Update: 27-Dec-2019

Title:
Single Crystal Growth of Relaxor Ferroelectric Ba2PrFeNb4O15 by the Optical Floating Zone Method
Authors:
Wang, BX, Zheng, H, Ren, Y, Krogstad, M, Mitchell, JF, Phelan, D
Source:
CRYST GROWTH DES 19 (12):7249 10.1021/acs.cgd.9b01147 DEC 2019
Abstract:
Uniaxial tungsten bronzes have received increasing interest because of their potential application as lead-free ferroelectrics as well as their flexibility-via chemical substitution. Here we demonstrate growth of single crystals of one such material, Ba2PrFeNb4O15, which possesses the tetragonal tungsten bronze structure, by the optical floating zone method. The challenge of this growth is to control the stability of the molten zone which allows the growth to persist for a long enough time to achieve large volume single crystals. Our work reveals that the use of a slight overpressure of air allows the molten zone to be maintained up to 7 h at a traveling speed of 4 mm/h. The obtained crystals were studied using high-resolution single crystal scattering, powder X-ray diffraction, and dielectric measurements. We find that Ba2PrFeNb4O15 possesses a rather complex average structure with a monoclinic symmetry in a P112/m space group and unit cell parameters of a = 12.49188(8) angstrom, b = 12.49232(8) angstrom, c = 3.92863(1) angstrom, and gamma = 90.056 degrees, with an additional incommensurate superstructural modulation superimposed. The temperature dependence of dielectric properties has been investigated by comparing as-grown, O-2-annealed, and Ar-annealed samples. A broad relaxation dielectric peak is observed around 150 K for the O-2-annealed sample, indicating a typical relaxor behavior below 150 K. A larger dielectric permittivity (epsilon' approximate to 1300) than those of corresponding ceramics (up to epsilon' approximate to 200) is found in the oxygen annealed crystals. We suggest that as-grown single crystals are oxygen deficient and that the oxygen vacancies can be eliminated by an oxygen annealing treatment.
Title:
Influence of weak frustration on quench dynamics of 1D spin-1/2 ANNNI model
Authors:
Cheraghi, H, Tafreshi, MJ, Mahdavifar, S
Source:
J MAGN MAGN MATER 497 10.1016/j.jmmm.2019.166078 MAR 1 2020
Abstract:
In this work we study the dynamical quantum phase transition in the 1D spin-1/2 transverse axial next-nearest-neighbor Ising (ANNNI) model by employing the mean field Jordan-Wigner approach. The NNN interaction breaks the integrability of the ANNNI model. We have focused on the induced dynamical effects of the frustration on quench dynamics of the system. The approach helps us to diagonalize the Hamiltonian in the region where the frustration is weak and the analytical method is reliable. First, the non-analyticity of the rate function is analyzed. It is found that only by quenching across the quantum critical point, regular nonanalyticitic behaviors at periodic instants are seen in the dynamics of the rate function. Here, our results confirm the existence of paramagnetic commensurate and paramagnetic incommensurate phases in the system. Second, the order parameter dynamics as a system's macroscopical property is investigated and the oscillatory behavior is reported. Third, the nonequilibrium dynamics of the quantum correlations as the entanglement and the quantum discord are studied. We have compared the efficiency of the quantum discord with respect to the entanglement in the detection of the occurrence of the dynamical quantum phase transition.
Title:
Quasicrystalline Chern insulators
Authors:
He, AL, Ding, LR, Zhou, Y, Wang, YF, Gong, CD
Source:
PHYS REV B 100 (21) 10.1103/PhysRevB.100.214109 DEC 11 2019
Abstract:
A Chern insulator or a quantum anomalous Hall state is a topological state with integer Hall conductivity but in absence of the Landau level. It had been well established on various two-dimensional lattices with periodic structure. Here, we report similar Chern insulators that can also be realized on a quasicrystal with fivefold rotational symmetry. Providing the staggered flux through plaquettes, we propose two types of quasicrystalline Chern insulators. Their topological characterizations are well identified by the robustness of edge states, nonzero real-space Chern number, and quantized conductance. We further find the failure of integer conductivity but with the quantized Chern number at some special energies. Our study, therefore, provides a new opportunity to searching topological materials in aperiodic systems.

Update: 12-Dec-2019

Title:
Single phase charge ordered stoichiometric CaFe3O5 with commensurate and incommensurate trimeron ordering
Authors:
Cassidy, SJ, Orlandi, F, Manuel, P, Clarke, SJ
Source:
NAT COMMUN 10 10.1038/s41467-019-13450-5 DEC 2 2019
Abstract:
Mixed-valent transition metal compounds display complex structural, electronic and magnetic properties which can often be exquisitely tuned. Here the charge-ordered state of stoichiometric CaFe3O5 is probed using neutron powder diffraction, Monte Carlo simulation and symmetry analysis. Magnetic ordering is dominated by the formation of ferromagnetic Fe3+-Fe2+-Fe3+ trimers which are evident above the magnetic ordering transition. Between T-N= 289 K and 281 K an incommensurate magnetically ordered phase develops due to magnetic frustration, but a spin Jahn-Teller distortion lifts the frustration and enables the magnetic ordering to lock in to a charge-ordered commensurate state at lower temperatures. Stoichiometric CaFe3O5 exhibits single phase behaviour throughout and avoids the phase separation into two distinct crystallographic phases with different magnetic structures and Fe valence distributions reported recently, which likely occurs due to partial Fe2+ for Ca2+ substitution. This underlines the sensitivity of the magnetism and chemistry of these mixed-valent systems to composition.
Title:
Antiferromagnetic order survives in the higher-order quasicrystal approximant
Authors:
Yoshida, S, Suzuki, S, Yamada, T, Fujii, T, Ishikawa, A, Tamura, R
Source:
PHYS REV B 100 (18) 10.1103/PhysRevB.100.180409 NOV 25 2019
Abstract:
We report the observation of antiferromagnetic (AFM) transitions in 1/1 and 2/1 quasicrystal approximants having slightly different electron-per-atom (e/a) ratios, in the same Au-Ga-Eu system, at Ned temperatures of 7.0 and 8.5 K, respectively. This clearly demonstrates that an antiferromagnetic order survives when the degree of approximation to the quasicrystals is raised provided that the e/a ratio is kept nearly the same. Since, unlike the 1/1 approximant, the 2/1 approximant has all the building blocks necessary for the construction of the quasicrystal, this finding can be a significant leap toward the long-sought realization of an AFM quasicrystal.
Title:
Emergent Quasicrystalline Symmetry in Light-Induced Quantum Phase Transitions
Authors:
Mivehvar, F, Ritsch, H, Piazza, F
Source:
PHYS REV LETT 123 (21) 10.1103/PhysRevLett.123.210604 NOV 22 2019
Abstract:
The discovery of quasicrystals with crystallographically forbidden rotational symmetries has changed the notion of the ordering in materials, yet little is known about the dynamical emergence of such exotic forms of order. Here we theoretically study a nonequilibrium cavity-QED setup realizing a zero-temperature quantum phase transition from a homogeneous Bose-Einstein condensate to a quasicrystalline phase via collective superradiant light scattering. Across the superradiant phase transition, collective light scattering creates a dynamical, quasicrystalline optical potential for the atoms. Remarkably, the quasicrystalline potential is " emergent" as its eightfold rotational symmetry is not present in the Hamiltonian of the system, rather appears solely in the low-energy states. For sufficiently strong two-body contact interactions between atoms, a quasicrystalline order is stabilized in the system, while for weakly interacting atoms the condensate is localized in one or few of the deepest minima of the quasicrystalline potential.
Title:
Twisted Graphene Bilayers and Quasicrystals: A Cut and Projection Approach
Authors:
Aragon, JL, Naumis, GG, Gomez-Rodriguez, A
Source:
CRYSTALS 9 (10) 10.3390/cryst9100519 OCT 2019
Abstract:
In this work, a modified version of the cut and projection approach is proposed to describe the structure of graphene bilayers with twist angles. With this method, the rotation between two graphene layers is viewed as a rotation of the projection space and the resulting projected structure is interpreted as the set of points of best fit between the two rotated structures. Additionally, focus is given to the pertinence of the many algebraic and geometric tools used in grain boundaries and in quasicrystals to graphene bilayer system (or any other bilayer system, for that matter) case.
Title:
Multiple Influences of Molybdenum on the Precipitation Process in a Martensitic PH Stainless Steel
Authors:
Thuvander, M, Andersson, M, Stiller, K
Source:
METALS-BASEL 9 (10) 10.3390/met9101118 OCT 2019
Abstract:
Molybdenum has been found to influence the complex precipitation process in a martensitic precipitation hardening stainless steel during aging at 475 degrees C in several different ways. Three steels with different Mo content (0, 1.2 and 2.3 at.%) were investigated. Studies of the microstructure were performed with atom probe tomography and energy filtered transmission electron microscopy. It is shown that, at the initial stage of aging, a faster nucleation of Cu-rich clusters takes place with increasing Mo content. The Cu-clusters act as precipitation sites for other solute elements and promote the nucleation of Ni-rich phases. During further aging, a higher Mo content in the material instead slows down the growth and coarsening of the Ni-rich phases, because Mo segregates to the interface between precipitate and matrix. Additionally, Mo promotes decomposition of the matrix into alpha and alpha' regions. After longer aging times (>40 h) quasicrystalline Mo-rich R' phase forms (to a greater extent in the material having the highest Mo content). The observations serve to understand the hardness evolution during aging.

Update: 5-Dec-2019

Title:
Magnetic structures
Authors:
Rodriguez-Carvajal, J, Villain, J
Source:
CR PHYS 20 (7-8):770 10.1016/j.crhy.2019.07.004 NOV-DEC 2019
Abstract:
While ferromagnetism has been known since many centuries, more complex magnetic structures have only been identified in the twentieth century: ferrimagnetism, antiferromagnetism, helimagnetism, modulated structures... Incommensurable or long-period structures have first been deduced as consequences of phenomenological models, e.g., the Heisenberg Hamiltonian. The more fundamental explanation of Rudermann, Kittel, Kasuya, and Yoshida relies on the general phenomenon of Friedel oscillations. The coexistence of crystallographic order and magnetic order is sometimes antagonistic and results in sequences of transitions that may be continuous or not. The most effective experimental technique to observe magnetic order is neutron diffraction, but the analysis is sometimes very complicated and requires sophisticated numerical methods involving group theory. In the case of incommensurable structures, it may be useful to consider the three-dimensional system as the section of a higher-dimensional crystal. The determination of magnetic structures from neutron scattering data is facilitated by computers and adequate programs. (C) 2019 Academie des sciences. Published by Elsevier Masson SAS.
Title:
Discovery of quasicrystals: The early days
Authors:
Gratias, D, Quiquandon, M
Source:
CR PHYS 20 (7-8):803 10.1016/j.crhy.2019.05.009 NOV-DEC 2019
Abstract:
This paper is a survey of the initial developments of the research on quasicrystals starting from their discovery by Daniel Shechtman (Nobel Prize in Chemistry in 2011) in 1982 at the National Bureau of Standards (now National Institute for Standard and Technology) in Gaithersburg (Maryland, USA) up to the beginning of the early 1990s, a time when the crystallographic methods were well developed and mastered enough to decipher the ultimate atomic structures of quasicrystals. These early works have enlarged our understanding of spatial order in solids through a strong multidisciplinary effort between mathematicians, physicists, chemists and material scientists. (C) 2019 Academie des sciences. Published by Elsevier Masson SAS.

Update: 28-Nov-2019

Title:
Verification of the de Wolff hypothesis concerning the symmetry of beta-MnO2
Authors:
Fabrykiewicz, P, Przenioslo, R, Sosnowska, I, Fauth, F, Oleszak, D
Source:
ACTA CRYSTALLOGR A 75:889 10.1107/S2053273319013408 NOV 2019
Abstract:
The symmetry lowering from tetragonal to orthorhombic is demonstrated using high-resolution diffraction and also justified by using the magnetic superspace groups formalism for the rutile-type compound beta-MnO2. The (lower) orthorhombic symmetry is observed at temperatures both below and above the Neel temperature. The magnetic ordering of beta-MnO2 is of spin density type and not screw-type helical. The results support the de Wolff [Acta Cryst. (1959), 12, 341-345] hypothesis about the orthorhombic symmetry of beta-MnO2.
Title:
C-60 adsorption on a dodecagonal oxide quasicrystal
Authors:
Zollner, EM, Schenk, S, Forster, S, Widdra, W
Source:
PHYS REV B 100 (20) 10.1103/PhysRevB.100.205414 NOV 14 2019
Abstract:
Quasicrystalline surfaces are potential templates for highly ordered but aperiodic molecular self-assemblies. Here, we report on the adsorption of C-60 molecules on a two-dimensional oxide quasicrystal (OQC) and its sigma-phase approximant at room temperature and 150 K. The molecular films have been characterized by means of scanning tunneling microscopy and low-energy electron diffraction. A weak interaction of the molecules with the dodecagonal oxide template is found, resulting in a low desorption temperature of 510 K. For low temperatures specific adsorption sites within the tiling of the OQC and the s-phase approximant have been identified as preferred nucleation sites. The narrow spacing between these sites introduces repulsive interaction between C60 molecules and restricts the epitaxial growth to small patches. At room temperature, C-60 nucleates in hcp islands of almost arbitrary rotational orientation on the OQC. A slight orientational preference for hexagonal islands with a 15 degrees rotation against the OQC tiling is discussed as a consequence of the preferential adsorption on the quadratic tiles.
Title:
A surface-stacking structural model for icosahedral quasicrystals
Authors:
Ajlouni, R
Source:
STRUCT CHEM 30 (6):2279 10.1007/s11224-019-01413-x DEC 2019
Abstract:
An original structural model for the description of icosahedral quasicrystals is proposed. This novel theoretical approach is based on a surface-stacking image of icosahedral quasicrystals and is in concert with the step-terrace morphology observed in many experimental investigations of real icosahedral surfaces. According to this model, the infinite icosahedral structure is constructed by stacking two arrangements of quasi-periodic surfaces along each of the 5-fold axis of the icosahedral symmetry. In this stacking order, the spacings between the layered surfaces are governed by Fibonacci sequence. The proposed model operates within the real physical (Euclidean) space and provides a direct three-dimensional visual representation of the icosahedral superstructure, which can be instrumental for conducting different modes of experimentations, analyses, and fabrication strategies; eliminating a major roadblock for researchers especially outside the fields of crystallography and material science. More importantly, understanding the long-range surface-stacking logic of the icosahedral structure will hopefully provide a deeper understanding of the structure of quasicrystals at an atomic scale and help achieve improved control over material compositions and structure.

Update: 21-Nov-2019

Title:
Antiferromagnetic Semiconductor BaFMn0.5Te with Unique Mn Ordering and Red Photoluminescence
Authors:
Chen, HJ, McClain, R, He, JG, Zhang, C, Olding, JN, dos Reis, R, Bao, JK, Hadar, I, Spanopoulos, I, Malliakas, CD, He, YH, Chung, DY, Kwok, WK, Weiss, EA, Dravid, VP, Wolverton, C, Kanatzidis, MG
Source:
J AM CHEM SOC 141 (43):17421 10.1021/jacs.9b09382 OCT 30 2019
Abstract:
Semiconductors possessing both magnetic and optoelectronic properties are rare and promise applications in opto-spintronics. Here we report the mixed-anion semiconductor BaFMn0.5Te with a band gap of 1.76 eV and a work function of 5.08 eV, harboring both antiferromagnetism (AFM) and strong red photoluminescence (PL). The synthesis of BaFMn0.5Te in quantitative yield was accomplished using the "panoramic synthesis" technique and synchrotron radiation to obtain the full reaction map, from which we determined that the compound forms upon heating at 850 degrees C via an intermediate unknown phase. The structure refinement required the use of a (3+1)-dimensional superspace group Cmme(alpha 01/2)0ss. The material crystallizes into a ZrCuSiAs-like structure with alternating [BaF](+) and [Mn0.5Te](-) layers and has a commensurately modulated structure with the q-vector of 1/6a* + 1/6b* + 1/2c* at room temperature arising from the unique ordering pattern of Mn2+ cations. Long-range AFM order emerges below 90 K, with two-dimensional short-range AFM correlations above the transition temperature. First-principles calculations indicate that BaFMn0.5Te is an indirect band gap semiconductor with the gap opening between Te 5p and Mn 3d orbitals, and the magnetic interactions between nearest-neighbor Mn2+ atoms are antiferromagnetic. Steady-state PL spectra show a broad strong emission centered at similar to 700 nm, which we believe originates from the energy manifolds of the modulated Mn2+ sublattice and its defects. Time-resolved PL measurements reveal an increase in excited-state lifetimes with longer probe wavelengths, from 93 ns (at 650 nm) to 345 ns (at 800 nm), and a delayed growth (6.5 +/- 0.3 ns) in the kinetics at 800 nm with a concomitant decay (4.1 +/- 0.1 ns) at 675 nm. Together, these observations suggest that there are multiple emissive states, with higher energy states populating lower energy states by energy transfer.
Title:
Ferromagnetic Ising chains in frustrated LnODCO(3): the influence of magnetic structure in magnetocaloric frameworks
Authors:
Dixey, RJC, Stenning, GBG, Manuel, P, Orlandi, F, Saines, PJ
Source:
J MATER CHEM C 7 (42):13111 10.1039/c9tc04980k NOV 14 2019
Abstract:
Probing the magnetic interactions in functional magnetic materials can reveal detailed insight into how to optimise the properties they possess while providing key understanding of the exotic phenomena they may host. This study probes the short and long range magnetic order in the LnODCO(3) (where Ln = Tb, Dy, Ho, and Er) framework magnetocalorics using variable-temperature neutron scattering measurements. Reverse Monte Carlo analysis of neutron scattering data shows that TbODCO3, DyODCO3 and HoODCO3 develop short range Ising-like magnetic order between 1.5 and 20 K, consistent with dominant ferromagnetic correlations within chains along the b-axis. Through magnetic susceptibility measurements we identify that long range magnetic order develops in TbODCO3 and HoODCO3 at similar to 1.2 and similar to 0.9 K, respectively. Neutron diffraction measurements were conducted on HoODCO3 revealing incommensurate magnetic order develops between 1.2 and 0.9 K, before a commensurate magnetic phases emerges at 0.8 K with long-range ferromagnetic order in the chains. The results suggest Ising-like ferromagnetic chains associated with frustration are responsible for the improved magnetocaloric properties, of some members in this family, at higher temperatures and low applied fields.

Update: 14-Nov-2019

Title:
New modulated structures of solid bromine at high pressure
Authors:
Li, PF, Du, XD, Gao, GY, Sun, RX, Zhang, LJ, Wang, WH
Source:
COMP MATER SCI 171 10.1016/j.commatsci.2019.109205 JAN 2020
Abstract:
Crystal structures of bromine under pressure have been studied through the advanced structure search method in combination with first-principles calculations. At 10 and 90 GPa, we successfully reproduced the experimentally observed molecular phase I and monatomic body-centred orthorhombic phase II, respectively. At 120 and 200 GPa, the lowest-enthalpy structures predicted are body centered tetragonal and face-centered cubic phase, respectively, which are also consistent with previously theoretical study. Interestingly, in the pressure range of 50-80 GPa, our structural searches predicted four structurally similar and modulated structures, oF20, oC24, oF28 and oC12, whose magnitude of the modulation vectors k are 2/5, 1/6, 2/7 and 1/3, respectively. Enthalpy calculations show that oF20, oC24, oF28 and oC12 are thermaldynamically stable in the pressure range of 52-53, 53-58, 58-65 and 65-79 GPa, respectively. Through comparison of the structural characterization and X-ray diffraction patterns of the predicted oF28, oC12 in bromine and the known incommensurate modulated phase V in iodine, we suggest that bromine might also adopt an incommensurate modulated structure. In addition, the prediction of two new phases (oF20 and oC24) between molecular phase I and incommensurate phases are consistent with Raman scattering and X-ray absorption spectroscopy (XAS) experimental results. For the first time, we presented the structure information between molecular phase I and monatomic phase II in bromine. The calculated elastic stiffness coefficients indicate that the four modulated phases are mechanically stable. The calculated electronic density of states for these four predicted phases show that they are all metallic.
Title:
Helical magnetic ordering in Sr(Co1-xNix)(2)As-2
Authors:
Wilde, JM, Kreyssig, A, Vaknin, D, Sangeetha, NS, Li, B, Tian, W, Orth, PP, Johnston, DC, Ueland, BG, McQueeney, RJ
Source:
PHYS REV B 100 (16) 10.1103/PhysRevB.100.161113 OCT 29 2019
Abstract:
SrCo2As2 is a peculiar itinerant magnetic system that does not order magnetically, but inelastic neutron-scattering experiments observe the same stripe-type antiferromagnetic (AF) fluctuations found in many of the Fe-based superconductors along with evidence of magnetic frustration. Here we present results from neutron diffraction measurements on single crystals of Sr(Co1-xNix)(2)As-2 that show the development of long-range AF order with Ni doping. However, the AF order is not stripe type. Rather, the magnetic structure consists of ferromagnetically aligned (FM) layers (with moments laying in the layer) that are AF arranged along c with an incommensurate propagation vector of (0 0 tau), i.e., a helix. Using high-energy x-ray diffraction, we find no evidence for a temperature-induced structural phase transition that would indicate a collinear AF order. This finding supports a picture of competing FM and AF interactions within the square transition-metal layers due to flat-band magnetic instabilities. However, the composition dependence of the propagation vector suggests that far more subtle Fermi surface and orbital effects control the interlayer magnetic correlations.
Title:
A commensurately modulated crystal structure and the physical properties of a novel polymorph of the caesium manganese phosphate CsMnPO4
Authors:
Bolotina, N, Yakubovich, O, Shvanskaya, L, Dimitrova, O, Volkov, A, Vasiliev, A
Source:
ACTA CRYSTALLOGR B 75:822 10.1107/S2052520619009296 OCT 2019
Abstract:
A novel modification of the CsMnPO4 beta-phase was achieved by hydrothermal synthesis at 553 K. The compound crystallizes in the monoclinic system with the basic unit-cell parameters a = 11.0699 (4), b = 11.0819 (6), c = 9.1106 (3) angstrom, gamma = 119.480 (5)degrees; the modulation vectors are q1 = 0.4a* and q2 = 0.4b*. The structure was determined based on single-crystal X-ray diffraction data obtained from a pseudo-merohedral twin using a superspace approach in the (3 + 2)D symmetry group P11a(a1,b1,0)0(a2,b2,0)0 and refined to R = 0.083 for 10 266 reflections with I > 3 sigma (I). It is considered as a low-temperature polymorph of CsMnPO4 with the same UUUDDD-type layer topology built by MnO4 and PO4 tetrahedra, and stacked in a framework in the same manner as beta-tridymite. Large open channels parallel to the [110] and [001] directions incorporate Cs atoms. All Cs atoms are distributed along the a(super) = 55.35 (1) and b(super) = 55.41 (1) axes of the large unit cell with pseudo periods of a(super)/5 and b(super)/5 which are broken mainly by the positions of oxygen atoms (orientation of Mn- and P-centered tetrahedra). The beta-phase is discussed as a member of the morphotropic series of manganese phosphates with large cations of AMnPO(4), where A = Cs, Rb, K and Ag. The title compound is an antiferromagnet with the Neel temperature T-N = 4.5K.

Update: 31-Oct-2019

Title:
Analysis of elastic-plastic fracture in two-dimensional decagonal quasicrystals using the displacement discontinuity method
Authors:
Dang, HY; Zhao, MH; Ren, JL; Fan, CY Author Full Names: Dang, HuaYang; Zhao, MingHao; Ren, JingLi; Fan, CuiYing
Source:
ENGINEERING ANALYSIS WITH BOUNDARY ELEMENTS, 108 366-371; 10.1016/j.enganabound.2019.07.021 NOV 2019
Abstract:
The generalized Dugdale model of cracks in two-dimensional decagonal quasicrystals is studied by developing the extended displacement discontinuity boundary element method. Expressions for the phonon and phason stress intensity factors and energy release rate are given in terms of the phonon and phason displacement discontinuities near the crack front. The extended displacement discontinuity boundary element method, with an iterative approach of determining the size of the yielding zone, is adopted to numerically simulate the nonlinear fracture problem. The effects of phonon and phason loadings, as well as the yield stress on the size of yielding zone and energy release rate, are discussed.
Title:
Structural Peculiarities of the Intermediate Phase in Zr-Rich Lead Zirconate Titanate
Authors:
Andronikova, DA; Bronwald, IA; Leontyev, NG; Leontyev, IN; Chernyshov, DY; Filimonov, AV; Vakhrushev, SB Author Full Names: Andronikova, D. A.; Bronwald, I. A.; Leontyev, N. G.; Leontyev, I. N.; Chernyshov, D. Yu; Filimonov, A., V; Vakhrushev, S. B.
Source:
PHYSICS OF THE SOLID STATE, 61 (10):1772-1778; 10.1134/S1063783419100056 OCT 2019
Abstract:
This paper presents the results of X-ray diffraction studies on a single crystal of lead zirconate titanate PbZr0.993Ti0.007O3 in the region of existence of an intermediate ferroelectric phase. In addition to the known superstructure reflections of the M type q(M) = {\frac{1}{2},\frac{1}{2},0} \right\}$$\end{document} and the first-order satellite reflections q(M) + {delta, delta, delta}, unknown second-order satellites have been observed near q(M) and near the Bragg reflections. Structural model of regular system of antiphase domains is used for diffraction calculation. The model is shown to describe the first- and second-orders satellite reflections in the vicinity of q(M), but it cannot explain the appearance of satellites around the main Bragg peaks. A possible origin of the system of the superstructures observed in the intermediate phase is discussed.
Title:
Crack Detection in High-Velocity Oxygen-Fuel-Sprayed Al59.2Cu25.5Fe12.3B3 Quasicrystalline Coatings Using Piezoelectric Active Sensors
Authors:
Gomes, R; Feitosa, FR; Souto, C; Lima, BA; Anselmo, J; Cunha, M; Sobrinho, JMB; Dubois, JM Author Full Names: Gomes, Rodinei; Feitosa, Francisco Riccelly; Souto, Cicero; Lima, Bruno Alessandro; Anselmo Junior, Jose; Cunha, Maxsuel; Basilio Sobrinho, Jose Marques; Dubois, Jean-Marie
Source:
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE, 28 (9):5649-5660; 10.1007/s11665-019-04298-3 SEP 2019
Abstract:
Quasicrystals have received some attention in recent years regarding their potential usefulness as low friction and wear resistant materials. When quasicrystalline (QC) coatings are exposed to different levels of external loading or are subjected to thermal stresses, crack nucleation, and propagation become life-limiting factors. In this investigation, Al59.2Cu25.5Fe12.3B3 QC coatings were deposited onto AISI-A36 steel substrates using the high-velocity oxygen-fuel (HVOF) technique. The coatings were deposited at different oxygen-to-fuel ratios. To characterize the integrity of the coatings, the active piezoceramic excitation technique was applied to detect the propagation of cracks during three-point bending tests. The piezoelectric transducer signal was processed using wavelet transformation analysis. The results revealed that the coated samples displayed different densities of cracks depending on the oxygen-to-fuel. The crack density was found higher for coatings formed using a slightly oxidizing flame. The opening of the pre-existing cracks in the coating was the main reason of signal attenuation during piezoelectric excitation. The HVOF-sprayed AlCuFeB quasicrystalline coating, with thickness between 150 and 180 mu m, withstands a flexural stress as high as 340 MPa. To the best of our knowledge, this study is the first that provides a quantitative assessment of the viability of QC coatings in mechanical applications in spite of their intrinsic brittleness.

Update: 24-Oct-2019

Title:
Lattice and magnetic dynamics in the polar, chiral, and incommensurate antiferromagnet Ni2InSbO6
Authors:
Prosnikov, MA; Smirnov, AN; Davydov, VY; Araki, Y; Arima, T; Pisarev, RV Author Full Names: Prosnikov, M. A.; Smirnov, A. N.; Davydov, V. Yu; Araki, Y.; Arima, T.; Pisarev, R., V
Source:
PHYSICAL REVIEW B, 100 (14):10.1103/PhysRevB.100.144417 OCT 10 2019
Abstract:
Complex systems with coexisting polarity, chirality, and incommensurate magnetism are of great interest because they open new degrees of freedom in the interaction between crystal and magnetic subsystems and therefore they host a plethora of intriguing physical properties. Here we report the optical properties and lattice and spin dynamics of Ni2InSbO6 single crystals. This material was studied with the use of polarized optical microscopy and micro-Raman spectroscopy in the temperature range 10-300 K. Ni2InSbO6 crystallizes in a polar structure described by the noncentrosymmetric space group R3 and the two types of structural domains were visualized due to the natural optical activity of opposite chirality. Raman tensor elements of most A and E phonons along with their symmetry were determined. The manifestation of LO-TO splitting was observed for the A modes. By tracking the temperature dependencies of phonon frequencies, the well pronounced spin-phonon interaction was observed for several modes below and above the Ned transition temperature T-N = 76 K. In the antiferromagnetic phase, a broad excitation centered at 247 cm(-1), was detected and assigned to the two-magnon mode and this value was used for estimating exchange parameters through linear spin-wave theory calculations.
Title:
Stability of three-dimensional icosahedral quasicrystals in multi-component systems
Authors:
Jiang, K; Si, W Author Full Names: Jiang, Kai; Si, Wei
Source:
PHILOSOPHICAL MAGAZINE, 10.1080/14786435.2019.1671997
Abstract:
The relative stability of three-dimensional icosahedral quasicrystals in multi-component systems has been investigated based on a phenomenological coupled-mode Swift-Hohenberg model with two-length scales. A recently developed projection method, which provides a unified numerical framework to study periodic crystals and quasicrystals, is used to compute free energy to high accuracy. Compared with traditional approaches, the advantage of the projection method has also been discussed in detail. A rigorous and systematic computation demonstrates that three-dimensional icosahedral quasicrystal and two-dimensional decagonal quasicrystal are both stable phases in such a simple multi-component coupled-mode Swift-Hohenberg model. The result extends the two-length scales interaction mechanism of stabilising quasicrystals from single-component to multi-component systems.
Title:
Equilibrium Configurations for Generalized Frenkel-Kontorova Models on Quasicrystals
Authors:
Trevino, R Author Full Names: Trevino, Rodrigo
Source:
COMMUNICATIONS IN MATHEMATICAL PHYSICS, 371 (1):1-17; 10.1007/s00220-019-03557-7 OCT 2019
Abstract:
I study classes of generalized Frenkel-Kontorova models whose potentials are given by almost-periodic functions which are closely related to aperiodic Delone sets of finite local complexity. Since such Delone sets serve as models for quasicrystals, this setup presents Frenkel-Kontorova models for the type of aperiodic crystals which have been discovered since Shechtman's discovery of quasicrystals. Here I consider models with configurations u:Zr -> Rd}, where d is the dimension of the quasicrystal, for any r and d. The almost-periodic functions used for potentials are called pattern-equivariant and I show that if the interactions of the model satisfies a mild end{document} requirement, and if the potential satisfies a mild non-degeneracy assumption, then there exist equilibrium configurations of any prescribed rotation rotation number/vector/plane. The assumptions are general enough to satisfy the classical Frenkel-Kontorova models and its multidimensional analoges. The proof uses the idea of the anti-integrable limit.

Update: 17-Oct-2019

Title:
Development of quasicrystal morphology in gas-atomized icosahedral-phase-strengthened aluminum alloy powders
Authors:
Leonard, HR; Rommel, S; Watson, TJ; Policandriotes, T; Aindow, M Author Full Names: Leonard, H. R.; Rommel, S.; Watson, T. J.; Policandriotes, T.; Aindow, M.
Source:
MATERIALS & DESIGN, 182 10.1016/j.matdes.2019.108094 NOV 15 2019
Abstract:
The microstructures in gas-atomized powders and in blind-die-compacted material from three AI-Cr-Mn-Co-Zr alloys have been studied using X-ray diffraction and electron microscopy. The materials consist of a mixture of FCC AI and icosahedral quasicrystalline phases, but three different phase distributions are observed which depend on the powder particle size, and hence on the cooling rate. The finest particles contain a nano-composite mixture of equiaxed Al grains and fine (<200 nm) quasicrystalline dispersoids. Coarser particles exhibit large cellular dendritic AI grains with thin films of Co- and Cr/Mn-rich phases at the cell boundaries and coarser (up to 2 mu m) quasicrystals at the particle surfaces. The largest particles contain coarse (up to 5 mu m) radial quasicrystalline growths within the particle. The same microstructures were observed for each alloy, but the volume fractions of the microstructural types varied with the alloy content. These effects are explained on the basis of competing nucleation and growth phenomena during solidification of the atomized droplets. Since these microstructures are retained in the bulk material following blind-die-compaction, they could have a profound influence on the mechanical and other properties of materials made from such powders. The importance of such effects for alloy and process design are discussed. (C) 2019 The Author(s). Published by Elsevier Ltd.
Title:
Topological Anderson insulator phase in a quasicrystal lattice
Authors:
Chen, R; Xu, DH; Zhou, B Author Full Names: Chen, Rui; Xu, Dong-Hui; Zhou, Bin
Source:
PHYSICAL REVIEW B, 100 (11):10.1103/PhysRevB.100.115311 SEP 27 2019
Abstract:
Motivated by the recent experimental realization of the topological Anderson insulator and research interest on the topological quasicrystal lattices, we investigate the effects of disorder on topological properties of a two-dimensional Penrose-type quasicrystal lattice that supports the quantum spin Hall insulator (QSHI) and normal insulator (NI) phases in the clean limit. It is shown that the helical edge state of the QSHI phase is robust against weak disorder. Most saliently, it is found that disorder can induce a phase transition from NI to QSHI phase in the quasicrystal system. The numerical results based on a two-terminal device show that a quantized conductance plateau can arise inside the energy gap of the NI phase for moderate Anderson disorder strength. Further, it is confirmed that the local current distributions of the disorder-induced quantized conductance plateau are located on the two edges of the sample. Finally, we identify this disorder-induced phase as topological Anderson insulator phase by computing the disorder-averaged spin Bott index.
Title:
Electronic band structure of a two-dimensional oxide quasicrystal
Authors:
Chiang, CT; Ellguth, M; Schumann, FO; Tusche, C; Kraska, R; Forster, S; Widdra, W Author Full Names: Chiang, Cheng-Tien; Ellguth, Martin; Schumann, Florian O.; Tusche, Christian; Kraska, Richard; Foerster, Stefan; Widdra, Wolf
Source:
PHYSICAL REVIEW B, 100 (12):10.1103/PhysRevB.100.125149 SEP 23 2019
Abstract:
The valence band electronic structure of a BaTiO3-derived oxide quasicrystal (OQC) is studied by photoemission using momentum microscopy. An upward-dispersive Q(2p) band is identified, and it can be assigned to a combination of in-plane orbitals according to the symmetry and the overlap of the wave functions. In addition, the signature of Ti-3d states near the Fermi level is observed, which results in a metallic character of the OQC with 3d(1) occupation. Our experiments reveal two-dimensional electronic states within the OQC based on a symmetry-adapted decomposition of photoelectron intensity distribution in the momentum space.
Title:
Fabrication and electrochemical hydrogen storage performance of Ti49Zr26Ni25 alloy covered with Cd/Pd core/shell particles
Authors:
Liu, H; Tan, LY; Guo, YL; Chen, P; Gao, S; Su, ZM; Liu, WQ; Zhao, JX Author Full Names: Liu, Heng; Tan, Liyuan; Guo, Yalan; Chen, Peng; Gao, Shang; Su, Zhongmin; Liu, Wanqiang; Zhao, Jianxun
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 44 (45):24800-24809; 10.1016/j.ijhydene.2019.07.094 SEP 20 2019
Abstract:
A facile two-step reduction method is employed to obtain the Cd/Pd core/shell particles. Mechanical alloying and subsequent annealing are used to fabricate the Ti49Zr26Ni25 quasicrystal. Composite materials of Ti49Zr26Ni25 mixed with different contents of Cd/Pd particles are obtained via ball-milling. The electrochemical performance and kinetics properties of the alloy electrodes for Ni/MH secondary batteries are studied. Ultimately, a maximum discharge capacity of 272.9 mA h/g is achieved for 7% additive content of Cd/Pd. Ti49Zr26Ni25 + Cd/Pd shows higher capacity than Ti49Zr26Ni25 + Pd (246.8 mA h/g) and original Ti49Zr26Ni25 (212.5 mA h/g). Moreover, the composites also exhibit improved cyclic stability and high-rate dischargeability. The Cd/Pd particles with special core/shell microstructure can enhance the electro-catalytic activity of Pd. The Cd/Pd material covered on the surface of alloy can further decrease the charge-transfer resistance and accelerate the hydrogen transmission, thus improving the electrochemical properties and reaction kinetics of the electrode. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Update: 10-Oct-2019

Title:
Elastic field for a blunt crack in a decagonal quasicrystalline material
Authors:
Wang, X; Schiavone, P Author Full Names: Wang, Xu; Schiavone, Peter
Source:
ENGINEERING FRACTURE MECHANICS, 220 10.1016/j.engfracmech.2019.106657 OCT 15 2019
Abstract:
We show that the full-field solution for the plane strain deformations of a decagonal quasicrystalline material with traction-free parabolic boundary can be used to directly obtain the elastic field describing phonon and phason stresses as well as displacements in the vicinity of a blunt crack tip in a decagonal quasicrystalline material. The aforementioned full-field solution is derived by applying complex variable methods to the boundary value problem in the physical plane without any recourse to conformal mapping and a corresponding image plane.
Title:
Fundamental solutions and analysis of the interface crack for two-dimensional decagonal quasicrystal bimaterial via the displacement discontinuity method
Authors:
Fan, CY; Lv, SY; Dang, HY; Yuan, YP; Zhao, MH Author Full Names: Fan, CuiYing; Lv, ShouYi; Dang, HuaYang; Yuan, YanPeng; Zhao, MingHao
Source:
ENGINEERING ANALYSIS WITH BOUNDARY ELEMENTS, 106 462-472; 10.1016/j.enganabound.2019.05.029 SEP 2019
Abstract:
The extended displacement discontinuity method is developed to analyze an interface line crack in a two-dimensional decagonal quasicrystal bimaterial. According to the general solutions and Fourier transform, fundamental solutions for phonon and phason displacement discontinuities and phonon and phason stresses are obtained. The delta function in the phonon and phason stresses is replaced by the Gaussian distribution function to eliminate the oscillatory singularity near the crack front. The expressions of phonon and phason stress intensity factors are given in terms of phonon and phason displacement discontinuities. The finite element analysis software COMSOL is used to validate the developed method.

Update: 3-Oct-2019

Title:
Magnetic ground state of the frustrated spin-1/2 chain compound beta-TeVO4 at high magnetic fields
Authors:
Pregelj, M; Zorko, A; Klanjsek, M; Zaharko, O; White, JS; Prokhnenko, O; Bartkowiak, M; Nojiri, H; Berger, H; Arcon, D Author Full Names: Pregelj, M.; Zorko, A.; Klanjsek, M.; Zaharko, O.; White, J. S.; Prokhnenko, O.; Bartkowiak, M.; Nojiri, H.; Berger, H.; Arcon, D.
Source:
PHYSICAL REVIEW B, 100 (9):10.1103/PhysRevB.100.094433 SEP 19 2019
Abstract:
Frustrated spin-1/2 chains, despite the apparent simplicity, exhibit a remarkably rich phase diagram comprising vector-chiral (VC), spin-density-wave (SDW), and multipolar/spin-nematic phases as a function of the magnetic field. Here we report a study of beta-TeVO4, an archetype of such compounds, based on magnetization and neutron diffraction measurements up to 25 T. We find the transition from the helical VC ground state to the SDW state at similar to 3 T for the magnetic field along the a and c crystal axes, and at similar to 9 T for the field along the b axis. The high-field (HF) state, existing above similar to 18 T, i.e., above similar to 1/2 of the saturated magnetization, is an incommensurate magnetically ordered state and not the spin-nematic state, as theoretically predicted for the isotropic frustrated spin-1/2 chain. The HF state is likely driven by sizable interchain interactions and symmetric intrachain anisotropies uncovered in previous studies. Consequently, the potential existence of the spin-nematic phase in beta-TeVO4 is limited to a narrow field range, i.e., a few tenths of a tesla bellow the saturation of the magnetization, as also found in other frustrated spin-1/2 chain compounds.
Title:
Metallic-mean quasicrystals as aperiodic approximants of periodic crystals
Authors:
Nakakura, J; Ziherl, P; Matsuzawa, J; Dotera, T Author Full Names: Nakakura, Joichiro; Ziherl, Primoz; Matsuzawa, Junichi; Dotera, Tomonari
Source:
NATURE COMMUNICATIONS, 10 10.1038/s41467-019-12147-z SEP 17 2019
Abstract:
Ever since the discovery of quasicrystals, periodic approximants of these aperiodic structures constitute a very useful experimental and theoretical device. Characterized by packing motifs typical for quasicrystals arranged in large unit cells, these approximants bridge the gap between periodic and aperiodic positional order. Here we propose a class of sequences of 2-D quasicrystals that consist of increasingly larger periodic domains and are marked by an ever more pronounced periodicity, thereby representing aperiodic approximants of a periodic crystal. Consisting of small and large triangles and rectangles, these tilings are based on the metallic means of multiples of 3, have a 6-fold rotational symmetry, and can be viewed as a projection of a non-cubic 4-D superspace lattice. Together with the non-metallic-mean three-tile hexagonal tilings, they provide a comprehensive theoretical framework for the complex structures seen, e.g., in some binary nanoparticles, oxide films, and intermetallic alloys.
Title:
High strain rate behaviour of nano-quasicrystalline Al93Fe3Cr2Ti2 alloy and composites
Authors:
Pedrazzini, S; Galano, M; Audebert, F; Siegkas, P; Gerlach, R; Tagarielli, VL; Smith, GDW Author Full Names: Pedrazzini, S.; Galano, M.; Audebert, F.; Siegkas, P.; Gerlach, R.; Tagarielli, V. L.; Smith, G. D. W.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 764 10.1016/j.msea.2019.138201 SEP 9 2019
Abstract:
We demonstrate the outstanding dynamic strength of nano-quasicrystalline Al93Fe3Cr2Ti2 at.% alloy and composites. Unlike most crystalline Al alloys, this alloy exhibits substantial strain rate sensitivity and retains ductility at high strain rates. This opens new pathways for use in safety-critical materials requiring impact resistance.
Title:
How Accurate Do X-ray Data Need To Be To Obtain a Reliable Order of Stability for Polymorphs? The Case Study of p-Hydroxyacetophenone Polymorphs
Authors:
Sztylko, M; Malinska, M; Petricek, V; Gutmann, MJ; Hoser, AA Author Full Names: Sztylko, Marcin; Malinska, Maura; Petricek, Vaclav; Gutmann, Matthias J.; Hoser, Anna A.
Source:
CRYSTAL GROWTH & DESIGN, 19 (9):5132-5141; 10.1021/acs.cgd.9b00518 SEP 2019
Abstract:
Technical progress in crystallographic instruments allows contemporary crystallographers to more routinely conduct excellent quality low-temperature diffraction measurements. As a result, even crystal structures that have been extensively studied at ambient conditions start to reveal their more complex nature. The importance of low-temperature measurements is discussed based on the new, modulated structures found for polymorphs of 4'-hydroxyacetophenone (HAP). Diffraction data for this polymorphic system have been collected in the temperature range from 40 K to 330 K. At 123 K, form II of HAP appears to be a new, commensurately modulated structure with a modulation vector q = [0.4, 0.0, 0.0]. The structure can be solved and refined with 10 molecules in the asymmetric unit. A further decrease of temperature to 40 K resulted in the discovery of a new, incommensurately modulated phase with four independent molecules in the P2(1) monoclinic space group with the modulation vector q = [0.37, 0.17, 0.0]. Consequences of modulation for the relative stability of polymorphs will be discussed.

Update: 26-Sep-2019

Title:
Structural correlation of magneto-electric coupling in polycrystalline TbMnO3 at low temperature
Authors:
Agarwal, H; Yadav, P; Lalla, NP; Alonso, JA; Srivastava, ON; Shaz, MA Author Full Names: Agarwal, Harshit; Yadav, Poonam; Lalla, N. P.; Alonso, J. A.; Srivastava, O. N.; Shaz, M. A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 806 510-519; 10.1016/j.jallcom.2019.07.228 OCT 25 2019
Abstract:
The present study is focused on the structural correlation of magneto-electric coupling that exists in polycrystalline TbMnO3. The X-ray diffraction patterns are collected at various conditions, which are (1) at 300 K without a magnetic field, (2) at 2 K without magnetic field and (3) at 2 K with 7 Tesla magnetic fields. The structural transition in TbMnO3 has been observed at 2 K and some lattice modulation after applying the magnetic field at 2 K. The Rietveld refinement of TbMnO3 confirms the orthorhombic phase with centrosymmetric space group Pnma at 300 K. We have observed that the inversion symmetry breaks at 2 K and the polycrystalline TbMnO3 has been refined using a non-centrosymmetric orthorhombic space group which can be either Pn2(1)a or P2(1)ma. This structural transition confirms the presence of a ferroelectric phase at 2 K. After the application of 7 Tesla magnetic field, the signature of an incommensurate phase has been observed in polycrystalline TbMnO3 at 2 K. The DC magnetization behaviour with temperature M(T) and field M(H) reveals the antiferromagnetic behaviour of polycrystalline TbMnO3 below 42 K. We have also measured magneto-dielectric property of polycrystalline TbMnO3 at the low temperature, which confirms the strong magneto-electric coupling in polycrystalline TbMnO3 below the transition temperature. (C) 2019 Elsevier B.V. All rights reserved.
Title:
Highly dispersive magnons with spin-gap-like features in the frustrated ferromagnetic S=1/2 chain compound Ca2Y2Cu5O10 detected by inelastic neutron scattering
Authors:
Matsuda, M; Ma, J; Garlea, VO; Ito, T; Yamaguchi, H; Oka, K; Drechsler, SL; Yadav, R; Hozoi, L; Rosner, H; Schumann, R; Kuzian, RO; Nishimoto, S Author Full Names: Matsuda, M.; Ma, J.; Garlea, V. O.; Ito, T.; Yamaguchi, H.; Oka, K.; Drechsler, S-L; Yadav, R.; Hozoi, L.; Rosner, H.; Schumann, R.; Kuzian, R. O.; Nishimoto, S.
Source:
PHYSICAL REVIEW B, 100 (10):10.1103/PhysRevB.100.104415 SEP 12 2019
Abstract:
We report inelastic neutron scattering experiments in Ca2Y2Cu5O10 and map out the full one-magnon dispersion which extends up to a record value of 53 meV for frustrated ferromagnetic (FM) edge-sharing CuO2 chain (FFESC) cuprates. A homogeneous spin-1/2 chain model with a FM nearest-neighbor (NN), an antiferromagnetic (AFM) next-nearest-neighbor (NNN) inchain, and two diagonal AFM interchain couplings (ICs) analyzed within linear spin-wave theory (LSWT) reproduces well the observed strong dispersion along the chains and a weak one perpendicularly. The ratio alpha = vertical bar J(a2)/J(a1)vertical bar fall of the FM NN and the AFM NNN couplings is found as similar to 0.23, close to the critical point alpha(c) = 1/4 which separates ferromagnetically and antiferromagnetically correlated spiral magnetic ground states in single chains, whereas alpha(c) > 0.25 for coupled chains is considerably upshifted even for relatively weak IC. Although the measured dispersion can be described by homogeneous LSWT, the scattering intensity appears to be considerably reduced at similar to 11.5 and similar to 28 meV. The gaplike feature at 11.5 meV is attributed to magnon-phonon coupling whereas based on density matrix renormalization group simulations of the dynamical structure factor the gap at 28 meV is considered to stem partly from quantum effects due to the AFM IC. Another contribution to that gap is ascribed to the intrinsic superstructure from the distorting incommensurate pattern of CaY cationic chains adjacent to the CuO2 ones. It gives rise to nonequivalent CuO4 units and Cu-O-Cu bond angles Phi and a resulting distribution of all exchange integrals. The J's fitted by homogeneous LSWT are regarded as average values. The record value of the FM NN integral J(1) = 24 meV among FFESC cuprates can be explained by a nonuniversal Phi(not equal 90 degrees) and Cu-O bond length dependent anisotropic mean direct FM Cu-O exchange (K) over bar (pd) similar to 120 meV, similar to a value of 105 meV for Li2CuO2, in accord with larger values for La2CuO4 and CuGeO3 (similar to 110 meV) reported by Braden et al. [Phys. Rev. B 54, 1105 (1996)] phenomenologically. Enhanced K-pd values are also needed to compensate a significant AFM J(dd) >= 6 meV from the dd channel, generic for FFESC cuprates but ignored so far.
Title:
Growth interactions between icosahedral quasicrystals
Authors:
Senabulya, N; Shahani, AJ Author Full Names: Senabulya, Nancy; Shahani, Ashwin J.
Source:
PHYSICAL REVIEW MATERIALS, 3 (9):10.1103/PhysRevMaterials.3.093403 SEP 11 2019
Abstract:
We investigate the solidification pathways of a population of icosahedral quasicrystals in a liquid through in situ synchrotron x-ray tomography. The wealth of three-dimensional space- and time-resolved data enables us to test the predictions of various models and theories of crystallization on a quasi-crystal-forming alloy. Remarkably, we find the general evolution equation-that accounts for the competing effects of growth, coalescence, and coarsening-fits well our experimental data on surface area concentration. Furthermore, we quantify the orientation selection, screening length, and coarsening rate of the dodecahedra, and compare these results to that of periodic crystals. The latter is a full order of magnitude smaller than that of elemental metal dendrites in the limit of zero volume fraction, a reflection of the low solid-liquid interfacial energy of the icosahedral phase. Our paper provides the critical input data for microstructural models used for integrated computational materials engineering of complex intermetallics, including quasicrystals.
Title:
Multiple charge density waves compete in ternary rare-earth nickel carbides, RNiC2 (R: Y, Dy, Ho, and Er)
Authors:
Maeda, H; Kondo, R; Nogami, Y Author Full Names: Maeda, Hiroyuki; Kondo, Ryusuke; Nogami, Yoshio
Source:
PHYSICAL REVIEW B, 100 (10):10.1103/PhysRevB.100.104107 SEP 9 2019
Abstract:
Single-crystal x-ray-diffraction experiments and electrical resistivity measurements were performed on intermetallic compounds of formula RNiC2 [rare earth (R): Y, Dy, Ho, and Er]. In the series of diffraction studies, we found three kinds of satellite reflections that had different wave vectors [incommensurate q(1)(ic):(0.5, 0.5 + eta, 0) and commensurate q(1)(c):(0.5, 0.5, 0) and q(2c):(0.5, 0.5, 0.5)] at temperatures where their resistivities show anomalies, such as a hump, a sharp increase, or a dent. Satellite reflections with nearly identical wave vectors have also been reported in RNiC2 composed of earlier lanthanide atoms (GdNiC2 and TbNiC2). These results indicate the formation of a charge density wave (CDW) also in RNiC2 studied in this paper. We found strong competition between the q(1ic) and the q(2c) CDWs in DyNiC2 and YNiC2, and that only the q(2c) CDW existed in HoNiC2 and ErNiC2. Based on the results obtained in the present paper and those of SmNiC2, GdNiC2, and TbNiC2 reported before, we discuss the CDW transitions in the RNiC2 family.
Title:
Formation of Incommensurate Charge Density Waves in Cuprates
Authors:
Miao, H; Fumagalli, R; Rossi, M; Lorenzana, J; Seibold, G; Yakhou-Harris, F; Kummer, K; Brookes, NB; Gu, GD; Braicovich, L; Ghiringhelli, G; Dean, MPM Author Full Names: Miao, H.; Fumagalli, R.; Rossi, M.; Lorenzana, J.; Seibold, G.; Yakhou-Harris, F.; Kummer, K.; Brookes, N. B.; Gu, G. D.; Braicovich, L.; Ghiringhelli, G.; Dean, M. P. M.
Source:
PHYSICAL REVIEW X, 9 (3):10.1103/PhysRevX.9.031042 SEP 6 2019
Abstract:
Although charge density waves (CDWs) are omnipresent in cuprate high-temperature superconductors, they occur at significantly different wave vectors, confounding efforts to understand their formation mechanism. Here, we use resonant inelastic x-ray scattering to investigate the doping- and temperature-dependent CDW evolution in La2-xBaxCuO4 (x = 0.115-0.155). We discover that the CDW develops in two stages with decreasing temperature. A precursor CDW with a quasicommensurate wave vector emerges first at high temperature. This doping-independent precursor CDW correlation originates from the CDW phase mode coupled with a phonon and "seeds" the low-temperature CDW with a strongly doping-dependent wave vector. Our observation reveals the precursor CDW and its phase mode as the building blocks of the highly intertwined electronic ground state in the cuprates.
Title:
Reply to comment on Couzi et al. (2018): a phenomenological model for structural phase transitions in incommensurate alkane/urea inclusion compounds
Authors:
Christensen, K; Williams, PA; Patterson, R; Palmer, BA; Couzi, M; Guillaume, F; Harris, KDM Author Full Names: Christensen, Kirsten; Williams, P. Andrew; Patterson, Rhian; Palmer, Benjamin A.; Couzi, Michel; Guillaume, Francois; Harris, Kenneth D. M.
Source:
ROYAL SOCIETY OPEN SCIENCE, 6 (8):10.1098/rsos.190518 AUG 2019
Abstract:
In a recentpaper (Couzi et al. 2018 R. Soc. open sci. 5, 180058. (doi: 10.1098/rsos.180058)), we proposed a new phenomenological model to account for the I <-> II <->"III" phase sequence in incommensurate n-alkane/urea inclusion compounds, which represents an alternative interpretation to that proposed in work of Toudic et al. In a Comment (Toudic et al. 2019 R. Soc. open sci. 6, 182073. (doi: 10.1098/rsos. 182073)), Toudic et al. have questioned our assignment of the superspace group of phase II of n-nonadecane/urea, which they have previously assigned, based on a (3 + 2)-dimensional superspace, as C222(1)(00 gamma)(10 delta). In this Reply, we present new results from a comprehensive synchrotron single-crystal X-ray diffraction study of n-nonadecane/urea, involving measurements as a detailed function of temperature across the I <-> II <->"III" phase transition sequence. Our results demonstrate conclusively that "main reflections" (h, k, l, 0) with h+k odd are observed in phase II of n-nonadecane/urea (including temperatures in phase II that are just below the transition from phase I to phase II), in full support of our assignment of the (3+ 1)-dimensional superspace group P212121(00.) to phase II. As our phenomenological model is based on phase II and phase '' III '' of this incommensurate material having the same (3+ 1)-dimensional superspace group P2(1)2(1)2(1)(00 gamma), it follows that the new X-ray diffraction results are in full support of our phenomenological model.
Title:
Comment on Couzi et al. (2018): a phenomenological model for structural transitions in incommensurate alkane/urea inclusion compounds
Authors:
Toudic, B; Guerin, L; Mariette, C; Frantsuzov, I; Rabiller, P; Ecolivet, C; Hollingsworth, MD Author Full Names: Toudic, B.; Guerin, L.; Mariette, C.; Frantsuzov, I.; Rabiller, P.; Ecolivet, C.; Hollingsworth, Mark D.
Source:
ROYAL SOCIETY OPEN SCIENCE, 6 (8):10.1098/rsos.182073 AUG 2019
Title:
Compression behavior of selected laser melted Al/quasicrystal composite lattice structure
Authors:
Kang, N; Lin, X; Xu, J; Joguet, D; Li, Q; Liao, HL; Huang, WD; Coddet, C Author Full Names: Kang, N.; Lin, X.; Xu, J.; Joguet, D.; Li, Q.; Liao, H. L.; Huang, W. D.; Coddet, C.
Source:
JOURNAL OF LASER APPLICATIONS, 31 (2):10.2351/1.5096152 MAY 2019
Abstract:
In this work, Al/quasicrystal (QC) composite lattice samples with several cellular sizes ranging from 1.5 to 5 mm were manufactured using selective laser melting (SLM). The porosity of all the designed lattice structure samples is fixed as 50%. The morphology of QC reinforcement on the top surface changes from micro desquamated to nano in situ reacted, as the cellular size increases. The result indicates that cellular size has a significant influence on the compressive behavior of SLM processed lattice samples. As the cellular size increases from 1.5 to 5 mm, the fractural mechanism changes from three stages of linear elastic-plateau-densification to two stages of elastic collapse. Moreover, both the first peak compressive strength and the strain at failure decrease, when the cellular size increases. Furthermore, the SLM processed lattice 3 sample, which possesses a large cellular size, broke into small fragments after the compression test.

Update: 18-Sep-2019

Title:
Supercell refinement: a cautionary tale
Authors:
Lovelace, J; Petricek, V; Murshudov, G; Borgstahl, GEO Author Full Names: Lovelace, Jeffrey; Petricek, Vaclav; Murshudov, Garib; Borgstahl, Gloria E. O.
Source:
ACTA CRYSTALLOGRAPHICA SECTION D-STRUCTURAL BIOLOGY, 75 852-860; 10.1107/S2059798319011082 9 SEP 2019
Abstract:
Theoretically, crystals with supercells exist at a unique crossroads where they can be considered as either a large unit cell with closely spaced reflections in reciprocal space or a higher dimensional superspace with a modulation that is commensurate with the supercell. In the latter case, the structure would be defined as an average structure with functions representing a modulation to determine the atomic location in 3D space. Here, a model protein structure and simulated diffraction data were used to investigate the possibility of solving a real incommensurately modulated protein crystal using a supercell approximation. In this way, the answer was known and the refinement method could be tested. Firstly, an average structure was solved by using the 'main' reflections, which represent the subset of the reflections that belong to the subcell and in general are more intense than the 'satellite' reflections. The average structure was then expanded to create a supercell and refined using all of the reflections. Surprisingly, the refined solution did not match the expected solution, even though the statistics were excellent. Interestingly, the corresponding superspace group had multiple 3D daughter supercell space groups as possibilities, and it was one of the alternate daughter space groups that the refinement locked in on. The lessons learned here will be applied to a real incommensurately modulated profilin-actin crystal that has the same superspace group.
Title:
Coordination shells and coordination numbers of the vertex graph of the Ammann-Beenker tiling
Authors:
Shutov, A; Maleev, A Author Full Names: Shutov, Anton; Maleev, Andrey
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 746-757; 10.1107/S2053273319008179 5 SEP 2019
Abstract:
The vertex graph of the Ammann-Beenker tiling is a well-known quasiperiodic graph with an eightfold rotational symmetry. The coordination sequence and coordination shells of this graph are studied. It is proved that there exists a limit growth form for the vertex graph of the Ammann-Beenker tiling. This growth form is an explicitly calculated regular octagon. Moreover, an asymptotic formula for the coordination numbers of the vertex graph of the Ammann-Beenker tiling is also proved.
Title:
Robust minimal matching rules for quasicrystals
Authors:
Kalugin, P; Katz, A Author Full Names: Kalugin, Pavel; Katz, Andre
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 669-693; 10.1107/S2053273319008180 5 SEP 2019
Abstract:
A unified framework is proposed for dealing with matching rules of quasiperiodic patterns, relevant for both tiling models and real-world quasicrystals. The approach is intended for extraction and validation of a minimal set of matching rules, directly from the phased diffraction data. The construction yields precise values for the spatial density of distinct atomic positions and tolerates the presence of defects in a robust way.
Title:
Twinning and incommensurate modulation in baumoite, Ba-0.5[(UO2)(3)O8Mo2(OH)(3)](H2O)(similar to 3), the first natural Ba uranyl molybdate
Authors:
Elliott, P; Plasil, J; Petricek, V; Cejka, J; Bindi, L Author Full Names: Elliott, Peter; Plasil, Jakub; Petricek, Vaclav; Cejka, Jiri; Bindi, Luca
Source:
MINERALOGICAL MAGAZINE, 83 (4):507-514; 10.1180/mgm.2019.20 AUG 2019
Abstract:
Baumoite, Ba-0.5[(UO2)(3)O8Mo2(OH)(3)](H2O)(similar to 3), is a new mineral found near Radium Hill, South Australia, where it occurs in a granite matrix associated with baryte, metatorbernite, phurcalite and kaolinite. Baumoite forms thin crusts of yellow to orange-yellow tabular to prismatic crystals. The mineral is translucent with a vitreous lustre and pale yellow streak. Crystals are brittle, the fracture is uneven and show one excellent cleavage. The Mohs hardness is similar to 21/2 . The calculated density is 4.61 g/cm(3). Optically, baumoite crystals are biaxial (-), with alpha = 1.716(4), beta= 1.761(4), gamma = 1.767(4) (white light); and 2V(calc) = 42.2 degrees. Electron microprobe analyses gave the empirical formula Ba0.87Ca0.03Al0.04U2.97Mo2.02P0.03O22H11.99, based on 22 O atoms per formula unit. The eight strongest lines in the powder X-ray diffraction pattern are [d(obs )angstrom (I) (hkl)]: 9.175(39)(12 (1) over bar), 7.450(100)(020), 3.554(20)(221), 3.365(31)(004, 202), 1255(31)(123, 30 (2) over bar), 3.209(28)(12 (4) over bar), 3.067(33)(30 (3) over bar, 222, 32 (2) over bar) and 2.977(20)(142). Single-crystal X-ray studies (R-1 = 5.85% for 1892 main reflections) indicate that baumoite is monoclinic, superspace group X2/m(a0g)0s with X = (0,1/2,0,1/2), with unit-cell parameters: a = 9.8337(3), b = 15.0436(5), c = 14.2055(6) angstrom, beta = 108.978(3)degrees, V= 1987.25(13) angstrom(3) and Z = 4. The crystal structure is twinned and incommensurately modulated and is based upon sheets of U6+ and Mo6+ polyhedra of unique topology. Four independent cationic sites partially occupied by Ba atoms are located between the sheets, together with H2O molecules.
Title:
Debye temperature of single-crystal Cr with incommensurate and commensurate magnetic structure
Authors:
Dubiel, SM; Zukrowski, J Author Full Names: Dubiel, Stanislaw M.; Zukrowski, Jan
Source:
EPL, 127 (2):10.1209/0295-5075/127/26002 JUL 2019
Abstract:
Single crystals of Cr and Cr3%Mn doped with similar to 0.2 at.% Sn-119 were studied by means of Sn-119-site Mossbauer spectroscopy. Mossbauer spectra recorded in the temperature range of 78-300 K were analyzed using a hyperfine field distribution method. Additionally, the spectra recorded on the Cr3%Mn sample were analyzed in terms of three sextets. Derived therefrom values of a center shift, CS, were fitted to the Debye model yielded values of the Debye temperature, T-D = 477(56) K for Cr and T-D = 282(16) :K for Cr3%Mn. The difference in the T-D-value can be regarded as evidence that a spin-phonon coupling is different for the incommensurate and commensurate antiferromagnetic magnetic structure of chromium. Copyright (C) EPLA, 2019

Update: 11-Sep-2019

Title:
Al-Cu-Fe quasicrystals as the anode for lithium ion batteries
Authors:
Lan, X; Wang, HJ; Sun, ZH; Jiang, XY Author Full Names: Lan, Xiao; Wang, Haijuan; Sun, Zhanhao; Jiang, Xunyong
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 805 942-946; 10.1016/j.jallcom.2019.07.148 OCT 15 2019
Abstract:
In this paper, Al-Cu-Fe quasicrystal alloy was used as the anode material for lithium-ion batteries. The first specific discharge capacity of quasicrystal was 204 mA h/g. Cyclic voltammetry showed that the oxidation peak of the Al-Cu-Fe quasicrystal was at about 1.4 V. The reduction peak was at 0.3 V. The Al-Cu-Fe quasicrystals had a higher Li-ion diffusion impedance and Warburg impedance in the first cycle. X-ray diffraction analysis demonstrated that Li atoms enter into the quasicrystal structure and can-not fully leave the quasicrystal during the first charge-discharge cycle, which induces an irreversible capacity. (C) 2019 Elsevier B.V. All rights reserved.
Title:
High-pressure structural change in the ferroelectric layered perovskite Sr2Nb2O7
Authors:
Alanis, J; Ojeda-Galvan, HJ; Rodriguez-Aranda, MC; Rodriguez, AG; Garcia, HM; Iniguez, J; Mendoza, ME; Navarro-Contreras, HR Author Full Names: Alanis, Javier; Joazet Ojeda-Galvan, Hiram; Rodriguez-Aranda, M. C.; Rodriguez, A. G.; Moreno Garcia, Harumi; Iniguez, Jorge; Eugenia Mendoza, Maria; Navarro-Contreras, Hugo R.
Source:
PHYSICAL REVIEW B, 100 (5):10.1103/PhysRevB.100.054110 AUG 26 2019
Abstract:
The structural changes of sintered powder samples of perovskite-slab layered polycrystalline Sr2Nb2O7 (SNO) ferroelectric compound subjected to high pressures are here investigated. The samples were prepared using a solid-state reaction in the presence (SNOE) or absence (SNO) of an applied electric field. Density functional theory (DFT) calculations including hydrostatic pressure indicate that SNO's ferroelectricity remains up to 25 GPa in the structure of space group Cmc2(1) derived from the condensation of one zone-center soft phonon. The predicted DFT theoretical structural changes are discussed and compared with the results of the experimental Raman spectra as a function of pressure. The pressure-dependent spectra were recorded from atmospheric pressure up to 11.5 and 13.5 GPa for SNOE and SNO, respectively. Both samples underwent a pressure induced phase transition from an incommensurate to a commensurate state at room temperature, SNO at Pi-c = 6.5 +/- 0.2 GPa, and SNOE at Pi-c = 6.9 +/- 0.3 GPa. The DFT calculations enable the identification of the change in phase to the orthorhombic structure with the space group Cmc2(1). The experimental values for Pi-c are in reasonably good agreement with the theoretical predicted value of similar to 7.3 GPa. After the critical pressures, the number of observable phonons decreases, that is, when the compound adopts a higher symmetry structure, several phonons vanish abruptly in both the SNO and SNOE samples, as expected. The Raman spectra for both samples show hysteresis effects, that is, after the pressure is removed, a few extra lines remain visible, as well as many relative intensity changes and broadenings for some phonon bands. The bulk moduli of the Sr2Nb2O7 before and after Pi-c are calculated resulting in 117.0 and 147.8 GPa, respectively. The Gruneisen parameters of the phonons observed are finally calculated and discussed.
Title:
Spin-Orbital Density Wave and a Mott Insulator in a Two-Orbital Hubbard Model on a Honeycomb Lattice
Authors:
Zhu, Z; Sheng, DN; Fu, L Author Full Names: Zhu, Zheng; Sheng, D. N.; Fu, Liang
Source:
PHYSICAL REVIEW LETTERS, 123 (8):10.1103/PhysRevLett.123.087602 AUG 23 2019
Abstract:
Inspired by the recent discovery of correlated insulating states in twisted bilayer graphene, we study a two-orbital Hubbard model on the honeycomb lattice with two electrons per unit cell. Based on the real-space density matrix renormalization group simulation, we identify a metal-insulator transition around U-c/t = 2.5-3. In the vicinity of U-c, we find strong spin-orbital density wave fluctuations at commensurate wave vectors, accompanied by weaker incommensurate charge density wave fluctuations. The spin-orbital density wave fluctuations are enhanced with increasing system sizes, suggesting the possible emergence of long-range order in the two-dimensional limit. At larger U, our calculations indicate a possible nonmagnetic Mott insulator phase without spin or orbital polarization. Our findings offer new insight into correlated electron phenomena in twisted bilayer graphene and other multiorbital honeycomb materials.
Title:
Pinched P-E hysteresis loops in Ba4Sm2Fe0.5Ti3Nb6.5O30 ceramic with tungsten bronze structure
Authors:
Li, C; Hong, JS; Huang, YH; Ma, X; Fu, MS; Li, J; Liu, XQ; Wu, YJ Author Full Names: Li, Cheng; Hong, Jiang Sheng; Huang, Yu Hui; Ma, Xiao; Fu, Mao Sen; Li, Juan; Liu, Xiao Qiang; Wu, Yong Jun
Source:
APPLIED PHYSICS LETTERS, 115 (8):10.1063/1.5111360 AUG 19 2019
Abstract:
In the present work, single-phase Ba4Sm2Fe0.5Ti3Nb6.5O30 ceramics with a tetragonal tungsten bronze structure (TTB) were synthesized. Pinched polarization-electric field (P-E) hysteresis loops are observed below the Curie temperature (T-c) in the as-synthesized ceramics. The origin of the loops was thoroughly studied using in situ TEM and XRD. The in situ selected area electron diffraction (SAED) patterns showed that the pinched loops originated from the coexistence of polar commensurate and nonpolar incommensurate superlattice reflections. In situ XRD results revealed increasing tetragonality with rising temperature, implying that the enhancement in octahedral tilting was closely related to the commensurate-incommensurate structural modulation.

Update: 5-Sep-2019

Title:
Low temperature magnetic and x-ray diffraction studies of YBa1-xSrxCuFeO5 (x=0, 0.5)
Authors:
Lai, S; Mukherjee, K; Yadav, CS Author Full Names: Lai, Surender; Mukherjee, K.; Yadav, C. S.
Source:
PHYSICA B-CONDENSED MATTER, 570 191-193; 10.1016/j.physb.2019.06.034 OCT 1 2019
Abstract:
We report low temperature magnetic and structural properties of Sr doped layered perovskite material YBaCuFeO5. YBaCuFeO5 is the antiferromagnetic compound with commensurate to incommensurate transition temperature at 200 K. Low temperature x-ray diffraction shows the lattice contraction effect with decreasing temperature. Below 15 K a strong bifurcation between the ZFC and FC curves has been observed in YBa0.5Sr0.5CuFeO5, which may arise due to lattice contraction effect which changes the interaction between the spin and the lattice.
Title:
Unique crystal structures and their applications as materials for Li1+x-yM1-x-3yTix+4yO3 (M = Nb or Ta, 0.07 <= x <= 0.33, 0 <= y <= 0.175)
Authors:
Nakano, H Author Full Names: Nakano, Hiromi
Source:
ADVANCED POWDER TECHNOLOGY, 30 (10):2003-2013; 10.1016/j.apt.2019.04.034 OCT 2019
Abstract:
In the Li2O-M2O5-TiO2 (M = Nb or Ta) system, Li1+x-yM1-x-3yTix+4yO3 (LMT) forms with a superstructure known as the M-phase, in which the periodical intergrowth layers are inserted in a matrix having a trigonal structure of LiMO3. We have been investigating this unique material focusing on its crystal structure, photoluminescence, and electrical properties. First, the formation area of the superstructure was compared between Nb- and Ta-systems and the difference was accurately analyzed. Second, to apply this unique material as a host material of phosphor, we synthesized new phosphors with various emission colors. Red phosphor, having a high PL intensity with an internal quantum efficiency of 98%, was successfully synthesized and used as a host material of the solid solution for the Ta system. Its high value was the result of the large centroid-to-cation distance of the Eu3+ position in the [(Li, Eu)O-12] polyhedral. Further still, toward application of the unique qualities of an electro-ceramic, we successfully fabricated oriented balk ceramics for the Nb system by slip casting in a strong magnetic field of 12 T. As a result, anisotropic electric properties were found along the c-axis, which were caused by the super-structure. We first clarified the mechanism showing that the anisotropic Qf value was due to anisotropic electron conductivity and anisotropic bonding strength within the superstructure. (C) 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
Title:
Structural, thermodynamic, thermal, and electron transport properties of single-crystalline LaPt2Si2
Authors:
Falkowski, M; Dolezal, P; Andreev, AV; Duverger-Nedellec, E; Havela, L Author Full Names: Falkowski, M.; Dolezal, P.; Andreev, A., V; Duverger-Nedellec, E.; Havela, L.
Source:
PHYSICAL REVIEW B, 100 (6):10.1103/PhysRevB.100.064103 AUG 20 2019
Abstract:
LaPt2Si2 in a single-crystalline form was subjected to structure, thermodynamic, thermal, and electron transport studies with a special emphasis on the structure phase transition appearing at T = 85 K. X-ray diffraction proves the noncentrosymmetric tetragonal structure of CaBe2Ge2-type (space group P4/nmm). The transition manifests as a small step of opposite sign in both lattice parameters, leaving almost no volume change. c decreases and a increases in the low-T phase, but the change of the c/a ratio does not exceed 0.1%. Additional periodicity, related to the supposed charge density wave (CDW) state, can be related to satellites corresponding to the wave vector q approximate to (0.36, 0, 0), which start to grow with temperature decreasing below 175 K and almost vanish (or relocate from the investigated ab plane) below the 85 K transition. Electrical resistivity reveals that the 85 K transition is hysteretic in temperature, with the difference between heating and cooling being almost 10 K, proving the first-order type of the transition. The transition dramatically enhances resistivity in the low-T state, pointing to a formation of a pseudogap. This, however, does allow a superconducting state, arising below T-c = 1.6 K. The temperature dependence up upper critical field is not compatible with the weak coupling BCS theory. Strong anisotropy of electronic structure and its dramatic changes at the structure transition are manifest also in thermal expansion and thermoelectric power. The Sommerfeld coefficient gamma = 7.8 mJ mol(-1) K-2 and Debye temperature of 205 K could be derived at low temperatures, but the specific heat has a strongly non-Debye like T dependence, which can be ascribed to a low-energy Einstein mode.
Title:
Superconducting phase diagram and nontrivial band topology of structurally modulated Sn1-xSbx
Authors:
Liu, B; Xiao, CC; Zhu, QQ; Wu, JF; Cui, YW; Wang, HD; Wang, ZC; Lu, YH; Ren, Z; Cao, GH Author Full Names: Liu, Bin; Xiao, Chengcheng; Zhu, Qinqing; Wu, Jifeng; Cui, Yanwei; Wang, Hangdong; Wang, Zhicheng; Lu, Yunhao; Ren, Zhi; Cao, Guang-han
Source:
PHYSICAL REVIEW MATERIALS, 3 (8):10.1103/PhysRevMaterials.3.084603 AUG 19 2019
Abstract:
We report the discovery of superconductivity in binary alloy Sn1-xSbx with x in the range of 0.43 to 0.6, which possesses a modulated rhombohedral structure due to the incommensurate ordering of Sn and Sb layers along the c axis. The specific heat measurements indicate a weakly coupled, fully gapped superconducting state in this homogeneity range with a maximum bulk T-c of 1.58 K at x = 0.46, though the electronic specific heat and Hall coefficients remain nearly x independent. The nonmonotonic dependence of the bulk T-c is discussed in relation to the effects of Sb-layer intercalation between the [Sn4Sb3] seven-layer lamellae that are the essential building blocks for superconductivity. On the other hand, a zero-resistivity transition is found to take place well above the bulk superconducting transition, and the corresponding T-c increases monotonically with x from 2.06 K to 3.29 K. This contrast, together with the uniform elements distribution revealed by energy dispersive x-ray mapping, implies that the resistive transition is due to the strain effect at the grain boundary rather than the compositional inhomogeneity. The first-principles calculations on the representative composition Sn 4 Sb 3 (x = 0.43) indicate that it is topologically nontrivial similar to Sb, but with different Z(2) invariants (0;111). Our results not only identify a second superconducting region in the Sn-Sb phase diagram, but also provide a viable platform to study the interplay between structural modulation, nontrivial band topology, and superconductivity.
Title:
Depth dependent ferroelectric to incommensurate/commensurate antiferroelectric phase transition in epitaxial lanthanum modified lead zirconate titanate thin films
Authors:
Gao, M; Tang, X; Dai, S; Li, JF; Viehland, D Author Full Names: Gao, Min; Tang, Xiao; Dai, Steve; Li, Jiefang; Viehland, D.
Source:
APPLIED PHYSICS LETTERS, 115 (7):10.1063/1.5113720 AUG 12 2019
Abstract:
Transmission electron microscopy was used to investigate the coexistence of ferroelectricity (FE) and antiferroelectricity (AFE) in (001) and (011) (Pb0.97, La0.02) (Zr0.95, Ti0.05) O3 (PLZT) epitaxial thin films. The depth resolved selected area electron diffraction (SAED) results revealed that the AFE phase was located in the near interface region, whereas the FE phase was found in the near surface region. A thickness dependent lattice parameter distribution was calculated using the SAED data, and a decrease in the c/a ratio was found to correlate with the transition from AFE to FE stability. Additionally, commensurate and incommensurate modulations in AFE PLZT were identified based on the observation of various superlattice reflections.

Update: 28-Aug-2019

Title:
Significantly improved cycling stability for electrochemical hydrogen storage in Ti1.4V0.6Ni alloy with TiN
Authors:
Yu, L; Lin, J; Liang, F; Wang, LM; Chang, LM; Wang, FK; Li, N Author Full Names: Yu, Lu; Lin, Jing; Liang, Fei; Wang, Limin; Chang, Limin; Wang, Fangkuo; Li, Na
Source:
MATERIALS RESEARCH BULLETIN, 118 10.1016/j.materresbull.2019.110509 OCT 2019
Abstract:
Ti1.4V0.6Ni alloy contained icosahedral quasicrystals can be electrochemically charged and discharged with the maximum capacity of approximately 270 mAh g(-1), however this alloy shows poor cycling stability, making it difficult to develop the practical application. Here, new TiN-added Ti1.4V0.6Ni composites are prepared by ball-milling. The electrochemical performance of the composites as negative active ingredient of Nickel-metal hydride(Ni-MH) battery is compared with Ti1.4V0.6Ni. Benefiting from the excellent catalysts for HER, electrical conductivity and resistance to oxidation/corrosion of TiN, TiN-added Ti1.4V0.6Ni composites exhibit excellent cycling stability as well as charge retention(89.7% after 24 h relaxation). The cycling capacity retention rate for these electrodes is approximately 80% after a preliminarytest of 50 continuous cycles. But meanwhile, the maxium discharge capacity falls into about 250 g(-1), and the electrocatalytic activity improvement is hightly demanded. This work presents a practical method for using TiN as an additive for enhancing the cycling stability of hydrogen storage alloy.
Title:
Whirling spin order in the quasicrystal approximant Au72Al14Tb
Authors:
Sato, TJ; Ishikawa, A; Sakurai, A; Hattori, M; Avdeev, M; Tamura, R Author Full Names: Sato, Taku J.; Ishikawa, Asuka; Sakurai, Akira; Hattori, Masashi; Avdeev, Maxim; Tamura, Ryuji
Source:
PHYSICAL REVIEW B, 100 (5):10.1103/PhysRevB.100.054417 AUG 13 2019
Abstract:
A neutron powder diffraction experiment has been performed on the quasicrystal approximant Au72Al14Tb14, a body-centered-cubic crystal of icosahedral spin clusters. The long-range antiferromagnetic order was confirmed at the transition temperature T-N = 10.4 K. The magnetic structure consists of noncoplanar whirling spins on the icosahedral clusters, arranged in an antiferroic manner. A simple icosahedral spin-cluster model with uniaxial anisotropy accounts well the whirling spin order as well as the in-field metamagnetic transition, indicating that the icosahedral symmetry is essential.
Title:
Theory of quantum oscillations in quasicrystals: Quantizing spiral Fermi surfaces
Authors:
Spurrier, S; Cooper, NR Author Full Names: Spurrier, Stephen; Cooper, Nigel R.
Source:
PHYSICAL REVIEW B, 100 (8):10.1103/PhysRevB.100.081405 AUG 13 2019
Abstract:
We show that electronic materials with disallowed rotational symmetries that enforce quasiperiodic order can exhibit quantum oscillations and that these are generically associated with exotic "spiral Fermi surfaces." These Fermi surfaces are self-intersecting, and characterized by a winding number of their surface tangent-a topological invariant-that is larger than one. We compute the nature of the quantum oscillations in two experimentally relevant settings which give rise to spiral Fermi surfaces: a "nearly-free-electron" quasicrystal, and 30 degrees twisted bilayer graphene.
Title:
The incommensurately modulated structures of volcanic plagioclase: displacement, ordering and phase transition
Authors:
Jin, SY; Xu, HF; Wang, XP; Zhang, DO; Jacobs, R; Morgan, D Author Full Names: Jin, Shiyun; Xu, Huifang; Wang, Xiaoping; Zhang, Dongzho; Jacobs, Ryan; Morgan, Dane
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 75 643-656; SI 10.1107/S2052520619006243 4 AUG 2019
Abstract:
Four basaltic phenocryst samples of plagioclase, with compositions ranging from An(48) (andesine) to An(64) (labradorite), have been studied with single-crystal X-ray and neutron diffraction techniques. The samples were also subjected to a heating experiment at 1100 degrees C for two weeks in an effort to minimize the Al-Si ordering in their structures. The average and the modulated structures of the samples (before and after the heating experiment) were compared, in order to understand the mechanism of the phase transition from the disordered C (1) over bar structure to the e-plagioclase structure. A comparison between the structures from neutron and X-ray diffraction data shows that the < T-O > distance does not solely depend on the Al occupancy as previously thought. A dramatic decrease of the Al-Si ordering is observed after heating at 1100 degrees C for two weeks for all four samples, with an obvious change in the intensities of the satellite reflections (e-reflections) in the diffraction pattern. Evident changes in the modulation period were also observed for the more calcic samples. No obvious change in the Ca-Na ordering was observed after the heating experiment. An in situ heating X-ray diffraction experiment was carried out on the andesine sample (An(48)) to study the change in the satellite intensity at high temperature. A dramatic weakening of the satellite peaks was observed between 477 degrees C and 537 degrees C, which strongly supports the displacive nature of the initiation of e2 ordering. Rigid-Unit Mode (RUM) analysis of the plagioclase structure suggests the initial position of the e-reflections is determined by the anti-RUMs in the framework.
Title:
Daliranite, PbHgAs2S5: determination of the incommensurately modulated structure and revision of the chemical formula
Authors:
Lanza, AE; Gemmi, M; Bindi, L; Mugnaioli, E; Paar, WH Author Full Names: Lanza, Arianna E.; Gemmi, Mauro; Bindi, Luca; Mugnaioli, Enrico; Paar, Werner H.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 75 711-716; SI 10.1107/S2052520619007340 4 AUG 2019
Abstract:
The incommensurately modulated crystal structure of the mineral daliranite has been determined using 3D electron diffraction data obtained on nanocrystalline domains. Daliranite is orthorhombic with a = 21, b = 4.3, c = 9.5 angstrom and shows modulation satellites along c. The solution of the average structure in the Pnma space group together with energy-dispersive X-ray spectroscopy data obtained on the same domains indicate a chemical formula of PbHgAs2S5, which has one S fewer than previously reported. The crystal structure of daliranite is built from columns of face-sharing PbS8 bicapped trigonal prisms laterally connected by Hg[2+4] polyhedra and (As23+S5)(4-) groups. The excellent quality of the electron diffraction data allows a structural model to be built for the modulated structure in superspace, which shows that the modulation is due to an alternated occupancy of a split As site.

Update: 22-Aug-2019

Title:
Comparison of quantum spin Hall states in quasicrystals and crystals
Authors:
Huang, HQ; Liu, F Author Full Names: Huang, Huaqing; Liu, Feng
Source:
PHYSICAL REVIEW B, 100 (8):10.1103/PhysRevB.100.085119 AUG 8 2019
Abstract:
We theoretically study the quantum spin Hall states in an Ammann-Beenker-type octagonal quasicrystal and a periodic snub-square crystal, both sharing the same basic building blocks. Although the bulk states show significant differences in localization and transport properties, the topological phases manifest similarly in the two systems. This indicates the robustness of the topological properties regardless of symmetry and periodicity. We characterize the topological nature of the two systems with a nonzero topological invariant (spin Bott index B-s and Z(2) invariant), robust metallic edge states, and quantized conductance. In spite of some quantitative differences, the topological phase diagram of the two systems also exhibits similar behaviors, indicating that the topological phase transition is mainly determined by similar interactions in the two systems regardless of their structural difference. This is also reflected by the observation that the transition point between the normal insulator and the quantum spin Hall state in both systems follows a universal linear scaling relation for topological phase transitions.
Title:
The origin of the modulated structure in Sr2CuO3+delta (delta=0.4): [CuO2] in-plane oxygen vacancy or apical oxygen vacancy?
Authors:
Shen, X; Cao, LP; Zhao, JF; Wang, WP; Liu, QQ; Yao, Y; Li, JJ; Gu, CZ; Chen, MW; Jin, CQ; Yu, RC Author Full Names: Shen, Xi; Cao, Li-Peng; Zhao, Jian-Fa; Wang, Wei-Peng; Liu, Qing-Qing; Yao, Yuan; Li, Jun-Jie; Gu, Chang-Zhi; Chen, Ming-Wei; Jin, Chang-Qing; Yu, Ri-Cheng
Source:
JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 10.1111/jace.16662
Abstract:
We propose the question of the modulated structures of copper oxide is caused by the [CuO2] in-plane oxygen vacancy or apical oxygen vacancy. Sr2CuO3+delta single-crystal samples were prepared using high-temperature and high-pressure methods. The major phase of Sr2CuO3+delta (delta = 0.4) single-crystal system is found to be constituted by the 5 root 2 a modulated structure with the Fmmm space group, which originates from the [CuO2] in-plane oxygen vacancy appearing in octahedral Cu-O. Besides, the presence of the [CuO2] in-plane oxygen vacancy may obliterate the superconductivity of the system. Experimental results deduce that the oxygen vacancy may appear in the apical oxygen sites in high-temperature copper oxide superconductors.
Title:
Formation of an Intermediate Valence Icosahedral Quasicrystal in the Au-Sn-Yb System
Authors:
Yamada, T; Nakamura, Y; Watanuki, T; Machida, A; Mizumaki, M; Nitta, K; Sato, A; Matsushita, Y; Tsai, AP Author Full Names: Yamada, Tsunetomo; Nakamura, Yoko; Watanuki, Tetsu; Machida, Akihiko; Mizumaki, Masaichiro; Nitta, Kiyofumi; Sato, Akira; Matsushita, Yoshitaka; Tsai, An-Pang
Source:
INORGANIC CHEMISTRY, 58 (14):9181-9186; 10.1021/acs.inorgchem.9b00801 JUL 15 2019
Abstract:
We report on the formation of a new icosahedral quasicrystal (iQC) in the Au-Sn-Yb alloy system. This iQC has a primitive icosahedral lattice with a lattice constant a(ico) of 0.5447(7) nm and a composition that was determined to be Au60.0Sn26.7Yb13.3. X-ray absorption spectroscopy measurement of the near Yb L-3 edge demonstrates that the Yb valence in the iQC is an intermediate valence between divalent (4f(14)) and trivalent (4f(13)) at ambient pressure and was determined to be 2.18+. The results are compared to those for a corresponding 2/1 cubic approximant crystal. The formation of this new iQC is discussed in terms of the atomic size factor (delta) and the valence electron-to-atom ratio (e/a).

Update: 15-Aug-2019

Title:
V-51-NMR study on the S=1/2 square lattice antiferromagnet K2V3O8
Authors:
Takeda, H; Yasuoka, H; Yoshida, M; Takigawa, M; Ghimire, NJ; Mandrus, D; Sales, BC Author Full Names: Takeda, H.; Yasuoka, H.; Yoshida, M.; Takigawa, M.; Ghimire, N. J.; Mandrus, D.; Sales, B. C.
Source:
PHYSICAL REVIEW B, 100 (5):10.1103/PhysRevB.100.054406 AUG 5 2019
Abstract:
Static and dynamic properties of the quasi-two-dimensional antiferromagnet K2V3O8 have been investigated by V-51-NMR experiments on nonmagnetic V5+ sites. Above the structural transition temperature T-S = 115 K, NMR spectra are fully compatible with the P4bm space-group symmetry. The formation of superstructure below T-S causes splitting of the NMR lines, which get broadened at lower temperatures so that individual peaks are not well resolved. Evolution of NMR spectra with magnetic field along the c axis below the magnetic transition temperature T-N similar to 4 K is qualitatively consistent with a simple Neel order and a spin-flop transition. However, a broad feature of the spectra does not rule out possible incommensurate spin structure. The spin-lattice relaxation rate 1/T-1 below T-N shows huge enhancement for a certain range of magnetic field, which is independent of temperature and attributed to cross relaxation due to anomalously large nuclear spin-spin coupling between V5+ and magnetic V4+ sites. The results indicate strong gapless spin fluctuations, which could arise from incommensurate orders or complex spin textures.
Title:
Interpretation of diffuse scattering using superspace crystallography
Authors:
Schmidt, EM; Neder, RB Author Full Names: Schmidt, Ella Mara; Neder, Reinhard B.
Source:
PHYSICAL REVIEW B, 100 (5):10.1103/PhysRevB.100.054201 AUG 2 2019
Abstract:
Single-crystal diffuse scattering is generally interpreted using correlation parameters that describe probabilities for certain configurations on a local scale. In this paper we present an interpretation of diffuse maxima using a disordered superspace approach. In (D + d)-dimensional superspace two modulation functions are disordered along the superspace axis a(s,i) for i = 1, . . . , D, while the periodicity along the internal dimensions is maintained. This simple approach allows the generation of substitutionally disordered model structures that show diffuse maxima of any width at any position in reciprocal space. The extinction rules that are introduced by superspace symmetry are also fulfilled by the diffuse maxima from structures generated using the disordered superspace approach. In this paper we demonstrate the disordered superspace approach using a simple two-dimensional binary substitutionally disordered system. The extension of the approach to (3 + d)-dimensional superspace is trivial. The treatment of displacement and magnetic disorder as well as size-effect-like distortions in a similar manner is possible.
Title:
Conduction electrons in aperiodic versus periodic structures: An ESR study of quasicrystalline i-Y(Gd)-Cd and its approximant Y(Gd)Cd-6
Authors:
Cabrera-Baez, M; Avila, MA; Rettori, C Author Full Names: Cabrera-Baez, M.; Avila, M. A.; Rettori, C.
Source:
PHYSICAL REVIEW B, 100 (1):10.1103/PhysRevB.100.014207 JUL 31 2019
Abstract:
A formal description of collective electronic states in condensed-matter systems lacking long-range periodicity remains a theoretical challenge. To experimentally explore the differences in electronic and magnetic behavior between metallic quasicrystals (QCs) and their conventional crystalline analogs [quasicrystal approximants (QCAs)], we have grown single crystals of Y1-xGdx-Cd6 (QCA) together with their QC counterparts i-Y1-xGdx-Cd for x = 0.006, 0.01, 0.1, and 1.00, and we carried out comparative T-dependent electron spin resonance (ESR) measurements. On the high Gd concentration side, x = 1.00, we confirm that GdCd6 adopts an antiferromagnetic ground state below T-N similar to 22 K, whereas i-Gd-Cd presents spin-glass-like behavior showing similar local and dynamical properties from the point of view of ESR. For the diluted samples, our ESR experimental results show similar local conduction electron polarization behavior at the Gd3+ site in all QC/QCA pairs investigated, supporting the validity of using QCAs as periodic representations of QCs in terms of short-range electronic interactions. However, there is a measurable difference in the Korringa relaxation rate (spin-flip relaxation process between the localized Gd3+ 4f electron and the delocalized s-type conduction electrons at the Fermi surface) between the QC/QCA pairs probably associated with the lack of periodicity. We expect that our comparative ESR study may provide support and motivation for the development of new theoretical approaches toward a generalized band-structure theory, contemplating condensed-matter systems beyond the scope of traditional periodicity.

Update: 8-Aug-2019

Title:
Elastic Properties of a FeGe2 Single Crystal
Authors:
Zainullina, RI; Milyaev, MA Author Full Names: Zainullina, R. I.; Milyaev, M. A.
Source:
PHYSICS OF THE SOLID STATE, 61 (7):1278-1283; 10.1134/S1063783419070321 JUL 2019
Abstract:
The report presents the results of studying the temperature dependences of the velocities of propagation of longitudinal and torsion waves and the internal friction in a tetragonal FeGe2 single crystal along crystallographic axes [100], [110], and [001]. At temperatures of magnetic phase transitions of T-1 approximate to 263 K and T-2 approximate to 289 K an abrupt decrease of sound velocities is detected. A high anisotropy of the internal friction is observed in the region of existence of an incommensurate magnetic structure (T-1 <= T <= T-2).
Title:
Transition Kinetics of Self-Assembled Supramolecular Dodecagonal Quasicrystal and Frank-Kasper sigma Phases in AB(n) Dendron-Like Giant Molecules
Authors:
Feng, XY; Liu, GX; Guo, D; Lang, KN; Zhang, RM; Huang, JH; Su, ZB; Li, YW; Huang, MJ; Li, T; Cheng, SZD Author Full Names: Feng, Xueyan; Liu, Gengxin; Guo, Dong; Lang, Kening; Zhang, Ruimeng; Huang, Jiahao; Su, Zebin; Li, Yiwen; Huang, Mingjun; Li, Tao; Cheng, Stephen Z. D.
Source:
ACS MACRO LETTERS, 8 (7):875-881; 10.1021/acsmacrolett.9b00287 JUL 2019
Abstract:
A series of noncrystalline AB dendron-like giant molecules DPOSS MPOSSn (n = 2-6, DPOSS: hydrophilic polyhedral oligomeric silsesquioxane (POSS) cage; MPOSS: hydrophobic POSS cage) were synthesized. These samples present a thermodynamically stable phase formation sequence from the hexagonal cylinder phase (plane group of P6mm), to the Frank Kasper (F-K) A15 phase (space group of Pm (3) over barn), and further to the F-K sigma phase (space group of P4(2)/mnm), with increasing the number of MPOSS in a single molecule (n, from 2 to 6). Moreover, for DPOSS MPOSS5 and DPOSS-MPOSS6, an intriguing dodecagonal quasicrystal (DQC) structure has been identified and revealed as a kinetic favorable metastable phase at lower temperatures, while the thermodynamically stable phase is the a phase. The detailed investigation of the transition kinetics between the DQC and a phase in these samples makes it possible to identify how the self-assembly directs the phase transition in terms of molecular and supramolecular aspects.

Update: 1-Aug-2019

Title:
TEM study of incommensurate superstructure in Pb1-0.5xNbx((Zr0.52Sn0.48)(0.955)Ti-0.045)(1-x)O-3 ceramics with 0-1 switching characteristic strain and high energy storage density
Authors:
Lyu, CG; Liu, YF; Lyu, YN; Qian, H; Li, M; Chen, FJ; Xi, H Author Full Names: Lyu, Chongguang; Liu, Yunfei; Lyu, Yinong; Qian, Hao; Li, Min; Chen, Fujun; Xi, Hao
Source:
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 30 (13):12375-12381; 10.1007/s10854-019-01595-4 JUL 2019
Abstract:
Pb1-0.5xNbx((Zr0.52Sn0.48)(0.955)Ti-0.045)(1-x)O-3(PNZST-100x (x=0.01, 0.02, 0.03, 0.04)) antiferroelectric (AFE) ceramics were prepared using a solid-state method. X-ray diffraction analysis indicates a structural evolution from the tetragonal phase to the pseudocubic phase. When x=0.02, the ceramic exhibits an enhanced energy storage density of 1.37J/cm(3), and a strain, with 0-1 switching characteristics, of 0.22%. Selected-area electron diffraction (SAED), high-resolution transmission electron microscopy imaging, and in-situ TEM analyses indicate that there are two kinds of superlattice reflections, including the 1/2(hkl) superlattice reflection (h, k, and l: all odd) and 1/6.67(a+b) one-dimensional incommensurate superlattice reflections. The origin of the 1/2(hkl) superlattice reflection was the tilting of a(-)a(-)a(-) oxygen octahedra. Therefore, the 1/2(hkl) reflections were no longer superlattice reflections, but fundamental reflections in the trigonal system; hence, the reciprocal vector was re-expressed as H, where h, k, and l are integers and (-h+k+l)=3n. The incommensurate structure of the PNZST-2 ceramic originated from the displacement of Pb2+.
Title:
Bridging the local configurations and crystalline counterparts of bulk metallic glass by nanocalorimetry
Authors:
Zhao, BG; Yang, B; Rodriguez-Viejo, J; Wu, MN; Schick, C; Zhai, QJ; Gao, YL Author Full Names: Zhao, Bingge; Yang, Bin; Rodriguez-Viejo, Javier; Wu, Mannan; Schick, Christoph; Zhai, Qijie; Gao, Yulai
Source:
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 8 (4):3603-3611; 10.1016/j.jmrt.2019.05.023 JUL-AUG 2019
Abstract:
The structural understanding of crystallization in bulk metallic glasses (BMGs) has attracted much attention while rapid crystallization occurring under controllable conditions is less involved. In this study, a Ce68Al10Cu20Co2 (at.%) BMG was thermally devitrified by differential scanning calorimetry (DSC) and nanocalorimetry. At a heating rate of 10 K/min by DSC, AlCe3 and Ce are the major crystalline phases after devitrification while Al13Co4 quasicrystals and Ce are the dominant phases in the crystallization products at a heating rate of 5000 K/s by nanocalorimetry. Attributing to the covalent-like bond in Al-Co atom pairs, Al13Co4 quasicrystals precipitate in the primary crystallization and work as the precursors associating local atomic configurations in the glassy state with crystalline phases after crystallization. Attributing to the enhanced mobility of Cu atoms, compositional redistribution occurs in the as-cast sample. On nanocalorimetry heating, an unambiguous discrepancy in the nucleation and growth of the nano-sized Al13Co4 quasicrystals is thus triggered, contributing to an obvious difference in the crystal size. This research unveils the distinct crystallization behaviors of Ce-based BMG on rapid heating. The formation of quasicrystals demonstrates the multi-stage crystallization on rapid heating and bridges the structural gap between local atomic configurations of metallic glasses and crystalline phases. (C) 2019 The Authors. Published by Elsevier B.V.

Update: 25-Jul-2019

Title:
New stable icosahedral quasicrystal in the system Al-Cu-Co-Fe
Authors:
Klyueva, M; Shulyatev, D; Andreev, N; Tabachkova, N; Sviridova, T; Suslov, A Author Full Names: Klyueva, Maria; Shulyatev, Dmitry; Andreev, Nikolay; Tabachkova, Natalia; Sviridova, Tatiana; Suslov, Alexey
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 801 473-477; 10.1016/j.jallcom.2019.06.056 SEP 15 2019
Abstract:
Based on the conceptual Al-Cu-(Fe + Co) phase diagram we found an optimal initial composition and developed a method to grow Al-Cu-Fe-Co single-grain quasicrystals. Our original two-stage cooling process includes (i) fast cooling of the melt down to the quasicrystalline single phase region with rate of similar to 165 K/h to prevent growing of nonquasicrystalline phases in the melt, and (ii) slow cooling down with rate of similar to 2-3 K/h to grow large (mm-size) single-grain quasicrystals. As a result a new stable quaternary Al-based icosahedral quasicrystal has been obtained. The chemical composition of the grown quasicrystal determined by both the energy dispersive X-ray analysis and inductively coupled plasma mass spectrometry was Al64.36Cu22.20CO3.05Fe10.39. Powder XRD and selected area electron diffraction were carried out for the phase identification and confirmed the icosahedral structure. The temperature dependencies of the electrical resistance measured on the oriented samples in the temperature range of 1.4 K-300 K is typical for icosahedral quasicrystals. (C) 2019 Elsevier B.V. All rights reserved.
Title:
Direct observation of growth and stability of Al-Cu-Fe quasicrystal thin films
Authors:
Parsamehr, H; Yang, CL; Liu, WT; Chen, SW; Chang, SY; Chen, LJ; Tsai, AP; Lai, CH Author Full Names: Parsamehr, Hadi; Yang, Chun-Liang; Liu, Wei-Ting; Chen, Shi-Wei; Chang, Shou-Yi; Chen, Lih-Juann; Tsai, An Pang; Lai, Chih-Huang
Source:
ACTA MATERIALIA, 174 1-8; 10.1016/j.actamat.2019.05.024 AUG 1 2019
Abstract:
Al-Cu-Fe based quasicrystal thin films exhibit unique surface and mechanical properties. To better understand the formation of the quasicrystal thin films, we observe direct growth of quasicrystals, prepared in a multilayer Al-Cu-Fe thin films with subsequent heat treatment, by in-situ synchrotron x-ray diffraction and in-situ transmission electron microscopy during heating and cooling. Using these two methods, we show that the ternary phase is more thermodynamically stable compared to the binary phases at temperature higher than 470 degrees C during the heating process, and quasicrystal formation occurs during the cooling process, specifically at 660 degrees C, after the sample has reached a liquid state. To distinguish quasicrystal from approximant crystals in the obtained thin film samples, we use high resolution x-ray diffraction to analyze the sample at room temperature. We reveal that the peak broadening increases monotonically along the twofold, threefold, and fivefold high-symmetry directions with the physical scattering vector but does not have systematic dependence on the phason momentum, which suggests that the thin film sample is indeed a quasicrystal instead of approximant crystals and it is almost free of phason strain. Our study provides a complete understanding of the growth mechanism for thin film Al-Cu-Fe quasicrystals, which is of particular importance for developing versatile applications of quasicrystal thin films. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Enhanced electrochemical hydrogen storage performance of Ti49Zr26Ni25 alloy by doping with Pd nanoparticles deposited MWCNTs
Authors:
Zhang, L; Zhang, YN; Lv, DF; Liu, H; Zhao, JX; Chen, P; Liu, WQ Author Full Names: Zhang, Lei; Zhang, Yinan; Lv, Dongfang; Liu, Heng; Zhao, Jianxun; Chen, Peng; Liu, Wanqiang
Source:
SOLID STATE SCIENCES, 94 138-144; 10.1016/j.solidstatesciences.2019.06.007 AUG 2019
Abstract:
Mechanical alloying and subsequent annealing are used to fabricate the Ti49Zr26Ni25 quasicrystal. A complexation-reduction method is employed to obtain the Pd deposited multiwall carbon nanotubes (Pd/MWCNTs). Composite of Ti49Zr26Ni25 mixed with Pd/MWCNTs is obtained via ball-milling. The composite alloy combines the characteristics of Pd in conjunction with the advantages of MWCNTs. Pd exhibits outstanding electrocatalytic activity and MWCNTs provide high conductivity and large specific surface area. The electrochemical performance and kinetics properties of the alloy electrodes for Ni/MH secondary batteries are studied. A maximum discharge capacity of 274.6 mAh/g is achieved for Ti49Zr26Ni25 + Pd/MWCNTs, remarkably higher than that for original Ti49Zr26Ni25 (208.9 mAh/g). In addition, the composite shows improved cyclic stability and high-rate dischargeability. The synergistic effect of Pd and MWCNTs can decrease charge-transfer resistance and accelerate the hydrogen transmission, thus improving the reaction kinetics and electrochemical activity of the electrode.
Title:
Conventional superconductivity in quasicrystals
Authors:
Araujo, RN; Andrade, EC Author Full Names: Araujo, Ronaldo N.; Andrade, Eric C.
Source:
PHYSICAL REVIEW B, 100 (1):10.1103/PhysRevB.100.014510 JUL 11 2019
Abstract:
Motivated by a recent experimental observation of superconductivity in the Al-Zn-Mg quasicrystal, we study the low-temperature behavior of electrons moving in the quasiperiodic potential of the Ammann-Beenker tiling in the presence of a local attraction. We employ the Bogoliubov-de Gennes approach for approximants of different sizes and determine the local pairing amplitude Delta(i) as well its spatial average, Delta(0), the superconducting order parameter. Due to the lack of periodicity of the octagonal tiling, the resulting superconducting state is inhomogeneous, but we find no evidence of the superconductivity islands, as observed in disordered systems, with Delta(i) -> 0 at T-c for all sites. In the weak-coupling regime, we find that the superconducting order parameter depends appreciably on the approximant size only if the Fermi energy sits at a pseudogap in the noninteracting density of states, with Delta(0) decreasing as the system size increases. These results are in line with the experimental observations for the Al-Zn-Mg quasicrystal, and they suggest that, despite their electronic structure, quasicrystals are prone to display conventional BCS-like superconductivity.
Title:
Tomonaga-Luttinger Liquid Spin Dynamics in the Quasi-One-Dimensional Ising-Like Antiferromagnet BaCo2V2O8
Authors:
Faure, Q; Takayoshi, S; Simonet, V; Grenier, B; Mansson, M; White, JS; Tucker, GS; Ruegg, C; Lejay, P; Giamarchi, T; Petit, S Author Full Names: Faure, Quentin; Takayoshi, Shintaro; Simonet, Virginie; Grenier, Beatrice; Mansson, Martin; White, Jonathan S.; Tucker, Gregory S.; Ruegg, Christian; Lejay, Pascal; Giamarchi, Thierry; Petit, Sylvain
Source:
PHYSICAL REVIEW LETTERS, 123 (2):10.1103/PhysRevLett.123.027204 JUL 10 2019
Abstract:
Combining inelastic neutron scattering and numerical simulations, we study the quasi-one-dimensional Ising anisotropic quantum antiferromagnet BaCo2V2O8 in a longitudinal magnetic field. This material shows a quantum phase transition from a Neel ordered phase at zero field to a longitudinal incommensurate spin density wave at a critical magnetic field of 3.8 T. Concomitantly, the excitation gap almost closes and a fundamental reconfiguration of the spin dynamics occurs. These experimental results are well described by the universal Tomonaga-Luttinger liquid theory developed for interacting spinless fermions in one dimension. We especially observe the rise of mainly longitudinal excitations, a hallmark of the unconventional low-field regime in Ising-like quantum antiferromagnetic chains.
Title:
Structural and electronic properties of the incommensurate host-guest Bi-III phase
Authors:
Kartoon, D; Makov, G Author Full Names: Kartoon, D.; Makov, G.
Source:
PHYSICAL REVIEW B, 100 (1):10.1103/PhysRevB.100.014104 JUL 9 2019
Abstract:
At high pressure, bismuth acquires a complex incommensurate host-guest structure, only recently discovered. Characterizing the structure and properties of this incommensurate phase from first principles is challenging owing to its nonperiodic nature. In this study we use large-scale density functional theory calculations to model commensurate approximants to the Bi-III phase, and in particular to describe the atomic modulations with respect to their ideal positions, shown here to strongly affect the electronic structure of the lattice and its stability. The equation of state and range of stability of Bi-III are reproduced in excellent agreement with experiment using a fully relativistic model. We demonstrate the importance of employing large unit cells for the accurate description of the geometric and electronic configuration of Bi-III. In contrast, accurate description of the equation of state of bismuth is found to be primarily sensitive to the choice of pseudopotential and exchange-correlation function, while almost completely insensitive to the commensurate approximation.
Title:
Effect of heat treatment on the microstructure and micromechanical properties of the rapidly solidified Mg61.7Zn34Gd4.3 alloy containing icosahedral phase
Authors:
Luo, WB; Xue, ZY; Mao, WM Author Full Names: Luo, Wen-bo; Xue, Zhi-yong; Mao, Wei-min
Source:
INTERNATIONAL JOURNAL OF MINERALS METALLURGY AND MATERIALS, 26 (7):869-877; 10.1007/s12613-019-1799-4 JUL 2019
Abstract:
In this paper, the microstructure evolution of the rapidly solidified (RS) Mg61.7Zn34Gd4.3 (at%, atomic ratio) alloy at high temperatures was investigated. The hardness and elastic modulus of the main precipitated phases were also analyzed and compared with those of the alpha-Mg matrix on the basis of nanoindentation tests. The results show that the RS alloy consists of either a petal-like icosahedral quasicrystal (IQC) phase (similar to 20 mu m) and block-shaped H1 phase (similar to 15 mu m) or IQC particles with an average grain size of similar to 107 nm as well as a small proportion of amorphous phase, which mainly depends on the holding time at the liquid temperature and the thickness of the ribbons. The IQC phase gradually transforms at 400 degrees C to a short-rod-shaped mu-phase (Mg28.6Zn63.8Gd7.7) with a hexagonal structure. The hardness of the IQC phase is higher than that of H1 phase, and both phases exhibit a higher hardness than the alpha-Mg matrix and the mu-phase. The elasticity of the H1 phase is superior to that of the alpha-Mg matrix. The IQC phase possesses a higher elastic modulus than H1 phase. The easily formed H1 phase exhibits the poorest plastic deformation capacity among these phases but a higher elastic modulus than the alpha-Mg matrix.

Update: 17-Jul-2019

Title:
Comprehensive study of the magnetic phase transitions in Tb3Co combining thermal, magnetic and neutron diffraction measurements
Authors:
Herrero, A; Oleaga, A; Gubkin, AF; Frontzek, MD; Salazar, A; Baranov, NV Author Full Names: Herrero, A.; Oleaga, A.; Gubkin, A. F.; Frontzek, M. D.; Salazar, A.; Baranov, N., V
Source:
INTERMETALLICS, 111 10.1016/j.intermet.2019.106519 AUG 2019
Abstract:
A comprehensive study of the magnetic phase transitions in Tb3Co has been undertaken combining different techniques. Using single crystal neutron diffraction in the paramagnetic state a weak crystal structure distortion from the room temperature orthorhombic structure of the Fe3C type described with the Pnma space group toward structure with lower symmetry has been observed with cooling below 100 K. At 81 K there is a second order phase transition to an antiferromagnetic incommensurate phase with the propagation vector k = (0.155, 0, 0). As derived from thermal diffusivity measurements, the critical exponents for this transition are very close to the 3D-Heisenberg universality class, proving that the magnetic interactions are short-range but with a deviation from perfect isotropy due to crystal field effects. At T-2 approximate to 70 K there is another magnetic phase transition to a ferromagnetic state whose character is shown to be weakly first order. The low temperature magnetic state has a non-coplanar ferromagnetic structure with strong ferromagnetic components of Tb magnetic moments along the crystallographic c-axis. The application of an external magnetic field B = 2 T along the c crystallographic axis suppresses the incommensurate antiferromagnetic phase and gives rise to the ferromagnetic phase. The magnetic entropy peak change as well as the refrigerant capacity indicate that Tb3Co is a competitive magnetocaloric material in this temperature range.
Title:
Significantly improved plasticity of bulk metallic glasses by introducing quasicrystal within high energy glass matrix
Authors:
Liu, BC; Zhang, QD; Wang, HJ; Li, XY; Zu, FQ Author Full Names: Liu, Bao-Chuan; Zhang, Qi-Dong; Wang, Hui-Juan; Li, Xiao-Yun; Zu, Fang-Qiu
Source:
INTERMETALLICS, 111 10.1016/j.intermet.2019.106504 AUG 2019
Abstract:
Many studies consistently report that quasicrystal-BMG (bulk metallic glass) composites usually exhibit limited plasticity. In this work, however, we demonstrate that quasicrystal embedded in high energy glass matrix could remarkably improve the plasticity of BMGs. By the method, a Zr-based quasicrystal-BMG composite successfully exhibits > 50.0% compressive plasticity and > 6.6% bending strain, which is much higher than similar to 3.0% compressive plasticity in the monolithic as-cast BMG. After introducing quasicrystal within high energy glass matrix, the lower formation energy and difficulty to propagate of shear bands contribute to the enhanced plasticity. This work provides a new strategy to overcome the brittleness of BMGs and greatly promotes the practical value of quasicrystal in improving plasticity of BMGs.
Title:
Microstructural evolution and age-hardening behavior of quasicrystal-reinforced Mg-Dy-Zn alloy
Authors:
Bi, GL; Han, YX; Jiang, J; Jiang, CH; Li, YD; Ma, Y Author Full Names: Bi, Guang-Li; Han, Yu-Xiang; Jiang, Jing; Jiang, Chun-Hong; Li, Yuan-Dong; Ma, Ying
Source:
RARE METALS, 38 (8):739-745; 10.1007/s12598-018-1089-8 AUG 2019
Abstract:
Microstructural evolution and age-hardening behavior of Mg-2Dy-6Zn (at%) alloy during solid-solution and aging treatment were investigated. The microstructure of as-cast alloy is composed of -Mg, Mg3DyZn6 (I) phase, Mg3Dy2Zn3 (W) phase, Mg(Zn,Dy) phase and a small amount of Mg0.97Zn0.03 phases. After solid-solution treatment (480 degrees C, 12h), all the I phases and most W phases dissolve into -Mg matrix and the remainder W phases transform into Mg(Dy,Zn) phase and MgDy3 phase. During aging treatment, I phase and small amounts of W phases co-precipitate from -Mg matrix, respectively. The alloy exhibits a peak hardness of HV 77.5 at 200 degrees C for 8h. The excellent age-hardening behavior of alloy is mainly attributed to the co-precipitation strengthening of I and W phases.
Title:
Microstructure and mechanical properties of AZ31 magnesium alloy reinforced by I-phase
Authors:
Wu, HR; Du, WB; Li, SB; Liu, K; Wang, ZH Author Full Names: Wu, Hai-Rong; Du, Wen-Bo; Li, Shu-Bo; Liu, Ke; Wang, Zhao-Hui
Source:
RARE METALS, 38 (8):733-738; 10.1007/s12598-014-0390-4 AUG 2019
Abstract:
The particles of Mg-Zn-Gd icosahedral quasi-crystal master alloy were added into the AZ31 alloy by the repeated plastic working (RPW) process in order to improve the mechanical properties of the AZ31 alloy at room temperature. The microstructure and tensile properties of composites were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and tensile testing machine at room temperature. The results suggest that the RPW process can effectively refine the matrix and make the I-phase particles distribute uniformly. The ultimate tensile strength and the yield strength of the composites reach their maximum values of 362.3 and 330.5MPa, respectively, when the amount of I-phase particles added is 10%. Meanwhile, the elongation of the composites decreases sharply.
Title:
Disordered Jahn-Teller-Polaron States in the Simple Perovskite Manganite Ca(1-x)La(x)nO(3) with 0.15 <= x <= 0.28
Authors:
Endo, T; Goto, T; Inoue, Y; Koyama, Y Author Full Names: Endo, Tomoki; Goto, Takamasa; Inoue, Yasuhide; Koyama, Yasumasa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 88 (7):10.7566/JPSJ.88.074708 JUL 15 2019
Abstract:
Among orbital-ordered states in manganites with strongly correlated electronic systems, both the C-type orbital-ordered (Ctype-OO) state and the charge- and orbital-ordered (COO) state have been reported in the simple perovskite Ca1-xLaxMnO3 (CLMO) with 0.15 <= x <= 0.28. To understand their formation from the disordered Pnma (DO) state with orthorhombic symmetry, the crystallographic features of prepared CLMO samples with 0.15 <= x <= 0.28 were examined mainly by transmission electron microscopy. When the temperature was lowered from the orthorhombic DO state for 0.15 <= x <= 0.23, referred to as Region I, the Ctype-OO state with monoclinic-P2(1)/m symmetry appeared via a disordered Jahn-Teller polaron (DJTP) state, which exhibited characteristic diffuse scattering around each DO reflection in electron diffraction patterns. For 0.23 <= x <= 0.28 as Region II, cooling from the DO state resulted in the appearance of the COO state via a similar DJTP state. In patterns obtained from the COO state, satellite reflections characterizing the state were confirmed to be due to both transverse and longitudinal lattice modulations. It was also found that the DJTP states in Regions I and II were present in T-N >= T >= T-Ct(yp)e-OO and T >= T-COO), respectively, and were identified as the precursor states, which appear prior to the formation of the Ctype-OO and COO states.
Title:
Emergent symmetries in block copolymer epitaxy
Authors:
Ding, Y; Gadelrab, KR; Rodriguez, KM; Huang, HJ; Ross, CA; Alexander-Katz, A Author Full Names: Ding, Yi; Gadelrab, Karim R.; Rodriguez, Katherine Mizrahi; Huang, Hejin; Ross, Caroline A.; Alexander-Katz, Alfredo
Source:
NATURE COMMUNICATIONS, 10 10.1038/s41467-019-10896-5 JUL 5 2019
Abstract:
The directed self-assembly (DSA) of block copolymers (BCPs) has shown promise in fabricating customized two-dimensional (2D) geometries at the nano- and meso-scale. Here, we discover spontaneous symmetry breaking and superlattice formation in DSA of BCP. We observe the emergence of low symmetry phases in high symmetry templates for BCPs that would otherwise not exhibit these phases in the bulk or thin films. The emergence phenomena are found to be a general behavior of BCP in various template layouts with square local geometry, such as 4(4) and 3(2)434 Archimedean tilings and octagonal quasicrystals. To elucidate the origin of this phenomenon and confirm the stability of the emergent phases, we implement self-consistent field theory (SCFT) simulations and a strong-stretching theory (SST)-based analytical model. Our work demonstrates an emergent behavior of soft matter and draws an intriguing connection between 2-dimensional soft matter self-assembly at the mesoscale and inorganic epitaxy at the atomic scale.
Title:
Magnetic phase diagram of the quantum spin chain compound SrCo2V2O8: a single-crystal neutron diffraction study
Authors:
Shen, L; Zaharko, O; Obirk, J; Jellyman, E; He, Z; Blackburn, E Author Full Names: Shen, L.; Zaharko, O.; Birk, J. O.; Jellyman, E.; He, Z.; Blackburn, E.
Source:
NEW JOURNAL OF PHYSICS, 21 10.1088/1367-2630/ab2b7a JUL 3 2019
Abstract:
We explore magnetic order in the quantum spin chain compound SrCo2V2O8 up to 14.9 T and down to 50 mK, using single-crystal neutron diffraction. Upon cooling in zero-field, commensurate antiferromagnetic (C-AFM) order with modulation vector k(C) = (0, 0, 1) develops below T-N similar or equal to 5.0 K. Applying an external magnetic field (H parallel to c axis) destabilizes this C-AFM order, leading to an order-disorder transition between T-N and similar to 1.5 K. Below 1.5 K, a commensurate to incommensurate (IC-AFM) transition occurs at 3.9 T, above which the magnetic reflections can be indexed by k(1C) = (0, 0,1 +/- delta l). The incommensurability N scales monotonically with H until the IC-AFM order disappears around 7.0 T. Magnetic reflections modulated by k(C) emerge again at higher fields. While the characters of the C-AFM, IC-AFM and the emergent AFM order in SrCo2V2O8 appear to fit the descriptions of the Neel, longitudinal spin density wave and transverse AFM order observed in the related compound BaCo2V2O8, our results also reveal several unique signatures that are not present in the latter, highlighting the inadequacy of mean-field theory in addressing the complex magnetic order in systems of this class.
Title:
X-ray magnetic diffraction under high pressure
Authors:
Wang, YS; Rosenbaum, TF; Feng, Y Author Full Names: Wang, Yishu; Rosenbaum, T. F.; Feng, Yejun
Source:
IUCRJ, 6 507-520; 10.1107/S2052252519007061 4 JUL 2019
Abstract:
Advances in both non-resonant and resonant X-ray magnetic diffraction since the 1980s have provided researchers with a powerful tool for exploring the spin, orbital and ion degrees of freedom in magnetic solids, as well as parsing their interplay. Here, we discuss key issues for performing X-ray magnetic diffraction on single-crystal samples under high pressure (above 40 GPa) and at cryogenic temperatures (4 K). We present case studies of both non-resonant and resonant X-ray magnetic diffraction under pressure for a spin-flip transition in an incommensurate spin-density-wave material and a continuous quantum phase transition of a commensurate all-in-all-out antiferromagnet. Both cases use diamond-anvil-cell technologies at third-generation synchrotron radiation sources. In addition to the exploration of the athermal emergence and evolution of antiferromagnetism discussed here, these techniques can be applied to the study of the pressure evolution of weak charge order such as charge-density waves, antiferro-type orbital order, the charge anisotropic tensor susceptibility and charge superlattices associated with either primary spin order or softened phonons.
Title:
Identification of Phase Transitions and Metastability in Dynamically Compressed Antimony Using Ultrafast X-Ray Diffraction
Authors:
Coleman, AL; Gorman, MG; Briggs, R; McWilliams, RS; McGonegle, D; Bolme, CA; Gleason, AE; Fratanduono, DE; Smith, RF; Galtier, E; Lee, HJ; Nagler, B; Granados, E; Collins, GW; Eggert, JH; Wark, JS; McMahon, MI Author Full Names: Coleman, A. L.; Gorman, M. G.; Briggs, R.; McWilliams, R. S.; McGonegle, D.; Bolme, C. A.; Gleason, A. E.; Fratanduono, D. E.; Smith, R. F.; Galtier, E.; Lee, H. J.; Nagler, B.; Granados, E.; Collins, G. W.; Eggert, J. H.; Wark, J. S.; McMahon, M. I.
Source:
PHYSICAL REVIEW LETTERS, 122 (25):10.1103/PhysRevLett.122.255704 JUN 28 2019
Abstract:
Ultrafast x-ray diffraction at the LCLS x-ray free electron laser has been used to resolve the structural behavior of antimony under shock compression to 59 GPa. Antimony is seen to transform to the incommensurate, host-guest phase Sb-II at similar to 11 GPa, which forms on nanosecond timescales with ordered guest-atom chains. The high-pressure bcc phase Sb-III is observed above similar to 15 GPa, some 8 GPa lower than in static compression studies, and mixed Sb-III/liquid diffraction are obtained between 38 and 59 GPa. An additional phase which does not exist under static compression, Sb-I', is also observed between 8 and 12 GPa, beyond the normal stability field of Sb-I, and resembles Sb-I with a resolved Peierls distortion. The incommensurate Sb-II high-pressure phase can be recovered metastably on release to ambient pressure, where it is stable for more than 10 ns.
Title:
Maximum supercooling studies in Ti39.5Zr39.5Ni21, Ti40Zr30Ni30, and Zr80Pt20 liquids-Connecting liquid structure and the nucleation barrier
Authors:
Sellers, ME; Van Hoesen, DC; Gangopadhyay, AK; Kelton, KF Author Full Names: Sellers, M. E.; Van Hoesen, D. C.; Gangopadhyay, A. K.; Kelton, K. F.
Source:
JOURNAL OF CHEMICAL PHYSICS, 150 (20):10.1063/1.5096188 MAY 28 2019
Abstract:
Almost three quarters of a century ago, Charles Frank proposed that the deep supercooling observed in metallic liquids is due to icosahedral short-range order (ISRO), which is incompatible with the long-range order of crystal phases. Some evidence in support of this hypothesis had been published previously. However, those studies were based on a small population of maximum supercooling measurements before the onset of crystallization. Here, the results of a systematic statistical study of several hundred maximum supercooling measurements on Ti39.5Zr39.5Ni21, Ti40Zr30Ni30, and Zr80Pt20 liquids are presented. Previous X-Ray and neutron scattering studies have shown that the structures of these liquid alloys contain significant amounts of ISRO. The results presented here show a small work of critical cluster formation (W* = 31-40 k(B)T) from the analysis of the supercooling data for the Ti39.5Zr39.5Ni21 liquid, which crystallizes to a metastable icosahedral quasicrystal. A much larger value (W* = 54-79 k(B)T and W* = 60-99 k(B)T) was obtained for the Ti40Zr30Ni30 and Zr80Pt20 liquids, respectively, which do not crystallize to an icosahedral quasicrystal. Taken together, these results significantly strengthen the validity of Frank's hypothesis. Published under license by AIP Publishing.
Title:
Chemical Bonding and Physical Properties in Quasicrystals and Their Related Approximant Phases: Known Facts and Current Perspectives
Authors:
Barber, EM Author Full Names: Macia Barber, Enrique
Source:
APPLIED SCIENCES-BASEL, 9 (10):10.3390/app9102132 MAY 2 2019
Abstract:
Quasicrystals are a class of ordered solids made of typical metallic atoms but they do not exhibit the physical properties that usually signal the presence of metallic bonding, and their electrical and thermal transport properties resemble a more semiconductor-like than metallic character. In this paper I first review a number of experimental results and numerical simulations suggesting that the origin of the unusual properties of these compounds can be traced back to two main features. For one thing, we have the formation of covalent bonds among certain atoms grouped into clusters at a local scale. Thus, the nature of chemical bonding among certain constituent atoms should play a significant role in the onset of non-metallic physical properties of quasicrystals bearing transition-metal elements. On the other hand, the self-similar symmetry of the underlying structure gives rise to the presence of an extended chemical bonding network due to a hierarchical nesting of clusters. This novel structural design leads to the existence of quite diverse wave functions, whose transmission characteristics range from extended to almost localized ones. Finally, the potential of quasicrystals as thermoelectric materials is discussed on the basis of their specific transport properties.
Title:
STATISTICAL DESCRIPTION OF DIFFRACTION PATTERN OF APERIODIC CRYSTALS
Authors:
Wolny, J; Buganski, I; Pytlik, L; Strzalka, R Author Full Names: Wolny, J.; Buganski, I; Pytlik, L.; Strzalka, R.
Source:
ARCHIVES OF METALLURGY AND MATERIALS, 64 (2):721-725; 10.24425/amm.2019.127604 2019
Abstract:
Modern crystallography faces a demanding challenge of describing atomic structure and diffraction pattern of quasicrystals, which, after 30 years of Shechtman's discovery, is still an open field of research. The classical approach based on the Braggs and Laue equations in three-dimensional space is useless, because the direct and the reciprocal lattices cannot be introduced for aperiodic systems. A standard solution to this problem, applied by number of scientists, is to retrieve periodicity in high dimensions. This is a purely mathematical approach with some difficulties from a point of view of physics. It is mathematically elegant, but not applicable to all aperiodic systems (e.g. Thue-Morse or Rudin-Shapiro sequences). It meets also a serious trouble in a proper description of structural defects, like phasons. In our opinion the most successful alternative to the multidimensional description is a statistical method of diffractional and structural analysis of aperiodic systems, also known as the average unit cell approach (AUC). In this work an application of the AUC method to selected aperiodic systems, including modulated structures, quasicrystals and covering clusters, is discussed in the form of a mini-review. A reader can find more details in the cited references.
Title:
Electronic properties of incommensurately modulated novel and complex materials
Authors:
Martino, E; Arakcheeva, A; Autes, G; Katrych, S; Yazyev, OV; Moll, PJW; Akrap, A; Forro, L Author Full Names: Martino, Edoardo; Arakcheeva, Alla; Autes, Gabriel; Katrych, Sergiv; Yazyev, Oleg V.; Moll, Philip J. W.; Akrap, Aim; Forro, Laszlo
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E96-E96; S 10.1107/S2053273318093798 AUG 2018
Title:
Investigation of the structure of the modulated doubly ordered perovskite NaLaCoWO6 and its reversible phase transition with a colossal temperature hysteresis
Authors:
Cohn, CV; Zuo, P; Darie, C; Klein, H Author Full Names: Cohn, Claire V.; Zuo, Peng; Darie, Celine; Klein, Holger
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E51-E51; S 10.1107/S2053273318094421 AUG 2018
Title:
Electron diffraction tomography of modulated minerals: the crystal structure of daliranite
Authors:
Gemmi, M; Lanza, A; Mugnaioli, E; Bindi, L; Paar, WH Author Full Names: Gemmi, Mauro; Lanza, Arianna; Mugnaioli, Enrico; Bindi, Luca; Paar, Werner H.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E321-E322; S 10.1107/S2053273318090356 AUG 2018
Title:
Application of the Generalized Penrose Tiling to the structure refinement of AICuRh decagonal quasicrystal
Authors:
Strzalka, R; Buganski, L; Chodyn, M; Wolny, J Author Full Names: Strzalka, Radoslaw; Buganski, Lreneusz; Chodyn, Maciej; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E98-E98; S 10.1107/S2053273318093762 AUG 2018
Title:
Multidimensional crossed cube tilings
Authors:
Ben-Abraham, S Author Full Names: Ben-Abraham, Shelomo
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E332-E332; S 10.1107/S2053273318090186 AUG 2018
Title:
Transitions toward complex electronic states and superperiodic structures in P4W16O56
Authors:
Duverger-Nedellec, E; Pautrat, A; Perez, O Author Full Names: Duverger-Nedellec, Elen; Pautrat, Alain; Perez, Olivier
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E95-E95; S 10.1107/S2053273318093816 AUG 2018
Title:
Exploring modulation in molecular crystals at low temperatures
Authors:
Sztylko, M; Hoser, A Author Full Names: Sztylko, Marcin; Hoser, Anna
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E327-E327; S 10.1107/S2053273318090289 AUG 2018
Title:
Aperidic structures and luminescent properties in the scheelite family
Authors:
Morozov, V; Abakumov, A; Hadermann, J; Khaikina, E; Deynekol, D; Lazoryak, B; Leonidov, I; Batuk, D; Batuk, M Author Full Names: Morozov, Vladimir; Abakumov, Artem; Hadermann, Joke; Khaikina, Elena; Deynekol, Dina; Lazoryak, Bogdan; Leonidov, Ivan; Batuk, Dmitry; Batuk, Maria
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E94-E94; S 10.1107/S2053273318093828 AUG 2018
Title:
On the symmetry of incommensurate magnetic structures
Authors:
Perez-Mato, JM; Elcoro, L; Madariaga, G; Aroyo, MI Author Full Names: Manuel Perez-Mato, J.; Elcoro, Luis; Madariaga, Gotzon; Aroyo, Mois I.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E100-E101; S 10.1107/S2053273318093737 AUG 2018
Title:
AlCuRh decagonal quasicrystal - new techniques for the refinement
Authors:
Buganski, I; Strzalka, R; Wolny, J Author Full Names: Buganski, Ireneusz; Strzalka, Radoslaw; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E328-E328; S 10.1107/S2053273318090265 AUG 2018
Title:
Clusters in the Al13TM4 quasicrystalline approximants : role on the surface structures and properties
Authors:
Gaudry, E Author Full Names: Gaudry, Emilie
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E96-E97; S 10.1107/S2053273318093786 AUG 2018

Update: 11-Jul-2019

Title:
Low-temperature thermal conductivity and magnetic transitions of the kagome-staircase compound Ni3V2O8
Authors:
Zhao, ZY; Li, QJ; Liu, XG; Rao, X; Che, HL; Chu, LG; He, ZZ; Zhao, X; Sun, XF Author Full Names: Zhao, Z. Y.; Li, Q. J.; Liu, X. G.; Rao, X.; Che, H. L.; Chu, L. G.; He, Z. Z.; Zhao, X.; Sun, X. F.
Source:
PHYSICAL REVIEW B, 99 (22):10.1103/PhysRevB.99.224428 JUN 25 2019
Abstract:
The kagome-staircase compound Ni3V2O8 is an attractive multiferroic material exhibiting rich phase diagrams. However, the magnetic properties and magnetic transitions have been studied only above 1.3 K. In this work, we study the thermal conductivity kappa of Ni3V2O8 single crystals at low temperatures down to 0.3 K and in magnetic fields up to 14 T. In zero field, the magnetic transitions from the low-temperature incommensurate (LTI) phase to the commensurate phase (C) and then to a second commensurate phase (C' yield anomalies in kappa(T) curves at T-LC = 3.7 K and T-CC' = 2.0 K, respectively, which indicates a significant phonon scattering by the critical spin fluctuations. When the field is applied along the a axis, the field dependence of kappa displays four anomalies associated with different magnetic transitions and reveals an undetected magnetic state at subkelvin temperatures. In addition, the kappa(B) curves are found to depend not only on the history but also on the magnitude of the applied field. When the field is applied along the b axis, a high-field phase located above the LTI and high-temperature incommensurate phases is revealed.
Title:
Stacking sequence variations in vaterite resolved by precession electron diffraction tomography using a unified superspace model
Authors:
Steciuk, G; Palatinus, L; Rohlicek, J; Ouhenia, S; Chateigner, D Author Full Names: Steciuk, Gwladys; Palatinus, Lukas; Rohlicek, Jan; Ouhenia, Salim; Chateigner, Daniel
Source:
SCIENTIFIC REPORTS, 9 10.1038/s41598-019-45581-6 JUN 24 2019
Abstract:
As a metastable phase, vaterite is involved in the first step of crystallization of several carbonate-forming systems including the two stable polymorphs calcite and aragonite. Its complete structural determination would consequently shed important light to understand scaling formation and biomineralization processes. While vaterite's hexagonal substructure (a(0) similar to 4.1 angstrom and c(0) similar to 8.5 angstrom) and the organization of the carbonate groups within a single layer is known, conflicting interpretations regarding the stacking sequence remain and preclude the complete understanding of the structure. To resolve the ambiguities, we performed precession electron diffraction tomography (PEDT) to collect single crystal data from 100 K to the ambient temperature. The structure was solved ab initio and described over all the temperature range using a unified modulated structure model in the superspace group C12/c1(alpha 0 gamma)00 with a = a(0) = 4.086(3) angstrom, b = root 3a(0) = 7.089(9) angstrom, c = c(0) = 8.439(9) angstrom, alpha=beta=gamma=90 degrees and q = 2/3a* + gamma c*. At 100 K the model presents a pure 4-layer stacking sequence with gamma = 1/2 whereas at the ambient temperature, ordered stacking faults are introduced leading to gamma < 1/2. The model was refined against PEDT data using the dynamical refinement procedure including modulation and twinning as well as against x-ray powder data by the Rietveld refinement.
Title:
Effect of exchange interaction on electronic instabilities in the honeycomb lattice: A functional renormalization group study
Authors:
O, SJ; Kim, YH; Rim, HY; Pak, HC; Im, SJ Author Full Names: O, Song-Jin; Kim, Yong-Hwan; Rim, Ho-Yong; Pak, Hak-Chol; Im, Song-Jin
Source:
PHYSICAL REVIEW B, 99 (24):10.1103/PhysRevB.99.245140 JUN 21 2019
Abstract:
The impact of local and nonlocal density-density interactions on the electronic instabilities in the honeycomb lattice is widely investigated. Some early studies proposed the emergence of interaction-induced topologically nontrivial phases, but recently, it was denied in several works including renormalization group calculations with refined momentum resolution. We use the truncated unity functional renormalization group to study the many-body instabilities of electrons on the half-filled honeycomb lattice, focusing on the effect of the exchange interaction. We show that varying the next-nearest-neighbor repulsion and nearest-neighbor exchange integral can lead to diverse ordered phases, namely, the quantum spin Hall, the spin-Kekule, and some spin- and charge-density-wave phases. The quantum spin Hall phase can be induced by a combination of the ferromagnetic exchange and pair hopping interactions. Another exotic phase, the spin-Kekule phase, develops in a very small region of the parameter space considered. We encounter the three-sublattice charge-density-wave phase in a large part of the parameter space. It is replaced by the incommensurate charge density wave when increasing the exchange integral. In order to reduce the computational effort, we derive the explicit symmetry relations for the bosonic propagators of the effective interaction and propose a linear-response-based approach for identifying the form factor of order parameter. Their efficiencies are confirmed by numerical calculations in our work.
Title:
Suppression of charge density wave order by disorder in Pd-intercalated ErTe3
Authors:
Straquadine, JAW; Weber, F; Rosenkranz, S; Said, AH; Fisher, AIR Author Full Names: Straquadine, J. A. W.; Weber, F.; Rosenkranz, S.; Said, A. H.; Fisher, And I. R.
Source:
PHYSICAL REVIEW B, 99 (23):10.1103/PhysRevB.99.235138 JUN 19 2019
Abstract:
Disorder is generically anticipated to suppress long range charge density wave (CDW) order. We report transport, thermodynamic, and scattering experiments on PdxErTe3, a model CDW system with disorder induced by intercalation. The pristine parent compound (x = 0) shows two separate, mutually perpendicular, incommensurate unidirectional CDW phases setting in at 270 K and 165 K. In this work we present measurements on a finely-spaced series of single crystal samples, in which we track the suppression of signatures corresponding to these two parent transitions as the Pd concentration increases. At the largest values of x, we observe complete suppression of long range CDW order in favor of superconductivity. We also report evidence from electron and x-ray diffraction which suggests a tendency toward short-range ordering along both wave vectors which persists even well above the crossover temperature and comment on the origin and consequences of this effect. Based on this work, PdxErTe3 appears to provide a promising model system for the study of the interrelation of charge order and superconductivity in the presence of quenched disorder, for pseudotetragonal materials.
Title:
Commensurate Nb2Zr5O15: Accessible Within the Field Nb2ZrxO2x+5 After All
Authors:
Wiedemann, D; Orthmann, S; Muhlbauer, MJ; Lerch, M Author Full Names: Wiedemann, Dennis; Orthmann, Steven; Muehlbauer, Martin J.; Lerch, Martin
Source:
CHEMISTRYOPEN, 8 (4):447-450; 10.1002/open.201900043 APR 2019
Abstract:
Doped niobium zirconium oxides are applied in field-effect transistors and as special-purpose coatings. Whereas their material properties are sufficiently known, their crystal structures remain widely uncharacterized. Herein, we report on the comparably mild sol-gel synthesis of Nb2Zr5O15 and the elucidation of its commensurately modulated structure via neutron diffraction. We describe the structure using the most appropriate superspace as well as the convenient supercell approach. It is part of an -PbO2-homeotypic field with the formula Nb2ZrxO2x+5, which has previously been reported only for x5.1, and is closely related to the structure of Hf3Ta2O11. The results, supported by X-ray diffraction and additional synthesis experiments, are contextualized within the existing literature. Via the sol-gel route, metastable Nb-Zr-O compounds and their heavier congeners are accessible that shed light on possible structures of these commercially utilized materials.

Update: 27-Jun-2019

Title:
Growth of layered Lu(2)Fe(3)O(7 )and Lu3Fe4O10 single crystals exhibiting long-range charge order via the optical floating-zone method
Authors:
Hammouda, SS; Angst, M Author Full Names: Hammouda, S. S.; Angst, M.
Source:
JOURNAL OF CRYSTAL GROWTH, 521 50-54; 10.1016/j.jcrysgro.2019.06.003 SEP 1 2019
Abstract:
We report the controlled growth of single crystals of intercalated layered Lu1+n Fe2+nO4+3n-delta(n = 1,2) with different oxygen stoichiometries delta. For the first time crystals sufficiently stoichiometric to exhibit superstructure reflections in X-ray diffraction attributable to charge ordering were obtained. The estimated correlation lengths tend to be smaller than for not intercalated LuFe2O4. For Lu2Fe3O7, two different superstructures were observed, one an incommensurate zigzag pattern similar to previous observations by electron diffraction, the other an apparently commensurate pattern with (1/31/30) propagation. Implications for the possible charge order in the bilayers are discussed. Magnetization measurements suggest reduced magnetic correlations and the absence of an antiferromagnetic phase.
Title:
Synthesis and characterization of Sn reinforced Al-Cu-Fe quasicrystalline matrix nanocomposite by mechanical milling
Authors:
Shadangi, Y; Shivam, V; Singh, MK; Chattopadhyay, K; Basu, J; Mukhopadhyay, NK Author Full Names: Shadangi, Yagnesh; Shivam, Vikas; Singh, Manish Kumar; Chattopadhyay, Kausik; Basu, Joysurya; Mukhopadhyay, N. K.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 797 1280-1287; 10.1016/j.jallcom.2019.05.128 AUG 15 2019
Abstract:
The influence of mechanical milling (MM), primarily on microstructure and phase evolution in Al62.5Cu25Fe12.5 (at%) quasicrystalline (IQC) matrix reinforced with varying volume fraction of Sn has been investigated by means of X-ray diffraction (XRD), scanning & transmission electron microscopy (SEM and TEM) and differential scanning calorimetry (DSC) methods. It was observed that with increasing the milling duration, the IQC phase transforms to crystalline B2 phase [Al (Cu, Fe) and Pm3m, a = 0.29 nm]. In SEM and TEM analysis, it was found that both IQC and Sn particles are refined during MM. The XRD and TEM results confirm the formation nanostructured matrix consisting of nanocrystalline B2 phase along with minor IQC phase reinforced with ultrafine grained Sn particles after 40 h of MM. The STEM-EDS results show a homogenous distribution of elements (Al, Cu, Fe). The Sn particles were immiscible in a matrix consisting of B2 and IQC phase as indicated by XRD and TEM investigations. (C) 2019 Elsevier B.V. All rights reserved.
Title:
Comprehensive magnetic phase diagrams of the polar metal Ca-3(Ru0.95Fe0.05)(2)O-7
Authors:
Lei, SM; Chikara, S; Puggioni, D; Peng, J; Zhu, MZ; Gu, MQ; Zhao, WW; Wang, Y; Yuan, YK; Akamatsu, H; Chan, MHW; Ke, XL; Mao, ZQ; Rondinelli, JM; Jaime, M; Singleton, J; Weickert, F; Zapf, VS; Gopalan, V Author Full Names: Lei, Shiming; Chikara, Shalinee; Puggioni, Danilo; Peng, Jin; Zhu, Mengze; Gu, Mingqiang; Zhao, Weiwei; Wang, Yu; Yuan, Yakun; Akamatsu, Hirofumi; Chan, Moses H. W.; Ke, Xianglin; Mao, Zhiqiang; Rondinelli, James M.; Jaime, Marcelo; Singleton, John; Weickert, Franziska; Zapf, Vivien S.; Gopalan, Venkatraman
Source:
PHYSICAL REVIEW B, 99 (22):10.1103/PhysRevB.99.224411 JUN 10 2019
Abstract:
Polar metals exist as a rather unique class of materials as they combine two seemingly mutually exclusive properties (polar order and metallicity) in one system. So far only a few polar metals have been unambiguously identified; the magnetic ones are exceptionally rare. Here we investigate a 5% Fe-doped polar metal Ca3Ru2O7, via electrical transport, magnetization, microstrain, and optical second-harmonic generation measurements. We report the full magnetic phase diagrams (in the field-temperature space) for magnetic field H parallel to a and H parallel to b, which exhibit distinct field-dependent magnetizations behavior. In particular, for H parallel to a we found a ferromagnetic incommensurate spin structure, which is absent in the pure Ca3Ru2O7. We propose a microscopic spin model to understand this behavior, highlighting the role of Fe doping in tipping the delicate balance of the underlying exchange-interaction energy in this system.
Title:
Experimental realization of a semiconducting quasicrystalline approximant in Al-Si-Ru system by band engineering
Authors:
Iwasaki, Y; Kitahara, K; Kimura, K Author Full Names: Iwasaki, Yutaka; Kitahara, Koichi; Kimura, Kaoru
Source:
PHYSICAL REVIEW MATERIALS, 3 (6):10.1103/PhysRevMaterials.3.061601 JUN 7 2019
Abstract:
We found that an Al-Si-Ru cubic quasicrystalline approximant has a semiconducting band structure by performing an orbital analysis based on density functional theory. These semiconducting transport properties have been confirmed in an experimentally synthesized sample. The temperature dependences of the electrical conductivity and the Seebeck coefficient were consistent with the trends of an intrinsic semiconductor with a band gap of 0.15 eV above 350 K. The lattice thermal conductivity had a low value of approximately 1.0 W m(-1) K-1 above 400 K, which is close to the theoretical minimum.
Title:
Incommensurate magnetism in K2MnS2-xSex and prospects for tunable frustration in a triangular lattice of pseudo-1D spin chains
Authors:
Bhutani, A; Behera, P; McAuliffe, RD; Cao, HB; Huq, A; Kirkham, MJ; dela Cruz, CR; Woods, T; Shoemaker, DP Author Full Names: Bhutani, Ankita; Behera, Piush; McAuliffe, Rebecca D.; Cao, Huibo; Huq, Ashfia; Kirkham, Melanie J.; dela Cruz, Clarina R.; Woods, Toby; Shoemaker, Daniel P.
Source:
PHYSICAL REVIEW MATERIALS, 3 (6):10.1103/PhysRevMaterials.3.064404 JUN 5 2019
Abstract:
We report a detailed investigation of K2MnS2 and K2MnSe2 from the K2MnS2 structure type and their magnetic solid solution K2MnS2-xSex and find that compounds of this structure type consist of strongly coupled pseudo-one-dimensional antiferromagnetic chains that collectively represent a frustrated two-dimensional triangular antiferromagnet. Bulk samples of K2MnS2-xSex with 0 <= x <= 2 are characterized using x-ray diffraction, neutron diffraction, magnetization, and heat-capacity measurements. An incommensurate cycloid magnetic structure with a magnetic propagation vector k = [0.58 0 1] is observed for all samples in K2MnS2-xSex, and the ordering is robust despite a 12% increase in cell volume. Geometric frustration of chains results in incommensurability along a and a two-step magnetic transition. The varying geometries accessible in compounds of this structure type are presented as promising avenues to tune frustration.
Title:
Emergent localization in dodecagonal bilayer quasicrystals
Authors:
Park, MJ; Kim, HS; Lee, S Author Full Names: Park, Moon Jip; Kim, Hee Seung; Lee, SungBin
Source:
PHYSICAL REVIEW B, 99 (24):10.1103/PhysRevB.99.245401 JUN 4 2019
Abstract:
Long range order in the absence of translational symmetry gives rise to drastic revolution of our common knowledge in condensed-matter physics. Quasicrystals, as such an unconventional system, became a plethora to test our insights and to find exotic states of matter. In particular, electronic properties in quasicrystals have gotten lots of attention along with their experimental realization and controllability in twisted bilayer systems. In this work, we study how quasicrystalline order in bilayer systems can induce unique localization of electrons without any extrinsic disorders. We focus on the dodecagonal quasicrystal that has been demonstrated in twisted bilayer graphene system in recent experiments. In the presence of a small gap, we show the localization generically occurs due to the nonperiodic nature of quasicrystals, which is evidenced by the inverse participation ratio and the energy-level statistics. We understand the origin of such localization by approximating the dodecagonal quasicrystals as an impurity scattering problem.
Title:
Study of Penrose Tiling Using Parameterization Method
Authors:
Shutov, AV; Maleev, AV Author Full Names: Shutov, A. V.; Maleev, A. V.
Source:
CRYSTALLOGRAPHY REPORTS, 64 (3):376-385; 10.1134/S1063774519030234 MAY 2019
Abstract:
A new description of Penrose tiling, based on parameterization of tiling rhombuses, has been obtained. A method making it possible to describe clusters and coordination environments in Penrose tiling in terms of parameters is developed. The parameters of all possible types of the first coordination environments in Penrose tiling are found. A new proof is obtained that the form of layer-by-layer growth of Penrose tiling is a regular decagon, and the vertices of this decagon are calculated.

Update: 19-Jun-2019

Title:
Control of wave propagation response using quasi crystals: A formulation based on spectral finite element
Authors:
Chellappan, V; Gopalakrishnan, S; Mani, V Author Full Names: Chellappan, Vinita; Gopalakrishnan, S.; Mani, V
Source:
MECHANICS OF ADVANCED MATERIALS AND STRUCTURES, 26 (7):579-600; 10.1080/15376494.2017.1410901 APR 3 2019
Abstract:
This paper presents wave propagation studies in quasi crystal structures and quasi crystal reinforced aluminium structures. The analysis is performed using frequency domain spectral finite element formulation. The analysis considers different 2-D decagonal and 3-D icosahedral quasi crystals. First, wave propagation analysis of quasi crystal structure alone is performed and the propagation of phonon and phason modes for different quasi crystals are studied. The study includes the propagation of axial and transverse wave responses in these quasi crystals. The study has found that the amplitude of the phason modes is very small compared to the phonon modes and the increase of the phason mode content (through increase in R) increases the phason mode amplitude, without affecting the phonon mode amplitudes. It is shown that the dominant axial phonon mode is non-dispersive and the dominant flexural phonon mode is dispersive. In the next study, the aluminium beam structure is reinforced with different quasi crystals in different configurations and the wave propagation of axial and transverse responses are studied. For all the combinations of quasi crystal aluminium beam combination, there is substantial suppression of responses both for the axial and the bending responses. Unsymmetrical configuration produces substantial non-dominant phonon modes which propagate dispersively. It is found that for a symmetric bi-morph configuration, the response is reduced significantly, about 68% and 75% for axial loading and 80% and 78% for flexural loading, respectively, for the 2-D decagonal quasi crystal and the 3-D icosahedral quasi crystal.
Title:
Microstructure and mechanical behavior of Al92Fe3Cr2X3 (X = Ce, Mn, Ti, and V) alloys processed by centrifugal force casting
Authors:
Koga, GY; Silva, AMBE; Wolf, W; Kiminami, CS; Bolfarini, C; Botta, WJ Author Full Names: Koga, Guilherme Yuuki; Branquinho e Silva, Ana Martha; Wolf, Witor; Kiminami, Claudio Shyinti; Bolfarini, Claudemiro; Botta, Walter Jose
Source:
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 8 (2):2092-2097; 10.1016/j.jmrt.2018.12.022 APR 2019
Abstract:
Microstructural and mechanical characterization of Al92Fe3Cr2X3 (X = Ce, Mn, Ti, and V) alloys were performed. The alloys were processed by a method that uses centrifugal force to cast the samples into a rotating copper mold. Microstructural characterization was carried out by means of x-ray diffraction, scanning electron microscopy, and differential scanning calorimetry. Compressive tests at room and at 300 degrees C were performed in selected samples to evaluate their mechanical properties. Microstructural characterization showed the formation of quasicrystalline phases as well as other intermetallic phases embedded within an Al-FCC matrix. The Ce-containing alloy exhibited promising results regarding quasicrystalline phase formation and stability as well as with respect to its mechanical properties at high temperatures. The quasicrystalline phase of this alloy appears to be stable up to 545 degrees C when the DSC reveals an exothermic transformation. In addition, the presence of a eutectic structure surrounding the Al-FCC grains enhanced the mechanical strength of this alloy. At 300 degrees C, the Ce-containing alloy showed yield strength and ultimate tensile strength of 180 MPa and 360 MPa, respectively. If compared to a commercial aluminum alloy 2024 at the T6 condition, close to 300 degrees C, the alloy studied here showed an increase of more than 4 times in the yield strength, and almost 7 times in the ultimate tensile strength. The high thermal stability and mechanical properties at high temperatures of this alloy open interesting possibilities for further studies and future applications of this Al-Fe-Cr-Ce alloy. (C) 2019 Published by Elsevier Editora Ltda. on behalf of Brazilian Metallurgical, Materials and Mining Association.
Title:
Effect of I(Mg3YZn6)-, W(Mg3Y2Zn3)- and LPSO(Mg12ZnY)- phases on tensile work-hardening and fracture behaviors of rolled Mg-Y-Zn alloys
Authors:
Yang, JY; Kim, WJ Author Full Names: Yang, Jun Yeong; Kim, Woo Jin
Source:
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 8 (2):2316-2325; 10.1016/j.jmrt.2019.04.016 APR 2019
Abstract:
The effects of secondary phases (W,Mg3Y2Zn3), long-period stacking-ordered (LPSO, Mg12ZnY) and icosahedral (I, Mg3YZn6) phases on the tensile properties and work- hardening behavior of Mg-Y-Zn alloys (Mg-1.32Zn-1.79Y, ZW12; Mg-4.4Zn-2.2Y, ZW42; and microstructures were studied at room temperature. The volume fractions of LPSO, W and I-phase in ZW12, ZW42 and ZW51 were 4.7, 6.3 and 4.8%, respectively. The rolled alloys exhibited a similar level of yield strength but different work hardening characteristics and tensile fracture behavior. The rolled ZW51 with I-phase particles exhibited the highest work-hardening rate and the largest tensile elongation (with ductile fracture). The ZW42 with W-phase particles exhibited a work-hardening rate slightly lower than that of the rolled ZW51, despite having the larger amount of secondary phase, and premature fracture occurred far before neck formation in ZW42, while fracture occured after neck formation occurred far before neck formation in ZW42, while fracture occured after neck formation in ZW51. The fractured surface showed that the coherent interface between the I-phase and Mg matrix phase is significantly more resistant to cracking than is the incoherent interface between the W-phase and Mg matrix phase. The rolled ZW12 with LPSO-phase, forming a coherent interface with the Mg matrix phase, exhibited a considerably lower work hardening rate than the rolled ZW51, though they had the similar amounts of secondary phase. Thus, the uniform strain of the rolled ZW12 was quite small compared with that of the rolled ZW51, though fracture occurred after necking in both alloys. The same work-hardening and tensile elongation behaviors were retained after annealing treatment on the rolled alloys. (C) 2019 The Authors. Published by Elsevier B.V.
Title:
Synthesis and Investigation of Quaternary Quasi-Crystalline Phase in Al - Cu - Fe - Cr Alloys
Authors:
Wang, YF; Hou, H; Zhao, YH; Tian, JZ Author Full Names: Wang, Yifan; Hou, Hua; Zhao, Yuhong; Tian, Jinzhong
Source:
METAL SCIENCE AND HEAT TREATMENT, 60 (11-12):770-776; 10.1007/s11041-019-00354-w MAR 2019
Abstract:
Formation of a quasi-crystalline phase under rapid solidification and heat treatment of alloys of the Al - Cu - Fe - Cr system is studied. The study is performed by x-ray diffractometry, optical, scanning and transmission electron microscopy and differential scanning calorimetry. It is shown that the quasi-crystalline Al65Cu20Fe10Cr5 phase is a mixture of icosahedral and decagonal phases. The substitution of iron with chromium destabilizes the icosahedral I-phase and promotes formation of a decagonal d-phase. After quenching from 880 degrees C, the Al64Cu24Fe10Cr2 alloy acquires a pure I-phase, and the Al64Cu24Fe8Cr4 alloy acquires a d-phase.

Update: 13-Jun-2019

Title:
Charge density wave and lock-in transitions of CuV2S4
Authors:
Ramakrishnan, S; Schonleber, A; Hubschle, CB; Eisele, C; Schaller, AM; Rekis, T; Bui, NHA; Feulner, F; van Smaalen, S; Bag, B; Ramakrishnan, S; Tolkiehn, M; Paulmann, C Author Full Names: Ramakrishnan, Sitaram; Schoenleber, Andreas; Huebschle, Christian B.; Eisele, Claudio; Schaller, Achim M.; Rekis, Toms; Nguyen Hai An Bui; Feulner, Florian; van Smaalen, Sander; Bag, Biplab; Ramakrishnan, Srinivasan; Tolkiehn, Martin; Paulmann, Carsten
Source:
PHYSICAL REVIEW B, 99 (19):10.1103/PhysRevB.99.195140 MAY 23 2019
Abstract:
The three-dimensional charge density wave (CDW) compound CuV2S4 is known to undergo phase transitions at similar to 91 and similar to 50 K. Employing single-crystal x-ray diffraction on an annealed crystal, we confirm the formation of an incommensurate CDW at T-CDW approximate to 91 K, and we establish the nature of the transition at Tlock-in approximate to 50 K as a lock-in transition toward a threefold superstructure. As-grown crystals develop the same incommensurate CDW as the annealed crystal does, but they fail to go through the lock-in transition. Instead, the length of the modulation wave vector continues to decrease down to low temperatures in as-grown crystals. These findings are corroborated by distinct temperature dependencies of the electrical resistivity, magnetic susceptibility, and specific heat measured on as-grown and annealed crystals. A superspace model for the crystal structure of the incommensurate CDW suggests that the formation of extended vanadium clusters is at the origin of the CDW. In the lock-in phase, short and long V-V distances persist, but clusters now percolate the entire crystal. The lowering toward orthorhombic symmetry appears to be responsible for the precise pattern of short and long V-V distances. However, the orthorhombic lattice distortion is nearly zero for the annealed crystal, while it is visible for the as-grown material, again suggesting the role of lattice defects in the latter.
Title:
Magnons in a Quasicrystal: Propagation, Extinction, and Localization of Spin Waves in Fibonacci Structures
Authors:
Lisiecki, F; Rychly, J; Kuswik, P; Glowinski, H; Klos, JW; Gross, F; Trager, N; Bykova, I; Weigand, M; Zelent, M; Goering, EJ; Schutz, G; Krawczyk, M; Stobiecki, F; Dubowik, J; Grafe, J Author Full Names: Lisiecki, Filip; Rychly, Justyna; Kuswik, Piotr; Glowinski, Hubert; Klos, Jaroslaw W.; Gross, Felix; Traeger, Nick; Bykova, Iuliia; Weigand, Markus; Zelent, Mateusz; Goering, Eberhard J.; Schuetz, Gislea; Krawczyk, Maciej; Stobiecki, Feliks; Dubowik, Janusz; Graefe, Joachim
Source:
PHYSICAL REVIEW APPLIED, 11 (5):10.1103/PhysRevApplied.11.054061 MAY 22 2019
Abstract:
Magnonic quasicrystals exceed the possibilities of spin-wave (SW) manipulation offered by regular magnonic crystals, because of their more complex SW spectra with fractal characteristics. Here, we report the direct x-ray microscopic observation of propagating SWs in a magnonic quasicrystal, consisting of dipolar coupled permalloy nanowires arranged in a one-dimensional Fibonacci sequence. SWs from the first and second band as well as evanescent waves from the band gap between them are imaged. Moreover, additional mini band gaps in the spectrum are demonstrated, directly indicating an influence of the quasiperiodicity of the system. Finally, the localization of SW modes within the Fibonacci crystal is shown. The experimental results are interpreted using numerical calculations and we deduce a simple model to estimate the frequency position of the magnonic gaps in quasiperiodic structures. The demonstrated features of SW spectra in one-dimensional magnonic quasicrystals allow utilizing this class of metamaterials for magnonics and make them an ideal basis for future applications.
Title:
Changes in spin and lattice dynamics induced by magnetic and structural phase transitions in multiferroic SrMn7O12
Authors:
Kamba, S; Goian, V; Kadlec, F; Nuzhnyy, D; Kadlec, C; Vit, J; Borodavka, F; Glazkova, IS; Belik, AA Author Full Names: Kamba, Stanislav; Goian, Veronica; Kadlec, Filip; Nuzhnyy, Dmitry; Kadlec, Christelle; Vit, Jakub; Borodavka, Fedir; Glazkova, Iana S.; Belik, Alexei A.
Source:
PHYSICAL REVIEW B, 99 (18):10.1103/PhysRevB.99.184108 MAY 20 2019
Abstract:
SrMn7O12 is a recently synthesized homolog of multiferroic CaMn7O12. Upon cooling, SrMn7O12 undergoes a series of structural and magnetic phase transitions from cubic to rhombohedral symmetry, and to an incommensurately modulated crystal structure, which is connected with charge and orbital ordering of the Mn cations. We report infrared, terahertz, and Raman spectra of SrMn7O12 ceramics reflecting corresponding changes in phonon selection rules, including new phonons appearing in spin-order-induced ferroelectric phases. The observed phonon activities are compared with the predictions from the factor-group analysis. In the high-temperature phase, more phonons are observed than the number predicted for the cubic symmetry. This is explained by the presence of rhombohedral clusters in the cubic phase. The strongest variations occur in THz spectra near the two magnetic phase transitions, at T-N1 = 87 K and T-N2 = 63 K. These activate new modes in the spectra, with resonance frequencies and intensities changing with temperature and magnetic field. Below T-N2, we observed a transfer of oscillator strengths from low-frequency phonons to these excitations, which we assign to electromagnons.
Title:
Microstructure and Mechanical Properties of Extruded Mg-7Sn-5Zn-xAl (x=0, 1, 2 and 3 wt.%) Alloy
Authors:
Jiang, J; Li, TQ; Bi, GL; Yan, FY; Cao, C; Li, YD; Ma, Y Author Full Names: Jiang, Jing; Li, Tingqu; Bi, Guang-Li; Yan, Feng-Yun; Cao, Chi; Li, Yuan-Dong; Ma, Ying
Source:
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE, 28 (5):2672-2680; 10.1007/s11665-019-04053-8 MAY 2019
Abstract:
Microstructure and mechanical properties of extruded Mg-7Sn-5Zn-xAl (x=0, 1, 2 and 3 wt.%) alloy were investigated. The as-cast Mg-7Sn-5Zn alloy mainly comprised alpha-Mg dendrites, Mg2Sn and nanosized Mg-Zn phases in a Mg matrix, whereas the quasicrystal (icosahedral (I)) phase precipitated with the addition of Al. After extrusion, the grain size decreased due to dynamic recrystallization and the resulting particles were crushed and distributed along the extrusion direction. The highest tensile strength was exhibited by the extruded Mg-7Sn-5Zn-2Al alloy, which had a yield strength, ultimate tensile strength and elongation to failure of 198, 343 MPa and 18.7%, respectively. The high tensile strength was mainly attributed to grain refinement and precipitation strengthening of the Mg2Sn and icosahedral phases.

Update: 6-Jun-2019

Title:
The influence of the incommensurately modulated structure on the physical properties of Fe1.35Ge
Authors:
Jacimovic, J; Popcevic, P; Arakcheeva, A; Pattison, P; Pisoni, A; Katrych, S; Prsa, K; Berger, H; Smontara, A; Forro, L Author Full Names: Jacimovic, J.; Popcevic, P.; Arakcheeva, A.; Pattison, P.; Pisoni, A.; Katrych, S.; Prsa, K.; Berger, H.; Smontara, A.; Forro, L.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 794 108-113; 10.1016/j.jallcom.2019.04.159 JUL 25 2019
Abstract:
Single crystal growth by chemical vapour transport has resulted samples with Fe1.35Ge stoichiometry. Structural study has shown that the large number of vacancies introduces an incommensuately modulated structure. The electrical resistivity is in the 200 mu Omega cm range at room temperature, and although the ferromagnetic transition temperature at 425 K is clearly visible, it hardly varies down to 4.2 K. It is suggested that the large number of vacancies (and the incommensurate modulation) introduce a strong backscattering, and the system is at the brink of a Mooij correlation. The thermal conductivity and Seebeck coefficient carry also the consequences of the high concentration of vacancies. (c) 2019 Elsevier B.V. All rights reserved.
Title:
Annealing induced precipitation of nanoscale icosahedral quasicrystals in aluminum based alloy
Authors:
Mochugovskiy, A; Tabachkova, N; Mikhaylovskaya, A Author Full Names: Mochugovskiy, Andrey; Tabachkova, Natalia; Mikhaylovskaya, Anastasia
Source:
MATERIALS LETTERS, 247 200-203; 10.1016/j.matlet.2019.03.126 JUL 15 2019
Abstract:
This study analyzes the precipitation phenomenon in the Al-3%Mg-1%Mn alloy and shows that low-temperature annealing at 360 degrees C enables the decomposition of an as-cast Mn-enriched supersaturated solid solution and precipitation of the quasicrystalline icosahedral phase. Icosahedrons are predominantly formed heterogeneously on the dislocations and dislocation walls. Precipitates with quasicrystalline structure contain Al and Mn, free of Si, and their size varies in a range of 17-71 nm. The Ashby-Brown contrast and the ordered positions of the precipitate and matrix reflections in the SAED and in high-resolution TEM images suggest partial coherency of the quasicrystalline precipitates and aluminum matrix. (C) 2019 Elsevier B.V. All rights reserved.
Title:
Incommensurate Magnetism Near Quantum Criticality in CeNiAsO
Authors:
Wu, S; Phelan, WA; Liu, L; Morey, JR; Tutmaher, JA; Neuefeind, JC; Huq, A; Stone, MB; Feygenson, M; Tam, DW; Frandsen, BA; Trump, B; Wan, C; Dunsiger, SR; McQueen, TM; Uemura, YJ; Broholm, CL Author Full Names: Wu, Shan; Phelan, W. A.; Liu, L.; Morey, J. R.; Tutmaher, J. A.; Neuefeind, J. C.; Huq, Ashfia; Stone, Matthew B.; Feygenson, M.; Tam, David W.; Frandsen, Benjamin A.; Trump, Benjamin; Wan, Cheng; Dunsiger, S. R.; McQueen, T. M.; Uemura, Y. J.; Broholm, C. L.
Source:
PHYSICAL REVIEW LETTERS, 122 (19):10.1103/PhysRevLett.122.197203 MAY 15 2019
Abstract:
We report the discovery of incommensurate magnetism near quantum criticality in CeNiAsO through neutron scattering and zero field muon spin rotation. For T < T-N1 = 8.7(3) K, a second order phase transition yields an incommensurate spin density with a wave vector k = (0.44(4), 0, 0). For T < T-N2 = 7.6(3) K, we find coplanar commensurate order with a moment of 0.37(5)mu(B), reduced to 30% of the saturation moment of the vertical bar +/- 1/2 > Kramers doublet ground state, which we establish through inelastic neutron scattering. Muon spin rotation in CeNiAs1-xPxO shows the commensurate order only exists for x <= 0.1 so we infer the transition at x(c) = 0.4(1) is between an incommensurate longitudinal spin density wave and a paramagnetic Fermi liquid.
Title:
Magnetic Phase Transitions to an Incommensurate Magnetic Structure in FeGe2 Compound
Authors:
Men'shenin, VV Author Full Names: Men'shenin, V. V.
Source:
PHYSICS OF THE SOLID STATE, 61 (3):421-432; 10.1134/S1063783419030211 MAR 2019
Abstract:
A symmetry analysis of possible magnetic structures in an incommensurate magnetic phase in FeGe2 compound, resulted from phase transitions from the paramagnetic phase, was performed based on a phenomenological consideration. It is shown that two possible approaches to a such an analysis, the first of which uses the magnetic representation of the space group, and the second one is based on the expansion of the magnetic moment in basis functions of irreducible representations of the space group of the paramagnetic phase, yield the same results. Space group irreducible representations are determined, according to which the transition to an incommensurate structure can occur. The set of these representations appears identical in both approaches. Ginzburg-Landau functionals for analyzing the transitions according to these representations are written. A renormalization group analysis of the second-order phase transitions from the paramagnetic state to the incommensurate magnetic structure is performed. It is shown that a helical magnetic structure can arise in the incommensurate phase as a result of two second-order phase transitions at the transitions temperature.

Update: 29-May-2019

Title:
Preparation of bulk metallic glasses by modifying local structure of icosahedral quasicrystals
Authors:
Li, ZJ; Pan, SP; Zhang, SH; Feng, SD; Li, MZ; Liu, RP; Tian, YJ; Wang, LM Author Full Names: Li, Zijing; Pan, Shaopeng; Zhang, Suhong; Feng, Shidong; Li, Maozhi; Liu, Riping; Tian, Yongjun; Wang, Li-min
Source:
INTERMETALLICS, 109 97-104; 10.1016/j.intermet.2019.03.007 JUN 2019
Abstract:
An attempt is carried out to design metallic glasses by modifying the local structure of icosahedral quasicrystals. A series of metallic glasses are prepared by introducing beryllium to the quasicrystal former, Zr40Ti40Ni20, and the maximum diameter of the glasses reaches 20 mm. A phase transformation diagram is constructed for the alloys of (Zr40Ti40Ni20)(100-x)Be-x, revealing the transition from stable crystal to quasicrystal and then to metallic glasses with the increased Be content. This study shows a connection between the formation of metallic glasses and the specific thermodynamics of the initially precipitated quasicrystals. Interestingly, both improvements in the forming ability for glasses and quasicrystals are observed over a wide composition range. Ab initio molecular dynamic simulations show the evolution of the structural features of the metallic melts for the optimised glass forming region, which guarantee the primary precipitation of quasicrystal.
Title:
Formation and stability of complex metallic phases including quasicrystals explored through combinatorial methods
Authors:
Wolf, W; Kube, SA; Sohn, S; Xie, YJ; Cha, JJ; Scanley, BE; Kiminami, CS; Bolfarini, C; Botta, WJ; Schroers, J Author Full Names: Wolf, Witor; Kube, Sebastian A.; Sohn, Sungwoo; Xie, Yujun; Cha, Judy J.; Ellen Scanley, B.; Kiminami, Claudio S.; Bolfarini, Claudemiro; Botta, Walter J.; Schroers, Jan
Source:
SCIENTIFIC REPORTS, 9 10.1038/s41598-019-43666-w MAY 9 2019
Abstract:
Aluminum-based quasicrystals typically form across narrow composition ranges within binary to quaternary alloys, which makes their fabrication and characterization challenging. Here, we use combinatorial approaches together with fast characterization techniques to study a wide compositional range including known quasicrystal forming compositions. Specifically, we use magnetron cosputtering to fabricate libraries of similar to 140 Al-Cu-Fe and similar to 300 Al-Cu-Fe-Cr alloys. The alloys compositions are measured through automated energy dispersive X-ray spectroscopy. Phase formation and thermal stability are investigated for different thermal processing conditions (as-sputtered and annealed at 400 degrees C, 520 degrees C and 600 degrees C for Al-Cu-Fe libraries; annealed at 600 degrees C for Al-Cu-Fe-Cr libraries) using automated X-ray diffraction and transmission electron microscopy. In both systems the compositional regions across which the quasicrystalline phase forms are identified. In particular, we demonstrate that the quasicrystalline phase forms across an unusually broad composition range in the Al-Cu-Fe-Cr system. Additionally, some of the considered alloys vitrify during sputtering, which also allows us to study their nucleation behavior. We find that phases with polytetrahedral symmetry, such as the icosahedral quasicrystal and the lambda-Al13Fe4 phase, exhibit higher nucleation rates but lower growth rates, as compared to other phases with a lower degree of polytetrahedral order. Altogether, the here used combinatorial approach is powerful to identify compositional regions of quasicrystals.
Title:
Lattice Discontinuities of 1T-TaS2 across First Order Charge Density Wave Phase Transitions
Authors:
Wang, W; Dietzel, D; Schirmeisen, A Author Full Names: Wang, Wen; Dietzel, Dirk; Schirmeisen, Andre
Source:
SCIENTIFIC REPORTS, 9 10.1038/s41598-019-43307-2 MAY 8 2019
Abstract:
Transition metal dichalcogenides are lamellar materials which can exhibit unique and remarkable electronic behavior due to effects of electron-electron and electron-phonon coupling. Among these materials, 1T-tantalum disulfide (1T-TaS2) has spurred considerable interest, due to its multiple first order phase transitions between different charge density wave (CDW) states. In general, the basic effects of charge density wave formation in 1T-TaS2 can be attributed to in plane re-orientation of Ta-atoms during the phase transitions. Only in recent years, an increasing number of studies has also emphasized the role of interlayer interaction and stacking order as a crucial aspect to understand the specific electronic behavior of 1T-TaS2, especially for technological systems with a finite number of layers. Obviously, continuously monitoring the out of plane expansion of the sample can provide direct inside into the rearrangement of the layer structure during the phase transition. In this letter, we therefore investigate the c-axis lattice discontinuities of 1T-TaS2 by atomic force microscopy (AFM) method under ultra-high vacuum conditions. We find that the c-axis lattice experiences a sudden contraction across the nearly-commensurate CDW (NC-CDW) phase to commensurate CDW (C-CDW) phase transition during cooling, while an expansion is found during the transition from the C-CDW phase to a triclinic CDW phase during heating. Thereby our measurements reveal, how higher order C-CDW phase can favor a more dense stacking. Additionally, our measurements also show subtler effects like e.g. two expansion peaks at the start of the transitions, which can provide further insight into the mechanisms at the onset of CDW phase transitions.
Title:
Crystal Structure and Photoluminescence Properties of an Incommensurate Phase in EuO- and P2O5-Doped Ca2SiO4
Authors:
Hiramatsu, Y; Michiue, Y; Funahashi, S; Hirosaki, N; Banno, H; Urushihara, D; Asaka, T; Fukuda, K Author Full Names: Hiramatsu, Yuya; Michiue, Yuichi; Funahashi, Shiro; Hirosaki, Naoto; Banno, Hiroki; Urushihara, Daisuke; Asaka, Toru; Fukuda, Koichiro
Source:
INORGANIC CHEMISTRY, 58 (9):6155-6160; 10.1021/acs.inorgchem.9b00408 MAY 6 2019
Abstract:
We have for the first time clarified the incommensurately modulated crystal structure as well as the photoluminescence properties of Eu2+ -activated Ca2SiO4 solid solution, the chemical formula of which is (Ca1.88Eu0.012+square(0.11))-(Si0.78P0.22)O-4, where square denotes vacancies in Ca sites with the replacement of Si4+ by P5+. The emission spectrum upon the 335 nm excitation showed a relatively broad band centered at ca. 490 nm and a full width at half-maximum of ca. 80 nm. The crystal structure was made up of the four types of beta-Ca2SiO4-like layers with one type of interlayer. The incommensurate modulation with superspace group Pnma(0 beta 0)00s was induced by the long-range stacking order of these layers. The modulation wavevector was 0.27404(2) x b*, with the basic unit-cell dimensions being a = 0.68355(2) nm, b = 0.54227(2) nm, and c = 0.93840(3) nm (Z = 4). The basic structure contained two nonequivalent Ca sites. One site was fully occupied by Ca2+ and free from Eu2+ in the overall incommensurate structure. The occupational modulation at the other site was so significant that the sum of site occupation factors for Ca2+ and Eu2+ as low as 0.5 was seen at the interlayer. This site was too large for accommodation of Ca2+ but was suitable for Eu2+. Thus, the Eu2+ ions would exclusively concentrate at the relevant site, which would cause the emission peak of the incommensurate phase to be shifted to the shorter wavelength ranges as compared with those of the other commensurate phases such as beta and alpha'(L).
Title:
Synthesis and Atomic Structure of the Yb-Ga-Au 1/1 Quasicrystal Approximant
Authors:
Yamada, T; Kurihara, T; Prots, Y; Sato, A; Matsushita, Y; Grin, Y; Tsai, AP Author Full Names: Yamada, Tsunetomo; Kurihara, Takuya; Prots, Yurii; Sato, Akira; Matsushita, Yoshitaka; Grin, Yuri; Tsai, An Pang
Source:
INORGANIC CHEMISTRY, 58 (9):6320-6327; 10.1021/acs.inorgchem.9b00513 MAY 6 2019
Abstract:
The Yb-Ga-Au 1/1 quasicrystal approximant (AP) composition ranges from Yb14.0Ga20.6Au65.4 to Yb-14.8Ga46.3Au38.9, and single crystals of the 1/1 AP having the composition Yb13.8Ga26.1Au60.1 were obtained by the self-flux technique. X-ray structural analysis demonstrated that the atomic structure [space group Im (3) over bar; a = 14.6889(9) angstrom] can be described by the body-centered packing of Tsai-type rhombic triacontahedron (RTH) clusters. The positional disorder in these clusters, interpreted as the average of an orientationally disordered tetrahedron and triangle, results in positional disorder in the outer shells. The elemental distributions and positions of mixtures of Au and Ga atoms in the RTH clusters correspond to those in the isostructural Yb15Al36Au49 1/1 AP.
Title:
Na3Sm(PO4)(2):(3+1)-dimensional commensurately modulated structure model and photoluminescence properties
Authors:
Zhang, RJ; Zhao, D; Zhong, Q; Xue, YL; Huang, GX Author Full Names: Zhang, Rui-Juan; Zhao, Dan; Zhong, Qiu; Xue, Ya-Li; Huang, Guang-Xu
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 234 (5):281-289; 10.1515/zkri-2018-2095 MAY 2019
Abstract:
For the first time, we determined the detailed crystal structure of Na3Sm(PO4)(2) using single crystal X-ray diffraction and established the commensurately modulated structure model using the superspace formalism. The structure adopts a (3+1)-dimensional superspace group Pca2(1)(0 beta 0)000 with the modulation vector q=1/3b*. At the same time, the photoluminescent properties of Na3Sm(PO4)(2) sintered at different temperatures between 800 and 1200 degrees C were studied. Under near-UV excitation (402 nm), Na3Sm(PO4)(2) shows intense characteristic emission bands of Sm3+ (561, 596, 642 nm) with the CIE coordinate of (0.5709, 0.4282), corresponding to orange color. The excitation spectrum covers a wide range from 350 nm to 470 nm, which indicates that Na3Sm(PO4)(2) can be efficiently activated by near-UV or visuable LED ship.
Title:
Influence of Ni Alloying on the Precipitation of Quasicrystal Phase in As-Cast Mg96.5Zn1Y1.5Mn1 Alloy
Authors:
Zhu, W; Liu, W; Zhang, YG; Ma, QQ; Zhang, JS; Xu, CX Author Full Names: Zhu, Wei; Liu, Wei; Zhang, Yong Gang; Ma, Qiang Qiang; Zhang, Jinshan; Xu, Chunxiang
Source:
ADVANCED ENGINEERING MATERIALS, 21 (4):10.1002/adem.201801238 APR 2019
Abstract:
Ni alloying is first adopted to explore the precipitation of quasicrystal phase (I phase) in Mg96.5Zn1Y1.5Mn1 alloy containing LPSO structure and W phase during solidification. Results show the component of I phase is Mg-3(Zn, Ni)(6)Y-1 which mainly distributes near the W phase. Besides, during the formation of I phase, Ni acts as Zn to participate in the precipitation process of I phase, making up for the deficiency of Zn. Meanwhile, an excellent strength-ductility balance with ultimate tensile strength (210MPa) and elongation (9.5%) is greatly optimized.
Title:
The Effect of Composition on the Formation of a BCC Approximant in Ti-Cr-Al-Si-O Alloys
Authors:
Firstov, SA; Gorban, VF; Karpets, MV; Krapivka, MO; Rokytska, OA; Samelyuk, AV Author Full Names: Firstov, S. A.; Gorban, V. F.; Karpets, M. V.; Krapivka, M. O.; Rokytska, O. A.; Samelyuk, A. V.
Source:
POWDER METALLURGY AND METAL CERAMICS, 57 (11-12):731-739; 10.1007/s11106-019-00038-3 MAR 2019
Abstract:
The microstructure, phase composition, and mechanical properties of Ti-Cr-Al-Si-O alloys in ascast state and after annealing at 800 degrees C have been studied. The as-cast alloys with 50 and 60 at.% Ti have two phases: a 1/1 (TiCrSi) cubic approximant of the quasicrystalline phase and an intermetallic Cr2Ti(C14) Laves phase in different ratios. The as-cast alloy with a high titanium amount (72 at.%) contains three phases: a 1/1(TiCrSi) approximant and two -Ti and -Ti solid solutions. The effect of annealing on the phase composition of the alloys has been studied. After annealing, the alloys with the lowest (50 at.%) and highest (72 at.%) Ti contents change their phase composition with the formation of Ti5Si3 silicide, while the alloy with 60 at.% Ti exhibits high thermal stabilityits phase composition remains unchanged. The changes in hardness of the starting and annealed alloys have been examined by automatic indentation. The highest hardness, 11.7 GPa, is shown by the as-cast Ti72Cr20Al2Si2(SiO2)(4) alloy. The hardness of the annealed Ti50Cr30Al13Si2(SiO2)(5) alloy increases to 14.8 GPa.

Update: 22-May-2019

Title:
Formation and crystallographic orientation study of quasicrystal, 2/1 and 1/1 approximants in Cd-Mg-Y system using electron backscatter diffraction (EBSD)
Authors:
Labib, F; Ohhashi, S; Tsai, AP Author Full Names: Labib, Farid; Ohhashi, Satoshi; Tsai, An-Pang
Source:
PHILOSOPHICAL MAGAZINE, 99 (12):1528-1550; 10.1080/14786435.2019.1585589 JUN 18 2019
Abstract:
A partial isothermal ternary phase diagram of the Cd-Mg-Y system including icosahedral quasicrystal (i-QC) and 1/1 approximant (APP) was obtained at 673 K. The stability of the i-QC and APPs in terms of composition and temperature was studied, as a result of which the 2/1 APP phase was discovered at 773 K. Moreover, the i-QC phase was found to be stable at lower Y concentrations of similar to 12-13 at.%, as compared to the 1/1 APP, which showed similar to 15-16 at.% Y. Single i-QC, 2/1 and 1/1 APP grains were also synthesized applying centrifuging system. Electron backscatter diffraction (EBSD) characterization of the obtained i-QC and APPs revealed almost the same Kikuchi patterns for the i-QC and 2/1 APP, indicating high resemblance of their structures. However, the Kikuchi pattern acquired from the 1/1 APP was distinguishable from the one obtained from the i-QC as it showed split bands. The occurrence of the split bands was associated with significant deviation from a perfect icosahedral symmetry. This was also confirmed by analysing calculated electron diffraction and Kikuchi patterns along pseudo-five-fold axes of the 2/1 and 1/1 APPs. Finally, orientation relationships between the i-QC, 1/1 APP and alpha-Mg were investigated by analysing acquired EBSD Kikuchi patterns from the respective domains. Accordingly, three perpendicular two-fold axes of the i-QC and {100} axes of the 1/1 APP occur along three mutually orthogonal {0001}, {10-10} and {11-20} axes of the alpha-Mg.
Title:
Effect of Ca Doping on Modulated Structures in Multiferroic Bi1-xCaxFeO3
Authors:
Hiroyama, T; Hirata, A; Inoue, Y; Horibe, Y; Koyama, Y Author Full Names: Hiroyama, Takumi; Hirata, Akihiko; Inoue, Yasuhide; Horibe, Yoichi; Koyama, Yasumasa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 88 (5):10.7566/JPSJ.88.054601 MAY 15 2019
Abstract:
The crystallographic features of Bi1-xCaxFeO3 samples with x = 0.10, 0.15, 0.20, and 0.30 compositions are investigated by transmission electron microscopy. Perovskite-based modulated structures are found in all the samples except for the x = 0.10 sample where a rhombohedral R3c BiFeO3-type structure is observed at room temperature. The in situ heating experiment indicates that the modulated structure appears even in the x = 0.10 sample at 673K or higher. At room temperature, the modulation direction is found to change at approximately x = 0.20. The models of the modulated structures are constructed by introducing periodic antiphase boundaries in terms of the M-3-type rotational displacements of the FeO6 octahedra. The electron diffraction patterns simulated from the models are in good agreement with the experimental results. The composition dependence of the modulated structures is also discussed.
Title:
Preparation and electro-catalytic activity of nanoporous palladium by dealloying rapidly-quenched Al70Pd17Fe13 quasicrystalline alloy
Authors:
Liu, XY; Wang, YM; Qiang, JB; Wang, BL; Ma, DG; Zhang, W; Dong, C Author Full Names: Liu, Xin-yi; Wang, Ying-min; Qiang, Jian-bing; Wang, Bao-lin; Ma, Dian-guo; Zhang, Wei; Dong, Chuang
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 29 (4):785-790; 10.1016/S1003-6326(19)64988-5 APR 2019
Abstract:
The formation of nanoporous Pd was studied by electro-chemical dealloying a rapidly-quenched Al70Pd17Fe13 quasicrystal alloy in dilute NaCl aqueous solution, and the electro-catalytic activity of the nanoporous Pd towards methanol electro-oxidation was evaluated by cyclic voltammetry in 1 mol/L KOH solution. XRD and TEM analyses revealed that nano-decomposition of quasicrystal grains occurred in the initial stage of dealloying, and the fully dealloyed sample was composed of FCC-Pd phase. Scanning electron microscopy observation indicated that a maze-like nanoporous pattern was formed in the dealloyed sample, consisting of percolated pores of 5-20 nm in diameter in a skeleton of randomly-orientated Pd nano-ligaments with a uniform thickness of similar to 5 nm. A retention of similar to 12 at.% Al in the Pd nano-ligments was determined by energy dispersive X-ray spectroscopy (EDS). The nanoporous Pd demonstrated obvious electro-catalytic activity towards methanol electro-oxidation in alkaline environment.
Title:
Analytic Solutions to Two-Dimensional Decagonal Quasicrystals with Defects Using Complex Potential Theory
Authors:
Cao, HB; Shi, YQ; Li, W Author Full Names: Cao, Haobai; Shi, Yiqing; Li, Wu
Source:
CRYSTALS, 9 (4):10.3390/cryst9040209 APR 2019
Abstract:
An analytical treatment for two-dimensional point group 10 mm decagonal quasicrystals with defects was suggested based on the complex potential method. On the basis of the assumption of linear elasticity, two new conformal maps were applied to two examples: the first was an arc with an elliptic notch inner surface in a decagonal quasicrystal, where the complex potentials could be exactly obtained; and the second was concerned with a decagonal point group 10 mm quasicrystalline strip weakened by a Griffith crack, which was subjected to a pair of uniform static pressures. Using the basic idea underlying crack theory, the extent of the stress intensity factors was analytically estimated. If the height was allowed to approach infinity, these results can be turned into the known results of an ordinary crystal with only phonon elastic parameters when the phason and phonon-phason elastic constants are eliminated.
Title:
Y3Ru2-x-A Representative of a Composite Modulated Family of Intermetallics
Authors:
Lidin, S; Folkers, L Author Full Names: Lidin, Sven; Folkers, Laura
Source:
CRYSTALS, 9 (4):10.3390/cryst9040189 APR 2019
Abstract:
The compound Y3Ru2-x was synthesized from the elements and the structure was solved from single crystal synchrotron data. The high quality of the data allowed the determination of the incommensurate ordering of the compound, previously reported as disordered, with respect to the second subsystem. The compound crystallizes in the super space group X-3(00)0 with the q-vector axial along c*, q = 00, = 0.4276(7) and the centering vectors (1/3 2/3 0 1/3), (2/3 1/3 0 2/3).
Title:
Formation of ethylene-vinyl acetate composites filled with Al-Cu-Fe and Al-Cu-Cr quasicrystallline particles
Authors:
Tcherdyntsev, VV; Stepashkin, AA; Chukov, DI; Olifirov, LK; Senatov, FS Author Full Names: Tcherdyntsev, Victor V.; Stepashkin, Andrey A.; Chukov, Dilyus, I; Olifirov, Leonid K.; Senatov, Fedor S.
Source:
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 18 (1):572-589; 10.1016/j.jmrt.2018.05.008 JAN-MAR 2019
Abstract:
Icosahedral Al65Cu23Fe12 and decagonal Al73Cu11Cr16 quasicrystalline powders were synthesized by the mechanical alloying and subsequent annealing. Morphology evolution at mechanical alloying of Al-based powders was found to be determined by competition between cold welding and fracture mechanisms. Mechanical alloying results in formation of coarse agglomerates consisting of fine particles. The chemical binding between the polymer matrix and quasicrystals, destruction of agglomerated at extrusion, and the uniform distribution of quasicrystals over the polymer melt were provided by surface treatment of quasicrystalline particles with silanes. The highly filled (up to 60 wt%) ethylene-vinyl acetate/quasicrystals composites were obtained, and their rheological characteristics were studied. It was shown that the fluidity of the melt is retained at a high level providing uniform distribution of quasicrystalline particles over the polymer. (C) 2018 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda.
Title:
Study of the surface properties of the epoxy/quasicrystal composite
Authors:
Barros, TPD; Cavalcante, DGD; de Oliveira, DF; Caluete, RE; de Lima, SJG Author Full Names: dos Santos Barros, Thayza Pacheco; de Lima Cavalcante, Danielle Guedes; de Oliveira, Danniel Ferreira; Caluete, Rafael Evaristo; Guedes de Lima, Severino Jackson
Source:
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 18 (1):590-598; 10.1016/j.jmrt.2018.04.015 JAN-MAR 2019
Abstract:
This work consists of the study of the surface and Hardness properties of epoxy/quasicrystal (QC) composites. The composites had volumetric proportions of 1%, 10%, 20% and 30%, where the comparison was made between the composites and the pure epoxy resin. Techniques of Shore D Hardness, Thermogravimetric Analysis Techniques, Roughness Test, Contact Angle Analysis and Scanning Electron Microscopy (SEM) were used. Wettability test allowed to analyze the surface of the composite under the influence of two liquids: saline water and paraffinic oil. Regarding the composite and the pure resin, the contact angle increased when the liquid used in the test was saline water and decreased when exposed to paraffinic oil. It could be ensured that this small variation of the contact angles in relation to the increase of the composition occurred due to the influence of the roughness. In relation to saline water, the roughness has operated in order to prevent the liquid from spreading on the composite. As for paraffinic oil, it influenced in an opposite way, absorbing the oil and reducing the angle formed. When analyzing the pure quasicrystal, the effect was contrary to that of the composite: when it was exposed to saline water the contact angle decreased, on the other hand when exposed to paraffinic oil the resulting angle increased. This effect is related to the low polarity of the Quasicrystal, which when exposed to an apolar liquid tends to repel, thus forming a greater contact angle. Through this study it is concluded that it was possible to obtain a composite QC/Epoxy with greater hardness and still maintain its surface characteristics. (C) 2018 Published by Elsevier Editora Ltda. on behalf of Brazilian Metallurgical, Materials and Mining Association.

Update: 15-May-2019

Title:
Density Wave Probes Cuprate Quantum Phase Transition
Authors:
Webb, TA; Boyer, MC; Yin, Y; Chowdhury, D; He, Y; Kondo, T; Takeuchi, T; Ikuta, H; Hudson, EW; Hoffman, JE; Hamidian, MH Author Full Names: Webb, Tatiana A.; Boyer, Michael C.; Yin, Yi; Chowdhury, Debanjan; He, Yang; Kondo, Takeshi; Takeuchi, T.; Ikuta, H.; Hudson, Eric W.; Hoffman, Jennifer E.; Hamidian, Mohammad H.
Source:
PHYSICAL REVIEW X, 9 (2):10.1103/PhysRevX.9.021021 MAY 1 2019
Abstract:
In cuprates, the strong correlations in proximity to the antiferromagnetic Mott insulating state give rise to an array of unconventional phenomena beyond high-temperature superconductivity. Developing a complete description of the ground-state evolution is crucial to decoding the complex phase diagram. Here we use the structure of broken translational symmetry, namely, d-form factor charge modulations in (Bi, Pb)(2) (Sr, La)(2)CuO6+delta as a probe of the ground-state reorganization that occurs at the transition from truncated Fermi arcs to a large Fermi surface. We use real space imaging of nanoscale electronic inhomogeneity as a tool to access a range of dopings within each sample, and we definitively validate the spectral gap Delta as a proxy for local hole doping. From the Delta dependence of the charge modulation wave vector, we discover a commensurate-to-incommensurate transition that is coincident with the Fermi-surface transition from arcs to large hole pocket, demonstrating the qualitatively distinct nature of the electronic correlations governing the two sides of this quantum phase transition. Furthermore, the doping dependence of the incommensurate wave vector on the overdoped side is at odds with a simple Fermi-surface-driven instability.
Title:
Reprogrammability and Scalability of Magnonic Fibonacci Quasicrystals
Authors:
Lisiecki, F; Rychly, J; Kuswik, P; Glowinski, H; Klos, JW; Gross, F; Bykova, I; Weigand, M; Zelent, M; Goering, EJ; Schutz, G; Gubbiotti, G; Krawczyk, M; Stobiecki, F; Dubowik, J; Grafe, J Author Full Names: Lisiecki, Filip; Rychly, Justyna; Kuswik, Piotr; Glowinski, Hubert; Klos, Jaroslaw W.; Gross, Felix; Bykova, Iuliia; Weigand, Markus; Zelent, Mateusz; Goering, Eberhard J.; Schuetz, Gisela; Gubbiotti, Gianluca; Krawczyk, Maciej; Stobiecki, Feliks; Dubowik, Janusz; Graefe, Joachim
Source:
PHYSICAL REVIEW APPLIED, 11 (5):10.1103/PhysRevApplied.11.054003 MAY 1 2019
Abstract:
Magnonic crystals are systems that can be used to design and tune the dynamic properties of magnetization. Here, we focus on one-dimensional Fibonacci magnonic quasicrystals. We confirm the existence of collective spin waves propagating through the structure as well as dispersionless modes; the reprogammability of the resonance frequencies, dependent on the magnetization order; and dynamic spin-wave interactions. With the fundamental understanding of these properties, we lay a foundation for the scalable and advanced design of spin-wave band structures for spintronic, microwave, and magnonic applications.
Title:
Incommensurate 2k(F) density wave quantum criticality in two-dimensional metals
Authors:
Halbinger, J; Pimenov, D; Punk, M Author Full Names: Halbinger, Johannes; Pimenov, Dimitri; Punk, Matthias
Source:
PHYSICAL REVIEW B, 99 (19):10.1103/PhysRevB.99.195102 MAY 1 2019
Abstract:
We revisit the problem of two-dimensional metals in the vicinity of a quantum phase transition to incommensurate Q = 2k(F) charge-density-wave order, where the order-parameter wave vector Q connects two hot spots on the Fermi surface with parallel tangents. Earlier theoretical works argued that such critical points are potentially unstable, if the Fermi surface at the hot spots is not sufficiently flat. Here we perform a controlled, perturbative renormalization-group analysis and find a stable fixed point corresponding to a continuous quantum phase transition, which exhibits a strong dynamical nesting of the Fermi surface at the hot spots. We derive scaling forms of correlation functions at the critical point and discuss potential implications for experiments with transition-metal dichalcogenides and rare-earth tellurides.
Title:
Quasicrystalline electronic states in 30 degrees rotated twisted bilayer graphene
Authors:
Moon, P; Koshino, M; Son, YW Author Full Names: Moon, Pilkyung; Koshino, Mikito; Son, Young-Woo
Source:
PHYSICAL REVIEW B, 99 (16):10.1103/PhysRevB.99.165430 APR 29 2019
Abstract:
The recently realized bilayer graphene system with a twist angle of 30 degrees offers a new type of quasicrystal which unites the dodecagonal quasicrystalline nature and graphene's relativistic properties. Here, we introduce a concise theoretical framework that fully respects both the dodecagonal rotational symmetry and the massless Dirac nature, to describe the electronic states of the system. We find that the electronic spectrum consists of resonant states labeled by 12-fold quantized angular momentum, together with the extended relativistic states. The resulting quasiband structure is composed of the nearly flat bands with spiky peaks in the density of states, where the wave functions exhibit characteristic patterns which fit to the fractal inflations of the quasicrystal tiling. We also demonstrate that the 12-fold resonant states appear as spatially localized states in a finite-size geometry, which is another hallmark of quasicrystal. The theoretical method introduced here is applicable to a broad class of "extrinsic quasicrystals" composed of a pair of two-dimensional crystals overlaid on top of the other with incommensurate configurations.

Update: 8-May-2019

Title:
Effect of thermal treatment upon the structure incommensurability and magnetism of the spin chain oxide Sr3CaMn2CoO9+delta
Authors:
Seikh, MM; Caignaert, V; Sakly, N; Perez, O; Raveau, B; Hardy, V Author Full Names: Seikh, Md. Motin; Caignaert, Vincent; Sakly, Nahed; Perez, Olivier; Raveau, Bernard; Hardy, Vincent
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 790 572-576; 10.1016/j.jallcom.2019.03.183 JUN 25 2019
Abstract:
Spin chain oxides with different incommensurate hexagonal composite structures have been obtained for a same cationic composition according to the formula Sr3CaMn2CoO9+delta by varying the thermal treatments in air. The cell parameters of these oxides, a-9.5 angstrom, c(1)similar to 2.5 angstrom and c(2)similar to 3.8 angstrom, decrease as the deviation from commensurability increases, i.e. as gamma = c(1)/c(2) decreases and falls away from 2/3. All the investigated samples exhibit a signature typical of single-ion magnet (SIM), as well as a competition between single-chain magnet (SCM) and short-range ordering (SRO) responses. The balance between the latter two features turns out to be clearly affected by the thermal treatment. The sample quenched at 1450 degrees C, which structure is almost commensurate (gamma = 0.6659, close to 2/3), exhibits a SCM behavior without sizeable indication of SRO, whereas, for the samples annealed at 1300 degrees C or furnace cooled from 1400 degrees C with an incommensurate structure (gamma = 0.6622-0.6631), the SRO character is strongly reinforced. These changes in the magnetic response are assumed to originate from incorporation of extra oxygen into the commensurate stoichiometric Sr3CaMn2CoO9 oxide, leading to the replacement of some trimeric units built up of two octahedra and one trigonal prism (Oh(2)Tp) by tetrameric units (Oh(3)Tp) containing one additional octahedron, with a concomitant appearance of cationic vacancies in the trigonal prismatic sites. (C) 2019 Elsevier B.V. All rights reserved.
Title:
Many-beam dynamical scattering simulations for scanning and transmission electron microscopy modalities for 2D and 3D quasicrystals
Authors:
Singh, S; Lenthe, WC; De Graef, M Author Full Names: Singh, Saransh; Lenthe, William C.; De Graef, Marc
Source:
PHILOSOPHICAL MAGAZINE, 10.1080/14786435.2019.1605217
Abstract:
We present a general theory of electron scattering from both 2D and 3D quasicrystals, applicable to both transmission (forescatter) and scanning (backscatter) geometries. Specifically, simulations of conventional zone axis diffraction patterns, convergent beam diffraction patterns and electron backscatter diffraction for decagonal AlNiCo are presented. As expected, the geometry of the diffraction pattern is similar to kinematical patterns, but the intensity distributions show strong dynamical effects in all the modalities. Experimental electron backscatter diffraction patterns for AlNiCo are compared to simulated patterns for this 2D quasicrystalline structure as well as one of its crystalline monoclinic approximant phases, CoAl. While the simulated patterns from the quasicrystalline and approximant phases are very similar to the experimental patterns, direct comparison shows a better agreement with the decagonal phase.
Title:
Looking for alternatives to the superspace description of icosahedral quasicrystals
Authors:
Madison, AE; Madison, PA Author Full Names: Madison, A. E.; Madison, P. A.
Source:
PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, 475 (2221):10.1098/rspa.2018.0667 JAN 2019
Abstract:
A multiple-cell approach is discussed as a possible alternative to the higher dimensional crystallography of icosahedral quasicrystals. It is based on the Socolar-Steinhardt tiling combined with the quasi-unit cell model. Quasi-unit cells fill the space without gaps and overlappings similar to those in periodic crystals. Similarly, the atoms can occupy general and special positions. The alloy stoichiometry and the packing density can be calculated through the relative tile frequencies, which in turn are determined as the components of the Perron-Frobenius eigenvector of the corresponding substitution matrix. The calculation of the diffraction pattern reduces to the Perron projection of a special matrix, the entries of which reflect the contribution of each type of quasi-unit cell to the coherent scattering.

Update: 2-May-2019

Title:
Characterization of aluminium matrix compositesreinforced by Al-Cu-Fe-Cr quasicrystalline particles
Authors:
Yuan, Y; Hou, H; Zhao, YH; Yan, F Author Full Names: Yuan, Ye; Hou, Hua; Zhao, Yuhong; Yan, Feng
Source:
MATERIALS RESEARCH EXPRESS, 6 (7):10.1088/2053-1591/ab15a4 JUL 2019
Abstract:
The Al63Cu25Fe9Cr3 quasicrystalline was prepared by conventional casting method. The microstructures and phase composition of Al63Cu25Fe12 quasi-crystalline and Al65Cu20Fe10Cr5 phases were characterized by XRD and SEM. Aluminium based composites was fabricated by using the Al63Cu25Fe9Cr3 quasicrystalline particles as the reinforcing phase and ZL101 as matrix with mechanical stirring. The effects of quasicrystals content, on the microstructure and mechanical properties of the obtained composite, were investigated. The results show that the as-cast quasicrystalline material is composed of d-phase(Al65Cu20Fe10Cr5), I-phase(Al63Cu25Fe12), lambda-Al3Fe, beta-AlFe3 and a small amount of eta-AlCu, theta-Al2Cu phases. After heat treatment, the quasicrystalline intermediate alloy composition tends to quasicrystal phase. In the composite material, the diffusion between the quasicrystalline and the matrix alloy caused the decomposition of the structure of quasicrystalline phase. With the increase of quasicrystalline content, the tensile strength of the composites increases. However, addition of the Cr element changes the acicular beta-Fe(Al80-85Fe6-9Si10-15) phase into a manlike or bone-like alpha-Fe(Al80-85Fe4-8Si6-8Cr3-5) phase which increases the elongation of the composite. The best comprehensive mechanical properties corresponded to the 7 wt% quasicrystalline particles. Strengthening mechanism of quasicrystal reinforced aluminum matrix composites, a model that model considers the dislocation strengthening mechanism and the effect of load transfers mechanism on the tensile strength of composites. This theory calculates the tensile strength of quasicrystalline reinforced aluminum matrix composites and verifies the effectiveness of the model through experiments.
Title:
Effect of selective post-aging treatment on subsurface damage of quasicrystal reinforced Al composite manufactured by selective laser melting
Authors:
Kang, N; El Mansori, M; Lu, JL; Lin, X; Huang, WD Author Full Names: Kang, N.; El Mansori, M.; Lu, J. L.; Lin, X.; Huang, W. D.
Source:
WEAR, 426 934-941; 10.1016/j.wear.2018.12.048 B APR 30 2019
Abstract:
In this work, Al-Fe-Cr quasicrystal reinforced Al matrix composite was in-situ prepared by using selective laser melting from powder mixture of Al-Cu-Fe-Cr quasicrystal and pure Al. The effect of selective post-aging treatment on microstructure and mechanical properties were determined with focus on the metastable phases. The microstructural analysis, which was determined by X-ray diffraction and scanning electron microscopy, indicates that the Al-based intermetallic is precipitated from supersaturated alpha-Al after the aging process. Moreover, the compression tests were performed on the samples in form of dense and lattice structures (50% porosity). The elastic modules of dense and lattice structural samples reduce from 21.3 GPa and 4.4-14.6 GPa and 3.6 GPa by using a low cooling-rated aging process. After aging process, the compressive deformation behavior of dense part changes from elastic-plastic-fracture mode to elastic-plastic-densification mode. On the other hand, the failure mechanism of lattice structural sample changes from rapid-single-stage to slow-double-stage with an improvement of the strain at failure.
Title:
Unconventional Charge Density Wave Order in the Pnictide Superconductor Ba(Ni1-xCox)(2)As-2
Authors:
Lee, S; de la Pena, G; Sun, SXL; Mitrano, M; Fang, YZ; Jang, HY; Lee, JS; Eckberg, C; Campbell, D; Collini, J; Paglione, J; de Groot, FMF; Abbamonte, P Author Full Names: Lee, Sangjun; de la Pena, Gilberto; Sun, Stella X-L; Mitrano, Matteo; Fang, Yizhi; Jang, Hoyoung; Lee, Jun-Sik; Eckberg, Chris; Campbell, Daniel; Collini, John; Paglione, Johnpierre; de Groot, F. M. F.; Abbamonte, Peter
Source:
PHYSICAL REVIEW LETTERS, 122 (14):10.1103/PhysRevLett.122.147601 APR 12 2019
Abstract:
Ba(Ni1-xCox)(2)As-2 is a structural homologue of the pnictide high temperature superconductor, Ba(Fe1-xCox)(2)As-2, in which the Fe atoms are replaced by Ni. Superconductivity is highly suppressed in this system, reaching a maximum T-c = 2.3 K, compared to 24 K in its iron-based cousin, and the origin of this T-c suppression is not known. Using x-ray scattering, we show that Ba(Ni1-xCox)(2)As-2 exhibits a unidirectional charge density wave (CDW) at its triclinic phase transition. The CDW is incommensurate, exhibits a sizable lattice distortion, and is accompanied by the appearance of alpha Fermi surface pockets in photoemission [B. Zhou et al., Phys. Rev. B 83, 035110 (2011)], suggesting it forms by an unconventional mechanism. Co doping suppresses the CDW, paralleling the behavior of antiferromagnetism in iron-based superconductors. Our study demonstrates that pnictide superconductors can exhibit competing CDW order, which may be the origin of T-c suppression in this system.
Title:
Electron diffraction study of crystal structures of (Sr1-xBax)(2)Nb2O7
Authors:
Aryal, B; Morikawa, D; Tsuda, K; Tsukada, S; Akishige, Y; Terauchi, M Author Full Names: Aryal, Bikas; Morikawa, Daisuke; Tsuda, Kenji; Tsukada, Shinya; Akishige, Yukikuni; Terauchi, Masami
Source:
PHYSICAL REVIEW MATERIALS, 3 (4):10.1103/PhysRevMaterials.3.044405 APR 12 2019
Abstract:
Selected-area electron diffraction and convergent-beam electron diffraction (CBED) techniques are used to reveal the Ba doping effect on the crystal structure of (Sr1-xBax)(2)Nb2O7 [SBN(x)] in the temperature range from 293 to 693 K. Ba doping of Sr2Nb2O7 (SN) causes weakening of the incommensurate modulation and deviation from the C-centered lattice. On the other hand, symmetries of fundamental reflections in CBED patterns of SBN(x) are seen to be the same as those of SN, showing a small structural deviation from Cmc2(1). Crystal symmetries above and below the temperature of a relaxorlike dielectric anomaly in SBN (x = 0.32) at 465 K remain unchanged. CBED experiments with a nanometer-sized electron probe do not show any indication of the presence of a nanodomain around this temperature. However, the presence of a few-micron-sized polar-inversion domains is found at around 573 K in SBN (x = 0.32). The origin of the reported relaxorlike dielectric anomaly in SBN (x = 0.32) is discussed on the basis of the experimental results of CBED.

Update: 25-Apr-2019

Title:
Influence of Ir Additions and Icosahedral Short Range Order (ISRO) on Nucleation and Growth Kinetics in Au-20.5Wt Pct Cu-4.5Wt PctAg Alloy
Authors:
Zollinger, J; Rouat, B; Guyon, J; Pillai, SK; Rappaz, M Author Full Names: Zollinger, J.; Rouat, B.; Guyon, J.; Pillai, S. K.; Rappaz, M.
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 50A (5):2279-2288; 10.1007/s11661-019-05176-2 MAY 2019
Abstract:
Based on detailed EBSD analyses, Kurtuldu et al. (Acta Mater. 70:240-248, 2014) have explained the grain refinement of Au-12.5 wt pctCu-12.5 wt pctAg (yellow gold) by the addition of minute amounts of Ir in terms of icosahedral quasicrystal (iQC)-mediated nucleation, i.e., Ir induced the formation of Icosahedral short range order (ISRO) of atoms in the liquid, leading to the formation of iQC on which the fcc-phase forms. In the present contribution, we show that: (i) this mechanism is also responsible of the grain refinement in Au-20.5 wt pctCu-4.5 wt pctAg (pink gold) with Ir addition; (ii) ISRO also influences the morphology and growth kinetics of the fcc phase: at solidification rate of a few mm/s, 100 dendrites are replaced by a cellular-type morphology growing along 111 when 100 wt ppm of Ir is added to the melt; (iii) iQC-mediated nucleation is accompanied by a spinodal decomposition of the liquid, which is revealed at high cooling rate by the formation of Cu-rich particles or dendrites, some of them being also twinned, in parallel to iQC-mediated grain refinement and twin formation. (C) The Minerals, Metals & Materials Society and ASM International 2019
Title:
Structural evolution of La2Ti2O7 at elevated temperatures
Authors:
Ishizawa, N; Ninomiya, K; Wang, J Author Full Names: Ishizawa, Nobuo; Ninomiya, Keisuke; Wang, Jun
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 75 10.1107/S2052520619002105 2 APR 2019
Abstract:
Structural evolution of a La2Ti2O7 ferroelectric compound possessing perovskite-type slabs at elevated temperatures was investigated using the single-crystal X-ray diffraction technique. The monoclinic low-temperature phase (L) transformed into the orthorhombic high-temperature phase (H) via an incommensurately modulated phase (IC) between similar to 989 and similar to 1080 K. The L-IC transition was considered to be of the first order, with the L+IC two-phase co-existing region between similar to 989 and similar to 1027 K. The structure of IC was determined from the (3+1)-dimensional superspace representation with a modulation vector q = alpha a(o) (alpha similar or equal to 0.49), where a o is the a-axis vector of the basic cell. The structural modulation originated from the variation of the tilt angle of the TiO6 octahedra in the perovskite-type slab in association with small positional displacements of La atoms. The IC-H transition took place at -1080 K and was close to the second order. During the IC-H transition, nanoscale flat plate domains having either a cell twin of the L-type structural modules or a cell twin of the alternating H- and L-type structural modules began to appear in the approximant structure of IC. The thickness of the flat plate domains then grew rapidly along the modulation vector in proportion to (1/2-alpha)(-1) as alpha approached 1/2 with decreasing temperature. In the two-phase L+IC co-existing region, the IC phase consisting of the two types of cell twins was gradually replaced with the low-temperature monoclinic phase L, which is not cell twinned but rather twinned macroscopically by the L-type structural modules.

Update: 17-Apr-2019

Title:
Distortion analysis of crystalline and locally quasicrystalline 2D photonic structures with grazing-incidence small-angle X-ray scattering
Authors:
Pfluger, M; Soltwisch, V; Xavier, J; Probst, J; Scholze, F; Becker, C; Krumrey, M Author Full Names: Pflueger, Mika; Soltwisch, Victor; Xavier, Jolly; Probst, Juergen; Scholze, Frank; Becker, Christiane; Krumrey, Michael
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 52 322-331; 10.1107/S1600576719001080 2 APR 2019
Abstract:
In this study, grazing-incidence small-angle X-ray scattering (GISAXS) is used to collect statistical information on dimensional parameters in an area of 20 x 15 mm on photonic structures produced by nanoimprint lithography. The photonic structures are composed of crystalline and locally quasicrystalline two-dimensional patterns with structure sizes between about 100 nm and 10 mu m to enable broadband visible light absorption for use in solar-energy harvesting. These first GISAXS measurements on locally quasicrystalline samples demonstrate that GISAXS is capable of showing the locally quasicrystalline nature of the samples while at the same time revealing the long-range periodicity introduced by the lattice design. The scattering is described qualitatively in the framework of the distorted-wave Born approximation using a hierarchical model mirroring the sample design, which consists of a rectangular and locally quasicrystalline supercell that is repeated periodically to fill the whole surface. The nanoimprinted samples are compared with a sample manufactured using electron-beam lithography and the distortions of the periodic and locally quasiperiodic samples are quantified statistically. Owing to the high sensitivity of GISAXS to deviations from the perfect lattice, the misalignment of the crystallographic axes was measured with a resolution of 0.015 degrees, showing distortions of up to +/- 0.15 degrees in the investigated samples.
Title:
Effects of semisolid treatment and ECAP on the microstructure and mechanical properties of Mg-6.52Zn-0.95Y alloy with icosahedral phase
Authors:
Li, KN; Zhang, YB; Zeng, Q; Huang, GH; Ji, B; Yin, DD Author Full Names: Li, K. N.; Zhang, Y. B.; Zeng, Q.; Huang, G. H.; Ji, B.; Yin, D. D.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 751 283-291; 10.1016/j.msea.2019.02.083 MAR 28 2019
Abstract:
The microstructure evolutions and mechanical properties of Mg-6.52Zn-0.95Y (wt%) alloy with icosahedral phase (I-phase) by semisolid treatment and equal channel angular processing (ECAP) were systematically investigated. After semisolid treatment, lamellar ultra-fine eutectic phases with spacing of 100 +/- 19 nm formed at the grain boundaries. After subsequent 4 passes ECAP, fine grains (2.9 +/- 0.4 gm) were obtained and the lamellar eutectic phases were fragmented into 50-500 nm granular particles. The best comprehensive mechanical properties with ultimate tensile strength (UTS) of 385 +/- 18 MPa, tensile yield strength (TYS) of 290 +/- 3 MPa and elongation to failure (EL) of 22.0 +/- 1.6% were obtained by the combination of semisolid treatment and subsequent 2 passes ECAP at 300 degrees C followed by 2 passes ECAP at 200 degrees C, compared with that by the initial alloy. The improvement of mechanical properties results from combined effects of the grain refinement, dispersion of nanoscale I-phase particles and weakened basal texture. In addition, the I-phase particles contributed to the grain refinement during dynamic recrystallization by particle stimulated nucleation (PSN), which contributed to both strength and ductility. The average Schmid factor (SF) of basal slip increased from 0.2 to 0.4 after semisolid treatment and ECAP processing, which benefit the ductility.
Title:
Influence of cobalt substitution on the magnetism of NiBr2
Authors:
Rai, BK; Christianson, AD; Mandrus, D; May, AF Author Full Names: Rai, Binod K.; Christianson, Andrew D.; Mandrus, David; May, Andrew F.
Source:
PHYSICAL REVIEW MATERIALS, 3 (3):10.1103/PhysRevMaterials.3.034005 MAR 25 2019
Abstract:
Co-substituted Ni1-xCoxBr2 (0 <= x <= 1) single crystals were synthesized using vapor transport. The physical properties of the crystals were characterized by x-ray powder diffraction, magnetization, and specific-heat measurements. Room-temperature x-ray powder diffraction data indicate that a change from the CdCl2 structure type to the CdI2 structure type occurs within 0.56 < x < 0.76. NiBr2 has a commensurate antiferromagnetic phase below TN approximate to 46 K and an incommensurate magnetic ground state below TIC approximate to 20 K. Both magnetic transitions are affected by cobalt substitution, and the incommensurate phase transition is present up to at least x = 0.56. The evolution of magnetism has been studied as a function of cobalt content and is summarized in the temperature-composition phase diagram.
Title:
A neutron diffraction demonstration of long-range magnetic order in the quasicrystal approximant DyCd6
Authors:
Ryan, DH; Cadogan, JM; Kong, T; Canfield, PC; Goldman, AI; Kreyssig, A Author Full Names: Ryan, D. H.; Cadogan, J. M.; Kong, T.; Canfield, P. C.; Goldman, A. I.; Kreyssig, A.
Source:
AIP ADVANCES, 9 (3):10.1063/1.5079991 MAR 2019
Abstract:
We have used neutron powder diffraction to demonstrate the existence of long-range antiferromagnetic order of Ising-like Dy moments in the DyCd6 quasicrystal approximant phase. This cubic compound undergoes a slight distortion to a monoclinic cell at low temperatures. The Neel temperature is 18.0(2) K and the magnetic order of the Dy sublattice may be described in the parent cubic Im (3) over bar structure using a combination of two propagation vectors, k(1) = [0 0 0] and k(2) = [1/2 0 1/2], yielding 'anti-I' order. Alternatively, when referred to the monoclinic C2/c cell, the magnetic structure may be described by a single propagation vector: k = [1 0 0]. (C) 2019 Author(s).
Title:
Modulated magnetic structure in Fe-57 doped orthorhombic YbMnO3: A Mossbauer study
Authors:
Duttine, M; Wattiaux, A; Balima, F; Decorse, C; Moutaabbid, H; Ryan, DH; Bonville, P Author Full Names: Duttine, Mathieu; Wattiaux, Alain; Balima, Felix; Decorse, Claudia; Moutaabbid, Hicham; Ryan, D. H.; Bonville, Pierre
Source:
AIP ADVANCES, 9 (3):10.1063/1.5077005 MAR 2019
Abstract:
In the orthorhombic manganites o-RMnO3, where R is a heavy rare earth (R = Gd-Yb), the Mn3+ sublattice is known to undergo two magnetic transitions. The low temperature phase has an antiferromagnetic structure (collinear or elliptical), which has been well characterized by neutron diffraction in most of these compounds. The intermediate phase, occurring in a narrow temperature range (a few K), is documented for R = Gd-Ho as a collinear modulated structure, incommensurate with the lattice spacings. We report here on a Fe-57 Mossbauer study of 2% Fe-57 doped o-YbMnO3, where the spin only Fe3+ ion plays the role of a magnetic probe. From the analysis of the shape of the magnetic hyperfine Mossbauer spectra, we show that the magnetic structure of the intermediate phase in o-YbMnO3 (38.0 K < T < 41.5 K) is also modulated and incommensurate. (C) 2019 Author(s).

Update: 10-Apr-2019

Title:
Relaxing Kondo-screened Kramers doublets in CeRhSi3
Authors:
Pasztorova, J; Howell, A; Songvilay, M; Sarte, PM; Rodriguez-Rivera, JA; Arevalo-Lopez, AM; Schmalzl, K; Schneidewind, A; Dunsiger, SR; Singh, DK; Petrovic, C; Hu, R; Stock, C Author Full Names: Pasztorova, J.; Howell, A.; Songvilay, M.; Sarte, P. M.; Rodriguez-Rivera, J. A.; Arevalo-Lopez, A. M.; Schmalzl, K.; Schneidewind, A.; Dunsiger, S. R.; Singh, D. K.; Petrovic, C.; Hu, R.; Stock, C.
Source:
PHYSICAL REVIEW B, 99 (12):10.1103/PhysRevB.99.125144 MAR 25 2019
Abstract:
CeRhSi3 is a superconductor under pressure coexisting with a weakly antiferromagnetic phase characterized by a Bragg peak at (q) over right arrow (0) = (similar to 0.2, 0, 0.5) [N. Aso et al., J. Magn. Magn. Mater. 310, 602 (2007)]. The compound is also a heavy-fermion material with a large specific heat coefficient gamma = 110 mJ mol(-1) K-2 and a high Kondo temperature of T-K = 50 K, indicating CeRhSi3 is in a strongly Kondo screened state. We apply high-resolution neutron spectroscopy to investigate the magnetic fluctuations in the normal phase, at ambient pressures, and at low temperatures. We measure a commensurate dynamic response centered around the (Q) over right arrow = (0, 0, 2) position that gradually evolves to H similar to 0.2 with decreasing temperature and/or energy transfers. The response is broadened both in momentum and energy and is not reminiscent of sharp spin wave excitations found in insulating magnets where the electrons are localized. We parametrize the excitation spectrum and temperature dependence using a heuristic model utilizing the random-phase approximation to couple relaxing Ce3+ ground-state Kramers doublets with a Kondo-like dynamic response. With a Ruderman-Kittel-Kasuya-Yosida exchange interaction within the ab plane and an increasing single-site susceptibility, we can qualitatively reproduce the neutron spectroscopic results in CeRhSi3 and, namely, the trade-off between scattering at commensurate and incommensurate positions. We suggest that the antiferromagnetic phase in CeRhSi3 is driven by weakly correlated relaxing localized Kramers doublets and that CeRhSi3 at ambient pressures is on the border between a Rudderman-Kittel-Yosida antiferromagnetic state and a Kondo-screened phase where static magnetism is predominately absent.

Update: 4-Apr-2019

Title:
Analysis solution method for 3D planar crack problems of two-dimensional hexagonal quasicrystals with thermal effects
Authors:
Li, Y; Zhao, MH; Qin, QH; Fan, CY Author Full Names: Li, Yuan; Zhao, MingHao; Qin, Qing-Hua; Fan, CuiYing
Source:
APPLIED MATHEMATICAL MODELLING, 69 648-664; 10.1016/j.apm.2019.01.004 MAY 2019
Abstract:
An analysis solution method (ASM) is proposed for analyzing arbitrarily shaped planar cracks in two-dimensional (2D) hexagonal quasicrystal (QC) media. The extended displacement discontinuity (EDD) boundary integral equations governing three-dimensional (3D) crack problems are transferred to simplified integral-differential forms by introducing some complex quantities. The proposed ASM is based on the analogy between these EDD boundary equations for 3D planar cracks problems of 2D hexagonal QCs and those in isotropic thermoelastic materials. Mixed model crack problems under combined normal, tangential and thermal loadings are considered in 2D hexagonal QC media. By virtue of ASM, the solutions to 3D planar crack problems under various types of loadings for 2D hexagonal QCs are formulated through comparison to the corresponding solutions of isotropic thermoelastic materials which have been studied intensively and extensively. As an application, analytical solutions of a penny-shaped crack subjected uniform distributed combined loadings are obtained. Especially, the analytical solutions to a penny-shaped crack subjected to the anti-symmetric uniform thermal loading are first derived for 2D hexagonal QCs. Numerical solutions obtained by EDD boundary element method provide a way to verify the validity of the presented formulation. The influences of phonon-phason coupling effect on fracture parameters of 2D hexagonal QCs are assessed. (C) 2019 Elsevier Inc. All rights reserved.
Title:
Rational Design and Self-Assembly of Two-Dimensional, Dodecagonal DNA Quasicrystals
Authors:
Liu, LF; Li, Z; Li, YL; Mao, CD Author Full Names: Liu, Longfei; Li, Zhe; Li, Yulin; Mao, Chengde
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 141 (10):4248-4251; 10.1021/jacs.9b00843 MAR 13 2019
Abstract:
Quasicrystals are a class of materials with long-range order but no translational periodicity. Though many quasicrystals have been discovered, rational design and engineering of quasicrystals remain a great challenge. Herein, we have developed a rational strategy to assemble two-dimensional (2D), dodecagonal quasicrystals from branched DNA nanomotifs. The key of our strategy is to balance the rigidity and flexibility of the motifs, which is controlled by the introduction of interbranch "bridges". By fine-tuning the experimental conditions, we are able to predictably produce either 2D quasicrystals or conventional crystals. This study presents a rational design, prediction and realization of quasicrystal formation.

Update: 27-Mar-2019

Title:
Spinodal decomposition in a melt-spun Cu-15Ni-8Sn alloy
Authors:
Kondo, S; Nakashima, H; Morimura, T Author Full Names: Kondo, Shin-ichiro; Nakashima, Hiromichi; Morimura, Takao
Source:
PHYSICA B-CONDENSED MATTER, 560 244-254; 10.1016/j.physb.2019.01.030 MAY 1 2019
Abstract:
We investigate the spinodal decomposition process in a melt-spun Cu-15Ni-8Sn alloy using X-ray diffraction (XRD), transmission electron microscopy (TEM), and electron diffraction analyses. In the XRD measurements, an aging treatment of more than 300 min at 350 degrees C was required to obtain the (200) sidebands. TEM observations of the melt-spun samples aged at 350 degrees C for 40, 60, and 300 min showed a modulated structure with a wavelength too small to be detected by TEM and aging for about 1200 min was required for the clear appearance of a modulated structure. The electron diffraction patterns showed only the disordered fcc phase with no satellite structures in the sample aged for 20 min at 350 degrees C, which implied that no spinodal decomposition occurred. Aging for 40 min at 350 degrees C was required before the super-lattice reflection of DO22 was observed. These experimental results indicate that the decomposition process in the melt-spun alloy was slow initially.
Title:
Analytical and numerical investigations of noncollinear magnetic ordering in the frustrated delafossite CuCrO2
Authors:
Albaalbaky, A; Kvashnin, Y; Patte, R; Ledue, D Author Full Names: Albaalbaky, Ahmed; Kvashnin, Yaroslav; Patte, Renaud; Ledue, Denis
Source:
PHYSICAL REVIEW B, 99 (10):10.1103/PhysRevB.99.104415 MAR 12 2019
Abstract:
The magnetic propagation vector in delafossite CuCrO2 with classical Heisenberg spins is calculated analytically as a function of exchange interactions up to fourth-nearest neighbors. Exchange interactions are estimated by a series of density functional theory calculations for several values of lattice distortion. Our calculations show that the magnetic propagation vector is directly affected by the considered distortions providing different stable commensurate or incommensurate magnetic configurations. A realistic set of exchange interactions corresponding to a 0.1% lattice distortion yields the experimental ground state with an incommensurate propagation vector q similar to (0.329, 0.329, 0). We find that a very weak antiferromagnetic interlayer interaction favors an incommensurate ordering even in the absence of lattice distortion. Moreover, the exchange energy of a magnetic configuration of a finite crystal of CuCrO2 with periodic boundary conditions is derived analytically. Based on that, highly accurate Monte Carlo simulations performed on CuCrO2 confirm both the proposed analytical calculations and the density functional theory estimations, where we obtain excellent convergence toward the experimental ground state with a magnetic propagation vector q = (0.3288, 0.3288, 0).
Title:
Size effect of soft phonon dispersion in nanosized ferroics
Authors:
Morozovska, AN; Eliseev, EA Author Full Names: Morozovska, Anna N.; Eliseev, Eugene A.
Source:
PHYSICAL REVIEW B, 99 (11):10.1103/PhysRevB.99.115412 MAR 11 2019
Abstract:
Using Landau-Ginsburg-Devonshire theory, we derive and analyze analytical expressions for the frequency dispersion of soft phonon modes in nanosized ferroics and perform numerical calculations for a thin SrTiO3 film. We revealed the pronounced "true" size effect in the dependence of soft phonon spatial dispersion on the film thickness and predict that it can lead to the "apparent" or "false" size effect of dynamic flexoelectric coupling constants. Also, we derived analytical expressions describing the influence of finite size effect on the appearance and properties of the incommensurate spatial modulation induced by the static flexoelectric effect in ferroic thin films. To verify the theoretical predictions experimental measurements of the soft phonon dispersion in nanosized ferroics seem urgent.
Title:
Magnetic-field-induced incommensurate to collinear spin order transition in NiBr2
Authors:
Babu, S; Prokes, K; Huang, YK; Radu, F; Mishra, SK Author Full Names: Babu, S.; Prokes, K.; Huang, Y. K.; Radu, F.; Mishra, S. K.
Source:
JOURNAL OF APPLIED PHYSICS, 125 (9):10.1063/1.5066625 MAR 7 2019
Abstract:
The triangular spin lattice of NiBr2 is a canonical example of the frustrated helimagnet that shows a collinear commensurate antiferromagnetic to an incommensurate spin helix phase transition on cooling. Herein, we have studied a self-flux grown NiBr2 single crystal by neutron diffraction and low temperature magnetization measurements at fields up to 14 T. Experimental findings enable the deduction of the driving force responsible for the spin spiral ordering. The neutron diffraction data reveal satellite peaks representing characteristic features of an incommensurate magnetic state. The satellites develop symmetrically below T-N = 44.0(1) K, replacing the main magnetic reflections. Interestingly, a field-induced incommensurate to commensurate spin phase transition has been successfully demonstrated, which enforces the spin helix to restore the high temperature compensated antiferromagnetic structure. This reorientation can be described by a spin-flop in the (a-b) basal plane of a triangular spin lattice system. The findings offer a novel way for spin helix control of incommensurate phases, having immense scientific and technological implications in the next generation data storage devices.

Update: 20-Mar-2019

Title:
Isothermal section of Ga-Co-Cu phase diagram at 830 degrees C and its peculiarities
Authors:
Priputen, P; Drienovsky, M; Noga, P; Kusy, M; Cernickova, I; Janovec, J Author Full Names: Priputen, P.; Drienovsky, M.; Noga, P.; Kusy, M.; Cernickova, I; Janovec, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 785 1173-1179; 10.1016/j.jallcom.2019.01.288 MAY 15 2019
Abstract:
Recently, the Ga-based ternary alloys have gained interest for the possibility of finding new quasicrystals. Inspired by the previously reported decagonal and icosahedral quasicrystals identified in the Ga50Co25Cu25 alloy at 830 degrees C, the phase equilibria of 27 alloys of various composition were investigated in this work. Based on the obtained results, an isothermal section of the Ga-Co-Cu phase diagram at 830 degrees C was proposed. However, neither decagonal nor icosahedral quasicrystals were found to be stable at 830 degrees C, but instead of that, a superalloy-like structure was found in the Ga35Co25Cu40 alloy consisting of beta-GaCo and beta-GaCug-GaCu. (C) 2019 Elsevier B.V. All rights reserved.
Title:
Band gap closure, incommensurability and molecular dissociation of dense chlorine
Authors:
Dalladay-Simpson, P; Binns, J; Pena-Alvarez, M; Donnelly, ME; Greenberg, E; Prakapenka, V; Chen, XJ; Gregoryanz, E; Howie, RT Author Full Names: Dalladay-Simpson, Philip; Binns, Jack; Pena-Alvarez, Miriam; Donnelly, Mary-Ellen; Greenberg, Eran; Prakapenka, Vitali; Chen, Xiao-Jia; Gregoryanz, Eugene; Howie, Ross T.
Source:
NATURE COMMUNICATIONS, 10 10.1038/s41467-019-09108-x MAR 8 2019
Abstract:
Diatomic elemental solids are highly compressible due to the weak interactions between molecules. However, as the density increases the intra-and intermolecular distances become comparable, leading to a range of phenomena, such as structural transformation, molecular dissociation, amorphization, and metallisation. Here we report, following the crystallization of chlorine at 1.15(30) GPa into an ordered orthorhombic structure (oC8), the existence of a mixed-molecular structure (mC8, 130(10)-241(10) GPa) and the concomitant observation of a continuous band gap closure, indicative of a transformation into a metallic molecular form around 200(10) GPa. The onset of dissociation of chlorine is identified by the observation of the incommensurate structure (i-oF4) above 200(10) GPa, before finally adopting a monatomic form (oI2) above 256(10) GPa.
Title:
Resonantly hybridized excitons in moire superlattices in van der Waals heterostructures
Authors:
Alexeev, EM; Ruiz-Tijerina, DA; Danovich, M; Hamer, MJ; Terry, DJ; Nayak, PK; Ahn, S; Pak, S; Lee, J; Sohn, JI; Molas, MR; Koperski, M; Watanabe, K; Taniguchi, T; Novoselov, KS; Gorbachev, RV; Shin, HS; Fal'ko, VI; Tartakovskii, AI Author Full Names: Alexeev, Evgeny M.; Ruiz-Tijerina, David A.; Danovich, Mark; Hamer, Matthew J.; Terry, Daniel J.; Nayak, Pramoda K.; Ahn, Seongjoon; Pak, Sangyeon; Lee, Juwon; Sohn, Jung Inn; Molas, Maciej R.; Koperski, Maciej; Watanabe, Kenji; Taniguchi, Takashi; Novoselov, Kostya S.; Gorbachev, Roman V.; Shin, Hyeon Suk; Fal'ko, Vladimir I.; Tartakovskii, Alexander I.
Source:
NATURE, 567 (7746):81-+; 10.1038/s41586-019-0986-9 MAR 7 2019
Abstract:
Atomically thin layers of two-dimensional materials can be assembled in vertical stacks that are held together by relatively weak van der Waals forces, enabling coupling between monolayer crystals with incommensurate lattices and arbitrary mutual rotation(1,2). Consequently, an overarching periodicity emerges in the local atomic registry of the constituent crystal structures, which is known as a moire superlattice(3). In graphene/hexagonal boron nitride structures(4), the presence of a moire superlattice can lead to the observation of electronic minibands(5-7), whereas in twisted graphene bilayers its effects are enhanced by interlayer resonant conditions, resulting in a superconductor-insulator transition at magic twist angles(8). Here, using semiconducting heterostructures assembled from incommensurate molybdenum diselenide (MoSe2) and tungsten disulfide (WS2) monolayers, we demonstrate that excitonic bands can hybridize, resulting in a resonant enhancement of moire superlattice effects. MoSe2 and WS2 were chosen for the near-degeneracy of their conduction-band edges, in order to promote the hybridization of intra- and interlayer excitons. Hybridization manifests through a pronounced exciton energy shift as a periodic function of the interlayer rotation angle, which occurs as hybridized excitons are formed by holes that reside in MoSe2 binding to a twist-dependent superposition of electron states in the adjacent monolayers. For heterostructures in which the monolayer pairs are nearly aligned, resonant mixing of the electron states leads to pronounced effects of the geometrical moire pattern of the heterostructure on the dispersion and optical spectra of the hybridized excitons. Our findings underpin strategies for bandstructure engineering in semiconductor devices based on van der Waals heterostructures(9).
Title:
Redox behaviour and solid solubility of cerium ortho-niobates
Authors:
Harris, CM; Skinner, SJ Author Full Names: Harris, Cassandra M.; Skinner, Stephen J.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 271 135-143; 10.1016/j.jssc.2018.12.042 MAR 2019
Abstract:
Using Ce L-III edge X-ray absorption near edge spectroscopy (XANES), it is shown that acceptor dopants introduced to cerium members of the rare earth ortho-niobate series, Ce1-xSrxNbO4 +/- delta and Ce1-xSrxNbO4 +/- delta, are charge compensated by the formation of holes on the cerium sublattice. These spectroscopic studies are complemented by structural studies, using X-ray and neutron powder diffraction, determining that the solubility limit of the strontium and calcium dopants within the CeNbO4+delta structure is similar to 10% and similar to 30% respectively. Under oxidising conditions, the Ce3+/Ce4+ redox couple facilitates reversible redox processes, and it is observed that the Ce1-xSrxNbO4 +/- delta and Ce1-xSrxNbO4 +/- delta materials form commensurate and incommensurately modulated oxygen hyperstoichiometric phases as a function of temperature. Under reducing atmospheres, this redox activity is suppressed, and charge-compensating Ce4+ holes are annihilated.
Title:
Kinetics of a Phonon-Mediated Laser-Driven Structural Phase Transition in Sn2P2Se6
Authors:
Kubli, M; Savoini, M; Abreu, E; Burganov, B; Lantz, G; Huber, L; Neugebauer, MJ; Boie, L; Esposito, V; Bothschafter, EM; Parchenko, S; Grubel, S; Porer, M; Rittmann, J; Beaud, P; Staub, U; Yabashi, M; Tanaka, Y; Katayama, T; Togashi, T; Kohutych, AA; Vysochanskii, YM; Johnson, SL Author Full Names: Kubli, Martin; Savoini, Matteo; Abreu, Elsa; Burganov, Bulat; Lantz, Gabriel; Huber, Lucas; Neugebauer, Martin J.; Boie, Larissa; Esposito, Vincent; Bothschafter, Elisabeth M.; Parchenko, Sergii; Gruebel, Sebastian; Porer, Michael; Rittmann, Jochen; Beaud, Paul; Staub, Urs; Yabashi, Makina; Tanaka, Yoshikazu; Katayama, Tetsuo; Togashi, Tadashi; Kohutych, Anton A.; Vysochanskii, Yulian M.; Johnson, Steven L.
Source:
APPLIED SCIENCES-BASEL, 9 (3):10.3390/app9030525 FEB 1 2019
Abstract:
We investigate the structural dynamics of the incommensurately modulated phase of Sn2P2Se6 by means of time-resolved X-ray diffraction following excitation by an optical pump. Tracking the incommensurable distortion in the time domain enables us to identify the transport effects leading to a complete disappearance of the incommensurate phase over the course of 100 ns. These observations suggest that a thin surface layer of the high-temperature phase forms quickly after photo-excitation and then propagates into the material with a constant velocity of 3.7 m/s. Complementary static structural measurements reveal previously unreported higher-order satellite reflection in the incommensurate phase. These higher-order reflections are attributed to cubic vibrational terms in the Hamiltonian.
Title:
Wood-Derived Dietary Fibers Promote Beneficial Human Gut Microbiota
Authors:
La Rosa, SL; Kachrimanidou, V; Buffetto, F; Pope, PB; Pudlo, NA; Martens, EC; Rastall, RA; Gibson, GR; Westereng, B Author Full Names: La Rosa, Sabina Leanti; Kachrimanidou, Vasiliki; Buffetto, Fanny; Pope, Phillip B.; Pudlo, Nicholas A.; Martens, Eric C.; Rastall, Robert A.; Gibson, Glenn R.; Westereng, Bjerge
Source:
MSPHERE, 4 (1):10.1128/mSphere.00554-18 JAN-FEB 2019
Abstract:
Woody biomass is a sustainable and virtually unlimited source of hemicellulosic polysaccharides. The predominant hemicelluloses in softwood and hardwood are galactoglucomannan (GGM) and arabinoglucuronoxylan (AGX), respectively. Based on the structure similarity with common dietary fibers, GGM and AGX may be postulated to have prebiotic properties, conferring a health benefit on the host through specific modulation of the gut microbiota. In this study, we evaluated the prebiotic potential of acetylated GGM (AcGGM) and highly acetylated AGX (AcAGX) obtained from Norwegian lignocellulosic feedstocks in vitro. In pure culture, both substrates selectively promoted the growth of Bifidobacterium, Lactobacillus, and Bacteroides species in a manner consistent with the presence of genetic loci for the utilization of beta-manno-oligosaccharides/beta-mannans and xylo-oligosaccharides/ xylans. The prebiotic potential of AcGGM and AcAGX was further assessed in a pH-controlled batch culture fermentation system inoculated with healthy adult human feces. Results were compared with those obtained with a commercial fructo-oligosaccharide (FOS) mixture. Similarly to FOS, both substrates significantly increased (P < 0.05) the Bifidobacterium population. Other bacterial groups enumerated were unaffected with the exception of an increase in the growth of members of the Bacteroides-Prevotella group, Faecalibacterium prausnitzii, and clostridial cluster IX (P < 0.05). Compared to the other substrates, AcGGM promoted butyrogenic fermentation whereas AcAGX was more propiogenic. Although further in vivo confirmation is necessary, these results demonstrate that both AcGGM and AcAGX from lignocellulosic feedstocks can be used to direct the promotion of beneficial bacteria, thus exhibiting a promising prebiotic ability to improve or restore gut health. IMPORTANCE The architecture of the gut bacterial ecosystem has a profound effect on the physiology and well-being of the host. Modulation of the gut microbiota and the intestinal microenvironment via administration of prebiotics represents a valuable strategy to promote host health. This work provides insights into the ability of two novel wood-derived preparations, AcGGM and AcAGX, to influence human gut microbiota composition and activity. These compounds were selectively fermented by commensal bacteria such as Bifidobacterium, Bacteroides-Prevotella, F. prausnitzii, and clostridial cluster IX spp. This promoted the microbial synthesis of acetate, propionate, and butyrate, which are beneficial to the microbial ecosystem and host colonic epithelial cells. Thus, our results demonstrate potential prebiotic properties for both AcGGM and AcAGX from lignocellulosic feedstocks. These findings represent pivotal requirements for rationally designing intervention strategies based on the dietary supplementation of AcGGM and AcAGX to improve or restore gut health.

Update: 13-Mar-2019

Title:
Mechanics of dislocations and metadislocations in quasicrystals and their approximants: power invariance and balance
Authors:
Mariano, PM Author Full Names: Mariano, Paolo Maria
Source:
CONTINUUM MECHANICS AND THERMODYNAMICS, 31 (2):373-399; 10.1007/s00161-018-0690-2 MAR 2019
Abstract:
We discuss the mechanics of a single dislocation in quasicrystals. We account for dislocation's core by means of a non-constant line energy. Above all, we focus attention on the origin of the balance equations involving the pertinent bulk and line actions. We derive all balances, including those of configurational actions along the dislocation line,from a unique invariance requirement for the so-called relative power; it is an axiom that furnishes also the action-reaction principle for the standard traction and the phason one, as well as the standard Cauchy theorem and, in addition, the existence of phason stress and self-action. The theoretical scheme presented here includes the description of the large core of metadislocations in quasicrystal's approximants (complex metallic alloys). Each metadislocation features thousands of atoms per unit thickness in the direct vicinity of the core, a circumstance suggesting to consider it as a sort of micro-rod, a view adopted in the present paper. In fact, from an abstract point of view, the results presented here describe the motion of a rod within a body with vectorial microstructure.
Title:
Principles of weakly ordered domains in intermetallics: the cooperative effects of atomic packing and electronics in Fe2Al5
Authors:
Vinokur, AI; Hilleke, KP; Fredrickson, DC Author Full Names: Vinokur, Anastasiya, I; Hilleke, Katerina P.; Fredrickson, Daniel C.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 297-306; 10.1107/S2053273318017461 2 MAR 2019
Abstract:
Many complex intermetallic structures feature a curious juxtaposition of domains with strict 3D periodicity and regions of much weaker order or incommensurability. This article explores the basic principles leading to such arrangements through an investigation of the weakly ordered channels of Fe2Al5. It starts by experimentally confirming the earlier crystallographic model of the high-temperature form, in which nearly continuous columns of electron density corresponding to disordered Al atoms emerge. Then electronic structure calculations on ordered models are used to determine the factors leading to the formation of these columns. These calculations reveal electronic pseudogaps near 16 electrons/Fe atom, an electron concentration close to the Al-rich side of the phase's homogeneity range. Through a reversed approximation Molecular Orbital (raMO) analysis, these pseudogaps are correlated with the filling of 18-electron configurations on the Fe atoms with the support of isolobal sigma Fe-Fe bonds. The resulting preference for 16 electrons/Fe requires a fractional number of Al atoms in the Fe2Al5 unit cell. Density functional theory-chemical pressure (DFT-CP) analysis is then applied to investigate how this nonstoichiometry is accommodated. The CP schemes reveal strong quadrupolar distributions on the Al atoms of the channels, suggestive of soft atomic motions along the undulating electron density observed in the Fourier map that allow the Al positions to shift easily in response to compositional changes. Such a combination of preferred electron counts tied to stoichiometry and continuous paths of CP quadrupoles could provide predictive indicators for the emergence of channels of disordered or incommensurately spaced atoms in intermetallic structures.
Title:
Ted Janssen and aperiodic crystals
Authors:
de Boissieu, M Author Full Names: de Boissieu, Marc
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 273-280; 10.1107/S2053273318016765 2 MAR 2019
Abstract:
This article reviews some of Ted Janssen's (1936-2017) major contributions to the field of aperiodic crystals. Aperiodic crystals are long-range ordered structures without 3D lattice translations and encompass incommensurately modulated phases, incommensurate composites and quasicrystals. Together with Pim de Wolff and Aloysio Janner, Ted Janssen invented the very elegant theory of superspace crystallography that, by adding a supplementary dimension to the usual 3D space, allows for a deeper understanding of the atomic structure of aperiodic crystals. He also made important contributions to the understanding of the stability and dynamics of aperiodic crystals, exploring their fascinating physical properties. He constantly interacted and collaborated with experimentalists, always ready to share and explain his detailed understanding of aperiodic crystals.
Title:
A side-by-side comparison of the solidification dynamics of quasicrystalline and approximant phases in the Al-Co-Ni system
Authors:
Han, I; Xiao, XH; Sun, HP; Shahani, AJ Author Full Names: Han, Insung; Xiao, Xianghui; Sun, Haiping; Shahani, Ashwin J.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 281-296; 10.1107/S2053273318017114 2 MAR 2019
Abstract:
Quasicrystals and their approximants have triggered widespread interest due to the challenge of solving their complex crystal structures as well as their possibly exceptional properties. The structural motifs of approximants are similar to those of the corresponding quasicrystals, but to what extent are their crystallization pathways the same? Unfortunately, there have been very few in situ experimental investigations to answer this question. Here, by leveraging the high penetrating power of hard X-rays, synchrotron-based X-ray tomography was conducted in order to capture the nucleation and growth of a decagonal quasicrystal and its related approximant. The combination of data-driven computational analysis with new thermodynamic databases allowed the characterization, with high precision, of the constitutional and kinetic driving forces for crystallization. The experimental results prove that the growth of both crystals from a liquid is dominated by first-order kinetics. Nevertheless, and somewhat surprisingly, significant differences were observed in their rates of nucleation and growth. The reasons for such divergent behaviours are discussed in light of contemporary theories of intermetallic crystallization.
Title:
Phason-flips refinement of and multiple-scattering correction for the d-AlCuRh quasicrystal
Authors:
Ruganski, I; Strzalka, R; Wolny, J Author Full Names: Ruganski, Ireneusz; Strzalka, Radoslaw; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 352-361; 10.1107/S2053273318017254 2 MAR 2019
Abstract:
The origin of the characteristic bias observed in a logarithmic plot of the calculated and measured intensities of diffraction peaks for quasicrystals has not yet been established. Structure refinement requires the inclusion of weak reflections; however, no structural model can properly describe their intensities. For this reason, detailed information about the atomic structure is not available. In this article, a possible cause for the characteristic bias, namely the lattice phason flip, is investigated. The derivation of the structure factor for a tiling with inherent phason flips is given and is tested for the AlCuRh decagonal quasicrystal. Although an improvement of the model is reported, the bias remains. A simple correction term involving a redistribution of the intensities of the peaks was tested, and successfully removed the bias from the diffraction data. This new correction is purely empirical and only mimics the effect of multiple scattering. A comprehensive study of multiple scattering requires detailed knowledge of the diffraction experiment geometry.
Title:
Aperiodic order coming of age: from inorganic materials to dynamic protein superstructures
Authors:
Borgstahl, G; Goldman, AI; Thiel, PA Author Full Names: Borgstahl, Gloria; Goldman, Alan I.; Thiel, Patricia A.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 212-213; 10.1107/S2053273319001165 2 MAR 2019
Title:
Full real-space analysis of a dodecagonal quasicrystal
Authors:
Schenk, S; Zollner, EM; Krahn, O; Schreck, B; Hammer, R; Forster, S; Widdra, W Author Full Names: Schenk, Sebastian; Zollner, Eva Maria; Krahn, Oliver; Schreck, Berit; Hammer, Rene; Foerster, Stefan; Widdra, Wolf
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 307-313; 10.1107/S2053273319000056 2 MAR 2019
Abstract:
The atomically resolved real-space structure of a long-range-ordered dodecagonal quasicrystal is determined based on scanning tunnelling microscopy. For the BaTiO3-derived oxide quasicrystal which spontaneously forms on a Pt(111) surface, 8100 atomic positions have been determined and are compared with an ideal Niizeki-Gahler tiling. Although the Niizeki-Gahler tiling has a complex three-element structure, the abundance of the triangle, square and rhomb tiling elements in the experimental data closely resembles the ideal frequencies. Similarly, the frequencies of all possible next-neighbour tiling combinations are, within the experimental uncertainty, identical to the ideal tiling. The angular and orientational distributions of all individual tiling elements show the characteristics of the dodecagonal quasicrystal. In contrast, the analysis of the orientation of characteristic and more complex tiling combinations indicates the partial decomposition of the quasicrystal into small patches with locally reduced symmetry. These, however, preserve the long-range quasicrystal coherence. The symmetry reduction from dodecagonal to sixfold is assigned to local interaction with the threefold substrate. It leads to atomic flips which preserve the number of quasicrystal tiling elements.
Title:
Characterizing modulated structures with first-principles calculations: a unified superspace scheme of ordering in mullite
Authors:
Klar, PB; Etxebarria, I; Madariaga, G Author Full Names: Klar, Paul Benjamin; Etxebarria, Inigo; Madariaga, Gotzon
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 260-272; 10.1107/S2053273319000846 2 MAR 2019
Abstract:
The benefit of computational methods applying density functional theory for the description and understanding of modulated crystal structures is investigated. A method is presented which allows one to establish, improve and test superspace models including displacive and occupational modulation functions from firstprinciples calculations on commensurate structures. The total energies of different configurations allow one to distinguish stable and less stable structure models. The study is based on a series of geometrically optimized superstructures of mullite (A(l4+2x)Si(2-2x)O(10-x)) derived from the superspace group Pham(alpha 01/2)0ss. Despite the disordered and structurally complex nature of mullite, the calculations on ordered superstructures are very useful for determining the ideal Al/Si ordering in mullite, extracting atomic modulation functions as well as understanding the SiO2-Al2O3 phase diagram. The results are compared with experimentally established models which confirm the validity and utility of the presented method.
Title:
Phase diagram of the Kondo model on the zigzag ladder
Authors:
Peschke, M; Woelk, LM; Potthoff, M Author Full Names: Peschke, Matthias; Woelk, Lena-Marie; Potthoff, Michael
Source:
PHYSICAL REVIEW B, 99 (8):10.1103/PhysRevB.99.085140 FEB 27 2019
Abstract:
The effect of next-nearest-neighbor hopping t(2) on the ground-state phase diagram of the one-dimensional Kondo lattice is studied with density-matrix renormalization-group techniques and by comparing with the phase diagram of the classical-spin variant of the same model. For a finite t(2), i.e., for a zigzag-ladder geometry, indirect antiferromagnetic interactions between the localized spins are geometrically frustrated. We demonstrate that t(2) at the same time triggers several magnetic phases which are absent in the model with nearest-neighbor hopping only. For strong J, we find a transition from antiferromagnetic to incommensurate magnetic short-range order, which can be understood entirely in the classical-spin picture. For weaker J, a spin-dimerized phase emerges, which spontaneously breaks the discrete translation symmetry. The phase is not accessible to perturbative means but is explained, on a qualitative level, by the classical-spin model as well. Spin dimerization alleviates magnetic frustration and is interpreted as a key to understand the emergence of quasi-long-range spiral magnetic order, which is found at weaker couplings. The phase diagram at weak J, with gapless quasi-long-range order on top of the twofold degenerate spin-dimerized ground state, competing with a nondegenerate phase with gapped spin (and charge) excitations, is unconventional and eludes an effective low-energy spin-only theory.
Title:
Gauge theory for the cuprates near optimal doping
Authors:
Sachdev, S; Scammell, HD; Scheurer, MS; Tarnopolsky, G Author Full Names: Sachdev, Subir; Scammell, Harley D.; Scheurer, Mathias S.; Tarnopolsky, Grigory
Source:
PHYSICAL REVIEW B, 99 (5):10.1103/PhysRevB.99.054516 FEB 25 2019
Abstract:
We describe the phase diagram of a 2+1-dimensional SU(2) gauge theory of fluctuating incommensurate spin density waves for the hole-doped cuprates. Our primary assumption is that all low-energy fermionic excitations are gauge neutral and electron-like, while the spin density wave order is fractionalized into Higgs fields transforming as adjoints of the gauge SU(2). The confining phase of the gauge theory is a conventional Fermi liquid with a large Fermi surface (and its associated d-wave superconductor). There is a quantum phase transition to a Higgs phase describing the "pseudogap" at lower doping. Depending on the quartic terms in the Higgs potential, the Higgs phase exhibits one or more of charge density wave, Ising-nematic, time-reversal odd scalar spin chirality, and Z(2) topological orders. It is notable that the emergent broken symmetries in our theory of fluctuating spin density waves coincide with those observed in diverse experiments. For the electron-doped cuprates, the spin density wave fluctuations are at wave vector (pi, pi), and then the corresponding SU(2) gauge theory only has a crossover between the confining and Higgs regimes, with an exponentially large confinement scale deep in the Higgs regime. On the Higgs side, for both the electron- and hole-doped cases, and at scales shorter than the confinement scale (which can be infinite when Z(2) topological order is present), the electron spectral function has a "fractionalized Fermi liquid" form with small Fermi surfaces. We also describe the deconfined quantum criticality of the Higgs transition in the limit of a large number of Higgs flavors, and perturbatively discuss its coupling to fermionic excitations.
Title:
Spin dynamics and field-induced magnetic phase transition in the honeycomb Kitaev magnet alpha-Li2IrO3
Authors:
Choi, S; Manni, S; Singleton, J; Topping, CV; Lancaster, T; Blundell, SJ; Adroja, DT; Zapf, V; Gegenwart, P; Coldea, R Author Full Names: Choi, Sungkyun; Manni, S.; Singleton, J.; Topping, C., V; Lancaster, T.; Blundell, S. J.; Adroja, D. T.; Zapf, V; Gegenwart, P.; Coldea, R.
Source:
PHYSICAL REVIEW B, 99 (5):10.1103/PhysRevB.99.054426 FEB 25 2019
Abstract:
The layered honeycomb iridate alpha-Li2IrO3 displays an incommensurate magnetic structure with counter-rotating moments on nearest-neighbor sites, proposed to be stabilized by strongly frustrated anisotropic Kitaev interactions between spin-orbit entangled Ir4+ magnetic moments. Here we report powder inelastic neutron scattering measurements that observe sharply dispersive low-energy magnetic excitations centered at the magnetic ordering wave vector, attributed to Goldstone excitations of the incommensurate order, as well as an additional intense mode above a gap Delta similar or equal to 2.3 meV. Zero-field muon-spin relaxation measurements show clear oscillations in the muon polarization below the Ned temperature T-N similar or equal to 15 K with a time-dependent profile consistent with bulk incommensurate long-range magnetism. Pulsed-field magnetization measurements observe that only about half the saturation magnetization value is reached at the maximum field of 64 T. A clear anomaly near 25 T indicates a transition to a phase with reduced susceptibility. The transition field has a Zeeman energy comparable to the zero-field gapped mode, suggesting gap suppression as a possible mechanism for the field-induced transition.
Title:
Static response of functionally graded multilayered one-dimensional hexagonal piezoelectric quasicrystal plates using the state vector approach
Authors:
Huang, YZ; Li, Y; Yang, LZ; Gao, Y Author Full Names: Huang, Yun-zhi; Li, Yang; Yang, Lian-zhi; Gao, Yang
Source:
JOURNAL OF ZHEJIANG UNIVERSITY-SCIENCE A, 20 (2):133-147; 10.1631/jzus.A1800472 FEB 2019
Abstract:
The effect of the non-homogeneity of material properties has been considered the important variation mechanism in the static responses of quasicrystal structures, but the existing theoretical model for it is unable to simulate the material change format beyond the exponential function. In this paper, we create a new model of functionally graded multilayered 1D piezoelectric quasicrystal plates using the state vector approach, in which varying functionally graded electro-elastic properties can be extended from exponential to linear and higher order in the thickness direction. Based on the state equations, an analytical solution for a single plate has been derived, and the result for the corresponding multilayered case is obtained utilizing the propagator matrix method. The present study shows, in particular, that coefficient orders of two varying functions (the power function and the exponential function) of the material gradient provide the ability to tailor the mechanical behaviors in the system's phonon, phason, and electric fields. Moreover, the insensitive points of phonon stress and electric potential under functionally graded effects in the quasicrystal layer are observed. In addition, the influences of stacking sequences and discontinuity of horizontal stress are explored in the simulation by the new model. The results are very useful for the design and understanding of the characterization of functionally graded piezoelectric quasicrystal materials in their applications to multilayered systems.
Title:
Elasto-hydrodynamics of quasicrystals with a crack under sudden impacts
Authors:
Zhou, YB; Li, XF Author Full Names: Zhou, Y. -B.; Li, X. -F.
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 98 (10):419-436; 10.1080/09500839.2019.1566796 2018
Abstract:
In this paper, a mode-III crack in one-dimensional (1D) hexagonal quasicrystals subjected to anti-plane impact loading is analyzed. The elasto-hydrodynamics of quasicrystals is adopted, where the phonon field obeys wave equation, and the phason field obeys diffusion equation. By introducing a new auxiliary function, the coupled wave-diffusion equations are converted to a single higher-order partial differential equation. With the aid of the Laplace transform, an associated mixed initial-boundary value problem is reduced to two sets of dual integral equations, and then transformed into two coupled Fredholm integral equations of the second kind. Numerical results of transient phonon and phason stress intensity factors and crack-centre displacement jump are obtained through the numerical inversion of the Laplace transform and are presented graphically to show the influences of the phason.

Update: 7-Mar-2019

Title:
Neutron diffraction study of a metallic kagome lattice, Tb3Ru4Al12
Authors:
Rayaprol, S; Hoser, A; Iyer, KK; Upadhyay, SK; Sampathkumaran, EV Author Full Names: Rayaprol, Sudhindra; Hoser, Andreas; Iyer, Kartik K.; Upadhyay, Sanjay K.; Sampathkumaran, E. V.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 477 83-87; 10.1016/j.jmmm.2018.12.104 MAY 1 2019
Abstract:
We present the results of neutron diffraction studies on polycrystals of a metallic kagome lattice, Tb3Ru4Al12, reported recently to undergo reentrant magnetism, with the onset of long range antiferromagnetic order below (T-N = 22 K) and spin-glass features below about 17 K. The present results reveal long-range antiferromagnetic order of an incommensurate type with the moments oriented along c-axis at all temperatures below T-N. There are however notable changes in the T-dependence of propagation vector along b-axis across 17 K. An observation of interest is that there is no decrease of intensity of magnetic Bragg peaks on entrance into the glassy phase (that is, below 17 K). This finding suggests that the magnetism of this compound is an exotic one.
Title:
Charge orbital and spin ordering transitions in La1-xSrxMnO3+delta(x=0.67 & 0.71)
Authors:
Shahee, A; Kaushik, SD; Lalla, NP Author Full Names: Shahee, Aga; Kaushik, S. D.; Lalla, N. P.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 782 277-287; 10.1016/j.jallcom.2018.11.404 APR 25 2019
Abstract:
Structural and magnetic phase-transitions in La1-xSrxMnO3+delta (x = 0.67 & 0.71) have been studied employing x-ray diffraction, neutron diffraction and transmission electron microscopy (TEM) in conjunction with electrical-transport and magnetic studies. These studies reveal a cubic to incommensurate (IC) charge-ordered (CO) tetragonal phase-transition in both the samples with k-vector varying with temperature and thus indicates charge density wave-like nature. Followed by magnetic transition from paramagnetic phase to incommensurate antiferromagnetic phase. The nearly equal expansion of the a,b axes in the ab plane and the contraction of the c-axis (i.e. type-I Jahn-Teller distortion (JTD)) indicate that the CO is accompanied by a planer ferro-ordering of 3d(x2-y2) orbitals in the ab plan, which is different from haring-bone type ordering of 3d(3x2-r2)/3d(3y2-r2) orbitals, commonly observed in narrow bandwidth CO manganites. For x = 0.71, a second phase-transition from type-I JTD-CO phase (c < a) to charge disorder type-II JTD tetragonal phase (c > a) was observed. Through EDAX analysis in TEM, a nanoscale marginal composition difference has been observed to lead to nanoscale phase-coexistence. These studies have revealed first microscopic evidence of CO and nano-scale multiphase coexistence in La1-xSrxMnO3+delta with x = 0.67 & 0.71. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Negative refraction in quasicrystalline multilayered metamaterials
Authors:
Morini, L; Eyzat, Y; Gei, M Author Full Names: Morini, Lorenzo; Eyzat, Yoann; Gei, Massimiliano
Source:
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, 124 282-298; 10.1016/j.jmps.2018.10.016 MAR 2019
Abstract:
Inspired by some recent results in elastodynamics of layered composites, we address here the problem of an antiplane elastic wave obliquely incident at the interface between a substrate and a periodic laminate with a quasicrystalline structure (generated by the Fibonacci substitution rule). The angles of refraction of the transmitted modes are computed by combining the transfer matrix method with the normal mode decomposition and evaluating the direction of the average Poynting vector. It is shown that, with respect to a periodic classical bilayer, on the one hand, beyond a certain frequency threshold, high order Fibonacci laminates can provide negative refraction for a wider range of angles of incidence, on the other, they allow negative wave refraction at lower frequencies. The outcome strongly relies on the Floquet-Bloch dynamic analysis of this class of laminates that is performed thoroughly. It is revealed that the corresponding spectra have a self-similar character linked to the specialisation of the Kohmoto's invariant, a function of the frequency that was recently studied by the authors for periodic one-dimensional quasicrystalline-generated waveguides. This function is able to explain two types of scaling occurring in dispersion diagrams. The attained results represent an important advancement towards the realisation of multilayered quasicrystalline metamaterials with the aim to control negatively refracted elastic waves. (C) 2018 Elsevier Ltd. All rights reserved.
Title:
Excess specific heat from the gapped sliding phonon modes in the incommensurate composite crystal Sr14Cu24O41
Authors:
Bag, R; Hazra, S; Kini, RN; Singh, S Author Full Names: Bag, Rabindranath; Hazra, Soumitra; Kini, Rajeev N.; Singh, Surjeet
Source:
PHYSICAL REVIEW B, 99 (5):10.1103/PhysRevB.99.054305 FEB 13 2019
Abstract:
We show that the low-temperature specific heat (C-p) of the incommensurate chain-ladder system {CuO2}(alpha){Sr2Cu2O3} = Sr14Cu24O41 (for alpha = 10/7) shows a rather large excess contribution of nonmagnetic origin. Diluted Al doping at the Cu site or annealing the crystal in an O-2 atmosphere suppresses this feature considerably. Using THz time-domain spectroscopy, we relate the occurrence of excess specific heat to the presence of very low-energy (similar to 1 meV) gapped phonon modes that originate from the sliding motion of oppositely charged {CuO2} chain and {Sr2Cu2O3} ladder sheets past each other.
Title:
Critical Properties of the Anisotropic Ising Model with Competitive Interactions in the Region of a Phase Transition from the Modulated Phase to the Paramagnetic One
Authors:
Murtazaev, AK; Ibaev, ZG Author Full Names: Murtazaev, A. K.; Ibaev, Zh. G.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 127 (6):1040-1045; 10.1134/S106377611812021X DEC 2018
Abstract:
Monte Carlo methods are used to study the anisotropic Ising model with competing interactions in the region of the phase transition from the modulated to the paramagnetic phase. Using histogram analysis of Monte Carlo data and the theory of finite-size scaling, it is shown that the transition from the modulated state to the paramagnetic one is a second-order phase transition. The critical parameters and temperatures of phase transitions in this region are calculated. It is shown that the modulated-paramagnetic phase transition cannot be described within the framework of the known universality classes of critical behavior.

Update: 27-Feb-2019

Title:
Microstructure and mechanical properties of an aluminum alloy reinforced by Al-Ni-Co-Mn quasi-crystalline
Authors:
Yuan, Y; Hou, H; Zhao, YH; Yan, F; Zhang, Y Author Full Names: Yuan, Ye; Hou, Hua; Zhao, Yu Hong; Yan, Feng; Zhang, Yu
Source:
MATERIALS RESEARCH EXPRESS, 6 (5):10.1088/2053-1591/ab014c MAY 2019
Abstract:
The Al72Ni13Co10Mn5 quasi-crystalline was prepared by conventional casting method. The microstructures and the phase composition of Al72Ni12Co16 quasi-crystalline, Al70Ni11Co12Mn7 and Al2Ni phases were characterized by XRD, SEM and DSC. The (Al72Ni13Co10Mn5)p/ZL101A aluminium based composite was fabricated by using the Al72Ni13Co10Mn5 quasicrystals particles as the reinforcing phase and ZL101A as the matrix with electromagnetic stirring. The results showed that the Al72Ni13Co10Mn5 is a QC(quasi-crystalline) phase and the hardness of Al72Ni13Co10Mn5 is higher than d-Al72Ni12Co16; the as-cast (Al72Ni13Co10Mn5)p/ZL101A composites are composed of alpha-Al, eutectic Si, theta, gamma and phi phase. With the increase of reinforcing particle fraction, the changed order for the morphology of coralline Si as follows: coral distribution -> partially converted into strips strip -> or thick sheet. The changes of mechanical properties were studied by tensile test and the resulting crystalline phase gamma and phi phases contribute to the improvement of the mechanical properties of the composite. After adding 4%wt% quasicrystalline particles, the tensile strength increased by 20.3%. However, when additional increased to 7 wt% will cause agglomeration and clusters of the theta phase, which leads to the decrease of the mechanical properties.
Title:
Analysis of migration maps and features of magnetic properties of LiNi0.9M0.1PO4 (M = Co, Mn) single crystals
Authors:
Urusova, N; Semkin, M; Kratochvilova, M; Barykina, J; Volegov, A; Park, JG; Lee, S; Pirogov, A Author Full Names: Urusova, N.; Semkin, M.; Kratochvilova, M.; Barykina, J.; Volegov, A.; Park, J. -G.; Lee, S.; Pirogov, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 781 571-581; 10.1016/j.jallcom.2018.12.089 APR 15 2019
Abstract:
Lithium orthophosphates of the LiMPO4 type (M = Ni, Co, Fe, and Mn) gain intensive development due to the potential applications as electrodes for lithium-ion batteries. The other remarkable property of LiMPO4 is the multiferroicity. We present a study of the crystal structure and magnetic properties, refined anisotropic thermal coefficients and Li-ion migration maps of the LiNi0.9M0.1PO4(M = Co, Mn) single crystals and compared results for the undoped LiNiPO4 and LiMnPO4 ones. All samples have been synthesized by the flux method. In LiNi0.9M0.1PO4(M = Co, Mn), doping increases the lattice constants, unit cell volume, valence bonds, and the anisotropic thermal coefficients. By means of X-ray diffraction and the program package TOPOS, the Li-cation migration maps were obtained. The Li-ions move along the [010] direction which can be clearly visualized in the mixed-metal LiNi0.9 M0.1PO4(M = Co, Mn) single crystals. It was found that the 10% doping of LiNiPO4 by cobalt ions leads to a decrease in the formation temperature and to the suppression of the incommensurate phase. The 10% doping of manganese ions increases the transition temperature, while the temperature range of the incommensurate phase narrows. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Magnetic properties of RCuAl3 (R = Pr and Nd) compounds
Authors:
Klicpera, M; Fikacek, J; Vlaskova, K; Puente-Orench, I; Divis, M; Javorsky, P Author Full Names: Klicpera, Milan; Fikacek, Jan; Vlaskova, Kristina; Puente-Orench, Ines; Divis, Martin; Javorsky, Pavel
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 781 1189-1197; 10.1016/j.jallcom.2018.12.077 APR 15 2019
Abstract:
( )Magnetic properties of PrCuAl3 and NdCuAl3 single crystals, adopting the tetragonal BaNiSn3 -structure-type, are reported. Our magnetization and specific heat measurements revealed no magnetic ordering in PrCuAl3, while NdCuAl3 orders antiferromagnetically below T-N = 2.45 K. The paramagnetic regime was investigated for both analogues revealing (i) the a-axis as the easy direction of magnetization with (ii) a relatively high uniaxial anisotropy energy of 13.2 meV for PrCuAl3 compared to a smaller value of 4.7 meV for NdCuAl3. The measured data are well explained by rare-earth ground state multiplet splitting in crystal electric field. A powder neutron diffraction experiment confirmed PrCuAl3 to remain paramagnetic down to 1.5 K. On the other hand, NdCuAl3 orders antiferromagnetically below T-N with an incommensurate magnetic structure described by two propagation vectors k(1) = (1/3 - delta(1), 0, 0) and k(2) = (1/7 - delta 2 , 1/7 - delta(2) , 0), where delta(1) = 0.035(1) and delta(2) = 0.007(1). The magnetic moments (of both magnetic modulations) are arranged within the basal plane with a small z-component moment allowed by the symmetry. Our results are discussed with respect to other RCuAl3 compounds. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Spontaneous and induced magnetic phase transitions in Tb0.9Er0.1Ni5
Authors:
Lee, HJ; Choi, YN; Lukoyanov, AV; Gerasimov, EG; Pirogov, AN Author Full Names: Lee, H-J; Choi, Y-N; Lukoyanov, A., V; Gerasimov, E. G.; Pirogov, A. N.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 475 593-601; 10.1016/j.jmmm.2018.12.004 APR 1 2019
Abstract:
Magnetic and neutron powder diffraction measurements have been carried out on Tb0.9Er0.1Ni5 intermetallic compound. The intermetallide crystallizes in the hexagonal CaCu5-type structure and possesses a long-range magnetic order at temperatures below 22 K. A fan-like magnetic structure is described by two propagation vectors: k(1) = 0 and k(2) = 2 pi/c(0, 0, 0.036), at 20 K. The total Tb-ion magnetic moment has the ferromagnetic and modulated components. The latter is a transverse spin wave. When the sample is cooled at a temperature below 8 K, the module of the k(2) vector does not change and is equal to k(2) = 2 pi/c(0, 0, 0.027). An "in-commensurate - lock-in" magnetic transition takes place at 8 K. The k(2) vector exhibits a temperature hysteresis of about (5-6) K, whereas the intensities of Bragg reflections and satellites do not show up appreciable changes. When an external magnetic field is applied to the sample, the satellites and the module of the k(2) vector decrease, while the Bragg intensities increase. The sample becomes a ferromagnetic at a field of similar to 2 kOe, and the Tb-ion magnetic moment is equal to 8.3 mu(B). A general notion of the Tb0.9Er0.1Ni5 magnetic state evolution with an external field is given using the field dependence of the background intensity in diffraction patterns. First principle calculations for TbNi5 and Tb0.9Er0.1Ni5 are performed including the 4f states into the orbital basis and accounting for strong electronic correlations and spin-orbital coupling. This allowed obtaining both spin and orbital moments of the effective Tb-ion moment and estimating also the value of Tb-Tb exchange interaction.
Title:
Direct observation of incommensurate magnetism in Hubbard chains (vol 565, pg 56, 2018)
Authors:
Salomon, G; Koepsell, J; Vijayan, J; Hilker, TA; Nespolo, J; Pollet, L; Bloch, I; Gross, C Author Full Names: Salomon, Guillaume; Koepsell, Joannis; Vijayan, Jayadev; Hilker, Timon A.; Nespolo, Jacopo; Pollet, Lode; Bloch, Immanuel; Gross, Christian
Source:
NATURE, 566 (7743):E5-E5; 10.1038/s41586-019-0906-z FEB 14 2019
Title:
Honeycomb lattice type charge density wave associated with interlayer Cu ions ordering in 1T-CuxTiSe2
Authors:
Kitou, S; Kobayashi, S; Kaneko, T; Katayama, N; Yunoki, S; Nakamura, T; Sawa, H Author Full Names: Kitou, Shunsuke; Kobayashi, Shintaro; Kaneko, Tatsuya; Katayama, Naoyuki; Yunoki, Seiji; Nakamura, Toshikazu; Sawa, Hiroshi
Source:
PHYSICAL REVIEW B, 99 (8):10.1103/PhysRevB.99.081111 FEB 11 2019
Abstract:
The phase transition phenomenon in a semimetallic 1T-TiSe2. has attracted attention as an excitonic insulator. However, as the phase transition accompanying superlattice peaks has the q vector connecting the Fermi surfaces of the three-dimensional shape of hole and electron pockets, it also assumes the charge density wave (CDW) state owing to the electron-phonon interaction. To understand the electronic state at the low temperature, control of the chemical potential was attempted by electronic doping through Cu+ intercalation. Physical properties measurements and synchrotron x-ray diffraction experiments in CuxTiSe2 (x = 0-0.35) were performed. The phase transition was determined to occur as a cooperative phenomenon between the honeycomb lattice type CDW corresponding to the nesting vector and the ordered state of the Cu+ ions between TiSe2 layers at a specific doping amount (x = 1/3). The behavior of Cu+ ions in highly doped regions suggests the occurrence of a two-dimensional liquid-solid state transition based on the temperature dependence of the x-ray diffuse scattering.
Title:
Crystallographic Relationship between the nu (Mn82Si18) and H (Mn7Si2V) Phases in the Mn-Si-V Alloy System
Authors:
Nakayama, K; Kurihara, D; Koyama, Y Author Full Names: Nakayama, Kei; Kurihara, Daichi; Koyama, Yasumasa
Source:
MATERIALS TRANSACTIONS, 59 (7):1051-1056; 10.2320/matertrans.MD201712 2018
Abstract:
There are the intermetallic-compound nu (Mn82Si18) and H (Mn7Si2V) phases in the Mn-Si-V alloy system. These two phases can be regarded as approximant phases of the dodecagonal quasicrystal, and their crystal structures involve similar structural hierarchies consisting of dodecagonal atomic columns and giant dodecagonal structural units. To understand the crystallographic relationship between these approximant phases, we examined their crystallographic features mainly by transmission electron microscopy. It was found that there is a simple orientation relationship of N(001)(nu)//N(0001)(H) and N(010)(nu)//N(01<(1)overbar>0)(H) between the nu and H structures. In addition, H-structure regions have an antiphase boundary with a pi phase shift along a column axis as a structural defect. A notable feature of the antiphase boundary is that it consists of decagonal columns, not dodecagonal columns present in the H structure, where both 11 dodecagonal columns and eight decagonal columns form one dodecagonal unit in the nu structure. The nu structure can thus be produced in the following two steps. First, eight outer dodecagonal columns in each dodecagonal unit in the H structure are replaced by eight decagonal columns. The second step is the periodic introduction of antiphase boundaries, consisting of decagonal columns present in the replacement.

Update: 20-Feb-2019

Title:
Benefits of intermediate-layer formation at the interface of Nb/Cu and Ta/Cu explosive clads
Authors:
Parchuri, P; Kotegawa, S; Yamamoto, H; Ito, K; Mori, A; Hokamoto, K Author Full Names: Parchuri, PradeepK.; Kotegawa, Shota; Yamamoto, Hajime; Ito, Kazuhiro; Mori, Akihisa; Hokamoto, Kazuyuki
Source:
MATERIALS & DESIGN, 166 10.1016/j.matdes.2019.107610 MAR 15 2019
Abstract:
A systematic, comparative study was carried out to quantitatively characterize the bending strength of wavy interfaces with and without an intermediate layer (IL) in Nb/Cu and Ta/Cu explosive clads. The clads having wavy interfaces with and without an IL were obtained at horizontal high and low collision velocities (HCV and LCV) in the explosive welding, respectively. The stress-strain curves of all the clads were similar in three-point bending tests, but the clads with an IL exhibited higher bending stress than those without an IL. Moreover, cracks were observed in the Nb plate of Nb/Cu clads without an IL, but nocracks in that with an IL. TEM observation confirmed coexistence of ultrafine refractory metal and Cu phases in the ILs. In addition, the Ta-Cu-based intermetallic compound or dodecagonal quasicrystal, which is a non-equilibrium phase, were also observed along with coexistence of Ta and Cu phases in the ILs of Ta/Cu interface. Cladding at HCV and a lower collision angle assisted in resultant less strain in refractory metal plates near the joint interfaces than those at LCV, due to IL formation. The ILs assisted in obtainment of interfaces of higher hardness, leading to higher bending-stress clads without losing large elongation. (C) 2019 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.
Title:
Formation and temporal evolution of modulated structure in high Nb-containing lamellar gamma-TiAl alloy
Authors:
Ren, GD; Dai, CR; Mei, W; Sun, J; Lu, S; Vitos, L Author Full Names: Ren, Guo-dong; Dai, Cheng-ren; Mei, Wei; Sun, Jian; Lu, Song; Vitos, Levente
Source:
ACTA MATERIALIA, 165 215-227; 10.1016/j.actamat.2018.11.041 FEB 15 2019
Abstract:
The formation and temporal evolution of the modulated structure in a lamellar gamma-based Ti-45Al-8.5Nb alloy have been investigated by transmission electron microscopy (TEM) in combination with first-principles theory in this work. The results show that the Nb-rich O phase as a constituent of the modulated structure is thermodynamically stable below 650 degrees C in the alpha(2) lamellae. The morphology of the O phase variants changes from thin plate-like shape with a low volume fraction at initial annealing to rectangle/square shape with a high volume fraction after a prolonged annealing, and the retransformed alpha(2), named as alpha(2-II) hereafter, emerges at intersections of the variants with two orthogonal habit planes due to their elastic interactions. The partitioning coefficient of Nb between the O phase and alpha(2) is about 2 at 600 degrees C. The diffusion coefficient of Nb derived from growth kinetics of the O phase is about (1.3 +/- 0.2) x 10(-22) m(2)s(-1) in the alpha(2) lamellae. Significant precipitation hardening effect of the O phase has been revealed for the alpha(2) lamellae and gamma/(alpha(2)+O) lamellar microstructure, which is supposed to be attributed to refining the alpha(2) lamellae associated with elastic strain energy from the alpha(2) -> O phase transformation and introducing the interface between the modulated lamella and adjacent gamma phase. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Room temperature structure and transport properties of the incommensurate modulated LaNb0.88W0.12O4.06
Authors:
Li, C; Pramana, SS; Skinner, SJ Author Full Names: Li, Cheng; Pramana, Stevin S.; Skinner, Stephen J.
Source:
DALTON TRANSACTIONS, 48 (5):1633-1646; 10.1039/c8dt03958e FEB 7 2019
Abstract:
The crystal structure of a (3 + 2)D incommensurate modulated LaNb0.88W0.12O4.06 phase, a novel oxygen ionic conductor, is refined using a combination of synchrotron X-ray diffraction and electron diffraction data. The superspace group I2/c(alpha(1)0(gamma 1))00(alpha(2)0(gamma 2))00 (a = 5.4131(1) angstrom, b = 11.6432(2) degrees, c = 5.2963(1) angstrom, beta = 91.540(1)degrees, q(1) = 0.2847(5)a* + 0.1098(9)c* and q(2) = -0.1266(9)a* + 0.2953(1)c*) was chosen for the refinement. Similar to other scheelite type modulated structures, the modulation of LaNb0.88W0.12O4.06 stems from the cation occupancy ordering in the xz plane. To facilitate the modulated cation sub-lattice, and to compensate for the difference in their size and charge, the B site polyhedra are distorted by stretching the B-O bond lengths. Consequently, an extension in the B site coordination number from 6 to 8 is observed in the modulated phase. An interconnected 3D network of BOx polyhedra, similar to that of modulated CeNbO4.25, is obtained as a result of the structure modulation, which is not available in the unmodulated parent structure. Tracer diffusivity measurements indicate that the composition is an oxygen ion conductor, which relies on an intersticalcy conduction mechanism. Oxygen tracer diffusivity of 2.46 x 10(-9) cm(2) s(-1), at 750 degrees C is reported.
Title:
In-Situ observation of local atomic structure of Al-Cu-Fe quasicrystal formation
Authors:
Parsamehr, H; Lu, YJ; Lin, TY; Tsai, AP; Lai, CH Author Full Names: Parsamehr, Hadi; Lu, Ying-Jiu; Lin, Tzu-Ying; Tsai, An-Pang; Lai, Chih-Huang
Source:
SCIENTIFIC REPORTS, 9 10.1038/s41598-018-37644-x FEB 4 2019
Abstract:
The phase and local environment, neighbouring atoms and coordination numbers (CN), for an Al-Cu-Fe multilayer were studied during heating (to 800 degrees C) and cooling (to room temperature) processes using in-situ X-Ray diffraction (XRD) and in-situ X-ray absorption spectroscopy (XAS) techniques to investigate the formation of Al-Cu-Fe quasicrystals (QCs). In-situ XRD clarified the transition of the omega-Al7Cu2Fe phase to a liquid state at the high temperature which transformed into the QC phase during cooling. The in-situ XAS showed a relatively small shift in distance between Cu-Al and Fe-Al during the phase evolution from RT to 700 degrees C. The distance between Cu-Cu, however, showed a significant increase from omega-phase at 700 degrees C to the liquid state at 800 degrees C, and this distance was maintained after QC formation. Furthermore, the CN of Fe-Al was changed to N = 9 during cooling. Through our observations of changes in CN, atomic distances and the atomic environment, we propose the local structural ordering of the quasicrystalline phase originated from a liquid state via omega-phase. In this study, we give a clear picture of the atomic environment from the crystalline to the quasicrystalline phase during the phase transitions, which provides a better understanding of the synthesis of functional QC nanomaterials.
Title:
Enhancing Morphology and Separation Performance of Polyamide 6,6 Membranes By Minimal Incorporation of Silver Decorated Graphene Oxide Nanoparticles
Authors:
Mahmoudi, E; Ng, LY; Ang, WL; Chung, YT; Rohani, R; Mohammad, AW Author Full Names: Mahmoudi, Ebrahim; Ng, Law Yong; Ang, Wei Lun; Chung, Ying Tao; Rohani, Rosiah; Mohammad, Abdul Wahab
Source:
SCIENTIFIC REPORTS, 9 10.1038/s41598-018-38060-x FEB 4 2019
Abstract:
Nanomaterials can be incorporated in the synthesis of membrane to obtain mixed-matrix membrane with marked improvement in properties and performance. However, stability and dispersion of the nanomaterials in the membrane matrix, as well as the need to use high ratio of nanomaterials for obvious improvement of membrane properties, remain a major hurdle for commercialization. Hence, this study aims to investigate the improvement of polyamide 6,6 membrane properties with the incorporation of silver nanoparticles decorated on graphene oxide (Ag-GO) nanoplates and at the same time focus is given to the issues above. Graphene oxide nanoplates were synthesized using the modified Hummers' method and decorated with silver before embedded into the polyamide 6,6 matrix. Physicochemical characterizations were conducted on both nanoplates and the mixed-matrix Ag-GO polyamide 6,6 membrane. The issues of Ag agglomeration and leaching were not observed, which could be attributed to the decoration of Ag on GO that helped to disperse the nanomaterials and provided a better anchor point for the attachment of Ag nanoparticles. The synthesized membrane showed marked improvement regarding flux (135% increment) and antifouling (40% lower irreversible fouling), which could be ascribed to the more negative charge of membrane surface (-14 +/- 6 to -31 +/- 3.8 mV) and hydrophilicity (46% enhancement) of the membranes. With minimal embedment of Ag nanoparticles, the membrane showed superior antibacterial property where the E. coli bacteria could not form a single colony on the membrane surface. Overall, the decoration of Ag on GO nanoplates could be a promising approach to resolve the agglomeration and leaching issues as well as reduce the amount of precious Ag in the synthesis of Ag-GO polyamide 6,6 membrane.
Title:
Energy-dispersive Laue experiments with X-ray tube and PILATUS detector: precise determination of lattice constants
Authors:
Kurdzesau, F Author Full Names: Kurdzesau, Fiodar
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 52 72-93; 10.1107/S1600576718017193 1 FEB 2019
Abstract:
A PILATUS detector in combination with a conventional sealed X-ray tube was used for the development of the energy-dispersive Laue diffraction technique, which can be applied for precise measurements of single-crystal lattice constants in transmission and reflection modes without moving the sample. Exploiting the ability of PILATUS detectors to suppress counting of X-ray photons below a certain energy threshold allows one to recover the wavelength of diffracted Bragg reflections, reconstruct the three-dimensional reciprocal-space pattern, index X-ray diffraction peaks, and find the orientation and lattice parameters of the crystal without any a priori information about the sample. By making some geometrical assumptions and using a set of fast in situ calibration procedures, it is possible to simultaneously refine lattice constants and hardware correction factors, which simplifies the sample preparation and measurement strategies. Several samples [silicon, quartz, fluorite (CaF2), o-Al13Co4 quasicrystal approximant, Laves (MgZn2) and Bergman (Mg-32(Al,Zn)(49)) phases] were studied with the developed technique, and 0.01 angstrom and 0.1 degrees precisions were routinely reached for lattice vector lengths and angles, respectively. The use of the developed methods is only limited by the energy resolution of the PILATUS detector, where lattice vectors with >27 angstrom length cannot be reliably resolved.
Title:
Damping Properties of As-Cast Mg-Zn-Y Alloy with / Phase
Authors:
Wan, DQ; Hu, YL; Li, ZM; Ye, ST Author Full Names: Wan Diqing; Hu Yinglin; Li Zhumin; Ye Shuting
Source:
RARE METAL MATERIALS AND ENGINEERING, 48 (1):71-76; JAN 2019
Abstract:
A conventional casting method was adopted to fabricate the alloys of Mg-Zn-Y, in which the dendritic morphology and its relation to the damping properties of as-cast Mg-Zn-Y alloy were studied based on the typical Mg93Zn6Y1 alloy containing icosahedral quasicrystal phase. By controlling the pouring temperature, the stirring speed and stirring time, the dendritic morphology with different parameters was obtained. The results show that the microstructure of the as-cast Mg93Zn6Y1 mainly consists of alpha-Mg dendritic crystal and icosahedral quasicrystal phase. After stirring, the primary alpha-Mg dendritic gradually have fractal characteristics in faith, and its size changes, affecting the damping capacity. The mechanism was discussed.
Title:
Porous Al63Cu25Fe12 quasicrystals covered with (Al11.5Fe13.9Cu19.7)O-54.9 nanosheets
Authors:
Zhang, F; Guo, HJ; Wang, LL; Ma, HK; Li, H; Zhang, L; He, ZB Author Full Names: Zhang, Fan; Guo, Huijie; Wang, Leilei; Ma, Haikun; Li, Hua; Zhang, Lei; He, Zhangbing
Source:
MATERIALS CHARACTERIZATION, 147 165-172; 10.1016/j.matchar.2018.10.026 JAN 2019
Abstract:
Porous Al63Cu25Fe12 quasicrystal alloys with the surfaces and the wall of pores covered with abundant (Al11.5Fe13.9Cu19.7)O-54.9 nanosheets were successfully fabricated through the combination of powder metallurgy and dealloying in NaOH solutions. Their compositions, microscopic morphology, and crystal structures were investigated using energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. We found that the composite of porous Al63Cu25Fe12 quasicrystal alloys and (Al11.5Fe13.9Cu19.7)O-54.9 nanosheets shows high catalytic performances in hydrogen production by methanol steam reforming at relatively low temperatures. X-ray photoelectron spectroscopy was used to analyze the catalytic mechanisms, and Cu was found to be the key element in this catalytic reaction.

Update: 13-Feb-2019

Title:
Helical Ordering of Spin Trimers in a Distorted Kagome Lattice of Gd3Ru4Al12 Studied by Resonant X-ray Diffraction
Authors:
Matsumura, T; Ozono, Y; Nakamura, S; Kabeya, N; Ochiai, A Author Full Names: Matsumura, Takeshi; Ozono, Yusaku; Nakamura, Shintaro; Kabeya, Noriyuki; Ochiai, Akira
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 88 (2):10.7566/JPSJ.88.023704 FEB 15 2019
Abstract:
Successive magnetic phase transitions at T-1 = 17.5 K and T-2 = 18.5 K in Gd3Ru4Al12, with a distorted kagome lattice of Gd ions, is studied using resonant X-ray diffraction with polarization analysis. It has been suggested that in this compound the S = 7/2 spins on the nearest-neighbor Gd-triangle form a ferromagnetic trimer and the Gd lattice can be effectively considered as an antiferromagnetic triangular lattice of S = 21/2 spin trimers [S. Nakamura et al., Phys. Rev. B 98, 054410 (2018)]. We show that the magnetic order in this system is described by an incommensurate wave vector q similar to (0.27,0, 0), which varies slightly with temperature. In the low temperature phase below T-1, the experimental results are well explained by considering that the spin timers form a helical order with both the c-axis and c-plane components. In the intermediate phase above T-1 the c-axis component vanishes, resulting in a sinusoical structure within the c-plane. The sinusoidal-helical transition at T-1, can be regarded as an ordering of chiral degree of freedom, which is degenerate in the intermediate phase.
Title:
Long-period structural modulation on the global length scale as the characteristic feature of the morphotropic phase boundaries in the Na0.5Bi0.5TiO3 based lead-free piezoelectrics
Authors:
Das Adhikary, G; Khatua, DK; Senyshyn, A; Ranjan, R Author Full Names: Das Adhikary, Gobinda; Khatua, Dipak Kumar; Senyshyn, Anatoliy; Ranjan, Rajeev
Source:
ACTA MATERIALIA, 164 749-760; 10.1016/j.actamat.2018.11.016 FEB 1 2019
Abstract:
The inherent structural disorder has a profound effect on the dielectric, ferroelectric and the electromechanical response of the Na0.5Bi0.5TiO3 (NBT) based lead-free piezoelectrics. While analogous to the lead-based classical morphotropic phase boundary (MPB) systems the existence of MPB has been recognized in some derivatives of NBT displaying enhanced electromechanical response, there is a lack of clarity on the structural state of the MPB compositions on NBT-based systems on the global length scale. We have examined this issue on the well known MPB system (1-x)Na0.5Bi0.5TiO3-(x)K0.5Bi0.5TiO3(NBT-KBT) by carrying out structural investigations on local and global length scales using Eu+3 photoluminiscence and high-resolution neutron powder diffraction techniques, respectively. Our study reveals that the MPB of this system is characterized by the onset of a long-period modulated structure with a periodicity of similar to 40 angstrom on the global scale. Temperature depedent neutron diffraction study revealed that the intermediate temperature P4bm phase which appears in NBT is suppressed for the MPB composition. The MPB composition rather develops a long-period modulated phase on cooling from the cubic phase. The ergodic-nonergodic relaxor ferroelectric transition occurs within this long-period modulated phase. In the non-ergodic regime, however, strong electric field irreversibly transforms the long-period modulated phase to the rhombohedral ferroelectric (R3c). We demonstrate that thermal depolarization of this system is a distinct structural event characterized by the system losing its field-induced long range rhombohedral (R3c) coherence and transforming back to the long-period modulated phase. Our study suggests that the long-period modulated phase is the primary structural feature of the MPB compositions in NBT-based piezoelectrics. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Symmetry-changing commensurate-incommensurate solid transition in the He-4 monolayer on 6,6,12-graphyne
Authors:
Ahn, J; You, M; Lee, G; Volkoff, T; Kwon, Y Author Full Names: Ahn, Jeonghwan; You, Mujin; Lee, Gwangyoung; Volkoff, Tyler; Kwon, Yongkyung
Source:
PHYSICAL REVIEW B, 99 (2):10.1103/PhysRevB.99.024113 JAN 30 2019
Abstract:
Path-integral Monte Carlo calculations have been carried out to investigate physical properties of a He-4 monolayer adsorbed on a single 6,6,12-graphyne sheet, which is one of the graphyne families possessing a rectangular symmetry. To characterize elusive quantum phases of an adsorbed He-4 monolayer on 6,6,12-graphyne, we model the He-4-graphyne interaction by the pairwise sum of empirical He-4-C interatomic potentials. At partially filled He-4 coverages, we identify three commensurate solids of the C-3/4, C-4/4, and C-6/4 structures from the two-dimensional density distribution. These solids show the rectangular symmetry inherited from the symmetry of 6,6,12-graphyne, which were confirmed with the analysis of their static structure factors. At high helium coverages near its completion, the He-4 monolayer is predicted to exhibit a transition from a rectangular commensurate structure to a triangular incommensurate structure, after going through inhomogeneous structures mixed with domains of triangular and rectangular orderings. This symmetry-changing transition has not been observed in He-4 monolayers adsorbed on other carbon substrates.
Title:
Microstructure, texture evolution and tensile properties of extruded Mg-4.58Zn-2.6Gd-0.16Zr alloy
Authors:
Xiao, L; Yang, GY; Chen, JM; Luo, SF; Li, JH; Jie, WQ Author Full Names: Xiao, Lei; Yang, Guangyu; Chen, Jieming; Luo, Shifeng; Li, Jiehua; Jie, Wanqi
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 744 277-289; 10.1016/j.msea.2018.11.142 JAN 28 2019
Abstract:
Microstructure, texture evolution and mechanical properties of extruded Mg-4.58Zn-2.6Gd-0.18Zr alloy were investigated at extrusion temperatures of 260 degrees C, 280 degrees C and 300 degrees C, extrusion ratios of 10, 15 and 30, and ram speeds of 3 mm s(-1) and 6 mm s(-1), respectively. The results indicated that the as-cast experimental alloy was composed of alpha-Mg matrix, coarse alpha-Mg + W(Mg3Zn3Gd2) eutectic and icosahedral quasicrystalline I(Mg3Zn6Gd) phase. A small amount of undissolved W phases were detected after the homogenization treatment at 505 degrees C up to 16 h, while most I phase dissolved into the alpha-Mg matrix. The initial crystallites before extrusion were randomly oriented, and showed a typical random texture. After extrusions, all samples exhibited a bimodal microstructure consisting of fine Dynamic recrystallization (DRX) grains and coarse elongated un-DRX grains, and the formation of ultra-fine DRX grains only occurred in the sample with an extrusion ratio of 10 at 260 degrees C, 3 mm s(-1), which was caused by the solute segregation in homogenized billets and non-uniformly distributed W phase during the extrusion process. A fiber texture with {0002} planes and < 1210 > directions paralleled to the extrusion direction was observed to be dominant in all the extruded samples. Furthermore, the increase of extrusion ratio was found to be beneficial for the DRX process and refinement of grain size, and the maximum texture intensity was accordingly weakened, which resulted in a decrease of tensile yield strength but an increase of elongation. With increasing the extrusion temperature or ram speed, both the grain size and DRX fraction gradually increased. Consequently, the texture was randomized and the maximum texture intensity decreased, which led to a reduction of the elongation and tensile yield strength. The tensile failure behaviors under different extrusion conditions were found to be related with the contraction twin lamellas formed in the un-DRX grains and the string-like W phases.
Title:
Comparing the anomalous Hall effect and the magneto-optical Kerr effect through antiferromagnetic phase transitions in Mn3Sn
Authors:
Balk, AL; Sung, NH; Thomas, SM; Rosa, PFS; McDonald, RD; Thompson, JD; Bauer, ED; Ronning, F; Crooker, SA Author Full Names: Balk, A. L.; Sung, N. H.; Thomas, S. M.; Rosa, P. F. S.; McDonald, R. D.; Thompson, J. D.; Bauer, E. D.; Ronning, F.; Crooker, S. A.
Source:
APPLIED PHYSICS LETTERS, 114 (3):10.1063/1.5066557 JAN 21 2019
Abstract:
In the non-collinear antiferromagnet Mn3Sn, we compare simultaneous measurements of the anomalous Hall effect (AHE) and the magneto-optical Kerr effect (MOKE) through two magnetic phase transitions: the high-temperature paramagnetic/antiferromagnetic (AF) phase transition at the Neel temperature (T-N approximate to 420 K) and a lower-temperature incommensurate magnetic ordering at T-1 approximate to 270 K. While both the AHE and MOKE are sensitive to the same underlying symmetries of the AF non-collinear spin order, we find that the transition temperatures measured by these two techniques unexpectedly differ by approximately 10 K. Moreover, the applied magnetic field at which the AF order reverses is significantly larger when measured by MOKE than when measured by AHE. These results point to a difference between the bulk and surface magnetic properties of Mn3Sn. Published under license by AIP Publishing.
Title:
Quasicrystal nucleation and Z module twin growth in an intermetallic glass-forming system
Authors:
Hornfeck, W; Kobold, R; Kolbe, M; Conrad, M; Herlach, D Author Full Names: Hornfeck, Wolfgang; Kobold, Raphael; Kolbe, Matthias; Conrad, Matthias; Herlach, Dieter
Source:
NATURE COMMUNICATIONS, 9 10.1038/s41467-018-06597-0 OCT 3 2018
Abstract:
While quasicrystals possess long-range orientational order they lack translation periodicity. Considerable advancements in the elucidation of their structures and formative principles contrast with comparatively uncharted interrelations, as studies bridging the spatial scales from atoms to the macroscale are scarce. Here, we report on the homogeneous nucleation of a single quasicrystalline seed from the undercooled melt of glass-forming NiZr and its continuous growth into a tenfold twinned dendritic microstructure. Observing a series of crystallization events on electrostatically levitated NiZr confirms homogeneous nucleation. Mapping the microstructure with electron backscatter diffraction suggests a unique, distortion-free structure merging a common structure type of binary alloys with a spiral growth mechanism resembling phyllotaxis. A general geometric description, relating all atomic loci, observed by atomic resolution electron microscopy, to a pentagonal Z module, explains how the seed's decagonal long-range orientational order is conserved throughout the symmetry breaking steps of twinning and dendritic growth.
Title:
Waves in one-dimensional quasicrystalline structures: dynamical trace mapping, scaling and self-similarity of the spectrum
Authors:
Morini, L; Gei, M Author Full Names: Morini, Lorenzo; Gei, Massimiliano
Source:
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, 119 83-103; 10.1016/j.jmps.2018.06.007 OCT 2018
Abstract:
Harmonic axial waves in quasiperiodic-generated structured rods are investigated. The focus is on infinite bars composed of repeated elementary cells designed by adopting generalised Fibonacci substitution rules, some of which represent examples of one-dimensional quasicrystals. Their dispersive features and stop/pass band spectra are computed and analysed by imposing Floquet-Bloch conditions and exploiting the invariance properties of the trace of the relevant transfer matrices. We show that for a family of generalised Fibonacci substitution rules, corresponding to the so-called precious means, an invariant function of the circular frequency, the Kohmoto's invariant, governs self-similarity and scaling of the stop/pass band layout within defined ranges of frequencies at increasing generation index. Other parts of the spectrum are instead occupied by almost constant ultrawide band gaps. The Kohmoto's invariant also explains the existence of particular frequencies, named canonical frequencies, associated with closed orbits on the geometrical three-dimensional representation of the invariant. The developed theory represents an important advancement towards the realisation of elastic quasicrystalline metamaterials. (C) 2018 Elsevier Ltd. All rights reserved.

Update: 6-Feb-2019

Title:
Observation of the nesting and defect-driven 1D incommensurate charge density waves phase in the 2D system
Authors:
Matetskiy, AV; Denisov, NV; Hsing, CR; Wei, CM; Zotov, AV; Saranin, AA Author Full Names: Matetskiy, A., V; Denisov, N., V; Hsing, C. R.; Wei, C. M.; Zotov, A., V; Saranin, A. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 31 (11):10.1088/1361-648X/aaf9ea MAR 20 2019
Abstract:
We report on the low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) study of the (Bi, Na)/Si(111) root 3 x root 3 reconstruction that is known to possess Fermi surface with apparently good nesting. We found that defects on this surface produce a one-dimensional-like pattern with the periodicity of 8.2 +/- 0.4 angstrom that is incommensurate with the root 3 x root 3 lattice period. The dI/dV mapping analysis reveals an occurrence of the k-dependent branch associated with quasi-particle interference and the k-independent branch associated with the nesting vector connecting the parallel segments of the (Bi,Na)/Si(111) root 3 x root 3 Fermi surface, the fingerprint of the charge-density-wave (CDW) phase. The STS data demonstrates that development of the CDW phase leads to reducing electron density of states at the Fermi level.
Title:
Coherent photo-induced phonon emission in the charge-density-wave state of K0.3MoO3
Authors:
Rabia, K; Meng, F; Thomson, MD; Bykov, M; Merlin, R; van Smaalen, S; Roskos, HG Author Full Names: Rabia, K.; Meng, F.; Thomson, M. D.; Bykov, M.; Merlin, R.; van Smaalen, S.; Roskos, H. G.
Source:
NEW JOURNAL OF PHYSICS, 21 10.1088/1367-2630/aaf81f JAN 18 2019
Abstract:
We report on the observation of coherent terahertz (THz) emission from the quasi-one-dimensional charge-density wave (CDW) system, blue bronze (K0.3MoO3), upon photo-excitation with ultrashort near-infrared optical pulses. The emission contains a broadband, low-frequency component due to the photo-Dember effect, which is present over the whole temperature range studied (30-300 K), as well as a narrow-band doublet centered at 1.5 THz, which is only observed in the CDW state and results from the generation of coherent transverse-optical phonons polarized perpendicular to the incommensurate CDW b-axis. As K0.3MoO3 is centrosymmetric, the lowest-order generation mechanism which can account for the polarization dependence of the phonon emission involves either a static surface field or quadrupolar terms due to the optical field gradients at the surface. This phonon signature is also present in the ground-state conductivity, and decays in strength with increasing temperature to vanish above T similar to 100 K, i.e. significantly below the CDW transition temperature. The temporal behavior of the phonon emission can be well described by a simple model with two coupled modes, which initially oscillate with opposite polarity.

Update: 23-Jan-2019

Title:
On the Characterization of a Hitherto Unreported Icosahedral Quasicrystal Phase in Additively Manufactured Aluminum Alloy AA7075
Authors:
Kairy, SK; Gharbi, O; Nicklaus, J; Jiang, D; Hutchinson, CR; Birbilis, N Author Full Names: Kairy, S. K.; Gharbi, O.; Nicklaus, J.; Jiang, D.; Hutchinson, C. R.; Birbilis, N.
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 50A (2):529-533; 10.1007/s11661-018-5025-1 FEB 2019
Abstract:
Aluminum alloy AA7075 (Al-Zn-Mg-Cu) specimens were prepared using selective laser melting, also known as powder bed fusion additive manufacturing. In the as-manufactured state, which represents a locally rapidly solidified condition, the prevalence of a previously unreported icosahedral quasicrystal with 5-fold symmetry was observed. The icosahedral quasicrystal, which has been termed -phase (nu-phase), was comprised of Zn, Cu, and Mg.
Title:
Topological Landscape of Competing Charge Density Waves in 2H-NbSe2
Authors:
Gye, G; Oh, E; Yeom, HW Author Full Names: Gye, Gyeongcheol; Oh, Eunseok; Yeom, Han Woong
Source:
PHYSICAL REVIEW LETTERS, 122 (1):10.1103/PhysRevLett.122.016403 JAN 9 2019
Abstract:
Despite decades of studies of the charge density wave (CDW) of 2H-NbSe2, the origin of its incommensurate CDW ground state has not been understood. We discover that the CDW of 2H-NbSe2 is composed of two different, energetically competing, structures. The lateral heterostructures of two CDWs are entangled as topological excitations, which give rise to a CDW phase shift and the incommensuration without a conventional domain wall. A partially melted network of topological excitations and their vertices explain an unusual landscape of domains. The unconventional topological role of competing phases disclosed here can be widely applied to various incommensuration or phase coexistence phenomena in materials.

Update: 17-Jan-2019

Title:
Anisotropic transient thermoelasticity analysis in a two-dimensional decagonal quasicrystal using meshless local Petrov-Galerkin (MLPG) method
Authors:
Hosseini, SM; Sladek, J; Sladek, V Author Full Names: Hosseini, Seyed Mahmoud; Sladek, Jan; Sladek, Vladimir
Source:
APPLIED MATHEMATICAL MODELLING, 66 275-295; 10.1016/j.apm.2018.09.024 FEB 2019
Abstract:
The meshless local Petrov-Galerkin (MLPG) method is employed for anisotropic transient thermoelasticity analysis of 2D decagonal quasicrystals (QCs) subjected to transient thermal and mechanical shock loadings. The wave type model and the elasto-hydrodynamic model are applied to derive the phonon and phason governing equations, respectively. The temperature affects only the phonon field. To find the temperature distributions on the assumed 2D domain, the anisotropic heat conduction problem is solved using the MLPG method. Also, the MLPG method is successfully employed to obtain the transient behaviors of both phonon and phason displacements by solving the governing equations in local integral equations (LIEs) forms. Making use a unit step function as the test functions in the local weak-form of governing equations, we derived the local integral equations (LIEs) considered on small subdomains identical with support domains of test functions around each node. The radial basis functions are used for approximation of the spatial variation of field variables. The Laplace-transform technique is utilized to discretize the time variations. (C) 2018 Elsevier Inc. All rights reserved.
Title:
Direct observation of incommensurate magnetism in Hubbard chains
Authors:
Salomon, G; Koepsell, J; Vijayan, J; Hilker, TA; Nespolo, J; Pollet, L; Bloch, I; Gross, C Author Full Names: Salomon, Guillaume; Koepsell, Joannis; Vijayan, Jayadev; Hilker, Timon A.; Nespolo, Jacopo; Pollet, Lode; Bloch, Immanuel; Gross, Christian
Source:
NATURE, 565 (7737):56-+; 10.1038/s41586-018-0778-7 JAN 3 2019
Abstract:
The interplay between magnetism and doping is at the origin of exotic strongly correlated electronic phases and can lead to novel forms of magnetic ordering. One example is the emergence of incommensurate spin-density waves, which have wavevectors that do not belong to the reciprocal lattice. In one dimension this effect is a hallmark of Luttinger liquid theory, which also describes the low-energy physics of the Hubbard model(1). Here we use a quantum simulator that uses ultracold fermions in an optical lattice(2-8) to directly observe such incommensurate spin correlations in doped and spin-imbalanced Hubbard chains using fully spin- and density-resolved quantum gas microscopy. Doping is found to induce a linear change in the spin-density wavevector, in excellent agreement with predictions from Luttinger theory. For non-zero polarization we observe a reduction in the wavevector with magnetization, as expected from the antiferromagnetic Heisenberg model in a magnetic field. We trace the microscopic-scale origin of these incommensurate correlations to holes, doublons (double occupancies) and excess spins, which act as delocalized domain walls for the antiferromagnetic order. In addition, by inducing interchain coupling we observe fundamentally different spin correlations around doublons and suppression of incommensurate magnetism at finite (low) temperature in the two-dimensional regime(9). Our results demonstrate how access to the full counting statistics of all local degrees of freedom can be used to study fundamental phenomena in strongly correlated many-body physics.
Title:
Crystal structure of the high-temperature form of the trisulfide Cs2S3 and the (3+1)D modulated structure of the telluride K37Te28
Authors:
Stuble, P; Berroth, A; Wortelkamp, F; Rohr, C Author Full Names: Stueble, Pirmin; Berroth, Angela; Wortelkamp, Fritz; Roehr, Caroline
Source:
ZEITSCHRIFT FUR NATURFORSCHUNG SECTION B-A JOURNAL OF CHEMICAL SCIENCES, 74 (1):33-47; SI 10.1515/znb-2018-0168 JAN 2019
Abstract:
The high-temperature polymorph of the trisulfide Cs2S3, which has been synthesized from Cs2S2 and elemental sulfur, crystallizes in a new structure type (monoclinic, space group P2(1)/c, a = 999.97(4), b = 1029.30(5), c = 2642.07(12) pm, beta = 90.083(2)degrees, Z = 16, R1 = 0.0324). The structure contains four crystallographically independent angled S-3(2-) trisulfide ions with S-S distances of 205.7-208.3 pm. The distorted b.c.c. packing of the anions and their insertion in the five-membered rings of 3.5(3) + 3.5.3.5. (1:1) Cs nets are similarly found in the r.t. form (Cmc2(1), K2S3-type structure) and the two polymorphs differ mainly in the orientation of the S-3 groups. The second title compound, K37Te28, was synthesized from stoichiometric melts of the elements. It forms a complex (3 + 1)D modulated tetragonal structure (space group I4(1)/amd (00 sigma(3))s0s0, q=(0, 0, 0.5143), a = 1923.22(2), c = 2626.66(4) pm, Z = 4, R1(all) = 0.0837). According to K37Te28 = K-37[Te(1X)](8)[Te(2X)(2)](6)[Te(3X)(8)] the structure contains three different types of Te anions: The two crystallographically different isolated telluride anions [Te(1X)](2-) are coordinated by 9/10 K+ cations. Three [Te(2X)(2)](2-) dumbbells (d(Te-Te) = 277.9/286.4 pm) are arranged to 'hexamers'. The Te(31) and Te(32) atoms are located in columns of face-sharing K square antiprisms. Their z position modulation, which is accompanied by a smaller shift of the surrounding K+ cations, results in the decomposition of the [Te(3X)(8)](2) chain in a sequence vertical bar:Te-3-Te-2-Te-2-Te-3-Te-2-Te-2-Te-2:vertical bar of dumbbells Te-2(2-) (d(Te-Te) = 304 pm) and hypervalent linear trimers Te-3(4- )(d(Te-Te) = 325 pm).
Title:
A Yoffe-type moving crack in one-dimensional hexagonal piezoelectric quasicrystals
Authors:
Zhou, YB; Li, XF Author Full Names: Zhou, Y. -B.; Li, X. -F.
Source:
APPLIED MATHEMATICAL MODELLING, 65 148-163; 10.1016/j.apm.2018.08.005 JAN 2019
Abstract:
A Yoffe-type moving crack in one-dimensional hexagonal piezoelectric quasicrystals is considered. The Fourier transform technique is used to solve a moving crack problem under the action of antiplane shear and inplane electric field. Full elastic stresses of phonon and phason fields and electric fields are derived for a crack running with constant speed in the periodic plane. Obtained results show that the coupled elastic fields inside piezoelectric quasicrystals depend on the speed of crack propagation, and exhibit the usual square-root singularity at the moving crack tip. Electric field and phason stresses do not have singularity and electric displacement and phonon stresses have the inverse square-root singularity at the crack tip for a permeable crack. The field intensity factors and energy release rates are obtained in closed form. The crack velocity does not affect the field intensity factors, but alters the dynamic energy release rate. Bifurcation angle of a moving crack in a 1D hexagonal piezoelectric quasicrystal is evaluated from the viewpoint of energy balance. Obtained results are helpful to better understanding crack advance in piezoelectric quasicrystals. (C) 2018 Elsevier Inc. All rights reserved.
Title:
The origin of the polar symmetry in huebnerite-type multiferroics
Authors:
Park, SH; Behal, D; Pedersen, B Author Full Names: Park, So-Hyun; Behal, David; Pedersen, Bjoern
Source:
PHYSICA B-CONDENSED MATTER, 551 118-121; 10.1016/j.physb.2017.11.034 DEC 15 2018
Abstract:
The magnetic structure of the multiferroic phase AF2 of huebnerite (MnWO4) has been re-investigated based on the polar space group P2, instead of P2/c widely accepted in literature. The site character between two independent sites for Mn2+, Mn-a and Mn-b, fairly differs from each other in terms of bond valence sums. This hidden intrinsic dipole moment is the true origin of the chiral magnetic order in AF2 in the polar superspace group P2.1' (alpha, 1/2, gamma)0s. From structure refinements using single crystal neutron diffraction data at 10 K the ellipticity of the spin helix could be determined to be 0.92 and 0.77 at Mn-a and Mn-b, respectively. The different contributions of two chiral spin-textures to electric polarisation microscopically measurable in the b axis (P-b) could be estimated with P-b (Mn-a) = 22.8 mu Cm-2 and P-b (Mn-b) = 12.2 mu Cm-2.

Update: 9-Jan-2019

Title:
Lattice Modulation and Structural Phase Transition in the Antiferromagnet EuAl4
Authors:
Shimomura, S; Murao, H; Tsutsui, S; Nakao, H; Nakamura, A; Hedo, M; Nakama, T; Onuki, Y Author Full Names: Shimomura, Susumu; Murao, Hiroki; Tsutsui, Satoshi; Nakao, Hironori; Nakamura, Ai; Hedo, Masato; Nakama, Takao; Onuki, Yoshichika
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 88 (1):10.7566/JPSJ.88.014602 JAN 15 2019
Abstract:
X-ray diffraction measurements on the antiferromagnet EuAl4 using synchrotron radiation have revealed that satellite peaks characterized by an incommensurate wave vector (0, 0, zeta) with zeta approximate to 0.18 appear below 145.1 K, suggesting the formation of a charge density wave. The value of zeta shows an inflection at an antiferromagnetic transition temperature of 15.4K, and it changes discontinuously at lower antiferromagnetic transition temperatures of 12.2 and 10.0K. The antiferromagnetic transition at 12.2 K is accompanied by a structural transition from the modulated structure on a tetragonal lattice to that on a lattice with lower symmetry such as an orthorhombic one.
Title:
Unique Helical Magnetic Order and Field-Induced Phase in Trillium Lattice Antiferromagnet EuPtSi
Authors:
Kaneko, K; Frontzek, MD; Matsuda, M; Nakao, A; Munakata, K; Ohhara, T; Kakihana, M; Haga, Y; Hedo, M; Nakama, T; Onuki, Y Author Full Names: Kaneko, Koji; Frontzek, Matthias D.; Matsuda, Masaaki; Nakao, Akiko; Munakata, Koji; Ohhara, Takashi; Kakihana, Masashi; Haga, Yoshinori; Hedo, Masato; Nakama, Takao; Onuki, Yoshichika
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 88 (1):10.7566/JPSJ.88.013702 JAN 15 2019
Abstract:
Magnetic transition phenomena in cubic chiral antiferromagnet EuPtSi with T-N = 4.0 K were investigated by means of single crystal neutron diffraction. At 0.3 K in the ground state, magnetic peaks emerge at positions represented by an ordering vector q(1) = (0.2, 0.3, 0) and its cyclic permutation. Upon heating, an additional magnetic peak splitting with hysteresis was uncovered at around T-N* similar to 2.5 K, indicating the presence of a first-order commensurate incommensurate transition with q(1)* = (0.2, 0.3, delta) (delta(max) similar or equal to 0.04) at T-N*. A half-polarized neutron scattering experiment for polarization parallel to the scattering vector revealed that polarization antiparallel to the scattering vector has stronger intensity in both magnetic phases. This feature clarifies the single chiral character of the helical structure with moments lying perpendicular to the ordering vector in both ordered states. Under a vertical magnetic field of 1.2 T for B parallel to [1, 1, 1] at 1.9 K entering into the so-called A phase, magnetic peaks form characteristic hexagonal patterns in the equatorial scattering plane around nuclear peaks. An ordering vector q(A) similar or equal to (+/- 0.09, +/- 0.20, -/+ 0.28) of the A-phase has similar periodic length as q(1), and could be the hallmark of a formation of skyrmion lattice in EuPtSi.
Title:
Hyperuniformity and anti-hyperuniformity in one-dimensional substitution tilings
Authors:
Oguz, EC; Socolar, JES; Steinhardt, PJ; Torquato, S Author Full Names: Oguz, Erdal C.; Socolar, Joshua E. S.; Steinhardt, Paul J.; Torquato, Salvatore
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 3-13; 10.1107/S2053273318015528 1 JAN 2019
Abstract:
This work considers the scaling properties characterizing the hyperuniformity (or anti-hyperuniformity) of long-wavelength fluctuations in a broad class of one-dimensional substitution tilings. A simple argument is presented which predicts the exponent alpha governing the scaling of Fourier intensities at small wavenumbers, tilings with alpha > 0 being hyperuniform, and numerical computations confirm that the predictions are accurate for quasiperiodic tilings, tilings with singular continuous spectra and limit-periodic tilings. Quasiperiodic or singular continuous cases can be constructed with alpha arbitrarily close to any given value between -1 and 3. Limit-periodic tilings can be constructed with alpha between -1 and 1 or with Fourier intensities that approach zero faster than any power law.
Title:
k-eIsocoronal tilings
Authors:
Taganap, E; De Las Penas, MLA Author Full Names: Taganap, Eduard; Antonette De Las Penas, Ma. Louise
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 94-106; 10.1107/S2053273318013992 1 JAN 2019
Abstract:
In this article, a framework is presented that allows the systematic derivation of planar edge-to-edge k-isocoronal tilings from tile-s-transitive tilings, s <= k. A tiling T is k-isocoronal if its vertex coronae form k orbits or k transitivity classes under the action of its symmetry group. The vertex corona of a vertex x of T is used to refer to the tiles that are incident to x. The k-isocoronal tilings include the vertex-k-transitive tilings (k-isogonal) and k-uniform tilings. In a vertex-k-transitive tiling, the vertices form k transitivity classes under its symmetry group. If this tiling consists of regular polygons then it is k-uniform. This article also presents the classification of isocoronal tilings in the Euclidean plane.

Update: 4-Jan-2019

Title:
Spatially localized quasicrystalline structures
Authors:
Subramanian, P; Archer, AJ; Knobloch, E; Rucklidge, AM Author Full Names: Subramanian, P.; Archer, A. J.; Knobloch, E.; Rucklidge, A. M.
Source:
NEW JOURNAL OF PHYSICS, 20 10.1088/1367-2630/aaf3bd DEC 14 2018
Abstract:
Soft matter systems have been observed to self-assemble, over a range of system parameters, into quasicrystalline structures. The resulting quasicrystals (QCs) may minimize the free energy, and be in thermodynamic coexistence with the liquid state. At such state points, the likelihood of finding the presence of spatially localized states with quasicrystalline structure within the liquid is increased. Here we report the first examples of metastable spatially localized QCs of varying sizes in both two and three dimensions. Implications of these results for the nucleation of quasicrystalline structures are discussed. Our conclusions apply to a broad class of soft matter systems and more generally to continuum systems exhibiting quasipatterns.

Update: 20-Dec-2018

Title:
Accurate Determination of Composite Crystal Structure of Incommensurately Modulated Sr14Cu24O41 Using the Akaike Information Criterion
Authors:
Gotoh, Y Author Full Names: Gotoh, Yoshito
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 87 (12):10.7566/JPSJ.87.124601 DEC 15 2018
Abstract:
The composite crystal structure of the spin-ladder compound Sr14Cu24O41 has been reinvestigated using the Akaike information criterion (AIC) to solve the possible overfitting of atomic positions in our previous work [Phys. Rev. B 68. 224108 (2003)]. The minimizing AIC method using the same data as before removes the splitting behavior of the Cu-O bonds along the one-dimensional Cu-O chain in the two-legged Cu2O3 ladder and reveals the importance of the Cu-O-Cu rung with a strong Cu-O bond. Nonsymmetric paths of hole transfer from the O atom in the CuO2 chain to the Cu-O-Cu rung in the ladder have been elucidated by the resulting new modulated structure. Bond-valence sum analysis of the modulated CuO2 substructure of Sr(14)Cu(24)O(41 )shows the role of large displacive modulation of the O atom in the CuO2 chain and the valence fluctuation of Cu atom with a periodicity almost 200 times that of the average CuO2 lattice. There is no discommensuration of the < Cu2+>-< Cu3+>-< Cu2+> arrangements in the CuO2 chain. The incommensurability between the average substructures is characterized as sigma = (0 0 0.6995) and the chemical formula should be exactly expressed as (Sr2Cu2O3)(0.6995)CuO2.
Title:
Magnetic order in the rare-earth ferroborate CeFe3(BO3)(4)
Authors:
Hayashida, S; Asai, S; Kato, D; Hasegawa, S; Avdeev, M; Cao, HB; Masuda, T Author Full Names: Hayashida, Shohei; Asai, Shinichiro; Kato, Daiki; Hasegawa, Shunsuke; Avdeev, Maxim; Cao, Huibo; Masuda, Takatsugu
Source:
PHYSICAL REVIEW B, 98 (22):10.1103/PhysRevB.98.224405 DEC 4 2018
Abstract:
We have studied the magnetic order of the rare-earth ferroborate CeFe3(BO3)(4) through the thermodynamic and the neutron diffraction measurements. The heat capacity and the magnetic susceptibility revealed antiferromagnetic magnetic ordering at 29 K. In the neutron powder diffraction data, we observed the magnetic Bragg peaks indexed by the commensurate (CM) propagation vector k(CM) = (0, 0, 3/2) and the incommensurate (ICM) vector k(ICM) = (0, 0, 3/2+delta). The incommensurability delta increases with decreasing the temperature, and is evaluated to be 0.04556(16) at 3.7 K. Magnetic structure analysis reveals that the magnetic moments aligning in the ab plane form the collinear antiferromagnetic structure having k(CM)( )and helical structure having k(ICM). Detailed measurements of the magnetic susceptibility exhibit an additional anomaly at 27 K. Furthermore, the temperature dependence of the neutron diffraction profile on the single-crystal sample shows that the ICM and CM ordering occurs at 29 and 26 K, respectively. These results suggest a phase separation state between the collinear and helical structures. The multiferroicity of CeFe3(BO3)(4) is discussed on the basis of the determined magnetic structure.
Title:
A seed-based structural model for constructing rhombic quasilattice with 7-fold symmetry
Authors:
Ajlouni, R Author Full Names: Ajlouni, Rima
Source:
STRUCTURAL CHEMISTRY, 29 (6):1875-1883; 10.1007/s11224-018-1169-2 DEC 2018
Abstract:
A seed-based theoretical model with built-in local degree of freedom for constructing rhombic quasilattice with 7-fold symmetry is presented. This new approach mitigates a key limitation with existing structural models for describing quasicrystals, which do not incorporate atomic fluctuations or phasonic flips in their approaches. Here, we propose a structural model that works in concert with the seed-initiated nucleation growth models of quasicrystals and incorporates a degree of flexibility that allows the lattice to rearrange locally without affecting the global long-range order. This approach suggests that the position of high-symmetry motifs locally and globally is defined by one long-range framework and not based on local rules (i.e., inflation, deflation, substitution, matching, overlapping, etc.). The proposed model is based on building a hierarchical network that allows the self-similar quasilattice to expand infinitely without any gaps, overlaps, or mismatches. The use of a global relational logic provides scientists, artists, and teachers with a simple method for creating a wide variety of complicated hierarchical quasilattice formations without the need for any specialized software or complicated mathematics and could possibly provide a deeper understanding of how the atoms interact to form their complicated long-range quasicrystalline formations.
Title:
Light-Tunable 1T-TaS2 Charge-Density-Wave Oscillators
Authors:
Zhu, C; Chen, Y; Liu, FC; Zheng, SJ; Li, XB; Chaturvedi, A; Zhou, JD; Fu, QD; He, YM; Zeng, QS; Fan, HJ; Zhang, H; Liu, WJ; Yu, T; Liu, Z Author Full Names: Zhu, Chao; Chen, Yu; Liu, Fucai; Zheng, Shoujun; Li, Xiaobao; Chaturvedi, Apoorva; Zhou, Jiadong; Fu, Qundong; He, Yongmin; Zeng, Qingsheng; Fan, Hong Jin; Zhang, Hua; Liu, Wen Jun; Yu, Ting; Liu, Zheng
Source:
ACS NANO, 12 (11):11203-11210; 10.1021/acsnano.8b05756 NOV 2018
Abstract:
w External stimuli-controlled phase transitions are essential for fundamental physics and design of functional devices. Charge density wave (CDW) is a metastable collective electronic phase featured by the periodic lattice distortion. Much attention has been attracted to study the external control of CDW phases. Although much work has been done in the electric field-induced CDW transition, the study of the role of Joule heating in the phase transition is insufficient. Here, using the Raman spectroscopy, the electric-field-driven phase transition is in situ observed in the ultrathin 1T-TaS2. By quantitative evaluation of the Joule heating effect in the electric-field-induced CDW transition, it is shown that Joule heating plays a secondary role in the nearly commensurate (NC) to incommensurate (IC) CDW transition, while it dominants the IC-NC CDW transition, providing a better understanding of the electric field-induced phase transition. More importantly, at room temperature, light illumination can modulate the CDW phase and thus tune the frequency of the ultrathin 1T-TaS2 oscillators. This light tunability of the CDW phase transition is promising for multifunctional device applications.
Title:
Thermal behavior of modulated hauyne from Eifel, Germany: In situ high-temperature single-crystal X-ray diffraction study
Authors:
Kuribayashi, T; Aoki, S; Nagase, T Author Full Names: Kuribayashi, Takahiro; Aoki, Satoshi; Nagase, Toshiro
Source:
JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES, 113 (1):51-55; 10.2465/jmps.161114d FEB 2018
Abstract:
In-situ high-temperature single-crystal X-ray diffraction experiments on modulated hauyne obtained from Ei-fel, Germany, were conducted to re-evaluate its thermal behavior. The linearity of its thermal expansion is lost between 600 and 700 degrees C. Satellite peaks, indicating the modulated structure, were clearly observed up to 600 degrees C, but disappeared at 700 degrees C. These results indicate that the modulated hauyne structure changed in this temperature region. In addition, according to the observation of X-ray oscillation images taken at ambient conditions, the modulated structure of the sample heat-treated below 1000 degrees C remained unchanged, whereas modulation of the parent crystal structure changed when the sample was heat-treated above 1000 degrees C. This structural change to the unique modulated structure can be attributed to be the possible rearrangement of Al/Si distribution in the tetrahedral sites forming the framework.

Update: 12-Dec-2018

Title:
In-situ synthesis of aluminum/nano-quasicrystalline Al-Fe-Cr composite by using selective laser melting
Authors:
Kang, N; El Mansori, M; Lin, X; Guittonneau, F; Liao, HL; Huang, WD; Coddet, C Author Full Names: Kang, N.; El Mansori, M.; Lin, X.; Guittonneau, F.; Liao, H. L.; Huang, W. D.; Coddet, C.
Source:
COMPOSITES PART B-ENGINEERING, 155 382-390; 10.1016/j.compositesb.2018.08.108 DEC 15 2018
Abstract:
In this research, Al-Fe-Cr quasicrystal (QC) reinforced Al-based metal matrix composites were in-situ manufactured by using selective laser melting (SLM) from the powder mixture. The parametrical optimization based on our previous work was performed with focus on laser scanning speed. From the optimized parameters, an almost dense (99.7%) free-crack sample was fabricated with an ultra-fine microstructure. A phase transition from decagonal QC Al65Cu25Fe10Cr5 to icosahedral QC Al91Fe4Cr5 could be observed as laser scanning speed decreases. Differential scanning calorimetry curves show that the QC phase is quiet stable until 500 degrees C. And then, the effects of annealing temperature on the microstructural and mechanical properties were determined. The results indicate that the recrystallization and growth behavior of alpha-Al grains could be prevented by QC particle during annealing. Furthermore, the growth of QC particle, which tends to form a porous structure, leads an improvement of Young modulus and decline of ductility.
Title:
Syntheses, modulated crystal structures of Ba6-2xU2+xAg4Se12 (x=0 and 0.5), and crystal structure and spectroscopy of Sr4Th2.78Cu4S12
Authors:
Mesbah, A; Prakash, J; Beard, JC; Malliakas, CD; Lebegue, S; Ibers, JA Author Full Names: Mesbah, Adel; Prakash, Jai; Beard, Jessica C.; Malliakas, Christos D.; Lebegue, Sebastien; Ibers, James A.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 268 30-35; 10.1016/j.jssc.2018.08.025 DEC 2018
Abstract:
Single crystals of Ba6-2xU2+xAg4Se12 (x = 0 and 0.5) and Sr4Th2.78Cu4S12 were obtained by standard solid-state chemistry methods at 1173 K. The Ba6-2xU2+xAg4Se12 structures are modulated. They were solved and refined in the monoclinic C2(alpha 0 gamma)0 super space group. The structure consists of layers formed by the connection of USe6 and AgSe4 polyhedra. The incommensurate nature of the structure arises from the disorder among Ba atoms and U atoms in the layers. The crystal structure of the Sr4Th2.78Cu4S12 was solved in space group Pmn2(1) of the orthorhombic system. The refinement of the structure reveals three partially occupied Th sites. The connection of ThS7 and CuS4 polyhedra form a channel structure filled by Sr atoms. From optical measurements Sr4Th2.78Cu4S12 is a semiconductor with an indirect band gap of 2.27(2) eV.
Title:
Basic and charge density wave modulated structures of NbS3-II
Authors:
Zupanic, E; van Midden, HJP; van Midden, MA; Sturm, S; Tchernychova, E; Pokrovskii, VY; Zybtsev, SG; Nasretdinova, VF; Zaitsev-Zotov, SV; Chen, WT; Pai, WW; Bennett, JC; Prodan, A Author Full Names: Zupanic, E.; van Midden, H. J. P.; van Midden, M. A.; Sturm, S.; Tchernychova, E.; Pokrovskii, V. Ya; Zybtsev, S. G.; Nasretdinova, V. F.; Zaitsev-Zotov, S., V; Chen, W. T.; Pai, Woei Wu; Bennett, J. C.; Prodan, A.
Source:
PHYSICAL REVIEW B, 98 (17):10.1103/PhysRevB.98.174113 NOV 27 2018
Abstract:
The basic and the charge density wave (CDW) structures of the monoclinic NbS3-II polymorph were studied by synchrotron x-ray diffraction, ab initio calculations, simulation of electron diffraction patterns, and by atomic-resolution transmission electron and low-temperature scanning tunneling microscopies. It is confirmed that the basic structure belongs to the space group P2(1)/ m and is described with a unit cell, formed of four pairs of symmetry-related trigonal prismatic (TP) columns [a(0) = 0.96509(8) nm, b(0) = 0.33459(2) nm, c(0) = 1.9850(1) nm, and beta(0) = 110.695(4)degrees]. The incommensurate components of the two CDWs, (q) over bar (1) = (0, 0.298, 0) and (q) over bar (2) = (0, 0.352, 0), are related as (q) over bar (1b) + 2q(2b) approximate to 1. Both CDWs form their own modulation patterns with unit cells (a(m) = 2a(0), b(m) = b(0)/q(jb), c(m) = c(0), beta(m) = beta(0)) and are ordered along adjacent isosceles TP columns either pairwise or with both columns modulated by either the (q) over bar (1) or (q) over bar (2) CDW only. The CDWs are ordered according to one of the two possible modulation pattern space groups, Cm or C2/ m. If considered as long-period commensurate, the entire modulated structure with both CDWs included is described within experimental error with an enlarged unit cell (a = 2a(0), b = 37b(0), c = c(0), and beta = beta(0)) and with all atoms displaced from their average positions in accord with the specified modulation pattern.
Title:
Crystal and Magnetic Structures and Properties of (Lu1-xMnx)MnO3 Solid Solutions
Authors:
Zhang, L; Donni, A; Pomjakushin, VY; Yamaura, K; Belik, AA Author Full Names: Zhang, Lei; Donni, Andreas; Pomjakushin, Vladimir Y.; Yamaura, Kazunari; Belik, Alexei A.
Source:
INORGANIC CHEMISTRY, 57 (22):14073-14085; 10.1021/acs.inorgchem.8b01470 NOV 19 2018
Abstract:
(Lu1-xMnx)MnO3 solid solutions, having the perovskite-type structure and Pnma space group, with 0 <= x <= 0.4 were synthesized by a high-pressure, high temperature method at 6 GPa and about 1670 K from Lu2O3 and Mn2O3. Their crystal and magnetic structures were studied by neutron powder diffraction. The degree of octahedral MnO6 tilting decreases in (Lu1-xMnx)MnO3 with increasing x. Only the incommensurate (IC) spin structure with a propagation vector of k = (k(0), 0, 0) and k(0) approximate to 0.44 remains in (Lu0.9Mn0.1)MnO3 in the whole temperature range below the Neel temperature T-N = 36 K, and the commensurate noncollinear E-type structure that has been reported in the literature for undoped o-LuMnO3 is not observed. (Lu1-xMnx)MnO3 samples with 0.2 <= x <= 0.4 have a ferrimagnetic structure with a propagation vector of k = (0, 0, 0) and ferromagnetic (FM) ordering of Mn3+ and Mn4+ cations at the B site, which are antiferromagnetically coupled to a noncollinear predominantly FM arrangement of Mn2+ at the A site. The ferrimagnetic Curie temperature, T-C, increases monotonically from 67 K for x = 0.2 to 118 K for x = 0.4. Magnetic and dielectric properties of (Lu1-xMnx)MnO3 and a composition-temperature phase diagram are also reported.
Title:
At the Gates: The Tantalum-Rich Phase Hf3Ta2O11 and its Commensurately Modulated Structure
Authors:
Wiedemann, D; Ludtke, T; Palatinus, L; Willinger, E; Willinger, MG; Muhlbauer, MJ; Lerch, M Author Full Names: Wiedemann, Dennis; Luedtke, Tobias; Palatinus, Lukas; Willinger, Elena; Willinger, Marc G.; Muehlbauer, Martin J.; Lerch, Martin
Source:
INORGANIC CHEMISTRY, 57 (22):14435-14442; 10.1021/acs.inorgchem.8b02642 NOV 19 2018
Abstract:
Generic mixtures in the system (Zr,Hf)O-2-(Nb,Ta)(2)O-5 are employed as tunable gate materials for field-effect transistors. Whereas production processes and target compositions are well-defined, resulting crystal structures are vastly unexplored. In this study, we summarize the sparse reported findings and present the new phase Hf3Ta2O11 as synthesized via a sol-gel route. Its commensurately modulated structure represents the hitherto unknown, metal(V)-richest member of the family (Zr,Hf)(x)(Nb,Ta)(2)O2x+5. Based on electron, neutron, and X-ray diffraction, the crystal structure is described within modern superspace [Hf1.2Ta0.8O4.4 Z = 2, a = 4.7834(13), b = 5.1782(17), c = 5.064(3) angstrom, q = 1/5c*, orthorhombic, superspace group Xmcm(00 gamma)s00] and supercell formalisms [Hf3Ta2O11, Z = 4, a = 4.7834(13), b = 5.1782(17), c = 25.320(13) angstrom, orthorhombic, space group Pbnm]. Transmission electron microscopy shows the microscopic structure from film-like aggregates down to atomic resolution. Cation ordering within the different available coordination environments is possible, but no significant hint at it is found within the limits of standard diffraction techniques. Hf3Ta2O11 is an unpredicted compound in the above-mentioned oxide systems, in which stability ranges have been disputably fuzzy and established only by syntheses via solid-state routes so far.
Title:
Magnetic structure of a non-centrosymmetric CePtSi3
Authors:
Ueta, D; Yoshida, M; Ikeda, Y; Liu, Y; Hong, T; Masuda, T; Yoshizawa, H Author Full Names: Ueta, D.; Yoshida, M.; Ikeda, Y.; Liu, Y.; Hong, T.; Masuda, T.; Yoshizawa, H.
Source:
AIP ADVANCES, 8 (11):10.1063/1.5042736 NOV 2018
Abstract:
Neutron diffraction experiments have been performed on single crystalline samples of CePtSi3. We found that the incommensurate magnetic propagation vector tau(1) = (+/- 0.283, 0, 0) in the phase I (2.2 similar to 4.8 K) switches to the commensurate vectors tau(2) = (+/- 0.25, 0, 0) and tau(3) = (+/- 0.25, 0, +/- 1) in the phase III (similar to 2.8 K) at zero field. Although the magnetic structure of CePtSi3 in the phase I is a spin density wave similar to those in CeRhSi3, CeIrSi3, and CePdSi3, the magnetic structure in the phase III is commensurate unlike other CeTSi3 (T = Rh, Ir, Pd) compounds. (c) 2018 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license

Update: 5-Dec-2018

Title:
New Ti-based bulk metallic glasses with exceptional glass forming ability
Authors:
Lin, SF; Liu, DM; Zhu, ZW; Li, D; Fu, HM; Zhuang, YX; Zhang, HW; Li, H; Wang, AM; Zhang, HF Author Full Names: Lin, Shifeng; Liu, Dingming; Zhu, Zhengwang; Li, Dan; Fu, Huameng; Zhuang, Yanxin; Zhang, Hongwei; Li, Hong; Wang, Aimin; Zhang, Haifeng
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 502 71-75; 10.1016/j.jnoncrysol.2018.06.038 DEC 15 2018
Abstract:
New Ti-based bulk metallic glasses (BMGs) of Ti32.8+xZr30.2-xNi5.3Cu9Be22.7 (3 <= vertical bar X vertical bar <= 15, at.%) with large size were prepared. The results reveal that the forming of primary icosahedral quasicrystal phase (I-phase) and the enthalpy of the primary crystallization (Delta H-1) were closely related to the glass forming abilities (GFAs). Thecrystallization product of the metallic glass alloys at primary crystallization state is a metastable I-phase. It is demonstrated that apparent activation energy for crystallization obtained by fitting the Kissinger equation at T-x temperature increases with the increase of Ti concentration, while GFAs deteriorate. The Delta H-1 of metallic glasses declines with the increase of Ti concentration. The Ti32.8+XZr30.2-XNi5.3Cu9Be22.7 possess high similar compressive fracture strength of about 1800 MPa, which is one of the best options as structural materials on account of high specific strength and low cost.
Title:
Magnetic ordering in multiferroic SmMn2O5 and GdMn2O5 studied by resonant soft x-ray scattering
Authors:
Ishii, Y; Horio, S; Yamamoto, H; Noda, Y; Nakao, H; Murakami, Y; Kimura, H Author Full Names: Ishii, Y.; Horio, S.; Yamamoto, H.; Noda, Y.; Nakao, H.; Murakami, Y.; Kimura, H.
Source:
PHYSICAL REVIEW B, 98 (17):10.1103/PhysRevB.98.174428 NOV 21 2018
Abstract:
Resonant soft x-ray scattering was used to study the magnetic ordering of the multiferroic materials SmMn2O5 and GdMn2O5. In the case of SmMn2O5, the results confirm that antiferromagnetic ordering of Mn magnetic moments occurs with magnetic propagation vector q(M) = (1/2, 0, 1/3 + delta') in the incommensurate magnetic phase, followed by the appearance of the commensurate magnetic phase with q(M) = (1/2, 0, 0) as the temperature is decreased. The energy spectrum around Mn L-II(,)III edges suggests that the Mn ions adopt unique electronic states in the CM phase of SmMn2O5. No evidence was found for spin polarization of oxygen ions through 2p-3d orbital hybridization between oxygen and Mn ions in this compound, although this phenomenon is clearly evident in GdMn2O5 and other RMn2O5 (R = Y, Er, Tb) compounds. The energy spectra around O K edge strongly suggest that electronic polarization resulting from charge transfer between oxygen and Mn ions has little contribution to the ferroelectricity while lattice distortion likely plays a key role in promoting ferroelectricity in SmMn2O5.
Title:
Synthesis of an Al-Mn-Based Alloy Containing In Situ-Formed Quasicrystals and Evaluation of Its Mechanical and Corrosion Properties
Authors:
Naglic, I; Samardzija, Z; Delijic, K; Kobe, S; Leskovar, B; Markoli, B Author Full Names: Naglic, Iztok; Samardzija, Zoran; Delijic, Kemal; Kobe, Spomenka; Leskovar, Blaz; Markoli, Bostjan
Source:
JOM, 70 (11):2698-2703; 10.1007/s11837-018-2945-6 NOV 2018
Abstract:
An Al-Mn alloy with additions of copper, magnesium, and silicon was prepared and cast into a copper mold. It contains in situ-formed icosahedral quasicrystals (iQCs), as confirmed by electron backscatter diffraction. The aim of this work is to present the mechanical and corrosion properties of this alloy and compare its properties with some conventional commercial materials. The compressive strength and compressive yield strength were 751MPa and 377MPa, while the compressive fracture strain was 19%. It was observed that intensive shearing caused the final fracture of the specimens and the fractured iQC dendrites still showed cohesion with the -Al matrix. The polarization resistance and corrosion rate of the artificially aged alloy were 7.30k and 1.2m/year. The evaluated properties are comparable to conventional, discontinuously reinforced aluminum metal-matrix composites and structural wrought aluminum alloys.
Title:
Influence of Minor Additions on Icosahedral Short-Range Order (ISRO) and Its Consequences on Nucleation and Solidification Growth Kinetics in fcc Alloys
Authors:
Zollinger, J; Rappaz, M Author Full Names: Zollinger, J.; Rappaz, M.
Source:
TRANSACTIONS OF THE INDIAN INSTITUTE OF METALS, 71 (11):2635-2638; SI 10.1007/s12666-018-1411-z NOV 2018
Abstract:
The present contribution reviews the recent progress related to the influence of icosahedral short-range order (ISRO) and icosahedral quasicrystal (iQC) formation on the solidification of fcc alloys through minor solute element additions. From intensive crystallographic analysis of multi-twinned region in as-cast Al-based and Au-based fcc alloys, it has been shown recently that a so-called iQC-mediated nucleation mechanism occurs when a few hundred ppm of Cr and Ir, respectively, are added to the melt (Kurtuldu et al. in Acta Mater 61(19):7098-7108, 2013; Acta Mater 70:240-248, 2014). Similarly, it appears that the growth directions of dendrites in Al-Zn/Cr are also influenced by ISRO in the liquid, thus showing an attachment kinetics effect (Kurtuldu in Influence of trace elements on the nucleation and solidification morphologies of fcc alloys and relationship with icosahedral quasicrystal formation, 2014). Similar observations have been made recently in pink gold alloys with Ir additions, when the solidification speed is increased (Zollinger et al. in Acta Mater, 2018).

Update: 28-Nov-2018

Title:
Effect of Cu and Mn content on solidification microstructure, T-phase formation and mechanical property of Al-Cu-Mn alloys
Authors:
Dar, SM; Liao, HC; Xu, AQ Author Full Names: Dar, Soban Muddassir; Liao, Hengcheng; Xu, Aiqun
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 774 758-767; 10.1016/j.jallcom.2018.09.362 FEB 5 2019
Abstract:
Solidification microstructure of two AlCuMn alloys (Alloy-1: Al-1.6Cu-0.3Mn, Alloy-2: Al-2.2Cu-0.8Mn) and their precipitation behavior during solutionizing and aging treatments were investigated by optical microscopy, X-ray diffraction, Scanning and Transmission Electron Microscopies. The influence of Cu/Mn content and ratio on mechanical properties was also discussed in this study. Results reveal that Cu/Mn content and ratio have considerable influence on the solidification microstructure of these alloys. In Alloy-1 with low Cu/Mn content and ratio, only small amount of theta-CuAl2 and T-phase (Al20Cu2Mn3) are formed within the interdendritic regions and grains boundaries during solidification. But in Alloy-2 with high Cu/Mn content and ratio, a great amount of bone-like and round multiphase structure is observed in interdendritic regions, which consists of alpha-Al, theta-CuAl2 and Al13Cu4Mn3 phases. The Al13Cu4Mn3 phase in multiphase structure is demonstrated to be an icosahedral quasicrystalline phase (I-phase). The formation of I-phase in a conventional casting of AlCuMn alloy is related to the stabilizing effect of Fe. Cu/Mn content and ratio also have considerable influence on precipitation behavior of AlCuMn alloy during solutionizing and aging treatment. In Alloy-2, two morphologies of T-phase are formed: large particulate one is transformed from the instability decomposition of I-phase at high temperature and the fine rod-like is precipitated from supersaturated Al solid solution. And further aging does not lead to new precipitates. At each test temperature, both the YS and UTS of Alloy-2 are higher than that of Alloy-1 which is related to the formation of a great amount of T-phase particles during solution treatment. (C) 2018 Published by Elsevier B.V.
Title:
Effect of refinement of grains and icosahedral phase on hot compressive deformation and processing maps of Mg-Zn-Y magnesium alloys with different volume fractions of icosahedral phase
Authors:
Kwak, TY; Kim, WJ Author Full Names: Kwak, T. Y.; Kim, W. J.
Source:
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY, 35 (1):181-191; 10.1016/j.jmst.2018.06.019 JAN 2019
Abstract:
The effect of the volume fraction of I-phase on the hot compressive behavior and processing maps of the extruded Mg-Zn-Y alloys was examined, and the obtained results were compared with those of the cast alloys in a previous work. The average grain sizes, fractions of dynamically recrystallized (DRXed) grains, and sizes of DRXed grains of the extruded alloys after compressive deformation were significantly smaller, higher and smaller, respectively, than those of the cast alloys after compressive deformation under the same experimental conditions. This was because the microstructures of the extruded alloys, having much more grain boundaries and more refined I-phase particles than the cast alloys, provided a larger number of nucleation sites for dynamic recrystallization than those of the cast alloys. The constitutive equations for high-temperature deformation of the extruded and cast alloys could be derived using the same activation energy for plastic flow, which was close to the activation energy for lattice diffusion in magnesium. Compared with the cast alloys, the onset of the power law breakdown (PLB) occurred at larger Zener-Holloman (Z) parameter values in the extruded alloys. This was because the extruded alloys had finer initial grain sizes and higher fractions of finer DRXed grains compared to the cast alloys, such that the onset of PLB caused by creation of excessive concentrations of deformation-induced vacancies was delayed to a higher strain rate and a lower temperature. The flow-stress difference between the extruded alloys and the cast alloys could be attributed to the difference in the fraction of DRXed grains. According to the processing maps, the extruded alloys exhibited higher power dissipation efficiency and flow stability than the cast alloys. This agreed with the microstructural observations. (C) 2018 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.
Title:
Electronic structure of commensurate, nearly commensurate, and incommensurate phases of 1T-TaS2 by angle-resolved photoelectron spectroscopy, scanning tunneling spectroscopy, and density functional theory
Authors:
Lutsyk, I; Rogala, M; Dabrowski, P; Krukowski, P; Kowalczyk, PJ; Busiakiewicz, A; Kowalczyk, DA; Lacinska, E; Binder, J; Olszowska, N; Kopciuszynski, M; Szalowski, K; Gmitra, M; Stepniewski, SR; Jalochowski, M; Kolodziej, JJ; Wysmolek, A; Klusek, Z Author Full Names: Lutsyk, I; Rogala, M.; Dabrowski, P.; Krukowski, P.; Kowalczyk, P. J.; Busiakiewicz, A.; Kowalczyk, D. A.; Lacinska, E.; Binder, J.; Olszowska, N.; Kopciuszynski, M.; Szalowski, K.; Gmitra, M.; Stepniewski, S. R.; Jalochowski, M.; Kolodziej, J. J.; Wysmolek, A.; Klusek, Z.
Source:
PHYSICAL REVIEW B, 98 (19):10.1103/PhysRevB.98.195425 NOV 19 2018
Abstract:
The electronic structure of 1T-TaS2 showing a metal-insulator transition and a sequence of different charge density wave (CDW) transformations was discussed in the frame of variable temperature angle-resolved photoelectron spectroscopy (ARPES), scanning tunneling spectroscopy (STS), and density functional theory (DFT) calculations. For the commensurate charge density wave phase (CCDW) the Mott gap was estimated to be 0.4 eV and energy gaps Delta(CCDW,1), Delta(CCDW,2), Delta(B3-HHB), Delta(B4-B3) were observed. For the nearly commensurate charge density wave phase (NCCDW), the reminiscent of higher and lower Hubbard bands and a very pronounced electronic state associated with the parabolic band at the (Gamma) over bar point in the Brillouin zone were identified. The incommensurate charge density wave phase (ICCDW) showed a high value of local density of states at the Fermi level and a very pronounced edge of the metallic surface state located in the range of 0.15-0.20 eV above the Fermi level. The obtained STS and ARPES results were consistent with our theoretical calculations performed within DFT formalism including spin-orbit coupling.
Title:
Femtosecond diffraction studies of solid and liquid phase changes in shock-compressed bismuth
Authors:
Gorman, MG; Coleman, AL; Briggs, R; McWilliams, RS; McGonegle, D; Bolme, CA; Gleason, AE; Galtier, E; Lee, HJ; Granados, E; Sliwa, M; Sanloup, C; Rothman, S; Fratanduono, DE; Smith, RF; Collins, GW; Eggert, JH; Wark, JS; McMahon, MI Author Full Names: Gorman, M. G.; Coleman, A. L.; Briggs, R.; McWilliams, R. S.; McGonegle, D.; Bolme, C. A.; Gleason, A. E.; Galtier, E.; Lee, H. J.; Granados, E.; Sliwa, M.; Sanloup, C.; Rothman, S.; Fratanduono, D. E.; Smith, R. F.; Collins, G. W.; Eggert, J. H.; Wark, J. S.; McMahon, M. I.
Source:
SCIENTIFIC REPORTS, 8 10.1038/s41598-018-35260-3 NOV 16 2018
Abstract:
Bismuth has long been a prototypical system for investigating phase transformations and melting at high pressure. Despite decades of experimental study, however, the lattice-level response of Bi to rapid (shock) compression and the relationship between structures occurring dynamically and those observed during slow (static) compression, are still not clearly understood. We have determined the structural response of shock-compressed Bi to 68 GPa using femtosecond X-ray diffraction, thereby revealing the phase transition sequence and equation-of-state in unprecedented detail for the first time. We show that shocked-Bi exhibits a marked departure from equilibrium behavior - the incommensurate Bi-III phase is not observed, but rather a new metastable phase, and the Bi-V phase is formed at significantly lower pressures compared to static compression studies. We also directly measure structural changes in a shocked liquid for the first time. These observations reveal new behaviour in the solid and liquid phases of a shocked material and give important insights into the validity of comparing static and dynamic datasets.

Update: 21-Nov-2018

Title:
A contribution to the ternary phase diagrams of Al with Co, Rh and Ir
Authors:
Grushko, B Author Full Names: Grushko, B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 772 399-408; 10.1016/j.jallcom.2018.09.066 JAN 25 2019
Abstract:
Phase equilibria were studied in Al-Co-Rh above 50 at.% Al at 1100 and 1000 degrees C and above 70 at.% Al at 900 degrees C; in Al-Co-Ir above 50 at.% Al at 1100 degrees C and above 70 at.% Al at 900 degrees C; in Al-Ir-Rh above 50 at.% Al at 1150 degrees C and above 70 at.% Al at 900 degrees C. Wide phase regions extended along about constant Al are common in these ternary alloy systems. A continuous ternary region was observed between isostructural Al9Co2, Al9Rh2 and Al9Ir2 (theta-phase), another region between Al5Co2 and Al5Rh2 (H-phase), and at elevated temperatures also between Al2.63Rh and Al2.75Ir (C-phase). The binary regions forming around equiatomic AlCo, AlRh and AlIr are probably connected by continuous ternary regions. The C-phase was found to extend up to at least 8 at.% Co in Al-Co-Rh and up to 10 at.% Co in Al-Co-Ir. The H-phase was found to extend up to at least 8 at.% Ir in Al-Co-Ir. The ternary extensions of m-Al13Co4 achieved similar to 11 at.% Ir and similar to 15 at.% Rh, and those of the Al-Co Z-phase up to similar to 4 at.% Ir and similar to 10 at.% Rh. O-Al13Co4 was found to dissolve up to similar to 2 at.% Rh or Ir. M-Al13Co4 was not observed at ternary compositions. The Al-Rh epsilon-region containing both epsilon(6) and epsilon(16) was found to extend up to similar to 8.5 at.% Co and up to similar to 20 at.% Ir, while the Al-Rh V-phase was found to extend up to 5.5 at.% Co and at least 13 at.% Ir. Of the Al-Ir phases, the phi-phase was found to dissolve up to 5 at.% Rh, and the chi-phase up to at least 12 at.% Rh but only similar to 5 at.% Co. Al3Ir was found to dissolve up to similar to 14.5 at.% Co but very little Rh. No ternary phases were revealed in Al-Ir-Rh. A ternary E-phase (Pbma, a = 2.3555, b = 1.6497, c = 2.0035 nm) was exposed around similar to Al77Co8Rh15. The same structure was also revealed at similar to Al77Co10.5-16.0Ir12.5-7.0. In addition, Al-Co-Ir contains ternary phases V, epsilon, W and D. The Al-Co-Ir V-phase and epsilon-phase are structurally interrelated with the Al-Rh V-phase and epsilon-phase, respectively. The former is formed at similar to Al71Co17.5Ir11.5, the latter at Al76Co7.5-10.5Ir16.5-13.5. The W-phase (Pmn2(1), a = 2.3736, b = 0.8153, c = 2.0757 nm for Al73Co21Ir6) occupies a region inside similar to Al73.0-71.5Co19.0-22Ir5.0-9.0 at 1100 degrees C and decomposes between 1000 and 1100 degrees C. At 1150 degrees C the same compositional region belongs to a decagonal D-phase, while at 1100 degrees C this phase exists at similar to Al74.5Co17.5-21.0Ir8.0-4.5 and at 900 degrees C around similar to Al74.5Co19,5Ir6.0. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Mechanical properties and Hall-Petch relationship of the extruded Mg-Zn-Y alloys with different volume fractions of icosahedral phase
Authors:
Kwak, TY; Kim, WJ Author Full Names: Kwak, T. Y.; Kim, W. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 770 589-599; 10.1016/j.jallcom.2018.08.121 JAN 5 2019
Abstract:
The effect of the volume fraction (0.6-8.4%) of the icosahedral phase (I-phase) on the microstructure, texture and mechanical properties of extruded Mg-Zn-Y alloys was examined. During extrusion, the eutectic and divorced eutectic I-phase in the cast microstructures was broken into small particles, and the particles were dispersed along the extrusion direction, forming parallel particle bands. The broken Iphase particles promoted grain refinement via a particle-stimulated nucleation mechanism and led to basal texture weakening through dynamic recrystallization. The work hardening rate increased with an increase in the volume fraction of I-phase. However, the strength decreased with an increase in the volume fraction of I-phase due to the texture softening effect. To incorporate the texture softening effect into the Hall-Petch relation, a modified Hall-Petch equation, which simultaneously considers the effects of grain size and texture on strength, was developed using the Schmid factors for basal slip. The proposed equation predicts smaller Hall-Petch slope, friction stress and yield strength with easier activation of basal slip, agreeing with the experimental observations. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Neutron Diffraction Studies on Valence Ordering Compound YbPd
Authors:
Oyama, K; Sugishima, M; Tanabe, K; Mitsuda, A; Wada, H; Ohoyama, K; Matsukawa, T; Yoshida, Y; Hoshikawa, A; Ishigaki, T; Iwasa, K Author Full Names: Oyama, Kohei; Sugishima, Masaki; Tanabe, Kousuke; Mitsuda, Akihiro; Wada, Hirofumi; Ohoyama, Kenji; Matsukawa, Takeshi; Yoshida, Yukihiko; Hoshikawa, Akinori; Ishigaki, Toru; Iwasa, Kazuaki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 87 (11):10.7566/JPSJ.87.114705 NOV 15 2018
Abstract:
The magnetic structure of YbPd was determined for a newly synthesized strain-free sample by neutron diffraction techniques. The sinusoidal magnetic structure characterized by an incommensurate wave vector k = (0.080 0 0.32) is observed in the magnetic-ordered phase between T-3 = 1.9K and T-4 = 0.5 K, which is composed of the magnetic-moment amplitude of 0.3 mu(B) parallel to the alpha-axis in the tetragonal crystal-structure phase. The modulated magnetic structure is consistent with the previously proposed Yb-ion valence ordered structure appearing below T-2 = 105 K, which consists of the periodic arrangement of magnetic and nonmagnetic Yb ions.
Title:
Unravelling Incommensurate Magnetism and Its Emergence in Iron-Based Superconductors
Authors:
Christensen, MH; Andersen, BM; Kotetes, P Author Full Names: Christensen, Morten H.; Andersen, Brian M.; Kotetes, Panagiotis
Source:
PHYSICAL REVIEW X, 8 (4):10.1103/PhysRevX.8.041022 NOV 9 2018
Abstract:
We focus on a broad class of tetragonal itinerant systems sharing a tendency towards the spontaneous formtion of incommensurate magnetism with ordering wave vectors Q(1,)(2) = (pi - delta, 0)/(0, pi - delta) or Q(1,2) = (pi, delta) 1 (-delta, pi). Employing a Landau approach, we obtain the generic magnetic phase diagram and identify the leading instabilities near the paramagnetic-magnetic transition. Nine distinct magnetic phases exist that either preserve or violate the assumed C-4 symmetry of the paramagnetic phase. These are single-and double-Q phases consisting of magnetic stripes, helices, and whirls, either in an individual or coexisting manner. These nine phases can be experimentally distinguished by polarized neutron scattering, or, e.g., by combining measurements of the induced charge order and magnetoelectric coupling. Within two representative five-orbital models, suitable for BaFe2As2 and LaFeAsO, we find that the incommensurate magnetic phases we discuss here are accessible in iron-based superconductors. Our investigation unveils a set of potential candidates for the unidentified C-2-symmetric magnetic phase that was recently observed in Ba1-xNaxFe2As2. Among the phases stabilized we find a spin-whirl crystal, which is a textured magnetic C-4-symmetric phase. The possible experimental observation of textured magnetic orders in iron-based superconductors opens new directions for realizing intrinsic topological superconductors.
Title:
Angle-dependent magnetization dynamics with mirror-symmetric excitations in artificial quasicrystalline nanomagnet lattices
Authors:
Bhat, VS; Grundler, D Author Full Names: Bhat, V. S.; Grundler, D.
Source:
PHYSICAL REVIEW B, 98 (17):10.1103/PhysRevB.98.174408 NOV 6 2018
Abstract:
We report angle-dependent spin-wave spectroscopy on aperiodic quasicrystalline magnetic lattices, i.e., Ammann, Penrose P2 and P3 lattices made of large arrays of interconnected Ni80Fe20 nanobars. Spin-wave spectra obtained in the nearly saturated state contain distinct sets of resonances with characteristic angular dependencies for applied in-plane magnetic fields. Micromagnetic simulations allow us to attribute detected resonances to mode profiles with specific mirror symmetries. Spectra in the reversal regime show systematic emergence and disappearance of spin-wave modes indicating reprogrammable magnonic characteristics.
Title:
Angle-dependent magnetoresistance as a sensitive probe of the charge density wave in quasi-one-dimensional semimetal Ta2NiSe7
Authors:
He, JM; Wen, LB; Wu, YS; Liu, JY; Tang, GX; Yang, YS; Xing, H; Mao, ZQ; Sun, H; Liu, Y Author Full Names: He, Jiaming; Wen, Libin; Wu, Yueshen; Liu, Jinyu; Tang, Guoxiong; Yang, Yusen; Xing, Hui; Mao, Zhiqiang; Sun, Hong; Liu, Ying
Source:
APPLIED PHYSICS LETTERS, 113 (19):10.1063/1.5058182 NOV 5 2018
Abstract:
The behavior of charge density waves (CDWs) in an external magnetic field is dictated by both orbital and Pauli (Zeeman) effects. A quasi-one-dimensional (Q1D) system features Q1D Fermi surfaces that allow these effects to be distinguished, which in turn can provide a sensitive probe to the underlying electronic states. Here, we studied the field dependence of an incommensurate CDW in a transition-metal chalcogenide Ta2NiSe7 with a Q1D chain structure. The angle-dependent magnetoresistance (MR) is found to be very sensitive to the relative orientation between the magnetic field and the chain direction. With an applied current fixed along the b axis (the chain direction), the angle-dependent MR shows a striking change of the symmetry below T-CDW only for a rotating magnetic field in the ac plane. In contrast, the symmetry axis remains unchanged for other configurations (H in ab and be planes). The orbital effect conforms to the lattice symmetry, while the Pauli effect in the form of mu B-B/(h) over barv(F) can be responsible for such symmetry change, provided that the Fermi velocity v(F) is significantly anisotropic and the nesting vector changes in a magnetic field, which is corroborated by our first-principles calculations. Our results show that the angle-dependent MR is a sensitive transport probe of CDW and can be useful for the study of lowdimensional systems in general. Published by AIP Publishing.
Title:
Previously unknown quasicrystal periodic approximant found in space
Authors:
Bindi, L; Pham, J; Steinhardt, PJ Author Full Names: Bindi, Luca; Pham, Joyce; Steinhardt, Paul J.
Source:
SCIENTIFIC REPORTS, 8 10.1038/s41598-018-34375-x NOV 2 2018
Abstract:
We report the discovery of Al34Ni9Fe2, the first natural known periodic crystalline approximant to decagonite (Al71Ni24Fe5), a natural quasicrystal composed of a periodic stack of planes with quasiperiodic atomic order and ten-fold symmetry. The new mineral has been approved by the International Mineralogical Association (IMA 2018-038) and officially named proxidecagonite, which derives from its identity to periodic approximant of decagonite. Both decagonite and proxidecagonite were found in fragments from the Khatyrka meteorite. Proxidecagonite is the first natural quasicrystal approximant to be found in the Al-Ni-Fe system. Within this system, the decagonal quasicrystal phase has been reported to transform at similar to 940 degrees C to Al-13(Fe,Ni)(4), Al-3(Fe,Ni)(2) and the liquid phase, and between 800 and 850 degrees C to Al-13(Fe,Ni)(4),Al-3(Fe,Ni) and Al-3(Fe,Ni)(2). The fact that proxidecagonite has not been observed in the laboratory before and formed in a meteorite exposed to high pressures and temperatures during impact-induced shocks suggests that it might be a thermodynamically stable compound at high pressure. The most prominent structural motifs are pseudo-pentagonal symmetry subunits, such as pentagonal bipyramids, that share edges and corners with trigonal bipyramids and which maximize shortest Ni-Al over Ni-Ni contacts.

Update: 14-Nov-2018

Title:
A tenfold twin of the CrB structure type
Authors:
Hornfeck, W Author Full Names: Hornfeck, Wolfgang
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 659-672; 10.1107/S2053273318011828 6 NOV 2018
Abstract:
NiZr crystallized from an amorphous matrix or solidified from an undercooled melt exhibits a tenfold twinned microstructure, which is explained by an ideal twin model utilizing special geometric properties of the CrB structure type. The model is unique in several ways: (i) it contains no adjustable parameters other than a scaling factor accounting for the smallest interatomic distance; (ii) it features an irrational shift in the translational part of the twin operation; and (iii) it has many traits commonly observed for quasicrystals, connected to the occurrence of decagonal long-range orientational order, making NiZr the first experimental example of the recently introduced concept of Z-module twinning. It is shown how these remarkable properties of the tenfold twin's structure model are related to one another and founded in number theory as well as in the mathematical theory of aperiodic order.
Title:
Thermal evolution of quasi-one-dimensional spin correlations within the anisotropic triangular lattice of alpha-NaMnO2
Authors:
Dally, RL; Chisnell, R; Harriger, L; Liu, YH; Lynn, JW; Wilson, SD Author Full Names: Dally, Rebecca L.; Chisnell, Robin; Harriger, Leland; Liu, Yaohua; Lynn, Jeffrey W.; Wilson, Stephen D.
Source:
PHYSICAL REVIEW B, 98 (14):10.1103/PhysRevB.98.144444 OCT 31 2018
Abstract:
Magnetic order on the spatially anisotropic triangular lattice of alpha-NaMnO2 is studied via neutron diffraction measurements. The transition into a commensurate, collinear antiferromagnetic ground state with k = (0.5, 0.5, 0) was found to occur below T-N = 22 K. Above this temperature, the transition is preceded by the formation of a coexisting, short-range ordered, incommensurate state below T-IC = 45 K whose two-dimensional propagation vector evolves toward k = (0.5, 0.5) as the temperature approaches T-N. At high temperatures (T > T-IC), quasielastic scattering reveals one-dimensional spin correlations along the nearest-neighbor Mn-Mn "chain direction" of the MnO6 planes. Our data are consistent with the predictions of a mean-field model of Ising-like spins on an anisotropic triangular lattice, as well as the predominantly one-dimensional Heisenberg spin Hamiltonian reported for this material.
Title:
Quasicrystal Tilings in Three Dimensions and Their Empires
Authors:
Hammock, D; Fang, F; Irwin, K Author Full Names: Hammock, Dugan; Fang, Fang; Irwin, Klee
Source:
CRYSTALS, 8 (10):10.3390/cryst8100370 OCT 2018
Abstract:
The projection method for constructing quasiperiodic tilings from a higher dimensional lattice provides a useful context for computing a quasicrystal's vertex configurations, frequencies, and empires (forced tiles). We review the projection method within the framework of the dual relationship between the Delaunay and Voronoi cell complexes of the lattice being projected. We describe a new method for calculating empires (forced tiles) which also borrows from the dualisation formalism and which generalizes to tilings generated projections of non-cubic lattices. These techniques were used to compute the vertex configurations, frequencies and empires of icosahedral quasicrystals obtained as a projections of the D-6 and Z(6) lattices to R-3 and we present our analyses. We discuss the implications of this new generalization.

Update: 8-Nov-2018

Title:
Effect of Ca Concentration on Microstructure and Mechanical Properties of As-Cast and As-Extruded Quasicrystal-Strengthened Mg-7.2Zn-2.4Gd Alloy
Authors:
Sun, JC; Ma, YL; Miao, HW; Li, KJ; Li, CH; Huang, H Author Full Names: Sun, Jianchun; Ma, Yilong; Miao, Hongwei; Li, Kejian; Li, Chunhong; Huang, Hua
Source:
ADVANCES IN MATERIALS SCIENCE AND ENGINEERING, 10.1155/2018/9138753 2018
Abstract:
Quasicrystal-strengthened Mg-Zn-RE (RE = rare-earth element) alloys have been investigated extensively due to their excellent mechanical properties. Here, we prepare quasicrystal-strengthened Mg-7.2Zn-2.4Gd (wt.%) alloy with different concentrations of Ca addition (0, 0.16, 0.32, and 0.64 wt.%) by traditional gravity casting, followed by extrusion at 573 K with the extrusion ratio of 9:1. lhe microstructure and room temperature tensile properties of as-cast and as-extruded alloys are characterized. With the addition of the trace amount of Ca, the I-phase tends to transfer into W-phase due to the appearance of Mg2Ca and Mg6Zn3Ca2. As a consequence, the mechanical properties of the as-cast Ca containing alloys are downgraded. After extrusion, in comparison to the as-cast alloys, microstructure of the four types of alloys is refined and mechanical property is enhanced greatly. With the increasing of Ca concentration, the grain size is decreased gradually. However, the yield strength of the alloys is decreased to about 230 MPa and then up to 269 MPa, while the elongation increases first from 12.9% to 13.6% yet then decreases to 9.9%.

Update: 1-Nov-2018

Title:
Identification of the incommensurate structure transition in biphenyl by Raman scattering
Authors:
Zhang, K; Chen, XJ Author Full Names: Zhang, Kai; Chen, Xiao-Jia
Source:
SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, 206 202-206; 10.1016/j.saa.2018.07.104 JAN 5 2019
Abstract:
Raman scattering measurements are performed on crystalline biphenyl at low temperatures. The properties of the vibrational modes focused on the intra- and intermolecular terms are analyzed in detail. Nearly all of the vibration modes exhibit hardening and simultaneously sharpen with decreasing temperature, whereas the modes at around 250 cm(-1) and 1280 cm(-1) soften their energies as temperature is decreased. Moreover, all the internal modes have anomalous reversals at around 45 K on the frequencies, widths, and intensities, and below 45 K, several new internal modes appear. Results of the analyses indicate that the reemergence of the interring tilt angle of the molecules at 45 K has a significant impact on the vibrational properties of biphenyl. Our work thus paves interesting and essential groundwork for the further study of biphenyl. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Magnetic phase coexistence in DyNiAl4
Authors:
White, R; Hutchison, WD; Avdeev, M Author Full Names: White, R.; Hutchison, W. D.; Avdeev, M.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 469 30-34; 10.1016/j.jmmm.2018.08.011 JAN 1 2019
Abstract:
The magnetic structure and properties of the rare earth intermetallic DyNiAl4 have been determined. Two magnetic phase transitions have been observed at T-N = 20.2(1) K and T-N, = 14.6(1) K. Analysis via neutron diffraction has revealed that these correspond to the formation of two distinct magnetic phases, a low temperature collinear antiferromagnetic phase with k(C) = (0, 1, 0) and a higher temperature incommensurate phase with k(I) = ( 0.1745(6), 1, 0.0313(6)). The incommensurate phase consists of a sinusoidal modulation of the magnetic moment along the a- and c-axis directions. In addition, both of these phases have been found to coexist between 14.5 K and 16.1 K.
Title:
A New Class of Ordered Structure Between Crystals and Quasicrystals
Authors:
Qin, GW; Xie, HB; Pan, HC; Ren, YP Author Full Names: Qin Gaowu; Xie Hongbo; Pan Hucheng; Ren Yuping
Source:
ACTA METALLURGICA SINICA, 54 (11):1490-1502; SI 10.11900/0412.1961.2018.00357 NOV 11 2018
Abstract:
This paper briefly reviews the development and research history of strutures of the solid matters, and highlight two new strcutures of precipitates in Mg alloys found by our group recently. (1) The isothermally aged (Mg, In)(2)Ca "Laves phase" contains two separate unit cells promoting the formation of five tiling patterns. The bonding of these patterns leads to the generation of the present phase but without any six-fold rotational symmetry in a long-range on the (0001)(L) basal plane, constrainted by the Penrose geometrical rule, completely different from the known Laves phases. (2) The MgZn five-fold nanodomain structure is self-assembled by two separate unit cells (72 degrees rhombus structure: MgZn2, and 72 degrees equilateral hexagon structure: MgZn) under the Penrose geomotrical constraints, containing 2D five-fold symmetry locally and short-range ordered C14 and C15 Laves structures. These two special structures without any translational symmetry on the normal plane while periodical arrangement along the normal direction, are a new class of intermediate structures between crystals and quasicrystals. And thus, they does not belong to any crystals or 2D ordered structures in quasicrystals or quasicrystal approximants.
Title:
Landau levels in quasicrystals
Authors:
Fuchs, JN; Mosseri, R; Vidal, J Author Full Names: Fuchs, Jean-Noel; Mosseri, Remy; Vidal, Julien
Source:
PHYSICAL REVIEW B, 98 (16):10.1103/PhysRevB.98.165427 OCT 19 2018
Abstract:
Two-dimensional tight-binding models for quasicrystals made of plaquettes with commensurate areas are considered. Their energy spectrum is computed as a function of an applied perpendicular magnetic field. Landau levels are found to emerge near band edges in the zero-field limit. Their existence is related to an effective zero-field dispersion relation valid in the continuum limit. For quasicrystals studied here, an underlying periodic crystal exists and provides a natural interpretation to this dispersion relation. In addition to the slope (effective mass) of Landau levels, we also study their width as a function of the magnetic flux and identify two fundamental broadening mechanisms: (i) tunneling between closed cyclotron orbits and (ii) individual energy displacement of states within a Landau level. Interestingly, the typical broadening of the Landau levels is found to behave algebraically with the magnetic field with a nonuniversal exponent.
Title:
Influence of the magnetic field on the stability of the multiferroic conical spin arrangement of Mn0.80Co0.20WO4
Authors:
Urcelay-Olabarria, I; Ressouche, E; Ivanov, VY; Skumryev, V; Wang, Z; Skourski, Y; Balbashov, AM; Popov, YF; Vorob'ev, GP; Qureshi, N; Garcia-Munoz, JL; Mukhin, AA Author Full Names: Urcelay-Olabarria, I.; Ressouche, E.; Ivanov, V. Y.; Skumryev, V.; Wang, Z.; Skourski, Y.; Balbashov, A. M.; Popov, Yu. F.; Vorob'ev, G. P.; Qureshi, N.; Garcia-Munoz, J. L.; Mukhin, A. A.
Source:
PHYSICAL REVIEW B, 98 (13):10.1103/PhysRevB.98.134430 OCT 17 2018
Abstract:
The evolution of the low temperature antiferromagnetic conical (characterized by two, commensurate and incommensurate propagation vectors), and the high temperature collinear spin arrangements of the 20% Co-doped MnWO4 multiferroic has been studied in the presence of magnetic field up to 60 T by means of macroscopic magnetic and pyroelectric measurements, and by neutron diffraction experiments in fields up to 12 T on a single crystal. The complete magnetoelectric phase diagrams for magnetic fields along distinct magnetic directions with respect to the spin structure have been constructed up to magnetic field values exceeding those necessary to induce a spin-flip transition into the paramagnetic state. The differences in the topology of the diagrams are discussed. The obtained results might be common for other magnetic materials possessing conical antiferromagnetic structures.
Title:
Grain extraction and microstructural analysis method for two-dimensional poly and quasicrystalline solids
Authors:
Hirvonen, P; La Boissoniere, GM; Fan, ZY; Achim, CV; Provatas, N; Elder, KR; Ala-Nissila, T Author Full Names: Hirvonen, Petri; La Boissoniere, Gabriel Martine; Fan, Zheyong; Vasile Achim, Cristian; Provatas, Nikolas; Elder, Ken R.; Ala-Nissila, Tapio
Source:
PHYSICAL REVIEW MATERIALS, 2 (10):10.1103/PhysRevMaterials.2.103603 OCT 16 2018
Abstract:
While the microscopic structure of defected solid crystalline materials has significant impact on their physical properties, efficient and accurate determination of a given polycrystalline microstructure remains a challenge. In this paper, we present a highly generalizable and reliable variational method to achieve this goal for two-dimensional crystalline and quasicrystalline materials. The method is benchmarked and optimized successfully using a variety of large-scale systems of defected solids, including periodic structures and quasicrystalline symmetries to quantify their microstructural characteristics, e.g., grain size and lattice misorientation distributions. We find that many microstructural properties show universal features independent of the underlying symmetries.
Title:
Structure and hydrogen absorption properties of Ti53Zr27Ni20(Pd,V) quasicrystals
Authors:
Lee, SH; Kim, J Author Full Names: Lee, Sang-hwa; Kim, Jaeyong
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 43 (41):19130-19140; 10.1016/j.ijhydene.2018.08.141 OCT 11 2018
Abstract:
The structure and hydrogen absorption properties of Pd and V doped TiZrNi quasicrystals were investigated in terms of the equilibrium vapor pressure of hydrogen, and the results were compared with those of undoped samples. Rapidly quenched Ti53Zr27Ni2o alloys formed quasicrystals and absorbed hydrogen H/M (hydrogen to host metal atom ratio) value of 1.79 at room temperature. This was attributed to their structure, which contains mostly tetrahedral interstitial sites that are chemically formed by atoms having a high affinity with hydrogen. However, the relatively low equilibrium vapor pressure of hydrogen, 0.14 Torr at 300 degrees C, prevents TiZrNi quasicrystals for the practical application on energy storage materials. To overcome this limitation, we replaced Ti with Pd and V to increase the vapor pressure of hydrogen and investigated the properties of hydrogen absorption behaviors. Results of XRD measurements revealed that the quasicrystal structure was maintained by the replacement of Ti with a maximum of 8 at. % of Pd and V. Total amounts of the absorbed hydrogen decreased from 1.33 to 1.06 and to 1.12 of the H/M values when the Ti was replaced by 8 at. % of Pd and V, respectively, at 300 degrees C. The pressure-composition-temperature data measured using an automatic gas-handling system revealed that the equilibrium vapor pressure increased from 0.14 to 0.21 and to 0.56 Torr at H/M value of 0.5 when Ti atoms were replaced by 8 at. % Pd, and V, respectively, without the appearance of an impurity phase. Our results demonstrate that the replacement of Ti with Pd and V is an effective method to increase the equilibrium vapor pressure of hydrogen without a phase transformation in a TiZrNi quasicrystal system. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Update: 24-Oct-2018

Title:
Coupling between Ho and Mn/Cr moments and its influence on the structural and magnetic properties of HoMn1-xCrxO3 (0 < x <= 1) compounds
Authors:
Prakash, P; Singh, R; Mishra, SK; Prajapat, CL; Kumar, A; Das, A Author Full Names: Prakash, Pulkit; Singh, Ripandeep; Mishra, S. K.; Prajapat, C. L.; Kumar, A.; Das, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 465 70-80; 10.1016/j.jmmm.2018.05.080 NOV 1 2018
Abstract:
The effect of doping non Jahn-Teller (JT) Cr3+ ion on the crystallographic structure and magnetic ordering has been studied in a series of polycrystalline compounds HoMn1-xCrxO3 (0 < x <= 1). These compounds crystallize in a mixture of hexagonal and orthorhombic phases for x < 0.125 whereas the orthorhombic phase is present for all higher concentrations. It is observed that Cr doping leads to decrease in the mismatch of the bond length in Mn-O-6 octahedra indicating reduction in the static orbital ordering due to JT effect. In addition, doping with Cr3+ introduces ferromagnetic Mn3+-O-Cr3+ interactions in an antiferromagnetic matrix consisting of Mn3+-OMn3+ and Cr3+-O-Cr3+ interactions. A change in the magnetic structure from Gamma(4) (A(x)F(y)G(z)) to Gamma(2) (C(x)G(y)F(z)) is observed in samples with x > 0.75, which is attributed to the anisotropic interactions between the Ho3+ and Cr3+ spins. An incommensurate magnetic order corresponding to the wave vector (0.4, 0, 0) is observed in the orthorhombic phase associated with the x = 0.05 sample. The hexagonal phase in the Mn-rich end exhibits a reduced magnetic ordering temperature of 55 K and a spin reorientation at 15 K, in comparison to h-HoMnO3. The temperature variation of dielectric data shows weak magnetodielectric coupling in these compounds.
Title:
Old and New Insights into Structure and Properties of Eu-2[SiO4]
Authors:
Funk, C; Koher, J; Lazar, I; Kajewski, D; Roleder, K; Nuss, J; Bussmann-Holder, A; Bamberger, H; van Slageren, J; Enseling, D; Justel, T; Schleid, T Author Full Names: Funk, Christian; Koeher, Juergen; Lazar, Iwona; Kajewski, Dariusz; Roleder, Krystian; Nuss, Juergen; Bussmann-Holder, Annette; Bamberger, Heiko; van Slageren, Joris; Enseling, David; Juestel, Thomas; Schleid, Thomas
Source:
CRYSTAL GROWTH & DESIGN, 18 (10):6316-6325; 10.1021/acs.cgd.8b01265 OCT 2018
Abstract:
Lemon-yellow single crystals of Eu-2[SiO4] were obtained by reaction of elemental europium with Eu2O3 in the presence of SiO2 carried out in evacuated silica ampules at 1373 K for 48 h followed by constant cooling to room temperature with 120 K per hour. Eu-2[SiO4] crystallizes at room temperature in the larnite-type structure of beta-Ca-2[SiO4] (monoclinic, P2(1)/n) with parameters a = 565.02(5), b = 709.15(6), c = 975.84(8) pm, beta = 92.614(3)degrees for Z = 4. At 452 K it undergoes a reversible phase transition to an incommensurate structure similar to the isotypic compounds Sr-2[SiO4] and K-2[SeO4]. The phase transition energy was determined to 0.54(2) J.g(-1) by DSC measurements and temperature dependent birefringence measurements show that the phase transition exhibits a significant hysteresis. Refinements of the structure of Eu-2[SiO4] based on single crystal X-ray diffraction data show that the high temperature modification crystallizes in the orthorhombic space group Pnma(alpha 00)0ss with a = 710.16(6), b = 566.93(5), c = 977.13(8) pm, and an incommensurate modulation along [100] with a modulation vector t = [0.293(4), 0, 0]. Eu-2[SiO4] exhibits a bright yellow photoluminescence and its permittivity increases substantially above 300 K. Magnetic susceptibility and EPR measurements show that Eu-2[SiO4] becomes ferromagnetic below 7 K with a g factor of 1.993.
Title:
Development of Mg-Zn-Y-Ca alloys containing icosahedral quasicrystal phase through trace addition of Y
Authors:
Nie, KB; Kang, XK; Deng, KK; Guo, YC; Han, JG; Zhu, ZH Author Full Names: Nie, Kaibo; Kang, Xinkai; Deng, Kunkun; Guo, Yachao; Han, Jungang; Zhu, Zhihao
Source:
JOURNAL OF MATERIALS RESEARCH, 33 (18):2806-2816; 10.1557/jmr.2018.267 SEP 28 2018
Abstract:
In this work, three Mg-Zn-Y-Ca alloys reinforced by icosahedral quasicrystal phase through trace Y addition were extruded at a low temperature of 503 K. With increasing the contents of Zn and Y, the grain size of the as-extruded alloy was significantly reduced while both the size and volume fraction of nanosized precipitates were increased. The grain refinement in the Mg-Zn-Y-Ca alloy was related to dynamical recrystallization during extrusion and the pinning effect of nanosized precipitates on the grain boundaries. After extrusion, the yield strength (YS) and ultimate tensile strength (UTS) of the three alloys were significantly increased. The YS of 294.0 MPa, UTS of 337.5 MPa, and elongation of 10.6% were obtained in the case of Mg-2.09Zn-0.26Y-0.12Ca (at.%) alloys. The improvement in the mechanical properties could mainly be due to the grain boundary strengthening and Orowan strengthening. The as-cast alloy exhibited a typical cleavage fracture while the as-extruded alloy possessed a mixture fracture of dimple fracture and cracking along the twinning.
Title:
Correlation between the atomic configurations and the amorphous-to-icosahedral phase transition in metallic glasses
Authors:
Geng, GH; Yan, ZJ; Hu, Y; Wang, Z; Ketov, SV; Eckert, J Author Full Names: Geng, Guihong; Yan, Zhijie; Hu, Yong; Wang, Zhi; Ketov, Sergey V.; Eckert, Juergen
Source:
JOURNAL OF MATERIALS RESEARCH, 33 (18):2775-2783; 10.1557/jmr.2018.187 SEP 28 2018
Abstract:
Positron annihilation spectroscopy and differential scanning calorimetry were used to evaluate the changes of the atomic configurations in Zr-based metallic glasses (MGs) due to alloying and plastic deformation. The correlation between the atomic configurations of MGs and the amorphous-to-icosahedral phase transition due to heating was investigated. The results indicate that the free volume frozen in the as-cast Zr60Al15Ni25, Zr65Al7.5Ni10Cu17.5, and Zr65Al7.5Ni10Cu17.5Ag5 MGs substantially decreases in sequence. More excess free volume is introduced in Zr65Al7.5Ni10Cu17.5Ag5 MG due to cold rolling and milling. The annihilation of free volume due to alloying considerably stabilizes the icosahedral structure of MGs, which enhances the nucleation and growth of quasicrystals upon heating. However, the nucleation and growth of quasicrystals are considerably suppressed in Zr65Al7.5Ni10Cu17.5Ag5 MG due to cold rolling and milling, during which the more introduced excess free volume results in substantial destruction of short-range order with 5-fold symmetry. The present work further provides direct evidence for the prevalence of icosahedral short-range order in MGs.

Update: 17-Oct-2018

Title:
Correlation between crystallographic and microstructural features and low hysteresis behavior in Ni50.0Mn35.25In14.75 melt-spun ribbons
Authors:
Yan, HL; Sanchez-Valdes, CF; Zhang, YD; Llamazares, JLS; Li, ZB; Yang, B; Esling, C; Zhao, X; Zuo, L Author Full Names: Yan, Haile; Sanchez-Valdes, C. F.; Zhang, Yudong; Sanchez Llamazares, J. L.; Li, Zongbin; Yang, Bo; Esling, Claude; Zhao, Xiang; Zuo, Liang
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 767 544-551; 10.1016/j.jallcom.2018.07.063 OCT 30 2018
Abstract:
In this work, crystallographic, microstructural and magnetocaloric investigations were performed on textured Ni50Mn35.25In14.75 melt-spun ribbons with low thermal (6 K) and magnetic-field induced hysteresis (-0.731 kg(-1) at 2 T) and moderate maximum magnetic entropy change Delta S-M(max)(11 J kg(-1) K-1 at 5 T) at room temperature (302 K). The austenite in the ribbons crystallizes into a L2(1) structure, whereas martensite has a monoclinic incommensurate 6 M modulated structure as determined with the super space theory. By means of electron backscatter diffraction technique, the morphological and crystallographic features of microstructure were systematically characterized. Ribbons possess a fine microstructure with an average grain size (initial austenite phase) of around 10 mu m, whereas the 6 M martensite has a self-accommodated microstructure with 4 kinds of twin-related martensite variants. During inverse martensitic transformation, the austenite prefers to nucleate at the grain boundaries of initial austenite. By means of cofactor conditions and crystallographic orientation analyses, the good geometrical compatibility between austenite and martensite was confirmed. Based on the crystal structure and microstructure information obtained, the reason of the low thermal hysteresis was discussed. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Exceptionally large areas of local tenfold symmetry in decagonal Al59Cr21Fe10Si10
Authors:
Ma, HK; He, ZB; Hou, LG; Steurer, W Author Full Names: Ma, Haikun; He, Zhanbing; Hou, Longgang; Steurer, Walter
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 765 753-756; 10.1016/j.jallcom.2018.05.084 OCT 15 2018
Abstract:
The decagonal diffraction symmetry of a decagonal quasicrystal (DQC) results from its particular auto-correlation (Patterson) function. Structural subunits ('clusters') with decagonal symmetry may exist but do not need to exist. By atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), we observed the so far largest tenfold symmetric structural subunits in decagonal Al59Cr21Fe10Si10 scaling up to 5.2 nm. This amazing result provides direct experimental evidence how the local tenfold symmetry of DQCs is expanded to a larger size. (C) 2018 Published by Elsevier B.V.
Title:
Formation and microstructure of quasicrystals in suction cast Al-6wt.% Mn alloys with additions of nickel and iron elements
Authors:
Chen, Z; Xie, B; Fan, Q Author Full Names: Chen, Z.; Xie, B.; Fan, Q.
Source:
MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, 49 (10):1236-1244; 10.1002/mawe.201700128 OCT 2018
Abstract:
The formation and microstructure of quasicrystals in suction cast Al-6wt.% Mn-2wt.% TM (TM=Ni, Fe) alloys were investigated by transmission electron microscopy, scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction. The suction cast Al-6wt.% Mn-2wt.% Ni alloy consists of a single decagonal phase of Al56Mn11Ni2, whereas the Al-6wt.% Mn alloy with 2wt.% iron addition comprises a primitive icosahedral phase and a decagonal phase of Al40Mn7Fe2. Thus, the addition of nickel or iron favors quasicrystal formation in the suction cast Al-6wt.% Mn alloys. Based on a 4:1 matching ratio of aluminum atoms to heavier atoms, the approximate electron to atom ratio is 1.85 in two decagonal phases of Al56Mn11Ni2 and Al40Mn7Fe2. Various morphologies of quasicrystals with a size of more than 5m were observed in the microstructure of suction cast Al-6wt.% Mn-2wt.% TM (TM=Ni, Fe) alloys. The decagonal Al40Mn7Fe2 phase nucleates epitaxially and grows on the icosahedral phase.
Title:
Nonuniformly Loaded Stack of Antiplane Shear Cracks in One-Dimensional Piezoelectric Quasicrystals
Authors:
Tupholme, GE Author Full Names: Tupholme, G. E.
Source:
ADVANCES IN MATERIALS SCIENCE AND ENGINEERING, 10.1155/2018/4847837 2018
Abstract:
Representations in a closed form are derived, using an extension to the method of dislocation layers, for the phonon and phason stress and electric displacement components in the deformation of one-dimensional piezoelectric quasicrystals by a nonuniformly loaded stack of parallel antiplane shear cracks. Their dependence upon the polar angle in the region close to the tip of a crack is deduced, and the field intensity factors then follow. These exhibit that the phenomenon of crack shielding is dependent upon the relative spacing of the cracks. The analogous analyses, that have not been given previously, involving non-piezoelectric or non-quasicrystalline or simply elastic materials can be straightforwardly considered as special cases. Even when the loading is uniform and the crack is embedded in a purely elastic isotropic solid, no explicit representations have been available before for the components of the field at points other than directly ahead of a crack. Typical numerical results are graphically displayed.

Update: 3-Oct-2018

Title:
Magnetic structures of the rare-earth quadruple perovskite manganites RMn7O12
Authors:
Johnson, RD; Khalyavin, DD; Manuel, P; Zhang, L; Yamaura, K; Belik, AA Author Full Names: Johnson, R. D.; Khalyavin, D. D.; Manuel, P.; Zhang, L.; Yamaura, K.; Belik, A. A.
Source:
PHYSICAL REVIEW B, 98 (10):10.1103/PhysRevB.98.104423 SEP 19 2018
Abstract:
We report a neutron powder diffraction study of RMn7O12 quadruple perovskite manganites with R = La, Ce, Nd, Sm, and Eu. We show that in all measured compounds concomitant magnetic ordering of the A and B manganese sublattices occurs on cooling below the Neel temperature. The respective magnetic structures are collinear, with one uncompensated Mn3+ moment per formula unit as observed in bulk magnetization measurements. We show that both LaMn7O12 and NdMn7O12 undergo a second magnetic phase transition at low temperature, which introduces a canting of the B-site sublattice moments that is commensurate in LaMn7O12 and incommensurate in NdMn7O12. This spin canting is consistent with a magnetic instability originating in the B-site orbital order. Furthermore, NdMn7O12 displays a third magnetic phase transition at which long-range ordering of the Nd sublattice modifies the periodicity of the incommensurate spin canting. Our results demonstrate a rich interplay between transition-metal magnetism, orbital order, and the crystal lattice, which may be fine-tuned by cation substitution and rare-earth magnetism.
Title:
Quantum Spin Hall Effect and Spin Bott Index in a Quasicrystal Lattice
Authors:
Huang, HQ; Liu, F Author Full Names: Huang, Huaqing; Liu, Feng
Source:
PHYSICAL REVIEW LETTERS, 121 (12):10.1103/PhysRevLett.121.126401 SEP 17 2018
Abstract:
Despite the rapid progress in the field of the quantum spin Hall (QSH) effect, most of the QSH systems studied up to now are based on crystalline materials. Here we propose that the QSH effect can be realized in quasicrystal lattices (QLs). We show that the electronic topology of aperiodic and amorphous insulators can be characterized by a spin Bott index B-s. The nontrivial QSH state in a QL is identified by a nonzero spin Bott index B-s = 1, associated with robust edge states and quantized conductance. We also map out a topological phase diagram in which the QSH state lies in between a normal insulator and a weak metal phase due to the unique wave functions of QLs. Our findings not only provide a better understanding of electronic properties of quasicrystals but also extend the search of the QSH phase to aperiodic and amorphous materials that arc experimentally feasible.

Update: 26-Sep-2018

Title:
Unraveling the complex magnetic structure of multiferroic pyroxene NaFeGe2O6: A combined experimental and theoretical study
Authors:
Ding, L; Manuel, P; Khalyavin, DD; Orlandi, F; Tsirlin, AA Author Full Names: Ding, Lei; Manuel, Pascal; Khalyavin, Dmitry D.; Orlandi, Fabio; Tsirlin, Alexander A.
Source:
PHYSICAL REVIEW B, 98 (9):10.1103/PhysRevB.98.094416 SEP 14 2018
Abstract:
Magnetic order and the underlying magnetic model of the multiferroic pyroxene NaFeGe2O6 are systematically investigated by neutron powder diffraction, thermodynamic measurements, density-functional band-structure calculations, and Monte Carlo simulations. Upon cooling, NaFeGe2O6 first reveals one-dimensional spin-spin correlations in the paramagnetic state below about 50 K, uncovered by magnetic diffuse scattering. The sinusoidal spin-density wave with spins along the a direction sets in at 13 K, followed by the cycloidal configuration with spins lying in the (ac) plane below 11.6 K. Microscopically, the strongest magnetic coupling runs along the structural chains, J(1) similar or equal to 12 K, which is likely related to the one-dimensional spin-spin correlations. The interchain couplings J(2) similar or equal to 3.8 K and J(3) similar or equal to 2.1 K are energetically well balanced and compete, thus giving rise to the incommensurate order, in sharp contrast to other transition-metal pyroxenes, in which one type of the interchain couplings prevails. The magnetic model of NaFeGe2O6 is further completed by the weak single-ion anisotropy along the a direction. Our results resolve the earlier controversies regarding the magnetic order in NaFeGe2O6 and establish relevant symmetries of the magnetic structures. These results, combined with symmetry analysis, enable us to identify the possible mechanisms of the magnetoelectric coupling in this compound. We also elucidate microscopic conditions for the formation of incommensurate magnetic order in pyroxenes.
Title:
Phase Formation of Mg-Zn-Gd Alloys on the Mg-rich Corner
Authors:
Luo, L; Liu, Y; Duan, M Author Full Names: Luo, Lan; Liu, Yong; Duan, Meng
Source:
MATERIALS, 11 (8):10.3390/ma11081351 AUG 2018
Abstract:
The phase constitutions of as-cast magnesium (Mg)-Zn-Gd alloys (Zn/Gd = 0.25 similar to 60, Zn 0 similar to 10 at.%, Gd 0 similar to 2 at.%, 48 samples) were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The Mg-Zn-Gd phase diagram focused on the Mg-rich corner (with up to 20 at.% Zn, 10 at.% Gd) has been set up. Five regions can be classified as follows: (I) alpha-Mg+W-phase+(binary compounds), (II) alpha-Mg+W-phase+I-phase(+binary compounds), (III) alpha-Mg+I-phase(+binary compounds), (IV) alpha-Mg+binary compounds, and (V) alpha-Mg. The phase diagram has been verified by solidification behaviors observation using differential thermal analysis (DTA). Moreover, the structures of I-phase and W-phase in the alloy were explored in details. In terms of the Hume-Rothery rules, I-phase is confirmed as FK-type quasicrystalline with a chemical stoichiometry as Mg30 +/- 1Zn62Gd8 +/- 1 (at.%). The composition and lattice parameter aW-phase (fcc structure, m (3) over barm) are affected by the composition of Mg-Zn-Gd alloys, especially by the Zn/Gd ratio of alloys. This work would be instructive for the design of Mg-Zn-Gd alloys to obtain the phase components, and then selected the strengthening ways, which could adjust its mechanical properties.

Update: 19-Sep-2018

Title:
Microstructure evolution, mechanical properties and diffusion behaviour of Mg-6Zn-2Gd-0.5Zr alloy during homogenization
Authors:
Xiao, L; Yang, GY; Liu, Y; Luo, SF; Jie, WQ Author Full Names: Xiao, Lei; Yang, Guangyu; Liu, Yang; Luo, Shifeng; Jie, Wanqi
Source:
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY, 34 (12):2246-2255; 10.1016/j.jmst.2018.05.003 DEC 2018
Abstract:
The microstructure evolution and mechanical properties of Mg-6Zn-2Gd-0.5Zr alloy during homogenization treatment were investigated. The as-cast alloy was found to be composed of dendritic primary alpha-Mg matrix, alpha-Mg +W (Mg3Zn3Gd2) eutectic along grain boundaries, and icosahedral quasicrystalline I (Mg3Zn6Gd) phase within alpha-Mg matrix. During homogenization process, alpha-Mg +W (Mg3Zn3Gd2) eutectic and I phase gradually dissolved into alpha-Mg matrix, while some rod-like rare earth hydrides (GdH2) formed within alpha-Mg matrix. Both the tensile yield strength and the elongation showed a similar tendency as a function of homogenization temperature and holding time. The optimized homogenization parameter was determined to be 505 degrees C for 16 h according to the microstructure evolution. Furthermore, the diffusion kinetics equation of the solute elements derived from the Gauss model was established to predict the segregation ratio of Gd element as a function of holding time, which was proved to be effective to evaluate the homogenization effect of the experimental alloy. (C) 2018 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.
Title:
Role of nanosize icosahedral quasicrystal of Mg-Al and Mg-Ca alloys in avoiding crystallization of liquid Mg: Ab initio molecular dynamics study
Authors:
Debela, TT; Abbas, HG Author Full Names: Debela, Tekalign T.; Abbas, Hafiz Ghulam
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 499 173-182; 10.1016/j.jnoncrysol.2018.07.010 NOV 1 2018
Abstract:
We have used highly accurate first-principles molecular dynamics simulations to explore the structural (both topological and chemical ordering) evolution during solidification of Mg90Ca10 and MgaoAlio liquids upon cooling. Using various structural analysis methods, we find that local atomic structure of both amorphous alloys are characterized by major distorted and perfect icosahedral symmetry. The fraction of fivefold icosahedra around Mg atoms in Mg-Ca alloy is higher than in Mg-Al alloy. Eutectic Mg90Ca50 alloy shows strong chemical short range order, which further increases upon cooling. In contrast, Mg90Al10 shows weak chemical short range ordering which seems to show weak temperature dependency behavior. The fraction of fivefold icosahedral symmetry, which is responsible for geometrical frustration, and the atomic size are responsible for the dynamic slowdown and causing glassy formation.
Title:
A Brownian quasi-crystal of pre-assembled colloidal Penrose tiles
Authors:
Wang, PY; Mason, TG Author Full Names: Wang, Po-Yuan; Mason, Thomas G.
Source:
NATURE, 561 (7721):94-+; 10.1038/s41586-018-0464-9 SEP 6 2018
Abstract:
Penrose's pentagonal P2 quasi-crystal(1-4) is a beautiful, hierarchically organized multiscale structure in which kite-and dart-shaped tiles are arranged into local motifs, such as pentagonal stars, which are in turn arranged into various close-packed superstructural patterns that become increasingly complex at larger length scales. Although certain types of quasi-periodic structure have been observed in hard and soft matter, such structures are difficult to engineer, especially over large areas, because generating the necessary, highly specific interactions between constituent building blocks is challenging. Previously reported soft-matter quasi-crystals of dendrimers(5), triblock copolymers(6), nanoparticles(7) and polymeric micelles(8) have been limited to 12- or 18-fold symmetries. Because routes for self-assembling complex colloidal building blocks(9-11) into low-defect dynamic superstructures remain limited(12), alternative methods, such as using optical and directed assembly, are being explored(13,14). Holographic laser tweezers(15) and optical standing waves(16) have been used to hold microspheres in local quasi-crystalline arrangements, and magnetic microspheres of two different sizes have been assembled into local five-fold-symmetric quasi-crystalline arrangements in two dimensions(17). But a Penrose quasi-crystal of mobile colloidal tiles has hitherto not been fabricated over large areas. Here we report such a quasi-crystal in two dimensions, created using a highly parallelizable method of lithographic printing and subsequent release of pre-assembled kite- and dart-shaped tiles into a solution-dispersion containing a depletion agent. After release, the positions and orientations of the tiles within the quasi-crystal can fluctuate, and these tiles undergo random, Brownian motion in the monolayer owing to frequent collisions between neighbouring tiles, even after the system reaches equilibrium. Using optical microscopy, we study both the equilibrium fluctuations of the system at high tile densities and also the 'melting' of the pattern as the tile density is lowered. At high tile densities we find signatures of a five-fold pentatic liquid quasi-crystalline phase, analogous to a six-fold hexatic liquid crystal. Our fabrication approach is applicable to tiles of different sizes and shapes, and with different initial positions and orientations, enabling the creation of two-dimensional quasi-crystalline systems (and other systems that possess multiscale complexity at high tile densities) beyond those of current self-or directed-assembly methods(18-20). We anticipate that our approach for generating lithographically pre-assembled monolayers could be extended to create three-dimensional Brownian systems of fluctuating particles with custom-designed shapes through holographic lithography(21,22) or stereolithography(23).

Update: 6-Sep-2018

Title:
Effects of Mg-Zn-Y quasicrystal addition on the microstructures, mechanical performances and corrosion behaviors of as-cast AM60 magnesium alloy
Authors:
Jia, P; Wu, M; Zhang, JY; Hu, X; Teng, XY; Zhao, DG; Wei, T; Dong, DH; Liu, Q; Wang, Y Author Full Names: Jia, Peng; Wu, Ming; Zhang, Jinyang; Hu, Xun; Teng, Xinying; Zhao, Degang; Wei, Tao; Dong, Dehua; Liu, Qing; Wang, Yi
Source:
MATERIALS RESEARCH EXPRESS, 5 (10):10.1088/2053-1591/aada70 OCT 2018
Abstract:
In this work, the as-cast Mg-50Zn-5Y (mass fraction) master alloy containing Mg42Zn50Y8(mole fraction) icosahedral quasicrystal phase (I-phase) was prepared. The influences of addition amount of the Mg-50Zn-5Y master alloy on the microstructure, mechanical performances and corrosion properties of AM60 alloys were studied, aiming to investigate the structure-activity relationship for optimizing the microstructures and properties of AM60 alloys. The results indicated that the continuous reticulation structure could be broken and the precipitated phases could be significantly refined by adding the Mg-50Zn-5Y quasicrystal master alloy. The quasicrystal-reinforced AM60 alloys exhibited better mechanical properties and corrosion resistance than unmodified one. The modified AM60 alloy with 6 wt% of the Mg-50Zn-5Y quasicrystal master alloy had the optimal mechanical performances and corrosion resistance such as a Brinell hardness of 74 HB (increased by 37.0%), an ultimate tensile strength of 205 MPa (increased by 24.3%), a yield strength of 99 MPa (increased by 32.0%) as well as a corrosion rate of 1.35 x 10(-2)mm.year(-1)(decreased by 93.1%). The broken of the continuous reticulation structure and the refinement of the precipitated phases were responsible for the improvement of mechanical performances and corrosion resistance.
Title:
Preparation and electrochemical hydrogen storage properties of MWCNTs-doped Ti49Zr26Ni25 alloy containing quasicrystal phase
Authors:
Liu, H; Zhai, XJ; Li, Z; Tao, X; Liu, WQ; Zhao, JX; Jiang, DY; Gao, S Author Full Names: Liu, Heng; Zhai, Xiaojie; Li, Zhe; Tao, Xing; Liu, Wanqiang; Zhao, Jianxun; Jiang, Dayong; Gao, Shang
Source:
SOLID STATE SCIENCES, 83 17-22; 10.1016/j.solidstatesciences.2018.06.012 SEP 2018
Abstract:
Mechanical alloying technique and subsequent annealing were used to prepare the Ti49Zr26Ni25 quasicrystal. Composite materials of multi-walled carbon nanotubes (MWCNT5) doped Ti49Zr26Ni25 alloys were obtained via ball-milling to improve the hydrogen storage performance of Ti49Zr26Ni25. X-ray diffraction, scanning electron microscopy and transmission electron microscopy were used to analyze the structural properties of the samples. The phase structures of the composite alloys were composed of icosahedral quasicrystal phase and Ti2Ni-type phase. Smaller alloy particles were obtained after doping MWCNT5. Moreover, a three-electrode battery system was carried out to test the electrochemical properties. The composites showed higher discharge capacity, stronger HRD, better cyclic stability and lower charge-transfer resistance than the original Ti49Zr26Ni25 alloy. In the composite electrodes, the optimal discharge capacity of 254.2 mAh/g and the highest capacity retention of 63.1% were achieved for 5 wt% additive content of MWCNTs. The electro-catalytic function of MWCNT5, the reduction of particle size and raise of specific surface area for Ti49Zr26Ni25 alloy may provide larger electrochemically accessible area and rapid channel for hydrogen transportation, which are crucial for improving the electrochemical performance of the alloy.
Title:
A molecular overlayer with the Fibonacci square grid structure
Authors:
Coates, S; Smerdon, JA; McGrath, R; Sharma, HR Author Full Names: Coates, Sam; Smerdon, Joseph A.; McGrath, Ronan; Sharma, Hem Raj
Source:
NATURE COMMUNICATIONS, 9 10.1038/s41467-018-05950-7 AUG 24 2018
Abstract:
Quasicrystals differ from conventional crystals and amorphous materials in that they possess long-range order without periodicity. They exhibit orders of rotational symmetry which are forbidden in periodic crystals, such as five-, ten-, and twelve-fold, and their structures can be described with complex aperiodic tilings such as Penrose tilings and Stampfli-Gaehler tilings. Previous theoretical work explored the structure and properties of a hypothetical four-fold symmetric quasicrystal-the so-called Fibonacci square grid. Here, we show an experimental realisation of the Fibonacci square grid structure in a molecular overlayer. Scanning tunnelling microscopy reveals that fullerenes (C-60) deposited on the two-fold surface of an icosahedral Al-Pd-Mn quasicrystal selectively adsorb atop Mn atoms, forming a Fibonacci square grid. The site-specific adsorption behaviour offers the potential to generate relatively simple quasicrystalline overlayer structures with tunable physical properties and demonstrates the use of molecules as a surface chemical probe to identify atomic species on similar metallic alloy surfaces.

Update: 29-Aug-2018

Title:
Incommensurate phase of the stuffed tridymite derivative BaSrFe4O8
Authors:
Ishii, Y; Kawaguchi, S; Asai, K; Mori, S Author Full Names: Ishii, Y.; Kawaguchi, S.; Asai, K.; Mori, S.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 265 314-318; 10.1016/j.jssc.2018.06.007 SEP 2018
Abstract:
We demonstrate a new modulation for a high-temperature polymorph of BaSrFe4O8 via synchrotron powder X-ray diffraction and transmission electron microscopy (TEM) experiments. Although the powder X-ray diffraction pattern was successfully analyzed using a structure model of space group Pnna, an unusually large isotropic atomic displacement parameter (U-iso) was observed for the O1 atom. A split atom model that was applied to the O1 site and the adjacent Ba/Sr site, both of which are on the two-fold axis along the c-axis, indicated that positional disorder occurred in these atoms along the c-axis. The electron diffraction pattern and high-resolution TEM observations combined with the structure refinements revealed an incommensurate structure with a modulation vector q = 0.4270(1)a* and a displacement vector perpendicular to the alpha-axis, which gave rise to the large U-iso value of the O1 atom. The modulation observed in this study may be a signature of structural instability, which has commonly been discussed in the stuffed tridymite-type oxides.
Title:
Spontaneous and field-induced magnetic phase transitions in Dy2Co3Al9: Effects of exchange frustration
Authors:
Gorbunov, DI; Henriques, MS; Qureshi, N; Ouladdiaf, B; Mejia, CS; Gronemann, J; Andreev, AV; Petricek, V; Green, EL; Wosnitza, J Author Full Names: Gorbunov, D. I.; Henriques, M. S.; Qureshi, N.; Ouladdiaf, B.; Mejia, C. Salazar; Gronemann, J.; Andreev, A. V.; Petricek, V.; Green, E. L.; Wosnitza, J.
Source:
PHYSICAL REVIEW MATERIALS, 2 (8):10.1103/PhysRevMaterials.2.084406 AUG 15 2018
Abstract:
Due to the long-range oscillatory character of RKKY exchange interactions, for Dy2Co3Al9 there exist positive and negative couplings between the Dy magnetic moments that lead to magnetic frustration. As a result, the ground state can be easily perturbed, and the system displays a number of spontaneous and field-induced phase transitions. We performed magnetization, magnetic-susceptibility, specific-heat, and electrical-resistivity measurements as well as neutron-diffraction experiments on a single crystal. We find two transitions to distinct incommensurate antiferromagnetic phases at 6.2 and 5.2 K that evolve to a commensurate phase at 3.7 K. In applied magnetic field, new phases emerge. Field-dependent magnetization exhibits a multistep metamagnetic process with sharp transitions accompanied by pronounced magnetoresistance changes. The large number of phases and their complex magnetic structures suggest that the physical properties of Dy2Co3Al9 are ruled by exchange frustration in the presence of a large magnetocrystalline anisotropy.
Title:
Effect of Mg-Based Quasicrystals Addition on Microstructure and Mechanical Properties of AM50 Magnesium Alloy
Authors:
Ma, DZ; Wang, F; Wang, Z; Liu, Z; Mao, PL Author Full Names: Ma Dezhi; Wang Feng; Wang Zhi; Liu Zheng; Mao Pingli
Source:
RARE METAL MATERIALS AND ENGINEERING, 47 (7):2166-2171; JUL 2018
Abstract:
The Mg-48Zn-13Y (MZY) quasicrystal master alloy with high volume fraction of the quasicrystalline phase was prepared by a conventional solidification method. The influences of the MZY quasicrystal on microstructures and mechanical properties of AM50 alloys were investigated by OM, SEM, EDS, XRD and tensile tests. The results indicate that with addition of the MZY quasicrystal to AM50 alloy, the Mg3Zn6Y quasicrystal phase can be retained in AM50 matrix alloy, and the microstructures are obviously refined. The beta phase in the microstructures is changed from coarse and continuous net-like to discontinuous strip-like and granular, and the amount is decreased. When the content of the MZY quasicrystal is 6%, the microstructure is greatly refined, and the ultimate tensile strength, yield strength and elongation of the alloy reach to the maximum, 202.92 MPa, 100.57 MPa and 10.8%, respectively, which are improved by 24.59%, 74.9% and 66.15%, respectively, compared with those of AM50 alloy. Mechanical properties of AM50 magnesium alloy can be improved significantly by addition of the MZY quasicrystal, which results from the microstructure refinement, the optimization of the morphology and amount of the beta phase, and the dispersion strengthening effect of the quasicrystal phase having good wettability with the magnesium alloy substrate.

Update: 22-Aug-2018

Title:
Formation of modulated structures induced by oxygen vacancies in alpha-Fe2O3 nanowires
Authors:
Li, T; Feng, HL; Wang, YQ; Wang, C; Zhu, WH; Yuan, L; Zhou, GW Author Full Names: Li, Tao; Feng, Honglei; Wang, Yiqian; Wang, Chao; Zhu, Wenhui; Yuan, Lu; Zhou, Guangwen
Source:
JOURNAL OF CRYSTAL GROWTH, 498 10-16; 10.1016/j.jcrysgro.2018.05.031 SEP 15 2018
Abstract:
Two modulated structures caused by long-range ordering of oxygen vacancies have been observed in alpha-Fe2O3 nanowires (NWs) produced after oxidation of Fe, one being ten times (30 (3) over bar0) interplanar spacing and the other being six times (11 (2) over bar0) interplanar spacing. Both types of oxygen vacancy ordering structures have a similar modulation periodicity of 1.45 or 1.50 nm with corresponding atomic ratios of Fe and O (Fe/O) of 0.7407 and 0.7273, respectively. The Fe/O ratios in the NWs with oxygen-vacancy ordering are very close to that of Fe3O4 (0.7500). The similar Fe/O ratio between NWs and Fe3O4 may explain the similar modulation periodicity of different oxygen-vacancy orderings. Electron energy-loss spectroscopy studies show that the Fe/O ratio of NWs is close to that of Fe3O4 when oxygen atoms are not sufficient, which makes the NWs energetically favorable. The elucidation of the mechanism governing the formation of the modulated structures in alpha-Fe2O3 NWs is critical for controlling the microstructure and correspondingly physicochemical properties of NWs.
Title:
Investigation of a nano-scale, incommensurate, modulated domain in a Ti-Fe alloy
Authors:
Zheng, YF; Huber, D; Fraser, HL Author Full Names: Zheng, Yufeng; Huber, Daniel; Fraser, Hamish L.
Source:
SCRIPTA MATERIALIA, 154 220-224; 10.1016/j.scriptamat.2018.06.010 SEP 2018
Abstract:
The microstructure of a Ti-Fe compositional gradient sample was investigated using transmission electron microscopy (TEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Different combinations of phases were observed to form depending on the local concentration of Fe. Interestingly, a nano-scale incommensurate modulated domain was detected in the alloy containing approximately 13.8 to 33.9 wt% Fe using selected area diffraction (SAD). The observed disordered structure with no fixed long range periodicity in the nano-scale incommensurate modulated domain in aberration-corrected HAADF-STEM imaging was found not related to the shuffle mechanism of the to phase. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Electronic phase separation and magnetic-field-induced phenomena in molecular multiferroic (ND4)(2)FeCl5 center dot D2O
Authors:
Tian, W; Cao, HB; Clune, AJ; Hughey, KD; Hong, T; Yan, JQ; Agrawal, HK; Singleton, J; Sales, BC; Fishman, RS; Musfeldt, JL; Fernandez-Baca, JA Author Full Names: Tian, W.; Cao, H. B.; Clune, Amanda J.; Hughey, Kendall D.; Hong, Tao; Yan, J. -Q.; Agrawal, Harish K.; Singleton, John; Sales, B. C.; Fishman, Randy S.; Musfeldt, J. L.; Fernandez-Baca, J. A.
Source:
PHYSICAL REVIEW B, 98 (5):10.1103/PhysRevB.98.054407 AUG 8 2018
Abstract:
Electronic phase separation has been increasingly recognized as an important phenomenon in understanding many of the intriguing properties displayed in transition metal oxides. It is believed to produce fascinating functional properties in otherwise chemically homogenous electronic systems, e.g., colossal magnetoresistance manganites and high-T-c cuprates. While many well-known electronically phase-separated systems are oxides, it has been argued that the same phenomenon should occur in other electronic systems with strong competing interactions. Here we report the observation of electronic phase separation in molecular (ND4)(2)FeCl5 center dot D2O, a type-II multiferroic. We show that two magnetic phases, one of which is commensurate and the other of which is incommensurate, coexist in this material. Their evolution under applied magnetic field produces emergent properties. In particular, our measurements reveal a field-induced exotic state linked to a direct transition from a paraelectric/paramagnetic phase to a ferroelectric/antiferromagnetic phase, a collective phenomenon that hasn't been seen in other magnetic multiferroics.
Title:
Incommensurately Modulated Structures in Zr-rich PZT: Periodic Nanodomains, Reciprocal Configuration, and Nucleation
Authors:
Fu, ZQ; Chen, XF; Lu, P; Zhu, CX; Nie, HC; Xu, FF; Wang, GS; Dong, XL Author Full Names: Fu, Zhengqian; Chen, Xuefeng; Lu, Ping; Zhu, Chenxi; Nie, Henchang; Xu, Fangfang; Wang, Genshui; Dong, Xianlin
Source:
CRYSTAL GROWTH & DESIGN, 18 (8):4395-4402; 10.1021/acs.cgd.8b00369 AUG 2018
Abstract:
Zr-rich PZT is one of the most representative materials with compositions located at the ferroelectric-antiferroelectric (FE-AFE) phase boundary. The study of its incommensurately modulated structure (IMS) is of fundamental importance in understanding the origin of its high-performance stored-energy properties and phase transformation between FE and AFE. In this study, the structural features of the IMS were investigated in detail by transmission electron microscopy. The IMS appears as submicron domains assembled by periodic arrays of two-dimensional nanodomains along a <111> direction with the domain width of about 30 {111} spacings. The nanodomains have dual attributes of both antiphase domains and electric domains. The displacement vector across the periodic antiphase boundaries was determined to be R = [001]. The reciprocal lattice of IMS was constructed and characterized by a set of strong basic reflections of pseudocubic unit cell together with 1/2{ooe} superlattice reflections where 1/2(ooe) superlattice reflections (located on the (001) reciprocal planes) do not split, while both 1/2(eoo) and 1/2(oeo) superlattice reflections (located on (100) and (010) reciprocal planes, respectively) split. In addition, the growth process of IMS and the visibility conditions for the periodic nanodomains and superlattice reflections splitting are presented.
Title:
Modulation in charge ordering structure of ferroelectric YbFe2O4 by magnetic ordering
Authors:
Nagata, T; Ikeda, N Author Full Names: Nagata, T.; Ikeda, N.
Source:
AIP ADVANCES, 8 (7):10.1063/1.5026921 JUL 2018
Abstract:
We report the modulation in charge ordering structure of ferroelectric YbFe2O4 by magnetic ordering from x-ray diffraction experiments and magnetic measurements. The incommensurate modulation was observed on (n n 3m+3/2) type diffraction signal around magnetic ordering temperature where n and m are integer. The modulation was also observed on charge ordering signal, indicating spin-charge coupling. The incommensurate modulation was observed only on (n/3 n/3 3m) type charge ordering signal. This selectivity can be explained by polar charge ordering models. (C) 2018 Author(s).

Update: 15-Aug-2018

Title:
Research on the formation of M1-type alite doped with MgO and SO3-A route to improve the quality of cement clinker with a high content of MgO
Authors:
Zhou, H; Gu, XM; Sun, JF; Yu, ZQ; Huang, H; Wang, QQ; Shen, XD Author Full Names: Zhou, Hao; Gu, Xiaomei; Sun, Jinfeng; Yu, Zhuqing; Huang, Hong; Wang, Qianqian; Shen, Xiaodong
Source:
CONSTRUCTION AND BUILDING MATERIALS, 182 156-166; 10.1016/j.conbuildmat.2018.06.078 SEP 10 2018
Abstract:
This paper discusses the effect of SO3 dopants on the M-1 polymorph formation and mechanical properties of alite containing a high content of MgO. The structure of the M-1 alite is identified by XRD, high-temperature XRD and TEM analysis. A characteristic XRD pattern of M-1 alite doped with MgO and SO3 is determined, and TEM results show that M-1 alite has an incommensurate modulated structure feature with 2.4 times the subcell dimension along [(2) over bar1 0 ](H)* and could be expressed as ha* + kb* + lc* + m/[2.4 (-2a* + b*)], where m = +/- 1. The First-Principles method is used to simulate the structure of M-1 alite, and the calculated Delta Cohesive Energy is approximately 11-12 eV between the M-1 and M-3 alite. Quantitative analysis is performed by the Rietveld method. The SO3/MgO (mass ratio from SO3 to MgO) and M-1% in alite (M1-C3S%/M1-C3S%+M3-C3S% x 100%) are shown to have a strong linear relationship, which can be defined as M1-C3S%/M1-C3S%+M3-C3S% x 100% = 24.73 + 108.11 * SO3/MgO (%). Mechanical properties results show that appropriate SO3 dopant can improve the compressive strength of alite containing high MgO while over dosed SO3 will lead to a contrary effect because of the decomposition of alite. The relationship between M-1% in the alite and the compressive strengths at different ages is also given. The optimal M-1% in alite is approximately 68% and the best SO3/MgO ratio is approximately 0.43 because the compressive strength could be maximized at each age. (C) 2018 Elsevier Ltd. All rights reserved.
Title:
Incommensurately Modulated Structures and Luminescence Properties of the AgxSm(2-x)/3WO4 (x=0.286, 0.2) Scheelites as Thermographic Phosphors
Authors:
Morozov, V; Deyneko, D; Basoyich, O; Khaikina, EG; Spassky, D; Morozov, A; Chernyshev, V; Abakumov, A; Hadermann, J Author Full Names: Morozov, Vladimir; Deyneko, Dina; Basoyich, Olga; Khaikina, Elena G.; Spassky, Dmitry; Morozov, Anatolii; Chernyshev, Vladimir; Abakumov, Artem; Hadermann, Joke
Source:
CHEMISTRY OF MATERIALS, 30 (14):4788-4798; 10.1021/acs.chemmater.8b02029 JUL 24 2018
Abstract:
Ag+ for Sm3+ substitution in the scheelite-type AgxSm(2-x)/3 square(1-2x)/3WO4 tungstates has been investigated for its influence on the cation-vacancy ordering and luminescence properties. A solid state method was used to synthesize the x = 0.286 and x = 0.2 compounds, which exhibited (3 + 1)D incommensurately modulated structures in the transmission electron microscopy study. Their structures were refined using high resolution synchrotron powder X-ray diffraction data. Under near-ultraviolet light, both compounds show the characteristic emission lines for (4)G(5/2) -> H-6(J) (J = 5/2, 7/2, 9/2, and 11/2) transitions of the Sm3+ ions in the range 550-720 nm, with the J = 9/2 transition at the similar to 648 nm region being dominant for all photoluminescence spectra. The intensities of the (4)G(5/2) -> H-6(9/2) and (4)G(5/2) -> H-6(7/2) bands have different temperature dependencies. The emission intensity ratios (R) for these bands vary reproducibly with temperature, allowing the use of these materials as thermographic phosphors.

Update: 8-Aug-2018

Title:
Effects of Microstructure of Quasicrystal Alloys on Their Mechanical and Tribological Performance
Authors:
Lee, K; Dai, W; Naugle, D; Liang, H Author Full Names: Lee, Kyungjun; Dai, Wei; Naugle, Donald; Liang, Hong
Source:
JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME, 140 (5):10.1115/1.4039528 SEP 2018
Abstract:
The current design of materials against wear considers hardness as the sole material property. As a result, the brittleness associated with increased hardness leads to severe damage. The purpose of this research is to understand the nature of conflicts between hardness and toughness of a new alloy composite. First, we designed Al-Cu-Fe alloys containing crystal structures of lambda, beta, and quasi-crystalline i-phase. These and their combination with others lead to a set of alloys with various hardness and fracture toughness. Experimental study was carried out using a noble and hard tungsten carbide (WC) ball against sample disks. The WC ball did not produce any wear. The wear rate of those alloys was found to be dependent not only on their hardness, but also the toughness, an alternative to the well-accepted Archard-based equations.
Title:
Re-entrant charge order in overdoped (Bi,Pb)(2.12)Sr1.88CuO6+delta outside the pseudogap regime
Authors:
Peng, YY; Fumagalli, R; Ding, Y; Minola, M; Caprara, S; Betto, D; Bluschke, M; De Luca, GM; Kummer, K; Lefrancois, E; Salluzzo, M; Suzuki, H; Le Tacon, M; Zhou, XJ; Brookes, NB; Keimer, B; Braicovich, L; Grilli, M; Ghiringhelli, G Author Full Names: Peng, Y. Y.; Fumagalli, R.; Ding, Y.; Minola, M.; Caprara, S.; Betto, D.; Bluschke, M.; De Luca, G. M.; Kummer, K.; Lefrancois, E.; Salluzzo, M.; Suzuki, H.; Le Tacon, M.; Zhou, X. J.; Brookes, N. B.; Keimer, B.; Braicovich, L.; Grilli, M.; Ghiringhelli, G.
Source:
NATURE MATERIALS, 17 (8):697-+; 10.1038/s41563-018-0108-3 AUG 2018
Abstract:
In the underdoped regime, the cuprate high-temperature superconductors exhibit a host of unusual collective phenomena, including unconventional spin and charge density modulations, Fermi surface reconstructions, and a pseudogap in various physical observables. Conversely, overdoped cuprates are generally regarded as conventional Fermi liquids possessing no collective electronic order. In partial contradiction to this widely held picture, we report resonant X-ray scattering measurements revealing incommensurate charge order reflections for overdoped (Bi,Pb)(2.12)Sr1.88CuO6+delta (Bi2201), with correlation lengths of 40-60 lattice units, that persist up to temperatures of at least 250 K. The value of the charge order wavevector decreases with doping, in line with the extrapolation of the trend previously observed in underdoped Bi2201. In overdoped materials, however, charge order coexists with a single, unreconstructed Fermi surface without nesting or pseudogap features. The discovery of re-entrant charge order in Bi2201 thus calls for investigations in other cuprate families and for a reconsideration of theories that posit an essential relationship between these phenomena.
Title:
Incommensurate atomic and magnetic modulations in the spin-frustrated beta-NaMnO2 triangular lattice
Authors:
Orlandi, F; Aza, E; Bakaimi, I; Kiefer, K; Klemke, B; Zorko, A; Arcon, D; Stock, C; Tsibidis, GD; Green, MA; Manuel, P; Lappas, A Author Full Names: Orlandi, Fabio; Aza, Eleni; Bakaimi, Ioanna; Kiefer, Klaus; Klemke, Bastian; Zorko, Andrej; Arcon, Denis; Stock, Christopher; Tsibidis, George D.; Green, Mark A.; Manuel, Pascal; Lappas, Alexandros
Source:
PHYSICAL REVIEW MATERIALS, 2 (7):10.1103/PhysRevMaterials.2.074407 JUL 24 2018
Abstract:
The layered beta-NaMnO2, a promising Na-ion energy-storage material, has been investigated for its triangular lattice capability to promote complex magnetic configurations that may release symmetry restrictions for the coexistence of ferroelectric and magnetic orders. The complexity of the neutron powder diffraction patterns underlines that the routinely adopted commensurate structural models are inadequate. Instead, a single-phase superspace symmetry description is necessary, demonstrating that the material crystallizes in a compositionally modulated q = (0.077(1), 0, 0) structure. Here Mn3+ Jahn-Teller distorted MnO6 octahedra form corrugated layer stacking sequences of the beta-NaMnO2 type, which are interrupted by flat sheets of the alpha-like oxygen topology. Spontaneous long-range collinear antiferromagnetic order, defined by the propagation vector k = (1/2,1/2,1/2), appears below T-N1 = 200 K. Moreover, a second transition into a spatially modulated proper-screw magnetic state (k +/- q) is established at T-N2 = 95 K, with an antiferromagnetic order parameter resembling that of a two-dimensional (2D) system. The evolution of Na-23 NMR spin-lattice relaxation identifies a magnetically inhomogeneous state in the intermediate T region (T-N2 < T < T-N1), while its strong suppression below T-N2 indicates that a spin gap opens in the excitation spectrum. High-resolution neutron inelastic scattering confirms that the magnetic dynamics are indeed gapped (Delta similar to 5 meV) in the low-temperature magnetic phase, while simulations on the basis of the single-mode approximation suggest that Mn spins residing on adjacent antiferromagnetic chains, establish sizable 2D correlations. Our analysis points out that novel structural degrees of freedom promote cooperative magnetism and emerging dielectric properties in this nonperovskite type of manganite.

Update: 1-Aug-2018

Title:
Easy-plane XY spin fluctuations in the cycloidal magnet UPtGe studied via field-orientation-dependent Pt-195 NMR
Authors:
Tokunaga, Y; Nakamura, A; Aoki, D; Shimizu, Y; Homma, Y; Honda, F; Sakai, H; Hattori, T; Kambe, S Author Full Names: Tokunaga, Y.; Nakamura, A.; Aoki, D.; Shimizu, Y.; Homma, Y.; Honda, F.; Sakai, H.; Hattori, T.; Kambe, S.
Source:
PHYSICAL REVIEW B, 98 (1):10.1103/PhysRevB.98.014425 JUL 23 2018
Abstract:
Pt-195 NMR measurements have been performed on a single crystal of the uranium-based compound UPtGe, which is the only 5f system known to possess an incommensurate helical (cycloidal) structure below T-N = 50 K. Knight shift measurement confirmed the isotropic character of the static spin susceptibilities in hexagonal-like ac crystal planes of the EuAuGe-type crystal structure. The hyperfine coupling constants were also found to be isotropic in the planes, estimated to be 59 kOe/mu B. Nuclear relaxation rate (1/T-1) measurement revealed the development of the antiferromagnetic spin fluctuations with XY character confined to the hexagonal-like plane below 200 K. The results present a clear contrast to the Ising anisotropy of the fluctuations in ferromagnetic superconductors UCoGe and URhGe.
Title:
Imaging the magnetic structures of artificial quasicrystal magnets using resonant coherent diffraction of circularly polarized X-rays
Authors:
Sung, D; Jung, C; Cho, BG; Jo, W; Han, HS; Lee, KS; Bhat, V; Farmer, B; De Long, LE; Lee, KB; Keavney, DJ; Lee, DR; Song, C Author Full Names: Sung, Daeho; Jung, Chulho; Cho, Byeong-Gwan; Jo, Wonhyuk; Han, Hee-Sung; Lee, Ki-Suk; Bhat, Vinayak; Farmer, Barry; De Long, L. E.; Lee, Ki Bong; Keavney, D. J.; Lee, Dong Ryeol; Song, Changyong
Source:
NANOSCALE, 10 (27):13159-13164; 10.1039/c8nr03733g JUL 21 2018
Abstract:
Unraveling nanoscale spin structures has long been an important activity addressing various scientific interests, that are also readily adaptable to technological applications. This has invigorated the development of versatile nanoprobes suitable for imaging specimens under native conditions. Here we have demonstrated the resonant coherent diffraction of an artificial quasicrystal magnet with circularly polarized X-rays. The nanoscale magnetic structure was revealed from X-ray speckle patterns by comparing with micromagnetic simulations, as a step toward understanding the intricate relationship between the chemical and spin structures in an aperiodic quasicrystal lattice. Femtosecond X-ray pulses from free electron lasers are expected to immediately extend the current work to nanoscale structure investigations of ultrafast spin dynamics, surpassing the present spatio-temporal resolution.
Title:
Structure and properties of composites based on polyphenylene sulfide reinforced with Al-Cu-Fe quasicrystalline particles
Authors:
Chukov, DI; Stepashkin, AA; Tcherdyntsev, VV; Olifirov, LK; Kaloshkin, SD Author Full Names: Chukov, D. I.; Stepashkin, A. A.; Tcherdyntsev, V. V.; Olifirov, L. K.; Kaloshkin, S. D.
Source:
JOURNAL OF THERMOPLASTIC COMPOSITE MATERIALS, 31 (7):882-895; 10.1177/0892705717729015 JUL 2018
Abstract:
Structural, mechanical, and thermal properties of polyphenylene sulfide (PPS) filled with Al-Cu-Fe quasicrystals particles were studied. It was shown that the introducing of quasicrystalline fillers into the polymer matrix results in the increase in Young's modulus, hardness, and toughness of the polymer. Quasicrystalline fillers can improve thermal properties of PPS, including heat resistance index, Vicat softening temperature, thermal diffusivity, and thermal conductivity.
Title:
Cylindrical bending analysis of a layered two-dimensional piezoelectric quasicrystal nanoplate
Authors:
Li, Y; Yang, LZ; Gao, Y; Pan, EN Author Full Names: Li, Yang; Yang, Lianzhi; Gao, Yang; Pan, Ernian
Source:
JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES, 29 (12):2660-2676; 10.1177/1045389X18770920 JUL 2018
Abstract:
The piezoelectric effect is a significant property of quasicrystal. In this article, the exact solution is derived for a layered piezoelectric quasicrystal nanoplate with nonlocal effect in cylindrical bending. Based on the nonlocal theory and the pseudo-Stroh formalism, the exact solution for a homogeneous simply supported nanoplate is obtained. With the aid of the propagator matrix, the exact solution for a multilayered nanoplate is achieved. Numerical examples are carried out to reveal the influences of span-to-thickness ratio, nonlocal parameter, and stacking sequence on piezoelectric quasicrystal nanoplates with their top surface subjected to two loadings. One is a z-direction mechanical loading and the other is an electric potential loading. These results can be served as benchmarks for the design, numerical modeling, and simulation of layered two-dimensional piezoelectric quasicrystal nanoplates under cylindrical bending.
Title:
EVOLUTION OF THE PHASES OF QUASICRYSTALLINE ALLOYS ICOSAHEDRAL/DECAGONAL Al62.2Cu25.3Fe12.5/Al65Ni15Co20 AND OXIDATIVE BEHAVIOR
Authors:
Jamshidi, LCLA; Rodbari, RJ Author Full Names: Lucena Agostinho Jamshidi, Lourdes Cristina; Rodbari, Reza Jamshidi
Source:
JOURNAL OF THE CHILEAN CHEMICAL SOCIETY, 63 (2):3928-3933; 10.4067/s0717-97072018000203928 JUN 2018
Abstract:
In this paper, we present an approach and investigation on the evolution of the icosahedral and decagonal phases of quasicrystalline alloys Al62.2Cu25.3Fe12.5 E Al65Ni15Co20, the oxidation behavior in them. The quantification of the quasicrystalline and crystalline phases present in the quasicrystals provides important information in the mass transport by diffusion, as well as the phase transformations that occurred. For this purpose, X-ray diffraction (XRD) and Rietveld Method Quantification, Scanning Electron Microscopy (SEM) / Dispersive Energy Spectroscopy (EDS), Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis). The results showed structural aspects of the two compositions of quasicrystals, these were elaborated and obtained in an arc induction furnace. The oxidation of the alloy Al62.2Cu25.3Fe12.5 showed intermetallic phases with associations of the elements of the alloy and above 735 degrees C was observed that the crystalline phase is stable in the icosahedral phase. The quasicrystals Al65Ni15Co20, with the interaction of oxygen, happens in the surface of symmetry 10 times plane perpendicular vector. The formation of a thin film of the aluminum oxide with a well ordered hexagonal shape structure, with a domain opposite the decagonal phase with lateral size at about 35 angstrom.
Title:
Electric-field-induced phase transition and pinched P-E hysteresis loops in Pb-free ferroelectrics with a tungsten bronze structure
Authors:
Li, K; Zhu, XL; Liu, XQ; Ma, X; Sen Fu, M; Kroupa, J; Kamba, S; Chen, XM Author Full Names: Li, Kun; Zhu, Xiao Li; Liu, Xiao Qiang; Ma, Xiao; Sen Fu, Mao; Kroupa, Jan; Kamba, Stanislav; Chen, Xiang Ming
Source:
NPG ASIA MATERIALS, 10 10.1038/s41427-018-0013-x APR 5 2018
Abstract:
Antiferroelectrics are of interest due to their high potential for energy storage. Here, we report the discovery of pinched, polarization-vs.-electric field (P-E) hysteresis loops in the lead-free tungsten bronze ferroelectrics Ba4Sm2Ti4Nb6O30 and Ba4Eu2Ti4Nb6O30, while a broad, single P-E hysteresis loop was observed in the analogue compound Ba4Nd2Ti4Nb6O30. Pinched P-E loops are similar to antiferroelectric hysteresis loops, but in perovskites, they are mostly caused by an extrinsic, internal bias field due to defects, which block domain wall motion. We show that the pinched P-E loops are caused by an intrinsic effect, i.e., by the electric-field-induced phase transition from a non-polar incommensurate to a polar commensurately modulated crystal structure. The in situ electron diffraction results show the coexistence of commensurate polar structural modulation and incommensurate non-polar modulation during the ferroelectric transition and within the ferroelectric phase below the transition temperature. This phase coexistence is the reason for the small remanent polarization. An external electric field transforms the incommensurate component into a commensurate one, and the polarization increases. This new mechanism for pinched P-E hysteresis loops in ferroelectrics not only indicates a new direction for the development of Pb-free ferroelectric materials for energy storage but also significantly contributes to the physical understanding of ferroelectricity in materials with a tungsten bronze structure.

Update: 26-Jul-2018

Title:
Charge density wave phase, Mottness, and ferromagnetism in monolayer 1T-NbSe2
Authors:
Pasquier, D; Yazyev, OV Author Full Names: Pasquier, Diego; Yazyev, Oleg V.
Source:
PHYSICAL REVIEW B, 98 (4):10.1103/PhysRevB.98.045114 JUL 10 2018
Abstract:
The recently investigated 1T polymorph of monolayer NbSe2 revealed an insulating behavior suggesting a star-of-David phase with root 13 x root 13 periodicity associated with a Mott insulator, reminiscent of 1 T-TaS2. We examine this novel two-dimensional material from first principles. We find an instability towards the formation of an incommensurate charge density wave (CDW) and establish the star-of-David phase as the most stable commensurate CDW. The Mottness in the star-of-David phase is confirmed and studied at various levels of theory: the spin-polarized generalized gradient approximation (GGA) and its extension involving the on-site Coulomb repulsion (GGA+U), as well as the dynamical mean-field theory. Finally, we estimate Heisenberg exchange couplings in this material and find a weak nearest-neighbor ferromagnetic coupling, at odds with most Mott insulators. We point out the close resemblance between this star-of-David phase and flat-band ferromagnetism models.
Title:
Multi-orbital nature of the spin fluctuations in Sr2RuO4
Authors:
Boehnke, L; Werner, P; Lechermann, F Author Full Names: Boehnke, Lewin; Werner, Philipp; Lechermann, Frank
Source:
EPL, 122 (5):10.1209/0295-5075/122/57001 JUN 2018
Abstract:
The spin susceptibility of strongly correlated Sr2RuO4 is known to display a rich structure in reciprocal space, with a prominent peak at Q(i) = (0.3,0.3,0). It is still debated if the resulting incommensurate spin-density-wave fluctuations foster unconventional superconductivity at low temperature or compete therewith. By means of density functional theory combined with dynamical mean-field theory, we reveal the realistic multi-orbital signature of the (dynamic) spin susceptibility beyond existing weak-coupling approaches. The experimental fluctuation spectrum up to 80 meV is confirmed by theory. Furthermore, the peak at Q(i) is shown to carry nearly equal contributions from each of the Ru(4d)-t(2)g orbitals, pointing to a cooperative effect resulting in the dominant spin fluctuations. Copyright (C) EPLA, 2018
Title:
Quasicrystal seen to superconduct
Authors:
Jarman, S Author Full Names: Jarman, Sam
Source:
PHYSICS WORLD, 31 (5):4-4; MAY 2018

Update: 18-Jul-2018

Title:
Persistent low-energy phonon broadening near the charge-order q vector in the bilayer cuprate Bi2Sr2CaCu2O8+delta
Authors:
He, Y; Wu, S; Song, Y; Lee, WS; Said, AH; Alatas, A; Bosak, A; Girard, A; Souliou, SM; Ruiz, A; Hepting, M; Bluschke, M; Schierle, E; Weschke, E; Lee, JS; Jang, H; Huang, H; Hashimoto, M; Lu, DH; Song, D; Yoshida, Y; Eisaki, H; Shen, ZX; Birgeneau, RJ; Yi, M; Frano, A Author Full Names: He, Y.; Wu, S.; Song, Y.; Lee, W-S; Said, A. H.; Alatas, A.; Bosak, A.; Girard, A.; Souliou, S. M.; Ruiz, A.; Hepting, M.; Bluschke, M.; Schierle, E.; Weschke, E.; Lee, J-S; Jang, H.; Huang, H.; Hashimoto, M.; Lu, D-H; Song, D.; Yoshida, Y.; Eisaki, H.; Shen, Z-X; Birgeneau, R. J.; Yi, M.; Frano, A.
Source:
PHYSICAL REVIEW B, 98 (3):10.1103/PhysRevB.98.035102 JUL 2 2018
Abstract:
We report a persistent low-energy phonon broadening around qB similar to 0.28 reciprocal lattice unit (r.l.u.)along the Cu-O bond direction in the high-T-c cuprate Bi2Sr2CaCu2O8+delta (Bi-2212). We show that such broadening exists both inside and outside the conventional charge-density wave (CDW) phase, via temperature-dependent measurements in both underdoped and heavily overdoped samples. Combining inelastic hard x-ray scattering, diffuse scattering, angle-resolved photoemission spectroscopy, and resonant soft x-ray scattering at the Cu L-3-edge, we exclude the presence of a CDW in the heavily overdoped Bi-2212 similar to that observed in the underdoped systems. Finally, we discuss the origin of such anisotropic low-energy phonon broadening and its potential precursory role to the CDW phase in the underdoped region.
Title:
Exploiting superspace to clarify vacancy and Al/Si ordering in mullite
Authors:
Klar, PB; Etxebarria, I; Madariaga, G Author Full Names: Klar, Paul Benjamin; Etxebarria, Inigo; Madariaga, Gotzon
Source:
IUCRJ, 5 497-509; 10.1107/S2052252518007467 4 JUL 2018
Abstract:
Synchrotron single-crystal X-ray diffraction has revealed diffuse scattering alongside sharp satellite reflections for different samples of mullite (Al4+2xSi2-2xO10-x). Structural models have been developed in (3+1)-dimensional superspace that account for vacancy ordering and Al/Si ordering based on harmonic modulation functions. A constraint scheme is presented which explains the crystal-chemical relationships between the split sites of the average structure. The modulation amplitudes of the refinements differ significantly by a factor of similar to 3, which is explained in terms of different degrees of ordering, i.e. vacancies follow the same ordering principle in all samples but to different extents. A new approach is applied for the first time to determine Al/Si ordering by combining density functional theory with the modulated volumes of the tetrahedra. The presence of Si-Si diclusters indicates that the mineral classification of mullite needs to be reviewed. A description of the crystal structure of mullite must consider both the chemical composition and the degree of ordering. This is of particular importance for applications such as advanced ceramics, because the physical properties depend on the intrinsic structure of mullite.
Title:
Sr2Pt8-x As: a layered incommensurately modulated metal with saturated resistivity
Authors:
Martino, E; Arakcheeva, A; Autes, G; Pisoni, A; Bachmann, MD; Modic, KA; Helm, T; Yazyev, OV; Moll, PJW; Forro, L; Katrych, S Author Full Names: Martino, Edoardo; Arakcheeva, Alla; Autes, Gabriel; Pisoni, Andrea; Bachmann, Maja D.; Modic, Kimberly A.; Helm, Toni; Yazyev, Oleg, V; Moll, Philip J. W.; Forro, Laszlo; Katrych, Sergiy
Source:
IUCRJ, 5 470-477; 10.1107/S2052252518007303 4 JUL 2018
Abstract:
The high-pressure synthesis and incommensurately modulated structure are reported for the new compound Sr2Pt8-xAs, with x = 0.715 (5). The structure consists of Sr2Pt3 As layers alternating with Pt-only corrugated grids. Ab initio calculations predict a metallic character with a dominant role of the Pt d electrons. The electrical resistivity (rho) and Seebeck coefficient confirm the metallic character, but surprisingly, rho showed a near-flat temperature dependence. This observation fits the description of the Mooij correlation for electrical resistivity in disordered metals, originally developed for statistically distributed point defects. The discussed material has a long-range crystallographic order, but the high concentration of Pt vacancies, incommensurately ordered, strongly influences the electronic conduction properties. This result extends the range of validity of the Mooij correlation to long-range ordered incommensurately modulated vacancies. Motivated by the layered structure, the resistivity anisotropy was measured in a focused-ion-beam micro-fabricated well oriented single crystal. A low resistivity anisotropy indicates that the layers are electrically coupled and conduction channels along different directions are intermixed.
Title:
A Markov theoretic description of stacking-disordered aperiodic crystals including ice and opaline silica
Authors:
Hart, AG; Hansen, TC; Kuhs, WF Author Full Names: Hart, A. G.; Hansen, T. C.; Kuhs, W. F.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 357-372; 10.1107/S2053273318006083 4 JUL 2018
Abstract:
This article reviews the Markov theoretic description of one-dimensional aperiodic crystals, describing the stacking-faulted crystal polytype as a special case of an aperiodic crystal. Under this description the centrosymmetric unit cell underlying a topologically centrosymmetric crystal is generalized to a reversible Markov chain underlying a reversible aperiodic crystal. It is shown that for the close-packed structure almost all stackings are irreversible when the interaction reichweite s > 4. Moreover, the article presents an analytic expression of the scattering cross section of a large class of stacking-disordered aperiodic crystals, lacking translational symmetry of their layers, including ice and opaline silica (opal CT). The observed stackings and their underlying reichweite are then related to the physics of various nucleation and growth processes of disordered ice. The article discusses how the derived expressions of scattering cross sections could significantly improve implementations of Rietveld's refinement scheme and compares this Q-space approach with the pair-distribution function analysis of stacking-disordered materials.
Title:
Primitive substitution tilings with rotational symmetries
Authors:
Say-awen, ALD; De las Penas, MLAN; Frettloh, D Author Full Names: Say-awen, April Lynne D.; De las Penas, Ma Louise Antonette N.; Frettloeh, Dirk
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 388-398; 10.1107/S2053273318006745 4 JUL 2018
Abstract:
This work introduces the idea of symmetry order, which describes the rotational symmetry types of tilings in the hull of a given substitution. Definitions are given of the substitutions sigma(6) and sigma(7) which give rise to aperiodic primitive substitution tilings with dense tile orientations and which are invariant under six- and sevenfold rotations, respectively; the derivation of the symmetry orders of their hulls is also presented.
Title:
A phenomenological model for structural phase transitions in incommensurate alkane/urea inclusion compounds
Authors:
Couzi, M; Guillaume, F; Harris, KDM Author Full Names: Couzi, Michel; Guillaume, Francois; Harris, Kenneth D. M.
Source:
ROYAL SOCIETY OPEN SCIENCE, 5 (6):10.1098/rsos.180058 JUN 2018
Abstract:
n-Alkane/urea inclusion compounds are crystalline materials in which n-alkane 'guest' molecules are located within parallel one-dimensional 'host' tunnels formed by a helical hydrogen-bonded arrangement of urea molecules. The periodic repeat distance of the guest molecules along the host tunnels is incommensurate with the periodic repeat distance of the host substructure. The structural properties of the high-temperature phase of these materials (phase I), which exist at ambient temperature, are described by a (3 + l)-dimensional superspace. Recent publications have suggested that, in the prototypical incommensurate composite systems, n-nonadecane/urea and n-hexadecane/urea, two low-temperature phases II and 'III' exist and that one or both of these phases are described by a (3 + 2)dimensional superspace. We present a phenomenological model based on symmetry considerations and developed in the frame of a pseudo-spin-phonon coupling mechanism, which accounts for the mechanisms responsible for the I <-> II <-> 'III' phase sequence. With reference to published experimental data, we demonstrate that, in all phases of these incommensurate materials, the structural properties are described by (3 + l)-dimensional superspace groups. Around the temperature of the II <-> 'III' transition, the macroscopic properties of the material are not actually associated with a phase transition, but instead represent a 'crossover' between two regimes involving different couplings between relevant order parameters.
Title:
Microstructural analysis, micro-hardness and wear resistance properties of quasicrystalline Al-Cu-Fe coatings on Ti-6Al-4V alloy
Authors:
Fatoba, OS; Akinlabi, SA; Akinlabi, ET; Gharehbaghi, R Author Full Names: Fatoba, O. S.; Akinlabi, S. A.; Akinlabi, E. T.; Gharehbaghi, R.
Source:
MATERIALS RESEARCH EXPRESS, 5 (6):10.1088/2053-1591/aaca70 JUN 2018
Abstract:
The need for engineering components with suitable functionality under harsh wear and aggressive environment subjected to high risk of deterioration, has led to the demand for surface treatment processes and high-performance materials. Ti-6Al-4V is one of the mostly used titanium alloys with more than 70% of the industrial applications in the aerospace, marine and automotive industries. Despite the exceptional properties of Ti-6Al-4V alloy, their low hardness, high susceptibility to corrosion, poor thermal stability and poor tribological properties have limited their viability in the field of engineering. In this research, laser metal deposition technique by incorporating quasicrystal-line Al-Cu-Fe coatings can be very beneficial in enhancing the surface properties of Ti-6Al-4V alloy. A 3 kW continuous wave ytterbium laser system (YLS) attached to a KUKA robot which controls the movement of the cladding process was utilized for the fabrication of the coatings. The titanium alloy cladded surfaces were investigated for its microstructure, mechanical and wear resistance properties at different laser processing conditions. The obtained results illustrated that geometrical properties height and width of the deposit increase with an increase in laser power. Increase in scanning speed results in a decrease in the geometrical properties. Ti reacted with increased amount of Al and Fe and less amount of Cu powders to form Al2Ti, Fe0.975Ti, Al0.9Fe3.1Ti0.025 and AlCu2Ti. The optimum performances were obtained for an alloy composition of Ti-6A-4V/Al-Cu-5Fe composite, at laser power of 800 W and scanning speed of 1.0 m min(-1). Its performance enhancement compared to the unprotected substrate comprised a significant increase in hardness from 302 to 2740 HV which translates to 89.14% in hardness values above that of the substrate. Coatings with higher hardness levels were achieved mainly due to the larger fraction of hard-intermetallic phases at lower laser scanning speeds. Finally, Ti-6Al-4V/Al-Cu-5Fe coating at laser power of 800 W and scanning speed of 1.0 m min(-1) shows the highest wear resistance performance compared to the substrate. Ti-6Al-4V/ Al-Cu-5Fe coating was 2.8 times the wear resistance performance of the substrate.

Update: 11-Jul-2018

Title:
Al-Fe-Ge: New ternary compounds and phase equilibria at 800 degrees C
Authors:
Reisinger, GR; Effenberger, HS; Richter, KW Author Full Names: Reisinger, Gabriel R.; Effenberger, Herta S.; Richter, Klaus W.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 762 849-857; 10.1016/j.jallcom.2018.05.214 SEP 25 2018
Abstract:
The isothermal sections of Al-Fe-Ge at 800 degrees C and 780 degrees C were studied by a combination of SEM/EDX with X-ray powder diffraction. Two new ternary compounds were structurally characterised by means of single-crystal XRD measurements: Al3-xFeGe2+x, I4/mcm, a = 6.2303(11) angstrom, c = 9.710(2) angstrom, V = 376.9 angstrom(3), Z = 4, R-int = 0.031, wR(2) = 0.038 and Al1+xFeGe1-x, Fddd, a = 8.627(2) angstrom, b = 4.9139(8) angstrom, c = 16.369(3) angstrom, V = 693.9 angstrom(3), Z = 16, R-int = 0.039, wR(2) = 0.053, which crystallise in the Ga5Pd and CuMg2 structure types, respectively. Considerable solid solution ranges mainly based on Al/Ge substitution were found for all binary and ternary phases present in this section. An apparently incommensurate superstructure of Al5Fe2 is triggered by Ge-additions. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Liquid Exfoliation of Icosahedral Quasicrystals
Authors:
Yadav, TP; Woellner, CF; Sinha, SK; Sharifi, T; Apte, A; Mukhopadhyay, NK; Srivastava, ON; Vajtai, R; Galvao, DS; Tiwary, CS; Ajayan, PM Author Full Names: Yadav, Thakur Prasad; Woellner, Cristiano F.; Sinha, Shyam K.; Sharifi, Tiva; Apte, Amey; Mukhopadhyay, Nilay Krishna; Srivastava, Onkar Nath; Vajtai, Robert; Galvao, Douglas S.; Tiwary, Chandra Sekhar; Ajayan, Pulickel M.
Source:
ADVANCED FUNCTIONAL MATERIALS, 28 (26):10.1002/adfm.201801181 JUN 27 2018
Abstract:
The realization of quasicrystals has attracted a considerable attention due to their unusual structures and properties. The concept of quasicrystals in the atomically thin materials is even more appealing due to the in-plane covalent bonds and weak interlayer interactions. Here, it is demonstrated that 2D quasicrystals can be created/isolated from bulk phases because of long-range interlayer ordered aperiodic arrangements. An ultrasonication-assisted exfoliation of polygrained icosahedral Al-Pd-Mn quasicrystals at room temperature shows the formation of a large area of mono- and few layers in threefold quasicrystalline plane. The formation of these layers from random grain orientation consistently indicates that the threefold plane is most stable in comparison to the twofold and fivefold planes in icosahedral clusters. The above experimental observations are further supported with help of theoretical simulations. The mono- and few-layered aperiodic planes render plentiful active sites for the catalysis of hydrogen evolution reaction. The threefold 2D quasicrystalline plane exhibits a hydrogen evolution reaction overpotential of approximate to 100 mV (160 times less than bulk counterpart) and long-term durability. These systems constitute the first demonstration of quasicrystalline monolayer ordering in a free-standing thin layer without requiring the support of periodic or aperiodic substrate.
Title:
Light Localization in Local Isomorphism Classes of Quasicrystals
Authors:
Lin, C; Steinhardt, PJ; Torquato, S Author Full Names: Lin, Chaney; Steinhardt, Paul J.; Torquato, Salvatore
Source:
PHYSICAL REVIEW LETTERS, 120 (24):10.1103/PhysRevLett.120.247401 JUN 14 2018
Abstract:
We study a continuum of photonic quasicrystal heterostructures derived from local isomorphism (LI) classes of pentagonal quasicrystal tilings. These tilings are obtained by direct projection from a five-dimensional hypercubic lattice. We demonstrate that, with the sole exception of the Penrose LI class, all other LI classes result in degenerate, effectively localized states, with precisely predictable and tunable properties (frequencies, frequency splittings, and densities). We show that localization and tunability are related to a mathematical property of the pattern known as "restorability," i.e., whether the tiling can be uniquely specified given only a set of rules that fix all allowed clusters smaller than some bound.
Title:
First-principles study of elastic and slip properties of non-canonical beta-based Al-Cu-Fe approximants
Authors:
Medvedeva, NI; Shalaeva, EV Author Full Names: Medvedeva, N. I.; Shalaeva, E. V.
Source:
PHILOSOPHICAL MAGAZINE, 98 (23):2135-2150; 10.1080/14786435.2018.1478145 2018
Abstract:
Ab initio calculations were carried out to compare the mechanical properties of beta-based non-canonical Al-Cu-Fe approximants of quasicrystals with cubic (beta), monoclinic (eta) and orthorhombic (xi 1, xi 2) structures, which all demonstrate high strengthening. The aim was to elucidate the competitive effects of the eta- and xi-ordering and iron content on deformation behaviour of these phases. We found that the Young's modulus, polycrystalline shear modulus, mechanical stability and shear elastic modulus G(n,m) for different slip planes decrease for beta-Al50Cu1-xFex with lowering iron content, but they grow from beta-Al50Cu31.25Fe18.75 to the ordered eta-Al50Cu45Fe5, and xi 2-Al45.5Cu50Fe4.5 that indicates a growing resistance to plastic deformation due to ordering and agrees well with our experimental finding. The preferable slip systems were predicted based on the calculated generalised stacking fault (GSF) energies in beta-(Cu,Fe)Al and eta-(Cu,Fe)Al with similar Fe concentration. The GSF energies confirmed also that the strengthening observed in eta-phase is related to ordering rather than the Fe effect in consistence with a stronger covalent bonding in eta-phase.
Title:
Interpretation of some Yb-based valence-fluctuating crystals as approximants to a dodecagonal quasicrystal
Authors:
Ishimasa, T; Mihalkovic, M; Deguchi, K; Sato, NK; de Boissieu, M Author Full Names: Ishimasa, Tsutomu; Mihalkovic, Marek; Deguchi, Kazuhiko; Sato, Noriaki K.; de Boissieu, Marc
Source:
PHILOSOPHICAL MAGAZINE, 98 (22):2018-2034; 10.1080/14786435.2018.1470339 2018
Abstract:
The hexagonal ZrNiAl-type (space group: P (6) over bar 2m) and the tetragonal Mo2FeB2-type (space group: P4/mbm) structures, which are formed in the same Yb-based alloys and exhibit physical properties related to valence-fluctuation, can be regarded as approximants of a hypothetical dodecagonal quasicrystal. Using Pd-Sn-Yb system as an example, a model of quasicrystal structure has been constructed, of which five-dimensional crystal (space group: P12/mmm, a(DD) = 5.66 angstrom and c = 3.72 angstrom) consists of four types of acceptance regions located at the following crystallographic sites; Yb [0 0 0 0 0], Pd[1/3 0 1/3 0 1/2], Pd[1/3 1/3 1/3 1/3 0] and Sn[1/2 00 1/2 1/2]. In the three-dimensional space, the quasicrystal is composed of three types of columns, of which c-projections correspond to a square, an equilateral triangle and a three-fold hexagon. They are fragments of two known crystals, the hexagonal alpha-YbPdSn and the tetragonal Yb2Pd2Sn structures. The model of the hypothetical quasicrystal may be applicable as a platform to treat in a unified manner the heavy fermion properties in the two types of Yb-based crystals.

Update: 4-Jul-2018

Title:
Evolution of Magneto-Orbital order Upon B-Site Electron Doping in Na1-xCaxMn7O12 Quadruple Perovskite Manganites
Authors:
Johnson, RD; Mezzadri, F; Manuel, P; Khalyavin, DD; Gilioli, E; Radaelli, PG Author Full Names: Johnson, R. D.; Mezzadri, F.; Manuel, P.; Khalyavin, D. D.; Gilioli, E.; Radaelli, P. G.
Source:
PHYSICAL REVIEW LETTERS, 120 (25):10.1103/PhysRevLett.120.257202 JUN 19 2018
Abstract:
We present the discovery and refinement by neutron powder diffraction of a new magnetic phase in the Na1-xCaxMn7O12 quadruple perovskite phase diagram, which is the incommensurate analogue of the wellknown pseudo-CE phase of the simple perovskite manganites. We demonstrate that incommensurate magnetic order arises in quadruple perovskites due to the exchange interactions between A and B sites. Furthermore, by constructing a simple mean field Heisenberg exchange model that generically describes both simple and quadruple perovskite systems, we show that this new magnetic phase unifies a picture of the interplay between charge, magnetic, and orbital ordering across a wide range of compounds.
Title:
Magnetoelastic phase diagram of TbNi2B2C
Authors:
Toft-Petersen, R; Jensen, TBS; Jensen, J; von Zimmermann, M; Sloth, S; Isaksen, FW; Christensen, NB; Chen, YZ; Siemensmeyer, K; Kawano-Furukawa, H; Takeya, H; Abrahamsen, AB; Andersen, NH Author Full Names: Toft-Petersen, Rasmus; Jensen, Thomas Bagger Stibius; Jensen, Jens; von Zimmermann, Martin; Sloth, Steffen; Isaksen, Frederik Werner; Christensen, Niels Bech; Chen, Yunzhong; Siemensmeyer, Konrad; Kawano-Furukawa, Hazuki; Takeya, Hiroyuki; Abrahamsen, Asger Bech; Andersen, Niels Hessel
Source:
PHYSICAL REVIEW B, 97 (22):10.1103/PhysRevB.97.224417 JUN 15 2018
Abstract:
The magnetic phase diagram of the quaternary borocarbide TbNi2B2C is investigated by direct means and by studying magnetically induced modifications of the crystal structure. Detailed superconducting quantum interference device measurements reveal a complex phase diagram with five distinct magnetic phases. The phase boundaries aremapped out comprehensively. Synchrotron hard x-raymeasurements in appliedmagnetic fields are employed to probe the magnetoelastic distortions throughout the phase diagram. The determination of the wave vectors of these field-induced lattice deformations suggests a range of commensurate spin-slip-type magnetic structures at low temperatures with wave vectors of the form (q, 0,0) with q = 6/11 and 5/9. The proposed magnetic structures yield values of magnetization well in-line with observations. The scattering intensity due to the magnetoelastic deformations exhibits a drastic jump at the phase boundary at 1.3 T and low temperatures.
Title:
Lattice Correspondence and Growth Structures of Monoclinic Mg4Zn7 Phase Growing on an Icosahedral Quasicrystal
Authors:
Singh, A; Rosalie, JM Author Full Names: Singh, Alok; Rosalie, Julian M.
Source:
CRYSTALS, 8 (5):10.3390/cryst8050194 MAY 2018
Abstract:
Mg4Zn7 phase, with a monoclinic unit cell, a layered structure and a unique axis showing pseudo-tenfold symmetry, grows over icosahedral quasicrystalline phase in a manner similar to a decagonal quasicrystal. In this study, the relationship of this phase to icosahedral quasicrystal is brought out by a transmission electron microscopy study of Mg4Zn7 phase growing on icosahedral phase in a cast Mg-Zn-Y alloy. Lattice correspondences between the two phases have been determined by electron diffraction. Planes related to icosahedral fivefold and pseudo-twofold symmetry are identified. Possible orthogonal cells bounded by twofold symmetry-related planes have been determined. Mg4Zn7 phase growing on an icosahedral phase exhibits a number of planar faults parallel to the monoclinic axis, presumably to accommodate the quasiperiodicity at the interface. Two faults were identified, which were on {200} and {201} planes. Their structures have been determined by high resolution imaging in TEM. They produce two different unit cells at the interface.
Title:
Crystallographic features of the approximant H (Mn7Si2V) phase in the Mn-Si-V alloy system
Authors:
Nakayama, K; Komatsuzaki, T; Koyama, Y Author Full Names: Nakayama, Kei; Komatsuzaki, Takumi; Koyama, Yasumasa
Source:
PHILOSOPHICAL MAGAZINE, 98 (20):1823-1847; 10.1080/14786435.2018.1459058 2018
Abstract:
The intermetallic compound H (Mn7Si2V) phase in the Mn-Si-V alloy system can be regarded as an approximant phase of the dodecagonal quasicrystal as one of the two-dimensional quasicrystals. To understand the features of the approximant H phase, in this study, the crystallographic features of both the H phase and the (sigma H) reaction in Mn-Si-V alloy samples were investigated, mainly by transmission electron microscopy. It was found that, in the H phase, there were characteristic structural disorders with respect to an array of a dodecagonal structural unit consisting of 19 dodecagonal atomic columns. Concretely, penetrated structural units consisting of two dodecagonal structural units were presumed to be typical of such disorders. An interesting feature of the (sigma H) reaction was that regions with a rectangular arrangement of penetrated structural units (RAPU) first appeared in the sigma matrix as the initial state, and H regions were then nucleated in contact with RAPU regions. The subsequent conversion of RAPU regions into H regions eventually resulted in the formation of the approximant H state as the final state. Furthermore, atomic positions in both the H structure and the dodecagonal quasicrystal were examined using a simple plane-wave model with 12 plane waves.

Update: 27-Jun-2018

Title:
Photoinduced discommensuration of the commensurate charge-density wave phase in 1T-TaS2
Authors:
Tanimura, K Author Full Names: Tanimura, Katsumi
Source:
PHYSICAL REVIEW B, 97 (24):10.1103/PhysRevB.97.245115 JUN 11 2018
Abstract:
The dynamics induced by femtosecond-laser excitation of the commensurate phase of the charge-density wave (CDW) in 1T -TaS2 have been studied using both time-resolved electron diffraction and the time-resolved spectroscopy of coherent-phonon dynamics. Electron diffraction results show that the commensurate CDW phase is transformed into a new phase with CDW order that is similar to the nearly commensurate phase with threshold-type transition rates; the threshold excitation density of 0.2 per 13 Ta atoms is evaluated. Coherent-phonon spectroscopy results show that, together with the amplitude mode of CDW with a frequency of 2.41 THz, two other modes with frequencies of 2.34 and 2.07 THz are excited in the photoexcited commensurate CDW phase over a timescale of several tens of picoseconds after excitation. Spectroscopic, temporal, and excitation-intensity dependent characteristics of the three coherent phonons reveal that a photoinduced decomposition of the commensurate CDW order into an ensemble of domains with different CDW orders is induced before the CDW-phase transition occurs. The physics underlying the photoinduced decomposition and evolution into discommensurations responsible for the CDW-order transformation are discussed.
Title:
Adaptive modulation in the Ni2Mn1.4In0.6 magnetic shape-memory Heusler alloy
Authors:
Devi, P; Singh, S; Dutta, B; Manna, K; D'Souza, SW; Ikeda, Y; Suard, E; Petricek, V; Simon, P; Werner, P; Chadhov, S; Parkin, SSP; Felser, C; Pandey, D Author Full Names: Devi, P.; Singh, Sanjay; Dutta, B.; Manna, K.; D'Souza, S. W.; Ikeda, Y.; Suard, E.; Petricek, V; Simon, P.; Werner, P.; Chadhov, S.; Parkin, Stuart S. P.; Felser, C.; Pandey, D.
Source:
PHYSICAL REVIEW B, 97 (22):10.1103/PhysRevB.97.224102 JUN 11 2018
Abstract:
The origin of incommensurate structural modulation in Ni-Mn based Heusler-type magnetic shape-memory alloys (MSMAs) is still an unresolved issue in spite of intense focus on it due to its role in the magnetic field induced ultrahigh strains. In the archetypal MSMA Ni2MnGa, the observation of "nonuniform displacement" of atoms from their mean positions in the modulated martensite phase, premartensite phase, and charge density wave as well as the presence of phason broadening of satellite peaks has been taken in support of the electronic instability model linked with a soft acoustic phonon. We present here results of a combined high-resolution synchrotron x-ray powder diffraction (SXRPD) and neutron powder diffraction (NPD) study on Ni2Mn1.4In0.6 using a (3+1)D superspace group approach, which reveals not only uniform atomic displacements in the modulated structure of the martensite phase with physically acceptable ordered magnetic moments in the antiferromagnetic phase at low temperatures, but also the absence of any premartensite phase and phason broadening of the satellite peaks. Our HRTEM studies and first-principles calculations of the ground state also support uniform atomic displacements predicted by powder diffraction studies. All these observations suggest that the structural modulation in the martensite phase of Ni(2)Mn(1.4)In(0.6 )MSMA can be explained in terms of the adaptive phase model. The present study underlines the importance of superspace group analysis using complementary SXRPD and NPD in understanding the physics of the origin of modulation as well as the magnetic and the modulated ground states of the Heusler-type MSMAs. Our work also highlights the fact that the mechanism responsible for the origin of modulated structure in different Ni-Mn based MSMAs may not be universal and it must be investigated thoroughly in different alloy compositions.
Title:
Breakdown of Magnetic Order in the Pressurized Kitaev Iridate beta-Li2IrO3
Authors:
Majumder, M; Manna, RS; Simutis, G; Orain, JC; Dey, T; Freund, F; Jesche, A; Khasanov, R; Biswas, PK; Bykova, E; Dubrovinskaia, N; Dubrovinsky, LS; Yadav, R; Hozoi, L; Nishimoto, S; Tsirlin, AA; Gegenwart, P Author Full Names: Majumder, M.; Manna, R. S.; Simutis, G.; Orain, J. C.; Dey, T.; Freund, F.; Jesche, A.; Khasanov, R.; Biswas, P. K.; Bykova, E.; Dubrovinskaia, N.; Dubrovinsky, L. S.; Yadav, R.; Hozoi, L.; Nishimoto, S.; Tsirlin, A. A.; Gegenwart, P.
Source:
PHYSICAL REVIEW LETTERS, 120 (23):10.1103/PhysRevLett.120.237202 JUN 8 2018
Abstract:
Temperature-pressure phase diagram of the Kitaev hyperhoneycomb iridate beta-Li2IrO3 is explored using magnetization, thermal expansion, magnetostriction, and muon spin rotation measurements, as well as single-crystal x-ray diffraction under pressure and ab initio calculations. The Neel temperature of beta-Li2IrO3 increases with the slope of 0.9 K/GPa upon initial compression, but the reduction in the polarization field Hc reflects a growing instability of the incommensurate order. At 1.4 GPa, the ordered state breaks down upon a first-order transition, giving way to a new ground state marked by the coexistence of dynamically correlated and frozen spins. This partial freezing in the absence of any conspicuous structural defects may indicate the classical nature of the resulting pressure-induced spin liquid, an observation paralleled to the increase in the nearest-neighbor off-diagonal exchange Gamma under pressure.
Title:
Dynamically enhanced magnetic incommensurability: Effects of local dynamics on nonlocal spin correlations in a strongly correlated metal
Authors:
Vilardi, D; Taranto, C; Metzner, W Author Full Names: Vilardi, Demetrio; Taranto, Ciro; Metzner, Walter
Source:
PHYSICAL REVIEW B, 97 (23):10.1103/PhysRevR.97.235110 JUN 7 2018
Abstract:
We compute the spin susceptibility of the two-dimensional Hubbard model away from half-filling, and analyze the impact of frequency-dependent vertex corrections as obtained from the dynamical mean field theory (DMFT). We find that the local dynamics captured by the DMFT vertex strongly affects nonlocal spin correlations, and thus the momentum dependence of the spin susceptibility. While the widely used random-phase approximation yields commensurate Neel-type antiferromagnetism as the dominant instability over a wide doping range, the vertex corrections favor incommensurate ordering wave vectors away from(pi,pi). Our results indicate that the connection between the magnetic ordering wave vector and the Fermi surface geometry, familiar for weakly interacting systems, can hold in a strongly correlated metal, too.
Title:
Structural phase transitions in YPtGe2 and GdPtGe2
Authors:
Janka, O; Hoffmann, RD; Heying, B; Pottgen, R Author Full Names: Janka, Oliver; Hoffmann, Rolf-Dieter; Heying, Birgit; Poettgen, Rainer
Source:
DALTON TRANSACTIONS, 47 (17):6075-6088; 10.1039/c8dt00815a MAY 7 2018
Abstract:
The germanides YPtGe2 and GdPtGe2 were synthesized from REGe2 precursor compounds and platinum by arc-melting and their structures were studied on the basis of temperature-dependent single crystal X-ray diffraction data. At room temperature both germanides adopt the orthorhombic YIrGe2 type structure, space group Immm, with enhanced U-11 displacement parameters for the Ge1 atoms. Below 174 and 145 K, respectively, satellite reflections emerge in the diffraction patterns, giving rise to modulations. The low-temperature structures were refined in the superspace group Pnnn(1/2,1/2,gamma)qq0 (48.1.11.3). The structural phase transition is also evident in the magnetic susceptibility, specific heat and resistivity data. The high-and low-temperature modifications are discussed on the basis of a group-subgroup scheme.

Update: 20-Jun-2018

Title:
Preparation and nanoscopic plastic deformation of toughened Al-Cu-Fe-based quasicrystal/vanadium multilayered coatings
Authors:
Chang, SY; Chen, BJ; Hsiao, YT; Wang, DS; Chen, TS; Leu, MS; Lai, HJ Author Full Names: Chang, Shou-Yi; Chen, Bo-Jien; Hsiao, Yu-Ting; Wang, Ding-Shiang; Chen, Tai-Sheng; Leu, Ming-Sheng; Lai, Hong-Jen
Source:
MATERIALS CHEMISTRY AND PHYSICS, 213 277-284; 10.1016/j.matchemphys.2018.04.045 JUL 1 2018
Abstract:
Ductile vanadium layers were alternately deposited with brittle aluminum-copper-iron-based quasicrystal-alloy layers to form multilayered coatings. The in-situ transmission electron microscopic observations of nanopillar compression revealed that the as-deposited single-layered amorphous aluminum-copper-iron alloy slightly deformed via shear banding. After annealing at 800 degrees C, brittle quasicrystal and intermetallic compounds were formed, so the single-layered coating cracked and peeled. In comparison, the multilayered coatings were effectively toughened. The multilayered nanopillars plastically deformed via dislocation activities and were work hardened owing to confined dislocation gliding. The as-deposited multilayered structure (amorphous alloy/crystalline vanadium) had a low 10% flow stress of 1.72 GPa, while the annealed multilayered structure (quasicrystal/vanadium) presented a high flow stress of 2.58 GPa owing to quasicrystal strengthening. Dislocation clusters were in-situ observed to glide laterally in the crystalline vanadium layers and move vertically through the vanadium and quasicrystal layers, yielding an improved plasticity. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Growth of two-dimensional decagonal colloidal quasicrystals
Authors:
Martinsons, M; Schmiedeberg, M Author Full Names: Martinsons, M.; Schmiedeberg, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 30 (25):10.1088/1361-648X/aac503 JUN 27 2018
Abstract:
The growth of quasicrystals, i.e. structures with long-range positional order but no periodic translational symmetry, is more complex than the growth of periodic crystals. By employing Brownian dynamics simulations in two dimensions for colloidal particles that interact according to an isotropic pair potential with two incommensurate lengths, we study the growth of quasicrystalline structures by sequentially depositing particles at their surface. We quantify the occurrence of quasicrystalline order as a function of the temperature and the rate of added particles. In addition, we explore defects like local triangular order or gaps within the quasicrystalline structure. Furthermore, we analyze the shapes of the surfaces in grown structures which tend to build straight lines along the symmetry axes of the quasicrystal. Finally, we identify phasonic flips which are rearrangements of the particles due to additional degrees of freedom. The number of phasonic flips decreases with the distance to the surface.
Title:
Identification of a secondary phase Ga2O3(ZnO)m in Ga-doped ZnO thermoelectric materials by a (3+1)-dimensional superspace model
Authors:
Michiue, Y; Mori, T Author Full Names: Michiue, Yuichi; Mori, Takao
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 51 924-927; 10.1107/S1600576718004119 3 JUN 2018
Abstract:
A unified structure model for the homologous compounds Ga2O3(ZnO)(m) in (3 + 1)-dimensional superspace was modified by refinements for samples of Ga2O3:ZnO = 1:n (n = 15, 23, 28, 33, 38). The first-order sine terms in the modulation functions decreased with increasing phase index m. The diffraction intensities of the thermoelectric material Ga2O3:ZnO = 1:98 were best fitted by a two-phase model containing the wurtzite structure (Ga-doped ZnO) and the homologous compound Ga2O3(ZnO)(s), where s = 38.
Title:
Commensurate versus incommensurate charge ordering near the superconducting dome in Ir1-xPtxTe2 revealed by resonant x-ray scattering
Authors:
Takubo, K; Yamamoto, K; Hirata, Y; Wadati, H; Mizokawa, T; Sutarto, R; He, F; Ishii, K; Yamasaki, Y; Nakao, H; Murakami, Y; Matsuo, G; Ishii, H; Kobayashi, M; Kudo, K; Nohara, M Author Full Names: Takubo, K.; Yamamoto, K.; Hirata, Y.; Wadati, H.; Mizokawa, T.; Sutarto, R.; He, F.; Ishii, K.; Yamasaki, Y.; Nakao, H.; Murakami, Y.; Matsuo, G.; Ishii, H.; Kobayashi, M.; Kudo, K.; Nohara, M.
Source:
PHYSICAL REVIEW B, 97 (20):10.1103/PhysRevB.97.205142 MAY 31 2018
Abstract:
The electronic-structural modulations of Ir1-xPtxTe2 (0 <= x <= 0.12) have been examined by resonant elastic x-ray scattering (REXS) and resonant inelastic x-ray scattering (RIXS) techniques at both the Ir and Te edges. Charge-density-wave-like superstructures with wave vectors of Q = (1/5 0 - 1/5), (1/8 0 - 1/8), and (1/6 0 - 1/6) are observed on the same sample of IrTe2 at the lowest temperature, the patterns of which are controlled by the cooling speeds. In contrast, superstructures around Q = (1/5 0 - 1/5) are observed for doped samples (0.02 <= x <= 0.05). The superstructure reflections persist to higher Pt substitution than previously assumed, demonstrating that a charge-density wave (CDW) can coexist with superconductivity. The analysis of the energy-dependent REXS and RIXS line shape reveals the importance of the Te 5p state rather than the Ir 5d states in the formation of the spatial modulation of these systems. The phase diagram reexamined in this work suggests that the CDW incommensurability may correlate with the emergence of superconducting states such as CuxTiSe2 and LixTaS2.
Title:
Dipole-dipole interactions and incommensurate order in perovskite structures
Authors:
Burkovsky, RG Author Full Names: Burkovsky, R. G.
Source:
PHYSICAL REVIEW B, 97 (18):10.1103/PhysRevB.97.184109 MAY 31 2018
Abstract:
Dipole-dipole (DD) interactions are known to play an important role in conditioning ferroelectricity in ABO(3) perovskite crystals. Their possible role in conditioning nonferroelectric (inhomogeneous) cation ordering is presently unexplored. I analyze the energy of DD interactions in perovskite structure for different inhomogeneous spatial patterns of electric dipoles localized at the lattice sites. I show that DD interactions can favor inhomogeneous ordering when other terms of the Hamiltonian allow large total polarizability of A sites, comparably large total polarizability of oxygen sites in A-O planes, and relatively weak total polarizability of oxygen sites in the B-O direction. These conditions are naturally expected in PbZrO3 crystals, for which the reason behind antiferroelectric and incommensurate inhomogeneous ordering is currently being debated.
Title:
Magnetic structure of Ho0.5Y0.5Mn6Sn6 compound studied by powder neutron diffraction
Authors:
Li, XY; Peng, LC; He, LH; Zhang, SY; Yao, JL; Zhang, Y; Wang, FW Author Full Names: Li, X-Y.; Peng, L-C.; He, L-H.; Zhang, S-Y.; Yao, J-L.; Zhang, Y.; Wang, F-W.
Source:
JOURNAL OF APPLIED PHYSICS, 123 (20):10.1063/1.5029707 MAY 28 2018
Abstract:
The crystallographic and magnetic structures of the HfFe6Ge6-type compound Ho0.5Y0.5Mn6Sn6 have been studied by powder neutron diffraction and in-situ Lorentz transmission electron microscopy. Besides the nonlinear thermal expansion of lattice parameters, an incommensurate conical spiral magnetic structure was determined in the temperature interval of 2-340 K. A spin reorientation transition has been observed from 50 to 300 K, where the alignment of the c-axis component of magnetic moments of the Ho sublattice and the Mn sublattice transfers from ferrimagnetic to ferromagnetic. Published by AIP Publishing.

Update: 13-Jun-2018

Title:
A study on spherical particles in Al65Cu20Fe15 alloy prepared by arc melting
Authors:
Li, CF; Carey, C; Li, DQ; Caputo, M; Bouch, R; Hampikian, H Author Full Names: Li, Chunfei; Carey, Christopher; Li, Dingqiang; Caputo, Matthew; Bouch, Ronald; Hampikian, Helen
Source:
MATERIALS CHARACTERIZATION, 140 162-171; 10.1016/j.matchar.2018.03.050 JUN 2018
Abstract:
Al-Cu-Fe alloys are important due to reports that stable icosahedral quasicrystalline phase with composition in the vicinity of Al65Cu20Fe15 can be prepared. However, it has been widely reported that the as-prepared alloy, very often by arc-melting, is porous, consisting of particles with different morphologies. Among these, one type of particles of a spherical shape is considered as pure cubic beta phase in previous reports. In this research, this spherical particle was studied using a Scanning Electron Microscope, Energy Dispersive X-ray Spectroscopy, Transmission Electron Microscope, and Electron Diffraction. It was found that the particles are not single phase, consisting of icosahedral quasicrystalline grains embedded inside single crystal matrix of tau phase. Additionally, there are places where the tau phase appears to have out-most layer enriched in Cu. The surface of the particles is faceted and the facets can be classified to three types according to their detailed structures. A close examination and analysis led to the conclusion that these three types are parallel to the atomic planes of {1 1 0}, {1 1 1}, and {1 0 0}, respectively. A model for the spherical particle formation is suggested and the reasons for the formation of facets are discussed. This report is valuable in clarifying some discrepancies in previous reports, and in understanding the phase development in an Al-Cu-Fe alloy system.

Update: 6-Jun-2018

Title:
Coexistence of charge density wave and incommensurate antiferromagnetism in the cubic phase of DyGe2.85 synthesised under high pressure
Authors:
Salamatin, DA; Sidorov, VA; Kichanov, SE; Velichkov, A; Salamatin, AV; Fomicheva, LN; Kozlenko, DP; Nikolaev, AV; Menzel, D; Budzynski, M; Tsvyashchenko, AV Author Full Names: Salamatin, D. A.; Sidorov, V. A.; Kichanov, S. E.; Velichkov, A.; Salamatin, A. V.; Fomicheva, L. N.; Kozlenko, D. P.; Nikolaev, A. V.; Menzel, D.; Budzynski, M.; Tsvyashchenko, A. V.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 755 10-14; 10.1016/j.jallcom.2018.04.319 JUL 30 2018
Abstract:
A novel metastable phase of DyGe2.85 synthesised in the AuCu3-structure under high pressure, has been studied by means of the magnetic susceptibility and electrical resistivity measurements (under the pressure P <= 3.1 GPa), neutron powder diffraction and time-differential gamma-gamma perturbed angular correlations (TDPAC) using Cd-111 nuclear probes. Two distinct phase transitions have been found in this compound as the temperature is lowered. We assign the first transition occurring at the temperature T-CDW = 80 K with charge density wave formation and the second transition at T-N approximate to 18 K with an antiferromagnetic spiral ordering of Dy magnetic moments, and discuss a close relationship between them. (C) 2018 Elsevier B.V. All rights reserved.
Title:
PERFECTLY ORDERED QUASICRYSTALS AND THE LITTLEWOOD CONJECTURE
Authors:
Haynes, A; Koivusalo, H; Walton, J Author Full Names: Haynes, Alan; Koivusalo, Henna; Walton, James
Source:
TRANSACTIONS OF THE AMERICAN MATHEMATICAL SOCIETY, 370 (7):4975-4992; 10.1090/tran/7136 JUL 2018
Abstract:
Linearly repetitive cut and project sets are mathematical models for perfectly ordered quasicrystals. In a previous paper we presented a characterization of linearly repetitive cut and project sets. In this paper we extend the classical definition of linear repetitivity to try to discover whether or not there is a natural class of cut and project sets which are models for quasicrystals which are better than 'perfectly ordered'. In the positive direction, we demonstrate an uncountable collection of such sets (in fact, a collection with large Hausdorff dimension) for every choice of dimension of the physical space. On the other hand, we show that, for many natural versions of the problems under consideration, the existence of these sets turns out to be equivalent to the negation of a well-known open problem in Diophantine approximation, the Littlewood conjecture.
Title:
Improved electrochemical hydrogen storage capacity of Ti45Zr38Ni17 quasicrystal by addition of ZrH2
Authors:
Zhao, JX; Zhai, XJ; Tao, X; Li, Z; Wang, QS; Liu, WQ; Wang, LM Author Full Names: Zhao, Jianxun; Zhai, Xiaojie; Tao, Xing; Li, Zhe; Wang, Qingshuang; Liu, Wanqiang; Wang, Limin
Source:
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY, 34 (6):995-998; 10.1016/j.jmst.2017.10.006 JUN 2018
Abstract:
Ti45Zr38Ni17 + xZrH(2) (x = 5, 10, 15 and 20 wt%) composite materials are produced by ball milling for 20 min. The results of XRD measurement show that the composite materials contain icosahedral quasicrystal phase (I-phase), FCC phase with a Ti2Ni type crystal and C14 Laves phase. After adding ZrH2, the composite materials include not only the individual phases mentioned above, but also the ZrH phase. These composite materials are used as the negative electrode material of the nickel-metal hydride batteries. The electrochemical hydrogen storage characteristics of the material after adding ZrH is investigated. The Ti45Zr38Ni17 + xZrH(2) (x = 5, 10, 15 and 20 wt%) composite material has reached the maximum discharge capacity (83.2 mA h/g) when x equals 10. This maximum discharge capacity is much higher than that of Ti(45)Zr(38)Ni(17 )alloy without ZrH. After adding ZrH2, the high-rate discharge ability and the cycling stability are enhanced simultaneously. The improvement of the electrochemical properties can be attributed to the synergistic effects of ZrH2, and the synergistic effects in the composite electrodes are probably attributed to the entry of most of hydrogen atoms from weakly bond strength of the Zr-H to the I-phase structure in electrochemical reaction. (C) 2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.
Title:
Epitaxial growth of a metastable icosahedral quasicrystal on a stable icosahedral quasicrystal substrate
Authors:
Leskovar, B; Sturm, S; Samardzija, Z; Ambrozic, B; Markoli, B; Naglic, I Author Full Names: Leskovar, Blaz; Sturm, Saso; Samardzija, Zoran; Ambrozic, Bojan; Markoli, Bostjan; Naglic, Iztok
Source:
SCRIPTA MATERIALIA, 150 92-95; 10.1016/j.scriptamat.2018.03.014 JUN 2018
Abstract:
This study confirms that the stable icosahedral quasicrystal (iQc) phase Al65Cu20Fe15(iQc-AlCuFe) can serve as a substrate for the nucleation of the metastable iQc-AlMnSi phase formed in rapidly solidified Al-Mn-Si alloys. The results reveal that a continuous, thin layer of the metastable iQc-AlMnSi phase can be formed on a stable iQc-AlCuFe particle. Electron backscatter diffraction patterns and selected-area electron diffraction patterns confirmed that epitaxy exists between the stable and the metastable iQc phases. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Magnetic field induced evolution of intertwined orders in the Kitaev magnet beta-Li2IrO3
Authors:
Rousochatzakis, I; Perkins, NB Author Full Names: Rousochatzakis, Ioannis; Perkins, Natalia B.
Source:
PHYSICAL REVIEW B, 97 (17):10.1103/PhysRevB.97.174423 MAY 24 2018
Abstract:
Recent scattering experiments in the 3D Kitaev magnet beta-Li2IrO3 have shown that a relatively weak magnetic field along the crystallographic b axis drives the system from its incommensurate counter-rotating order to a correlated magnet, with a significant uniform 'zigzag' component superimposing the magnetization along the field. Here it is shown that the zigzag order is not emerging from its linear coupling to the field (via a staggered, off-diagonal element of the g tensor) but from its intertwining with the incommensurate order and the longitudinal magnetization. The emerging picture explains all qualitative experimental findings at zero and finite fields, including the rapid decline of the incommensurate order with field and the so-called intensity sum rule. The latter are shown to be independent signatures of the smallness of the Heisenberg exchange J, compared to the Kitaev coupling K and the off-diagonal anisotropy Gamma. Remarkably, in the regime of interest, the field H* at which the incommensurate component vanishes, depends essentially only on J, which allows us to extract an estimate of J similar or equal to 4 K from reported measurements of H*. We also comment on recent experiments in pressurized beta-Li2IrO3 and conclude that J decreases with pressure.
Title:
Polarized neutron scattering study of the multiple order parameter system NdB4
Authors:
Metoki, N; Yamauchi, H; Matsuda, M; Fernandez-Baca, JA; Watanuki, R; Hagihala, M Author Full Names: Metoki, N.; Yamauchi, H.; Matsuda, M.; Fernandez-Baca, J. A.; Watanuki, R.; Hagihala, M.
Source:
PHYSICAL REVIEW B, 97 (17):10.1103.PhysRevB.97.174416 MAY 17 2018
Abstract:
Neutron polarization analysis has been carried out in order to clarify the magnetic structures of multiple order parameter f-electron system NdB4. We confirmed the noncollinear "all-in all-out" structure (Gamma(4)) of the in-plane moment, which is in good agreement with our previous neutron powder diffraction study. We found that the magnetic moment along the c-axis m(c) showed diagonally antiferromagnetic structure (Gamma(10)), inconsistent with previously reported "vortex" structure (Gamma(2)). The microscopic mixture of these two structures with (q) over right arrow 0 = (0,0,0) appears in phase II and remains stable in phases III and IV, where an incommensurate modulation coexists. The unusual magnetic ordering is phenomenologically understood via Landau theory with the primary order parameter Gamma(4) coupled with higher-order secondary order parameter Gamma(10). The magnetic moments were estimated to be 1.8 +/- 0.2 and 0.2 +/- 0.05 mu B at T = 7.5 K for Gamma(4) and Gamma(10), respectively. We also found along-penod incommensurate modulation of the (q) over right arrow1 = (0,0,1 /2) antiferromagnetic structure of m(c) with the propagation (q) over right arrow (s1)= (0.14, 0.14, 0.1) and <(q) over right arrow>(s2) = (0.2,0,0.1) in phase III and IV, respectively. The amplitude of sinusoidal modulation was about m(c) = 1.0 +/- 0.2 mu B at T=1.5 K. The local (0,0,1 /2) structure consists of in-plane ferromagnetic and out-of-plane antiferromagnetic coupling of m(c), opposite to the coexisting Gamma(10). The m(c) of Gamma(10) is significantly enhanced up to 0.6 mu B at T=1.5 K, which is accompanied by the incommensurate modulations. The Landau phenomenological approach indicates that the higher-order magnetic and/or multipole interactions based on the pseudoquartet f-electron state play important roles.
Title:
Structural and electronic properties of the alkali metal incommensurate phases
Authors:
Woolman, G; Robinson, VN; Marques, M; Loa, I; Ackland, GJ; Hermann, A Author Full Names: Woolman, Gavin; Robinson, Victor Naden; Marques, Miriam; Loa, Ingo; Ackland, Graeme J.; Hermann, Andreas
Source:
PHYSICAL REVIEW MATERIALS, 2 (5):10.1103/PhysRevMaterials.2.053604 MAY 11 2018
Abstract:
Under pressure, the alkali elements sodium, potassium, and rubidium adopt nonperiodic structures based on two incommensurate interpenetrating lattices. While all elements form the same "host" lattice, their "guest" lattices are all distinct. The physical mechanism that stabilizes these phases is not known, and detailed calculations are challenging due to the incommensurability of the lattices. Using a series of commensurate approximant structures, we tackle this issue using density functional theory calculations. In Na and K, the calculations prove accurate enough to reproduce not only the stability of the host-guest phases, but also the complicated pressure dependence of the host-guest ratio and the two guest-lattice transitions. We find Rb-IV to be metastable at all pressures, and suggest it is a high-temperature phase. The electronic structure of these materials is unique: they exhibit two distinct, coexisting types of electride behavior, with both fully localized pseudo anions and electrons localized in 1D wells in the host lattice, leading to low conductivity. While all phases feature pseudogaps in the electronic density of states, the perturbative free-electron picture applies to Na, but not to K and Rb, due to significant d-orbital population in the latter.

Update: 23-May-2018

Title:
Dzyaloshinskii-Moriya interaction and magnetic anisotropies in Uranium compounds
Authors:
Sandratskii, LM Author Full Names: Sandratskii, L. M.
Source:
PHYSICA B-CONDENSED MATTER, 536 512-515; 10.1016/j.physb.2017.11.014 MAY 1 2018
Abstract:
We report on the first-principles study of complex noncollinear magnetic structures in Uranium compounds. We contrast two cases. The first is the periodic magnetic structure of U2Pd2In with exactly orthogonal atomic moments, the second is an incommensurate plane spiral structure of UPtGe where the angle between atomic moments of nearest neighbors is also close to 90 degrees. We demonstrate that the hierarchy of magnetic interactions leading to the formation of the magnetic structure is opposite in the two cases. In U2Pd2In, the magnetic anisotropy plays the leading role, followed by the Dzyaloshinskii-Moriya interaction (DMI) interaction specifying the chirality of the structure. Here, the interatomic exchange interaction does not play important role. In UPtGe the hierarchy of the interactions is opposite. The leading interaction is the interatomic exchange interaction responsible for the formation of the incommensurate spiral structure followed by the DMI responsible for the selected chirality of the helix. The magnetic anisotropy is very weak that is a prerequisite for keeping the distortion of the helical structure weak.
Title:
Magnetic excitations in the orbital disordered phase of MnV2O4
Authors:
Matsuura, K; Sagayama, H; Uehara, A; Nii, Y; Kajimoto, R; Kamazawa, K; Ikeuchi, K; Ji, S; Abe, N; Arima, TH Author Full Names: Matsuura, Keisuke; Sagayama, Hajime; Uehara, Amane; Nii, Yoichi; Kajimoto, Ryoichi; Kamazawa, Kazuya; Ikeuchi, Kazuhiko; Ji, Sungdae; Abe, Nobuyuki; Arima, Taka-hisa
Source:
PHYSICA B-CONDENSED MATTER, 536 372-376; 10.1016/j.physb.2017.09.085 MAY 1 2018
Abstract:
We have investigated the temperature dependence of magnetic dynamics in a spinel-type vanadium oxide MnV2O4 by inelastic neutron scattering. The scattering intensity of excitation around 20 meV disappears in the collinear intermediate-temperature cubic-ferrimagnetic phase, which reveals that this excitation should be peculiar to the orbital ordered phase. We have found a weakly dispersive mode emergent from a non-integer wavevector (1.4,1.4,0) at 56 K, which lies in the cubic-ferrimagnetic phase between non-coplanar ferrimagnetic and paramagnetic phases. This indicates that the probable presence of an incommensurate instability in the simple collinear structure.
Title:
Magnetic and thermodynamic studies on the charge and spin ordering in the highly-doped La2-xSrxCoO4
Authors:
Yoshida, M; Ueta, D; Ikeda, Y; Yokoo, T; Itoh, S; Yoshizawa, H Author Full Names: Yoshida, Masahiro; Ueta, Daichi; Ikeda, Yoichi; Yokoo, Tetsuya; Itoh, Shinichi; Yoshizawa, Hideki
Source:
PHYSICA B-CONDENSED MATTER, 536 338-341; 10.1016/j.physb.2017.10.081 MAY 1 2018
Abstract:
We report magnetic studies on the charge and spin ordering in La2-xSrxCoO4 for x = 1/3, 0.60, and 0.75. The magnetic susceptibility displays a clear cusp which we attribute to a spin glass freezing transition in all three compositions stduied. The behaviors of the evaluated effective magnetic moment and Curie-Weiss temperature indicate that the antiferromagnetic (AFM) interaction among Co2+ ions surrounded by the non-magnetic Co3+ weakens with increasing the doping concentration x. In addition, we have found that the incommensurate AFM short range order is frozen at T-g which is further below the onset temperature TIC of the neutron intensity of the incommensurate AFM correlation.
Title:
Detailed study of the structure of the low-energy magnetic excitations in overdoped La1.75Sr0.25CuO4
Authors:
Ikeuchi, K; Kikuchi, T; Nakajima, K; Kajimoto, R; Wakimoto, S; Fujita, M Author Full Names: Ikeuchi, Kazuhiko; Kikuchi, Tatsuya; Nakajima, Kenji; Kajimoto, Ryoichi; Wakimoto, Shuichi; Fujita, Masaki
Source:
PHYSICA B-CONDENSED MATTER, 536 717-719; 10.1016/j.physb.2017.11.022 MAY 1 2018
Abstract:
To examine the detailed structure of low-energy magnetic excitations in a high-transition-temperature superconducting cuprate with heavily hole-doping, we performed inelastic neutron scattering experiments on La1.75Sr0.25CuO4. We observed clear dispersion relations of the previously reported incommensurate (IC) magnetic correlations at Qtet = (0.5 +/- d, 0.5)/(0.5, 0.5 +/- delta) [1]. In addition, we show the emergence of continuum magnetic excitations with a ring shape centered at G point Q(tet) = (0.5, 0.5) in a constant energy spectrum at Gamma = 50K. The radius of the ring (r = 0.109) is smaller than the incommensurability (delta = 0.118). This suggests that the origin of the ring-like excitations is different from that of the IC magnetic correlations, and the low-energy magnetic excitations of the La2-xSrxCuO4 system are inherently composed of these two kinds of excitations.
Title:
Fluctuation effects at the onset of the 2k(F) density wave order with one pair of hot spots in two-dimensional metals
Authors:
Sykora, J; Holder, T; Metzner, W Author Full Names: Sykora, Jachym; Holder, Tobias; Metzner, Walter
Source:
PHYSICAL REVIEW B, 97 (15):10.1103/PhysRevB.97.155159 APR 30 2018
Abstract:
We analyze quantum fluctuation effects at the onset of charge or spin density wave order in two-dimensional metals with an incommensurate 2k(F) wave vector connecting a single pair of hot spots on the Fermi surface. We compute the momentum and frequency dependence of the fermion self-energy near the hot spots to leading order in a fluctuation expansion (one loop). Non-Fermi liquid behavior with anomalous frequency scaling and a vanishing quasiparticle weight is obtained. The momentum dependence yields a divergent renormalization of the Fermi velocity and a flattening of the Fermi surface near the hot spots. Going beyond the leading-order calculation, we find that the one-loop result is not self-consistent. We show that any momentum-independent self-energy with a non-Fermi liquid frequency exponent wipes out the peak of the polarization function at the 2k(F) wave vector, and thus destroys the mechanism favoring 2k(F) density waves over those with generic wave vectors. However, a 2k(F) density wave quantum critical point might survive in presence of a sufficiently flat renormalized Fermi surface.
Title:
Refinement of the Modulated Structures of Pb-Free and Pb-Doped Bi-2223 HTSC
Authors:
Shcherban, O; Akselrud, L; Giannini, E; Gladyshevskii, R Author Full Names: Shcherban, O.; Akselrud, L.; Giannini, E.; Gladyshevskii, R.
Source:
ACTA PHYSICA POLONICA A, 133 (4):1027-1029; 10.12693/APhysPolA.133.1027 APR 2018
Abstract:
The incommensurate modulated structures of Pb-free and Pb-doped Bi-2223 phases were refined on single crystal X-ray diffraction data.

Update: 16-May-2018

Title:
First-principles study of giant thermoelectric power in incommensurate TlInSe2
Authors:
Ishikawa, M; Nakayama, T; Wakita, K; Shim, YG; Mamedov, N Author Full Names: Ishikawa, M.; Nakayama, T.; Wakita, K.; Shim, Y. G.; Mamedov, N.
Source:
JOURNAL OF APPLIED PHYSICS, 123 (16):10.1063/1.5011337 APR 28 2018
Abstract:
Ternary thallium compound TlInSe2 exhibits a giant Seebeck effect below around 410 K, where Tl atoms form one dimensional incommensurate (IC) arrays. To clarify the origin of large thermoelectric power in the IC phase, the electronic properties of Tl-atom super-structured TlInSe2 were studied using the first-principles calculations. It was shown that the super-structures induce strong binding states between Se-p orbitals in the nearest neighboring layers and produce large density of states near lower conduction bands, which might be one of the origins to produce large thermoelectric power. Published by AIP Publishing.
Title:
The Effect of Doping on the Corrosion Behavior of Quasi-Crystalline Alloys in the Al-Cu-Fe-Cr System
Authors:
Chugunov, DB; Klyuchagina, AN; Meshkov, LL; Osipov, AK Author Full Names: Chugunov, D. B.; Klyuchagina, A. N.; Meshkov, L. L.; Osipov, A. K.
Source:
PROTECTION OF METALS AND PHYSICAL CHEMISTRY OF SURFACES, 54 (2):301-307; 10.1134/S2070205118020041 MAR 2018
Abstract:
The electrochemical behavior of five alloys of variable compositions in the Al65Cu25Fe10-N... Cr (N...) system in dependence on the number of QC phases in acidic and alkaline media has been investigated by the potentiodynamic method. It has been established that the samples' corrosion stabilities increase along with the increase of the solution pH. Higher stability was manifested by alloys with a predominant quasi-crystalline (dexagonal and icosahedral) structural component.

Update: 9-May-2018

Title:
Field-induced magnetic phase transitions and metastable states in Tb3Ni
Authors:
Gubkin, AF; Wu, LS; Nikitin, SE; Suslov, AV; Podlesnyak, A; Prokhnenko, O; Prokes, K; Yokaichiya, F; Keller, L; Baranov, NV Author Full Names: Gubkin, A. F.; Wu, L. S.; Nikitin, S. E.; Suslov, A. V.; Podlesnyak, A.; Prokhnenko, O.; Prokes, K.; Yokaichiya, F.; Keller, L.; Baranov, N. V.
Source:
PHYSICAL REVIEW B, 97 (13):10.1103/PhysRevB.97.134425 APR 26 2018
Abstract:
In this paper we report the detailed study of magnetic phase diagrams, low-temperature magnetic structures, and the magnetic field effect on the electrical resistivity of the binary intermetallic compound Tb3Ni. The incommensurate magnetic structure of the spin-density-wave type described with magnetic superspace group P112(1)/a1'(ab0)0ss and propagation vector k(IC) = [0.506, 0.299,0] was found to emerge just below Neel temperature T-N = 61 K. Further cooling below 58 K results in the appearance of multicomponent magnetic states: (i) a combination of k(1) = [1/2, 1/2, 0] and k(IC) in the temperature range 51 < T < 58 K; (ii) a mixed magnetic state of k(IC), k(1), and k(2) = [1/2, 1/4, 0] with the partially locked-in incommensurate component in the temperature range 48 < T < 51 K; and (iii) a low-temperature magnetic structure that is described by the intersection of two isotropy subgroups associated with the irreducible representations of two coupled primary order parameters (OPs) k(2) = [1/2, 1/4, 0] and k(3) = [1/2, 1/3, 0] and involves irreducible representations of the secondary OPs k(1) = [1/2, 1/2, 0] and k(4) = [1/2, 0, 0] below 48 K. An external magnetic field suppresses the complex low-temperature antiferromagnetic states and induces metamagnetic transitions towards a forced ferromagnetic state that are accompanied by a substantial magnetoresistance effect due to the magnetic superzone effect. The forced ferromagnetic state induced after application of an external magnetic field along the b and c crystallographic axes was found to be irreversible below 3 and 8 K, respectively.
Title:
Improved electrochemical hydrogen storage performance of Ti49Zr26Ni25 quasicrystal alloy by doping with mesoporous alpha-Fe2O3 particles
Authors:
Liu, H; Zhai, XJ; Li, Z; Tao, X; Liu, WQ; Zhao, JX Author Full Names: Liu, Heng; Zhai, Xiaojie; Li, Zhe; Tao, Xing; Liu, Wanqiang; Zhao, Jianxun
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 43 (15):7447-7455; 10.1016/j.ijhydene.2018.02.149 APR 12 2018
Abstract:
A Ti49Zr26Ni25 quasicrystal alloy was prepared by mechanical alloying and subsequent annealing. Mesoporous alpha-Fe2O3 particles were obtained via a hydro-thermal procedure using chitosan as the template. Composites of Ti49Zr26Ni25 mixed with different amounts of mesoporous alpha-Fe2O3 were synthesized to enhance the electrochemical properties of Ti49Zr26Ni25. The structural characteristics of the alloy and composites were investigated using XRD, SEM, TEM and BET analysis. The electrochemical properties of the composite electrodes were tested using a three-electrode battery system at room temperature. The discharge capacities for the composites were higher than those for the Ti49Zr26Ni25 alloy and reached a maximum (259.6 mAh/g) for 5% additive content of alpha-Fe2O3. Moreover, the composites showed enhanced high-rate dischargeability. The capacity decay rate and charge-transfer resistance decreased after alpha-Fe2O3 loading. The preferable performance of the composite alloys may be attributed to the doping of mesoporous alpha-Fe2O3, which may play a catalytic effect in the kinetics of the electrochemical reactions. The large surface area and mesoporous structure of alpha-Fe2O3 may also be advantageous for rapid transmission of hydrogen in the interior of the alloy, thus improving the discharge capacity of the alloy electrode. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Update: 2-May-2018

Title:
The Tetrachloridoaurates(III) of Zinc(II) and Cadmium(II)
Authors:
Landvogt, C; Beck, J Author Full Names: Landvogt, Christian; Beck, Johannes
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 644 (7):391-396; 10.1002/zaac.201700455 APR 17 2018
Abstract:
The first salt-like compounds of dications with [AuCl4](-) anions are reported. The compounds Zn[AuCl4](2)(AuCl3)(1.115) (1) and Cd[AuCl4](2) (2) are obtained from reactions of MCl2 (M = Zn, Cd) and elemental gold in liquid chlorine at ambient temperature under autogenous pressure and subsequent annealing at 230 degrees C. The structure of 1 represents an incommensurately modulated composite [superspace group C2/c(0)0s] built of two subsystems. The first subsystem contains chains of zinc(II) tetrachloridoaurate(III), which feature a slightly distorted octahedral coordination of Zn and can be described by the Niggli formula (1){Zn[AuCl4](1/1)[AuCl4](2/2)}. The second subsystem consists of Au2Cl6 molecules, which are located in channels built up by the first subsystem. The structural parameters of the hosted Au2Cl6 molecules show only small deviations from neat AuCl3. The crystal structure of Cd[AuCl4](2) (2) consists of chains built of Cd2+ ions coordinated by bridging [AuCl4](-) anions and alternating Cd-Au sequence. Cd has a distorted octahedral coordination environment.

Update: 25-Apr-2018

Title:
Large-sized quasi-crystals with continuously adjustable compositions
Authors:
Li, ZJ; Zhao, LR; Pan, SP; Fan, CZ; Qiang, JB; Dong, C; Wang, LM Author Full Names: Li, Zijing; Zhao, Linran; Pan, Shaopeng; Fan, Changzeng; Qiang, Jianbing; Dong, Chuang; Wang, Li-Min
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 746 356-360; 10.1016/j.jallcom.2018.02.341 MAY 25 2018
Abstract:
The quasi-crystal-forming alloys with adjustable compositions were prepared by element-addition to a pre-existing pure quasi-crystalline system. The protocol alloy Zr40Ti40Ni20 was chosen as the parent alloy, and beryllium was used as the additive element. The quasi-crystal forming ability was found to be enhanced with Be content within a wide composition range of (Zr40Ti40Ni20)(100-x)Be-x (0 <= x <= 16). A maximum size of up to 10mm in diameter of pure quasi-crystalline rod was attained at a composition of (Zr40Ti40Ni20)(84)Be-16. Structural analyses show that Be-addition continuously reduces the interplanar spacing. The mechanism of the enhanced quasi-crystal forming ability was also discussed. (c) 2018 Elsevier B.V. All rights reserved.
Title:
Effects of crystalline electronic field and onsite interorbital interaction in Yb-based quasicrystal and approximant crystal
Authors:
Watanabe, S; Miyake, K Author Full Names: Watanabe, Shinji; Miyake, Kazumasa
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 30 (18):10.1088/1361-648X/aab817 MAY 10 2018
Abstract:
To get an insight into a new type of quantum critical phenomena recently discovered in the quasicrystal Yb15Al34Au51 and approximant crystal (AC) Yb14Al35Au51 under pressure, we discuss the property of the crystalline electronic field (CEF) at Yb in the AC and show that uneven CEF levels at each Yb site can appear because of the Al/Au mixed sites. Then we construct the minimal model for the electronic state on the AC by introducing the onsite Coulomb repulsion between the 4f and 5d orbitals at Yb. Numerical calculations for the ground state shows that the lattice constant dependence of the Yb valence well explains the recent measurement done by systematic substitution of elements of Al and Au in the quasicrystal and AC, where the quasicrystal Yb15Al34Au51 is just located at the point from where the Yb-valence starts to change drastically. Our calculation convincingly demonstrates that this is indeed the evidence that this material is just located at the quantum critical point of the Yb-valence transition.
Title:
Partially-devitrified icosahedral quasicrystalline phase in Ti33.33Zr33.33Hf13.33Ni20 and Zr30Hf30Ni15Cu10Ti15 amorphous alloys with near equi-atomic compositions
Authors:
Takeuchi, A; Amiya, K; Yubuta, K Author Full Names: Takeuchi, A.; Amiya, K.; Yubuta, K.
Source:
MATERIALS CHEMISTRY AND PHYSICS, 210 245-250; SI 10.1016/j.matchemphys.2017.10.057 MAY 1 2018
Abstract:
Ti33.33Zr33.33Hf13.33Ni20 and Zr30Hf30Ni15Cu10Ti15 alloys were investigated for their possibility to be formed into a high-entropy alloy (HEA) with a quasicrystalline (QC) structure that contains an icosahedral-(I-) phase. The melt-spun alloys quenched at a circumference speed of 39 m/s were formed into an amorphous single phase. The amorphous alloys annealed up to a temperature between the first and second crystallization temperatures exhibited mixed phases of I- and remaining amorphous phases. Observation of the Zr30Hf30Ni15Cu10Ti15 amorphous alloy heated up to 745 K with transmission electron microscope revealed the presence of precipitates with diameters ranging 10-20 nm. Nano-beam diffraction demonstrated that the precipitates were identified to be the I-phase with the five-, three and two-fold symmetries. The Ti33.33Zr33.33Hf13.33Ni20 and Zr30Hf30Ni15Cu10Ti15 alloys were not formed into a single quasicrystalline phase as HEAs, but the discussions of the current and early experimental data led to provide the way to approach high-entropy quasicrystalline alloys (HE-QCs). (C) 2017 Elsevier B.V. All rights reserved.
Title:
Phase diagram of antimony up to 31 GPa and 835 K
Authors:
Coleman, AL; Stevenson, M; McMahon, MI; Macleod, SG Author Full Names: Coleman, A. L.; Stevenson, M.; McMahon, M. I.; Macleod, S. G.
Source:
PHYSICAL REVIEW B, 97 (14):10.1103/PhysRevB.97.144107 APR 13 2018
Abstract:
X-ray powder diffraction experiments using resistively heated diamond anvil cells have been conducted in order to establish the phase behavior of antimony up to 31 GPa and 835 K. The dip in the melting curve at 5.7 GPa and 840 K is identified as the triple point between the Sb-I, incommensurate Sb-II, and liquid phases. No evidence of the previously reported simple cubic phase was observed. Determination of the phase boundary between Sb-II and Sb-III suggests the existence of a second triple point in the region of 13 GPa and 1200 K. The incommensurate composite structure of Sb-II was found to remain ordered to the highest temperatures studies-no evidence of disordering of the guest-atom chains was observed. Indeed, the modulation reflections that arise from interactions between the host and guest subsystems were found to be present to the highest temperatures, suggesting such interactions remain relatively strong in Sb even in the presence of increased thermal motion. Finally, we show that the incommensurately modulated structure recently reported as giving an improved fit to diffraction data from incommensurate Ba-IV can be rejected as the structure of Sb-II using a simple density argument.
Title:
Phase transitions in ferroelectric 4-amino-pyridinium tetrachloroantimonate(III) - revisited
Authors:
Gagor, A Author Full Names: Gagor, Anna
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 74 217-225; 10.1107/S2052520618003669 2 APR 2018
Abstract:
New X-ray diffraction studies on the crystal structure of ferroelectric [4-NH2C5H4NH][SbCl4] indicate that in the broad temperature range from 240 to 304 K covering the three intermediate phases, the crystal structure is modulated. Phase II is incommensurately modulated with modulation vector q = beta b*, beta varying from 0.60 to 0.66 and monoclinic C2/c(0 beta 0)s0 superspace group. Ferroelectric phase III is commensurate with q = 2/3b* and Cc(0 beta 0)0 symmetry. Polar phase IV is incommensurately modulated with beta varying from 0.66 to 0.70 and Cc(0 beta 0)0 superspace group. In all phases only first-order satellites are observed along the b* direction. Two types of periodic deformation are present in the structure of modulated phases. The 4-aminopyridinium cations are subjected to occupation modulation whereas [SbCl4](n)(-) chains are displacively modulated. The paraelectric-ferroelectric phase transition is an example of the incommensurate-commensurate transition of the lock-in type. A new mechanism for this transformation is proposed.
Title:
Revisiting the I(1)over-bar structures of high-temperature Ca-rich plagioclase feldspar - a single-crystal neutron and X-ray diffraction study
Authors:
Jin, SY; Wang, XP; Xu, HF Author Full Names: Jin, Shiyun; Wang, Xiaoping; Xu, Huifang
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 74 152-164; 10.1107/S2052520618003219 2 APR 2018
Abstract:
The I (1) over bar structures of four natural Ca-rich plagioclase feldspars formed at high temperature were analysed using single-crystal neutron and X-ray diffraction. The neutron time-of-flight Laue diffractometer at the ORNL Spallation Neutron Source (Tennessee, USA) combined with a single-crystal X-ray diffraction instrument were able to reveal some new details about these already intensively studied structures. The split oxygen atoms refined from the neutron diffraction data show the underlying mechanism of Ca-Na ordering and the anisotropic P (1) over bar ordering along the c-axis. The compositional ranges covered by the samples studied are quite rare for I (1) over bar structures. The incommensurately modulated e2 structure of some plagioclase samples can easily be confused with an I (1) over bar structure from the diffraction pattern, which puts some previously published I (1) over bar structures into question. An incomplete phase diagram for Ca-rich plagioclase feldspar is proposed to explain the rarity of the I (1) over bar structure in this compositional range, and a time-temperature-transformation diagram for the composition similar to An(66) is provided accordingly.

Update: 18-Apr-2018

Title:
Incommensurately modulated phase and charge ordering transition in nanocrystalline Nd0.5Sr0.5MnO3 perovskite
Authors:
Shankar, U; Pandey, R; Singh, AK Author Full Names: Shankar, Uma; Pandey, Rishikesh; Singh, Akhilesh Kumar
Source:
JOURNAL OF APPLIED PHYSICS, 123 (12):10.1063/1.5007199 MAR 28 2018
Abstract:
We report here the "incommensurate modulated" phase along with the ferromagnetic character in nanocrystalline Nd0.5Sr0.5MnO3 perovskite. The Rietveld analysis of powder X-ray diffraction data reveals that the structure of nanocrystalline Nd0.5Sr0.5MnO3 ceramic can be described as a modulated phase in the monoclinic structure with space group Pm and lattice parameters a(m) approximate to 2a(o), b(m) approximate to b(o), and c(m) approximate to 3c(o), where a(o), b(o), and c(o) correspond to the lattice parameters of the parent ortho-rhombic structure for the bulk sample at room temperature. Increasing the crystallite size converts the modulated monoclinic structure to an orthorhombic structure with the Imma space group for the bulk Nd0.5Sr0.5MnO3 sample. The magnetic measurements on nanocrystalline samples reveal ferromagnetic behaviour and the absence of charge ordering transition at low temperatures. The nanocrystalline samples also exhibit Griffith phase like behaviour near the paramagnetic to ferromagnetic phase transition. The Powder X-ray diffraction study of bulk Nd0.5Sr0.5MnO3 in the temperature range of 13 K-300K reveals the transition from the orthorhombic to the monoclinic structure in the P2(1)/m space group with the coexistence of the two phases in a wide temperature range below room temperature. Published by AIP Publishing.

Update: 11-Apr-2018

Title:
Thermal transport properties, magnetic susceptibility and neutron diffraction studies of the (Cr100-xAlx)(95)Mo-5 alloy system
Authors:
Muchono, B; Sheppard, CJ; Venter, AM; Prinsloo, ARE Author Full Names: Muchono, B.; Sheppard, C. J.; Venter, A. M.; Prinsloo, A. R. E.
Source:
PHYSICA B-CONDENSED MATTER, 537 212-224; 10.1016/j.physb.2018.02.018 MAY 15 2018
Abstract:
Previous electrical resistivity (rho) and specific heat (C-P) studies on the ternary (Cr100-xAlx)(95)Mo-5 alloy system suggested that it harbours two quantum critical points (QCPs). This study reports comprehensive investigations of this alloy system through Seebeck coefficient oSthorn, thermal conductivity (kappa) magnetic susceptibility o.thorn and neutron diffraction oNDthorn measurements in the concentration range 0 <= x 8.6. The results of (kappa) and (chi) show that spin-density-wave (SDW) antiferromagnetism is suppressed to temperatures below 2 K for concentrations in the range 1.4 <= x <= 4.4. Plots of dS= dT in the limit as T -> 2 K depict two minima, i. e. just above x = 1.4 and 4.4. This parameter has been used as a key indicator of quantum critical behaviour (QCB) in Cr alloys. Analyses against the Nordheim-Gorter relationship demonstrates a positive slope for the incommensurate (I) SDW alloys and a negative slope for the commensurate (C) SDW alloys. Extrapolations of these two slopes intercept at a concentration of 3.2 at.% Al indicating the occurrence of band structure modifications when Al is added into the Cr95Mo5 base alloy. The Lorenz number oLthorn for the alloys with x = 0 and 0.5 shows interesting anomalous behaviour associated with band structure effects and SDW magnetic ordering. ND measurements as a function of temperature confirm that alloys with x < 1.4 order in the incommensurate (I) SDW phase whilst alloys with x > 4.4 show commensurate (C) SDW order. Power law fits of the form T-N alpha(1.40 - x)(0.35) (+/-0.05) for the ISDW to P phase transition and T-N alpha (x- 4. 40)(0.63) (+/-0.03) for the P to CSDW phase transition rendered the critical exponents 0: 35 +/- 0: 05 and 0: 63 +/- 0: 03 respectively. Overall the results of S,.,. and ND corroborate the existence of two QCPs at x approximate to 1.4 and 4.4.
Title:
Microphases deriving from Ba2ZrF8 structure type: II: Crystal structure of Sr17Zr9F70 and Sr(17.145)ZT(9)F(70.29)
Authors:
Laval, JP; Rafik, H; Trolliard, G Author Full Names: Laval, Jean-Paul; Rafik, Hamid; Trolliard, Gilles
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 260 151-158; 10.1016/j.jssc.2018.01.005 APR 2018
Abstract:
In the domain Sr1-xZrxF2+2 (x) studied at 670 degrees C between the limits 0.333 <= x <= 0.353, Sr2ZrF8 (x = 0.333) cannot be obtained under our synthesis conditions but a new phase Sr17Zr9F70 (x = 0.346) is characterized which clearly shows a great analogy with Ba2ZrF8 and Pb2ZrF8 already described. It presents the same Pnma space group and derives from this basic type by the relation: a = 28.812(10) angstrom = 3 x a(Ba2ZrF8); b = 16.566(6) angstrom = 3 x b(Ba2ZrF8); c = 11.433(4)angstrom = c(Ba2ZrF8). The superlattice along a results from a change in the step of zigzag parallel rows of respectively Sr cations and ZrF8 polyhedra. The zigzag step is not composition-dependent but more likely depends on the size of the M2+ cation. The superlattice along b results from an ordered creation of Sr vacancies of multiplicity m = 3 (1 vacancy for 3 Sr) in some Sr raws which changes the Sr/Zr ratio from 2/1 to 1.889/1 (x = 0.346). Then the superstructure along b accommodates the change in stoichiometry in Sr within this phase from Sr18Zr9F72 (9 x "Sr2ZrF8") to Sr17Zr9F70. A second structure of close composition (x = 0.344) shows that the vacant Sr site can be partially occupied in a disordered way by a small proportion of Sr, giving a composition slightly closer to "Sr2ZrF8". Compared to Sr17Zr8F70, the over-stoichiometry mechanism is a solid solution model. For Zr contents comprised between x = 0.346 and 0.353, a series of modulated phases corresponding to various more or less ordered sequences of Sr cations and Sr vacancies along b are characterized by electron diffraction and TEM lattice imaging. They can be interpreted as intermediate between limit phases Sr17Zr9F70 (x = 0.346) and Sr11Zr6F46 (x = 0.353), of respective multiplicities m = 3 and m = 2 along the same b direction and of modulation vectors q = 1/3b* and q = 1/2b*. Several modulated phases with q modulation vector comprised between 1/3 b* and 1/2 b* can be characterized.
Title:
Stairlike Aurivillius Phases in the Pseudobinary Bi5Nb3O15-ABi(2)Nb(2)O(9) (A = Ba and Sr) System: A Comprehensive Analysis Using Superspace Group Formalism
Authors:
Steciuk, G; Barrier, N; Pautrat, A; Boullay, P Author Full Names: Steciuk, Gwladys; Barrier, Nicolas; Pautrat, Alain; Boullay, Philippe
Source:
INORGANIC CHEMISTRY, 57 (6):3107-3115; 10.1021/acs.inorgchem.7b03026 MAR 19 2018
Abstract:
We report the possibility of extending the so-called stairlike Aurivilius phases in the pseudobinary Bi5Nb3O15-ABi(2)Nb(2)O(9) (A = Ba and Sr) over a wide range of compositions. These phases are characterized by a discontinuous stacking of [Bi2O2] slabs and perovskite blocks, leading to long-period intergrowths stabilized as a single phase. When analyses from precession electron diffraction tomography and Xray and neutron powder diffraction are combined, the monoclinic incommensurately modulated structure with q = alpha a* + gamma c* previously proposed for the ABi(7)Nb(5)O(24) composition could be generalized to the Bi5Nb3O15-ABi(2)Nb(2)O(9) (A = Ba and Sr) compounds. Considering the compositions expressed as (A,Bi)(1-x)NbxO3-3x, the stacking sequence associated with compositions ranging from x = 2/5 to 3/8 is governed by the component gamma of the modulation vector and can be predicted following a Farey tree hierarchy independently to the A cation. The length of the steps, characteristic of the stairlike nature, is controlled by the alpha component and depends on the substitution ratio A/Bi and the nature of A (A = Ba and Sr). This study highlights the compositional flexibility of stairlike Aurivillius phases.
Title:
Kinetically Controlled Formation and Decomposition of Metastable [(BiSe)(1+delta)](m)[TiSe2](m) Compounds
Authors:
Lygo, AC; Hamann, DM; Moore, DB; Merrill, DR; Ditto, J; Esters, M; Orlowicz, J; Wood, SR; Johnson, DC Author Full Names: Lygo, Alexander C.; Hamann, Danielle M.; Moore, Daniel B.; Merrill, Devin R.; Ditto, Jeffrey; Esters, Marco; Orlowicz, Jacob; Wood, Suzannah R.; Johnson, David C.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 140 (9):3385-3393; 10.1021/jacs.7b13398 MAR 7 2018
Abstract:
Preparing homologous series of compounds allows chemists to rapidly discover new compounds with predictable structure and properties. Synthesizing compounds within such a series involves navigating a free energy landscape defined by the interactions within and between constituent atoms. Historically, synthesis approaches are typically limited to forming only the most thermodynamically stable compound under the reaction conditions. Presented here is the synthesis, via self-assembly of designed precursors, of isocompositional incommensurate layered compounds[(BiSe)(1+delta)](m)[TiSe2](m) , with m = 1, 2, and 3. The structure of the BiSe bilayer in the m = 1 compound is not that of the binary compound, and this is the first example of compounds where a BiSe layer thicker than a bilayer in heterostructures has been prepared. Specular and in-plane X-ray diffraction combined with high-resolution electron microscopy data was used to follow the formation of the compounds during low-temperature annealing and the subsequent decomposition of the m = 2 and 3 compounds into [(BiSe)(1+delta)](1)[TiSe2](1) at elevated temperatures. These results show that the structure of the precursor can be used to control reaction kinetics, enabling the synthesis of kinetically stable compounds that are not accessible via traditional techniques. The data collected as a function of temperature and time enabled us to schematically construct the topology of the free energy landscape about the local free energy minima for each of the products.
Title:
The Mystery of the Auln 1:1 Phase and Its Incommensurate Structural Variations
Authors:
Folkers, LC; Simonov, A; Wang, F; Lidin, S Author Full Names: Folkers, Laura C.; Simonov, Arkadiy; Wang, Fei; Lidin, Sven
Source:
INORGANIC CHEMISTRY, 57 (5):2791-2796; 10.1021/acs.inorgchem.7b03206 MAR 5 2018
Abstract:
In this communication, the AuIn 1:1 phase (Naturwissenschaften, 1953, 40, 437, DOI: 10.1007/BF00590353), and its ordering behavior at various temperatures is investigated. To enable the growth of a X-ray suitable specimen, a tempering routine was established by the interpretation of a differential scanning calorimetry (DSC) study. In this way, good quality single crystals were grown and measured at the Crystal beamline at Synchrotron SOLEIL. From the acquired data, three variations of this structure could be found at temperatures of 400 degrees C and 300 degrees C and room temperature, with differing degrees of incommensurate modulation. Diffuse scattering found at 400 degrees C was interpreted with the help of a three-dimensional difference pair distribution function (3D-Delta PDF) study.
Title:
Formation of Quasicrystalline Phases and Their Close Approximants in Cast Al-Mn Base Alloys Modified by Transition Metals
Authors:
Stan-Glowinska, K Author Full Names: Stan-Glowinska, Katarzyna
Source:
CRYSTALS, 8 (2):10.3390/cryst8020061 FEB 2018
Abstract:
The aim of the presented research was to study the influence of Cr, Co, Ni, and Cu additions on the formation of quasicrystalline particles in the 94Al-6Mn base alloy during casting at intermediate cooling rates. Based on the obtained results, Cu and Ni enhance quasicrystalline phase nucleation compared to the unmodified binary composition. In the case of Cu addition, formation of a quasicrystalline phase takes place along whole thickness of the prepared casting, but its fraction and morphology depends on the cooling rates present in different parts of the sample. Based on the previous works on the beneficial effect of Fe addition, a quaternary alloy containing both Fe and Cu was prepared to evaluate the effect of the simultaneous presence of these elements on the microstructure of the obtained castings.
Title:
Possible nucleus of the Bergman cluster in the Zn-Mg-Y alloy system
Authors:
Nakayama, K; Nakagawa, M; Koyama, Y Author Full Names: Nakayama, Kei; Nakagawa, Masaya; Koyama, Yasumasa
Source:
PHILOSOPHICAL MAGAZINE, 98 (3):219-236; 10.1080/14786435.2017.1400703 2018
Abstract:
To understand the formation of the Bergman cluster in the F-type icosahedral quasicrystal (IQ), crystallographic relations between the quasicrystal and the intermetallic-compound H and Zn23Y6 phases in the ZnMgY alloy system were investigated mainly by transmission electron microscopy. It was found that, although sample rotations of about 1 degrees were required to obtain simple crystallographic relations, the orientation relationship was established among the cubic-Fmm Zn23Y6 structure, the hexagonal-P6(3)/mmc H structure and the F-type IQ; that is, [(1) over bar 1 3](c) // the five-fold axis in the IQ // N(2 (1) over bar(1) over bar0)(H), and [1 1 1](c) // the two-fold axis in the IQ // N(0 5 (5) over bar3)(H), where N(h k m l)(H) means the normal direction of the (h k m l)(H) plane in the H structure. The correspondences between atomic positions in the Bergman cluster and in the Zn23Y6 structure and between those in the cluster and in the H structure were investigated on the basis of the established relationship. As a result, an assembly of six short-penetrated-decagonal columns was identified as an appropriate nucleus in the formation of the Bergman cluster from these two structures.

Update: 4-Apr-2018

Title:
Spin wave propagation spectra in Octonacci one-dimensional magnonic quasicrystals
Authors:
Valeriano, AP; Costa, CH; Bezerra, CG Author Full Names: Valeriano, Analine P.; Costa, Carlos H.; Bezerra, Claudionor G.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 456 228-235; 10.1016/j.jmmm.2018.02.042 JUN 15 2018
Abstract:
In this paper, we study spin wave propagation in quasiperiodic magnonic superlattices that follow the so-called Octonacci quasiperiodic sequence, where the N-th stage can be obtained through the recurrence rule S-N = SN-1SN-2SN-1, for N >= 3, and starting with S-1 = A and S-2 = B. The multilayered magnonic nanostructure is composed of two simple cubic ferromagnetic materials, labeled A and B, which interact through bilinear and biquadratic exchange couplings at their interfaces. The ferromagnetic materials are described by the Heisenberg model, and a transfer matrix treatment is employed, with the calculations performed for the exchange-dominated regime, taking the random phase approximation (RPA) into account. The obtained numerical results show the effects of both (i) the Octonacci quasiperiodic sequence and (ii) the biquadratic exchange coupling on the band structure and transmission spectra of spin waves. Comparisons are also performed with the spectra found in other periodic and quasiperiodic structures. (C) 2018 Elsevier B.V. All rights reserved.
Title:
Building 2D quasicrystals from 5-fold symmetric corannulene molecules
Authors:
Kalashnyk, N; Ledieu, J; Gaudry, E; Cui, C; Tsai, AP; Fournee, V Author Full Names: Kalashnyk, Nataliya; Ledieu, Julian; Gaudry, Emilie; Cui, Can; Tsai, An-Pang; Fournee, Vincent
Source:
NANO RESEARCH, 11 (4):2129-2138; 10.1007/s12274-017-1830-x APR 2018
Abstract:
The formation of long-range ordered aperiodic molecular films on quasicrystalline substrates is a new challenge that provides an opportunity for further surface functionalization. This aim can be realized through the smart selection of molecular building blocks, based on symmetry-matching between the underlying quasicrystal and individual molecules. It was previously found that the geometric registry between the C-60 molecules and the 5- and 10-fold surfaces was key to the growth of quasiperiodic organic layers. However, an attempt to form a quasiperiodic C-60 network on i-Ag-In-Yb substrates was unsuccessful, resulting in disordered molecular films. Here we report the growth of 5-fold symmetric corannulene C20H10 molecules on the 5-fold surfaces of i-Ag-In-Yb quasicrystals. Low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) revealed long-range quasiperiodic order and 5-fold rotational symmetry in self-assembled corannulene films. Recurrent decagonal molecular rings were seen, resulting from the decoration of specific adsorption sites with local pentagonal symmetry by corannulenes, adsorbed with their bowl-openings pointing away from the surface. They were identified as (Ag, In)-containing rhombic triacontahedral (RTH) cluster centers and pentagonal Yb motifs, which cannot be occupied simultaneously due to steric hindrance. It is proposed that symmetry-matching between the molecule and specific substrate sites drives this organization. Alteration of the molecular rim by the introduction of CH substituents appeared to increase molecule mobility on the potential energy surface and facilitate trapping at these specific sites. This finding suggests that rational selection of molecular moiety enables the templated self-assembly of molecules leading to an ordered aperiodic corannulene layer.
Title:
SU(5) grand unified theory, its polytopes and 5-fold symmetric aperiodic tiling
Authors:
Koca, M; Koca, NO; Al-Siyabi, A Author Full Names: Koca, Mehmet; Koca, Nazife Ozdes; Al-Siyabi, Abeer
Source:
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS, 15 (4):10.1142/S0219887818500561 APR 2018
Abstract:
We associate the lepton-quark families with the vertices of the 4D polytopes 5-cell (0001) (A4) and the rectified 5-cell (0100) (A4) derived from the SU(5) Coxeter-Dynkin diagram. The off-diagonal gauge bosons are associated with the root polytope (1001) A(4) whose facets are tetrahedra and the triangular prisms. The edge-vertex relations are interpreted as the SU(5) charge conservation. The Dynkin diagram symmetry of the SU(5) diagram can be interpreted as a kind of particle-antiparticle symmetry. The Voronoi cell of the root lattice consists of the union of the polytopes (1000) (A4) + (0100) (A4) + (0010) (A4) + (0001) (A4) whose facets are 20 rhombohedra. We construct the Delone (Delaunay) cells of the root lattice as the alternating 5-cell and the rectified 5-cell, a kind of dual to the Voronoi cell. The vertices of the Delone cells closest to the origin consist of the root vectors representing the gauge bosons. The faces of the rhombohedra project onto the Coxeter plane as thick and thin rhombs leading to Penrose-like tiling of the plane which can be used for the description of the 5-fold symmetric quasicrystallography. The model can be extended to SO(10) and even to SO(11) by noting the Coxeter-Dynkin diagram embedding A(4) subset of D-5 subset of B-5. Another embedding can be made through the relation A(4) subset of D-5 subset of E-6 for more popular GUT's. Appendix A includes the quaternionic representations of the Coxeter-Weyl groups W(A(4)) subset of W(H-4) which can be obtained directly from W(E-8) by projection. This leads to relations of the SU(5) polytopes with the quasicrystallography in 4D and E-8 polytopes. Appendix B discusses the branching of the polytopes in terms of the irreducible representations of the Coxeter-Weyl group W(A(4)) approximate to S-5.
Title:
Charge Order and Superconductivity in Underdoped YBa2Cu3O7-delta under Pressure
Authors:
Putzke, C; Ayres, J; Buhot, J; Licciardello, S; Hussey, NE; Friedemann, S; Carrington, A Author Full Names: Putzke, Carsten; Ayres, Jake; Buhot, Jonathan; Licciardello, Salvatore; Hussey, Nigel E.; Friedemann, Sven; Carrington, Antony
Source:
PHYSICAL REVIEW LETTERS, 120 (11):10.1103/PhysRevLett.120.117002 MAR 16 2018
Abstract:
In underdoped cuprates, an incommensurate charge density wave (CDW) order is known to coexist with superconductivity. A dip in T-c at the hole doping level where the CDW is strongest (n(p) similar or equal to 0.12) suggests that CDW order may suppress superconductivity. We investigate the interplay of charge order with superconductivity in underdoped YBa2Cu3O7-d(delta) by measuring the temperature dependence of the Hall coefficient R-H(T) at high magnetic field and at high hydrostatic pressure. We find that, although pressure increases T-c by up to 10 K at 2.6 GPa, it has very little effect on R-H(T). This suggests that pressure, at these levels, only weakly affects the CDW and that the increase in T-c with pressure cannot be attributed to a suppression of the CDW. We argue, therefore, that the dip in T-c at n(p) similar or equal to 0.12 at ambient pressure is probably not caused by the CDW formation.

Update: 28-Mar-2018

Title:
Simultaneous localization of photons and phonons in defect-free dodecagonal phoxonic quasicrystals
Authors:
Xu, BH; Wang, Z; Tan, YX; Yu, TB Author Full Names: Xu, Bihang; Wang, Zhong; Tan, Yixiang; Yu, Tianbao
Source:
MODERN PHYSICS LETTERS B, 32 (7):10.1142/S0217984918500963 MAR 10 2018
Abstract:
In dodecagonal phoxonic quasicrytals (PhXQCs) with a very high rotational symmetry, we demonstrate numerically large phoxonic band gaps (PhXBGs, the coexistence of photonic and phononic band gaps). By computing the existence and dependence of PhXBGs on the choice of radius of holes, we find that PhXQCs can possess simultaneous photonic and phononic band gaps over a rather wide range of geometric parameters. Furthermore, localized modes of THz photons and tens of MHz phonons may exist inside and outside band gaps in defect-free PhXQCs. The electromagnetic and elastic field can be confined simultaneously around the quasicrytals center and decay in a length scale of several basic cells. As a kind of quasiperiodic structures, 12-fold PhXQCs provide a good candidate for simultaneously tailoring electromagnetic and elastic waves. Moreover, these structures exhibit some interesting characteristics due to the very high symmetry.

Update: 21-Mar-2018

Title:
Two spin-canting textures in the antiferromagnetic phase AF1 of MnWO4 based on the new polar atomistic model in P2
Authors:
Park, SH; Liu, BQ; Behal, D; Pedersen, B; Schneidewind, A Author Full Names: Park, S-H; Liu, B-Q; Behal, D.; Pedersen, B.; Schneidewind, A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 30 (13):10.1088/1361-648X/aaaeae APR 4 2018
Abstract:
The low temperature antiferromagnetic (AF) phase of MnWO4 (the so-called AF1 phase) exhibits different spin-canting configurations at two Mn2+ sublattices of the (3 + 1)-dimensional magnetic structure. The suggested superspace group P2.1'(alpha, 1/2, gamma)0s is a significant consequence of the polar space group P2 true for the nuclear structure of MnWO4. Density functional theory calculations showed that its ground state prefers this two spin-canting system. The structural difference between two independent atomic sites for Mn (Mn-a, Mn-b) is too small to allow microscopically detectable electric polarisation. However, this hidden intrinsic polar character allows AF1 two commensurately modulated spin-canting textures. This is considered as the prerequisite onset of the improper ferroelectricity enhanced by the helical spin order in the multiferroic phase AF2 of MnWO4.
Title:
The incommensurately modulated crystal structure of roshchinite, Cu0.09Ag1.04Pb0.65Sb2.82As0.37S6.08
Authors:
Makovicky, E; Stoger, B; Topa, D Author Full Names: Makovicky, Emil; Stoger, Berthold; Topa, Dan
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 233 (3-4):255-267; 10.1515/zkri-2017-2126 MAR 2018
Abstract:
The Pb-Ag-Sb sulfide roshchinite, Cu0.09Ag1.04Pb0.65Sb2.82As0.37S6.08, is a lillianite homologue N = 4 with a complex incommensurate superstructure in the 8.46 angstrom direction of the orthorhombic crystal lattice with a 19.0804(1) angstrom, b 8.4591(2) angstrom and c 12.9451(3) angstrom, superspace group Pbcn(0 sigma(2)0)00s, q = 0.41458(3) b*. A structure solution and refinement in (3+1) superspace, based on 10,019 observed reflections and 437 refined parameters was terminated at R-obs (wR) equal to 7.27 (8.07)% using satellites up to second order; R-obs is 4.82 for main reflections only. The Pb atoms in trigonal coordination prisms on planes of unit-cell twinning are semiperiodically replaced by antimony. The marginal columns of (311)(PbS) slabs of the Sb-Ag based structure which is based on PbS-like topology contain Sb, Ag(Cu) and mixed Ag/Sb sites in a complicated sequence. Central portions of the slabs are occupied by Sb-S crankshaft chains, best exposed on the (100) PbS planes, which run diagonally across the slabs. In these planes, in their majority the chains display Sb3S4 form and two opposing orientations, zig-zagging along the [010] direction. Every six chains, a parallel configuration of two chains occurs, but occasionally this interval is reduced to five chains. This, together with related compositional changes in the Pb- and Ag-Sb column, explains the one-dimensionally incommensurate character of roshchinite. Modestly elevated contents of As replacing Sb are the probable reason of modulation and non-commensurability in roshchinite.
Title:
The (3+3) commensurately modulated structure of the uranyl silicate mineral swamboite-(Nd), Nd-0.333[(UO2)(SiO3OH)](H2O)(2.41)
Authors:
Plasil, J; Petricek, V; Locock, AJ; Skoda, R; Burns, PC Author Full Names: Plasil, Jakub; Petricek, Vaclav; Locock, Andrew J.; Skoda, Radek; Burns, Peter C.
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 233 (3-4):223-231; 10.1515/zkri-2017-2119 MAR 2018
Abstract:
The uranyl mineral swamboite has been redefined to swamboite-(Nd) and its structure has been solved and refined as a commensurate structure in six-dimensional superspace. The structure is monoclinic, superspace group P2(1)/m(a1, b1, g1) 00(-a1, b1, g1) 00 (a2,0,g2)0s, cell parameters a = 6.6560(3), b = 6.9881(5), c = 8.8059(6), c = 11.3361(16) angstrom, beta = 102.591(5)degrees, modulation wave-vectors q(1) = 1/3 1/3 0; q(2) = - 1/3 1/3 0; q(3) = 1/2 0 1/2. The structure was refined from 8717 reflections to a final R = 0.0610. The model includes modulation both of atomic positions and displacement parameters, as well as occupancy waves. The structure is based upon uranyl-silicate sheets of uranophane topology alternating with an inter-layer of partly occupied Nd3+ sites and H2O molecules. The strong (3 + 3) dimensional modulation of the structure originates from the distribution of the Nd-dominated sites and further accommodation of the suitable geometry within the sheets and charge distribution within the structure. The separation distances between the corres-ponding occupied Nd sites are rationals of the super-cell vectors corresponding to the modulation vectors of the structure. The case of swamboite-(Nd) is the first example of a modulated structure within the oxysalts of U6+.
Title:
Frustration and thermalization in an artificial magnetic quasicrystal
Authors:
Shi, D; Budrikis, Z; Stein, A; Morley, SA; Olmsted, PD; Burnell, G; Marrows, CH Author Full Names: Shi, Dong; Budrikis, Zoe; Stein, Aaron; Morley, Sophie A.; Olmsted, Peter D.; Burnell, Gavin; Marrows, Christopher H.
Source:
NATURE PHYSICS, 14 (3):309-+; 10.1038/s41567-017-0009-4 MAR 2018
Abstract:
Artificial frustrated systems offer a playground to study the emergent properties of interacting systems. Most work to date has been on spatially periodic systems, known as artificial spin ices when the interacting elements are magnetic. Here we have studied artificial magnetic quasicrystals based on quasiperiodic Penrose tiling patterns of interacting nanomagnets. We construct a low-energy configuration from a step-by-step approach that we propose as a ground state. Topologically induced emergent frustration means that this configuration cannot be constructed from vertices in their ground states. It has two parts, a quasione- dimensional 'skeleton' that spans the entire pattern and is capable of long-range order, surrounding ` flippable' clusters of macrospins that lead to macroscopic degeneracy. Magnetic force microscopy imaging of Penrose tiling arrays revealed superdomains that are larger for more strongly coupled arrays, especially after annealing the array above its blocking temperature.
Title:
Coordination numbers of the vertex graph of a Penrose tiling
Authors:
Shutov, A; Maleev, A Author Full Names: Shutov, Anton; Maleev, Andrey
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 112-122; 10.1107/S2053273318000062 2 MAR 2018
Abstract:
A new approach to study coordination shells and coordination sequences of quasiperiodic graphs is suggested. The structure of the coordination shells in the vertex graph of a Penrose tiling is described. An asymptotic formula for its coordination numbers is obtained. An essentially different behaviour of the coordination numbers for even and odd shells is revealed.
Title:
Deformation Behavior and Structure of i-Al-Cu-Fe Quasicrystalline Alloy in Vicinity of Nanoindenter Indentation
Authors:
Shalaeva, EV; Selyanin, IO; Smirnova, EO; Smirnov, SV; Novachek, DD Author Full Names: Shalaeva, E. V.; Selyanin, I. O.; Smirnova, E. O.; Smirnov, S. V.; Novachek, D. D.
Source:
PHYSICS OF THE SOLID STATE, 60 (2):312-319; 10.1134/S1063783418020233 FEB 2018
Abstract:
The nanoindentation tests have been carried out for the quasicrystalline polygrain Al62.4Cu25.3Fe12.3 alloy with the icosahedral structure i; the load P-displacement h diagrams have been used to estimate the contributions of plastic deformation (monotonic and intermittent), and the structures of the transverse microscopic sections have been studied in the vicinity of indentations by electron microscopy. It is shown that several systems of deformation bands are formed in the elasto-plastic zone in the vicinity of the indentations along the close-packed planes of the i lattice with the five-fold and two-fold symmetry axes; the bands often begin from cracks and manifest the signs of the dislocation structure. The traces of the phase transformation with the formation of the beta-phase areas are observed only in a thin layer under an indenter. The effects of intermittent deformation are up to 50% of the total inelastic deformation and are related to the plastic behavior of the quasicrystal-activation and passage of deformation bands and also the formation of undersurface micro- and nanosized cracks.

Update: 14-Mar-2018

Title:
Melt holding time as an important factor on the formation of quasicrystal phase in Mg67Zn30Gd3 alloy
Authors:
Zhang, JY; Jia, P; Zhao, DG; Teng, XY Author Full Names: Zhang, Jinyang; Jia, Peng; Zhao, Degang; Teng, Xinying
Source:
PHYSICA B-CONDENSED MATTER, 533 28-32; 10.1016/j.physb.2017.12.052 MAR 15 2018
Abstract:
In the present work, the content of icosahedral quasicrystal phase (I-phase) and melt holding time shows a mono peak curve: a small amount of I-phase and lots of Mg-3(Gd, Zn) phase are presented for t < 21 min, however a great deal of I-phase is observed for t > 21 min, and the volumetric fraction of I-phase has the maximum of 49.50% for t = 41 min. This strategy of formation of quasicrystal phase makes us realize that melt thermal treatment could significantly affect the phase types in Mg-Zn-Gd alloy.
Title:
Multi-q Mesoscale Magnetism in CeAuSb2
Authors:
Marcus, GG; Kim, DJ; Tutmaher, JA; Rodriguez-Rivera, JA; Birk, JO; Niedermeyer, C; Lee, H; Fisk, Z; Broholm, CL Author Full Names: Marcus, Guy G.; Kim, Dae-Jeong; Tutmaher, Jacob A.; Rodriguez-Rivera, Jose A.; Birk, Jonas Okkels; Niedermeyer, Christof; Lee, Hannoh; Fisk, Zachary; Broholm, Collin L.
Source:
PHYSICAL REVIEW LETTERS, 120 (9):10.1103/PhysRevLett.120.097201 FEB 28 2018
Abstract:
We report the discovery of a field driven transition from a single-q to multi-q spin density wave (SDW) in the tetragonal heavy fermion compound CeAuSb2. Polarized along c, the sinusoidal SDW amplitude is 1.8(2)mu(B)/Ce for T << T-N = 6.25(10)K with a wave vector q(1) = (eta, eta, 1/2) [eta = 0.136(2)]. For H parallel to c, harmonics appearing at 2q(1) evidence a striped magnetic texture below mu H-degrees(1) = 2.78(1)T. Above H-1, these are replaced by coupled harmonics at q(1) + q(2) = (2 eta, 0, 0) + c* until mu H-degrees(2) = 5.42(5)T, where satellites vanish and magnetization nonlinearly approaches saturation at 1.64(2)mu(B)/Ce for mu H-degrees approximate to 7T.
Title:
High-strength Mg-6Zn-1Y-1Ca (wt%) alloy containing quasicrystalline I-phase processed by a powder metallurgy route
Authors:
Medina, J; Perez, P; Garces, G; Stark, A; Schell, N; Adeva, P Author Full Names: Medina, J.; Perez, P.; Garces, G.; Stark, A.; Schell, N.; Adeva, P.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 715 92-100; 10.1016/j.msea.2017.12.111 FEB 7 2018
Abstract:
A high-strength Mg-6Zn-1Y-1Ca (wt%) alloy has been processed by a powder metallurgy route. Rapidly solidified powders with a particle size below 100 tun were used as a way for preventing formation of ternary MgZnCa compounds during subsequent extrusion at 250 degrees C. The microstructure of the extruded alloy consists of an ultrafine-grain magnesium matrix, with an average grain size of 444 nm, embedding a high volume fraction of fine I-phase particles aligned along the extrusion direction. The alloy combines an excellent ductility (14% of elongation to failure) with a high strength (ultimate strength of 469 MPa and yield stress of 461 MPa) at room temperature, mainly due to grain size refinement (around 70% of the yield stress). The strength is kept high up to 150 degrees C (yield stress of 279 MPa). Above this temperature, the mechanical strength falls to very low values but the ability to deform plastically is considerably enhanced, exhibiting superplastic behaviour from 200 to 350 degrees C, with a maximum elongation of 477% at 350 degrees C.
Title:
Parallels in Structural Chemistry between the Molecular and Metallic Realms Revealed by Complex Intermetallic Phases
Authors:
Fredrickson, DC Author Full Names: Fredrickson, Daniel C.
Source:
ACCOUNTS OF CHEMICAL RESEARCH, 51 (2):248-257; 10.1021/acs.accounts.7b00625 FEB 2018
Abstract:
CONSPECTUS: The structural diversity of intermetallic phases poses a great challenge to chemical theory and materials design. In this Account, two examples are used to illustrate how a focus on the most complex of these structures (and their relationships to simpler ones) can reveal how chemical principles underlie structure for broad families of compounds. First, we show how experimental investigations into the Fe-Al-Si system, inspired by host-guest like features in the structure of Fe25Al78Si20, led to a theoretical approach to deriving isolobal analogies between molecular and intermetallic compounds and a more general electron counting rule. Specifically, the Fe(8)Al(17.6)Si(7.4)compound obtained in these syntheses was traced to a fragmentation of the fluorite-type structure (as adopted by NiSi2), driven by the maintenance of 18-electron configurations on the transition metal centers.& para;& para;The desire to quickly generalize these conclusions to a broader range of phases motivated the formulation of the reversed approximation Molecular Orbital (raMO) approach. The application of raMO to a diverse series of compounds allowed us recognize the prevalence of electron pair sharing in multicenter functions isolobal to classical covalent bonds and to propose the 18 - n electron rule for transition metal-main group (T-E) intermetallic compounds. These approaches provided a framework for understanding the 14-electron rule of the Nowotny Chimney Ladder phases, a temperature-driven phase transition in GdCoSi2, and the bcc-structure of group VI transition metals.& para;& para;In the second story, we recount the development of the chemical pressure approach to analyzing atomic size and packing effects in intermetallic structures. We begin with how the stability of the Yb2Ag7-type structure of Ca2Ag7 over the more common CaCu(5 )type highlights the pressing need for approaches to assessing the role of atomic size in crystal structures, and inspired the development of the DFT-Chemical Pressure (CP) method. Examples of structural phenomena elucidated by this approach are then given, including the Y/Co(2 )dumbbell substitution in the Th2Zn17-type phase Y2Co17, and local icosahedral order in the Tsai-type quasicrystal approximant CaCd6. We next discuss how deriving relationships between the CP features of a structure and its phonon modes provided a way of both validating the method and visualizing how local arrangements can give rise to soft vibrational modes. The themes of structural mechanisms for CP relief and soft atomic motions merge in the discovery and elucidation of the incommensurately modulated phase CaPd5. In the conclusion of this Account, we propose combining raMO and CP methods for focused predictions of structural phenomena.
Title:
In Situ Synthesis and Single Crystal Synchrotron X-ray Diffraction Study of ht-Sn3Sb2: An Example of How Complex Modulated Structures Are Becoming Generally Accessible
Authors:
Lidin, S; Folkers, LC Author Full Names: Lidin, Sven; Folkers, Laura C.
Source:
ACCOUNTS OF CHEMICAL RESEARCH, 51 (2):223-229; 10.1021/acs.accounts.7b00508 FEB 2018
Abstract:
Recent developments in X-ray sources and detectors and the parallel development of software for nonstandard crystallography has made analysis of very complex structural problems accessible to nonexperts. Here, we report the successful solution of the structure of ht-Sn3Sb2, an analysis that presents several challenges but that is still manageable in a relatively straightforward way. This compound exists only in a narrow temperature regime and undergoes an unquenchable phase transformation on cooling to room temperature; it contains two elements with close to identical scattering factors, and the structure is incommensurately modulated with four symmetry dependent modulation wave vectors. In this study, an attempt was first made to synthesize the title compound by in-house crystal growth in the stability region of ht-Sn3Sb2, followed by cooling to room temperature. This is known to produce mutiply twinned stistaite and elemental tin, and this sample, freshly prepared, was then reheated in situ at the single crystal materials beamline Crystal at the synchrotron Soleil. This method was unsuccessful as reheating the sample led to loss of Sn from stistaite as revealed by a change in the measured modulation wave vector. The compound was instead successfully synthesized in situ at the beamline by the topochemical reaction of single crystalline stistaite and liquid tin. A well-formed crystal of stistaite was enclosed in a quartz capillary together with a large excess of tin and heated above the melting point of tin but below the melting point of ht-Sn3Sb2. The structure was probed by sychrotron X-ray diffraction using a wavelength close to the absorption edge of Sn to maximize elemental contrast. In the diffraction patterns, first order satellites were observed, making the structure of ht-Sn3Sb2 incommensurately modulated. Further analysis exposes four q-vectors running along the body diagonals of the cubic unit cell (q(1)' = alpha alpha alpha, q(2)' = -alpha alpha -alpha, q3' = -alpha -alpha alpha, q(4)' = alpha-alpha-alpha). To facilitate the analysis, the q vectors were instead treated as axial (q(1) = alpha 0 0, q(2) = 0 alpha 0, q(3) = 0 0 alpha) and an F-type extinction condition for satellites was introduced so that only reflections with hklmnp, mnp all odd or all even, were considered. Further, the modulation functions F(q(i)) were set to zero, and only modulation functions of the type F(q(i)') were refined. The final model uses the four modulation functions, F(q(1)'), F(q(2)'), F(q(3)'), and F(q(4)'), to model occupancy Sn/Sb and positional modulation. The model shows a structure that comprises small NaCl type clusters, typically 7 x 7 x 7 atoms in extension, interspersed between single layers of elemental tin. The terminating layers of tin are slightly puckered, emulating an incipient deformation toward the structure of the layers perpendicular to the [001] direction in elemental tin. It is notable that this model is complementary to that of stistaite. In stistaite, two-dimensionally infinite slabs of rock salt are interspersed between layers of antimony along the trigonal [001] direction, so that the terminating Sb layers are the puckered bilayers typical for elemental Sb. Since all modulation functions are simple first-order harmonics, the structural model describes a locally disordered and most probably dynamic ordering.

Update: 7-Mar-2018

Title:
Shear localization and size-dependent strength of YCd6 quasicrystal approximant at the micrometer length scale
Authors:
Song, G; Kong, T; Dusoe, KJ; Canfield, PC; Lee, SW Author Full Names: Song, Gyuho; Kong, Tai; Dusoe, Keith J.; Canfield, Paul C.; Lee, Seok-Woo
Source:
JOURNAL OF MATERIALS SCIENCE, 53 (9):6980-6990; 10.1007/s10853-018-2043-8 MAY 2018
Abstract:
Mechanical properties of materials are strongly dependent of their atomic arrangement as well as the sample dimension, particularly at the micrometer length scale. In this study, we investigated the small-scale mechanical properties of single-crystalline YCd6, which is a rational approximant of the icosahedral Y-Cd quasicrystal. In situ microcompression tests revealed that shear localization always occurs on {101} planes, but the shear direction is not constrained to any particular crystallographic directions. Furthermore, the yield strengths show the size dependence with a power law exponent of 0.4. Shear localization on {101} planes and size-dependent yield strength are explained in terms of a large interplanar spacing between {101} planes and the energetics of shear localization process, respectively. The mechanical behavior of the icosahedral Y-Cd quasicrystal is also compared to understand the influence of translational symmetry on the shear localization process in both YCd6 and Y-Cd quasicrystal micropillars. The results of this study will provide an important insight in a fundamental understanding of shear localization process in novel complex intermetallic compounds.
Title:
Precipitation of binary quasicrystals along dislocations
Authors:
Yang, ZQ; Zhang, LF; Chisholm, MF; Zhou, XZ; Ye, HQ; Pennycook, SJ Author Full Names: Yang, Zhiqing; Zhang, Lifeng; Chisholm, Matthew F.; Zhou, Xinzhe; Ye, Hengqiang; Pennycook, Stephen J.
Source:
NATURE COMMUNICATIONS, 9 10.1038/s41467-018-03250-8 FEB 23 2018
Abstract:
Dislocations in crystals naturally break the symmetry of the bulk, introducing local atomic configurations with symmetries such as fivefold rings. But dislocations do not usually nucleate aperiodic structure along their length. Here we demonstrate the formation of extended binary quasicrystalline precipitates with Penrose-like random-tiling structures, beginning with chemical ordering within the pentagonal structure at cores of prismatic dislocations in Mg-Zn alloys. Atomic resolution observations indicate that icosahedral chains centered along [0001] pillars of Zn interstitial atoms are formed templated by the fivefold rings at dislocation cores. They subsequently form columns of rhombic and elongated hexagonal tiles parallel to the dislocation lines. Quasicrystalline precipitates are formed by random tiling of these rhombic and hexagonal tiles. Such precipitation may impact dislocation glide and alloy strength.
Title:
From Quasicrystals to Crystals with Interpenetrating Icosahedra in Ca-Au-Al: In Situ Variable-Temperature Transformation
Authors:
Pham, J; Meng, FQ; Lynn, M; Ma, T; Kreyssig, A; Kramer, MJ; Goldman, AI; Miller, GJ Author Full Names: Pham, Joyce; Meng, Fanqiang; Lynn, Matthew.; Ma, Tao; Kreyssig, Andreas; Kramer, Matthew J.; Goldman, Alan I.; Miller, Gordon J.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 140 (4):1337-1347; 10.1021/jacs.7b10358 JAN 31 2018
Abstract:
The irreversible transformation from an icosahedral quasicrystal (i-QC) CaAu4.39Al1.61 to its cubic 2/1 crystalline approximant (CA) Ca13Au56.31 Al-(3)(21.69) (CaAu4.33(1)Al1.67, Pa (3) over bar (No. 205); Pearson symbol: cP728; a = 23.8934(4)), starting at similar to 570 degrees C and complete by similar to 650 degrees C, is discovered from in situ, high-energy, variable-temperature powder X-ray diffraction (PXRD), thereby providing direct experimental evidence for the relationship between QCs and their associated CAs. The new cubic phase crystallizes in a Tsai-type approximant structure under the broader classification of polar intermetallic compounds, in which atoms of different electronegativities, viz., electronegative Au + Al vs electropositive Ca, are arranged in concentric shells. From a structural chemical perspective, the outermost shell of this cubic approximant may be described as interpenetrating and edge-sharing icosahedra, a perspective that is obtained by splitting the traditional structural description of this shell as a 92-atom rhombic triacontahedron into an 80-vertex cage of primarily Au [Au59.86(2)Al17.14 square(3.00)] and an icosahedral shell of only Al [Al-10.5 square(1.5)]. Following the proposal that the cubic 2/1 CA approximates the structure of the i-QC and on the basis of the observed transformation, an atomic site analysis of the 2/1 CA, which shows a preference to maximize the number of heteroatomic Au-Al nearest neighbor contacts over homoatomic Al-Al contacts, implies a similar outcome for the i-QC structure. Analysis of the most intense reflections in the diffraction pattern of the cubic 2/1 CA that changed during the phase transformation shows correlations with icosahedral symmetry, and the stability of this cubic phase is assessed using valence electron counts. According to electronic structure calculations, a cubic 1/1 CA, "Ca24Au88Al (64)" (CaAu3.67Al2.67) is proposed.

Update: 1-Mar-2018

Title:
On the kinetic and equilibrium shapes of icosahedral Al71Pd19Mn10 quasicrystals
Authors:
Senabulya, N; Xiao, XH; Han, I; Shahani, AJ Author Full Names: Senabulya, Nancy; Xiao, Xianghui; Han, Insung; Shahani, Ashwin J.
Source:
SCRIPTA MATERIALIA, 146 218-221; 10.1016/j.scriptamat.2017.11.049 MAR 15 2018
Abstract:
The dynamics of growth and relaxation of icosahedral single quasicrystals in a liquid phase were investigated using in situ synchrotron-based X-ray tomography. Our 4D studies (i.e., space- and time-resolved) provide direct evidence that indicates the growth process of an Al71Pd19Mn10 quasicrystal is governed predominantly by bulk transport rather than attachment kinetics. This work is in agreement with theoretical predictions, which show that the pentagonal dodecahedron is not the minimum energy structure in Al-Pd-Mn icosahedral quasicrystals, but merely a growth shape characterized by non-zero anisotropic velocity. This transient shape transforms into a truncated dodecahedral Archimedian polyhedron once equilibrium has been attained. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
A Cesium Rare-Earth Silicate Cs3RESi6O15 (RE = Dy-Lu, Y, In): The Parent of an Unusual Structural Class Featuring a Remarkable 57 angstrom Unit Cell Axis
Authors:
Terry, R; Vinton, D; McMillen, CD; Kolis, JW Author Full Names: Terry, Rylan; Vinton, Daniel; McMillen, Colin D.; Kolis, Joseph W.
Source:
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 57 (8):2077-2080; 10.1002/anie.201708798 FEB 19 2018
Abstract:
The structure of Cs3RESi6O15, where RE=Dy-Lu, Y, In, is unusual in that it contains octahedrally coordinated rare-earth ions; their relative orientation dictates the structure, as they rotate about the c-axis supported by the cyclic Si6O15 framework. The repeat unit of the rotation is eight units generating a very long (ca. 57 angstrom) unit cell axis. This unusual repeat unit is created by the structural flexibility of the hexasilicate ring, which is in turn affected by the size of the rare earth ion as well as the size of alkali ion residing within the silicate layers. Previous work showed for the smaller Sc3+ ion, the rotation of the octahedra is not sufficient to achieve closure at an integral repeat unit and an incommensurate structure results. The products are prepared as large, high quality single crystals using a high-temperature (650 degrees C) hydrothermal method with CsOH and F- mineralizers. The presence of fluoride is essential to the formation of the product.
Title:
Enhancement and destruction of spin-Peierls physics in a one-dimensional quantum magnet under pressure
Authors:
Rotundu, CR; Wen, JJ; He, W; Choi, Y; Haskel, D; Lee, YS Author Full Names: Rotundu, Costel R.; Wen, Jiajia; He, Wei; Choi, Yongseong; Haskel, Daniel; Lee, Young S.
Source:
PHYSICAL REVIEW B, 97 (5):10.1103/PhysRevB.97.054415 FEB 15 2018
Abstract:
The application of pressure reveals a rich phase diagram for the quantum S = 1/2 spin chain material TiOCl. We performed x-ray diffraction on single-crystal samples in a diamond-anvil cell down to T = 4 K and pressures up to 14.5 GPa. Remarkably, the magnetic interaction scale increases dramatically with increasing pressure, as indicated by the high onset temperature of the spin-Peierls phase. The spin-Peierls phase was probed at similar to 6 GPa up to 215 K but possibly extends in temperature to above T = 300 K, indicating the possibility of a quantum singlet state at room temperature. Near the critical pressure for the transition to the more metallic phase, coexisting phases are exemplified by incommensurate order in two directions. Further comparisons are made with the phase diagrams of related spin-Peierls systems that display metallicity and superconductivity under pressure.
Title:
Effect of imperfections on the hyperuniformity of many-body systems
Authors:
Kim, J; Torquato, S Author Full Names: Kim, Jaeuk; Torquato, Salvatore
Source:
PHYSICAL REVIEW B, 97 (5):10.1103/PhysRevB.97.054105 FEB 12 2018
Abstract:
A hyperuniform many-body system is characterized by a structure factor S(k) that vanishes in the small-wave-number limit or equivalently by a local number variance sigma(2)(N) (R) associated with a spherical window of radius R that grows more slowly than R-d in the large-R limit. Thus, the hyperuniformity implies anomalous suppression of long-wavelength density fluctuations relative to those in typical disordered systems, i.e., sigma(2)(N) (R) similar to R-d as R -> infinity. Hyperuniform systems include perfect crystals, quasicrystals, and special disordered systems. Disordered hyperuniform systems are amorphous states of matter that lie between a liquid and crystal [S. Torquato et al., Phys. Rev. X 5, 021020 (2015)], and have been the subject of many recent investigations due to their novel properties. In the same way that there is no perfect crystal in practice due to the inevitable presence of imperfections, such as vacancies and dislocations, there is no "perfect" hyperuniform system, whether it is ordered or not. Thus, it is practically and theoretically important to quantitatively understand the extent to which imperfections introduced in a perfectly hyperuniform system can degrade or destroy its hyperuniformity and corresponding physical properties. This paper begins such a program by deriving explicit formulas for S(k) in the small-wave-number regime for three types of imperfections: (1) uncorrelated point defects, including vacancies and interstitials, (2) stochastic particle displacements, and (3) thermal excitations in the classical harmonic regime. We demonstrate that our results are in excellent agreement with numerical simulations. We find that "uncorrelated" vacancies or interstitials destroy hyperuniformity in proportion to the defect concentration p. We show that "uncorrelated" stochastic displacements in perfect lattices can never destroy the hyperuniformity but it can be degraded such that the perturbed lattices fall into class III hyperuniform systems, where sigma(2)(N) (R) similar to Rd-alpha as R -> infinity and 0 < alpha < 1. By contrast, we demonstrate that certain "correlated" displacements can make systems nonhyperuniform. For a perfect (ground-state) crystal at zero temperature, increase in temperature T introduces such correlated displacements resulting from thermal excitations, and thus the thermalized crystal becomes nonhyperuniform, even at an arbitrarily low temperature. It is noteworthy that imperfections in disordered hyperuniform systems can be unambiguously detected. Our work provides the theoretical underpinnings to systematically study the effect of imperfections on the physical properties of hyperuniform materials.
Title:
Magnetoelectric and Raman spectroscopic studies of monocrystalline MnCr2O4
Authors:
Lin, GT; Wang, YQ; Luo, X; Ma, J; Zhuang, HL; Qian, D; Yin, LH; Chen, FC; Yan, J; Zhang, RR; Zhang, SL; Tong, W; Song, WH; Tong, P; Zhu, XB; Sun, YP Author Full Names: Lin, G. T.; Wang, Y. Q.; Luo, X.; Ma, J.; Zhuang, H. L.; Qian, D.; Yin, L. H.; Chen, F. C.; Yan, J.; Zhang, R. R.; Zhang, S. L.; Tong, W.; Song, W. H.; Tong, P.; Zhu, X. B.; Sun, Y. P.
Source:
PHYSICAL REVIEW B, 97 (6):10.1103/PhysRevB.97.064405 FEB 12 2018
Abstract:
MnCr2O4 that exhibits spin frustration and complex spiral spin order is of great interest from both fundamental as well as application-oriented perspectives. Unlike CoCr2O4, whose ground state presents the coexistence of commensurate spiral spin order (CSSO) and ferroelectric order, MnCr2O4 shows no multiferroicity. One reason is that the spiral spin order is highly sensitive to the oxygen concentration in MnCr2O4. Here, we have successfully grown high-quality single-crystalline MnCr2O4 by the chemical vapor transport method. We observe a first-order magnetic transition from the incommensurate spiral spin order (ICSSO) at 19.4 K to the CSSO at 17.4 K. This magnetic transition is verified by magnetization, specific heat, and magnetoelectric measurements, which also confirm that the ground state exhibits the coexistence of the CSSO and magnetoelectricity below 17.4 K. Interestingly, the temperature evolution of Raman spectra between 5.4 and 300 K suggests that the structure remains the same. We also find that the phase-transition temperature of the CSSO decreases as applied magnetic field increases up to 45 kOe.
Title:
Magnetic state selected by magnetic dipole interaction in the kagome antiferromagnet NaBa2Mn3F11
Authors:
Hayashida, S; Ishikawa, H; Okamoto, Y; Okubo, T; Hiroi, Z; Avdeev, M; Manuel, P; Hagihala, M; Soda, M; Masuda, T Author Full Names: Hayashida, Shohei; Ishikawa, Hajime; Okamoto, Yoshihiko; Okubo, Tsuyoshi; Hiroi, Zenji; Avdeev, Maxim; Manuel, Pascal; Hagihala, Masato; Soda, Minoru; Masuda, Takatsugu
Source:
PHYSICAL REVIEW B, 97 (5):10.1103/PhysRevB.97.054411 FEB 12 2018
Abstract:
We haved studied the ground state of the classical kagome antiferromagnet NaBa2Mn3F11. Strong magnetic Bragg peaks observed for d spacings shorter than 6.0 angstrom were indexed by the propagation vector of k(0) = (0,0,0). Additional peaks with weak intensities in the d-spacing range above 8.0 angstrom were indexed by the incommensurate vector of k(1) = [0.3209(2), 0.3209(2), 0] and k(2) = [0.3338(4), 0.3338(4), 0]. Magnetic structure analysis unveils a 120 degrees. structure with the tail-chase geometry having k(0) modulated by the incommensurate vector. A classical calculation of the Heisenberg kagome antiferromagnet with antiferromagnetic second-neighbor interaction, for which the ground state a k(0) 120 degrees. degenerated structure, reveals that the magnetic dipole-dipole (MDD) interaction including up to the fourth neighbor terms selects the tail-chase structure. The observed modulation of the tail-chase structure is attributed to a small perturbation such as the long-range MDD interaction or the interlayer interaction.
Title:
Magnetic structure of the swedenborgite CaBa(Co3Fe)O-7 derived by unpolarized neutron diffraction and spherical neutron polarimetry
Authors:
Qureshi, N; Diaz, MTF; Chapon, LC; Senyshyn, A; Schweika, W; Valldor, M Author Full Names: Qureshi, N.; Diaz, M. T. Fernandez; Chapon, L. C.; Senyshyn, A.; Schweika, W.; Valldor, M.
Source:
PHYSICAL REVIEW B, 97 (6):10.1103/PhysRevB.97.064404 FEB 9 2018
Abstract:
We present a study that combines polarized and unpolarized neutrons to derive the magnetic structure of the swedenborgite compound CaBa(Co3Fe)O-7. Integrated intensities from a standard neutron diffraction experiment and polarization matrices from spherical neutron polarimetry have been simultaneously analyzed revealing a complex order, which differs from the usual spin configurations on a kagome lattice. We find that the magnetic structure is well described by a combination of two one-dimensional representations corresponding to themagnetic superspace symmetry P2(1)' and it consists of spins rotating around an axis close to the [110] direction. Due to the propagation vector q = (1/300), this modulation has cycloidal and helicoidal character rendering this system a potential multiferroic. The resulting spin configuration can be mapped onto the classical root 3 x root 3 structure of a kagome lattice, and it indicates an important interplay between the kagome and the triangular layers of the crystal structure.
Title:
Atomic channel occupation in disordered eta-Al5Fe2 and in two of its low-temperatures phases, eta '' and eta '''
Authors:
Becker, H; Leineweber, A Author Full Names: Becker, Hanka; Leineweber, Andreas
Source:
INTERMETALLICS, 93 251-262; 10.1016/j.intermet.2017.09.021 FEB 2018
Abstract:
High-temperature, disordered n-Al5Fe2 intermetallic and its low-temperature long-range ordered structures have been investigated in the whole homogeneity range from 70.6 to 73.0 at.% Al based on selected area electron diffraction data and powder X-ray diffraction data. Using these data, the channel site occupation in the disordered eta phase has been revised and a composition-dependent model with mixed occupation of the channels by both Al and Fe atoms was derived. It leads to an average number of atoms per channel and unit cell of approx. 1.5 in the whole homogeneity range. Below about 350 degrees C, four different phases exhibiting long-range order of the channel atoms appear to exist. Here the atomic ordering in the Al-poorest and Al-richest of these low-temperature phases, eta '' and eta ''' is reported. Both these phases can be characterized as incommensurately modulated composite crystal structures. Thereby, in both phases, the first composite subsystem contains atoms of the framework structure generating channels which are filled by atoms described by the second composite subsystem. The subsystems of the eta '' phase have orthorhombic superspace groups Xmcm(00g)0s0 and Inunm(00g)0s0 keeping the basic metric of the parent eta phase. The subsystems of the eta ''' can be described by the monoclinic superspace groups P2(1)/c(0b0)00 and P2(1)/c(0b0)s0 providing a lattice correspondence a(m) = 1/2(a + b), b(m) = c and c(m) = a +b to the orthorhombic parent eta phase. Although the number of atoms per channel is approx. 1.5 in eta '' and eta ''' phases, the channels are differently correlated with each other which is attributed to different Fe content in the channels inherited from the channel occupation in the disordered eta phase.
Title:
Observation of a dodecagonal oxide quasicrystal and its complex approximant in the SrTiO3-Pt(111) system
Authors:
Schenk, S; Forster, S; Meinel, K; Hammer, R; Leibundgut, B; Paleschke, M; Pantzer, J; Dresler, C; Schumann, FO; Widdra, W Author Full Names: Schenk, Sebastian; Foerster, Stefan; Meinel, Klaus; Hammer, Rene; Leibundgut, Bettina; Paleschke, Maximilian; Pantzer, Jonas; Dresler, Christoph; Schumann, Florian O.; Widdra, Wolf
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (13):10.1088/1361-648X/aa5bdb APR 5 2017
Abstract:
We report on the formation of a SrTiO3-derived dodecagonal oxide quasicrystal (OQC) at the interface to Pt(111). This is the second observation of a two-dimensional quasicrystal in the class of oxides. The SrTiO3-derived OQC exhibits strong similarities to the BaTiO3-derived OQC with respect to the local tiling geometry. However, the characteristic length scale of the SrTiO3-derived OQC is 1.8% smaller. Coexisting with the OQC a large scale approximant structure with a monoclinic unit cell is identified. It demonstrates the extraordinary level of complexity that oxide approximant structures can reach.

Update: 21-Feb-2018

Title:
A non-uniformly loaded anti-plane crack embedded in a half-space of a one-dimensional piezoelectric quasicrystal
Authors:
Tupholme, G Author Full Names: Tupholme, G. E.
Source:
MECCANICA, 53 (4-5):973-983; 10.1007/s11012-017-0759-1 MAR 2018
Abstract:
Closed-form representations are obtained using an extension of the classical continuous dislocation layer method combined with a method of images for the components of the phonon and phason stress and electric displacement fields around a generally loaded strip crack in a half-space of one-dimensional hexagonal piezoelectric quasicrystalline material parallel to its free surface. Representative numerical data are presented graphically.
Title:
Similar local order in disordered fluorite and aperiodic pyrochlore structures
Authors:
Shamblin, J; Tracy, CL; Palomares, RI; O'Quinn, EC; Ewing, RC; Neuefeind, J; Feygenson, M; Behrens, J; Trautmann, C; Lang, M Author Full Names: Shamblin, Jacob; Tracy, Cameron L.; Palomares, Raul I.; O'Quinn, Eric C.; Ewing, Rodney C.; Neuefeind, Joerg; Feygenson, Mikhail; Behrens, Jason; Trautmann, Christina; Lang, Maik
Source:
ACTA MATERIALIA, 144 60-67; 10.1016/j.actamat.2017.10.044 FEB 1 2018
Abstract:
A major challenge to understanding the response of materials to extreme environments (e.g., nuclear fuels/waste forms and fusion materials) is to unravel the processes by which a material can incorporate atomic-scale disorder, and at the same time, remain crystalline. While it has long been known that all condensed matter, even liquids and glasses, possess short-range order, the relation between fully-ordered, disordered, and aperiodic structures over multiple length scales is not well understood. For example, when defects are introduced (via pressure or irradiation) into materials adopting the pyrochlore structure, these complex oxides either disorder over specific crystallographic sites, remaining crystalline, or become aperiodic. Here we present neutron total scattering results characterizing the irradiation response of two pyrochlores, one that is known to disorder (Er2Sn2O7) and the other to amorphize (Dy2Sn2O7) under ion irradiation. The results demonstrate that in both cases, the local pyrochlore structure is transformed into similar short range configurations that are best fit by the orthorhombic weberite structure, even though the two compositions have distinctly different structures, aperiodic vs. disordered-crystalline, at longer length scales. Thus, a material's resistance to amorphization may not depend primarily on local defect formation energies, but rather on the structure's compatibility with meso-scale modulations of the local order in a way that maintains long-range periodicity. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Cesium immobilization in (Ba,Cr)-hollandites: Effects on structure
Authors:
Tumurugoti, P; Sundaram, SK; Misture, ST Author Full Names: Tumurugoti, Priyatham; Sundaram, S. K.; Misture, Scott T.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 258 72-78; 10.1016/j.jssc.2017.10.008 FEB 2018
Abstract:
Hollandites with compositions Ba1.15-xCs2xCr2.3Ti5.7O16 (0 <= x <= 1.15) intended for the immobilization of cesium (Cs) from nuclear waste have been prepared, characterized, and analyzed for Cs retention properties. Sol-gel synthesized powders were used for structural characterization using a combination of X-ray, neutron, and electron diffraction techniques. Phase-pure hollandites adopting tetragonal (I4/m) or monoclinic symmetry (I2/m) were observed to form in the compositional range 0 <= x <= 0.4. Structural models for the compositions, x = 0, 0.15, and 0.25 were developed from Rietveld analysis of powder diffraction data. Refined anisotropic displacement parameters (beta(ij)) for the Ba and Cs ions in the hollandite tunnels indicate local disorder of Ba/Cs along the tunnel direction. In addition, weak superlattice reflections were observed in X-ray and electron diffraction patterns that were due to the compositional modulation i.e., ordering of ions and vacancies along tunnel direction. Our overall observations suggest the phase-pure hollandites studied assumed supercell structures with ordered tunnel cations, which in turn have positional disorder in individual supercells.
Title:
Phase relations in the pseudo ternary system In2O3-TiO2-BO (B: Zn, Co and Ni) at 1200 degrees C in air
Authors:
Brown, F; Jacobo-Herrera, IE; Alvarez-Montano, VE; Kimizuka, N; Hirano, T; Sekine, R; Denholme, SJ; Miyakawa, N; Kudo, A; Iwase, A; Michiue, Y Author Full Names: Brown, Francisco; Edmundo Jacobo-Herrera, Ivan; Emmanuel Alvarez-Montano, Victor; Kimizuka, Noboru; Hirano, Tomonosuke; Sekine, Ryotaro; Denholme, Saleem J.; Miyakawa, Nobuaki; Kudo, Akihiko; Iwase, Akihide; Michiue, Yuichi
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 258 865-875; 10.1016/j.jssc.2017.12.020 FEB 2018
Abstract:
Phase relations in the pseudo ternary systems In2O3-TiO2-ZnO, In2O3-TiO2-CoO and In2O3-TiO2-NiO at 1200 degrees C in air were determined by means of a classic quenching method. In6Ti6BO22 (B: Zn, Co and Ni) which has the monoclinic In(Fe1/4Ti3/4)O-27/8-type of structure with a 4-dimensional super space group exists in a stable form. There exist homologous phases In1-x(Ti1/2Zn1/2)(1-x)O-3(ZnO)(m) (m: natural number, 0 m (No. 166) for m = odd or P63/mmc (No. 194) for m = even in space group. Lattice constants for each of the homologous compounds as a hexagonal setting and In6Ti6BO22 as the monoclinic system were determined by means of the powder X-ray diffraction method at room temperature. The temperature dependence of resistivity for In1-x(Ti1/2Zn1/2)(1-x)(ZnO)(4) (0.15 <= x <= 1) showed semiconducting like behavior for all samples examined at T(K) = 2-300. The resistivity increased systematically with decreasing x (0.7 <= x <= 1), and it was found that samples where x <= 0.7 became insulators. The optical band gap E-g (eV) of In1+x(Ti1/2Zn1/2)(1-x)(ZnO)(4) has been estimated from the diffuse reflection spectra for the whole range of x (0.15 <= x <= 1). A minimum value of 2.0717 eV for x = 1 and a maximum one of 3.066 eV for x = 0.15 were observed. Dependence of the crystal structures of the InAO(3)(BO), In(Ti1/2B1/2)O-3(B'O) and stability of In6Ti6BO22 upon the constituent cations in the pseudo quaternary system In2O3-TiO2-A(2)O(3)-BO (A: Fe, Ga and Cr; B, B': Mg, Zn, Co, Ni, Ca and Sr) were discussed in terms of their ionic radii and site preference effects.
Title:
Hybrid aluminium matrix composites containing boron carbide and quasicrystals: manufacturing and characterisation
Authors:
Khan, M; Zulfaqar, M; Ali, F; Subhani, T Author Full Names: Khan, Mahmood; Zulfaqar, Muhammad; Ali, Fahad; Subhani, Tayyab
Source:
MATERIALS SCIENCE AND TECHNOLOGY, 33 (16):1955-1963; 10.1080/02670836.2017.1342017 2017
Abstract:
Hybrid composites of boron carbide (B4C) and Al62.5Cu25Fe12.5 quasicrystals (QCs) were prepared by ball milling and pressureless sintering in aluminium matrix to investigate their individual and hybrid effects on microstructural and mechanical properties. Hybrid composite contained B4C and QCs in 3 wt-% each, making a total of 6 wt-%. For reference, specimens of pure aluminium and two composites containing 6 wt-% B4C and 6 wt-% QCs were prepared. Microstructural characterisation was performed using optical, scanning electron microscopy and X-ray diffraction, while evaluation of mechanical properties was carried out by hardness and compression tests. Uniform dispersion of reinforcements in composites was observed along with significant increase in the mechanical properties. The composite containing 6 wt-% QCs demonstrated the highest hardness, while the hybrid composite showed better compressive properties.
Title:
Microstructure and mechanical properties of Mg-Zn-Y alloy under a steady magnetic field
Authors:
Zhang, L; Jin, F; Zhan, W; Hu, PH; Zhou, Q Author Full Names: Zhang, L.; Jin, F.; Zhan, W.; Hu, P. H.; Zhou, Q.
Source:
MATERIALS SCIENCE AND TECHNOLOGY, 33 (18):2197-2202; 10.1080/02670836.2017.1353662 2017
Abstract:
This study examined the effect of steady magnetic field on the microstructure and mechanical properties of Mg-Zn-Y alloy reinforced by icosahedral quasicrystal phase. Results show that the microstructure of Mg-Zn-Y alloy was further refined as the magnetic field intensity increased. However, the primary alpha-Mg gradually became coarse over a certain value. No significant effect on the refinement of icosahedral quasicrystal phase was observed. The (10 (1) over bar1) plane of the alloy treated by steady magnetic field was substituted by the (0002) plane as the primary plane. The (10 (1) over bar2) plane was intensified gradually as the intensity of the magnetic field increased. The mechanical properties of Mg-Zn-Y alloy also improved with steady magnetic field treatment.

Update: 15-Feb-2018

Title:
Relaxor nature in Ba5RZr3Nb7O30 (R = La, Nd, Sm) tetragonal tungsten bronze new system
Authors:
Feng, WB; Zhu, XL; Liu, XQ; Fu, MS; Ma, X; Jia, SJ; Chen, XM Author Full Names: Feng, Wen Bin; Zhu, Xiao Li; Liu, Xiao Qiang; Fu, Mao Sen; Ma, Xiao; Jia, Shu Jing; Chen, Xiang Ming
Source:
JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 101 (4):1623-1631; 10.1111/jace.15332 APR 2018
Abstract:
Ba5RZr3Nb7O30(R=La, Nd, Sm) lead-free relaxor ferroelectrics were prepared by a standard solid-state reaction process, and the influence of A and B site ion occupation on the dielectric characteristics especially the relaxor nature were investigated systematically. Tetragonal tungsten bronze structure with space group P4/mbm was determined for all compositions, ion cross distribution by Ba2+ and R3+ in A1 site was observed, while A2 site was only occupied by Ba2+. Selected area electron diffraction patterns confirmed the existence of incommensurate superlattice modulation. Furthermore, temperature and frequency dependences of the dielectric properties showed a broad permittivity peak with strong frequency dispersion, following well the Vogel-Fulcher relationship. The maximum dielectric constant temperature increased gradually with decreasing A1 site ion size. Slim P-E hysteresis loops were obtained at room temperature for all compositions. Meanwhile, micro ferroelectric domains were observed in Ba5SmZr3Nb7O30. For Ba4R2Zr4Nb6O30 and Ba5RZr3Nb7O30 (R=Nd, Sm), the transition from normal ferroelectric to relaxor behavior originates from the increased t(A1), which is a result of cross distribution at A1 site. Compared with Ba5RTi3Nb7O30, Zr substitution at B site enhances the relaxor nature.
Title:
Crystallite size effect on the monoclinic deformation of the bcc crystal structure of chromium
Authors:
Przenioslo, R; Fabrykiewicz, P; Sosnowska, I; Wardecki, D; Slawinski, WA; Playford, HY; Hempelmann, R; Bukowski, M Author Full Names: Przenioslo, R.; Fabrykiewicz, P.; Sosnowska, I.; Wardecki, D.; Slawinski, W. A.; Playford, H. Y.; Hempelmann, R.; Bukowski, M.
Source:
PHYSICA B-CONDENSED MATTER, 530 183-190; 10.1016/j.physb.2017.10.086 FEB 1 2018
Abstract:
The modulated spin density wave magnetic orderings observed in chromium suggests that the crystal structure of chromium cannot be described by the cubic space group Im3m. Our experimental studies of polycrystalline and nanocrystalline chromium by synchrotron radiation (SR) and neutron powder diffraction show a hkl-dependent Bragg peak broadening which can be interpreted by the low-symmetry monoclinic space group P2(1)/n instead of the high symmetry cubic space group Im3m. Themonoclinic angle is beta(m) = 90.05(1)degrees and 90.29(1)degrees for polycrystalline Cr and nanocrystalline Cr, respectively. The relative monoclinic distortion observed in chromium is 5 times larger than those reported for several oxides: BiFeO3, alpha-Fe2O3, Cr2O3 and calcite. The symmetry of the magnetic transverse spin density wave (TSDW) and the longitudinal spin density wave (LSDW) observed in Cr are described by using the superspace groups P2(1)/n(0 beta 0)00 and P2'(1)/n'(0 beta 0)00, respectively. These superspace groups describe both the magnetic modulations and the atomic position modulations reported in the literature. The monoclinic symmetry of chromium is a robust effect which is observed in the paramagnetic as well as in the TSDW and LSDW phases.

Update: 7-Feb-2018

Title:
Field-induced magnetic phase transitions and memory effect in bilayer ruthenate Ca3Ru2O7 with Fe substitution
Authors:
Zhu, M; Hong, T; Peng, J; Zou, T; Mao, ZQ; Ke, X Author Full Names: Zhu, M.; Hong, T.; Peng, J.; Zou, T.; Mao, Z. Q.; Ke, X.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 30 (7):10.1088/1361-648X/aaa626 FEB 21 2018
Abstract:
Bilayer ruthenate Ca-3(Ru(1-x)Fex)(2)O-7 (x = 0.05) exhibits an incommensurate magnetic soliton lattice driven by the Dzyaloshinskii-Moriya interaction. Here we report complex field-induced magnetic phase transitions and memory effect in this system via single-crystal neutron diffraction and magnetotransport measurements. We observe first-order incommensurateto- commensurate magnetic transitions upon applying the magnetic field both along and perpendicular to the propagation axis of the incommensurate spin structure. Furthermore, we find that the metastable states formed upon decreasing the magnetic field depend on the temperature and the applied field orientation. We suggest that the observed field-induced metastability may be ascribable to the quenched kinetics at low temperature.
Title:
Two superstructures of Ce3Rh4Ge4
Authors:
Vosswinkel, D; Hoffmann, RD; Svitlyk, V; Hermes, W; Greiwe, M; Niehaus, O; Chevalier, B; Matar, SF; Al Alam, AF; Nakhl, M; Ouaini, N; Pottgen, R Author Full Names: Vosswinkel, Daniel; Hoffmann, Rolf-Dieter; Svitlyk, Volodymyr; Hermes, Wilfried; Greiwe, Magnus; Niehaus, Oliver; Chevalier, Bernard; Matar, Samir F.; Al Alam, Adel F.; Nakhl, Michel; Ouaini, Naim; Poettgen, Rainer
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 233 (2):81-95; 10.1515/zkri-2017-2092 FEB 2018
Abstract:
Two different samples of Ce3Rh4Ge4 were synthesized from different starting compositions by melting of the elements in an arc-melting furnace followed by annealing sequences in a sealed tantalum ampoule in a muffle furnace. The structures of two different stacking variants were refined on the basis of temperature dependent single-crystal X-ray diffractometer data. At high temperature Ce3Rh4Ge4 adopts the U3Ni4Si4 type structure with strongly enhanced anisotropic displacement parameters for the Rh1 atoms. For the two different crystals, additional reflections start to appear at different temperatures. The first crystal showed additional reflections already at room temperature (stacking variant I) and the second one showed additional reflections emerging below 270 K (stacking variant II). Stacking variant I could be described with the (3 + 1)D superspace group I2/m(alpha 0 gamma)00; alpha = 1/2a*, gamma = 1/2c*; (Z = 2), 1252 F-2 values, 48 variables, wR = 0.0306 for the main and wR = 0.0527 for 440 1st order satellite reflections, similar to Pr3Rh4Ge4. For stacking variant II the (3 + 1) D superspace group is Immm(alpha 00)00s; alpha = 1/2a*; (Z = 2). The structure could be refined with 1261 F-2 values, 53 variables and residuals of wR = 0.0331 for the main reflections and wR = 0.1755 (R1(obs) = 0.0788) for the 1st order satellite reflections, [a = 406.2(1), b = 423.7(1) and c = 2497.1(1) pm]. The commensurate description could be transformed to a three-dimensional (3D)supercell with space group Pnma and Z = 4: a = 812.5(1), b = 423.7(1), c = 2497.1(2) pm, 1261 F-2 values, 69 variables and wR = 0.0525. The relation of the U3Ni4Si4 type structure, the (3 + 1) D modulated and the 3D supercells are discussed on the basis of group-subgroup schemes. Ab initio electronic structure calculations are in line with the diffraction experiments, revealing the lowest total energy for the Pnma phase.
Title:
Incommensurate Phonon Anomaly and the Nature of Charge Density Waves in Cuprates
Authors:
Miao, H; Ishikawa, D; Heid, R; Le Tacon, M; Fabbris, G; Meyers, D; Gu, GD; Baron, AQR; Dean, MPM Author Full Names: Miao, H.; Ishikawa, D.; Heid, R.; Le Tacon, M.; Fabbris, G.; Meyers, D.; Gu, G. D.; Baron, A. Q. R.; Dean, M. P. M.
Source:
PHYSICAL REVIEW X, 8 (1):10.1103/PhysRevX.8.011008 JAN 18 2018
Abstract:
While charge density wave (CDW) instabilities are ubiquitous to superconducting cuprates, the different ordering wave vectors in various cuprate families have hampered a unified description of the CDW formation mechanism. Here, we investigate the temperature dependence of the low-energy phonons in the canonical CDW-ordered cuprate La1.875Ba0.125CuO4. We discover that the phonon softening wave vector associated with CDW correlations becomes temperature dependent in the high-temperature precursor phase and changes from a wave vector of 0.238 reciprocal lattice units (r.l.u.) below the ordering transition temperature to 0.3 r.l.u. at 300 K. This high-temperature behavior shows that "214"-type cuprates can host CDW correlations at a similar wave vector to previously reported CDW correlations in non-214-type cuprates such as YBa2Cu3O6+delta. This indicates that cuprate CDWs may arise from the same underlying instability despite their apparently different low-temperature ordering wave vectors.
Title:
The partial substitution of Y with Gd on microstructures and mechanical properties of as-cast and as-extruded Mg-10Zn-6Y-0.5Zr alloy
Authors:
Jiang, HS; Qiao, XG; Zheng, MY; Wu, K; Xu, C; Kamado, S Author Full Names: Jiang, H. S.; Qiao, X. G.; Zheng, M. Y.; Wu, K.; Xu, C.; Kamado, S.
Source:
MATERIALS CHARACTERIZATION, 135 96-103; 10.1016/j.matchar.2017.11.025 JAN 2018
Abstract:
Mg-10Zn-6Y-0.5Zr (wt%) alloy and Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy with medium RE content have been fabricated by conventional casting and indirect extrusion. The as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy shows a bimodal microstructure containing dynamic recrystallized (DRXed) grains with average grain size of 2 mu m and deformed regions. In addition to the fragmented W phase particle bands distributing along the extrusion direction, large amount of nano W phase and small amount of nano beta(2)' phase are precipitated in the matrix. While the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy exhibits completely dynamic recrystallized microstructure with average grain size of 3 mu m. The broken W phase particles are distributed homogeneously in the matrix. Icosahedral quasicrystal phase layer is observed at the surface of some W phase particles in the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr alloy. The as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy exhibits yield strength of 341 MPa, ultimate tensile strength of 368 MPa and elongation to failure of 6.8%. While the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy shows lower yield strength of 247 MPa, ultimate tensile strength of 330 MPa and higher elongation to failure of 19.8%. The higher strength in the as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy is mainly attributed to higher area fraction of unDRXed regions with strong texture and the precipitation of nano W and beta(2)' phase. The fully recrystallized microstructure with weak texture and the formation of icosahedral quasi crystal phases with good coherent bond with alpha-Mg contribute to the good ductility of the as-extruded Mg-10Zn3Y-3Gd-0.5Zr alloy.

Update: 1-Feb-2018

Title:
Comment on "The true structural periodicities and superspace group descriptions of the prototypical incommensurate composite materials: Alkane/urea inclusion compounds" by Couzi M. et al
Authors:
Toudic, B; Guerin, L; Mariette, C; Frantsuzov, I; Rabiller, P; Ecolivet, C; Janssen, T; Hollingsworth, MD Author Full Names: Toudic, B.; Guerin, L.; Mariette, C.; Frantsuzov, I.; Rabiller, P.; Ecolivet, C.; Janssen, T.; Hollingsworth, Mark D.
Source:
EPL, 119 (6):10.1209/0295-5075/119/66004 SEP 2017

Update: 25-Jan-2018

Title:
Discovery of superconductivity in quasicrystal
Authors:
Kamiya, K; Takeuchi, T; Kabeya, N; Wada, N; Ishimasa, T; Ochiai, A; Deguchi, K; Imura, K; Sato, NK Author Full Names: Kamiya, K.; Takeuchi, T.; Kabeya, N.; Wada, N.; Ishimasa, T.; Ochiai, A.; Deguchi, K.; Imura, K.; Sato, N. K.
Source:
NATURE COMMUNICATIONS, 9 10.1038/s41467-017-02667-x JAN 11 2018
Abstract:
Superconductivity is ubiquitous as evidenced by the observation in many crystals including carrier-doped oxides and diamond. Amorphous solids are no exception. However, it remains to be discovered in quasicrystals, in which atoms are ordered over long distances but not in a periodically repeating arrangement. Here we report electrical resistivity, magnetization, and specific-heat measurements of Al-Zn-Mg quasicrystal, presenting convincing evidence for the emergence of bulk superconductivity at a very low transition temperature of T-c congruent to 0: 05 K. We also find superconductivity in its approximant crystals, structures that are periodic, but that are very similar to quasicrystals. These observations demonstrate that the effective interaction between electrons remains attractive under variation of the atomic arrangement from periodic to quasiperiodic one. The discovery of the superconducting quasicrystal, in which the fractal geometry interplays with superconductivity, opens the door to a new type of superconductivity, fractal superconductivity.
Title:
Unidirectional spin density wave state in metallic (Sr1-xLax)(2)IrO4
Authors:
Chen, X; Schmehr, JL; Islam, Z; Porter, Z; Zoghlin, E; Finkelstein, K; Ruff, JPC; Wilson, SD Author Full Names: Chen, Xiang; Schmehr, Julian L.; Islam, Zahirul; Porter, Zach; Zoghlin, Eli; Finkelstein, Kenneth; Ruff, Jacob P. C.; Wilson, Stephen D.
Source:
NATURE COMMUNICATIONS, 9 10.1038/s41467-017-02647-1 JAN 9 2018
Abstract:
Materials that exhibit both strong spin-orbit coupling and electron correlation effects are predicted to host numerous new electronic states. One prominent example is the J(eff) = 1/2 Mott state in Sr2IrO4, where introducing carriers is predicted to manifest high temperature superconductivity analogous to the S = 1/2 Mott state of La2CuO4. While bulk super-conductivity currently remains elusive, anomalous quasiparticle behaviors paralleling those in the cuprates such as pseudogap formation and the formation of a d-wave gap are observed upon electron-doping Sr2IrO4. Here we establish a magnetic parallel between electron-doped Sr2IrO4 and hole-doped La2CuO4 by unveiling a spin density wave state in electron-doped Sr2IrO4. Our magnetic resonant X-ray scattering data reveal the presence of an incommensurate magnetic state reminiscent of the diagonal spin density wave state observed in the monolayer cuprate (La1-xSrx)(2)CuO4. This link supports the conjecture that the quenched Mott phases in electron-doped Sr2IrO4 and hole-doped La2CuO4 support common competing electronic phases.
Title:
Lattice Distortions in TlInSe2 Thermoelectric Material Studied by X-Ray Absorption Fine Structure
Authors:
Hosokawa, S; Stellhorn, JR; Ikemoto, H; Mimura, K; Wakita, K; Mamedov, N Author Full Names: Hosokawa, Shinya; Stellhorn, Jens Ruediger; Ikemoto, Hiroyuki; Mimura, Kojiro; Wakita, Kazuki; Mamedov, Nazim
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 215 (1):10.1002/pssa.201700416 JAN 2018
Abstract:
Tl L-II and In K X-ray absorption fine structure (XAFS) measurements were performed on a TlInSe2 thermoelectric material in the temperature range of 25-300K including the incommensurate-commensurate phase transition temperature of about 135K. Most of the bond lengths obtained from the present XAFS measurements are in good agreement with existing X-ray diffraction data at room temperature, while only the Tl-Tl correlation shows inconsistent values indicating the commensurate properties of the Tl chains expected from the thermodynamic properties. The present XAFS data clearly support positional fluctuations of the Tl atoms found in three-dimensional atomic images reconstructed from X-ray fluorescence holography.
Title:
Hyperuniformity variation with quasicrystal local isomorphism class (vol 29, 204003, 2017)
Authors:
Lin, C; Steinhardt, PJ; Torquato, S Author Full Names: Lin, C.; Steinhardt, P. J.; Torquato, S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (47):10.1088/1361-648X/aa8430 NOV 29 2017

Update: 17-Jan-2018

Title:
Spin waves in planar quasicrystal of Penrose tiling
Authors:
Rychly, J; Mieszczak, S; Klos, JW Author Full Names: Rychly, J.; Mieszczak, S.; Klos, J. W.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 450 18-23; 10.1016/j.jmmm.2017.03.029 MAR 15 2018
Abstract:
We investigated two-dimensional magnonic structures which are the counterparts of photonic quasicrystals forming Penrose tiling. We considered the slab composed of Ni (or Py) disks embedded in Fe (or Co) matrix. The disks are arranged in quasiperiodic Penrose-like structure. The infinite quasicrystal was approximated by its rectangular section with periodic boundary conditions applied. This approach allowed us to use the plane wave method to find the frequency spectrum of eigenmodes for spin waves and their spatial profiles. The calculated integrated density of states shows more distinctive magnonic gaps for the structure composed of materials of high magnetic contrast (Ni and Fe) and relatively high filling fraction. This proves the impact of quasiperiodic long-range order on the spectrum of spin waves. We also investigated the localization of spin wave eingenmodes resulting from the quasiperiodicity of the structure. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Defects in Static Elasticity of Quasicrystals
Authors:
Xu, Q; Lu, J; Li, W Author Full Names: Xu, Qin; Lu, Jing; Li, Wu
Source:
CRYSTALS, 7 (12):10.3390/cryst7120373 DEC 2017
Abstract:
A review on mathematical elasticity of quasicrystals is given. In this review, the focus is on various defects of quasicrystals. Dislocation and crack are two classes of typical topological defects, while their existence has great influence on the mechanical behavior of quasicrystals. The analytic and numerical solutions of dislocations and crack in quasicrystals are the core of the static and dynamic elasticity theory, and this paper gives a comprehensive review on the solutions for dislocations and crack with different configurations in different various important quasicrystalline systems. We review some results in linear elasticity of quasicrystals, referring to different boundary value problems. We also add some new achievements.
Title:
Structurally Complex Frank-Kasper Phases and Quasicrystal Approximants: Electronic Origin of Stability
Authors:
Degtyareva, VF; Afonikova, NS Author Full Names: Degtyareva, Valentina F.; Afonikova, Natalia S.
Source:
CRYSTALS, 7 (12):10.3390/cryst7120359 DEC 2017
Abstract:
Metal crystals with tetrahedral packing are known as Frank-Kasper phases, with large unit cells with the number of atoms numbering from hundreds to thousands. The main factors of the formation and stability of these phases are the atomic size ratio and the number of valence electrons per atom. The significance of the electronic energy contribution is analyzed within the Fermi sphere-Brillouin zone interaction model for several typical examples: Cu4Cd3, Mg2Al3 with over a thousand atoms per cell, and for icosahedral quasicrystal approximants with 146-168 atoms per cell. Our analysis shows that to minimize the crystal energy, it is important that the Fermi sphere (FS) is in contact with the Brillouin zones that are related to the strong diffraction peaks: the zones either inscribe the FS or are circumscribed by the FS creating contact at edges or vertices.

Update: 11-Jan-2018

Title:
Influence of Ag replacement on supercooled liquid region and icosahedral phase precipitation of Zr65Al7.5Ni10Cu17.5-xAgx (x=0-17.5 at%) glassy alloys
Authors:
Li, MM; Inoue, A; Han, Y; Kong, FL; Zhu, SL; Shalaan, E; Al-Marzouki, F Author Full Names: Li, M. M.; Inoue, A.; Han, Y.; Kong, F. L.; Zhu, S. L.; Shalaan, E.; Al-Marzouki, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 735 1712-1721; 10.1016/j.jallcom.2017.11.203 FEB 25 2018
Abstract:
The glass transition phenomenon for Zr65Al7.5Ni10Cu17.5-xAgx (x = 5-17.5 at%) glassy alloys was observed in the Ag content range below about 15% and the icosahedral phase precipitated as the heating-induced primary phase in the limited Ag content range. In the higher Ag content range where glass transition is not clearly observed, the primary precipitation phase changed to mixed phases of tetragonal Zr3Ag + tetragonal Zr2Ni + hexagonal Zr4Al3. The good correspondence between the appearance of glass transition and the icosahedral phase precipitation was recognized in the multicomponent glassy alloys containing the immiscible type atomic pairs of Ni-Ag and Cu-Ag. Although neither glass transition nor supercooled liquid region is observed for Zr65Al7.5Ni10Ag17.5 and no icosahedral phase is formed, a modified Zr65Al7.5Ni17.5Ag10 alloy with higher Ni/Ag content ratio exhibits glass transition and supercooled liquid region and the primary precipitates also changes to an icosahedral phase. The good correspondence can be interpreted on the basis of the previous knowledge that the appearance of glass transition and supercooled liquid state originates from icosahedral-like medium range ordered atomic configurations. Besides, the 6% Ag-containing alloy keeps high glass-forming ability which is high enough to form a bulk glassy alloy rod of 6 mm by suction casting. The close correlation between the appearance of glass transition phenomenon and the primary precipitation of icosahedral phase is expected to provide a useful knowledge on the role of icosahedral-like atomic configuration in the achievement of bulk glass-forming ability through the stabilization of supercooled liquid. (C) 2017 Elsevier B.V. All rights reserved.
Title:
The role of hydrogen bonds in order-disorder transition of a new incommensurate low temperature phase beta-[Zn-(C7H4NO4)(2)]center dot 3H(2)O
Authors:
Tabatabaee, M; Poupon, M; Eigner, V; Vanek, P; Dusek, M Author Full Names: Tabatabaee, Masoumeh; Poupon, Morgane; Eigner, Vaclav; Vanek, Premysl; Dusek, Michal
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 233 (1):17-25; 10.1515/zkri-2016-2013 JAN 2018
Abstract:
The room temperature structure with P2(1)/c symmetry of the zinc(II) complex of pyridine-2,6-dicarboxylic acid was published by Okabe and Oya (N. Okabe, N. Oya, Copper(II) and zinc(II) complexes of pyridine-2,6-dicarboxylic acid. Acta Crystallogr. C. 2000, 56, 305). Here we report crystal structure of the low temperature phase beta-[Zn(pydcH)(2)]center dot 3H(2)O, pydc = C7H3NO4, resulting from the phase transition around 200 K. The diffraction pattern of the low temperature phase revealed satellite reflections, which could be indexed with q-vector 0.4051(10)b* corresponding to (3 + 1)D incommensurately modulated structure. The modulated structure was solved in the superspace group X2(1)/c(0b0)s0, where X stands for a nonstandard centring vector (1/2, 0, 0, 1/2), and compared with the room temperature phase. It is shown that hydrogen bonds are the main driving force of modulation.
Title:
Spatially modulated magnetic structure of EuS due to the tetragonal domain structure of SrTiO3
Authors:
Rosenberg, AJ; Katmis, F; Kirtley, JR; Gedik, N; Moodera, JS; Moler, KA Author Full Names: Rosenberg, Aaron J.; Katmis, Ferhat; Kirtley, John R.; Gedik, Nuh; Moodera, Jagadeesh S.; Moler, Kathryn A.
Source:
PHYSICAL REVIEW MATERIALS, 1 (7):10.1103/PhysRevMaterials.1.074406 DEC 15 2017
Abstract:
The combination of ferromagnets with topological superconductors or insulators allows for new phases of matter that support excitations such as chiral edge modes and Majorana fermions. EuS, a wide-bandgap ferromagnetic insulator with a Curie temperature around 16 K, and SrTiO3 (STO), an important substrate for engineering heterostructures, may support these phases. We present scanning superconducting quantum interference device measurements of EuS grown epitaxially on STO that reveal micron-scale variations in ferromagnetism and paramagnetism. These variations are oriented along the STO crystal axes and only change their configuration upon thermal cycling above the STO cubic-to-tetragonal structural transition temperature at 105 K, indicating that the observed magnetic features are due to coupling between EuS and the STO tetragonal structure. We speculate that the STO tetragonal distortions may strain the EuS, altering the magnetic anisotropy on a micron scale. This result demonstrates that local variation in the induced magnetic order from EuS grown on STO needs to be considered when engineering new phases of matter that require spatially homogeneous exchange.

Update: 13-Dec-2017

Title:
Mechanical and surface properties of Aluminum-Copper-Iron quasicrystal thin films
Authors:
Parsamehr, H; Chang, SY; Lai, CH Author Full Names: Parsamehr, Hadi; Chang, Shou-Yi; Lai, Chih-Huang
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 732 952-957; 10.1016/j.jallcom.2017.10.229 JAN 25 2018
Abstract:
We show quasicrystal formation by annealing multilayers of Al, Cu and Fe. The mechanical and surface properties of quasicrystals are affected by the parameters of annealing process. Here, multilayer Al-Cu-Fe thin film samples with different compositions were sputtered on Si/SiO2 substrates and subjected to a two-step annealing process for different durations (5, 10 and 15 h). X-ray diffraction analyses indicated that the 15-h annealed sample had a sharper quasicrystal peak, which was more stable than any other phases. From the XRD data, the amount of each phase was calculated; the sample with longer annealing duration revealed a high amount of phi-phase (84.3% crystallinity of quasicrystal) with a small amount of cubic Al-50 (CuFe) (50) phase. Nanoindentation tests and contact angle measurements showed that this sample also had the greatest hardness (similar to 11 GPa) and the highest contact angle (127 degrees), respectively. (C) 2017 Elsevier B.V. All rights reserved.
Title:
The formation of quasicrystals in Al-Cu-Fe-(M=Cr, Ni) melt-spun ribbons
Authors:
Wolf, W; Coury, FG; Kaufman, MJ; Bolfarini, C; Kiminami, CS; Botta, WJ Author Full Names: Wolf, W.; Coury, F. G.; Kaufman, M. J.; Bolfarini, C.; Kiminami, C. S.; Botta, W. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 731 1288-1294; 10.1016/j.jallcom.2017.09.139 JAN 15 2018
Abstract:
The influence of Cr and Ni additions in rapidly-solidified Al-Cu-Fe alloys was investigated. Four compositions, namely, Al64Cu20Fe13Ni3, Al63Cu18Fe10Ni9, Al65Cu22Fe10Cr3 and Al67Cu20Fe5Cr8 were selected based on a methodology in which the average valence electron per atom (e/a) ratio of the ternary Al-Cu-Fe quasicrystal was maintained constant. Melt-spun ribbons of all four alloys were produced and then examined by X-ray diffraction, transmission electron microscopy and energy dispersive X-ray spectroscopy. The results indicate that the Al-Cu-Fe icosahedral quasicrystalline phase has limited solubility for Ni such that with increasing Ni content, the fraction of the quasicrystalline phase decreased drastically and two primitive B2 cubic phases were formed instead. Additions of Cr resulted in the formation of a decagonal quasicrystal at the expense of the icosahedral phase. At 3 at% Cr, both icosahedral and decagonal phases were observed, with the former having the major volume fraction. For the alloy containing 8 at% Cr, only the decagonal phase was observed. (C) 2017 Elsevier B.V. All rights reserved.

Update: 7-Dec-2017

Title:
In-situ neutron diffraction of a quasicrystal-containing Mg alloy interpreted using a new polycrystal plasticity model of hardening due to {10.2} tensile twinning
Authors:
Agnew, SR; Singh, A; Calhoun, CA; Mulay, RP; Bhattacharyya, JJ; Somekawa, H; Mukai, T; Clausen, B; Wu, PD Author Full Names: Agnew, S. R.; Singh, A.; Calhoun, C. A.; Mulay, R. P.; Bhattacharyya, J. J.; Somekawa, H.; Mukai, T.; Clausen, B.; Wu, P. D.
Source:
INTERNATIONAL JOURNAL OF PLASTICITY, 100 34-51; 10.1016/j.ijplas.2017.09.005 JAN 2018
Abstract:
Due to the excellent balance of strength and ductility exhibited by some Mg-Zn-RE (Y subgroup rare earth element) alloys, which contain icosahedral quasicrystalline precipitates, it is of interest to examine their deformation mechanisms. The internal strain evolution Mg-3at%Zn-0.5 at%Y with 4 vol% i-phase was measured using in-situ neutron diffraction. The extruded samples exhibit an initially weak <10.0> parallel to extrusion direction "rod texture," distinct from the normally strong texture of extruded Mg alloys, but the grain size is unexceptional (16.7 +/- 2.1 mu m). The initially weak texture contributes to a nearly symmetric yielding response between tension and compression. The hardening responses are asymmetric, however, since {10.2} extension twinning is significantly more active during compressive straining, despite the initially weak texture. In-situ neutron diffraction tension and compression experiments parallel to the extrusion direction, together with elasto-plastic self-consistent (EPSC) crystal plasticity modeling, reveal the strength and hardening behavior of individual slip and twinning modes. The previously published twinning-detwinning (TDT) model is implemented within the EPSC framework, and it is proven effective for describing the observed, mild tension-compression asymmetry. This is not possible with previous EPSC-based models of twinning. Finally, the description of hardening within the TDT model is modified, in order to accurately describe the evolution of internal strains within the twins. (C) 2017 Elsevier Ltd. All rights reserved.
Title:
Revealing the Topology of Quasicrystals with a Diffraction Experiment
Authors:
Dareau, A; Levy, E; Aguilera, MB; Bouganne, R; Akkermans, E; Gerbier, F; Beugnon, J Author Full Names: Dareau, A.; Levy, E.; Aguilera, M. Bosch; Bouganne, R.; Akkermans, E.; Gerbier, F.; Beugnon, J.
Source:
PHYSICAL REVIEW LETTERS, 119 (21):10.1103/PhysRevLett.119.215304 NOV 22 2017
Abstract:
Topological properties of crystals and quasicrystals is a subject of recent and growing interest. This Letter reports an experiment where, for certain quasicrystals, these properties can be directly retrieved from diffraction. We directly observe, using an interferometric approach, all of the topological invariants of finite-length Fibonacci chains in their diffraction pattern. We also quantitatively demonstrate the stability of these topological invariants with respect to structural disorder.
Title:
Rational Design of a Commensurate (3+3)-D Modulated Structure within the Fast-Ion Conducting Stabilized delta-Bi2O3 Series
Authors:
Wind, J; Polt, J; Zhang, Z; Blom, DA; Vogt, T; Withers, RL; Ling, CD Author Full Names: Wind, Julia; Polt, Julia; Zhang, Zhaoming; Blom, Douglas A.; Vogt, Thomas; Withers, Ray L.; Ling, Chris D.
Source:
CHEMISTRY OF MATERIALS, 29 (21):9171-9181; 10.1021/acs.chemmater.7b03012 NOV 14 2017
Abstract:
We report the systematic design, preparation, and characterization of the first commensurate member of the oxide-ionic conducting, (3 + 3)-D modulated, Type II phases of doped delta-Bi2O3. The incommensurate Type II modulation vector epsilon was previously described as continuously variable, but high-resolution synchrotron X-ray powder diffraction data show that close to the composition Bi23CrNb3O45, it "locks in" to epsilon = 1/3. The space group of the resulting 3 X 3 X 3 fluorite type supercell was found to be F $(4) over bar $ 3m by selected-area electron diffraction, and the structure was solved and Rietveld-refined against neutron powder diffraction data in conjunction with local structural information from X-ray absorption spectroscopy, high-resolution transmission electron microscopy, and ab initio geometry optimization calculations. The result unambiguously validates the crystal-chemical model of the Type II phases as being based on the local ordering of oxygen around transition metals M into tetrahedral clusters of MO6 octahedra and isolated MO4 tetrahedra, separating relatively disordered fluorite-type regions that facilitate the highest oxide-ionic conduction among transition metal-doped delta-Bi2O3 phases.

Update: 30-Nov-2017

Title:
Structural signature and size-dependent mechanical response of frozen-in icosahedral phase in bulk metallic glasses
Authors:
Chang, HJ; Oh, HS; Lee, JI; Park, ES Author Full Names: Chang, Hye Jung; Oh, Hyun Seok; Lee, Je In; Park, Eun Soo
Source:
MATERIALS & DESIGN, 138 129-139; 10.1016/j.matdes.2017.10.049 JAN 15 2018
Abstract:
In the present study, we report structural signature and size-dependent mechanical response of frozen-in icosahedral phase (I-phase) embedded in Zr-(Ti, Nb, Al)-(Cu, Ni) bulkmetallic glass (BMG)-forming alloys, which exhibit a narrowcomposition range overlapping between glass and I-phase forming region. Thus, the different sizes of the I-phase from tens of nanoscale precipitates to enhanced icosahedral short-range order in MG matrix can be obtained by controlling cooling history. I-phase particles with tens of nanoscale in BMGs do not contribute to extrinsic ductility due to limited blocking of the propagation of shear band. The shear band passes through the particle, splitting it into two pieces. On the other hand, BMGs with enhanced icosahedral short-range order, which can be evaluated by EXAFS analysis as well as calorimetric signal during isothermal annealing, exhibit enhanced ductility without strength reduction. Indeed, we examine the cut-off size of strain bursts and deformation dynamics of shear-avalanches through the statistical analysis of serration behavior. Icosahedral short-range order (ISRO)-embedded MGs exhibit weakened jammed state of the self-organized deformed zones, which results in the formation of numerous catastrophic deformed zones under relatively chaotic dynamics, and consequently multiple shear bands. These results would help deepen our understanding of the underlying mechanism that determines intrinsic ductility in BMGs via frozen-in ISRO, and ultimately give us a guideline for the design of promising BMGs with improved intrinsic ductility by manipulating local structural instability. (C) 2017 Elsevier Ltd. All rights reserved.
Title:
Model refinement of quasicrystals
Authors:
Wolny, J; Buganski, I; Strzalka, R Author Full Names: Wolny, Janusz; Buganski, Ireneusz; Strzalka, Radoslaw
Source:
CRYSTALLOGRAPHY REVIEWS, 24 (1):22-64; 10.1080/0889311X.2017.1340276 2018
Abstract:
From the discovery of quasicrystals, exhibiting rotational symmetries forbidden by the classical crystallography, the idea of a quasicrystalline geometry spreads out to a great variety of scientific fields, including soft matter physics, optics, or nanotechnology. However, the atomic structure of quasicrystals is still unclear and many questions are unanswered, including the most peculiar one asked by Per Bak: Where are the atoms?' [Icosahedral crystals: where are the atoms? Phys Rev Lett. 1986;56:861-864]. To answer those questions, more detailed structural analysis needs to be done. Two approaches to the structural description and refinement are used for aperiodic crystals: the higher dimensional method, well established in the community, and the statistical method. We introduce the essence of the crystallography of quasicrystals, giving the historical background and fundamentals of the higher dimensional modelling, but focus is put on the details and application of the statistical approach. We present also a case study of the decagonal Al-Cu-{Co,Ir,Rh} phase, which is an example of the crystal structure solved using the statistical method. In the last chapter, a brief discussion of the recently developed approach of a phasonic corrective factor, alongside the effect of phonons on the atomic distribution function, is given.
Title:
Hall effect in cuprates with an incommensurate collinear spin-density wave
Authors:
Charlebois, M; Verret, S; Foley, A; Simard, O; Senechal, D; Tremblay, AMS Author Full Names: Charlebois, M.; Verret, S.; Foley, A.; Simard, O.; Senechal, D.; Tremblay, A. -M. S.
Source:
PHYSICAL REVIEW B, 96 (20):10.1103/PhysRevB.96.205132 NOV 16 2017
Abstract:
The presence of incommensurate spiral spin-density waves (SDW) has been proposed to explain the p (hole doping) to 1 + p jump measured in the Hall number n(H) at a doping p*. Here we explore incommensurate collinear SDW as another possible explanation of this phenomenon, distinct from the incommensurate spiral SDW proposal. We examine the effect of different SDW strengths and wave vectors, and we find that the n(H) similar to p behavior is hardly reproduced at low doping. Furthermore, the calculated n(H) and Fermi surfaces give characteristic features that should be observed; thus, the lack of these features in experiment suggests that the incommensurate collinear SDW is unlikely to be a good candidate to explain the n(H) similar to p observed in the pseudogap regime.
Title:
Shock Synthesis of Decagonal Quasicrystals
Authors:
Oppenheim, J; Ma, C; Hu, J; Bindi, L; Steinhardt, PJ; Asimow, PD Author Full Names: Oppenheim, J.; Ma, C.; Hu, J.; Bindi, L.; Steinhardt, P. J.; Asimow, P. D.
Source:
SCIENTIFIC REPORTS, 7 10.1038/s41598-017-15229-4 NOV 15 2017
Abstract:
The Khatyrka meteorite contains both icosahedral and decagonal quasicrystals. In our previous studies, icosahedral quasicrystals have been synthesized and recovered from shock experiments at the interface between CuAl5 and stainless steel 304 alloys. In this study, we report a new shock recovery experiment aimed at synthesizing decagonal quasicrystals similar to decagonite, natural Al71Ni24Fe5. Aluminum 2024 and permalloy 80 alloys were stacked together and shocked in a stainless steel 304 recovery chamber. Abundant decagonal quasicrystals of average composition Al73Ni19Fe4Cu2Mg0.6Mo0.4Mn0.3 with traces of Si and Cr were found along the recovered interface between the Al and permalloy. The experiment also synthesized AlNiFe alloy with the B2 (CsCl-type) structure and the metastable Al9Ni2 phase. We present chemical (scanning electron microscopy and electron microprobe) and structural (electron backscatter diffraction and transmission electron microscopy) characterization of the recovered phases and discuss the implications of this shock synthesis for the stability of quasicrystals during high-pressure shocks and for the interpretation of the phase assemblage found in Khatyrka.
Title:
Unusual Long-Range Ordering Incommensurate Structural Modulations in an Organic Molecular Ferroelectric
Authors:
Sun, ZH; Li, J; Ji, CM; Sun, JL; Hong, MC; Luo, JH Author Full Names: Sun, Zhihua; Li, Jian; Ji, Chengmin; Sun, Junliang; Hong, Maochun; Luo, Junhua
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 139 (44):15900-15906; 10.1021/jacs.7b08950 NOV 8 2017
Abstract:
The incommensurate (IC) behaviors of ferroelectrics have been widely investigated in inorganic oxides as an exciting branch for aperiodic materials, whereas it still remains a great challenge to achieve such intriguing effects in organic systems. Here, we present that successive ordering of dynamic dipoles in an organic molecular ferroelectric, N-isopropylbenzylaminium trichloroacetate (1), enables unusual incommensurately modulated structures between its paraelectric phase and ferroelectric phase. In particular, 1 exhibits three distinct IC states coupling with a long-range ordering modulation. That is, the incommensurately modulated lattice is similar to 7 times as large as its periodic prototype, and the IC structure is well solved using a (3 + 1)D superspace group with the modulated wavevector q = (0, 0, 0.1589). To the best of our knowledge, 1 is the first organic ferroelectric showing such a long-range ordering IC structural modulation. In addition, structural analyses reveal that slowing down dynamic motions of anionic moieties accounts for its modulation behaviors, which also results in dramatic reorientation of dipolar moments and concrete ferroelectric polarization of 1 (similar to 0.65 mu C/cm(2)). The combination of unique IC structural modulations and ferroelectricity makes 1 a potential candidate for the assembly of an artificially modulated lattice, which will allow for a deep understanding of the underlying chemistry and physics of aperiodic materials.

Update: 23-Nov-2017

Title:
Frustrated spin-1/2 ladder with ferro- and antiferromagnetic legs
Authors:
Maiti, D; Dey, D; Kumar, M Author Full Names: Maiti, Debasmita; Dey, Dayasindhu; Kumar, Manoranjan
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 446 170-176; 10.1016/j.jmmm.2017.09.025 JAN 15 2018
Abstract:
Two-leg spin-1/2 ladder systems consisting of a ferromagnetic leg and an antiferromagnetic leg are considered where the spins on the legs interact through antiferromagnetic rung couplings J(1). These ladders can have two geometrical arrangements either zigzag or normal ladder and these systems are frustrated irrespective of their geometry. This frustration gives rise to incommensurate spin density wave, dimer and spin fluid phases in the ground state. The magnetization in the systems decreases linearly with J(1)(2), and the systems show an incommensurate phase for 0.0 < J(1) < 1.0. The spin-spin correlation functions in the incommensurate phase follow power law decay which is very similar to Heisenberg antiferromagnetic chain in external magnetic field. In large J(1) limit, the normal ladder behaves like a collection of singlet dimers, whereas the zigzag ladder behaves as a one dimensional spin-1/2 antiferromagnetic chain. (C) 2017 Elsevier B.V. All rights reserved.

Update: 15-Nov-2017

Title:
New State of Matter: Heavy Fermion Systems, Quantum Spin Liquids, Quasicrystals, Cold Gases, and High-Temperature Superconductors
Authors:
Shaginyan, VR; Stephanovich, VA; Msezane, AZ; Schuck, P; Clark, JW; Amusia, MY; Japaridze, GS; Popov, KG; Kirichenko, EV Author Full Names: Shaginyan, V. R.; Stephanovich, V. A.; Msezane, A. Z.; Schuck, P.; Clark, J. W.; Amusia, M. Ya.; Japaridze, G. S.; Popov, K. G.; Kirichenko, E. V.
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS, 189 (5-6):410-450; 10.1007/s10909-017-1801-3 DEC 2017
Abstract:
We report on a new state of matter manifested by strongly correlated Fermi systems including various heavy fermion (HF) metals, two-dimensional quantum liquids such as He films, certain quasicrystals, and systems behaving as quantum spin liquids. Generically, these systems can be viewed as HF systems or HF compounds, in that they exhibit typical behavior of HF metals. At zero temperature, such systems can experience a so-called fermion condensation quantum phase transition (FCQPT). Combining analytical considerations with arguments based entirely on experimental grounds, we argue and demonstrate that the class of HF systems is characterized by universal scaling behavior of their thermodynamic, transport, and relaxation properties. That is, the quantum physics of different HF compounds is found to be universal, emerging irrespective of the individual details of their symmetries, interactions, and microscopic structure. This observed universal behavior reveals the existence of a new state of matter manifest in HF compounds. We propose a simple, realistic model to study the appearance of flat bands in two-dimensional ensembles of ultracold fermionic atoms, interacting with coherent resonant light. It is shown that signatures of these flat bands may be found in peculiarities in their thermodynamic and spectroscopic properties. We also show that the FCQPT, in generating flat bands and altering Fermi surface topology, is an essential progenitor of the exotic behavior of the overdoped high-temperature superconductors represented by , whose superconductivity differs from that predicted by the classical Bardeen-Cooper-Schrieffer theory. The theoretical results presented are in good agreement with recent experimental observations, closing the colossal gap between these empirical findings and Bardeen-Cooper-Schrieffer-like theories.

Update: 9-Nov-2017

Title:
High electrochemical performance of nanoporous Fe3O4/CuO/Cu composites synthesized by dealloying Al-Cu-Fe quasicrystal
Authors:
Liu, H; Wang, XL; Wang, JX; Xu, H; Yu, WS; Dong, XT; Zhang, HB; Wang, LM Author Full Names: Liu, Huan; Wang, Xinlu; Wang, Jinxian; Xu, Hang; Yu, Wensheng; Dong, Xiangting; Zhang, Hongbo; Wang, Limin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 729 360-369; 10.1016/j.jallcom.2017.09.111 DEC 30 2017
Abstract:
Quasicrystal, an attractive type of material with special physical and chemical properties, has been considered as one of the most promising functional materials. Herein, Al65Cu23Fe12 quasicrystal precursor alloy ribbons were prepared by arc-melting subsequently melt-spinning under a protective argon atmosphere. Unique Fe3O4/CuO/Cu with bicontinuous ligaments and nanopore channels structure was fabricated by a facile one-step chemical dealloying method in 2 M NaOH solutions at room temperature with controlled dealloying times (12 h, 24 h, 48 h, and 96 h). X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) analysis, transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM) are employed to study the crystal structure and microstructural evolution of these Fe3O4/CuO/Cu composites. The unique composites combined both advantages of Fe3O4/CuO with high capacities and Cu with excellent conductive as anode material for lithium ion batteries. Remarkably, the successful integration of Fe3O4, CuO and Cu as well as the specific 3D ligament-pore structure, which could alleviate the volume changes during the repeating charge and discharge cycles, endowed the as-prepared electrode material with higher reversible capacity, excellent cycle life, and good rate performance due to the synergetic effect. Cyclic voltammetry (CV) and galvanostatic chargeedischarge measurements had been aimed at evaluating the lithium storage performances of the Fe3O4/CuO/Cu composites. A high specific capacity of 738.4 mAh g(-1) could be achieved up to 550 cycles at a current density of 200 mA g(-1). Therefore, the as synthesized Fe3O4/CuO/Cu composites exhibit excellent electrochemical stability and reactivity, which might open a new avenue to explore the application of quasicrystals. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Phase transitions of Cu3+xSi observed by temperature-dependent x-ray powder diffraction
Authors:
Correa, CA; Poupon, M; Kopecek, J; Kral, R; Zemenova, P; Lecourt, J; Barrier, N; Brazda, P; Klementova, M; Palatinus, L Author Full Names: Correa, Cinthia Antunes; Poupon, Morgane; Kopecek, Jaromir; Kral, Robert; Zemenova, Petra; Lecourt, Jerome; Barrier, Nicolas; Brazda, Petr; Klementova, Mariana; Palatinus, Lukas
Source:
INTERMETALLICS, 91 129-139; 10.1016/j.intermet.2017.07.003 DEC 2017
Abstract:
Phases in the system Cu3+xSi were analyzed by temperature-dependent x-ray powder diffraction and differential scanning calorimetry on samples with nominal composition Cu74Si26 and Cu78Si22 in the temperature range between 30 degrees C and 700 degrees C. Contrary to previous works, which report three phases in the system, we identified six distinct phases, labeled, in order of increasing temperature, eta"', eta", eta(3) eta(2), eta(1),. All these phases can be indexed with a similar basic unit cell. However, each phase has a different superstructure or modulation vectors.
Title:
Z-module defects in crystals
Authors:
Sirindil, A; Quiquandon, M; Gratias, D Author Full Names: Sirindil, Abdullah; Quiquandon, Marianne; Gratias, Denis
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 73 427-437; 10.1107/S2053273317013882 6 NOV 2017
Abstract:
An analysis is presented of the new types of defects that can appear in crystalline structures where the positions of the atoms and the unit cell belong to the same Z-module, i.e. are irrational projections of an N > 3-dimensional (N-D) lattice Lambda as in the case of quasicrystals. Beyond coherent irrationally oriented twins already discussed in a previous paper [Quiquandon et al. (2016). Acta Cryst. A72, 55-61], new two-dimensional translational defects are expected, the translation vectors of which, being projections of nodes of Lambda, have irrational coordinates with respect to the unitcell reference frame. Partial dislocations, called here module dislocations, are the linear defects bounding these translation faults. A specific case arises when the Burgers vector B is the projection of a non-zero vector of Lambda that is perpendicular to the physical space. This new kind of dislocation is called a scalar dislocation since, because its Burgers vector in physical space is zero, it generates no displacement field and has no interaction with external stress fields and other dislocations.
Title:
The monoclinic superstructure of the M2Pt6Al15 series (M = Ca, Sc, Y, La, Lu)
Authors:
Radzieowski, M; Stegemann, F; Hoffmann, RD; Janka, O Author Full Names: Radzieowski, Mathis; Stegemann, Frank; Hoffmann, Rolf-Dieter; Janka, Oliver
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 232 (10):675-687; 10.1515/zkri-2017-2050 OCT 2017
Abstract:
The five ternary intermetallic compounds M2Pt6Al15 (M = Ca, Sc, Y, La, Lu) were prepared from the elements by arc-melting. The crystal structure was determined via single crystal X-ray diffraction. The title compounds crystallize in a superstructure of the RE0.67Pt2Al5 type structure (P6(3)/mmc) in the monoclinic crystal system with space group P12(1)/m1 (Sc2Pt6Al15 : a= 734.19(2), b = 1628.96(10), c = 734.19(2) pm, beta = 119.999(3)degrees; wR = 0.0356, 3034 F-2 values, 68 variables). The superstructure can be derived by the superspace formalism using (3 + 2)D or (3 + 1)D interpretations of the diffraction data. The structural relation to the subcell structure is discussed on the basis of a group-subgroup scheme. In the crystal structure strongly bonded [Pt2Al4](delta-) slabs are alternatingly stacked with ordered layers containing M atoms and Al-3 triangles.
Title:
Modeling of dodecagonal quasicrystal lattices
Authors:
Smolyakov, AV; Girzhon, VV Author Full Names: Smolyakov, A. V.; Girzhon, V. V.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 125 (3):443-450; 10.1134/S1063776117080106 SEP 2017
Abstract:
We consider a method for constructing dodecagonal quasi-lattices, which involves the recurrent multiplication of the initial group of sites that are vertices of a regular dodecagon. The algorithm of modeling of reciprocal lattices of dodecagonal quasicrystals has been analyzed. The proposed modeling method is compared with the traditional projection method. We have performed indexing of the diffraction pattern from dodecagonal quasicrystals, which is analogous to indexing proposed by Cahn for icosahedral quasicrystals. The ambiguity of the choice of the basis vectors of the quasicrystal reciprocal lattice has been considered.

Update: 1-Nov-2017

Title:
Phase equilibria in the nominally Al65Cu23Fe12 system at 3, 5 and 21 GPa: Implications for the quasicrystal-bearing Khatyrka meteorite
Authors:
Stagno, V; Bindi, L; Steinhardt, PJ; Fei, YW Author Full Names: Stagno, Vincenzo; Bindi, Luca; Steinhardt, Paul J.; Fei, Yingwei
Source:
PHYSICS OF THE EARTH AND PLANETARY INTERIORS, 271 47-56; 10.1016/j.pepi.2017.08.005 OCT 2017
Abstract:
Two of the three natural quasiperiodic crystals found in the Khatyrka meteorite show a composition within the Al-Cu-Fe system. Icosahedrite, with formula Al63Cu24Fe13, coexists with the new Al62Cu31Fe2 quasicrystal plus additional Al-metallic minerals such as stolperite (AlCu), kryachkoite [(AlCu)(6)(Fe, Cu)], hollisterite (AlFe3), khatyrkite (Al2Cu) and cupalite (AlCu), associated to high-pressure phases like ringwoodite/ahrensite, coesite, and stishovite. These high-pressure minerals represent the evidence that most of the Khatyrka meteoritic fragments formed at least at 5 GPa and 1200 degrees C, if not at more extreme conditions. On the other hand, experimental studies on phase equilibria within the representative Al-Cu Fe system appear mostly limited to ambient pressure conditions, yet. This makes the interpretation of the coexisting mineral phases in the meteoritic sample quite difficult. We performed experiments at 3,5 and 21 GPa and temperatures of 800-1500 degrees C using the multi-anvil apparatus to investigate the phase equilibria in the Al65Cu23Fe12 system representative of the first natural quasicrystal, icosahedrite. Our results, supported by single-crystal X-ray diffraction and analyses by scanning electron microscopy, confirm the stability of icosahedrite at high pressure and temperature along with additional coexisting Al-bearing phases representative of khatyrkite and stolperite as those found in the natural meteorite. One reversal experiment performed at 5 GPa and 1200 degrees C shows the formation of the icosahedral quasicrystal from a pure Al, Cu and Fe mixture, a first experimental synthesis of icosahedrite under those conditions. Pressure appears to not play a major role in the distribution of Al, Cu and Fe between the coexisting phases, icosahedrite in particular. Results from this study extend our knowledge on the stability of icosahedral AlCuFe at higher temperature and pressure than previously examined, and provide a new constraint on the stability of icosahedrite. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Elevated temperature mechanical behaviour of nanoquasicrystalline Al93Fe3Cr2Ti2 alloy and composites
Authors:
Pedrazzini, S; Galano, M; Audebert, F; Smith, GDW Author Full Names: Pedrazzini, S.; Galano, M.; Audebert, F.; Smith, G. D. W.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 705 352-359; 10.1016/j.msea.2017.08.075 SEP 29 2017
Abstract:
Rapidly solidified nano-quasicrystalline Al93Fe3Cr2Ti2 at% alloy has previously shown outstanding tensile and compressive strength and microstructural stability up to elevated temperatures. Despite this, no study had previously assessed the effect of plastic deformation at elevated temperature to simulate thermal-mechanical forging processes for the production of engineering components. The present work analysed bars consisting of a nano-quasicrystalline Al93Fe3Cr2Ti2 at% alloy matrix, with the addition of 10 and 20 vol% pure Al ductilising fibres, produced through gas atomisation and warm extrusion. The microstructure was made primarily of nanometre-sized icosahedral particles in an alpha-Al matrix. Compression tests were performed across a range of temperatures and strain rates. The measured yield strength at 350 degrees C was over 3x that of "high strength" 7075 T6 Al alloy, showing outstanding thermal stability and mechanical performance. However, the microstructure was shown by XRD to undergo a phase transformation which resulted in the decomposition of the icosahedral phase around 500 degrees C into more stable intermetallic phases. Serrated flow associated with dynamic strain ageing was observed and a semi-quantitative analysis matching elemental diffusion speeds with dislocation speed at specific strain rates was performed, which tentatively identified Ti as the solute species responsible within the selected range of temperatures and strain rates.

Update: 26-Oct-2017

Title:
The Construction of Nonlinear Elasticity Tensors for Crystals and Quasicrystals
Authors:
Astapov, Y; Khristich, D; Markin, A; Sokolova, M Author Full Names: Astapov, Yuri; Khristich, Dmitrii; Markin, Alexey; Sokolova, Marina
Source:
INTERNATIONAL JOURNAL OF APPLIED MECHANICS, 9 (6):10.1142/S1758825117500806 SEP 2017
Abstract:
The problem of construction of constitutive relations in nonlinear elasticity theory for crystals and quasicrystals is associated with finding the construction of the structure of tensors of elastic modules of 2nd and 3rd orders. In the case of linear constitutive relations, the problem is entirely solved for crystals and some quasicrystals. In the case of nonlinear relations, the quantity of nonzero elastic modules of the 3rd order is known only for some classes of crystals. The problem of construction of nonlinear constitutive relations for quasicrystal materials has not been considered. In this article, representations of linear and nonlinear elastic properties of crystals and quasicrystals in the form of decompositions by special invariant tensor bases are considered. This allows us to concretize constitutive relations for icosahedral and axial quasicrystals. It is shown that axial quasicrystals' behavior towards elastic properties coincides with transversal-isotropic materials. Icosahedral quasicrystals' behavior matches with the isotropic materials' one. On the basis of the obtained decompositions of nonlinear elasticity tensors for axial quasicrystals having a symmetry plane and for graphene films with and without defects, the analysis of their mechanical behavior at some types of loading is fulfilled. It is shown that differences in the behavior of these materials appear only in the second order effects.

Update: 20-Oct-2017

Title:
Formation of incommensurate long-range magnetic order in the Dzyaloshinskii-Moriya antiferromagnet Ba-2 CuGe2O7 studied by neutron diffraction
Authors:
Muhlbauer, S; Brandl, G; Mansson, M; Garst, M Author Full Names: Muehlbauer, S.; Brandl, G.; Mansson, M.; Garst, M.
Source:
PHYSICAL REVIEW B, 96 (13):10.1103/PhysRevB.96.134409 OCT 6 2017
Abstract:
Neutron diffraction on a triple-axis spectrometer and a small-angle neutron scattering instrument is used to study the magnetic phase transition in tetragonal Ba2CuGe2O7 at zero magnetic field. In addition to the incommensurate cycloidal antiferromagnetic (AFM) long-range order, we establish that weak incommensurate ferromagnetism (FM) also arises below the transition temperature T-N identified by sharp Bragg peaks close to the Gamma point. The intensities of both the incommensurate AFM and FM Bragg peaks vanish abruptly at T-N, which is indicative of a weak first-order transition. Above TN, evidence is presented that the magnetic intensity within the tetragonal (a, b) plane is distributed on a ring in momentum space whose radius is determined by the incommensurate wave vector of the cycloidal order. We speculate that the associated soft fluctuations are at the origin of the weak first-order transition in the spirit of a scenario proposed by Brazovskii.
Title:
Low-temperature behaviour of K2Sc[Si2O6]F: determination of the lock-in phase and its relationships with fresnoite-and melilite-type compounds
Authors:
Hejny, C; Bindi, L Author Full Names: Hejny, C.; Bindi, L.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 923-930; 10.1107/S2052520617010241 5 OCT 2017
Abstract:
K2Sc[Si2O6]F exhibits, at room temperature, a (3 + 2)-dimensional incommensurately modulated structure [a = 8.9878 (1), c = 8.2694 (2) angstrom, V = 668.01 (2) angstrom(3); superspace group P4(2)/mnm(alpha, alpha,0) 000s(-alpha, alpha,0) 0000] with modulation wave-vectors q(1) = 0.2982 (4)(a* + b*) and q(2) = 0.2982 (4)(-a* + b*). Its low-temperature behaviour has been studied by single-crystal X-ray diffraction. Down to 45 K, the irrational component alpha of the modulation wave-vectors is quite constant varying from 0.2982 (4) (RT), through 0.2955 (8) (120 K), 0.297 (1) (90 K), 0.298 (1) (75 K), to 0.299 (1) (45 K). At 25 K it approaches the commensurate value of one-third [i.e. 0.332 (3)]: thus indicating that the incommensurate-commensurate phase transition takes place between 45 K and 25 K. The commensurate lock-in phase of K2Sc[Si2O6] F has been solved and refined with a 3 x 3 x 1 supercell compared with the tetragonal incommensurately modulated structure stable at room temperature. This corresponds to a 3 x 1 x 3 supercell in the pseudo-orthorhombic monoclinic setting of the low-temperature structure, space group P2/m, with lattice parameters a = 26.786 (3), b = 8.245 (2) c = 26.824 (3) angstrom, beta = 90.00 (1)degrees. The structure is a mixed tetrahedral-octahedral framework composed of chains of [ScO4F2] octahedra that are interconnected by [Si4O12] rings with K atoms in fourfold to ninefold coordination. Distorted [ScO4F2] octahedra are connected to distorted Si tetrahedra to form octagonal arrangements closely resembling those observed in the incommensurate structure of fresnoite-and melilite-type compounds.
Title:
A commensurately modulated structure of parabutlerite, (FeSO4)-S-III(OH)center dot 2H(2)O
Authors:
Plasil, J; Petricek, V; Majzlan, J Author Full Names: Plasil, Jakub; Petricek, Vaclav; Majzlan, Juraj
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 856-862; 10.1107/S2052520617007156 5 OCT 2017
Abstract:
Parabutlerite, orthorhombic (FeSO4)-S-III(OH)center dot 2H(2)O, has been reinvestigated using single-crystal X-ray diffraction. The structure of parabutlerite is commensurately modulated, with a = 20.0789 (8), b = 7.4024 (7), c = 7.2294 (15) angstrom and q = 0.4b*. The superstructure has been determined, using a superspace approach, as having the superspace group Pnma(0 beta 0)s0s and t(0) = 1/20, and refined to R = 0.0295 for 2392 main reflections with I > 3 sigma(I). The structure consists of infinite chains of Fe octahedra that are linked via vertices (OH groups); these chains are encased from both sides by SO4 tetrahedra. The displacive modulation of atoms in parabutlerite is connected with a tilt of the chains around the b axis towards the adjacent chains due to the accommodation of an energetically more favorable hydrogen-bond geometry.
Title:
Structural changes of relaxor ferroelectric Sr0.52Ba0.48Nb2O6 (SBN52) on quenching and reheating
Authors:
Graetsch, HA Author Full Names: Graetsch, Heribert A.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 820-826; 10.1107/S2052520617007880 5 OCT 2017
Abstract:
Quenching of Sr0.52Ba0.48Nb2O6 (SBN52) from temperatures above 700 degrees C causes small modifications in the strontium distribution over the large cation sites (Me1 and Me2), changed off-centre shifts of the Nb atoms and slightly increased modulation amplitudes. The higher disorder of cation incorporation can explain the enhanced ferroelectric properties. The quenched structural disorder can be healed by reheating followed by slow cooling. A change of the modulation dimension on quenching such as for CaxBa1-xNb2O6 (CBN) mixed crystals was not observed.
Title:
Incommensurately modulated structure of morpholinium tetrafluoroborate and configurational versus chemical entropies at the incommensurate and lock-in phase transitions
Authors:
Noohinejad, L; van Smaalen, S; Petricek, V; Schoenleber, A Author Full Names: Noohinejad, Leila; van Smaalen, Sander; Petricek, Vaclav; Schoenleber, Andreas
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 836-843; 10.1107/S2052520617009398 5 OCT 2017
Abstract:
Morpholinium tetrafluoroborate, [C4H10NO](+)[BF4](-), belongs to a class of ferroelectric compounds ABX(4). However, [C4H10NO](+)[BF4](-) does not develop ferroelectric properties because the incommensurate phase below T-c,T-I = 153 K is centrosymmetric with superspace group Pnam(sigma(1)00)00s and sigma(1) = 0.42193 (12) at T = 130 K; the threefold superstructure below T-c,T-II = 117-118 K possesses the acentric but non-ferroelectric space group P2(1)2(1)2(1). At ambient conditions, [C4H10NO](+)[BF4](-) comprises orientationally disordered [BF4](-) anions accommodated in cavities between four morpholinium cations. A structure model for the incommensurately modulated phase, which involves modulated orientational ordering of [BF4](-) together with modulated distortions and displacements of the morpholinium ions is reported. A mechanism is proposed for the phase transitions, whereby at low temperatures morpholinium cations are shaped around the tetrafluoroborate anion in order to optimize the interactions with one orientation of this anion and, thus, forcing [BF4](-) into this orientation. This mechanism is essentially different from a pure order-disorder phase transition. It is supported by consideration of the transition entropy. The difference in configurational entropy between the disordered and incommensurate phases has been computed from the structure models. It is shown to be much smaller than the experimental transition entropy reported by Owczarek et al. [Chem. Phys. (2011), 381, 11-20]. These features show that the order-disorder contribution is only a minor contribution to the transition entropy and that other factors, such as conformational changes, play a larger role in the phase transitions.
Title:
Flexocoupling-induced soft acoustic modes and the spatially modulated phases in ferroelectrics
Authors:
Morozovska, AN; Glinchuk, MD; Eliseev, EA; Vysochanskii, YM Author Full Names: Morozovska, Anna N.; Glinchuk, Maya D.; Eliseev, Eugene A.; Vysochanskii, Yulian M.
Source:
PHYSICAL REVIEW B, 96 (9):10.1103/PhysRevB.96.094111 SEP 29 2017
Abstract:
Using the Landau-Ginzburg-Devonshire theory and one component approximation, we examined the conditions of the soft acoustic phonon mode (A-mode) appearance in a ferroelectric (FE) depending on the magnitude of the flexoelectric coefficient f and temperature T. If the flexocoefficient f is equal to the temperature-dependent critical value f(cr)(T) at some temperature T = T-IC, theA-mode frequency tends to zero atwave vector k = k(0)(cr), and the spontaneous polarization becomes spatially modulated in the temperature rangeT < T-IC, where T-IC is turned into the transition temperature to the incommensurate spatially modulated phase (SMP). When f > f(cr)(T-IC), the A-mode becomes zero for two wave vectors k = k(1,2)(cr), and does not exist in the range of wave vectors k(1)(cr) < k < k(2)(cr), indicating the transition to SMP. The corresponding temperature dependence of the dielectric susceptibility is in agreement with experimental data in ferroics with SMPs. This gives us a background to predict flexocoupling-induced soft acoustic amplitudon-type modes in FEs with SMPs of type II. The available experimental results on neutron scattering in organic incommensurate FE betaine calcium chloride dihydrate are in semiquantitative agreement with our theoretical results.
Title:
The Equivalence Between Unit-Cell Twinning and Tiling in Icosahedral Quasicrystals
Authors:
Prodan, A; Hren, RD; van Midden, MA; van Midden, HJP; Zupanic, E Author Full Names: Prodan, Albert; Hren, Ram Dusic; van Midden, Marion A.; van Midden, Herman J. P.; Zupanic, Erik
Source:
SCIENTIFIC REPORTS, 7 10.1038/s41598-017-12669-w SEP 29 2017
Abstract:
It is shown that tiling in icosahedral quasicrystals can also be properly described by cyclic twinning at the unit cell level. The twinning operation is applied on the primitive prolate golden rhombohedra, which can be considered a result of a distorted face-centered cubic parent structure. The shape of the rhombohedra is determined by an exact space filling, resembling the forbidden five-fold rotational symmetry. Stacking of clusters, formed around multiply twinned rhombic hexecontahedra, keeps the rhombohedra of adjacent clusters in discrete relationships. Thus periodicities, interrelated as members of a Fibonacci series, are formed. The intergrown twins form no obvious twin boundaries and fill the space in combination with the oblate golden rhombohedra, formed between clusters in contact. Simulated diffraction patterns of the multiply twinned rhombohedra and the Fourier transform of an extended model structure are in full accord with the experimental diffraction patterns and can be indexed by means of three-dimensional crystallography. The alternative approach is fully compatible to the rather complicated descriptions in a hyper-space.

Update: 12-Oct-2017

Title:
Influence of chemical leaching on Al-Cu-Co decagonal quasicrystals
Authors:
Mishra, SS; Pandey, SK; Yadav, TP; Srivastava, ON Author Full Names: Mishra, S. S.; Pandey, Sunita K.; Yadav, T. P.; Srivastava, O. N.
Source:
MATERIALS CHEMISTRY AND PHYSICS, 200 23-32; 10.1016/j.matchemphys.2017.07.068 OCT 1 2017
Abstract:
In the present investigation, the chemical leaching of the poly-grain Al65Cu15Co20 and Al65Cu20Co15 decagonal quasicrystalline alloys have been studied. The polished surfaces of as-cast Al65Cu15Co20 and Al65Cu20Co15 alloys have been leached by 10 moltlitre (mol/L) concentrated NaOH alkaline solutions. The X-ray diffraction, Scanning electron microscopy and Transmission electron microscopy techniques have been used for the structural and microstructural characterization of the samples and the chemical composition were characterized using Energy-dispersive X-ray spectroscopy. Chemical leaching exclusively removes the Al from the surfaces of the Al65Cu15Co20 and Al65Cu20Co15 decagonal quasicrystalline alloys, consequentially the formation of porous structure containing nano size particles of Cu, Co and Co3O4 have been observed on the leached surface. The leached surface of Al65Cu15Co20 was more porous compared to Al65Cu20Co15 alloy, however the size of the precipitated nano-particles i.e. Cu, Co and Co3O4 were smaller in the case of Al65Cu20Co15 alloy. The elemental mapping through energy dispersive X-ray spectroscopy suggests that the distribution of Cu and Co were formed on the leached surface, however in some regions the oxygen was also detected. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Bronze-mean hexagonal quasicrystal
Authors:
Dotera, T; Bekku, S; Ziherl, P Author Full Names: Dotera, Tomonari; Bekku, Shinichi; Ziherl, Primoz
Source:
NATURE MATERIALS, 16 (10):987-+; 10.1038/NMAT4963 OCT 2017
Abstract:
The most striking feature of conventional quasicrystals is their non-traditional symmetry characterized by icosahedral, dodecagonal, decagonal or octagonal axes(1-6). The symmetry and the aperiodicity of these materials stem from an irrational ratio of two or more length scales controlling their structure, the best-known examples being the Penrose(7,8) and the Ammann-Beenker(9,10) tiling as two-dimensional models related to the golden and the silver mean, respectively. Surprisingly, no other metallic-mean tilings have been discovered so far. Here we propose a self-similar bronze-mean hexagonal pattern, which may be viewed as a projection of a higher-dimensional periodic lattice with a Koch-like snowflake projection window. We use numerical simulations todemonstrate that a disordered variant(11) of this quasicrystal can be materialized in soft polymeric colloidal particles with a core-shell architecture(12-17). Moreover, by varying the geometry of the pattern we generate a continuous sequence of structures, which provide an alternative interpretation of quasicrystalline approximants observed in several metal-silicon alloys(18).
Title:
Layer-by-layer growth of vertex graph of Penrose tiling
Authors:
Shutov, AV; Maleev, AV Author Full Names: Shutov, A. V.; Maleev, A. V.
Source:
CRYSTALLOGRAPHY REPORTS, 62 (5):683-691; 10.1134/S1063774517050194 SEP 2017
Abstract:
The growth form for the vertex graph of Penrose tiling is found to be a regular decagon. The lower and upper bounds for this form, coinciding with it, are strictly proven. A fractal character of layer-by-layer growth is revealed for some subgraphs of the vertex graph of Penrose tiling.

Update: 28-Sep-2017

Title:
Metastable quasicrystals in Al-Mn alloys containing copper, magnesium and silicon
Authors:
Naglic, I; Samardzija, Z; Delijic, K; Kobe, S; Dubois, JM; Leskovar, B; Markoli, B Author Full Names: Naglic, Iztok; Samardzija, Zoran; Delijic, Kemal; Kobe, Spomenka; Dubois, Jean-Marie; Leskovar, Blaz; Markoli, Bostjan
Source:
JOURNAL OF MATERIALS SCIENCE, 52 (23):13657-13668; 10.1007/s10853-017-1477-8 DEC 2017
Abstract:
We prepared three Al-Mn-based alloys with different copper, magnesium and silicon contents by casting into cylindrical copper molds. All the alloys exhibited primary metastable quasicrystals (QCs). In order to confirm the presence of either primary decagonal QCs (dQCs) or icosahedral QCs (iQCs) and to determine their compositions, the castings were characterized by means of light microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDS), electron-backscatter diffraction and X-ray diffraction. The dQCs are present in the Al-Mn-based alloys containing copper. In the case of the combined presence of copper and magnesium, iQCs are present in the edge region and dQCs are present in the central region. In the alloy containing copper, magnesium and silicon, iQCs are present in the casting. The average metallic radius (AMR) and electron-to-atom ratio of these primary phases were calculated by taking into account the composition of these primary phases, as determined by EDS. The AMR shows different values in the cases of dQCs and iQCs. Equal mean values of the AMR were found in iQCs with markedly different compositions. Furthermore, all the metastable QCs in this work show electron concentrations close to 2.6.
Title:
Tricritical wings and modulated magnetic phases in LaCrGe3 under pressure
Authors:
Kaluarachchi, US; Bud'ko, SL; Canfield, PC; Taufour, V Author Full Names: Kaluarachchi, Udhara S.; Bud'ko, Sergey L.; Canfield, Paul C.; Taufour, Valentin
Source:
NATURE COMMUNICATIONS, 8 10.1038/s41467-017-00699-x SEP 15 2017
Abstract:
Experimental and theoretical investigations on itinerant ferromagnetic systems under pressure have shown that ferromagnetic quantum criticality is avoided either by a change of the transition order, becoming of the first order at a tricritical point, or by the appearance of modulated magnetic phases. In the first case, the application of a magnetic field reveals a wing-structure phase diagram as seen in itinerant ferromagnets such as ZrZn2 and UGe2. In the second case, no tricritical wings have been observed so far. Here, we report on the discovery of wing-structure as well as the appearance of modulated magnetic phases in the temperature-pressure-magnetic field phase diagram of LaCrGe3. Our investigation of LaCrGe3 reveals a double-wing structure indicating strong similarities with ZrZn2 and UGe2. But, unlike these simpler systems, LaCrGe3 also shows modulated magnetic phases similar to CeRuPO. This finding provides an example of an additional possibility for the phase diagram of metallic quantum ferromagnets.
Title:
Periodic layers of a dodecagonal quasicrystal and a floating hexagonal crystal in sedimentation-diffusion equilibria of colloids
Authors:
Pattabhiraman, H; Dijkstra, M Author Full Names: Pattabhiraman, Harini; Dijkstra, Marjolein
Source:
JOURNAL OF CHEMICAL PHYSICS, 147 (10):10.1063/1.4993521 SEP 14 2017
Abstract:
We investigate the behaviour of a system of colloidal particles interacting with a hard-core and a repulsive square shoulder potential under the influence of a gravitational field using event-driven Brownian dynamics simulations. We use a fixed square shoulder diameter equal to 1.4 times the hardcore diameter of the colloids, for which we have previously calculated the equilibrium phase diagram considering two-dimensional disks [H. Pattabhiraman et al., J. Chem. Phys. 143, 164905 (2015) and H. Pattabhiraman and M. Dijkstra, J. Phys.: Condens. Matter 20, 094003 (2017)]. The parameters in the simulations are chosen such that the pressure at the bottom of the sediment facilitates the formation of phases in accordance with the calculated phase diagram of the two-dimensional system. It is surprising that we observe the formation of layers with dodecagonal, square, and hexagonal symmetries at the relevant pressures in the three-dimensional sedimentation column. In addition, we also observe a re-entrant behaviour exhibited by the colloidal fluid phase, engulfing a hexagonal crystal phase, in the sedimentation column. In other words, a floating crystal is formed between the colloidal fluid regions. Published by AIP Publishing.

Update: 21-Sep-2017

Title:
Interaction between infinitely many dislocations and a semi-infinite crack in one-dimensional hexagonal quasicrystal
Authors:
Liu, GT; Yang, LY Author Full Names: Liu, Guan-Ting; Yang, Li-Ying
Source:
CHINESE PHYSICS B, 26 (9):10.1088/1674-1056/26/9/094601 AUG 2017
Abstract:
By means of analytic function theory, the problems of interaction between infinitely many parallel dislocations and a semi-infinite crack in one-dimensional hexagonal quasicrystal are studied. The analytic solutions of stress fields of the interaction between infinitely many parallel dislocations and a semi-infinite crack in one-dimensional hexagonal quasicrystal are obtained. They indicate that the stress concentration occurs at the dislocation source and the tip of the crack, and the value of the stress increases with the number of the dislocations increasing. These results are the development of interaction among the finitely many defects of quasicrystals, which possesses an important reference value for studying the interaction problems of infinitely many defects in fracture mechanics of quasicrystal.

Update: 13-Sep-2017

Title:
On the microstructure, hardness and wear behavior of Al-Fe-Cr quasicrystal reinforced Al matrix composite prepared by selective laser melting
Authors:
Kang, N; Fu, YQ; Coddet, P; Guelorget, B; Liao, HL; Coddet, C Author Full Names: Kang, Nan; Fu, Yingqing; Coddet, Pierre; Guelorget, Bruno; Liao, Hanlin; Coddet, Christian
Source:
MATERIALS & DESIGN, 132 105-111; 10.1016/j.matdes.2017.06.060 OCT 15 2017
Abstract:
Al91Fe4Cr5 quasicrystal (QC) reinforced alpha-Al matrix composite materials from the mixture of pure aluminum and Al65Cu20Fe10Cr5 QC powders were prepared by Selective Laser Melting (SLM) which can produce parts with sophisticated form and fine microstructure with near-zeromaterial waste. The effects of process parameters (such as laser power and scanning speed) on the microstructure, hardness and wear behavior of SLMed composites were investigated with a special focus on the size and morphology of Al91Fe4Cr5 QC reinforcement. After laser melting process, an Al-rich QC phase (Al91Fe4Cr5) is formed. The grain size increases and its morphology changes from spherical to irregular with increment of laser power. Additionally, the sample obtained at relatively low laser power presents a mixed microstructure (partially melted QC, micro-QC and nano-QC) and high wear resistance. The instrumented indentation tests indicate that the partially melted QC particle present higher hardness than that of the other structure in the composite. Moreover, the wear mechanism changes from oxidation to delamination as the laser power increases. (C) 2017 Elsevier Ltd. All rights reserved.
Title:
First Observation of Heavy Fermion Behavior in Ce-Based Icosahedral Approximant
Authors:
Imura, K; Nobe, K; Deguchi, K; Matsunami, M; Miyazaki, H; Yasui, A; Ikenaga, E; Sato, NK Author Full Names: Imura, Keiichiro; Nobe, Kohei; Deguchi, Kazuhiko; Matsunami, Masaharu; Miyazaki, Hidetoshi; Yasui, Akira; Ikenaga, Eiji; Sato, Noriaki K.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 86 (9):10.7566/JPSJ.86.093702 SEP 15 2017
Abstract:
Since the discovery of unconventional quantum criticality in the Au-Al-Yb quasicrystal and pressure-induced quantum criticality in its approximant, quasicrystals and approximants with an icosahedral cluster of atoms have attracted much attention. Here we report magnetic, thermodynamic, transport, and hard x-ray photoemission spectroscopy experiments on the Ce-based approximant Ag-In-Ce. These results indicate the heavy fermion behavior of the 4f electrons and provide convincing evidence of a magnetic phase transition into a spin-glass-like short-rangeordered state at a low temperature. The Ag-In-Ce alloy is the first Ce-based heavy fermion approximant to a Tsai-type quasicrystal. Reflecting its unique crystal structure, the approximant shows an electrical resistivity distinct from that of traditional Kondo lattices.
Title:
Formation pathways of mesoporous silica nanoparticles with dodecagonal tiling
Authors:
Sun, Y; Ma, K; Kao, T; Spoth, KA; Sai, H; Zhang, DH; Kourkoutis, LF; Elser, V; Wiesner, U Author Full Names: Sun, Yao; Ma, Kai; Kao, Teresa; Spoth, Katherine A.; Sai, Hiroaki; Zhang, Duhan; Kourkoutis, Lena F.; Elser, Veit; Wiesner, Ulrich
Source:
NATURE COMMUNICATIONS, 8 10.1038/s41467-017-00351-8 AUG 15 2017
Abstract:
Considerable progress in the fabrication of quasicrystals demonstrates that they can be realized in a broad range of materials. However, the development of chemistries enabling direct experimental observation of early quasicrystal growth pathways remains challenging. Here, we report the synthesis of four surfactant-directed mesoporous silica nanoparticle structures, including dodecagonal quasicrystalline nanoparticles, as a function of micelle pore expander concentration or stirring rate. We demonstrate that the early formation stages of dodecagonal quasicrystalline mesoporous silica nanoparticles can be preserved, where precise control of mesoporous silica nanoparticle size down to <30 nm facilitates comparison between mesoporous silica nanoparticles and simulated single-particle growth trajectories beginning with a single tiling unit. Our results reveal details of the building block size distributions during early growth and how they promote quasicrystal formation. This work identifies simple synthetic parameters, such as stirring rate, that may be exploited to design other quasicrystal-forming self-assembly chemistries and processes.
Title:
X-ray Study of Phason Strains in an AlCuFeMn Decagonal Phase
Authors:
Yang, W; Ando, T; Yamamoto, K Author Full Names: Yang, Wang; Ando, Tomoyo; Yamamoto, Kazuki
Source:
MATERIALS TRANSACTIONS, 58 (6):847-851; 10.2320/matertrans.M2016446 2017
Abstract:
The peak profiles, shifts, and splittings of Bragg reflections, which are inherent in the phason strain of a quasicrystal, are carefully examined using a precise powder X-ray diffraction method for a wide range of different AlCuFeMn alloys and annealing temperatures. Based on the peak-shift dependences of the Bragg reflections on the phason momentum Q(perpendicular to), two kinds of new approximant phases are identifled. These phases have linear phason strains theta(1) = tau(-6) and theta(2) = tau(-5), and theta(1) = tau(-10) and theta(2) =tau(-5), corresponding to lattice spacings a=3.814 nm and b = 2.005 nm, and a = 9.985 nm and b = 2.005 nm in the quasiperiodic plane of the orthorhombic system, respectively.

Update: 6-Sep-2017

Title:
Quantum incommensurate skyrmion crystals and commensurate to in-commensurate transitions in cold atoms and materials with spin-orbit couplings in a Zeeman field
Authors:
Sun, FD; Ye, JW; Liu, WM Author Full Names: Sun, Fadi; Ye, Jinwu; Liu, Wu-Ming
Source:
NEW JOURNAL OF PHYSICS, 19 10.1088/1367-2630/aa7ce5 AUG 16 2017
Abstract:
In this work, we study strongly interacting spinor atoms in a lattice subject to a two dimensional (2d) anisotropic Rashba type of spin orbital coupling (SOC) and an Zeeman field. We find the interplay between the Zeeman field and the SOC provides a new platform to host rich and novel classes of quantum commensurate and in-commensurate phases, excitations and phase transitions. These commensurate phases include two collinear states at low and high Zeeman field, two co-planar canted states at mirror reflected SOC parameters respectively. Most importantly, there are non-coplanar incommensurate Skyrmion (IC-SkX) crystal phases surrounded by the four commensurate phases. New excitation spectra above all the five phases, especially on the IC-SKX phase are computed. Three different classes of quantum commensurate to in-commensurate transitions from the IC-SKX to its four neighboring commensurate phases are identified. Finite temperature behaviors and transitions are discussed. The critical temperatures of all the phases can be raised above that reachable by current cold atom cooling techniques simply by tuning the number of atoms N per site. In view of recent impressive experimental advances in generating 2d SOC for cold atoms in optical lattices, these new many-body phenomena can be explored in the current and near future cold atom experiments. Applications to various materials such as MnSi, Fe-0.5 Co0.5Si, especially the complex incommensurate magnetic ordering in Li2IrO3 are given.

Update: 30-Aug-2017

Title:
Atomic-scale configurations of variant twin boundaries of a pseudo-decagonal quasicrystal approximant in Al60Cr20Fe10Si10 alloy
Authors:
Ma, HK; Li, H; He, ZB Author Full Names: Ma, Haikun; Li, Hua; He, Zhanbing
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 723 736-742; 10.1016/j.jallcom.2017.06.183 NOV 5 2017
Abstract:
Twin boundaries (TBs) of decagonal quasicrystal approximants generally exhibit structural characteristics that are peculiar compared with traditional crystals with small lattice parameters. Herein, the TBs of the orthorhombic (3/2,2/1) 2 decagonal approximant in the quaternary Al60Cr20Fe10Si10 alloy were investigated, and four types of ( 101) TBs were found using atomic-resolution high-angle annular dark-field scanning transmission electron microscopy. The structural features of these TBs at the atomic level were revealed and the corresponding projected structural models along the pseudo-tenfold axis were proposed and discussed. These results demonstrate that the diversifications of the TBs of decagonal approximants are closely related to the rich combinations of substructural blocks, and this may trigger further interest in the planar defects present in other decagonal approximants. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Continual approach at T=0 in the mean field theory of incommensurate magnetic states in the frustrated Heisenberg ferromagnet with an easy axis anisotropy
Authors:
Martynov, SN; Tugarinov, VI; Martynov, AS Author Full Names: Martynov, S. N.; Tugarinov, V. I.; Martynov, A. S.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 440 47-49; 10.1016/j.jmmm.2016.12.086 OCT 15 2017
Abstract:
The algorithm of approximate solution was developed for the differential equation describing the anharmonical change of the spin orientation angle in the model of ferromagnet with the exchange competition between nearest and next nearest magnetic neighbors and the easy axis exchange anisotropy. The equation was obtained from the collinearity constraint on the discrete lattice. In the low anharmonicity approximation the equation is resulted to an autonomous form and is integrated in quadratures. The obvious dependence of the angle velocity and second derivative of angle from angle and initial condition was derived by expanding the first integral of the equation in the Taylor series in vicinity of initial condition. The ground state of the soliton solutions was calculated by a numerical minimization of the energy integral. The evaluation of the used approximation was made for a triple point of the phase diagram.
Title:
Hierarchical porous CoNi/CoO/NiO composites derived from dealloyed quasicrystals as advanced anodes for lithium-ion batteries
Authors:
Liu, H; Wang, XL; Wang, JX; Xu, H; Yu, WS; Dong, XT; Zhang, HB; Wang, LM Author Full Names: Liu, Huan; Wang, Xinlu; Wang, Jinxian; Xu, Hang; Yu, Wensheng; Dong, Xiangting; Zhang, Hongbo; Wang, Limin
Source:
SCRIPTA MATERIALIA, 139 30-33; 10.1016/j.scriptamat.2017.06.011 OCT 2017
Abstract:
Three-dimensional (3D) hierarchical porous CoNi/CoO/NiO composites have been elaborately designed by selectively dealloying of Al-Ni-Co quasicrystals (QCs) alloy. The CoNi/CoO/NiO electrode combines the excellent conductivity and strong stability of CoNi with the high theoretical capacities of CoO/NiO together. When applied as anode materials for lithium-ion batteries (LIBs), the CoNi/CoO/NiO delivers a high specific capacity of 578 mAh g(-1) at a current density of 200 mA g(-1) after 600 cycles. Furthermore, this facile and efficient strategy not only provides an opportunity for rational designing advanced battery anodes, but also open a promising avenue to explore the application of QCs. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Interplay of phase sequence and electronic structure in the modulated martensites of Mn2NiGa from first-principles calculations
Authors:
Kundu, A; Gruner, ME; Siewert, M; Hucht, A; Entel, P; Ghosh, S Author Full Names: Kundu, Ashis; Gruner, Markus E.; Siewert, Mario; Hucht, Alfred; Entel, Peter; Ghosh, Subhradip
Source:
PHYSICAL REVIEW B, 96 (6):10.1103/PhysRevB.96.064107 AUG 14 2017
Abstract:
We investigate the relative stability, structural properties, and electronic structure of various modulated martensites of the magnetic shape memory alloy Mn2NiGa by means of density functional theory. We observe that the instability in the high-temperature cubic structure first drives the system to a structure where modulation shuffles with a period of six atomic planes are taken into account. The driving mechanism for this instability is found to be the nesting of the minority band Fermi surface, in a similar way to that established for the prototype system Ni2MnGa. In agreement with experiments, we find 14M modulated structures with orthorhombic and monoclinic symmetries having energies lower than other modulated phases with the same symmetry. In addition, we also find energetically favorable 10M modulated structures which have not been observed experimentally for this system yet. The relative stability of various martensites is explained in terms of changes in the electronic structures near the Fermi level, affected mostly by the hybridization of Ni and Mn states. Our results indicate that the maximum achievable magnetic field-induced strain in Mn2NiGa would be larger than in Ni2MnGa. However, the energy costs for creating nanoscale adaptive twin boundaries are found to be one order of magnitude higher than that in Ni2MnGa.
Title:
Latest trends in quasicrystal research
Authors:
Takemori, N; Singh, A Author Full Names: Takemori, Nayuta; Singh, Alok
Source:
CURRENT SCIENCE, 113 (3):377-379; AUG 10 2017
Title:
Universal self-assembly of one-component three-dimensional dodecagonal quasicrystals
Authors:
Ryltsev, R; Chtchelkatchev, N Author Full Names: Ryltsev, Roman; Chtchelkatchev, Nikolay
Source:
SOFT MATTER, 13 (29):5076-5082; 10.1039/c7sm00883j AUG 7 2017
Abstract:
Using molecular dynamics simulations, we study computational self-assembly of one-component threedimensional dodecagonal (12-fold) quasicrystals in systems with two-length-scale potentials. Existing criteria for three-dimensional quasicrystal formation are quite complicated and rather inconvenient for particle simulations. So to localize numerically the quasicrystal phase, one should usually simulate over a wide range of system parameters. We show how to universally localize the parameter values at which dodecagonal quasicrystal order may appear for a given particle system. For that purpose, we use a criterion recently proposed for predicting decagonal quasicrystal formation in one-component two-length-scale systems. The criterion is based on two dimensionless effective parameters describing the fluid structure which are extracted from the radial distribution function. The proposed method allows reduction of the time spent for searching the parameters favoring a certain solid structure for a given system. We show that the method works well for dodecagonal quasicrystals; this result is verified on four systems with different potentials: the Dzugutov potential, the oscillating potential which mimics metal interactions, the repulsive shoulder potential describing effective interactions for the core/shell model of colloids and the embedded-atom model potential for aluminum. Our results suggest that the mechanism of dodecagonal quasicrystal formation is universal for both metallic and soft-matter systems and it is based on competition between interparticle scales.

Update: 23-Aug-2017

Title:
How to assign a (3+1)-dimensional superspace group to an incommensurately modulated biological macromolecular crystal
Authors:
Porta, J; Lovelace, J; Borgstahl, GEO Author Full Names: Porta, Jason; Lovelace, Jeff; Borgstahl, Gloria E. O.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 50 1200-1207; 10.1107/S1600576717007294 4 AUG 2017
Abstract:
Periodic crystal diffraction is described using a three-dimensional (3D) unit cell and 3D space-group symmetry. Incommensurately modulated crystals are a subset of aperiodic crystals that need four to six dimensions to describe the observed diffraction pattern, and they have characteristic satellite reflections that are offset from the main reflections. These satellites have a non-integral relationship to the primary lattice and require q vectors for processing. Incommensurately modulated biological macromolecular crystals have been frequently observed but so far have not been solved. The authors of this article have been spearheading an initiative to determine this type of crystal structure. The first step toward structure solution is to collect the diffraction data making sure that the satellite reflections are well separated from the main reflections. Once collected they can be integrated and then scaled with appropriate software. Then the assignment of the superspace group is needed. The most common form of modulation is in only one extra direction and can be described with a (3 + 1) D superspace group. The (3 + 1) D superspace groups for chemical crystallographers are fully described in Volume C of International Tables for Crystallography. This text includes all types of crystallographic symmetry elements found in small-molecule crystals and can be difficult for structural biologists to understand and apply to their crystals. This article provides an explanation for structural biologists that includes only the subset of biological symmetry elements and demonstrates the application to a real-life example of an incommensurately modulated protein crystal.
Title:
Microstructural and crystallographic characteristics of modulated martensite, non-modulated martensite, and pre-martensitic tweed austenite in Ni-Mn-Ga alloys
Authors:
Zhou, L; Schneider, MM; Giri, A; Cho, K; Sohn, Y Author Full Names: Zhou, Le; Schneider, Matthew M.; Giri, Anit; Cho, Kyu; Sohn, Yongho
Source:
ACTA MATERIALIA, 134 93-103; 10.1016/j.actamat.2017.05.050 AUG 1 2017
Abstract:
A combinatorial approach using diffusion couples and TEM analyses was carried out to investigate the composition-dependent martensitic transformation in NiMnGa alloys. The compositions cover a large portion of the off-stoichiometric Ni2MnGa compositions and some Mn-rich compositions. Crystallographic variations of the martensitic phase, including non-modulated (NM) martensite, modulated (5M or 7M) martensite, and austenitic phase were identified in the diffusion couples and investigated with respect to their microstructure and crystallography. The 5M and 7M martensitic structures were only found near the interphase boundary between austenite and martensite, while the NM martensitic structures were found mostly away from the interphase boundary. The tetragonality ratio (c/a) for NM martensite generally increases with e/a ratio, but was also dependent on the composition. The habit plane and martensitic microstructure that consists of twinned variants with differing orientations were documented using electron diffraction. The pre-martensitic state was observed in the austenitic phase that was located near the interphase boundary between austenite and martensite, with distinctive tweed microstructure and a strain field originating from the local lattice distortions. The combinatorial approach proves to be efficient and systematic in studying the composition-dependent martensitic transformation in NiMnGa alloys and can be potentially applied to other shape memory alloys. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Crystal structures of eta ''-Cu3+xSi and eta '''-Cu3+xSi
Authors:
Correa, CA; Perez, O; Kopecek, J; Brazda, P; Klementova, M; Palatinus, L Author Full Names: Correa, Cinthia Antunes; Perez, Olivier; Kopecek, Jaromir; Brazda, Petr; Klementova, Mariana; Palatinus, Lukas
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 767-774; SI 10.1107/S2052520617006163 4 AUG 2017
Abstract:
The binary phase diagram of Cu-Si is unexpectedly complex in the vicinity of Cu3+xSi. The low-temperature region contains three closely related incommensurately modulated phases denoted, in order of increasing temperature of stability, eta''', eta '' and eta'. The structure analysis of eta' has been reported previously [Palatinus et al. (2011). Inorg. Chem. 50, 3743]. Here the structure model for the phases eta '' and eta''' is reported. The structures could be solved in superspace, but no superspace structure model could be constructed due to the complexity of the modulation functions. Therefore, the structures were described in a supercell approximation, which involved a 4 x 4 x 3 supercell for the eta '' phase and a 14 x 14 x 3 supercell for the eta''' phase. Both structures are very similar and differ only by a subtle symmetry lowering from eta '' to eta'''. A comparison of the structure models of eta '' and eta''' with the reported structure of eta' suggests that the reported structure model of eta' contains an incorrect assignment of atomic types.

Update: 17-Aug-2017

Title:
Local cluster networks and the number of valence states in aluminium-transition metal face-centred icosahedral quasicrystals
Authors:
Kitahara, K; Kimura, K Author Full Names: Kitahara, Koichi; Kimura, Kaoru
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 232 (7-9):507-513; 10.1515/zkri-2016-2035 JUL 2017
Abstract:
Coordination environments of a special class of clusters which are related to the valence states in aluminium-transition metal face-centred icosahedral quasicrystals were analysed on the basis of the six-dimensional model of Katz and Gratias for the atomic sites and that of Yamamoto for the centres of the clusters. The number of the clusters per atom in the model (approximate to 0.263) is comparable with that of Al-Cu-Ir cubic approximant crystal (approximate to 0.258), and it indicates that the model reasonably represents the distribution of the clusters. We identified all the possible local cluster networks of short distances, which are related to the inter-cluster bonds, and evaluated the number of the valence states by assuming two possible configurations of inter-cluster bonds. The number of the valence states per atom was derived as a function of the fraction of transition-metal atoms, and the value is in good agreement with that expected from the compositions of real quasicrystals. Notably, the number of the part of the valence states which do not depend on the fraction of transition-metal atoms is numerically similar to the electron to atom ratio known as e/ a, which is phenomenologically related to the stability of quasicrystals.
Title:
Anisotropic electrical, thermal and magnetic properties of Al13Ru4 decagonal quasicrystalline approximant
Authors:
Wencka, M; Vrtnik, S; Kozelj, P; Jaglicic, Z; Gille, P; Dolinsek, J Author Full Names: Wencka, Magdalena; Vrtnik, Stanislav; Kozelj, Primoz; Jaglicic, Zvonko; Gille, Peter; Dolinsek, Janez
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 232 (7-9):647-652; 10.1515/zkri-2016-2039 JUL 2017
Abstract:
We present measurements of the anisotropic electrical and thermal transport coefficients (the electrical resistivity, the thermoelectric power, the thermal conductivity), the magnetization and the specific heat of the Al13Ru4 monoclinic approximant to the decagonal quasicrystal, in comparison to the isostructural Al13Fe4. The electrical and thermal transport parameters of Al13Ru4 were found to exhibit significant anisotropy, qualitatively similar to that found previously in the Al13Fe4 (P. Popcevic, et al., Phys. Rev. B 2010, 81, 184203). The crystallographic b direction, corresponding to the stacking direction of the (a,c) atomic planes, is the most conducting direction for the electricity and heat. The thermopower is strongly anisotropic with a complicated temperature dependence, exhibiting maxima, minima, crossovers and sign change. The electronic density of states (DOS) at the Fermi energy is reduced to 35% of the DOS of Al metal. The magnetic susceptibility is diamagnetic and the diamagnetism is by a factor of 2 stronger for the magnetic field along the stacking b direction.s

Update: 3-Aug-2017

Title:
Three-Dimensional Modeling of Quasicrystal Structures from X-ray Diffraction: An Icosahedral Al-Cu-Fe Alloy
Authors:
Hong, ST Author Full Names: Hong, Seung-Tae
Source:
INORGANIC CHEMISTRY, 56 (13):7354-7359; 10.1021/acs.inorgchem.7b00245 JUL 3 2017
Abstract:
Quasicrystals (QCs) are well-ordered but aperiodic crystals with classically forbidden symmetries (such as 5-fold). High-dimensional (HD) crystallography is a standard method to locate atom positions explicitly. However, in practice, it is still challenging because of its complexity. Here, we report a new simple approach to three-dimensional (3D) atomic modeling derived from X-ray diffraction data, and apply it to the icosahedral QC Al0.63Cu0.25Fe0.12. Electron density maps were calculated directly from 3D diffraction data indexed with noninteger (fractional) numbers as measured, with proper phases; each of 2(5) = 32 possible phase assignments for the five strongest reflections was used for Fourier synthesis. This resulted in an initial phasing model based on chemically sensible electron density maps. The following procedure was exactly the same as that used to determine ordinary crystal structures, except that fractional indices were assigned to the reciprocal vectors relative to the three orthogonal 2-fold axes in icosahedral (I-h) symmetry to which the observed diffraction data conformed. Finally, similar to 30 000 atoms were located within a sphere of a,similar to 48 angstrom radius. Structural motifs or basic repeating units with a hierarchical nature can be found. Isolated icosahedral clusters are surrounded by a concentric dodecahedron, beyond which there is a concentric truncated icosahedron. These are strikingly similar to those obtained via HI) crystallography, but show very clear real-space relationships between the clusters.
Title:
Microstructural and Mechanical Characterization of Hybrid Aluminum Matrix Composite Containing Boron Carbide and Al-Cu-Fe Quasicrystals
Authors:
Khan, M; Zulfaqar, M; Ali, F; Subhani, T Author Full Names: Khan, Mahmood; Zulfaqar, Muhammad; Ali, Fahad; Subhani, Tayyab
Source:
METALS AND MATERIALS INTERNATIONAL, 23 (4):813-822; 10.1007/s12540-017-6619-7 JUL 2017
Abstract:
Hybrid aluminum matrix composites containing particles of boron carbide and quasicrystals were manufactured to explore the combined effect of reinforcements on microstructural evolution and mechanical performance of the composites. The particles were incorporated at a loading of 6 wt% each making a total of 12 wt% reinforcement in pure aluminum. For comparison, two composites containing individually reinforced 12 wt% particles were also prepared along with a reference specimen of pure aluminum. Ball milling technique was employed to mix the composite constituents. The green bodies of composite powders were prepared by uniaxial pressing at room temperature followed by consolidation by pressureless sintering under inert atmosphere. The microstructural characterization was performed using scanning electron microscopy while phase identification was carried out by X-ray diffraction. The mechanical characterization was performed by Vickers hardness and compression tests. Hybrid composites showed increased compressive properties while the composites containing solely quasicrystals demonstrated improved hardness. The increase in mechanical performance was related to the microstructural evolution due to the presence and uniform dispersion of binary particles.
Title:
Orthorhombic intermediate phase originating from {110} nanotwinning in Ni50.0Mn28.7Ga21.3 modulated martensite
Authors:
Straka, L; Drahokoupil, J; Vertat, P; Kopecek, J; Zeleny, M; Seiner, H; Heczko, O Author Full Names: Straka, Ladislav; Drahokoupil, Jan; Vertat, Petr; Kopecek, Jaromir; Zeleny, Martin; Seiner, Hanus; Heczko, Oleg
Source:
ACTA MATERIALIA, 132 335-344; 10.1016/j.actamat.2017.04.048 JUN 15 2017
Abstract:
The temperature evolution of the structure of Ni50.0Mn28.7Ga21.3, single crystals exhibiting magnetic shape memory effect was investigated near the martensitic transformation by X-ray diffraction. Upon heating, five-layered modulated monoclinic martensite (10M) with a = 0.5974 nm, b = 0.5949 nm, c = 0.5589 nm, and 7 = 90.34 at room temperature (297 K) changed to an intermediate (10M') phase with a = b = 0.5945 nm, c = 0.5616 nm, and gamma = 90.25 degrees at a few tenths of kelvin below the transformation to austenite at T-A = 327 K. This previously unreported 10M' phase between 10M martensite and austenite can be described as orthorhombic using axes diagonal to the original a and b axes derived from the cubic L2(1) cell. Upon cooling, the phase remained stable in a broader temperature interval down to temperature T = 318 K at which it transformed back to monoclinic 10M structure with a not equal b. The transformation temperature coincided with the martensitic transformation temperature T-M = 318 K. The SEM observations and theoretical X-ray diffraction calculations indicate that the intermediate phase is actually the nanotwinned original 10M phase. This {110} nanotwinning with approximate to 20 nm mean twin width originates from the complex hierarchical branching on the austenite nucleus-martensite interface. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Influence of Fe addition on the formation of a quasicrystalline phase in bulk Al-rich Al-Mn base alloys
Authors:
Stan-Glowinska, K; Litynska-Dobrzynska, L; Rogal, L Author Full Names: Stan-Glowinska, K.; Litynska-Dobrzynska, L.; Rogal, L.
Source:
MATERIALS CHARACTERIZATION, 128 203-208; 10.1016/j.matchar.2017.04.006 JUN 2017
Abstract:
This work evaluates the effect of Fe addition on the formation of a quasicrystalline phase in the 94A1-6Mn base alloys obtained by wedge casting. Different Mn to Fe ratios (1, 1.4, 2, 5) were used to estimate Fe content that leads to formation of a quasicrystalline icosahedral phase (I-phase) at the selected Al concentration (94 at.%). Based on the obtained results, Fe enhances I-phase nucleation in the studied ternary alloys compared to the non modified binary composition. Although the maximum thickness of the cast wedge at which the I -phase was formed in the prepared alloys varied with Fe content, its nucleation was always limited to a certain range of cooling rates above 10(3) K/s. Hardness increased significantly for areas composed of Al matrix and I -phase particles. The highest HV values were obtained for parts of castings where the microstructure consisted of very fine I-phase/A1 eutectic.

Update: 26-Jul-2017

Title:
Effects of hot-compaction on the structure and properties of Al-Mn-Fe-X alloys strengthened with quasi-crystalline icosahedral phase
Authors:
Stan-Glowinska, K; Litynska-Dobrzynska, L; Kania, B; Dutkiewicz, J; Rogal, L; Skuza, W; Wojewoda-Budka, J; Gordillo, MA; Wiezorek, JM Author Full Names: Stan-Glowinska, K.; Litynska-Dobrzynska, L.; Kania, B.; Dutkiewicz, J.; Rogal, L.; Skuza, W.; Wojewoda-Budka, J.; Gordillo, M. A.; Wiezorek, J. M.
Source:
MATERIALS & DESIGN, 126 162-173; 10.1016/j.matdes.2017.04.043 JUL 15 2017
Abstract:
Melt-spun ribbons of Al91Mn6Fe2X1 (X= Mn, Mo, V) were used as a feedstock to obtain bulk materials by mechanical milling and subsequent hot-pressing compaction. Modifications of the chemical composition of the Al-Fe-Mn base ternary alloy with the transition metals Mo and V facilitated hot-compaction based preparation of bulk samples with microstructures that retained significant fractions of the quasicrystalline I-phase. The transition metal modified bulk alloy samples exhibited enhanced values of compressive strength and high hardness.
Title:
EXISTENCE RESULTS IN THE LINEAR DYNAMICS OF QUASICRYSTALS WITH PHASON DIFFUSION AND NONLINEAR GYROSCOPIC EFFECTS
Authors:
Bisconti, L; Mariano, PM Author Full Names: Bisconti, Luca; Mariano, Paolo Maria
Source:
MULTISCALE MODELING & SIMULATION, 15 (2):745-767; 10.1137/15M1049580 2017
Abstract:
Quasicrystals are characterized by quasi-periodic arrangements of atoms. The description of their mechanics involves deformation and a (so-called phason) vector field accounting at macroscopic scale for local phase changes, due to atomic flips necessary to match quasi periodicity under the action of the external environment. Here we discuss the mechanics of quasicrystals, commenting on a shift from its initial formulation, as standard elasticity in a space with dimension twice the ambient one, to a more elaborated setting, which seems to account more deeply for the physics at hand. In the new setting we tackle two problems. First we discuss the linear dynamics of quasicrystals including a phason diffusion. We prove existence of weak solutions and their uniqueness under rather general boundary and initial conditions. We then consider phason rotational inertia, nonlinearly coupled with the curl of the macroscopic velocity, and prove once again existence of weak solutions to the pertinent balance equations.

Update: 19-Jul-2017

Title:
Towards the growth of single quasicrystalline grains in Al-Cu-(Fe,Cr) alloys after mechanical alloying and subsequent high temperature heating
Authors:
Salimon, AI; Stepashkin, AA; Tcherdyntsev, VV; Olifirov, LK; Klyueva, MV; Kaloshkin, SD Author Full Names: Salimon, A. I.; Stepashkin, A. A.; Tcherdyntsev, V. V.; Olifirov, L. K.; Klyueva, M. V.; Kaloshkin, S. D.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 720 95-104; 10.1016/j.jallcom.2017.05.249 OCT 5 2017
Abstract:
Coarse grains growth in Al65Cu23Fe12 and Al73Cu11Cr16 mechanically alloyed powders was studied. Heating up to 950 degrees C and further rapid cooling produces a range of single quasicrystalline grains having different sizes, shapes and the degree of perfection. In the Al-Cu-Fe system both secondary recrystallization in the solid state and crystallization from liquid state were found. Contrary to the mechanism of nucleation in the liquid state and further growth of nuclei we demonstrate another mechanism - the ready nuclei which survived after the short heating are incorporating the molten material, which results in the formation of perfectly shaped single grains. In the Al-Cu-Cr system only secondary recrystallization in the solid state and no crystallization from liquid state were found. (C) 2017 Elsevier B.V. All rights reserved.

Update: 13-Jul-2017

Title:
Analysis of cracks in one-dimensional hexagonal quasicrystals with the heat effect
Authors:
Fan, CY; Yuan, YP; Pan, YB; Zhao, MH Author Full Names: Fan, CuiYing; Yuan, YanPeng; Pan, YiBo; Zhao, MingHao
Source:
INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 120 146-156; 10.1016/j.ijsolstr.2017.04.036 AUG 1 2017
Abstract:
The extended displacement discontinuity (EDD) method is proposed to analyze cracks in the periodical plane of one-dimensional (1D) hexagonal quasicrystals with the heat effect. Based on the operator theory and the Fourier transform, the fundamental solutions for EDDs are derived, where the EDD5 include phonon and phason displacement discontinuities and the temperature discontinuity. The EDD boundary integral equation method is used to analyze the singularities of the near-crack tip fields, and the extended stress intensity factor (ESIF) expressions are obtained in terms of the EDD5 across the crack faces. The EDD boundary element method is proposed to calculate the ESIFs of cracks in 1D hexagonal quasicrystals. COMSOL software is used to validate the developed method. The influences of applied mechanical and heat loads on cracks in a finite plate are investigated. (C) 2017 Elsevier Ltd. All rights reserved.

Update: 6-Jul-2017

Title:
On magnetism in the quasicrystalline Ti45Zr38Ni17 alloy
Authors:
Czub, J; Przewoznik, J; Zywczak, A; Takasaki, A; Hoser, A; Gondek, L Author Full Names: Czub, J.; Przewoznik, J.; Zywczak, A.; Takasaki, A.; Hoser, A.; Gondek, L.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 470 108-111; 10.1016/j.jnoncrysol.2017.05.007 AUG 15 2017
Abstract:
Magnetism of 3D quasicrystals is extensively researched, mainly for rare-earth or iron-based alloys. In this contribution, magnetic properties of the icosahedral Ti45Zr38Ni17 quasicrystal are reported. Namely, the results of magnetometric and neutron diffraction studies in the broad temperature ranges of 1.5-300 K and 2-700 K respectively are discussed. The magnetometric studies reveal that the alloy exhibits an extremely weak ferromagnetic signal, however it is associated with the traces of nickel clusters at the grains boundaries. The neutron scattering studies, including diffraction in external magnetic field, indicate no possibility of long-rage magnetic ordering in the icosahedral Ti45Zr38Ni17 alloy. According to our studies, the investigated material exhibits Pauli-like paramagnetic behaviour.
Title:
Effects of calcium, manganese and cerium-rich mischmetal additions on the mechanical properties of extruded Mg-Zn-Y alloy reinforced by quasicrystalline I-phase
Authors:
Medina, J; Perez, P; Garces, G; Adeva, P Author Full Names: Medina, Judit; Perez, Pablo; Garces, Gerardo; Adeva, Paloma
Source:
MATERIALS CHARACTERIZATION, 129 195-206; 10.1016/j.matchar.2017.04.033 JUL 2017
Abstract:
The effect of calcium, manganese and cerium mischmetal additions on the mechanical properties of the extruded Mg-6Zn-1Y (wt%) alloy reinforced by quasicrystalline I-phase has been investigated. The tensile behaviour at room temperature can be rationalized on the basis of microstructural changes induced by the different elements added to the ternary alloy. The highest yield stress value corresponds to the material modified with cerium-rich mischmetal. Manganese addition leads to the best balance between strength and ductility while calcium addition has a negligible effect on the mechanical properties of ternary alloy. The analysis of the contributions of the different strengthening mechanisms operating during deformation reveals that grain size refinement is the main hardening contribution in all alloys mechanism followed by the strengthening due to coarse second phases. The hardening due to basal texture conferred by the existence of coarse non-recrystallized grains depends on the overall hardening induced by the rest of strengthening mechanisms.
Title:
Imaging quasiperiodic electronic states in a synthetic Penrose tiling
Authors:
Collins, LC; Witte, TG; Silverman, R; Green, DB; Gomes, KK Author Full Names: Collins, Laura C.; Witte, Thomas G.; Silverman, Rochelle; Green, David B.; Gomes, Kenjiro K.
Source:
NATURE COMMUNICATIONS, 8 10.1038/ncomms15961 JUN 22 2017
Abstract:
Quasicrystals possess long-range order but lack the translational symmetry of crystalline solids. In solid state physics, periodicity is one of the fundamental properties that prescribes the electronic band structure in crystals. In the absence of periodicity and the presence of quasicrystalline order, the ways that electronic states change remain a mystery. Scanning tunnelling microscopy and atomic manipulation can be used to assemble a two-dimensional quasicrystalline structure mapped upon the Penrose tiling. Here, carbon monoxide molecules are arranged on the surface of Cu(111) one at a time to form the potential landscape that mimics the ionic potential of atoms in natural materials by constraining the electrons in the two-dimensional surface state of Cu(111). The real-space images reveal the presence of the quasiperiodic order in the electronic wave functions and the Fourier analysis of our results links the energy of the resonant states to the local vertex structure of the quasicrystal.
Title:
Static charge-density-wave order in the superconducting state of La2-xBaxCuO4
Authors:
Thampy, V; Chen, XM; Cao, Y; Mazzoli, C; Barbour, AM; Hu, W; Miao, H; Fabbris, G; Zhong, RD; Gu, GD; Tranquada, JM; Robinson, IK; Wilkins, SB; Dean, MPM Author Full Names: Thampy, V.; Chen, X. M.; Cao, Y.; Mazzoli, C.; Barbour, A. M.; Hu, W.; Miao, H.; Fabbris, G.; Zhong, R. D.; Gu, G. D.; Tranquada, J. M.; Robinson, I. K.; Wilkins, S. B.; Dean, M. P. M.
Source:
PHYSICAL REVIEW B, 95 (24):10.1103/PhysRevB.95.241111 JUN 21 2017
Abstract:
Charge-density-wave (CDW) correlations feature prominently in the phase diagram of the cuprates, motivating competing theories of whether fluctuating CDW correlations aid superconductivity or whether static CDW order coexists with superconductivity in inhomogeneous or spatially modulated states. Here we report Cu L-edge resonant x-ray photon correlation spectroscopy measurements of CDW correlations in superconducting La2-xBaxCuO4, x = 0.11. Static CDW order is shown to exist in the superconducting state at low temperatures and to persist up to at least 85% of the CDW transition temperature. We discuss the implications of our observations for how nominally competing order parameters can coexist in the cuprates.
Title:
High-field magnetization and magnetic phase diagram of alpha-Cu2V2O7
Authors:
Gitgeatpong, G; Suewattana, M; Zhang, SW; Miyake, A; Tokunaga, M; Chanlert, P; Kurita, N; Tanaka, H; Sato, TJ; Zhao, Y; Matan, K Author Full Names: Gitgeatpong, G.; Suewattana, M.; Zhang, Shiwei; Miyake, A.; Tokunaga, M.; Chanlert, P.; Kurita, N.; Tanaka, H.; Sato, T. J.; Zhao, Y.; Matan, K.
Source:
PHYSICAL REVIEW B, 95 (24):10.1103/PhysRevB.95.245119 JUN 16 2017
Abstract:
High-field magnetization of the spin-1/2 antiferromagnet alpha-Cu2V2O7 was measured in pulsed magnetic fields of up to 56 T in order to study its magnetic phase diagram. When the field was applied along the easy axis (the a axis), two distinct transitions were observed at H-c1 = 6.5 T and H-c2 = 18.0 T. The former is a spin-flop transition typical for a collinear antiferromagnet and the latter is believed to be a spin-flip transition of canted moments. The canted moments, which are induced by the Dzyaloshinskii-Moriya interactions, anti-align for H-c1 < H < H-c2 due to the anisotropic exchange interaction that favors the antiferromagnetic arrangement along the a axis. Above H-c2, the Zeeman energy of the applied field overcomes the antiferromagnetic anisotropic interaction and the canted moments are aligned along the field direction. Density functional theory was employed to compute the exchange interactions, which were used as inputs for quantum Monte Carlo calculations and then further refined by fitting to the magnetic susceptibility data. Contrary to our previous report in Phys. Rev. B 92, 024423 (2015), the dominant exchange interaction is between the third nearest-neighbor spins, which form zigzag spin chains that are coupled with one another through an intertwining network of the nonnegligible nearest and second nearest-neighbor interactions. In addition, elastic neutron scattering under the applied magnetic fields of up to 10 T reveals the incommensurate helical spin structure in the spin-flop state.
Title:
Ultrafast Formation of a Charge Density Wave State in 1T-TaS2: Observation at Nanometer Scales Using Time-Resolved X-Ray Diffraction
Authors:
Laulhe, C; Huber, T; Lantz, G; Ferrer, A; Mariager, SO; Grubel, S; Rittmann, J; Johnson, JA; Esposito, V; Lubcke, A; Huber, L; Kubli, M; Savoini, M; Jacques, VLR; Cario, L; Corraze, B; Janod, E; Ingold, G; Beaud, P; Johnson, SL; Ravy, S Author Full Names: Laulhe, C.; Huber, T.; Lantz, G.; Ferrer, A.; Mariager, S. O.; Grubel, S.; Rittmann, J.; Johnson, J. A.; Esposito, V.; Lubcke, A.; Huber, L.; Kubli, M.; Savoini, M.; Jacques, V. L. R.; Cario, L.; Corraze, B.; Janod, E.; Ingold, G.; Beaud, P.; Johnson, S. L.; Ravy, S.
Source:
PHYSICAL REVIEW LETTERS, 118 (24):10.1103/PhysRevLett.118.247401 JUN 16 2017
Abstract:
Femtosecond time-resolved x-ray diffraction is used to study a photoinduced phase transition between two charge density wave (CDW) states in 1T-TaS2, namely the nearly commensurate (NC) and the incommensurate (I) CDW states. Structural modulations associated with the NC-CDW order are found to disappear within 400 fs. The photoinduced I-CDW phase then develops through a nucleation and growth process which ends 100 ps after laser excitation. We demonstrate that the newly formed I-CDW phase is fragmented into several nanometric domains that are growing through a coarsening process. The coarsening dynamics is found to follow the universal Lifshitz-Allen-Cahn growth law, which describes the ordering kinetics in systems exhibiting a nonconservative order parameter.
Title:
Analysis of a three-dimensional arbitrarily shaped interface crack in a one-dimensional hexagonal thermo-electro-elastic quasicrystal bi-material. Part 1: Theoretical solution
Authors:
Zhao, MH; Dang, HY; Fan, CY; Chen, ZT Author Full Names: Zhao, MingHao; Dang, HuaYang; Fan, CuiYing; Chen, ZengTao
Source:
ENGINEERING FRACTURE MECHANICS, 179 59-78; 10.1016/j.engfracmech.2017.04.019 JUN 15 2017
Abstract:
The extended displacement discontinuity boundary integral-differential equation method is adapted to analyze a three-dimensional interface crack of arbitrary shape in a one-dimensional, hexagonal thermo-electro-elastic quasicrystals bi-material. The extended displacement discontinuities include phonon and phason displacement discontinuities, electric potential discontinuity, as well as temperature discontinuity across the interface crack; while the extended stresses represent phonon and phason stresses, electric displacement and heat flux, respectively. An analysis method is proposed based on the analogy between the governing equations for one-dimensional hexagonal electro-thermo-elastic quasicrystals and three-dimensional transversely isotropic magnetoelectrothermoelastic media. By using the analogy method, the fundamental solutions for unit-point extended displacement discontinuities on the interface are obtained. Using the superposition principal, the extended displacement discontinuity boundary integral-differential equations are established. The singular indices and the singular behaviors of the near crack border fields are studied, and the combined extended stress intensity factors (SIFs) are derived in terms of the EDDs. (c) 2017 Elsevier Ltd. All rights reserved.
Title:
Study on structure variations of incommensurately modulated labradorite feldspars with different cooling histories
Authors:
Jin, SY; Xu, HF Author Full Names: Jin, Shiyun; Xu, Huifang
Source:
AMERICAN MINERALOGIST, 102 (6):1328-1339; 10.2138/am-2017-6003 JUN 2017
Abstract:
The incommensurately modulated structures of three intermediate plagioclase feldspars with compositions of similar to An(51) are determined by single-crystal X-ray diffraction analyses. The samples selected cover a range of different cooling rate, from relatively fast to extremely slow. The structures show various ordering states that are directly correlated with the cooling histories of the samples. The slowest cooled sample shows an e1 structure with strong density modulation, along with nanoscale exsolution lamellae. The fastest cooled sample displays an e2 structure, without second-order satellite reflections (f-reflections) and density modulation. The sample with intermediate cooling rate shows a less ordered e1 structure with weak density modulation, but the modulation period and orientation are the same as in e2 structure. The comparison of the structures with the same composition reveals the ordering process and phase transitions during the cooling of plagioclase within the compositional range of Boggild intergrowth. New parameters from modulation waves can be used for quantifying the ordering state of plagioclase feldspars. Proposed phase relationship and T-T-T diagram for similar to An(51) plagioclase feldspars are illustrated for explaining the relationship among Cl, e1 and e2 structures, and relative cooling rates of their host rocks.
Title:
Enhanced electrochemical hydrogen storage performance of Ti-V-Ni composite employing NaAlH4
Authors:
Liang, F; Lin, J; Wu, YM; Wang, LM Author Full Names: Liang, Fei; Lin, Jing; Wu, Yaoming; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 42 (21):14633-14640; 10.1016/j.ijhydene.2017.04.202 MAY 25 2017
Abstract:
The Ti1.41V0.6Ni doped with NaAlH4 composites were prepared by ball-milling method and the phase composition and electrochemical hydrogen storage properties of the composites were investigated. The phase contains icosahedral quasicrystalline (i-phase), Ti2Ni and V based solid-solution phase primarily. The NaAlH4 phase is not evident for the composite, and the NaAlH4 phase should be decomposed to help form porous structure on the surface of the composites. The electrochemical hydrogen storage properties of composites has been enhanced with doped NaAlH4, and the maximum electrochemical hydrogen discharge capacity is 299.2 mAh/g, and keeps above 220 mAh/g after 80 cycles for 1 wt.% doping. The high-rate discharge ability of the composite electrode could achieve 79.8% at the discharge current density of 240 mA/g compared with that of 30 mA/g. The enhancement could be attributed to decoration of the composites surface, increase of entropy variation and improvement of H-kinetics on the strength of new porous structure in the composites. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Title:
Effect of Icosahedral Phase on Crystallographic Texture and Mechanical Anisotropy of Mg-4%Li Based Alloys
Authors:
Li, CQ; Xu, DK; Yu, S; Sheng, LY; Han, EH Author Full Names: Li, C. Q.; Xu, D. K.; Yu, S.; Sheng, L. Y.; Han, E. H.
Source:
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY, 33 (5):475-480; 10.1016/j.jmst.2016.10.003 MAY 2017
Abstract:
Through investigating and comparing the microstructure and mechanical properties of the as-extruded Mg alloys Mg-4%Li and Mg-4%Li-6%Zn-1.2%Y (in wt%), it demonstrates that although the formation of I-phase (Mg3Zn6Y, icosahedral structure) could weaken the crystallographic texture and improve the mechanical strength, the mechanical anisotropy in terms of strength remains in Mg-4%Li-6%Zn-1.2%Y alloy. Failure analysis indicates that for the Mg-4%Li alloy, the fracture surfaces of the tensile samples tested along transverse direction (TD) contain a large number of plastic dimples, whereas the fracture surface exhibits quasi-cleavage characteristic when tensile samples were tested along extrusion direction (ED). For the Mg-4%Li-6%Zn-1.2%Y alloy, typical ductile fracture surfaces can be observed in both "TD" and "ED" samples. Moreover, due to the zonal distribution of broken I-phase particles, the fracture surface of "TD" samples is characterized by the typical "woody fracture". Copyright (C) 2017, The editorial office of Journal of Materials Science & Technology. Published by Elsevier Limited.

Update: 29-Jun-2017

Title:
Heat capacity, resistivity, and angular dependent magnetization studies of single crystal Nd1+epsilon Fe4B4 for epsilon approximate to 1/7
Authors:
Conner, BS; Susner, MA; Lampen-Kelley, P; May, AF; McGuire, MA; Yan, JQ; Sales, BC Author Full Names: Conner, B. S.; Susner, M. A.; Lampen-Kelley, P.; May, A. F.; McGuire, M. A.; Yan, J. -Q.; Sales, B. C.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 435 100-106; 10.1016/j.jmmm.2017.04.002 AUG 1 2017
Abstract:
Advances in crystal growth have allowed for synthesis of large single crystals of Nd1+epsilon Fe4B4, a wellknown phase with a modulated structure. As a result we are able to report heat capacity and resistivity measurements on a single crystal Nd1+epsilon Fe4B4 sample with a distribution of epsilon that skews towards the solubility limit of Nd near epsilon approximate to 1/7. Heat capacity measurements show evidence of crystal field splitting at temperatures higher than the long-range ferromagnetic Curie temperature. Heat capacity, resistivity, and magnetization measurements all confirm a Curie temperature of 7 K which is lower than previously reported values in the Nd1+epsilon Fe4B4 system. We also perform measurements of the angular dependence of the magnetization and discover behavior associated with the magnetic anisotropy that is inconsistent with the simple description previously proposed. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Fe-57 Mossbauer study of unusual magnetic structure of multiferroic 3R-AgFeO2
Authors:
Sobolev, A; Rusakov, V; Moskvin, A; Gapochka, A; Belik, A; Glazkova, I; Akulenko, A; Demazeau, G; Presniakov, I Author Full Names: Sobolev, A.; Rusakov, V.; Moskvin, A.; Gapochka, A.; Belik, A.; Glazkova, I.; Akulenko, A.; Demazeau, G.; Presniakov, I.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (27):10.1088/1361-648X/aa70ae JUL 12 2017
Abstract:
We report new results of a Fe-57 Mossbauer study of hyperfine magnetic interactions in the layered multiferroic 3R-AgFeO2 demonstrating two magnetic phase transitions at TN1 and TN2. The asymptotic value beta* approximate to 0.34 for the critical exponent obtained from the temperature dependence of the hyperfine field H-hf(T) at Fe-57 the nuclei below TN1 approximate to 14 K indicates that 3R-AgFeO2 shows quasi-3D critical behavior. The spectra just above TN1 (TN1 < T < T* approximate to 41 K) demonstrate a relaxation behavior due to critical spin fluctuations which indicates the occurrence of short-range correlations. At the intermediate temperature range, TN2 < T < TN1, the Fe-57 Mossbauer spectra are described in terms of collinear spin-density-waves (SDW) with the inclusion of many high-order harmonics, indicating that the real magnetic structure of the ferrite appears to be more complicated than a pure sinusoidally modulated SDW. Below T < TN2 approximate to 9 K, the hyperfine field Hhf reveals a large spatial anisotropy (Delta H-anis approximate to 30 kOe) which is related with a local intra-cluster (FeO6) spin-dipole term that implies a conventional contribution of the polarized oxygen ions. We proposed a simple two-parametric formula to describe the dependence of H-anis on the distortions of the (FeO6) clusters. Analysis of different mechanisms of spin and hyperfine interactions in 3R-AgFeO2 and its structural analogue CuFeO2 points to a specific role played by the topology of the exchange coupling and the oxygen polarization in the delafossite-like structures.
Title:
Quantitative atomic force microscopy
Authors:
Songen, H; Bechstein, R; Kuhnle, A Author Full Names: Soengen, Hagen; Bechstein, Ralf; Kuehnle, Angelika
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (27):10.1088/1361-648X/aa6f8b JUL 12 2017
Abstract:
A variety of atomic force microscopy (AFM) modes is employed in the field of surface science. The most prominent AFM modes include the amplitude modulation (AM) and the frequency modulation (FM) mode. Over the years, different ways for analyzing data acquired with different AFM modes have been developed, where each analysis is usually based on mode-specific assumptions and approximations. Checking the validity of the seemingly different approximations employed in the various analysis methods can be a tedious task. Moreover, a straightforward comparison of data analyzed with different methods can, therefore, be challenging. Here, we combine the existing evaluation methods which have been separately developed for the different AFM modes and present a unifying set of three equations. These three AFM equations allow for a straightforward analysis of AFM data within the harmonic approximation, regardless of the AFM mode. The three AFM equations provide the three and only pieces of information about the tip-sample force available within the harmonic approximation. We demonstrate the generality of our approach by quantitatively analyzing three-dimensional AFM data obtained in both the AM and FM mode.
Title:
Engineering of many-body Majorana states in a topological insulator/s-wave superconductor heterostructure
Authors:
Hung, HH; Wu, JS; Sun, K; Chiu, CK Author Full Names: Hung, Hsiang-Hsuan; Wu, Jiansheng; Sun, Kuei; Chiu, Ching-Kai
Source:
SCIENTIFIC REPORTS, 7 10.1038/s41598-017-02493-7 JUN 14 2017
Abstract:
We study a vortex chain in a thin film of a topological insulator with proximity-induced superconductivity-a promising platform to realize Majorana zero modes (MZMs)-by modeling it as a two-leg Majorana ladder. While each pair of MZMs hybridizes through vortex tunneling, we hereby show that MZMs can be stabilized on the ends of the ladder with the presence of tilted external magnetic field and four-Majorana interaction. Furthermore, a fruitful phase diagram is obtained by controlling the direction of magnetic field and the thickness of the sample. We reveal many-body Majorana states and interaction-induced topological phase transitions and also identify trivialsuperconducting and commensurate/ incommensurate charge-density-wave states in the phase diagram.
Title:
Crossover from an incommensurate singlet spiral state with a vanishingly small spin gap to a valence-bond solid state in dimerized frustrated ferromagnetic spin chains
Authors:
Agrapidis, CE; Drechsler, SL; van den Brink, J; Nishimoto, S Author Full Names: Agrapidis, Clio Efthimia; Drechsler, Stefan-Ludwig; van den Brink, Jeroen; Nishimoto, Satoshi
Source:
PHYSICAL REVIEW B, 95 (22):10.1103/PhysRevB.95.220404 JUN 13 2017
Abstract:
Motivated by the magnetic properties of the spin-chain compounds LiCuSbO4 equivalent to LiSbCuO4 and Rb2Cu2Mo3O12, we study the ground state of the Heisenberg chain with dimerized nearest-neighbor ferromagnetic (FM) (J(1), J'(1) < 0) and next-nearest-neighbor antiferromagnetic (J(2) > 0) couplings. Using the density-matrix renormalization group technique and spin-wave theory, we find a first-order transition between a fully polarized FM and an incommensurate spiral state at 2 alpha = beta/(1 + beta), where alpha is the frustration ratio J(2)/|J(1)| and beta the degree of dimerization J'(1)/J(1). In the singlet spiral state the spin-gap is vanishingly small in the vicinity of the FM transition, corresponding to a situation of LiCuSbO4. For larger alpha, corresponding to Rb2Cu2Mo3O12, and smaller beta there is a crossover from this frustration induced incommensurate state to an Affleck-Lieb-Kennedy-Tasaki-type valence-bond solid state with substantial spin gaps.
Title:
Deformation behavior and texture randomization of Mg-Zn-Gd alloys reinforced with icosahedral quasicrystal
Authors:
Huang, H; Miao, HW; Yuan, GY; Chen, CL; Zhang, H; Pei, J; Wang, ZC Author Full Names: Huang, Hua; Miao, Hongwei; Yuan, Guangyin; Chen, Chunlin; Zhang, Hua; Pei, Jia; Wang, Zhongchang
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, 108 (6):455-464; 10.3139/146.111500 JUN 2017
Abstract:
We report hot deformation behavior of icosahedral quasicrystalline phase reinforced Mg-1.50Zn-0.25Gd (at.%) alloys fabricated by a traditional gravity casting approach. The exponential law constitutive equation is applied to describe their flow stress behavior and the average activation energy is determined to be 187.70 kJ mol(-1). We also find that I-phase forms and grows in the alloys when the deformation strain is increasingly applied and that twinning contributes to high basal texture at early stage of deformation. Basal texture is weakened when the applied strain is strong owing to the dynamic recrystallization and also to the particle stimulation nucleation (PSN) effects of I-phase at late stage of deformation. High temperature is found to contribute to recrystallization but restrain I-phase precipitation and also weaken PSN effects of I-phase. Moreover, we find that a large strain rate not only promotes non-basal dislocation glide/twinning but also contributes to basal texture randomization, while a moderate strain rate is harmful for deformation due to the generation of strong basal texture. Furthermore, I-phase is found to be more effective for basal texture randomization than other strengthening secondary phases in Mg alloys, which is due to the presence of many orientation relationships and also because the interface between I-phase and Mg matrix is coherent or semi-coherent.
Title:
On the Mechanisms of Modulation of Crystal Structures
Authors:
Borisov, SV; Magarill, SA; Pervukhina, NV Author Full Names: Borisov, S. V.; Magarill, S. A.; Pervukhina, N. V.
Source:
CRYSTALLOGRAPHY REPORTS, 62 (3):349-354; 10.1134/S1063774517030038 MAY 2017
Abstract:
Based on the assumption that crystal structures of a number of sulfides are the result of modulation of cationic lattices by anionic lattices, the versions of their conjugation in direct and reciprocal spaces have been analyzed using common translational lattices. The concept of this phenomenon, developed within the superspace formalism, is supplemented by a proposed interpretation of the real modulation of the structures.

Update: 21-Jun-2017

Title:
Magnetism of PrFeAsO parent compound for iron-based superconductors: Mossbauer spectroscopy study
Authors:
Komedera, K; Pierzga, A; Blachowski, A; Ruebenbauer, K; Budziak, A; Katrych, S; Karpinski, J Author Full Names: Komedera, K.; Pierzga, A.; Blachowski, A.; Ruebenbauer, K.; Budziak, A.; Katrych, S.; Karpinski, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 717 350-355; 10.1016/j.jallcom.2017.05.049 SEP 15 2017
Abstract:
Mossbauer spectroscopy measurements were performed for the temperature range between 4.2 K and 300 K in a transmission geometry applying 14.41-keV resonant line in Fe-57 for PrFeAsO the latter being a parent compound of the iron-based superconductors belonging to the '1111' family. It was found that an itinerant 3d magnetic order develops at about 165 K and it is accompanied by an orthorhombic distortion of the chemical unit cell. A complete longitudinal 3d incommensurate spin density wave (SDW) order develops at about 140 K. Transferred hyperfine magnetic field generated by the praseodymium magnetic order on iron nuclei is seen at 12.8 K and below, i.e., below magnetic order of praseodymium magnetic moments. It is oriented perpendicular to the field of SDW on iron nuclei. The shape of SDW is almost rectangular at low temperatures and it transforms into roughly triangular form around "nematic" transition at about 140 K. Praseodymium magnetic order leads to the substantial enhancement of SDW due to the large orbital contribution to the magnetic moment of praseodymium. A transferred field indicates presence of strong magnetic susceptibility anisotropy in the [b-c] plane while following rotation of praseodymium magnetic moments in this plane with lowering temperature. It was found that "nematic" phase region is a region of incoherent spin density wavelets typical for a critical region. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Stacking order dynamics in the quasi-two-dimensional dichalcogenide 1T-TaS2 probed with MeV ultrafast electron diffraction
Authors:
Le Guyader, L; Chase, T; Reid, AH; Li, RK; Svetin, D; Shen, X; Vecchione, T; Wang, XJ; Mihailovic, D; Durr, HA Author Full Names: Le Guyader, L.; Chase, T.; Reid, A. H.; Li, R. K.; Svetin, D.; Shen, X.; Vecchione, T.; Wang, X. J.; Mihailovic, D.; Durr, H. A.
Source:
STRUCTURAL DYNAMICS, 4 (4):10.1063/1.4982918 JUL 2017
Abstract:
Transitions between different charge density wave (CDW) states in quasi-twodimensional materials may be accompanied also by changes in the inter-layer stacking of the CDW. Using MeV ultrafast electron diffraction, the out-of-plane stacking order dynamics in the quasi-two-dimensional dichalcogenide 1T-TaS2 is investigated for the first time. From the intensity of the CDW satellites aligned around the commensurate l = 1/6 characteristic stacking order, it is found out that this phase disappears with a 0.3 ps time constant. Simultaneously, in the same experiment, the emergence of the incommensurate phase, with a slightly slower 2.0 ps time constant, is determined from the intensity of the CDW satellites aligned around the incommensurate l = 1/3 characteristic stacking order. These results might be of relevance in understanding the metallic character of the laser-induced metastable "hidden" state recently discovered in this compound. (C) 2017 Author(s).
Title:
Dynamic diffraction effects and coherent breathing oscillations in ultrafast electron diffraction in layered 1T-TaSeTe
Authors:
Wei, LL; Sun, SS; Guo, C; Li, ZW; Sun, K; Liu, Y; Lu, WJ; Sun, YP; Tian, HF; Yang, HX; Li, JQ Author Full Names: Wei, Linlin; Sun, Shuaishuai; Guo, Cong; Li, Zhongwen; Sun, Kai; Liu, Yu; Lu, Wenjian; Sun, Yuping; Tian, Huanfang; Yang, Huaixin; Li, Jianqi
Source:
STRUCTURAL DYNAMICS, 4 (4):10.1063/1.4979643 JUL 2017
Abstract:
Anisotropic lattice movements due to the difference between intralayer and interlayer bonding are observed in the layered transition-metal dichalcogenide 1T-TaSeTe following femtosecond laser pulse excitation. Our ultrafast electron diffraction investigations using 4D-transmission electron microscopy (4D-TEM) clearly reveal that the intensity of Bragg reflection spots often changes remarkably due to the dynamic diffraction effects and anisotropic lattice movement. Importantly, the temporal diffracted intensity from a specific crystallographic plane depends on the deviation parameter s, which is commonly used in the theoretical study of diffraction intensity. Herein, we report on lattice thermalization and structural oscillations in layered 1T-TaSeTe, analyzed by dynamic diffraction theory. Ultrafast alterations of satellite spots arising from the charge density wave in the present system are also briefly discussed. (C) 2017 Author(s).
Title:
Magnetic structures and excitations in CePd2(Al,Ga)(2) series: Development of the "vibron" states
Authors:
Klicpera, M; Boehm, M; Dolezal, P; Mutka, H; Koza, MM; Rols, S; Adroja, DT; Orench, IP; Rodriguez-Carvajal, J; Javorsky, P Author Full Names: Klicpera, M.; Boehm, M.; Dolezal, P.; Mutka, H.; Koza, M. M.; Rols, S.; Adroja, D. T.; Orench, I. Puente; Rodriguez-Carvajal, J.; Javorsky, P.
Source:
PHYSICAL REVIEW B, 95 (8):10.1103/PhysRevB.95.085107 FEB 3 2017
Abstract:
CePd2Al2-xGax compounds crystallizing in the tetragonal CaBe2Ge2-type structure (space group P4/nmm) and undergoing a structural phase transition to an orthorhombic structure (Cmme) at low temperatures were studied by means of neutron scattering. The amplitude-modulated magnetic structure of CePd2Al2 is described by an incommensurate propagation vector (k) over right arrow = (delta(x), 1/2 + delta(y), 0) with delta(x) = 0.06 and delta(y) = 0.04. The magnetic moments order antiferromagnetically within the ab planes stacked along the c axis and are arranged along the direction close to the orthorhombic a axis with a maximum value of 1.5(1) mu(B)/Ce3+. CePd2Ga2 reveals a magnetic structure composed of two components: the first is described by the propagation vector (k) over right arrow (1) = (1/2,1/2,0), and the second one propagates with (k) over right arrow (2) = (0,1/2,0). The magnetic moments of both components are aligned along the same direction-the orthorhombic [100] direction-and their total amplitude varies depending on the mutual phase of magnetic moment components on each Ce site. The propagation vectors (k) over right arrow (1) and (k) over right arrow (2) describe also the magnetic structure of substituted CePd2Al2-xGax compounds, except the one with x = 0.1. CePd2Al1.9Ga0.1 with magnetic structure described by (k) over right arrow and (k) over right arrow (1) stays on the border between pure CePd2Al2 and the rest of the series. Determined magnetic structures are compared with other Ce 112 compounds. Inelastic neutron scattering experiments disclosed three nondispersive magnetic excitations in the paramagnetic state of CePd2Al2, while only two crystal field (CF) excitations are expected from the splitting of ground state J = 5/2 of the Ce3+ ion in a tetragonal/orthorhombic point symmetry. Three magnetic excitations at 1.4, 7.8, and 15.9 meV are observed in the tetragonal phase of CePd2Al2. A structural phase transition to an orthorhombic structure shifts the first excitation up to 3.7 meV, while the other two excitations remain at almost the same energy. The presence of an additional magnetic peak is discussed and described within the Thalmeier-Fulde CF-phonon coupling (i.e., magnetoelastic coupling) model generalized to the tetragonal point symmetry. The second parent compound CePd2Ga2 does not display any sign of additional magnetic excitation. The expected two CF excitations were observed. The development of magnetic excitations in the CePd2Al2-xGax series is discussed and crystal field parameters determined.
Title:
Sr1/2Ce5/14 square 1/7WO4: a new modulated ternary scheelite compound
Authors:
dos Passos, RHD; Arab, M; de Souza, CP; Leroux, C Author Full Names: Damascena dos Passos, Rafael Hernandez; Arab, Madjid; de Souza, Carlson Pereira; Leroux, Christine
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 466-473; 10.1107/S2052520617002827 3 JUN 2017
Abstract:
For the first time, a ternary tetragonal scheelite structure tungstate with strontium and cerium cations, (Sr, Ce)WO4, was synthesized. As much as 35% Ce could be inserted into the structure, leaving 1/7 of the (Sr, Ce) cation sites vacant. Partial ordering of Sr and Ce, with atomic displacements, were shown by high-resolution electron microscopy. Two-dimensional incommensurate modulations occur in this material, in small domains 20 nm in size. The band gap of this compound is significantly lower than the band gap of SrWO4 and this was related to the distortions of WO4 and (Sr,Ce)O-8 polyhedra. The band gap value of 3.2 eV makes Sr1/2Ce5/14 square 1/7WO4 a promising candidate for violet luminescence.
Title:
Could incommensurability in sulfosalts be more common than thought? The case of meneghinite, CuPb13Sb7S24
Authors:
Bindi, L; Petricek, V; Biagioni, C; Plasil, J; Moelo, Y Author Full Names: Bindi, Luca; Petricek, Vaclav; Biagioni, Cristian; Plasil, Jakub; Moelo, Yves
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 369-376; 10.1107/S2052520617002657 3 JUN 2017
Abstract:
The structure of meneghinite (CuPb13Sb7S24), from the Bottino mine in the Apuan Alps (Italy), has been solved and refined as an incommensurate structure in four-dimensional superspace. The structure is orthorhombic, superspace group Pnma(0 beta 0)00s, cell parameters a = 24.0549 (3), b = 4.1291 (6), c = 11.3361 (16) angstrom, modulation vector q = 0.5433 (4) b*. The *structure* was refined from 6604 reflections to a final R = 0.0479. The model includes modulation of both atomic positions and displacement parameters, as well as occupational waves. The driving forces stabilizing the modulated structure of meneghinite are linked to the occupation modulation of Cu and some of the Pb atoms. As a consequence of the Cu/[] and Pb/Sb modulations, three-to sevenfold coordinations of the M cations (Pb/Sb) occur in different parts of the structure. The almost bimodal distribution of the occupation of Cu/[] and Pb/Sb at M5 conforms with the coupled substitution Sb3+ + [] -> Pb2+ + Cu+, thus corroborating the hypothesis deduced previously for the incorporation of copper in the meneghinite structure. The very small departure (similar to 0.54 versus 0.50) from the commensurate value of the modulation raises the question of whether other sulfosalts considered superstructures have been properly described, and, in this light, if incommensurate modulation in sulfosalts could be much more common than thought.
Title:
Ordered vacancy distribution in 2/1 mullite: a superspace model
Authors:
Klar, PB; de la Pinta, N; Lopez, GA; Etxebarria, I; Breczewski, T; Madariaga, G Author Full Names: Klar, Paul B.; de la Pinta, Noelia; Lopez, Gabriel A.; Etxebarria, Inigo; Breczewski, Tomasz; Madariaga, Gotzon
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 377-388; 10.1107/S2052520617001652 3 JUN 2017
Abstract:
A mullite single crystal with composition Al4.84Si1.16O9.58 (2) exhibiting sharp satellite reflections was investigated by means of X-ray diffraction. For the refinement of a superspace model in the superspace group Pbam(alpha 01/2)0ss different scale factors for main and satellite reflections were used in order to describe an ordered mullite structure embedded in a disordered polymorph. The ordered fraction of the mullite sample exhibits a completely ordered vacancy distribution and can be described as a block structure of vacancy blocks (VBs) that alternate with vacancy-free blocks (VFBs) along a and c. The incommensurate nature of mullite originates from a modulation of the block size, which depends on the composition. The displacive modulation is analyzed with respect to the vacancy distribution and a possible Al/Si ordering scheme is derived, although the measurement itself is not sensitive to the Al/Si distribution. An idealized, commensurate approximation for 2/1 mullite is also presented. Comparison of the ordered superspace model with different preceding models reconciles many key investigations of the last decades with partly contradicting conclusions, where mullite was usually treated as either ordered or disordered instead of considering simultaneously different states of order.

Update: 15-Jun-2017

Title:
Enhancement in magnetocaloric properties of NiMnGa alloy through stoichiometric tuned phase transformation and magneto-thermal transitions
Authors:
Dey, S; Roy, RK; Ghosh, M; Mallick, AB; Mitra, A; Panda, AK Author Full Names: Dey, Sushmita; Roy, R. K.; Ghosh, M.; Mallick, A. Basu; Mitra, A.; Panda, A. K.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 439 305-311; 10.1016/j.jmmm.2017.04.088 OCT 1 2017
Abstract:
The investigation is focussed on phase generation and magnetocaloric properties of a series of Ni77-XMnXGa23 (x = 22, 23, 24, 25, 27) alloys prepared through arc melting furnace. With increase in Mn content, the alloys showed systematic transition from a non-modulated martensite (NM) to a fully austenitic parent phase through an appearance and coexistence of modulated (M) structure. Intermediate Mn containing alloy (#Mn-24) not only displayed high magnetic entropy change (Delta S-M) of -7.7 J/kg(-1)K(-1) but also large Refrigerant Capacity (RC) of 169 J.Kg(-1) at magnetic field change of 3 T compared to other alloys. The coexisting martensite (NM, M) and parent austenite as well as overlapping thermomagnetic and structural transformation was deliverable through tuning of alloy chemistry wherein Ni was systematically substituted by Mn. Transmission electron microscopy (TEM) supported the proposition with existence of martensite plates of different morphology in Mn-24 alloy exhibiting superior magnetocaloric properties. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Interlayer coupling and electronic structure of misfit-layered bismuth-based cobaltites
Authors:
Takakura, S; Yamamoto, I; Tanaka, E; Azuma, J; Maki, M Author Full Names: Takakura, Sho-ichi; Yamamoto, Isamu; Tanaka, Eishi; Azuma, Junpei; Maki, Makoto
Source:
PHYSICAL REVIEW B, 95 (19):10.1103/PhysRevB.95.195166 MAY 30 2017
Abstract:
The [Bi2M2O4](p) CoO2 materials (M = Ca, Sr, and Ba) were studied to clarify the effect of the lattice incommensurability on electronic properties using angle-resolved photoemission spectroscopy and transmission electron microscopy (TEM). Results show that the insulating behavior is characterized by a spectral weight for binding energies higher than 2.0 eV. Moreover, the spectral shape is modified as a function of the incident photon energy, demonstrating a close relationship between the electrical properties and interlayer coupling. TEM results show that the effect of the lattice mismatch differs for different misfit parameters p. We therefore conclude that the carrier concentration and the chemical environment at the misfit interface, which depend on the degree of incommensurability, mutually determine the electronic properties of the system.
Title:
Fracture analysis of one-dimensional hexagonal quasicrystals: Researches of a finite dimension rectangular plate by boundary collocation method
Authors:
Cheng, JX; Sheng, DF; Shi, PP Author Full Names: Cheng Jiaxing; Sheng Dongfa; Shi Pengpeng
Source:
JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY, 31 (5):2373-2383; 10.1007/s12206-017-0434-4 MAY 2017
Abstract:
As an important supplement and development to crystallography, the applications about quasicrystal materials have played a core role in many fields, such as manufacturing and the space industry. Due to the sensitivity of quasicrystals to defects, the research on the fracture problem of quasicrystals has attracted a great deal of attention. We present a boundary collocation method to research fracture problems for a finite dimension rectangular one-dimensional hexagonal quasicrystal plate. Because mode I and mode II problems for onedimensional hexagonal quasicrystals are like that for the classical elastic materials, only the anti-plane problem is discussed in this paper. The correctness of the present numerical method is verified through a comparison of the present results and the existing results. And then, the size effects on stress field, stress intensity factor and energy release rate are discussed in detail. The obtained results can provide valuable references for the fracture behavior of quasicrystals.
Title:
Interplay between charge density wave and antiferromagnetic order in GdNiC2
Authors:
Hanasaki, N; Shimomura, S; Mikami, K; Nogami, Y; Nakao, H; Onodera, H Author Full Names: Hanasaki, N.; Shimomura, S.; Mikami, K.; Nogami, Y.; Nakao, H.; Onodera, H.
Source:
PHYSICAL REVIEW B, 95 (8):10.1103/PhysRevB.95.085103 FEB 2 2017
Abstract:
The correlation between the charge density wave (CDW) and f local moments is observed in GdNiC2 by means of x-ray diffraction in a magnetic field. Various kinds of electronic states exist in the magnetic field. The intensity of the CDW peak changes in the successive transitions and the commensurate-incommensurate transition of the CDW takes place as well. The successive transitions are explained in terms of a cooperative effect of the Peierls instability and the spin Friedel oscillation, in which the antiferromagnetic order of the f local moments is coupled to the spin density wave coexisting with the CDW of the conduction electron.
Title:
Effects of oxygen-deficiency on crystal structure, dielectric and ferroelectric properties in Sr5SmTi3+2xNb7-2xO30-x with tungsten bronze structure
Authors:
Deng, BL; Zhu, XL; Liu, XQ; Chen, XM Author Full Names: Deng, Bao Li; Zhu, Xiao Li; Liu, Xiao Qiang; Chen, Xiang Ming
Source:
RSC ADVANCES, 7 (44):27370-27376; 10.1039/c7ra03870d 2017
Abstract:
Oxygen-deficient tungsten bronze ceramics with general formula Sr5SmTi3+ 2xNb7-2xO30-x (x = 0, 0.1, 0.25) are prepared. The effects of oxygen deficiency on the crystal structure, dielectric and ferroelectric properties are investigated. With increasing oxygen deficiency, the crystal structure becomes less stable and the lattice shrinks, while the ferroelectricity is weakened, and the low temperature relaxation enhanced. Commensurate superlattices observed in Sr5SmTi3+ 2xNb7-2xO30-x , corresponding to the onset of the ferroelectric transition as reported previously. In compositions with x = 0.1 and 0.25, two factors that Asite cross occupancies and disturbance of oxygen vacancies on the ferroelectric order are noticed and related to the change from ferroelectric behavior to diffuse one. Three orders of incommensurate superlattice reflections are observed in x = 0.1 and 0.25 compositions. The first-order incommensurate superlattice reflections appear at positions (h + 1/4 - delta, k + 1/4 - delta, l + 1/2), reflecting the common feature in tungsten bronzes with relaxor or diffuse ferroelectric nature. The second-order incommensurate superlattice reflections are observed on the (00l) (l = 0, 1, 2, 3,.) planes around the (h + 1/2, k + 1/2, l) positions, while the third-order incommensurate superlattice reflections are observed on the (00l) (l = 1/2, 3/2,.) planes, by the side of the first-order ones. The appearance of higher-order is believed to reduce the high structural energy induced by the oxygen deficiency.

Update: 7-Jun-2017

Title:
Copper nanocubes on Al65Cu20Fe15 quasicrystalline surface
Authors:
Yadav, TP; Mishra, SS; Srivastava, ON Author Full Names: Yadav, T. P.; Mishra, S. S.; Srivastava, O. N.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 712 134-138; 10.1016/j.jallcom.2017.04.058 JUL 25 2017
Abstract:
A simple leaching method was developed to synthesize Cu nanocubes having edge length in the range of 50-80 nm on a quasicrystalline surface. The Al65Cu20Fe15(at%) quasicrystalline ribbons (similar to 2 mm wide, 5 cm long and similar to 20 mu m thick) have been synthesized by melt spinning techniques. The copper nanocubes were formed by leaching these quasicrystalline ribbons with a 5 M aqueous solution of NaOH. Leaching was performed at various times ranging from 1 to 8 hours (h). The samples were characterized using x-ray diffraction, scanning and transmission electron microscopy as well as energy-dispersive x-ray spectroscopy which confirm the presence of copper nanocubes on the surface of quasicrystal after 8 h of leaching. (C) 2017 Elsevier B.V. All rights reserved.
Title:
An investigation on selective laser melting of Al-Cu-Fe-Cr quasicrystal: From single layer to multilayers
Authors:
Fu, YQ; Kang, N; Liao, HL; Gao, Y; Coddet, C Author Full Names: Fu, Yingqing; Kang, Nan; Liao, Hanlin; Gao, Yang; Coddet, Christian
Source:
INTERMETALLICS, 86 51-58; 10.1016/j.intermet.2017.03.012 JUL 2017
Abstract:
In this study, the effects of processing parameters on the microstructure of Al-Cu-Fe-Cr quasicrystalline (QC) coatings fabricated by selective laser melting (SLM) are investigated. A qualitative analysis on the XRD patterns indicates that the phase composition for the SLM processed coating mainly consisted of Al-Cu-Fe-Cr quasicrystals and alpha-Al (CuFeCr) solid solution, and with increasing laser energy input or coating thickness, the volume fraction of QC i-Al91Fe4Cr5 reduced and those of QC d-Al65Cu20Fe10Cr5 and crystalline 0-Al2Cu increased. The formation of cracks during the coating building procedure from single layer to multilayers is also discussed. For the coatings with the same layer number, the pores and balling particles diminish as laser power increases, due to the growth of melting degree. At the early stage of fabrication, with increment of layer number (or coating thickness), pores and balling particles decrease considerably because the molten pool solidified more "slowly". However, after the layer number increases continuously from 10 to 20, the porosity no longer decreases, and some big size pores, micro-cracks and fractures appear, especially for the sample obtained at lower laser power. A wavy-like pattern composed chiefly of Al and QC phases, is formed at the interfacial region between substrate and coating due to Marangoni effect. (C) 2017 Elsevier Ltd. All rights reserved.
Title:
Salt fog corrosion behavior in a powder-processed icosahedral-phase-strengthened aluminum alloy
Authors:
Watson, TJ; Gordillo, MA; Ernst, AT; Bedard, BA; Aindow, M Author Full Names: Watson, T. J.; Gordillo, M. A.; Ernst, A. T.; Bedard, B. A.; Aindow, M.
Source:
CORROSION SCIENCE, 121 133-138; 10.1016/j.corsci.2017.03.010 JUN 2017
Abstract:
The pitting corrosion resistance has been evaluated for a powder-processed Al-Cr-Mn-Co-Zr alloy which contains approximate to 35% by volume of an icosahedral quasi-crystalline phase and a little Al9Co2 in an Al matrix. ASTM standard salt fog exposure tests show that the alloy exhibits far lower corrosion pit densities and depths than commercial high-strength aerospace Al alloys under the same conditions. Electron microscopy data show that the salt fog exposure leads to the selective oxidation of the face-centered cubic Al matrix around the other phases, and to the development of a porous outer oxide scale. (C) 2017 Elsevier Ltd. All rights reserved.
Title:
Strain modulated ferromagnetic to antiferromagnetic transition in FeRh/BaTiO3 (001) heterostructures
Authors:
Chen, JH; Ma, J; Zhang, YJ; Bao, SY; Wu, L; Liu, C; Nan, CW Author Full Names: Chen, Jiahui; Ma, Jing; Zhang, Yujun; Bao, Shanyong; Wu, Liang; Liu, Chen; Nan, Ce-Wen
Source:
JOURNAL OF APPLIED PHYSICS, 121 (19):10.1063/1.4983361 MAY 21 2017
Abstract:
We report the elastically induced magnetic phase transition of FeRh thin films on BaTiO3 (001) at the successive phase transitions of BaTiO3, which is accompanied by abrupt variations of magnetization and resistance of FeRh at saturated magnetic fields. In-situ X-ray diffraction at different temperatures reveal that the compressive strains are induced accompanied by the tetragonal to orthorhombic and the orthorhombic to rhombohedral structural phase transition of BaTiO3 during cooling, due to the changes in the lattice constant and domain structure in different phases. The compressive strain further stabilizes the antiferromagnetic phase of FeRh and accounts for the magnetization and resistance changes. Published by AIP Publishing.
Title:
Dimensional Crossover in a Charge Density Wave Material Probed by Angle-Resolved Photoemission Spectroscopy
Authors:
Nicholson, CW; Berthod, C; Puppin, M; Berger, H; Wolf, M; Hoesch, M; Monney, C Author Full Names: Nicholson, C. W.; Berthod, C.; Puppin, M.; Berger, H.; Wolf, M.; Hoesch, M.; Monney, C.
Source:
PHYSICAL REVIEW LETTERS, 118 (20):10.1103/PhysRevLett.118.206401 MAY 18 2017
Abstract:
High-resolution angle-resolved photoemission spectroscopy data reveal evidence of a crossover from one-dimensional (1D) to three-dimensional (3D) behavior in the prototypical charge density wave (CDW) material NbSe3. In the low-temperature 3D regime, gaps in the electronic structure are observed due to two incommensurate CDWs, in agreement with x-ray diffraction and electronic-structure calculations. At higher temperatures we observe a spectral weight depletion that approaches the power-law behavior expected in one dimension. From the warping of the quasi-1D Fermi surface at low temperatures, we extract the energy scale of the dimensional crossover. This is corroborated by a detailed analysis of the density of states, which reveals a change in dimensional behavior dependent on binding energy. Our results offer an important insight into the dimensionality of excitations in quasi-1D materials.
Title:
Effect of Atomic Disorder and Temperature on Incommensurate Helical Spin Waves in the Anderson-Hubbard Model
Authors:
Groshev, AG; Arzhnikov, AK Author Full Names: Groshev, A. G.; Arzhnikov, A. K.
Source:
PHYSICS OF THE SOLID STATE, 59 (5):890-897; 10.1134/S1063783417050146 MAY 2017
Abstract:
Based on the single-band t-t' Anderson-Hubbard model, the effect of disorder on the parameters and ranges of existence of incommensurate helical spin waves is studied. The problem is solved within the functional integration theory in static approximation, taking into account longitudinal fluctuations of the magnetic moment. Magnetic phase diagrams and parameters of incommensurate helical spin waves are obtained as functions of temperatures and electron and impurity concentrations. It is shown that disorder can lead to the first-order transition from the antiferromagnetic phase to the (Q, pi) phase and the metal-dielectric transition from antiferromagnetic metal to antiferromagnetic dielectric far from the half-filled band. The results obtained are used to explain the incommensurate magnetic order observed in cuprates in the overdoped mode.

Update: 1-Jun-2017

Title:
The order-disorder evolution in quasicrystals through phason flips
Authors:
Buganski, I; Chodyn, M; Strzalka, R; Wolny, J Author Full Names: Buganski, Ireneusz; Chodyn, Maciej; Strzalka, Radoslaw; Wolny, Janusz
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 710 92-101; 10.1016/j.jallcom.2017.03.251 JUL 5 2017
Abstract:
The problem of incorporating phason flips in the structural investigation of aperiodic systems is still an open question and a challenge in crystallography. Phasons are understood both as atomic fluctuation and positional disorder of the quasicrystalline lattice. Popular correction to diffraction peaks' intensities takes the form of generalized Debye-Waller factor, assuming Gaussian distribution of fluctuations in the perpendicular space of higher-dimensional periodic lattice. Although proven to work in case of random tiling types of structures recent evidence indicates improper handling of peaks with high perpendicular space scattering vector whenever structure is far from random tiling regime. We introduce the concept of a series expansion of the characteristic function of the statistical distribution to properly correct the peaks' intensities with respect to phasonic fluctuations. Calculations are performed upon Penrose tiling. Such approximation of the structure factor works correctly even in cases for which the Debye-Waller correction fails. Even more we investigate transition to random tiling through phason flips by means of the statistical approach which results in interesting scaling properties (ordered -> disordered -> random -> amorphous structure). (C) 2017 Elsevier B.V. All rights reserved.
Title:
Three-dimensional exact electric-elastic analysis of a multilayered two-dimensional decagonal quasicrystal plate subjected to patch loading
Authors:
Yang, LZ; Li, Y; Gao, Y; Pan, E; Waksmanski, N Author Full Names: Yang, Lianzhi; Li, Yang; Gao, Yang; Pan, Ernian; Waksmanski, Natalie
Source:
COMPOSITE STRUCTURES, 171 198-216; 10.1016/j.compstruct.2017.02.036 JUL 1 2017
Abstract:
An exact electric-elastic analysis of a multilayered two-dimensional decagonal quasicrystal plate subjected to patch loading with simply supported boundary conditions is presented. The pseudo-Stroh formalism and propagator matrix method are used to obtain the exact three-dimensional mechanical behaviors of the plate. By expressing the patch loading in the form of a double Fourier series expansion an exact closed-form solution with a concise and elegant expression is deduced. Three different kinds of patch surface loadings are applied to the surface of the plate and the response of the plate is investigated. Comprehensive numerical results are shown for a sandwich plate subjected to the three patch loadings with two different stacking sequences. The results show that the stacking sequences, patch loading areas, and patch loading types have a great influence on the stress, displacement and electric components of the plate. Also, different coupling constants between the phonon and phason fields will influence the physical quantities. The useful features observed from numerical results can be used in the design of composite laminates made of two-dimensional piezoelectric quasicrystals. The numerical results can also serve as a reference in convergence studies of other numerical methods and for verification of existing or future plate theories. (C) 2017 Elsevier Ltd. All rights reserved.
Title:
Non-close-packed three-dimensional quasicrystals
Authors:
Damasceno, PF; Glotzer, SC; Engel, M Author Full Names: Damasceno, Pablo F.; Glotzer, Sharon C.; Engel, Michael
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (23):10.1088/1361-648X/aa6cc1 JUN 14 2017
Abstract:
Quasicrystals are frequently encountered in condensed matter. They are important candidates for equilibrium phases from the atomic scale to the nanoscale. Here, we investigate the computational self-assembly of four quasicrystals in a single model system of identical particles interacting with a tunable isotropic pair potential. We reproduce a known icosahedral quasicrystal and report a decagonal quasicrystal, a dodecagonal quasicrystal, and an octagonal quasicrystal. The quasicrystals have low coordination number or occur in systems with mesoscale density variations. We also report a network gel phase.
Title:
Exchange bias and strain effect co-modulated magnetic symmetry in La0.6Sr0.4MnO3/orthorhombic-YMnO3 multiferroic heterostructures
Authors:
Zheng, DX; Gong, JL; Jin, C; Li, P; Feng, LF; Bai, HL Author Full Names: Zheng, Dongxing; Gong, Junlu; Jin, Chao; Li, Peng; Feng, Liefeng; Bai, Haili
Source:
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 50 (21):10.1088/1361-6463/aa69ab JUN 1 2017
Abstract:
The exchange bias and strain effect co-modulated magnetic symmetry in all oxide La0.6Sr0.4MnO3 (LSMO) and orthorhombic YMnO3 (YMO) multiferroic heterostructures were studied. Because of the lattice mismatch between the LSMO and YMO layers, the LSMO layer exhibits a 90 degrees rotation growth on the YMO layer. The strain induced growth not only leads to a 90 degrees phase shift in the anisotropic magnetoresistance (AMR) curves, but also brings a two-fold symmetric magnetoelastic coupling energy along the LSMO [1 1 0] direction. With the incorporation of magnetoelastic coupling energy and exchange coupling energy, the exchange bias induced torque shows a phase shift and causes the asymmetry of the peak position and value in the AMR curves. This work illustrates a modulated magnetic symmetry in ferromagnetic/multiferroic systems by interfacial exchange coupling and strain effect, which will benefit the design of magnetoelectric devices.
Title:
Influence of Cr on local order and dynamic properties of liquid and undercooled Al-Zn alloys
Authors:
Pasturel, A; Jakse, N Author Full Names: Pasturel, A.; Jakse, N.
Source:
JOURNAL OF CHEMICAL PHYSICS, 146 (18):10.1063/1.4982887 MAY 14 2017
Abstract:
Using ab initio molecular dynamics, we present a systematic study of structural and transport properties of liquid Al90Zn10 and Al83Zn10Cr7 alloys. In the liquid phase, we find that Cr additions promote the formation of a heterogeneous local ordering characterized by a strong five-fold symmetry (icosahedral short-range order (ISRO)) around Cr atoms. In the undercooled phase, we observe the extension of ISRO to icosahedral medium-range order (IMRO) length scale referring to Cr atoms. In examining dynamic properties, we show that this Cr induced structural heterogeneity leads to a substantial decoupling of Cr diffusion from the diffusion of Al and Zn components by a factor of 3 at 1000 K, the liquidus temperature. Below this temperature, the formation of IMRO gives rise to a non-Arrhenian temperature dependence of diffusivity and viscosity, a breakdown of the Stokes-Einstein relation, as well as the onset of dynamic heterogeneities. Using the isoconfigurational ensemble method, we evidence that the structural origin of dynamics heterogeneities is clearly related to IMRO. Finally we discuss the role of IMRO in a quasicrystal-enhanced nucleation mechanism discovered recently in Al-Zn-Cr alloys. Published by AIP Publishing.
Title:
Evidence of cross-cutting and redox reaction in Khatyrka meteorite reveals metallic-Al minerals formed in outer space
Authors:
Lin, C; Hollister, LS; MacPherson, GJ; Bindi, L; Ma, C; Andronicos, CL; Steinhardt, PJ Author Full Names: Lin, Chaney; Hollister, Lincoln S.; MacPherson, Glenn J.; Bindi, Luca; Ma, Chi; Andronicos, Christopher L.; Steinhardt, Paul J.
Source:
SCIENTIFIC REPORTS, 7 10.1038/s41598-017-01445-5 MAY 9 2017
Abstract:
We report on a fragment of the quasicrystal-bearing CV3 carbonaceous chondrite Khatyrka recovered from fine-grained, clay-rich sediments in the Koryak Mountains, Chukotka (Russia). We show higher melting-point silicate glass cross-cutting lower melting-point Al-Cu-Fe alloys, as well as unambiguous evidence of a reduction-oxidation reaction history between Al-Cu-Fe alloys and silicate melt. The redox reactions involve reduction of FeO and SiO2 to Fe and Fe-Si metal, and oxidation of metallic Al to Al2O3, occurring where silicate melt was in contact with Al-Cu-Fe alloys. In the reaction zone, there are metallic Fe and Fe-Si beads, aluminous spinel rinds on the Al-Cu-Fe alloys, and Al2O3 enrichment in the silicate melt surrounding the alloys. From this and other evidence, we demonstrate that Khatyrka must have experienced at least two distinct events: first, an event as early as 4.564 Ga in which the first Al-Cu-Fe alloys formed; and, second, a more recent impact-induced shock in space that led to transformations of and reactions between the alloys and the meteorite matrix. The new evidence firmly establishes that the Al-Cu-Fe alloys (including quasicrystals) formed in outer space in a complex, multi-stage process.
Title:
Competing Phases Involving Spin-State and Ligand Structural Orderings in a Multistable Two-Dimensional Spin Crossover Coordination Polymer
Authors:
Zhang, DP; Trzop, E; Valverde-Munoz, FJ; Pineiro-Lopez, L; Munoz, MC; Collet, E; Real, JA Author Full Names: Zhang, Daopeng; Trzop, Elzbieta; Valverde-Munoz, Francisco J.; Pineiro-Lopez, Lucia; Munoz, M. Carmen; Collet, Eric; Real, Jose A.
Source:
CRYSTAL GROWTH & DESIGN, 17 (5):2736-2745; 10.1021/acs.cgd.7b00218 MAY 2017
Abstract:
Competition between spin-crossover and structural ligand ordering is identified as responsible for multistability and generation of six different phases in a rigid two-dimensional coordination polymer formulated {Fe-II[Hg-II(SCN)(3)](2) mu-(4,4'-bipy)(2)}(n) (1) (4,4'-bipy = 4,4'-bipyridine). The structure of 1 consists of infinite linear [Fe(mu-4,4'-bipy)](n)(2n+) chains linked by in situ formed {[Hg-II(SCN)(3)](2)(mu-4,4'-bipy)}(2n-) anionic dimers. The thermal dependence of the high-spin fraction, his, features four magnetic phases defined by steps following the sequence gamma(HS) = 1 (phase 1) <-> gamma(HS) = 1/2 (phase 2) <-> gamma(HS) approximate to 1/3 (phase 3) <-> gamma(HS) = 0 (phase 4) These four magnetic states are consistent with structural ordering stemming from the different commensurate or incommensurate high and low-spin populations [HS] <-> [HS:LS], <-> approximate to [HS:2LS] <-> [LS1] inferred from single crystal-analysis. Furthermore, two additional phases are generated at low temperature. One, LS2 (gamma(HS) = 0, phase 5); is due to spontaneous symmetry breaking of the : LS-1 state below 85 K The other results from irradiating the low-temperature-LS2 Phase at 15 K with red light to photogenerate a HS phase of low symmetry (HS*) (gamma(HS) = 1, phase 6). Detailed structural studies of the six phases-unravd the pivotal role-played by the internal dihedral angle of the 4,4'-bipy ligands in the microscopic. mechanism responsible for multistability and multistep behavior in 1.
Title:
Theory of charge density wave depinning by electromechanical effect
Authors:
Quemerais, P Author Full Names: Quemerais, P.
Source:
EPL, 117 (5):10.1209/0295-5075/117/57004 MAR 2017
Abstract:
We discuss the first theory for the depinning of low-dimensional, incommensurate, charge density waves (CDWs) in the strong electron-phonon (e-p) regime. Arguing that most real CDWs systems invariably develop a gigantic dielectric constant (GDC) at very low frequencies, we propose an electromechanical mechanism which is based on a local field effect. At zero electric field and large enough e-p coupling the structures are naturally pinned by the lattice due to its discreteness, and develop modulation functions which are characterized by discontinuities. When the electric field is turned on, we show that it exists a finite threshold value for the electric field above which the discontinuities of the modulation functions vanish due to CDW deformation. The CDW is then free to move. The signature of this pinning/depinning transition as a function of the increasing electric field can be directly observed in the phonon spectrum by using inelastic neutrons or X-rays experiments. Copyright (C) EPLA, 2017

Update: 25-May-2017

Title:
Mechanical alloying as a solid state route for fabrication of Al-Cu-M(=Fe, Cr) quasicrystalline phases
Authors:
Salimon, AI; Shevchukov, AP; Stepashkin, AA; Tcherdyntsev, VV; Olifirov, LK; Kaloshkin, SD Author Full Names: Salimon, A. I.; Shevchukov, A. P.; Stepashkin, A. A.; Tcherdyntsev, V. V.; Olifirov, L. K.; Kaloshkin, S. D.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 707 315-320; 10.1016/j.jallcom.2016.11.173 JUN 15 2017
Abstract:
Almost single phase quasicrystalline powders consisting of icosahedral Al65Cu23Fe12 and decagonal Al73Cu11Cr16 phases were produced by mechanical alloying (MA) and subsequent heat-treatment. Microstructure, particle size distribution, chemical and phase composition of crystalline powder precursors forming under MA from elemental powders of Al, Cu, Fe and Cr were investigated. Phase transformations leading to formation of quasicrystals during heating of precursors were determined by differential thermal analysis and X-ray diffraction. The growth of quasicrystalline grains studied by SEM is discussed. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Effect of Cr addition on the formation of the decagonal quasicrystalline phase of a rapidly solidified Al-Ni-Co alloy
Authors:
Wolf, W; Sitta, BO; Martini, LM; Jorge, AM; Bolfarini, C; Kiminami, CS; Botta, WJ Author Full Names: Wolf, W.; Sitta, B. O.; Martini, L. M.; Jorge, A. M., Jr.; Bolfarini, C.; Kiminami, C. S.; Botta, W. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 707 41-45; 10.1016/j.jallcom.2016.10.050 JUN 15 2017
Abstract:
The influence of Cr addition in a rapidly solidified Al-Ni-Co alloy was investigated. Melt spun samples of atomic composition Al71Ni20Co9, Al72Ni19Co7Cr2 and Al72Ni20Co5Cr3 were studied by X-ray diffraction and transmission electron microscopy. Aiming to develop quasicrystalline compositions enriched in corrosion resistant elements such as Cr and Ni this work presents, for the first time, the effect of Cr addition on the quasicrystalline phase formation of a high-Ni Al-Ni-Co rapidly solidified alloy chosen to be within the range of formation of the decagonal quasicrystalline phase observed in this ternary system. The composition of the quaternary alloys was chosen by reducing the Co content in favor of Cr on the ternary alloy and keeping the average valence electron per atom (e/a) around 1.86. The phase constitution of the ternary alloy consisted of the decagonal phase along with two intermetallic phases, Al3Ni and Al3Ni2. The addition of Cr resulted in the formation of a second quasicrystalline decagonal phase, rich in Cr. This was due to the low Cr solubility on the ternary Al-Ni-Co decagonal and intermetallic phases, which rejected Cr and resulted on the formation of the Cr-rich quasicrystal. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Characterization of nano-quasicrystal-formation in correlation to the local structure in Zr-based metallic glasses containing Pd
Authors:
Saida, J; Yamada, R; Kozikowski, P; Imafuku, M; Sato, S; Ohnuma, M Author Full Names: Saida, Junji; Yamada, Rui; Kozikowski, Pawel; Imafuku, Muneyuki; Sato, Shigeo; Ohnuma, Masato
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 707 46-50; 10.1016/j.jallcom.2016.10.270 JUN 15 2017
Abstract:
The effect of a noble metal (Pd) on the local atomic structure of the glassy state and the transformation behavior of quasicrystal (QC) precipitation in Zr-70(Cu and Ni)(30-x)Pd-x (x = 0, 5, 10, 20) alloys were investigated. A QC phase precipitates in Zr-Cu glassy alloys at Pd concentrations of 5-20 at.% and in Zr-Ni glassy alloys at Pd concentrations of 10-20 at.%. The radial distribution function (RDF) indicates a change in the local atomic structure upon the addition of Pd. The QC phase is abruptly formed from the glassy structure above a certain temperature. The activation energy for nucleation is much larger than that for the precipitation of conventional intermetallic compounds. The QC growth is suddenly suppressed when their diameter reaches approximately 20 nm. The cooperative motion of icosahedral clusters as the precipitation mechanism was discussed. It was assumed that QC nucleus has a Zr-centered icosahedral medium-range order (MRO) as its core, and it grows by the aggregation of surrounding small icosahedral clusters. Noble metals might play a role of stabilizing the individual Zr-centered icosahedral MROs. (C) 2016 Elsevier B.V. All rights reserved.
Title:
On the lubricity of transition metal dichalcogenides: an ab initio study
Authors:
Irving, BJ; Nicolini, P; Polcar, T Author Full Names: Irving, Benjamin J.; Nicolini, Paolo; Polcar, Tomas
Source:
NANOSCALE, 9 (17):5597-5607; 10.1039/c7nr00925a MAY 7 2017
Abstract:
Owing to specific characteristics engendered by their lamellar structures, transition metal dichalcogenides are posited as being some of the best dry lubricants available. Herein, we report a density functional investigation into the sliding properties and associated phenomena of these materials. Calculated potential energy and charge transfer profiles are used to highlight the dependence of shear strength on chemical composition and bilayer orientation (sliding direction). Furthermore, our calculations underscore the intrinsic relationship between incommensurate crystals and the oft-touted superlubric behaviour of molybdenum disulfide.
Title:
Domain state of the axial next-nearest-neighbor Ising model in two dimensions
Authors:
Matsubara, F; Shirakura, T; Suzuki, N Author Full Names: Matsubara, Fumitaka; Shirakura, Takayuki; Suzuki, Nobuo
Source:
PHYSICAL REVIEW B, 95 (17):10.1103/PhysRevB.95.174409 MAY 5 2017
Abstract:
We have examined the spin ordering of an axial next-nearest-neighbor Ising model in two dimensions (2D) near above the antiphase (< 2 > phase). We considered an N-R-replica system and calculated an overlap function qm between different replicas, having used a cluster heat bath Monte Carlo method. We determined transition temperature between the < 2 > phase and a floating incommensurate (IC) phase as T-C2/J = 0.89 +/- 0.01 with frustration ratio k(= -J(2)/J(1)) = 0.6. We found that the spin state at T greater than or similar to T-C2 may be called a domain state, because the spin structure is characterized by a sequentially arranged four types of domains with different < 2 > structures. In the domain state, the 2D XY symmetry of the spin correlation in the IC phase weakly breaks, and the diversity of the spin arrangement increases as T -> T-C2. The Binder ratio gL exhibits a depression at T similar to T-C2 and the quasiperiodic spin structure, which is realized in the IC phase, becomes diverse at T greater than or similar to T-C2. We discussed that the domain state is stable against the thermal fluctuation which brings a two-stage development of the spin structure at low temperatures.
Title:
NMR determination of an incommensurate helical antiferromagnetic structure in EuCo2As2
Authors:
Ding, QP; Higa, N; Sangeetha, NS; Johnston, DC; Furukawa, Y Author Full Names: Ding, Q. -P.; Higa, N.; Sangeetha, N. S.; Johnston, D. C.; Furukawa, Y.
Source:
PHYSICAL REVIEW B, 95 (18):10.1103/PhysRevB.95.184404 MAY 5 2017
Abstract:
We report Eu-153, As-75, and Co-59 nuclear magnetic resonance (NMR) results on EuCo2As2 single crystal. Observations of Eu-153 and As-75 NMR spectra in zero magnetic field at 4.3 K below an antiferromagnetic (AFM) ordering temperature T-N = 45 K and its external magnetic field dependence clearly evidence an incommensurate helical AFM structure in EuCo2As2. Furthermore, based on Co-59 NMR data in both the paramagnetic and the incommensurate AFM states, we have determined the model-independent value of the AFM propagation vector k = (0,0,0.73 +/- 0.07)2 pi/c, where c is the c lattice parameter. Thus the incommensurate helical AFM state was characterized by only NMR data with model-independent analyses, showing NMR to be a unique tool for determination of the spin structure in incommensurate helical AFMs.
Title:
The interaction between a screw dislocation and a wedge-shaped crack in one-dimensional hexagonal piezoelectric quasicrystals
Authors:
Jiang, LJ; Liu, GT Author Full Names: Jiang, Li-Juan; Liu, Guan-Ting
Source:
CHINESE PHYSICS B, 26 (4):10.1088/1674-1056/26/4/044601 APR 2017
Abstract:
Based on the fundamental equations of piezoelasticity of quasicrystal material, we investigated the interaction between a screw dislocation and a wedge-shaped crack in the piezoelectricity of one-dimensional hexagonal quasicrystals. Explicit analytical solutions are obtained for stress and electric displacement intensity factors of the crack, as well as the force on dislocation. The derivation is based on the conformal mapping method and the perturbation technique. The influences of the wedge angle and dislocation location on the image force are also discussed. The results obtained in this paper can be fully reduced to some special cases already available or deriving new ones.

Update: 18-May-2017

Title:
Nucleation of recrystallized magnesium grains over quasicrystalline phase during severe plastic deformation of a Mg-Zn-Y alloy at room temperature
Authors:
Singh, A; Basha, DA; Somekawa, H; Tsuchiya, K Author Full Names: Singh, Alok; Basha, Dudekula Aithaf; Somekawa, Hidetoshi; Tsuchiya, Koichi
Source:
SCRIPTA MATERIALIA, 134 80-84; 10.1016/j.scriptamat.2017.02.039 JUN 2017
Abstract:
We show by high pressure torsion at room temperature and transmission electron microscopy that nucleation of recrystallized alpha-Mg grains occurs preferentially over quasicrystalline i-phase particles at an early stage of recrystallization in a Mg-3.0Zn-0.5Y (at%) alloy. alpha-Mg grains nucleated on i-phase surfaces by torsional rotation N = 1/2 (at 5GPa pressure), and show definite orientation relationships with the i-phase. These orientation relationships are asymmetrical variations of those reported for as-cast and extruded alloys. The nucleated grains show a planar interface with the i-phase and are often faceted as they grow into a yet unrecrystallized matrix. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Effects of grain boundaries and defects on anisotropic magnon transport in textured Sr14Cu24O41
Authors:
Chen, X; Jarvis, K; Sullivan, S; Li, YT; Zhou, JS; Shi, L Author Full Names: Chen, Xi; Jarvis, Karalee; Sullivan, Sean; Li, Yutao; Zhou, Jianshi; Shi, Li
Source:
PHYSICAL REVIEW B, 95 (14):10.1103/PhysRevB.95.144310 APR 27 2017
Abstract:
The strong spin-spin exchange interaction in some low-dimensional magnetic materials can give rise to a high group velocity and thermal conductivity contribution from magnons. Examples are the incommensurate layered compounds (Sr,Ca,La)(14)Cu24O41. The effects of grain boundaries and defects on quasi-one-dimensional magnon transport in these compounds are not well understood. Here we report the microstructural and anisotropic thermal transport properties of textured Sr14Cu24O41, which is prepared by solid-state reaction followed by spark plasma sintering. Transmission electron microscopy clearly reveals nanolayered grains and the presence of dislocations and planar defects. The thermal conductivity contribution and mean free paths of magnons in the textured samples are evaluated with the use of a kinetic model for one-dimensional magnon transport and found to be suppressed significantly compared to single crystals at low temperatures. The experimental results can be explained by a one-dimensional magnon-defect scattering model, provided that the magnon-grain boundary scattering mean free path in the anisotropic magnetic structure is smaller than the average length of these nanolayers along the c axis. The finding suggests low transmission coefficients for energy-carrying magnons across grain boundaries.
Title:
Tuning the competing phases of bilayer ruthenate Ca3Ru2O7 via dilute Mn impurities and magnetic field
Authors:
Zhu, M; Peng, J; Tian, W; Hong, T; Mao, ZQ; Ke, X Author Full Names: Zhu, M.; Peng, J.; Tian, W.; Hong, T.; Mao, Z. Q.; Ke, X.
Source:
PHYSICAL REVIEW B, 95 (14):10.1103/PhysRevB.95.144426 APR 21 2017
Abstract:
We have systematically investigated the evolution of the magnetic structure of the bilayer ruthenate Ca-3(Ru1-xMnx)(2)O-7 induced uponMndoping. For 0 < x <= 0.03, thematerials exhibit the same spin structure as that of the parent compound at low temperature, while an incommensurate cycloidal magnetic structure emerges at T slightly above the metal-insulator transition (MIT) temperature (T-MIT). In contrast, for x >= 0.04 the ground state becomes a G-type antiferromagnetic Mott insulator. Furthermore, we have observed magnetic-field-induced transitions in Ca-3(Ru0.96Mn0.04)(2)O-7, which is positioned at the phase boundary. Below T-MIT, the magnetic transition is accompanied by a structural transition, as well as a dramatic change in the electronic properties from a Mott insulator to a localized phase. On the contrary, an incommensurate-to-commensurate spin structure transition is observed for T-MIT < T < T-ICM. Our results suggest strong competing magnetic tendencies in this bilayer ruthenate system that are very susceptible to 3d transition-metal substitution and magnetic field.
Title:
Kitaev-Heisenberg model in a magnetic field: Order-by-disorder and commensurate-incommensurate transitions
Authors:
Chern, GW; Sizyuk, Y; Price, C; Perkins, NB Author Full Names: Chern, Gia-Wei; Sizyuk, Yuriy; Price, Craig; Perkins, Natalia B.
Source:
PHYSICAL REVIEW B, 95 (14):10.1103/PhysRevB.95.144427 APR 21 2017
Abstract:
We present a theoretical study of field-induced magnetic phases in the honeycomb Kitaev-Heisenberg model, which is believed to describe the essential physics of Mott insulators with strong spin-orbit coupling such as A(2)IrO(3) and alpha-RuCl3. We obtain a rich finite temperature phase diagram in which the competition between the Zeeman coupling and thermal fluctuations gives rise to both collinear zigzag phases and noncoplanar magnetic orders. Our large-scale classical Monte Carlo simulations also unveil intriguing commensurate-incommensurate transitions and multiple-Q incommensurate phases at high field. Experimental implications are also discussed.
Title:
Field-induced metastability of the modulation wave vector in a magnetic soliton lattice
Authors:
Zhu, M; Peng, J; Hong, T; Prokes, K; Zou, T; Mao, ZQ; Ke, X Author Full Names: Zhu, M.; Peng, J.; Hong, T.; Prokes, K.; Zou, T.; Mao, Z. Q.; Ke, X.
Source:
PHYSICAL REVIEW B, 95 (13):10.1103/PhysRevB.95.134429 APR 19 2017
Abstract:
We present magnetic-field-induced metastability of the magnetic soliton lattice in a bilayer ruthenate Ca-3(Ru1-xFex)(2)O-7(x = 0.05) through single-crystal neutron diffraction study. We show that the incommensurability of the modulation wave vector at zero field strongly depends on the history of magnetic field at low temperature, and that the equilibrium ground state can be achieved by warming above a characteristic temperature Tg similar to 37 K. We suggest that such metastability might be associated with the domain wall pinning by the magnetic Fe dopants.
Title:
Incommensurate magnetic order in a quasicubic structure of the double-perovskite compound Sr2NiIrO6
Authors:
Rolfs, K; Toth, S; Pomjakushina, E; Adroja, DT; Khalyavin, D; Conder, K Author Full Names: Rolfs, K.; Toth, S.; Pomjakushina, E.; Adroja, D. T.; Khalyavin, D.; Conder, K.
Source:
PHYSICAL REVIEW B, 95 (14):10.1103/PhysRevB.95.140403 APR 10 2017
Abstract:
In Sr2NiIrO6, a metastable compound, the magnetic structure could be elucidated. The magnetic susceptibility data of the compound suggests a three-dimensional Heisenberg behavior. Moreover, neutron diffraction reveals a novel incommensurate magnetic order, requiring exchange interactions beyond second neighbor to stabilize this phase. An incommensurate propagation vector of k = (0, k, k) with k = 0.356 was observed in such a pseudocubic system. This can be an example of how to induce an incommensurate ground state and a possible type-II multiferroicity in double perovskites.
Title:
Emergent incommensurate correlations in frustrated ferromagnetic spin-1 chains
Authors:
Lee, HJ; Choi, M; Jeon, GS Author Full Names: Lee, Hyeong Jun; Choi, MooYoung; Jeon, Gun Sang
Source:
PHYSICAL REVIEW B, 95 (2):10.1103/PhysRevB.95.024424 JAN 23 2017
Abstract:
We study frustrated ferromagnetic spin-1 chains, where the ferromagnetic nearest-neighbor coupling competes with the antiferromagnetic next-nearest-neighbor coupling. We use the density-matrix renormalization group to obtain the ground states. Through the analysis of spin-spin correlations we identify the double Haldane phase as well as the ferromagnetic phase. It is shown that the ferromagnetic coupling leads to incommensurate correlations in the double Haldane phase. Such short-range correlations transform continuously into the ferromagnetic instability at the transition to the ferromagnetic phase. We also compare the results with the spin-1/2 and classical spin systems and discuss the string orders in the system.

Update: 10-May-2017

Title:
Formation of a quasicrystalline phase in Al-Mn base alloys cast at intermediate cooling rates
Authors:
Stan-Glowinska, K; Rogal, L; Goral, A; Wierzbicka-Miernik, A; Wojewoda-Budka, J; Schell, N; Litynska-Dobrzynska, L Author Full Names: Stan-Glowinska, Katarzyna; Rogal, Lukasz; Goral, Anna; Wierzbicka-Miernik, Anna; Wojewoda-Budka, Joanna; Schell, Norbert; Litynska-Dobrzynska, Lidia
Source:
JOURNAL OF MATERIALS SCIENCE, 52 (13):7794-7807; 10.1007/s10853-017-1011-z JUL 2017
Abstract:
Al-rich 94Al-6Mn and 94Al-4Mn-2Fe alloys were suction-cast to evaluate the feasibility of obtaining bulk quasicrystal-strengthened Al-alloys at intermediate cooling rates alloyed with non-toxic, easily accessible and affordable additions. The influence of different cooling rates on the potential formation of a quasicrystalline phase was examined by means of scanning and transmission electron microscopy, X-ray diffraction and differential scanning calorimetry. Increased cooling rates in the thinnest castings entailed a change in sample phase composition. The highest cooling rates turned out to be insufficient to form an icosahedral quasicrystalline phase (I-phase) in the binary alloy. Instead, an orthorhombic approximant phase occurred (L-phase). The addition of Fe to the 94Al-6Mn binary alloy enhanced the formation of a quasicrystalline phase. At intermediate cooling rates of 10(2)-10(3) K/s, various metastable phases were formed, including decagonal and icosahedral quasicrystals and their approximants. Rods (1 mm in diameter) composed of I-phase particles embedded in Al matrix exhibited a hardness of 1.5 GPa, much higher than the 1.1 GPa of 94Al-6Mn.
Title:
Magnetic texturing due to the partial ordering of Fe+3 and Cu+2 in NdBaCuFeO5
Authors:
Pissas, M Author Full Names: Pissas, M.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 432 224-230; 10.1016/j.jmmm.2017.01.083 JUN 15 2017
Abstract:
The crystal and magnetic structure of the oxygen deficient double perovskite NdBaCuFeO5 was studied, using neutron powder diffraction data. The structure was refined from neutron powder diffraction data using the space groups P4/ mmm and P4mm. For 2 K <= T <= T-N2 = 260 K three families of magnetic Bragg peaks exist. These peaks can be indexed with commensurate propagation vectors k(1) = [1/2 1/2 1/2 ], k(2) = [1/2 1/2 0] and the incommensurate k(3) = [1/2 1/2 0.4] Above T-N2 only magnetic Bragg peaks originated from k(1) and k(2) propagation, were observed. The incommensurate magnetic structure can be attributed to a circular inclined spiral ordering as in YBaCuFeO5 compound. (C)2017 Elsevier B. V. All rights reserved.
Title:
Hyperuniformity variation with quasicrystal local isomorphism class
Authors:
Lin, C; Steinhardt, PJ; Torquato, S Author Full Names: Lin, C.; Steinhardt, P. J.; Torquato, S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (20):10.1088/1361-648X/aa6944 MAY 24 2017
Abstract:
Hyperuniformity is the suppression of long-wavelength density fluctuations, relative to typical structurally disordered systems. In this paper, we examine how the degree of hyperuniformity [(Lambda) over bar (infinity)] in quasicrystals depends on the local isomorphism class. By studying the continuum of pentagonal quasicrystal tilings obtained by direct projection from a five-dimensional hypercubic lattice, we find that (Lambda) over bar (infinity) is dominantly determined by the local distribution of vertex environments (e.g. as measured by Voronoi cells) but also exhibits a non-negligible dependence on the restorability. We show that the highest degree of hyperuniformity [smallest (Lambda) over bar (infinity)] corresponds to the Penrose local isomorphism class. The difference in the degree of hyperuniformity is expected to affect physical characteristics, such as transport properties.
Title:
Structure and magnetism in the bond-frustrated spinel ZnCr2Se4
Authors:
Zajdel, P; Li, WY; van Beek, W; Lappas, A; Ziolkowska, A; Jaskiewicz, S; Stock, C; Green, MA Author Full Names: Zajdel, P.; Li, W. -Y.; van Beek, W.; Lappas, A.; Ziolkowska, A.; Jaskiewicz, S.; Stock, C.; Green, M. A.
Source:
PHYSICAL REVIEW B, 95 (13):10.1103/PhysRevB.95.134401 APR 3 2017
Abstract:
The crystal and magnetic structures of stoichiometric ZnCr2Se4 have been investigated using synchrotron x-ray and neutron powder diffraction, muon spin relaxation (mu SR), and inelastic neutron scattering. Synchrotron x-ray diffraction shows a spin-lattice distortion from the cubic Fd (3) over barm spinel to a tetragonal I4(1)/amd lattice below T-N = 21 K, where powder neutron diffraction confirms the formation of a helical magnetic structure with magnetic moment of 3.04( 3) mu(B) at 1.5 K, close to that expected for high-spin Cr3+. mu SR measurements show prominent local spin correlations that are established at temperatures considerably higher (< 100 K) than the onset of long-range magnetic order. The stretched exponential nature of the relaxation in the local spin-correlation regime suggests a wide distribution of depolarizing fields. Below T-N, unusually fast (> 100 mu s(-1)) muon relaxation rates are suggestive of rapid site hopping of the muons in static field. Inelastic neutron scattering measurements show a gapless mode at an incommensurate propagation vector of k = [000.4648( 2)] in the low-temperature magnetic ordered phase that extends to 0.8 meV. The dispersion is modeled by a two-parameter Hamiltonian, containing ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions with a J(nnn)/J(nn) = -0.337.
Title:
Enhancement of Mechanical Properties of Aluminum and 2124 Aluminum Alloy by the Addition of Quasicrystalline Phases
Authors:
Wolf, W; Aliaga, LCR; Travessa, DN; Afonso, CRM; Bolfarini, C; Kiminami, CS; Botta, WJ Author Full Names: Wolf, Witor; Rodriguez Aliaga, Luis Cesar; Travessa, Dilermando Nagle; Moreira Afonso, Conrado Ramos; Bolfarini, Claudemiro; Kiminami, Claudio Shyinti; Botta, Walter Jose
Source:
MATERIALS RESEARCH-IBERO-AMERICAN JOURNAL OF MATERIALS, 19 74-79; 1 10.1590/1980-5373-MR-2016-0088 DEC 2016
Abstract:
A structural and mechanical characterization of pure aluminum and 2124 T6 aluminum alloy reinforced with quasicrystalline phases of composition Al65Cu20Fe15 and Al70.5Pd21Mn8.5 (% at.) were performed. The quasicrystalline phases were synthesized by arc melting and then milled to produce powder of the alloys, which were then mechanical mixed with the starting powders of aluminum and 2124 aluminum alloy. The composites were produced by hot extrusion of a mechanical mixture containing 20% (% wt.) of the reinforcing phases on the metallic matrix. The structural characterization of the composites was carried out by X- ray diffraction, scanning electron microscopy and transmission electron microscopy. Mechanical characterization was carried out by Vickers hardness measurements and torsion tests at room temperature. The pure aluminum/ quasicrystal composite showed the presence of the same phases from the starting powder mixture while for the 2124 aluminum alloy/Al65Cu20Fe15 the quasicrystalline phase transformed to the tetragonal w-Al7Cu2 Fe during the solution heat treatment. Mechanical strength of the composites presented a substantial increase in comparison to the original matrix metal. While the equivalent ultimate tensile strength of the Al/ quasicrystal composites reached values up to 215MPa and Vickers hardness up to 60HV, the 2124/ quasicrystal composites reached values up to 670MPa and Vickers hardness up to 190HV.

Update: 4-May-2017

Title:
Incommensurately modulated twin structure of nyerereite Na1.64K0.36Ca(CO3)(2)
Authors:
Bolotina, NB; Gavryushkin, PN; Korsakov, AV; Rashchenko, SV; Seryotkin, YV; Golovin, AV; Moine, BN; Zaitsev, AN; Litasov, KD Author Full Names: Bolotina, Nadezhda B.; Gavryushkin, Pavel N.; Korsakov, Andrey V.; Rashchenko, Sergey V.; Seryotkin, Yurii V.; Golovin, Alexander V.; Moine, Bertrand N.; Zaitsev, Anatoly N.; Litasov, Konstantin D.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 73 276-284; SI 10.1107/S2052520616020680 2 APR 2017
Abstract:
The incommensurately modulated twin structure of nyerereite Na1.64K0.36Ca(CO3)(2) has been first determined in the (3 + 1)- dimensional symmetry group Cmcm(alpha 00)00s with modulation vector q = 0.383a*. Unit-*cell* values are a = 5.062 (1), b = 8.790 (1), c = 12.744 (1) angstrom. Three orthorhombic components are related by threefold rotation about [001]. Discontinuous crenel functions are used to describe the occupation modulation of Ca and some CO3 groups. The strong displacive modulation of the O atoms in vertexes of such CO3 groups is described using x- harmonics in crenel intervals. The Na, K atoms occupy mixed sites whose occupation modulation is described in two ways using either complementary harmonic functions or crenels. The nyerereite structure has been compared both with the commensurately modulated structure of K-free Na2Ca(CO3)(2) and with the widely known incommensurately modulated structure of gamma-Na2CO3.
Title:
IN SITU TEM STUDY OF PRECIPITATION IN A QUASICRYSTAL-STRENGTHENED Al-ALLOY
Authors:
Boncina, T; Zupanic, F Author Full Names: Boncina, T.; Zupanic, F.
Source:
ARCHIVES OF METALLURGY AND MATERIALS, 62 (1):5-9; 10.1515/amm-2017-0001 2017
Abstract:
Precipitation kinetics and mechanisms within an Al-Mn-Be-Cu quasicrystal strengthened alloy at 300 degrees C were studied using in-situ transmission electron microscopy. The alloy was cast into a copper mould. Quasicrystalline precipitates formed throughout the Al-rich solid solution, whilst heterogeneous formations of Al2Cu and T-phase occurred on icosahedral quasicrystalline particles formed during solidification. The formation of quasicrystalline particles and T-phase was limited by manganese diffusivity, whilst that of Al2Cu by copper diffusivity. The precipitation produced only a small hardening effect.

Update: 27-Apr-2017

Title:
Effect of cation vacancies on the crystal structure and luminescent properties of Ca0.85-1.5xGdxEu0.1 square 0.05+0.5xWO4(0 <= x <= 0.567) scheelite-based red phosphors
Authors:
Batuk, D; Batuk, M; Morozov, VA; Meert, KW; Smet, PF; Poelman, D; Abakumov, AM; Hadermann, J Author Full Names: Batuk, Dmitry; Batuk, Maria; Morozov, Vladimir A.; Meert, Katrien W.; Smet, Philippe F.; Poelman, Dirk; Abakumov, Artem M.; Hadermann, Joke
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 706 358-369; 10.1016/j.jallcom.2017.02.154 JUN 5 2017
Abstract:
The Ca0.85-1.5xGdxEu0.1+0.05 square 0.5xWO4(0 <= x <= 0.567) series of cation-deficient scheelites is investigated to unveil the influence of the cation vacancies on the crystal structure and luminescent properties. The concentration of the vacancies is varied by the heterovalent substitution of Gd3+ for Ca2+, keeping the concentration of the Eu3+ luminescent centers constant in all compounds of the series. The crystal structure of the materials is studied using a combination of transmission electron microscopy and synchrotron X-ray powder diffraction. At low vacancy concentration (x - 0.1, 0.2), cations and cation vacancies are randomly distributed in the structure, and the materials preserve the I4(1)/alpha symmetry of the parent scheelite structure [x = 0.1: a = 5.25151(1) angstrom, c = 11.39479(2) angstrom; x = 0.2: a = 5.25042(1) angstrom, c = 11.41335(2) angstrom]. At higher concentration, the cation-vacancy ordering gives rise to incommensurately modulated structures. The x = 0.3 structure has a (3 + 2) D tetragonal symmetry [superspace group I4(1)/alpha(alpha,beta, 0)00(-beta,alpha,0)00, a = 5.24700(1) angstrom, c = 11.45514(3) angstrom, q(1) = 0.51637(14)a* + 0.80761(13)b*, q(2) = -0.80761a* + 0.51637b*]. At x = 0.4, the scheelite basic cell undergoes a monoclinic distortion with the formation of the (3 + 1) D structure [superspace group I-2/b(alpha,beta,0)00, a = 5.23757(1) angstrom, b = 5.25035(1) angstrom, c = 11.45750(2) angstrom, gamma = 90.5120(2) angstrom, q = 0.54206(8)a* + 0.79330(8)b*]. In both structures, the antiphase Ca and (Gd, Eu) occupancy modulations indicate that the ordering between the A cations and vacancies also induces partial Ca/(Gd, Eu) cation ordering. Further increase of the Gd3+ content up to x = 0.567 leads to the formation of a monoclinic phase (space group C2/c) with the Eu2/ 3WO4-type structure. Despite the difference in the cation-vacancy ordering patterns, all materials in the series demonstrate very similar quantum efficiency and luminescence decay lifetimes. However, the difference in the local coordination environment of the A cation species noticeably affects the line width and the multiplet splitting of the 4f(6)-4f(6) transitions. (C) 2017 Elsevier B.V. All rights reserved.
Title:
New quantum criticality revealed under pressure
Authors:
Watanabe, S; Miyake, K Author Full Names: Watanabe, Shinji; Miyake, Kazumasa
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS, 56 (5):3 10.7567/JJAP.56.05FA01 MAY 2017
Abstract:
Unconventional quantum critical phenomena observed in Yb-based periodic crystals such as YbRh2Si2 and beta-YbAlB4 have been one of the central issues in strongly correlated electron systems. The common criticality has been discovered in the quasicrystal Yb15Au51Al34, which surprisingly persists under pressure at least up to P = 1.5GPa. The T/H scaling where the magnetic susceptibility can be expressed as a single scaling function of the ratio of the temperature T to the magnetic field H has been discovered in the quasicrystal, which is essentially the same as that observed in beta-YbAlB4. Recently, the T/ H scaling as well as the common criticality has also been observed even in the approximant crystal Yb15Au51Al34 under pressure. The theory of critical Yb-valence fluctuation gives a natural explanation for these striking phenomena in a unified way. (C) 2017 The Japan Society of Applied Physics
Title:
International Journal of Biological Macromolecules
Authors:
Abidi, M; Iram, A; Furkan, M; Naeem, A Author Full Names: Abidi, Minhal; Iram, Afshin; Furkan, Mohammad; Naeem, Aabgeena
Source:
INTERNATIONAL JOURNAL OF BIOLOGICAL MACROMOLECULES, 98 459-468; 10.1016/1flbiomac.2017.01.086 MAY 2017
Abstract:
Glucoamylase (EC 3.2.1.3) from Aspergillus niger possesses 31% alpha-helix, 36% beta structure and rest aperiodic structure. A transition of glucoamylase structure in the presence of varying concentrations of glyoxal (GO) and trifluoroethanol (TFE) was studied by using multi-methodological approaches. At 20% GO, glucoamylase exists as molten globule state as evident by high tryptophan and ANS fluorescence, retention of secondary structure and loss of native tertiary structure. This state precedes the onset of the aggregation process and maximum is achieved at the highest concentration i.e. at 90% of GO. In parallel study TFE, on increasing concentration up to 25% induces secondary structure transformation leading to accumulation of intermolecular 13 sheets, altered tryptophan environment, high ANS and ThT fluorescence resulting in the formation of glucoamylase aggregates. Isothermal titration calorimetric curve is sigmoidal, indicating the weak binding of GO/TFE and glucoamylase. TEM studies showed that glucoamylase exists as globular and amorphous aggregates at 90% glyoxal and 25% TFE respectively. Further, TFE at 70% causes inhibition of enzyme aggregates; the majority of secondary structures observed at this concentration are a helices. Alpha helices being the main key player relocates glucoamylase native environment as evident by CD, FTIR and TEM. Hence induction of 6 sheet promotes protein aggregation and a helices inhibits protein aggregation. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Enhanced thermal stability of a quasicrystalline phase in rapidly solidified Al-Mn-Fe-X alloys
Authors:
Stan-Glowinska, K; Litynska-Dobrzynska, L; Morgiel, J; Goral, A; Gordillo, MA; Wiezorek, JM Author Full Names: Stan-Glowinska, K.; Litynska-Dobrzynska, L.; Morgiel, J.; Goral, A.; Gordillo, M. A.; Wiezorek, J. M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 702 216-228; 10.1016/j.jallcom.2016.12383 APR 25 2017
Abstract:
A series of rapidly solidified Al-Mn-Fe-X alloys, where X is one of Mo, W or V, were prepared using a melt spinning technique. Microstructures of obtained ribbons comprised of an aluminium solid solution matrix containing metastable quasicrystalline particles of icosahedral type (I-phase). Micro-analytical studies by X-ray diffraction, transmission and scanning transmission electron microscopy after various heat treatments, including in situ TEM heating experiments, have been performed to elucidate details of the I-phase decomposition mechanisms. Results of these investigations and values of activation energies of the transition calculated based on differential scanning calorimeter measurements indicated that V modified alloys exhibit significantly increased thermal stability of the I-phase relative to Mo- and W modified alloys and the un-modified ternary Al-Mn-Fe benchmark. In V-modified alloys the quasicrystalline particle transformations resulted in formation of the Al-45(Mn, Fe, V)(7) intermetallic phase, while the Ally(Mn, Fe, X = Mo, W) crystalline product formed during annealing of Mo- and W-modified alloys. Notably, the Al-45(Mn, Fe, V)(7) intermetallic phase shows considerable structural similarity to the quasi crystalline I-phase. This correlates with a small value of measured heat release during the I-phase decomposition and implies the stabilization of icosahedral structural ordering by V addition. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Non-collinear magnetic structure of manganese quadruple perovskite CdMn7O12
Authors:
Guo, H; Fernandez-Daz, MT; Zhou, L; Yin, Y; Long, Y; Komarek, AC Author Full Names: Guo, H.; Fernandez-Daz, M. T.; Zhou, L.; Yin, Y.; Long, Y.; Komarek, A. C.
Source:
SCIENTIFIC REPORTS, 7 10.1038/srep45939 APR 5 2017
Abstract:
We report on the magnetic structure of CdMn7O12 determined by powder neutron diffraction. We were able to measure the magnetic structure of this Cd containing and highly neutron absorbing material by optimizing the sample geometry and by blending the CdMn7O12 with Aluminum powder. Below its Neel temperature TN1 all magnetic reflections can be indexed by a single commensurate propagation vector k = (0, 0, 1). This is different to the case of CaMn7O12 where the propagation vector is incommensurate and where an in-plane helical magnetic structure has been found. We observe a commensurate noncollinear magnetic structure in CdMn7O12 with in-plane aligned magnetic moments resembling the ones in CaMn7O12. However, the commensurate propagation vector prevents the appearance of a helical magnetic structure in CdMn7O12. Finally, we also observe a third structural phase transition below similar to 60 K that can be attributed to phase separation.
Title:
Incommensurate atomic density waves in the high-pressure IVb phase of barium
Authors:
Arakcheeva, A; Bykov, M; Bykova, E; Dubrovinsky, L; Pattison, P; Dmitriev, V; Chapuis, G Author Full Names: Arakcheeva, Alla; Bykov, Maxim; Bykova, Elena; Dubrovinsky, Leonid; Pattison, Phil; Dmitriev, Vladimir; Chapuis, Gervais
Source:
IUCRJ, 4 152-157; 10.1107/S2052252517000264 2 MAR 2017
Abstract:
The host-guest structures of elements at high pressure discovered a decade ago still leave many open questions due to the lack of precise models based on full exploitation of the diffraction data. This concerns in particular Ba IV, which is stable in the range 12-45 GPa. With the example of phase Ba IVb, which is characterized here for the first time, a systematic analysis is presented of possible host-guest structure models based on high-quality single-crystal diffraction data obtained with synchrotron radiation at six different pressures between 16.5 and 19.6 GPa. It is shown that a new incommensurately modulated (IM) structure model better fits the experimental data. Unlike the composite models which are commonly reported for the Ba IV phases, the IM model reveals a density wave and its pressure-dependent evolution. The crucial role played by the selected model in the interpretation of structure evolution under pressure is discussed. The findings give a new experimental basis for a better understanding of the nature of host-guest structures.
Title:
Breakthrough in the high-pressure structures of Ba based on full exploitation of aperiodic symmetry
Authors:
Boldyreva, EV Author Full Names: Boldyreva, Elena V.
Source:
IUCRJ, 4 104-105; 10.1107/S2052252517001427 2 MAR 2017
Title:
Ordering effect on the mechanical, electronic and magnetic properties of the beta-based non-canonical approximant phases: beta-Al50Cu33Fe17, eta-Al50Cu44Fe6 and phi-Al47.5Cu49.5Fe3
Authors:
Shalaeva, EV; Medvedeva, NI; Prekul, AF; Smirnova, EO; Smirnov, SV; Shchegolikhina, NI; Selyanin, IO Author Full Names: Shalaeva, E. V.; Medvedeva, N. I.; Prekul, A. F.; Smirnova, E. O.; Smirnov, S. V.; Shchegolikhina, N. I.; Selyanin, I. O.
Source:
PHILOSOPHICAL MAGAZINE, 97 (13):1024-1046; 10.1080/14786435.2017.1287970 A 2017
Abstract:
Using transmission electron microscopy and X-ray diffraction, we established that the ordered eta 1-Al50Cu44Fe6 and phi-Al47.5Cu49.5Fe3 (Fmm2) alloys with nano-sized domain structure are formed by slowly cooling, whereas beta-solid solutions with a short-range order were found in quenched states. The phi'-modification which exhibits the additional long-period superstructure was also observed in Al47.5Cu49.5Fe3. The studies of low temperature magnetic susceptibility and heat capacity did not reveal any another phase transitions in these alloys. The indentation test showed that hardness and Young's modulus consistently grow as beta-Al50Cu33Fe17 -> eta 1-Al50Cu44Fe6 -> (phi+phi')-Al47.5Cu49.5Fe3 and approach to those in icosahedral phase. The same trend in the Young's modulus was obtained for alloys containing beta-solid solution with a short-range order. Ab initio calculations, however, predicted the opposite tendency in cubic beta-Al50Cu50-xFex with a decrease in x, which was explained by the weakening of the covalent Fe 3d-Al sp bonding. This discrepancy between the results for beta- and ordered phases, we related to a crucial effect of ordering which is accompanied by a progressive distortion of cubic local structure in the series beta-Al50Cu33Fe17 -> eta 1-Al50Cu44Fe6 -> phi-Al47.5Cu49.5Fe3. As we demonstrated for eta-Al(Cu,Fe), these distortions lead to the strengthening of the both covalent FeAl and Cu-Al bonds and the higher modules.
Title:
Enhancement of Mechanical Properties of Aluminum and 2124 Aluminum Alloy by the Addition of Quasicrystalline Phases
Authors:
Wolf, W; Aliaga, LCR; Travessa, DN; Afonso, CRM; Bolfarini, C; Kiminami, CS; Botta, WJ Author Full Names: Wolf, Witor; Rodriguez Aliaga, Luis Cesar; Travessa, Dilermando Nagle; Moreira Afonso, Conrado Ramos; Bolfarini, Claudemiro; Kiminami, Claudio Shyinti; Botta, Walter Jose
Source:
MATERIALS RESEARCH-IBERO-AMERICAN JOURNAL OF MATERIALS, 19 74-79; 1 10.1590/1980-5373-MR-2016-0088 DEC 2016
Abstract:
A structural and mechanical characterization of pure aluminum and 2124 T6 aluminum alloy reinforced with quasicrystalline phases of composition Al65Cu20Fe15 and Al70.5Pd21Mn8.5 (% at.) were performed. The quasicrystalline phases were synthesized by arc melting and then milled to produce powder of the alloys, which were then mechanical mixed with the starting powders of aluminum and 2124 aluminum alloy. The composites were produced by hot extrusion of a mechanical mixture containing 20% (% wt.) of the reinforcing phases on the metallic matrix. The structural characterization of the composites was carried out by X- ray diffraction, scanning electron microscopy and transmission electron microscopy. Mechanical characterization was carried out by Vickers hardness measurements and torsion tests at room temperature. The pure aluminum/ quasicrystal composite showed the presence of the same phases from the starting powder mixture while for the 2124 aluminum alloy/Al65Cu20Fe15 the quasicrystalline phase transformed to the tetragonal w-Al7Cu2 Fe during the solution heat treatment. Mechanical strength of the composites presented a substantial increase in comparison to the original matrix metal. While the equivalent ultimate tensile strength of the Al/ quasicrystal composites reached values up to 215MPa and Vickers hardness up to 60HV, the 2124/ quasicrystal composites reached values up to 670MPa and Vickers hardness up to 190HV.

Update: 20-Apr-2017

Title:
Geometry of adaptive martensite in Ni-Mn- based Heusler alloys
Authors:
Niemann, R; Fahler, S Author Full Names: Niemann, Robert; Faehler, Sebastian
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 703 280-288; 10.1016/j.jallcom.2017.01.189 MAY 5 2017
Abstract:
Modulated martensites play an important role in magnetic shape memory alloys, because all functional properties are closely connected to the twin microstructure and the phase boundary. The nature of the modulated martensites is still unclear. One approach is the concept of adaptive martensite, which regards all modulated phases as nanotwinned microstructures. In this article, we use the Ni-Mn-based shape memory alloys as an example to show the geometric rationale behind this concept using analytic equations based on the phenomenological theory of martensite. This could enhance discussions about the implications of the adaptive martensite by showing the exact relations between the various unit cells used to describe the structure. We use the concept to discuss the compatibility at the habit plane, the nature of high-order twin boundaries and the dependence of the lattice constants on the different types of modulation. (C) 2017 Elsevier B.V. All rights reserved.

Update: 13-Apr-2017

Title:
Magnetic ordering and dielectric relaxation in the double perovskite YBaCuFeO5
Authors:
Lai, YC; Du, CH; Lai, CH; Liang, YH; Wang, CW; Rule, KC; Wu, HC; Yang, HD; Chen, WT; Shu, GJ; Chou, FC Author Full Names: Lai, Yen-Chung; Du, Chao-Hung; Lai, Chun-Hao; Liang, Yu-Hui; Wang, Chin-Wei; Rule, Kirrily C.; Wu, Hung-Cheng; Yang, Hung-Duen; Chen, Wei-Tin; Shu, G. J.; Chou, F-C
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (14):10.1088/1361-648X/aa5708 APR 12 2017
Abstract:
Using magnetization, dielectric constant, and neutron diffraction measurements on a high quality single crystal of YBaCuFeO5 (YBCFO), we demonstrate that the crystal shows two antiferromagnetic transitions at T-N1 similar to 475 K and T-N2 similar to 175 K, and displays a giant dielectric constant with a characteristic of the dielectric relaxation at T-N2. It does not show the evidence of the electric polarization for the crystal used for this study. The transition at T-N1 corresponds with a paramagnetic to antiferromagnetic transition with a magnetic propagation vector doubling the unit cell along three crystallographic axes. Upon cooling, at T-N2, the commensurate spin ordering transforms to a spiral magnetic structure with a propagation vector of (h/2 k/2 l/2 +/- delta), where h, k, and l are odd, and the incommensurability d is temperature dependent. Around the transition boundary at T-N2, both commensurate and incommensurate spin ordering coexist.
Title:
Stability of icosahedral quasicrystals in a simple model with two-length scales
Authors:
Jiang, K; Zhang, PW; Shi, AC Author Full Names: Jiang, Kai; Zhang, Pingwen; Shi, An-Chang
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (12):10.1088/1361-648X/aa586b MAR 29 2017
Abstract:
The phase behaviour of a free energy functional with two length scales is examined by comparing the free energy of different candidate phases including three-dimensional icosahedral quasicrystals. Accurate free energy of the quasicrystals has been obtained using the recently developed projection method. The results reveal that the icosahedral quasicrystal and body-centred-cubic spherical phase are the stable ordered phases of the model. Furthermore, the difference between the results obtained from the projection method and the one-mode approximation has been analyzed in detail. The present study extends previous results on two-dimensional systems, demonstrating that the interactions between density waves at two length scales can stabilize two-and three-dimensional quasicrystals.
Title:
Effects of Cu addition on the microstructure and mechanical properties of as-cast and heat treated Mg-6Zn-4Al magnesium alloy
Authors:
Zhu, SZ; Luo, TJ; Zhang, TG; Li, YJ; Yang, YS Author Full Names: Zhu, Shaozhen; Luo, Tianjiao; Zhang, Tingan; Li, Yingju; Yang, Yuansheng
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 689 203-211; 10.1016/j.msea.2017.02.061 MAR 24 2017
Abstract:
The microstructure and mechanical properties of as-cast and heat treated Mg-6Zn-4Al-xCu (x=0, 0.5, 1.0 and 1.5 wt%) alloys were investigated in this work. The results show that the grain sizes of the alloys decrease considerably with increasing Cu addition, and the eutectics are refined with 0.5% Cu addition. The icosahedral quasi-crystalline phase is observed in Mg-6Zn-4Al and Cu-containing alloys, and the MgAlCu phase forms in the Cu-containing alloys because of Cu addition. Compared with Mg-6Zn-4Al alloy, the Cu-containing alloys exhibit improved age-hardening response during single-aging treatment. In addition, high-density fine precipitates are formed in the matrix during double-aging treatment, resulting in remarkable improvement of the tensile strength. The double aged Mg-6Zn-4Al-0.5Cu alloy shows the relatively optimal tensile properties. The yield strength, ultimate tensile strength and elongation are 202 MPa, 312 MPa and 7%, respectively, which is attributed to the combined effects of fine grains and the uniform distribution of high-density fine precipitates. It is noticed that the ductility of as-aged Cu-containing alloys is lower than that of the as-aged Mg-6Zn-4Al alloy due to the stress concentration during the tensile stress caused by the residual phases distributed along the grain boundaries after solution treatment.
Title:
Phase behaviour of quasicrystal forming systems of core-corona particles
Authors:
Pattabhiraman, H; Dijkstra, M Author Full Names: Pattabhiraman, Harini; Dijkstra, Marjolein
Source:
JOURNAL OF CHEMICAL PHYSICS, 146 (11):10.1063/1.4977934 MAR 21 2017
Abstract:
Using Monte Carlo simulations and free-energy calculations, we study the phase behaviour of a two-dimensional system of particles interacting with a hard core of diameter sigma(HD) and a repulsive square shoulder potential. The interest in this system lies in the formation of quasicrystals of different symmetries at specific square-shoulder widths delta as previously reported by Dotera et al. [Nature 506, 208 (2014)]. However, an insight into other possible periodic phases formed in these systems and the thermodynamic stability of both the periodic and quasicrystal phases is yet to be addressed. Here, we study the phase behaviour and map out the phase diagrams for three different shoulder widths delta = 1.27 sigma(HD), 1.40 sigma(HD), and 1.60 sigma(HD), where octadecagonal, dodecagonal, and decagonal quasicrystals were previously reported. In addition, we verify the thermodynamic stability of these quasicrystals with respect to their periodic approximants. In general, we find that the system at all three shoulder widths forms hexagonal phases in two distinct density ranges due to the two characteristic length scales in the interaction potential. Further, we find that the dodecagonal and octadecagonal quasicrystals are stable in between two crystal phase regimes. In contrast, the decagonal quasicrystal is not bounded by a low-density crystal phase regime due to the lower density of this quasicrystal. From the free-energy calculations, we find indications that the decagonal and dodecagonal quasicrystals are thermodynamically stable with respect to their approximants, and the octadecagonal quasicrystal is stabilised by a configurational entropy contribution. Published by AIP Publishing.
Title:
Enhancement of Ferroelectricity for Orthorhombic (TB0.861Mn0.121)MnO3-delta by Copper Doping
Authors:
Deng, JM; Farid, MA; Zhang, M; Yang, AM; Zhang, HX; Zhang, H; Tian, GF; Wu, MM; Liu, LJ; Sun, JL; Li, GB; Liao, FH; Lin, JH Author Full Names: Deng, Jianming; Farid, Muhammad Asim; Zhang, Meng; Yang, Aimei; Zhang, Hongxing; Zhang, Hao; Tian, Gengfang; Wu, Meimei; Liu, Laijun; Sun, Junliang; Li, Guobao; Liao, Fuhui; Lin, Jianhua
Source:
INORGANIC CHEMISTRY, 56 (6):3475-3482; 10.1021/acs.inorgchem.6b03024 MAR 20 2017
Abstract:
Copper-doped (Tb0.861MnO0.121)Mn0(3-delta) has been synthesized by the conventional solid state reaction method. X-ray, neutron, and electron diffraction data indicate that they crystallize in Pnma space group at room temperature. Two magnetic orderings are found for this series by neutron diffraction. One is the ICAM (incommensurate canted antiferromagnetic) ordering of Mn with a wave vector q(Mn) = (similar to 0.283, 0, 0) with a approximate to 5.73A,b approximate to 5.31 A, and c approximate to 7.41 A, and the other is the CAM (canted antiferromagneiic) ordering of both Tb and Mn in the magnetic space group Pn'a2(1)' with a approximate to 5.73 A, b approximate to 5.31 A, and c approximate to 7:41 A. A dielectric peak around 40 K is found for the samples doped with Cu, which is higher than that for orthorhombic TbMnO3.
Title:
Opening a nodal gap by fluctuating spin-density wave in lightly doped La2-xSrxCuO4
Authors:
Kapon, I; Ellis, DS; Drachuck, G; Bazalitski, G; Weschke, E; Schierle, E; Strempfer, J; Niedermayer, C; Keren, A Author Full Names: Kapon, Itzik; Ellis, David S.; Drachuck, Gil; Bazalitski, Galina; Weschke, Eugen; Schierle, Enrico; Strempfer, Joerg; Niedermayer, Christof; Keren, Amit
Source:
PHYSICAL REVIEW B, 95 (10):10.1103/PhysRevB.95.104512 MAR 14 2017
Abstract:
We investigate whether the spin or charge degrees of freedom are responsible for the nodal gap in underdoped cuprates by performing inelastic neutron scattering and x-ray diffraction measurements on La2-xSrxCuO4, which is on the edge of the antiferromagnetic phase. We found that a fluctuating incommensurate spin-density wave (SDW) with a bottom part of an hourglass dispersion exists even in this magnetic sample. The strongest component of these fluctuations diminishes at the same temperature where the nodal gap opens. X-ray scattering measurements on the same crystal show no signature of a charge-density wave (CDW). Therefore, we suggest that the nodal gap in the electronic band of this cuprate opens due to fluctuating SDW with no contribution from CDW.
Title:
E-type noncollinear magnetic ordering in multiferroic o-LuMnO3
Authors:
Mukherjee, S; Donni, A; Nakajima, T; Mitsuda, S; Tachibana, M; Kitazawa, H; Pomjakushin, V; Keller, L; Niedermayer, C; Scaramucci, A; Kenzelmann, M Author Full Names: Mukherjee, Saumya; Donni, Andreas; Nakajima, Taro; Mitsuda, Setsuo; Tachibana, Makoto; Kitazawa, Hideaki; Pomjakushin, Vladimir; Keller, Lukas; Niedermayer, Christof; Scaramucci, Andrea; Kenzelmann, Michel
Source:
PHYSICAL REVIEW B, 95 (10):10.1103/PhysRevB.95.104412 MAR 13 2017
Abstract:
Multiferroic orthorhombic o-LuMnO3 exhibits large ferroelectric polarization induced by an E-type magnetic order. Recently, the E-type magnetic phase in LuMnO3 was proposed to feature magnetic moments tilted away from the collinear ordering. We employed neutron diffraction to determine the symmetry of the magnetic order in o-LuMnO3. We observed that below T-N = 39 K, the Mn3+ spins order into an incommensurate amplitudemodulated phase that obeys the Pbnm crystal symmetry and is paraelectric. The incommensurate phase locks into a commensurate phase at T-C = 35.5 K described by a fully antiferromagnetic and noncollinear E-type order. This noncollinear E-type ordering breaks the spatial inversion symmetry and induces a spontaneous polarization at TC. At T = 2 K, an appreciably large electric polarization was observed similar to that of other orthorhombic manganites featuring E-type magnetic order. We also present a Pbnm symmetry-allowed Dzyaloshinskii-Moriya interaction that explains the noncollinear E-type order in the commensurate phase. These results are in qualitative agreement with the type of distortions from collinear E-type antiferromagnetic order found using Monte Carlo simulation for rare-earth manganites
Title:
Sodium layer chiral distribution and spin structure of Na2Ni2TeO6 with a Ni honeycomb lattice
Authors:
Karna, SK; Zhao, Y; Sankar, R; Avdeev, M; Tseng, PC; Wang, W; Shu, GJ; Matan, K; Guo, GY; Chou, FC Author Full Names: Karna, Sunil K.; Zhao, Y.; Sankar, R.; Avdeev, M.; Tseng, P. C.; Wang, W.; Shu, G. J.; Matan, K.; Guo, G. Y.; Chou, F. C.
Source:
PHYSICAL REVIEW B, 95 (10):10.1103/PhysRevB.95.104408 MAR 8 2017
Abstract:
The nature of Na ion distribution, diffusion path, and the spin structure of P2-type Na2Ni2TeO6 with a Ni honeycomb lattice has been explored. The nuclear density distribution of Na ions reveals a two-dimensional (2D) chiral pattern within Na layers without breaking the original 3D crystal symmetry, which has been achieved uniquely via an inverse Fourier transform (iFT)-assisted neutron-diffraction technique. The Na diffusion pathway described by the calculated isosurface of the Na ion bond valence sum (BVS) map is found consistent to a chiral diffusion mechanism. The Na site occupancy and Ni2+ spin ordering were examined in detail with the neutron diffraction, magnetic susceptibility, specific heat, thermal conductivity, and transport measurements. Signatures of both strong incommensurate (ICM) and weak commensurate (CM) antiferromagnetic (AFM) spin ordering were identified in the polycrystalline sample studied, and the CM-AFM spin ordering was confirmed by using a single-crystal sample through the k scan in the momentum space corresponding to the AFM peak of (1/2,0,1).
Title:
Formation of the Structure and Physicomechanical Properties of a Quasicrystalline Al-Cu-Fe Alloy upon Plasma Spraying
Authors:
Lepeshev, AA; Karpov, IV; Ushakov, AV Author Full Names: Lepeshev, A. A.; Karpov, I. V.; Ushakov, A. V.
Source:
PHYSICS OF THE SOLID STATE, 59 (3):438-442; 10.1134/S1063783417030210 MAR 2017
Abstract:
Quasicrystalline coatings prepared under various thermal conditions of spraying have been studied. Initial quasicrystalline powders with dispersion of 10-50 mu m were prepared in a low-pressure arc discharge plasma. The coatings have been sprayed on copper rings using a swinging plasmatron. It is found that the increase in the quenching rate of melt droplets increases the chemical homogeneity and leads to formation of nanostructured formations. The precipitation of nanostructured grains (d < 100 nm) in the sprayed alloy leads to an increase in the mechanical characteristics (hardness, deformation, and ductility) and can be considered as an additional factor of hardening of the material.
Title:
Mossbauer Studies of Spatial Spin-Modulated Structure and Hyperfine Interactions in Multiferroic (BiFe0.10Fe0.85Cr0.05O3)-Fe-57
Authors:
Pokatilov, VS; Rusakov, VS; Sigov, AS; Belik, AA; Matsnev, ME; Komarov, AE Author Full Names: Pokatilov, V. S.; Rusakov, V. S.; Sigov, A. S.; Belik, A. A.; Matsnev, M. E.; Komarov, A. E.
Source:
PHYSICS OF THE SOLID STATE, 59 (3):443-449; 10.1134/S1063783417030271 MAR 2017
Abstract:
Results of Mossbauer investigations on Fe-57 nuclei in multiferroic material (BiFe0.10Fe0.85Cr0.05O3)-Fe-57 in the temperature range from 5.2 to 300 K are presented. Bulk rhombohedral samples were obtained by solid-state synthesis at high pressure. Mossbauer spectra were analyzed using the model of spatial incommensurate spin-modulated structure of the cycloidal type. Information on the influence of substituting Cr cations for Fe cations on hyperfine spectral parameters was obtained: the shift and quadrupolar shift of a Mossbauer line, and isotropic and anisotropic contributions into the hyperfine magnetic field. The anharmonicity parameter m of the spatial spin-modulated structure increases almost 1.7 times at 5.2 K when BiFeO3 is doped with chromium. The data on m were used for calculation of the uniaxial magnetic anisotropy constants and their temperature dependences for pure and chromium-doped BiFeO3.ß

Update: 6-Apr-2017

Title:
Charge Density Wave in the New Polymorphs of RE2Ru3Ge5 (RE = Pr, Sm, Dy)
Authors:
Bugaris, DE; Malliakas, CD; Han, F; Calta, NP; Sturza, M; Krogstad, MJ; Osborn, R; Rosenkranz, S; Ruff, JPC; Trimarchi, G; Bud'ko, SL; Balasubramanian, M; Chung, DY; Kanatzidis, MG Author Full Names: Bugaris, Daniel E.; Malliakas, Christos D.; Han, Fei; Calta, Nicholas P.; Sturza, Mihai; Krogstad, Matthew J.; Osborn, Raymond; Rosenkranz, Stephan; Ruff, Jacob P. C.; Trimarchi, Giancarlo; Bud'ko, Sergey L.; Balasubramanian, Mahalingam; Chung, Duck Young; Kanatzidis, Mercouri G.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 139 (11):4130-4143; 10.1021/jacs.7b00284 MAR 22 2017
Abstract:
A new polymorph of the RE2Ru3Ge5 (RE = Pr, Sm, Dy) compounds has been grown as single crystals via an indium flux. These compounds crystallize in tetragonal space group P4/mnc with the Sc2Fe3Si5-type structure, having lattice parameters a = 11.020(2) angstrom and c = 5.853(1) angstrom for RE = Pr, a = 10.982(2) angstrom and c = 5.777(1) angstrom for RE = Sm, and a = 10.927(2) angstrom and c = 5.697(1) angstrom for RE = Dy. These materials exhibit a structural transition at low temperature, which is attributed to an apparent charge density wave (CDW). Both the high-temperature average crystal structure and the low-temperature incommensufately Modulated crystal structure (for Sm2Ru3Ge5 as a representative) have been solved. The charge density wave order is manifested by periodic distortions of the one-dimensional zigzag Ge chains. From X-ray diffraction, charge transport (electrical resistivity, Hall effect, magnetoresistance), magnetic measurements, and heat capacity, the ordering temperatures (T-CDW) observed, in the Pr and Sm analogues are similar to 200 and similar to 175 K, respectively. The charge transport measurement results indicate an electronic state transition happening simultaneously with the CDW transition. X-ray absorption near-edge spectroscopy (XANES) and electronic band structure results are also reported.
Title:
Improved tensile properties of an equal channel angular pressed (ECAPed) Mg-8Sn-6Zn-2A1 alloy by prior aging treatment
Authors:
Cheng, WL; Tian, L; Wang, HX; Bian, LP; Yu, H Author Full Names: Cheng, Weili; Tian, Liang; Wang, Hongxia; Bian, Liping; Yu, Hui
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 687 148-154; 10.1016/jansea.2017.01.054 FEB 27 2017
Abstract:
This paper demonstrates that aging prior to ECAP (APE) can greatly enhance the tensile properties of an ECAPed Mg-8Sn-6Zn-2(wt%)Al (TZA862) alloy. Both fine Mg2Sn and icosahedral quasicrystal phase (I -phase) precipitates that formed during the APE treatment could reduce the average size of dynamically recrystallized (DRXed) grains as well as increase the fraction of fine particles after ECAP. Furthermore, the APE treatment resulted in increased basal texture intensity as well as a decreased amount of large non-deformed particles. Therefore, the tensile strength and ductility of ECAPed TZA862 alloy were improved simultaneously by the APE treatment.
Title:
Subpicometer-scale atomic displacements and magnetic properties in the oxygen-isotope substituted multiferroic DyMnO3
Authors:
Narayanan, N; Graham, PJ; Reynolds, N; Li, F; Rovillain, P; Hester, J; Kimpton, J; Yethiraj, M; McIntyre, GJ; Hutchison, WD; Ulrich, C Author Full Names: Narayanan, N.; Graham, P. J.; Reynolds, N.; Li, F.; Rovillain, P.; Hester, J.; Kimpton, J.; Yethiraj, M.; McIntyre, G. J.; Hutchison, W. D.; Ulrich, C.
Source:
PHYSICAL REVIEW B, 95 (7):10.1103/PhysRevB.95.075154 FEB 27 2017
Abstract:
We have investigated DyMn O-16(3) and its isotopically substituted counterpart DyMn O-18(3) by neutron powder diffraction, x-ray diffraction, and heat capacity measurements to investigate the mechanism leading to its magnetically induced electric polarization. O-18 isotope substitution does not influence the magnetic ordering temperature of the Mn ions T-N,(Mn) or the multiferroic ordering temperature T-l coinciding with the onset of the spin spiral phase; however, it does reduce the ordering temperature of Dy into its incommensurate magnetic state T-N,T-Dy from 7.0(1) K to 5.9(1) K. The temperature dependence of the magnetic propagation vector, q(IC), changes with O-18 substitution, while T-l remains almost constant, independent of q(IC). Pronounced changes in the lattice parameters occur at the various phase transitions. Furthermore, distinct subpicometer-scale distortions of the MnO6 octahedra and displacements of the Dy ions are observed below the ferroelectric phase transition at T-l in both samples, pointing toward the mechanism for electric polarization and its coupling to the orbital degrees of freedom.
Title:
Hyperuniformity of quasicrystals
Authors:
Oguz, EC; Socolar, JES; Steinhardt, PJ; Torquato, S Author Full Names: Oguz, Erdal C.; Socolar, Joshua E. S.; Steinhardt, Paul J.; Torquato, Salvatore
Source:
PHYSICAL REVIEW B, 95 (5):10.1103/PhysRevB.95.054119 FEB 23 2017
Abstract:
Hyperuniform systems, which include crystals, quasicrystals, and special disordered systems, have attracted considerable recent attention, but rigorous analyses of the hyperuniformity of quasicrystals have been lacking because the support of the spectral intensity is dense and discontinuous. We employ the integrated spectral intensity Z(k) to quantitatively characterize the hyperuniformity of quasicrystalline point sets generated by projection methods. The scaling of Z(k) as k tends to zero is computed for one-dimensional quasicrystals and shown to be consistent with independent calculations of the variance, sigma(2)(R), in the number of points contained in an interval of length 2R. We find that one-dimensional quasicrystals produced by projection from a two-dimensional lattice onto a line of slope 1/tau fall into distinct classes determined by the width of the projection window. For a countable dense set of widths, Z(k) similar to k(4); for all others, Z(k) similar to k(2). This distinction suggests that measures of hyperuniformity define new classes of quasicrystals in higher dimensions as well.
Title:
Field-induced reentrant magnetoelectric phase in LiNiPO4
Authors:
Toft-Petersen, R; Fogh, E; Kihara, T; Jensen, J; Fritsch, K; Lee, J; Granroth, GE; Stone, MB; Vaknin, D; Nojiri, H; Christensen, NB Author Full Names: Toft-Petersen, Rasmus; Fogh, Ellen; Kihara, Takumi; Jensen, Jens; Fritsch, Katharina; Lee, Jooseop; Granroth, Garrett E.; Stone, Matthew B.; Vaknin, David; Nojiri, Hiroyuki; Christensen, Niels Bech
Source:
PHYSICAL REVIEW B, 95 (6):10.1103/PhysRevB.95.064421 FEB 21 2017
Abstract:
Using pulsed magnetic fields up to 30 T we have measured the bulk magnetization and electrical polarization of LiNiPO4 and have studied its magnetic structure by time-of-flight neutron Laue diffraction. Our data establish the existence of a reentrant magnetoelectric phase between 19 T and 21 T. We show that a magnetized version of the zero field commensurate structure explains the magnetoelectric response quantitatively. The stability of this structure suggests a field-dependent spin anisotropy. Above 21 T, amagnetoelectrically inactive, short-wavelength incommensurate structure is identified. Our results demonstrate the combination of pulsed fields with epithermal neutron Laue diffraction as a powerful method to probe even complex phase diagrams in strong magnetic fields.
Title:
Cell-quintupling: Structural phase transition in a molecular crystal, bis(trans-4-butylcyclohexyl) methanol
Authors:
Saito, K; Ikeda, T; Yamamura, Y; Saitoh, H; Hishida, M; Kobayashi, Y; Fujita, T; Ichikawa, J Author Full Names: Saito, Kazuya; Ikeda, Takaaki; Yamamura, Yasuhisa; Saitoh, Hideki; Hishida, Mafumi; Kobayashi, Yutaro; Fujita, Takeshi; Ichikawa, Junji
Source:
JOURNAL OF CHEMICAL PHYSICS, 146 (7):10.1063/1.4976318 FEB 21 2017
Abstract:
Astructural phase transition at 151.6 K of the title compound [bis(trans-4-butylcyclohexyl) methanol] is examined by X-ray diffraction crystallography, Fourier-transform infrared spectroscopy, and adiabatic calorimetry. A general consideration on possible superstructures indicates that a single modulation wave is sufficient to drive this cell-quintupling transition. The entropy of transition determined calorimetrically indicates that two conformations are dominant in the room-temperature phase in contrast to the fivefold disorder expected from the structure of the low-temperature phase. Published by AIP Publishing.
Title:
Four-Dimensional Incommensurate Modulation and Luminescent Properties of Host Material Na3La(PO4)(2)
Authors:
Zhao, D; Ma, FX; Ma, SQ; Zhang, AY; Nie, CK; Huang, M; Zhang, L; Fan, YC Author Full Names: Zhao, Dan; Ma, Fa-Xue; Ma, Shu-Qi; Zhang, Ai-Yun; Nie, Cong-Kui; Huang, Min; Zhang, Lei; Fan, Yun-Chang
Source:
INORGANIC CHEMISTRY, 56 (4):1835-1845; 10.1021/acs.inorgchem.6b02241 FEB 20 2017
Abstract:
A series of orthophosphates Na(3)Ln(PO4)(2) (Ln = lanthanoids) have for a long time been known as good luminescent materials, yet their crystal structures have not been studied in full detail. In this work, compound Na3La(PO4)(2) was prepared using molten salt (flux) method and for the first time was structurally determined on X-ray single-crystal diffraction data. Interestingly, it crystallizes in the four-dimensional incommensurately modulated structure with orthorhombic superspace group Pca(21)(0 beta 0)000 and modulation wave vector q = 0.387b*. Furthermore, to evaluate the potentiality of Na3La(PO4)(2) to be used as a luminescent host material, 5 mol % Eu3+, Tb3+, and Dy3+ doped phosphors were prepared, respectively. The excitation spectra, emission spectra, decay time, quantum efficiency, and the color purity of prepared phosphors, Na3La0.95Eu0.05(PO4)(2), Na3La0.95Tb0.05(PO4)(2), and Na3La0.95Dy0.05(PO4)(2), were studied.
Title:
Anomalous lattice compression and magnetic ordering in CuO at high pressures: A structural study and first-principles calculations
Authors:
Kozlenko, DP; Druzbicki, K; Kichanov, SE; Lukin, EV; Liermann, HP; Glazyrin, KV; Savenko, BN Author Full Names: Kozlenko, D. P.; Druzbicki, K.; Kichanov, S. E.; Lukin, E. V.; Liermann, H. -P.; Glazyrin, K. V.; Savenko, B. N.
Source:
PHYSICAL REVIEW B, 95 (5):10.1103/PhysRevB.95.054115 FEB 17 2017
Abstract:
The structural and magnetic properties of multiferroic CuO have been studied by means of neutron and x-ray powder diffraction at pressures up to 11 and 38 GPa, respectively, and by first-principles theoretical calculations. Anomalous lattice compression is observed, with enlargement of the lattice parameter a, reaching a maximum at P = 13 GPa, followed by its reduction at higher pressures. The lattice distortion of the monoclinic structure at high pressures is accompanied by a progressive change of the oxygen coordination around Cu atoms from the square fourfold towards the octahedral sixfold coordination. The pressure-induced evolution of the structural properties and electronic structure of CuO was successfully elucidated in the framework of full-electronic density functional theory calculations with range-separated HSE06, and meta-generalized gradient approximation hybrid M06 functionals. The antiferromagnetic (AFM) ground state with a propagation vector q = (0.5,0, -0.5) remains stable in the studied pressure range. From the obtained structural parameters, the pressure dependencies of the principal superexchange magnetic interactions were analyzed, and the pressure behavior of the Neel temperature as well as the magnetic transition temperature from the intermediate incommensurate AFM multiferroic state to the commensurate AFM ground state were evaluated. The estimated upper limit of the Neel temperature at P = 38 GPa is about 260 K, not supporting the previously predicted existence of the multiferroic phase at room temperature and high pressure.
Title:
Fabrication of a Quasicrystal Electrode at a Low Processing Temperature via Electrohydrodynamic and Transfer Printing for use in Multifunctional Electronics
Authors:
Park, S; Park, S; Park, S; Ryu, H; Park, JJ Author Full Names: Park, Seoungwoong; Park, Siyong; Park, Sangki; Ryu, Hochung; Park, Jong-Jin
Source:
ADVANCED ELECTRONIC MATERIALS, 3 (2):10.1002/aelm.201600440 FEB 2017
Abstract:
Fabrication of a quasicrystal electrode at a low processing temperature via electrohydrodynamic and transfer printing for use in multifunctional electronics is demonstrated using an electrohydrodynamic narrow nozzle-to-substrate distance printing method to obtain a quasicrystal electrode (transferred electrode), which can increase electrode durability with a better surface roughness and lower processing cost with low-temperature processing, for use in multifunctional electronics.
Title:
Dynamic response of an icosahedral quasi-crystalline medium with a Griffith crack under mechanical loadings
Authors:
Qiao, LP; Wu, L; Fan, TY Author Full Names: Qiao, Liangping; Wu, Li; Fan, Tianyou
Source:
ADVANCES IN MECHANICAL ENGINEERING, 9 (2):10.1177/1687814016688850 FEB 1 2017
Abstract:
Elastodynamic response of three-dimensional icosahedral quasi-crystals under mechanical loadings is presented in this article. Two kinds of cases are considered here, in which the plane problem and anti-plane problem are included. The phonon and phason elastic fundamental fields along with their coupling effect in crack analysis are explicitly presented in terms of the theoretical and numerical analyses. Using the finite difference method, some numerical results of stresses, displacements, and normalized dynamic stress intensity factor are obtained. By comparing the results of quasi-crystals, this article reveals the influence of phonon and phason elastic fundamental fields, which occupy an important position in dynamic deformation behavior of quasi-crystals. Of course, phonon-phason coupling effect also should not be neglected.

Update: 30-Mar-2017

Title:
Shield-like tile and its application to the decagonal quasicrystal-related structures in Al-Cr-Fe-Si alloys
Authors:
Li, H; Ma, HK; Hou, LG; Guo, MX; He, ZB Author Full Names: Li, Hua; Ma, Haikun; Hou, Longgang; Guo, Mingxing; He, Zhanbing
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 701 494-498; 10.1016/j.jallcom.2017.01.105 APR 15 2017
Abstract:
A shield-like tile (SLT) consisting of one star tile and two hexagon tiles was used as one structural block to describe the tilings of quasicrystal approximants in our previous work [J. All. Compds. 647 (2015) 797- 801.] because of its merits compared with the hexagon-boat-star model. In this paper, we aim to elucidate the rules of connection and the orientations of SLTs. Two examples of high-angle annular dark field scanning transmission electron microscopy images are provided to support these rules. The SLT orientation mapping of the quasicrystal-related structures along the pseudo-tenfold axis was achieved, and the structural characterizations were revealed intuitively. Furthermore, some new quasicrystal approximants were discussed based on the changeable rows of SLTs. (C) 2017 Elsevier B.V. All rights reserved.
Title:
Nanoquasicrystalline Al-Fe-Cr-Ti alloy matrix/gamma-Al2O3 nanocomposite powders: The effect of the ball milling process
Authors:
Xu, W; Galano, M; Audebert, F Author Full Names: Xu, W.; Galano, M.; Audebert, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 701 342-349; 10.1016/j.jallcom.2016.11.412 APR 15 2017
Abstract:
Quasicrystalline aluminium alloys and aluminium based nanocomposites with the advantage of high strength over commercial aluminium alloys have been studied for many years. In this work a nano-quasicrystalline Al-Fe-Cr-Ti alloy powder and a nanocomposite consisting of a mixture of a nano-quasicrystalline alloy and nanosize gamma-Al2O3 powders were produced through mechanical milling with different milling speeds. It has been observed that a higher milling time or milling speed can improve the homogeneity of the gamma-Al2O3 distribution. The alpha-Al crystallite size decreases and the hardness increases with the milling time. The smallest crystallite size (14 nm) and the highest hardness value (638 HV10g) were obtained for the nanocomposite after 30 h of milling at 250 rpm. As the alpha-Al crystallite size is the main change in the microstructure during the ball milling process, the change in the hardness of the milled powders was found to follow a Hall-Fetch type relation with an exponent of 0.25. (C) 2016 Published by Elsevier B.V.
Title:
The effect of temperature, interaction range, and pair potential on the formation of dodecagonal quasicrystals in core-corona systems
Authors:
Pattabhiraman, H; Dijkstra, M Author Full Names: Pattabhiraman, Harini; Dijkstra, Marjolein
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (9):10.1088/1361-648X/aa5530 MAR 8 2017
Abstract:
A two-dimensional dodecagonal quasicrystal was previously reported by Dotera et al (2014 Nature 506 208) in a system of particles interacting with a hard core of diameter s and a repulsive square shoulder of diameter delta = 1.40 sigma. In the current work, we examine the formation of this quasicrystal using bond orientational order parameters, correlation functions and tiling distributions. We find that this dodecagonal quasicrystal forms from a fluid phase. We further study the effect of the width of the repulsive shoulder by simulating the system over a range of values of d. For the range of densities and temperatures considered, we observe the formation of the dodecagonal quasicrystal between delta = 1.30 sigma and 1.44 sigma. We also study the effect of shape of the interaction potential by simulating the system using three other interaction potentials with two length scales, namely hard-core plus a linear ramp, modified exponential, or Buckingham (exp-6) potential. We observe the presence of the quasicrystal in all three systems. However, depending on the shape of the potential, the formation of the quasicrystal takes place at lower temperatures (or higher interaction strengths). Using free-energy calculations, we demonstrate that the quasicrystal is thermodynamically stable in the square-shoulder and linear-ramp system.
Title:
New insights into the multiferroic properties of Mn3TeO6
Authors:
Ivanov, SA; Ritter, C; Nordblad, P; Tellgren, R; Weil, M; Carolus, V; Lottermoser, T; Fiebig, M; Mathieu, R Author Full Names: Ivanov, S. A.; Ritter, C.; Nordblad, P.; Tellgren, R.; Weil, M.; Carolus, V.; Lottermoser, Th; Fiebig, M.; Mathieu, R.
Source:
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 50 (8):10.1088/1361-6463/aa5621 MAR 1 2017
Abstract:
Mn3TeO6 has a trigonal corundum related structure (space group R (3) over bar), and orders in an incommensurate antiferromagnetic (AFM) structure at T-N approximate to 24 K. A weak ferroelectric order below T* similar to 21 K has recently been reported. In order to investigate possible structural changes below T-N leading to the observed dipole order, we have performed a detailed study of the crystal and magnetic structures of Mn3TeO6 using neutron powder diffraction (NPD) in the temperature range of 5-40 K. Complementary low-temperature second harmonic generation (SHG) measurements were performed in order to confirm the reported dipole order at T*. No change in the rhombohedral symmetry associated with a possible displacive phase transition at T* was observed in the long-range *structural* correlations, and it appears that Mn3TeO6 keeps the same incommensurately modulated magnetic spin structure with the propagation vector k = (0; 0; 0.43) in the whole temperature range from 5 to 24 K.
Title:
Competing electronic instabilities of extended Hubbard models on the honeycomb lattice: A functional renormalization group calculation with high-wave-vector resolution
Authors:
de la Pena, DS; Lichtenstein, J; Honerkamp, C Author Full Names: de la Pena, D. Sanchez; Lichtenstein, J.; Honerkamp, C.
Source:
PHYSICAL REVIEW B, 95 (8):10.1103/PhysRevB.95.085143 FEB 27 2017
Abstract:
We investigate the quantum many-body instabilities for electrons on the honeycomb lattice at half filling with extended interactions, motivated by a description of graphene and related materials. We employ a recently developed fermionic functional renormalization group scheme, which allows for highly resolved calculations of wave-vector dependences in the low-energy effective interactions. We encounter the expected anti-ferromagnetic spin densitywave for a dominant on-site repulsion between electrons, and charge orderwith different modulations for dominant pure nth nearest-neighbor repulsive interactions. Novel instabilities towards incommensurate charge density waves take place when nonlocal density interactions among several bond distances are included simultaneously. Moreover, for more realistic Coulomb potentials in graphene including enough nonlocal terms there is a suppression of charge order due to competition effects between the different charge ordering tendencies, and if the on-site term fails to dominate, the semimetallic state is rendered stable. The possibility of a topological Mott insulator being the favored tendency for dominating second-nearest-neighbor interactions is not realized in our results with high momentum resolution.
Title:
Quasiperiodic Frank-Kasper phases derived from the square-triangle dodecagonal tiling
Authors:
Sadoc, JF; Mosseri, R Author Full Names: Sadoc, Jean-Francois; Mosseri, Remy
Source:
STRUCTURAL CHEMISTRY, 28 (1):63-73; SI 10.1007/s11224-016-0846-2 FEB 2017
Abstract:
Frank-Kasper (F-K) phases form an important set of large-cell crystalline structures describing many intermetallic alloys. They are usually described in term of their atomic environments, with atoms having 12, 14, 15 and 16 neighbours, coded into the canonical Z(p) cells (with p the coordination number), the case p = 12 corresponding to a local icosahedral environment. In addition, the long-range structure is captured by the geometry of a network (called either "major skeleton" or "disclination network") connecting only the non-icosahedral sites (with p 6 not equal 12). Another interesting description, valid for the so-called layered F-K phases, amounts to give simple rules to decorate specific periodic 2d tilings made of triangles and squares and eventually get the 3d periodic F-K phases. Quasicrystalline phases can sometime be found in the vicinity, in the phase diagram, of the F-K crystalline alloys; it is therefore of interest to understand whether and how the standard F-K construction rules can be generalized on top of an underlying quasiperiodic structure. It is in particular natural to investigate how well square-triangle quasiperiodic tilings with dodecagonal symmetry, made of square and (equilateral) triangles, can be used as building frames to generate some F-K-like quasicrystalline structures. We show here how to produce two types of such structures, which are quasiperiodic in a plane and periodic in the third direction, and containing (or not) Z(16) sites.
Title:
Are periodicity and symmetry the properties of a discrete space? (On one paradox of cellular automata)
Authors:
Shevchenko, VY; Krivovichev, SV Author Full Names: Shevchenko, Vladimir Ya; Krivovichev, Sergey V.
Source:
STRUCTURAL CHEMISTRY, 28 (1):45-50; SI 10.1007/s11224-016-0844-4 FEB 2017
Abstract:
We consider a three-color cellular automaton (CA) that acts on a square lattice. In ternary numeral system, the CA has the number 111010011111110111011102010, which corresponds to 3704707887996 in the decimal system. With the finite size of the input row, CA-3704707887996 generates aperiodic structures with repeating self-similar patterns. In order to investigate the formation of periodic patterns by the CA-3704707887996, the input row was used that represents a periodic structure containing variable number of cells. The behavior of the CA-3704707887996 work for the input rows with periods up to 21 cells was studied. All generated patterns were analyzed from the viewpoint of their periodicity along the vertical direction. It was found out that the behavior of the system depending upon the length (l(input)) and structure of the periodic input row is strongly nonlinear. The complexity C of a pattern considered as a size of a unit cell increases exponentially with the increasing l(input) value and can be described by the function C = 1.8986 exp [0.3334 l(input)], with the correlation coefficient R-2 = 0.8967. As a rule, initially the CA generates a metastable aperiodic structure and then adopts a stable regime of generation of a stable periodic pattern. The abstract properties of the CA-3704707887996 have several important consequences for structural chemistry: (1) relatively simple schemes of local interactions of particles may result in the formation of very complex structures depending upon the initial conditions and abstract properties of the interactions; (2) symbolic complexity of the generated patterns increases exponentially depending upon the structure of initial conditions; (3) under certain initial conditions, explosive fluctuations of complexity are possible that lead to the formation of giant superstructures with extremely large periods; and (4) under certain conditions, the border between aperiodic and periodic structures virtually disappears.
Title:
Generalized reciprocal vector sets
Authors:
Gomez-Rodriguez, A; Aragon, JL Author Full Names: Gomez-Rodriguez, A.; Aragon, J. L.
Source:
STRUCTURAL CHEMISTRY, 28 (1):235-238; SI 10.1007/s11224-016-0848-0 FEB 2017
Abstract:
In this work, we present a short review on generalized reciprocal vectors, a field created by Alan L. Mackay. In particular, we discuss the concept of generalized reciprocal vectors, its relation with eutactic stars used in quasicrystallography and their calculation using Moore-Penrose pseudoinverses. Additionally, we propose a plain Gaussian algorithm for this same purpose.
Title:
Tiling approach for the description of the sevenfold symmetry in quasicrystals
Authors:
Madison, AE Author Full Names: Madison, A. E.
Source:
STRUCTURAL CHEMISTRY, 28 (1):57-62; SI 10.1007/s11224-016-0793-y FEB 2017
Abstract:
An example of substitution rules for the construction of heptagonal rhombic tilings is proposed. Rigorous inflation/deflation rules make it possible to expand the tiling up to infinity without additional ad hoc rearrangements. The derived tilings are self-similar and consist of characteristic patterns with seven-pointed stars surrounded by similar seven-pointed stars.
Title:
Mackay clusters and beyond in icosahedral quasicrystals seen from 6D space
Authors:
Sirindil, A; Quiquandon, M; Gratias, D Author Full Names: Sirindil, Abdullah; Quiquandon, Marianne; Gratias, Denis
Source:
STRUCTURAL CHEMISTRY, 28 (1):123-132; SI 10.1007/s11224-016-0843-5 FEB 2017
Abstract:
It is a great pleasure and honour for us to participate to the celebration of the 90th birthday of Alan Mackay, one of the most inspired crystallographers of our time who has been the authentic predecessor of the quasicrystal discovery. We discuss here several ways to construct Mackay-type atomic clusters and others for describing quasicrystalline structures from the standard 6D framework. We show that they are several simple solutions for both the 6D natural cluster and the original Mackay derivation that are consistent with special points of the basic icosahedral 6D lattice and the actually determined clusters in usual cubic 1/1 approximants of the icosahedral phases. This technique works as well for describing the two first shells of the so-called Bergman clusters but the situation is far more complicated for the so-called Tsai cluster that cannot be directly obtained from the icosahedral cut and projection of the simple 6D lattice special points without significantly large differences in the radii of the various orbits with respect to their actual positions in the YbCd icosahedral-type alloys. This shows that the 6D approach using special points as locations of the mean atomic surfaces-although very efficient for constructing initial simple models of the icosahedral phases-requires subsequent refinement techniques, especially in the actual locations and sizes of the various atomic orbits of the implied clusters, for leading to final acceptable structural models.
Title:
Kurt Bruckner's view on the Penrose tiling
Authors:
Steurer, W; Arlitt, S Author Full Names: Steurer, Walter; Arlitt, Sabine
Source:
STRUCTURAL CHEMISTRY, 28 (1):51-56; SI 10.1007/s11224-016-0790-1 FEB 2017
Abstract:
We demonstrate the potential of Kurt Bruckner's 'addition algorithm', which is based on the substitution rule for the generation of the Robinson triangle tiling, a variant of the Penrose tiling. The artist Kurt Bruckner developed his straightforward approach intuitively for the creation of quasiperiodic ornaments. This versatile method can be used for the construction of achiral, homochiral and racemic quasiperiodic ornaments, as well as for the generation of decorated two-level (two-color) Penrose tilings. Therefore, the underlying tiling is always the same kind of Penrose tiling, which is invariant under the action of specific mirror and black/white mirror operations in contrast to unit tiles that are decorated in specific ways. Compared to the underlying classical substitution method the advantage of Kurt Bruckner's approach is its simplicity and versatility for the creation of decorated tilings. Using a vector graphics editor, large and arbitrarily complex quasiperiodic ornaments can be easily generated manually.
Title:
Generalizing crystallography: a tribute to Alan L. Mackay at 90
Authors:
Hargittai, I Author Full Names: Hargittai, Istvan
Source:
STRUCTURAL CHEMISTRY, 28 (1):1-16; SI 10.1007/s11224-016-0766-1 FEB 2017
Abstract:
Alan L. Mackay, one of the rare generalists of our time, was a disciple and follower of J. Desmond Bernal. Mackay has contributed decisively to the development of the science of structures and taught generations to look at the broader picture when determining crystal and molecular structures. He was constantly seeking coherence and regularities in observations and in thought experiments and was aiming at creating concepts on the basis of those regularities. His inquiries prompted him to predict the existence of regular but not periodic crystal structures that are known today as quasicrystals.
Title:
The philosophical significance of Alan Mackay's theoretical discovery of quasicrystals
Authors:
Gilead, A Author Full Names: Gilead, Amihud
Source:
STRUCTURAL CHEMISTRY, 28 (1):249-256; SI 10.1007/s11224-016-0742-9 FEB 2017
Abstract:
Dan Shechtman was the first to discover an actual quasicrystal (on April 8, 1982). He was, however, not the first to discover the pure possibility of this novel structure (the theoretical discovery), which had been excluded from the range of the possibilities of crystals (as it had been fixed by both theoretical and empirical means in the beginning of the twentieth century). Penrose and Mackay, in particular, had contributed to the discovery of the pure possibilities of quasicrystals quite some time before their actual discovery. These pure possibilities are mathematical-structural, and like purely mathematical entities, they do not exist spatiotemporally and causally, whereas actual quasicrystals exist only spatiotemporally and causally. The pure possibilities of quasicrystals do not depend on their actualities, and without them, these actualities would have been theoretically groundless, meaningless, and could not be correctly identified if at all. Hence, Mackay's contribution to the meaning and theoretical basis of the discovery of actual quasicrystals is indispensable.
Title:
Microstructure and electrical resistivity in the GdNi5-xCux intermetallic series
Authors:
Bajorek, A; Chelkowska, G Author Full Names: Bajorek, Anna; Chelkowska, Grazyna
Source:
JOURNAL OF RARE EARTHS, 35 (1):71-78; 10.1016/S1002-0721(16)60176-X JAN 2017
Abstract:
The effect of the Ni/Cu substitution on the electrical resistivity and microstructure of the polycrystalline GdNi5-xCux series was studied. The value of temperature of phase transition (T-ph) estimated from temperature dependence of electrical resistance varied non-linearly across copper doping from 32.5 K (x=0.0) to 29.1 K (x=5.0). The value of residual resistivity (rho(o)) estimated at low temperature range decreased from 27.28 mu Omega cm (x=0.0) to 9.44 mu Omega cm (x=5.0), which was discussed as the influence of microstructure. In order to describe the temperature dependence of resistivity rho(T) a variety of approaches were applied due to different scattering mechanisms occurring at high and low temperature ranges. The change within rho(T) curvature was evidenced at low temperature range across copper doping. The temperature variation of the resistivity was quite peculiar for Cu-rich compounds (x=4.8, x=5.0), which might be correlated with the incommensurate magnetic structure derived from the weakly negative interaction between the nearest neighbours of Gd. The correlation between microstructure and resistivity was observed.

Update: 16-Mar-2017

Title:
Interfacial free energy and medium range order: Proof of an inverse of Frank's hypothesis
Authors:
Lee, GW; Cho, YC; Lee, B; Kelton, KF Author Full Names: Lee, Geun Woo; Cho, Yong Chan; Lee, Byeongchan; Kelton, Kenneth F.
Source:
PHYSICAL REVIEW B, 95 (5):10.1103/PhysRevB.95.054202 FEB 13 2017
Abstract:
We study the relation of crystal-liquid interfacial free energy and medium range order in the quasicrystal-forming Ti37Zr42Ni21 liquid from undercooling experiment and ab initio molecular dynamics (MD) simulation. Adding a small amount of Ag to the liquid significantly reduces the degree of undercooling, which is suggestive of small interfacial free energy, and thus very similar atomic configuration between the liquid and the icosahedral quasicrystal phases. Using ab initioMDstudy, we find that Ag atoms predominantly form a bond with Zr atoms in the short range and, further, Ag-Zr pairs are extended in the liquid, as amedium range orderwhich is identical to the global structural feature reported recently [Liu et al., Phys. Rev. Lett. 105, 155501 (2010)]. This result may expect extremely small undercooling if the icosahedral medium range order exists in a liquid forming an icosahedral quasicrystal, which implies the ambiguity of clear distinction of heterogeneous and homogeneous nucleation.
Title:
Non-Fermi surface nesting driven commensurate magnetic ordering in Fe-doped Sr(2)RuO4
Authors:
Zhu, M; Shanavas, KV; Wang, Y; Zou, T; Sun, WF; Tian, W; Garlea, VO; Podlesnyak, A; Matsuda, M; Stone, MB; Keavney, D; Mao, ZQ; Singh, DJ; Ke, X Author Full Names: Zhu, M.; Shanavas, K. V.; Wang, Y.; Zou, T.; Sun, W. F.; Tian, W.; Garlea, V. O.; Podlesnyak, A.; Matsuda, M.; Stone, M. B.; Keavney, D.; Mao, Z. Q.; Singh, D. J.; Ke, X.
Source:
PHYSICAL REVIEW B, 95 (6):10.1103/PhysRevB.95.054413 FEB 10 2017
Abstract:
Sr2RuO4, an unconventional superconductor, is known to possess an incommensurate spin-density wave instability driven by Fermi surface nesting. Here we report a static spin-density wave ordering with a commensurate propagation vector q(c) = ( 0.25 0.25 0) in Fe-doped Sr2RuO4, despite the magnetic fluctuations persisting at the incommensurate wave vectors q(ic) = ( 0.30.3L) as in the parent compound. The latter feature is corroborated by the first-principles calculations, which showthat Fe substitution barely changes the nesting vector of the Fermi surface. These results suggest that in addition to the known incommensurate magnetic instability, Sr2RuO4 is also in proximity to a commensurate magnetic tendency that can be stabilized via Fe doping.
Title:
Non-Fermi surface nesting driven commensurate magnetic ordering in Fe-doped Sr2RuO4
Authors:
Zhu, M; Shanavas, KV; Wang, Y; Zou, T; Sun, WF; Tian, W; Garlea, VO; Podlesnyak, A; Matsuda, M; Stone, MB; Keavney, D; Mao, ZQ; Singh, DJ; Ke, X Author Full Names: Zhu, M.; Shanavas, K. V.; Wang, Y.; Zou, T.; Sun, W. F.; Tian, W.; Garlea, V. O.; Podlesnyak, A.; Matsuda, M.; Stone, M. B.; Keavney, D.; Mao, Z. Q.; Singh, D. J.; Ke, X.
Source:
PHYSICAL REVIEW B, 95 (5):10.1103/PhysRevB.95.054413 FEB 10 2017
Abstract:
Sr2RuO4, an unconventional superconductor, is known to possess an incommensurate spin-density wave instability driven by Fermi surface nesting. Here we report a static spin-density wave ordering with a commensurate propagation vector q(c) = (0.25 0.25 0) in Fe-doped Sr2RuO4, despite the magnetic fluctuations persisting at the incommensurate wave vectors q(ic) = (0.30.3L) as in the parent compound. The latter feature is corroborated by the first-principles calculations, which show that Fe substitution barely changes the nesting vector of the Fermi surface. These results suggest that in addition to the known incommensurate magnetic instability, Sr2RuO4 is also in proximity to a commensurate magnetic tendency that can be stabilized via Fe doping.
Title:
Incommensurate charge ordered states in the t-t '-J model
Authors:
Choubey, P; Tu, WL; Lee, TK; Hirschfeld, PJ Author Full Names: Choubey, Peayush; Tu, Wei-Lin; Lee, Ting-Kuo; Hirschfeld, P. J.
Source:
NEW JOURNAL OF PHYSICS, 19 10.1088/1367-2630/19/1/013028 JAN 20 2017
Abstract:
We study the incommensurate charge ordered states in the t-t'-J model using the Gutzwiller mean field theory on large systems. In particular, we explore the properties of incommensurate charge modulated states referred to as nodal pair density waves (nPDW) in the literature. nPDW states intertwine site and bond charge order with modulated d-wave pair order, and are characterized by a nonzero amplitude of uniform pairing; they also manifest a dominant intra-unit cell d-density wave form factor. To compare with a recent scanning tunneling microscopy (STM) study (Hamidian et al 2015 Nat. Phys. 12 150) of the cuprate superconductor BSCCO-2212, we compute the continuum local density of states (LDOS) at a typicalSTM tip height using the Wannier function based approach. By Fourier transforming Cu and O sub-lattice LDOS we also obtain bias-dependent intra-unit cell form factors and spatial phase difference. We find that in then PDW state the behavior of form factors and spatial phase difference as a function of energy agrees remarkably well with the experiment. This is in contrast to commensurate charge modulated states, which we show do not agree with experiment. We propose that then PDW states are good candidates for the charge density wave phase observed in the superconducting state of underdoped cuprates.

Update: 9-Mar-2017

Title:
Tuning Crystal Structures and Thermoelectric Properties through Al Doping in ReSi1.75
Authors:
Wang, F; Veremchuk, I; Lidin, S Author Full Names: Wang, Fei; Veremchuk, Igor; Lidin, Sven
Source:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 2017 (1):47-55; 10.1002/ejic.201600792 JAN 2017
Abstract:
Binary rhenium silicide, ReSi1.75, and its aluminium-doped variants have been synthesized. Their crystal structures were characterized by X-ray diffraction, solved and refined through the use of superspace group models. The binary un-doped ReSi1.75 is a commensurate (supercell) structure of the previously well-known MoSi2-type structure. Al doping renders an incommensurate structure that was solved and refined, and reported for the first time. The thermoelectric properties of these compounds were also measured, including their electrical resistivities, thermal conductivities, and Seebeck coefficients. Compared with the commensurate structure of binary ReSi1.75, the Al-doped incommensurate phase exhibits lower lattice thermal conductivity, lower electrical resistivity, a higher Seebeck coefficient, and ultimately a much higher figure of merit (ZT). The cause of the structural incommensuration by Al doping was studied through the use of first-principle calculations. The relationship between the incommensurability and the improved thermoelectric properties is also discussed.
Title:
The true structural periodicities and superspace group descriptions of the prototypical incommensurate composite materials: Alkane/urea inclusion compounds
Authors:
Couzi, M; Guillaume, F; Harris, KDM; Palmer, BA; Christensen, K; Collins, SP Author Full Names: Couzi, Michel; Guillaume, Francois; Harris, Kenneth D. M.; Palmer, Benjamin A.; Christensen, Kirsten; Collins, Stephen P.
Source:
EPL, 116 (5):10.1209/0295-5075/116/56001 DEC 2016
Abstract:
The prototypical family of incommensurate composite materials are the n-alkane/urea inclusion compounds, in which n-alkane guest molecules are arranged in a periodic manner along one-dimensional tunnels in a urea host structure, with an incommensurate relationship between the periodicities of the host and guest substructures along the tunnel. We develop interpretations of the structural periodicities, superspace group descriptions and symmetry properties of the low-temperature phases of n-alkane/urea inclusion compounds, based in part on a high-resolution synchrotron single-crystal X-ray diffraction study of n-nonadecane/urea. Specifically, we prove that, on passing from phase I to phase II, the C-centering of the orthohexagonal unit cell is lost for both the host and guest substructures, and that the symmetries of all phases I, II and III are described completely by (3+1)-dimensional superspace groups. Copyright (C) EPLA, 2016
Title:
Commensurate-incommensurate transition and domain wall dynamics of adsorbed overlayers on a honeycomb substrate
Authors:
Elder, KR; Achim, CV; Granato, E; Ying, SC; Ala-Nissila, T Author Full Names: Elder, K. R.; Achim, C. V.; Granato, E.; Ying, S. C.; Ala-Nissila, T.
Source:
EPL, 116 (5):10.1209/0295-5075/116/56002 DEC 2016
Abstract:
We introduce an effective one-mode phase-field crystal model for studying the commensurate-incommensurate transition and domain wall dynamics of the (root 3 x root 3) R30 degrees. phase found in systems such as Xe/Pt(111), or Xe and Kr on graphite. The model allows us to study large systems where the domain walls can be separated over large macroscopic distances and at the same time incorporate the microscopic details of the domain wall structures. The resulting phase diagram shows that an intermediate stripe incommensurate phase always separates the commensurate phase from the honeycomb incommensurate phases. The energy of the domain wall crossing is investigated. We also find that near a step edge, the domain walls tend to align perpendicularly to the step edge, in agreement with recent experimental observations. Copyright (C) EPLA, 2016
Title:
Thermoelectric properties of layered calcium cobaltite Ca3Co4O9 from hybrid functional first-principles calculations
Authors:
Lemal, S; Varignon, J; Bilc, DI; Ghosez, P Author Full Names: Lemal, Sebastien; Varignon, Julien; Bilc, Daniel I.; Ghosez, Philippe
Source:
PHYSICAL REVIEW B, 95 (7):10.1103/PhysRevB.95.075205 FEB 9 2017
Abstract:
Using a combination of first-principles calculations based on density functional theory and Boltzmann semiclassical transport theory, we compute and study the properties of pristine layered calcium cobaltite Ca3Co4O9. We model the system with the B1WC hybrid functional. Two supercells of increasing size which approximate the incommensurate crystallographic structure of the compound are studied and we determine their structural, magnetic, and electronic properties. It is found that the B1WC hybrid functional is appropriate to reproduce the structural, electronic, and magnetic properties, which are then extensively discussed. From the electronic band structure, the Seebeck (S) and electrical resistivity (rho) tensors are computed using Boltzmann transport theory within the constant relaxation-time approximation. The differences between the diagonal components are detailed and reveal a strong in-plane anisotropy of the properties. The qualitative behavior of the averaged in-plane properties, S-// and rho(//), is consistent with the measurements reported in the literature. Our calculation clarifies and provides a broad picture of the evolution of the thermoelectric properties with both carrier density and temperature, and suggests that the change in S-// and rho(//) around 100 K is not necessarily related to the magnetic transitions occurring around 100 K.
Title:
Quasicrystalline nanocrystal superlattice with partial matching rules
Authors:
Ye, XC; Chen, J; Irrgang, ME; Engel, M; Dong, AG; Glotzer, SC; Murray, CB Author Full Names: Ye, Xingchen; Chen, Jun; Irrgang, M. Eric; Engel, Michael; Dong, Angang; Glotzer, Sharon C.; Murray, Christopher B.
Source:
NATURE MATERIALS, 16 (2):214-219; 10.1038/NMAT4759 FEB 2017
Abstract:
Expanding the library of self-assembled superstructures provides insight into the behaviour of atomic crystals and supports the development of materials with mesoscale order(1,2). Here we build on recent findings of soft matter quasicrystals (3-6) and report a quasicrystalline binary nanocrystal superlattice that exhibits correlations in the form of partial matching rules reducing tiling disorder. We determine a three-dimensional structure model through electron tomography(7,8) and direct imaging of surface topography. The 12-fold rotational symmetry of the quasicrystal is broken in sublayers, forming a random tiling of rectangles, large triangles and small triangles with 6-fold symmetry. We analyse the geometry of the experimental tiling and discuss factors relevant for the stabilization of the quasicrystal. Our joint experimental-computational study demonstrates the power of nanocrystal superlattice engineering and further narrows the gap between the richness of crystal structures found with atoms and in soft matter assemblies.

Update: 22-Feb-2017

Title:
Critical scattering and incommensurate phase transition in antiferroelectric PbZrO3 under pressure
Authors:
Burkovsky, RG; Bronwald, I; Andronikova, D; Wehinger, B; Krisch, M; Jacobs, J; Gambetti, D; Roleder, K; Majchrowski, A; Filimonov, AV; Rudskoy, AI; Vakhrushev, SB; Tagantsev, AK Author Full Names: Burkovsky, R. G.; Bronwald, I.; Andronikova, D.; Wehinger, B.; Krisch, M.; Jacobs, J.; Gambetti, D.; Roleder, K.; Majchrowski, A.; Filimonov, A. V.; Rudskoy, A. I.; Vakhrushev, S. B.; Tagantsev, A. K.
Source:
Scientific Reports, 7 10.1038/srep41512 JAN 30 2017
Abstract:
Antiferroelectric lead zirconate is the key ingredient in modern ferroelectric and piezoelectric functional solid solutions. By itself it offers opportunities in new-type non-volatile memory and energy storage applications. A highly useful and scientifically puzzling feature of this material is the competition between the ferro- and antiferroelectric phases due to their energetic proximity, which leads to a challenge in understanding of the critical phenomena driving the formation of the antiferroelectric structure. We show that application of hydrostatic pressure drastically changes the character of critical lattice dynamics and enables the soft-mode-driven incommensurate phase transition sequence in lead zirconate. In addition to the long known cubic and antiferroelectric phases we identify the new non-modulated phase serving as a bridge between the cubic and the incommensurate phases. The pressure effect on ferroelectric and incommensurate critical dynamics shows that lead zirconate is not a single-instability-driven system.
Title:
Observation of a Charge Density Wave Incommensuration Near the Superconducting Dome in CuxTiSe2
Authors:
Kogar, A; de la Pena, GA; Lee, S; Fang, Y; Sun, SXL; Lioi, DB; Karapetrov, G; Finkelstein, KD; Ruff, JPC; Abbamonte, P; Rosenkranz, S Author Full Names: Kogar, A.; de la Pena, G. A.; Lee, Sangjun; Fang, Y.; Sun, S. X. -L.; Lioi, D. B.; Karapetrov, G.; Finkelstein, K. D.; Ruff, J. P. C.; Abbamonte, P.; Rosenkranz, S.
Source:
PHYSICAL REVIEW LETTERS, 118 (2):10.1103/PhysRevLett.118.027002 JAN 11 2017
Abstract:
X-ray diffraction was employed to study the evolution of the charge density wave (CDW) in CuxTiSe2 as a function of copper intercalation in order to clarify the relationship between the CDW and superconductivity. The results show a CDWincommensuration arising at an intercalation value coincident with the onset of superconductivity at around x = 0.055(5). Additionally, it was found that the charge density wave persists to higher intercalant concentrations than previously assumed, demonstrating that the CDW does not terminate inside the superconducting dome. A charge density wave peak was observed in samples up to x = 0.091(6), the highest copper concentration examined in this study. The phase diagram established in this work suggests that charge density wave incommensuration may play a role in the formation of the superconducting state.

Update: 16-Feb-2017

Title:
Multiple quasicrystal approximants with the same lattice parameters in Al-Cr-Fe-Si alloys
Authors:
He, ZB; Li, H; Ma, HK; Li, GW Author Full Names: He, Zhanbing; Li, Hua; Ma, Haikun; Li, Guowu
Source:
SCIENTIFIC REPORTS, 7 10.1038/srep40510 JAN 13 2017
Abstract:
By means of atomic-resolution high-angle annular dark-field scanning transmission electron microscopy, we found three types of giant approximants of decagonal quasicrystal in Al-Cr-Fe-Si alloys, where each type contains several structural variants possessing the same lattice parameters but different crystal structures. The projected structures of these approximants along the pseudo-tenfold direction were described using substructural blocks. Furthermore, the structural relationship and the plane crystallographic groups in the (a, c) plan of these structural variants was also discussed. The diversity of quasicrystal approximants with the same lattice parameters was shown to be closely related to the variety of shield-like tiles and their tiling patterns.
Title:
A general algorithm for generating isotropy subgroups in superspace
Authors:
Stokes, HT; Campbell, BJ Author Full Names: Stokes, Harold T.; Campbell, Branton J.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 73 4-13; 10.1107/S2053273316017629 1 JAN 2017
Abstract:
This paper presents a general algorithm for generating the isotropy subgroups of superspace extensions of crystallographic space groups involving arbitrary superpositions of multi-k order parameters from incommensurate and commensurate k vectors. Several examples are presented in detail in order to illuminate each step of the algorithm. The practical outcome is that one can now start with any commensurate parent crystal structure and generate a structure model for any conceivable incommensurate modulation of that parent, fully parameterized in terms of order parameters of irreducible representations at the relevant wavevectors. The resulting modulated structures have (3 + d)-dimensional superspace-group symmetry. Because incommensurate structures are now commonly encountered in the context of many scientifically and technologically important functional materials, the opportunity to apply the powerful methods of group representation theory to this broader class of structural distortions is very timely.
Title:
To superspace and beyond
Authors:
Senn, MS Author Full Names: Senn, Mark S.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 73 1-3; 10.1107/S2053273316019902 1 JAN 2017

Update: 8-Feb-2017

Title:
Field-induced magnetic states in holmium tetraboride
Authors:
Brunt, D; Balakrishnan, G; Wildes, AR; Ouladdiaf, B; Qureshi, N; Petrenko, OA Author Full Names: Brunt, D.; Balakrishnan, G.; Wildes, A. R.; Ouladdiaf, B.; Qureshi, N.; Petrenko, O. A.
Source:
PHYSICAL REVIEW B, 95 (2):10.1103/PhysRevB.95.024410 JAN 11 2017
Abstract:
A study of the zero field and field induced magnetic states of the frustrated rare earth tetraboride HoB4 has been carried out using single crystal neutron diffraction complemented by magnetization measurements. In zero field, HoB4 shows magnetic phase transitions at T-N1 = 7.1 K to an incommensurate state with a propagation vector (delta, delta, delta'), where delta = 0.02 and delta' = 0.43 and at T-N2 = 5.7 K to a noncollinear commensurate antiferromagnetic structure. Polarized neutron diffraction measurements in zero field have revealed that the incommensurate reflections, albeit much reduced in intensity, persist down to 1.5 K despite antiferromagnetic ordering at 5.7 K. At lower temperatures, application of a magnetic field along the c axis initially re-establishes the incommensurate phase as the dominant magnetic state in a narrow field range, just prior to HoB4 ordering with an up-up-down ferrimagnetic structure characterized by the (h k 1/3)-type reflections between 18 and 24 kOe. This field range is marked by the previously reported M/M-sat = 1 3 magnetization plateau, which we also see in our magnetization measurements. The region between 21 and 33 kOe is characterized by the increase in the intensity of the antiferromagnetic reflections, such as (100), the maximum of which coincides with the appearance of the narrow magnetization plateau with M/M-sat approximate to 3/5. Further increase of the magnetic field results in the stabilization of a polarized state above 33 kOe, while the incommensurate reflections are clearly present in all fields up to 59 kOe. We propose the H-T phase diagram of HoB4 for the H parallel to c containing both stationary and transitionary magnetic phases which overlap and show significant history dependence.
Title:
Gapped excitation in dense Kondo lattice CePtZn
Authors:
Harriger, L; Disseler, SM; Gunasekera, J; Rodriguez-Rivera, J; Pixley, J; Manfrinetti, P; Dhar, SK; Singh, DK Author Full Names: Harriger, L.; Disseler, S. M.; Gunasekera, J.; Rodriguez-Rivera, J.; Pixley, J.; Manfrinetti, P.; Dhar, S. K.; Singh, D. K.
Source:
PHYSICAL REVIEW B, 95 (4):10.1103/PhysRevB.95.041102 JAN 10 2017
Abstract:
We report on neutron scattering and muon spin relaxation measurements of dense Kondo lattice CePtZn. The system develops long-range incommensurate magnetic order as the temperature is reduced below T-N = 1.75 K. Interestingly, a Q-independent gap at E = 0.65 meV in the energy spectrum is found to co-exist with the long-range magnetic order. The gap persists to a very high temperature of T similar or equal to 100 K. The Q-independent characteristic and its persistence to high temperature hint that the gapped excitation may be manifesting the excited state of the ground-state doublet of the crystal-field energy levels. However, the observed broadness in the linewidth with distinct temperature and field dependencies makes it a nontrivial phenomenon. Qualitative analysis of the experimental data suggests the possible co-existence of a local critical behavior, which is onset near the critical field of H similar or equal to 3 T, with the crystal-field excitation in the dynamic properties.
Title:
Mixed-mode crack tip loading and crack deflection in 1D quasicrystals
Authors:
Wang, Z; Scheel, J; Ricoeur, A Author Full Names: Wang, Zhibin; Scheel, Johannes; Ricoeur, Andreas
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 122 (12):10.1007/s00339-016-0570-1 DEC 2016
Abstract:
Quasicrystals (QC) are a new class of materials besides crystals and amorphous solids and have aroused much attention of researchers since they were discovered. This paper presents a generalized fracture theory including the J-integral and crack closure integrals, relations between J(1), J(2) and the stress intensity factors as well as the implementation of the near-tip stress and displacement solutions of 1D QC. Different crack deflection criteria, i.e. the J-integral and maximum circumferential stress criteria, are investigated for mixed-mode loading conditions accounting for phonon-phason coupling. One focus is on the influence of phason stress intensity factors on crack deflection angles.

Update: 1-Feb-2017

Title:
Electronic structure and X-ray magnetic circular dichroism in the Ni-Mn-Ga Heusler alloys
Authors:
Antonov, VN; Bekenov, LV; Uba, S; Bonda, A; Uba, L Author Full Names: Antonov, V. N.; Bekenov, L. V.; Uba, S.; Bonda, A.; Uba, L.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 695 1826-1837; 10.1016/j.jallcom.2016.11.016 FEB 25 2017
Abstract:
The electronic structure and X-ray magnetic circular dichroism (XMCD) spectra of the Ni2MnGa and Cu doped Ni2MnGa Heusler alloys were investigated theoretically from first principles, using the fully relativistic Dirac linear MT-orbital (LMTO) band structure method. Densities of valence states, orbital and spin magnetic moments are analyzed and discussed. The electronic and magnetic structure of Ni-Mn-Ga Heusler alloys were investigated for the cubic austenitic and modulated 7M-like incommensurate martensitic phases. The X-ray absorption spectra ( XAS) and XMCD at the Mn, Ni, Ga, and Cu L-2,L-3,L- and Mn, Ni, and Ga K edges were investigated theoretically from first principles. The origin of the XMCD spectra in the Ni2MnGa compound is examined. The ab initio calculations reproduce well experimental XAS and XMCD spectra. The XAS at the Mn L-2,L-3 edges remains mostly unchanged through martensitic phase transition. A fingerprint of the martensitic phase transition has been found in the Ni L-2,L-3 XAS spectra. The experimental Ni L-3 XAS has a pronounced shoulder at the L-3 peak at around 853 eV. This peak is nearly suppressed in the martensitic state in comparison with the austenitic phase due to the lifting of the degeneracy in the Ni 3d related unoccupied electronic states. The XMCD of the martensitic phase is increased compared to the XMCD of the austenite phase at the Ni and Mn L-2,L-3 edges. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Incommensurately modulated structure and spectroscopic properties of CaGd2(MoO4)(4):Ho3+/Yb3+ phosphors for up-conversion applications
Authors:
Lim, CS; Atuchin, VV; Aleksandrovsky, AS; Molokeev, MS; Oreshonkov, AS Author Full Names: Lim, Chang Sung; Atuchin, Victor V.; Aleksandrovsky, Aleksandr S.; Molokeev, Maxim S.; Oreshonkov, Aleksandr S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 695 737-746; 10.1016/j.jallcom.2016.06.134 FEB 25 2017
Abstract:
CaGd2(MoO4)(4):Ho3+/Yb3+ phosphors doped by Ho3+ and Yb3+ (Ho3+ = 0 and 0.05, and Yb3+ = 0, 0.35, 0.40, 0.45 and 0.50) were successfully synthesized by the microwave sol-gel method. The synthesized particles, being formed after heat-treatment at 900 degrees C for 16 h, showed a well crystallized morphology. All compounds are (3 + 2)D incommensurately modulated with superspace group I4(1)/alpha(alpha,beta,0)00(-beta,alpha,0)00. It was found that parameter (alpha(2) + beta(2))(1)/(2) is proportional to cell parameter a for all studied compositions and, therefore, modulation vector k is the same for all known CaRE2(MoO4)(4) compounds. The modulation vector invariance is a specific and valuable feature of this type of the structure. Under the excitation at 980 nm, the doped particles exhibited the yellow emission composed of green (545-nm) and red (655-nm) emission bands due to frequency upconversion (UC). The pump power dependence and CIE chromaticity of the UC emission were evaluated. The shape of UC bands in CaGd2(MoO4)(4):Ho3+/Yb3+ is dependent on the Yb content due to the influence of the crystal field affecting a holmium ion. 13 Raman-active modes of the CaGd2(MoO4)(4) lattice were identified via a comparison of experimental Raman spectra and the lattice dynamics simulation results. Four additional Raman lines were found in the region of stretching vibrations and, at least, two additional modes are present in the bending mode region. These additional modes are ascribed to incommensurate crystal lattice modulation. Luminescence bands of Ho ions are severely broadened due to a statistical disorder in the CaGd2-xYby (MoO4)(4) lattice. (C) 2016 Published by Elsevier B.V.
Title:
Commensurate-incommensurate magnetic phase transition in the new Yb1-xLuxMn6Sn6 compounds
Authors:
Eichenberger, L; Venturini, G; Malaman, B; Nataf, L; Baudelet, F; Mazet, T Author Full Names: Eichenberger, L.; Venturini, G.; Malaman, B.; Nataf, L.; Baudelet, F.; Mazet, T.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 695 286-293; 10.1016/j.jallcom.2016.10.191 FEB 25 2017
Abstract:
We investigate the magnetic properties of the new Yb1-xLuxMn6Sn6 (0.00 <= x <= 1.00) alloys from AC/DC magnetization and powder neutron diffraction experiments. Room-temperature XANES measurements at Yb L-3 edge indicate that Yb is in an intermediate valent state (upsilon(Yb) similar to 2.6) in the whole Yb1-xLuxMn6Sn6 series. In these compounds only the Mn sublattice magnetically orders with an atomic Mn moment close to m(Mn) similar to 2.2 mu(B) at 2 K throughout the series. Lu substitution yields a crossover from ferromagnetism to antiferromagnetism of the Mn sublattice. In RMn6Sn6 compounds, this is the first time that such transition of the Mn sublattice is induced by substitution on the R site. The enhancement of the antiferromagnetic interactions likely results from modification in valence electron concentration since intermediate valent Yb is replaced by trivalent Lu. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Pushing the limits of crystallography
Authors:
Wolny, J; Buganski, I; Kuczera, P; Strzalka, R Author Full Names: Wolny, Janusz; Buganski, Ireneusz; Kuczera, Pawel; Strzalka, Radoslaw
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 2106-2115; 10.1107/S160057671601637X 6 DEC 2016
Abstract:
A very serious concern of scientists dealing with crystal structure refinement, including theoretical research, pertains to the characteristic bias in calculated versus measured diffraction intensities, observed particularly in the weak reflection regime. This bias is here attributed to corrective factors for phonons and, even more distinctly, phasons, and credible proof supporting this assumption is given. The lack of a consistent theory of phasons in quasicrystals significantly contributes to this characteristic bias. It is shown that the most commonly used exponential Debye-Waller factor for phasons fails in the case of quasicrystals, and a novel method of calculating the correction factor within a statistical approach is proposed. The results obtained for model quasiperiodic systems show that phasonic perturbations can be successfully described and refinement fits of high quality are achievable. The standard Debye-Waller factor for phonons works equally well for periodic and quasiperiodic crystals, and it is only in the last steps of a refinement that different correction functions need to be applied to improve the fit quality.
Title:

Update: 19-Jan-2017

Title:
K8Nb7P7O39: a new type of complicated incommensurately modulated structure and photoluminescence properties of Eu3+-doped solid solutions
Authors:
Zhao, D; Cui, JY; Han, HX; Li, C Author Full Names: Zhao, Dan; Cui, Jun-Yan; Han, Hong-Xian; Li, Can
Source:
JOURNAL OF MATERIALS CHEMISTRY C, 4 (48):11436-11448; 10.1039/c6tc03022j 2016
Abstract:
A new type of potassium niobium phosphate, K8Nb7P7O39, has been prepared and its structure has been determined by single crystal X-ray diffraction analysis. The results show that it crystallizes in a novel (3 + 1)-dimensional incommensurately modulated structure with a triclinic superspace group P (1) over bar(alpha beta gamma)O and modulation vector q = -0.35281a* + 0.17630b* + 0.25807c*. The structure of K8Nb7P7O39 contains [K-3.66](infinity) N, [K-4.34](infinity) N and [Nb7P7O39](infinity) N layers alternately stacked along the c-axis. In this structure, seven not fully occupied K atoms (six of them come from the [K-3.66](infinity) N layer and the remaining one comes from the [K-4.34]infinity N layer) are thought to be the dominant factors in driving the structural modulation. The strong occupational modulation in combination with positional modulation of these seven K atoms can be described by crenel-type modulation functions. Furthermore, elemental composition, UV-Vis absorption spectrum, SEM morphology and photoluminescence properties induced by Eu3+-doping have been studied for K8Nb7P7O39. The excitation spectrum covers a wide range from 362 to 465 nm and it matches well with the emission of near-UV InGaN-based LED chips and bluish-green LED chips, indicating that K8Nb7P7O39: Eu3+ has potential as a red-emitting phosphor for LED applications.
Title:
Generation of Basis Vectors for Magnetic Structures and Displacement Modes
Authors:
Davies, ZL; Wills, AS Author Full Names: Davies, Z. L.; Wills, A. S.
Source:
ADVANCES IN CONDENSED MATTER PHYSICS, 10.1155/2016/3960145 2016
Abstract:
Increasing attention is being focused on the use of symmetry-adapted functions to describe magnetic structures, structural distortions, and incommensurate crystallography. Though the calculation of such functions iswell developed, significant difficulties can arise such as the generation of too many or too few basis functions to minimally span the linear vector space. We present an elegant solution to these difficulties using the concept of basis sets and discuss previous work in this area using this concept. Further, we highlight the significance of unitary irreducible representations in this method and provide the first validation that the irreducible representations of the crystallographic space groups tabulated by Kovalev are unitary.
Title:
K8Nb7P7O39: a new type of complicated incommensurately modulated structure and photoluminescence properties of Eu3+-doped solid solutions
Authors:
Zhao, D; Cui, JY; Han, HX; Li, C Author Full Names: Zhao, Dan; Cui, Jun-Yan; Han, Hong-Xian; Li, Can
Source:
JOURNAL OF MATERIALS CHEMISTRY C, 4 (48):11436-11448; 10.1039/c6tc03022j 2016
Abstract:
A new type of potassium niobium phosphate, K8Nb7P7O39, has been prepared and its structure has been determined by single crystal X-ray diffraction analysis. The results show that it crystallizes in a novel (3 + 1)-dimensional incommensurately modulated structure with a triclinic superspace group P (1) over bar(alpha beta gamma)O and modulation vector q = -0.35281a* + 0.17630b* + 0.25807c*. The structure of K8Nb7P7O39 contains [K-3.66](infinity) N, [K-4.34](infinity) N and [Nb7P7O39](infinity) N layers alternately stacked along the c-axis. In this structure, seven not fully occupied K atoms (six of them come from the [K-3.66](infinity) N layer and the remaining one comes from the [K-4.34]infinity N layer) are thought to be the dominant factors in driving the structural modulation. The strong occupational modulation in combination with positional modulation of these seven K atoms can be described by crenel-type modulation functions. Furthermore, elemental composition, UV-Vis absorption spectrum, SEM morphology and photoluminescence properties induced by Eu3+-doping have been studied for K8Nb7P7O39. The excitation spectrum covers a wide range from 362 to 465 nm and it matches well with the emission of near-UV InGaN-based LED chips and bluish-green LED chips, indicating that K8Nb7P7O39: Eu3+ has potential as a red-emitting phosphor for LED applications.
Title:
Generation of Basis Vectors for Magnetic Structures and Displacement Modes
Authors:
Davies, ZL; Wills, AS Author Full Names: Davies, Z. L.; Wills, A. S.
Source:
ADVANCES IN CONDENSED MATTER PHYSICS, 10.1155/2016/3960145 2016
Abstract:
Increasing attention is being focused on the use of symmetry-adapted functions to describe magnetic structures, structural distortions, and incommensurate crystallography. Though the calculation of such functions iswell developed, significant difficulties can arise such as the generation of too many or too few basis functions to minimally span the linear vector space. We present an elegant solution to these difficulties using the concept of basis sets and discuss previous work in this area using this concept. Further, we highlight the significance of unitary irreducible representations in this method and provide the first validation that the irreducible representations of the crystallographic space groups tabulated by Kovalev are unitary.

Update: 12-Jan-2017

Title:
Incommensurate spin density wave as a signature of spin-orbit coupling and precursor of topological superconductivity
Authors:
Farrell, A; Wu, PK; Kao, YJ; Pereg-Barnea, T Author Full Names: Farrell, Aaron; Wu, P. -K.; Kao, Y. -J.; Pereg-Barnea, T.
Source:
PHYSICAL REVIEW B, 94 (21):10.1103/PhysRevB.94.214424 DEC 22 2016
Abstract:
On a square lattice, the Hubbard model at half filling reduces to the Heisenberg model and exhibits antiferromagnetism. When doped away from half filling this model gives rise to d-wave superconductivity. This behavior is reminiscent of the phenomenology of the cuprate family with their high T(c)d-wave superconductivity and their antiferromagnetic parent compound. It is therefore interesting to study an extension of the Hubbard model which includes spin orbit coupling. We have previously studied this model away from half filling [see, for example, Farrell and Pereg-Barnea, Phys. Rev. B 89, 035112 (2014)] and found that the addition of spin-orbit coupling and Zeeman field leads to topological superconductivity with d + id pairing function. In this paper we are interested in the 'parent compound' of this state. Namely, we study the half filling, strong coupling limit of the square lattice Hubbard model with spin orbit coupling and Zeeman field. The strong coupling expansion of the model is a spin model which contains compass anisotropy and Dzyaloshinsky-Moriya interaction on top of the usual Heisenberg term. We analyze this spin model classically and find an incommensurate spin density wave (ISDW) for low Zeeman fields. This ISDWhas a wave vector (Q) over right arrow which deviates from (pi, pi) by an amount which is proportional to the spin-orbit coupling and can therefore serve as a signature. We study the stability of the ISDW phase using spin wave theory and find a stable and an unstable region. At higher but moderate Zeeman fields we find a tilted antiferromagnet and a ferromagnet at high Zeeman fields.
Title:
Anisotropic spin fluctuations in Sr2RuO4: Role of spin-orbit coupling and induced strain
Authors:
Cobo, S; Ahn, F; Eremin, I; Akbari, A Author Full Names: Cobo, Sergio; Ahn, Felix; Eremin, Ilya; Akbari, Alireza
Source:
PHYSICAL REVIEW B, 94 (22):10.1103/PhysRevB.94.224507 DEC 14 2016
Abstract:
We analyze the spin anisotropy of themagnetic susceptibility of Sr2RuO4 in the presence of spin-orbit coupling and anisotropic strain using quasi-two-dimensional tight-binding parametrization fitted to the angle-resolved photoemission spectroscopy results. Similar to the previous observations we find the in-plane polarization of the low-q magnetic fluctuations and the out-of-plane polarization of the incommensurate magnetic fluctuation at the nestingwave-vector Q(1) = (2/3 pi, 2/3 pi) but also nearly isotropic fluctuations nearQ(2) = (pi/6, pi/6). Furthermore, one finds that, apart from the high-symmetry direction of the tetragonal Brillouin zone, the magnetic anisotropy is maximal, i. e., chi(xx) not equal chi(yy) not equal chi(zz) reflected in the x polarization of the intraband nestingwave-vectorQ(3) = (pi/2, pi). This is a consequence of the orbital anisotropy of the t(2g) orbitals in momentum space. We also study how the magnetic anisotropy evolves in the presence of the strain and find strong Ising-like ferromagnetic fluctuations near the Lifshitz transition for the xy band.
Title:
Vacancy pairing and superstructure in the high-pressure silicate K1.5Mg2Si2O7H0.5: a new potential host for potassium in the deep Earth
Authors:
Welch, MD; Bindi, L; Petricek, V; Plasil, J Author Full Names: Welch, M. D.; Bindi, L.; Petricek, V.; Plasil, J.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 822-827; 10.1107/S2052520616014049 6 DEC 2016
Abstract:
The high-pressure silicate K1.5Mg2Si2O7H0.5, synthesized and characterized by Welch et al. [(2012), Am. Mineral. 97, 1849-1857], has been re-examined with the aim of determining the nature of the superstructure noted in their study. The composition corresponds to a 1:1 combination of KMg2Si2O7H and K2Mg2Si2O7 end-members, but it is not a solid solution. Single-crystal X-ray diffraction data for one of the original K1.5Mg2Si2O7H0.5 crystals synthesized at 16 GPa/1573 K, has been collected using a much longer exposure time in order to improve the intensity statistics of weak superlattice reflections identified by Welch et al. (2012). The superstructure has been determined using a superspace approach as having the superspace group Cmcm(0,beta,0)00s and t(0) = 1/16 with refined parameters a = 8.7623 (10), b = 5.0703 (7), c = 13.2505 (11) angstrom, V = 588.69 (12) angstrom(3). This structure corresponds to one with the conventional space group Pbnm and unit-cell parameters a = 8.7623 (10), b = 20.281 (3), c = 13.2505 (11) angstrom, V=2354.7 (5) angstrom(3) and is based upon a super-sheet motif in which ordering involves rows of pairs of vacant interlayer K sites. This is the third topologically distinct structure type for the KMg2Si2O7H-K2Mg2Si2O7 join and suggests that there is very limited solid solution, and so it can be expected that each of the three structures (P6(3)cm, P (3) over bar 1m and Pbnm) has its own stability field, rather than being part of a continuous compositional series based upon a single structure type. As such, K1.5Mg2Si2O7H0.5 should be considered as a potentially significant host of K in the Earth's mantle.
Title:
Incommensurate density modulation in a Na-rich plagioclase feldspar: Z-contrast imaging and single-crystal X-ray diffraction study
Authors:
Xu, HF; Jin, SY; Noll, BC Author Full Names: Xu, Huifang; Jin, Shiyun; Noll, Bruce C.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 904-915; 10.1107/S205252061601578X 6 DEC 2016
Abstract:
Plagioclase feldspars are the most abundant mineral in the Earth's crust. Intermediate plagioclase feldspars commonly display incommensurately modulated or aperiodic structures. Z-contrast images show both Ca-Na ordering and density modulation. The local structure of lamellae domains has I1-like symmetry. The neighboring lamellae domains are in an inversion twinning relationship. With a state-of-the-art X-ray diffraction unit, second-order satellite reflections (f-reflections) are observed for the first time in andesine (An(45)), a Na-rich e-plagioclase. The f-reflections indicate a structure with a density modulation which is close to a Ca-rich e-plagioclase. The similarity between this e-andesine structure and previously solved e-labradorite structure is confirmed. Refinement of the structure shows density modulation of similar to 7 mol% in compositional variation of the anorthite (An) component. The results from Z-contrast imaging and low-temperature single X-ray diffraction (XRD) provide a structure consistent with density modulation. The discovery of f-reflections in Na-rich e-plagioclase extends the composition range of e1 structure with density modulation to as low as at least An45, which is the lower end of the composition range of Boggild intergrowth. The new result supports the loop-shaped solvus for Boggild intergrowth, below which is a homogenous stable area for e1 structure in the phase diagram. The phase transition between e2 structure without density modulation and e1 structure with density modulation should happen at low temperature. There is a change in modulation period accompanying the phase transition, as well as higher occupancy of AL in the T(1)o site. The andesine with density modulation also indicates extremely slow cooling of its host rock.
Title:
Elasto-Dynamics of Quasicrystals
Authors:
Li, W; Fan, TY Author Full Names: Li, Wu; Fan, Tianyou
Source:
CRYSTALS, 6 (11):10.3390/cryst6110152 NOV 2016
Abstract:
A review on elasto-dynamics of quasicrystals (QCs) and their applications based on mathematical elasticity is given. In this study, recent studies on elasto-dynamics of QCs are reviewed, in which the focus of the problem lies in the role of phason variables and the coupling effect between phonons and phasons in the dynamic deformation process. On summarizing and describing the development of the elastic dynamics of QCs, this review mainly presents theelasto-dynamics of QCs and their application in a variety of research areas, ranging from problems with different QCs, including one-, two-, and three-dimensional QCs to various coupling problems. The plane elasticity and anti-plane elasticity of quasicrystals are included in this review.
Title:
Quasicrystals and Other Aperiodic Structures in Mineralogy
Authors:
Pina, CM; Lopez-Acevedo, V Author Full Names: Pina, Carlos M.; Lopez-Acevedo, Victoria
Source:
CRYSTALS, 6 (11):10.3390/cryst6110137 NOV 2016
Abstract:
In this article, we first present and discuss eighteenth-century descriptions of minerals that contributed decisively to the development of crystallography. Remarkably, these old crystallographic descriptions included morphologies with symmetries incompatible with an internal periodic order of atoms, which, however, have been recognised to be characteristics of quasicrystals. Moreover, we also review a number of studies of minerals with aperiodic crystal structures, including recently reported natural quasicrystals of extra-terrestrial origin. Finally, we discuss the current investigations addressing the search for new quasicrystalline minerals in nature.
Title:
Neutron diffraction study of low-temperature magnetic phase diagram of an isosceles-triangular-lattice Ising antiferromagnet CoNb2O6
Authors:
Kobayashi, S; Mitsuda, S; Hosaka, S; Tamatsukuri, H; Nakajima, T; Koorikawa, H; Prokes, K; Kiefer, K Author Full Names: Kobayashi, S.; Mitsuda, S.; Hosaka, S.; Tamatsukuri, H.; Nakajima, T.; Koorikawa, H.; Prokes, K.; Kiefer, K.
Source:
PHYSICAL REVIEW B, 94 (13):10.1103/PhysRevB.94.134427 OCT 27 2016
Abstract:
A low-temperature magnetic phase diagram under magnetic fields along the orthorhombic a axis of an isosceles-triangular-lattice antiferromagnet CoNb2O6 was investigated through single-crystal neutron diffraction measurements made at temperatures down to T = 0.5K. We produced a phase diagram that consists of three magnetically ordered phases, i.e., the antiferromagnetic (AF), the incommensurate sinusoidal magnetic (IC), and the induced ferromagnetic (IFM) phases, which were characterized by the propagation wave vectors Q = (01/20), (0 q 0), and (0 0 0), respectively. We found that a field-induced ferrimagnetic phase with Q = (01/40) that had been observed by previous neutron diffraction studies down to T = 1.8K [H. Weitzel et al., Phys. Rev. B 62, 12146 (2000)] does not exist as a single equilibrium phase, but rather it always coexists with the other ordered phases near the triple point where the AF, IC, and IFM phases meet. We also found that the relaxation time of the system becomes extremely long below T = 0.6 K in comparison with our observation time; this was considered to possibly be the reason for magnetization plateaus appearing at T = 0.5K. These plateaus have a half-saturation magnetization, from which another field-induced state was inferred in previous magnetization measurements [J. Phys. Soc. Jpn. 63, 2706 (1994)].
Title:
An Icosahedral Quasicrystal and Its 1/0 Crystalline Approximant in the Ca-Au-Al System
Authors:
Pham, J; Kreyssig, A; Goldman, AI; Miller, GJ Author Full Names: Pham, Joyce; Kreyssig, Andreas; Goldman, Alan I.; Miller, Gordon J.
Source:
INORGANIC CHEMISTRY, 55 (20):10425-10437; 10.1021/acs.inorgchem.6b01636 OCT 17 2016
Abstract:
A new icosahedral quasicrystalline phase, CaAu4.5-xAl1.5+x [0.11 <= x <= 0.40(6); CaAu4.4Al1.6, a(QC) = 5.383(4) angstrom, and Pm (3) over bar(5) over bar], and its lowest-order 1/0 cubic crystalline approximant phase, CaAu3+xAl1-x [0 <= x <= 0.31(1); a = 9.0766(5)-9.1261(8) angstrom, Pa (3) over bar (No. 205), and Pearson symbol cP40], have been discovered in the Ca-poor region of the Ca-Au-Al system. In the crystalline approximant, eight [Au3-xAl1+x] tetrahedra fill the unit cell, and each tetrahedron is surrounded by four Ca atoms, thus forming a three-dimensional network of {Ca-4/4[Au3-xAl1+x]} tetrahedral stars. A computational study of Au and Al site preferences concurs with the experimental results, which indicate a preference for near-neighbor Au-Al interactions over Au-Au and Al-Al interactions. Analysis of the electronic density of states and the associated crystal orbital Hamilton population curves was used to rationalize the descriptions of CaAu4.5-xAl1.5+x [0.11 <= x <= 0.46(6)] and CaAu3+xAl1-x [0 <= x <= 0.31(1)] as polar intermetallic species, whereby Ca atoms engage in polar covalent bonding with the electronegative, electron-deficient [Au3-xAl1+x] tetrahedral clusters and the observed phase width of the crystalline approximant.
Title:
Quantum Simulation of a 2D Quasicrystal with Cold Atoms
Authors:
Mace, N; Jagannathan, A; Duneau, M Author Full Names: Mace, Nicolas; Jagannathan, Anuradha; Duneau, Michel
Source:
CRYSTALS, 6 (10):10.3390/cryst6100124 OCT 2016
Abstract:
We describe a way to obtain a two-dimensional quasiperiodic tiling with eight-fold symmetry using cold atoms. One can obtain a series of such optical tilings, related by scale transformations, for a series of specific values of the chemical potential of the atoms. A theoretical model for the optical system is described and compared with that of the well-known cut-and-project method for the Ammann-Beenker tiling. The relation between the two tilings is discussed. This type of cold atom structure should allow the simulation of several important lattice models for interacting quantum particles and spins in quasicrystals.
Title:
Detection of a Cooper-pair density wave in Bi2Sr2CaCu2O8+x
Authors:
Hamidian, MH; Edkins, SD; Joo, SH; Kostin, A; Eisaki, H; Uchida, S; Lawler, MJ; Kim, EA; Mackenzie, AP; Fujita, K; Lee, J; Davis, JCS Author Full Names: Hamidian, M. H.; Edkins, S. D.; Joo, Sang Hyun; Kostin, A.; Eisaki, H.; Uchida, S.; Lawler, M. J.; Kim, E. -A.; Mackenzie, A. P. .; Fujita, K.; Lee, Jinho; Davis, J. C. Seamus
Source:
NATURE, 532 (7599):343-+; 10.1038/nature17411 APR 21 2016
Abstract:
The quantum condensate of Cooper pairs forming a superconductor was originally conceived as being translationally invariant. In theory, however, pairs can exist with finite momentum Q, thus generating a state with a spatially modulated Cooper-pair density(1,2). Such a state has been created in ultracold Li-6 gas(3) but never observed directly in any superconductor. It is now widely hypothesized that the pseudogap phase (4) of the copper oxide superconductors contains such a 'pair density wave' state(5-21). Here we report the use of nanometre-resolution scanned Josephson tunnelling microscopy (22-24) to image Cooper pair tunnelling from a d-wave superconducting microscope tip to the condensate of the superconductor Bi2Sr2CaCu2O8+x. We demonstrate condensate visualization capabilities directly by using the Cooper-pair density variations surrounding zinc impurity atoms(25) and at the Bi2Sr2CaCu2O8+x crystal supermodulation(26). Then, by using Fourier analysis of scanned Josephson tunnelling images, we discover the direct signature of a Cooper-pair density modulation at wavevectors Q(P) approximate to (0.25, 0)2 pi/a(0) and (0, 0.25)2 pi/a(0) in Bi2Sr2CaCu2O8+x. The amplitude of these modulations is about five per cent of the background condensate density and their form factor exhibits primarily s or s' symmetry. This phenomenology is consistent with Ginzburg-Landau theory(5,13,14) when a charge density wave(5,27) with d-symmetry form factor(28-30) and wavevector Q(C) = Q(P) coexists with a d-symmetry superconductor; it is also predicted by several contemporary microscopic theories for the pseudogap phase (18-21).

Update: 4-Jan-2017

Title:
Monoclinic superstructure of Pr3Rh4Ge4
Authors:
Vosswinkel, D; Hoffmann, RD; Greiwe, M; Eul, M; Pottgen, R Author Full Names: Vosswinkel, Daniel; Hoffmann, Rolf-Dieter; Greiwe, Magnus; Eul, Matthias; Poettgen, Rainer
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (11):641-651; 10.1515/zkri-2016-1992 NOV 2016
Abstract:
Pr3Rh4Ge4 was synthesized by melting of the elements in an arc-melting furnace followed by annealing in a sealed tantalum ampoule in a muffle furnace. Structure refinement was based on temperature dependent single-crystal X-ray diffractometer data. At ambient temperature Pr3Rh4Ge4 adopts the U3Ni4Si4 type structure with strongly enhanced anisotropic displacement parameters for Rh1. Below 230 K additional reflections start to appear and at 110 K the structure could be described with the (3+1)D superspace group I2/m(alpha 0 gamma)00; alpha = 1/2, gamma = 1/2; (Z = 2). This commensurately *modulated structure* could be refined with 1448 F-2 values, 39 variables and residuals of wR = 0.0417 for the main reflections and wR = 0.1520 for the satellites of 1st order, [a = 408.36(2), b = 421.12(3) and c = 2504.4(2) pm]. The commensurate description could be transformed to a 3D supercell with space group A2/m and Z = 4: a = 816.72(2), b = 421.12(3), c = 2537.5(1) pm, beta = 99.26(1)degrees, 1448 F-2 values, 69 variables and wR = 0.0499. The relation of the U3Ni4Si4 type structure, the (3+ 1)D modulated and the 3D supercell is discussed on the basis of a group-subgroup scheme. Temperature dependent magnetic susceptibility data reveal Curie-Weiss paramagnetism with an experimental moment of 3.72(2) mu(B) /Pr atom and a Weiss constant of -12.6(5) K. No magnetic ordering is evident down to 3 K.

Update: 29-Dec-2016

Title:
Collisions in outer space produced an icosahedral phase in the Khatyrka meteorite never observed previously in the laboratory
Authors:
Bindi, L; Lin, C; Ma, C; Steinhardt, PJ Author Full Names: Bindi, Luca; Lin, Chaney; Ma, Chi; Steinhardt, Paul J.
Source:
Scientific Reports, 6 10.1038/srep38117 DEC 8 2016
Abstract:
We report the first occurrence of an icosahedral quasicrystal with composition Al-62.0(8) Cu-31.2(8) Fe-6.8(4), outside the measured equilibrium stability field at standard pressure of the previously reported Al-Cu-Fe quasicrystal (AlxCuyFez, with x between 61 and 64, y between 24 and 26, z between 12 and 13%). The new icosahedral mineral formed naturally and was discovered in the Khatyrka meteorite, a recently described CV3 carbonaceous chondrite that experienced shock metamorphism, local melting (with conditions exceeding 5 GPa and 1,200 degrees C in some locations), and rapid cooling, all of which likely resulted from impact-induced shock in space. This is the first example of a quasicrystal composition discovered in nature prior to being synthesized in the laboratory. The new composition was found in a grain that has a separate metal assemblage containing icosahedrite (Al63Cu24Fe13), currently the only other known naturally occurring mineral with icosahedral symmetry (though the latter composition had already been observed in the laboratory prior to its discovery in nature). The chemistry of both the icosahedral phases was characterized by electron microprobe, and the rotational symmetry was confirmed by means of electron backscatter diffraction.
Title:
Spin-lattice coupling mediated multiferroicity in (ND4)(2)FeCl5 center dot D2O
Authors:
Tian, W; Cao, H; Wang, J; Ye, F; Matsuda, M; Yan, JQ; Liu, Y; Garlea, VO; Agrawal, HK; Chakoumakos, BC; Sales, BC; Fishman, RS; Fernandez-Baca, JA Author Full Names: Tian, W.; Cao, Huibo; Wang, Jincheng; Ye, Feng; Matsuda, M.; Yan, J. -Q.; Liu, Yaohua; Garlea, V. O.; Agrawal, Harish K.; Chakoumakos, B. C.; Sales, B. C.; Fishman, Randy S.; Fernandez-Baca, J. A.
Source:
PHYSICAL REVIEW B, 94 (21):10.1103/PhysRevB.94.214405 DEC 7 2016
Abstract:
We report a neutron diffraction study of the multiferroic mechanism in (ND4)(2)FeCl5 center dot D2O, a molecular compound that exhibits magnetically induced ferroelectricity. This material exhibits two successive magnetic transitions on cooling: a long-range order transition to an incommensurate (IC) collinear sinusoidal spin state at T-N = 7.3 K, followed by a second transition to an IC cycloidal spin state at T-FE = 6.8 K, the latter of which is accompanied by spontaneous ferroelectric polarization. The cycloid structure is strongly distorted by spin-lattice coupling, as evidenced by the observations of both odd and even higher-order harmonics associated with the cycloid wave vector, and a weak commensurate phase that coexists with the IC phase. The second-order harmonic appears at TFE, thereby providing unambiguous evidence that the onset of the electric polarization is accompanied by a lattice modulation due to spin-lattice interaction. The neutron results, in conjunction with the negative thermal expansion and large magnetostriction observed in Ref. [19], indicate that spin-lattice coupling plays a critical role in the ferroelectric mechanism of (ND4)(2)FeCl5 center dot D2O.
Title:
Hofstadter butterfly of a quasicrystal
Authors:
Fuchs, JN; Vidal, J Author Full Names: Fuchs, Jean-Noel; Vidal, Julien
Source:
PHYSICAL REVIEW B, 94 (20):10.1103/PhysRevB.94.205437 NOV 28 2016
Abstract:
The energy spectrum of a tight-binding Hamiltonian is studied for the two-dimensional quasiperiodic Rauzy tiling in a perpendicular magnetic field. This spectrum known as a Hofstadter butterfly displays a very rich pattern of bulk gaps that are labeled by four integers, instead of two for periodic systems. The role of phason-flip disorder is also investigated in order to extract genuinely quasiperiodic properties. This geometric disorder is found to only preserve main quantum Hall gaps.
Title:
Magnetic field-temperature phase diagrams of multiferroic (Ni0.9Co0.1)(3)V2O8
Authors:
Qureshi, N; Ressouche, E; Mukhin, AA; Ivanov, VY; Barilo, SN; Shiryaev, SV; Skumryev, V Author Full Names: Qureshi, N.; Ressouche, E.; Mukhin, A. A.; Ivanov, V. Yu.; Barilo, S. N.; Shiryaev, S. V.; Skumryev, V.
Source:
PHYSICAL REVIEW B, 94 (17):10.1103/PhysRevB.94.174441 NOV 28 2016
Abstract:
We present macroscopic and neutron diffraction data on multiferroic lightly Co doped Ni3V2O8. The magnetic H-T phase diagrams have been derived from magnetization and electric polarization measurements with field directions parallel to the principal crystallographic axes. While the phase diagram for H parallel to b is very similar to that of the parent compound Ni3V2O8 for the commonly involved phases, the zero-field phases in (Ni0.9Co0.1)(3)V2O8 show a stronger instability for applied magnetic fields along the a or c axis. Neutron single-crystal diffraction revealed the magnetic structure of the field-induced phase for H parallel to c with a collinear spin alignment along the a and b axes for the two magnetically inequivalent sites. A pronounced irreversibility has been observed for the transition between the zero-field spin cycloid and the field-induced phase, which is manifested in a propagation vector change from q = (0.322 0 0) to q = (0.306 0 0), with slight modifications of the magnetic structure after reentering the zero-field phase. The reentrant phase is characterized by a significantly larger b component of the cross-tie site spin, therefore showing remanent features of the high-field phase. For H parallel to a the magnetization data reveal anomalies, one of which was proved to reflect a field-induced transition from the cycloidally to the sinusoidally modulated magnetic structure.

Update: 21-Dec-2016

Title:
Enhancement of glass-forming ability and mechanical property of Zr-based Zr-Al-Ni bulk metallic glasses with addition of Pd
Authors:
Hua, NB; Chen, WZ Author Full Names: Hua, Nengbin; Chen, Wenzhe
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 693 816-824; 10.1016/j.jallcom.2016.09.263 FEB 5 2017
Abstract:
The effects of partial substitution of Ni by Pd in the high-Zr-based Zr65Al10Ni25-xPdx (at.%, x = 0, 5 and 10) alloys on their glass-forming ability (GFA), crystallization kinetics and mechanical property were investigated. The critical diameter for glass formation is increased from 3 mm for Zr65Al10Ni25 alloy to 5 mm for Zr65Al10Ni15Pd10. An icosahedral quasicrystal phase precipitates in the amorphous matrix in the first crystallization step of Zr-Al-Ni-Pd BMGs, implying that strong icosahedral short/medium-range order (IS/MRO) may exist in the Pd-containing alloys. In additional, Pd-bearing Zr-based BMGs present a lower Avrami exponent n indicating the higher stabilization of the supercooled liquid. Moreover, the Zr-Al-Ni-Pd BMGs exhibit larger compressive plasticity, higher notch toughness and Poisson's ratio than those of Zr65Al10Ni25 alloy, which can be correlated with the existence of strong IS/MRO clusters in amorphous phase. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Microstructure evolution and mechanical properties of quasicrystal-reinforced Mg-Zn-Y alloy subjected to ultrasonic vibration
Authors:
Fang, XG; Wu, SS; Lu, SL; Wang, J; Yang, X Author Full Names: Fang, Xiaogang; Wu, Shusen; Lu, Shulin; Wang, Jing; Yang, Xiong
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 679 372-378; 10.1016/j.msea.2016.10.035 JAN 2 2017
Abstract:
Although the icosahedral quasicrystal phase found in Mg-Zn-Y alloys has some outstanding characteristics, the coarse alpha-Mg dendrites and the agglomeration of the secondary phases in as-cast microstructure restrict the improvements in the mechanical properties. In this study, the semisolid slurry of Mg-6Zn-1.4Y alloy was obtained with ultrasonic vibration (UV) treatment and then formed by rheo-squeeze casting (RSC) process. The effects of UV on the microstructure evolution and mechanical properties were systematically investigated. With UV, primary a-Mg grains and the agglomerated Mg-Zn-Y compounds were significantly refined. Notably, a large mass of fine and granular quasicrystal I-phase particles precipitate in the grains at the later stage of solidification. The RSC alloy subjected to 6 W/mL UV exhibited the optimal mechanical properties, with the yield strength of 129 MPa, the ultimate tensile strength of 231 MPa and the elongation of 18.5%. Compared with the samples without UV, they are increased by 18.3%, 14.9% and 55.5%, respectively.
Title:
Intertwined nematic orders in a frustrated ferromagnet
Authors:
Iqbal, Y; Ghosh, P; Narayanan, R; Kumar, B; Reuther, J; Thomale, R Author Full Names: Iqbal, Yasir; Ghosh, Pratyay; Narayanan, Rajesh; Kumar, Brijesh; Reuther, Johannes; Thomale, Ronny
Source:
PHYSICAL REVIEW B, 94 (22):10.1103/PhysRevB.94.224403 DEC 2 2016
Abstract:
We investigate the quantum phases of the frustrated spin-1/2 J(1)-J(2)-J(3) Heisenberg model on the square lattice with ferromagnetic J(1) and antiferromagnetic J(2) and J(3) interactions. Using the pseudofermion functional renormalization group technique, we find an intermediate paramagnetic phase located between classically ordered ferromagnetic, stripy antiferromagnetic, and incommensurate spiral phases. We observe that quantum fluctuations lead to significant shifts of the spiral pitch angles compared to the classical limit. By computing the response of the system with respect to various spin rotation and lattice symmetry-breaking perturbations, we identify a complex interplay between different nematic spin states in the paramagnetic phase. While retaining time-reversal invariance, these phases either break spin-rotation symmetry, lattice-rotation symmetry, or a combination of both. We therefore propose the J(1)-J(2)-J(3) Heisenberg model on the square lattice as a paradigmatic example where different intimately connected types of nematic orders emerge in the same model.
Title:
Cation distribution in nanocrystalline (Co, Ni)Al2O4 Spinel
Authors:
Agarwal, H; Yadav, TP; Srivastava, ON; Shaz, MA Author Full Names: Agarwal, Harshit; Yadav, T. P.; Srivastava, O. N.; Shaz, M. A.
Source:
CERAMICS INTERNATIONAL, 42 (16):19429-19432; 10.1016/j.ceramint.2016.08.193 DEC 2016
Abstract:
In the present study, the cations Co2+/Ni2+ and Al3+ distribution in nanocrystalline (Co, Ni)Al2O4 spinel have been investigated using X-ray and transmission electron microscopy. The nanocrystalline (Co, Ni) Al2O4 spinet has been synthesized using mechanically activated Al70Co15Ni15 quasicrystalline precursor through annealing at 600 degrees C in controlled oxygen atmosphere. The mechanical activation of single phasic decagonal Al70Co15Ni15 quasicrystal was carried out in a high energy attritor ball mill for 40 h with 40:1 ball to powder ratio using toluene as a process control agent. The high resolution x-ray diffraction data has been refined by the Rietveld method using JANA2006 and subsequently, the corresponding structure has been constructed using Diamond4.0. The structure was also confirmed by analysis of transmission electron microscopy linearized diffraction pattern profile of D-values and corresponding plane. These analyses indicate that the cations Co2+ and Ni2+ distributed in the tetrahedral coordinated sites are the dominant species in the normal spinel phase. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Title:
Commensurate Superstructure of the {Cu(NO3)(H2O)}(HTae)(Bpy) Coordination Polymer: An Example of 2D Hydrogen-Bonding Networks as Magnetic Exchange Pathway
Authors:
de Luis, RF; Larrea, ES; Orive, J; Lezama, L; Arriortua, MI Author Full Names: Fernandez de Luis, Roberto; Larrea, Edurne S.; Orive, Joseba; Lezama, Luis; Arriortua, Maria I.
Source:
INORGANIC CHEMISTRY, 55 (22):11662-11675; 10.1021/acs.inorgchem.6b01199 NOV 21 2016
Abstract:
The average and commensurate superstructures of the one-dimensional coordination polymer {Cu(NO3)(H2O)}(HTae)(Bpy) (H(2)Tae = 1,1,2,2-tetraacetylethane, Bpy = 4,4'-bipyridine) were determined by single-crystal X-ray diffraction, and the possible symmetry relations between the space group of the average structure and the superstructure were checked. The crystal structure consists in parallel and oblique {Cu(HTae)(Bpy)} zigzag metal organic chains stacked along the [100] crystallographic direction. The origin of the fivefold c axis in the commensurate superstructure is ascribed to a commensurate modulation of the coordination environment of the copper atoms. The commensurately ordered nitrate groups and coordinated water molecules establish a twodimensional hydrogen-bonding network. Moreover, the crystal structure shows a commensurate to incommensurate transition at room temperature. The release of the coordination water molecules destabilizes the crystal framework, and the compound shows an irreversible structure transformation above 100 degrees C. Despite the loss of crystallinity, the spectroscopic studies indicate that the main building blocks of the crystal framework are retained after the transformation. The hydrogen-bonding network not only plays a crucial role stabilizing the crystal structure but also is an important pathway for magnetic exchange transmission. In fact, the magnetic susceptibility curves indicate that after the loss of coordinated water molecules, and hence the collapse of the hydrogen-bonding network, the weak anti-ferromagnetic coupling observed in the initial compound is broken. The electron paramagnetic resonance spectra are the consequence of the average signals from Cu(II) with different orientations, indicating that the magnetic coupling is effective between them. In fact, X- and Q-band data are reflecting different situations; the X-band spectra show the characteristics of an exchange g-tensor, while the Qband signals are coming from both the exchange and the molecular g-tensors.
Title:
The Moment Series Expansion for Quasicrystal with Phason Disorder
Authors:
Buganski, I; Strzalka, R; Wolny, J Author Full Names: Buganski, I.; Strzalka, R.; Wolny, J.
Source:
ACTA PHYSICA POLONICA A, 130 (4):833-835; 10.12693/APhysPolA.130.833 OCT 2016
Abstract:
The novel method for structural analysis of quasicrystals with phason flips is presented. The correction for diffraction peaks' intensities can be made within average unit cell approach by modification of the statistical distribution of atomic positions. Characteristic function of the distribution expanded into moment series, involving only even moments, estimates the envelope function and therefore the flip ratio can be evaluated.
Title:
Crystal Structure of the High Temperature Phase of Strontium Barium Niobate
Authors:
Paszkowski, R; Zubko, M; Wokulska, K; Kusz, J; Dec, J Author Full Names: Paszkowski, R.; Zubko, M.; Wokulska, K.; Kusz, J.; Dec, J.
Source:
ACTA PHYSICA POLONICA A, 130 (4):856-858; 10.12693/APhysPolA.130.856 OCT 2016
Abstract:
Pure and undoped strontium-barium niobate Sr0.40Ba0.60Nb2O6 (SBN40) single crystals grown by the Czochralski method were investigated by single crystal X-ray diffraction methods. The study below T-C (429 K for SBN40) confirmed the structure with P4bm space group. Above this temperature the structure transforms into the paraelectric, centrosymmetric one with P4/mbm space group. Analysis of the recorded diffraction patterns allowed to observe several signs of crystal structure modulation. On the registered diffraction images satellite reflections were found. A modulation vector q = (delta, +/-delta,), where delta = 0.3075(6) (at room temperature) was found and it was similar to that occurring in the SBN61. In addition, above the phase transition temperature on the (hk) planes with l integer a weak diffuse scattering was observed.
Title:
Solution and Refinement of Magnetic Structures with Jana2006
Authors:
Petricek, V; Henriques, MS; Dusek, M Author Full Names: Petricek, V.; Henriques, M. S.; Dusek, M.
Source:
ACTA PHYSICA POLONICA A, 130 (4):848-851; 10.12693/APhysPolA.130.848 OCT 2016
Abstract:
The program Jana2006 allows the solution and refinement of regular, twinned, modulated, and composite structures against different diffraction data sets. Recently a new option for solving and refining magnetic structures from powder and single crystal neutron diffraction data has been developed.
Title:
Fitting the Long-Range Order of a Decagonal Quasicrystal
Authors:
Chodyn, M; Kuczera, P; Wolny, J Author Full Names: Chodyn, M.; Kuczera, P.; Wolny, J.
Source:
ACTA PHYSICA POLONICA A, 130 (4):845-847; 10.12693/APhysPolA.130.845 OCT 2016
Abstract:
The generalized Penrose tiling is an infinite set of decagonal tilings. It is constructed with the same rhombs (thick and thin) as the conventional Penrose tiling, but its long-range order depends on the so-called shift parameter s is an element of < 0,1). The formula for structure factor, calculated within the average unit cell approach, works in physical space only and is directly dependent on the s parameter. It allows to straightforwardly change the long-range order of the refined structure just by changing the s parameter and keeping the tile decoration unchanged. The possibility and viability of using the shift as one of the refinement parameters during structure refinement was tested for a numerically generated simple binary decagonal quasicrystal.
Title:
Simple Decoration Model of Icosahedral Quasicrystals in Statistical Approach
Authors:
Strzalka, R; Buganski, I; Wolny, J Author Full Names: Strzalka, R.; Buganski, I.; Wolny, J.
Source:
ACTA PHYSICA POLONICA A, 130 (4):841-844; 10.12693/APhysPolA.130.841 OCT 2016
Abstract:
The statistical approach based on the average unit cell concept was recently successfully applied to structural modelling of icosahedral quasicrystals. The structure factor for arbitrarily decorated icosahedral structure was derived for model Ammann tiling (3D Penrose tiling). It is a fully physical-space model where no higher-dimensional description is needed. In the present paper we show the application of the model to the so-called simple decoration scheme - atomic decoration in the nodes, at mid-edges and along body-diagonal of structural units of 3D Penrose tiling. By analyzing the obtained calculated diffraction patterns we show the correctness of the model and its applicability to binary and ternary icosahedral phases.
Title:
Phononic and Phasonic Debye-Waller Factors for 1D Quasicrystals
Authors:
Wolny, J; Buganski, I; Strzalka, R Author Full Names: Wolny, J.; Buganski, I.; Strzalka, R.
Source:
ACTA PHYSICA POLONICA A, 130 (4):836-840; 10.12693/APhysPolA.130.836 OCT 2016
Abstract:
The main purpose of crystallography is to solve and refine crystal structures based on measured diffraction data. One of important corrections crucial in the refinement process is the Debye-Waller factor correction for phonons in physical, and phasons in perpendicular space. In our paper we show the limitations of the standard approaches to the Debye-Waller correction in case of quasicrystals and propose new approach based on the statistical method. For the model 1D quasicrystal we show that in case of phonons there is no significant objection against classical (exponential) Debye-Waller factor, however using different forms can slightly improve the results of a refinement. In case of phasons the classical formula gives no rise to the efficiency of the refinement and completely new approach is required. We propose a redefinition of the Debye-Waller factor in terms of the statistical approach and show its effectiveness.
Title:
Precession Electron Diffraction Studies of SrxBa1-xNb2O6 and CaxBa1-xNb2O6 Single Crystals
Authors:
Wspaniala-Rak, J; Zubko, M; Stroz, D; Rak, J; Dec, J Author Full Names: Wspaniala-Rak, J.; Zubko, M.; Stroz, D.; Rak, J.; Dec, J.
Source:
ACTA PHYSICA POLONICA A, 130 (4):830-832; 10.12693/APhysPolA.130.830 OCT 2016
Abstract:
Crystal structures of two single crystals SrxBa1-xNb2O6 and CaxBa1-xNb2O6 have been reinvestigated using automated electron diffraction tomography method with beam precession. 3D reciprocal space has been reconstructed based on recorded tilt series. For both samples the crystal structure was refined and the tetragonal symmetry with space group P4bm was confirmed. The three dimensional reciprocal space allowed to observe and to study satellite reflections in both materials.
Title:
FOUR-DIMENSIONAL INCOMMENSURATELY MODULATED STRUCTURE OF THULIUM POLYPHOSPHATE
Authors:
Ma, FX; Zhao, D; Yang, H; Chen, PF; Yang, RJ; Wu, SX Author Full Names: Ma, Fa-Xue; Zhao, Dan; Yang, Hong; Chen, Peng-Fei; Yang, Rui-Juan; Wu, Shan-Xuan
Source:
JOURNAL OF THE CHILEAN CHEMICAL SOCIETY, 61 (2):3005-3008; JUN 2016
Abstract:
Single crystal of rare-earth polyphosphate Tm(PO3)(3) has been grown under high temperature molten-salt method and structurally characterized by single crystal X-ray diffraction analysis. Using the four-dimensional superspace formalism for aperiodic structures, we performed the crystal structure refinement of Tm(PO3)(3) as (3+ 1)-dimensional incommensurately modulated structure with monoclinic superspace group C2/c(0, 0.358,0)s0 and a = 14.0620 (12)angstrom, b = 6.6612 (6) angstrom, c = 10.0191 (9) angstrom, beta = 127.6043 (9)degrees, V = 743.51 (11) angstrom(3), Z = 4, M-r = 405.8, D-c = 3.626 g/cm(3), F(000) = 744, mu((MoKa)) = 12.60 mm(-1), R = 0.048 and omega R = 0.050. The structure features infinite chains of corner-sharing PO4 tetrahedra which are affected by positional modulation running along the b-axis. The final structure model was reasonable and did not show any unusual features.

Update: 14-Dec-2016

Title:
Soft-phonon-driven orbital order in CaMn7O12
Authors:
Souliou, SM; Li, Y; Du, X; Le Tacon, M; Bosak, A Author Full Names: Souliou, S. M.; Li, Y.; Du, X.; Le Tacon, M.; Bosak, A.
Source:
PHYSICAL REVIEW B, 94 (18):10.1103/PhysRevB.94.184309 NOV 22 2016
Abstract:
We use variable-temperature x-ray thermal diffuse scattering and inelastic scattering to investigate the lattice dynamics in single crystals of multiferroic CaMn7O12 which undergo a series of orbital and magnetic transitions at low temperatures. Upon approaching the charge and orbital ordering temperature T-o = 250 K from above, we observe intense diffuse scattering features and a pronounced optical phonon softening centered around the superstructure reflections of the incommensurately modulated structure. The phonon anomaly appears well above T-o and continuously increases upon cooling, following a canonical power-law temperature dependence that confirms the transition at T-o to be of second order and related to a soft-phonon lattice instability. Microscopic mechanisms for the incommensurate charge and orbital ordering based on competing interactions and on momentum-dependent electron-phonon coupling could both account for the observed extended momentum width of the phonon softening. Our results highlight the importance of the lattice interactions in the physics of this magnetically induced ferroelectric system.
Title:
High-Pressure Phase Transformations in TiPO4: A Route to Pentacoordinated Phosphorus
Authors:
Bykov, M; Bykova, E; Hanfland, M; Liermann, HP; Kremer, RK; Glaum, R; Dubrovinsky, L; van Smaalen, S Author Full Names: Bykov, Maxim; Bykova, Elena; Hanfland, Michael; Liermann, Hanns-Peter; Kremer, Reinhard K.; Glaum, Robert; Dubrovinsky, Leonid; van Smaalen, Sander
Source:
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 55 (48):15053-15057; 10.1002/anie.201608530 NOV 21 2016
Abstract:
Titanium(III) phosphate, TiPO4, is a typical example of an oxyphosphorus compound containing covalent P-O bonds. Single-crystal X-ray diffraction studies of TiPO4 reveal complex and unexpected structural and chemical behavior as a function of pressure at room temperature. A series of phase transitions lead to the high-pressure phase V, which is stable above 46 GPa and features an unusual oxygen coordination of the phosphorus atoms. TiPO4-V is the first inorganic phosphorus-containing compound that exhibits fivefold coordination with oxygen. Up to the highest studied pressure of 56 GPa, TiPO4-V coexists with TiPO4-IV, which is less dense and might be kinetically stabilized. Above a pressure of about 6 GPa, TiPO4-II is found to be an incommensurately modulated phase whereas a lock-in transition at about 7 GPa leads to TiPO4-III with a fourfold superstructure compared to the structure of TiPO4-I at ambient conditions. TiPO4-II and TiPO4-III are similar to the corresponding low-temperature incommensurate and commensurate magnetic phases and reflect the strong pressure dependence of the spin-Peierls interactions.
Title:
Influence of elastic strain gradient on the upper limit of flexocoupling strength, spatially modulated phases, and soft phonon dispersion in ferroics
Authors:
Morozovska, AN; Eliseev, EA; Scherbakov, CM; Vysochanskii, YM Author Full Names: Morozovska, Anna N.; Eliseev, Eugene A.; Scherbakov, Christian M.; Vysochanskii, Yulian M.
Source:
PHYSICAL REVIEW B, 94 (17):10.1103/PhysRevB.94.174112 NOV 21 2016
Abstract:
Using the Landau-Ginzburg-Devonshire theory, we established the role of the flexoelectric coupling between the gradients of elastic strain and polarization in the stability of spatially modulated phases in ferroics, such as incipient and proper ferroelectrics with commensurate and incommensurate long-range-ordered phases. We included the square of elastic strain gradient in the Landau-Ginzburg-Devonshire functional because this term provides the functional stability for all values of the strain gradient. Analytical expressions for polarization, strain, dielectric susceptibility, and stability threshold were derived for a one-dimensional case. The expressions show that the maximal possible values of the static flexoelectric effect coefficients (upper limits) established by Yudin, Ahluwalia, and Tagantsev without the square of elastic strain gradient and other higher order gradients terms lose their direct meaning. Considering the gradients, the temperature dependent condition for the flexocoupling magnitude exists instead of the upper limits. Also, we established that spatially modulated phases appear and become stable in commensurate ferroelectrics if the flexocoupling constant exceeds a critical value. The critical value depends on the electrostriction and elastic constants, temperature, and gradient coefficients in the Landau-Ginzburg-Devonshire functional. We calculated soft phonon dispersion in commensurate and incommensurate long-range-ordered phases of ferroelectrics with the square of elastic strain gradient, static, and dynamic flexocoupling. It appeared that the dispersion of the optical mode is slightly sensitive to the flexocoupling, and the dispersion of acoustic mode strongly depends on the coupling magnitude. Obtained results demonstrate that nontrivial differences in the dispersion of optical and acoustic modes occur with the change of flexocoupling constant. Therefore, experimental determination of soft phonon dispersion might be very informative to study the influence of strain gradients and flexocoupling on the spatially modulated phase in ferroelectrics with commensurate and incommensurate long-range order.
Title:
MAGNDATA: towards a database of magnetic structures. I. The commensurate case
Authors:
Gallego, SV; Perez-Mato, JM; Elcoro, L; Tasci, ES; Hanson, RM; Momma, K; Aroyo, MI; Madariaga, G Author Full Names: Gallego, Samuel V.; Manuel Perez-Mato, J.; Elcoro, Luis; Tasci, Emre S.; Hanson, Robert M.; Momma, Koichi; Aroyo, Mois I.; Madariaga, Gotzon
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 1750-1776; 10.1107/S1600576716012863 5 OCT 2016
Abstract:
A free web page under the name MAGNDATA, which provides detailed quantitative information on more than 400 published magnetic structures, has been developed and is available at the Bilbao Crystallographic Server (http://www. cryst.ehu.es). It includes both commensurate and incommensurate structures. This first article is devoted to explaining the information available on commensurate magnetic structures. Each magnetic structure is described using magnetic symmetry, i.e. a magnetic space group (or Shubnikov group). This ensures a robust and unambiguous description of both atomic positions and magnetic moments within a common unique formalism. A non-standard setting of the magnetic space group is often used in order to keep the origin and unit-cell orientation of the paramagnetic phase, but a description in any desired setting is possible. Domain-related equivalent structures can also be down-loaded. For each structure its magnetic point group is given, and the resulting constraints on any macroscopic tensor property of interest can be consulted. Any entry can be retrieved as a magCIF file, a file format under development by the International Union of Crystallography. An online visualization tool using Jmol is available, and the latest versions of VESTA and Jmol support the magCIF format, such that these programs can be used locally for visualization and analysis of any of the entries in the collection. The fact that magnetic structures are often reported without identifying their symmetry and/or with ambiguous information has in many cases forced a reinterpretation and transformation of the published data. Most of the structures in the collection possess a maximal magnetic symmetry within the constraints imposed by the magnetic propagation vector(s). When a lower symmetry is realized, it usually corresponds to an epikernel (isotropy subgroup) of one irreducible representation of the space group of the parent phase. Various examples of the structures present in this collection are discussed.
Title:
Temperature and cooling field dependent exchange coupling in [Cr/Gd](5) multilayers
Authors:
Jiao, ZW; Chen, HJ; Jiang, WD; Wang, JF; Yu, SJ; Hou, YL; Lu, B; Ye, QL Author Full Names: Jiao, Z. W.; Chen, H. J.; Jiang, W. D.; Wang, J. F.; Yu, S. J.; Hou, Y. L.; Lu, B.; Ye, Q. L.
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 213 (9):2531-2536; 10.1002/pssa.201600025 SEP 2016
Abstract:
Exchange coupling has been investigated in the [Cr/Gd](5) multilayers deposited at 25, 200, and 400 degrees C, where the Neel temperature (TN) of antiferromagnetic Cr is slightly higher than the Curie temperature (T-C) of ferromagnetic Gd. It was found that the exchange coupling existed not only at T-C < T < T-N, but also above the temperature (T-N) of antiferromagnetic orderings with incommensurate spin-density wave structures transiting to paramagnetic state. These results can be discussed in terms of the crucial role played by the antiferromagnetic spins of Cr with commensurate spin-density wave structures in the vicinity of the Cr/Gd interfaces. Moreover, the exchange coupling of the multilayers grown at different temperatures exhibited different dependencies on the measuring temperature and the cooling field, respectively. Positive exchange bias was observed in the multilayers grown at 200 and 400 degrees C. The interfacial roughness, grain size, and the antiferromagnetic orderings of Cr may be responsible for the anomalous exchange coupling of the multilayers. In addition, the competition between the exchange coupling at Cr/Gd interfaces and the external field-Cr surface magnetic coupling can explain the appearance of negative or positive exchange bias. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Update: 8-Dec-2016

Title:
Self-assembly of two-dimensional binary quasicrystals: a possible route to a DNA quasicrystal
Authors:
Reinhardt, A; Schreck, JS; Romano, F; Doye, JPK Author Full Names: Reinhardt, Aleks; Schreck, John S.; Romano, Flavio; Doye, Jonathan P. K.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (1):10.1088/0953-8984/29/1/014006 JAN 11 2017
Abstract:
We use Monte Carlo simulations and free-energy techniques to show that binary solutions of penta-and hexavalent two-dimensional patchy particles can form thermodynamically stable quasicrystals even at very narrow patch widths, provided their patch interactions are chosen in an appropriate way. Such patchy particles can be thought of as a coarse-grained representation of DNA multi-arm 'star' motifs, which can be chosen to bond with one another very specifically by tuning the DNA sequences of the protruding arms. We explore several possible design strategies and conclude that DNA star tiles that are designed to interact with one another in a specific but not overly constrained way could potentially be used to construct soft quasicrystals in experiment. We verify that such star tiles can form stable dodecagonal motifs using oxDNA, a realistic coarse-grained model of DNA.
Title:
Electrochemical and kinetic properties of Ti41.5Zr41.5Ni17 quasicrystal and LiH composite materials
Authors:
Zhai, XJ; Wang, QS; Luo, TH; Zhao, Z; DongyanLiu; Xing, C; Shen, XD; Liu, WQ; LiminWang Author Full Names: Zhai, Xiaojie; Wang, Qingshuang; Luo, Tianhao; Zhao, Zhen; DongyanLiu; Xing, Cheng; Shen, Xiande; Liu, Wanqiang; LiminWang
Source:
MATERIALS RESEARCH BULLETIN, 85 196-201; 10.1016/j.materresbull.2016.09.021 JAN 2017
Abstract:
We report the effect of LiH on the discharge performance of electrodes which are consist of Ti41.5Zr41.5Ni17 quasicrystal in this paper. The Ti41.5Zr41.5Ni17 alloy ribbons are prepared by arc-melting and melt spinning technique subsequently. The final product of Ti41.5Zr41.5Ni17 and LiH composite materials is produced by mechanical alloying (MA) for 20 min, and it is investigated by a three-electrode cell at room temperature. The maximum discharge capacity can achieve 146.6 mAh/g around for Ti41.5Zr41.5Ni17 and LiH composite materials electrode at the first discharge process, which is higher than 96.5 mAh/g of Ti41.5Zr41.5Ni17 quasicrystal at the third discharge process. High-rate dischargeability and cycling stability are improved by adding LiH, which may attribute to the reversible reaction of LiH that enhances the electrochemical reaction activity in the process of electrochemical reaction. The discharge process is also characterized by electrochemical impedance spectroscopy. (C) 2016 Elsevier Ltd. All rights reserved.
Title:
Polarization curling and flux closures in multiferroic tunnel junctions
Authors:
Peters, JJP; Apachitei, G; Beanland, R; Alexe, M; Sanchez, AM Author Full Names: Peters, Jonathan J. P.; Apachitei, Geanina; Beanland, Richard; Alexe, Marin; Sanchez, Ana M.
Source:
NATURE COMMUNICATIONS, 7 10.1038/ncomms13484 NOV 16 2016
Abstract:
Formation of domain walls in ferroelectrics is not energetically favourable in low-dimensional systems. Instead, vortex-type structures are formed that are driven by depolarization fields occurring in such systems. Consequently, polarization vortices have only been experimentally found in systems in which these fields are deliberately maximized, that is, in films between insulating layers. As such configurations are devoid of screening charges provided by metal electrodes, commonly used in electronic devices, it is wise to investigate if curling polarization structures are innate to ferroelectricity or induced by the absence of electrodes. Here we show that in unpoled Co/PbTiO3/(La, Sr)MnO3 ferroelectric tunnel junctions, the polarization in active PbTiO3 layers 9 unit cells thick forms Kittel-like domains, while at 6 unit cells there is a complex flux-closure curling behaviour resembling an incommensurate phase. Reducing the thickness to 3 unit cells, there is an almost complete loss of switchable polarization associated with an internal gradient.
Title:
Semiclassical ground-state phase diagram and multi-Q phase of a spin-orbit-coupled model on triangular lattice
Authors:
Liu, CL; Yu, R; Wang, XQ Author Full Names: Liu, Changle; Yu, Rong; Wang, Xiaoqun
Source:
PHYSICAL REVIEW B, 94 (17):10.1103/PhysRevB.94.174424 NOV 15 2016
Abstract:
Motivated by recent experiments on the frustrated quantum magnetic compound YbMgGaO4, we study an effective spin model on triangular lattice taking into account the effects of the spin-orbit coupling. We determine the classical ground-state phase diagram of this model, which includes a 120 degrees Neel and two collinear antiferromagnetic phases. In the vicinity of the phase boundary between the Neel and collinear phases, we identify three intermediate noncollinear antiferromagnetic phases. In each of them the magnetic moments are ordered at multiple incommensurate wave vector Q values. We further study the effects of quantum fluctuations in this model via a linear spin-wave theory. We find that the spin excitation gap of the noncollinear multi-Q antiferromagnetic states is vanishingly small. We also find that multi-Q states are most fragile against quantum fluctuations, and hence most unstable toward spin liquid phases.
Title:
Effect of cooling rate and Mg addition on the structural evaluation of rapidly solidified Al-20wt%Cu-12wt%Fe alloy
Authors:
Karakose, E; Colak, H Author Full Names: Karakose, Ercan; Colak, Hakan
Source:
MATERIALS CHARACTERIZATION, 121 68-75; 10.1016/j.matchar.2016.09.030 NOV 2016
Abstract:
The present work examines the effect of Mg contents and cooling rate on the morphology and mechanical properties of Al20Cu12Fe quasicrystalline alloy. The microstructure of the alloys was analyzed by scanning electron microscopy and the phase composition was identified by X-ray diffractometry. The melting characteristics were studied by differential thermal analysis under an Ar atmosphere. The mechanical features of the melt-spun and conventionally solidified alloys were tested by tensile-strength test and Vickers micro-hardness test. It was found that the final microstructure of the Al20Cu12Fe samples mainly depends on the cooling rate and Mg contents, which suggests that different cooling rates and Mg contents produce different microstructures and properties. The average grain sizes of the melt spun samples were about 100-300 nm at 35 m/s. The nanosize, dispersed, different shaped quasicrystal particles possessed a remarkable effect to the mechanical characteristics of the rapidly solidified ribbons. The microhardness values of the melt spun samples were approximately 18% higher than those of the conventionally counterparts. (C) 2016 Elsevier Inc. All rights reserved.
Title:
Magnetic structure and effect of magnetic field on its domain structure in magnetoelectric Ba1.3Sr0.7CoZnFe11AlO22
Authors:
Ueda, H; Tanaka, Y; Nakajima, H; Mori, S; Ohta, K; Haruki, K; Hirose, S; Wakabayashi, Y; Kimura, T Author Full Names: Ueda, H.; Tanaka, Y.; Nakajima, H.; Mori, S.; Ohta, K.; Haruki, K.; Hirose, S.; Wakabayashi, Y.; Kimura, T.
Source:
APPLIED PHYSICS LETTERS, 109 (18):10.1063/1.4966623 OCT 31 2016
Abstract:
The magnetic structure and the effect of a magnetic field on its domain structure were investigated in a magnetoelectric Y-type hexaferrite, Ba1.3Sr0.7CoZnFe11AlO22, by means of mapping with a micro-focused and circularly polarized X-ray beam in the resonant X-ray diffraction. It was revealed that this hexaferrite exhibits a magnetic order characterized by two distinct antiferromagnetic components: incommensurate helical and commensurate collinear ones, which can be explained as the development of the so-called alternating longitudinal conical structure. A multidomain state due to the handedness of the helical component, i.e., spin-chirality, is transformed into nearly a mono-domain one by using only a magnetic field. Furthermore, the sign of the spin-chirality in the mono-domain state is reversed by reversing the sign of a magnetic field. These results demonstrate that the spin-chirality in this hexaferrite can be manipulated by a magnetic field alone at room temperature. Published by AIP Publishing.
Title:
Structure and Electrical Conductivity of Ag-Doped TiZrNi Quasicrystals
Authors:
Lee, SH; Park, T; Yi, W; Kim, J Author Full Names: Lee, Sang-Hwa; Park, Taehee; Yi, Whikun; Kim, Jaeyong
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 16 (10):10532-10534; 10.1166/jnn.2016.13189 OCT 2016
Abstract:
To investigate the structure and electrical conductivity of Ag-doped TiZrNi quasicrystals, alloys of (Ti53Zr27Ni20)(100) Ag-x(x) (where, x = 0, 4 and 8) were arc-melted and rapidly quenched in an Ar atmosphere. After optimum quenching, the results of the X-ray diffraction (XRD) measurements revealed that the samples have a pure quasicrystal structure. The quasicrystal structure remained to the maximum 8 at.% of Ag without a significant change in the quasi-lattice constant value, 5.12 angstrom. The specific electrical resistance values of the quasicrystals increased from 4.21 to 5.47x10(-4) Omega. cm with increasing Ag contents from 0 to 8 at.% whereas the coherence lengths decreased from 119 to 93 angstrom accordingly. It is interesting to note that the reduction in the electrical conductivity with the increase in Ag contents is mainly due to the structural incoherence factor, not the atomic conductivity of Ag.
Title:
Direct observation of incommensurate structure in Mo3Si
Authors:
Gulec, A; Yu, XX; Taylor, M; Perepezko, JH; Marks, L Author Full Names: Gulec, Ahmet; Yu, Xiaoxiang; Taylor, Matthew; Perepezko, John H.; Marks, Laurence
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 72 660-666; 10.1107/S2053273316012286 6 OCT 2016
Abstract:
Z-contrast imaging, electron diffraction, atom-probe tomography (APT) and density functional theory calculations were used to study the crystal structure of the Mo3Si phase which was previously reported to have an A15 crystal structure. The results showed that Mo3Si has an incommensurate crystal structure with a non-cubic unit cell. The small off-stoichiometry in composition of the sample which was revealed by APT and atomic resolution Z-contrast imaging suggested that site substitution caused the development of split atomic positions, disorder and vacancies.
Title:
Structure determination of modulated structures by powder X-ray diffraction and electron diffraction
Authors:
Zhou, ZY; Palatinus, L; Sun, JL Author Full Names: Zhou, Zhengyang; Palatinus, Lukas; Sun, Junliang
Source:
INORGANIC CHEMISTRY FRONTIERS, 3 (11):1351-1362; 10.1039/c6qi00219f 2016
Abstract:
Since the first discovery and description of materials, whose structures are not periodic, enormous efforts have been made in studying these aperiodic structures. With these efforts including the development of superspace group theory and structure solution algorithms, numerous incommensurately modulated structures which represent the vast majority of known aperiodic structures have been determined with single crystal X-ray diffraction data. However, the determination of modulated structures remains very difficult for polycrystalline materials. Powder X-ray diffraction and electron microscopy techniques yield remarkable information for polycrystalline materials. By combining these two methods, modulated structures of polycrystalline materials that impede solution by conventional methods can be determined. The power of these methods is illustrated with the examples of the determination of modulated structures of polycrystalline materials.

Update: 23-Nov-2016

Title:
Crystallographic Features and State Stability of the Decagonal Quasicrystal in the Al-Co-Cu Alloy System
Authors:
Nakayama, K; Mizutani, A; Koyama, Y Author Full Names: Nakayama, Kei; Mizutani, Akito; Koyama, Yasumasa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (11):10.7566/JPSJ.85.114602 NOV 15 2016
Abstract:
In the Al-Co-Cu alloy system, both the decagonal quasicrystal with the space group of P (10) over bar m2 and its approximant Al13Co4 phase with monoclinic Cm symmetry are present around 20 at. % Co-10 at. % Cu. In this study, we examined the crystallographic features of prepared Al-(30 - x) at. % Co-x at. % Cu samples mainly by transmission electron microscopy in order to make clear the crystallographic relation between the decagonal quasicrystal and the monoclinic Al13Co4 structure. The results revealed a coexistence state consisting of decagonal quasicrystal and approximant Al13Co4 regions in Al-20 at. % Co-10 at. % Cu alloy samples. With the help of the coexistence state, the orientation relationship was established between the monoclinic Al13Co4 structure and the decagonal quasicrystal. In the determined relationship, the crystallographic axis in the quasicrystal was found to be parallel to the normal direction of the (010) m plane in the Al13Co4 structure, where the subscript m denotes the monoclinic system. Based on data obtained experimentally, the state stability of the decagonal quasicrystal was also examined in terms of the Hume-Rothery (HR) mechanism on the basis of the nearly-free-electron approximation. It was found that a model based on the HR mechanism could explain the crystallographic features such as electron diffraction patterns and atomic arrangements found in the decagonal quasicrystal. In other words, the HR mechanism is most likely appropriate for the stability of the decagonal quasicrystal in the Al-Co-Cu alloy system.
Title:
Prediction of entropy stabilized incommensurate phases in the system MoS2-MoTe2
Authors:
Burton, BP; Singh, AK Author Full Names: Burton, B. P.; Singh, A. K.
Source:
JOURNAL OF APPLIED PHYSICS, 120 (15):10.1063/1.4964868 OCT 21 2016
Abstract:
A first principles phase diagram calculation, that included van der Waals interactions, was performed for the 3D bulk system (1 X).MoS2 (X) . MoTe2. Surprisingly, the predicted phase diagram has at least two ordered phases, at X approximate to 0: 46, even though all calculated formation energies are positive; in a ground-state analysis that examined all configurations with 16 or fewer anion sites. The lower-temperature I-phase is predicted to transform to a higher-temperature I'-phase at T approximate to 500 K, and I0 disorders at T approximate to 730 K. Both these transitions are predicted to be first-order, and there are broad two-phase fields on both sides of the ordered regions. Both the I-and I'-phases are predicted to be incommensurate, i. e., aperiodic: I-phase in three dimensions; and I'-phase in two dimensions.
Title:
Structural transformations in highly oriented seven modulated martensite Ni-Mn-Ga thin films on an Al2O3 (11(2)over-bar0) substrate
Authors:
Sharma, A; Mohan, S; Suwas, S Author Full Names: Sharma, Amit; Mohan, Sangeneni; Suwas, Satyam
Source:
JOURNAL OF MATERIALS RESEARCH, 31 (19):3016-3026; 10.1557/jmr.2016.317 OCT 2016
Abstract:
Highly oriented Ni-Mn-Ga thin film with multiple variants and room temperature orthorhombic martensite structure were prepared on a single crystalline Al2O3 (11 (2) over bar0) substrate by DC magnetron sputtering. X-ray diffraction and rocking curve measurements reveal the film as (202)(7M) oriented with an excellent crystal quality ( = 1.8 degrees). Spot-like pole figures indicate that the Ni-Mn-Ga film grows with a strong in-plane preferred orientation. An in-depth analysis of the measured pole figure reveals the presence of a retained austenite phase in the film. Two phase transformations, M-S approximate to 345 K and T-C approximate to 385 K, are observed and are attributed to first order structural transformation from cubic to orthorhombic, and second order phase transformation from ferromagnetic to paramagnetic, respectively. In situ high temperature x-ray diffraction measurements provide a clear indication of a thermally-induced martensite austenite reversible structural phase transformation in the film. The presence of martensite plates with seven modulated orthorhombic structure and adaptive nano-twins are some of the important microscopic features observed in the film with transmission electron microscopy investigations.

Update: 16-Nov-2016

Title:
A guide to lifting aperiodic structures
Authors:
Baake, M; Ecija, D; Grimm, U Author Full Names: Baake, Michael; Ecija, David; Grimm, Uwe
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (9):507-515; 10.1515/zkri-2016-1982 SEP 2016
Abstract:
The embedding of a given point set with non-crystallographic symmetry into higher-dimensional space is reviewed, with special emphasis on the Minkowski embedding known from number theory. This is a natural choice that does not require an a priori construction of a lattice in relation to a given symmetry group. Instead, some elementary properties of the point set in physical space are used, and explicit methods are described. This approach works particularly well for the standard symmetries encountered in the practical study of quasicrystalline phases. We also demonstrate this with a recent experimental example, taken from a sample with square-triangle tiling structure and (approximate) 12-fold symmetry.
Title:
Effect of Pt addition to Ag-Au bimetallic nanoclusters: A molecular dynamics study of Ag-Au-Pt ternary system
Authors:
Akbarzadeh, H; Shamkhali, AN; Abbaspour, M; Salemi, S; Hajizadeh, Z Author Full Names: Akbarzadeh, Hamed; Shamkhali, Amir Nasser; Abbaspour, Mohsen; Salemi, Sirous; Hajizadeh, Zohreh
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 692 647-657; 10.1016/j.jallcom.2016.09.066 JAN 25 2017
Abstract:
In this work addition of Pt atoms to Ag0.5Au0.5 nanoclusters and formation of Ag0.5-chi Au0.5-chi Pt2 chi (with chi - 0.1, 0.17, 0.2, 0.25, 0.3, and 0.4) and total number of atoms equal to 1415 and 2057 ternary nanoclusters is studied by molecular dynamics simulation. The results indicated that at low concentrations of Pt, nanoclusters exhibit a local-ordered structure in such a way that (Pt-Ag-n-Au-2n) cores are surrounded by extra Ag atoms. By increase of Pt concentration total order of the nanocluster also increases. For nanoclusters with 0.0 < chi(Pt) < 0.4 total order of the system is decreased due to lower concentration of Ag-Pt and Au-Pt interactions. For chi(Pt) - 0.4 system, total order of the nanocluster again increases considerably which represents a Pt-rich nanocluster with some Ag and Au impurity. Also, all nanoclusters with chi(Pt) > 0.0 exhibit an icosahedral-fcc phase transition before melting and temperature of this phase transition is decreased by increase of Pt concentration. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Controlling Magnetic Ordering in Ca1-xEuxCo2As2 by Chemical Compression
Authors:
Tan, XY; Yaroslavtsev, AA; Cao, HB; Geondzhian, AY; Menushenkov, AP; Chernikov, RV; Nataf, L; Garlea, VO; Shatruk, M Author Full Names: Tan, Xiaoyan; Yaroslavtsev, Alexander A.; Cao, Huibo; Geondzhian, Andrey Y.; Menushenkov, Alexey P.; Chernikov, Roman V.; Nataf, Lucie; Garlea, V. Ovidiu; Shatruk, Michael
Source:
CHEMISTRY OF MATERIALS, 28 (20):7459-7469; 10.1021/acs.chemmater.6b03184 OCT 25 2016
Abstract:
To investigate the interplay between electronic structure and itinerant magnetism, Ca1-xEuxCo2As2 solid solutions (x = 0, 0.1, 0.3, 0.4, 0.5, 0.6, 0.65, 0.7, 0.9, 1.0) were prepared by reactions between constituent elements in molten Bi. All of the samples crystallize in the ThCr2Si2 structure type. The crystal structure refinement revealed the formation of Co vacancies, the concentration of which decreases as the Eu content increases. The Eu site exhibits mixed valence in all samples. X-ray absorption near-edge structure spectroscopy revealed that the average Eu oxidation state decreases from +2.17 at 0 < x <= 0.6 to +2.14 at x >= 0.65. The same borderline behavior is observed in magnetic properties. The substitution of Eu for Ca causes the transition from the antiferromagnetic (AFM) ordering of Co moments in CaCo2As2 to ferromagnetic (FM) ordering of Co moments in Ca1-xEuxCo2As2 with 0.1 <= x <= 0.6. At higher Eu content, AFM ordering of Eu moments is observed, whereas the Co sublattice exhibits only paramagnetic behavior. Single-crystal neutron diffraction studies revealed that both Co and Eu sublattices order FM in Ca0.5Eu0.5Co2As2 with the magnetic moments aligned along the tetragonal c axis. In the AFM phases with x >= 0.65, only Eu moments are ordered in a helical spin structure defined by an incommensurate propagation vector k = [00q], with the moment lying in the ab plane. The changes in magnetic behavior are well-justified by the analysis of the electronic density of states and crystal orbital Hamilton population.
Title:
Role of Structure- and Defect Chemistry in High-Performance Thermoelectric Bismuth Strontium Cobalt Oxides
Authors:
Baran, JD; Kepaptsoglou, D; Molinari, M; Kulwongwit, N; Azough, F; Freer, R; Ramasse, QM; Parker, SC Author Full Names: Baran, Jakub D.; Kepaptsoglou, Demie; Molinari, Marco; Kulwongwit, Nuth; Azough, Feridoon; Freer, Robert; Ramasse, Quentin M.; Parker, Stephen C.
Source:
CHEMISTRY OF MATERIALS, 28 (20):7470-7478; 10.1021/acs.chemmater.6b03200 OCT 25 2016
Abstract:
[Bi0.87SrO2](2)[CoO2](1.82) (BSCO) is one of the best p-type thermoelectric oxides but its structural and electronic properties are still poorly understood. BSCO is a misfit-layered compound consisting of an incommensurate stacking of hexagonal CoO2 and double rock-salt BiSrO2 layers. Here we combine experimental and computational approaches to investigate its crystallographic and electronic structure as well as thermoelectric transport properties. Considering different approximations for the subsystems stacking, we present a structural model that agrees well with both bulk and atomic-scale experimental data. This model, which suggests a level of Bi deficiency in the rock-salt layers, is then used to discuss the material's electronic, magnetic, and transport properties. We show that Bi deficiency leads to a band gap opening and increases p-type electronic conductivity due to the formation of Co4+ species that serve as itinerant holes within the predominantly Co3+ framework of the CoO2 layer. We validate these predictions using electron energy loss spectroscopy in the scanning transmission electron microscope. The relationship between the hole-doping mechanism and the changes of the local structure (in particular the level of Bi deficiency) is evaluated. The reliability of the simulations is supported by the calculated temperature dependence of the Seebeck coefficient, in good agreement with experimental measurements.
Title:
Weak coupling of pseudoacoustic phonons and magnon dynamics in the incommensurate spin-ladder compound Sr14Cu24O41
Authors:
Chen, X; Bansal, D; Sullivan, S; Abernathy, DL; Aczel, AA; Zhou, JS; Delaire, O; Shi, L Author Full Names: Chen, Xi; Bansal, Dipanshu; Sullivan, Sean; Abernathy, Douglas L.; Aczel, Adam A.; Zhou, Jianshi; Delaire, Olivier; Shi, Li
Source:
PHYSICAL REVIEW B, 94 (13):10.1103/PhysRevB.94.134309 OCT 21 2016
Abstract:
Intriguing lattice dynamics have been predicted for aperiodic crystals that contain incommensurate substructures. Here we report inelastic neutron scattering measurements of phonon and magnon dispersions in Sr14Cu24O41, which contains incommensurate one-dimensional (1D) chain and two-dimensional (2D) ladder substructures. Two distinct pseudoacoustic phonon modes, corresponding to the sliding motion of one sublattice against the other, are observed for atomic motions polarized along the incommensurate axis. In the long wavelength limit, it is found that the sliding mode shows a remarkably small energy gap of 1.7-1.9 meV, indicating very weak interactions between the two incommensurate sublattices. The measurements also reveal a gapped and steep linear magnon dispersion of the ladder sublattice. The high group velocity of this magnon branch and weak coupling with acoustic and pseudoacoustic phonons can explain the large magnon thermal conductivity in Sr14Cu24O41 crystals. In addition, the magnon specific heat is determined from the measured total specific heat and phonon density of states and exhibits a Schottky anomaly due to gapped magnon modes of the spin chains. These findings offer new insights into the phonon and magnon dynamics and thermal transport properties of incommensurate magnetic crystals that contain low-dimensional substructures.
Title:
Helicity-dependent photocurrent in a Bi2Se3 thin film probed by terahertz emission spectroscopy
Authors:
Hamh, SY; Park, SH; Jerng, SK; Jeon, JH; Chun, SH; Lee, JS Author Full Names: Hamh, Sun Young; Park, Soon-Hee; Jerng, Sahng-Kyoon; Jeon, Jae Ho; Chun, Seung-Hyun; Lee, Jong Seok
Source:
PHYSICAL REVIEW B, 94 (16):10.1103/PhysRevB.94.161405 OCT 20 2016
Abstract:
We investigate photocarrier dynamics in a Bi2Se3 thin film via terahertz (THz) emission spectroscopy. We report amplitude and phase modulations of the emitted THz wave under the variations in a polarization of an input laser beam and sample azimuth. Photon-helicity-dependent responses are manifested in both time and frequency domains, and azimuth dependence of such circular anisotropy exhibits a clear threefold periodicity. We analyze these results based on the symmetry of the bulk and the surface of Bi2Se3 and demonstrate that the observed helicity-dependent photocurrent originates from the circular photon drag effect, namely, linear and angular momentum transfers from photons to photocarriers.
Title:
Crystallographic computing system Jana2006: solution and refinement of twinned structures
Authors:
Petricek, V; Dusek, M; Plasil, J Author Full Names: Petricek, Vaclav; Dusek, Michal; Plasil, Jakub
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (10):583-599; SI 10.1515/zkri-2016-1956 OCT 2016
Abstract:
Twinning is a phenomenon complicating structure analysis of single crystals of standard as well as modulated structures. Jana2006 as a software for advanced structure analysis contains tools for recognition and refinement of twins including most complicated cases of modulated and magnetic structures. In order to efficiently use the tools of Jana2006 related to twinning, we explain the basic terminology and the underlying theory, especially the symmetry of the diffraction patterns affected by twinning. We present typical diffraction patterns of twins and show how twinning can be recognized or detected by various tools and described with twinning matrices. Data processing of twins and ways of how they can be imported to Jana2006 are also discussed. Two examples demonstrate the solution of typical twins: twinning by metric merohedry and twinning by reticular merohedry, followed by the third example demonstrating twinning in a commensurately *modulated structure*. The relationship between the dimensionality of the structure and twinning is discussed, too.

Update: 10-Nov-2016

Title:
Competing magnetic ground states and their coupling to the crystal lattice in CuFe2Ge2
Authors:
May, AF; Calder, S; Parker, DS; Sales, BC; McGuire, MA Author Full Names: May, Andrew F.; Calder, Stuart; Parker, David S.; Sales, Brian C.; McGuire, Michael A.
Source:
SCIENTIFIC REPORTS, 6 10.1038/srep35325 OCT 14 2016
Abstract:
Identifying and characterizing systems with coupled and competing interactions is central to the development of physical models that can accurately describe and predict emergent behavior in condensed matter systems. This work demonstrates that the metallic compound CuFe2Ge2 has competing magnetic ground states, which are shown to be strongly coupled to the lattice and easily manipulated using temperature and applied magnetic fields. Temperature-dependent magnetization M measurements reveal a ferromagnetic-like onset at 228 (1) K and a broad maximum in M near 180 K. Powder neutron diffraction confirms antiferromagnetic ordering below T-N approximate to 175 K, and an incommensurate spin density wave is observed below approximate to 125 K. Coupled with the small refined moments (0.5-1 mu B/Fe), this provides a picture of itinerant magnetism in CuFe2Ge2. The neutron diffraction data also reveal a coexistence of two magnetic phases that further highlights the near-degeneracy of various magnetic states. These results demonstrate that the ground state in CuFe2Ge2 can be easily manipulated by external forces, making it of particular interest for doping, pressure, and further theoretical studies.
Title:
Charge density wave modulation and gap measurements in CeTe3
Authors:
Ralevic, U; Lazarevic, N; Baum, A; Eiter, HM; Hackl, R; Giraldo-Gallo, P; Fisher, IR; Petrovic, C; Gajic, R; Popovic, ZV Author Full Names: Ralevic, U.; Lazarevic, N.; Baum, A.; Eiter, H. -M.; Hackl, R.; Giraldo-Gallo, P.; Fisher, I. R.; Petrovic, C.; Gajic, R.; Popovic, Z. V.
Source:
PHYSICAL REVIEW B, 94 (16):10.1103/PhysRevB.94.165132 OCT 14 2016
Abstract:
We present a study of charge density wave (CDW) ordering in CeTe3 at room temperature using a scanning tunneling microscope and Raman spectroscopy. Two characteristic CDW ordering wave vectors obtained from the Fourier analysis are assessed to be |c* - q| = 4.19 nm(-1) and |q| = 10.26 nm(-1) where |c*| = 2 Pi/c is the reciprocal lattice vector. The scanning tunneling spectroscopy measurements, along with inelastic light ( Raman) scattering measurements, show a CDWgap Delta(max) of approximately 0.37 eV. In addition to the CDW modulation, we observe an organization of the Te sheet atoms in an array of alternating V- and N-shaped groups along the CDW modulation, as predicted in the literature.
Title:
Remarkable Stability of Charge Density Wave Order in La1.875Ba0.125CuO4
Authors:
Chen, XM; Thampy, V; Mazzoli, C; Barbour, AM; Miao, H; Gu, GD; Cao, Y; Tranquada, JM; Dean, MPM; Wilkins, SB Author Full Names: Chen, X. M.; Thampy, V.; Mazzoli, C.; Barbour, A. M.; Miao, H.; Gu, G. D.; Cao, Y.; Tranquada, J. M.; Dean, M. P. M.; Wilkins, S. B.
Source:
PHYSICAL REVIEW LETTERS, 117 (16):10.1103/PhysRevLett.117.167001 OCT 11 2016
Abstract:
The occurrence of charge-density-wave (CDW) order in underdoped cuprates is now well established, although the precise nature of the CDW and its relationship with superconductivity is not. Theoretical proposals include contrasting ideas such as that pairing may be driven by CDW fluctuations or that static CDWs may intertwine with a spatially modulated superconducting wave function. We test the dynamics of CDW order in La1.825Ba0.125CuO4 by using x-ray photon correlation spectroscopy at the CDW wave vector, detected resonantly at the Cu L-3 edge. We find that the CDW domains are strikingly static, with no evidence of significant fluctuations up to 2 (3)/(4) h. We discuss the implications of these results for some of the competing theories.
Title:
Structure of the Al13Co4(100) surface: Combination of surface x-ray diffraction and ab initio calculations
Authors:
Gaudry, E; Chatelier, C; McGuirk, GM; Loli, LNS; de Weerd, MC; Ledieu, J; Fournee, V; Felici, R; Drnec, J; Beutier, G; de Boissieu, M Author Full Names: Gaudry, E.; Chatelier, C.; McGuirk, G. M.; Serkovic Loli, L. N.; de Weerd, M. -C.; Ledieu, J.; Fournee, V.; Felici, R.; Drnec, J.; Beutier, G.; de Boissieu, M.
Source:
PHYSICAL REVIEW B, 94 (16):10.1103/PhysRevB.94.165406 OCT 10 2016
Abstract:
The structure of the quasicrystalline approximant Al13Co4(100) has been determined by surface x-ray diffraction (SXRD) and complementary density-functional-theory (DFT) calculations. Thanks to the use of a two-dimensional pixel detector, which speeds up the data acquisition enormously, an exceptionally large set of experimental data, consisting of 124 crystal truncation rods, has been collected and used to refine this complex structure of large unit cell and low symmetry. Various models were considered for the SXRD analysis. The best fit is consistent with a surface termination at the puckered type of planes but with a depletion of the protruding Co atoms. The surface energy of the determined surface model was calculated using DFT, and it takes a rather low value of 1.09 J/m(2). The results for the atomic relaxation of surface planes found by SXRD or DFT were in excellent agreement. This work opens up additional perspectives for the comprehension of related quasicrystalline surfaces.
Title:
Communication between cation environments in aluminosilicate frameworks: incommensurately modulated crystal structure of an e-plagioclase
Authors:
Fredrickson, RT; Fredrickson, DC Author Full Names: Fredrickson, Rie T.; Fredrickson, Daniel C.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 787-801; 10.1107/S2052520616010350 5 OCT 2016
Abstract:
Despite being one of the most common minerals in the earth's crust the crystal structure of intermediate e-plagioclase remains only partially understood, due in a large part to its complex diffraction patterns including satellite reflections. In this article we present a detailed analysis of the structure of e-plagioclase (An44) using single-crystal X-ray diffraction measured at ambient and low temperature (T = 100 K), in which the full modulated structure is successfully refined. As in earlier studies, the diffraction pattern exhibits strong main a-reflections and weak e-satellite reflections. The average structure could be solved in terms of an albite-like basic cell with the triclinic centrosymmetric and non-centrosymmetric space groups P (1) over bar and P1 (treated in its C (1) over bar and C1 setting, respectively, to follow conventions in the literature), while the incommensurately modulated structure was modeled in (3 + 1) D superspace, employing both the centro-and noncentrosymmetric superspace groups X (1) over bar(alpha beta gamma)0 and X1(alpha beta gamma) 0, where X refers to a special (3 + 1) D lattice centering with centering vectors (0 0 1/2 1/2), (1/2 1/2 0 1/2), and (1/2 1/2 1/2 0). Individual positional and occupational modulations for Ca/Na were refined with deeper insights being revealed in the non-centrosymmetric structure model. Through the structural details emerging from this model, the origin of the modulation can be traced to the communication between Ca/Na site positions through their bridging aluminosilicate (Si/Al) O-4 tetrahedra.
Title:
Charge and spin coupling in magnetoresistive oxygen-vacancy strontium ferrate SrFeO3-delta
Authors:
Lee, SH; Frawley, TW; Yao, CH; Lai, YC; Du, CH; Hatton, PD; Wang, MJ; Chou, FC; Huang, DJ Author Full Names: Lee, S. H.; Frawley, T. W.; Yao, C. H.; Lai, Y. C.; Du, Chao-Hung; Hatton, P. D.; Wang, M. J.; Chou, F. C.; Huang, D. J.
Source:
NEW JOURNAL OF PHYSICS, 18 10.1088/1367-2630/18/9/093033 SEP 20 2016
Abstract:
Using magnetization, conductivity and x-ray scattering measurements, we demonstrate that the giant magnetoresistance of the oxygen-deficient ferrite SrFeO2.875+0.02 is a consequence of the coupling between the charge and spin order parameters and the tetragonal to monoclinic structural distortion. Upon cooling the sample at T similar or equal to 120 K we find a shoulder in both field-cool and zero field cool magnetization data and the simultaneous appearance of incommensurate structural satellites observed using x-ray diffraction. These satellites are shown to be due to incommensurate charge ordering with the high temperature delocalized Fe3.5+ ions becoming localized with a charge disproportion forming an incommensurate charge-ordered phase. Strong resonant enhancement of these satellites at the Fe L-III absorption edge confirms that this charge ordering is occurring at the Fe(2) sites. Further cooling increases the charge order correlation until T similar or equal to 62Kwhere there is a full structural transition from the tetragonal phase to a mononclinic phase. This causes a jump in the charge order wavevector from an incommensurate value of 0.610 to a commensurate ground state position of 5/8. This first-order structural transition displays considerable hysteresis as well as dramatic reductions in the magnetization, resistivity and magnetoresistance. The transition also causes an antiferromagnetic spin-ordering with a doubled unit cell along the c-axis. Well as observing new commensurate magnetic reflections at the Fe-III edge we also observed resonant enhancement at the oxygen K-edge showing considerable hybridization between the Fe 3d and oxygen 2p states at low temperatures. Our results show that the formation of a magnetic long-rage ordered ground state drives the charge ordering from an incommensurate ordering to a commensurate ground state. This is evidence of a strong coupling between the magnetic and charge order parameters which is the basis for the unusual magnetoresistive effects observed at the transition.

Update: 3-Nov-2016

Title:
Ab-initio, Mossbauer spectroscopy, and magnetic study of the approximant Al72Ni9Fe19 to a decagonal Al-Ni-Fe quasicrystal
Authors:
Nejadsattari, F; Stadnik, ZM; Przewoznik, J; Grushko, B Author Full Names: Nejadsattari, Farshad; Stadnik, Zbigniew M.; Przewoznik, Janusz; Grushko, Benjamin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 689 726-732; 10.1016/j.jallcom.2016.08.021 DEC 25 2016
Abstract:
We report the results of ab-initio electronic structure and electric field gradient calculations and of X-ray diffraction, Fe-57 Mossbauer spectroscopy, and magnetic studies of the approximant Al72Ni9Fe19 to a decagonal Al-Ni-Fe quasicrystal. The approximant crystallizes in the hexagonal space group P63/mmc with the lattice parameters a = 7.6989(2) A ($) over circle and c = 7.6724(2) A ($) over circle. A pseudogap in the density of states, centered at similar to 0.30 eV above the Fermi level and with a width of similar to 0.35 eV, is found. Evidence for the covalent nature of the chemical bonding and good metallicity of Al72Ni9Fe19 is provided. The Mossbauer spectra and a 1/T-like dependence of the magnetic susceptibility indicate that Al72Ni9Fe19 is a paramagnet down to 2.0 K. The shape of the Mossbauer spectra is accounted for by a superposition of two quadrupole doublets corresponding to Fe atoms located at two inequivalent crystallographic sites. A sudden change of the quadrupole splittings of the two doublets at similar to 200 K indicates a possible structural phase transition. Excellent agreement between the calculated and measured quadrupole splittings is observed. The Debye temperature of Al72Ni9Fe19 is found to be 431 (3) K. (C) 2016 Elsevier B. V. All rights reserved.
Title:
High temperature phases with wurtzite-derived structure in Zn2LiGaO4-ZnO alloy system
Authors:
Kita, M; Fukada, T; Yamaguchi, S; Omata, T Author Full Names: Kita, Masao; Fukada, Tomoaki; Yamaguchi, Shu; Omata, Takahisa
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 688 69-76; 10.1016/j.jallcom.2016.06.249 A DEC 15 2016
Abstract:
We investigated the structural phase transformations of Zn2LiGaO4, which is a quaternary oxide semiconductor with a wide band gap of 4.0 eV, and its alloys with ZnO by using in-situ high-temperature X-ray diffraction (XRD), room-temperature XRD and selected-area electron diffraction of samples quenched from high temperatures of >873 K. Three types of phases with the wurtzite-derived structure were found in the y(Zn2LiGaO4)(1/4)-(1-y)ZnO alloy system. First is the low-temperature phase, phase I, in which constituent cations are ordered similarly to those in a Cd2AgGaS4-type structure. Phase I has an incommensurate modulation vector of 1.04b* and is stable at <1070 K and compositions of 0.96 <= y <= 1 and is stable at room temperature for y = 0.92. The second phase, phase II, appears at intermediate temperatures of 773-1373 K at 0.96 <= y <= 1, and its incommensurate modulation vector is 1.08b*. *Phase* III, which has no long-range cation ordering but still has short-range cation ordering, is stable for 0.92 <= y < 1 at high temperatures and for 0.2 < y < 0.92 from room temperature to high temperatures. We discuss the driving force of the transformations among the three phases in terms of their crystal structure and the mismatch in thermal expansion between -Zn-O-Zn-O- and -Li-O-Ga-O- linkages. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Anisotropy of the electric transport properties of decagonal Al-Cu-Co(Fe) quasicrystals
Authors:
Shulyatev, DA; Klyueva, MV; Devaradjan, U Author Full Names: Shulyatev, D. A.; Klyueva, M. V.; Devaradjan, U.
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 117 (9):883-888; 10.1134/S0031918X16070152 SEP 2016
Abstract:
The method of growth from a melt solution was used to obtain iron-alloyed (0.08 at %) Al-Cu-Co single crystals with a decagonal symmetry. The temperature dependences of the electrical resistivity in magnetic fields of 0-18 T were measured using samples oriented in the periodic direction (rho (p) (T)) and in the quasi-periodic plane (rho (q) (T)). A strong anisotropy of the resistivity was observed; the rho (p) (T) curve is linear, whereas the rho (q) (T) curve is approximated well by a second-order polynomial. A strong anisotropy of the magnetoresistance was also observed; a positive magnetoresistance Delta rho/rho similar to 10(-3) for the current flowing in the quasiperiodic plane; and a weak (close to zero) negative magnetoresistance for the current flowing along the periodic direction.

Update: 27-Oct-2016

Title:
Application of electron backscatter diffraction (EBSD) to quasicrystal-containing microstructures in the Mg-Cd-Yb system
Authors:
Tanaka, R; Ohhashi, S; Fujita, N; Demura, M; Yamamoto, A; Kato, A; Tsai, AP Author Full Names: Tanaka, R.; Ohhashi, S.; Fujita, N.; Demura, M.; Yamamoto, A.; Kato, A.; Tsai, A. P.
Source:
ACTA MATERIALIA, 119 193-202; 10.1016/j.actamat.2016.08.011 OCT 15 2016
Abstract:
We develop a new analysis system for identifying orientation of an icosahedral quasicrystal (iQc) in a SEM installed with an electron backscatter diffraction (EBSD) instrument. The system is successfully applied to determine the orientation of any given iQc grain by reading and assigning the Kikuchi bands obtained with the EBSD. This enables us to analyze relative orientations of iQc and alpha Mg grains in a eutectic structure obtained through a unidirectional solidification process for the Mg-Cd-Yb system. According to EBSD analysis, growth direction of the eutectic structure is shown to be clearly parallel to a two-fold axis of the iQc and {10-10} of alpha Mg, and a unique orientation relationship in iQc and alpha Mg grains is verified in all iQc-alpha Mg coexisting regions. The similarity between primary inter-planar spacings of the iQc and alpha Mg phases is a key factor for stabilizing the interface of two phases and favoring the formation of eutectic structure. This stabilization mechanism is supported by a simple argument on the energetics of a quasiperiodic/periodic lattice interface. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Two-Level Electron Excitations and Distinctive Physical Properties of Al-Cu-Fe Quasicrystals
Authors:
Prekul, A; Shchegolikhina, N Author Full Names: Prekul, Alexandre; Shchegolikhina, Natalya
Source:
CRYSTALS, 6 (9):10.3390/cryst6090119 SEP 2016
Abstract:
This article is not a review in the conventional sense. Rather, it is a monographic study of the implications of detection in Al-Cu-Fe quasicrystals of the electronic heat capacity contributions associated with the two-level electron excitations. Our aim was to reveal correlations between these contributions, on the one hand, and specific features of electron transport, magnetic susceptibility, Hall-effect, tunnelling and optical spectra, on the other hand. It is shown that the full range of these features can be understood in the framework of the unified conceptual scheme based on two-level electron excitations.
Title:
Statistical Approach to Diffraction of Periodic and Non-Periodic Crystals-Review
Authors:
Strzalka, R; Buganski, I; Wolny, J Author Full Names: Strzalka, Radoslaw; Buganski, Ireneusz; Wolny, Janusz
Source:
CRYSTALS, 6 (9):10.3390/cryst6090104 SEP 2016
Abstract:
In this paper, we show the fundamentals of statistical method of structure analysis. Basic concept of a method is the average unit cell, which is a probability distribution of atomic positions with respect to some reference lattices. The distribution carries complete structural information required for structure determination via diffraction experiment regardless of the inner symmetry of diffracting medium. The shape of envelope function that connects all diffraction maxima can be derived as the Fourier transform of a distribution function. Moreover, distributions are sensitive to any disorder introduced to ideal structure-phonons and phasons. The latter are particularly important in case of quasicrystals. The statistical method deals very well with phason flips and may be used to redefine phasonic Debye-Waller correction factor. The statistical approach can be also successfully applied to the peak's profile interpretation. It will be shown that the average unit cell can be equally well applied to a description of Bragg peaks as well as other components of diffraction pattern, namely continuous and singular continuous components. Calculations performed within statistical method are equivalent to the ones from multidimensional analysis. The atomic surface, also called occupation domain, which is the basic concept behind multidimensional models, acquires physical interpretation if compared to average unit cell. The statistical method applied to diffraction analysis is now a complete theory, which deals equally well with periodic and non-periodic crystals, including quasicrystals. The method easily meets also any structural disorder.
Title:
A Review of Transmission Electron Microscopy of Quasicrystals-How Are Atoms Arranged?
Authors:
Li, RT; Li, Z; Dong, ZL; Khor, KA Author Full Names: Li, Ruitao; Li, Zhong; Dong, Zhili; Khor, Khiam Aik
Source:
CRYSTALS, 6 (9):10.3390/cryst6090105 SEP 2016
Abstract:
Quasicrystals (QCs) possess rotational symmetries forbidden in the conventional crystallography and lack translational symmetries. Their atoms are arranged in an ordered but non-periodic way. Transmission electron microscopy (TEM) was the right tool to discover such exotic materials and has always been a main technique in their studies since then. It provides the morphological and crystallographic information and images of real atomic arrangements of QCs. In this review, we summarized the achievements of the study of QCs using TEM, providing intriguing structural details of QCs unveiled by TEM analyses. The main findings on the symmetry, local atomic arrangement and chemical order of QCs are illustrated.
Title:
Elastodynamic Analysis of a Hollow Cylinder with Decagonal Quasicrystal Properties: Meshless Implementation of Local Integral Equations
Authors:
Hosseini, SM; Sladek, J; Sladek, V Author Full Names: Hosseini, Seyed Mahmoud; Sladek, Jan; Sladek, Vladimir
Source:
CRYSTALS, 6 (8):10.3390/cryst6080094 AUG 2016
Abstract:
A meshless approximation and local integral equation (LIE) formulation are proposed for elastodynamic analysis of a hollow cylinder made of quasicrystal materials with decagonal quasicrystal properties. The cylinder is assumed to be under shock loading. Therefore, the general transient elastodynamic problem is considered for coupled phonon and phason displacements and stresses. The equations of motion in the theory of compatible elastodynamics of wave type for phonons and wave-telegraph type for phasons are employed and can be easily modified to the elasto-hydro dynamic equations for quasicrystals (QCs). The angular dependence of the tensor of phonon-phason coupling coefficients handicaps utilization of polar coordinates, when the governing equations would be given by partial differential equations with variable coefficients. Despite the symmetry of the geometrical shape, the local weak formulation and meshless approximation are developed in the Cartesian coordinate system. The response of the cylinder in terms of both phonon and phason stress fields is obtained and studied in detail.
Title:
A ZrNiAl related high-pressure modification of CeRuSn
Authors:
Niehaus, O; Heymann, G; Huppertz, H; Rodewald, UC; Chevalier, B; Matar, SF; Hoffmann, RD; Pottgen, R Author Full Names: Niehaus, Oliver; Heymann, Gunter; Huppertz, Hubert; Rodewald, Ute Ch.; Chevalier, Bernard; Matar, Samir F.; Hoffmann, Rolf-Dieter; Poettgen, Rainer
Source:
DALTON TRANSACTIONS, 45 (36):14216-14229; 10.1039/c6dt02294d 2016
Abstract:
Monoclinic CeRuSn with its own structure type transforms to a high-pressure modification at 11.5 GPa and 1470 K (1000 t press, Walker type module). The structure of the high-pressure phase was refined from X-ray single crystal diffractometer data at room temperature. The HP-CeRuSn subcell structure adopts the ZrNiAl type: P (6) over bar 2m, a = 751.4(3) and c = 394.6(2) pm, wR2 = 0.0787, 310 F-2 values and 15 variables. The Ru2 atoms within the Sn-6 trigonal prisms show a strongly enhanced U-33 parameter. Weak satellite reflections indicate a commensurate modulation: (3 + 1)D superspace group P31m(1/3,1/3,gamma)000, a = 751.4(3) and c = 394.6(2) pm, gamma = -1/3, wR2 = 0.0786, 1584 F-2 values, 32 variables for the main reflections and wR2 = 0.3757 for the satellites of 1st order. A description of this new superstructure variant of the ZrNiAl type is possible in a transformed 3D supercell with the space group R3m and Z = 9. The driving force for formation of the modulation is strengthening of Ru-Sn bonding within the comparatively large Ru@Sn-6 trigonal prisms. Electronic structure calculations point to an almost depleted Ce 4f shell. This is substantiated by temperature-dependent magnetic susceptibility data. Fitting of the data within the inter-configuration fluctuation model (ICF) resulted in cerium valences of 3.41 at 10 K and 3.31 at 350 K. Temperature dependent specific heat data underline the absence of magnetic ordering.

Update: 20-Oct-2016

Title:
Complex magnetic ordering in Tm3Cu4Si4
Authors:
Baran, S; Szytula, A; Kaczorowski, D; Damay, F Author Full Names: Baran, S.; Szytula, A.; Kaczorowski, D.; Damay, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 688 577-584; 10.1016/j.jallcom.2016.07.241 B DEC 15 2016
Abstract:
Tm3Cu4Si4 crystalizes in the orthorhombic Gd3Cu4Ge4-type crystal structure with trivalent Tm atoms occupying 2(d) and 4(e) Wyckoff sites. Neutron diffraction data shows that at 1.7 K the Tm magnetic moments form a commensurate magnetic structure defined by the propagation vectors (k) over right arrow (2d) = [0,1/2,0] and (k) over right arrow (4e) = [1/4,0,1/2] for the 2(d) and 4(e) sites, respectively. With increasing temperature, the magnetic order in the 4(e) sublattice undergoes near 2.5 K an order-order transition into an incommensurate magnetic structure and then disappears at 2.9 K. Similar changes in the magnetic structure occur in the 2(d) sublattice at 3.3 and 3.8 K, respectively. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Al-rich region of Al-Cu-Mn
Authors:
Grushko, B; Mi, SB Author Full Names: Grushko, B.; Mi, S. B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 688 957-963; 10.1016/j.jallcom.2016.07.075 B DEC 15 2016
Abstract:
The Al-Cu-Mn alloy system was studied above 45 at.% Al between 550 and 910 degrees C by scanning electron microscopy, powder X-ray diffraction and differential thermal analysis. A wide ternary region of the so-called beta-phase extending along similar to 50 at.% Al was confirmed. It has a CsCl-type structure with a approximate to 0.292-0.298 nm. The total gamma(1)/gamma(2)-region extends from Al-Mn up to similar to 17 at.% Cu and the high-temperature T-Al3Mn phase (Pnma, a approximate to 1.48, b approximate to 1.24, c approximate to 1.25 nm) extends up to similar to 15 at.% Cu. The so-called R-phase (Bbmm, a approximate to 2.41, b approximate to 1.25, c approximate to 0.76 nm) was found to exist in a compositional region of Al74-80Cu5-12.5Mn12.5-18. The ternary phase earlier reported at Al57.9Cu26.3Mn15.8 was confirmed. It exists below 697 degrees C in a compositional region of Al55-58Cu29-Mn-37(7.5-14). The decagonal D-3-phase was concluded to be stable in a compositional region of Al61.5-68.5Cu19-29.5Mn9-16. Below 631 degrees C an fcc phase (a = 0.5814 nm) was revealed around similar to Al60Cu36.5Mn3.5. Partial isothermal sections at 550, 600, 650, 750, 850 and 910 degrees C were constructed. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Microstructural characteristics and mechanical properties of Mg-Zn-Y alloy containing icosahedral quasicrystals phase treated by pulsed magnetic field
Authors:
Zhang, L; Zhou, W; Hu, PH; Zhou, Q Author Full Names: Zhang, L.; Zhou, W.; Hu, P. H.; Zhou, Q.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 688 868-874; 10.1016/j.jallcom.2016.07.280 B DEC 15 2016
Abstract:
Pulsed magnetic field (PMF) has been imposed during solidification of Mg-Zn-Y alloy containing icosahedral quasicrystals phase (I-phase) in this work. The effects of vibration power on the solidification microstructure and mechanical properties of Mg93Zn6Y alloy were studied. The results show that the solidification microstructure of the Mg93Zn6Y alloy was further refined with increasing vibration power. The primary alpha-Mg in the alloy treated by PMF was changed from dendrites with the average grain size more than 1 mm untreated by PMF to rosette-like and polyhedral morphology with the average grain size of 122 mm. Moreover, the I-phase was changed from continuous thick skeletal to discontinuous fine reticular and particle-like morphology. The fraction of I-phase in the alloy treated by PMF was also reduced due to the increase of concentrations of Zn and Y elements inside grains. The mechanical properties of Mg93Zn6Y alloy treated by PMF were also improved significantly. The yield strength, ultimate tensile strength and elongation of the alloy treated by PMF at a vibration power of 350 Wat room temperature were 162 MPa, 221 MPa and 1.99%, which were increased by 65%, 66% and 124% respectively, compared to those of the alloy untreated by PMF. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Laser-Induced Charge-Density-Wave Transient Depinning in Chromium
Authors:
Jacques, VLR; Laulhe, C; Moisan, N; Ravy, S; Le Bolloc'h, D Author Full Names: Jacques, V. L. R.; Laulhe, C.; Moisan, N.; Ravy, S.; Le Bolloc'h, D.
Source:
PHYSICAL REVIEW LETTERS, 117 (15):10.1103/PhysRevLett.117.156401 OCT 3 2016
Abstract:
We report on time-resolved x-ray diffraction measurements following femtosecond laser excitation in pure bulk chromium. Comparing the evolution of incommensurate charge-density-wave (CDW) and atomic lattice reflections, we show that, a few nanoseconds after laser excitation, the CDW undergoes different structural changes than the atomic lattice. We give evidence for a transient CDW shear strain that breaks the lattice point symmetry. This strain is characteristic of sliding CDWs, as observed in other incommensurate CDW systems, suggesting the laser-induced CDW sliding capability in 3D systems. This first evidence opens perspectives for unconventional laser-assisted transport of correlated charges.
Title:
Phase transition of solid bismuth under high pressure
Authors:
Chen, HY; Xiang, SK; Yan, XZ; Zheng, LR; Zhang, Y; Liu, SG; Bi, Y Author Full Names: Chen, Hai-Yan; Xiang, Shi-Kai; Yan, Xiao-Zhen; Zheng, Li-Rong; Zhang, Yi; Liu, Sheng-Gang; Bi, Yan
Source:
CHINESE PHYSICS B, 25 (10):10.1088/1674-1056/25/10/108103 OCT 2016
Abstract:
As a widely used pressure calibrator, the structural phase transitions of bismuth from phase I, to phase II, to phase III, and then to phase V with increasing pressure at 300 K have been widely confirmed. However, there are different structural versions for phase III, most of which are determined by x-ray diffraction (XRD) technology. Using x-ray absorption fine structure (XAFS) measurements combined with ab initio calculations, we show that the proposed incommensurate composite structure of bismuth of the three configurations is the best option. An abnormal continuous increase of the nearest-neighbor distance of phase III with elevated pressure is also observed. The electronic structure transformation from semimetal to metal is responsible for the complex behavior of structure transformation.
Title:
Collapse and reappearance of magnetic orderings in spin frustrated TbMnO3 induced by Fe substitution
Authors:
Hong, F; Yue, BB; Wang, JL; Studer, A; Fang, CS; Wang, XL; Dou, SX; Cheng, ZX Author Full Names: Hong, Fang; Yue, Binbin; Wang, Jianli; Studer, Andrew; Fang, Chunsheng; Wang, Xiaolin; Dou, Shixue; Cheng, Zhenxiang
Source:
APPLIED PHYSICS LETTERS, 109 (10):113-117; 10.1063/1.4962465 SEP 5 2016
Abstract:
We studied the temperature dependent magnetic phase evolution in spin frustrated TbMnO3 affected by Fe doping via powder neutron diffraction. With the introduction of Fe (10% and 20%), the long range incommensurate magnetic orderings collapse. When the Fe content is increased to 30%, a long-range antiferromagnetic ordering develops, while a spin reorientation transition is found near 35K from a canted G-type antiferromagnetic ordering to a collinear G-type antiferromagnetic ordering. This work demonstrates the complex magnetic interactions existing in transition metal oxides, which helps to understand the frustrated spin states in other similar systems and design magnetic materials as well. Published by AIP Publishing.

Update: 13-Oct-2016

Title:
Crystallization behavior and mechanical properties of (Al90Fe5Ce5)(100-x)Ti-x amorphous alloys
Authors:
Singh, D; Singh, D; Mandal, RK; Srivastava, ON; Tiwari, RS Author Full Names: Singh, Dharmendra; Singh, Devinder; Mandal, R. K.; Srivastava, O. N.; Tiwari, R. S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 687 990-998; 10.1016/j.jallcom.2016.06.272 DEC 5 2016
Abstract:
The crystallization behavior and mechanical properties of melt-spun (Al90Fe5Ge5)(100-x)Ti-x (x = 0, 4, 8 and 12 at.%) alloys have been investigated. The amorphous phase seems to be stable up to x = 8. The crystallization products for the amorphous alloys with x = 0-8 mainly composed of fcc-Al and icosahedral phases in the glassy matrix. The load dependent hardness behavior of amorphous alloys with and without Ti addition has been studied. The hardness value of the amorphous alloys has been found to be 3.72 and 3.07 GPa for x = 0 and 8 at 100 g load respectively. The annealed ribbons have higher hardness and strength as compared to that of as-synthesized ribbons. The enhanced values of hardness of the (Al90Fe5Ce5)(100-x)Ti-x (x = 0, 4 and 8) alloys are attributed to the combined effects of icosahedral nano particles and Al nanoparticles in amorphous matrix. The absence of cracks around the indentation area up to 500 g of load for amorphous alloys suggests better capability to resist crack propagation in comparison to the annealed alloys. The formation of shear bands around the indentation periphery has been observed. The number of visible shear bands for the as-synthesized ribbons is higher in comparison to those of annealed ribbons. The values of yield strength and Meyer exponent of these alloys are also compared. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Spatially modulated spin structure (SMSS) in BiFeO3-30 years later
Authors:
Sosnowska, IM Author Full Names: Sosnowska, I. M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (42):10.1088/0953-8984/28/42/421002 OCT 26 2016
Title:
Martensitic transition, structure and magnetic anisotropy of martensite in Ni-Mn-Sn single crystal
Authors:
Czaja, P; Szczerba, MJ; Chulist, R; Balanda, M; Przewoznik, J; Chumlyakov, YI; Schell, N; Kapusta, C; Maziarz, W Author Full Names: Czaja, P.; Szczerba, M. J.; Chulist, R.; Balanda, M.; Przewoznik, J.; Chumlyakov, Y. I.; Schell, N.; Kapusta, Cz.; Maziarz, W.
Source:
ACTA MATERIALIA, 118 213-220; 10.1016/j.actamat.2016.07.059 OCT 1 2016
Abstract:
The structural and magnetic properties of Ni50Mn37.5Sn12.5 single crystal were investigated. The alloy undergoes martensitic transformation at 308 K from the austenite phase to the structurally modulated tetragonal 4M martensite phase with lattice parameters a(4M) = 6.177 angstrom, c(4M) = 5.669 angstrom. The alloy shows 7.9% pre-strain upon uniaxial compression along the (001) direction, which is near the theoretical 8.2% maximum twinning strain. Magnetization measurements reveal that the magnetic anisotropy of the martensite phase is uniaxial with the easy magnetization axis corresponding to the shortest c axis of the tetragonally distorted unit cell, while its a axis is the hard magnetization direction. The magnetic anisotropy constant K-u saturates at low temperature around 7 x 10(4) j/m(3) and then gradually decreases with increasing temperature as the system approaches the Curie temperature of martensite at 215 K. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Er1.33Pt3Ga8: A modulated variant of the Er4Pt9Al24-structure type
Authors:
Oswald, IWH; Gourdon, O; Bekins, A; Evans, J; Treadwell, LJ; Chan, JY; Macaluso, RT Author Full Names: Oswald, Iain W. H.; Gourdon, Olivier; Bekins, Amy; Evans, Jess; Treadwell, LaRico J.; Chan, Julia Y.; Macaluso, Robin T.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 242 161-167; SI 10.1016/j.jssc.2016.04.009 2 OCT 2016
Abstract:
Single crystals of Er1.33Pt3Ga8 were synthesized in a molten Ga flux. Er1.33Pt3Ga8 can be considered to be a modulated variant of the Er4Pt9Al24-structure type, where the partial occupancies are ordered. Indeed, the presence of weak satellite reflections indicates a complex organization and distribution of the Er and Ga atoms within the [ErGa] slabs. The structure has been solved based on single crystal X-ray diffraction data in the monoclinic superspace group X2/m(0 beta 0)00 with a commensurate modulated vector q=1/3b*. Precession images also indicate diffusion in the perpendicular direction indicating a partial disorder of this arrangement from layer to layer. In addition, Er1.33Pt3Ga8 shows antiferromagnetic ordering at T-N similar to 5 K. (C) 2016 Elsevier Inc. All rights reserved.
Title:
Strong magnetoelastic coupling at the transition from harmonic to anharmonic order in NaFe(WO4)(2) with 3d(5) configuration
Authors:
Holbein, S; Ackermann, M; Chapon, L; Steffens, P; Gukasov, A; Sazonov, A; Breunig, O; Sanders, Y; Becker, P; Bohaty, L; Lorenz, T; Braden, M Author Full Names: Holbein, S.; Ackermann, M.; Chapon, L.; Steffens, P.; Gukasov, A.; Sazonov, A.; Breunig, O.; Sanders, Y.; Becker, P.; Bohaty, L.; Lorenz, T.; Braden, M.
Source:
PHYSICAL REVIEW B, 94 (10):10.1103/PhysRevB.94.104423 SEP 21 2016
Abstract:
The crystal structure of the double tungstate NaFe(WO4)(2) arises from that of the spin-driven multiferroic MnWO4 by inserting nonmagnetic Na layers. NaFe(WO4)(2) exhibits a three-dimensional incommensurate spin-spiral structure at low temperature and zero magnetic field, which, however, competes with commensurate order induced by magnetic field. The incommensurate zero-field phase corresponds to the condensation of a single irreducible representation but it does not imply ferroelectric polarization because spirals with opposite chirality coexist. Sizable anharmonic modulations emerge in this incommensurate structure, which are accompanied by large magnetoelastic anomalies, while the onset of the harmonic order is invisible in the thermal-expansion coefficient. In magnetic fields applied along the monoclinic axis, we observe a first-order transition to a commensurate structure that again is accompanied by large magnetoelastic effects. The large magnetoelastic coupling, a reduction of the b lattice parameter, is thus associated only with the commensurate order. Upon releasing the field at low temperature, the magnetic order transforms to another commensurate structure that considerably differs from the incommensurate low-temperature phase emerging upon zero-field cooling. The latter phase, which exhibits a reduced ordered moment, seems to be metastable.
Title:
Unusual Relaxor Ferroelectric Behavior in Stairlike Aurivillius Phases
Authors:
Steciuk, G; Boullay, P; Pautrat, A; Barrier, N; Caignaert, V; Palatinus, L Author Full Names: Steciuk, Gwladys; Boullay, Philippe; Pautrat, Alain; Barrier, Nicolas; Caignaert, Vincent; Palatinus, Lukas
Source:
INORGANIC CHEMISTRY, 55 (17):8881-8891; 10.1021/acs.inorgchem.6b01373 SEP 5 2016
Abstract:
New ferroelectric layered materials were found in the pseudobinary system Bi5Nb3O15-ABi(2)Nb(2)O(9) (A= Ba, Sr and Pb). Preliminary observations made by transmission electron microscopy indicate that these compounds exhibit a complex incommensurately modulated structure. A (3 + 1)D structural model is obtained using ab initio phasing by charge flipping based on the analysis of precession electron diffraction tomography data. The (3 + 1)D structure is further validated by a refinement against neutron powder diffraction. These materials possess a layered structure with discontinuous [Bi2O2] slabs and perovskite blocks. While these structural units are characteristics of Aurivillius phases, the existence of periodic crystallographic shear planes offers strong similarities with collapsed or stairlike structures known in high-Tc superconductors and related compounds. Using dielectric spectroscopy, we study the phase transitions of these new layered materials. For A = Ba and Sr, a Vogel-Fulcher-like behavior characteristic of the so-called relaxor ferroelectrics is observed and compared to "canonical" relaxors. For A = Sr, the absence of a Bums temperature separated from the freezing temperature appears as a rather unusual behavior.
Title:
An exceptional series of phase transitions in hydrophobic amino acids with linear side chains
Authors:
Gorbitz, CH; Karen, P; Dusek, M; Petricek, V Author Full Names: Gorbitz, Carl Henrik; Karen, Pavel; Dusek, Michal; Petricek, Vaclav
Source:
IUCRJ, 3 341-353; 10.1107/S2052252516010472 5 SEP 2016
Abstract:
The solid-state phase transitions and intermediate structures of S-2-aminobutanoic acid (L-2-aminobutyric acid), S-2-aminopentanoic acid (L-norvaline), S-2-aminohexanoic acid (L-norleucine) and L-methionine between 100 and 470 K, identified by differential scanning calorimetry, have been characterized in a comprehensive single-crystal X-ray diffraction investigation. Unlike other enantiomeric amino acids investigated until now, this group featuring linear side chains displays up to five distinct phases. The multiple transitions between them involve a number of different processes: alteration of the hydrogen-bond pattern, to our knowledge the first example of this observed for an amino acid, sliding of molecular bilayers, seen previously only for racemates and quasiracemates, concerted side-chain rearrangements and abrupt as well as gradual modifications of the side-chain disorder. Ordering of L-norleucine upon cooling even proceeds via an incommensurately modulated structure. L-Methionine has previously been described as being fully ordered at room temperature. An accurate refinement now reveals extensive disorder for both molecules in the asymmetric unit, while two previously unknown phases occur above room temperature.
Title:
Heuristic Description of Magnetoelectricity of Cu2OSeO3
Authors:
Milde, P; Neuber, E; Bauer, A; Pfleiderer, C; Berger, H; Eng, LM Author Full Names: Milde, Peter; Neuber, Erik; Bauer, Andreas; Pfleiderer, Christian; Berger, Helmuth; Eng, Lukas M.
Source:
NANO LETTERS, 16 (9):5612-5618; 10.1021/acs.nanolett.6b02167 SEP 2016
Abstract:
CuO2SeO3 is an insulating material that hosts topologically nontrivial spin whirls, so-called skyrmions, and exhibits magnetoelectric coupling allowing to manipulate these skyrmions by means of electric fields. We report magnetic force microscopy imaging of the real-space spin structure on the surface of a.. bulk single crystal of CuO2SeO3. Based on measurements of the electric polarization using Kelvin-probe force microscopy, we develop a heuristic description of the magnetoelectric properties in CuO2SeO3. The model successfully describes the dependency of the electric polarization on the magnetization in all magnetically modulated phases.

Update: 6-Oct-2016

Title:
Multi-phase quasicrystalline alloys for superior wear resistance
Authors:
Lee, K; Hsu, JL; Naugle, D; Liang, H Author Full Names: Lee, Kyungjun; Hsu, Jialin; Naugle, Donald; Liang, Hong
Source:
MATERIALS & DESIGN, 108 440-447; 10.1016/j.matdes.2016.06.113 OCT 15 2016
Abstract:
Highly wear-resistant alloys are important in many engineering and biomedical applications. In this research, a multi-phase quasicrystal-based alloy was developed using a rapid arc-melting technique. The alloy contains three characteristic phases, hard lambda-Al13Fe4, quasicrystal icosahedral (i-phase), and ductile tau-AlCu. The Vickers micro hardness of each was 828, 795, and 552, respectively, with an overall hardness of 334 (HR15T). Due to the co-existence of these three phases, this alloy exhibits both hardness and ductility. As such, the new material has favorable wear and crack resistance. The approaches used in this study are beneficial for the future design and development of this class of quasicrystalline alloys. (C) 2016 Elsevier Ltd. All rights reserved.
Title:
Quantization of states and strain-induced transformation of charge-density waves in the quasi-one-dimensional conductor TaS3
Authors:
Zybtsev, SG; Pokrovskii, VY Author Full Names: Zybtsev, S. G.; Pokrovskii, V. Ya.
Source:
PHYSICAL REVIEW B, 94 (11):10.1103/PhysRevB.94.115140 SEP 16 2016
Abstract:
We report studies of low-field conductivity, sigma, of nanosized samples of orthorhombic TaS3 as a function of strain, epsilon. The sigma(epsilon) curves show steplike changes associated with the "quantization" of the wave vector, q, of the charge-density wave. Based on the effect we have revealed the change of the q-vector with strain: its in-chain component (normalized by the reciprocal lattice constant) is found to increase with sample stretch. A similar q(epsilon) dependence results from the analysis of the sigma(epsilon) hysteresis for macroscopic samples. This means that the strain-induced anomalies cannot be explained by the transition of the CDW to fourfold commensurability with the pristine lattice (lock-in transition), as it was supposed earlier. We also discuss the metastable length states and the elastic anomalies in TaS3 in light of the observed q(epsilon) dependence.
Title:
Thermoelastic analysis of a two-dimensional decagonal quasicrystal with a conductive elliptic hole
Authors:
Guo, JH; Yu, J; Xing, YM; Pan, EN; Li, LH Author Full Names: Guo, Junhong; Yu, Jing; Xing, Yongming; Pan, Ernian; Li, Lianhe
Source:
ACTA MECHANICA, 227 (9):2595-2607; 10.1007/s00707-016-1657-7 SEP 2016
Abstract:
A general solution in terms of the Stroh-type formalism for quasicrystals is developed for two-dimensional thermoelastic deformation. The solution is then applied to analyze the deformation of a conductive elliptic hole embedded in the decagonal quasicrystal plane which is under a remotely uniform heat flow. The hoop stresses around the elliptic hole are derived in an exact closed form. When the thermal conductivity inside the hole is neglected, the present results are reduced to the existing solutions in the literature. Some numerical examples are provided to show the effects of the geometrical shape of the hole and the thermal conductivity inside the hole on the hoop stresses. The results show that along the hole the variations of the hoop stress of the phonon field are completely different from those of the phason field. Compared to the corresponding insulated case, consideration of a conductive elliptic hole would lead to very different and interesting thermoelastic behaviors.
Title:
Microstructural changes in an extruded Mg-Zn-Y alloy reinforced by quasicrystalline I-phase by small additions of calcium, manganese and cerium-rich mischmetal
Authors:
Medina, J; Perez, P; Garces, G; Tolnai, D; Stark, A; Schell, N; Adeva, P Author Full Names: Medina, J.; Perez, P.; Garces, G.; Tolnai, D.; Stark, A.; Schell, N.; Adeva, P.
Source:
MATERIALS CHARACTERIZATION, 118 186-198; 10.1016/j.matchar.2016.05.019 AUG 2016
Abstract:
The effects of calcium, manganese and cerium-rich mischmetal additions on the microstructure and texture of the extruded Mg-6Zn-1Y (wt.%) alloy have been investigated. The microstructure of the alloys consisted of a magnesium matrix embedding second phase particles aligned along the extrusion direction. The nature and volume fraction of the second phases depended on the alloying element. Thus, Ce-rich mischmetal promoted the formation of T-phase while calcium additions resulted in the formation of a ternary Mg-Zn-Ca compound. Only, manganese additions did not affect the existence of the I-phase present in the ternary alloy. The texture was measured and it was found that calcium addition has a significant effect weakening the extrusion texture. (C) 2016 Elsevier Inc. All rights reserved.
Title:
First Step Towards a Devil's Staircase in Spin-Crossover Materials
Authors:
Trzop, E; Zhang, DP; Pineiro-Lopez, L; Valverde-Munoz, FJ; Munoz, MC; Palatinus, L; Guerin, L; Cailleau, H; Real, JA; Collet, E Author Full Names: Trzop, Elzbieta; Zhang, Daopeng; Pineiro-Lopez, Lucia; Valverde-Munoz, Francisco J.; Carmen Munoz, M.; Palatinus, Lukas; Guerin, Laurent; Cailleau, Herve; Antonio Real, Jose; Collet, Eric
Source:
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 55 (30):8675-8679; 10.1002/anie.201602441 JUL 18 2016
Abstract:
The unprecedented bimetallic 2D coordination polymer {Fe[(Hg(SCN)(3))(2)](4,4'-bipy)(2)}(n) exhibits a thermal high-spin (HS)<-> low-spin (LS) staircase-like conversion characterized by a multi-step dependence of the HS molar fraction gamma(HS). Between the fully HS (gamma(HS)= 1) and LS (gamma(HS)= 0) phases, two steps associated with different ordering appear in terms of spin-state concentration waves (SSCW). On the gamma(HS). 0.5 step, a periodic SSCW forms with a HS-LS-HS-LS sequence. On the gamma(HS) approximate to 0.34 step, the 4D superspace crystallography structural refinement reveals an aperiodic SSCW, with a HS-LS sequence incommensurate with the molecular lattice. The formation of these different long-range spatially ordered structures of LS and HS states during the multi-step spin-crossover is discussed within the framework of "Devil's staircase"-type transitions. Spatially modulated phases are known in various types of materials but are uniquely related to molecular HS/LS bistability in this case.
Title:
Atomic-scale mapping of twins and relevant defective structures in Al20Cu2Mn3 decagonal approximant
Authors:
Wang, J; Zhang, B; He, ZB; Wu, B; Ma, XL Author Full Names: Wang, J.; Zhang, B.; He, Z. B.; Wu, B.; Ma, X. L.
Source:
PHILOSOPHICAL MAGAZINE, 96 (23):2457-2467; 10.1080/14786435.2016.1205229 2016
Abstract:
Twins or multiple twins occur frequently in the orthorhombic Al20Cu2Mn3 approximant of decagonal quasi crystal (DQC). Due to the specific structural units, the twins in the Al20Cu2Mn3 approximant usually exhibit the glide-reflection characteristics. Using aberration-corrected transmission electron microscope at the atomic scale, we have observed not only glide-reflection twins but also simple mirror-reflection twins in the Al20Cu2Mn3 approximant. The two twinning modes are found to coexist in the present sample. These twins exhibit variant configurations at the twin boundaries where the tessellations of local subunits are imaged at an atomic scale. At the twin boundaries, diversified tiles such as star-like (S), bowtie-shaped and boat-shaped (B) are observed. The diversified tiles stacking with various manners allow the coexistence of the DQC and the approximant. Furthermore, the variants of B and S tiles are also found.

Update: 29-Sep-2016

Title:
Structure and mechanical properties in a powder-processed icosahedral-phase-strengthened aluminum alloy
Authors:
Watson, TJ; Gordillo, MA; Cernatescu, I; Aindow, M Author Full Names: Watson, Thomas J.; Gordillo, Mauricio A.; Cernatescu, Iuliana; Aindow, Mark
Source:
SCRIPTA MATERIALIA, 123 51-54; 10.1016/j.scriptamat.2016.05.037 OCT 2016
Abstract:
Nanocomposite powder particles of aluminum with dispersed icosahedral quasicrystals were produced by gas atomization from an Al-Cr-Mn-Co-Zr alloy. Bulk dispersion -strengthened material was obtained from the powder by blind-die compaction and forging. The material exhibited an attractive combination of room temperature mechanical properties with a dynamic elastic modulus of 90.5 GPa, a tensile yield strength of 690 MPa with 6% elongation to failure, and a high cycle fatigue life of 109 cycles at 207 MPa applied stress. The material also exhibited significant potential for elevated temperature applications with a modulus of 75 GPa and yield strength of 400 MPa at 300 degrees C. (C) 2016 Elsevier Ltd. All rights reserved.
Title:
Strengthening mechanisms in an Al-Fe-Cr-Ti nano-quasicrystalline alloy and composites
Authors:
Pedrazzini, S; Galano, M; Audebert, F; Collins, DM; Hofmann, F; Abbey, B; Korsunsky, AM; Lieblich, M; Escorial, AG; Smith, GDW Author Full Names: Pedrazzini, S.; Galano, M.; Audebert, F.; Collins, D. M.; Hofmann, F.; Abbey, B.; Korsunsky, A. M.; Lieblich, M.; Garcia Escorial, A.; Smith, G. D. W.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 672 175-183; 10.1016/j.msea.2016.07.007 AUG 30 2016
Abstract:
We report a study of the structure-processing-property relationships in a high strength Al93Fe3Cr2Ti2 nano-quasicrystalline alloy and composites containing 10 and 20 vol% ductilising pure Al fibres. The superimposed contributions of several different strengthening mechanisms have been modelled analytically using data obtained from systematic characterisation of the monolithic alloy bar. An observed yield strength of 544 MPa has been substantiated from a combination of solid solution strengthening, work hardening, precipitation hardening and Hall-Petch grain size dependent effects. These materials have been shown by other authors in previous published work to be highly sensitive to the size distribution of particles in the powder from which they are made, and the subsequent thermomechanical processing conditions. The processing condition employed in this study provided micron-sized grains with a strong [111] preferential orientation along the extrusion direction and a bimodal size distribution of the icosahedral nano-quasicrystalline precipitates. Both were deemed to be a significant contributor to the high yield strength observed. The addition of pure Al fibres was found to decrease the yield strength linearly with increasing Al content, and to auginent the ductility of the composites. (C) 2016 The Authors. Published by Elsevier B.V.
Title:
Observation and Structure Determination of an Oxide Quasicrystal Approximant
Authors:
Forster, S; Trautmann, M; Roy, S; Adeagbo, WA; Zollner, EM; Hammer, R; Schumann, FO; Meinel, K; Nayak, SK; Mohseni, K; Hergert, W; Meyerheim, HL; Widdra, W Author Full Names: Foerster, S.; Trautmann, M.; Roy, S.; Adeagbo, W. A.; Zollner, E. M.; Hammer, R.; Schumann, F. O.; Meinel, K.; Nayak, S. K.; Mohseni, K.; Hergert, W.; Meyerheim, H. L.; Widdra, W.
Source:
PHYSICAL REVIEW LETTERS, 117 (9):10.1103/PhysRevLett.117.095501 AUG 24 2016
Abstract:
We report on the first observation of an approximant structure to the recently discovered two-dimensional oxide quasicrystal. Using scanning tunneling microscopy, low-energy electron diffraction, and surface x-ray diffraction in combination with ab initio calculations, the atomic structure and the bonding scheme are determined. The oxide approximant follows a 3(2.)4.3.4 Archimedean tiling. Ti atoms reside at the corners of each tiling element and are threefold coordinated to oxygen atoms. Ba atoms separate the TiO3 clusters, leading to a fundamental edge length of the tiling 6.7 angstrom.
Title:
Polymorphism in Zintl Phases ACd(4)Pn(3): Modulated Structures of NaCd(4)Pn(3) with Pn = P, As
Authors:
Grotz, C; Baumgartner, M; Freitag, KM; Baumer, F; Nilges, T Author Full Names: Grotz, Carolin; Baumgartner, Maximilian; Freitag, Katharina M.; Baumer, Franziska; Nilges, Tom
Source:
INORGANIC CHEMISTRY, 55 (15):7764-7776; 10.1021/acs.inorgchem.6b01233 AUG 1 2016
Abstract:
NaCd4P3 and NaCd4As3 were synthesized via short-way transport using the corresponding elements and CdI2 as mineralizer. At room temperature, the two beta-polymorphs adopt the RbCd4As3 structure type which has been recently reported for alkali metal (A)-d(10) transition metal (T)-pnictides (Pn). The title compounds crystallize rhombohedrally in space group R (3) over barm at room temperature and show reversible phase transitions to incommensurately modulated alpha-polymorphs at lower temperatures. The low-temperature phases are monoclinic and can be described in space group Cm(alpha 0 gamma)s with q vectors of q = (-0.04,0,0.34) for alpha-NaCd4P3 and q(1) = (-0.02,0,0.34) for alpha-NaCd4As3. Thermal properties, Raman spectroscopy, and electronic structures have been determined. Both compounds are Zintl phases with band gaps of 1.05 eV for beta-NaCd4P3 and similar to 0.4 eV for beta-NaCd4As3.
Title:
Crystal structure of modulated martensite and crystallographic correlations between martensite variants of Ni50Mn38Sn12 alloy
Authors:
Lin, CQ; Yan, HL; Zhang, YD; Esling, C; Zhao, X; Zuo, L Author Full Names: Lin, Chunqing; Yan, Haile; Zhang, Yudong; Esling, Claude; Zhao, Xiang; Zuo, Liang
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 1276-1283; 10.1107/S1600576716010372 4 AUG 2016
Abstract:
A comprehensive study on the crystal structure, the microstructure and the crystallographic features of the martensite in an Ni50Mn38Sn12 alloy has been conducted in the present work. The results show that the martensite possesses a 4O modulated structure. The martensite is organized into broad plates in the original austenite grain. The plates contain irregularly shaped colonies with two characteristic microstructural patterns: a classical lamellar pattern and a herringbone pattern. Crystallographic analyses by scanning electron microscopy/electron backscatter diffraction demonstrate that in each colony there are four orientation variants (A, B, C and D) and they form three types of twins (type I, type II and compound twin). The interfaces between corresponding variants are coincident with their twinning plane K1. The interface planes of the compound twin pairs A&D and B&C can have one or two different orientations, which leads to the two microstructural patterns. The corresponding variants in neighboring colonies within one broad plate (intra-plate colonies) possess close orientations, but the type I and the type II twin relationships are interchanged. The variants in neighboring colonies situated in adjacent plates (inter-plate colonies) are type I or type II twin related but with some angular deviations. The plate interface is defined by the {221} plane of the variant pair with largest thickness. The results of the present work provide comprehensive microstructural and crystallographic information on modulated martensite in NiMnSn alloys that is useful for the understanding of their specific functionalities and helpful for further investigation on property optimization of these materials.
Title:
Superior room-temperature ductility of typically brittle quasicrystals at small sizes
Authors:
Zou, Y; Kuczera, P; Sologubenko, A; Sumigawa, T; Kitamura, T; Steurer, W; Spolenak, R Author Full Names: Zou, Yu; Kuczera, Pawel; Sologubenko, Alla; Sumigawa, Takashi; Kitamura, Takayuki; Steurer, Walter; Spolenak, Ralph
Source:
NATURE COMMUNICATIONS, 7 10.1038/ncomms12261 AUG 2016
Abstract:
The discovery of quasicrystals three decades ago unveiled a class of matter that exhibits long-range order but lacks translational periodicity. Owing to their unique structures, quasicrystals possess many unusual properties. However, a well-known bottleneck that impedes their widespread application is their intrinsic brittleness: plastic deformation has been found to only be possible at high temperatures or under hydrostatic pressures, and their deformation mechanism at low temperatures is still unclear. Here, we report that typically brittle quasicrystals can exhibit remarkable ductility of over 50% strains and high strengths of similar to 4.5 GPa at room temperature and sub-micrometer scales. In contrast to the generally accepted dominant deformation mechanism in quasicrystals-dislocation climb, our observation suggests that dislocation glide may govern plasticity under high-stress and low-temperature conditions. The ability to plastically deform quasicrystals at room temperature should lead to an improved understanding of their deformation mechanism and application in small-scale devices.
Title:
Magnetism and superconductivity in a quasi-2D anisotropic system doped with charge carriers
Authors:
Palistrant, ME Author Full Names: Palistrant, M. E.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 123 (1):86-97; 10.1134/S1063776116050198 JUL 2016
Abstract:
The theory of multiband superconducting systems with variable density of charge carriers is analyzed. The possibility of emergence of nonphonon high-temperature superconductivity due to the predominance of electron-electron interband interactions over intraband interactions, as well as due to the fact that the thermodynamic and magnetic properties of multiband systems in the superconducting phase differ qualitatively from those of single-band systems, is indicated. Phase transitions in a quasi-2D anisotropic medium upon a change in the carrier concentration, i.e., a transition from the commensurate to the incommensurate state of the spin density wave, are analyzed. Such a transition is observed when the Umklapp processes in the lattice structure are taken into account. These processes facilitate a deviation of wavevector Q of the spin density wave from 2k (F) , as well as a displacement of the bandgap relative to the Fermi surface. This leads to the generation of free charge carriers and the possibility of superconductivity. It is shown that superconductivity accompanies the magnetism. The conditions for the coexistence of these two phenomena are determined.
Title:
Direct imaging of incommensurate wave pockets in the charge-density-wave state of LaTe2
Authors:
Yang, HX; Cai, Y; Ma, C; Li, J; Long, YJ; Chen, GF; Tian, HF; Wei, LL; Li, JQ Author Full Names: Yang, H. X.; Cai, Y.; Ma, C.; Li, J.; Long, Y. J.; Chen, G. F.; Tian, H. F.; Wei, L. L.; Li, J. Q.
Source:
EPL, 114 (6):10.1209/0295-5075/114/67002 JUN 2016
Abstract:
We herein report the study of the atomic structure for a fully incommensurate CDW in LaTe2 using Cs-corrected scanning transmission electron microscopy (STEM). It is directly revealed for the first time that the atomic displacements adopt an incommensurate wave-pocket structure along each Te chain. This pocket structure has a long periodicity determined by the CDW incommensurability. We can use the sinusoidal waves as the first-order approximation to characterize the atomic motions within the pocket pattern, which can yield atomic displacements in good agreement with the theoretical model commonly used for studying CDW. These facts demonstrate that the incommensurate pocket patterns should be an essential structural nature in the CDW states and play a critical role for developing the mechanism of the CDW transitions. Copyright (C) EPLA, 2016

Update: 22-Sep-2016

Title:
Microstructure and Mechanical Properties of Squeeze Casting Quasicrystal Reinforced AZ91D Magnesium Matrix Composites
Authors:
Yang, L; Hou, H; Zhao, YH; Yang, XM Author Full Names: Yang Ling; Hou Hua; Zhao Yuhong; Yang Xiaomin
Source:
RARE METAL MATERIALS AND ENGINEERING, 45 (8):1978-1982; AUG 2016
Abstract:
To improve the mechanical properties of AZ91D alloy, a squeeze casting process was employed to fabricate AZ91D magnesium matrix composites reinforced with stable icosahedral quasicrystal particles which were introduced as Mg-Zn-Y quasicrystal master alloy. The effects of quasicrystal master alloy content on the microstructure and mechanical properties of the composites were investigated. The results show that the squeeze casting process is an effective method to refine grain size. The composites comprise alpha-Mg matrix, beta-Mg17Al12 phases that disperse on grain boundaries and Mg3Zn6Y quasicrystal particles. A stable interface between the quasicrystal particles and the Mg matrix is observed. The composite exhibits the maximum ultimate tensile strength of 194.3 MPa and the maximum elongation of 9.2%, when the mass fraction of quasicrystal master alloy is 5%. The reinforcement mechanism is concluded as fine-grain strengthening and quasicrystal particle strengthening.

Update: 15-Sep-2016

Title:
Fatigue properties and microstructure of quasicrystalline AlFeCrTi alloy
Authors:
Chlupova, A; Chlup, Z; Kruml, T Author Full Names: Chlupova, Alice; Chlup, Zdenek; Kruml, Tomas
Source:
INTERNATIONAL JOURNAL OF FATIGUE, 91 251-256; 10.1016/j.ijfatigue.2016.06.007 1 OCT 2016
Abstract:
Aluminium based material having chemical composition of Al93Fe3Ti2Cr2 (at.%) was prepared by hot extrusion of gas atomised powder. Microstructure consisting of aluminium matrix and icosahedral quasicrystalline particles was investigated by scanning and transmission electron microscopy a X-ray spectroscopy. Size, distribution and inner structure of quasicrystalline particles were determined. When quasicrystalline particles having submicron size were present in the microstructure together with fine-grained aluminium matrix, it resulted in enhancement of mechanical properties. Fatigue experiments were performed in load controlled regime with positive mean stress and fatigue life data for this quasicrystalline material were compared with similar results for commercially available aluminium alloys. Longer fatigue life together with higher fatigue strength reaching value of 350 MPa was observed. It is approx. 100 MPa higher than for commercially produced coarse-grained aluminium alloys. Fractographic observations revealed presence of fish eye fracture patterns and validity of weakest link fracture mechanism acting in this type of material under investigation. (C) 2016 Elsevier Ltd. All rights reserved.
Title:
Quasi-ordered C-60 molecular films grown on the pseudo-ten-fold (100) surface of the Al13Co4 quasicrystalline approximant
Authors:
Fournee, V; Gaudry, E; Ledieu, J; de Weerd, MC; Diehl, RD Author Full Names: Fournee, V.; Gaudry, E.; Ledieu, J.; de Weerd, M-C; Diehl, R. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (35):10.1088/0953-8984/28/35/355001 SEP 7 2016
Abstract:
The growth of C-60 films on the pseudo-ten-fold (1 0 0) surface of the orthorhombic Al13Co4 quasicrystalline approximant was studied experimentally by scanning tunneling microscopy, low-energy electron diffraction and photoemission spectroscopy. The (1 0 0) surface terminates at bulk-planes presenting local atomic configurations with five-fold symmetry-similar to quasicrystalline surfaces. While the films deposited at room temperature were found disordered, high-temperature growth (up to 693 K) led to quasi-ordered molecular films templated on the substrate rectangular unit mesh. The most probable adsorption sites and geometries were investigated by density functional theory (DFT) calculations. A large range of adsorption energies was determined, influenced by both symmetry and size matching at the molecule-substrate interface. The quasi-ordered structure of the film can be explained by C-60 adsorption at the strongest adsorption sites which are too far apart compared to the distance minimizing the intermolecular interactions, resulting in some disorder in the film structure at a local scale. Valence band photoemission indicates a broadening of the molecular orbitals resulting from hybridization between the substrate and overlayer electronic states. Dosing the film at temperature above 693 K led to molecular damage and formation of carbide thin films possessing no azimuthal order with respect to the substrate.
Title:
Exchange anisotropy as mechanism for spin-stripe formation in frustrated spin chains
Authors:
Pregelj, M; Zaharko, O; Herak, M; Gomilsek, M; Zorko, A; Chapon, LC; Bourdarot, F; Berger, H; Arcon, D Author Full Names: Pregelj, M.; Zaharko, O.; Herak, M.; Gomilsek, M.; Zorko, A.; Chapon, L. C.; Bourdarot, F.; Berger, H.; Arcon, D.
Source:
PHYSICAL REVIEW B, 94 (8):10.1103/PhysRevB.94.081114 AUG 29 2016
Abstract:
We investigate the spin-stripe mechanism responsible for the peculiar nanometer modulation of the incommensurate magnetic order that emerges between the vector-chiral and the spin-density-wave phase in the frustrated zigzag spin-1/2 chain compound beta-TeVO4. A combination of magnetic-torque, neutron-diffraction, and spherical-neutron-polarimetry measurements is employed to determine the complex magnetic structures of all three ordered phases. Based on these results, we develop a simple phenomenological model, which exposes the exchange anisotropy as the key ingredient for the spin-stripe formation in frustrated spin systems.
Title:
Electronic structure and magneto-optical Kerr effect spectra of ferromagnetic shape-memory Ni-Mn-Ga alloys: Experiment and density functional theory calculations
Authors:
Uba, S; Bonda, A; Uba, L; Bekenov, LV; Antonov, VN Author Full Names: Uba, S.; Bonda, A.; Uba, L.; Bekenov, L. V.; Antonov, V. N.
Source:
PHYSICAL REVIEW B, 94 (5):10.1103/PhysRevB.94.054427 AUG 25 2016
Abstract:
In this joint experimental and ab initio study, we focused on the influence of the chemical composition and martensite phase transition on the electronic, magnetic, optical, and magneto-optical properties of the ferromagnetic shape-memory Ni-Mn-Ga alloys. The polar magneto-optical Kerr effect (MOKE) spectra for the polycrystalline sample of the Ni-Mn-Ga alloy of Ni60Mn13Ga27 composition were measured by means of the polarization modulation method over the photon energy range 0.8 <= hv <= 5.8 eV in magnetic field up to 1.5 T. The optical properties (refractive index n and extinction coefficient k) were measured directly by spectroscopic ellipsometry using the rotating analyzer method. To complement experiments, extensive first-principles calculations were made with two different first-principles approaches combining the advantages of a multiple scattering Green function method and a spin-polarized fully relativistic linear-muffin-tin-orbital method. The electronic, magnetic, and MO properties of Ni-Mn-Ga Heusler alloys were investigated for the cubic austenitic and modulated 7M-like incommensurate martensitic phases in the stoichiometric and off-stoichiometric compositions. The optical and MOKE properties of Ni-Mn-Ga systems are very sensitive to the deviation from the stoichiometry. It was shown that the ab initio calculations reproduce well experimental spectra and allow us to explain the microscopic origin of the Ni2MnGa optical and magneto-optical response in terms of interband transitions. The band-by-band decomposition of the Ni2MnGa MOKE spectra is presented and the interband transitions responsible for the prominent structures in the spectra are identified.
Title:
Reflection quasilattices and the maximal quasilattice
Authors:
Boyle, L; Steinhardt, PJ Author Full Names: Boyle, Latham; Steinhardt, Paul J.
Source:
PHYSICAL REVIEW B, 94 (6):10.1103/PhysRevB.94.064107 AUG 25 2016
Abstract:
We introduce the concept of a reflection quasilattice, the quasiperiodic generalization of a Bravais lattice with irreducible reflection symmetry. Among their applications, reflection quasilattices are the reciprocal (i.e., Bragg diffraction) lattices for quasicrystals and quasicrystal tilings, such as Penrose tilings, with irreducible reflection symmetry and discrete scale invariance. In a follow-up paper, we will show that reflection quasilattices can be used to generate tilings in real space with properties analogous to those in Penrose tilings, but with different symmetries and in various dimensions. Here we explain that reflection quasilattices only exist in dimensions two, three, and four, and we prove that there is a unique reflection quasilattice in dimension four: the "maximal reflection quasilattice" in terms of dimensionality and symmetry. Unlike crystallographic Bravais lattices, all reflection quasilattices are invariant under rescaling by certain discrete scale factors. We tabulate the complete set of scale factors for all reflection quasilattices in dimension d > 2, and for all those with quadratic irrational scale factors in d = 2.
Title:
Atomic structure of the i-R-Cd quasicrystals and consequences for magnetism
Authors:
Yamada, T; Takakura, H; Kong, T; Das, P; Jayasekara, WT; Kreyssig, A; Beutier, G; Canfield, PC; de Boissieu, M; Goldman, AI Author Full Names: Yamada, T.; Takakura, H.; Kong, T.; Das, P.; Jayasekara, W. T.; Kreyssig, A.; Beutier, G.; Canfield, P. C.; de Boissieu, M.; Goldman, A. I.
Source:
PHYSICAL REVIEW B, 94 (6):10.1103/PhysRevB.94.060103 AUG 15 2016
Abstract:
We report on the six-dimensional (6D) structural refinement of three members of the i-R-Cd quasicrystals (R = Gd, Dy, Tm) via synchrotron x-ray diffraction from single-grain samples, and show that this series is isostructural to the i-YbCd5.7 quasicrystal. However, our refinements suggest that the R occupancy on the Yb icosahedron sites within the Tsai-type atomic cluster is approximately 80%, with the balance taken up by Cd. Similarities between the i-R-Cd series and i-ScZn7.33, and their differences with i-YbCd5.7 and i-Ca15Cd85, indicate that there are at least two subclasses of Tsai-type icosahedral quasicrystals. We further show from x-ray resonant magnetic scattering (XRMS) measurements on a set of closely related Tb1-xYxCd6 1/1 approximants that the dilution of themagnetic R ions on the icosahedron within the Tsai-type cluster by nonmagnetic Y disrupts the commensurate magnetic ordering in the approximant phase.
Title:
Three-Dimensional Icosahedral Phase Field Quasicrystal
Authors:
Subramanian, P; Archer, AJ; Knobloch, E; Rucklidge, AM Author Full Names: Subramanian, P.; Archer, A. J.; Knobloch, E.; Rucklidge, A. M.
Source:
PHYSICAL REVIEW LETTERS, 117 (7):10.1103/PhysRevLett.117.075501 AUG 8 2016
Abstract:
We investigate the formation and stability of icosahedral quasicrystalline structures using a dynamic phase field crystal model. Nonlinear interactions between density waves at two length scales stabilize three-dimensional quasicrystals. We determine the phase diagram and parameter values required for the quasicrystal to be the global minimum free energy state. We demonstrate that traits that promote the formation of two-dimensional quasicrystals are extant in three dimensions, and highlight the characteristics required for three-dimensional soft matter quasicrystal formation.
Title:
Modulated crystal structure of InMo4O6
Authors:
Schultz, P; Simon, A; Oeckler, O Author Full Names: Schultz, Peter; Simon, Arndt; Oeckler, Oliver
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 642-649; SI 10.1107/S205252061600874X 4 AUG 2016
Abstract:
The (3 + 1)-dimensional modulated crystal structure of the metal-rich cluster compound InMo4O6 was solved and refined from single-crystal data in the superspace group P4/mbm(00 gamma)00ss [q = 0, 0, 0.1536 (4); a = 9.6664 (9), c = 2.8645 (3) angstrom; R1(all) = 0.046, wR(all) = 0.076]. The crystal structure is closely related to the NaMo4O6 structure type. It is built from rods of Mo-6 clusters condensed via trans edges. These form channels parallel to [001], in which In-6 and In-7 oligomers alternate. Weak diffuse planes parallel to (001)* interconnect the *satellite* *reflections*; they occur due to two-dimensional rod disorder of the In oligomer chains.
Title:
Magnetic anisotropy in the frustrated spin-chain compound beta-TeVO4
Authors:
Weickert, F; Harrison, N; Scott, BL; Jaime, M; Leitmae, A; Heinmaa, I; Stern, R; Janson, O; Berger, H; Rosner, H; Tsirlin, AA Author Full Names: Weickert, F.; Harrison, N.; Scott, B. L.; Jaime, M.; Leitmae, A.; Heinmaa, I.; Stern, R.; Janson, O.; Berger, H.; Rosner, H.; Tsirlin, A. A.
Source:
PHYSICAL REVIEW B, 94 (6):10.1103/PhysRevB.94.064403 AUG 1 2016
Abstract:
Isotropic and anisotropic magnetic behavior of the frustrated spin-chain compound beta-TeVO4 is reported. Three magnetic transitions observed in zero magnetic field are tracked in fields applied along different crystallographic directions using magnetization, heat capacity, and magnetostriction measurements. Qualitatively different temperature-field diagrams are obtained below 10 T for the field applied along a or b and along c, respectively. In contrast, a nearly isotropic high-field phase emerges above 18 T and persists up to the saturation that occurs around 22.5 T. Upon cooling in low fields, the transitions at T-N1 and T-N2 toward the spin-density-wave and stripe phases are of the second order, whereas the transition at T-N3 toward the helical state is of the first order and entails a lattice component. Our microscopic analysis identifies frustrated J(1)-J(2) spin chains with a sizable antiferromagnetic interchain coupling in the bc plane and ferromagnetic couplings along the a direction. The competition between these ferromagnetic interchain couplings and the helical order within the chain underlies the incommensurate order along the a direction, as observed experimentally. While a helical state is triggered by the competition between J(1) and J(2) within the chain, the plane of the helix is not uniquely defined because of competing magnetic anisotropies. Using high-resolution synchrotron diffraction and Te-125 nuclear magnetic resonance, we also demonstrate that the crystal structure of beta-TeVO4 does not change down to 10 K, and the orbital state of V4+ is preserved.
Title:
Internal field emission nature of the fine structure of tunnel spectra in icosahedral quasicrystals
Authors:
Prekul, AF; Schegolikhina, NI Author Full Names: Prekul, A. F.; Schegolikhina, N. I.
Source:
JETP LETTERS, 103 (9):603-606; 10.1134/S0021364016090071 MAY 2016
Abstract:
Calorimetric and tunnel data for the icosahedral phases of the Al-Cu-Fe system have been jointly analyzed. It has been found that the field-dependent part of the tunnel conductance can be represented as the sum of elementary terms similar in nature to thermal Schottky anomalies. As a result, the features of the fine structure of tunnel spectra in the form of zero-bias anomalies, peaks, and humps can be due to the internal field emission and can indicate a wide distribution of two-level electron traps in the electronic structure of quasicrystals. It was previously assumed that these features constitute a direct image of the density of single-electron states of the conduction band.

Update: 9-Sep-2016

Title:
Long-range charge-density-wave proximity effect at cuprate/manganate interfaces
Authors:
Frano, A; Blanco-Canosa, S; Schierle, E; Lu, Y; Wu, M; Bluschke, M; Minola, M; Christiani, G; Habermeier, HU; Logvenov, G; Wang, Y; van Aken, PA; Benckiser, E; Weschke, E; Le Tacon, M; Keimer, B Author Full Names: Frano, A.; Blanco-Canosa, S.; Schierle, E.; Lu, Y.; Wu, M.; Bluschke, M.; Minola, M.; Christiani, G.; Habermeier, H. U.; Logvenov, G.; Wang, Y.; van Aken, P. A.; Benckiser, E.; Weschke, E.; Le Tacon, M.; Keimer, B.
Source:
NATURE MATERIALS, 15 (8):831-+; 10.1038/NMAT4682 AUG 2016
Abstract:
The interplay between charge density waves (CDWs) and high-temperature superconductivity is currently under intense investigation(1-10). Experimental research on this issue is difficult because CDW formation in bulk copper oxides is strongly influenced by random disorder(11-13), and a long-range-ordered CDW state in high magnetic fields(14-16) is difficult to access with spectroscopic and diffraction probes. Here we use resonant X-ray scattering in zero magnetic field to show that interfaces with the metallic ferromagnet La2/3Ca1/3MnO3 greatly enhance CDW formation in the optimally doped high-temperature superconductor YBa2Cu3O6+delta (delta similar to 1), and that this effect persists over several tens of nanometres. The wavevector of the incommensurate CDW serves as an internal calibration standard of the charge carrier concentration, which allows us to rule out any significant influence of oxygen non-stoichiometry, and to attribute the observed phenomenon to a genuine electronic proximity effect. Long-range proximity effects induced by heterointerfaces thus offer a powerful method to stabilize the charge-density-wave state in the cuprates and, more generally, to manipulate the interplay between different collective phenomena in metal oxides.

Update: 1-Sep-2016

Title:
Electron diffraction study of cobalt-rich Hf-Co
Authors:
Li, XZ; Jin, YL; Wang, MY; Shield, JE; Skomski, R; Sellmyer, DJ Author Full Names: Li, X. -Z.; Jin, Y. -L.; Wang, M. -Y.; Shield, J. E.; Skomski, R.; Sellmyer, D. J.
Source:
INTERMETALLICS, 75 54-61; 10.1016/j.intermet.2016.06.002 AUG 2016
Abstract:
Intermetallic compounds having compositions from HfCo4 to HfCo8 were investigated by transmission electron microscopy, selected-area electron diffraction, and energy-dispersive x-ray spectroscopy. A major crystalline phase, closely related to the orthorhombic Zr2Co11 phase in structure, has been observed in the samples with the composition ranges from HfCo6 to HfCo8. The phase, referred to as either Hf2Co11 or HfCo7 phase in the literature, is actually one common phase, having a broad composition range and referred to as mu-phase in the present paper. In addition to the mu-phase, we have found coexisted fcc-Co phase and a minor Hf2Co7 phase. The Hf6Co23 phase has been identified in the HfCo4 and HfCo5 samples. Tilt-series electron diffraction revealed that the mu-phase is a one-dimensional incommensurate structure, which can be described approximately as B-centered orthorhombic with a = 0.47 nm, b = 0.82 nm, and c = 3.86 nm. (C) 2016 Elsevier Ltd. All rights reserved.
Title:
Low temperature heat capacity and electrical resistivity of the Ti40Zr25Cu12Ni3Be20 glass forming alloy
Authors:
Liu, BB; Ye, F Author Full Names: Liu, Binbin; Ye, Feng
Source:
INTERMETALLICS, 75 31-35; 10.1016/j.intermet.2016.05.010 AUG 2016
Abstract:
Gaining knowledge of electronic structure provides useful information for understanding unique properties of metallic glasses. In this study, low temperature heat capacity and electrical resistivity of the glass forming Ti40Zr25Cu12Ni3Be20 alloy with glassy, quasicrystalline, or crystalline states below 300 K were investigated. The precipitation of the I-phase was revealed in the initial crystallization process of the Ti40Zr25Cu12Ni3Be20 BMG. The glassy state has higher state density at Fermi level than its quasi crystalline or crystalline counterparts, which could be interpreted by the electron localization in glassy state as well as a pseudo-Brillouin zone formed nearby Fermi surface in the quasicrystalline state. None of the three states showed superconductivity phenomenon down to 1.9 K. Temperature dependence of resistivity for both the glassy state and the quasicrystalline state exhibited negative temperature coefficient and was less sensitive to temperature than the crystalline state. The electrical resistivity showed a smaller value for the I-phase than that for the glass due to lower structural integrity of I -phase. Electrical resistivity as well as heat capacity measurements indicated that the electronic structure of the quasi crystalline state is quite similar to glassy state but far from crystalline state. (C) 2016 Elsevier Ltd. All rights reserved.
Title:
2D materials and van der Waals heterostructures
Authors:
Novoselov, KS; Mishchenko, A; Carvalho, A; Neto, AHC Author Full Names: Novoselov, K. S.; Mishchenko, A.; Carvalho, A.; Castro Neto, A. H.
Source:
SCIENCE, 353 (6298):461-+; 10.1126/science.aac9439 JUL 29 2016
Abstract:
The physics of two-dimensional ( 2D) materials and heterostructures based on such crystals has been developing extremely fast. With these new materials, truly 2D physics has begun to appear ( for instance, the absence of long-range order, 2D excitons, commensurate-incommensurate transition, etc.). Novel heterostructure devices-such as tunneling transistors, resonant tunneling diodes, and light-emitting diodes-are also starting to emerge. Composed from individual 2D crystals, such devices use the properties of those materials to create functionalities that are not accessible in other heterostructures. Here we review the properties of novel 2D crystals and examine how their properties are used in new heterostructure devices.

Update: 25-Aug-2016

Title:
Prediction of Host-Guest Na-Fe Intermetallics at High Pressures
Authors:
Zhou, YY; Wang, H; Zhu, CY; Liu, HY; Tse, JS; Ma, YM Author Full Names: Zhou, Yuanyuan; Wang, Hui; Zhu, Chunye; Liu, Hanyu; Tse, John S.; Ma, Yanming
Source:
INORGANIC CHEMISTRY, 55 (14):7026-7032; 10.1021/acs.inorgchem.6b00881 JUL 18 2016
Abstract:
High pressure can fundamentally alter the electronic structure of elemental metals, leading to the unexpected formation of intermetallics with unusual structural features. In the present study, the phase stabilities and structural changes of Na-Fe intermetallics under pressure were studied using unbiased structure searching methods, combined with density functional theory calculations. Two intermetallics with stoichiometries Na3Fe and Na4Fe are found to be thermodynamically stable at pressures above 120 and 155 GPa, respectively. An interesting structural feature is that both have form a host guest-like structure with Na sublattices constructed from small and large polygons similar to the host framework of the self-hosting incommensurate phases observed in Group I and II elements. Apart from the one-dimensional (1D) Fe chains running through the large channels, more interestingly, electrides are found to localize in the small channels between the layers. Electron topological analysis shows secondary bonding interactions between the Fe atoms and the interstitial electrides help to stabilize these structures.

Update: 18-Aug-2016

Title:
Influence of icosahedral short range order on diffusion in liquids: A study on Al-Zn-Cr alloys
Authors:
Kurtuldu, G; Jarry, P; Rappaz, M Author Full Names: Kurtuldu, Guven; Jarry, Philippe; Rappaz, Michel
Source:
ACTA MATERIALIA, 115 423-433; 10.1016/j.actamat.2016.05.051 AUG 15 2016
Abstract:
It has been shown recently that minute additions of Cr in Al-Zn alloys refine the solidified grain structure and induce multiply-twinned grains which can only be explained if the icosahedral symmetry is considered (Kurtuldu et al., 2013). It has been suggested that Cr addition to Al-Zn alloys promotes the formation of icosahedral short-range order (ISRO) in the liquid, leading to the formation of icosahedral quasicrystals (iQC) acting then as a template for the nucleation of the fcc Al-phase. If ISRO exists in liquid Al-Zn-Cr alloys, this should influence diffusion of solute elements in the liquid. The present study focuses on the effect of Cr addition on Zn diffusion in liquid Al-Zn-Cr alloys. The solute diffusion coefficients of Zn and Cr in the liquid were deduced from the solute profiles in the quenched liquid ahead of a planar solid liquid interface. By comparison with the same measurement in Al-Zn alloys, it is shown that Cr indeed slows down the diffusion (and mobility) of Zn atoms, an effect which reinforces the hypothesis of ISRO in Al-Zn liquid induced by Cr. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Structure and microstructure of Ni-Mn-Ga single crystal exhibiting magnetic shape memory effect analysed by high resolution X-ray diffraction
Authors:
Heczko, O; Cejpek, P; Drahokoupil, J; Holy, V Author Full Names: Heczko, Oleg; Cejpek, Petr; Drahokoupil, Jan; Holy, Vaclav
Source:
ACTA MATERIALIA, 115 250-258; 10.1016/j.actamat.2016.05.047 AUG 15 2016
Abstract:
Subtle changes of (micro-) structure can have far-reaching consequences for magnetic shape memory (MSM) effect, also called magnetic induced reorientation (MIR). Detailed X-ray structure analysis using reciprocal mapping of Ni-Mn-Ga single crystals exhibiting MIR at room temperature and prepared in single macrotwin orientation revealed 10M modulated structure. It indicated that the modulation was harmonic, i.e. commensurate, but it also showed that the difference when compared to non commensurate mode or even to adaptive model was very small. The distinction between commensurate and non-commensurate modulation could not be reliably resolved due to large broadening of diffraction peaks. The broadening was caused by small size (less than 100 nm) of structurally coherent L2(1) ordered domains. The small size of these coherent domains is a result of large concentration of antiphase boundaries. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
The 7 x 1 Fermi Surface Reconstruction in a Two-dimensional f-electron Charge Density Wave System: PrTe3
Authors:
Lee, E; Kim, DH; Kim, HW; Denlinger, JD; Kim, H; Kim, J; Kim, K; Min, BI; Min, BH; Kwon, YS; Kang, JS Author Full Names: Lee, Eunsook; Kim, D. H.; Kim, Hyun Woo; Denlinger, J. D.; Kim, Heejung; Kim, Junwon; Kim, Kyoo; Min, B. I.; Min, B. H.; Kwon, Y. S.; Kang, J. -S.
Source:
SCIENTIFIC REPORTS, 6 10.1038/srep30318 JUL 25 2016
Abstract:
The electronic structure of a charge density wave (CDW) system PrTe3 and its modulated structure in the CDW phase have been investigated by employing ARPES, XAS, Pr 4 f RPES, and first-principles band structure calculation. Pr ions are found to be nearly trivalent, supporting the CDW instability in the metallic Te sheets through partial filling. Finite Pr 4 f spectral weight is observed near the Fermi level, suggesting the non-negligible Pr 4 f contribution to the CDW formation through the Pr 4 f-Te 5p hybridization. The two-fold symmetric features in the measured Fermi surface (FS) of PrTe3 are explained by the calculated FS for the assumed 7 x 1 CDW supercell formation in Te sheets. The shadow bands and the corresponding very weak FSs are observed, which originate from both the band folding due to the 3D interaction of Te sheets with neighboring Pr-Te layers and that due to the CDW-induced FS reconstruction. The straight vertical FSs are observed along k(z), demonstrating the nearly 2D character for the near-E-F states. The observed linear dichroism reveals the in-plane orbital character of the near-E-F Te 5p states.

Update: 11-Aug-2016

Title:
Structure and multiferroic properties of multi-doped Bi1-xErxFe0.96Mn0.02Co0.02O3 thin films
Authors:
Zheng, YJ; Tan, GQ; Xia, A; Ren, HJ Author Full Names: Zheng, Yujuan; Tan, Guoqiang; Xia, Ao; Ren, Huijun
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 684 438-444; 10.1016/j.jallcom.2016.05.193 NOV 5 2016
Abstract:
Multiferroic Bi1-xErxFe0.96Mn0.02Co0.02O3 (BExFMCO, x = 0.08-0.12) thin films have been successfully prepared on fluorine doped tin oxide (FTO) substrates by the chemical solution deposition method. The structural characteristics of the thin films were investigated by X-ray diffraction (XRD), Rietveld refinement and Raman spectra, indicating a structural transition from typical rhombohedral-R3c:H (BFO) to two-phase coexistence of triclinic-P1 and orthorhombic-Pbmn (BE0.12FMCO). XPS analyses suggest there is the coexistence of Fe2+ and Fe3+ ions in all the thin films. The multi-doping exhibits small effects on oxygen vacancies due to the complex effects of doping ions. Intensive super exchange between Fe2+ and Fe3+ and the decreased leakage current densities are observed in BE0.1FMCO thin films. Multi-doped thin films show the superior ferroelectric properties with a giant remanent polarization (the BE0.1FMCO thin film with P-r similar to 104.43 mu C/cm(2)). The enhanced ferroelectric properties of BExFMCO thin films can be mainly attributed to the structural transition via doping. The highest magnetization values of M-s similar to 9.78 emu/cm(3) and M-r similar to 2.1 emu/cm(3) are obtained in the BE0.1FMCO thin films, which can be attributed to the super exchange between Fe2+ and Fe3+ ions and the altered space modulated spin structure due to structural transition. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Chemical Pressure-Driven Incommensurability in CaPd5: Clues to High-Pressure Chemistry Offered by Complex Intermetallics
Authors:
Kilduff, BJ; Fredrickson, DC Author Full Names: Kilduff, Brandon J.; Fredrickson, Daniel C.
Source:
INORGANIC CHEMISTRY, 55 (13):6781-6793; 10.1021/acs.inorgchem.6b01124 JUL 4 2016
Abstract:
While composition and pressure are generally considered orthogonal parameters in the synthesis and optimization of solid state materials, their distinctness is blurred by the concept of chemical pressure (CP): microscopic pressure arising from lattice constraints rather than an externally applied force. In this article, we describe the first cycle of an iterative theoretical/experimental investigation into this connection. We begin by theoretically probing the ability of physical pressure to promote structural transitions in CaCu5-type phases that are driven by CP in other systems. Our results point to the instability of the reported CaCu5-type CaPd5 phase to such a transition even at ambient pressure, suggesting that new structural chemistry should arise at only modest pressures. We thus attempted to synthesize CaPd5 as a starting material for high-pressure experiments. However, rather than obtaining the expected CaCu5-type phase, we encountered crystals of an incommensurately modulated variant CaCu5+q/2, whose composition is related to its satellite spacing, q = qb(basic)* with q approximate to 0.44. Its structure was solved and refined in the (3 + 1)D superspace group Cmcm(0 beta 0)s00, revealing CaCu5-type slabs separated by distorted Pd hexagonal nets with an incommensurate periodicity. DFT-CP analysis on a commensurate model for CaPd5+q/2 indicates that the new Pd nets serve to relieve intense negative CPs that the Ca atoms would experience in a CaCu5-type CaPd5 phase but suffer from a desire to contract relative to the rest of the structure. In this way, both the Pd layer substitution and incommensurability in CaPd5+q/2 are anticipated by the CP schemes of simpler model systems, with CP quadrupoles tracing the paths of the favorable atomic motions. This picture offers predictions for how elemental substitution and physical pressure should affect these structural motifs, which could be applicable to the magnetic phase Zr2Co11 whose previously proposed structures show close parallels to CaPd5+q/2.

Update: 4-Aug-2016

Title:
Distributed Hybridization Model for Quantum Critical Behavior in Magnetic Quasicrystals
Authors:
Otsuki, J; Kusunose, H Author Full Names: Otsuki, Junya; Kusunose, Hiroaki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (7):10.7566/JPSJ.85.073712 JUL 15 2016
Abstract:
A quantum critical behavior of the magnetic susceptibility was observed in a quasicrystal containing ytterbium. At the same time, a mixed-valence feature of Yb ions was reported, which appears to be incompatible with the magnetic instability. We derive the magnetic susceptibility by expressing the quasiperiodicity as the distributed hybridization strength between Yb 4f and conduction electrons. Assuming a wide distribution of the hybridization strength, the most f electrons behave as renormalized paramagnetic states in the Kondo or mixed-valence regime, but a small number of f moments remain unscreened. As a result, the bulk magnetic susceptibility exhibits a nontrivial power-law-like behavior, while the average f-electron occupation is that of mixed-valence systems. This model thus resolves two contradictory properties of Yb quasicrystals.
Title:
Incommensurate Magnetic Structure in the Cubic Noncentrosymmetric Ternary Compound Pr5Ru3Al2
Authors:
Makino, K; Okuyama, D; Avdeev, M; Sato, TJ Author Full Names: Makino, Koya; Okuyama, Daisuke; Avdeev, Maxim; Sato, Taku J.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (7):10.7566/JPSJ.85.073705 JUL 15 2016
Abstract:
Magnetic susceptibility and neutron powder diffraction experiments have been performed on the noncentrosymmetric ternary compound Pr5Ru3Al2. The previously reported ferromagnetic transition at 24K was not detected in our improved-quality samples. Instead, magnetic ordering was observed in the DC magnetic susceptibility at T-c similar or equal to 3.8 K. The neutron powder diffraction experiment further indicates that an incommensurate magnetic structure is established below T-c with the magnetic modulation vector q similar or equal to (0.066, 0.066, 0.066) (r.l.u.). A candidate for the magnetic structure is proposed using representation analysis.
Title:
Local growth of icosahedral quasicrystalline tilings
Authors:
Hann, CT; Socolar, JES; Steinhardt, PJ Author Full Names: Hann, Connor T.; Socolar, Joshua E. S.; Steinhardt, Paul J.
Source:
PHYSICAL REVIEW B, 94 (1):10.1103/PhysRevB.94.014113 JUL 14 2016
Abstract:
Icosahedral quasicrystals (IQCs) with extremely high degrees of translational order have been produced in the laboratory and found in naturally occurring minerals, yet questions remain about how IQCs form. In particular, the fundamental question of how locally determined additions to a growing cluster can lead to the intricate long-range correlations in IQCs remains open. In answer to this question, we have developed an algorithm that is capable of producing a perfectly ordered IQC yet relies exclusively on local rules for sequential, face-to-face addition of tiles to a cluster. When the algorithm is seeded with a special type of cluster containing a defect, we find that growth is forced to infinity with high probability and that the resultant IQC has a vanishing density of defects. The geometric features underlying this algorithm can inform analyses of experimental systems and numerical models that generate highly ordered quasicrystals.
Title:
Unique magnetic structure of YbCo2Si2
Authors:
Mufti, N; Kaneko, K; Hoser, A; Gutmann, M; Geibel, C; Krellner, C; Stockert, O Author Full Names: Mufti, N.; Kaneko, K.; Hoser, A.; Gutmann, M.; Geibel, C.; Krellner, C.; Stockert, O.
Source:
PHYSICAL REVIEW B, 94 (4):10.1103/PhysRevB.94.045116 JUL 14 2016
Abstract:
We report on the results of powder and single-crystal neutron diffraction to investigate the magnetic order in YbCo2Si2 below the Neel temperature T-N = 1.7 K in detail. Two different magnetically ordered phases can clearly be distinguished. At lowest temperatures a commensurate magnetic structure with a propagation vector k(1) = (0.25 0.25 1) is found, while the intermediate phase (T > 0.9 K) is characterized by an incommensurate magnetic structure with k(2) = (0.25 0.086 1). The magnetic structure in YbCo2Si2 is in marked contrast to all other known RCo2Si2 compounds (R = rare earth element) likely due to some itineracy of the Yb 4f states being responsible for the magnetism.
Title:
Reinterpretation of the zero-temperature conductivity in icosahedral AlPdRe
Authors:
Rapp, O Author Full Names: Rapp, O.
Source:
PHYSICAL REVIEW B, 94 (2):10.1103/PhysRevB.94.024202 JUL 13 2016
Abstract:
The zero-temperature conductivity sigma(0) of icosahedral (i)-AlPdRe has been found to be simply related to the resistance ratio R = rho(4.2 K)/rho(295 K) by a power law, sigma(0) similar to R (1.74), over four orders of magnitude in sigma(0). This relation includes metallic single grain samples, and polygrain samples of different morphologies which are metallic for small R values, and insulatinglike at large R. Electronic transport properties of single grain i-AlPdRe samples are thus found to be on common ground with polygrain i-AlPdRe. The relation between R and sigma(0) can be qualitatively understood from published band-structure calculations on quasicrystalline approximants.
Title:
Commensurate and incommensurate magnetic order in spin-1 chains stacked on the triangular lattice in Li2NiW2O8
Authors:
Ranjith, KM; Nath, R; Majumder, M; Kasinathan, D; Skoulatos, M; Keller, L; Skourski, Y; Baenitz, M; Tsirlin, AA Author Full Names: Ranjith, K. M.; Nath, R.; Majumder, M.; Kasinathan, D.; Skoulatos, M.; Keller, L.; Skourski, Y.; Baenitz, M.; Tsirlin, A. A.
Source:
PHYSICAL REVIEW B, 94 (1):10.1103/PhysRevB.94.014415 JUL 13 2016
Abstract:
We report the thermodynamic properties, magnetic ground state, and microscopic magnetic model of the spin-1 frustrated antiferromagnet Li2NiW2O8, showing successive transitions at T-N1 similar or equal to 18 K and T-N2 similar or equal to 12.5 K in zero field. Nuclear magnetic resonance and neutron diffraction reveal collinear and commensurate magnetic order with the propagation vector k = (1/2,0,1/2) below T-N2. The ordered moment of 1.8 mu(B) at 1.5 K is directed along [0.89(9), - 0.10(5), - 0.49(6)] and matches the magnetic easy axis of spin-1 Ni2+ ions, which is determined by the scissor-like distortion of the NiO6 octahedra. Incommensurate magnetic order, presumably of spin-density-wave type, is observed in the region between T-N2 and T-N1. Density-functional band-structure calculations put forward a three-dimensional spin lattice with spin-1 chains running along the [01 (1) over bar] direction and stacked on a spatially anisotropic triangular lattice in the ab plane. We show that the collinear magnetic order in Li2NiW2O8 is incompatible with the triangular lattice geometry and thus driven by a pronounced easy-axis single-ion anisotropy of Ni2+.
Title:
Static magnetic order on the metallic triangular lattice in CrSe2 detected by mu+SR
Authors:
Sugiyama, J; Nozaki, H; Umegaki, I; Uyama, T; Miwa, K; Brewer, JH; Kobayashi, S; Michioka, C; Ueda, H; Yoshimura, K Author Full Names: Sugiyama, Jun; Nozaki, Hiroshi; Umegaki, Izumi; Uyama, Takeshi; Miwa, Kazutoshi; Brewer, Jess H.; Kobayashi, Shintaro; Michioka, Chishiro; Ueda, Hiroaki; Yoshimura, Kazuyoshi
Source:
PHYSICAL REVIEW B, 94 (1):10.1103/PhysRevB.94.014408 JUL 7 2016
Abstract:
The magnetic nature of a metallic two-dimensional triangular compound, CrSe2, has been investigated by muon spin rotation and relaxation (mu+SR) measurements using both powder and single crystal samples. It is found that CrSe2 enters into a static antiferromagnetic (AF) ordered state below 157 K (=T-N). Furthermore, the AF state is slightly changed below around 20 K (=T-N2). Based on the analysis of the internal magnetic fields at the muon sites predicted with DFT calculations, collinear AF and helical 120 degrees AF are clearly eliminated for the ground state of CrSe2. The most probable one is an incommensurate spin density wave order.
Title:
Atomic structure and phason modes of the Sc-Zn icosahedral quasicrystal
Authors:
Yamada, T; Takakura, H; Euchner, H; Gomez, CP; Bosak, A; Fertey, P; de Boissieu, M Author Full Names: Yamada, Tsunetomo; Takakura, Hiroyuki; Euchner, Holger; Gomez, Cesar Pay; Bosak, Alexei; Fertey, Pierre; de Boissieu, Marc
Source:
IUCRJ, 3 247-258; 10.1107/S2052252516007041 4 JUL 2016
Abstract:
The detailed atomic structure of the binary icosahedral (i) ScZn7.33 quasicrystal has been investigated by means of high-resolution synchrotron single-crystal X-ray diffraction and absolute scale measurements of diffuse scattering. The average atomic structure has been solved using the measured Bragg intensity data based on a six-dimensional model that is isostructural to the i-YbCd5.7 one. The structure is described with a quasiperiodic packing of large Tsai-type rhombic triacontahedron clusters and double Friauf polyhedra (DFP), both resulting from a close-packing of a large (Sc) and a small (Zn) atom. The difference in chemical composition between i-ScZn7.33 and i-YbCd5.7 was found to lie in the icosahedron shell and the DFP where in i-ScZn7.33 chemical disorder occurs on the large atom sites, which induces a significant distortion to the structure units. The intensity in reciprocal space displays a substantial amount of diffuse scattering with anisotropic distribution, located around the strong Bragg peaks, that can be fully interpreted as resulting from phason fluctuations, with a ratio of the phason elastic constants K-2/K-1 = -0.53, i.e. close to a threefold instability limit. This induces a relatively large perpendicular (or phason) Debye-Waller factor, which explains the vanishing of 'high-Q(perp)' reflections.
Title:
Mysteries of icosahedral quasicrystals: how are the atoms arranged?
Authors:
Ishimasa, T Author Full Names: Ishimasa, Tsutomu
Source:
IUCRJ, 3 230-231; 10.1107/S2052252516009842 4 JUL 2016

Update: 28-Jul-2016

Title:
Defects forming the optical absorption edge in TlGaSe2 layered crystal
Authors:
Seyidov, MY; Suleymanov, RA; Sale, Y Author Full Names: Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Sale, Yasin
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 96-97 17-21; 10.1016/j.jpcs.2016.04.009 SEP-OCT 2016
Abstract:
In this work, we present the results of optical experiments designed to investigate the changes in optical absorption spectra of TlGaSe2 ferroelectric-semiconductor with incommensurate (INC) phase in experimental conditions where crystal is kept several hours within the INC-phase (the regime of so called "memory" effect). The fundamental absorption of TlGaSe2, experimentally investigated by optical transmission measurements performed in the temperature range 15-300 K. An extraordinary modification of the optical absorption edge in the range of Urbach's tail is discovered as a result of the annealing within the INC-phase. The role of native defects forming the band edge in the observed phenomena in TlGaSe2 is discussed. (C) 2016 Elsevier Ltd. All rights reserved.
Title:
Phase transitions and magnetic structures in MnW1-xMoxO4 compounds (x <= 0.2)
Authors:
Hardy, V; Payen, C; Damay, F; Meddar, L; Josse, M; Andre, G Author Full Names: Hardy, Vincent; Payen, Christophe; Damay, Francoise; Meddar, Lynda; Josse, Michael; Andre, Gilles
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (33):10.1088/0953-8984/28/33/336003 AUG 24 2016
Abstract:
Temperature-dependent specific heat, magnetization and neutron diffraction data have been collected in zero magnetic field for polycrystalline samples of MnW1-xMoxO4 (x <= 0.2) solid solution whose end-member MnWO4 exhibits a magnetoelectric multiferroic phase (AF2 phase) between T-1 approximate to 8 K and T-2 = 12.5 K. In MnW1-xMoxO4, diamagnetic W6+ are replaced with diamagnetic Mo6+ cations and magnetic couplings among Mn2+ (3d(5), S = 5/2) ions are modified due the doping-induced tuning of the orbital hybridization between Mn 3d and O 2p states. It was observed that magnetic phase transition temperatures which are associated with the second-order AF3-to-paramagnetic (T-N) and AF2-to-AF3 (T-2) transitions in pure MnWO4 slightly increase with the Mo content x. Magnetic specific heat data also indicate that the first-order AF1-to-AF2 phase transition at T-1 survives a weak doping x <= 0.05. This latter phase transition becomes invisible above the base temperature 2 K for higher level of doping x >= 0.10. Neutron powder diffraction datasets collected above 1.5 K for a sample of MnW0.8Mo0.2O4 were analyzed using the Rietveld method. The magnetic structure below approximate to 14 K is a helical incommensurate spin order with a temperature-independent propagation vector k = (-0.217(6), 0.5, 0.466(4)). This cycloidal magnetic structure is similar to the polar AF2 structure observed in MnWO4. The AF1 up-up-down-down collinear spin arrangement observed in MnWO4 is absent in our MnW0.8Mo0.2O4 sample.
Title:
Shock synthesis of quasicrystals with implications for their origin in asteroid collisions
Authors:
Asimow, PD; Lin, C; Bindi, L; Ma, C; Tschauner, O; Hollister, LS; Steinhardt, PJ Author Full Names: Asimow, Paul D.; Lin, Chaney; Bindi, Luca; Ma, Chi; Tschauner, Oliver; Hollister, Lincoln S.; Steinhardt, Paul J.
Source:
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 113 (26):7077-7081; 10.1073/pnas.1600321113 JUN 28 2016
Abstract:
We designed a plate impact shock recovery experiment to simulate the starting materials and shock conditions associated with the only known natural quasicrystals, in the Khatyrka meteorite. At the boundaries among CuAl5, (Mg0.75Fe0.252+)(2)SiO4 olivine, and the stainless steel chamber walls, the recovered specimen contains numerous micron-scale grains of a quasicrystalline phase displaying face-centered icosahedral symmetry and low phason strain. The compositional range of the icosahedral phase is Al68-73Fe11-16Cu10-12Cr1-4Ni1-2 and extends toward higher Al/(Cu+Fe) and Fe/Cu ratios than those reported for natural icosahedrite or for any previously known synthetic quasicrystal in the Al-Cu-Fe system. The shock-induced synthesis demonstrated in this experiment reinforces the evidence that natural quasicrystals formed during a shock event but leaves open the question of whether this synthesis pathway is attributable to the expanded thermodynamic stability range of the quasicrystalline phase at high pressure, to a favorable kinetic pathway that exists under shock conditions, or to both thermodynamic and kinetic factors.
Title:
Dynamic stabilities of icosahedral-like clusters and their ability to form quasicrystals
Authors:
Liang, XG; Hamid, I; Duan, HM Author Full Names: Liang, Xiaogang; Hamid, Ilyar; Duan, Haiming
Source:
AIP ADVANCES, 6 (6):10.1063/1.4954741 JUN 2016
Abstract:
The dynamic stabilities of the icosahedral-like clusters containing up to 2200 atoms are investigated for 15 metal elements. The clusters originate from five different initial structures (icosahedron, truncated decahedron, octahedron, closed-shell fragment of an HCP structure, and non-closed-shell fragment of an HCP structure). The obtained order of the dynamic stabilities of the icosahedral-like clusters can be assigned to three groups, from stronger to weaker, according to the size ranges involved: (Zr, Al, Ti) > (Cu, Fe, Co, Ni, Mg, Ag) > (Pb, Au, Pd, Pt, Rh, Ir), which correspond to the predicted formation ability of the quasicrystals. Thedifferences of the sequences can be explained by analyzing the parameters of the Gupta-type manybody inter-atomic potentials. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Update: 22-Jul-2016

Title:
Complex incommensurate helicoidal magnetic ordering of EuNiGe3
Authors:
Ryan, DH; Cadogan, JM; Rejali, R; Boyer, CD Author Full Names: Ryan, D. H.; Cadogan, J. M.; Rejali, Rasa; Boyer, C. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (26):10.1088/0953-8984/28/26/266001 JUL 6 2016
Abstract:
Eu-151 Mossbauer spectroscopy and neutron powder diffraction are combined to show that the tetragonal (I4mm #107) compound EuNiGe3 orders magnetically below T-N similar to 14 K and adopts a complex incommensurate helicoidal magnetic structure at 3.6 K, with a propagation vector k =[0.255(1), 0.054(14), 0] and a Eu moment of 7.1(2)mu B. On warming through 6 K an incommensurate sinusoidal modulation develops and dominates the magnetic order by 12 K.

Update: 14-Jul-2016

Title:
Microstructural control and hardening response of Mg-6Zn-0.5Er-0.5Ca alloy
Authors:
Zheng, XB; Liu, K; Wang, ZH; Li, SB; Du, WB Author Full Names: Zheng, Xiao-Bing; Liu, Ke; Wang, Zhao-Hui; Li, Shu-Bo; Du, Wen-Bo
Source:
RARE METALS, 35 (7):526-531; 10.1007/s12598-015-0462-0 JUL 2016
Abstract:
The effects of heat treatment on microstructures and hardening response of Mg-6Zn-0.5Er-0.5Ca (wt%) alloy were investigated by optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM) in this paper. The results show that the Mg-6Zn-0.5Er-0.5Ca alloy contains Mg3Zn6Er1 quasicrystalline phase (I-phase) and Ca2Mg6Zn3 phase under as-cast condition. Most of the Ca2Mg6Zn3 phases and I-phases dissolve into matrix during heat treatment at 475 degrees C for 5 h. After the as-solution alloy was aged at 175 degrees C for 36 h, a large amount of MgZn2 precipitate with several nanometers precipitate. It is suggested that the trace addition of Ca results in refining the size of the precipitate, and the presence of the nanoscale MgZn2 phase is the main factor to improve the peak-aged hardness greatly to 87 HV, which increases about 40 % compared with that of as-cast alloy.
Title:
Atomistic simulation of frictional anisotropy on quasicrystal approximant surfaces
Authors:
Ye, ZJ; Martini, A; Thiel, P; Lovelady, HH; McLaughlin, K; Rabson, DA Author Full Names: Ye, Zhijiang; Martini, Ashlie; Thiel, Patricia; Lovelady, Heather H.; McLaughlin, Keith; Rabson, David A.
Source:
PHYSICAL REVIEW B, 93 (23):10.1103/PhysRevB.93.235438 JUN 23 2016
Abstract:
J. Y. Park et al. [Science 309, 1354 (2005)] have reported eight times greater atomic-scale friction in the periodic than in the quasiperiodic direction on the twofold face of a decagonal Al-Ni-Co quasicrystal. We present results of molecular-dynamics simulations intended to elucidate mechanisms behind this giant frictional anisotropy. Simulations of a bare atomic-force-microscope tip on several model substrates and under a variety of conditions failed to reproduce experimental results. On the other hand, including the experimental passivation of the tip with chains of hexadecane thiol, we reproduce qualitatively the experimental anisotropy in friction, finding evidence for entrainment of the organic chains in surface furrows parallel to the periodic direction.
Title:
Magnetic correlations in a periodic Anderson model with nonuniform conduction electron coordination
Authors:
Hartman, N; Chiu, WT; Scalettar, RT Author Full Names: Hartman, N.; Chiu, W. -T.; Scalettar, R. T.
Source:
PHYSICAL REVIEW B, 93 (23):10.1103/PhysRevB.93.235143 JUN 21 2016
Abstract:
The periodic Anderson model is widely studied to understand strong correlation physics and especially the competition of antiferromagnetism and singlet formation. In this paper we extend quantum Monte Carlo work on lattices with uniform numbers of neighbors to geometries in which the conduction electron sites can have variable coordination z. This situation is relevant both to recently discovered magnetic quasicrystals and also to magnetism in doped heavy fermion systems. Our key results are the presence of antiferromagnetic order at weak interorbital hybridization Vfd, and a delay in singlet formation to larger values of Vfd on sites with larger z. The staggered magnetization tends to be larger on sites with higher z, providing insight into the behavior to be expected in crown, dice, and CaVO lattices.
Title:
Weak crystallization theory of metallic alloys
Authors:
Martin, I; Gopalakrishnan, S; Demler, EA Author Full Names: Martin, Ivar; Gopalakrishnan, Sarang; Demler, Eugene A.
Source:
PHYSICAL REVIEW B, 93 (23):10.1103/PhysRevB.93.235140 JUN 20 2016
Abstract:
Crystallization is one of the most familiar, but hardest to analyze, phase transitions. The principal reason is that crystallization typically occurs via a strongly first-order phase transition, and thus rigorous treatment would require comparing energies of an infinite number of possible crystalline states with the energy of liquid. A great simplification occurs when crystallization transition happens to be weakly first order. In this case, weak crystallization theory, based on unbiased Ginzburg-Landau expansion, can be applied. Even beyond its strict range of validity, it has been a useful qualitative tool for understanding crystallization. In its standard form, however, weak crystallization theory cannot explain the existence of a majority of observed crystalline and quasicrystalline states. Here we extend the weak crystallization theory to the case of metallic alloys. We identify a singular effect of itinerant electrons on the form of weak crystallization free energy. It is geometric in nature, generating strong dependence of free energy on the angles between ordering wave vectors of ionic density. That leads to stabilization of fcc, rhombohedral, and icosahedral quasicrystalline (iQC) phases, which are absent in the generic theory with only local interactions. As an application, we find the condition for stability of iQC that is consistent with the Hume-Rothery rules known empirically for the majority of stable iQC; namely, the length of the primary Bragg-peak wave vector is approximately equal to the diameter of the Fermi sphere.
Title:
Effect of MWNTs-addition on cathodic performance of Ti-V-Ni composites for Ni-MH batteries
Authors:
Lin, J; Sun, LS; Liang, F; Wu, YM; Cao, ZY; Wang, LM Author Full Names: Lin, Jing; Sun, Lianshan; Liang, Fei; Wu, Yaoming; Cao, Zhanyi; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 41 (22):9471-9475; 10.1016/j.ijhydene.2016.03.211 JUN 15 2016
Abstract:
Composites of Ti1.4V0.6Ni alloy and various amounts of multiwalled carbon nanotubes (MWNTs) have been synthesized by high energy mechanical ball-milling method. The composites mainly contain icosahedral quasicrystal and TiNi-type phases. In contrast to Ti1.4V0.6Ni, all milled composites have excellent activation properties activated at the first charge/discharge cycle, together with excellent rate discharge abilities. The composites are able to deliver outstanding maximum discharge capacities of 295.5 mAh g(-1) enhanced by 68.2 mAh g(-1) in comparison to Ti1.4V0.6Ni alloy, and good cycling stabilities with capacity retention of more than 40% after 100 charge/discharge cycles higher than Ti1.4V0.6Ni alloy. Experimental and theoretical investigations suggest that the unusual electrochemical performance of this composite is depended on the copacetic electrocatalytic activity of MWNTs addition and the enhancement of hydrogen diffusion progress. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Title:
Fundamental solutions and analysis of three-dimensional cracks in one-dimensional hexagonal piezoelectric quasicrystals
Authors:
Fan, CY; Li, Y; Xu, GT; Zhao, MH Author Full Names: Fan, CuiYing; Li, Yuan; Xu, GuangTao; Zhao, MingHao
Source:
MECHANICS RESEARCH COMMUNICATIONS, 74 39-44; 10.1016/j.mechrescom.2016.03.009 JUN 2016
Abstract:
In this study, three-dimensional cracks in one-dimensional hexagonal piezoelectric quasicrystals are investigated. Based on the general solutions and Hankel transform, the fundamental solutions for unit point extended displacement discontinuities (including the phonon and phason displacement discontinuities and the electric potential discontinuity) are derived. The extended displacement discontinuity boundary integral equations for a planar crack of arbitrary shape in the periodic plane of one-dimensional hexagonal piezoelectric quasicrystals are established in terms of the extended displacement discontinuities. Using the boundary integral equation method, the singularities of near-crack border fields are obtained and the stress and electric displacement intensity factors are derived. (C) 2016 Elsevier Ltd. All rights reserved.

Update: 7-Jul-2016

Title:
Characterization of SrBiMn2-xTixO6 perovskites: Local ordering influence on the dielectric and magnetic response
Authors:
Alonso-Dominguez, D; Alvarez-Serrano, I; Lopez, ML; Cuello, GJ; Asensio, E; Garcia-Hernandez, M; Veiga, ML; Pico, C Author Full Names: Alonso-Dominguez, D.; Alvarez-Serrano, I.; Lopez, M. L.; Cuello, Gabriel J.; Asensio, Eloy; Garcia-Hernandez, Mar; Veiga, M. L.; Pico, C.
Source:
CERAMICS INTERNATIONAL, 42 (10):11889-11900; 10.1016/j.ceramint.2016.04.111 AUG 1 2016
Abstract:
Two new phases in the (SrTiO3)-(BiMnO3) perovskite type system were studied. These SrBiMn2-xTixO6 (x=0.5 and 0.75) ceramics were prepared by the liquid-mix method as polycrystalline powders. They were characterized by neutron diffraction (ND), electrical and magnetic measurements and these results were analysed in connection with the x=0.25 phase, previously described by us. Their crystal structures were fitted in the tetragonal 14/mcm space group, with additional superstructure reflections suggesting local ordering. Electron microscopy results revealed these ordering effects are actually present concerning both perovskite sublattices. The electrical response pointed to a mechanism consisting in variable range hopping of polarons. A relaxor ferroelectric behaviour dependent on the pellets thickness was found with T-m in the 140-240 K range. The magnetic structures imply an incommensurable modulation of the magnetic moments along the c or a directions, depending on the substitution degree x. A cluster picture in terms of chemically different nanoregions responsible of the macroscopic response is discussed. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Title:
Quasicrystallinity expressed in two-dimensional coordination networks
Authors:
Urgel, JI; Ecija, D; Lyu, GQ; Zhang, R; Palma, CA; Auwarter, W; Lin, NA; Barth, JV Author Full Names: Urgel, Jose I.; Ecija, David; Lyu, Guoqing; Zhang, Ran; Palma, Carlos-Andres; Auwaerter, Willi; Lin, Nian; Barth, Johannes V.
Source:
NATURE CHEMISTRY, 8 (7):657-662; 10.1038/nchem.2507 JUL 2016
Abstract:
The recognition of quasicrystals, which exhibit long-range order but lack translational symmetry, represented both the introduction of a new class of materials and a transformative breakthrough in crystallography. Concomitant with the exploration of quasicrystallinity, metal-organic architectures emerged as promising and versatile systems with significant application potential. Their building principles have been studied extensively and become manifest in a multitude of intricate amorphous and crystalline phases. To date, however, indications for quasicrystalline order have been elusive in metal-organic coordination networks (MOCNs). Here we employ rare-earth-directed assembly to construct a two-dimensional tiling with quasicrystalline characteristics at a well-defined gold substrate. By careful stoichiometry control over europium centres and functional linkers, we produced a porous network, including the simultaneous expression of four-fold, five-fold and six-fold vertices. The pertaining features were directly inspected by scanning tunnelling microscopy, and the molecule-europium reticulation was recognized as square-triangle tessellation with dodecagonal symmetry. Our findings introduce quasicrystallinity in surface-confined MOCNs with a nanoporous structure and anticipate functionalities that arise from quasicrystalline ordering of the coordinative spheres.
Title:
Microstructure and mechanical properties of aluminium matrix composites reinforced by Al62Cu25.5Fe12.5 melt spun ribbon
Authors:
Litynska-Dobrzynska, L; Mitka, M; Goral, A; Stan-Glowinska, K; Dutkiewicz, J Author Full Names: Litynska-Dobrzynska, Lidia; Mitka, Mikolaj; Goral, Anna; Stan-Glowinska, Katarzyna; Dutkiewicz, Jan
Source:
MATERIALS CHARACTERIZATION, 117 127-133; 10.1016/j.matchar.2016.04.025 JUL 2016
Abstract:
Aluminium matrix composites containing 15, 30 and 50 vol.% of pulverized Al62Cu25.5Fe12.5 (in at.%) melt spun ribbons have been prepared by a vacuum hot pressing (T = 673 K, P = 600 MPa). The microstructure of the initial ribbon and the composites was investigated using X-ray, scanning and transmission electron microscopy. In the as-spun ribbon the quasicrystalline icosahedral phase (i-phase) coexisted with the cubic copper rich beta-Al(Cu, Fe) intermetallic compound. The phase composition of Al-Cu-Fe particles changed after consolidation process and the i-phase transformed partially to the omega-Al70Cu20Fe10 phase. Additionally, the Theta-Al2Cu phase formed at the alpha(Al)/Al-Cu-Fe particle interfaces. With an increase in volume fraction of the reinforcement the hardness of the composites increased up to HV = 180 for the highest amount of added particles. The ultimate compression strength of the same sample reached the value of 545 MPa. (C) 2016 Elsevier Inc. All rights reserved.
Title:
Exploring metamagnetism of single crystalline EuNiGe3 by neutron scattering
Authors:
Fabreges, X; Gukasov, A; Bonville, P; Maurya, A; Thamizhavel, A; Dhar, SK Author Full Names: Fabreges, X.; Gukasov, A.; Bonville, P.; Maurya, A.; Thamizhavel, A.; Dhar, S. K.
Source:
PHYSICAL REVIEW B, 93 (21):10.1103/PhysRevB.93.214414 JUN 15 2016
Abstract:
We present here a neutron diffraction study, both in zero field and as a function of magnetic field, of the magnetic structure of the tetragonal intermetallic EuNiGe3 on a single crystalline sample. This material is known to undergo a cascade of transitions, first at 13.2 K towards an incommensurate modulated magnetic structure, then at 10.5 K to an antiferromagnetic structure. We show here that the low-temperature phase presents a spiral moment arrangement with wave vector k = (1/4, delta, 0). For a magnetic field applied along the tetragonal c axis, the square root of the scattering intensity of the (1 0 1) reflection matches very well the complex metamagnetic behavior of the magnetization along c measured previously. For the magnetic field applied along the b axis, two magnetic transitions are observed below the transition to a fully polarized state.
Title:
Commensurate and incommensurate spin-density waves in heavy electron systems
Authors:
Schlottmann, P Author Full Names: Schlottmann, P.
Source:
AIP ADVANCES, 6 (5):10.1063/1.4942549 MAY 2016
Abstract:
The nesting of the Fermi surfaces of an electron and a hole pocket separated by a nesting vector Q and the interaction between electrons gives rise to itinerant antiferromagnetism. The order can gradually be suppressed by mismatching the nesting and a quantum critical point (QCP) is obtained as the Neel temperature tends to zero. The transfer of pairs of electrons between the pockets can lead to a superconducting dome above the QCP (if Q is commensurate with the lattice, i.e. equal to G/2). If the vector Q is not commensurate with the lattice there are eight possible phases: commensurate and incommensurate spin and charge density waves and four superconductivity phases, two of them with modulated order parameter of the FFLO type. The renormalization group equations are studied and numerically integrated. A re-entrant SDW phase (either commensurate or incommensurate) is obtained as a function of the mismatch of the Fermi surfaces and the magnitude of vertical bar Q - G/2 vertical bar. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Update: 30-Jun-2016

Title:
The Z '=12 superstructure of A-cobalt(III) sepulchrate trinitrate governed by C-H center dot center dot center dot O hydrogen bonds
Authors:
Dey, S; Schonleber, A; Mondal, S; Prathapa, SJ; van Smaalen, S; Larsen, FK Author Full Names: Dey, Somnath; Schoenleber, Andreas; Mondal, Swastik; Prathapa, Siriyara Jagannatha; van Smaalen, Sander; Larsen, Finn Krebs
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 372-380; 10.1107/S2052520616005503 3 JUN 2016
Abstract:
A-Cobalt(III) sepulchrate trinitrate crystallizes in P6(3)22 with Z = 2 (Z' = 1/6) at room temperature. Slabs perpendicular to the hexagonal axis comprise molecules Co(sepulchrate) alternating with nitrate groups A and B. Coordinated by six sepulchrate molecules, highly disordered nitrate groups C are accommodated between the slabs. Here we report the fully ordered, low temperature crystal structure of Co(sep)(NO3)(3). It is found to be a high-Z' structure with Z' = 12 of the 12-fold 6a(h) x root 3b(h) x c(h) superstructure with monoclinic symmetry P2(1) (c unique). Correlations between structural parameters are effectively removed by refinements within the superspace approach. Superstructure formation is governed by a densification of the packing in conjunction with ordering of nitrate group C, the latter assuming different orientations for each of the Z' = 12 independent copies in the superstructure. The Co(sep) moiety exhibits small structural variations over its 12 independent copies, while orientations of nitrate groups A and B vary less than the orientations of the nitrate group C do. Molecular packing in the superstructure is found to be determined by short C-H center dot center dot center dot H-C contacts, with H center dot center dot center dot H distances of 2.2-2.3 angstrom, and by short C H center dot center dot center dot O contacts, with H center dot center dot center dot O distances down to 2.2 angstrom. These contacts presumably represent weak C-H center dot center dot center dot O hydrogen bonds, but in any case they prevent further densification of the structure and strengthening of weak N-H center dot center dot center dot O hydrogen bonds with observed H center dot center dot center dot O distances of 2.4-2.6 angstrom.
Title:
New insight on bismuth cuprates with incommensurate modulated structures
Authors:
Mironov, AV; Petricek, V; Khasanova, NR; Antipov, EV Author Full Names: Mironov, Andrei V.; Petricek, Vaclav; Khasanova, Nellie R.; Antipov, Evgeny V.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 395-403; 10.1107/S2052520616005643 3 JUN 2016
Abstract:
The incommensurate modulated crystal structure of Bi2.27Sr1.73CuO6+delta (2201) phase [a = 5.3874 (5), b = 5.3869 (4), c = 24.579 (3) angstrom; beta = 90.01 (1)degrees, q = 0.2105 (3)a* + 0.538 (4)c*, Z = 4, the (3 + 1) -dimensional monoclinic A2/a(alpha 0 gamma) group] has been refined with R = 0.041, wR = 0.052 from X-ray single-crystal data including up to third-order satellite reflections. The same structure has also been considered as incommensurate composite with a(2) = 2.437, b(2) = 5.387, c(2) = 24.614, beta(2) = 93.06, q(2) = 0.4524a(2)* -0.243c(2)* and the (3 + 1)-dimensional A2/m(alpha 0 gamma)0s group for the second component. Both approaches give quite similar results. The structure possesses oxygen disorder in the oxygen-rich region of the BiO layer. An extra 0 atom is determined in the bridging position shifted similar to 0.6 angstrom from BiO towards the SrO layer. Its presence is the cause of the tremendous increase of the bismuth U-11 atomic displacement parameter in similar to 20% of the unit cells (t = -0.05-0.15). Vacancies are determined in the oxygen site of the SrO layer, which may result in the oxygen content variation with annealing at different oxygen pressures. The total refined oxygen content 6.18 (1) corresponds to the results of chemical analysis.

Update: 23-Jun-2016

Title:
Thermo-mechanical study of bulk glass forming Zr-Cu-Ni-Al alloys
Authors:
Spassov, T; Gyurov, S; Stefanov, G; Rangelov, A; Drenchev, L; Russew, K Author Full Names: Spassov, Tony; Gyurov, Stoyko; Stefanov, Georgi; Rangelov, Antoan; Drenchev, Lyudmil; Russew, Krassimir
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 443 103-107; 10.1016/j.jnoncrysol.2016.04.006 JUL 1 2016
Abstract:
The thermal stability and viscous flow behavior of bulk glass forming Zr(68)Cu(13)Ni(11.5)A(17.5) and Zr69Cu12.5Ni11Al7.5 alloys are studied. The viscosity experimental results are interpreted based on the free volume model (FVM). The values of the obtained model parameters are used to estimate the glass forming ability (GFA) in terms of Angell parameter, and the fracture strength of the alloys based on its correlation with the glass transition temperature (T-g). The viscosity data are compared with DSC measurements. The two glasses, having similar composition, revealed comparable T-g, but one of them (Zr68Cu13Ni11.5Al7.5) showed substantially lower crystallization temperature due to quasicrystals formation. Higher GFA was obtained for Zr69Cu12.5Ni11Al7.5 alloy. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Origin of Quantum Criticality in Yb-Al-Au Approximant Crystal and Quasicrystal
Authors:
Watanabe, S; Miyake, K Author Full Names: Watanabe, Shinji; Miyake, Kazumasa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (6):10.7566/JPSJ.85.063703 JUN 15 2016
Abstract:
To get insight into the mechanism of emergence of unconventional quantum criticality observed in quasicrystal Yb15Al34Au51, the approximant crystal Yb14Al35Au51 is analyzed theoretically. By constructing a minimal model for the approximant crystal, the heavy quasiparticle band is shown to emerge near the Fermi level because of strong correlation of 4f electrons at Yb. We find that charge-transfer mode between 4f electron at Yb on the 3rd shell and 3p electron at Al on the 4th shell in Tsai-type cluster is considerably enhanced with almost flat momentum dependence. The mode-coupling theory shows that magnetic as well as valence susceptibility exhibits chi similar to T-0.5 for zero-field limit and is expressed as a single scaling function of the ratio of temperature to magnetic field T/B over four decades even in the approximant crystal when some condition is satisfied by varying parameters, e.g., by applying pressure. The key origin is clarified to be due to strong locality of the critical Yb-valence fluctuation and small Brillouin zone reflecting the large unit cell, giving rise to the extremely-small characteristic energy scale. This also gives a natural explanation for the quantum criticality in the quasicrystal corresponding to the infinite limit of the unit-cell size.
Title:
Pressure-Driven Quantum Criticality and T/H Scaling in the Icosahedral Au-Al-Yb Approximant
Authors:
Matsukawa, S; Deguchi, K; Imura, K; Ishimasa, T; Sato, NK Author Full Names: Matsukawa, Shuya; Deguchi, Kazuhiko; Imura, Keiichiro; Ishimasa, Tsutomu; Sato, Noriaki K.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (6):10.7566/JPSJ.85.063706 JUN 15 2016
Abstract:
We report on ac magnetic susceptibility measurements under pressure of the Au-Al-Yb alloy, a crystalline approximant to the icosahedral quasicrystal that shows unconventional quantum criticality. In describing the susceptibility as chi(T)(-1) - chi(0)(-1) alpha T-gamma, we find that chi(0)(-1) decreases with increasing pressure and vanishes to zero at the critical pressure P-c similar or equal to 2 GPa, with gamma (similar or equal to 0.5) unchanged. We suggest that this quantum criticality emerges owing to critical valence fluctuations. Above P-c, the approximant undergoes a magnetic transition at T similar or equal to 100 mK. These results are contrasted with the fact that, in the quasicrystal, the quantum criticality is robust against the application of pressure. The applicability of the so-called T/H scaling to the approximant is also discussed.
Title:
d-Density Wave Scenario Description of the New Hidden Charge Order in Cuprates
Authors:
Makhfudz, I Author Full Names: Makhfudz, Imam
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (6):10.7566/JPSJ.85.064701 JUN 15 2016
Abstract:
In this paper, we show that the theory of high T-c superconductivity based on a microscopic model with d-density wave (DDW) scenario in the pseudogap phase is able to reproduce some of the most important features of the recent experimentally discovered hidden charge order in several families of Cuprates. In particular, by computing and comparing energies of charge orders of different modulation directions derived from a full microscopic theory with d-density wave scenario, the axial charge order phi(X(Y)) with wavevector Q = (Q(0), 0)((0, Q(0))) is shown to be unambiguously energetically more favorable over the diagonal charge order phi(X+Y) with wavevector Q = (Q(0), +/- Q(0)) at least in commensurate limit, to be expected also to hold even to more general incommensurate case, in agreement with experiment. The two types of axial charge order phi(X) and phi(Y) are degenerate by symmetry. We find that within the superconducting background, biaxial (checkerboard) charge order is energetically more favorable than uniaxial (stripe) charge order, and therefore checkerboard axial charge order should be the one observed in experiments, assuming a single domain of charge ordered state on each CuO2 plane.
Title:
Superlubricity in quasicrystalline twisted bilayer graphene
Authors:
Koren, E; Duerig, U Author Full Names: Koren, Elad; Duerig, Urs
Source:
PHYSICAL REVIEW B, 93 (20):10.1103/PhysRevB.93.201404 MAY 31 2016
Abstract:
The unique atomic positions in quasicrystals lead to peculiar self-similarity and fractal-like structural morphology. Accordingly, many of the material properties are supposed to manifest exceptional characteristics. In this Rapid Communication, we explain through numerical simulations the fundamental and peculiar aspects of quasicrystals wearless friction manifested in a 30 degrees twisted bilayer graphene system. In particular, the sliding force exhibits a fractal structure with distinct area correlations due to the natural mixture between both periodic and aperiodic lateral modulations. In addition, zero power scaling of the sliding force with respect to the contact area is demonstrated for a geometric sequence of dodecagonal elements.
Title:
Temperature dependences of the electric polarization and wave number of incommensurate structures in multiferroics
Authors:
Pikin, SA Author Full Names: Pikin, S. A.
Source:
CRYSTALLOGRAPHY REPORTS, 61 (3):449-455; 10.1134/S1063774516030214 MAY 2016
Abstract:
It is shown that the electric polarization and wave number of incommensurate modulations, proportional to each other, increase according to the Landau law in spin multiferroic cycloids near the N,el temperature. In this case, the constant magnetization component (including the one for a conical spiral) is oriented perpendicular to the spin incommensurability wave vector. A similar temperature behavior should manifest itself for spin helicoids, the axes of which are oriented parallel to the polarization vector but their spin rotation planes are oriented perpendicular to the antiferromagnetic order plane. When the directions of axes of the magnetization helicoid and polarization vector coincide, the latter is quadratic with respect to magnetization and linearly depends on temperature, whereas the incommensurate-modulation wave number barely depends on temperature. Structural distortions of unit cells for multiferroics of different types determine their axial behavior.

Update: 20-Jun-2016

Title:
Determination of shapes and preferred growth directions of icosahedral quasicrystals from the 2D-sections
Authors:
Zupanic, F; Boncina, T Author Full Names: Zupanic, Franc; Boncina, Tonica
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 681 532-540; 10.1016/j.allcom.2016.04.255 OCT 5 2016
Abstract:
The icosahedral quasicrystalline phases have been present in many alloys either as nearly regular polyhedra or dendrites. This work provides a systematic approach for the determination of shapes of polyhedra with icosahedral symmetry, and the determination of preferred growth directions of icosahedral dendrites from their 2D-sections; i.e. from the surface of polished samples. The possible shapes of polyhedra and dendrites by differently oriented intersecting planes are presented within the icosahedral stereographic triangle. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Incommensurate counterrotating magnetic order stabilized by Kitaev interactions in the layered honeycomb alpha-Li2IrO3
Authors:
Williams, SC; Johnson, RD; Freund, F; Choi, S; Jesche, A; Kimchi, I; Manni, S; Bombardi, A; Manuel, P; Gegenwart, P; Coldea, R Author Full Names: Williams, S. C.; Johnson, R. D.; Freund, F.; Choi, Sungkyun; Jesche, A.; Kimchi, I.; Manni, S.; Bombardi, A.; Manuel, P.; Gegenwart, P.; Coldea, R.
Source:
PHYSICAL REVIEW B, 93 (19):10.1103/PhysRevB.93.195158 MAY 26 2016
Abstract:
The layered honeycomb magnet alpha-Li2IrO3 has been theoretically proposed as a candidate to display unconventional magnetic behaviour associated with Kitaev interactions between spin-orbit entangled j(eff) = 1/2 magnetic moments on a honeycomb lattice. Here we report single crystal magnetic resonant x-ray diffraction combined with powder magnetic neutron diffraction to reveal an incommensurate magnetic order in the honeycomb layers with Ir magnetic moments counterrotating on nearest-neighbor sites. This unexpected type of magnetic structure for a honeycomb magnet cannot be explained by a spin Hamiltonian with dominant isotropic (Heisenberg) couplings. The magnetic structure shares many key features with the magnetic order in the structural polytypes beta- and gamma-Li2IrO3, understood theoretically to be stabilized by dominant Kitaev interactions between Ir moments located on the vertices of three-dimensional hyperhoneycomb and stripyhoneycomb lattices, respectively. Based on this analogy and a theoretical soft-spin analysis of magnetic ground states for candidate spin Hamiltonians, we propose that Kitaev interactions also dominate in alpha-Li2IrO3, indicative of universal Kitaev physics across all three members of the harmonic honeycomb family of Li2IrO3 polytypes.
Title:
Strong enhancement of superconductivity at high pressures within the charge-density-wave states of 2H-TaS2 and 2H-TaSe2
Authors:
Freitas, DC; Rodiere, P; Osorio, MR; Navarro-Moratalla, E; Nemes, NM; Tissen, VG; Cario, L; Coronado, E; Garcia-Hernandez, M; Vieira, S; Nunez-Regueiro, M; Suderow, H Author Full Names: Freitas, D. C.; Rodiere, P.; Osorio, M. R.; Navarro-Moratalla, E.; Nemes, N. M.; Tissen, V. G.; Cario, L.; Coronado, E.; Garcia-Hernandez, M.; Vieira, S.; Nunez-Regueiro, M.; Suderow, H.
Source:
PHYSICAL REVIEW B, 93 (18):10.1103/PhysRevB.93.184512 MAY 24 2016
Abstract:
We present measurements of the superconducting and charge-density-wave (CDW) critical temperatures (T-c and T-CDW) as a function of pressure in the transition metal dichalchogenides 2H-TaSe2 and 2H-TaS2. Resistance and susceptibility measurements show that T-c increases from temperatures below 1 K up to 8.5 K at 9.5 GPa in 2H-TaS2 and 8.2 K at 23 GPa in 2H-TaSe2. We observe a kink in the pressure dependence of T-CDW at about 4 GPa that we attribute to the lock-in transition from incommensurate CDW to commensurate CDW. Above this pressure, the commensurate TCDW slowly decreases, coexisting with superconductivity within our full pressure range.
Title:
Self-lubricating, low-friction, wear-resistant Al-based quasicrystalline coatings
Authors:
de Lima, BASG; Gomes, RM; de Lima, SJG; Dragoe, D; Barthes-Labrousse, MG; Kouitat-Njiwa, R; Dubois, JM Author Full Names: Silva Guedes de Lima, Bruno Alessandro; Gomes, Rodinei Medeiros; Guedes de Lima, Severino Jackson; Dragoe, Diana; Barthes-Labrousse, Marie-Genevieve; Kouitat-Njiwa, Richard; Dubois, Jean-Marie
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 17 (1):71-79; 10.1080/14686996.2016.1152563 2016
Abstract:
After gas atomization, a quasicrystalline powder based on aluminium was used to prepare a thick coating by high-velocity oxygen-fuel flame torch spraying. This layer was deposited on top of a bond-coat layer on a steel plate. A post-spraying annealing treatment turned the two layers to their stable state, a.-brass crystal and an icosahedral quasicrystal, respectively. The projection parameters were selected in such a way that the coating behaved like a self-lubricating material, which offered very good wear resistance (duration of pin-on-disk tests superior to 5 km with negligible material loss) and low friction (mu <= 6% against sintered tungsten carbide), in contrast to the state of the art. This property was achieved thanks to, on the one hand, excellent bonding to the substrate via the bound coat, and on the other hand, presence at the boundaries between quasicrystalline flakes of a mixture of both threefold and fourfold coordinated carbon originating from spray processing. Application to hard materials used in mechanical devices is appealing, especially because soft, lubricating additives may not be needed, thus considerably increasing the lifetime of the devices and reducing waste of materials.

Update: 8-Jun-2016

Title:
Evolution of the magnetic structure of TbRu2Al10 in applied field
Authors:
White, R; Hutchison, WD; Mizushima, T; Studer, AJ Author Full Names: White, R.; Hutchison, W. D.; Mizushima, T.; Studer, A. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 679 169-176; 10.1016/j.jallcom.2016.04.039 SEP 15 2016
Abstract:
TbRu2Al10 is found to undergo two magnetic phase transitions as a function of temperature and three as a function of applied field at low temperature. The Tb3+ magnetic moments order antiferromagnetically along the c-axis at 15.0(3) K, with an incommensurate sinusoidally modulated structure with a propagation vector of k = (0, 0.759(1), 0). At 6.5(3) K the structure switches to square wave order. Analysis of single crystal TbRu2Al10 has revealed that this square wave structure is altered to a 'pulse wave' on application of a 1.30 T magnetic field along the c-axis, with two in fifty of the magnetic moments across the structure changing direction to be aligned parallel with the direction of the field. At 1.85 T a further three moments flip, leading to a duty cycle of 60% and resulting in a total change of one in ten moments from the starting square wave structure. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Two iridates, two models, and two approaches: A comparative study on magnetism in three-dimensional honeycomb materials
Authors:
Lee, EKH; Rau, JG; Kim, YB Author Full Names: Lee, Eric Kin-Ho; Rau, Jeffrey G.; Kim, Yong Baek
Source:
PHYSICAL REVIEW B, 93 (18):10.1103/PhysRevB.93.184420 MAY 17 2016
Abstract:
Two recent theoretical works studied the role of Kitaev interactions in the newly observed incommensurate magnetic order in the hyper-honeycomb (beta-Li2IrO3) and stripy-honeycomb (gamma-Li2IrO3) iridates. Each of these works analyzed a different model (JK Gamma versus coupled zigzag chain model) using a contrasting method (classical versus soft-spin analysis). The lack of commonality between these works precludes meaningful comparisons and a proper understanding of these unusual orderings. In this study, we complete the unfinished picture initiated by these two works by solving both models with both approaches for both three-dimensional (3D) honeycomb iridates. Through comparisons between all combinations of models, techniques, and materials, we find that the bond-isotropic JK Gamma model consistently predicts the experimental phase of beta-Li2IrO3 regardless of the method used, while the experimental phase of gamma-Li2IrO3 can be generated by the soft-spin approach with eigenmode mixing irrespective of the model used. To gain further insights, we solve a one-dimensional (1D) quantum spin-chain model related to both 3D models using the density matrix renormalization group method to form a benchmark. We discover that in the 1D model, incommensurate correlations in the classical and soft-spin analysis survive in the quantum limit only in the presence of the symmetric-off-diagonal exchange Gamma found in the JK Gamma model. The relevance of these results to the real materials is also discussed.

Update: 1-Jun-2016

Title:
Ternary phases forming adjacent to Al3Mn-Al4Mn in Al-Mn-TM (TM = Fe, Co, Ni, Cu, Zn, Pd)
Authors:
Grushko, B; Pavlyuchkov, D; Mi, SB; Balanetskyy, S Author Full Names: Grushko, B.; Pavlyuchkov, D.; Mi, S. B.; Balanetskyy, S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 677 148-162; 10.1016/j.jallcom.2016.03.220 AUG 25 2016
Abstract:
The Al-Mn alloy system contains complex intermetallics in its Al-rich part, and this was the first system where quasiperiodic structures were recognized. In the present work, the solubility of TMs (TM = Fe, Co, Ni, Cu, Zn and Pd) in the stable binaries, the stabilization effect of these elements on the metastable binaries and the formation of ternary compounds are specified and compared. While the solubility of all these TMs in hexagonal mu-Al4Mn and lambda-Al4Mn is low, the high-temperature orthorhombic T-Al3Mn dissolves up to at least 14.5, 12, 16 and 7.5 at.% Fe, Cu, Zn and Pd, respectively. The metastable hexagonal phi-Al10Mn3 is stabilized by Fe, Co and Ni in wide ternary compositional regions, and in Al-Co-Mn such a region propagates up to Al5Co2. In alloys with Fe, Co and Ni, a ternary hexagonal phase isostructural to the Al-Cr-Ni zeta-phase (P6(3)/m, a approximate to 1.76, c approximate to 1.25 nm) is formed along similar to 80 at.% Al, while in alloys with Cu and Pd the orthorhombic so-called R-phase (Bbmm, a approximate to 2.41, b approximate to 1.25, c approximate to 0.76 nm) was found at similar compositions. This structure is also known in Al-Zn-Mn but at much lower-Al Al68Zn14.5Mn17.5, while in the range of 75-80 at.% Al a monoclinic phase isostructural to eta-Al11Cr2 (C2/c, a approximate to 1.76, b approximate to 3.04, c approximate to 1.76 nm, beta approximate to 90 degrees) is formed. In addition to the stable decagonal D-3-phase in Al-Fe-Mn and Al-Pd-Mn reported earlier, the stabilization of binary Al-Mn D-3-phase was revealed around Al64Cu20Mn16. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Medium-range structure and glass forming ability in Zr-Cu-Al bulk metallic glasses
Authors:
Zhang, P; Maldonis, JJ; Besser, MF; Kramer, MJ; Voyles, PM Author Full Names: Zhang, Pei; Maldonis, Jason J.; Besser, M. F.; Kramer, M. J.; Voyles, Paul M.
Source:
ACTA MATERIALIA, 109 103-114; 10.1016/j.actamat.2016.02.006 MAY 1 2016
Abstract:
Fluctuation electron microscopy experiments combined with hybrid reverse Monte Carlo modeling show a correlation between medium-range structure at the nanometer scale and glass forming ability in two Zr-Cu-Al bulk metallic glass (BMG) alloys. Both Zr50Cu35Al15 and Zr50Cu45Al5 exhibit two nanoscale structure types, one icosahedral and the other more crystal-like. In Zr50Cu35Al15, the poorer glass former, the crystal-like structure is more stable under annealing below the glass transition temperature, T-g, than in Zr50Cu45Al5. Variable resolution fluctuation microscopy of the MRO clusters show that in Zr50Cu35Al15 on sub-T-g annealing, the crystal-like clusters shrink even as they grow more ordered, while icosahedral-like clusters grow. Overall, the results suggest that achieving better glass forming ability in this alloy system may depend more on destabilizing crystal-like structures than enhancing non-crystalline structures. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Influence of pre-strain on the aging hardening effect of the Mg-9.02Zn-1.68Y alloy
Authors:
Ye, J; Lin, XP; Zhao, TB; Liu, NN; Xie, HB; Niu, Y; Teng, F Author Full Names: Ye, Jie; Lin, Xiao-ping; Zhao, Tian-bo; Liu, Ning-ning; Xie, Hong-bin; Niu, Yi; Teng, Fei
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 663 49-55; 10.1016/j.msea.2016.03.115 APR 29 2016
Abstract:
The solid-solution state Mg-7.68Zn-1.68Y alloy was pre-compressed before the isothermal aging treatment at 200 degrees C, then the pre-induced twinning and its influence on the aging microstructure and aging hardening effect were investigated using EBSD, TEM and SEM. Results showed that: about 15% (area fraction) lenticular (1012) tensile twinning were induced into the matrix when the alloy was compressed by 3% pre-strain; and when the amount of pre-strain increased, area fraction of twinning would increase, average size of twinning would decrease, morphology and structure of twinning would change: when the pre-strain reached 15%, about 28% (area fraction) of narrow double twinning (10 (1) over bar1)-(10 (1) over bar2)would be induced, while the anamorphosis of double twinning were mostly inter-crossing. In addition, twinning could become an effective substrate for nucleation. And different from precipitates in the matrix, which is rod-shaped beta'(1)1-MgZn2 growing along a certain direction, precipitates in the twin boundaries were granular icosahedral quasi -crystal phase with 5 -times rotational symmetric diffraction pattern. And when the pre-strain was in the range of 3-15%, aging hardening effect increased with pre-strain; when pre-strain were 10-15%, the peak hardness arrived 110HV, 28% improved compared to that of the not pre-deformed one (86HV); when the pre-strain exceeded 20%, the aging hardening effect would decrease. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Determination of the zero-field magnetic structure of the helimagnet MnSi at low temperature
Authors:
de Reotier, PD; Maisuradze, A; Yaouanc, A; Roessli, B; Amato, A; Andreica, D; Lapertot, G Author Full Names: de Reotier, P. Dalmas; Maisuradze, A.; Yaouanc, A.; Roessli, B.; Amato, A.; Andreica, D.; Lapertot, G.
Source:
PHYSICAL REVIEW B, 93 (14):10.1103/PhysRevB.93.144419 APR 22 2016
Abstract:
Below a temperature of approximately 29 K the manganese magnetic moments of the cubic binary compound MnSi order to a long-range incommensurate helical magnetic structure. Here we quantitatively analyze a high-statistic zero-field muon spin rotation spectrum recorded in the magnetically ordered phase of MnSi by exploiting the result of representation theory as applied to the determination of magnetic structures. Instead of a gradual rotation of the magnetic moments when moving along a (111) axis, we find that the angle of rotation between the moments of certain subsequent planes is essentially quenched. It is the magnetization of pairs of planes which rotates when moving along a (111) axis, thus preserving the overall helical structure.
Title:
Incommensurate-commensurate transitions in the monoaxial chiral helimagnet driven by the magnetic field
Authors:
Laliena, V; Campo, J; Kishine, JI; Ovchinnikov, AS; Togawa, Y; Kousaka, Y; Inoue, K Author Full Names: Laliena, Victor; Campo, Javier; Kishine, Jun-Ichiro; Ovchinnikov, Alexander S.; Togawa, Yoshihiko; Kousaka, Yusuke; Inoue, Katsuya
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134424 APR 20 2016
Abstract:
The zero-temperature phase diagram of the monoaxial chiral helimagnet in the magnetic-field plane formed by the components parallel and perpendicular to the helical axis is thoroughly analyzed. The nature of the transition to the commensurate state depends on the angle between the field and the helical axis. For field directions close to the directions parallel or perpendicular to the helical axis the transition is continuous, while for intermediate angles the transition is discontinuous and the incommensurate and commensurate states coexist on the transition line. The continuous and discontinuous transition lines are separated by two tricritical points with specific singular behavior. The location of the continuous and discontinuous lines and of the tricritical points depend strongly on the easy-plane anisotropy, the effect of which is analyzed. For high anisotropy the conical approximation locates the transition line very accurately, although it does not predict the continuous transitions and the tricritical behavior. It is shown that for high anisotropy, as in CrNb3S6, the form of the transition line is universal, that is, independent of the sample, and obeys a simple equation. The position of the tricritical points, which is not universal, is theoretically estimated for a sample of CrNb3S6.
Title:
Low-Temperature Oxidation of Fine UO2 Powders: A Process of Nanosized Domain Development
Authors:
Leinders, G; Pakarinen, J; Delville, R; Cardinaels, T; Binnemans, K; Verwerft, M Author Full Names: Leinders, Gregory; Pakarinen, Janne; Delville, Remi; Cardinaels, Thomas; Binnemans, Koen; Verwerft, Marc
Source:
INORGANIC CHEMISTRY, 55 (8):3915-3927; 10.1021/acs.inorgchem.6b00127 APR 18 2016
Abstract:
The nanostructure and phase evolution in low-temperature oxidized (40-250 degrees C), fine UO2 powders (<200 nm) have been investigated by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). The extent of oxidation was also measured via in situ thermogravimetric analysis. The oxidation of fine powders was found to, proceed differently as compared to oxidation of coarse grained UO2. No discrete surface oxide layer was observed and no U3O8 was formed, despite the high degree of oxidation (up to O/U = 2.45). Instead, nanosized (5-15 nm) amorphous nuclei (interpreted as amorphous UO3), unmodulated and modulated U4O9, and a continuous range of U3O7-z phases with varying tetragonal distortion (c/a > 1) were observed. Oxidation involves formation of higher uranium oxides in nanodomains near the grain surface which, initially, have a disordered defect structure ("disordered U4O9"). As oxidation progresses, domain growth increases and the long period modulated structure of U4O9 develops ("ordered U4O9"). A similar mechanism is understood to happen also in U3O7-z.
Title:
Disorder-promoted C-4-symmetric magnetic order in iron-based superconductors
Authors:
Hoyer, M; Fernandes, RM; Levchenko, A; Schmalian, J Author Full Names: Hoyer, Mareike; Fernandes, Rafael M.; Levchenko, Alex; Schmalian, Joerg
Source:
PHYSICAL REVIEW B, 93 (14):10.1103/PhysRevB.93.144414 APR 18 2016
Abstract:
In most iron-based superconductors, the transition to the magnetically ordered state is closely linked to a lowering of structural symmetry from tetragonal (C-4) to orthorhombic (C-2). However, recently, a regime of C-4-symmetric magnetic order has been reported in certain hole-doped iron-based superconductors. This novel magnetic ground state can be understood as a double-Q spin density wave characterized by two order parameters M-1 and M-2 related to each of the two Q vectors. Depending on the relative orientations of the order parameters, either a noncollinear spin-vortex crystal or a nonuniform charge-spin density wave could form. Experimentally, Mossbauer spectroscopy, neutron scattering, and muon spin rotation established the latter as the magnetic configuration of some of these optimally hole-doped iron-based superconductors. Theoretically, low-energy itinerant models do support a transition from single-Q to double-Q magnetic order, but with nearly degenerate spin-vortex crystal and charge-spin density wave states. In fact, extensions of these low-energy models including additional electronic interactions tip the balance in favor of the spin-vortex crystal, in apparent contradiction with the recent experimental findings. In this paper we revisit the phase diagram of magnetic ground states of low-energy multiband models in the presence of weak disorder. We show that impurity scattering not only promotes the transition from C-2 to C-4-magnetic order, but it also favors the charge-spin density wave over the spin-vortex crystal phase. Additionally, in the single-Q phase, our analysis of the nematic coupling constant in the presence of disorder supports the experimental finding that the splitting between the structural and stripe-magnetic transition is enhanced by disorder.
Title:
Low-temperature magnetic phase transitions in the multiferroic Nd0.9Dy0.1Fe3(BO3)(4). Part 1. Transitions induced by magnetic fields directed along the trigonal symmetry axis. Spontaneous transitions with temperature changes
Authors:
Zvyagina, GA; Zhekov, KR; Bilych, IV; Kolodyazhnaya, MP; Zvyagin, AA; Bludov, AN; Pashchenko, VA; Gudim, IA Author Full Names: Zvyagina, G. A.; Zhekov, K. R.; Bilych, I. V.; Kolodyazhnaya, M. P.; Zvyagin, A. A.; Bludov, A. N.; Pashchenko, V. A.; Gudim, I. A.
Source:
LOW TEMPERATURE PHYSICS, 42 (4):273-279; 10.1063/1.4947480 APR 2016
Abstract:
The elastic and magnetic characteristics of single-crystal Nd0.9Dy0.1Fe3(BO3)(4) are studied at low temperatures in zero magnetic field and in external fields H vertical bar vertical bar C-3. The temperature dependences of the acoustic mode velocities and the magnetic susceptibility manifest a transition of the magnetic subsystem into a magnetically ordered state and two successive, spontaneous spin-reorientation phase transitions. The possibility of a spontaneous transition into an incommensurate (spiral) magnetic phase in the crystal is discussed. It is shown that an external magnetic field directed along the trigonal axis of the crystal induces a sequence of spin-reorientation phase transitions. An H-T phase diagram (H vertical bar vertical bar C-3) is constructed for this compound. Published by AIP Publishing.
Title:
3D Morphology and Formation Process of the Icosahedral Quasicrystalline Phase in Rapidly Solidified Al-Mn Alloy
Authors:
Kang, HJ; Hu, ZL; Gao, XX; Chen, ZN; Lu, YP; Jie, JC; Guo, JJ Author Full Names: Kang, Hui-Jun; Hu, Zhong-Lue; Gao, Xiao-Xia; Chen, Zong-Ning; Lu, Yi-Ping; Jie, Jin-Chuan; Guo, Jing-Jie
Source:
ACTA METALLURGICA SINICA-ENGLISH LETTERS, 29 (1):28-31; 10.1007/s40195-015-0357-y JAN 2016
Abstract:
Three-dimensional morphology and formation process of icosahedral quasicrystal phase have been investigated in a melt-spun Al-18Mn alloy (in wt%). Three distinct layers corresponding to varying temperature gradient have been observed on the cross section of the ribbons. 3D morphologies of cellular and dendritic icosahedral phase have been obtained through electro-etching. A model has been proposed to describe the formation process of the icosahedral phase and alpha-Al during the rapid solidification. The icosahedral phases are primarily precipitated from the melt into fine cellular and dendritic particles, and subsequently engulfed by the alpha-Al which propagates in a planar morphology.
Title:
Diffraction pattern of modulated structures described by Bessel functions
Authors:
Wolny, J; Buganski, I; Strzalka, R Author Full Names: Wolny, Janusz; Buganski, Ireneusz; Strzalka, Radoslaw
Source:
PHILOSOPHICAL MAGAZINE, 96 (13):1344-1359; 10.1080/14786435.2016.1161859 2016
Abstract:
We performed detailed analysis of 1D modulated structure (MS) with harmonic modulation within the statistical approach. By applying two-mode Fourier transform, we were able to derive analytically the structure factor for MS with single harmonic modulation component. We confirmed in a very smooth way that ordinary Bessel functions of the first kind define envelopes tuning the intensities of the diffraction peaks. This applies not only to main reflections of the diffraction pattern but also to all satellites. In the second part, we discussed in details the similarities between harmonically modulated structures with multiple modulations and 1D model quasicrystal. The Fourier expansion of the nodes' positions in the Fibonacci chain gives direct numerical definition of the atomic arrangement in MS. In that sense, we can define 1D quasicrystal as a MS with infinite number of harmonic modulations. We prove that characteristic measures (like v(u) relation typical for statistical approach and diffraction pattern) calculated for MS asymptotically approach their counterparts for 1D quasicrystal as large enough number of modulation terms is taken into account.
Title:
The Effect of the Drop Tube Process for the Quasicrystal Fine Particles Formation
Authors:
Takeda, Y; Kawamura, T; Nagayama, K Author Full Names: Takeda, Yuya; Kawamura, Tadaharu; Nagayama, Katsuhisa
Source:
JOURNAL OF THE JAPAN INSTITUTE OF METALS, 80 (4):273-279; 10.2320/jinstmet.JBW201506 2016
Abstract:
In general, quasicrystalline structures are produced by liquid quenching using a single roll, Bridgman and Czochralski method, which is typical for the production of single crystals. However, there are few reports of the quasicrystal formation using a containerless process; therefore, the effect of such a process is unclear. In this study, we have investigated the production of quasicrystalline fine particles and the formation ability of Al63Cu25Fe12, Al65Cu20Fe15, and Al70Ni15Co15 ternary alloys using a drop tube apparatus with a free fall length of 2.5 m. In addition, we have aimed to examine the effectiveness of the drop tube process for quasicrystal formation. The formation of dodecahedron crystals, which are considered a quasicrystalline phase, was observed in Al63Cu25Fe12 ternary fine particle samples prepared using the drop tube process under a He atmosphere (1 atm). Based on the heat flux, the calculated results suggested that the icosahedral phase was formed at high cooling rates of similar to 10(5) K/s. In the Al70Ni15Co15 ternary fine particle sample, aggregation of prismatic crystals was observed in the fine particle samples prepared using the drop tube process under an atmosphere of He (1 atm) and Ar (1 atm). Furthermore, formation of prismatic crystals was observed on the surface of fine particle samples prepared under a low-pressure Ar atmosphere (0.5 atm), under which the formation ability of quasicrystals was observed to be the highest. From these results, the formation ability of the Al-Ni-Co-based decagonal phase is suggested to increase with decreasing cooling rates. This result is different from that of the Al-Cu-Fe-based icosahedral quasicrystals.

Update: 27-May-2016

Title:
Self-consistent theory of nanodomain formation on nonpolar surfaces of ferroelectrics
Authors:
Morozovska, AN; Ievlev, AV; Obukhovskii, VV; Fomichov, Y; Varenyk, OV; Shur, VY; Kalinin, SV; Eliseev, EA Author Full Names: Morozovska, Anna N.; Ievlev, Anton V.; Obukhovskii, Vyacheslav V.; Fomichov, Yevhen; Varenyk, Oleksandr V.; Shur, Vladimir Ya.; Kalinin, Sergei V.; Eliseev, Eugene A.
Source:
PHYSICAL REVIEW B, 93 (16):10.1103/PhysRevB.93.165439 APR 28 2016
Abstract:
We propose a self-consistent theoretical approach capable of describing the features of the anisotropic nanodomain formation induced by a strongly inhomogeneous electric field of a charged scanning probe microscopy tip on nonpolar cuts of ferroelectrics. We obtained that a threshold field, previously regarded as an isotropic parameter, is an anisotropic function that is specified from the polar properties and lattice pinning anisotropy of a given ferroelectric in a self-consistent way. The proposed method for the calculation of the anisotropic threshold field is not material specific, thus the field should be anisotropic in all ferroelectrics with the spontaneous polarization anisotropy along the main crystallographic directions. The most evident examples are uniaxial ferroelectrics, layered ferroelectric perovskites, and low-symmetry incommensurate ferroelectrics. Obtained results quantitatively describe the differences at several times in the nanodomain length experimentally observed on X and Y cuts of LiNbO3 and can give insight into the anisotropic dynamics of nanoscale polarization reversal in strongly inhomogeneous electric fields.
Title:
Incommensurate spin correlations in highly oxidized cobaltates La2-xSrxCoO4
Authors:
Li, ZW; Drees, Y; Kuo, CY; Guo, H; Ricci, A; Lamago, D; Sobolev, O; Rutt, U; Gutowski, O; Pi, TW; Piovano, A; Schmidt, W; Mogare, K; Hu, Z; Tjeng, LH; Komarek, AC Author Full Names: Li, Z. W.; Drees, Y.; Kuo, C. Y.; Guo, H.; Ricci, A.; Lamago, D.; Sobolev, O.; Ruett, U.; Gutowski, O.; Pi, T. W.; Piovano, A.; Schmidt, W.; Mogare, K.; Hu, Z.; Tjeng, L. H.; Komarek, A. C.
Source:
SCIENTIFIC REPORTS, 6 10.1038/srep25117 APR 27 2016
Abstract:
We observe quasi-static incommensurate magnetic peaks in neutron scattering experiments on layered cobalt oxides La2-xSrxCoO4 with high Co oxidation states that have been reported to be paramagnetic. This enables us to measure the magnetic excitations in this highly hole-doped incommensurate regime and compare our results with those found in the low-doped incommensurate regime that exhibit hourglass magnetic spectra. The hourglass shape of magnetic excitations completely disappears given a high Sr doping. Moreover, broad low-energy excitations are found, which are not centered at the incommensurate magnetic peak positions but around the quarter-integer values that are typically exhibited by excitations in the checkerboard charge ordered phase. Our findings suggest that the strong inter-site exchange interactions in the undoped islands are critical for the emergence of hourglass spectra in the incommensurate magnetic phases of La2-xSrxCoO4.
Title:
Electronic nature of the lock-in magnetic transition in CeXAl4Si2
Authors:
Gunasekera, J; Harriger, L; Dahal, A; Maurya, A; Heitmann, T; Disseler, SM; Thamizhavel, A; Dhar, S; Singh, DJ; Singh, DK Author Full Names: Gunasekera, J.; Harriger, L.; Dahal, A.; Maurya, A.; Heitmann, T.; Disseler, S. M.; Thamizhavel, A.; Dhar, S.; Singh, D. J.; Singh, D. K.
Source:
PHYSICAL REVIEW B, 93 (15):10.1103/PhysRevB.93.155151 APR 25 2016
Abstract:
We have investigated the underlying magnetism in newly discovered single crystal Kondo lattices CeXAl4Si2, where X = Rh, Ir. We show that the compound undergoes an incommensurate-to-commensurate magnetic transition at T-c = 9.19 K (10.75 K in Ir). The spin correlation in the incommensurate phase is described by a spin density wave configuration of Ce ions, which locks in to the long-range antiferromagnetic order at T = T-c. The analysis of the experimental data, combined with the calculation of the electronic properties, suggests the role of the Fermi surface nesting as the primary mechanism behind this phenomenon.
Title:
Direct imaging of coexisting ordered and frustrated sublattices in artificial ferromagnetic quasicrystals
Authors:
Farmer, B; Bhat, VS; Balk, A; Teipel, E; Smith, N; Unguris, J; Keavney, DJ; Hastings, JT; De Long, LE Author Full Names: Farmer, B.; Bhat, V. S.; Balk, A.; Teipel, E.; Smith, N.; Unguris, J.; Keavney, D. J.; Hastings, J. T.; De Long, L. E.
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134428 APR 25 2016
Abstract:
We have used scanning electron microscopy with polarization analysis and photoemission electron microscopy to image the two-dimensional magnetization of permalloy films patterned into Penrose P2 tilings (P2T). The interplay of exchange interactions in asymmetrically coordinated vertices and short-range dipole interactions among connected film segments stabilize magnetically ordered, spatially distinct sublattices that coexist with frustrated sublattices at room temperature. Numerical simulations that include long-range dipole interactions between sublattices agree with images of as-grown P2T samples and predict a magnetically ordered ground state for a two-dimensional quasicrystal lattice of classical Ising spins.
Title:
Confinement transition to density wave order in metallic doped spin liquids
Authors:
Patel, AA; Chowdhury, D; Allais, A; Sachdev, S Author Full Names: Patel, Aavishkar A.; Chowdhury, Debanjan; Allais, Andrea; Sachdev, Subir
Source:
PHYSICAL REVIEW B, 93 (16):10.1103/PhysRevB.93.165139 APR 25 2016
Abstract:
Insulating quantum spin liquids can undergo a confinement transition to a valence bond solid via the condensation of topological excitations of the associated gauge theory. We extend the theory of such transitions to fractionalized Fermi liquids (FL*): These are metallic doped spin liquids in which the Fermi surfaces only have gauge neutral quasiparticles. Using insights from a duality transform on a doped quantum dimer model for the U(1)-FL* state, we show that projective symmetry group of the theory of the topological excitations remains unmodified, but the Fermi surfaces can lead to additional frustrating interactions. We propose a theory for the confinement transition of Z2-FL* states via the condensation of visons. A variety of confining, incommensurate density wave states are possible, including some that are similar to the incommensurate d-form factor density wave order observed in several recent experiments on the cuprate superconductors.
Title:
Two Kinds of Contact Problems in Dodecagonal Quasicrystals of Point Group 12 mm
Authors:
Zhao, XF; Li, X; Ding, SH Author Full Names: Zhao, Xuefen; Li, Xing; Ding, Shenghu
Source:
ACTA MECHANICA SOLIDA SINICA, 29 (2):167-177; APR 2016
Abstract:
In this paper, two kinds of contact problems in 2-D dodecagonal quasicrystals were discussed using the complex variable function method: one is the finite frictional contact problem, the other is the adhesive contact problem. The analytic expressions of contact stresses in the phonon and phason fields were obtained for a flat rigid punch, which showed that: (1) for the finite frictional contact problem, the contact stress exhibited power-type singularities at the edge of the contact zone; (2) for the adhesive contact problem, the contact stress exhibited oscillatory singularities at the edge of the contact zone. The distribution regulation of contact stress under punch was illustrated; and the low friction property of quasicrystals was verified graphically.
Title:
Structure modulation, band structure, density of states and luminescent properties of columbite-type ZnNb2O6
Authors:
Zhao, D; Ma, FX; Zhang, RJ; Li, FF; Zhang, L; Yang, J; Fan, YC; Xin, X Author Full Names: Zhao, Dan; Ma, Fa-Xue; Zhang, Rui-Juan; Li, Fei-Fei; Zhang, Lei; Yang, Juan; Fan, Yun-Chang; Xin, Xia
Source:
CRYSTENGCOMM, 18 (16):2929-2936; 10.1039/c5ce01828e 2016
Abstract:
Zinc niobate ZnNb2O6, with a columbite-type structure, is a promising dielectric, photocatalytic and luminescent material, but the crystal structure has not been studied in detail. For the first time, we redetermined the crystal structure using single crystal X-ray diffraction and established the commensurately modulated structure model through high-dimensional formalism. The structure features a (3 + 1)-dimensional superspace group Pbcn(alpha 00)00s with the modulation vector q = 1/3a*. At the same time, calculations of the band structure and the density of states were performed using density functional theory to reveal the electronic origins of the optical transitions. In addition, the photoluminescent properties of ZnNb2O6 were studied, showing that a broad emission band at approximately 470 nm can achieve a high quantum efficiency of up to 64% with an optimal sintered temperature of 950 degrees C.

Update: 18-May-2016

Title:
Point contact tunneling spectroscopy of the density of states in Tb-Mg-Zn quasicrystals
Authors:
Escudero, R; Morales, F Author Full Names: Escudero, R.; Morales, F.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 439 46-50; 10.1016/j.jnonaysol.2016.02.019 MAY 1 2016
Abstract:
According to theoretical predictions the quasicrystalline (QC) electronic density of states (DOS) must have a rich and fine spiky structure which actually has resulted elusive. The problem with its absence may be related to poor structural characteristics of the studied specimens, and/or to the non-existence of this spike characteristic. Recent calculations have shown that the fine structure indeed exists, but only for two dimensional approximants phases. The aim of the present study is to show our recent experimental studies with point contact tunnel junction spectroscopy performed in samples of very high quality. The studies were performed in icosahedral QC alloys with composition Tb9Mg35Zn56. We found the presence of a pseudogap feature at the Fermi level, small as compared to the pseudogap of other icosahedral materials. This study made in different spots on the QC shows quite different spectroscopic features, where the observed DOS was a fine non-spiky structure, distinct to theoretical predictions. In some regions of the specimens the spectroscopic features could be related to Kondo characteristics due to Tb magnetic atoms acting as impurities. Additionally, we observed that the spectroscopic features vanished under magnetic field. (C) 2016 Elsevier B.V. All rights reserved.

Update: 12-May-2016

Title:
Quasicrystal as a Catalyst for the Synthesis of Carbon Nanotubes
Authors:
Kajiwara, K; Matsui, Y; Yadav, TP; Mukhopadhyay, NK; Srivastava, ON Author Full Names: Kajiwara, K.; Matsui, Y.; Yadav, T. P.; Mukhopadhyay, N. K.; Srivastava, O. N.
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 16 (3):3084-3089; 10.1166/jnn.2016.12468 MAR 2016
Abstract:
The present report describes the catalytic activity of mechanically activated nano quasicrystalline Al65Cu20Fe15 and related nano crystalline Al50Cu28Fe22 for the synthesis of carbon nanotubes (CNTs). CNTs are synthesized by catalytic decomposition of ethanol through nano quasicrystalline Al65Cu20Fe15 and related crystalline Al50Cu28Fe22 alloys as a catalyst. The synthesized multi-walled CNTs exhibits tube diameter ranging from 5 to 25 nm. The synthesized CNTs are characterized by scanning and transmission electron microscopy. It is found that Al65Cu20Fe15 nanoquasicystal shows better catalytic behaviour as compared to nano-crystalline Al50Cu28Fe22 alloys for decomposition of ethanol during the synthesis of multi-walled CNTs.

Update: 5-May-2016

Title:
Long-period modulated structure and electric-field-induced structural transformation in Na0.5Bi0.5TiO3-based lead-free piezoelectrics
Authors:
Khatua, DK; Senyshyn, A; Ranjan, R Author Full Names: Khatua, Dipak Kumar; Senyshyn, Anatoliy; Ranjan, Rajeev
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134106 APR 14 2016
Abstract:
Na0.5Bi0.5TiO3- based lead-free piezoelectrics exhibiting giant piezostrain are technologically interesting materials for actuator applications. The lack of clarity with regard to the structure of the nonpolar phase of this system has hindered the understanding of the structural mechanism associated with the giant piezostrain and other related phenomena. In this paper, we have investigated the structure and field-induced phase transformation behavior of a model system (0.94 - x) Na0.5Bi0.5TiO3-0.06BaTiO(3)-xK(0.5)Na(0.5)NbO(3) (0.0 <= x <= 0.025). A detailed structural analysis using neutron powder diffraction revealed that the nonpolar phase is neither cubic nor a mixture of rhombohedral (R3c) and tetragonal (P4bm) phases as commonly reported in literature but exhibits a long-period modulated structure, which is most probably of the type root 2 x root 2 x n with n = 16. Our results suggest that the giant piezoelectric strain is associated with a field-induced phase transformation of the long-period modulated structure to rhombohedral R3c structure above a critical field. We also demonstrate that the giant piezostrain is lost if the system retains a fraction of the field-induced R3c phase. A possible correlation among depolarization temperature, giant piezostrain, and its electrical fatigue behavior has also been indicated.
Title:
Temperature-dependent Fermi surface of the misfit cobaltite [Bi2Sr2O4](0.51)CoO2: A comparison with [Bi2Ba2O4](0.50)CoO2
Authors:
Takakura, S; Yamamoto, I; Koga, E; Ichikawa, F; Azuma, J; Maki, M Author Full Names: Takakura, Sho-ichi; Yamamoto, Isamu; Koga, Emi; Ichikawa, Fusao; Azuma, Junpei; Maki, Makoto
Source:
PHYSICAL REVIEW B, 93 (16):10.1103/PhysRevB.93.165118 APR 14 2016
Abstract:
Angle-resolved photoemission spectroscopy has been performed to investigate the Fermi surface (FS) and the electronic structure of misfit cobaltites, by comparing [Bi2Sr2O4](p)CoO2 with [Bi2Ba2O4](0.50)CoO2. In [Bi2Sr2O4](0.51)CoO2, we observed a suppression of spectral weight near the Fermi energy. Nevertheless, the FS can be mapped out by measuring the photoelectron intensity distribution. The FS size changes with temperature. Additionally, results show that the electronic band structure at a higher binding energy was changed by changing the sample temperature. Our results provide insight into the characteristics of the pseudogap state in the misfit-layered cobaltites. The unusual properties are probably related to the local deformations of the incommensurate structure.
Title:
Structure modulations in nonlinear optical (NLO) materials Cs2TB4O9 (T = Ge, Si)
Authors:
Zhou, ZY; Xu, X; Fei, R; Mao, JG; Sun, JL Author Full Names: Zhou, Zhengyang; Xu, Xiang; Fei, Rao; Mao, Jianggao; Sun, Junliang
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 194-200; 10.1107/S2052520615019733 2 APR 2016
Abstract:
Incommensurately modulated borate structures of a new type were studied in detail in the nonlinear optical (NLO) materials Cs2TB4O9 (T = Ge, Si) using single-crystal X-ray diffraction techniques. The structures were solved by the charge-flipping algorithm in the superspace group I2(alpha beta 0)0. The refinement results strongly suggest that the main structure modulation feature of Cs2TB4O9 is the ordering of the O atoms. With these modulated structure models, the unreasonable B-O distances in the average structures were explained as the ordering of BO4 and BO3.
Title:
Melilite-like modulation and temperature-dependent evolution in the framework structure of K2Sc[Si2O6]F
Authors:
Hejny, C; Kahlenberg, V; Eberhard, T; Kruger, H Author Full Names: Hejny, Clivia; Kahlenberg, Volker; Eberhard, Tim; Krueger, Hannes
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 209-222; 10.1107/S2052520615024865 2 APR 2016
Abstract:
The crystal structure of synthetic K2Sc[Si2O6] F has been solved and refined as an incommensurately modulated structure in (3 + 2)-dimensional superspace. This paper describes the tetragonal structure in the superspace group P4(2)/mnm(alpha, alpha,0) 000s(-alpha, alpha,0) 0000 [a = 8.9878 (1), c = 8.2694 (2) angstrom, V = 668.01 (2) angstrom(3)] with modulation wavevectors q(1) = 0.2982 (4)(a* + b*) and q(2) = 0.2982 (4)(-a* + b*). Structure refinement taking into account the modulation of positional and ADP parameters for all atoms from 3074 observed main hkl00 and satellite reflections hklmn of first order with single, m.n = 0, and mixed, m.n = +/- 1, indices converged to a final R value of 0.0514. The structure is a mixed octahedral-tetrahedral framework composed of [ScO4F2] octahedra, [Si4O12] rings and K in variable coordination. Due to the modulation the O atoms move into and out of the first coordination sphere of K leading to a minimum of five and a maximum of 10 interatomic K-O distances up to 3.1 angstrom Although this feature is comparable to observations in modulated fresnoite and melilite group compounds, these structures differ from K2Sc[Si2O6] F with respect to their topology. On temperature increase the intensity of the satellite reflections decreases until they disappear just above 443 K. The high-temperature normal structure, in space group P4(2)/mnm, is identical to the room-temperature average structure of K2Sc[Si2O6]F.

Update: 29-Apr-2016

Title:
Metastable phase formation in ternary Mg-Gd-Zn alloys
Authors:
Grobner, J; Zhu, SM; Nie, JF; Gibson, MA; Schmid-Fetzer, R Author Full Names: Groebner, Joachim; Zhu, Suming; Nie, Jian-Feng; Gibson, Mark A.; Schmid-Fetzer, Rainer
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 675 149-157; 10.1016/j.jallcom.2016.03.106 AUG 5 2016
Abstract:
Two metastable phases have been identified in as-cast Mg-rich Mg-Gd-Zn alloys by TEM characterization. The I-phase was found to have a composition close to Gd11Mg29Zn60 with an icosahedral structure (a(R) = 0.524 nm). The H2-phase, with a composition close to Gd16Mg14Zn70, was identified to have a hexagonal structure (a = 0.937 nm and c = 0.977 nm). An extension of the thermodynamic description of the ternary Mg-Gd-Zn phase diagram to incorporate the formation of these metastable phases has been modelled. Thermodynamic simulation of metastable phase formation has been conducted by suppressing the formation of more stable phases in a constrained Scheil solidification simulation to form I and H2 phases. The results of these solidification simulations are compared with reported as-cast alloy structures. Limiting values for the Gd/Zn atomic ratio, similar to< 0.55 and similar to> 1.4, are found to be crucial for phase selection. An application to Mg-Zn-Gd-Y alloys is discussed briefly. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Phenomenological Magnetic Model in Tsai-Type Approximants
Authors:
Sugimoto, T; Tohyama, T; Hiroto, T; Tamura, R Author Full Names: Sugimoto, Takanori; Tohyama, Takami; Hiroto, Takanobu; Tamura, Ryuji
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (5):10.7566/JPSJ.85.053701 MAY 15 2016
Abstract:
Motivated by the recent discovery of canted ferromagnetism in the Tsai-type approximants Au-Si-REs (RE = Tb, Dy, and Ho), we propose a phenomenological magnetic model reproducing their magnetic structure and thermodynamic quantities. In the model, the cubic symmetry (m (3) over bar) of the approximately regular icosahedra plays a key role in the peculiar magnetic structure determined by a neutron diffraction experiment. Our magnetic model does not only explain magnetic behaviors in the quasicrystal approximants, but also provides a good starting point for the possibility of the coexistence between the magnetic long-range order and the aperiodicity in quasicrystals.
Title:
Low temperature magneto-structural transitions in Mn3Ni20P6
Authors:
Cedervall, J; Beran, P; Vennstrom, M; Danielsson, T; Ronneteg, S; Hoglin, V; Lindell, D; Eriksson, O; Andre, G; Andersson, Y; Nordblad, P; Sahlberg, M Author Full Names: Cedervall, Johan; Beran, Premysl; Vennstrom, Marie; Danielsson, Therese; Ronneteg, Sabina; Hoglin, Viktor; Lindell, David; Eriksson, Olle; Andre, Gilles; Andersson, Yvonne; Nordblad, Per; Sahlberg, Martin
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 237 343-348; 10.1016/j.jssc.2016.02.028 MAY 2016
Abstract:
X-ray and neutron powder diffraction has been used to determine the crystal and magnetic structure of Mn3Ni20P6. The crystal structure can be described as cubic with space group Fm (3) over barm (225) without any nuclear phase transformation within studied temperature interval from room temperature down to 4 K. The magnetic structure of Mn3Ni20P6 is complex with two independent magnetic positions for the Mn atoms and the compound passes three successive magnetic phase transitions during cooling. At 30 K the spins of the Mn atoms on the Wyckoff 4a site (Mn1) order to form a primitive cubic anti ferromagnetic structure with propagation vector k=(0 0 1). Between 29 and 26 K the Mn atoms on the Wyckoff 8c site (Mn2) order independently on already ordered Mn1 magnetic structure forming a commensurate antiferromagnetic structure with propagation vector k= (0 0 1/2) and below 26 K, both Mn positions order to form an incommensurate helical structure with propagation vector k=(0 0 similar to 0.45). Magnetization vs. temperature curve of Mn3Ni20P6 shows a steep increase indicating some magnetic ordering below 230 K and a sharp field dependent anomaly in a narrow temperature range around 30 K. (C) 2016 Elsevier Inc. All rights reserved.
Title:
Europium and manganese magnetic ordering in EuMn2Ge2
Authors:
Ryan, DH; Rejali, R; Cadogan, JM; Flacau, R; Boyer, CD Author Full Names: Ryan, D. H.; Rejali, Rasa; Cadogan, J. M.; Flacau, R.; Boyer, C. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (16):10.1088/0953-8984/28/16/166003 APR 27 2016
Abstract:
The antiferromagnetic structures of both the manganese and europium sublattices in EuMn2Ge2 have been determined using thermal neutron diffraction. T-N(Mn) = 714(5) K with the 3.35(5) mu(B) (at 285 K) Mn moments ordering according to the I4 '/m ' m ' m space group. The Eu order is incommensurate with the 6.1(2) mu(B) (at 3.6 K) Eu moments oriented parallel to the c-axis with a propagation vector of k = [0.153(2) 0 0]. Both neutron diffraction and Eu-151 Mossbauer spectroscopy reveal evidence of magnetic short-range ordering of the Eu sublattice around and above T-N(Eu) similar to 10 K. The ordering temperature of the Eu sublattice is strongly affected by the sample's thermal history and rapid quenching from the melting point may lead to a complete suppression of that ordering.
Title:
Quantum diffusion of electrons in quasiperiodic and periodic approximant lattices in the rare earth-cadmium system
Authors:
Armstrong, NMR; Mortimer, KD; Kong, T; Bud'ko, SL; Canfield, PC; Basov, DN; Timusk, T Author Full Names: Armstrong, N. M. R.; Mortimer, K. D.; Kong, T.; Bud'ko, S. L.; Canfield, P. C.; Basov, D. N.; Timusk, T.
Source:
PHILOSOPHICAL MAGAZINE, 96 (11):1122-1130; 10.1080/14786435.2016.1150612 APR 12 2016
Abstract:
Icosahedral quasicrystals are characterised by the absence of a distinct Drude peak in their low-frequency optical conductivity and the same is true of their crystalline approximants. We have measured the optical conductivity of i-GdCd [GRAPHICS] , an icosahedral quasicrystal, and two approximants, GdCd [GRAPHICS] and YCd [GRAPHICS] . We find that there is a significant difference in the optical properties of these compounds. The approximants have a zero frequency peak, characteristic of a metal, whereas the quasicrystal has a striking minimum. This is the first example where the transport properties of a quasicrystal and its approximant differ in such a fundamental way. Using a generalised Drude model introduced by Mayou, we find that our data are well described by this model. It implies that the quantum diffusion of electron wave packets through the periodic and quasiperiodic lattices is responsible for these dramatic differences: in the approximants, the transport is superdiffusive, whereas the quasicrystals show subdiffusive motion of the electrons.
Title:
Electromagnons, magnons, and phonons in Eu1-xHoxMnO3
Authors:
Chen, ZY; Schmidt, M; Wang, Z; Mayr, F; Deisenhofer, J; Mukhin, AA; Balbashov, AM; Loidl, A Author Full Names: Chen, Zhenyu; Schmidt, M.; Wang, Zhe; Mayr, F.; Deisenhofer, J.; Mukhin, A. A.; Balbashov, A. M.; Loidl, A.
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134406 APR 6 2016
Abstract:
Here we present a detailed study of the terahertz and far-infrared response of the mixed perovskite manganite system Eu1-xHoxMnO3 for holmium concentrations x = 0.1 and 0.3. We compare the magnetic excitations of the four different magnetically ordered phases (A-type antiferromagnetic, sinusoidally modulated collinear, helical phases with spin planes perpendicular to the crystallographic a and c axes). The transition between the two latter phases goes hand in hand with a switching of the ferroelectric polarization from P parallel to a to P parallel to c. Special emphasis is paid to the temperature dependence of the excitations at this transition. We find a significant change of intensity indicating that the exchange-striction mechanism may not be the only mechanism to induce dipolar weight to spin-wave excitations. We also focus on excitations within the incommensurate collinear antiferromagnetic phase and find an excitation close to 40 cm(-1). A detailed analysis of optical weight gives a further unexpected result: In the multiferroic phase with P parallel to c all the spectral weight of the electromagnons comes from the lowest-phonon mode. However, for the phase with the polarization P parallel to a additional spectral weight must be transferred from higher frequencies.
Title:
Effect of platinum substitution on the structural and magnetic properties of Ni2MnGa ferromagnetic shape memory alloy
Authors:
Singh, S; D'Souza, SW; Nayak, J; Caron, L; Suard, E; Chadov, S; Felser, C Author Full Names: Singh, Sanjay; D'Souza, S. W.; Nayak, J.; Caron, L.; Suard, E.; Chadov, S.; Felser, C.
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134102 APR 6 2016
Abstract:
Ni2MnGa exhibits ideal ferromagnetic shape memory properties, however, brittleness and a low-temperature martensite transition hinder its technological applications motivating the search for novel materials showing better mechanical properties as well as higher transition temperatures. In this work, the crystal structure, phase transitions, and the magnetic properties of quaternary Ni2-x Pt-x MnGa(0 <= x <= 1) shape memory alloys were studied experimentally by x-ray diffraction, magnetization measurements, and neutron diffraction and compared to ab initio calculations. Compositions within 0 <= x <= 0.25 exhibit the cubic austenite phase at room temperature. The x approximate to 0.3 composition exhibits a seven-layer modulated monoclinic martensite structure. Within 0.4 <= x <= 1, the system stabilizes in the nonmodulated tetragonal structure. The martensite transition has very narrow thermal hysteresis 0 <= x <= 0.3, which is a typical characteristic of a shape memory alloy. By increasing x, the temperature of the martensite transition increases, while that of the magnetic transition decreases. The x = 1 composition (NiPtMnGa) in the martensite phase undergoes a para-to-ferrimagnetic transition. The saturation magnetization exhibits a nontrivial behavior with increasing up to x approximate to 0.25, above which, it suddenly decreases. Powder neutron diffraction reveals the presence of antisite disorder, with about 17% of the original Ga sites being occupied by Mn. Computations suggest that the antisite disorder triggers an antiferromagnetic coupling between two Mn atoms in different crystallographic positions, resulting into a sudden drop of the saturation magnetization for higher x.
Title:
Comparative study of the field-induced and spontaneous AF2 ' multiferroic phases in MnWO4 and Mn0.90Co0.10WO4 within the magnetic symmetry framework
Authors:
Urcelay-Olabarria, I; Garcia-Munoz, JL; Ressouche, E; Mukhin, AA; Skumryev, V Author Full Names: Urcelay-Olabarria, Irene; Luis Garcia-Munoz, Jose; Ressouche, Eric; Mukhin, Alexander A.; Skumryev, Vassil
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 520-527; 10.1107/S1600576716000881 2 APR 2016
Abstract:
(Mn,Co)WO4 compounds are regarded as reference spin-induced multiferroics. A comparative study is presented here, within the magnetic symmetry framework, of the incommensurate magnetic orders responsible for the ferroelectric phases of (i) MnWO4 under a magnetic field (H vertical bar vertical bar b) and (ii) Mn0.90Co0.10WO4 in the absence of an external field. On the one hand, although these two ferroelectric phases are stabilized under different external physical conditions, both present the same Xc1'(alpha 0 gamma)ss magnetic symmetry and practically the same modulation vector. The magnetic ordering in both phases is an elliptical helix with the magnetic moments (as the polarization vector, P) perpendicular to the b axis, although in most of the ferroelectric compositions of the (Mn,Co)WO4 family the spins rotate in planes containing b (and have P vertical bar vertical bar b). On the other hand, the anisotropy of the resulting magnetic modulations is extraordinarily different in the two phases. This is described and explained in the light of the different anisotropies of Co and Mn ions.
Title:
Structure determination of a pseudo-decagonal quasicrystal approximant by the strong-reflections approach and rotation electron diffraction
Authors:
Singh, D; Yun, YF; Wan, W; Grushko, B; Zou, XD; Hovmoller, S Author Full Names: Singh, Devinder; Yun, Yifeng; Wan, Wei; Grushko, Benjamin; Zou, Xiaodong; Hovmoller, Sven
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 433-441; 10.1107/S1600576716000042 2 APR 2016
Abstract:
The structure of a complicated pseudo-decagonal (PD) quasicrystal approximant in the Al-Co-Ni alloy system, denoted as PD1, was solved by the strong-reflections approach on three-dimensional rotation electron diffraction (RED) data, using the phases from the known PD2 structure. RED shows that the PD1 crystal is primitive and orthorhombic, with a = 37.3, b = 38.8, c = 8.2 angstrom. However, as with other approximants in the PD series, the superstructure reflections (corresponding to c = 8.2 angstrom) are much weaker than those of the main reflections (corresponding to c = 4.1 angstrom), so it was decided to solve the PD1 structure in the smaller primitive unit cell first, i.e. with unit-cell parameters a = 37.3, b = 38.8, c = 4.1 angstrom and space group Pnam. A density map of PD1 was calculated from only the 15 strongest unique reflections. It contained all 31 Co/Ni atoms and many weaker peaks corresponding to Al atoms. The structure obtained from the strong-reflections approach was confirmed by applying direct methods to the complete RED data set. Successive refinement using the RED data set resulted in 108 unique atoms (31 Co/Ni and 77 Al). This is one of the most complicated approximant structures ever solved by electron diffraction. As with other approximants in the PD series, PD1 is built of characteristic 2 nm wheel clusters with fivefold rotational symmetry, which agrees with results from high-resolution electron microscopy images. The simulated electron diffraction patterns for the structure model are in good agreement with the experimental electron diffraction patterns obtained by RED.
Title:
Jacques Friedel and the physics of metals and alloys
Authors:
Villain, J; Lavagna, M; Bruno, P Author Full Names: Villain, Jacques; Lavagna, Mireille; Bruno, Patrick
Source:
COMPTES RENDUS PHYSIQUE, 17 (3-4):276-290; 10.1016/j.crhy.2015.12.010 MAR-APR 2016
Abstract:
This is an introduction to the theoretical physics of metals for students and physicists from other specialities. Certain simple consequences of the Fermi statistics in pure metals are first addressed, namely the Peierls distortion, Kohn anomalies and the Labbe-Friedel distortion. Then the physics of dilute alloys is discussed. The analogy with nuclear collisions was a fruitful starting point, which suggested one should analyze the effects of impurities in terms of a scattering problem with the introduction of phase shifts. Starting from these concepts, Friedel derived a theory of the resistivity of alloys, and a celebrated sum rule relating the phase shifts at the Fermi level to the number of electrons in the impurity, which turned out to play a prominent role later in the context of correlated impurities, as for instance in the Kondo effect. Friedel oscillations are also an important result, related to incommensurate magnetic structures. It is shown how they can be derived in various ways: from collision theory, perturbation theory, self-consistent approximations and Green's function methods. While collision theory does not permit to take the crystal structure into account, which is responsible for electronic bands, those effects can be included in other descriptions, using for instance the tight binding approximation. (C) 2015 The Authors. Published by Elsevier Masson SAS on behalf of Academie des sciences.

Update: 22-Apr-2016

Title:
X-ray study of the anomalous thermal hystereses of the modulation wavevectors in Cs2HgCl4
Authors:
Bagautdinov, B; Shaw, Z; Orlov, A; Aliev, MA Author Full Names: Bagautdinov, Bagautdin; Shaw, Zachery; Orlov, Andrii; Aliev, Marat A.
Source:
PHASE TRANSITIONS, 89 (5):471-479; 10.1080/01411594.2015.1080258 MAY 3 2016
Abstract:
A rich sequence of structural modulations in Cs2HgCl4 as a function of temperature was studied by means of X-ray diffraction. Accurate satellite-position measurements on the cooling and heating paths of the crystal revealed abnormal thermal hystereses for incommensurate phases and coexistences of neighboring commensurate phases. A well-defined X-ray picture of the a-axis modulated phases in the range of 221-184K were observed on the heating path, while the c-axis modulated phases existing below 184K were definitely detected on the cooling path. The proper conditions for a precise phase diagram of Cs2HgCl4 can be correlated with relatively defect-free transformations of a-axis modulations at heating and of c-axis modulations at cooling. The peculiarity of Cs2HgCl4 to switch modulation direction among the a- and c-axes at 184K allows us deliberately accumulate and thus control a majority of mobile defects on the mutually perpendicular (100) or (001) planes by possessing crystal within temperature domain of a- or c-axes modulations, respectively.
Title:
Phase transformation behavior of Cu-10Ni-3Al-0.8Si alloy
Authors:
Shen, LN; Li, Z; Zhao, YY; Wang, Y; Dong, QY; Wang, MY Author Full Names: Shen, Leinuo; Li, Zhou; Zhao, Yuyuan; Wang, Yang; Dong, Qiyi; Wang, Mengying
Source:
MATERIALS CHEMISTRY AND PHYSICS, 173 421-428; 10.1016/j.matchemphys.2016.02.033 APR 15 2016
Abstract:
Microstructure evolution of solution treated Cu-10Ni-3Al-0.8Si alloy aged at different temperatures was investigated and different transformation products were observed: modulated structure resulting from spinodal decomposition, L1(2) ordering of matrix, continuous Ni3Al precipitates, continuous delta-Ni2Si precipitates and discontinuous precipitates. Modulated structure, L1(2) ordering of matrix and micro-twins formed initially at 450 degrees C, while continuous Ni3Al and delta-Ni2Si particles precipitated soon. Increasing temperature led to the formation of discontinuous precipitates, dissolution of Ni3Al and cellular decomposition. The alloy showed excellent over-aging resistance at 450 degrees C because the Ni3Al and delta-Ni2Si precipitates grew very slowly and the addition of silicon hindered the precipitation of the coarsening NiAl phase. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Interplay of charge density wave and multiband superconductivity in 2H-PdxTaSe2
Authors:
Bhoi, D; Khim, S; Nam, W; Lee, BS; Kim, C; Jeon, BG; Min, BH; Park, S; Kim, KH Author Full Names: Bhoi, D.; Khim, S.; Nam, W.; Lee, B. S.; Kim, Chanhee; Jeon, B. -G.; Min, B. H.; Park, S.; Kim, Kee Hoon
Source:
SCIENTIFIC REPORTS, 6 10.1038/srep24068 APR 5 2016
Abstract:
2H-TaSe2 has been one of unique transition metal dichalcogenides exhibiting several phase transitions due to a delicate balance among competing electronic ground states. An unusual metallic state at high-T is sequentially followed by an incommensurate charge density wave (ICDW) state at approximate to 122 K and a commensurate charge density wave (CCDW) state at approximate to 90 K, and superconductivity at T-C similar to 0.14 K. Upon systematic intercalation of Pd ions into TaSe2, we find that CCDW order is destabilized more rapidly than ICDW to indicate a hidden quantum phase transition point at x similar to 0.09-0.10. Moreover, T-C shows a dramatic enhancement up to 3.3 K at x = 0.08, similar to 24 times of T-C in 2H-TaSe2, in proportional to the density of states N(E-F). Investigations of upper critical fields H-C2 in single crystals reveal evidences of multiband superconductivity as temperature-dependent anisotropy factor gamma(H) = H-C2(ab)/HHC2C, quasi-linear increase of H-C2(C) (T), and an upward, positive-curvature in H-C2(ab) (T) near T-C. Furthermore, analysis of temperature-dependent electronic specific heat corroborates the presence of multiple superconducting gaps. Based on above findings and electronic phase diagram vs x, we propose that the increase of N(E-F) and effective electron-phonon coupling in the vicinity of CDW quantum phase transition should be a key to the large enhancement of T-C in PdxTaSe2.
Title:
Synthesis and anisotropic properties of single crystalline Ln(2)Ru(3)Al(15+x) (Ln=Gd, Tb)
Authors:
Morrison, G; Prestigiacomo, J; Haldolaarachchige, N; Rai, BK; Young, DP; Stadler, S; Morosan, E; Chan, JY Author Full Names: Morrison, Gregory; Prestigiacomo, Joseph; Haldolaarachchige, Neel; Rai, Binod K.; Young, David P.; Stadler, Shane; Morosan, Emilia; Chan, Julia Y.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 236 186-194; SI 10.1016/j.jssc.2015.08.009 APR 2016
Abstract:
Single crystals of Ln(2)Ru(3)Al(15+x)(Ln=Gd, Tb) have been grown using the self-flux method under Ru-poor conditions. The structure of the Gd analog is found to be highly dependent on the synthesis method. Gd2Ru3Al15.08 orders antiferromagnetically at 17.5 K. Tb2Ru3Al15.05 enters an antiferromagnetic state at 16.6 K followed by a likely incommensurate-to-commensurate transition at 14.9 K for crystals oriented with HI lab. For crystals oriented with H//c, a broad maximum is observed in the temperature dependent M/H indicative of a highly anisotropic magnetic system with the hard axis in the c-direction. The magnetization as a function of field and magnetoresistance along the ab-direction of Tb2Ru3Al15.05 display a stepwise behavior and indicate strong crystalline electric field effects. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Crystal growth of incommensurate members of 2H-hexagonal perovskite related oxides: Ba4MzPt3-zO9 (M=Co, Ni, Cu, Zn, Mg, Pt)
Authors:
Ferreira, T; Morrison, G; Yeon, J; zur Loye, HC Author Full Names: Ferreira, Timothy; Morrison, Gregory; Yeon, Jeongho; zur Loye, Hans-Conrad
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 236 2-9; SI 10.1016/j.jssc.2015.10.040 APR 2016
Abstract:
Millimeter sized crystals of six oxides of approximate composition Ba4MzPt3-zO9 (M=Co, Ni, Cu, Zn, Mg, Pt) were grown from molten K2CO3 fluxes and found to crystallize in a 2H hexagonal perovskite-related structure type. The compositions of these incommensurate structures, which belong to the A(3n+3m)A'(n) B3m+nO9m+6n family of 2H hexagonal perovskite related oxides, were characterized by X-ray diffraction, energy dispersive spectroscopy, and magnetic susceptibility measurements. The specific synthetic considerations, crystal growth conditions, and magnetic susceptibility measurements are discussed. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Interplay between multiple charge-density waves and the relationship with superconductivity in PdxHoTe3
Authors:
Lou, R; Cai, YP; Liu, ZH; Qian, T; Zhao, LX; Li, Y; Liu, K; Han, ZQ; Zhang, DD; He, JB; Chen, GF; Ding, H; Wang, SC Author Full Names: Lou, Rui; Cai, Yipeng; Liu, Zhonghao; Qian, Tian; Zhao, Lingxiao; Li, Yu; Liu, Kai; Han, Zhiqing; Zhang, Dandan; He, Junbao; Chen, Genfu; Ding, Hong; Wang, Shancai
Source:
PHYSICAL REVIEW B, 93 (11):10.1103/PhysRevB.93.115133 MAR 21 2016
Abstract:
HoTe3, a member of the rare-earth tritelluride (RTe3) family, and its Pd-intercalated compounds, PdxHoTe3, where superconductivity (SC) sets in as the charge-density wave (CDW) transition is suppressed by the intercalation of a small amount of Pd, are investigated using angle-resolved photoemission spectroscopy (ARPES) and electrical resistivity. Two incommensurate CDWs with perpendicular nesting vectors are observed in HoTe3 at low temperatures. With a slight Pd intercalation (x = 0.01), the large CDW gap decreases and the small one increases. The momentum dependence of the gaps along the inner Fermi surface (FS) evolves from orthorhombicity to near tetragonality, manifesting the competition between two CDW orders. At x = 0.02, both CDW gaps decrease with the emergence of SC. Further increasing the content of Pd for x = 0.04 will completely suppress the CDW instabilities and give rise to the maximal SC order. The evolution of the electronic structures and electron-phonon couplings (EPCs) of the multiple CDWs upon Pd intercalation are carefully scrutinized. We discuss the interplay between multiple CDW orders, and the competition between CDW and SC in detail.

Update: 15-Apr-2016

Title:
Cycloid spirals and cycloid cone transition in the HoMn6-xCrxGe6 (T, x) magnetic phase diagramm by neutron diffraction
Authors:
Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Buschow, KHJ Author Full Names: Schobinger-Papamantellos, P.; Rodriguez-Carvajal, J.; Buschow, K. H. J.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 408 233-243; 10.1016/j.jmmm.2016.02.018 JUN 15 2016
Abstract:
The structures and magnetic properties of the antiferromagnetic hexagonal pseudo ternary compounds HoMn6-xCrxGe6 (x=1, 1.5 and 2) are studied by neutron diffraction in the temperature range 1.5-300 K. The substitution of nonmagnetic Cr for Mn greatly affects the magnetic properties of HoMn6Ge6 by reducing the ordering temperature from 466 K to 278 K, 205 K and 130 K for (x=0, 1, 1.5 and 2) respectively, increasing the c/a ratio, suppressing the high temperature (HT) commensurate phase with q(2)=(0, 0, 1/2) and changing the high temperature (LT) q(1)=(0, 0, q(1z)) skew spiral rotation plane. HoMn5CrGe6 and HoMn4Cr2Ge6 display in the entire magnetically ordered regime cycloid spiral structures with the wave vector: q=(0, 0, q(z)), q(z) approximate to 0.18(3) r.l.u. and q(z) approximate to 64.8 degrees turn angle. The Ho and Mn/ Cr (001) layers have ferromagnetic arrangements coupled antiferromagnetically. The Ho moments in the z=0 layer are oriented in a direction opposite to the line bisecting the angle 2 phi(Mn) approximate to 2 x 28 degrees of the Mn layers at z = +/-similar to 0.25. This triple unit changes orientation collectively in the direction of q within the (b, c) plane containing the wave vector. Above 50 K, the wave vector length increases linearly from 0.24 to 0.28 (1) r.l.u. below T-N. The HT HoMn4.5Cr1.5Ge6 cycloid spiral, is stable in the range T-t < T < T-N (q(1)=(0,0,q(1z)), q(1z)=0.1711(3) r. I.u., Phi(s), =61.6 degrees at 40 K). At variance to the other compounds, crossing Try 36 K from above, it undergoes a first order magnetoelastic transition from a cycloid HT q(1) to a LT longitudinal cone structure: q(2)=(0, 0, q2z), q2z=0.149 r.l.u., Phi(s)=53.6 degrees and cone angle Phi(c)=47 degrees. The q(1) and q(2) phases coexist in the LT range down to 1.5 K <= T <= T-t in varying amounts with T. This transition is directly manifested by the splitting of the HT magnetic satellites and the increase of characteristic nuclear intensities. The results are summarised in a (T, x) magnetic phase diagram. (C) 2016 Elsevier B.V. All rights reserved.
Title:
Neutron scattering studies of spin-phonon hybridization and superconducting spin gaps in the high-temperature superconductor La2-x(Sr, Ba)(x)CuO4
Authors:
Wagman, JJ; Carlo, JP; Gaudet, J; Van Gastel, G; Abernathy, DL; Stone, MB; Granroth, GE; Kolesnikov, AI; Savici, AT; Kim, YJ; Zhang, H; Ellis, D; Zhao, Y; Clark, L; Kallin, AB; Mazurek, E; Dabkowska, HA; Gaulin, BD Author Full Names: Wagman, J. J.; Carlo, J. P.; Gaudet, J.; Van Gastel, G.; Abernathy, D. L.; Stone, M. B.; Granroth, G. E.; Kolesnikov, A. I.; Savici, A. T.; Kim, Y. J.; Zhang, H.; Ellis, D.; Zhao, Y.; Clark, L.; Kallin, A. B.; Mazurek, E.; Dabkowska, H. A.; Gaulin, B. D.
Source:
PHYSICAL REVIEW B, 93 (9):10.1103/PhysRevB.93.094416 MAR 14 2016
Abstract:
We present time-of-flight neutron scattering measurements on single crystals of La2-xBaxCuO4 (LBCO) with 0 <= x <= 0.095 and La2-xSrxCuO4 (LSCO) with x = 0.08 and 0.11. This range of dopings spans much of the phase diagram relevant to high-temperature cuprate superconductivity, ranging from insulating, three-dimensional commensurate long-range antiferromagnetic order, for x <= 0.02, to two-dimensional (2D) incommensurate antiferromagnetism coexisting with superconductivity for x >= 0.05. Previous work on lightly doped LBCO with x = 0.035 showed a clear enhancement of the inelastic scattering coincident with the low-energy crossings of the highly dispersive spin excitations and quasi-2D optic phonons. The present work extends these measurements across the phase diagram and shows this enhancement to be a common feature to this family of layered quantum magnets. Furthermore, we show that the low-temperature, low-energy magnetic spectral weight is substantially larger for samples with nonsuperconducting ground states relative to any of the samples with superconducting ground states. Spin gaps, suppression of low-energy magnetic spectral weight as a function of decreasing temperature, are observed in both superconducting LBCO and LSCO samples, consistent with previous observations for superconducting LSCO.

Update: 7-Apr-2016

Title:
A Partial Isothermal Section at 1000 A degrees C of Al-Mn-Fe Phase Diagram in Vicinity of Taylor Phase and Decagonal Quasicrystal
Authors:
Priputen, P; Cernickova, I; Lejcek, P; Janickovic, D; Janovec, J Author Full Names: Priputen, P.; Cernickova, I.; Lejcek, P.; Janickovic, D.; Janovec, J.
Source:
JOURNAL OF PHASE EQUILIBRIA AND DIFFUSION, 37 (2):130-134; 10.1007/s11669-015-0432-0 APR 2016
Abstract:
Altogether 19 alloys of an Al-Mn-Fe system with compositions near to the Taylor phase and/or the decagonal quasicrystal were characterised by the x-ray diffraction and the energy-dispersive x-ray spectroscopy coupled with the scanning electron microscopy, after annealing at 1000 A degrees C for 330 h. The obtained experimental results were used to propose a partial isothermal section at 1000 A degrees C of the Al-Mn-Fe phase diagram. The ternary T-phase area of an untypical saddle shape was found to touch the Al-Mn binary one. The gamma(2)- phase was found to be stable between 2 and 30 at.% of Fe at 1000 A degrees C and boundaries between gamma(1)- and gamma(2)-areas are expected to be located very close to the Al-Mn binary.

Update: 1-Apr-2016

Title:
Evidence of multiferroicity in NdMn2O5
Authors:
Chattopadhyay, S; Baledent, V; Damay, F; Gukasov, A; Moshopoulou, E; Auban-Senzier, P; Pasquier, C; Andre, G; Porcher, F; Elkaim, E; Doubrovsky, C; Greenblatt, M; Foury-Leylekian, P Author Full Names: Chattopadhyay, S.; Baledent, V.; Damay, F.; Gukasov, A.; Moshopoulou, E.; Auban-Senzier, P.; Pasquier, C.; Andre, G.; Porcher, F.; Elkaim, E.; Doubrovsky, C.; Greenblatt, M.; Foury-Leylekian, P.
Source:
PHYSICAL REVIEW B, 93 (10):10.1103/PhysRevB.93.104406 MAR 8 2016
Abstract:
Recently, RMn2O5 (R = rare earth, Bi, Y) type multiferroics have drawn considerable attention, because of magnetically induced ferroelectricity along with an extremely large magnetoelectric coupling. Here, we present a detailed study on NdMn2O5 which is a crucial composition between the nonferroelectric PrMn2O5 and ferroelectric SmMn2O5. We report the results of heat capacity, magnetization, dielectric permittivity, and electric polarization measurements along with an accurate description of the structural and microscopic magnetic properties obtained from high resolution x-ray and neutron diffraction studies. We show that NdMn2O5 is ferroelectric, although the magnitude of polarization is much weaker than that of the other multiferroic members. The direction of the polarization is along the crystallographic b axis and its magnitude can be tuned with the application of a magnetic field. Moreover, unlike the other multiferroic members of this series, ferroelectricity in NdMn2O5 emerges in an incommensurate magnetic state. The present study also provides evidence in support of the influence of the rare-earth size on the magnetoelectric phase diagram.
Title:
Thermally and Electrochemically Driven Topotactical Transformations in Sodium Layered Oxides NaxVO2
Authors:
Didier, C; Guignard, M; Suchomel, MR; Carlier, D; Darriet, J; Delmas, C Author Full Names: Didier, Christophe; Guignard, Marie; Suchomel, Matthew R.; Carlier, Dany; Darriet, Jacques; Delmas, Claude
Source:
CHEMISTRY OF MATERIALS, 28 (5):1462-1471; 10.1021/acs.chemmater.5b04882 MAR 8 2016
Abstract:
Phase diagrams and structural transformations in the complex NaxVO2 system have been studied using electrochemical (de)intercalation and in situ and operando high resolution synchrotron powder diffraction. Starting from O'3-Na1/2VO2 obtained by sodium electrochemical deintercalation of O'3-NaVO2, the structural details of irreversible and reversible thermally driven transformations to P'3 and P3 type structures are presented. Subsequently, these P'3-NaxVO(2) phases provide a platform for operando studies exploring the NaxVO2 phase diagram as a function of sodium electrochemical (de) intercalation. In this system, three single phase domains have been found: a line phase P'3-Na1/2VO2, one solid solution for 0.53 <= x <= 0.55 characterized by an incommensurate modulated structure, and a second solid solution for 0.63 <= x <= 0.65 with a defective structure resulting from a random stack of O'3 and P'3 layers. With further sodium intercalation (x > 0.65), the structure irreversibly transforms to the starting parent phase O3-NaVO2. This work reveals new details about the diverse structural polymorphs found in sodium layered oxides used as electrode battery materials and the transitional pathways between them as a function of temperature and composition.
Title:
Tailoring Magnetic Behavior in the Tb-Au-Si Quasicrystal Approximant System
Authors:
Gebresenbut, GH; Andersson, MS; Nordblad, P; Sahlberg, M; Gomez, CP Author Full Names: Gebresenbut, Girma H.; Andersson, Mikael S.; Nordblad, Per; Sahlberg, Martin; Gomez, Cesar Pay
Source:
INORGANIC CHEMISTRY, 55 (5):2001-2008; 10.1021/acs.inorgchem.5b02286 MAR 7 2016
Abstract:
A novel synthesis method, "arc-melting-self-flux", has been developed and a series of five Tsai-type 1/1 approximant crystals in the Tb-Au-Si system have been synthesized. The synthesis method, by employing a temperature program which oscillates near the melting and nucleation points of the approximants, has provided high-quality and large single crystals in comparison to those obtained from the standard arc-melting-annealing and self-flux methods. The atomic structures of the approximants have been determined from single-crystal X-ray diffraction data and described using concentric atomic clusters with icosahedral symmetry. The compounds are nearly isostructural with subtle variations; two types of atomic clusters which mainly vary at their cluster centers are observed. One type contains a Tb site at the center, and the other contains a disordered tetrahedron decorated with Au/Si mixed sites. Both cluster types can be found coexisting in the approximants. The compounds have different average weighted ratios of central Tb to disordered tetrahedron in the bulk material. Furthermore, a strategy for chemically tuning magnetic behavior is presented. Magnetic property measurements on the approximants revealed that the magnetic transition temperature (T-c) decreases as the occupancy of the central Tb site increases. T-c decreased from 11.5 K for 0% occupancy of the central Tb to 8 K for 100% occupancy. Enhanced magneto crystalline anisotropy is observed for the approximants with higher central Tb occupancy in comparison to their low central Tb occupancy counterparts. Hence, the previously reported "ferrimagnetic-like" magnetic structure model remains valid.
Title:
Athermal and deformation-induced omega-phase transformations in biomedical beta-type alloy Ti-9Cr-0.20
Authors:
Liu, HH; Niinomi, M; Nakai, M; Cho, K Author Full Names: Liu, Huihong; Niinomi, Mitsuo; Nakai, Masaaki; Cho, Ken
Source:
ACTA MATERIALIA, 106 162-170; 10.1016/j.actamat.2016.01.008 MAR 2016
Abstract:
The alloy Ti-9Cr-0.20 has been developed as a potential material for implant rods used in spinal fixation applications, since it exhibits good mechanical properties and a remarkably "changeable Young's modulus", which is achieved by suppressing the athermal omega-phase formed upon quenching and enhancing the deformation-induced omega-phase transformation. In this study, athermal and deformation induced omega-phase transformations in Ti-9Cr-0.20 were investigated systematically by transmission electron microscopy. This was done in order to understand the nature of these omega-phase transformations, as well as the specific functionality the "changeable Young's modulus" resulting from them. In solution-treated alloy samples, in addition to ideal omega-structures, structures considered as initial omega-structures associated with incommensurate omega-phase were observed. This might be attributed to the composition heterogeneity, heterogeneity of oxygen distribution, and/or the inhomogeneous distribution of defects such as vacancies and locally strained areas. Following cold rolling, some of the selected area electron diffraction patterns of the alloy showed that the reflections of one omega-variant had increased significantly in intensity while those of the other omega-variant had decreased sharply. This vanishing of one type of variant omega-structures is attributable to two possible mechanisms: (i) a reversal mechanism, under which the particular <111> partial dislocations transform the corresponding omega-variants back into beta-phase or (ii) a re-orientation mechanism, according to which the omega-variants unfavorable with regard to the loading direction re-orient and turn into the preferred omega-variants. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
SrPt2Al2 - A(3+2)D-incommensurately modulated variant of the CaBe2Ge2 type structure
Authors:
Hoffmann, RD; Stegemann, F; Janka, O Author Full Names: Hoffmann, Rolf-Dieter; Stegemann, Frank; Janka, Oliver
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (3):127-142; 10.1515/zkri-2015-1891 MAR 2016
Abstract:
The first ternary compound in the Sr-Pt-Al system, SrPt2Al2, was synthesized by melting of the elements in a sealed niobium tube in a high frequency furnace. The structure of SrPt2Al2 was determined by single-crystal X-ray diffraction on the basis of data sets recorded at 90, 150, 210, 270 and 300 K. The compound crystallizes in an incommensurately modulated (3+2)D structure being related to the tetragonal primitive CaBe2Ge2 type structure. The structure was refined in the orthorhombic superspace group Pmmn(alpha, 0,0) 0s0(0,beta,0) s00 (alpha = 0.222(1) a*, beta = 0.224(1) b*, a = b = 436.89(5), c = 1010.16(13) pm at 90 K) with R-M = 0.0403, R-S,R-1 = 0.0597 and R-S,R-2 = 0.2046. The structural relation with CaBe2Ge2 along with a refinement in the tetragonal superspace group P4/nmm(alpha, 0,0)-0000(0,alpha,0)00s0 is discussed with respect to the temperature dependence of the q-vectors and by group-subgroup relations. The modulation, from the standpoint of the crystal chemistry, is mainly caused by the distortion of the Pt arrangements within the pseudo-tetragonal ab plane.
Title:
The modulated structure of intermediate-valent CeCoGa
Authors:
Niehaus, O; Hoffmann, RD; Chevalier, B; Pottgen, R Author Full Names: Niehaus, Oliver; Hoffmann, Rolf-Dieter; Chevalier, Bernard; Poettgen, Rainer
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (3):143-153; 10.1515/zkri-2015-1882 MAR 2016
Abstract:
CeCoGa was synthesized by melting of the elements in an arc-melting furnace as well as in a sealed niobium tube in an induction furnace. A further annealing step improves the purity and crystallinity of the samples significantly. Its structure was refined on the basis of single-crystal X-ray diffractometer data at different temperatures. Already at room temperature CeCoGa crystallizes in a superstructure of the HT-CeCoAl type. This superstructure can be described in the (3 + 1)D superspace group C2/m(alpha 0 gamma) 00; alpha = 2/3, gamma = 1/3 with a temperature independent q-vector (Z = 4). For the 300 K data (also for 90 K) the commensurate *modulated structure* could be refined with 1336 F-2 values, 56 variables and residuals of wR = 0.0348 for the main and wR = 0.0605 for the satellites of 1st order [a = 1101.7(1), b = 436.0(1) and c = 482.4(1) pm, beta = 103.2(1)degrees]. Furthermore a description in a transformed 3D supercell with the space group C2/m and Z = 12 is possible. For the 90 K data this 3D supercell was refined with 1289 F-2 values, 56 variables and a residual of wR = 0.0409 [a = 1618.8(1), b = 435.3(1) and c = 1094.1(1) pm, beta = 119.3(1)degrees]. The relation of the HT-CeCoAl type structure, the (3 + 1)D modulated and the 3D supercell structure are discussed on the basis of a group-subgroup relation. By thermal analysis and magnetic measurements the phase transition temperature to the HT-CeCoAl type structure is stated slightly above 475 K. Furthermore intermediate cerium valence was identified by the magnetic susceptibility.
Title:
The estimation of phason flips in 1D quasicrystal from the diffraction pattern
Authors:
Buganski, I; Strzalka, R; Wolny, J Author Full Names: Buganski, Ireneusz; Strzalka, Radoslaw; Wolny, Janusz
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 253 (3):450-457; 10.1002/pssb.201552426 MAR 2016
Abstract:
The statistical approach based on the average unit-cell concept and the envelop functions for the diffraction pattern were used to estimate the number of phason flips in the model 1D quasicrystal (Fibonacci chain). The characteristic function of a statistical distribution expanded to a power series with distribution moments as coefficients can be used to retrieve phases of diffraction peaks. In addition, the number of flips in the structure can be designated in two ways: with the value of the second moment's value and directly from the shape of a probability density function retrieved from the diffraction pattern. In this paper, all calculations are performed for a nondecorated Fibonacci chain. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Title:
Schottky effect in the i-Zn-Ag-Sc-Tm icosahedral quasicrystal and its 1/1 Zn-Sc-Tm approximant
Authors:
Jazbec, S; Kashimoto, S; Kozelj, P; Vrtnik, S; Jagodic, M; Jaglicic, Z; Dolinsek, J Author Full Names: Jazbec, S.; Kashimoto, S.; Kozelj, P.; Vrtnik, S.; Jagodic, M.; Jaglicic, Z.; Dolinsek, J.
Source:
PHYSICAL REVIEW B, 93 (5):10.1103/PhysRevB.93.054208 FEB 23 2016
Abstract:
The analysis of low-temperature specific heat of rare-earth (RE)-containing quasicrystals and periodic approximants and consequent interpretation of their electronic properties in the T -> 0 limit is frequently hampered by the Schottky effect, where crystalline electric fields lift the degeneracy of the RE-ion Hund's rule ground state and introduce additional contribution to the specific heat. In this paper we study the low-temperature specific heat of a thulium-containing i-Zn-Ag-Sc-Tm icosahedral quasicrystal and its 1/1 Zn-Sc-Tm approximant, both being classified as "Schottky" systems. We have derived the crystal-field Hamiltonian for pentagonal symmetry of the crystalline electric field, pertinent to the class of Tsai-type icosahedral quasicrystals and their approximants, where the RE ions are located on fivefold axes of the icosahedral atomic cluster. Using the leading term of this Hamiltonian, we have calculated analytically the Schottky specific heat in the presence of an external magnetic field and made comparison to the experimental specific heat of the investigated quasicrystal and approximant. When the low-temperature specific heat C is analyzed in a C/T versus T-2 scale (as it is customarily done for metallic specimens), the Schottky specific heat yields an upturn in the T -> 0 limit that cannot be easily distinguished from a similar upturn produced by the electron-electron interactions in exchange-enhanced systems and strongly correlated systems. Our results show that extraction of the electronic properties of RE-containing quasicrystals from their low-temperature specific heat may be uncertain in the presence of the Schottky effect.
Title:
Mechanical and tribological properties of AlCuFe quasicrystal and Al(Si)CuFe approximant thin films
Authors:
Olsson, S; Broitman, E; Garbrecht, M; Birch, J; Hultman, L; Eriksson, F Author Full Names: Olsson, Simon; Broitman, Esteban; Garbrecht, Magnus; Birch, Jens; Hultman, Lars; Eriksson, Fredrik
Source:
JOURNAL OF MATERIALS RESEARCH, 31 (2):232-240; 10.1557/jmr.2015.384 JAN 28 2016
Abstract:
Multilayered thin films of Al/Cu/Fe have been prepared by magnetron sputtering and annealed into quasicrystalline and approximant phases on Al2O3 and Si substrates, respectively. The nanomechanical and nanotribological properties, such as hardness, elastic modulus, friction, and toughness, have been measured using a triboindenter and analytical methods. The approximant phase was proved to be slightly harder than the quasicrystalline phase with a hardness of about 15.6 GPa, and with a similar elastic modulus of about 258 GPa. These values however decreased rapidly with an increasing amount of Si in the approximant. The indentation toughness of the approximant, <0.1 MPa/m(1/2), was however inferior to that of the quasicrystals with 1.5 MPa/m(1/2). Friction coefficients were measured in a range of 0.10-0.14 for both the quasicrystalline and approximant thin films.

Update: 24-Mar-2016

Title:
Design and Synthesis of a Geopolymer-Enhanced Quasi-Crystalline Composite for Resisting Wear and Corrosion
Authors:
Ozaydin, MF; Liang, H Author Full Names: Ozaydin, M. Fevzi; Liang, Hong
Source:
JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME, 138 (2):10.1115/1.4031400 APR 2016
Abstract:
Multiphase composites are attractive for improved mechanical performance and corrosion resistance. In this research, a new composite consisting quasi-crystalline Al75Mn14Si7Fe4 alloy of icosahedral, cubic alpha-AlMnSiFe, monoclinic Al13Fe4 phases, and ferro-silico-aluminate geopolymer was synthesized using rapid solidification and thermal treatment methods. The concentration of icosahedral phase (i-phase) was controlled and the formation of geopolymer was obtained through heat treatment. Characterization showed that the microhardness and wear resistance were increased with the amount of i-phase. The corrosion resistance, on the other hand, was improved with the existence of the geopolymer. This research demonstrates an effective approach in processing a multi-phase composite that has desired properties and performance through multiphase design and composition.
Title:
Coexistence of Incommensurate Magnetism and Superconductivity in the Two-Dimensional Hubbard Model
Authors:
Yamase, H; Eberlein, A; Metzner, W Author Full Names: Yamase, Hiroyuki; Eberlein, Andreas; Metzner, Walter
Source:
PHYSICAL REVIEW LETTERS, 116 (9):10.1103/PhysRevLett.116.096402 MAR 4 2016
Abstract:
We analyze the competition of magnetism and superconductivity in the two-dimensional Hubbard model with a moderate interaction strength, including the possibility of incommensurate spiral magnetic order. Using an unbiased renormalization group approach, we compute magnetic and superconducting order parameters in the ground state. In addition to previously established regions of Neel order coexisting with d-wave superconductivity, the calculations reveal further coexistence regions where superconductivity is accompanied by incommensurate magnetic order.
Title:
Evolution of the charge density wave superstructure in ZrTe3 under pressure
Authors:
Hoesch, M; Garbarino, G; Battaglia, C; Aebi, P; Berger, H Author Full Names: Hoesch, Moritz; Garbarino, Gaston; Battaglia, Corsin; Aebi, Philipp; Berger, Helmuth
Source:
PHYSICAL REVIEW B, 93 (12):10.1103/PhysRevB.93.125102 MAR 1 2016
Abstract:
The material ZrTe3 is a well-known example of an incommensurate periodic lattice distortion (PLD) at low temperatures due to a charge density wave (CDW). Previous studies have found a sharp boundary as a function of pressure between CDW below 5 GPa and bulk superconductivity above this value. We present a study of low-temperature-high-pressure single crystal x-ray diffraction along with ab initio density functional theory calculations. The modulation vector q(CDW) is found to change smoothly with pressure until the PLD is lost. Fermi surface calculations reproduce these changes, but neither these nor the experimental crystal lattice structure show a particular step change at 5 GPa, thus leading to the conclusion that the CDW is lost accidentally by tipping the balance of CDW formation in the Fermi surface nesting that stabilizes it.
Title:
Incommensurate spin-density-wave antiferromagnetism in CeRu2Al2B
Authors:
Bhattacharyya, A; Khalyavin, DD; Kruger, F; Adroja, DT; Strydom, AM; Kockelmann, WA; Hillier, AD Author Full Names: Bhattacharyya, A.; Khalyavin, D. D.; Krueger, F.; Adroja, D. T.; Strydom, A. M.; Kockelmann, W. A.; Hillier, A. D.
Source:
PHYSICAL REVIEW B, 93 (6):10.1103/PhysRevB.93.060410 FEB 29 2016
Abstract:
The newly discovered Ising-type ferromagnet CeRu2Al2B exhibits an additional phase transition at T-N = 14.2 K before entering the ferromagnetic ground state at T-C = 12.8 K. We clarify the nature of this transition through high resolution neutron diffraction measurements. The data reveal the presence of a longitudinal incommensurate spin-density wave (SDW) in the temperature range of T-C < T < T-N. The propagation vector q similar to (0,0,0.148) is nearly temperature independent in this region and discontinuously locks into q = 0 at T-C. Mean-field calculations of an effective Ising model indicate that the modulated SDW phase is stabilized by a strong competition between ferromagnetic and antiferromagnetic exchange interactions. This makes CeRu2Al2B a particularly attractive model system to study the global phase diagram of ferromagnetic heavy-fermion metals under the influence of magnetic frustration.

Update: 17-Mar-2016

Title:
The modulated structures of La2-xPrxO2MnSe2 (0 <= x <= 1) and La2-xNdxO2MnSe2 (0 <= x <= 0.6)
Authors:
Peschke, S; Johrendt, D Author Full Names: Peschke, Simon; Johrendt, Dirk
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (2):89-95; 10.1515/zkri-2015-1883 FEB 2016
Abstract:
The solid solutions La2-xPrxO2MnSe2 (0 <= x <= 1) and La2-xNdxO2MnSe2 (0 <= x <= 0.6) were synthesized in a NaI/KI flux between 800 and 900 degrees C. The selenide oxides adopt a ZrCuSiAs-related structure with modulated [MnSe2](2)(-)- layers which consist of a mixture of edge- and corner-sharing MnSe4/2-tetrahedra. The crystal structures are described with a (3+1)D model in superspace group Cmme(alpha 01/2)0s0. The modulation vector q can be-controlled by partial substitution of La3+ for Pr3+ and Nd3+ via the unit cell volume leading to, amongst others, (La0.55Pr0.45)(2)O2MnSe2 with alpha = 1/6, which allows the projection onto 3D space by using a simple sixfold a axis.
Title:
M2PO3N (M = Ca, Sr): ortho-Oxonitridophosphates with beta-K2SO4 Structure Type
Authors:
Marchuk, A; Schultz, P; Hoch, C; Oeckler, O; Schnick, W Author Full Names: Marchuk, Alexey; Schultz, Peter; Hoch, Constantin; Oeckler, Oliver; Schnick, Wolfgang
Source:
INORGANIC CHEMISTRY, 55 (2):974-982; 10.1021/acs.inorgchem.5b02647 JAN 18 2016
Abstract:
Two novel oxonitridophosphates M2PO3N with M = Ca and Sr were synthesized under high-pressure high-temperature (7 GPa and 1100 degrees C) using the multianvil technique or by solid-state reaction in the silica ampules (1100 degrees C) from amorphous phosphorus oxonitride (PON) and the respective alkaline earth oxides MO (M = Ca, Sr). The products represent the first examples of alkaline earth ortho-oxonitridophosphates containing noncondensed [PO3N](4-) ions. The crystal structures were elucidated by single-crystal X-ray diffraction. Sr2PO3N [space group Pnma (No. 62), Z = 4, a = 7.1519(5) angstrom, b = 5.5778(3) angstrom, c = 9.8132(7) angstrom, R1 = 0.020, wR2 = 0.047] crystallizes in the beta-K2SO4 structure type. The structure of Ca2PO3N was solved and refined in the (3 + 1)D superspace group Pnma(a00)0ss [Z = 4, a = 6.7942(7) angstrom, b = 5.4392(6) angstrom, c = 9.4158(11) angstrom, R1 = 0.041, wR2 = 0.067]. It exhibits an incommensurate modulation along [100] with a modulation vector q = [0.287(5), 0, 0]. Rietveld refinements support the structural models as well as the phase purity of the products. Upon doping with Eu2+, Ca2PO3N exhibits luminescence in the green range (lambda(em) = 525 nm) of the visible spectrum if excited by near-UV light (lambda(exc) = 400 nm).

Update: 11-Mar-2016

Title:
Incommensurate crystal supercell and polarization flop observed in the magnetoelectric ilmenite MnTiO3
Authors:
Silverstein, HJ; Skoropata, E; Sarte, PM; Mauws, C; Aczel, AA; Choi, ES; van Lierop, J; Wiebe, CR; Zhou, HD Author Full Names: Silverstein, Harlyn J.; Skoropata, Elizabeth; Sarte, Paul M.; Mauws, Cole; Aczel, Adam A.; Choi, Eun Sang; van Lierop, Johan; Wiebe, Christopher R.; Zhou, Haidong
Source:
PHYSICAL REVIEW B, 93 (5):10.1103/PhysRevB.93.054416 FEB 19 2016
Abstract:
MnTiO3 has been studied for many decades, but it was only in the last few years that its magnetoelectric behavior had been observed. Here, we use neutron scattering on two separately grown single crystals and two powder samples to show the presence of a supercell that breaks R (3) over bar symmetry. We also present the temperature and field dependence of the dielectric constant and pyroelectric current and show evidence of nonzero off-diagonal magnetoelectric tensor elements (forbidden by R (3) over bar symmetry) followed by a polarization flop accompanying the spin flop transition at mu H-0(SF) = 6.5T. Mossbauer spectroscopy on MnTiO3 gently doped with Fe-57 was used to help shed light on the impact of the supercell on the observed behavior. Although the full supercell structure could not be solved at this time due to a lack of visible reflections, the full scope of the results presented here suggest that the role of local spin-lattice coupling in the magnetoelectric properties of MnTiO3 is likely more important than previously thought.
Title:
Magnetic ordering in pressure-induced phases with giant spin-driven ferroelectricity in multiferroic TbMnO3
Authors:
Terada, N; Khalyavin, DD; Manuel, P; Osakabe, T; Kikkawa, A; Kitazawa, H Author Full Names: Terada, Noriki; Khalyavin, Dmitry D.; Manuel, Pascal; Osakabe, Toyotaka; Kikkawa, Akiko; Kitazawa, Hideaki
Source:
PHYSICAL REVIEW B, 93 (8):10.1103/PhysRevB.93.081104 FEB 16 2016
Abstract:
In order to clarify the mechanism associated with pressure/magnetic-field-induced giant ferroelectric polarization in TbMnO3, this work investigated changes in magnetic ordering brought about by variations in temperature, magnetic field, and pressure. This was accomplished by means of neutron diffraction analyses under high pressures and high magnetic fields, employing a single crystal. The incommensurate magnetic ordering of a cycloid structure was found to be stable below the reported critical pressure of 4.5 GPa. In contrast, a commensurate E-type spin ordering of Mn spins and a noncollinear configuration of Tb spins with k = (0, 1/2,0) appeared above 4.5 GPa. The application of a magnetic field along the a axis (H-parallel to a) under pressure induces a k = (0,0,0) antiferromagnetic structure in the case of Tb spins above H-parallel to a, enhancing the ferroelectric polarization, while the E-type ordering of Mn spins is stable even above the critical field. From the present experimental findings, we conclude that the E-type ordering of Mn spins induces giant ferroelectric polarization through an exchange striction mechanism. The H-parallel to a-induced polarization enhancement can be understood by considering that the polarization, reduced by the polar ordering of Tb moments in a zero field, can be recovered through a field-induced change to nonpolar k = (0,0,0) ordering at H-parallel to a similar to 2 T.
Title:
Alumina nanowire growth by water decomposition and the peritectic reaction of decagonal Al65Cu15Co20 quasicrystals
Authors:
Tellez-Vazquez, JO; Patino-Carachure, C; Rosas, G Author Full Names: Tellez-Vazquez, J. O.; Patino-Carachure, C.; Rosas, G.
Source:
MATERIALS CHARACTERIZATION, 112 155-159; 10.1016/j.matchar.2015.12.023 FEB 2016
Abstract:
In this paper, the results of the Al2O3 nanowires' growth through a chemical reaction between Al and water vapor at 1050 degrees C are presented. Our approach is based on two primary considerations. First, at room temperature, the Al65Cu15Co20 alloy is affected by the following mechanism: 2AI (s) + 3H(2)O (g) -> Al2O3 (s) + H-2 (g). In this reaction, the released hydrogen induces cleavage fracture of the material to form small particles. Second, the Al65Cu15Co20 quasicrystalline phase is transformed on heating to liquid + Al (Cu, Co) cubic phase through a peritectic reaction at 1050 degrees C. The Al-rich liquid then reacts with water vapor, forming Al2O3 nanowires. X-ray diffraction (XRD) analysis shows that the formed nanowires have a hexagonal structure, and infrared analysis further confirms the presence of alpha-Al2O3 phase in the final products. Transmission electron microscopy observations show that nanoparticles are present at the end of nanowires, suggesting the VLS growth mechanism. Elemental analysis by energy dispersive spectroscopy (EDS) indicates that the particles at the tip of the nanowires are mainly formed by Co and Cu alloying elements and small amounts of Al. Electron microscopy observations showed nanowires with diameters ranging from 20 to 70 nm; the average diameter was 37 nm and the nanowire lengths were up to several micrometers. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Structure and reactivity with oxygen of Pr2NiO4+delta: an in situ synchrotron X-ray powder diffraction study
Authors:
Broux, T; Prestipino, C; Bahout, M; Paofai, S; Elkaim, E; Vibhu, V; Grenier, JC; Rougier, A; Bassat, JM; Hernandez, O Author Full Names: Broux, Thibault; Prestipino, Carmelo; Bahout, Mona; Paofai, Serge; Elkaim, Erik; Vibhu, Vaibhav; Grenier, Jean-Claude; Rougier, Aline; Bassat, Jean-Marc; Hernandez, Olivier
Source:
DALTON TRANSACTIONS, 45 (7):3024-3033; 10.1039/c5dt03482e 2016
Abstract:
The promising SOFC cathode material Pr2NiO4.22 has been studied in situ under a pure oxygen atmosphere from 25 to 950 degrees C by high resolution synchrotron X-ray powder diffraction. At room temperature (RT) delta = 0.22(1), the average crystal structure turns out to be monoclinic. The subtle monoclinic distortion (gamma = 90.066(1)degrees at RT), retained up to 460 degrees C, is interpreted in terms of specific tilt schemes of the NiO6 octahedra. It is also shown that Pr2NiO4.22 is incommensurately structurally modulated already at room temperature, in the same manner as the homologous cobaltate La2CoO4.14. The phase transition to the High Temperature Tetragonal (HTT) phase was completed at 480 degrees C without any evidence for the Low Temperature Orthorhombic (LTO) phase allowing clarifying the phase diagram of this K2NiF4-type ternary oxide. Moreover, it turns out that above 800 degrees C, the HTT phase transforms reversibly into two coexisting isomorphous tetragonal phases. The incommensurate modulation subsists up to 950 degrees C, although modified concomitantly with the two abovementioned phase transformations. In addition, the role of kinetics on the decomposition process is highlighted through thermo-gravimetric analyses.

Update: 3-Mar-2016

Title:
Analysis of modulated Ho2PdSi3 crystal structure at Pd K and Ho L absorption edges using resonant elastic X-scattering
Authors:
Nentwich, M; Zschornak, M; Richter, C; Novikov, D; Meyer, DC Author Full Names: Nentwich, Melanie; Zschornak, Matthias; Richter, Carsten; Novikov, Dmitri; Meyer, Dirk C.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (6):10.1088/0953-8984/28/6/066002 FEB 17 2016
Abstract:
Replacing Si atoms with a transition metal in rare earth disilicides results in a family of intermetallic compounds with a variety of complex magnetic phase transitions. In particular, the family R2PdSi3 shows interesting magnetic behavior arising from the electronic interaction of the R element with the transition metal in the Si network, inducing the specific structure of the related phase. Within this series, the highest degree of superstructural order was reported for the investigated representative Ho2PdSi3, although several competing superstructures have been proposed in literature. The diffraction anomalous fine structure (DAFS) method is highly sensitive to the local structure of chosen atoms at specific positions within the unit cell of a crystalline phase. In combination with x-ray absorption fine structure (XAFS), this sophisticated synchrotron method has been applied in the present work to several selected reflections, i.a. a satellite reflection. Extensive electronic modeling was used to test the most relevant structure proposals. The 2 x 2 x 8 superstructure has been strongly confirmed, although a small amount of disorder in the modulation is very probable.
Title:
Effect of LiH on electrochemical hydrogen storage properties of Ti55V10Ni35 quasicrystal
Authors:
Liu, DY; Zhao, Z; Luo, TH; Xing, C; Fei, L; Lin, J; Hou, JH; Jiang, DY; Liu, WQ; Wang, LM Author Full Names: Liu, Dongyan; Zhao, Zhen; Luo, Tianhao; Xing, Cheng; Fei, Liang; Lin, Jing; Hou, Jianhua; Jiang, Dayong; Liu, Wanqiang; Wang, Limin
Source:
SOLID STATE SCIENCES, 52 19-22; 10.1016/j.solidstatesciences.2015.12.002 FEB 2016
Abstract:
The electrochemical hydrogen storage properties and mechanisms of the Ti55V10Ni35 quasicrystal + xLiH(x = 3, 6 and 9 wt.%) system are investigated and discussed in this paper. A composite material in the Ti55V10Ni35 quasicrystal and system has been synthesized moderately by means of mechanical milling under an argon atmosphere, which can avoid reaction of releasing of hydrogen during the process of milling. The results indicate that the addition of LiH significantly improves the electrochemical characteristics of composite material. The maximum discharge capacity increases from 220.1 mAh/g to 292.3 mAh/g on Ti55V10Ni35 + 6 wt.% LiH, and the cycling stability is also enhanced too. In addition, the high rate dischargeability (HRD) is ameliorated remarkably, and the value of HRD value at 240 mA/g rises by 78.1%-87.8% for Ti55V10Ni35 + 6 wt.% LiH alloy electrodes. The improvement of characteristics of the electrochemical hydrogen storage characteristics may be attributed to LiH, which has excellent electrochemical activity. (C) 2015 Elsevier Masson SAS. All rights reserved.
Title:
Synthesis, structure, and magnetic characterization of Cr4US8
Authors:
Ward, MD; Chan, IY; Malliakas, CD; Lee, M; Choi, ES; Ibers, JA Author Full Names: Ward, Matthew D.; Chan, Ian Y.; Malliakas, Christos D.; Lee, Minseong; Choi, Eun Sang; Ibers, James A.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 233 67-74; 10.1016/j.jssc.2015.10.009 JAN 2016
Abstract:
The compound Cr4US8 has been synthesized at 1073 K and its crystal structure has been determined at 100 K. The structure is modulated with a two-fold commensurate supercell. The subcell may be indexed in an orthorhombic cell but weak supercell reflections lead to the monoclinic superspace group P2(1)/c (0 alpha gamma)0s with two Cr sites, one U site, and four S sites. The structure comprises a three-dimensional framework of CrS6 octahedra with channels that are partially occupied by U atoms. Each U atom in these channels is coordinated by eight S atoms in a bicapped trigonal-prismatic arrangement. The magnetic behavior of Cr4US8 is complex. At temperatures above similar to 120 K at all measured fields, there is little difference between field-cooled and zero field-cooled data and chi(T) decreases monotonously with temperature, which is reminiscent of the Curie-Weiss law. At lower temperatures, the temperature dependence of chi(T) is complex and strongly dependent on the magnetic field strength. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Electronic transport in polycrystalline samples of icosahedral phases
Authors:
Vekilov, YK; Chernikov, MA; Dolinichek, Y Author Full Names: Vekilov, Yu. Kh.; Chernikov, M. A.; Dolinichek, Ya.
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 117 (1):16-21; 10.1134/S0031918X15110113 JAN 2016
Abstract:
The low-temperature electronic transport in polycrystals of quasicrystalline phases with an icosahedral structure has been analyzed within the model of the granular electronic system. In this model, the grains (drops) of a metallic icosahedral phase are surrounded by extended defects and grain boundaries, which create an insulating environment. The electron transport in this model is determined by the size quantization of electronic states inside metallic grains, by intergranular tunneling, and by electrostatic barriers. Depending on the temperature and structural state of the system, the hopping conductivity with variable lengths of jumps in the Efros-Shklovskii or Mott regime is observed with predominantly elastic cotunneling. In the case of strong intergranular coupling, the system passes into the metallic regime with the exponential temperature dependence of the electrical conductivity.

Update: 25-Feb-2016

Title:
From an electron micrograph to a postage stamp
Authors:
Hargittai, I Author Full Names: Hargittai, Istvan
Source:
STRUCTURAL CHEMISTRY, 27 (1):5-7; SI 10.1007/s11224-015-0629-1 FEB 2016
Abstract:
Soon following Dan Shechtman's discovery of quasicrystals, Agnes Csanady and her associates started producing beautiful quasicrystals of flowerlike morphology. The image of one of their specimen appeared on the Israeli postage stamp honoring Shechtman's discovery, his Nobel Prize, and the International Year of Crystallography.
Title:
Ultrafast resonant soft x-ray diffraction dynamics of the charge density wave in TbTe3
Authors:
Moore, RG; Lee, WS; Kirchman, PS; Chuang, YD; Kemper, AF; Trigo, M; Patthey, L; Lu, DH; Krupin, O; Yi, M; Reis, DA; Doering, D; Denes, P; Schlotter, WF; Turner, JJ; Hays, G; Hering, P; Benson, T; Chu, JH; Devereaux, TP; Fisher, IR; Hussain, Z; Shen, ZX Author Full Names: Moore, R. G.; Lee, W. S.; Kirchman, P. S.; Chuang, Y. D.; Kemper, A. F.; Trigo, M.; Patthey, L.; Lu, D. H.; Krupin, O.; Yi, M.; Reis, D. A.; Doering, D.; Denes, P.; Schlotter, W. F.; Turner, J. J.; Hays, G.; Hering, P.; Benson, T.; Chu, J. -H.; Devereaux, T. P.; Fisher, I. R.; Hussain, Z.; Shen, Z. -X.
Source:
PHYSICAL REVIEW B, 93 (2):10.1103/PhysRevB.93.024304 JAN 25 2016
Abstract:
Understanding the emergence of collective behavior in correlated electron systems remains at the forefront of modern condensed matter physics. Disentangling the degrees of freedom responsible for collective behavior can lead to insights into the microscopic origins of emergent properties and phase transitions. Utilizing an optical pump, resonant soft x-ray diffraction probe we are able to track, in real time, the dynamics of the charge density wave (CDW) in TbTe3, a model system that violates traditional views of a Fermi surface nested CDW. We observe coherent oscillations corresponding to the CDW amplitude mode at 2.4 THz and a coherent optical phonon mode at similar to 1.7 THz. We show how such observations reveal the anisotropic energy optimization between in-plane Te charge density modulations and the three-dimensional lattice coupling.
Title:
Ti-V-Ni with graphene-mixing icosahedral quasicrystalline composites: Preparation, structure and its application in Ni-MH rechargeable batteries
Authors:
Lin, J; Lu, C; Sun, LS; Liang, F; Cao, ZY; Wang, LM Author Full Names: Lin, Jing; Lu, Chong; Sun, Lianshan; Liang, Fei; Cao, Zhanyi; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 41 (2):1098-1103; 10.1016/j.ijhydene.2015.11.067 JAN 12 2016
Abstract:
The Ti-V-Niquasicrystalline was prepared by arc-melting and subsequent melt-spinning technique, and the Ti1.4V0.6Ni + x graphene (x = 3, 5, 7, 10 and 13, wt%) composites were obtained by mechanical ball-milling method. The structures and electrochemical hydrogen storage properties of the composites were investigated. The results showed that, the structures of the composites contained icosahedral quasicrystal, Ti2Ni-type, NiTi and graphene phases. The electrochemical hydrogen storage properties of the composites were improved with graphene addition. The cycling stabilities after 50 charging/discharging cycles of Ti1.4V0.6Ni + x graphene composites were improved obviously, especially the Ti1.4V0.6Ni + 10 graphene composite showed the best cycling stability of 70.3%, increased by 6.5%, compared with the Ti1.4V0.6Ni electrode. The high-rate discharge abilities of the composites were also increased appreciably. The improvement in the hydrogen storage characteristics should own to the proper graphene addition and that could cause copacetic electrocatalytic activity and anti-corrosion ability. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Title:
Orientation Relations and Conversion Matrix Between M3 Supercell and Pseudohexagonal Subcell in Tricalcium Silicate Solid Solution
Authors:
Min, HH; Xu, F; Lu, YN; Yang, J; Ding, LF; Su, F; Zhu, JM Author Full Names: Min Hui-Hua; Xu Feng; Lu Yi-Nong; Yang Jing; Ding Lin-Fei; Su Fan; Zhu Jian-Min
Source:
CHINESE JOURNAL OF INORGANIC CHEMISTRY, 32 (1):145-152; JAN 10 2016
Abstract:
A M3 modification of tricalcium silicate (C3S) solid solution was investigated using transmission electron microscope (TEM). Selected area electron diffraction (SAED) patterns and high resolution transmission electron microscopy (HRTEM) images were analyzed based on a pseudohexagonal subcell (Space group R3m; a=0.705 9 nm, b=0.705 5 nm, c=2.492 4 nm, alpha=89.79 degrees,beta=90.04 degrees, gamma=120.14 degrees). Reflections caused by the superstructure were proven to occur along the modulation wave vector [(1) over bar .17](H)(*) with one-dimensional type and could be expressed as ha+kb+lc*+m/[6(-a+b+7C*)], where m=+/- 1,+/- 2 and +/- 3. SAED patterns and HRTEM images based on the M3 supercell (Space group Cm; a=3.310 8 nm, b=0.703 6 nm, c=1.852 1 nm, beta=94.137 degrees) were simulated and finally the orientation relations between M3 supercell and pseudohexagonal subcell were established as follows: (600)(M3), (020)(M3) and (006)(M3) were equivalent to ((1) over bar1 (2) over bar)(H), ((1) over bar(1) over bar0)(H) and ((1) over bar 17)(H)* respectively, and [100](M3)//[(7) over bar7 (2) over bar](H), [010](M3)// [(1) over bar(1) over bar0](H), and [001](M3)//[(1) over bar 11](H): Furthermore, the conversion matrix between M3 supercell and pseudohexagonal subcell was established.
Title:
Soft spherical nanostructures with a dodecagonal quasicrystal-like order
Authors:
Rochal, SB; Konevtsova, OV; Shevchenko, IA; Lorman, VL Author Full Names: Rochal, S. B.; Konevtsova, O. V.; Shevchenko, I. A.; Lorman, V. L.
Source:
SOFT MATTER, 12 (4):1238-1247; 10.1039/c5sm02265g 2016
Abstract:
We develop a theory which predicts curvature-related structural peculiarities of soft spherical nanostructures with a dodecagonal local arrangement of subunits. Spherical templates coated with a thin film of a soft quasicrystal (QC)-forming material constitute the most promising direction to realize these nanostructures. Disordered and perfect spherical nanostructures are simulated using two approaches. The first of them models a random QC-like spherical nanostructure with extended curvature-induced topological defects similar to scars in colloidal spherical crystals. The second approach is inspired by the physics of viral capsids. It deals with the most regular spherical nanostructures with a local QC-like order derived from three well-known planar dodecagonal tilings. We explain how the additional QC-like degrees of freedom assist the nanostructure stabilization and determine the point defect number and location without extended scar formation. Unusual for nanoassemblies snub cube geometry is shown to be the most energetically favorable global organization of these spherical QC nanostructures.
Title:
Thermal conductivity of solid thiophene in an incommensurate orientational state
Authors:
Korolyuk, OA; Krivchikov, AI; Vdovichenko, GA; Romantsova, OO; Horbatenko, YV Author Full Names: Korolyuk, O. A.; Krivchikov, A. I.; Vdovichenko, G. A.; Romantsova, O. O.; Horbatenko, Yu. V.
Source:
LOW TEMPERATURE PHYSICS, 42 (1):68-73; 10.1063/1.4940993 JAN 2016
Abstract:
The thermal conductivity of solid thiophene at equilibrium vapor pressure between 2K < T < 170K, has been measured in a sequence of incommensurate metastable orientationally disordered phases II, II1, II2, and II2g with different degrees of orientational ordering of the molecules. It is found that in phase states II, II1 and II2 with dynamic orientational disorder of the molecules, the thermal conductivity does not depend on the temperature. It is shown that the temperature dependence of the thermal conductivity kappa(T) of orientational glass V-g and II2g (incommensurate) does not have any of the anomalies that are typical for amorphous materials and glasses. The temperature dependence kappa(T) of the incommensurate state of orientational glass II2g is bell-shaped, which is typical for the thermal conductivity of crystals with long-range orientational order. In the II2g state, as temperature drops from T-g to almost 10K, the thermal conductivity increases according to kappa(T) = A/T + B, where the first term describes the input of the propagating phonons, wherein the average length of their mean free path is greater than half of the phonon wavelength. The B term is associated with the input of localized short-wave, or "diffuse" vibrational modes. At low temperatures T <= 7K, kappa(T) proportional to T-3 is observed with increasing temperatures, which corresponds to the boundary scattering of phonons. (C) 2016 AIP Publishing LLC.
Title:
Synthesis of quasi-crystalline phases in the Al-Cu-Fe-Cr system
Authors:
Chugunov, DB; Meshkov, LL; Kalmykov, KB; Osipov, AK Author Full Names: Chugunov, D. B.; Meshkov, L. L.; Kalmykov, K. B.; Osipov, A. K.
Source:
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY, 61 (1):11-17; 10.1134/S003602361601006X JAN 2016
Abstract:
Phase equilibria in the Al-Cu-Fe system alloyed with 5% Cr were studied. Based on the data of X-ray powder diffraction analysis, electron microscopy, and differential thermal analysis, the effect of temperature on i a double dagger" d phase transitions in alloys Al65Cu25Fe5Cr5 and Al70Cu20Fe5Cr5. In the Al-Cu-Fe-Cr system, multiphase structures were detected; these structures are mixtures of quasi-crystalline and approximant phases, the contents and morphologies of which depend on the composition of the initial mixture and the crystallization rate.
Title:
STRUCTURE AND MECHANICAL PROPERTIES OF QUASICRYSTALLINE AND APPROXIMANT PHASES OBTAINED FROM TITANIUM-BASED QUINARY ALLOY
Authors:
Firstov, SA; Gorban', VF; Karpets, MV; Krapivka, NA; Danilenko, NI; Pechkovskii, EP; Rokitskaya, EA Author Full Names: Firstov, S. A.; Gorban', V. F.; Karpets, M. V.; Krapivka, N. A.; Danilenko, N. I.; Pechkovskii, E. P.; Rokitskaya, E. A.
Source:
STRENGTH OF MATERIALS, 47 (6):781-788; 10.1007/s11223-015-9714-3 NOV 2015
Abstract:
The paper presents the investigation of influence of cooling rate and conditions of melt crystallization on the change in phase composition and physical and mechanical properties of alloy Ti60Cr30Al3Si2(SiO2)(5). The influence of thermal treatment on the stability and properties of quasicrystalline and approximant phases is studied. Using the method of high-temperature indentation it is found that the diffusive mechanism of plastic strain of the alloy is strongly observed at 800 degrees C (0.68T(m)).

Update: 18-Feb-2016

Title:
Structural and electrocaloric properties of multiferroic-BiFeO3 doped 0.94Bi(0.5)Na(0.5)TiO(3)-0.06BaTiO(3) solid solutions
Authors:
Zheng, GP; Uddin, S; Zheng, XC; Yang, JH Author Full Names: Zheng, Guang-Ping; Uddin, Sarir; Zheng, Xiucheng; Yang, Junhe
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 663 249-255; 10.1016/j.jallcom.2015.12.056 APR 5 2016
Abstract:
Single-phase (1-x)(0.94Bi(0.5)Na(0.5)TiO(3)-0.06BaTiO(3))-xBiFeO(3) (BNT-BT-xBF, x = 0.05, 0.1 and 0.15) solid solutions are fabricated using a modified citrate method. The structural, ferroelectric and electrocaloric properties are significantly affected by the multiferroic BiFe03 doping, which is found to favor the antiferroelectric (AFE) state of the solid solutions. The dynamic mechanical analysis suggests that the BiFeO3 induced ordering of oxygen octahedrons plays a dominant role in the formation of AFE incommensurate phases and leads to the enhanced negative electrocaloric effect (ECE). A maximum ECE temperature change of 1.65 degrees C under an applied field of 70 kV/cm is observed. It is suggested that the magnetoelectric coupling is effective in enhancing the negative ECE in BNT-BT-xBF. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Indirect assessment of the surface energy of the Al-Cu-Fe quasicrystal
Authors:
de Lima, DCG; Dos Passos, TA; de Weerd, MC; Kenzari, S; Medeiros, RG; de Lima, SJG; Dubois, JM Author Full Names: Guedes de Lima, Danielle Cavalcante; Dos Passos, Tiberio Andrade; de Weerd, Marie-Cecile; Kenzari, Samuel; Medeiros, Rodinei Gomes; Guedes de Lima, Severino Jackson; Dubois, Jean-Marie
Source:
JOURNAL OF MATERIALS SCIENCE, 51 (8):4070-4078; 10.1007/s10853-016-9728-7 APR 2016
Abstract:
This work summarizes an attempt to estimate the surface energy of the stable, icosahedral Al-Cu-Fe quasicrystal (i-ACF hereafter). To this end, samples of i-ACF were prepared by sintering a powder produced by ball milling and heat treating a master ingot of composition Al59Cu25.5Fe12.5B3 (at.%), icosahedral lattice structure, and containing negligibly small amounts of contaminating crystalline phases. This powder was then sintered in the shape of a cylinder appropriate for pin-on-disk tests in ambient air. Variable amounts of either Sn or Bi were added to the powder prior to sintering. These elements do not dissolve in the quasicrystal and form small pockets of pure Sn or Bi that are either isolated or percolating, depending on the added volume of metal. Analysis of pin-on-disk data deduced from tests performed at room temperature allows us to conclude that the surface energy of the quasicrystal itself falls between the respective surface energies of the pure metals: gamma(Bi) a parts per thousand currency sign gamma(QC) a parts per thousand currency sign gamma(Sn) or 0.5 a parts per thousand currency sign gamma(i-ACF) a parts per thousand currency sign 0.8 J/m(2).
Title:
Flexoelectricity, incommensurate phases and the Lifshitz point
Authors:
Pottker, H; Salje, EKH Author Full Names: Poettker, Henning; Salje, Ekhard K. H.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (7):10.1088/0953-8984/28/7/075902 FEB 24 2016
Abstract:
The solutions for the minimizers of the energy density f(q, p) = Aq(2) + Bq(4) + p(2) + g(A,B) + beta(q'p-p'q) + vertical bar q'vertical bar(2) + k vertical bar p'vertical bar(2) describe the flexoelectric effect with a flexoelectric coupling coefficient beta. The order parameters q and p can be visualized as strain and polarisation, respectively. The parameter k denotes the ratio of intrinsic length scales for q and p. We show that the structural ground-states include 3 phases, namely the paraelastic state q = p = 0, the ferroelastic state where polarization exists inside and near twin boundaries, and the incommensurate (modulated) phases with a very rich array of structural modulations ranging from nearly pure sine waves to kink arrays and ripple states. The phases coincide in the multicritical Lifshitz point. Linear flexoelectricity p similar to q' is encountered only approximately inside the ferroelastic phase and near the phase boundary between the paraelastic phase and the incommensurate phase. The relationship between the polarisation and the strain gradient is highly non-linear in all other states. The spatial profiles and energy distributions are discussed in detail.
Title:
Muon-spin relaxation study of the double perovskite insulators Sr2BOsO6 (B = Fe, Y, In)
Authors:
Williams, RC; Xiao, F; Thomas, IO; Clark, SJ; Lancaster, T; Cornish, GA; Blundell, SJ; Hayes, W; Paul, AK; Felser, C; Jansen, M Author Full Names: Williams, R. C.; Xiao, F.; Thomas, I. O.; Clark, S. J.; Lancaster, T.; Cornish, G. A.; Blundell, S. J.; Hayes, W.; Paul, A. K.; Felser, C.; Jansen, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (7):10.1088/0953-8984/28/7/076001 FEB 24 2016
Abstract:
We present the results of zero-field muon-spin relaxation measurements made on the double perovskite insulators Sr2BOsO6 (B = Fe, Y, In). Spontaneous muon-spin precession indicative of quasistatic long range magnetic ordering is observed in Sr2FeOsO6 within the AF1 antiferromagnetic phase for temperatures below T-N = 135 +/- 2 K. Upon cooling below T-2 approximate to 67 K the oscillations cease to be resolvable owing to the coexistence of the AF1 and AF2 phases, which leads to a broader range of internal magnetic fields. Using density functional calculations we identify a candidate muon stopping site within the unit cell, which dipole field simulations show to be consistent with the proposed magnetic structure. The possibility of incommensurate magnetic ordering is discussed for temperatures below T-N = 53 K and 25 K for Sr2YOsO6 and Sr2InOsO6, respectively.
Title:
B-cation effect on relaxor behavior and electric properties in Sr2NaNb5-xSbxO15 tungsten bronze ceramics
Authors:
Fan, JY; Yang, B; Wei, LL; Wang, ZM Author Full Names: Fan, Jianyong; Yang, Bian; Wei, Lingling; Wang, Zhongming
Source:
CERAMICS INTERNATIONAL, 42 (3):4054-4062; 10.1016/j.ceramint.2015.11.077 FEB 15 2016
Abstract:
Sr2NaNb5-xSbxO15 ceramics (SNNS, x=0.0, 0.3, 0.5, 1.0) with 'filled' tungsten bronze structure were prepared by the conventional solid-state reaction method. Effects of introducing Sb concentration in B-sites on the microstructure, dielectric and ferroelectric properties were investigated in detail. With increasing of Sb concentration, the crystal structure of SNNS ceramics distorted slightly from the TB orthorhombic Ccm2 phase to tetragonal P4bm phase, and then to paraelectric P4/mbm phase at room temperature. The smaller ionic radius of Sb5+ (0.60 angstrom) compared with that of Nb5+ (0.64 angstrom) contributed to the shrinkage of crystal structure. It was found that accompanying with the introduction of Sb, some unique dielectric and ferroelectric behavior emerged for SNNS ceramics. Only the samples with x < 0.5 showed additional dielectric anomaly in low temperature range, which was attributed to the incommensurate superstructure ICS-associated dielectric dispersion process caused by local structural fluctuation. With increasing of Sb concentration, T-c shifted to lower temperatures, and the diffuse phase transition and relaxor behavior appeared to be exceptionally induced around T-c at higher Sb concentration. The underlying mechanisms of relaxor behavior induced by different Sb concentration in B-sites for SNNS ceramics were clarified in detail. Moreover, the ferroelectric properties deteriorated and even disappeared at higher Sb concentration, because the ceramics showed P4/mbm phase structure as a result of decreasing of T-c to lower than room temperature. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Title:
Glass-like Lattice Thermal Conductivity and Thermoelectric Properties of Incommensurate Chimney-Ladder Compound FeGe gamma
Authors:
Sato, N; Ouchi, H; Takagiwa, Y; Kimura, K Author Full Names: Sato, Naoki; Ouchi, Hideyasu; Takagiwa, Yoshiki; Kimura, Kaoru
Source:
CHEMISTRY OF MATERIALS, 28 (2):529-533; 10.1021/acs.chemmater.5b03952 JAN 26 2016
Abstract:
We have characterized the thermoelectric properties of FeGe gamma which is one of the promising Nowotny chimney-ladder compounds. A glass-like low lattice thermal conductivity below 1.0 W m(-1) K-1 is observed around 373 K because of its complex structural nature, i.e., incommensurate structure. A first-principles band structure calculation implies that a narrow band gap of similar to 0.2 eV is formed near the Fermi level for a hypothetical composition of Fe2Ge3 with a Ru2Sn3-type structure, leading to a large power factor of 1.90 mW m(-1) K-2 near 600 K. The maximum dimensionless figure-of-merit of 0.57 is attractive as a starting point; calculation using the Boltzmann transport equation under a constant relaxation time approximation predicts that a further enhancement of ZT exceeding unity at 600-700 K can be achieved by optimizing the valence electron count per transition metal and further reduction of the lattice thermal conductivity.
Title:
Modulated structures and associated microstructures in the ferroelectric phase of Ba1-xSrxAl2O4 for 0.7 <= x <= 1.0
Authors:
Tsukasaki, H; Ishii, Y; Tanaka, E; Kurushima, K; Mori, S Author Full Names: Tsukasaki, Hirofumi; Ishii, Yui; Tanaka, Eri; Kurushima, Kosuke; Mori, Shigeo
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS, 55 (1):10.7567/JJAP.55.011502 JAN 2016
Abstract:
In order to understand the ferroelectric and ferroelastic phases in Ba1-xSrxAl2O4 for 0.7 <= x <= 1.0, we have investigated the crystal structures and their associated microstructures of the ferroelectric and ferroelastic phases mainly by transmission electron microscopy (TEM) and scanning transmission electron microscopy-high-angle angular dark-field (STEM-HAADF) experiments, combined with powder X-ray diffraction experiments. Electron diffraction experiments showed that the ferroelectric and ferroelastic phases of Ba1-xSrxAl2O4 for 0.7 <= x <= 1.0 should be characterized as a modulated structure with the modulation vector of q = 0, 1/2, 0, whose space group should be monoclinic P2(1). High-resolution TEM experiments revealed that the microstructures in the monoclinic phase can be characterized as twin structures and nanometer-sized planar defects due to the monoclinic structure with the modulated structures, which are responsible for anomalous elastic behaviors and mechanoelectro-optical properties. In addition, subatomic-resolution STEM-HAADF images clearly indicated that the displacement of Al3+ ions involved in the AlO4 tetrahedra should play a crucial role in the formation of the modulated structures and twin structures. (C) 2016 The Japan Society of Applied Physics
Title:
Influence of high energy milling on the microstructure and magnetic properties of the AlCu-Fe phases: the case of the i-Al64Cu23Fe13 quasicrystalline and the omega-Al70Cu20Fe10 crystalline phases
Authors:
Quispe, MP; Landauro, CV; Vergara, MZP; Quispe-Marcatoma, J; Rojas-Ayala, C; Pena-Rodriguez, VA; Baggio-Saitovitch, E Author Full Names: Pillaca Quispe, Mirtha; Landauro, Carlos V.; Pinto Vergara, Milida Z.; Quispe-Marcatoma, Justiniano; Rojas-Ayala, Chachi; Pena-Rodriguez, Victor A.; Baggio-Saitovitch, Elisa
Source:
RSC ADVANCES, 6 (7):5367-5376; 10.1039/c5ra21093c 2016
Abstract:
The effect of mechanical milling in i-Al64Cu23Fe13 quasicrystalline and omega-Al70Cu20Fe10 crystalline phases is systematically investigated in the present work. The Al-Cu-Fe samples were obtained by arc furnace technique and then nanostructured by means of mechanical milling. The results indicate that the solid samples present a weak ferromagnetic behavior at 300 K, showing a saturation magnetization of 0.124 emu g(-1) for the icosahedral phase (i-phase) and 0.449 emu g(-1) for the tetragonal phase (omega phase). These small values could be an indication that only a few percentage of Fe atoms carry magnetic moment. The magnetic response in the nanostructured u-phase increases up to 3.5 times higher than its corresponding solid counterpart. Whereas for the i-phase this increment is about 16 times higher. Moreover, the speed of the variation of the studied physical parameters after reducing the average grain size has been obtained from the exponent (alpha) of a power law fit of the experimental data. The values of a, corresponding to the magnetic response, are slightly different in each phase, which should be related to the different chemical composition and/or the type of long range order. Additionally, we also search for a critical grain size. However, this critical value has not been observed in the studied samples.

Update: 10-Feb-2016

Title:
Magnetic structures in TmPdIn and TmAgSn
Authors:
Baran, S; Szytula, A; Kaczorowski, D; Damay, F Author Full Names: Baran, S.; Szytula, A.; Kaczorowski, D.; Damay, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 662 11-15; 10.1016/j.jallcom.2015.11.200 MAR 25 2016
Abstract:
Low temperature antiferromagnetic structures of TmPdIn and TmAgSn have been derived from powder neutron diffraction data. The magnetic structure of TmPdIn is a commensurate one and related to a propagation vector (k) over right arrow = [1/3, 1/3, 1/2] while the incommensurate sine-modulated structure of TmAgSn is connected with (k) over right arrow = [k(x), -k(x), 0] where k(x) = 0.1314(2). The thulium magnetic moments are constrained within the basal plane and show 'triangular' arrangement. Validity of obtained magnetic structures is discussed on the basis of symmetry analysis. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Mossbauer spectroscopy, magnetic, and ab-initio study of the approximant Al76Ni9Fe15 to a decagonal Al-Ni-Fe quasicrystal
Authors:
Nejadsattari, F; Stadnik, ZM; Przewoznik, J; Grushko, B Author Full Names: Nejadsattari, Farshad; Stadnik, Zbigniew M.; Przewoznik, Janusz; Grushko, Benjamin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 662 612-620; 10.1016/j.jallcom.2015.12.115 MAR 25 2016
Abstract:
The structural, magnetic, and Mossbauer spectral properties of the approximant Al76Ni9Fe15 to a decagonal Al-Ni-Fe quasicrystal, complemented by ab-initio electronic structure and the hyperfine-interaction parameters calculations, are reported. The approximant studied crystallizes in the monoclinic space group C2/m with the lattice parameters a = 15.3898(3) angstrom, b = 8.0840(2) angstrom, c = 12.4169(2) angstrom, and beta = 107.870(2)degrees. The existence of a pseudogap in the calculated electronic density of states slightly above the Fermi level suggests electronic stabilization according to the Hume-Rothery-type mechanism. High metallicity of Al76Ni9Fe15 is predicted. Both the Mossbauer spectra and magnetic susceptibility data indicate that Al76Ni9Fe15 is a paramagnet down to 2.0 K. The presence of the distribution of the electric quadrupole splitting in the Mossbauer spectra measured in the temperature range 4.5-296.1 K is observed. The increase of the average quadrupole splitting with decreasing temperature is well described by a T-3/2 power-law relation. The Debye temperature of Al76Ni9Fe15 is found to be 431(3) K. (C) 2015 Elsevier B.V. All rights reserved.
Title:
The Use and Abuse of Transcranial Magnetic Stimulation to Modulate Corticospinal Excitability in Humans (vol 10, e0144151, 2015)
Authors:
Heroux, ME; Taylor, JL; Gandevia, SC Author Full Names: Heroux, Martin E.; Taylor, Janet L.; Gandevia, Simon C.
Source:
PLOS ONE, 11 (1):10.1371/journal.pone.0147890 JAN 21 2016
Title:
Composition-driven spin glass to ferromagnetic transition in the quasicrystal approximant Au-Al-Gd
Authors:
Ishikawa, A; Hiroto, T; Tokiwa, K; Fujii, T; Tamura, R Author Full Names: Ishikawa, A.; Hiroto, T.; Tokiwa, K.; Fujii, T.; Tamura, R.
Source:
PHYSICAL REVIEW B, 93 (2):10.1103/PhysRevB.93.024416 JAN 21 2016
Abstract:
We investigated the composition dependence of the magnetic susceptibility of the quasicrystal approximant Au-Al-Gd. A composition-driven ferromagnetic transition is observed in a quasicrystal approximant, which is attributed to the Ruderman-Kittel-Kasuya-Yosida (RKKY) oscillation via a variation in the Fermi wave vector. The ferromagnetic transition is most simply understood as a result of the close matching of the nearest and second-nearest spin distances with the maximum positions of the RKKY potential. The present work provides an idea that allows us to tailor the magnetic order via the electron concentration in quasicrystal approximants as well as in quasicrystals.
Title:
Complex phase diagram of Ba1-xNaxFe2As2: A multitude of phases striving for the electronic entropy
Authors:
Wang, L; Hardy, F; Bohmer, AE; Wolf, T; Schweiss, P; Meingast, C Author Full Names: Wang, L.; Hardy, F.; Boehmer, A. E.; Wolf, T.; Schweiss, P.; Meingast, C.
Source:
PHYSICAL REVIEW B, 93 (1):10.1103/PhysRevB.93.014514 JAN 19 2016
Abstract:
The low-temperature electronic phase diagram of Ba1-xNaxFe2As2, obtained using high-resolution thermal-expansion and specific-heat measurements, is shown to be considerably more complex than previously reported, containing nine different phases. Besides the magnetic C-2 and reentrant C-4 phases, we find evidence for an additional, presumably magnetic, phase below the usual spin-density-wave transition, as well as a possible incommensurate magnetic phase. All these phases coexist and compete with superconductivity, which is particularly strongly suppressed by the C-4-magnetic phase due to a strong reduction of the electronic entropy available for pairing in this phase.
Title:
Use of frit-disc crucibles for routine and exploratory solution growth of single crystalline samples
Authors:
Canfield, PC; Kong, T; Kaluarachchi, US; Jo, NH Author Full Names: Canfield, Paul C.; Kong, Tai; Kaluarachchi, Udhara S.; Jo, Na Hyun
Source:
PHILOSOPHICAL MAGAZINE, 96 (1):84-92; 10.1080/14786435.2015.1122248 JAN 2 2016
Abstract:
Solution growth of single crystals from high temperature solutions often involves the separation of residual solution from the grown crystals. For many growths of intermetallic compounds, this separation has historically been achieved with the use of plugs of silica wool. Whereas this is generally efficient in a mechanical sense, it leads to a significant contamination of the decanted liquid with silica fibres. In this paper, we present a simple design for frit-disc alumina crucible sets that has made their use in the growth single crystals from high temperature solutions both simple and affordable. An alumina frit-disc allows for the clean separation of the residual liquid from the solid phase. This allows for the reuse of the decanted liquid, either for further growth of the same phase, or for subsequent growth of other, related phases. In this paper, we provide examples of the growth of isotopically substituted TbCd6 and icosahedral i-RCd quasicrystals, as well as the separation of (i) the closely related Bi2Rh3S2 and Bi2Rh3.5S2 phases and (ii) PrZn11 and Pr2Zn17.
Title:
Mn3TeO6 - a new multiferroic material with two magnetic substructures
Authors:
Zhao, L; Hu, ZW; Kuo, CY; Pi, TW; Wu, MK; Tjeng, LH; Komarek, AC Author Full Names: Zhao, Li; Hu, Zhiwei; Kuo, Chang-Yang; Pi, Tun-Wen; Wu, Maw-Kuen; Tjeng, Liu Hao; Komarek, Alexander C.
Source:
PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS, 9 (12):730-734; 10.1002/pssr.201510347 DEC 2015
Abstract:
From magnetic susceptibility, dielectric permittivity, electric polarization and specific heat measurements we discover spin-induced ferroelectricity and magnetoelectric coupling in Mn3TeO6 and observe two successive magnetic transitions at low temperatures. A non-ferroelectric intermediate magnetic state occurs below 23 K and a multiferroic ground state emerges below 21 K. Moreover, Mn3TeO6 is a candidate for a multiferroic material where two types of incommensurate spin structures, cycloidal and helical, coexist. Theoretically, both spin substructures may contribute to the macro electric polarization via different mechanisms. This could open new ways of manipulating the ferroelectric polarization in a multiferroic material. (c) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Update: 4-Feb-2016

Title:
Highly modulated structure and upconversion photoluminescence properties of PbGd2(MoO4)(4):Er3+/Yb3+ phosphors
Authors:
Lim, CS Author Full Names: Lim, Chang Sung
Source:
MATERIALS RESEARCH BULLETIN, 75 211-216; 10.1016/j.materresbull.2015.11.058 MAR 2016
Abstract:
Double molybdate of PbGd2-x(MoO4)(4):Er3+/Yb3+ phosphors with the correct doping concentrations of Er3+ and Yb3+ (x= Er3+ + Yb3+, Er3+ = 0.05, 0.1, 0.2 and Yb3+ = 0.2, 0.45) were successfully synthesized by microwave sol-gel process. The highly modulated structure and the upconversion photoluminescence properties were investigated in detail. The synthesized particles, formed after heat-treatment at 900 degrees C for 16 h, showed a well ctystallized morphology with particle sizes of 2-5 mu m. Under excitation at 980 nm, the PbGd1.7(MoO4)(4):Er(0.1)Ybo(0.2) and PbGd1.5(MoO4)(4):Er0.05Yb0.45 particles exhibited a strong 525-nm emission band, a weak 550-nm emission band in the green region, and a very weak 655-nm emission band in the red region. The Raman spectra of the doped particles indicated the disordered structures of PbGd2-x(MoO4)(4) by the incorporation of the Er3+ and Yb3+ ions into the crystal lattice, which resulted in the highly modulated structure as well as a concentration quenching effect of Er3+ ions. (C) 2015 Published by Elsevier Ltd.
Title:
Gabor frames for quasicrystals, K-theory, and twisted gap labeling
Authors:
Kreisel, M Author Full Names: Kreisel, Michael
Source:
JOURNAL OF FUNCTIONAL ANALYSIS, 270 (3):1001-1030; 10.1016/j.jfa.2015.11.011 FEB 1 2016
Abstract:
We study the connection between Gabor frames for quasicrystals, the topology of the hull of a quasicrystal A, and the K-theory of an associated twisted groupoid algebra. In particular, we construct a finitely generated projective module over this algebra, and any multiwindow Gabor frame for A can be used to construct an idempotent representing this module in K-theory. For lattice subsets in dimension two, this allows us to prove a twisted version of Bellissard's gap labeling theorem. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Observation of nonequilibrium behavior near the Lifshitz point in ferroelectrics with incommensurate phase
Authors:
Rushchanskii, KZ; Molnar, A; Bilanych, R; Yevych, R; Kohutych, A; Vysochanskii, YM; Samulionis, V; Banys, J Author Full Names: Rushchanskii, K. Z.; Molnar, A.; Bilanych, R.; Yevych, R.; Kohutych, A.; Vysochanskii, Yu. M.; Samulionis, V.; Banys, J.
Source:
PHYSICAL REVIEW B, 93 (1):10.1103/PhysRevB.93.014101 JAN 14 2016
Abstract:
We have investigated nonequilibrium properties of proper uniaxial Sn2P2(SexS1-x)(6) ferroelectrics with the type II incommensurate phase above Lifshitz point x(LP) similar to 0.28. We performed measurements of dielectric susceptibility in cooling and heating regimes with the rate ranging 0.002-0.1 K/min, as well as high-resolution ultrasound investigation and hypersound Brillouin scattering experiments. For samples with x >= 0.28 clear anomalies are observed at incommensurate second-order transition (T-i) and at first-order lock-in transition (T-c) in the regime of very slow cooling rate, whereas the intermediate incommensurate phase is not observed when the rate is faster than 0.1 K/min. In general, increasing the cooling rate leads to smearing of the anomaly at T-c. We relate this effect to cooling rate dependence of domain-wall concentration and their size: domain width decreases when cooling rate increases. At certain conditions, the size of domain is comparable to the incommensurate phase modulation period, which is in the micrometer range in the vicinity of Lifshitz point and leads to pinning of the modulation period by domain walls.
Title:
Spatial spin-modulated structure and hyperfine interactions of Fe-57 nuclei in multiferroics BiFe1-x T (x) O-3 (T = Sc, Mn; x=0, 0.05)
Authors:
Rusakov, VS; Pokatilov, VS; Sigov, AS; Matsnev, ME; Gapochka, AM; Kiseleva, TY; Komarov, AE; Shatokhin, MS; Makarova, AO Author Full Names: Rusakov, V. S.; Pokatilov, V. S.; Sigov, A. S.; Matsnev, M. E.; Gapochka, A. M.; Kiseleva, T. Yu.; Komarov, A. E.; Shatokhin, M. S.; Makarova, A. O.
Source:
PHYSICS OF THE SOLID STATE, 58 (1):102-107; 10.1134/S1063783416010261 JAN 2016
Abstract:
The results of the Mossbauer studies on Fe-57 nuclei in multiferroics BiFe1-x T (x) O-3 (T = Sc, Mn; x = 0, 0.05) in the temperature range of 5.2-300 K have been presented. The Mossbauer spectra have been analyzed in terms of the model of an incommensurate spatial spin-*modulated structure* of cycloid type. Information has been obtained about the effect of the substitution of Sc and Mn atoms for Fe atoms on the hyperfine parameters of the spectrum: the shift and the quadrupole shift of the Mossbauer line, the isotropic and anisotropic contributions to the hyperfine magnetic field, and also the parameter of anharmonicity of the spatial spin-modulated structure.
Title:
Multilayered sandwich-like architecture containing large-scale faceted Al-Cu-Fe quasicrystal grains
Authors:
Wei, DX; He, ZB Author Full Names: Wei, Dongxia; He, Zhanbing
Source:
MATERIALS CHARACTERIZATION, 111 154-161; 10.1016/j.matchar.2015.11.027 JAN 2016
Abstract:
Faceted quasicrystals are structurally special compared with traditional crystals. Although the application of faceted quasicrystals has been expected, wide-scale application has not occurred owing to the limited exposure of the facets. Using a facile method of heat treatment, we synthesize a multilayered sandwich-like structure with each layer composed of large-scale pentagonal-dodecahedra of Al-Cu-Fe quasicrystals. Moreover, there are channels between the adjacent Al-Cu-Fe layers that serve to increase the exposure of the facets of quasicrystals. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction are used to characterize the multilayered architecture, and the generation mechanisms of this special structure are also discussed. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Effect of applied pressure on microstructure and mechanical properties of Mg-Zn-Y quasicrystal-reinforced AZ91D magnesium matrix composites prepared by squeeze casting
Authors:
Yang, L; Hou, H; Zhao, YH; Yang, XM Author Full Names: Yang, Ling; Hou, Hua; Zhao, Yu-hong; Yang, Xiao-min
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 25 (12):3936-3943; 10.1016/S1003-6326(15)64041-9 DEC 2015
Abstract:
The Mg-Zn-Y quasicrystal-reinforced AZ91D magnesium matrix composites were prepared by squeeze casting process. The effects of applied pressure on microstructure and mechanical properties of the composites were investigated. The results show that squeeze casting process is an effective method to refine the grain. The composites are mainly composed of alpha-Mg, beta-Mg17Al12 and Mg3Zn6Y icosahedral quasicrystal phase (I-phase). With the increase of applied pressure, the contents of beta-Mg17Al12 phase and Mg3Zn6Y quasicrystal particles increase, further matrix grain refinement occurs and coarse dendritic alpha-Mg transforms into equiaxed grain structure. The composite exhibits the maximum ultimate tensile strength and elongation of 194.3 MPa and 9.2% respectively when the applied pressure is 100 MPa, and a lot of dimples appear on the tensile fractography. Strengthening mechanisms of quasicrystal-reinforced AZ91D magnesium matrix composites are chiefly fine-grain strengthening and quasicrystal particles strengthening.

Update: 28-Jan-2016

Title:
Controlling many-body states by the electric-field effect in a two-dimensional material
Authors:
Li, LJ; O'Farrell, ECT; Loh, KP; Eda, G; Ozyilmaz, B; Neto, AHC Author Full Names: Li, L. J.; O'Farrell, E. C. T.; Loh, K. P.; Eda, G.; Ozyilmaz, B.; Neto, A. H. Castro
Source:
NATURE, 529 (7585):185-U129; 10.1038/nature16175 JAN 14 2016
Abstract:
To understand the complex physics of a system with strong electron-electron interactions, the ideal is to control and monitor its properties while tuning an external electric field applied to the system (the electric-field effect). Indeed, complete electric-field control of many-body states in strongly correlated electron systems is fundamental to the next generation of condensed matter research and devices(1-3). However, the material must be thin enough to avoid shielding of the electric field in the bulk material. Two-dimensional materials do not experience electrical screening, and their charge-carrier density can be controlled by gating. Octahedral titanium diselenide (1T-TiSe2) is a prototypical two-dimensional material that reveals a charge-density wave (CDW) and superconductivity in its phase diagram(4), presenting several similarities with other layered systems such as copper oxides(5), iron pnictides(6), and crystals of rare-earth elements and actinide atoms(7). By studying 1T-TiSe2 single crystals with thicknesses of 10 nanometres or less, encapsulated in two-dimensional layers of hexagonal boron nitride, we achieve unprecedented control over the CDW transition temperature (tuned from 170 kelvin to 40 kelvin), and over the superconductivity transition temperature (tuned from a quantum critical point at 0 kelvin up to 3 kelvin). Electrically driving TiSe2 over different ordered electronic phases allows us to study the details of the phase transitions between many-body states. Observations of periodic oscillations of magnetoresistance induced by the Little-Parks effect show that the appearance of superconductivity is directly correlated with the spatial texturing of the amplitude and phase of the superconductivity order parameter, corresponding to a two-dimensional matrix of superconductivity. We infer that this superconductivity matrix is supported by a matrix of incommensurate CDW states embedded in the commensurate CDW states. Our results show that spatially modulated electronic states are fundamental to the appearance of two-dimensional superconductivity.
Title:
Structure of periodic crystals and quasicrystals in ultrathin films of Ba-Ti-O
Authors:
Cockayne, E; Mihalkovic, M; Henley, CL Author Full Names: Cockayne, Eric; Mihalkovic, Marek; Henley, Christopher L.
Source:
PHYSICAL REVIEW B, 93 (2):10.1103/PhysRevB.93.020101 JAN 7 2016
Abstract:
We model the remarkable thin-film Ba-Ti-O structures formed by heat treatment of an initial perovskite BaTiO3 thin film on a Pt(111) surface. All structures contain a rumpled Ti-O network with all Ti threefold coordinated with O and with Ba occupying the larger. mainly Ti7O7, pores. The quasicrystal structure is a simple decoration of three types of tiles: square, triangle, and 30 degrees. rhombus, with edge lengths 6.85 angstrom, joined edge-to-edge in a quasicrystalline pattern; observed periodic crystals in ultrathin film Ba-Ti-O are built from these and other tiles. Simulated STM images reproduce the patterns seen experimentally and identify the bright protrusions as Ba atoms. The models are consistent with all experimental observations.
Title:
Ultrafast Metamorphosis of a Complex Charge-Density Wave
Authors:
Haupt, K; Eichberger, M; Erasmus, N; Rohwer, A; Demsar, J; Rossnagel, K; Schwoerer, H Author Full Names: Haupt, Kerstin; Eichberger, Maximilian; Erasmus, Nicolas; Rohwer, Andrea; Demsar, Jure; Rossnagel, Kai; Schwoerer, Heinrich
Source:
PHYSICAL REVIEW LETTERS, 116 (1):10.1103/PhysRevLett.116.016402 JAN 6 2016
Abstract:
Modulated phases, commensurate or incommensurate with the host crystal lattice, are ubiquitous in solids. The transition between such phases involves formation and rearrangement of domain walls and is generally slow. Using ultrafast electron diffraction, we directly record the photoinduced transformation between a nearly commensurate and an incommensurate charge-density-wave phase in 1T-TaS2. The transformation takes place on the picosecond time scale, orders of magnitude faster than previously observed for commensurate-to-incommensurate transitions. The transition speed and mechanism can be linked to the peculiar nanoscale structure of the photoexcited nearly commensurate phase.
Title:
Phase diagram of the Kondo lattice model on the kagome lattice
Authors:
Ghosh, S; Brien, PO; Henley, CL; Lawler, MJ Author Full Names: Ghosh, Shivam; Brien, Patrick O'; Henley, Christopher L.; Lawler, Michael J.
Source:
PHYSICAL REVIEW B, 93 (2):10.1103/PhysRevB.93.024401 JAN 4 2016
Abstract:
We consider the potential for novel forms of magnetism arising from the subtle interplay between electrons and spins in the underscreened kagome Kondo lattice model. At weak coupling, we show that incommensurate noncoplanar multiwave vector magnetic orders arise at nearly all fillings and that this results from Fermi surface effects that introduce competing interactions between the spins. At strong coupling, we find that such a complex order survives near half filling despite the presence of ferromagnetism at all other fillings. We show this arises due to state selection among a massive degeneracy of states at infinite coupling. Finally, we show that at intermediate filling only commensurate orders seem to survive, but these orders still include noncoplanar magnetism. So, the mere presence of both local moments and itinerant electrons enables complex orders to form unlike any currently observed in kagome materials.
Title:
Incommensurate to commensurate antiferromagnetism in CeRhAl4Si2: An Al-27 NMR study
Authors:
Sakai, H; Hattori, T; Tokunaga, Y; Kambe, S; Ghimire, NJ; Ronning, F; Bauer, ED; Thompson, JD Author Full Names: Sakai, H.; Hattori, T.; Tokunaga, Y.; Kambe, S.; Ghimire, N. J.; Ronning, F.; Bauer, E. D.; Thompson, J. D.
Source:
PHYSICAL REVIEW B, 93 (1):10.1103/PhysRevB.93.014402 JAN 4 2016
Abstract:
Al-27 nuclear magnetic resonance (NMR) experiments have been performed on a single crystal of CeRhAl4Si2, which is an antiferromagnetic Kondo-lattice compound with successive antiferromagnetic transitions of T-N1 = 14 K and T-N2 = 9 K at zero external field. In the paramagnetic state, the Knight shifts, quadrupolar frequency, and asymmetric parameter of electrical field gradient on the Al sites have been determined, which have local orthorhombic symmetry. The transferred hyperfine coupling constants are also determined. Analysis of the NMR spectra indicates that a commensurate antiferromagnetic structure exists below T-N2, but an incommensurate modulation of antiferromagnetic moments is present in the antiferromagnetic state between T-N1 and T-N2. The spin-lattice relaxation rate suggests that the 4 f electrons behave as local moments at temperatures above T-N1.
Title:
Trapping of Oxygen Vacancies at Crystallographic Shear Planes in Acceptor-Doped Pb-Based Ferroelectrics
Authors:
Batuk, D; Batuk, M; Tsirlin, AA; Hadermann, J; Abakumov, AM Author Full Names: Batuk, Dmitry; Batuk, Maria; Tsirlin, Alexander A.; Hadermann, Joke; Abakumov, Artem M.
Source:
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 54 (49):14787-14790; 10.1002/anie.201507729 DEC 1 2015
Abstract:
The defect chemistry of the ferroelectric material PbTiO3 after doping with Fe-III acceptor ions is reported. Using advanced transmission electron microscopy and powder X-ray and neutron diffraction, we demonstrate that even at concentrations as low as circa 1.7% (material composition approximately ABO(2.95)), the oxygen vacancies are trapped into extended planar defects, specifically crystallographic shear planes. We investigate the evolution of these defects upon doping and unravel their detailed atomic structure using the formalism of superspace crystallography, thus unveiling their role in nonstoichiometry in the Pb-based perovskites.

Update: 14-Jan-2016

Title:
Dislocations in icosahedral quasicrystalline phase embedded in hot-deformed Mg alloys
Authors:
Huang, H; Tian, Y; Yuan, GY; Chen, CL; Wang, ZC; Ding, WJ; Inoue, A Author Full Names: Huang, Hua; Tian, Yuan; Yuan, Guangyin; Chen, Chunlin; Wang, Zhongchang; Ding, Wenjiang; Inoue, Akihisa
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 658 483-487; 10.1016/j.jallcom.2015.10.284 FEB 15 2016
Abstract:
We perform a systematic structural investigation of the I-phase particles embedded in Mg matrix in I-phase-reinforced Mg-3.5Zn-0.6Gd alloy and offer evidence to the presence of dislocations in the I-phase particles. Such dislocations are found to be formed on the (0001) plane of Mg matrix, which is attributed to their slipping into the 5-fold and 2-fold planes of I-phase particles. We also discuss how deformation conditions of wrought Mg alloys affect the deformation behaviors of the I-phase and how deformation behavior of I-phase affect the mechanical properties of wrought Mg alloys. The bonding between the I-phase and Mg matrix was also confirmed to be strong. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Microstructures and phase transformations in as-aged Mn2.04NiGa Heusler alloy
Authors:
Du, ZW; Han, XL; Li, T; Liu, EK; Ma, XD; Xiong, JC; Wu, GH Author Full Names: Du, Z. W.; Han, X. L.; Li, T.; Liu, E. K.; Ma, X. D.; Xiong, J. C.; Wu, G. H.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 657 443-449; 10.1016/j.jallcom.2015.10.111 FEB 5 2016
Abstract:
The room-temperature microstructures and phase transformation of Mn2.04NiGa alloy were investigated by transmission electron microscopy (TEM), electron backscattered diffraction (EBSD) and high-angle annular dark field scanning-TEM (HAADF-STEM). The Mn2.04NiGa alloy annealed at 1073 K for 72 h is mainly austenite phase with Hg2CuTi-type structure. After 623 K/72 h ageing, nano-scaled MnNiGa precipitates considered as Ni2In-type hexagonal structure were found by TEM. A crystalline orientation relationship between precipitates and austensite can be described by ((22) over bar4)(A)//(0 (1) over bar 10)(H), [1 (1) over bar0](A)//[2 (11) over bar0](H). These precipitates are accompanying with Mn-rich martensite lamellae. Both non-modulated and nearly 16-layered modulated structures are generally in coexistence in one martensite lath. A crystalline orientation relationship between the ageing-induced martensite and austenite is (111)(A)//(110)(M), [011](A)//[1 (1) over bar2]M. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Origin of modulated phases and magnetic hysteresis in TmB4
Authors:
Wierschem, K; Sunku, SS; Kong, T; Ito, T; Canfield, PC; Panagopoulos, C; Sengupta, P Author Full Names: Wierschem, Keola; Sunku, Sai Swaroop; Kong, Tai; Ito, Toshimitsu; Canfield, Paul C.; Panagopoulos, Christos; Sengupta, Pinaki
Source:
PHYSICAL REVIEW B, 92 (21):10.1103/PhysRevB.92.214433 DEC 23 2015
Abstract:
We investigate the low-temperature magnetic phases in TmB4, a metallic quantum magnet on the geometrically frustrated Shastry-Sutherland lattice, using coordinated experimental and theoretical studies. Our results provide an explanation for the appearance of the intriguing fractional plateau in TmB4 and accompanying magnetic hysteresis. Together with observation of the bump in the half plateau, our results support the picture that the magnetization plateau structure in TmB4 is strongly influenced by the zero-field modulated phases. We present a phenomenological model to explain the appearance of the modulated phases and a microscopic Hamiltonian that captures the complete magnetic behavior of TmB4.

Update: 7-Jan-2016

Title:
Magnetic properties and complex magnetic phase diagram in non-centrosymmetric EuRhGe3 and EuIrGe3 single crystals
Authors:
Maurya, A; Bonville, P; Kulkarni, R; Thamizhavel, A; Dhar, SK Author Full Names: Maurya, Arvind; Bonville, P.; Kulkarni, R.; Thamizhavel, A.; Dhar, S. K.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 401 823-831; 10.1016/j.jmmm.2015.10.134 MAR 1 2016
Abstract:
We report the magnetic properties of two Eu based compounds, single crystalline EuIrGe3 and EuRhGe3, inferred from magnetisation, electrical transport, heat capacity and Eu-151 Mossbauer spectroscopy. These previously known compounds crystallise in the non-centrosymmetric, tetragonal, I4 mm, BaNiSn3-type structure. Single crystals of EuIrGe3 and EuRhGe3 were grown using a high temperature solution growth method using In as flux. EuIrGe3 exhibits two magnetic transition temperatures T-N1 = 12.4 K, and T(N)2 = 7.3 K, whereas EuRhGe3 presents a single one at T-N = 12K. Eu-151 Mossbauer spectra show evidence for a cascade of transitions from paramagnetic to incommensurate amplitude modulated followed by an equal moment phase at lower temperature in EuIrGe3. This latter phase alone occurs in EuRhGe3. In both compounds, the magnetisation measured up to 14 T suggests that the equal moment magnetic phase has a spiral spin arrangement. The field induced reorientations are also well documented in the magnetotransport data. A superzone gap is observed for the current density J vertical bar vertical bar [001], which is enhanced by a transverse magnetic field. The magnetic phase diagram constructed from all the data is complex, revealing the presence of many phases in the H - T space. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Structural and magnetic phase transitions in CeCu6-xT(x) (T = Ag, Pd)
Authors:
Poudel, L; de la Cruz, C; Payzant, EA; May, AF; Koehler, M; Garlea, VO; Taylor, AE; Parker, DS; Cao, HB; McGuire, MA; Tian, W; Matsuda, M; Jeen, H; Lee, HN; Hong, T; Calder, S; Zhou, HD; Lumsden, MD; Keppens, V; Mandrus, D; Christianson, AD Author Full Names: Poudel, L.; de la Cruz, C.; Payzant, E. A.; May, A. F.; Koehler, M.; Garlea, V. O.; Taylor, A. E.; Parker, D. S.; Cao, H. B.; McGuire, M. A.; Tian, W.; Matsuda, M.; Jeen, H.; Lee, H. N.; Hong, T.; Calder, S.; Zhou, H. D.; Lumsden, M. D.; Keppens, V.; Mandrus, D.; Christianson, A. D.
Source:
PHYSICAL REVIEW B, 92 (21):10.1103/PhysRevB.92.214421 DEC 15 2015
Abstract:
The structural and the magnetic properties of CeCu6-xAgx(0 <= x <= 0.85) and CeCu6-xPdx (0 <= x <= 0.4) have been studied using neutron diffraction, resonant ultrasound spectroscopy (RUS), x-ray diffraction measurements, and first principles calculations. The structural and magnetic phase diagrams of CeCu6-xAgx and CeCu6-xPdx as a function of Ag/Pd composition are reported. The end member, CeCu6, undergoes a structural phase transition from an orthorhombic (Pnma) to a monoclinic (P2(1)/c) phase at 240 K. In CeCu6-xAgx, the structural phase transition temperature (T-s) decreases linearly with Ag concentration and extrapolates to zero at x(S) approximate to 0.1. The structural transition in CeCu6-xPd (x) remains unperturbed with Pd substitution within the range of our study. The lattice constant b slightly decreases with Ag/Pd doping, whereas a and c increase with an overall increase in the unit cell volume. Both systems, CeCu6-xAgx and CeCu6-xPdx, exhibit a magnetic quantum critical point (QCP), at x approximate to 0.2 and x approximate to 0.05, respectively. Near the QCP, long range antiferromagnetic ordering takes place at an incommensurate wave vector (delta(1) 0 delta(2)), where delta(1) similar to 0.62, delta 2 similar to 0.25, x = 0.125 for CeCu6-xPdx and delta(1) similar to 0.64, delta(2) similar to 0.3, x = 0.3 for CeCu6-xAgx. The magnetic structure consists of an amplitude modulation of the Ce moments which are aligned along the c axis of the orthorhombic unit cell.
Title:
Overcoming magnetic frustration and promoting half-metallicity in spinel CoCr2O4 by doping with Fe
Authors:
Ganguly, S; Chimata, R; Sanyal, B Author Full Names: Ganguly, Shreemoyee; Chimata, Raghuveer; Sanyal, Biplab
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224417 DEC 14 2015
Abstract:
In this paper, we present a systematic study of the effects of Fe doping on the electronic and magnetic structures of spinel CoCr2O4 by ab initio density functional theory and atomistic spin dynamics calculations. Our calculated magnetic structure for pristine CoCr2O4 correctly reproduces the experimental one with a q-vector of (0.67, 0.67,0.0), establishing the accuracy of the calculated interatomic exchange interactions. We show that the noncollinear spin structure with a nonzero q-vector in the spinel structure is driven towards collinearity by Fe doping by a complex interplay between interatomic exchange interactions. In the inverse spinel structure with 100% Fe doping, a collinear antiferromagnetic order develops along with a half-metallic electronic structure, which evolves due to the chemical disorder between Fe and Co in the B sites described by the coherent potential approximation. This is a comprehensive theoretical study to understand the evolution of magnetic and electronic properties of multiferroic CoCr2O4 doped with Fe.

Update: 31-Dec-2015

Title:
Decoupling of the antiferromagnetic and insulating states in Tb-doped Sr2IrO4
Authors:
Wang, JC; Aswartham, S; Ye, F; Terzic, J; Zheng, H; Haskel, D; Chikara, S; Choi, Y; Schlottmann, P; Custelcean, R; Yuan, SJ; Cao, G Author Full Names: Wang, J. C.; Aswartham, S.; Ye, Feng; Terzic, J.; Zheng, H.; Haskel, Daniel; Chikara, Shalinee; Choi, Yong; Schlottmann, P.; Custelcean, Radu; Yuan, S. J.; Cao, G.
Source:
PHYSICAL REVIEW B, 92 (21):10.1103/PhysRevB.92.214411 DEC 8 2015
Abstract:
Sr2IrO4 is a spin-orbit-coupled insulator with an antiferromagnetic (AFM) transition at T-N = 240 K. We report results of a comprehensive study of single-crystal Sr2Ir1-xTbxO4 (0 <= x <= 0.03). This study found that a mere 3% (x = 0.03) of tetravalent Tb4+ (4f(7)) substituting for Ir4+ (rather than Sr2+) completely suppresses the long-range collinear AFM transition but retains the insulating state, leading to a phase diagram featuring a decoupling of the magnetic interactions and charge gap. The insulating state at x = 0.03 is characterized by an unusually large specific heat at low temperatures and an incommensurate magnetic state having magnetic peaks at (0.95,0,0) and (0,0.95,0) in the neutron diffraction, suggesting a spiral or spin-density-wave order. It is apparent that Tb doping effectively changes the relative strength of the spin-orbit interaction (SOI) and the tetragonal crystal electric field and enhances the Hund's rule coupling that competes with the SOI, and destabilizes the AFM state. However, the disappearance of the AFM is accompanied by no metallic state chiefly because an energy level mismatch for the Ir and Tb sites weakens charge carrier hopping and causes a persistent insulating state. This work highlights an unconventional correlation between the AFM and insulating states in which the magnetic transition plays no critical role in the formation of the charge gap in the iridate.
Title:
Long-range magnetic order in models for rare-earth quasicrystals
Authors:
Thiem, S; Chalker, JT Author Full Names: Thiem, Stefanie; Chalker, J. T.
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224409 DEC 7 2015
Abstract:
We take a two-step theoretical approach to study magnetism of rare-earth quasicrystals by considering Ising spins on quasiperiodic tilings, coupled via Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. First, we compute RKKY interactions from a tight-binding Hamiltonian defined on the two-dimensional quasiperiodic tilings. We find that the magnetic interactions are frustrated and strongly dependent on the local environment. This results in the formation of clusters with strong bonds at certain patterns of the tilings that repeat quasiperiodically. Second, we examine the statistical mechanics of Ising spins with these RKKY interactions, using extensive Monte Carlo simulations. Although models that have frustrated interactions and lack translational invariance might be expected to display spin-glass behavior, we show that the spin system has a phase transition to low-temperature states with long-range quasiperiodic magnetic order. Additionally, we find that in some of the systems spin clusters can fluctuate much below the ordering temperature.
Title:
One-Dimensional Quasicrystals from Incommensurate Charge Order
Authors:
Flicker, F; van Wezel, J Author Full Names: Flicker, Felix; van Wezel, Jasper
Source:
PHYSICAL REVIEW LETTERS, 115 (23):10.1103/PhysRevLett.115.236401 DEC 3 2015
Abstract:
Artificial quasicrystals are nowadays routinely manufactured, yet only two naturally occurring examples are known. We present a class of systems with the potential to be realized both artificially and in nature, in which the lowest energy state is a one-dimensional quasicrystal. These systems are based on incommensurately charge-ordered materials, in which the quasicrystalline phase competes with the formation of a regular array of discommensurations as a way of interpolating between incommensurate charge order at high temperatures and commensurate order at low temperatures. The nonlocal correlations characteristic of the quasicrystalline state emerge from a free-energy contribution localized in reciprocal space. We present a theoretical phase diagram showing that the required material properties for the appearance of such a ground state allow for one-dimensional quasicrystals to form in real materials. The result is a potentially wide class of one-dimensional quasicrystals.
Title:
Disorder in the composite crystal structure of the manganese 'disilicide' MnSi1.73 from powder X-ray diffraction data
Authors:
Akselrud, L; Gil, RC; Wagner-Reetz, M; Grin, Y Author Full Names: Akselrud, L.; Gil, R. Cardoso; Wagner-Reetz, M.; Grin, Yu.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 (6):707-712; SI 10.1107/S2052520615019757 DEC 2015
Abstract:
The crystal structure of the higher manganese silicide MnSi1.7 (known in the literature as HMS) is investigated in samples with different compositions obtained by different techniques at temperatures not higher than 1273 K. Powder X-ray diffraction was applied. The crystal structure is described as incommensurate composite. In addition to the ordered model already known in the literature, the partial disorder in the silicon substructure was detected and described introducing an additional atomic site with a different modulation function.
Title:
Type II Bi-1 (-) xWxO1.5 (+) (1.5x): a (3+3)-dimensional commensurate modulation that stabilizes the fast-ion conducting delta phase of bismuth oxide
Authors:
Wind, J; Auckett, JE; Withers, RL; Piltz, RO; Maljuk, A; Ling, CD Author Full Names: Wind, Julia; Auckett, Josie E.; Withers, Ray L.; Piltz, Ross O.; Maljuk, Andrey; Ling, Chris D.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 (6):679-687; SI 10.1107/S2052520615018351 DEC 2015
Abstract:
The Type II phase in the Bi1 - xWxO1.5 (+) (1.5x) system is shown to have a (3 + 3)-dimensional modulated delta-Bi2O3-related structure, in which the modulation vector epsilon 'locks in' to a commensurate value of 1/3. The structure was refined in a 3 x 3 x 3 supercell against single-crystal Laue neutron diffraction data. Ab initio calculations were used to test and optimize the local structure of the oxygen sublattice around a single mixed Bi/W site. The underlying crystal chemistry was shown to be essentially the same as for the recently refined (3 + 3)-dimensional modulated structure of Type II Bi-1 (-) xNbxO1.5 (+) (x) (Ling et al., 2013), based on a transition from fluorite-type to pyrochlore-type via the appearance of W4O18 'tetrahedra of octahedra' and chains of corner-sharing WO6 octahedra along < 110 >(F) directions. The full range of occupancies on this mixed Bi/W site give a hypothetical solid-solution range bounded by Bi23W4O46.5 (x = 0.148) and Bi22W5O48 (x = 0.185), consistent with previous reports and with our own synthetic and analytical results.
Title:
Determination of the incommensurate modulated structure of Bi2Sr1.6La0.4CuO6+delta by aberration-corrected transmission electron microscopy
Authors:
Ge, BH; Wang, YM; Luo, HQ; Wen, HH; Yu, R; Cheng, ZY; Zhu, J Author Full Names: Ge, Binghui; Wang, Yumei; Luo, Huiqian; Wen, Haihu; Yu, Rong; Cheng, Zhiying; Zhu, Jing
Source:
ULTRAMICROSCOPY, 159 67-72; 10.1016/j.ultramic.2015.08.004 1 DEC 2015
Abstract:
The incommensurate modulated structure (IMS) of Bi2Sr1.6La0.4Cu6+delta (BSLCO) has been studied by aberration-corrected transmission electron microscopy in combination with a high-dimensional (HD) space description. Two images are deconvoluted in the negative Cs imaging (NCSI) and positive Cs imaging (PCSI) modes. Similar results for the IMS have been obtained from two corresponding projected potential maps (PPMs), and the size of the dots representing atoms in the NCSI PPM is found to be smaller than that in the PCSI PPM. Considering that the object size is one of the factors that influence the precision of the structural determination, modulation functions for all unoverlapped atoms in BSLCO were determined on the basis of the NCSI PPM in combination with the HD space description. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Crystal Structure and Thermoelectric Properties of Chimney-Ladder Higher Manganese Silicides
Authors:
Miyazaki, Y Author Full Names: Miyazaki, Yuzuru
Source:
JOURNAL OF THE JAPAN INSTITUTE OF METALS, 79 (11):530-537; SI 10.2320/jinstmet.JA201508 2015
Abstract:
Crystal structure, electronic structure and thermoelectric (TE) properties of Nowotny chimney-ladder (NCL) higher manganese silicides (HMSs) are reviewed. According to a (3+1). dimensional superspace approach, HMSs are revealed to belong to incommensurate composite crystals, wherein [Mn] and [Si] subsystems possess an irrational c-axis ratio gamma=c(Mn)/c(Si). The gamma parameter, also represents a stoichiometry of the HMSs as MnSi gamma, dictates the electronic structure, directly relating to a valence electron counting number, VEC. The p-type TE performance can be enhanced by a partial substitution of V, Cr, etc., while n-type HMSs can be obtained by heavily substituting Mn with Fe, etc., to realize VEC > 14. A unique thermal expansion has been discovered at T similar to 800 K, which would deteriorate TE performance and hence to be avoided from a practical application point of view.
Title:
Electronic vs. structural ordering in a manganese(III) spin crossover complex
Authors:
Fitzpatrick, AJ; Trzop, E; Muller-Bunz, H; Dirtu, MM; Garcia, Y; Collet, E; Morgan, GG Author Full Names: Fitzpatrick, Anthony J.; Trzop, Eliza; Mueller-Bunz, Helge; Dirtu, Marinela M.; Garcia, Yann; Collet, Eric; Morgan, Grace G.
Source:
CHEMICAL COMMUNICATIONS, 51 (99):17540-17543; 10.1039/c5cc05129k 2015
Abstract:
A symmetry breaking spin transition in a Mn(III) complex is reported with three structural phases, a high symmetry high temperature S = 2 phase, an intermediate S = 1/S = 2 ordered phase and an aperiodic low temperature phase with S = 1 cations. The aperiodicity is interpreted as resulting from long-range ordering of the NTf2- anions.
Title:
Effects of Initial States on the Spinodal Decomposition of Quenched and Melt-Spun Cu-15Ni-8Sn Alloy
Authors:
Kondo, S; Masusaki, A; Ogawa, K; Morimura, T; Nakashima, H Author Full Names: Kondo, Shin-ichiro; Masusaki, Akinori; Ogawa, Kento; Morimura, Takao; Nakashima, Hiromichi
Source:
JOURNAL OF THE JAPAN INSTITUTE OF METALS, 79 (12):664-671; 10.2320/jinstmet.J2015012 2015
Abstract:
We investigate early stages of spinodal decomposition in a melt. spun Cu-15Ni-8Sn alloy (melt-spun samples) by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and electron diffraction analysis through comparison against a quenched alloy of the same composition (quenched samples). In XRD measurements, no sidebands of (200) planes are found in the melt-spun sample after aging at 350 degrees C for 120 min, whereas they are found in the quenched sample after a heat treatment at 350 degrees C for 60 min. TEM observations of a quenched sample after aging at 350 degrees C for 60 min indicate the presence of a modulated structure (lambda= 5-10 nm) in the matrix, whereas those of a melt-spun sample after the same heat treatment also indicate the presence of a modulated structure (lambda: too small to measure). Electron diffraction patterns reveal satellite structures in both samples, although with superlattice reflections from ordering phases visible in the quenched sample. These differences are presumably due to a difference in the size of clusters present in their respective quenched states; in melt. spun samples, cluster size was much smaller as a result of a high cooling rate (approximate to 8 x 10(5 degrees)C/s).

Update: 24-Dec-2015

Title:
Single-Crystal Neutron Diffraction Study of the Heavy-Electron Superconductor CeNiGe3
Authors:
Ikeda, Y; Ueta, D; Yoshizawa, H; Nakao, A; Munakata, K; Ohhara, T Author Full Names: Ikeda, Yoichi; Ueta, Daichi; Yoshizawa, Hideki; Nakao, Akiko; Munakata, Koji; Ohhara, Takashi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (12):10.7566/JPSJ.84.123701 DEC 15 2015
Abstract:
A single-crystal neutron diffraction study was performed on anomalous antiferromagnetic ordering in the heavyelectron superconductor CeNiGe3. We observed incommensurate magnetic Bragg reflections characterized by the incommensurate propagation vector k(2) = (0, 0.41, 1/2) below the Neel temperature of 5K, but no significant magnetic reflection with the commensurate propagation vector k(1) = (1, 0, 0), at which another magnetic reflection was observed in a previous neutron diffraction study with a polycrystalline sample. From the single-crystal study, we suggest that the magnetic phase of CeNiGe3 at ambient pressure is characterized only by the incommensurate propagation vector k(2).
Title:
Electronic Properties of Incommensurate Atomic Layers
Authors:
Koshino, M; Moon, P Author Full Names: Koshino, Mikito; Moon, Pilkyung
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (12):10.7566/JPSJ.84.121001 DEC 15 2015
Abstract:
We present a brief theoretical overview of electronic properties of incommensurate multilayer systems, i.e., a pair of two-dimensional atomic layers stacked in an arbitrary orientation. We introduce the general theoretical scheme to describe the interlayer interaction between incommensurate crystal structures, and apply the formula to two specific examples, the twisted bilayer graphene and graphene-hBN composite bilayer. In each case, we calculate the electronic band structure and demonstrate that the low-energy electronic properties are significantly modified by the interlayer interaction, particularly when the two lattice structures are close to each other. We also study the energy spectrum and the quantum Hall effect in magnetic fields, where we see that the spectral structure exhibits a fractal nature, as known as the Hofstadter butterfly. We argue about the optical absorption properties of the twisted bilayer graphene and show that the interlayer interaction gives rise to the characteristic spectroscopic features in zero magnetic field and also in strong magnetic field.
Title:
Amorphous hydrides of the Ti45Zr38Ni17-xCox nano-powders
Authors:
Zywczak, A; Rusinek, D; Czub, J; Sikora, M; Stepien, J; Gondek, L; Takasaki, A; Hoser, A Author Full Names: Zywczak, A.; Rusinek, D.; Czub, J.; Sikora, M.; Stepien, J.; Gondek, L.; Takasaki, A.; Hoser, A.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 40 (45):15534-15539; 10.1016/j.ijhydene.2015.09.136 DEC 7 2015
Abstract:
The Ti-Zr-Ni alloys can be synthesized in crystalline, amorphous and quasicrystalline phases. They are produced by mechanical alloying or melt-spinning and they are good candidate materials for hydrogen storage applications. In this communication we modified the Ti45Zr38Ni17 compounds by substituting 3d metals (cobalt) for Ni to obtain amorphous phase. The cobalt atoms are located at the same positions as nickel. We describe a series of phase transitions associated with a hydrogen uptake in the amorphous Ti45Zr38Ni17-xCox alloys that were prepared by mechanical alloying. The investigated alloys exhibited a high capacity for gaseous H-2 reaching 2.2 wt.% at elevated temperatures. It has been found, that the amorphous powders were decomposed into simple hydrides being exposed to H-2 at temperatures above 200 degrees C. In order to overcome that problem, a processing route to obtain the amorphous hydrides was established. The heated amorphous hydrides underwent an unusual and fascinating transformation into the glassy quasicrystal phase with no hydrogen loss. A further temperature increase triggered another structural transformation into the cubic phase, which was associated with hydrogen release from the structure. The crystal structure evolution was characterized by the variety of diffraction techniques. Thermodynamic properties were studied by differential scanning calorimetry and thermal desorption spectroscopy. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Title:
Static and quasielastic properties of the spiral magnet Ba2CuGe2O7 studied by neutron resonance spin echo spectroscopy and neutron Larmor labeling
Authors:
Muhlbauer, S; Kindervater, J; Hassler, W Author Full Names: Muehlbauer, S.; Kindervater, J.; Haessler, W.
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224406 DEC 4 2015
Abstract:
We provide a route to use elastic and quasielastic neutron spin echo spectroscopy (Larmor labeling) for a unified approach to study both the static and dynamic properties of incommensurate magnetic structures with small propagation vectors. The archetypal noncentrosymmetric spiral magnet Ba2CuGe2O7 serves as a model system for our study. We show how Larmor labeling can efficiently decouple instrumental wavelength resolution and effective-(Q) over right arrow resolution and give high-precision access to the structural properties of the incommensurate domains of Ba2CuGe2O7.
Title:
Two types of nematicity in the phase diagram of the cuprate superconductor YBa2Cu3Oy
Authors:
Cyr-Choiniere, O; Grissonnanche, G; Badoux, S; Day, J; Bonn, DA; Hardy, WN; Liang, R; Doiron-Leyraud, N; Taillefer, L Author Full Names: Cyr-Choiniere, O.; Grissonnanche, G.; Badoux, S.; Day, J.; Bonn, D. A.; Hardy, W. N.; Liang, R.; Doiron-Leyraud, N.; Taillefer, Louis
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224502 DEC 2 2015
Abstract:
Nematicity has emerged as a key feature of cuprate superconductors, but its link to other fundamental properties such as superconductivity, charge order, and the pseudogap remains unclear. Here we use measurements of transport anisotropy in YBa2Cu3Oy to distinguish two types of nematicity. The first is associated with short-range charge-density-wave modulations in a doping region near p = 0.12. It is detected in the Nernst coefficient, but not in the resistivity. The second type prevails at lower doping, where there are spin modulations but no charge modulations. In this case, the onset of in-plane anisotropy-detected in both the Nernst coefficient and the resistivity-follows a line in the temperature-doping phase diagram that tracks the pseudogap energy. We discuss two possible scenarios for the latter nematicity.
Title:
Direct observation of an optically induced charge density wave transition in 1T-TaSe2
Authors:
Sun, SS; Wei, LL; Li, ZW; Cao, GL; Liu, Y; Lu, WJ; Sun, YP; Tian, HF; Yang, HX; Li, JQ Author Full Names: Sun, Shuaishuai; Wei, Linlin; Li, Zhongwen; Cao, Gaolong; Liu, Y.; Lu, W. J.; Sun, Y. P.; Tian, Huanfang; Yang, Huaixin; Li, Jianqi
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224303 DEC 2 2015
Abstract:
Four-dimensional ultrafast transmission electron microscopy measurements reveal a rich variety of structural dynamic phenomena at a phase transition in the charge density wave (CDW) of 1T-TaSe2. Under photoexcitation, remarkable changes in both the CDW intensity and orientation are clearly observed, associated with the transformation from a commensurate (C) phase into an incommensurate (IC) phase in a time scale of picoseconds. Moreover, the transient states reveal a notable "structural isosbestic point" at a wave vector of q(iso) where the C and IC phases yield their diffracting efficiencies in equal ratio. This observation reveals that the crystal planes parallel to q(iso) adopt a common dynamic feature in the CDW phases throughout whole nonequilibrium transition. The second-order characteristics observed in this nonequilibrium phase transition have also been analyzed based on time-resolved structural data.
Title:
Ancient Metal Mirror Alloy Revisited: Quasicrystalline Nanoparticles Observed
Authors:
Sekhar, JA; Mantri, AS; Yamjala, S; Saha, S; Balamuralikrishnan, R; Rao, PR Author Full Names: Sekhar, J. A.; Mantri, A. S.; Yamjala, S.; Saha, Sabyasachi; Balamuralikrishnan, R.; Rao, P. Rama
Source:
JOM, 67 (12):2976-2983; 10.1007/s11837-015-1524-3 DEC 2015
Abstract:
This article presents, for the first time, evidence of nanocrystalline structure, through direct transmission electron microscopy (TEM) observations, in a Cu-32 wt.% Sn alloy that has been made by an age-old, uniquely crafted casting process. This alloy has been used as a metal mirror for centuries. The TEM images also reveal five-sided projections of nano-particles. The convergent beam nano-diffraction patterns obtained from the nano-particles point to the nano-phase being quasicrystalline, a feature that has never before been reported for a copper alloy, although there have been reports of the presence of icosahedral 'clusters' within large unit cell intermetallic phases. This observation has been substantiated by x-ray diffraction, wherein the observed peaks could be indexed to an icosahedral quasi-crystalline phase. The mirror alloy casting has been valued for its high hardness and high reflectance properties, both of which result from its unique internal microstructure that include nano-grains as well as quasi-crystallinity. We further postulate that this microstructure is a consequence of the raw materials used and the manufacturing process, including the choice of mold material. While the alloy consists primarily of copper and tin, impurity elements such as zinc, iron, sulfur, aluminum and nickel are also present, in individual amounts not exceeding one wt.%. It is believed that these trace impurities could have influenced the microstructure and, consequently, the properties of the metal mirror alloy.
Title:
Mathematical crystallography in the 21st century
Authors:
Senechal, M Author Full Names: Senechal, Marjorie
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 230 (12):691-698; SI 10.1515/zkri-2015-1870 DEC 2015
Abstract:
As crystallography merges with materials science and engineering, mathematical crystallography is growing in new directions, including: Characterizing new materials with unusual properties; Imaging, including but not limited to diffraction; Exploring and exploiting superspaces; Mapping the aperiodic landscape, from chaos to classical periodicity and beyond; Re-modeling the structures of real crystals, both periodic and aperiodic; Modeling self-assembly and self-reorganization on the nanoscale. In short, it's not (just) about space groups and tilings anymore.
Title:
Incommensurate charge density wave modulated by period of Hubbard superlattices
Authors:
Zhang, LL; Huang, J; Duan, CB; Wang, WZ Author Full Names: Zhang, Liang-Liang; Huang, Jin; Duan, Cheng-Bo; Wang, Wei-Zhong
Source:
MODERN PHYSICS LETTERS B, 29 (32):10.1142/S0217984915502085 NOV 30 2015
Abstract:
The charge structure factor of the half-filled Hubbard superlattices with one on-site repulsive site and L-0 free sites per unit cell is investigated numerically. The behaviors of charge structure reveal a kind of evenodd L-0 disparity. For even L-0, we always observe a commensurate charge density wave (CDW). For odd L-0, we observe a commensurateincommensurate CDW transition at a critical on-site repulsion around the particlehole symmetric point. This transition results from the competition between the local charge correlations with odd distance and even distance.
Title:
Incommensurate-commensurate magnetic phase transition in SmRu2Al10
Authors:
Takai, S; Matsumura, T; Tanida, H; Sera, M Author Full Names: Takai, Shun; Matsumura, Takeshi; Tanida, Hiroshi; Sera, Masafumi
Source:
PHYSICAL REVIEW B, 92 (17):10.1103/PhysRevB.92.174427 NOV 30 2015
Abstract:
Magnetic properties of single crystalline SmRu2Al10 have been investigated by electrical resistivity, magnetic susceptibility, and specific heat. We have confirmed the successive magnetic phase transitions at T-N = 12.3 K and T-M = 5.6 K. Resonant x-ray diffraction has also been performed to study the magnetic structures. Below TN, the Sm3+ moments order in an incommensurate structure with q(1) = (0,0.759,0). The magnetic moments are oriented along the orthorhombic b axis, which coincides with the magnetization easy axis in the paramagnetic phase. A very weak third harmonic peak is also observed at q(3) = (0,0.278,0). The transition at T-M is a lock-in transition to the commensurate structure described by q(1) = (0,0.75,0). A well-developed third harmonic peak is observed at q(3) = (0,0.25,0). From the discussion of the magnetic structure, we propose that the long-range RKKY interaction plays an important role, in addition to the strong nearest-neighbor antiferromagnetic interaction.
Title:
Microstructure and High Damping Properties of Mg-Zn-Y Alloys Containing LPSO Phase and I Phase
Authors:
Wan, DQ; Li, JJ; Yu, T Author Full Names: Wan Diqing; Li Junjie; Yu Tian
Source:
RARE METAL MATERIALS AND ENGINEERING, 44 (11):2651-2655; NOV 2015
Abstract:
A high damping Mg-Zn-Y alloy containing LPSO phase and I phase was investigated. The microstructure of a high damping Mg80Y4Zn16 (at%) alloy was examined by optical microscopy (OM) and SEM. Furthermore, the differential thermal analysis (DTA) was used to analyze its phase transformation. Microstructure evolution and damping properties under the conditions of the different solid solution time (3, 6, 9 h) were studied. The results show that the main phase component of the Mg80Y4Zn16 alloy is alpha-Mg, Mg12ZnY (X phase), Mg3Zn6Y (I phase) and Mg10ZnY2 phase (LPSO phase), in which I phase and LPSO phase coexistence is firstly reported. The average damping value of the alloy is 0.03, indicating that it is a high damping alloy. The damping is strain amplitude dependent. The high damping mechanism was also discussed.

Update: 17-Dec-2015

Title:
On the adaptability of 1/1 cubic approximant structure in the Mg-Al-Zn system with the particular example of Mg32Al12Zn37
Authors:
Montagne, P; Tillard, M Author Full Names: Montagne, Pierre; Tillard, Monique
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 656 159-165; 10.1016/j.jallcom.2015.09.201 JAN 25 2016
Abstract:
Intermetallic Mg alloys are of interest in the development of light materials with specific properties and some of them are crystalline approximants of quasicrystalline materials. Mg32Al12Zn37 single crystal structure, cubic, Im (3) over bar, a = 14.1845(1) angstrom, is disordered and belongs to the well known 1/1 approximant structural type commonly called Mg-32(Al1-xZnx)(49) or T-phase. In this family, Mg32Al12Zn37 is a new member remarkable for its very special composition nearby intersection of the 2/1 and 1/1 lines that mark composition domains of cubic 2/1 and 1/1 approximants. Structural features are discussed comparatively with literature data to emphasize the great adaptability through atom disorder of the 1/1 structure. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Icosahedral hydrides of the Ti45Zr38Ni17-xCox nano-powders
Authors:
Zywczak, A; Rusinek, D; Czub, J; Sikora, M; Stepien, J; Gondek, L; Gajewska, M; Takasaki, A; Hoser, A Author Full Names: Zywczak, A.; Rusinek, D.; Czub, J.; Sikora, M.; Stepien, J.; Gondek, L.; Gajewska, M.; Takasaki, A.; Hoser, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 656 702-706; 10.1016/j.jallcom.2015.09.278 JAN 25 2016
Abstract:
In this communication we report the phase transitions associated with a hydrogen uptake in the quasicrystalline Ti45Zr38Ni17-xCox alloys that were prepared by mechanical alloying. The crystal structure evolution of the alloys was characterized by means of the variety of diffraction techniques (X-ray, neutron, and electron) as well as extended X-ray absorption fine structure spectroscopy (EXAFS). That analysis was supported by the results of the thermodynamic measurements, namely differential scanning calorimetry (DSC) and thermal desorption spectroscopy (TDS). According to the neutron diffraction results, the transformation of the amorphous Ti45Zr38Ni17-xCox phases into the quasicrystalline state starts at the temperature of 475 degrees C. At 525 degrees C the icosahedral phase (the i-phase) is well-developed. At higher temperatures the i-phase transforms into the approximant w-phase and eventually into the cubic phase (the c-phase). The investigated icosahedral nano-powders exhibit a high capacity for gaseous H-2 reaching 2.2 wt.% at elevated temperatures. After a hydrogen uptake, a complex phase constitution including the simple hydrides is evidenced. Although the i-phases form again after hydrogen desorption, they are accompanied by the additional Zr3Co phase. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Thermal diffusivity and 3D-XY critical behavior of ferroelectric semiconductors (PbxSn1-x)(2)P2Se6
Authors:
Shvalya, V; Oleaga, A; Salazar, A; Kohutych, AA; Vysochanskii, YM Author Full Names: Shvalya, V.; Oleaga, A.; Salazar, A.; Kohutych, A. A.; Vysochanskii, Yu. M.
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 88 78-84; 10.1016/j.jpcs.2015.10.004 JAN 2016
Abstract:
An ac photopyroelectric calorimeter has been used to study the thermal diffusivity of the ferroelectric semiconductors family (PbxSn1 (-) (x))(2)P2Se6 (x=0-1) from 30 K to room temperature. Phase transitions have been found for x=0, 0.05, 0.2, 0.47 but not for x=1 in the full temperature range. A continuous phase transition has been found for x=0, 0.05, 0.2 and 0.47 which corresponds to the paraelectric commensurate to incommensurate phase. It has been possible to study the critical behavior of this transition for x=0, 0.05 and the critical parameters obtained have been alpha=-0.019, A(+)/A(-)=1.00 and alpha=-0.026, A(+)/A(-) A(-)=1.03, respectively, having fitted at the same time both the low and high temperature branches of the transition as rigorous critical theory indicates; these results agree with the theoretical prediction from renormalization group theory that this kind of transition complies with the 3D-XY universality class (alpha(theor)=-0.014, A(+)/A(-)=1.06), which has been experimentally confirmed only in a few materials. A first order incommensurate to ferroelectric phase transition has been characterized in x=0, 0.05 at lower temperature. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Planar lattices with tailorable coefficient of thermal expansion and high stiffness based on dual-material triangle unit
Authors:
Wei, K; Chen, HS; Pei, YM; Fang, DN Author Full Names: Wei, Kai; Chen, Haosen; Pei, Yongmao; Fang, Daining
Source:
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, 86 173-191; 10.1016/j.jmps.2015.10.004 JAN 2016
Abstract:
The unexpected thermal distortions and failures in engineering raise the big concern about thermal expansion controlling. Thus, design of tailorable coefficient of thermal expansion (CTE) is urgently needed for the materials used in large temperature variation circumstance. Here, inspired by multi-fold rotational symmetry in crystallography, we have devised six kinds of periodic planar lattices, which incorporate tailorable CTE and high specific biaxial stiffness. Fabrication process, which overcame shortcomings of welding or adhesion connection, was developed for the dual-material planar lattices. The analytical predictions agreed well with the CTE measurements. It is shown that the planar lattices fabricated from positive CTE constituents, can give large positive, near zero and even negative CIEs. Furthermore, a generalized stationary node method was proposed for aperiodic lattices and even arbitrary structures with desirable thermal expansion. As an example, aperiodic quasicrystal lattices were designed and exhibited zero thermal expansion property. The proposed method for the lattices of lightweight, robust stiffness, strength and tailorable thermal expansion is useful in the engineering applications. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Magnetic structures of R5Ni2In4 and R11Ni4In9 (R = Tb and Ho): strong hierarchy in the temperature dependence of the magnetic ordering in the multiple rare-earth sublattices
Authors:
Ritter, C; Provino, A; Manfrinetti, P; Pecharsky, VK; Gschneidner, KA; Dhar, SK Author Full Names: Ritter, C.; Provino, A.; Manfrinetti, P.; Pecharsky, V. K.; Gschneidner, K. A., Jr.; Dhar, S. K.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (47):10.1088/0953-8984/27/47/476001 DEC 2 2015
Abstract:
The magnetic properties and magnetic structures of the R5Ni2In4 and the microfibrous R11Ni4In9 compounds with R = Tb and Ho have been examined using magnetization, heat capacity, and neutron diffraction data. Rare earth atoms occupy three and five symmetrically inequivalent rare earth sites in R5Ni2In4 and R11Ni4In9 compounds, respectively. As a result of the intra-and inter-magnetic sublattice interactions, the magnetic exchange interactions are different for various rare earth sites; this leads to a cascade of magnetic transitions with a strong hierarchy in the temperature dependence of the magnetic orderings. A transition at T-C = 125 K in Tb5Ni2In4 [kappa(1) = (0, 0, 0)] leads to a ferro/ferrimagnetic order where the magnetic ordering in one of the three R-sublattices leads to the ordering of another one; the third sublattice stays non-magnetic. New magnetic Bragg peaks appearing below T-N = 20 K can be indexed with the incommensurate magnetic propagation vector kappa(2) = (0, 0.636, 1/2); at T-N = 20 K a cycloidal spin order, which acts mostly upon the third R-sublattice, occurs. Ho5Ni2In4 establishes first antiferromagnetism [kappa = (0, 0, 0)] at T-N = 31 K on two R-sublattices; then the system becomes ferro/ferrimagnetic at T-C = 25 K with the third sublattice ordering as well. Tb11Ni4In9 has three magnetic transitions at T-C = 135 K, T-N1 = 35 K and at T-N2 = 20 K; they are respectively coupled to the appearance of different propagation vectors [kappa(1) = (0, 0, 0), kappa(2) = (0, 0, 1/2), kappa(3) = (0, 1, 1/2)], which themselves are operating differently on the five different R-sublattices. Two sublattices remain mostly ferromagnetic down to lowest temperature while the three others are predominantly coupled antiferromagnetically. In Ho11Ni4In9 a purely antiferromagnetic order, described by four different magnetic propagation vectors [kappa(1) = (0, 0.62, 0), kappa(2) = (0, 1, 0), kappa(3) = (0, 0, 1/2), kappa(4) = (0, 1, 1/2)], succeedingly includes all five different sublattices on cooling through transitions at T-N1 = 22 K, T-N2 = 12 K, T-N3 = 8 K and T-N4 = 7 K. The strength of the magnetic interactions of the different sublattices can be linked to structural details for both R5Ni2In4 and R11Ni4In9 compounds.
Title:
Spiral magnetism in the single-band Hubbard model: the Hartree-Fock and slave-boson approaches
Authors:
Igoshev, PA; Timirgazin, MA; Gilmutdinov, VF; Arzhnikov, AK; Irkhin, VY Author Full Names: Igoshev, P. A.; Timirgazin, M. A.; Gilmutdinov, V. F.; Arzhnikov, A. K.; Irkhin, V. Yu
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (44):10.1088/0953-8984/27/44/446002 NOV 11 2015
Abstract:
The ground-state magnetic phase diagram is investigated within the single-band Hubbard model for square and different cubic lattices. The results of employing the generalized non-correlated mean-field (Hartree-Fock) approximation and generalized slave-boson approach by Kotliar and Ruckenstein with correlation effects included are compared. We take into account commensurate ferromagnetic, antiferromagnetic, and incommensurate (spiral) magnetic phases, as well as phase separation into magnetic phases of different types, which was often lacking in previous investigations. It is found that the spiral states and especially ferromagnetism are generally strongly suppressed up to non-realistically large Hubbard U by the correlation effects if nesting is absent and van Hove singularities are well away from the paramagnetic phase Fermi level. The magnetic phase separation plays an important role in the formation of magnetic states, the corresponding phase regions being especially wide in the vicinity of half-filling. The details of non-collinear and collinear magnetic ordering for different cubic lattices are discussed.
Title:
Quasicrystals at extreme conditions: The role of pressure in stabilizing icosahedral A(163)Cu(24)Fe(13) at high temperature
Authors:
Stagno, V; Bindi, L; Park, CY; Tkachev, S; Prakapenka, VB; Mao, HK; Hemley, RJ; Steinhardt, PJ; Fei, YW Author Full Names: Stagno, Vincenzo; Bindi, Luca; Park, Changyong; Tkachev, Sergey; Prakapenka, Vitali B.; Mao, H. -K.; Hemley, Russell J.; Steinhardt, Paul J.; Fei, Yingwei
Source:
AMERICAN MINERALOGIST, 100 (11-12):2412-2418; 10.2138/am-2015-5412 NOV-DEC 2015
Abstract:
Icosahedrite, the first natural quasicrystal with composition Al63Cu24Fe13, was discovered in several grains of the Khatyrka meteorite, a CV3 carbonaceous chondrite. The presence of icosahedrite associated with high-pressure phases like ahrensite and stishovite indicates formation at high pressures and temperatures due to an impact-induced shock. Previous experimental studies on the stability of synthetic icosahedral AlCuFe have either been limited to ambient pressure, for which they indicate incongruent melting at similar to 1123 K, or limited to room-temperature, for which they indicate structural stability up to about 35 GPa. These data are insufficient to experimentally constrain the formation and stability of icosahedrite under the conditions of high pressure and temperature that formed the Khatyrka meteorite. Here we present the results of room-temperature, high-pressure diamond-anvil cells measurements of the compressional behavior of synthetic icosahedrite up to 50 GPa. High P-T experiments were also carried out using both laser-heated diamond-anvil cells combined with in situ synchrotron X-ray diffraction (at 42 GPa) and multi-anvil apparatus (at 21 GPa) to investigate the structural evolution and crystallization of possible coexisting phases. The results demonstrate that the quasiperiodic order of icosahedrite is retained over the P-T range explored. We find that pressure acts to stabilize the icosahedral symmetry at temperatures much higher than previously reported. Direct solidification of AlCuFe quasicrystals from an unusual Al-Cu-rich melt is possible but it is limited to a narrow temperature range. Alternatively, quasicrystals may form after crystallization through solid-solid reactions of Al-rich phases. In either case, our results show that quasicrystals can preserve their structure even after hypervelocity impacts spanning a broad range of pressures and temperatures.
Title:
New horizon in quasicrystals
Authors:
Samavat, F; Kiani, M Author Full Names: Samavat, F.; Kiani, M.
Source:
CRYSTALLOGRAPHY REPORTS, 60 (6):935-938; 10.1134/S1063774515060280 NOV 2015
Abstract:
Quasicrystals (QCs) are aperiodic intermetallic alloys that possess a long range positional order. They often exhibit crystallographically forbidden symmetries, most commonly fivefold and tenfold. The forbidden symmetry is related to the fact that the atoms are arranged quasiperiodically. Quasiperiodic translational order has physical consequences. For example, since electrons and phonons in quasicrystals do not encounter a periodic potential, quasicrystals have unusual resistive and elastic properties, and these have been exploited in several applications. The purpose of this introduction is to present certain properties that are relevant to the surface science of quasicrystals, as a launching point for the other articles in this special issue of progress in surface science.
Title:
Penrose tilings as model sets
Authors:
Shutov, AV; Maleev, AV Author Full Names: Shutov, A. V.; Maleev, A. V.
Source:
CRYSTALLOGRAPHY REPORTS, 60 (6):797-804; 10.1134/S1063774515060322 NOV 2015
Abstract:
The Baake construction, based on generating a set of vertices of Penrose tilings as a model set, is refined. An algorithm and a corresponding computer program for constructing an uncountable set of locally indistinguishable Penrose tilings are developed proceeding from this refined construction. Based on an analysis of the parameters of tiling vertices, 62 versions of rhomb combinations at the tiling center are determined. The combinatorial structure of Penrose tiling worms is established. A concept of flip transformations of tilings is introduced that makes it possible to construct Penrose tilings that cannot be implemented in the Baake construction.
Title:
Birefringence of mechanically stressed Rb2ZnCl4 crystals
Authors:
Kurlyak, VY; Stadnyk, VY; Stakhura, VB; Kohut, ZO Author Full Names: Kurlyak, V. Yu.; Stadnyk, V. Yo.; Stakhura, V. B.; Kohut, Z. O.
Source:
CRYSTALLOGRAPHY REPORTS, 60 (6):929-934; 10.1134/S1063774515060164 NOV 2015
Abstract:
The spectral and temperature dependences of the birefringence of mechanically free and uniaxially stressed Rb2ZnCl4 crystals have been investigated. It is shown that annealing a crystal leads to step changes in the birefringence at the phase transition from the incommensurate to commensurate phase, whereas the birefringence of as-prepared crystals changes continuously. It is established that the birefringence of Rb2ZnCl4 crystal is sensitive to uniaxial pressure; however, uniaxial stress does not change the character of its dispersion and temperature dependences. A new "pseudoisotropic" state of this crystal and a baric shift of the points of paraelectric phase-incommensurate phase-commensurate phase transitions to different temperature regions are found.
Title:
Refinement of Thermodynamic Parameters of the Mg24Y5, W and H Phases in the Mg-Zn-Y System
Authors:
Minamoto, S; Horiuchi, T; Miura, S Author Full Names: Minamoto, Satoshi; Horiuchi, Toshiaki; Miura, Seiji
Source:
MATERIALS TRANSACTIONS, 56 (10):60-64; 10.2320/matertrans.MH201418 OCT 2015
Abstract:
The Mg-Zn-Y alloy shows excellent mechanical properties which can be achieved by combining LPSO phase (known as X phase) and an icosahedral quasicrystal phase (land Z phases) in Mg solid solution (a phase). Thermodynamic data for the binary/ternary compounds Mg24Y5, X, Wand H have to be critically assessed to obtain accurate information of three-phase equilibrium in order to understand equilibria among these phases. In this research, we focused on developing CALPHAD (CALculation of PHAse Diagrams) thermodynamic database to evaluate phase diagrams for the Mg-Zn-Y system. Especially thermodynamic models for the Mg24Y5, W and H phases have been determined based on crystallographic data. Then thermodynamic parameters have been assessed to yield experimental data from EPMA/WDS, SEM, TEM and X-Ray diffraction.
Title:
Dielectric Properties and Phase Diagram of (Sr1-xBax)(2)Nb2O7 Single Crystals
Authors:
Akishige, Y; Kamata, M; Tsukada, S Author Full Names: Akishige, Yukikuni; Kamata, Misako; Tsukada, Shinya
Source:
FERROELECTRICS, 485 (1):73-79; SI 10.1080/00150193.2015.1060832 AUG 26 2015
Abstract:
Dielectric constants, epsilon(b) and epsilon(c) along the crystallographic b and c axes respectively, were measured in a temperature range of 10 - 700K on Ba-substituted Sr2Nb2O7 single crystals with different Ba concentrations up to x = 0.32. When x = 0, two dielectric anomalies were observed at T-I = 489K and at T-L = 100K, owing to the incommensurate phase transition and the low-temperature ferroelectric phase transition, respectively. Both T-I and T-L decrease with Ba-content x at initial slopes of ca. -19 and -37K/mol%, respectively, and become broad at x = 0.04 and almost disappear at x = 0.08. Furthermore, Ba-substitution induces a weak and broad dielectric maximum in epsilon(b)' vs. T curve at approximately T-m = 465K for x > 0.2. Phase diagram of this system was proposed.

Update: 10-Dec-2015

Title:
Smearing-type wear behavior of Al62Cu25.5Fe12.5 quasicrystal abrasive on soft metals
Authors:
Chen, YJ; Qiang, JB; Dong, C Author Full Names: Chen, Yongjun; Qiang, Jianbin; Dong, Chuang
Source:
INTERMETALLICS, 68 23-30; 10.1016/j.intermet.2015.09.001 JAN 2016
Abstract:
The abrasive polishing behavior of Al62Cu25.5Fe12.5 quasicrystal on Cu, Al and austenite stainless steel alloys were investigated, to compare with commonly used hard abrasives such as diamond, alumina and silica. The quasicrystal abrasive showed a dominating smearing-type wear mechanism, in sharp contrast to all the other three abrasives, as reflected by large indent size shrinking with respect to surface removal depth. The quasicrystal abrasive polishing, producing a flattened surface with minor depth removal, may open new application fields where low-wearing and fine surface finishing are demanded. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
X-ray diffraction study of the icosahedral AlCuFe quasicrystal at megabar pressures
Authors:
Takagi, S; Kyono, A; Mitani, S; Sugano, N; Nakamoto, Y; Hirao, N Author Full Names: Takagi, Sota; Kyono, Atsushi; Mitani, Saki; Sugano, Neo; Nakamoto, Yuki; Hirao, Naohisa
Source:
MATERIALS LETTERS, 161 13-16; 10.1016/j.matlet.2015.08.057 DEC 15 2015
Abstract:
We report in-situ synchrotron X-ray diffraction study of icosahedral (i)-AlCuFe quasicrystal (QC) at high pressure up to 104 GPa under ambient temperature using the diamond anvil technique. With compression, there is no obvious change of the diffraction pattern within the measured pressure range. Five characteristic peaks from the i-AlCuFe QC maintain up to 104 GPa. The unit cell volume of the i-AlCuFe QC decreases monotonously until 72 GPa. The experimental P-V compression curve below 72 GPa was fitted to the Birch-Murnaghan equation of state with V-0=2023(19) angstrom(3), K-0=131(7) GPa, K'=4.0 (fixed). The resulting EoS parameters are approximately consistent with those observed in previous study. A discontinuous volume change is observed between 72 and 75 GPa. These observed results indicate a phase transition from i-AlCuFe QC to an approximant crystal (AC) which has a similar local atomic arrangement as the QC. This study suggests that i-AlCuFe QC maintains its structure at least up to 72 GPa and then transforms to AC with small displacement of atoms. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Ni coated Ti1.4V0.6Ni composite as the negative electrode in Ni-MH battery
Authors:
Sun, LS; Lin, J; Liang, F; Cao, ZY; Wang, LM Author Full Names: Sun, Lianshan; Lin, Jing; Liang, Fei; Cao, Zhanyi; Wang, Limin
Source:
MATERIALS LETTERS, 161 686-689; 10.1016/j.matlet.2015.09.081 DEC 15 2015
Abstract:
Ti1.4V0.6Ni composite is synthesized by arc-melting and subsequent melt-spinning techniques. An improved electrochemical stability of Ti14V0.6Ni composite is obtained by chemical plating Ni. The phase structures of the composite contain icosahedral quasicrystal phase (i-phase) and TiNi-type phase. Different amount of Ni is coated on the surface of the composite particles. When Ti14V0.6Ni is plated with 19 wt% Ni, the discharge capacity retention ratio is promoted. Ni coating layer inhibits the dissolution of V from the composite and also promotes the high rate discharge property. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Antiphase Boundaries in the Turbostratically Disordered Misfit Compound (BiSe)(1+delta)NbSe2
Authors:
Mitchson, G; Falmbigl, M; Ditto, J; Johnson, DC Author Full Names: Mitchson, Gavin; Falmbigl, Matthias; Ditto, Jeffrey; Johnson, David C.
Source:
INORGANIC CHEMISTRY, 54 (21):10309-10315; 10.1021/acs.inorgchem.5b01648 NOV 2 2015
Abstract:
(BiSe)(1+delta)NbSe2 ferecrystals were synthesized in order to determine whether structural modulation in BiSe layers, characterized by periodic antiphase boundaries and Bi-Bi bonding, occurs. Specular X-ray diffraction revealed the formation of the desired compound with a c-axis lattice parameter of 1.21 nm from precursors with a range of initial compositions and initial periodicities. In-plane X-ray diffraction scans could be indexed as hk0 reflections of the constituents, with a rectangular basal BiSe lattice and a trigonal basal NbSe2 lattice. Electron micrographs showed extensive turbostratic disorder in the samples and the presence of periodic antiphase boundaries (approximately 1.5 nm periodicity) in BiSe layers oriented with the [110] direction parallel to the zone axis of the microscope. This indicates that the structural modulation in the BiSe layers is not due to coherency strain resulting from commensurate in-plane lattices. Electrical transport measurements indicate that holes are the dominant charge carrying species, that there is a weak decrease in resistivity as temperature decreases, and that minimal charge transfer occurs from the BiSe to NbSe2 layers. This is consistent with the lack of charge transfer from the BiX to the TX2 layers reported in misfit layer compounds where antiphase boundaries were observed. This suggests that electronic considerations, i.e., localization of electrons in the Bi-Bi pairs at the antiphase boundaries, play a dominant role in stabilizing the structural modulation.
Title:
Unravelling structural ambiguities in lithium- and manganese-rich transition metal oxides
Authors:
Shukla, AK; Ramasse, QM; Ophus, C; Duncan, H; Hage, F; Chen, GY Author Full Names: Shukla, Alpesh Khushalchand; Ramasse, Quentin M.; Ophus, Colin; Duncan, Hugues; Hage, Fredrik; Chen, Guoying
Source:
NATURE COMMUNICATIONS, 6 10.1038/ncomms9711 OCT 2015
Abstract:
Although Li- and Mn-rich transition metal oxides have been extensively studied as high-capacity cathode materials for Li-ion batteries, the crystal structure of these materials in their pristine state is not yet fully understood. Here we apply complementary electron microscopy and spectroscopy techniques at multi-length scale on well-formed Li-1.2(Ni0.13Mn0.54Co0.13)O-2 crystals with two different morphologies as well as two commercially available materials with similar compositions, and unambiguously describe the structural make-up of these samples. Systematically observing the entire primary particles along multiple zone axes reveals that they are consistently made up of a single phase, save for rare localized defects and a thin surface layer on certain crystallographic facets. More specifically, we show the bulk of the oxides can be described as an aperiodic crystal consisting of randomly stacked domains that correspond to three variants of monoclinic structure, while the surface is composed of a Co- and/or Ni-rich spinel with antisite defects.
Title:
Fermi states and anisotropy of Brillouin zone scattering in the decagonal Al-Ni-Co quasicrystal
Authors:
Rogalev, VA; Groning, O; Widmer, R; Dil, JH; Bisti, F; Lev, LL; Schmitt, T; Strocov, VN Author Full Names: Rogalev, V. A.; Groening, O.; Widmer, R.; Dil, J. H.; Bisti, F.; Lev, L. L.; Schmitt, T.; Strocov, V. N.
Source:
NATURE COMMUNICATIONS, 6 10.1038/ncomms9607 OCT 2015
Abstract:
Quasicrystals (QCs) are intermetallic alloys that have excellent long-range order but lack translational symmetry in at least one dimension. The valence band electronic structure near the Fermi energy E-F in such materials is of special interest since it has a direct relation to their unusual physical properties. However, the Fermi surface (FS) topology as well as the mechanism of QC structure stabilization are still under debate. Here we report the first observation of the three-dimensional FS and valence band dispersions near E-F in decagonal Al70Ni20Co10 (d-AlNiCo) QCs using soft X-ray angle-resolved photoemission spectroscopy. We show that the FS, formed by dispersive Al sp-states, has a multicomponent character due to a large contribution from high-order bands. Moreover, we discover that the magnitude of the gap at the FS related to the interaction with Brillouin zone boundary (Hume-Rothery gap) critically differs for the periodic and quasiperiodic directions.

Update: 3-Dec-2015

Title:
Microstructure and mechanical properties of laser beam welded Al-Li alloy 2060 with Al-Mg filler wire
Authors:
Zhang, XY; Yang, WX; Xiao, RS Author Full Names: Zhang, Xinyi; Yang, Wuxiong; Xiao, Rongshi
Source:
MATERIALS & DESIGN, 88 446-450; 10.1016/j.matdes.2015.08.144 DEC 25 2015
Abstract:
Alloy 2060-T8 is a newly developed high-strength Al-Li alloy for applications in aircraft industry. Crack-free welds were obtained in laser beam welding with 5087 filler wire under optimized welding conditions. In this paper, fusion zone microstructure and joint mechanical properties were investigated. Microstructure typical for the weld metal consists of alpha-Al matrix with a few nanoscale precipitates inside and a coarse icosahedral quasi-crystalline T-2 phase at the dendritic and grain boundaries. The quasicrystalline occurred normally in Al-Li-Cu alloys with higher Li contents. Our investigations show that the icosahedral quasicrystalline phase T-2 phase forms in the laser-welded Al-Li alloy 2060 with lower Li content as a result of segregation and replacement of Mg element. The joint tensile strength in as-welded condition is around 317 MPa, about 63% of that of the base metal, and fracture occurs within the fusion zone. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Explosively welded multilayer Ni-Al composites
Authors:
Bataev, IA; Ogneva, TS; Bataev, AA; Mali, VI; Esikov, MA; Lazurenko, DV; Guo, Y; Jorge, AM Author Full Names: Bataev, I. A.; Ogneva, T. S.; Bataev, A. A.; Mali, V. I.; Esikov, M. A.; Lazurenko, D. V.; Guo, Y.; Jorge Junior, A. M.
Source:
MATERIALS & DESIGN, 88 1082-1087; 10.1016/j.matdes.2015.09.103 DEC 25 2015
Abstract:
In this study, the structure of explosively welded Ni-Al multilayer composites was investigated. In particular, the interface between Ni and Al plates was studied using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). Continuous interlayers of mixed Al and Ni were found at the interface. The Al and Ni in these zones were heated above their melting temperatures, non-uniformly mixed, and rapidly solidified. Several intermetallic phases, including the decagonal phase and metastable Al9Ni2, were observed in these zones using electron diffraction. A cellular dislocation structure formed in the Ni plates and a polygonized dislocation structure formed in the Al plates due to the extremely high strain rate deformation and heating. Subsequent heat treatment at 620 degrees C led to the rapid formation of stable intermetallic layers at the interfaces. The growth of the intermetallic layers was considerably faster in the explosively welded composite than in the reference sample. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Effect of icosahedral phase on the crystallographic texture and mechanical anisotropy of duplex structured Mg-Li alloys
Authors:
Xu, DK; Li, CQ; Wang, BJ; Han, EH Author Full Names: Xu, D. K.; Li, C. Q.; Wang, B. J.; Han, E. H.
Source:
MATERIALS & DESIGN, 88 88-97; 10.1016/j.matdes.2015.08.123 DEC 25 2015
Abstract:
Through comparing the microstructure and mechanical properties of Mg-6%Li and Mg-6%Li-6%Zn-1.2%Y alloys, the difference in their mechanical anisotropy have been deeply investigated. Due to the formation of I-phase (Mg3Zn6Y, icosohedral structure), the volume fraction of beta-Li phases formed in Mg-6%Li-6%Zn-1.2%Y alloy was two times higher than that in Mg-6%Li alloy even these two alloys having the same Li content. Texture analysis demonstrated that I-phase particle stimulated nucleation of recrystallization (PSN) and the formation of higher volume fraction of beta-Li phases can remarkably weaken the basal texture of alpha-Mg phases, resulting in a very weak mechanical anisotropy. On the contrary, the basal texture of the alpha-Mg phases in Mg-6%Li alloy was quite strong and obvious mechanical anisotropy between differently oriented samples can be observed. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Phase Formation in the Rapidly Solidified Al70-xGaxPd13Mn17 Alloys
Authors:
Yadav, TP; Shaz, MA; Mukhopadhyay, NK; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Shaz, M. A.; Mukhopadhyay, N. K.; Tiwari, R. S.; Srivastava, O. N.
Source:
TRANSACTIONS OF THE INDIAN INSTITUTE OF METALS, 68 (6):1145-1149; 10.1007/s12666-015-0660-3 DEC 2015
Abstract:
In the present investigation, the effect of Ga substitution at Al site on the phase formation and stabilization of decagonal quasicrystalline phase in the rapidly solidified Al70-xGaxPd13Mn17 alloys have been studied by employing X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive x-ray analysis. The as-cast and rapidly solidified alloys with x = 0, 2.5 and 5 have been investigated. The melt-spinning technique has been used for rapid solidification of the as-cast alloys. The alloys up to 5 at.% Ga exhibit the formation of small amount of icosahedral quasicrystalline phases along with major amount of decagonal phase in the rapidly solidied ribbons. The energy dispersive X-ray analysis investigations suggest the homogeneous presence of Ga in the quasicrystalline alloys.
Title:
Three-dimensional charge density wave order in YBa2Cu3O6.67 at high magnetic fields
Authors:
Gerber, S; Jang, H; Nojiri, H; Matsuzawa, S; Yasumura, H; Bonn, DA; Liang, R; Hardy, WN; Islam, Z; Mehta, A; Song, S; Sikorski, M; Stefanescu, D; Feng, Y; Kivelson, SA; Devereaux, TP; Shen, ZX; Kao, CC; Lee, WS; Zhu, D; Lee, JS Author Full Names: Gerber, S.; Jang, H.; Nojiri, H.; Matsuzawa, S.; Yasumura, H.; Bonn, D. A.; Liang, R.; Hardy, W. N.; Islam, Z.; Mehta, A.; Song, S.; Sikorski, M.; Stefanescu, D.; Feng, Y.; Kivelson, S. A.; Devereaux, T. P.; Shen, Z. -X.; Kao, C. -C.; Lee, W. -S.; Zhu, D.; Lee, J. -S.
Source:
SCIENCE, 350 (6263):949-952; 10.1126/science.aac6257 NOV 20 2015
Abstract:
Charge density wave (CDW) correlations have been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured with x-ray scattering at zero and low fields. We combined a pulsed magnet with an x-ray free-electron laser to characterize the CDW in YBa2Cu3O6.67 via x-ray scattering in fields of up to 28 tesla. While the zero-field CDW order, which develops at temperatures below similar to 150 kelvin, is essentially two dimensional, at lower temperature and beyond 15 tesla, another three-dimensionally ordered CDW emerges. The field-induced CDW appears around the zero-field superconducting transition temperature; in contrast, the incommensurate in-plane ordering vector is field-independent. This implies that the two forms of CDW and high-temperature superconductivity are intimately linked.
Title:
Tuning of magnetic ordering by Y substitution onto Tb site in the nanocrystalline TbMnO3
Authors:
Chakraborty, KR; Shukla, R; Kaushik, SD; Mukadam, MD; Siruguri, V; Tyagi, AK; Yusuf, SM Author Full Names: Chakraborty, Keka R.; Shukla, Rakesh; Kaushik, S. D.; Mukadam, M. D.; Siruguri, V.; Tyagi, A. K.; Yusuf, S. M.
Source:
JOURNAL OF APPLIED PHYSICS, 118 (16):10.1063/1.4934251 OCT 28 2015
Abstract:
We report the magnetic properties, of nano-crystalline powders Tb1-xYxMnO3 (x = 0, 0.1, 0.2, 0.3 and 0.4), as perceived by neutron diffraction, and elucidate the effect of Tb site substitution on the magnetic structure of TbMnO3. All samples crystallized in the orthorhombic structure conforming to space group Pnma, and exhibited an incommensurate collinear antiferromagnetic ordering of the Mn ions below similar to 40 K. Furthermore, at T <= 20 K, all these samples showed a change in magnetic structure (of Mn moments) to a spiral ordering down to 2K, the lowest measured temperature. For the samples with x = 0, 0.1, and 0.2, a short-ranged two dimensional (2D) ordering of Tb moments was also observed at 2K. However, for the other samples (x-0.3 and 0.4), no magnetic ordering of Tb moments was found down to 2K. So with Y substitution, a crossover from 2D ordering to a disordering of Tb moments was observed. The moments at the Mn site were found to be lower than the full Mn3+(4 mu B) moment for all the samples below 40 K. The magnetic properties of all the samples studied by us in nano form are more pronounced than those of the reported single crystals of same compositions [V. Yu. Ivanov et al., JETP Lett. 91, 392-397 (2010)]. (C) 2015 AIP Publishing LLC.
Title:
Exchange integrals of commensurate and incommensurate structures of MFe4Al8 (M = U, Sc)
Authors:
Recko, K Author Full Names: Recko, K.
Source:
JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 17 (9-10):1403-1409; SEP-OCT 2015
Abstract:
The appearance of the commensurability of UFe4Al8 alloy considering incommensurability of ScFe4Al8 compound is analysed on the basis of Heisenberg Hamiltonian. The influence of Dzyaloshinskii - Moriya and Ruderman-Kittel-Kasuya-Yoshida as well as the dipolar interactions as the main reasons of the noncollinearity and incommensurability of the alloys belonging to ThMn12 family is investigated. The values and directions of the spin ordering found by magnetic diffraction are compared to that one's deriving from grand state configurations obtained by a simulated annealing algorithm. The lock-in magnetic modulations due to substitution of scandium by uranium atoms is discussed based on an appropriate exchange constants ratios.
Title:
The Incommensurate Phase Transformation in TlInS2 Ferroelectric
Authors:
Salnik, A; Gololobov, YP; Borovoy, NA Author Full Names: Salnik, A.; Gololobov, Yu. P.; Borovoy, N. A.
Source:
FERROELECTRICS, 484 (1):62-68; SI 10.1080/00150193.2015.1059716 AUG 5 2015
Abstract:
The features of the crystal structure of c and 2c TlInS2 polytypes have been studied by single-crystal X-ray diffraction method in the temperature range 180 K-300 K. In the c polytype the appearance of the incommensurate phase with modulation vector q. d; 0; 0: 25/. dD0: 04/was observed at the temperature of 238 K (on cooling). The active phase formation occurred between 213 K and 217 K. The incommensurability parameter d decreases monotonically to the zero as the temperature approaches 195 K. For the 2c polytype the modulation satellites for both incommensurate and commensurate phases were not observed in the temperature range 180 K-300 K.

Update: 26-Nov-2015

Title:
Superconductivity in the orthorhombic phase of thermoelectric CsPbxBi4-xTe6 with 0.3 <= x <= 1.0
Authors:
Zhang, RX; Yang, HX; Tian, HF; Chen, GF; Wu, SL; Wei, LL; Li, JQ Author Full Names: Zhang, R. X.; Yang, H. X.; Tian, H. F.; Chen, G. F.; Wu, S. L.; Wei, L. L.; Li, J. Q.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 232 50-55; 10.1016/j.jssc.2015.08.050 DEC 2015
Abstract:
Experimental measurements clearly reveal the presence of bulk superconductivity in the CsPbxBi4-xTe6 (0.3 <= x <= 1.0) materials, i.e. the first member of the thermoelectric series of Cs[PbmBi3Te5+m], these materials have the layered orthorhombic structure containing infinite anionic [PbBi3Te6]- slabs separated with Cs+ cations. Temperature dependences of electrical resistivity, magnetic susceptibility, and specific heat have consistently demonstrated that the superconducting transition in Cs0.96Pb0.25Bi3.75Te6.04 occurs at T-c=3.1 K, with a superconducting volume fraction close to 100% at 1.8 K. Structural study using aberration-corrected STEM/TEM reveals a rich variety of microstructural phenomena in correlation with the Pb-ordering and chemical inhomogeneity. The superconducting material CS0.96Pb0.25Bi3.75Te6.04 with the highest T-c shows a clear ordered structure with a modulation wave vector of q approximate to a*/2+c*/1.35 on the a-c plane. Our study evidently demonstrates that superconductivity deriving upon doping of narrow-gap semiconductor is a viable approach for exploration of novel superconductors. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Phason space analysis and structure modelling of 100 angstrom-scale dodecagonal quasicrystal in Mn-based alloy
Authors:
Ishimasa, T; Iwami, S; Sakaguchi, N; Oota, R; Mihalkovic, M Author Full Names: Ishimasa, Tsutomu; Iwami, Shuhei; Sakaguchi, Norihito; Oota, Ryo; Mihalkovic, Marek
Source:
PHILOSOPHICAL MAGAZINE, 95 (33):3745-3767; 10.1080/14786435.2015.1095365 NOV 22 2015
Abstract:
The dodecagonal quasicrystal classified into the five-dimensional space group P12(6)/mmc, recently discovered in a Mn-Cr-Ni-Si alloy, has been analysed using atomic-resolution spherical aberration-corrected electron microscopy, i.e. high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and conventional transmission electron microscopy. By observing along the 12-fold axis, non-periodic tiling consisting of an equilateral triangle and a square has been revealed, of which common edge length is a=4.560 angstrom. These tiles tend to form a network of dodecagons of which size is (2+root 3)a approximate to 17 angstrom in diameter. The tiling was interpreted as an aggregate of 100 angstrom-scale oriented domains of high- and low-quality quasicrystals with small crystallites appearing at their boundaries. The quasicrystal domains exhibited a densely filled circular acceptance region in the phason space. This is the first observation of the acceptance region in an actual dodecagonal quasicrystal. Atomic structure model consistent with the electron microscopy images is a standard Frank-Kasper decoration of the triangle and square tiles that can be inferred from the crystal structures of Zr4Al3 and Cr3Si. Four kinds of layers located at z = 0, +/- 1/4 and 1/2 are stacked periodically along the 12-fold axis, and the atoms at z = 0 and 1/2 form hexagonal anti-prisms consistently with the 12(6)-screw axis. The validity of this structure model was examined by means of powder X-ray diffraction.
Title:
Effect of Ca and CaO on the microstructure and hot compressive deformation behavior of Mg-9.5Zn-2.0Y alloy
Authors:
Kwak, TY; Lim, HK; Kim, WJ Author Full Names: Kwak, T. Y.; Lim, H. K.; Kim, W. J.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 648 146-156; 10.1016/j.msea.2015.09.014 NOV 11 2015
Abstract:
In this study, the effect of adding 0.3 wt% Ca to a Mg-9.5Zn-2.0Y alloy with icosahedral (I) phase (Mg3Zn6Y) was examined. The Ca alloying was done by two different routes, either through a master alloy produced with Mg and CaO (which is convenient from the points of view of safety and cost) or by direct addition of powdered Ca to the molten alloy. The small addition of Ca (CaO) effectively increased the ignition temperature of the alloys (by about 90 K), which is promising for fire suppression and safe handling with the molten alloys, but it led to the formation of Ca2Mg5Zn13 phase at grain boundaries or interdendritic interfaces, causing partial melting and intergranular cracking during compressive deformation near similar to 615 K. As a result, the upper limit of hot workability temperature decreased to 598 K, which is lower than that of the Mg-9.5Zn-2.0Y alloy by 125 K. The cast Mg-9.5Zn-2.0Y-03Ca alloys prepared using the two different routes exhibited high similarity in ignition temperature, chemical composition, microstructure, hot compressive behaviors and processing maps, indicating that the use of CaO is as effective as the use of Ca in producing the same quality of Ca containing Mg alloys. The flow stresses during hot compressive deformation and the activation energy for plastic flow remained unaffected by the Ca (CaO) alloying, but decreased the strain rate sensitivity at high strain rates over 10(-3) s(-1) due to the initiation of either power-law breakdown or partial melting by adiabatic heating. Because of this, the Ca containing alloy lost hot workability at high strain rates by comparison to the Ca-free alloy. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Incommensurateness in nanotwinning models of modulated martensites
Authors:
Benesova, B; Frost, M; Kampschulte, M; Melcher, C; Sedlak, P; Seiner, H Author Full Names: Benesova, Barbora; Frost, Miroslav; Kampschulte, Malte; Melcher, Christof; Sedlak, Petr; Seiner, Hanus
Source:
PHYSICAL REVIEW B, 92 (18):10.1103/PhysRevB.92.180101 NOV 6 2015
Abstract:
We study the formation of modulated martensites in ferromagnetic shape memory alloys by a mathematical model originating from the nanotwinning concept. The results show that the incommensurateness, systematically observed in experiments for the modulated phases, may be understood as a precursor effect of the intermartensitic transitions, and its appearance does not contradict the nanotwinning concept itself. The model sufficiently explains the different levels of incommensurateness reported from different experimental observations for the 14-layered and 10-layered martensites of the Ni-Mn-Ga alloy and outlines the mechanism of formation of faults in the stacking sequences of these materials.
Title:
Quantum phase transitions and decoupling of magnetic sublattices in the quasi-two-dimensional Ising magnet Co3V2O8 in a transverse magnetic field
Authors:
Fritsch, K; Ehlers, G; Rule, KC; Habicht, K; Ramazanoglu, M; Dabkowska, HA; Gaulin, BD Author Full Names: Fritsch, K.; Ehlers, G.; Rule, K. C.; Habicht, K.; Ramazanoglu, M.; Dabkowska, H. A.; Gaulin, B. D.
Source:
PHYSICAL REVIEW B, 92 (18):10.1103/PhysRevB.92.180404 NOV 5 2015
Abstract:
The application of a magnetic field transverse to the easy axis, Ising direction in the quasi-two-dimensional kagome staircase magnet, Co3V2O8, induces three quantum phase transitions at low temperatures, ultimately producing a novel high field polarized state, with two distinct sublattices. New time-of-flight neutron scattering techniques, accompanied by large angular access, high magnetic field infrastructure allow the mapping of a sequence of ferromagnetic and incommensurate phases and their accompanying spin excitations. At least one of the transitions to incommensurate phases at mu H-0(c1) similar to 6.25 T and mu H-0(c2) similar to 7 T is discontinuous, while the final quantum critical point at mu H-0(c3) similar to 13 T is continuous.
Title:
Fluctuating orders and quenched randomness in the cuprates
Authors:
Nie, LM; Sierens, LEH; Melko, RG; Sachdev, S; Kivelson, SA Author Full Names: Nie, Laimei; Sierens, Lauren E. Hayward; Melko, Roger G.; Sachdev, Subir; Kivelson, Steven A.
Source:
PHYSICAL REVIEW B, 92 (17):10.1103/PhysRevB.92.174505 NOV 4 2015
Abstract:
We study a quasi-two-dimensional classical Landau-Ginzburg-Wilson effective field theory in the presence of quenched disorder in which incommensurate charge-density wave and superconducting orders are intertwined. The disorder precludes long-range charge-density wave order, but not superconducting or nematic order. We select three representative sets of input parameters and compute the corresponding charge-density wave structure factors using both large-N techniques and classical Monte Carlo simulations. Where nematicity and superconductivity coexist at low temperature, the peak height of the charge-density wave structure factor decreases monotonically as a function of increasing temperature, unlike what is seen in x-ray experiments on YBa2Cu3O6+x. Conversely, where the thermal evolution of the charge-density wave structure factor qualitatively agrees with experiments, the nematic correlation length, computed to one-loop order, is shorter than the charge-density wave correlation length.
Title:
Symmetries and color symmetries of a family of tilings with a singular point
Authors:
Evidente, IF; Felix, RP; Loquias, MJC Author Full Names: Evidente, Imogene F.; Felix, Rene P.; Loquias, Manuel Joseph C.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 71 583-591; 10.1107/S2053273315016137 6 NOV 2015
Abstract:
Tilings with a singular point are obtained by applying conformal maps on regular tilings of the Euclidean plane and their symmetries are determined. The resulting tilings are then symmetrically colored by applying the same conformal maps on colorings of regular tilings arising from sublattice colorings of the centers of the tiles. In addition, conditions are determined in order that the coloring of a tiling with singularity that is obtained in this manner is perfect.
Title:
Unusual Strong Incommensurate Modulation in a Tungsten-Bronze-Type Relaxor PbBiNb5O15
Authors:
Lin, K; Zhou, ZY; Liu, LJ; Ma, HQ; Chen, J; Deng, JX; Sun, JL; You, L; Kasai, H; Kato, K; Takata, M; Xing, XR Author Full Names: Lin, Kun; Zhou, Zhengyang; Liu, Laijun; Ma, Hongqiang; Chen, Jun; Deng, Jinxia; Sun, Junliang; You, Li; Kasai, Hidetaka; Kato, Kenichi; Takata, Masaki; Xing, Xianran
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137 (42):13468-13471; 10.1021/jacs.5b08230 OCT 28 2015
Abstract:
Pb- or Bi-based perovskite oxides have been widely studied and used because of their large ferroelectric polarization features induced by stereochemically active 6s(2) lone pair electrons. It is intriguing whether this effect could exist in other related systems. Herein, we designed and synthesized a mixed Pb and Bi A site polar compound, PbBiNb5O15, with the TTB framework. The as-synthesized material turns out to be a relaxor with weak macroscopic ferroelectricity but adopts strong local polarizations. What's more, unusual five orders of incommensurate satellite reflections with strong intensities were observed under the electron diffraction, suggesting that the modulation is highly developed with large amplitudes. The structural modulation was solved with a (3 + 1)D superspace group using high-resolution synchrotron radiation combined with anomalous dispersion X-ray diffraction technique to distinguish Pb from Bi. We show that the strong modulation mainly originates from lone-pair driven Pb2+-Bi3+ ordering in the large pentagonal caves, which can suppress the local polarization in x-y plane in long ranges. Moreover, the as-synthesized ceramics display strong relaxor ferroelectric feature with transition temperature near room temperature and moderate dielectric properties, which could be functionalized to be electromechanical device materials.
Title:
On the stability of a quasicrystal and its crystalline approximant in a system of hard disks with a soft corona
Authors:
Pattabhiraman, H; Gantapara, AP; Dijkstra, M Author Full Names: Pattabhiraman, Harini; Gantapara, Anjan P.; Dijkstra, Marjolein
Source:
JOURNAL OF CHEMICAL PHYSICS, 143 (16):10.1063/1.4934499 OCT 28 2015
Abstract:
Using computer simulations, we study the phase behavior of a model system of colloidal hard disks with a diameter sigma and a soft corona of width 1.4 sigma. The particles interact with a hard core and a repulsive square-shoulder potential. We calculate the free energy of the random-tiling quasicrystal and its crystalline approximants using the Frenkel-Ladd method. We explicitly account for the configurational entropy associated with the number of distinct configurations of the random-tiling quasicrystal. We map out the phase diagram and find that the random tiling dodecagonal quasicrystal is stabilised by entropy at finite temperatures with respect to the crystalline approximants that we considered, and its stability region seems to extend to zero temperature as the energies of the defect-free quasicrystal and the crystalline approximants are equal within our statistical accuracy. (C) 2015 AIP Publishing LLC.
Title:
Corrosion Behavior of Psi and beta Quasicrystalline Al-Cu-Fe Alloy
Authors:
Torres, A; Serna, S; Patino, C; Rosas, G Author Full Names: Torres, Alvaro; Serna, Sergio; Patino, Cristobal; Rosas, Gerardo
Source:
ACTA METALLURGICA SINICA-ENGLISH LETTERS, 28 (9):1117-1122; 10.1007/s40195-015-0302-0 SEP 2015
Abstract:
Two nanostructured Al-Cu-Fe alloys, Al64Cu24Fe12 and Al62.5Cu25.2Fe12.3, have been studied. Icosahedral quasicrystalline (psi) Al64Cu24Fe12 and crystalline cubic (beta) Al62.5Cu25.2Fe12.3 cylindrical ingots were first produced using normal casting techniques. High-energy mechanical milling was then conducted to obtain psi icosahedral and beta intermetallic nanostructured powders. Electrochemical impedance spectroscopy, linear polarization resistance, and potentiodynamic polarization were used to investigate the electrochemical corrosion characteristics of the powders in solutions with different pH values. Current density (i(corr)), polarization resistance (R-p), and impedance modulus (vertical bar Z vertical bar) were determined. The results showed that regardless of pH value, increasing the solution temperature enhanced the corrosion resistance of the both phases. However, the electrochemical behavior of the psi phase indicated that its stability depends on the submerged exposure time in neutral and alkaline environments. This behavior was related to the type of corrosion products present on the surfaces of the particles along with the diffusion and charge-transfer mechanisms of the corrosion process.

Update: 19-Nov-2015

Title:
Large coincidence lattice on Au/Fe3O4 incommensurate structure for spintronic applications
Authors:
Munoz-Noval, A; Rubio-Zuazo, J; Salas-Colera, E; Serrano, A; Rubio-Marcos, F; Castro, GR Author Full Names: Munoz-Noval, Alvaro; Rubio-Zuazo, Juan; Salas-Colera, Eduardo; Serrano, Aida; Rubio-Marcos, Fernando; Castro, German R.
Source:
APPLIED SURFACE SCIENCE, 355 698-701; 10.1016/j.apsusc.2015.07.158 NOV 15 2015
Abstract:
The design of metallic hybrid systems for spintronics has been widely studied during the past decade, motivated by the promising technological applications of these materials. Nevertheless, the importance of preserving the native structure and properties of the interfaces is often ignored. Here, we present the fabrication of nanocrystalline Au(001) onto a single oriented Fe3O4 (0 0 1) thin film as a promising hybrid system to develop spintronic devices by growing Au over the Fe3O4 by using a simple one-pot Pulsed Laser Deposition (PLD) approach. The structural coupling between Au nanocrystals and Fe3O4 layer results in the development of an incommensurate structure based on a coincidence lattice of order 35, which preserves the intrinsic properties of the Au nanocrystals, the Fe3O4 matrix and the interface between them. The general strategy described in the present work preserves the structure and main intrinsic properties of the constituting materials, being a fundamental issue for the future development of spintronic devices. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Unoccupied electronic structure of Ni2MnGa ferromagnetic shape memory alloy
Authors:
Maniraj, M; D'Souza, SW; Rai, A; Schlagel, DL; Lograsso, TA; Chakrabarti, A; Barman, SR Author Full Names: Maniraj, M.; D'Souza, S. W.; Rai, Abhishek; Schlagel, D. L.; Lograsso, T. A.; Chakrabarti, Aparna; Barman, S. R.
Source:
SOLID STATE COMMUNICATIONS, 222 1-4; 10.1016/j.ssc.2015.08.003 NOV 2015
Abstract:
Momentum resolved inverse photoemission spectroscopy measurements show that the dispersion of the unoccupied bands of Ni(2)MaGa is significant in the austenite phase. In the martensite phase, it is markedly reduced, which is possibly related to the structural transition to an incommensurate modulated state in the martensite phase. Based on the first principle calculations of the electronic structure of Ni-Mn-Ga, we show that the modification of the spectral shape with surface composition is related to change in the hybridization between the Mn 3d and Ni 3d-like states that dominate the unoccupied conduction band. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Local cluster symmetry of a highly ordered quasicrystalline Al58Cu26Ir16 extracted through multivariate analysis of STEM images
Authors:
Seki, T; Abe, E Author Full Names: Seki, Takehito; Abe, Eiji
Source:
MICROSCOPY, 64 (5):341-349; 10.1093/jmicro/dfv035 OCT 2015
Abstract:
The structure of a highly ordered Al58Cu26Ir16 decagonal quasicrystal (d-QC), which is constructed by a periodic stack of quasiperiodic atomic planes, was investigated using aberration-corrected scanning transmission electron microscopy. The entire quasiperiodic structure can be well described based on the pentagonal Penrose lattice decorated with a decagonal columnar cluster 2 nm across, and the individual clusters apparently showed up with localized atomic disorder to various degree that blurs the underlying cluster symmetry. Multivariate analysis of the cluster images with principal component analysis has successfully extracted two fundamental clusters, which are with definite mirror and 10-fold-rotation symmetries; this is the first solid example of the d-QC composed of multiple fundamental clusters with different symmetry. Consequently, it is found that all the observed variations can be reasonably interpreted by a linear combination between these two fundamental clusters of mirror and 10-fold symmetries, indicating that the possible atomic disorder is strongly restricted by these particular symmetries. Characteristic distributions of the mirror/10-fold clusters on the pentagonal Penrose lattice are also described.

Update: 12-Nov-2015

Title:
Magnetic anisotropy in FeSb studied by Fe-57 Mossbauer spectroscopy
Authors:
Komedera, K; Jasek, AK; Blachowski, A; Ruebenbauer, K; Krzton-Maziopa, A Author Full Names: Komedera, K.; Jasek, A. K.; Blachowski, A.; Ruebenbauer, K.; Krzton-Maziopa, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 399 221-227; 10.1016/j.jmmm.2015.09.076 FEB 1 2016
Abstract:
The Fe1+xSb compound has been synthesized close to stoichiometry with x=0.023(8). The compound was investigated by Fe-57 Mossbauer spectroscopy in the temperature range 4.2-300 K. The anti-ferromagnetic ordering temperature was found as 232 K i.e. much higher than for the less stoichiometric material. Regular iron was found to occupy two different positions in proportion 2:1. They differ by the electric quadrupole coupling constants and both of them exhibit extremely anisotropic electric field gradient tensor (EFG) with the asymmetry parameter eta approximate to 1. The negative component of both EFGs is aligned with the c-axis of the hexagonal unit cell, while the positive component is aligned with the (120) direction. Hence, a model describing deviation from the NiAs P6(3)/mmc symmetry group within Fe-planes has been proposed. Spectra in the magnetically ordered state could be explained by introduction of the incommensurate spin spirals propagating through the iron atoms in the direction of the c-axis with a complex pattern of the hyperfine magnetic fields distributed within a-b plane. Hyperfine magnetic field pattern of spirals due to major regular iron is smoothed by the spin polarized itinerant electrons, while the minor regular iron exhibits hyperfine field pattern characteristic of the highly covalent bonds to the adjacent antimony atoms. The excess interstitial iron orders magnetically at the same temperature as the regular iron, and magnetic moments of these atoms are likely to form two-dimensional spin glass with moments lying in the a-b plane. The upturn of the hyperfine field for minor regular iron and interstitial iron is observed below 80 K. Magneto-elastic effects are smaller than for FeAs, however the recoilless fraction increases significantly upon transition to the magnetically ordered state. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Flat and conical incommensurate magnetic structures in the two-subsystem partially frustrated Heisenberg ferrimagnet
Authors:
Martynov, SN Author Full Names: Martynov, S. N.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 398 121-126; 10.1016/j.jmmm.2015.09.046 JAN 15 2016
Abstract:
The phase transitions into flat and conical incommensurate magnetic structures are considered for a ferrimagnet with the dominant nonfrustrated exchange between the spins in one crystallographic position, competing exchanges between the spins in another position and frustrated exchange between the spins in different positions. The appearance conditions and the temperatures of the second order phase transitions are analytically obtained in the mean field approximation. The first order phase transition between these states is studied and the phase diagrams of temperature vs frustrated exchanges are calculated by the numerical minimization of free energy. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Temperature dependence of the propagation vector in Ni3-xCoxV2O8 with x=0.1 and 0.5
Authors:
Lee, S; Lee, H; Choi, YN; Semkin, MA; Teplykh, AE; Skryabin, YN; Li, WH; Pirogov, AN Author Full Names: Lee, Seongsu; Lee, Heeju; Choi, Yong Nam; Semkin, M. A.; Teplykh, A. E.; Skryabin, Yu. N.; Li, Wen-Hsien; Pirogov, A. N.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 397 225-229; 10.1016/j.jmmm.2015.08.106 JAN 1 2016
Abstract:
We present the susceptibility and neutron diffraction data on multiferroic Ni3-xCoxV2O8 with x=0.1 and 0.5. The temperature dependence of the susceptibility indicates that the magnetic order-disorder transition occurs at T-HTI=8.5 K in both samples. Below T-HTI, the high-temperature incommensurate magnetic structure is realized, which undergoes a transition to the low-temperature incommensurate phase when the sample is cooled. The temperature evolution of the propagation vector k for x=0.1 is very weak, which confirms previous studies showing that substitution of 3.5% Ni ions by Co ions suppresses the explicit temperature dependence of k that is observed in the parent compound. On the other hand, we found that the vector k for x=0.5 exhibits a definite temperature dependence, which differs from the case of the undopal sample (x=0)., (C) 2015 Elsevier By. All rights reserved.
Title:
Microstructure of mechanically alloyed and annealed Al62Cu25.5Fe12.5 powder
Authors:
Mitka, M; Goral, A; Rogal, L; Litynska-Dobrzynska, L Author Full Names: Mitka, Mikolaj; Goral, Anna; Rogal, Lukasz; Litynska-Dobrzynska, Lidia
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 653 47-53; 10.1016/j.jallcom.2015.08.250 DEC 25 2015
Abstract:
The influence of mechanical alloying (MA) of Al62Cu25.5Fe12.5 (at.%) powder obtained with different milling speeds and milling time and subsequent annealing on its microstructure and phase composition was investigated by means X-ray diffraction, scanning and transmission electron microscopy (SEM and TEM) methods. The power was milled in a high energy planetary ball mill at the rotation speed 250, 300 and 350 rpm for 3, 6, 10 and 20 h using WC milling media. The annealing of milled powders was performed at 800 degrees C for 4 h. Nano-quasicrystalline icosahedral phase (i-phase) was obtained in the as-milled powder at a speed 350 rpm, while the lower milling speed resulted in the formation of cubic beta-Al(Cu, Fe) phase. In all annealed powders the i-phase coexisting with the ordered lambda-Al(Cu, Fe) phase and small amount of the l-Al13Fe4 phase has been observed. The highest volume fraction of i-phase was found in the annealed powder milled at 250 rpm. After annealing the grain size increases compared to the as-milled powder. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Fabrication and properties of Ti-Zr-Ni quasicrystal and bulk composite materials by high pressure sintering
Authors:
Han, QG; Zhong, JL; Zhang, Q; Liu, B; Wang, LM Author Full Names: Han, Qi-Gang; Zhong, Ji-Lun; Zhang, Qiang; Liu, Biao; Wang, Li-Min
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 428 62-67; 10.1016/j.jnoncrysol.2015.08.008 NOV 15 2015
Abstract:
The overall composition of Ti40.83Zr40.83Ni18.34 quasicrystal powders that consist of the stable icosahedral phase (I-phase) was prepared by mechanical alloying and the subsequent heat treatment in a vacuum furnace. Then, bulk composite materials (BCMs) with the composition of Ti40.83Zr40.83Ni18.34 I-phase quasicrystal powders and carbonyl nickel powders as metal bonding agent (20 wt.%), have been fabricated by high pressure sintering. The Vickers hardness, compressive strength, deformation at fracture, Young's modulus, and wear resistance of the BCMs have been studied in detail, after being sintered at different pressure and temperature. It indicates that high pressure sintering enables us to produce the BCMs (about 10 mm in diameter and 3 mm in height) with a short sintered time of 10 mm and high pressure of 3.0 GPa. In addition, the optimum sintered condition is 3.0 GPa-600 degrees C, which is beneficial of the improvement of the performances of BCM, such as the Vickers hardness of 389, the compressive strength of 430 MPa, the deformation at fracture of 2.20%, the Young's modulus of 19 GPa, the lowest value of friction coefficient at 0.45 +/- 0.13, and wear mass losses of 024 mm(3). This work shows a promise in practical fabrication of BCM that consist of the stable Ti-Zr-Ni icosahedral quasicrystalline phase may be developed. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Nanosized helical magnetic domains in strongly frustrated Fe3PO4O3
Authors:
Ross, KA; Bordelon, MM; Terho, G; Neilson, JR Author Full Names: Ross, K. A.; Bordelon, M. M.; Terho, G.; Neilson, J. R.
Source:
PHYSICAL REVIEW B, 92 (13):10.1103/PhysRevB.92.134419 OCT 26 2015
Abstract:
Fe3PO4O3 forms a noncentrosymmetric lattice structure (space group R3m) comprising triangular motifs of Fe3+ coupled by strong antiferromagnetic interactions (vertical bar circle dot(CW)vertical bar > 900 K). Neutron diffraction from polycrystalline samples shows that strong frustration eventually gives way to an ordered helical incommensurate structure below T-N = 163 K, with the helical axis in the hexagonal ab plane and a modulation length to similar to 86 angstrom. The magnetic structure consists of an unusual needlelike correlation volume that extends past 900 angstrom along the hexagonal c axis but is limited to similar to 70 angstrom in the ab plane, despite the three-dimensional nature of the magnetic sublattice topology. The small in-plane correlation length, which persists to at least T = T-N/40, indicates a robust blocking of long-range order of the helical magnetic structure, and therefore stable domain walls, or other defect spin textures, must be abundant in Fe3PO4O3. Temperature-dependent neutron powder diffraction reveals small negative thermal expansion below T-N. No change in lattice symmetry is observed on cooling through TN, as revealed by high-resolution synchrotron x-ray diffraction. The previously reported reduced moment of the Fe3+ ions (S = 5/2), mu similar to 4.2 mu(B), is confirmed here through magnetization studies of a magnetically diluted solid solution series of compounds, Fe(3-x)GaxPO4O3, and is consistent with the refined magnetic moment from neutron diffraction 4.14(2) mu(B). We attribute the reduced moment to a modified spin density distribution arising from ligand charge transfer in this insulating oxide.
Title:
Solitonic Spin-Liquid State Due to the Violation of the Lifshitz Condition in Fe1+yTe
Authors:
Materne, P; Koz, C; Rossler, UK; Doerr, M; Goltz, T; Klauss, HH; Schwarz, U; Wirth, S; Rossler, S Author Full Names: Materne, Ph.; Koz, C.; Roessler, U. K.; Doerr, M.; Goltz, T.; Klauss, H. H.; Schwarz, U.; Wirth, S.; Roessler, S.
Source:
PHYSICAL REVIEW LETTERS, 115 (17):10.1103/PhysRevLett.115.177203 OCT 21 2015
Abstract:
A combination of phenomenological analysis and Mossbauer spectroscopy experiments on the tetragonal Fe1+yTe system indicates that the magnetic ordering transition in compounds with higher Fe excess, y >= 0.11, is unconventional. Experimentally, a liquidlike magnetic precursor with quasistatic spin order is found from significantly broadened Mossbauer spectra at temperatures above the antiferromagnetic transition. The incommensurate spin-density wave order in Fe1+yTe is described by a magnetic free energy that violates the weak Lifshitz condition in the Landau theory of second-order transitions. The presence of multiple Lifshitz invariants provides the mechanism to create multidimensional, twisted, and modulated solitonic phases.
Title:
Rare earth ferrites LuFe2O4 +/- x polymorphism, polytypism and metastable phases
Authors:
Hervieu, M; Damay, F; Maignan, A; Martin, C Author Full Names: Hervieu, M.; Damay, F.; Maignan, A.; Martin, C.
Source:
SOLID STATE SCIENCES, 48 A1-A16; 10.1016/j.solidstatesciences.2015.07.013 OCT 2015
Abstract:
This work is a compendium of the structural properties of layered LnFe(2)O(4 +/- x) ferrites, focussed on recently discovered polymorphs and their transitions through five complex commensurate and incommensurate modulated structures. These phases are obtained varying the oxygen content (reversibly from O-4.0 to O-4.5) or applying high pressure (up to 15 GPa). The relationships between the different structures are discussed and models are proposed. These ferrites, which contain magnetic cations and exhibit remarkable 3D flexibility, open the road for magnetic, electric, catalytic or energy materials. (C) 2015 Elsevier Masson SAS. All rights reserved.
Title:
Low temperature oxygen diffusion mechanisms in Nd2NiO4+delta and Pr2NiO4+delta via large anharmonic displacements, explored by single crystal neutron diffraction
Authors:
Ceretti, M; Wahyudi, O; Cousson, A; Villesuzanne, A; Meven, M; Pedersen, B; Bassat, JM; Paulus, W Author Full Names: Ceretti, M.; Wahyudi, O.; Cousson, A.; Villesuzanne, A.; Meven, M.; Pedersen, B.; Bassat, J. M.; Paulus, W.
Source:
JOURNAL OF MATERIALS CHEMISTRY A, 3 (42):21140-21148; 10.1039/c5ta05767a 2015
Abstract:
We investigated the structure of Nd2NiO4+delta and Pr2NiO4+delta by single crystal neutron diffraction studies. While the real structure of both compounds is incommensurate, the scattering density of the respective average structures was explored using the Maximum Entropy Method. Unusually high displacement factors were found for the equatorial and apical oxygen atoms showing respectively large displacement amplitudes towards [001] and [110] with respect to the F-symmetry cell. The shifts of the apical oxygen atoms reach up to 1 angstrom from their average position, corresponding to a 25 degrees tilt of the NiO6 octahedra. At 400 degrees C, i.e. slightly above the orthorhombic-tetragonal phase transition, the anharmonic apical oxygen displacements towards [110] in the commensurate tetragonal parent structure are strongly enhanced, showing a double-well potential and pointing towards the interstitial vacancy sites, creating a quasi continuous shallow energy diffusion pathway between apical and interstitial oxygen sites. These large displacement amplitudes are considered to be - at least partially - of dynamical origin, which is consistent with a phonon assisted diffusion mechanism, already activated at very moderate temperatures.

Update: 5-Nov-2015

Title:
Effects of cyclic extrusion and compression parameters on microstructure and mechanical properties of Mg-1.50Zn-0.25Gd alloy
Authors:
Huang, H; Tang, ZB; Tian, Y; Jia, GZ; Niu, JL; Zhang, H; Pei, J; Yuan, GY; Ding, WJ Author Full Names: Huang, Hua; Tang, Zibo; Tian, Yuan; Jia, Gaozhi; Niu, Jialin; Zhang, Hua; Pei, Jia; Yuan, Guangyin; Ding, Wenjiang
Source:
MATERIALS & DESIGN, 86 788-796; 10.1016/j.matdes.2015.07.155 DEC 5 2015
Abstract:
Mg-1.50Zn-0.25Gd (at.%) alloy reinforced by icosahedral quasicrystalline phase (I-phase) was fabricated and then subjected to cyclic extrusion and compression (CEC) at 250, 300, 350 and 400 degrees C, respectively. The effects of CEC parameters including passes and temperatures on microstructure evolution and room temperature tensile mechanical properties were characterized and discussed. The results show that more passes are beneficial for secondary phase precipitation, grain refinement and basal texture weakening; while moderate temperature is beneficial for secondary phase precipitation and basal texture weakening by particle stimulated recrystallization nucleation (PSN), and lower temperature is beneficial for grain refinement. The alloy has the highest yield strength after CEC at 250 degrees C because of grain refinement and basal texture strengthening, while it has the highest elongation after being processed with 8 passes of CEC due to grain refinement and basal texture weakening. The processing passes have more important effects on microstructure evolution and mechanical properties than that of temperature during CEC. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Evolution of the dense packings of spherotetrahedral particles: from ideal tetrahedra to spheres
Authors:
Jin, WW; Lu, P; Li, SX Author Full Names: Jin, Weiwei; Lu, Peng; Li, Shuixiang
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep15640 OCT 22 2015
Abstract:
Particle shape plays a crucial role in determining packing characteristics. Real particles in nature usually have rounded corners. In this work, we systematically investigate the rounded corner effect on the dense packings of spherotetrahedral particles. The evolution of dense packing structure as the particle shape continuously deforms from a regular tetrahedron to a sphere is investigated, starting both from the regular tetrahedron and the sphere packings. The dimer crystal and the quasicrystal approximant are used as initial configurations, as well as the two densest sphere packing structures. We characterize the evolution of spherotetrahedron packings from the ideal tetrahedron (s = 0) to the sphere (s = 1) via a single roundness parameter s. The evolution can be partitioned into seven regions according to the shape variation of the packing unit cell. Interestingly, a peak of the packing density Phi is first observed at s approximate to 0.16 in the Phi-s curves where the tetrahedra have small rounded corners. The maximum density of the deformed quasicrystal approximant family (Phi approximate to 0.8763) is slightly larger than that of the deformed dimer crystal family (Phi approximate to 0.8704), and both of them exceed the densest known packing of ideal tetrahedra (Phi approximate to 0.8563).
Title:
Neutron diffraction investigation of the H - T phase diagram above the longitudinal incommensurate phase of BaCo2V2O8
Authors:
Grenier, B; Simonet, V; Canals, B; Lejay, P; Klanjsek, M; Horvatic, M; Berthier, C Author Full Names: Grenier, B.; Simonet, V.; Canals, B.; Lejay, P.; Klanjsek, M.; Horvatic, M.; Berthier, C.
Source:
PHYSICAL REVIEW B, 92 (13):10.1103/PhysRevB.92.134416 OCT 20 2015
Abstract:
The quasi-one-dimensional antiferromagnetic Ising-like compound BaCo2V2O8 has been shown to be describable by the Tomonaga-Luttinger liquid theory in its gapless phase induced by a magnetic field applied along the Ising axis. Above 3.9 T, this leads to an exotic field-induced low-temperature magnetic order, made of a longitudinal incommensurate spin-density wave, stabilized by weak interchain interactions. By single-crystal neutron diffraction we explore the destabilization of this phase at a higher magnetic field. We evidence a transition at around 8.5 T towards a more conventional magnetic structure with antiferromagnetic components in the plane perpendicular to the magnetic field. The phase diagram boundaries and the nature of this second field-induced phase are discussed with respect to previous results obtained by means of nuclear magnetic resonance and electron spin resonance, and in the framework of the simple model based on the Tomonaga-Luttinger liquid theory, which obviously has to be refined in this complex system.
Title:
Microscopic adjustment of misfit strain and charge segregation in [Bi2Sr2O4](0.51)CoO2
Authors:
Maki, M; Takakura, S; Nishizaki, T; Ichikawa, F Author Full Names: Maki, Makoto; Takakura, Sho-ichi; Nishizaki, Terukazu; Ichikawa, Fusao
Source:
PHYSICAL REVIEW B, 92 (16):10.1103/PhysRevB.92.165117 OCT 16 2015
Abstract:
From scanning tunneling microscopy of the misfit-layered cobaltate [Bi2Sr2O4](0.51)CoO2 single crystals, we observed structural short corrugations oriented in the direction inclined with respect to the incommensurate axis. Results show that the spatial distribution of the electronic charge density is also modified in relation to the atomic displacement. Our data strongly suggest that the rocksalt structure flexibly mounted on the CoO2 layer affects the electronic properties of this system.
Title:
Phase Diagram of Modulated Structures in Ferroelectric Crystals Based on Quantum Ising Model with Third-Neighbor Interactions
Authors:
Mashiyama, H Author Full Names: Mashiyama, Hiroyuki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (10):10.7566/JPSJ.84.104712 OCT 15 2015
Abstract:
Incommensurate commensurate phase transitions are analyzed using a model derived from the normal coordinate Hamiltonian for a crystal lattice. The Hamiltonian consists of a local self-potential and effective third-neighbor interactions. Free energies of various modulated phases are calculated with a mean-field approximation under the condition that two quantum states within the local potential are important at low temperature. It is demonstrated that the quantum effect works to stabilize the incommensurate phase rather than the commensurate phase. Even at zero temperature, the incommensurate phase can occupy a finite region in the phase diagram. This situation is similar to quantum paraelectricity in some ferroelectrics, and can be expected as a general feature of modulated structures of dielectric crystals. The phase diagram for ferroic first- and third-neighbor interactions but antiferroic second-neighbor interactions is constructed theoretically and is discussed in detail to explain qualitatively the low-temperature behavior of some ferroelectric crystals.
Title:
Competing magnetic and structural states in multiferroic YMn2O5 at high pressure
Authors:
Kozlenko, DP; Dang, NT; Kichanov, SE; Lukin, EV; Pashayev, AM; Mammadov, AI; Jabarov, SH; Dubrovinsky, LS; Liermann, HP; Morgenroth, W; Mehdiyeva, RZ; Smotrakov, VG; Savenko, BN Author Full Names: Kozlenko, D. P.; Dang, N. T.; Kichanov, S. E.; Lukin, E. V.; Pashayev, A. M.; Mammadov, A. I.; Jabarov, S. H.; Dubrovinsky, L. S.; Liermann, H. -P.; Morgenroth, W.; Mehdiyeva, R. Z.; Smotrakov, V. G.; Savenko, B. N.
Source:
PHYSICAL REVIEW B, 92 (13):10.1103/PhysRevB.92.134409 OCT 12 2015
Abstract:
The magnetic, structural, and vibrational properties of YMn2O5 multiferroic have been studied by means of neutron, x-ray powder diffraction, and Raman spectroscopy at pressures up to 6 and 30 GPa, respectively. Application of high pressure, P > 1 GPa, leads to a gradual suppression of the commensurate and incommensurate antiferromagnetic (AFM) phases with a propagation vector q = (1/2,0, q(z) similar to 1/4) and appearance of the commensurate AFM phase with q = (1/2,0,1/2). This observation is sharply contrasting to general trend towards stabilization of commensurate AFM phase with q = (1/2,0,1/4) found in other RMn2O5 compounds upon lattice compression. At P similar to 16 GPa a structural phase transformation accompanied by anomalies in lattice compression and pressure behavior of vibrational modes was observed. The comparative analysis of high-pressure and R-cation radius variation effects clarified a role of particular magnetic interactions in the formation of the magnetic states of RMn2O5 compounds.

Update: 29-Oct-2015

Title:
First-order commensurate-incommensurate magnetic phase transition in the coupled FM spin-1/2 two-leg ladders
Authors:
Jahangiri, J; Hadipour, H; Mandavifar, S; Shayesteh, SF Author Full Names: Jahangiri, J.; Hadipour, H.; Mandavifar, S.; Shayesteh, S. Farjami
Source:
PHYSICA B-CONDENSED MATTER, 476 24-28; 10.1016/j.physb.2015.07.012 NOV 1 2015
Abstract:
We consider the spin-1/2 two-leg ladders with ferromagnetic (FM) interactions along legs and rungs. Using the stochastic series expansion QMC method, we study the low-temperature magnetic behavior of the system. An isolated spin-1/2 FM two-leg ladder is in the gapped saturated FM phase at zero temperature. As soon as the spin-1/2 FM two-leg ladders are connected with antiferromagnetic (AFM) inter-ladder interaction, a first-order commensurate-incommensurate quantum phase transition occurs in the ground state magnetic phase diagram. In fact a jump in the magnetization curve is observed. We found that, coupled spin-1/2 FM two-leg ladders are in a nonmagnetic phase at zero temperature. Applying a magnetic field, the ground state of coupled spin-1/2 FM two-leg ladders remains in the nonmagnetic phase up to a quantum saturate critical field. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Predicting complex mineral structures using genetic algorithms
Authors:
Mohn, CE; Kob, W Author Full Names: Mohn, Chris E.; Kob, Walter
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (42):10.1088/0953-8984/27/42/425201 OCT 28 2015
Abstract:
We show that symmetry-adapted genetic algorithms are capable of finding the ground state of a range of complex crystalline phases including layered- and incommensurate superstructures. This opens the way for the atomistic prediction of complex crystal structures of functional materials and mineral phases.
Title:
Incommensurate modulation and thermal expansion of Sr3B2 (+) Si-x(1) (-) O-x(8) (-) (x/2) solid solutions
Authors:
Volkov, S; Bubnova, R; Bolotina, N; Krzhizhanovskaya, M; Belousova, O; Filatov, S Author Full Names: Volkov, Sergey; Bubnova, Rimma; Bolotina, Nadezhda; Krzhizhanovskaya, Maria; Belousova, Olga; Filatov, Stanislav
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 489-497; 10.1107/S2052520615011713 5 OCT 2015
Abstract:
Crystal structures of Sr3B2 (+) Si-x(1) (-) O-x(8) (- x/2) solid solutions with nominal compositions x = 0.28, 0.53, 0.78 in the Sr3B2SiO8-Sr2B2O5 section of the SrO-B2O3-SiO2 system are refined using single-crystal X-ray diffraction data. Incommensurate structure modulations are mainly associated with various orientations of corner-sharing (B,Si)-polyhedra. Preference is given to the (3 + 2)-dimensional symmetry group Pnma(0 beta gamma)000(0 beta gamma)000 for a single crystal compared with an alternate model of a twin formed by monoclinic components, each of them corresponding to the (3 + 1)-dimensional symmetry group P2(1)/n(0 beta gamma). Single-phase polycrystalline samples of solid solutions are investigated by high-temperature X-ray powder diffraction in air. Orientation preferences of the BO3 units lead to a strong anisotropy of thermal expansion. Negative expansion is observed along the a axis over the temperature range 303-753 K. Anisotropy decreases both on heating and decreasing of the boron content.
Title:
Decagonite, Al71Ni24Fe5, a quasicrystal with decagonal symmetry from the Khatyrka CV3 carbonaceous chondrite
Authors:
Bindi, L; Yao, N; Lin, C; Hollister, LS; Andronicos, CL; Distler, VV; Eddy, MP; Kostin, A; Kryachko, V; MacPherson, GJ; Steinhardt, WM; Yudovskaya, M; Steinhardt, PJ Author Full Names: Bindi, Luca; Yao, Nan; Lin, Chaney; Hollister, Lincoln S.; Andronicos, Christopher L.; Distler, Vadim V.; Eddy, Michael P.; Kostin, Alexander; Kryachko, Valery; MacPherson, Glenn J.; Steinhardt, William M.; Yudovskaya, Marina; Steinhardt, Paul J.
Source:
AMERICAN MINERALOGIST, 100 (10):2340-2343; 10.2138/am-2015-5423 OCT 2015
Abstract:
Decagonite is the second natural quasicrystal, after icosahedrite (Al63Cu24Fe13), and the first to exhibit the crystallographically forbidden decagonal symmetry. It was found as rare fragments up to similar to 60 mu m across in one of the grains (labeled number 126) of the Khatyrka meteorite, a CV3 carbonaceous chondrite. The meteoritic grain contains evidence of a heterogeneous distribution of pressures and temperatures that occurred during impact shock, in which some portions of the meteorite reached at least 5 GPa and 1200 degrees C. Decagonite is associated with Al-bearing trevorite, diopside, forsterite, ahrensite, clinoenstatite, nepheline, coesite, pentlandite, Cu-bearing troilite, icosahedrite, khatyrkite, taenite, Al-bearing taenite, and steinhardtite. Given the exceedingly small size of decagonite, it was not possible to determine most of the physical properties for the mineral. A mean of seven electron microprobe analyses (obtained from three different fragments) gave the formula Al70.2(3)Ni24.5(4)Fe5.3(2), on the basis of 100 atoms. A combined TEM and single-crystal X-ray diffraction study revealed the unmistakable signature of a decagonal quasicrystal: a pattern of sharp peaks arranged in straight lines with 10-fold symmetry together with periodic patterns taken perpendicular to the 10-fold direction. For quasicrystals, by definition, the structure is not reducible to a single three-dimensional unit cell, so neither cell parameters nor Z can be given. The likely space group is P10(5)/mine, as is the case for synthetic A(17)Ni(24)Fe(5). The five strongest powder-diffraction lines [d in angstrom (I/I-0)] are: 2.024 (100), 3.765 (50), 2.051 (45), 3.405 (40), 1.9799 (40). The new mineral has been approved by the IMA-NMNC Commission (IMA2015-017) and named decagonite for the 10-fold symmetry of its structure. The finding of a second natural quasicrystal informs the longstanding debate about the stability and robustness of quasicrystals among condensed matter physicists and demonstrates that mineralogy can continue to surprise us and have a strong impact on other disciplines.
Title:
Secondary phases in quasicrystal-reinforced Mg-3.5Zn-0.6Gd Mg alloy
Authors:
Huang, H; Tian, Y; Yuan, GY; Chen, CL; Wang, ZC; Ding, WJ; Inoue, A Author Full Names: Huang, Hua; Tian, Yuan; Yuan, Guangyin; Chen, Chunlin; Wang, Zhongchang; Ding, Wenjiang; Inoue, Akihisa
Source:
MATERIALS CHARACTERIZATION, 108 132-136; 10.1016/j.matchar.2015.09.005 OCT 2015
Abstract:
The secondary phases in quasicrystal-reinforced Mg-Zn-Gd alloys are investigated by transmission electron microscopy. The orientation relationships between the dendritic I-phase and the Mg matrix are identified to be [1 1 (2) over bar 0](Mg)parallel to[2-fold](I-phase) and (0001)(Mg)parallel to(5-fold)(I-phase). We also find that the dendritic I-phase is brittle along 2-fold, 5-fold, and 3-fold atomic planes during hot extrusion. Moreover, new orientation relations [(1) over bar 101](Mg)parallel to[mirror 2-fold](I-phase) and (0 (1) over bar 1 1)(Mg)parallel to(5-fold)(I-phase) are found between nanoscale I-phase and Mg matrix. The findings have implications for our understanding of excellent mechanical properties of the I-phase-strengthened Mg alloys. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Strain induced incommensurate structures in vicinity of reconstructive phase transitions
Authors:
Korzhenevskii, AL; Dmitriev, V Author Full Names: Korzhenevskii, A. L.; Dmitriev, V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (37):10.1088/0953-8984/27/37/375401 SEP 23 2015
Abstract:
General conditions controlling the formation of incommensurate phases in crystals undergoing reconstructive phase transitions are analyzed in the framework of a model-free phenomenological approach. A universal trend to stabilizing such intermediate phases in the vicinity of reconstructive phase transitions stems from the fact that certain high-order improper Lifshitz invariants reduce at such transformations to ones bi-linearly coupling critical displacement gradients and strains or even to the proper Lifshitz invariant. The approach developed here introduces a universal mechanism for the formation both of premartensite incommensurate phases and complex structures with giant unit cells, as found in some elemental crystals at high pressure.
Title:
Characteristics of 5M modulated martensite in Ni-Mn-Ga magnetic shape memory alloys
Authors:
Cakir, A; Acet, M; Righi, L; Albertini, F; Farle, M Author Full Names: Cakir, A.; Acet, M.; Righi, L.; Albertini, F.; Farle, M.
Source:
AIP ADVANCES, 5 (9):10.1063/1.4932233 SEP 2015
Abstract:
The applicability of the magnetic shape memory effect in Ni-Mn-based martensitic Heusler alloys is closely related to the nature of the crystallographically modulated martensite phase in these materials. We study the properties of modulated phases as a function of temperature and composition in three magnetic shape memory alloys Ni49.8Mn25.0Ga25.2, Ni49.8Mn27.1Ga23.1 and Ni49.5Mn28.6Ga21.9. The effect of substituting Ga for Mn leads to an anisotropic expansion of the lattice, where the b-parameter of the 5M modulated structure increases and the a and c-parameters decrease with increasing Ga concentration. The modulation vector is found to be both temperature and composition dependent. The size of the modulation vector corresponds to an incommensurate structure for Ni49.8Mn25.0Ga25.2 at all temperatures. For the other samples the modulation is incommensurate at low temperatures but reaches a commensurate value of q approximate to 0.400 close to room temperature. The results show that commensurateness of the 5M modulated structure is a special case of incommensurate 5M at a particular temperature. (C) 2015 Author(s).

Update: 22-Oct-2015

Title:
Thermoelectric properties of Tsai-type Au-Al-RE (RE: Yb, Tm, Gd) quasicrystals and approximants
Authors:
Takagiwa, Y; Kimura, K; Sawama, K; Hiroto, T; Nishio, K; Tamura, R Author Full Names: Takagiwa, Y.; Kimura, K.; Sawama, K.; Hiroto, T.; Nishio, K.; Tamura, R.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 652 139-144; 10.1016/j.jallcom.2015.08.081 DEC 15 2015
Abstract:
The thermoelectric properties of Tsai-type Au-Al-RE (RE: Yb, Tm, Gd) icosahedral quasicrystals (QCs) and their approximant crystals (ACs) have been investigated from 373 K to 873 K. Comparison of their thermoelectric properties above room temperature is of great interest since resonant states are likely to be present in the electronic density of states near the Fermi level for the Au-Al-Yb QC, which should influence the thermoelectric properties and, hence, the dimensionless figure of merit. The electrical conductivity of Au-Al-Yb ACs varies significantly, i.e. from 3000 Omega(-1) cm(-1) to 5200 Omega(-1) cm(-1), with changing the Au/Al composition whereas the other compounds have conductivities of similar to 3000 Omega(-1) cm(-1). Such an anomalous behavior of the Au-Al-Yb ACs is understood to be due to the existence of a resonant peak originating from hybridization of Yb f-states and Au/Al sp-states. A maximum power factor of 230 mu Wm(-1) K-2 at 873 K is obtained in 1/1-Au48Al37Yb15 AC, which is significantly higher than those of Al-based icosahedral phases at the same temperature. On the other hand, the room-temperature thermal conductivities for Au-Al-RE compounds range from 3 to 4 W m(-1) K-1, reflecting their complex crystal structures with a large unit cell and mixed and/or partially occupied sites. Consequently, both 1/1-Au50Al35Yb15 and Au48Al37Yb15 ACs have similar maximum figures of merit of 0.014 at 873 K. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Deformation mechanism of Ni54Mn25Ga20.9Gd0.1 high-temperature shape memory alloy
Authors:
Zhang, X; Sui, JH; Cai, W; Liu, QS; Liu, AL Author Full Names: Zhang, Xin; Sui, Jiehe; Cai, Wei; Liu, Qingsuo; Liu, Ailian
Source:
INTERMETALLICS, 67 52-55; 10.1016/j.intermet.2015.07.017 DEC 2015
Abstract:
Ni54Mn25Ga20.9Gd0.1 Polycrystalline high-temperature shape memory alloy displayed high compressive fracture strain of 24.6% and large shape memory effect of 7.5%. However, its deformation mechanism was still unknown. In this paper, the structure revolution characterized by XRD and TEM indicated a new deformation mechanism different before was found. The deformation process of Ni54Mn25Ga20.9Gd0.1 alloy could be divided into four stages, including elastic deformation of non-modulated tetragonal martensite (T), stress-induced T to seven-layered modulated martensite (7 M) transformation, variants reorientation of 7 M, and elastic plastic deformation of reoriented 7 M. The 7 M formed by compression deformation disappeared completely after heating to the temperature above A(f). (C) 2015 Elsevier Ltd. All rights reserved.
Title:
From crystal morphology to molecular and scale crystallography
Authors:
Janner, A; Janssen, T Author Full Names: Janner, A.; Janssen, T.
Source:
PHYSICA SCRIPTA, 90 (8):10.1088/0031-8949/90/8/088007 AUG 2015
Abstract:
A number of topics, ranging from morphology of aperiodic crystals to indexed enclosing forms of axial-symmetric proteins, nucleic acids and viruses, have been selected among those investigated by the authors in 50 years of research. The basic symmetries involved in fields like superspace, molecular and scale crystallography, are considered from a personal point of view in their time evolution. A number of specific subjects follow, chosen among a few highlights and presented according to the experience of the authors: snow crystals, calaverite AuTe2, the incommensurately modulated crystals Rb2ZnBr4, [N(CH3)(4)](2)ZnCl4 and the mitochondrial ferritin.
Title:
Atomic structure of icosahedral quasicrystals: stacking multiple quasi-unit cells
Authors:
Madison, AE Author Full Names: Madison, Alexey E.
Source:
RSC ADVANCES, 5 (97):79279-79297; 10.1039/c5ra13874d 2015
Abstract:
An effective tiling approach is proposed for the structural description of icosahedral quasicrystals based on the original substitution algorithm. The atomic structure of icosahedral quasicrystals may by derived by using the iterative and recursive inflation/deflation procedure with subsequent decoration of quasi-unit cells. The quasi-unit cells are stacked in three-dimensional space face-to-face without any gaps between them producing the whole infinite icosahedral structure in the same manner as the usual periodic crystals are generated by multiplication of their unit cells containing one or more atoms in a specific spatial arrangement. A variety of examples illustrating the efficiency of the general algorithm is presented. Stacking of quasi-unit cells along the five-fold axis, as well as the arrangement of cells normal to the five-fold, three-fold, and two-fold axes are presented. The possible atomic structure of an icosahedral single-component quasicrystal is derived. Three types of inequivalent sites with exact icosahedral symmetry may simultaneously exist in the quasicrystalline structure. The structure of characteristic clusters enforced by the compatibility with the quasicrystalline type of ordering is discussed.

Update: 15-Oct-2015

Title:
Solid-state formation of icosahedral quasicrystals at Zn3Mg3Y2/Mg interfaces in a Mg-Zn-Y alloy
Authors:
Liu, JF; Yang, ZQ; Ye, HQ Author Full Names: Liu, J. F.; Yang, Z. Q.; Ye, H. Q.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 650 65-69; 10.1016/j.jallcom.2015.07.254 NOV 25 2015
Abstract:
Solid-state formation of Zn6Mg3Y icosahedral quasicrystals was observed at interfaces between Mg and W-Zn3Mg3Y2 crystals in a Mg-Zn-Y alloy by in situ transmission electron microscopy investigations. The quasicrystals were formed at about 593 K which is about 130 K below the peritectic temperature. Thermally driven interdiffusion of atoms across the W/Mg interface firstly produces local regions with Zn:Mg:Y close to 6:3:1 at the surface of W phase particles, where the cuboctahedral packing of atoms in W phase transforms to icosahedral packing through slight rearrangement of atoms, leading to the nucleation and growth of icosahedral clusters. The icosahedral clusters act as nuclei for the growth of icosahedral quasicrystals. Both valence electron concentration and the densest packing of atoms play important roles in the formation of Zn6Mg3Y quasicrystals. Solid-state formation of icosahedral quasicrystals at W/Mg interfaces provide a feasible way to modify the weakly bonded W/Mg interfaces, which is thus believed to be able to improve the magnesium alloy's mechanical properties. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Properties of Ti40.83Zr40.83Ni18.34 quasicrystalline alloys sintered by Spark Plasma Sintering
Authors:
Han, QG; Chen, ML; Zhang, Q; Sun, LS; Lin, J; Wang, LM Author Full Names: Han, Qi-Gang; Chen, Meng-Lu; Zhang, Qiang; Sun, Lian-Shan; Lin, Jing; Wang, Li-Min
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 650 154-158; 10.1016/j.jallcom.2015.07.297 NOV 25 2015
Abstract:
The quasicrystalline alloy powders with the composition of Ti40.83Zr40.83Ni18.34 are prepared by mechanical alloying (MA) techniques, and the bulk part is obtained by Spark Plasma Sintering (SPS) method. The structure, mechanical properties, friction and wear properties of the bulk part are investigated. The results showed that the structure of the bulk part is pure icosahedral quasicrystalline phase (I-phase). The Vickers Hardness of the bulk part is 7.03 GPa. The maximum compression strength, the elastic deformation and Young modulus is (662 +/- 50) MPa, 2.7 +/- 0.1% and (30 +/- 3) GPa, respectively. The lowest value of friction coefficient is 0.40 at a normal load of 100 N, a sliding velocity of 10 mm/s, a sliding time of 10 min and an ambient temperature of 293.15 K. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Electrochemical hydrogen storage properties of Ti1.4V0.6Ni alloy comprising quasicrystal coating with Cu
Authors:
Sun, LS; Lin, J; Cao, ZY; Liang, F; Wang, LM Author Full Names: Sun, Lianshan; Lin, Jing; Cao, Zhanyi; Liang, Fei; Wang, Limin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 650 15-21; 10.1016/j.jallcom.2015.07.252 NOV 25 2015
Abstract:
The Ti1.4V0.6Ni alloy ribbons are prepared by arc-melting and subsequently melt spinning technique. Different percentage compositions of x Cu (x = 1, 3, 5 and 10 wt%) are covered on the surface of the alloy particles utilizing electro-less plating method. The phase structures of the Ti1.4V0.6Ni alloy contain icosahedral quasicrystal phase (I-phase), fcc-Ti2Ni-type phase and bcc-V-based solid solution phase. With increasing x value, the maximum electrochemical hydrogen storage capacity reaches 260 mAh g(-1) when x = 10. After 100 cycles, 23% capacity retention rate is promoted by covering 10 wt% Cu on the alloy than the bare Ti1.4V0.6Ni. Cu offers well electrical conductivity and corrosion resistance, especially it also inhibits the dissolution of V from the alloys. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Investigation on incommensurate modulation structure and T-c in Ca-doped Bi-2201 system
Authors:
Sun, BZ; Zhang, M; Wang, RY; Jiang, YL; Wang, H; Qi, Y Author Full Names: Sun, B. Z.; Zhang, M.; Wang, R. Y.; Jiang, Y. L.; Wang, H.; Qi, Y.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 650 430-435; 10.1016/j.jallcom.2015.08.015 NOV 25 2015
Abstract:
A series of samples with the nominal composition of Bi2Sr2-xCaxCuO6+delta (x = 0.2, 0.4, 0.6, 0.8, 1.0) ceramics are synthesized by sol-gel growth. The microstructure and the incommensurate modulation structure (IMS) were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD) methods. The superconductivity and the onset temperature of superconducting transition (T-c,T-onset) were analysed. In the whole Ca-doping range, an IMS in b-c planes can be identified and the values of T-c,T-onset are all exceed 80 K. With an increase of chi, the b-component of modulation vector q*, the basic *structural* parameters b and c of Bi-2201 phase have a trend of fall first then rise, whereas the c-component of modulation vector, the angle theta between q* and b* vectors and the values of T-c,T-onset are reversely varied. It can be verified that Ca concentration x = 0.6 is an extreme value, at which the distortion of the CuO2 layers makes the concentration of mobile carriers and the value of T-c,(onset) optimizing. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Approximants of Al-Cr-Fe-Si decagonal quasicrystals described by single structural block
Authors:
He, ZB; Wei, DX; Shen, X; Chen, Y; Ma, HK; Wang, LL; Du, K; Yao, Y; Yu, RC Author Full Names: He, Zhanbing; Wei, Dongxia; Shen, Xi; Chen, Yuan; Ma, Haikun; Wang, Leilei; Du, Kui; Yao, Yuan; Yu, Richeng
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 647 797-801; 10.1016/j.jallcom.2015.06.165 OCT 25 2015
Abstract:
The orthorhombic (3/2, 2/1) approximant with a = 3.06 nm, b = 1.23 nm, c = 2.24 nm, and the coexisting (2/1, 3/2) approximant of decagonal quasicrystals with a = 1.90 nm, c = 3.64 nm, and beta congruent to 90 degrees are found in Al-Cr-Fe-Si alloys by aberration-corrected transmission electron microscope. The structural relationships of these two approximants are analyzed and discussed based on the high-angle annular dark-field scanning transmission electron microscopy images at atomic resolution. We find that both of their structural tiling along the [010] direction can be described by one shield-like tile, with the superiority over the previous HBS tiling model due to the clarity. Combining the shield-like tile and HBS tiling model, the domains of approximants are clearly demonstrated. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Incommensurate antiferromagnetism induced by a charge density wave in the cubic phase of TbGe2.85
Authors:
Tsvyashchenko, AV; Salamatin, DA; Sidorov, VA; Petrova, AE; Fomicheva, LN; Kichanov, SE; Salamatin, AV; Velichkov, A; Kozlenko, DR; Nikolaev, AV; Ryasny, GK; Makarova, OL; Menzel, D; Budzynski, M Author Full Names: Tsvyashchenko, A. V.; Salamatin, D. A.; Sidorov, V. A.; Petrova, A. E.; Fomicheva, L. N.; Kichanov, S. E.; Salamatin, A. V.; Velichkov, A.; Kozlenko, D. R.; Nikolaev, A. V.; Ryasny, G. K.; Makarova, O. L.; Menzel, D.; Budzynski, M.
Source:
PHYSICAL REVIEW B, 92 (10):10.1103/PhysRevB.92.104426 SEP 23 2015
Abstract:
Temperature dependencies of the electrical resistivity, magnetic susceptibility, and heat capacity have been obtained in the cubic phase of TbGe2.85 (the AuCu3 structure), synthesized at high pressure. The macroscopic measurements indicate that a charge density wave is formed below 145 K and an antiferromagnetic ordering is realized below 19 K. Hyperfine interaction data obtained with the time differential perturbed angular correlation method with Cd-111 probes inserted in the TbGe2.85 lattice suggest that the charge density wave is incommensurate in the temperature region 19-145 K, but becomes commensurate below 19 K. The neutron diffraction reveals a complex antiferromagnetic spiral structure in the magnetically ordered phase. We discuss relations between the charge density wave and helical ordering in TbGe2.85 and TbPd3.
Title:
Direct evidence of an incommensurate phase in NaNbO3 and its implication in NaNbO3-based lead-free antiferroelectrics
Authors:
Guo, HZ; Shimizu, H; Randall, CA Author Full Names: Guo, Hanzheng; Shimizu, Hiroyuki; Randall, Clive A.
Source:
APPLIED PHYSICS LETTERS, 107 (11):10.1063/1.4930067 SEP 14 2015
Abstract:
Hot-stage in situ transmission electron microscopy was employed to investigate the temperature-induced complex sequence of phase transitions in NaNbO3 polycrystalline. In addition to the commonly recognized P (Pbma) -> R (Pmnm) -> S (Pnmm) phase transitions, incommensurate phases were observed to exist in P and R phase regions. The former (in the P -> R transition region) is coincident with a diffused dielectric peak appearing at similar to 170 degrees C, and the latter (in the R -> S transition region) serves as an intermediate structure to bridge the two sub-phases in the R phase region. The incommensurate phase in the P phase region can be inferred from the polarization current density and differential dielectric permittivity anomalies, and it provides the bridge structure during the electric field-induced polarization reversal and antiferroelectric-to-ferroelectric transition in NaNbO3 solid solutions. (C) 2015 AIP Publishing LLC.
Title:
Structure and electrical properties of tetragonal tungsten bronze Ba2CeFeNb4O15
Authors:
Ma, HQ; Lin, K; Liu, LJ; Yang, BL; Rong, YC; Chen, J; Deng, JX; Kawaguchi, S; Kato, K; Xing, XR Author Full Names: Ma, Hongqiang; Lin, Kun; Liu, Laijun; Yang, Baoling; Rong, Yangchun; Chen, Jun; Deng, Jinxia; Kawaguchi, Shogo; Kato, Kenichi; Xing, Xianran
Source:
RSC ADVANCES, 5 (94):76957-76962; 10.1039/c5ra16115k 2015
Abstract:
The crystal structure and electrical microstructure of a tetragonal tungsten bronze (TTB) ceramic, BaCeFeNb4O15 (BCFN), were investigated by high-resolution synchrotron X-ray powder diffraction (SPD), selected area electron diffraction (SAED), and AC impedance spectroscopy. SPD and SAED reveal that the BCFN has a tetragonal structure with space group P4/mbm, and includes an incommensurate modulated behavior. Impedance and AC conductivity tests in the range of 200-360 degrees C suggest thermally activated electrical behavior which originates from both the bulk and the grain boundary elements of the ceramics. The dielectric relaxation in the grain boundaries is due to the trap-controlled ac conduction around doubly ionized oxygen vacancies while the relaxation of the bulk may be associated with the localized electron hopping between the transition-metal ions. These results could be helpful in understanding the electrical conduction and relaxation processes in Fe-containing TTB-type oxides.

Update: 8-Oct-2015

Title:
Oxygen vacancy ordering and its mobility in YMnO3
Authors:
Zhang, QH; Shen, X; Yao, Y; Wang, YG; Jin, CQ; Yu, RC Author Full Names: Zhang, Q. H.; Shen, X.; Yao, Y.; Wang, Y. G.; Jin, C. Q.; Yu, R. C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 648 253-257; 10.1016/j.jallcom.2015.07.032 NOV 5 2015
Abstract:
Oxygen vacancy (V-O) ordering and its mobility in YMnO3 have been studied via electron-beam irradiation. By controlling the beam intensity, three commensurate (A, B and C-type) and one incommensurate V-O-orderings can be formed. The transformation from the A-type to the C-type ordering has also been revealed, which could be attributed to the migration of V-O from the apical V-O site to the planar V-O site. Further, intense irradiation can introduce more V(O)s and make a breakdown of the ferroelectric displacements of Y ions. These results suggest that the V(O)s in YMnO3 system are highly active in several ordered ways and also have a high mobility. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Evolution of atomic distribution during devitrification of bulk metallic glass investigated by atom probe microscopy
Authors:
Mridha, S; Jaeger, DL; Arora, HS; Banerjee, R; Mukherjee, S Author Full Names: Mridha, Sanghita; Jaeger, David L.; Arora, Harpreet Singh; Banerjee, Rajarshi; Mukherjee, Sundeep
Source:
MATERIALS LETTERS, 158 99-103; 10.1016/j.matlet.2015.05.034 NOV 1 2015
Abstract:
Evolution of atomic distribution during devitrification of a zirconium-based bulk metallic glass, Zr41.2Ti13.8Cu12.5Ni10.0Be22.5, was investigated using three-dimensional atom probe microscopy. Atom probe analysis showed uniform distribution of constituent elements for the as-cast alloy, with no phase separation. The metallic glass was annealed at different temperatures to study the crystallization pathways and the length scale, distribution, and morphology of the phases formed. Devitrification was found to proceed via the formation of a metastable icosahedral phase. The devitrification pathway is explained based on "strong-liquid" behavior of this alloy. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Conduction mechanisms and enhanced multiferroic properties of Sr doped Bi0.85-xPr0.15SrxFe0.97Mn0.03O3 thin films
Authors:
Yan, X; Tan, GQ; Ye, W; Ren, HJ; Xia, A Author Full Names: Yan, Xia; Tan, Guoqiang; Ye, Wei; Ren, Huijun; Xia, Ao
Source:
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 26 (10):7407-7414; 10.1007/s10854-015-3371-y OCT 2015
Abstract:
Pure BiFeO3 (BFO) and Bi0.85-xPr0.15SrxFe0.97Mn0.03O3 (BPSxFMO, x = 0.02-0.05) thin films were deposited on fluorine-doped SnO2 (FTO/glass) substrates by a sol-gel method. The systematic studies of crystalline structure, surface morphologies, leakage conduction mechanisms, ferroelectric and magnetic properties of pure BiFeO3 and Bi0.85-xPr0.15SrxFe0.97Mn0.03O3 thin films were investigated. X-ray diffraction patterns, Rietveld analysis and Raman scattering spectra reveal that the (Pr, Sr and Mn) co-doped BiFeO3 thin films give rise to a trigonal (R3m: R) structure transition with respect to the original rhombohedral structure of pure BiFeO3 film. Fowler-Nordheim tunneling conduction mechanism dominates the leakage current of all the films in the relatively high electric field. The significantly enhanced ferroelectric properties of the Bi0.85-xPr0.15SrxFe0.97Mn0.03O3 thin films were observed in comparison with pure BiFeO3 film. In addition, the BPS2FMO film shows the enhanced ferromagnetism with the saturation magnetization (M (s) similar to 1.97 emu cm(-3)), which is almost three times larger than that of pure BFO film (M (s) similar to 0.67 emu cm(-3)), as a result of the small grain size effect and the collapse of space modulated spin structure by the structure transition.
Title:
Crystalline and Spin Chiralities in Multiferroics with Langasite-type Structure and Fe1-xCoxSi Crystals
Authors:
Pikin, SA; Lyubutin, IS; Dudka, AP Author Full Names: Pikin, S. A.; Lyubutin, I. S.; Dudka, A. P.
Source:
CRYSTALLOGRAPHY REPORTS, 60 (5):729-736; 10.1134/S1063774515050077 SEP 2015
Abstract:
It is shown that, when magnetic ordering occurs in layered iron-containing langasites (sp. gr. P321), one of the reasons for spin chiralities of different signs is the presence of structural chirality (the existence of inversion twins), which, in turn, is due to the nonsymmetricity of these crystals. Spin helicoids arise in these multiferroics at split sites of Fe3+ ions below the N,el point. The direction of electric polarization vectors coincides with the direction of the magnetic helicoid axes because of the piezoelectric properties of these materials. Due to the magnetostriction effects, structural chirality wave vector k (z) exceeds the magnetic helicoid wave vector by a factor of 2: k (z) = 2q (z). The temperatures of transitions to the chiral structural and chiral magnetic states may differ. In particular, if the structural transition initial temperature exceeds the magnetic transition temperature (T-U > T-M ), structural displacements may arise in the absence of magnetism at T-M < T < T-U. In noncentrosymmetric Fe1-xCoxSi crystals (sp. gr. P2(1)3), which are not multiferroics, magnetic chirality is due to the Dzyaloshinski-Moriya interaction. The dependence of the moduli of incommensurate wave number of the corresponding helicoid on the atomic composition of the crystals under consideration is nonmonotonic.

Update: 1-Oct-2015

Title:
Strongly anisotropic and complex magnetic behavior in EuRhGe3
Authors:
Bednarchuk, O; Kaczorowski, D Author Full Names: Bednarchuk, Oleksandr; Kaczorowski, Dariusz
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 646 291-297; 10.1016/j.jallcom.2015.06.125 OCT 15 2015
Abstract:
Single crystals of EuRhGe3 were studied by means of magnetic susceptibility, magnetization, heat capacity, resistivity and magnetoresistance measurements, performed in wide ranges of temperature and magnetic field strength. The compound was characterized as a Curie-Weiss paramagnet, due to divalent Eu ions, that orders antiferromagnetically at T-N = 11.3 K. In the ordered state, EuRhGe3 exhibits strong magnetic anisotropy. The magnetic moments are probably nearly confined within the ab plane of the tetragonal crystallographic unit cell, and the magnetic propagation vector is likely perpendicular to this plane. The bulk thermodynamic and transport data concordantly suggest that in zero magnetic field the magnetic structure of EuRhGe3 is incommensurate with the chemical one and bears an amplitude-modulated character. In external magnetic field applied within the easy magnetization plane, two other magnetic structures were detected, each of them having an antiferromagnetic nature. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Electrochemical synthesis of Co7Ni3 and Co6Ni4 nanorods with controlled crystalline phase. Application to methanol electro-oxidation
Authors:
Vilana, J; Escalera-Lopez, D; Gomez, E; Valles, E Author Full Names: Vilana, Joan; Escalera-Lopez, Daniel; Gomez, Elvira; Valles, Elisa
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 646 669-674; 10.1016/j.jallcom.2015.06.134 OCT 15 2015
Abstract:
CoNi nanorods with modulated crystalline phase have been synthesised by means of a potentiostatic deposition method, using a single electrolytic bath, by only varying the electrodeposition potential. The growth of the nanorods in the interior on the nanochannels of the membrane is mainly controlled by the limited transport of the Co(II) and Ni(II) ions to the growth front. Two types of CoNi nanorods of several microns long, with similar composition but different crystalline phases depending on the applied potential, have been obtained. The potentials for the electrosynthesis of the nanorods have been selected to induce different deposition rates and, as a consequence, different crystalline phases, hcp for the lower deposition rates and fcc (+hcp) for the highest ones. For each selected potential, the nanorods present the same composition and crystalline phase along the rods. The test of the two types of nanorods for the methanol electro-oxidation demonstrated both the specific electrocatalytic behaviour of each one and the promising behaviour of the nanorods as electrocatalysts in direct methanol fuel cells in basic medium, due to their higher surface/volume ratio than that of thin films and the superior stability than that of nanoparticles. The influence of the crystalline phase in the methanol electro-oxidation has been also corroborated from pure-hcp and pure-fcc CoNi films. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Structural phase transitions in the Ti45Zr38Ni17-xFex nano-alloys and their deuterides
Authors:
Rusinek, D; Czub, J; Niewolski, J; Gondek, L; Gajewska, M; Takasaki, A; Hoser, A; Zywczak, A Author Full Names: Rusinek, D.; Czub, J.; Niewolski, J.; Gondek, L.; Gajewska, M.; Takasaki, A.; Hoser, A.; Zywczak, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 646 90-95; 10.1016/j.jallcom.2015.06.023 OCT 15 2015
Abstract:
The mechanically alloyed Ti-Zr-Ni materials are extensively studied due to their promising properties concerning biomedical, electronic or hydrogen related applications (for example the gaseous hydrogen storage and the MNiH batteries). In this paper we address the very crucial issue of the structural properties and transformations of the amorphous and quasicrystalline Ti45Zr38Ni17-xFex (x = 0, 4, 8) and their hydrides. According to the neutron diffraction results, the transformation of the amorphous Ti45Zr38Ni17 phase into the icosahedral quasicrystalline state (the i-phase) is quasi-continuous and starts at the relatively low temperature of 300 degrees C. At 500 degrees C the i-phase is well-developed. At higher temperatures the i-phase transforms into the approximant w-phase and eventually into the cubic phase (the c-phase). Interestingly, the deuterided i-phase exhibits completely different thermal evolution. Namely, this phase decomposes into the simple intermetallic compounds above 625 degrees C. What is worth-mentioning is that the release of deuterium is strictly related to that structural decomposition. The possibility of hydrogenation of the amorphous Ti45Zr38Ni17-xFe (x) phases with maintaining the amorphous nature of the alloys is the other extremely important field of our interest. We established a processing route to meet our goal. Finally, we show that introducing deuterium triggers an exciting phase transition from the deuterided amorphous phase into the unknown before, partially disordered, quasicrystallinelike phase (the glassy quasicrystal) without releasing of deuterium. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Reassessment of the effects of Ce on quasicrystal formation and microstructural evolution in rapidly solidified Al-Mn alloys
Authors:
Coury, FG; Botta, WJ; Bolfarini, C; Kiminami, CS; Kaufman, MJ Author Full Names: Coury, F. G.; Botta, W. J.; Bolfarini, C.; Kiminami, C. S.; Kaufman, M. J.
Source:
ACTA MATERIALIA, 98 221-228; 10.1016/j.actamat.2015.07.046 OCT 1 2015
Abstract:
Rapidly solidified Al-Mn-Ce alloys have been reported to exhibit desirable properties due to the uniform distribution of quasicrystalline (QC) particles in an Al matrix. In this study, several ternary alloy compositions that encompassed the alloys reported in the previous reports, namely Al-6Mn-2Ce, Al-6Mn-4Ce, AI-8Mn-4Ce, Al-12Mn-2Ce and Al-10Mn-5Ce, were prepared by melt spinning and their microstructures were characterized by electron microscopy and X-ray diffraction. The results are in direct contrast with the previous reports available in the literature in that the formation of QCs was only observed in the Al-12Mn-2Ce alloy; in the others, the dispersed phase was not the QC; rather, the structural and compositional information presented in this paper together with data recently published in the literature enabled a reinterpretation of the effect of Ce on rapidly solidified Al-Mn alloys. The main conclusion is that Ce favors the formation of a ternary metastable phase with approximate stoichiometry Al20Mn2Ce. This phase forms in a wide portion of the Al-rich region of the ternary phase diagram and can even coexist with the QC phase in alloys containing low amounts of Ce; in this case, the QC contains no detectable Ce by TEM/EDS, consistent with the conclusion that Ce does not favor QC formation in contrast to the previous reports. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Discovery of a Sodium-Ordered Form of Na3V2(PO4)(3) below Ambient Temperature
Authors:
Chotard, JN; Rousse, G; David, R; Mentre, O; Courty, M; Masquelier, C Author Full Names: Chotard, Jean-Noel; Rousse, Gwenaelle; David, Renald; Mentre, Olivier; Courty, Matthieu; Masquelier, Christian
Source:
CHEMISTRY OF MATERIALS, 27 (17):5982-5987; 10.1021/acs.chemmater.5b02092 SEP 8 2015
Abstract:
The crystal structure of the NASICON Na3V2(PO4)(3) phase (NVP) has been investigated as a function of temperature. Combining laboratory and synchrotron X-ray powder diffraction with single crystal X-ray diffraction, we demonstrate the presence of four polymorphs of NVP from 30 to 225 degrees C. While the high temperature gamma-NVP crystallizes in the classical rhombohedral cell (S.G. R (3) over barc, a = 8.73382(4) angstrom, c = 21.91438(17) angstrom), the low temperature alpha-NVP undergoes a monoclinic distortion (S.G. C2/c, a = 15.1244(6) angstrom, b = 8.7287(3) angstrom, c = 21.6143(8) angstrom, beta = 90.163(2)degrees) together with an ordering of the Na atoms. In the middle temperature range, two incommensurate modulated structures (beta- and beta '-NVP) are also reported for the first time.
Title:
Intermediate-valent CeCoAl - a commensurate modulated structure with short Ce-Co distances
Authors:
Niehaus, O; Hoffmann, RD; Tence, S; Chevalier, B; Poettgen, R Author Full Names: Niehaus, Oliver; Hoffmann, Rolf-Dieter; Tence, Sophie; Chevalier, Bernard; Poettgen, Rainer
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 230 (9-10):579-591; 10.1515/zkri-2015-1856 SEP 2015
Abstract:
CeCoAl was synthesized by melting of the elements in a sealed niobium tube in an induction furnace. Annealing of the sample gave access to a single phase sample. Its structure was refined on the basis of single-crystal X-ray diffractometer data at different temperatures. Above 271 K CeCoAl crystallizes in its own structure type in the space group C2/m [a = 1107.4(2), b = 440.6(1) and c = 479.6(1) pm, beta = 104.6(1)degrees]. Data obtained at 300 K lead to 511 F-2 values with 20 variables and a residual of [I >= 3 sigma(I)] wR = 0.0539. Below 271 K satellites give rise to the superspace group C2/m(alpha 0 gamma) 00; alpha = 2/3, gamma = 2/5 with a temperature independent q-vector. For the 90 K data (also for 180 and 220 K) the commensurate modulated structure could be refined with 4817 F-2 values, 129 variables and residuals of wR = 0.0347 (main), wR = 0.1927 (satellites 1st order), wR = 0.1541 (satellites 2nd order) and wR = 0.1768 (satellites 3rd order) [a = 1107.5(1), b = 440.3(1) and c = 479.0(1) pm, beta = 104.7(1)degrees]. For the three temperatures only minor variations of the modulation amplitudes are observed. The relation of the low temperature (3+1)D 3a x 5c approximant and the room temperature 3D structure is discussed on the basis of a group-subgroup relation. By investigation of the heat capacity, the phase transition could be identified as a second order one with a transition temperature of 271 K. Magnetic measurements clearly prove the intermediate cerium valence which is in line with the short Ce-Co distances.
Title:
The birth of time-of-flight (TOF) neutron powder diffraction at pulsed neutron source (invited)
Authors:
Sosnowska, IM Author Full Names: Sosnowska, Izabela M.
Source:
CRYSTAL RESEARCH AND TECHNOLOGY, 50 (9-10):705-715; 10.1002/crat.201400439 SEP 2015
Abstract:
Behind every improvement there is a story. The early history of the TOF neutron powder diffraction technique is presented. Successes and problems in the application of this technique in material science are reported. Powder diffraction technique is very useful when materials, in a single crystal form, reveal complicated electric and magnetic domain structures. Finding and describing the magnetic structure of multiferroics is the great success of ultra-high resolution TOF neutron diffraction. This unique role of the TOF method in discovery of the modulated magnetic structure of BiFeO3 is presented. To date, the TOF powder neutron diffraction technique gives the richest information on the long period modulated magnetic structure of BiFeO3 and its solid solutions. Determination of magnetic moment direction in a crystal lattice is the unique area of application of the TOF technique. The current status and perspectives of the application of the TOF neutron powder diffraction technique in material science are presented in the review.

Update: 24-Sep-2015

Title:
HREM observation and high-pressure composition isotherm measurement of Ti45Zr38Ni17 quasicrystal powders synthesized by mechanical alloying
Authors:
Tominaga, T; Takasaki, A; Shibato, T; Swierczek, K Author Full Names: Tominaga, Tomoki; Takasaki, Akito; Shibato, Tsuyoshi; Swierczek, Konrad
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 645 S292-S294; 1 10.1016/j.jallcom.2014.12.200 OCT 5 2015
Abstract:
Elemental powders consisted of chemical composition of Ti45Zr38Ni17 were mechanical alloyed and annealed subsequently, and the microstructures were characterized by high-resolution electron microscopy (HREM) and an X-ray diffractometry, and hydrogen absorption and desorption pressure-composition (PC) isotherms were measured at 523 K, 573 K and 623 K by a Sieverts type apparatus. The annealing after mechanical alloying (MA) caused formation of an icosahedral quasicrystal with a Ti2Ni type crystal phases. 5 or 10-fold rotational symmetry, which is prohibited to normal crystals, was observed by HREM in a digital diffractogram and an simulated atomic arrangement derived from the digital diffractogram. The hydrogen storage capacity (hydrogen to metal atom ratio: H/M) at 523 K was about 1.3, which decreased with increasing hydrogenation temperatures. All the PC isotherms were steep, and no plateau pressure was observed. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Hydrogen storage properties for Mg-Zn-Y quasicrystal and ternary alloys
Authors:
Luo, XL; Grant, DM; Walker, GS Author Full Names: Luo, Xuanli; Grant, David M.; Walker, Gavin S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 645 S23-S26; 1 10.1016/j.jallcom.2015.01.266 OCT 5 2015
Abstract:
Three Zn-Mg-Y alloys with nominal compositions of Zn50Mg42Y8 and Zn60Mg30Y10 were prepared by induction melting or gas atomisation. XRD and SEM analysis shows samples ZMY-1 and ZMY-2 consisted of multiple phases including icosahedral quasicrystal (QC) i-phase, hexagonal H-phase and Mg7Zn3, whilst ZMY-3 contained QC only. The hydrogen storage properties of the Zn-Mg-Y quasicrystal and ternary alloys were investigated for the first time. The quasicrystal sample ZMY-3 hydrogenated at 300 degrees C had 0.3 wt.% capacity and the DSC decomposition peak temperature was 503 degrees C. Amongst the three samples, the highest hydrogen storage capacity (0.9 wt.%) and the lowest decomposition peak temperature (445 degrees C) was achieved by sample ZMY-1. The pressure-composition-isotherm (PCI) curve of ZMY-1 sample showed a flat plateau gave a plateau pressure of 3.5 bar at 300 degrees C, which indicates a lower dehydrogenation enthalpy than MgH2. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Electrochemical properties of Ti49Zr26Ni25-xPdx (x=0-6) quasicrystal electrodes produced by mechanical alloying
Authors:
Ariga, Y; Takasaki, A; Kimijima, T; Swierczek, K Author Full Names: Ariga, Youhei; Takasaki, Akito; Kimijima, Tsubasa; Swierczek, Konrad
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 645 S152-S154; 1 10.1016/j.jallcom.2015.01.114 OCT 5 2015
Abstract:
Elemental powders consisted of chemical composition of Ti49Zr26Ni25 Pd-x(x) (x = 0, 1, 3, 6) were mechanically alloyed and annealed subsequently, and the discharge performance of the electrodes was measured by a three-electrode cell at room temperature. The annealing after mechanical alloying caused a formation of the icosahedral quasicrystal phase with a Ti2Ni type crystal, C14 Laves and alpha-Ti/Zr phases. The quasilattice constant increased with increasing amount of Pd substituted for Ni up to 3 at.% due to difference in atomic radius between Pd and Ni. The maximum discharge capacity achieved was about 220 mA h/g from a (Ti49Zr26Ni22Pd3) electrode at the first discharge process. (C) 2015 Elsevier B.V. All rights reserved.
Title:
TEM study of the (SbS)(1+delta)(NbS2)(n), (n=1, 2, 3; delta similar to 1.14, 1.20) misfit layer phases
Authors:
Gomez-Herrero, A; Landa-Canovas, AR; Otero-Diaz, LC Author Full Names: Gomez-Herrero, A.; Landa-Canovas, A. R.; Otero-Diaz, L. C.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 230 357-368; 10.1016/j.jssc.2015.07.029 OCT 2015
Abstract:
In the Sb-Nb-S system four new misfit layer phases have been found and carefully investigated via Transmission Electron Microscopy (TEM). Their structures are of composite modulated structure type with stoichiometries that can be formulated as (SbS)(1+delta)(NbS2)(n); for n=1, delta similar to 1.14 and 1.19; for n=2, delta similar to 1.18 and for n=3, delta similar to 1.19. Selected Area Electron Diffraction (SAED) patterns show an almost commensurate fit between the pseudo-tetragonal (SbS) and the pseudo-orthohexagonal (NbS2)(n) subcells along the misfit direction a, with 3(SbS) approximate to 5(NbS2), being b the same for both sub-lattices and c the stacking direction. For n=1, a commensurate phase with 4a(SbS)=7a(NbS2) has also been observed. In addition to the characteristic misfit and associated modulation of the two sub-structures, a second modulation is also present which appears to be primarily associated with the (SbS) sub-structure of both the n=1 and n=2 phases. High Resolution Transmission Electron Microscopy (HRTEM) images show ordered stacking sequences between the (SbS) and (NbS2)(n) lamellae for each of the four phases, however, disordered intergrowths were also occasionally found. Most of the crystals showed different kinds of twinning defects on quite a fine scale. Many crystals showed curled up edges. In some cases the lamellar crystals were entirely folded giving rise to similar diffraction patterns as found for cylindrical crystals. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Enhancement of superconductivity at the onset of charge-density-wave order in a metal
Authors:
Wang, YX; Chubukov, AV Author Full Names: Wang, Yuxuan; Chubukov, Andrey V.
Source:
PHYSICAL REVIEW B, 92 (12):10.1103/PhysRevB.92.125108 SEP 4 2015
Abstract:
We analyze superconductivity in the cuprates near the onset of an incommensurate charge-density-wave (CDW) order with momentum Q = (Q, 0)/(0, Q), as observed in experiments. We first consider a semiphenomenological charge-fermion model in which hot fermions, separated by Q, attract each other by exchanging soft CDW fluctuations. We find that in a quantum-critical region near the CDW transition, T-c = A (g) over bar (c), where (g) over bar (c) is charge-fermion coupling and Ais the prefactor, which we explicitly compute. We then consider the particular microscopic scenario in which the CDW order parameter emerges as a composite field made of primary spin-density-wave fields. We show that charge-fermion coupling (g) over bar (c) is of the order of spin-fermion coupling (g) over bar (s). As a consequence, superconducting Tc is substantially enhanced near the onset of CDW order. Finally, we analyze the effect of an external magnetic field H. We show that, as H increases, the optimal Tc decreases and the superconducting dome becomes progressively more confined to the CDW quantum-critical point. These results are consistent with experiments.
Title:
Quasiperiodicity and 2D topology in 1D charge-ordered materials
Authors:
Flicker, F; van Wezel, J Author Full Names: Flicker, F.; van Wezel, Jasper
Source:
EPL, 111 (3):10.1209/0295-5075/111/37008 AUG 2015
Abstract:
The mathematical description of 1D quasicrystals has recently been linked to that of 2D quantum Hall states. The topological classification of 1D quasicrystals and the corresponding interpretation of their observed charge transport have been widely discussed. We demonstrate the equivalence of both 1D quasicrystals and 2D quantum Hall states to a mean-field treatment of charge order. Using the fractal nature of the spectrum of charge-ordered states we consider incommensurate order as a limit of commensurate. The topological properties of both are identical, arising from a 2D parameter space of phase and wave vector, and fit into class A of the Tenfold Way. The topological nature of all the systems can be tested by measuring a quantized particle transport upon dragging the charge order. Copyright (C) EPLA, 2015

Update: 17-Sep-2015

Title:
Low temperature superplasticity of ultrafine grained Mg-9.25Zn-1.66Y alloy with an icosahedral quasicrystalline phase
Authors:
Kim, WJ; Yoo, YJ Author Full Names: Kim, W. J.; Yoo, Y. J.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 643 47-50; 10.1016/j.msea.2015.07.022 SEP 3 2015
Abstract:
The ultrafine grained Mg-9.25Zn-1.66Y alloy sheet with I-phase prepared by directly applying high-ratio differential speed rolling to the as-cast microstructure exhibited excellent low-temperature super-plasticity (386-888% at 443-473 K) at a moderately high strain rate of 10(-3) s(-1). A criterion for achieving low temperature superplasticity was proposed. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Premartensite to martensite transition and its implications for the origin of modulation in Ni2MnGa ferromagnetic shape-memory alloy
Authors:
Singh, S; Bednarcik, J; Barman, SR; Felser, C; Pandey, D Author Full Names: Singh, Sanjay; Bednarcik, J.; Barman, S. R.; Felser, C.; Pandey, Dhananjai
Source:
PHYSICAL REVIEW B, 92 (5):10.1103/PhysRevB.92.054112 AUG 28 2015
Abstract:
We present results of a temperature-dependent high-resolution synchrotron x-ray powder diffraction study of sequence of phase transitions in Ni2MnGa. Our results show that the incommensurate martensite phase results from the incommensurate premartensite phase and not from the austenite phase assumed in the adaptive phase model. The premartensite phase transforms to the martensite phase through a first order phase transition with coexistence of the two phases in a broad temperature interval (similar to 40 K), discontinuous change in the unit cell volume as also in the modulation wave vector across the transition temperature, and considerable thermal hysteresis in the characteristic transition temperatures. The temperature variation of the modulation wave vector q shows smooth analytic behavior with no evidence for any devilish plateau corresponding to an intermediate or ground state commensurate lock-in phase. The existence of the incommensurate 7M-like modulated structure down to 5 K suggests that the incommensurate 7M-like modulation is the ground state of Ni2MnGa and not the Bain distorted tetragonal L1(0) phase or any other lock-in phase with a commensurate modulation. These findings can be explained within the framework of the soft phonon model.
Title:
KEu(MoO4)(2): Polymorphism, Structures, and Luminescent Properties
Authors:
Morozov, VA; Arakcheeva, AV; Pattison, P; Meert, KW; Smet, PF; Poelman, D; Gauquelin, N; Verbeeck, J; Abakumov, AM; Hadermann, J Author Full Names: Morozov, Vladimir A.; Arakcheeva, Alla V.; Pattison, Philip; Meert, Katrien W.; Smet, Philippe F.; Poelman, Dirk; Gauquelin, Nicolas; Verbeeck, Johan; Abakumov, Artem M.; Hadermann, Joke
Source:
CHEMISTRY OF MATERIALS, 27 (16):5519-5530; 10.1021/acs.chemmater.5b01622 AUG 25 2015
Abstract:
In this paper, with the example of two different polymorphs of KEu(MoO4)(2), the influence of the ordering of the A-cations on the luminescent properties in scheelite related compounds (A',A '') [(B',B '')O-4](m) is investigated. The polymorphs were synthesized using a solid state method. The study confirmed the existence of only two polymorphic forms at annealing temperature range 923-1203 K and ambient pressure: a low temperature anorthic alpha-phase and a monoclinic high temperature beta-phase with an incommensurately *modulated structure*. The *structures* of both polymorphs were solved using transmission electron microscopy and refined from synchrotron powder X-ray diffraction data. The monoclinic beta-KEu(MoO4)(2) has a (3+1)-dimensional incommensurately modulated structure (superspace group I2/b(alpha beta 0)00, a = 5.52645(4) angstrom, b = 5.28277(4) angstrom, c = 11.73797(8) angstrom, gamma = 91.2189(4)degrees, q = 0.56821(2)a*-0.12388(3)b*), whereas the anorthic alpha-phase is (3+1)-dimensional commensurately modulated (superspace group I (1) over bar(alpha beta gamma)0, a = 5.58727(22) angstrom, b = 5.29188(18)angstrom, c = 11.7120(4) angstrom, alpha = 90.485(3)degrees, beta = 88.074(3)degrees, gamma = 91.0270(23)degrees, q = 1/2a* + 1/2c*). In both cases the modulation arises due to Eu/K cation ordering at the A site: the formation of a 2-dimensional Eu3+ network is characteristic for the alpha-phase, while a 3-dimensional Eu3+-framework is observed for the beta-phase structure. The luminescent properties of KEu(MoO4)(2) samples prepared under different annealing conditions were measured, and the relation between their optical properties and their structures is discussed.
Title:
Precipitates in a quasicrystal-strengthened Al-Mn-Be-Cu alloy
Authors:
Zupanic, F; Wang, D; Gspan, C; Boncina, T Author Full Names: Zupanic, Franc; Wang, Di; Gspan, Cristian; Boncina, Tonica
Source:
MATERIALS CHARACTERIZATION, 106 93-99; 10.1016/j.matchar.2015.05.013 AUG 2015
Abstract:
In this work, an Al-Mn-Be-Cu alloy was studied containing a primary and eutectic icosahedral quasicrystalline phase in the as-cast microstructure. Special attention was given to a transmission electron microscopy investigation of precipitates formed within the aluminium solid solution (Al-ss) at different temperatures. At 200 degrees C, only binary Al-Cu precipitates (theta') were formed. At 300 degrees C, icosahedral quasicrystalline (IQC) precipitates prevailed with a crystallographic orientation relationship with the Al-ss. The rods of the T-phase (Al20Mn3Cu2) which were precipitated above 400 degrees C, also had a specific orientation relationship with the Al-ss. The primary and eutectic IQC microstructural constituent started to transform rapidly to the T-phase and Be4Al(Mn,Cu) at 500 degrees C. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Self-assembly of the decagonal quasicrystalline order in simple three-dimensional systems
Authors:
Ryltsev, R; Klumov, B; Chtchelkatchev, N Author Full Names: Ryltsev, Roman; Klumov, Boris; Chtchelkatchev, Nikolay
Source:
SOFT MATTER, 11 (35):6991-6998; 10.1039/c5sm01397f 2015
Abstract:
Using molecular dynamics simulations we show that a one-component system can be driven to a three-dimensional decagonal (10-fold) quasicrystalline state just by purely repulsive, isotropic and monotonic interaction pair potential with two characteristic length scales; no attraction is needed. We found that self-assembly of a decagonal quasicrystal from a fluid can be predicted by two dimensionless effective parameters describing the fluid structure. We demonstrate stability of the results under changes of the potential by obtaining the decagonal order for three particle systems with different interaction potentials, both purely repulsive and attractive, but with the same values of the effective parameters. Our results suggest that soft matter quasicrystals with decagonal symmetry can be experimentally observed for the same systems demonstrating the dodecagonal order for an appropriate tuning of the effective parameters.

Update: 10-Sep-2015

Title:
The Effect of Icosahedral Phase on Dynamic Recrystallization Evolution and Hot Workability of Mg-2.0Zn-0.3Zr-0.2Y Alloy
Authors:
Lv, BJ; Peng, J; Chu, Z Author Full Names: Lv, Bin-Jiang; Peng, Jian; Chu, Zhong
Source:
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE, 24 (9):3502-3512; 10.1007/s11665-015-1604-0 SEP 2015
Abstract:
The effect of Icosahedral phase (I-phase) on hot deformation behavior, dynamic recrystallization (DRX) evolution, and hot workability of Mg-2.0Zn-0.3Zr-0.2Y alloy has been investigated in the temperature range of 300-500 A degrees C and strain rate range of 0.001-1 s(-1) using Gleeble 3500D thermo-mechanical simulator. Based on regression analysis for Arrhenius-type equation of flow behavior, the average activation energy of deformation was determined as Q = 277.8 kJ/mol. The model of DRX evolution is . The DRX model agreed well with the microstructure evolution of the alloy at all deformation conditions. At lower strain rates (0.001-0.01 s(-1)), continuous DRX (CDRX) is the main DRX mechanism that occurred near the original grain boundaries. Twin-dynamic recrystallization (TDRX) began to occur at lower deformation temperatures and higher strain rates (0.1-1 s(-1)). At a deformation temperature range of 250 to 350 A degrees C and a strain rate of 1 s(-1), the main DRX mechanism is TDRX, and the density of twins decreased, and CDRX began to occur near the original grain boundaries. When the deformation temperature increased to 400 A degrees C, TDRX disappeared and CDRX occurred near original grain boundaries and I-phase particles. According to the flow stress behavior and DRX model, the processing maps have exhibited the optimum deformation conditions to be 450 A degrees C and the strain rate range of 0.01-0.001 s(-1).
Title:
Crystal chemistry of layered structures formed by linear rigid silyl-capped molecules
Authors:
Lumpi, D; Kautny, P; Stoger, B; Frohlich, J Author Full Names: Lumpi, Daniel; Kautny, Paul; Stoeger, Berthold; Froehlich, Johannes
Source:
IUCRJ, 2 584-600; 10.1107/S2052252515011665 5 SEP 2015
Abstract:
The crystallization behavior of methylthio-or methylsulfonyl-containing spacer extended Z, Z-bis-ene-yne molecules capped with trimethylsilyl groups obtained by (tandem) thiophene ring fragmentation and of two non-spacer extended analogs were investigated. The rigid and linear molecules generally crystallized in layers whereby the flexibility of the layer interfaces formed by the silyl groups leads to a remarkably rich crystal chemistry. The molecules with benzene and thiophene spacers both crystallized with C2/c symmetry and can be considered as merotypes. Increasing the steric bulk of the core by introduction of ethylenedioxythiophene (EDOT) gave a structure incommensurately modulated in the [010] direction. Further increase of steric demand in the case of a dimethoxythiophene restored periodicity along [010] but resulted in a doubling of the c vector. Two different polytypes were observed, which feature geometrically different layer interfaces (non-OD, order-disorder, polytypes), one with a high stacking fault probability. Oxidation of the methylthio groups of the benzene-based molecule to methylsulfonyl groups led to three polymorphs (two temperature-dependent), which were analyzed by Hirshfeld surface d(e)/d(i) fingerprint plots. The analogously oxidized EDOT-based molecule crystallized as systematic twins owing to its OD polytypism. Shortening of the backbone by removal of the aryl core resulted in an enantiomorphic structure and a further shortening by removal of a methylthio-ene fragment again in a systematically twinned OD polytype.
Title:
Good reproductive preparation method of Li-intercalated hexagonal boron nitride and transmission electron microscopy - Electron energy loss spectroscopy analysis
Authors:
Sumiyoshi, A; Hyodo, H; Sato, Y; Terauchi, M; Kimura, K Author Full Names: Sumiyoshi, A.; Hyodo, H.; Sato, Y.; Terauchi, M.; Kimura, K.
Source:
SOLID STATE SCIENCES, 47 68-72; 10.1016/j.solidstatesciences.2015.04.011 SEP 2015
Abstract:
A Li-intercalated hexagonal boron nitride (Li-h-BNIC) phase was synthesized using a highly reproducible method that involves annealing an Li3N and h-BN mixture at 1220 K. Powder X-ray diffraction, electrical conductivity measurements, transmission electron microscopy (TEM) and electron energy loss spectroscopy were performed. The stacking of BN atomic layers in the Li-h-BNIC phase is not the same as the two-layer stacking periodicity of h-BN. TEM observation suggests the existence of incommensurate periodicity along the intralayer direction. From the low-loss and core-loss spectra, the Li-h-BNIC phase is not metal as predicted by the first-principle calculations. Satellite peaks of 1 s to pi* transition in the B K-edge core-loss spectrum indicate the presence of N atom vacancies modified by O atoms in the h-BN atomic layer. (C) 2015 Elsevier Masson SAS. All rights reserved.
Title:
Cluster-Based Solidification and Growth Algorithm for Decagonal Quasicrystals
Authors:
Kuczera, P; Steurer, W Author Full Names: Kuczera, P.; Steurer, W.
Source:
PHYSICAL REVIEW LETTERS, 115 (8):10.1103/PhysRevLett.115.085502 AUG 21 2015
Abstract:
A novel approach is used for the simulation of decagonal quasicrystal (DQC) solidification and growth. It is based on the observation that in well-ordered DQCs the atoms are largely arranged along quasiperiodically spaced planes parallel to the tenfold axis, running throughout the whole structure in five different directions. The structures themselves can be described as quasiperiodic arrangements of decagonal columnar clusters (cluster covering) that partially overlap in a systematic way. Based on these findings, we define a cluster interaction model within the mean field approximation, with effectively asymmetric interactions ranging beyond the nearest neighbors. In our Monte Carlo simulations, this leads to a long-range ordered quasiperiodic ground state. Indications of two finite-temperature unlocking phase transitions are observed, and are related to the two fundamental length scales that are characteristic for the system.
Title:
Complex variable method for an anti-plane elliptical cavity of one-dimensional hexagonal piezoelectric quasicrystals
Authors:
Yu, J; Guo, JH; Xing, YM Author Full Names: Yu Jing; Guo Junhong; Xing Yongming
Source:
CHINESE JOURNAL OF AERONAUTICS, 28 (4):1287-1295; 10.1016/j.cja.2015.04.013 AUG 2015
Abstract:
Based on the fundamental equations of piezoelasticity of quasicrystal media, using the symmetry operations of point groups, the linear piezoelasticity behavior of one-dimensional (1D) hexagonal quasicrystals is investigated and the piezoelasticity problem of 1D hexagonal quasicrystals is decomposed into two uncoupled problems, i.e., the classical plane elasticity problem of conventional hexagonal crystals and the phonon-phason-electric coupling elasticity problem of 1D hexagonal quasicrystals. The final governing equations are derived for the phonon-phason-electric coupling anti-plane elasticity of 1D hexagonal quasicrystals. The complex variable method for an anti-plane elliptical cavity in 1D hexagonal piezoelectric quasicrystals is proposed and the exact solutions of complex potential functions, the stresses and displacements of the phonon and the phason fields, the electric displacements and the electric potential are obtained explicitly. Reducing the cavity into a crack, the explicit solutions in closed forms of electro-elastic fields, the field intensity factors and the energy release rate near the crack tip are derived. (C) 2015 The Authors.

Update: 27-Aug-2015

Title:
(3+1)-Dimensional incommensurately modulated structure and photoluminescence property of polyphosphate Ho(PO3)(3)
Authors:
Zhao, D; Zhang, RH; Ma, FX; Li, FF Author Full Names: Zhao, Dan; Zhang, Rong-Hua; Ma, Fa-Xue; Li, Fei-Fei
Source:
MATERIALS LETTERS, 157 219-221; 10.1016/j.matlet.2015.05.125 OCT 15 2015
Abstract:
Single-crystal of polyphosphate Ho(PO3)(3) has been prepared under high temperature molten-salt method and its structure has been characterized by single crystal X-ray diffraction analysis. In-commensurately modulated structure of compound Ho(PO3)(3) was perfectly modeled using high-dimensional approach with centrosymmetric superspace group C2/c(0 beta 0)s0 and modulation vector q=0.362b*. The basic structure features infinite 1-D zigzag chains of (PO3)infinity running along the c-axis, which are further interconnected by HoO6 octahedra. Although with high concentration of Ho3+ ion, the emission spectrum shows the characteristic 4f transitions of Ho3+ ion of S-5(2)-> I-5(8) at about 566 nm, making it as a promising green emitting phosphor. (C) 2015 Elsevier B.V. All rights reserved.

Update: 20-Aug-2015

Title:
Field-induced spin density wave and spiral phases in a layered antiferromagnet
Authors:
Stone, MB; Lumsden, MD; Garlea, VO; Grenier, B; Ressouche, E; Samulon, EC; Fisher, IR Author Full Names: Stone, M. B.; Lumsden, M. D.; Garlea, V. O.; Grenier, B.; Ressouche, E.; Samulon, E. C.; Fisher, I. R.
Source:
PHYSICAL REVIEW B, 92 (2):10.1103/PhysRevB.92.020415 JUL 28 2015
Abstract:
We determine the low-field ordered magnetic phases of the S = 1 dimerized antiferromagnet Ba3Mn2O8 using single-crystal neutron diffraction. We find that for magnetic fields between mu H-0 = 8.80 T and 10.56 T applied along the [1 (1) over bar0] direction the system exhibits spin density wave order with incommensurate wave vectors of type (eta,eta,epsilon). For mu H-0 > 10.56 T, the magnetic order changes to a spiral phase with incommensurate wave vectors only along the [hh0] direction. For both field-induced ordered phases, the magnetic moments are lying in the plane perpendicular to the field direction. The nature of these two transitions is fundamentally different: the low-field transition is a second-order transition to a spin density wave ground state, while the one at higher field, toward the spiral phase, is of first order.
Title:
Symmetry-Based Computational Tools for Magnetic Crystallography
Authors:
Perez-Mato, JM; Gallego, SV; Tasci, ES; Elcoro, L; de la Flor, G; Aroyo, MI Author Full Names: Perez-Mato, J. M.; Gallego, S. V.; Tasci, E. S.; Elcoro, L.; de la Flor, G.; Aroyo, M. I. Edited by: Clarke DR
Source:
ANNUAL REVIEW OF MATERIALS RESEARCH, VOL 45, 45 217-248; 10.1146/annurev-matsci-070214-021008 2015 Book Series: Annual Review of Materials Research
Abstract:
In recent years, two important advances have opened new doors for the characterization and determination of magnetic structures. Firstly, researchers have produced computer-readable listings of the magnetic or Shubnikov space groups. Secondly, they have extended and applied the superspace formalism, which is presently the standard approach for the description of nonmagnetic incommensurate structures and their symmetry, to magnetic structures. These breakthroughs have been the basis for the subsequent development of a series of computer tools that allow a more efficient and comprehensive application of magnetic symmetry, both commensurate and incommensurate. Here we briefly review the capabilities of these computation instruments and present the fundamental concepts on which they are based, providing various examples. We show how these tools facilitate the use of symmetry arguments expressed as either a magnetic space group or a magnetic superspace group and allow the exploration of the possible magnetic orderings associated with one or more propagation vectors in a form that complements and goes beyond the traditional representation method. Special focus is placed on the programs available online at the Bilbao Crystallographic Server (http://www. cryst.ehu.es).

Update: 13-Aug-2015

Title:
Thermodynamic Aspects of Homogeneous Nucleation Enhanced by Icosahedral Short Range Order in Liquid Fcc-Type Alloys
Authors:
Rappaz, M; Kurtuldu, G Author Full Names: Rappaz, Michel; Kurtuldu, Gueven
Source:
JOM, 67 (8):1812-1820; 10.1007/s11837-015-1328-5 AUG 2015
Abstract:
We have recently shown that minute solute element additions to liquid metallic alloys can strongly influence the nucleation of the fcc phase and act as a grain refinement method. Electron back-scattered diffraction observations revealed a concomitant increase in the percentage of nearest neighbor (nn) grains that are in a twin relationship. Furthermore, multiple-twinned (MT) nn grain configurations with a fivefold symmetry around a common < 110 > direction have been identified, an occurrence that can be explained when the symmetry of the icosahedron is accounted for. It was then conjectured that a new nucleation mechanism occurs in two steps: first, the formation of small icosahedral quasicrystals in the melt, followed by heteroepitaxy of the fcc phase on facets of these quasicrystals. In the present contribution, based on thermodynamics arguments, it is proposed that the first step occurs by spinodal decomposition of the liquid, in a manner similar to Guinier-Preston zones formation in solid state precipitation, while the second step is a transformation of these quasicrystal precursors into MT-fcc nanocrystals once the driving force for this transformation is sufficient to overcome the fcc-liquid interfacial energy and the elastic strains associated with MT-fcc nanoparticles. This explanation sets up guidelines for finding solute elements and composition ranges that favor this grain refinement mechanism.
Title:
Symmetry of icosahedral quasicrystals
Authors:
Madison, AE Author Full Names: Madison, A. E.
Source:
STRUCTURAL CHEMISTRY, 26 (4):923-942; 10.1007/s11224-014-0559-3 AUG 2015
Abstract:
The concept of infinitely fragmented fractal tiling is proposed for the description of the structure and symmetry of quasicrystals. Fractal tilings may serve as unique "parent" structures for the corresponding local isomorphism class. The generating symmetry elements and some special features of the resulting symmetry groups of the fractal tilings are analyzed. Simple inflation/deflation rules for icosahedral quasicrystals are proposed, and natural local matching rules are derived.
Title:
Incommensurate spin density wave at a ferromagnetic quantum critical point in a three-dimensional parabolic semimetal
Authors:
Murray, JM; Vafek, O; Balents, L Author Full Names: Murray, James M.; Vafek, Oskar; Balents, Leon
Source:
PHYSICAL REVIEW B, 92 (3):10.1103/PhysRevB.92.035137 JUL 21 2015
Abstract:
We explore the ferromagnetic quantum critical point in a three-dimensional semimetallic system with upwardand downward-dispersing bands touching at the Fermi level. Evaluating the static spin susceptibility to leading order in the coupling between the fermions and the fluctuating ferromagnetic order parameter, we find that the ferromagnetic quantum critical point is masked by an incommensurate, longitudinal spin density wave phase. We first analyze an idealized model that, despite having strong spin-orbit coupling, still possesses O(3) rotational symmetry generated by the total angular momentum operator. In this case, the direction of the incommensurate spin density wave propagation can point anywhere, while the magnetic moment is aligned along the direction of propagation. Including symmetry-allowed anisotropies in the fermion dispersion and the coupling to the order parameter field, however, we find that the ordering wavevector instead breaks a discrete symmetry and aligns along either the [111] or [100] direction, depending on the signs and magnitudes of these two types of anisotropy.
Title:
Spin- and Pair-Density-Wave Glasses
Authors:
Mross, DF; Senthil, T Author Full Names: Mross, David F.; Senthil, T.
Source:
PHYSICAL REVIEW X, 5 (3):10.1103/PhysRevX.5.031008 JUL 20 2015
Abstract:
Spontaneous breaking of translational symmetry, known as density-wave order, is common in nature. However, such states are strongly sensitive to impurities or other forms of frozen disorder leading to fascinating glassy phenomena. We analyze impurity effects on a particularly ubiquitous form of broken translation symmetry in solids: a spin-density wave (SDW) with spatially modulated magnetic order. Related phenomena occur in pair-density-wave (PDW) superconductors where the superconducting order is spatially modulated. For weak disorder, we find that the SDW or PDW order can generically give way to a SDWor PDW glass-new phases of matter with a number of striking properties, which we introduce and characterize here. In particular, they exhibit an interesting combination of conventional (symmetry-breaking) and spin-glass (Edwards-Anderson) order. This is reflected in the dynamic response of such a system, which-as expected for a glass-is extremely slow in certain variables, but, surprisingly, is fast in others. Our results apply to all uniaxial metallic SDW systems where the ordering vector is incommensurate with the crystalline lattice. In addition, the possibility of a PDW glass has important consequences for some recent theoretical and experimental work on La2-xBaxCu2O4.
Title:
A magnetocaloric effect arising from a ferromagnetic transition in the martensitic state in Heusler alloy of Ni50Mn36Sb8Ga6
Authors:
Tian, FH; Zeng, YY; Xu, MW; Yang, S; Lu, T; Wang, JQ; Chang, TY; Adil, M; Zhang, Y; Zhou, C; Song, XP Author Full Names: Tian, Fanghua; Zeng, Yuyang; Xu, Minwei; Yang, Sen; Lu, Tao; Wang, Jieqiong; Chang, Tieyan; Adil, Murtaza; Zhang, Yin; Zhou, Chao; Song, Xiaoping
Source:
APPLIED PHYSICS LETTERS, 107 (1):10.1063/1.4926411 JUL 6 2015
Abstract:
We report a magnetocaloric effect with nearly zero thermal hysteresis in Heusler alloy of Ni50Mn36Sb8Ga6 around room temperature due to a ferromagnetic transition in martensitic state (FTMS). The refrigerant capacity value of this ferromagnetic transition in the vicinity of onset temperature T-M(C) can arrive at 163.8 J/kg, much higher than that of first-order magnetically martensitic transition in the same alloy. Such a magnetocaloric effect in FTMS is attributed to a second-order (or a weak first-order) transition from an antiferromagnetic phase with modulated 7M orthorhombic structure to a ferromagnetic phase with modulated 4O orthorhombic structure. (C) 2015 AIP Publishing LLC.

Update: 6-Aug-2015

Title:
Microstructural transformation of quasicrystalline AlFeCrTi extruded bars upon long thermal treatments
Authors:
Garcia-Escorial, A; Natale, E; Cremaschi, VJ; Todd, I; Lieblich, M Author Full Names: Garcia-Escorial, A.; Natale, E.; Cremaschi, V. J.; Todd, I.; Lieblich, M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 643 S199-S203; 1 10.1016/j.jallcom.2014.12.164 SEP 15 2015
Abstract:
Bulk Al93Fe3Cr2Ti2 bars extruded from gas atomised powder particles present a microstructure of an aluminium matrix reinforced with a spherical nanoquasicrystalline phase. In this work the evolution of the microstructure of Al93Fe3Cr2Ti2 extruded bars upon heating at 400 degrees C for up to 1000 h is investigated by means of X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. According to our observations we propose that the quasicrystalline alloy evolves in two steps: a first step consists in the decomposition of the supersaturated solid solution of the matrix and the quasicrystals, and a second step in the transformation of the quasicrystals into the equilibrium phases. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Characterization of aluminium matrix composites reinforced by Al-Cu-Fe quasicrystalline particles
Authors:
Litynska-Dobrzynska, L; Dutkiewicz, J; Stan-Glowinska, K; Wajda, W; Dembinski, L; Langlade, C; Coddet, C Author Full Names: Litynska-Dobrzynska, L.; Dutkiewicz, J.; Stan-Glowinska, K.; Wajda, W.; Dembinski, L.; Langlade, C.; Coddet, C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 643 S114-S118; 1 10.1016/j.jallcom.2014.11.125 SEP 15 2015
Abstract:
Aluminium matrix composites were consolidated from elemental Al powder and atomised Al65Cu20Fe15 particles by vacuum hot pressing technique. The spherical Al65Cu20Fe15 particles consisted of icosahedral quasicrystalline dendrites or cells and cubic tau-AlCu(Fe) phase located in interdendritic areas. The composites with different content of the reinforcement particles (20, 40 and 60 wt%) were prepared. All composites showed density about 99% and a good bonding between the Al65Cu20Fe15 particles and the matrix. It was shown that the phase composition of the atomised particles did not change after consolidation for the composite containing 20% and 40% added particles while Al2Cu precipitates formed at the Al/Al65Cu20Fe15 interfaces and inside the matrix in the composite with 60% of Al65Cu20Fe15 particles. With the increase of the volume fraction of the reinforcement in the composite the hardness as well as compressive strength increased reaching the value of 173 HV0.5 and 370 MPa, respectively for 60% of Al65Cu20Fe15 particles. The friction coefficient slightly varied in the range 0.5-0.7 depending on the composition. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Formation of Complex Intermetallics in the Al-Rich Part of Al-Pt-Ru
Authors:
Kapush, D; Samuha, S; Meshi, L; Velikanova, TY; Grushko, B Author Full Names: Kapush, D.; Samuha, S.; Meshi, L.; Velikanova, T. Ya.; Grushko, B.
Source:
JOURNAL OF PHASE EQUILIBRIA AND DIFFUSION, 36 (4):327-332; 10.1007/s11669-015-0385-3 AUG 2015
Abstract:
The study confirmed the stability of the previously reported ternary C-phase (, a = 0.77353(3) nm for Al73.5Pt10Ru16.5), whose composition was found to range between Al73Pt6Ru21 and Al73.5Pt14.5Ru12. The thermodynamically stable decagonal phase was revealed for the first time at 700-900 A degrees C in a small compositional region around Al78Pt6Ru16. It belongs to the D-4 structural type (1.65 nm periodicity in the specific direction). The metastable Al-Pt chi-phase (P31c) is stabilized by the addition of only similar to 1.5 at.% Ru and extends up to similar to 12 at.% Ru. The lattice parameters for Al76Pt18.6Ru5.4 are a = 1.2256(4) and c = 2.7331(4) nm.
Title:
Periodic almost-Schrodinger equation for quasicrystals
Authors:
Blinov, IV Author Full Names: Blinov, Igor V.
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep11492 JUL 24 2015
Abstract:
A new method for finding electronic structure and wavefunctions of electrons in quasiperiodic potential is introduced. To obtain results it uses slightly modified Schrodinger equation in spaces of dimensionality higher than physical space. It enables to get exact results for quasicrystals without expensive non-exact calculations.
Title:
Complex antiferromagnetic structure in the intermediate-valence intermetallic Ce-2 RuZn4
Authors:
Hartwig, S; Prokes, K; Hansen, T; Ritter, C; Gerke, B; Pottgen, R; Mydosh, JA; Forster, T Author Full Names: Hartwig, Steffen; Prokes, Karel; Hansen, Thomas; Ritter, Clemens; Gerke, Birgit; Poettgen, Rainer; Mydosh, J. A.; Foerster, Tobias
Source:
PHYSICAL REVIEW B, 92 (2):10.1103/PhysRevB.92.024420 JUL 17 2015
Abstract:
Neutron powder diffraction experiments were performed on the intermediate-valence Ce-2 RuZn4 intermetallic compound and combined with magnetic bulk measurements including high magnetic field experiments up to 58 T. Previous theoretical studies suggest that only one (here Ce1) out of two inequivalent Ce sites is magnetically active. Ce-2 RuZn4 orders antiferromagnetically at T-N = 2.3 K. The magnetic structure is characterized by an incommensurate propagation vector q(m) = (0.384, 0.384, 1/2). Assuming that the Ce2 site does not carry any substantial moment, Ce1 magnetic moments are confined to the (110)-type planes and transversely modulated with an amplitude of 1.77(3) mu(B).
Title:
Commensurate and incommensurate spin-density waves and the superconductivity dome in heavy electron systems
Authors:
Schlottmann, P Author Full Names: Schlottmann, P.
Source:
PHYSICAL REVIEW B, 92 (4):10.1103/PhysRevB.92.045115 JUL 16 2015
Abstract:
The nesting of the Fermi surfaces of an electron and a hole pocket separated by a nesting vector Q and the interaction between electrons gives rise to itinerant antiferromagnetism. The order can gradually be suppressed by mismatching the nesting and a quantum critical point is obtained as the Neel temperature tends to zero. If the vector Q is commensurate with the lattice (umklapp with Q = G/2), pairs of electrons can be transferred between the pockets and a superconducting dome above the quantum critical point may arise. If the vector Q is not commensurate with the lattice, there are eight phases that need to be considered: commensurate and incommensurate spin and charge density waves and four superconductivity phases, two of them with a modulated order parameter of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) type. The renormalization group equations are studied and numerically integrated. The phase diagram is obtained as a function of the mismatch of the Fermi surfaces and the magnitude of vertical bar Q - G/2 vertical bar.
Title:
Non-Fermi-Liquid Behavior in Metallic Quasicrystals with Local Magnetic Moments
Authors:
Andrade, EC; Jagannathan, A; Miranda, E; Vojta, M; Dobrosavljevic, V Author Full Names: Andrade, Eric C.; Jagannathan, Anuradha; Miranda, Eduardo; Vojta, Matthias; Dobrosavljevic, Vladimir
Source:
PHYSICAL REVIEW LETTERS, 115 (3):10.1103/PhysRevLett.115.036403 JUL 14 2015
Abstract:
Motivated by the intrinsic non-Fermi-liquid behavior observed in the heavy-fermion quasicrystal Au51Al34Yb15, we study the low-temperature behavior of dilute magnetic impurities placed in metallic quasicrystals. We find that a large fraction of the magnetic moments are not quenched down to very low temperatures T, leading to a power-law distribution of Kondo temperatures P(T-K) similar to T-K(alpha-1), with a nonuniversal exponent alpha, in a remarkable similarity to the Kondo-disorder scenario found in disordered heavy-fermion metals. For alpha < 1, the resulting singular P(T-K) induces non-Fermi-liquid behavior with diverging thermodynamic responses as T -> 0.

Update: 30-Jul-2015

Title:
Effect of Ti addition on the glass forming ability, crystallization, and plasticity of (Zr64.13Cu15.75Ni10.12Al10)(100-x)Ti-x bulk metallic glasses
Authors:
Shi, B; Xu, YL; Ma, WL; Li, C; Estefania, CV; Li, JG Author Full Names: Shi, Bo; Xu, Yuanli; Ma, Wenli; Li, Chao; Estefania, Carmen Verge; Li, Jiangong
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 639 345-349; 10.1016/j.msea.2015.04.100 JUL 15 2015
Abstract:
A series of (Zr(64.13)Cu(15.7)sNi(10.12)Al(10))(100-x)Ti-x (x=0-7) bulk metallic glasses were prepared by water-cooled copper mold casting method. The glass forming ability, crystallization behavior, and plasticity of the (Zr64.13Cu15.75Ni10.12Al10)(100-x)Ti-x alloys with different Ti contents were studied. The reduced glass transition temperature increases with Ti addition and a maximum value of 0.562 is achieved at x=5, indicating that the glass forming ability increases with Ti addition. Compared with that of one crystallization step for the sample without Ti addition, the Ti (x >= 2) containing alloys exhibit a two-step crystallization behavior. In addition, the initial crystallization temperature decreases from 744 to 684 K as x increases from 0 to 7. Icosahedral quasicrystal phase was found to precipitate in the amorphous matrix in the first crystallization step, implying that strong icosahedral short-range order may exist in the Ti (x >= 2) containing alloys. moreover, the (Zr64.13Cu15.75Ni10.12Al10)(100-x)Ti-x bulk metallic glasses exhibit excellent plasticity, i.e., a plastic engineering strain in compression larger than 80% for x <= 6. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Effects of Al-Cr-Fe Quasicrystal Content on Tribological Properties of Cold-Sprayed Titanium Composite Coatings
Authors:
Khun, NW; Li, RT; Loke, K; Khor, KA Author Full Names: Khun, N. W.; Li, R. T.; Loke, K.; Khor, K. A.
Source:
TRIBOLOGY TRANSACTIONS, 58 (4):616-624; 10.1080/10402004.2014.991860 2015
Abstract:
Titanium (Ti) composite coatings were prepared on commercially available Ti substrates via a cold-spray process. Quasicrystalline Al-Cr-Fe particles were incorporated in the cold-sprayed Ti matrices at different contents to form a new type of wear-resistant Ti composite coating. The tribological properties of the Ti composite coatings were systematically investigated using steel ball-on-disc microtribological testing. The incorporation of 10 wt% Al-Cr-Fe particles gave rise to the higher wear resistance of the Ti composite coating than that of the Ti coating due to the higher wear resistance of the Al-Cr-Fe particles than that of the Ti matrix. As a result, an increase in the Al-Cr-Fe particle content to 20 wt% increased the wear resistance of the Ti composite coating. However, the wear resistance of the Ti composite coating decreased with a further increase in the Al-Cr-Fe particle content to 30 wt% due to the significantly increased volume of micropores in the composite coating. It could be concluded that the Ti composite coating with 20 wt% Al-Cr-Fe particles had the highest wear resistance among the cold-sprayed coatings used in this study.
Title:
Complex physical properties of EuMgSi - a complementary study by neutron powder diffraction and Eu-151 Mossbauer spectroscopy
Authors:
Niehaus, O; Ryan, DH; Flacau, R; Lemoine, P; Chernyshov, D; Svitlyk, V; Cuervo-Reyes, E; Slabon, A; Nesper, R; Schellenberg, I; Pottgen, R Author Full Names: Niehaus, O.; Ryan, D. H.; Flacau, R.; Lemoine, P.; Chernyshov, D.; Svitlyk, V.; Cuervo-Reyes, E.; Slabon, A.; Nesper, R.; Schellenberg, I.; Poettgen, R.
Source:
JOURNAL OF MATERIALS CHEMISTRY C, 3 (27):7203-7215; 10.1039/c5tc01017a 2015
Abstract:
X-ray pure samples of EuMgSi were synthesized by reactions of the elements in sealed niobium tubes using a high frequency and subsequently a resistance furnace. The structure was investigated by single crystal X-ray diffraction: TiNiSi-type, Pnma, a = 769.5(2), b = 455.0(1), c = 836.9(2) pm, wR(2) = 0.033 [I > 2 sigma(I)], and 705 F-2 values with 20 variables. Powder synchrotron radiation diffraction experiments did not reveal any structural changes down to 4.3 K. Magnetic susceptibility data and Eu-151 Mossbauer spectra clearly indicate a stable Eu2+ configuration. Two distinct magnetic anomalies around 12 and 14 K can be observed for different samples with dc- and ac-susceptibility, heat capacity and resistivity measurements. Fitting of hyperfine field splitting as a function of temperature (Eu-151 Mossbauer spectroscopy data) with a Brillouin function also leads to a magnetic ordering around 14 K. Electronic structure calculations in coincidence with the resistivity measurement prove narrow (or nearly zero) gap-semiconducting behaviour. The calculated band gap energy of 0.03 eV should be considered with precautions due to the accuracy of this method. An incommensurate magnetic structure with the propagation vector k = [q(x) approximate to 0.37, 0, 0] was determined using neutron diffraction data at 5.5 K. In consensus of dc- and ac-susceptibility and neutron powder diffraction a complex combination of antiferromagnetic and ferromagnetic interactions, most likely by super-exchange, is confirmed. These cause two magnetic ordering temperatures, though only one independent crystallographic Eu site in terms of the crystal structure is present in EuMgSi.

Update: 23-Jul-2015

Title:
Microstructure and mechanical properties of sand mold cast Mg-4.58Zn-2.6Gd-0.18Zr magnesium alloy after different heat treatments
Authors:
Liu, SJ; Yang, GY; Luo, SF; Jie, WQ Author Full Names: Liu, S. J.; Yang, G. Y.; Luo, S. F.; Jie, W. Q.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 644 846-853; 10.1016/j.jallcom.2015.05.062 SEP 25 2015
Abstract:
Microstructure and mechanical properties of sand mold cast Mg-4.58Zn-2.6Gd-0.18Zr magnesium alloy after different heat treatments were investigated. As-cast alloy was composed of alpha(Mg) matrix, interdendritic alpha(Mg) + W(Mg3Zn3Gd2) eutectic, icosahedral quasicrystalline I(Mg3Zn6Gd) phase and Mg3Gd particles within alpha(Mg) matrix. After solution treatment at 505 degrees C for 16 h, most of alpha(Mg) + W(Mg3Zn3Gd2) eutectic dissolved into alpha(Mg) matrix, but a new phase, Zn2Zr3, precipitated within alpha(Mg) matrix. The appropriate aging treatment was done at 220 degrees C for 16 h, after which some dispersive fine eutectics re-precipitated along the grain boundary. Furthermore, rod-like beta(1)' and plate-like beta(2)' formed within alpha(Mg) matrix. The ultimate tensile strength, yield strength and elongation of the experimental alloy in the T6 state at room temperature were 280 MPa, 175 MPa and 7.5%, respectively. According to strengthening contribution calculation, it is revealed that both the second phase strengthening and the solid solution strengthening played important roles in improving the mechanical properties after T6 treatment. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Hot compression characteristics and processing maps of a cast Mg-9.5Zn-2.0Y alloy with icosahedral quasicrystalline phase
Authors:
Kwak, TY; Lim, HK; Kim, WJ Author Full Names: Kwak, T. Y.; Lim, H. K.; Kim, W. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 644 645-653; 10.1016/j.jallcom.2015.04.158 SEP 25 2015
Abstract:
Hot compressive characteristics and processing maps of a cast Mg-9.5Zn-2.0Y alloy with I-phase (ZW92) were studied in the temperature range between 523 and 723 K and in the strain rate range between 10(-3) and 10 s(-1). According to the analysis of deformation behavior, the rate-controlling mechanism governing deformation during entire compression process was lattice diffusion controlled dislocation climb creep and power-law breakdown. Comparison of the processing maps of ZW92 with those of the cast Mg-Zn-Y alloys with different types of intermetallic compounds (W- and long period stacking ordered phases) and the cast Mg-Al-Zn alloy (AZ80) alloy with beta-Mg17Al12 phase in terms of eta values and the domain sizes of the unstable regime indicated that ZW92 exhibited a better hot workability at high strain rates above 1 s-1. This result was attributed to the suppression of power law breakdown in ZW92 due to occurrence of extensive dynamic recrystallization at high strain rates, which was facilitated by the effective fragmentation and dispersion of I-phase during deformation at high strain rates. A fully recrystallized microstructure composed of defect-free fine grains (9.34 mu m) with high fraction of high angle grain boundaries (0.81) was obtained at 623 K - 10 s(-1). (C) 2015 Elsevier B.V. All rights reserved.

Update: 16-Jul-2015

Title:
Structural crossover from nonmodulated to long-period modulated tetragonal phase and anomalous change in ferroelectric properties in the lead-free piezoelectric Na1/2Bi1/2TiO3-BaTiO3
Authors:
Rao, BN; Khatua, DK; Garg, R; Senyshyn, A; Ranjan, R Author Full Names: Rao, Badari Narayana; Khatua, Dipak Kumar; Garg, Rohini; Senyshyn, Anatoliy; Ranjan, Rajeev
Source:
PHYSICAL REVIEW B, 91 (21):10.1103/PhysRevB.91.214116 JUN 29 2015
Abstract:
The highly complex structure-property interrelationship in the lead-free piezoelectric (x) Na1/2Bi1/2TiO3 - (1 - x) BaTiO3 is a subject of considerable contemporary debate. Using comprehensive x-ray, neutron diffraction, dielectric, and ferroelectric studies, we have shown the existence of a new criticality in this system at x = 0.80, i.e., well within the conventional tetragonal phase field. This criticality manifests as a nonmonotonic variation of the tetragonality and coercivity and is shown to be associated with a crossover from a nonmodulated tetragonal phase (for x < 0.8) to a long-period modulated tetragonal phase (for x > 0.80). It is shown that the stabilization of long-period modulation introduces a characteristic depolarization temperature in the system. While differing qualitatively from the two-phase model often suggested for the critical compositions of this system, our results support the view with regard to the tendency in perovskites to stabilize long-period modulated structures as a result of complex interplay of antiferrodistortive modes [Bellaiche and Iniguez, Phys. Rev. B 88, 014104 ( 2013); Prosandeev, Wang, Ren, Iniguez, ands Bellaiche, Adv. Funct. Mater. 23, 234 (2013)].
Title:
Crystal structure, incommensurate magnetic order, and ferroelectricity in Mn1-xCuxWO4 (0 <= x <= 0.19)
Authors:
Kumar, CMN; Xiao, Y; Lunkenheimer, P; Loidl, A; Ohl, M Author Full Names: Kumar, C. M. N.; Xiao, Y.; Lunkenheimer, P.; Loidl, A.; Ohl, M.
Source:
PHYSICAL REVIEW B, 91 (23):10.1103/PhysRevB.91.235149 JUN 29 2015
Abstract:
We have carried out a systematic study on the effect of Cu doping on nuclear, magnetic, and dielectric properties in Mn1-xCuxWO4 for 0 <= x <= 0.19 by a synergic use of different techniques, viz, heat capacity, magnetization, dielectric, and neutron powder diffraction measurements. Via heat capacity and magnetization measurements we show that with increasing Cu concentration magnetic frustration decreases, which leads to the stabilization of commensurate magnetic ordering. This was further verified by temperature-dependent unit cell volume changes derived from neutron diffraction measurements which was modeled by the Gruneisen approximation. Dielectric measurements show a low temperature phase transition below about 9-10 K. Furthermore, magnetic refinements reveal no changes below this transition indicating a possible spin-flop transition which is unique to the Cu doped system. From these combined studies we have constructed a magnetoelectric phase diagram of this compound.
Title:
Interplay between magnetic order at Mn and Tm sites alongside the structural distortion in multiferroic films of o-TmMnO3
Authors:
Windsor, YW; Ramakrishnan, M; Rettig, L; Alberca, A; Bothschafter, EM; Staub, U; Shimamoto, K; Hu, Y; Lippert, T; Schneider, CW Author Full Names: Windsor, Y. W.; Ramakrishnan, M.; Rettig, L.; Alberca, A.; Bothschafter, E. M.; Staub, U.; Shimamoto, K.; Hu, Y.; Lippert, T.; Schneider, C. W.
Source:
PHYSICAL REVIEW B, 91 (23):10.1103/PhysRevB.91.235144 JUN 26 2015
Abstract:
We employ resonant soft x-ray diffraction to individually study the magnetic ordering of the Mn and the Tm sublattices in single-crystalline films of orthorhombic (o-)TmMnO3. The same magnetic ordering wave vector of (0 q 0) with q approximate to 0.46 is found for both ionic species, suggesting that the familiar antiferromagnetic order of the Mn ions induces a magnetic order on the Tm unpaired 4f electrons. Indeed, intensity variations of magnetic reflections with temperature corroborate this scenario. Calculated magnetic fields at the Tm sites are used as a model magnetic structure for the Tm, which correctly predicts intensity variations at the Tm resonance upon azimuthal rotation of the sample. The model allows ruling out a bc-cycloid modulation of the Mn ions as the cause for the incommensurate ordering, as found in TbMnO3. The structural distortion, which occurs in the ferroelectric phase below T-C, was followed through nonresonant diffraction of structural reflections forbidden by the high-temperature crystal symmetry. The (0 q 0) magnetic reflection appears at the Mn resonance well above T-C, indicating that this reflection is sensitive also to the intermediate sinusoidal magnetic phase. The model presented suggests that the Tm 4f electrons are polarized well above the ferroelectric transition and are possibly not affected by the transition at T-C. The successful description of the induced order observed at the Tm resonance is a promising example for future element-selective studies in which "spectator" ions may allow access to previously unobtainable information about other constituent ions.
Title:
Superspace crystallography: a key to the chemistry and properties
Authors:
Pinheiro, CB; Abakumov, AM Author Full Names: Pinheiro, Carlos Basilio; Abakumov, Artem M.
Source:
IUCRJ, 2 137-154; 10.1107/S2052252514023550 1 JAN 2015
Abstract:
An overview is given of the recent advances in the field of modulated molecular and inorganic crystals with an emphasis on the links between incommensurability, intermolecular and interatomic interactions and, wherever possible, the properties of the materials. The importance of detailed knowledge on the modulated structure for understanding the crystal chemistry and the functional properties of modulated phases is shown using selected examples of incommensurate modulations in organic molecular compounds and inorganic complex oxides.
Title:
A CENTURY OF X-RAY CRYSTALLOGRAPHY AND 2014 INTERNATIONAL YEAR OF X-RAY CRYSTALLOGRAPHY
Authors:
Kojic-Prodic, B Author Full Names: Kojic-Prodic, Biserka
Source:
MACEDONIAN JOURNAL OF CHEMISTRY AND CHEMICAL ENGINEERING, 34 (1):19-32; 2015
Abstract:
The 100(th) anniversary of the Nobel prize awarded to Max von Laue in 1914 for his discovery of diffraction of X-rays on a crystal marked the beginning of a new branch of science - X-ray crystallography. The experimental evidence of von Laue's discovery was provided by physicists W. Friedrich and P. Knipping in 1912. In the same year, W. L. Bragg described the analogy between X-rays and visible light and formulated the Bragg's law, a fundamental relation that connected the wave nature of X-rays and fine structure of a crystal at atomic level. In 1913 the first simple diffractometer was constructed and structure determination started by the Braggs, father and son. In 1915 their discoveries were acknowledged by a Nobel Prize in physics. Since then, X-ray diffraction has been the basic method for determination of three-dimensional structures of synthetic and natural compounds. The three-dimensional structure of a substances defines its physical, chemical, and biological properties. Over the past century the significance of X-ray crystallography has been recognized by about forty Nobel prizes. X-ray structure analysis of simple crystals of rock salt, diamond and graphite, and later of complex biomolecules such as B12-vitamin, penicillin, haemoglobin/myoglobin, DNA, and biomolecular complexes such as viruses, chromatin, ribozyme, and other molecular machines have illustrated the development of the method. Among these big discoveries the double helix DNA structure was an epochal achievement of the 20(th) century. These discoveries, together with many others of the X-ray crystallography, have completely changed our views and helped to develop other new fields of science such as molecular genetics, biophysics, structural molecular biology, material science, and many others. During the last decade, the implementation of free electron X-ray lasers, a new experimental tool, has opened up femtosecond dynamic crystallography. This highly advanced methodology enables to solve the structures and dynamics of the most complex biological assemblies involved in a cell metabolism. The advancements of science and technology over the 20th and 21(st) centuries are of great influence on our views in almost all human activities. The importance of Xray crystallography for science and technology advocates for its high impact on a wide area of research and declares it as a highly interdisciplinary science. In short, crystallography has defined the shape of the modern world. Focusing on single crystal diffraction, this essay tackles only one field of crystallography; the comprehensive review on X-ray crystallography can hardly be fitted into a single article. The aim with this review was to highlight the most striking examples illustrating some of the milestones over the past century.
Title:
A modulation wave approach to the order hidden in disorder
Authors:
Withers, R Author Full Names: Withers, Ray
Source:
IUCRJ, 2 74-84; 10.1107/S2052252514022556 1 JAN 2015
Abstract:
The usefulness of a modulation wave approach to understanding and interpreting the highly structured continuous diffuse intensity distributions characteristic of the reciprocal spaces of the very large family of inherently flexible materials which exhibit ordered 'disorder' is pointed out. It is shown that both longer range order and truly short-range order are simultaneously encoded in highly structured diffuse intensity distributions. The long-range ordered crystal chemical rules giving rise to such diffuse distributions are highlighted, along with the existence and usefulness of systematic extinction conditions in these types of structured diffuse distributions.

Update: 9-Jul-2015

Title:
Microwave sol-gel synthesis and upconversion photoluminescence properties of CaGd2(WO4)(4):Er3+/Yb3+ phosphors with incommensurately modulated structure
Authors:
Lim, CS; Aleksandrovsky, A; Molokeev, M; Oreshonkov, A; Atuchin, V Author Full Names: Lim, Chang Sung; Aleksandrovsky, Aleksandr; Molokeev, Maxim; Oreshonkov, Aleksandr; Atuchin, Victor
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 228 160-166; 10.1016/j.jssc.2015.04.032 AUG 2015
Abstract:
CaGd2-x(WO4)(4):Er3+/Yb3+ phosphors with the doping concentrations of Er3+ and Yb3+ (x=Er3++Yb3+, Er3+=0.05, 0.1, 0.2 and Yb3+=0.2, 0.45) have been successfully synthesized by the microwave sol-gel method. The crystal structure of CaGd2-x(WO4)(4):Er3+/Yb3+ tungstates have been refined, and upconversion photoluminescence properties have been investigated. The synthesized particles, being formed after the heat-treatment at 900 degrees C for 16 h, showed a well crystallized morphology. Under the excitation at 980 nm, CaGd2(WO4)(4):Er3+/Yb3+ particles exhibited a strong 525-nm and a weak 550-nm emission bands in the green region and a very weak 655-nm emission band in the red region. The Raman spectrum of undoped CaGd2(WO4)(4) revealed about 12 narrow lines. The strongest band observed at 903 cm(-1) was assigned to the v(1) symmetric stretching vibration of WO4 tetrahedrons. The spectra of the samples doped with Er and Yb obtained under the 514.5 nm excitation were dominated by Er3+ luminescence preventing the recording of these samples Raman spectra. Concentration quenching of the erbium luminescence at H-2(11/2)-> I-4(15/2) transition is weak in the range of erbium doping level x(Er)=0.05-0.2, while, for transition S-4(3/2)-> 4I(15/2), the signs of concentration quenching become pronounced at x(Er)=0.2. (C) 2015 Elsevier Inc. All rights reserved.
Title:
Direct evidence for stress-induced transformation between coexisting multiple martensites in a Ni-Mn-Ga multifunctional alloy
Authors:
Huang, L; Cong, DY; Wang, ZL; Nie, ZH; Dong, YH; Zhang, Y; Ren, Y; Wang, YD Author Full Names: Huang, L.; Cong, D. Y.; Wang, Z. L.; Nie, Z. H.; Dong, Y. H.; Zhang, Y.; Ren, Y.; Wang, Y. D.
Source:
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 48 (26):10.1088/0022-3727/48/26/265304 JUL 8 2015
Abstract:
The structural response of coexisting multiple martensites to stress field in a Ni-Mn-Ga multifunctional alloy was investigated by the in situ high-energy x-ray diffraction technique. Stress-induced transformation between coexisting multiple martensites was observed at 110 K, at which five-layered modulated (5M), seven-layered modulated (7M) and non-modulated (NM) martensites coexist. We found that a tiny stress of as low as 0.5 MPa could trigger the transformation from 5M and 7M martensites to NM martensite and this transformation is partly reversible. Besides the transformation between coexisting multiple martensites, rearrangement of martensite variants also occurs during loading, at least at high stress levels. The present study is instructive for designing advanced multifunctional alloys with easy actuation.
Title:
Quasicrystal dissolution and performance of isothermally heat-treated Mg-Zn-Y alloy
Authors:
Wan, DQ; Luo, X; Liu, YJ; Yu, T Author Full Names: Wan, Di-Qing; Luo, Xian; Liu, Ya-Juan; Yu, Tian
Source:
RARE METALS, 34 (7):452-456; 10.1007/s12598-013-0119-9 JUL 2015
Abstract:
Conventional casting method was employed to prepare Mg-Zn-Y alloy only with alpha-Mg+I-phase; however, the grain size of quasicrystal is quite large in the as-cast state. Therefore, isothermal treatment was applied to refine the quasicrystal phase. The result shows that after the Mg-Zn-Y alloy was isothermally treated at 500 degrees C for several hours, the coarse quasicrystal can be gradually dissolved and thus refined. Generally, the dissolving processes of quasicrystal are slow first and then accelerate; after isothermally treated with 8 h at 500 degrees C, the quasicrystal is almost completely dissolved into the matrix only with 1-5 mu m tiny quasicrystals remained. Refinement of quasicrystal can markedly reduce the wear resistance, but increase the corrosion resistance.
Title:
How important is the {103} plane of stable Ge2Sb2Te5 for phase-change memory?
Authors:
Zhang, W; Zheng, WT; Kim, JG; Cui, XQ; Li, L; Qi, JG; Kim, YJ; Song, SA Author Full Names: Zhang, W.; Zheng, W. T.; Kim, J. -G.; Cui, X. Q.; Li, L.; Qi, J. G.; Kim, Y. -J.; Song, S. A.
Source:
JOURNAL OF MICROSCOPY, 259 (1):10-15; 10.1111/jmi.12242 JUL 2015
Abstract:
Closely correlating with {200} plane of cubic phase, {103} plane of hexagonal phase of Ge2Sb2Te5 plays a crucial role in achieving fast phase change process as well as formation of modulation structures, dislocations and twins in Ge2Sb2Te5. The behaviors of {103} plane of hexagonal phase render the phase-change memory process as a nanoscale shape memory. Lay description Exploring the phase-change mechanism, structures and properties of chalcogenides has been currently one of the hot topics. Ge-Sb-Te chalcogenides are of tremendous technological importance ranging from optical data storage to PRAM. Exhibiting the best performance for DVD-RAM in terms of speed and stability, Ge2Sb2Te5 is currently the most important phase-change alloy. There exist three solid phases in Ge2Sb2Te5: amorphous, metastable rocksalt (FCC) and stable hexagonal (Hex) phases. The whole switching operation in optical data storage and electronic memories is based on the following rapid cycling processes by either laser or electric heating: amorphousFCC (Erase/SET process)Hexliquidamorphous (Write/RESET process). The stable Hex is an indispensable concern to bridge the aforementioned whole cycling framework. In this work, structural correlations between the two crystalline phases were analyzed and the rich structural phenomena were unraveled. Closely correlated with {200} plane of FCC phase, {103} plane of Hex phase of Ge2Sb2Te5 plays a crucial role in achieving fast phase change process as well as formation of modulation structures, dislocations and twins in Ge2Sb2Te5. We propose that from a point view of maintaining the ultra-high transition speed, (103) of Hex phase can effectively facilitate phase-change memory. This leads to a novel concept that phase-change process can be treated as a nanoscale shape-memory, towards essential understanding of the relevant structural features of Ge-Sb-Te chalcogenides.
Title:
Antiferromagnetic Dichroism in a Complex Multisublattice Magnetoelectric CuB2O4
Authors:
Boldyrev, KN; Pisarev, RV; Bezmaternykh, LN; Popova, MN Author Full Names: Boldyrev, K. N.; Pisarev, R. V.; Bezmaternykh, L. N.; Popova, M. N.
Source:
PHYSICAL REVIEW LETTERS, 114 (24):10.1103/PhysRevLett.114.247210 JUN 19 2015
Abstract:
Magnetic control of the crystal chirality was announced by Saito et al. [Phys. Rev. Lett. 101, 117402 (2008)] on the ground of experiments in CuB2O4. This claim has raised a sharp dispute in the literature because it seemed to contradict the fundamental symmetry principles. We settle this dispute on the basis of a high-resolution optical spectroscopy study of excitonic transitions in CuB2O4. We find that a large sublattice-sensitive antiferromagnetic linear dichroism (LD) emerges at the Neel temperature T-N = 21 K and show how it could simulate a "magnetic-field control of the crystal chirality." We prove that the discovered LD is related microscopically to the magnetic Davydov splitting. This LD is highly sensitive to subtle changes in the spin subsystems, which allowed us to observe a splitting of the phase transition into an incommensurate magnetic phase into two transitions (T-1* = 8.5 and T-2* = 7.9 K) and to suggest elliptical spiral structures below T-1*, instead of a simple circular helix proposed earlier.
Title:
Lattice vibrations in the Frenkel-Kontorova model. I. Phonon dispersion, number density, and energy
Authors:
Meng, QP; Wu, LJ; Welch, DO; Zhu, YM Author Full Names: Meng, Qingping; Wu, Lijun; Welch, David O.; Zhu, Yimei
Source:
PHYSICAL REVIEW B, 91 (22):10.1103/PhysRevB.91.224305 JUN 17 2015
Abstract:
We studied the lattice vibrations of two interpenetrating atomic sublattices via the Frenkel-Kontorova (FK) model of a linear chain of harmonically interacting atoms subjected to an on-site potential using the technique of thermodynamic Green's functions based on quantum field-theoretical methods. General expressions were deduced for the phonon frequency-wave-vector dispersion relations, number density, and energy of the FK model system. As the application of the theory, we investigated in detail cases of linear chains with various periods of the on-site potential of the FK model. Some unusual but interesting features for different amplitudes of the on-site potential of the FK model are discussed. In the commensurate structure, the phonon spectrum always starts at a finite frequency, and the gaps of the spectrum are true ones with a zero density of modes. In the incommensurate structure, the phonon spectrum starts from zero frequency, but at a nonzero wave vector; there are some modes inside these gap regions, but their density is very low. In our approximation, the energy of a higher-order commensurate state of the one-dimensional system at a finite temperature may become indefinitely close to the energy of an incommensurate state. This finding implies that the higher-order incommensurate-commensurate transitions are continuous ones and that the phase transition may exhibit a "devil's staircase" behavior at a finite temperature.
Title:
Lattice vibrations in the Frenkel-Kontorova Model. II. Thermal conductivity
Authors:
Meng, QP; Wu, LJ; Welch, DO; Zhu, YM Author Full Names: Meng, Qingping; Wu, Lijun; Welch, David O.; Zhu, Yimei
Source:
PHYSICAL REVIEW B, 91 (22):10.1103/PhysRevB.91.224306 JUN 17 2015
Abstract:
We applied the formulas for the phonon spectral-density function that we presented in the previous paper of this series to analyze the thermal conductivity of the lattice in the framework of the Frenkel-Kontorova (FK) model. We found that two extra mechanisms of phonon scattering (different from the point impurities, three-phonon processes, and boundary scattering typical of all crystals), viz., resonance, and anharmonic scattering, that mainly influences the thermal conductivity of the lattice. The frequencies of resonance scattering are discrete, and their number increases from a finite number to infinity with their transition from the commensurate to the incommensurate state. Changing the amplitude and period of the FK model changes the frequencies and the frequency number of resonance scattering and the intensity of anharmonic scattering. We analyze these changes in detail. Our theory can explain all existing numerical results on this problem and suggest strategies to reduce the thermal conductivity of the lattice of layered materials.
Title:
Characterization of deep level defects and thermally stimulated depolarization phenomena in La-doped TlInS2 layered semiconductor
Authors:
Seyidov, MY; Suleymanov, RA; Mikailzade, FA; Kargin, EO; Odrinsky, AP Author Full Names: Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Mikailzade, Faik A.; Kargin, Elif Orhan; Odrinsky, Andrei P.
Source:
JOURNAL OF APPLIED PHYSICS, 117 (22):10.1063/1.4922347 JUN 14 2015
Abstract:
Lanthanum-doped high quality TlInS2 (TlInS2: La) ferroelectric-semiconductor was characterized by photo-induced current transient spectroscopy (PICTS). Different impurity centers are resolved and identified. Analyses of the experimental data were performed in order to determine the characteristic parameters of the extrinsic and intrinsic defects. The energies and capturing cross section of deep traps were obtained by using the heating rate method. The observed changes in the Thermally Stimulated Depolarization Currents (TSDC) near the phase transition points in TlInS2: La ferroelectric-semiconductor are interpreted as a result of self-polarization of the crystal due to the internal electric field caused by charged defects. The TSDC spectra show the depolarization peaks, which are attributed to defects of dipolar origin. These peaks provide important information on the defect structure and localized energy states in TlInS2: La. Thermal treatments of TlInS2: La under an external electric field, which was applied at different temperatures, allowed us to identify a peak in TSDC which was originated from La-dopant. It was established that deep energy level trap BTE43, which are active at low temperature (T <= 156 K) and have activation energy 0.29 eV and the capture cross section 2.2 x 10(-14) cm(2), corresponds to the La dopant. According to the PICTS results, the deep level trap center B5 is activated in the temperature region of incommensurate (IC) phases of TlInS2: La, having the giant static dielectric constant due to the structural disorders. From the PICTS simulation results for B5, native deep level trap having an activation energy of 0.3 eV and the capture cross section of 1.8 x 10(-16) cm(2) were established. A substantial amount of residual space charges is trapped by the deep level localized energy states of B5 in IC-phase. While the external electric field is applied, permanent dipoles, which are originated from the charged B5 deep level defects, are aligned in the direction of the applied electric field and the equilibrium polarization can be reached in a relatively short time. When the polarization field is maintained, while cooling the temperature of sample to a sufficiently low degrees, the relaxation times of the aligned dipoles drastically increases. Practically, frozen internal electric field or electrets states remain inside the TlInS2: La when the applied bias field is switched off. The influence of deep level defects on TSDC spectra of TlInS2: La has been revealed for the first time. (C) 2015 AIP Publishing LLC.
Title:
Coexistence of the spin and electron-hole quantum liquids in frustrated manganites La1-y Sm (y) MnO3+delta
Authors:
Bukhanko, FN; Bukhanko, AF Author Full Names: Bukhanko, F. N.; Bukhanko, A. F.
Source:
PHYSICS OF THE SOLID STATE, 57 (6):1114-1127; 10.1134/S1063783415060062 JUN 2015
Abstract:
The structural, electronic, and magnetic phase transformations induced in the temperature range of 4.2-300 K by the isovalent substitution of the rare-earth Sm3+ ion for the La3+ ion with a larger radius have been investigated in the system of self-doped manganites La1-y Sm (y) MnO3+delta (delta similar to 0.1, 0 a parts per thousand currency sign y a parts per thousand currency sign 1). It has been found using the X-ray diffraction analysis that the substitution La -> Sm is accompanied by a significant increase of the GdFeO3-type and Jahn-Teller-type lattice distortions. At a temperature of 300 K, an increase in the Sm concentration y leads to a concentration phase transition from the pseudocubic O* phase to the orthorhombic O phase, as well as to the appearance of an s-shaped anomaly of the lattice parameter a at concentrations y a parts per thousand yen 0.4 and an anomalous peak in the concentration dependence of the electrical resistance R(y) near y a parts per thousand 0.85. The magnetic T-y-aOE (c) r (A) phase diagrams of the La1-y Sm (y) MnO3+delta system in the temperature range of 4.2-250 K have been constructed according to the results of measurements of the temperature dependences of the direct-current (dc) magnetization M(T). It has been revealed that the samples with y a parts per thousand yen 0.8 exhibit signs of the melting of the A- and CE-type modulated antiferromagnetic (AFM) structures in the form of an anomalous decrease both in the critical temperature of the transition to a frustrated AFM state and in the magnetization of the samples with an increase in the concentration y. The anomalies observed in the temperature dependences of the alternating-current (ac) dielectric permittivity of the La1-y Sm (y) MnO3+delta samples have been explained within the existing concepts of the Bose-Einstein condensation of an electron-hole liquid in the form of metallic droplets in an excitonic insulator.

Update: 2-Jul-2015

Title:
Ni- and Cu-free Ti-based metallic glasses with potential biomedical application
Authors:
Guo, Y; Bataev, I; Georgarakis, K; Jorge, AM; Nogueira, RP; Pons, M; Yavari, AR Author Full Names: Guo, Y.; Bataev, I.; Georgarakis, K.; Jorge, A. M., Jr.; Nogueira, R. P.; Pons, M.; Yavari, A. R.
Source:
INTERMETALLICS, 63 86-96; 10.1016/j.intermet.2015.04.004 AUG 2015
Abstract:
In the present work Ti-Fe-Si and Ti-Fe-Si-X (X = Zr, Pd, Ge) glassy alloys are discussed as potential biomedical materials. Depending on composition and experimental conditions these alloys possess glassy, quasicrystalline or crystalline structure. The glassy state and crystallization behavior of the melt spun ribbons were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and the Hank's solution was used as simulated body fluid for corrosion tests. Ternary Ti-Fe-Si alloys near the Ti65Fe30Si5 eutectic point were prone to form quasicrystals if the cooling rate was not high enough to retain amorphous structure. The compositions on the steeper side of the eutectic point could be vitrified. The results indicate that small additions of Zr can have a positive effect on glass formation, while additions of Ge, Pd may have a detrimental effect by promoting crystallization. Ti Fe Si and Ti Fe Si Zr alloys exhibited high corrosion properties, superior to that of pure Ti and most of Ti-based glassy alloys reported in the literature. Being free of Ni and Cu this group of alloys may be considered for possible biomedical application. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Amorphous-i phase-big cube-amorphous cyclic phase transformation of mechanically alloyed Zr75Ni20Al5 system
Authors:
El-Eskandarany, MS Author Full Names: El-Eskandarany, M. Sherif
Source:
INTERMETALLICS, 63 27-36; 10.1016/j.intermet.2015.01.010 AUG 2015
Abstract:
Cyclic glassy-metastable-glassy phase transformations were investigated during mechanical alloying of Zr75Ni20Al5 powders, using high-energy ball milling technique. After 20 h of continuous milling, a single glassy phase was obtained. The synthesized glassy powder, which is homogeneous in structure and composition, showed a glass transition temperature lied at 510 degrees C and a large supercooled liquid region extended to 86.5 degrees C. This glassy phase, which crystallized through a single sharp exothermic peak at 596.5 degrees C, tended to transformed into icosahedral (i-phase) nano-quasicrystalline grains upon further milling to 30 h. This i-phase showed serious instability against the mechanical deformations generated by the milling tools, and hence transformed into big cube phase with increasing the milling time to 45 h. In a cyclic phase transformation the obtained big cube phase subsequently transformed into the same glassy phase after 60 h of milling. This observed cyclic phase transformation was observed twice upon further milling to 90 h without serious compositional changes. The iron contamination contents in the ball-milled powders had constant values of about 0.16 wt.% and did not change with changing the structure of the powders. The present work shows that this phenomenon does not have any obvious analogues with the periodic redox reactions or with diffusive-reactive phenomena known in chemistry. On the basis of our results, the destabilizing effect of the defects created by the milling media (balls), which leads to the cyclic transformations, depends on the milling time. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Direct observation of solid-state reversed transformation from crystals to quasicrystals in a Mg alloy
Authors:
Liu, JF; Yang, ZQ; Ye, HQ Author Full Names: Liu, Jian-Fang; Yang, Zhi-Qing; Ye, Heng-Qiang
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep09816 JUN 12 2015
Abstract:
Phase transformation of quasicrystals is of interest in various fields of science and technology. Interestingly, we directly observed unexpected solid-state epitaxial nucleation and growth of Zn6Mg3Y icosahedral quasicrystals in a Mg alloy at about 573 K which is about 300 K below the melting point of Zn6Mg3Y, in contrast to formation of quasicrystals through solidification that was usually found in many alloys. Maximizing local packing density of atoms associated with segregation of Y and Zn in Mg adjacent to Mg/Zn3MgY interfaces triggered atomic rearrangement in Mg to form icosahedra coupled epitaxially with surface distorted icosahedra of Zn3MgY, which plays a critical role in the nucleation of icosahedral clusters. A local Zn: Mg: Y ratio close to 6:3:1, corresponding to a valence electron concentration of about 2.15, should have been reached to trigger the formation of quasicrystals at Mg/Zn3MgY interfaces. The solid-state icosahedral ordering in crystals opens a new window for growing quasicrystals and understanding their atomic origin mechanisms. Epitaxial growth of quasicrystals onto crystals can modify the surface/interface structures and properties of crystalline materials.
Title:
Bulk electronic structure of Zn-Mg-Y and Zn-Mg-Dy icosahedral quasicrystals
Authors:
Nayak, J; Maniraj, M; Gloskovskii, A; Krajci, M; Sebastian, S; Fisher, IR; Horn, K; Barman, SR Author Full Names: Nayak, J.; Maniraj, M.; Gloskovskii, A.; Krajci, M.; Sebastian, S.; Fisher, I. R.; Horn, K.; Barman, S. R.
Source:
PHYSICAL REVIEW B, 91 (23):10.1103/PhysRevB.91.235116 JUN 11 2015
Abstract:
We use bulk sensitive hard x-ray photoelectron spectroscopy to provide unambiguous evidence for a pseudogap in the density of states around the Fermi level in icosahedral Zn-Mg-Y and Zn-Mg-Dy quasicrystals, in agreement with our density functional theory calculations. The pseudogap in these Zn-based quasicrystals is less pronounced compared to the Al-based ones such as Al-Pd-Mn and Al-Cu-Fe [J. Nayak et al., Phys. Rev. Lett. 109, 216403 ( 2012)]. This observation is in agreement with transport studies that indicate a larger charge carrier concentration in the Zn-based quasicrystals. Compared to Zn-Mg-Dy, the pseudogap is somewhat deeper in Zn-Mg-Y. The larger width of the Mg 1s and Zn 2p core-level spectra in Zn-Mg-Y is explained by different configurations of the local atomic surrounding compared to Zn-Mg-Dy.
Title:
Synthesis, structures and magnetic properties of the dimorphic Mn2CrSbO6 oxide
Authors:
Dos Santos-Garcia, AJ; Solana-Madruga, E; Ritter, C; Avila-Brande, D; Fabelo, O; Saez-Puche, R Author Full Names: Dos Santos-Garcia, Antonio J.; Solana-Madruga, Elena; Ritter, Clemens; Avila-Brande, David; Fabelo, Oscar; Saez-Puche, Regino
Source:
DALTON TRANSACTIONS, 44 (23):10665-10672; 10.1039/c4dt03849e 2015
Abstract:
The perovskite polymorph of Mn2CrSbO6 compound has been synthesized at 8 GPa and 1473 K. It crystallizes in the monoclinic P2(1)/n space group with cell parameters a = 5.2180 (2) angstrom, b = 5.3710(2) angstrom, c = 7.5874(1) angstrom and alpha = 90.36(1)degrees. Magnetic susceptibility and magnetization measurements show the simultaneous antiferromagnetic ordering of Mn2+ and Cr3+ sublattices below T-N = 55 K with a small canting. Low temperature powder neutron diffraction reveals a commensurate magnetic structure with spins confined to the ac-plane and a propagation vector kappa = [1/2 0 1/2]. The thermal treatment of this compound induces an irreversible phase transition to the ilmenite polymorph, which has been isolated at 973 K and crystallizes in R (3) over bar space group with cell parameters a = 5.2084 (4) angstrom and c = 14.4000 (11) angstrom. Magnetic susceptibility, magnetization and powder neutron diffraction data confirm the antiferromagnetic helical ordering of spins in an incommensurate magnetic structure with kappa = [00 0.46] below 60 K, and the temperature dependence of the propagation vector up to kappa = [00 0.54] at about 10 K.
Title:
Ordering effects in the crystal structure and electrochemical properties of the Gd0.5Ba0.5Mn0.5Fe0.5O3-delta perovskite
Authors:
Munoz-Gil, D; Avila-Brande, D; Urones-Garrote, E; Garcia-Martin, S Author Full Names: Munoz-Gil, Daniel; Avila-Brande, David; Urones-Garrote, Esteban; Garcia-Martin, Susana
Source:
DALTON TRANSACTIONS, 44 (23):10867-10874; 10.1039/c4dt03873h 2015
Abstract:
Layered-type ordering and oxygen vacancies ordering are revealed in GdBaMnFeO6-delta perovskite. Selected area electron diffraction and high-resolution transmission electron microscopy results indicate a modulation of the crystal structure. Ba and Gd ordering in (001)(p) layers is confirmed by high angle annular dark field scanning transmission electron microscopy and electron energy-loss spectroscopy. These techniques also revealed formation of layer-stacking defects in the crystals. Direct imaging of the oxygen sublattice is obtained by phase image reconstruction. Location of the oxygen vacancies in the (GdO)(x) layers is achieved by analysis of the intensity of the averaged phase image. Physical properties of the GdBaMnFeO6-delta perovskite, are likely to be strongly affected by its ordering effects and crystal microstructure. In this sense, layered-type GdBaMnFeO6-delta perovskite show better electrochemical properties as cathodes in SOFCs than ion disordered Gd0.5Ba0.5Mn0.5Fe0.5O3-delta perovskite.

Update: 25-Jun-2015

Title:
Symplectic approach for the plane elasticity problem of quasicrystals with point group 10 mm
Authors:
Wang, H; Li, LH; Huang, JJ; Chen, A Author Full Names: Wang, Hua; Li, Lianhe; Huang, Junjie; Chen, Alatancang
Source:
APPLIED MATHEMATICAL MODELLING, 39 (12):3306-3316; 10.1016/j.apm.2014.10.060 JUN 15 2015
Abstract:
The symplectic approach is introduced into the plane elasticity problem of quasicrystals with point group 10 mm. The basic equations of the problem are equivalently written as the Hamiltonian dual equations. It is shown that the generalized eigenvector system of the corresponding Hamiltonian operator matrix is complete in the Cauchy Principal Value (CPV) sense. The analytical solution and related numerical results of the problem are then given. (C) 2014 Elsevier Inc. All rights reserved.
Title:
Magnetic structure and multiferroic coupling in pyroxene NaFeSi2O6
Authors:
Baum, M; Komarek, AC; Holbein, S; Fernandez-Diaz, MT; Andre, G; Hiess, A; Sidis, Y; Steffens, P; Becker, P; Bohaty, L; Braden, M Author Full Names: Baum, M.; Komarek, A. C.; Holbein, S.; Fernandez-Diaz, M. T.; Andre, G.; Hiess, A.; Sidis, Y.; Steffens, P.; Becker, P.; Bohaty, L.; Braden, M.
Source:
PHYSICAL REVIEW B, 91 (21):10.1103/PhysRevB.91.214415 JUN 9 2015
Abstract:
By comprehensive neutron diffraction measurements we have studied the magnetic structure of aegirine (NaFeSi2O6) in and above its multiferroic phase. Natural aegirine exhibits two magnetic transitions into incommensurate magnetic order with a propagation vector of (k) over right arrow (inc) = (0, similar to 0.78,0). Between 9 and 6 K, we find a transverse spin-density wave with moments pointing near the c direction. Below 6 K, magnetic order becomes helical and spins rotate in the ac plane. The same irreducible representation is involved in the two successive transitions. In addition, the ferroelectric polarization (P) over right arrow appearing along the b direction cannot be described by the most common multiferroic mechanism but follows (P) over right arrow proportional to ($) over right arrow (i) x (S) over right arrow (j). Synthetic NaFeSi2O6 does not exhibit the pure incommensurate helical order but shows coexistence of this order with a commensurate magnetic structure. By applying moderate pressure to natural aegirine, we find that the incommensurate magnetic ordering partially transforms to the commensurate one, underlining the nearly degenerate character of the two types of order in NaFeSi2O6.
Title:
Matrix product state approach to a frustrated spin chain with long-range interactions
Authors:
Li, ZH; Wang, AM Author Full Names: Li, Zhi-Hua; Wang, An-Min
Source:
PHYSICAL REVIEW B, 91 (23):10.1103/PhysRevB.91.235110 JUN 8 2015
Abstract:
We make extensive simulations over a spin chain model that combines the frustrated J(1) - J(2) spin chain and the long-range nonfrustrated (-1)((r-1))r(-alpha) decay interactions through the variational matrix product state method for both finite and infinite lengths. We study both the ground-state entanglement and phase diagram. We find that it is most entangled in the rotation invariant long-range ordered antiferromagnetic phase, where the entanglement scales approximately logarithmically. We determine the development of the Majudar-Ghosh point to a disorder line from entanglement. And we approximately determine the transition from the dimerized and incommensurate phase of the J(1) - J(2) model to a decoupled phase by studying spin correlation and the dimerization order parameter. Some implications for entanglement in systems with long-range interactions are stated.
Title:
Influence of Ti doping on the incommensurate charge density wave in 1T-TaS2
Authors:
Chen, XM; Miller, AJ; Nugroho, C; de la Pena, GA; Joe, YI; Kogar, A; Brock, JD; Geck, J; MacDougall, GJ; Cooper, SL; Fradkin, E; Van Harlingen, DJ; Abbamonte, P Author Full Names: Chen, X. M.; Miller, A. J.; Nugroho, C.; de la Pena, G. A.; Joe, Y. I.; Kogar, A.; Brock, J. D.; Geck, J.; MacDougall, G. J.; Cooper, S. L.; Fradkin, E.; Van Harlingen, D. J.; Abbamonte, P.
Source:
PHYSICAL REVIEW B, 91 (24):10.1103/PhysRevB.91.245113 JUN 8 2015
Abstract:
We report temperature-dependent transport and x-ray diffraction measurements of the influence of Ti hole doping on the charge density wave (CDW) in 1T-Ta1-xTixS2. Confirming past studies, we find that even trace impurities eliminate the low-temperature commensurate (C) phase in this system. Surprisingly, the magnitude of the in-plane component of the CDW wave vector in the nearly commensurate (NC) phase does not change significantly with Ti concentration, as might be expected from a changing Fermi surface volume. Instead, the angle of the CDWin the basal plane rotates, from 11.9 degrees at x = 0 to 16.4 degrees at x = 0.12. Ti substitution also leads to an extended region of coexistence between incommensurate (IC) and NC phases, indicating heterogeneous nucleation near the transition. Finally, we explain a resistive anomaly originally observed by Di Salvo [F. J. Di Salvo et al., Phys. Rev. B 12, 2220 (1975)] as arising from pinning of the CDW on the crystal lattice. Our study highlights the importance of commensuration effects in the NC phase, particularly at x similar to 0.08.
Title:
Dispersionless Spin Waves and Underlying Field-Induced Magnetic Order in Gadolinium Gallium Garnet
Authors:
d'Ambrumenil, N; Petrenko, OA; Mutka, H; Deen, PP Author Full Names: d'Ambrumenil, N.; Petrenko, O. A.; Mutka, H.; Deen, P. P.
Source:
PHYSICAL REVIEW LETTERS, 114 (22):10.1103/PhysRevLett.114.227203 JUN 2 2015
Abstract:
We report the results of neutron diffraction and inelastic neutron scattering on a powder sample of Gd3Ga5O12 at high magnetic fields. Analysis of the diffraction data shows that in high fields (B greater than or similar to 1.8 T) the spins are not fully aligned, but are canted slightly as a result of the dipolar interaction. The magnetic phase for fields less than or similar to 1.8 T is characterized by antiferromagnetic peaks at (210) and an incommensurate wave vector. The dominant contribution to inelastic scattering at large momentum transfers is from a band of almost dispersionless excitations. We show that these correspond to the spin waves localized on ten site rings, expected on the basis of nearest neighbor exchange interaction, and that the spectrum at high fields B greater than or similar to 1.8 T is well described by a spin wave theory.
Title:
Aperiodic crystals and beyond
Authors:
Grimm, U Author Full Names: Grimm, Uwe
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 258-274; 10.1107/S2052520615008409 3 JUN 2015
Abstract:
Crystals are paradigms of ordered structures. While order was once seen as synonymous with lattice periodic arrangements, the discoveries of incommensurate crystals and quasicrystals led to a more general perception of crystalline order, encompassing both periodic and aperiodic crystals. The current definition of crystals rests on their essentially point-like diffraction. Considering a number of recently investigated toy systems, with particular emphasis on non-crystalline ordered structures, the limits of the current definition are explored.
Title:
Structures beyond superspace
Authors:
Senechal, M Author Full Names: Senechal, Marjorie
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 250-251; 10.1107/S2052520615009907 3 JUN 2015
Title:
The modulated average structure of mullite
Authors:
Birkenstock, J; Petricek, V; Pedersen, B; Schneider, H; Fischer, RX Author Full Names: Birkenstock, Johannes; Petricek, Vaclav; Pedersen, Bjoern; Schneider, Hartmut; Fischer, Reinhard X.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 358-368; 10.1107/S205252061500757X 3 JUN 2015
Abstract:
Homogeneous and inclusion-free single crystals of 2: 1 mullite (Al4.8Si1.2O9.6) grown by the Czochralski technique were examined by X-ray and neutron diffraction methods. The observed diffuse scattering together with the pattern of satellite reflections confirm previously published data and are thus inherent features of the mullite structure. The ideal composition was closely met as confirmed by microprobe analysis (Al-4.82 (3) Si-1.18 (1) O-9.59 (5)) and by average structure refinements. 8 (5) to 20 (13)% of the available Si was found in the T* position of the tetrahedra triclusters. The strong tendencey for disorder in mullite may be understood from considerations of hypothetical superstructures which would have to be n-fivefold with respect to the three-dimensional average unit cell of 2: 1 mullite and n-fourfold in case of 3: 2 mullite. In any of these the possible arrangements of the vacancies and of the tetrahedral units would inevitably be unfavorable. Three directions of incommensurate modulations were determined: q(1) = [0.3137 (2) 0 1/2], q(2) = [0 0.4021 (5) 0.1834 (2)] and q(3) = [0 0.4009 (5) -0.1834 (2)]. The one-dimensional incommensurately modulated crystal structure associated with q1 was refined for the first time using the superspace approach. The modulation is dominated by harmonic occupational modulations of the atoms in the di- and the triclusters of the tetrahedral units in mullite. The modulation amplitudes are small and the harmonic character implies that the modulated structure still represents an average structure in the overall disordered arrangement of the vacancies and of the tetrahedral structural units. In other words, when projecting the local assemblies at the scale of a few tens of average mullite cells into cells determined by either one of the modulation vectors q(1), q(2) or q(3) a weak average modulation results with slightly varying average occupation factors for the tetrahedral units. As a result, the real structure of mullite is locally ordered (as previously known), but on the long-range its average is not completely disordered, the modulated structure of mullite may be denoted the true 'average structure of mullite'.
Title:
Neutron Laue and X-ray diffraction study of a new crystallographic superspace phase in n-nonadecane-urea
Authors:
Zerdane, S; Mariette, C; McIntyre, GJ; Lemee-Cailleau, MH; Rabiller, P; Guerin, L; Ameline, JC; Toudic, B Author Full Names: Zerdane, S.; Mariette, C.; McIntyre, G. J.; Lemee-Cailleau, M. -H.; Rabiller, P.; Guerin, L.; Ameline, J. C.; Toudic, B.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 293-299; 10.1107/S2052520615005442 3 JUN 2015
Abstract:
Aperiodic composite crystals present long-range order without translational symmetry. These materials may be described as the intersection in three dimensions of a crystal which is periodic in a higher-dimensional space. In such materials, symmetry breaking must be described as structural changes within these crystallographic superspaces. The increase in the number of superspace groups with the increase in the dimension of the superspace allows many more structural solutions. This is illustrated in n-nonadecane-urea, revealing a fifth higher-dimensional phase at low temperature.
Title:
One-Third Magnetization Plateau with a Preceding Novel Phase in Volborthite
Authors:
Ishikawa, H; Yoshida, M; Nawa, K; Jeong, M; Kramer, S; Horvatic, M; Berthier, C; Takigawa, M; Akaki, M; Miyake, A; Tokunaga, M; Kindo, K; Yamaura, J; Okamoto, Y; Hiroi, Z Author Full Names: Ishikawa, H.; Yoshida, M.; Nawa, K.; Jeong, M.; Kraemer, S.; Horvatic, M.; Berthier, C.; Takigawa, M.; Akaki, M.; Miyake, A.; Tokunaga, M.; Kindo, K.; Yamaura, J.; Okamoto, Y.; Hiroi, Z.
Source:
PHYSICAL REVIEW LETTERS, 114 (22):10.1103/PhysRevLett.114.227202 JUN 1 2015
Abstract:
We have synthesized high-quality single crystals of volborthite, a seemingly distorted kagome antiferromagnet, and carried out high-field magnetization measurements up to 74 T and V-51 NMR measurements up to 30 T. An extremely wide 1/3 magnetization plateau appears above 28 T and continues over 74 T at 1.4 K, which has not been observed in previous studies using polycrystalline samples. NMR spectra reveal an incommensurate order (most likely a spin-density wave order) below 22 T and a simple spin structure in the plateau phase. Moreover, a novel intermediate phase is found between 23 and 26 T, where the magnetization varies linearly with magnetic field and the NMR spectra indicate an inhomogeneous distribution of the internal magnetic field. This sequence of phases in volborthite bears a striking similarity to those of frustrated spin chains with a ferromagnetic nearest-neighbor coupling J(1) competing with an antiferromagnetic next-nearest-neighbor coupling J(2)
Title:
Pressure-induced normal-incommensurate and incommensurate-commensurate phase transitions in CrOCl
Authors:
Bykov, M; Bykova, E; Dubrovinsky, L; Hanfland, M; Liermann, HP; van Smaalen, S Author Full Names: Bykov, Maxim; Bykova, Elena; Dubrovinsky, Leonid; Hanfland, Michael; Liermann, Hanns-Peter; van Smaalen, Sander
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep09647 MAY 21 2015
Abstract:
The high-pressure behavior of layered CrOCl is shown to be governed by non-bonded interactions between chlorine atoms in relation to a rigid framework composed of Cr and O atoms. The competition between optimizing intra-and interlayer Cl-Cl distances and the general trend towards denser packing defines a novel mechanism for high-pressure phase transitions of inorganic materials. CrOCl possesses an incommensurate phase for 16-51 GPa. Single-crystal x-ray diffraction in a diamond anvil cell provides an accurate description of the evolution of the incommensurate wave with pressure. It thus demonstrates a continuous increase of the amplitude up to 30 GPa, followed by a decrease of the wavelength until a lock-in transition occurs at 51 GPa.
Title:
Magnetism in rare-earth quasicrystals: RKKY interactions and ordering
Authors:
Thiem, S; Chalker, JT Author Full Names: Thiem, Stefanie; Chalker, J. T.
Source:
EPL, 110 (1):10.1209/0295-5075/110/17002 APR 2015
Abstract:
We study magnetism in simple models for rare-earth quasicrystals, by considering Ising spins on a quasiperiodic tiling, coupled via RKKY interactions. Computing these interactions from a tight-binding model on the tiling, we find that they are frustrated and strongly dependent on the local environment. Although such features are often associated with spin glass behaviour, we show using Monte Carlo simulations that the spin system has a phase transition to a low-temperature state with long-range quasiperiodic magnetic order. Copyright (C) EPLA, 2015
Title:
Synthesis and structure of the new pentanary uranium (VI) silicate, K4CaUSi4O14, a member of a structural family related to fresnoite
Authors:
Morrison, G; Smith, MD; Tran, TT; Halasyamani, PS; Loye, HCZ Author Full Names: Morrison, Gregory; Smith, Mark D.; Tran, T. Thao; Halasyamani, P. Shiv; Loye, Hans-Conrad Zur
Source:
CRYSTENGCOMM, 17 (22):4218-4224; 10.1039/c5ce00504c 2015
Abstract:
Single crystals of K4CaUSi4O14 have been grown from a eutectic CaF2-KF flux. K4CaUSi4O14 crystallizes in a new structure which exhibits a 49-fold superstructure believed to be due to a modulation of the uranium and silicon polyhedra. We report the sub-cell of the structure which adopts the tetragonal space group P (4) over bar n2 with lattice parameters a = 9.2862(2) angstrom c = 8.3796(4) angstrom, and V = 722.60(5)angstrom(3). K4CaUSi4O14 is a member of a structural family related to the mineral fresnoite which we describe here. Finally, we report UV-vis absorbance and SHG measurements on the compound, which is non-centrosymmetric.
Title:
The symmetry of the thermoelastic properties of quasicrystals
Authors:
Sokolova, MY; Khristich, DV Author Full Names: Sokolova, M. Yu.; Khristich, D. V.
Source:
PMM JOURNAL OF APPLIED MATHEMATICS AND MECHANICS, 78 (5):524-528; 10.1016/j.jappmathmech.2015.03.012 2014
Abstract:
The thermoelastic properties of quasicrystals, possessing 5-th, 8-th, 10-th and 12-th order rotational axes, not characteristic of crystalline bodies, are considered. Using group analysis, canonical representations of the second and fourth rank tensors, characterizing the properties of quasicrystals, are constructed. The fact that orthogonal, decagonal and dodecagonal quasicrystals belong to the class of transversely isotropic materials and the isotropy of icosahedric quasicrystals and fullerenes are proved. (C) 2015 Elsevier Ltd. All rights reserved.

Update: 18-Jun-2015

Title:
Magnetostructural transitions in Mn-rich Heusler Mn-Ni-In melt-spun ribbons with enhanced magnetocaloric effect
Authors:
Li, HW; Feng, ST; Ren, J; Zhai, QJ; Fu, JX; Luo, ZP; Zheng, HX Author Full Names: Li, Hongwei; Feng, Shutong; Ren, Jian; Zhai, Qijie; Fu, Jianxun; Luo, Zhiping; Zheng, Hongxing
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 391 17-21; 10.1016/j.jmmm.2015.04.098 OCT 1 2015
Abstract:
The magnetostructural transition behavior and magnetocaloric effect of Mn-rich Heusler Mn-Ni-In melt spun ribbons have been investigated in the present study. Experimental results showed that the martensitic transition temperatures decreased by substituting small amounts of Ni with Mn in Mn49+xNi42-xIn9 (x=0,1,2). Within a temperature range from 100 K to 380 K, the Mn(49)Ni(41)ln(9) underwent a martensitic transformation from a paramagnetic L2(1)-type cubic austenite to a ferromagnetic modulated fourteen layered monoclinic (14M) martensite, followed with a ferromagnetic -> weak-magnetic transition in martensite upon cooling. While for both Mn50Ni41In9 and Mn51Ni40In9, the paramagnetic -> ferromagnetic transition in austenite occurred prior to the martensitic transformation upon cooling. Under a magnetic field change of 30 kOe, the maximum magnetic entropy changes of the Mn50Ni41In9 melt spun ribbons were found to be 5.7 J/kg K and -2.3 J/kg K in the vicinity of martensitic transformation and magnetic transition of austenite, respectively. An enhanced total effective refrigeration capacity as high as 184.2 J/kg was obtained in the Mn50Ni41In9 melt spun ribbons. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Microstructure and phase transformation of forged Mg-3.7Zn-0.3Y-0.3Gd quasicrystal alloy
Authors:
Yang, Y; Zhang, K; Ma, ML; Li, XG Author Full Names: Yang, Yang; Zhang, Kui; Ma, Minglong; Li, Xinggang
Source:
JOURNAL OF MATERIALS RESEARCH, 30 (10):1693-1700; 10.1557/jmr.2015.97 MAY 28 2015
Abstract:
An alloy with the composition of Mg-3.7Zn-0.3Y-0.3Gd (in at.%) which contains quasicrystal phase was studied by multiple means. The as-cast alloy has dendritic structure and consists of -Mg, I-phase, W-phase, and Mg-Zn precipitations. The alloy was forged one pass and annealed at 440 degrees C for 4 h, then followed by two passes of compressions. Eutectics were crushed and partially dissolved after deformation and annealing. The tensile strength increased after each forge pass. Submicron scale particles precipitated all around the grains during the deformations, and the amount of precipitations was proportional to the amount of deformations. These precipitated particles were observed by high resolution transmission electron microscopy (TEM). The existence of rhomboid W'-phase with face center cubic (FCC) structure and globular I-phase was confirmed. A quasi-periodicity lamellar phase combined with I-phase was founded, which was considered to be the transient phase between I-phase and I-phase.
Title:
Effect of substrate and orientation on charge ordering behaviors in epitaxial Pr0.5Ca0.35Sr0.15MnO3 films
Authors:
Yang, HW; Wang, C; Cai, RS; Hu, FX; Wang, YQ; Sun, JR Author Full Names: Yang, H. W.; Wang, C.; Cai, R. S.; Hu, F. X.; Wang, Y. Q.; Sun, J. R.
Source:
JOURNAL OF APPLIED PHYSICS, 117 (17):10.1063/1.4913731 MAY 7 2015
Abstract:
The charge ordering (CO) behaviors of Pr0.5Ca0.35Sr0.15MnO3 films grown on STO(100), STO(110) and LAO(100) are systematically investigated by transport measurements and transmission electron microscopy (TEM) examinations. From the transport measurements, the CO transition temperatures of all the three films are much higher than those of the bulk materials, showing that the film strain could enhance the CO transition. From TEM observations, many superlattice spots appear in the electron diffraction patterns taken from the films, indicating the appearance of the CO modulation structures at room temperature. The modulation vectors are determined to be (1/2, 0, 0) for STO (100), (1/2, 1/2, 1/2) for STO (110), and both (0, 1/2, 0) and (1/2, 1/2, 0) for LAO (100). It is shown that both the substrate orientation and the film strain have a great effect on the CO modulation structures. The CO state is much easier to appear in the compressive strain direction which is due to the Mn-O-Mn angle tilting. (C) 2015 AIP Publishing LLC.
Title:
Spin reorientation in multiferroic spinel Co0.5Fe0.5Cr2O4 with Mossbauer spectroscopy
Authors:
Myoung, BR; Kim, CS Author Full Names: Myoung, Bo Ra; Kim, Chul Sung
Source:
JOURNAL OF APPLIED PHYSICS, 117 (17):10.1063/1.4918968 MAY 7 2015
Abstract:
We studied the magnetic properties of multiferroic spinel Co0.5Fe0.5Cr2O4, especially focusing on the spin-ordering, spin-reorientation, and charge re-distribution effects. From the Rietveld refinement analysis, the crystal structure was identified to be a normal cubic spinel of Fd-3m. Based on the temperature-dependent measurements of the magnetization and magnetic hyperfine field (H-hf), Curie temperature (T-C) of Co0.5Fe0.5Cr2O4 was determined to be around 86K where H-hf (sic) 0. From the change of slope in the M-T curve, the conical-spiral magnetic ordering temperature was determined to be 20 K, which coincides with H-hf measurement. Also, we have observed the decrease in the slope of the electric quadrupole splitting (Delta E-Q) curve above 20K, suggesting that the change in Delta E-Q around T-S is originated from charge redistribution due to the spin-relocation associated with the distortion of each tetrahedral site around Fe2+ ion above T-S. This indicates that Co0.5Fe0.5Cr2O4 has the noncollinear conical-spiral spin ordering with incommensurate spin structure below T-S, while above T-S, it has ferrimagnetic spin ordering with commensuration in the collinear state. In addition, the Jahn-teller distortion temperature is measured to be around 155K, since both Delta E-Q and Delta(1) of T-5(2g) band decrease rapidly with increasing temperature and disappear around 155 K. (C) 2015 AIP Publishing LLC.
Title:
Zone-Folded Phonons and the Commensurate-Incommensurate Charge-Density-Wave Transition in 1T-TaSe2 Thin Films
Authors:
Samnakay, R; Wickramaratne, D; Pope, TR; Lake, RK; Salguero, TT; Balandin, AA Author Full Names: Samnakay, R.; Wickramaratne, D.; Pope, T. R.; Lake, R. K.; Salguero, T. T.; Balandin, A. A.
Source:
NANO LETTERS, 15 (5):2965-2973; 10.1021/nl504811s MAY 2015
Abstract:
Bulk 1T-TaSe2 exhibits unusually high charge density wave (CDW) transition temperatures of 600 and 473 K below which the material exists in the incommensurate (I-CDW) and the commensurate (C-CDW) charge-density-wave phases, respectively. The (13)(1/2) x (13)(1/2), C-CDW reconstruction of the lattice coincides with new Raman peaks resulting from zone-folding of phonon modes from middle regions of the original Brillouin zone back to Gamma. The C-CDW transition temperatures as a function of film thickness are determined from the evolution of these new Raman peaks, and they are found to decrease from 473 to 413 K as the film thicknesses decrease from 150 to 35 nm. A comparison of the Raman data with ab initio calculations of both the normal and C-CDW phases gives a consistent picture of the zone-folding of the phonon modes following lattice reconstruction, The Raman peak at similar to 154 cm(-1) originates from the zone-folded phonons in the C-CDW phase. In the I-CDW phase, the loss of translational symmetry coincides with a strong suppression and broadening of the Raman peaks. The observed,change: in the C-CDW transition temperature is consistent with total energy calculations of bulk and monolayer 1T-TaSe2.
Title:
Temperature-Pressure Phase Diagram for Rb2ZnCl4 Crystals
Authors:
Kurlyak, VY; Stadnyk, VY; Stakhura, V Author Full Names: Kurlyak, V. Yu.; Stadnyk, V. Yo.; Stakhura, V.
Source:
JOURNAL OF APPLIED SPECTROSCOPY, 82 (2):228-233; 10.1007/s10812-015-0090-3 MAY 2015
Abstract:
We have studied the effect of uniaxial stress along the principal crystallophysical directions on the temperature variations in the birefringence Delta n (i) and the refractive indices ni for Rb2ZnCl4 crystals in the region of phase transitions from the paraelectric phase to the incommensurate phase and then to the commensurate ferroelectric phase. We have established that Delta n (i) and n (i) are rather sensitive to the action of uniaxial stresses. We have observed a significant pressure-induced shift of the paraelectric - incommensurate - ferroelectric phase transition points in different temperature regions, depending on the direction of the uniaxial compression.

Update: 11-Jun-2015

Title:
Effect of Li on electrochemical properties of Ti1.4V0.6Ni quasicrystal alloy produced by rapid quenching
Authors:
Ouyang, ZT; Liu, K; Shang, JM; Xing, C; Liu, WQ; Wang, LM Author Full Names: Ouyang, Zhongtao; Liu, Kun; Shang, Jinming; Xing, Cheng; Liu, Wanqiang; Wang, Limin
Source:
INTERMETALLICS, 62 50-55; 10.1016/j.intermet.2015.03.010 JUL 2015
Abstract:
The effect of Li on the electrochemical performance of electrodes consisting of Ti1.4V0.6Ni quasicrystal was investigated at room temperature in three-electrode cell set-up. The quasicrystal sample was initially synthesized by arc melting, followed by melt-spinning, and then infiltrated with Li atoms by electroosmosis. According to X-ray diffraction, all ribbon samples were determined to be icosahedral quasicrystal phase (I-phase), V-based solid solution phase with BCC structure and face centered cubic (FCC) phase with Ti2Ni-type structure. After infiltrating some Li atoms into the Ti1.4V0.6Ni quasicrystal lattice under the condition of an electroosmosis current of 0.6 A, we could observe the appearance of Li diffraction peaks. Importantly, the slight shift to the left observed in the diffraction peaks indicated that lattice expansion was caused by the infiltration of Li. The discharge capacity of Ti1.4V0.6Ni-Li material was higher than that of Ti1.4V0.6Ni.The maximum discharge capacity of 307.1 mAh/g was recorded for Ti1.4V0.6Ni Li at a current density of 30 mAh/g. Both high-rate dischargeability and cycling stability were enhanced as a result of infiltrating Li. The lithium could get into the lattice, which resulted in the formation of microspores on surface of alloy, thus improving electrochemical activity of the alloy electrode. At the same time, the electrochemical reaction kinetics of alloy electrodes was also researched. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Synthesis and Characterization of Bulk Al-Cu-Fe Based Quasicrystals and Composites by Spray Forming
Authors:
Mukhopadhyay, NK; Uhlenwinkel, V; Srivastava, VC Author Full Names: Mukhopadhyay, N. K.; Uhlenwinkel, V.; Srivastava, V. C.
Source:
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE, 24 (6):2172-2178; SI 10.1007/s11665-015-1442-0 JUN 2015
Abstract:
The bulk quasicrystalline (QC) materials and their composites have attracted considerable interest due to their promising mechanical properties. In the present investigation, spray forming has been used to synthesize bulk single-phase icosahedral quasicrystals and composites in Al62.5Cu25Fe12.5 system as well as in quaternary system containing 10% Sn. The elemental materials were induction melted under nitrogen cover and a billet of 250 mm in diameter and 350 mm in height was spray formed. The phase constitution of the spray-formed materials showed a bulk single-phase icosahedral quasicrystal as a major phase along with other crystalline phases. A large number of annealing twins were observed in the microstructure in ternary AlCuFe alloys. It is interesting to note that due to addition of Sn, the volume fraction of beta-Al(CuFe) phase was found to increase and annealing twins were almost absent. The hardness of the single-phase AlCuFe alloy and Sn-containing composites was found to be 8.6 and 6.0 GPa, respectively, at a load of 300 g. In general, the hardness decreases with heat treatment at high temperatures. However, in case of Sn-ontaining alloy, hardness increases with low-temperature heat treatment. Long and hair-like cracks (Palmqvist type) are observed to form from the corner of the indentations of the ternary alloys, whereas in Sn-containing composites, the cracks are not sharp and long suggesting the enhancement of fracture toughness in the composites. Attempts have been made to understand the effect of Sn on the evolution of icosahedral phase, other crystalline phases and their composite effects on the mechanical properties.
Title:
Superconductivity and the electronic phase diagram of LaPt2-xGe2+x
Authors:
Maeda, S; Matano, K; Yatagai, R; Oguchi, T; Zheng, GQ Author Full Names: Maeda, S.; Matano, K.; Yatagai, R.; Oguchi, T.; Zheng, Guo-qing
Source:
PHYSICAL REVIEW B, 91 (17):10.1103/PhysRevB.91.174516 MAY 22 2015
Abstract:
In many cases, unconventional superconductivity are realized by suppressing another order parameter, such as charge density wave (CDW) or spin density wave (SDW). This suggests that the fluctuations of these order parameters play an important role in producing superconductivity. LaPt2Ge2 undergoes a tetragonal-to-monoclinic structural phase transition (SPT) at T-s = 394 K, accompanying a double period modulation in the a-axis direction, and superconducts at T-c = 0.41 K. We performed band calculations and found 2D (two dimensional)-like Fermi surfaces with partial nesting. A reduction in the density of states in the monoclinic phase was found in the calculation and confirmed by Pt-195-NMR. We suggest a CDW as a possible cause for the SPT. By changing the stoichiometry between Pt and Ge, we succeeded in suppressing T-s and increasing T-c in LaPt2-xGe2+x. Comparison of La-139- and Pt-195-NMR data reveals moderate fluctuations associated with SPT. From La-139-NQR measurements at zero field, we found that an isotropic superconducting gap is realized in LaPt2-xGe2+x (x = 0.20). We discuss the relationship between superconductivity and the SPT order/fluctuations.
Title:
Oxygen octahedra distortion induced structural and magnetic phase transitions in Bi1-xCaxFe1-xMnxO3 ceramics
Authors:
Kumar, P; Shankhwar, N; Srinivasan, A; Kar, M Author Full Names: Kumar, Pawan; Shankhwar, Nisha; Srinivasan, A.; Kar, Manoranjan
Source:
JOURNAL OF APPLIED PHYSICS, 117 (19):10.1063/1.4921433 MAY 21 2015
Abstract:
The co-doping of Ca and Mn in respective Bi and Fe-sites of BiFeO3 lattice leads to structural transition from rhombohedral (R3c space group) to orthorhombic (Pbnm space group) crystal symmetry. The tilt angle for anti-phase rotation of the oxygen octahedra of BiFeO3 at room temperature is observed to be similar to 13.8 degrees. It decreases with the increase in the co-doping percentage which suggests the composition-driven structural phase transition. The remnant magnetization for sample with 15% of co-doping becomes about 16 times that of BiFeO3. It may be attributed to the suppression of cycloid spin structure and uncompensated spins at the surface of nanocrystallites. Further increase in co-doping percentage results in the sharp reduction of remnant magnetization due to the dominant contribution from the collinear antiferromagnetic ordering in the Pbnm space group. The Arrott plot analysis clearly indicates the composition-driven crossover from the antiferromagnetic to weak ferromagnetic ordering and vice versa. Electron spin resonance results provide the evidence for the composition-driven phase transitions from an incommensurate spin cycloidal modulated state to one with nearly homogeneous spin order. The band gap (2.17 eV) of BiFeO3 measured using UV-Vis spectra was supported by the resonance Raman spectra. (C) 2015 AIP Publishing LLC.
Title:
Coexistence of Charge-Density-Wave and Pair-Density-Wave Orders in Underdoped Cuprates
Authors:
Wang, YX; Agterberg, DF; Chubukov, A Author Full Names: Wang, Yuxuan; Agterberg, Daniel F.; Chubukov, Andrey
Source:
PHYSICAL REVIEW LETTERS, 114 (19):10.1103/PhysRevLett.114.197001 MAY 15 2015
Abstract:
We analyze incommensurate charge-density-wave (CDW) and pair-density-wave (PDW) orders with transferred momenta (+/- Q, 0)/(0, +/- Q) in underdoped cuprates within the spin-fermion model. Both orders appear due to an exchange of spin fluctuations before magnetic order develops. We argue that the ordered state with the lowest energy has nonzero CDW and PDW components with the same momentum. Such a state breaks C-4 lattice rotational symmetry, time-reversal symmetry, and mirror symmetries. We argue that the feedback from CDW/PDW order on fermionic dispersion is consistent with ARPES data. We discuss the interplay between the CDW/PDWorder and d(x2-y2) superconductivity and make specific predictions for experiments.
Title:
Incommensurate Systems as Model Compounds for Disorder Revealing Low-Temperature Glasslike Behavior
Authors:
Remenyi, G; Sahling, S; Biljakovic, K; Staresinic, D; Lasjaunias, JC; Lorenzo, JE; Monceau, P; Cano, A Author Full Names: Remenyi, G.; Sahling, S.; Biljakovic, K.; Staresinic, D.; Lasjaunias, J. -C.; Lorenzo, J. E.; Monceau, P.; Cano, A.
Source:
PHYSICAL REVIEW LETTERS, 114 (19):10.1103/PhysRevLett.114.195502 MAY 14 2015
Abstract:
We show that the specific heat of incommensurately modulated crystals with broken translational periodicity presents similar features at low temperatures to those of amorphous and glass materials. Here we demonstrate that the excess to the constant C-p(T)/T-3 law (or Debye limit) is made up of an upturn below 1 K and of a broad bump at T approximate to 10 K that directly originates from the gapped phase and amplitude modes of the incommensurate structure. We argue that the low-energy dynamics of incommensurate systems constitute a plausible simplification of the landscape of interactions present in glasses, giving rise to their low-temperature anomalies.
Title:
A Crystal-Chemical Framework for Relaxor versus Normal Ferroelectric Behavior in Tetragonal Tungsten Bronzes
Authors:
Zhu, X; Fu, M; Stennett, MC; Vilarinho, PM; Levin, I; Randall, CA; Gardner, J; Morrison, FD; Reaney, IM Author Full Names: Zhu, X.; Fu, M.; Stennett, M. C.; Vilarinho, P. M.; Levin, I.; Randall, C. A.; Gardner, J.; Morrison, F. D.; Reaney, I. M.
Source:
CHEMISTRY OF MATERIALS, 27 (9):3250-3261; 10.1021/acs.chemmater.5b00072 MAY 12 2015
Abstract:
Tetragonal tungsten bronzes (TTBs), an important class of oxides known to exhibit ferroelectricity, undergo complex distortions, including rotations of,oxygen octahedra, which give rise to either incommensurately or commensurately modulated superstructures. Many TTBs display broad, frequency-dependent relaxor dieletric behavior rather than sharper frequency-independent normal ferroelectric anomalies, but the exact reasons that favor a particular type of dielectric response for a given composition remain unclear. In this contribution the influence of incommensurate/commensurate dispiacive modulations on the onset of relaxor/ferroelectric behavior in TTBs is assessed in the context of basic crystal-chemical factors, such as positional disorder, ionic radii and polarizabilities, and point defects. We present a predictive crystal-chemical model that rationalizes composition structure properties relations for a broad range of TTB systems.
Title:
Structural transformation in quasicrystal-forming Al-Cu-Fe alloys
Authors:
Boularas, H; Debili, MY; Alleg, S Author Full Names: Boularas, H.; Debili, M. Y.; Alleg, S.
Source:
METALLURGICAL RESEARCH & TECHNOLOGY, 112 (2):10.1051/metal/2015008 2015
Abstract:
Three Al-Cu-Fe alloys with various iron contents (6 at.%, 12 at.% and 15 at.%), were synthesized by fusion under high-frequency magnetic induction and characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry(DSC). The microstructure evolution was carried out both in the as-quenched state as well after heat treatment at 500 degrees C in relation to iron composition. Particular attention was been paid to the alloy containing 15%, and we were been able to determine by DSC that a massive transformation from crystal (beta) to quasicrystal i-psi (Al6Fe2Cu) occurs for this composition.
Title:
Formation of an Icosahedral Quasicrystal and Its Approximant in Au-Al-Sc System
Authors:
So, YG; Kimoto, K; Edagawa, K Author Full Names: So, Yeong-Gi; Kimoto, Koji; Edagawa, Keiichi
Source:
MATERIALS TRANSACTIONS, 56 (4):495-499; 10.2320/matertrans.M2014421 2015
Abstract:
The formation of the icosahedral (i-) and 1/1-approximant (1/1-) phases in the Au-Al-Sc system has been investigated. A primitive-type i-phase was found to form in an Au45Al40Sc15 alloy. This i-phase was shown to be thermodynamically stable at 973 K. A stable 1/1-phase was found to form at 1173K for compositions of Au44+xAl41-xSc15 (x = 0, 1, 2, 3). High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) revealed that the 1/1-phase consists of Tsai-type icosahedral clusters. Similar local structures were observed in the HAADF-STEM image for the i-phase, indicating that the i-phase consists of Tsai-type clusters identical to the clusters in the 1/1-phase. The composition of the Au-Al-Sc i-phase is consistent with the formation conditions, including those in the valence electrons per atom ratio and in the atomic size factor, which has been shown previously for other Tsai-type i-phases. This fact demonstrates the importance of these conditions for stabilization of Tsai-type i-phases.

Update: 3-Jun-2015

Title:
The study of Al-3(Mn, Pd) crystal and Al-Mn-Pd decagonal quasicrystal by spherical aberration-corrected scanning transmission microscopy and atomic-resolution energy dispersive X-ray spectroscopy
Authors:
Yasuhara, A; Hiraga, K Author Full Names: Yasuhara, Akira; Hiraga, Kenji
Source:
PHILOSOPHICAL MAGAZINE, 95 (14):1511-1523; 10.1080/14786435.2015.1039623 MAY 13 2015
Abstract:
An Al3Mn-type Al-3(Mn, Pd) crystal and an Al-Mn-Pd decagonal quasicrystal (DQC) in an Al70Mn20Pd10 alloy are studied using a spherical aberration (Cs)-corrected scanning transmission electron microscope (STEM) with high-angle annular dark-field (HAADF) and annular bright-field (ABF) techniques, together with atomic-resolution energy dispersive X-ray spectroscopy (EDS). Mn and Pd atomic positions in the Al-3(Mn, Pd) structure projected along the b-axis (pseudo-tenfold rotational axis) are represented by separate bright dots in observed HAADF-STEM images. Besides, Al as well as Mn and Pd atomic positions are represented as dark dots in ABF-STEM images. Most Mn and Pd atomic positions in the Al-3(Mn, Pd) structure can be observed on atomic-resolution EDS maps. On the basis of the good correlation between the STEM images and the EDS maps, and also considering the structure of the Al-3(Mn, Pd) crystal, which was determined by X-ray diffraction using a single crystal, observed HAADF and ABF-STEM images of the Al-Mn-Pd DQC have been interpreted. Pd and Mn atomic positions in the Al-Mn-Pd DQC can be detected on the observed EDS maps. It can be seen that Pd is enriched around the centre of the columnar clusters, having a decagonal section with 2nm in diameter. It can therefore be concluded that Pd plays an important role in the stabilization of the decagonal clusters, which form the Al-Mn-Pd DQC structure.
Title:
The structure of an Al-Rh-Cu decagonal quasicrystal studied by spherical aberration (Cs)-corrected scanning transmission electron microscopy
Authors:
Hiraga, K; Yasuhara, A; Yamamoto, K; Yubuta, K Author Full Names: Hiraga, Kenji; Yasuhara, Akira; Yamamoto, Kazuki; Yubuta, Kunio
Source:
PHILOSOPHICAL MAGAZINE, 95 (14):1524-1535; 10.1080/14786435.2015.1039624 MAY 13 2015
Abstract:
The structure of an Al-Rh-Cu decagonal quasicrystal formed with two quasiperiodic planes along the periodic axis in an Al63Rh18.5Cu18.5 alloy has been studied by spherical aberration (Cs)-corrected high-angle annular detector dark-field (HAADF)- and annular bright-field (ABF)-scanning transmission electron microscopy (STEM). Heavy atoms of Rh and mixed sites (MSs) of Al and Cu atoms projected along the periodic axis can be clearly represented as separate bright dots in observed HAADF-STEM images, and consequently arrangements of Rh atoms and MSs on the two quasiperiodic planes can be directly determined from those of bright dots in the observed HAADF-STEM image. The Rh atoms are arranged in pentagonal tiling formed with pentagonal and star-shaped pentagonal tiles with an edge-length of 0.76nm, and also MSs with a pentagonal arrangement are located in the pentagonal tiles with definite orientations. The star-shaped pentagonal tiles in the pentagonal tiling are arranged in tau(2)(tau: golden ratio)-inflated pentagonal tiling with a bond-length of 2nm. From arrangements of Rh atoms placed in pentagonal tilings with a bond-length of 2nm, which are generated by the projection of a five-dimensional hyper-cubic lattice, occupation domains in the perpendicular space are derived. Al atoms as well as Rh atoms and MSs are represented as dark dots in an observed ABF-STEM image, and arrangements of Al atoms in well-symmetric regions are discussed.

Update: 28-May-2015

Title:
Refinement of the icosahedral quasicrystalline phase and the grain size of Mg-9.25Zn-1.66Y alloy by high-ratio differential speed rolling
Authors:
Kwak, TY; Lim, HK; Han, SH; Kim, WJ Author Full Names: Kwak, T. Y.; Lim, H. K.; Han, S. H.; Kim, W. J.
Source:
SCRIPTA MATERIALIA, 103 49-52; 10.1016/j.scriptamat.2015.03.004 JUL 1 2015
Abstract:
Differential speed rolling was applied to a Mg-9.25Zn-1.66Y alloy with an icosahedral quasicrystalline (I) phase to refine its cast microstructure by severe plastic deformation. The grain size was reduced to gm. A higher speed ratio, which produces a higher shear strain, was more effective in breaking up the eutectic I phase structure and dispersing the broken particles into the matrix. The processed alloy exhibited a high yield stress of 337 MPa and a good elongation of 10.7%. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Evidence for magneto-electric and spin-lattice coupling in PbFe0.5Nb0.5O3 through structural and magneto-electric studies
Authors:
Matteppanavar, S; Rayaprol, S; Singh, K; Reddy, VR; Angadi, B Author Full Names: Matteppanavar, Shidaling; Rayaprol, Sudhindra; Singh, Kiran; Reddy, V. Raghavendra; Angadi, Basavaraj
Source:
JOURNAL OF MATERIALS SCIENCE, 50 (14):4980-4993; 10.1007/s10853-015-9046-5 JUL 2015
Abstract:
Neutron diffraction (ND) studies were carried out on polycrystalline single-phase multiferroic Pb(Fe0.5Nb0.5)O-3 (PFN) in the temperature range of 290-2 K to understand the structural and magnetic properties as a function of temperature. ND data were refined using the Rietveld refinement method for both crystallographic and magnetic structures. The structure at room temperature was found to be monoclinic, in Cm space group. No structural transition was observed till 2 K. At low temperatures (i.e., from T < T (N); T (N) = 155 K), an additional peak appears at scattering vector, Q = 1.35 (-1), indicating the onset of antiferromagnetic ordering. The magnetic structure was found to be commensurate with the crystallographic structure and could be refined using the propagation vector, k = [0.125, 0.5, and 0.5]. Magnetization, ferroelectric P-E loops, and dielectric measurements on PFN reveal a strong anomaly at the antiferromagnetic transition temperature (T (N)) indicating the magneto-electric coupling. The refined temperature-dependent structural parameters such as unit cell volume and monoclinic distortion angle (beta) reveal pronounced anomalies at the magnetic ordering temperature (T (N)), which indicates strong spin-lattice coupling. An anomaly in lattice volume was observed with a small negative thermal expansion below and a large thermal expansion above the T (N), respectively. It shows the occurrence of isostructural phase transition accompanying the magnetic ordering below T (N) 155 K, leading to significant change in ionic polarization, octahedral tilt angle, and lattice strain around T (N). We have used refined atomic positional coordinates from the nuclear and magnetic structures, to obtain ionic polarization. These detailed studies confirm the magneto-electric and spin-lattice coupling in PFN across T-N.
Title:
Pressure-induced successive magnetic and structural phase transitions in Fe1.087Te
Authors:
Jorgensen, JE; Hansen, TC Author Full Names: Jorgensen, Jens-Erik; Hansen, Thomas Christian
Source:
EUROPEAN PHYSICAL JOURNAL B, 88 (5):10.1140/epjb/e2015-50713-6 MAY 11 2015
Abstract:
The crystal and magnetic structures of Fe1.087Te have been studied by neutron powder diffraction in the temperature range from 5 to 170 K at pressures in the range from approximate to 0.8 to approximate to 7 GPa. The p, T-phase diagram contains three phases with monoclinic, orthorhombic and tetragonal symmetry. The monoclinic and orthorhombic phases are both antiferromagnetically ordered and stable at temperatures below approximate to 69 K while the non-magnetic tetragonal phase is stable above this temperature. The monoclinic phase is stable for p less than or similar to 1.2 GPa while the orthorhombic phase is stable for 1.2 less than or similar to p less than or similar to 1.7 GPa and the tetragonal phase becomes stable at higher pressures at the lowest measured temperatures. The magnetic ordering is antiferromagnetic bicollinear and commensurate in the monoclinic phase but incommensurate and pressure dependent in the orthorhombic phase. The pressure-induced collapse of magnetic order at approximate to 1.7 GPa is accompanied by abrupt changes in volume and compressibility, suggestive of a spin state change of the Fe2+ ions in the FeTe layers.
Title:
Amount of valence charge of Al- and Zn-based quasicrystals and related approximant crystals evaluated by chemical shift observations and Bader analysis
Authors:
Koshiya, S; Terauchi, M Author Full Names: Koshiya, S.; Terauchi, M.
Source:
PHILOSOPHICAL MAGAZINE, 95 (13):1462-1470; 10.1080/14786435.2015.1033486 MAY 3 2015
Abstract:
The amounts of decreased charge at Al sites of Al-based (Al-Pd-Cr-Fe, Al-Si-Mn, and Al-Re-Si) and at Zn sites of Zn-based (Zn-Mg-Zr) quasicrystals and approximant crystals were estimated. The evaluation was done by comparisons between chemical shifts experimentally observed by soft-X-ray emission spectroscopy and the amount of valence charge obtained by Bader analysis for first principle calculations of reference materials (Al, alpha-Al2O3, Zn, and ZnO). Decreased charges at Al sites of Al-based quasicrystals and at Zn sites of Zn-based quasicrystals were evaluated to be 1.0-2.5 e(-)/atom and 1.1-1.2 e(-)/atom, respectively. A covalent bonding nature alloy of Al-Re-Si also showed a decrease in valence charge at Al sites.
Title:
Infinitely Adaptive Transition Metal Oxychalcogenides: The Modulated Structures of Ce2O2MnSe2 and (Ce0.78La0.22)(2)O2MnSe2
Authors:
Wang, CH; Ainsworth, CM; Gui, DY; McCabe, EE; Tucker, MG; Evans, IR; Evans, JSO Author Full Names: Wang, Chun-Hai; Ainsworth, Chris M.; Gui, Dong-Yun; McCabe, Emma E.; Tucker, Matthew G.; Evans, Ivana R.; Evans, John S. O.
Source:
CHEMISTRY OF MATERIALS, 27 (8):3121-3134; 10.1021/acs.chemmaer.5b00666 APR 28 2015
Abstract:
This article reports the syntheses, structures, and physical properties of the oxychalcogenides (Ce1-xLax)(2)O2MnSe2 with x = 0-0.7. These materials have a layered structure related to that of the LaOFeAs-derived superconductors but with the transition metal sites 50% occupied. Ce2O2MnSe2 contains alternating layers of composition: [Ce2O2](2+) and [MnSe2](2-). The size mismatch between the layers leads to an incommensurate structure with a modulation vector of q = ae+ Ob*+0.5c* with a = 0.158(1), which can be described with a (3 + 1)D superspace structural model in superspace group Cmme(a,0,(1) / OM [67.12]. There is a strong modulation of Mn site occupancies, leading to a mixture of corner- and edge-sharing MnSe4/2 tetrahedra in the [MnSe2](2-) layers. The modulation vector can be controlled by partial substitution of Ce3+ for larger La3+, and a simple commensurate (Ce0.78La0.22)(2)O2MnSe2 with a = 1/6. The materials respond to the change in relative size of the oxide and chalcogenide blocks by varying the ratio of corner- to edge-sharing tetrahedra. The superspace model lets us unify the structural description of the five different ordering patterns reported to date for different Ln(2)O(2)MSe(2) (Ln = lanthanide) materials. Mn moments in Ce2O2MnSe2 and (Ce0.78La0.22)(2)O2MnSe2 order antiferromagnetically below TN = 150 K, and Ce moments order below similar to 70 K. The magnetic structures of both materials have been determined using neutron diffraction. Both materials are semiconductors; Ce2O2MnSe2 has a = 9 x 10(-6) Omega(-1) cm(-1) at room temperature and an activation energy for charge carrier mobility from RT to 170 degrees C of -,0.4 eV.
Title:
Effect of Pd Substitution on Phase Formation and Stability in Ti-Zr-Ni Quasicrystalline Alloys
Authors:
Huang, HG; Chen, L; Xu, QY Author Full Names: Huang Huogen; Chen Liang; Xu Qinying
Source:
RARE METAL MATERIALS AND ENGINEERING, 44 (4):821-825; APR 2015
Abstract:
Pd can be used as an adding element to improve hydrogenation properties of Ti-Zr-Ni quasicrystalline alloys. However, the action mechanism of Pd addition is unclear yet. The effects of Pd substituting Ti and Zr in Ti45Zr38Ni17 and Ti40Zr40Ni20 alloys were studied by means of XRD, TEM and DSC examination. The results show that icosahedral quasicrystal can be formed purely through 4%similar to 6% Pd substitution for Ti or 4% for Zr in the Ti45Zr38Ni17 alloy, as well as 3%similar to 4% for Ti or possibly below 3% for Zr in the Ti40Zr40Ni20 alloy. This indicates a higher substitution limit for Ti in order for the heritance of the quasicrystal phase. Two derived quasicrystals Ti39Zr38Ni17Pd6 and Ti36Zr40Ni20Pd4 can be transformed into crystalline phases after annealing at 400 degrees C, demonstrating their lower thermo-stabilities in comparison to such Ti-Zr-Ni alloys being stable at about 700 degrees C. Both the replacement tendency and the decrease of the thermostability of quasicrystal phase might be ascribed to appropriate atomic size of Pd.
Title:
X-ray induced lock-in transition of cycloidal magnetic order in a multiferroic perovskite manganite
Authors:
Yamasaki, Y; Nakao, H; Murakami, Y; Nakajima, T; Sampietro, AL; Ohsumi, H; Takata, M; Arima, T; Tokura, Y Author Full Names: Yamasaki, Y.; Nakao, H.; Murakami, Y.; Nakajima, T.; Sampietro, A. Lafuente; Ohsumi, H.; Takata, M.; Arima, T.; Tokura, Y.
Source:
PHYSICAL REVIEW B, 91 (10):10.1103/PhysRevB.91.100403 MAR 24 2015
Abstract:
We report the x-ray photoexcitation effects on cycloidal magnetic order in a multiferroic perovskite-type manganite Gd0.5Tb0.5MnO3. The material exhibits a competition between the P (electric polarization)parallel to a ferroelectric state with the commensurate (C) ab-plane cycloidal and the P parallel to c ferroelectric state with the incommensurate (IC) bc-plane cycloidal spin structure. The phase transition between these two phases can be induced by an application of a magnetic field. We found that the x-ray irradiation can induce the bidirectional and persistent phase transition between IC and C phases. The nonresonant x-ray magnetic diffraction revealed that both the initial and the x-ray induced phases have the bc-plane cycloidal magnetic structure, whereas the magnetic wave number varies between IC and C. The x-ray induced bc-plane cycloidal C phase is thus the hidden multiferroic phase in the Gd1-xTbxMnO3 system, which does not show up with the application of any static field.

Update: 20-May-2015

Title:
High-resolution Brillouin scattering studies of phase transitions in Ca2MgSi2O7 and Ca2ZnSi2O7 silicates
Authors:
Maczka, M; Hanuza, J; Kaminskii, A; Kojima, S Author Full Names: Maczka, Miroslaw; Hanuza, Jerzy; Kaminskii, Alexander; Kojima, Seiji
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 638 34-37; 10.1016/j.jallcom.2015.03.055 JUL 25 2015
Abstract:
Temperature-dependent Micro-Brillouin scattering studies of Ca2MgSi2O7 and Ca2ZnSi2O7 single crystals were performed. Step-like decrease of Brillouin shifts and strong broadening of Brillouin bands corresponding to the c(33) elastic constant were observed at 351 K for Ca2MgSi2O7 and 407 K for Ca2ZnSi2O7. This behavior was attributed to coupling of strain to the square of the order parameter due to structural transitions into incommensurate phases. Analysis of the observed acoustic anomalies showed critical slowing down behavior of the relaxation time characterizing interaction between the order parameter and acoustic phonon. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Investigation of multiferroic behaviour of TbMnO3 nanoplates
Authors:
Acharya, SA; Khule, SM; Gaikwad, VM Author Full Names: Acharya, S. A.; Khule, S. M.; Gaikwad, V. M.
Source:
MATERIALS RESEARCH BULLETIN, 67 111-117; 10.1016/j.materresbull.2015.03.013 JUL 2015
Abstract:
In the present study, hydrothermally prepared TbMnO3 in plates-like morphology at nanoscale are investigated in multiferroic view point. X-ray diffraction study confirms the orthorhombic phase of as-synthesized TbMnO3. Microstructural features studied by Scanning Electron Microscopy and Transmission Electron Microscopy show the plates-like morphology of as-synthesized TbMnO3 at nanoscale. Local distortions investigated by FT-Raman exhibits redshift in T mode by about 20 cm(-1) as compared to that of the single crystal. The redshift in T mode is mainly due to defect by tilting of octahedra and respective changes in bond angle of Mn-O(1)-Mn. This is assigned to the size-morphology induced defects. The temperature dependent zero-field-cooled and field-cooled magnetization are measured at H=50 Oe and in the temperature range 2-300 K. The anomalies in magnetization are obtained at 8 and 42 K. Bifurcation of the ZFC and FC curves are observed very close to magnetic transition temperature 42 K. The 42 K anomaly is related to the sine wave ordering of Mn3+ moment; and 8K anomaly is associated with magnetic ordering of the Tb3+-sublattice propagation vector. The anomalies in the electric properties, epsilon' (T), tan delta (T), which are noticed within the 28K range, coincide with the temperature of incommensurate-commensurate (or lock-in) magnetic transition of TbMnO3. This study confirms that multiferroic behavior is retained in TbMnO3 nanoplates. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Spatial decay of the phason field in quasicrystal linear elasticity
Authors:
Mariano, PM; Salvatori, L Author Full Names: Mariano, Paolo Maria; Salvatori, Luca
Source:
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING, 23 (4):10.1088/0965-0393/23/4/045004 JUN 2015
Abstract:
We present numerical simulations showing that a conservative phason self-action, i.e. the stationary part of the phason diffusion, promotes in quasicrystal linear elasticity the phason spatial decay. The proof of the possible existence of such a phason self-action is based on the invariance requirements of the external power of all actions over a quasicrystal, with respect to isometry-based changes in observers in the physical and phason spaces. The numerical result confirms a 2011 theoretical prevision by Colli and Mariano.
Title:
Phase equilibria and transformations in ternary Mg-Gd-Zn alloys
Authors:
Grobner, J; Kozlov, A; Fang, XY; Zhu, SM; Nie, JF; Gibson, MA; Schmid-Fetzer, R Author Full Names: Groebner, Joachim; Kozlov, Artem; Fang, Xi-Ya; Zhu, Suming; Nie, Jian-Feng; Gibson, Mark A.; Schmid-Fetzer, Rainer
Source:
ACTA MATERIALIA, 90 400-416; 10.1016/j.actamat.2015.02.044 MAY 15 2015
Abstract:
Phase equilibria and transformations in ternary Mg-Gd-Zn alloys were studied experimentally by investigating 22 samples with up to 40 at.% Gd and 60 at.% Zn. These results, combined with a critical review of literature data, were used to develop thermodynamic descriptions of the Gd Zn and the Mg-Gd-Zn systems and to calculate the Mg-Gd-Zn phase diagram in the entire composition range. In the ternary system the hexagonal long-period stacking ordered structure 14H, the hexagonal phase H1, Gd11Mg24Zn64, and five solid solution phases with ternary compositions, GdMg5, GdMg3, GdMg2, Gd(Mg,Zn), and W are found to be stable, whereas the icosahedral phase I, GdMg3Zn6, and other hexagonal phases are metastable. In addition, a new stable phase Gd20Mg19Zn81 with a face-centered cubic structure is identified in the Mg Gd Zn system. Based on the thermodynamic description obtained in this work, the microstructures and phase transformations previously observed in the as-cast, solution heat treated and aged conditions are discussed. It is shown that the current thermodynamic predictions are in good accord with the experimental findings, suggesting the viability of such an approach for the microstructure design of Mg-Gd-Zn alloys. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Spectroscopic study of metallic magnetism in single-crystalline Nb1-yFe2+y
Authors:
Rauch, D; Kraken, M; Litterst, FJ; Sullow, S; Luetkens, H; Brando, M; Forster, T; Sichelschmidt, J; Neubauer, A; Pfleiderer, C; Duncan, WJ; Grosche, FM Author Full Names: Rauch, D.; Kraken, M.; Litterst, F. J.; Suellow, S.; Luetkens, H.; Brando, M.; Foerster, T.; Sichelschmidt, J.; Neubauer, A.; Pfleiderer, C.; Duncan, W. J.; Grosche, F. M.
Source:
PHYSICAL REVIEW B, 91 (17):10.1103/PhysRevB.91.174404 MAY 6 2015
Abstract:
We have investigated single crystals and polycrystals from the series Nb1-yFe2+y, -0.004 <= y <= 0.018, by electron spin resonance, muon spin relaxation, and Mossbauer spectroscopy. Our data establish that at lowest temperatures all samples exhibit bulk magnetic order. Slight Fe excess induces low-moment ferromagnetism, consistent with bulk magnetometry, while Nb-rich and stoichiometric NbFe2 display spin density wave order with small magnetic moment amplitudes of order similar to 0.001-0.01 mu(B)/Fe. This provides microscopic evidence for a modulated magnetic state on the border of ferromagnetism in NbFe2.
Title:
Long-range modulation of a composite crystal in a five-dimensional superspace
Authors:
Guerin, L; Mariette, C; Rabiller, P; Huard, M; Ravy, S; Fertey, P; Nichols, SM; Wang, B; Mannsfeld, SCB; Weber, T; Hollingsworth, MD; Toudic, B Author Full Names: Guerin, Laurent; Mariette, Celine; Rabiller, Philippe; Huard, Michael; Ravy, Sylvain; Fertey, Pierre; Nichols, Shane M.; Wang, Bo; Mannsfeld, Stefan C. B.; Weber, Thomas; Hollingsworth, Mark D.; Toudic, Bertrand
Source:
PHYSICAL REVIEW B, 91 (18):10.1103/PhysRevB.91.184101 MAY 5 2015
Abstract:
The intergrowth crystal of n-tetracosane/urea presents a misfit parameter, defined by the ratio gamma = c(h)/c(g) (c(host)/c(guest)), that is very close to a commensurate value (gamma congruent to 1/3). High-resolution diffraction studies presented here reveal an aperiodic misfit parameter of gamma = 0.3369, which is found to be constant at all temperatures studied. A complex sequence of structural phases is reported. The high temperature phase (phase I) exists in the four-dimensional superspace group P6(1)22(00 gamma). At T-c1 = 179(1) K, a ferroelastic phase transition increases the dimension of the crystallographic superspace. This orthorhombic phase (phase II) is characterized by the five-dimensional (5D) superspace group C222(1)(00 gamma)(10 delta) with a modulation vector a(o)* + c(m)* = a(o)* + delta . c(h)*, in which the supplementary misfit parameter is delta = 0.025(1) in host reciprocal units. This corresponds to the appearance of a modulation of very long period (about 440 +/- 16 angstrom). At T-c2 = 163.0(5) K, a 5D to 5D phase transition leads to the crystallographic superspace group P2(1)2(1)2(1)(00 gamma)(00 delta) with a very similar value of delta. This phase transition reveals a significant hysteresis effect.
Title:
X-ray investigation of lateral hetero-structures of inversion domains in LiNbO3, KTiOPO4 and KTiOAsO4
Authors:
Lyford, TS; Collins, SP; Fewster, PF; Thomas, PA Author Full Names: Lyford, Thomas S.; Collins, Stephen P.; Fewster, Paul F.; Thomas, Pamela A.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 71 255-267; 10.1107/S2053273315001503 3 MAY 2015
Abstract:
In this paper periodically domain-inverted (PDI) ferroelectric crystals are studied using high-resolution X-ray diffraction. Rocking curves and reciprocal-space maps of the principal symmetric Bragg reflections in LiNbO3 (LN) (Lambda = 5 mu m), KTiOPO4 (KTP) (Lambda = 9 mu m) and KTiOAsO4 (KTA) (Lambda = 39 mu m) are presented. For all the samples strong satellite reflections were observed as a consequence of the PDI structure. Analysis of the satellites showed that they were caused by a combination of coherent and incoherent scattering between the adjacent domains. Whilst the satellites contained phase information regarding the structure of the domain wall, this information could not be rigorously extracted without a priori knowledge of the twinning mechanism. Analysis of the profiles reveals strain distributions of Delta d/d = 1.6 x 10(-4) and 2.0 x 10(-4) perpendicular to domain walls in KTP and LN samples, respectively, and lateral correlation lengths of 63 mu m (KTP), 194 mu m (KTA) and 10 mu m (LN). The decay of crystal truncation rods in LN and KTP was found to support the occurrence of surface corrugations.
Title:
Structure factor for an icosahedral quasicrystal within a statistical approach
Authors:
Strzalka, R; Buganski, I; Wolny, J Author Full Names: Strzalka, Radoslaw; Buganski, Ireneusz; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 71 279-290; 10.1107/S2053273315001473 3 MAY 2015
Abstract:
This paper describes a detailed derivation of a structural model for an icosahedral quasicrystal based on a primitive icosahedral tiling (three-dimensional Penrose tiling) within a statistical approach. The average unit cell concept, where all calculations are performed in three-dimensional physical space, is used as an alternative to higher-dimensional analysis. Comprehensive analytical derivation of the structure factor for a primitive icosahedral lattice with monoatomic decoration (atoms placed in the nodes of the lattice only) presents in detail the idea of the statistical approach to icosahedral quasicrystal structure modelling and confirms its full agreement with the higher-dimensional description. The arbitrary decoration scheme is also discussed. The complete structure-factor formula for arbitrarily decorated icosahedral tiling is derived and its correctness is proved. This paper shows in detail the concept of a statistical approach applied to the problem of icosahedral quasicrystal modelling.
Title:
Path-independent integral in fracture mechanics of quasicrystals
Authors:
Sladek, J; Sladek, V; Atluri, SN Author Full Names: Sladek, J.; Sladek, V.; Atluri, S. N.
Source:
ENGINEERING FRACTURE MECHANICS, 140 61-71; 10.1016/j.engfracmech.2015.03.039 MAY 2015
Abstract:
Path-independent integrals are successfully utilized for accurate evaluation of fracture parameters in crystalic materials, where atomic arrangement is periodic. In quasicrystals (QC) the atomic arrangement is quasiperiodic in one-, two-or three-directions. The 2-d elastic problem for quasicrystal is described by coupled governing equations for phonon and phason displacements. Conservation laws for quasicrystals are utilized to derive path-independent integrals for cracks. The relation between the energy release and stress intensity factor for a crack under the mode I is given for decagonal QCs. The path-independent integral formulation is valid also for cracks in QCs with continuously varying material properties. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
Density functional theory calculations of the turbostratically disordered compound [(SnSe)(1+y)](m)(VSe2)(n)
Authors:
Rudin, SP; Johnson, DC Author Full Names: Rudin, Sven P.; Johnson, David C.
Source:
PHYSICAL REVIEW B, 91 (14):10.1103/PhysRevB.91.144203 APR 30 2015
Abstract:
Among composite materials that layer constituent substances of nanoscale thicknesses, [(SnSe)(1+y)](m)(VSe2)(n) emerges as an example where the constituents retain incommensurate lattice structures. Perpendicular to the stacking direction, the system exhibits random translations and random rotations on average, i.e., turbostratic disorder, with local regions showing twelvefold diffraction patterns. Earlier theoretical work on these structures showed that combining density functional theory with an empirical treatment of the van der Waals interaction gave structural parameters in good agreement with experiment, but no attempt was made to examine the relative orientations. Here we approximate the extended system with one extended constituent and one finite constituent, which allows the treatment of all relative orientations on equal footing. The calculations show how the twelvefold periodicity follows from how the ions of the SnSe layer lock in with favored positions relative to the VSe2 layer, and the associated energy scale supports arguments for the overall turbostratic disorder. The success of this approximation in describing the structural parameters of the extended [(SnSe)(1+y)](m)(VSe2)(n) system encourages its use for other properties and for other similar systems with other chemistries.
Title:
Linear spin wave theory for single-Q incommensurate magnetic structures
Authors:
Toth, S; Lake, B Author Full Names: Toth, S.; Lake, B.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (16):10.1088/0953-8984/27/16/166002 APR 29 2015
Abstract:
Linear spin wave theory provides the leading term in the calculation of the excitation spectra of long-range ordered magnetic systems as a function of 1/root S. This term is acquired using the Holstein-Primakoff approximation of the spin operator and valid for small dS fluctuations of the ordered moment. We propose an algorithm that allows magnetic ground states with general moment directions and single-Q incommensurate ordering wave vector using a local coordinate transformation for every spin and a rotating coordinate transformation for the incommensurability. Finally we show, how our model can determine the spin wave spectrum of the magnetic C-site langasites with incommensurate order.
Title:
Soft chemical control of the crystal and magnetic structure of a layered mixed valent manganite oxide sulfide
Authors:
Blandy, JN; Abakumov, AM; Christensen, KE; Hadermann, J; Adamson, P; Cassidy, SJ; Ramos, S; Free, DG; Cohen, H; Woodruff, DN; Thompson, AL; Clarke, SJ Author Full Names: Blandy, Jack N.; Abakumov, Artem M.; Christensen, Kirsten E.; Hadermann, Joke; Adamson, Paul; Cassidy, Simon J.; Ramos, Silvia; Free, David G.; Cohen, Harry; Woodruff, Daniel N.; Thompson, Amber L.; Clarke, Simon J.
Source:
APL MATERIALS, 3 (4):10.1063/1.4918973 APR 2015
Abstract:
Oxidative deintercalation of copper ions from the sulfide layers of the layered mixed-valent manganite oxide sulfide Sr2MnO2Cu1.5S2 results in control of the copper-vacancy modulated superstructure and the ordered arrangement of magnetic moments carried by the manganese ions. This soft chemistry enables control of the structures and properties of these complex materials which complement mixed-valent perovskite and perovskite-related transition metal oxides. (C) 2015 Author(s).
Title:
Periodic and incommensurately modulated phases in a (2-methylimidazolium) tetraiodobismuthate(III) thermochromic organic-inorganic hybrid
Authors:
Gagor, A; Weclawik, M; Bondzior, B; Jakubas, R Author Full Names: Gagor, A.; Weclawik, M.; Bondzior, B.; Jakubas, R.
Source:
CRYSTENGCOMM, 17 (17):3286-3296; 10.1039/c5ce00046g 2015
Abstract:
A(2-methylimidazolium) tetraiodobismuthate(III) (abbreviated as (2-MIm)BiI4) hybrid undergoes structural phase transition to an incommensurately modulated phase at 308 K. The relative coordinates of the modulation q-vector do not change down to 150 K indicating the stability of the incommensurate crystal packing that may be modeled by the sinusoidal waves of displacements. The transformation is triggered by the deformation of [BiI4-](n) chains which entails ordering of 2-MIm(+) counterions that couple to the anionic substructure via weak hydrogen bond interactions. Differential scanning calorimetry (DSC) and dielectric spectroscopy methods confirm the phase transition at 308 K (phase I -> phase II). Two dielectric relaxation processes that may be assigned to the dynamics of the polar 2-MIm(+) cations are present: a low frequency relaxator close to T-c and a high frequency one in a wide temperature region over phase II. The compound shows significant thermochromism characteristics for direct gap semiconductors. DOS calculations, together with the asymmetric local environment of bismuth ions, imply the presence of the stereo-chemically active bismuth lone pair 6s(2) electrons in both phases.

Update: 14-May-2015

Title:
Magnetic anisotropy in the incommensurate ScFe4Al8 system
Authors:
Recko, K; Dobrzynski, L; Waliszewski, J; Szymanski, K Author Full Names: Recko, K.; Dobrzynski, L.; Waliszewski, J.; Szymanski, K.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 388 82-89; 10.1016/j.jmmm.2015.03.096 AUG 15 2015
Abstract:
Neutron scattering and magnetization data are used for estimation of the spin ordering in ScFe4Al8. Results of experimental measurements are compared with the ground state configurations obtained by simulated annealing algorithms. The origins of the magnetocrystalline anisotropy of the scandium intermetallic alloy and the conditions of the coexistence of two different magnetic modulations as a function of the exchange integrals are discussed. The influence of the dipolar interactions for the noncollinearity and incommensurability in ScFe4Al8 was determined. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Thermal expansion of a Au - Al - Yb intermediate valence quasicrystal
Authors:
Watanuki, T; Kashimoto, S; Ishimasa, T; Machida, A; Yamamoto, S; Tanaka, Y; Mizumaki, M; Kawamura, N; Watanabe, S Author Full Names: Watanuki, T.; Kashimoto, S.; Ishimasa, T.; Machida, A.; Yamamoto, S.; Tanaka, Y.; Mizumaki, M.; Kawamura, N.; Watanabe, S.
Source:
SOLID STATE COMMUNICATIONS, 211 19-22; 10.1016/1.ssc2015.03.008 JUN 2015
Abstract:
The thermal expansion of a Au - Al - Yb intermediate-valence quasicrystal has been studied. X-ray diffraction measurements showed zero thermal expansion below 50 K. By comparison with an isostructural Au - Al - Tm quasicrystal, the contribution of the Yb valence variation was extracted, and it was shown that its negative thermal expansion component compensated for the positive thermal expansion of the original lattice. On cooling, the Yb contribution grew steeply below approximately 155 K down to the lowest experimental temperature of 5 K, due to enlargement of the Yb atomic radius, which was caused by the valence shift toward the divalent state. Additionally, a larger Yb contribution to the thermal expansion was demonstrated in a crystalline approximant to this quasicrystal. The magnitude of this contribution was approximately 1.4 Limes larger than in the case of the quasicrystal itself, resulting in a slight negative thermal expansion below 50 K. A heterogeneous valence model for the quasicrystal that we proposed previously accounts for this magnitude difference. (C) 2015 Elsevier Ltd. All rights reserved.
Title:
The unusual normal state and charge-density-wave order in 2H-NbSe2
Authors:
Koley, S; Mohanta, N; Taraphder, A Author Full Names: Koley, S.; Mohanta, N.; Taraphder, A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (18):10.1088/0953-8984/27/18/185601 MAY 13 2015
Abstract:
Competition between collective states like charge-density-wave and superconductivity, unencumbered by the spin degrees of freedom, is played out in some of the transition metal dichalcogenides. Although 2H-NbSe2 has received much less attention than some of the other members of the family (such as 1T-TiSe2 and 2H-TaSe2) of late, it shows superconductivity at 7.2 K and incommensurate charge ordering at 33 K. Recent experiments, notably angle resolved photoemission spectroscopy, have cast serious doubts on the theories based on Fermi surface nesting and electron-phonon interaction. The normal state has been found to be a poor, incoherent metal and remarkably, the coherence increases in the broken symmetry state. From a preformed excitonic liquid scenario, we show that there exists a natural understanding of the experimental data on 2H-NbSe2, based on electron-electron interaction. The collective instabilities, in this scenario, are viewed as a condensation of an incoherent excitonic liquid already present at high temperature.
Title:
Muon spin rotation and neutron scattering study of the noncentrosymmetric tetragonal compound CeAuAl3
Authors:
Adroja, DT; de la Fuente, C; Fraile, A; Hillier, AD; Daoud-Aladine, A; Kockelmann, W; Taylor, JW; Koza, MM; Burzuri, E; Luis, F; Arnaudas, JI; del Moral, A Author Full Names: Adroja, D. T.; de la Fuente, C.; Fraile, A.; Hillier, A. D.; Daoud-Aladine, A.; Kockelmann, W.; Taylor, J. W.; Koza, M. M.; Burzuri, E.; Luis, F.; Arnaudas, J. I.; del Moral, A.
Source:
PHYSICAL REVIEW B, 91 (13):10.1103/PhysRevB.91.134425 APR 24 2015
Abstract:
We have investigated the noncentrosymmetric tetragonal heavy fermion compound CeAuAl3 using muon spin rotation (mu SR), neutron diffraction (ND), and inelastic neutron scattering (INS) measurements. We have also revisited the magnetic, transport, and thermal properties. Themagnetic susceptibility reveals an antiferromagnetic transition at 1.1 K with, possibly, another magnetic transition near 0.18 K. The heat capacity shows a sharp lambda-type anomaly at 1.1 K in zero field, which broadens and moves to a higher temperature in an applied magnetic field. Our zero-field mu SR and ND measurements confirm the existence of a long-range magnetic ground state below 1.2 K. Further, the ND study reveals an incommensurate magnetic order with a magnetic propagation vector k = (0,0,0.52(1)) and a spiral structure of Ce moments coupled ferromagnetically within the ab plane. Our INS study reveals the presence of two well-defined crystal electric field (CEF) excitations at 5.1 and 24.6 meV in the paramagnetic phase of CeAuAl3 that can be explained on the basis of the CEF theory and the Kramer's theorem for a Ce ion having a 4f(1) electronic state. Furthermore, low energy quasielastic excitations show a Gaussian line shape below 30 K compared to a Lorentzian line shape above 30 K, indicating a slowdown of spin fluctuations below 30 K. We have estimated a Kondo temperature of T-K = 3.5 K from the quasielastic linewidth, which is in good agreement with that estimated from the heat capacity. This study also indicates the absence of any CEF-phonon coupling unlike that observed in isostructural CeCuAl3 The CEF parameters, energy level scheme, and their wave functions obtained from the analysis of INS data explain satisfactorily the single crystal susceptibility in the presence of two-ion anisotropic exchange interaction in CeAuAl3.
Title:
One-dimensional chain melting in incommensurate potassium
Authors:
McBride, EE; Munro, KA; Stinton, GW; Husband, RJ; Briggs, R; Liermann, HP; McMahon, MI Author Full Names: McBride, E. E.; Munro, K. A.; Stinton, G. W.; Husband, R. J.; Briggs, R.; Liermann, H. -P.; McMahon, M. I.
Source:
PHYSICAL REVIEW B, 91 (14):10.1103/PhysRevB.91.144111 APR 22 2015
Abstract:
Between 19 and 54 GPa, potassium has a complex composite incommensurate host-guest structure which undergoes two intraphase transitions over this pressure range. The temperature dependence of these host-guest phases is further complicated by the onset of an order-disorder transition in their guest chains. Here, we report single-crystal, quasi-single-crystal, and powder synchrotron x-ray diffraction measurements of this order-disorder phenomenon in incommensurate potassium to 47 GPa and 750 K. The so-called chain melting transition is clearly visible over a 22 GPa pressure range, and there are significant changes in the slope of the phase boundary which divides the ordered and disordered phases, one of which results from the intraphase transitions in the guest structure.
Title:
Structures of spherical viral capsids as quasicrystalline tilings
Authors:
Konevtsova, OV; Lorman, VL; Rochal, SB Author Full Names: Konevtsova, O. V.; Lorman, V. L.; Rochal, S. B.
Source:
PHYSICS OF THE SOLID STATE, 57 (4):810-814; 10.1134/S1063783415040125 APR 2015
Abstract:
Spherical viral shells with icosahedral symmetry have been considered as quasicrystalline tilings. Similarly to known Caspar-Klug quasi-equivalence theory, the presented approach also minimizes the number of conformations necessary for the protein molecule bonding with its neighbors in the shell, but is based on different geometrical principles. It is assumed that protein molecule centers are located at vertices of tiles with identical edges, and the number of different tile types is minimal. Idealized coordinates of nonequivalent by symmetry protein positions in six various capsid types are obtained. The approach describes in a uniform way both the structures satisfying the well-known Caspar-Klug geometrical model and the structures contradicting this model.

Update: 7-May-2015

Title:
The question of intrinsic origin of the metal-insulator transition in i-AlPdRe quasicrystal
Authors:
Delallaye, J; Berger, C Author Full Names: Delallaye, Julien; Berger, Claire
Source:
EUROPEAN PHYSICAL JOURNAL B, 88 (4):10.1140/epjb/e2015-50720-7 APR 15 2015
Abstract:
The icosahedral (i-) AlPdRe is the most resistive quasicrystalline alloy discovered so far. Resistivities (rho) of 1 Omega cm at 4 K and correlated resistance ratios (RRR = rho(4) kappa/rho(300) K) of more than 200 are observed in polycrystalline samples. These values are two orders of magnitude larger than for the isomorphous i-AlPdMn phase. We discuss here the controversial microscopic origin of the i-AlPdRe alloy electrical specificity. It has been proposed that the high resistivity values are due to extrinsic parameters, such as secondary phases or oxygen contamination. From comprehensive measurements and data from the literature including electronic transport correlated with micro structural and micro chemical analysis, we show that on the contrary there is mounting evidence in support of an origin intrinsic to the i-phase. Similarly to the other quasicrystalline alloys, the electrical resistivity of the i-AlPdRe samples depends critically on minute changes in the structural quality and chemical composition. The low resistivity in i-AlPdRe single-grains compared to polycrystaline samples can be explained by difference in chemical composition, heterogeneity and thermal treatment.
Title:
Beyond Entropy: Magnetic Forces Induce Formation of Quasicrystalline Structure in Binary Nanocrystal Superlattices
Authors:
Yang, ZJ; Wei, JJ; Bonville, P; Pileni, MP Author Full Names: Yang, Zhijie; Wei, Jingjing; Bonville, Pierre; Pileni, Marie-Paule
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137 (13):4487-4493; 10.1021/jacs.5b00332 APR 8 2015
Abstract:
Here, it is shown that binary superlattices of Co/Ag nanocrystals with the same size, surface coating, differing by their type of crystallinity are governed by Co-Co magnetic interactions. By using 9 nm amorphous-phase Co nanocrystals and 4 nm polycrystalline Ag nanocrystals at 25 degrees C, triangle-shaped NaCl-type binary nanocrystal superlattices are produced driven by the entropic force, maximizing the packing density. By contrast, using ferromagnetic 9 nm single domain (hcp) Co nanocrystals instead of amorphous-phase Co, dodecagonal quasicrystalline order is obtained, together with less-packed phases such as the CoAg13 (NaZn13-type), CoAg (AuCu-type), and CoAg3 (AuCu3-type) structures. On increasing temperature to 65 degrees C, 9 nm hcp Co nanocrystals become superparamagnetic, and the system yields the CoAg3 (AuCu3-type) and CoAg2 (AlB2-type) structures, as observed with 9 nm amorphous Co nanocrystals. Furthermore, by decreasing the Co nanocrystal size from 9 to 7 nm, stable AlB2-type binary nanocrystal superlattices are produced, which remain independent of the crystallinity of Co nanocrystals with the superparamagnetic state.
Title:
Incommensurate and commensurate modulations of Ba5RTi3Nb7O30 (R = La, Nd) tungsten bronzes and the ferroelectric domain structures
Authors:
Mao, MM; Li, K; Zhu, XL; Chen, XM Author Full Names: Mao, Min Min; Li, Kun; Zhu, Xiao Li; Chen, Xiang Ming
Source:
JOURNAL OF APPLIED PHYSICS, 117 (13):10.1063/1.4916723 APR 7 2015
Abstract:
Incommensurate and commensurate structural modulations of Ba5RTi3Nb7O30 (R=La, Nd) tungsten bronze ceramics were investigated by using a cooling holder equipped transmission electron microscopy in the temperature range from 100 K to 363 K. The incommensurate modulation was observed in both Ba5LaTi3Nb7O30 and Ba5NdTi3Nb7O30 at room temperature, while there was a transition from incommensurate tilted structure to commensurate superstructure for Ba5NdTi3Nb O-7(30) with decreasing temperature. The incommensurate and commensurate modulations were determined by the A-site occupancy of Ba and R cations. The A-site disorder resulted in larger incommensurability parameter delta and the diffusion of the *satellite reflection* spots. The effect of A-site disorder on the coupling between long-range dipolar order and the commensurate modulation was also discussed. The obvious ferroelectric 180 degrees domains with spike-like shape parallel to c axis were observed for Ba5NdTi3Nb7O30, while no macro ferroelectric domain was determined for Ba5LaTi3Nb7O30. (C) 2015 AIP Publishing LLC.
Title:
Periodically distributed objects with quasicrystalline diffraction pattern
Authors:
Wolny, J; Kuczera, P; Strzalka, R Author Full Names: Wolny, Janusz; Kuczera, Pawel; Strzalka, Radoslaw
Source:
APPLIED PHYSICS LETTERS, 106 (13):10.1063/1.4916830 MAR 30 2015
Abstract:
It is possible to construct fully periodically distributed objects with a diffraction pattern identical to the one obtained for quasicrystals. These objects are probability distributions of distances obtained in the statistical approach to aperiodic structures distributed periodically. The diffraction patterns have been derived by using a two-mode Fourier transform-a very powerful method not used in classical crystallography. It is shown that if scaling is present in the structure, this two-mode Fourier transform can be reduced to a regular Fourier transform with appropriately rescaled scattering vectors and added phases. Detailed case studies for model sets 1D Fibonacci chain and 2D Penrose tiling are discussed. Finally, it is shown that crystalline, quasicrystalline, and approximant structures can be treated in the same way. (C) 2015 AIP Publishing LLC.

Update: 30-Apr-2015

Title:
Correlation effects and non-collinear magnetism in the doped Hubbard model
Authors:
Igoshev, PA; Timirgazin, MA; Gilmutdinov, VF; Arzhnikov, AK; Irkhin, VY Author Full Names: Igoshev, P. A.; Timirgazin, M. A.; Gilmutdinov, V. F.; Arzhnikov, A. K.; Irkhin, V. Yu
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 383 2-7; 10.1016/j.jmmm.2014.10.031 JUN 1 2015
Abstract:
The ground-state magnetic phase diagram is investigated for the two- and three-dimensional t-t' Hubbard model. We take into account commensurate ferro-, antiferromagnetic, and incommensurate (spiral) magnetic phases, as well as phase separation into magnetic phases of different types, which was often missed in previous investigations. We trace the influence of correlation effects on the stability of both spiral and collinear magnetic order by comparing the results of employing both the generalized non-correlated mean-field (Hartree-Fock) approximation and generalized slave boson approach by Kotliar and Ruckenstein with correlation effects included. We found that the spiral states and especially ferromagnetism are generally strongly suppressed up to non-realistic large Hubbard U, if the correlation effects are taken into account. The electronic phase separation plays an important role in the formation of magnetic states and corresponding regions are wide, especially in the vicinity of half-filling. The details of magnetic ordering for different cubic lattices are discussed. (C) 2014 Elsevier B.V. All rights reserved
Title:
Structural, vibrational, and dielectric properties of Ruddlesden-Popper Ba2ZrO4 from first principles
Authors:
Louis, L; Nakhmanson, SM Author Full Names: Louis, Lydie; Nakhmanson, Serge M.
Source:
PHYSICAL REVIEW B, 91 (13):10.1103/PhysRevB.91.134103 APR 13 2015
Abstract:
Using first-principles computational techniques, we have investigated the structural, vibrational, and dielectric properties of a Ruddlesden-Popper-type layered oxide Ba2ZrO4 subjected to a wide range of biaxial strains emulating epitaxial thin-film environment. Under compressive strains, this compound experiences an incommensurate distortion characterized by planar displacements of individual perovskite slabs away from their high symmetry positions. On the other hand, under increasing epitaxial tension, the original centrosymmetric structure becomes unstable-first, with respect to antiferrodistortive oxygen cage rotations and then also with respect to in-plane polar distortions. Both the incommensurate-to-commensurate and the nonpolar-to-polar phase transformations are accompanied by anomalies of the static dielectric response, however, only in the latter case a divergence of the in-plane dielectric constant is observed. Remarkably, even after the transition into the ferroelectric state (with polarization of up to 0.12 C/m(2) at 3.5% tension) dielectric permittivity of Ba2ZrO4 remains unusually high, which is explained by an emergence of a Goldstone-like excitation in the system manifested through an in-plane libration of the polarization vector. Since Ba2ZrO4 displays a yet poorly understood tendency to absorb small molecules, such as water and CO2, acquiring better insights into the physical underpinnings of its behavior can produce more efficient functional materials for applications in advanced technologies for carbon sequestration.
Title:
Charge-Density Wave in Ca-Intercalated Bilayer Graphene Induced by Commensurate Lattice Matching
Authors:
Shimizu, R; Sugawara, K; Kanetani, K; Iwaya, K; Sato, T; Takahashi, T; Hitosugi, T Author Full Names: Shimizu, Ryota; Sugawara, Katsuaki; Kanetani, Kohei; Iwaya, Katsuya; Sato, Takafumi; Takahashi, Takashi; Hitosugi, Taro
Source:
PHYSICAL REVIEW LETTERS, 114 (14):10.1103/PhysRevLett.114.146103 APR 7 2015
Abstract:
We report the emergence of a charge-density wave (CDW) in Ca-intercalated bilayer graphene (C6CaC6), the thinnest limit of superconducting C6Ca, observed by low-temperature, high-magneticfield scanning tunneling microscopy or spectroscopy, and angle-resolved photoemission spectroscopy. While the possible superconductivity was not observed in epitaxially grown C6CaC6 on a SiC substrate, a CDW order different from that observed on the surface of bulk C6Ca was observed. It is inferred that the CDW state is induced by the potential modulation due to the commensurate lattice matching between the C6CaC6 film and the SiC substrate.
Title:
Microstructure and phase transformation of as-cast and annealed Mg-4Zn-1Y alloy containing quasi-crystal phase
Authors:
Yang, Y; Zhang, K; Li, XG; Li, YJ; Ma, ML; Shi, GL; Yuan, JW Author Full Names: Yang, Yang; Zhang, Kui; Li, Xing-Gang; Li, Yong-Jun; Ma, Ming-Long; Shi, Guo-Liang; Yuan, Jia-Wei
Source:
RARE METALS, 34 (4):239-244; 10.1007/s12598-014-0443-8 APR 2015
Abstract:
By means of optical microscope (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses, the microstructures of as-cast and heat-treated Mg-4Zn-1Y (wt%) alloy containing quasi-crystal phase were studied. The microstructure of the as-cast alloy consists of alpha-Mg solid solution grains, intermetallic particles and eutectic phases (W-phase and I-phase), and huge grains with serious dendritic segregation are clearly observed. After heat treatment, phase transformation and dissolution occur in the alloy and many phases remain. When the alloy was treated above 410 A degrees C, the eutectic phases transform into spherical shape as the I-phase turns to W-phase. After heat treatment for long time, the alloy is over burnt and the W-phase decomposes to Mg-Y binary phase.
Title:
Microstructural changes in quasicrystalline Al - Mn - Be - Cu alloy after various heat treatments
Authors:
Strekelj, N; Naglic, I; Klancnik, G; Nagode, A; Markoli, B Author Full Names: Strekelj, Neva; Naglic, Iztok; Klancnik, Grega; Nagode, Ales; Markoli, Bostjan
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, 106 (4):342-351; 10.3139/146.111195 APR 2015
Abstract:
In this study we investigated the microstructural changes after a variety of heat treatments of the quasicrystalline Al - Mn - Be - Cu alloy. In addition, we report on Vickers microhardness measurements and tensile-test results for the same materials. The samples were produced in a conventional manner, i.e., melting in an electrical resistance furnace in air and a gravitational casting process using a round copper die, which was in the form of a tensile-test specimen with a diameter of 5 mm. After the casting, some of the samples were just solution treated (annealed) and then quenched in water, while others were additionally aged (artificially - T6, or naturally - T4) or directly aged after the casting. In comparison to the as-cast state, the Vickers microhardness values of the aluminum-based matrix and the tensile properties of the samples decreased when just the solution treatment, T4 or T6 treatment was performed. The tensile properties also decreased after the heat treatments. A microstructural inspection revealed that the microstructural changes occurred already during the solution treatment, i.e., the formation of the phases Be4Al(Mn,Cu) and tau(1)-Al29Mn6Cu4 on the approximant H-Al4Mn and quasicrystalline i-phase particles' edges and the occurrence of precipitates in the alpha(Al) matrix. The precipitates that would additionally contribute to the hardening of the alloy did not form. The directly aged samples showed little or no increase in microhardness values in comparison to the as-cast samples, but possibilities of theta '' precipitates being formed from the already saturated matrix after the casting could not be excluded. After all the heat treatments the quasicrystalline i-phase, as a primary and eutectic phase, was preserved.
Title:
Influence of I-phase and W-phase on microstructure and mechanical properties of Mg-8Li-3Zn alloy
Authors:
Wei, GB; Peng, XD; Zhang, B; Hadadzadeh, A; Xu, TC; Xie, WD Author Full Names: Wei, Guo-bing; Peng, Xiao-dong; Zhang, Bao; Hadadzadeh, Amir; Xu, Tian-cai; Xie, Wei-dong
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 25 (3):713-720; 10.1016/S1003-6326(15)63656-1 MAR 2015
Abstract:
Microstructures and mechanical properties of LZ83-xY alloys containing I-phase and W-phase were investigated by XRD, OM, SEM and EDS. The experimental results show that the content of I-phase and W-phase changes by varying Zn/Y mass ratio in the LZ83-xY alloys. The cohesion of I-phase/alpha-Mg eutectic pockets can enhance the strength in the as-cast LZ83-0.5Y and LZ83-1.0Y alloys, while the W-phase has no obvious strengthening effect on the LZ83-1.5Y alloy. In the extruded alloys, the I-phase and W-phase were extruded into the particles with nanoscale size in the beta-Li matrix phase. The dispersion strengthening of W-phase was more obvious because of the higher volume fraction. The ultimate tensile strength of extruded LZ83-1.5Y alloy is up to 238 MPa while the elongation is up to 20%.
Title:
Topological Hofstadter insulators in a two-dimensional quasicrystal
Authors:
Tran, DT; Dauphin, A; Goldman, N; Gaspard, P Author Full Names: Tran, Duc-Thanh; Dauphin, Alexandre; Goldman, Nathan; Gaspard, Pierre
Source:
PHYSICAL REVIEW B, 91 (8):10.1103/PhysRevB.91.085125 FEB 27 2015
Abstract:
We investigate the properties of a two-dimensional quasicrystal in the presence of a uniform magnetic field. In this configuration, the density of states (DOS) displays a Hofstadter-butterfly-like structure when it is represented as a function of the magnetic flux per tile. We show that the low-DOS regions of the energy spectrum are associated with chiral edge states, in direct analogy with the Chern insulators realized with periodic lattices. We establish the topological nature of the edge states by computing the topological Chern number associated with the bulk of the quasicrystal. This topological characterization of the nonperiodic lattice is achieved through a local (real-space) topological marker. This work opens a route for the exploration of topological-insulating materials in a wide range of nonperiodic lattice systems, including photonic crystals and cold atoms in optical lattices.
Title:
The refined theory of 2D quasicrystal deep beams based on elasticity of quasicrystals
Authors:
Gao, Y; Yu, LY; Yang, LZ; Zhang, LL Author Full Names: Gao, Yang; Yu, Lian-Ying; Yang, Lian-Zhi; Zhang, Liang-Liang
Source:
STRUCTURAL ENGINEERING AND MECHANICS, 53 (3):411-427; FEB 10 2015
Abstract:
Based on linear elastic theory of quasicrystals, various equations and solutions for quasicrystal beams are deduced systematically and directly from plane problem of two-dimensional quasicrystals. Without employing ad hoc stress or deformation assumptions, the refined theory of beams is explicitly established from the general solution of quasicrystals and the Lur'e symbolic method. In the case of homogeneous boundary conditions, the exact equations and exact solutions for beams are derived, which consist of the fourth-order part and transcendental part. In the case of non-homogeneous boundary conditions, the exact governing differential equations and solutions under normal loadings only and shear loadings only are derived directly from the refined beam theory, respectively. In two illustrative examples of quasicrystal beams, it is shown that the exact or accurate analytical solutions can be obtained in use of the refined theory.
Title:
Low-Temperature Physical Properties of Single-Crystalline EuCoGe3 and EuRhGe3
Authors:
Bednarchuk, O; Kaczorowski, D Author Full Names: Bednarchuk, O.; Kaczorowski, D.
Source:
ACTA PHYSICA POLONICA A, 127 (2):418-420; FEB 2015
Abstract:
Since a few years europium-based intermetallics have been attracting more and more attention due to their intriguing physical properties with anomalous behaviours in magnetically ordered states. Here, we report on the formation and the bulk physical properties of two tetragonal compounds EuCoGe3 and EuRhGe3, studied on high-quality single-crystalline specimens. In both materials, the Eu ions are in their divalent state, which gives rise to an antiferromagnetic ordering below T-N = 15.4 K and T-N = 11.3 K, respectively. In addition, EuCoGe3 exhibits a successive antiferromagnetic phase transition at T-2 = 13.4 K. Based on some characteristic features in the temperature variations of the magnetic susceptibility, specific heat and electrical resistivity, we suggest that in both germanides an amplitude modulated magnetic structure develops below the respective T-N, with the Eu magnetic moments directed along the crystallographic [001] axis in EuCoGe3 and perpendicular to this direction in EuRhGe3.
Title:
The J(1)-J(2) Model on the Anisotropic Triangular and the Square Lattice: Similarities and Differences
Authors:
Schmidt, B; Thalmeier, P Author Full Names: Schmidt, B.; Thalmeier, P.
Source:
ACTA PHYSICA POLONICA A, 127 (2):324-326; FEB 2015
Abstract:
The Heisenberg model on a triangular lattice is a prime example for a geometrically frustrated spin system. However most experimentally accessible compounds have spatially anisotropic exchange interactions. As a function of this anisotropy, ground states with different magnetic properties can be realized. On the other hand, the J(1)-J(2) model on the square lattice is a well-known example for frustration induced by competing exchange. The classical phase diagrams of the two models are related in a broad range of the control parameter phi - tan(-1)(J(2)/J(1)). In both cases three different types of ground states are realized, each model having a ferromagnetic and an antiferromagnetic region in the phase diagram, and a third phase with columnar magnetic order for the square lattice and an in general incommensurate spiral structure for the triangular lattice. Quantum effects lift degeneracies in the non-FM phases and lead to additional nonmagnetic regions in the phase diagrams. The contribution of zero point fluctuations to ground state energy, wave vector, and ordered moment is discussed.
Title:
Reconstruction of the Exchange Integrals Map of ScFe4Al8 Magnetic Structure
Authors:
Recko, K; Dobrzynski, L; Waliszewski, J; Szymanski, K Author Full Names: Recko, K.; Dobrzynski, L.; Waliszewski, J.; Szymanski, K.
Source:
ACTA PHYSICA POLONICA A, 127 (2):424-426; FEB 2015
Abstract:
The influence of the dipolar as well as crystal field interaction as the main reasons of the noncollineaxity and incommensurability of the 3d-3d-3p alloy belonging to ThMn12 family is investigated. Available data on the single crystal neutron scattering experiments for ScFe4Al8 compound are discussed. The values and directions of the spin ordering found by magnetic diffraction are compared to that one derived from ground state configurations obtained by a simulated annealing algorithm.

Update: 23-Apr-2015

Title:
Crystal structure determination of incommensurate modulated martensite in Ni-Mn-In Hensler alloys
Authors:
Yan, HL; Zhang, YD; Xu, N; Senyshyn, A; Brokmeier, HG; Esling, C; Zhao, X; Zuo, L Author Full Names: Yan, Haile; Zhang, Yudong; Xu, Nan; Senyshyn, Anatoliy; Brokmeier, Heinz-Guenter; Esling, Claude; Zhao, Xiang; Zuo, Liang
Source:
ACTA MATERIALIA, 88 375-388; 10.1016/j.actamat.2015.01.025 APR 15 2015
Abstract:
The crystal structure of modulated martensite in Mn-rich off-stoichiometric Ni2Mn1.44In0.56 alloy was determined with high-resolution powder neutron diffraction and synchrotron X-ray diffraction in the frame of (3 + 1)-dimensional superspace theory. The average crystal structure and the modulation wave vector were firstly derived by analyzing the reflection separations induced by the martensitic transformation on the basis of the transformation orientation inheritance. This treatment could be applied to predetermine the modulated structures of materials with displacive structural transformation. The crystal structure of modulated martensite was finally refined by the Rietveld method. Results show that the martensite possesses an incommensurate 6M modulated structure of superspace group I2/m(alpha 0 gamma)00, with lattice parameters a= 4.3919(4) angstrom, b = 5.6202(1) angstrom, c = 4.3315(7) angstrom, and beta = 93.044(1)degrees, and the modulation wave vector q = 0.343(7) c.* The detailed site occupations for extra-Mn atoms with respect to the stoichiometric case were investigated by ab initio calculations. The extra-Mn atoms have a preference to be uniformly dispersed. A threefold layered superstructure in the 3-dimensional space was proposed to approximately describe the incommensurate modulated structure. This 6M superstructure model is considered to be representative for off-stoichiometric Ni-(Co)-Mn-In modulated martensite with martensitic transformation around room temperature. The present study is expected to offer an important basis for reliable crystallographic and microstructural characterizations on Ni-Mn-In alloys, so as to understand the underlying mechanisms of their multifunctional magneto-responsive properties. (c) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Magnetic structures in the magnetic phase diagram of Ho2RhIn8
Authors:
Cermak, P; Prokes, K; Ouladdiaf, B; Boehm, M; Kratochvilova, M; Javorsky, P Author Full Names: Cermak, Petr; Prokes, Karel; Ouladdiaf, Bachir; Boehm, Martin; Kratochvilova, Marie; Javorsky, Pavel
Source:
PHYSICAL REVIEW B, 91 (14):10.1103/PhysRevB.91.144404 APR 7 2015
Abstract:
The magnetic phase diagram of the tetragonal Ho2RhIn8 compound has similar features to many related systems, revealing a zero magnetic field AF1 and a field-induced AF2 phases. Details of the magnetic order in the AF2 phase were not reported yet for any of the related compounds. In addition, only the Ho2RhIn8 phase diagram contains a small region of the incommensurate zero-field AF3 phase. We have performed a number of neutron diffraction experiments on single crystals of Ho2RhIn8 using several diffractometers including experiments in both horizontal and vertical magnetic fields up to 4 T. We present details of the magnetic structures in all magnetic phases of the rich phase diagram of Ho2RhIn8. The Ho magnetic moments point along the tetragonal c axis in every phase. The ground-state AF1 phase is characterized by propagation vector k = (1/2,0,0). The more complex ferrimagnetic AF2 phase is described by four propagation vectors k(0) = ( 0,0,0), k(1) = (1/2,0,0), k(2) = ( 0,1/ 2,1/2), k(3) = (1/2,1/2,1/2). The magnetic structure in the AF3 phase is incommensurate with k(AF3) = ( 0.5, delta, 0). Our results are consistent with theoretical calculations based on crystal field theory.
Title:
Taking a closer look for a broader view: combining powder diffraction with electron crystallography for a better understanding of modulated structures
Authors:
Palatinus, L Author Full Names: Palatinus, Lukas
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 125-126; 10.1107/S2052520615005910 2 APR 2015
Title:
Resonance-stabilized partial proton transfer in hydrogen bonds of incommensurate phenazine-chloranilic acid
Authors:
Noohinejad, L; Mondal, S; Ali, SI; Dey, S; van Smaalen, S; Schonleber, A Author Full Names: Noohinejad, Leila; Mondal, Swastik; Ali, Sk Imran; Dey, Somnath; van Smaalen, Sander; Schoenleber, Andreas
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 228-234; 10.1107/S2052520615004084 2 APR 2015
Abstract:
The co-crystal of phenazine (Phz) and chloranilic acid (H(2)ca) becomes ferroelectric upon cooling through the loss of inversion symmetry. Further cooling results in the development of an incommensurate ferroelectric phase, followed by a lock-in transition towards a twofold superstructure. Here we present the incommensurately modulated crystal structure of Phz-H(2)ca at T = 139 K with a symmetry given by the superspace group P2(1)(1/2 sigma(2) 1/2)0 and sigma(2) = 0.5139. The modulation mainly affects the positions of the protons within half of the intermolecular hydrogen bonds that are responsible for the spontaneous polarization in all three low-temperature phases. Evidence for proton transfer in part of the hydrogen bonds is obtained from the correlated dependence on the phase of the modulation of the lengths of bonds involved in resonance stabilization of the acidic anion, and much smaller variations of bond lengths of atoms not involved in the resonance mechanism. Incommensurability is explained as competition between proton transfer favored for single hydrogen bonds on the basis of pK(a) values and avoiding unfavorable Coulomb repulsion within the lattice of the resulting ionic molecules.
Title:
Synergy between transmission electron microscopy and powder diffraction: application to modulated structures
Authors:
Batuk, D; Batuk, M; Abakumov, AM; Hadermann, J Author Full Names: Batuk, Dmitry; Batuk, Maria; Abakumov, Artem M.; Hadermann, Joke
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 127-143; 10.1107/S2052520615005466 2 APR 2015
Abstract:
The crystal structure solution of modulated compounds is often very challenging, even using the well established methodology of single-crystal Xray crystallography. This task becomes even more difficult for materials that cannot be prepared in a single-crystal form, so that only polycrystalline powders are available. This paper illustrates that the combined application of transmission electron microscopy (TEM) and powder diffraction is a possible solution to the problem. Using examples of anion-deficient perovskites modulated by periodic crystallographic shear planes, it is demonstrated what kind of local structural information can be obtained using various TEM techniques and how this information can be implemented in the crystal structure refinement against the powder diffraction data. The following TEM methods are discussed: electron diffraction (selected area electron diffraction, precession electron diffraction), imaging (conventional high-resolution TEM imaging, high-angle annular dark-field and annular bright-field scanning transmission electron microscopy) and state-of-the-art spectroscopic techniques (atomic resolution mapping using energy-dispersive X-ray analysis and electron energy loss spectroscopy).
Title:
Magnetic ordering and ferroelectricity in multiferroic 2H-AgFeO2: Comparison between hexagonal and rhombohedral polytypes
Authors:
Terada, N; Khalyavin, DD; Manuel, P; Tsujimoto, Y; Belik, AA Author Full Names: Terada, Noriki; Khalyavin, Dmitry D.; Manuel, Pascal; Tsujimoto, Yoshihiro; Belik, Alexei A.
Source:
PHYSICAL REVIEW B, 91 (9):10.1103/PhysRevB.91.094434 MAR 30 2015
Abstract:
Magnetic and dielectric properties of the hexagonal triangular lattice antiferromagnet 2H-AgFeO2 have been studied by neutron diffraction, magnetic susceptibility, specific heat, pyroelectric current, and dielectric constant measurements. The ferroelectric polarization, P similar or equal to 5 mu C/m(2), has been found to appear below 11 K due to a polar nature of the magnetic ground state of the system. In the temperature range of 11 K <= T <= 18 K, an incommensurate spin density wave (ICM1) with the nonpolar magnetic point group mmm1' and the k(1) = (0, q(b)(1),0; q(b)(1) = 0.390-0.405) propagation vector takes place. Below 14 K, a proper screw ordering (ICM2) and k(2) = (0, q(b)(2),0; q(b)(2) = 0.385-0.396) appears as a minor phase which coexists with ICM1 and the ground state down to the lowest measured temperature 5.5 K. No ferroelectric polarization associated with the ICM2 phase was observed in agreement with its nonpolar point group 2221'. Finally, a spiral order with cycloid and proper screw components (ICM3), and k(3) = (q(a)(3), q(b)(3),0; q(a)(3) = 0.0467, q(b)(3) = 0.349) emerges below 11 K as the ground state of the system. Based on the deduced magnetic point group 21', we conclude that the ferroelectric polarization in ICM3 is parallel to the c axis and is caused by the inverse Dzyloshinskii-Moriya effect with p(1) proportional to r(ij) x (S-i x S-j). Unlike the rhombohedral 3R-AgFeO2 polytype, the additional contribution to the macroscopic polarization p(2) proportional to S-i x S-j is not allowed in the present case due to the symmetry constraints imposed by the hexagonal lattice of 2H-AgFeO2.
Title:
Field effects with H vertical bar vertical bar b on the incommensurate magnetic structures of multiferroic MnWO4 studied within the superspace formalism
Authors:
Urcelay-Olabarria, I; Garcia-Munoz, JL; Mukhin, AA Author Full Names: Urcelay-Olabarria, I.; Garcia-Munoz, J. L.; Mukhin, A. A.
Source:
PHYSICAL REVIEW B, 91 (10):10.1103/PhysRevB.91.104429 MAR 30 2015
Abstract:
We investigate the magnetic-field-induced (H vertical bar vertical bar b) transition in the reference improper multiferroic MnWO4 using superspace formalism. The distinct superspace group symmetries are determined from single-crystal neutron diffraction. The study of the full magnetic symmetry of the incommensurate magnetic phases under field provides the keys for understanding its magnetic and ferroelectric behavior up to 12 T. At moderate fields, below the transition, the magnetic modulations of the two Mn sites in the simple cell are independent. At the field-induced transition between multiferroic phases, the electric polarization undergoes a flip from the monoclinic b axis to the ac plane. An additional component in the polarization is predicted along the c axis, due to a point symmetry change from 2(y) 1' to m(y)1'. In contrast with the low-field phase, above the transition the influence of the magnetic field results in the coupling between the magnetic modulations of the two Mn sites of the original monoclinic cell.
Title:
Updating the phase diagram of the archetypal frustrated magnet Gd3Ga5O12
Authors:
Deen, PP; Florea, O; Lhotel, E; Jacobsen, H Author Full Names: Deen, P. P.; Florea, O.; Lhotel, E.; Jacobsen, H.
Source:
PHYSICAL REVIEW B, 91 (1):10.1103/PhysRevB.91.014419 JAN 15 2015
Abstract:
The applied magnetic field and temperature phase diagram of the archetypal frustrated magnet, Gd3Ga5O12, has been reinvestigated using single-crystal magnetometry and polarized neutron diffraction. The updated phase diagram is substantially more complicated than previously reported and can be understood in terms of competing interactions with loops of spins, trimers, and decagons, in addition to competition and interplay between antiferromagnetic, incommensurate, and ferromagnetic order. Several additional distinct phase boundaries are presented. The phase diagram centers around a multiphase convergence to a single point at 0.9 T and similar to 0.35 K, below which, in temperature, a very narrow magnetically disordered region exists. These data illustrate the richness and diversity that arise from frustrated exchange on the three-dimensional hyperkagome lattice.
Title:
Chemical ordering of Co and Ni in a W-(AlCoNi) crystalline approximant related to Al-Co-Ni decagonal quasicrystals studied by atomic resolution energy-dispersive X-ray spectroscopy
Authors:
Yasuhara, A; Hiraga, K Author Full Names: Yasuhara, Akira; Hiraga, Kenji
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 95 (1):52-57; 10.1080/09500839.2015.1006705 JAN 2 2015
Abstract:
A W-(AlCoNi) crystalline approximant, which is closely related to Al-Co-Ni decagonal quasicrystals, in an Al72.5Co20Ni7.5 alloy has been studied by atomic resolution energy-dispersive X-ray spectroscopy (EDS), in an instrument attached to a spherical aberration (Cs)-corrected scanning transmission electron microscope. On high-resolution EDS maps of Co and Ni elements, obtained by integrating many sets of EDS data taken from undamaged areas, chemical ordering of Co and Ni is clearly detected. In the structure of the W-(AlCoNi) phase, consisting of arrangements of transition-metal (TM) atoms located at vertices of pentagonal tilings and pentagonal arrangements of mixed sites (MSs) of TM and Al atoms, Co atoms occupy the TM atom positions with the pentagonal tiling and Ni is enriched in part of the pentagonal arrangements of MSs.

Update: 16-Apr-2015

Title:
Nematic fluctuations and their wave vector in two-dimensional metals
Authors:
Punk, M Author Full Names: Punk, Matthias
Source:
PHYSICAL REVIEW B, 91 (11):10.1103/PhysRevB.91.115131 MAR 17 2015
Abstract:
We revisit the problem of electrons on a square lattice below half-filling close to an Ising-nematic quantum critical point. For Fermi surfaces with sufficiently strong antinodal nesting, the static nematic susceptibility is maximal at the antinodal nesting wave vector within a simple random phase approximation calculation. We present a detailed analysis of the nematic susceptibility within Eliashberg theory and show that the strong interaction between fermions in the antinodal regions shifts the maximum of the nematic susceptibility to slightly larger wave vectors. The corresponding order is akin to the incommensurate charge-density wave with d-wave form factor found recently in some underdoped cuprate materials. At sufficiently high temperatures around T/t similar to 0.1, nematic fluctuations are strongest at zero wave vector.
Title:
Ferroelectricity induced by ferriaxial crystal rotation and spin helicity in a B-site-ordered double-perovskite multiferroic In2NiMnO6
Authors:
Terada, N; Khalyavin, DD; Manuel, P; Yi, W; Suzuki, HS; Tsujii, N; Imanaka, Y; Belik, AA Author Full Names: Terada, Noriki; Khalyavin, Dmitry D.; Manuel, Pascal; Yi, Wei; Suzuki, Hiroyuki S.; Tsujii, Naohito; Imanaka, Yasutaka; Belik, Alexei A.
Source:
PHYSICAL REVIEW B, 91 (10):10.1103/PhysRevB.91.104413 MAR 17 2015
Abstract:
We have performed dielectric measurements and neutron diffraction experiments on the double perovskite In2NiMnO6. A ferroelectric polarization, P similar or equal to 30 mu C/m(2), is observed in a polycrystalline sample below T-N = 26 K where a magnetic phase transition occurs. The neutron diffraction experiment demonstrates that a complex noncollinear magnetic structure with " cycloidal" and " proper screw" components appears below T-N, which has the incommensurate propagation vector k = (k(a),0, k(c); k(a) similar or equal to 0.274, k(c) similar or equal to - 0.0893). The established magnetic point group 21' implies that the macroscopic ferroelectric polarization is along the monoclinic b axis. Recent theories based on the inverse Dzyaloshinskii- Moriya effect allow us to specify two distinct contributions to the polarization of In2NiMnO6. One of them is associated with the cycloidal component, p(1) proportional to r(ij) x (S-i x S-j)(perpendicular to), and the other with the proper screw component, p(2) proportional to [r(ij) center dot ( S-i x S-j)(parallel to)] A. The latter is explained by coupling between spin helicity and " ferriaxial" crystal rotation with macroscopic ferroaxial vector A, characteristic of the B- site ordered perovskite systems with out- of- plane octahedral tilting.
Title:
X-ray standing wave study of Si clusters on a decagonal Al-Co-Ni quasicrystal surface
Authors:
Woodruff, DP; Ledieu, J; Lovelock, KRJ; Jones, RG; Deyko, A; Wearing, LH; McGrath, R; Chaudhuri, A; Li, HI; Su, SY; Mayer, A; Stanisha, NA; Diehl, RD Author Full Names: Woodruff, D. P.; Ledieu, J.; Lovelock, K. R. J.; Jones, Robert G.; Deyko, A.; Wearing, L. H.; McGrath, R.; Chaudhuri, A.; Li, H. I.; Su, S. Y.; Mayer, A.; Stanisha, N. A.; Diehl, R. D.
Source:
PHYSICAL REVIEW B, 91 (11):10.1103/PhysRevB.91.115418 MAR 12 2015
Abstract:
Quantitative adsorption structure determinations on quasicrystals are scarce because most techniques for measuring surface structures are not well suited to the complex and infinite unit cells of quasicrystals. The normal incidence standing x-ray wave field technique presents a solution to these problems because it can be made inherently surface sensitive and does not involve extensive computational effort. We describe a method for applying this technique to adsorbates on quasicrystals, with specific application to a submonolayer of Si atoms on a decagonal Al-Co-Ni surface. We demonstrate the sensitivity of the technique to both adsorption site and geometry, leading to the conclusion that the Si atoms, which form six-atom pentagonal clusters, have an average height of 1.77 +/- 0.05 angstrom above pentagonal hollow sites, with a significant height variation among the Si atoms in the cluster. In particular, the central Si atom sits more deeply than the five surrounding Si atoms, which are, on average, 2.7 angstrom away from the central Si atom. Although this study was performed on a decagonal quasicrystal that is periodic perpendicular to the surface, we describe how the technique can be applied to cases with no periodicity.
Title:
Effect of pointlike impurities on d(x2-y2) charge-density waves in cuprate superconductors
Authors:
Atkinson, WA; Kampf, AP Author Full Names: Atkinson, W. A.; Kampf, A. P.
Source:
PHYSICAL REVIEW B, 91 (10):MAR 12 2015
Abstract:
Many cuprate superconductors possess an unusual charge- ordered phase that is characterized by an approximate dx2 - y2 intraunit cell form factor and a finite modulation wave vector q*. We study the effects of impurities on this charge- ordered phase via a single- band model in which bond order is the analog of charge order in the cuprates. Impurities are assumed to be pointlike and are treated within the self- consistent t- matrix approximation. We show that suppression of bond order by impurities occurs through the local disruption of the dx2 - y2 form factor near individual impurities. Unlike d- wave superconductors, where the sensitivity of Tc to impurities can be traced to a vanishing average of the dx2 - y2 order parameter over the Fermi surface, the response of bond order to impurities is dictated by a few Fermi surface " hotspots." The bond order transition temperature Tbo thus follows a different universal dependence on impurity concentration ni than does the superconducting Tc. In particular, Tbo decreases more rapidly than Tc with increasing ni when there is a nonzero Fermi surface curvature at the hotspots. Based on experimental evidence that the pseudogap is insensitive to Zn doping, we conclude that a direct connection between charge order and the pseudogap is unlikely. Furthermore, the enhancement of stripe correlations in the La- based cuprates by Zn doping is evidence that this charge order is also distinct from stripes.
Title:
Influence of leaching on surface composition, microstructure, and valence band of single grain icosahedral Al-Cu-Fe quasicrystal
Authors:
Lowe, M; Yadav, TP; Fournee, V; Ledieu, J; McGrath, R; Sharma, HR Author Full Names: Lowe, M.; Yadav, T. P.; Fournee, V.; Ledieu, J.; McGrath, R.; Sharma, H. R.
Source:
JOURNAL OF CHEMICAL PHYSICS, 142 (9):10.1063/1.4913567 MAR 7 2015
Abstract:
The use of quasicrystals as precursors to catalysts for the steam reforming of methanol is potentially one of the most important applications of these new materials. To develop application as a technology requires a detailed understanding of the microscopic behavior of the catalyst. Here, we report the effect of leaching treatments on the surface microstructure, chemical composition, and valence band of the icosahedral (i-) Al-Cu-Fe quasicrystal in an attempt to prepare a model catalyst. The high symmetry fivefold surface of a single grain i-Al-Cu-Fe quasicrystal was leached with NaOH solution for varying times, and the resulting surface was characterized by x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The leaching treatments preferentially remove Al producing a capping layer consisting of Fe and Cu oxides. The subsurface layer contains elemental Fe and Cu in addition to the oxides. The quasicrystalline bulk structure beneath remains unchanged. The subsurface gradually becomes Fe3O4 rich with increasing leaching time. The surface after leaching exhibits micron sized dodecahedral cavities due to preferential leaching along the fivefold axis. Nanoparticles of the transition metals and their oxides are precipitated on the surface after leaching. The size of the nanoparticles is estimated by high resolution transmission microscopy to be 5-20 nm, which is in agreement with the AFM results. Selected area electron diffraction (SAED) confirms the crystalline nature of the nanoparticles. SAED further reveals the formation of an interface between the high atomic density lattice planes of nanoparticles and the quasicrystal. These results provide an important insight into the preparation of model catalysts of nanoparticles for steam reforming of methanol. (C) 2015 AIP Publishing LLC.
Title:
Flux Synthesis, Modulated Crystal Structures, and Physical Properties of REMn0.5SeO (RE = La, Ce)
Authors:
Peschke, S; Nitsche, F; Johrendt, D Author Full Names: Peschke, Simon; Nitsche, Fabian; Johrendt, Dirk
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 641 (3-4):529-536; 10.1002/zaac.201400603 MAR 2015
Abstract:
The selenide oxides REMn0.5SeO (RE = La, Ce) were synthesized by heating RE2O3, RE, Mn, and Se in a NaI/KI flux at 800 degrees C, and their modulated crystal structures determined by X-ray single crystal and powder diffraction {P 1 1 2/n(1/2)0s, Z = 2, LaMn0.5SeO: a = 405.7(1), b = 405.7(1), c = 915.2(1) pm, = 90 degrees, q = [1/10, -1/10, 1/2]; CeMn0.5SeO: a = 402.0(1), b = 401.8(1), c = 910.7(1) pm, = 90.000(4)degrees, q = [0.0789(2), -0.0783(2), 1/2]}. The structures are related to the ZrCuSiAs-type structure with ordered vacancies at the manganese sites. The resulting modulations of the checkerboard pattern in the [Mn0.5Se] layers can be approximated by 10ax10bx2c and 51ax51bx2c supercells in LaMn0.5SeO and CeMn0.5SeO, respectively. Both compounds are insulators. The optical bandgap of LaMn0.5SeO was determined to 2.13 eV from the Kubelka-Munk function. Magnetic measurements indicate antiferromagnetic ordering of the Mn2+ moments with Neel points well above room temperature, as known from related manganese compounds.
Title:
Microstructure and phase compositions of as-cast Mg-3.9Zn-0.6RE (Gd, Y) alloy with different Gd/Y ratios
Authors:
Yang, Y; Zhang, K; Ma, ML; Yuan, JW Author Full Names: Yang, Yang; Zhang, Kui; Ma, Ming-Long; Yuan, Jia-Wei
Source:
RARE METALS, 34 (3):160-163; 10.1007/s12598-014-0444-7 MAR 2015
Abstract:
Mg-Zn-RE (Gd, Y) alloys with different Gd/Y atomic ratios were prepared by conventional casting, and the microstructure of the alloys was studied by multiple means. Icosahedral quasicrystal phases are observed in all alloys. The different Gd/Y atomic ratios affect the microstructures of the alloys irregularly. The alloy with more Gd has large dendritic structure and more complicated phase composition which are composed of I-phase lamellar eutectic, W-phase divorced eutectic, Mg-RE cuboid particles and Mg-Zn binary phases. Other two alloys show similar microstructures and phase compositions with very thin lamellar eutectics which distribute along the interdendritic region, and the lamellar eutectics are formed by I-phase and Mg. The element contents of the I-phases and Mg-RE phases are partially controlled by the Gd/Y atomic ratio.
Title:
Coupling between an incommensurate antiferromagnetic structure and a soft ferromagnet in the archetype multiferroic BiFeO3/cobalt system (vol 91, 014402, 2015)
Authors:
Elzo, M; Moubah, R; Blouzon, C; Sacchi, M; Grenier, S; Belkhou, R; Dhesi, S; Colson, D; Torres, F; Kiwi, M; Viret, M; Jaouen, N Author Full Names: Elzo, Marta; Moubah, Reda; Blouzon, Camille; Sacchi, Maurizio; Grenier, Stephane; Belkhou, Rachid; Dhesi, Sarnjeet; Colson, Dorothee; Torres, Felipe; Kiwi, Miguel; Viret, Michel; Jaouen, Nicolas
Source:
PHYSICAL REVIEW B, 91 (1):10.1103/PhysRevB.91.019903 JAN 30 2015

Update: 9-Apr-2015

Title:
Synthesis and structural analysis of C-60-C-70 two-component fullerene nanowhiskers
Authors:
Konno, T; Wakahara, T; Miyazawa, K Author Full Names: Konno, Toshio; Wakahara, Takatsugu; Miyazawa, Kun'ichi
Source:
JOURNAL OF CRYSTAL GROWTH, 416 41-46; 10.1016/j.jcrysgro.2014.12.016 APR 15 2015
Abstract:
C-60-C-70 two-component fullerene nanowhiskers (C-60-C(70)NWs) were synthesized by liquid-liquid interfacial precipitation (LLIP) using various ratios of C-70 to C-60 and then analyzed using a focused ion beam processing apparatus (FIB-SEM), scanning electron microscopy (SEM). Raman spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, X-ray diffraction (XRD) and high-performance liquid chromatography (HPLC). Both C-60 and C-70 were saturated in the supernatant solutions with fullerene compositions in the mother solutions ranging from 124 mass% C-70 to 73.4 mass% C-70. C-60-C(70)NWs contained a small amount of rhombohedral phase, indicating polymerization of C-60. The solid solubility limit of C-70 in the C-60 matrix was found to be 13.7 mass%. In addition to fine C-60-C(70)NWs, thick C-60-C-70 needle-like crystals were formed. The thick C-60-C-70 needle-like crystals were fractured using a molybdenum probe in the FIB. The fractured surfaces of the C-60-C-70 needle-like crystals showed modulated structures with chemical compositions characteristic of spinodal decomposition. The activation energy of diffusion was determined to be 37.1 kJ/mol. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Broken translational and rotational symmetry via charge stripe order in underdoped YBa2Cu3O6+y
Authors:
Comin, R; Sutarto, R; Neto, EHDS; Chauviere, L; Liang, R; Hardy, WN; Bonn, DA; He, F; Sawatzky, GA; Damascelli, A Author Full Names: Comin, R.; Sutarto, R.; Neto, E. H. da Silva; Chauviere, L.; Liang, R.; Hardy, W. N.; Bonn, D. A.; He, F.; Sawatzky, G. A.; Damascelli, A.
Source:
SCIENCE, 347 (6228):1335-1339; 10.1126/science.1258399 MAR 20 2015
Abstract:
After the discovery of stripelike order in lanthanum-based copper oxide superconductors, charge-ordering instabilities were observed in all cuprate families. However, it has proven difficult to distinguish between unidirectional (stripes) and bidirectional (checkerboard) charge order in yttrium-and bismuth-based materials. We used resonant x-ray scattering to measure the two-dimensional structure factor in the superconductor YBa2Cu3O6+y in reciprocal space. Our data reveal the presence of charge stripe order (i.e., locally unidirectional density waves), which may represent the true microscopic nature of charge modulation in cuprates. At the same time, we find that the well-established competition between charge order and superconductivity is stronger for charge correlations across the stripes than along them, which provides additional evidence for the intrinsic unidirectional nature of the charge order.
Title:
Synchronized collapse and formation of long-period stacking and chemical orders in Mg85Zn6Y9
Authors:
Matsushita, M; Bednarcik, J; Sakata, Y; Akamatsu, S; Nishiyama, N; Michalikoya, J; Yamasaki, M; Kawamura, Y Author Full Names: Matsushita, Masafumi; Bednarcik, Jozef; Sakata, Yuya; Akamatsu, Shutaro; Nishiyama, Norimasa; Michalikoya, Jana; Yamasaki, Michiaki; Kawamura, Yoshihito
Source:
PHYSICA B-CONDENSED MATTER, 461 147-153; 10.1016/j.physb.2014.12.021 MAR 15 2015
Abstract:
Phase transformation of the long period stacking order (LPSO) synchronized with the chemical concentration in Mg85Zn6Y9 has been investigated during both heating and cooling via in situ X-ray diffraction analysis. With increasing temperature, above 800 K, 10H-type LPSO phase collapsed firstly. 10H structural modulation collapsed earlier than the chemical modulation of 5 layers per period. The in plane ordering consisted of aligned L1(2)-type clusters vanished before the collapse of chemical and structural modulation of 18R-type LPSO. After, the chemical and structural modulation of 18R-type LPSO show synchronize collapse. During cooling, the 14H-type LPSO emerged in addition to the 18R-type LPSO. The growths of chemical and structural modulation start at the same temperature. After that, the formation of in plane order consisting of aligned L1(2)-type Zn-Y clusters emerged. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Natural quasicrystal with decagonal symmetry
Authors:
Bindi, L; Yao, N; Lin, C; Hollister, LS; Andronicos, CL; Distler, VV; Eddy, MP; Kostin, A; Kryachko, V; MacPherson, GJ; Steinhardt, WM; Yudovskaya, M; Steinhardt, PJ Author Full Names: Bindi, Luca; Yao, Nan; Lin, Chaney; Hollister, Lincoln S.; Andronicos, Christopher L.; Distler, Vadim V.; Eddy, Michael P.; Kostin, Alexander; Kryachko, Valery; MacPherson, Glenn J.; Steinhardt, William M.; Yudovskaya, Marina; Steinhardt, Paul J.
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep09111 MAR 13 2015
Abstract:
We report the first occurrence of a natural quasicrystal with decagonal symmetry. The quasicrystal, with composition Al71Ni24Fe5, was discovered in the Khatyrka meteorite, a recently described CV3 carbonaceous chondrite. Icosahedrite, Al63Cu24Fe13, the first natural quasicrystal to be identified, was found in the same meteorite. The new quasicrystal was found associated with steinhardtite (Al38Ni32Fe30), Fe-poor steinhardtite (Al50Ni40Fe10), Al-bearing trevorite (NiFe2O4) and Al-bearing taenite (FeNi). Laboratory studies of decagonal Al71Ni24Fe5 have shown that it is stable over a narrow range of temperatures, 1120 K to 1200 K at standard pressure, providing support for our earlier conclusion that the Khatyrka meteorite reached heterogeneous high temperatures [1100 < T(K) <= 1500] and then rapidly cooled after being heated during an impact-induced shock that occurred in outer space 4.5 Gya. The occurrences of metallic Al alloyed with Cu, Ni, and Fe raises new questions regarding conditions that can be achieved in the early solar nebula.
Title:
Group-theoretical analysis of aperiodic tilings from projections of higher-dimensional lattices B-n
Authors:
Koca, M; Koca, NO; Koc, R Author Full Names: Koca, Mehmet; Koca, Nazife Ozdes; Koc, Ramazan
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 71 175-185; 10.1107/S2053273314025492 2 MAR 2015
Abstract:
A group-theoretical discussion on the hypercubic lattice described by the affine Coxeter-Weyl group W-a(B-n) is presented. When the lattice is projected onto the Coxeter plane it is noted that the maximal dihedral subgroup D-h of W(B-n) with h = 2n representing the Coxeter number describes the h-fold symmetric aperiodic tilings. Higher-dimensional cubic lattices are explicitly constructed for n = 4, 5, 6. Their rank-3 Coxeter subgroups and maximal dihedral subgroups are identified. It is explicitly shown that when their Voronoi cells are decomposed under the respective rank-3 subgroupsW(A(3)), W(H-2) x W(A(1)) and W(H-3) one obtains the rhombic dodecahedron, rhombic icosahedron and rhombic triacontahedron, respectively. Projection of the lattice B-4 onto the Coxeter plane represents a model for quasicrystal structure with eightfold symmetry. The B-5 lattice is used to describe both fivefold and tenfold symmetries. The lattice B-6 can describe aperiodic tilings with 12-fold symmetry as well as a three-dimensional icosahedral symmetry depending on the choice of subspace of projections. The novel structures from the projected sets of lattice points are compatible with the available experimental data.
Title:
Thermodynamic and neutron diffraction studies on multiferroic NdMn2O5
Authors:
Chattopadhyay, S; Baledent, V; Auban-Senzier, P; Pasquier, C; Doubroysky, C; Greenblatt, M; Foury-Leylekian, P Author Full Names: Chattopadhyay, S.; Baledent, V.; Auban-Senzier, P.; Pasquier, C.; Doubroysky, C.; Greenblatt, M.; Foury-Leylekian, P.
Source:
PHYSICA B-CONDENSED MATTER, 460 214-217; SI 10.1016/j.physb.2014.11.074 MAR 1 2015
Abstract:
Magnetically frustrated RMn2O5 oxides have attracted considerable attention in recent years, because most of the members of this family show spin ordering induced dielectric polarization along with strong magneto-electric coupling. Although the true origin of the ferroelectricity is still a matter of debate, it has been observed that the magneto-electric phase diagram can be substantially tuned with the variation of rare earth elements. In this work, we have chosen NdMn2O5 as the compound of our interest since it lies exactly in between the ferroelectric and non-ferroelectric members of this family and also, because there are few investigations performed on RMn2O5 systems with large rare earth atoms. With the combination of heat capacity, magnetic susceptibility, dielectric permittivity, powder X-ray diffraction, and powder neutron diffraction measurements, it has been found that NdMn2O5 undergoes an incommensurate magnetic ordering around 30 K followed by a possible ferroelectric-like transition at similar to 26 K. Another lock-in kind of magnetic transition appears when the temperature is decreased to similar to 15 K. With further lowering of temperature, an antiferromagnetic ordering, which is presumably associated with the Nd3+, is achieved near 4 K. This study thus sheds light on a new compound of the RMn2O5 series presenting different multiferroic properties. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Generalized Penrose tiling as a quasilattice for decagonal quasicrystal structure analysis
Authors:
Chodyn, M; Kuczera, P; Wolny, J Author Full Names: Chodyn, Maciej; Kuczera, Pawel; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 71 161-168; 10.1107/S2053273314024917 2 MAR 2015
Abstract:
The generalized Penrose tiling is, in fact, an infinite set of decagonal tilings. It is constructed with the same rhombs (thick and thin) as the conventional Penrose tiling, but its long-range order depends on the so-called shift parameter (s is an element of < 0; 1)). The structure factor is derived for the arbitrarily decorated generalized Penrose tiling within the average unit cell approach. The final formula works in physical space only and is directly dependent on the s parameter. It allows one to straightforwardly change the long-range order of the refined structure just by changing the s parameter and keeping the tile decoration unchanged. This gives a great advantage over the higher-dimensional method, where every change of the tiling (change in the s parameter) requires the structure model to be built from scratch, i.e. the fine division of the atomic surfaces has to be redone.
Title:
Analytical electron microscopy study on gallium nitride systems doped with manganese and iron
Authors:
Meingast, A; Quezada, AN; Devillers, T; Kovacs, A; Albu, M; Fladischer, S; Bonanni, A; Kothleitner, G Author Full Names: Meingast, Arno; Quezada, Andrea Navarro; Devillers, Thibaut; Kovacs, Andras; Albu, Mihela; Fladischer, Stefanie; Bonanni, Alberta; Kothleitner, Gerald
Source:
SEMICONDUCTOR SCIENCE AND TECHNOLOGY, 30 (3):10.1088/0268-1242/30/3/035002 MAR 2015
Abstract:
Modulated structures of gallium nitride (GaN) doped with transition metal ions (here Fe, Mn) are investigated by analytical (scanning) transmission electron microscopy to gain insight into the structural arrangement and chemical composition of the material, known to be critically correlated to the magnetic response and hence the functionality of these technologically relevant systems. Three classes of samples are considered: (i) homogeneous (dilute) (Ga, Mn) N; (ii) delta-Mn-doped (Ga, delta-Mn) N and phase separated (Ga, Fe) N, containing Fe-rich nanocrystals. The combination of various microscopic techniques employed, allows for a quantitative determination of the distribution of the magnetic ions in the samples, providing essential information on the structural and chemical asset of these systems.
Title:
Direct observation of single-electron solitons and Friedel oscillations in a quasi-one dimensional material with incommensurate charge-density waves
Authors:
Brun, C; Brazovskii, S; Wang, ZZ; Monceau, P Author Full Names: Brun, Christophe; Brazovskii, Serguei; Wang, Zhao-Zhong; Monceau, Pierre
Source:
PHYSICA B-CONDENSED MATTER, 460 88-92; SI 10.1016/j.physb.2014.11.046 MAR 1 2015
Abstract:
We have performed scanning tunneling microscopy experiments in the quasi-one dimensional charge density wave (CDW) system NbSe3, where we could image and study in detail individual solitons corresponding to the self-trapping of a single electron. Our analysis shows that the type of soliton we observed is an "Amplitude Soliton", characterized by a vanishing CDW amplitude at the soliton center and by a pi-shift of its phase along the chain direction. Pairs of solitons or multiple solitons were also observed. Such observations could be made only in the high-temperature COW phase. Additionally, one-dimensional Friedel oscillations around charged defects could also be imaged and are found to be superimposed to the COW. The distinction between amplitude solitons and Friedel oscillations can be made without any ambiguity. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Topological Hofstadter insulators in a two-dimensional quasicrystal
Authors:
Tran, DT; Dauphin, A; Goldman, N; Gaspard, P Author Full Names: Tran, Duc-Thanh; Dauphin, Alexandre; Goldman, Nathan; Gaspard, Pierre
Source:
PHYSICAL REVIEW B, 91 (8):10.1103/PhysRevB.91.085125 FEB 27 2015
Abstract:
We investigate the properties of a two-dimensional quasicrystal in the presence of a uniform magnetic field. In this configuration, the density of states (DOS) displays a Hofstadter-butterfly-like structure when it is represented as a function of the magnetic flux per tile. We show that the low-DOS regions of the energy spectrum are associated with chiral edge states, in direct analogy with the Chern insulators realized with periodic lattices. We establish the topological nature of the edge states by computing the topological Chern number associated with the bulk of the quasicrystal. This topological characterization of the nonperiodic lattice is achieved through a local (real-space) topological marker. This work opens a route for the exploration of topological-insulating materials in a wide range of nonperiodic lattice systems, including photonic crystals and cold atoms in optical lattices.
Title:
Effects of Initial States on the Spinodal Decomposition of Quenched and Melt-Spun Cu-15Ni-8Sn Alloy
Authors:
Kondo, SI; Masusaki, A; Ogawa, K; Morimura, T; Nakashima, H Author Full Names: Kondo, Shin-ichiro; Masusaki, Akinori; Ogawa, Kento; Morimura, Takao; Nakashima, Hiromichi
Source:
MATERIALS TRANSACTIONS, 56 (1):23-29; 10.2320/matertrans.M2014234 JAN 2015
Abstract:
We investigate early stages of spinodal decomposition in a melt-spun Cu-15Ni-8Sn alloy (melt-spun samples) by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and electron diffraction analysis through comparison against a non-melt-spun alloy of the same composition (quenched samples). In XRD measurements, no sidebands of (200) planes are found in the melt-spun sample after aging at 350 degrees C for 120 min, whereas they are found in the quenched sample after a heat treatment at 350 degrees C for 60 min. TEM observations of a quenched sample after aging at 350 degrees C for 60 mm indicate the presence of a modulated structure (lambda = 5-10 nm) in the matrix, whereas those of a melt-spun sample after the same heat treatment also indicate the presence of a modulated structure (lambda: too small to measure). Electron diffraction patterns reveal satellite structures in both samples, although with superlattice reflections from ordering phases visible in the quenched sample. These differences are presumably due to a difference in the size of clusters present in their respective quenched states; in melt-spun samples, cluster size was much smaller as a result of a high cooling rate (approximate to 8 x 10(5)degrees C/s).

Update: 2-Apr-2015

Title:
First-principles study of structurally modulated multiferroic CaMn7O12
Authors:
Cao, K; Johnson, RD; Perks, N; Giustino, F; Radaelli, PG Author Full Names: Cao, Kun; Johnson, Roger D.; Perks, Natasha; Giustino, Feliciano; Radaelli, Paolo G.
Source:
PHYSICAL REVIEW B, 91 (6):10.1103/PhysRevB.91.064422 FEB 27 2015
Abstract:
study the electronic and magnetic structures of multiferroic CaMn7O12 by first-principles calculations, based on the experimentally determined modulated crystal structure. We confirm the presence of a 3d orbital modulation of the Mn2 (Mn3+) sites, previously inferred from the Jahn-Teller crystal distortions. Our results indicate that in the multiferroic phase themagnetic structure of the Mn3 (Mn4+) sites is anharmonically modulated via orbitally mediated coupling with the structural modulation, and that the Dzyaloshinskii-Moriya and exchange striction mechanisms contribute equally to the polarization.
Title:
Disorder from order among anisotropic next-nearest-neighbor Ising spin chains in SrHo2O4
Authors:
Wen, JJ; Tian, W; Garlea, VO; Koohpayeh, SM; McQueen, TM; Li, HF; Yan, JQ; Rodriguez-Rivera, JA; Vaknin, D; Broholm, CL Author Full Names: Wen, J. -J.; Tian, W.; Garlea, V. O.; Koohpayeh, S. M.; McQueen, T. M.; Li, H. -F.; Yan, J. -Q.; Rodriguez-Rivera, J. A.; Vaknin, D.; Broholm, C. L.
Source:
PHYSICAL REVIEW B, 91 (5):10.1103/PhysRevB.91.054424 FEB 26 2015
Abstract:
We describe why Ising spin chains with competing interactions in SrHo2O4 segregate into ordered and disordered ensembles at low temperatures (T). Using elastic neutron scattering, magnetization, and specific heat measurements, the two distinct spin chains are inferred to have Neel (up arrow down arrow up arrow down arrow) and double-Neel (up arrow up arrow down arrow down arrow) ground states, respectively. Below T-N = 0.68(2) K, the Neel chains develop three-dimensional long range order (LRO), which arrests further thermal equilibration of the double-Neel chains so they remain in a disordered incommensurate state for T below T-S = 0.52(2) K. SrHo2O4 distills an important feature of incommensurate low dimensional magnetism: kinetically trapped topological defects in a quasi-d-dimensional spin system can preclude order in d + 1 dimensions.
Title:
Quantum critical behavior in heavily doped LaFeAsO1-xHx pnictide superconductors analyzed using nuclear magnetic resonance
Authors:
Sakurai, R; Fujiwara, N; Kawaguchi, N; Yamakawa, Y; Kontani, H; Iimura, S; Matsuishi, S; Hosono, H Author Full Names: Sakurai, R.; Fujiwara, N.; Kawaguchi, N.; Yamakawa, Y.; Kontani, H.; Iimura, S.; Matsuishi, S.; Hosono, H.
Source:
PHYSICAL REVIEW B, 91 (6):10.1103/PhysRevB.91.064509 FEB 19 2015
Abstract:
We studied the quantum critical behavior of the second antiferromagnetic (AF) phase in the heavily electron-doped high-T-c pnictide, LaFeAsO1-x H-x, by using a As-75 and H-1 nuclear magnetic resonance (NMR) technique. In the second AF phase, we observed a spatially modulated spin-density-wave-like state up to x = 0.6 from the NMR spectral line shape and detected a low-energy excitation gap from the nuclear relaxation time T-1 of As-75. The excitation gap closes at the AF quantum critical point (QCP) at x approximate to 0.49. The superconducting phase in a lower-doping regime contacts the second AF phase only at the AF QCP, and both phases are segregated from each other. The absence of AF critical fluctuations and the enhancement of the in-plane electric anisotropy are key factors for the development of superconductivity.
Title:
Disruption of quantum oscillations by an incommensurate charge density wave
Authors:
Zhang, Y; Maharaj, AV; Kivelson, S Author Full Names: Zhang, Yi; Maharaj, Akash V.; Kivelson, Steven
Source:
PHYSICAL REVIEW B, 91 (8):10.1103/PhysRevB.91.085105 FEB 9 2015
Abstract:
Because a material with an incommensurate charge density wave (ICDW) is only quasiperiodic, Bloch's theorem does not apply and there is no sharply defined Fermi surface. We will show that, as a consequence, there are no quantum oscillations which are truly periodic functions of 1/B (where B is the magnitude of an applied magnetic field). For a weak ICDW, there exist broad ranges of 1/B in which approximately periodic variations occur, but with frequencies that vary inexorably in an unending cascade with increasing 1/B. For a strong ICDW, e.g., in a quasicrystal, no quantum oscillations survive at all. Rational and irrational numbers really are different.
Title:
Direct observation of Ca-Na ordering and structure polarity in Ca-rich intermediate plagioclase feldspar with incommensurate modulated structure
Authors:
Xu, HF Author Full Names: Xu, Huifang
Source:
AMERICAN MINERALOGIST, 100 (2-3):510-515; 10.2138/am-2015-5022 FEB-MAR 2015
Abstract:
Ca-Na ordering and structural polarity of subcells in an intermediate plagioclase with modulated structure have been observed using Z-contrast imaging with an aberration-corrected scanning transmission electron microscope. Neighboring lamellar domains with I1 symmetry are related by inversion twin operation, instead of anti-phase domain boundaries (or APBs) as in all previously reported structure models. The boundaries between lamellar domains have I (1) over bar symmetry instead of C (1) over bar symmetry. Modulated plagioclase has unique Ca-Na and Al-Si ordering structure that is different from those in end-member structures of anorthite and low albite. The modulated structures of intermediate plagioclase are not metastable structures formed during phase transition, but instead thermodynamically stable structures at low temperature due to Ca-Na ordering within the subcells with I1 symmetry.

Update: 26-Mar-2015

Title:
Charge order and resistivity transition of Zn-doped cuprate superconductors
Authors:
de Mello, EVL; Mockli, D Author Full Names: de Mello, E. V. L.; Moeckli, David
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (9):10.1088/0953-8984/27/9/095702 MAR 11 2015
Abstract:
Impurity doping using Zn atoms was largely studied in cuprates because this process substantially reduces the superconducting critical temperature T-c without any effect on the pseudogap onset T*. Earlier theories missed the recently established ubiquitous presence of incommensurate charge modulations in these materials. The charge order is a consequence of a phase separation transition which we describe by a continuity equation of the local free energy density. The Zn atoms generate a local magnetic moment, freezing their neighbors' spins, slowing down the electronic segregation process. Then the Zn-doped properties are that of a granular superconductor whose size of the charge order modulations are dictated by the degree of phase separation.
Title:
Effect of Li on structure and electrochemical hydrogen storage properties of Ti55V10Ni35 quasicrystal alloy
Authors:
Liu, CF; Duan, YH; Ouyang, ZT; Shang, JM; Liu, K; Xing, C; Fu, YG; Liu, WQ; Wang, LM Author Full Names: Liu, Chaofan; Duan, Yuhan; Ouyang, Zhongtao; Shang, Jinming; Liu, Kun; Xing, Cheng; Fu, Yuegang; Liu, Wanqiang; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 40 (7):3015-3022; 10.1016/j.ijhydene.2014.12.133 FEB 23 2015
Abstract:
The Ti55V10Ni35 quasicrystal ribbons are synthesized by arc melting and subsequent melt-spinning technique and then Li atoms are infiltrated into this quasicrystal material by the way of electroosmosis. X-ray diffraction results indicate that the pristine quasicrystal Ti55V10Ni35 mainly consists of the icosahedral quasicrystal (I-phase), V-based solid solution phase with BBC structure and face centered cubic (FCC) phase with Ti2Ni-type structure. After infiltrating some amount of Li atoms into Ti55V10Ni35 quasicrystal lattice voids at different electroosmosis current density (A/mg) of 0.3, 0.6 and 0.9 respectively, phase structure investigations show that the main phase structures do not change greatly except for the additional lithium phase, which demonstrates that Li does not destroy the phase structure of Ti55V10Ni35 quasicrystal. Ti55V10Ni35 alloy shows the best discharge capacity is 219.8 mAh g(-1) at a current density of 30 mA g(-1). The negative electrode made by Ti55V10Ni35 Li quasicrystal alloys (Li atoms are infiltrated into Ti55V10Ni35 quasicrystal alloy at different the electroosmosis current density (A/mg) of 0.3, 0.6 and 0.9 has a maximum discharge capacity of 257.7 mAh g(-1), 301.8 mAh g(-1) and 238.7 mAh g(-1) at a discharge current density of 30 mA g(-1), respectively. And the high rate discharge ability of alloy electrodes is higher than that of Ti55V10Ni35 quasicrystal alloy at 240 mA g(-1). The Effect of Li on structure of Ti55V10Ni35 quasicrystal has been discussed by measuring the place, mass ratio and chemical state that Li infiltrated into quasicrystal Ti55V10Ni35 lattice. In addition, the electrochemical reaction kinetics of Ti55V10Ni35-Li quasicrystal alloy electrodes is also studied by measuring both the electrochemical impedance spectroscopy and hydrogen diffusion coefficient. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Title:
Density-matrix renormalization group study of the extended Kitaev-Heisenberg model
Authors:
Shinjo, K; Sota, S; Tohyama, T Author Full Names: Shinjo, Kazuya; Sota, Shigetoshi; Tohyama, Takami
Source:
PHYSICAL REVIEW B, 91 (5):10.1103/PhysRevB.91.054401 FEB 4 2015
Abstract:
We study an extended Kitaev-Heisenberg model including additional anisotropic couplings by using the two-dimensional density-matrix renormalization group method. Calculating the ground-state energy, entanglement entropy, and spin-spin correlation functions, we make a phase diagram of the extended Kitaev-Heisenberg model around the spin-liquid phase. We find a zigzag antiferromagnetic phase, a ferromagnetic phase, a 120. antiferromagnetic phase, and two kinds of incommensurate phases around the Kitaev spin-liquid phase. Furthermore, we study the entanglement spectrum of the model, and we find that entanglement levels in the Kitaev spin-liquid phase are degenerate forming pairs, but those in the magnetically ordered phases are nondegenerate. The Schmidt gap defined as the energy difference between the lowest two levels changes at the phase boundary adjacent to the Kitaev spin-liquid phase. However, we find that phase boundaries between magnetically ordered phases do not necessarily agree with the change of the Schmidt gap.
Title:
Modification of the phase composition and structure of the quasicrystalline Al-Cu-Fe alloy prepared by plasma spraying
Authors:
Lepeshev, AA; Bayukov, OA; Rozhkova, EA; Karpov, IV; Ushakov, AV; Fedorov, LY Author Full Names: Lepeshev, A. A.; Bayukov, O. A.; Rozhkova, E. A.; Karpov, I. V.; Ushakov, A. V.; Fedorov, L. Yu.
Source:
PHYSICS OF THE SOLID STATE, 57 (2):255-259; 10.1134/S1063783415020249 FEB 2015
Abstract:
The structural-phase state of quasicrystalline coatings of the Al-Cu-Fe alloy produced under different thermal conditions of plasma spraying (different contact temperatures T (k) of the substrate) has been investigated. It has been shown that sprayed coatings are heterophase with the dominant content of the icosahedral psi and cubic beta phases, the formation and fractional ratio of which depend on spraying conditions. The distribution of probabilities P(QS) of quadrupole splitting in experimental gamma-resonance spectra has been analyzed. The dependence of hyperfine interaction parameters (QS, A) on spraying conditions of the coating has been established. Five nonequivalent positions of resonant iron atoms, the appearance and filling of which are determined by spraying conditions, have been revealed.
Title:
Incommensurate Structure and Phase Transitions in Epitaxial Multiferroic Films
Authors:
Gareeva, ZV; Popkov, AF; Kulagin, NE; Soloviov, SV; Zvezdin, AK Author Full Names: Gareeva, Z. V.; Popkov, A. F.; Kulagin, N. E.; Soloviov, S. V.; Zvezdin, A. K.
Source:
FERROELECTRICS, 475 (1):1-9; SI 10.1080/00150193.2015.994973 JAN 25 2015
Abstract:
We investigate transformations of space modulated structure in BiFeO3 films induced by change of magnetic anisotropy, strain, or temperature and applied magnetic field. We show that critical field of the transition between incommensurate and commensurate structures is lower in films as compared with single crystals. There are two incommensurate phases at H parallel to[111]: plane and conical cycloidal phases with the second order transition between them. An important feature of this transition is softening of spin wave activation mode localized on spin cycloid. Cycloidal spin wave spectrum contains a countable number of branches, thus BiFeO3 can be considered as a magnonic crystal.

Update: 19-Mar-2015

Title:
Electrochemical hydrogen storage properties of Ti1.4V0.6Ni quasicrystal and TiH composite materials
Authors:
Liu, K; Shang, JM; Ouyang, ZT; Duan, YH; Xing, C; Fu, YG; Liang, F; Lin, J; Liu, WQ; Wang, LM Author Full Names: Liu, Kun; Shang, Jinming; Ouyang, Zhongtao; Duan, Yuhan; Xing, Cheng; Fu, Yuegang; Liang, Fei; Lin, Jing; Liu, Wanqiang; Wang, Limin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 630 158-162; 10.1016/j.jallcom.2015.01.062 MAY 5 2015
Abstract:
In this study, we use arc-melting and subsequent melt-spinning techniques to prepare Ti1.4V0.6Ni alloy ribbons. The Ti1.4V0.6Ni + xTiH (x = 5, 10, 15 and 20 wt.%) mixture powders are obtained by mechanical ball-milling. Also, we investigate the structure and electrochemical hydrogen storage properties of composite materials. Besides I-phase, FCC and BCC phase, the XRD of composite materials indicates it contains TiH phase. After adding TiH, the discharge capacities of Ti1.4V0.6Ni alloy electrode increase first and then decrease with increasing amount of Ti. The achieved maximum discharge capacity is about 339.8 mA h/g (x = 15 wt.%) at the first discharge cycle. Additionally, composite materials lead to significant improvement in the high-rate dischargeability (HRD) as well as the cyclic stability. (C) 2015 Elsevier B.V. All rights reserved.
Title:
Wave propagation of phonon and phason displacement modes in quasicrystals: Determination of wave parameters
Authors:
Chellappan, V; Gopalakrishnan, S; Mani, V Author Full Names: Chellappan, Vinita; Gopalakrishnan, S.; Mani, V.
Source:
JOURNAL OF APPLIED PHYSICS, 117 (5):10.1063/1.4907212 FEB 7 2015
Abstract:
The paper presents the study of wave propagation in quasicrystals. Our interest is in the computation of the wavenumber (k(n)) and group speed (c(g)) of the phonon and phason displacement modes of one, two, and three dimensional quasicrystals. These wave parameter expressions are derived and computed using the elasto-hydrodynamic equations for quasicrystals. For the computation of the wavenumber and group speeds, we use Fourier transform approximation of the phonon and the phason displacement modes. The characteristic equations obtained are a polynomial equation of the wavenumber (k(n)), with frequency as a parameter. The corresponding group speeds (c(g)) for different frequencies are then computed from the wavenumber k(n). The variation of wavenumber and group speeds with frequency is plotted for the 1-D quasicrystal, 2-D decagonal Al-Ni-Co quasicrystals, and 3-D icosahedral Al-Pd-Mn and Zn-Mg-Sc quasicrystals. From the wavenumber and group speeds plots, we obtain the cut-off frequencies for different spatial wavenumber eta(m). The results show that for 1-D, 2-D, and 3-D quasicrystals, the phonon displacement modes are non-dispersive for low values of eta(m) and becomes dispersive for increasing values of eta(m). The cut-off frequencies are not observed for very low values of eta(m), whereas the cut-off frequency starts to appear with increasing eta(m). The group speeds of the phason displacement modes are orders of magnitude lower than that of the phonon displacement modes, showing that the phason modes do not propagate, and they are essentially the diffusive modes. The group speeds of the phason modes are also not influenced by eta(m). The group speeds for the 2-D quasicrystal at 35 kHz is also simulated numerically using Galerkin spectral finite element methods in frequency domain and is compared with the results obtained using wave propagation analysis. The effect of the phonon and phason elastic constants on the group speeds is studied using 3-D icosahedral Al-Pd-Mn and Zn-Mg-Sc quasicrystals. It is also shown that the phason elastic constants and the coupling coefficient do not affect the group speeds of the phonon displacement modes. (C) 2015 AIP Publishing LLC.

Update: 12-Mar-2015

Title:
Spin-Glass Behavior and Incommensurate Modulation in High-Pressure Perovskite BiCr0.5Ni0.5O3
Authors:
Arevalo-Lopez, AM; Dos Santos-Garcia, AJ; Levin, JR; Attfield, JP; Alario-Franco, MA Author Full Names: Arevalo-Lopez, Angel M.; Dos Santos-Garcia, Antonio J.; Levin, Jessica R.; Attfield, J. Paul; Alario-Franco, Miguel A.
Source:
INORGANIC CHEMISTRY, 54 (3):832-836; 10.1021/ic502012p FEB 2 2015
Abstract:
The BiCr0.5Ni0.5O3 perovskite has been obtained at high pressure. Neutron and synchrotron diffraction data show a Pnma orthorhombic structure with a = 5.5947(1) angstrom, b = 7.7613(1) angstrom, and c = 5.3882(1) angstrom at 300 K and random B-site Cr/Ni distribution. Electron diffraction reveals an incommensurate modulation parallel to the b axis. The combination of either Cr-O-Ni (J > 0) or Cr-O-Cr/Ni-O-Ni (J < 0) nearest-neighbor spin interactions results in a random-bond spin-glass configuration. Magnetization, neutron diffraction, and muon-spin-relaxation measurements demonstrate that variations in the local bonding and charge states contribute to the magnetic frustration.
Title:
Structural Modulations in the Rare-Earth Metal Digermanides REAl1-x,Ge-2 (RE = Gd-Tm, Lu, Y; 0.8
Authors:
Zhang, JL; Wang, YM; Bobev, S Author Full Names: Zhang, Jiliang; Wang, Yingmin; Bobev, Svilen
Source:
INORGANIC CHEMISTRY, 54 (3):722-732; 10.1021/ic501002j FEB 2 2015
Abstract:
Rare-earth metal aluminum germanides with the general formula REAl1-xGe2 (RE = Gd, Tb, Dy, Ho, Er, Tm, Lu, and Y) have been synthesized by direct fusion of the corresponding elements. The structures have been studied by single-crystal X-ray diffraction and selected-area electron diffraction (SAED). The average structure represents a randomly stuffed variant of the orthorhombic ZrSi2 structure type, also known as the CeNi1-xSi2 type (Pearson symbol oC16; space group Cmcm). The SAED patterns for selected members of the family suggest the coexistence of commensurate and incommensurate structural modulations. The most prominent model for long-range vacancy ordering is the Tb4FeGe8 type (Pearson symbol mP26; space group P2(1)/n), which is the commensurate 4-fold superstructure of CeNi1-xSi2 (x = 3/4). Short-range correlations cause additional deviations in the 4-fold superlattice. These results shed more light on the structural complexity as a function of the aluminum vacancies and size of the rare-earth metal. Magnetic susceptibility measurements are presented and discussed. The measured ordering temperatures and calculated ones based on empirical rules and Ruderman-Kittel-Kasuya-Yosida interactions are shown to be in close agreement.
Title:
Fabrication and structural characterization of bismuth niobate thin films grown by chemical solution deposition
Authors:
Goncalves, LF; Cortes, JA; Ranieri, MGA; Destro, FB; Ramirez, MA; Simoes, AZ Author Full Names: Goncalves, L. F.; Cortes, J. A.; Ranieri, M. G. A.; Destro, F. B.; Ramirez, M. A.; Simoes, A. Z.
Source:
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 26 (2):1142-1150; 10.1007/s10854-014-2518-6 FEB 2015
Abstract:
Bi3NbO7 (BNO) thin films were deposited on Pt/TiO2/SiO2/Si (100) substrates at room temperature from the polymeric precursor method. X-ray powder diffraction and transmission electron microscopy were used to investigate the formation characteristics and stability range of the tetragonal modification of a fluorite-type solid solution. The results showed that this tetragonal, commensurately modulated phase forms through the intermediate formation of the incommensurately modulated cubic fluorite phase followed by the incommensurate-commensurate transformation. The 200 nm thick BNO films exhibit crystalline structure, a dielectric constant of 170, capacitance density of 200 nF/cm(2), dielectric loss of 0.4 % at 1 MHz, and a leakage current density of approximately 1 x 10(-7) A/cm(2) at 5 V. They show breakdown strength of about 0.25 MV/cm. The leakage mechanism of BNO film in high field conduction is well explained by the Schottky and Poole-Frenkel emission models. The 200 nm thick BNO film is suitable for embedded decoupling capacitor applications directly on a printed circuit board.
Title:
On the Origin of Nanochessboard Super lattices in A-Site-Deficient Ca-Stabilized Nd2/3TiO3
Authors:
Azough, F; Kepaptsoglou, D; Ramasse, QM; Schaffer, B; Freer, R Author Full Names: Azough, Feridoon; Kepaptsoglou, Demie; Ramasse, Quentin M.; Schaffer, Berhnard; Freer, Robert
Source:
CHEMISTRY OF MATERIALS, 27 (2):497-507; 10.1021/cm5036985 JAN 27 2015
Abstract:
A-site deficient Nd2/3TiO3 ceramics stabilized with CaTiO3, with an overall composition of 0.9 Nd2/3TiO3-0.1 CaTiO3, were synthesized by the mixed oxide route. Synchrotron X-ray diffraction was used to identify the basic perovskite structure and revealed cross-type superlattice reflections. An incommensurate superlattice structure with dimensions of a approximate to b approximate to 20ap and c = 2a(p) (where a(p) is the cell parameter for the parent perovskite phase) was identified, giving rise to contrast features resembling a nanochessboard pattern in electron microscopy images. The superlattice was further characterized by aberration-corrected scanning transmission electron microscopy (STEM): atomically resolved lattice images were obtained along ?100? orientations to visualize the A-site (Ca, Nd, and vacancies) and B-site (Ti) cation column intensities, in correlation with observations of the nanochessboard superlattice. Electron energy loss spectroscopy (EELS) was used to precisely determine the distribution of Nd and Ca across the structure, confirming the absence of long-range elemental segregation or phase separation across the nanochessboard superstructure. Closer inspection of the chemical maps in two orthogonal directions, however, suggests the presence of localized ordering of cations and vacancies. The chessboard pattern superlattice is thus likely to be caused by periodic octahedral tilt distortions of the O sublattice, possibly induced by these short-range chemical variations, as a result of a complex interplay between cation and vacancy ordering in three dimensions.
Title:
Cation ordering in A-site-deficient Li-ion conducting perovskites La(1-x)/3LixNbO3
Authors:
Gao, X; Fisher, CAJ; Ikuhara, YH; Fujiwara, Y; Kobayashi, S; Moriwake, H; Kuwabara, A; Hoshikawa, K; Kohama, K; Iba, H; Ikuhara, Y Author Full Names: Gao, Xiang; Fisher, Craig A. J.; Ikuhara, Yumi H.; Fujiwara, Yasuyuki; Kobayashi, Shunsuke; Moriwake, Hiroki; Kuwabara, Akihide; Hoshikawa, Keigo; Kohama, Keiichi; Iba, Hideki; Ikuhara, Yuichi
Source:
JOURNAL OF MATERIALS CHEMISTRY A, 3 (7):3351-3359; 10.1039/c4ta07040b 2015
Abstract:
Cation-deficient perovskites exhibit complex local atomic arrangements which cannot be adequately described by average crystal structure models. By combining reciprocal-space electron diffraction analysis and direct observations of atom positions using state-of-the-art scanning transmission electron microscopy, we clarify the nature of the cation ordering within A-site-deficient perovskite single crystals of La(1-x)/3LixNbO3 (x = 0 and x = 0.04). Both materials are found to have complex modulated crystal structures with two types of A-cation ordering, namely a long-range layer ordering in alternate (001)(p) planes and a short-range (intra-domain) columnar ordering within La-rich (001)(p) layers. The columnar ordering (occupational modulation) produces modulated displacements of Nb and O atoms. It is also found that substitution of even a small amount of Li for La can affect significantly the columnar ordering, leading to a series of structural and microstructural changes that are likely to have a deleterious effect on the Li-ion conductivity of this material.
Title:
Magnetic resonance and spin-reorientation transitions in the Nd0.75Ho0.25Fe3(BO3)(4) multiferroic
Authors:
Kobets, MI; Dergachev, KG; Gnatchenko, SL; Khatsko, EN; Bezmaternykh, LN; Gudim, IA Author Full Names: Kobets, M. I.; Dergachev, K. G.; Gnatchenko, S. L.; Khatsko, E. N.; Bezmaternykh, L. N.; Gudim, I. A.
Source:
LOW TEMPERATURE PHYSICS, 41 (1):75-79; 10.1063/1.4906338 JAN 2015
Abstract:
A presentation of experimental study results obtained by antiferromagnetic resonance (AFMR) of the high-frequency properties of the multiferroic Nd0.75Ho0.25Fe3(BO3)(4) in a broad range of temperatures and frequencies. We studied the effect of substituting the Nd3+ ions with Ho3+, on the resonance properties of the Nd0.75Ho0.25Fe3(BO3)(4) solid solution. In addition, we investigated the particularities of magnetic-field induced spin-reorientation phase transitions for H parallel to c and H parallel to a directions, in which the anisotropy of the magnetic system is measured from "easy-axis" anisotropy to "easy-plane." The AFMR modes of a Fe3+ subsystem are revealed. New information about the most important characteristics of AFM is obtained, including: frequency-field dependence of the AFMR spectrum, gaps in the spin-wave spectrum, effective magnetic anisotropy values, and fields of spin-reorientation transitions. It is shown that "easy-plane" anisotropy prevails in this magnet, with a weak anisotropy in the basal plane. For the first time there are observed features in the AFMR spectra that could be tied to the presence of a spatially modulated spin structure (incommensurate phase) in AFM Nd0.75Ho0.25Fe3(BO3)(4). (C) 2015 AIP Publishing LLC.
Title:
Single-molecule probing of incommensurate biphenyl (vol 36, pg 448, 2010)
Authors:
Pars, M; Palm, V; Kikas, J Author Full Names: Paers, M.; Palm, V.; Kikas, J.
Source:
LOW TEMPERATURE PHYSICS, 41 (1):80-80; 10.1063/1.4906339 JAN 2015
Title:
Effect of shape on the self-assembly of faceted patchy nanoplates with irregular shape into tiling patterns
Authors:
Millan, JA; Ortiz, D; Glotzer, SC Author Full Names: Millan, Jaime A.; Ortiz, Daniel; Glotzer, Sharon C.
Source:
SOFT MATTER, 11 (7):1386-1396; 10.1039/c4sm01612b 2015
Abstract:
Recent reports of the synthesis and assembly of faceted nanoplates with a wide range of shapes and composition motivates the possibility of a new class of two-dimensional materials with specific patterns targeted for a host of exciting properties. Yet, studies of how nanoplate shape controls their assembly knowledge necessary for their inverse design from target structures - has been performed for only a handful of systems. By constructing a general framework in which many known faceted nanoplates may be described in terms of four anisotropy dimensions, we discover design rules to guide future synthesis and assembly. We study via Monte Carlo simulations attractive polygons whose shape is altered systematically under the following four transformations: faceting, pinching, elongation and truncation. We report that (i) faceting leads to regular porous structures (ii) pinching stabilizes complex structures such as dodecagonal quasicrystals (iii) elongation leads to asymmetric phase behavior, where low and high aspect ratio nanoplates self-assemble completely different structures and (iv) low and high degrees of truncation transform a complex self-assembler into a disk-like assembler, providing design ideas that could lead to switchable structures. We provide important insight into how the shape and attractive interactions of a nanoplate can be exploited or designed to target specific classes of structures, including space-filling, porous, and complex tilings.
Title:
Ultrathin Two-Dimensional Inorganic Materials: New Opportunities for Solid State Nanochemistry
Authors:
Sun, YF; Gao, S; Lei, FC; Xiao, C; Xie, Y Author Full Names: Sun, Yongfu; Gao, Shan; Lei, Fengcai; Xiao, Chong; Xie, Yi
Source:
ACCOUNTS OF CHEMICAL RESEARCH, 48 (1):3-12; 10.1021/ar500164g JAN 2015
Abstract:
CONSPECTUS: The ultimate goal of solid state chemistry is to gain a clear correlation between atomic, defect, and electronic structure and intrinsic properties of solid state materials. Solid materials can generally be classified as amorphous, quasicrystalline, and crystalline based on their atomic arrangement, in which crystalline materials can be further divided into single crystals, microcrystals, and nanocrystals. Conventional solid state chemistry mainly focuses on studying single crystals and microcrystals, while recently nanocrystals have become a hot research topic in the field of solid state chemistry. As more and more nanocrystalline materials have been artificially fabricated, the solid state chemistry for studying those nanosolids has become a new subdiscipline: solid state nanochemistry. However, solid state nanochemistry, usually called "nanochemistry" for short, primarily studies the microstructures and macroscopic properties of a nanomaterial's aggregation states. Due to abundant microstructures in the aggregation states, it is only possible to build a simple but imprecise correlation between the microscopic morphology and the macroscopic properties of the nanostructures. Notably, atomically thin two-dimensional inorganic materials provide an ideal platform to establish clear structure-property relationships in the field of solid state nanochemistry, thanks to their homogeneous dispersion without the assistance of a capping ligand. In addition, their atomic structures including coordination number, bond length, and disorder degree of the examined atoms can be clearly disclosed by X-ray absorption fine structure spectroscopy. Also, their more exposed interior atoms would inevitably induce the formation of various defects, which would have a non-negligible effect on their physicochemical properties. Based on the obtained atomic and defect structural characteristics, density-functional calculations are performed to study their electronic structures. Then, after the properties of the individual ultrathin two-dimensional materials or their assembled highly oriented thin film-based nanodevices are measured, the explicit relationship between atomic, defect, and electronic structure and intrinsic properties could be established. In this Account, we focus on our recent advances in the field of solid state nanochemistry, including atomic structure characterization of ultrathin two-dimensional inorganic materials by X-ray absorption fine structure spectroscopy, characterization of their different types of structural defects by positron annihilation spectra and electron spin resonance, and investigation of their electronic structure by density-functional calculations. In addition, we summarize the close correlation between atomic, defect, and electronic structure variations and the optoelectronic, electrical, magnetic, and thermal properties of ultrathin two-dimensional materials. Finally, we also propose the major challenges and opportunities that face solid state nanochemistry. We believe that all the past achievements in ultrathin two-dimensional materials could bring new opportunities for solid state nanochemistry.

Update: 5-Mar-2015

Title:
An enhancement ZT and spin state transition of Ca3Co4O9 with Pb doping
Authors:
Demirel, S; Altin, E; Oz, E; Altin, S; Bayri, A Author Full Names: Demirel, S.; Altin, E.; Oz, E.; Altin, S.; Bayri, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 627 430-437; 10.1016/j.jallcom.2014.11.200 APR 5 2015
Abstract:
We reported the structural, electrical, thermal and magnetic properties of Pb-doped Ca3Co4O9 in the range of 300-5 K. DTA analysis showed that the stability of the Ca3Co4O9 was increased with Pb doping. According to XRD analysis, it is found that Pb ions were successfully doped in the Ca3Co4O9 structure. The temperature of resistivity minima, T-min, increased by increasing the Pb doping level and it is seen that incommensurate spin density wave state becomes more stable with Pb doping. The enhancement of thermopower was explained that Pb doping in Ca sites caused a decrease of Co4+ fraction such that Co4+ ions transformed into Co3+ or Co2+. The room temperature ZT value of the polycrystalline sample reaches about 16 times larger value than that of the un-doped polycrystalline sample which is the promising candidate for high temperatures in the thin film applications. According to magnetic susceptibility measurement, the increase of effective magnetic moment by Pb concentration was explained by spin state transition of Co3+ from low spin to intermediate spin and high spin state together with some orbital angular momentum contribution which comes from T-5(2) term due to a decrease of the ligand field splitting energy. (C) 2014 Elsevier B. V. All rights reserved.
Title:
Localized Electron Magnetism in the Icosahedral Au-Al-Tm Quasicrystal and Crystalline Approximant
Authors:
Nakayama, M; Tanaka, K; Matsukawa, S; Deguchi, K; Imura, K; Ishimasa, T; Sato, NK Author Full Names: Nakayama, Mika; Tanaka, Katsumasa; Matsukawa, Shuya; Deguchi, Kazuhiko; Imura, Keiichiro; Ishimasa, Tsutomu; Sato, Noriaki K.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (2):10.7566/JPSJ.84.024721 FEB 15 2015
Abstract:
We report the magnetic, thermal, and transport properties of the Au-Al-Tm quasicrystal, which is isostructural to the first and only quasicrystal Au-Al-Yb that shows a novel quantum critical behavior. The Tm-based quasicrystal undergoes a spin-glass-like freezing below T-f similar to 0.4 K. We also synthesize the Au-Al-Tm approximant to the quasicrystal and find that it shows a similar spin-glass-like freezing below T-f similar to 0.3 K. Both the quasicrystal and the approximant follow the Curie-Weiss law in a wide temperature range above T-f, indicating that the 4f electrons are well localized on the vertices of the icosahedron. The interspin interaction is antiferromagnetic and its magnitude is as small as similar to 1 K. The spin-glass-like freezing is presumably driven by the combined effect of the chemical disorder of Au/Al ions and the frustrated nature of the icosahedron. On the basis of these results, we discuss a possible origin of the unusual quantum criticality observed in the Yb-based system.
Title:
Superconductivity of Au-Ge-Yb Approximants with Tsai-Type Clusters
Authors:
Deguchi, K; Nakayama, M; Matsukawa, S; Imura, K; Tanaka, K; Ishimasa, T; Sato, NK Author Full Names: Deguchi, Kazuhiko; Nakayama, Mika; Matsukawa, Shuya; Imura, Keiichiro; Tanaka, Katsumasa; Ishimasa, Tsutomu; Sato, Noriaki K.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (2):10.7566/JPSJ.84.023705 FEB 15 2015
Abstract:
We report the emergence of bulk superconductivity in Au64.0Ge22.0Yb14.0 and Au63.5Ge20.5Yb16.0 below 0.68 and 0.36 K, respectively. This is the first observation of superconductivity in Tsai-type crystalline approximants of quasicrystals. The Tsai-type cluster center is occupied by Au and Ge ions in the former approximant, and by an Yb ion in the latter. For magnetism, the latter system shows a larger magnetization than the former. To explain this observation, we propose a model that the cluster-center Yb ion is magnetic. The relationship between the magnetism and the superconductivity is also discussed.
Title:
Incommensurate magnetic structure, Fe/Cu chemical disorder, and magnetic interactions in the high-temperature multiferroic YBaCuFeO5
Authors:
Morin, M; Scaramucci, A; Bartkowiak, M; Pomjakushina, E; Deng, G; Sheptyakov, D; Keller, L; Rodriguez-Carvajal, J; Spaldin, NA; Kenzelmann, M; Conder, K; Medarde, M Author Full Names: Morin, M.; Scaramucci, A.; Bartkowiak, M.; Pomjakushina, E.; Deng, G.; Sheptyakov, D.; Keller, L.; Rodriguez-Carvajal, J.; Spaldin, N. A.; Kenzelmann, M.; Conder, K.; Medarde, M.
Source:
PHYSICAL REVIEW B, 91 (6):10.1103/PhysRevB.91.064408 FEB 6 2015
Abstract:
Motivated by the recent observations of incommensurate magnetic order and electric polarization in YBaCuFeO5 up to temperatures T-N2 as high as 230 K [B. Kundys et al., Appl. Phys. Lett. 94, 072506 (2009); Y. Kawamura et al., J. Phys. Soc. Jpn 79, 073705 (2010)], we report here for the first time a model for the incommensurate magnetic structure of this material, which we complement with ab initio calculations of the magnetic exchange parameters. Using neutron powder diffraction, we show that the appearance of polarization below TN2 is accompanied by the replacement of the high-temperature collinear magnetic order by a circular inclined spiral with propagation vector k(i) = (1/2,1/2,1/2 +/- q). Moreover, we find that the polarization approximately scales with the modulus of the magnetic modulation vector q down to the lowest temperature investigated (similar to 3 K). Further, we observe occupational Fe/Cu disorder in the FeO5-CuO5 bipyramids, although a preferential occupation of such units by Fe-Cu pairs is supported by the observed magnetic order and by density functional calculations. We calculate exchange coupling constants for different Fe/Cu distributions and show that, for those containing Fe-Cu dimers, the resulting magnetic order is compatible with the experimentally observed collinear magnetic structure [k(c) = (1/2,1/2,1/2), T-N2 > T > T-N1 = 440 K]. Based on these results, we discuss possible origins for the incommensurate modulation and its coupling with ferroelectricity.
Title:
Critical behaviour of Sn2P2S6 and Sn2P2(Se0.28S0.72)(6) crystals under high hydrostatic pressures
Authors:
Zapeka, B; Kostyrko, M; Martynyuk-Lototska, I; Vlokh, R Author Full Names: Zapeka, B.; Kostyrko, M.; Martynyuk-Lototska, I.; Vlokh, R.
Source:
PHILOSOPHICAL MAGAZINE, 95 (4):382-393; 10.1080/14786435.2015.1006295 FEB 1 2015
Abstract:
Basing on the temperature dependences of optical birefringence for Sn2P2S6 and Sn2P2(Se0.28S0.72)(6) crystals subjected to hydrostatic pressures, we prove unambiguously that Sn2P2S6 reveals a tricritical point on its (p, T)- phase diagram with the coordinates (p, T) = (4.3kbar, 259K), so that the second-order phase transition transforms into the first-order one whenever the pressure increases above 4.3kbar. We also find that increasing hydrostatic pressure applied to Sn2P2(Se0.28S0.72)(6) leads to the change in the phase transition character from tricritical to first order. Further increase in the pressure up to ~2.5kbar imposes splitting of the first-order paraelectric-to-ferroelectric phase transition into two phase transitions, a second-order paraelectric-to-incommensurate one and a first-order incommensurate-to-ferroelectric transition.
Title:
Phase Diagram of (Li1-xFex)OHFeSe: A Bridge between Iron Selenide and Arsenide Superconductors
Authors:
Dong, XL; Zhou, HX; Yang, HX; Yuan, J; Jin, K; Zhou, F; Yuan, DN; Wei, LL; Li, JQ; Wang, XQ; Zhang, GM; Zhao, ZX Author Full Names: Dong, Xiaoli; Zhou, Huaxue; Yang, Huaixin; Yuan, Jie; Jin, Kui; Zhou, Fang; Yuan, Dongna; Wei, Linlin; Li, Jianqi; Wang, Xinqiang; Zhang, Guangming; Zhao, Zhongxian
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137 (1):66-69; 10.1021/ja511292f JAN 14 2015
Abstract:
Previous experimental results have shown important differences between iron selenide and arsenide superconductors which seem to suggest that the high-temperature superconductivity in these two subgroups of iron-based families may arise from different electronic ground states. Here we report the complete phase diagram of a newly synthesized superconducting (SC) system, (Li1-xFex)OHFeSe, with a structure similar to that of FeAs-based superconductors. In the non-SC samples, an antiferromagnetic (AFM) spin-density-wave (SDW) transition occurs at similar to 127 K. This is the first example to demonstrate such an SDW phase in an FeSe-based superconductor system. Transmission electron microscopy shows that a well-known O5xO5 iron vacancy ordered state, resulting in an AFM order at similar to 500 K in A(y)Fe(2-x)Se(2) (A = metal ions) superconductor systems, is absent in both non-SC and SC samples, but a unique superstructure with a modulation wave vector q = 1/2(1,1,0), identical to that seen in the SC phase of KyFe2-xSe2, is dominant in the optimal SC sample (with an SC transition temperature T-c = 40 K). Hence, we conclude that the high-T-c superconductivity in (Li1-xFex)OHFeSe stems from the similarly weak AFM fluctuations as FeAs-based superconductors, suggesting a universal physical picture for both iron selenide and arsenide superconductors.
Title:
Row of shear cracks moving in one-dimensional hexagonal quasicrystalline materials
Authors:
Tupholme, GE Author Full Names: Tupholme, G. E.
Source:
ENGINEERING FRACTURE MECHANICS, 134 451-458; 10.1016/j.engfracmech.2014.07.002 JAN 2015
Abstract:
Representations for the stress fields created around an infinite row of collinear, antiplane shear cracks moving within one-dimensional hexagonal quasicrystals, and the resulting stress intensity factors and the J-integral, are determined in closed-form and discussed, using an extended method of dislocation layers. The solutions for a finite quasicrystalline plate containing a single moving crack and a plate with a moving edge crack are also provided by this analysis. (C) 2014 Elsevier Ltd. All rights reserved.

Update: 26-Feb-2015

Title:
Electrochemical hydrogen storage properties of TixV65-xNi35 (x=45, 55) alloys produced by rapid-quenching
Authors:
Liu, CF; Liu, WQ; Wang, LM; Liang, F; Lin, J; Shen, Y; Jiang, DY Author Full Names: Liu, Chaofan; Liu, Wanqiang; Wang, Limin; Liang, Fei; Lin, Jing; Shen, Yu; Jiang, Dayong
Source:
MATERIALS LETTERS, 141 291-293; 10.1016/j.matlet.2014.11.108 FEB 15 2015
Abstract:
Electrochemical discharge performances of TixV65-xNi35 (x=45, 55) alloy are measured by electrochemical measurements at galvanostatic conditions, and alloy ribbon is prepared by rapid-quenching under argon atmosphere. XRD analysis of TixV65-xNi35 (x=45) alloy shows that the Ti45V20Ni35 (x=45) is mostly the amorphous phase, V-based solid solution phase with BCC structure phase and a negligible amount of (Ni, V) phase. While x=55, namely the Ti55V10Ni35 alloy, mainly consists of the icosahedral quasicrystal (I-phase), face centered cubic (FCC) phase with Ti2Ni-type structure and V-based solid solution phase with BCC structure phase. In the electrochemical tests, the maximum discharge capacity of Ti45V20Ni35 is about 150.4 mAh/g at a current density of 30 mA/g. However, Ti55V10Ni35 alloy shows that the best discharge capacity is 221.8 mAh/g under the same condition. In addition, it exhibits extraordinary cycling stability of 87.2% at 30 charge-discharge cycles. It can be found that the discharge capacity of the amorphous electrode is lower than those of the I-phase ones under the similar composition levels. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Strain-induced dimensionality crossover of precursor modulations in Ni2MnGa
Authors:
Nie, ZH; Wang, YD; Shang, SL; Zeng, QS; Ren, Y; Liu, DM; Yang, WG; Wang, Y; Liu, ZK Author Full Names: Nie, Zhihua; Wang, Yandong; Shang, Shunli; Zeng, Qiaoshi; Ren, Yang; Liu, Dongmei; Yang, Wenge; Wang, Yi; Liu, Zi-Kui
Source:
APPLIED PHYSICS LETTERS, 106 (2):10.1063/1.4906333 JAN 12 2015
Abstract:
Precursor modulations often occur in functional materials like magnetic shape memory alloys, ferroelectrics, and superconductors. In this letter, we have revealed the underlying mechanism of the precursor modulations in ferromagnetic shape memory alloys Ni2MnGa by combining synchrotron-based x-ray diffraction experiments and first-principles phonon calculations. We discovered the precursor modulations along [011] direction can be eliminated with [001] uniaxial loading, while the precursor modulations or premartensite can be totally suppressed by hydrostatic pressure condition. The TA(2) phonon anomaly is sensitive to stress induced lattice strain, and the entire TA(2) branch is stabilized along the directions where precursor modulations are eliminated by external stress. Our discovery bridges precursor modulations and phonon anomalies, and sheds light on the microscopic mechanism of the two-step superelasticity in precursor martensite. (C) 2015 AIP Publishing LLC.
Title:
Static friction scaling of physisorbed islands: the key is in the edge
Authors:
Varini, N; Vanossi, A; Guerra, R; Mandelli, D; Capozza, R; Tosatti, E Author Full Names: Varini, Nicola; Vanossi, Andrea; Guerra, Roberto; Mandelli, Davide; Capozza, Rosario; Tosatti, Erio
Source:
NANOSCALE, 7 (5):2093-2101; 10.1039/c4nr06521b 2015
Abstract:
The static friction preventing the free sliding of nanosized rare gas solid islands physisorbed on incommensurate crystalline surfaces is not completely understood. Simulations modeled on Kr/Pb(111) highlight the importance and the scaling behavior of the island's edge contribution to static friction.

Update: 19-Feb-2015

Title:
Distinct itinerant spin-density waves and local-moment antiferromagnetism in an intermetallic ErPd2Si2 single crystal
Authors:
Li, HF; Cao, CD; Wildes, A; Schmidt, W; Schmalzl, K; Hou, BY; Regnault, LP; Zhang, C; Meuffels, P; Loser, W; Roth, G Author Full Names: Li, Hai-Feng; Cao, Chongde; Wildes, Andrew; Schmidt, Wolfgang; Schmalzl, Karin; Hou, Binyang; Regnault, Louis-Pierre; Zhang, Cong; Meuffels, Paul; Loeser, Wolfgang; Roth, Georg
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep07968 JAN 22 2015
Abstract:
Identifying the nature of magnetism, itinerant or localized, remains a major challenge in condensed-matter science. Purely localized moments appear only in magnetic insulators, whereas itinerant moments more or less co-exist with localized moments in metallic compounds such as the doped-cuprate or the iron-based superconductors, hampering a thorough understanding of the role of magnetism in phenomena like superconductivity or magnetoresistance. Here we distinguish two antiferromagnetic modulations with respective propagation wave vectors at Q(+/-) = (H +/- 0.557(1), 0, L +/- 0.150(1)) and Q(C) = (H +/- 0.564(1), 0, L), where (H, L) are allowed Miller indices, in an ErPd2Si2 single crystal by neutron scattering and establish their respective temperature-and field-dependent phase diagrams. The modulations can co-exist but also compete depending on temperature or applied field strength. They couple differently with the underlying lattice albeit with associated moments in a common direction. The Q(+/-)modulation may be attributed to localized 4f moments while the Q(C) correlates well with itinerant conduction bands, supported by our transport studies. Hence, ErPd2Si2 represents a new model compound that displays clearly-separated itinerant and localized moments, substantiating early theoretical predictions and providing a unique platform allowing the study of itinerant electron behavior in a localized antiferromagnetic matrix.
Title:
Exploring the magnetic phase diagram of dysprosium with neutron diffraction
Authors:
Yu, J; LeClair, PR; Mankey, GJ; Robertson, JL; Crow, ML; Tian, W Author Full Names: Yu, J.; LeClair, P. R.; Mankey, G. J.; Robertson, J. L.; Crow, M. L.; Tian, W.
Source:
PHYSICAL REVIEW B, 91 (1):10.1103/PhysRevB.91.014404 JAN 5 2015
Abstract:
With one of the highest intrinsic magnetic moments (10.6 mu(B)/atom) among the heavy rare-earth elements, dysprosium exhibits a rich magnetic phase diagram, including several modulated magnetic phases. Aided by the Ruderman-Kittel-Kasuya-Yosida interaction, the magnetic modulations propagate coherently over a long range. Neutron diffraction experiments were performed to determine the microscopic magnetic origin of the field induced phases in bulk Dy as a function of temperature, covering regions of the well-known ferromagnetic, helical antiferromagnetic, fan phases, and several possible new phases suggested by previous studies. A short-range ordered fan phase was identified as the intermediate state between ferromagnetism and long-range ordered fan. In a field of 1 T applied along the a axis, the temperature range of a coexisting helix/fan phase was determined. The magnetic phase diagram of Dy was thus refined to include the detailed magnetic origin and the associated phase boundaries. Based on the period of the magnetic modulation and the average magnetization, the evolution of the spin arrangement upon heating was derived quantitatively for the modulated magnetic phases.
Title:
Coupling between an incommensurate antiferromagnetic structure and a soft ferromagnet in the archetype multiferroic BiFeO3/cobalt system
Authors:
Elzo, M; Moubah, R; Blouzon, C; Sacchi, M; Grenier, S; Belkhou, R; Dhesi, S; Colson, D; Torres, F; Kiwi, M; Viret, M; Jaouen, N Author Full Names: Elzo, Marta; Moubah, Reda; Blouzon, Camille; Sacchi, Maurizio; Grenier, Stephane; Belkhou, Rachid; Dhesi, Sarnjeet; Colson, Dorothee; Torres, Felipe; Kiwi, Miguel; Viret, Michel; Jaouen, Nicolas
Source:
PHYSICAL REVIEW B, 91 (1):10.1103/PhysRevB.91.014402 JAN 5 2015
Abstract:
Multiferroic materials are mostly antiferromagnets, often containing incommensurate magnetic arrangements stemming from the magnetoelectric interaction. Using soft x-ray resonant magnetic scattering, we show that these long-range structures induce a magnetization wriggle in cobalt layers deposited on top of BiFeO3 single crystals. This is understood using a simple interface exchange interactions model. It leads to the appearance of a magnetic anisotropy axis, which, in the particular BiFeO3/Co system, can be manipulated using an electric field. More generally, it is demonstrated here that through interfacial magnetic exchange, antiferromagnets can leave an imprint revealing some of their hidden properties, thus providing much richer effects than mere exchange bias.
Title:
Modulated spin structure responsible for the magnetic-field-induced polarization switching in multiferroic TbMn2O5
Authors:
Lee, JH; Jang, HM Author Full Names: Lee, Jung-Hoon; Jang, Hyun Myung
Source:
PHYSICAL REVIEW B, 91 (1):10.1103/PhysRevB.91.014403 JAN 5 2015
Abstract:
Orthorhombic TbMn2O5 (o-TMO) is a well-known multiferroic manganite with the remarkable property of polarization switching at 3 K under a bias magnetic (H) field along the a axis of Pb2(1)m. To theoretically account for this outstanding observation, we have proposed a modulated spin structure under the saturated bias H field by considering the relative strength of the three relevant exchange parameters in o-TMO. The proposed modulated structure based on density-functional theory (DFT) calculations is described in terms of the spin angle phi between the neighboring Mn4+-Mn3+ spin moments on the a-b plane. We have shown that the computed DFT polarization plotted as a function of f satisfactorily accounts for the observed H-field-induced polarization switching. We have further theoretically shown that the square of the critical field strength (H-c) needed for the polarization switching is inversely proportional to the degree of the extrinsic magnetoelectric coupling. The computed partial charge density demonstrates that the H-field-induced polarization switching also accompanies with the switching in the sign of the excess valence-electron density.
Title:
Molecular disorder effects in the thermal conductivity of solid thiophene
Authors:
Vdovichenko, GA; Krivchikov, AI; Korolyuk, OA; Romantsova, OO Author Full Names: Vdovichenko, G. A.; Krivchikov, A. I.; Korolyuk, O. A.; Romantsova, O. O.
Source:
LOW TEMPERATURE PHYSICS, 40 (12):1112-1115; 10.1063/1.4904001 DEC 2014
Abstract:
The temperature dependence of the thermal conductivity kappa(T) of solid thiophene is measured in a sequence of stable orientationally disordered phases with different degrees of orientational ordering of the molecules: in orientational glass (V-g); in phase V with large angular librational molecular vibrations; in incommensurate phase IV with a static orientational disorder; and in orientationally disordered crystalline phase III with dynamic orientational disorder of the molecules. Measurements are made at the saturated vapor pressure in a temperature range of 2-180 K. It is found that the thermal conductivity of thiophene is practically independent of temperature in phases III and V with dynamic orientational disorder of the molecules. In the orientational glass state and in the incommensurate state, the temperature dependence of the thermal conductivity of thiophene has a form typical of crystals with a long-range orientational order. A distinct hysteresis of the thermal conductivity is found at temperatures slightly below the temperature of the transition from phase IV into phase V. (C) 2014 AIP Publishing LLC.

Update: 12-Feb-2015

Title:
Magnetic and structural phase transitions and the tetragonality of thermoelastic martensite in quasi-binary Heusler alloys Ni2+x Mn1-x Ga
Authors:
Pushin, VG; Kourov, NI; Korolev, AV; Marchenkova, EB; Kuranova, NN; Belosludtseva, ES Author Full Names: Pushin, V. G.; Kourov, N. I.; Korolev, A. V.; Marchenkova, E. B.; Kuranova, N. N.; Belosludtseva, E. S.
Source:
PHYSICS OF THE SOLID STATE, 57 (1):45-52; 10.1134/S1063783415010242 JAN 2015
Abstract:
This paper reports on the results of investigations into the structure of martensite and the electronic and magnetic properties of Ni2 + x Mn1 - x Ga alloys in the concentration range 0.12 a parts per thousand currency sign x a parts per thousand currency sign 0.39. The concentration dependences of the critical temperatures and the anomalous behavior of the degree of tetragonal distortion of the martensite have been discussed, as well as the changes in the parameters characterizing the electronic and magnetic subsystems in the thermoelastic martensitic transition L2(1) a dagger' M, which occurs in atomically ordered L2(1)-type alloys upon doping in the range 0.12 a parts per thousand currency sign x a parts per thousand currency sign 0.39 at different temperatures. The temperature and concentration dependences of the magnetic properties have been determined for the state of the single-phase L2(1) austenite (at T > T (C) and A (f)) and martensite (at T > T (C) and M (f)), which undergoes the transition from a modulated 10M- or 14M-type structure to a nonmodulated (NM) tetragonal structure.
Title:
The Synthesis, Structure, and Electrical Characterization of (SnSe)(1.2)TiSe2
Authors:
Merrill, DR; Moore, DB; Ditto, J; Sutherland, DR; Falmbigl, M; Winkler, M; Pernau, HF; Johnson, DC Author Full Names: Merrill, Devin R.; Moore, Daniel B.; Ditto, Jeffrey; Sutherland, Duncan R.; Falmbigl, Matthias; Winkler, Markus; Pernau, Hans-Fridtjof; Johnson, David C.
Source:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, (1):83-91; 10.1002/ejic.201402814 JAN 2015
Abstract:
(SnSe)(1.2)TiSe2 was found to self-assemble from a precursor containing modulated layers of Sn-Se and Ti-Se over a surprisingly large range of layer thicknesses and compositions. The constituent lattices form an alternating layer superstructure with rotational disorder present between the layers. This compound was found to have the highest Seebeck coefficient measured for analogous TiX2 containing misfit layered compounds to date, suggesting potential for low-temperature thermoelectric applications. Electrical characterization suggests that electrons transferred from SnSe to TiSe2 are responsible for the higher carrier concentration observed relative to bulk TiSe2. The transfer of charge from one constituent to the other may provide a mechanism for doping layered dichalcogenides for various applications without negatively affecting carrier mobility.
Title:
Very large thermal rectification in bulk composites consisting partly of icosahedral quasicrystals
Authors:
Takeuchi, T Author Full Names: Takeuchi, Tsunehiro
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (6):10.1088/1468-6996/15/6/064801 DEC 2014
Abstract:
The bulk thermal rectifiers usable at a high temperature above 300 K were developed by making full use of the unusual electron thermal conductivity of icosahedral quasicrystals. The unusual electron thermal conductivity was caused by a synergy effect of quasiperiodicity and by a narrow pseudogap at the Fermi level. The rectification ratio, defined by TRR = vertical bar J(large)vertical bar/vertical bar J(small)vertical bar, reached vary large values exceeding 2.0. This significant thermal rectification would lead to new practical applications for the heat management.

Update: 5-Feb-2015

Title:
Microstructure evolution and mechanical properties of quasicrystal-reinforced Mg-Zn-Gd alloy processed by cyclic extrusion and compression
Authors:
Tian, Y; Huang, H; Yuan, GY; Ding, WJ Author Full Names: Tian, Yuan; Huang, Hua; Yuan, Guangyin; Ding, Wenjiang
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 626 42-48; 10.1016/j.jallcom.2014.11.167 MAR 25 2015
Abstract:
Mg-1.5Zn-0.25Gd (at.%) alloy reinforced by icosahedral quasicrystalline phase (I-phase) was fabricated and subjected to cyclic extrusion and compression (CEC) at 350 degrees C to investigate the microstructure evolution during CEC and its effect on the mechanical properties. It is observed that, during CEC, the microstructure of the alloy was greatly refined by dynamic recrystallization (DRX), large numbers of I-phase particles precipitated and then grew up, the texture of the alloy was obviously weakened. These changes in microstructure improved the mechanical properties of the alloy significantly and the alloy processed by 8 passes CEC exhibited outstanding plasticity of 31.4% and moderate yield strength of 161 MPa. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Substitution rules for icosahedral quasicrystals
Authors:
Madison, AE Author Full Names: Madison, Alexey E.
Source:
RSC ADVANCES, 5 (8):5745-5753; 10.1039/c4ra09524c 2015
Abstract:
An original well-defined substitution algorithm on how to construct the icosahedral packings is proposed, simple inflation/deflation rules for icosahedral quasicrystals are described, and natural local matching rules are derived.

Update: 29-Jan-2015

Title:
The modulated antiferromagnetic structures in multiferroic FeVO4: A Fe-57 Mossbauer spectroscopy investigation
Authors:
Colson, D; Forget, A; Bonville, P Author Full Names: Colson, D.; Forget, A.; Bonville, P.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 378 529-534; 10.1016/j.jmmm.2014.11.078 MAR 15 2015
Abstract:
We present an investigation of the two incommensurate magnetic phases in the multiferroic material FeVO4 using magnetic susceptibility and Fe-57 Mossbauer spectroscopy measurements. The susceptibility shows anomalies at the phase transitions at 15.7 and 23 K. We devise Mossbauer lineshapes appropriate for planar elliptical and collinear modulated magnetic structures and show that they reproduce very well the Mossbauer spectra in FeVO4, in full qualitative agreement with a previous neutron diffraction study. Quantitatively, our spectra provide precise determinations of the characteristics of the elliptical and modulated structures which match rather well the neutron diffraction results. We find that the hyperfine field elliptical modulation persists as T -> 0, which we attribute to an anisotropy of the hyperfine interaction since a moment modulation is forbidden at T=0 for a spin only ion like Fe3+. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Crystal Structure of Superconducting 1/1 Cubic Au-Ge-Yb Approximant with Tsai-Type Cluster
Authors:
Deguchi, K; Nakayama, M; Matsukawa, S; Imura, K; Tanaka, K; Ishimasa, T; Sato, NK Author Full Names: Deguchi, Kazuhiko; Nakayama, Mika; Matsukawa, Shuya; Imura, Keiichiro; Tanaka, Katsumasa; Ishimasa, Tsutomu; Sato, Noriaki K.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (1):10.7566/JPSJ.84.015002 JAN 15 2015
Abstract:
We report the synthesis of a single-phase sample of the superconducting crystalline approximant Au64.0Ge22.0Yb14.0 and present a structure model refined by Rietveld analysis for X-ray diffraction data.
Title:
Semimetallic Band Structure and Cluster-Based Description of a Cubic Quasicrystalline Approximant in the Al-Cu-Ir System
Authors:
Kitahara, K; Takagiwa, Y; Kimura, K Author Full Names: Kitahara, Koichi; Takagiwa, Yoshiki; Kimura, Kaoru
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (1):10.7566/JPSJ.84.014703 JAN 15 2015
Abstract:
Density functional calculations were performed for a cubic quasicrystalline approximant in the Al-Cu-Ir system. A semimetallic band structure was developed and analyzed on the basis of Wannier functions constructed from the valence and a part of the conduction band manifold. The Wannier functions were s-and p-like orbitals centered on either the centers of conventional clusters or the icosahedron-like vertices of pseudo-Mackay clusters, and d-like orbitals centered on the transition metals. Grouping the orbitals according to their center, we considered a small cluster for each group of the orbitals. Most of the orbitals contribute to the density of states only within the valence bands, i.e., they are valence states. The exceptions are some of p-like orbitals centered on the icosahedron-like vertices of the pseudo-Mackay clusters, and they contribute to both valence and conduction bands. Each of these p-like orbitals forms a covalent bond with one centered on the neighboring small cluster. The resulting bonding and antibonding orbitals are valence and conduction states, respectively. The number of valence bands (173) of our Al39Cu8Ir15 model was then decomposed in terms of the numbers of transition metals (23), clusters (16), and covalent bonds between the clusters (6) as 23 x 5 + 16 x 4 -6 = 173. The description for the valence-band formation may also be applicable to some of the group 13 element-transition metal intermetallic compounds, such as RuAl2.
Title:
Detailed study of the magnetic ordering in FeMnP0.75Si0.25
Authors:
Hoglin, V; Hudl, M; Caron, L; Beran, P; Solby, MH; Nordblad, P; Andersson, Y; Sahlberg, M Author Full Names: Hoglin, Viktor; Hudl, Matthias; Caron, Luana; Beran, Premysl; Solby, Magnus H.; Nordblad, Per; Andersson, Yvonne; Sahlberg, Martin
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 221 240-246; 10.1016/j.jssc.2014.10.013 JAN 2015
Abstract:
Magnetic and crystallographic properties of FeMnP0.75Si0.25 in the hexagonal Fe2P-type structure have been investigated by X-ray powder diffraction, neutron powder diffraction and magnetic measurements. The room temperature diffractograms reveal co-existence of two distinct structural phases in the samples with small, but significant, differences only in the unit cell dimensions. The volume ratio between the two phases is governed by the annealing conditions. One of the phases orders ferromagnetically (T-C=250 K) and the other in an incommensurate antiferromagnetic structure at low temperatures (q(x) = 0.363(1), T-N=150 K). (C) 2014 Elsevier Inc. All rights reserved.
Title:
Multiple twins of a decagonal approximant embedded in S-Al2CuMg phase resulting in pitting initiation of a 2024Al alloy
Authors:
Wang, J; Zhang, B; Zhou, YT; Ma, XL Author Full Names: Wang, J.; Zhang, B.; Zhou, Y. T.; Ma, X. L.
Source:
ACTA MATERIALIA, 82 22-31; 10.1016/j.actamat.2014.09.001 JAN 1 2015
Abstract:
The pitting of Al-Cu-Mg alloy is believed to originate from the local dissolution of S-Al2CuMg particles, and the dissolution activity differs from one particle to another. Nevertheless, the initial site where the dissolution of the S phase preferentially occurs and the cause of the heterogeneity in the electrochemical dissolution activity remain unknown, hindering our understanding of pitting initiation of Al-Cu-Mg alloys. In this work, we have applied in situ ex-environmental transmission electron microscopy and identified a large number of nanosized Al20Cu2Mn3 approximants of the decagonal quasicrystal embedded in the S phase. We find that the S phase with Al20Cu2Mn3 inclusions is more active than those free of the approximants. Such a preference is clarified to result from the decomposition of Al20Cu2Mn3 approximant prior to the dissolution of the S phase. In addition, we also find that the electrochemical behavior of Al20Cu2Mn3 approximants is different. The approximants with multiple twins are more active than those with few planar defects. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
New RMnO3+delta (R=Y, Ho; delta approximate to 0.35) phases with modulated structure
Authors:
Parkkima, O; Malo, S; Hervieu, M; Rautama, EL; Karppinen, M Author Full Names: Parkkima, Outi; Malo, Sylvie; Hervieu, Maryvonne; Rautama, Eeva-Leena; Karppinen, Maarit
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 221 109-115; 10.1016/j.jssc.2014.09.012 JAN 2015
Abstract:
A series of hexagonal RMnO3 (R=Y, Ho-Lu) compounds are first annealed in various highly oxidizing conditions to show that for the largest R constituents, Y and Ho, it is possible to load the phases with large amounts of excess oxygen. Within the oxygen-annealed samples we identify new heavily-oxygenated phases, that is, YMnO3.33 and HoMnO3.34. The former is then thoroughly characterized by thermogravimetric analysis, X-ray diffraction and electron diffraction. These studies evidence a hexagonal sub-cell (a(s) approximate to 3.578 angstrom (a(H)/root 3), c(S)approximate to 11.18 angstrom, space group P6(3)mc) and satellites, associated with two modulation vectors q(1)(->*)approximate to 0.41 a(S)(->*)+ 0.41 b(S)(->*)+1/3 c(S)(->*) and q(2)(->*) = (1/2). The results are interpreted by the formation of a modulated composite structure, resulting from the evolution of the hexagonal parent YMnO3+delta structure toward a reduced pyrochlore-type structure Y2Mn2O7-x, in long-and short-range ordering. (C) 2014 Elsevier Inc. All rights reserved.
Title:
Closely related magnetic and dielectric transitions in the "114" magnetoelectric Zn-doped CaBaCo4O7
Authors:
Seikh, MM; Caignaert, V; Suard, E; Meher, KRSP; Maignan, A; Raveau, B Author Full Names: Seikh, Md Motin; Caignaert, V.; Suard, E.; Meher, K. R. S. Preethi; Maignan, A.; Raveau, B.
Source:
JOURNAL OF APPLIED PHYSICS, 116 (24):10.1063/1.4905033 DEC 28 2014
Abstract:
We report on the impact of zinc doping upon the magneto-electric properties of CaBaCo4O7. We show that the presence of less than 1% Zn at the Co sites decreases T-C from 64K to 48K and generates two magnetic transitions, concomitant with changes of slope of dielectric permittivity, at 54K and 77K, respectively. Powder neutron diffraction and magnetic data show the existence of an incommensurate magnetic phase and a spin-flop transition in this temperature range. The crossover of the magnetodielectric effect of this oxide, from positive below 50K to negative above this temperature emphasizes the primordial role of the incommensurate magnetic phase in the evolution of these properties. (C) 2014 AIP Publishing LLC.
Title:
Tiling Phosphorene
Authors:
Guan, J; Zhu, Z; Tomanek, D Author Full Names: Guan, Jie; Zhu, Zhen; Tomanek, David
Source:
ACS NANO, 8 (12):12763-12768; 10.1021/nn5059248 DEC 2014
Abstract:
We present a scheme to categorize the structure of different layered phosphorene allotropes by mapping their nonplanar atomic structure onto a two-color 2D triangular tiling pattern. In the buckled structure of a phosphorene monolayer, we assign atoms in top positions to dark tiles and atoms in bottom positions to light tiles. Optimum sp(3) bonding is maintained throughout the structure when each triangular tile is surrounded by the same number N of like-colored tiles, with 0 = N = 2. Our ab initio density functional calculations indicate that both the relative stability and electronic properties depend primarily on the structural index N. The proposed mapping approach may also be applied to phosphorene structures with nonhexagonal rings and 2D quasicrystals with no translational symmetry, which we predict to be nearly as stable as the hexagonal network.
Title:
Spatial control of functional properties via octahedral modulations in complex oxide superlattices
Authors:
Moon, EJ; Colby,; Wang, Q; Karapetrova, E; Schleputz, CM; Fitzsimmons, MR; May, SJ Author Full Names: Moon, E. J.; R., Colby; Wang, Q.; Karapetrova, E.; Schlepuetz, C. M.; Fitzsimmons, M. R.; May, S. J.
Source:
NATURE COMMUNICATIONS, 5 10.1038/ncomms6710 DEC 2014
Abstract:
Control of atomic structure, namely the topology of the corner-connected metal-oxygen octahedra, has emerged as an important route to tune the functional properties at oxide interfaces. Here we investigate isovalent manganite superlattices (SLs), [(La0.7Sr0.3MnO3) n/(Eu0.7Sr0.3MnO3) n] x m, as a route to spatial control over electronic bandwidth and ferromagnetism through the creation of octahedral superstructures. Electron energy loss spectroscopy confirms a uniform Mn valence state throughout the SLs. In contrast, the presence of modulations of the MnO6 octahedral rotations along the growth direction commensurate with the SL period is revealed by scanning transmission electron microscopy and X-ray diffraction. We show that the Curie temperatures of the constituent materials can be systematically engineered via the octahedral superstructures leading to a modulated magnetization in samples where the SL period is larger than the interfacial octahedral coupling length scale, whereas a single magnetic transition is observed in the short-period SLs.
Title:
Magnetic structure and domain conversion of the quasi-2D frustrated antiferromagnet CuCrO2 probed by NMR
Authors:
Sakhratov, YA; Svistov, LE; Kuhns, PL; Zhou, HD; Reyes, AP Author Full Names: Sakhratov, Yu A.; Svistov, L. E.; Kuhns, P. L.; Zhou, H. D.; Reyes, A. P.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 119 (5):880-890; 10.1134/S1063776114110181 NOV 2014
Abstract:
We have carried out Cu-63,Cu-65 NMR spectra measurements in a magnetic field up to about 15.5 T on a single crystal of the multiferroic triangular-lattice antiferromagnet CuCrO2. The measurements were performed for perpendicular and parallel orientations of the magnetic field with respect to the c axis of the crystal, and the detailed angle dependence of the spectra on the magnetic field direction in the ab plane was studied. The shape of the spectra can be well described in the model of spiral spin structure proposed by recent neutron diffraction experiments. When the field is rotated perpendicular to the crystal c axis, we observed, directly for the first time, a remarkable reorientation of the spin plane simultaneous with rotation of the incommensurate wavevector, by quantitatively deducing the conversion of the energetically less favorable domain to a more favorable one. At high enough fields parallel to the c axis, the data are consistent with either a field-induced commensurate spiral magnetic structure or an incommensurate spiral magnetic structure with a disorder in the c direction, suggesting that high fields may have influence on interplanar ordering.
Title:
Modeling quasi-lattice with octagonal symmetry
Authors:
Girzhon, VV; Smolyakov, OV; Zakharenko, MI Author Full Names: Girzhon, V. V.; Smolyakov, O. V.; Zakharenko, M. I.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 119 (5):854-860; 10.1134/S1063776114110053 NOV 2014
Abstract:
We prove the possibility to use the method of modeling of a quasi-lattice with octagonal symmetry similar to that proposed earlier for the decagonal quasicrystal. The method is based on the multiplication of the groups of basis sites according to specified rules. This model is shown to be equivalent to the method of the periodic lattice projection, but is simpler because it considers merely two-dimensional site groups. The application of the proposed modeling procedure to the reciprocal lattice of octagonal quasicrystals shows a fairly good matching with the electron diffraction pattern. Similarly to the decagonal quasicrystals, the possibility of three-index labeling of the diffraction reflections is exhibited in this case. Moreover, the ascertained ratio of indices provides information on the intensity of diffraction reflections.
Title:
Single-Crystal Neutron Diffraction Study of Superstructure Ordering and Domain Behaviour in Brownmillerite-Type Ca2Fe2O5
Authors:
Auckett, JE; Studer, AJ; Ling, CD Author Full Names: Auckett, Josie E.; Studer, Andrew J.; Ling, Chris D.
Source:
AUSTRALIAN JOURNAL OF CHEMISTRY, 67 (12):1824-1828; 10.1071/CH14358 2014
Abstract:
We show that large single crystals of brownmillerite-type Ca2Fe2O5 can be grown using the floating-zone method under ambient pressure conditions, provided that the feed rods are pre-annealed to a very high density. Neutron diffraction data collected from these crystals show the emergence of a long-range ordered incommensurate phase at high temperature. The observation of this phase for the first time using neutrons proves that the incommensurate ordering of tetrahedral chains upon heating Ca2Fe2O5 is a truly long-range and bulk phenomenon. The results are used to compare and contrast the structures of Ca2Fe2O5 and Sr2Fe2O5, and are consistent with experimental observations of significantly higher oxide ionic conduction in the latter material.

Update: 21-Jan-2015

Title:
The creation of modulated monoclinic aperiodic composites in n-alkane/urea compounds
Authors:
Mariette, C; Guerin, L; Rabiller, P; Chen, YS; Bosak, A; Popov, A; Hollingsworth, MD; Toudic, B Author Full Names: Mariette, Celine; Guerin, Laurent; Rabiller, Philippe; Chen, Yu-Sheng; Bosak, Alexei; Popov, Alexander; Hollingsworth, Mark D.; Toudic, Bertrand
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 230 (1):5-11; 10.1515/zkri-2014-1773 JAN 2015
Abstract:
n-Dodecane/urea is a member of the prototype series of n-alkane/urea inclusion compounds. At room temperature, it presents a quasi-one dimensional liquid-like state for the confined guest molecules within the rigid, hexagonal framework of the urea host. At lower temperatures, we report the existence of two other phases. Below T-c=248 K there appears a phase with rank four superspace group P6(1)22(00 gamma), the one typically observed at room temperature in n-alkane/urea compounds with longer guest molecules. A misfit parameter, defined by the ratio gamma=C-h/C-g (C-host/C-guest), is found to be 0.632 +/- 0.005. Below T-c1=123 K, a monoclinic modulated phase is created with a constant shift along c of the guest molecules in adjacent channels. The maximal monoclinic space group for this structure is P12(1)1(alpha 0 gamma). Analogies and differences with n-heptane/urea, which also presents a monoclinic, modulated low-temperature phase, are discussed.
Title:
Incommensurate modulations in stoichiometric Ni2MnGa ferromagnetic shape memory alloy: an overview
Authors:
Singh, S; Barman, SR; Pandey, D Author Full Names: Singh, Sanjay; Barman, S. R.; Pandey, Dhananjai
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 230 (1):13-22; 10.1515/zkri-2014-1784 JAN 2015
Abstract:
This article presents a brief overview of our recent work on the nature of long period modulation in the premartensite and martensite phases of Ni2MnGa ferromagnetic shape memory alloy using high resolution synchrotron x-ray powder diffraction patterns. The commensurate structure model using the Pnnm space group is unable to account for the peak positions of the satellite reflections that appear due to modulations correctly. LeBail and Rietveld refinements using the (3+1)-D super space group Immm(00 gamma)s00 show that the peak positions of all the reflections, including the satellites, can be explained satisfactorily using incommensurate modulations for both the premartensite and martensite phases. The incommensurate modulation vectors are found to be q=0.33761(5)c*=(1/3+delta(1))c* and 0.43160(3)c*=(3/7+delta(2))c*, where delta(1) and delta(2) are the degrees of incommensuration for the premartensite and martensite phases, respectively. The periodicity of the closest rational approximant of the premartensite and martensite phases are confirmed to be 3 M and 7 M, respectively, in agreement with single crystal diffraction results.
Title:
Insights from STEM and NBED studies into the local structure and growth mechanism of misfit layered compounds prepared using modulated reactants
Authors:
Hausler, I; Atkins, R; Falmbigl, M; Rudin, SP; Neumann, W; Johnson, DC Author Full Names: Haeusler, Ines; Atkins, Ryan; Falmbigl, Matthias; Rudin, Sven P.; Neumann, Wolfgang; Johnson, David C.
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 230 (1):45-54; 10.1515/zkri-2014-1761 JAN 2015
Abstract:
X-ray diffraction and transmission electron microscopy were used to probe the structure of the misfit compound [(SnSe)(1.15)](1)(VSe2)(1) grown using an elementally modulated precursor. The specular X-ray diffraction pattern contained only 00l reflections, which yielded a c lattice parameter of 1.203(1) nm. Cross-section STEM revealed alternating layers of SnSe and VSe2, in agreement with the structure model refined from the X-ray diffraction pattern using Rietveld refinement. Plan-view transmission electron microscopy revealed the in-plane grain structure of the films, yielding grain sizes in agreement with previously reported in plane X-ray diffraction studies and the cross-section STEM images. The plan view images also contained Moire fringes resulting from grains with different relative tilting on both sides of interfaces as well as Moire fringes resulting from different relative rotations between domains. An energy-filtered nano-beam electron diffraction pattern obtained from at least one domain in the [(SnSe)(1.15)](1) (VSe2)(1) sample investigated in cross section contained a series of resolvable supercell reflections along the c axis that indicated that the supercell c-axis lattice parameter was a multiple of three times that determined using X-ray diffraction. Energy filtered NBED of plan-view samples showed diffraction patterns from select regions with 12-fold symmetry, indicating that the arrangement of the layers is not rotationally random from layer to layer. This suggests that during the self-assembly of the amorphous modulated elemental precursor, the SnSe and VSe2 constituent layers must nucleate off the adjacent interfaces of the growing crystal, yielding layers that are locally rotationally aligned with growing crystal. Different processing conditions during the precursor to crystal self-assembly might enable the domain size and/or the extent of order to be controlled.
Title:
The modulated structure of labradorite
Authors:
Boysen, H; Kek, S Author Full Names: Boysen, Hans; Kek, Stefan
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 230 (1):23-35; 10.1515/zkri-2014-1749 JAN 2015
Abstract:
The crystal structure of labradorite is characterized by two modulation waves with largely different periods of about 1500 angstrom and 50 angstrom, giving rise to s- and e-satellites, respectively. The problems to determine the true structure by diffraction methods are discussed. Since each s-lamella has its own e-modulation, common experiments are not sufficient. Using only s-satellites around main reflections assumes e-averaged structures of the s-lamellae. On the other hand, using only averaged e-satellites and main reflections integrated over the s-satellites leads to a hypothetical, idealised structure such as if there were no s-modulation. For this reason the analysis of an extensive data set, including e-satellites up to third order, cannot resolve the Ca/Na modulation unambiguously, although the Si/Al modulation can be determined consistently from directly refined occupancies and T-O bond lengths.
Title:
LEED studies on modulated surface structures
Authors:
Moritz, W Author Full Names: Moritz, Wolfgang
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 230 (1):37-43; 10.1515/zkri-2014-1787 JAN 2015
Abstract:
The problems occurring in structure analyses of modulated surfaces by LEED or X-ray diffraction are briefly discussed. In previous LEED studies of modulated surfaces a commensurate unit cell and Fourier coefficients to describe the modulation function has been used. The wave length of the modulation and the size of the supercell are limited in this way by the computational effort of the multiple scattering calculations. To overcome this problem an approximation is proposed allowing the analysis of commensurate or incommensurate surface modulations with long wave lengths.
Title:
Density-wave instabilities of fractionalized Fermi liquids
Authors:
Chowdhury, D; Sachdev, S Author Full Names: Chowdhury, Debanjan; Sachdev, Subir
Source:
PHYSICAL REVIEW B, 90 (24):10.1103/PhysRevB.90.245136 DEC 22 2014
Abstract:
Recent experiments in the underdoped regime of the hole-doped cuprates have found evidence for an incommensurate charge density-wave state. We present an analysis of the charge ordering instabilities in a metal with antiferromagnetic correlations, where the electronic excitations are coupled to the fractionalized excitations of a quantum fluctuating antiferromagnet on the square lattice. The resulting charge density-wave state emerging out of such a fractionalized Fermi liquid (FL*)has wave vectors of the form (+/- Q(0),0),(0, +/- Q(0)), with a predominantly d-form factor, in agreement with experiments on a number of different families of the cuprates. In contrast, as previously shown, the charge density-wave instability of a nearly antiferromagnetic metal with a large Fermi surface, interacting via short-range interactions, has wave vectors of the type (+/- Q(0), +/- Q(0)). Our results show that the observed charge density-wave appears as a low-energy instability of a fractionalized metallic state linked to the proximity to an antiferromagnetic insulator, and the pseudogap regime can be described by such a metal at least over intermediate length and energy scales.
Title:
BaGe6 and BaGe6-x : Incommensurately Ordered Vacancies as Electron Traps
Authors:
Akselrud, L; Wosylus, A; Castillo, R; Aydemir, U; Prots, Y; Schnelle, W; Grin, Y; Schwarz, U Author Full Names: Akselrud, Lev; Wosylus, Aron; Castillo, Rodrigo; Aydemir, Umut; Prots, Yurii; Schnelle, Walter; Grin, Yuri; Schwarz, Ulrich
Source:
INORGANIC CHEMISTRY, 53 (24):12699-12705; 10.1021/ic5021065 DEC 15 2014
Abstract:
We report the high-pressure high-temperature synthesis of the germanium-based framework compounds BaGe6 (P = 15 GPa, T = 1073 K) and BaGe6-x (P = 10 GPa, T = 1073 K) which are metastable at ambient conditions. In BaGe6-x, partial fragmentation of the BaGe6 network involves incommensurate modulations of both atomic positions and site occupancy. Bonding analysis in direct space reveals that the defect formation in BaGe6-x is associated with the establishment of free electron pairs around the defects. In accordance with the electron precise composition of BaGe6-x for x = 0.5, physical measurements evidence semiconducting electron transport properties which are combined with low thermal conductivity.
Title:
Structural phase transition associated with van Hove singularity in 5d transition metal compound IrTe2
Authors:
Qian, T; Miao, H; Wang, ZJ; Shi, X; Huang, YB; Zhang, P; Xu, N; Zeng, LK; Ma, JZ; Richard, P; Shi, M; Xu, G; Dai, X; Fang, Z; Fang, AF; Wang, NL; Ding, H Author Full Names: Qian, T.; Miao, H.; Wang, Z. J.; Shi, X.; Huang, Y. B.; Zhang, P.; Xu, N.; Zeng, L. K.; Ma, J. Z.; Richard, P.; Shi, M.; Xu, G.; Dai, X.; Fang, Z.; Fang, A. F.; Wang, N. L.; Ding, H.
Source:
NEW JOURNAL OF PHYSICS, 16 10.1088/1367-2630/16/12/123038 DEC 15 2014
Abstract:
We have investigated the electronic states of IrTe2 by using angle-resolved photoemission spectroscopy to elucidate the origin of the structural phase transition. Both the Ir 4f and Te 4d core level spectra exhibit dramatic splitting below the phase transition temperature T-s, suggesting that there exist two inequivalent Ir and Te sites with distinctly different electronic states in the distorted phase. The band related to the saddle points at the Fermi level (E-F) is strongly reconstructed, which removes the van Hove singularity from E-F below T-s. The wavevector connecting the adjacent saddle points is consistent with the in-plane superstructure modulation wavevector. These results indicate that the phase transition in IrTe2 is intimately associated with the saddle points. As the van Hove singularity mainly originates from the Te p(x)+p(y) orbitals, the Te 5p electronic states play a dominant role in the structural phase transition.
Title:
Diagnostics of a spatial spin-modulated structure using nuclear magnetic resonance and Mossbauer spectroscopy
Authors:
Rusakov, VS; Pokatilov, VS; Sigov, AS; Matsnev, ME; Gubaidulina, TV Author Full Names: Rusakov, V. S.; Pokatilov, V. S.; Sigov, A. S.; Matsnev, M. E.; Gubaidulina, T. V.
Source:
JETP LETTERS, 100 (7):463-469; 10.1134/S0021364014190102 DEC 2014
Abstract:
Methods of the diagnostics of the spatial spin-modulated structure of the cycloidal type in multiferroics based on nuclear magnetic resonance and Mossbauer spectroscopy have been considered. It has been established that Mossbauer spectroscopy makes it possible to determine the anharmonicity parameter of the spatial spin-modulated structure of the cycloidal type with no worse accuracy than nuclear magnetic resonance with higher resolution. Mossbauer spectroscopy, being sensitive to the hyperfine quadrupole interaction of the nucleus in the excited state, makes it possible to obtain additional information on the features of the spatial spin-modulated structure.
Title:
Effects of Au-Addition on Plastic Deformation Ability of Zr-Cu-Ni-Al Bulk Metallic Glasses
Authors:
Yamada, M; Yamasaki, T; Fujita, K; Yokoyama, Y; Kim, DH Author Full Names: Yamada, Masahiro; Yamasaki, Tohru; Fujita, Kazutaka; Yokoyama, Yoshihiko; Kim, Do Hyang
Source:
JOURNAL OF THE JAPAN INSTITUTE OF METALS, 78 (12):449-458; 10.2320/jinstmet.J2014042 DEC 2014
Abstract:
Effects of Au-addition on plastic deformation ability of Zr-Cu-Ni-Al bulk metallic glasses (BMGs) during compression and tensile tests have been examined. Zr65Cu20Ni5Al10 BMG(Zr-65) and Zr60+xCu22-xNi5Al10Au3(x= 0, 5, 6.5, 8, 9 at.) BMGs (Zr60Au3-Zr69Au3) have been prepared by a tilt casting method. By the Au. addition on the BMGs containing Zr. content of 65 at. and more, precipitation of icosahedral quasicrystalline phase (I. phase) in supercooled liquids was observed, resulting in large increase of viscosity in the supercooled liquids. Compression and tensile tests were carried out in these BMGs under various strain rates of 1 similar to 5x10 (4)/s at room temperature. In the compression test of the Zr65 BMG, plastic strain at fracture was about 10. and only several localized shear bands were observed. In the Zr65Au3 and Zr66.5Au3 BMGs, plastic strains at fracture were largely increased to 20. and above. In these cases, initial plastic strains of about 5. with large number of shear band were observed as macroscopically homogeneous deformation, and successive plastic strains along main shear band was observed. In the tensile test, large plastic strain at fracture of about 0.5% was also observed for the Zr66.5Au3 BMG. By transmission electron microscopic observations of the Au. addition BMGs, precipitation of nano. crystallites having about 10 nm in diameter was observed near the fractured surfaces of the compressive and tensile test specimens. Viscosity of supercooled liquids in shear bands was estimated by the stress. drop of serrations in the compressive stress. strain curves. It is considered that the large increase of the plastic strain is due to the drastic increase of the viscosity of the supercooled liquids formed inside shear bands during plastic deformation.
Title:
Spin reorientation and magnetic structure of HoCo12B6 ferrimagnetic compound
Authors:
Diop, LVB; Isnard, O Author Full Names: Diop, L. V. B.; Isnard, O.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (2):10.1088/0953-8984/27/2/026004 JAN 21 2014
Abstract:
The magnetic phase diagram is determined by combining magnetization measurements, ac susceptibility and neutron diffraction. The crystal and magnetic structures are also investigated. The HoCo12B6 compound exhibits ferrimagnetic behavior below T-C = 147 K. Two antiferromagnetically coupled sublattices cancel out at the compensation temperature T-Comp = 46 K. HoCo12B6 undergoes a spin reorientation transition at T-SR = 76 K; the easy magnetization axis changes from axial to basal plane upon heating. The magnitude of the magnetic moments and their orientation are described and discussed. It is revealed that HoCo12B6 compound exhibits a commensurate magnetic structure below T-SR and an incommensurate one slightly above T-SR. Significantly different magnetic moments have been observed on the two Co crystal sites, a very low magnetic moment of 0.14(mu B) being refined on the Co 18 g position. In addition, the second order crystal electric-field parameter A(2)(0) at the rare-earth site is determined. This result is discussed and used to explain the observed spin reorientation transition by a competition between the Co and Ho sublattice anisotropy.

15-Jan-2015

Title:
A modulation wave approach to the order hidden in disorder
Authors:
Withers, R.
Source:
IUCrJ (2015) 2, 74-84
Abstract:
The usefulness of a modulation wave approach to understanding and interpreting the highly structured continuous diffuse intensity distributions characteristic of the reciprocal spaces of the very large family of inherently flexible materials which exhibit ordered `disorder' is pointed out. It is shown that both longer range order and truly short-range order are simultaneously encoded in highly structured diffuse intensity distributions. The long-range ordered crystal chemical rules giving rise to such diffuse distributions are highlighted, along with the existence and usefulness of systematic extinction conditions in these types of structured diffuse distributions.
Title:
Superspace crystallography: a key to the chemistry and properties
Authors:
Pinheiro, C. B; Abakumov, A. M.
Source:
IUCrJ (2015) 2, 137-154
Abstract:
An overview is given of the recent advances in the field of modulated molecular and inorganic crystals with an emphasis on the links between incommensurability, intermolecular and interatomic interactions and, wherever possible, the properties of the materials. The importance of detailed knowledge on the modulated structure for understanding the crystal chemistry and the functional properties of modulated phases is shown using selected examples of incommensurate modulations in organic molecular compounds and inorganic complex oxides.
Title:
Computational self-assembly of a one-component icosahedral quasicrystal
Authors:
Engel, M; Damasceno, PF; Phillips, CL; Glotzer, SC Author Full Names: Engel, Michael; Damasceno, Pablo F.; Phillips, Carolyn L.; Glotzer, Sharon C.
Source:
NATURE MATERIALS, 14 (1):109-116; 10.1038/NMAT4152 JAN 2015
Abstract:
Icosahedral quasicrystals (IQCs) are a form of matter that is ordered but not periodic in any direction. All reported IQCs are intermetallic compounds and either of face-centred-icosahedral or primitive-icosahedral type, and the positions of their atoms have been resolved from diffraction data. However, unlike axially symmetric quasicrystals, IQCs have not been observed in non-atomic (that is, micellar or nanoparticle) systems, where real-space information would be directly available. Here, we show that an IQC can be assembled by means of molecular dynamics simulations from a one-component system of particles interacting via a tunable, isotropic pair potential extending only to the third-neighbour shell. The IQC is body-centred, self-assembles from a fluid phase, and in parameter space neighbours clathrates and other tetrahedrally bonded crystals. Our findings elucidate the structure and dynamics of the IQC, and suggest routes to search for it and design it in soft matter and nanoscale systems.
Title:
ICOSAHEDRAL QUASICRYSTALS Assembled with one component
Authors:
Boissieu, M Author Full Names: de Boissieu, Marc
Source:
NATURE MATERIALS, 14 (1):18-19; 10.1038/nmat4183 JAN 2015
Title:
Entropy-driven formation of large icosahedral colloidal clusters by spherical confinement
Authors:
de Nijs, B; Dussi, S; Smallenburg, F; Meeldijk, JD; Groenendijk, DJ; Filion, L; Imhof, A; van Blaaderen, A; Dijkstra, M Author Full Names: de Nijs, Bart; Dussi, Simone; Smallenburg, Frank; Meeldijk, Johannes D.; Groenendijk, Dirk J.; Filion, Laura; Imhof, Arnout; van Blaaderen, Alfons; Dijkstra, Marjolein
Source:
NATURE MATERIALS, 14 (1):56-60; 10.1038/NMAT4072 JAN 2015
Abstract:
Icosahedral symmetry, which is not compatible with truly long-range order, canbefoundinmany systems, such as liquids, glasses, atomic clusters, quasicrystals and virus-capsids(1-12). To obtain arrangements with a high degree of icosahedral order from tens of particles or more, interparticle attractive interactions are considered to be essential(1,3,6-12). Here, we report that entropy and spherical confinement suffice for the formation of icosahedral clusters consisting of up to 100,000 particles. Specifically, by using real-space measurements on nanometre- and micrometre-sized colloids, as well as computer simulations, we show that tens of thousands of hard spheres compressed under spherical confinement spontaneously crystallize into icosahedral clusters that are entropically favoured over the bulk face-centred cubic crystal structure (13,14). Our findings provide insights into the interplay between confinement and crystallization and into how these are connected to the formation of icosahedral structures.
Title:
Frustration and multicriticality in the antiferromagnetic spin-1 chain
Authors:
Pixley, JH; Shashi, A; Nevidomskyy, AH Author Full Names: Pixley, J. H.; Shashi, Aditya; Nevidomskyy, Andriy H.
Source:
PHYSICAL REVIEW B, 90 (21):10.1103/PhysRevB.90.214426 DEC 15 2014
Abstract:
The antiferromagnetic spin-1 chain has a venerable history and has been thought to be well understood. Here, we show that inclusion of both next-nearest-neighbor (alpha) and biquadratic (beta) interactions results in a rich phase diagram with a multicritical point that has not been observed before. We study the problem using a combination of the density matrix renormalization group (DMRG), an analytic variational matrix product state wave function, and conformal field theory. For negative beta < beta*, we establish the existence of a spontaneously dimerized phase, separated from the Haldane phase by the critical line alpha(c) (beta) of second-order phase transitions. In the opposite regime, beta > beta*, the transition from the Haldane phase becomes first order into the next-nearest-neighbor (NNN) AKLT phase. Based on the field theoretical arguments and DMRG calculations, we find that these two regimes are separated by a multicritical point (beta*, alpha*) of a different universality class, described by the level-4 SU(2) Wess-Zumino-Witten conformal theory. From the DMRG calculations, we estimate this multicritical point to lie in the range -0.2 < beta* < -0.15 and 0.47 < alpha* < 0.53. We further find that the dimerized and NNN-AKLT phases are separated from each other by a line of first-order phase transitions that terminates at the multicritical point. We establish that transitions out of the Haldane phase into the dimer or NNN-AKLT phases are topological in nature and occur either with or without closing of the bulk gap, respectively. We also study short-range incommensurate-to-commensurate transitions in the resulting phase diagram. Inside the Haldane phase, we show the existence of two incommensurate crossovers: the Lifshitz transition and the disorder transition of the first kind, marking incommensurate correlations in momentum and real space, respectively. Notably, these crossover lines stretch across the entire (beta, alpha) phase diagram, merging into a single incommensurate-to-commensurate transition line for negative beta less than or similar to beta* inside the dimer *phase*. This behavior is qualitatively similar to that seen in classical frustrated two-dimensional spin models, by way of the quantum (1+ 1) D to classical 2D correspondence.
Title:
Isothermal section of Mg-rich corner in Mg-Zn-Al ternary system at 335 degrees C
Authors:
Ren, YP; Sun, SN; Wang, LQ; Guo, Y; Li, HX; Li, S; Qin, GW Author Full Names: Ren, Yu-ping; Sun, Shi-neng; Wang, Li-qing; Guo, Yun; Li, Hong-xiao; Li, Song; Qin, Gao-wu
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 24 (11):3405-3412; 10.1016/S1003-6326(14)63483-X NOV 2014
Abstract:
The phase equilibria and compositions at the Mg-rich corner of the Mg-Zn-Al ternary system at 335 degrees C were systemically investigated through the equilibrated alloy method by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) assisted with energy dispersive spectroscopy of X-ray (EDS). It is experimentally testified that the alpha-Mg solid solution is not in equilibrium with the Mg-32(Al, Zn)(49) (tau) ternary intermetallic compound or q quasicrystalline phase, but only in equilibrium with one ternary intermetallic compound Al5Mg11Zn4 (phi). The whole composition range of the phi phase was also obtained at 335 degrees C, i.e., 52.5%-56.4% Mg, 13.6%-24.0% Al, 19.6%-33.9% Zn (mole fraction). The solubility of Al in the MgZn phase is remarkably more than that in the Mg7Zn3 phase, and the maximum is about 8.6% Al. Aluminum and zinc are simultaneously soluble in the alpha-Mg solid solution.
Title:
The alpha <-> beta phase transitions of Zn2P2O7 revisited: existence of an additional intermediate phase with an incommensurately modulated structure
Authors:
Stoger, B; Weil, M; Dusek, M Author Full Names: Stoeger, Berthold; Weil, Matthias; Dusek, Michal
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 539-554; SI 10.1107/S205252061401049X 3 JUN 2014
Abstract:
Zn2P2O7 crystallizes in a thortveitite-like structure and features temperature-dependent polymorphism. At high temperatures (T > 500 K), the aristotype phase beta-Zn2P2O7 (C2/m, Z = 2, a similar or equal to 6.60, b similar or equal to 8.28, c similar or equal to 4.53 angstrom, beta similar or equal to 105.4 degrees) is stable. At lower temperatures the lock-in phase alpha(1)-Zn2P2O7 [at 350 K: I2/c, Z = 12, a = 20.1131 (13), b = 8.2769 (6), c = 9.109 (3) angstrom, beta = 106.338 (16)degrees], a sixfold superstructure with commensurate modulation vector q = (1/3, 0, 1/2), is stable. Between the stability ranges of the alpha(1)- and beta-phases exists the intermediate, *incommensurately modulated* alpha(2)-Zn2P2O7 phase with modulation wavevector q similar or equal to (0.33, 0, 0.40) and C2/m(alpha, 0, gamma)0s superspace group symmetry. The alpha(1) -> alpha(2) lock-in phase transition at T-L = 408 K is of first-order and features virtually no hysteresis. It is immediately followed by the second-order alpha(2) -> beta transition to the non-modulated phase at T-I similar or equal to 430 K. This transformation is sluggish and even at T = 500 K very weak satellite reflections of the alpha(2)- phase were observed. Both phase transitions were analyzed with differential scanning calorimetry and high-temperature powder and single-crystal X-ray diffraction. The crystal structures of the alpha(1)- and alpha(2)- phases were refined from single crystal data collected at T = 350, 400, 405, 410, 415, 420, 425, 430, 450 and 500 K. Different models describing the slow transition from the *incommensurately modulated* alpha(2)- to the non-modulated beta-phase were tested. In the model resulting in the best residuals, the bridging O atom of the [P2O7] group, which is located on a 2/m position in the basic structure, is described as an overlap of an atom ordered in internal space and one atom disordered around the mirror plane. The occupancy of the ordered atom decreases with temperature until at T = 500 K virtually only the disordered atom remains. Simultaneously, the amplitude of the modulation functions of the remaining atoms decreases, so that the T = 500 K structure can be considered as the C2/m aristotype structure, although the diffraction pattern still features *satellite reflections* of first order with very low intensities.
Title:
Understanding the structure details when drying hydrate crystals of pharmaceuticals - interpretations from diffuse scattering and inter-modulation satellites of a partially dehydrated crystal
Authors:
Chan, EJ; Gao, Q; Dabros, M Author Full Names: Chan, E. J.; Gao, Q.; Dabros, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 555-567; SI 10.1107/S2052520614005125 3 JUN 2014
Abstract:
Simplified models for the crystal lattice of the sesquihydrate form of the hemi-sulfate salt of (5S, 6S, 9R)-5-amino-6-(2,3-difluorophenyl)-6,7,8,9-tetrahydro-5H-cyclohepta[b]py ridin9-yl 4-(2-oxo-2,3-dihydro-1H-imidazol[4,5b]pyridin-1-yl)-1piperidine carboxylate (BMS-927711, C28H29F2N6O3+) are used to calculate diffuse diffraction features in order to develop a mechanistic understanding of the dehydration process with respect to disruption of the lattice, since a Bragg model cannot be established. The model demonstrates that what we observe when the water leaves the crystal is partial transformation from the parent form to a child form (a new form, less hydrated and structurally related to the parent). Yet this 'dried' structure is not a pure phase. It consists of semi-random layers of both child, parent and an interfacial layer which has a *modulated structure* that represents a transitory *phase*. Understanding the fact that a single 'dried' crystal can have the disordered layer structure described as well as understanding mechanistic relationships between the phases involved can have implications in understanding the effect of common large scale bulk drying procedures. During the development of BMS-927711, difficulties did arise during characterization of the dried bulk when using only routine solid-state analysis. The material is now better understood from this diffraction study. The diffraction experiments also reveal intermodulation satellites, which upon interpretation yield even more structural information about the crystal transformation. The model suggests the mechanism of transformation is laminar in which layers of the crystal are driven to approach a stable B-centered supercell phase of lower water content.

Update: 8-Jan-2015

Title:
Incommensurate-to-incommensurate phase transition in Eu metal at high pressures
Authors:
Husband, RJ; Loa, I; Munro, KA; McBride, EE; Evans, SR; Liermann, HP; McMahon, MI Author Full Names: Husband, R. J.; Loa, I.; Munro, K. A.; McBride, E. E.; Evans, S. R.; Liermann, H. -P.; McMahon, M. I.
Source:
PHYSICAL REVIEW B, 90 (21):10.1103/PhysRevB.90.214105 DEC 8 2014
Abstract:
High pressure x-ray powder-diffraction experiments were performed on europium metal up to similar to 70 GPa. Above 38 GPa, europium transforms from the incommensurately modulated Eu-IV phase to a second phase with an incommensurately modulated crystal structure, Eu-V. This is a previously unseen incommensurately modulated to incommensurately modulated transition in the elements at high pressure. High-pressure high-temperature experiments were also performed up to 449 K in order to make an initial estimate of the positions of the phase boundaries of the incommensurate phases.
Title:
Toward the Understanding of Modulation in Molecular Materials: Barluenga's Reagent and its Analogues.
Authors:
Kim, Y; Mckinley, EJ; Christensen, KE; Rees, NH; Thompson, AL Author Full Names: Kim, Yejin; Mckinley, Emma J.; Christensen, Kirsten E.; Rees, Nicholas H.; Thompson, Amber L.
Source:
CRYSTAL GROWTH & DESIGN, 14 (12):6294-6301; 10.1021/cg500983s DEC 2014
Abstract:
Investigations into the phase transition of Barluengas reagent revealed a transient incommensurately modulated phase; the structures are presented herein. To understand the origin of the modulated phase and the chemistry that can affect it, analogues of Barluengas reagent were synthesized and studied. In this context, the halogen and anion can easily be exchanged. Studying different analogues led to the development of the Ratchet Model to describe the behavior in the solid state leading to a better understanding of modulation in this class of molecular crystal structure.
Title:
Breakdown of the Fermi arcs in underdoped cuprates by incommensurate charge density waves
Authors:
Gor'kov, LP Author Full Names: Gor'kov, L. P.
Source:
JETP LETTERS, 100 (6):403-406; 10.1134/S0021364014180040 NOV 2014
Abstract:
Interactions between the coherent excitations on disconnected arcs along a "bare" Fermi surface (the socalled Fermi arcs FAs) seen by angle-resolved photo emission spectroscopy (ARPES) in several underdoped (UD) cuprates and incommensurate charge density wave (IC CDW) ordering at lowering of the temperature have been studied. The carriers on FAs scatter strongly on the short-wavelength potential of CDW. The large momentum transfer relates FAs with the electronic states lying deeply under the chemical potential thus involving into consideration the Fermi liquid interactions. At low temperatures IC CDW may fully destroy low lying excitations on the Fermi arcs, leaving electrons on the pocket at the I" point as the only charged elementary excitations in the CDW phase in UD cuprates. The results infer competition between superconducting and CDW order parameters.
Title:
Magnetic shape memory effect and highly mobile twin boundaries
Authors:
Heczko, O Author Full Names: Heczko, O.
Source:
MATERIALS SCIENCE AND TECHNOLOGY, 30 (13A):1559-1578; 10.1179/1743284714Y.0000000599 NOV 2014
Abstract:
The magnetic shape memory effect can be classified as an example of the multiferroic effect combining ferro-elasticity and (ferro) magnetism. After short overview of all known effects the focus is on magnetic field induced structure reorientation (MIR) in the martensite of Ni-Mn-Ga. In this material giant deformations of up to 12% have been observed in moderate magnetic fields. The phenomenology of the effect is first discussed and a model presented. The properties of Ni-Mn-Ga relevant to MIR are then considered. One necessary condition for MIR is a highly mobile twin boundary or interface between two differently oriented martensite variants (ferroelastic domains). In 10M modulated martensite, two types of mobile twin boundary (type I and type II) are observed with complex layered microstructures consisting of a hierarchy of twinning systems. The boundaries strongly differ according to the magnitude and temperature dependence of the twinning stress. Finally, the nature of these boundaries and their different behaviour is reviewed.
Title:
Linear magneto-optical effect in the incommensurate phase of antiferromagnetic LiNiPO4
Authors:
Kharchenko, YM; Miloslavskaya, OV; Kharchenko, MF Author Full Names: Kharchenko, Yu. M.; Miloslavskaya, O. V.; Kharchenko, M. F.
Source:
LOW TEMPERATURE PHYSICS, 40 (11):1029-1031; 10.1063/1.4901407 NOV 2014
Abstract:
A linear magneto-optical effect, birefringence of linearly polarized light that is directly proportional to magnetic field strength, is observed in magnetoelectric crystals of the orthophosphate LiNiPO4. This effect is especially pronounced in the incommensurate antiferromagnetic phase of the crystal. The linear magneto-optical effect indicates that the magnetic symmetry groups of the incommensurate, as well as the commensurate, phases of antiferromagnetic LiNiPO4 lack an anti-inversion operation. This fact is consistent with the existence of ultraweak ferromagnetism in the crystal and indicates that this antiferromagnet has more complicated magnetic structures than those found in neutron diffraction experiments. (C) 2014 AIP Publishing LLC.
Title:
Mechanical Alloying of Al73Cu11Cr16 Alloy from Ion Irradiated Powders
Authors:
Medvedeva, EV; Tcherdyntsev, VV; Makhin'ko, FF; Gushchina, NV; Ovchinnikov, VV Author Full Names: Medvedeva, E. V.; Tcherdyntsev, V. V.; Makhin'ko, F. F.; Gushchina, N. V.; Ovchinnikov, V. V.
Source:
ACTA PHYSICA POLONICA A, 126 (4):979-983; OCT 2014
Abstract:
Al73Cu11Cr16 alloys were prepared by mechanical alloying of the irradiated by Ar+ ions elemental powders. Evolution of alloy structure at ball milling, as well as during the further annealing, was investigated using X-ray diffraction and differential scanning calorimetry. It was shown that ball milling leads to the Cu dissolution in Al and Cr and to the formation of Al2Cu intermetallic phase. An increase of the milling duration leads to an increase of the Al2Cu phase content in the samples. Ion irradiation of initial elemental powders results in an increase of their interaction rate at milling. In the case of irradiated powders using as initial materials, a content of Al2Cu phase after milling is higher than in the case of using non-irradiated elemental powders. No effect of irradiation of initial elemental powders on the phase transformation at heating was observed. The annealing results in the decomposition of Al- and Cr-based supersaturated solid solutions. An increase in the Al2Cu phase content at heating was observed only in the samples, which were milled for 4 h. In the samples milled for 14 h, nearly no increase in Al2Cu phase content at heating was observed. Heating up to 500-600 degrees C results in the single-phase decagonal quasicrystalline phase formation for all of the studied samples.

Update: 1-Jan-2015

Title:
Brillouin scattering, DSC, dielectric and X-ray diffraction studies of phase transitions in antiferroelectric PbHfO3:Sn
Authors:
Maczka, M; Kim, TH; Gagor, A; Jankowska-Sumara, I; Majchrowski, A; Kojima, S Author Full Names: Maczka, Miroslaw; Kim, Tae Hyun; Gagor, Anna; Jankowska-Sumara, Irena; Majchrowski, Andrzej; Kojima, Seiji
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 622 935-941; 10.1016/j.jallcom.2014.11.020 FEB 15 2015
Abstract:
Specific heat, dielectric, powder X-ray diffraction and Brillouin scattering studies of phase transitions in antiferroelectric PbHf0.975Sn0.025O3 crystal were performed. The specific heat data revealed clear anomalies at T-1 = 473.5 and T-2 = 426.3 K on cooling, which could be attributed to onset of first order phase transitions from the paraelectric (PE) phase to an intermediate antiferroelectric phase (AFE2) and the AFE2 phase to another antiferroelectric phase (AFE1), respectively. The estimated entropy changes at T-1 and T-2 pointed to mainly an order-disorder and displacive character of these transitions, respectively. X-ray diffraction data showed a complex superstructure of the intermediate phase with a = 11.895(6) angstrom, b = 11.936(4) angstrom, c = 8.223(3)angstrom at 453 K. Brillouin studies revealed pronounced softening of longitudinal acoustic (LA) mode in the PE phase associated with its broadening. The broadening and softening exhibited maximum values at T-1. Additional acoustic anomalies, that is, abrupt frequency shifts for LA and transverse acoustic (TA) modes were also observed at T-2. Brillouin scattering data also showed presence of a broad central peak (CP) that exhibited highest intensity at T-1. The observed temperature dependences of acoustic modes and CP indicate order-disorder character of the FE to AFE2 phase transition and importance of polar precursor clusters in the PE phase. The obtained data also suggest that the intermediate antiferroelectric phases in Sn4+ doped PbHfO3 and PbZrO3 may have very similar structures with incommensurate modulations. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Atomic structure solution of the complex quasicrystal approximant Al77Rh15Ru8 from electron diffraction data
Authors:
Samuha, S; Mugnaioli, E; Grushko, B; Kolb, U; Meshi, L Author Full Names: Samuha, Shmuel; Mugnaioli, Enrico; Grushko, Benjamin; Kolb, Ute; Meshi, Louisa
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 999-1005; 10.1107/S2052520614022033 6 DEC 2014
Abstract:
The crystal structure of the novel Al77Rh15Ru8 phase (which is an approximant of decagonal quasicrystals) was determined using modern direct methods (MDM) applied to automated electron diffraction tomography (ADT) data. The Al77Rh15Ru8 E-phase is orthorhombic [Pbma, a = 23.40 (5), b = 16.20 (4) and c = 20.00 (5) angstrom] and has one of the most complicated intermetallic structures solved solely by electron diffraction methods. Its structural model consists of 78 unique atomic positions in the unit cell (19 Rh/Ru and 59 Al). Precession electron diffraction (PED) patterns and high-resolution electron microscopy (HRTEM) images were used for the validation of the proposed atomic model. The structure of the E-phase is described using hierarchical packing of polyhedra and a single type of tiling in the form of a parallelogram. Based on this description, the structure of the E-phase is compared with that of the epsilon(6)-phase formed in Al-Rh-Ru at close compositions.
Title:
Field-Induced Spin-Flop in Antiferromagnetic Semiconductors with Commensurate and Incommensurate Magnetic Structures: Li2FeGeS4 (LIGS) and Li2FeSnS4 (LITS)
Authors:
Brant, JA; dela Cruz, C; Yao, JL; Douvalis, AP; Bakas, T; Sorescu, M; Aitken, JA Author Full Names: Brant, Jacilynn A.; dela Cruz, Clarina; Yao, Jinlei; Douvalis, Alexios P.; Bakas, Thomas; Sorescu, Monica; Aitken, Jennifer A.
Source:
INORGANIC CHEMISTRY, 53 (23):12265-12274; 10.1021/ic5011693 DEC 1 2014
Abstract:
Li2FeGeS4 (LIGS) and Li2FeSnS4 (LITS), which are among the first magnetic semiconductors with the wurtz-kesterite structure, exhibit antiferromagnetism with TN 6 and 4 K, respectively. Both compounds undergo a conventional metamagnetic transition that is accompanied by a hysteresis; a reversible spin-flop transition is dominant. On the basis of constant-wavelength neutron powder diffraction data, we propose that LIGS and LITS exhibit collinear magnetic structures that are commensurate and incommensurate with propagation vectors k(m) = [(1)/(2), (1)/(2), (1)/(2)] and [0, 0, 0.546(1)], respectively. The two compounds exhibit similar magnetic phase diagrams, as the critical fields are temperature-dependent. The nuclear structures of the bulk powder samples were verified using time-of-flight neutron powder diffraction along with synchrotron X-ray powder diffraction. (57)Fe and (119)Sn Mossbauer spectroscopy confirmed the presence of Fe2+ and Sn4+ as well as the number of crystallographically unique positions. LIGS and LITS are semiconductors with indirect and direct bandgaps of 1.42 and 1.86 eV, respectively, according to optical diffuse-reflectance UV-vis-NIR spectroscopy.
Title:
Structure and Magnetic Behaviours of Melt-Spun Ti1.4V0.6Ni Alloy Containing Icosahedral Quasicrystalline Phase
Authors:
Hu, W; Yin, C; Ma, ZY; Liu, WQ; Wang, LM Author Full Names: Hu, W.; Yin, C.; Ma, Z. Y.; Liu, W. Q.; Wang, L. M.
Source:
ASIAN JOURNAL OF CHEMISTRY, 26 (17):5821-5823; A SEP 2014
Abstract:
The ribbons of Ti1.4V0.6Ni and TiVNi alloys were synthesized by arc-melting and subsequent melt-spinning techniques. The structures and magnetic properties were investigated. The results showed that the icosahedral quasicrystal (I-phase), Ti2Ni-type face centered cubic (FCC) phase and body centered cubic (BCC) structural solid solution phase existed in Ti1.4V0.6Ni alloy and the Ti2Ni-type FCC phase and BCC solid solution phase presented in TiVNi alloy. The relationships of M-H (magnetization -magnetic field) and M-T (magnetization-temperature) of the alloy ribbons were investigated by using SQUID (superconductivity quantum interference device). The results demonstrated that the magnetic behaviour was different, which is the Ti1.4V0.6Ni alloy ribbons exhibited higher ferromagnetic properties than those of TiVNi alloy ribbons both at 15 and 300 K.

Update: 25-Dec-2014

Title:
In situ transmission electron microscopy investigation of quasicrystal-crystal transformations in Mg-Zn-Y alloys
Authors:
Liu, JF; Yang, ZQ; Ye, HQ Author Full Names: Liu, J. F.; Yang, Z. Q.; Ye, H. Q.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 621 179-188; 10.1016/j.jallcom.2014.09.177 FEB 5 2015
Abstract:
Evolution of icosahedral quasicrystals (IQC) in Mg-Zn-Y alloys during annealing was investigated by in situ transmission electron microscopy (TEM), in combination with differential thermal analysis and X-ray diffraction. In bulk samples, the IQC phase transformed to face-centered cubic phase W and hexagonal phase H at 720 K and 727 K, respectively. In TEM samples, IQC started to transform to W at 673 K and H at 688 K during heating, and H transformed to W at 623 K on cooling. Quantitative analysis of the in situ transformation process reveals that growth of both H and W is controlled by diffusion, agreeing with the Avrami's model. The transformed products have specific orientation relationships with the parent phases: 3-fold(IQC)//[0001](H)//[111](W) and 2- fold(IQC)//11 (2) over bar0](H)//[0 (1) over bar1](W). The specific orientation relationships are attributed to close structural correlation among icosahedron, distorted icosahedron and cuboctahedron in IQC, H and W phases. The close structure relationship among IQC, H and W phases on the unit-cell level plays an important role in the phase transformations. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Microstructure and tensile properties of as-extruded Mg-Li-ZnGd alloys reinforced with icosahedral quasicrystal phase
Authors:
Zhang, Y; Zhang, J; Wu, GH; Liu, WC; Zhang, L; Ding, WJ Author Full Names: Zhang, Yang; Zhang, Jie; Wu, Guohua; Liu, Wencai; Zhang, Liang; Ding, Wenjiang
Source:
MATERIALS & DESIGN, 66 162-168; 10.1016/j.matdes.2014.10.049 A FEB 5 2015
Abstract:
Mg-Li-Zn-Gd alloys reinforced with icosahedral quasicrystal phase (I-phase) were prepared by casting and deformed by hot extrusion. The microstructure and tensile properties of as-extruded Mg-Li-Zn-Gd alloys were investigated. It is found that I-phase formed in as-cast Mg-Li-Zn-Gd alloys and was broken into small particles during extrusion. After hot extrusion, both alpha-Mg and beta-Li phases were elongated along the extrusion direction. Dynamic recrystallization occurred in as-extruded Mg-Li-Zn-Gd alloys. Compared with Mg-9Li (L9) alloy, the improvement in mechanical properties especially the tensile strength of the as-extruded Mg-Li-Zn-Gd alloys was mainly ascribed to the formation of I-phase and their volume fraction. Moreover, the finely recrystallized grain structure can also attribute to the strength enhancement of the alloy. (C) 2014 Elsevier Ltd. All rights reserved.
Title:
Field dependence of the magnetic structure of TbMn2O5
Authors:
Chatterji, T; Brown, PJ Author Full Names: Chatterji, T.; Brown, P. J.
Source:
JOURNAL OF APPLIED PHYSICS, 116 (20):10.1063/1.4902840 NOV 28 2014
Abstract:
The evolution of the magnetic propagation vector of the magnetically ordered phases of TbMn2O5 has been studied as a function of magnetic field applied parallel to both [010] and [100] axes. The results have been used to construct (H, T) phase diagrams showing the regions of stability of the three distinct phases IC1, C, and IC2 known to exist in zero field. Application of magnetic field along [010] increases the stability range of the commensurate C phase at the expense of the two incommensurate phases IC1 and IC2, whereas applying the field along [100] has the opposite effect. The evolution with field of the magnetic structure of the C phase has been determined from the integrated intensities of sets of magnetic reflections measured with different field values. With the field along [010], there are no significant changes in structure in fields up to 6 T. Applying the field parallel to [100] leads to an apparently continuous increase in the z component of the propagation vector from 0.25 in zero field to approximate to 0.3 in 6 T. This change is accompanied by increasing ferromagnetic polarisation of the Tb sublattices. Polarised neutron measurements made on the fundamental reflections show that there is no significant ferromagnetic polarisation of any the Mn sublattices in fields of up to 6 T. (C) 2014 AIP Publishing LLC.
Title:
Structural Evolution of GdBaCo2O5+delta (delta=7/18) at Elevated Temperatures
Authors:
Ishizawa, N; Asaka, T; Kudo, T; Fukuda, K; Yasuhara, A; Abe, N; Arima, T Author Full Names: Ishizawa, Nobuo; Asaka, Toru; Kudo, Tatsunari; Fukuda, Koichiro; Yasuhara, Akira; Abe, Nobuyuki; Arima, Taka-hisa
Source:
CHEMISTRY OF MATERIALS, 26 (22):6503-6517; 10.1021/cm503132e NOV 25 2014
Abstract:
The structural chemistry of the double-layered perovskite-type gadolinium barium cobaltate, GdBaCo2O5+delta (0 < delta < 1/2), is not well-known, in comparison to the representative end-member phases alpha at delta = 0 and beta at delta = 1/2. This study unveils the structural evolution of the room-temperature stable phase gamma at delta = 7/18, using in situ single-crystal X-ray diffraction at elevated temperatures and electron microscopy. The gamma phase is essentially charge-ordered with Co3+ and Co2+ in a ratio of 8:1 and is incommensurately modulated in the five-dimensional superspace. The approximant of the modulated structure reveals the presence of island-like charge-ordered square cell domains interleaved with a discommensurate zone. The gamma phase underwent a reversible first-order phase transition at similar to 380 K to the commensurate phase beta, without any change in composition at delta = 7/18. The charge ordering of Co in gamma ceased in beta, in combination with a redistribution of oxygen atoms (O3) in the [GdO delta] layer and a change in the spin state of Co. Further heating of beta induced partial oxygen detachment at similar to 700 K, causing a change in d from 7/18 (similar to 0.389) to 0.19 in the nitrogen flow atmosphere. The crystal irreversibly turned into a tetragonal prototypal phase a. A peristaltic oxygen transport mechanism in GdBaCo2O5+delta (0 <= delta <= 1/2) accompanied by electron transfer and resulting in polaronic local structure relaxation is also proposed. This mechanism underpins a usefulness of the compound for application to solid oxide fuel cells as revealed in recent years.

Update: 18-Dec-2014

Title:
Automated effective band structures for defective and mismatched supercells
Authors:
Brommer, P; Quigley, D Author Full Names: Brommer, Peter; Quigley, David
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (48):10.1088/0953-8984/26/48/485501 DEC 3 2014
Abstract:
In plane-wave density functional theory codes, defects and incommensurate structures are usually represented in supercells. However, interpretation of E versus (k) over right arrow band structures is most effective within the primitive cell, where comparison to ideal structures and spectroscopy experiments are most natural. Popescu and Zunger recently described a method to derive effective band structures (EBS) from supercell calculations in the context of random alloys. In this paper, we present bs_sc2pc, an implementation of this method in the CASTEP code, which generates an EBS using the structural data of the supercell and the underlying primitive cell with symmetry considerations handled automatically. We demonstrate the functionality of our implementation in three test cases illustrating the efficacy of this scheme for capturing the effect of vacancies, substitutions and lattice mismatch on effective primitive cell band structures.
Title:
Wear assessment of composite surface layers in Al-6Mg alloy reinforced with AlCuFe quasicrystalline particles: Effects of particle size, microstructure and hardness
Authors:
Mordyuk, BN; Prokopenko, GI; Milman, YV; Iefimov, MO; Grinkevych, KE; Sameljuk, AV; Tkachenko, IV Author Full Names: Mordyuk, B. N.; Prokopenko, G. I.; Milman, Yu. V.; Iefimov, M. O.; Grinkevych, K. E.; Sameljuk, A. V.; Tkachenko, I. V.
Source:
WEAR, 319 (1-2):84-95; 10.1016/j.wear.2014.07.011 NOV 15 2014
Abstract:
Aluminium alloys reinforced with ceramic, intermetallic or quasicrystalline particles can fill the needs of automotive and aerospace industries due to their superior properties. In this paper, near-surface layers in Al-6Mg alloy specimens were modified using an ultrasonic impact treatment (UIT) process, which induces mechanical mixing of matrix and reinforces quasicrystalline (QC) Al63Cu25Fe12 particles to be introduced into a zone of severe plastic deformation. The wear and friction behaviours of the matrix alloy and QC reinforced layers were investigated in quasi-static and dynamic conditions with particular attention to the effects of QC particles size and test type on wear resistance and microhardness of subsurface composite layers in Al-6Mg alloy. XRD and SEM analyses show that the layers of 40-50 mu m dispersed fine QC(F) (0.5-3 mu m) or coarse QC(C) (similar to 15 mu m) particles, with volume fractions V-f of about 9% and 22%, respectively. In comparison to the annealed Al-6Mg alloy, noticeable increment in wear resistance was registered only for the composite layer reinforced with QC(F) particles. On the contrary, the QC(C) particles being fractured at the fabrication process and/or at the wear tests facilitate three-body abrasive wear conditions and deteriorate the wear resistance of the alloy. SEM and confocal laser microscopy show changes in wear mechanism from microcutting/ploughing in the QC(F) reinforced layer to microcracking/fracturing in the case of QC(C) reinforcement. Fine QC(F) particles are preferred for better wear resistance both at the quasi-static and dynamic conditions. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Photocatalytic and magnetic behaviors of BiFeO3 thin films deposited on different substrates
Authors:
Xu, HM; Wang, HC; Shen, Y; Lin, YH; Nan, CW Author Full Names: Xu, Hao-Min; Wang, Huan-Chun; Shen, Yang; Lin, Yuan-Hua; Nan, Ce-Wen
Source:
JOURNAL OF APPLIED PHYSICS, 116 (17):10.1063/1.4901066 NOV 7 2014
Abstract:
Single phase polycrystalline BiFeO3 thin films were grown on three different substrates via chemical solution deposition. Our results indicate that the band gap of as-prepared BiFeO3 films can be tuned (2.02-2.67eV) by the grain size effects caused by the substrates. These BiFeO3 films show good photocatalytic properties by the degradation of Congo red solution under visible-light irradiation (lambda>400 nm). Additionally, weak ferromagnetic behaviors can be observed at room temperature in all the films, which should be correlated to the destruction of the incommensurate cycloid spin structure of BiFeO3 phase and the coexistence of Fe3+ and Fe2+ as confirmed by X-ray photoelectron spectroscopy. (C) 2014 AIP Publishing LLC.
Title:
Formation of less-known structurally complex zeta(b) and orthorhombic quasicrystalline approximant epsilon(n) on solidification of selected Al-Pd-Cr alloys
Authors:
Adamech, M; Cernickova, I; Duriska, L; Kolesar, V; Drienovsky, M; Bednarcik, J; Svoboda, M; Janovec, J Author Full Names: Adamech, M.; Cernickova, I.; Duriska, L.; Kolesar, V.; Drienovsky, M.; Bednarcik, J.; Svoboda, M.; Janovec, J.
Source:
MATERIALS CHARACTERIZATION, 97 189-198; 10.1016/j.matchar.2014.10.001 NOV 2014
Abstract:
The evolution of phases was investigated on cooling of Al71Pd24Cr5, Al73Pd20Cr7, and Al73Pd23Cr4 alloys from 1350 degrees C down to ambient temperature with the rate of 10 degrees C.min(-1). To perform the investigation, differential thermal analysis, synchrotron X-ray powder diffraction, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy were used. In all the investigated alloys structurally complex phases epsilon(n) (epsilon(6) + epsilon(28)) and zeta(b), as well as the delta-phase were identified. Based on the results of differential thermal analysis, sequences of phase transformations were determined. The Al71Pd24Cr4 alloy started to solidify at 1031.4 degrees C through beta. Primary dendrites of zeta(b) were observed in Al73Pd20Cr7 and Al73Pd23Cr4 alloys. In the second step of solidification delta and/or zeta(b) were formed. The peritectic reaction, liquid + zeta(b) + delta -> epsilon(n) + zeta(b) + delta, leading to the formation of the quasicrystalline approximant epsilon(n) (epsilon(6) + epsilon(28)) took place in the final step of solidification at approximately 792 degrees C. (C) 2014 Published by Elsevier Inc.
Title:
Microstructure and compression deformation behavior in the quasicrystal-reinforced Mg-8Zn-1Y alloy solidified under super-high pressure
Authors:
Dong, Y; Lin, XP; Xu, R; Zheng, RG; Fan, ZB; Liu, SJ; Wang, Z Author Full Names: Dong Yun; Lin Xiaoping; Xu Rui; Zheng Runguo; Fan Zhibin; Liu Shijun; Wang Zhe
Source:
JOURNAL OF RARE EARTHS, 32 (11):1048-1055; 10.1016/S1002-0721(14)60182-4 NOV 2014
Abstract:
The microstructure of Mg-8Zn-1Y alloy solidified under super-high pressure was analyzed through X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). And, compression deformation behavior at room-temperature was studied. The results showed that the microstructure of Mg-8Zn-1Y alloy solidified under ambient pressure and super-high pressure was both mainly composed of alpha-Mg and quasicrystal I-Mg3Zn6Y. Solidification under super-high pressure contributed to refining solidified microstructure and changing morphology of the intergranular second phase. The morphology of intergranular second phase (quasicrystal I-Mg3Zn6Y) was transformed from continuous network (ambient pressure) to long island (high pressure) and finally to granular (super-high pressure) with the increase in pressure. The compressive strength, yield strength and rupture strain of the samples solidified under ambient pressure were significantly improved from 262.6 MPa, 244.4 MPa and 13.3% to 437.3 MPa, 368.9 MPa and 24.7% under the pressure of 6 GPa, respectively. Under ambient pressure, cleavage plane on compressive fracture was large and smooth. When it was solidified under the pressure ranging from 4 to 6 GPa, cleavage plane on compressive fracture was small and coarse. In addition, dimple, tear ridge and lobate patterns existed.
Title:
Anti-plane problem analysis for icosahedral quasicrystals under shear loadings
Authors:
Li, W; Chai, YZ Author Full Names: Li Wu; Chai Yu-Zhen
Source:
CHINESE PHYSICS B, 23 (11):10.1088/1674-1056/23/11/116201 NOV 2014
Abstract:
The present paper is concerned with the longitudinal shear elasticity of three-dimensional icosahedral quasicrystals. By virtue of the Dugdale hypothesis along with the method of complex potential theory, it involves two defect problems of the icosahedral quasicrystals. The first one is the calculation of stress intensity factors and the size of the cohesive force zone in a half-infinite crack. Meanwhile, the crack tip tearing displacements can be exactly derived. The other is the demonstration of the generalized stress intensity factors induced by a sharp V-notch as an extension of a crack. The generalized E-integral around the notch tip gives the energy release rate when the V-notch degenerates into a crack. Apart from their own usefulness in carrying out some simplified crack analyses, the results obtained in this work can particularly serve as a basis for fracture mechanics of anti-plane defect problems of icosahedral quasicrystals.
Title:
Tailoring microstructure of Mg-Zn-Y alloys with quasicrystal and related phases for high mechanical strength
Authors:
Singh, A Author Full Names: Singh, Alok
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (4):10.1088/1468-6996/15/4/044803 AUG 2014
Abstract:
The occurrence of a stable icosahedral (i-) phase, which is quasicrystalline with an icosahedral (fivefold) symmetry, on the equilibrium phase diagram of Mg-Zn-RE (RE = Y, Gd, Tb, Dy, Ho or Er) alloys opened up an interesting possibility of developing a new series of magnesium alloys for structural applications. Alloys based on the i-phase have been studied for the past 14 years. Ultra-high strengths combined with good ductility have been shown. Here we show two strategies for tailoring microstructures for very high strengths in Mg-Zn-Y alloys. One of them involves strengthening by a fine distribution of rod-like beta(')(1) precipitates, where the matrix grain size is not critical. The alloy is solutionized at a high temperature of 480 degrees C to dissolve a large part of the i-phase, followed by a high temperature extrusion (similar to 430 degrees C) and a low temperature ageing to reprecipitate phases with fine size distribution. At first, phase transformations involved in this procedure are described. The closeness of the structure of the beta(')(1) precipitates to the i-phase is brought out. By this procedure, tensile yield strengths of over 370 MPa are obtained in grain sizes of 20 mu m. In another strategy, the alloys are chill cast and then extruded at low temperatures of about 250 degrees C. Ultra-fine grains are produced by enhanced recrystallization due to presence of the i-phase. At the same time nano-sized precipitates are precipitated dynamically during extrusion from the supersaturated matrix. Ultra-high tensile strengths of up to 400 MPa are obtained in combination with ductility of 12 to 16%. Analysis of the microstructure shows that strengthening by the i-phase occurs by enhanced recrystallization during extrusion. It produces ultra-fine grain sizes to give very high strengths, and moderate texture for good ductility. Fine distribution of the i-phase and precipitates contribute to strengthening and provide microstructre stability. Ultra-high strength over a very wide range of grain sizes is thus demonstrated, by utilizing different strengthening effects.
Title:
Metallic-covalent bonding conversion and thermoelectric properties of Al-based icosahedral quasicrystals and approximants
Authors:
Takagiwa, Y; Kimura, K Author Full Names: Takagiwa, Yoshiki; Kimura, Kaoru
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (4):10.1088/1468-6996/15/4/044802 AUG 2014
Abstract:
In this article, we review the characteristic features of icosahedral cluster solids, metallic-covalent bonding conversion (MCBC), and the thermoelectric properties of Al-based icosahedral quasicrystals and approximants. MCBC is clearly distinguishable from and closely related to the well-known metal-insulator transition. This unique bonding conversion has been experimentally verified in 1/1-AlReSi and 1/0-Al12Re approximants by the maximum entropy method and Rietveld refinement for powder x-ray diffraction data, and is caused by a central atom inside the icosahedral clusters. This helps to understand pseudogap formation in the vicinity of the Fermi energy and establish a guiding principle for tuning the thermoelectric properties. From the electron density distribution analysis, rigid heavy clusters weakly bonded with glue atoms are observed in the 1/1-AlReSi approximant crystal, whose physical properties are close to icosahedral Al-Pd-TM (TM: Re, Mn) quasicrystals. They are considered to be an intermediate state among the three typical solids: metals, covalently bonded networks (semiconductor), and molecular solids. Using the above picture and detailed effective mass analysis, we propose a guiding principle of weakly bonded rigid heavy clusters to increase the thermoelectric figure of merit (ZT) by optimizing the bond strengths of intra-and intericosahedral clusters. Through element substitutions that mainly weaken the inter-cluster bonds, a dramatic increase of ZT from less than 0.01 to 0.26 was achieved. To further increase ZT, materials should form a real gap to obtain a higher Seebeck coefficient.
Title:
Magnetism in icosahedral quasicrystals: current status and open questions
Authors:
Goldman, AI Author Full Names: Goldman, Alan I.
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (4):10.1088/1468-6996/15/4/044801 AUG 2014
Abstract:
Progress in our understanding of the magnetic properties of R-containing icosahedral quasicrystals (R = rare earth element) from over 20 years of experimental effort is reviewed. This includes the much studied R-Mg-Zn and R-Mg-Cd ternary systems, as well as several magnetic quasicrystals that have been discovered and investigated more recently including Sc-Fe-Zn, R-Ag-In, Yb-Au-Al, the recently synthesized R-Cd binary quasicrystals, and their periodic approximants. In many ways, the magnetic properties among these quasicrystals are very similar. However, differences are observed that suggest new experiments and promising directions for future research.

Update: 11-Dec-2014

Title:
Structural and electrical properties of a new ([SnSe](1.16))(1)(NbSe2)(1) polytype
Authors:
Alemayehu, MB; Falmbigl, M; Grosse, C; Ta, K; Fischer, SF; Johnson, DC Author Full Names: Alemayehu, Matti B.; Falmbigl, Matthias; Grosse, Corinna; Ta, Kim; Fischer, Saskia F.; Johnson, David C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 619 861-868; 10.1016/j.jallcom.2014.09.084 JAN 15 2015
Abstract:
A new polytype of the misfit layer compound ([SnSe](1.16))(1)(NbSe2)(1) with extensive rotational disorder was prepared from designed modulated elemental reactants. This polytype, previously referred to as a ferecrystal due to the extensive rotational disorder, formed over a range of compositions and precursor thicknesses and the resulting c-axis lattice parameters ranged from 1.2210(4) to 1.2360(4) nm. These values bracket the value published for the crystalline misfit layer compound prepared at high temperature. The a- and b-axis in-plane lattice parameters of both the SnSe and NbSe2 constituents were incommensurate, which differs from the misfit layer compound formed via high temperature reaction that has a common b-axis lattice parameter for the two constituents. The in-plane area per unit cell of the ferecrystal is 1-2% larger than the compound formed at high temperature. The ferecrystalline ([SnSe](1.16))(1)(NbSe2)(1) compound is 1.6 times more conductive than the misfit layer compound. Hall effect measurements indicate that the ferecrystal is a p-type metal and that the higher conductivity is a consequence of higher mobility of carriers in the ferecrystalline compound. (C) 2014 Elsevier B.V. All rights reserved.
Title:
The Al-rich region of the Al-Fe-Mn alloy system
Authors:
Balanetskyy, S; Pavlyuchkov, D; Velikanova, T; Grushko, B Author Full Names: Balanetskyy, S.; Pavlyuchkov, D.; Velikanova, T.; Grushko, B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 619 211-220; 10.1016/j.jallcom.2014.08.232 JAN 15 2015
Abstract:
Phase equilibria in the Al-rich region of the Al-Fe-Mn alloy system were studied at 1070, 1020, 950, 875, 800, 740, 695 and 650 degrees C. The continuous region of the bcc solid solution was estimated between the Al-Mn and Al-Fe terminals. Also the isostructural high-temperature Al-Mn and Al-Fe gamma(1)- phases (gamma-brass type structure) form continuous regions. The Al6Mn, high-temperature T-Al11Mn4 and low-temperature gamma(2) phases dissolve up to 9.0, 14.5 and 31.0 at.% Fe, respectively, while the M-Al13Fe4, Al5Fe2 and Al2Fe phases dissolve up to 15.5, 11.5 and 10.0 at.% Mn, respectively. The thermodynamically stable decagonal D-3-phase with periodicity of 1.25 nm in the specific direction and two periodic intermetallics designated phi(P6(3)/mmc; a = 0.7554, c = 0.7872 nm) and kappa (P6(3)/m; a = 1.7630, c = 1.2506 nm) were identified. An additional ternary phase of unknown structure was also revealed. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Neutron and X-ray Scattering Studies of Rb2CoCl4 and Successive Phase Transition in A(2)BX(4)-type Crystals
Authors:
Shigematsu, H; Nishiyama, K; Kawamura, Y; Mashiyama, H Author Full Names: Shigematsu, Hirotake; Nishiyama, Katsura; Kawamura, Yukihiko; Mashiyama, Hiroyuki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 83 (12):10.7566/JPSJ.83.124601 DEC 15 2014
Abstract:
Soft phonon modes, which are related to the normal-incommensurate phase transition at T-i = 294 K and the lowest-temperature phase transition at T-3 = 66 K in Rb2CoCl4, have been measured by inelastic neutron scattering. For the normal-incommensurate phase transition, phonon dispersion curves have been determined in the low-temperature commensurate phases, and the phase mode has been observed far below T-i. The soft mode is fully overdamped above T-i. Moreover, another soft phonon mode, which contributes to the phase transition at T3, has been observed. Furthermore, the space group of the lowest phase is directly confirmed to be C1c1 by verifying extinction rules of X-ray diffraction. It has been recognized that the ratio of the ionic radius of A(+) to the average bond length B-X in the tetrahedral BX42- ion can control the phase transition sequence. Rb2CoCl4 belongs to the group in which this ratio is in the range from 0.69 to 0.85, and the transition temperature decreases loosely with increasing the lattice parameter ratio c(0)/a(0), where a(0) and c(0) are the lattice parameters of the normal phase.
Title:
Controllable 3D morphology and growth mechanism of quasicrystalline phase in directionally solidified Al-Mn-Be alloy
Authors:
Kang, HJ; Wang, TM; Lu, YP; Jie, JH; Li, XZ; Su, YQ; Guo, JJ Author Full Names: Kang, Huijun; Wang, Tongmin; Lu, Yiping; Jie, Jinchuan; Li, Xinzhong; Su, Yanqing; Guo, Jingjie
Source:
JOURNAL OF MATERIALS RESEARCH, 29 (21):2547-2555; 10.1557/jmr.2014.287 NOV 14 2014
Abstract:
Three-dimensional (3D) morphological evolution and growth mechanisms of primary I-phase particles have been investigated in directionally solidified Al-6Mn-2.5Be (wt%) alloy at a wide range of growth rates (100-1500 mu m/s). At relatively low growth rates (100-600 mu m/s), the I-phase particles exhibit faceted growth with strong anisotropy, forming a hierarchical flower-like aggregate with icosahedral morphological symmetry composed of several attached irregular polyhedrons or pentagonal dodecahedrons. At higher growth rates (e.g., 1000 mu m/s), the interface of the I-phases becomes unstable along the edges and corners of the pentagonal dodecahedron, thereby arousing growth perturbations. Correspondingly, a transition from faceted to nonfaceted growth occurs with increasing growth rate. Further increase of the growth rate leads to the formation of I-phase columnar dendrites' preferential growth along the 3-fold axis. The configurations of the flower-like aggregates can be adequately illustrated by a geometrical model in terms of the perfect and elongated pentagonal dodecahedrons. A growth mechanism for the flower-like aggregates has been proposed based on the clear understanding of the 3D morphological evolution of the I-phase particles.
Title:
Commensurate structural modulation in the charge- and orbitally ordered phase of the quadruple perovskite (NaMn3)Mn4O12
Authors:
Prodi, A; Daoud-Aladine, A; Gozzo, F; Schmitt, B; Lebedev, O; van Tendeloo, G; Gilioli, E; Bolzoni, F; Aruga-Katori, H; Takagi, H; Marezio, M; Gauzzi, A Author Full Names: Prodi, A.; Daoud-Aladine, A.; Gozzo, F.; Schmitt, B.; Lebedev, O.; van Tendeloo, G.; Gilioli, E.; Bolzoni, F.; Aruga-Katori, H.; Takagi, H.; Marezio, M.; Gauzzi, A.
Source:
PHYSICAL REVIEW B, 90 (18):10.1103/PhysRevB.90.180101 NOV 10 2014
Abstract:
By means of synchrotron x-ray and electron diffraction, we studied the structural changes at the charge order transition T-CO = 176 K in the mixed-valence quadruple perovskite (NaMn3)Mn4O12. Below T-CO we find satellite peaks indicating a commensurate structural modulation with the same propagation vector q = ( 1/2,0,-1/2) of the CE magnetic structure that orders at low temperatures, similarly to the case of simple perovskites such as La0.5Ca0.5MnO3. In the present case, the modulated structure, together with the observation of a large entropy change at T-CO, gives evidence of a rare case of full Mn3+/Mn4+ charge and orbital order, consistent with the Goodenough-Kanamori model.
Title:
Noncoplanar and Counterrotating Incommensurate Magnetic Order Stabilized by Kitaev Interactions in gamma-Li2IrO3
Authors:
Biffin, A; Johnson, RD; Kimchi, I; Morris, R; Bombardi, A; Analytis, JG; Vishwanath, A; Coldea, R Author Full Names: Biffin, A.; Johnson, R. D.; Kimchi, I.; Morris, R.; Bombardi, A.; Analytis, J. G.; Vishwanath, A.; Coldea, R.
Source:
PHYSICAL REVIEW LETTERS, 113 (19):10.1103/PhysRevLett.113.197201 NOV 6 2014
Abstract:
Materials that realize Kitaev spin models with bond-dependent anisotropic interactions have long been searched for, as the resulting frustration effects are predicted to stabilize novel forms of magnetic order or quantum spin liquids. Here, we explore the magnetism of gamma-Li2IrO3, which has the topology of a three-dimensional Kitaev lattice of interconnected Ir honeycombs. Using magnetic resonant x-ray diffraction, we find a complex, yet highly symmetric incommensurate magnetic structure with noncoplanar and counterrotating Ir moments. We propose a minimal Kitaev-Heisenberg Hamiltonian that naturally accounts for all key features of the observed magnetic structure. Our results provide strong evidence that gamma-Li2IrO3 realizes a spin Hamiltonian with dominant Kitaev interactions.
Title:
Original Crystal-Chemical Behaviors in (Ba,Sr)(2)Ln(Fe,Nb,Ta)(5)O-15 Tetragonal Tungsten Bronze: Anion-Driven Properties Evidenced by Cationic Substitutions
Authors:
Josse, M; Heijboer, P; Albino, M; Molinari, F; Porcher, F; Decourt, R; Michau, D; Lebraud, E; Veber, P; Velazquez, M; Maglione, M Author Full Names: Josse, Michael; Heijboer, Pierre; Albino, Marjorie; Molinari, Flora; Porcher, Florence; Decourt, Rodolphe; Michau, Dominique; Lebraud, Eric; Veber, Philippe; Velazquez, Matias; Maglione, Mario
Source:
CRYSTAL GROWTH & DESIGN, 14 (11):5428-5435; 10.1021/cg5006049 NOV 2014
Abstract:
From room-temperature composite multiferroics to relaxor to ferroelectric crossovers, many original behaviors were recently evidenced in compounds and/or solid solutions related to the Ba(2)LnFeNb(4)O(15) (Ln = rare earth) family of tetragonal tungsten bronze (TTB) materials. We show how an empirical crystal chemistry approach, while yielding unexpected results, allowed for a better understanding of these original and sometimes specific behaviors. A survey of the dielectric properties of four solid solutions derived from the Ba2NdFeNb4O15 ferroelectric TTB is presented. We also show how the diversity of compositions and chemical substitution patterns unveils the anionic driving force behind the relaxor to ferroelectric crossovers. We finally discuss the probable involvement of aperiodic modulations in these crossovers and the fact that these modulations may constitute an additional degree of freedom to control the properties of TTB structured functional materials.
Title:
Twelvefold symmetric quasicrystallography from the lattices F-4, B-6 and E-6
Authors:
Koca, NO; Koca, M; Koc, R Author Full Names: Koca, Nazife O.; Koca, Mehmet; Koc, Ramazan
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 70 605-615; 10.1107/S2053273314015812 6 NOV 2014
Abstract:
One possible way to obtain the quasicrystallographic structure is the projection of the higher-dimensional lattice into two- or three-dimensional subspaces. Here a general technique applicable to any higher-dimensional lattice is introduced. The Coxeter number and the integers of the Coxeter exponents of a Coxeter-Weyl group play a crucial role in determining the plane onto which the lattice is to be projected. The quasicrystal structures display the dihedral symmetry of order twice that of the Coxeter number. The eigenvectors and the corresponding eigenvalues of the Cartan matrix are used to determine the set of orthonormal vectors in n-dimensional Euclidean space which lead to suitable choices for the projection subspaces. The maximal dihedral subgroup of the Coxeter-Weyl group is identified to determine the symmetry of the quasicrystal structure. Examples are given for 12-fold symmetric quasicrystal structures obtained by projecting the higher-dimensional lattices determined by the affine Coxeter-Weyl groups W-a(F-4), W-a(B-6) and W-a(E-6). These groups share the same Coxeter number h = 12 with different Coxeter exponents. The dihedral subgroup D-12 of the Coxeter groups can be obtained by defining two generators R-1 and R-2 as the products of generators of the Coxeter-Weyl groups. The reflection generators R-1 and R-2 operate in the Coxeter planes where the Coxeter element R1R2 of the Coxeter-Weyl group represents the rotation of order 12. The canonical (strip, equivalently, cut-and-project technique) projections of the lattices determine the nature of the quasicrystallographic structures with 12-fold symmetry as well as the crystallographic structures with fourfold and sixfold symmetry. It is noted that the quasicrystal structures obtained from the lattices W-a(F-4) and W-a(B-6) are compatible with some experimental results.
Title:
A study of one-dimensional incommensurate modulated structure determination in high-resolution transmission electron microscopy
Authors:
Li, XM; Ge, BH; Li, FH; Luo, HQ; Wen, HH Author Full Names: Li, Xueming; Ge, Binghui; Li, Fanghua; Luo, Huiqian; Wen, Haihu
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 70 563-571; 10.1107/S2053273314012005 6 NOV 2014
Abstract:
The methods for determining incommensurate modulated structures (IMSs) in high-resolution transmission electron microscopy have been studied and improved to a level more perfect than before. This is demonstrated by means of the IMS determination for Bi2.31Sr1.69CuO6+ as an example. First, as previously, the projected potential map (PPM) of the IMS with resolution 0.2nm was obtained after image deconvolution from a [100] image. Secondly, the resolution of the PPM was enhanced to 0.1nm through phase extension combined with the electron-diffraction data so that the substitutional and displacive modulation functions could be determined. Thirdly, a (2+1)- dimensional structure model that corresponds to the [100] projected IMS was built for calculating the related partial structure factors that were utilized to correct the experimental electron-diffraction intensities for both main and satellite reflections. After three cycles of diffraction-intensity correction and phase extension, all unoverlapped atoms projected along the [100] direction in Bi2.31Sr1.69CuO6+ were resolved, and the modulations of substitution and displacement could be observed clearly. The substitution of Bi for Sr atoms at the Sr(O) columns was seen in the final PPM and verified by high-dimensional image simulation.
Title:
Dielectric Studies of Thiourea, SC(NH2)(2), Embedded into Molecular Sieves
Authors:
Baryshnikov, SV; Charnaya, EV; Milinskiy, AY Author Full Names: Baryshnikov, S. V.; Charnaya, E. V.; Milinskiy, A. Yu.
Source:
FERROELECTRICS, 471 (1):109-117; 10.1080/00150193.2014.963428 OCT 26 2014
Abstract:
Studies of temperature dependences of linear permittivity and third harmonic generation were carried out for ferroelectric thiourea, SC(NH2)(2), particles embedded into molecular sieves SBA-15 and \MC\M-41 with pore sizes of 7.5nm and 4.0nm, respectively. Temperatures of the ferroelectric phase transition and transition from the incommensurate phase into paraphase were shown to be higher than in bulk thiourea. The shifts of the transitions increased with decreasing pore size. Both phase transitions were strongly diffused. The obtained data evidenced that the third harmonic generation can be used to find temperatures of the diffused ferroelectric transition.

Update: 4-Dec-2014

Title:
B19 phase in Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy
Authors:
Song, L; Xu, XJ; You, L; Liang, YF; Lin, JP Author Full Names: Song, L.; Xu, X. J.; You, L.; Liang, Y. F.; Lin, J. P.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 618 305-310; 10.1016/j.jallcom.2014.08.137 JAN 5 2015
Abstract:
The B19 phase is widely observed in the alpha(2) laths in Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy, forming a modulated structure together with the alpha(2) phase. The distortion between the alpha(2) and B19 phases exists only along the [1 (1) over bar 0 0](alpha 2) direction and is very difficult to detect. Thin gamma laths precipitate regularly within the alpha(2) + B19 structure to accommodate the lattice misfit, whereas the sizes of the gamma laths are limited to a small scale. The B19 phase, however, is unstable and was eliminated after annealing at 900 degrees C for 30 min, followed by air-cooling. The pure alpha(2) phase observed in the air-cooled sample is not in the equilibrium state. The B19 phase can be a stable phase in some temperatures below 900 degrees C but be repressed under rapid cooling. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Microstructure of an Al-Mn-Be-B alloy
Authors:
Zupanic, F; Boncina, T Author Full Names: Zupanic, F.; Boncina, T.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 617 174-179; 10.1016/j.jallcom.2014.07.212 DEC 25 2014
Abstract:
The aim of this work was to determine the effect of boron on the solidification and processes taking place during heat treatment of an Al-Mn-Be-based alloy. Several phases formed upon slow cooling of the investigated alloy Al89Mn2Be2B7: BeB12, AlBeB, T-Al15Mn3Be2, Al6Mn and aluminium solid solution (Al-ss). An icosahedral quasicrystalline phase (IQC) was formed during rapid solidification by melt spinning; partly dissolving Be and B, while the remaining Be and B precipitated as a ternary compound AlBeB. The primary IQC persisted within the microstructure up to 400 degrees C, whilst at temperatures above 450 degrees C the initial microstructure started to transform quickly into AlBeB, Al6Mn and Al-ss, which appeared to be the stable phases below the alloy's solidus temperature. The hardness remained almost unchanged up to 400 degrees C, whilst at temperatures above 450 degrees C it dropped abruptly. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Incommensurate structure of a new Nowotny phase in Fe-Ge system
Authors:
Li, WF; Li, Y; Ma, XL; Zhang, ZD Author Full Names: Li, Wanfeng; Li, Ying; Ma, Xiuliang; Zhang, Zhidong
Source:
MATERIALS CHEMISTRY AND PHYSICS, 148 (3):490-493; 10.1016/j.matchemphys.2014.08.023 DEC 15 2014
Abstract:
We studied post-annealed Fe-Ge alloy by X-ray diffraction and transmission electron microscopy. A new Nowotny chimney ladder phase has been discovered in such Fe-Ge system. The crystal structure and the composition have been calculated based on selected area electron diffraction. The formation of the incommensurate structure is attributed to the shrinkage of the Ge sublattice to meet the 14 electrons rule. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Hydrogen Absorption and Structural Analysis of TiZrNiV Quasicrystals
Authors:
Lee, SH; Jo, Y; Kim, J Author Full Names: Lee, Sang-Hwa; Jo, Youngsoo; Kim, Jaeyong
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 14 (12):9373-9376; 10.1166/jnn.2014.10126 DEC 2014
Abstract:
Ti-based quasicrystals are known to store a high capacity of hydrogen exceeding the density of liquid hydrogen. Because TiZrNi quasicrystals contain a large number of tetrahedral sites formed with Ti and Zr atoms that are chemically favorable to hydrogen, these materials retain strong advantages for hydrogen storage applications in structurally and chemically. In fact, TiZrNi quasicrystals are known to absorb hydrogen maximum of the hydrogen to host metal ratio (H/M) value of near 2.0. The critical disadvantage, however, is that the equilibrium vapor pressure of hydrogen is very low (less than 1 Torr). To overcome this engineering drawback, we added a small amount of vanadium (V) in Ti53-XZr27Ni20Vx, alloys (where x = 0 to 15) and rapidly quenched the molten ingots to form quasicrystals, and investigated the effects of V in terms of changes of structure, the H/M values, and an equilibrium vapor pressure of hydrogen. As the results, an equilibrium vapor pressure significantly increased from 0.84 to 2.16 Torr while the maximum H/M value decreased from 1.32 to 1.11 as increasing x = 0 to 8. After hydrogenation, the main peaks shifted evenly to the lower angle of 2 theta in X-ray diffraction patterns with uniform expansion of the quasilattice constants which demonstrates that hydrogen atoms homogeneously diffused into the samples. A Laves phase starts to form at x = 13 and the samples completely transformed to the phase at x = 15 suggesting the similarity between the quasicrystal and the Laves phase.
Title:
The electronic structure and magnetism of CaFeAs2: First principles calculations
Authors:
Wang, GT; Shi, XB; Zhang, L; Yi, X Author Full Names: Wang, Guangtao; Shi, Xianbiao; Zhang, Lin; Yi, Xia
Source:
SOLID STATE COMMUNICATIONS, 200 61-65; 10.1016/j.ssc.2014.09.025 DEC 2014
Abstract:
The electronic structure, magnetism and Fermi surface (FS) nesting of the recently discovered superconductive parent material CaFeAs2 are studied by the first-principles, based on the GGA and GGA+U methods. In the nonmagnetic state, the density of states at the Fermi level are mostly derived from the d(xy), d(yz) and d(zx) orbits, just like LaOFeAs. The Fermi surfaces consist of four hole like FS sheets around the Gamma-point, two electron like sheets near the Brillouin zone corner M-point, and small pockets near X-point. The hole like Fermi surfaces will strongly overlap with the electron like FS sheets, if they are shifted by the q-vector q = (pi, pi, 0). Such FS nesting will induce the magnetic instability and spin density wave (SDW), which has been confirmed to be more stable than other states by the calculated total energy. The calculated bare susceptibility chi(0)(q) peaked at M-point, and was obviously suppressed with the electron doping. This explains the emergence of the superconductivity in the electron-doped compound Ca1-xLaxFeAs2, because the electron doping suppressed the SDW and induced the superconductivity. (C) 2014 Elsevier Ltd. All rights reserved.
Title:
Superspace application on magnetic structure analysis of the Pb2MnWO6 double perovskite system
Authors:
Orlandi, F; Righi, L; Ritter, C; Pernechele, C; Solzi, M; Cabassi, R; Bolzoni, F; Calestani, G Author Full Names: Orlandi, Fabio; Righi, Lara; Ritter, Clemens; Pernechele, Chiara; Solzi, Massimo; Cabassi, Riccardo; Bolzoni, Fulvio; Calestani, Gianluca
Source:
JOURNAL OF MATERIALS CHEMISTRY C, 2 (43):9215-9223; 10.1039/c4tc01450b NOV 21 2014
Abstract:
The commensurate crystal structure of the magnetic phase occurring below 7 K of the multiferroic Pb2MnWO6 perovskite has been solved by the introduction of the superspace approach. This lead based double perovskite is characterized by a complex ferrielectric non-centrosymmetric nuclear structure with orthorhombic symmetry stable in a wide temperature range. As indicated from the analysis of powder neutron diffraction data, the low temperature antiferromagnetic structure showing a propagation vector kappa = [1/4 0 0] is stabilized by a multi-step process involving the evolution from incommensurate to commensurate spin ordering with a concomitant change of the magnetic symmetry. The determination of the Pb2MnWO6 magnetic structure offers a meaningful example of the superspace application and provides a detailed phase diagram of the involved magnetic states. Nowadays this ordered perovskite could be considered as a new type of multiferroic material combining ferrielectric properties and a long period antiferromagnetic structure.
Title:
Synthesis and crystal structure of a series of incommensurately modulated composite oxohalide compounds
Authors:
Zimmermann, I; Corgnet, A; Johnsson, M; Lidin, S Author Full Names: Zimmermann, Iwan; Corgnet, Alexis; Johnsson, Mats; Lidin, Sven
Source:
DALTON TRANSACTIONS, 43 (42):15812-15817; 10.1039/c4dt02084g NOV 14 2014
Abstract:
Transparent, needle-like single crystals of the isostructural compounds [Sb4O7+3 delta X4][Zn-3](1+delta) = CL Br, I) delta approximate to 0.2 were obtained from chemical reactions in evacuated and sealed silica tubes. First, the average structure was solved in P211n but the model refined poorly and a lowering of the symmetry to the 3 + 1 dimensional space group P2(1)(alpha 0 gamma)0 gave a significantly better fit to the data. This model used second order positional modulations for all the atoms. Whereas Sb, Cl (Br, I) and most 0 positions were well behaved, there was a mismatch with Zn that was better described in a sub-cell, thus yielding a composite structure. The composite nature of the structure leads to a charge imbalance that is compensated by oxygen vacancies.
Title:
Complex magnetic ordering in CeGe1.76 studied by neutron diffraction
Authors:
Jayasekara, WT; Tian, W; Hodovanets, H; Canfield, PC; Bud'ko, SL; Kreyssig, A; Goldman, AI Author Full Names: Jayasekara, W. T.; Tian, W.; Hodovanets, H.; Canfield, P. C.; Bud'ko, S. L.; Kreyssig, A.; Goldman, A. I.
Source:
PHYSICAL REVIEW B, 90 (13):10.1103/PhysRevB.90.134423 OCT 29 2014
Abstract:
Neutron diffraction measurements on a single crystal of CeGe1.76 reveal a complex series of magnetic transitions at low temperature. At T-N approximate to 7 K, there is a transition from a paramagnetic state at higher temperature to an incommensurate magnetic structure characterized by a magnetic propagation vector ( 0 0 tau) with tau approximate to 1/4 and the magnetic moment along the a axis of the orthorhombic unit cell. Below T-LI approximate to 5 K, the magnetic structure locks in to a commensurate structure with tau = 1/4 and the magnetic moment remains along the a axis. Below T* approximate to 4 K, we find additional half-integer and integer indexed magnetic Bragg peaks consistent with a second commensurately ordered antiferromagnetic state.
Title:
Feedback of superconducting fluctuations on charge order in the underdoped cuprates
Authors:
Chowdhury, D; Sachdev, S Author Full Names: Chowdhury, Debanjan; Sachdev, Subir
Source:
PHYSICAL REVIEW B, 90 (13):10.1103/PhysRevB.90.134516 OCT 24 2014
Abstract:
Metals interacting via short-range antiferromagnetic fluctuations are unstable to sign-changing superconductivity at low temperatures. For the cuprates, this leading instability leads to the well-known d-wave superconducting state. However, there is also a secondary instability to an incommensurate charge-density wave, with a predominantly d-wave form factor, arising from the same antiferromagnetic fluctuations. Recent experiments in the pseudogap regime of the hole-doped cuprates have found strong evidence for such a charge-density wave order and, in particular, the predicted d-wave form factor. However, the observed wave vector of the charge order differs from the leading instability in Hartree-Fock theory, and is that of a subleading instability. In this paper, we examine the feedback of superconducting fluctuations on these different charge-density wave states, and find that over at least a small temperature window, they prefer the experimentally observed wave vector.
Title:
Non-Fermi-liquid behavior at the onset of incommensurate 2k(F) charge- or spin-density wave order in two dimensions
Authors:
Holder, T; Metzner, W Author Full Names: Holder, Tobias; Metzner, Walter
Source:
PHYSICAL REVIEW B, 90 (16):10.1103/PhysRevB.90.161106 OCT 21 2014
Abstract:
We analyze the influence of quantum critical fluctuations on single-particle excitations at the onset of incommensurate 2k(F) charge- or spin-density wave order in two-dimensional metals. The case of a single pair of hot spots at high symmetry positions on the Fermi surface needs to be distinguished from the case of two hot spot pairs. We compute the fluctuation propagator and the electronic self-energy perturbatively in leading order. The energy dependence of the single-particle decay rate at the hot spots obeys non-Fermi-liquid power laws, with an exponent 2/3 in the case of a single hot spot pair, and exponent one for two hot spot pairs. The prefactors of the linear behavior obtained in the latter case are not particle-hole symmetric.
Title:
Structural and magnetic dynamics in the magnetic shape-memory alloy Ni2MnGa
Authors:
Mariager, SO; Dornes, C; Johnson, JA; Ferrer, A; Grubel, S; Huber, T; Caviezel, A; Johnson, SL; Eichhorn, T; Jakob, G; Elmers, HJ; Beaud, P; Quitmann, C; Ingold, G Author Full Names: Mariager, S. O.; Dornes, C.; Johnson, J. A.; Ferrer, A.; Gruebel, S.; Huber, T.; Caviezel, A.; Johnson, S. L.; Eichhorn, T.; Jakob, G.; Elmers, H. J.; Beaud, P.; Quitmann, C.; Ingold, G.
Source:
PHYSICAL REVIEW B, 90 (16):10.1103/PhysRevB.90.161103 OCT 10 2014
Abstract:
Magnetic shape-memory Heusler alloys are multiferroics stabilized by the correlations between electronic, magnetic, and structural order. To study these correlations we use time-resolved x-ray diffraction and magneto-optical Kerr effect experiments to measure the laser induced dynamics in a Heusler alloy Ni2MnGa film and reveal a set of time scales intrinsic to the system. We observe a coherent phonon which we identify as the amplitudon of the modulated structure and an ultrafast phase transition leading to a quenching of the incommensurate modulation within 300 fs with a recovery time of a few ps. The thermally driven martensitic transition to the high temperature cubic phase proceeds via nucleation within a few ps and domain growth limited by the speed of sound. The demagnetization time is 320 fs, which is comparable to the quenching of the structural modulation.
Title:
Fine structure of the incommensurate antiferromagnetic fluctuations in single-crystalline LiFeAs studied by inelastic neutron scattering
Authors:
Qureshi, N; Steffens, P; Lamago, D; Sidis, Y; Sobolev, O; Ewings, RA; Harnagea, L; Wurmehl, S; Buchner, B; Braden, M Author Full Names: Qureshi, N.; Steffens, P.; Lamago, D.; Sidis, Y.; Sobolev, O.; Ewings, R. A.; Harnagea, L.; Wurmehl, S.; Buechner, B.; Braden, M.
Source:
PHYSICAL REVIEW B, 90 (14):10.1103/PhysRevB.90.144503 OCT 8 2014
Abstract:
We present an inelastic neutron scattering study on single-crystalline LiFeAs devoted to the characterization of the incommensurate antiferromagnetic fluctuations at Q = (0.5 +/- delta, 0.5 -/+ delta, ql). Time-of-flight measurements show the presence of these magnetic fluctuations up to an energy transfer of 60 meV, while polarized neutrons in combination with a longitudinal polarization analysis on a triple-axis spectrometer prove the pure magnetic origin of this signal. The normalization of the magnetic scattering to an absolute scale yields that magnetic fluctuations in LiFeAs are by a factor of 8 weaker than the resonance signal in nearly optimally Co-doped BaFe2As2, although a factor of 2 is recovered due to the split peaks owing to the incommensurability. The longitudinal polarization analysis indicates weak spin-space anisotropy with a slightly stronger out-of-plane component between 6 and 12 meV. Furthermore, our data suggest a fine structure of the magnetic signal most likely arising from superposing nesting vectors.
Title:
CeCu2Ge2: Challenging our understanding of quantum criticality
Authors:
Zeng, B; Zhang, QR; Rhodes, D; Shimura, Y; Watanabe, D; Baumbach, RE; Schlottmann, P; Ebihara, T; Balicas, L Author Full Names: Zeng, B.; Zhang, Q. R.; Rhodes, D.; Shimura, Y.; Watanabe, D.; Baumbach, R. E.; Schlottmann, P.; Ebihara, T.; Balicas, L.
Source:
PHYSICAL REVIEW B, 90 (15):10.1103/PhysRevB.90.155101 OCT 3 2014
Abstract:
In the zero temperature limit, the zero-point quantum fluctuations of certain degrees of freedom (or quantum criticality) are claimed to describe the collective fluctuations of systems undergoing a second-order phase transition. To date, some of the best studied examples of quantum phase transitions, and concomitant anomalous physical behavior, involve f-electron magnetism in heavy-fermion metals, where quantum criticality (QC) is ascribed to either the suppression of a spin-density wave (SDW) ground state or the Kondo effect. Here, we unveil evidence for a quantum phase transition in CeCu2Ge2 which displays both an incommensurate SDW ground state, and a strong renormalization of the quasiparticle effective masses (mu) due to the Kondo effect. For all angles theta between an external magnetic field (H) and the crystallographic c axis, the application of H leads to the suppression of the SDW state through a second-order phase transition at a theta-dependent critical field H-p(theta) leading to the observation of small Fermi surfaces (FSs) in the paramagnetic state. For the H vertical bar vertical bar c axis, these FSs are characterized by light mu's pointing also to the suppression of the Kondo effect at H-p with, surprisingly, no experimental evidence for QC. But as H is rotated towards the a axis, these mu's increase considerably becoming undetectable for theta > 56 degrees between H and the c axis. Around H-p(a) similar to 30 T the resistivity becomes alpha T which, coupled to the divergence of mu, indicates the existence of a field-induced QC point at H-p(a) (T = 0 K). This observation, suggesting FS hot spots associated with the SDW nesting vector, is at odds with current QC scenarios for which the continuous suppression of all relevant energy scales at H-p(theta, T) should lead to a line of quantum-critical points in the H-theta plane. Finally, we show that the complexity of its magnetic phase diagram(s) makes CeCu2Ge2 an ideal system to explore field-induced quantum tricritical and QC end points.
Title:
Competing Exchange Interactions on the Verge of a Metal-Insulator Transition in the Two-Dimensional Spiral Magnet Sr3Fe2O7
Authors:
Kim, JH; Jain, A; Reehuis, M; Khaliullin, G; Peets, DC; Ulrich, C; Park, JT; Faulhaber, E; Hoser, A; Walker, HC; Adroja, DT; Walters, AC; Inosov, DS; Maljuk, A; Keimer, B Author Full Names: Kim, J. -H.; Jain, Anil; Reehuis, M.; Khaliullin, G.; Peets, D. C.; Ulrich, C.; Park, J. T.; Faulhaber, E.; Hoser, A.; Walker, H. C.; Adroja, D. T.; Walters, A. C.; Inosov, D. S.; Maljuk, A.; Keimer, B.
Source:
PHYSICAL REVIEW LETTERS, 113 (14):10.1103/PhysRevLett.113.147206 OCT 3 2014
Abstract:
We report a neutron scattering study of the magnetic order and dynamics of the bilayer perovskite Sr3Fe2O7, which exhibits a temperature-driven metal-insulator transition at 340 K. We show that the Fe4+ moments adopt incommensurate spiral order below T-N = 115 K and provide a comprehensive description of the corresponding spin-wave excitations. The observed magnetic order and excitation spectra can be well understood in terms of an effective spin Hamiltonian with interactions ranging up to third-nearest-neighbor pairs. The results indicate that the helical magnetism in Sr3Fe2O7 results from competition between ferromagnetic double-exchange and antiferromagnetic superexchange interactions whose strengths become comparable near the metal-insulator transition. They thus confirm a decades-old theoretical prediction and provide a firm experimental basis for models of magnetic correlations in strongly correlated metals.
Title:
Oxide ion distribution, vacancy ordering and electrical behaviour in the Bi3NbO7-Bi3YbO6 pseudo-binary system
Authors:
Leszczynska, M; Liu, X; Wrobel, W; Malys, M; Dygas, JR; Norberg, ST; Hull, S; Krok, F; Abrahams, I Author Full Names: Leszczynska, M.; Liu, X.; Wrobel, W.; Malys, M.; Dygas, J. R.; Norberg, S. T.; Hull, S.; Krok, F.; Abrahams, I.
Source:
JOURNAL OF MATERIALS CHEMISTRY A, 2 (43):18624-18634; 10.1039/c4ta03225j 2014
Abstract:
Oxide ion distribution, vacancy ordering and electrical conductivity has been examined in the Nb/Yb double substituted bismuth oxide based system Bi3Nb1-xYbxO7-x, using X-ray and neutron powder diffraction, reverse Monte Carlo modelling of total neutron scattering data and a. c. impedance spectroscopy. Transference number measurements confirm the system to be predominantly ionically conducting above ca. 450 degrees C. Niobium rich compositions show incommensurate ordering of the fluorite subcell, while increasing ytterbium content results in a commensurate fluorite, with fully disordered cation and anion sublattices. Oxide ion distribution shows both compositional and thermal dependencies. The latter is discussed with respect to its effect on the thermal variation of cubic lattice parameter. Substitution of bismuth by niobium and ytterbium in the cation sublattice of bismuth oxide leads to the creation of Frenkel interstitial oxide ions, which increase the tetrahedral vacancy concentration. The high vacancy concentration is confirmed in both Rietveld and RMC analyses of neutron data. Examination of vacancy ordering, in the x - 0.6 composition, indicates a favouring of < 100 > vacancy pair alignment.

Update: 26-Nov-2014

Title:
Magnetic properties of nanoscaled paramelaconite Cu4O3-x (x=0.0 and 0.5)
Authors:
Djurek, D; Prester, M; Drobac, D; Ivanda, M; Vojta, D Author Full Names: Djurek, D.; Prester, M.; Drobac, Dj.; Ivanda, M.; Vojta, D.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 373 183-187; JAN 1 2015
Abstract:
Pure paramelaconite Cu4O3-x has been prepared in the form of nanoparticles with 56 nm in diameter. This mixed valency oxide crystallizes in a tetragonal lattice with 4 unit formulae and forms a pyrochlore structure which manifests in two stoichiometric forms; Cu4O3 and Cu4O2.5, the latter form having two oxygen vacancies per unit cell. Magnetic lattice consists of Cu spin 1/2, and both stoichiometric forms obey transition to the antiferromagnetic state at T-N=45-55 K. Defect free Cu4O3 is indicated by an inversion symmetry and exhibits both antiferromagnetic and ferromagnetic state, where the latter is supposedly due to the superexchange interaction in Cu-O(1n)-Cu bonds. An additional magnetic transition was observed in Cu4O3 at T=120 K, probably as a result of an incommensurate ordering. Absence of an inversion symmetry in the oxygen defect Cu4O2.5 results in a long range Dzyaloshinsky-Moriya interaction accompanied by the strong superparamagnetism. (C) 2014 Elsevier B.V. All rights reserved
Title:
Interacting magnetic cluster-spin glasses and strain glasses in Ni-Mn based Heusler structured intermetallics
Authors:
Entel, P; Gruner, ME; Comtesse, D; Sokolovskiy, VV; Buchelnikov, VD Author Full Names: Entel, Peter; Gruner, Markus E.; Comtesse, Denis; Sokolovskiy, Vladimir V.; Buchelnikov, Vasiliy D.
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 251 (10):2135-2148; SI 10.1002/pssb.201451059 OCT 2014
Abstract:
Magnetic Ni-Mn based Heusler intermetallics show complex magnetic behavior in connection with martensitic transformations (see, for instance, the phase diagram of Ni-Co-Mn-Sn on the right-hand side). The cubic austenitic phase at high temperature shows long-range ferromagnetic order which can considerably be weakened by the appearance of competing antiferromagnetic interactions which are induced by Mn excess and chemical disorder. With decreasing temperature a martensitic/magnetostructural transformation takes place from cubic to non-modulated/modulated tetragonal/monoclinic or orthorhombic structure, where long-range ferromagnetic order can no longer be maintained, leading to superparamagnetic behavior. At still lower temperatures superparamagnetism changes to superspin glass because of strong competition of ferromagnetic and antiferromagnetic interactions and chemical disorder. In addition, disorder and local structural distortions can lead to strain glass in austenite, as observed for some nonmagnetic martensitic systems. The magnetic intermetallics are of technological importance in view of their functional properties involving magnetic shape-memory and exchangebias effects as well as magnetocaloric effects. The ` ferroic cooling' is of particular relevance since it avoids the use of ozone-depleting and greenhouse chemicals compared with conventional fluid-compression technology. Experimental phase diagram of Ni50-xCoxMn39Sn11 for 0 <= x <= 10. Here, TC is the Curie temperature of austenite; at T-M the system transforms to paramagnetic martensite and at T-S to superparamagnetic martensite (SPM) and then to superspin-glass martensite (SSG) at T-P. The possible strainglass phases (labeled by question marks) are predicted because of kinetic arrest phenomena and local distortions associated with the magnetostructural transition and ergodicity breaking by field-cooling/zero-field-cooling experiments. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Title:
Elastic fields around a nanosized elliptic hole in decagonal quasicrystals
Authors:
Li, LH; Yun, GH Author Full Names: Li Lian-He; Yun Guo-Hong
Source:
CHINESE PHYSICS B, 23 (10):10.1088/1674-1056/23/10/106104 OCT 2014
Abstract:
Based on the variational principle, a continuum theory of surface elasticity and new boundary conditions for quasicrystals is proposed. The effect of the residual surface stress on a decagonal quasicrystal that is weakened by a nanoscale elliptical hole is considered. The explicit expressions for the hoop stress along the edge of the hole are obtained using the Stroh formalism. The results show that the residual surface stress and the shape of the hole have a significant effect on the elastic state around the hole.
Title:
Two-coupled structural modulations in charge-density-wave state of SrPt2As2 superconductor
Authors:
Wang, L; Wang, Z; Shi, HL; Chen, Z; Chiang, FK; Tian, HF; Yang, HX; Fang, AF; Wang, NL; Li, JQ Author Full Names: Wang Li; Wang Zhen; Shi Hong-Long; Chen Zhen; Chiang Fu-Kuo; Tian Huan-Fang; Yang Huai-Xin; Fang Ai-Fang; Wang Nan-Lin; Li Jian-Qi
Source:
CHINESE PHYSICS B, 23 (8):10.1088/1674-1056/23/8/086103 AUG 2014
Abstract:
Transmission electron microscopy (TEM) study of SrPt2As2 reveals two incommensurate modulations appearing in the charge-density-wave (CDW) state below T-CDW approximate to 470 K. These two structural modulations can be well explained in terms of condensations of two-coupled phonon modes with wave vectors of q(1) = 0.62a on the a-b* plane and q(2) = 0.23a on the a-c* plane. The atomic displacements occur along the b-axis direction for q(1) and along the c-axis direction for q(2), respectively. Moreover, the correlation between q(1) and q(2) can be generally written as q(1) = (q(2) + a*)/2 in the CDW state, suggesting the presence of essential coupling between q(1) and q(2). A small fraction of Ir doping on the Pt site in Sr(Pt1-xIrx)(2)As-2 (x < 0.06) could moderately change these CDW modulations and also affect their superconductivities.

Update: 19-Nov-2014

Title:
The use of Nb in rapid solidified Al alloys and composites
Authors:
Audebert, F; Galano, M; Saporiti, F Author Full Names: Audebert, F.; Galano, M.; Saporiti, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 615 S621-S626; 1 10.1016/j.jallcom.2013.12.129 DEC 5 2014
Abstract:
The worldwide requirements for reducing the energy consumption and pollution have increased the demand of new and high performance lightweight materials. The development of nanostructured Al-based alloys and composites is a key direction towards solving this demand. High energy prices and decreased availability of some alloying elements open up the opportunity to use non-conventional elements in Al alloys and composites. In this work the application of Nb in rapid solidified Al-based alloys and Al alloys matrix composites is reviewed. New results that clarify the effect of Nb on rapid solidified Al alloys and composites are also presented. It is observed that Nb stabilises the icosahedral Al-Fe/Cr clusters, enhances the glass forming ability and shifts the icosahedral phase decomposition towards higher temperatures. Nb provides higher corrosion resistance with respect to the pure Al and Al-Fe-RE (RE: rare earth) alloys in the amorphous and crystalline states. The use of Nb as a reinforcement to produce new Al alloy matrix composites is explored. It is observed that Nb provides higher strength, ductility and toughness to the nanoquasicrystalline matrix composite. Nb appears as a new key element that can improve several properties in rapid solidified Al alloys and composites. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Effect of Ti, Zr and Hf addition on microstructure and properties of rapidly solidified Al-Mn-Fe alloy
Authors:
Stan, K; Litynska-Dobrzynska, L; Ochin, P; Garzel, G; Wierzbicka-Miernik, A; Wojewoda-Budka, J Author Full Names: Stan, K.; Litynska-Dobrzynska, L.; Ochin, P.; Garzel, G.; Wierzbicka-Miernik, A.; Wojewoda-Budka, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 615 S607-S611; 1 10.1016/j.jallcom.2013.11.160 DEC 5 2014
Abstract:
In this work, the influence of alloying elements Ti, Zr and Hf on microstructure and properties of Al91Mn7Fe2 melt spun ribbons, strengthened with quasicrystalline particles was studied. It was found that Zr improves significantly the microhardness of the alloy in as spun state by precipitation of metastable L1(2)-Al3Zr phase in matrix grains. Both Hf and Zr additions retain higher microhardness values after annealing at 673 K by formation of stable Al3X precipitates, even though the quasicrystalline phase being the main strengthening phase in the alloy starts to decompose. Comparison of the results from differential scanning calorimetry, thermo-mechanical analysis and microhardness measurements after annealing showed correlation between phase transformations and mechanical properties. Based on TEM studies, drop of microhardness and increase in Young's modulus with temperature for all samples was attributed to significant change in samples microstructure, especially to decomposition of quasicrystalline particles and formation of different intermetallic phases. (C) 2013 Elsevier B.V. All rights reserved.
Title:
High-resolution electron microscopy and electron diffraction of perovskite-type superconducting copper oxides
Authors:
Oku, T Author Full Names: Oku, Takeo
Source:
NANOTECHNOLOGY REVIEWS, 3 (5):413-444; SI 10.1515/ntrev-2014-0003 OCT 2014
Abstract:
High-resolution electron microscopy and electron diffraction are quite useful for structural characterization of perovskite-type superconducting copper oxides on the atomic scale. Valuable information on the crystal structures and the microstructures could be obtained from observed high-resolution images if severe conditions such as thinner crystals and definite defocus values are satisfied. The structure images and electron diffraction patterns include information not only on accurate atomic coordinates of cations but also on ordered arrangements of oxygen atoms and oxygen vacancies. Crystal structures of the various perovskite-type copper oxides were analyzed from the observed structure images. Modulated structures, defects, intergowth, surfaces, and interfaces were also investigated.
Title:
Dual-phase glassy/nanoscale icosahedral phase materials in Cu-Zr-Ti-Pd system alloys
Authors:
Louzguine-Luzgin, DV; Churyumov, AY Author Full Names: Louzguine-Luzgin, Dmitri V.; Churyumov, A. Yu.
Source:
MATERIALS CHARACTERIZATION, 96 6-12; 10.1016/j.matchar.2014.07.014 OCT 2014
Abstract:
The present work is devoted to an investigation of the formation kinetics, stability and homogeneity area of the nanoscale icosahedral phase formed on heating in the dual-phase glassy/quasicrystalline phase Cu-Zr-Ti-Pd alloys. The data obtained indicate that the Cu-Zr-Ti-Pd icosahedral phase is not a Cu-rich part of the compositional homogeneity area of the Zr-Cu-Pd one. Moreover, Ti, as well as Pd, is found to be an important element stabilizing quasicrystalline phase in the Cu-Zr-Ti-Pd alloys. The formation criteria for Cu- and Zr/Hf-based icosahedral phases are discussed based on the quasilattice constant to average atomic diameter ratio. Deviation from a certain ratio leads to destabilization of the icosahedral phase. By using the isothermal calorimetry traces transformation kinetics above and below the glass-transition region was analyzed. Some difference in the transformation kinetics above and below the glass-transition region allows us to suggest that possible structure changes occur upon glass-transition. (C) 2014 Elsevier Inc. All rights reserved.
Title:
Partially amorphous (metamict) titanite: a silicate mineral in a natural radiation induced non-equilibrium phase
Authors:
Beirau, T Author Full Names: Beirau, Tobias
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 229 (8):543-549; 10.1515/zkri-2014-1745 AUG 2014
Abstract:
The present review will give a brief overview mainly focused on studies during the past 5 years on the mineral titanite (end-member composition CaTiSiO5) which could incorporate radioactive elements in its crystal structure. Aspects of investigations were the structural damage resulting from the radioactive decay, the thermally induced recrystallization process and the elastic properties of the mineral. During the radiation induced damage process, namely the metamictization, titanite becomes partially amorphous with coexisting defect enriched crystalline and aperiodic regions. Within these crystalline regions a P2(1)/c to C2/c phase transition (similar to at 500 K) occurs. Resulting from radiation induced structural damage, titanite shows elastic properties close to those of titanite glass. During recrystallization on annealing an initial softening of the titanite structure takes place (up to temperature similar to 950 K) resulting from the formation of soft interfaces. Thermal annealing at higher temperatures leads to increasing structural order and the hardening of the mineral.

Update: 13-Nov-2014

Title:
Multicomponent and High Entropy Alloys
Authors:
Cantor, B Author Full Names: Cantor, Brian
Source:
ENTROPY, 16 (9):4749-4768; 10.3390/e16094749 SEP 2014
Abstract:
This paper describes some underlying principles of multicomponent and high entropy alloys, and gives some examples of these materials. Different types of multicomponent alloy and different methods of accessing multicomponent phase space are discussed. The alloys were manufactured by conventional and high speed solidification techniques, and their macroscopic, microscopic and nanoscale structures were studied by optical, X-ray and electron microscope methods. They exhibit a variety of amorphous, quasicrystalline, dendritic and eutectic structures.
Title:
Structural origin of the different devitrification behaviors between ZrCu and ZrPd metallic glasses
Authors:
Huang, P; Zou, DH; Guo, GQ; Yang, L Author Full Names: Huang, Po; Zou, De-Hui; Guo, Gu-Qing; Yang, Liang
Source:
EPL, 107 (6):10.1209/0295-5075/107/66002 SEP 2014
Abstract:
The microstructures of Zr70Pd30 and Zr70Cu30 metallic glasses (MGs) were investigated via the synchrotron radiation techniques combined with the reverse Monte Carlo simulations. It is revealed that, compared with Zr70Cu30, Zr70Pd30 has more fruitful icosahedral-like clusters, which have a relatively high geometrical regularity closer to that of the ideal icosahedron. Therefore, clusters in Zr70Pd30 are prone to change into the structural units of icosahedral quasicrystal phase. This should be the structural origin of the amorphous-to-quasicrystal transformation found in Zr70Pd30 while such phase change never appears when heating Zr70Cu30 MG. This work provides an understanding of the devitrification mechanism from the atomic level in this class of glassy materials. Copyright (C) EPLA, 2014
Title:
The alpha <-> beta phase transitions of Zn2P2O7 revisited: existence of an additional intermediate phase with an incommensurately modulated structure
Authors:
Stoger, B; Weil, M; Dusek, M Author Full Names: Stoeger, Berthold; Weil, Matthias; Dusek, Michal
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 539-554; SI 10.1107/S205252061401049X 3 JUN 2014
Abstract:
Zn2P2O7 crystallizes in a thortveitite-like structure and features temperature-dependent polymorphism. At high temperatures (T > 500 K), the aristotype phase beta-Zn2P2O7 (C2/m, Z = 2, a similar or equal to 6.60, b similar or equal to 8.28, c similar or equal to 4.53 angstrom, beta similar or equal to 105.4 degrees) is stable. At lower temperatures the lock-in phase alpha(1)-Zn2P2O7 [at 350 K: I2/c, Z = 12, a = 20.1131 (13), b = 8.2769 (6), c = 9.109 (3) angstrom, beta = 106.338 (16)degrees], a sixfold superstructure with commensurate modulation vector q = (1/3, 0, 1/2), is stable. Between the stability ranges of the alpha(1)- and beta-phases exists the intermediate, incommensurately modulated alpha(2)-Zn2P2O7 phase with modulation wavevector q similar or equal to (0.33, 0, 0.40) and C2/m(alpha, 0, gamma)0s superspace group symmetry. The alpha(1) -> alpha(2) lock-in phase transition at T-L = 408 K is of first-order and features virtually no hysteresis. It is immediately followed by the second-order alpha(2) -> beta transition to the non-modulated phase at T-I similar or equal to 430 K. This transformation is sluggish and even at T = 500 K very weak satellite reflections of the alpha(2)-phase were observed. Both phase transitions were analyzed with differential scanning calorimetry and high-temperature powder and single-crystal X-ray diffraction. The crystal structures of the alpha(1)- and alpha(2)-phases were refined from single crystal data collected at T = 350, 400, 405, 410, 415, 420, 425, 430, 450 and 500 K. Different models describing the slow transition from the incommensurately modulated alpha(2)- to the non-modulated beta-phase were tested. In the model resulting in the best residuals, the bridging O atom of the [P2O7] group, which is located on a 2/m position in the basic structure, is described as an overlap of an atom ordered in internal space and one atom disordered around the mirror plane. The occupancy of the ordered atom decreases with temperature until at T = 500 K virtually only the disordered atom remains. Simultaneously, the amplitude of the modulation functions of the remaining atoms decreases, so that the T = 500 K structure can be considered as the C2/m aristotype structure, although the diffraction pattern still features satellite reflections of first order with very low intensities.
Title:
Understanding the structure details when drying hydrate crystals of pharmaceuticals - interpretations from diffuse scattering and inter-modulation satellites of a partially dehydrated crystal
Authors:
Chan, EJ; Gao, Q; Dabros, M Author Full Names: Chan, E. J.; Gao, Q.; Dabros, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 555-567; SI 10.1107/S2052520614005125 3 JUN 2014
Abstract:
Simplified models for the crystal lattice of the sesquihydrate form of the hemi-sulfate salt of (5S, 6S, 9R)-5-amino-6-(2,3-difluorophenyl)-6,7,8,9-tetrahydro-5H-cyclohepta[b]py ridin9-yl 4-(2-oxo-2,3-dihydro-1H-imidazol[4,5b]pyridin-1-yl)-1piperidine carboxylate (BMS-927711, C28H29F2N6O3+) are used to calculate diffuse diffraction features in order to develop a mechanistic understanding of the dehydration process with respect to disruption of the lattice, since a Bragg model cannot be established. The model demonstrates that what we observe when the water leaves the crystal is partial transformation from the parent form to a child form (a new form, less hydrated and structurally related to the parent). Yet this 'dried' structure is not a pure phase. It consists of semi-random layers of both child, parent and an interfacial layer which has a modulated structure that represents a transitory phase. Understanding the fact that a single 'dried' crystal can have the disordered layer structure described as well as understanding mechanistic relationships between the phases involved can have implications in understanding the effect of common large scale bulk drying procedures. During the development of BMS-927711, difficulties did arise during characterization of the dried bulk when using only routine solid-state analysis. The material is now better understood from this diffraction study. The diffraction experiments also reveal intermodulation satellites, which upon interpretation yield even more structural information about the crystal transformation. The model suggests the mechanism of transformation is laminar in which layers of the crystal are driven to approach a stable B-centered supercell phase of lower water content.

Update: 5-Nov-2014

Title:
High temperature X-ray diffraction study on incommensurate composite crystal MnSi gamma - (3+1)-dimensional superspace approach
Authors:
Kikuchi, Y; Nakajo, T; Hayashi, K; Miyazaki, Y Author Full Names: Kikuchi, Y.; Nakajo, T.; Hayashi, K.; Miyazaki, Y.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 616 263-267; 10.1016/j.jallcom.2014.07.106 DEC 15 2014
Abstract:
The (3 + 1)-dimensional crystal structure of a higher manganese silicide (MnSi gamma) phase is revealed using in situ high temperature powder X-ray diffraction (XRD) above room temperature. The compound consists of two tetragonal subsystems of [Mn] and [Si] with an irrational c-axis ratio gamma = c(Mn)/c(Si). The in situ XRD results show that the MnSi gamma phase is stable, in a vacuum of similar to 1 Pa, up to 1093 K and partially decomposes into the monosilicide (MnSi) phase with further increase in temperature. Refined a- and c(Mn)-axis lengths increase linearly and the thermal expansion coefficients are comparable with those of typical metallic electrode materials. In contrast, c(Si)-axis length changes its increment against temperature at T-BD similar to 773 K. As a result, the temperature dependence of gamma starts to decrease gradually above T-BD, from 1.7387(1) (at 773 K) to 1.7244(1) (at 1173 K). This finding implies that the MnSi gamma phase consecutively changes its irrational composition above T-BD, a typical temperature where the silicides exhibit a maximum figure-of-merit. An increase in hole carrier concentration is expected according to the valence electron counting concept. Although the nearest Mn-Mn and Mn-Si distances increase monotonically with temperature, the nearest Si-Si distance much increases by similar to 0.05 angstrom from 2.439(4) angstrom at 773 K to 2.493(7) angstrom at 1173 K. The latter increase is considered to be caused by the introduction of excited electron carriers into the anti-bonding orbital, due to the bipolar diffusion (BD). (C) 2014 Elsevier B.V. All rights reserved.
Title:
Effects of S-Se substitution and magnetic field on magnetic order in Fe0.5Ti(S,Se)(2) layered compounds
Authors:
Gubkin, AF; Sherokalova, EM; Keller, L; Selezneva, NV; Proshkin, AV; Proskurina, EP; Baranov, NV Author Full Names: Gubkin, A. F.; Sherokalova, E. M.; Keller, L.; Selezneva, N. V.; Proshkin, A. V.; Proskurina, E. P.; Baranov, N. V.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 616 148-154; 10.1016/j.jallcom.2014.06.195 DEC 15 2014
Abstract:
Powder neutron diffraction and specific heat measurements have been employed to study the evolution of an antiferromagnetic (AFM) structure in the intercalated Fe0.5TiS2-ySey compounds with S-Se substitution and under application of a magnetic field. In Fe0.5TiS2 (y = 0), the magnetic structure just below T-N similar or equal to 140 K is incommensurate while it becomes commensurate with further cooling below T-t similar or equal to 125 K. The presence of two magnetic phase transitions at T-t and T-N in Fe0.5TiS2 is confirmed by specific heat measurements. The field-induced AFM-FM transitions occurring in Fe0.5TiS2 within temperature interval T-t < T < T-N and below T-t are evidenced by neutron diffraction measurements under application of a magnetic field. Unlike Fe0.5TiS2 having a quadruplicated AFM structure, the compounds with the Se concentrations y > 0.5 are observed to exhibit an AFM structure with the doubled magnetic unit cell along a and c crystallographic directions of the monoclinic crystal lattice (I12/m1 space group). In the transition region around the critical Se concentration y(c) approximate to 0.5, the magnetic structure of Fe0.5TiS2-ySey is found to be incommensurate. The appearance of the AFM order with decreasing temperature in Fe0.5TiS2-ySey is accompanied by anisotropic deformations of the crystal lattice. At low temperatures, the Fe magnetic moments in all Fe0.5TiS2-ySey form an angle 14-16 degrees to the c crystallographic direction, which can be ascribed to the crystal field effects and spin-orbit couplings. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Cu3Sn - understanding the systematic absences
Authors:
Muller, CJ; Lidin, S Author Full Names: Muller, Carola J.; Lidin, Sven
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 879-887; 10.1107/S205252061401806X 5 OCT 2014
Abstract:
The intermetallic compound Cu3Sn has previously been described as a long-period antiphase boundary superstructure of the Cu3Ti structure type. While the compound itself has been reported as a tenfold and an eightfold superstructure, ternary doped alloys show shorter repetitions. Interestingly, the diffraction patterns of these compounds show noncrystallographic absences that cannot be explained using the superstructure models. Since the compound exhibits phase broadening, these models are not satisfactory because the paucity of observed data does not allow for a refinement of the composition. Here, an alternative, superspace model in the orthorhombic space group Xmcm(0 beta 0)000 is proposed, with the centering vectors (0,0,0,0) and (1/2,0,0,1/2). The presence of the non-crystallographic absences is explained as a result of a dominating occupational modulation that is accompanied by a weaker displacive modulation. In consistency with the EDXS results, the composition has been refined to Cu3 + xSn from single-crystal X-ray diffraction data. It is further demonstrated that by varying the length and the direction of the modulation wavevector in the superspace model, the ternary Cu3Sn compounds and other colored hexagonal close packing (h.c.p.) structures can be produced.
Title:
Mackay icosahedron explaining orientation relationship of dispersoids in aluminium alloys
Authors:
Muggerud, AMF; Li, YJ; Holmestad, R; Andersen, SJ Author Full Names: Muggerud, Astrid Marie F.; Li, Yanjun; Holmestad, Randi; Andersen, Sigmund J.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 888-896; 10.1107/S2052520614017880 5 OCT 2014
Abstract:
The orientation relations (ORs) of the cubic icosahedral quasicrystal approximant phase alpha-Al(Fe,Mn)Si have been studied after low temperature annealing of a 3xxx wrought aluminium alloy by transmission electron microscopy. From diffraction studies it was verified that the most commonly observed OR for the alpha-Al(Fe,Mn)Si dispersoids is [1 (1) over bar1]alpha // [1 (1) over bar1]Al, (5 (2) over bar(7) over bar)alpha // (011)Al. This orientation could be explained by assuming that the internal Mackay icosahedron (MI) in the alpha-phase has a fixed orientation in relation to Al, similar to that of the icosahedral quasi-crystals existing in this alloy system. It is shown that mirroring of the normal-to-high-symmetry icosahedral directions of the MI explains the alternative orientations, which are therefore likely to be caused by twinning of the fixed MI. Only one exception was found, which was related to the Bergman icosahedron internal to the T-phase of the Al-Mg-Zn system.
Title:
The ac-magnetic susceptibility and dielectric response of complex spin ordering processes in Mn3O4
Authors:
Thota, S; Singh, K; Nayak, S; Simon, C; Kumar, J; Prellier, W Author Full Names: Thota, Subhash; Singh, Kiran; Nayak, Sanjib; Simon, Ch.; Kumar, Jitendra; Prellier, Wilfrid
Source:
JOURNAL OF APPLIED PHYSICS, 116 (10):10.1063/1.4895054 SEP 14 2014
Abstract:
We report a meticulous study of the ac-magnetization dynamics (chi(ac)(T)), relative dielectric permittivity epsilon(r)(T), and magneto-dielectric (Delta epsilon(r)/epsilon(r)(H)) response of various complex magnetic transitions that occur below the ferrimagnetic Neel temperature T-N of Mn3O4. Besides the known sequence of transitions at T-N similar to 42.75 K, T-1 similar to 39 K, and T-2 similar to 34 K, the existence of a new anomaly reported recently at 38 K (T*) has been successfully probed by chi(ac)(T) and epsilon(r)(T) measurements. The effect of external dc-bias fields (H-DC) and driving frequency (f) on the above mentioned transitions has been investigated in consonance with the epsilon(r)(T) and Delta epsilon(r)/epsilon(r)(T, H) results. For the first time, we observed a clear hysteresis of about 5.15 K in the zero-field epsilon(r)(T) across the incommensurate-to-commensurate transition T-2 similar to 34 K, which provides evidence to the first-order nature of this transition. The Arrott plot (H/M vs. M-2) criterion has been used to distinguish the nature of all the sequential transitions that take place below T-N. (C) 2014 AIP Publishing LLC.
Title:
Structural changes and microstructures in stuffed tridymite-type compounds Ba1-xSrxAl2O4
Authors:
Tanaka, E; Ishii, Y; Teukasaki, H; Taniguchi, H; Mori, S Author Full Names: Tanaka, Eri; Ishii, Yui; Teukasaki, Hirofumi; Taniguchi, Hiroki; Mori, Shigeo
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS, 53 (9):SI 10.7567/JJAP.53.09PB01 SEP 2014
Abstract:
Crystal structures and microstructures in Ba1-xSrxAl2O4 solid solutions between the end members of BaAl2O4 and SrAl2O4 have been carefully investigated by powder X-ray diffraction, electron diffraction and transmission electron microscopy (TEM) imaging experiments. With the help of fast Fourier transform (FFT) calculation, high-resolution TEM images suggested that diffuse streaks along three equivalent (110) directions in the (001) plane, which appear in the P6(3) structure of Ba1-xSrxAl2O4 for x = 0.4, originate from the large structural fluctuation of the AlO4 tetrahedral network. On the other hand, the monoclinic P2(1) structure in Ba1-xSrxAl2O4 with x = 0.7 was found to consist of a modulated structure with q = 0,1/2,0. The present experimental results reveal that a structural phase boundary exists at approximately x = 0.6 between the P6(3) structure with a large structural fluctuation and a monoclinic P2(1) phase with the single-q modulated structure. (C) 2014 The Japan Society of Applied Physics
Title:
Strongly localized modes in one-dimensional defect-free magnonic quasicrystals
Authors:
Chen, CH; Qiu, RZ; Chang, CH; Hsueh, WJ Author Full Names: Chen, C. H.; Qiu, R. Z.; Chang, C. H.; Hsueh, W. J.
Source:
AIP ADVANCES, 4 (8):10.1063/1.4892164 AUG 2014
Abstract:
Signal storage in magnonic quasicrystals using a slow spin-wave mode, rather than the quasinormal mode of traditional periodic magnonic crystals, is proposed, which is analogous to the slow light mode in the field of optics. Compared to traditional materials, richer and more wavelength-selective sharp resonances are achieved using the quasicrystals with a fewer number of layers, because of the peculiar fractal transmission spectra of quasicrystals. The number of sharp resonance and the quality factor for the sharp resonances in the transmission spectra also increases as the generation order of the magnonic quasicrystal increases. This generic nature allows the storage of signals using spin wave, for a wide range of quasiperiodic systems. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
Title:
Crystal structure and magnetic properties of Bi(0.8)A(0.2)FeO(3) (A = La, Ca, Sr, Ba) multiferroics using neutron diffraction and Mossbauer spectroscopy
Authors:
Rangi, M; Agarwal, A; Sanghi, S; Singh, R; Meena, SS; Das, A Author Full Names: Rangi, Manisha; Agarwal, Ashish; Sanghi, Sujata; Singh, Ripandeep; Meena, S. S.; Das, A.
Source:
AIP ADVANCES, 4 (8):10.1063/1.4893241 AUG 2014
Abstract:
Bi(0.8)A(0.2)FeO(3) (A = La, Ca, Sr, Ba) multiferroics were studied using x-ray, neutron diffraction and magnetization techniques. All the samples crystallized in rhombohedral structure with space group R3c. The compounds exhibit antiferromagnetic (AFM) ordering at 300 K and no evidence of further structural or magnetic transition was observed on lowering of temperature below it. The magnetic structure of these substituted compounds are found to be collinear G-type AFM structure as against the non collinear incommensurate magnetic structure reported in the case of parent compound. The moments on Fe at 6 K are aligned along the a-axis in the case of Ca-doped sample. With increase in the ionic radii of dopant, the moments are found to be aligned in the ac plane and the angle of tilt away from the a-axis increases. The observed change in the magnetic structure with substitution is attributed to the intrinsic structural distortion as evidenced by the change in the bond angle (Fe-O-Fe) and bond distances (Bi-O, Fe-O). It has been found that heterovalent substitution A(2+) results in the formation of oxygen vacancies in the parent lattices as the possibility of Fe4+ ruled out by Mossbauer spectra recorded at room temperature. Higher value of remnant magnetization (0.4187 emu/g) and coercivity (4.7554kOe) is observed in Bi0.8Ba0.2FeO3 sample in comparison to other substituted samples revealing a strong correlation between ionic radii and magnetization. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
Title:
The alpha <-> beta phase transitions of Zn2P2O7 revisited: existence of an additional intermediate phase with an incommensurately modulated structure
Authors:
Stoger, B; Weil, M; Dusek, M Author Full Names: Stoeger, Berthold; Weil, Matthias; Dusek, Michal
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 539-554; SI 10.1107/S205252061401049X 3 JUN 2014
Abstract:
Zn2P2O7 crystallizes in a thortveitite-like structure and features temperature-dependent polymorphism. At high temperatures (T > 500 K), the aristotype phase beta-Zn2P2O7 (C2/m, Z = 2, a similar or equal to 6.60, b similar or equal to 8.28, c similar or equal to 4.53 angstrom, beta similar or equal to 105.4 degrees) is stable. At lower temperatures the lock-in phase alpha 1-Zn2P2O7 [at 350 K: I2/c, Z = 12, a = 20.1131 (13), b = 8.2769 (6), c = 9.109 (3) angstrom, beta = 106.338 (16)degrees], a sixfold superstructure with commensurate modulation vector q = (1/3, 0, 1/2), is stable. Between the stability ranges of the alpha(1)- and beta-phases exists the intermediate, *incommensurately modulated* alpha(2)-Zn2P2O7 phase with modulation wavevector q similar or equal to (0.33, 0, 0.40) and C2/m(alpha, 0, gamma)0s superspace group symmetry. The alpha(1) -> alpha(2) lock-in phase transition at T-L = 408 K is of first-order and features virtually no hysteresis. It is immediately followed by the second-order alpha(2) -> beta transition to the non-modulated phase at T-I similar or equal to 430 K. This transformation is sluggish and even at T = 500 K very weak satellite reflections of the alpha(2)- phase were observed. Both phase transitions were analyzed with differential scanning calorimetry and high-temperature powder and single-crystal X-ray diffraction. The crystal structures of the alpha(1)- and alpha(2)- phases were refined from single crystal data collected at T = 350, 400, 405, 410, 415, 420, 425, 430, 450 and 500 K. Different models describing the slow transition from the *incommensurately modulated* alpha(2)- to the non-modulated beta-phase were tested. In the model resulting in the best residuals, the bridging O atom of the [P2O7] group, which is located on a 2/m position in the basic structure, is described as an overlap of an atom ordered in internal space and one atom disordered around the mirror plane. The occupancy of the ordered atom decreases with temperature until at T = 500 K virtually only the disordered atom remains. Simultaneously, the amplitude of the modulation functions of the remaining atoms decreases, so that the T = 500 K structure can be considered as the C2/m aristotype structure, although the diffraction pattern still features *satellite reflections* of first order with very low intensities.
Title:
Understanding the structure details when drying hydrate crystals of pharmaceuticals - interpretations from diffuse scattering and inter-modulation satellites of a partially dehydrated crystal
Authors:
Chan, EJ; Gao, Q; Dabros, M Author Full Names: Chan, E. J.; Gao, Q.; Dabros, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 555-567; SI 10.1107/S2052520614005125 3 JUN 2014
Abstract:
Simplified models for the crystal lattice of the sesquihydrate form of the hemi-sulfate salt of (5S,6S,9R)-5-amino-6-(2,3-difluorophenyl)-6,7,8,9-tetrahydro-5H-cyclohep ta[b]pyridin9-yl 4-(2-oxo-2,3-dihydro-1H-imidazol[4,5b] pyridin-1-yl)-1-piperidine carboxylate (BMS-927711, C28H29F2N6O3+) are used to calculate diffuse diffraction features in order to develop a mechanistic understanding of the dehydration process with respect to disruption of the lattice, since a Bragg model cannot be established. The model demonstrates that what we observe when the water leaves the crystal is partial transformation from the parent form to a child form (a new form, less hydrated and structurally related to the parent). Yet this 'dried' structure is not a pure phase. It consists of semi-random layers of both child, parent and an interfacial layer which has a modulated structure that represents a transitory phase. Understanding the fact that a single 'dried' crystal can have the disordered layer structure described as well as understanding mechanistic relationships between the phases involved can have implications in understanding the effect of common large scale bulk drying procedures. During the development of BMS-927711, difficulties did arise during characterization of the dried bulk when using only routine solid-state analysis. The material is now better understood from this diffraction study. The diffraction experiments also reveal intermodulation satellites, which upon interpretation yield even more structural information about the crystal transformation. The model suggests the mechanism of transformation is laminar in which layers of the crystal are driven to approach a stable B-centered supercell phase of lower water content.
Title:
Studies on icosahedral Ag-In-Yb: a prototype for Tsai-type quasicrystals
Authors:
Cui, C; Shimoda, M; Tsai, AP Author Full Names: Cui, Can; Shimoda, Masahiko; Tsai, An Pang
Source:
RSC ADVANCES, 4 (87):46907-46921; 10.1039/c4ra07980a 2014
Abstract:
Tsai-type icosahedral quasicrystals (i-QCs) are present in numerous alloy systems. Among them, the icosahedral Ag-In-Yb quasicrystal (i-Ag-In-Yb) is regarded as a prototype for studying various features of QCs, such as crystalline structure and physical properties, due to its good average structural order, good stability both in air and in ultra-high vacuum, amenability to growth of large single grains, and lack of elements with high vapor pressure or toxicity. Here we present a review on recent studies of i-Ag-In-Yb, including studies on bulk structure, crystal growth, physical properties, surface structure and thin film growth on quasicrystalline surface. We believe the results will encourage studies on other QCs.

Update: 29-Oct-2014

Title:
Fusion: a General Framework for Hierarchical Tilings
Authors:
Frank, NP Author Full Names: Frank, N. P.
Source:
ACTA PHYSICA POLONICA A, 126 (2):461-466; AUG 2014
Abstract:
One well studied way to construct quasicrystalline tilings is via inflate-and-subdivide (a.k.a. substitution) rules. These produce self-similar tilings the Penrose, octagonal, and pinwheel tilings are famous examples. We present a different model for generating hierarchical tilings we call "fusion rules". Inflate-and-subdivide rules are a special case of fusion rules, but general fusion rules are more flexible and allow for defects, changes in geometry, and even constrained randomness. A condition that produces homogeneous structures and a method for computing frequency for fusion tiling spaces are discussed.
Title:
Quasicrystal-Polymer Composites for Additive Manufacturing Technology
Authors:
Kenzari, S; Bonina, D; Degiovanni, A; Dubois, JM; Fournee, V Author Full Names: Kenzari, S.; Bonina, D.; Degiovanni, A.; Dubois, J. M.; Fournee, V.
Source:
ACTA PHYSICA POLONICA A, 126 (2):449-452; AUG 2014
Abstract:
We present a new niche application of quasicrystalline powders that leads to a commercially successful development of polymer-matrix composites. The process is based upon selective laser sintering, which is one of the current most powerful additive manufacturing technologies in use in the mechanical industries. Characteristics of the materials produced, such as porosity, friction and wear against hard steel, are evaluated and compared to the state of the art. Insight into the production of metal-matrix composites, using a variant of the technology, is also given.
Title:
Electronic Properties and Complexity of Al-Based Complex Metallic Alloys
Authors:
Dubois, JM; Belin-Ferre, E Author Full Names: Dubois, J. -M.; Belin-Ferre, E.
Source:
ACTA PHYSICA POLONICA A, 126 (2):453-457; AUG 2014
Abstract:
As a consequence of their structural complexity, the electron transport properties of Al-based complex metallic alloys scale as simple power laws of the number of atoms in the primitive unit cell. Furthermore, presence in energy space of localised, d-like states below the Fermi level is systematically observed, even in the absence of any transition metal constituting element. The relative intensity of this contribution to the total density of states correlates with the structural complexity of the compound. Thus, complexity plays a key role, via Hume-Rothery, hybridization effects and most probably hopping, in the selection, formation and stability of Al-based complex metallic alloys. The results are interpreted in terms of self-organized criticality. In order to promote discussion about the essence of the quasicrystalline state ("why are the atoms where they are?"), a speculative model is suggested.
Title:
Hyperbolic Icosahedral Tilings by Buckyballs
Authors:
Luck, R; Frettloh, D Author Full Names: Lueck, R.; Frettloeh, D.
Source:
ACTA PHYSICA POLONICA A, 126 (2):524-526; AUG 2014
Abstract:
Hyperbolic icosabedral filings by Hockyballs with 4 or 8 Buckyballs sharing a vertex are considered as an example of tilings by Archimedean polyhedra. Representation requires Poincare balls; colour symmetry may be derived by GAP. Colour symmetries preserving both rotation and reflection symmetry as well as only rotation symmetry are discussed.
Title:
Leaching Effect on Multiple Surfaces of a Single Grain Decagonal Al-Ni-Co Quasicrystal
Authors:
Lowe, M; Gille, P; McGrath, R; Sharma, HR Author Full Names: Lowe, M.; Gille, P.; McGrath, R.; Sharma, H. R.
Source:
ACTA PHYSICA POLONICA A, 126 (2):520-523; AUG 2014
Abstract:
We have studied the effect of leaching treatments on the surface microstructure and chemical composition on the two different twofold surfaces, (10000) and (10 (1) over bar 00), and the tenfold surface (00001) of a decagonal (d-) Al-Ni-Co quasicrystal. A sample exposing the three surfaces was leached with NaOH solution and then studied using atomic force microscopy and scanning electron microscopy combined with energy dispersive X-ray analysis. The leaching treatment preferentially removes the Al present in the crystal surface leaving a mixture of transition metal and their associated oxides. The high symmetry, tenfold axis was found to be less resistant to leaching than either of the twofold axes, providing further information regarding the effect of crystallographic direction on leaching kinetic.
Title:
Fermi Surface-Brillouin Zone Interactions in 2/1-2/1-2/1 Bergman-Type Approximant Na27Au27Ga31
Authors:
Mizutani, U; Sato, H; Inukai, M; Zijlstra, ES; Lin, Q; Corbett, JD; Miller, GJ Author Full Names: Mizutani, U.; Sato, H.; Inukai, M.; Zijlstra, E. S.; Lin, Q.; Corbett, J. D.; Miller, G. J.
Source:
ACTA PHYSICA POLONICA A, 126 (2):535-538; AUG 2014
Abstract:
The X-ray diffraction studies on a newly synthesized Na26Au25Ga29 single crystal revealed the formation of a single phase 2/1-2/1-2/1 Bergman-type approximant and the presence of Au/Ga mixed occupancies in its unit cell containing 680 atoms. The structure model of the 2/1-2/1-2/1 approximant with composition Na27Au27Ga31 was constructed by eliminating the chemical disorder with a minimum sacrifice of composition displacement. The full potential linearized augmented plane wave electronic structure calculations with subsequent full potential linearized augmented plane wave-Fourier analysis were performed for the 2/1-2/1-2/1 approximant Na27Au27Ga31 with space group Pa (3) over bar. The square of the Fermi diameter (2kF)(2), electrons per atom ratio e/a and the critical reciprocal lattice vector vertical bar G vertical bar(2) are determined. A shallow pseudogap at the Fermi level was interpreted as originating from interference of electrons having (2kF)(2) = 109.2 +/- 1.0 with sets of lattice planes with vertical bar G vertical bar(2)s centered at 108. The effective e/a value for the compound is found to be 1.76 in good agreement with 1.73 derived from a composition average of (e/a)Na = 1.0, (e/a)Au = 1.0 and (e/a)Ga = 3.0.
Title:
Aperiodicity in Equilibrium Systems: Between Order and Disorder
Authors:
van Enter, ACD Author Full Names: van Enter, A. C. D.
Source:
ACTA PHYSICA POLONICA A, 126 (2):621-624; AUG 2014
Abstract:
Spatial aperiodicity occurs in various models and materials. Although today the most well-known examples occur in the area of quasicrystals, other applications might also be of interest. Here we discuss some issues related to the notion and occurrence of aperiodic order in equilibrium statistical mechanics. In particular, we consider some spectral characterisations, and shortly review what is known about the occurrence of aperiodic order in lattice models at zero and nonzero temperatures. At the end some more speculative connections to the theory of (spin-)glasses are indicated.
Title:
Nanoquasicrystalline Phase in Mechanically Alloyed and Heat-Treated Al73Cu11Cr16
Authors:
Sviridova, TA; Shevchukov, AP; Shelekhov, EV; Diakonov, DL; Gorshenkov, MV; Kaloshkin, SD; Tcherdyntsev, VV; Li, Z; Fan, G Author Full Names: Sviridova, T. A.; Shevchukov, A. P.; Shelekhov, E. V.; Diakonov, D. L.; Gorshenkov, M. V.; Kaloshkin, S. D.; Tcherdyntsev, V. V.; Li, Z.; Fan, G.
Source:
ACTA PHYSICA POLONICA A, 126 (2):599-602; AUG 2014
Abstract:
X-ray diffraction analysis, scanning and transmission electron microscopy, thermal analysis and measurement of chemical composition were implemented to determine structure, thermal stability and chemical composition of the decagonal quasicrystal in Al73Cu11Cr16 alloy produced by long-term mechanical alloying of elemental powders followed by annealing at 700 C. According to the TEM investigation such a technique permits to produce a single-phase nanostructural quasicrystal with grain size about 60 nm. Differential thermal analysis revealed that the decagonal phase does not exist above 923 degrees C and undergoes incongruent two-stage melting coming to the end at 1100 degrees C.
Title:
Periodic Series of Peaks in Diffraction Patterns of Aperiodic Structures
Authors:
Wolny, J; Kozakowski, B; Kuczera, P; Pytlik, L; Strzalka, R; Wnek, A Author Full Names: Wolny, J.; Kozakowski, B.; Kuczera, P.; Pytlik, L.; Strzalka, R.; Wnek, A.
Source:
ACTA PHYSICA POLONICA A, 126 (2):625-628; AUG 2014
Abstract:
Quasicrystals are aperiodic structures with no periodicity both in direct and reciprocal space. The diffraction pattern of quasicrystals consists however of the periodic series of peaks in the scattering vector space. The intensities of the peaks of all series reduced in a proper way build up the so-called envelope function common for the whole pattern. The Fourier transformed envelope gives the average unit cell which is the statistical distribution of atomic positions in physical space. The distributions lifted to high dimensions correspond to atomic surfaces - the basic concept of structural quasicrystals modeling within higher-dimensional approach.
Title:
Electronic Structure and Transport in Approximants of the Penrose Tiling
Authors:
de Laissardiere, GT; Szallas, A; Mayou, D Author Full Names: de Laissardiere, G. Trambly; Szallas, A.; Mayou, D.
Source:
ACTA PHYSICA POLONICA A, 126 (2):617-620; AUG 2014
Abstract:
We present numerical calculations of electronic structure and transport in the Penrose approximants. The electronic structure of perfect approximants shows a spiky density of states and a tendency to localization that is more pronounced in the middle of the band. Near the band edges the behavior is more similar to that of free electrons. These calculations of band structure and in particular the band scaling suggest an anomalous quantum diffusion when compared to normal ballistic crystals. This is confirmed by a numerical calculation of quantum diffusion which shows a crossover from normal ballistic propagation at long times to anomalous, possibly insulator-like, behavior at short times. The time scale t* (E) for this crossover is computed for several approximants and is detailed. The consequences for electronic conductivity are discussed in the context of the relaxation time approximation. The metallic-like or non-metallic-like behavior of the conductivity is dictated by the comparison between the scattering time due to defects and the time scale t* (E).
Title:
Characterization of Rapidly Solidified Al65Cu20Fe15 Alloy in Form of Powder or Ribbon
Authors:
Litynska-Dobrzynska, L; Dutkiewicz, J; Stan-Glowinska, K; Dembinski, L; Coddet, C; Ochin, P Author Full Names: Litynska-Dobrzynska, L.; Dutkiewicz, J.; Stan-Glowinska, K.; Dembinski, L.; Coddet, C.; Ochin, P.
Source:
ACTA PHYSICA POLONICA A, 126 (2):512-515; AUG 2014
Abstract:
The Al65Cu20Fe15 alloy has been prepared by conventional casting to the mould and by melt spinning or atomisation techniques. The melt spun ribbon was in the form of fragmented, brittle flakes, atomized powder has spherical shape with average size 17.2 mu m. It was found that icosahedral I-phase was the main phase in all types of prepared samples. In the conventionally cast alloy the following phases have been identified additionally: lambda-Al13Fe4, tau-AlCu(Fe) and eta(2)-AlCu. In the melt-spun ribbon the formation of eta(2) is avoided, while in the atomised powder the I-phase coexists with small amount of copper rich tau-phase. In the cast ingot the I-phase form as a product of peritectic reaction lambda + L, while in the ribbon and in the powder quasicrystal solidified from the undercooled melt as primary phase and next metastable cubic tau-AlCu(Fe) was formed at the interdendritic areas. Single I-phase grains of the sizes about 1 mu m are observed in the ribbon close to the wheel side.
Title:
N-H center dot center dot center dot O and C-H center dot center dot center dot F hydrogen bonds in the incommensurately modulated crystal structure of adamantan-1-ammonium 4-fluorobenzoate
Authors:
Schonleber, A; van Smaalen, S; Weiss, HC; Kesel, AJ Author Full Names: Schoenleber, Andreas; van Smaalen, Sander; Weiss, Hans-Christoph; Kesel, Andreas J.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 652-659; 10.1107/S2052520614007707 4 AUG 2014
Abstract:
At low temperatures the organic salt adamantan-1-ammonium 4-fluorobenzoate, C10H18N+center dot C7H4FO2-, possesses an incommensurately modulated crystal structure. The effect of the modulation on the atomic arrangement and intermolecular interactions is studied by analysing single-crystal X-ray diffraction data within the (3 + 1)-dimensional superspace approach and superspace group P2(1)/n(alpha 0 gamma)00. The modulation strongly affects the position of the atoms as well as their atomic displacement parameters. Nevertheless, the molecular cations and anions are built by rigid moieties, which vary their orientation with respect to each other as a function of the phase of the modulation t. Cations and anions are connected into slabs by dense N-H center dot center dot center dot O and C-H center dot center dot center dot F hydrogen-bonded networks, which are characterized by being rather rigid and which show only a little variation as a function of the phase of the modulation t.
Title:
Formation of the Icosahedral Al-Cu-Fe Phase by Solid State Reaction
Authors:
Shulyatev, DA; Nigmatulin, AS; Chernikov, MA; Klyueva, MV; Shaitura, DS; Golovkova, EA Author Full Names: Shulyatev, D. A.; Nigmatulin, A. S.; Chernikov, M. A.; Klyueva, M. V.; Shaitura, D. S.; Golovkova, E. A.
Source:
ACTA PHYSICA POLONICA A, 126 (2):581-584; AUG 2014
Abstract:
Al-Cu-Fe alloys with a nominal composition of Al63Cu24Fe13, Al62Cu25.5Fe12.5 and Al65Cu20Fe15 have been fabricated by solid-state reaction at 550, 650, and 750 degrees C. The synthesized alloys mainly consist of icosahedral Al65Cu20Fe15, body-centered cubic beta-AlFe(Cu) and monoclinic lambda-Al13Fe4 phases. After synthesis under optimal conditions the fraction of the icosahedral phase was 100, 80, and 85 weight per cent in Al63Cu24Fe13, Al62Cu25.5Fe12.5, and Al65Cu20Fe15, respectively.
Title:
Inhomogeneous Electronic Localization in Icosahedral Quasicrystals
Authors:
Prekul, A; Schegolikhina, N; Shalaeva, E Author Full Names: Prekul, A.; Schegolikhina, N.; Shalaeva, E.
Source:
ACTA PHYSICA POLONICA A, 126 (2):556-559; AUG 2014
Abstract:
Experimental results indicating that the electronic inhomogeneity may be a fundamental property of icosahedral quasicrystals and their approximants are presented.
Title:
Direct and Reciprocal Space Properties of the Generalized Penrose Tiling
Authors:
Chodyn, M; Kuczera, P; Wolny, J Author Full Names: Chodyn, M.; Kuczera, P.; Wolny, J.
Source:
ACTA PHYSICA POLONICA A, 126 (2):442-445; AUG 2014
Abstract:
We have constructed a generalized Penrose tiling by the cut-and-project method and compared its structure with that of the regular Penrose tiling. We derived the structure factor of the generalized Penrose tiling and applied it to calculate the diffraction pattern of a non-decorated structure.
Title:
Development of Composites with Icosahedral Phase in Al-Cu-Fe Quasicrystalline Alloys Obtained by the Bridgman Method
Authors:
Krawczyk, J Author Full Names: Krawczyk, J.
Source:
ACTA PHYSICA POLONICA A, 126 (2):501-504; AUG 2014
Abstract:
The composites were obtained by the Bridgman method through solidification of Al61Cu27Fe12 alloy (numbers indicate at.%). The microstructure of composites with crystal matrix and quasicrystal reinforcement was studied. The crystalline beta-phase was the matrix and the quasicrystaline i-phase was the reinforcement of obtained composites. The shape and spatial distribution of reinforcement fibres were specified. Some geometrical relations of the fibres arrangement were defined. Obtained composite samples were subjected to X-ray phase analysis, optical, and scanning electron microscopy observations, chemical microanalysis and the Laue diffraction.
Title:
Structure of decagonal Al-Ni-Rh
Authors:
Logvinovich, D; Simonov, A; Steurer, W Author Full Names: Logvinovich, Dmitry; Simonov, Arkadiy; Steurer, Walter
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 732-742; 10.1107/S2052520614010750 4 AUG 2014
Abstract:
The crystal structure of the decagonal phase in the system Al-Ni-Rh (d-Al-Ni-Rh) was analyzed in the five-dimensional embedding approach based on single-crystal synchrotron X-ray diffraction data. The structure can be described as a quasiperiodic packing of partially overlapping decagonal and pentagonal columnar clusters with similar to 21 angstrom diameter and similar to 4 angstrom period along the tenfold axis.
Title:
Evolution of the beta Phase Flux Dissolution during Quasicrystal Formation
Authors:
Surowiec, M; Bogdanowicz, W; Sozanska, M Author Full Names: Surowiec, M.; Bogdanowicz, W.; Sozanska, M.
Source:
ACTA PHYSICA POLONICA A, 126 (2):594-596; AUG 2014
Abstract:
This study focuses mainly on the verification of a peritectic reaction during the crystallization of quasicrystals. The beta and lambda phases apparently provide the necessary material for crystallization of the quasicrystalline psi phase. We present results of an experimental visualization of the evolution of the flux dissolution process of the high temperature beta phase. Solidified droplets of the beta phase, formed primarily by the surface tension of the liquid within a bubble or a shrinkage, after crumbling during the flux dissolution may contribute to the quasicrystal formation process according to a peritectic reaction: beta(c) + lambda + L ->psi where beta(c) denotes the crumbled beta phase immersed in the liquid.
Title:
Compositions of Al-Based Quasicrystals Interpreted by Cluster Formulae
Authors:
Chen, H; Qiang, JB; Wang, YM; Dong, C Author Full Names: Chen, H.; Qiang, J. B.; Wang, Y. M.; Dong, C.
Source:
ACTA PHYSICA POLONICA A, 126 (2):446-448; AUG 2014
Abstract:
It is known previously that bulk metallic glass compositions satisfy cluster formulae [cluster](glue atom)(1,3) of 24 valence electrons as deduced from our cluster-resonance model. In the present work, it is further shown that compositions of Al-based binary and ternary quasicrystals are also explained by 24-electron cluster formulae of the types [icosahedron](glue atom)(0,1), where the icosahedral cluster is identified from a corresponding crystalline approximant according to dense atomic packing and cluster isolation criteria, and the glue atom site is either vacant for an icosahedral quasicrystal or equal to one for a decagonal quasicrystal. Ternary quasicrystals are formulated with the same formulae as their basic binary ones but the icosahedron shell sites are substituted by third elements. The 24-electron cluster formulae are then the chemical and electronic structural units of quasicrystals, mimicking the molecular formulae of chemical substances.
Title:
An Icosahedral Quasicrystal as a Packing of Regular Tetrahedra
Authors:
Fang, F; Kovacs, J; Sadler, G; Irwin, K Author Full Names: Fang, F.; Kovacs, J.; Sadler, G.; Irwin, K.
Source:
ACTA PHYSICA POLONICA A, 126 (2):458-460; AUG 2014
Abstract:
We present the construction of a dense, quasicrystalline packing of regular tetrahedra with icosahedral symmetry. This quasicrystalline packing was achieved through two independent approaches. The first approach originates in the Elser Sloane 4D quasicrystal. A 3D slice of the quasicrystal contains a few types of prototiles. An initial structure is obtained by decorating these prototiles with tetrahedra. This initial structure is then modified using the Elser Sloane quasicrystal itself as a guide. The second approach proceeds by decorating the prolate and oblate rhombohedra in a 3-dimensional Ammann tiling. The resulting quasicrystal has a packing density of 59.783%. We also show a variant of the quasicrystal that has just 10 "plane classes" (compared with the 190 of the original), defined as the total number of distinct orientations of the planes in which the faces of the tetrahedra are contained. This small number of plane classes was achieved by a certain "golden rotation" of the tetrahedra.
Title:
Transport Properties of the Au-Al-Yb Quasicrystal and Approximant under Hydrostatic Pressure
Authors:
Matsukawa, S; Tanaka, K; Nakayama, M; Kunikata, S; Deguchi, K; Imura, K; Ishimasa, T; Sato, NK Author Full Names: Matsukawa, S.; Tanaka, K.; Nakayama, M.; Kunikata, S.; Deguchi, K.; Imura, K.; Ishimasa, T.; Sato, N. K.
Source:
ACTA PHYSICA POLONICA A, 126 (2):527-530; AUG 2014
Abstract:
The mixed-valence Au-Al-Yb quasicrystal exhibits unusual quantum criticality. Its crystalline approximant behaves like a conventional heavy fermion metal. Due to these novel features, they have attracted much attention recently. To examine the sample dependence of this new type of materials, we have prepared several samples and measured the electrical resistivity both at ambient and high pressures as well as the magnetic susceptibility at ambient pressure. The residual resistivity ratio of the quasicrystals is almost sample independent while the power law exponent n of the electrical resistivity varies from sample to sample. The effective magnetic moment p(eff) of the quasicrystals is also sample dependent, ranging from about 3.4 to 3.9 mu(B)/Yb, and these values are all smaller than the free Yb3+ ion value, confirming the mixed-valence nature. Although the magnitude of n and p(eff) is sample-dependent, the principal feature of the mixed-valence is confirmed in all the samples studied thus far. A combination of these results indicates correlation between n and p(eff) suggesting that the 4f electrons may contribute to a scattering mechanism of the conduction electrons. External pressure increases the magnitude of the electrical resistivity and decreases the index n of both the quasicrystal and the approximant. Up to the highest pressure measured in the present study no experimental evidence for a phase transition was found.
Title:
Topology of the Random Fibonacci Tiling Space
Authors:
Gahler, F; Miro, E Author Full Names: Gaehler, F.; Miro, E.
Source:
ACTA PHYSICA POLONICA A, 126 (2):564-567; AUG 2014
Abstract:
We look at the topology of the tiling space of locally random Fibonacci substitution, which is defined as a -> ba with probability p, a -> ab with probability 1-p and b -> a for 0 < p < 1. We show that its Cech cohomology group is not finitely generated, in contrast to the case where random substitutions are applied globally.
Title:
Coincidences of a Shifted Hexagonal Lattice and the Hexagonal Packing
Authors:
Arias, JCH; Gabinete, ED; Loquias, MJC Author Full Names: Arias, J. C. H.; Gabinete, E. D.; Loquias, M. J. C.
Source:
ACTA PHYSICA POLONICA A, 126 (2):516-519; AUG 2014
Abstract:
A geometric study of twin and grain boundaries in crystals and quasicrystals is achieved via coincidence site lattices and coincidence site modules, respectively. Recently, coincidences of shifted lattices and multilattices (i.e. finite unions of shifted copies of a lattice) have been investigated. Here, we solve the coincidence problem for a shifted hexagonal lattice. This result allows us to analyze the coincidence isometrics of the hexagonal packing by viewing the hexagonal packing as a multilattice.
Title:
From Colorings to Weavings
Authors:
Miro, E; Garciano, A; Zambrano, A Author Full Names: Miro, E.; Garciano, A.; Zambrano, A.
Source:
ACTA PHYSICA POLONICA A, 126 (2):560-563; AUG 2014
Abstract:
We present a methodology for constructing weavings from 2-colorings of the plane. In particular, we consider tilings T of the plane by triangles and their corresponding triangle groups G. We derive 2-colorings of T using the index 2 subgroups of G.
Title:
Structure Model for Icosahedral Quasicrystal Based on Ammann Tiling
Authors:
Strzalka, R; Wolny, J Author Full Names: Strzalka, R.; Wolny, J.
Source:
ACTA PHYSICA POLONICA A, 126 (2):585-587; AUG 2014
Abstract:
We derive a structure model for icosahedral quasicrystals. The model is based on a statistical approach involving the concept of average unit cell. This approach enables limiting calculations to real space as opposed to higher-dimensional analysis involving to unphysical atomic surface modeling. We start with the three-dimensional Ammann tiling with its two rhombohedral prototiles. For monoatomic decoration of the lattice nodes the perfect agreement with the higher-dimensional description was recently shown. In this paper we discuss the shape of the average unit cell and the first attempts for decoration scheme.
Title:
RKKY Interactions and Low-Temperature Behaviour of Spins in Quasiperiodic Tilings
Authors:
Thiem, S Author Full Names: Thiem, S.
Source:
ACTA PHYSICA POLONICA A, 126 (2):613-616; AUG 2014
Abstract:
We study the structure of the Ruderman Kittel Kasuya Yosida interactions for selected quasiperiodic tilings. The interaction energies between the magnetic impurities in these systems are computed by a continued fraction expansion for the Green function of the conduction electrons. Based on these results we study the alignment of the magnetic moments in the Ammann Beenker tiling by Monte Carlo simulations. In particular, we are interested in the structure of the magnetic ground state and the low-temperature behaviour for the Ising model.
Title:
Proceedings of the 12th International Conference on Quasicrystals (ICQ12) Krakow, Poland, September 1-6, 2013 Preface
Authors:
Wolny, J; Surowiec, M Author Full Names: Wolny, Janusz; Surowiec, Marian
Source:
ACTA PHYSICA POLONICA A, 126 (2):429-429; AUG 2014
Title:
Tight-Binding Models in a Quasiperiodic Optical Lattice
Authors:
Jagannathan, A; Duneau, M Author Full Names: Jagannathan, A.; Duneau, M.
Source:
ACTA PHYSICA POLONICA A, 126 (2):490-492; AUG 2014
Abstract:
This paper describes how one can use four standing wave laser fields to realize a two dimensional optical quasicrystal with eight-fold symmetry, closely related to the well-known octagonal or Ammann-Beenker tiling quasicrystal. We describe the structure and we outline the main features of an effective tight-binding model for atoms in this optical quasicrystal. Such a system, if realized experimentally, should provide valuable insights into the quantum properties of quasicrystals.
Title:
Recent Progress in Mathematical Diffraction
Authors:
Grimm, U; Baake, M Author Full Names: Grimm, U.; Baake, M.
Source:
ACTA PHYSICA POLONICA A, 126 (2):474-478; AUG 2014
Abstract:
A brief summary of recent developments in mathematical diffraction theory is given. Particular emphasis is placed on systems with aperiodic order and continuous spectral components. We restrict ourselves to some key results and refer to the literature for further details.
Title:
Tiling Vertices and the Spacing Distribution of Their Radial Projection
Authors:
Jakobi, T Author Full Names: Jakobi, T.
Source:
ACTA PHYSICA POLONICA A, 126 (2):493-496; AUG 2014
Abstract:
The Fourier-based diffraction approach is an established method to extract order and symmetry properties from a given point set. We want to investigate a different method for planar sets which works in direct space and relies on reduction of the point set information to its angular component relative to a chosen reference frame. The object of interest is the distribution of the spacings of these angular components, which can for instance be encoded as a density function on R+. In fact, this radial projection method is not entirely new, and the most natural choice of a point set, the integer lattice Z(2), is already well understood. We focus on the radial projection of aperiodic point sets and study the relation between the resulting distribution and properties of the underlying tiling, like symmetry, order and the algebraic type of the inflation multiplier.
Title:
F-AlCoPdGe Alloy with Three Types of Pseudo-Mackay Clusters
Authors:
Sugiyama, K; Yubuta, K; Yokoyama, Y; Suzuki, S; Simura, R Author Full Names: Sugiyama, K.; Yubuta, K.; Yokoyama, Y.; Suzuki, S.; Simura, R.
Source:
ACTA PHYSICA POLONICA A, 126 (2):588-593; AUG 2014
Abstract:
The structure of an F-AlCoPdGe alloy was determined by single-crystal X-ray diffraction analysis: space group Pa (3) over bar (No. 205), Pearson symbol cP1128-142.4, a = 24.4338(4) angstrom; R1 = 0.0526 for the observed 5106 reflections with Fo > 4.0 sigma(F-0). The F-AlCoPdGe alloy exhibited three types of pseudo-Mackay clusters (pMCs). The first shell of the Co(13)-pMC at 24d indicated a coordination polyhedron typically found in Al Co binary approximants; the second shell was a combination of an M icosahedron and an Al icosidodecahedron, where M is a mixed site of Pd and/or Co. The first shell of the Co(14)-pMC at 4b consisted of 20 partially occupied Al positions arranged in a dodecahedral fashion; its second shell was also composed of an M icosahedron and an Al icosidodecahedron. The first shell of the Al(18)-pMC at 4a consisted of a combination of an M cube and an Al octahedron, resulting in the rhombic dodecahedral arrangement; its outer shell structure was similar to those of the other pMCs. The structure of the F-AlCoPdGe phase comprised an arrangement of these three types of pMCs together with interstitially placed Al icosahedra around the Pd/Al(1) and Pd/Al(2) sites.
Title:
Phason Contribution to the Dislocation Loop Bias in Quasicrystals
Authors:
Lavrova, GN; Turkin, AA; Bakai, AS Author Full Names: Lavrova, G. N.; Turkin, A. A.; Bakai, A. S.
Source:
ACTA PHYSICA POLONICA A, 126 (2):505-507; AUG 2014
Abstract:
We develop a model of the absorption of vacancies and self-interstitial atoms by dislocation loops and associated phason defects in quasicrystals under irradiation. The capture efficiency and the bias of the loop for radiation point defects are evaluated for variable loop sizes. Numerical calculation of these quantities is performed for comparison. It is shown that phason defects decrease the total bias of the dislocation loop in a quasicrystal.
Title:
Surface Decorations of Al-Cu-Fe and Al-Cu-Co Single Quasicrystals
Authors:
Surowiec, M; Bogdanowicz, W; Krawczyk, J; Sozanska, M Author Full Names: Surowiec, M.; Bogdanowicz, W.; Krawczyk, J.; Sozanska, M.
Source:
ACTA PHYSICA POLONICA A, 126 (2):597-598; AUG 2014
Abstract:
We studied surface decorations of faceted icosahechal Al-Cu-Fe and decagonal Al-Cu-Co single quasicrystals by the scanning electron microscopy using primary and secondary electrons. Both types of single quasicrystals exhibited decorations on their facets, however the character of the decorations was totally different. Three kinds of decorations has been developed. On icosahech-al Al60Cu26Fe14 quasicrystals we found three kinds of decorations: cellular, cavity type and fractal-like. There was no evident difference in chemical composition between the inner dodecahedra and the decorations of all types. Surface decorations found on decagonal Al73.5Cu17.5Co9 quasicrystals formed a kind of irregular dench-itic stars on the separate bright islands.
Title:
The Structure of the (100) Surface of Ag-In-Gd 1/1 Approximant
Authors:
Hars, SS; Sharma, HR; Smerdon, JA; Yadav, TP; Tamura, R; Shimoda, M; McGrath, R Author Full Names: Hars, S. S.; Sharma, H. R.; Smerdon, J. A.; Yadav, T. P.; Tamura, R.; Shimoda, M.; McGrath, R.
Source:
ACTA PHYSICA POLONICA A, 126 (2):479-481; AUG 2014
Abstract:
Scanning tunneling microscopy is employed to characterise the structure and morphology of the (100) surface of the Ag-In-Gd 1/1 approximant. The surface prepared by the usual method of sputter-annealing produces stepterrace structure. Observed step heights are consistent with the lattice constant of the bulk. Scanning tunneling microscopy on terraces reveals cluster-like protrusions arranged with a square unit cell as expected from the bulk. It has not been possible to assign the terraces to the specific bulk planes because of lack of atomic resolution on terraces.
Title:
Quotient Cohomology of Certain 1-and 2-Dimensional Substitution Tiling Spaces
Authors:
Bugarin, EP; Gahler, F Author Full Names: Bugarin, E. P.; Gaehler, F.
Source:
ACTA PHYSICA POLONICA A, 126 (2):438-441; AUG 2014
Abstract:
The quotient cohomology of tiling spaces is a topological invariant that relates a tiling space to one of its factors, viewed as topological dynamical systems. In particular, it is a relative version of the tiling cohomology that distinguishes factors of tiling spaces. In this work, the quotient cohomologies within certain families of substitution tiling spaces in 1 and 2 dimensions are determined. Specifically, the quotient cohomologies for the family of the generalised Thue Morse sequences and generalised chair tilings are presented.
Title:
Incommensurate modulations of relaxor ferroelectric Ca0.24Ba0.76Nb2O6 (CBN24) and Ca0.31Ba0.69Nb2O6 (CBN31)
Authors:
Graetsch, HA; Pandey, CS; Schreuer, J; Burianek, M; Muhlberg, M Author Full Names: Graetsch, Heribert A.; Pandey, Chandra Shehkar; Schreuer, Juergen; Burianek, Manfred; Muehlberg, Manfred
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 743-749; 10.1107/S2052520614011676 4 AUG 2014
Abstract:
CBN crystals show a one- and a two-dimensionally modulated modification. The former is isotypic with orthorhombic Ba4Na2Nb10O30 and the latter with the tetragonal tungsten bronze type of crystal structure. The orthorhombic form irreversibly transforms to the tetragonal polymorph at the ferroelectric phase transition near 603 K. Orthorhombic and tetragonal CBN24 slightly differ in the distribution of the Ba and Ca atoms over the incompletely filled Me1 and Me2 sites. The tetragonal symmetry is further broken in orthorhombic CBN24 by different amplitudes of the positional modulations of O atoms which are symmetrically equivalent in the TTB structure. A similar orthorhombic phase of CBN31 could be obtained by quenching from 1473 K.
Title:
Magnetic Properties of Icosahedral (Au,Cu)-Al-Yb Quasicrystals
Authors:
Oki, S; Hiroto, T; Muro, Y; Tamura, R Author Full Names: Oki, S.; Hiroto, T.; Muro, Y.; Tamura, R.
Source:
ACTA PHYSICA POLONICA A, 126 (2):553-555; AUG 2014
Abstract:
We have synthesized Cu-substituted (Au,Cu) Al Yb quasicrystals in order to investigate the relationship between the quasilattice constant and the magnetic property. The quasilattice constant a R is found to decrease as Au is replaced by Cu, and the maximum reduction of 2.18% in aR was observed for x = 0.60 in (Au1-xCux)(49)Al34Yb17. Magnetic measurements of (Au1-xCux)(49)Al34Yb17 (x = 0, 0.10, 0.20, 0.50) show that the intermediate-valence state of Yb persists in all the studied compositions. The effective magnetic moment is found to depend on (r) over bar /a(R) rather than on the quasilattice constant a(R). This suggests that f/ari can be regarded as a measure of the chemical pressure induced on the Yb atoms.
Title:
Electric-Elastic Field Induced by a Straight Dislocation in One-Dimensional Quasicrystals
Authors:
Yang, LZ; Gao, Y; Pan, E; Waksmanski, N Author Full Names: Yang, L. -Z.; Gao, Y.; Pan, E.; Waksmanski, N.
Source:
ACTA PHYSICA POLONICA A, 126 (2):467-470; AUG 2014
Abstract:
By using the generalized Stroh formalism, the electric-elastic field induced by a straight dislocation parallel to a periodic axis of a one-dimensional quasicrystal is obtained. The derivation is concise and the solution is in an exact closed form. As an illustration, the electric-elastic fields around a straight dislocation in a one-dimensional hexagonal quasicrystal are studied. Besides the interesting numerical results presented, the generalized Stroh formalism can be applied to more complicated dislocation problems in quasicrystals.
Title:
Tsai-Type Quasicrystal and Its Approximant in Au-Al-Tm Alloys
Authors:
Tanaka, K; Tanaka, Y; Ishimasa, T; Nakayama, M; Matsukawa, S; Deguchi, K; Sato, NK Author Full Names: Tanaka, K.; Tanaka, Y.; Ishimasa, T.; Nakayama, M.; Matsukawa, S.; Deguchi, K.; Sato, N. K.
Source:
ACTA PHYSICA POLONICA A, 126 (2):603-607; AUG 2014
Abstract:
A P-type icosahedral quasicrystal with a six-dimensional lattice parameter a(6D) = 7.411 angstrom is formed as an equilibrium phase in Au-Al-Tm alloy, of which composition was analyzed to be Au(46)AL(38)Tm(16) by electron probe microanalysis. This quasicrystal is observed as a predominant phase in both as-cast and Au49Al34Tm17 alloys annealed at 910 degrees C, and as one of main phases in the alloy slowly cooled from 1020 degrees C. A 1/1 approximant, Au48Al38Tm14, is also formed near the composition of the quasicrystal. This is a body-centered cubic structure (space group: /m(3)) with a lattice parameter a = 14.458 angstrom that is an isostructure to the recently reported 1/1 Tsai-type approximant in Au-Al-Yb. This approximant is characterized by disorderly arranged four Au-Al atoms centered at the Tsai-type cluster, presence of atoms at 8c site, and chemical ordering of Au and Al at sites forming a partial triacontahedron.
Title:
Temperature Dependence of Ag Film Roughening during Deposition on Quasicrystal and Approximant Surfaces
Authors:
Unal, B; Evans, JW; Thiel, PA Author Full Names: Uenal, B.; Evans, J. W.; Thiel, P. A.
Source:
ACTA PHYSICA POLONICA A, 126 (2):608-612; AUG 2014
Abstract:
The temperature (T) dependence of roughening as assessed by scanning tunneling microscopy is compared for growth of Ag films on an 5-fold icosahedral Al-Pd-Mn quasicrystal surface and on an xi'-approximant. Growth on the quasicrystal corresponds to a version of the Volmer Weber growth, but modified by quantum size effects, and also by kinetic smoothening at low T and low coverages (theta). Growth on the approximant corresponds to a version of the Stranski Krastanov growth modified by kinetic roughening at low T and low theta. For larger theta, i.e., for thicker films, distinct behavior is observed.
Title:
Colloidal Trajectories in Two-Dimensional Light-Induced Quasicrystals with 14-Fold Symmetry due to Phasonic Drifts
Authors:
Martinsons, M; Sandbrink, M; Schmiedeberg, M Author Full Names: Martinsons, M.; Sandbrink, M.; Schmiedeberg, M.
Source:
ACTA PHYSICA POLONICA A, 126 (2):568-571; AUG 2014
Abstract:
Quasicrystals are structures that are not periodic but possess a long range positional order. They can have any rotational symmetry including those that are forbidden in periodic crystals. The symmetry is classified by the point group and the rank D. In quasicrystals, phasons as additional hydrodynamic modes cause correlated rearrangements of the particles. The number of phasonic degrees of freedom depends on the rank. For colloidal quasicrystals that are induced by laser fields, specific phasonic displacements can be realized by changing the phases of the laser beams in a well-determined way. The arising trajectories of colloids in two-dimensional light-induced colloidal quasicrystals with rank D = 4 have already been analyzed in detail. Here, we analyze the colloidal trajectories in two-dimensional quasicrystals with 14-fold symmetry having rank D = 6. We observe complex paths of the colloids consisting of straight and winding lines as well as jumps.
Title:
Structure of an Al-Fe-Ni Decagonal Quasicrystal Studied by Cs-Corrected STEM
Authors:
Yasuhara, A; Yamamoto, K; Yubuta, K; Hiraga, K Author Full Names: Yasuhara, A.; Yamamoto, K.; Yubuta, K.; Hiraga, K.
Source:
ACTA PHYSICA POLONICA A, 126 (2):637-640; AUG 2014
Abstract:
The structure of an Al-Fe-Ni decagonal quasicrystal with two quasiperiodic planes along the periodic axis in an Al72Ni24Fe4 alloy has been examined by spherical aberration (Cs)-corrected scanning transmission electron microscopy with high-angle annular dark-field and annular bright-field techniques. The transition-metal atoms and mixed sites (MSs) of Al and transition-metal atoms are represented as separated bright dots in the observed high-angle annular dark-field scanning transmission electron microscopy images, and consequently the arrangements of transition-metal atoms and mixed sites on the two quasiperiodic planes can be directly determined. The transition-metal atoms are arranged on a pentagonal tiling of an edge-length of 0.76 nm. The close examination of observed annular bright-field- and high-angle annular dark-field scanning transmission electron microscopy images indicates the existence of large decagonal columnar clusters with 3.2 nm diameter, and their arrangement on pentagonal, thin rhombic and squashed hexagonal tiles with an edge-length of 3.2 nm. The arrangements of transition-metal atoms in these three tiles are placed on an ideal pentagonal tiling with an edge-length of 3.2 nm, which is generated by the projection of a five-dimensional hyper-cubic lattice. The vertices are denoted by 5D hyper-cubic indices and then they are projected on the occupation domains in perpendicular space. The arrangement of Al atoms as well as transition-metal atoms and mixed sites in the large decagonal atom cluster with about 3.2 nm diameter is interpreted from the observed high-angle annular dark-field- and annular bright-field scanning transmission electron microscopy ABF-STEM images.
Title:
Tiling Spaces of Taylor-Socolar Tilings
Authors:
Lee, JY Author Full Names: Lee, J. -Y.
Source:
ACTA PHYSICA POLONICA A, 126 (2):508-511; AUG 2014
Abstract:
The Taylor Socolar tiling has been introduced as an aperiodic mono-tile tiling. We consider a tiling space which consists of all the tilings that are locally indistinguishable from a Taylor-Socolar tiling and study its structure. It turns out that there is a bijective map between the space of the Taylor-Socolax tilings and a compact Abelian group of a Q-adic space ((Q) over bar) except at a dense set of points of measure 0 in ((Q) over bar). From this we can derive that the Taylor Socolar tilings have quasicrystalline structures. We make a parity tiling from the Taylor Socolar tiling identifying all the rotated versions of a tile in the Taylor-Socolax tiling by white tiles and all the reflected versions of the tile by gray tiles. It turns out that the Taylor-Socolax tiling is mutually locally derivable from this parity tiling.
Title:
Aperiodic crystals and superspace concepts
Authors:
Janssen, T; Janner, A Author Full Names: Janssen, T.; Janner, A.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 617-651; 10.1107/S2052520614014917 4 AUG 2014
Abstract:
For several decades the lattice periodicity of crystals, as shown by Laue, was considered to be their essential property. In the early sixties of the last century compounds were found which for many reasons should be called crystals, but were not lattice periodic. This opened the field of aperiodic crystals. An overview of this development is given. Many materials of this kind were found, sometimes with very interesting properties. In the beginning the development was slow, but the number of structures of this type increased enormously. In the meantime hundreds of scientists have contributed to this field using a multi-disciplinary approach.
Title:
Finite Element Method for Static Problems of Cubic Quasicrystals
Authors:
Yang, LZ; He, FM; Gao, Y Author Full Names: Yang, L. -Z.; He, F. -M.; Gao, Y.
Source:
ACTA PHYSICA POLONICA A, 126 (2):471-473; AUG 2014
Title:
Curie Temperature and Density of States at the Fermi Level for Al-Cu-Fe Phases: beta-Solid State
Authors:
Shalaeva, EV; Prekul, AF; Shchegolikhina, NI; Medvedeva, NI Author Full Names: Shalaeva, E. V.; Prekul, A. F.; Shchegolikhina, N. I.; Medvedeva, N. I.
Source:
ACTA PHYSICA POLONICA A, 126 (2):572-576; AUG 2014
Abstract:
A consistent reduction in the absolute value of the negative paramagnetic Curie temperature was found in a series of Al-Cu-Fe phases: beta(CsCl)- solid state solution, noncanonical approximant (eta-AlCu(Fe) phase), rational approximants (P1+P2-pentagonal phases) and icosahechal quasicrystal. For these Al-Cu-Fe phases, the decrease in the Curie temperature correlates with a reduction of the density of states at the Fermi level which was estimated from the low-temperature heat capacity measurements and first-principles calculations. The observed correlation was related to the antiferromagnetic indirect exchange interaction (Ruderman Kittel Kasuya Yosida interaction) between the localized magnetic moments on Fe induced by the intrinsic structural defects in the Al-Cu-Fe phases. The weakening of Fe 3d-Al s,p hybridization owing to the intrinsic structural defects such as vacancies, antisite defects and distortions of coordination polyhedrons is suggested to be the main mechanism of appearance of localized magnetic moments on Fe atoms.
Title:
Shape Limit in Triangular Spiral Tilings
Authors:
Sushida, T; Hizume, A; Yamagishi, Y Author Full Names: Sushida, T.; Hizume, A.; Yamagishi, Y.
Source:
ACTA PHYSICA POLONICA A, 126 (2):633-636; AUG 2014
Abstract:
Phyllotaxis is the study of arrangements of leafs and florets. The topology of triangular spiral (multiple) tilings with opposed parastichy pairs is intimately related to the phyllotaxis theory and continued fractions. It is shown that, if the divergence angle of the genetic spiral is given as a quadratic irrational and fixed, then the limit set of the shape parameters of triangular tiles, as the parastichy numbers tend to infinity, is a finite set. In particular, the limit is the golden section if the divergence angle is 'ultimately golden'.
Title:
Inverse Hall Petch Like Mechanical Behaviour in Nanophase Al-Cu-Fe Quasicrystals: A New Phenomenon
Authors:
Mukhopadhyay, NK; Ali, F; Scudino, S; Khoshkhoo, MS; Stoica, M; Srivastava, VC; Uhlenwinkel, V; Vaughan, G; Suryanarayana, C; Eckert, J Author Full Names: Mukhopadhyay, N. K.; Ali, F.; Scudino, S.; Khoshkhoo, M. Samadi; Stoica, M.; Srivastava, V. C.; Uhlenwinkel, V.; Vaughan, G.; Suryanarayana, C.; Eckert, J.
Source:
ACTA PHYSICA POLONICA A, 126 (2):543-548; AUG 2014
Abstract:
The structural and mechanical stability of quasicrystals are important issues due to their potential for possible applications at high temperatures and stresses. The aim of the present work is, therefore, to review the earlier works on conventional crystalline and quasicrystalline materials and also to report the results and the analysis on the Hall Petch and inverse Hall Petch like behavior of nanoquasicrystalline Al62.5Cu25Fe12.5 alloys. It was observed that, at large grain sizes, the hardness increases with decreasing grain size, exhibiting the conventional Hall Petch relationship, whereas for smaller grains, inverse Hall Petch behavior was identified. The inverse Hall Fetch behavior in the nanoquasicrystalline phase could be attributed to thermally activated shearing of the grain boundaries, leading to grain boundary sliding in nanostructures of quasicrystalline grains. These results were analyzed based on the dislocation pile-up model as well as the grain boundary shearing models applicable to nanomaterials.
Title:
Leaching of Al-Based Polygrain Quasicrystalline and Related Crystalline Surfaces
Authors:
Yadav, TP; Mishra, SS; Pandey, SK; Singh, D; Lowe, M; Tamura, R; Mukhopadhyay, NK; Srivastava, ON; McGrath, R; Sharma, HR Author Full Names: Yadav, T. P.; Mishra, S. S.; Pandey, S. K.; Singh, D.; Lowe, M.; Tamura, R.; Mukhopadhyay, N. K.; Srivastava, O. N.; McGrath, R.; Sharma, H. R.
Source:
ACTA PHYSICA POLONICA A, 126 (2):629-632; AUG 2014
Abstract:
In the present investigation, we have studied leaching on polygrain Al-based quasicrystalline (i-Al63Cu25Fe12) as well as crystalline (B2 phase; Al55Cu30Fe15) alloy surfaces using a 10 mole NaOH solution. The surface was leached at varying times from 30 mm to 8 h and subsequently characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray analysis. Leaching of the samples for 30 min generated a homogeneous layer. However further leaching for 1-8 h yielded nano-size particles on the surface. Spherical microstructure has been observed on the Al-Cu-Fe crystalline surface whereas on the quasicrystalline surface a petal-like microstructure appeared. The implications of the evolution of different microstructures in the context of structure, stability and activity are discussed. The results are compared with the microstructure of leached polygrained samples containing a mixture of different surface orientations.

Update: 23-Oct-2014

Title:
Influence of yttrium content on phase formation and strain hardening behavior of Mg-Zn-Mn magnesium alloy
Authors:
Tahreen, N; Zhang, DF; Pan, FS; Jiang, XQ; Li, C; Li, DY; Chen, DL Author Full Names: Tahreen, N.; Zhang, D. F.; Pan, F. S.; Jiang, X. Q.; Li, C.; Li, D. Y.; Chen, D. L.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 615 424-432; 10.1016/j.jallcom.2014.06.211 DEC 5 2014
Abstract:
The aim of this study was to identify the effect of yttrium (Y) addition on the phase development and strain hardening behavior of an extruded Mg-Zn-Mn (ZM31) magnesium alloy. The addition of a small amount (0.3 wt.%) of Y in the alloy led to the formation of icosahedral quasicrystalline I (Mg3YZn6) phase. Both I-phase and W-phase (Mg3Y2Zn3) were present in the extruded ZM31+3.2Y alloy, while long period stacking ordered (LPSO) X-phase (Mg12YZn) and Mg24Y5 were observed in the extruded ZM31+6Y alloy. The Y addition significantly refined grains in the extruded state. The presence of I-phase in the extruded ZM31+0.3Y alloy increased hardness, compressive yield strength, and Stage B strain hardening rate. The extruded ZM31+3.2Y alloy exhibited a lower hardness and Stage B hardening rate due to the formation of W-phase. Both extruded ZM31+0.3Y and ZM31+3.2Y alloys showed a yield point phenomenon with an initial negative strain hardening rate. The extruded ZM31+6Y alloy had a high hardness and compressive yield strength without Stage B hardening, suggesting a change of major deformation mode from twinning to slip mainly due to the role of LPSO X-phase. After solution treatment and aging, the hardness and compressive yield strength gradually increased with increasing Y content, while the strain hardening exponent and the extent of Stage B strain hardening decreased due to the dissolution of I- and W-phases and the presence of LPSO X-phase. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Synthesis of an icosahedral quasicrystalline phase in the Al-Cu-Fe system via mechanical activation
Authors:
Chugunov, DB; Filippova, SE; Portnoi, VK; Meshkov, LL Author Full Names: Chugunov, D. B.; Filippova, S. E.; Portnoi, V. K.; Meshkov, L. L.
Source:
INORGANIC MATERIALS, 50 (11):1083-1092; 10.1134/S0020168514110053 NOV 2014
Abstract:
A quasicrystalline compound of composition Al64Cu24Fe12 has been prepared through mechanical activation. We have studied the morphology of powder particles after heat treatment under various conditions, identified the sequence of phase transformations in Al-Cu-Fe alloys in the stability region of the ico-phase, and optimized conditions for the preparation of powders containing the maximum possible percentage of the quasicrystalline phase.
Title:
Dielectric properties of the ferroelectric composite (NaNO2)(0.9)/(BaTiO3)(0.1)
Authors:
Baryshnikov, S; Stukova, E; Koroleva, E Author Full Names: Baryshnikov, S.; Stukova, E.; Koroleva, E.
Source:
COMPOSITES PART B-ENGINEERING, 66 190-193; 10.1016/j.compositesb.2014.05.005 NOV 2014
Abstract:
The temperature and frequency dependences of dielectric properties of the ferroelectric composite (NaNO2)(0.9)/(BaTiO3)(0.1) have been studied. It was shown that in the composites the mutual influence of the components may lead to the expansion of incommensurate phase existence in NaNO2. The greatest contribution to the low-frequency dielectric constant of the composite is due to the Maxwell-Wagner polarization. (C) 2014 Elsevier Ltd. All rights reserved.
Title:
Magnetic structure of the Eu2+ moments in superconducting EuFe2(As1-xPx)(2) with x=0.19
Authors:
Nandi, S; Jin, WT; Xiao, Y; Su, Y; Price, S; Schmidt, W; Schmalzl, K; Chatterji, T; Jeevan, HS; Gegenwart, P; Bruckel, T Author Full Names: Nandi, S.; Jin, W. T.; Xiao, Y.; Su, Y.; Price, S.; Schmidt, W.; Schmalzl, K.; Chatterji, T.; Jeevan, H. S.; Gegenwart, P.; Brueckel, Th.
Source:
PHYSICAL REVIEW B, 90 (9):10.1103/PhysRevB.90.094407 SEP 9 2014
Abstract:
The magnetic structure of the Eu2+ moments in the superconducting EuFe2(As1-xPx)(2) sample with x = 0.19 has been determined using neutron scattering. We conclude that the Eu2+ moments are aligned along the c direction below T-C = 19.0(1) K with an ordered moment of 6.6(2) mu(B) in the superconducting state. An impurity phase similar to the underdoped phase exists within the bulk sample which orders antiferromagnetically below T-N = 17.0(2) K. We found no indication of iron magnetic order, nor any incommensurate magnetic order of the Eu2+ moments in the sample.
Title:
Structure of a crystalline approximant related to Al-Co-Ni decagonal quasicrystals studied by spherical aberration (Cs)-corrected scanning transmission electron microscopy and atomic-resolution energy dispersive X-ray spectroscopy
Authors:
Yasuhara, A; Yubuta, K; Hiraga, K Author Full Names: Yasuhara, Akira; Yubuta, Kunio; Hiraga, Kenji
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 94 (9):539-547; 10.1080/09500839.2014.944604 2014
Abstract:
Six types of decagonal quasicrystals (DQCs) found in Al-Co-Ni alloys with a wide compositional ratio of Co/Ni are considered to be stabilized by chemical ordering of Co and Ni, but the elucidation of this ordering has never been performed on alloys containing neighbouring elements Co and Ni. In order to examine the chemical ordering, an Al-Co-Ni crystalline phase, the PD3c phase, which is an important approximant for understanding the structures of ordered Al-Co-Ni DQCs, in an Al71.5Co16Ni12.5 alloy has been studied by spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM) and atomic-resolution energy dispersive X-ray spectroscopy (EDXS). From the combination of observed high-angle annular dark-field and annular bright-field STEM observations, an atomic arrangement of the crystalline approximant can be directly derived. The chemical ordering of Co and Ni in the arrangement of transition-metal (TM) atoms and mixed sites (MSs) of TM and Al atoms can be clearly detected on atomic-resolution EDXS maps obtained with the special technique. Co atoms are located at the TM atom positions arranged in pentagonal tiling with a bond length of 0.76 nm, whereas Ni is enriched in the MSs located in pentagonal tiles of Co atoms. It can be concluded that the change of an area ratio of Co-rich clusters to Ni-rich MSs produces various types of DQCs with different compositional Ni/Co ratios.

Update: 15-Oct-2014

Title:
Incommensurate helical spin ground states on the hollandite lattice
Authors:
Mandal, S; Andreanov, A; Crespo, Y; Seriani, N Author Full Names: Mandal, S.; Andreanov, A.; Crespo, Y.; Seriani, N.
Source:
PHYSICAL REVIEW B, 90 (10):10.1103/PhysRevB.90.104420 SEP 24 2014
Abstract:
We present a model of classical Heisenberg spins on a hollandite lattice, which has been developed to describe the magnetic properties of alpha-MnO2 and similar compounds. The model has only nearest-neighbor interacting spins, however, the strength and the sign of spin-spin interactions is anisotropic and depends on the nature of the bonds. Our analysis shows that the hollandite lattice supports four different incommensurate and helical magnetic ground states depending on the relative strengths and signs of spin-spin interactions. We show that the incommensurate helical ground states appear due to the geometrical frustration present in the model. We demonstrate that each of the four helical incommensurate magnetic phases are continuously connected to four different collinear antiferromagnetic ground states as the strength of spin-spin interaction along some bonds is increased. The present results give support to the presence of helical states that have been previously suggested experimentally for hollandite compounds. We provide an in-depth analysis of the magnetic form factors for each helical phase and describe how it could be used to identify each of these phases in neutron diffraction experiments.
Title:
Spiral order in the honeycomb iridate Li2IrO3
Authors:
Reuther, J; Thomale, R; Rachel, S Author Full Names: Reuther, Johannes; Thomale, Ronny; Rachel, Stephan
Source:
PHYSICAL REVIEW B, 90 (10):10.1103/PhysRevB.90.100405 SEP 12 2014
Abstract:
The honeycomb iridates A(2)IrO(3) (A = Na, Li) constitute promising candidate materials to realize the Heisenberg-Kitaev model (HKM) in nature, hosting unconventional magnetic as well as spin-liquid phases. Recent experiments suggest, however, that Li2IrO3 exhibits a magnetically ordered state of incommensurate spiral type which has not been identified in the HKM. We show that these findings can be understood in the context of an extended Heisenberg-Kitaev scenario satisfying all tentative experimental evidence: (i) the maximum of the magnetic susceptibility is located inside the first Brillouin zone, (ii) the Curie-Weiss temperature is negative relating to dominant antiferromagnetic fluctuations, and (iii) significant second-neighbor spin exchange is involved.
Title:
Magnetic and nonmagnetic phases in doped AB(2) t-J Hubbard chains
Authors:
Montenegro, RR; Coutinho, MD Author Full Names: Montenegro-Filho, R. R.; Coutinho-Filho, M. D.
Source:
PHYSICAL REVIEW B, 90 (11):10.1103/PhysRevB.90.115123 SEP 11 2014
Abstract:
We discuss the rich phase diagram of doped AB(2) t-J chains by using data from density matrix renormalization group and exact diagonalization techniques. The J vs delta (hole doping) phase diagram exhibits regions of itinerant ferrimagnetism, incommensurate, resonating valence bond and Nagaoka states, phase separation, and Luttinger liquid (LL) physics. Several features are highlighted, such as the modulated ferrimagnetic structure, the occurrence of Nagaoka spin polarons in the underdoped regime and small values of J = 4t(2)/U, where t is the first-neighbor hopping amplitude and U is the on-site repulsive Coulomb interaction, incommensurate structures with nonzero magnetization, and strong-coupling LL physics in the high-doped regime. We also verify that relevant findings are in agreement with the corresponding findings in square and n-leg ladder lattices. In particular, we mention the instability of Nagaoka ferromagnetism against J and delta.
Title:
Renormalization group analysis of a fermionic hot-spot model
Authors:
Whitsitt, S; Sachdev, S Author Full Names: Whitsitt, Seth; Sachdev, Subir
Source:
PHYSICAL REVIEW B, 90 (10):10.1103/PhysRevB.90.104505 SEP 10 2014
Abstract:
We present a renormalization group (RG) analysis of a fermionic "hot-spot" model of interacting electrons on the square lattice. We truncate the Fermi-surface excitations to linearly dispersing quasiparticles in the vicinity of eight hot spots on the Fermi surface, with each hot spot separated from another by the wave vector (pi, pi). This is motivated by the importance of these Fermi-surface locations to the onset of antiferromagnetic order; however, we allow for all possible quartic interactions between the fermions, and also for all possible ordering instabilities. We compute the RG equations for our model, which depend on whether or not the hot spots are perfectly nested, and relate our results to earlier models. We also compute the RG flow of the relevant order parameters for both Hubbard and J, V interactions, and present our results for the dominant instabilities in the nested and non-nested cases. In particular, we find that non-nested hot spots with J, V interactions have competing singlet d(x2) (-) (y2) superconducting and d-form factor incommensurate density wave instabilities. We also investigate the enhancement of incommensurate density waves near experimentally observed wave vectors, and find dominant d-form factor enhancement for a range of couplings.
Title:
Formation of Tsai-type 1/1 approximants in In-Pd-RE (RE: rare earth metal) alloys
Authors:
So, YG; Saruhashi, F; Kimoto, K; Tamura, R; Edagawa, K Author Full Names: So, Yeong-Gi; Saruhashi, Fukuaki; Kimoto, Koji; Tamura, Ryuji; Edagawa, Keiichi
Source:
PHILOSOPHICAL MAGAZINE, 94 (26):2980-2991; 10.1080/14786435.2014.944607 2014
Abstract:
The formation of the 1/1 crystal approximant phase (1/1 phase) to the icosahedral phase (i phase) in In-Pd-RE (RE: rare earth metal) systems has been investigated. A new series of 1/1 phases were found in In53Pd33RE14 (RE; Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm) alloys. For Y, Sm, Gd, Tb, Dy, and Ho, the 1/1 phases were found in annealed alloys, indicating that they are thermodynamically stable. The atomic structure of the 1/1 phases was directly observed by high-angle annular dark-field imaging performed via scanning transmission electron microscopy, revealing that the 1/1 phases consisted of a periodic arrangement of Tsai-type icosahedral clusters. Further, the atomic size effect on i phase formation, as well as formation conditions previously reported for other Tsai-type i and 1/1 phases were examined. It was found that the ratio of the atomic radius of base metals such as In and Pd affects i phase formation. Moreover, the appropriate range of the radius ratio for i phase formation was narrower than that for 1/1 phase formation.

Update: 9-Oct-2014

Title:
The triplite-triploidite supergroup: structural modulation in wagnerite, discreditation of magniotriplite, and the new mineral hydroxylwagnerite
Authors:
Chopin, C; Armbruster, T; Grew, ES; Baronnet, A; Leyx, C; Medenbach, O Author Full Names: Chopin, Christian; Armbruster, Thomas; Grew, Edward S.; Baronnet, Alain; Leyx, Catherine; Medenbach, Olaf
Source:
EUROPEAN JOURNAL OF MINERALOGY, 26 (4):553-565; 10.1127/0935-1221/2014/0026-2386 AUG 2014
Abstract:
Electron-microprobe analysis, single-crystal X-ray diffraction with an area detector, and high-resolution transmission electron microscopy show that minerals related to wagnerite, triplite and triploidite, which are monoclinic Mg, Fe and Mn phosphates with the formula Me2+ 2PO4(F,OH), constitute a modulated series based on the average triplite structure. Modulation occurs along b and may be commensurate with (2b periodicity) or incommensurate but generally close to integer values (similar to 3b, similar to 5b, similar to 7b, similar to 9b), i.e. close to polytypic behaviour. As a result, the Mg- and F-dominant minerals magniotriplite and wagnerite can no longer be considered polymorphs of Mg2PO4F, i.e., there is no basis for recognizing them as distinct species. Given that wagnerite has priority (1821 vs. 1951), the name magniotriplite should be discarded in favour of wagnerite. Hydroxylwagnerite, end-member Mg2PO4OH, occurs in pyrope megablasts along with talc, clinochlore, kyanite, rutile and secondary apatite in two samples from lenses of pyrope-kyanite-phengite-quartz-schist within metagranite in the coesite-bearing ultrahigh-pressure metamorphic unit of the Dora-Maira Massif, western Alps, Vallone di Gilba, Val Varaita, Piemonte, Italy. Electron microprobe analyses of holotype hydroxylwagnerite and of the crystal with the lowest F content gave in wt%: P2O5 44.14, 43.99; SiO2 0.28, 0.02; SO3 -, 0.01; TiO2 0.20, 0.16; Al2O3 0.06, 0.03; MgO 48.82, 49.12; FeO 0.33, 0.48; MnO 0.01, 0.02; CaO 0.12, 0.10; Na2O 0.01, -; F 5.58, 4.67; H2O (calc) 2.94, 3.36; -O = F 2.35, 1.97; Sum 100.14, 99.98, corresponding to (Mg1.954Fe0.007Ca0.003Ti0.004Al0.002Na0.001)(Sigma=1.971)(P1.003Si0.008) (Sigma=1.011)O-4(OH0.526F0.474)(Sigma=1) and (Mg1.971Fe0.011Ca0.003Ti0.003Al0.001)(Sigma=1.989)(P1.002Si0.001)(Sigma= 1.003)O-4(OH0.603F0.397)(Sigma=1), respectively. Due to the paucity of material, H2O could not be measured, so OH was calculated from the deficit in F assuming stoichiometry, i.e., by assuming F + OH = 1 per formula unit. Holotype hydroxylwagnerite is optically biaxial (+), alpha 1.584(1), beta 1.586(1), gamma 1.587(1) (589 nm); 2V(Z) (meas.) = 43(2)degrees; orientation Y = b. Single-crystal X-ray diffraction gives monoclinic symmetry, space group P2(1)/c, a = 9.646(3) angstrom, b = 12.7314(16) angstrom, c = 11.980(4) angstrom, beta = 108.38(4)degrees, V = 1396.2(8) angstrom(3,) Z = 16, i.e., hydroxylwagnerite is the OH-dominant analogue of wagnerite [beta-Mg2PO4(OH)] and a high-pressure polymorph of althausite, holtedahlite, and alpha- and epsilon-Mg2PO4(OH). We suggest that the group of minerals related to wagnerite, triplite and triploidite constitutes a triplite-triploidite super-group that can be divided into F-dominant phosphates (triplite group), OH-dominant phosphates (triploidite group), O-dominant phosphates (stanekite group) and an OH-dominant arsenate (sarkinite). The distinction among the three groups and a potential fourth group is based only on chemical features, i.e., occupancy of anion or cation sites. The structures of these minerals are all based on the average triplite structure, with a modulation controlled by the ratio of Mg, Fe2+, Fe3+ and Mn2+ ionic radii to (O,OH,F) ionic radii.
Title:
Orbital correlations and dimensional crossover in epitaxial Pr0.5Ca0.5MnO3/La0.5Sr0.5MnO3 superlattices
Authors:
Wadati, H; Okamoto, J; Garganourakis, M; Scagnoli, V; Staub, U; Sakai, E; Kumigashira, H; Sugiyama, T; Ikenaga, E; Nakamura, M; Kawasaki, M; Tokura, Y Author Full Names: Wadati, H.; Okamoto, J.; Garganourakis, M.; Scagnoli, V.; Staub, U.; Sakai, E.; Kumigashira, H.; Sugiyama, T.; Ikenaga, E.; Nakamura, M.; Kawasaki, M.; Tokura, Y.
Source:
NEW JOURNAL OF PHYSICS, 16 10.1088/1367-2630/16/7/073044 JUL 30 2014
Abstract:
We studied the charge-orbital ordering in the superlattice of charge-ordered insulating Pr0.5Ca0.5MnO3 and ferromagnetic metallic La0.5Sr0.5MnO3 by resonant soft x-ray diffraction (RSXD) and hard x-ray photoemission spectroscopy (HXPES). A temperature-dependent incommensurability is found in the orbital ordering by RSXD. In addition, a large hysteresis is observed that is caused by phase competition between the insulating charge ordered and metallic ferromagnetic states. No magnetic phase transitions are observed in contrast to pure Pr0.5Ca0.5MnO3 thin films, confirming the unique character of the superlattice. Mn 2p HXPES spectra revealed a hysteresis in the metalicity, supporting the picture of phase competition. The deviation from the commensurate orbital order can be directly related to the decrease of ordered-layer thickness that leads to dimensional crossover from three-dimensional to two-dimensional orbital ordering.

Update: 1-Oct-2014

Title:
Unusual doping effect of non-magnetic ion on magnetic properties of CuFe1-xGaxO2
Authors:
Shi, LR; Jin, Z; Chen, BR; Xia, NM; Zuo, HK; Wang, YS; Ouyang, ZW; Xia, ZC Author Full Names: Shi, Liran; Jin, Zhao; Chen, Borong; Xia, Nianming; Zuo, Huakun; Wang, Yeshuai; Ouyang, Zhongwen; Xia, Zhengcai
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 372 7-11; 10.1016/j.jmmm.2014.07.014 DEC 2014
Abstract:
The structural and magnetic properties of nonmagnetic Ga3+ ion doped CuFe1-xGaxO2 (x=0, 0.02, 0.03, and 0.05) single crystal samples have been investigated. In pulsed high magnetic fields, the field-induced multi-step transitions were observed in all the samples. Compared with pure CuFeO2, the transition temperatures, critical magnetic fields decrease and the magnetic hysteresis of the doped samples become small, which may result from the partial release of the spin frustration and the changes of the magnetic coupling both inter- and intra-planes due to the Ga3+ dopant. The magnetization measurements show an abnormal dilution behavior, especially in a lower temperature region, the magnetic moment was enhanced due to the nonmagnetic Ga3+ ion doping, the enhancement becomes more obviously in the sample with the Ga3+ doping level of x=0.03. These results may connected with the substitution of nonmagnetic Ga3+ ions destroying the stability of ground state and affecting the stability of the ferroelectricity incommensurate phase. Based on the experimental results, a super-cell model and their magnetic diagram were assumed. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Composition dependent phase stability of Ni-Mn-Ga alloys studied by ab initio calculations
Authors:
Xu, N; Raulot, JM; Li, ZB; Zhang, YD; Bai, J; Peng, W; Meng, XY; Zhao, X; Zuo, L; Esling, C Author Full Names: Xu, N.; Raulot, J. M.; Li, Z. B.; Zhang, Y. D.; Bai, J.; Peng, W.; Meng, X. Y.; Zhao, X.; Zuo, L.; Esling, C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 614 126-130; 10.1016/j.jallcom.2014.06.079 NOV 25 2014
Abstract:
Composition dependent phase stability of Ni-Mn-Ga magnetic shape memory alloys was studied by first-principles density-functional calculations. It is demonstrated that the three kinds of doping (Ni substitution for Mn, Ni for Ga, and Mn for Ga) destabilize all the three structures. However, Ni-doping relatively stabilizes the non-modulated martensite (NM) with simple tetragonal crystal structure, whereas proper Mn-doping relatively stabilizes the monoclinic seven-layered modulated (7M) martensite with monoclinic structure. Comparing the energy difference between the parent and the product phases, we found that martensitic transformation experiences much larger driving force than that of the intermar-tensitic transformation. Chemical bonds between Ni and Mn are observed not only with the stoichiometric Mn, but also with the excess ones. Bonds between Ni and Mn in modulated martensite is stronger than that of the non-modulated martensite, which is beneficial to the stability of the modulated martensite. The present result provides useful information for further development of magnetic shape memory alloys that is difficult to be obtained from experiments. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Impact of Quenched Oxygen Disorder on Charge Density Wave Order in YBa2Cu3O6+x
Authors:
Achkar, AJ; Mao, X; McMahon, C; Sutarto, R; He, F; Liang, RX; Bonn, DA; Hardy, WN; Hawthorn, DG Author Full Names: Achkar, A. J.; Mao, X.; McMahon, Christopher; Sutarto, R.; He, F.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Hawthorn, D. G.
Source:
PHYSICAL REVIEW LETTERS, 113 (10):10.1103/PhysRevLett.113.107002 SEP 4 2014
Abstract:
The competition between superconductivity and charge density wave (CDW) order in underdoped cuprates has now been widely reported, but the role of disorder in this competition has yet to be fully resolved. A central question is whether disorder sets the length scale of the CDW order, for instance by pinning charge density fluctuations or disrupting an otherwise long-range order. Using resonant soft x-ray scattering, we investigate the sensitivity of CDW order in YBa2Cu3O6+x (YBCO) to varying levels of oxygen disorder. We find that quench cooling YBCO6.67 (YBCO6.75) crystals to destroy their o-V and o-VIII (o-III) chains decreases the intensity of the CDW superlattice peak by a factor of 1.9 (1.3), but has little effect on the CDW correlation length, incommensurability, and temperature dependence. This reveals that while quenched oxygen disorder influences the CDW order parameter, the spatial extent of the CDW order is insensitive to the level of quenched oxygen disorder and may instead be a consequence of competition with superconductivity.
Title:
Cation Ordering and Flexibility of the BO42- Tetrahedra in Incommensurately Modulated CaEu2(BO4)(4) (B = Mo, W) Scheelites
Authors:
Abakumov, AM; Morozov, VA; Tsirlin, AA; Verbeeck, J; Hadermann, J Author Full Names: Abakumov, Artem M.; Morozov, Vladimir A.; Tsirlin, Alexander A.; Verbeeck, Johan; Hadermann, Joke
Source:
INORGANIC CHEMISTRY, 53 (17):9407-9415; 10.1021/ic5015412 SEP 1 2014
Abstract:
The factors mediating cation ordering in the scheelite-based molybdates and tungstates are discussed on the basis of the incommensurately modulated crystal structures of the CaEu2(BO4)(4) (B = Mo, W) red phosphors solved from high-resolution synchrotron powder X-ray diffraction data. Monoclinic CaEu2(WO4)(4) adopts a (3 + 1)-dimensionally modulated structure [superspace group I2/b(alpha beta 0)00, a = 5.238 73(1)A, b = 5.266 35(1) A, c = 11.463 19(9) A, gamma = 91.1511(2)degrees, q = 0.56153(6)a* + 0.7708(9)b*, R-F = 0.050, R-p = 0.069], whereas tetragonal CaEu2(MoO4)(4) is (3 + 2)-dimensionally modulated [superspace group I4(1)/ a(alpha beta 0)00(-beta alpha 0)00, a = 5.238 672(7) A, c = 11.548 43(2) A, q(1) = 035331(8)a* + 0.82068(9)b*, q(2) = -0.82068(9)a* + 0.55331(8)b*, R-F = 0.061, R-p = 0.082]. In both cases the modulation arises from the ordering of the Ca/Eu cations and the cation vacancies at the A-sublattice of the parent scheelite ABO(4) structure. The cation ordering is incomplete and better described with harmonic rather than with steplike occupational modulation functions. The structures respond to the variation of the effective charge and cation size at the A-position through the flexible geometry of the MoO42- and WO42- tetrahedra demonstrating an alternation of stretching the B-O bond lengths and bending the O-B-O bond angles. The tendency towards A-site cation ordering in scheelites is rationalized using the difference in ionic radii and concentration of the A-site vacancies as parameters and presented in the form of a structure map.
Title:
Controlled Self-Assembly of Periodic and Aperiodic Cluster Crystals
Authors:
Barkan, K; Engel, M; Lifshitz, R Author Full Names: Barkan, Kobi; Engel, Michael; Lifshitz, Ron
Source:
PHYSICAL REVIEW LETTERS, 113 (9):10.1103/PhysRevLett.113.098304 AUG 28 2014
Abstract:
Soft particles are known to overlap and form stable clusters that self-assemble into periodic crystalline phases with density-independent lattice constants. We use molecular dynamics simulations in two dimensions to demonstrate that, through a judicious design of an isotropic pair potential, one can control the ordering of the clusters and generate a variety of phases, including decagonal and dodecagonal quasicrystals. Our results confirm analytical predictions based on a mean-field approximation, providing insight into the stabilization of quasicrystals in soft macromolecular systems, and suggesting a practical approach for their controlled self-assembly in laboratory realizations using synthesized soft-matter particles.
Title:
Quantum spin chain as a potential realization of the Nersesyan-Tsvelik model
Authors:
Balz, C; Lake, B; Luetkens, H; Baines, C; Guidi, T; Abdel-Hafiez, M; Wolter, AUB; Buchner, B; Morozov, IV; Deeva, EB; Volkova, OS; Vasiliev, AN Author Full Names: Balz, C.; Lake, B.; Luetkens, H.; Baines, C.; Guidi, T.; Abdel-Hafiez, M.; Wolter, A. U. B.; Buechner, B.; Morozov, I. V.; Deeva, E. B.; Volkova, O. S.; Vasiliev, A. N.
Source:
PHYSICAL REVIEW B, 90 (6):10.1103/PhysRevB.90.060409 AUG 25 2014
Abstract:
It is well established that long-range magnetic order is suppressed in magnetic systems whose interactions are low dimensional. The prototypical example is the S-1/2 Heisenberg antiferromagnetic chain (S-1/2 HAFC) whose ground state is quantum critical. In real S-1/2 HAFC compounds interchain coupling induces long-range magnetic order although with a suppressed ordered moment and reduced Neel temperature compared to the Curie-Weiss temperature. Recently, it was suggested that order can also be suppressed if the interchain interactions are frustrated, as for the Nersesyan-Tsvelik model. Here, we study the new S-1/2 HAFC, (NO)[Cu(NO3)(3)]. This material shows extreme suppression of order which furthermore is incommensurate revealing the presence of frustration consistent with the Nersesyan-Tsvelik model.
Title:
Excess-hole induced high temperature polarized state and its correlation with the multiferroicity in single crystalline DyMnO3
Authors:
Zou, T; Dun, ZL; Cao, HB; Zhu, MZ; Coulter, D; Zhou, HD; Ke, XL Author Full Names: Zou, Tao; Dun, Zhiling; Cao, Huibo; Zhu, Mengze; Coulter, Daniel; Zhou, Haidong; Ke, Xianglin
Source:
APPLIED PHYSICS LETTERS, 105 (5):10.1063/1.4892470 AUG 4 2014
Abstract:
Controlling the ferroelectricity and magnetism in multiferroic materials has been an important research topic. We report the formation of a highly polarized state in multiferroic DyMnO3 single crystals which develops well above the magnetic transition temperatures, and we attribute it to the thermally stimulated depolarization current effect of excess holes forming Mn4+ ions in the system. We also show that this high temperature polarized state intimately correlates with the lower temperature ferroelectric state that is induced by the incommensurate spiral magnetic order of Mn spins. This study demonstrates an efficient approach to tune the multiferroicity in the manganite system. (C) 2014 AIP Publishing LLC.
Title:
Short-range cluster spin glass near optimal superconductivity in BaFe2-xNixAs2
Authors:
Lu, XY; Tam, DW; Zhang, CL; Luo, HQ; Wang, M; Zhang, R; Harriger, LW; Keller, T; Keimer, B; Regnault, LP; Maier, TA; Dai, PC Author Full Names: Lu, Xingye; Tam, David W.; Zhang, Chenglin; Luo, Huiqian; Wang, Meng; Zhang, Rui; Harriger, Leland W.; Keller, T.; Keimer, B.; Regnault, L. -P.; Maier, Thomas A.; Dai, Pengcheng
Source:
PHYSICAL REVIEW B, 90 (2):10.1103/PhysRevB.90.024509 JUL 11 2014
Abstract:
High-temperature superconductivity in iron pnictides occurs when electrons are doped into their antiferromagnetic (AF) parent compounds. In addition to inducing superconductivity, electron doping also changes the static commensurate AF order in the undoped parent compounds into short-range incommensurate AF order near optimal superconductivity. Here we use neutron scattering to demonstrate that the incommensurate AF order in BaFe2-xNixAs2 is not a spin-density wave arising from the itinerant electrons in nested Fermi surfaces, but is consistent with a cluster spin glass in the matrix of the superconducting phase. Therefore, optimal superconductivity in iron pnictides coexists and competes with a mesoscopically separated cluster spin glass phase, much different from the homogeneous coexisting AF and superconducting phases in the underdoped regime.

Update: 24-Sep-2014

Title:
Exchange bias in non-collinear spin-spiral system Co(Cr1-xCox)(2)O-4(x=0.0-0.1)
Authors:
Padam, R; Ravi, S; Ramakrishnan, S; Grover, AK; Pal, D Author Full Names: Padam, R.; Ravi, S.; Ramakrishnan, S.; Grover, A. K.; Pal, D.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 371 144-148; 10.1016/j.jmmm.2014.07.052 DEC 2014
Abstract:
We report structural and magnetic properties of Co(Cr1-xCox)(2)O-4 (x = 0.0-0.1). The thermal hysteresis has been observed both across magnetostructural transition (T-S) and lock-in transition (T-L). We observe noticeable Exchange bias (EB) only below the lock-in transition, T-L. The value or coercivity also shows the dramatical increase below T-L. These results have been discussed in the context or incommensurate to commensurate non-collinear spin-spiral transitions across T-L. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Exact diagonalization study of the anisotropic triangular lattice Heisenberg model using twisted boundary conditions
Authors:
Thesberg, M; Sorensen, ES Author Full Names: Thesberg, Mischa; Sorensen, Erik S.
Source:
PHYSICAL REVIEW B, 90 (11):10.1103/PhysRevB.90.115117 SEP 8 2014
Abstract:
The spin-1/2 anisotropic triangular model, which is believed to describe the materials Cs2CuCl4 and Cs2CuBr4, among others, is dominated by incommensurate spiral physics and is thus extremely resistant to numerical analysis on small system sizes. In this paper, we use twisted boundary conditions and exact diagonalization techniques to study the ground state of this model as a function of exchange parameter strength. With these boundary conditions we are able to extract the inter-and intrachain ordering q vectors for the J '/J < 1 region finding very close agreement with recent DMRG results on much larger systems. Our results suggest a phase transition between a long-range incommensurate spiral ordered phase, and a more subtle phase with short-range spiral correlations with the q vector describing the incommensurate correlations varying smoothly through the transition. In the latter phase correlations between next-nearest chains exhibit an extremely close competition between predominantly antiferromagnetic and ferromagnetic correlations. Further analysis suggests that the antiferromagnetic next-nearest chain correlations may be slightly stronger than the ferromagnetic ones. This difference is found to be slight but in line with previous renormalization group predictions of a collinear antiferromagnetic ordering in this region.
Title:
Unoccupied electronic states of icosahedral Al-Pd-Mn quasicrystals: Evidence of image potential resonance and pseudogap
Authors:
Maniraj, M; Rai, A; Barman, SR; Krajci, M; Schlagel, DL; Lograsso, TA; Horn, K Author Full Names: Maniraj, M.; Rai, Abhishek; Barman, S. R.; Krajci, M.; Schlagel, D. L.; Lograsso, T. A.; Horn, K.
Source:
PHYSICAL REVIEW B, 90 (11):10.1103/PhysRevB.90.115407 SEP 5 2014
Abstract:
We study the unoccupied region of the electronic structure of the fivefold symmetric surface of an icosahedral (i) Al-Pd-Mn quasicrystal. A feature that exhibits parabolic dispersion with an effective mass of (1.15 +/- 0.1)m(e) and tracks the change in the work function is assigned to an image potential resonance because our density functional calculation shows an absence of band gap in the respective energy region. We show that Sn grows pseudomorphically on i-Al-Pd-Mn as predicted by density functional theory calculations, and the energy of the image potential resonance tracks the change in the work function with Sn coverage. The image potential resonance appears much weaker in the spectrum from the related crystalline Al-Pd-Mn surface, demonstrating that its strength is related to the compatibility of the quasiperiodic wave functions in i-Al-Pd-Mn with the free-electron-like image potential states. Our investigation of the energy region immediately above E-F provides unambiguous evidence for the presence of a pseudogap, in agreement with our density functional theory calculations.
Title:
Quantitative Adsorbate Structure Determination for Quasicrystals Using X-Ray Standing Waves
Authors:
Diehl, RD; Li, HI; Su, SY; Mayer, A; Stanisha, NA; Ledieu, J; Lovelock, KRJ; Jones, RG; Deyko, A; Wearing, LH; McGrath, R; Chaudhuri, A; Woodruff, DP Author Full Names: Diehl, R. D.; Li, H. I.; Su, S. Y.; Mayer, A.; Stanisha, N. A.; Ledieu, J.; Lovelock, K. R. J.; Jones, Robert G.; Deyko, A.; Wearing, L. H.; McGrath, R.; Chaudhuri, A.; Woodruff, D. P.
Source:
PHYSICAL REVIEW LETTERS, 113 (10):10.1103/PhysRevLett.113.106101 SEP 3 2014
Abstract:
The quantitative structure determination of adsorbed species on quasicrystal surfaces has so far appeared to present insurmountable problems. The normal incidence standing x-ray wave field technique offers a simple solution, without extensive data sets or large computations. Its application to quasicrystals raises several conceptual difficulties that are related to the phase problem in x-ray diffraction. We demonstrate their solution for the case of Si atoms adsorbed on the decagonal Co-rich modification of the Al-Co-Ni quasicrystal to determine the local structure, comprising 6-atom clusters in particular hollow sites.
Title:
Nonmagnetic Impurity Effect on Magnetic Phase Transitions in an Isosceles Triangular Lattice Ising Chain Antiferromagnet CoNb2O6
Authors:
Nakajima, T; Mitsuda, S; Okano, H; Inomoto, Y; Kobayashi, S; Prokes, K; Gerischer, S; Smeibidl, P Author Full Names: Nakajima, Taro; Mitsuda, Setsuo; Okano, Hidekazu; Inomoto, Yu; Kobayashi, Satoru; Prokes, Karel; Gerischer, Sebastian; Smeibidl, Peter
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 83 (9):10.7566/JPSJ.83.094723 SEP 2014
Abstract:
We have investigated nonmagnetic impurity effect on the H-parallel to c-T magnetic phase diagram of an isosceles triangular lattice Ising antiferromagnet CoNb2O6, by means of neutron diffraction measurements using single crystals of Co1-x-MgxNb2O6 with x = 0, 0.004, and 0.008. We have found that the commensurate antiferromagnetic (AF) ground state disappears by substituting only 0.8% of nonmagnetic Mg2+ ions for the magnetic Co2+ ions. On the other hand, the phase boundaries between the other phases, namely the field-induced ferrimagnetic phase, thermally-induced incommensurate (IC) magnetic phase and the paramagnetic phase, are hardly affected by the small amount of nonmagnetic substitution. We have also performed Monte Carlo simulations for the isosceles triangular lattice Ising model to understand the extremely high sensitivity to the nonmagnetic substitution. Consequently, we have revealed that the disappearance of the AF phase is not because the small amount of nonmagnetic impurities destabilize the AF phase, but because the phase transition from the IC phase to the AF phase is strongly suppressed by a pinning effect due to the impurities.
Title:
Possible coupling between magnons and phonons in multiferroic CaMn7O12
Authors:
Kadlec, F; Goian, V; Kadlec, C; Kempa, M; Vanek, P; Taylor, J; Rols, S; Prokleska, J; Orlita, M; Kamba, S Author Full Names: Kadlec, Filip; Goian, Veronica; Kadlec, Christelle; Kempa, Martin; Vanek, Premysl; Taylor, Jon; Rols, Stephane; Prokleska, Jan; Orlita, Milan; Kamba, Stanislav
Source:
PHYSICAL REVIEW B, 90 (5):10.1103/PhysRevB.90.054307 AUG 28 2014
Abstract:
Spin and lattice dynamics of CaMn7O12 ceramics were investigated using infrared, THz, and inelastic neutron scattering (INS) spectroscopies in the temperature range 2 to 590 K, and, at low temperatures, in applied magnetic fields of up to 12 T. On cooling, we observed phonon splitting accompanying the structural phase transition at T-C = 450 K as well as the onset of the incommensurately modulated structure at 250 K. In the two antiferromagnetic phases below T-N1 = 90 K and T-N2 = 48 K, several infrared-active excitations emerge in the meV range; their frequencies correspond to the maxima in the magnon density of states obtained by INS. At the magnetic phase transitions, these modes display strong anomalies and, for some of them, a transfer of dielectric strength from the higher-frequency phonons is observed. We propose that these modes are electromagnons. Remarkably, at least two of these modes remain active also in the paramagnetic phase; for this reason, we call them paraelectromagnons. In accordance with this observation, quasielastic neutron scattering revealed short-range magnetic correlations persisting within temperatures up to 500 K above T-N1.
Title:
Structural, magnetic, and dielectric studies on Gd0.7Y0.3MnO3
Authors:
Sarguna, RM; Sridharan, V; Samatham, SS; Ganesan, V; Bhardwaj, S; Awasthi, AM; Mukadam, MD; Yusuf, SM; Sinha, AK; Subramanian, N Author Full Names: Sarguna, R. M.; Sridharan, V.; Samatham, S. Shanmukharao; Ganesan, V.; Bhardwaj, S.; Awasthi, A. M.; Mukadam, M. D.; Yusuf, S. M.; Sinha, A. K.; Subramanian, N.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (34):10.1088/0953-8984/26/34/345901 AUG 27 2014
Abstract:
Structural, magnetic, specific heat, and dielectric studies were carried out on Y substituted (30 at. %) GdMnO3 compound as a function of temperature. Anomalies occur at similar to 41 and 18 K, in the specific heat measurements and are ascribed to paramagnetic, to sinusoidal incommensurate antiferromagnetic transition (ICAFM) and ICAFM to commensurate antiferromagnetic transitions, respectively. Changes in the lattice parameters across these temperatures indicate magneto-elastic coupling present in the compound. However, in the dielectric measurements, an anomaly at 18 K alone is observed and is ascribed to a ferroelectric transition, giving rise to spontaneous ferroelectric ordering at low temperatures. This observation is supported by an anomaly in lattice parameters, across the transition temperature. From the frequency dependent dielectric studies, a strong coupling between Gd3+ and Mn3+ magnetic sublattices is inferred and Y substitution results in substantial changes in the relaxation process compared to that of GdMnO3.
Title:
Uniaxial-pressure control of geometrical spin frustration in an Ising antiferromagnet CoNb2O6 via anisotropic deformation of the isosceles lattice
Authors:
Kobayashi, S; Hosaka, S; Tamatsukuri, H; Nakajima, T; Mitsuda, S; Prokes, K; Kiefer, K Author Full Names: Kobayashi, S.; Hosaka, S.; Tamatsukuri, H.; Nakajima, T.; Mitsuda, S.; Prokes, K.; Kiefer, K.
Source:
PHYSICAL REVIEW B, 90 (6):10.1103/PhysRevB.90.060412 AUG 26 2014
Abstract:
We report neutron diffraction measurement results for an Ising antiferromagnet CoNb2O6 under uniaxial pressure along the geometrically frustrated isosceles-triangular-lattice direction. We find that an onset incommensurate wave number at the Neel temperature increases with pressure from 0.378 to 0.411 at 400 MPa. The observations suggest that the anisotropic deformation of the lattice by the uniaxial pressure significantly modifies the spin frustration, leading to an increase in the nearest-neighbor to next-nearest-neighbor interaction ratio from 1.33 to 1.81.
Title:
Phases of a Triangular-Lattice Antiferromagnet Near Saturation
Authors:
Starykh, OA; Jin, W; Chubukov, AV Author Full Names: Starykh, Oleg A.; Jin, Wen; Chubukov, Andrey V.
Source:
PHYSICAL REVIEW LETTERS, 113 (8):10.1103/PhysRevLett.113.087204 AUG 21 2014
Abstract:
We consider 2D Heisenberg antiferromagnets on a triangular lattice with spatially anisotropic interactions in a high magnetic field close to the saturation. We show that this system possesses a rich phase diagram in a field or anisotropy plane due to competition between classical and quantum orders: an incommensurate noncoplanar spiral state, which is favored classically, and a commensurate coplanar state, which is stabilized by quantum fluctuations. We show that the transformation between these two states is highly nontrivial and involves two intermediate phases-the phase with coplanar incommensurate spin order and the one with noncoplanar double-Q spiral order. The transition between the two coplanar states is of commensurate-incommensurate type, not accompanied by softening of spin-wave excitations. We show that a different sequence of transitions holds in triangular antiferromagnets with exchange anisotropy, such as Ba3CoSb2O9.
Title:
Competing charge, spin, and superconducting orders in underdoped YBa2Cu3Oy
Authors:
Hucker, M; Christensen, NB; Holmes, AT; Blackburn, E; Forgan, EM; Liang, RX; Bonn, DA; Hardy, WN; Gutowski, O; von Zimmermann, M; Hayden, SM; Chang, J Author Full Names: Huecker, M.; Christensen, N. B.; Holmes, A. T.; Blackburn, E.; Forgan, E. M.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Gutowski, O.; v Zimmermann, M.; Hayden, S. M.; Chang, J.
Source:
PHYSICAL REVIEW B, 90 (5):10.1103/PhysRevB.90.054514 AUG 21 2014
Abstract:
To explore the doping dependence of the recently discovered charge-density-wave (CDW) order in YBa2Cu3Oy, we present a bulk-sensitive high-energy x-ray study for several oxygen concentrations, including strongly underdoped YBa2Cu3O6.44. Combined with previous data around the so-called 1/8 doping, we show that bulk CDW order exists at least for hole concentrations (p) in the CuO2 planes of 0.078 less than or similar to p less than or similar to 0.132. This implies that CDW order exists in close vicinity to the quantum critical point for spin-density-wave (SDW) order. In contrast to the pseudogap temperature T*, the onset temperature of CDW order decreases with underdoping to T-CDW similar to 90 K in YBa2Cu3O6.44. Together with a weakened order parameter this suggests a competition between CDW and SDW orders. In addition, the CDW order in YBa2Cu3O6.44 shows the same type of competition with superconductivity as a function of temperature and magnetic field as samples closer to p = 1/8. At low p the CDW incommensurability continues the previously reported linear increasing trend with underdoping. In the entire doping range the in-plane correlation length of the CDW order in b axis direction depends only very weakly on the hole concentration, and appears independent of the type and correlation length of the oxygen-chain order. The onset temperature of the CDW order is remarkably close to a temperature T-dagger that marks the maximum of 1/(T1T) in planar Cu-63 NQR/NMR experiments, potentially indicating a response of the spin dynamics to the formation of the CDW. Our discussion of these findings includes a detailed comparison to the charge stripe order in La2-xBaxCuO4.
Title:
Resonant x-ray scattering study of charge-density wave correlations in YBa2Cu3O6+x
Authors:
Blanco-Canosa, S; Frano, A; Schierle, E; Porras, J; Loew, T; Minola, M; Bluschke, M; Weschke, E; Keimer, B; Le Tacon, M Author Full Names: Blanco-Canosa, S.; Frano, A.; Schierle, E.; Porras, J.; Loew, T.; Minola, M.; Bluschke, M.; Weschke, E.; Keimer, B.; Le Tacon, M.
Source:
PHYSICAL REVIEW B, 90 (5):10.1103/PhysRevB.90.054513 AUG 21 2014
Abstract:
We report the results of a comprehensive study of charge-density wave (CDW) correlations in untwinned YBa2Cu3O6+x single crystals with 0.4 <= x <= 0.99 using CuL3 edge resonant x-ray scattering (RXS). Evidence of CDW formation is found for 0.45 <= x <= 0.93 (hole-doping levels 0.086 less than or similar to p less than or similar to 0.163), but not for samples with x <= 0.44 (p less than or similar to 0.084) that exhibit incommensurate spin-density-wave order, and in slightly overdoped samples with x = 0.99 (p similar to 0.19). This suggests the presence of two proximate zero-temperature CDW critical points at p(c1) similar to 0.08 and p(c2) similar to 0.18. Remarkably, pc(2) is close to the doping level that is optimal for superconductivity. The CDW reflections are observed at incommensurate in-plane wave vectors (delta(a), 0) and (0, delta(b)) with delta(a) less than or similar to delta(b). Both delta(a) and delta(b) decrease linearly with increasing doping, in agreement with recent reports on Bi-based high-T-c superconductors, but in sharp contrast to the behavior of the La2-x(Ba,Sr)(x)CuO4 family. The CDW intensity and correlation length exhibit maxima at p similar to 0.12, coincident with a plateau in the superconducting transition temperature T-c. The onset temperature of the CDW reflections depends nonmonotonically on p, with a maximum of similar to 160 K for p similar to 0.12. The RXS reflections exhibit a uniaxial intensity anisotropy. Whereas in strongly underdoped samples the reflections at (delta(a), 0) are much weaker than those at (0, delta(b)), the anisotropy is minimal for p similar to 0.12, and reversed close to optimal doping. We further observe a depression of CDW correlations upon cooling below T-c, and (for samples with p >= 0.09) an enhancement of the signal when an external magnetic field up to 6 T is applied in the superconducting state. For samples with p similar to 0.08, where prior work has revealed a field-enhancement of incommensurate magnetic order, the RXS signal is field independent. This supports a previously suggested scenario in which incommensurate charge and spin orders compete against each other, in addition to individually competing against superconductivity [Blanco-Canosa et al., Phys. Rev. Lett. 110, 187001 (2013)]. We discuss the relationship of these results to prior observations of "stripe" order in La2-x(Ba,Sr)(x)CuO4, the "pseudogap" phenomenon, superconducting fluctuations, and quantum oscillations, as well as their implications for the mechanism of high-temperature superconductivity.
Title:
High-resolution synchrotron x-ray powder diffraction study of the incommensurate modulation in the martensite phase of Ni2MnGa: Evidence for nearly 7M modulation and phason broadening
Authors:
Singh, S; Petricek, V; Rajput, P; Hill, AH; Suard, E; Barman, SR; Pandey, D Author Full Names: Singh, Sanjay; Petricek, V.; Rajput, Parasmani; Hill, Adrian H.; Suard, E.; Barman, S. R.; Pandey, Dhananjai
Source:
PHYSICAL REVIEW B, 90 (1):10.1103/PhysRevB.90.014109 JUL 31 2014
Abstract:
The modulated structure of the martensite phase of Ni2MnGa is revisited using high-resolution synchrotron x-ray powder diffraction measurements, which reveal higher-order *satellite reflections* up to the third order and phason broadening of the satellite peaks. The structure refinement, using the (3+1) dimensional superspace group approach, shows that the *modulated structure* of Ni2MnGa can be described by orthorhombic *superspace* group Immm(00 gamma)s00 with lattice parameters a = 4.218 61(2) angstrom, b = 5.546 96(3) angstrom, and c = 4.187 63(2) angstrom, and an incommensurate modulation wave vector q = 0.431 60(3)c* = (3/7 + delta)c*, where delta = 0.003 03(3) is the degree of incommensuration of the modulated structure. Additional satellite peak broadening, which could not be accounted for in terms of the anisotropic strain broadening based on a lattice parameter distribution, has been modeled in terms of phasons using fourth-rank covariant strain-tensor representation for incommensurate structures. The simulation of single-crystal diffraction patterns from the refined structural parameters unambiguously reveals a rational approximant structure with 7M modulation. The inhomogeneous displacement of different atomic sites on account of incommensurate modulation and the presence of phason broadening clearly rule out the adaptive phase model proposed recently by Kaufmann et al. [S. Kaufmann, U. K. Rossler, O. Heczko, M. Wuttig, J. Buschbeck, L. Schultz, and S. Fahler, Phys. Rev. Lett. 104, 145702 (2010)] and suggest that the modulation in Ni2MnGa originates from soft-mode phonons.
Title:
Charge-density-wave order with momentum (2Q,0) and (0,2Q) within the spin-fermion model: Continuous and discrete symmetry breaking, preemptive composite order, and relation to pseudogap in hole-doped cuprates
Authors:
Wang, YX; Chubukov, A Author Full Names: Wang, Yuxuan; Chubukov, Andrey
Source:
PHYSICAL REVIEW B, 90 (3):10.1103/PhysRevB.90.035149 JUL 31 2014
Abstract:
We analyze charge order in hole-doped cuprates within the the spin-fermion model. We show that a magnetically mediated interaction, which is known to give rise to d-wave superconductivity and charge order with momentum along zone diagonal, also gives rise to charge order with momenta Q(x) = (2Q,0) and Q(y) = (0,2Q) consistent with the experiments. We show that an instability towards Delta(Q)(k) = < c(k+Q)(dagger)c(k-Q)> with Q = Q(x) or Q(y) is a threshold phenomenon, but the dimensionless spin-fermion coupling is above the threshold, if the magnetic correlation length xi exceeds a certain critical value. At a critical xi, the onset temperature for the charge order terminates at a quantum-critical point distant from the magnetic one. We argue that the charge order with Q(x) or Q(y) changes sign under k -> k + (pi, pi), but vertical bar Delta(Q)(k)vertical bar not equal vertical bar Delta(Q)(k+(pi,pi))vertical bar. In real space, such an order has both bond and site components; the bond one is larger. We further argue that Delta(Q)(k) and Delta(Q)(-k) are not equivalent, and their symmetric and antisymmetric combinations describe, in real space, incommensurate density modulations and incommensurate bond current, respectively. We derive the Ginzburg-Landau functional for four-component U(1) order parameters Delta(Q)(k) with Q = Q(x) or Q(y) and analyze it first in mean-field theory and then beyond mean field. Within mean field we find two types of charge-density-wave (CDW) states, I and II, depending on system parameters. In state I, density and current modulations emerge with the same Q = Q(x) or Q(y), breaking Z(2) lattice rotational symmetry, and differ in phase by +/-pi/2. The selection of pi/2 or -pi/2 additionally breaks Z(2) time-reversal symmetry, such that the total order parameter manifold is U(1) x Z(2) x Z(2). In state II, density and current modulations emerge with different Q and the order parameter manifold is U(1) x U(1) x Z(2), where in the two realizations of state II, Z(2) corresponds to either lattice rotational or time-reversal symmetry breaking. We extend the analysis beyond mean field and argue that discrete symmetries get broken before long-range charge order sets in. For state I, which, we argue, is related to hole-doped cuprates, we show that, upon lowering the temperature, the system first breaks Z(2) lattice rotational symmetry (C-4 -> C-2) at T = T-n and develops a nematic order, then breaks Z(2) time-reversal symmetry at T-t < T-n and locks the relative phase between density and current fluctuations, and finally breaks U(1) symmetry of a common phase of even and odd components of Delta(Q)(k) at T = T-CDW < T-t < T-n and develops a true charge order. We argue that at a mean field, T-CDW is smaller than superconducting T-SC, but preemptive composite order lifts T-CDW and reduces T-SC such that at large xi charge order develops prior to superconductivity. We obtain the full phase diagram and present quantitative comparison of our results with ARPES data for hole-doped cuprates.
Title:
Metastable host-guest structure of carbon
Authors:
Zhu, Q; Feya, OD; Boulfelfel, SE; Oganov, AR Author Full Names: Zhu, Q.; Feya, O. D.; Boulfelfel, S. E.; Oganov, A. R.
Source:
JOURNAL OF SUPERHARD MATERIALS, 36 (4):246-256; 10.3103/S1063457614040030 JUL 2014
Abstract:
A family of metastable host-guest structures, the prototype of which is a tetragonal tP9 structure with 9 atoms per cell has been found. It is composed of an 8-atoms tetragonal host, with atoms filling channels oriented along the c-axis. The tP9 structure has a strong analogy with the recently discovered Ba-IV- and Rb-IV-type incommensurate structures. By considering modulations of the structure due to the variations of the host/guest ratio, it has been concluded that the most stable representative of this family of structures has a guest/host ratio of 2/3 and 26 atoms in the unit cell (space group P4(2)/m). This structure is 0.39 eV/atom higher in energy than diamond. We predict it to have band gap 4.1 eV, bulk modulus 384 GPa, and hardness 61-71 GPa. Due to the different local environments of the host and guest atoms, we considered the possibility of replacing carbon atoms in the guest sublattice by Si atoms in the tP9 prototype and study the properties of the resulting compound SiC8, which was found to have remarkably high bulk modulus 361.2 GPa and hardness 46.2 GPa.

Update: 18-Sep-2014

Title:
Ordered vacancies in the commensurately modulated structure of SrPt1.833 square Sn-0.167(2)
Authors:
Schwickert, C; Hoffmann, RD; Winter, F; Pottgen, R Author Full Names: Schwickert, Christian; Hoffmann, Rolf-Dieter; Winter, Florian; Poettgen, Rainer
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 229 (7):525-535; 10.1515/zkri-2014-1759 2014
Abstract:
The stannide SrPt1.833 square Sn-0.167(2) was synthesized from the elements in a sealed niobium tube in a high-frequency furnace. Its structure was determined by and refined on the basis of single crystal X-ray diffraction data at 300 and 90K. The refinement of 1177/1169 F-2 values with 34/37 variables leads to residuals [I >= 3 sigma(I)] R-M=0.026 (375) and R-S=0.075 (53)/R-M=0.0211 (408) and R-S=0.0503 (128) for the 300/90 K data sets, respectively. SrPt1.833 square Sn-0.167(2) crystallizes with an orthorhombic (3+1)D structure with the supercentered superspace group C(c)mme(O beta O)sOO [beta=1/3 b*, a=655.25(15), b=656.7(4), c=2062.3(5) pm]. It is related to the tetragonal CaBe2Ge2 type structure. The crystal chemistry is described and the structure solution is discussed based on (3+2)D-(3+1)D-3D group-subgroup relations in the Barnighausen formalism. Sn-119 Mossbauer spectra at ambient temperature and 78 K revealed a single signal with isomer shifts of delta=1.78(1) and delta=1.83(1) mm s(-1) with quadropole splitting of Delta E-Q=0.71(1) and 0.86(1) mm s(-1), respectively reflecting the low-symmetric site symmetry of the tin atoms. SrPt1.833 square Sn-0.167(2) was classified as a Pauliparamagnet by magnetic susceptibility measurements. Its specific heat capacity is C-pm=121.4(1) J mol(-1)K(-1) at 300 K.

Update: 11-Sep-2014

Title:
Temperature dependence of the electrical resistivity of Mg-Zn-Y quasicrystal alloy
Authors:
Geng, JW; Teng, XY; Zhou, GR; Zhao, DG Author Full Names: Geng, Jiwei; Teng, Xinying; Zhou, Guorong; Zhao, Degang
Source:
MATERIALS LETTERS, 132 334-337; 10.1016/j.matlet.2014.06.076 OCT 1 2014
Abstract:
Resistivity of Mg63.5Zn34Y2.5 alloy including icosahedral quasicrystalline phase (I-phase) was measured. It shows that the quasicrystal alloy has a negative temperature coefficient of resistivity (TCR) before melting of I-phase. The TCR shows a reversible transition at similar to 1073 K during heating and cooling processes, involving evolution of icosahedral short-range orders (ISROs) inheriting from I-phase. The pre-existing ISROs act as templates in liquid and promote the nucleation of I-phase. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Pairing Symmetry, Spin Gap, and More in HTSC Cuprates
Authors:
Dayan, M Author Full Names: Dayan, Moshe
Source:
JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 27 (9):1973-1981; 10.1007/s10948-014-2549-5 SEP 2014
Abstract:
This work is based on the double correlated linear aggregations of holes in checkerboard geometry. It is proved that the pairing function symmetry is -d (x2 - y2), as been observed experimentally. It is also shown that there is a "superconductive spin gap" for the observation of the magnetic incommensurate modulation peaks, in agreement with the experiment. In addition, the unperturbed Hamiltonian and its related propagator are reanalyzed and modified.
Title:
Evidence of a short-range incommensurate d-wave charge order from a fermionic two-loop renormalization group calculation of a 2D model with hot spots
Authors:
de Carvalho, VS; Freire, H Author Full Names: de Carvalho, Vanuildo S.; Freire, Hermann
Source:
ANNALS OF PHYSICS, 348 32-49; 10.1016/j.aop.2014.05.009 SEP 2014
Abstract:
The two-loop renormalization group (RG) calculation is considerably extended here for the two-dimensional (2D) fermionic effective field theory model, which includes only the so-called "hot spots" that are connected by the spin-density-wave (SDW) ordering wavevector on a Fermi surface generated by the 2D t - t' Hubbard model at low hole doping. We compute the Callan-Symanzik RG equation up to two loops describing the flow of the single-particle Green's function, the corresponding spectral function, the Fermi velocity, and some of the most important order-parameter susceptibilities in the model at lower energies. As a result, we establish that - in addition to dearly dominant SDW correlations - an approximate (pseudospin) symmetry relating a short-range incommensurate d-wave charge order to the d-wave superconducting order indeed emerges at lower energy scales, which is in agreement with recent works available in the literature addressing the 2D spin-fermion model. We derive implications of this possible electronic phase in the ongoing attempt to describe the phenomenology of the pseudogap regime in underdoped cuprates. (C) 2014 Elsevier Inc. All rights reserved.
Title:
Long range ordered magnetic and atomic structures of the quasicrystal approximant in the Tb-Au-Si system
Authors:
Gebresenbut, G; Andersson, MS; Beran, P; Manuel, P; Nordblad, P; Sahlberg, M; Gomez, CP Author Full Names: Gebresenbut, Girma; Andersson, Mikael Svante; Beran, Premysl; Manuel, Pascal; Nordblad, Per; Sahlberg, Martin; Gomez, Cesar Pay
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (32):10.1088/0953-8984/26/32/322202 AUG 13 2014
Abstract:
The atomic and magnetic structure of the 1/1 Tb(14)Au(70)Si(16) quasicrystal approximant has been solved by combining x-ray and neutron diffraction data. The atomic structure is classified as a Tsai-type 1/1 approximant with certain structural deviations from the prototype structures; there are additional atomic positions in the so-called cubic interstices as well as in the cluster centers. The magnetic property and neutron diffraction measurements indicate the magnetic structure to be ferrimagnetic-like below 9 K in contrast to the related Gd(14)Au(70)Si(16) structure that is reported to be purely ferromagnetic.
Title:
Structure of Bergman-type W-TiZrNi approximants to quasicrystal, analyzed by lattice inversion method
Authors:
Huang, H; Meng, DQ; Lai, XC; Liu, TW; Long, Y; Hu, QM Author Full Names: Huang, H.; Meng, D. Q.; Lai, X. C.; Liu, T. W.; Long, Y.; Hu, Q. M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (31):10.1088/0953-8984/26/31/315003 AUG 6 2014
Abstract:
The combined interatomic pair potentials of TiZrNi, including Morse and Inversion Gaussian, are successfully built by the lattice inversion method. Some experimental controversies on atomic occupancies of sites 6-8 in W-TiZrNi are analyzed and settled with these inverted potentials. According to the characteristics of composition and site preference occupancy of W-TiZrNi, two stable structural models of W-TiZrNi are proposed and the possibilities are partly confirmed by experimental data. The stabilities of W-TiZrNi mostly result from the contribution of Zr atoms to the phonon densities of states in lower frequencies.
Title:
Self-similarity and self-inversion of quasicrystals
Authors:
Madison, AE Author Full Names: Madison, A. E.
Source:
PHYSICS OF THE SOLID STATE, 56 (8):1706-1716; 10.1134/S1063783414080162 AUG 2014
Abstract:
The discovery of quasicrystals played a revolutionary role in the condensed matter science and forced to renounce the dogma of the classical crystallography that the regular filling of the space by identical blocks is reduced solely to the Fedorov space groups. It is shown that aperiodic crystals, apart from the similarity, exhibit the self-inversion property. In a broadened sense, the self-inversion implies the possible composition of the inversion with translations, rotations, and homothety, whereas pure reflection by itself in a circle can be absent as an independent symmetry element. It is demonstrated that the symmetry of aperiodic tilings is described by Schottky groups (which belong to a particular type of Kleinian groups generated by the linear fractional Mobius transformations); in the theory of aperiodic crystals, the Schottky groups play the same role that the Fedorov groups play in the theory of crystal lattices. The local matching rules for the Penrose fractal tiling are derived, the problem of choice of the fundamental region of the group of motions of a quasicrystal is discussed, and the relation between the symmetry of aperiodic tilings and the symmetry of constructive fractals is analyzed.
Title:
Charge density wave fluctuations in La2-xSrxCuO4 and their competition with superconductivity
Authors:
Croft, TP; Lester, C; Senn, MS; Bombardi, A; Hayden, SM Author Full Names: Croft, T. P.; Lester, C.; Senn, M. S.; Bombardi, A.; Hayden, S. M.
Source:
PHYSICAL REVIEW B, 89 (22):10.1103/PhysRevB.89.224513 JUN 19 2014
Abstract:
We report hard (14 keV) x-ray diffraction measurements on three compositions (x = 0.11,0.12,0.13) of the high-temperature superconductor La2-xSrxCuO4. All samples show charge density wave (CDW) order with onset temperatures in the range 51-80 K and ordering wave vectors close to (0.23,0,0.5). The CDW is strongest with the longest in-plane correlation length near 1/8 doping. On entering the superconducting state the CDW is suppressed, demonstrating the strong competition between the charge order and superconductivity. CDW order coexists with incommensurate magnetic order and the wave vectors of the two modulations have the simple relationship delta(charge) = 2 delta(spin). The intensity of the CDW Bragg peak tracks the intensity of the low-energy (quasielastic) spin fluctuations. We present a phase diagram of La2-xSrxCuO4 including the pseudogap phase, CDW, and magnetic order.

Update: 3-Sep-2014

Title:
Effect of microstructure on strength and ductility of high strength quasicrystal phase dispersed Mg-Zn-Y alloys
Authors:
Singh, A; Osawa, Y; Somekawa, H; Mukai, T Author Full Names: Singh, Alok; Osawa, Yoshiaki; Somekawa, Hidetoshi; Mukai, Toshiji
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 611 242-251; 10.1016/j.msea.2014.05.091 AUG 12 2014
Abstract:
Recently, magnesium alloys with a dispersion of quasicrystalline icosahedral i-phase have been shown to exhibit very high strengths combined with ductility. However, effect of the i-phase and its amount has not been investigated comprehensively. To make a systematic investigation, two alloys of composition Mg-6x Zn-x Y, where x=0.5 and 1 at%, were chill cast and extruded at three different temperatures to produce various grain sizes with a dispersion of i-phase. The extruded alloys were tested in tension and compression. Very fine grains of micron and submicron size have been obtained, resulting in very high yield strengths of up to about 400 MPa accompanied by total elongations of over 12%. Microstructural features such as precipitation and texture have been studied, and mechanical properties such as strength and ductility in tension and compression have been determined. As the grain size is refined, depending on the alloy composition and extrusion temperature, the texture is also modified, such that a higher strength resulting from finer grain size is accompanied by a reasonable elongation, of over 12%. In aged condition the Hall-Petch plots for tensile and compressive yield strengths are nearly parallel, with slopes in the range of 237-307 MPa mu m(-1/2). The Hall-Petch slopes of critically resolved shear stress of slip and twinning are nearly the same at about 63 MPa mu m(-1/2). (C) 2014 Elsevier B.V. All rights reserved.
Title:
Effect of annealing on the microstructure and mechanical properties of Mg-2.5Zn-0.5Y alloy
Authors:
Zhang, L; Liu, Z; Mao, PL Author Full Names: Zhang, Li; Liu, Zheng; Mao, Ping-li
Source:
INTERNATIONAL JOURNAL OF MINERALS METALLURGY AND MATERIALS, 21 (8):779-784; 10.1007/s12613-014-0971-0 AUG 2014
Abstract:
The microstructure and mechanical properties of extruded Mg-2.5Zn-0.5Y alloy before and after annealing treatments were investigated. The as-extruded alloy exhibits a yield tensile strength (YTS) of 305.9 MPa and an ultimate tensile strength (UTS) of 354.8 MPa, whereas the elongation is only 4%. After annealing, the YTS and UTS decrease to 150 MPa and 240 MPa, respectively, and the elongation increases to 28%. Interestingly, the annealed alloy maintains an acceptable stress level even after a much higher ductility is achieved. These excellent mechanical properties stem from the combined effects of fine alpha-Mg dynamic recrystallization (DRX) grains and a homogeneously distributed icosahedral quasicrystalline phase (I-phase) in the alpha-Mg DRX grains. In particular, the superior ductility originates from the coherent interface of I-phase and alpha-Mg and from the formation of the secondary twin {10 (1) over bar 1}-{10 (1) over bar 2}(38 degrees < 1 <(2)over bar> 10>) in the tension twin {10 (1) over bar 2}.
Title:
Ferroelectricity of Phenazine-Chloranilic Acid at K
Authors:
Noohinejad, L; Mondal, S; Wolfel, A; Ali, SI; Schonleber, A; van Smaalen, S Author Full Names: Noohinejad, Leila; Mondal, Swastik; Woelfel, Alexander; Ali, Sk Imran; Schoenleber, Andreas; van Smaalen, Sander
Source:
JOURNAL OF CHEMICAL CRYSTALLOGRAPHY, 44 (8):387-393; 10.1007/s10870-014-0527-1 AUG 2014
Abstract:
The co-crystal of phenazine (Phz) and chloroanilic acid is ferroelectric below the temperature K (FE-I phase). Upon cooling, two more phase transitions involve a further reduction of symmetry, until Phz-Hca is triclinic in the second ferroelectric phase (FE-II phase) stable below 137 K. Ferroelectricity in all low-temperature phases is believed to be related to partial proton transfer within the hydrogen bonds between the molecules Phz and . Here we present the crystal structure of the FE-II phase at K. Experimental positions of hydrogen atoms indicate that ferroelectricity is mainly governed by half of the hydrogen-bonded chains, whereby proton transfer is observed within one of the two hydrogen bonds in which each molecule participates. A simple point charge model quantitatively reproduces the polarisation of this material. However, a possible contribution to the polarisation is proposed of the O-HN hydrogen bonds of the second half of the mixed chains, which show elongated O-H bonds similar to those in the FE-I phase. The twofold superstructure with symmetry was successfully solved as commensurately modulated structure employing the monoclinic superspace group . The latter shows that the distortions at low temperatures follow a single normal mode of the space group of the FE-I phase, and it thus explains that the direction of the polarisation remains close to the monoclinic axis, despite the lowering towards triclinic symmetry.
Title:
Structure of an Al-Cu-Co Decagonal Quasicrystal Studied by Cs-Corrected STEM
Authors:
Yubuta, K; Yamamoto, K; Yasuhara, A; Hiraga, K Author Full Names: Yubuta, Kunio; Yamamoto, Kazuki; Yasuhara, Akira; Hiraga, Kenji
Source:
MATERIALS TRANSACTIONS, 55 (6):866-870; 10.2320/matertrans.M2014008 JUN 2014
Abstract:
The structure of an Al-Cu-Co decagonal quasicrystal (DQC) with two quasiperiodic planes in an annealed Al64Cu22Co14 alloy has been studied by spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM) with high-angle annular detector dark-field (HAADF) and annular bright-field (ABF) techniques. The observed HAADF-STEM images taken with the incident beam parallel to the periodic axis clearly represent individual transition-metal (TM) Cu/Co atoms and mixed sites (MSs) of Al and TM atoms as separated bright dots, and consequently arrangements of TM atoms and MSs on the two quasiperiodic planes can be directly determined. The TM atoms on the two quasiperiodic planes are arranged in pentagonal tiling with an edge-length of 0.76nm, and also the TM atoms and MSs are located at vertices of Penrose tiling with an edge-length of 0.25 nm, and so they are arranged with a bond orientational order (BOO). Pentagonal frames with definite directions in the pentagonal tiling of TM atoms are also arranged in tau(2)-inflated pentagonal tiling with an edge-length of 2 nm. Arrangements of TM atoms derived from the observed HAADF-STEM image are placed in ideal pentagonal Penrose tiling with an edge-length of 2 nm, which is generated by the projection of five-dimensional (5D) hyper-cubic lattice, and are projected on occupation domains (ODs) in the perpendicular space. The arrangement of Al atoms and TM atoms and MSs in a well-symmetric region is interpreted from the observed HAADF- and ABF-STEM images.

Update: 28-Aug-2014

Title:
Effect of group 5 elements on the formation and corrosion behavior of Ti-based BMG matrix composites reinforced by icosahedral quasicrystalline phase
Authors:
Debnath, MR; Chang, HJ; Fleury, E Author Full Names: Debnath, Mukta Rani; Chang, Hye-Jung; Fleury, Eric
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 612 134-142; 10.1016/j.jallcom.2014.05.049 NOV 5 2014
Abstract:
The addition of a low concentration of group 5 elements to the Ti40Zr29Be16Cu8Ni7 BMG alloys resulted in the formation of particles with icosahedral quasiciystalline symmetry of different size and volume fraction embedded in BMG matrices. Since the i-phase is known for its excellent corrosion resistance, the properties of the TM-containing Ti-based BMGs, with 0 <= TM <= 5 at.%, have been investigated in aerated 1 M H2SO4 + 2 ppm F- solution with 80 degrees C by means of potentio-dynamic, potentio-static and chemical immersion. The addition of 3 at.% Ta provided an alloys with properties similar to those of Ti-6Al-4V alloy in a solution simulating the environment of a bipolar plate in polymer electrolyte membrane. The high corrosion resistances of the in situ BMG matrix composites are attributed to the similarity in the composition of the i-phase and amorphous matrices as well as the formation of protective oxide layers rich in Ti, Zr and V/Ta/Nb. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Magnetic ordering of ScMn6Ge6 by neutron diffraction
Authors:
Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Buschow, KHJ Author Full Names: Schobinger-Papamantellos, P.; Rodriguez-Carvajal, J.; Buschow, K. H. J.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 369 243-248; 10.1016/j.jmmm.2014.06.052 NOV 2014
Abstract:
The compound ScMn6Ge6 (Hffe(6)Ge(6)-type, P6/mmm) orders antiferromagnetically below T-N=516 K. Neutron powder diffraction at various temperatures 1.5-309 K shows the existence of two distinct magnetic ordering ranges described by the commensurate q(1)=(0, 0, 1/2) and the incommensurate q(2)=(0, 0, q(z)) vectors: (i) the HT (high temperature) T-t approximate to 100 K < T < 309 K range described by cut, corresponds to an easy axis antiferromagnetic stacking of the Mn ferromagnetic (0 0 1) layers ( + - - +) at z(Mn) similar to 1/4, 3/4, 5/4, 7/4, the Mn moments being confined to the c-axis. (ii) The LT (low temperature) T-t > T > 1.5 K range has an easy double-cone incommensurately modulated structure described by two vectors (q(1), q(2)). At 1.5 K q(2)=(0, 0, 0.405(1)), the spiral angle is Phi=145.8 degrees the cone half angle is a alpha approximate to 8 degrees and the ordered moment value mu(Mn)=2.12(2)mu(B) is the same as for the isomorphic RMn6Ge6 (R=heavy rare earth) compounds. The 1.5 K q(2) satellites are very weak as the in-plane moment component measures only 0.31 mu(B). (C) 2014 Elsevier B.V. All rights reserved
Title:
Magnetic transitions in the spin-5/2 frustrated magnet BiMn2PO6 and strong lattice softening in BiMn2PO6 and BiZn2PO6 below 200 K
Authors:
Nath, R; Ranjith, KM; Roy, B; Johnston, DC; Furukawa, Y; Tsirlin, AA Author Full Names: Nath, R.; Ranjith, K. M.; Roy, B.; Johnston, D. C.; Furukawa, Y.; Tsirlin, A. A.
Source:
PHYSICAL REVIEW B, 90 (2):10.1103/PhysRevB.90.024431 JUL 30 2014
Abstract:
The crystallographic, magnetic, and thermal properties of polycrystalline BiMn2PO6 and its nonmagnetic analog BiZn2PO6 are investigated by x-ray diffraction, magnetization M, magnetic susceptibility., heat capacity C-p, and P-31 nuclear magnetic resonance (NMR) measurements versus applied magnetic field H and temperature T as well as by density-functional band theory and molecular-field calculations. Both compounds show a strong monotonic lattice softening on cooling, where the Debye temperature decreases by a factor of two from Theta(D) similar to 650 K at T = 300 K to Theta(D) similar to 300 K at T = 2 K. The chi(T) data for BiMn2PO6 above 150 K follow a Curie-Weiss law with a Curie constant consistent with a Mn+2 spin S = 5/2 with g factor g = 2 and an antiferromagnetic (AFM) Weiss temperature theta(CW) similar or equal to -78 K. The. data indicate long-range AFM ordering below T-N similar or equal to 30 K, confirmed by a sharp lambda-shaped peak in C-p(T) at 28.8 K. The magnetic entropy at 100 K extracted from the C-p(T) data is consistent with spin S = 5/2 for the Mn+2 cations. The band-theory calculations indicate that BiMn2PO6 is an AFM compound with dominant interactions J(1)/k(B) similar or equal to 6.7 K and J(3)/k(B) similar or equal to 5.6 K along the legs and rungs of a Mn two-leg spin-ladder, respectively. However, sizable and partially frustrating interladder couplings lead to an anisotropic three-dimensional magnetic behavior with long-range AFM ordering at T-N similar or equal to 30 K observed in the chi, C-p, and NMR measurements. A second magnetic transition at approximate to 10 K is observed from the chi and NMR measurements but is not evident in the C-p data. The C-p data at low T suggest a significant contribution from AFM spin waves moving in three dimensions and the absence of a spin-wave gap. A detailed analysis of the NMR spectra indicates commensurate magnetic order between 10 and 30 K, while below 10 K additional features appear that may arise from an incommensurate modulation and/or spin canting. The commensurate order is consistent with microscopic density functional calculations that yield a collinear Neel-type AFM spin arrangement both within and between the ladders, despite the presence of multiple weak interactions frustrating this magnetic structure of the Mn spins. Frustration for AFM ordering and the one-dimensional spatial anisotropy of the three-dimensional spin interactions are manifested in the frustration ratio f = |theta(CW)|/T-N similar or equal to 2.6, indicating a suppression of T-N from 68 K in the absence of these effects to the observed value of about 30 K in BiMn2PO6.
Title:
Icosahedral AlCuFe quasicrystal at high pressure and temperature and its implications for the stability of icosahedrite
Authors:
Stagno, V; Bindi, L; Shibazaki, Y; Tange, Y; Higo, Y; Mao, HK; Steinhardt, PJ; Fei, YW Author Full Names: Stagno, Vincenzo; Bindi, Luca; Shibazaki, Yuki; Tange, Yoshinori; Higo, Yuji; Mao, H. -K.; Steinhardt, Paul J.; Fei, Yingwei
Source:
SCIENTIFIC REPORTS, 4 10.1038/srep05869 JUL 29 2014
Abstract:
The first natural-occurring quasicrystal, icosahedrite, was recently discovered in the Khatyrka meteorite, a new CV3 carbonaceous chondrite. Its finding raised fundamental questions regarding the effects of pressure and temperature on the kinetic and thermodynamic stability of the quasicrystal structure relative to possible isochemical crystalline or amorphous phases. Although several studies showed the stability at ambient temperature of synthetic icosahedral AlCuFe up to similar to 35 GPa, the simultaneous effect of temperature and pressure relevant for the formation of icosahedrite has been never investigated so far. Here we present in situ synchrotron X-ray diffraction experiments on synthetic icosahedral AlCuFe using multianvil device to explore possible temperature-induced phase transformations at pressures of 5 GPa and temperature up to 1773 K. Results show the structural stability of i-AlCuFe phase with a negligible effect of pressure on the volumetric thermal expansion properties. In addition, the structural analysis of the recovered sample excludes the transformation of AlCuFe quasicrystalline phase to possible approximant phases, which is in contrast with previous predictions at ambient pressure. Results from this study extend our knowledge on the stability of icosahedral AlCuFe at higher temperature and pressure than previously examined, and provide a new constraint on the stability of icosahedrite.
Title:
Effects of Y on Microstructures and Properties of Mg-Zn-Y Alloys Prepared by Conventional Solidification
Authors:
Yang, L; Zhao, YH; Hou, H; Yang, XM Author Full Names: Yang Ling; Zhao Yuhong; Hou Hua; Yang Xiaomin
Source:
RARE METAL MATERIALS AND ENGINEERING, 43 (7):1754-1758; JUL 2014
Abstract:
Mg-45Zn-xY (x=1.0, 4.0, 5.5, 8.0 wt%) alloys were prepared by a conventional solidification technique. The influences of Y on microstructures and properties of Mg-45Zn-xY alloys were investigated by means of SEM, EDS, OM, TEM, XRD, DSC and hardness tests. The formation mechanism of quasicrystal was also analyzed. The results show that microstructures of Mg-45Zn-xY alloys consist of alpha-Mg particle or dendritic crystal, petal-like Mg3Zn6Y quasicrystalline phase (I-phase), lamellar (I-phase+alpha-Mg) eutectic structure and Mg7Zn3 phase. The morphology, the amount and distribution of quasicrystalline phase are closely related to the content of Y. With the increase of Y content, the amount of petal-like quasicrystalline phase increases and when Y content is 5.5 wt%, the alloy has the most petal-like quasicrystalline phase and its hardness reaches the maximum value of HB 1557 MPa. When Y content is 8.0 wt%, the petal-like quasicrystalline phase disappears. Quasicrystalline phase exists in two forms: eutectic structure and petal-like structure, and the special morphology of petal-like structure is the result of icosahedron's growth along five-axis direction.
Title:
Incommensurate Phases of the MgSiF6 center dot 6H(2)O Crystals: EPR and Group-Theoretical Studies
Authors:
Skrylnik, PG; Ziatdinov, AM Author Full Names: Skrylnik, Peter G.; Ziatdinov, Albert M.
Source:
APPLIED MAGNETIC RESONANCE, 45 (7):623-640; 10.1007/s00723-014-0542-6 JUL 2014
Abstract:
The group-theoretical study of the structural phase transition to incommensurate state of MgSiF6 center dot 6H(2)O crystals, revealed by the electron paramagnetic resonance (EPR) method, as well as analysis of the EPR results, are presented. The consideration of temperature dependences of Mn2+ admixture ion EPR spectrum symmetry and parameters leads to the conclusion that at T-i1 = 370 +/- 0.3 K they undergo second-order structural phase transition to incommensurately modulated state, the order parameter of this transition may be the angle of [Mg(H2O)(6)](2+) octahedra rotation around crystal C-3 axis. At temperature decreasing below Ti1 the gradual transformation of plane-wave modulation of lattice displacements into soliton mode occurs, which is interrupted by the first-order phase transition at T-i2 = 343 +/- 0.3 K accompanied by abrupt decrease in modulation amplitude. At T-c = 298.5 +/- 0.3 K the first-order improper ferroelastic phase transition into monoclinic phase occurs. The group-theoretical analysis of the phase transition at T-i1 in the investigated crystals, carried out for the first time, has shown that the existence of the *incommensurately modulated* *phase* is conditioned by the fundamental reasons (presence of Lifshitz invariant). The conclusions of this analysis on the nature of order parameter, the structural motifs of incommensurate phase and the possible character of temperature evolution of the structure are in agreement with the EPR investigation data.
Title:
Effects of Water-Cooling on Quasicrystal Formation of As-Cast Mg-Zn-Zr-Y Alloys and the Microstructure
Authors:
Lu, BJ; Peng, J; Han, W; Tang, AT; Pan, FS Author Full Names: Lu Binjiang; Peng Jian; Han Wei; Tang Aitao; Pan Fusheng
Source:
RARE METAL MATERIALS AND ENGINEERING, 43 (7):1643-1648; JUL 2014
Abstract:
Mg-Zn-Zr-Y alloys containing quasicrystal phase were prepared by an as-cast method with water-cooling. On this base, the effects of different Zn and Y content (the same Zn/Y ratio) on microstructure and micro-hardness were also discussed. The results show that the increase of cooling rate by water-cooling can increase the volume fraction of quasicrystal phase (I-phase, Mg3YZn6) of Mg-Zn-Zr-Y alloy. The decreasing of grain sizes of the as-cast alloy is due to the increase of constitutional supercooling by Y addition. The solid solubility of Zn in alpha-Mg matrix mainly affects the hardness of the matrix, and the hardness of I-phase is much higher than that of the matrix. The liquidus temperature decreases substantially while the solid temperature does not change with Y addition, which weakens the hot cracking tendency of the ingot due to the decrease of freezing range.

Update: 21-Aug-2014

Title:
Room temperature inverse magnetocaloric effect in Pd substituted Ni50Mn37Sn13 Heusler alloys
Authors:
Saha, R; Nigam, AK Author Full Names: Saha, Ritwik; Nigam, A. K.
Source:
PHYSICA B-CONDENSED MATTER, 448 263-266; 10.1016/j.physb.2014.04.011 SEP 1 2014
Abstract:
The structural, magnetic and magnetocaloric effects for Ni50-xPdxMn37Sn13 Heusler alloys have been investigated around both structural and magnetic transitions. The room temperature X-ray diffraction indicates 10 M modulated martensitic structure with an orthorhombic unit cell for x=0 and 1. However, the superstructure reflections for x=2 alloy imply that the pattern is related to the L2(1) phase. The maximum entropy change occurring at the martensitic transition is found to be 21 j kg(-1) K-1 for Ni50Mn37Sn13 alloy around room temperature. Despite the smaller change in entropy around room temperature, 3.8 times larger value of refrigerant capacity (184.6 jfkg) is achieved for 2% substitution of Pd, due to occurrence of magnetic entropy change in a broader temperature region. (C) 2014 Elsevier B.V. All rights reserved,
Title:
Friction and solid-solid adhesion on complex metallic alloys
Authors:
Dubois, JM; Belin-Ferre, E Author Full Names: Dubois, Jean-Marie; Belin-Ferre, Esther
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (3):10.1088/1468-6996/15/3/034804 JUN 2014
Abstract:
The discovery in 1987 of stable quasicrystals in the Al-Cu-Fe system was soon exploited to patent specific coatings that showed reduced friction in ambient air against hard antagonists. Henceforth, it was possible to develop a number of applications, potential or commercially exploited to date, that will be alluded to in this topical review. A deeper understanding of the characteristics of complex metallic alloys (CMAs) may explain why material made of metals like Al, Cu and Fe offers reduced friction; low solid-solid adhesion came later. It is linked to the surface energy being significantly lower on those materials, in which translational symmetry has become a weak property, that is determined by the depth of the pseudo-gap at the Fermi energy. As a result, friction is anisotropic in CMAs that builds up according to the translation symmetry along one direction, but is aperiodic along the other two directions. A review is given in this article of the most salient data found along these lines during the past two decades or so.

Update: 14-Aug-2014

Title:
Orthorhombic Zr2Co11 phase revisited
Authors:
Li, XZ; Zhang, WY; Sellmyer, DJ; Zhao, X; Nguyen, MC; Wang, CZ; Ho, KM Author Full Names: Li, X. -Z.; Zhang, W. Y.; Sellmyer, D. J.; Zhao, X.; Nguyen, M. C.; Wang, C. Z.; Ho, K. M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 611 167-170; 10.1016/j.jallcom.2014.05.072 OCT 25 2014
Abstract:
The structure of the orthorhombic Zr2Co11 phase was revisited in the present work. Selected-area electron diffraction (SAED) and high-resolution electron microscopy (HREM) techniques were used to investigate the structure. They show the orthorhombic Zr2Co11 phase has a 1-D incommensurate modulated structure. The structure can be approximately described as a B-centered orthorhombic lattice. The lattice parameters of the orthorhombic Zr2Co11 phase have been determined by a tilt series of SAED patterns. A hexagonal network with a modulation wave has been observed in the HREM image and the hexagonal motif is considered as the basic structural unit. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Magnetic and transport properties of i-R-Cd icosahedral quasicrystals (R=Y, Gd-Tm)
Authors:
Kong, T; Budko, SL; Jesche, A; McArthur, J; Kreyssig, A; Goldman, AI; Canfield, PC Author Full Names: Kong, Tai; Budko, Sergey L.; Jesche, Anton; McArthur, John; Kreyssig, Andreas; Goldman, Alan I.; Canfield, Paul C.
Source:
PHYSICAL REVIEW B, 90 (1):10.1103/PhysRevB.90.014424 JUL 18 2014
Abstract:
We present a detailed characterization of the recently discovered i-R-Cd (R = Y, Gd-Tm) binary quasicrystals by means of x-ray diffraction, temperature-dependent dc and ac magnetization, temperature-dependent resistance, and temperature-dependent specific heat measurements. Structurally, the broadening of x-ray diffraction peaks found for i-R-Cd is dominated by frozen-in phason strain, which is essentially independent of R. i-Y-Cd is weakly diamagnetic and manifests a temperature-independent susceptibility. i-Gd-Cd can be characterized as a spin glass below 4.6 K via dc magnetization cusp, a third order nonlinear magnetic susceptibility peak, a frequency-dependent freezing temperature, and a broad maximum in the specific heat. i-R-Cd (R = Ho-Tm) is similar to i-Gd-Cd in terms of features observed in thermodynamic measurements. i-Tb-Cd and i-Dy-Cd do not show a clear cusp in their zero-field-cooled dc magnetization data, but instead show a more rounded, broad local maximum. The resistivity for i-R-Cd is of order 300 mu Omega cm and weakly temperature dependent. The characteristic freezing temperatures for i-R-Cd (R = Gd-Tm) deviate from the de Gennes scaling, in a manner consistent with crystal electric field splitting induced local moment anisotropy.
Title:
Switching of the magnetic order in CeRhIn5-xSnx in the vicinity of its quantum critical point
Authors:
Raymond, S; Buhot, J; Ressouche, E; Bourdarot, F; Knebel, G; Lapertot, G Author Full Names: Raymond, S.; Buhot, J.; Ressouche, E.; Bourdarot, F.; Knebel, G.; Lapertot, G.
Source:
PHYSICAL REVIEW B, 90 (1):10.1103/PhysRevB.90.014423 JUL 18 2014
Abstract:
We report neutron diffraction experiments performed in the tetragonal antiferromagnetic heavy fermion system CeRhIn5-xSnx in its (x, T) phase diagram up to the vicinity of the critical concentration x(c) approximate to 0.40, where long range magnetic order is suppressed. The propagation vector of the magnetic structure is found to be k(IC) = (1/2,1/2,k(l)) with k(l) increasing from k(l) = 0.298 to k(l) = 0.410 when x increases from x = 0 to x = 0.26. Surprisingly, for x = 0.30, the order has changed drastically and a commensurate antiferromagnetism with k(C) = (1/2,1/2,0) is found. This concentration is located in the proximity of the quantum critical point where superconductivity is expected.
Title:
Transformation between spin-Peierls and incommensurate fluctuating phases of Sc-doped TiOCl
Authors:
Zhang, J; Wolfel, A; Bykov, M; Schonleber, A; van Smaalen, S; Kremer, RK; Williamson, HL Author Full Names: Zhang, Jian; Woelfel, Alexander; Bykov, Maxim; Schoenleber, Andreas; van Smaalen, Sander; Kremer, Reinhard K.; Williamson, Hailey L.
Source:
PHYSICAL REVIEW B, 90 (1):10.1103/PhysRevB.90.014415 JUL 15 2014
Abstract:
Single crystals of ScxTi1-xOCl (x = 0.005) have been grown by the vapor phase transport technique. Specific heat measurements prove the absence of phase transitions for 4-200 K. Instead, an excess entropy is observed over a range of temperatures that encompasses the incommensurate phase transition at 90 K and the spin-Peierls transition at 67 K of pure TiOCl. Temperature-dependent x-ray diffraction on ScxTi1-xOCl gives broadened diffraction maxima at incommensurate positions between T-cl = 61.5 (3) and similar to 90 K, and at commensurate positions below 61.5 K. These results are interpreted as due to the presence of an incommensurate phase without long-range order at intermediate temperatures, and of a highly disturbed commensurate phase without long-range order at low temperatures. The commensurate phase is attributed to a fluctuating spin-Peierls state on an orthorhombic lattice. The monoclinic symmetry and local structure of the fluctuations are equal to the symmetry and structure of the ordered spin-Peierls state of TiOCl. A novel feature of ScxTi1-xOCl (x = 0.005) is a transformation from one fluctuating phase (the incommensurate phase at intermediate temperatures) to another fluctuating phase (the spin-Peierls-like phase). This transformation is not a phase transition occurring at a critical temperature, but it proceeds gradually over a temperature range of similar to 10 K wide. The destruction of long-range order requires much lower levels of doping in TiOCl than in other low-dimensional electronic crystals, like the canonical spin-Peierls compound CuGeO3. An explanation for the higher sensitivity to doping has not been found, but it is noticed that it may be the result of an increased two-dimensional character of the doped magnetic system. The observed fluctuating states with long correlation lengths are reminiscent of Kosterlitz-Thouless-type phases in two-dimensional systems.
Title:
Magnetocaloric effect in multiferroic Y-type hexaferrite Ba0.5Sr1.5Zn2(Fe0.92Al0.08)(12)O-22
Authors:
Xu, WF; Yang, J; Shen, YD; Bai, W; Zhang, YY; Liu, J; Tang, K; Wang, Z; Duan, CG; Tang, XD; Chu, JH Author Full Names: Xu, Wenfei; Yang, Jing; Shen, Yude; Bai, Wei; Zhang, Yuanyuan; Liu, Jia; Tang, Kai; Wang, Zhi; Duan, Chun-Gang; Tang, Xiaodong; Chu, Junhao
Source:
AIP ADVANCES, 4 (6):10.1063/1.4883235 JUN 2014
Abstract:
Magnetocaloric effect is investigated in multiferroic Ba0.5Sr1.5Zn2(Fe0.92Al0.08)(12)O-22 ceramic with Y-type hexagonal system. Three magnetic transitions, from alternating longitudinal conical to mixed conical at similar to 240 K, to ferrimagnetic at similar to 297 K, further to paramagnetic at similar to 702 K, are unambiguously determined. Furthermore, obvious MCE is shown, and the maximum values of the magnetic entropy change and relative cooling power are evaluated to be 1.53 JKg(-1)K(-1) and 280 JKg(-1) for a field change of 7 T, respectively. In addition, inverse MCE is also observed, which might be associated with the first-order magnetic phase transition between two incommensurate longitudinal conical phases. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Update: 7-Aug-2014

Title:
Crystal structure, disorder and composition of the 2/1 approximant in the Al-Mg-Zn system revisited
Authors:
Berthold, R; Mihalkovic, M; Burkhardt, U; Prots, Y; Amarsanaa, A; Kreiner, G Author Full Names: Berthold, Rico; Mihalkovic, Marek; Burkhardt, Ulrich; Prots, Yurii; Amarsanaa, Altangerel; Kreiner, Guido
Source:
INTERMETALLICS, 53 67-84; 10.1016/j.intermet.2014.02.022 OCT 2014
Abstract:
The tau(1) and tau(2) phases in the Al-Mg-Zn system are famous examples for complex intermetallic alloy phases. They are 1/1 and 2/1 approximants of a quasicrystalline phase. The crystal structure of the tau(2) phase has been studied several times but the reported results are inconsistent. In this work, the tau(2) phase has been investigated in order to determine the homogeneity range at 330 degrees C and 360 degrees C and to revisit its crystal structure. The tau(2) phase is a ternary solid solution phase, which is able to vary its composition by about 5 at.% Al, 2 at.% Mg and 6 at.% Zn at 330 degrees C. Heterogeneous equilibria with the five phases Phi, tau(1), beta, MB21Zn25 and (Mg) have been observed. The Zn-rich beta phase is a new intermetallic compound with a large cubic unit cell. At 360 degrees C, the variation of the Zn content is slightly larger (8 at.%) and the two phases Phi and (Mg) are exchanged in heterogeneous equilibria by a liquid and a quasicrystalline phase. The crystal structure of the tau(2) phase has been studied at the composition Al15.4Mg42.0Zn42.6 by a combined refinement of X-ray and neutron data. Total energy calculations at 0 K reveal two stable variants at the compositions Al14.8Mg40.8Zn44.4 and Al13.0Mg40.8Zn46.2. The chemical and structural disorder can be illustrated with the help of a Henley-Elser decoration of a canonical cell tiling. The crystal data are close to those reported previously reported by Spiekermann, but not in agreement with the results of Sugiyama et al. and Lin et al., which have reported compositions outside the homogeneity range. (C) 2014 Elsevier Ltd. All rights reserved.
Title:
Nanoscale icosahedral quasicrystal phase precipitation mechanism during annealing for Mg-Zn-Gd-based alloys
Authors:
Tian, Y; Huang, H; Yuan, GY; Chen, CL; Wang, ZC; Ding, WJ Author Full Names: Tian, Yuan; Huang, Hua; Yuan, Guangyin; Chen, Chunlin; Wang, Zhongchang; Ding, Wenjiang
Source:
MATERIALS LETTERS, 130 236-239; 10.1016/j.matlet.2014.05.131 SEP 1 2014
Abstract:
We have performed a systematic transmission electron microscopy study of precipitated particles in Mg-Zn-Gd-based alloys after annealing. We find that the Mg-Zn phases and ellipsoidal-shaped icosahedral quasicrystal phases (I-phase) are precipitated and distributed by partition in the grains, which can be attributed to the composition segregation of the alloying elements in the as-cast alloys. The content of alloying element is found to be crucial to the precipitation of nanoscale I-phase. The nanoscale I-phase ranges in size from a few to dozens of nanometers, revealing that the precipitation process satisfies the classical nucleation and growth theory. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Crystal structure and potential interstitial oxide ion conductivity of LnNbO(4) and LnNb(0.92) W0.08O4.04 (Ln = La, Pr, Nd)
Authors:
Li, C; Bayliss, RD; Skinner, SJ Author Full Names: Li, Cheng; Bayliss, Ryan D.; Skinner, Stephen J.
Source:
SOLID STATE IONICS, 262 530-535; SI 10.1016/j.ssi.2013.12.023 SEP 1 2014
Abstract:
Single phase LnNbO(4) and LnNb(0.92) W0.08O4.04 (Ln = La, Pr and Nd) were prepared via solid state reaction. The crystal structure of the materials has been investigated by X-ray diffraction and Rietveld refinement. PrNb0.92 W0.08O4.04 and NdNb0.92 W0.08O4.04 were found to have the same crystal structure as the parent phases whereas LaNb0.92W0.08O4.04 has a modulated structure. Electrical conductivity was studied by AC impedance spectroscopy. Substantial improvements in total conductivity were achieved by W doping on the B-site, with LaNb0.92 W0.08O4.04 having the highest overall conductivity of 3.0 x 10(-3) Scm(-1) at 800 degrees C. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Mesenchymal stromal cell transplantation modulates neuroinflammatory milieu in amyotrophic lateral sclerosis
Authors:
Connick, P; Chandran, S Author Full Names: Connick, Peter; Chandran, Siddharthan
Source:
CYTOTHERAPY, 16 (8):1031-1032; 10.1016/j.jcyt.2014.06.001 AUG 2014
Title:
Crystallographic insights into the intermartensitic transformation in Ni-Mn-Ga alloys
Authors:
Li, ZB; Yang, B; Zhang, YD; Esling, C; Zou, NF; Zhao, X; Zuo, L Author Full Names: Li, Zongbin; Yang, Bo; Zhang, Yudong; Esling, Claude; Zou, Naifu; Zhao, Xiang; Zuo, Liang
Source:
ACTA MATERIALIA, 74 9-17; 10.1016/j.actamat.2014.04.025 AUG 1 2014
Abstract:
Ferromagnetic shape memory alloys such as Ni-Mn-Ga usually undergo intermartensitic transformation upon cooling or heating. Here, an attempt is made to explore the microstructural features and orientation relationships associated with the intermartensitic transformation from seven-layered modulated (7M) martensite to non-modulated (NM) martensite in a polycrystalline Ni53Mn22Ga25 alloy. Based on electron backscatter diffraction analysis, it is demonstrated that the intermartensitic transformation proceeds in an in-plate manner (through atomic reshuffling and lattice distortion) with specific orientation relationships between the two martensitic phases, i.e. (0 0 1)(7M)//(1 1 2)(NM) and [1 0 0](7M)//[1 1 (1) over bar](NM) as well as (0 0 1)(7M)//(1 1 2)(NM) and [(1) over bar 0 0](7M)//[1 1 (1) over bar](NM), accompanied by the thickening of martensite plates and the surface relief effect. Consequently, one 7M variant (plate) evolves into one NM plate consisting of two twin-related fine variants, and four differently oriented 7M variants in one variant group result in a total of eight NM variants. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Phonon and thermal transport properties of the misfit-layered oxide thermoelectric Ca3Co4O9 from first principles
Authors:
Rebola, A; Klie, RF; Zapol, P; Ogut, S Author Full Names: Rebola, Alejandro; Klie, Robert F.; Zapol, Peter; Oeguet, Serdar
Source:
APPLIED PHYSICS LETTERS, 104 (25):10.1063/1.4885389 JUN 23 2014
Abstract:
The full phonon spectra of two rational approximants to the incommensurate thermoelectric oxide material Ca3Co4O9 (CCO) are calculated from first principles within density functional theory (DFT) and its DFT + U extension. The computed phonon dispersion curves are then used to evaluate the constant volume heat capacity, as well as the full and partial (subsystem-projected) lattice thermal conductivity of CCO. The results are discussed in terms of the effects of the Hubbard U on the computed properties, the size of the rational approximants used to model CCO, the relative contributions of the two subsystems that comprise the misfit-layered material, and the anisotropic nature of the computed thermal conductivity. We obtain good agreement with available experimental data. (C) 2014 AIP Publishing LLC.
Title:
Mapping of strained graphene into one-dimensional Hamiltonians: Quasicrystals and modulated crystals
Authors:
Naumis, GG; Roman-Taboada, P Author Full Names: Naumis, Gerardo G.; Roman-Taboada, Pedro
Source:
PHYSICAL REVIEW B, 89 (24):10.1103/PhysRevB.89.241404 JUN 11 2014
Abstract:
The electronic properties of graphene under any arbitrary uniaxial strain field are obtained by an exact mapping of the corresponding tight-binding Hamiltonian into an effective one-dimensional modulated chain. For a periodic modulation, the system displays a rich behavior, including quasicrystals and modulated crystals with a complex spectrum, including gaps and peaks at the Fermi energy and localization transitions. All these features are explained by the incommensurate or commensurate nature of the potential, which leads to a dense filling by diffraction spots of the reciprocal space in the former case. The essential features of strain are made specially clear by analyzing a special momenta that uncouples the model into dimers.
Title:
Hidden one-dimensional spin modulation in a three-dimensional metal
Authors:
Feng, YJ; Wang, JY; Palmer, A; Aguiar, JA; Mihaila, B; Yan, JQ; Littlewood, PB; Rosenbaum, TF Author Full Names: Feng, Yejun; Wang, Jiyang; Palmer, A.; Aguiar, J. A.; Mihaila, B.; Yan, J. -Q.; Littlewood, P. B.; Rosenbaum, T. F.
Source:
NATURE COMMUNICATIONS, 5 10.1038/ncomms5218 JUN 2014
Abstract:
Pressure can transform a transparent material into an opaque one, quench the moments in a magnet and force solids to flow like liquids. At 15 GPa, the pressure found 500 km below the earth's surface, the semiconductors silicon and germanium superconduct. Yet, at this same pressure, we show here that the magnetism in metallic GdSi remains completely robust even as it shrinks by one-seventh of its volume. Non-resonant X-ray magnetic diffraction in a specially designed diamond anvil cell, combined with band structure calculations, reveal the stability of the incommensurate spin density wave, which can be traced to a persistently nested portion of the Fermi surface that becomes increasingly one-dimensional under pressure. A cooperative interaction between nested, itinerant spins and local magnetic moments provides the organizing principle for the modulated magnetic order, salient both for its insights into the role of topology in ordered states and its potential functionality.
Title:
Electronic and magnetic properties of BiFeO3 with intrinsic defects: First-principles prediction
Authors:
Yang, RP; Lin, SX; Fang, XG; Qin, MH; Gao, XS; Zeng, M; Liu, JM Author Full Names: Yang Rui-Peng; Lin Si-Xian; Fang Xiao-Gong; Qin Ming-Hui; Gao Xing-Sen; Zeng Min; Liu Jun-Ming
Source:
CHINESE PHYSICS B, 23 (6):10.1088/1674-1056/23/6/067102 JUN 2014
Abstract:
The electronic structure, magnetism, and dielectric functions of BiFeO3 with intrinsic vacancies, including Bi-, Fe-, and O-vacancies (denoted as V-Fe, V-Bi, and V-O, respectively) are investigated using the first-principles density functional theory plus U calculations. It is revealed that the structural distortions associated with those vacancies impose significant influences on the total density of state and magnetic behaviors. The existence of V-Bi favors the excitation of the O-2p state into the band gap at 0.4 eV, while the O-2p and Fe-3d orbitals are co-excited into the band gap around 0.45 eV in V-Fe. Consequently, a giant net magnetic moment of 1.96 mu(B) is generated in VFe, and a relatively small moment of 0.13 mu B is induced in V-Bi, whereas VO seems magnetically inactive. The giant magnetic moment generated in V-Fe originates from the suppression of the spatially modulated antiferromagnetic spin structure. Furthermore, V-Fe and V-Bi have strong influences on dielectric function, and induce some strong peaks to occur in the lower energy level. In contrast, V-O has a small effect.
Title:
Impact-induced shock and the formation of natural quasicrystals in the early solar system
Authors:
Hollister, LS; Bindi, L; Yao, N; Poirier, GR; Andronicos, CL; MacPherson, GJ; Lin, C; Distler, VV; Eddy, MP; Kostin, A; Kryachko, V; Steinhardt, WM; Yudovskaya, M; Eiler, JM; Guan, YB; Clarke, JJ; Steinhardt, PJ Author Full Names: Hollister, Lincoln S.; Bindi, Luca; Yao, Nan; Poirier, Gerald R.; Andronicos, Christopher L.; MacPherson, Glenn J.; Lin, Chaney; Distler, Vadim V.; Eddy, Michael P.; Kostin, Alexander; Kryachko, Valery; Steinhardt, William M.; Yudovskaya, Marina; Eiler, John M.; Guan, Yunbin; Clarke, Jamil J.; Steinhardt, Paul J.
Source:
NATURE COMMUNICATIONS, 5 10.1038/ncomms5040 JUN 2014
Abstract:
The discovery of a natural quasicrystal, icosahedrite (Al63Cu24Fe13), accompanied by khatyrkite (CuAl2) and cupalite (CuAl) in the CV3 carbonaceous chondrite Khatyrka has posed a mystery as to what extraterrestrial processes led to the formation and preservation of these metal alloys. Here we present a range of evidence, including the discovery of high-pressure phases never observed before in a CV3 chondrite, indicating that an impact shock generated a heterogeneous distribution of pressures and temperatures in which some portions reached at least 5GPa and 1,200 degrees C. The conditions were sufficient to melt Al-Cu-bearing minerals, which then rapidly solidified into icosahedrite and other Al-Cu metal phases. The meteorite also contains heretofore unobserved phases of iron-nickel and iron sulphide with substantial amounts of Al and Cu. The presence of these phases in Khatyrka provides further proof that the Al-Cu alloys are natural products of unusual processes that occurred in the early solar system.
Title:
Networks of superconducting nano-puddles in 1/8 doped YBa2Cu3O6.5+y controlled by thermal manipulation
Authors:
Ricci, A; Poccia, N; Campi, G; Coneri, F; Barba, L; Arrighetti, G; Polentarutti, M; Burghammer, M; Sprung, M; Zimmermann, MV; Bianconi, A Author Full Names: Ricci, Alessandro; Poccia, Nicola; Campi, Gaetano; Coneri, Francesco; Barba, Luisa; Arrighetti, Gianmichele; Polentarutti, Maurizio; Burghammer, Manfred; Sprung, Michael; Zimmermann, Martin V.; Bianconi, Antonio
Source:
NEW JOURNAL OF PHYSICS, 16 10.1088/1367-2630/16/5/053030 MAY 14 2014
Abstract:
While it is known that the nature and the arrangement of defects in complex oxides have an impact on the material functionalities, little is known about control of superconductivity by oxygen interstitial organization in cuprates. Here we report direct compelling evidence for the control of T-c by manipulation of the superconducting granular networks of nanoscale puddles, made of ordered oxygen stripes, in a single crystal of YBa2Cu3O6.5+y with average formal hole doping p close to 1/8. Upon thermal treatments we were able to switch from a first network of oxygen defect striped puddles with OVIII modulation ((qOVIII)(a*) = (h + 3/8, k, 0) and (qOVIII)(a*) = (h + 5/8, k, 0)) to a second network characterized by OXVI modulation ((qOXVI)(a*) = (h + 7/16, k, 0) and (qox-VI)(a*) = (h + 9/16, k, 0)) and finally to a third network with puddles of OV periodicity ((qOV)(a*) = (4/10, 1, 0) and (qOV)(a*) = (6/10, 1, 0)). We map the microscopic spatial evolution of the out of plane OVIII, OXVI and OV puddle nanosize distribution via scanning micro-diffraction measurements. In particular, we calculated the number of oxygen chains (n) and the charge density (hole concentration p) inside each puddle, analyzing areas of 160 x 80 mu m(2), and recording 12 800 diffraction patterns to reconstruct each spatial map. The high spatial inhomogeneity shown by all the reconstructed spatial maps reflects the intrinsic granular structure that characterizes cuprates and iron chalcogenides, disclosing the presence of several complex networks of coexisting superconducting domains with different lattice modulations, charge densities and gaps as in the proposed multi-gap scenario called superstripes.
Title:
Internal Friction of an Ag-In-Yb Icosahedral Quasicrystal
Authors:
Handa, K; So, YG; Kamimura, Y; Tamura, R; Edagawa, K Author Full Names: Handa, Kenma; So, Yeong-Gi; Kamimura, Yasushi; Tamura, Ryuji; Edagawa, Keiichi
Source:
MATERIALS TRANSACTIONS, 55 (5):754-757; 10.2320/matertrans.M2013448 MAY 2014
Abstract:
Internal friction has been measured for an Ag-In-Yb Tsai-type icosahedral (i-) quasicrystal to investigate an energy-dissipation mechanism by phason relaxation, possibly operating in quasicrystals. A fairly large peak of the magnitude Q(-1) approximate to 0.022 was observed, which was shown to be of the thermally-activated relaxation type. The frequency factor and activation enthalpy were evaluated to be 10(20)s(-1) and 2.6 x 10(-19)J (1.6 eV), respectively. The observed peak was analyzed on the assumption that it is of phason-origin. The magnitude of the phonon-phason coupling constant was estimated to be 0.008 mu (mu: shear modulus), based on the model of the phonon-phason elastodynamics previously proposed. This value is comparable to those previously reported for Mackay-type i-phases such as i-Al-Pd-Mn and i-Al-Cu-Fe.

Update: 31-Jul-2014

Title:
Growth Modes of Quasicrystals
Authors:
Achim, CV; Schmiedeberg, M; Lowen, H Author Full Names: Achim, C. V.; Schmiedeberg, M.; Loewen, H.
Source:
PHYSICAL REVIEW LETTERS, 112 (25):10.1103/PhysRevLett.112.255501 JUN 26 2014
Abstract:
The growth of quasicrystals, i.e., aperiodic structures with long-range order, seeded from the melt is investigated using a dynamical phase field crystal model. Depending on the thermodynamic conditions, two different growth modes are detected, namely defect-free growth of the stable quasicrystal and a mode dominated by phasonic flips which are incorporated as local defects into the grown structure such that random tilinglike ordering emerges. The latter growth mode is unique to quasicrystals and can be verified in experiments on one-component mesoscopic systems.
Title:
Commensurate-incommensurate magnetic phase transition in the Fe-doped bilayer ruthenate Ca3Ru2O7
Authors:
Ke, X; Peng, J; Tian, W; Hong, T; Zhu, M; Mao, ZQ Author Full Names: Ke, X.; Peng, J.; Tian, W.; Hong, Tao; Zhu, M.; Mao, Z. Q.
Source:
PHYSICAL REVIEW B, 89 (22):10.1103/PhysRevB.89.220407 JUN 23 2014
Abstract:
Neutron diffraction studies have revealed an uncommon commensurate-incommensurate magnetic phase transition with decreasing temperature in the (similar to 5%) Fe-doped bilayer ruthenate Ca-3(Ru,Fe)(2)O-7. An incommensurate phase formed of a cycloidal spiral spin structure coexists with a commensurate one below the phase transition at 42 K and persists down to the lowest temperature, accompanied by higher-order magnetic satellite peaks which indicate the formation of a magnetic soliton lattice. We ascribe these findings to the competing magnetic interactions in this system. This study demonstrates an effective approach to tune novel magnetic and electronic properties of ruthenates via 3d magnetic transition-metal substitution.
Title:
Charge- and spin-density waves observed through their spatial fluctuations by coherent and simultaneous x-ray diffraction
Authors:
Jacques, VLR; Pinsolle, E; Ravy, S; Abramovici, G; Le Bolloc'h, D Author Full Names: Jacques, V. L. R.; Pinsolle, E.; Ravy, S.; Abramovici, G.; Le Bolloc'h, D.
Source:
PHYSICAL REVIEW B, 89 (24):10.1103/PhysRevB.89.245127 JUN 23 2014
Abstract:
Spatial fluctuations of spin-density wave (SDW) and charge-density wave (CDW) in chromium have been compared by combining coherent and simultaneous x-ray diffraction experiments. Despite their close relationship, spatial fluctuations of the spin and of the charge-density waves display a very different behavior: the satellite reflection associated to the charge density displays speckles while the spin one displays an impressive long-range order. This observation is hardly compatible with the commonly accepted magneto-elastic origin of CDW in chromium and is more consistent with a purely electronic scenario where CDW is the second harmonic of SDW. A BCS model taking into account a second-order nesting predicts correctly the existence of a CDW and explains why the CDW is more sensitive to punctual defects.
Title:
On Symplectic Analysis for the Plane Elasticity Problem of Quasicrystals with Point Group 12 mm
Authors:
Wang, H; Chen, JR; Zhang, XY Author Full Names: Wang, Hua; Chen, Jianrui; Zhang, Xiaoyu
Source:
ABSTRACT AND APPLIED ANALYSIS, 10.1155/2014/367018 2014
Abstract:
The symplectic approach, the separation of variables based on Hamiltonian systems, for the plane elasticity problem of quasicrystals with point group 12 mm is developed. By introducing appropriate transformations, the basic equations of the problem are converted to two independent Hamiltonian dual equations, and the associated Hamiltonian operator matrices are obtained. The study of the operator matrices shows the feasibility of the method. Without any assumptions, the general solution is presented for the problem with mixed boundary conditions.

Update: 24-Jul-2014

Title:
Modulating the Li+/Ni2+ replacement and electrochemical performance optimizing of layered Lithium-rich Li1.2Ni0.2Mn0.6O2 by minor Co dopant
Authors:
Huang, XL; Wang, M; Che, RC Author Full Names: Huang, Xiaolan; Wang, Min; Che, Renchao
Source:
JOURNAL OF MATERIALS CHEMISTRY A, 2 (25):9656-9665; 10.1039/c4ta01217h JUL 7 2014
Abstract:
The influences of the Li+/Ni2+ replacement modulated by minor Co dopant on cyclic capacity and rate performance of lithium-rich cathode material Li1.2Ni0.2-z/2Mn0.6-z/2CozO2 (z = 0, 0.02, 0.04, 0.10) were investigated from the microstructural point of view by comprehensive techniques of high-resolution transmission electron microscopy (HRTEM) imaging, atomic-resolution electron energy loss spectroscopy (EELS), selected-area electron diffraction (SAED), and X-ray diffraction (XRD). It is found that Co played a vital role in decreasing the Li+/Ni2+ replacement ratio in the hexagonal layered Li1 2Ni0.2-z/2Mn0.6-z/2CozO2 (R (3) over barm), which is closely related to the electrochemical performance. An evident cationic ordering in the transition metal layers and a stacking sequence vertical to the Li+ diffusion orientation were observed in the Li1.2Ni0.2-z/2Mn0.6-z/2CozO2 (z > 0) system rather than in the Li1.2Ni0.2Mn0.6O2 system. Compared with Li1.2Ni0 2Mn0.6O2, Li1.2Ni0.18Mn0.58Co0.04O2 showed excellent electrochemical performance with increase in discharge capacity to 288.3 mA h g(-1) from 166.3 mA h g(-1), improvement in capacity retention to 98.6% from 73.9% at a current density of 0.1 C after 40 cycles, and enhancement in capacity to 161.4 mA h g(-1) from 113 mA h g(-1) at a higher rate of 2 C. The largest interlayer spacing (0.218 nm of O-Li-O layer), highest proportion of Mn4+ ion component, and the most remarkable superstructure diffraction spots were found for Li1.2Ni0.18Mn0.58Co0.04O2 among all specimens, as confirmed by XRD refinement, EELS, HRTEM, and SAED. Three superstructure vectors modulated by 1/4 (q) over right arrow, 2/4 (q) over right arrow, 3/4 (q) over right arrow ((q) over right arrow = [0 (1) over bar1]) were simultaneously observed for Li1.2Ni0.18Mn0.58Co0.04O2, indicating a high degree of ordering. Our findings might shed new insights into the understanding of the Li+/Ni2+ replacement by doping minor amounts of Co for optimizing the electrochemical performance in Li-ion batteries cathode material from the microstructural point of view.
Title:
Al-Cr-Fe phase diagram. Isothermal Sections in the region above 50 at% Al
Authors:
Pavlyuchkov, D; Przepiorzynski, B; Kowalski, W; Velikanova, TY; Grushko, B Author Full Names: Pavlyuchkov, D.; Przepiorzynski, B.; Kowalski, W.; Velikanova, T. Ya.; Grushko, B.
Source:
CALPHAD-COMPUTER COUPLING OF PHASE DIAGRAMS AND THERMOCHEMISTRY, 45 194-203; 10.1016/j.calphad.2013.12.007 JUN 2014
Abstract:
The Al-Cr-Fe phase diagram was studied in the compositional range of 50-100 at% Al and partial isothermal sections were determined at 1160, 1100, 1075, 1042, 1000, 900, 800 and 700 degrees C In the low-Al part of the studied compositional region the isostructural high-temperature Al-Cr and Al-Fe gamma(1)- phases form a continuous region of solid solutions. Both binary Al13Fe4 and Al5Fe2 were found to dissolve up to 6.5 at% Cr while Al2Fe was found to extend up to 4.1 at% Cr. The solid solutions based on the Al-Cr gamma(2) and mu phases were determined to reach 35.2 and 1.3 at% Fe, respectively. The dissolution of Cr in the Al-Fe binaries only slightly influences their Al concentrations, while the Al-Cr binaries exhibit decreasing Al concentration with increasing Fe concentration. The Al-Cr eta-phase dissolves up to 5 at% Fe, which results in a sharp decrease of its Al concentration and increase of melting temperatures. The earlier reported existence of a ternary decagonal D-3-phase and three complex periodic phases O-1, H and e was confirmed and their compositions at different temperatures were specified. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Atomic clusters and atomic surfaces in icosahedral quasicrystals
Authors:
Quiquandon, M; Portier, R; Gratias, D Author Full Names: Quiquandon, Marianne; Portier, Richard; Gratias, Denis
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 70 229-238; 10.1107/S2053273314004665 3 MAY 2014
Abstract:
This paper presents the basic tools commonly used to describe the atomic structures of quasicrystals with a specific focus on the icosahedral phases. After a brief recall of the main properties of quasiperiodic objects, two simple physical rules are discussed that lead one to eventually obtain a surprisingly small number of atomic structures as ideal quasiperiodic models for real quasicrystals. This is due to the fact that the atomic surfaces (ASs) used to describe all known icosahedral phases are located on high-symmetry special points in six-dimensional space. The first rule is maximizing the density using simple polyhedral ASs that leads to two possible sets of ASs according to the value of the six-dimensional lattice parameter A between 0.63 and 0.79 nm. The second rule is maximizing the number of complete orbits of high symmetry to construct as large as possible atomic clusters similar to those observed in complex intermetallic structures and approximant phases. The practical use of these two rules together is demonstrated on two typical examples of icosahedral phases, i-AlMnSi and i-CdRE (RE = Gd, Ho, Tm). (C) 2014 International Union of Crystallography
Title:
Fluorinated mixed valence Fe(II)-Fe(III) phosphites with channels templated by linear tetramine chains. Structural and magnetic implications of partial replacement of Fe(II) by Co(II)
Authors:
Orive, J; de Luis, RF; Fernandez, JR; Legarra, E; Plazaola, F; Arriortua, MI Author Full Names: Orive, Joseba; de Luis, Roberto Fernandez; Fernandez, Jesus Rodriguez; Legarra, Estibaliz; Plazaola, Fernando; Arriortua, Maria I.
Source:
CRYSTENGCOMM, 16 (27):6066-6079; 10.1039/c4ce00264d 2014
Abstract:
Three new fluorinated mixed valence Fe(II)-Fe(III) phosphites were synthesized by employing mild hydrothermal conditions. (H(4)baepn) (0.5)[(Fe2.3Fe1.7II)-Fe-III(H2O)(2)(HPO3)(4)-((x+y))(HPO4)x(PO4)yF(4)] (x similar or equal to 0.13, y similar or equal to 0.3) (1) (baepn = N,N'-bis(2-aminoethyl)-1,3-propanediamine (C7N4H20)) and the Co(II)-substituted phase with the formula (H(4)baepn)(0.5)[(Fe2.0FeI0.71Co1.29II)-Fe-III-Co-I(H2O)(2)(HPO3)(4-x)(H PO4)xF(4)] (x similar or equal to 0.38) (2) were studied by single crystal X-ray diffraction. The phase with the major content of Co(II), (H(4)baepn)(0.5)[(Fe2.0Fe0.62Co1.38II)-Fe-III-Co-II(H2O)(2)(HPO3)(4-x)(H PO4)xF(4)] (x similar or equal to 0.38) (3) was obtained as a polycrystalline powder and studied by Rietveld refinement by using the structural model of 2. These compounds were characterized by ICP-Q-MS, thermogravimetric and thermodiffractometric analyses, and XPS, IR, UV/ vis and Mssbauer spectroscopy. The single crystal data indicate that phases 1 and 2 crystallize in the P2(1)/c space group with lattice parameters a = 13.6808(4), b = 12.6340(2), c = 12.7830(3) angstrom and beta = 116.983(4)degrees for 1 and a = 13.6823(4), b = 12.6063(3), c = 12.7535(4) angstrom and beta = 116.988(4)degrees for 2, with Z = 4. The reciprocal space of 1 shows satellite reflections with a modulation wavevector q = 0.284(2)a* which indicate an *incommensurate* long-range order. The average structure of these compounds is built up by a 3D lattice constructed by inorganic layers of Fe(III) chains and Fe(II) and Co(II) dimers joined by phosphite groups partially substituted by HPO4 and PO4 tetrahedral groups. These anionic layers stack along the [100] direction encapsulating linear tetramines in eight-membered open channels involving host-guest interactions. Magnetic measurements of 1 and 3 showed antiferromagnetic coupling as the major interactions, exhibiting a weak ferromagnetic component together with a spin glass transition at low temperature in the case of 1. Heat capacity measurements showed a small anomaly at 20.5 K for 1 and a sharp magnetic peak at 28 K for 3. Unexpectedly, the small anomaly observed in 1 increased with the magnetic field and became better defined.

Update: 10-Jul-2014

Title:
Pressure-induced polar phases in multiferroic delafossite CuFeO2
Authors:
Terada, N; Khalyavin, DD; Manuel, P; Osakabe, T; Radaelli, PG; Kitazawa, H Author Full Names: Terada, Noriki; Khalyavin, Dmitry D.; Manuel, Pascal; Osakabe, Toyotaka; Radaelli, Paolo G.; Kitazawa, Hideaki
Source:
PHYSICAL REVIEW B, 89 (22):10.1103/PhysRevB.89.220403 JUN 13 2014
Abstract:
The pressure effect on the frustrated magnetic system CuFeO2 exhibiting multiferroic behavior has been studied by means of time-of-flight single crystal neutron diffraction combined with a hybrid-anvil-type pressure cell. The nonpolar collinear magnetic ground state (CM1 phase) with propagation vector k = (0, 1/2, 1/2) turns into a proper screw magnetic ordering with incommensurate modulation k = (0, q, 1/2; q similar or equal to 0.4) and a polar 21 ' magnetic point group (ICM2 phase), between 3 and 4 GPa. This spin structure is similar to the ferroelectric phase induced by magnetic field or chemical doping under ambient pressure. Above, 4 GPa, a magnetic phase (ICM3) appears, with an incommensurate propagation vector that is unique for the CuFeO2 system, k = (qa, qb, qc; qa similar or equal to 0, qb similar or equal to 0.34, qc similar or equal to 0.43). This propagation vector at the general point results in triclinic magnetic symmetry which implies an admixture of both cycloidal and proper screw spin configurations. The ICM3 phase is stable in a narrow pressure range, and above 6 GPa, the spin-density collinear structure (ICM1 phase), similar to the first ordered state at ambient pressure, takes place. Comparing the degree of lattice distortions among the magnetic phases observed at ambient pressure, we discuss the origin of the pressure-induced magnetic phase transitions in CuFeO2.
Title:
Synthesis of [(SnSe)(1.16-1.09)](1)[(NbxMo1-x)Se-2](1) Ferecrystal Alloys
Authors:
Westover, RD; Atkins, RA; Ditto, JJ; Johnson, DC Author Full Names: Westover, Richard D.; Atkins, Ryan A.; Ditto, Jeffrey J.; Johnson, David C.
Source:
CHEMISTRY OF MATERIALS, 26 (11):3443-3449; 10.1021/cm500720x JUN 10 2014
Abstract:
Modification of the modulated elemental reactant method allowed the first reported synthesis of quaternary [(MX)(z)](m)[(TxT'(1-x))X-2](n), compounds with controlled compositions. Metastable ferecrystal compounds, [(SnSe)(1.16-1.09)](1)[(NbxMo1-x)Se-2](1) with x = 0, 0.26, 0.49, 0.83, and 1, were synthesized and characterized by X-ray diffraction, electron probe microanalysis (EPMA), and scanning transmission electron microscopy (STEM). Misfit layer dichalcogenide analogues, showing controlled alloying of the dichalcogenide layers, have not been reported. Changes in lattice parameters, as a function of x, were similar to literature observations for the (NbxMo1-x)Se-2 system. The c-lattice parameters of the ferecrystal alloys decreased linearly from 12.53(2) angstrom for [(SnSe)(1.09)](1)(MoSe2)(1) to 12.27(2) angstrom for [(SnSe)(1.6)](1)(NbSe2)(1). The a-lattice parameters of the dichalcogenide constituent increased from 3.329(8) angstrom for [(SnSe)(1.09)](1)(MoSe2)(1) to 3.461(4) angstrom for [(SnSe)(1.6)](1)(NbSe2)(1). The a-lattice parameter of the rocksalt constituent remained constant resulting in a linear increase in misfit parameter with increased Nb content. Temperature dependent electrical resistivity measurements showed a transition from semiconducting to metallic behavior as the Nb content of the alloys increased.
Title:
Conduction-band electronic structure of 1T-TaS2 revealed by angle-resolved inverse-photoemission spectroscopy
Authors:
Sato, H; Arita, M; Utsumi, Y; Mukaegawa, Y; Sasaki, M; Ohnishi, A; Kitaura, M; Namatame, H; Taniguchi, M Author Full Names: Sato, Hitoshi; Arita, Masashi; Utsumi, Yuki; Mukaegawa, Yutaka; Sasaki, Minoru; Ohnishi, Akimasa; Kitaura, Mamoru; Namatame, Hirofumi; Taniguchi, Masaki
Source:
PHYSICAL REVIEW B, 89 (15):10.1103/PhysRevB.89.155137 APR 28 2014
Abstract:
We have investigated the conduction-band electronic structure of 1T-TaS2 in the incommensurate (IC) and commensurate (C) charge-density-wave (CDW) phases by means of angle-resolved inverse-photoemission spectroscopy (ARIPES) along the Gamma (A)-M (L) direction. In the ARIPES spectra for the ICCDW phase, a continuous and dispersive Ta 5d band is clearly observed near the Fermi level (E-F). For the CCDW phase, on the other hand, the Ta 5d band splits up and down into two manifolds around the M (L) point, reflecting formation of the root 13 x root 13 superstructure of the Ta plane. In addition, the CCDW-ARIPES spectrum around the M (L) points exhibits a shoulder structure at 0.7 eV above E-F, ascribed to the upper Hubbard band folded from the Gamma (Lambda) point. We have also observed an energy gap of similar to 100 meV in the unoccupied density of states in the CCDW phase.

Update: 2-Jul-2014

Title:
Development of Very High Strength and Ductile Dilute Magnesium Alloys by Dispersion of Quasicrystal Phase
Authors:
Singh, A; Osawa, Y; Somekawa, H; Mukai, T; Parrish, CJ; Shih, DS Author Full Names: Singh, Alok; Osawa, Yoshiaki; Somekawa, Hidetoshi; Mukai, Toshiji; Parrish, Catherine J.; Shih, Donald S.
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 45A (8):3232-3240; 10.1007/s11661-013-2056-5 JUL 2014
Abstract:
Very high strengths, with tensile yield strength from 377 to 405 MPa, combined with elongation to failure of over 12 pct, have been achieved in Mg-Zn-Y dilute alloys by direct extrusion. Alloys Mg-6xZn-xY, where x = 0.2, 0.35, and 0.5 (at. pct) were chill cast in a steel mold and direct extruded at a temperature in the range 508 K to 528 K (235 A degrees C to 255 A degrees C), which produced an average grain size of about 1 mu m. Quasicrystalline i-phase particles were dispersed in the matrix with size ranging from 50 nm to 1 mu m. In addition, high density of nano-precipitates of average size 15 nm was dispersed in matrix. Thus we have developed magnesium alloys of very high strength combined with ductility by a simple process using extrusion with very little addition of yttrium. (C) The Minerals, Metals & Materials Society and ASM International 2013
Title:
Localization and Impact of Pb-Non-Bonded Electronic Pair on the Crystal and Electronic Structure of Pb2YSbO6
Authors:
Larrogola, SA; Alonso, JA; de la Pena-O'Shea, VA; Sheptyakov, D; Pomjakushin, V; Fernandez-Diaz, MT; Pedregosa, JC Author Full Names: Larregola, Sebastian A.; Alonso, Jose A.; de la Pena-O'Shea, Victor A.; Sheptyakov, Denis; Pomjakushin, Vladimir; Fernandez-Diaz, Maria T.; Pedregosa, Jose C.
Source:
INORGANIC CHEMISTRY, 53 (11):5609-5618; 10.1021/ic500278y JUN 2 2014
Abstract:
The synthesis and crystal structure evolution of the double perovskite Pb2YSbO6 is reported for the first time. The structure has been analyzed in the temperature range between 100 and 500 K by using a combination of synchrotron and neutron powder diffraction. This compound shows two consecutive first order phase transformations as previously observed for a subgroup of Pb2RSbO6 perovkites (R = rare earths). The thermodynamic parameters associated with the phase transitions were calculated using differential scanning calorimetry (DSC), and the role of the diverse cations of the structure was studied from DFT calculations for the room temperature polymorph. The crystal structure evolves from a C2/c monoclinic structure (a(-)b(-)b(-) tilting system in Glazer's notation) to another monoclinic P2(1)/n (a(-)a(-)b(+))phase with an incommensurate modulation and finally to a cubic Fm (3) over barm perovskite (a(0)a(0)a(0)). The highly distorted nature of the room temperature crystal structure seems to be driven by the polarization of the Pb lone pair which shows a marked local effect in the atomic spatial arrangements. Moreover, the lone pairs have been localized from DFT calculations and show an antiferroelectric ordering along the b monoclinic axis.
Title:
Emergence of charge density wave domain walls above the superconducting dome in 1T-TiSe2
Authors:
Joe, YI; Chen, XM; Ghaemi, P; Finkelstein, KD; de la Pena, GA; Gan, Y; Lee, JCT; Yuan, S; Geck, J; MacDougall, GJ; Chiang, TC; Cooper, SL; Fradkin, E; Abbamonte, P Author Full Names: Joe, Y. I.; Chen, X. M.; Ghaemi, P.; Finkelstein, K. D.; de la Pena, G. A.; Gan, Y.; Lee, J. C. T.; Yuan, S.; Geck, J.; MacDougall, G. J.; Chiang, T. C.; Cooper, S. L.; Fradkin, E.; Abbamonte, P.
Source:
NATURE PHYSICS, 10 (6):421-425; 10.1038/NPHYS2935 JUN 2014
Abstract:
Superconductivity in so-called unconventional superconductors is nearly always found in the vicinity of another ordered state, such as antiferromagnetism, charge density wave (CDW), or stripe order. This suggests a fundamental connection between superconductivity and fluctuations in some other order parameter. To better understand this connection, we used high-pressure X-ray scattering to directly study the CDW order in the layered dichalcogenide TiSe2, which was previously shown to exhibit superconductivity when the CDW is suppressed by pressure(1) or intercalation of Cu atoms(2). We succeeded in suppressing the CDW fully to zero temperature, establishing for the first time the existence of aquantum critical point (QCP) at P-c = 5.1 +/- 0.2 GPa, which is more than 1 GPa beyond the end of the superconducting region. Unexpectedly, at P = 3 GPa we observed a reentrant, weakly first order, incommensurate phase, indicating the presence of a Lifshitz tricritical point somewhere above the superconducting dome. Our study suggests that superconductivity in TiSe2 may not be connected to the QCP itself, but to the formation of CDW domain walls.
Title:
The alpha <-> beta phase transitions of Zn2P2O7 revisited: existence of an additional intermediate phase with an incommensurately modulated structure
Authors:
Stoger, B; Weil, M; Dusek, M Author Full Names: Stoeger, Berthold; Weil, Matthias; Dusek, Michal
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 539-554; SI 10.1107/S205252061401049X 3 JUN 2014
Abstract:
Zn2P2O7 crystallizes in a thortveitite-like structure and features temperature-dependent polymorphism. At high temperatures (T > 500 K), the aristotype phase beta-Zn2P2O7 (C2/m, Z = 2, a similar or equal to 6.60, b similar or equal to 8.28, c similar or equal to 4.53 angstrom, beta similar or equal to 105.4 degrees) is stable. At lower temperatures the lock-in phase alpha(1)-Zn2P2O7 [at 350 K: I2/c, Z = 12, a = 20.1131 (13), b = 8.2769 (6), c = 9.109 (3) angstrom, beta = 106.338 (16)degrees], a sixfold superstructure with commensurate modulation vector q = (1/3, 0, 1/2), is stable. Between the stability ranges of the alpha(1)- and beta-phases exists the intermediate, incommensurately modulated alpha(2)-Zn2P2O7 phase with modulation wavevector q similar or equal to (0.33, 0, 0.40) and C2/m(alpha, 0, gamma)0s superspace group symmetry. The alpha(1) -> alpha(2) lock-in phase transition at T-L = 408 K is of first-order and features virtually no hysteresis. It is immediately followed by the second-order alpha(2) -> beta transition to the non-modulated phase at T-I similar or equal to 430 K. This transformation is sluggish and even at T = 500 K very weak satellite reflections of the alpha(2)- phase were observed. Both phase transitions were analyzed with differential scanning calorimetry and high-temperature powder and single-crystal X-ray diffraction. The crystal structures of the alpha(1)- and alpha(2)- phases were refined from single crystal data collected at T = 350, 400, 405, 410, 415, 420, 425, 430, 450 and 500 K. Different models describing the slow transition from the incommensurately modulated alpha(2)- to the non-modulated beta-phase were tested. In the model resulting in the best residuals, the bridging O atom of the [P2O7] group, which is located on a 2/m position in the basic structure, is described as an overlap of an atom ordered in internal space and one atom disordered around the mirror plane. The occupancy of the ordered atom decreases with temperature until at T = 500 K virtually only the disordered atom remains. Simultaneously, the amplitude of the modulation functions of the remaining atoms decreases, so that the T = 500 K structure can be considered as the C2/m aristotype structure, although the diffraction pattern still features satellite reflections of first order with very low intensities.
Title:
Phase transformation and mechanical properties of as-cast Ti41.5Zr41.5Ni17 quasicrystalline composites
Authors:
Park, GH; Hong, SH; Kim, JT; Park, HJ; Seo, Y; Suh, JY; Hong, S; Park, JM; Kim, KB Author Full Names: Park, G. H.; Hong, S. H.; Kim, J. T.; Park, H. J.; Seo, Y.; Suh, J. Y.; Hong, S.; Park, J. M.; Kim, K. B.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 392 6-10; 10.1016/j.jnoncryso1.2014.03.024 JUN 1 2014
Abstract:
Phase transformation behavior of the quasicrystalline icosahedral phase (I-phase) and mechanical properties in a Ti41.5Zr41.5Ni17, alloy have been investigated using suction-casted bulk samples with various sample sizes (phi = 2, 3 and 5 mm). For 2 and 3 mm diameter rod samples, micrometer size dendritic beta-(Ti,Zr) phases are precipitated in the matrix and continuously I-phases are developed in the vicinity of the primary beta-(Ti,Zr) phases. With further increase of the sample size (i.e. decrease of cooling rate; phi = 5 mm), the length scale and volume fraction of primary beta-(Ti,Zr) dendritic phase are continuously increased and the constitution of matrix phase is changed from I-phase to eutectic lamella composed of bcc beta-(Ti,Zr) and hcp C14 Laves phases. The characterization of mechanical properties was carried out by compression and microhardness tests at room temperature. Depending on the selection, size and volume fraction of constituent phases, the values of hardness and compressive fracture strength are varied. The fracture surface morphologies of failed samples exhibit cleavage and quasi-cleavage patterns revealing the typical brittle failure characteristics. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Commensurate-incommensurate transition in graphene on hexagonal boron nitride
Authors:
Woods, CR; Britnell, L; Eckmann, A; Ma, RS; Lu, JC; Guo, HM; Lin, X; Yu, GL; Cao, Y; Gorbachev, RV; Kretinin, AV; Park, J; Ponomarenko, LA; Katsnelson, MI; Gornostyrev, YN; Watanabe, K; Taniguchi, T; Casiraghi, C; Gao, HJ; Geim, AK; Novoselov, KS Author Full Names: Woods, C. R.; Britnell, L.; Eckmann, A.; Ma, R. S.; Lu, J. C.; Guo, H. M.; Lin, X.; Yu, G. L.; Cao, Y.; Gorbachev, R. V.; Kretinin, A. V.; Park, J.; Ponomarenko, L. A.; Katsnelson, M. I.; Gornostyrev, Yu. N.; Watanabe, K.; Taniguchi, T.; Casiraghi, C.; Gao, H-J.; Geim, A. K.; Novoselov, K. S.
Source:
NATURE PHYSICS, 10 (6):451-456; 10.1038/NPHYS2954 JUN 2014
Abstract:
When a crystal is subjected to a periodic potential, under certain circumstances it can adjust itself to follow the periodicity of the potential, resulting in a commensurate state. Of particular interest are topological defects between the two commensurate phases, such as solitons and domain walls. Here we report a commensurate-incommensurate transition for graphene on top of hexagonal boron nitride (hBN). Depending on the rotation angle between the lattices of the two crystals, graphene can either stretch to adapt to a slightly different hBN periodicity (for small angles, resulting in a commensurate state) or exhibit little adjustment (the incommensurate state). In the commensurate state, areas with matching lattice constants are separated by domain walls that accumulate the generated strain. Such soliton-like objects are not only of significant fundamental interest, but their presence could also explain recent experiments where electronic and optical properties of graphene-hBN heterostructures were observed to be considerably altered.
Title:
Understanding the structure details when drying hydrate crystals of pharmaceuticals - interpretations from diffuse scattering and inter-modulation satellites of a partially dehydrated crystal
Authors:
Chan, EJ; Gao, Q; Dabros, M Author Full Names: Chan, E. J.; Gao, Q.; Dabros, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 555-567; SI 10.1107/S2052520614005125 3 JUN 2014
Abstract:
Simplified models for the crystal lattice of the sesquihydrate form of the hemi-sulfate salt of (5S, 6S, 9R)-5-amino-6-(2,3-difluorophenyl)-6,7,8,9-tetrahydro-5H-cyclohepta[b]py ridin9-yl 4-(2-oxo-2,3-dihydro-1H-imidazol[4,5b]pyridin-1-yl)-1piperidine carboxylate (BMS-927711, C28H29F2N6O3+) are used to calculate diffuse diffraction features in order to develop a mechanistic understanding of the dehydration process with respect to disruption of the lattice, since a Bragg model cannot be established. The model demonstrates that what we observe when the water leaves the crystal is partial transformation from the parent form to a child form (a new form, less hydrated and structurally related to the parent). Yet this 'dried' structure is not a pure phase. It consists of semi-random layers of both child, parent and an interfacial layer which has a modulated structure that represents a transitory phase. Understanding the fact that a single 'dried' crystal can have the disordered layer structure described as well as understanding mechanistic relationships between the phases involved can have implications in understanding the effect of common large scale bulk drying procedures. During the development of BMS-927711, difficulties did arise during characterization of the dried bulk when using only routine solid-state analysis. The material is now better understood from this diffraction study. The diffraction experiments also reveal intermodulation satellites, which upon interpretation yield even more structural information about the crystal transformation. The model suggests the mechanism of transformation is laminar in which layers of the crystal are driven to approach a stable B-centered supercell phase of lower water content.
Title:
Solidification Process and Formation of Quasi-crystal Phase in Mg-6Zn-1Y Alloy under Pressure in the Order of GPa
Authors:
Dong, Y; Lin, XP; Xu, R; Liu, SJ; Tian, SS Author Full Names: Dong Yun; Lin Xiaoping; Xu Rui; Liu Shijun; Tian Shasha
Source:
RARE METAL MATERIALS AND ENGINEERING, 43 (5):1117-1122; MAY 2014
Abstract:
The solidification path in the Mg-6Zn-1Y alloy was calculated by FactSage thermodynamic software and Mg-database. The solidification process and the formation of quasi-crystal phase in the Mg-6Zn-1Y alloy were analyzed using OM, SEM equipped with EDS, XRD, and DSC. The results show that the microstructure of the alloy solidified under the ambient pressure is consisted of the lamellar quasi-crystal I-Mg3YZn6 distributed in the interdendritic region of the coarse alpha-Mg dendrite and the thermodynamic calculation is well agreed with the experimental analyses of the solidification process. The microstructure of the super-fined dendrite can be obtained and the morphology of interdendritic lamellar phases can be improved when the alloy solidifies under super-high pressure in the order of GPa. The transition of dendritic morphology occurs from interdendritic network or banding to "long island" as well as "granule" with the increasing of solidified pressure. In particular, the amount of interdendritic quasi-crystal I-Mg3YZn6 increases remarkably and the volume fraction of the phase is up to 40%. Meanwhile, the new ternary Mg-Zn-Y phase with high Y content is dispersively distributed in the matrix with the size in the order of nanometer.
Title:
Crystallographic Computing System JANA2006: General features
Authors:
Petricek, V; Dusek, M; Palatinus, L Author Full Names: Petricek, Vaclav; Dusek, Michal; Palatinus, Lukas
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 229 (5):345-352; 10.1515/zkri-2014-1737 2014
Abstract:
JANA2006 is a freely available program for structure determination of standard, modulated and magnetic samples based on X-ray or neutron single crystal/powder diffraction or on electron diffraction. The system has been developed for 30 years from specialized tool for refinement of modulated structures to a universal program covering standard as well as advanced crystallography. The aim of this article is to describe the basic features of JANA2006 and explain its scope and philosophy. It will also serve as a basis for future publications detailing tools and methods of JANA.
Title:
The incommensurate crystal structure of the Pd(5)b(1-z) phase; B ordering driven by elastic interaction between B atoms
Authors:
Leineweber, A; Berger, TG; Udyansky, A; Bugaev, VN; Duppel, V Author Full Names: Leineweber, Andreas; Berger, Tilmann Georg; Udyansky, Alexander; Bugaev, Volodymyr N.; Duppel, Viola
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 229 (5):353-367; 10.1515/zkri-2013-1710 2014
Abstract:
The atomic structure of the incommensurate Pd5B1-z phase has been analysed in detail by selected area electron diffraction and neutron-powder diffraction. That structure is based on a close-packed cubic arrangement of Pd atoms with the B atoms occupying the octahedral sites in a long-range ordered fashion. The ordering pattern of B is an incommensurately modulated one with a modulation vector of a length which changes with the B content (similar to PdB0.18-0.19) to adapt the ordering pattern continuously to the actual composition. The structure can be conceived to be constituted from "isolated" BPd6 units (also occurring in the previously reported Pd6B phase) and edge-sharing B2Pd10 octahedra units, which occur in a ratio reflecting the actual B content. As predicted on the basis of elastic interactions between B atoms, nearest neighbour B-B pairs occur (the B2Pd10 double octahedra units) in the structure of the Pd5B1-z phase, whereas occurrence of second-nearest neighbour B-B pairs is avoided. For the ideal composition Pd5B the crystal structure of the Pd5B1-z, phase corresponds to that of monoclinic UCl5 with U playing the role of B and Cl that of Pd.

Update: 25-Jun-2014

Title:
Al-based metal matrix composites reinforced with Al-Cu-Fe quasicrystalline particles: Strengthening by interfacial reaction
Authors:
Ali, F; Scudino, S; Anwar, MS; Shahid, RN; Srivastava, VC; Uhlenwinkel, V; Stoica, M; Vaughan, G; Eckert, J Author Full Names: Ali, F.; Scudino, S.; Anwar, M. S.; Shahid, R. N.; Srivastava, V. C.; Uhlenwinkel, V.; Stoica, M.; Vaughan, G.; Eckert, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 607 274-279; 10.1016/j.jallcom.2014.04.086 SEP 15 2014
Abstract:
The interfacial reaction between the Al matrix and the Al62.5Cu25Fe12.5 quasicrystalline (QC) reinforcing particles to form the Al7Cu2Fe omega-phase has been used to further enhance the strength of the Al/QC composites. The QC-to-omega phase transformation during heating was studied by in situ X-ray diffraction using a high-energy monochromatic synchrotron beam, which permits to follow the structural evolution and to correlate it with the mechanical properties of the composites. The mechanical behavior of these transformation-strengthened composites is remarkably improved as the QC-to-x phase transformation progresses: the yield strength increases from 195 MPa for the starting material reinforced exclusively with QC particles to 400 MPa for the material where the QC-to-x reaction is complete. The reduction of the matrix ligament size resulting from the increased volume fraction of the reinforcing phase during the transformation can account for most of the observed improvement in strength, whereas the additional strengthening can be ascribed to the possible presence of nanosized omega-phase particles as well as to the improved interfacial bonding between matrix and particles caused by the compressive stresses arising in the matrix. (C0 2014 Elsevier B.V. All rights reserved.
Title:
Field-induced incommensurate phase in the strong-rung spin ladder with ferromagnetic legs
Authors:
Yamaguchi, H; Miyagai, H; Yoshida, M; Takigawa, M; Iwase, K; Ono, T; Kase, N; Araki, K; Kittaka, S; Sakakibara, T; Shimokawa, T; Okubo, T; Okunishi, K; Matsuo, A; Hosokoshi, Y Author Full Names: Yamaguchi, H.; Miyagai, H.; Yoshida, M.; Takigawa, M.; Iwase, K.; Ono, T.; Kase, N.; Araki, K.; Kittaka, S.; Sakakibara, T.; Shimokawa, T.; Okubo, T.; Okunishi, K.; Matsuo, A.; Hosokoshi, Y.
Source:
PHYSICAL REVIEW B, 89 (22):10.1103/PhysRevB.89.220402 JUN 9 2014
Abstract:
We report magnetization, specific heat, and NMR measurements of 3-Br-4-F-V [=3-(3-bromo-4-fluorophenyl)-1,5-diphenylverdazyl], a strong-rung S = 1/2 Heisenberg spin ladder with ferromagnetic leg interactions. We explain the magnetic and thermodynamic properties based on the strong-rung regime. Furthermore, we find a field-induced successive phase transition in the specific heat and the nuclear spin-lattice relaxation rate 1/T-1. F-19-NMR spectra for higher-and lower-temperature phases indicate partial magnetic order and incommensurate long-range order, respectively, evidencing the presence of frustration due to weak interladder couplings.
Title:
Raman study of phonons in CaMn7O12: Effects of structural modulation and structural transition
Authors:
Iliev, MN; Hadjiev, VG; Gospodinov, MM; Nikolova, RP; Abrashev, MV Author Full Names: Iliev, M. N.; Hadjiev, V. G.; Gospodinov, M. M.; Nikolova, R. P.; Abrashev, M. V.
Source:
PHYSICAL REVIEW B, 89 (21):10.1103/PhysRevB.89.214302 JUN 5 2014
Abstract:
Polarized Raman spectra of oriented CaMn7O12 single crystals have been studied in a broad temperature range (5-500 K) covering the crystallographic, ferroelectric, and magnetic transitions. From the spectra obtained at room temperature (RT) 10 out of the total 12 Raman active 6A(g) + 6E(g) modes of the trigonal R (3) over bar phase have been identified and assigned to definite atomic motions in close comparison to results of lattice-dynamics modeling. With the decrease in temperature below 250 K some Raman bands split, and additional spectral features, not expected for the R (3) over bar structure, arise well above the magnetic transitions near 90 and 50 K. Their appearance, however, correlates with the transformation due to incommensurate structural modulation revealed by recent x-ray and neutron-diffraction studies. As temperature increases above RT the intensity of the Raman lines strongly decreases, and entering the high-temperature Im (3) over bar phase the spectrum transforms its shape to that expected for a structure with disordered Jahn-Teller distortions.
Title:
Concomitant charge-density-wave and unit-cell-doubling structural transitions in Dy5Ir4Si10
Authors:
Lee, MH; Chen, CH; Tseng, CM; Lue, CS; Kuo, YK; Yang, HD; Chu, MW Author Full Names: Lee, M. H.; Chen, C. H.; Tseng, C. M.; Lue, C. S.; Kuo, Y. K.; Yang, H. D.; Chu, M. -W.
Source:
PHYSICAL REVIEW B, 89 (19):10.1103/PhysRevB.89.195142 MAY 29 2014
Abstract:
The tetragonal rare-earth transition-metal silicide system with three-dimensional crystallographic structure R5T4Si10, where R is Dy, Ho, Er, Tm, and Lu, and T = Ir and Rh, has been shown to exhibit fascinating charge-density-wave (CDW) phase transitions, a phenomenon largely found in otherwise low-dimensional systems. In this study, we report the investigations of CDW in Dy5Ir4Si10 at different temperatures using transmission electron microscopy techniques including electron diffraction and dark-field imaging. Incommensurate superlattice spots along the c axis were observed in the electron-diffraction patterns when the sample was cooled below the CDW transition temperature at similar to 208 K. CDW becomes commensurate with further cooling and configurations of CDW dislocations convincingly show that the CDW phase transition is accompanied by a concomitant cell-doubling crystallographic structural phase transition. Intriguingly, the cell-doubling transition is featured by a broken inversion symmetry along the c axis and a disparity in the CDW-modulation vectors with opposite signs, which gives rise to two sets of CDW domains with reversed contrasts. The profound physics underlining this notable domain-contrast behavior is discussed.
Title:
Neutron powder diffraction and Mossbauer spectroscopy (Sn-119 and Gd-155) studies of the CeScSi-type GdMgSn and GdMgPb compounds
Authors:
Lemoine, P; Lee-Hone, NR; Ryan, DH; Verniere, A; Malaman, B; Le Caer, G Author Full Names: Lemoine, P.; Lee-Hone, N. R.; Ryan, D. H.; Verniere, A.; Malaman, B.; Le Caer, G.
Source:
PHYSICAL REVIEW B, 89 (17):10.1103/PhysRevB.89.174428 MAY 28 2014
Abstract:
The magnetic structures of the CeScSi-type GdMgSn and GdMgPb compounds have been studied by both neutron powder diffraction and Mossbauer spectroscopy (Sn-119 and Gd-155). The neutron diffraction results show that the two compounds adopt incommensurate antiferromagnetic structures at 5.4 K with propagation vectors (k) over right arrow = [0.910,0.077,0] for GdMgSn and (k) over right arrow = [0.892,0,0] for GdMgPb. The magnetic moments lie in the basal plane, which is confirmed by both Sn-119 and Gd-155 Mossbauer spectroscopy. Mossbauer spectroscopy refinements and simulations reveal that the magnetic structure of GdMgSn is cycloidal at low temperature and undergoes a transition to a modulated magnetic structure above T similar to 40 K. A similar magnetic transition is inferred for GdMgPb. The magnetic structures of GdMgSn and GdMgPb are compared with those of other CeScSi-type compounds.
Title:
Magnetic and ferroelectric orderings in multiferroic alpha-NaFeO2
Authors:
Terada, N; Khalyavin, DD; Perez-Mato, JM; Manuel, P; Prabhakaran, D; Daoud-Aladine, A; Radaelli, PG; Suzuki, HS; Kitazawa, H Author Full Names: Terada, Noriki; Khalyavin, Dmitry D.; Perez-Mato, Juan M.; Manuel, Pascal; Prabhakaran, Dharmalingam; Daoud-Aladine, Aziz; Radaelli, Paolo G.; Suzuki, Hiroyuki S.; Kitazawa, Hideaki
Source:
PHYSICAL REVIEW B, 89 (18):10.1103/PhysRevB.89.184421 MAY 28 2014
Abstract:
The triangular based antiferromagnet alpha-NaFeO2 has been studied by magnetization, dielectric, and neutron diffraction measurements as a function of temperature and magnetic field. The appropriate (H - T) phase diagram was constructed revealing a complex behavior due to a competition between several magnetic phases. In zero field, the system undergoes a sequence of magnetostructural transitions; initially from paramagnetic R (3) over bar m1' phase to the incommensurate spin density wave (ICM1) at T-N1 = 11 K with the nonpolar (3 + 1) magnetic superspace group C2/m1' (0, beta, 1/2)s0s, then, below T-N2 = 7.5 K, the ICM1 phase coexists with the polar cycloidal ordering (ICM2) possessing the Cm1'(0, beta, 1/2)0s superspace symmetry and finally the commensurate collinear ordering (CM) with the nonpolar magnetic space group P(a)2(1)/m develops below T-N3 = 5.5 K as the ground state of the system. A small amount of ICM2 coexists with the ICM1 and CM phases resulting in a nonzero measured polarization below T-N2. Magnetic field destabilizes the collinear ground state and promotes the polar ICM2 phase resulting in a drastic increase of the polarization. The symmetry of the zero field cycloidal structure allows the two orthogonal components p(1) proportional to r(ij) x (S-i x S-j) and p(2) proportional to S-i x S-j to contribute to the macroscopic polarization through the inverse DM effect. The applied magnetic field reduces the symmetry of the ICM2 phase down to the triclinic P-1(alpha, beta, gamma)0, resulting in admixture of another cycloidal and helical components both generating magnetic field switchable polarization p(3) perpendicular to p(1) and p(2).
Title:
Influence of the Structure on the Properties of NaxEuy(MoO4)(z) Red Phosphors
Authors:
Morozov, VA; Lazoryak, BI; Shmurak, SZ; Kiselev, AP; Lebedev, OI; Gauquelin, N; Verbeeck, J; Hadermann, J; Van Tendeloo, G Author Full Names: Morozov, Vladimir A.; Lazoryak, Bogdan I.; Shmurak, Semen Z.; Kiselev, Aleksander P.; Lebedev, Oleg I.; Gauquelin, Nicolas; Verbeeck, Johan; Hadermann, Joke; Van Tendeloo, Gustaaf
Source:
CHEMISTRY OF MATERIALS, 26 (10):3238-3248; 10.1021/cm500966g MAY 27 2014
Abstract:
Scheelite related compounds (A',A '')(n)[(B',B '')O-4](m) with B', B '' = W and/or Mo are promising new materials for red phosphors in pc-WLEDs (phosphor-converted white-light-emitting-diode) and solid-state lasers. Cation substitution in CaMoO4 of Ca2+ by the combination of Na+ and Eu3+, with the creation of A cation vacancies, has been investigated as a factor for controlling the scheelite-type structure and the luminescent properties. Na5Eu(MoO4)(4) and NaxEu(2-x)/33+square(2-x)/3MoO4 (0.138 <= x <= 0.5) phases with a scheelite-type structure were synthesized by the solid state method; their structural characteristics were investigated using transmission electron microscopy. Contrary to powder synchrotron X-ray diffraction before, the study by electron diffraction and high resolution transmission electron microscopy in this paper revealed that Na0.286Eu0.571MoO4 has a (3 + 2)D incommensurately modulated structure and that (3 + 2)D incommensurately modulated domains are present in Na0.200Eu0.600MoO4. It also confirmed the (3 + 1)D incommensurately modulated character of Na(0.138)Eu(0.621)Mo04. The luminescent properties of all phases under near-ultraviolet (n-UV) light have been investigated. The excitation spectra of these phosphors show the strongest absorption at about 395 nm, which matches well with the commercially available n-UV-emitting GaN-based LED chip. The emission spectra indicate an intense red emission due to the D-5(0) -> F-7(2) transition of Eu3+, with local minima in the intensity at Na0.286Eu0.571MoO4 and Na0.200Eu0.600MoO4 for similar to 613 nm and similar to 616 nm bands. The phosphor Na5Eu(MoO4)(4) shows the brightest red light emission among the phosphors in the Na2MoO4-Eu2/3MoO4 system and the maximum luminescence intensity of Na5Eu(MoO4)(4) (lambda(ex) = 395 nm) in the D-5(0) -> F-7(2) transition region is close to that of the commercially used red phosphor YVO4:Eu3+ (lambda(ex) = 326 nm). Electron energy loss spectroscopy measurements revealed the influence of the structure and Na/Eu cation distribution on the number and positions of bands in the UV-optical-infrared regions of the EELS spectrum.

Update: 19-Jun-2014

Title:
Acid-Base Chemistry in the Formation of Mackay-Type Icosahedral Clusters: mu(3)-Acidity Analysis of Sc-Rich Phases of the Sc-Ir System
Authors:
Guo, YM; Stacey, TE; Fredrickson, DC Author Full Names: Guo, Yiming; Stacey, Timothy E.; Fredrickson, Daniel C.
Source:
INORGANIC CHEMISTRY, 53 (10):5280-5293; 10.1021/ic500510s MAY 19 2014
Abstract:
The crystal structures of intermetallic phases offer a wealth of geometrical features (helices, multishelled clusters, and host guest motifs) whose formation has yet to be explained or predicted by chemical theory. A recently developed extension of the acid base concept to metallic systems, the mu(3)-acidity model, provides an avenue for developing this understanding for intermetallics formed from transition metals. In this Article, we illustrate how this approach can be used to understand one of the most striking geometrical entities to emerge in intermetallic chemistry, the Mackay cluster of icosahedral quasicrystals. We present mu(3)-acidity analyses, based on DFT-calibrated Huckel calculations, for a series of Sc-Ir intermetallics: ScIr (CsCl-type), Sc2Ir (Ti2Ni-type), Sc11Ir4, and the Mackay cluster containing phases Sc57Ir13 and Sc44Ir7. We begin by illustrating that a mu(3)-acidity model correctly predicts that each of these phases is stable relative to disproportionation into their neighboring compounds when a common set of Huckel parameters and d-orbital occupancies is used. Next, we explain these results by developing a relationship between the distance distribution of homoatomic contacts within an atom's coordination sphere and the mu(3)-neutralization it experiences. For a given average homoatomic distance, the role of heteroatomic contacts is higher when the distribution of homoatomic contacts is narrower. This effect is key to the strength of the acid base neutralization of the Sc-rich phases, where the Sc atoms find a scarcity of Ir atoms from which to obtain neutralization. Under these circumstances, Sc-Ir contacts should be maximized, whereas the number and distance variations of the Sc Sc contacts should be minimized. These expectations are borne out by the observed crystal structures. In particular, the Mackay clusters of Sc57Ir13 and Sc44Ir7, in which a central Ir atom is icosahedrally coordinated by a pentagonal dodecahedral array of face-sharing Sc octahedra, represent a natural way of merging the competing needs for enhancing Sc-Ir interactions while diminishing those between the Sc atoms.
Title:
Crystalline and quasicrystalline allotropes of Pb formed on the fivefold surface of icosahedral Ag-In-Yb
Authors:
Sharma, HR; Smerdon, JA; Nugent, PJ; Ribeiro, A; McLeod, I; Dhanak, VR; Shimoda, M; Tsai, AP; McGrath, R Author Full Names: Sharma, H. R.; Smerdon, J. A.; Nugent, P. J.; Ribeiro, A.; McLeod, I.; Dhanak, V. R.; Shimoda, M.; Tsai, A. P.; McGrath, R.
Source:
JOURNAL OF CHEMICAL PHYSICS, 140 (17):10.1063/1.4873596 MAY 7 2014
Abstract:
Crystalline and quasicrystalline allotropes of Pb are formed by evaporation on the fivefold surface of the icosahedral (i) Ag-In-Yb quasicrystal under ultra-high vacuum. Lead grows in three dimensional quasicrystalline order and subsequently forms fivefold-twinned islands with the fcc(111) surface orientation atop of the quasicrystalline Pb. The islands exhibit specific heights (magic heights), possibly due to the confinement of electrons in the islands. We also study the adsorption behavior of C-60 on the two allotropes of Pb. Scanning tunneling microcopy reveals that a high corrugation of the quasicrystalline Pb limits the diffusion of the C-60 molecules and thus produces a disordered film, similar to adsorption behavior of the same molecules on the clean substrate surface. However, the sticking coefficient of C-60 molecules atop the Pb islands approaches zero, regardless of the overall C-60 coverage. (C) 2014 AIP Publishing LLC.
Title:
Icosahedral quasicrystals solids with an elliptic hole under uniform heat flow
Authors:
Li, LH; Liu, GT Author Full Names: Li Lian-He; Liu Guan-Ting
Source:
CHINESE PHYSICS B, 23 (5):10.1088/1674-1056/23/5/056101 MAY 2014
Abstract:
The complex variable method for solving the two-dimensional thermal stress problem of icosahedral quasicrystals is stated. The closed-form solutions for icosahedral quasicrystals containing an elliptical hole subjected to a remote uniform heat flow are obtained. When the hole degenerates into a crack, the explicit solutions for the stress intensity factors is presented.
Title:
Finite size specimens with cracks of icosahedral Al-Pd-Mn quasicrystals
Authors:
Yang, LZ; Andreas, R; He, FM; Gao, Y Author Full Names: Yang Lian-Zhi; Andreas, Ricoeur; He Fan-Min; Gao Yang
Source:
CHINESE PHYSICS B, 23 (5):10.1088/1674-1056/23/5/056102 MAY 2014
Abstract:
Icosahedral quasicrystals are the most important and thermodynamically stable in all about 200 kinds of quasicrystals currently observed. Beyond the scope of classical elasticity, apart from a phonon displacement field, there is a phason displacement field in the elasticity of the quasicrystal, which induces an important effect on the mechanical properties of the material and makes an analytical solution difficult to obtain. In this paper, a finite element algorithm for the static elasticity of icosahedral quasicrystals is developed by transforming the elastic boundary value problem of the icosahedral quasicrystals into an equivalent variational problem. Analytical and numerical solutions for an icosahedral Al-Pd-Mn quasicrystal cuboid subjected to a uniaxial tension with different phonon-phason coupling parameters are given to verify the validity of the numerical approach. A comparison between the analytical and numerical solutions of the specimen demonstrates the accuracy and efficiency of the present algorithm. Finally, in order to reveal the fracture behavior of the icosahedral Al-Pd-Mn quasicrystal, a cracked specimen with a finite size of matter is investigated, both with and without phonon-phason coupling. Meanwhile, the geometry factors are calculated, including the stress intensity factor and the crack opening displacement for the finite-size specimen. Computational results reveal the importance of phonon-phason coupling effect on the icosahedral Al-Pd-Mn quasicrystal. Furthermore, the finite element procedure can be used to solve more complicated boundary value problems.
Title:
A Novel Approach to Improve Properties of BiFeO3 Nanomultiferroics
Authors:
Arya, G; Kotnala, RK; Negi, NS Author Full Names: Arya, Ghanshyam; Kotnala, Ravinder K.; Negi, Nainjeet Singh
Source:
JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 97 (5):1475-1480; 10.1111/jace.12782 MAY 2014
Abstract:
In this study we report the synthesis of Bi1-xInxFe1-yTiyO3 (0x0.1, 0y0.05) nanoparticles by a simple cost effective solution combustion method. Pure BFO samples shows distorted rhombohedral perovskite structure with space group R3c which is also supported by Fourier transform infrared spectra study. The codoping of In and Ti at A-B sites of BFO (BIFTO) partially distorts the crystal structure, increases the lattice strain, reduces the average particle size (14nm), and increases the Fe3+/Fe2+ ratio which significantly affect the observed results. The saturation magnetization increases significantly upon codoping (4.60emu/gm) by about 12 times than that of pure BFO (0.4emu/gm). The improved ferromagnetic properties upon codoping is further manifestated in large value of linear magnetoelectric coupling coefficient (4.8mV/cmOe) which further provides an indirect evidence for the collapse of space modulated spin structure. The activation energy increases with codoping (0.68eV), although less than 1eV which indicates that the conduction is still dominated by charged defects.
Title:
Coupled Skyrmion Sublattices in Cu2OSeO3
Authors:
Langner, MC; Roy, S; Mishra, SK; Lee, JCT; Shi, XW; Hossain, MA; Chuang, YD; Seki, S; Tokura, Y; Kevan, SD; Schoenlein, RW Author Full Names: Langner, M. C.; Roy, S.; Mishra, S. K.; Lee, J. C. T.; Shi, X. W.; Hossain, M. A.; Chuang, Y. -D.; Seki, S.; Tokura, Y.; Kevan, S. D.; Schoenlein, R. W.
Source:
PHYSICAL REVIEW LETTERS, 112 (16):10.1103/PhysRevLett.112.167202 APR 25 2014
Abstract:
We report the observation of a Skyrmion lattice in the chiral multiferroic insulator Cu2OSeO3 using Cu L-3-edge resonant soft x-ray diffraction. We observe the unexpected existence of two distinct Skyrmion sublattices that arise from inequivalent Cu sites with chemically identical coordination numbers but different magnetically active orbitals. The Skyrmion sublattices are rotated with respect to each other, implying a long wavelength modulation of the lattice. The modulation vector is controlled with an applied magnetic field, associating this moirelike phase with a continuous phase transition. Our findings will open up a new class of science involving manipulation of quantum topological states.
Title:
Quasicrystal-reinforced Mg alloys
Authors:
Kim, YK; Kim, WT; Kim, DH Author Full Names: Kim, Young Kyun; Kim, Won Tae; Kim, Do Hyang
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (2):10.1088/1468-6996/15/2/024801 APR 2014
Abstract:
The formation of the icosahedral phase (I-phase) as a secondary solidification phase in Mg-Zn-Y and Mg-Zn-Al base systems provides useful advantages in designing high performance wrought magnesium alloys. The strengthening in two-phase composites (I-phase + alpha-Mg) can be explained by dispersion hardening due to the presence of I-phase particles and by the strong bonding property at the I-phase/matrix interface. The presence of an additional secondary solidification phase can further enhance formability and mechanical properties. In Mg-Zn-Y alloys, the co-presence of I and Ca2Mg6Zn3 phases by addition of Ca can significantly enhance formability, while in Mg-Zn-Al alloys, the co-presence of the I-phase and Mg2Sn phase leads to the enhancement of mechanical properties. Dynamic and static recrystallization are significantly accelerated by addition of Ca in Mg-Zn-Y alloy, resulting in much smaller grain size and more random texture. The high strength of Mg-Zn-Al-Sn alloys is attributed to the presence of finely distributed Mg2Sn and I-phase particles embedded in the alpha-Mg matrix.
Title:
Complex metallic alloys as new materials for additive manufacturing
Authors:
Kenzari, S; Bonina, D; Dubois, JM; Fournee, V Author Full Names: Kenzari, Samuel; Bonina, David; Dubois, Jean Marie; Fournee, Vincent
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (2):10.1088/1468-6996/15/2/024802 APR 2014
Abstract:
Additive manufacturing processes allow freeform fabrication of the physical representation of a three-dimensional computer-aided design (CAD) data model. This area has been expanding rapidly over the last 20 years. It includes several techniques such as selective laser sintering and stereolithography. The range of materials used today is quite restricted while there is a real demand for manufacturing lighter functional parts or parts with improved functional properties. In this article, we summarize recent work performed in this field, introducing new composite materials containing complex metallic alloys. These are mainly Al-based quasicrystalline alloys whose properties differ from those of conventional alloys. The use of these materials allows us to produce light-weight parts consisting of either metal-matrix composites or of polymer-matrix composites with improved properties. Functional parts using these alloys are now commercialized.
Title:
On the equations of motion of dislocations in quasicrystals
Authors:
Agiasofitou, E; Lazar, M Author Full Names: Agiasofitou, Eleni; Lazar, Markus
Source:
MECHANICS RESEARCH COMMUNICATIONS, 57 27-33; 10.1016/j.mechrescom.2014.01.006 APR 2014
Abstract:
In this work we investigate the theory of dynamics of dislocations in quasicrystals. We consider three models: the elastodynamic model of wave type, the elasto-hydrodynamic model, and the elastodynamic model of wave-telegraph type. Similarities and differences between the three models are pointed out and discussed. Using the framework of linear incompatible elastodynamic theory, the equations of motion of dislocations are deduced for these three models. Especially, the equations of motion for the phonon and phason elastic distortion tensors and elastic velocity vectors are derived, where the source fields are given in terms of the phonon and phason dislocation density and dislocation current tensors in analogy to the classical theory of elastodynamics of dislocations. The equations of motion for the displacement fields are also obtained. (C) 2014 Elsevier Ltd. All rights reserved.
Title:
A New Mechanism of the Incommensurate Phase Transition
Authors:
Ishibashi, Y; Iwata, M Author Full Names: Ishibashi, Y.; Iwata, M.
Source:
FERROELECTRICS, 461 (1):1-9; SI 10.1080/00150193.2014.889521 MAR 12 2014
Abstract:
A new mechanism of incommensurate (INC) phase transition will be mentioned. The INC phase may be stabilized by freezing of a soft mode on the [k, k, 0] or [k, k, 1/2] branch induced by the parabolic splitting of the doubly degenerate modes at the Brillouin zone boundary (1/2, 1/2, 0) or (1/2, 1/2, 1/2). A simple model theory of the incommensurate phase transition of this type is proposed, which easily reproduces a special feature for the INC phase that the macroscopic symmetry changes at the INC phase transition.

Update: 11-Jun-2014

Title:
EuNiGe3, an anisotropic antiferromagnet
Authors:
Maurya, A; Bonville, P; Thamizhavel, A; Dhar, SK Author Full Names: Maurya, A.; Bonville, P.; Thamizhavel, A.; Dhar, S. K.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (21):10.1088/0953-8984/26/21/216001 MAY 28 2014
Abstract:
Single crystals of EuNiGe3, crystallizing in the non-centrosymmetric BaNiSn3-type structure, were grown using In flux, enabling us to explore the anisotropic magnetic properties, which was not possible with previously reported polycrystalline samples. The EuNiGe3 single crystalline sample is found to order antiferromagnetically at 13.2 K, as revealed from the magnetic susceptibility, heat capacity and electrical resistivity data. The low temperature magnetization M (H) is distinctly different for the field parallel to the ab-plane and c-axis; the ab-plane magnetization varies almost linearly with the field before the occurrence of an induced ferromagnetic (FM) phase (spin-flip) at 6.2 Tesla. On the other hand M (H) along the c-axis is accompanied by two metamagnetic transitions followed by a spin-flip at 4.1 T. A model including anisotropic exchange and dipole-dipole interactions reproduces the main features of magnetization plots but falls short of full representation. (H,T) phase diagrams have been constructed for the field applied along the principal directions. From the Eu-151 Mssbauer spectra, we determine that the 13.2 K transition leads to an incommensurate antiferromagnetic (AFM) intermediate phase followed by a transition near 10.5 K to a commensurate AFM configuration.
Title:
Sign of canted ferromagnetism in the quasicrystal approximants Au-SM-R (SM = Si, Ge and Sn/R = Tb, Dy and Ho)
Authors:
Hiroto, T; Tokiwa, K; Tamura, R Author Full Names: Hiroto, T.; Tokiwa, K.; Tamura, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (21):10.1088/0953-8984/26/21/216004 MAY 28 2014
Abstract:
Magnetic susceptibility and magnetization of the quasicrystal approximants Au-SM-R (SM = Si, Ge or Sn / R = Gd, Tb, Dy or Ho) are investigated. Ferromagnetic transitions are observed in all of these compounds, in contrast to the spin-glass behavior reported in similar compounds, Ag-In-R (R = Eu, Gd, Tb or Dy). Au-SM-Gd (SM = Si, Ge or Sn) exhibit a simple ferromagnetic transition at 22.5, 13 and 9 K, respectively, whereas Au-Si-(Tb, Dy or Ho) show indications of a canted ferromagnetic transition at 8.3, 5.9 and 3.8 K, respectively. The latter are attributed to a crystal electric field effect that is absent in the Gd-bearing compounds. The ferromagnetic behavior in Au-SM-R may be understood to be a consequence of the short R-R distances compared to those for Cd-R and Ag-In-R.
Title:
Chemical shifts of metallic and non-metallic Al-Re-Si approximant crystals studied by EELS and SXES
Authors:
Koshiya, S; Terauchi, M; Takagiwa, Y; Yamada, K; Kanazawa, I; Kimura, K Author Full Names: Koshiya, S.; Terauchi, M.; Takagiwa, Y.; Yamada, K.; Kanazawa, I.; Kimura, K.
Source:
PHILOSOPHICAL MAGAZINE, 94 (15):1711-1718; 10.1080/14786435.2014.894648 MAY 24 2014
Abstract:
Chemical shifts of approximant crystals of 1/0-Al12Re (1/0-metallic), 1/1-Al73Re15Si12 (1/1-metallic) and 1/1-Al73Re17Si10 (1/1-non-metallic) were examined by using electron energy-loss spectroscopy (EELS) and soft-X-ray emission spectroscopy (SXES). Al L-shell excitation EELS spectra of these alloys showed an apparent chemical shift only for the 1/1-non-metallic alloy to the larger binding energy side by 0.2 eV. Al-K alpha, Re-M alpha and Si-K alpha emission SXES spectra also showed a shift to the larger binding energy side only for 1/1-non-metallic alloy. 1/0-metallic and 1/1-metallic alloys did not show any chemical shift in EELS and SXES experiments. Chemical shifts were observed only in larger binding energy side compared with pure materials. This implies the decrease of valence charge at constituent atomic sites of 1/1-non-metallic alloy compared with 1/0-metallic, 1/1-metallic and pure materials. The decreased charges should distribute intermetallic sites, which should be related to a formation of covalent bonding among Al atomic sites reported by maximum-entropy method (MEM)/Rietveld analysis on this material. This relation between chemical shift and covalent bonding nature of this approximant alloy may support the presence of covalent bonding in Al-based quasicrystals.
Title:
Structural Phase Transition and Microstructures in Stuffed Tridymite-Type Compounds; Ba(Al, Fe)(2)O-4
Authors:
Mori, S; Katsumura, S; Ozaki, T; Tanaka, E; Ishii, Y; Kurushima, K; Kubota, Y; Taniguchi, H Author Full Names: Mori, S.; Katsumura, S.; Ozaki, T.; Tanaka, E.; Ishii, Y.; Kurushima, K.; Kubota, Y.; Taniguchi, H.
Source:
FERROELECTRICS, 464 (1):116-121; SI 10.1080/00150193.2014.893160 MAY 19 2014
Abstract:
We have investigated structural phase transition and changes of microstrucrtures in BaAl2O4 with the tridymite tetrahedral framework structure by transmission electron microscopy experiments in the temperature range between 100K and 298K. In our polycrystalline samples the transition from the paraelectric phase with the P6(3)22 space group to the ferroelectric (FE) phase took place around 250K, which accompanies with the appearance of the modulated structure with the three equivalent modulation wave vectors, q = 1/2. Real-space images revealed that the FE phase should consist of nanodomains with the 10 similar to 20nm size. In addition, it is revealed that partial substitution of Fe3+ for Al3+ in BaAl2O4 induced structural phase transition to the modulated structure with q = 1/3 around x similar to 0.50 in Ba(Al1-xFex)(2)O-4.
Title:
Influence of flexoelectric coupling on domain patterns in ferroelectrics
Authors:
Ahluwalia, R; Tagantsev, AK; Yudin, P; Setter, N; Ng, N; Srolovitz, DJ Author Full Names: Ahluwalia, Rajeev; Tagantsev, Alexander K.; Yudin, Petr; Setter, Nava; Ng, Nathaniel; Srolovitz, David J.
Source:
PHYSICAL REVIEW B, 89 (17):10.1103/PhysRevB.89.174105 MAY 14 2014
Abstract:
Using Ginzburg-Landau theory and two-dimensional (2D) phase field simulations, we analyze the influence of flexoelectric coupling on the domain patterns in ferroelectrics. The phase field simulations predict that a high strength of the flexoelectric coupling leads to formation of a fine structure in domain patterns in ferroelectrics. The fine structure forms when the coupling strength exceeds a critical value and is related to local transition into an incommensurate phase. Depending on the parameters, a structure with stripe patterns with antiparallel polarizations or another one, not seen before, with two-dimensional arrays of alternating vortices is found. Complex domain configurations with coexisting phases and unusual domain walls between them are observed. Although the incommensurate phase does not form for weaker couplings, the influence of flexoelectricity on bulk domain patterns can still be significant. The results of the calculations are rationalized using an analytical model. Directions for the modulation wave vectors in the fine structure are found in the framework of a linear analysis, while the type of the structure-stripes or vortices-is determined by anharmonicity.
Title:
Ab-initio tiling and atomic structure for decagonal ZnMgY quasicrystal
Authors:
Mihalkovic, M; Richmond-Decker, J; Henley, CL; Oxborrow, M Author Full Names: Mihalkovic, M.; Richmond-Decker, J.; Henley, C. L.; Oxborrow, M.
Source:
PHILOSOPHICAL MAGAZINE, 94 (14):1529-1541; 10.1080/14786435.2014.888499 MAY 13 2014
Abstract:
We discover the detailed atomic structure of -MgZnY, a stable decagonal quasicrystal alloy of the layered Frank-Kasper type, and related phases, using the 'tiling and decoration' approach. The atoms have invariable sites in the rectangle and triangle tiles of a 10-fold-symmetric planar tiling. To discover the lowest-energy structures, we combine the methods of density functional theory (DFT) total energy calculations, empirical oscillating pair potentials (fitted to DFT), fitting effective Hamiltonians for tilings, and discovering optimum tiling structures using a nonlocal tile-reshuffling algorithm. We find a family of almost stable binary compounds with varying composition, including the decagonal quasicrystal and the known MgZn; in addition, we show the ternary versions can be stable: -MgZnY at high temperature, and -MgZnSc even at .
Title:
Spin fluctuations and frustrated magnetism in multiferroic FeVO4
Authors:
Zhang, J; Ma, L; Dai, J; Zhang, YP; He, ZZ; Normand, B; Yu, WQ Author Full Names: Zhang, J.; Ma, L.; Dai, J.; Zhang, Y. P.; He, Zhangzhen; Normand, B.; Yu, Weiqiang
Source:
PHYSICAL REVIEW B, 89 (17):10.1103/PhysRevB.89.174412 MAY 12 2014
Abstract:
We report V-51 nuclear magnetic resonance (NMR) studies on single crystals of the multiferroic material FeVO4. The high-temperature Knight shift shows Curie-Weiss behavior K-51 = a/(T + theta), with a large Weiss constant theta approximate to 116 K. However, the V-51 spectrum shows no ordering near these temperatures, splitting instead into two peaks below 65 K, which suggests only short-ranged magnetic order on the NMR time scale. Two magnetic transitions are identified from peaks in the spin-lattice relaxation rate 1/T-51(1) at temperatures T-N1 approximate to 19 K and T-N2 approximate to 13 K, which are lower than the estimates obtained from polycrystalline samples. In the low-temperature incommensurate spiral state, the maximum ordered moment is estimated as 1.95 mu(B)/Fe, or 1/3 of the local moment. Strong low-energy spin fluctuations are also indicated by the unconventional power-law temperature dependence 1/T-51(1) proportional to T-2. The largeWeiss constant, short-range magnetic correlations far above T-N1, small ordered moment, significant low-energy spin fluctuations, and incommensurate ordered phases all provide explicit evidence for strong magnetic frustration in FeVO4.
Title:
Ferro-Orbital Ordering Transition in Iron Telluride Fe1+yTe
Authors:
Fobes, D; Zaliznyak, IA; Xu, ZJ; Zhong, RD; Gu, GD; Tranquada, JM; Harriger, L; Singh, D; Garlea, VO; Lumsden, M; Winn, B Author Full Names: Fobes, David; Zaliznyak, Igor A.; Xu, Zhijun; Zhong, Ruidan; Gu, Genda; Tranquada, John M.; Harriger, Leland; Singh, Deepak; Garlea, V. Ovidiu; Lumsden, Mark; Winn, Barry
Source:
PHYSICAL REVIEW LETTERS, 112 (18):10.1103/PhysRevLett.112.187202 MAY 9 2014
Abstract:
Fe1+yTe with y less than or similar to 0.05 exhibits a first-order phase transition on cooling to a state with a lowered structural symmetry, bicollinear antiferromagnetic order, and metallic conductivity, dp/dT > 0. Here, we study samples with y = 0.09(1), where the frustration effects of the interstitial Fe decouple different orders, leading to a sequence of transitions. While the lattice distortion is closely followed by incommensurate magnetic order, the development of bicollinear order and metallic electronic coherence is uniquely associated with a separate hysteretic first-order transition, at a markedly lower temperature, to a phase with dramatically enhanced bond-order wave (BOW) order. The BOW state suggests ferro-orbital ordering, where electronic delocalization in ferromagnetic zigzag chains decreases local spin and results in metallic transport.
Title:
Hardness of Al-based quasicrystals evaluated via cluster-plus-glue-atom model
Authors:
Chen, H; Luo, LJ; Qiang, JB; Wang, YM; Dong, C Author Full Names: Chen, Hua; Luo, Lingjie; Qiang, Jianbing; Wang, Yingmin; Dong, Chuang
Source:
PHILOSOPHICAL MAGAZINE, 94 (13):1463-1477; 10.1080/14786435.2014.887863 MAY 3 2014
Abstract:
In this paper, the hardness of ternary Al-based quasicrystals was assessed through an application of the cluster-plus-glue-atom model. In this model, any structure is decomposed into a first-neighbour strongly bonded cluster part and second-neighbour weakly bonded glue-atom part so that the overall structural information is condensed into a local structural unit [cluster](glue atom)(x). For quasicrystals, the averaged local units are formulated as [icosahedron] TM0,1(Transition Metal) and could be visualized as single icosahedron packing. Then, the hardness of quasicrystals was related to the rupture of weak inter-cluster bonds. Typically, theoretical hardness values of 8-9 GPa were obtained using 19 broken inter-cluster bonds, which accounts for about half of all the surface bonds of an icosahedron in the Mackay-type environment. The unit cluster formulas would act as rigid units during deformation and cracking.
Title:
Templated Quasicrystalline Molecular Ordering
Authors:
Smerdon, JA; Young, KM; Lowe, M; Hars, SS; Yadav, TP; Hesp, D; Dhanak, VR; Tsai, AP; Sharma, HR; McGrath, R Author Full Names: Smerdon, J. A.; Young, K. M.; Lowe, M.; Hars, S. S.; Yadav, T. P.; Hesp, D.; Dhanak, V. R.; Tsai, A. P.; Sharma, H. R.; McGrath, R.
Source:
NANO LETTERS, 14 (3):1184-1189; 10.1021/nl403947b MAR 2014
Abstract:
Quasicrystals are materials with long-range ordering but no periodicity. We report scanning tunneling microscopy (STM) observations of quasicrystalline molecular layers on 5-fold quasicrystal surfaces. The molecules adopt positions and orientations on the surface consistent with the quasicrystalline ordering of the substrate. Carbon-60 adsorbs atop sufficiently separated Fe atoms on icosahedral Al-Cu-Fe to form a unique quasicrystalline lattice, whereas further C-60 molecules decorate remaining surface Fe atoms in a quasi-degenerate fashion. Pentacene (Pn) adsorbs at 10-fold symmetric points around surface-bisected rhombic triacontahedral the first demonstrations of quasicrystalline molecular ordering on clusters in icosahedral Ag-In-Yb. These systems constitute a template.

Update: 5-Jun-2014

Title:
Icosahedral quasicrystal-enhanced nucleation of the fcc phase in liquid gold alloys
Authors:
Kurtuldu, G; Sicco, A; Rappaz, M Author Full Names: Kurtuldu, Gueven; Sicco, Alberto; Rappaz, Michel
Source:
ACTA MATERIALIA, 70 240-248; 10.1016/j.actamat.2014.02.037 MAY 15 2014
Abstract:
Although the grain refinement of yellow gold alloys with Jr has been used in industry and known for nearly half a century, the basic mechanism is still unknown. The present contribution shows that the mechanism is the same as that evidenced recently in Al-Zn alloys, when small amounts of Cr (1000 ppm) are added to the melt (Kurtuldu et al., 2013). The reduced face-centered cubic (fcc) crystal size, the abnormal fraction of twin, or near-twin, grain boundaries and the 5-fold symmetry crystallographic orientation of multiple nearestneighbor grains reproduce the symmetry of icosahedral quasicrystals (iQCs) with the following heteroepitaxial relationships: {111}(fcc)< 110 >(fcc) perpendicular to 3-fold/2-fold symmetry axes of iQCs. While iQCs and the approximant stable Al45Cr7 phase, which contains several 5-fold symmetry building blocks in its unit cell, are known to exist in Al Cr alloys, no such phases have been reported for yellow gold +Ir. Nevertheless, when minute amounts of Jr ( less than or similar to 200 ppm) are added to the gold alloy melt, it is shown that the grain refinement from 248 to 30 mu m is accompanied by a spectacular increase in the fraction of twinned grain boundaries, i.e. from less than 1% without Jr to 11% with 200 ppm Ir. Furthermore, up to 9 grains have been shown to reproduce the six 5-fold symmetry axes of the icosahedron, while many other grain configurations exhibit this heteroepitaxial relationship with the icosahedron or interlocked icosahedron. This confirms that fcc crystals can form in a supercooled liquid by heteroepitaxial growth from an iQC template. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd.
Title:
Magneto-optical spectroscopy of ferromagnetic shape-memory Ni-Mn-Ga alloy
Authors:
Veis, M; Beran, L; Zahradnik, M; Antos, R; Straka, L; Kopecek, J; Fekete, L; Heczko, O Author Full Names: Veis, M.; Beran, L.; Zahradnik, M.; Antos, R.; Straka, L.; Kopecek, J.; Fekete, L.; Heczko, O.
Source:
JOURNAL OF APPLIED PHYSICS, 115 (17):10.1063/1.4867754 MAY 7 2014
Abstract:
Magneto-optical properties of single crystal of Ni50.1Mn28.4Ga21.5 magnetic shape memory alloy in martensite and austenite phase were systematically studied. Crystal orientation was approximately along {100} planes of parent cubic austenite. At room temperature, the sample was in modulated 10M martensite phase and transformed to cubic austenite at 323 K. Spectral dependence of polar magneto-optical Kerr effect was obtained by generalized magneto-optical ellipsometry with rotating analyzer in the photon energy range from 1.2 to 4 eV, and from room temperature to temperature above the Curie point. The Kerr rotation spectra exhibit prominent features typical for complexes containing Mn atoms. Significant spectral changes during transformation to austenite can be explained by different optical properties caused by changes in density of states near the Fermi energy. (C) 2014 AIP Publishing LLC.
Title:
Ferromagnetic resonance study of eightfold artificial ferromagnetic quasicrystals
Authors:
Bhat, VS; Sklenar, J; Farmer, B; Woods, J; Ketterson, JB; Hastings, JT; De Long, LE Author Full Names: Bhat, V. S.; Sklenar, J.; Farmer, B.; Woods, J.; Ketterson, J. B.; Hastings, J. T.; De Long, L. E.
Source:
JOURNAL OF APPLIED PHYSICS, 115 (17):10.1063/1.4859035 MAY 7 2014
Abstract:
We have performed broadband (10 MHz-18 GHz) and narrowband (9.7 GHz) ferromagnetic resonance (FMR) measurements on permalloy thin films patterned with quasiperiodic Ammann tilings having eightfold rotational symmetry. We observed highly reproducible mode structures in the low-frequency, hysteretic regime in which domain walls and unsaturated magnetization textures exist. A minimum of 10 robust modes were observed in patterned samples, compared to the single uniform mode observed in unpatterned permalloy films. The field dependence and approximate eightfold rotational symmetry of the FMR spectra are in good agreement with micromagnetic simulations that confirm the importance of patterning for controlling static and dynamic magnetic response. (C) 2014 AIP Publishing LLC.
Title:
Growth mechanism of an icosahedral quasicrystal and solute partitioning in a Mg-rich Mg-Zn-Y alloy
Authors:
Geng, JW; Teng, XY; Zhou, GR; Zhao, DG; Leng, JF Author Full Names: Geng, Jiwei; Teng, Xinying; Zhou, Guorong; Zhao, Degang; Leng, Jinfeng
Source:
JOURNAL OF MATERIALS RESEARCH, 29 (8):942-949; 10.1557/jmr.2014.81 APR 28 2014
Abstract:
The growth mechanism of an icosahedral quasicrystal and solute partitioning in a Mg-rich Mg-Zn-Y alloy were investigated. It is found that the preferred growth directions of the icosahedral quasicrystalline phase (I-phase) are along 5-fold axes and the planes perpendicular to the 5-fold axes grow in a facet manner. Due to the local compositional change at the solid/liquid interface, the planar growth is gradually replaced by cellular growth. During the nucleation of the primary I-phase, on a microscale, the distribution of the Y element is changed and concentrated along 5-fold directions in the remaining liquid. If the cooling rate is relatively slow, there will be more Y element in the remaining liquid after the formation of the primary I-phase. It causes that (I-phase + alpha-Mg) eutectic structures form around the primary I-phase. Almost all the Y element is exhausted after this stage. Especially, under a relatively slow cooling rate, the solute partitioning occurs during the growth process of the primary I-phase, which leads to the microshrinkage cavity and crack defects at the edge of the primary I-phase.
Title:
Spin density waves in the Hubbard model: A DMFT approach
Authors:
Peters, R; Kawakami, N Author Full Names: Peters, Robert; Kawakami, Norio
Source:
PHYSICAL REVIEW B, 89 (15):10.1103/PhysRevB.89.155134 APR 24 2014
Abstract:
We analyze spin density waves (SDWs) in the Hubbard model on a square lattice within the framework of inhomogeneous dynamical mean field theory (IDMFT). Doping the half-filled Hubbard model results in a change of the antiferromagnetic Neel state, which exists exactly at half filling, to a phase of incommensurate SDWs. Previous studies of this phase mainly rely on static mean field calculations. In this paper, we will use large-scale IDMFT calculations to study properties of SDWs in the Hubbard model. A great advantage of IDMFT over static mean field approaches is the inclusion of local screening effects and the easy access to dynamical correlation functions. Furthermore, this technique is not restricted to the Hubbard model, but can be easily used to study incommensurate phases in various strongly correlated materials.
Title:
Unusual spin fluctuations and magnetic frustration in olivine and non-olivine LiCoPO4 detected by P-31 and Li-7 nuclear magnetic resonance
Authors:
Baek, SH; Klingeler, R; Neef, C; Koo, C; Buchner, B; Grafe, HJ Author Full Names: Baek, S. -H.; Klingeler, R.; Neef, C.; Koo, C.; Buechner, B.; Grafe, H. -J.
Source:
PHYSICAL REVIEW B, 89 (13):10.1103/PhysRevB.89.134424 APR 24 2014
Abstract:
We report P-31 and Li-7 nuclear magnetic resonance (NMR) studies in new non-olivine LiZnPO4-type LiCoPO4tetra microcrystals, where the Co2+ ions are tetrahedrally coordinated. Olivine LiCoPO4, which was directly transformed from LiCoPO4tetra by an annealing process, was also studied and compared. The uniform bulk magnetic susceptibility and the P-31 Knight shift obey the Curie-Weiss law for both materials with a high spin Co2+ (3d(7), S = 3/2), but the Weiss temperature Theta and the effective magnetic moment mu(eff) are considerably smaller in LiCoPO4tetra. The spin-lattice relaxation rate T-1(-1) reveals a quite different nature of the spin dynamics in the paramagnetic state of both materials. Our NMR results imply that strong geometrical spin frustration occurs in tetrahedrally coordinated LiCoPO4, which may lead to the incommensurate magnetic ordering.
Title:
Structural Diversity of Hydrogen-Bonded Networks of [Co(NH3)(6)](3+) Complex Cations and Acetylenedicarboxylic Acid Anions
Authors:
Seidel, RW; Goddard, R; Gramm, V; Ruschewitz, U Author Full Names: Seidel, Ruediger W.; Goddard, Richard; Gramm, Verena; Ruschewitz, Uwe
Source:
ZEITSCHRIFT FUR NATURFORSCHUNG SECTION B-A JOURNAL OF CHEMICAL SCIENCES, 69 (3):277-288; 10.5560/ZNB.2014-3272 MAR 2014
Abstract:
The crystal structure of [Co(NH3)(6)](ADC)(HADC) center dot 2 H2O (1) (ADC(2-) = acetylenedicarboxylate) (P2(1)/n, Z = 4) was mistakenly described as containing the [Co(H2O)(6)](3+) ion [I. Stein, U. Ruschewitz, Z. Nattuforsch. 2011, 66b, 471-478]. A revision is reported. While attempting to reproduce 1, we isolated phase-pure crystalline material of [Co(NH3)(6)]Cl-2(HADC) center dot H2O (2), the crystal structure of which was also reported in the article above. Upon standing in the aqueous mother liquor at room temperature for several days, the needle-shaped crystals of 2 disappear, while block-shaped crystals of the formerly unknown compound [Co(NH3)(6)](ADC)(HADC) (3) grow. Satellite peaks in the X-ray diffraction frames indicate that the crystal structure is incommensurately modulated. Dissolving crystals of 3 in water at elevated temperature leads to plate-shaped crystals of the new compound [Co(NH3)(6)](2) (ADC)(3) center dot 3 H2O (4) upon slow cooling to room temperature. Compounds 2-4 were investigated by elemental analysis, powder X-ray diffraction and infrared spectroscopy. Structural characterization of 4 by single-crystal X-ray analysis was also achieved (P (1) over bar, Z = 2). Complex 1, however, could not be reproduced.

Update: 29-May-2014

Title:
Mg-doped Bi0.8Ca0.2FeO3 with enhanced ferromagnetic properties
Authors:
Xu, JL; Xie, D; Yin, C; Feng, TT; Zhang, XW; Zhao, HM; Li, G; Ren, TL; Guan, YJ; Gao, XS; Pan, W Author Full Names: Xu, Jianlong; Xie, Dan; Yin, Cong; Feng, Tingting; Zhang, Xiaowen; Zhao, Haiming; Li, Gang; Ren, Tian-Ling; Guan, Yujie; Gao, Xingsen; Pan, Wei
Source:
MATERIALS LETTERS, 122 139-142; 10.1016/j.matlet.2014.01.127 MAY 1 2014
Abstract:
We report the structural and enhanced ferromagnetic properties of Mg doped Bi0.8Ca0.2FEO3 ceramics. Oxygen vacancies are introduced into Bi0.8Ca0.2Fe1-xMgxO3 ceramics doping confirmed by XRD and Raman spectra, which induce a significantly enhanced macroscopic ferromagnetism from antiferromagnetism to ferromagnetism. The enhanced ferromagnetism can be ascribed to the creation of unbalanced Fe3+ spins induced by the collapse of the space modulated cycloidal spin structure and relative long-range coupling mediated by the oxygen vacancies trapped localized electrons. The improved ferromagnetic properties obtained by co-doping demonstrate the possibility of bulk BFO in practical multiferroic applications. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Mechanical and damping properties of thermal treated Mg-Zn-Y-Zr alloys reinforced with quasicrystal phase
Authors:
Ma, R; Dong, XP; Yan, BS; Chen, SQ; Li, ZB; Pan, Z; Ling, HJ; Fan, ZT Author Full Names: Ma, Rong; Dong, Xuanpu; Yan, Bangsong; Chen, Shuqun; Li, Zhangbo; Pan, Zhang; Ling, Hongjiang; Fan, Zitian
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 602 11-18; 10.1016/j.msea.2014.02.055 APR 25 2014
Abstract:
The effects of annealing, T4 and T6 heat treatment on microstructure, mechanical properties and damping capacities of a quasicrystal-reinforced Mg-Zn-Y-Zr alloy (the ZWK3 alloy) were investigated in this study. The structural results show that the Mg0.97Zn0.03 phase could transform to Mg7Zn3 phase during annealing and only primary phase and the I-Mg3YZn6 quasicrystal phase exist in the T4 treated ZWK3 alloy. Further aging in T6 treatment precipitates a large amount of nanoscaled MgZn2 phase. The thermal treatment could improve the tensile strength of the ZWK3 alloy greatly, while a large reduction in elongation and high strain amplitude damping are obtained compared with that of the as-cast alloy. In spite of this, the damping values of three heat treated ZWK3 alloys all exceed 0.01, representing our studied alloys still belong to high damping magnesium alloys. Decrease of mobility of dislocations, resulting from tanglement and pinning, is responsible for damping decline. We also find that twins only observed in the T6 treated ZWK3 alloy could produce new damping sources besides dislocation. (C) 2014 Published by Elsevier B.V.
Title:
Effect of Mg-Zn-Nd Quasicrystal Addition on Corrosion Resistance of AZ91 Alloys
Authors:
Zhao, ZW; Teng, XY; Zhou, GR; Leng, JF; Geng, JW Author Full Names: Zhao Zhenwei; Teng Xinying; Zhou Guorong; Leng Jinfeng; Geng Jiwei
Source:
RARE METAL MATERIALS AND ENGINEERING, 43 (4):791-795; APR 2014
Abstract:
The purpose of this study is to improve the corrosion resistance of AZ91 alloys through adding different contents of Mg-Zn-Nd quasicrystal master alloy. The microstructure and the corrosion behavior of AZ91 alloys with addition of Mg-Zn-Nd (MZN) quasicrystal master alloy were investigated by scanning electron microscopy (SEM) equipped with electron dispersive spectroscopy (EDS), X-ray diffractometry (XRD), mass loss tests and potentiodynamic polarization measurements. The results show that the microstructures of AZ91 alloys are significantly refined, and the morphology of beta-Mg17Al12 phase changes from a continuous net to a discrete net or even to particles after adding MZN quasicrystal master alloy. Moreover, the amount of beta-Mg17Al12 phase is reduced. The alloy with 6wt% MZN quasicrystal master alloy has the best corrosion resistance, and the corrosion rate is 0.8 (mg.cm(-2))/d, only 1/15 of that of common AZ91 alloy, but the excessive MZN quasicrystal master alloy could result in a poorer corrosion resistance of AZ91 alloy.
Title:
Penrose nanotiles: design of the thin and thick rhomb molecules to self-assemble into a quasicrystal
Authors:
Laikov, DN Author Full Names: Laikov, Dimitri N.
Source:
RSC ADVANCES, 4 (34):17925-17930; 10.1039/c4ra01354a 2014
Abstract:
New organic molecules are designed, with synthesis in mind, to fit the shape of the thin and thick rhombs of the Penrose tiling and selfassemble by hydrogen bonding into nearly flat sheets (that may stack face-to-face) following the matching rules.

Update: 22-May-2014

Title:
Mechanical properties of Al-Cu-Fe quasicrystalline and crystalline phases: An analogy
Authors:
Laplanche, G; Bonneville, J; Joulain, A; Gauthier-Brunet, V; Dubois, S Author Full Names: Laplanche, G.; Bonneville, J.; Joulain, A.; Gauthier-Brunet, V.; Dubois, S.
Source:
INTERMETALLICS, 50 54-58; 10.1016/j.intermet.2014.02.004 JUL 2014
Abstract:
The mechanical properties of the omega-Al7Cu2Fe crystalline phase have been investigated over a large temperature range (650-1000 K). Despite of its antinomic structure with the icosahedral Al-Cu-Fe quasicrystalline phase, i.e. periodic vs non-periodic, its mechanical properties are very similar to those of the quasicrystalline phase, which strongly suggest similar deformation mechanisms. Consequently, as for the quasicrystalline structure, we propose that dislocation climb might control the plastic deformation of the omega-phase. However, in the present case, the specificities of the quasiaystalline structure cannot be invoked to justify the predominance of dislocation climb, which questions the role of quasiperiodicity on dislocation mobility. We suggest that this deformation mode certainly results from specific non-planar extensions of the dislocation core. (C) 2014 Elsevier Ltd. All rights reserved.
Title:
Crystal structures of orthorhombic, hexagonal, and cubic compounds of the Sm(x)Yb(2-x)TiO5 series
Authors:
Aughterson, RD; Lumpkin, GR; Reyes, MD; Sharma, N; Ling, CD; Gault, B; Smith, KL; Avdeev, M; Cairney, JM Author Full Names: Aughterson, Robert D.; Lumpkin, Gregory R.; Reyes, Massey de Los; Sharma, Neeraj; Ling, Christopher D.; Gault, Baptiste; Smith, Katherine L.; Avdeev, Maxim; Cairney, Julie M.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 213 182-192; 10.1016/j.jssc.2014.02.029 MAY 2014
Abstract:
A series of single phase compounds with nominal stoichiometry Sm(x)Yb(2-x)TiO5 (x=2,1.4, 1, 0.6, and 0) have been successfully fabricated to generate a range of crystal structures covering the most common polymorphs previously discovered in the Ln(2)TiO(5) series (Ln=lanthanides and yttrium). Four of the five samples have not been previously fabricated in bulk, single phase form so their crystal structures are refined and detailed using powder synchrotron and single crystal x-ray diffraction, neutron diffraction and transmission electron microscopy. Based on the phase information from diffraction data, there are four crystal structure types in this series; orthorhombic Pnma, hexagonal P6(3)/mmc, cubic (pyrochlore-like) Fd-3m and cubic (fluorite-like) Fm-3m. The cubic materials show modulated structures with variation between long and short range ordering and the variety of diffraction techniques were used to describe these complex crystal structure types. Crown Copyright (C) 2014 Published by Elsevier Inc. All rights reserved.
Title:
Local Crystal Structure of Antiferroelectric Bi2Mn4/3Ni2/3O6 in Commensurate and Incommensurate Phases Described by Pair Distribution Function (PDF) and Reverse Monte Carlo (RMC) Modeling
Authors:
Szczecinski, RJ; Chong, SY; Chater, PA; Hughes, H; Tucker, MG; Claridge, JB; Rosseinsky, MJ Author Full Names: Szczecinski, Robert J.; Chong, Samantha Y.; Chater, Philip A.; Hughes, Helen; Tucker, Matthew G.; Claridge, John B.; Rosseinsky, Matthew J.
Source:
CHEMISTRY OF MATERIALS, 26 (7):2218-2232; 10.1021/cm4038439 APR 8 2014
Abstract:
The functional properties of materials can arise from local structural features that are not well determined or described by crystallographic methods based on long-range average structural models. The room temperature (RT) structure of the Bi perovskite Bi2Mn4/3Ni2/3O6 has previously been modeled as a locally polar structure where polarization is suppressed by a long-range incommensurate antiferroelectric modulation. In this study we investigate the short-range local structure of Bi2Mn4/3Ni2/3O6, determined through reverse Monte Carlo (RMC) modeling of neutron total scattering data, and compare the results with the long-range incommensurate structure description. While the incommensurate structure has equivalent B site environments for Mn and Ni, the local structure displays a significantly Jahn-Teller distorted environment for Mn3+. The local structure displays the rock-salt-type Mn/Ni ordering of the related Bi2MnNiO6 high pressure phase, as opposed to Mn/Ni clustering observed in the long-range average incommensurate model. RMC modeling reveals short-range ferroelectric correlations between Bi3+ cations, giving rise to polar regions that are quantified for the first time as existing within a distance of approximately 12 A. These local correlations persist in the commensurate high temperature (HT) phase, where the long-range average structure is nonpolar. The local structure thus provides information about cation ordering and B site structural flexibility that may stabilize Bi3+ on the A site of the perovskite structure and reveals the extent of the local polar regions created by this cation.
Title:
Spin Exchange and Magnetic Dipole Dipole Interactions Leading to the Magnetic Superstructures of MAs2O6 (M = Mn, Co, Ni)
Authors:
Koo, HJ; Whangbo, MH Author Full Names: Koo, Hyun-Joo; Whangbo, Myung-Hwan
Source:
INORGANIC CHEMISTRY, 53 (7):3812-3817; 10.1021/ic500156e APR 7 2014
Abstract:
The three isostructural magnetic oxides MAs2O6 (M = Mn, Co, Ni) containing high-spin M2+ ions undergo a long-range antiferromagnetic ordering below 30 K, but their ordered magnetic structures are not identical. While CoAs2O6 and NiAs2O6 adopt the commensurate superstructure of q(1) = (0, 0, 1/2), MnAs2O6 has the incommensurate superstructure of q(2) = (0.055, 0.389, 0.136). The cause for this difference was examined by calculating their spin exchange and magnetic dipole-dipole interaction energies. In CoAs2O6 and NiAs2O6, the strongest M-O center dot center dot center dot O-M spin exchange, J(1), dominates over other exchanges, hence leading to the q(1) superstructure. For MnAs2O6, the spin exchanges are not a deciding factor leading to its magnetic superstructure, being all weak and comparable in strengths, but the magnetic dipole-dipole interactions are.

Update: 14-May-2014

Title:
Effect of different element doping on the structure and magnetic properties of composite crystal Sr-14(Cu1-xMx)(24)O-41 (M=Zn, Ni, Co)
Authors:
Wang, J; Zou, HM; Li, Y; Xie, H; Hu, N; Wang, LL; Shi, J Author Full Names: Wang, Jun; Zou, Huamin; Li, Yang; Xie, Hui; Hu, Ni; Wang, Lili; Shi, Jing
Source:
PHYSICA B-CONDENSED MATTER, 441 6-11; 10.1016/j.physb.2014.01.045 MAY 15 2014
Abstract:
The Zn2+, Ni2+ and Co3+ doped Sr-14(Cu1 - xMx)(24)O-41 composite crystals were synthesized by a standard solid state reaction method. The temperature dependence of magnetic properties was measured for every sample. The Curie coefficient, Weiss temperature, number of dimers in CuO2 chain per formula unit (Lu.) and dimer coupling constant are obtained by fitting the temperature dependence of the magnetic susceptibility. Meantime, selected area electron diffraction patter no (EDPs) show that the diffraction spots corresponding to the CuO2 chain substnicture are extended to streaks along a and b directions for all the samples, while the diffraction spots produced merely by the Cu2O3 ladder substructure are still very sharp. This means that the periodicities of chains in a and b directions are partially destroyed upon doping of Zn, Ni and Co due to that the initial phase of each chain becomes a random variable. Considering the effect of different ions substitution for Cu on the magnetic susceptibility, it is found that the degree of initial phase disorder is related to the order degree of magnetic sequence in CuO2 chain. For the un-doped sample, the decoupling of (timers is weak, the magnetic sequence is slightly destroyed, and the streaks in EDP are also very weak, which implies the degree of initial phase disorder in CuO2 chain is very low. When Zn2+ and Ni2+ ions are doped, the number of dimers per Eu, decreases, and the intensity of diffraction streaks increases. Furthermore, when the high spin magnetic ions Co3+ are doped, the number of holes in Sr-14(Cu1- xCox)(24)O-41 decreases, the magnetic sequence is destroyed very seriously, and the spots in EDP are extended to streaks almost completely. The phenomenon that the diffraction spots of CuO2 chain extend to streaks in EDP appears as evidence that the magnetic sequence in the CuO2 chain is destroyed by doping of Zn, Ni, Co. (C) 2014 Elsevier BA/. All rights reserved.
Title:
Mg-based bulk metallic glass composite containing in situ microsized quasicrystalline particles
Authors:
Zhao, YY; Men, H; Estevez, D; Liu, Y; Wang, XM; Li, RW; Chang, CT Author Full Names: Zhao, Yuan-Yun; Men, He; Estevez, Diana; Liu, Yan; Wang, Xinmin; Li, Run-Wei; Chang, Chuntao
Source:
SCRIPTA MATERIALIA, 78-79 21-24; 10.1016/j.scriptamat.2014.01.019 MAY 2014
Abstract:
A novel in situ forming Mg66Zn29Ca4Y1 composite comprising microsized icosahedral quasicrystal phase (I-phase) particles dispersed within a Mg-based metallic glass matrix was synthesized. The size and volume fraction of the I-phase particles are similar to 25-35 mu m and similar to 10%, respectively. The I-phase particles can noticeably improve both the strength and plasticity of the composite. The mechanism of the hard I-phase particles on the deformation and fracture behaviors of the composite and the synthesis strategy of the composite are discussed. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
The 1D Spin-1/2 XXZ Model in Transverse Uniform and Staggered Magnetic Fields
Authors:
Moradmard, H; Naseri, MS; Mahdavifar, S Author Full Names: Moradmard, H.; Naseri, M. Shahri; Mahdavifar, S.
Source:
JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 27 (5):1265-1271; 10.1007/s10948-013-2429-4 MAY 2014
Abstract:
We have studied the ground state magnetic phase diagram of the one-dimensional anisotropic spin-1/2 XXZ model in the presence of transverse uniform and staggered magnetic fields. We have suggested that the presence study can be applied to a real magnet with the Dzyaloshinskii-Moriya interaction. In the absence of the staggered magnetic field, the phase diagram is divided into four regions. Using the numerical Lanczos method, we have done an accurate numerical experiment. We have presented a detailed numerical analysis of the low energy spectrum and the ground state magnetic phase diagram. Our numerical results show the staggered-field-induced effects depend on in which one of the four regions the system is. In one of the regions, we have identified two quantum phase transitions, which belong to the universality class of the commensurate-incommensurate phase transition.
Title:
Formation mechanism of quasicrystals at the nanoscale during hot compression of Mg alloys
Authors:
Huang, H; Tian, Y; Yuan, GY; Chen, CL; Ding, WJ; Wang, ZC Author Full Names: Huang, Hua; Tian, Yuan; Yuan, Guangyin; Chen, Chunlin; Ding, Wenjiang; Wang, Zhongchang
Source:
SCRIPTA MATERIALIA, 78-79 61-64; 10.1016/j.scriptamat.2014.01.035 MAY 2014
Abstract:
A comprehensive transmission electron microscopy investigation was conducted to gain insights into how the secondary phases in Mg-1.50Zn-0.25Gd alloys are transformed during hot compression. It was found that needle-like Mg4Zn7 phases precipitate in Mg matrix, yet vanish during compression, forming nano-quasicrystals. These nano-quasicrystals are found to nucleate on the Mg4Zn7 phase with orientation relationships [1 1 (2) over bar 0](Mg) parallel to [(1) over bar 0 7](Mg4Zn7) parallel to [2-fold](I-phase), indicating that the crystal phase can transform to the quasicrystalline phase. The formation mechanism of the quasicrystals in Mg alloys at the nanoscale is also discussed. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
The Splitting of SDW State into Commensurable and Incommensurables Ones and the Peculiarities of the Behavior of Thermodynamic Quantities in a Magnetic Field Arbitrarily Oriented to Magnetization in Quasi Two-Dimensional Systems
Authors:
Palistrant, ME; Ursu, VA; Calalb, M Author Full Names: Palistrant, M. E.; Ursu, V. A.; Calalb, M.
Source:
JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 27 (5):1299-1308; 10.1007/s10948-013-2431-x MAY 2014
Abstract:
The quasi-two-dimensional system in which magnetism is caused by spin density wave (SDW) with an anisotropic energy spectrum (with defined impurity concentration x) is examined. The wave vector is supposed to be different from 2k (F) and the umklapp scattering (U-processes) is taken into account. The system is placed in a magnetic field arbitrarily oriented with respect to the vector . The basic equations for order parameters are obtained and the system of these equations is transformed taking into account the U-processes. The particular cases and and the case of small arbitrarily oriented magnetic fields are examined in detail. The conditions of the system transition to commensurable and incommensurable SDW state are analyzed. The phase diagram (T,x) at H=0 is traced. The influence of the magnetic field on the temperature of magnetic transition is researched and the aspect of the phase diagram in magnetic field in the cases H (z) H (sigma) =0 is presented. The longitudinal magnetic susceptibility chi (ayen) which demonstrates that at x < x (c) the temperature behavior is similar to the case when the system has a gap, and at x > x (c) to a gapless case. At x similar to x (c) in the dependence X (ayen)(T) a local maximum appears. The influence of the energy spectrum anisotropy on the system's properties is researched. Also the angular anisotropy of the quantity chi (ayen) at different values of T and x is determined.
Title:
Brillouin zone labelling for quasicrystals
Authors:
Gambaudo, JM; Vignolo, P Author Full Names: Gambaudo, Jean-Marc; Vignolo, Patrizia
Source:
NEW JOURNAL OF PHYSICS, 16 10.1088/1367-2630/16/4/043013 APR 15 2014
Abstract:
We propose a scheme to determine the energy-band dispersion of quasicrystals that does not require any periodic approximation and directly provides the correct structure of the extended Brillouin zones. From the gap labelling viewpoint, this allows us to transpose the measurement of the integrated density of states with that of the effective Brillouin zone areas, which are uniquely determined by the position of the Bragg peaks. Moreover, we show that the Bragg vectors can be determined by stability analysis of the law of recurrence used to generate the quasicrystal. Our analysis of gap labelling in the quasimomentum space opens the way to experimental proof of gap labelling itself within the framework of optics experiments, polaritons, or with ultracold atoms.

Update: 7-May-2014

Title:
High-pressure synthesis, crystal chemistry and physics of perovskites with small cations at the A site
Authors:
Belik, AA; Yi, W Author Full Names: Belik, Alexei A.; Yi, Wei
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (16):10.1088/0953-8984/26/16/163201 APR 23 2014
Abstract:
ABO(3) perovskites with small cations at the A site (A = Sc3+, In3+ and Mn2+ and B = Al3+ and transition metals) are reviewed. They extend the corresponding families of perovskites with A(3+) = Y, La-Lu, and Bi and A(2+) = Cd, Ca, Sr and Ba and exhibit the largest structural distortions. As a result of these large distortions, they show, in many cases, distinct structural and magnetic properties. These are manifested in: B-site-ordered monoclinic structures of ScMnO3 and 'InMnO3'; an unusual superstructure of ScRhO3 and InRhO3; antiferromagnetic ground states and multiferroic properties of Sc2NiMnO6 and In2NiMnO6; two magnetic transitions in ScCrO3 and InCrO3 with very close transition temperatures; a Pnma-to-P-1 structural transition and k = (1/2, 0, 1/2) magnetic ordering in ScVO3; and incommensurate magnetic ordering of Mn2+ spins in metallic MnVO3. A large number of simple ScBO3, InBO3 and MnBO3 perovskites has not been synthesized yet, and the number of experimental and theoretical works on each known ScBO3, InBO3 and MnBO3 perovskites counts to only one or two (except for ScAlO3). The synthesis, crystal chemistry and physics of perovskites with small cations at the A site is an emerging field in perovskite science.
Title:
Phase formation and stability of quasicrystal/alpha-Mg interfaces in the Mg-Cd-Yb system
Authors:
Ohhashi, S; Suzuki, K; Kato, A; Tsai, AP Author Full Names: Ohhashi, S.; Suzuki, K.; Kato, A.; Tsai, A. P.
Source:
ACTA MATERIALIA, 68 (15):116-126; 10.1016/j.actamat.2014.01.009 APR 2014
Abstract:
Phase formation involving icosahedral quasicrystals (iQc) in the Mg-Cd-Yb system was investigated. The phase diagrams obtained revealed that the iQc is in equilibrium with either (Mg, Cd)(2)Yb or an alpha-Mg phase over a wide composition range at 673 K. A eutectic reaction, where the melt decomposed to a rod-like lamella structure consisting of iQc and alpha-Mg phases was observed for Mg68Cd24Yb8 at 735 K. High-angle annular dark-field scanning transmission microscopy observation of the iQc in Mg96Cd3Yb1 verified the atomic positions of the Yb icosahedra and confirmed that the i-MgCdYb is isostructural to the i-CdYb. The formation of the eutectic structure is responsible for the high stability of the iQc/alpha-Mg interfaces because of good lattice matching; which is coincident interplanar spacing over several planes for the two phases. This coincidence in interplanar spacing was further confirmed in the real atomic structure, for which the twofold planes of the iQc, and the [0002] and [2-1-10] planes of alpha-Mg are dominant factors in determining the stability of the interfaces. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
QUASICRYSTALS Making ends meet
Authors:
Verberck, B Author Full Names: Verberck, Bart
Source:
NATURE PHYSICS, 10 (4):246-246; 10.1038/nphys2944 APR 2014
Title:
Effect of aluminum on the microstructure and properties of two refractory high-entropy alloys
Authors:
Senkov, ON; Senkova, SV; Woodward, C Author Full Names: Senkov, O. N.; Senkova, S. V.; Woodward, C.
Source:
ACTA MATERIALIA, 68 (15):214-228; 10.1016/j.actamat.2014.01.029 APR 2014
Abstract:
The microstructure, phase composition and mechanical properties of the AlMo0.5NbTa0.5TiZr and Al0.4Hf0.6NbTaTiZr high-entropy alloys are reported. The AlMo0.5NbTa0.5TiZr alloy consists of two body-centered cubic (bcc) phases with very close lattice parameters, a(1) = 326.8 pm and a(2) = 332.4 pm. One phase was enriched with Mo, Nb and Ta and another phase was enriched with Al and Zr. The phases formed nano-lamellae modulated structure inside equiaxed grains. The alloy had a density of rho = 7.40 g cm(-3) and Vickers hardness H-v = 5.8 GPa. Its yield strength was 2000 MPa at 298 K and 745 MPa at 1273 K. The Al0.4Hf0.6NbTaTiZr had a single-phase bcc structure, with the lattice parameter a= 336.7 pm. This alloy had a density rho = 9.05 g cm(-3), Vickers microhardness H-v = 4.9 GPa, and its yield strength at 298 K and 1273 K was 1841 MPa and 298 MPa, respectively. The properties of these Al-containing alloys were compared with the properties of the parent CrMo0.5NbTa0.5TiZr and HfNbTaTiZr alloys and the beneficial effects from the Al additions on the microstructure and properties were outlined. A thermodynamic calculation of the solidification and equilibrium phase diagrams was conducted for these alloys and the calculated results were compared with the experimental data. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Crystallographic account of nano-scaled intergrowth of M2B-type borides in nickel-based superalloys
Authors:
Hu, XB; Zhu, YL; Ma, XL Author Full Names: Hu, X. B.; Zhu, Y. L.; Ma, X. L.
Source:
ACTA MATERIALIA, 68 (15):70-81; 10.1016/j.actamat.2014.01.002 APR 2014
Abstract:
M2B-type borides in nickel-based superalloys containing boron subjected to long-term aging treatments were investigated by means of analytical transmission electron microscopy. Contrast analysis and electron diffraction show that the boride precipitations have dual-phase structures (I4/mcm, C16; Fddd, C-b) with a high density of stacking faults. The faulted planes and displacement vectors are determined as (110)(C16) and [1 (1) over bar1](C16)/4 in C16 structure and (100)(Cb) and [011](Cb)/4 in C-b structure. Structural models based on a polyhedron of square anti-prisms are proposed not only to rationalize the stacking faults, 60 degrees rotation twin and the intergrowth of structural variants, but also to interpret the newly observed structure in M2B-type borides. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Structural phase transitions of robust insulating Bi1-xLaxFe1-yTiyO3 multiferroics
Authors:
Zhang, LL; Yu, J; Itoh, M Author Full Names: Zhang, Linlin; Yu, Jian; Itoh, Mitsuru
Source:
JOURNAL OF APPLIED PHYSICS, 115 (12):10.1063/1.4869743 MAR 28 2014
Abstract:
In contrast to leaky BiFeO3, of which two structural phase transitions of cycloidal modulated antiferromagnetic-paramagnetic and ferroelectric-paraelectric are observed below 850 degrees C, chemical co-substitution to form Bi1-xLaxFe1-yTiyO3 ternary solid solution makes these multiferroic ceramics become robust insulating low dielectric loss and exhibit rich structural phase transitions. Differential thermal analysis and temperature-dependent X-ray diffraction measurements probe four first-order structural phase transitions, e. g., T-H = 305 degrees C, T-N = 365 degrees C, T-C = 810 degrees C, and T-S = 830 degrees C observed in the Bi0.98La0.02Fe0.99Ti0.01O3 system, which are reasonably attributed to Brazovskii-type cycloidal modulated antiferromagnetic-helimagnetic (at T-H) and helimagnetic-paramagnetic (at T-N) magnetic phase transitions, ferroelectric-paraelectric (at T-C) and rhombohedral-cubic (at T-S) structural phase transitions, respectively. Magnetic phase transition temperatures change a little but ferroelectric and lattice structural phase transition temperatures decrease gradually with increasing co-substitution up to composition-induced rhombohedral-(pseudo-)cubic structural phase boundary. The first-order nature of magnetic phase transition and emergence of helimagnetic phase were attributed to Ti3+ d(1) magnetic disorder distribution in the Fe3+ d(5) -O-Fe3+ d(5) chains, while the first-order nature becomes weak with increasing co-substitution, owing to decreased ferroelectric rhombohedral lattice distortion. An intermediate rhombohedral paraelectric phase is discovered intervening between ferroelectric rhombohedral and paraelectric cubic phase, of which the temperature range defined by difference between TC and TS increases with increasing co-substitution. It was found that TC and TS are able to be predicted quantitatively by reduced mass of unit cell. These findings enrich our understanding of ferroic phase transitions and advance designing novel high temperature multiferroic compounds. (C) 2014 AIP Publishing LLC.
Title:
Dynamic behavior of magnetoelectric coupling of CuFeO2 induced by a high magnetic field
Authors:
Xia, NM; Shi, LR; Xia, ZC; Chen, BR; Jin, Z; Wang, YS; Ouyang, ZW; Zuo, HK; Shen, YN Author Full Names: Xia, Nianming; Shi, Liran; Xia, Zhengcai; Chen, Borong; Jin, Zhao; Wang, Yeshuai; Ouyang, Zhongwen; Zuo, Huakun; Shen, Yining
Source:
JOURNAL OF APPLIED PHYSICS, 115 (11):10.1063/1.4868578 MAR 21 2014
Abstract:
Magnetoelectric effects and their dynamic behavior in a CuFeO2 single crystal grown by the floating zone technique are investigated at low temperature in pulsed high magnetic fields. Experimental results show that the magnetization, dielectric polarization, and magnetoelectric coupling are anisotropic. In the magnetization, a field-induced multi-step-like transition with hysteresis is observed, in which the critical magnetic fields are independent of the field sweep rate. In the dielectric polarization, the field-induced dielectric polarization with hysteresis (or partial irreversible) is only observed in the incommensurate-noncollinear phase. In particular, no obvious spontaneous dielectric polarization is observed in the lower magnetic field regime. Using a pulsed high magnetic field with various magnetic field strength and field sweep rates, the coupling behavior between the magnetic moment and the dielectric polarization is investigated. Experimental results show that the dielectric polarization is weakly related to the field sweep rate. In the field-decreasing branch, the magnetic field is higher, the magnetic field region of the dielectric polarization remains is lower, indicating that the pulsed high magnetic field has an effect on the enhancement of the spontaneous dielectric polarization. (C) 2014 AIP Publishing LLC.

Update: 1-May-2014

Title:
An exact solution for a multilayered two-dimensional decagonal quasicrystal plate
Authors:
Yang, LZ; Gao, Y; Pan, E; Waksmanski, N Author Full Names: Yang, Lian-Zhi; Gao, Yang; Pan, Ernian; Waksmanski, Natalie
Source:
INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 51 (9):1737-1749; 10.1016/j.ijsolstr.2014.01.018 MAY 1 2014
Abstract:
By extending the pseudo-Stroh formalism to two-dimensional decagonal quasicrystals, an exact closed-form solution for a simply supported and multilayered two-dimensional decagonal quasicrystal plate is derived in this paper. Based on the different relations between the periodic direction and the coordinate system of the plate, three internal structure cases for the two-dimensional quasicrystal layer are considered. The propagator matrix method is also introduced in order to treat efficiently and accurately the multilayered cases. The obtained exact closed-form solution has a concise and elegant expression. Two homogeneous quasicrystal plates and a sandwich plate made of a two-dimensional quasicrystal and a crystal with two stacking sequences are investigated using the derived solution. Numerical results show that the differences of the periodic direction have strong influences on the stress and displacement components in the phonon and phason fields; different coupling constants between the phonon and phason fields will also cause differences in physical quantities; the stacking sequences of the multilayer plates can substantially influence all physical quantities. The exact closed-form solution should be of interest to the design of the two-dimensional quasicrystal homogeneous and laminated plates. The numerical results can also be employed to verify the accuracy of the solution by numerical methods, such as the finite element and difference methods, when analyzing laminated composites made of quasicrystals. (C) 2014 Elsevier Ltd. All rights reserved.
Title:
Np-237 Mossbauer effect study on NpFeAsO
Authors:
Gaczynski, P; Klimczuk, T; Walker, H; Springell, R; Colineau, E; Eloirdi, R; Griveau, JC; Caciuffo, R Author Full Names: Gaczynski, P.; Klimczuk, T.; Walker, H.; Springell, R.; Colineau, E.; Eloirdi, R.; Griveau, J-C; Caciuffo, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (15):10.1088/0953-8984/26/15/156002 APR 16 2014
Abstract:
We report Np-237 Mossbauer measurements on NpFeAsO. The Np atoms were found to occupy only one crystallographic site. The value of the isomer shift (delta similar to 9.1 mm s(-1) versus NpAl2) indicates a 5f(4) electronic configuration (Np3+ ions). The magnetic ordering of the Np sublattice below 60 K is established and the saturated ordered magnetic moment is determined to be 1.73 mu(B) at 3.6 K. The unique set of hyperfine parameters exclude a modulated magnetic structure or spin waves on the Np site. The neptunium magnetic moments mu(Np) are found to lie along the tetragonal c-axis.
Title:
High-temperature structural study of decagonal Al-Cu-Rh
Authors:
Kuczera, P; Wolny, J; Steurer, W Author Full Names: Kuczera, Pawel; Wolny, Janusz; Steurer, Walter
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 306-314; 10.1107/S2052520613032575 2 APR 2014
Abstract:
The structure of decagonal Al-Cu-Rh has been studied as a function of temperature by in-situ single-crystal X-ray diffraction in order to contribute to the discussion on energy or entropy stabilization of quasicrystals. The experiments were performed at 293, 1223, 1153, 1083 and 1013 K. A common subset of 1460 unique reflections was used for the comparative structure refinements at each temperature. A comparison of the high-temperature datasets suggests that the best quasiperiodic ordering should exist between 1083 and 1153 K. However, neither the refined structures nor the phasonic displacement parameter vary significantly with temperature. This indicates that the phasonic contribution to entropy does not seem to play a major role in the stability of this decagonal phase in contrast to other kinds of structural disorder, which suggests that, in this respect, this decagonal phase would be similar to other complex intermetallic high-temperature phases.
Title:
Moroccan ornamental quasiperiodic patterns constructed by the multigrid method
Authors:
Aboufadil, Y; Thalal, A; Raghni, MAE Author Full Names: Aboufadil, Youssef; Thalal, Abdelmalek; El Idrissi Raghni, My Ahmed
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 47 630-641; 10.1107/S1600576714001691 2 APR 2014
Abstract:
The similarity between the structure of Islamic decorative patterns and quasicrystals has aroused the interest of several crystallographers. Many of these patterns have been analysed by different approaches, including various kinds of ornamental quasiperiodic patterns encountered in Morocco and the Alhambra (Andalusia), as well as those in the eastern Islamic world. In the present work, the interest is in the quasiperiodic patterns found in several Moroccan historical buildings constructed in the 14th century. First, the zellige panels (fine mosaics) decorating the Madrasas (schools) Attarine and Bou Inania in Fez are described in terms of Penrose tiling, to confirm that both panels have a quasiperiodic structure. The multigrid method developed by De Bruijn [Proc. K. Ned. Akad. Wet. Ser. A Math. Sci. (1981), 43, 39-66] and reformulated by Gratias [Tangente (2002), 85, 34-36] to obtain a quasiperiodic paving is then used to construct known quasiperiodic patterns from periodic patterns extracted from the Madrasas Bou Inania and Ben Youssef (Marrakech). Finally, a method of construction of heptagonal, enneagonal, tetradecagonal and octadecagonal quasiperiodic patterns, not encountered in Moroccan ornamental art, is proposed. They are built from tilings (skeletons) generated by the multigrid method and decorated by motifs obtained by craftsmen.
Title:
The quasiperiodic average structure of highly disordered decagonal Zn-Mg-Dy and its temperature dependence
Authors:
Ors, T; Takakura, H; Abe, E; Steurer, W Author Full Names: Ors, Taylan; Takakura, Hiroyuki; Abe, Eiji; Steurer, Walter
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 315-330; 10.1107/S2052520614001115 2 APR 2014
Abstract:
A single-crystal X-ray diffraction structure analysis of decagonal Zn-Mg-Dy, a Frank-Kasper-type quasicrystal, was performed using the higher-dimensional approach. For this first Frank-Kasper (F-K) decagonal quasicrystal studied so far, significant differences to the decagonal Al-TM-based (TM: transition metal) phases were found. A new type of twofold occupation domain is located on certain edge centers of the five-dimensional unit cell. The structure can be described in terms of a two-cluster model based on a decagonal cluster (similar to 23 angstrom diameter) arranged on the vertices of a pentagon-Penrose tiling (PPT) and a star-like cluster covering the remaining space. This model is used for the five-dimensional refinements, which converged to an R value of 0.126. The arrangement of clusters is significantly disordered as indicated by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). In order to check the structure and stability at higher temperatures, in-situ high-temperature (HT) single-crystal X-ray diffraction experiments were conducted at 598 and 648 K (i.e. slightly below the decomposition temperature). The structure does not change significantly, however, the best quasiperiodic order is found at 598 K. The implication of these results on the stabilization mechanism of quasicrystals is discussed.
Title:
LiZn4-x (x=0.825) as a (3+1)-dimensional modulated derivative of hexagonal close packing
Authors:
Pavlyuk, V; Chumak, I; Akselrud, L; Lidin, S; Ehrenberg, H Author Full Names: Pavlyuk, Volodymyr; Chumak, Ihor; Akselrud, Lev; Lidin, Sven; Ehrenberg, Helmut
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 212-217; 10.1107/S2052520613030709 2 APR 2014
Abstract:
The (3+1)-dimensional modulated structure of the LiZn4 - x (x = 0.825) binary compound has been determined in the superspace. The compound crystallizes in the orthorhombic superspace group Cmcm(alpha 00)0s0 with a = 2.7680 (6), b = 4.7942 (6), c = 4.3864 (9) angstrom, modulation wavevector: q similar or equal to 4/7a*. The structure is a derivative from the hexagonal close packing. The cubo-octahedron as a coordination polyhedron (c.n. = 12) is typical for all atoms. Bonding between atoms is explored by means of the TB-LMTO-ASA program package. The absence of strong interatomic interactions in LiZn4 - x is the main reason for the possible structure transformations.
Title:
Charge Density Wave Accompanied by Spin Density Wave in Mn3Si
Authors:
Tomiyoshi, S; Ohsumi, H; Kobayashi, H; Yamamoto, A Author Full Names: Tomiyoshi, Shoichi; Ohsumi, Hiroyuki; Kobayashi, Hisao; Yamamoto, Akiji
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 83 (4):10.7566/JPSJ.83.044715 APR 2014
Abstract:
The displacement modulation due to the charge density wave (CDW) in Mn3Si, which occurs as second harmonics of the spin density wave (SDW), has been investigated by synchrotron x-ray diffraction and the existence of CDW below Neel temperature of 23 K has been confirmed. High resolution measurement revealed the splitting of the satellite peaks deviating very little from the [111] axis toward [110] direction, suggesting the possibility of a single or double q CDW state. The temperature dependence of the satellites indicates the existence of the phase transition at T-t = 8.5 K, in agreement with the neutron diffraction result [Phys. Rev. B 73, 224416 (2006)]. The analysis of reflection intensities using a single q model, which is a limiting case of no splitting, shows that in both phases Si and Mn-II have larger displacement than that of Mn-I. The formation of single and double q SDWs and their nesting mechanism are discussed.
Title:
Superspace description of wagnerite-group minerals (Mg,Fe,Mn)(2)(PO4)(F,OH)
Authors:
Lazic, B; Armbruster, T; Chopin, C; Grew, ES; Baronnet, A; Palatinus, L Author Full Names: Lazic, Biljana; Armbruster, Thomas; Chopin, Christian; Grew, Edward S.; Baronnet, Alain; Palatinus, Lukas
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 243-258; 10.1107/S2052520613031247 2 APR 2014
Abstract:
Reinvestigation of more than 40 samples of minerals belonging to the wagnerite group (Mg, Fe, Mn)(2)(PO4)(F,OH) from diverse geological environments worldwide, using single-crystal X-ray diffraction analysis, showed that most crystals have incommensurate structures and, as such, are not adequately described with known polytype models (2b), (3b), (5b), (7b) and (9b). Therefore, we present here a unified superspace model for the structural description of periodically and aperiodically modulated wagnerite with the (3+1)-dimensional superspace group C2/c(0 beta 0)s0 based on the average triplite structure with cell parameters a similar or equal to 12.8, b similar or equal to 6.4, c similar or equal to 9.6 angstrom, beta similar or equal to 117 degrees and the modulation vectors q = beta b*. The superspace approach provides a way of simple modelling of the positional and occupational modulation of Mg/Fe and F/OH in wagnerite. This allows direct comparison of crystal properties.
Title:
The Tenth Ewald Prize and aperiodic crystals
Authors:
Mukhopadhyay, NK Author Full Names: Mukhopadhyay, N. K.
Source:
CURRENT SCIENCE, 106 (6):793-793; MAR 25 2014
Title:
Rheological properties of palygorskite-bentonite and sepiolite-bentonite mixed clay suspensions
Authors:
Chemeda, YC; Christidis, GE; Khan, NMT; Koutsopoulou, E; Hatzistamou, V; Kelessidis, VC Author Full Names: Chemeda, Yadeta C.; Christidis, George E.; Khan, N. M. Tauhid; Koutsopoulou, Eleni; Hatzistamou, Vicky; Kelessidis, Vassilios C.
Source:
APPLIED CLAY SCIENCE, 90 165-174; 10.1016/j.clay.2013.12.013 MAR 2014
Abstract:
This study examines the influence of layer charge and smectite content on the rheological properties of mixed bentonite-palygorskite suspensions. Eight bentonite samples containing smectite with layer charge ranging between 0.38 and 0.54 e/huc were used to prepare 5% w/v mixed palygorskite-bentonite aqueous suspension at pH 7. The influence of smectite on the apparent viscosity and yield point of palygorskite suspensions depends on the proportion of the smectite in the mixture and the layer charge and charge localization of the smectite. The interaction between the two end member clay minerals is maximum at low percentage (10 to 20%) of bentonite in the mixture. Low charge and high charge smectite tended to improve and deteriorate, respectively, the yield point and apparent viscosity of the suspension. This behaviour seemed to be related to the influence of layer charge of smectite on the degree of delamination and the thickness of smectite quasicrystals, which consequently determine the number of particles involved in the interaction and the strength of particle-particle linkages. (C) 2014 Elsevier B.V. All rights reserved.
Title:
Frequency dependence of the characteristic temperatures in PbSc0.5Ta0.36Nb0.14O3 relaxor ferroelectrics crystals seen via acoustic emission
Authors:
Dul'kin, E; Mihailova, B; Gospodinov, M; Roth, M Author Full Names: Dul'kin, E.; Mihailova, B.; Gospodinov, M.; Roth, M.
Source:
JOURNAL OF APPLIED PHYSICS, 115 (8):10.1063/1.4864036 FEB 28 2014
Abstract:
PbSc0.5Ta0.36Nb0.14O3 relaxor ferroelectrics crystals were investigated in a wide temperature range of 200-700K using acoustic emission. The intermediate temperature T* as well as the Burns temperature T-d were successfully detected at 480K and 581 K, respectively. Another acoustic emission burst was detected at T-n(l) similar to 211K, which is below the temperature of the dielectric-permittivity maximum T-m similar to 257K but it is accompanied by a slight anomaly in the dielectric permittivity. T-n(l) is attributed to the low-temperature boundary of an incommensurately modulated antiferroelectric phase transition taking place over a temperature range. All characteristic temperatures exhibit frequency dispersion in the range of 0.1-10 kHz, which is considerably stronger for T* and T-d than for T-m and T-n(l). In addition, T-n(l) depends linearly on frequency, whereas both T* and T-d resemble the non-linear frequency dependence of Tm typical of relaxors. The nature of the frequency dispersion of T* and T-d is discussed from the viewpoint of complex behavior of low-energy polar modes intrinsic of relaxor ferroelectrics. (C) 2014 AIP Publishing LLC.
Title:
In-situ high-pressure X-ray diffraction on the Zn6Sc 1/1 periodic cubic approximant to a quasicrystal
Authors:
Yamada, T; Garbarino, G; Takakura, H; Gomez, CP; Tamura, R; de Boissieu, M Author Full Names: Yamada, Tsunetomo; Garbarino, Gaston; Takakura, Hiroyuki; Gomez, Cesar Pay; Tamura, Ryuji; de Boissieu, Marc
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 229 (3):230-235; SI 10.1515/zkri-2013-1684 2 2014
Abstract:
The Zn6Sc 1/1 cubic approximant to a quasicrystal has been studied in-situ at high pressures by single-crystal X-ray diffraction. This phase can be described as a bcc packing of Tsai-type icosahedral clusters whose center is occupied by a disordered Zn-4 tetrahedron. At ambient pressure the Zn6Sc undergoes a structural phase transition at 159 K to a monoclinic superstructure in which the Zn-4 tetrahedra are orientationally ordered along the [101] direction of the high-temperature bcc phase. In the pressure range up to 35 GPa, two new superstructures have been observed. The second phase corresponds to a four-fold pseudo cubic superstructure, i.e. a very large unit cell with a lattice parameter of about 5.5 nm. The resulting pressure-temperature phase diagram is different from that of Cd6Yb, which was reported by Watanuki et al. (2006).

Update: 23-Apr-2014

Title:
Bulk synthesis by spray forming of Al-Cu-Fe and Al-Cu-Fe-Sn alloys containing a quasicrystalline phase
Authors:
Srivastava, VC; Huttunen-Saarivirta, E; Cui, C; Uhlenwinkel, V; Schulz, A; Mukhopadhyay, NK Author Full Names: Srivastava, V. C.; Huttunen-Saarivirta, E.; Cui, C.; Uhlenwinkel, V.; Schulz, A.; Mukhopadhyay, N. K.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 597 258-268; 10.1016/j.jallcom.2014.01.241 JUN 5 2014
Abstract:
In this study, Al-Cu-Fe alloys without and with the addition of Sn and containing a quasicrystalline phase were spray deposited. The spray-deposited bulk materials were characterized in terms of microstructure and hardness. The results showed that the Al62.5Cu25Fe12.5 alloy contains the icosahedral quasicrystalline phase (i-phase) along with the minor lambda-Al13Fe4 phase, whereas the Al62.5Cu25Fe12.5 + Sn alloy contains five phases: the major i-phase and the crystalline phases of Sn, theta-Al2Cu, lambda-Al13Fe4 and beta-AlFe(Cu) phases. These results have been corroborated by X-ray diffraction (XRD), scanning and transmission electron microscopies (SEM and TEM) and differential scanning calorimetry (DSC). The hardness value of the Al-Cu-Fe alloy reached 10.5 GPa at 50 g load and then decreased steadily with increase in the applied load, while that for Al-Cu-Fe-Sn alloy it was originally somewhat lower, then decreased dramatically with slight increase in the applied load but stayed constant with further load increase. The hardness indentations in Al-Cu-Fe alloy introduced cracking in the material, whereas in the case of Al-Cu-Fe-Sn alloy the Sn-rich areas inhibited the crack growth. The present study provides an insight into the mechanism of phase and microstructural evolutions during spray forming of the studied alloys. Furthermore, the role of Sn in terms of microstructure and properties is highlighted. (C) 2014 Elsevier B. V. All rights reserved.
Title:
Exotic Magnetism on the Quasi-fcc Lattices of the d(3) Double Perovskites La2NaB ' O-6 (B ' = Ru, Os)
Authors:
Aczel, AA; Baker, PJ; Bugaris, DE; Yeon, J; Loye, HCZ; Guidi, T; Adroja, DT Author Full Names: Aczel, A. A.; Baker, P. J.; Bugaris, D. E.; Yeon, J.; Loye, H. -C. Zur; Guidi, T.; Adroja, D. T.
Source:
PHYSICAL REVIEW LETTERS, 112 (11):10.1103/PhysRevLett.112.117603 MAR 20 2014
Abstract:
We find evidence for long-range and short-range (zeta = 70 angstrom at 4 K) incommensurate magnetic order on the quasi-face-centered-cubic (fcc) lattices of the monoclinic double perovskites La2NaRuO6 and La2NaOsO6, respectively. Incommensurate magnetic order on the fcc lattice has not been predicted by mean field theory, but may arise via a delicate balance of inequivalent nearest neighbor and next nearest neighbor exchange interactions. In the Ru system with long-range order, inelastic neutron scattering also reveals a spin gap Delta similar to 2.75 meV. Magnetic anisotropy is generally minimized in the more familiar octahedrally coordinated 3d(3) systems, so the large gap observed for La2NaRuO6 may result from the significantly enhanced value of spin-orbit coupling in this 4d(3) material.
Title:
Influence of the thickness of [N(CH3)(4)](2)Zn0.75Mn0.25Cl4 crystal on the *phase-*transition temperature
Authors:
Sveleba, SA; Karpa, IV; Katerynchuk, IM; Kunyo, IM; Phitsych, EI Author Full Names: Sveleba, S. A.; Karpa, I. V.; Katerynchuk, I. M.; Kunyo, I. M.; Phitsych, E. I.
Source:
CRYSTALLOGRAPHY REPORTS, 59 (2):229-237; 10.1134/S1063774514020266 MAR 2014
Abstract:
The change in the phase-transition temperature of [N(CH3)(4)](2)Zn0.75Mn0.25Cl4 crystal as a function of its size (3500 mu m-1 mu m) has been investigated. It is established that a decrease in crystal sizes along the spontaneous-polarization axis is accompanied by several effects: a shift of the initial *phase-*incommensurate phase transition point to higher temperatures, an increase in the temperature range of existence of incommensurate phase, an increase in the temperature range of existence of metastable states of incommensurate structure, the occurrence of new long-period commensurate phases, and an increase in *phase-*transition temperature hysteresis at T (c) and T (3). The possibility that a size effect exists in the phase diagram of this crystal is discussed.
Title:
Modulated quasi-two-dimensional antiferromagnetic structures in La1-y Nd (y) MnO3+delta manganites
Authors:
Bukhanko, FN Author Full Names: Bukhanko, F. N.
Source:
PHYSICS OF THE SOLID STATE, 56 (3):473-486; 10.1134/S106378341403007X MAR 2014
Abstract:
The structural, electronic, and magnetic phase transitions induced by the isovalent substitution of the rare-earth Nd3+ ion for the La3+ ion with a larger radius have been investigated in the system of self-doped manganites La1 - y Nd (y) MnO3 + delta (0 a parts per thousand currency sign y a parts per thousand currency sign 1; delta similar to 0.1). For the average radius of the ions in A-sites of the lattice aOE (c) r (A) > aOE (c) 1.19 (y > 0.5), the phenomena revealed in the manganites are as follows: the ordering of Mn e (g) orbitals, the transition from the pseudocubic O* phase to the orthorhombic O' phase, the opening of the dielectric Jahn-Teller gap, the frustration of the collinear ferromagnetic (FM) state, and the transition from the lowtemperature canted FM to canted antiferromagnetic (AFM) state of Mn spins. It is assumed that, in samples with neodymium concentrations y = 0.9 and 1.0 (aOE (c) r (A) > a parts per thousand 1.16 ) at temperatures T < 12 K, there coexist A- and E-type modulated AFM states similar to the sinusoidal and helical structures of Mn spins, which were previously studied in RMnO3 multiferroics. The magnetic T-H phase diagrams of these samples are characteristic of quasi-two-dimensional antiferromagnets with a very low (zero) magnetic anisotropy in the ab planes. Under these conditions, the phase transition from the A-type AFM phase to the spin-flop state occurs in a relatively weak magnetic field. The AFM ordering of the Nd magnetic moments with a critical phase transition temperature T (Nd) a parts per thousand OE 6 K is induced in magnetic fields with a strength H a parts per thousand yen 3.5 kOe. For the NdMnO3 + delta manganite in a magnetic field H = 10.7 kOe, the curves M(T) are characterized by additional very narrow peaks near temperatures T (1) a parts per thousand OE 4.5 K and T (2) a parts per thousand OE 5 K. The additional features revealed for the first time in the magnetization near T = 0 are assumed to be caused by the quantization of the spectrum of free holes in the ab planes by a strong magnetic field.
Title:
Electronic band structure and Fermi surfaces of the quasi-two-dimensional monophosphate tungsten bronze, P4W12O44
Authors:
Paul, S; Ghosh, A; Sato, T; Sarma, DD; Takahashi, T; Wang, E; Greenblatt, M; Raj, S Author Full Names: Paul, S.; Ghosh, A.; Sato, T.; Sarma, D. D.; Takahashi, T.; Wang, E.; Greenblatt, M.; Raj, S.
Source:
EPL, 105 (4):10.1209/0295-5075/105/47003 FEB 2014
Abstract:
The electronic structure of quasi-two-dimensional monophosphate tungsten bronze, P4W12O44, has been investigated by high-resolution angle-resolved photoemission spectroscopy and density functional theoretical calculations. Experimental electron-like bands around Gamma point and Fermi surfaces have similar shapes as predicted by calculations. Fermi surface mapping at different temperatures shows a depletion of density of states at low temperature in certain flat portions of the Fermi surfaces. These flat portions of the Fermi surfaces satisfy the partial nesting condition with incommensurate nesting vectors q(1) and q(2), which leads to the formation of charge density waves in this phosphate tungsten bronzes. The setting up of charge density wave in these bronzes can well explain the anomaly observed in its transport properties. Copyright (C) EPLA, 2014

Update: 17-Apr-2014

Title:
Local orderings in long-range-disordered bismuth-layered intergrowth structure
Authors:
Zhang, FQ; Li, YX; Gu, H; Gao, X Author Full Names: Zhang, Faqiang; Li, Yongxiang; Gu, Hui; Gao, Xiang
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 212 165-170; 10.1016/j.jssc.2014.01.031 APR 2014
Abstract:
A series of intergrowth bismuth-layered (Bi3TiNbO9)(2)(Bi4Ti3O12) (2(2)3) ceramics were prepared by conventional solid-state reaction to study the characteristics of the local orderings in long-range-disordered intergrowth structures. High-resolution high-angle annular dark-field (HAADF) imaging reveals the intergrowth structure composed of mixtures of -23-, -223-, -2223- and -22- sequences, while the -223- structure is the thermodynamic stable state of this intergrowth system. It was confirmed by the crystals of recurrent -223- structure prepared by self-flux method and the nature of the local ordering was discussed from their differences in repeating units. The statistics show that when repeating units reach 4 or higher, the independent -223- intergrowth ordering emerges clearly among the competing associated orderings. We infer it is the kinetic factor that induces local compositional variance to result in long-range disordered intergrowth structures. (C) 2014 Elsevier Inc. All rights reserved.
Title:
Angular Fluctuations of a Multicomponent Order Describe the Pseudogap of YBa2Cu3O6+x
Authors:
Hayward, LE; Hawthorn, DG; Melko, RG; Sachdev, S Author Full Names: Hayward, Lauren E.; Hawthorn, David G.; Melko, Roger G.; Sachdev, Subir
Source:
SCIENCE, 343 (6177):1336-1339; 10.1126/science.1246310 MAR 21 2014
Abstract:
The hole-doped cuprate high-temperature superconductors enter the pseudogap regime as their superconducting critical temperature, T-c, falls with decreasing hole density. Recent x-ray scattering experiments in YBa2Cu3O6+x observe incommensurate charge-density wave fluctuations whose strength rises gradually over a wide temperature range above T-c, but then decreases as the temperature is lowered below T-c. We propose a theory in which the superconducting and charge-density wave orders exhibit angular fluctuations in a six-dimensional space. The theory provides a natural quantitative fit to the x-ray data and can be a basis for understanding other characteristics of the pseudogap.
Title:
Magnetic ordering in TmGa
Authors:
Cadogan, JM; Stewart, GA; Perez, SM; Cobas, R; Hansen, BR; Avdeev, M; Hutchison, WD Author Full Names: Cadogan, J. M.; Stewart, G. A.; Perez, S. Munoz; Cobas, R.; Hansen, B. R.; Avdeev, M.; Hutchison, W. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (11):10.1088/0953-8984/26/11/116002 MAR 19 2014
Abstract:
We have determined the magnetic structure of the intermetallic compound TmGa by high-resolution neutron powder diffraction and Tm-169 Mossbauer spectroscopy. This compound crystallizes in the orthorhombic (Cmcm) CrB-type structure and its magnetic structure is characterized by magnetic order of the Tm sublattice along the a-axis. The initial magnetic ordering occurs at 15(1) K and yields an incommensurate antiferromagnetic structure described by the propagation vector k1 = [0.0.275(2)0]. At 12 K the dominant ferromagnetic ordering of the Tm sublattice along the a-axis develops in what appears to be a first-order transition. At 3 K the magnetic structure of TmGa is predominantly ferromagnetic but a weakened incommensurate component remains. The ferromagnetic Tm moment reaches 6.7(2) mu B at 3 K and the amplitude of the remaining incommensurate component is 2.7(4) mu B. The Tm-169 hyperfine magnetic field at 5 K is 631(1) T.
Title:
RESEARCH PROGRESS OF FIVE-FOLD SYMMETRY CLUSTERS
Authors:
Li, GF; Shu, XY; Liu, JW Author Full Names: Li, G. F.; Shu, X. Y.; Liu, J. W.
Source:
REVIEWS ON ADVANCED MATERIALS SCIENCE, 36 (1):21-28; FEB 2014
Abstract:
Since 1984, Shechtman et al. published a paper which marked the discovery of quasicrystals. The local five fold symmetry (LFFS) structure is becoming an unsocial hero, who walks a muricated way against classical crystallography. As well known, the LFFS clusters have largely potential application prospect in catalysis, in recomposing physical, mechanical and thermal performance of bulk metallic glasses, in composing "super atom" materials, in some creative manufacture technologies of crystal metal from amorphous straightly. In this paper, we summarize the ubiquitous existence, particularity, performance and research progress of LFFS clusters in metallic glasses, and put forward some urgent problems.
Title:
Comprehensive study of the spin-charge interplay in antiferromagnetic La-2 - xSrxCuO4
Authors:
Drachuck, G; Razzoli, E; Bazalitski, G; Kanigel, A; Niedermayer, C; Shi, M; Keren, A Author Full Names: Drachuck, Gil; Razzoli, Elia; Bazalitski, Galina; Kanigel, Amit; Niedermayer, Christof; Shi, Ming; Keren, Amit
Source:
NATURE COMMUNICATIONS, 5 10.1038/ncomms4390 FEB 2014
Abstract:
The origin of the pseudogap and its relationship with superconductivity in the cuprates remains vague. In particular, the interplay between the pseudogap and magnetism is mysterious. Here we investigate the newly discovered nodal gap in hole-doped cuprates using a combination of three experimental techniques applied to one, custom made, single crystal. The crystal is an antiferromagnetic La2 - xSrxCuO4 with x = 1.92%. We perform angle-resolved photoemission spectroscopy measurements as a function of temperature and find: quasi-particle peaks, Fermi surface, anti-nodal gap and below 45 K a nodal gap. Muon spin rotation measurements ensure that the sample is indeed antiferromagnetic and that the doping is close, but below, the spin-glass phase boundary. We also perform elastic neutron scattering measurements and determine the thermal evolution of the commensurate and incommensurate magnetic order, where we find that a nodal gap opens well below the commensurate ordering at 140 K, and close to the incommensurate spin density wave ordering temperature of 30 K.

Update: 9-Apr-2014

Title:
A novel quasicrystal-resin composite for stereolithography
Authors:
Sakly, A; Kenzari, S; Bonina, D; Corbel, S; Fournee, V Author Full Names: Sakly, Adnene; Kenzari, Samuel; Bonina, David; Corbel, Serge; Fournee, Vincent
Source:
MATERIALS & DESIGN, 56 280-285; 10.1016/j.matdes.2013.11.025 APR 2014
Abstract:
Laser stereolithography (SL) is an additive manufacturing technology which is increasingly being used to produce customized end-user parts of any complex shape. It requires the use of a photo-curable resin which can be loaded with ceramic powders or carbon fibers to produce composite parts. However, the range of available materials compatible with the SL process is rather limited. In particular, photo-curable resins reinforced by metal particles are difficult to process, because of fundamental limitations related to the high reflectivity of intermetallics in the UV-visible range. In this work, the unique properties of Al-based quasicrystalline alloys are being used to develop a new UV-curable resin reinforced by such metal particles. The optical properties of the quasicrystalline particles and of the filled resin are studied and they are found to be compatible with the SL process. The volume fraction of the filler particles in the liquid resin is optimized to increase the polymerization depth while preserving suitable rheological behaviour. Finally, 3D composite parts are being built by SL. The composite parts have improved mechanical properties compared to the unfilled resin (higher hardness, reduced wear losses and lower friction coefficient) and compete favourably with the other commercial photo-curable resins. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Elastic field in an infinite medium of one-dimensional hexagonal quasicrystal with a planar crack
Authors:
Li, XY Author Full Names: Li, X. -Y.
Source:
INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 51 (6):1442-1455; 10.1016/j.ijsolstr.2013.12.030 MAR 15 2014
Abstract:
This present work is concerned with planar cracks embedded in an infinite space of one-dimensional hexagonal quasicrystals. The potential theory method together with the general solutions is used to develop the framework of solving the crack problems in question. The model problems of three common planar cracks (a penny-shaped crack, an external circular crack and a half-infinite crack) are solved in a systematic manner. The phonon and phason elastic fundamental fields along with some important parameters in crack analysis are explicitly presented in terms of elementary functions. Several examples are given to show the applications of the present fundamental solutions. The validity of the present solutions is discussed both analytically and numerically. The derived analytical solutions of crack will not only play an important role in understanding the phonon-phason coupling behavior in quasicrystals, but also serve as benchmarks for future numerical studies and simplified analyses. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Pressure effect on magnetism and multiferroicity in Mn2GeO4
Authors:
Honda, T; Aoyama, T; White, JS; Strassle, T; Keller, L; Kenzelmann, M; Honda, F; Miyake, A; Shimizu, K; Wakabayashi, Y; Kimura, T Author Full Names: Honda, T.; Aoyama, T.; White, J. S.; Straessle, Th; Keller, L.; Kenzelmann, M.; Honda, F.; Miyake, A.; Shimizu, K.; Wakabayashi, Y.; Kimura, T.
Source:
PHYSICAL REVIEW B, 89 (10):10.1103/PhysRevB.89.104405 MAR 10 2014
Abstract:
The effect of high pressure exceeding 6 GPa on magnetism and multiferroicity was investigated for the olivine Mn2GeO4 that shows successive magnetic transitions at ambient pressure and a ferroelectric ground state driven by spin- spiral order. We measured heat capacity, dielectric constant, and electric polarization at various pressures using a diamond anvil cell. The pressure evolution of the magnetic structures was also investigated by powder neutron diffraction measurements using a Paris- Edinburgh press. We found that all of the magnetic transition temperatures are enhanced monotonically by applying pressure. Furthermore, the spin- driven ferroelectricity persists up to about 6 GPa but suddenly vanishes by 6.3 GPa. A consistent description of all data is achieved if an incommensurate- commensurate phase transition occurs with pressurization and causes the suppression of ferroelectricity. We discuss the origin of the observed pressure effects on the magnetism and multiferroicity in Mn2GeO4 in terms of a pressure- induced change in the superexchange magnetic interactions.
Title:
Observation of a new type of magnetic excitations in NdFe3(BO3)(4) ferroborate
Authors:
Kobets, M; Dergachev, K; Kovalev, A; Gnatchenko, S; Khatsko, E Author Full Names: Kobets, M.; Dergachev, K.; Kovalev, A.; Gnatchenko, S.; Khatsko, E.
Source:
LOW TEMPERATURE PHYSICS, 40 (2):151-155; 10.1063/1.4865568 FEB 2014
Abstract:
AFMR spectra of single crystal NdFe3(BO3)(4) are studied over frequencies of 15-32.2 GHz and temperatures of 2.17-10 K in fields H
Title:
Activation of Al-Cu-Fe quasicrystalline surface: fabrication of a fine nanocomposite layer with high catalytic performance
Authors:
Kameoka, S; Tanabe, T; Satoh, F; Terauchi, M; Tsai, AP Author Full Names: Kameoka, Satoshi; Tanabe, Toyokazu; Satoh, Futami; Terauchi, Masami; Tsai, An Pang
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (1):10.1088/1468-6996/15/1/014801 FEB 2014
Abstract:
A fine layered nanocomposite with a total thickness of about 200 nm was formed on the surface of an Al63Cu25Fe12 quasicrystal (QC). The nanocomposite was found to exhibit high catalytic performance for steam reforming of methanol. The nanocomposite was formed by a self-assembly process, by leaching the Al-Cu-Fe QC using a 5 wt% Na2CO3 aqueous solution followed by calcination in air at 873 K. The quasiperiodic nature of the QC played an important role in the formation of such a structure. Its high catalytic activity originated from the presence of highly dispersed copper and iron species, which also suppressed the sintering of nanoparticles.

Update: 3-Apr-2014

Title:
Anomalous triple point effects in the spin-density-wave Cr1-xAlx alloy system
Authors:
Sheppard, CJ; Prinsloo, ARE; Alberts, HL; Muchono, B; Strydom, AM Author Full Names: Sheppard, C. J.; Prinsloo, A. R. E.; Alberts, H. L.; Muchono, B.; Strydom, A. M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 595 164-177; 10.1016/j.jallcom.2014.01.129 MAY 15 2014
Abstract:
It was recently suggested that for the Cr1-xAlx alloy system the Sommerfeld specific heat coefficient (gamma) as a function of x may peak at the triple point (TP) concentration (x(t)) of the x-T magnetic phase diagram. The TP at (x(t), T-t) represents the intersection point of three magnetic phase transition lines at which incommensurate (I) and commensurate (C) spin-density-wave (SDW) phases are expected to coexist with the paramagnetic (P) phase. A comprehensive experimental study on the physical properties of single crystalline Cr1-xAlx alloys in the concentration range 0 <= x <= 0.034, that encloses x(t), is reported here for further investigations of the above conjecture and possible anomalous behaviour in other physical properties near x(t). The measurements include the electrical resistivity (rho), Seebeck coefficient (S), specific heat (C-p), Hall coefficient (R-H), magnetic susceptibility (chi) and thermal conductivity (kappa). All these properties, except for kappa, depict anomalous temperature and concentration dependencies of SDW origin for x close to x(t). The present study indicates a value of x(t) rather close to x = 0.022. The x-dependence of gamma exhibits an extraordinary large and sharp peak near this concentration. This observation is interpreted as indication that the temperature of the TP is likely situated at 0 K. A new magnetic phase diagram is therefore proposed for the Cr1-xAlx alloy system for x in the region of x(t). This study presents novel experimental evidence of exceptional anomalous magnetic behaviour around the TP concentration of the Cr1-xAlx system. It should incite similar studies on other Cr alloy systems with a TP on their magnetic phase diagrams. (C) 2014 Elsevier B. V. All rights reserved.
Title:
Magnetic properties of LaCo12B6 compound as probed by neutron diffraction and by magnetization study under high pressures
Authors:
Diop, LVB; Arnold, Z; Isnard, O; Kamarad, J Author Full Names: Diop, L. V. B.; Arnold, Z.; Isnard, O.; Kamarad, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 593 163-168; 10.1016/j.jallcom.2013.12.216 APR 25 2014
Abstract:
The magnetic properties have been studied by magnetization measurements and the crystal and magnetic structure investigated by neutron diffraction. It is shown that LaCo12B6 compound exhibits an incommensurate conical type magnetic structure. Significantly different magnetic moments have been observed on the two Co crystal sites. The ambient pressure data are compared to that of YCo12B6 isotype and Landau coefficients have been derived from the magnetization curves for both compounds as well as their temperature dependence. The LaCo12B6 compound undergoes a transition from ordered to paramagnetic state at 160 K. The volume dependence of intrinsic magnetic properties of the LaCo12B6 compound has been determined by studies under hydrostatic pressure up to 10 kbar in temperature range 5-200 K. Both the Curie temperature T-C and the spontaneous magnetization M-S decreases with increasing pressure. The observed decrease of M-S with pressure (dM(S)/dp = -7.4 x 10(-3) mu(B)/kbar at 5 K) can be attributed to the pressure induced decrease of Co magnetic moments. The decrease of T-C with pressure (dT(C)/dp = -0.49 K/kbar) is comparable to the decrease observed on RCo12B6 compounds with non-magnetic R and can be attributed to the volume dependence of Co-Co exchange interactions. The remarkable role of the hybridization as a consequence of small distances between Co and B atoms could be a background of this rather unexpected volume stability of magnetic properties. (C) 2014 Elsevier B.V. All rights reserved.
Title:
(3+1)-dimensional crystal and antiferromagnetic structures in CeRuSn
Authors:
Prokes, K; Petricek, V; Ressouche, E; Hartwig, S; Ouladdiaf, B; Mydosh, JA; Hoffmann, RD; Huang, YK; Pottgen, R Author Full Names: Prokes, K.; Petricek, V.; Ressouche, E.; Hartwig, S.; Ouladdiaf, B.; Mydosh, J. A.; Hoffmann, R-D; Huang, Y-K; Poettgen, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (12):10.1088/0953-8984/26/12/122201 MAR 26 2014
Abstract:
At 320 K, the crystal structure of CeRuSn is commensurate with the related CeCoAl-type of structure by the doubling of the c lattice parameter. However, with lowering the temperature it becomes incommensurate with x and z position parameters at all three elemental sites being modulated as one moves along the c-axis. The resulting crystal structure can be conveniently described within the superspace formalism in (3 + 1) dimensions. The modulation vector, after initially strong temperature dependence, approaches a value close to q(nuc) = (0 0 0.35). Below T-N = 2.8 (1) K, CeRuSn orders antiferromagnetically with a propagation vector q(mag) = (0 0 0.175), i.e. with the magnetic unit cell doubled along the c-axis direction with respect to the incommensurate crystal structure. Ce moments appear to be nearly collinear, confined to the a-c plane, forming ferromagnetically coupled pairs. Their magnitudes are modulated between 0.11 and 0.95 mu B as one moves along the c-axis.
Title:
Self-assembly of hydrogen-bonded two-dimensional quasicrystals
Authors:
Wasio, NA; Quardokus, RC; Forrest, RP; Lent, CS; Corcelli, SA; Christie, JA; Henderson, KW; Kandel, SA Author Full Names: Wasio, Natalie A.; Quardokus, Rebecca C.; Forrest, Ryan P.; Lent, Craig S.; Corcelli, Steven A.; Christie, John A.; Henderson, Kenneth W.; Kandel, S. Alex
Source:
NATURE, 507 (7490):86-+; 10.1038/nature12993 MAR 6 2014
Abstract:
The process of molecular self-assembly on solid surfaces is essentially one of crystallization in two dimensions, and the structures that result depend on the interplay between intermolecular forces and the interaction between adsorbates and the underlying substrate(1). Because a single hydrogen bond typically has an energy between 15 and 35 kilojoules per mole, hydrogen bonding can be a strong driver of molecular assembly; this is apparent from the dominant role of hydrogen bonding in nucleic-acid base pairing, as well as in the secondary structure of proteins. Carboxylic acid functional groups, which provide two hydrogen bonds, are particularly promising and reliable in creating and maintaining surface order, and self-assembled monolayers of benzoic acids produce structure that depends on the number and relative placement of carboxylic acid groups(2-6). Here we use scanning tunnelling microscopy to study self-assembled monolayers of ferrocenecarboxylic acid (FcCOOH), and find that, rather than producing dimeric or linear structures typical of carboxylic acids, FcCOOH forms highly unusual cyclic hydrogen-bonded pentamers, which combine with simultaneously formed FcCOOH dimers to form two-dimensional quasicrystallites that exhibit local five-fold symmetry and maintain translational and rotational order (without periodicity) for distances of more than 400 angstroms.
Title:
Ordering and growth of rare gas films (Xe, Kr, Ar, and Ne) on the pseudo-ten-fold quasicrystalline approximant Al13Co4(100) surface
Authors:
Petucci, J; Karimi, M; Huang, YT; Curtarolo, S; Diehl, RD Author Full Names: Petucci, J.; Karimi, M.; Huang, Y-T; Curtarolo, S.; Diehl, R. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (9):10.1088/0953-8984/26/9/095003 MAR 5 2014
Abstract:
Adsorption of the rare gases Kr, Ar, and Ne on the complex alloy surface Al13Co4(100) was studied using grand canonical Monte Carlo (GCMC) computer simulations. This surface is an approximant to the ten-fold decagonal Al-Ni-Co quasicrystalline surface, on which rare gas adsorption was studied previously. Comparison of adsorption results on the periodic Al13Co4(100) surface with those of the quasiperiodic Al-Ni-Co surface indicates some similarities, such as layer-by-layer growth, and some dissimilarities, such as the formation of Archimedes tiling phases (Mikhael et al 2008 Nature 454 501, Shechtman et al 1984 Phys. Rev. Lett. 53 1951, Macia 2006 Rep. Prog. Phys. 69 397, Schmiedeberg et al 2010 Eur. Phys. J. E 32 25-34, Kromer et al 2012 Phys. Rev. Lett. 108 218301, Schmiedeberg and Stark 2008 Phys. Rev. Lett. 101 218302). The conditions under which Archimedes tiling phases (ATP) emerge on Al13Co4(100) are examined and their presence is related to the gas-gas and gas-surface interaction parameters.
Title:
What periodicities can be found in diffraction patterns of quasicrystals?
Authors:
Wolny, J; Kozakowski, B; Kuczera, P; Pytlik, L; Strzalka, R Author Full Names: Wolny, Janusz; Kozakowski, Bartlomiej; Kuczera, Pawel; Pytlik, Lucjan; Strzalka, Radoslaw
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 70 181-185; 10.1107/S2053273313034384 2 MAR 2014
Abstract:
The structure of quasicrystals is aperiodic. Their diffraction patterns, however, can be considered periodic. They are composed solely of series of peaks which exhibit a fully periodic arrangement in reciprocal space. Furthermore, the peak intensities in each series define the so-called 'envelope function'. A Fourier transform of the envelope function gives an average unit cell, whose definition is based on the statistical distribution of atomic coordinates in physical space. If such a distribution is lifted to higher-dimensional space, it becomes the so-called atomic surface - the most fundamental feature of higher-dimensional analysis.
Title:
Hydrogen storage properties of Ti1.4V0.6Ni + x Mg (x=1-3, wt.%) alloys
Authors:
Lin, J; Mang, F; Wu, YM; Liu, WQ; Wang, LM Author Full Names: Lin, Jing; Mang, Fei; Wu, Yaoming; Liu, Wanqiang; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 39 (7):3313-3319; 10.1016/j.ijhydene.2013.12.059 FEB 25 2014
Abstract:
We prepared Ti1.4V0.6Ni ribbons by arc-melting and subsequent melt-spinning techniques. Ti1.4V0.6Ni + x Mg (x = 1, 1.5, 2, 2.5 and 3, wt.%) composite alloys were obtained by the mechanical ball-milling method. The structures and hydrogen storage properties of alloys were investigated. Ti1.4V0.6Ni + x Mg composite alloys contained icosahedral quasicrystalline phase, Ti2Ni-type phase, beta-Ti solid-solution phase and metallic Mg. The electrochemical and gaseous hydrogen storage properties of alloys were improved with Mg addition. Ti1.4V0.6Ni + 2 Mg alloy showed maximum electrochemical discharge capacity of 282.5 mAh g(-1) as well as copacetic high-rate discharge ability of 82.3% at the discharge current density of 240 mA g(-1) compared with that of 30 mA g(-1), and the cycling life achieved above 200 mAh g(-1) after 50 consecutive cycles of charging and discharging. The hydrogen absorption/desorption properties of Ti1.4V0.6Ni + x Mg (x = 1, 2 and 3, wt.%) alloys were better than Ti1.4V0.6Ni. Ti1.4V0.6Ni + 3 Mg alloy also exhibited a favorable hydrogen absorption capacity of 1.53 wt.%. The improvement in the hydrogen storage characteristics caused by adding Mg may be ascribed to better hydrogen diffusion and anti-corrosion ability. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Title:
Chemical pressure effects on structural, dielectric and magnetic properties of solid solutions Mn3-xCoxTeO6
Authors:
Ivanov, SA; Mathieu, R; Nordblad, P; Ritter, C; Tellgren, R; Golubko, N; Mosunov, A; Politova, ED; Weil, M Author Full Names: Ivanov, S. A.; Mathieu, R.; Nordblad, P.; Ritter, C.; Tellgren, R.; Golubko, N.; Mosunov, A.; Politova, E. D.; Weil, M.
Source:
MATERIALS RESEARCH BULLETIN, 50 42-56; 10.1016/j.materresbull.2013.10.016 FEB 2014
Abstract:
The effects of Co2+ doping on the structural, magnetic and dielectric properties of the multiferroic frustrated antiferromagnet Mn3TeO6 have been investigated. Ceramic samples of the solid solution series Mn3-xCoxTeO6 were prepared by a solid-state reaction route. X-ray and neutron powder diffraction and electron microscopy techniques were combined with calorimetric, dielectric and magnetic measurements to investigate the dependence of the crystal structure and physical properties on temperature and composition. It is shown that the compounds with x <= 2.4 adopt the trigonal corundum-related structure of pure Mn3TeO6 (space group 18) in the temperature range 5-295 K and that the lattice parameters a and c and the unit-cell volume V decrease linearly with increasing Co2+ concentration. The low-temperature magnetic susceptibility and heat capacity data evidence the antiferromagnetic ordering of all samples. The Neel temperature linearly increases with Co2+ concentration x. Curie-Weiss fits of the high temperature susceptibility indicate that the magnetic frustration decreases with x. The derived magnetic structure of Mn3TeO6 can be described as an incommensurately modulated magnetic spin state with k = [0, 0, k(z)] and an elliptical spin-spiral order of spins within the chains of MnO6 octahedra. With increasing Co2+ concentration the propagation vector kz changes from 0.453 (x = 0) to 0.516 (x = 2.4). The magnetic anisotropy changes as well, leading to a reorientation of the spiral-basal plane. A possible coexistence of long-range order of electrical dipoles and magnetic moments in Mn3-xCoxTeO6 is discussed. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Observation of exchange bias below incommensurate antiferromagnetic (ICAFM) to canted A-type antiferromagnetic (cAAFM) transition in nanocrystalline orthorhombic EuMnO3
Authors:
Das, R; Poddar, P Author Full Names: Das, Raja; Poddar, Pankaj
Source:
RSC ADVANCES, 4 (21):10614-10618; 10.1039/c3ra45435e 2014
Abstract:
Detailed ac and dc magnetic properties of orthorhombic EuMnO3 were studied using a nanocrystalline powder sample. Orthorhombic EuMnO3 nanoparticles of 45 nm average size were synthesised using a hydrothermal method. Zero field cooled (ZFC) and field cooled (FC) magnetisation shows anomalies at similar to 53, 44 and 24 K attributed to paramagnetic (PM) to an incommensurate antiferromagnetic phase (ICAFM), ICAFM to a canted A-type antiferromagnetic order (cAAFM) and spin reorientation transitions, respectively. No indication of a PM to ICAFM transition was observed in either the real or imaginary part of ac magnetisation. The real part of the ac magnetisation curve showed a peak at similar to 24.7 K and anomalies at similar to 46.8 and 21.8 K were observed in the imaginary part of ac magnetisation. Reduction in the width of the thermal hysteresis between the field cooling and heating magnetisation curve was observed with the nanocrystallites (similar to 1 K) compared with the bulk phase (similar to 3 K) EuMnO3. Isothermal magnetisation showed a large value of the exchange bias (2799 Oe at 3 K) below the ICAFM to cAAFM transition temperature.
Title:
Lattice dynamical signature of charge density wave formation in underdoped YBa2Cu3O6+x
Authors:
Bakr, M; Souliou, SM; Blanco-Canosa, S; Zegkinoglou, I; Gretarsson, H; Strempfer, J; Loew, T; Lin, CT; Liang, R; Bonn, DA; Hardy, WN; Keimer, B; Le Tacon, M Author Full Names: Bakr, M.; Souliou, S. M.; Blanco-Canosa, S.; Zegkinoglou, I.; Gretarsson, H.; Strempfer, J.; Loew, T.; Lin, C. T.; Liang, R.; Bonn, D. A.; Hardy, W. N.; Keimer, B.; Le Tacon, M.
Source:
PHYSICAL REVIEW B, 88 (21):10.1103/PhysRevB.88.214517 DEC 31 2013
Abstract:
We report a detailed Raman scattering study of the lattice dynamics in detwinned single crystals of the underdoped high-temperature superconductor YBa2Cu3O6+x (x = 0.75, 0.6, 0.55, and 0.45). Whereas at room temperature the phonon spectra of these compounds are similar to that of optimally doped YBa2Cu3O6.99, additional Raman-active modes appear upon cooling below similar to 170-200Kin underdoped crystals. The temperature dependence of these new features indicates that they are associated with the incommensurate charge density wave state recently discovered using synchrotron x-ray scattering techniques on the same single crystals. Raman scattering thus has the potential to explore the evolution of this state under extreme conditions.

Update: 26-Mar-2014

Title:
Valence Change Driven by Constituent Element Substitution in the Mixed-Valence Quasicrystal and Approximant Au-Al-Yb
Authors:
Matsukawa, S; Tanaka, K; Nakayama, M; Deguchi, K; Imura, K; Takakura, H; Kashimoto, S; Ishimasa, T; Sato, NK Author Full Names: Matsukawa, Shuya; Tanaka, Katsumasa; Nakayama, Mika; Deguchi, Kazuhiko; Imura, Keiichiro; Takakura, Hiroyuki; Kashimoto, Shiro; Ishimasa, Tsutomu; Sato, Noriaki K.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 83 (3):10.7566/JPSJ.83.034705 MAR 2014
Abstract:
Quantum criticality has been considered to be specific to crystalline materials such as heavy fermions. Very recently, however, the Tsai-type quasicrystal Au51Al34Yb15 has been reported to show unusual quantum critical behavior. To obtain a deeper understanding of this new material, we have searched for other Tsai-type cluster materials. Here, we report that the metal alloys Au44Ga41Yb15 and Ag47Ga38Yb15 are members of the 1/1 approximant to the Tsai-type quasicrystal and that both possess no localized magnetic moment. We suggest that the Au-Al-Yb system is located near the border of the divalent and trivalent states of the Yb ion; we also discuss a possible origin of the disappearance of magnetism, associated with the valence change, by the substitution of the constituent elements.
Title:
Ordering and dynamical properties of superbright C-60 molecules on Ag(111)
Authors:
Li, HI; Abreu, GJP; Shukla, AK; Fournee, V; Ledieu, J; Loli, LNS; Rauterkus, SE; Snyder, MV; Su, SY; Marino, KE; Diehl, RD Author Full Names: Li, H. I.; Abreu, G. J. P.; Shukla, A. K.; Fournee, V.; Ledieu, J.; Loli, L. N. Serkovic; Rauterkus, S. E.; Snyder, M. V.; Su, S. Y.; Marino, K. E.; Diehl, R. D.
Source:
PHYSICAL REVIEW B, 89 (8):10.1103/PhysRevB.89.085428 FEB 28 2014
Abstract:
C-60 monolayers grown on Ag(111) at room temperature form incommensurate lattices that convert into a commensurate (2 root 3 x 2 root 3)R30 degrees phase upon annealing. The C-60 molecules in the commensurate phase have been observed to exist in three different states on Ag(111), namely bright, dim, and superbright (SB). All three species are in dynamical equilibrium at 280 < T < 440 K. The bright and dim species were the subject of an earlier low-energy electron diffraction study that determined their geometries on the surface and the dynamics of the switching between those two states. The study presented here takes a closer look at the SB molecules, which appear and disappear at temperature-dependent rates with a measured activation barrier of 1.5 eV. The SB molecules in the commensurate phase comprise about 0.5% of the molecules and have a spatially random distribution. The evidence suggests that the formation of the three different states of C-60 on Ag(111) is a result of stress imposed by the substrate as the C-60 adopts the commensurate spacing that is slightly smaller than its natural spacing. In the incommensurate phases, there is no bright-dim contrast, but SB C-60 molecules form and organize into ordered arrays that appear to correspond to the moire patterns that are produced by the mutually incommensurate lattices. This suggests that the substrate responds to the nonuniform forces imposed by the C-60 molecules by producing raised islands of Ag atoms at the vertices of the moire structure. A similar island structure may account for the SB molecules in the commensurate phase.
Title:
Nanotubes from Chalcogenide Misfit Compounds: Sn-S and Nb-Pb-S
Authors:
Radovsky, G; Popovitz-Biro, R; Stroppa, DG; Houben, L; Tenne, R Author Full Names: Radovsky, Gal; Popovitz-Biro, Ronit; Stroppa, Daniel G.; Houben, Lothar; Tenne, Reshef
Source:
ACCOUNTS OF CHEMICAL RESEARCH, 47 (2):406-416; 10.1021/ar400138h FEB 18 2014
Abstract:
Carbon fullerenes and nanotubes revolutionized understanding of the reactivity of nanoscale compounds. Subsequently, our group and others discovered analogous inorganic compounds with hollow, dosed nanostructures. Such inorganic nanostructures offer many applications, particularly in the energy and electronics industries. One way to create inorganic nanostructures is via misfit layered compounds (MLC), which are stacks of alternating two-dimensional molecular slabs, typically held together via weak van der Waals forces. They contain "misfits" in their a-b plane structures that can make them unstable, leading to collapse of the slabs into tubular nanostructures. For example, metal chalcogenide MLCs of the general formula (MX)(1+y)/TX2 (M = Sn, Pb, Bi, Sb, and other rare earths; T= Sn, Ti, V, Cr, Nb,Ta, etc; X = S or Se) consist of a superstructure of alternating layers where the MX unit belongs to a (distorted NaCl) orthorhombic symmetry group (O), the TX2 layer possesses trigonal (T) or octahedral symmetry, and the two layers are held together via both van der Waals and polar forces. A misfit in the a axis or both a and b axes of the two sublattices may lead to the formation of nanostructures as the lattices relax via scrolling. Previous research has also shown that the abundance of atoms with dangling bonds in the rims makes nanoparticles of compounds with layered structure unstable in the planar form, and they tend to fold into hollow closed structures such as nanotubes. This Account shows that combining these two triggers, misfits and dangling bond annihilation in the slab rims, leads to new kinds of nanotubes from MLCs. In particular, we report the structure of two new types of nanotubes from misfits, namely, the SnS/SnS2 and PbS/NbS2 series. To decipher the complex structures of these nanotubes, we use a range of methods: high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), selected area electron diffraction (SAED) analyses, scanning electron microscopy (SEM), and Cs-corrected scanning transmission electron microscopy (STEM) in the high-angle annular dark-field mode (HAADF). In both new types, the lattice mismatch between the two alternating sublayers dictates the relative layer-stacking order and leads to a variety of chiral tubular structures. In particular, the incommensuration (a type of misfit) of the SnS2/SnS system in both the (in plane) a and b directions leads to a variety of relative in-plane orientation and stacking orders along the common c-axis. Thus the SnS/SnS2 nanotubes form superstructures with the sequence O-T and O-T-T, and mixtures thereof. We also report nanotubes of the misfit layered compound (PbS)(1.14)NbS2, and of NbS2 intercalated with Pb atoms, with the chemical formula PbNbS2. Thus, the possibility to use two kinds of folding mechanisms jointly offers a new apparatus for the synthesis of unique 1-D nanostructures of great complexity and a potentially large diversity of physicochemical properties.
Title:
On the nature of phase transitions in the tetragonal tungsten bronze GdK2Nb5O15 ceramics
Authors:
Gagou, Y; Amira, Y; Lukyanchuk, I; Mezzane, D; Courty, M; Masquelier, C; Yuzyuk, YI; El Marssi, M Author Full Names: Gagou, Y.; Amira, Y.; Lukyanchuk, I.; Mezzane, D.; Courty, M.; Masquelier, C.; Yuzyuk, Yu. I.; El Marssi, M.
Source:
JOURNAL OF APPLIED PHYSICS, 115 (6):10.1063/1.4865741 FEB 14 2014
Abstract:
Phase transitions in gadolinium potassium niobate GdK2Nb5O15 (GKN) ceramics have been investigated by x-ray diffraction, dielectric susceptibility, differential scanning calorimetry, and Raman scattering. The results of our complementary studies show that GKN exhibits two phase transitions at T-c1 = 238 degrees C and T-c2 = 375 degrees C attributed to the ferroelectric-antiferroelectric-paraelectric (FE-AFE-PE) phase transitions. According to the x-ray diffraction analysis, the FE and PE phases were refined in the polar P4bm and centrosymmetric P4/mbm space groups. For the intermediate phase, the structure is refined in the space group P4nc with doubling of the c unit cell parameter, which is compatible with an AFE phase. This result was confirmed by Raman spectroscopy since new low-frequency lines are activated in the AFE phase due to the Brillouin zone-folding effect, typical for the modulated phases. The presence of the AFE phase between the FE and PE phases and the complex nature of tetragonal tungsten bronze crystal structure can explain the large thermal hysteresis observed at the FE-AFE transition between heating and cooling cycle and the strong depression of the Curie-Weiss temperature T-0. The semi-phenomenological Ising-like model based on the obtained experimental data is proposed to account for the observed FE-AFE-PE transition sequence. (C) 2014 AIP Publishing LLC.
Title:
High magnetic field evolution of ferroelectricity in CuCrO2
Authors:
Mun, E; Frontzek, M; Podlesnyak, A; Ehlers, G; Barilo, S; Shiryaev, SV; Zapf, VS Author Full Names: Mun, Eundeok; Frontzek, M.; Podlesnyak, A.; Ehlers, G.; Barilo, S.; Shiryaev, S. V.; Zapf, Vivien S.
Source:
PHYSICAL REVIEW B, 89 (5):10.1103/PhysRevB.89.054411 FEB 12 2014
Abstract:
CuCrO2 offers insights into the different types of spiral magnetic orderings that can form spontaneously due to frustration in triangular-lattice antiferromagnets. We explore the magnetic phase diagram up to 65 T along all the principal axes, and also use electric polarization to probe changes in the spiral order at high magnetic fields. It is known that at zero magnetic field a proper-screw spiral of the Cr S = 3/2 spins forms that in turn induces electric polarization with six possible orientations in the ab plane. Applied magnetic fields in the (hard) ab plane have been shown to induce a transition to cycloidal-spiral magnetic order above 5.3 T in those domains that have spins perpendicular to the applied magnetic field. We show that the cycloidal order remains unchanged all the way up to 65 T, which is one quarter of the extrapolated saturation magnetization. On the other hand, for magnetic fields along the (easy) c axis, we observe a transition in the electric polarization near 45 T, and it is followed by a series of steps and/or oscillations in the electric polarization. The data are consistent with a proper-screw-to-cycloidal transition that is pushed from 5.3 to 45 T by easy-axis anisotropy, and is in turn followed by stretching of the magnetic spiral through commensurate and incommensurate wave vectors. This work also highlights the ability of the magnetically induced electric polarization to probe complex magnetic orders in regimes of phase space that are difficult to reach with neutron diffraction.
Title:
Self-generation of dissipative solitons in magnonic quasicrystal active ring resonator
Authors:
Grishin, SV; Beginin, EN; Morozova, MA; Sharaevskii, YP; Nikitov, SA Author Full Names: Grishin, S. V.; Beginin, E. N.; Morozova, M. A.; Sharaevskii, Yu. P.; Nikitov, S. A.
Source:
JOURNAL OF APPLIED PHYSICS, 115 (5):10.1063/1.4864133 FEB 7 2014
Abstract:
Self-generation of dissipative solitons in the magnonic quasicrystal (MQC) active ring resonator is studied theoretically and experimentally. The developed magnonic crystal has quasiperiodic Fibonacci type structure. Frequency selectivity of the MQC together with the parametric three-wave decay of magnetostatic surface spin wave (MSSW) leads to the dissipative soliton self-generation. The transfer matrix method is used to describe MQC transmission responses. Besides, the model of MQC active ring resonator is suggested. The model includes three coupled differential equations describing the parametric decay of MSSW and two differential equations of linear oscillators describing the frequency selectivity of MQC. Numerical simulation results of dissipative soliton self-generation are in a fair agreement with experimental data. (C) 2014 AIP Publishing LLC.
Title:
Spin-density-wave ordering in Ca0.5Sr1.5RuO4 studied by neutron scattering
Authors:
Kunkemoller, S; Nugroho, AA; Sidis, Y; Braden, M Author Full Names: Kunkemoeller, S.; Nugroho, A. A.; Sidis, Y.; Braden, M.
Source:
PHYSICAL REVIEW B, 89 (4):10.1103/PhysRevB.89.045119 JAN 14 2014
Abstract:
The spin-density-wave ordering in Ca0.5Sr1.5RuO4 was studied by polarized and unpolarized neutron diffraction experiments. Below about 20 K Ca0.5Sr1.5RuO4 exhibits quasistatic correlations at exactly the incommensurate wave vector at which pure Sr2RuO4 shows strong inelastic fluctuations driven by Fermi-surface nesting. The magnetic character of the signal and the orientation of the ordered moments along the c direction can be ascertained by neutron polarization analysis. The magnetic ordering at low temperature is very similar to that found upon minor Ti substitution of Sr2RuO4, underlining that this incommensurate spin density wave is the dominant magnetic instability of the unconventional superconductor Sr2RuO4.
Title:
Vector-spin-chirality order in a dimerized frustrated spin-1/2 chain
Authors:
Ueda, H; Onoda, S Author Full Names: Ueda, Hiroshi; Onoda, Shigeki
Source:
PHYSICAL REVIEW B, 89 (2):10.1103/PhysRevB.89.024407 JAN 10 2014
Abstract:
A frustrated spin-1/2 XXZ chain model comprising a ferromagnetic nearest-neighbor coupling with the bond alternation, J(1)(1 +/- delta) < 0, and an antiferromagnetic second-neighbor exchange coupling J(2) > 0 is studied at zero and weak magnetic fields by means of density-matrix renormalization-group calculations of order parameters, correlation functions, and the entanglement entropy, as well as an Abelian bosonization analysis. At zero magnetic field, the bond alternation delta > 0 suppresses the gapless phase characterized by a vector-chiral (VC) long-range order (LRO) and a quasi-LRO of an incommensurate spin spiral, whereas this phase occupies a large region in the space of J(1)/J(2) and the easy-plane exchange anisotropy for delta = 0 [S. Furukawa et al., Phys. Rev. Lett. 105, 257205 (2010)]. Then, four gapped phases are found to appear as the exchange anisotropy varies from the SU(2)-symmetric case to the U(1)-symmetric case: the Haldane dimer (D+) phase with the same sign of the x, y- and z-component dimer order parameters, two VC dimer (VCD+/VCD-) phases with the sign of the z-component dimer order parameter being unaltered/reversed, and the even-parity dimer (D-) phase. At small magnetic fields, a field-induced ring-exchange interaction, which is proportional to a staggered scalar chirality and a magnetic flux penetrating the associated triangle, drives a transition from the D- phase into a VC-Neel-dimer (VCND) phase, but not from the D+ phase. This VCND phase is stable up to the large magnetic field at which the Zeeman term closes the spin gap. A possible relevance to Rb2Cu2Mo3O12 is discussed.
Title:
Collective modes in quasi-one-dimensional charge-density wave systems probed by femtosecond time-resolved optical studies
Authors:
Schaefer, H; Kabanov, VV; Demsar, J Author Full Names: Schaefer, H.; Kabanov, V. V.; Demsar, J.
Source:
PHYSICAL REVIEW B, 89 (4):10.1103/PhysRevB.89.045106 JAN 6 2014
Abstract:
The interplay between the electronic and structural subsystems has strong implications on the character of collective excitations in cooperative systems. Their detailed understanding can provide important information on the coupling mechanisms and coupling strengths in such systems. With the recent developments in femtosecond time-resolved optical probes, numerous advantages with respect to conventional time-integrated probes have been put forward. Owing to their high dynamic range, high-frequency resolution, fast data acquisition, and an inherent access to phases of coherent excitations, they provide direct access to the interplay between various degrees of freedom. In this paper, we present a detailed analysis of time-resolved optical data on blue bronzes (K0.3MoO3 and Rb0.3MoO3), prototype quasi-one-dimensional charge-density wave (CDW) systems. Numerous coherent (Raman active) modes appear upon the phase transition into the CDW state. We analyze the temperature dependence of mode frequencies, their damping times, as well as their oscillator strengths and phases using the time-dependent Ginzburg-Landau model. We demonstrate that these low-temperature modes are a result of linear coupling between the Fermi surface nesting driven modulation of the conduction electron density and the normal-state phonons at the CDW wave vector, and determine their coupling strengths. Moreover, we are able to identify the nature of excitation of these coupled modes, as well as the nature of the probing mechanisms in this type of experiments. We demonstrate that in incommensurate CDW systems, femtosecond optical excitation initially suppresses the electronic density modulation, while the reflectivity changes at frequencies far above the CDW induced gap in the single-particle excitation spectrum are governed by the modulation of interband transitions caused by lattice motion. This approach can be readily extended to more complex systems with spatially modulated ground states.
Title:
Wear and Friction Properties of Mg-Zn-Y Alloy with Dispersion of Quasi-Crystalline Phase
Authors:
Somekawa, H; Shimoda, A; Hirayama, T; Matsuoka, T; Mukai, T Author Full Names: Somekawa, Hidetoshi; Shimoda, Atsushi; Hirayama, Tomoko; Matsuoka, Takashi; Mukai, Toshiji
Source:
MATERIALS TRANSACTIONS, 55 (7):216-219; 10.2320/matertrans.M2013301 JAN 2014
Abstract:
The wear and friction properties of the Mg-Zn-Y alloys with a dispersion of the quasi-crystalline phase were investigated using the pin-on-disk configuration. The wear loss rates and the friction coefficient were obtained to be 1.95 x 10(-5)mm(3)/mm and 0.26 in the casted alloy, 1.75 x 10(-5)mm(3)/mm and 0.24 in the heat-treated alloy, 2.40 x 10(-5)mm(3)/mm and 0.24 in the extruded alloy, respectively, under the dry wear condition. An effective method to enhance the wear properties in the magnesium alloys was determined to be a homogenous distribution of the quasi-crystalline phase in the coarse-grained matrix. Meanwhile, the grain refinement was not suitable due to grain boundary sliding, i.e., materials softening.
Title:
Geometrically frustrated magnetism of spins on icosahedral clusters: The Gd3Au13Sn4 quasicrystalline approximant
Authors:
Kozelj, P; Jazbec, S; Vrtnik, S; Jelen, A; Dolinsek, J; Jagodic, M; Jaglicic, Z; Boulet, P; de Weerd, MC; Ledieu, J; Dubois, JM; Fournee, V Author Full Names: Kozelj, P.; Jazbec, S.; Vrtnik, S.; Jelen, A.; Dolinsek, J.; Jagodic, M.; Jaglicic, Z.; Boulet, P.; de Weerd, M. C.; Ledieu, J.; Dubois, J. M.; Fournee, V.
Source:
PHYSICAL REVIEW B, 88 (21):10.1103/PhysRevB.88.214202 DEC 26 2013
Abstract:
By investigating the magnetism of spins on a quasiperiodic lattice, we present an experimental study of static and dynamic magnetic properties, specific heat, and magnetic entropy of the Gd3Au13Sn4 quasicrystalline approximant. The magnetic sublattice of Gd3Au13Sn4 is a periodic arrangement of nonoverlapping spin clusters of almost perfect icosahedral symmetry, where gadolinium localized f magnetic moments are distributed on equilateral triangles. The absence of disorder on the magnetic sublattice and the antiferromagnetic (AFM) interactions between the nearest-neighbor spins distributed on triangles result in geometrical frustration of spin-spin interactions. Thus, the Gd3Au13Sn4 phase can be viewed as a prototype site-ordered, geometrically frustrated spin system on icosahedral clusters. The zero-field-cooled and field-cooled magnetic susceptibilities, the alternating current susceptibility, the thermoremanent magnetization, the memory effect, the magnetic specific heat, and the magnetic entropy all show that the spin system undergoes at low temperatures a transition to a nonergodic state at the spin freezing temperature T-f approximate to 2.8 K. Below this, the ergodicity is broken on the experimental timescale, because the thermally activated correlation times for the spin reorientations become macroscopically long. The magnetic state achieved at low temperatures by continuous cooling in low magnetic fields is likely a superposition of (1) metastable states with randomly frozen spins that have no long-range order yet undergo gradual spin-freezing dynamics and (2) an AFM-like magnetically ordered state with critical slowing dynamics. The magnetic properties of the site-ordered, geometrically frustrated Gd3Au13Sn4 system are discussed in comparison to site-disordered spin glasses that contain both randomness and frustration.

Update: 20-Mar-2014

Title:
The incommensurate modulations of stoichiometric Ni2MnGa
Authors:
Mariager, SO; Huber, T; Ingold, G Author Full Names: Mariager, S. O.; Huber, T.; Ingold, G.
Source:
ACTA MATERIALIA, 66 192-198; 10.1016/j.actamat.2013.11.077 MAR 2014
Abstract:
We use X-ray diffraction to confirm that the 5M phase of the stoichiometric Hensler alloy Ni2MnGa has an incommensurate modulation with wavevector q = [0.428 0.428 0]. We find the crystal to be macroscopically twinned with a structure well described by the theory of martensitic phase transitions, though theoretical calculations of the X-ray diffraction rule out the existence of an adaptive phase. The premartensite phase is found to be slightly incommensurate with q =[0.341 0.341 0]. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Pressure-Induced Quantum Critical and Multicritical Points in a Frustrated Spin Liquid
Authors:
Thede, M; Mannig, A; Mansson, M; Huvonen, D; Khasanov, R; Morenzoni, E; Zheludev, A Author Full Names: Thede, M.; Mannig, A.; Mansson, M.; Huevonen, D.; Khasanov, R.; Morenzoni, E.; Zheludev, A.
Source:
PHYSICAL REVIEW LETTERS, 112 (8):10.1103/PhysRevLett.112.087204 FEB 25 2014
Abstract:
The quantum spin-liquid compound (C4H12N2)Cu2Cl6 is studied by muon spin relaxation under hydrostatic pressures up to 23.6 kbar. At low temperatures, pressure-induced incommensurate magnetic order is detected beyond a quantum critical point at P-c similar to 4.3 kbar. An additional phase transition to a different ordered phase is observed at P-1 similar to 13.4 kbar. The data indicate that the high-pressure phase may be a commensurate one. The established (P-T) phase diagram reveals the corresponding pressure-induced multicritical point at P-1, T-1 = 2.0 K.
Title:
Generic Spin Model for the Honeycomb Iridates beyond the Kitaev Limit
Authors:
Rau, JG; Lee, EKH; Kee, HY Author Full Names: Rau, Jeffrey G.; Lee, Eric Kin-Ho; Kee, Hae-Young
Source:
PHYSICAL REVIEW LETTERS, 112 (7):10.1103/PhysRevLett.112.077204 FEB 20 2014
Abstract:
Recently, realizations of Kitaev physics have been sought in the A(2)IrO(3) family of honeycomb iridates, originating from oxygen-mediated exchange through edge-shared octahedra. However, for the j(eff) = 1/2 Mott insulator in these materials, exchange from direct d-orbital overlap is relevant, and it was proposed that a Heisenberg term should be added to the Kitaev model. Here, we provide the generic nearest-neighbor spin Hamiltonian when both oxygen-mediated and direct overlap are present, containing a bond-dependent off-diagonal exchange in addition to Heisenberg and Kitaev terms. We analyze this complete model using a combination of classical techniques and exact diagonalization. Near the Kitaev limit, we find new magnetic phases, 120 degrees and incommensurate spiral order, as well as extended regions of zigzag and stripy order. Possible applications to Na2IrO3 and Li2IrO3 are discussed.
Title:
Origin of {332} twinning in metastable beta-Ti alloys
Authors:
Tobe, H; Kim, HY; Inamura, T; Hosoda, H; Miyazaki, S Author Full Names: Tobe, Hirobumi; Kim, Hee Young; Inamura, Tomonari; Hosoda, Hideki; Miyazaki, Shuichi
Source:
ACTA MATERIALIA, 64 345-355; 10.1016/j.actamat.2013.10.048 FEB 2014
Abstract:
In this paper, the origin of {3 3 2}< 1 1 (3) over bar > twinning, which is a unique twinning mode in metastable beta-Ti alloys, was investigated. The possible twinning modes in metastable beta-Ti alloys are derived by considering lattice instability in addition to the theory of the crystallography of deformation twinning. In order to consider lattice instability in the body-centered-cubic (bcc) structure, a modulated structure was proposed. We then clarify how the modulated structure facilitates {3 3 2}< 1 1 (3) over bar > twinning preferentially compared to other possible twinning modes by evaluating the magnitude of twinning shear and the complexity of shuffle. It was found that the lattice instability makes {1 1 2}<(1) over bar (1) over bar 1 > twinning, which is a major twinning mode observed in alloys with stable bcc structure, unlikely to occur because the lattice modulation causes additional shuffling to form the {1 1 2}<(1) over bar (1) over bar 1 > twin. It was also found that {3 3 2}<(1) over bar (1) over bar 3 > twinning is the most possible twinning mode in the modulated structure in terms of the magnitude of twinning shear and the complexity of shuffle. The new formation model of the {3 3 2} < 1 1 (3) over bar > twin presented in this study can explain how the lattice instability preferentially activates the {3 3 2}< 1 1 (3) over bar > twinning in metastable beta-Ti alloys. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Growth and Characterization of Ba(2)LnFeNb(4)O(15) (Ln = Pr, Nd, Sm, Eu) Relaxor Single Crystals
Authors:
Albino, M; Veber, P; Pechev, S; Labrugere, C; Velazquez, M; Maglione, M; Josse, M Author Full Names: Albino, Marjorie; Veber, Philippe; Pechev, Stanislav; Labrugere, Christine; Velazquez, Matias; Maglione, Mario; Josse, Michael
Source:
CRYSTAL GROWTH & DESIGN, 14 (2):500-512; 10.1021/cg401181j FEB 2014
Abstract:
Ba(2)LnFeNb(4)O(15) (Ln = Pr, Nd, Sm, and Eu) single crystals were grown from high-temperature solution under controlled atmosphere. Chemical, structural, and dielectric characterizations were performed on four crystals with tetragonal tungsten bronze (TTB) structure. The main difference between the four crystals' compositions is the proportion of rare-earth, as well as vacancies, located in the square site. All crystals displayed an incommensurately modulated structure at room temperature in the paraelectric state. The corresponding basic structures were refined using the P4/mbm space group (R = 0.0274; 0.0416; 0.0328; 0.0357 for Ln = Pr, Nd, Sm, and Eu, respectively). Examination of the structural parameters confirmed the central role played by square-shaped channels in the crystal chemistry of these materials. All crystals display a relaxor behavior with T-m (1 MHz) ranging from 110 to 270 K. The chemical, structural, and physical properties of the crystals are discussed and compared, for the latter, with those of corresponding ceramics.
Title:
Effect of mechanical processing on the stability of metastable icosahedral quasicrystalline nanoparticles in zirconium and hafnium based metallic glasses
Authors:
Li, CF; Li, DQ; Solomon, V; Bauer, M; McCauley, T; Berrier, S Author Full Names: Li, Chunfei; Li, Dingqiang; Solomon, Virgil; Bauer, Michael; McCauley, Tyler; Berrier, Shannon
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 381 68-72; 10.1016/j.jnoncrysol.2013.09.023 DEC 1 2013
Abstract:
Metastable icosahedral quasicrystalline nanoparticles precipitate in the initial crystallization processes of some selected zirconium and hafnium based metallic glasses. All such particles reported so far are embedded in residual glassy matrix. It is predicted that, if these are separated as free standing particles, they can be applied in a variety of fields. Breaking the suitably annealed metallic glasses to small pieces by mechanical approaches is considered to be the first step toward this goal. The result of such an attempt is reported here. Several previously reported metallic glasses such as Zr70Cu27.5Rh2.5 and Hf69.5Al7.5Ni11Cu12 have been abraded by using regular sandpapers and diamond papers, scraped with diamond scratchers, and sliced by using microtome. Thus obtained small pieces have been examined by Scanning Electron Microscope, Transmission Electron Microscope, and Energy Dispersive X-ray Spectroscopy. It has been revealed that the mechanical breaking processes cause an undesired phase transformation Of the quasicrystalline nanoparticles to the crystalline phases. The reason for this undesired phase transformation was analyzed and the appropriate procedures to avoid this negative effect for future work were suggested. (C) 2013 Elsevier B.V. All rights reserved.

Update: 12-Mar-2014

Title:
Understanding the multiple magnetic structures of the intermetallic compound NdMn1.4Co0.6Si2
Authors:
Halder, M; Bera, AK; Kumar, A; Keller, L; Yusuf, SM Author Full Names: Halder, Madhumita; Bera, A. K.; Kumar, Amit; Keller, L.; Yusuf, S. M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 592 86-91; 10.1016/j.jallcom.2013.12.247 APR 15 2014
Abstract:
Magnetic phases for the intermetallic compound NdMn1.4Co0.6Si2 have been investigated at various temperatures by dc magnetization, neutron diffraction and neutron depolarization. Our study shows multiple magnetic phase transitions with temperature (T) over 1.5-300 K. In agreement with dc-magnetization and neutron depolarization results, the temperature dependence of the neutron diffraction patterns shows five distinct regions with different magnetic phases. These temperature regions are (i) T >= 215 K, (ii) 215 K > T >= 50 K, (iii) 50 K > T >= 40 K, (iv) 40 K > T > 15 K, and (v) T <= 15 K. The corresponding magnetic structures are paramagnetic, commensurate collinear antiferromagnetic (AFM-I), incommensurate AFM (AFM-II), mixed ferromagnetic and AFM (FM + AFM-II), and incommensurate AFM (AFM-II), respectively. (C) 2014 Elsevier B.V. All rights reserved.
Title:
The elastodynamic model of wave-telegraph type for quasicrystals
Authors:
Agiasofitou, E; Lazar, M Author Full Names: Agiasofitou, Eleni; Lazar, Markus
Source:
INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 51 (5):923-929; 10.1016/j.ijsolstr.2013.11.016 MAR 1 2014
Abstract:
In this work we propose the elastodynamic model of wave-telegraph type for the description of dynamics of quasicrystals. Phonons are represented by waves, and phasons by waves damped in time and propagating with finite velocity. Therefore, the equations of motion for the phonon fields are of wave type and for the phason fields are of telegraph type. The proposed model constitutes a unified theory in the sense that already established models in the literature can be recovered as asymptotic cases of it. The equations of motion for the displacement fields in the theory of incompatible and compatible elastodynamics of wave-telegraph type of quasicrystals are derived. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Anomalous electronic transport in quasicrystals and related complex metallic alloys
Authors:
de Laissardiere, GT; Mayou, D Author Full Names: de Laissardiere, Guy Trambly; Mayou, Didier
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):70-81; 10.1016/j.crhy.2013.09.010 JAN 2014
Abstract:
We analyse the transport properties in approximants of quasicrystals alpha-AlMnSi, 1/1-AlCuFe and for the complex metallic phase lambda-AlMn. These phases present strong analogies in their local atomic structures and are related to existing quasicrystalline phases. Experimentally, they present unusual transport properties with low conductivities and a mix of metallic-like and insulating-like characteristics We compute the band structure and the quantum diffusion in the perfect structure without disorder and introduce simple approximations that allow us to treat the effect of disorder. Our results demonstrate that the standard Bloch-Boltzmann theory is not applicable to these intermetallic phases. Indeed their dispersion relations are flat, indicating small band velocities, and corrections to quantum diffusion, which are not taken into account in the semi-classical Bloch-Boltzmann scheme, become dominant. We call this regime the small velocity regime. A simple relaxation time approximation to treat the effect of disorder allows us to reproduce the main experimental facts on conductivity qualitatively and even quantitatively. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Prolegomena of quasicrystals
Authors:
Friedel, J Author Full Names: Friedel, Jacques
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):3-5; 10.1016/j.crhy.2013.09.001 JAN 2014
Abstract:
The first published observations of quasicrystals in metallic alloys were in harmony with the increasing complexity of the structural description of possible solid phases, due to specific properties of the magnetic and electric charges of electrons. This led to the complex crystal phases of Frank and Kasper and Meyer's prediction of quasicrystalline structures with original diffraction properties in the reciprocal space and local symmetries not allowed for crystals. The initial works on two-dimensional tilings by Penrose and others clarified the problems involved. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Crystal chemistry and chemical order in ternary quasicrystals and approximants
Authors:
Gomez, CP; Tsai, AP Author Full Names: Gomez, Cesar Pay; Tsai, An Pang
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):30-39; 10.1016/j.crhy.2013.10.007 JAN 2014
Abstract:
In this work we review our current understanding of structure, stability and formation of icosahedral quasicrystals and approximants. The work has special emphasis on Cd-Yb type phases, but several concepts are generalized to other families of icosahedral quasicrystals and approximants. The paper handles topics such as chemical order and site preference at the cluster level for ternary phases, valence electron concentration and its influence on formation and composition, fundamental building blocks and cluster linkages, and the similarities and differences between different families of icosahedral quasicrystals and approximants. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Dynamics of quasicrystals
Authors:
Janssen, T; de Boissieu, M Author Full Names: Janssen, Ted; de Boissieu, Marc
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):58-69; 10.1016/j.crhy.2013.09.011 JAN 2014
Abstract:
The (lattice) dynamics of quasicrystals differs in many aspects from that of lattice periodic systems. This they have in common with other aperiodic crystals. The dynamics of quasicrystals is discussed here in the context of these general aperiodic crystals, but the special features of quasicrystals are stressed. The lattice dynamics is now fairly well understood. Especially for aperiodic crystals, there are excitations related to the possibility to describe the systems in superspace. These 'phasons' are discussed in particular. (C) 2013 Published by Elsevier Masson SAS on behalf of Academie des sciences.
Title:
Surfaces of quasicrystals
Authors:
Ledieu, J; Fournee, V Author Full Names: Ledieu, Julian; Fournee, Vincent
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):48-57; 10.1016/j.crhy.2013.09.009 JAN 2014
Abstract:
The remarkable surface properties of quasicrystals have motivated extensive investigations of their intrinsic atomic and electronic structures. In this article, we summarize some of the main conclusions obtained so far. We also describe adsorption experiments where quasiperiodic surfaces are used as templates to grow thin films with novel structures. Finally we discuss some of their useful properties of current interest. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Decagonal quasicrystals - What has been achieved?
Authors:
Steurer, W; Deloudi, S Author Full Names: Steurer, Walter; Deloudi, Sofia
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):40-47; 10.1016/j.crhy.2013.09.007 JAN 2014
Abstract:
Where are we now, 25 years after the discovery of the first stable decagonal quasicrystal (DQC)? In this critical review, the status of research into these axial quasicrystals, which are quasiperiodic in two dimensions and periodic along the third, is discussed, and some of the open questions are addressed. We conclude that the structures of DQC are essentially known now, a few of them even as a function of temperature. Some hypotheses concerning DQC formation, growth and stability have still to be confirmed. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Quasicrystals, model sets, and automatic sequences
Authors:
Allouche, JP; Meyer, Y Author Full Names: Allouche, Jean-Paul; Meyer, Yves
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):6-11; 10.1016/j.crhy.2013.09.002 JAN 2014
Abstract:
We survey mathematical properties of quasicrystals, first from the point of view of harmonic analysis, then from the point of view of morphic and automatic sequences. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
About the atomic structures of icosahedral quasicrystals
Authors:
Quiquandon, M; Gratias, D Author Full Names: Quiquandon, Marianne; Gratias, Denis
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):18-29; 10.1016/j.crhy.2013.09.008 JAN 2014
Abstract:
This paper is a survey of the crystallographic methods that have been developed these last twenty five years to decipher the atomic structures of the icosahedral stable quasicrystals since their discovery in 1982 by D. Shechtman. After a brief recall of the notion of quasiperiodicity and the natural description of Z-modules in 3-dim as projection of regular lattices in N > 3-dim spaces, we give the basic geometrical ingredients useful to describe icosahedral quasicrystals as irrational 3-dim cuts of ordinary crystals in 6-dim space. Atoms are described by atomic surfaces (ASs) that are bounded volumes in the internal (or perpendicular) 3-dim space and the intersections of which with the physical space are the actual atomic positions. The main part of the paper is devoted to finding the major properties of quasicrystalline icosahedral structures. As experimentally demonstrated, they can be described with a surprisingly few high symmetry ASs located at high symmetry special points in 6-dim space. The atomic structures are best described by aggregations and intersections of high symmetry compact interpenetrating atomic clusters. We show here that the experimentally relevant clusters are derived from one generic cluster made of two concentric triacontahedra scaled by tau and an external icosidodecahedron. Depending on which ones of the orbits of this cluster are eventually occupied by atoms, the actual atomic clusters are of type Bergman, Mackay, Tsai and others.... (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Dislocations and mechanical properties of icosahedral quasicrystals
Authors:
Mompiou, F; Caillard, D Author Full Names: Mompiou, Frederic; Caillard, Daniel
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):82-89; 10.1016/j.crhy.2013.09.003 JAN 2014
Abstract:
In this article we interpret the mechanical properties of icosahedral quasicrystals with the dislocation theory. After having defined the concept of dislocation in a periodic crystal, we extend this notion to quasicrystals in the 6-dimensional space. We show that perfect dislocations and imperfect dislocations trailing a phason fault can be defined and observed in transmission electron microscopy (TEM). In-situ straining TEM experiments at high temperature show that dislocations move solely by climb, a non-conservative motion-requiring diffusion. This behavior at variance with that of crystals which deform mainly by glide is explained by the atypical nature of the atomic structure of icosahedral quasicrystals. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Quasicrystals and atomic clusters
Authors:
Guyot, P; Audier, M Author Full Names: Guyot, Pierre; Audier, Marc
Source:
COMPTES RENDUS PHYSIQUE, 15 (1):12-17; 10.1016/j.crhy.2013.10.005 JAN 2014
Abstract:
Historically, two principal approaches exist to determine the quasicrystal atomic structures: one is derived directly from diffraction experiments, using cut and projection of higher dimensional space-representation techniques; the other one takes use of the similarity between so-called approximant crystalline phases, observed to co-exist with quasicrystals. The known structure of these phases is shown to be the starting point of building a quasicrystal model in terms of constitutive polyatomic clusters of icosahedral symmetry. It requires to apply inflation properties of quasiperiodicity, and decoration of elementary building tiles. One example is detailed and discussed, in terms of a two-cluster model, in the case of AlLiCu. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Spin wave spectra and spatially modulated structures in BiFeO3
Authors:
Popkov, AF; Kulagin, NE; Soloviov, SV; Gareeva, ZV; Zvezdin, AK Author Full Names: Popkov, A. F.; Kulagin, N. E.; Soloviov, S. V.; Gareeva, Z. V.; Zvezdin, A. K.
Source:
LOW TEMPERATURE PHYSICS, 40 (1):58-64; 10.1063/1.4862464 JAN 2014
Abstract:
The spin wave spectra of antiferromagnetic BiFeO3-type multiferronics are analyzed theoretically. The presence of a spatially modulated cycloidal antiferromagnetic structure leads to a countable number of frequency branches of two oscillatory modes (Goldstone and activation) for spin waves propagating along a cycloid. When there is no magnetic field and anisotropy, the magnon spectrum is characterized by the absence of frequency gaps. The spectral features of the spin oscillations with changing anisotropy and application of a magnetic field are identified and the limits on the existence of an antiferromagnetic cycloid are established up to its transformation into a conical structure. In the transverse direction the spin oscillations have a mixed character which indicates that the cycloid is stable with respect to bending throughout its domain of existence. (C) 2014 AIP Publishing LLC.

Update: 26-Feb-2014

Title:
Lattice dynamics of the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and the cubic 1/1-approximant Zn6Sc
Authors:
Euchner, H; Yamada, T; Rols, S; Ishimasa, T; Ollivier, J; Schober, H; Mihalkovic, M; de Boissieu, M Author Full Names: Euchner, H.; Yamada, T.; Rols, S.; Ishimasa, T.; Ollivier, J.; Schober, H.; Mihalkovic, M.; de Boissieu, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (5):10.1088/0953-8984/26/5/055402 FEB 5 2014
Abstract:
A comparison of periodic approximants and their quasicrystalline counterparts offers the opportunity to better understand the structure, physical properties and stabilizing mechanisms of these complex phases. We present a combined experimental and computational study of the lattice dynamics of the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and compare these to the lattice dynamics of the cubic 1/1-approximant Zn6Sc. The two phases, quasicrystal and approximant, are built up from the same atomic clusters, which are packed either quasiperiodically or on a body centered cubic lattice, respectively. Using inelastic neutron scattering and atomic scale simulations, we show that the vibrational spectra of these three systems are very similar, however, they contain a clear signature of the increasing structural complexity from approximant to quasicrystal.
Title:
A complex pseudo-decagonal quasicrystal approximant, Al-37(Co,Ni)(15.5), solved by rotation electron diffraction
Authors:
Singh, D; Yun, YF; Wan, W; Grushko, B; Zou, XD; Hovmoller, S Author Full Names: Singh, Devinder; Yun, Yifeng; Wan, Wei; Grushko, Benjamin; Zou, Xiaodong; Hovmoller, Sven
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 47 215-221; 10.1107/S1600576713029294 1 JAN 2014
Abstract:
Electron diffraction is a complementary technique to single-crystal X-ray diffraction and powder X-ray diffraction for structure solution of unknown crystals. Crystals too small to be studied by single-crystal X-ray diffraction or too complex to be solved by powder X-ray diffraction can be studied by electron diffraction. The main drawbacks of electron diffraction have been the difficulties in collecting complete three-dimensional electron diffraction data by conventional electron diffraction methods and the very time-consuming data collection. In addition, the intensities of electron diffraction suffer from dynamical scattering. Recently, a new electron diffraction method, rotation electron diffraction (RED), was developed, which can overcome the drawbacks and reduce dynamical effects. A complete three-dimensional electron diffraction data set can be collected from a sub-micrometre-sized single crystal in less than 2 h. Here the RED method is applied for ab initio structure determination of an unknown complex intermetallic phase, the pseudo-decagonal (PD) quasicrystal approximant Al-37.0(Co,Ni)(15.5), denoted as PD2. RED shows that the crystal is F-centered, with a = 46.4, b = 64.6, c = 8.2 angstrom. However, as with other approximants in the PD series, the reflections with odd l indices are much weaker than those with l even, so it was decided to first solve the PD2 structure in the smaller, primitive unit cell. The basic structure of PD2 with unit-cell parameters a = 23.2, b = 32.3, c = 4.1 angstrom and space group Pnmm has been solved in the present study. The structure with c = 8.2 angstrom will be taken up in the near future. The basic structure contains 55 unique atoms (17 Co/Ni and 38 Al) and is one of the most complex structures solved by electron diffraction. PD2 is built of characteristic 2 nm wheel clusters with fivefold rotational symmetry, which agrees with results from high-resolution electron microscopy images. Simulated electron diffraction patterns for the structure model are in good agreement with the experimental electron diffraction patterns obtained by RED.
Title:
Co-4 clusters in the high-temperature phase La18Co28In3
Authors:
Galadzhun, YV; Rodewald, UC; Svitlyk, V; Kalychak, Y; Pottgen, R Author Full Names: Galadzhun, Yaroslav V.; Rodewald, Ute Ch.; Svitlyk, Volodymyr; Kalychak, Yaroslav; Poettgen, Rainer
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 228 (12):650-655; 10.1524/zkri.2013.1695 2013
Abstract:
The metal-rich indide La18Co28In3 was synthesized by melting of the elements in a high-frequency furnace and characterized by X-ray diffraction on powders and single crystals. This high-temperature phase crystallizes with a new structure type: 14/mmm, a = 1432.56(8), c = 984.35(6) pm, wR(2) = 0.1054, 1027 F-2 values, 43 variables at 295 K. The structure is built up by a complex three-dimensional network of Co-4 tetrahedra which arc condensed via further cobalt atoms with a broad range of Co-Co distances (242-262 pin). This network leaves larger channels which are filled by the lanthanum and indium centered polyhedra. The two crystallographically independent indium atoms have exclusively lanthanum neighbors within the channels. They form infinite (In-In2-In2) chains along c with mill In1-In2 and In2-In2 distances of 332 and 319 pm, respectively. These chains are only weakly bonded to their lanthanum neighbors with La-In distances ranging from 344 to 368 pm. Both indium sites show enhanced displacements along the c axis. Temperature dependent diffraction studies and similarities to the incommensurate La1.18Rh3In2 structure are discussed.

Update: 19-Feb-2014

Title:
Double symmetry breaking in TmFe4Ge2 compared to RFe4Ge2 (R=Y, Lu, Er, Ho, Dy) magnetic behaviour
Authors:
Schobinger-Papamantellos, P; Buschow, KHJ; Rodriguez-Carvajal, J Author Full Names: Schobinger-Papamantellos, P.; Buschow, K. H. J.; Rodriguez-Carvajal, J.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 355 104-120; 10.1016/j.jmmm.2013.11.020 APR 2014
Abstract:
TmFe4Ge(2) undergoes a double magneto-elastic first order transition at T-N,T-C where the high temperature (HT) tetragonal phase disproportionate into two distinct orthorhombic low temperature (LT) phases with commensurate and incommensurate magnetic wave vectors respectively: P4(2)/mnm (HT) T-N, T-C -> Cmmm q(1) = (0, 1/2, 0) + Pnnm (q(2) = (0, q(y), 0), q(y) approximate to 2/11(LT) Neutron diffraction shows the relative portions of the LT Cmmm and Pnnm competing phases change linearly with T. The amount of the majority IIT phase Nom (54% at 30 K) decreases linearly to 30% clown to 10 K in favour of the Cmmm phase that dominates the range 26-1.5 K. The Tm moments point along the c-axis in both phases while the Fe moments have canted arrangements. The mu(Tm) = 3.54(3) mu(B)/atom at 15 K is strongly reduced below the Tm3+ free ion value g(J)J = 7 mu(B) for the q(1) phase. The q(2) phase corresponds to a 3D canted sinusoidal arrangement. The results are summarised on a phase diagram and compared to the findings in RFe4Ge2 (R = Y, Lu, Er, Ho, Dy) that are reviewed. The multitude of transition paths occurring in those systems arise from the competing magnetoelastic mechanisms involving the R-crystal field anisotropy, the exchange interactions R-R, R-Fe, Fe-Fe of the two sublattices and their coupling to the lattice strain. The geometrical frustration emerging from the compact tetrahedral Fe arrangement with antiferromagnetic interactions leads to 2D and 3D canted, incommensurate and nonmagnetic states. The Cmmm transition is triggered by dominating R-R and R-Fe interactions becoming stronger at LT while the Pnnm phase is promoted by Fe-Fe and R-Fe interactions that prevail at HT. Included is also the magnetic structure of the ferromagnetic impurity phase Fe3Ge. (C) 2013 Elsevier B.V. All rights reserved
Title:
The structural stability and magnetic properties of the ferromagnetic Heusler alloy Ni-Mn-Sn: A first principle investigation
Authors:
Wang, X; Shang, JX; Wang, FH; Jiang, CB; Xu, HB Author Full Names: Wang, Xu; Shang, Jia-Xiang; Wang, Fu-He; Jiang, Cheng-Bao; Xu, Hui-Bin
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 355 173-179; 10.1016/j.jmmm.2013.12.017 APR 2014
Abstract:
The phase stability and magnetic properties of the cubic phase L2(1) and modulated four- and five layered orthorhombic (40. 5M) and unmodulated tetragonal (L1(0)) martensite of Ni-Mn-Sn alloys are investigated using the first-principle calculations. The results show that for Ni2Mn1+xSn1-x the martensite phases can be stable only at x >= 0.05. The stability of L2(1) phase decreases while it increases for L1(0) with the increasing of Mn contents. The anti-ferromagnetic order is stable for both L2(1) and martensite phases. The modulated 5M and 40 structures are determined accurately and the displacement of the atoms exhibits a sine-like oscillation along the stacking direction. Furthermore, a regular oscillation can also be observed in the distribution of the magnetic moments. With the analysis of the electronic structures, the origin of the effect of the modulation on the system can be explained. The modulation induced displacement of the atoms enhances the charge accumulation between the Ni and Mn/Mn', which lead to a stronger interaction and more structural stability. Accordingly, the calculated results may help in gaining the comprehensive and detailed information on the structural and magnetic properties of the modulated martensite structures, for better understanding of the basic transformation in Ni-Mn-Sn alloys. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Giant frictional dissipation peaks and charge-density-wave slips at the NbSe2 surface
Authors:
Langer, M; Kisiel, M; Pawlak, R; Pellegrini, F; Santoro, GE; Buzio, R; Gerbi, A; Balakrishnan, G; Baratoff, A; Tosatti, E; Meyer, E Author Full Names: Langer, Markus; Kisiel, Marcin; Pawlak, Remy; Pellegrini, Franco; Santoro, Giuseppe E.; Buzio, Renato; Gerbi, Andrea; Balakrishnan, Geetha; Baratoff, Alexis; Tosatti, Erio; Meyer, Ernst
Source:
NATURE MATERIALS, 13 (2):173-177; 10.1038/NMAT3836 FEB 2014
Abstract:
Understanding nanoscale friction and dissipation is central to nanotechnology(1-4). The recent detection of the electronicfriction drop caused by the onset of superconductivity in Nb (ref. 5) by means of an ultrasensitive non-contact pendulum atomic force microscope (AFM) raised hopes that a wider variety of mechanical-dissipation mechanisms become accessible. Here, we report a multiplet of AFM dissipation peaks arising a few nanometres above the surface of NbSe2-a layered compound exhibiting an incommensurate chargedensity wave (CDW). Each peak appears at a well-defined tip-surface interaction force of the order of a nanonewton, and persists up to 70 K, where the short-range order of CDWs is known to disappear. Comparison of the measurements with a theoretical model suggests that the peaks are associated with local, tip-induced 2 pi phase slips of the CDW, and that dissipation maxima arise from hysteretic behaviour of the CDW phase as the tip oscillates at specific distances where sharp local slips occur.
Title:
A new modulated structure in Sr2CuO3+delta superconductor synthesized under high pressure
Authors:
Liu, Y; Shen, X; Liu, QQ; Li, X; Feng, SM; Yu, RC; Uchida, S; Jin, CQ Author Full Names: Liu, Y.; Shen, X.; Liu, Q. Q.; Li, X.; Feng, S. M.; Yu, R. C.; Uchida, S.; Jin, C. Q.
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 497 34-37; 10.1016/j.physc.2013.09.004 FEB 2014
Abstract:
A Sr2CuO3+delta superconductor with a new modulated structure has been synthesized using high pressure technique. Two superconducting transitions with Tc similar to 75 K and similar to 48 K respectively were found in Sr2CuO3+delta superconductor. The superconducting volume fraction is calculated to be 85% at 2 K, which is much higher than anyone else reported before. A new type of modulated phase with a periodicity of 2 root 2a(p) x 2 root 2a(p) x c(p) of Pmmm symmetry is found in the sample by using transmission electron microscopy. Our experimental results suggest that the new Pmmm modulated phase is responsible for superconductivity with Tc at 48 K, while C2/m modulated phase for that with Tc at 75 K found previously. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Partial Spin Ordering and Complex Magnetic Structure in BaYFeO4: A Neutron Diffraction and High Temperature Susceptibility Study
Authors:
Thompson, CM; Greedan, JE; Garlea, VO; Flacau, R; Tan, M; Nguyen, PHT; Wrobel, F; Derakhshan, S Author Full Names: Thompson, Corey M.; Greedan, John E.; Garlea, V. Ovidiu; Flacau, Roxana; Tan, Malinda; Nguyen, Phuong-Hieu T.; Wrobel, Friederike; Derakhshan, Shahab
Source:
INORGANIC CHEMISTRY, 53 (2):1122-1127; 10.1021/ic4026798 JAN 20 2014
Abstract:
The novel iron-based compound, BaYFeO4, crystallizes in the Pnma space group with two distinct Fe3+ sites, that are alternately corner-shared [FeO5](7-) square pyramids and [FeO6](9-) octahedra, forming into [Fe4O18](24-) rings, which propagate as columns along the b-axis. A recent report shows two discernible antiferromagnetic (AFM) transitions at 36 and 48 K in the susceptibility, yet heat capacity measurements reveal no magnetic phase transitions at these temperatures. An upturn in the magnetic susceptibility measurements up to 400 K suggests the presence of short-range magnetic behavior at higher temperatures. In this Article, variable-temperature neutron powder diffraction and high-temperature magnetic susceptibility measurements were performed to clarify the magnetic behavior. Neutron powder diffraction confirmed that the two magnetic transitions observed at 36 and 48 K are due to long-range magnetic order. Below 48 K, the magnetic structure was determined as a spin-density wave (SDW) with a propagation vector, k = (0, 0, 1/3), and the moments along the b-axis, whereas the structure becomes an incommensurate cycloid [k = (0, 0, 0.35)] below 36 K with the moments within the bc-plane. However, for both cases the ordered moments on Fe3+ are only of the order similar to 3.0 mu(B), smaller than the expected values near 4.5 mu(B), indicating that significant components of the Fe moments remain paramagnetic to the lowest temperature studied, 6 K. Moreover, new high-temperature magnetic susceptibility measurements revealed a peak maximum at similar to 550 K indicative of short-range spin correlations. It is postulated that most of the magnetic entropy is thus removed at high temperatures which could explain the absence of heat capacity anomalies at the long-range ordering temperatures. Published spin dimer calculations, which appear to suggest a k = (0, 0, 0) magnetic structure, and allow for neither low dimensionality nor geometric frustration, are inadequate to explain the observed complex magnetic structure.
Title:
Labile Degree of Disorder in Bismuth-Oxophosphate Compounds: Illustration through Three New Structural Types
Authors:
Aliev, A; Endara, D; Huve, M; Colmont, M; Roussel, P; Delevoye, L; Tran, TT; Halasyamani, PS; Mentre, O Author Full Names: Aliev, A.; Endara, D.; Huve, M.; Colmont, M.; Roussel, P.; Delevoye, L.; Tran, T. T.; Halasyamani, P. S.; Mentre, O.
Source:
INORGANIC CHEMISTRY, 53 (2):861-871; 10.1021/ic402930d JAN 20 2014
Abstract:
Here, we analyze the crystal structures of three new Bi/M oxophosphates, focusing on the ambiguity between order and disorder in different structural subunits. The three structures are original but systematically built on the assembly of O(Bi,M)(4) tetrahedra into various 1D-oxocenterd units, separated by PO4 groups that create cationic channels. Two main subunits show versatile degrees of disorder, i.e., the cationic channels and some of the terminal O(Bi,M)(4) entities. (a) In the compound [Bi-2(Bi1.56K0.44)O-dis(3)]K-0.88(dis)(PO4)(2), the K/K and K/Bi disorder is total on both nano- and micro-sized domains. (b) In the incommensurately modulated [Bi-10(Bi similar to 0.5Cd similar to 0.5)(8)O-dis(16)](Bi0.6Cd0.8)(2)(ord)(PO4)(8), only the cationic channels show an ordered Bi/Cd arrangement which can be modified by minor stoichiometric changes between domains. (c) In [Bi18Zn10O21](ord)zn(5)(ord)(PO4)(14), both subunits are almost perfectly ordered (complex Bi/Zn sequence) into a 7-fold supercell, but this order strongly depends on the observation scale and is mainly lost in micronic-grains also due to slight compositional changes. However, the refined noncentrosymmetric organization is maintained (SHG tests) in the bulk. The relative stability of ordered versus disordered sites is discussed on the basis of the existence of two possible mixed sites and probably depends on the M chemical nature. Disorder was characterized by use of solid-state P-31 NMR probing for the first two cases. Finally, the observed disordered or long periodicities along the infinite dimension suggest the sketch of a periodic/rigid skeleton of O(Bi,M)(4) units with counterions filling the interspace in more or less disordered arrangements.

Update: 5-Feb-2014

Title:
Effects of minor Gd addition on microstructures and mechanical properties of the high strain-rate rolled Mg-Zn-Zr alloys
Authors:
Yu, HY; Yan, HG; Chen, JH; Su, B; Zheng, Y; Shen, YJ; Ma, ZJ Author Full Names: Yu, Haiyang; Yan, Hongge; Chen, Jihua; Su, Bin; Zheng, Yi; Shen, Yanjin; Ma, Zhaojie
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 586 757-765; 10.1016/j.jallcom.2013.10.005 FEB 15 2014
Abstract:
Effects of minor Gd addition (0, 0.2, 0.5 and 0.8 mass%) on microstructure and mechanical properties of the high strain-rate rolled (HSRR) Mg-5.5Zn-0.6Zr-based alloys are investigated by OM, XRD, SEM, TEM and mechanical testing. The Mg-5.5Zn-0.6Zr alloy consists of the alpha-Mg matrix and the Mg7Zn3 phase. Minor Gd addition can effectively refine grains and change phase compositions. The quasicrystal I-phases (Mg-Zn-Gd ternary phase) are formed and mainly aggregated along the grain boundaries in the Mg-5.5Zn-0.6Zr-based alloys with minor Gd addition. The amount of the I-phase increases with the increase of Gd addition, but the amount of the Mg7Zn3 phase decreases. With the Gd addition up to 0.8 mass%, the main phases of the alloy are the alpha-Mg matrix and I-phases. The Gd addition can reduce the stacking fault energy of the alpha-Mg matrix and thus promote the dynamic recrystallization (DRX) during the HSRR process. The broken quasicrystal I-phase particles resulted from the HSRR process play a role in promoting the nucleation of DRX, inhibiting the growth of the DRX grains and refining grains. Meanwhile, the dispersion strengthening and precipitation strengthening of the I-phase particles contribute to the enhanced strength. The as-rolled Mg-5.5Zn-0.6Zr-0.8Gd alloy exhibits an optimal strength-ductility balance, with the ultimate tensile strength of 327 MPa, the yield strength of 242 MPa and the elongation to rupture of 22%, respectively. The addition of Gd can effectively weaken the recrystallization texture and modify the tensile fracture mechanism from quasi-cleavage to ductile. (C) 2013 Elsevier B. V. All rights reserved.
Title:
Electronic density of states and metastability of icosahedral Au-Al-Yb quasicrystal
Authors:
Jazbec, S; Vrtnik, S; Jaglicic, Z; Kashimoto, S; Ivkov, J; Popcevic, P; Smontara, A; Kim, HJ; Kim, JG; Dolinsek, J Author Full Names: Jazbec, S.; Vrtnik, S.; Jaglicic, Z.; Kashimoto, S.; Ivkov, J.; Popcevic, P.; Smontara, A.; Kim, Hae Jin; Kim, Jin Gyu; Dolinsek, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 586 343-348; 10.1016/j.jallcom.2013.10.073 FEB 15 2014
Abstract:
The recently discovered icosahedral quasicrystal (i-QC) in the ternary Au-Al-Yb system at the composition Au51Al34Yb15 is formed only in as-cast alloys and is metastable with decomposition to other crystalline phases upon annealing at 700 degrees C. Measuring the electronic transport coefficients (electrical resistivity, thermoelectric power, Hall coefficient), magnetic susceptibility and specific heat, we addressed the question of metastability of the i-Au-Al-Yb quasicrystalline phase by reconstructing the shape of the electronic density of states (DOS) in the vicinity of Fermi level epsilon(F) with the aim to find out whether there exists a pseudogap in the DOS that could contribute to electronic stabilization of the icosahedral phase. The results have revealed that the DOS in the vicinity of epsilon(F) exhibits a pronounced valley on a 100 meV energy scale with a sharp feature on a 10 meV scale, both being centered almost exactly at epsilon(F). This pseudogap is apparently not wide enough to ensure sufficient electronic energy gain of the order of a few 10 kJ/mol needed for the electronic stabilization of the icosahedral phase. A possible origin of metastability of the i-Au-Al-Yb quasicrystal and thermodynamic stability of its 1/1 cubic approximant of very similar composition is discussed. The sharp feature in the DOS at epsilon(F) is proposed to originate from indirect interaction between localized Yb f-moments due to overlap of their polarization clouds in the presence of hybridization of the f and s states, which leads to a sharp resonance peak. (C) 2013 Elsevier B. V. All rights reserved.

Update: Nezname datum (ma se nacist z hlavicek e-mailu)

Title:
Magnetic ordering in NdMn2O5 studied by the neutron diffraction
Authors:
Zobkalo, IA; Gavrilov, SV; Nyi, NZS; Barilo, SN; Shiryaev, SV Author Full Names: Zobkalo, I. A.; Gavrilov, S. V.; Nyi, N. Z. Saw; Barilo, S. N.; Shiryaev, S. V.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 354 85-89; 10.1016/j.jmmm.2013.10.034 MAR 2014
Abstract:
The magnetic ordering in NdMn2O5 single crystal has been studied by the neutron scattering, including XYZ-polarization analysis. At T-N approximate to 30 K the onset of the long-range magnetic order with incommensurate wave vector k = (0.5 0 similar to 0.36) is observed. Below 30 K two magnetic phases are observed with propagation vectors close to each other: k(1)=(0.5 0 k(z1)), k(2)=(0.5 0 k(z2)). k(z1), k(z2) components increase monotonously with temperature decrease down to 25 K, then remain to be constant with values k(z1)=0.384(2), k(z2)=0.395(2). Two reorientation transitions were observed at similar to 20 K and at similar to 5 K. (C) 2013 Published by Elsevier B.V.
Title:
Interpretation of magnetoelectric phase states using the praphase concept and exchange symmetry
Authors:
Ter-Oganessian, NV; Sakhnenko, VP Author Full Names: Ter-Oganessian, N. V.; Sakhnenko, V. P.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (3):10.1088/0953-8984/26/3/036003 JAN 22 2014
Abstract:
The majority of magnetoelectric crystals show complex temperature-magnetic field or temperature-pressure phase diagrams with alternating antiferromagnetic incommensurate, magnetoelectric, and commensurate phases. Such phase diagrams occur as a result of successive magnetic instabilities with respect to different order parameters, which usually transform according to different irreducible representations (IRs) of the space group of the crystal. Therefore, in order to build a phenomenological theory of phase transitions in such magnetoelectrics one has to employ several order parameters and assume the proximity of various instabilities on the thermodynamic path. In this work we analyze the magnetoelectrics MnWO4, CuO, NaFeSi2O6, NaFeGe2O6, Cu3Nb2O8, alpha-CaCr2O4 and FeTe2O5Br using the praphase concept and the symmetry of the exchange Hamiltonian. We find that in all the considered cases the appearing magnetic structures are described by IRs entering into a single exchange multiplet, whereas in the cases of MnWO4 and CuO by a single IR of the space group of the praphase structure. Therefore, one can interpret the complex phase diagrams of magnetoelectrics as induced by a single IR either of the praphase or of the symmetry group of the exchange Hamiltonian. Detailed temperature-magnetic field phase diagrams of MnWO4 and CuO for certain field directions are obtained and the magnetic structures of the field-induced phases are determined.
Title:
Temperature hysteresis of magnetic phase transitions in Tb1-xCexMn2O5 (x = 0, 0.20, 0.25)
Authors:
Zobkalo, IA; Gavrilov, SV; Sanina, VA; Golovenchits, EI Author Full Names: Zobkalo, I. A.; Gavrilov, S. V.; Sanina, V. A.; Golovenchits, E. I.
Source:
PHYSICS OF THE SOLID STATE, 56 (1):51-56; 10.1134/S1063783414010405 JAN 2014
Abstract:
The temperature evolution of the magnetic structure of multiferroics Tb1 - x Ce (x) Mn2O5 (x = 0, 0.20, 0.25) has been investigated using the neutron scattering methods. It has been found that, despite the qualitative similarity of the magnetic states and the series of phase transitions for pure TbMn2O5 (TMO) and doped crystals Tb1 - x Ce (x) Mn2O5 (TCMO, x = 0.20 and 0.25), there are significant differences in their properties. In contrast to TMO, where there are three magnetic phases, TCMO can include two magnetic phases that coexist in a wide temperature range and exhibit a rather wide temperature hysteresis. One of these phases with wave vector k (1) = (0.5, 0, k (z1)), k (z1) = 0.25, is commensurate and arises at temperatures below T (N) similar to 39 K (for x = 0.2) and T (N) similar to 38 K (x = 0.25). The second phase is incommensurate with wave vector k (2) = (1/2, 0, k (z2)), k (z2) = 0.256(2), and appears upon cooling at T = 21 K (x = 0.2) and T = 19 K (x = 0.25). Upon further cooling to 16 K, the component k (z2) increases to 0.292(2) and then remains constant. The component k (z1) increases to the value of 0.280(2) upon cooling in the range from 15 to 10 K and then remains constant down to 1.5 K. With an increase in the temperature, the components k (z1) and k (z2) undergo reverse changes to their initial values, but these changes occur at temperatures 7 K higher than those observed with a decrease in the temperature. For TMO, two phases also coexist, but the temperature hysteresis in this case is considerably smaller than for TCMO. This is explained by different densities of domain walls and different sizes of domains in pure and doped crystals.
Title:
Spatially modulated magnetic structure of AgFeO2: Mossbauer study on Fe-57 nuclei
Authors:
Rusakov, VS; Presnyakov, IA; Sobolev, AV; Gapochka, AM; Matsnev, ME; Belik, AA Author Full Names: Rusakov, V. S.; Presnyakov, I. A.; Sobolev, A. V.; Gapochka, A. M.; Matsnev, M. E.; Belik, A. A.
Source:
JETP LETTERS, 98 (9):544-550; 10.1134/S0021364013220098 JAN 2014
Abstract:
The results of the Mossbauer study of ferrite AgFeO2 manifesting multiferroic properties (at T a parts per thousand currency sign T (N2)) have been presented. The hyperfine interaction parameters of Fe-57 nuclei have been analyzed in a wide temperature range including the points of two magnetic phase transitions (T (N2) a parts per thousand 7-9 K and T (N1) a parts per thousand 15-16 K). It has been shown that the Mossbauer spectra of the Fe-57 nuclei are sensitive to the variations of the character of the magnetic ordering of Fe3+ ions in the studied ferrite. The results of the model identification of a series of spectra (4.7 K a parts per thousand currency sign T a parts per thousand currency sign T (N2)) under the assumption of the cycloid magnetic structure of ferrite AgFeO2 have been presented. The analysis of the results has been performed in comparison with the literature data for other oxide multiferroics.

Update: 23-Jan-2014

Title:
Magnetic Order in Ce0.95Nd0.05CoIn5: The Q-Phase at Zero Magnetic Field
Authors:
Raymond, S; Ramos, SM; Aoki, D; Knebel, G; Mineev, VP; Lapertot, G Author Full Names: Raymond, Stephane; Ramos, Scheilla M.; Aoki, Dai; Knebel, Georg; Mineev, Vladimir P.; Lapertot, Gerard
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 83 (1):10.7566/JPSJ.83.013707 JAN 2014
Abstract:
We report neutron scattering experiment results revealing the nature of the magnetic order occurring in the heavy fermion superconductor Ce0.95Nd0.05CoIn5. In this system, an antiferromagnetic state is stabilized at a temperature below the superconducting transition one. We evidence that it is an incommensurate order and its propagation vector is found to be identical to that of the magnetic field induced antiferromagnetic order occurring in the stoichiometric superconductor CeCoIn5, the so-called Q-phase. The commonality between these two cases suggests that d-wave superconductivity is playing a key role for the formation of this kind of magnetic order. The proposed mechanism is the enhancement of the nesting condition by an order parameter with nodes in the nesting area.

Update: 16-Jan-2014

Title:
Depth dependent order/disorder transitions in iron-rich thin films grown on i-Al-Pd-Mn studied by medium energy ion scattering
Authors:
Noakes, TCQ; Parle, J; Nugent, P; Sharma, HR; Smerdon, JA; Bailey, P; McGrath, R Author Full Names: Noakes, T. C. Q.; Parle, J.; Nugent, P.; Sharma, H. R.; Smerdon, J. A.; Bailey, P.; McGrath, R.
Source:
SURFACE SCIENCE, 620 59-64; 10.1016/j.susc.2013.09.023 FEB 2014
Abstract:
This paper reports a medium energy ion scattering study of the room temperature deposition of Fe on the fivefold surface of i-Al70Pd21Mn9. At low coverage (similar to 1 ML) growth results in a disordered alloy film with significant Al content. At higher coverage (similar to 11 ML) again an alloy film is formed, but this time with an average composition that slowly varies through the film but is close to stoichiometric Fe3Al. This composition is consistent with magnetic ordering which has been observed in previous experiments on this system. Structural analysis indicates five domains of bcc-like structure in the film, which is oriented with (110) type planes parallel to the five-fold quasicrystal surface. There is a distinct structural transition within the film between a compressed layer near the surface and a slightly expanded layer directly above the quasicrystalline substrate. The sub-surface layer has considerable disorder and the change in layer spacing is attributed to this order/disorder transition within the film. Annealing to 300 degrees C for 10 min induces a small amount of further up-diffusion of Al into the film and also some segregation of Al to the surface, although structurally the film remains essentially unchanged, with the order/disorder transition occurring at a similar depth. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.
Title:
Icosahedral gold-platinum alloy nanocrystals in hollow silica: a highly active and stable catalyst for Ullmann reactions
Authors:
Wu, XL; Tan, LF; Chen, D; Meng, XW; Tang, FQ Author Full Names: Wu, Xiaoli; Tan, Longfei; Chen, Dong; Meng, Xianwei; Tang, Fangqiong
Source:
CHEMICAL COMMUNICATIONS, 50 (5):539-541; 10.1039/c3cc46383d 2014
Abstract:
Icosahedral Au-Pt alloy nanocrystals are prepared in porous hollow silica nanospheres via a hydrothermal method without using capping agents. These nanoparticles with unique shape and structure exhibit excellent catalytic activity and stability in Ullmann reactions.
Title:
Sintering, structure, and physicomechanical properties of Al-Cu-Fe quasicrystals compacted at high pressure
Authors:
Ekimov, EA; Sirotinkin, VP; Petrzhik, MI; Gromnitskaya, EL Author Full Names: Ekimov, E. A.; Sirotinkin, V. P.; Petrzhik, M. I.; Gromnitskaya, E. L.
Source:
INORGANIC MATERIALS, 50 (1):52-57; 10.1134/S002016851401004X JAN 2014
Abstract:
Bulk samples of Al-Cu-Fe quasicrystals with excellent mechanical and tribological properties were prepared by high-pressure compaction followed by pressureless sintering. Cold pressing at 8-9 GPa was shown to cause severe plastic deformation of the Al-Cu-Fe quasicrystals.
Title:
Interfacial magnetism and exchange coupling in BiFeO3-CuO nanocomposite
Authors:
Chakrabarti, K; Sarkar, B; Ashok, VD; Das, K; Chaudhuri, SS; De, SK Author Full Names: Chakrabarti, Kaushik; Sarkar, Babusona; Ashok, Vishal Dev; Das, Kajari; Chaudhuri, Sheli Sinha; De, S. K.
Source:
NANOTECHNOLOGY, 24 (50):10.1088/0957-4484/24/50/505711 DEC 20 2013
Abstract:
Ferromagnetic BiFeO3 nanocrystals of average size 9 nm were used to form a composite with antiferromagnetic CuO nanosheets, with the composition (x) BiFeO3/(100 - x )CuO, x D 0, 20, 40, 50, 60, 80 and 100. The dispersion of BiFeO3 nanocrystals into the CuO matrix was confirmed by x-ray diffraction and transmission electron microscopy. The ferromagnetic ordering as observed in pure BiFeO3 occurs mainly due to the reduction in the particle size as compared to the wavelength (62 nm) of the spiral modulated spin structure of the bulk BiFeO3. Surface spin disorder of BiFeO3 nanocrystals gives rise to an exponential behavior of magnetization with temperature. Strong magnetic exchange coupling between the BiFeO3 nanocrystal and the CuO matrix induces an interfacial superparamagnetic phase with a blocking temperature of about 80 K. Zero field and field cooled magnetizations are analyzed by a ferromagnetic core and disordered spin shell model. The temperature dependence of the calculated saturation magnetization exhibits three magnetic contributions in three temperature regimes. The BiFeO3/CuO nanocomposites reveal an exchange bias effect below 170 K. The maximum exchange bias field HEB is 1841 Oe for x D 50 at 5 K under field cooling of 50 kOe. The exchange bias coupling results in an increase of coercivity of 1934 Oe at 5 K. Blocked spins within an interfacial region give rise to a remarkable exchange bias effect in the nanocomposite due to strong magnetic exchange coupling between the BiFeO3 nanocrystals and the CuO nanosheets.
Title:
Universal emergence of spatially modulated structures induced by flexoantiferrodistortive coupling in multiferroics
Authors:
Eliseev, EA; Kalinin, SV; Gu, YJ; Glinchuk, MD; Khist, V; Borisevich, A; Gopalan, V; Chen, LQ; Morozovska, AN Author Full Names: Eliseev, Eugene A.; Kalinin, Sergei V.; Gu, Yijia; Glinchuk, Maya D.; Khist, Victoria; Borisevich, Albina; Gopalan, Venkatraman; Chen, Long-Qing; Morozovska, Anna N.
Source:
PHYSICAL REVIEW B, 88 (22):10.1103/PhysRevB.88.224105 DEC 19 2013
Abstract:
We proved the existence of a universal flexoantiferrodistortive coupling as a necessary complement to the well-known flexoelectric coupling. The coupling is universal for all antiferrodistortive systems and can lead to the formation of incommensurate, spatially modulated phases in multiferroics. Our analysis can provide a self-consistent mesoscopic explanation for a broad range of modulated domain structures observed experimentally in multiferroics.
Title:
Analysis of Structure and P-c-T Curve of Hydrogenated Ti53Zr27-xNi20Pdx Quasicrystals
Authors:
Jo, Y; Lee, SH; Shin, HS; Kim, J Author Full Names: Jo, Youngsoo; Lee, Sang-Hwa; Shin, Hong Sik; Kim, Jaeyong
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 13 (12):7959-7962; 10.1166/jnn.2013.8124 DEC 2013
Abstract:
The potential application of TiZrNi quasicrystals was evaluated by measuring the pressure-composition-temperature curves after replacing Zr by Pd to the limit maintaining the host structure for the samples made with Ti53Zr27-xNi20Pdx, where 0 <= x <= 8. The results of X-ray diffraction data revealed that the samples keep the pure quasicrystal structure to the maximum value of x = 8. All diffracted peaks uniformly shifted to the low angle of 2 theta in X-ray diffraction pattern suggesting that hydrogen atoms homogeneously diffuse in the quasicrystals and uniformly expand the quasilattice constants without modification of the structure. After hydrogenation at elevated temperature, the quasi-lattice constants increased from 5.12 to 5.34 angstrom for the samples made with x = 0 without appearing an impurity phase. When Zr was replaced by 8 at.% of Pd, the equilibrium vapor pressures significantly increased to 3.41 from 0.41 Torr at 300 degrees C although the total amount of hydrogen decreased as increasing Pd concentration. These results demonstrate that Pd will play a critical role in application for the TiZrNi quasicrystals as hydrogen storage materials.
Title:
Effect of Ce on electrochemical properties of the TiVNi quasicrystal material as an anode for Ni/MH batteries
Authors:
Liu, WQ; Duan, Q; Liang, F; Lin, J; Jiang, DY; Wang, LM Author Full Names: Liu, Wanqiang; Duan, Qian; Liang, Fei; Lin, Jing; Jiang, Dayong; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 38 (34):14810-14815; 10.1016/j.ijhydene.2013.09.015 NOV 13 2013
Abstract:
In order to investigate effect of Ce on electrochemical properties of the Ti1.4V/Ni-0.6 quasi-crystal, (Ti1.4V0.6Ni)(99.4)Ce-0.6 alloy ribbon is prepared by arc melting and subsequent melt-spinning technique. The electrochemical properties of the Ti1.4V0.6Ni and (Ti1.4V0.6Ni)(99.4)Ce-0.6 are studied as negative electrode for nickel-metal hydride batteries in aqueous KOH solution. The structures of the alloys were characterized by XRD and TEM. Phase structure investigations of the (Ti1.4V0.6Ni)(99) Ce-4(0.6) show that alloy mainly consist of the icosahedral quasicrystal (I-phase) and face centered cubic (FCC) phase with Ti2Ni-type structure. The electrochemical measurements demonstrated that the negative electrode made by (Ti1.4V0.6Ni)(99.4)Ce-0.6 alloy showed an improved electrochemical reversibility and a considerably higher charge-discharge capacity when compared to the Ce-free base alloy. Its maximum discharge capacity is about 300 mAh/g, which is higher than that of Ti1.4V0.6Ni, and remains 270 mAh/g after 30 cycles at a current density of 30 mA/g. The discharge process is also characterized by electrochemical impedance spectroscopy. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Update: 8-Jan-2014

Title:
Metastable primary precipitation phases in multicomponent glass forming Fe-base alloys with metalloids
Authors:
Lyasotsky, IV; Dyakonova, NB; Dyakonov, DL Author Full Names: Lyasotsky, I. V.; Dyakonova, N. B.; Dyakonov, D. L.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 586 S20-S23; 1 10.1016/j.jallcom.2013.03.112 FEB 15 2014
Abstract:
Structure transformations at the initial stages of devitrification have been investigated for alloys with good glass forming ability on the base of Fe-B-Si, Fe-P-C, Fe-P-B-C systems with various additions. Systematization of the metastable phases formed in these alloys showed that: (a) metastable phases at the initial stages of crystallization are tetrahedrally close packed (TCP) or aperiodic structures and possess compositions close to the mean composition of the alloy; (b) the observed TCP phases belong to one family of structures related to alpha-Mn for essentially different types of alloying systems, having in common a high glass forming ability; (c) for alloys based on the same system with different small alloying additions, structure of the metastable phase can change within this family of related phases. The obtained results show that Fe-based metallic glasses with metalloids are not essentially different from metal-metal type glasses. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Vitrification and devitrification processes in metallic glasses
Authors:
Louzguine-Luzgin, DV Author Full Names: Louzguine-Luzgin, D. V.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 586 S2-S8; 1 10.1016/j.jallcom.2012.09.057 FEB 15 2014
Abstract:
The phenomenon of vitrification on cooling, also called the glass-transition still remains not fully understood. Recent studies by different techniques were performed in order to shed light on this and on the converse phenomenon of devitrification. Devitrification may either lead to the formation of a supercooled liquid, a crystal(s) or a quasicrystal(s). The present paper is a review of recent findings on the processes of vitrification and devitrification in metallic glasses. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Development of antifriction composites based on polypyromellitimide matrix
Authors:
Olifirov, LK; Kaloshkin, SD; Tcherdyntsev, VV; Danilov, VD Author Full Names: Olifirov, L. K.; Kaloshkin, S. D.; Tcherdyntsev, V. V.; Danilov, V. D.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 586 S446-S450; 1 10.1016/j.jallcom.2013.02.119 FEB 15 2014
Abstract:
A method of polypyromellitimide powder production from PM-A film was proposed and a possibility of fabricating bulk composites based on polypyromellitimide matrix was investigated. The powders were prepared by the treatment of PM-A films in a planetary ball mill. The compositions based on polypyromellitimide containing additives of Al65Cu23Fe12 quasicrystals, graphite, polytetrafluoroethylene and PI-PR-20 polyimide were prepared by the solid-state mixing in an IKA M20 batch mill. The bulk samples were fabricated by the compression molding technique. Thus produced materials were characterized by using the methods of sieve analysis, scanning electron microscopy, Fourier-transform infrared spectroscopy, dynamo-mechanical analysis and tribological tests. It was found that the PM-A polypyromellitimide powder had a low sinterability and, therefore, the bulk samples of unfilled PM-A and also the composites based on PM-A containing additives of Al65Cu23Fe12 quasicrystals, graphite and polytetrafluoroethylene exhibited a high brittleness and show unstable behavior in the tribological tests. It was found that an addition of 15 wt.% PI-PR-20 polyimide improved the sinterability of PM-A and also provides excellent antifriction properties. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Microstructure and mechanical properties of a Mg-Zn-Y alloy produced by a powder metallurgy route
Authors:
Asgharzadeh, H; Yoon, EY; Chae, HJ; Kim, TS; Lee, JW; Kim, HS Author Full Names: Asgharzadeh, H.; Yoon, E. Y.; Chae, H. J.; Kim, T. S.; Lee, J. W.; Kim, H. S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 586 S95-S100; 1 10.1016/j.jallcom.2012.10.108 FEB 15 2014
Abstract:
In this paper, a bulk Mg-Zn-Y alloy reinforced by quasicrystalline particles was produced by hot extrusion of rapidly-solidified powders. MgZn4.3Y0.7 powders with different particle sizes were prepared by an inert gas atomizer and then extruded at 380 degrees C with extrusion ratios of 10:1, 15:1, and 20:1. Microstructural studies were performed using an optical microscope, scanning electron microscope, transmission electron microscope, and X-ray diffraction. The mechanical strength and hardness of the extruded materials were enhanced by employing finer Mg alloy powders. More uniform deformation of powders in extruded billets with good tensile properties was achieved at higher extrusion ratios, especially for finer powders. The high strength of the MgZn4.3Y0.7 alloy was preserved at elevated temperatures due to the presence of icosahedral phase nanoparticles. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Decagonal quasicrystalline phase in as-cast and mechanically alloyed Al-Cu-Cr alloys
Authors:
Shevchukov, AP; Sviridova, TA; Kaloshkin, SD; Tcherdyntsev, VV; Gorshenkov, MV; Churyukanova, MN; Zhang, D; Li, Z Author Full Names: Shevchukov, A. P.; Sviridova, T. A.; Kaloshkin, S. D.; Tcherdyntsev, V. V.; Gorshenkov, M. V.; Churyukanova, M. N.; Zhang, D.; Li, Z.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 586 S391-S394; 1 10.1016/j.jallcom.2013.02.043 FEB 15 2014
Abstract:
Microstructure and phase composition of three Al-rich as-cast alloys of Al-Cu-Cr system were investigated by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The decagonal quasi-crystalline phase is contained in all alloys under study and has grains with faceted shape, its composition lies in the range of 71-73 at.% Al, 11-12 at.% Cu and 15-18 at.% Cr. The heating in calorimeter of the mechanically alloyed Al73Cu11Cr16 powder up to 600 degrees C leads to the formation of the pure decagonal phase. Total thermal effect in the temperature range 250-600 degrees C corresponding to the quasicrystalline phase formation is about 15 kJ/mol. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Effect of Mo on stability of quasicrystalline phase in Al-Mn-Fe alloy
Authors:
Stan, K; Litynska-Dobrzynska, L; Labar, JL; Goral, A Author Full Names: Stan, Katarzyna; Litynska-Dobrzynska, Lidia; Labar, Janos L.; Goral, Anna
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 586 S395-S399; 1 10.1016/j.jallcom.2012.12.013 FEB 15 2014
Abstract:
Microstructure evolution in rapidly solidified Al91Mn6Fe2Mo1 ribbons after annealing was investigated using X-ray diffraction, scanning electron microscopy and analytical transmission electron microscopy including in situ heating experiment in TEM. As spun ribbons consisted of icosahedral quasicrystalline particles enriched in Fe, Mn and Mo embedded in an aluminium matrix. A small amount of quasicrystals containing Fe and Mn which coexisted with the Al-3(Fe, Mn) phase was also observed between the aluminium grains. Further annealing experiments and subsequent analysis of microstructure changes in the sample showed that the quasicrystalline particles underwent a transformation into stable crystalline phases at temperatures which depended on their composition. It was observed that quasicrystals enriched in Mn and Fe transformed at much lower temperatures than primary quasicrystals with Mo content. It was noticed that two different crystalline phases formed in dependence on the temperature of annealing. The Al-6(Mn, Fe) phase appeared first at the quasicrystal/matrix interface. At higher temperature, the Al-12(Mn, Mo) phase formed due to reaction of the Al-6(Mn, Fe) phase with the aluminium matrix. Microstructural and DSC investigations showed that addition of molybdenum improved thermal stability of the quasicrystals in Al-Mn-Fe system. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Effect of mechanical milling on electrochemical properties of Ti45Zr38xNi17+x (x=0, 8) quasicrystals produced by rapid-quenching
Authors:
Baster, D; Takasaki, A; Kuroda, C; Hanc, E; Lee, SH; Swierczek, K; Szmyd, JS; Kim, JY; Molenda, J Author Full Names: Baster, Dominika; Takasaki, Aldto; Kuroda, Chihiro; Hanc, Emil; Lee, Sang-Hwa; Swierczek, Konrad; Szmyd, Janusz S.; Kim, Jae-Yong; Molenda, Janina
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 580 S238-S242; 1 10.1016/j.jallcom.2013.03.272 DEC 15 2013
Abstract:
The effect of mechanical milling on the discharge performance of electrodes consisting of Ti45Zr38-xNi17+x (x = 0, 8) quasictystals, which were produced by a rapid-quenching, was investigated at room temperature in three-electrode cell set-up. All of the obtained ribbons were identified to contain mostly icosahedral (i) quasicrystal phase (i-phase). The measured discharge capacity for Ti45Zr30Ni25 material was higher than the one for Ti45Zr38Ni17. The maximum discharge capacity equal 86 mA h g(-1) was achieved for Ti45Zr30Ni25, which was mechanically milled for 15 h. This value was obtained at the third discharge process. The recorded discharge performance was quite stable on cycling up to 30 cycles for Ti45Zr38Ni17 material, but slight decrease after 15th cycle was observed for Ti45Zr30Ni25 phase. It should be highlighted that the quasioystal i-phase remained stable also after 25 h of mechanical milling for both studied materials. However, a formation of (Ti, Zr)H-2 hydride phase was observed after charge/discharge cycles for both of the materials. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Hydrogen storage characteristics of Ti45Zr38Ni17-xCox (x=4, 8) alloy and quasicrystal powders produced by mechanical alloying
Authors:
Takasaki, A; Zywczak, A; Gondek, L; Figiel, H Author Full Names: Takasaki, Akito; Zywczak, A.; Gondek, L.; Figiel, H.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 580 S216-S218; 1 10.1016/j.jallcom.2013.03.145 DEC 15 2013
Abstract:
The effect of substitution of Co for Ni on hydrogen storage characteristics of Ti-Zr-Ni/Co powders (Ti-45- Zr38Ni17-xCox (x = 4, 8)) produced by mechanical alloying (MA) was investigated. The final product after MA was amorphous for all the powders, but subsequent annealing caused the formation of the icosahedral quasicrystal (i) phase with a Ti2Ni type crystal and a C14 like Laves phases. The amount of i-phase decreased, and reversely those of Ti2Ni and the Laves phases increased with increasing the amount of Co. After hydrogenation at 573 K and at an initial hydrogen pressure of 3.8 MPa, the maximum hydrogen concentration for the annealed powders reached was about 58 at%, and all the phases in the powders transformed to metallic hydrides ((Zr,Ti)H-2, Ni(Zr,Ti)H-3 and Co(Zr,Ti)H-3). Because of the formation of several hydrides, accelerated hydrogen desorption occurred at several temperatures. The activation energies for hydrogen desorption varied from about 70 kJ/mol to 180 kJ/mol. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Electrochemical properties of Ti45-xZr30+xNi25 (x=4, 0, 4) quasicrystal and amorphous electrodes produced by mechanical alloying
Authors:
Ariga, Y; Takasaki, A; Kuroda, C; Kulka, A Author Full Names: Ariga, Youhei; Takasaki, Akito; Kuroda, Cihiro; Kulka, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 580 S251-S254; 1 10.1016/j.jallcom.2013.03.224 DEC 15 2013
Abstract:
The effect of substitution of Zr for Ti on the discharge performance of electrodes consisted of Ti45-xZr30+xNi25 (x = -4, 0, 4) powders produced by mechanical alloying (MA) and subsequent annealing was investigated by a three-electrode cell at room temperature. All the powders after MA were amorphous, but a subsequent annealing caused the formation of the icosahedral (i) quasicrystal phase with a Ti2Ni type crystal phase as the second phase. The discharge capacities for both the amorphous and the i-phase electrodes decreased with increasing amount of Zr substituted for Ti. The maximum discharge capacity achieved was about 130 mA h/g from a (Ti49Zr26Ni25) i-phase electrode at the first discharge process. The discharge capacities of the amorphous electrodes were lower than those of the i-phase ones if the composition levels were alike. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Physical, Mechanical, and Tribological Properties of Quasicrystalline Al-Cu-Fe Coatings Prepared by Plasma Spraying
Authors:
Lepeshev, AA; Rozhkova, EA; Karpov, IV; Ushakov, AV; Fedorov, LY Author Full Names: Lepeshev, A. A.; Rozhkova, E. A.; Karpov, I. V.; Ushakov, A. V.; Fedorov, L. Yu.
Source:
PHYSICS OF THE SOLID STATE, 55 (12):2531-2536; 10.1134/S1063783413120202 DEC 2013
Abstract:
The physical, mechanical, and tribological properties of quasicrystalline coatings based on the Al65Cu23Fe12 alloy prepared by plasma spraying have been investigated. The specific features of the phase formation due to the competitive interactions of the icosahedral psi and cubic beta phases have been elucidated. A correlation between the microhardness and the content of the icosahedral phase in the coating has been determined. The decisive role of the quasicrystalline phase in the formation of high tribological characteristics of the coatings has been revealed and tested.
Title:
Measurement of Unique Magnetic and Superconducting Phases in Oxygen-Doped High-Temperature Superconductors La2-xSrxCuO4+y
Authors:
Udby, L; Larsen, J; Christensen, NB; Boehm, M; Niedermayer, C; Mohottala, HE; Jensen, TBS; Toft-Petersen, R; Chou, FC; Andersen, NH; Lefmann, K; Wells, BO Author Full Names: Udby, L.; Larsen, J.; Christensen, N. B.; Boehm, M.; Niedermayer, Ch.; Mohottala, H. E.; Jensen, T. B. S.; Toft-Petersen, R.; Chou, F. C.; Andersen, N. H.; Lefmann, K.; Wells, B. O.
Source:
PHYSICAL REVIEW LETTERS, 111 (22):10.1103/PhysRevLett.111.227001 NOV 25 2013
Abstract:
We present a combined magnetic neutron scattering and muon spin rotation study of the nature of the magnetic and superconducting phases in electronically phase separated La2-xSrxCuO4+y, x = 0.04, 0.065, 0.09. For all samples, we find long- range modulated magnetic order below TN similar or equal to Tc = 39 K. In sharp contrast to oxygen- stoichiometric La-2 -xSrxCuO4, we find that the magnetic propagation vector as well as the ordered magnetic moment is independent of Sr content and consistent with that of the "striped" cuprates. Our study provides direct proof that superoxygenation in La2-xSrxCuO4+y allows the spin stripe ordered phase to emerge and phase separate from superconducting regions with the hallmarks of optimally doped oxygen- stoichiometric La2-xSrxCuO4.

Update: 25-Dec-2013

Title:
Differently mobile twin boundaries and magnetic shape memory effect in 10 M martensite of Ni-Mn-Ga
Authors:
Heczko, O; Kopecek, J; Straka, L; Seiner, H Author Full Names: Heczko, O.; Kopecek, J.; Straka, L.; Seiner, H.
Source:
MATERIALS RESEARCH BULLETIN, 48 (12):5105-5109; SI 10.1016/j.materresbull.2013.04.034 DEC 2013
Abstract:
We investigated twin boundaries with sharply different mobility or twinning stress in five-layered modulated (10 M) martensite of Ni-Mn-Ga exhibiting magnetic shape memory effect or magnetically induced reorientation. Different mobility is ascribed to the different microstructures of the macrotwin planar interface. In monoclinic approximation the mobile boundaries are of Type 1 and Type 11 with complex microstructure of adjoining variants. These boundaries respond differently to magnetic field. For Type II boundary the reorientation takes place at very low field 250 Oe. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
New Roles for Icosahedral Clusters in Intermetallic Phases: Micelle-like Segregation of Ca-Cd and Cu-Cd Interactions in Ca10Cd27Cu2
Authors:
Hadler, AB; Harris, NA; Fredrickson, DC Author Full Names: Hadler, Amelia B.; Harris, Nicholas A.; Fredrickson, Daniel C.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 135 (46):17369-17378; 10.1021/ja407291t NOV 20 2013
Abstract:
Despite significant progress in the structural characterization of the quasicrystalline state, the chemical origins of long- and short-range icosahedral order remain mysterious and a subject of debate. In this Article, we present the crystal structure of a new complex intermetallic phase, Ca10Cd27Cu2 (mC234.24), whose geometrical features offer clues to the driving forces underlying the icosahedral clusters that occur in Bergman-type quasicrystals. Ca10Cd27Cu2 adopts a C-centered monoclinic superstructure of the 1/1 Bergman approximant structure, in which [110] layers of Bergman clusters in the 1/1 structure are separated through the insertion of additional atoms (accompanied by substantial positional disorder). An examination of the coordination environments of Ca and Cu (in the ordered regions) reveals that the structure can be viewed as a combination of coordination polyhedra present in the nearest binary phases in the Ca-Cd-Cu compositional space. A notable feature is the separation of Ca-Cd and Cu-Cd interactions, with Bergman clusters emerging as Ca-Cd Friauf polyhedra (derived from the MgZn2-type CaCd2 phase) encapsulate a Cu-Cd icosahedron similar to those appearing in Cu2Cd5. DFT chemical pressure calculations on nearby binary phases point to the importance of this segregation of Ca-Cd and Cu-Cd interactions. The mismatch in atomic size between Cu and Cd leads to an inability to satisfy Ca Cu and Ca Cd interactions simultaneously in the Friauf polyhedra of the nearby Laves phase CaCd2. The relegation of the Cu atoms to icosahedra prevents this frustration while nucleating the formation of Bergman clusters.
Title:
Grain size softening effect in Al62.5Cu25Fe12.5 nanoquasicrystals
Authors:
Mukhopadhyay, NK; Ali, F; Scudino, S; Khoshkhoo, MS; Stoica, M; Srivastava, VC; Uhlenwinkel, V; Vaughan, G; Suryanarayana, C; Eckert, J Author Full Names: Mukhopadhyay, N. K.; Ali, F.; Scudino, S.; Khoshkhoo, M. Samadi; Stoica, M.; Srivastava, V. C.; Uhlenwinkel, V.; Vaughan, G.; Suryanarayana, C.; Eckert, J.
Source:
APPLIED PHYSICS LETTERS, 103 (20):10.1063/1.4831737 NOV 11 2013
Abstract:
Inverse Hall-Petch (IHP) behavior in nano-quasicrystalline Al62.5Cu25Fe12.5 is reported. Powders with varying grain sizes were produced by mechanical milling of spray-formed quasicrystals. The hardness of the milled powders increased with decreasing grain size down to about 40 nm and decreased with further refinement, demonstrating the IHP behavior. This critical grain size was found to be larger compared to other metallic nanocrystalline alloys. This IHP behaviour has been attributed to the structural complexity in quasicrystals and to thermally activated shearing events of atoms at the grain boundaries. (C) 2013 AIP Publishing LLC.
Title:
Influence of Cr on the nucleation of primary Al and formation of twinned dendrites in Al-Zn-Cr alloys: Can icosahedral solid clusters play a role?
Authors:
Kurtuldu, G; Jarry, P; Rappaz, M Author Full Names: Kurtuldu, Gueven; Jarry, Philippe; Rappaz, Michel
Source:
ACTA MATERIALIA, 61 (19):7098-7108; 10.1016/j.actamat.2013.07.056 NOV 2013
Abstract:
The equiaxed solidification of Al-20 wt.% Zn alloys revealed an unexpectedly large number of fine grains which are in a twin, or near-twin, relationship with their nearest neighbors when minute amounts of Cr (1000 ppm) are added to the melt. Several occurrences of neighboring grains sharing a nearly common < 1 1 0 > direction with a fivefold symmetry multi-twinning relationship have been found. These findings are a very strong indication that the primary face-centered cubic Al phase forms on either icosahedron quasicrystals or nuclei of the parent stable Al45Cr7 phase, which exhibits several fivefold symmetry building blocks in its large monoclinic unit cell. They are further supported by thermodynamic calculations and by grains sometimes exhibiting orientations compatible with the so-called interlocked icosahedron. These results are important, not only because they provide an explanation of the nucleation of twinned dendrites in Al alloys, a topic that has remained unclear over the past 60 years despite several recent investigations, but also because they identify a so far neglected nucleation mechanism in aluminum alloys, which could also apply to other metallic systems. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Templated three-dimensional growth of quasicrystalline lead
Authors:
Sharma, HR; Nozawa, K; Smerdon, JA; Nugent, PJ; McLeod, I; Dhanak, VR; Shimoda, M; Ishii, Y; Tsai, AP; McGrath, R Author Full Names: Sharma, H. R.; Nozawa, K.; Smerdon, J. A.; Nugent, P. J.; McLeod, I.; Dhanak, V. R.; Shimoda, M.; Ishii, Y.; Tsai, A. P.; McGrath, R.
Source:
NATURE COMMUNICATIONS, 4 10.1038/ncomms3715 NOV 2013
Abstract:
Quasicrystals, materials with aperiodic long-range order, have been found in intermetallics, soft materials such as colloids and supermolecules, and also in two-dimensional monolayer films. Here we present the first example of three-dimensional growth of a single-element quasicrystalline film. Using a hitherto unexplored template, the icosahedral Ag-In-Yb quasi-crystal, and various experimental techniques combined with theoretical calculations of adsorption energies, we find that lead atoms deposited on the surface occupy the positions of atoms in the rhombic triacontahedral cluster, the building block of the substrate, and thus grow in layers with different heights and adsorption energies. We show that the adlayer-adlayer interaction is crucial for stabilizing this epitaxial quasicrystalline structure. The finding opens an avenue for further investigation of the impact of the aperiodic atomic order over periodic order on the physical and chemical properties of materials.
Title:
About the reason of electric polarization flop in TbMnO3
Authors:
Chupis, IE; Kovtun, HA Author Full Names: Chupis, I. E.; Kovtun, H. A.
Source:
APPLIED PHYSICS LETTERS, 103 (18):10.1063/1.4824929 OCT 28 2013
Abstract:
The phenomenological analysis of incommensurate magnetic states in multiferroic TbMnO3 in magnetic field along the modulation wave vector is provided. The incommensurate state of manganese spins after the polarization flop (reorientation of electric polarization by 90 degrees) is assumed. The key role of magnetic anisotropic energy of the fourth order in polarization flop and existence of tricritical point on the phase diagram is shown. The competition between different terms of the fourth order of anisotropic energy is a reason of the reorientation of spin cycloid plane, leading to polarization flop. Calculated phase diagram is in a good agreement with the experimental data. (c) 2013 AIP Publishing LLC.
Title:
Rosette patterns - a common description for both crystalline and quasicrystalline structures
Authors:
Ruhnow, M Author Full Names: Ruhnow, M.
Source:
CRYSTAL RESEARCH AND TECHNOLOGY, 48 (9):612-621; 10.1002/crat.201300175 SEP 2013
Abstract:
Crystalline structures are generally considered to be the normal case and quasicrystals a rare peculiarity. An attempt has been made to find a generalized view for both of these long range ordered atomic arrangements. It has been shown that they can be understood in terms of an angle-periodic rosette pattern. The three-dimensional wall paper design patterns, normally used to describe crystalline structures, are a large subgroup of this rosette pattern supergroup, which have the additional characteristics of translational periodicity. The topic is dealt with from a combined crystallographic and solid state physics point of view. The covalent bonding in the quasicrystals is an important prerequisite for their appearance. (C) 2013 WILEY- VCH Verlag GmbH & Co. KGaA, Weinheim
Title:
The parameters that play role in numerical parameter variation in two-center holographic recording in photorefractive lithium niobate (LiNbO3) and strontium barium niobate (SrxBa1-xNb2O6)
Authors:
Demirbilek, R; Kilic, M Author Full Names: Demirbilek, Riza; Kilic, Mehmet
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 210 (8):1641-1646; 10.1002/pssa.201228800 AUG 2013
Abstract:
We have conducted a numerical study of the dependence of nonvolatile data storage on the holographic parameter variation for a two-center holographic recording (TCHR) process. Parameters of the photorefractive crystals and the experimental conditions such as the electron mobility in the conduction band, the level concentrations, the electron-recombination coefficients, the bulk photovoltaic coefficient, the spatial period of modulation, the dielectric constant, and the modulation depth are studied numerically. The results of the numerical calculations showed that the significant parameters are the electron mobility in the conduction band, the electron-recombination coefficient, and the concentrations of the dopant levels (levels created due to the dopants) in the TCHR process. It seems that the electron-recombination coefficient for deep levels plays a more important role than the other parameters.
Title:
1-Periodic Nanostructures
Authors:
Diudea, MV; Bucila, VR; Proserpio, DM Author Full Names: Diudea, Mircea V.; Bucila, Virginia R.; Proserpio, Davide M.
Source:
MATCH-COMMUNICATIONS IN MATHEMATICAL AND IN COMPUTER CHEMISTRY, 70 (2):545-564; 2013
Abstract:
Triply periodic structures are the usual subjects of crystallographic studies while the objects of these are the crystals or reticulations. There are amorphous materials with no ordered atomic arrays and some ordered structures with no translational periodicity, eventually called quasicrystals. This study presents a variety of five-fold symmetry molecular networks with 1-periodicity. The construction and topology (the genus calculation included) of these structures is described in terms of the net parameters, in a crystallographic manner.

Update: 18-Dec-2013

Title:
Production of Al-Cu-Fe metallic foams without foaming agents or space holders
Authors:
Suarez, MA; Figueroa, IA; Gonzalez, G; Lara-Rodriguez, GA; Novelo-Peralta, O; Alfonso, I; Calvo, IJ Author Full Names: Suarez, M. A.; Figueroa, I. A.; Gonzalez, G.; Lara-Rodriguez, G. A.; Novelo-Peralta, O.; Alfonso, I.; Calvo, I. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 585 318-324; 10.1016/j.jallcom.2013.08.015 FEB 5 2014
Abstract:
This investigation presents a study on the intrinsic formation of Al68Cu20Fe12 alloy foams, i.e. without the need of foaming agents or space holders. This alloy was slowly solidified in the furnace crucible, producing a multiphase microstructure, mainly composed by the lambda-Al13Fe4, I-icosahedral, theta-Al2Cu and omega-Al7Cu2Fe phases. Several heat treatments were carried out to a number of as-cast alloy samples in order to produce foams with porosities above 60%. The microstructure, thermal properties, pore morphology and porosity were characterized by means of SEM, DTA, Image analyzer and Archimedes principle, respectively. The highest amount of macro porosity of up to 65% and a density of 1.5 g/cm(3) in the treated sample were found at 900 degrees C for 360 min. At this temperature, a highly porous structure formed mainly by the lambda-Al13Fe4, I-icosahedral and omega-Al7Cu2Fe phase was obtained. The proposed mechanism for the intrinsic porosity formation is based on the high amount of liquid phase generated by the melting of the Cu-rich phases and the peritectic reaction. The reaction between the lambda-Al13Fe4 and the liquid phases formed the highly dense omega-Al7Cu2Fe and I-icosahedral phases. Thus, the space that is left behind caused the highly porous structure in this material. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Effect of quasicrystal phase on mechanical properties and damping capacities of Mg-Zn-Y-Zr alloys
Authors:
Ma, R; Dong, XP; Chen, SQ; Pan, Z; Ling, HJ; Fan, ZT Author Full Names: Ma, Rong; Dong, Xuanpu; Chen, Shuqun; Pan, Zhang; Ling, Hongjiang; Fan, Zitian
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 587 328-335; 10.1016/j.msea.2013.07.035 DEC 10 2013
Abstract:
Four Mg-5x%Zn-x%Y-0.6%Zr alloys reinforced with the I-Mg3YZn6 quasiaystal phase were fabricated by introducing Zn and Y elements into Mg-0.6%Zr alloys under conventional solidification condition. Due to the coherent lattice relationship between the I-Mg3YZn6 phase and the alpha-Mg matrix, the grain sizes of the Mg-Zn-Y-Zr alloys are obviously refined and the tensile strengths are largely improved to a maximum value of 216 MPa. The fracture mechanism transformed from cleavage fracture to quasi-cleavage fracture with increasing amount of I-Mg3YZn6 phase. The damping capacities of the Mg-Zn-Y-Zr alloys decrease with the increasing I-Mg3YZn6 phase and the damping behavior can be explained with the G-L dislocation model. The forming of the I-Mg3YZn6 phase makes more grain boundaries, phases and interfaces generate in the alloys. And the dislocation densities in the alloys hardly changes as little residual stress or entanglement of dislocation generates at the interface between the I-Mg3YZn6 phase and the alpha-Mg matrix. So the damping values are reduced accordingly with the strong pinning points on dislocations increasing tremendously. (C) 2013 Published by Elsevier B.V.
Title:
Interplay of Charge-Density Wave and Magnetic Order in Ternary Rare-Earth Nickel Carbides, RNiC2 (R = Pr and Nd)
Authors:
Yamamoto, N; Kondo, R; Maeda, H; Nogami, Y Author Full Names: Yamamoto, Nobuki; Kondo, Ryusuke; Maeda, Hiroyuki; Nogami, Yoshio
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (12):10.7566/JPSJ.82.123701 DEC 2013
Abstract:
The electrical and structural properties of NdNiC2 and PrNiC2 are examined in single-crystalline samples in order to investigate the interplay of charge-density wave (CDW) and magnetic order in ternary rare-earth nickel carbides, RNiC2, where R is a rare-earth element. PrNiC2 (no magnetic order down to 1.5 K) and NdNiC2 [antiferromagnetic (AF) transition at 17.2 K] show resistance anomalies at 89 and 121 K, respectively, which are revealed to be CDW transitions by observing X-ray satellite reflections. NdNiC2 also shows a gradual decrease in both resistivity and CDW amplitude below the Neel temperature. In the AF phase, the magnetoresistance sharply decreases where a ferromagnetic (FM) order occurs, which is realized above the spin-flop magnetic field. These results clearly suggest that the relationships between CDW and magnetic order in RNiC2 depend on whether the magnetic order is AF or FM.
Title:
Competing Magnetic Anisotropy Fields and Double Polarization Flops in Multiferroic Mn1-xCoxWO4
Authors:
Song, YS; Chung, JH; Chun, SH; Kim, KH; Schefer, J Author Full Names: Song, Young-Sang; Chung, Jae-Ho; Chun, Sae Hwan; Kim, Kee Hoon; Schefer, Juerg
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (12):10.7566/JPSJ.82.124716 DEC 2013
Abstract:
We report the cobalt doping dependencies of the ferroelectric polarization and underlying incommensurate spiral magnetic ordering in multiferroic Mn1-xCoxWO4 (0 <= x < 0.18). The spiral ordering changed its rotational plane upon cobalt doping (x similar to 0.1), followed by heliconical ordering at higher doping (x > 0.15). These consecutive changes were accompanied by simultaneous 90 degrees flops of ferroelectric polarizations. Such doping dependencies are driven by the competitions between the anisotropy fields of MnWO4 and CoWO4, the spatial distributions of which are nearly orthogonal to each other. We propose a model that can consistently describe the two consecutive flops based on a combined picture of magnetic anisotropy and biquadratic exchange.
Title:
Theory of Antiferromagnetic Order in High-T-c Oxides: An Approach Based on Ginzburg-Landau Expansion
Authors:
Hayashi, M; Tanuma, Y; Kuboki, K Author Full Names: Hayashi, Masahiko; Tanuma, Yasunari; Kuboki, Kazuhiro
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (12):10.7566/JPSJ.82.124705 DEC 2013
Abstract:
The mean-field phase diagram of antiferromagnetic order in t-J model has been examined, using the free energy obtained by Ginzburg-Landau (GL) expansion. We extended the usual GL theory in two ways: First, we have included higher order terms with respect to the spatial derivative (or wave number) to incorporate the incommensurate antiferromagnetic order. Second, we have also included higher order terms with respect to the order parameter amplitude, in order to treat the first order phase transition between paramagnetic and antiferromagnetic phase, which appears at some doping rates. We found the possibility of tricritical point and critical endpoint in the magnetic phase diagram of the high-T-c oxides associated with the commensurate and incommensurate antiferromagnetic order. The possible effects of thermal fluctuations and randomness (spin glass) are also discussed qualitatively based on the GL free energy.
Title:
Ultrathin quasicrystals
Authors:
Taroni, A Author Full Names: Taroni, Andrea
Source:
NATURE MATERIALS, 12 (12):1080-1080; DEC 2013
Title:
Complex magnetic couplings in Co3TeO6
Authors:
Wang, CW; Lee, CH; Li, CY; Wu, CM; Li, WH; Chou, CC; Yang, HD; Lynn, JW; Huang, QZ; Harris, AB; Berger, H Author Full Names: Wang, Chin-Wei; Lee, Chi-Hung; Li, Chi-Yen; Wu, Chun-Ming; Li, Wen-Hsien; Chou, Chih-Chieh; Yang, Hung-Duen; Lynn, Jeffrey W.; Huang, Qingzhen; Harris, A. Brooks; Berger, Helmuth
Source:
PHYSICAL REVIEW B, 88 (18):10.1103/PhysRevB.88.184427 NOV 26 2013
Abstract:
We report powder and single-crystal neutron diffractionmeasurements, combinedwith x-ray powder diffraction data, to unravel the complex magnetic phase diagram and exchange coupling in Co3TeO6. The magnetic structures of the various phases differ markedly from those proposed by Ivanov et al. [Mater. Res. Bull. 47, 63 (2012)] on the basis of only powder diffraction data. The dominant exchange interactions are identified by considering the geometrical arrangement of severely distorted CoO6 octahedra and CoO4 tetrahedra, which naturally divide into two different types of layers, one of which consists of zigzag chains. These zigzag chains are the first to develop magnetic order at T-M1 = 26 K, which is incommensurate in nature. The other separate layer of Co spins develops antiferromagnetic order of Gamma 4 symmetry at zero wave vector at T-M2 = 19.5 K. Our results are consistent with the previous findings of a spontaneous polarization below T-M3 = 18 K. Our neutron powder diffraction data indicate that the increase in the single-crystal (600) Bragg peak is due to a relief of extinction rather than to magnetic effects associated with the observed anomalous variation in the incommensurate wave vector at T-M4 = 16 K. The commensurate order parameter is shown to have a small dependence on the applied electric field, whereas no such effect is found for the incommensurate ordering. Below T-M3, the thermal expansion is negative, and it also exhibits anomalies at T-M2 and T-M4. A symmetry analysis and comprehensive phase diagram are given.
Title:
Electronic phase separation in iron pnictides
Authors:
Sboychakov, AO; Rozhkov, AV; Kugel, KI; Rakhmanov, AL; Nori, F Author Full Names: Sboychakov, A. O.; Rozhkov, A. V.; Kugel, K. I.; Rakhmanov, A. L.; Nori, Franco
Source:
PHYSICAL REVIEW B, 88 (19):10.1103/PhysRevB.88.195142 NOV 22 2013
Abstract:
A mechanism for electronic phase separation in iron pnictides is proposed. It is based on the competition between commensurate and incommensurate spin-density-wave phases in a system with an imperfect doping-dependent nesting of a multisheeted Fermi surface. We model the Fermi surface by two elliptical electron pockets and three circular hole pockets. The interaction between a charge carrier in a hole band and a carrier in an electron band leads to the formation of spin-density-wave order. The commensurate spin density wave in the parent compound transforms to the incommensurate phase when doping is introduced. We show that, for certain parameter values, the uniform state is unstable with respect to phase separation. The resulting inhomogeneous state consists of regions of commensurate and incommensurate spin-density-wave phases. Our results are in qualitative agreement with recent observations of incommensurate spin density waves and electronic inhomogeneity in iron pnictides.
Title:
Incommensurate Modulation and Luminescence in the CaGd2(1-x)Eu-2x(MoO4)(4(1-y))(WO4)(4y) (0 <= x <= 1, 0 <= y <= 1) Red Phosphors
Authors:
Morozov, VA; Bertha, A; Meert, KW; Van Rompaey, S; Batuk, D; Martinez, GT; Van Aert, S; Smet, PF; Raskina, MV; Poelman, D; Abakumov, AM; Hadermann, J Author Full Names: Morozov, Vladimir A.; Bertha, Anne; Meert, Katrien W.; Van Rompaey, Senne; Batuk, Dmitry; Martinez, Gerardo T.; Van Aert, Sandra; Smet, Philippe F.; Raskina, Maria V.; Poelman, Dirk; Abakumov, Artem M.; Hadermann, Joke
Source:
CHEMISTRY OF MATERIALS, 25 (21):4387-4395; 10.1021/cm402729r NOV 12 2013
Abstract:
Scheelite related compounds (A',A '') [(B',B '')O-4], with B', B '' = W and/or Mo are promising new light-emitting materials for photonic applications, including phosphor converted LEDs (light-emitting diodes). In this paper, the creation and ordering of A-cation vacancies and the effect of cation substitutions in the scheelite-type framework are investigated as a factor for controlling the scheelite-type structure and luminescent properties. CaGd2(1-x)Eu2x(MoO4)(4(1-y))(WO4)(4y) (0 <= x <= 1, 0 <= y <= 1) solid solutions with scheelite-type structure were synthesized by a solid state method, and their structures were investigated using a combination of transmission electron microscopy techniques and powder X-ray diffraction. Within this series all complex molybdenum oxides have (3 + 2)D incommensurately modulated structures with superspace group I4(1)/a(alpha,beta,0)00(-beta,alpha,0)00, while the structures of all tungstates are (3 + 1)D incommensurately modulated with superspace group I2/b(alpha beta 0)00. In both cases the modulation arises because of cation-vacancy ordering at the A site. The prominent structural motif is formed by columns of A-site vacancies running along the c-axis. These vacant columns occur in rows of two or three aligned along the [110] direction of the scheelite subcell. The replacement of the smaller Gd3+ by the larger Eu3+ at the A-sublattice does not affect the nature of the incommensurate modulation, but an increasing replacement of Mo6+ by W6+ switches the modulation from (3 + 2)D to (3 + 1)D regime. Thus, these solid solutions can be considered as a model system where the incommensurate modulation can be monitored as a function of cation nature while the number of cation vacancies at the A sites remain constant upon the isovalent cation replacement. All compounds' luminescent properties were measured, and the optical properties were related to the structural properties of the materials. CaGd2(1-x)(MoO4)(4(1-y))(WO4)(4y) phosphors emit intense red light dominated by the D-5(0)-F-7(2) transition at 612 nm, along with other transitions from the D-5(1) and D-5(0) excited states. The intensity of the 5D0-7F2 transition reaches a maximum at x = 0.5 for y = 0 and 1.
Title:
Crystal structures of X-phase in the Sb-Te binary alloy system
Authors:
Kifune, K; Fujita, T; Tachizawa, T; Kubota, Y; Yamada, N; Matsunaga, T Author Full Names: Kifune, K.; Fujita, T.; Tachizawa, T.; Kubota, Y.; Yamada, N.; Matsunaga, T.
Source:
CRYSTAL RESEARCH AND TECHNOLOGY, 48 (11):1011-1021; 10.1002/crat.201300252 NOV 2013
Abstract:
It is well known that the Sb-Te binary system has a large number of incommensurately or commensurately modulated structures between Sb and Sb2Te3 compounds. These structures, which are long-period trigonal stacking structures, possess their own modulation period , according to their composition in the thermal equilibrium. However, the structure of sputtered Sb-Te films with various compositions between the two compounds at both ends formed in a non-thermal equilibrium showed smaller values, than those expected from their compositions without exception. A smaller value implies that its structure is closer to that of Sb with the shortest period in all Sb-Te modulated structures. With increase in temperature, all these transient structures with smaller , however, became stable, accompanying an increase of to acquire their original modulated structures.

Update: 12-Dec-2013

Title:
Effect of quasicrystalline phase on improving the corrosion resistance of a duplex structured Mg-Li alloy
Authors:
Xu, DK; Han, EH Author Full Names: Xu, D. K.; Han, E. H.
Source:
SCRIPTA MATERIALIA, 71 21-24; 10.1016/j.scriptamat.2013.09.025 JAN 15 2014
Abstract:
The in situ formation of I-phase improves the corrosion resistance of the duplex structured Mg-6% Li alloy. Corrosion attack on the surfaces of Mg-6% Li alloy is very inhomogeneous and severe pits and filiform corrosion clearly occur on the surfaces after immersion in 0.1 M NaCl solution. For the I-phase-containing Mg-6% Li-6% Zn-1.2% Y alloy, the corrosion attack is homogeneous and no severe pits and filiform corrosion can be observed. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Modulated crystal structure of Pr2SbO2
Authors:
Magdysyuk, OV; Nuss, J; Jansen, M Author Full Names: Magdysyuk, Oxana V.; Nuss, Juergen; Jansen, Martin
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 69 547-555; 10.1107/S2052519213029436 6 DEC 2013
Abstract:
The crystal structure of commensurately modulated Pr2SbO2 was solved in the orthorhombic superspace group Immm(0 beta 0)000, q = 3/4b*, a = 13.5790 (15), b = 3.9818 (18), c = 4.0041 (18) angstrom (T = 40 K) from a crystal twinned by reticular pseudomerohedry applying the twin law (1 0 0, 0 0 1, 0-10), corresponding to a rotation by 90 degrees along the reciprocal a axis. The formation of Zintl- type Sb2--Sb2- dumbbells in Pr-2(3+) Sb2-O22- is considered to be accountable for its semiconducting properties, as observed previously. The space group for the three- dimensional commensurate super-cell a = 13.5790 (15), b = 15.9272 (18), c = 4.0041 (18) angstrom (T = 40 K) is Pmnm.
Title:
Spin-Peierls distortions in TiPO4
Authors:
Bykov, M; Zhang, J; Schonleber, A; Wolfel, A; Ali, SI; van Smaalen, S; Glaum, R; Koo, HJ; Whangbo, MH; Reuvekamp, PG; Law, JM; Hoch, C; Kremer, RK Author Full Names: Bykov, Maxim; Zhang, Jian; Schoenleber, Andreas; Woelfel, Alexander; Ali, Sk Imran; van Smaalen, Sander; Glaum, R.; Koo, H. -J.; Whangbo, M. -H.; Reuvekamp, P. G.; Law, J. M.; Hoch, C.; Kremer, R. K.
Source:
PHYSICAL REVIEW B, 88 (18):10.1103/PhysRevB.88.184420 NOV 19 2013
Abstract:
On the basis of single-crystal x-ray diffraction we show that TiPO4 undergoes a spin-Peierls distortion below 74.5(5) K, with a dimerization of the Ti chains along the c axis. Between 74.5(5) and 111.6(3) K, TiPO4 develops an incommensurate (IC) phase with temperature-dependent q vector (sigma(1),0,0). Density functional calculations strongly suggest that the IC phase results from a frustration of the lock-in spin-Peierls transition due to the competition of three energetically almost degenerate crystal structures and elastic coupling of the Ti chains via the bridging PO4 units. The phase transition into the IC phase is of second order, but the lock-in transition into the spin-Peierls distortion below 74.5 K is of weak first order in nature.
Title:
Crystal and Magnetic Structure in Co-Substituted BiFeO3
Authors:
Sosnowska, I; Azuma, M; Przenioslo, R; Wardecki, D; Chen, WT; Oka, K; Shimakawa, Y Author Full Names: Sosnowska, Izabela; Azuma, Masaki; Przenioslo, Radoslaw; Wardecki, Dariusz; Chen, Wei-tin; Oka, Kengo; Shimakawa, Yuichi
Source:
INORGANIC CHEMISTRY, 52 (22):13269-13277; 10.1021/ic402427q NOV 18 2013
Abstract:
Ultra-high-resolution neutron diffraction studies of BiFe0.8Co0.2O3 show a transition from a cycloidal space modulated spin structure at T = 10 K to a collinear G-type antiferromagnetic structure at T = 120 K. The model of antiparallel directions of Fe3+ and Co3+ magnetic moments at the shared Wyckoff position describes well the observed neutron diffraction intensities. On heating above RT, the crystal structure of BiFe0.8Co0.2O3 changes from a rhombohedral R3c to a monoclinic Cm. At 573 K only the Cm phase is present. The collinear C-type antiferromagnetic structure is present in the Cm phase of BiFe0.8Co0.2O3 at RT after annealing.
Title:
Problem Solving with Pentagons: Tsai-Type Quasicrystal as a Structural Response to Chemical Pressure
Authors:
Berns, VM; Fredrickson, DC Author Full Names: Berns, Veronica M.; Fredrickson, Daniel C.
Source:
INORGANIC CHEMISTRY, 52 (22):12875-12877; 10.1021/ic402412k NOV 18 2013
Abstract:
Even after significant advances in the structural characterization of quasicrystals-phases whose diffraction patterns combine the sharp peaks normally associated with lattice periodicity and rotational symmetries antithetical to such periodicity this new form of long-range order remains enigmatic. Here, we present DFT-chemical pressure calculations on the Tsai-type quasicrystal approximant CaCd6, which reveal how its icosahedral clusters can be traced to simple CaCu5-type (hP6) intermetallics. The results indicate that the Tsai-type clusters emerge from an atomic-size-driven transformation from planar arrangements to spherical clusters, recalling the relationship between graphene and C-60.
Title:
Incommensurately Modulated delta ''-Au1+xCd2-x Formed by an Unquenchable Phase Transformation from the gamma-Brass delta '-Phase
Authors:
Jana, PP; Lidin, S Author Full Names: Jana, Partha P.; Lidin, Sven
Source:
INORGANIC CHEMISTRY, 52 (22):12980-12985; 10.1021/ic4013608 NOV 18 2013
Abstract:
The synthesis and structural determination of the compound delta"-Au1-xCd2-x, (0.07 <= x <= 0.08) is reported. The structure may be formally derived from that of xi-CoZn13, but elemental ordering causes an incommensurate modulation as determined by single-crystal X-ray diffraction at room temperature. The compound delta"-Au3.23Cd5.76 crystallizes in the monoclinic super space group C2/m(0 beta 1/2)00 with lattice parameters a = 14.790(2) angstrom, b = 8.251(1) angstrom, c = 12.744(1) angstrom, beta = 115.182(9)degrees and a q-vector q = (0 beta 1/2), beta = 0.579b*. The delta ''-phase is stable up to 652(1) K.
Title:
Interlayer Magnetoresistance due to Chiral Soliton Lattice Formation in Hexagonal Chiral Magnet CrNb3S6
Authors:
Togawa, Y; Kousaka, Y; Nishihara, S; Inoue, K; Akimitsu, J; Ovchinnikov, AS; Kishine, J Author Full Names: Togawa, Y.; Kousaka, Y.; Nishihara, S.; Inoue, K.; Akimitsu, J.; Ovchinnikov, A. S.; Kishine, J.
Source:
PHYSICAL REVIEW LETTERS, 111 (19):10.1103/PhysRevLett.111.197204 NOV 7 2013
Abstract:
We investigate the interlayer magnetoresistance (MR) along the chiral crystallographic axis in the hexagonal chiral magnet CrNb3S6. In a region below the incommensurate-commensurate phase transition between the chiral soliton lattice and the forced ferromagnetic state, a negative MR is obtained in a wide range of temperature, while a small positive MR is found very close to the Curie temperature. Normalized data of the negative MR almost falls into a single curve and is well fitted by a theoretical equation of the soliton density, meaning that the origin of the MR is ascribed to the magnetic scattering of conduction electrons by a nonlinear, periodic, and countable array of magnetic soliton kinks.
Title:
Superspace approach to high pressure superstructures
Authors:
Bykov, M; Bykova, E; Hanfland, M; Liermann, HP; van Smaalen, S Author Full Names: Bykov, Maxim; Bykova, Elena; Hanfland, Michael; Liermann, Hanns-Peter; van Smaalen, Sander
Source:
HIGH PRESSURE RESEARCH, 33 (3):501-510; SI 10.1080/08957959.2013.822076 AUG 20 2013
Abstract:
Single-crystal X-ray diffraction in a diamond anvil cell has proven to be a powerful tool for studying matter at extreme conditions. Displacive zone-boundary phase transitions between a high-symmetry low pressure structure and a low-symmetry high pressure superstructure represent a significant part of pressure-induced processes. However, the analysis of such superstructures is usually complicated by low angular resolution and limited reciprocal space coverage. This leads to unfavorable data/parameter ratio during the structure solution and refinement. The superspace approach is an established method to describe commensurately modulated structures, however it is not often applied to high pressure phase transitions. Here, we discuss the advantages of the superspace approach for the description and crystal-chemical analysis of high pressure superstructures. The main ideas of this approach are illustrated by the examples of isostructural FeOCl and CrOCl, forming different superstructures above 15 GPa.
Title:
Determining complex crystal structures from high pressure single-crystal diffraction data collected on synchrotron sources
Authors:
McMahon, MI; Loa, I; Stinton, GW; Lundegaard, LF Author Full Names: McMahon, M. I.; Loa, I.; Stinton, G. W.; Lundegaard, L. F.
Source:
HIGH PRESSURE RESEARCH, 33 (3):485-500; SI 10.1080/08957959.2013.831087 AUG 20 2013
Abstract:
As part of a Long Term Project, single-crystal diffraction techniques have been developed for use at the high pressure beamlines ID09 and ID27 at the European Synchrotron Radiation Facility, and have been utilised to determine the crystal structures of various high pressure phases, including those with incommensurate structures, at both high and low temperatures. The same techniques have also been used to determine the structures of high pressure phases at the SRS, Diamond and Petra-III synchrotron sources. In this paper, we describe technical details of the methods developed, and describe some of the considerations necessary for planning experiments and collecting and processing the data. We then illustrate the quality of data that can be obtained, and the complexity of the structures that can be refined, using recent results obtained from complex high pressure phases of N-2 and Ba.
Title:
The Anisotropic Glassy Properties of Decagonal Quasicrystals
Authors:
Anghel, DV; Churochkin, DV Author Full Names: Anghel, Dragos-Victor; Churochkin, Dmitry V.
Source:
ADVANCES IN CONDENSED MATTER PHYSICS, 10.1155/2013/419202 2013
Abstract:
We use an extended version of the standard tunnelingmodel to explain the anisotropic sound absorption in decagonal quasicrystals. The glassy properties are determined by an ensemble of two level systems (TLSs), arbitrarily oriented. The TLS is characterized by a 3 x 3 symmetric tensor, [T], which couples to the strain field, [S], through a 3 x 3 x 3 x 3 tensor of coupling constants, [R]. The structure of [R] reflects the symmetry of the quasicrystal. We also analyze the probability distributions of the elements of [T] in this particular model for a better understanding of the characteristics of "isotropic" and "anisotropic" distributions of the ensemble of TLSs. We observe that the distribution of the elements is neither simple nor intuitive and therefore it is difficult to guess it a priory, using qualitative arguments based on the symmetry properties.

Update: 4-Dec-2013

Title:
Numerical methods for quasicrystals
Authors:
Jiang, K; Zhang, PW Author Full Names: Jiang, Kai; Zhang, Pingwen
Source:
JOURNAL OF COMPUTATIONAL PHYSICS, 256 428-440; 10.1016/j.jcp.2013.08.034 JAN 1 2014
Abstract:
Quasicrystals are one kind of space-filling structures. The traditional crystalline approximant method utilizes periodic structures to approximate quasicrystals. The errors of this approach come from two parts: the numerical discretization, and the approximate error of Simultaneous Diophantine Approximation which also determines the size of the domain necessary for accurate solution. As the approximate error decreases, the computational complexity grows rapidly, and moreover, the approximate error always exits unless the computational region is the full space. In this work we focus on the development of numerical method to compute quasicrystals with high accuracy. With the help of higher-dimensional reciprocal space, a new projection method is developed to compute quasicrystals. The approach enables us to calculate quasicrystals rather than crystalline approximants. Compared with the crystalline approximant method, the projection method overcomes the restrictions of the Simultaneous Diophantine Approximation, and can also use periodic boundary conditions conveniently. Meanwhile, the proposed method efficiently reduces the computational complexity through implementing in a unit cell and using pseudospectral method. For illustrative purpose we work with the Lifshitz-Petrich model, though our present algorithm will apply to more general systems including quasicrystals. We find that the projection method can maintain the rotational symmetry accurately. More significantly, the algorithm can calculate the free energy density to high precision. (C) 2013 Elsevier Inc. All rights reserved.
Title:
Crystal-quasicrystal transition depending on cooling rates in directionally solidified Al-3Mn-7Be (at.%) alloy
Authors:
Kang, HJ; Li, XZ; Wang, TM; Liu, DM; Su, YQ; Hu, ZL; Guo, JJ; Fu, HZ Author Full Names: Kang, Huijun; Li, Xinzhong; Wang, Tongmin; Liu, Dongmei; Su, Yanqing; Hu, Zhonglve; Guo, Jingjie; Fu, Hengzhi
Source:
INTERMETALLICS, 44 101-105; 10.1016/j.intermet.2013.09.004 JAN 2014
Abstract:
The transition of primary phases from the crystalline approximant phase to icosahedral quasicrystal phase (I-phase) is observed in the directional solidified Al-3Mn-7Be (at.%) alloy. The structures of I-phase and approximant phases are characterized by SEM, TEM and HRTEM. The addition of Be significantly enhances the formation ability of I-phase, combining with the directional solidification method where the growth rates and temperature gradients can be separately controlled, giving rise to a promising way to prepare quasicrystal-reinforced Al-matrix composite. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Switching kinetics of the ferroelectric transition in K2SeO4 studied by stroboscopic gamma-ray diffraction
Authors:
Leist, J; Gibhardt, H; Eckold, G Author Full Names: Leist, J.; Gibhardt, H.; Eckold, G.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (46):10.1088/0953-8984/25/46/465901 NOV 20 2013
Abstract:
The kinetics of the ferroelectric lock-in transition in potassium selenate (K2SeO4) was studied on a millisecond timescale using high-resolution gamma-ray diffraction. A large change of the line width and wavevector of the first order satellite is observed during the switching process. This is attributed to a loss of long-range order under the influence of the electric field. In addition, the incommensurate phase is stabilized by the pulsed field and the transition to the pure commensurate phase is shifted to lower temperatures. Strains that may build up during the rapid switching process are supposed to be the reason for this behaviour.
Title:
Short-range order and singularities of the electronic structure of icosahedral quasicrystals
Authors:
Prekul, AF; Shchegolikhina, NI Author Full Names: Prekul, A. F.; Shchegolikhina, N. I.
Source:
PHYSICS OF THE SOLID STATE, 55 (11):2260-2266; 10.1134/S106378341311019X NOV 2013
Abstract:
For icosahedral phases of the Al-Cu-Fe system, components of the electrical conductivity, magnetic susceptibility, Hall effect, and heat capacity associated with thermally induced charge carriers for the first time have been considered jointly over a wide temperature range. It has been shown that the full range of thermal effects can be understood in the framework of the unified concept, which is based on an inhomogeneous system of two-level electronic excitations. A model of the inhomogeneous electronic state and the mechanism of its formation with the dominant role of short-range order have been proposed.
Title:
"Bite like a Rottweiler"
Authors:
Remenyi, C; Koster, V; Shechtman, D Author Full Names: Remenyi, Christian; Koester, Vera; Shechtman, Dan
Source:
NACHRICHTEN AUS DER CHEMIE, 61 (11):1107-1108; 10.1002/nadc.201390359 NOV 2013
Abstract:
2011 Nobel prize laureate Dan Shechtman talks about quasicrystals, jewelry and being stubborn.
Title:
Lamellar structure and nanomechanical properties of quasicrystalline Al-Cu-Fe alloys
Authors:
Shalaeva, EV; Chernyshev, YV; Smirnova, EO; Smirnov, SV Author Full Names: Shalaeva, E. V.; Chernyshev, Yu. V.; Smirnova, E. O.; Smirnov, S. V.
Source:
PHYSICS OF THE SOLID STATE, 55 (11):2205-2214; 10.1134/S106378341311022X NOV 2013
Abstract:
The kinetics of structural phase transformations in quasicrystal-forming Al-Cu-Fe alloys with compositions in the region of stability of the icosahedral (i) phase has been investigated. It has been shown that, depending on the development of metastable transformations i -> pentagonal phases P1 and P2, a homogeneous lamellar structure (i + P1 + P2) or a polygrain i-phase is formed in the alloys. The P-h diagrams obtained upon nanoindentation, atomic force microscopy, and scanning electron microscopy of indentations have demonstrated signs of elasto-plastic deformation of the alloys with lamellar and polygrain icosahedral structures. It has been found that, in contrast to the polygrain icosahedral alloys with a normal size effect of nanoindentation, the alloys with a lamellar structure are characterized by a nonmonotonic dependence of the hardness (H) on the maximum load (P (max)) and exhibit the effect of strain hardening in the range of loads 50 mN a parts per thousand currency sign P (max) < 500 mN. The strain hardening is considered as the result of resistance exerted by boundaries of the lamellar structure to the development of plastic deformation.
Title:
beta-Technetium Dichloride: Solid-State Modulated Structure, Electronic Structure, and Physical Properties
Authors:
Malliakas, CD; Poineau, F; Johnstone, EV; Weck, PF; Kim, E; Scott, BL; Forster, PM; Kanatzidis, MG; Czerwinski, KR; Sattelberger, AP Author Full Names: Malliakas, Christos D.; Poineau, Frederic; Johnstone, Erik V.; Weck, Philippe F.; Kim, Eunja; Scott, Brian L.; Forster, Paul M.; Kanatzidis, Mercouri G.; Czerwinski, Kenneth R.; Sattelberger, Alfred P.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 135 (42):15955-15962; 10.1021/ja408459k OCT 23 2013
Abstract:
A second polymorph of technetium dichloride, beta-TcCl2, has been synthesized from the reaction of Tc metal and chlorine in a sealed tube at 450 degrees C. The crystallographic structure and physical properties of beta-TcCl2 have been investigated. The structure of beta-TcCl2 consists of infinite chains of face sharing [Tc2Cl8] units; within a chain, the Tc Tc vectors of two adjacent [Tc2Cl8] units are ordered in the long-range where perpendicular and/or parallel arrangement of Tc Tc vectors yields a modulated structure. Resistivity and Seebeck measurements performed on a beta-TcCl2 single crystal indicate the compound to be a p-type semiconductor while a magnetic susceptibility measurement shows technetium dichloride to be diamagnetic. A band gap of 0.12(2) eV was determined by reflectance spectroscopy measurements. Theoretical calculations at the density functional level were utilized for the investigation of other possible stable forms of TcCl2.

Update: 27-Nov-2013

Title:
de Haas-van Alphen effect and Fermi surface properties of single-crystal CrB2
Authors:
Brasse, M; Chioncel, L; Kunes, J; Bauer, A; Regnat, A; Blum, CGF; Wurmehl, S; Pfleiderer, C; Wilde, MA; Grundler, D Author Full Names: Brasse, M.; Chioncel, L.; Kunes, J.; Bauer, A.; Regnat, A.; Blum, C. G. F.; Wurmehl, S.; Pfleiderer, C.; Wilde, M. A.; Grundler, D.
Source:
PHYSICAL REVIEW B, 88 (15):10.1103/PhysRevB.88.155138 OCT 31 2013
Abstract:
We report the angular dependence of three distinct de Haas-van Alphen (dHvA) frequencies of the torque magnetization in the itinerant antiferromagnet CrB2 at temperatures down to 0.3 K and magnetic fields up to 14 T. Comparison with the Fermi surface calculations considering an incommensurate cycloidal magnetic order suggests that two of the observed dHvA oscillations arise from electronlike Fermi surface sheets formed by bands with strong B-p(x,y) character. The third orbit could correspond to a Cr-d derived Fermi surface sheet. The measured effective masses of these Fermi surface sheets display strong enhancements of a factor of about 2 over the calculated band masses which can be attributed to electron-phonon coupling and electronic correlations. Signatures of further heavy d-electron bands that are predicted by the calculations are not observed in the temperature and field range studied. In the view that the B-p bands are at the heart of conventional high-temperature superconductivity in the isostructural MgB2, we consider possible implications of our findings for nonmagnetic CrB2 and an interplay of itinerant antiferromagnetism with superconductivity.
Title:
Effect of Lone-Electron-Pair Cations on the Orientation of Crystallographic Shear Planes in Anion-Deficient Perovskites
Authors:
Batuk, D; Batuk, M; Abakumov, AM; Tsirlin, AA; McCammon, C; Pubrovinsky, L; Hadermann, J Author Full Names: Batuk, Dmitry; Batuk, Maria; Abakumov, Artem M.; Tsirlin, Alexander A.; McCammon, Catherine; Pubrovinsky, Leonid; Hadermann, Joke
Source:
INORGANIC CHEMISTRY, 52 (17):10009-10020; 10.1021/ic4012845 SEP 2 2013
Abstract:
Factors affecting the structure and orientation of the crystallographic shear (CS) planes in anion-deficient perovskites were investigated using the (Pb1-,Srz),-xFe(1+x),,, "perovskites as a model system. The isovalent substitution of Sr2+ for Pb2+ highlights the-influence of the A cation electronic strUcture because these cations exhibit very close ionic radii. Two compositional ranges have been identified in the system: 0.05 <= z <= 0.2, where the CS plane orientation gradually varies but stays close to (203)p, and 0.3 <= z <= 0.45 with (101)p CS,planes. The incommensurately modulated structure of Pb0.792Sro.,68Fel.0,002.629 was refined from neutron powder diffraction data using the (3+ 1)D approach (space group X2/rn(alpha 0(gamma)), X -= C / 2, V2, I/2), a = 3.9512(1) A, b = 3.9483(1) A, c =3.9165(1) k, = 93.268(2)6, q =0.0879(1)a* +0.1276(1)c*, R-F = 0.023, R-p = 0.029, and T = 900 K). A comparison of the compounds with different CS planes indicates that the orientation of the CS planes is governed mainly by the stereochemical "activity of the lone-electron-pair cations inside the perovskite blocks.
Title:
Magnetic Tri-Axial Grain Alignment Achieved in Bismuth-Based Cuprate Superconductors
Authors:
Horii, S; Nagai, R; Yamaki, M; Maeda, T; Shimoyama, J; Doi, T Author Full Names: Horii, Shigeru; Nagai, Ryotaro; Yamaki, Momoko; Maeda, Toshihiko; Shimoyama, Jun-ichi; Doi, Toshiya
Source:
APPLIED PHYSICS EXPRESS, 6 (9):10.7567/APEX.6.093102 SEP 2013
Abstract:
We demonstrate the tri-axial magnetic alignment of Bi2Sr2CaCu2Oy [Bi2212] and Bi1.7Pb0.35Sr2Ca2Cu3Oy [(Bi1.7Pb0.35)2223] and report the semi-quantitative tri-axial magnetic anisotropy of Bi2212. A modulated rotating magnetic field of 10 tesla achieved degrees of in-plane and c-axis orientations of <9 and similar to 4 degrees, respectively. Conversion of magnetization axes of Bi2212 by slight Er-doping suggests that the incommensurate modulated crystal structures observed in the Bi-based cuprates induced generation of weak but strictly tri-axial magnetic anisotropy. Our present results indicate the possibility of fabricating tri-axially grain-oriented bulks and thick films without applying epitaxial growth methods, such as melt solidification and thin-film deposition. (c) 2013 The Japan Society of Applied Physics

Update: 20-Nov-2013

Title:
Microscopic coexistence of a two-component incommensurate spin density wave with superconductivity in underdoped NaFe0.983Co0.017As
Authors:
Oh, S; Mounce, AM; Lee, JA; Halperin, WP; Zhang, CL; Carr, S; Dai, PC; Reyes, AP; Kuhns, PL Author Full Names: Oh, Sangwon; Mounce, A. M.; Lee, Jeongseop A.; Halperin, W. P.; Zhang, C. L.; Carr, S.; Dai, Pengcheng; Reyes, A. P.; Kuhns, P. L.
Source:
PHYSICAL REVIEW B, 88 (13):10.1103/PhysRevB.88.134518 OCT 25 2013
Abstract:
We have performed As-75 and Na-23 nuclear magnetic resonance (NMR) measurements on a single crystal of NaFe0.9835Co0.0165As and found microscopic coexistence of superconductivity with a two-component spin density wave (SDW). Using Na-23 NMRwemeasured the spatial distribution of local magnetic fields. The SDWwas found to be incommensurate with a major component having magnetic moment (similar to 0.2 mu(B)/Fe) and a smaller component with magnetic moment (similar to 0.02 mu(B)/Fe). Spin lattice relaxation experiments reveal that this coexistence occurs at a microscopic level.
Title:
Electron doping evolution of the magnetic excitations in BaFe2-xNixAs2
Authors:
Luo, HQ; Lu, XY; Zhang, R; Wang, M; Goremychkin, EA; Adroja, DT; Danilkin, S; Deng, GC; Yamani, Z; Dai, PC Author Full Names: Luo, Huiqian; Lu, Xingye; Zhang, Rui; Wang, Meng; Goremychkin, E. A.; Adroja, D. T.; Danilkin, Sergey; Deng, Guochu; Yamani, Zahra; Dai, Pengcheng
Source:
PHYSICAL REVIEW B, 88 (14):10.1103/PhysRevB.88.144516 OCT 25 2013
Abstract:
We use inelastic neutron scattering (INS) spectroscopy to study the magnetic excitations spectra throughout the Brillouin zone in electron-doped iron pnictide superconductors BaFe2-xNixAs2 with x = 0.096,0.15,0.18. While the x = 0.096 sample is near optimal superconductivity with T-c = 20 K and has coexisting static incommensurate magnetic order, the x = 0.15,0.18 samples are electron overdoped with reduced T-c of 14 and 8 K, respectively, and have no static antiferromagnetic (AF) order. In previous INS work on undoped (x = 0) and electron optimally doped (x = 0.1) samples, the effect of electron doping was found to modify spin waves in the parent compound BaFe2As2 below similar to 100 meV and induce a neutron spin resonance at the commensurate AF ordering wave vector that couples with superconductivity. While the new data collected on the x = 0.096 sample confirm the overall features of the earlier work, our careful temperature dependent study of the resonance reveals that the resonance suddenly changes its Q width below T-c similar to that of the optimally hole-doped iron pnictides Ba0.67K0.33Fe2As2. In addition, we establish the dispersion of the resonance and find it to change from commensurate to transversely incommensurate with increasing energy. Upon further electron doping to overdoped iron pnictides with x = 0.15 and 0.18, the resonance becomes weaker and transversely incommensurate at all energies, while spin excitations above similar to 100 meV are still not much affected. Our absolute spin excitation intensity measurements throughout the Brillouin zone for x = 0.096,0.15,0.18 confirm the notion that the low-energy spin excitation coupling with itinerant electron is important for superconductivity in these materials, even though the high-energy spin excitations are weakly doping dependent.
Title:
Stable All-Nitrogen Metallic Salt at Terapascal Pressures
Authors:
Sun, J; Martinez-Canales, M; Klug, DD; Pickard, CJ; Needs, RJ Author Full Names: Sun, Jian; Martinez-Canales, Miguel; Klug, Dennis D.; Pickard, Chris J.; Needs, Richard J.
Source:
PHYSICAL REVIEW LETTERS, 111 (17):10.1103/PhysRevLett.111.175502 OCT 24 2013
Abstract:
The phase diagram and equation of state of dense nitrogen are of interest in understanding the fundamental physics and chemistry under extreme conditions, including planetary processes, and in discovering new materials. We predict several stable phases of nitrogen at multi-TPa pressures, including a P4/nbm structure consisting of partially charged N-2(delta+) pairs and N-5(delta-) tetrahedra, which is stable in the range 2.5-6.8 TPa. This is followed by a modulated layered structure between 6.8 and 12.6 TPa, which also exhibits a significant charge transfer. The P4/nbm metallic nitrogen salt and the modulated structure are stable at high pressures and temperatures, and they exhibit strongly ionic features and charge density distortions, which is unexpected in an element under such extreme conditions and could represent a new class of nitrogen materials. The P-T phase diagram of nitrogen at TPa pressures is investigated using quasiharmonic phonon calculations and ab initio molecular dynamics simulations.
Title:
Magnetic Structures of LiMBO3 (M = Mn, Fe, Co) Lithiated Transition Metal Borates
Authors:
Tao, L; Neilson, JR; Melot, BC; McQueen, TM; Masquelier, C; Rousse, G Author Full Names: Tao, Liang; Neilson, James R.; Melot, Brent C.; McQueen, Tyrel M.; Masquelier, Christian; Rousse, Gwenaelle
Source:
INORGANIC CHEMISTRY, 52 (20):11966-11974; 10.1021/ic401671m OCT 21 2013
Abstract:
The magnetic ordering within LiMBO3 compounds (M = Mn, Fe, and Co) has been explored re by magnetization measurements and neutron powder diffraction. For all M, an incommensurately ordered magnetic phase is established on cooling, followed by a change to a commensurate long-range antiferromagnetic state below T-N2 = 12(1) K for LiMnBO3, T-N2 = 25(1) K for LiFeBO3, and T-N2 = 12(1) K for LiCoBO3. For LiMnBO3, the magnetic ordering at T = 2 K exhibits a propagation vector k = (1, 0, 0) and consists of antiferromagnetic chains that are coupled antiferromagnetically to each other, the magnetic moments being oriented along the [001] direction. In contrast, the magnetic order at T=2 K in LiFeBO3 and LiCoBO3 exhibits a propagation vector of k = (1/2, 1/2, 1/2) and consists of ferromagnetic chains that are antiferromagnetically coupled. The magnetic moments lie roughly along the [02 (3) over bar] direction within the bc plane for LiFeBO3, and along the [30 (1) over bar] direction within the ac plane for LiCoBO3. The moment orientations in both LiMnBO3 and LiFeBO3 suggest an Ising character arising from unquenched orbital momentum due to unusual trigonal bipyrimidal coordination environments. No evidence of Ising behavior is found in the case of LiCoBO3.
Title:
Magnetic fluctuations and effective magnetic moments in gamma-iron due to electronic structure peculiarities
Authors:
Igoshev, PA; Efremov, AV; Poteryaev, AI; Katanin, AA; Anisimov, VI Author Full Names: Igoshev, P. A.; Efremov, A. V.; Poteryaev, A. I.; Katanin, A. A.; Anisimov, V. I.
Source:
PHYSICAL REVIEW B, 88 (15):10.1103/PhysRevB.88.155120 OCT 18 2013
Abstract:
Applying the local density and dynamical mean field approximations to paramagnetic gamma-iron we revisit the problem of the theoretical description of its magnetic properties in a wide temperature range. We show that contrary to alpha-iron, the frequency dependence of the electronic self-energy has a quasiparticle form for both t(2g) and e(g) states. In the temperature range T = 1200-1500 K, where gamma-iron exists in nature, this substance can be nevertheless characterized by temperature-dependent effective local moments, which yield relatively narrow peaks in the real part of the local magnetic susceptibility as a function of frequency. At the same time, at low temperatures gamma-iron (which is realized in precipitates) is better described in terms of the itinerant picture. In particular, the nesting features of the Fermi surfaces yield the maximum of the static magnetic susceptibility at the incommensurate wave vector q(max) belonging in the direction q(X) - q(W) (q(X) (2 pi/a)(1,0,0), q(W) (2 pi/a)(1,1/2,0), a is a lattice parameter) in agreement with the experimental data. This state is found, however, to compete closely with the states characterized by magnetic wave vectors along the directions q(X) - q(L) - q(K), where q(L) (2 pi/a)(1/2,1/2,1/2), q(K) (2 pi/a)(3/4,3/4,0). From the analysis of the uniform magnetic susceptibility we find that contrary to alpha-iron, the Curie-Weiss law is not fulfilled in a broad temperature range, although the inverse susceptibility is nearly linear in the moderate-temperature region (1200-1500 K). The nonlinearity of the inverse uniform magnetic susceptibility in a broader temperature range is due to the density of states peak located close to the Fermi level. The effective exchange integrals in the paramagnetic phase are estimated on the base of momentum-dependent susceptibility.
Title:
Hartree-Fock Ground State Phase Diagram of Jellium
Authors:
Baguet, L; Delyon, F; Bernu, B; Holzmann, M Author Full Names: Baguet, L.; Delyon, F.; Bernu, B.; Holzmann, M.
Source:
PHYSICAL REVIEW LETTERS, 111 (16):10.1103/PhysRevLett.111.166402 OCT 14 2013
Abstract:
We calculate the ground state phase diagram of the homogeneous electron gas in three dimensions within the Hartree-Fock approximation and show that broken symmetry states are energetically favored at any density against the homogeneous Fermi gas state with isotropic Fermi surface. At high density, we find metallic spin-unpolarized solutions where electronic charge and spin density form an incommensurate crystal having more crystal sites than electrons. For r(s) -> 0, our solutions approach pure spin-density waves, whereas the commensurate Wigner crystal is favored at lower densities, r(s) greater than or similar to 3.4. Decreasing the density, the system undergoes several structural phase transitions with different lattice symmetries. The polarization transition occurs around r(s) approximate to 8.5.
Title:
System-dependent melting behavior of icosahedral anti-Mackay nanoalloys
Authors:
Oderji, HY; Behnejad, H; Ferrando, R; Ding, HB Author Full Names: Oderji, Hassan Yousefi; Behnejad, Hassan; Ferrando, Riccardo; Ding, Hongbin
Source:
RSC ADVANCES, 3 (44):21981-21993; 10.1039/c3ra43401j 2013
Abstract:
Anti-Mackay icosahedral clusters of composition Ag32M13, where M is either Cu, Ni, or Co, have been recently shown to possess special structural stability both by calculations and experiments. These nanoalloys assume a core-shell arrangement, with an icosahedral core of 13 M atoms surrounded by an Ag shell of anti-Mackay structure. In this paper we study the melting of these three nanoalloys, showing that, despite the close similarity of the structures, melting takes place through quite different mechanisms. In particular, we find that Ag32Co13 and Ag32Ni13 present a premelting phenomenon which involves only the shell of the cluster while the core melts at higher temperatures, in agreement with previous calculations. On the contrary, in Ag32Cu13, melting occurs through stages that involve the shell and the core at the same time. These findings are rationalized in terms of the different features of the energy landscape of these nanoalloys. Our simulations, in which special care has been devoted to avoid non-ergodicity problems, show also that the particles keep their core-shell structures even in the liquid phase, indicating an incomplete miscibility of Ag with Ni, Co or Cu at the nanoscale up to quite high temperatures.

Update: 13-Nov-2013

Title:
The Influence of Alloying Elements on Adhesive Properties of Epoxy-Quasicrystal Composites
Authors:
Altidis, JD; Lima, SJG; Torres, SM; Lima, BASG; Medeiros, ES; de Barros, S Author Full Names: Altidis, J. D.; Lima, S. J. G.; Torres, S. M.; Lima, B. A. S. G.; Medeiros, E. S.; de Barros, S.
Source:
JOURNAL OF ADHESION, 90 (1):41-49; SI 10.1080/00218464.2013.806212 JAN 2 2014
Abstract:
Quasicrystals (QC) are materials that exhibit good surface properties such as high hardness, low surface energy, low friction coefficient, and good resistance to oxidation and corrosion. Despite these properties, QC alloys are highly brittle, discouraging their uses in applications requiring mechanical stresses. Hence, the development of composites using quasicrystalline materials as reinforcement to ductile matrices is an interesting alternative. In this work, Al-Cu-Fe quasicrystals were used as a reinforcement to epoxy resin in order improve adhesion with metallic substrates. Adhesive properties were evaluated by single lap joint (SLJ) tests and the QC/epoxy interface was analyzed by scanning electron microscopy (SEM). Aluminum, copper, and iron, individual elements, were used to investigate the contribution of each element to the adhesive. Results show that it was possible to significantly enhance adhesion properties when 25% QC was added to epoxy and that the effect of QC amount on SLJ bond strength did not follow a linear trend. Moreover, the contribution of each alloying element was important to explain the influence of QC addition on adhesive properties of the epoxy-based composites.
Title:
Uniaxial-Pressure Effects on Spin-Driven Lattice Distortions in Geometrically Frustrated Magnets CuFe1-xGaxO2 (x=0, 0.035)
Authors:
Nakajima, T; Iguchi, Y; Tamatsukuri, H; Mitsuda, S; Yamasaki, Y; Nakao, H; Terada, N Author Full Names: Nakajima, Taro; Iguchi, Yusuke; Tamatsukuri, Hiromu; Mitsuda, Setsuo; Yamasaki, Yuichi; Nakao, Hironori; Terada, Noriki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (11):10.7566/JPSJ.82.114711 NOV 2013
Abstract:
The triangular lattice antiferromagnet CuFeO2 (CFO) is a spin-lattice coupled system, whose magnetic phase transitions are accompanied by crystal lattice distortions to relieve the geometrical spin frustration. Recent neutron diffraction and magnetic susceptibility measurements on CFO have revealed that the application of uniaxial pressure (up to 100 MPa) in the triangular lattice plane shifts the magnetic phase transition temperatures to higher values [Nakajima et al.: J. Phys. Soc. Jpn. 81 (2012) 094710]. In the present study, we have performed synchrotron radiation x-ray diffraction measurements on CFO and CuFe1-xGaxO2 (CFGO) with x = 0.035 under applied uniaxial pressure in order to directly observe the uniaxial-pressure effects on the lattice. As a result, we have revealed that the applied uniaxial pressure certainly affects the crystal structure so that the structural transition temperatures increase as well as the magnetic phase transition temperatures. We have also found that CFO exhibits a pronounced lattice instability in the vicinity of the phase transition from the paramagnetic phase with a trigonal structure to an incommensurate magnetic phase with a monoclinic structure. In addition, the present results for CFGO (x = 0.035) have revealed that the lattice instability is suppressed by the substitution of a small amount of nonmagnetic Ga3+ ions for the magnetic Fe3+ ions. This indicates that the spin degree of freedom plays an important role in the lattice instability in this system.
Title:
Incommensurate Crystallography
Authors:
Chapuis, G Author Full Names: Chapuis, Gervais
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 620-621; 10.1107/S010876731301951X 6 NOV 2013
Title:
Ferromagnetism and re-entrant spin-glass transition in quasicrystal approximants Au-SM-Gd (SM = Si, Ge)
Authors:
Hiroto, T; Gebresenbut, GH; Gomez, CP; Muro, Y; Isobe, M; Ueda, Y; Tokiwa, K; Tamura, R Author Full Names: Hiroto, T.; Gebresenbut, G. H.; Gomez, C. Pay; Muro, Y.; Isobe, M.; Ueda, Y.; Tokiwa, K.; Tamura, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (42):10.1088/0953-8984/25/42/426004 OCT 23 2013
Abstract:
Magnetic susceptibility and specific heat measurements on quasicrystalline approximants Au-Si-Gd and Au-Ge-Gd reveal that a ferromagnetic (FM) transition occurs at T-c = 22.5(5) K for Au-Si-Gd and at T-c = 13(1) K for Au-Ge-Gd, which are the first examples of ferromagnetism in crystalline approximants. In addition, a re-entrant spin-glass (RSG) transition is observed at T-RSG = 3.3 K for Au-Ge-Gd in contrast to Au-Si-Gd. The different behaviors are understood based on the recent structural models reported by Gebresenbut et al (2013 J. Phys.: Condens. Matter 25 135402). The RSG transition in Au-Ge-Gd is attributed to a random occupation of the center of the Gd-12 icosahedron by Gd atoms; a central Gd spin hinders the long-range FM order.
Title:
QUASICRYSTALLINE OXIDES
Authors:
[Anonymous] Author Full Names: [Anonymous]
Source:
CHEMICAL & ENGINEERING NEWS, 91 (41):30-30; OCT 14 2013
Title:
TRANSPORT PROPERTIES IN MISFIT-LAYERED Ca2Co2O5 COMPOUND
Authors:
Lan, JL; Zhan, B; Lin, YH; Nan, CW; Liu, YC Author Full Names: Lan, Jinle; Zhan, Bin; Lin, Yuan-Hua; Nan, Ce-Wen; Liu, Yao-Chun
Source:
FUNCTIONAL MATERIALS LETTERS, 6 (5):10.1142/S1793604713400018 OCT 2013
Abstract:
The low temperature transport and magnetic properties were investigated in the misfit-layered Ca2Co2O5 compound. The compound exhibits incommensurate spin-density-wave (SDW) state in the d(chi)(-1)/dT curve at 20K, which is confirmed by the resistivity (rho) characterization. The resistivity shows an upturn from metallic to insulating behavior at TM-I (130 K) and strong Fermi liquid behaviors with rho similar to T-2 relation between TM-I and T*(225 K). The Seebeck coefficient shows abnormal temperature dependence at T-p (40 K), which is suggested to origin from the long order of atomic in [Ca2CoO3] sublayer and spin fluctuation of Co ions. Moreover, large Seebeck coefficient (120 mu V/K) and low thermal conductivity (2.5 W/mK) were obtained at room temperature, indicating that it is a promising p-type thermoelectric material for energy conversion.
Title:
Non-centro-symmetric electron diffraction pattern of icosahedral quasicrystal induced by combination of linear phason strain and curvature of Ewald sphere
Authors:
Xiong, DX; Lu, L; Wang, JB; Zhao, DS; Sun, YF Author Full Names: Xiong, Dongxia; Lu, Lu; Wang, Jianbo; Zhao, Dongshan; Sun, Yufeng
Source:
MICRON, 52-53 45-48; 10.1016/j.micron.2013.08.004 SEP-OCT 2013
Abstract:
Non-centro-symmetric characteristics are observed in the experimental electron diffraction patterns (EDPs) from the icosahedral quasicrystalline precipitates in ZrAlNiCuNb alloys. Different from the well-known breaking of the Friedel's law, where a strong dynamical effect will reveal in EDPs the concealed non-centro-symmetry originated from the crystal structures themselves, the current results can be interpreted in terms of changes in deviation parameters due to a delicate combination of the linear phason strain characteristic of quasicrystals and the curvature of Ewald sphere. After taking this effect into consideration, the corresponding simulated EDPs fit quite well to the experimental data. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Structural and magnetic characterization of the intermartensitic phase transition in NiMnSn Heusler alloy ribbons
Authors:
Llamazares, JLS; Flores-Zuniga, H; Rios-Jara, D; Sanchez-Valdes, CF; Garcia-Fernandez, T; Ross, CA; Garcia, C Author Full Names: Sanchez Llamazares, J. L.; Flores-Zuniga, H.; Rios-Jara, D.; Sanchez-Valdes, C. F.; Garcia-Fernandez, T.; Ross, C. A.; Garcia, C.
Source:
JOURNAL OF APPLIED PHYSICS, 113 (17):10.1063/1.4800836 MAY 7 2013
Abstract:
Phase transitions and structural and magnetic properties of rapidly solidified Ni50Mn38Sn12 alloy ribbons have been studied. Ribbon samples crystallize as a single-phase, ten-layered modulated (10M) monoclinic martensite with a columnar-grain microstructure and a magnetic transition temperature of 308 K. By decreasing the temperature, martensite undergoes an intermartensitic phase transition around 195 K. Above room temperature, the high temperature martensite transforms into austenite. Below 100 K, magnetization hysteresis loops shift along the negative H-axis direction, confirming the occurrence of an exchange bias effect. On heating, the thermal dependence of the coercive field H-C shows a continuous increase, reaching a maximum value of 1017 Oe around 50 K. Above this temperature, H-C declines to zero around 195 K. But above this temperature, it increases again up to 20 Oe falling to zero close to 308 K. The coercivity values measured in both temperature intervals suggest a significant difference in the magnetocrystalline anisotropy of the two martensite phases. (C) 2013 AIP Publishing LLC.

Update: 7-Nov-2013

Title:
Bending analyses of 1D orthorhombic quasicrystal plates
Authors:
Sladek, J; Sladek, V; Pan, E Author Full Names: Sladek, J.; Sladek, V.; Pan, E.
Source:
INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 50 (24):3975-3983; 10.1016/j.ijsolstr.2013.08.006 NOV 2013
Abstract:
The meshless Petrov-Galerkin method (MLPG) is applied to plate bending analysis in 1D orthorhombic quasicrystals (QCs) under static and transient dynamic loads. The Bak and elasto-hydrodynamic models are applied for phason governing equation in the elastodynamic case. The phason displacement for the orthorhombic QC in the first-order shear deformation plate theory depends only on the in-plane coordinates on the mean plate surface. Nodal points are randomly distributed over the mean surface of the considered plate. Each node is the center of a circle surrounding this node. The coupled governing partial differential equations are satisfied in a weak-form on small fictitious subdomains. The spatial variations of the phonon and phason displacements are approximated by the moving least-squares (MLS) scheme. After performing the spatial MLS approximation, a system of ordinary differential equations (ODEs) for nodal unknowns is obtained. The system of the ODEs of the second order is solved by the Houbolt finite-difference scheme. Our numerical examples demonstrate clearly the effect of the coupling parameter on both static and dynamic phonon/phason deflections. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Competition Between Antiferromagnetism and Ferromagnetism in Sr2RuO4 Probed by Mn and Co Doping
Authors:
Ortmann, JE; Liu, JY; Hu, J; Zhu, M; Peng, J; Matsuda, M; Ke, X; Mao, ZQ Author Full Names: Ortmann, J. E.; Liu, J. Y.; Hu, J.; Zhu, M.; Peng, J.; Matsuda, M.; Ke, X.; Mao, Z. Q.
Source:
SCIENTIFIC REPORTS, 3 10.1038/srep02950 OCT 15 2013
Abstract:
Spin-triplet superconductivity in Sr2RuO4 has attracted enormous interest. Like other unconventional superconductors, superconductivity in Sr2RuO4 is in close proximity to magnetic instability. Undoped Sr2RuO4 exhibits incommensurate antiferromagnetic (AFM) fluctuations, which can evolve into static, short-range AFM order via Ti doping. Moreover, weak ferromagnetic (FM) coupling in Sr2RuO4 has also been suggested by NMR/neutron scattering experiments and studies on Ca2-xSrxRuO4 and Sr2-yLayRuO4, implying orbital dependent magnetism. We report bulk static, short-range FM order in Sr2RuO4 triggered by <2% Co doping, showing superconductivity in Sr2RuO4 is much closer to FM instability than previously reported in Ca2-xSrxRuO4. We also find Mn doping can effectively establish incommensurate AFM order, with T-N similar to 50 K for 3% Mn doping. These new results place Sr2RuO4 in a unique situation where superconductivity lies directly on the borderline of two distinct magnetic states, highlighting the important role of competing magnetic fluctuations in determining superconducting properties of Sr2RuO4.
Title:
Quasicrystalline structure formation in a classical crystalline thin-film system
Authors:
Forster, S; Meinel, K; Hammer, R; Trautmann, M; Widdra, W Author Full Names: Foerster, Stefan; Meinel, Klaus; Hammer, Rene; Trautmann, Martin; Widdra, Wolf
Source:
NATURE, 502 (7470):215-+; 10.1038/nature12514 OCT 10 2013
Abstract:
The discovery of quasicrystals(1)-crystalline structures that show order while lacking periodicity-forced a paradigm shift in crystallography. Initially limited to intermetallic systems(1-4), the observation of quasicrystalline structures has recently expanded to include 'soft' quasicrystals in the fields of colloidal and supermolecular chemistry(5-9). Here we report an aperiodic oxide that grows as a two-dimensional quasicrystal on a periodic single-element substrate. On a Pt(111) substrate with 3-fold symmetry, the perovskite barium titanate BaTiO3 forms a high-temperature interface-driven structure with 12-fold symmetry. The building blocks of this dodecagonal structure assemble with the theoretically predicted Stampfli-Gahler tiling(10,11) having a fundamental length-scale of 0.69 nm. This example of interface-driven formation of ultrathin quasicrystals from a typical periodic perovskite oxide potentially extends the quasicrystal concept to a broader range of materials. In addition, it demonstrates that frustration at the interface between two periodic materials can drive a thin film into an aperiodic quasicrystalline phase, as proposed previously(12). Such structures might also find use as ultrathin buffer layers for the accommodation of large lattice mismatches in conventional epitaxy(13).
Title:
Magnetic orders, excitations, and phase transitions in Fe1+yTe
Authors:
Chen, G; Choi, S; Radzihovsky, L Author Full Names: Chen, G.; Choi, S.; Radzihovsky, L.
Source:
PHYSICAL REVIEW B, 88 (16):10.1103/PhysRevB.88.165117 OCT 10 2013
Abstract:
We study the magnetic properties of Fe1+yTe, a parent compound of the iron-based high-temperature superconductors. Motivated by recent neutron scattering experiments, we show that a spin S = 1 exchange model, supplemented by a single-ion spin anisotropy, accounts well for the experimentally observed low-temperature magnetic phase diagram, that exhibits a commensurate bicollinear order at low Fe dopings (y less than or similar to 0.12) and an incommensurate spin-spiral order at high Fe dopings (y greater than or similar to 0.12). We suggest that the commensurate incommensurate transition at y similar or equal to 0.12 is due to the competition between the exchange interaction and the local spin anisotropy. At low Fe dopings, the single-ion spin anisotropy is strong and pins the spins along the easy axis, which, together with the spatially anisotropic exchanges, induces a unusual bicollinear commensurate magnetic order. The low-energy spin-wave excitation is gapped due to the explicit breaking of spin-rotational symmetry by the local spin anisotropy. At high Fe dopings, the single-ion anisotropy is weak, and the exchange favors an incommensurate coplanar state. The incommensurate magnetic wave vector averages out the spin anisotropy so that a gapless low-energy spin-wave excitation is obtained. We also analyze the low-energy hydrodynamic model and use it to describe the magnetostructural transition and the static and dynamical spin structure factors across the magnetic ordering transitions.
Title:
Evolution of incommensurate spin order with magnetic field and temperature in the itinerant antiferromagnet GdSi
Authors:
Feng, YJ; Silevitch, DM; Wang, JY; Palmer, A; Woo, N; Yan, JQ; Islam, Z; Suslov, AV; Littlewood, PB; Rosenbaum, TF Author Full Names: Feng, Yejun; Silevitch, D. M.; Wang, Jiyang; Palmer, A.; Woo, Nayoon; Yan, J. -Q.; Islam, Z.; Suslov, A. V.; Littlewood, P. B.; Rosenbaum, T. F.
Source:
PHYSICAL REVIEW B, 88 (13):10.1103/PhysRevB.88.134404 OCT 7 2013
Abstract:
GdSi exhibits spin-density-wave (SDW) order arising from the cooperative interplay of sizeable local moments and a partially nested Fermi sea of itinerant electrons. Using magnetotransport, magnetization, and nonresonant magnetic x-ray diffraction techniques, we determine the H-T phase diagrams of GdSi for magnetic fields up to 21 T, where antiferromagnetic order is no longer stable, and field directions along each of the three major crystal axes. While the incommensurate magnetic ordering vector that characterizes the SDW is robust under magnetic field, the multiple spin structures of this compound are highly flexible and rotate relative to the applied field via either canting or spin-flop processes. The antiferromagnetic spin densities always arrange themselves transverse to the applied magnetic field direction. The phase diagrams are delineated by two types of phase boundaries: one separates a collinear from a planar spin structure associated with a lattice structural transition, and the other defines a spin flop transition that is only weakly temperature dependent. The major features of the phase diagrams along each of the crystal axes can be explained by the combination of local moment and global Fermi surface physics at play.
Title:
Critical behavior of RMn2O5 oxides near the magnetic phase transition to a structure incommensurate in two spatial directions
Authors:
Men'shenin, VV Author Full Names: Men'shenin, V. V.
Source:
PHYSICS OF THE SOLID STATE, 55 (10):2051-2056; 10.1134/S1063783413100235 OCT 2013
Abstract:
A phase transition from the paramagnetic state to the long-period magnetic structure in RMn2O5 oxides with the star of the wave vector determining the incommensurability of long-range magnetic order in two spatial directions has been investigated. An effective Hamiltonian of the system that allows one to describe this transition in the framework of the renormalization group approach has been constructed. It has been shown that there is a stable critical point of transformations of this group at which there occurs a second-order phase transition. The critical indices have been found. The obtained results have been compared with the results for phase transitions occurring in these oxides in accordance with the star of the wave vector, which provides incommensurability in one of the spatial directions. It has been found that fluctuations of the four-component order parameter due to the low spatial symmetry of these compounds do not change the order of the phase transition, which was found in terms of the Landau theory.
Title:
Effects of Strain and Ordering of Rare-Earth Element Moments on Magnetic-Reordering in Orthorhombic Multiferroic Manganites
Authors:
Hsiao, YF; Lai, JY; Lin, JY; Fang, HW; Hung, YT; Luo, CW; Wu, KH; Uen, TM; Lin, JY; Juang, JY Author Full Names: Hsiao, Yen-Fu; Lai, Jun-Yo; Lin, Jun-Yu; Fang, Hau-Wei; Hung, Yi-Tse; Luo, Chih-Wei; Wu, Kaung-Hsiung; Uen, Tzeng-Ming; Lin, Jiunn-Yuan; Juang, Jenh-Yih
Source:
APPLIED PHYSICS EXPRESS, 6 (10):10.7567/APEX.6.103201 OCT 2013
Abstract:
Orthorhombic multiferroic manganite thin films with various orientations and strain states were prepared to show the effects of anisotropic strain and antiferromagnetic (AFM) ordering of rare-earth f-electrons on the orientation of the incommensurate-to-commensurate AFM reordering. Systematic analyses suggest that the low-temperature AFM ordering of the rare-earth f-electrons may have played a decisive role in causing the orientation changes in AFM reordering, although the b-axis strain does have a significant influence on the zero-field magnetization behaviors. (C) 2013 The Japan Society of Applied Physics
Title:
Mechanical properties of the icosahedral phase reinforced duplex Mg-Li alloy both at room and elevated temperatures
Authors:
Xu, DK; Zu, TT; Yin, M; Xu, YB; Han, EH Author Full Names: Xu, D. K.; Zu, T. T.; Yin, M.; Xu, Y. B.; Han, E. H.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 582 161-166; 10.1016/j.jallcom.2013.08.020 JAN 5 2013
Abstract:
Through investigating tensile properties of the duplex Mg-Li alloys with and without I-phase (Mg3Zn6Y, icosahedral quasicrystal structure) tested both at ambient and elevated temperatures, it demonstrates that I-phase can not only improve the tensile strength at room temperature, but also be beneficial for the mechanical improvement at elevated temperatures. Based on the microstructural observations of the sample surfaces before and after tests, the I-phase particles can effectively suppress the plastic flow of beta phase at 220 degrees C, resulting in the I-phase reinforced duplex Mg-Li alloy having higher mechanical properties at elevated temperatures. (c) 2013 Elsevier B.V. All rights reserved.
Title:
Arrangements of Transition-Metal Atoms in Three Types of Al-Co-Ni Decagonal Quasicrystals Studied by Cs-Corrected HAADF-STEM
Authors:
Hiraga, K; Yasuhara, A Author Full Names: Hiraga, K.; Yasuhara, A.
Source:
MATERIALS TRANSACTIONS, 54 (4):493-497; 10.2320/matertrans.M2012340 2013
Abstract:
Three types of Al-Co-Ni decagonal quasicrystals in Al72.5Co11Ni16.5, Al71Co14.5Ni14.5 and Al71.5Co16Ni12.5 alloys have been examined by Cs-corrected high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM), which has an enough resolution to represent individual TM atoms as bright dots in observed images of decagonal quasicrystals. On the basis of the structure of a W-(AlNiCo) crystalline approximant, transition-metal (TM) atoms and mixed sites (MSs) of Al and TM atoms are separately distinguished in HAADF-STEM images. Most of TM atoms are arranged with pentagonal tilings of a bond-length of 0.76 nm, and MSs are located inside of pentagonal frames with definite orientations. All of the TM atoms and MSs are located at lattice points of a Penrose lattice of an edge-length of 0.25 nm, and arranged with a bond-orientational order. The present result shows that the structures of Al-Co-Ni decagonal quasicrystals should be characterized as BOO arrangements of transition-metal atoms, instead of previous models of BOO arrangements of 2 nm atom clusters.

Update: 31-Oct-2013

Title:
Role of magnetic chirality in polarization flip upon a commensurate-incommensurate magnetic phase transition in YMn2O5
Authors:
Wakimoto, S; Kimura, H; Sakamoto, Y; Fukunaga, M; Noda, Y; Takeda, M; Kakurai, K Author Full Names: Wakimoto, Shuichi; Kimura, Hiroyuki; Sakamoto, Yuma; Fukunaga, Mamoru; Noda, Yukio; Takeda, Masayasu; Kakurai, Kazuhisa
Source:
PHYSICAL REVIEW B, 88 (14):10.1103/PhysRevB.88.140403 OCT 10 2013
Abstract:
We have performed simultaneous measurements of magnetic chirality by using polarized neutrons and electric polarization along the b axis of single crystals of YMn4+(Mn1-xGax)O-3+(5) with x = 0.047 and 0.12, in which nonmagnetic Ga ions dilute Mn3+ spins. The x = 0.047 sample exhibits high-temperature incommensurate (HT-ICM), commensurate (CM), and low-temperature incommensurate (LT-ICM) magnetic phases in order of decreasing temperature, whereas the x = 0.12 sample exhibits only HT-ICM and LT-ICM phases. Here, the CM and LT-ICM phases are ferroelectric and weak ferroelectric, respectively. Measurements conducted under zero-field heating after various field-cooling conditions evidence that the microscopic mechanisms of the spin-driven ferroelectricity in the CM and LT-ICM phases are different: The magnetic chirality of Mn4+ cycloidal spins plays a dominant role in the LT-ICM phase, whereas the magnetic exchange striction by the Mn4+-Mn3+ chain plays a dominant role in the CM phase. The polarization of YMn2O5 flips upon a CM to LT-ICM phase transition because the ferroelectricity driven by the magnetic chirality and the exchange striction provides opposite directions of polarization.
Title:
Magnetic and structural properties near the Lifshitz point in Fe1+xTe
Authors:
Rodriguez, EE; Sokolov, DA; Stock, C; Green, MA; Sobolev, O; Rodriguez-Rivera, JA; Cao, H; Daoud-Aladine, A Author Full Names: Rodriguez, E. E.; Sokolov, D. A.; Stock, C.; Green, M. A.; Sobolev, O.; Rodriguez-Rivera, Jose A.; Cao, H.; Daoud-Aladine, A.
Source:
PHYSICAL REVIEW B, 88 (16):10.1103/PhysRevB.88.165110 OCT 7 2013
Abstract:
We construct a phase diagram of the parent compound Fe1+xTe as a function of interstitial iron x in terms of the electronic, structural, and magnetic properties. For a concentration of x < 10%, Fe1+xTe undergoes a "semimetal" to metal transition at approximately 70 K that is also first-order and coincident with a structural transition from a tetragonal to a monoclinic unit cell. For x approximate to 14%, Fe1+xTe undergoes a second-order phase transition at approximately 58 K corresponding to a semimetal to semimetal transition along with a structural orthorhombic distortion. At a critical concentration of x approximate to 11%, Fe1+xTe undergoes two transitions: the higher-temperature one is a second-order transition to an orthorhombic phase with incommensurate magnetic ordering and temperature-dependent propagation vector, while the lower-temperature one corresponds to nucleation of a monoclinic phase with a nearly commensurate magnetic wave vector. While both structural and magnetic transitions display similar critical behavior for x < 10% and near the critical concentration of x approximate to 11%, samples with large interstitial iron concentrations show a marked deviation between the critical response indicating a decoupling of the order parameters. Analysis of temperature dependent inelastic neutron data reveals incommensurate magnetic fluctuations throughout the Fe1+xTe phase diagram are directly connected to the "semiconductor"-like resistivity above T-N and implicates scattering from spin fluctuations as the primary reason for the semiconducting or poor metallic properties. The results suggest that doping driven Fermi surface nesting maybe the origin of the gapless and incommensurate spin response at large interstitial concentrations.
Title:
Observation of atomic scale compositional and displacive modulations in incommensurate melilite electrolytes
Authors:
Wei, FX; Williams, T; An, T; Baikie, T; Kloc, C; Wei, J; White, T Author Full Names: Wei, Fengxia; Williams, Tim; An, Tao; Baikie, Tom; Kloc, Christian; Wei, Jun; White, Tim
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 203 291-296; 10.1016/j.jssc.2013.04.039 JUL 2013
Abstract:
The paradigm that functional materials are adequately described as three-dimensional crystal structures is not universally tenable. Gallate melilites are efficient oxide ion conductors at intermediate temperatures (similar to 750 degrees C) with non-rational crystallographic modulations presumed to play a key role in significantly enhancing oxygen mobility. Lattice distortions associated with incommensuration are usually extrapolated from diffraction analysis of volumes greatly exceeding the scale of modulation. Therefore, opportunities for making direct nanometric measurements are exceptionally valuable for correlating structure with function. In [CaLn](2)[Ga](2)[Ga2O7](2) (Ln=Nd, La) melilites, atomic displacive and compositional modulation waves can be imaged by high angle annular dark field and bright field scanning transmission electron microscopy with contrast quantified through electron scattering simulation. Here, we present atomic scale observations of (3+2)-dimensional modulations in gallate melilites which expands our understanding of the ion conduction mechanism and provides guidance for enhancing the performance of solid oxide fuel cells through crystal chemical tailoring. (C) 2013 Elsevier Inc. All rights reserved.

Update: 23-Oct-2013

Title:
SWAXS analysis on some quasicrystalline alloys: Nanoclusters and nanoaggregates
Authors:
Tukel, C; Ide, S; Yildirim, L; Erbudak, M Author Full Names: Tukel, Caner; Ide, Semra; Yildirim, Leyla; Erbudak, Mehmet
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 581 860-866; 10.1016/j.jallcom.2013.07.175 DEC 25 2013
Abstract:
Mesoscopic structure of two decagonal quasicrystalline samples, Al-Co-Ni and Al-Co-Cu, is investigated by XRD and SEM. Simultaneous SAXS and WAXS (SWAXS) measurements give information on the shape, size, and pair-distance distributions of nanometer-size aggregates contained in the analyzed volume. Decagonal single quasicrystal structures, quasicrystalline approximants, and nanometer-size domain structures are found to coexist in the samples. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Characterisation of nano-sized Al-Mn-(Mg) particles in AZ91 and their effect on Mg17Al12 precipitation
Authors:
Zeng, R; Chiu, Y; Jones, IP Author Full Names: Zeng, R.; Chiu, Y.; Jones, I. P.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 579 34-38; 10.1016/j.jallcom.2013.04.179 DEC 5 2013
Abstract:
Al-Mn-(Mg) particles in the size range of 20-200 nm have been found in a sand cast AZ91 magnesium alloy. Their morphologies, chemical composition and structures were investigated using transmission electron microscopy. It was found that these particles have a chemical composition of (Al6.52Mn)(1-x)Mg-x (x < 0.13) and a decagonal quasi-crystalline structure. These particles were stable during a solution treatment at 420 degrees C for 72 h and acted as preferential nucleation sites for Mg17Al12 precipitates during the subsequent ageing. The potential effect of these Al-Mn-(Mg) particles on the strengthening of AZ91 magnesium alloys is discussed. (c) 2013 Elsevier B.V. All rights reserved.
Title:
C6H4S2AsCl: description and interpretation of an incommensurately modulated molecular crystal structure
Authors:
Bakus, RC; Atwood, DA; Parkin, S; Brock, CP; Petricek, V Author Full Names: Bakus, Ronald C., II; Atwood, David A.; Parkin, Sean; Brock, Carolyn P.; Petricek, Vaclav
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 69 496-508; 10.1107/S205251921301782X 5 OCT 2013
Abstract:
Crystals of 2-chloro-benzo-1,3,2-dithiarsole have a strongly modulated structure that can be solved and refined with relative ease in a P (1) over bar, Z' = 17 approximate supercell but that is better described as incommensurate. Two conventional refinements (different superstructure approximations that differ in the placement of their crystallographic inversion centers) and a (3 + 1)-dimensional superspace refinement are all nearly equally successful, at least as measured by the usual agreement factors; the data integration, however, shows that the incommensurate description is preferable. The overall packing is determined by the stacking of the aromatic rings and probably by the segregation of As and Cl atoms to give short As center dot center dot center dot Cl contacts. A refinement of the average (Z' = 1) structure shows that there are two basic orientations of the C6S2 plane, but that those orientations must be correlated in several directions to avoid impossibly short intermolecular contacts. Along the modulation vector q the orientation of the C6S2 plane varies smoothly, but q is not a direction in which the molecules are in contact. Along the directions in which the molecules are in contact the orientation of the C6S2 plane alternates; there are also positional shifts. The single modulation q relieves packing problems in several different directions well enough that crystals that diffract well can be grown.
Title:
Dzyaloshinskii-Moriya driven helical-butterfly structure in Ba3NbFe3Si2O14
Authors:
Scagnoli, V; Huang, SW; Garganourakis, M; de Souza, RA; Staub, U; Simonet, V; Lejay, P; Ballou, R Author Full Names: Scagnoli, V.; Huang, S. W.; Garganourakis, M.; de Souza, R. A.; Staub, U.; Simonet, V.; Lejay, P.; Ballou, R.
Source:
PHYSICAL REVIEW B, 88 (10):10.1103/PhysRevB.88.104417 SEP 18 2013
Abstract:
We have used soft x-ray magnetic diffraction at the Fe3+ L-2,L-3 edges to examine to what extent the Dzyaloshinsky-Moriya interaction in Ba3NbFe3Si2O14 influences its low-temperature magnetic structure. A modulated component of the moments along the c axis is present, adding to the previously proposed helical magnetic configuration of coplanar moments in the a, b plane. This leads to a "helical-butterfly" structure and suggests that both the multiaxial in-plane and the uniform out-of-plane Dzyaloshinsky-Moriya vectors are relevant. A nonzero orbital magnetic signal is also observed at the oxygen K edge, which reflects the surprisingly strong hybridization between iron 3d and oxygen 2p states, given the nominal spherical symmetry of the Fe3+ half-filled shell.
Title:
Rotational disorder of bis(mesitylene)vanadium in channels of a triazine inclusion compound
Authors:
Barbon, A; Hauser, J; Berger, R; Brustolon, M; Hulliger, J Author Full Names: Barbon, Antonio; Hauser, Juerg; Berger, Ricarda; Brustolon, Marina; Hulliger, Juerg
Source:
CRYSTENGCOMM, 15 (40):8110-8115; 10.1039/c3ce41102h 2013
Abstract:
Electron paramagnetic resonance (EPR) was applied to study rotational disorder of bis(mesitylene)vanadium (VBM, S = 1/2) in channels of 2,4,6-tris(4-Br-phenoxy)-1,3,5-triazine. To ensure a magnetically dilute system, decamethylbis(cyclopentadienyl) ruthenium was used as a main guest to fill the channels. X-ray diffraction confirmed inclusion formation, resulting in an incommensurate host-guest system. EPR spectra were measured using prismatic single crystals oriented to have B-o either parallel to the channel axis c or at any angle in between c and the perpendicular direction. Temperature-dependent spectra were recorded down to 80 K. The analysis revealed two types of paramagnetic guest entities, i.e. VBM (I) and VBM (II). Both showed dynamical effects due to a reorientational motion. VBM (I) is confined to show a molecular axis z distributed around c by a small angle (+/- 1.25 degrees), whereas for VBM (II) the distribution is completely disordered. The reorientational motions are frozen at low temperature giving for VBM (II) a powder-like EPR spectrum. Analysing EPR intensities allowed us to conclude that the ratio of (I)/(II) species is of the order of 1.5.

Update: 17-Oct-013

Title:
Phases in the Al-Corner of the Al-Mn-Be System
Authors:
Zupanic, F; Markoli, B; Naglic, I; Weingartner, T; Meden, A; Boncina, T Author Full Names: Zupanic, Franc; Markoli, Bostjan; Naglic, Iztok; Weingaertner, Tobias; Meden, Anton; Boncina, Tonica
Source:
MICROSCOPY AND MICROANALYSIS, 19 (5):1308-1316; 10.1017/S1431927613001852 OCT 2013
Abstract:
This work studied the phases in the Al corner of the Al-Mn-Be phase diagram in the as-cast state and heat-treated conditions. Metallographic investigations, X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy were used for identifying the phases. The Be contents in the identified phases were precisely determined using Auger electron spectroscopy. The results indicated that Al6Mn does not dissolve Be, whilst lambda-Al4Mn dissolves up to 7 at.% Be. The average composition of the T phase, which is normally designated as Al15Mn3Be2, was 72 at.% Al, 19 at.% Mn, and 9 at.% Be. The phase with the nominal composition Be4AlMn contained more Al than Mn. The atomic ratio Al: Mn was between 1.3: 1 and 2: 1. The hexagonal Be-rich phase did not dissolve any Al and Mn. The icosahedral quasicrystalline (IQC) phase contained up to 45 at.% Be. The compositions of T phase, lambda-Al4Mn, IQC, and Be4AlMn may vary, however, the ratio (Al + Be):Mn remained constant, and was close either to four or six indicating substitution of Al atoms with Be atoms in these phases.
Title:
Experimental Study of Al-Co-Cu Phase Diagram in Temperature Range of 800-1050 A degrees C
Authors:
Priputen, P; Liu, TY; Cernickova, I; Janickovic, D; Kolesar, V; Janovec, J Author Full Names: Priputen, P.; Liu, T. Y.; Cernickova, I.; Janickovic, D.; Kolesar, V.; Janovec, J.
Source:
JOURNAL OF PHASE EQUILIBRIA AND DIFFUSION, 34 (5):425-429; 10.1007/s11669-013-0253-y OCT 2013
Abstract:
Partial isothermal sections of the Al-Co-Cu phase diagram at 800, 1020, and 1050 A degrees C were proposed based on both literature data and own experimental results. By means of x-ray diffraction, electron backscattered diffraction, electron diffraction, high-resolution scanning electron microscopy, transmission electron microscopy, and energy dispersive x-ray spectroscopy altogether five phases (Al5Co2, m-Al13Co4, D, B2, and rapidly solidified liquid) were identified in a number of investigated alloys falling within compositional ranges Al58-67Co18-34Cu7-20. The single-phase area corresponding in the isothermal sections to the decagonal quasicrystalline phase (D) was found to reduce in size, and to shift to lower Cu and higher Al bulk contents, both with increasing temperature. The single-phase m and Al5Co2 areas showed only small temperature-dependent changes in size and location. Moreover, an increase in temperature caused both a slow decrease of the copper solubility in B2 and an increase of the liquid stability.
Title:
Direction of atom displacement in incommensurate state of Ti-32Pd-18Fe shape memory alloy
Authors:
Todai, M; Fukuda, T; Kakeshita, T Author Full Names: Todai, Mitsuharu; Fukuda, Takashi; Kakeshita, Tomoyuki
Source:
MATERIALS LETTERS, 108 293-296; 10.1016/j.matlet.2013.07.018 OCT 1 2013
Abstract:
Displacement of atoms causing diffuse satellites in a Ti-32Pd-18Fe alloy (in at%) has been investigated by transmission electron microscopy (TEM). In this alloy, diffuse satellites appear at incommensurate positions given by g(B2)+q when the zone axis is [111] and [001], but they are missing when [110]. This results imply that the satellites appear because of a transverse wave with a propagation vector of q similar to 1/5 * and displacement in (110) direction. Possibly, this transverse wave occurs as a result of phonon softening of the TA(2) phonon branch, which is a common feature for B2-type Ti-based shape memory alloys. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Dynamic spin correlations in the frustrated cubic phase of MnV2O4
Authors:
Chung, JH; Song, YS; Kim, JH; Suzuki, T; Katsufuji, T; Matsuda, M; Lee, SH Author Full Names: Chung, Jae-Ho; Song, Young-Sang; Kim, J. -H.; Suzuki, T.; Katsufuji, T.; Matsuda, M.; Lee, S. -H.
Source:
PHYSICAL REVIEW B, 88 (9):10.1103/PhysRevB.88.094430 SEP 23 2013
Abstract:
The ferrimagnetic spinel MnV2O4 undergoes an orbital-induced cubic-to-tetragonal distortion at T-YK = 58 K, below which noncollinear commensurate ferrimagnetic ordering occurs. Using inelastic neutron scattering, we investigated low-energy dynamics in its cubic phase above TYK. We observed two types of coexisting short-range magnetic excitations: the dispersive spin waves centered around the Brillouin-zone centers, k(0) = (0, 0, 0), and quasielastic spin fluctuations centered at incommensurate wave vectors, k(incom) = (xi,xi, 0). The coexistence of the two distinct features can be understood as a dynamic realization of the conical spiral order observed in cubic spinels such as CoCr2O4.
Title:
Fabrication and magnetic properties of single-crystalline La0.33Pr0.34Ca0.33MnO3/MgO nanowires
Authors:
Li, L; Li, H; Zhai, XF; Zeng, CG Author Full Names: Li, Lin; Li, Hui; Zhai, Xiaofang; Zeng, Changgan
Source:
APPLIED PHYSICS LETTERS, 103 (11):10.1063/1.4819828 SEP 9 2013
Abstract:
Single crystalline La0.33Pr0.34Ca0.33MnO3/MgO core-shell nanowires with diameters about tens of nanometers are synthesized by a two-step process. Structure and morphology characterizations confirm the epitaxial growth of La0.33Pr0.34Ca0.33MnO3 shell layers on MgO core layers. Clear interfaces are observed between the core and shell layers. Magnetic measurements suggest the existence of electronic phase separation in the one dimensional nanowires similar to the bulk. However, the nanowires exhibit significantly increased amount of magnetically frozen phase and increased coercivity, which are attributed to the strongly modulated magnetic structure in the one dimensional structure. (C) 2013 AIP Publishing LLC.
Title:
AlCuFe(Cr) and AlCoFeCr coatings for improvement of elevated temperature oxidation resistance of a near-alpha titanium alloy
Authors:
Moskalewicz, T; Dubiel, B; Wendler, B Author Full Names: Moskalewicz, Tomasz; Dubiel, Beata; Wendler, Bogdan
Source:
MATERIALS CHARACTERIZATION, 83 161-169; 10.1016/j.matchar.2013.06.018 SEP 2013
Abstract:
In this work, an AlCuFe, AlCuFeCr and AlCoFeCr multicomponent coatings were deposited on a near-alpha titanium alloy, TIMETAL 834, by a non-reactive magnetron sputtering. A microstructure, phase composition, coatings adhesion to the substrate, micro-mechanical properties and oxidation resistance were investigated. The AlCuFe coating was quasicrystalline and consisted of icosahedral psi-Al65Cu20Fe15 phase grains. The AlCuFeCr coating consisted mainly of decagonal d-AlCuFeCr phase and some Al6.1Cu1.2Ti2.7 phase grains. The AlCoFeCr coating microstructure was composed of AlCrFe2 nanocrystals embedded in an Al13Co4 matrix. It was established that all multicomponent coatings exhibit higher hardness and elastic moduli than the titanium alloy substrate. Among all investigated coatings, the AlCoFeCr one exhibits the best adhesion to the substrate. It was found that a very brittle, non-protective scale formed on the uncoated alloy during isothermal oxidation consisted of TiO2 (rutile) grains. The oxidation resistance of the TIMETAL 834 alloy at elevated temperature (750 degrees C) was significantly improved by the coatings deposition. The smallest weight gain during oxidation test, 82% lower than in the case of uncoated sample, was found for the AlCoFeCr coated alloy. The microstructure investigation of the specimen after oxidation test was performed by SEM and TEM. It was found that the improvement of oxidation resistance of TIMETAL 834 by the coatings deposited in the present work is mainly due to an occurrence of the protective alpha-Al2O3 scale. (C) 2013 Elsevier Inc. All rights reserved.
Title:
Incommensurate magnetic structures in rhombohedral Heisenberg antiferromagnet
Authors:
Martynov, SN Author Full Names: Martynov, S. N.
Source:
JETP LETTERS, 98 (1):19-23; 10.1134/S0021364013140099 SEP 2013
Abstract:
The phase diagram of the ground state has been calculated for a rhombohedral antiferromagnet of the R3m symmetry with frustrated exchange in the base plane and competition of exchanges between the nearest and next-nearest planes. The diagram contains phases of collinear antiferromagnetic ordering of various types separated by five incommensurate magnetic states of the helicoidal type, differing in the ordering type and in the direction of the modulation vector. The commensurate and incommensurate phases converge at multi-critical points lying on a line corresponding to an antiferromagnet with an undistorted simple cubic lattice.
Title:
Icosahedral stereographic projections in three dimensions for use in dark field TEM
Authors:
Bourdillon, AJ Author Full Names: Bourdillon, Antony J.
Source:
MICRON, 51 21-25; 10.1016/j.micron.2013.06.004 AUG 2013
Abstract:
Thermodynamics require that rapidly cooled crystals and quasicrystals are relatively defective. Yet, without convenient 3-dimensional indexation both at crystal poles and in diffraction planes, or Kikuchi maps, it is difficult to identify the defects by dark field transmission electron microscopy. For two phase Al6Mn, these maps are derived. They relate i-Al6Mn to the standard face centered cubic, matrix crystals. An example of their usefulness in determining interfacial characteristics is described. Indices are integral powers on an irrational number. (c) 2013 Elsevier Ltd. All rights reserved.
Title:
Bond Order in Two-Dimensional Metals with Antiferromagnetic Exchange Interactions
Authors:
Sachdev, S; La Placa, R Author Full Names: Sachdev, Subir; La Placa, Rolando
Source:
PHYSICAL REVIEW LETTERS, 111 (2):10.1103/PhysRevLett.111.027202 JUL 9 2013
Abstract:
We present an unrestricted Hartree-Fock computation of charge-ordering instabilities of two-dimensional metals with antiferromagnetic exchange interactions, allowing for arbitrary ordering wave vectors and internal wave functions of the particle-hole pair condensate. We find that the ordering has a dominant d symmetry of rotations about lattice points for a range of ordering wave vectors, including those observed in recent experiments at low temperatures on YBa2Cu3Oy. This d symmetry implies the charge ordering is primarily on the bonds of the Cu lattice, and we propose incommensurate bond order parameters for the underdoped cuprates. The field theory for the onset of Neel order in a metal has an emergent pseudospin symmetry which "rotates" d-wave Cooper pairs to particle-hole pairs [M. A. Metlitski and S. Sachdev, Phys. Rev. B82, 075128 ( 2010)]; our results show that this symmetry has consequences even when the spin correlations are short ranged and incommensurate.

Update: 9-Oct-2013

Title:
Scanning tunneling microscopy of a polygrain Al-Pd-Re quasicrystal: study of the relative surface stability
Authors:
Tamura, R; Yadav, TP; McLeod, IM; Hesp, D; Young, KM; Nakamura, T; Nishio, K; Dhanak, VR; McGrath, R; Sharma, HR Author Full Names: Tamura, R.; Yadav, T. P.; McLeod, I. M.; Hesp, D.; Young, K. M.; Nakamura, T.; Nishio, K.; Dhanak, V. R.; McGrath, R.; Sharma, H. R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (39):10.1088/0953-8984/25/39/395007 OCT 2 2013
Abstract:
Scanning tunneling microscopy and x-ray photoemission spectroscopy on a polygrain icosahedral (i-) Al-Pd-Re quasicrystal (QC) show the formation of the twofold surfaces with symmetry and composition expected from the bulk. The predominant occurrence of the twofold surface on the polygrain i-QC having random grain orientation, as well as preferential formation of terrace edges, kinks and voids along the twofold axes, consistently indicates that the twofold surface, which has the highest atomic density, is the most stable among all the crystallographic planes.
Title:
Topological equivalence of crystal and quasicrystal band structures
Authors:
Madsen, KA; Bergholtz, EJ; Brouwer, PW Author Full Names: Madsen, Kevin A.; Bergholtz, Emil J.; Brouwer, Piet W.
Source:
PHYSICAL REVIEW B, 88 (12):10.1103/PhysRevB.88.125118 SEP 11 2013
Abstract:
A number of recent articles have reported the existence of topologically nontrivial states and associated end states in one-dimensional incommensurate lattice models that would usually only be expected in higher dimensions. Using an explicit construction, we here argue that the end states have precisely the same origin as their counterparts in commensurate models and that incommensurability does not in fact provide a meaningful connection to the topological classification of systems in higher dimensions. In particular, we show that it is possible to smoothly interpolate between states with commensurate and incommensurate modulation parameters without closing the band gap and without states crossing the band gap.
Title:
Optical spectroscopy and electronic structure of the face-centered icosahedral quasicrystals Zn-Mg-R (R = Y, Ho, Er)
Authors:
Karpus, V; Tumenas, S; Suchodolskis, A; Arwin, H; Assmus, W Author Full Names: Karpus, V.; Tumenas, S.; Suchodolskis, A.; Arwin, H.; Assmus, W.
Source:
PHYSICAL REVIEW B, 88 (9):10.1103/PhysRevB.88.094201 SEP 9 2013
Abstract:
Results of optical spectroscopy studies of the face-centered icosahedral (fci) single-grain Zn-Mg-Y, Zn-Mg-Ho, and Zn-Mg-Er quasicrystals (QCs) are presented. The dielectric function of the QCs was measured in the 0.01-6 eV spectral range by IR-UV spectroscopic ellipsometry and far infrared reflection spectroscopy techniques. A theoretical scheme of optical conductivity calculations is extended to account for the Fermi level positions within and below a pseudogap. The model of the QC electron energy spectrum, based on a band structure hypothesis, is suggested, which treats the electronic subsystem as a nearly free electron gas affected by intersections of the Fermi surface with several families of Bragg planes. The experimental optical spectra are reproduced in detail by theoretical calculations carried out within the framework of the model. The parameters of the electron energy spectrum deduced from an analysis of optical data are close to those previously determined in an analysis of fci Zn-Mg-R valence band photoemission spectra.
Title:
Atom probe tomography investigation of lath boundary segregation and precipitation in a maraging stainless steel
Authors:
Thuvander, M; Andersson, M; Stiller, K Author Full Names: Thuvander, Mattias; Andersson, Marcus; Stiller, Krystyna
Source:
ULTRAMICROSCOPY, 132 265-270; 10.1016/j.ultramic.2012.10.014 SEP 2013
Abstract:
Lath boundaries in a maraging stainless steel of composition 13Cr-8Ni-2Mo-2Cu-1Ti-0.7Al-0.3Mn-0.2Si-0.03C (at%) have been investigated using atom probe tomography following aging at 475 degrees C for up to 100 h. Segregation of Mo, Si and P to the lath boundaries was observed already after 5 min or aging, and the amount or segregation increases with aging time At lath boundaries also precipitation or eta-Ni-3(Ti, Al) and Cu-rich 9R, in contact with each other, takes place. These co-precipitates grow with time and because of coarsening the area number density decreases. After 100 h or aging a similar to 5 nm thick film-like precipitation of a Mo-rich phase was observed at the lath boundaries. From the composition or the film it is suggested that the phase in question is the quasicrystalline R' phase. The film is perforated with Cu-rich OR and eta-Ni-3(Ti, Al) co-precipiLaLes. Not all precipitate types present in the matrix do precipitate at the lath boundaries; the Si-containing G phase and gamma'-Ni-3(Ti, Al, Si) and the Cr-rich alpha' phase were not observed at the lath boundaries. (C) 2012 Elsevier B.V. All rights reserved.

Update: 3-Oct-2013

Title:
Nanoquasicrystalline Al-Fe-Cr-Nb alloys produced by powder metallurgy
Authors:
Audebert, F; Galano, M; Rios, CT; Kasama, H; Peres, M; Kiminami, C; Botta, WJ; Bolfarini, C Author Full Names: Audebert, F.; Galano, M.; Triveno Rios, C.; Kasama, H.; Peres, M.; Kiminami, C.; Botta, W. J.; Bolfarini, C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 577 650-657; 10.1016/j.jallcom.2013.06.162 NOV 15 2013
Abstract:
Nano-quasicrystalline Al-Fe-Cr based alloys produced by rapid solidification processes exhibit high strength at elevated temperatures. Nevertheless, the quasicrystalline particles in these systems become unstable at high temperature limiting the industrial applications. In early works, it was observed that the use of Nb or Ta increases the stability of the Al-Fe-Cr quasicrystalline phase delaying the microstructural transformation to higher temperatures. Thus, these nano-quasicrystalline Al-based alloys have become promising new high strength material to be used at elevated temperatures in the automotive and aeronautical industries. In previous works, nano-quasicrystalline Al-Fe-Cr-Nb based alloys were obtained by rapid solidification using the melt-spinning technique. In order to obtain bulk alloys for industrial applications other fabrication routes such as powder production by gas atomization followed by compaction and extrusion are required. In the present work, the production of Al-Fe-Cr-Nb based alloys by powder atomization at laboratory scale was investigated. The powders obtained were sieved in different ranges of sizes and the microstructures were characterised by means of X-ray diffraction, scanning and transmission electron microscopy, and energy dispersive of X-ray analysis. Mechanical properties have been measured by compression tests at room temperature and at 250 degrees C. It was observed that a very high temperature is required to produce these alloys by gas atomization; the icosahedral quasicrystalline phase can be retained after the atomization in powder sizes typically under 75 mu m, and also after the extrusion at 375 degrees C. The extruded bars were able to retain a very high strength at elevated temperature, around 60% of the yield stress at room temperature, in contrast with the 10-30% typically obtained for many commercial Al alloys. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Microstructure transformations in the heat-treated Mg-Zn-Y alloy
Authors:
Geng, JW; Teng, XY; Zhou, GR; Zhao, DG Author Full Names: Geng, Jiwei; Teng, Xinying; Zhou, Guorong; Zhao, Degang
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 577 498-506; 10.1016/j.jallcom.2013.07.009 NOV 15 2013
Abstract:
Mg-Zn-Y icosahedral quasicrystals have been prepared from the Mg63.5Zn34Y2.5 (at.%) alloy by copper and steel molds casting respectively. The phase transformations under different heat treatments have been investigated successively. Although the cooling rates of the two samples are quite different, the icosahedral quasicrystalline (I-phase) can precipitate from liquid directly almost at the same temperature. The eutectic structure (alpha-Mg + I-phase) forms at the later stage, while the Mg7Zn3 phase forms under a larger cooling rate (copper mold). Moreover, with a lower cooling speed, micro shrinkage cavities and cracks are easily caused by solute partitioning at the edge of petals-like I-phase. The volume fraction of I-phase is effectively increased after heat treatment at 350 degrees C for 50 h because I-phase can grow further in a facet manner during the heat treatment process. The I-phase in the Mg63.5Zn34Y2.5 alloy is thermodynamically unstable at 420 degrees C, and therefore transformations of the I-phase to the W or H-phase occur due to slow transformation kinetics and low thermodynamics driving force. In addition, few decagonal quasicrystalline phases (D-phases) can form on the I-phase/Mg7Zn3 interface. Atomic diffusion and concentration also play a crucial role in these transformations. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Relative orientation of the magnetic moments in modulated multiferroic CaMn7O12
Authors:
Przenioslo, R; Wardecki, D; Slawinski, W; Sosnowska, I; Keller, L Author Full Names: Przenioslo, Radoslaw; Wardecki, Dariusz; Slawinski, Wojciech; Sosnowska, Izabela; Keller, Lukas
Source:
PHYSICA B-CONDENSED MATTER, 428 27-29; 10.1016/j.physb.2013.07.008 NOV 1 2013
Abstract:
The modulated magnetic ordering in the multiferroic manganite CaMn7O12 has been studied by using the neutron powder diffraction technique. The relative orientation of the magnetic moments of Mn4+ and Mn3+ ions located in Mn3 sublattice at (0,0,112) and Mn2 sublattice at (112,0,112) is shown to be antiparallel, i.e. their relative orientation angle Phi=pi. This result differs from that given by other authors who propose another relative orientation with a value of Phi=0.84(4)pi. The relative orientation angle is an important parameter used in model studies based on effective hamiltonians. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Origin of the phase transition in IrTe2: Structural modulation and local bonding instability
Authors:
Cao, HB; Chakoumakos, BC; Chen, X; Yan, JQ; McGuire, MA; Yang, H; Custelcean, R; Zhou, HD; Singh, DJ; Mandrus, D Author Full Names: Cao, Huibo; Chakoumakos, Bryan C.; Chen, Xin; Yan, Jiaqiang; McGuire, Michael A.; Yang, Hui; Custelcean, Radu; Zhou, Haidong; Singh, David J.; Mandrus, David
Source:
PHYSICAL REVIEW B, 88 (11):10.1103/PhysRevB.88.115122 SEP 12 2013
Abstract:
We used x-ray and neutron diffraction to determine the low-temperature structure of IrTe2. A structural modulation was observed with a wave vector of k = (1/5,0,1/5) below T-s approximate to 285 K, accompanied by a structural transition from a trigonal to a triclinic lattice. We also performed first-principles calculations for high-temperature and low-temperature structures, which elucidate the nature of the phase transition and the low-temperature structure. A local bonding instability associated with the Te 5p states is likely the origin of the structural phase transition in IrTe2.
Title:
EFFECT OF ALLOYING ELEMENTS ON MICROSTRUCTURE AND PROPERTIES OF Al-Mn-Fe RIBBON
Authors:
Stan, K; Litynska-Dobrzynska, L; Ochin, P; Wierzbicka-Miernik, A; Goral, A; Wojewoda-Budka, J Author Full Names: Stan, K.; Litynska-Dobrzynska, L.; Ochin, P.; Wierzbicka-Miernik, A.; Goral, A.; Wojewoda-Budka, J.
Source:
ARCHIVES OF METALLURGY AND MATERIALS, 58 (2):341-346; 10.2478/v10172-012-0195-0 2013
Abstract:
Influence of Ti, V, Cr, Zr, and Mo additions on microstructure and mechanical properties of the Al91Mn7Fe2 quasicrystalline alloy produced by the melt spinning technique has been studied. It was found that the microstructure of obtained all ribbons was similar and consists of spherical or dendritic icosahedral quasicrystalline particles embedded in an aluminium matrix coexisting with small fraction of intermetallic phase. Comporing DSC curves obtained for each sample it was observed that the alloy with Mo addition exhibits the best thermal stability among prepared alloys. Addition of molybdenum caused a significant shift of the main exothermic peak corresponding to temperature of quasicrystalline phase decomposition from 450 degrees C for ternary alloy to about 550 degrees C for quaternary composition. Microhardness measured for all prepared alloys were similar with the mean value of about 200 HV only alloy with Zr addition exhibited higher microhardness of about 270 HV caused by strengthening effect of Zr localized in the grains of aluminium matrix.

Update: 26-Sep-2013

Title:
STM and XPS investigation of the oxidation of the Al-4(Cr,Fe) quasicrystal approximant
Authors:
Parle, JK; Beni, A; Dhanak, VR; Smerdon, JA; Schmutz, P; Warde, M; Barthes-Labrousse, MG; Bauer, B; Gille, P; Sharma, HR; McGrath, R Author Full Names: Parle, J. K.; Beni, A.; Dhanak, V. R.; Smerdon, J. A.; Schmutz, P.; Warde, M.; Barthes-Labrousse, M. -G.; Bauer, B.; Gille, P.; Sharma, H. R.; McGrath, R.
Source:
APPLIED SURFACE SCIENCE, 283 276-282; 10.1016/j.apsusc.2013.06.101 OCT 15 2013
Abstract:
The oxidation of the Al-4(Cr, Fe) quasicrystal approximant has been studied using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). STM data indicate that the initial oxidation on the (1 0 0) surface proceeds in a highly ordered fashion. Oxygen preferentially adsorbs onto the surface of terraces, and step edges remain intact. The STM images show ordered stripes after initial oxidation. XPS data indicate that only Al is oxidised, with at least two oxidation states present. The Cr and Fe peaks remain unchanged. The oxidation of Al, rather than Cr or Fe, is consistent with the enthalpies of formation for each oxide. The stripes visible on the STM images are therefore identified to be the initial stages of aluminium oxide formation. XPS performed after higher O-2 exposure indicates that the (1 0 0) termination shows hindered Al oxide film thickness growth rates compared to the (0 1 0) and (0 0 1) surfaces. Crown Copyright (c) 2013 Published by Elsevier B.V. All rights reserved.
Title:
Excellent mechanical properties of an ultrafine-grained quasicrystalline strengthened magnesium alloy with multi-modal microstructure
Authors:
Huang, H; Yuan, GY; Chen, CL; Ding, WJ; Wang, ZC Author Full Names: Huang, Hua; Yuan, Guangyin; Chen, Chunlin; Ding, Wenjiang; Wang, Zhongchang
Source:
MATERIALS LETTERS, 107 181-184; 10.1016/j.matlet.2013.06.006 SEP 15 2013
Abstract:
In this study, we have developed an excellent mechanical properties of an ultrafine-grained quasicrystalline strengthened magnesium alloys by conventional extruding as-casted Mg-1.5Zn-0.25Gd (at%) ingot at 373 K with an extrusion ratio of about 9:1. After extrusion, multi-modal microstructure was formed, i.e. exhibited large deformed grains surrounded by fine dynamical recrystallization grains and the mean grain sizes smaller than I pal. The extruded sample shows excellent tensile properties at ambient temperature with ultimate tensile strength of 417 MPa, 0.2% proof stress of 395 MPa and elongation to failure of 8.3%. The notable improvement in strength mainly attributed to the grain refinement, dense distribution of the fine precipitates inside the fine dynamical recrystallization grains and the high intensity of typical basal texture. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Layered pnictide-oxide Na(2)Ti(2)Pn(2)O (Pn = As, Sb): a candidate for spin density waves
Authors:
Yan, XW; Lu, ZY Author Full Names: Yan, Xun-Wang; Lu, Zhong-Yi
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (36):10.1088/0953-8984/25/36/365501 SEP 11 2013
Abstract:
From first-principles calculations, we have studied the electronic and magnetic structures of compound Na(2)Ti(2)Pn(2)O (Pn = As or Sb), whose crystal structure is a bridge between or a combination of those of high-T-c superconducting cuprates and iron pnictides. We find that in the ground state Na2Ti2As2O is a novel blocked checkerboard antiferromagnetic semiconductor with a small band gap of about 0.15 eV. In contrast, Na2Ti2Sb2O is a bi-collinear antiferromagnetic semimetal, with a small moment of about 0.5 mu B around each Ti atom. We show that there is a strong Fermi surface nesting in Na(2)Ti(2)Pn(2)O, and we verify that the blocked checkerboard and bi-collinear antiferromagnetic states both are the spin density waves induced by the Fermi surface nesting. A tetramer structural distortion is found in company with the formation of a blocked checkerboard antiferromagnetic order, in good agreement with the experimentally observed commensurate structural distortion but with space group symmetry retained after the anomaly happens.
Title:
Phonon and magnon Raman scattering in CuB2O4
Authors:
Ivanov, VG; Abrashev, MV; Todorov, ND; Tomov, V; Nikolova, RP; Litvinchuk, AP; Iliev, MN Author Full Names: Ivanov, V. G.; Abrashev, M. V.; Todorov, N. D.; Tomov, V.; Nikolova, R. P.; Litvinchuk, A. P.; Iliev, M. N.
Source:
PHYSICAL REVIEW B, 88 (9):10.1103/PhysRevB.88.094301 SEP 3 2013
Abstract:
The Brillouin-zone-center phonons and two-magnon excitations in CuB2O4 are studied experimentally by polarized Raman spectroscopy. Most of the expected modes are clearly pronounced and their symmetry unambiguously identified from the polarization selection rules. The experimentally observed transverse optical phonon frequencies are in good agreement with those obtained by means of density functional theory. The two-magnon scattering band is centered at 82 cm(-1) and is clearly identified at temperatures below the Neel temperature T-N. The spectral shape of the two-magnon band confirms the existing theoretical models of magnon dispersion in the commensurate phase of CuB2O4 and suggests an exchange integral of J = 33 cm(-1) (48 K) between the nearest-neighbor Cu(A) ions. The quantitative line-shape analysis of the two-magnon band evidences for additional magnon self-energy contributions below the temperature T* of the commensurate-to-incommensurate phase transition.
Title:
Anisotropic Spin Fluctuations in the Quasi One-Dimensional Frustrated Magnet LiCuVO4
Authors:
Nawa, K; Takigawa, M; Yoshida, M; Yoshimura, K Author Full Names: Nawa, Kazuhiro; Takigawa, Masashi; Yoshida, Makoto; Yoshimura, Kazuyoshi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (9):10.7566/JPSJ.82.094709 SEP 2013
Abstract:
We report results of NMR experiments on a single crystal of the quasi one-dimensional frustrated magnet LiCuVO4 The NMR spectra of Li-7 and V-51 nuclei indicate a helical spin order in a magnetic field of 4 T with the helical spin plane perpendicular to the field and a spin-density-wave (SDW) order at 10 T with modulation in the magnitude of the moments aligned along the field, in agreement with earlier reports. The nuclear spin-lattice relaxation rate 1/T-1 at V-51 nuclei, which is selectively coupled to the transverse spin fluctuations perpendicular to the field, shows a pronounced peak near the helical ordering temperature in the field of 4 T applied along the a-axis. In the field of 10 T, however, such a peak is absent. Instead 1/T-1 at Li-7 nuclei probing longitudinal spin fluctuations shows divergent behavior towards the SDW ordering temperature. These results are qualitatively consistent with the theoretical description that the SDW correlation is due to bound magnon pairs, which produce an energy gap in the transverse spin excitation spectrum.
Title:
Field-induced phase transitions in the helimagnet Ba2CuGe2O7
Authors:
Chovan, J; Marder, M; Papanicolaou, N Author Full Names: Chovan, J.; Marder, M.; Papanicolaou, N.
Source:
PHYSICAL REVIEW B, 88 (6):10.1103/PhysRevB.88.064421 AUG 26 2013
Abstract:
We present a theoretical study of the two-dimensional spiral antiferromagnet Ba2CuGe2O7 in the presence of an external magnetic field. We employ a suitable nonlinear sigma model to calculate the T = 0 phase diagram and the associated low-energy spin dynamics for arbitrary canted magnetic fields, in general agreement with experiment. In particular, when the field is applied parallel to the c axis, a previously anticipated Dzyaloshinskii-type incommensurate-to-commensurate phase transition is actually mediated by an intermediate phase, in agreement with our earlier theoretical prediction confirmed by the recent observation of the so-called double-k structure. The sudden pi/2 rotations of the magnetic structures observed in experiment are accounted for by a weakly broken U(1) symmetry of our model. Finally, our analysis suggests a nonzero weak-ferromagnetic component in the underlying Dzyaloshinskii-Moriya anisotropy, which is important for quantitative agreement with experiment.
Title:
Landau theory of crystallization and self-assembly of octagonal quasicrystals
Authors:
Konevtsova, OV; Rochal, SB; Lorman, VL Author Full Names: Konevtsova, O. V.; Rochal, S. B.; Lorman, V. L.
Source:
PHYSICS OF THE SOLID STATE, 55 (8):1596-1601; 10.1134/S1063783413080143 AUG 2013
Abstract:
The theory of crystallization of quasicrystal structures that does not use the concept of multidimensional crystallography for describing the quasicrystal order has been proposed. It has been shown using the structure of the MnSiAl octagonal quasicrystal as an example that the coordinates of the sites in the corresponding quasicrystal lattice can be calculated by conditional minimization of the Landau free energy. The abandonment of the unconditional minimization of the free energy has been justified by special features of the local atomic order in the considered structure. The proposed theory gives a new physical meaning to the traditional concepts of multidimensional crystallography and can also be used for explaining the formation of quasicrystal structures with other quasicrystal lattices.

Update: 19-Sep-2013

Title:
Powder neutron diffraction study of HoCoGa5
Authors:
Kobayashi, R; Kaneko, K; Wakimoto, S; Chi, SX; Sanada, N; Watanuki, R; Suzuki, K Author Full Names: Kobayashi, Riki; Kaneko, Koji; Wakimoto, Shuichi; Chi, Songxue; Sanada, Naoyuki; Watanuki, Ryuta; Suzuki, Kazuya
Source:
JOURNAL OF THE KOREAN PHYSICAL SOCIETY, 63 (3):337-340; SI 10.3938/jkps.63.337 AUG 2013
Abstract:
We have studied successive magnetic transitions of HoCoGa5 at T (N1) = 9.6 K and T (N2) = 7.5 K by using powder neutron diffraction. Apparent superlattice peaks were observed at temperatures below T (N1). With further decreases temperature, the patterns exhibit a substantial change at temperatures below T (N2). The observed magnetic peaks at 8 K (AntiFerromagnetic InCommensurate (AFIC) phase: T (N2) aOE (c) T < T (N1)) can be represented by the propagation vector q (L) = (1/2 0 tau) with tau = 0.35(2). In contrast, the magnetic structure becomes commensurate with q (C) = (1/2 0 1/2) at 4 K (AntiFerromagnetic Commensurate (AFC) phase: T < T (N2)). The temperature dependence of magnetic intensity shows an apparent temperature hysteresis at T (N2), indicates a first-order transition at T (N2). Analysis of the integrated intensity at 4 K reveals that the Ho moment with a size of 8.6(2) A mu(B), oriented parallel to the c-axis in the AFC phase. While the successive transitions of HoCoGa5 are different from those of TbCoGa5, the magnetic structure in the AFC phase of HoCoGa5 is the same as the AF (I) (Tb) of TbCoGa5, and may indicate an additional transition at a lower temperature in HoCoGa5.
Title:
Structural and Magnetic Phase Transitions in the A(n)B(n)O(3n-2) Anion-Deficient Perovskites Pb2Ba2BiFe5O13 and Pb1.5Ba2.5Bi2Fe6O16
Authors:
Abakumov, AM; Batuk, M; Tsirlin, AA; Tyablikov, OA; Sheptyakov, DV; Filimonov, DS; Pokholok, KV; Zhidal, VS; Rozova, MG; Antipov, EV; Hadermann, J; Van Tendeloo, G Author Full Names: Abakumov, A. M.; Batuk, M.; Tsirlin, A. A.; Tyablikov, O. A.; Sheptyakov, D. V.; Filimonov, D. S.; Pokholok, K. V.; Zhidal, V. S.; Rozova, M. G.; Antipov, E. V.; Hadermann, J.; Van Tendeloo, G.
Source:
INORGANIC CHEMISTRY, 52 (14):7834-7843; 10.1021/ic3026667 JUL 15 2013
Abstract:
Novel anion-deficient perovskite-based ferrites Pb2Ba2BiFe5O13 and Pb1.5Ba2.5Bi2Fe6O16 were synthesized by solid-state reaction in air. Pb2Ba2BiFe5O13 and Pb1.5Ba2.5Bi2Fe6O16 belong to the perovskite-based A(n)B(n)O(3n-2) homologous series with n = 5 and 6, respectively, with a unit cell related to the perovskite subcell a(p) as a(p)root 2 x a(p) x na(p) root 2. Their structures are derived from the perovsldte one by slicing it with 1/2[110](p)((1) over bar 01)(p) crystallographic shear (CS) planes. The CS operation results in ((1) over bar 01)(p)-shaped perovsldte blocks with a thickness of (n - 2) FeO6 octahedra connected to each other through double chains of edge-sharing FeO5 distorted tetragonal pyramids which can adopt two distinct mirror-related configurations. Ordering of chains with a different configuration provides an extra level of structure complexity. Above T approximate to 750 K for Pb2Ba2BiFe5O13 and T approximate to 400 K for Pb1.5Ba2.5Bi2Fe6O16 the chains have a disordered arrangement. On cooling, a second-order structural phase transition to the ordered state occurs in both compounds. Symmetry changes upon phase transition are analyzed using a combination of superspace crystallography and group theory approach. Correlations between the chain ordering pattern and octahedral tilting in the perovskite blocks are discussed. Pb2Ba2BiFe5O13 and Pb1.5Ba2.5Bi2Fe6O16 undergo a transition into an antiferromagnetically (AFM) ordered state, which is characterized by a G-type AFM ordering of the Fe magnetic moments within the perovsldte blocks. The AFM perovsldte blocks are stacked along the CS planes producing alternating FM and AFM-aligned Fe-Fe pairs. In spite of the apparent frustration of the magnetic coupling between the perovskite blocks, all n = 4, 5, 6 A(n)Fe(n)O3(n-2) (A = Pb, Bi, Ba) feature robust antiferromagnetism with similar Neel temperatures of 623-632 K.
Title:
Surface-enhanced charge-density-wave instability in underdoped Bi2Sr2-xLaxCuO6+delta
Authors:
Rosen, JA; Comin, R; Levy, G; Fournier, D; Zhu, ZH; Ludbrook, B; Veenstra, CN; Nicolaou, A; Wong, D; Dosanjh, P; Yoshida, Y; Eisaki, H; Blake, GR; White, F; Palstra, TTM; Sutarto, R; He, F; Pereira, AF; Lu, Y; Keimer, B; Sawatzky, G; Petaccia, L; Damascelli, A Author Full Names: Rosen, J. A.; Comin, R.; Levy, G.; Fournier, D.; Zhu, Z. -H.; Ludbrook, B.; Veenstra, C. N.; Nicolaou, A.; Wong, D.; Dosanjh, P.; Yoshida, Y.; Eisaki, H.; Blake, G. R.; White, F.; Palstra, T. T. M.; Sutarto, R.; He, F.; Pereira, A. Frano; Lu, Y.; Keimer, B.; Sawatzky, G.; Petaccia, L.; Damascelli, A.
Source:
NATURE COMMUNICATIONS, 4 10.1038/ncomms2977 JUL 2013
Abstract:
Neutron and X-ray scattering experiments have provided mounting evidence for spin and charge ordering phenomena in underdoped cuprates. These range from early work on stripe correlations in Nd-LSCO to the latest discovery of charge-density-waves in YBa2Cu3O6 + x. Both phenomena are characterized by a pronounced dependence on doping, temperature and an externally applied magnetic field. Here, we show that these electron-lattice instabilities exhibit also a previously unrecognized bulk-surface dichotomy. Surface-sensitive electronic and structural probes uncover a temperature-dependent evolution of the CuO2 plane band dispersion and apparent Fermi pockets in underdoped Bi-2 Sr2-x La-x CuO6 + delta (Bi2201), which is directly associated with an hitherto-undetected strong temperature dependence of the incommensurate superstructure periodicity below 130 K. In stark contrast, the structural modulation revealed by bulk-sensitive probes is temperature-independent. These findings point to a surface-enhanced incipient charge-density-wave instability, driven by Fermi surface nesting. This discovery is of critical importance in the interpretation of single-particle spectroscopy data, and establishes the surface of cuprates and other complex oxides as a rich playground for the study of electronically soft phases.

Update: 12-Sep-2013

Title:
Two-dimensional alloy of immiscible Pb and Sn atoms on Ru(0001)
Authors:
Yuhara, J; Ishikawa, Y; Matsui, T Author Full Names: Yuhara, J.; Ishikawa, Y.; Matsui, T.
Source:
SURFACE SCIENCE, 616 131-136; 10.1016/j.susc.2013.05.018 OCT 2013
Abstract:
We investigated the atomic arrangements and phase diagrams of single and binary two-dimensional (2D) films of Pb and Sn on Ru(0001) using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). The Pb films formed the (root 7 x root 7) and c(2 x 4) structures in the saturated and unsaturated coverages, respectively, and their arrangements of Pb atoms were identified as hexagonal and rectangular structures. The Sn films formed the c(2 x 8) and incommensurate ("root 6 x root 3"), namely IC-1, at low coverages. Upon increasing the coverage, the IC-1 phase transformed into the commensurate (root 7 x root 3) structure and gradually extended to an incommensurate ("root 10 x root 3") structure, namely IC-2, at saturated coverages. The atomic arrangements of the Sn atoms were primarily rectangular-like structures. The 2D binary film exhibited an incommensurate structure close to (root 7 x root 7) at the Pb and Sn coverages of 0.15 +/- 0.05 ML and 0.40 +/- 0.05 ML, respectively. Atomically resolved STM images of the 2D binary films revealed a highly ordered hexagonal arrangement of Pb and Sn atoms with an average composition of PbSn3. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Antiferromagnetic order and the structural order-disorder transition in the Cd6Ho quasicrystal approximant
Authors:
Kreyssig, A; Beutier, G; Hiroto, T; Kim, MG; Tucker, GS; de Boissieu, M; Tamura, R; Goldman, AI Author Full Names: Kreyssig, Andreas; Beutier, Guillaume; Hiroto, Takanobu; Kim, Min Gyu; Tucker, Gregory S.; de Boissieu, Marc; Tamura, Ryuji; Goldman, Alan I.
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 93 (9):512-520; 10.1080/09500839.2013.815375 SEP 1 2013
Abstract:
It has generally been accepted that the orientational ordering of the Cd-4 tetrahedron within the Cd6R quasicrystal approximants is kinetically inhibited for R=Ho, Er, Tm and Lu by steric constraints. Our high-resolution X-ray scattering measurements of the Cd6Ho quasicrystal approximant, however, reveal an abrupt (first-order) transition to a monoclinic structure below T-S=178K for samples that have aged' at room temperature for approximately one year, reopening this question. Using X-ray resonant magnetic scattering at the Ho L-3-edge we have elucidated the nature of the antiferromagnetic ordering below T-N=8.5K in Cd6Ho. The magnetic Bragg peaks are found at the charge forbidden H+K+L=2n+1 positions, referenced to the high-temperature body-centred cubic structure. In general terms, this corresponds to antiferromagnetic arrangements of the Ho moments on adjacent clusters in the unit cell as previously found for Cd6Tb.
Title:
Local structure and hyperfine interactions of Fe-57 in NaFeAs studied by Mossbauer spectroscopy
Authors:
Presniakov, I; Morozov, I; Sobolev, A; Roslova, M; Boltalin, A; Son, V; Volkova, O; Vasiliev, A; Wurmehl, S; Buchner, B Author Full Names: Presniakov, I.; Morozov, I.; Sobolev, A.; Roslova, M.; Boltalin, A.; Son, V.; Volkova, O.; Vasiliev, A.; Wurmehl, S.; Buechner, B.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (34):10.1088/0953-8984/25/34/346003 AUG 28 2013
Abstract:
Detailed Fe-57 Mossbauer spectroscopy measurements on superconducting NaFeAs powder samples have been performed in the temperature range 13 K <= T < 300 K. The Fe-57 spectra recorded in the paramagnetic range (T > T-N approximate to 46 K) are discussed supposing that most of the Fe2+ ions are located in distorted (FeAs4) tetrahedra of NaFeAs phase, while an additional minor (< 10%) component of the spectra corresponds to impurity or intergrowth NaFe2As2 phase with a nominal composition near NaFe2As2. Our results reveal that the structural transition (T-S approximate to 55 K) has a weak effect on the electronic structure of iron ions, while at T <= T-N the spectra show a continuous distribution of hyperfine fields H-Fe. The shape of these spectra is analyzed in terms of two models: (i) an incommensurate spin density wave modulation of iron magnetic structure, (ii) formation of a microdomain structure or phase separation. It is shown that the hyperfine parameters obtained using these two methods have very similar values over the whole temperature range. Analysis of the temperature dependence H-Fe (T) with the Bean-Rodbell model leads to zeta = 1.16 +/- 0.05, suggesting that the magnetic phase transition is first order in nature. A sharp evolution of the V-ZZ(T) and eta(T) parameters of the full Hamiltonian of hyperfine interactions near T approximate to (T-N, T-S) is interpreted as a manifestation of the anisotropic electron redistribution between the d(xz)-, d(yz)- and d(xy)-orbitals of the iron ions.
Title:
Surface modification of Mg-67-Zn-30-Y-3 quasicrystal alloy by high current pulsed electron beam
Authors:
Gao, B; Hao, Y; Tu, GF; Li, SW; Yu, FX; Zuo, L; Hu, L Author Full Names: Gao, Bo; Hao, Yi; Tu, Ganfeng; Li, Shiwei; Yu, Fuxiao; Zuo, Liang; Hu, Liang
Source:
SURFACE & COATINGS TECHNOLOGY, 229 42-45; 10.1016/j.surfcoat.2012.06.026 AUG 25 2013
Abstract:
The HCPEB (high current pulsed electron beam) irradiation gives rise to rapid heating, melting and cooling of material surfaces, thereby improving surface properties of materials. In this paper, the surfaces of a Mg67Zn30Y3 quasicrystal alloy (Zn 50.86 wt.%, Y 7.02 wt.%, Mg balance) were bombarded by HCPEB. The surface microstructure variations of the Mg67Zn30Y3 alloy before and after HCPEB treatment were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM). The results show that the initial structure of the Mg67Zn30Y3 alloy consists of matrix Mg7Zn3, rich Mg phase (alpha-Mg) and quasicrystal Mg3Zn6Y. Under multiple HCPEB treatments, the phase boundaries become indistinct. The chemical composition of the surface layer tends to be a homogeneous distribution due to interdiffusion of alloying elements. Mg largely dissolved in the matrix by analyzing XRD patterns, causing the formation of supersaturated solid solution in surface layer. Besides, a nano-structured quasiaystal layer (grain size of 10-30 nm) is obtained after HCPEB treatment. By wear tests, the wear resistance of the HCPEB-treated samples is improved by a factor of 1.2 compared with that of the initial sample and the main reason can be attributed to the formation of a metastable structure during the HCPEB process. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Valence ordering in the intermediate-valence magnet YbPd
Authors:
Takahashi, R; Honda, T; Miyake, A; Kagayama, T; Shimizu, K; Ebihara, T; Kimura, T; Wakabayashi, Y Author Full Names: Takahashi, Ryo; Honda, Takashi; Miyake, Atsushi; Kagayama, Tomoko; Shimizu, Katsuya; Ebihara, Takao; Kimura, Tsuyoshi; Wakabayashi, Yusuke
Source:
PHYSICAL REVIEW B, 88 (5):10.1103/PhysRevB.88.054109 AUG 19 2013
Abstract:
An x-ray diffraction study reveals the valence-ordering structure in an intermediate-valence magnet YbPd with a CsCl structure. The valence of the Yb ions forms an incommensurate structure, characterized by the wave vector (+/- 0.07 +/- 0.07 1/2) below 130 K. At 105 K, the incommensurate structure turns into a commensurate structure, characterized by the wave vector (0 0 1/2). Based on the resonant x-ray diffraction spectra of the superlattice reflections, the valences of the Yb ions below 105 K are found to be 3+ and 2.6+. The origin of the long-wavelength modulation is discussed with the aid of an Ising model having next-nearest-neighbor interaction.
Title:
Phase transitions and their co-existence in TlGaSe2-TlCrS2(Se-2) systems
Authors:
Veliyev, RG; Seyidov, MHY; Kerimova, EM; Sadykhov, RZ; Asadov, YG; Seyidov, FM; Gasanov, NZ Author Full Names: Veliyev, R. G.; Seyidov, Mir Hasan Yu; Kerimova, E. M.; Sadykhov, R. Z.; Asadov, Yu G.; Seyidov, F. M.; Gasanov, N. Z.
Source:
BULLETIN OF MATERIALS SCIENCE, 36 (4):693-698; 10.1007/s12034-013-0530-8 AUG 2013
Abstract:
Investigation of dielectric properties of layered compound, TlGaSe2, showed that it is a ferroelectric (T (c) = 105 center dot 5 K) with an intermediate incommensurate phase (T (i) = 114 center dot 5 K). Our magnetic studies of layered compounds, TlCrS2 and TlCrSe2, for the first time revealed that the magnetic phase transition in these compounds are quasi two-dimensional ferromagnetic in nature and magnetic characteristics are T (C) = 90 K, T = 115 K, mu (eff) = 3 center dot 26 mu (B) and T (C) = 105 K, T = 120 K, mu (eff) = 3 center dot 05 mu (B) , respectively. Using the method of DTA, areas of homogeneous and heterogeneous coexistence of ferroelectric and ferromagnetic phase transitions in the systems, TlGaSe2-TlCrS2 and TlGaSe (2)-TlCrSe2, were identified. The low-dimensional solid solutions and eutectic alloys in these systems can be used as basic materials for plenty of functional recorders.
Title:
On the special points on the (P,T,x)- phase diagram for Sn2P2(Se x S1- x )(6) crystals: acoustic studies of Sn2P2(Se0.28S0.72)(6)
Authors:
Mys, O; Martynyuk-Lototska, I; Zapeka, B; Vlokh, R Author Full Names: Mys, O.; Martynyuk-Lototska, I.; Zapeka, B.; Vlokh, R.
Source:
PHILOSOPHICAL MAGAZINE, 93 (6):648-660; FEB 1 2013
Abstract:
On the basis of temperature dependences of the acoustic wave velocity and the acoustic attenuation in Sn2P2(Se0.28S0.72)(6) crystals under normal conditions and hydrostatic pressures, we show that increasing pressure causes these crystals to move away from the tricritical point and enter into the region of first-order phase transitions (PTs) in (P,T,x)-space. Still higher hydrostatic pressures lead to an increase in the attenuation of the acoustic wave with the velocity v(22) and broadening of its anomaly in the PT region, thus hinting at splitting of the PT, with the appearance of an intermediate incommensurate phase approximately at P=3.3kbar. We offer a (P,T,x)- phase diagram for the solid solutions Sn2P2(Se (x) S1- (x) )(6), which includes two special lines of PTs, tricritical and triple ones, which can intersect at the Lifshitz point at negative hydrostatic pressures. The variations of the surface of acoustic wave velocities occurring with changing temperature are obtained for Sn2P2(Se0.28S0.72)(6) crystals under the atmospheric pressure.
Title:
On the special points on the (P,T,x)- phase diagram for Sn2P2(Se x S1- x )6 crystals: acoustic studies of Sn2P2(Se0.28S0.72)(6)
Authors:
Mys, O; Martynyuk-Lototska, I; Zapeka, B; Vlokh, R Author Full Names: Mys, O.; Martynyuk-Lototska, I.; Zapeka, B.; Vlokh, R.
Source:
PHILOSOPHICAL MAGAZINE, 93 (6):648-660; 10.1080/14786435.2012.728010 FEB 1 2013
Abstract:
On the basis of temperature dependences of the acoustic wave velocity and the acoustic attenuation in Sn2P2(Se0.28S0.72)(6) crystals under normal conditions and hydrostatic pressures, we show that increasing pressure causes these crystals to move away from the tricritical point and enter into the region of first-order phase transitions (PTs) in (P,T,x)-space. Still higher hydrostatic pressures lead to an increase in the attenuation of the acoustic wave with the velocity v(22) and broadening of its anomaly in the PT region, thus hinting at splitting of the PT, with the appearance of an intermediate incommensurate phase approximately at P=3.3kbar. We offer a (P,T,x)- phase diagram for the solid solutions Sn2P2(Se (x) S1- (x) )(6), which includes two special lines of PTs, tricritical and triple ones, which can intersect at the Lifshitz point at negative hydrostatic pressures. The variations of the surface of acoustic wave velocities occurring with changing temperature are obtained for Sn2P2(Se0.28S0.72)(6) crystals under the atmospheric pressure.
Title:
A review of phase transitions in RbIn-molybdate
Authors:
Zapart, MB; Zapart, W Author Full Names: Zapart, Maria B.; Zapart, Wlodzimierz
Source:
NUKLEONIKA, 58 (3):365-370; 2013
Abstract:
The paper gives a brief review of the results of EPR temperature studies of RbIn(MoO4)(2) crystal. A sequence of several structural phase transitions has been found in this crystal in the temperature region 84-163 K. The transition at T-1 = 163 K leads to an incommensurate triply modulated state, whereas ferroelastic phases start below T-2 = 143 K. All the low temperature phases in the temperature region 84-143 K are examples of simultaneously ferroelastic and incommensurate ones. The transition observed at T-5 = 84 K seems to suppress the ferroelastic properties of the crystal.
Title:
Elliptic holes in octagonal quasicrystals
Authors:
Li, LH Author Full Names: Li Lian-He
Source:
CHINESE PHYSICS B, 22 (1):10.1088/1674-1056/22/1/016102 JAN 2013
Abstract:
The stress potential function theory for the plane elasticity of octagonal quasicrystals is developed. By introducing stress functions, a large number of basic equations involving the elasticity of octagonal quasicrystals are reduced to a single partial differential equation. Furthermore, we develop the complex variable function method (Lekhnitskii method) for anisotropic elasticity theory to that for quasicrystals. With the help of conformal transformation, an exact solution for the elliptic hole of quasicrystals is presented. The solution of the Griffith crack problem, as a special case of the results, is obtained. As a consequence, the phonon stress intensity factor is derived analytically.

Update: 5-Sep-2013

Title:
Crystal and magnetic structure of TbFe0.25Ge2 compound
Authors:
Gil, A; Hoser, A; Penc, B; Szytula, A Author Full Names: Gil, A.; Hoser, A.; Penc, B.; Szytula, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 344 167-170; 10.1016/j.jmmm.2013.05.055 OCT 2013
Abstract:
The crystal and magnetic structure of polycrystalline TbFe0.25Ge2 sample have been determined. X-ray and neutron diffraction studies indicate that this compound has the orthorhombic CeNiSi2-type crystal structure (space group Cmcm). The magnetic ordering, based on the neutron diffraction data in low temperature, is described by two components: a collinear antiferromagnetic G-type and a cosine-wave modulated one. In the collinear G-type structure the Tb magnetic moment is equal to 3.81(5) mu(B) and it is parallel to the c-axis. The modulated structure is described by the propagation vector k=(0.460(8), 0, 0.305(1)), the Tb magnetic moment equals 7.75(8) mu(B), lies in b-c and forms an angle 23(2)degrees with the c-axis. The collinear component decreases to zero at 22.6 K while the modulated one at 190.8 K. (C) 2013 Elsevier BY. All rights reserved.
Title:
Magnetic ordering in GdNi2B2C revisited by resonant x-ray scattering: Evidence for the double-q model
Authors:
Normile, PS; Rotter, M; Detlefs, C; Jensen, J; Canfield, PC; Blanco, JA Author Full Names: Normile, P. S.; Rotter, M.; Detlefs, C.; Jensen, J.; Canfield, P. C.; Blanco, J. A.
Source:
PHYSICAL REVIEW B, 88 (5):10.1103/PhysRevB.88.054413 AUG 14 2013
Abstract:
Recent theoretical efforts aimed at understanding the nature of antiferromagnetic ordering in GdNi2B2C predicted double-q ordering. Here we employ resonant elastic x-ray scattering to test this theory against the formerly proposed, single-q ordering scenario. Our study reveals a satellite reflection associated with a mixed-order component propagation wave vector, viz., (q(a),2q(b), 0) with q(b) = q(a) approximate to 0.55 reciprocal lattice units, the presence of which is incompatible with single-q ordering but is expected from the double-q model. A (3q(a),0,0) wave vector (i.e., third-order) satellite is also observed, again in line with the double-q model. The temperature dependencies of these along with that of a first-order satellite are compared with calculations based on the double-q model and reasonable qualitative agreement is found. By examining the azimuthal dependence of first-order satellite scattering, we show the magnetic order to be, as predicted, elliptically polarized at base temperature and find the temperature dependence of the "out of a-b plane" moment component to be in fairly good agreement with calculation. Our results provide qualitative support for the double-q model and thus in turn corroborate the explanation for the "magnetoelastic paradox" offered by this model.
Title:
Observation of a reentrant phase transition in incommensurate potassium
Authors:
Lundegaard, LF; Stinton, GW; Zelazny, M; Guillaume, CL; Proctor, JE; Loa, I; Gregoryanz, E; Nelmes, RJ; McMahon, MI Author Full Names: Lundegaard, L. F.; Stinton, G. W.; Zelazny, M.; Guillaume, C. L.; Proctor, J. E.; Loa, I.; Gregoryanz, E.; Nelmes, R. J.; McMahon, M. I.
Source:
PHYSICAL REVIEW B, 88 (5):10.1103/PhysRevB.88.054106 AUG 14 2013
Abstract:
The phase transitions in the host-guest composite structure of potassium have been determined between 19 and 54 GPa by a combination of x-ray powder and single-crystal diffraction. The guest component of the incommensurate composite phase K-III undergoes an "intraphase" transition at 30.0(7) GPa from a C-centered tetragonal structure to an A-centered orthorhombic form. At 39.7(5) GPa, the guest component undergoes a reentrant transition back to the C-centered tetragonal form. This is the first such reentrant transition observed in the composite structures of the elements. The transition in the guest at 30.0(7) GPa is preceded by a loss of the c-glide symmetry of the host component of the structure, and this is not recovered until some 3 GPa after the reentrant transition at 39.7 GPa.
Title:
Controlled Magnetic Reversal in Permalloy Films Patterned into Artificial Quasicrystals
Authors:
Bhat, VS; Sklenar, J; Farmer, B; Woods, J; Hastings, JT; Lee, SJ; Ketterson, JB; De Long, LE Author Full Names: Bhat, V. S.; Sklenar, J.; Farmer, B.; Woods, J.; Hastings, J. T.; Lee, S. J.; Ketterson, J. B.; De Long, L. E.
Source:
PHYSICAL REVIEW LETTERS, 111 (7):10.1103/PhysRevLett.111.077201 AUG 12 2013
Abstract:
We have patterned novel Permalloy thin films with quasicrystalline Penrose P2 tilings and measured their dc magnetization and ferromagnetic resonance absorption. Reproducible anomalies in the hysteretic, low-field data signal a series of abrupt transitions between ordered magnetization textures, culminating in a smooth evolution into a saturated state. Micromagnetic simulations compare well to experimental dc hysteresis loops and ferromagnetic resonance spectra and indicate that systematic control of magnetic reversal and domain wall motion can be achieved via tiling design, offering a new paradigm of magnonic quasicrystals.
Title:
Caged clusters in Al11Ir4: Structural transition and insulating phase
Authors:
Mihalkovic, M; Henley, CL Author Full Names: Mihalkovic, Marek; Henley, C. L.
Source:
PHYSICAL REVIEW B, 88 (6):10.1103/PhysRevB.88.064201 AUG 2 2013
Abstract:
Using pair potentials fitted to an ab initio database, combined with replica-exchange simulated annealing, we show that the complex, quasicrystal-related Al11Ir4 compound contains a nonstandard version of the "pseudo-Mackay" icosahedral cluster, with nonicosahedral inner Al10Ir and/or Al9Ir clusters that exist in various orientations and account for partial occupancies in the reported structure. We found two different compositions with different orientationally ordered grounds, each doubling the (cubic) unit cell and each reached by a first-order thermal transition. One of these is metallic and the other is insulating.
Title:
Computing Phase Diagrams for a Quasicrystal-Forming Patchy-Particle System
Authors:
Reinhardt, A; Romano, F; Doye, JPK Author Full Names: Reinhardt, Aleks; Romano, Flavio; Doye, Jonathan P. K.
Source:
PHYSICAL REVIEW LETTERS, 110 (25):10.1103/PhysRevLett.110.255503 JUN 20 2013
Abstract:
We introduce an approach to computing the free energy of quasicrystals, which we use to calculate phase diagrams for systems of two-dimensional patchy particles with five regularly arranged patches that have previously been shown to form dodecagonal quasicrystals. We find that the quasicrystal is a thermodynamically stable phase for a wide range of conditions and remains a robust feature of the system as the potential's parameters are varied. We also demonstrate that the quasicrystal is entropically stabilized over its crystalline approximants.
Title:
Elliptic holes in octagonal quasicrystals
Authors:
Li, LH Author Full Names: Li Lian-He
Source:
CHINESE PHYSICS B, 22 (1):10.1088/1674-1056/22/1/016102 JAN 2013
Abstract:
The stress potential function theory for the plane elasticity of octagonal quasicrystals is developed. By introducing stress functions, a large number of basic equations involving the elasticity of octagonal quasicrystals are reduced to a single partial differential equation. Furthermore, we develop the complex variable function method (Lekhnitskii method) for anisotropic elasticity theory to that for quasicrystals. With the help of conformal transformation, an exact solution for the elliptic hole of quasicrystals is presented. The solution of the Griffith crack problem, as a special case of the results, is obtained. As a consequence, the phonon stress intensity factor is derived analytically.

Update: 29-Aug-2013

Title:
Microstructure, texture and mechanical properties of as-extruded Mg-Zn-Er alloys
Authors:
Wang, QF; Du, WB; Liu, K; Wang, ZH; Li, SB; Wen, K Author Full Names: Wang, Qingfeng; Du, Wenbo; Liu, Ke; Wang, Zhaohui; Li, Shubo; Wen, Kai
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 581 31-38; 10.1016/j.msea.2013.05.055 OCT 1 2013
Abstract:
In the present work, the microstructure, texture and mechanical properties of the as-extruded Mg-xZn-yEr (x=3, 6 and 9; y=0.5,1 and 1.5; x/y= 6) alloys were investigated. The results showed that the I-phase in the as-cast alloys was destroyed and lots of nano-scale quasicrystalline particles were precipitated within the matrix during hot extrusion process. With the increase in the volume fraction of the primary I-phase, the particle-stimulated nucleation (PSN) of recrystallization was activated. It was suggested that the recrystallization via PSN should lead to the nucleation of new grains with a high orientation mismatch to the parent grains, making the texture gradually weaken. Significant strengthening is achieved in the Mg-9Zn-1.5Er alloy, of which the ultimate tensile strength (sigma(b)) and the yield tensile strength (sigma(0.2)) were 319 MPa and 192 MPa, respectively, with an elongation of 22.3%. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Effect of pretreatment and annealing on microstructure and mechanical properties of Mg-1.5Zn-0.25Gd (at%) alloys reinforced with quasicrystal
Authors:
Huang, H; Chen, CL; Wang, ZC; Li, YP; Yuan, GY Author Full Names: Huang, Hua; Chen, Chunlin; Wang, Zhongchang; Li, Yunping; Yuan, Guangyin
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 581 73-82; 10.1016/j.msea.2013.06.003 OCT 1 2013
Abstract:
Mg-1.5Zn-025Gd-based alloys containing the icosahedral quasicrystalline phase (I-phase) were fabricated to investigate the effect of heat treatment on the microstructure, mechanical properties and anisotropy of the as-extruded alloys. The results show that compared with the samples extruded without homogenized annealing, the samples extruded after homogenized annealing show larger grains, lower strength and elongation, which can be attributed to the secondary-phase particles precipitated in the matrix after homogenized annealing and to the fact that only a few volume fraction of nano-scale I-phase is precipitated in the matrix during extrusion. Moreover, the anisotropy is mitigated in the alloys extruded at as-cast condition because of the grain refinement and the I-phase precipitation. We also find that after annealing at 473 K or 673 K, yield strength decreases while the elongation increases slightly, indicating that annealing has a small effect on the improvement of room-temperature strength, especially the one at relatively higher temperature. The choice of appropriate annealing temperature only imposes a little impact on the ductility enhancement of the extruded samples. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Modulated structure of Lu4AlCu2B9O23 from low-temperature single-crystal X-ray data
Authors:
Bolotina, N; Plachinda, P; Belokoneva, E Author Full Names: Bolotina, Nadezhda; Plachinda, Paul; Belokoneva, Elena
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 69 329-335; 10.1107/S2052519213014231 4 AUG 2013
Abstract:
A second-order phase transition with both displacive and disorder mechanisms was discovered in Lu4AlCu2B9O23 using single-crystal X-ray diffraction techniques by cooling down the sample to 110 K. Low-temperature structure modulations are mainly associated with Cu atoms surrounded by O atoms. The fivefold asymmetric environment leads to a special copper position splitting into a pair of general ones so that four O atoms coordinate each of them. Each copper site is 50% occupied at room temperature, but at lower temperature statistical disorder gives occupation and displacive modulations with a wavevector of q = 0.132c*. Tetragonal P (4) over bar2(1)m symmetry of the non-modulated phase transforms into an orthorhombic (3+1)-dimensional symmetry, P2(1)2(1)2(00 gamma)00s, whereas the (4) over bar axis becomes the twinning axis.
Title:
Symmetry Rule of the Landau Free Energy in the Phonon-Originating Phase Transition
Authors:
Kubo, H; Khazaei, M Author Full Names: Kubo, Hiroshi; Khazaei, Mohammad
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (8):10.7566/JPSJ.82.084601 AUG 2013
Abstract:
We propose a pseudopotential model of the Landau free energy. A novel symmetry rule is manifested in the microscopic description of the model. Followed by ab initio calculations, a method of analyzing the mechanism of a weakly first-order phase transition is established. The model is applied to the pre-omega phase transition in Zr metal and in Zr-20% Nb (Zr-20Nb) alloy. The criterion is elucidated for the commensurate (C) omega-to-incommensurate (IC) omega phase transition by estimating the soliton (anti-omega phase wall) formation energy of the IC omega phase. The quantitative calculation of the reaction path in the thermodynamical potential field has explained the crystal structural difference of the pre-omega phase between Zr metal (C structure) and Zr-20Nb alloy (IC structure). The results of the phase stability are summarized in a energy-phase diagram.
Title:
Phonon anomalies and lattice dynamics in the superconducting oxychlorides Ca2-xCuO2Cl2
Authors:
d'Astuto, M; Yamada, I; Giura, P; Paulatto, L; Gauzzi, A; Hoesch, M; Krisch, M; Azuma, M; Takano, M Author Full Names: d'Astuto, Matteo; Yamada, Ikuya; Giura, Paola; Paulatto, Lorenzo; Gauzzi, Andrea; Hoesch, Moritz; Krisch, Michael; Azuma, Masaki; Takano, Mikio
Source:
PHYSICAL REVIEW B, 88 (1):10.1103/PhysRevB.88.014522 JUL 24 2013
Abstract:
We present a comprehensive study of the phonon dispersion in an underdoped, superconducting Ca2-xCuO2Cl2 crystal. We interpret the results using lattice dynamical calculations based on a shell model, and we compare the results to other hole-doped cuprates, in particular, to the ones isomorphic to La2-xSrxCuO4 (LSCO). We found that an anomalous dip in the Cu-O bond stretching dispersion develops in oxychlorides with a simultaneous marked broadening of the mode. The broadening is maximum at approximate to[pi/(2a) 0 0], which corresponds to the charge-modulation propagation vector. Our analysis also suggests that screening effects in calculations may cause an apparent cosine-shaped bending of the Cu-O bond-stretching dispersion along both the (q 0 0) and (q q 0) directions, which is not observed on the data close to optimal doping. This observation suggests that the discrepancy between experimental data and ab initio calculations on this mode originates from an overestimation of the doping effects on the mode.
Title:
The electronic structure and magnetism of BaTi2Sb2O
Authors:
Wang, GT; Zhang, HP; Zhang, L; Liu, C Author Full Names: Wang, Guangtao; Zhang, Huiping; Zhang, Lin; Liu, Chang
Source:
JOURNAL OF APPLIED PHYSICS, 113 (24):10.1063/1.4812489 JUN 28 2013
Abstract:
The electronic structure and magnetic structures of recently discovered BaTi2Sb2O were studied from first-principles calculations. In the nonmagnetic state, the density of states at the Fermi level are mostly derived from the d(z2); d(x2-y2), and d(xy) orbitals. The Fermi surface (FS) consists of three sheets. The first FS sheet (along X-R line) will nest with the third FS sheet (along M-A line) by the q-vector (q) over right arrow (1) = (pi/a, 0, 0) or (q) over right arrow (2) = (0, pi/a, 0) shift. The calculated bare susceptibility chi(0)(q) peaked at X-point, rather than at the M-point in the FeAs-based superconductor. Such peaked susceptibility induces the spin density wave, and the magnetic ground state is nearly two degenerate antiferromagnetism the bi-collinear antiferromagnetism (AF3) or the blocked checkerboard antiferromagnetism (AF4). The peak of susceptibility chi(0)(q) is obviously suppressed and become slightly in-commensurate with hole doping, but increased with electron doping. When the spin fluctuation is suppressed, the superconductivity appears. This can explain that why the superconductivity appears only in the hole-doped compounds, not in the electron-doped ones. (C) 2013 AIP Publishing LLC.
Title:
Interaction of a dislocation with an elliptical hole in icosahedral quasicrystals
Authors:
Li, LH; Liu, GT Author Full Names: Li, Lian He; Liu, Guan Ting
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 93 (3):142-151; 10.1080/09500839.2012.752883 MAR 1 2013
Abstract:
The interaction between a dislocation and an elliptical hole in icosahedral quasicrystals is considered. An explicit expression for the complex potential is derived using the extended Stroh formalism. Based on the conformal mapping method and a perturbation technique, closed-form solutions are obtained. The field intensity factors at a crack tip and the image forces on the dislocation arising from the crack are calculated. The effects of phonon-phason elastic coupling on the mechanical behavior are also observed.

Update: 21-Aug-2013

Title:
Lead nitroprusside: A new precursor for the synthesis of the multiferroic Pb2Fe2O5, an anion-deficient perovskite
Authors:
Gil, DM; Nieva, G; Franco, DG; Gomez, MI; Carbonio, RE Author Full Names: Gil, Diego M.; Nieva, Gladys; Franco, Diego G.; Ines Gomez, Maria; Carbonio, Raul E.
Source:
MATERIALS CHEMISTRY AND PHYSICS, 141 (1):355-361; 10.1016/j.matchemphys.2013.05.022 AUG 15 2013
Abstract:
In order to investigate the formation of multiferroic oxide Pb2Fe2O5, the thermal decomposition of Pb [Fe(CN)(5)NO] has been studied. The complex precursor and the thermal decomposition products were characterized by IR and Raman spectroscopy, thermal analysis, powder X-ray diffraction (PXRD), scanning electron microscopy and magnetic measurements. The crystal structure of Pb[Fe(CN)(5)NO] was refined by Rietveld analysis. It crystallizes in the orthorhombic system, space group Pnma. The thermal decomposition in air produces highly pure Pb2Fe2O5 as final product. This oxide is an anion deficient perovskite with an incommensurate superstructure. The magnetic measurements confirm that Pb2Fe2O5 shows a weak ferromagnetic signal probably due to disorder in the perfect antiferromagnetic structure or spin canting. The estimated ordering temperature from the fit of a phenomenological model was 520 K. The SEM images reveal that the thermal decomposition of Pb[Fe(CN)(5)NO] produces Pb2Fe2O5 with small particle size. (C) 2013 Elsevier B.V. All rights reserved.
Title:
QUASICRYSTALS Model structures
Authors:
de Boissieu, M Author Full Names: de Boissieu, Marc
Source:
NATURE MATERIALS, 12 (8):692-693; 10.1038/nmat3725 AUG 2013
Title:
A family of binary magnetic icosahedral quasicrystals based on rare earths and cadmium
Authors:
Goldman, AI; Kong, T; Kreyssig, A; Jesche, A; Ramazanoglu, M; Dennis, KW; Bud'ko, SL; Canfield, PC Author Full Names: Goldman, Alan I.; Kong, Tai; Kreyssig, Andreas; Jesche, Anton; Ramazanoglu, Mehmet; Dennis, Kevin W.; Bud'ko, Sergey L.; Canfield, Paul C.
Source:
NATURE MATERIALS, 12 (8):714-718; 10.1038/NMAT3672 AUG 2013
Abstract:
Examples of stable binary icosahedral quasicrystals are relatively rare, and at present there are no known examples featuring localized magnetic moments. These would represent an ideal model system for attaining a deeper understanding of the nature of magnetic interactions in aperiodic lattices. Here we report the discovery of a family of at least seven rare earth icosahedral binary quasicrystals, i-R-Cd (R = Gd to Tm, Y), six of which bear localized magnetic moments. Our work highlights the importance of carefully motivated searches through phase space(1) and supports the proposal that, like icosahedral Sc12Zn88 (ref. 2), binary quasicrystalline phases may well exist nearby known crystalline approximants, perhaps as peritectically forming compounds with very limited liquidus surfaces, offering very limited ranges of composition/temperature for primary solidification.
Title:
Pseudo-Fivefold Diffraction Symmetries in Tetrahedral Packing
Authors:
Lee, S; Henderson, R; Kaminsky, C; Nelson, Z; Nguyen, J; Settje, NF; Schmidt, JT; Feng, J Author Full Names: Lee, Stephen; Henderson, Ryan; Kaminsky, Corey; Nelson, Zachary; Jeffers Nguyen; Settje, Nick F.; Schmidt, Joshua Teal; Feng, Ji
Source:
CHEMISTRY-A EUROPEAN JOURNAL, 19 (31):10244-10270; 10.1002/chem.201203758 JUL 29 2013
Abstract:
We review the way in which atomic tetrahedra composed of metallic elements pack naturally into fused icosahedra. Orthorhombic, hexagonal, and cubic intermetallic crystals based on this packing are all shown to be united in having pseudo-fivefold rotational diffraction symmetry. A unified geometric model involving the 600-cell is presented: the model accounts for the observed pseudo-fivefold symmetries among the different Bravais lattice types. The model accounts for vertex-, edge-, polygon-, and cell-centered fused-icosahedral clusters. Vertex-centered and edge-centered types correspond to the well-known pseudo-fivefold symmetries in I-h and D-5h quasicrystalline approximants. The concept of a tetrahedrally-packed reciprocal space cluster is introduced, the vectors between sites in this cluster corresponding to the principal diffraction peaks of fused-icosahedrally-packed crystals. This reciprocal-space cluster is a direct result of the pseudosymmetry and, just as the real-space clusters, can be rationalized by the 600-cell. The reciprocal space cluster provides insights for the Jones model of metal stability. For tetrahedrally-packed crystals, Jones zone faces prove to be pseudosymmetric with one another. Lower and upper electron per atom bounds calculated for this pseudosymmetry-based Jones model are shown to accord with the observed electron counts for a variety of Group 10-12 tetrahedrally-packed structures, among which are the four known Cu/Cd intermetallic compounds: CdCu2, Cd-3 Cu-4, Cu-5 Cd-8, and Cu3Cd10. The rationale behind the Jones lower and upper bounds is reviewed. The crystal structure of Zn11Au15Cd23, an example of a 1: 1 MacKay cubic quasicrystalline approximant based solely on Groups 10-12 elements is presented. This compound crystallizes in Im (3) over bar (space group no. 204) with a= 13.842(2) angstrom. The structure was solved with R-1= 3.53%, I> 2 sigma;= 5.33%, all data with 1282/0/38 data/restraints/parameters.

Update: 15_Aug_2013

Title:
On importance of higher non-linear interactions in the theory of type II incommensurate systems
Authors:
Korda, VY; Berezovsky, SV; Molev, AS; Korda, LP; Klepikov, VF Author Full Names: Korda, V. Yu.; Berezovsky, S. V.; Molev, A. S.; Korda, L. P.; Klepikov, V. F.
Source:
PHYSICA B-CONDENSED MATTER, 425 31-33; 10.1016/j.physb.2013.05.021 SEP 15 2013
Abstract:
We reveal that the role of the higher non-linear local interactions in the conventional theoretical models developed to describe phase transitions in type II incommensurate systems is underestimated. Their consistent consideration in the thermodynamic potential expansion allows one to remove key contradictions in explanation of the experimental data for ferroelectric Sn2P2Se6 in the vicinity of the modulated-commensurate phase transition point. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Topological floating phase in a spatially anisotropic frustrated Ising model
Authors:
Kalz, A; Chitov, GY Author Full Names: Kalz, Ansgar; Chitov, Gennady Y.
Source:
PHYSICAL REVIEW B, 88 (1):10.1103/PhysRevB.88.014415 JUL 16 2013
Abstract:
We present results for the ordering process of a two-dimensional Ising model with anisotropic frustrating next-nearest-neighbor interactions. We concentrate on a specific wide temperature and parameter region to confirm the existence of two particular phases of the model. The first phase is an incommensurate algebraically ordered (floating) phase emerging at the transition from the paramagnetic high-temperature phase. Then the model undergoes a transition to an antiferromagnetically ordered second phase with diagonal ferromagnetic stripes [ordering wave vector q = (pi/2, pi/2)]. We analyze the unconventional features appearing in several observables, e.g., energy, structure factors, and correlation functions, by means of extensive Monte Carlo simulations and examine carefully the influence of the lattice sizes. For the analytical study of the intermediate phase the Villain-Bak theory is adapted for the present model. Combining both the numerical and analytical work we present the quantitative phase diagram of the model, and, in particular, argue in favor of an intermediate topological floating phase.
Title:
Frustrated Octahedral Tilting Distortion in the Incommensurately Modulated Li3xNd2/3-xTiO3 Perovskites
Authors:
Abakumov, AM; Erni, R; Tsirlin, AA; Rossell, MD; Batuk, D; Nenert, G; Van Tendeloo, G Author Full Names: Abakumov, Artem M.; Erni, Rolf; Tsirlin, Alexander A.; Rossell, Marta D.; Batuk, Dmitry; Nenert, Gwilherm; Van Tendeloo, Gustaaf
Source:
CHEMISTRY OF MATERIALS, 25 (13):2670-2683; 10.1021/cm4012052 JUL 9 2013
Abstract:
Perovskite-structured titanates with layered A-site ordering form remarkably complex superstructures. Using transmission electron microscopy, synchrotron X-ray and neutron powder diffraction, and ab initio structure relaxation, we present the structural solution of the incommensurately modulated Li3xNd2/3-xTiO3 perovskites (x = 0.05, superspace group Pmmm(alpha(1),1/2,0)000(1/2,beta(2) 0)000, a = 3.831048(5) angstrom, b = 3.827977(4) angstrom, c = 7.724356(8) angstrom, q(1) = 0.45131(8)a* + 1/2b*, q(2) = 1/2a* + 0.41923(4)b*). In contrast to earlier conjectures on the nanoscale compositional phase separation in these materials, all peculiarities of the superstructure can be understood in terms of displacive modulations related to an intricate octahedral tilting pattern. It involves fragmenting the pattern of the out-of-phase tilted TiO6 octahedra around the a- and b-axes into antiphase domains, superimposed on the pattern of domains with either, pronounced or suppressed in-phase tilt component around the c-axis. The octahedral tilting competes with the second order Jahn-Teller distortion of the TiO6 octahedra. This competition is considered as the primary driving force for the modulated structure. The A cations are suspected to play a role in this modulation affecting it mainly through the tolerance factor and the size variance. The reported crystal structure calls for a revision of the structure models proposed for the family of layered A-site ordered perovskites exhibiting a similar type of modulated structure.
Title:
Dissipative soliton generation in an active ring resonator based on magnonic quasicrystal with Fibonacci type structure
Authors:
Grishin, SV; Beginin, EN; Sharaevskii, YP; Nikitov, SA Author Full Names: Grishin, S. V.; Beginin, E. N.; Sharaevskii, Yu. P.; Nikitov, S. A.
Source:
APPLIED PHYSICS LETTERS, 103 (2):10.1063/1.4813411 JUL 8 2013
Abstract:
This study reports on the experimental investigations of a magnetostatic surface wave (MSSW) propagation in a magnonic quasicrystal (MQC) with Fibonacci type structure. It is shown that such structure has a greater number of band gaps and narrower pass bands located between them than a periodic structure. These features of the MQC and three-wave decay of the MSSW are used in a MQC active ring resonator for the eigenmode selection and dissipative soliton self-generation. (C) 2013 AIP Publishing LLC.
Title:
Critical exponents of ferroelectric transitions in modulated SrTiO3: Consequences of quantum fluctuations and quenched disorder
Authors:
Wang, JX; Liu, MF; Yan, ZB; Liu, JM Author Full Names: Wang Jing-Xue; Liu Mei-Feng; Yan Zhi-Bo; Liu Jun-Ming
Source:
CHINESE PHYSICS B, 22 (7):10.1088/1674-1056/22/7/077701 JUL 2013
Abstract:
The ferroelectric transitions of several SrTiO3-based ferroelectrics are investigated experimentally and theoretically, with special attention to the critical scaling exponents associated with the phase transitions, in order to understand the competition among quantum fluctuations (QFs), quenched disorder, and ferroelectric ordering. Two representative systems with sufficiently strong QFs and quenched disorders in competition with the ferroelectric ordering are investigated. We start from non-stoichiometric SrTiO3 (STO) with the Sr/Ti ratio deviating slightly from one, which is believed to maintain strong QFs. Then, we address Ba/Ca co-doped Sr1-x(Ca0.6389Ba0.3611)(x)TiO3 (SCBT) with the averaged Sr-site ionic radius identical to the Sr2+ ionic radius, which is believed to offer remarkable quenched disorder associated with the Sr-site ionic mismatch. The critical exponents associated with polarization P and dielectric susceptibility e, respectively, as functions of temperature T close to the critical point T-c, are evaluated. It is revealed that both non-stoichiometric SrTiO3 and SCBT exhibit much bigger critical exponents than the Landau mean-field theory predictions. These critical exponents then decrease gradually with increasing doping level or deviation of Sr/Ti ratio from one. A transverse Ising model applicable to the Sr-site doped STO (e.g., Sr1-xCaxTiO3) at low level is used to explain the observed experimental data. It is suggested that the serious deviation of these critical exponents from the Landau theory predictions in these STO-based systems is ascribed to the significant QFs and quenched disorder by partially suppressing the long-range spatial correlation of electric dipoles around the transitions. The present work thus sheds light on our understanding of the critical behaviors of ferroelectric transitions in STO in the presence of quantum fluctuations and quenched disorder, whose effects have been demonstrated to be remarkable.
Title:
The composite modulated structure of cupropearceite and cupropolybasite and its behavior toward low temperature
Authors:
Bindi, L; Schaper, AK; Kurata, H; Menchettii, S Author Full Names: Bindi, Luca; Schaper, Andreas K.; Kurata, Hiroki; Menchettii, Silvio
Source:
AMERICAN MINERALOGIST, 98 (7):1279-1284; 10.2138/am.2013.4380 JUL 2013
Abstract:
Cupropearceite, [(Cu3.51Ag2.50Fe0.01)(Sigma 6.02)(AS(1.72)Sb(0.24))(Sigma 1.96)S-7[Ag9CuS4], and cupropolybasite, [(Cu3.82Ag2.42Zn0.02Pb0.01)(Sigma 6.27)(Sb1.19As0.73)(Sigma 1.92)S-7][Ag9CuS4], both exhibit fast-ion conduction at very low temperatures. The structural relationship between the various phases is not fully understood as yet and is addressed in this study. Samples of these materials were studied by means of synchrotron radiation at room temperature and transmission electron microscopy at room temperature and low temperature (both liquid N-2 and liquid He) to have a better understanding of the stabilization of the fast-ion conducting form at low and ultra-low temperature in these minerals. The study at room temperature did not evidence any doubling of unit-cell parameters with respect to the basic Tac unit cell, of the type typically observed for minerals of the pearceite-polybasite group. On the other hand, relatively strong and well-defined satellite reflections relating to the pseudo-hexagonal arrangement of the Ag+ ions at G +/- similar to 1.39(1) < 110 >* positions of the reciprocal space, where G represents the average structure Bragg reflections, were clearly observed. Although this seems to suggest that the Ag+ ion distribution can adequately be described by a two-dimensional displacive modulation of the average P (3) over bar ml structure (Tac polytype) with the incommensurate modulation wave vectors of the *satellite reflections* q(1) = similar to 0.39(1) (a(F)* + b(F)*) and q(2) = similar to 0.39(I)(a(F)* - b(F)*), where the subscript F indicates the framework substructure, the structure observed is better described as a composite modulated structure because of the intensity asymmetry of the satellite reflections. Low-temperature TEM investigations show that the satellites are still present at both 90 and 4.2 K, with a remarkable temperature-dependent shift in their positions giving rise to a variation of the coefficient a of the modulation vectors from 0.39 at room temperature, trough similar to 0.40 at 90 K to similar to 0.5 at 4.2 K. Thus, the incommensurate modulation, strengthened by the very low temperature, approaches almost the alpha similar to 0.5 value, indicative of a commensurate modulation. The 4.2 K structure could thus be a low-temperature commensurate superstructure ("lock-in phase"), observed for the first time in the minerals of the pearceite-polybasite group.
Title:
Concentrational *commensurate-*incommensurate magnetic phase transition in Y1-x Tb (x) Mn6Sn6
Authors:
Bogdanov, SG; Mushnikov, NV; Terent'ev, PB; Gerasimov, EG; Grogor'ev, SV; Okorokov, AI; Chetverikov, YO; Ekerleb, G; Pranzas, K; Pirogov, AN Author Full Names: Bogdanov, S. G.; Mushnikov, N. V.; Terent'ev, P. B.; Gerasimov, E. G.; Grogor'ev, S. V.; Okorokov, A. I.; Chetverikov, Yu. O.; Ekerleb, G.; Pranzas, K.; Pirogov, A. N.
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 114 (7):566-572; 10.1134/S0031918X13070028 JUL 2013
Abstract:
The magnetic state of Y1 - x Tb (x) Mn6Sn6 (with x a parts per thousand currency sign 0.25) alloy is studied at different temperatures and magnetic fields by neutron diffraction. The alloy with x (c) = 0.22 exhibits an incommensurate-to-commensurate structure phase transition. The transition is accompanied by a decrease in the unit-cell volume. The weak dependence of the intensity of satellites on the x concentration and the monotonic displacement of their angular positions with increasing x allow us to conclude that the antiferromagnet -> ferrimagnet transition occurs through the uniform magnetic state. The incommensurate phase in YMn6Sn6 exhibits four satellites, which are observed in the low-angle range of X-ray diffraction pattern and demonstrate different behavior with changing temperature. At 293 K, the antiferromagnet -> ferromagnet transition in the Y1 -x Tb (x) Mn6Sn6 compound can be induced by applied magnetic field, in particular, the field mu(0) H = 0.3 T induces the transition in Tb0.15Y0.85Mn6Sn6.
Title:
Synthesis, Structure, and Properties of Turbostratically Disordered (PbSe)(1.18)(TiSe2)(2)
Authors:
Moore, DB; Beekman, M; Disch, S; Zschack, P; Hausler, I; Neumann, W; Johnson, DC Author Full Names: Moore, Daniel B.; Beekman, Matt; Disch, Sabrina; Zschack, Paul; Haeusler, Ines; Neumann, Wolfgang; Johnson, David C.
Source:
CHEMISTRY OF MATERIALS, 25 (12):2404-2409; 10.1021/cm400090f JUN 25 2013
Abstract:
Synthesis and structural characterization of a turbostratically disordered polymorph of (PbSe)(1.18)(TiSe2)(2) is reported. The structure of this compound consists of an intergrowth between one distorted rock salt structured PbSe bilayer and two transition metal dichalcogenide structured Se-Ti-Se trilayers. In addition to the lattice mismatch, there is extensive rotational disorder between these constituents. The electrical resistivity of (PbSe)(1.18)(TiSe2)(2) is a factor of 9 lower at room temperature, and the Seebeck coefficient is almost double that reported for the crystalline misfit layered compound analogue.

Update: 8-Aug-2013

Title:
Impact of beryllium additions on thermal and mechanical properties of conventionally solidified and melt-spun Al-4.5 wt.%Mn-x wt.%Be (x=0, 1, 3, 5) alloys
Authors:
Oz, T; Karakose, E; Keskin, M Author Full Names: Oz, Turan; Karakose, Ercan; Keskin, Mustafa
Source:
MATERIALS & DESIGN, 50 399-412; 10.1016/j.matdes.2013.03.024 SEP 2013
Abstract:
The influence of beryllium (Be) addition on the quasicrystal-forming ability, thermal and mechanical properties of Al-4.5 wt.%Mn-x wt.%Be (x = 0, 1, 3, 5) alloys was investigated in this study. Quasicrystalline Al-Mn-Be alloys were synthesized by the conventionally casting and melt spinning techniques. The microstructures of the samples were characterized by scanning electron microscopy (SEM) and the phase composition was identified by X-ray diffractometry (XRD). The phase transition during the solidification process was studied by differential scanning calorimetry (DSC) and differential thermal analysis (DTA) under an Ar atmosphere. The mechanical properties of the conventionally solidified (CS) and melt-spun (MS) samples were measured by a Vickers micro-hardness indenter and tensile-strength tests. The Al-4.5 wt.%Mn alloy has a hexagonal structure and minor dendritic icosahedral quasicrystalline phase (IQC) precipitates surrounded by an alpha-Al matrix. Addition of Be into the Al-4.5 wt.%Mn alloy generates intermetallic Be4AlMn and IQC phases with the extinction of the hexagonal phase, and the fraction of IQC increases continuously with the increase in Be content. A considerable improvement in microhardness and tensile strength values was observed due to the addition of Be in different percentages into the composition. (c) 2013 Elsevier Ltd. All rights reserved.
Title:
Band gaps and transmission spectra in generalized Fibonacci sigma(p, q) one-dimensional magnonic quasicrystals
Authors:
Costa, CHO; Vasconcelos, MS Author Full Names: Costa, C. H. O.; Vasconcelos, M. S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (28):10.1088/0953-8984/25/28/286002 JUL 17 2013
Abstract:
We employ a microscopic theory to investigate spin wave (magnon) propagation through their dispersion and transmission spectra in magnonic crystals arranged to display deterministic disorder. In this work the quasiperiodic arrangement investigated is the well-known generalized Fibonacci sequence, which is characterized by the sigma(p, q) parameter, where p and q are non-zero integers. In order to determine the bulk modes and transmission spectra of the spin waves, the calculations are carried out for the exchange dominated regime within the framework of the Heisenberg model and taking into account the random phase approximation. We have considered magnetic materials that have a ferromagnetic order, and the transfer-matrix treatment is applied to simplify the algebra. The results reveal that spin wave spectra display a rich and interesting magnonic pass- and stop-bands structures, including an almost symmetric band gap distribution around of a mid-gap frequency, which depends on the Fibonacci sequence type.
Title:
Two-dimensional incommensurate and three-dimensional commensurate magnetic order and fluctuations in La2-xBaxCuO4
Authors:
Wagman, JJ; Van Gastel, G; Ross, KA; Yamani, Z; Zhao, Y; Qiu, Y; Copley, JRD; Kallin, AB; Mazurek, E; Carlo, JP; Dabkowska, HA; Gaulin, BD Author Full Names: Wagman, J. J.; Van Gastel, G.; Ross, K. A.; Yamani, Z.; Zhao, Y.; Qiu, Y.; Copley, J. R. D.; Kallin, A. B.; Mazurek, E.; Carlo, J. P.; Dabkowska, H. A.; Gaulin, B. D.
Source:
PHYSICAL REVIEW B, 88 (1):10.1103/PhysRevB.88.014412 JUL 12 2013
Abstract:
We present neutron-scattering measurements on single crystals of lightly doped La2-xBaxCuO4, with 0 <= x <= 0.035. These reveal the evolution of the magnetism in this prototypical doped Mott insulator from a three-dimensional (3D) commensurate (C) antiferromagnetic ground state, which orders at a relatively high T-N, to a two-dimensional (2D) incommensurate (IC) ground state with finite-ranged static correlations, which appear below a relatively low effective T-N. At low temperatures, the 2D IC magnetism coexists with the 3D C magnetism for doping concentrations as low as similar to 0.0125. We find no signal of a 3D C magnetic ground state by x similar to 0.025, consistent with the upper limit of x similar to 0.02 observed in the sister family of doped Mott insulators, La2-xSrxCuO4. The 2D IC ground states observed for 0.0125 <= x <= 0.035 are diagonal, and are rotated by 45 degrees within the orthorhombic basal plane compared with those previously reported for samples with superconducting ground states: La2-xBaxCuO4, with 0.05 <= x <= 0.095. We construct a phase diagram based solely on magnetic order-parameter measurements, which displays much of the complexity of standard high-temperature superconductivity phase diagrams discussed in the literature. Analysis of high-energy resolution inelastic neutron scattering at moderately low temperatures shows a progressive depletion of the very low-energy dynamic magnetic susceptibility as x increases from 0.0125 to 0.035. This low-energy, dynamic susceptibility falls off with increasing temperature on a scale much higher than the effective 2D IC T-N appropriate to these materials. Appreciable dynamic 2D IC magnetic fluctuations inhabit much of the "pseudogap" regime of the phase diagram.
Title:
Incommensurate spin spiral of the geometrically-frustrated antiferromagnet CdCr2O4
Authors:
Chung, JH; Song, YS; Park, S; Ueda, H; Ueda, Y; Lee, SH Author Full Names: Chung, Jae-Ho; Song, Young Sang; Park, Sungil; Ueda, Hiroaki; Ueda, Yutaka; Lee, Seung-Hun
Source:
JOURNAL OF THE KOREAN PHYSICAL SOCIETY, 62 (12):1900-1904; 10.3938/jkps.62.1900 JUL 2013
Abstract:
CdCr2O4 is a cubic spinel with geometrically-frustrated antiferromagnetic interactions between Cr3+ ions. We investigated the structural and magnetic phase transitions in powder samples by using magnetization and neutron diffraction measurements. An antiferromagnetic phase transition was observed at T (N) = 8.1 K, below which the crystallographic unit cell was tetragonal (c < a = b). Its incommensurate antiferromagnetic ordering below T (N) resembles dimerized spin chains in the ab planes with the propagation vector k = (0, 0.088, 1). We argue that the Dzyaloshinskii-Moriya interaction and the magnetic frustration play important roles in establishing the observed magnetic ordering.
Title:
Ho-doping effect on the incommensurate magnetic order in La1.88Sr0.12CuO4
Authors:
Fujita, M; Enoki, M; Tsutsumi, K; Iikubo, S; Yamada, K Author Full Names: Fujita, Masaki; Enoki, Masanori; Tsutsumi, Kenji; Iikubo, Satoshi; Yamada, Kazuyoshi
Source:
JOURNAL OF THE KOREAN PHYSICAL SOCIETY, 62 (12):1840-1843; 10.3938/jkps.62.1840 JUL 2013
Abstract:
We have performed elastic neutron scattering experiments on the superconductor La1.85Ho0.03Sr0.12CuO4 to study the effect of substitution of a cation with a large magnetic moment at La site on the static spin correlation. In the Ho-free sample with a hole concentration of 0.12, the spatially-modulated magnetic order is known to be stabilized at temperature below T (spin) similar to 30 K. In the present Ho-doped sample, we found the appearance of magnetic peaks at (0.5, 0.5 +/- 0.119, 0) positions below T (spin) similar to 35 K, which is similar to the observation in the pristine sample. Furthermore, the volume-corrected intensities in the Ho-free and Ho-doped samples are comparable, suggesting a negligible effect of Ho-substitution at La sites. These results are quite a contrast to the huge enhancement of the magnetic intensity and the increase of T (spin) by substituting a comparable amounts of magnetic Fe3+ ions onto CuO2 planes. Therefore, the stability of the stripe order induced by the cation substitution is sensitive to the site at which the substitution occurs.
Title:
Molecular dynamics simulation of radiation damage in CaCd6 quasicrystal cubic approximant up to 10 keV
Authors:
Chen, PH; Avchachov, K; Nordlund, K; Pussi, K Author Full Names: Chen, P. H.; Avchachov, K.; Nordlund, K.; Pussi, K.
Source:
JOURNAL OF CHEMICAL PHYSICS, 138 (23):10.1063/1.4811183 JUN 21 2013
Abstract:
Due to the peculiar nature of the atomic order in quasicrystals, examining phase transitions in this class of materials is of particular interest. Energetic particle irradiation can provide a way to modify the structure locally in a quasicrystal. To examine irradiation-induced phase transitions in quasicrystals on the atomic scale, we have carried out molecular dynamics simulations of collision cascades in CaCd6 quasicrystal cubic approximant with energies up to 10 keV at 0 and 300 K. The results show that the threshold energies depend surprisingly strongly on the local coordination environments. The energy dependence of stable defect formation exhibits a power-law dependence on cascade energy, and surviving defects are dominated by Cd interstitials and vacancies. Only a modest effect of temperature is observed on defect survival, while irradiation temperature increases lead to a slight increase in the average size of both vacancy clusters and interstitial clusters. (C) 2013 AIP Publishing LLC.
Title:
The Structure of an Al-Co-Ni Decagonal Quasicrystal in an Al72Co8Ni20 Alloy Studied by Cs-Corrected Scanning Transmission Electron Microscopy
Authors:
Hiraga, K; Yasuhara, A Author Full Names: Hiraga, K.; Yasuhara, A.
Source:
MATERIALS TRANSACTIONS, 54 (5):720-724; 10.2320/matertrans.M2012333 MAY 2013
Abstract:
The structure of an Al-Co-Ni decagonal quasicrystal in an Al72Co8Ni20 alloy has been examined by Cs-corrected high-angle annular detector dark-field (HAADF)- and annular bright-field (ABF)-scanning transmission electron microscopy (STEM) observations with the incident beam parallel to the periodic axis. Observed ABF- and HAADF-STEM images clearly show the existence of large columnar clusters of a decagonal section with an about 3.2 nm in diameter and their arrangement with bond-orientational order (BOO) of a bond-length of 3.2 nm. Individual transition-metal (TM) atoms and mixed sites (MSs) of Al and TM atoms are represented as separated bright dots in observed HAADF-STEM images, and consequently arrangements of TM atoms and MSs on two quasiperiodic planes can be directly determined. The TM atoms and MSs are located at lattice points of a Penrose lattice with an edge-length of 0.25 nm, and so they are arranged with BOO on the two quasiperiodic planes. An atomic arrangement including Al atoms in the 3.2 nm cluster is speculated from observed HAADF- and ABF-STEM images.
Title:
Cu/Te substitution effects on superconductivity and microstructure of phase-separated K0.8Fe1.75Se2
Authors:
Wang, Z; Cai, Y; Wang, ZW; Sun, ZA; Yang, HX; Tian, HF; Ma, C; Zhang, B; Li, JQ Author Full Names: Wang, Z.; Cai, Y.; Wang, Z. W.; Sun, Z. A.; Yang, H. X.; Tian, H. F.; Ma, C.; Zhang, B.; Li, J. Q.
Source:
EPL, 102 (3):10.1209/0295-5075/102/37010 MAY 2013
Abstract:
Two series of K0.8Fe1.75-xCuxSe2 (0 <= x <= 0.15) and K0.8Fe1.75Se2-yTey (0 <= y <= 0.5) single crystals of nominal composition have been prepared and their physical properties and microstructural features have been studied. Resistivity measurements demonstrate that the superconducting transition temperature decreases gradually with the increase of the substitution level and zero resistivity finally disappears in both systems. Systematic TEM, SEM and XRD structural analyses, in combination with the magnetic experimental data, reveal a rich variety of structural phenomena resulting from different types of substitution. Cu substitution gives rise to the volume of a new non-superconducting Cu-rich phase with modulation q(3) = 1/3[2a* + b*] coexisting with the q(2) = 1/2[a* + b*] superconducting stripe domain. With the increase of the ratio of the new non-superconducting phase along with doping, the superconducting path is finally cut off, and results in the absence of zero resistivity. In contrast, the absence of superconductivity in Te-substituted materials is correlated with the complete disappearance of the q2 superconducting phase due to the suppression of phase separation. Copyright (C) EPLA, 2013

Update: 1-Aug-2013

Title:
Hall, Seebeck, and Nernst Coefficients of Underdoped HgBa2CuO4+delta : Fermi-Surface Reconstruction in an Archetypal Cuprate Superconductor
Authors:
Doiron-Leyraud, N; Lepault, S; Cyr-Choiniere, O; Vignolle, B; Grissonnanche, G; Laliberte, F; Chang, J; Barisic, N; Chan, MK; Ji, L; Zhao, X; Li, Y; Greven, M; Proust, C; Taillefer, L Author Full Names: Doiron-Leyraud, Nicolas; Lepault, S.; Cyr-Choiniere, O.; Vignolle, B.; Grissonnanche, G.; Laliberte, F.; Chang, J.; Barisic, N.; Chan, M. K.; Ji, L.; Zhao, X.; Li, Y.; Greven, M.; Proust, C.; Taillefer, Louis
Source:
PHYSICAL REVIEW X, 3 (2):10.1103/PhysRevX.3.021019 JUN 28 2013
Abstract:
Charge-density-wave order has been observed in cuprate superconductors whose crystal structure breaks the square symmetry of the CuO2 planes, such as orthorhombic YBa2Cu3Oy (YBCO), but not so far in cuprates that preserve that symmetry, such as tetragonal HgBa2CuO4+delta (Hg1201). We have measured the Hall (R-H), Seebeck (S), and Nernst (nu) coefficients of underdoped Hg1201 in magnetic fields large enough to suppress superconductivity. The high-field R-H(T) and S(T) are found to drop with decreasing temperature and become negative, as also observed in YBCO at comparable doping. In YBCO, the negative R-H and S are signatures of a small electron pocket caused by Fermi-surface reconstruction, attributed to charge-density-wave modulations observed in the same range of doping and temperature. We deduce that a similar Fermi-surface reconstruction takes place in Hg1201, evidence that density-wave order exists in this material. A striking similarity is also found in the normal-state Nernst coefficient nu(T), further supporting this interpretation. Given the model nature of Hg1201, Fermi-surface reconstruction appears to be common to all hole-doped cuprates, suggesting that density-wave order is a fundamental property of these materials.
Title:
Common quantum phase transition in quasicrystals and heavy-fermion metals
Authors:
Shaginyan, VR; Msezane, AZ; Popov, KG; Japaridze, GS; Khodel, VA Author Full Names: Shaginyan, V. R.; Msezane, A. Z.; Popov, K. G.; Japaridze, G. S.; Khodel, V. A.
Source:
PHYSICAL REVIEW B, 87 (24):10.1103/PhysRevB.87.245122 JUN 24 2013
Abstract:
Extraordinary new materials named quasicrystals and characterized by noncrystallographic rotational symmetry and quasiperiodic translational properties have attracted scrutiny. Study of quasicrystals may shed light on the most basic notions related to the quantum critical state observed in heavy-fermion metals. We show that the electronic system of some quasicrystals is located at the fermion condensation quantum phase transition without tuning. In that case the quasicrystals possess the quantum critical state with the non-Fermi-liquid behavior which in magnetic fields transforms into the Landau Fermi-liquid one. Remarkably, the quantum critical state is robust despite the strong disorder experienced by the electrons. We also demonstrate for the first time that quasicrystals exhibit the typical scaling behavior of their thermodynamic properties such as the magnetic susceptibility, and belong to the famous family of heavy-fermion metals. Our calculated thermodynamic properties are in good agreement with recent experimental observations.
Title:
Avoided Quantum Criticality and Magnetoelastic Coupling in BaFe2-xNixAs2
Authors:
Lu, XY; Gretarsson, H; Zhang, R; Liu, XR; Luo, HQ; Tian, W; Laver, M; Yamani, Z; Kim, YJ; Nevidomskyy, AH; Si, QM; Dai, PC Author Full Names: Lu, Xingye; Gretarsson, H.; Zhang, Rui; Liu, Xuerong; Luo, Huiqian; Tian, Wei; Laver, Mark; Yamani, Z.; Kim, Young-June; Nevidomskyy, A. H.; Si, Qimiao; Dai, Pengcheng
Source:
PHYSICAL REVIEW LETTERS, 110 (25):10.1103/PhysRevLett.110.257001 JUN 18 2013
Abstract:
We study the structural and magnetic orders in electron-doped BaFe2-xNixAs2 by high-resolution synchrotron x-ray and neutron scatterings. Upon Ni doping x, the nearly simultaneous tetragonal-to-orthorhombic structural (T-s) and antiferromagnetic (T-N) phase transitions in BaFe2As2 are gradually suppressed and separated, resulting in T-s > T-N with increasing x, as was previously observed. However, the temperature separation between T-s and T-N decreases with increasing x for x >= 0.065, tending toward a quantum bicritical point near optimal superconductivity at x approximate to 0.1. The zero-temperature transition is preempted by the formation of a secondary incommensurate magnetic phase in the region 0: 088 less than or similar to x less than or similar to 0.104, resulting in a finite value of T-N approximate to T-c + 10 K above the superconducting dome around x approximate to 0.1. Our results imply an avoided quantum critical point, which is expected to strongly influence the properties of both the normal and superconducting states.
Title:
Characteristic chemical shifts of quasicrystalline Zn-Mg-Zr alloys studied by EELS and SXES
Authors:
Koshiya, S; Terauchi, M; Ohhashi, S; Tsai, AP Author Full Names: Koshiya, S.; Terauchi, M.; Ohhashi, S.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE, 93 (18):2250-2258; 10.1080/14786435.2013.765994 JUN 1 2013
Abstract:
Chemical shifts of the constituent atoms of primitive icosahedral quasicrystal (P-QC), face-centred icosahedral quasicrystal (F-QC) and 1/1-approximant (1/1-AP) of F-QC Zn-Mg-Zr alloys were investigated for the first time using high energy-resolution electron energy-loss spectroscopy (EELS) and soft-X-ray emission spectroscopy (SXES). Among Zn M-shell and Mg L-shell excitation EELS spectra of P-QC, F-QC and 1/1-AP alloys, only the quasicrystalline alloys showed a chemical shift towards the larger binding energy side. In Zn-L and Zr-L emission SXES spectra, the P-QC and F-QC alloys showed a chemical shift towards larger binding energy side. The magnitudes of the shifts in the Zn-L emission spectra of the quasicrystalline alloys were almost the same as for ZnO. These results strongly suggest a decrease in valence charge in quasicrystalline states. Therefore, it should be concluded that bonding in quasicrystalline states involves a characteristic increase in covalency compared with bonding in corresponding approximant and standard metal crystals.
Title:
Microstructure of bilayer manganite PrCa2Mn2O7 showing charge/orbital ordering
Authors:
He, ZB; Tian, H; Deng, GC; Xu, Q; Van Tendeloo, G Author Full Names: He, Zhanbing; Tian, He; Deng, Guochu; Xu, Qiang; Van Tendeloo, Gustaaf
Source:
APPLIED PHYSICS LETTERS, 102 (21):10.1063/1.4807758 MAY 27 2013
Abstract:
The microstructure of the charge/orbital ordering Ruddleden-Popper phase PrCa2Mn2O7 was studied by transmission electron microscopy along both the [001] and the [110] orientation. Three coexisting charge/orbital ordering phases CO1, CO2, and CO3 were observed along the [001] orientation at room temperature. Different from the one-dimensional modulation in the CO1 and CO2 phase, the CO3 phase is characterized by two sets of mutually perpendicular structural modulations. From [110] high angle annular dark field-scanning transmission electron microscopy, we found that the Pr atoms locate in-between the bilayer MnO6 octahedra, which is different from the previous reports. (C) 2013 AIP Publishing LLC.
Title:
Nanocrystallization of Coarse Primary Phases in Al- and Mg-Based Alloys Induced by HCPEB Treatment
Authors:
Gao, B; He, JD; Tu, GF; Hu, L Author Full Names: Gao Bo; He Jidong; Tu Ganfeng; Hu Liang
Source:
JOURNAL OF NANOMATERIALS, 10.1155/2013/815384 2013
Abstract:
This paper reports on a phenomenon associated with high-current pulsed electron beam (HCPEB) treatment: surface nanocrystallization of coarse primary phase in hypereutectic Al17.5Si and quasicrystal alloys after multiple pulses of HCPEB irradiation. The HCPEB treatment induces superfast heating and diffusion of alloying elements and heterogeneous nucleation in a melting solution, followed by rapid solidification and cooling of the material surfaces. Consequently, nanostructured surface layers can be achieved easily. Nano-Si phase and nano-quasicrystal phase formation on the modified surface layer of hypereutectic Al17.5Si alloy and quasicrystal alloy (Mg37Zn60Y3) show a potential for surface nanocrystallization of materials with enhanced properties by HCPEB treatment.

Update: 24-Jul-2013

Title:
Magnetic lock-in phase transition in Tb0.95Er0.05Ni5 driven by low magnetic fields
Authors:
Lee, H; Choi, YN; Pirogov, AN; Kazantsev, VA; Gerasimov, EG Author Full Names: Lee, Heeju; Choi, Y. N.; Pirogov, A. N.; Kazantsev, V. A.; Gerasimov, E. G.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 341 129-132; 10.1016/j.jmmm.2013.04.010 SEP 2013
Abstract:
The magnetic properties of a mixed inter-metallic compound, Tb0.95Er0.05Ni5, were investigated using a neutron diffraction method at low temperatures. These compounds were known to have a successive magnetic phase transition from the paramagnetic state at high temperature to a lock-in phase at low temperature through intermediate phases, i.e., PM(paramagnetic)-FM(ferromagnetic)-IC(incommensurate)-L(lock-in) in reverse order of temperature. A meta-magnetic phase transition between an IC phase and a FM phase at 9 K was observed with the critical field, H-MT similar to 200 mT. A new magnetic phase between the new phase (lock-in phase) and an IC phase has been observed. From the field dependence of the Bragg reflections and their satellite peaks at low temperatures (3-12 K), weak field driven first-order magnetic phase transitions were recorded at six fixed temperatures. The critical magnetic field decreases exponentially with the temperature. From these experimental results, we obtained a magnetic phase diagram of Tb0.95Er0.05Ni5 at a low temperature region for the first time. (c) 2013 The Authors. Published by Elsevier B.V. All rights reserved.
Title:
Thermodynamic and transport properties of RSn2 (R=Tb-Tm, Lu, Y) single crystals
Authors:
Zhao, LL; Mehlman, MS; Besara, T; Siegrist, T; Morosan, E Author Full Names: Zhao, Liang L.; Mehlman, Michael S.; Besara, Tiglet; Siegrist, Theo; Morosan, E.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 341 6-16; 10.1016/j.jmmm.2013.03.033 SEP 2013
Abstract:
We report the anisotropic magnetization, heat capacity and resistivity measurements for isostructural RSn2 (R=Tb-Tm, Lu, Y) single crystals. The R=Tb-Tm compounds exhibit long range antiferromagnetic ordering with T-N ranging from 26.3 K to 3.6 K. An additional incommensurate-to-commensurate transition at a lower critical temperature T-1 is observed for R=Tb-Ho. Field-induced metamagnetic transitions have also been observed for all magnetic rare earth compounds. The resistivity has a typical metallic character with a relatively high residual resistivity ratio. Both the AFM ordering temperature and spin disordered resistivity scale with the de Gennes factor. The magnetic heat capacity data indicate partially lifted ground state degeneracies associated with crystal electric field splitting. (c) 2013 Elsevier B.V. All rights reserved.
Title:
Elastic constants of incommensurate solid He-4 from diffusion Monte Carlo simulations
Authors:
Cazorla, C; Lutsyshyn, Y; Boronat, J Author Full Names: Cazorla, Claudio; Lutsyshyn, Yaroslav; Boronat, Jordi
Source:
PHYSICAL REVIEW B, 87 (21):10.1103/PhysRevB.87.214522 JUN 28 2013
Abstract:
We study the elastic properties of incommensurate solid He-4 in the limit of zero temperature. Specifically, we calculate the pressure dependence of the five elastic constants (C-11, C-12, C-13, C-33, and C-44), longitudinal and transversal speeds of sound, and the T = 0 Debye temperature of incommensurate and commensurate hcp He-4 using the diffusion Monte Carlo method. Our results show that under compression, the commensurate crystal is globally stiffer than the incommensurate, however at pressures close to melting (i.e., P similar to 25 bar) some of the elastic constants accounting for strain deformations of the hcp basal plane (C-12 and C-13) are slightly larger in the incommensurate solid. Also, we find that upon the introduction of tiny concentrations of point defects, the shear modulus of He-4 (C-44) undergoes a small reduction.
Title:
Three-dimensional Dirac fermions in quasicrystals as seen via optical conductivity
Authors:
Timusk, T; Carbotte, JP; Homes, CC; Basov, DN; Sharapov, SG Author Full Names: Timusk, T.; Carbotte, J. P.; Homes, C. C.; Basov, D. N.; Sharapov, S. G.
Source:
PHYSICAL REVIEW B, 87 (23):10.1103/PhysRevB.87.235121 JUN 17 2013
Abstract:
The optical conductivity of quasicrystals is characterized by two features not seen in ordinary metallic systems. There is an absence of the Drude peak and the interband conductivity rises linearly from a very low value up to normal metallic levels over a wide range of frequencies. The absence of a Drude peak has been attributed to a pseudogap at the Fermi surface but a detailed explanation of the linear behavior has not been found. Here we show that the linear conductivity, which seems to be universal in all Al based icosahedral quasicrystal families, as well as their periodic approximants, follows from a simple model that assumes that the entire Fermi surface is gapped except at a finite set of Dirac points. There is no evidence of a semiconducting gap in any of the materials suggesting that the Dirac spectrum is massless, protected by topology leading to a Weyl semimetal. This model gives rise to a linear conductivity with only one parameter, the Fermi velocity. This picture suggests that decagonal quasicrystals should, like graphene, have a frequency independent conductivity, without a Drude peak. This is in accord with the experimental data as well.
Title:
Incommensurability and spin dynamics in the low-temperature phases of Ni3V2O8
Authors:
Ehlers, G; Podlesnyak, AA; Hahn, SE; Fishman, RS; Zaharko, O; Frontzek, M; Kenzelmann, M; Pushkarev, AV; Shiryaev, SV; Barilo, S Author Full Names: Ehlers, G.; Podlesnyak, A. A.; Hahn, S. E.; Fishman, R. S.; Zaharko, O.; Frontzek, M.; Kenzelmann, M.; Pushkarev, A. V.; Shiryaev, S. V.; Barilo, S.
Source:
PHYSICAL REVIEW B, 87 (21):10.1103/PhysRevB.87.214418 JUN 17 2013
Abstract:
Magnetic order and low-energy spin dynamics in the zero field ground state of Ni3V2O8 are revealed in elastic and inelastic neutron scattering experiments. Neutron diffraction shows that below T = 2.3 K the Ni2+ moments (spin S = 1) order in a cycloid pattern with incommensurate wave vector k(ICM) = (0,1, tau), where tau = 0.4030 +/- 0.0004, which is superimposed on a commensurate antiferromagnetic spin arrangement with k(CM) = (0,0,0). Three spin wave modes are discerned below E similar to 3 meV in inelastic measurements and qualitatively described by a model Hamiltonian that involves near neighbor exchange, local anisotropy, and a small biquadratic coupling between the spine and cross-tie sites. Results from both elastic and inelastic scattering experiments suggest that the two sublattices on spine and cross-tie sites are largely decoupled.
Title:
Field-induced phase transitions and phase diagrams in BiFeO3-like multiferroics
Authors:
Gareeva, ZV; Popkov, AF; Soloviov, SV; Zvezdin, AK Author Full Names: Gareeva, Z. V.; Popkov, A. F.; Soloviov, S. V.; Zvezdin, A. K.
Source:
PHYSICAL REVIEW B, 87 (21):10.1103/PhysRevB.87.214413 JUN 12 2013
Abstract:
We explore incommensurate magnetic structures and phase diagrams of multiferroics through accurate micromagnetic analysis, taking into account the spin flexoelectric interaction (the so-called Lifshitz invariant). We consider BiFeO3 single crystals and epitaxial films grown on (111) substrates. The main control parameters of these systems are the magnetic field, magnetic anisotropy, and, in the case of thin films, epitaxial strain. We construct phase diagrams representing stability regions for the homogeneous magnetic states and incommensurate structures for two geometries of the field (parallel to the principal crystal axis H parallel to C-3 and perpendicular to this direction H perpendicular to C-3). It is shown that the direction of applied magnetic field substantially affects the magnetic phases, the properties of incommensurate structures, and the character of phase transitions. A conical type of cycloidal ordering is revealed to exist during the transition from the incommensurate cycloidal structure to the homogeneous magnetic state. Constructed phase diagrams provide the combination of control parameters required to suppress the cycloidal ordering. Our results show that the critical magnetic field for suppression of the cycloid is lower in thin films than in single crystals, and can also be lowered by appropriate selection of applied magnetic field orientation. These results provide a stronger understanding of the complex magnetic ordering in BiFeO3 and can be useful for strain engineering of new multiferroic materials on demand.
Title:
X-ray Diffraction Study of BaTiO3/(Ba1-xSrx)TiO3 Artificial Superlattices
Authors:
Zakharchenko, IN; Bunina, OA; Maslova, OA; Yuzyuk, YI; Ortega, N; Kumar, A; Katiyar, RS Author Full Names: Zakharchenko, I. N.; Bunina, O. A.; Maslova, O. A.; Yuzyuk, Yu. I.; Ortega, N.; Kumar, A.; Katiyar, R. S.
Source:
FERROELECTRICS, 444 (1):1-8; 10.1080/00150193.2013.785833 JAN 1 2013
Abstract:
We report x-ray diffraction investigation of two sets of artificial BaTiO3/Ba1-xSrxTiO3 (BT/BST-x) superlattices (SLs) grown on MgO substrates. The first set of SLs was deposited with the constant periodicity (about 150 angstrom) and the variable Ba/Sr content in BST layers. In the second set, the modulation period was varied between 30 angstrom < < 110 angstrom while Ba content was equal 0 in BST layers. It is shown that, fabrication of the artificial SLs with variable composition of the constituting layers even with large modulation period may provide enhanced variation of the ferroelectric properties comparing to the SLs with variable layers thickness.

Update: 17-Jul-2013

Title:
Incommensurate crystallography without additional dimensions
Authors:
Kocian, P Author Full Names: Kocian, Philippe
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 374-387; 10.1107/S0108767313005990 4 JUL 2013
Abstract:
It is shown that the Euclidean group of translations, when treated as a Lie group, generates translations not only in Euclidean space but on any space, curved or not. Translations are then not necessarily vectors (straight lines); they can be any curve compatible with the parameterization of the considered space. In particular, attention is drawn to the fact that one and only one finite and free module of the Lie algebra of the group of translations can generate both modulated and non-modulated lattices, the modulated character being given only by the parameterization of the space in which the lattice is generated. Moreover, it is shown that the diffraction pattern of a structure is directly linked to the action of that free and finite module. In the Fourier transform of a whole structure, the Fourier transform of the electron density of one unit cell (i.e. the structure factor) appears concretely, whether the structure is modulated or not. Thus, there exists a neat separation: the geometrical aspect on the one hand and the action of the group on the other, without requiring additional dimensions.
Title:
Tabulation of irreducible representations of the crystallographic space groups and their superspace extensions
Authors:
Stokes, HT; Campbell, BJ; Cordes, R Author Full Names: Stokes, Harold T.; Campbell, Branton J.; Cordes, Ryan
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 388-395; 10.1107/S0108767313007538 4 JUL 2013
Abstract:
New tables of irreducible representations (IRs) are introduced for the 230 crystallographic space groups (SGs) in three-dimensional space, at both special and non-special k vectors, and for their extensions to (3 + d)-dimensional superspace ('superspace-extended SGs' or SSESGs). Neither a tabulation of SG IR matrices for non-special k vectors nor a tabulation of SSESG IR matrices for d > 1 have been previously published. These tabulations are made possible by a new form in which the IR matrices of SGs are separated as a product of a translation part T and a point-operation part P, and where the IR matrices of SSESGs are separated as a product of a phase-shift part Q and a point-operation part P-s. Both T and Q have a simple prescribed form that does not need to be tabulated. Also, the new IR matrices are in a convenient block form which allows one to see by inspection which parts of the matrices and the associated order parameters belong to which arm of the star of k. In addition to complex IR matrices, real physically irreducible representation (PIR) matrices are tabulated. The new IR and PIR tables are available on the ISO-IR website (http://stokes.byu.edu/iso/irtables.php) in both convenient human-readable and computer-readable forms.
Title:
Signatures of quantum criticality in the thermopower of Ba(Fe1-xCox)(2)As-2
Authors:
Arsenijevic, S; Hodovanets, H; Gaal, R; Forro, L; Bud'ko, SL; Canfield, PC Author Full Names: Arsenijevic, S.; Hodovanets, H.; Gaal, R.; Forro, L.; Bud'ko, S. L.; Canfield, P. C.
Source:
PHYSICAL REVIEW B, 87 (22):10.1103/PhysRevB.87.224508 JUN 18 2013
Abstract:
We demonstrate that the thermopower (S) can be used to probe the spin fluctuations (SFs) in proximity to the quantum critical point (QCP) in Fe-based superconductors. The sensitivity of S to the entropy of charge carriers allows us to observe an increase of S/T in Ba(Fe1-x Co-x)(2)As-2 close to the spin-density-wave (SDW) QCP. This behavior is due to the coupling of low-energy conduction electrons to two-dimensional SFs, similar to heavy-fermion systems. The low-temperature enhancement of S/T in the Co substitution range 0.02 < x < 0.1 is bordered by two Lifshitz transitions, and it corresponds to the superconducting region, where a similarity between the electron and nonreconstructed hole pockets exists. The maximal S/T is observed in proximity to the *commensurate-to-*incommensurate SDW transition, for critical x(c) approximate to 0.05, close to the highest superconducting T-c. This analysis indicates that low-T thermopower is influenced by critical spin fluctuations which are important for the superconducting mechanism.
Title:
Disorder line and incommensurate floating phases in the quantum Ising model on an anisotropic triangular lattice
Authors:
Iglovikov, VI; Scalettar, RT; Singh, RRP; Oitmaa, J Author Full Names: Iglovikov, V. I.; Scalettar, R. T.; Singh, R. R. P.; Oitmaa, J.
Source:
PHYSICAL REVIEW B, 87 (21):10.1103/PhysRevB.87.214415 JUN 13 2013
Abstract:
We present a quantum Monte Carlo study of the Ising model in a transverse field on a square lattice with nearest-neighbor antiferromagnetic exchange interaction J and one diagonal second-neighbor interaction J', interpolating between square-lattice (J' = 0) and triangular-lattice (J' = J) limits. At a transverse field of B-x = J, the disorder line first introduced by Stephenson [J. Math. Phys. 5, 1009 (1964)], where the correlations go from Neel to incommensurate, meets the zero-temperature axis at J' approximate to 0.7 J. Strong evidence is provided that the incommensurate phase at larger J', at finite temperatures, is a floating phase with power-law decaying correlations. We sketch a general phase-diagram for such a system and discuss how our work connects with the previous quantum Monte Carlo work by Isakov and Moessner [Phys. Rev. B 68, 104409 (2003)] for the isotropic triangular lattice (J' = J). For the isotropic triangular lattice, we also obtain the entropy function and constant entropy contours using a mix of quantum Monte Carlo, high-temperature series expansions and high-field expansion methods and show that phase transitions in the model in the presence of a transverse field occur at very low entropy.
Title:
Doping dependence of the spin excitations in the Fe-based superconductors Fe1+yTe1-xSex
Authors:
Christianson, AD; Lumsden, MD; Marty, K; Wang, CH; Calder, S; Abernathy, DL; Stone, MB; Mook, HA; McGuire, MA; Sefat, AS; Sales, BC; Mandrus, D; Goremychkin, EA Author Full Names: Christianson, A. D.; Lumsden, M. D.; Marty, K.; Wang, C. H.; Calder, S.; Abernathy, D. L.; Stone, M. B.; Mook, H. A.; McGuire, M. A.; Sefat, A. S.; Sales, B. C.; Mandrus, D.; Goremychkin, E. A.
Source:
PHYSICAL REVIEW B, 87 (22):10.1103/PhysRevB.87.224410 JUN 12 2013
Abstract:
The Fe1+yTe1-xSex series of materials is one of the prototype families of Fe-based superconductors. To provide further insight into these materials, we present systematic inelastic neutron scattering measurements of the low-energy spin excitations for x = 0.27, 0.36, 0.40, and 0.49. These measurements show an evolution of incommensurate spin excitations towards the (1/2,1/2,0) wave vector with doping. Concentrations (x = 0.40 and 0.49) which exhibit the most robust superconducting properties have spin excitations closest to (1/2,1/2,0) and also exhibit a strong spin resonance in the spin excitation spectrum below T-c. The resonance signal appears to be closer to (1/2,1/2,0) than the underlying spin excitations. We discuss the possible relationship between superconductivity and spin excitations at the (1/2,1/2,0) wave vector and the role that interstitial Fe may play.
Title:
Electronic Instability in a Zero-Gap Semiconductor: The Charge-DensityWave in (TaSe4)(2)I
Authors:
Tournier-Colletta, C; Moreschini, L; Autes, G; Moser, S; Crepaldi, A; Berger, H; Walter, AL; Kim, KS; Bostwick, A; Monceau, P; Rotenberg, E; Yazyev, OV; Grioni, M Author Full Names: Tournier-Colletta, C.; Moreschini, L.; Autes, G.; Moser, S.; Crepaldi, A.; Berger, H.; Walter, A. L.; Kim, K. S.; Bostwick, A.; Monceau, P.; Rotenberg, E.; Yazyev, O. V.; Grioni, M.
Source:
PHYSICAL REVIEW LETTERS, 110 (23):10.1103/PhysRevLett.110.236401 JUN 4 2013
Abstract:
We report a comprehensive study of the paradigmatic quasi-1D compound (TaSe4)(2)I performed by means of angle-resolved photoemission spectroscopy (ARPES) and first-principles electronic structure calculations. We find it to be a zero-gap semiconductor in the nondistorted structure, with non-negligible interchain coupling. Theory and experiment support a Peierls-like scenario for the charge-density wave formation below T-CDW = 263 K, where the incommensurability is a direct consequence of the finite interchain coupling. The formation of small polarons, strongly suggested by the ARPES data, explains the puzzling semiconductor-to-semiconductor transition observed in transport at T-CDW.
Title:
Synthesis, structure and electrical properties of a new tin vanadium selenide
Authors:
Atkins, R; Disch, S; Jones, Z; Haeusler, I; Grosse, C; Fischer, SF; Neumann, W; Zschack, P; Johnson, DC Author Full Names: Atkins, Ryan; Disch, Sabrina; Jones, Zachary; Haeusler, Ines; Grosse, Corinna; Fischer, Saskia F.; Neumann, Wolfgang; Zschack, Paul; Johnson, David C.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 202 128-133; 10.1016/j.jssc.2013.03.008 JUN 2013
Abstract:
The turbostratically disordered misfit layer compound (SnSe)(1.15)VSe2 was synthesized and structurally characterized. Electrical transport measurements suggest this compound undergoes a charge or spin density wave (CDW or SDW) transition, which has not been observed in previous misfit layer compounds. The (SnSe)(1.15)VSe2 compound, created through the modulated elemental reactants technique, contains highly oriented intergrowths of SnSe bilayers and VSe2 structured Se-V-Se trilayers with abrupt interfaces between them perpendicular to the c-axis. X-ray diffraction data and transmission electron microscope images show that each constituent has in-plane crystallinity but that there is a random rotational disorder between the constituent layers. Temperature-dependent electrical resistivity data and Hall measurements are consistent with (SnSe)(1.15)VSe2 being a metal, however an abrupt increase in the resistivity occurs between 30 and 100 K. The carrier concentration decreases by approximately 1 carrier per vanadium atom during this temperature interval. (C) 2013 Elsevier Inc. All rights reserved.
Title:
Microstructure and Physical Properties of Two Charge Density Wave States in NbSe3 Nanowires
Authors:
Shi, HL; Yang, HX; Tian, HF; Wang, ZW; Qin, YB; Song, YJ; Luo, MT; Wang, WZ; Li, JQ Author Full Names: Shi, Honglong; Yang, Huaixin; Tian, Huanfang; Wang, Zhiwei; Qin, Yunbin; Song, Yuanjun; Luo, Minting; Wang, Wenzhong; Li, Jianqi
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 13 (6):4123-4128; 10.1166/jnn.2013.7472 JUN 2013
Abstract:
The whisker-like niobium triselenide (NbSe3) nanowires were synthesized using the traditional solid state reaction. X-ray diffraction experiment suggested the monoclinic structure (P2(1)/m), and crystal morphology analysis indicated that the band-like shape is the stable morphology. Two charge density wave (CDW) states were observed at around 140 K and 50 K, respectively, and the nonlinear effect was detected in the CDW states from the R-T and I-V measurements. The doped Fe atoms, as pinning centers, play an important role in the nonlinear properties of the CDW state. Electron diffraction and HRTEM experiments were carried out at different temperatures in order to investigate the structural features and their evolution. The sets of incommensurate modulation spots with modulation vector q(1) similar to (h, k 0.243, I) appeared below 145 K, and other sets of complex superstructure spots with modulation vector q(2) similar to (h, k + 0.3, I + 1.3424), q(3) similar to (h, k-0.3137, 1.5685), = (1/3, k, 1) and q(5) = (0.5, 0.25, 0.5) were observed at [1 0 0] and [3 0 1] zone axis at about 20 K, respectively, suggesting the complex inconnmensurately modulated structures in this material.
Title:
Structural Properties in Incommensurately Modulated Spinel Compound CuV2S4
Authors:
Kawaguchi, S; Ishibashi, H; Tsuji, N; Kim, J; Kato, K; Takata, M; Kubota, Y Author Full Names: Kawaguchi, Shogo; Ishibashi, Hiroki; Tsuji, Naruki; Kim, Jungeun; Kato, Kenichi; Takata, Masaki; Kubota, Yoshiki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (6):10.7566/JPSJ.82.064603 JUN 2013
Abstract:
We have studied the incommensurate crystal structure of the spinel compound CuV2S4 at low temperatures using the synchrotron powder diffraction technique. The powder diffraction pattern at 70 K shows that the splitting of the fundamental 800 reflection peak and the weak superlattice reflections with a modulation vector q similar to 3/4[110] due to the structural phase transition at 90 K were observed. It is found that the crystal structure at 70 K has an orthorhombic unit cell with the superspace-group Imm2(0 beta 0) with a modulation vector q = 0.7391(5)b*. By Rietveld analysis including the *incommensurate* *modulation* along the b-axis, large static atomic displacements were found at the positions of V atoms, suggesting that V atoms play an important role in a charge-density wave (CDW) transition. The atomic displacements indicate that V1 atoms at the 4c site form dimers along the a-axis, suggesting that a commensurate CDW forms along the a-axis. Furthermore, the V2 atoms at the 4d site tend to approach V1 dimers, giving rise to the formation of V clusters such as trimers and tetramer-like clusters. The arrangements of V clusters form a pattern along the b-axis with a period of nearly four fundamental cells, which may induce the formation of an incommensurate CDW along the b-axis.
Title:
Mechanically driven phase transformation in single phase Al62.5Cu25Fe12.5 quasi-crystals: Effect of milling intensity
Authors:
Ali, F; Scudino, S; Gorantla, SM; Srivastava, VC; Shahid, HR; Uhlenwinkel, V; Stoica, M; Vaughan, G; Mukhopadhyay, NK; Eckert, J Author Full Names: Ali, F.; Scudino, S.; Gorantla, S. M.; Srivastava, V. C.; Shahid, H. R.; Uhlenwinkel, V.; Stoica, M.; Vaughan, G.; Mukhopadhyay, N. K.; Eckert, J.
Source:
ACTA MATERIALIA, 61 (10):3819-3830; 10.1016/j.actamat.2013.03.020 JUN 2013
Abstract:
In this work the effect of mechanical milling on the structure, thermal stability and hardness of single phase Al62.5Cu25Fe12.5 icosahedral quasi-crystals has been investigated for different milling intensities. The results indicate that, irrespective of the milling intensity used, the quasi-crystals transform to a body-centered cubic (bcc) phase during milling. This transformation starts when the grain size of the QC phase is about 10 nm, which represents the critical grain size initiating the phase transformation. Upon heating the milled powder displays grain growth of the bcc phase at low temperatures, followed by transformation to the original icosahedral QC phase at higher temperatures. The phase transformations occurring during milling and subsequent annealing have a remarkable effect on the indentation hardness, which can be tuned within a wide range (7-10 GPa) as a function of the volume fractions of the different phases. This suggests that a composite material with optimized mechanical properties can be produced by appropriate thermo-mechanical treatments. (c) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Composition-dependent ground state of martensite in Ni-Mn-Ga alloys
Authors:
Li, ZB; Xu, N; Zhang, YD; Esling, C; Raulot, JM; Zhao, X; Zuo, L Author Full Names: Li, Zongbin; Xu, Nan; Zhang, Yudong; Esling, Claude; Raulot, Jean-Mare; Zhao, Xiang; Zuo, Liang
Source:
ACTA MATERIALIA, 61 (10):3858-3865; 10.1016/j.actamat.2013.03.024 JUN 2013
Abstract:
For Ni-Mn-Ga alloys, giant magnetic-field-induced strains may be achieved in a modulated martensitic state, offering attractive chances for academic and practical exploration. However, the metastability of modulated martensite imposes a severe constraint on the capacity of these alloys as promising materials for sensors and actuators. In the present work, we conduct both experimental examinations and ab initio calculations to seek potential remedies of this critical problem through composition tuning. Results show that, for Group II alloys having modulated martensite at reasonable temperatures, the increase in Ni addition results in an enhanced tendency to the formation of non-modulated (NM) martensite, whereas the proper Mn addition leads to the stabilization of seven-layered modulated (7M) martensite, which serves as the structural ground state of martensite. By correlating the microstructural evolutions with the two-stage phase transformation (i.e. austenite -> 7M martensite -> NM martensite), it is demonstrated that the 7M martensite possesses lower energy barriers in terms of the lattice distortion of parent austenite and the interfacial energy of martensitic variants, which plays a vital role in bridging the austenite to NM martensite transformation. This result is expected to provide useful information for the design of these new functional materials. (c) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
High-Field Magnetism of the S = 5/2 Triangular-Lattice Antiferromagnet CuFe1-xGaxO2 (x=0-0.028)
Authors:
Fujita, T; Kimura, S; Kida, T; Kotetsu, T; Hagiwara, M Author Full Names: Fujita, Takahito; Kimura, Shojiro; Kida, Takanori; Kotetsu, Takahiro; Hagiwara, Masayuki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (6):10.7566/JPSJ.82.064712 JUN 2013
Abstract:
We have performed multifrequency electron spin resonance (ESR), electric polarization, and magnetization measurements on single crystals of the triangular-lattice antiferromagnet CuFe1-xGaxO2 (x = 0.000-0.028) in high magnetic fields. We compared ESR results with the other results (electric polarization and magnetization measurements) to clarify the origin of the expansion of a ferroelectric and incommensurate (FEIC) phase induced by the doping of nonmagnetic Ga3+ ions. We observed a rapid increase in the ESR linewidth and a large shift of the transition field from a four-sublattice collinear phase to the FEIC phase accompanied with a magnetization jump and a spontaneous electric polarization with slight doping of Ga3+ ions. We have found that the ESR linewidth is highly correlated with this shift. As a result, we have succeeded in explaining the origin of the expansion of the FEIC phase as well as the change of the transition field induced by broadening of the lowest excitation branch with an increase in Ga content.
Title:
Icosahedral quasicrystalline (Ti1.6V0.4Ni)(100-x)Sc-x alloys: Synthesis, structure and their application in Ni-MH batteries
Authors:
Hu, W; Yi, JH; Zheng, BJ; Wang, LM Author Full Names: Hu, Wen; Yi, Jianhong; Zheng, Biju; Wang, Limin
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 202 1-5; 10.1016/j.jssc.2013.03.006 JUN 2013
Abstract:
Thanks to the revolutionary discovery of 5-fold symmetry contributed by Shechtman, quasicrystal is now recognized as another solid-state existing form. As the second largest class of quasicrystals, titanium-based icosahedral quasicrystals are very promising for hydrogen storage applications owing to their inherent abundant interstitial sites and favorable hydrogen-metal chemistry. In this context, (Ti1.6V0.4Ni)(100-x)Sc-x (x=0.5-6) quaternary icosahedral quasicrystals have been successfully synthesized via arc-melting and subsequent melt-spinning techniques, and then their electrochemical performance toward hydrogen is explored. When the molar ratio of Sc addition is under 1%, a maximum discharge capacity of about 270 mA h g(-1) can be delivered. With further increasing Sc amount to 6%, good cycling stability as well as significantly retarded self-discharge rate (capacity retention 94% after 24 h relaxation) is observed. But meanwhile, the discharge capacities fall into 250-240 mA h g(-1), and the electrocatalytic activity improvement is highly demanded. (C) 2013 Elsevier Inc. All rights reserved.
Title:
Superconductivity Induced by Breaking Te-2 Dimers of AuTe2
Authors:
Kudo, K; Ishii, H; Takasuga, M; Iba, K; Nakano, S; Kim, J; Fujiwara, A; Nohara, M Author Full Names: Kudo, Kazutaka; Ishii, Hiroyuki; Takasuga, Masaya; Iba, Keita; Nakano, Seiya; Kim, Jungeun; Fujiwara, Akihiko; Nohara, Minoru
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 82 (6):10.7566/JPSJ.82.063704 JUN 2013
Abstract:
Mineral calaverite AuTe2 is a layered compound with an incommensurately modulated structure. The modulation is characterized by the formation of molecular-like Te-2 dimers. We have found that the breaking of Te-2 dimers that occurs in Au1-xPtxTe2 results in the emergence of superconductivity at T-c = 4.0 K.

Update: 11-Jul-2013

Title:
THE MULTIFERROIC PROPERTIES OF Bi(Fe1/2Cr1/2)O-3 COMPOUND
Authors:
Zhu, JL; Yang, HX; Feng, SM; Wang, LJ; Liu, QQ; Jin, CQ; Wang, XH; Li, LT; Yu, J Author Full Names: Zhu, J. L.; Yang, H. X.; Feng, S. M.; Wang, L. J.; Liu, Q. Q.; Jin, C. Q.; Wang, X. H.; Li, L. T.; Yu, J.
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B, 27 (15):SI 10.1142/S0217979213620233 JUN 20 2013
Abstract:
Dense Bi(Fe1/2Cr1/2)O-3 ceramics with R 3c crystal structure were synthesized by solid-state reaction under high pressure. Transmission electron microscope observations revealed an incommensurable superstructure along < 110 > direction. Magnetization measurements indicated a transition to a cooperative magnetic state below similar to 130 K. Dielectric properties of Bi(Fe1/2Cr1/2)O-3 showed a dielectric constant anomaly located at similar to 140 K indicating the giant dielectric relaxation in multiferroic Bi(Fe1/2Cr1/2)O-3 compound, which can be explained by the enhanced conductivity and possible Maxwell-Wagner contribution. Large dielectric frequency dispersion was observed at 140-185 K, and was supposed to be a thermal activated intrinsic process.
Title:
Magnetic phase diagrams, domain switching, and quantum phase transition of the quasi-one-dimensional Ising-like antiferromagnet BaCo2V2O8
Authors:
Niesen, SK; Kolland, G; Seher, M; Breunig, O; Valldor, M; Braden, M; Grenier, B; Lorenz, T Author Full Names: Niesen, S. K.; Kolland, G.; Seher, M.; Breunig, O.; Valldor, M.; Braden, M.; Grenier, B.; Lorenz, T.
Source:
PHYSICAL REVIEW B, 87 (22):10.1103/PhysRevB.87.224413 JUN 14 2013
Abstract:
In the effective Ising spin-1/2 antiferromagnetic chain system BaCo2V2O8 the magnetic-field influence is highly anisotropic. For magnetic fields along the easy axis c, the Neel order is strongly suppressed already at low fields and an incommensurate order is entered above 4 T. We present a detailed study of the magnetic phase diagrams for different magnetic field directions, which are derived from magnetization data, high-resolution thermal expansion, and magnetostriction measurements as well as from the thermal conductivity. Zero-field thermal-expansion data reveal that the magnetic transition is accompanied by an orthorhombic distortion within the ab plane. Under ambient conditions the crystals are heavily twinned, but the domain orientation can be influenced either by applying uniaxial pressure or a magnetic field along the [100] direction. In addition, our data reveal a pronounced in-plane magnetic anisotropy for fields applied within the ab plane. For H parallel to [110], the magnetic field influence on T-N is weak, whereas for magnetic fields applied along [100], T-N vanishes at about 10 T and the zero-field Neel order is completely suppressed as is confirmed by neutron diffraction data. The second-order phase transition strongly suggests a quantum critical point being present at H similar or equal to 10 T parallel [100].
Title:
Coexistence of spiral magnetic state and weak ferromagnetism in a multiferroic, cross-controlled by external magnetic and electric fields
Authors:
Lyubutin, IS; Pikin, SA Author Full Names: Lyubutin, I. S.; Pikin, S. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (23):10.1088/0953-8984/25/23/236001 JUN 12 2013
Abstract:
The influence of external magnetic and electric fields on the properties of a multiferroic with a helical magnetic structure is described. Thermodynamics of the phase transition from the antiferromagnetic ferroelectric to the new magnetic state is described for a multiferroic with a perovskite-type structure. In this magnetic state a spiral spin structure and weak ferromagnetism can exist simultaneously. Such a state is a result of the first-order phase transition at a certain temperature below T-N when, due to the Dzyaloshinskii-Moriya effect, a helical magnetic structure occurs. In this state the vectors of electrical polarization and the helicoid of magnetic moments in perovskites are mutually perpendicular and lie in the basic (ab) plane perpendicular to the main c axis. In this case an additional electrical polarization proportional to the square of magnetization appears in the (ab) plane which reduces the common polarization of the ferroelectric. It is shown that a weak ferromagnetic moment m occurs along the c axis in an applied magnetic field in addition to a modulated magnetic structure appearing in the (ab) plane. The dependence of these phenomena on the applied electric field is considered. It is shown that a sign-alternating electric field causes a linear-in-the-field variation of the magnetic moment opposite in sign to the electric field variation (i.e., the greater is the electric field, the smaller is the magnetic moment m). The observed hysteresis phenomena determining the temperature ranges of overheating and overcooling of each phase under applied magnetic and electrical fields are explained.
Title:
Magnetic phase diagram of Sr3Fe2O7-delta
Authors:
Peets, DC; Kim, JH; Dosanjh, P; Reehuis, M; Maljuk, A; Aliouane, N; Ulrich, C; Keimer, B Author Full Names: Peets, D. C.; Kim, J. -H.; Dosanjh, P.; Reehuis, M.; Maljuk, A.; Aliouane, N.; Ulrich, C.; Keimer, B.
Source:
PHYSICAL REVIEW B, 87 (21):10.1103/PhysRevB.87.214410 JUN 10 2013
Abstract:
Magnetometry, electrical transport, and neutron scattering measurements were performed on single crystals of the Fe4+-containing perovskite-related phase Sr3Fe2O7-delta as a function of oxygen content. Although both the crystal structure and electron configuration of this compound are closely similar to those of well-studied ruthenates and manganates, it exhibits very different physical properties. The fully oxygenated compound (delta = 0) exhibits a charge-disproportionation transition at T-D = 340 K, and an antiferromagnetic transition at T-N = 115 K. For temperatures T <= T-D, the material is a small-gap insulator; the antiferromagnetic order is incommensurate, which implies competing exchange interactions between the Fe4+ moments. The fully deoxygenated compound (delta = 1) is highly insulating, and its Fe3+ moments exhibit commensurate antiferromagnetic order below T-N similar to 600 K. Compounds with intermediate delta exhibit different order with lower T-N, likely as a consequence of frustrated exchange interactions between Fe3+ and Fe4+ sublattices. A previous proposal that the magnetic transition temperature reaches zero is not supported.
Title:
Chemistry, morphology and structural characteristics of synthetic Al-Ni and Al-Co-lizardites
Authors:
Bentabol, M; Cruz, MDR Author Full Names: Bentabol, Maria; Ruiz Cruz, Maria Dolores
Source:
APPLIED CLAY SCIENCE, 77-78 68-78; 10.1016/j.clay.2013.04.001 JUN 2013
Abstract:
Al-Ni and Al-Co lizardites have been synthesized at hydrothermal conditions. The two phases display different morphologies: thin, dominantly curved platelets (Al-Ni); and stacks of very thin platy particles (Al-Co). The X-ray diffraction and transmission/analytical electron microscopy studies have been used to make accurate distinctions among different structural types and chemical populations. Al-Ni bearing lizardite includes a 1M polytype and probably very subordinate amounts of chlorite. Al-Co bearing lizardite includes two 1M polytypes with different cell-parameters, one of these consisting of an apparently modulated structure. Chemically, Al-Ni- and specially Al-Co lizardite consist of a mixture of two populations with tetrahedral compositions similar to Si1.8Al0.2 and Si-2.0. In contrast with previously described Al-rich serpentines, our serpentines are characterized by an asymmetrical Al distribution, with Al-VI on the order of 1.0 atom per formula u nit. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Structural transformation and enhancement in magnetic properties of single-phase Bi1-xPrxFeO3 nanoparticles
Authors:
Srivastav, SK; Gajbhiye, NS; Banerjee, A Author Full Names: Srivastav, Simant Kumar; Gajbhiye, N. S.; Banerjee, A.
Source:
JOURNAL OF APPLIED PHYSICS, 113 (20):10.1063/1.4807928 MAY 28 2013
Abstract:
Single-phase Bi1-xPrxFeO3 (x = 0.0, 0.05, and 0.10) nanoparticles have been synthesized by propylene glycol-gel route at a temperature of 400 degrees C. Rietveld refinement of X-ray diffraction data and Raman spectra reflect a structural phase transition from rhombohedral for x = 0 to triclinic for x = 0.10. Magnetic measurements reveal that Pr-doped BiFeO3 nanoparticles for x = 0.10 have enhanced remnant magnetization about 10 times as compared to pure BiFeO3 nanoparticles. It has been shown by Fe-57 Mossbauer spectroscopy that the observed enhancement in magnetic properties of BiFeO3 with Pr doping is mainly due to suppression of modulated spiral spin structure near x = 0.10 and not due to Fe multiple valence, i.e., oxygen deficiency. (C) 2013 AIP Publishing LLC.
Title:
Precession Electron Diffraction Tomography for Solving Complex Modulated Structures: the Case of Bi5Nb3O15
Authors:
Boullay, P; Palatinus, L; Barrier, N Author Full Names: Boullay, Philippe; Palatinus, Lukas; Barrier, Nicolas
Source:
INORGANIC CHEMISTRY, 52 (10):6127-6135; 10.1021/ic400529s MAY 20 2013
Abstract:
The crystal structure of the ID incommensurately modulated phase Bi5Nb3O15 [superspace group X2mb(0b0)000, a = 5.46781(7) angstrom, b = 5.47381(8) angstrom, c = 41.9005(5) angstrom, and q = 0.17588(8)b*] is solved by *electron* *diffraction* using a tomography technique combined with precession of the *electron* beam. The (3 + 1)D structure is further validated by a refinement against powder X-ray diffraction (PXRD). A coherent picture of the true nature of this compound is obtained, conciliating experimental observations made by different groups using transmission electron microscopy and PXRD. Bi5Nb3O15 does not have a mixed-layer Aurivillius-type structure but does contain structural elements, [Bi2O2](2+) slabs, and perovsldte-like blocks, characteristic of Aurivillius phases. The presence of aperiodic crystallographic shear planes (CSPs) along the modulated direction b leads to the formation of an original layered structure containing both continuous and discontinuous [Bi2O2](2+) and perovskite-like octahedral layers. Between CSPs, the stacking of these two structural elements exhibits an unprecedented nonuniform sequence referring to Aurivillius phases.
Title:
Structure, Atomistic Simulations, and Phase Transition of Stoichiometric Yeelimite
Authors:
Cuesta, A; De la Torre, AG; Losilla, ER; Peterson, VK; Rejmak, P; Ayuela, A; Frontera, C; Aranda, MAG Author Full Names: Cuesta, Ana; De la Torre, Angeles G.; Losilla, Enrique R.; Peterson, Vanessa K.; Rejmak, Pawel; Ayuela, Andres; Frontera, Carlos; Aranda, Miguel A. G.
Source:
CHEMISTRY OF MATERIALS, 25 (9):1680-1687; 10.1021/cm400129z MAY 14 2013
Abstract:
Yeelimite, Ca-4[Al6O12]SO4, is outstanding as an aluminate sodalite, being the framework of these type of materials flexible and dependent on ion sizes and anion ordering/disordering. On the other hand, yeelimite is also important from an applied perspective as it is the most important phase in calcium sulfoaluminate cements. However, its crystal structure is not well studied. Here, we characterize the room temperature crystal structure of stoichiometric yeelimite through joint Rietveld refinement using neutron and Xray powder diffraction data coupled with chemical soft-constraints. Our structural study shows that yeelimite has a lower symmetry than that of the previously reported tetragonal system, which we establish to likely be the acentric orthorhombic space group Pcc2, with a root 2a x root 2a X a superstructure based on the cubic sodalite structure. Final unit cell values were a = 13.0356(7) angstrom, b = 13.0350(7) angstrom, and c = 9.1677(2) angstrom. We determine several structures using density functional theory calculations, with the lowest energy structure being Pcc2 in agreement with our experimental result. Yeelimite undergoes a reversible phase transition to a higher-symmetry phase which has been characterized to occur at 470 degrees C by thermodiffractometry. The higher-symmetry phase is likely cubic or pseudocubic possessing an incommensurate superstructure, as suggested by our theoretical calculations which show a phase transition from an orthorhombic to a tetragonal structure. Our theoretical study also predicts a pressure-induced phase transition to a cubic structure of space group 1 (4) under bar 3m. Finally, we show that our reported crystal structure of yeelimite enables better mineralogical phase analysis of commercial calcium sulfoaluminate cements, as shown by R-F values for this phase, 6.9% and 4.8% for the previously published orthorhombic structure and for the one reported in this study, respectively.
Title:
Elastohydrodynamic problems in quasicrystal elasticity theory and wave propagation
Authors:
Li, XF Author Full Names: Li, X. F.
Source:
PHILOSOPHICAL MAGAZINE, 93 (13):1500-1519; 10.1080/14786435.2012.745655 MAY 1 2013
Abstract:
Elastohydrodynamic problems of decagonal quasicrystals are analysed where the phonon field obeys wave equation and the phason field obeys diffusive wave equation. Basic equations are solved in the quasiperiodic plane and periodic plane, respectively. Final governing equations of dynamic behaviours of decagonal quasicrystals are obtained. A general solution is derived in terms of introduced three auxiliary functions, where two individually satisfy a fourth-order partial differential equation and one satisfies a second-order hyperbolic diffusion equation. Using the derived governing equations, elastic waves propagating in the quasiperiodic plane and a plane containing the period axis are analysed. Secular equations are obtained. It is found that differing from conventional crystals, at least four branches of elastic waves exist when the phononphason coupling is present. Moreover, acoustic waves have attenuation during wave propagation. Phason fluctuations exhibit! exponential decaying behaviour due to kinematic viscosity and damping. The phase speeds are isotropic in the quasiperiodic plane and anisotropic in a plane with the periodic axis. The section of the slowness surfaces is plotted.
Title:
Hydrogen Absorption Study of Ti-based Alloys Performed by Melt-spinning
Authors:
Ribeiro, RM; Lemus, LF; dos Santos, DS Author Full Names: Ribeiro, R. M.; Lemus, L. F.; dos Santos, D. S.
Source:
MATERIALS RESEARCH-IBERO-AMERICAN JOURNAL OF MATERIALS, 16 (3):679-682; 10.1590/S1516-14392013005000049 MAY-JUN 2013
Abstract:
The hydrogen absorption and desorption of Ti53Zr27Ni20 icosahedral quasicrystal (ICQ) and Ti50Ni50 shape memory alloy (SMA) melt-spun ribbons was studied. Samples were exposed to hydrogen gas at 623 K and 4 MPa for 1000 minutes. The total capacity of hydrogen obtained for Ti53Zr27Ni20 and Ti50Ni50 was 3.2 and 2.4 wt. % respectively. The Thermal Desorption Spectrometry (TDS) of the hydrogenated alloys shows that both alloys start to desorb hydrogen around 750 K. X-ray diffraction (XRD) patterns, performed after hydrogenation, indicate a complete amorphization of the Ti53Zr27Ni20 i-phase alloy, while the Ti50Ni50 alloy remained crystalline after hydride formation.

Update: 4-Jul-2013

Title:
(3+1)D superspace description of the incommensurate modulation in the premartensite phase of Ni2MnGa: a high resolution synchrotron x-ray powder diffraction study
Authors:
Singh, S; Nayak, J; Rai, A; Rajput, P; Hill, AH; Barman, SR; Pandey, D Author Full Names: Singh, Sanjay; Nayak, J.; Rai, Abhishek; Rajput, Parasmani; Hill, Adrian H.; Barman, S. R.; Pandey, Dhananjai
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (21):10.1088/0953-8984/25/21/212203 MAY 29 2013
Abstract:
Le Bail and Rietveld analysis of high resolution synchrotron x-ray powder diffraction (SXRPD) data shows unambiguous signatures of the failure of the commensurate 3M modulation model. Using (3 + 1) dimensional superspace group formalism, we have not only confirmed the incommensurate modulation in the premartensite phase with a modulation wavevector of q = 0.337 61(5)c* but also determined the superspace group (Immm(00 gamma)s00), atomic positions and amplitude of modulations for the incommensurate premartensite phase of Ni2MnGa for the first time. Our results may have important implications in the understanding of the martensitic transition and hence the magnetic field induced strains.
Title:
Cu/Te substitution effects on superconductivity and microstructure of phase-separated K0.8Fe1.75Se2
Authors:
Wang, Z; Cai, Y; Wang, ZW; Sun, ZA; Yang, HX; Tian, HF; Ma, C; Zhang, B; Li, JQ Author Full Names: Wang, Z.; Cai, Y.; Wang, Z. W.; Sun, Z. A.; Yang, H. X.; Tian, H. F.; Ma, C.; Zhang, B.; Li, J. Q.
Source:
EPL, 102 (3):10.1209/0295-5075/102/37010 MAY 2013
Abstract:
Two series of K0.8Fe1.75-xCuxSe2 (0 <= x <= 0.15) and K0.8Fe1.75Se2-yTey (0 <= y <= 0.5) single crystals of nominal composition have been prepared and their physical properties and microstructural features have been studied. Resistivity measurements demonstrate that the superconducting transition temperature decreases gradually with the increase of the substitution level and zero resistivity finally disappears in both systems. Systematic TEM, SEM and XRD structural analyses, in combination with the magnetic experimental data, reveal a rich variety of structural phenomena resulting from different types of substitution. Cu substitution gives rise to the volume of a new non-superconducting Cu-rich phase with modulation q(3) = 1/3[2a* + b*] coexisting with the q(2) = 1/2[a* + b*] superconducting stripe domain. With the increase of the ratio of the new non-superconducting phase along with doping, the superconducting path is finally cut off, and results in the absence of zero resistivity. In contrast, the absence of superconductivity in Te-substituted materials is correlated with the complete disappearance of the q2 superconducting phase due to the suppression of phase separation. Copyright (C) EPLA, 2013
Title:
Discovery of stable icosahedral quasicrystals: progress in understanding structure and properties
Authors:
Tsai, AP Author Full Names: Tsai, An-Pang
Source:
CHEMICAL SOCIETY REVIEWS, 42 (12):5352-5365; 10.1039/c3cs35388e 2013
Abstract:
The geometrical concept and structural framework of quasicrystals (QCs) were established shortly after the discovery of QCs. Specifically, the static and dynamic properties of the atoms and the electronic structures of quasiperiodic lattices were theoretically developed. Experimental studies lagged behind theoretical progress due to the lack of suitable samples. This situation changed with the discovery of several highly ordered stable QCs. Studies of these new QCs have provided new insights into the structure and properties of QCs. This article chronologically reviews the discoveries of various stable icosahedral QCs and subsequent studies that determined their structures, properties, and stabilization mechanisms.

Update: 26-Jun-2013

Title:
Magnetic field and pressure effects on magnetism of bond-frustrated ZnCr2S4
Authors:
Xie, YM; Yang, ZR; Zhang, ZT; Shen, C; Li, L; Ling, LS; Pi, L; Sun, YP; Zhang, YH Author Full Names: Xie, Y. M.; Yang, Z. R.; Zhang, Z. T.; Shen, C.; Li, L.; Ling, L. S.; Pi, L.; Sun, Y. P.; Zhang, Y. H.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 339 81-83; 10.1016/j.jmmm.2013.03.010 AUG 2013
Abstract:
In this paper, magnetic field and hydrostatic pressure effects on magnetism of ZnCr2S4 were investigated. Upon cooling the sample at 0.5 T to 2 K then warming back, the magnetization displays irreversibility between the cooling and warming sequence at temperatures around incommensurate-commensurate antiferromagnetic transition T-N2. With increasing magnetic field or hydrostatic pressure, the irreversibility is gradually suppressed, although the thermal hysteresis is shifted to higher temperatures under pressure. The observed thermal hysteresis is attributed to a structural transition and evolution of different magnetic phases upon cooling and warming. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Solidification and microstructure of as-cast Mg65Zn32Y3 quasicrystal alloy
Authors:
Geng, JW; Teng, XY; Zhou, GR; Zhao, ZW Author Full Names: Geng, Jiwei; Teng, Xinying; Zhou, Guorong; Zhao, Zhenwei
Source:
PHYSICA B-CONDENSED MATTER, 420 64-69; 10.1016/j.physb.2013.03.035 JUL 1 2013
Abstract:
Stable icosahedral quasicrystal with a nominal composition of Mg30Zn60Y10 (at%) was prepared by an as-cast method. Applying X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques, the equilibrium solidification microstructures of Mg65Zn32Y3 (at%) quasicrystal alloy in Mg-rich corner of the Mg-Zn-Y system was investigated. Since resistivity is one of the physical properties sensitive to structures, it is suggested that there is a reversible temperature-induced solid-liquid structural transition. Quasicrystal possesses quasi-periodic lattice structure and especial electronic structure, which indicates the resistivity of Mg65Zn32Y3 quasicrystal alloy will change greatly during the melting or solidification processes. The temperature dependence on resistivity exhibits a clear turning point. Measuring resistivity-temperature curve (rho-T curve) and comparing with differential scanning calorimetry (DSC) first time, a study on the solidifi cation process of quasicrystal was carried out. The icosahedral quasicrystalline phase (I-phase) surrounded by eutectic microstructure (alpha-Mg+decagonal quasicrystalline phase (D-phase)) is reported first time. During the solidification process, the I-phase is formed at about 423 degrees C undergoing a peritectic reaction, and decagonal quasicrystal eutectic microstructure is formed at the later stage. The phase involved in this peritectic reaction has a composition of Mg28.93M46.62Y24.35 (W-phase). Furthermore, the quasicrystals with various characteristics morphologies exist some degree micro-segregation. And the microsegregation phenomenon in rod-like quasicrystalline phase is more serious than that in petals-like quasicrystalline phase. (c) 2013 Elsevier B.V. All rights reserved.
Title:
Simulation of modulated protein crystal structure and diffraction data in a supercell and in superspace
Authors:
Lovelace, JJ; Simone, PD; Petricek, V; Borgstahl, GEO Author Full Names: Lovelace, Jeffrey J.; Simone, Peter D.; Petricek, Vaclav; Borgstahl, Gloria E. O.
Source:
ACTA CRYSTALLOGRAPHICA SECTION D-BIOLOGICAL CRYSTALLOGRAPHY, 69 1062-1072; 10.1107/S0907444913004630 6 JUN 2013
Abstract:
The toolbox for computational protein crystallography is full of easy-to-use applications for the routine solution and refinement of periodic diffraction data sets and protein structures. There is a gap in the available software when it comes to aperiodic crystallographic data. Current protein crystallography software cannot handle modulated data, and small-molecule software for aperiodic crystallography cannot work with protein structures. To adapt software for modulated protein data requires training data to test and debug the changed software. Thus, a comprehensive training data set consisting of atomic positions with associated modulation functions and the modulated structure factors packaged as both a three-dimensional supercell and as a modulated structure in (3+1)D superspace has been created. The (3+1)D data were imported into Jana2006; this is the first time that this has been performed for protein data.
Title:
Structural phase transition and related electronic properties in quasi-one-dimensional (NbSe4)(10/3)
Authors:
Zubko, M; Kusz, J; Prodan, A; Sturm, S; van Midden, HJP; Bennett, JC; Dubin, G; Zupanic, E; Bohm, H Author Full Names: Zubko, Maciej; Kusz, Joachim; Prodan, Albert; Sturm, Saso; van Midden, Herman J. P.; Bennett, J. Craig; Dubin, Grzegorz; Zupanic, Erik; Boehm, Horst
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 69 229-237; 10.1107/S2052519213010336 3 JUN 2013
Abstract:
The real crystal structure of the (NbSe4)(10/3)I charge density wave (CDW) compound is studied by simulation of the X-ray diffuse scattering. The average structure of the low-temperature twinned phase is determined and the phase transition is attributed to the formation of a CDW. The diffuse streaking, present in X-ray diffraction patterns above and below the transition at T = 282 K, is shown to be a projection of diffuse concentric rings perpendicular to the c* direction. The simulated patterns, based on a mismatch model between infinite NbSe4 chains, correlated by I atoms, are in good accordance with the experimental patterns. In addition to the experiments, the electronic properties of the high-and the low-temperature phases are calculated with the extended Huckel tight-binding method. The Fermi surfaces of the average structures above and below the phase transition appear very similar. Their shapes support a nesting instability and a CDW for! mation. The weak incommensurate CDW satellites, present below the phase transition, are at 100 K properly described by a modulation wavevector q = [0.06 (1), 0, 0.55 (1)].
Title:
Observation of Electronic Inhomogeneity and Charge Density Waves in a Bilayer La2-2xSr1+2xMn2O7 Single Crystal
Authors:
Kim, J; Huang, JW; Zhou, JS; Goodenough, JB; Zheng, H; Mitchell, JF; de Lozanne, A Author Full Names: Kim, Jeehoon; Huang, Junwei; Zhou, J. -S.; Goodenough, J. B.; Zheng, H.; Mitchell, J. F.; de Lozanne, Alex
Source:
PHYSICAL REVIEW LETTERS, 110 (21):10.1103/PhysRevLett.110.217203 MAY 20 2013
Abstract:
We employed a scanning tunneling microscope to image the (001) surface topography and local density of states (LDOS) in La2-2xSr1+2xMn2O7 (x = 0.32, LSMO) single crystals below the Curie temperature (T-C approximate to 120 K). The LDOS maps revealed a stripelike modulation propagating along the tetragonal a axis with a wavelength of about 16 angstrom, which is indicative of a charge density wave (CDW). The observed CDW in the x = 0.32 sample is far from the Fermi surface nesting instability as compared with the data of angle resolved photoemission spectroscopy in an x = 0.40 sample. The stripe model developed previously for cuprates can explain the observed CDW in our LSMO sample, indicating that competing interactions between localized and itinerant phases are the origin of the spatial modulations present intrinsically in cuprates and manganites.
Title:
Structural and magnetic characterization of the intermartensitic phase transition in NiMnSn Heusler alloy ribbons
Authors:
Llamazares, JLS; Flores-Zuniga, H; Rios-Jara, D; Sanchez-Valdes, CF; Garcia-Fernandez, T; Ross, CA; Garcia, C Author Full Names: Sanchez Llamazares, J. L.; Flores-Zuniga, H.; Rios-Jara, D.; Sanchez-Valdes, C. F.; Garcia-Fernandez, T.; Ross, C. A.; Garcia, C.
Source:
JOURNAL OF APPLIED PHYSICS, 113 (17):10.1063/1.4800836 MAY 7 2013
Abstract:
Phase transitions and structural and magnetic properties of rapidly solidified Ni50Mn38Sn12 alloy ribbons have been studied. Ribbon samples crystallize as a single-phase, ten-layered modulated (10M) monoclinic martensite with a columnar-grain microstructure and a magnetic transition temperature of 308 K. By decreasing the temperature, martensite undergoes an intermartensitic phase transition around 195 K. Above room temperature, the high temperature martensite transforms into austenite. Below 100 K, magnetization hysteresis loops shift along the negative H-axis direction, confirming the occurrence of an exchange bias effect. On heating, the thermal dependence of the coercive field H-C shows a continuous increase, reaching a maximum value of 1017 Oe around 50 K. Above this temperature, H-C declines to zero around 195 K. But above this temperature, it increases again up to 20 Oe falling to zero close to 308 K. The coercivity values measured in both temperature intervals suggest a significant difference in the magnetocrystalline anisotropy of the two martensite phases. (C) 2013 AIP Publishing LLC.
Title:
Coexistence of incommensurate and commensurate spiral orders and pressure effect on polycrystalline CoCr2O4
Authors:
Chen, XL; Yang, ZR; Xie, YM; Huang, ZH; Ling, LS; Zhang, SL; Pi, L; Sun, YP; Zhang, YH Author Full Names: Chen, Xuliang; Yang, Zhaorong; Xie, Yuanmiao; Huang, Zhonghao; Ling, Langsheng; Zhang, Shile; Pi, Li; Sun, Yuping; Zhang, Yuheng
Source:
JOURNAL OF APPLIED PHYSICS, 113 (17):10.1063/1.4796172 MAY 7 2013
Abstract:
In this paper, we have investigated the magnetism of multiferroic CoCr2O4. With decreasing temperature, CoCr2O4 first undergoes a ferrimagnetic transition at T-C then a long-range spiral spin transition at T-S followed by a magnetic lock-in transition at T-L. Coercive force manifests different slopes in different magnetic phases. Upon cooling the sample at 100 Oe to 5 K then warming back, the magnetization displays irreversibility between the cooling and warming sequence at temperatures below T-L. The irreversible behavior under the thermal-cycling is inert to magnetic field up to 45 kOe, indicating the coexistence of incommensurate and commensurate spiral orders. Both T-S and T-L are increased with the application of high pressure, which implies that the magnetic frustration is enhanced upon the shrinkage of lattice. The spin-lattice coupling is also revealed by infrared spectrum. (C) 2013 American Institute of Physics.
Title:
Magnetic structure of GdNiSn
Authors:
Lee-Hone, NR; Lemoine, P; Ryan, DH; Verniere, A; Malaman, B Author Full Names: Lee-Hone, N. R.; Lemoine, P.; Ryan, D. H.; Verniere, A.; Malaman, B.
Source:
JOURNAL OF APPLIED PHYSICS, 113 (17):10.1063/1.4793642 MAY 7 2013
Abstract:
The magnetic structure of the TiNiSi-type GdNiSn compound has been studied by both Gd-155 Mossbauer spectrocopy and neutron powder diffraction. The results suggest a square-wave modulated magnetic structure characterized by the propagation vector k = [0.426, 0.351, 0] and Gd magnetic moments of 6.52(15) mu B (at 3.6 K) oriented along the c-axis. The results are compared with those of the isotypic RNiSn compounds and with the possible magnetic structures of GdNiSn proposed from earlier Gd-155 Mossbauer work. (C) 2013 American Institute of Physics.
Title:
Growth and Characterization of Centimeter-Sized Ba2LaFeNb4O15 Crystals from High-Temperature Solution under a Controlled Atmosphere
Authors:
Albino, M; Veber, P; Castel, E; Velazquez, M; Schenk, K; Chapuis, G; Lahaye, M; Pechev, S; Maglione, M; Josse, M Author Full Names: Albino, Marjorie; Veber, Philippe; Castel, Elias; Velazquez, Matias; Schenk, Kurt; Chapuis, Gervais; Lahaye, Michel; Pechev, Stanislav; Maglione, Mario; Josse, Michael
Source:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, (15):2817-2825; 10.1002/ejic.201300008 MAY 2013
Abstract:
Centimeter-sized single crystals of Ba2LaFeNb4O15 were grown from a high-temperature solution by using LiBO2 flux and a sealed platinum assembly. The obtained single crystals display the same physical properties as their ceramic counterparts. A frequency-dependent dielectric permittivity maximum was found (Tm = 100 K at 5 kHz), which indicates relaxor behavior. Magnetic susceptibility measurements revealed purely paramagnetic behavior between 10 and 350 K. X-ray diffraction measurements of Ba2LaFeNb4O15 single crystals revealed an incommensurate structure at room temperature with a bidimensional modulation characterized by vectors q1 = (, , 1/2) and q2 = (, , 1/2) with = 0.295(1). This crystal growth method offers a promising elaboration route to centimeter-sized crystals of niobate-based compounds, which may not be grown from the pure liquid phase, especially those with a tetragonal tungsten bronze (TTB) structure.

Update: 19-Jun-2013

Title:
Momentum-Dependent Charge Correlations in YBa2Cu3O6+delta Superconductors Probed by Resonant X-Ray Scattering: Evidence for Three Competing Phases
Authors:
Blanco-Canosa, S; Frano, A; Loew, T; Lu, Y; Porras, J; Ghiringhelli, G; Minola, M; Mazzoli, C; Braicovich, L; Schierle, E; Weschke, E; Le Tacon, M; Keimer, B Author Full Names: Blanco-Canosa, S.; Frano, A.; Loew, T.; Lu, Y.; Porras, J.; Ghiringhelli, G.; Minola, M.; Mazzoli, C.; Braicovich, L.; Schierle, E.; Weschke, E.; Le Tacon, M.; Keimer, B.
Source:
PHYSICAL REVIEW LETTERS, 110 (18):10.1103/PhysRevLett.110.187001 MAY 1 2013
Abstract:
We use resonant x-ray scattering to determine the momentum-dependent charge correlations in YBa2Cu3O6.55 samples with highly ordered chain arrays of oxygen acceptors (ortho-II structure). The results reveal nearly critical, biaxial charge density wave (CDW) correlations at in-plane wave vectors (0.315, 0) and (0, 0.325). The corresponding scattering intensity exhibits a strong uniaxial anisotropy. The CDW amplitude and correlation length are enhanced as superconductivity is weakened by an external magnetic field. Analogous experiments are carried out on a YBa2Cu3O6.6 crystal with a dilute concentration of spinless (Zn) impurities, which had earlier been shown to nucleate incommensurate magnetic order. Compared to pristine crystals with the same doping level, the CDW amplitude and correlation length are found to be strongly reduced. These results indicate a three-phase competition between spin-modulated, charge-modulated, and superconducting states in underdoped YBa2Cu3O6+del! ta.
Title:
Commensurate and incommensurate states of a spin density wave in a quasi-two-dimensional system with an anisotropic energy spectrum in an external magnetic field of arbitrary direction relative to magnetization
Authors:
Palistrant, ME; Ursu, VA Author Full Names: Palistrant, M. E.; Ursu, V. A.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 116 (4):641-656; 10.1134/S1063776113040080 APR 2013
Abstract:
A theory of thermodynamic properties of a spin density wave (SDW) in a quasi-two-dimensional system (with a preset impurity concentration x) is constructed. We choose an anisotropic dispersion relation for the electron energy and assume that external magnetic field H has an arbitrary direction relative to magnetic moment M (Q) . The system of equations defining order parameters M (Q) (z) , M (Q) (sigma) , M (z) , and M (sigma) is constructed and transformed with allowance for the Umklapp processes. Special cases when H aEuro- M (Q) and H aSyen M (Q) (H (Z) H (sigma) = 0) are considered in detail as well as cases of weak fields H of arbitrary direction. The condition for the transition of the system to the commensurate and incommensurate states of the SDW is analyzed. The concentration dependence of magnetic transition temperature T (M) is calculated, and the components of the order parameter for the incommensurate phase are determined. The phase diagram (T,similar to x) is constructed. The effect of the magnetic field on magnetic transition temperature T (M) is analyzed for H (Z) H (sigma) = 0, and longitudinal magnetic susceptibility chi aEuro- is calculated; this quantity demonstrates the temperature dependence corresponding to a system with a gap for x < x (c) and to a gapless state for x > x (c) . In the immediate vicinity of the critical impurity concentration (x similar to x (c) ), the temperature dependence of the magnetic susceptibility acquires a local maximum. The effect of anisotropy of the electron energy spectrum on the investigated physical quantities is also analyzed.

Update: 12-Jun-2013

Title:
Conspicuous variation of the lattice unit cell in the pavonite homologous series and its relation with cation/anion occupational modulations
Authors:
Perez-Mato, JM; Elcoro, L; Makovicky, E; Topa, D; Peticek, V; Madariaga, G Author Full Names: Perez-Mato, J. M.; Elcoro, Luis; Makovicky, Emil; Topa, Dan; Petricek, Vaclav; Madariaga, Gotzon
Source:
MATERIALS RESEARCH BULLETIN, 48 (6):2166-2174; 10.1016/j.materresbull.2013.02.008 JUN 2013
Abstract:
The pavonites is a homologous series of sulfosalts with galena-like modules of variable size. A survey of their unit cells reveals that they are severely constrained by the metrics of an underlying common average sublattice. The unit cell of any compound of the series accommodates with high precision an integer number of approximately equal subcells. This explains a peculiar non-uniform variation of the unit cell parameters within the series and evidences that the interface between the galena-like modules, despite having a very different topology, approximately maintains the subperiodicity of the modules, and must therefore be subject to strong steric restrictions. It also implies that cations and anions occupy the nodes of the observed common underlying average sublattice according to a striking alternate cation/anion occupational modulation. This is the starting point for a description of these materials as modulated structures, which can make a proficient use of the approximate atomic positional non-crystallographic correlations caused by their modular character. Under this approach only four parameters suffice to define a realistic approximate model of any member of the series. A full structural characterization of any of the compounds only requires the determination of additional small/smooth modulations. As an example, the case of the P-7 pavonite Ag3Bi6.2Pb0 8S12, is analyzed. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Short- and long-range ordering during the phase transition of the Zn6Sc 1/1 cubic approximant
Authors:
Yamada, T; Euchner, H; Gomez, CP; Takakura, H; Tamura, R; de Boissieu, M Author Full Names: Yamada, Tsunetomo; Euchner, Holger; Gomez, Cesar Pay; Takakura, Hiroyuki; Tamura, Ryuji; de Boissieu, Marc
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (20):10.1088/0953-8984/25/20/205405 MAY 22 2013
Abstract:
Using in situ x-ray scattering and synchrotron radiation, we have experimentally elucidated the mechanism of the cubic to monoclinic phase transition in the Zn6Sc 1/1 approximant to an icosahedral quasicrystal. The high-temperature cubic phase is described as a bcc packing of a large Tsai-type icosahedral cluster whose center is occupied by an orientationally disordered Zn-4 tetrahedron. A clear monoclinic distortion has been found to take place within 2 K around T-c = 157 K, in excellent agreement with the observed anomalies in the electrical resistivity and heat capacity. Also, a rapid variation of the super-structure reflection intensity is observed. The low-temperature monoclinic phase, as determined by single-crystal x-ray diffraction at 40 K, has been confirmed to consist of ordered Zn-4 tetrahedra, oriented in an anti-parallel way along the [(1) over bar 01] direction. Above T-c, a diffuse scattering signal is observed at the position of the super-structure reflections, which evidences that a short-range ordering of the Zn-4 tetrahedra takes place. In a way similar to a second-order phase transition, the correlation length describing this short-range ordering increases rapidly when the temperature diminishes and almost diverges when the temperature is close to T-c, going from 200 angstrom at 220 K to reach the very large value of 1200 angstrom at 161 K. Finally, using single-crystal x-ray diffraction, the atomic structure of the low-temperature monoclinic super-structure (space group C2/c) could be solved. The ordering of the Zn-4 tetrahedra is accompanied by a strong distortion of the surrounding shells.
Title:
Magnetic and crystal structure determination of Mn2FeSbO6 double perovskite
Authors:
Dos Santos-Garcia, AJ; Ritter, C; Solana-Madruga, E; Saez-Puche, R Author Full Names: Dos Santos-Garcia, A. J.; Ritter, C.; Solana-Madruga, E.; Saez-Puche, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (20):10.1088/0953-8984/25/20/206004 MAY 22 2013
Abstract:
The perovskite form of the Mn2FeSbO6 oxide has been obtained at 5.5 GPa and 1523 K. X-ray and neutron diffraction data reveal that this compound crystallizes in the monoclinic P2(1)/n space group with a = 0.5234 nm, b = 0.5389 nm, c = 0.7642 nm and beta = 90.372 degrees lattice parameters. AC and DC magnetic susceptibility measurements suggest the existence of a complex magnetic behavior below 200 K. The magnetic structure has been determined and can be described on the basis of an elliptical spiral with an incommensurate propagation vector, k = [0, 0.426, 0], where the magnetic moments of 2Mn(2+) and Fe3+ cations are confined to the ac-plane.
Title:
A (3+3)-Dimensional "Hypercubic" Oxide-Ionic Conductor: Type II Bi2O3-Nb2O5
Authors:
Ling, CD; Schmid, S; Blanchard, PER; Petricek, V; McIntyre, GJ; Sharma, N; Maljuk, A; Yaremchenko, AA; Kharton, VV; Gutmann, M; Withers, RL Author Full Names: Ling, Chris D.; Schmid, Siegbert; Blanchard, Peter E. R.; Petricek, Vaclav; McIntyre, Garry J.; Sharma, Neeraj; Maljuk, Andrey; Yaremchenko, Aleksey A.; Kharton, Vladislav V.; Gutmann, Matthias; Withers, Ray L.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 135 (17):6477-6484; 10.1021/ja3109328 MAY 1 2013
Abstract:
The high-temperature cubic form of bismuth oxide, delta-Bi2O3, is the best intermediate-temperature oxide-ionic conductor known. The most elegant way of stabilizing delta-Bi2O3 to room temperature, while preserving a large part of its conductivity, is by doping with higher valent transition metals to create wide solid-solutions fields with exceedingly rare and complex (3 + 3)-dimensional incommensurately modulated "hypercubic" structures. These materials remain poorly understood because no such structure has ever been quantitatively solved and refined, due to both the complexity of the problem and a lack of adequate experimental data. We have addressed this by growing a large (centimeter scale) crystal using a novel refluxing floating-zone method, collecting high-quality single-crystal neutron diffraction data, and treating its structure together with X-ray diffraction data within the superspace symmetry formalism. The structure can be understood as an "inflated" pyrochlore, in which corner-connected NbO6 octahedral chains move smoothly apart to accommodate the solid solution. While some oxide vacancies are ordered into these chains, the rest are distributed throughout a continuous three-dimensional network of wide delta-Bi2O3-like channels, explaining the high oxide-ionic conductivity compared to commensurately modulated phases in the same pseudobinary system.
Title:
Correlation between structures and properties in (Zr65Cu15Ni10Al10)(90)Nb-10 alloys
Authors:
Zhang, JL; Wang, YM; Shek, CH Author Full Names: Zhang, Ji Liang; Wang, Ying Min; Shek, Chan Hung
Source:
JOURNAL OF MATERIALS RESEARCH, 28 (9):1218-1223; 10.1557/jmr.2013.22 MAY 2013
Abstract:
A quasicrystal (QC)-based alloy composite was made by copper mold casting under a low-vacuum level condition at the bulk metallic glass (BMG)- forming composition (Zr65Cu15Al10Ni10)(90)Nb-10. The QC alloy consisted of a majority of icosahedral quasicrystal phase and a small amount Zr-rich glassy phase. Under uniaxial compression at room temperature, the BMG alloy exhibits a certain plastic strain; the QC alloy is much stronger but brittle. The icosahedral glass model was used to describe the I-phase structure. The structure-property relations of the BMG and QC alloys are discussed assuming the common preferential icosahedral atomic structure in both cases and the existence of local glue structure in the BMG structure.
Title:
Symmetry of Quasicrystals
Authors:
Madison, AE Author Full Names: Madison, A. E.
Source:
PHYSICS OF THE SOLID STATE, 55 (4):855-867; 10.1134/S1063783413040185 APR 2013
Abstract:
The definition of an aperiodic crystal (quasicrystal) as a solid that is characterized by the forbidden symmetry suggests the existence of an unsolved problem, because, in a mutually exclusive manner, it appeals to the fundamental theorem of classical crystallography. Using the Penrose tiling as an example, we have investigated the symmetry properties of aperiodic tilings for the purpose to establish the allowed symmetry groups of quasicrystals. The filling of the Euclidean space according to an aperiodic law is considered as the action of an infinite number of group elements on a fundamental domain in the non-Euclidean space. It is concluded that all locally equivalent tilings have a common "parent" structure and, consequently, the same symmetry group. An idealized object, namely, an infinitely refined tiling, is introduced. It is shown that the symmetry operations of this object are operations of the similarity (rotational homothety). A positive answer is given to the question about a possible composition of operations of the similarity with different singular points. It is demonstrated that the transformations of orientation-preserving aperiodic crystals are isomorphic to a discrete subgroup of the Mobius group PSL(2, C); i.e., they can be realized as discrete subgroups of the full group of motions in the Lobachevsky space. The problem of classification of the allowed types of aperiodic tilings is reduced to the procedure of enumeration of the aforementioned discrete subgroups.

Update: 5-Jun-2013

Title:
Pd2Cd11-delta (0.21 <= delta <= 0.51)-a partly disordered gamma-brass type phase and Pd0.238Cd0.762-a gamma-brass related incommensurate phase in the palladium-cadmium system
Authors:
Jana, PP; Lidin, S Author Full Names: Jana, Partha Pratim; Lidin, Sven
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 201 244-249; 10.1016/j.jssc.2013.01.044 MAY 2013
Abstract:
The Cd rich part of the Cd-Pd phase diagram was reassessed by means of synthesis and single crystal and powder X-ray diffraction. The region contains two phases that have been reported to have substantial compositional widths, Cd11Pd2 and Cd4Pd. The phase Cd11Pd2 that has previously been reported to be a disordered gamma-brass crystallizing is space group P (4) over bar 3m is here shown to crystallize in I (4) over bar 3m and the mechanism for compositional variation is explained. The phase Pd4Cd has previously been shown to constitute a phase field or a phase bundle of modulated structures and here we determine the structure of a compound Pd0.238Cd0.762 which crystallizes in the orthorhombic superspace group Fmmm(alpha 00)0s0 (F=[(1/2, 1/2, 0, 0); (1/2, 0, 1/2, 0); (0, 1/2, 1/2, 0)] with the fundamental cell dimensions a=4.687(2) angstrom, b=10.000(1) angstrom, c=14.140(2) angstrom, q=0.6432(6)a*. (C) 2013 Elsevier Inc. All rights reserved.
Title:
Magnetic transition in K4Cu4OCl10: A model system of three-dimensional spin-1/2 tetrahedra
Authors:
Fujihala, M; Zheng, XG; Morodomi, H; Kawae, T; Watanabe, I Author Full Names: Fujihala, Masayoshi; Zheng, Xu-Guang; Morodomi, Hiroki; Kawae, Tatsuya; Watanabe, Isao
Source:
PHYSICAL REVIEW B, 87 (14):10.1103/PhysRevB.87.144425 APR 30 2013
Abstract:
Isolated spin tetrahedral systems with weak intertetrahedral couplings, as have been reported for Cu2Te2O5X2 (X = Cl, Br) and the related compound Cu4Te5O12Cl4, have received much attention recently because they represent an interesting class of magnets that consist of weakly coupled magnetic clusters and, in particular, they can directly demonstrate the interplay of intertetrahedral couplings with built-in tetrahedral frustration. However, there is much debate about the structural low dimensionality of the Cu-Te-O-Cl(Br) compounds and its effect on the magnetism of the material. Here, we present a model spin tetrahedral system K4Cu4OCl10, with almost isotropic magnetic coupling within the tetrahedron and three-dimensional connection of the tetrahedra. The system enters a spin-singlet state with a susceptibility maximum at T-max = 11 K, and then enters an antiferromagnetic order at T-N = 4.4 K. The ratio T-N/T-max = 0.40 is close to the T-N/T-max = 0.38 for Cu2Te2O5Br2, which is viewed as an indicator of closeness to quantum criticality. Evidence in muon-spin rotation or relaxation suggests an incommensurate ordering. This work shows that the previously revealed ground state in anisotropically structured Cu2Te2O5X2 compounds also exists in an isotropic spin tetrahedral system. DOI: 10.1103/PhysRevB.87.144425

Update: 30-May-2013

Title:
Phase Diagrams of He-4 on Flat and Curved Environments
Authors:
Gordillo, MC; Boronat, J Author Full Names: Gordillo, M. C.; Boronat, J.
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS, 171 (5-6):606-612; 10.1007/s10909-012-0790-5 JUN 2013
Abstract:
By means of diffusion Monte Carlo calculations, we obtained the phase diagrams of a first and second layer of He-4 on graphene and on the outside of different isolated armchair carbon nanotubes with radii in the range 3.42 to 10.85 . That corresponds to tubes between the (5, 5) and (16, 16) in standard nomenclature. In both cases, the ground state is either a liquid (second layer on graphene and on nanotubes whose radii is greater than similar to 7 ) or an incommensurate solid (for thinner tubes). In the former case, upon a density increase, the system undergoes a first-order phase transition to another incommensurate solid. A study of the influence of the C-He potential (isotropic or anisotropic) on the phase diagrams is also presented.
Title:
Effect of Icosahedral Quasicrystalline Fraction and Extrusion Ratio on Microstructure, Mechanical Properties, and Anisotropy of Mg-Zn-Gd-Based Alloys
Authors:
Huang, H; Yuan, GY; Wang, ZC; Chen, CL; Ding, WJ Author Full Names: Huang, Hua; Yuan, Guangyin; Wang, Zhongchang; Chen, Chunlin; Ding, Wenjiang
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 44A (6):2725-2734; 10.1007/s11661-013-1609-y JUN 2013
Abstract:
We have fabricated three types of Mg-Zn-Gd-based alloys containing the icosahedral quasicrystalline phase (I-phase) to investigate how volume fraction of the I-phase and extrusion ratio can have an impact on the microstructure, mechanical properties, and anisotropy of the as-extruded alloys. We find that grains are refined and that the ultimate tensile strength and elongation are improved as either the volume fraction of I-phase or the extrusion ratio is increased, which can be attributed to the secondary phase particle stimulate recrystallization nucleation and restrained grain boundary motion. Moreover, anisotropy is mitigated in all of the alloys as either the I-phase fraction or the extrusion ratio is increased owing to the coeffect of texture weakening and grain refinement as well as to the effect of I-phase on twinning. We also find that with the increase in the amount of the I-phase, the yield strength (YS) is decreased for the alloys extruded at a low ratio owing to the texture weakening, yet it is increased for the alloys extruded at high ratio owing to the strengthening originating from the I-phase and refined grains. The mechanical properties are improved for the alloys extruded at high ratio, which is due to their fine grains and uniform microstructure.
Title:
H-2 Physisorbed on Graphane
Authors:
Carbonell-Coronado, C; de Soto, F; Cazorla, C; Boronat, J; Gordillo, MC Author Full Names: Carbonell-Coronado, C.; de Soto, F.; Cazorla, C.; Boronat, J.; Gordillo, M. C.
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS, 171 (5-6):619-625; 10.1007/s10909-012-0828-8 JUN 2013
Abstract:
We study the zero-temperature phase diagrams of H-2 adsorbed on the three structures predicted for graphane (chair, boat and washboard graphane), using a diffusion Monte Carlo technique. Graphane is the hydrogenated version of graphene, in which each carbon atom changes its hybridization to sp (3) and forms a covalent bond with a hydrogen atom. Our results show that the ground state of H-2 adsorbed on all three types of graphane is a solid, similar to the structures found both for H-2 and D-2 on graphene. When the H-2 density increases, the system undergoes a first order phase transition to a triangular incommensurate solid. This change is direct in the case of washboard graphane, but indirect via different commensurate structures in the other cases. The total hydrogen weight percentage on the three graphane types in their ground states is in the range 10 % to 12 %, depending on if one or both graphane surfaces are covered with H-2.
Title:
Structural and Superfluid Properties of the He-4 Monolayer on a C-28 Molecule
Authors:
Kim, B; Kwon, Y Author Full Names: Kim, Byeongjoon; Kwon, Yongkyung
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS, 171 (5-6):599-605; 10.1007/s10909-012-0732-2 JUN 2013
Abstract:
We have performed path-integral Monte Carlo calculations to study the adsorption of N He-4 atoms on a single C-28 fullerene molecule. Radial density distributions show a layer-by-layer growth of He-4 with the first adlayer being located at a distance of 5.3 from the center of C-28. The monolayer is found to show a commensurate structure at N=16 with each of the 16 adsorption sites on the molecular surface being occupied by one He-4 atom. As more helium atoms are adsorbed beyond N=16, the adlayer is in a mixed state consisting of 4 localized atoms at the hexagonal faces and the other atoms delocalized over the pentagonal faces. Another structurally-ordered state is observed at N=32, where the helium layer shows the same crystalline structure with an icosahedral symmetry as observed for 32 He-4 atoms on a C-60 molecule. It is found that more He-4 atoms can be squeezed into the first layer to disrupt this icosahedral structure when enough He-4 atoms are added in the second layer. Finally we observe the reentrant superfluid response of the monolayer with superfluidity being quenched completely at the ordered states of N=16 and 32.
Title:
Investigation of the electromagnon excitations in the multiferroic TbMn2O5
Authors:
Petit, S; Baledent, V; Doubrovsky, C; Lepetit, MB; Greenblatt, M; Wanklyn, B; Foury-Leylekian, P Author Full Names: Petit, S.; Baledent, V.; Doubrovsky, C.; Lepetit, M. B.; Greenblatt, M.; Wanklyn, B.; Foury-Leylekian, P.
Source:
PHYSICAL REVIEW B, 87 (14):10.1103/PhysRevB.87.140301 APR 25 2013
Abstract:
Multiferroic materials in which magnetism and ferroelectricity coexist are a time-honored subject of study, opening the route for the next generation of electronic devices. Understanding the pronounced interplay between these properties is a current challenge, especially for the realization of multiferroic devices. One of the largest reversible magnetoelectric couplings has been evidenced in TbMn2O5, the reference compound of the so-called RMn2O5 multiferroics. The origin of this strong coupling has been intensively studied from the static properties. Here we report an inelastic neutron scattering investigation of the dynamic properties in this famous compound. Our work sheds light on the electromagnon, a hybrid mode theoretically predicted in multiferroics, which couples magnetic excitations with polar lattice degrees of freedom. We were able to determine in TbMn2O5 the exchange constants of a model Heisenberg Hamiltonian and to identify the spin excitation that transforms in the electromagnon on passing from the ferroelectric and magnetically collinear phase to the low temperature incommensurate and weakly ferroelectric one. Our results point to the unusual feature of the dynamic magnetoelectric coupling in this series of multiferroics. DOI: 10.1103/PhysRevB.87.140301
Title:
Phase transitions in europium at high pressures
Authors:
Husband, RJ; Loa, I; Stinton, GW; Ackland, GJ; McMahon, MI Author Full Names: Husband, R. J.; Loa, I.; Stinton, G. W.; Ackland, G. J.; McMahon, M. I.
Source:
HIGH PRESSURE RESEARCH, 33 (1):158-164; 10.1080/08957959.2013.775280 MAR 1 2013
Abstract:
For several decades, x-ray diffraction studies on europium (Eu) metal at high pressure were complicated by the presence of a rhombo-hedral contaminant phase, hR6, which has been recognised as such only recently. Using x-ray powder diffraction, we have determined the hR6 contaminant to undergo a phase transition to a cubic phase, cI12, at 34.8(12)GPa. Consideration of the volume per Eu atom of the two contaminant phases at the same pressure suggests that they have different stoichiometries or chemical compositions. We also report a phase transition in pure Eu from the incommensurately-modulated Eu-IV phase to Eu-V between 38 and 42GPa.

Update: 22-May-2013

Title:
Magnetism of the chromium thio-spinels Fe1-xCuxCr2S4 studied using muon spin rotation and relaxation
Authors:
Kalvius, GM; Krimmel, A; Wappling, R; Hartmann, O; Litterst, FJ; Wagner, FE; Tsurkan, V; Loidl, A Author Full Names: Kalvius, G. M.; Krimmel, A.; Wappling, R.; Hartmann, O.; Litterst, F. J.; Wagner, F. E.; Tsurkan, V.; Loidl, A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (18):10.1088/0953-8984/25/18/186001 MAY 8 2013
Abstract:
Powder samples of Fe1-xCuxCr2S4 with x = 0, 0.2, 0.5, 0.8 were studied, between 5 and 300 K. The results reveal that for x < 1, the magnetic order in the series is more varied than the simple collinear ferrimagnetic structure traditionally assumed to exist everywhere from the Curie point to T -> 0. In FeCr2S4 several ordered magnetic phases are present, with the ground state likely to have an incommensurate cone-like helical structure. Fe0.8Cu0.2Cr2S4 is the compound for which simple collinear ferrimagnetism is best developed. In Fe0.5Cu0.5Cr2S4 the ferrimagnetic spin structure is not stable, causing spin reorientation around 90 K. In Fe0.2Cu0.8Cr2S4 the ferrimagnetic structure is at low temperatures considerably distorted locally, but with rising temperature this disorder shows a rapid reduction, coupled to increased spin fluctuation rates. In summary, the present data show that the changes induced by the replacement of Fe by Cu have more profound influences on the magnetic properties of the Fe1-xCuxCr2S4 compounds than merely a shift of Curie temperature, saturation magnetization and internal field magnitude.
Title:
Incommensurate phases in the statistical theory of the crystalline state
Authors:
Golovko, VA Author Full Names: Golovko, V. A.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 341-354; 10.1107/S0108767313003619 3 MAY 2013
Abstract:
The paper is devoted to the elaboration of a mathematical apparatus for studying second-order phase transitions, both commensurate and incommensurate, and the properties of emerging phases on the basis of the approach in equilibrium statistical mechanics proposed earlier by the author. It is shown that the preliminary symmetry analysis for a concrete crystal can be performed analogously with the one in the Landau phenomenological theory of phase transitions. The analysis enables one to deduce a set of transcendental equations that describe the emerging phases and corresponding phase transitions. The treatment of an incommensurate phase is substantially complicated because the symmetry of the phase cannot be described in terms of customary space groups. For this reason, a strategy of representing the incommensurate phase as the limit of a sequence of long-period commensurate phases whose period tends to infinity is worked out.
Title:
Periodic entanglement I: networks from hyperbolic reticulations
Authors:
Evans, ME; Robins, V; Hyde, ST Author Full Names: Evans, Myfanwy E.; Robins, Vanessa; Hyde, Stephen T.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 241-261; 10.1107/S0108767313001670 3 MAY 2013
Abstract:
High-symmetry free tilings of the two-dimensional hyperbolic plane (H-2) can be projected to genus-3 3-periodic minimal surfaces (TPMSs). The three-dimensional patterns that arise from this construction typically consist of multiple catenated nets. This paper presents a construction technique and limited catalogue of such entangled structures, that emerge from the simplest examples of regular ribbon tilings of the hyperbolic plane via projection onto four genus-3 TPMSs: the P, D, G(yroid) and H surfaces. The entanglements of these patterns are explored and partially characterized using tools from TOPOS, GAVROG and a new tightening algorithm.
Title:
Quasirandom quasicrystals
Authors:
Hornfeck, W Author Full Names: Hornfeck, Wolfgang
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 355-364; 10.1107/S0108767313005412 3 MAY 2013
Abstract:
Two-dimensional point sets derived from pairs of quasirandom numbers generated by the bit-reversal method introduced by van der Corput exhibit features well known from the quasiperiodic binary substitution tilings derived from the rhombic tilings of Penrose and Ammann-Beenker. The concept of geometric discrepancy, a measure describing the uniformity of distribution of quasirandom sequences or point sets, is discussed from the perspective of structural chemistry.
Title:
Cluster-packing geometry for Al-based F-type icosahedral alloys
Authors:
Fujita, N; Takano, H; Yamamoto, A; Tsai, AP Author Full Names: Fujita, Nobuhisa; Takano, Hikari; Yamamoto, Akiji; Tsai, An-Pang
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 322-340; 10.1107/S0108767313005035 3 MAY 2013
Abstract:
This paper presents a new, highly stable, periodic approximant to the Al-based F-type icosahedral quasicrystals, i-Al-Pd-TM (TM = transition metals). The structure of this intermetallic Al-Pd-Cr-Fe compound is determined ab initio using single-crystal X-ray diffraction, where the space group is identified to be Pa (3) over bar and the lattice constant 40.5 angstrom. The structure is well described as a dense packing of clusters of two kinds, which are called the pseudo-Mackay-type and the mini-Bergman-type clusters. Adjacent clusters can be markedly interpenetrated, while the structure requires no glue atoms to fill in the gaps between the clusters. It is shown that the clusters are centred at the vertices of a canonical cell tiling, which corresponds to a 2 x 2 x 2 superstructure of Henley's cubic 3/2 packing, and that the parity of each vertex determines the kind of associated cluster. The proper quasi-lattice constant for describing the cluster packing is 1/tau (tau = golden mean) times the conventional one used to describe Al-based P-type icosahedral alloys. The superstructure ordering of the present approximant turns out to be of a different kind from the P-type superstructure ordering previously reported in i-Al-Pd-Mn. The present results will greatly improve the understanding of atomic structures of F-type icosahedral quasicrystals and their approximants.
Title:
Crack analysis in decagonal quasicrystals by the MLPG
Authors:
Sladek, J; Sladek, V; Krahulec, S; Zhang, C; Wunsche, M Author Full Names: Sladek, J.; Sladek, V.; Krahulec, S.; Zhang, Ch.; Wuensche, M.
Source:
INTERNATIONAL JOURNAL OF FRACTURE, 181 (1):115-126; 10.1007/s10704-013-9825-4 MAY 2013
Abstract:
A meshless method based on the local Petrov-Galerkin approach is proposed to solve initial-boundary-value crack problems in decagonal quasicrystals. These quasicrystals belong to the class of two-dimensional (2-d) quasicrystals, where the atomic arrangement is quasiperiodic in a plane, and periodic in the perpendicular direction. The ten-fold symmetries occur in these quasicrystals. The 2-d crack problem is described by a coupling of phonon and phason displacements. Both stationary governing equations and dynamic equations represented by the Bak's model with oscillations for phasons are analyzed here. Nodal points are spread on the analyzed domain, and each node is surrounded by a small circle for simplicity. The spatial variation of phonon and phason displacements is approximated by the moving least-squares scheme. After performing the spatial integrations, one obtains a system of ordinary differential equations for certain nodal unknowns. That system is solved numerically by the Houbolt finite-difference scheme as a time-stepping method.
Title:
Effects of frustration on magnetic excitations in a two-leg spin-ladder system
Authors:
Sugimoto, T; Mori, M; Tohyama, T; Maekawa, S Author Full Names: Sugimoto, Takanori; Mori, Michiyasu; Tohyama, Takami; Maekawa, Sadamichi
Source:
PHYSICAL REVIEW B, 87 (15):10.1103/PhysRevB.87.155143 APR 24 2013
Abstract:
We theoretically study the magnetic excitations in a frustrated two-leg spin-ladder system, in which antiferromagnetic exchange interactions act on the nearest-neighbor and next-nearest-neighbor bonds in the leg direction, and on the nearest-neighbor bonds in the rung direction. A dynamical spin correlation function at zero temperature is calculated using the dynamical density-matrix renormalization-group method for possible magnetic phases, i.e., columnar-dimer and rung-singlet phases. The columnar-dimer phase is characterized by multispinon excitations with a spin gap, whereas the rung-singlet phase is dominated by the triplet excitation in the rung direction. One major difference found between these two phases appears in the spectral weight of magnetic excitations, in particular, the bonding and antibonding modes in the rung direction. Therefore, we can distinguish one phase from the other by the difference in the spectral weight. Furthermore, we examine the effect of frustration on both modes in the rung-singlet phase with a perturbation theory from the strong coupling limit. The antibonding mode is shown to be stable against frustration, and a wave number with minimum excitation energy is shifted from being commensurate to being incommensurate. In contrast, the bonding mode is merged into the continuum excitation of multiple triplet excitations by increasing frustration. By comparing our results with inelastic neutron scattering experiments for BiCu2PO6, the magnitude of the magnetic exchange interactions and the ground state will be determined. DOI: 10.1103/PhysRevB.87.155143
Title:
Spin Density Wave Fluctuations and p-Wave Pairing in Sr2RuO4
Authors:
Huo, JW; Rice, TM; Zhang, FC Author Full Names: Huo, Jia-Wei; Rice, T. M.; Zhang, Fu-Chun
Source:
PHYSICAL REVIEW LETTERS, 110 (16):10.1103/PhysRevLett.110.167003 APR 18 2013
Abstract:
Recently, a debate has arisen over which of the two distinct parts of the Fermi surface of Sr2RuO4 is the active part for the chiral p-wave superconductivity exhibited. Early theories proposed p-wave pairing on the two-dimensional gamma band, whereas a recent proposal focuses on the one-dimensional (alpha, beta) bands whose nesting pockets are the source of the strong incommensurate spin density wave (SDW) fluctuations. We apply a renormalization group theory to study quasi-one-dimensional repulsive Hubbard chains and explain the form of SDW fluctuations, reconciling the absence of long-range order with their nesting Fermi surface. The mutual exclusion of p-wave pairing and SDW fluctuations in repulsive Hubbard chains favors the assignment of the two-dimensional gamma band as the source of p-wave pairing. DOI: 10.1103/PhysRevLett.110.167003
Title:
On similarity of structure of icosahedral viral capsids and shells of metallic nanoclusters
Authors:
Shevchenko, VY; Blatov, VA; Ilyushin, GD Author Full Names: Shevchenko, V. Ya.; Blatov, V. A.; Ilyushin, G. D.
Source:
GLASS PHYSICS AND CHEMISTRY, 39 (2):101-104; 10.1134/S1087659613020144 MAR 2013
Abstract:
TOPOS software has been applied for searching for topological types of viral capsids-virus shells generated by self-assembly of proteins into geometrically ordered structure (VIPERdb database). Three topological capsid types that characterize packing of capsomeres (1) in the form of 12-vertex icosahedron (its vertex are occupied with pentamers), (2) in the form of 32-vertex polyhedron (12-pentamers + 20-hexamers), and (3) in the form of 62-vertex polyhedron (12-pentamers + 50-hexamers) have been outlined. The three mentioned polyhedral shells have been presented in the form of graphs of edge nets and applied for searching for relevant nanocluster fragments in the developed database of intermetallic compounds (25808 structures). It has been established that local structures in the form of icosahedral shells can be met in 6403 (27.1%) intermetallic compounds. Thirty-two atom shells have been found in 469 (2.0%) intermetallic compounds; furthermore, they are always the second shells of Bergman nanoclusters where the first shell is icosahedron. Sixty-two atom polyhedral shells in intermetallic compounds have not been found in intermetallic compounds; however, a modified 110-atom shell has been obtained on its basis, which is a polyhedron with 72 pentagonal faces. Such a shell has been established in 18 intermetallic compounds, including quasicrystal approximants AlCa3Cd17, CaCd6, Eu3Cd19, HfNi2.15Ca3.85, etc.
Title:
Phason-induced dynamics of colloidal particles on quasicrystalline substrates
Authors:
Kromer, JA; Schmiedeberg, M; Roth, J; Stark, H Author Full Names: Kromer, Justus A.; Schmiedeberg, Michael; Roth, Johannes; Stark, Holger
Source:
EUROPEAN PHYSICAL JOURNAL E, 36 (3):10.1140/epje/i2013-13025-0 MAR 2013
Abstract:
Phasons are special hydrodynamic modes that occur in quasicrystals. The trajectories of particles due to a phasonic drift were recently studied by Kromer et al. (Phys. Rev. Lett. 108, 218301 (2012)) for the case where the particles stay in the minima of a quasicrystalline potential. Here, we study the mean motion of colloidal particles in quasicrystalline laser fields when a phasonic drift or displacement is applied and also consider the cases where the colloids cannot follow the potential minima. While the mean square displacement is similar to the one of particles in a random potential with randomly changing potential wells, there also is a net drift of the colloids that reverses its direction when the phasonic drift velocity is increased. Furthermore, we explore the dynamics of the structural changes in a laser-induced quasicrystal during the rearrangement process that is caused by a steady phasonic drift or an instantaneous phasonic displacement.
Title:
Crystal-Structure Studies of Mononuclear Iron(II) Complexes with Two-Step Spin Crossover: [Fe{5-NO2-sal-N(1,4,7,10)}] Revisited
Authors:
Kusz, J; Nowak, M; Gutlich, P Author Full Names: Kusz, Joachim; Nowak, Maria; Guetlich, Philipp
Source:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, (5-6):832-842; SI 10.1002/ejic.201201467 FEB 2013
Abstract:
In the region of the spin transition of spin-crossover (SCO) compounds there coexist molecules in both high-spin (HS) and low-spin (LS) states. In the case of two-step spin transition, theoretical predictions and computer simulations have shown that HS and LS complex molecules should be ordered in the plateau region. Several examples that support this hypothesis are already presented in the literature. Herein, we discuss a mononuclear complex of iron(II) with two-step spin transition in terms of long-range ordering of HS and LS molecules. In such compounds, spin transition is associated with the formation of a superstructure. However, previous studies of the [Fe{5-NO2-sal-N(1,4,7,10)}] [5-NO2-sal-N(1,4,7,10) = 5-nitrosalicylaldehyde-1,4,7,10-tetraazadecane] coordination complex have not revealed the occurrence of the satellite reflections in the SCO plateau region as a typical sign of the formation of a superstructure. Re-investigations of this complex by using strong X-ray sources and a charge-coupled device (CCD) camera show that satellite reflections appear in the plateau region. This is evidence that also in this case the superstructure is formed in the plateau region with long-range ordering of the HS and LS molecules. The two-step spin transition is connected to the change of the conformer and a dramatic change in the hydrogen-bonding system.

Update: 15-May-2013

Title:
A modulated structure derived from the sigma phase in the Mo-Ni-Re system
Authors:
Yaqoob, K; Guenee, L; Cerny, R; Joubert, JM Author Full Names: Yaqoob, Khurram; Guenee, Laure; Cerny, Radovan; Joubert, Jean-Marc
Source:
INTERMETALLICS, 37 42-45; 10.1016/j.intermet.2013.01.018 JUN 2013
Abstract:
The crystal structure identification of a new Mo-Ni-Re phase was carried out. The chemical characterisation of the studied composition was performed with the help of electron probe microanalysis (EPMA) whereas X-ray diffraction (XRD) and single crystal diffraction techniques were used for structural characterisation. The characterisation results revealed that this new Mo-Ni-Re phase has a modulated phase structure. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Structural evolution and magnetization enhancement of Bi1-xTbxFeO3
Authors:
Zhang, J; Wu, YJ; Chen, XK; Chen, XJ Author Full Names: Zhang, Jing; Wu, Yu-Jie; Chen, Xiao-Kun; Chen, Xiao-Jia
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 74 (6):849-853; 10.1016/j.jpcs.2013.01.030 JUN 2013
Abstract:
The structural, vibrational, and magnetic properties of well prepared Bi1-xTbxFeO3 (x=0-0.2) powders are investigated by combining the X-ray diffraction, Raman scattering, and magnetometry measurements. It is found that partial substitution of Tb (10-12.5%) in Bi site results in a structural transformation from the rhombohedral R3c symmetry to the orthorhombic Pnma phase, accompanied by a ferroelectric-paraelectric phase transition. The magnetization of Bi1-xTbxFeO3 first gradually increases before reaching maximum at the polar-nonpolar phase boundary and then decreases for x >= 0.125 until x=0.20. The enhancement of the remnant magnetization is attributed to the suppression of the space-modulated spin structure in the rhombohedral R3c phase. Meanwhile, the reduction of the remnant magnetization in the orthorhombic Pnma phase is suggested to result from the establishment of well parallel antiferromagnetic ordering. (C) 2013 Elsevier Ltd. All rights reserved.
Title:
Evolution of magnetic and crystal structures in the multiferroic FeTe2O5Br
Authors:
Pregelj, M; Jeglic, P; Zorko, A; Zaharko, O; Apih, T; Gradisek, A; Komelj, M; Berger, H; Arcon, D Author Full Names: Pregelj, M.; Jeglic, P.; Zorko, A.; Zaharko, O.; Apih, T.; Gradisek, A.; Komelj, M.; Berger, H.; Arcon, D.
Source:
PHYSICAL REVIEW B, 87 (14):10.1103/PhysRevB.87.144408 APR 9 2013
Abstract:
Neutron diffraction and nuclear quadrupole resonance (NQR) measurements were employed to investigate magnetic order in the nonferroelectric phase preceding the low-temperature multiferroic state in FeTe2O5Br. Refinement of the neutron diffraction data and simulations of Br-79,Br-81 NQR spectra reveal that the incommensurate magnetic ordering in the nonferroelectric state comprises amplitude-modulated magnetic moments, similar to that seen in the multiferroic state. The two ordered states differ in the orientation of the magnetic moments and phase shifts between modulation waves. Surprisingly, all symmetry restrictions for the electric polarization are absent in both states. The different ferroelectric responses of the two states are thus argued to arise from the differences in the phase shifts between certain modulation waves, which cancel out in the nonferrolectric state. DOI: 10.1103/PhysRevB.87.144408
Title:
Binary Superlattices from Colloidal Nanocrystals and Giant Polyoxometalate Clusters
Authors:
Bodnarchuk, MI; Erni, R; Krumeich, F; Kovalenko, MV Author Full Names: Bodnarchuk, Maryna I.; Erni, Rolf; Krumeich, Frank; Kovalenko, Maksym V.
Source:
NANO LETTERS, 13 (4):1699-1705; 10.1021/nl4002475 APR 2013
Abstract:
We report a new kind of long-range ordered binary superlattices comprising atomically defined inorganic clusters and colloidally synthesized nanocrystals. In a model system, we combined surfactant-encapsulated, nearly spherical giant polyoxometalate clusters containing 2.9 nm polyoxomolybdate or 2.5 nm polyoxovanadomolybdate cores with monodisperse colloidal semiconductor nanocrystals (PbS, CdSe, PbS/CdS; 4-11 nm). The results are rationalized on the basis of dense packing principles of sterically stabilized particles with predominantly hard-spherelike interparticle interactions. By varying the size-ratios and relative concentrations of constituents, we obtained known thermodynamically stable binary packings of hard-spheres such as NaCl, AlB2, and NaZn13 lattices and also CaCu5-type lattice and aperiodic quasicrystals with 12-fold symmetry. These results suggest that other kinds of cluster materials such as fullerenes and magic-sized metallic and semiconductor clusters can also be integrated into supramolecular assemblies with nanocrystals. Furthermore, synergistic effects are expected from the combination of redox and catalytic properties of polyoxometalates with excitonic and plasmonic properties of inorganic nanocrystals.
Title:
Microstructure and mechanical properties of as-cast and solution-treated Mg-Zn-Gd-based alloys reinforced with quasicrystals
Authors:
Huang, H; Yuan, GY; Tong, J; Ding, WJ Author Full Names: Huang, Hua; Yuan, Guangyin; Tong, Jian; Ding, Wenjiang
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, 104 (4):380-385; 10.3139/146.110880 APR 2013
Abstract:
The microstructure and mechanical properties of as-cast and solution-treated Mg-xZn-yGd (x/y = 6, at.%) alloys reinforced with quasicrystals have been investigated. The results indicate that with the increase in the alloying elements contents, the dendritic microstructure is refined, the corresponding strength gradually increased, and the elongation gradually decreased as the increase in the second phase sizes leads to stress concentration under as-cast and solution-treated conditions. For as-cast alloys, micro-cracks originated in the alpha-Mg matrix and quasicrystals interface. The fracture mode exhibits intergranular fracture characteristics. After solution treatment, the yield strength decreased, and the ultimate tensile strength and elongation increased clearly due to the Mg2Zn3 phase dissolution and the second phase sizes decreasing. The fracture mode changes to transgranular fracture.
Title:
Linear perturbation renormalization group method for Ising-like spin systems
Authors:
Sznajd, J Author Full Names: Sznajd, J.
Source:
CONDENSED MATTER PHYSICS, 16 (1):10.5488/CMP.16.13704 2013
Abstract:
The linear perturbation group transformation (LPRG) is used to study the thermodynamics of the axial next-nearest-neighbor Ising model with four spin interactions (extended ANNNI) in a field. The LPRG for weakly interacting Ising chains is presented. The method is used to study finite field para-ferrimagnetic phase transitions observed in layered uranium compounds, UAs1-xSex, UPd2Si2 or UNi2Si2. The above-mentioned systems are made of ferromagnetic layers and the spins from the nearest-neighbor and next-nearest-neighbor layers are coupled by the antiferromagnetic interactions J(1) < 0 and J(2) < 0, respectively. Each of these systems exhibits a triple point in which two ordered phases (ferrimagnetic and incommensurate) meet the paramagnetic one, and all undergo the high field phase transition from para- to ferrimagnetic (+ + -) phase. However, if in UAs1-xSex the para-ferri phase transition is of the first order as expected from the symmetry reason, in UT2Si2 (T = Pd, Ni) this transition seems to be a continuous one, at least in the vicinity of the multicritical point. Within the MFA, the critical character of the finite field para-ferrimagnetic transition at least at one isolated point can be described by the ANNNI model supplemented by an additional, e.g., four-spin interaction. However, in LPRG approximation for the ratio kappa = J(2)/J(1) around 0.5 there is a critical value of the field for which an isolated critical point also exists in the original ANNNI model. The positive four-spin interaction shifts the critical point towards higher fields and changes the shape of the specific heat curve. In the latter case for the fields small enough, the specific heat exhibits two-peak structure in the paramagnetic phase.
Title:
Influence of heat treatment on electrochemical properties of Ti1.4V0.6Ni alloy electrode containing icosahedral quasicrystalline phase
Authors:
Liu, WQ; Zhang, SS; Wang, LM Author Full Names: Liu Wan-qiang; Zhang Shan-shan; Wang Li-min
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 22 (12):3034-3038; 10.1016/S1003-6326(11)61567-7 DEC 2012
Abstract:
The structures and electrochemical properties of the Ti1.4V0.6Ni ribbon before and after heat treatment are investigated systematically. The structure of the sample is characterized by X-ray powder diffraction analysis. Electrochemical properties including the discharge capacity, the cyclic stability and the high-rate discharge ability are tested. X-ray powder diffraction analysis shows that after heat treatment at 590 degrees C for 30 min, all samples mainly consist of the icosahedral quasicrystal phase (I-phase), Ti2Ni phase (FCC), V-based solid solution phase (BCC) and C14 Laves phase (hexagonal). Electrochemical measurements show that the maximum discharge capacity of the alloy electrode after heat treatment is 330.9 mA.h/g under the conditions that the discharge current density is 30 mA/g and the temperature is 30 degrees C. The result indicates that the cyclic stability and the high-rate discharge ability are all improved. In addition, the electrochemical kinetics of the alloy electrode is also studied by electrochemical impedance spectroscopy (EIS) and hydrogen diffusion coefficient (D).

Update: 8-May-2013

Title:
Monophosphate tungsten bronzes with pentagonal tunnels: reinvestigation through the peephole of the superspace
Authors:
Perez, O; Elcoro, L; Perez-Mato, JM; Petricek, V Author Full Names: Perez, Olivier; Elcoro, Luis; Perez-Mato, J. M.; Petricek, Vaclav
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 69 122-136; 10.1107/S0108768113002826 2 APR 2013
Abstract:
The large family of monophosphate tungsten bronzes with pentagonal tunnels (MPTBp), (PO2)4(WO3)2m with m ranging from 4 to 14, can be considered as modular structures via a description with (PO2)2(WO3)m modules related together by a symmetry operation and alternating along the z axis. Following the success of the application of the superspace for the description of the lillianites homologous series, a (3+1)-dimensional superspace model is efficiently defined to unify the structural analysis of the MPTBp. The (3+1)-dimensional model reveals hidden common characteristics such as the symmetry. An evaluation of the model for six well known members of the series was carried out from experimental data collected to this aim.
Title:
Control of magnetic interaction and ferroelectricity by nonmagnetic Ga substitution in multiferroic YMn2O5
Authors:
Kimura, H; Sakamoto, Y; Fukunaga, M; Hiraka, H; Noda, Y Author Full Names: Kimura, H.; Sakamoto, Y.; Fukunaga, M.; Hiraka, H.; Noda, Y.
Source:
PHYSICAL REVIEW B, 87 (10):10.1103/PhysRevB.87.104414 MAR 29 2013
Abstract:
We have studied the effects of substituting nonmagnetic Ga3+ for Mn3+ on dielectric and magnetic properties in multiferroic YMn2O5. Upon Ga substitution, whereby only the Mn3+ ions are selectively replaced, the commensurate magnetic phase eventually disappeared owing to the disconnection of the magnetic interaction between Mn3+ and Mn4+ ions. In contrast, the low-temperature incommensurate magnetic phase is hardly affected by Ga substitution. Precise crystal structure analyses of Ga-substituted YMn2O5 have revealed that the bonds between Mn ions along the ab plane changed markedly with increasing Ga concentration, while those along the c axis did not change at all. This indicates that the magnetic interactions along the ab plane were altered dramatically, while those along the c axis were robust against Ga substitution. From the dielectric and magnetic phase diagrams as a function of Ga substitution, we conclude that the electric polarization is predominantly induced by exchange-striction in the commensurate magnetic phase, and by an inverse Dzyaloshinskii-Moriya interaction in the incommensurate phase. DOI: 10.1103/PhysRevB.87.104414

Update: 2-May-2013

Title:
X-Ray Diffraction Observations of a Charge-Density-Wave Order in Superconducting Ortho-II YBa2Cu3O6.54 Single Crystals in Zero Magnetic Field
Authors:
Blackburn, E; Chang, J; Hucker, M; Holmes, AT; Christensen, NB; Liang, RX; Bonn, DA; Hardy, WN; Rutt, U; Gutowski, O; von Zimmermann, M; Forgan, EM; Hayden, SM Author Full Names: Blackburn, E.; Chang, J.; Huecker, M.; Holmes, A. T.; Christensen, N. B.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Ruett, U.; Gutowski, O.; v Zimmermann, M.; Forgan, E. M.; Hayden, S. M.
Source:
PHYSICAL REVIEW LETTERS, 110 (13):10.1103/PhysRevLett.110.137004 MAR 28 2013
Abstract:
X-ray diffraction measurements show that the high-temperature superconductor YBa2Cu3O6.54, with ortho-II oxygen order, has charge-density-wave order in the absence of an applied magnetic field. The dominant wave vector of the charge density wave is q(CDW) = (0, 0.328(2), 0.5), with the in-plane component parallel to the b axis (chain direction). It has a similar incommensurability to that observed in ortho-VIII and ortho-III samples, which have different dopings and oxygen orderings. Our results for ortho-II contrast with recent high-field NMR measurements, which suggest a commensurate wave vector along the a axis. We discuss the relationship between spin and charge correlations in YBa2Cu3Oy and recent high-field quantum oscillation, NMR, and ultrasound experiments. DOI: 10.1103/PhysRevLett.110.137004
Title:
Spin and Dipole Ordering in Ni2InSbO6 and Ni2ScSbO6 with Corundum-Related Structure
Authors:
Ivanov, SA; Mathieu, R; Nordblad, P; Tellgren, R; Ritter, C; Politova, E; Kaleva, G; Mosunov, A; Stefanovich, S; Weil, M Author Full Names: Ivanov, S. A.; Mathieu, R.; Nordblad, P.; Tellgren, R.; Ritter, C.; Politova, E.; Kaleva, G.; Mosunov, A.; Stefanovich, S.; Weil, M.
Source:
CHEMISTRY OF MATERIALS, 25 (6):935-945; 10.1021/cm304095s MAR 26 2013
Abstract:
The complex metal oxides Ni2InSbO6 (NISO) and Ni2ScSbO6 (NSSO) have been prepared in the form of polycrystalline powders by a solid state reaction route. The crystal structure and magnetic properties of the compounds were investigated using a combination of X-ray and neutron powder diffraction, electron microscopy, calorimetric, and magnetic measurements. The compounds adopt a trigonal structure, space group R3, of the corundum related Ni3TeO6 (NTO) type. Only one of the octahedral Ni positions (Ni(2)) of the NTO structure was found to be occupied by In (Sc). NTO has noncentrosymmetric structure and is ferroelectric below 1000 K; dielectric and second harmonic measurements suggest that also NISO and NSSO are correspondingly ferroelectric. Magnetization measurements signified antiferromagnetic ordering below T-N = 60 K (NSSO) and 76 K (NISO). The magnetic structure is formed by two antiferromagnetically coupled incommensurate helices with the spiral axis along the b-axis and propagation vector k = [0, k(y),0] with k(y) = 0.036(1) (NSSO) and k(y) = 0.029(1) (NISO). The observed structural and magnetic properties of NISO and NSSO are discussed and compared with those of NTO.

Update: 25-Apr-2013

Title:
Antiferromagnetic order in TmRhGa
Authors:
Baran, S; Hoser, A; Szytula, A Author Full Names: Baran, S.; Hoser, A.; Szytula, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 335 97-100; 10.1016/j.jmmm.2013.01.039 JUN 2013
Abstract:
Magnetic properties of ternary TmRhGa intermetallic compound were investigated by means of ac and dc magnetic susceptibility, dc magnetization and neutron diffraction at low-temperatures. The compound is an antiferromagnet with the Neel temperature equal to 3.9(2) K. At 1.5 K the Tm magnetic moments form an incommensurate sine-wave modulated structure (propagation vector (k) over right arrow = [0,0.4222(3),0]) with amplitude of modulation equal to 7.15(11)mu(B). The moments are parallel to the c-axis. (C) 2013 Elsevier B.V. All rights reserved.
Title:
Primary Transformation Kinetics in Zr-Al-Ni-Cu-Pd Bulk Metallic Glass Correlated with Relaxation State
Authors:
Saida, J; Setyawan, AD Author Full Names: Saida, Junji; Setyawan, Albertus D.
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 44A (5):1998-2003; 10.1007/s11661-012-1321-3 MAY 2013
Abstract:
The primary transformation kinetics of nanoicosahedral quasicrystalline (QC) phase formation were investigated in Zr65Al7.5Ni10Cu12.5Pd5 bulk metallic glass (BMG) in various relaxation states. A less relaxed (unrelaxed) BMG exhibited higher activation energy for atomic diffusion in the glassy structure than that of a relaxed one, which represents a change in the nucleation and grain growth kinetics of the primary phase with the relaxation state. Actually, the grain growth rate of a QC particle near the crystallization temperature was approximately 1 x 10(-9) m/s in the less relaxed BMGs, which was less than half of that in the relaxed BMGs. In contrast, the calculated homogeneous nucleation rate significantly increased in the less relaxed samples. It increased with the volume fraction transformed in the early stage. It is concluded that the relaxation state of glassy alloys markedly affects the primary transformation kinetics. The current study also indicates a necessity of development of the relaxation state for structure controlling in industrial applications of BMGs. DOI: 10.1007/s11661-012-1321-3 (C) The Minerals, Metals & Materials Society and ASM International 2012
Title:
Anionic Depolymerization Transition in IrTe2
Authors:
Oh, YS; Yang, JJ; Horibe, Y; Cheong, SW Author Full Names: Oh, Yoon Seok; Yang, J. J.; Horibe, Y.; Cheong, S. -W.
Source:
PHYSICAL REVIEW LETTERS, 110 (12):10.1103/PhysRevLett.110.127209 MAR 22 2013
Abstract:
Selenium substitution drastically increases the transition temperature of iridium ditelluride (IrTe2) to a diamagnetic superstructure from 278 to 560 K. Transmission electron microscopy experiments revealed that this enhancement is accompanied by the evolution of nonsinusoidal structure modulations from q = 1/5(10 (1) over bar) to q = 1/6(10 (1) over bar) types. These comprehensive results are consistent with the concept of the destabilization of polymeric Te-Te bonds at the transition, the temperature of which is increased by chemical and hydrostatic pressure and by the substitution of Te with the more electronegative Se. This temperature-induced depolymerization transition in IrTe2 is unique in crystalline inorganic solids. DOI: 10.1103/PhysRevLett.110.127209
Title:
Antiferromagnetic ordering in a mixed-valent cerium compound CeRuSn
Authors:
Prokes, K; Mydosh, JA; Prokhnenko, O; Stein, WD; Landsgesell, S; Hermes, W; Feyerherm, R; Pottgen, R Author Full Names: Prokes, K.; Mydosh, J. A.; Prokhnenko, O.; Stein, W. -D.; Landsgesell, S.; Hermes, W.; Feyerherm, R.; Poettgen, R.
Source:
PHYSICAL REVIEW B, 87 (9):10.1103/PhysRevB.87.094421 MAR 22 2013
Abstract:
We report the results of extensive neutron powder diffraction experiments on a ternary compound CeRuSn in a temperature range from 2 to 520 K. At room temperature CeRuSn orders in a monoclinic structure that is related to the CeCoAl type by the doubling of the c-axis parameter caused by the splitting of the original single sites for each element into two sites. Upon cooling a very broad hysteretic structural transition has been observed in CeRuSn leading to the presence of higher-ordered variants having multiple c-axis parameters. Depending on the temperatures, one or the other variant seems to be more stable, but the sample as a whole becomes multiphase. We find also evidence for further symmetry lowering at low temperatures. CeRuSn is found to exhibit an antiferromagnetic order below T-N = 2.8(1) K. The order is described by two incommensurate propagation vectors q(1) = (0,0, approximate to 0.30) and q(2) = (0,0, approximate to 0.43) with respect to the doubled crystal structure variant. Although the details of themagnetic structure remain elusive, the best agreement has been found for a complicated distorted cycloidal magnetic structure with Ce moments of approximate to 0.7 mu(B) being confined to the ac plane. DOI: 10.1103/PhysRevB.87.094421
Title:
Mercury Bismuth Chalcohalides, Hg(3)Q(2)Bi(2)Cl(8) (Q = S, Se, Te): Syntheses, Crystal Structures, Band Structures, and Optical Properties
Authors:
Wibowo, AC; Malliakas, CD; Chung, DY; Im, J; Freeman, AJ; Kanatzidis, MG Author Full Names: Wibowo, Arief C.; Malliakas, Christos D.; Chung, Duck Young; Im, Jino; Freeman, Arthur J.; Kanatzidis, Mercouri G.
Source:
INORGANIC CHEMISTRY, 52 (6):2973-2979; 10.1021/ic3023826 MAR 18 2013
Abstract:
Three quaternary mercury bismuth chalcohalides, Hg(3)Q(2)Bi(2)Cl(8) (Q = S, Se, Te), are reported along with their syntheses, crystal structures, electronic band structures, and optical properties. The compounds are structurally similar with a layer comprised of a hole perforated sheet network of [Hg(3)Q(2)](2+) (Q = S and Te) that forms by fused cyclohexane, chairlike Hg(6)Q(6) rings. The cationic charge in the network is balanced by edge-sharing monocapped trigonal-prismatic anions of [Bi2Cl8](2-) that form a two-dimensional network located between layers. Compound 1, Hg(3)Q(2)Bi(2)Cl(8), crystallizes in the monoclinic space group C12/m1 with a = 12.9381(9) angstrom, b = 7.3828(6) angstrom, c = 9.2606(6) angstrom, and beta = 116.641(5)degrees. Compound 2, Hg(3)Q(2)Bi(2)Cl(8), crystallizes in the monoclinic space group C12/c1 with a = 17.483(4) angstrom, b = 7.684(2) angstrom, c = 13.415(3) angstrom, and beta = 104.72(3)degrees. The crystals of the Hg(3)Q(2)Bi(2)Cl(8) analogue exhibit complex modulations and structural disorder, which complicated its structural refinement. Compounds 1 and 2 melt incongruently and show band gaps of 3.26 and 2.80 eV, respectively, which are in a good agreement with those from band-structure density functional theory calculations.
Title:
The Modulated Structure of Co3Al4Si2: Incommensurability and Co-Co Interactions in Search of Filled Octadecets
Authors:
Fredrickson, RT; Fredrickson, DC Author Full Names: Fredrickson, Rie T.; Fredrickson, Daniel C.
Source:
INORGANIC CHEMISTRY, 52 (6):3178-3189; 10.1021/ic302650r MAR 18 2013
Abstract:
Incommensurate modulations are increasingly being recognized as a common phenomenon in solid-state compounds ranging from inorganic materials to molecular crystals. The origins of such modulations are often mysterious, but appear to be as diverse as the compounds in which they arise. In this Article, we describe the crystal structure and bonding of Co3Al4Si2, the delta phase of the Co-Si-Al system, whose modulated structure can be traced to a central concept of inorganic chemistry: the 18 electron rule. The structure is monoclinic, conforming to the 3 + 1D superspace group C/2m(0 beta 0)s0. The basis of the crystal structure is a rod packing of columns of the fluorite (CaF2) type, a theme that is shared by the recently determined structure of Fe8Al17.4Si7.6. The columns are arranged into sheets, within which the fluorite structure's primitive cubic network of Si/Al atoms continues uninterrupted from column to column. Between the sheets, layers of interstitial Si/Al atoms occur, some of which are arranged with a periodicity incommensurate with that of the fluorite-type columns. Strong modulations in the interstitial layers result. Electronic structure calculations, using a DFT-calibrated Huckel model on a commensurate approximate structure, reveal that the complex pattern of atoms within these interstitial layers serves to distribute Si/Al atoms around the Co atoms in order to reach 18 electron counts (filled octadecets). Central to this bonding scheme is the covalent sharing of electron pairs between Co atoms. The shared electron pairs occupy orbitals that are isolobal to classical Co-Co sigma and pi bonds, but whose stability is tied to multicenter character involving bridging Si/Al atoms. Through these features, Co3Al4Si2 expands the structural and electronic manifestations of the 18 electron rule in solid-state inorganic compounds.
Title:
Quasicrystals: a brief history of the impossible
Authors:
Steinhardt, PJ Author Full Names: Steinhardt, Paul J.
Source:
RENDICONTI LINCEI-SCIENZE FISICHE E NATURALI, 24 S85-S91; 1 10.1007/s12210-012-0203-3 MAR 2013
Abstract:
The 30-year history of quasicrystals is one in which, time after time, the conventional scientific view about what is possible has been proven wrong. First, quasicrystals were thought to be mathematically impossible; then, physically impossible; then, impossible unless synthesised in the laboratory under carefully controlled conditions. One by one, these strongly held views have been disproven, the last only recently as the result of the discovery of a natural quasicrystal found in a meteorite dating back to the formation of the solar system. This paper is a brief personal perspective on this history of misunderstanding and discovery.
Title:
The aperiodic nature of incommensurately modulated structures
Authors:
Chapuis, G; Arakcheeva, A Author Full Names: Chapuis, Gervais; Arakcheeva, Alla
Source:
RENDICONTI LINCEI-SCIENZE FISICHE E NATURALI, 24 S77-S84; 1 10.1007/s12210-012-0221-1 MAR 2013
Abstract:
The discovery of aperiodic crystals is perhaps one of the most important event which has changed our vision on crystalline architectures since the discovery of diffraction 100 years ago. It was the merit of a Dutch crystallographer, P.M. de Wolff, to interpret their diffraction pattern as a three dimensional projection of a higher dimensional reciprocal lattice, idea which led directly to the generalization of the concept of crystal. Aperiodic crystals are currently described as periodic objects in higher-dimensional space, i.e. the superspace and their structures can be described in terms of 3-d cuts. Incommensurate structures, composite structures and quasicrystals all belong to aperiodic structures. Many interesting properties of superspace have been discovered which are also directly applicable to crystals in the conventional sense, i.e. crystals with 3-d periodicity. In particular the concept of structure type can be extended for a better understanding of structure relations. The notion of solid solution has also benefited from superspace considerations. Moreover, superspace is a very powerful tool for a better understanding of structure-property relations in material science, e.g. luminescence properties could be directly associated to the description of structures in superspace. Recently, this concept has been used for the prediction of new structural modifications including polytypes and even polytypic modifications of a well-known pharmaceutical product.
Title:
Effects of phase dislocations on the charge density wave dynamics in quasi-one-dimensional conductors
Authors:
Habiballah, N; Qjani, M; Arbaoui, A; Dumas, J Author Full Names: Habiballah, N.; Qjani, M.; Arbaoui, A.; Dumas, J.
Source:
SYNTHETIC METALS, 164 52-54; 10.1016/j.synthmet.2012.12.027 JAN 15 2013
Abstract:
We report in this letter a numerical simulations study of the effects of phase dislocations on the dynamic properties of charge density waves (CDW) conductors, using the one-dimensional Fukuyama, Lee and Rice (FLR) model for a weakly pinned incommensurate CDW. The results show that the CDW phase dislocations affect the local dynamical properties of CDW. (c) 2013 Elsevier B.V. All rights reserved.
Title:
Structure Determination of gamma-Brass-Related Composite Structures in the Ni-Zn System: A Guided Tour by a (3+1)-Dimensional Space Description
Authors:
Jana, PP; Lidin, S Author Full Names: Jana, Partha Pratim; Lidin, Sven
Source:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, (1):91-98; 10.1002/ejic.201200780 JAN 2013
Abstract:
Three incommensurately modulated gamma-brass-related composite structures in the Ni-Zn system have been solved from Xray single crystal diffraction data using a 3+1 dimensional super space description. The compounds at the end points of the compositional domain NiZn3-delta (-0.09 <= delta <= 0.34) and NiZn3.30 crystallize in the orthorhombic superspace group Fmmm(alpha 00) 0s0 {F = [(1/2, 1/2, 0, 0); (1/2, 0, 1/2, 0); (0, 1/2, 1/2, 0)]} with the following fundamental cell dimensions a = 4.165(1) angstrom, b = 8.883(2) angstrom, c = 12.545(3) angstrom, q approximate to 0.6311a*; a = 4.161(2) angstrom, b = 8.876(3) angstrom, c = 12.535(4) angstrom, q approximate to 0.6314a* and a = 4.177(2) angstrom, b = 8.899(1) angstrom, c = 12.570(2) angstrom, q approximate to 0.6378a*.

Update: 17-Apr-2013

Title:
Characterization of mobile type I and type II twin boundaries in 10M modulated Ni-Mn-Ga martensite by electron backscatter diffraction
Authors:
Chulist, R; Straka, L; Lanska, N; Soroka, A; Sozinov, A; Skrotzki, W Author Full Names: Chulist, R.; Straka, L.; Lanska, N.; Soroka, A.; Sozinov, A.; Skrotzki, W.
Source:
ACTA MATERIALIA, 61 (6):1913-1920; 10.1016/j.actamat.2012.12.012 APR 2013
Abstract:
Mobile type I and type II twin boundaries mediating the magnetic field-induced strain in five-layered modulated (10M) Ni-Mn-Ga martensite were analyzed by electron backscatter diffraction. Taking into account the slight monoclinic distortion of the pseudo-tetragonal lattice, the electron backscatter diffraction study reveals domains of 0.01-1 mm thickness adjacent to the type I and type II twin boundaries. The domains differing in the modulation direction are {1 0 0) compound twins and their effect on twinning stress is discussed. Detailed analysis of type II twin boundary reveals that the domains are further internally twinned by compound {1 1 0) twins 1-15 mu m in size. An additional example of a complex twin microstructure combining type I and type II twin boundaries is presented. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Unconventional Magnetostructural Transition in CoCr2O4 at High Magnetic Fields
Authors:
Tsurkan, V; Zherlitsyn, S; Yasin, S; Felea, V; Skourski, Y; Deisenhofer, J; von Nidda, HAK; Wosnitza, J; Loidl, A Author Full Names: Tsurkan, V.; Zherlitsyn, S.; Yasin, S.; Felea, V.; Skourski, Y.; Deisenhofer, J.; von Nidda, H. -A. Krug; Wosnitza, J.; Loidl, A.
Source:
PHYSICAL REVIEW LETTERS, 110 (11):10.1103/PhysRevLett.110.115502 MAR 12 2013
Abstract:
The magnetic-field and temperature dependencies of the ultrasound propagation and magnetization of single-crystalline CoCr2O4 have been studied in static and pulsed magnetic fields up to 14 and 62 T, respectively. Distinct anomalies with significant changes in the sound velocity and attenuation are found in this spinel compound at the onset of long-range incommensurate-spiral-spin order at T-s = 27 K and at the transition from the incommensurate to the commensurate states at T-l = 14 K, evidencing strong spin-lattice coupling. While the magnetization evolves gradually with the field, steplike increments in the ultrasound clearly signal a transition into a new magnetostructural state between 6.2 and 16.5 K and at high magnetic fields. We argue that this is a high-symmetry phase with only the longitudinal component of the magnetization being ordered, while the transverse helical component remains disordered. This phase is metastable in an extended H - T phase space. DOI: 10.1103/PhysRevLett.110.115502
Title:
Microstructure and corrosion behavior of rapidly solidified Mg-Zn-Y alloys
Authors:
Nam, SW; Kim, WT; Kim, DH; Kim, TS Author Full Names: Nam, S. W.; Kim, W. T.; Kim, D. H.; Kim, T. S.
Source:
METALS AND MATERIALS INTERNATIONAL, 19 (2):205-209; 10.1007/s12540-013-2010-5 MAR 2013
Abstract:
The effect of a minor change in alloy composition on the microstructure and corrosion properties of melt spun Mg98.3-xZnxY1.7 ribbons with x=9-12 is studied by X-ray diffractometry, differential scanning calorimetry, transmission electron microscopy and a dynamic polarization test. The ribbon specimens with x=9-10 revealed an in-situ composite microstructure consisting of icosahedral quasicrystalline phase (I-phase) particles distributed in an alpha-Mg matrix. The ribbon specimens with x=11 and 12 contained a minor MgZn2 phase together with an alpha-Mg phase and I-phase. With increasing Zn content, the corrosion potential increased because of a mixed potential effect, but the formation of a MgZn2 phase deteriorated the corrosion property through preferential attack, causing an irregular boundary between the corrosion product and the substrate. These results indicate that it is important to control alloy chemistry not to form the MgZn2 phase in developing an I-phase strengthened Mg-Zn-Y alloy for structural applications.
Title:
Effect of substrate orientation on charge ordering behavior in Sm0.5Ca0.5MnO3 epitaxial films
Authors:
Li, CY; Wang, YQ; Cai, RS; Chen, YZ; Sun, JR Author Full Names: Li, C. Y.; Wang, Y. Q.; Cai, R. S.; Chen, Y. Z.; Sun, J. R.
Source:
MATERIALS LETTERS, 95 70-73; 10.1016/j.matlet.2012.12.097 MAR 1 2013
Abstract:
The effect of anisotropic strain induced by SrTiO3 (STO) substrate with different orientations on charge ordering (CO) behavior in epitaxial Sm0.5Ca0.5MnO3 (SCMO) films was investigated using cross-sectional transmission electron microscopy at 103 K. Incommensurate modulated structure caused by CO transition was observed in the SCMO film grown on a [101]-oriented STO substrate while none were found for SCMO film grown on a [100]-oriented STO substrate. This distinctive orientation-dependent CO transition is correlated with anisotropic strain in the films induced by lattice mismatch, confirming the previous results for growth on different substrates. (C) 2013 Elsevier B.V. All rights reserved.

Update: 10-Apr-2013

Title:
Field induced incommensurate-to-commensurate magnetic phase transition in Ca3Co1.8Fe0.2O6: a neutron diffraction study
Authors:
Yusuf, SM; Jain, A; Keller, L Author Full Names: Yusuf, S. M.; Jain, Anil; Keller, L.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (14):10.1088/0953-8984/25/14/146001 APR 10 2013
Abstract:
Neutron powder diffraction experiments have been performed to investigate the nature of magnetic ordering, as a function of temperature (1.5-100 K) and magnetic field (0, 2 and 4 T), in the compound Ca3Co1.8Fe0.2O6. In zero applied field, the compound orders magnetically in the incommensurate spin density wave (SDW) structure (T-N similar to 20 K). Under an applied field of similar to 2 T, an incommensurate-to-commensurate magnetic phase transition has been observed. With a further increase in the magnetic field (similar to 4 T), the commensurate magnetic structure transforms into a ferrimagnetic structure. In zero applied field, magnetic short-range ordering (SRO) coexists with the SDW long-range ordering (LRO) at all temperatures below T-N. In an applied magnetic field (2 and 4 T), SRO is converted into LRO only over the temperature range 12-20 K; however, below similar to 12 K, an increase in the volume fraction of the SRO has been observed. The correlation length for the SRO (below similar to 12 K) also gets affected by the application of a field.
Title:
Structural Phase Transition and Magnetic-Field Effect on the Modulated Structure in GdBaCo2O5+delta (delta < 0.5)
Authors:
Asaka, T; Abe, N; Kudo, T; Fukuda, K; Kimoto, K; Matsui, Y; Ishizawa, N; Arima, T Author Full Names: Asaka, T.; Abe, N.; Kudo, T.; Fukuda, K.; Kimoto, K.; Matsui, Y.; Ishizawa, N.; Arima, T.
Source:
PHYSICAL REVIEW LETTERS, 110 (12):10.1103/PhysRevLett.110.125502 MAR 19 2013
Abstract:
We investigated the crystal structures of an ordered perovskite-type cobaltate, GdBaCo2O5+delta (delta < 0.5), at elevated temperatures by transmission electron microscopy. Above the magnetic ordering temperature, we observed a first-order structural phase transition between the low-temperature tetragonal 3a(p) x 3a(p) and high-temperature orthorhombic 1a(p) x 2a(p) superstructure phases (where a(p) is the perovskite-unit cell). Upon the application of a magnetic field, an incommensurate phase emerges around the structural phase-transition temperature, which indicates a magnetic-field-induced structural phase transition via no magnetic ordering in the ordered perovskite-type cobaltate. DOI: 10.1103/PhysRevLett.110.125502
Title:
Entropic Commensurate-Incommensurate Transition
Authors:
Nikola, N; Hexner, D; Levine, D Author Full Names: Nikola, Nikolai; Hexner, Daniel; Levine, Dov
Source:
PHYSICAL REVIEW LETTERS, 110 (12):10.1103/PhysRevLett.110.125701 MAR 19 2013
Abstract:
The equilibrium properties of a minimal tiling model are investigated. The model has extensive ground state entropy, with each ground state having a quasiperiodic sequence of rows. It is found that the transition from the ground state to the high temperature disordered phase proceeds through a sequence of periodic arrangements of rows, in analogy with the commensurate-incommensurate transition. We show that the effective free energy of the model resembles the Frenkel-Kontorova Hamiltonian, but with temperature playing the role of the strength of the substrate potential, and with the competing lengths not explicitly present in the basic interactions. DOI: 10.1103/PhysRevLett.110.125701
Title:
Stabilized helical spin order and multiferroic phase coexistence in MnWO4: Consequence of 4d Ru substitution of Mn
Authors:
Yu, HW; Liu, MF; Li, X; Li, L; Lin, L; Yan, ZB; Liu, JM Author Full Names: Yu, H. W.; Liu, M. F.; Li, X.; Li, L.; Lin, L.; Yan, Z. B.; Liu, J. -M.
Source:
PHYSICAL REVIEW B, 87 (10):10.1103/PhysRevB.87.104404 MAR 11 2013
Abstract:
Most earlier work on the effect of chemical substitution in multiferroic MnWO4 has focused on the 3d transition metal substitution of Mn. In this paper, we investigate the Ru substitution of Mn in polycrystalline Mn1-xRux/2 WO4 in order to unveil the consequence of 4d transition metal substitution in terms of magnetic transitions and ferroelectricity. It is found that the Ru substitution substantially reshuffles the magnetic frustration and stabilizes the incommensurate helical spin-order phase (AF2) by partially suppressing the collinear spin-order phase (AF1 phase). The coexistence of the AF2 and AF1 phases at low temperature is suggested. Consequently, the ferroelectric polarization is remarkably enhanced, accompanied with significant response of the polarization to magnetic field. It is argued that the structural distortion and enhanced spin-orbital coupling associated with the Ru substitution may be responsible for this ferroelectricity enhancement. DOI: 10.1103/PhysRevB.87.104404
Title:
A Dugdale-Barenblatt model for a strip with a semi-infinite crack embedded in decagonal quasicrystals
Authors:
Li, W; Xie, LY Author Full Names: Li Wu; Xie Ling-Yun
Source:
CHINESE PHYSICS B, 22 (3):10.1088/1674-1056/22/3/036201 MAR 2013
Abstract:
The present study is to determine the solution of a strip with a semi-infinite crack embedded in decagonal quasicrystals, which transforms a physically and mathematically daunting problem. Then cohesive forces are incorporated into a plastic strip in the elastic body for nonlinear deformation. By superposing the two linear elastic fields, one is evaluated with internal loadings and the other with cohesive forces, the problem is treated in Dugdale-Barenblatt manner. A simple but yet rigorous version of the complex analysis theory is employed here, which involves a conformal mapping technique. The analytical approach leads to the establishment of a few equations, which allows the exact calculation of the size of cohesive force zone and the most important physical quantity in crack theory: stress intensity factor. The analytical results of the present study may be used as the basis of fracture theory of decagonal quasicrystals.
Title:
Geometry of metadislocations in approximants of quasicrystals
Authors:
Gratias, D; Quiquandon, M; Caillard, D Author Full Names: Gratias, Denis; Quiquandon, Marianne; Caillard, Daniel
Source:
PHILOSOPHICAL MAGAZINE, 93 (1-3):304-313; SI 10.1080/14786435.2012.706372 JAN 1 2013
Abstract:
We propose a simple geometrical definition of metadislocations based on the N-dim description of quasicrystals and their approximants, as being the traces of quasicrystalline dislocations with a non-zero component of their N-dim Burgers vector in the perpendicular space of the approximant. Examples are given in the octagonal canonical tiling.

Update: 3-Apr-2013

Title:
Syntheses optimization, structural and thermoelectric properties of 1/1 Tsai-type quasicrystal approximants in RE-Au-SM systems (RE = Yb, Gd and SM = Si, Ge)
Authors:
Gebresenbut, GH; Tamura, R; Eklof, D; Gomez, CP Author Full Names: Gebresenbut, Girma Hailu; Tamura, Ryuji; Eklof, Daniel; Gomez, Cesar Pay
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (13):10.1088/0953-8984/25/13/135402 APR 3 2013
Abstract:
Yb-Cd (Tsai-type) quasicrystals constitute the largest icosahedral quasicrystal family where Yb can be replaced by other rare earth elements (RE) and Cd by pairs of p- and d-block elements. YbCd6 is a prototype 1/1 Tsai-type approximant phase which has a similar local structure to the Yb-Cd quasicrystal. In this study, the syntheses of Yb15.78Au65.22Ge19.00, Gd14.34Au67.16Ge18.5 and Gd14.19Au69.87Si15.94 Tsai-type 1/1 quasicrystal approximants are optimized using the self-flux technique. The crystal structures of the compounds are refined by collecting single crystal x-ray diffraction data. The structural refinements indicated that the compounds are essentially isostructural with some differences at their cluster centers. The basic polyhedral cluster unit in all the three compounds can be described by concentric shells of icosahedra symmetry and of disordered tetrahedra and/or a rare earth atom at the cluster center. Furthermore, the thermoelectric properties of the compounds are probed and their dimensionless figures of merit are calculated at different temperatures. A significant difference is observed in their thermoelectric properties, which could arise due to the slight difference in their crystal structure and chemical composition, as we move from Ge to Si and/or Gd to Yb. Therefore, this study shows the systematic effect of the chemical substitution of structurally similar materials on their thermoelectric properties.
Title:
Impact of intermetallic precipitates on the tribological and/or corrosion performance of cast aluminium alloys: a short review
Authors:
Culliton, D; Betts, AJ; Kennedy, D Author Full Names: Culliton, D.; Betts, A. J.; Kennedy, D.
Source:
INTERNATIONAL JOURNAL OF CAST METALS RESEARCH, 26 (2):65-71; 10.1179/1743133612Y.0000000038 APR 2013
Abstract:
The role of various intermetallic precipitates (IMPs), or secondary phase particles, in governing the wear and corrosion performance characteristics of cast aluminium alloys is outlined in this brief review. Such alloys are especially important in transport applications where their low weight, low cost and recyclability make them very attractive. However, alloy wear and/or corrosion behaviour often limit their industrial application, and more work needs to be carried out to extend their use into other areas. Careful control of IMP nucleation and growth rates may be beneficial, especially in alloys exposed to corrosive environments. Silicon, copper and magnesium are all important elements for enhanced mechanical strength and tribological performance but often to the detriment of alloy corrosion resistance. Other elements such as iron may also play a significant role in deleterious IMP formation. Use of dispersoids based on novel (quasicrystals) seed alloys with similar lattice characteristics to the alpha-Al matrix may result in further exploitation of these alloys.
Title:
An x-ray scattering study of Sn2P2S6: absence of incommensurate phase up to 1 GPa
Authors:
Ondrejkovic, P; Guennou, M; Kempa, M; Vysochanskii, Y; Garbarino, G; Hlinka, J Author Full Names: Ondrejkovic, P.; Guennou, M.; Kempa, M.; Vysochanskii, Y.; Garbarino, G.; Hlinka, J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (11):10.1088/0953-8984/25/11/115901 MAR 20 2013
Abstract:
The ferroelectric phase transition in a semiconductor Sn2P2S6 single crystal has been studied by means of high-resolution synchrotron x-ray diffraction in the pressure-temperature range where an incommensurate modulated phase has been anticipated for many years. In contrast with the predictions, the present measurements reveal only a direct ferroelectric-paraelectric phase transition close to T = 100 K, p = 1.1 GPa. In the vicinity of this phase transition, a characteristic critical diffuse scattering was observed, but no satellite peaks could be resolved there. It is concluded that the earlier hypothesis about the presence of an incommensurate phase and associated Lifshitz point in the temperature-pressure phase diagram of Sn2P2S6 is incorrect.
Title:
Tetrahedron dynamics in the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and the cubic 1/1-approximant Zn6Sc
Authors:
Euchner, H; Yamada, T; Rols, S; Ishimasa, T; Kaneko, Y; Ollivier, J; Schober, H; Mihalkovic, M; de Boissieu, M Author Full Names: Euchner, H.; Yamada, T.; Rols, S.; Ishimasa, T.; Kaneko, Y.; Ollivier, J.; Schober, H.; Mihalkovic, M.; de Boissieu, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (11):10.1088/0953-8984/25/11/115405 MAR 20 2013
Abstract:
A comparison of periodic approximants and their quasicrystalline counterparts offers the opportunity to better understand the structure, physical properties and stabilizing mechanisms of these complex phases. We present a combined experimental and molecular dynamics study of the lattice dynamics of the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and compare it to recently published results obtained for the cubic 1/1-approximant Zn6Sc [1]. Both phases, quasicrystal and approximant, are built up from large atomic clusters which contain a tetrahedral shell at the cluster centre and are packed either quasiperiodically or on a bcc lattice. Using quasielastic neutron scattering and atomic scale simulations, we show that in the quasicrystal the tetrahedra display a dynamics similar to that observed in the 1/1-approximant: the tetrahedra behave as a 'single molecule' and reorient dynamically on a timescale of the order of a few ps. The tetrahedra reorientation is accompanied by a large distortion of the surrounding cluster shells which provide a unique dynamical flexibility to the quasicrystal. However, whereas in the 1/1-approximant the tetrahedron reorientation is observed down to T-c = 160 K, where a phase transition takes place, in the quasicrystal the tetrahedron dynamics is gradually freezing from 550 to 300 K, similarly to a glassy system.
Title:
On the Structure of alpha-BiFeO3
Authors:
Wang, H; Yang, CX; Lu, J; Wu, MM; Su, J; Li, K; Zhang, JR; Li, GB; Jin, TN; Kamiyama, T; Liao, FH; Lin, JH; Wu, YC Author Full Names: Wang, Hui; Yang, Chengxu; Lu, Jun; Wu, Meimei; Su, Jie; Li, Kuo; Zhang, Junrong; Li, Guobao; Jin, Tounan; Kamiyama, Takashi; Liao, Fuhui; Lin, Jianhua; Wu, Yicheng
Source:
INORGANIC CHEMISTRY, 52 (5):2388-2392; 10.1021/ic302047z MAR 4 2013
Abstract:
Polycrystalline and monocrystalline alpha-BiFeO3 crystals have been synthesized by solid state reaction and flux growth method, respectively. X-ray, neutron, and electron diffraction techniques are used to study the crystallographic and magnetic structure of alpha-BiFeO3. The present data show that alpha-BiFeO3 crystallizes in space group PI with a = 0.563 17(1) nm, b = 0.563 84(1) nm, c = 0.563 70(1) nm, alpha = 59.33(1)degrees, beta = 59.35(1)degrees, gamma = 59.38(1)degrees, and the magnetic structure of alpha-BiFeO3 can be described by space group PI with magnetic modulation vector in reciprocal space q = 0.0045a* - 0.0045b*, which is the magnetic structure model proposed by I. Sosnowska(1) applied to the new PI crystal symmetry of alpha-BiFeO3
Title:
Indentation on one-dimensional hexagonal quasicrystals: general theory and complete exact solutions
Authors:
Wu, YF; Chen, WQ; Li, XY Author Full Names: Wu, Y. F.; Chen, W. Q.; Li, X. Y.
Source:
PHILOSOPHICAL MAGAZINE, 93 (8):858-882; 10.1080/14786435.2012.735772 MAR 1 2013
Abstract:
This paper presents a general account of the indentation responses of a one-dimensional hexagonal quasicrystal half-space pressed by an axisymmetric rigid punch. Based on Green's functions of the half-space subjected to point sources on the surface, the mixed boundary value problem is transformed to integral equations and solved exactly using the results of the potential theory method. Explicit expressions for the generalised pressures and indentation forces are derived for three common indenters (cylinder, cone and approximate sphere) in a systematic manner. For conical and spherical indenters, relations between the contact radius and indentation loads are determined. The coupling phononphason fields in the half-space under indentation are accurately expressed in terms of elementary functions. Numerical calculations are performed and discussions on related physical phenomena are given. The present exact solutions can serve as benchmarks for approximate or numerical analyses and can guide the experimental characterisation of material properties of quasicrystals.
Title:
Incommensurate antiferromagnetism in a pure spin system via cooperative organization of local and itinerant moments
Authors:
Feng, YJ; Wang, JY; Silevitch, DM; Mihaila, B; Kim, JW; Yan, JQ; Schulze, RK; Woo, N; Palmer, A; Ren, Y; van Wezel, J; Littlewood, PB; Rosenbaum, TF Author Full Names: Feng, Yejun; Wang, Jiyang; Silevitch, D. M.; Mihaila, B.; Kim, J. W.; Yan, J. -Q.; Schulze, R. K.; Woo, Nayoon; Palmer, A.; Ren, Y.; van Wezel, Jasper; Littlewood, P. B.; Rosenbaum, T. F.
Source:
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 110 (9):3287-3292; 10.1073/pnas.1217292110 FEB 26 2013
Abstract:
Materials with strong correlations are prone to spin and charge instabilities, driven by Coulomb, magnetic, and lattice interactions. In materials that have significant localized and itinerant spins, it is not obvious which will induce order. We combine electrical transport, X-ray magnetic diffraction, and photoemission studies with band structure calculations to characterize successive anti-ferromagnetic transitions in GdSi. GdSi has both sizable local moments and a partially nested Fermi surface, without confounding contributions from orbital effects. We identify a route to incommensurate order where neither type of moment dominates, but is rooted in cooperative feedback between them. The nested Fermi surface of the itinerant electrons induces strong interactions between local moments at the nesting vector, whereas the ordered local moments in turn provide the necessary coupling for a spin-density wave to form among the itinerant electrons. This mechanism echoes the cooperative interactions between electrons and ions in charge-density-wave materials, and should be germane across a spectrum of transition-metal and rare-earth intermetallic compounds.
Title:
Morphology-controlled synthesis, characterization, and luminescence properties of KEu(MoO4)(2) microcrystals
Authors:
Wu, T; Liu, YF; Lu, YN; Wei, L; Gao, H; Chen, H Author Full Names: Wu, Tao; Liu, Yunfei; Lu, Yinong; Wei, Ling; Gao, Hong; Chen, Hu
Source:
CRYSTENGCOMM, 15 (14):2761-2768; 10.1039/c3ce27073d 2013
Abstract:
Large-scale one-dimensional (1D) rod-like and octagonal-like KEu(MoO4)(2) microcrystals were successfully synthesized by a simple, environmental friendly, and low cost molten salt method using halons (KCl or KBr) as flux. The as-prepared products were characterized by X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED) and photoluminescence (PL) spectrometry. The results show that the reaction parameters, including reaction temperature and reaction time, played important roles on the phase structures and morphologies of the final products. The possible growth process of 1D rod-like KEu(MoO4)(2) was proposed based on the time-dependent shape evolution and HRTEM analysis, which followed oriented aggregation and Ostwald ripening. The results of SAED and HRTEM investigations indicated an incommensurate modulated structure in the rod-like KEu(MoO4)(2), and all the reflections can be expressed as ha* + kb* + lc* + mq, where m is an integer, and modulated vector q = 0.182b* + 0.156c*. Room temperature photoluminescence spectra of KEu(MoO4)(2) microcrystals reveal a strong red emission via D-5(0) -> F-7(2) transition at 615 nm, and the 1D rod-like microcrystals own the enhanced intensity compared with the octagonal-like ones.
Title:
Synthesis, growth and characterization of 4-bromo-4 '-nitrobenzylidene aniline (BNBA): a novel nonlinear optical material with a (3+1)-dimensional incommensurately modulated structure
Authors:
Subashini, A; Leela, S; Ramamurthi, K; Arakcheeva, A; Stoeckli-Evans, H; Petricek, V; Chapuis, G; Pattison, P; Reji, P Author Full Names: Subashini, Ashokkumar; Leela, Sundararaman; Ramamurthi, Kandasamy; Arakcheeva, Alla; Stoeckli-Evans, Helen; Petricek, Vaclav; Chapuis, Gervais; Pattison, Philip; Reji, Philip
Source:
CRYSTENGCOMM, 15 (13):2474-2481; 10.1039/c3ce26663j 2013
Abstract:
The organic nonlinear optical material of 4-bromo-4'-nitrobenzylidene aniline (BNBA, C13H9BrN2O2), a new derivative of benzylideneaniline family, was synthesized and purified by repeated recrystallization. Single crystals of BNBA were grown in acetone solvent by slow evaporation at room temperature. Its (3+1-)dimensional incommensurately modulated structure was elucidated from single crystal X-ray diffraction data obtained at 173 K. The non-centrosymmetric structure was solved and refined in the monoclinic superspace group A2(alpha 0 gamma)0; the unit cell parameters are a = 10.5217(10) angstrom, b = 16.2535(16) angstrom, c = 7.4403(7) angstrom, beta = 110.709(7)degrees, modulation vector q = 0.0658(1)a(star)-0.2658(1)c(star). At 290 K, the structure is partially disordered, however, the local structure of domains is identical to that at 173 K. The H-1 and C-13 NMR and Fourier Transform Infrared and FT-Raman spectroscopic studies confirmed the molecular structure. The Kurtz powder second-harmonic generation (SHG) test reveals that the SHG efficiency of BNBA is about 9.4 times higher than that of potassium dihydrogen phosphate. According to the thermogravimetric, differential thermal and differential scanning calorimetric analyses, BNBA is a stable phase starting from room temperature and up to the melting point, 436 K. The optical nonlinearity of BNBA was investigated at 532 nm using 5 ns laser pulses, employing the open aperture Z-scan technique.

Update: 27-Mar-2013

Title:
Critical phenomena in higher dimensional spaces: The hexagonal-to-orthorhombic phase transition in aperiodic n-nonadecane/urea
Authors:
Mariette, C; Guerin, L; Rabiller, P; Ecolivet, C; Garcia-Orduna, P; Bourges, P; Bosak, A; de Sanctis, D; Hollingsworth, MD; Janssen, T; Toudic, B Author Full Names: Mariette, C.; Guerin, L.; Rabiller, P.; Ecolivet, C.; Garcia-Orduna, P.; Bourges, P.; Bosak, A.; de Sanctis, D.; Hollingsworth, Mark D.; Janssen, T.; Toudic, B.
Source:
PHYSICAL REVIEW B, 87 (10):10.1103/PhysRevB.87.104101 MAR 4 2013
Abstract:
Upon cooling, the aperiodic inclusion compound n-nonadecane/urea presents a hexagonal-to-orthorhombic group-subgroup phase transition at T-cl that increases the structure's superspace dimensionality from four to five. This paper reports on pretransitional phenomena in such a high-dimensional space, generalizing the critical results previously reported at a lower dimensionality. Very high-resolution diffraction data reveal anomalously large correlation lengths along the aperiodic direction, with all correlation lengths diverging at T-cl. This could be explained by low-frequency phason excitations that soften at T-cl at the critical wave vector, in accordance with an increase in the critical diffuse scattering intensity. DOI: 10.1103/PhysRevB.87.104101
Title:
The composite structure of mixed tau-(Ag, Cu)(x)V2O5 bronzes Evidence for T dependant guest-species ordering and mobility
Authors:
Hermes, W; Dolle, M; Rozier, P; Lidin, S Author Full Names: Hermes, Wilfred; Dolle, Mickael; Rozier, Patrick; Lidin, Sven
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 199 84-89; 10.1016/j.jssc.2012.11.029 MAR 2013
Abstract:
The complex structural behavior of tau-[AgCu](similar to 0.92)V4O10 has been elucidated by single crystal X-ray diffraction and thermal analysis. The tau-phase region is apparently composed of several distinct phases and this study identifies at least three: tau(1rt) tau(2rt) and tau(1t), tau(1rt) and tau(2rt) have slightly different compositions and crystal habits. Both phases transform to Tit at low temperature. The room temperature modification tau(1rt) crystallizes in an incommensurately modulated structure with monoclinic symmetry C2(0 beta 1/2) [equivalent to no 5.4, B2(01/2 gamma) in the Intnl. Tables for Crystallography, Volume C] and the cell parameters a=11.757(4) angstrom, b=3.6942(5) angstrom c = 9.463(2) beta=114.62(2)degrees and the q-vector (0 0.92 1/2), but it is more convenient to transform this to a setting with a non-standard centering X=(1/2 1/20 0; 0 0 1/2 1/2; 1/2 1/2 1/2 1/2;) and an axial q vector (00.92 0). The structure features a vanadate host lattice with Cu and Ag guests forming an incommensurate composite. The structural data indicates perfect Ag/Cu ordering. At low temperature this modification is replaced by a triclinic phase characterized by two independent q-vectors. The tau(2rt) phase is similar to the low temperature modification tau(lt) but the satellite reflections are generally more diffuse. (C) 2012 Elsevier Inc. All rights reserved.

Update: 20-Mar-2013

Title:
Influence of gamma ' nanometric particles on martensitic transformation and twinning structure of L1(0) martensite in Co-Ni-Ga ferromagnetic shape memory single crystals
Authors:
Kireeva, IV; Pons, J; Picornell, C; Chumlyakov, YI; Cesari, E; Kretinina, IV Author Full Names: Kireeva, I. V.; Pons, J.; Picornell, C.; Chumlyakov, Yu. I.; Cesari, E.; Kretinina, I. V.
Source:
INTERMETALLICS, 35 60-66; 10.1016/j.intermet.2012.10.018 APR 2013
Abstract:
Ageing treatments at 620 K performed in ferromagnetic Co49Ni21Ga30 shape memory single crystals have been found to generate dense dispersions of nanometric gamma' precipitates in the austenitic matrix. These particles have a strong influence on the B2-L1(0) martensitic transformation, decreasing the overall transformation temperatures and enhancing the transformation range (difference between the temperatures for start and finish of transformation) and hysteresis. The martensitic microstructure is strongly affected as well, in such a way that the thickness of martensitic twins depends on the size and shape of particles (spherical or elongated). The results indicate that, in case of precipitation of spherical particles with diameters similar to 3-5 nm, the martensitic twins can absorb the particles and the twin thickness is still considerably larger than the precipitate diameter, while growth of larger and elongated particles with a length of 10-25 nm leads to the formation of tiny twins in between the particles with thickness of similar to 3-4 nm. These small martensite twins present an additional internal modulation and satellite spots in the diffraction pattern. (C) 2012 Elsevier Ltd. All rights reserved.
Title:
Distribution of cations at two tetrahedral sites in Ca2MgSi2O7-Ca2Fe3+AlSiO7 series synthetic melilite and its relation to incommensurate structure
Authors:
Hamada, M; Akasaka, M Author Full Names: Hamada, Maki; Akasaka, Masahide
Source:
PHYSICS AND CHEMISTRY OF MINERALS, 40 (3):259-270; 10.1007/s00269-013-0566-8 MAR 2013
Abstract:
Synthetic melilites on the join Ca2MgSi2O7 (Ayenkermanite: Ak)-Ca2Fe3+AlSiO7 (ferrialuminium gehlenite: FAGeh) were studied using X-ray powder diffraction and Fe-57 Mossbauer spectroscopic methods to determine the distribution of Fe3+ between two different tetrahedral sites (T1 and T2), and the relationship between ionic substitution and incommensurate (IC) structure. Melilites were synthesized from starting materials with compositions of Ak(100), Ak(80)FAGeh(20), Ak(70)FAGeh(30) and Ak(50)FAGeh(50) by sintering at 1,170-1,350 A degrees C and 1 atm. The average chemical compositions and end-member components, Ak, FAGeh and Geh (Ca2Al2SiO7), of the synthetic melilites were Ca2.015Mg1.023Si1.981O7 (Ak(100)), Ca2.017Mg0.788Fe (0.187) (3+) Al0.221Si1.791O7 (Ak(78)FAGeh(19)Geh(3)), Ca1.995Mg0.695Fe (0.258) (3+) Al0.318Si1.723O7 (Ak(69)FAGeh(25)Geh(6)) and Ca1.982Mg0.495Fe (0.449) (3+) Al0.519Si1.535O7 (Ak(49)FAGeh(44)Geh(7)), respectively. Rietveld refinements using X- ray powder diffraction data measured using CuK (alpha) -radiation at room temperature converged successfully with goodness-of-fits of 1.15-1.26. The refined Fe occupancies at the T1 and T2 sites and the Mg and Si contents determined by electron microprobe analysis gave the site populations of [0.788Mg + 0.082Fe(3+) + 0.130Al](T1)[0.104Fe(3+) + 0.104Al + 1.792Si](T2) for Ak(78)FAGeh(19)Geh(3), [0.695Mg + 0.127Fe(3+) + 0.178Al](T1)[0.132Fe(3+) + 0.144Al + 1.724Si](T2) for Ak(69)FAGeh(25)Geh(6) and [0.495Mg + 0.202Fe(3+) + 0.303Al](T1)[0.248Fe(3+) + 0.216Al + 1.536Si](T2) for Ak(49)FAGeh(44)Geh(7) (apfu: atoms per formula unit), respectively. The results indicate that Fe3+ is distributed at both the T1 and the T2 sites. The mean T1-O distance decreases with the substitution of Fe3+ + Al3+ for Mg2+ at the T1 site, whereas the mean T2-O distance increases with substitution of Fe3+ + Al3+ for Si4+ at the T2 site, causing decrease in the a dimension and increase in the c dimension. However, in spite of the successful Rietveld refinements for the X-ray powder diffraction data measured using CuK (alpha)-radiation at room temperature, each Bragg reflection measured using CuK (alpha 1)-radiation at room temperature showed weak shoulders, which were not observed in those measured at 200 A degrees C. The Mossbauer spectra of the melilites measured at room temperature consist of two doublets assigned to Fe3+ at the T1 site and two or three doublets to Fe3+ at the T2 site, implying the existence of multiple T1 and T2 sites with different site distortions. These facts can be interpreted in terms of the IC structure in all synthetic melilites at room temperature, respectively. The results of Mossbauer analysis indicate that the IC structure in melilite is caused by not only known multiple T1 site, but also multiple T2 site at room temperature.
Title:
Energy-dependent crossover from anisotropic to isotropic magnetic dispersion in lightly doped La1.96Sr0.04CuO4
Authors:
Matsuda, M; Granroth, GE; Fujita, M; Yamada, K; Tranquada, JM Author Full Names: Matsuda, M.; Granroth, G. E.; Fujita, M.; Yamada, K.; Tranquada, J. M.
Source:
PHYSICAL REVIEW B, 87 (5):10.1103/PhysRevB.87.054508 FEB 21 2013
Abstract:
Inelastic neutron-scattering experiments have been performed on lightly doped La1.96Sr0.04CuO4, which shows diagonal incommensurate spin correlations at low temperatures. We previously reported that this crystal, with a single orthorhombic domain, exhibits the "hourglass" dispersion at low energies [Phys. Rev. Lett. 101, 197001 (2008)]. In this paper, we investigate in detail the energy evolution of the magnetic excitations up to 65 meV. It is found that the anisotropic excitations at low energies, dispersing only along the spin modulation direction, cross over to an isotropic, conical dispersion that resembles spin waves in the parent compound La2CuO4. The change from twofold to full symmetry on crossing the waist of the hourglass reproduces behavior first identified in studies of underdoped YBa2Cu3O6+x. We discuss the significance of these results. DOI: 10.1103/PhysRevB.87.054508
Title:
Wavefunctions, quantum diffusion, and scaling exponents in golden-mean quasiperiodic tilings
Authors:
Thiem, S; Schreiber, M Author Full Names: Thiem, Stefanie; Schreiber, Michael
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (7):10.1088/0953-8984/25/7/075503 FEB 20 2013
Abstract:
We study the properties of wavefunctions and the wavepacket dynamics in quasiperiodic tight-binding models in one, two, and three dimensions. The atoms in the one-dimensional quasiperiodic chains are coupled by weak and strong bonds aligned according to the Fibonacci sequence. The associated d-dimensional quasiperiodic tilings are constructed from the direct product of d such chains, which yields either the hypercubic tiling or the labyrinth tiling. This approach allows us to consider fairly large systems numerically. We show that the wavefunctions of the system are multifractal and that their properties can be related to the structure of the system in the regime of strong quasiperiodic modulation by a renormalization group (RG) approach. We also study the dynamics of wavepackets to get information about the electronic transport properties. In particular, we investigate the scaling behaviour of the return probability of the wavepacket with time. Applying again the RG approach we show that in the regime of strong quasiperiodic modulation the return probability is governed by the underlying quasiperiodic structure. Further, we also discuss lower bounds for the scaling exponent of the width of the wavepacket and propose a modified lower bound for the absolute continuous regime.
Title:
Correlating scanning tunneling spectroscopy with the electrical resistivity of Al-based quasicrystals and approximants
Authors:
Mader, R; Widmer, R; Groning, P; Steurer, W; Groning, O Author Full Names: Maeader, Ruben; Widmer, Roland; Groening, Pierangelo; Steurer, Walter; Groening, Oliver
Source:
PHYSICAL REVIEW B, 87 (7):10.1103/PhysRevB.87.075425 FEB 19 2013
Abstract:
We present detailed low-temperature scanning tunneling spectroscopy (STS) investigations of the local electronic density of states (DOS) on the fivefold and twofold i-Al70Pd21Mn9; pseudo tenfold. xi'-Al72Pd25Mn3; tenfold d-Al77Ni17Co6; twofold-(12110) d-Al72.9Ni10.4Co16.7; (100) Y-Al75.8Ni2.1Co22.1; and (111) Al surface in the range of +/- 1 eV around the Fermi energy. All these quasicrystals and approximants exhibit the theoretically predicted electronic pseudogap. We observe no evidence for a correlation between the depth of this pseudogap, as measured by STS, and the remarkably high electrical resistivity of the investigated quasicrystals and approximants. A parametrization of the spatial variability of STS spectra is introduced as a measure of the magnitude of the electron localization for a given system. The resulting (S) over cap parameter is found to be proportional to the square root of the electrical resistivity. This finding supports the validity of interpreting spatial variations of fine-structure features in the STS spectra of Al-based quasicrystals and approximants in terms of electron localization. DOI: 10.1103/PhysRevB.87.075425
Title:
Phase separation of antiferromagnetic ground states in systems with imperfect nesting
Authors:
Rakhmanov, AL; Rozhkov, AV; Sboychakov, AO; Nori, F Author Full Names: Rakhmanov, A. L.; Rozhkov, A. V.; Sboychakov, A. O.; Nori, Franco
Source:
PHYSICAL REVIEW B, 87 (7):10.1103/PhysRevB.87.075128 FEB 19 2013
Abstract:
We analyze the phase diagram for a system of weakly coupled electrons having an *electron-* and a hole-band with imperfect nesting. Namely, both bands have spherical Fermi surfaces, but their radii are slightly different, with a mismatch proportional to the doping. Such a model is used to describe the antiferromagnetism of chromium and its alloys, pnictides, AA-stacked graphene bilayers, as well as other systems. Here we show that the uniform ground state of this model is unstable with respect to electronic phase separation in a wide range of model parameters. Physically, this instability occurs due to the competition between commensurate and incommensurate antiferromagnetic states and could be of importance for other models with imperfect nesting. DOI: 10.1103/PhysRevB.87.075128
Title:
Nb-Nb Interactions Define the Charge Density Wave Structure of 2H-NbSe2
Authors:
Malliakas, CD; Kanatzidis, MG Author Full Names: Malliakas, Christos D.; Kanatzidis, Mercouri G.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 135 (5):1719-1722; 10.1021/ja3120554 FEB 6 2013
Abstract:
2H-NbSe2 is a canonical Charge-Density-Wave (CDW) layered material the structural details of which remained elusive. We report the detailed structure of 2H-NbSe2 below the CDW transition using a (3 + 2)-dimensional crystallographic approach on single crystal X-ray diffraction data collected at 15 K. Intensities of main reflections as well as CDW satellites of first order were measured. Quantitative information about the magnitude of the structural distortions and clustering of Nb atoms were extracted from the refined model. The Nb-Nb distances were found to distort between 3.4102(8) and 3.4928(8) angstrom in the CDW phase from the average undistorted distance of 3.4583(4) angstrom.
Title:
Precipitation of quasicrystal approximant phases in an Al-Mg-Cu-Ge alloy
Authors:
Xia, JH; Sha, G; Chen, ZG; Liao, XZ; Liu, HW; Ringer, SP Author Full Names: Xia, J. H.; Sha, G.; Chen, Z. G.; Liao, X. Z.; Liu, H. W.; Ringer, S. P.
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 93 (2):77-84; 10.1080/09500839.2012.745016 FEB 1 2013
Abstract:
Cube-shaped precipitates in the peak-aged Al4.0Mg1.5Cu0.25Ge (wt.%) alloy were found to exhibit a pseudo five-fold symmetry in their electron diffraction patterns along the ?110? and ?113? zone axes of the Al matrix. These strengthening precipitates, designated as the Z, possess a structure in a transition state from an icosahedral quasicrystal phase to a face-centred cubic (FCC) quasicrystal approximant phase. After prolonged ageing, the Z phase transforms into the FCC equilibrium Z phase having atoms in a periodic icosahedral arrangement.
Title:
Stabilization of Decatellurium Molecules in Isolated and Concatenated Clusters
Authors:
Gunther, A; Isaeva, A; Ruck, M Author Full Names: Guenther, Anja; Isaeva, Anna; Ruck, Michael
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 639 (2):254-260; SI 10.1002/zaac.201200430 FEB 2013
Abstract:
Black, shiny crystals of the molecular cluster compounds (Te10)[M(TeX4)(TeX3)]2 (M/X = Rh/Cl (1), Ir/Br (2)), (Te10)[Ru(TeI4)(TeI2)]2 (3), (Te10)[M(TeI4)(TeI2)]2(TeI4)(Te2I2) (M = Rh (4), Ir (5)) as well as the one-dimensional cluster polymer (Te10I2)[Ir(TeI4)]2(Te4)I2 (6) were synthesized by melting reactions of an electron-rich transition metal M (M = Ru, Rh, Ir) with tellurium and TeX4 (X = Cl, Br, I). X-ray diffraction on single-crystals revealed that the compounds crystallize in the triclinic space group type P$\bar{1}$. 4 and 5 show [3+1]-dimensional modulations of their structures. All compounds contain binuclear complexes with central -4:4-bridging Te10 units and terminal halogenidotellurate(II) groups. Each of the transition metal cations is in a slightly distorted octahedral coordination by six tellurium atoms; the two [MTe6] octahedra share a common edge. With the tellurium atoms acting as electron-pair donors, the 18 electron rule is fulfilled for the electrophilic M atoms. The central tricyclo[5.1.1.13, 5]-decatellurium molecule consists of two ecliptically stacked Te4 rings, which are linked through two tellurium atoms. The symmetric or asymmetric 3c4e bonds along these almost linear bridges are in analogy to polyanionic forms of tellurium, while the tricyclic conformation is stabilized by the strong bonding to the transition-metal cations. Multi-center bonding (3c4e) is also present in the terminal square [Te+IIX4]2 and the T-shaped [Te+IIX3] groups. The crystal structures of 4 and 5 are organized in layers of (Te10)[M(TeI4)(TeI2)]2n+ clusters (n 2) that are quite robust upon oxidation or reduction as shown by molecular calculations. These clusters alternate with incommensurately modulated layers that probably consist of TeI42 anions and a previously unknown Te2I2 molecule. The uncertainty arises primarily from equal scattering powers of I and Te atoms as well as from the known flexibility of the electron count of the Te10 unit. In 6, neutral Te4 rings concatenate (Te10I2)[Ir(TeI4)]2 clusters into chains, which run parallel to the a axis.
Title:
Magnetoelectric coupling driven by inverse magnetostriction in multiferroic BiMn3Mn4O12
Authors:
Gauzzi, A; Rousse, G; Mezzadri, F; Calestani, GL; Andre, G; Bouree, F; Calicchio, M; Gilioli, E; Cabassi, R; Bolzoni, F; Prodi, A; Bordet, P; Marezio, M Author Full Names: Gauzzi, A.; Rousse, G.; Mezzadri, F.; Calestani, G. L.; Andre, G.; Bouree, F.; Calicchio, M.; Gilioli, E.; Cabassi, R.; Bolzoni, F.; Prodi, A.; Bordet, P.; Marezio, M.
Source:
JOURNAL OF APPLIED PHYSICS, 113 (4):10.1063/1.4789350 JAN 28 2013
Abstract:
Inserting both polar A and magnetic B ions in a same crystalline phase, such as A = Bi3+, B = Fe3+ or Mn3+ in simple perovskites ABO(3), has been successful in achieving multiferroic properties with large ferroelectric and magnetic orders. However, modest magnetoelectric couplings have been hitherto reported, thus preventing any application for future electronics. By means of neutron diffraction, we found a large uniform C-type modulation of an E-type antiferromagnetic structure of the Mn3+ ions in the quadruple perovskite BiMn3Mn4O12. A symmetry analysis indicates that this modulation is induced by the internal strain created by the polar Bi3+ ion, which gives evidence of a large magnetoelectric coupling driven by inverse magnetostriction. This modulation is indeed absent in the isomorphic and isovalent compound LaMn3Mn4O12 containing the nonpolar La3+ ion. Our analysis indicates that this coupling mechanism is effective owing to the symmetry-limited structural distortions and inhomogeneities characteristic of the quadruple perovskite structure, thus preventing the release of the strain. We conclude that internal strain is a key control parameter to achieve large magnetoelectric couplings in proper ferroelectrics. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4789350]

Update: 14-Mar-2013

Title:
Magnetic structures of Er5Rh4Ge10 compound
Authors:
Penc, B; Hofmann, M; Sikora, W; Szytula, A Author Full Names: Penc, B.; Hofmann, M.; Sikora, W.; Szytula, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 332 114-117; 10.1016/j.jmmm.2012.11.036 APR 2013
Abstract:
A powder neutron diffraction measurement of Er5Rh4Ge10 is reported. This compound crystallizes in the tetragonal Sc5Co4Si10-type structure (space group P4/mbm) in which the Er atoms occupy three different sites. The neutron diffraction measurements indicate antiferromagnetic order with the Neel temperature T-N=5.5 K. Below T-N an additional phase transition connected with the change of the magnetic structure is observed at 4.3 K. At low temperatures the Er moments form a sine-wave modulated structure with the propagation vector k=(1/4, 1/4, 0) for 1.5 K < T < 4.2 K and (113, 113, 0) for 4.2 K up to T-N. The values of the magnetic moments are different in the different sublattices and all are parallel to the c-axis. Determined magnetic structures are compared to the results from symmetry analysis. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Fifty years of aperiodic crystals (vol A68, pg 667, 2012)
Authors:
Janssen, T Author Full Names: Janssen, T.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 207-207; 10.1107/S0108767313000238 Part 2 MAR 2013
Title:
Convex polyhedral tilings hidden in crystals and quasicrystals
Authors:
Oda, T Author Full Names: Oda, Tadao
Source:
REVISTA DE LA REAL ACADEMIA DE CIENCIAS EXACTAS FISICAS Y NATURALES SERIE A-MATEMATICAS, 107 (1):123-143; SI 10.1007/s13398-012-0078-2 MAR 2013
Abstract:
Alattice in a Euclidean space gives rise to facet-to-facet and space-filling convex polyhedral tilings called the Voronoi tiling and its dual Delaunay tiling of the Euclidean space. Given a subspace of the Euclidean space, we develop a systematic way of constructing facet-to-facet and space-filling convex polyhedral tilings of the subspace called the Namikawa tilings, which are generalization of the Delaunay tiling. Our results here amplify the author's previous work with Seshadri that was obtained as a by-product of Geometric Invariant Theory in algebraic geometry. In the orthonormal setting where the lattice is spanned by an orthonormal basis of the ambient Euclidean space, the method of Namikawa tilings turns out to be the "cut and project" method relevant not only to periodic convex polyhedral tilings hidden in crystals but also to aperiodic convex polyhedral tilings hidden in quasicrystals. In another paper, the author showed that a Voronoi tiling is hidden in the "standard realization", in the sense of Kotani and Sunada, of crystals in the case of maximal abelian covering of finite graphs. In this connection, we give an affirmative answer to a question raised by Kotani to the effect that the crystal lies in the 1-skeleton of a nondegenerate convex polyhedral tiling that is a subdivision of the Voronoi tiling appearing in the other paper of the author.
Title:
Multidimensional paperfolding systems
Authors:
Ben-Abraham, SI; Quandt, A; Shapira, D Author Full Names: Ben-Abraham, Shelomo I.; Quandt, Alexander; Shapira, Dekel
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 123-130; 10.1107/S010876731204531X Part 2 MAR 2013
Abstract:
Algorithms for constructing aperiodic structures produce templates for the nanofabrication of arrays for applications in photonics, phononics and plasmonics. Here a general multidimensional recursion rule is presented for the regular paperfolding structure by straightforward generalization of the one-dimensional rule. As an illustrative example the two-dimensional version of the paperfolding structure is explicitly constructed, its symbolic complexity referred to rectangles computed and its Fourier transform shown. The paperfolding structures readily yield novel 'paperfolding' tilings. Explicit formulas are put forward to count the number of folds in any dimension. Finally, possible generalizations of the dragon curve are discussed.
Title:
Enhanced fatigue durability of Al-6 Mg alloy by applying ultrasonic impact peening: Effects of surface hardening and reinforcement with AlCuFe quasicrystalline particles
Authors:
Mordyuk, BN; Prokopenko, GI; Milman, YV; Iefimov, MO; Sameljuk, AV Author Full Names: Mordyuk, B. N.; Prokopenko, G. I.; Milman, Yu V.; Iefimov, M. O.; Sameljuk, A. V.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 563 138-146; 10.1016/j.msea.2012.11.061 FEB 15 2013
Abstract:
Composite layer reinforced with quasicrystalline (QC) Al63Cu25Fe12 particles was fabricated on the surface of Al-6 Mg alloy specimens by ultrasonic impact peening (UIP). Stress-controlled fatigue response of the specimens was studied and compared with those for the annealed and UIP-treated specimens. The notch effect of the UIP induced surface roughness calculated in terms of the stress concentration factor does not exceed similar to 10%. XRD, OM and SEM analyses were used to characterize formed surface layers and fatigue fracture surfaces. Surface composite layer of 40-50 mu m thick contains the homogeneously dispersed QC particles (the volume fraction V-f similar to 0.15) trapped by high compressive residual stresses. The layer demonstrates almost triple increase in microhardness comparing to that for the annealed alloy and twice exceeding of that for the UIP-treated specimen. Superior fatigue endurance of Al-6 Mg alloy after the UIP process and the UIP-induced f! ormation of the composite layer is explained by sub-surface fatigue cracks' initiation promoted with high compressive residual stresses and tight interfacial bonding of QC reinforcement and the matrix alloy. The improved fatigue behavior of the UIP-treated specimens in both the low cycle and high cycle regimes can be ensured by combination of the following favorable characteristics: (i) sufficiently high ductility and resistance to fatigue damage and crack growth in the core parent material along with (ii) superior fatigue strength supported by high microhardness and compressive stresses in the surface layer, which contains fine grained matrix and/or uniformly distributed and tightly bonded QC reinforcements. (c) 2012 Elsevier B.V. All rights reserved.
Title:
Chiral magnetism and helimagnons in a pyrochlore antiferromagnet
Authors:
Choi, ES; Chern, GW; Perkins, NB Author Full Names: Choi, Eunsong; Chern, Gia-Wei; Perkins, Natalia B.
Source:
PHYSICAL REVIEW B, 87 (5):10.1103/PhysRevB.87.054418 FEB 15 2013
Abstract:
Recent neutron scattering measurements on the spinel CdCr2O4 revealed a rare example of helical magnetic order in geometrically frustrated pyrochlore antiferromagnet. The spin spiral characterized by an incommensurate wave vector Q = 2 pi( 0, delta, 1) with delta approximate to 0.09 is accompanied by a tetragonal distortion. Here we conduct a systematic study on the magnetic ground state resulting from the interplay between the Dzyaloshinskii-Moriya interaction and further neighbor exchange couplings, two of the most important mechanisms for stabilizing incommensurate spin orders. We compute the low-energy spin-wave spectrum based on a microscopic spin Hamiltonian and find a dispersion relation characteristic of the helimagnons. By numerically integrating the Landau-Lifshitz-Gilbert equation with realistic model parameters, an overall agreement between experiment and the numerical spectrum, lending further support to the view that a softened optical phonon triggers the magnetic transition and endows the lattice a chirality. DOI: 10.1103/PhysRevB.87.054418
Title:
Spin-Nematic and Spin-Density-Wave Orders in Spatially Anisotropic Frustrated Magnets in a Magnetic Field
Authors:
Sato, M; Hikihara, T; Momoi, T Author Full Names: Sato, Masahiro; Hikihara, Toshiya; Momoi, Tsutomu
Source:
PHYSICAL REVIEW LETTERS, 110 (7):10.1103/PhysRevLett.110.077206 FEB 15 2013
Abstract:
We develop a microscopic theory of finite-temperature spin-nematic orderings in three-dimensional spatially anisotropic magnets consisting of weakly coupled frustrated spin-1/2 chains with nearest-neighbor and next-nearest-neighbor couplings in a magnetic field. Combining a field theoretical technique with density-matrix renormalization group results, we complete finite-temperature phase diagrams in a wide magnetic-field range that possess spin-bond-nematic and incommensurate spin-density-wave ordered phases. The effects of a four-spin interaction are also studied. The relevance of our results to quasi-one-dimensional edge-shared cuprate magnets such as LiCuVO4 is discussed. DOI: 10.1103/PhysRevLett.110.077206
Title:
Manipulating Majorana fermions in quantum nanowires with broken inversion symmetry
Authors:
Liu, XJ; Lobos, AM Author Full Names: Liu, Xiong-Jun; Lobos, Alejandro M.
Source:
PHYSICAL REVIEW B, 87 (6):10.1103/PhysRevB.87.060504 FEB 15 2013
Abstract:
We study a Majorana-carrying quantum wire, driven into a trivial phase by breaking the spatial inversion symmetry with a tilted magnetic field. Interestingly, we predict that a supercurrent applied in the proximate superconductor is able to restore the topological phase and therefore the Majorana end states. Using Abelian bosonization, we further confirm this result in the presence of electron-electron interactions and show a profound connection of this phenomenon to the commensurate-incommensurate transition in one-dimensional doped Mott insulators. These results have important applications in, e. g., realizing a supercurrent-assisted braiding of Majorana fermions, which proves highly useful in topological quantum computation with realistic Majorana networks. DOI: 10.1103/PhysRevB.87.060504
Title:
Field-induced magnetic behavior in quasi-one-dimensional Ising-like antiferromagnet BaCo2V2O8: A single-crystal neutron diffraction study
Authors:
Canevet, E; Grenier, B; Klanjsek, M; Berthier, C; Horvatic, M; Simonet, V; Lejay, P Author Full Names: Canevet, E.; Grenier, B.; Klanjsek, M.; Berthier, C.; Horvatic, M.; Simonet, V.; Lejay, P.
Source:
PHYSICAL REVIEW B, 87 (5):10.1103/PhysRevB.87.054408 FEB 13 2013
Abstract:
BaCo2V2O8 is a nice example of a quasi-one-dimensional quantum spin system that can be described in terms of Tomonaga-Luttinger liquid physics. This is explored in the present study where the magnetic field-temperature phase diagram is thoroughly established up to 12 T using single-crystal neutron diffraction. The transition from the Neel phase to the incommensurate longitudinal spin density wave (LSDW) phase through a first-order transition, as well as the critical exponents associated with the paramagnetic-Neel phase transition, and the magnetic order both in the Neel and in the LSDW phase are determined, thus providing a stringent test for the theory. DOI: 10.1103/PhysRevB.87.054408
Title:
Incomplete Devil's Staircase in the Magnetization Curve of SrCu2(BO3)(2)
Authors:
Takigawa, M; Horvatic, M; Waki, T; Kramer, S; Berthier, C; Levy-Bertrand, F; Sheikin, I; Kageyama, H; Ueda, Y; Mila, F Author Full Names: Takigawa, M.; Horvatic, M.; Waki, T.; Kraemer, S.; Berthier, C.; Levy-Bertrand, F.; Sheikin, I.; Kageyama, H.; Ueda, Y.; Mila, F.
Source:
PHYSICAL REVIEW LETTERS, 110 (6):10.1103/PhysRevLett.110.067210 FEB 8 2013
Abstract:
We report on NMR and torque measurements on the frustrated quasi-two-dimensional spin-dimer system SrCu2(BO3)(2) in magnetic fields up to 34 T that reveal a sequence of magnetization plateaus at 1/8, 2/15, 1/6, and 1/4 of the saturation and two incommensurate phases below and above the 1/6 plateau. The magnetic structures determined by NMR involve a stripe order of triplets in all plateaus, suggesting that the incommensurate phases originate from proliferation of domain walls. We propose that the magnetization process of SrCu2(BO3)(2) is best described as an incomplete devil's staircase. DOI: 10.1103/PhysRevLett.110.067210
Title:
Varied linear phason strain and its induced domain structure in quasicrystalline precipitates of Zr-Al-Ni-Cu-Nb bulk metallic glass matrix composites (vol 27, pg 3041, 2012)
Authors:
Lu, L; Xiong, DX; Wang, JB; Zhao, DS; Sun, YF Author Full Names: Lu, Lu; Xiong, Dongxia; Wang, Jianbo; Zhao, Dongshan; Sun, Yufeng
Source:
JOURNAL OF MATERIALS RESEARCH, 28 (4):658-658; 10.1557/jmr.2012.427 FEB 2013
Title:
Hydrodynamic structure factor for two-dimensional decagonal quasicrystals
Authors:
Chatzopoulos, A; Trebin, HR; Ishii, Y Author Full Names: Chatzopoulos, Andreas; Trebin, Hans-Rainer; Ishii, Yasushi
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 250 (2):291-304; 10.1002/pssb.201248275 FEB 2013
Abstract:
The dynamic and static structure factors for two-dimensional decagonal quasicrystals (QCs) are calculated based on the hydrodynamic model. Explicit formulae with algebraic decay, which is characteristic in lower dimensions, are obtained. The sound-wave and diffusive-mode contributions are analyzed separately. It is shown that the phononphason coupling yields the characteristic anisotropy in the structure factors. If one assumes the phasonic diffusion constant of the order of magnitude typical for metallic QCs, however, the phasonic contribution is expected only at very small frequencies and hence more likely to be observed in the time domain than in the frequency domain.
Title:
Hidden ferromagnetic order in underdoped cuprates
Authors:
Seibold, G; Capati, M; Di Castro, C; Grilli, M; Lorenzana, J Author Full Names: Seibold, G.; Capati, M.; Di Castro, C.; Grilli, M.; Lorenzana, J.
Source:
PHYSICAL REVIEW B, 87 (3):10.1103/PhysRevB.87.035138 JAN 30 2013
Abstract:
We study a model for low-doped cuprates where holes aggregate into oriented stripe segments which have a magnetic vortex and antivortex at the extremes. We argue that due to the interaction between segments a ferronematic state with macroscopic polarization is stabilized. This state can be characterized as a charge nematic which, due to the net polarization, breaks inversion symmetry and also exhibits an incommensurate spin modulation. Our calculation can reproduce the doping-dependent spin structure factor of lanthanum cuprates in excellent agreement with experiment and allows to rationalize experiments in which the incommensurability has an order-parameter-like temperature dependence. DOI: 10.1103/PhysRevB.87.035138
Title:
Synthesis, Structural Characterization, and Physical Properties of the Early Rare-Earth Metal Digermanides REGe2-x (x approximate to 1/4) [RE = La-Nd, Sm]. A Case Study of Commensurately and Incommensurately Modulated Structures
Authors:
Zhang, JL; Tobash, PH; Pryz, WD; Buttey, DJ; Hur, N; Thompson, JD; Sarrao, JL; Bobev, S Author Full Names: Zhang, Jiliang; Tobash, Paul H.; Pryz, William D.; Buttey, Douglas J.; Hur, Namjung; Thompson, Joe D.; Sarrao, John L.; Bobev, Svilen
Source:
INORGANIC CHEMISTRY, 52 (2):953-964; 10.1021/ic3021645 JAN 21 2013
Abstract:
Rare-earth metal germanides with the general formula RE4Ge2 (RE = La, Ce, Pr, Nd, Sm) have been synthesized using the In-flux technique. Their structures have been established from single-crystal and powder X-ray diffraction, and the structural elucidation has been aided by electron diffraction. These compounds represent superstructures of the alpha-ThSi2 structure type through the long- and/or short-range vacancy ordering. RE4Ge7 (RE = Pr, Nd, Sm) appear to be commensurately modulated 4-fold superstructure of REGe2-x (x = 1/4), while coexistence of commensurate and incommensurate modulation is revealed in the La- and Ce-analogues. These results shed more light on the structural evolution of the REGe2-x phases as function of the vacancy concentration and nature of the rare-earth metal. Measurements of the magnetic susceptibilities on well-characterized single-crystals show ferromagnetic, antiferromagnetic, and even spin-glass-like behaviors. Mean-field theory is used to evaluate the correlations between structural and magnetic property data. Measurements on the electrical resistivities and the heat capacities are also presented and discussed.
Title:
Effects of heat treatment on microstructure and mechanical properties of Mg-5Zn-0.63Er alloy
Authors:
Zhao, XF; Li, SB; Wang, QF; Du, WB; Liu, K Author Full Names: Zhao, Xian-feng; Li, Shu-bo; Wang, Qing-feng; Du, Wen-bo; Liu, Ke
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 23 (1):59-65; 10.1016/S1003-6326(13)62429-2 JAN 2013
Abstract:
The microstructure evolution of the Mg-5Zn-0.63Er (mass fraction, %) alloy containing quasicrystalline phase (I-phase) under the as-cast condition was investigated via different heat treatments. The results show that apart from the precipitation of the W-phase particles, the I-phase almost dissolves into the matrix after solid solution treatment at 480 degrees C for 10 h (T4 state). The solution-treated alloy was aged at 175 degrees C for 6-100 h (T6 state). The ultimate tensile strength of the peak-aged alloy is approximately 261 MPa companying with an elongation of 10.5%. The improvement of the tensile strength is mainly attributed to the presence of the rod-like MgZn2 particles.

Update: 7-Mar-2013

Title:
Room temperature structure and multiferroic properties in Bi0.7La0.3FeO3 ceramics
Authors:
Carvalho, TT; Fernandes, JRA; de la Cruz, JP; Vidal, JV; Sobolev, NA; Figueiras, F; Das, S; Amaral, VS; Almeida, A; Moreira, JA; Tavares, PB Author Full Names: Carvalho, T. T.; Fernandes, J. R. A.; Perez de la Cruz, J.; Vidal, J. V.; Sobolev, N. A.; Figueiras, F.; Das, S.; Amaral, V. S.; Almeida, A.; Agostinho Moreira, J.; Tavares, P. B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 554 97-103; 10.1016/j.jallcom.2012.11.018 MAR 25 2013
Abstract:
Single phase Bi0.7La0.3FeO3 ceramic samples were successfully synthesized by sol-gel combustion and co-precipitation methods, performing a final sintering at 820-870 degrees C from 10 up to 180 min. Rietveld refinements of the XRD data detected small satellite peaks that were successfully indexed by an incommensurated modulated structure model. Lanthanum doping improves magnetic response, reduces the leakage current and dielectric losses. The piezoelectric coefficient was reported for the first time in the Bi0.7La0.3FeO3 composition. (C) 2012 Elsevier B. V. All rights reserved.
Title:
Acene adsorption on a Fibonacci-modulated Cu film
Authors:
Young, KM; Smerdon, JA; Sharma, HR; Lahti, M; Pussi, K; McGrath, R Author Full Names: Young, K. M.; Smerdon, J. A.; Sharma, H. R.; Lahti, M.; Pussi, K.; McGrath, R.
Source:
PHYSICAL REVIEW B, 87 (8):10.1103/PhysRevB.87.085407 FEB 6 2013
Abstract:
The adsorption of pentacene (Pn) on the fivefold surface of an i-Al-Pd-Mn quasicrystal and on a one-dimensionally aperiodic Cu multilayer formed thereon is observed with scanning tunneling microscopy. The molecule has a strong interaction with the clean quasicrystal surface, leading to the formation of a disordered layer. On the Cu film, a molecular layer assembles, with the Cu rows acting as a template. At lower coverages, there is a repulsive interaction between the molecules, leading to a dispersed homogeneous arrangement. At higher coverages, the steric interaction of the Pn molecules counterbalances the aperiodic template, which results in a short-range periodic "checkerboard" arrangement of molecules. Density functional theory calculations using lower order acenes are used to probe the details of the interactions with the aperiodic Cu surface and it is found that adsorption with molecules parallel to Cu rows is preferred, in agreement with experimental results. DOI: 10.1103/PhysRevB.87.085407
Title:
Thermal study of the interplay between spin and lattice in CoCr2O4 and CdCr2O4
Authors:
Kitani, S; Tachibana, M; Taira, N; Kawaji, H Author Full Names: Kitani, Suguru; Tachibana, Makoto; Taira, Naoya; Kawaji, Hitoshi
Source:
PHYSICAL REVIEW B, 87 (6):10.1103/PhysRevB.87.064402 FEB 4 2013
Abstract:
The interplay between spin and lattice degrees of freedom in the spinels CoCr2O4 and CdCr2O4 has been investigated by heat capacity and thermal expansion measurements. In CoCr2O4, sharp anomalies are observed at the magnetic phase transition temperatures of 13, 26, and 93 K. A large pressure dependence of the transition temperature at 13 K, which is calculated from the heat capacity and thermal expansion, indicates strong spin-lattice coupling in the incommensurate phase. This result provides the possibility of the reduction of lattice symmetry from cubic at the phase transition. In CdCr2O4, negative thermal expansion due to spin-lattice coupling emerges in temperature from 140 to 45 K, which is followed by strong positive thermal expansion at lower temperature. The magnetostructural transition at 7.8 K is observed as a large anomaly with an indication for a large pressure dependence of the transition temperature. The unusual thermal expansion suggests the importance of other perturbations besides exchange interactions between Cr ions for the formation of the spin clusters. Our results demonstrate that thermal measurements can help to further understand the frustrated systems with strong spin-lattice coupling. DOI: 10.1103/PhysRevB.87.064402
Title:
Superionic transitions and conductivity anisotropy in Na4.6FeP2O8.6F0.4 single crystals
Authors:
Sorokin, NI Author Full Names: Sorokin, N. I.
Source:
PHYSICS OF THE SOLID STATE, 55 (2):306-308; 10.1134/S1063783413020315 FEB 2013
Abstract:
The cation conductivity in the directions parallel (sigma(aEuro-[001])) and perpendicular (sigma(aSyen[001])) to the [001] crystallographic direction of Na4.6FeP2O8.6F0.4 single crystals has been investigated at 293-734 K. The specific features of the ionic conductivity have been studied near two phase transitions at T (tr, 1) similar to 450 K and T (tr, 2) similar to 545 K. At T = T (tr, 1), the activation enthalpy for the dependences sigma(aEuro-[001])(T) and sigma(aSyen[001])(T) decreases from 0.45 +/- 0.01 to 0.33 +/- 0.02 eV, and the sigma(aEuro-[001])(T) curve has a jump of the ionic conductivity by a factor of almost two at T = T (tr, 2); the jump is related to a manifestation of commensurate modulation of the crystal structure. In the Na4.6FeP2O8.6F0.4 crystals, the ionic transport is anisotropic with the ratio sigma(aEuro-[001])/sigma(aSyen[001]) = 7.7, 5.2, and 6.6 at 293 K (T < T (tr, 1)), 500 K (T (tr, 1) < T < T (tr, 2)), and 700 K (T < T (tr, 2)), respectively. The mechanism of cation conductivity in the Na4.6FeP2O8.6F0.4 crystals is discussed.
Title:
Electronic spectra of [N(CH3)(4)](2)CoCl4 microcrystals in thin films
Authors:
Karpa, IV; Sveleba, SA; Katerynchuk, IN; Kunyo, IM; Phitsych, EI; Shymkiv, RM; Furgala, YM Author Full Names: Karpa, I. V.; Sveleba, S. A.; Katerynchuk, I. N.; Kunyo, I. M.; Phitsych, E. I.; Shymkiv, R. M.; Furgala, Yu. M.
Source:
JOURNAL OF APPLIED SPECTROSCOPY, 79 (6):888-895; 10.1007/s10812-013-9690-y JAN 2013
Abstract:
Optical absorption spectroscopy was used to study [N(CH3)(4)](2)CoxZn1-xCl4 (x = 0.75, 0.50, 0.25) and [N(CH3)(4)](2)CoCl4 microcrystals in the thickness range 10 a parts per thousand currency sign d < 100 mu m. Weakening of the crystal field was observed with a decrease in the [N(CH3)(4)](2)CoCl4 crystal thickness. Both the reason for the dependence of the absorption band shifts in the visible region on the [N(CH3)(4)](2)CoCl4 crystal thickness and the manifestation of a size effect in crystals with an incommensurate superstructure were considered.
Title:
Elliptic holes in octagonal quasicrystals
Authors:
Li, LH Author Full Names: Li Lian-He
Source:
CHINESE PHYSICS B, 22 (1):10.1088/1674-1056/22/1/016102 JAN 2013
Abstract:
The stress potential function theory for the plane elasticity of octagonal quasicrystals is developed. By introducing stress functions, a large number of basic equations involving the elasticity of octagonal quasicrystals are reduced to a single partial differential equation. Furthermore, we develop the complex variable function method (Lekhnitskii method) for anisotropic elasticity theory to that for quasicrystals. With the help of conformal transformation, an exact solution for the elliptic hole of quasicrystals is presented. The solution of the Griffith crack problem, as a special case of the results, is obtained. As a consequence, the phonon stress intensity factor is derived analytically.

Update: 28-Feb-2013

Title:
A composite based on Fe substituted TiVNi alloy: Synthesis, structure and electrochemical hydrogen storage property
Authors:
Liu, WQ; Kawabe, Y; Liang, F; Okuyama, R; Lin, J; Wang, LM Author Full Names: Liu, Wanqiang; Kawabe, Yoshiteru; Liang, Fei; Okuyama, Ryoichi; Lin, Jing; Wang, Limin
Source:
INTERMETALLICS, 34 18-22; 10.1016/j.intermet.2012.11.001 MAR 2013
Abstract:
The TiV(1-x)NiFex (x = 0, 0.1, 0.2, 0.3 and 0.4) alloy ribbons are synthesized by arc-melting and subsequent melt-spinning techniques. The structure of the alloys is characterized by XRD. The electrochemical properties including the maximum discharge capacity, cyclic stability and the high rate dischargeability, etc. are tested. The results show that the structure of all TiVNi alloy mainly consists of the icosahedral quasicrystal (I-phase), Ti2Ni-type face centered cubic (FCC) phase and body centered cubic (BCC) solid solution phase. After adding some amount of Fe to TiVNi alloys, for TiV0.9NiFe0.1 (x = 0.1) alloy, the XRD pattern is characterized by the FCC and the BCC phase, while the structure of TiV1-xNiFex alloys (x = 0.2, 0.3 and 0.4) consists of the BCC solid solution phase alloy. The maximum discharge capacity of the alloy electrodes increases firstly and then decreases with increasing x, the same as the high-rate dischargeability. The optimal value of C-240/C-30 is 84.2%, corresponding to x being 0.2 and the discharge current density is 240 mA/g. In addition, the electrochemical reaction kinetics of the alloy electrodes is also studied by electrochemical impedance spectroscopy and hydrogen diffusion coefficient (D). (C0 2012 Elsevier Ltd. All rights reserved.
Title:
Incommensurate structure of GdBaCo2O5+delta (delta similar to 0.38)
Authors:
Ishizawa, N; Asaka, T; Kudo, T; Fukuda, K; Abe, N; Arima, T Author Full Names: Ishizawa, N.; Asaka, T.; Kudo, T.; Fukuda, K.; Abe, N.; Arima, T.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 198 532-541; 10.1016/j.jssc.2012.11.004 FEB 2013
Abstract:
The incommensurate structure of the GdBaCo2O5+delta (delta similar to 0.38) paramagnetic phase was studied using the single-crystal X-ray diffraction. The basic structure of the compound is a double-layered perovskite with an alternating layer sequence of [GdO delta]-[CoO2]-[BaO]-[CoO2] along the c axis. The crystal belongs to the five-dimensional superspace group P4/mmm(alpha 00)0000(0 alpha 0)0000, alpha=0.3368(1), with a 1 x 1 x 2-type tetragonal fundamental unit cell of alpha=3.8934(1) angstrom and c=7.5267(1)angstrom. The structure was refined to R=0.028 for all the observed 2216 reflections with I > 3 sigma(I), including 331 main reflections (R=0.017), 1039 observed first-order satellites (R=0.033), and 846 observed second-order satellites (R=0.045). The crystal has oxygen deficiency that occurs only in the [GdO delta] layer; however, it causes many positional modulations of the constituent atoms throughout the crystal in association with a valence fluctuation of Co between the divalent and trivalent states. Because the value of alpha was very close to 1/3, the structure was also investigated using both the commensurately modulated approach and the conventional three-dimensional approach assuming a 3 x 3 x 2 supercell of P4/mmm symmetry. These approaches successfully reproduced a prime structure of the compound that consists of intersecting CoO5 pyramidal arrays parallel to alpha or b axes. The bond valence sum and the charge neutrality principle suggested that the divalent and trivalent cobalt cations are distributed in an ordered way. The incommensurate approach also indicated the possible presence of a local disorder having a structural similarity with that of a high-temperature modification. (c) 2012 Elsevier Inc. All rights reserved.
Title:
Particle and crystallite size effects on the modulated structure of multiferroic CaMn7O12
Authors:
Slawinski, W; Przenioslo, R; SosnowskaA, I; Wardecki, D; Fitch, AN; Bieringer, M; Jasinski, JB Author Full Names: Slawinski, Wojciech; Przenioslo, Radoslaw; SosnowskaA, Izabela; Wardecki, Dariusz; Fitch, Andy N.; Bieringer, Mario; Jasinski, Jacek B.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 198 392-398; 10.1016/j.jssc.2012.10.024 FEB 2013
Abstract:
A systematic study of the atomic position modulation in polycrystalline CaMn7O12 with different particle sizes (determined from scanning electron microscopy) and crystallite sizes (determined from X-ray diffraction) is reported. The morphology and phase composition are characterised by scanning electron microscopy, selected area electron diffraction and energy dispersive X-ray spectroscopy. The crystal structure and the atomic position modulation in polycrystalline CaMn7O12 samples are explored with high-resolution synchrotron radiation based powder X-ray diffraction. The modulation vector and the modulation amplitudes observed at T=10 K do not change as a function of particle size, crystallite size and microstrain fluctuations. In addition, we report and discuss the formation of the additional CaMn4O8 nanowire phase during high temperature annealing. (C) 2012 Elsevier Inc. All rights reserved.
Title:
Frustration by competing interactions in the highly distorted double perovskites La2NaB ' O-6 (B ' = Ru, Os)
Authors:
Aczel, AA; Bugaris, DE; Li, L; Yan, JQ; de la Cruz, C; zur Loye, HC; Nagler, SE Author Full Names: Aczel, A. A.; Bugaris, D. E.; Li, L.; Yan, J-Q; de la Cruz, C.; zur Loye, H-C; Nagler, S. E.
Source:
PHYSICAL REVIEW B, 87 (1):10.1103/PhysRevB.87.014435 JAN 31 2013
Abstract:
The usual classical behavior of S = 3/2, B-site ordered double perovskites generally results in simple, commensurate magnetic ground states. In contrast, combined magnetic susceptibility, heat capacity, and neutron powder diffraction measurements for the S = 3/2 systems La2NaB'O-6 (B' = Ru, Os) reveal an incommensurate magnetic ground state for La2NaRuO6 and a drastically suppressed ordered moment for La2NaOsO6. This behavior is attributed to the large monoclinic structural distortions of these double perovskites. The distortions have the effects of creating inequivalent nearest neighbor (NN) superexchange interactions and weakening them on average, possibly to an energy scale that is comparable with the average next nearest neighbor (NNN) superexchange. The exotic ground states in these materials can then arise from a competition between some combination of inequivalent NN and NNN exchange interactions, providing an unusual mechanism for achieving frustration in the double perovskite family. DOI: 10.1103/PhysRevB.87.014435
Title:
Effect of high pressure on the crystal structure, magnetic, and vibrational properties of multiferroic RbFe(MoO4)(2)
Authors:
Kozlenko, DP; Kichanov, SE; Lukin, EV; Dang, NT; Dubrovinsky, LS; Bykova, EA; Kamenev, KV; Liermann, HP; Morgenroth, W; Shapiro, AY; Savenko, BN Author Full Names: Kozlenko, D. P.; Kichanov, S. E.; Lukin, E. V.; Dang, N. T.; Dubrovinsky, L. S.; Bykova, E. A.; Kamenev, K. V.; Liermann, H. -P.; Morgenroth, W.; Shapiro, A. Ya.; Savenko, B. N.
Source:
PHYSICAL REVIEW B, 87 (1):10.1103/PhysRevB.87.014112 JAN 22 2013
Abstract:
The structural, magnetic, and vibrational properties of RbFe(MoO4) 2 have been studied by means of x-ray and neutron powder diffraction, magnetic susceptibility measurements, and Raman spectroscopy at pressures up to 10 GPa. The gradual structural phase transition from the initial trigonal P (3) over bar m1 phase to the monoclinic C2/c phase via the intermediate P (3) over bar phase was observed at P similar to 1 GPa. The triangular antiferromagnetic order with a propagation vector q = (1/3, 1/3, q(z)) in the suppressed trigonal phase remains incommensurate, and the q(z) value increases from 0.45 to 0.48 in the pressure range 0- 2 GPa at T = 2 K. The pressure coefficient of the Neel temperature is equal to (1/T-N)dT(N)/dP = 0.09 GPa(-1). No evidence of the formation of the long-range magnetic order in the monoclinic phase was found. The pressure dependencies of the vibrational modes for the trigonal and monoclinic phases were obtained.
Title:
Optical features of A(2)BX(4) ferroic nanocomposites with the incommensurate phase
Authors:
Lakshminarayana, G; Plucinski, KJ Author Full Names: Lakshminarayana, G.; Plucinski, K. J.
Source:
MATERIALS LETTERS, 91 345-347; 10.1016/j.matlet.2012.09.116 JAN 15 2013
Abstract:
In this paper, we report on the experimental studies of optical birefringence of A(2)BX(4) (K2ZnCl4, Rb2ZnCl4, and K2SeO4) type of crystals in a wide temperature range which show para-electric, ferroelectric properties with incommensurate phases for the 633 nm wavelength. We found that with the decrease of the nanocrystallite sizes, temperature range of the incommensurate phase is enhanced. At the same time the ferroelectricity disappeared at crystallite sizes below 8 nm due to nano-confinement effects which change the electron-phonon anharmonic interactions which are responsible for such kinds of phase transitions. Additional superposition of the external electric field leads to drastic changes in the relative amount of the ferroelectrics and incommensurate phases. The effect is explained within the Landau-Ginzburg phenomenological approach with Lifshitz invariant. Additional confirmation of the observed effects was obtained by optical second harmonic generation. During the decrease of the nanocrystallite sizes below 12 nm there occurs some harmonic soliton waves which are propagated in several directions parallel to the crystallographic axes. Despite the absence of the long-range disorder there occurs some non-centrosymmetry. (c) 2012 Elsevier B.V. All rights reserved.
Title:
Modulated crystal structures of phases VII and V in (NH4)(3)H(SO4)(2). Neutron Laue diffraction
Authors:
McIntyre, GJ; Smirnov, LS; Baranov, AI; Dolbinina, VV; Frontasyeva, MV; Pavlov, SS; Pankratova, YS Author Full Names: McIntyre, G. J.; Smirnov, L. S.; Baranov, A. I.; Dolbinina, V. V.; Frontasyeva, M. V.; Pavlov, S. S.; Pankratova, Yu. S.
Source:
CRYSTALLOGRAPHY REPORTS, 58 (1):78-80; 10.1134/S1063774513010239 JAN 2013
Abstract:
A study of the crystal structure of the phases VII and V of (NH4)(3)H(SO4)(2) by mean of neutron Laue diffraction was carried out at temperatures from 5 to 300 K. It is found that the crystal structures of phases VII and V are incommensurately modulated with different periods, and that the phase transition from phase VII to phase V is of first order.
Title:
Size effects in [N(CH3)(4)](2)Zn0.58Cu0.42Cl4 crystals
Authors:
Sveleba, SA; Karpa, IV; Katerynchuk, IN; Furgala, YM; Semotyuk, OV; Kunyo, IM; Fitsych, EI; Pankivskyi, YI Author Full Names: Sveleba, S. A.; Karpa, I. V.; Katerynchuk, I. N.; Furgala, Yu. M.; Semotyuk, O. V.; Kunyo, I. M.; Fitsych, E. I.; Pankivskyi, Yu. I.
Source:
CRYSTALLOGRAPHY REPORTS, 58 (1):122-128; 10.1134/S1063774513010124 JAN 2013
Abstract:
The temperature dependences of birefringence in thin [N(CH3)(4)](2)Zn0.58Cu0.42Cl4 crystals in the thickness range 20 x 10(-6) a parts per thousand currency sign d a parts per thousand currency sign 500 a dagger 3/4 10(-6) m have been investigated. An increase in the temperatures of the parent phase-incommensurate phase and incommensurate phase-ferroelectric phase transitions has been found. The reasons for the shift in the phase transition temperatures with a decrease in the thickness of [N(CH3)(4)](2)Zn0.58Cu0.42Cl4 crystal and the size effect in crystals with an incommensurate superstructure are discussed.

Update: 21-Feb-2013

Title:
Structural, tribological and resistivity studies of Ga substituted (Al71-xGax) Pd21Mn8 icosahedral and other intermetallic phases
Authors:
Bohra, M; de Weerd, MC; Fournee, V; Mandal, RK; Mukhopadhyay, NK; Chatterjee, R; Sastry, GVS Author Full Names: Bohra, Murtaza; de Weerd, M. C.; Fournee, Vincent; Mandal, R. K.; Mukhopadhyay, N. K.; Chatterjee, Ratnamala; Sastry, G. V. S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 551 274-278; 10.1016/j.jallcom.2012.09.130 FEB 25 2013
Abstract:
We report the formation of icosahedral phase in Al-71 xGaxPd21Mn8 (x = 0, 4, 6, 8, and 10 at.%) by adopting powder metallurgical route. Such a variation in Ga substitution in the alloy composition gave rise to a nearly single phase face centred icosahedral phase for x = 6. All other Ga substituted compositions displayed formation of intermetallic phases in addition to the icosahedral quasicrystals. The 6d hypercubic lattice parameter for the Ga substituted icosahedral phase is higher than that of Al71Pd21Mn8 composition. The change in the lattice parameter is non-monotonic. Such a change in lattice parameter has been explained based on the mixed valence states of Ga on Al site. The electrical resistivity of x = 6 sample is comparable to those of earlier studies pertaining to flux grown icosahedral composition of Al(Ga) PdMn alloy. Further, x = 6 sample has displayed highest value of static friction coefficient. This has been understood in terms of the shift of Fermi level from the pseudo-gap location owing to mixed valence states of Ga. (C) 2012 Elsevier B. V. All rights reserved.
Title:
Generalization of the Mooij correlation to quasicrystals
Authors:
Rapp, O Author Full Names: Rapp, O.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (6):10.1088/0953-8984/25/6/065701 FEB 13 2013
Abstract:
The Mooij correlation has been generalized to include quasicrystals. The average temperature dependence of the electrical resistivity rho(T), as estimated from the difference rho(4.2 K)-rho(295 K), was found to be correlated with rho(295 K) over seven orders of magnitude. This relation remains robust for modifications of the samples such as approximants, single grain samples, and samples with properties that vary strongly with annealing. An interesting subset of data is metallic alloys of the type Al-Cu-M (M = Li, Li(Mg), Cu Ru, Os), where rho(4.2 K)-rho(295 K) similar to [rho(295 K)](2).
Title:
Magnetic structures and physical properties of Tm3Cu4Ge4 and Tm3Cu4Sn4
Authors:
Baran, S; Kaczorowski, D; Szytula, A; Gil, A; Hoser, A Author Full Names: Baran, S.; Kaczorowski, D.; Szytula, A.; Gil, A.; Hoser, A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (6):10.1088/0953-8984/25/6/066012 FEB 13 2013
Abstract:
Tm3Cu4Ge4 crystallizes in the orthorhombic Gd3Cu4Ge4-type crystal structure (space group Immm) whereas Tm3Cu4Sn4 crystallizes in a distorted variant of this structure (monoclinic space group C2/m). The compounds were studied by means of neutron diffraction, specific heat, electrical resistivity and magnetic measurements. Analysis of experimental data revealed the presence of an antiferromagnetic order below 2.8 K in both compounds. In Tm3Cu4Ge4 the magnetic unit cell is doubled in respect to the crystal unit cell and the magnetic structure can be described by a propagation vector (k) over right arrow = [0, 1/2, 0]. A larger magnetic unit cell was found in Tm3Cu4Sn4, given by a propagation vector (k) over right arrow = [1/2, 1/2, 0] (for simplicity the orthorhombic description is used for both the germanide and the stannide). Close to 2 K, in each compound an incommensurate antiferromagnetic order develops. This low-temperature magnetic phase is characterized by a propagation vector (k) over right arrow = [1/4, 0, k(z)], where k(z) is close to 0.49 and 0.47 in Tm3Cu4Ge4 and Tm3Cu4Sn4, respectively. The antiferromagnetic phase transitions are clearly seen in the bulk magnetic and specific heat data of both compounds.
Title:
The charge-flipping algorithm in crystallography
Authors:
Palatinus, L Author Full Names: Palatinus, Lukas
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 69 1-16; 10.1107/S0108768112051361 Part 1 FEB 2013
Abstract:
The charge-flipping algorithm (CFA) is a member of the diverse family of dual-space iterative phasing algorithms. These algorithms use alternating modifications in direct and reciprocal space to find a solution to the phase problem. The current state-of-the-art CFA is reviewed and it is put in the context of related dual-space algorithms with relevance for crystallography. The CFA has found applications in many crystallographic problems. The principal applications in various fields are described with sections devoted to routine structure solution, the solution of complex structures from powder diffraction data, the solution of incommensurately modulated crystals and quasicrystals, macromolecular crystallography and single-particle imaging.
Title:
Ultrafast filling of an electronic pseudogap in an incommensurate crystal
Authors:
Brouet, V; Mauchain, J; Papalazarou, E; Faure, J; Marsi, M; Lin, PH; Taleb-Ibrahimi, A; Le Fevre, P; Bertran, F; Cario, L; Janod, E; Corraze, B; Phuoc, VT; Perfetti, L Author Full Names: Brouet, V.; Mauchain, J.; Papalazarou, E.; Faure, J.; Marsi, M.; Lin, P. H.; Taleb-Ibrahimi, A.; Le Fevre, P.; Bertran, F.; Cario, L.; Janod, E.; Corraze, B.; Phuoc, V. Ta; Perfetti, L.
Source:
PHYSICAL REVIEW B, 87 (4):10.1103/PhysRevB.87.041106 JAN 28 2013
Abstract:
We investigate the quasiperiodic crystal (LaS)(1.196)VS2 by angle and time resolved photoemission spectroscopy. The dispersion of electronic states is in qualitative agreement with the band structure calculated for the VS2 slab without incommensurate distortion. Nonetheless, the spectra display a temperature dependent pseudogap instead of quasiparticle crossing. The sudden photoexcitation at 50 K induces a partial filling of the electronic pseudogap within less than 80 fs. The electronic energy flows into the lattice modes on a comparable time scale. We attribute this surprisingly short time scale to a very strong electron-phonon coupling to the incommensurate distortion. This result sheds light on the electronic localization arising in aperiodic structures and quasicrystals. DOI: 10.1103/PhysRevB.87.041106
Title:
Magnetoelectric responses induced by domain rearrangement and spin structural change in triangular-lattice helimagnets NiI2 and CoI2
Authors:
Kurumaji, T; Seki, S; Ishiwata, S; Murakawa, H; Kaneko, Y; Tokura, Y Author Full Names: Kurumaji, T.; Seki, S.; Ishiwata, S.; Murakawa, H.; Kaneko, Y.; Tokura, Y.
Source:
PHYSICAL REVIEW B, 87 (1):10.1103/PhysRevB.87.014429 JAN 25 2013
Abstract:
Dielectric and magnetic properties have been investigated for single crystals of triangular-lattice antiferromagnets NiI2 and CoI2. For NiI2, the proper screw spin order with the magnetic modulation vector q similar to (0.138, 0, 1.457) induces electric polarization (P) along the in-plane direction with respect to the triangular lattice basal plane. The P shows monotonic increase as a function of the poling magnetic field (H) along the in-plane direction, suggesting the H-induced rearrangement of the multiferroic domain out of six possible domains. For CoI2, both in-plane and out-of-plane components of P emerge in the helimagnetic ground state, in which two cycloidal magnetic phases with q(1) = (1/12, 1/12, 1/2) and q(2) = (1/8, 0, 1/2) are supposed to coexist. The application of the in-plane H induces two-step metamagneticlike transitions, which probably goes through another ferroelectric helimagnetic phase as well as a paraelectric spin-collinear phase. Such distinctive magnetoelectric responses in the two simple triangular lattice antiferromagnets demonstrate that even a slight difference in the balance of magnetic interactions leads to a dramatic change of resultant magnetoelectric response in frustrated magnets. DOI: 10.1103/PhysRevB.87.014429
Title:
Effects of quasicrystal formation on the crystallization of (Ti36.1Zr33.2Ni5.8Be24.9)(100-x)Cu-x (x=5, 7, 9, 11, 13, 15, 17) metallic glasses
Authors:
Sha, PF; Zhu, ZW; Tang, MQ; Fu, HM; Li, ZK; Li, H; Wang, AM; Zhang, HW; Zhang, HF; Hu, ZQ Author Full Names: Sha, P. F.; Zhu, Z. W.; Tang, M. Q.; Fu, H. M.; Li, Z. K.; Li, H.; Wang, A. M.; Zhang, H. W.; Zhang, H. F.; Hu, Z. Q.
Source:
JOURNAL OF APPLIED PHYSICS, 113 (3):10.1063/1.4775836 JAN 21 2013
Abstract:
The crystallization behaviors of the (Ti36.1Zr33.2Ni5.8Be24.9)(100-x)Cu-x (x = 5, 7, 9, 11, 13, 15, 17; at. %) metallic glasses are investigated under both the continuous heating and isothermal conditions by the differential scanning calorimetry. Quasicrystals are found in the crystallization products under both conditions by X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy. The evolution of the primary crystallization products of these alloys is discussed in detail. The effects of the increasing distortion energy of the icosahedral shortrange order with the increasing Cu content in the(Ti36.1Zr33.2Ni5.8Be24.9)(100-x)Cu-x (x = 5, 7, 9, 11, 13, 15, 17) alloys are found to be responsible for the evolution of the crystallization products. The isothermal crystallization kinetics deviates from the Johnson-Mehl-Avrami-Kolmogoroff (JMAK) model. A modified JMAK model with an impingement parameter is found to be suitable for the isothermal crystallization kinetics of the current alloys. The effects of quasicrystal formation on the crystallization kinetics are disscussed in detail. And it is found that the isothermal crystallization kinetics are influenced by both of the "soft impingement" effect and the formation of the quasicrystals. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4775836]
Title:
Aperiodic crystals
Authors:
Mukhopadhyay, NK Author Full Names: Mukhopadhyay, N. K.
Source:
CURRENT SCIENCE, 103 (12):1392-1394; DEC 25 2012
Title:
Toward theories of friction and adhesion on quasicrystals
Authors:
Rabson, DA Author Full Names: Rabson, D. A.
Source:
PROGRESS IN SURFACE SCIENCE, 87 (9-12):253-271; 10.1016/j.progsurf.2012.10.001 SEP-DEC 2012
Abstract:
It has long been known that quasicrystal surfaces show low sliding friction and adhesion, features that have led to practical applications, notably in cookware. Several mechanisms have been proposed for how quasiperiodicity might result in low friction and low adhesion. These include mechanical characteristics (stiffness and hardness), electronic properties, phonon propagation, surface topography at atomic length scales, and relatively irrational spacings between the atoms of the two sliding surfaces ("superlubricity"). Recent work by Park et al. finds an eightfold anisotropy in the coefficient of sliding friction between a decagonal quasicrystal surface and a passivated probe. This giant anisotropy epitomizes in a single experiment the difference between periodicity and aperiodicity, yet theoretical explanations of the effect remain controversial. (C) 2012 Elsevier Ltd. All rights reserved.

Update: 13-Feb-2013

Title:
Effects of Ag addition on crystallization, microstructure and mechanical properties of Zr-Cu-Ni-Al-Ag bulk metallic glasses
Authors:
Zhou, W; Lin, X; Li, JF Author Full Names: Zhou, W.; Lin, X.; Li, J. F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 552 102-106; 10.1016/j.jallcom.2012.10.101 MAR 5 2013
Abstract:
The composition dependences of crystallization, microstructure and mechanical properties have been investigated. When the Ag content is in the range of 0-8 at%, the BMGs with two or three-step of crystallization process exhibit remarkable plasticity, of which primary phase is an icosahedral phase. However, when the Ag concentration reaches 12-16 at%, the BMGs with single-step of crystallization mode display relatively limited plasticity, whose precipitation phase is Zr2Cu and/or Zr2Ni intermetallic compounds. Structural analyses reveal that the presence of icosahedral medium-range order clusters, which, in turn leads to the heterogeneity of free volume distribution, is responsible for the improvement of plasticity. The present results suggest that, under appropriate microstructural design by the introduction of icosahedral medium-range order clusters, BMG has extensive application prospect as structural material. (C) 2012 Elsevier B. V. All rights reserved.
Title:
Cimetidine, C10H16N6S, form C: crystal structure and modelling of polytypes using the superspace approach
Authors:
Arakcheeva, A; Pattison, P; Bauer-Brandl, A; Birkedal, H; Chapuis, G Author Full Names: Arakcheeva, Alla; Pattison, Philip; Bauer-Brandl, Annette; Birkedal, Henrik; Chapuis, Gervais
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 46 (1):99-107; 10.1107/S0021889812048133 FEB 2013
Abstract:
The H2 antagonist cimetidine forms many polymorphs, several of which have resisted structural analysis thus far. Using single-crystal X-ray measurements obtained from synchrotron radiation, the crystal structure of cimetidine form C has been solved. This layered structure crystallizes in space group C2/c with an unusually large lattice parameter, a = 82.904 angstrom. The thickness of each layer L is equal to a' = a/6 = 13.82 angstrom, and a = 6a' originates from a sixfold LLLL'L'L' sequence with L and L' differing by 0.5b. This packing is reminiscent of polytypic stacking in metals. A (3 + 1)-dimensional superspace model is derived and used to explain and predict many polytypic modifications. This model is characterized by (i) the (3 + 1)-dimensional symmetry group X2/c(alpha 0 gamma)00, where X = 0 1/2 0 1/2; (ii) the lattice parameter a' and modulation vector q = 1/n(a'*); (iii) the atomic positions of a single molecule of cimetidine form C; (iv) the primary variable, 1/n. The model reproduces the previously solved structure, the 6M polytype, and generates the related polytypes nM with lattice parameter a(nM) = na' for n = 1, 2, 3, 4 and 5. A comparison of powder X-ray diffraction patterns available for cimetidine form C with those simulated for the nM polytypes suggests that the powder samples published previously probably contain a mixture of various polytypes.
Title:
Incommensurate magnetic structures of multiferroic MnWO4 studied within the superspace formalism
Authors:
Urcelay-Olabarria, I; Perez-Mato, JM; Ribeiro, JL; Garcia-Munoz, JL; Ressouche, E; Skumryev, V; Mukhin, AA Author Full Names: Urcelay-Olabarria, I.; Perez-Mato, J. M.; Ribeiro, J. L.; Garcia-Munoz, J. L.; Ressouche, E.; Skumryev, V.; Mukhin, A. A.
Source:
PHYSICAL REVIEW B, 87 (1):10.1103/PhysRevB.87.014419 JAN 15 2013
Abstract:
The magnetic structures of the incommensurate phases of the prototypic multiferroic MnWO4 are analyzed using superspace symmetry formalism. This approach shows in a very simple way the relation between the magnetic symmetry of the incommensurate phases and any tensorial property, such as ferroelectricity. The magnetic structures have been redetermined by single-crystal neutron diffraction experiments, which revealed fine details of the AF3 and AF2 magnetic structures. The spin modulations of the two manganese ions of the basic unit cell are symmetry-related in the paraelectric incommensurate-magnetic structure (AF3)-they are not forced to be collinear but they must have opposite chirality-while in the multiferroic phase (AF2) they become symmetry independent. It is due to this symmetry break that the electric polarization arises along the b axis. DOI: 10.1103/PhysRevB.87.014419
Title:
New Layered Tin(II) Thiophosphates ASnPS(4) (A = K, Rb, Cs): Synthesis, Structure, Glass Formation, and the Modulated CsSnPS4
Authors:
Banerjee, S; Malliakas, CD; Kanatzidis, MG Author Full Names: Banerjee, Santanu; Malliakas, Christos D.; Kanatzidis, Mercouri G.
Source:
INORGANIC CHEMISTRY, 51 (21):11562-11573; 10.1021/ic301456m NOV 5 2012
Abstract:
The layered compounds KSnPS4 (1), RbSnPS4 (2), and CsSnPS4 (3) were synthesized using the chalcophosphate flux technique at high temperature and are rare examples of divalent Sn(II) thiophosphates. Orange polyhedral crystals of compound 1 crystallize in the monoclinic space group P2(1)/c with a = 6.6673(13) angstrom, b = 11.9697(24) angstrom, c = 8.7604(18), and beta=127.347(8)degrees in a 2-dimensional layered structure. Compound 2 is isostructural to 1. Yellow block shaped crystals of compound 3 crystallize in the monoclinic superspace group P2(1)(alpha beta 0)0 with a commensurate q-vector at 1/4a* + 1/4c* with a = 18.0477(14) angstrom, b = 6.2021(5) angstrom, and c = 6.8415(5) angstrom. The structure of all three compounds contains SnS3 pyramids, which is an extremely rare solid state chalcogenide coordination environment. All three compounds are semiconductors having well-defined band-gaps between 2.0 and 2.2 eV. The compounds are congruently melting and can be obtained as glasses by rapid quenching of the melt, which subsequently crystallize upon heating.

Update: 6-Feb-2013

Title:
Single crystal growth of antiferromagnetic Mn3Si by a two-phase RF floating-zone method
Authors:
Hermann, R; Wendrock, H; Rodan, S; Rossler, UK; Blum, CGF; Wurmehl, S; Buchner, B Author Full Names: Hermann, R.; Wendrock, H.; Rodan, S.; Roessler, U. K.; Blum, C. G. F.; Wurmehl, S.; Buechner, B.
Source:
JOURNAL OF CRYSTAL GROWTH, 363 1-6; 10.1016/j.jcrysgro.2012.09.029 JAN 15 2013
Abstract:
The floating-zone growth of massive intermetallic single crystals is very often unsuccessful due to unfavorable solidliquid interface geometry and insufficient mixing of the melt which depends on the flow in the molten zone. A tailored magnetic two-phase stirrer system with radio frequency (RF) heating has been developed which enables the control of the melt flow by a significant change of the flow field. The magnetic system was used for the crystal growth of the Heusler compound Mn3Si due to their interesting properties such an itinerant antiferromagnetic and incommensurate spin-density wave state. The grown crystals were oriented and cut to samples with the crystallographic orientations (100) and (110) normal to a plane. Measurements of the temperature dependence of magnetization and specific heat are discussed in terms of contributions of other thermodynamic phases and phase transitions. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Microstructure and mechanical properties of double continuously extruded Mg-Zn-Gd-based magnesium alloys
Authors:
Huang, H; Yuan, GY; Chu, ZH; Ding, WJ Author Full Names: Huang, Hua; Yuan, Guangyin; Chu, Zhenhua; Ding, Wenjiang
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 560 241-248; 10.1016/j.msea.2012.09.063 JAN 10 2013
Abstract:
Double continuous extrusion (DCE) is proposed here as a novel thermomechanical process which means that the sample is continuously extruded twice by one process. The microstructures and mechanical properties of Mg98Zn1.92Gd0.08 (at%, Alloy 1) and Mg96.83Zn2.7Gd0.47 (at%, Alloy 2) after conventional extrusion and DCE at 373 K were investigated. The results show that the major secondary phase in Alloy 1 is Mg2Zn3 and that in Alloy 2 is icosahedral quasicrystals phase (I-phase). After DCE, the microstructure is refined, and the average grain sizes of the both alloys are smaller than 1 mu m, and this further improves the mechanical properties. Both the alloys exhibit excellent mechanical properties, and the ultimate tensile strength, yield strength and elongation to failure are 434 MPa, 410 MPa and 14.6%, respectively, for Alloy 1; and 444 MPa, 417 MPa and 13.1%, respectively, for Alloy 2. The possible strengthening mechanisms were discussed and it was found that DCE is an effective method for Mg-based alloys strengthening by grain refinement and secondary phase dispersion. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Different microstructures of mobile twin boundaries in 10 M modulated Ni-Mn-Ga martensite
Authors:
Heczko, O; Straka, L; Seiner, H Author Full Names: Heczko, O.; Straka, L.; Seiner, H.
Source:
ACTA MATERIALIA, 61 (2):622-631; 10.1016/j.actamat.2012.10.007 JAN 2013
Abstract:
The morphology and microstructure of a single, macroscopically straight twin interface with a twinning stress of about 1 MPa was analysed in detail by differential interference contrast optical microscopy and X-ray diffraction. The interface was identified as a Type I macrotwin boundary between two variants with a/b-laminates and constant modulation direction, in contrast with a highly mobile twinned interface consisting of Type II macrotwin boundary segments with changing modulation direction and a/b-laminate reported earlier. Theoretical analysis using elastic continuum theory shows that only pure Type I or Type II boundaries are fully compatible with a/b-laminate. Other hypothetical twin microstructures combining these two mobile interfaces are shown to be incompatible to various degrees. A weakly incompatible combination of Type I and II boundaries was experimentally observed. The large difference in mobility between Type I and Type II macrotwin boundaries cr! eated at the same location of the same sample indicates that the mobility depends on the internal structure of these boundaries. A possible origin of this different mobility is discussed. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
A new cluster-based cubic phase in the Al-Cu-Ir system
Authors:
Dshemuchadse, J; Kuczera, P; Steurer, W Author Full Names: Dshemuchadse, Julia; Kuczera, Pawel; Steurer, Walter
Source:
INTERMETALLICS, 32 337-343; 10.1016/j.intermet.2012.08.027 JAN 2013
Abstract:
The structure of the intermetallic phase cF244-Al63.3Cu12.3Ir24.4, a superstructure of a 1/0-approximant to an icosahedral quasicrystal, was determined by single-crystal X-ray diffraction. It can be described as a packing of endohedral clusters with a significant amount of disorder in the innermost shells. Similarities to the structures of related intermetallic compounds and quasicrystal approximants are discussed. (C) 2012 Elsevier Ltd. All rights reserved.
Title:
Roles of icosahedral and crystal-like order in the hard spheres glass transition
Authors:
Leocmach, M; Tanaka, H Author Full Names: Leocmach, Mathieu; Tanaka, Hajime
Source:
NATURE COMMUNICATIONS, 3 10.1038/ncomms1974 JUL 2012
Abstract:
A link between structural ordering and slow dynamics has recently attracted much attention from the context of the origin of glassy slow dynamics. Candidates for such structural order are icosahedral, exotic amorphous and crystal-like. Each type of order is linked to a different scenario of glass transition. Here we experimentally access local structural order in polydisperse hard spheres by particle-level confocal microscopy. We identify the key structures as icosahedral and FCC-like order, both statistically associated with slow particles. However, when approaching the glass transition, the icosahedral order does not grow in size, whereas crystal-like order grows. It is the latter that governs the dynamics and is linked to dynamic heterogeneity. This questions the direct role of the local icosahedral ordering in glassy slow dynamics and suggests that the growing length scale of structural order is essential for the slowing down of dynamics and t! he non-local cooperativity in particle motion.

Update: 31-Jan-2013

Title:
Spin density wave in (FexV3-x)S-4 and the coexistence of normal and condensate states: A Mossbauer study
Authors:
Embaid, BP; Gonzalez-Jimenez, F Author Full Names: Embaid, B. P.; Gonzalez-Jimenez, F.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 330 134-140; 10.1016/j.jmmm.2012.10.030 MAR 2013
Abstract:
Iron-vanadium sulfides of the monoclinic system FexV3-xS4 (1.0 <= x <= 2.0) have been investigated by Fe-57 Mossbauer Spectroscopy in the temperature range 30-300 K. Incommensurate spin density waves (SDW) have been found in this system. An alternative treatment of the spectra allows a direct measurement of the temperature evolution of condensate density of the SDW state which follows the Maki-Virosztek formula. For composition (x=1.0) the SDW condensate is unpinned while for compositions (x > 1.0) the SDW condensate is pinned. Possible causes of the pinning-unpinning SDW will be discussed. (C) 2012 Elsevier B.V. All rights reserved.
Title:
An x-ray absorption spectroscopy study of Ni-Mn-Ga shape memory alloys
Authors:
Sathe, VG; Dubey, A; Banik, S; Barman, SR; Olivi, L Author Full Names: Sathe, V. G.; Dubey, Aditi; Banik, Soma; Barman, S. R.; Olivi, L.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (4):10.1088/0953-8984/25/4/046001 JAN 30 2013
Abstract:
The austenite to martensite phase transition in Ni-Mn-Ga ferromagnetic shape memory alloys was studied by extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) spectroscopy. The spectra at all the three elements', namely, Mn, Ga and Ni, K-edges in several Ni-Mn-Ga samples (with both Ni and Mn excess) were analyzed at room temperature and low temperatures. The EXAFS analysis suggested a displacement of Mn and Ga atoms in opposite direction with respect to the Ni atoms when the compound transforms from the austenite phase to the martensite phase. The first coordination distances around the Mn and Ga atoms remained undisturbed on transition, while the second and subsequent shells showed dramatic changes indicating the presence of a modulated structure. The Mn rich compounds showed the presence of antisite disorder of Mn and Ga. The XANES results showed remarkable changes in the unoccupied partial density of states corresponding to Mn and Ni, while the electronic structure of Ga remained unperturbed across the martensite transition. The post-edge features in the Mn K-edge XANES spectra changed from a double peak like structure to a flat peak like structure upon phase transition. The study establishes strong correlation between the crystal structure and the unoccupied electronic structure in these shape memory alloys.
Title:
The impact of oxygen on the morphology of gas-phase prepared Au nanoparticles
Authors:
Pohl, D; Surrey, A; Schultz, L; Rellinghaus, B Author Full Names: Pohl, D.; Surrey, A.; Schultz, L.; Rellinghaus, B.
Source:
APPLIED PHYSICS LETTERS, 101 (26):10.1063/1.4773203 DEC 24 2012
Abstract:
We present an easy procedure for the synthesis of single crystalline gold nanoparticles with a mean diameter of 4 nm using a DC-sputtering in an argon-oxygen gas mixture. Morphology population statistics have been determined to quantify the influence of oxygen. It is found that the particles undergo a structural transition from predominantly icosahedral to single crystalline particles with increasing amount of oxygen. Aberration-corrected high-resolution transmission electron microscopy investigation proves that likewise prepared single crystalline nanoparticles are defect and oxygen free. In contrast, the icosahedral particles prepared with pure argon show the presence of edge dislocations pointing to an energetic disfavoring already at these relatively small particle sizes. This morphology control of clean and uncovered Au nanoparticles provides a high application potential, e. g., for studying the influence of the particle morphology on plasmonic and catalytic propert! ies. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4773203]
Title:
Aperiodic Spin State Ordering of Bistable Molecules and Its Photoinduced Erasing
Authors:
Collet, E; Watanabe, H; Brefuel, N; Palatinus, L; Roudaut, L; Toupet, L; Tanaka, K; Tuchagues, JP; Fertey, P; Ravy, S; Toudic, B; Cailleau, H Author Full Names: Collet, E.; Watanabe, H.; Brefuel, N.; Palatinus, L.; Roudaut, L.; Toupet, L.; Tanaka, K.; Tuchagues, J. -P.; Fertey, P.; Ravy, S.; Toudic, B.; Cailleau, H.
Source:
PHYSICAL REVIEW LETTERS, 109 (25):10.1103/PhysRevLett.109.257206 DEC 21 2012
Abstract:
We describe a novel type of ordering phenomenon associated with the incommensurate occupational modulation of bistable molecular magnetic state in a spin-crossover material. This unusual type of aperiodicity resulting from the ordering of multistable electronic states opens new possibilities for addressing such materials by light. Here we show that light can switch the crystal from four-to three-dimensional periodic structure. Mixing aperiodicity, multistability, and photoinduced phenomena opens new perspectives for directing complex order and function in material science. DOI: 10.1103/PhysRevLett.109.257206
Title:
Structural incommensurate modulation rule in hexagonal Ba(Ti1-xMx)O3-delta (M = Mn, Fe) multiferroics
Authors:
Wei, XK; Zhang, QH; Jin, CQ; Yu, RC Author Full Names: Wei, X. K.; Zhang, Q. H.; Jin, C. Q.; Yu, R. C.
Source:
AIP ADVANCES, 2 (4):10.1063/1.4766181 DEC 2012
Abstract:
The structural incommensurate modulation (SIM) rule in hexagonal Ba(Ti1-xMx)O3-delta (1/18 <= x <= 1/3, M = Mn, Fe) multiferroic ceramics is investigated using transmission electron microscope (TEM). Our systematic analysis on the modulation characteristics in the electron diffraction patterns, especially along [001] direction, reveals that three types of anti-phase domain boundaries (APBs) dominate the SIMs. According to the derived APB models, the calculated oxygen vacancies at both O1 (face sharing) and O2 (corner sharing) sites qualitatively agree quite well with our previous results. Analysis on the high-resolution TEM images reveals that complex dislocation structures also play important roles in the formation of the SIMs. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4766181]
Title:
Evidence for a monoclinic incommensurate superstructure in modulated martensite
Authors:
Li, ZB; Zhang, YD; Esling, C; Zhao, X; Zuo, L Author Full Names: Li, Zongbin; Zhang, Yudong; Esling, Claude; Zhao, Xiang; Zuo, Liang
Source:
ACTA MATERIALIA, 60 (20):6982-6990; 10.1016/j.actamat.2012.09.001 DEC 2012
Abstract:
Structural modulation of martensitic phases is regarded as a prerequisite for magnetically or electrically induced reversible strains in shape-memory alloys. Controversy surrounds the crystal structure of modulated martensite. Here, we explore this critical issue through combined spatially resolved microstructural and crystallographic characterizations of a polycrystalline Ni53Mn22Ga25 alloy, by comparing the high-resolution Kikuchi patterns with those predicted according to various hypotheses-7M(IC) or nanotwin combination structure-on the modulated martensite. Detailed analysis has demonstrated that the modulated martensite plates may possess a monoclinic incommensurate superstructure, other than the nanotwinned tetragonal non-modulated structure. Such an incommensurate superstructure can generate a more favorable plate interface configuration for field-driven twinning/detwinning, capable of producing large reversible actuation strain. Moreover, the thermodynamically metastable modulated martensite may transform into the non-modulated martensite by further local lattice distortion, which would degrade the magnetic shape-memory effect. By taking into account the microstructure-property correlation, the ambiguity concerning the modulated martensitic structure could be clarified, which is essential to the understanding of the stability of modulated martensitic phases and their functionality as shape-memory materials. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 23-Jan-2013

Title:
Structure of Turbostratically Disordered Misfit Layer Compounds [(PbSe)0.99]1[WSe2]1, [(PbSe)1.00]1[MoSe2]1, and [(SnSe)1.03]1[MoSe2]1
Authors:
Smeller, MM; Heideman, CL; Lin, QY; Beekman, M; Anderson, MD; Zschack, P; Anderson, IM; Johnson, DC Author Full Names: Smeller, Mary M.; Heideman, Colby L.; Lin, Qiyin; Beekman, Matt; Anderson, Michael D.; Zschack, Paul; Anderson, Ian M.; Johnson, David C.
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 638 (15):2632-2639; SI 10.1002/zaac.201200408 DEC 2012
Abstract:
The structures of three new misfit layer compounds, [(PbSe)0.99]1[WSe2]1, [(PbSe)1.00]1[MoSe2]1, and [(SnSe)1.03]1[MoSe2]1, prepared as thin films from designed elementally modulated reactant precursors, have been investigated by synchrotron X-ray diffraction and scanning transmission electron microscopy. This is the second report of a misfit layer compound based on tin selenide and the first structure determinations of tungsten- and molybdenum-containing misfit layer compounds. The compounds have mismatches in both the a- and b-axis (in-plane) lattice parameters of the component structural units, which result in misfit parameters, d, both greater and smaller than zero. Pole figures of hk0-type reflections indicate that c-axis-oriented (basal plane) dichalcogenide-structured units are randomly oriented within the a-b plane. The widths of diffraction peaks of type hk0, 00l, and hkl (h, k ? 0; l ? 0) indicate coherence lengths of approximately (6 to 7) nm within the a-b plane, the full thickness of the film along the c-axis, and (1 to 2) nm in mixed-index directions, respectively, consistent with random rotational disorder between the constituents, commonly termed turbostratic disorder in the clay literature. The intensities of 00l- and hk0-type diffraction peaks were modeled to determine the structure of atomic planes along the c axis and the projection of the constituent structures onto the a-b plane, respectively.
Title:
High-pressure effects on Ti-Zr-Ni metallic glass and its corresponding quasicrystal
Authors:
Fang, YK; Jiang, JZ Author Full Names: Fang, Yuankan; Jiang, Jianzhong
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 358 (23):3212-3215; 10.1016/j.jnoncrysol.2012.09.022 DEC 1 2012
Abstract:
The room-temperature high-pressure effects on Ti38Zr38Ni24 metallic glass and its corresponding icosahedral quasicrystal have been investigated by in-situ angle-dispersive synchrotron radiation. It is demonstrated that the thermodynamic metastable metallic glass and icosahedral quasicrystal retain their structures up to 42.9 and 46.0 GPa. respectively. For the Ti38Zr38Ni24 quasicrystal, disorders are likely developed during compression. However, no special behaviors are detected in its amorphous counterpart although thermal analyses suggest that the metallic glass is possibly in microquasicrystalline nature. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Allowable irreducible representations of the point groups with five-fold rotational axes
Authors:
Rao, KRM; Simhachalam, B; Rao, PH Author Full Names: Rao, Rama Mohana K.; Simhachalam, B.; Rao, Hemagiri P.
Source:
PRAMANA-JOURNAL OF PHYSICS, 79 (6):1533-1541; 10.1007/s12043-012-0334-1 DEC 2012
Abstract:
Allowable irreducible representations of the point groups with five-fold rotations - that represent the symmetry of the quasicrystals in two and three dimensions - are derived by employing the little group technique in conjunction with the solvability property. The point groups D and are taken to illustrate the method.
Title:
High-Pressure Syntheses of Lanthanide Polysulfides and Polyselenides LnX1.9 (Ln = Gd-Tm, X = S, Se)
Authors:
Muller, CJ; Schwarz, U; Doert, T Author Full Names: Mueller, Carola J.; Schwarz, Ulrich; Doert, Thomas
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 638 (15):2477-2484; SI 10.1002/zaac.201200304 DEC 2012
Abstract:
The polysulfides LnS1.9 and polyselenides LnSe1.9 of the lanthanide metals from gadolinium to thulium were prepared by high-pressure high-temperature synthesis. The compounds adopt the tetragonal CeSe1.9 structure type in space group P42/n (No. 86) with lattice parameters of 8.531 angstrom = a = 8.654 angstrom and 15.563 angstrom = c = 15.763 angstrom for the sulfides and 8.869 angstrom = a = 9.076 angstrom and 16.367 angstrom = c = 16.611 angstrom for the selenides. The atomic pattern consists of puckered double slabs [LnX]+ and planar chalcogenide layers with ten possible chalcogen positions, of which eight are occupied by chalcogen atoms forming dinuclear X22 dianions, one by a single X2 ion and one remaining vacant. This resembles a v5x5?x?2 superstructure of the ZrSSi aristotype. Structural relationships to the aristotype and the related lanthanide polychalcogenides LnX2d (Ln = LaTm, X = STe, d = 0 0.3) are discussed. The samples synthesized under high-pressure conditions (p > 1 GPa) decompose slowly under release of sulfur or selenium at ambient conditions. The crystal structure of a partially degraded thulium-polysulfide sample can be described as an incommensurate variant of the original TmS1.9 motif. Additionally, the isostructural ternary compound Gd(S1xSex)1.9 was synthesized and characterized by powder X-ray diffraction.

Update: 16-Jan-2013

Title:
P2-NaxVO2 system as electrodes for batteries and electron-correlated materials
Authors:
Guignard, M; Didier, C; Darriet, J; Bordet, P; Elkaim, E; Delmas, C Author Full Names: Guignard, Marie; Didier, Christophe; Darriet, Jacques; Bordet, Pierre; Elkaim, Erik; Delmas, Claude
Source:
NATURE MATERIALS, 12 (1):74-80; 10.1038/NMAT3478 JAN 2013
Abstract:
Layered oxides are the subject of intense studies either for their properties as electrode materials for high-energy batteries or for their original physical properties due to the strong electronic correlations resulting from their unique structure. Here we present the detailed phase diagram of the layered P2-NaxVO2 system determined from electrochemical intercalation/deintercalation in sodium batteries and in situ X-ray diffraction experiments. It shows that four main single-phase domains exist within the 0.5 <= x <= 0.9 range. During the sodium deintercalation (intercalation), they differ from one another in the sodium/vacancy ordering between the VO2 slabs, which leads to commensurable or incommensurable superstructures. The electrochemical curve reveals that three peculiar compositions exhibit special structures for x = 1/2, 5/8 and 2/3. The detailed structural characterization of the P2-Na1/2VO2 phase shows that the Na+ ions are perfectly ordered to minimize Na+/Na+ electrostatic repulsions. Within the VO2 layers, the vanadium ions form pseudo-trimers with very short V-V distances (two at 2.581 angstrom and one at 2.687 angstrom). This original distribution leads to a peculiar magnetic behaviour with a low magnetic susceptibility and an unexpected low Curie constant. This phase also presents a first-order structural transition above room temperature accompanied by magnetic and electronic transitions. This work opens up a new research domain in the field of strongly electron-correlated materials. From the electrochemical point of view this system may be at the origin of an entire material family optimized by cationic substitutions.
Title:
Electrochemical hydrogen storage characteristics of TiVNi-quasicrystalline composite materials
Authors:
Liu, WQ; Zhang, SS; Hu, W; Wang, LM Author Full Names: Liu, Wanqiang; Zhang, Shanshan; Hu, Wen; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF NANOTECHNOLOGY, 10 (1-2):80-88; 10.1504/IJNT.2013.050884 2013
Abstract:
The Ti1.4V0.6Ni ribbon alloy and VTZN (V5Ti9Zr26.7Ni38Cr5Mn16Sn0.3) alloy ingot are prepared by melt- spinning technique and induction levitation melting technique, respectively. The Ti1.4V0.6Ni + 20 wt.% VTZN mixture powders are synthesised by ball-milling the above prepared alloy ingots, and their structures and the electrochemical hydrogen storage properties are investigated. It is found that the icosahedral quasicrystal, FCC and BCC structural solid solution phase are all presented in the composite material. The maximum electrochemical discharge capacity of the composite electrode is 308.2 mAh/g at the discharge current density of 30 mA/g and 303 K. In addition, the electrode made of Ti1.4V0.6Ni and AB(3) composite holds better high- rate discharge ability than that of Ti1.4V0.6Ni.
Title:
Equivalence of superspace groups
Authors:
van Smaalen, S; Campbell, BJ; Stokes, HT Author Full Names: van Smaalen, Sander; Campbell, Branton J.; Stokes, Harold T.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 69 75-90; 10.1107/S0108767312041657 Part 1 JAN 2013
Abstract:
An algorithm is presented which determines the equivalence of two settings of a (3 + d)-dimensional superspace group (d = 1, 2, 3). The algorithm has been implemented as a web tool findssg on SSG(3 + d)D, providing the transformation of any user-given superspace group to the standard setting of this superspace group in SSG(3 + d)D. It is shown how the standard setting of a superspace group can be directly obtained by an appropriate transformation of the external-space lattice vectors (the basic structure unit cell) and a transformation of the internal-space lattice vectors (new modulation wavevectors are linear combinations of old modulation wavevectors plus a three-dimensional reciprocal-lattice vector). The need for non-standard settings in some cases and the desirability of employing standard settings of superspace groups in other cases are illustrated by an analysis of the symmetries of a series of compounds, comparing published and standard settings and the transformations between them. A compilation is provided of standard settings of compounds with two-and three-dimensional modulations. The problem of settings of superspace groups is discussed for incommensurate composite crystals and for chiral superspace groups.
Title:
Spatially modulated antiferromagnetic structures in a multiferroic with biaxial anisotropy
Authors:
Popkov, AF; Solov'ev, SV; Kulagin, NE; Zvezdin, AK Author Full Names: Popkov, A. F.; Solov'ev, S. V.; Kulagin, N. E.; Zvezdin, A. K.
Source:
SEMICONDUCTORS, 46 (13):1568-1572; 10.1134/S1063782612130155 DEC 2012
Abstract:
Possible types of spatially modulated periodic antiferromagnetic structures in a uniaxial rhombohedral multiferroic with BiFeO3 crystal symmetry are studied depending on the ratio of the parameters of uniaxial and basal anisotropy and on magnetoelectric coupling. DOI: 10.1134/S1063782612130155
Title:
Room Temperature Modulated Structure of Ca and K co-Doped LaMnO3
Authors:
Hou, CM; Huang, KK; Hu, B; Yuan, HM; Feng, SH Author Full Names: Hou Chang-min; Huang Ke-ke; Hu Bin; Yuan Hong-ming; Feng Shou-hua
Source:
CHEMICAL RESEARCH IN CHINESE UNIVERSITIES, 28 (5):784-787; SEP 2012
Abstract:
A series of perovskite compounds of La1-x-yCaxKyMnO3 was prepared by hydrothermal disproportionation reaction of MnO2. The three oxidation states of manganese(Mn3+, Mn4+ and Mn5+) can stably exist in the compounds. Under room temperature conditions, twice and three times modulated structure produced by the charge ordering can be observed by X-ray diffraction (XRD), select area electron diffraction (SAED) and high resolution transmission electron microscopy (HR-TEM). The splits of the diffraction peaks of the single crystals confirmed by synchrotron X-ray diffraction experiment are in accordance with those of the powder sample. The existence of the different oxidation states of Mn3+, Mn4+ and Mn5+ can be considered to be the dominating reason of the complicated room temperature modulated structure.

Update: 9-Jan-2013

Title:
Rapidly solidified high-temperature aluminum alloys. I. Structure
Authors:
Krainikov, AV; Neikov, OD Author Full Names: Krainikov, A. V.; Neikov, O. D.
Source:
POWDER METALLURGY AND METAL CERAMICS, 51 (7-8):399-411; 10.1007/s11106-012-9448-8 NOV 2012
Abstract:
The paper examines the phase composition of a number of high-temperature aluminum alloys formed in rapid solidification. The main strengthening phases and associated phase transitions in Al-Fe-Ce, Al-Fe-Cr-(TM), Al-Cr-Zr(Mn), and Al-Fe-V(Mo)-Si alloys have been studied. The phase composition of the alloys is shown to be critically dependent on the cooling rate. High-temperature materials are particularly sensitive to the solidification rate since they are doped by nonsoluble elements. Fine quasicrystalline phases, which make a significant contribution to strengthening at low and high temperatures, are present in rapidly solidified materials doped with iron. Besides these phases, Al3TM intermetallics characterized by high thermal stability and low coarsening rate play an important role in modern materials.
Title:
Morphology Evolution of MZY Quasicrystal Particle in AZ91 Alloy Strengthened by MZY Quasicrystal Alloy
Authors:
Liu, T; Teng, XY; Liu, LY; Zhao, ZW Author Full Names: Liu Teng; Teng Xinying; Liu Liyan; Zhao Zhenwei
Source:
RARE METAL MATERIALS AND ENGINEERING, 41 28-31; 2 SEP 2012
Abstract:
The influence of holding time on the microstructures of MZY quasicrystal particle in AZ91 alloy strengthened by quasicrystals alloy was studied using SEM equipped with energy dispersive spectrometer (EDS). The results show that holding time could obviously influence the microstructures of MZY quasicrystal particle in AZ91 alloy strengthened by quasicrystals alloy. When holding time is within 2 min, the five petals-like quasicrystals could be left well in AZ91 matrix alloy; for the holding time of 4 min, the smooth petal's top of Mg3Zn6Y quasicrystal particle becomes sharp and its petals change for polygons; as holding time of 6 similar to 8 min, the petals of Mg3Zn6Y quasicrystals particle begin to desquamate, the phenomena of groomed fracture would appear in a single petals; for the holding time of 10 min and more, the petals of Mg3Zn6Y quasicrystal particle are not obvious and the petals with stamen form the oval quasicrystal particles.

Update: 2-Jan-2013

Title:
Temperature-dependent IR and Raman scattering studies of phase transitions in K2MgWO2 (PO4)(2)
Authors:
Maczka, M; Majchrowski, A; Hanuza, J; Kojima, S Author Full Names: Maczka, M.; Majchrowski, A.; Hanuza, J.; Kojima, S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 25 (2):10.1088/0953-8984/25/2/025901 JAN 16 2013
Abstract:
Temperature-dependent Raman scattering and IR experiments were performed on K2MgWO2(PO4)(2), which is derived from KTP by the replacement of two Ti4+ ions with Mg2+ and W6+ cations. These studies revealed significant changes in phonon properties of these materials with increasing temperature due to the onset of phase transitions at 436, 537 and 637 K. Analysis of the obtained data showed that disordering processes in the sublattice of potassium ions play a significant role in the mechanism of these phase transitions. However, these transitions are also accompanied by weak tilts of the nearly rigid PO4, WO6 and MgO6 groups. Present results also provide strong arguments that the phase transition at 637 K can be classified as occurring from the normal high-temperature phase with D-4 point symmetry into a modulated or incommensurate phase with the same D-4 point symmetry. Our results also show that the order disorder (displacive) contribution to the phase transition mechanism is significantly stronger (weaker) in K2MgWO2(PO4)(2) when compared to KTP.
Title:
Light wave states in quasiperiodic metallic structures
Authors:
Wang, K Author Full Names: Wang, Kang
Source:
PHYSICAL REVIEW B, 86 (23):10.1103/PhysRevB.86.235110 DEC 10 2012
Abstract:
We investigate the light wave states in the octagonal and decagonal quasiperiodic metallic structures by considering their respective approximants at different orders. The mechanisms underlying the light wave behaviors are studied in relation to various structure parameters and configurations. We show that the formation of the first passbands, that delimit the photonic band gaps and determine the plasma gaps, involves only the lowest frequency resonance modes inside the fat tiles, and that light localization occurs due to resonances in high symmetry local centers as well as in the fragments of such centers, formed by the skinny tiles. The structure filling rate affects the localized state frequencies relative to the first passbands, as well as the plasma frequency levels, by modulating the frequency levels of the resonance modes and the widths of the passbands. The results of this study can be generalized to other metallic quasiperiodic and related structures.
Title:
Neutron scattering study of ferroelectric Sn2P2S6 under pressure
Authors:
Ondrejkovic, P; Kempa, M; Vysochanskii, Y; Saint-Gregoire, P; Bourges, P; Rushchanskii, KZ; Hlinka, J Author Full Names: Ondrejkovic, P.; Kempa, M.; Vysochanskii, Y.; Saint-Gregoire, P.; Bourges, P.; Rushchanskii, K. Z.; Hlinka, J.
Source:
PHYSICAL REVIEW B, 86 (22):10.1103/PhysRevB.86.224106 DEC 7 2012
Abstract:
Ferroelectric phase transition in the semiconductor Sn2P2S6 single crystal has been studied by means of neutron scattering in the pressure-temperature range adjacent to the anticipated tricritical Lifshitz point (p approximate to 0.18 GPa, T approximate to 296 K). The observations reveal a direct ferroelectric-paraelectric phase transition in the whole investigated pressure range (0.18-0.6 GPa). These results are in a clear disagreement with phase diagrams assumed in numerous earlier works, according to which a hypothetical intermediate incommensurate phase extends over several or even tens of degrees in the 0.5 GPa pressure range. Temperature dependence of the anisotropic quasielastic diffuse scattering suggests that polarization fluctuations present above T-C are strongly reduced in the ordered phase. Still, the temperature dependence of the ((2) over bar 00) Bragg reflection intensity at p = 0.18 GPa can be remarkably well modeled assuming the order-parameter amplitude growth according to the power law with logarithmic corrections predicted for a uniaxial ferroelectric transition at the tricritical Lifshitz point.
Title:
Unusual Urbach tail in TlGaSe2 ferroelectric-semiconductor with incommensurate phase
Authors:
Seyidov, MY; Suleymanov, RA; Sale, Y Author Full Names: Seyidov, MirHasan Yu; Suleymanov, Rauf A.; Sale, Yasin
Source:
JOURNAL OF APPLIED PHYSICS, 112 (10):10.1063/1.4765736 NOV 15 2012
Abstract:
An analysis of temperature behavior of optical absorption edge is performed for TlGaSe2 ferroelectric-semiconductor with incommensurate phase. Unusual behavior of the Urbach tail manifested by the shift of the absorption edge toward the higher energies with increasing temperature was observed. It was shown that such behavior is due to the specific temperature interval where Urbach energy decreases with the temperature. This interval corresponds to the incommensurate phase-commensurate phase transition region. Unusual behavior of the Urbach energy can be explained interpreting the incommensurate phase as some type of disordered state, and TlGaSe2 crystal as a disordered semiconductor with controllable disorder. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4765736]
Title:
Formation of Al67Cu23Fe10 quasicrystals by microwave heating
Authors:
Mihoc, C; Schick, D; Lutgens, M; Lathe, C; Burkel, E Author Full Names: Mihoc, Carmen; Schick, Daniel; Luetgens, Matthias; Lathe, Christian; Burkel, Eberhard
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, 103 (11):1340-1344; 10.3139/146.110786 NOV 2012
Abstract:
The present work was carried out to compare the formation of single icosahedral phase during conventional heating and microwave processing. Al67Cu23Fe10 alloy powder was synthesized from high purity (99.9%) powder elements by mechanical alloying. Differential scanning calorimetry combined with in-situ synchrotron energy dispersive X-ray diffraction was used to identify the main solid state reactions and the phase evolution of the powders. Inductive microwave processing in the magnetic field anti-node was performed to obtain the quasicrystalline phase in only a few seconds. Due to the rapid cooling of the sample it was possible to stabilize the icosahedral phase against its competing quasicrystalline approximants. Laboratory X-ray diffraction analysis was used to characterise the atomic structure of the specimen and scanning electron microscopy was used to characterise the microstructure after the microwave processing.

Update: 27-Dec-2012

Title:
Vanishing of the metal-insulator Peierls transition in pressurized BaVS3
Authors:
Bernu, S; Fertey, P; Itie, JP; Berger, H; Foury-Leylekian, P; Pouget, JP Author Full Names: Bernu, S.; Fertey, P.; Itie, J. -P.; Berger, H.; Foury-Leylekian, P.; Pouget, J. -P.
Source:
PHYSICAL REVIEW B, 86 (23):10.1103/PhysRevB.86.235105 DEC 5 2012
Abstract:
BaVS3 presents a metal-to-insulator (MI) transition at ambient pressure due to the stabilization of a 2k(F) commensurate charge density wave (CDW) Peierls ground state built on the dz(2) V orbitals. The MI transition vanishes under pressure at a quantum critical point (QCP) where the electronic properties exhibit a non-Fermi liquid behavior. In this paper, we determine the CDW phase diagram under pressure and show that it combines both the vanishing of the second-order Peierls transition and a commensurate-incommensurate first-order delocking transition of the 2k(F) wave vector. We explain quantitatively the drop of the MI critical temperature by the decrease of the electron-hole pair lifetime of the CDW condensate due to an enhancement of the hybridization between the dz(2) and e(t(2g)) levels of the V under pressure.
Title:
Interfacial energies on quasicrystals
Authors:
Braides, A; Causin, A; Solci, M Author Full Names: Braides, Andrea; Causin, Andrea; Solci, Margherita
Source:
IMA JOURNAL OF APPLIED MATHEMATICS, 77 (6):816-836; SI 10.1093/imamat/hxs046 DEC 2012
Abstract:
We consider nearest-neighbour ferromagnetic energies defined on a quasicrystal modeled following the so-called cut-and-project approach as a portion of a regular lattice contained in a possibly irrational stripe defined as a neighborhood of a k-dimensional subspace in an n-dimensional space. The overall properties of this system are described by an effective surface energy on a k-dimensional space obtained as Gamma-limit of the scaled discrete energies.
Title:
Confirmation of the Random Tiling Hypothesis for a Decagonal Quasicrystal
Authors:
Kiselev, A; Engel, M; Trebin, HR Author Full Names: Kiselev, Alexander; Engel, Michael; Trebin, Hans-Rainer
Source:
PHYSICAL REVIEW LETTERS, 109 (22):10.1103/PhysRevLett.109.225502 NOV 29 2012
Abstract:
Mechanisms that stabilize quasicrystals are much discussed but not finally resolved. We confirm the random tiling hypothesis and its predictions in a fully atomistic decagonal quasicrystal model by calculating the free energy and the phason elastic constants over a wide range of temperatures. The Frenkel-Ladd method is applied for the phonon part, and an approach of uncorrelated phason flips is applied for the configurational part. When lowering the temperature, a phase transition to an approximant occurs. Close to the transition temperature, one of the phason elastic constants becomes soft.
Title:
Molecular dynamics simulation of reversibly self-assembling shells in solution using trapezoidal particles
Authors:
Rapaport, DC Author Full Names: Rapaport, D. C.
Source:
PHYSICAL REVIEW E, 86 (5):10.1103/PhysRevE.86.051917 Part 1 NOV 29 2012
Abstract:
The self-assembly of polyhedral shells, each constructed from 60 trapezoidal particles, is simulated using molecular dynamics. The spatial organization of the component particles in this shell is similar to the capsomer proteins forming the capsid of a T = 1 virus. Growth occurs in the presence of an atomistic solvent and, under suitable conditions, achieves a high yield of complete shells. The simulations provide details of the structure and lifetime of the particle clusters that appear as intermediate states along the growth pathway, and the nature of the transitions between them. In certain respects the growth of size-60 shells from trapezoidal particles resembles the growth of icosahedral shells from triangular particles studied previously, with reversible bonding playing a major role in avoiding incorrect assembly, although the details differ due to particle shape and bond organization. The strong preference for maximal bonding exhibited by the triangular pa! rticle clusters is also apparent for trapezoidal particles, but this is now confined to early growth and is less pronounced as shells approach completion along a variety of pathways.
Title:
Vortex dynamics in ferromagnetic superconductors: Vortex clusters, domain walls, and enhanced viscosity
Authors:
Lin, SZ; Bulaevskii, LN; Batista, CD Author Full Names: Lin, Shi-Zeng; Bulaevskii, Lev N.; Batista, Cristian D.
Source:
PHYSICAL REVIEW B, 86 (18):10.1103/PhysRevB.86.180506 NOV 28 2012
Abstract:
We demonstrate that there is a long-range vortex-vortex attraction in ferromagnetic superconductors due to polarization of the magnetic moments. Vortex clusters are then stabilized in the ground state for low vortex densities. The motion of vortex clusters driven by the Lorentz force excites magnons. This regime becomes unstable at a threshold velocity above which domain walls are generated for slow relaxation of the magnetic moments and the vortex configuration becomes modulated. This dynamics of vortices and magnetic moments can be probed by transport measurements.
Title:
Self-Similar Micron-Size and Nanosize Drops of Liquid Generated by Surface Acoustic Waves
Authors:
Taller, D; Go, DB; Chang, HC Author Full Names: Taller, Daniel; Go, David B.; Chang, Hsueh-Chia
Source:
PHYSICAL REVIEW LETTERS, 109 (22):10.1103/PhysRevLett.109.224301 NOV 27 2012
Abstract:
A planar surface acoustic wave on a solid substrate and its radiated sound into a static liquid drop produce time-averaged, exponentially decaying acoustic and electric Maxwell pressures near the contact line. These localized contact-line pressures are shown to generate two sequences of hemispherical satellite droplets at the tens of microns and submicron scales, both obeying self-similar exponential scaling but with distinct exponents that correspond to viscous dissipation and field leakage length scales, respectively. The acoustic pressure becomes dominant when the film thickness exceeds (1/4 pi) of the surface acoustic wave wavelength and it affects the shape and stability of the mother drop. The Maxwell pressure of the nanodrops, which exceeds ten atmospheres, is sensitive to the contact angle.
Title:
Persistent Spin Dynamics Intrinsic to Amplitude-Modulated Long-Range Magnetic Order
Authors:
Pregelj, M; Zorko, A; Zaharko, O; Arcon, D; Komelj, M; Hillier, AD; Berger, H Author Full Names: Pregelj, M.; Zorko, A.; Zaharko, O.; Arcon, D.; Komelj, M.; Hillier, A. D.; Berger, H.
Source:
PHYSICAL REVIEW LETTERS, 109 (22):10.1103/PhysRevLett.109.227202 NOV 27 2012
Abstract:
An incommensurate elliptical helical magnetic structure in the frustrated coupled-spin-chain system FeTe2O5Br is surprisingly found to persist down to 53(3) mK (T/T-N similar to 1/200), according to neutron scattering and muon spin relaxation. In this state, finite spin fluctuations at T -> 0 are evidenced by muon depolarization, which is in agreement with specific-heat data indicating the presence of both gapless and gapped excitations. We thus show that the amplitude-modulated magnetic order intrinsically accommodates contradictory persistent spin dynamics and long-range order and can serve as a model structure to investigate their coexistence.
Title:
Effects of icosahedral phase formation on the microstructure and mechanical improvement of Mg alloys: A review
Authors:
Xu, DK; Han, EH Author Full Names: Xu, D. K.; Han, E. H.
Source:
PROGRESS IN NATURAL SCIENCE-MATERIALS INTERNATIONAL, 22 (5):364-385; 10.1016/j.pnsc.2012.09.005 OCT 2012
Abstract:
Icosahedral phase (I-phase) is a relatively excellent strengthening phase in Mg alloys. Depending on their volume fraction, the yield strength of Mg-Zn-Y-Zr alloys can vary from 150 to 450 MPa at room temperature. Recently, the formation of I-phase has been considered as one of the most effective methods for developing high strength lightweight Mg alloys for automotive and aerospace applications. In this review article, a series of research work about I-phase containing Mg alloys have been systematically investigated including I-phase formation mechanism and their effects on mechanical properties of Mg alloys. Particular emphases have been given to: (1) Structure of I-phase and its orientation relationship with the alpha-Mg matrix. (2) Influence of alloying elements and solidification conditions on I-phase formation. (3) Effects of I-phase on microstructural evolution and mechanical improvement of Mg-Zn-Y-(Zr) alloys. Moreover, the applications of I-phase for the mechanical improvement of other Mg alloys such as AZ91 and super-lightweight Mg-Li alloys are also reviewed. (c) 2012 Chinese Materials Research Society. Production and hosting by Elsevier Ltd. All rights reserved.
Title:
CHARACTERIZATION OF AS-SPUN AND ANNEALED Al-Mn-Fe RIBBONS
Authors:
Stan, K; Litynska-Dobrzynska, L; Goral, A; Wierzbicka-Miernik, A Author Full Names: Stan, K.; Litynska-Dobrzynska, L.; Goral, A.; Wierzbicka-Miernik, A.
Source:
ARCHIVES OF METALLURGY AND MATERIALS, 57 (3):651-656; 10.2478/v10172-012-0069-5 2012
Abstract:
Microstructure of conventionally cast and melt spun Al91Mn7Fe2 alloy was examined by X-ray diffraction, SEM and TEM techniques. Three different phases were found in a mould cast ingot: Al-6(Mn, Fe), Al-4(Mn, Fe) and aluminium solid solution. Rapidly quenched ribbons cast using melt spinning technique with different speed values of rotating wheel: 25, 30 and 36 m/s had average width in a range of 30-50 mu m. It was found that ribbons contain quasicrystalline particles with different sizes and shapes including large dendrites in a range of micrometers and smaller spherical particles below 1 mu m embedded in an aluminium matrix. Composition of these particles was similar to the Al-4(Mn, Fe) phase. Also quasicrystals in the form of eutectic were observed with slightly different composition close to the Al-6(Mn, Fe) phase. All observed particles revealed 2, 3 and 5- fold symmetry, typical for icosahedral quasicrystals. Increase in microhardness up to 274 HV for melt spun ribbon comparing to 141 HV for the as-cast ingot was observed due to a change in phase composition and refinement of the phases. Thermal stability of quasicrystalline phase in the ribbon was examined by annealing in different temperatures. Temperatures for thermal treatment were chosen based on DSC curve which contains the exothermic peak in the temperature range 300-500 degrees C. Analysis of ribbons annealed for 30 minutes at 400 degrees C showed that transformation of quasicrystals to stable crystalline phase starts at quasicrystal/Al-matrix interfaces. After annealing for 4 hours at 500 degrees C only the Al-6(Mn, Fe) phase and aluminium solid solution were observed in the ribbon microstructure.

Update: 20-Dec-2012

Title:
Compositional uniformity, domain patterning and the mechanism underlying nano-chessboard arrays
Authors:
Gonzalez, S; Perez-Mato, JM; Elcoro, L; Garcia, A; Withers, RL; Bourgeois, L Author Full Names: Gonzalez, Santiago; Perez-Mato, J. M.; Elcoro, Luis; Garcia, Alberto; Withers, Ray L.; Bourgeois, Laure
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (49):10.1088/0953-8984/24/49/495301 DEC 12 2012
Abstract:
We propose that systems exhibiting compositional patterning at the nanoscale, so far assumed to be due to some kind of ordered phase segregation, can be understood instead in terms of coherent, single phase ordering of minority motifs, caused by some constrained drive for uniformity. The essential features of this type of arrangement can be reproduced using a superspace construction typical of uniformity-driven orderings, which only requires the knowledge of the modulation vectors observed in the diffraction patterns. The idea is discussed in terms of a simple two-dimensional lattice-gas model that simulates a binary system in which the dilution of the minority component is favoured. This simple model already exhibits a hierarchy of arrangements similar to the experimentally observed nano-chessboard and nano-diamond patterns, which are described as occupational modulated structures with two independent modulation wavevectors and simple step-like occupation modulation functions.
Title:
HAADF-STEM study of chemical ordering in Al-Pd-Sc 1/1-crystal approximant
Authors:
So, YG; Nagao, M; Nagai, T; Kimoto, K Author Full Names: So, Yeong-Gi; Nagao, Masahiro; Nagai, Takuro; Kimoto, Koji
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 543 7-11; 10.1016/j.jallcom.2012.07.119 DEC 5 2012
Abstract:
The atomic structure of the Al54Pd31Sc15 1/1-crystal approximant to the icosahedral quasicrystal has been studied using high-angle annular dark-field (HAADF) imaging in a scanning transmission electron microscopy (STEM). HAADF imaging directly reveals that the 1/1-phase has a periodic arrangement of Tsai-type atomic clusters, which consist of three successive shells with icosahedral symmetry as well as a disordered tetrahedron at the cluster center. In the 1/1-phase, the chemical ordering of Al and Pd is observed in the glue sites between the clusters, similar to that of Al and Au in the recently discovered Al35Au51Yb14 1/1-phase, indicating a common structural feature of ternary Tsai-type approximants. Moreover, the preferential introduction of structural disorder into the second dodecahedral shell is observed in the HAADF images, which causes symmetry breaking of the 1/1-phase. On the basis of a comparison with the experimental and simulated images, a preliminary model for the atomic structure of the 1/1-phase is presented. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Comparative structural study of decagonal quasicrystals in the systems Al-Cu-Me (Me = Co, Rh, Ir)
Authors:
Kuczera, P; Wolny, J; Steurer, W Author Full Names: Kuczera, Pawel; Wolny, Janusz; Steurer, Walter
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 68 578-589; 10.1107/S0108768112041134 Part 6 DEC 2012
Abstract:
A comparative single-crystal X-ray diffraction structure analysis of the family of Al-Cu-Me (Me = Co, Rh and Ir) decagonal quasicrystals is presented. In contrast to decagonal Al-Cu-Co, the other two decagonal phases do not show any structured disorder diffuse scattering indicating a higher degree of order. Furthermore, the atomic sites of Rh and Ir can be clearly identified, while Cu and Co cannot be distinguished because of their too similar atomic scattering factors. The structure models, derived from charge-flipping/low-density elimination results, were refined within the tiling-decoration method but also discussed in the five-dimensional embedding approach. The basic structural building units of the closely related structures are decagonal clusters with 33 angstrom diameter, which are consistent with the available electron-microscopic images. The refined structure models agree very well with the experimental data.
Title:
Varied linear phason strain and its induced domain structure in quasicrystalline precipitates of Zr-Al-Ni-Cu-Nb bulk metallic glass matrix composites
Authors:
Lu, L; Xiong, DX; Wang, JB; Zhao, DS; Sun, YF Author Full Names: Lu, Lu; Xiong, Dongxia; Wang, Jianbo; Zhao, Dongshan; Sun, Yufeng
Source:
JOURNAL OF MATERIALS RESEARCH, 27 (23):3041-3048; 10.1557/jmr.2012.351 DEC 2012
Abstract:
Quasicrystalline precipitates in ZrAlNiCuNb alloy were systematically studied by transmission electron microscopy. It was found that precipitates always contain various linear phason strains. By electron diffraction analysis, two types of linear phason strain with two different directions perpendicular to the incident beam described by strain matrices with only one nonzero element were identified. After measuring the deviations of diffraction spots and quantitatively fitting against their perpendicular components of the reciprocal lattice vectors, the phason strain matrices were obtained. Domain structures formed as a result of linear phason strain variants along directions with equal probability. Electron diffraction and high-resolution electron imaging provide supportive evidence of this result.
Title:
Quantum critical state in a magnetic quasicrystal
Authors:
Deguchi, K; Matsukawa, S; Sato, NK; Hattori, T; Ishida, K; Takakura, H; Ishimasa, T Author Full Names: Deguchi, Kazuhiko; Matsukawa, Shuya; Sato, Noriaki K.; Hattori, Taisuke; Ishida, Kenji; Takakura, Hiroyuki; Ishimasa, Tsutomu
Source:
NATURE MATERIALS, 11 (12):1013-1016; 10.1038/NMAT3432 DEC 2012
Abstract:
Quasicrystals are metallic alloys that possess long-range, aperiodic structures with diffraction symmetries forbidden to conventional crystals. Since the discovery of quasicrystals by Schechtman et al. in 1984(1), there has been considerable progress in resolving their geometric structure. For example, it is well known that the golden ratio of mathematics and art occurs over and over again in their crystal structure. However, the characteristic properties of the electronic states-whether they are extended as in periodic crystals or localized as in amorphous materials-are still unresolved. Here we report the first observation of quantum (T = 0) critical phenomena of the Au-Al-Yb quasicrystal-the magnetic susceptibility and the electronic specific heat coefficient arising from strongly correlated 4f electrons of the Yb atoms diverge as T -> 0. Furthermore, we observe that this quantum critical phenomenon is robust against hydrostatic pressure. By contrast, there is no such divergence in a crystalline approximant, a phase whose composition is close to that of the quasicrystal and whose unit cell has atomic decorations (that is, icosahedral clusters of atoms) that look like the quasicrystal. These results clearly indicate that the quantum criticality is associated with the unique electronic state of the quasicrystal, that is, a spatially confined critical state. Finally we discuss the possibility that there is a general law underlying the conventional crystals and the quasicrystals.
Title:
Structural transformation of Sb-based high-speed phase-change material
Authors:
Matsunaga, T; Kojima, R; Yamada, N; Kubota, Y; Kifune, K Author Full Names: Matsunaga, Toshiyuki; Kojima, Rie; Yamada, Noboru; Kubota, Yoshiki; Kifune, Kouichi
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 68 559-570; 10.1107/S0108768112039961 Part 6 DEC 2012
Abstract:
The crystal structure of a phase-change recording material (the compound Ag3.4In3.7Sb76.4Te16.5) enclosed in a vacuum capillary tube was investigated at various temperatures in a heating process using a large Debye-Scherrer camera installed in BL02B2 at SPring-8. The amorphous phase of this material turns into a crystalline phase at around 416 K; this crystalline phase has an A7-type structure with atoms of Ag, In, Sb or Te randomly occupying the 6c site in the space group. This structure was maintained up to around 545 K as a single phase, although thermal expansion of the crystal lattice was observed. However, above this temperature, phase separation into AgInTe2 and Sb-Te transpired. The first fragment, AgInTe2, reliably maintained its crystal structure up to the melting temperature. On the other hand, the atomic configuration of the Sb-Te gradually varied with increasing temperature. This gradual structural transformation can be described as a continuous growth of the modulation period gamma.
Title:
Bulk Electronic Structure of Quasicrystals
Authors:
Nayak, J; Maniraj, M; Rai, A; Singh, S; Rajput, P; Gloskovskii, A; Zegenhagen, J; Schlagel, DL; Lograsso, TA; Horn, K; Barman, SR Author Full Names: Nayak, J.; Maniraj, M.; Rai, Abhishek; Singh, Sanjay; Rajput, Parasmani; Gloskovskii, A.; Zegenhagen, J.; Schlagel, D. L.; Lograsso, T. A.; Horn, K.; Barman, S. R.
Source:
PHYSICAL REVIEW LETTERS, 109 (21):10.1103/PhysRevLett.109.216403 NOV 20 2012
Abstract:
We use hard x-ray photoemission to resolve a controversial issue regarding the mechanism for the formation of quasicrystalline solids, i.e., the existence of a pseudogap at the Fermi level. Our data from icosahedral fivefold Al-Pd-Mn and Al-Cu-Fe quasicrystals demonstrate the presence of a pseudogap, which is not observed in surface sensitive low energy photoemission because the spectrum is affected by a metallic phase near the surface. In contrast to Al-Pd-Mn, we find that in Al-Cu-Fe the pseudogap is fully formed; i.e., the density of states reaches zero at E-F indicating that it is close to the metal-insulator phase boundary.
Title:
Magnetic phase transitions in PrMn2O5: Importance of ion-size threshold size effects in RMn2O5 compounds (R = rare earth)
Authors:
Doubrovsky, C; Andre, G; Gukasov, A; Auban-Senzier, P; Pasquier, CR; Elkaim, E; Li, M; Greenblatt, M; Damay, F; Foury-Leylekian, P Author Full Names: Doubrovsky, C.; Andre, G.; Gukasov, A.; Auban-Senzier, P.; Pasquier, C. R.; Elkaim, E.; Li, M.; Greenblatt, M.; Damay, F.; Foury-Leylekian, P.
Source:
PHYSICAL REVIEW B, 86 (17):10.1103/PhysRevB.86.174417 NOV 19 2012
Abstract:
A detailed investigation of the thermodynamic, structural, and magnetic properties of high quality polycrystalline PrMn2O5 samples are presented. In contrast with members of the RMn2O5 family with smaller rare-earth ions, PrMn2O5 is not ferroelectric and does not undergo a transition to an incommensurate (q(x), 0, q(z)) magnetic phase: It exhibits two magnetic transitions, corresponding to commensurate magnetic orderings at T-1 = 25 +/- 1 K and T-2 = 18 +/- 1 K. These two magnetic transitions are characterized by two orthogonal propagation vectors q(1) = (1/2,0,0) and q(2) = (0,0,1/2), respectively, which coexist below (T)2. The refinement of the neutron data show that Mn3+ order primarily at T-1, following q(1); below T-2, the Mn4+ sublattice orders following q(2).
Title:
Effects of hydrogen on the magnetic properties of TiZrNi quasicrystals
Authors:
Shin, H; Lee, SH; Jo, Y; Kim, J Author Full Names: Shin, Hongsik; Lee, Sang-hwa; Jo, Youngsoo; Kim, Jaeyong
Source:
JOURNAL OF THE KOREAN PHYSICAL SOCIETY, 61 (9):1541-1544; 10.3938/jkps.61.1541 NOV 2012
Abstract:
The magnetic properties of hydrogenated metastable TiZrNi quasicrystals and their structures were studied. After hydrogenation, the quasi-lattice constants uniformly increased from 5.12 to 5.40 with a narrower peak width in X-ray diffraction, suggesting that hydrogen atoms diffuse homogeneously in different pieces of the metallic ribbon samples. The magnetization values measured by using a superconducting quantum interference device (SQUID) revealed that the magnetic susceptibilities of the hydrogenated quasicrystals strongly depended on the temperature so that the enhanced magnetic coercivities at low temperatures (< 9 K) were the result of a combination of hydrogen and temperature while the reduced magnetization values at temperatures above 9 K were attributed to the structural factor rather than the temperature. In fact, hydrogen contributes to the significant decrease in the magnetization values from 0.0236 to 0.0163 emu/g at room temperature. The reasons for the decreased magnetization after hydrogenation are understood to be the reduced interactions of magnetic moments between Ni atoms induced by the lattice expansion after hydrogen absorption.

Update: 12-Dec-2012

Title:
Transformation and slip behavior of Ni2FeGa
Authors:
Sehitoglu, H; Wang, J; Maier, HJ Author Full Names: Sehitoglu, H.; Wang, J.; Maier, H. J.
Source:
INTERNATIONAL JOURNAL OF PLASTICITY, 39 61-74; 10.1016/j.ijplas.2012.05.011 DEC 2012
Abstract:
Ni2FeGa is a relatively new shape memory alloy (SMA) and exhibits superior characteristics compared to other SMAs. Its favorable properties include low transformation stress, high reversible strains and small hysteresis. The first stage of stress-induced martensitic transformation is from a cubic to a modulated monoclinic phase. The energy barriers associated with the transformation from L2(1) (cubic) to modulated martensite (10M-martensite) incorporating shear and shuffle are established via atomistic simulations. In addition, the slip resistance in the [111] direction and the dissociation of full dislocations into partials as well as slip in the [001] direction are studied. The unstable stacking fault energy barriers for slip by far exceeded the transformation transition state barrier permitting transformation to occur with little irreversibility. Experiments at the mesa-scale on single crystals and transmission electron microscopy were conducted to provide further proof of the pseudoelastic (reversible) behavior and the presence of anti-phase boundaries. The results have implications for design of new shape memory alloys that possess low energy barriers for transformation coupled with high barriers for dislocation slip. (c) 2012 Elsevier Ltd. All rights reserved.
Title:
Variational Iteration Method for the Time-Fractional Elastodynamics of 3D Quasicrystals
Authors:
Yaslan, HC Author Full Names: Yaslan, H. Cerdik
Source:
CMES-COMPUTER MODELING IN ENGINEERING & SCIENCES, 86 (1):29-38; JUL 2012
Abstract:
This paper presents the approximate analytical solutions to the time fractional differential equations of elasticity for 3D quasicrystals with initial conditions. These equations are written in the form of a vector partial differential equation of the second order. The time fractional vector partial differential equations with initial conditions are solved by variational iteration method (VIM). The fractional derivatives are described in the Caputo sense. Numerical example shows that the proposed method is quite effective and convenient for solving kinds of time fractional system of partial differential equations.

Update: 6-Dec-2012

Title:
Complex magnetic order in Pr2Pd3Ge5: a single crystal study
Authors:
Anand, VK; Thamizhavel, A; Ramakrishnan, S; Hossain, Z Author Full Names: Anand, V. K.; Thamizhavel, A.; Ramakrishnan, S.; Hossain, Z.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (45):10.1088/0953-8984/24/45/456003 NOV 14 2012
Abstract:
We have investigated the magnetic and electronic transport properties of single crystal Pr2Pd3Ge5 grown by the Czochralski method. Complex magnetic behaviour (multiple magnetic transitions) is clearly seen in this compound from the magnetic susceptibility chi(T), isothermal magnetization M(H)and electrical resistivity rho(T) data. For the magnetic field applied along the crystallographic c-axis (H parallel to [001]) the chi(T) data exhibit two sharp transitions at 6.9 and 6.3 K and a broad hump near 8 K. Four anomalies at 8.0, 7.3, 6.2 and 4.9 K are observed for the magnetic field along both a- and b-directions (H parallel to [100] and H parallel to [010]). Further, the ordered state chi(T) presents a large anisotropy with an easy axis along the c-axis. The presence of magnetocrystalline anisotropy is also inferred from the isothermal M(H) data. The M(H) data measured at 1.9 K for H parallel to [001] exhibit a step-like increase due to field-induced metamagnetic transitions at H-c1(c) = 2.0 T and H-c2(c) = 4.0 T. For H parallel to [100] and H parallel to [010] sharp step-like field-induced metamagnetic transitions occur at H-c1(a) = H-c1(b) = 1.6 T and H-c2(a) = H-c2(b) = 1.8 T which are accompanied by a weak S-shaped spin-flop metamagnetic transition at H-c3(a) = H-c3(b) similar to 4 T. We have extracted the H-T phase diagram from the M(H) data collected at different temperatures in the magnetically ordered state which shows the existence of three magnetic phases below T-N for H parallel to [100] and H parallel to [010], and two magnetic phases for H parallel to [001]. A sharp transition due to the onset of long range antiferromagnetic order is also seen in the rho(T) data which also exhibit anisotropic behaviour. The observation of an upturn near T-N in the rho(T) data suggests the formation of a super-zone gap and hence the existence of incommensurate magnetic structure. Further, in the ordered state, the rho(T) data present a gap in the excitation spectrum of magnons with a characteristic energy gap Delta similar to 0.23 meV.
Title:
The atomic structure of the threefold surface of the icosahedral Ag-In-Yb quasicrystal
Authors:
Cui, C; Nugent, PJ; Shimoda, M; Ledieu, J; Fournee, V; Tsai, AP; McGrath, R; Sharma, HR Author Full Names: Cui, C.; Nugent, P. J.; Shimoda, M.; Ledieu, J.; Fournee, V.; Tsai, A. P.; McGrath, R.; Sharma, H. R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (44):10.1088/0953-8984/24/44/445011 NOV 7 2012
Abstract:
We report a study of the atomic structure of the threefold icosahedral (i-)Ag-In-Yb quasicrystal surface using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The LEED confirms that the surface exhibits quasicrystalline long-range order with the threefold symmetry expected from the bulk. The STM reveals large atomically flat terraces separated by steps of different heights. A comparison of atomically resolved STM images for the terraces and the step-height distribution with the bulk structure of isostructural i-Cd-Yb shows that the terraces are formed at bulk planes intersecting the centers of the rhombic triacontahedral clusters that make up the bulk structure of the system. However, the stability of particular terraces may be influenced by the density of atoms in the interstices (glue atoms that bind the clusters) in the terraces and also by the chemical environment in the underlying atomic plane. The surface exhibits screw dislocations, which is explained in terms of a continuous atomic density along the threefold axis.
Title:
Modeling the strengthening effect of Al-Cu-Fe quasicrystalline particles in Al-based metal matrix composites
Authors:
Ali, F; Scudino, S; Liu, G; Srivastava, VC; Mukhopadhyay, NK; Khoshkhoo, MS; Prashanth, KG; Uhlenwinkel, V; Calin, M; Eckert, J Author Full Names: Ali, F.; Scudino, S.; Liu, G.; Srivastava, V. C.; Mukhopadhyay, N. K.; Khoshkhoo, M. Samadi; Prashanth, K. G.; Uhlenwinkel, V.; Calin, M.; Eckert, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 536 S130-S133; 1 10.1016/j.jallcom.2011.12.022 SEP 25 2012
Abstract:
In this work, a model that simultaneously considers the combined strengthening contributions of load bearing, dislocation strengthening and matrix ligament size effects, which has been found to accurately describe the mechanical behavior of Al-based composites reinforced with complex intermetallic particles (Scudino et al. (2009) [8]), has been used to predict the mechanical properties of Al-based metal matrix composites containing different amounts of Al62.5Cu25Fe12.5 quasicrystalline reinforcing particles. The present results further demonstrate the validity of this model and confirm the importance of the characteristic matrix ligament size for explaining the strengthening effect of the composites containing large volume fractions of reinforcement. (c) 2011 Elsevier B.V. All rights reserved.

Update: 29-Nov-2012

Title:
Thermally induced structural changes in incommensurate calcium barium niobate Ca0.28Ba0.72Nb2O6 (CBN28)
Authors:
Graetsch, HA; Schreuer, J; Burianek, M; Muhlberg, M Author Full Names: Graetsch, H. A.; Schreuer, J.; Burianek, M.; Muehlberg, M.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 196 255-266; 10.1016/j.jssc.2012.06.028 DEC 2012
Abstract:
The incommensurately modulated crystal structure of relaxor ferroelectric CBN28 was refined at elevated temperatures up to 330 degrees C in the 3+2 dimensional superspace group P4bm(alpha alpha 1/2, -alpha alpha 1/2). The structural modulations mainly consisting of cooperative tilting of NbO6 octahedra and an occupational modulation of the large cation site Me2 persist beyond the diffuse ferroelectric transition with slightly reduced amplitudes. A change of symmetry was not observed. Both symmetrically non-equivalent NbO6 octahedra are distorted by off center shifts of the Nb atoms in the same direction along the tetragonal c-axis. The displacements of the Nb atoms are gradually reduced with increasing temperatures until one of the Nb atoms crosses the center of its coordination polyhedron near the transition temperature T-M adopting an uncompensated anti-ferroelectric configuration. This change is accompanied by enhanced thermal motions of the Nb atoms along the c-axis. Structural distortions and electric polarization do not completely vanish at TM but may persist in fluctuating polar nanodomains. (C) 2012 Elsevier Inc. All rights reserved.
Title:
Collective pinning dynamics of charge-density waves in 1T-TaS2
Authors:
Su, JD; Sandy, AR; Mohanty, J; Shpyrko, OG; Sutton, M Author Full Names: Su, Jun-Dar; Sandy, Alec R.; Mohanty, Jyoti; Shpyrko, Oleg G.; Sutton, Mark
Source:
PHYSICAL REVIEW B, 86 (20):10.1103/PhysRevB.86.205105 NOV 5 2012
Abstract:
Using high-resolution x-ray scattering and x-ray photon correlation spectroscopy (XPCS), we have investigated the structure and dynamics of charge density wave (CDW) dynamics in pure and titanium-doped 1T-TaS2. Time-averaged scattering measurements of pure and doped samples reveal that 1T-TaS2 is a weakly pinned two-dimensional CDW system. Using XPCS, we find that after long anneals the CDW domain structure in the incommensurate phase is pinned and stable against spontaneous fluctuations thus rejecting phasons as spontaneous excitations in higher-dimensional CDW systems. By examining the dynamics of deeply quenched samples upon heating, we find that metastable CDW configurations collectively rearrange in a nonequilibrium manner. For nominally pure samples, we determine an energy barrier to relaxation of 4600 K that is considerably greater than that found for lower-dimensional CDWs.
Title:
Phason strained quasicrystalline and crystalline precipitates in Zr-Al-Ni-Cu-Nb bulk metallic glass matrix composites
Authors:
Xiong, DX; Wang, JB; Lu, L; Zhao, DS; Sun, YF Author Full Names: Xiong, Dongxia; Wang, Jianbo; Lu, Lu; Zhao, Dongshan; Sun, Yufeng
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 358 (22):3007-3011; 10.1016/j.jnoncrysol.2012.07.031 NOV 1 2012
Abstract:
Quasicrystalline and crystalline precipitates in isothermally annealed bulk metallic glass (Zr65Al10Ni10Cu15)(93)Nb-7 are investigated by transmission electron microscopy techniques. The great majority of the precipitates are icosahedral quasicrystal with primitive icosahedral lattice. The linear phason strain widely existed in the quasicrystal phase is determined quantitatively by electron diffraction analysis. Precise measuring of the diffraction spots' deviation and the quantitative data fitting provides the phason strain matrix. Besides, nano-scaled crystallite inclusions are confirmed as rutile TiO2 assembling with (10 (1) over bar) twinning. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Magnetoelastic coupling in the incommensurate antiferromagnetic phase of FeOCl
Authors:
Zhang, J; Wolfel, A; Li, L; van Smaalen, S; Williamson, HL; Kremer, RK Author Full Names: Zhang, Jian; Woelfel, Alexander; Li, Liang; van Smaalen, Sander; Williamson, Hailey L.; Kremer, Reinhard K.
Source:
PHYSICAL REVIEW B, 86 (13):10.1103/PhysRevB.86.134428 OCT 26 2012
Abstract:
The antiferromagnetic phase transition of FeOCl has been studied by temperature-dependent x-ray-diffraction experiments, magnetic susceptibility, heat capacity, and dielectric measurements. The magnetic phase transition is found to be accompanied by a monoclinic lattice distortion, affecting the angle gamma between crystallographic axes parallel to the layers comprising the quasi-two-dimensional magnetic system. The temperature-dependent magnitude of gamma shows the phase transition to be of second order. Satellite reflections occur in x-ray diffraction with twice the magnetic modulation wave vector. These positions are temperature dependent, providing evidence for an incommensurate character of the magnetic order. The observed Neel temperature is T-N = 81.0 (2) K.
Title:
Complex metallic alloys: new materials for rapid manufacturing
Authors:
Kenzari, S; Bonina, D; Dubois, JM; Fournee, V Author Full Names: Kenzari, Samuel; Bonina, David; Dubois, Jean Marie; Fournee, Vincent
Source:
ACTUALITE CHIMIQUE, (366):36-41; SEP 2012
Abstract:
Complex metallic alloys: new materials for rapid manufacturing Rapid manufacturing processes allow freeform fabrication of the physical representation of a three dimensional CAD data model. This area has been expanding rapidly over the last twenty years. It includes several rapid prototyping techniques such as selective laser sintering and stereolithography. The range of materials used today is quite restricted while there is a real demand for manufacturing lighter functional parts. This article summarizes recent works performed in this field at the Jean Lamour Institute, introducing new materials based on complex metallic alloys. These are mainly Al-based alloys that are weakly periodic - or even aperiodic in the case of quasicrystals - whose properties differ from those of conventional alloys. The use of these materials allows us to produce light-weight parts consisting of either metal-intermetallic composites or of polymer-based composites with improved properties. Functional parts using these alloys are now commercialized.

Update: 22-Nov-2012

Title:
Fifty years of aperiodic crystals
Authors:
Janssen, T Author Full Names: Janssen, T.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 68 667-674; 10.1107/S0108767312033715 Part 6 NOV 2012
Abstract:
Historians often have debates about the beginning and end of a certain era. The same discussion can be had about the history of aperiodic crystals. There are reasons to claim that in 2012 one may celebrate the 50th anniversary of this field. A short description is given of the development of this branch of crystallography. It is argued that the most important point in its history is the discovery of quasicrystals, which has been recognized by awarding the Nobel Prize in Chemistry 2011 to Dan Shechtman.
Title:
Effects of Transition Metal Substitutions on the Incommensurability and Spin Fluctuations in BaFe2As2 by Elastic and Inelastic Neutron Scattering
Authors:
Kim, MG; Lamsal, J; Heitmann, TW; Tucker, GS; Pratt, DK; Khan, SN; Lee, YB; Alam, A; Thaler, A; Ni, N; Ran, S; Bud'ko, SL; Marty, KJ; Lumsden, MD; Canfield, PC; Harmon, BN; Johnson, DD; Kreyssig, A; McQueeney, RJ; Goldman, AI Author Full Names: Kim, M. G.; Lamsal, J.; Heitmann, T. W.; Tucker, G. S.; Pratt, D. K.; Khan, S. N.; Lee, Y. B.; Alam, A.; Thaler, A.; Ni, N.; Ran, S.; Bud'ko, S. L.; Marty, K. J.; Lumsden, M. D.; Canfield, P. C.; Harmon, B. N.; Johnson, D. D.; Kreyssig, A.; McQueeney, R. J.; Goldman, A. I.
Source:
PHYSICAL REVIEW LETTERS, 109 (16):10.1103/PhysRevLett.109.167003 OCT 19 2012
Abstract:
The spin fluctuation spectra from nonsuperconducting Cu-substituted, and superconducting Co-substituted, BaFe2As2 are compared quantitatively by inelastic neutron scattering measurements and are found to be indistinguishable. Whereas diffraction studies show the appearance of incommensurate spin-density wave order in Co and Ni substituted samples, the magnetic phase diagram for Cu substitution does not display incommensurate order, demonstrating that simple electron counting based on rigid-band concepts is invalid. These results, supported by theoretical calculations, suggest that substitutional impurity effects in the Fe plane play a significant role in controlling magnetism and the appearance of superconductivity, with Cu distinguished by enhanced impurity scattering and split-band behavior.
Title:
Deuterium storage of Ti40Zr40Ni20 icosahedral quasicrystal
Authors:
Huang, HG; Liu, TW; Zhang, Z; Ye, XQ; Luo, LZ; Zhang, XD Author Full Names: Huang, Huogen; Liu, Tianwei; Zhang, Zhi; Ye, Xiaoqiu; Luo, Lizhu; Zhang, Xiangdong
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 37 (20):15204-15209; 10.1016/j.ijhydene.2012.07.127 OCT 2012
Abstract:
Ti40Zr40Ni20 icosashedral quasicrystal was observed to load hydrogen in a much lower capacity than similar Ti-Zr-Ni alloys. To verify the result, the alloy is further studied by using deuterium instead of hydrogen in this work. With a home-made gas-solid reaction system, XRD and XPS techniques, the investigation was conducted on deuterium absorption and desorption properties of Ti40Zr40Ni20 alloy and its phase stability during the deuteration course. It is shown that the quasicrystal can load deuterium rapidly in an elevated volume of 11.5 mmol.D-2/g.M (D-2 denotes deuterium molecular and M the metal). After the full storage of deuterium, the quasicrystal phase remained, however the quasilattice expanded at a rate of 6.28%, revealing the occurrence of severe quasilattice stress. The solution of deuterium in the alloy caused the increase of binding energy of the metal elements, as much as 0.4 eV for Ti, 0.6 eV for Zr and 0.1 eV for Ni, which reflects the location of deuterium near Ti and Zr. The deuterium release was very slow at low temperature and could be complete at least above 610 degrees C. Based on the gained results, the quasilattice shrink would be more reasonable to explain the big difficulty of the desorption. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Title:
Attainment of quasicrystalline phase in Al-Cu-Fe alloy via melting and mechanical alloying
Authors:
Esquivel, R; Suarez, MA; Diaz-Barriga, L; Chavez, F Author Full Names: Esquivel, Rosalba; Suarez, Miguel A.; Diaz-Barriga, Lucia; Chavez, Federico
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, 103 (9):1137-1143; 10.3139/146.110808 SEP 2012
Abstract:
Al62Cu25.5Fe12.5 (A) and Al65Cu20Fe15 (B) alloys were fabricated via melting and experimentally studied in both as-cast and annealed conditions. Alloy (B) was also fabricated using mechanical alloying and an annealing treatment. The melted alloys were characterized to investigate the distribution of alloying elements Fe and Cu on the icosahedral and coexisting phases, as well as the hardness of all phases. The as-cast alloys showed the highest amount of icosahedral phase with up to 47 % of ingot (A), but this increased after heat treatment to 99% and 75% of ingots in (A) and (B) alloys respectively. During heat treatment the iron content was increased in all phases, while the copper content decreased. As a consequence, the hardness of the icosahedral phase increased by 23% in (A) Al62Cu25.5Fe12.5 alloy and 33% in (B) Al65Cu20Fe15 alloy. On the other hand, the effect of heat treatment on samples obtained from mechanical alloying caused a modification in the iron and copper contents, leading to the formation of iron-rich phases such as lambda-(Al,Cu)(13)Fe-4 phase for all milling times and the icosahedral phase after 35 h.
Title:
Mechanical behavior of the cold-rolled Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 metallic glass-quasicrystalline composite
Authors:
Beitelschmidt, D; Scudino, S; Prashanth, KG; Kuhn, U; Eckert, J Author Full Names: Beitelschmidt, Denise; Scudino, Sergio; Prashanth, Konda Gokuldoss; Kuehn, Uta; Eckert, Juergen
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, 103 (9):1113-1116; 10.3139/146.110783 SEP 2012
Abstract:
The as-cast Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 glass-quasicrystalline composite exhibits high strength, good elasticity but no macroscopic room temperature plastic deformability. Significant improvement in plastic deformability to a strain of about 5% can be achieved after cold-rolling of the as-cast material. This behavior can be ascribed the anisotropic and inhomoeeneous stress distribution developing during the mechanical test along with the creation of an extensive system of shear bands.
Title:
Conventional and Stuffed Bergman-Type Phases in the Na-Au-T (T=Ga, Ge, Sn) Systems: Syntheses, Structures, Coloring of Cluster Centers, and Fermi Sphere-Brillouin Zone Interactions
Authors:
Lin, QS; Smetana, V; Miller, GJ; Corbett, JD Author Full Names: Lin, Qisheng; Smetana, Volodymyr; Miller, Gordon J.; Corbett, John D.
Source:
INORGANIC CHEMISTRY, 51 (16):8882-8889; 10.1021/ic300866q AUG 20 2012
Abstract:
Bergman-type phases in the Na-Au-T (T = Ga, Ge, and Sn) systems were synthesized by solid-state means and structurally characterized by single-crystal X-ray diffraction studies. Two structurally related (1/1) Bergman phases were found in the Na-Au-Ga system: (a) a conventional Bergman-type (CB) structure, Na26AuxGa54-x, which features empty innermost icosahedra, as refined with x = 18.1 (3), Im (3) over bar, a = 14.512(2) angstrom, and Z = 2; (b) a stuffed Bergman-type (SB) structure, Na26AuyGa55-y, which contains Ga-centered innermost icosahedra, as refined with y = 36.0 (1), Im (3) over bar, a = 14.597(2) angstrom, and Z = 2. Although these two subtypes have considerable phase widths along with respective tie lines at Na approximate to 32.5 and 32.1 atom %, they do not merge into a continuous solid solution. Rather, a quasicrystalline phase close to the Au-poor CB phase and an orthorhombic derivative near the Au-rich SB phase lie between them. In contrast, only Au-rich SB phases exist in the Ge and Sn systems, in which the innermost icosahedra are centered by Au rather than Ge or Sn. These were refined for Na26Au40.93(5)Ge14.07(5) (Im (3) over bar, a = 14.581(2) angstrom, and Z = 2) and Na26Au39.83(6)Sn15.17(6) (Im (3) over bar, a = 15.009(2) angstrom, and Z = 2), respectively. Occupations of the centers of Bergman clusters are rare. Such centering and coloring correlate with the sizes of the neighboring icosahedra, the size ratios between electropositive and electronegative components, and the values of the average valence electron count per atom (e/a). Theoretical calculations revealed that all of these phases are Hume-Rothery phases, with evident pseudogaps in the density of states curves that arise from the interactions between Fermi surface and Brillouin zone boundaries corresponding to a strong diffraction intensity.

Update: 14-Nov-2012

Title:
Distinct Charge Orders in the Planes and Chains of Ortho-III-Ordered YBa2Cu3O6+delta Superconductors Identified by Resonant Elastic X-ray Scattering
Authors:
Achkar, AJ; Sutarto, R; Mao, X; He, F; Frano, A; Blanco-Canosa, S; Le Tacon, M; Ghiringhelli, G; Braicovich, L; Minola, M; Sala, MM; Mazzoli, C; Liang, RX; Bonn, DA; Hardy, WN; Keimer, B; Sawatzky, GA; Hawthorn, DG Author Full Names: Achkar, A. J.; Sutarto, R.; Mao, X.; He, F.; Frano, A.; Blanco-Canosa, S.; Le Tacon, M.; Ghiringhelli, G.; Braicovich, L.; Minola, M.; Sala, M. Moretti; Mazzoli, C.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Keimer, B.; Sawatzky, G. A.; Hawthorn, D. G.
Source:
PHYSICAL REVIEW LETTERS, 109 (16):10.1103/PhysRevLett.109.167001 OCT 17 2012
Abstract:
Recently, charge density wave (CDW) order in the CuO2 planes of underdoped YBa2Cu3O6+delta was detected using resonant soft x-ray scattering. An important question remains: is the chain layer responsible for this charge ordering? Here, we explore the energy and polarization dependence of the resonant scattering intensity in a detwinned sample of YBa2Cu3O6.75 with ortho-III oxygen ordering in the chain layer. We show that the ortho-III CDW order in the chains is distinct from the CDWorder in the planes. The ortho-III structure gives rise to a commensurate superlattice reflection at Q = [0.33 0 L] whose energy and polarization dependence agrees with expectations for oxygen ordering and a spatial modulation of the Cu valence in the chains. Incommensurate peaks at [0.30 0 L] and [0 0.30 L] from the CDW order in the planes are shown to be distinct in Q as well as their temperature, energy, and polarization dependence, and are thus unrelated to the structure of the chain layer. Moreover, the energy dependence of the CDW order in the planes is shown to result from a spatial modulation of energies of the Cu 2p to 3d(x2-y2) transition, similar to stripe-ordered 214 cuprates.
Title:
Magnetic Field Splitting of the Spin Resonance in CeCoIn5
Authors:
Stock, C; Broholm, C; Zhao, Y; Demmel, F; Kang, HJ; Rule, KC; Petrovic, C Author Full Names: Stock, C.; Broholm, C.; Zhao, Y.; Demmel, F.; Kang, H. J.; Rule, K. C.; Petrovic, C.
Source:
PHYSICAL REVIEW LETTERS, 109 (16):10.1103/PhysRevLett.109.167207 OCT 17 2012
Abstract:
Neutron scattering in strong magnetic fields is used to show the spin resonance in superconducting CeCoIn5 (T-c = 2.3 K) is a doublet. The underdamped resonance ((h) over bar Gamma = 0.069 +/- 0.019 meV) Zeeman splits into two modes at E-+/- = (h) over bar Omega(0) +/- mu H-B mu 0 with alpha = 0.96 +/- 0: 05. A linear extrapolation of the lower peak reaches zero energy at 11.2 +/- 0.5 T, near the critical field for the incommensurate "Q phase." Kenzelmann et al. [Science 321, 1652 (2008)] This, taken with the integrated weight and polarization of the low-energy mode (E-), indicates that the Q phase can be interpreted as a Bose condensate of spin excitons.
Title:
Magnetic ordering and multiferroicity in MnI2
Authors:
Wu, XX; Cai, YX; Xie, Q; Weng, HM; Fan, H; Hu, JP Author Full Names: Wu, Xianxin; Cai, Yingxiang; Xie, Qing; Weng, Hongming; Fan, Heng; Hu, Jiangping
Source:
PHYSICAL REVIEW B, 86 (13):10.1103/PhysRevB.86.134413 OCT 15 2012
Abstract:
Density-functional calculations are carried out to investigate incommensurate magnetic structures and ferroelectric polarization in the newly discovered multiferroic material MnI2. The exchange interactions among local moments on Mn are parameterized by mapping the mean-field Heisenberg model on to the total energy difference of several magnetic ordering states. The experimentally observed noncollinear magnetic states are well reproduced by using this model and exchange interaction parameters. The direction of polarization experimentally measured is also consistent with the result derived from the symmetry analysis of the magnetically ordered state. In particular, we find that the interplane magnetic exchange coupling is pivotal to the emergence of the spiral magnetic structure. This noncollinear magnetic structure, combined with spin-orbit coupling mainly from I ions, is responsible for the appearance of ferroelectric polarization.
Title:
Metal-insulator transition in the Hubbard model with incommensurate magnetic structures
Authors:
Timirgazin, MA; Arzhnikov, AK; Irkhin, VY Author Full Names: Timirgazin, M. A.; Arzhnikov, A. K.; Irkhin, V. Yu
Source:
JETP LETTERS, 96 (3):171-175; 10.1134/S002136401215012X OCT 2012
Abstract:
The metal-insulator transition for the square, simple cubic, and body centered cubic lattices has been studied within the Hubbard model at half-filling taking into account nearest- and next-nearest-neighbor electron hopping. Both staggered antiferromagnetic and incommensurate magnetic states (spin-spiral wave) have been considered. The inclusion of the latter states for the three-dimensional lattices does not change the general pattern of the metal-insulator transition, but opens the fundamentally new possibility of the metal-insulator transition of the first order between the magnetically ordered states for the square lattice.

Update: 7-Nov-2012

Title:
Extra-electron induced covalent strengthening and generalization of intrinsic ductile-to-brittle criterion
Authors:
Niu, HY; Chen, XQ; Liu, PT; Xing, WW; Cheng, XY; Li, DZ; Li, YY Author Full Names: Niu, Haiyang; Chen, Xing-Qiu; Liu, Peitao; Xing, Weiwei; Cheng, Xiyue; Li, Dianzhong; Li, Yiyi
Source:
SCIENTIFIC REPORTS, 2 10.1038/srep00718 OCT 9 2012
Abstract:
Traditional strengthening ways, such as strain, precipitation, and solid-solution, come into effect by pinning the motion of dislocation. Here, through first-principles calculations we report on an extra-electron induced covalent strengthening mechanism, which alters chemical bonding upon the introduction of extra-valence electrons in the matrix of parent materials. It is responsible for the brittle and high-strength properties of Al12W-type compounds featured by the typical fivefold icosahedral cages, which are common for quasicrystals and bulk metallic glasses (BMGs). In combination with this mechanism, we generalize ductile-to-brittle criterion in a universal hyperbolic form by integrating the classical Pettifor's Cauchy pressure with Pugh's modulus ratio for a wide variety of materials with cubic lattices. This study provides compelling evidence to correlate Pugh's modulus ratio with hardness of materials and may have implication for understanding the intrinsic brittleness of quasicrystals and BMGs.
Title:
Effect of A-site La and Ba doping on threshold field and characteristic temperatures of PbSc0.5Ta0.5O3 relaxor studied by acoustic emission
Authors:
Dul'kin, E; Mihailova, B; Gospodinov, M; Roth, M Author Full Names: Dul'kin, E.; Mihailova, B.; Gospodinov, M.; Roth, M.
Source:
JOURNAL OF APPLIED PHYSICS, 112 (6):10.1063/1.4752400 SEP 15 2012
Abstract:
The structural transitions in Pb1-xLaxSc(1+x)/2Ta(1-x)/2O3, x = 0.08 (PLST) relaxor crystals were studied by means of acoustic emission (AE) under an external electric field (E) and compared with those observed in pure PbSc0.5Ta0.5O3 (PST) and Pb0.78Ba0.22Sc0.5Ta0.5O3 (PBST) [E. Dul'kin et al., EPL 94, 57002 (2011)]. Similar to both the PST and PBST compounds, in zero field PLST exhibits AE corresponding to a para-to-antiferroelectric incommensurate phase transition at T-n = 276 K, lying in the vicinity of dielectric temperature maximum (T-m). This AE signal exhibits a nontrivial behavior when applying E resembling the electric-field-dependence of T-n previously observed for both the PST and PBST, namely, T-n initially decreases with the increase of E, attains a minimum at a threshold field E-th = 0.5 kV/cm, accompanied by a pronounced maximum of the AE count rate (N) over dot = 12 s(-1), and then starts increasing as E enhances. The similarities and difference between PST, PLST, and PBST with respect to T-n, E-th, and (N) over dot are discussed from the viewpoint of three mechanisms: (i) chemically induced random local electric field due to the extra charge on the A-site ion, (ii) disturbance of the system of stereochemically active lone-pair electrons of Pb2+ by the isotropic outermost electron shell of substituting ion, and (iii) change in the tolerance factor and elastic field to the larger ionic radius of the substituting A-site ion due to the different radius of the substituting ion. The first two mechanisms influence the actual values of T-n and E-th, whereas the latter is shown to affect the normalized (N) over dot, indicating the fractions undergoing a field-induced crossover from a modulated antiferroelectric to a ferroelectric state. Creation of secondary random electric field, caused by doping-induced A-site-O ionic chemical bonding, is discussed. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4752400]
Title:
Diffraction study of bending-induced polysynthetic twins in 10M modulated Ni-Mn-Ga martensite
Authors:
Chulist, R; Sozinov, A; Straka, L; Lanska, N; Soroka, A; Lippmann, T; Oertel, CG; Skrotzki, W Author Full Names: Chulist, R.; Sozinov, A.; Straka, L.; Lanska, N.; Soroka, A.; Lippmann, T.; Oertel, C-G.; Skrotzki, W.
Source:
JOURNAL OF APPLIED PHYSICS, 112 (6):10.1063/1.4754017 SEP 15 2012
Abstract:
Detailed conventional and synchrotron x-ray and electron backscatter diffraction experiments were performed to investigate bending-induced polysynthetic twins in a Ni-Mn-Ga single crystal with five-layered (10M) martensite crystal structure. It was proved that the twin microstructure produced in such a way is composed of type I twins. The type I twins exhibit a relatively high twinning stress of about 0.8 MPa, which limits the performance of bending-induced twins in magnetic actuation. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4754017]

Update: 31-Oct-2012

Title:
Ordering and dynamics of the central tetrahedron in the 1/1 Zn6Sc periodic approximant to quasicrystal
Authors:
Euchner, H; Yamada, T; Schober, H; Rols, S; Mihalkovic, M; Tamura, R; Ishimasa, T; de Boissieu, M Author Full Names: Euchner, Holger; Yamada, Tsunetomo; Schober, Helmut; Rols, Stephane; Mihalkovic, Marek; Tamura, Ryuji; Ishimasa, Tsutomu; de Boissieu, Marc
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (41):10.1088/0953-8984/24/41/415403 OCT 17 2012
Abstract:
Periodic approximants to quasicrystals offer a unique opportunity to better understand the structure, physical properties and stabilizing mechanisms of their quasicrystal counterparts. We present a detailed study of the order-disorder phase transition occurring at about 160 K in the Zn6Sc cubic approximant to the icosahedral quasicrystal i-MgZnSc. This transition goes along with an anti-parallel ordering of the tetrahedra located at the centres of large atomic clusters, which are packed on a bcc lattice. Single crystal x-ray diffuse scattering shows that the tetrahedra display pre-transitional short range ordering above T-c (Yamada et al 2012 in preparation). Using quasielastic neutron scattering (QENS) we clearly evidence this short range order to be dynamical in nature above T-c. The QENS data are consistent with a model of tetrahedra 'jumping' between almost equivalent positions, which is supported by molecular dynamics simulations. This demonstrates a unique dynamical flexibility of the Zn6Sc structure even at room temperature.
Title:
Spin polarized and density modulated phases in symmetric electron-electron and electron-hole bilayers
Authors:
Kumar, K; Moudgil, RK Author Full Names: Kumar, Krishan; Moudgil, R. K.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (41):10.1088/0953-8984/24/41/415601 OCT 17 2012
Abstract:
We have studied symmetric electron-electron and electron-hole bilayers to explore the stable homogeneous spin phase and the feasibility of inhomogeneous charge-/spin-density ground states. The former is resolved by comparing the ground-state energies in states of different spin polarizations, while the latter is resolved by searching for a divergence in the wavevector-dependent static charge/spin susceptibility. For this endeavour, we have used the dielectric approach within the self-consistent mean-field theory of Singwi et al. We find that the inter-layer interactions tend to change an abrupt spin-polarization transition of an isolated layer into a nearly gradual one, even though the partially spin-polarized phases are not clearly stable within the accuracy of our calculation. The transition density is seen to decrease with a reduction in layer spacing, implying a suppression of spin polarization by inter-layer interactions. Indeed, the suppression shows up distinctly in the spin susceptibility computed from the spin-polarization dependence of the ground-state energy. However, below a critical layer spacing, the unpolarized liquid becomes unstable against a charge-density-wave (CDW) ground state at a density preceding full spin polarization, with the transition density for the CDW state increasing on further reduction in the layer spacing. Due to attractive e-h correlations, the CDW state is found to be more pronounced in the e-h bilayer. On the other hand, the static spin susceptibility diverges only in the long-wavelength limit, which simply represents a transition to the homogeneous spin-polarized phase.
Title:
Magnetic ordering phenomena of interacting quantum spin Hall models
Authors:
Reuther, J; Thomale, R; Rachel, S Author Full Names: Reuther, Johannes; Thomale, Ronny; Rachel, Stephan
Source:
PHYSICAL REVIEW B, 86 (15):10.1103/PhysRevB.86.155127 OCT 15 2012
Abstract:
The two-dimensional Hubbard model defined for topological band structures exhibiting a quantum spin Hall effect poses fundamental challenges in terms of phenomenological characterization and microscopic classification. In the limit of infinite coupling U at half filling, the spin model Hamiltonians resulting from a strong-coupling expansion show various forms of magnetic ordering phenomena depending on the underlying spin-orbit coupling terms. We investigate the infinite-U limit of the Kane-Mele-Hubbard model with z-axis intrinsic spin-orbit coupling as well as its generalization to a generically multidirectional spin-orbit term which has been claimed to account for the physical scenario in monolayer Na2IrO3. We find that the axial spin symmetry which is kept in the former but broken in the latter has a fundamental impact on the magnetic phase diagram as we vary the spin-orbit coupling strength. While the Kane-Mele spin model shows a continuous evolution from conventional honeycomb Neel to XY antiferromagnetism which avoids the frustration imposed by the increased spin-orbit coupling, the multidirectional spin-orbit term induces a commensurate to incommensurate transition at intermediate coupling strength, and yields a complex spiral state with a 24 site unit cell in the limit of infinite spin-orbit coupling. From our findings, we conjecture that in the case of broken axial spin symmetry there is a large propensity for an additional phase at sufficiently large spin-orbit coupling and intermediate U.
Title:
The structure of dodecagonal (Ta,V)(1.6)Te imaged by phase-contrast scanning transmission electron microscopy
Authors:
Krumeich, F; Muller, E; Wepf, RA; Conrad, M; Reich, C; Harbrecht, B; Nesper, R Author Full Names: Krumeich, F.; Mueller, E.; Wepf, R. A.; Conrad, M.; Reich, C.; Harbrecht, B.; Nesper, R.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 194 106-112; 10.1016/j.jssc.2012.04.050 OCT 2012
Abstract:
While HRTEM is the well-established method to characterize the structure of dodecagonal tantalum (vanadium) telluride quasicrystals and their periodic approximants, phase-contrast imaging performed on an aberration-corrected scanning transmission electron microscope (STEM) represents a favorable alternative. The (Ta,V)(151)Te-74 clusters, the basic structural unit in all these phases, can be visualized with high resolution. A dependence of the image contrast on defocus and specimen thickness has been observed. In thin areas, the projected crystal potential is basically imaged with either dark or bright contrast at two defocus values close to Scherzer defocus as confirmed by image simulations utilizing the principle of reciprocity. Models for square-triangle tilings describing the arrangement of the basic clusters can be derived from such images. (C) 2012 Elsevier Inc. All rights reserved.
Title:
Incommensurate Orbital Modulation behind Ferroelectricity in CuFeO2
Authors:
Tanaka, Y; Terada, N; Nakajima, T; Taguchi, M; Kojima, T; Takata, Y; Mitsuda, S; Oura, M; Senba, Y; Ohashi, H; Shin, S Author Full Names: Tanaka, Yoshikazu; Terada, Noriki; Nakajima, Taro; Taguchi, Munetaka; Kojima, Taro; Takata, Yasutaka; Mitsuda, Setsuo; Oura, Masaki; Senba, Yasunori; Ohashi, Haruhiko; Shin, Shik
Source:
PHYSICAL REVIEW LETTERS, 109 (12):10.1103/PhysRevLett.109.127205 SEP 19 2012
Abstract:
CuFeO2 is one of the multiferroic materials and is the first case that the electric polarization is not explained by the magnetostriction model or the spin-current model. We have studied this material using soft x-ray resonant diffraction and found that superlattice reflection 0 1 - 2q 0 appears in the ferroelectric and incommensurate magnetic ordered phase at the Fe L-2,L-3 absorption edges and moreover that the rotation of the x-ray polarization such as from sigma to pi or from pi to sigma is allowed at this reflection. These findings definitely provide direct evidence that the 3d t(2g down arrow) orbital state of Fe ions has a long-range order in the ferroelectric state. The spin-orbit interaction in Fe ions plays a crucial role to the ferroelectricity in CuFeO2, coupling two nontrivial spin and orbital orders, both of which break the crystal symmetry.
Title:
Structural Impact of Platinum on the Incommensurably Modulated gamma-Brass Related Composite Structure Pd15Zn54
Authors:
Jana, PP; Lidin, S Author Full Names: Jana, Partha P.; Lidin, Sven
Source:
INORGANIC CHEMISTRY, 51 (18):9893-9901; 10.1021/ic301326p SEP 17 2012
Abstract:
The crystal structure of three incommensurately modulated gamma-brass related composite structures in the Pd-Zn-Pt system has been solved from X-ray single crystal diffraction data using a 3 + 1-dimensional super space description. The compounds PtxPd15-xZn54 (x approximate to 6, 7, 10) crystallize in orthorhombic superspace group Fmmm(alpha 00)0s0 (F = [(1/2, 1/2, 0, 0); (1/2, 0, 1/2, 0); (0, 1/2, 1/2, 0)] with the following fundamental cell dimensions: a = 4.265(1) angstrom, b = 9.132(1) angstrom, c = 12.928(2) angstrom, q approximate to 0.629a*; a = 4.284(1) angstrom, b = 9.151(2) angstrom, c = 12.948(4) angstrom, q approximate to 0.628a*; and a = 4.288(1) angstrom, b = 9.140(4) angstrom, c = 12.926(7) angstrom, q approximate to 0.627a*. Each structure is built by two sub-lattices-pentagonal antiprismatic columns parallel to [100] and a zigzag chain of Zn atoms running along the center of the column.
Title:
Structural Modulation and Phase Transitions in La2CoO4.14 Investigated by Synchrotron X-ray and Neutron Single-Crystal Diffraction
Authors:
Le Dreau, L; Prestipino, C; Hernandez, O; Schefer, J; Vaughan, G; Paofai, S; Perez-Mato, JM; Hosoya, S; Paulus, W Author Full Names: Le Dreau, Loic; Prestipino, Carmelo; Hernandez, Olivier; Schefer, Juerg; Vaughan, Gavin; Paofai, Serge; Perez-Mato, Juan Manuel; Hosoya, Shoichi; Paulus, Werner
Source:
INORGANIC CHEMISTRY, 51 (18):9789-9798; 10.1021/ic301165a SEP 17 2012
Abstract:
We report a combined synchrotron X-ray and neutron diffraction study on as-grown La2CoO4.14 single-crystal from 10 to 470 K. Unprecedented structural features in terms of a (3 + 2)D incommensurate modulation have been detected and characterized in the Low Temperature Orthorhombic (LTO) phase already at room temperature despite the complex twinning that was unravelled. A new intermediate phase between the LTO and High Temperature Tetragonal (HTT) phases has been observed for the first time (in the range of 413-433 K). The transformation from LTO to this so-called HTLO (High Temperature Less Orthorhombic) phase is associated to a lowering of orthorhombicity and a loss of one modulation vector, yielding a (3 + 1)D incommensurate modulation. Conversely, above 433 K the HTT phase appears as nonmodulated but exhibits a strong dynamic disorder of CoO6 octahedra, which has been characterized in detail by reconstruction of nuclear densities via the Maximum Entropy Method (MEM).
Title:
Topological States and Adiabatic Pumping in Quasicrystals
Authors:
Kraus, YE; Lahini, Y; Ringel, Z; Verbin, M; Zilberberg, O Author Full Names: Kraus, Yaacov E.; Lahini, Yoav; Ringel, Zohar; Verbin, Mor; Zilberberg, Oded
Source:
PHYSICAL REVIEW LETTERS, 109 (10):10.1103/PhysRevLett.109.106402 SEP 4 2012
Abstract:
The unrelated discoveries of quasicrystals and topological insulators have in turn challenged prevailing paradigms in condensed-matter physics. We find a surprising connection between quasicrystals and topological phases of matter: (i) quasicrystals exhibit nontrivial topological properties and (ii) these properties are attributed to dimensions higher than that of the quasicrystal. Specifically, we show, both theoretically and experimentally, that one-dimensional quasicrystals are assigned two-dimensional Chern numbers and, respectively, exhibit topologically protected boundary states equivalent to the edge states of a two-dimensional quantum Hall system. We harness the topological nature of these states to adiabatically pump light across the quasicrystal. We generalize our results to higher-dimensional systems and other topological indices. Hence, quasicrystals offer a new platform for the study of topological phases while their topology may better explain their surface properties.
Title:
Incommensurate Sinusoidal Oxygen Modulations in Layered Manganites La1-xSr1+xMnO4 (x >= 0.5)
Authors:
Garcia, J; Herrero-Martin, J; Subias, G; Blasco, J; Andreu, JS; Sanchez, MC Author Full Names: Garcia, Joaquin; Herrero-Martin, Javier; Subias, Gloria; Blasco, Javier; Andreu, J. S.; Concepcion Sanchez, M.
Source:
PHYSICAL REVIEW LETTERS, 109 (10):10.1103/PhysRevLett.109.107202 SEP 4 2012
Abstract:
We have studied the incommensurate-ordered phase in overdoped La0.4Sr1.6MnO4 by resonant x-ray diffraction at the Mn K edge. Weak resonant superlattice (h +/- 0.2 h +/- 0.2 0) and (h +/- 0.4 h +/- 0.4 0) reflections of the tetragonal structure were found below similar to 240 K. The energy, azimuth angle, and polarization dependencies of the resonant scattering have revealed sinusoidal modulations of the oxygen motions that are transverse and longitudinal to the tetragonal [110] direction. This result discards (Mn3+, Mn4+)-like stripe-type order but point to a charge-density-modulation picture.
Title:
The Crystalline Structure of O-AlFePd
Authors:
Sugiyama, K; Obata, T; Hiraga, K Author Full Names: Sugiyama, Kazumasa; Obata, Tatsuo; Hiraga, Kenji
Source:
MATERIALS TRANSACTIONS, 53 (8):1357-1362; 10.2320/matertrans.M2012130 AUG 2012
Abstract:
The structure of O-AlFePd has been analyzed by single-crystal X-ray diffraction, yielding space group Cmca (No. 64), a = 0.8130(1) nm, b = 1.5474(2) nm, c = 2.3868(4) nm, atoms/cell = 204, F(000) = 3339, D-eal, = 5.621 Mg m(-3) and R = 0.0294 for the 2117 observed reflections with F-obs > 4.0 sigma(F-obs). The structure consists of four Fe sites, one Fe/Pd mixed site, and fifteen Al sites, and the corresponding structural formula is Al-13(Fe,Pd)(4) (Z = 8). The O-AlFePd phase is a new type of approximant of decagonal quasicrystals with a periodicity of 0.8 nm, and the alternation of flat and puckered layers at an interval of about 0.2 nm is the fundamental structural feature. The structure could be also described by a linkage of pentagonal atom columns similar to that found in monoclinic Al13Fe4. Nevertheless, the columnar linkage for the O-AlFePd phase is unique, and this allows us to advance an idea explaining the fine (001) glide twins freque ntly found in the Al13Fe4 phase. [doi:10.2320/matertrans.M2012130]

Update: 25-Oct-2012

Title:
SHAPES OF THE ICOSAHEDRAL QUASICRYSTALLINE PHASE IN MELT-SPUN RIBBONS
Authors:
Boncina, T Author Full Names: Boncina, T.
Source:
METALURGIJA, 52 (1):65-67; JAN-MAR 2013
Abstract:
The shapes of icosahedral quasicrystalline (IQC) particles were determined in melt-spun ribbons of alloys based on the Al-Mn-Be alloy system. The sizes of the quasicrystalline particles ranged from a few tenths of nanometres up to 1 mu m. Therefore, different methods were employed for characterizing their shapes: projection of quasicrystalline particles using transmission electron microscopy (TEM), cross-sections of IQCs on metallographically polished surfaces, and observation of deep-etched samples and extracted particles using a scanning electron microscope (SEM). It was discovered that icosahedral quasicrystalline particles preferentially grow in three-fold directions and have a tendency for faceting and adopting the shape of a pentagonal dodecahedron. The evolution of quasicrystalline shapes is systematically presented.
Title:
On the fundamental equations of piezoelasticity of quasicrystal media
Authors:
Altay, G; Dokmeci, MC Author Full Names: Altay, Gulay; Dokmeci, M. Cengiz
Source:
INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 49 (23-24):3255-3262; 10.1016/j.ijsolstr.2012.06.016 NOV 15 2012
Abstract:
The three-dimensional fundamental equations of elasticity of quasicrystals with extension to quasi-static electric effect are expresses in both differential and variational invariant forms for a regular region of quasicrystal material. The principle of conservation of energy is stated for the regular region and the constitutive relations are obtained for the piezoelasticity of material. A theorem is proved for the uniqueness in solutions of the fundamental equations by means of the energy argument. The sufficient boundary and initial conditions are enumerated for the uniqueness. Hamilton's principle is stated for the regular region and a three-field variational principle is obtained under some constraint conditions. The constraint conditions, which are generally undesirable in computation, are removed by applying an involutory transformation. Then, a unified variational principle is obtained for the regular region, with one or more fixed internal surface of discontinuity. The variational principle operating on all the field variables generates all the fundamental equations of piezoelasticity of quasicrystals under the symmetry conditions of the phonon stress tensor and the initial conditions. The resulting equations, which are expressible in any system of coordinates and may be used through simultaneous approximation upon all the field variables in a direct method of solutions, pave the way to the study of important dislocation, fracture and interface problems of both elasticity and piezoelasticity of quasicrystal materials. (C) 2012 Elsevier Ltd. All rights reserved.
Title:
Neutron scattering studies on stripe phases in non-cuprate materials
Authors:
Ulbrich, H; Braden, M Author Full Names: Ulbrich, Holger; Braden, Markus
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 481 31-45; 10.1016/j.physc.2012.04.039 NOV 2012
Abstract:
Several non-cuprates layered transition-metal oxides exhibit clear evidence for stripe ordering of charges and magnetic moments. Therefore, stripe order should be considered as the typical consequence of doping a layered Mott insulator, but only in cuprates stripe order or fluctuating stripes coexist with metallic properties. A linear relationship between the charge concentration and the incommensurate structural and magnetic modulations can be considered as the finger print of stripe ordering with localized degrees of freedom. In nickelates and in cobaltates with K2NiF4 structure, doping suppresses the nearest-neighbor antiferromagnetism and induces stripe order. The higher amount of doping needed to induce stripe phases in these non-cuprates series can be attributed to reduced charge mobility. Also manganites exhibit clear evidence for stripe phases with further enhanced complexity, because orbital degrees of freedom are involved. Orbital ordering is the key element of stripe order in manganites since it is associated with the strongest structural distortion and with the perfectly fulfilled relation between doping and incommensurability. Magnetic excitations in insulating stripe phases exhibit strong similarity with those in the cuprates, but only for sufficiently short magnetic correlation lengths reflecting well-defined magnetic stripes that are only loosely coupled. (C) 2012 Elsevier B. V. All rights reserved.
Title:
Transmission electron microscopy observations of structural modulation in the phase transition from alpha-Zr to omega-Zr induced by shear strain
Authors:
Shen, X; Yu, PF; Jing, Q; Yao, Y; Gu, L; Wang, YG; Duan, XF; Yu, RC; Liu, RP Author Full Names: Shen, X.; Yu, P. F.; Jing, Q.; Yao, Y.; Gu, L.; Wang, Y. G.; Duan, X. F.; Yu, R. C.; Liu, R. P.
Source:
SCRIPTA MATERIALIA, 67 (7-8):653-656; 10.1016/j.scriptamat.2012.07.017 OCT 2012
Abstract:
Pure alpha-Zr samples were processed using unconstrained die sets at 5 and 6 GPa with different numbers of revolutions. The microstructural characteristics of Zr deformed by high pressure torsion was studied using transmission electron microscopy. It was found that shear strain can induce distortion of the hcp structure, which can, in addition, give rise to a variety of modulated structures. Most importantly, one possible phase transition route from alpha-Zr to omega-Zr is proposed involving intermediate steps with structural modulations. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Heliconical magnetic order and field-induced multiferroicity of the Co2Y-type hexaferrite Ba0.3Sr1.7Co2Fe12O22
Authors:
Lee, HB; Chun, SH; Shin, KW; Jeon, BG; Chai, YS; Kim, KH; Schefer, J; Chang, H; Yun, SN; Joung, TY; Chung, JH Author Full Names: Lee, Hak Bong; Chun, Sae Hwan; Shin, Kwang Woo; Jeon, Byung-Gu; Chai, Yi Sheng; Kim, Kee Hoon; Schefer, Juerg; Chang, Hun; Yun, Sae-Na; Joung, Tae-Young; Chung, Jae-Ho
Source:
PHYSICAL REVIEW B, 86 (9):10.1103/PhysRevB.86.094435 SEP 27 2012
Abstract:
Using magnetoelectric measurements and neutron diffraction, we investigated multiferroic properties of Co2Y hexaferrite Ba0.3Sr1.7Co2Fe12O22 in zero and finite magnetic field (H perpendicular to c). Upon zero-field cooling, a longitudinal heliconical magnetic structure was observed below 280 K, which involves incommensurate planar helical ordering. When the magnetic field was applied perpendicular to its c axis, electric polarization was observed and the incommensurate ordering was replaced by a commensurate one as commonly observed in other hexaferrites. Electric polarization remained at its maximum during field reversal at 10 K, which indicates that magnetic anisotropy within the basal planes stabilizes the field-induced electric polarization.
Title:
In search of natural quasicrystals
Authors:
Steinhardt, PJ; Bindi, L Author Full Names: Steinhardt, Paul J.; Bindi, Luca
Source:
REPORTS ON PROGRESS IN PHYSICS, 75 (9):10.1088/0034-4885/75/9/092601 SEP 2012
Abstract:
The concept of quasicrystals was first introduced twenty-eight years ago and, since then, over a hundred types have been discovered in the laboratory under precisely controlled physical conditions designed to avoid crystallization. Yet the original theory suggested that quasicrystals can potentially be as robust and stable as crystals, perhaps even forming naturally. These considerations motivated a decade-long search for a natural quasicrystal culminating in the discovery of icosahedrite (Al63Cu24Fe13), an icosahedral quasicrystal found in a rock sample composed mainly of khatyrkite (crystalline (Cu,Zn)Al-2) labeled as coming from the Koryak Mountains of far eastern Russia. In this paper, we review the search and discovery, the analysis showing the sample to be of extraterrestrial origin and the initial results of an extraordinary geological expedition to the Koryak Mountains to seek further evidence.
Title:
Beats in the Magnetic Modulation of Multiferroic CaMn7O12
Authors:
Slawinski, W; Przenioslo, R; Sosnowska, I; Chrobak, A Author Full Names: Slawinski, Wojciech; Przenioslo, Radoslaw; Sosnowska, Izabela; Chrobak, Artur
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 81 (9):10.1143/JPSJ.81.094708 SEP 2012
Abstract:
The modulated magnetic ordering and the atomic position modulation are studied in the case of the multiferroic CaCuxMn7-xO12 by neutron and SR powder diffraction methods. Below the magnetic transition temperature of T-N2 = 50 K both orderings are described by using the magnetic superspace group R31'(00 gamma)ts. For the magnetic ordering two different incommensurate modulation vectors are used: (0, 0, q(m)(1)) and (0, 0, q(m)(2)). For the atomic position modulation only one modulation vector is needed (0, 0, q(p)). The magnetic ordering is of helical screw-type showing beats in the magnetic moment spatial distribution. The values of q(m)(1) and q(m)(2) change with temperature below T-N2 = 50 K but the average value fulfil the relation (1/2)(q(m)(1) + q(m)(2)) = (1/2)q(p) = const: This relation underlines the importance of the magnetoelastic coupling in CaCuxMn7-xO12 compounds below T-N2 = 50 K.
Title:
Uniaxial-Pressure Control of Magnetic Phase Transitions in a Frustrated Magnet CuFe1-xGaxO2 (x=0, 0.018)
Authors:
Nakajima, T; Mitsuda, S; Takahashi, K; Yoshitomi, K; Masuda, K; Kaneko, C; Honma, Y; Kobayashi, S; Kitazawa, H; Kosaka, M; Aso, N; Uwatoko, Y; Terada, N; Wakimoto, S; Takeda, M; Kakurai, K Author Full Names: Nakajima, Taro; Mitsuda, Setsuo; Takahashi, Keiichiro; Yoshitomi, Keisuke; Masuda, Kazuya; Kaneko, Chikafumi; Honma, Yuki; Kobayashi, Satoru; Kitazawa, Hideaki; Kosaka, Masashi; Aso, Naofumi; Uwatoko, Yoshiya; Terada, Noriki; Wakimoto, Shuichi; Takeda, Masayasu; Kakurai, Kazuhisa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 81 (9):10.1143/JPSJ.81.094710 SEP 2012
Abstract:
We have investigated effects of applied uniaxial pressure (p) on magnetic phase transitions in a triangular lattice antiferromagnet CuFeO2 (CFO) and a slightly Ga-substituted compound CuFe1-xGaxO2 (CFGO) with x = 0.018. We have performed neutron diffraction, spherical neutron polarimetry, magnetic susceptibility and pyroelectric measurements under p up to 100 MPa applied on the [1 (1) over bar0] surfaces of the single crystal samples. As a result, we have revealed that in both of CFO and CFGO (x = 0.018), the application of p significantly increases the transition temperature from the paramagnetic phase to a collinear incommensurate antiferromagnetic phase, at which these systems exhibit a crystal structural distortion associated with the magnetic ordering. This suggests that the application of p beaks equilateral symmetry of the triangular lattice above the original transition temperature, and partially relieves geometrical spin frustration, which generally suppresses long-range magnetic orderings even at low temperatures. In CFGO (x = 0.018), we have also found that the ferroelectric helimagnetic phase, which originally shows up as an intermediate phase in zero pressure, partly remains down to low temperatures under applied p. These results have demonstrated that uniaxial pressure can be an effective tool to control magnetic phase transitions in frustrated magnets.
Title:
Doping Effect on Interlocked Ferroelectric and Structural Antiphase Domains in YMnO3
Authors:
Kobayashi, K; Koyama, T; Kamo, H; Togawa, Y; Horibe, Y; Cheong, SW; Mori, S Author Full Names: Kobayashi, Keisuke; Koyama, Tsukasa; Kamo, Hideki; Togawa, Yoshihiko; Horibe, Yoichi; Cheong, Sang Wook; Mori, Shigeo
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS, 51 (9):SI 10.1143/JJAP.51.09LE09 Part 2 SEP 2012
Abstract:
Changes in ferroelectric and structural antiphase domain structure by the partial substitution of nonmagnetic Ti4+ ions at the Mn site were investigated carefully by electron diffraction, dark-field imaging, and high-resolution lattice imaging experiments. The ferroelectric and structural antiphase domains are revealed to be mutually interlocked in YMnO3 and, on the other hand, when x was increased up to x similar to 0.30 in YMn1-xTixO3, the ferroelectric domains disappeared and the size of the structural antiphase domains decreased to approximately 10nm at x similar to 0.30. High-resolution lattice images clearly demonstrate the coexisting state of nanodomains characterized by the modulated structure due to the structural trimerization and the nonmodulated structures. Our experimental results suggest that a partial substitution of Ti4+ ions suppressed the ferroelectric displacement along the [001] direction and the correlation length of the Mn3+ trimerization decreased. (c) 2012 The Japan Society of Applied Physics
Title:
The Formation of Quasicrystal Phase in Al-Cu-Fe System By Mechanical Alloying
Authors:
Travessa, DN; Cardoso, KR; Wolf, W; Jorge, AM; Botta, WJ Author Full Names: Travessa, Dilermando Nagle; Cardoso, Katia Regina; Wolf, Witor; Jorge, Alberto Moreira, Jr.; Botta, Walter Jose
Source:
MATERIALS RESEARCH-IBERO-AMERICAN JOURNAL OF MATERIALS, 15 (5):749-752; 10.1590/S1516-14392012005000046 SEP-OCT 2012
Abstract:
In order to obtain quasicrystalline (QC) phase by mechanical alloying (MA) in the Al-Cu-Fe system, mixtures of elementary Al, Cu and Fe in the proportion of 65-20-15 (at. %) were produced by high energy ball milling (HEBM). A very high energy type mill (spex) and short milling times (up to 5 hours) were employed. The resulting powders were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). QC phase was not directly formed by milling under the conditions employed in this work. However, phase transformations identified by DSC analysis reveals that annealing after HEBM possibly results in the formation of the psi QC phase.
Title:
Modulated structure and molecular dissociation of solid chlorine at high pressures
Authors:
Li, PF; Gao, GY; Ma, YM Author Full Names: Li, Peifang; Gao, Guoying; Ma, Yanming
Source:
JOURNAL OF CHEMICAL PHYSICS, 137 (6):10.1063/1.4742152 AUG 14 2012
Abstract:
Among diatomic molecular halogen solids, high pressure structures of solid chlorine (Cl-2) remain elusive and least studied. We here report first-principles structural search on solid Cl-2 at high pressures through our developed particle-swarm optimization algorithm. We successfully reproduced the known molecular Cmca phase (phase I) at low pressure and found that it remains stable up to a high pressure 142 GPa. At 150 GPa, our structural searches identified several energetically competitive, structurally similar, and modulated structures. Analysis of the structural results and their similarity with those in solid Br-2 and I-2, it was suggested that solid Cl-2 adopts an incommensurate modulated structure with a modulation wave close to 2/7 in a narrow pressure range 142-157 GPa. Eventually, our simulations at >157 GPa were able to predict the molecular dissociation of solid Cl-2 into monatomic phases having body centered orthorhombic (bco) and face-centered cubic (fcc) structures, respectively. One unique monatomic structural feature of solid Cl-2 is the absence of intermediate body centered tetragonal (bct) structure during the bco -> fcc transition, which however has been observed or theoretically predicted in solid Br-2 and I-2. Electron-phonon coupling calculations revealed that solid Cl-2 becomes superconductors within bco and fcc phases possessing a highest superconducting temperature of 13.03 K at 380 GPa. We further probed the molecular Cmca -> incommensurate phase transition mechanism and found that the softening of the A(g) vibrational (rotational) Raman mode in the Cmca phase might be the driving force to initiate the transition. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4742152]
Title:
Magnetic Properties of Hydrogen-Included TiZrNiPd Quasicrystals
Authors:
Shin, H; Lee, SH; Jo, Y; Kim, JY Author Full Names: Shin, Hongsik; Lee, Sang-Hwa; Jo, Youngsoo; Kim, Jae-Yong
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 12 (7):6085-6088; 10.1166/jnn.2012.6318 JUL 2012
Abstract:
Quasicrystals prepared by rapid quenching of Pd-added TiZrNi ingots were hydrogenated, and effects of hydrogen for magnetic properties were compared with the unhydrogenated ones under magnetic fields from -10000 to 10000 Oe. The magnetization values obtained from vibrating sample magnetometer (VSM) were analyzed with the combination of powder X-ray diffraction (XRD) data. While its contribution is larger than that of Pd, hydrogen decreases the magnetic moments of both Pd-doped and undoped quasicrystals. As increasing the amount of absorbed hydrogen which is represented by H/M (hydrogen to host metal atom ratio) values from 0 to 1.19, the magnetization values of Ti53Zr27Ni20 quasicrystals measured at 10000 Oe significantly decreased from 0.301 to 0.212 emu/g. A careful analysis of XRD data demonstrated that the reduced interactions of magnetic dipole moments between Ni atoms, as the product of the expansion of the quasilattice constants after hydrogenation, are responsible for the decreased magnetization values in hydrogenated TiZrNiPd quasicrystal samples.
Title:
Properties- and applications of quasicrystals and complex metallic alloys
Authors:
Dubois, JM Author Full Names: Dubois, Jean-Marie
Source:
CHEMICAL SOCIETY REVIEWS, 41 (20):6760-6777; 10.1039/c2cs35110b 2012
Abstract:
This article aims at an account of what is known about the potential for applications of quasicrystals and related compounds, the so-called family of Complex Metallic Alloys (CMAs double dagger). Attention is focused at aluminium-based CMAs, which comprise a large number of crystalline compounds and quasicrystals made of aluminium alloyed with transition metals (like Fe or Cu) or normal metals like Mg. Depending on composition, the structural complexity varies from a few atoms per unit cell up to thousands of atoms. Quasicrystals appear then as CMAs of ultimate complexity and exhibit a lattice that shows no periodicity anymore in the usual 3-dimensional space. Properties change dramatically with lattice complexity and turn the metal-type behaviour of simple Al-based crystals into a far more complex behaviour, with a fingerprint of semi-conductors that may be exploited in various applications, potential or realised. An account of the ones known to the author is given in the light of the relevant properties, namely light absorption, reduced adhesion and friction, heat insulation, reinforcement of composites for mechanical devices, and few more exotic ones. The role played by the search for applications of quasicrystals in the development of the field is briefly addressed in the concluding section.
Title:
Dislocations in icosahedral quasicrystals
Authors:
Feuerbacher, M Author Full Names: Feuerbacher, Michael
Source:
CHEMICAL SOCIETY REVIEWS, 41 (20):6745-6759; 10.1039/c2cs35150a 2012
Abstract:
Dislocations in quasicrystals, as a direct result of the lack of translational symmetry in these materials, possess various salient features. The Burgers vector of a dislocation in an icosahedral quasicrystal is a 6-dimensional vector, which reflects the fact that the dislocation, besides the phonon-type strain field analogous to dislocations in ordinary crystals, is associated inseparably with a further type of defect, the phasons. Phasons are critically involved in the formation and motion of dislocations in quasicrystals and govern the macroscopic plastic behaviour of these materials. In this article the properties of dislocations in icosahedral quasicrystals are comprehensively reviewed, starting from a continuum-mechanical description, via core-structure simulation, to their full experimental characterization. The experimental results presented address the icosahedral phases in the well explored systems Al-Pd-Mn and Zn-Mg-Dy.
Title:
Electron microscopy of quasicrystals - where are the atoms?
Authors:
Abe, E Author Full Names: Abe, Eiji
Source:
CHEMICAL SOCIETY REVIEWS, 41 (20):6787-6798; 10.1039/c2cs35303b 2012
Abstract:
Quasicrystals represent aperiodically ordered form of solids with symmetries long thought forbidden in nature. Since their discovery, the fundamental key question has been "where are the atoms?" in these novel aperiodic solids, and electron microscopy has indeed provided images of real atomic arrangements in quasicrystals. In this tutorial review, we describe the microscopic view of quasicrystals using state-of-the-art scanning transmission electron microscopy, providing intriguing details that had never been unveiled by the early diffraction-based structural analyses.
Title:
Fascinating quasicrystals
Authors:
Steurer, W Author Full Names: Steurer, Walter
Source:
CHEMICAL SOCIETY REVIEWS, 41 (20):6717-6718; 10.1039/c2cs90077g 2012
Title:
Electrical and thermal transport properties of icosahedral and decagonal quasicrystals
Authors:
Dolinsek, J Author Full Names: Dolinsek, Janez
Source:
CHEMICAL SOCIETY REVIEWS, 41 (20):6730-6744; 10.1039/c2cs35036j 2012
Abstract:
Electrical and thermal transport properties of quasicrystals are reviewed on the examples of i-Ag-In-Yb and i-Al-Cu-Fe icosahedral phases and d-Al-Co-Ni decagonal phase. Using samples of single-grain morphology and high structural quality, and performing the measurements along well-defined crystallographic directions, the following basic questions in the context of physical properties of quasicrystals are addressed, both experimentally and theoretically: (1) are the unusual transport properties of quasicrystals introduced by the quasiperiodicity of the structure or are they a consequence of complex local atomic order with no direct relationship to the quasiperiodicity; (2) what is the role of the electronic structure of quasicrystals in their electronic transport properties, especially the pseudogap in the electronic density of states in the vicinity of the Fermi energy; (3) what is the anisotropy of the transport coefficients along different crystallographic directions for icosahedral and decagonal quasicrystals and (4) what are the true intrinsic properties of quasicrystalline phases?
Title:
Mathematical diffraction of aperiodic structures
Authors:
Baake, M; Grimm, U Author Full Names: Baake, Michael; Grimm, Uwe
Source:
CHEMICAL SOCIETY REVIEWS, 41 (20):6821-6843; 10.1039/c2cs35120j 2012
Abstract:
Kinematic diffraction is well suited for a mathematical approach via measures, which has substantially been developed since the discovery of quasicrystals. The need for further insight emerged from the question of which distributions of matter, beyond perfect crystals, lead to pure point diffraction, hence to sharp Bragg peaks only. More recently, it has become apparent that one also has to study continuous diffraction in more detail, with a careful analysis of the different types of diffuse scattering involved. In this review, we summarise some key results, with particular emphasis on non-periodic structures. We choose an exposition on the basis of characteristic examples, while we refer to the existing literature for proofs and further details.
Title:
Comments on the Unsettled Problems Related to the Origin of the Incommensurate Phase of Quartz
Authors:
Shigenari, T; Abe, K; Yajima, M; Nagamine, M; Semagin, D; Aslanyan, TA; Dmitriev, SV Author Full Names: Shigenari, T.; Abe, K.; Yajima, M.; Nagamine, M.; Semagin, D.; Aslanyan, T. A.; Dmitriev, S. V.
Source:
FERROELECTRICS, 433 1-11; 10.1080/00150193.2012.678098 2012
Abstract:
It is shown that there are several experimental and theoretical results which are not compatible with the currently accepted model for the incommensurate (INC) phase of quartz. In this paper, we comment on the unsettled problems obtained from the light scattering spectra and computational simulations related to the new model for the INC phase.
Title:
Adhesion Tests Using Epoxy Quasicrystal Composites
Authors:
Altidis, JD; Lima, SJG; Gomes, RM; Sampaio, EM; Torres, SM; De Barros, S Author Full Names: Altidis, J. D.; Lima, S. J. G.; Gomes, R. M.; Sampaio, E. M.; Torres, S. M.; De Barros, S.
Source:
JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY, 26 (10-11):1443-1451; 10.1163/156856111X618317 2012
Abstract:
Quasicrystals (QC) are usually complex metal alloys with atypical structures. Due to their physical, mechanical and surface properties, quasicrystals have been widely studied. Although methods to manufacture quasicrystalline materials are well known, much effort has been expended in obtaining suitable quasicrystalline materials for use in industry. As quasicrystalline materials are very brittle, they are usually used in powder form as a reinforcement for additives in composites as well as in coating technology. In this work, Al-Cu-Fe quasicrystalline powder was used as a reinforcement in epoxy resin and the influence of the quasicrystal particles incorporation on the adhesive properties of the epoxy was investigated. Single lap joints (SLJ) adhesion tests were performed in order to assess the shear mode bond strength. Results show that the effect of QC reinforcement is not linear with respect to the adherence of the composites. (C) Koninklijke Brill NV, Leiden, 2012

Update: 17-Oct-2012

Title:
Magnetic order and spin-flop transitions in the cobalt-doped multiferroic Mn1-xCoxWO4
Authors:
Ye, F; Chi, SX; Fernandez-Baca, JA; Cao, HB; Liang, KC; Wang, YQ; Lorenz, B; Chu, CW Author Full Names: Ye, Feng; Chi, Songxue; Fernandez-Baca, Jaime A.; Cao, Huibo; Liang, K. -C.; Wang, Yaqi; Lorenz, Bernd; Chu, C. W.
Source:
PHYSICAL REVIEW B, 86 (9):10.1103/PhysRevB.86.094429 SEP 24 2012
Abstract:
We present a comprehensive single-crystal neutron diffraction investigation of the Mn1-xCoxWO4 with 0.02 <= x <= 0.30. At lower concentration x <= 0.05, the system is quickly driven into the multiferroic phase with spin structure forming an elliptical spiral order similar to the parent compound. The reduction of electric polarization is ascribed to the tilting of the spiral plane. For x similar to 0.075, the magnetic structure undergoes a spin-flop transition that is characterized by a sudden rotation of the spin helix envelope into the ac plane. This spin structure persists for concentration up to x = 0.15, where additional competing magnetic orders appear at low temperature. For 0.17 <= x <= 0.30, the system experiences another spin-flop transition and recovers the low-x spiral spin configuration. A simple commensurate spin structure with (q) over right arrow = (0.5,0,0) is found to coexist with the incommensurate spiral order. The complex evolution of magnetic structure in Co doped MnWO4 contrasts sharply with other transition metal ion doped Mn(1-x)A(x)WO(4) (A = Zn, Mg, Fe) where the chemical substitutions stabilize only one type of magnetic structure. The rich phase diagram of Mn1-xCoxWO4 results from the interplay between magnetic frustration and spin anisotropy of the Co ions.
Title:
Composition and local atomic arrangement of decagonal Al-Co-Cu quasicrystal surfaces
Authors:
Zenkyu, R; Yuhara, J; Matsui, T; Zaman, SS; Schmid, M; Varga, P Author Full Names: Zenkyu, R.; Yuhara, J.; Matsui, T.; Zaman, S. Shah; Schmid, M.; Varga, P.
Source:
PHYSICAL REVIEW B, 86 (11):10.1103/PhysRevB.86.115422 SEP 17 2012
Abstract:
We investigated the composition of decagonal Al-Co-Cu surface by Auger electron spectroscopy (AES) and low-energy ion scattering (LEIS). The surface composition after annealing was Al richer and Co poorer compared to that after sputtering or bulk composition. Two types of the characteristic clusters were observed by scanning tunneling microscopy (STM) and no bias voltage dependence of the image was observed. On the other hand, scanning tunneling spectroscopy revealed a subtle difference of local density of states in unoccupied states between different sites. Structural optimization using ab initio calculations based on density functional theory (DFT) was performed on several compositional models, which are based on the W-(AlCoNi) bulk model. The surface structures of two types of the characteristic clusters were determined by comparison of the STM image and the simulated image of the structures obtained by DFT. The topmost layer was composed of Al and Cu atoms, and the compositional ratio was consistent with the AES and LEIS results.
Title:
Magnetic and Neutron Diffraction Studies of the Polycrystalline and Nanoparticle TbMnO3
Authors:
Bazela, W; Dul, M; Dyakonov, V; Gondek, L; Hoser, A; Hoffmann, JU; Penc, B; Szytula, A; Kravchenko, Z; Nosalev, I; Zarzycki, A Author Full Names: Bazela, W.; Dul, M.; Dyakonov, V.; Gondek, L.; Hoser, A.; Hoffmann, J. -U.; Penc, B.; Szytula, A.; Kravchenko, Z.; Nosalev, I.; Zarzycki, A.
Source:
ACTA PHYSICA POLONICA A, 122 (2):384-390; AUG 2012
Abstract:
This paper reports on investigations of magnetic properties, crystal and magnetic structures on TbMnO3 prepared in various ways, namely, as conventional polycrystalline sample and two nano particle specimens (synthesized with a sol gel method at temperatures of 800 and 850 degrees C). The X-ray and neutron diffraction data confirm the orthorhombic crystal structure (space group Pbnm, No. 62) without noticeable differences of the lattice parameters for poly- and nanocompounds. For the polycrystalline sample, a subsequent ordering of the Mn and Tb sublattices with decreasing temperature was observed. Namely, the Mn sublattice exhibits a modulated magnetic structure with the propagation vector k = (0, k(x), 0) in between 41-5 K. Below T = 21 K, a change from a collinear (A(y) mode) into non-collinear (A(y)G(z) mode) structure was evidenced. Further decreasing of temperature below 10 K results in magnetic ordering of the Tb sublattice (modulated G(x)A(y)F(z) mode). For nanoparticle compounds, magnetic ordering in the Mn and Tb sublattices is described by propagation vector k = (0, k(y), 0), with k(y) components higher than observed for polycrystalline sample. The magnetic ordering in the Mn sublattice is described by a collinear A(y) mode down to 1.6 K where the Tb moment becomes ordered (G(x)A(y) mode). The observed broadening of the Bragg peaks connected to the Tb sublattice suggests the cluster-like character of its magnetic structure.

Update: 10-Oct-2012

Title:
Magnetic structure of the Sm5Ge4-type Tb2Ti3Ge4
Authors:
Morozkin, AV; Nirmala, R; Malik, SK; Isnard, O Author Full Names: Morozkin, A. V.; Nirmala, R.; Malik, S. K.; Isnard, O.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 324 (23):4030-4033; 10.1016/j.jmmm.2012.07.009 NOV 2012
Abstract:
The orthorhombic Sm5Ge4-type Tb2Ti3Ge4 shows square modulated non-collinear magnetic ordering with wave vector K=[+/- 1/3, 1/2, 1/2] at 2 K. The terbium magnetic moments lie in the bc plane and magnetic moment value of 7.5(2) mu(B)/Tb is obtained at 2 K. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Oxygen displacements and magnetoelectric coupling in LuMnO3
Authors:
Tong, P; Louca, D; Lee, N; Cheong, SW Author Full Names: Tong, P.; Louca, Despina; Lee, Nara; Cheong, S. -W.
Source:
PHYSICAL REVIEW B, 86 (9):10.1103/PhysRevB.86.094419 SEP 14 2012
Abstract:
The hexagonal multiferroic LuMnO3 transforms to the P6(3)cm symmetry upon entering the ferroelectric phase. Using neutron diffraction and the pair density function analysis, it is shown that short-range local atomic distortions are present, calling for a lower symmetry, such as the P6(3), for the following reasons. With cooling, the MnO5 bipyramid tilting becomes more enhanced than previously determined. This splits the in-plane Mn-O-Mn angles especially below T-N, leading to inequivalent magnetic coupling constants J between the in-plane Mn ions. Additionally, below T-N, several weak incommensurate magnetic phases appear in response to the reminiscent frustration from the triangular Mn lattice. The complex magnetic structure may be the driving mechanism for the lower crystal symmetry.
Title:
Impact of dynamic orbital correlations on magnetic excitations in the normal state of iron-based superconductors
Authors:
Lee, WC; Lv, WC; Tranquada, JM; Phillips, PW Author Full Names: Lee, Wei-Cheng; Lv, Weicheng; Tranquada, J. M.; Phillips, Philip W.
Source:
PHYSICAL REVIEW B, 86 (9):10.1103/PhysRevB.86.094516 SEP 14 2012
Abstract:
We show here that orbital degrees of freedom produce a distinct signature in the magnetic excitation spectrum of iron-based superconductors above the magnetic ordering temperature. Because d(xz) and d(yz) orbitals are strongly connected with Fermi surface topology, the nature of magnetic excitations can be modified significantly due to the presence of either static or fluctuating orbital correlations. Within a five-orbital itinerant model, we show that static orbital order generally leads to an enhancement of commensurate magnetic excitations even when the original Fermi surface lacks nesting at (pi,0) or (0,pi). When long-range orbital order is absent, Gaussian fluctuations beyond the standard random-phase approximation capture the effects of fluctuating orbital correlations on the magnetic excitations. We find that commensurate magnetic excitations can also be enhanced if the orbital correlations are strong. Our results offer a natural explanation for the incommensurate-to-commensurate transformation observed in a recent neutron scattering measurement (Xu et al., arXiv:1201.4404), and we propose that this unusual transformation is an important signature to distinguish orbital from spin physics in the normal state of pnictides. Implications for the magnetic and superconducting states are discussed.
Title:
Effects of Al substitution on the multiferroic properties of TbMnO3
Authors:
Cuartero, V; Blasco, J; Rodriguez-Velaman, JA; Garcia, J; Subias, G; Ritter, C; Stankiewicz, J; Canadillas-Delgado, L Author Full Names: Cuartero, Vera; Blasco, Javier; Alberto Rodriguez-Velaman, J.; Garcia, Joaquin; Subias, Gloria; Ritter, Clemens; Stankiewicz, Jolanta; Canadillas-Delgado, Laura
Source:
PHYSICAL REVIEW B, 86 (10):10.1103/PhysRevB.86.104413 SEP 10 2012
Abstract:
The effect of a small substitution of Mn with Al in TbMnO3 has been studied. We report results of heat capacity, magnetization, and dielectric constant studies in TbMn1-xAlxO3 compounds (x <= 0.1). Al has the same valence as substituted Mn but is nonmagnetic and its small size gives rise to microstructural strain which affects the multiferroic properties of the parent compound. Long-range antiferromagnetic ordering is observed in all compounds but the transition temperature decreases as the Al content increases. TbMn0.95Al0.05O3 exhibits a ferroelectric phase transition which is absent in TbMn0.9Al0.1O3. The dielectric constant of the latter compound reveals a relaxor behavior suggesting the presence of nanosize polar domains for this compound. A neutron diffraction study on a single crystal of TbMn0.9Al0.1O3 reveals that Mn shows a sinusoidal incommensurate ordering down to low temperature. Tb moments exhibit an incommensurate short-range ordering but the application of a magnetic field leads to metamagnetic transitions. In particular, a field parallel to the b axis induces a commensurate long-range ordering of Tb of type CxFy. The magnetic field also affects the magnetic structure of Mn3+ moments at low temperature which develop an incommensurate cycloid ordering in the ab plane. This result suggests that dilution of a magnetic multiferroic with a small nonmagnetic atom might yield materials with a relaxor to ferroelectric transition driven by a magnetic field.
Title:
MESOPOROUS SILICA Holey quasicrystals
Authors:
Tolbert, SH Author Full Names: Tolbert, Sarah H.
Source:
NATURE MATERIALS, 11 (9):749-751; 10.1038/nmat3414 SEP 2012

Update: 3-Oct-2012

Title:
Determining the magnetic ground state of TbNi5 single crystal using polarized neutron scattering technique
Authors:
Pirogov, AN; Bogdanov, SG; Lee, S; Park, JG; Choi, YN; Lee, H; Grigorev, SV; Sikolenko, VV; Sherstobitova, EA; Schedler, R Author Full Names: Pirogov, A. N.; Bogdanov, S. G.; Lee, Seongsu; Park, Je-Geun; Choi, Y. -N.; Lee, H.; Grigorev, S. V.; Sikolenko, V. V.; Sherstobitova, E. A.; Schedler, R.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 324 (22):3811-3816; 10.1016/j.jmmm.2012.06.019 NOV 2012
Abstract:
The TbNi5 compound shows an interesting magnetic phase transition with an incommensurate structure below 23 K, whose true nature remains unresolved. In order to solve this question, we have carried out polarized neutron diffraction experiments by measuring temperature and field dependence of the intensities of satellites and Bragg reflections. From the temperature dependence of both satellite peaks and Bragg reflection, we demonstrated that it has only one magnetic structure at a given temperature. Furthermore, unlike previous reports, we found that both ferromagnetic and modulated components of the Tb ion magnetic moments should be collinear to each other. Our data also show strong depolarisation effects that are most likely to arise from domain structure of ferromagnetic component. A critical field, which destroyers a modulated magnetic structure is found to be lower than a field value to saturate the ferromagnetic component, in which the intensity of Bragg ferromagnetic r! eflections reaches saturation. (C) 2012 Elsevier By. All rights reserved.
Title:
Intermediate-valence icosahedral Au-Al-Yb quasicrystal
Authors:
Watanuki, T; Kashimoto, S; Kawana, D; Yamazaki, T; Machida, A; Tanaka, Y; Sato, TJ Author Full Names: Watanuki, Tetsu; Kashimoto, Shiro; Kawana, Daichi; Yamazaki, Teruo; Machida, Akihiko; Tanaka, Yukinori; Sato, Taku J.
Source:
PHYSICAL REVIEW B, 86 (9):10.1103/PhysRevB.86.094201 SEP 10 2012
Abstract:
A quasiperiodic intermediate-valence (IV) system is realized in an icosahedral Au-Al-Yb quasicrystal. X-ray absorption spectroscopy near the Yb L-3 edge indicates that quasiperiodically arranged Yb ions assume a mean valence of 2.61, between a divalent state (4f(14), J = 0) and a trivalent one (4f(13), J = 7/2). Magnetization measurements demonstrate that the 4f holes in this quasicrystal have a localized character. The magnetic susceptibility shows a Curie-Weiss behavior above similar to 100 K with an effective magnetic moment of 3.81 mu(B) per Yb. Moreover, a crystalline approximant to this quasicrystal is an IV compound. We propose a heterogeneous IV model for the quasicrystal, whereas the crystalline approximant is most likely a homogeneous IV system. At temperatures below similar to 10 K, specific heat and magnetization measurements reveal non-Fermi-liquid behavior in both the quasicrystal and its crystalline approximant without either doping, pressure, or field tuning.
Title:
Spin density wave and superconductivity in CaFe1-xCoxAsF studied by nuclear magnetic resonance
Authors:
Tsutsumi, S; Fujiwara, N; Matsuishi, S; Hosono, H Author Full Names: Tsutsumi, S.; Fujiwara, N.; Matsuishi, S.; Hosono, H.
Source:
PHYSICAL REVIEW B, 86 (6):10.1103/PhysRevB.86.060515 AUG 29 2012
Abstract:
We performed nuclear magnetic resonance measurements to investigate the evolution of spin-density-wave (SDW) and superconducting (SC) states upon electron doping in CaFe1-xCoxAsF, which exhibits an intermediate phase diagram between those of LaFeAsO1-xFx and Ba(Fe1-xCox)(2)As-2. We found that homogeneous coexistence of the incommensurate SDW and SC states occurs only in a narrow doping region around the crossover regime, which supports S+--wave symmetry. However, only the structural phase transition survives upon further doping, which agrees with predictions from orbital fluctuation theory. The transitional features upon electron doping imply that both spin and orbital fluctuations are involved in the superconducting mechanism.
Title:
Europium-IV: An Incommensurately Modulated Crystal Structure in the Lanthanides
Authors:
Husband, RJ; Loa, I; Stinton, GW; Evans, SR; Ackland, GJ; McMahon, MI Author Full Names: Husband, R. J.; Loa, I.; Stinton, G. W.; Evans, S. R.; Ackland, G. J.; McMahon, M. I.
Source:
PHYSICAL REVIEW LETTERS, 109 (9):10.1103/PhysRevLett.109.095503 AUG 27 2012
Abstract:
High-resolution x-ray powder-diffraction experiments were performed on europium metal at high pressure up to 50 GPa. At variance with previous reports, the hcp phase of Eu was observed to be stable not only to 18 GPa, but to 31.5 GPa. At 31.5(5) GPa, europium transforms to a phase (Eu-IV) with an incommensurately modulated monoclinic crystal structure with superspace group C2/c(q(1)0q(3))00. This new phase was observed to be stable to similar to 37.0 GPa, where another phase transition was observed. Eu-IV is the first phase in the lanthanide elements with an incommensurate crystal structure.
Title:
Micrometer-sized quasicrystals in the Al85Ni5Y6Co2Fe2 metallic glass: A TEM study and a brief discussion on the formability of quasicrystals in bulk and marginal glass-forming alloys
Authors:
Yan, M; Wang, JQ; Kong, C; Schaffer, GB; Qian, M Author Full Names: Yan, M.; Wang, J. Q.; Kong, C.; Schaffer, G. B.; Qian, M.
Source:
JOURNAL OF MATERIALS RESEARCH, 27 (16):2131-2139; 10.1557/jmr.2012.140 AUG 2012
Abstract:
Large quasicrystals up to similar to 10 mu m in size with a volume fraction of similar to 30% have been identified in a nitrogen gas-atomized marginal glass-forming alloy Al85Ni5Y6Co2Fe2 by detailed transmission electron microscopy. The formation of the large quasicrystal (Q) phase is discussed through the configuration of the valence electrons of its constituent elements, and the thermodynamic and kinetic factors associated with the solidification of this marginal glass-forming alloy during gas atomization. The finding leads to an important inference that marginal glass-forming alloys could be ideal systems for the formation of bulk quasicrystals under appropriate kinetic conditions. The Q phase is stable up to similar to 500 degrees C and decomposes thereafter. The activation energy for the decomposition of the Q phase is similar to the self-diffusion of Al. Two new intermetallic phases associated with the formation and decomposition of the Q phase have also been identified and characterized.

Update: 26-Sep-2012

Title:
X-ray diffraction study on the microstructure of a Mg-Zn-Y alloy consolidated by high-pressure torsion
Authors:
Jenei, P; Gubicza, J; Yoon, EY; Kim, HS Author Full Names: Jenei, Peter; Gubicza, Jeno; Yoon, Eun Yoo; Kim, Hyoung Seop
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 539 32-35; 10.1016/j.jallcom.2012.05.100 OCT 25 2012
Abstract:
Mg95Zn4.3Y0.7 (at.%) alloy powder produced by an inert gas-atomizer was consolidated by high-pressure torsion (HPT) at room temperature and 373 K. The phase composition and the microstructure were investigated by X-ray diffraction and the microstructural parameters were correlated to the yield strength. HPT-processing yielded an ultrafine-grained microstructure with high dislocation density, leading to a large yield strength of the samples. Both the gas-atomized powder and the consolidated samples contained an icosahedral Mg3YZn6 phase (I-phase) besides the main phase of alpha-Mg. It turned out that the I-phase dispersoids strengthen the consolidated material indirectly by increasing the dislocation density due to their pinning effect. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Epitaxial Bi allotropes on quasicrystal surfaces as templates for adsorption of pentacene and fullerene
Authors:
Sharma, HR; Smerdon, JA; Young, KM; McGrath, R Author Full Names: Sharma, H. R.; Smerdon, J. A.; Young, K. M.; McGrath, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (35):10.1088/0953-8984/24/35/354012 SEP 5 2012
Abstract:
The growth of Bi on surfaces of Al-based quasicrystals yields a quasicrystalline monolayer which is followed by the formation of crystalline islands of various forms depending on coverage, deposition flux and substrate temperature. We have used the Bi thin films consisting of both crystalline and quasicrystalline allotropes as substrates to study the deposition of C-60 and pentacene molecules. Scanning tunneling microscopy (STM) reveals substrate-dependent differences in molecular adsorption.
Title:
Crystallization and compressive behaviors of Ti40Zr25Ni8Cu9Be18 BMG cast from different liquid states
Authors:
Zhou, X; Kou, HC; Wang, J; Li, JS; Zhou, L Author Full Names: Zhou, Xun; Kou, Hongchao; Wang, Jun; Li, Jinshan; Zhou, Lian
Source:
INTERMETALLICS, 28 45-50; 10.1016/j.intermet.2012.03.061 SEP 2012
Abstract:
The initial microstructure of Ti40Zr25Ni8Cu9Be18 metallic glass is sensitive to preparation condition. The Ti40Zr25Ni8Cu9Be18 metallic glasses, prepared at different liquid temperature by copper mold casting, would possess different first crystallization product because of difference in initial microstructure. During first crystallization, Crystallization product is mainly metastable icosahedral phase for metallic glass prepared at relative low liquid temperature. However, the mixture of alpha-Ti + icosahedral + unknown phase precipitates from metallic glass prepared at relative high liquid temperature. Moreover, the difference in initial microstructure also has a significant influence on compressive properties. Ti40Zr25Ni8Cu9Be18 metallic glasses prepared at relative low temperature exhibit better plasticity. One of important reasons is that dominant icosahedral short range order (SRO) increases shear viscosity of shear band, and the possibility of catastrophic failure caused by fast and continuous slide of shear band is depressed. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.

Update: 20-Sep-2012

Title:
Magnetic dilution and steric effects in the multiferroic delafossite CuCrO2
Authors:
Pachoud, E; Singh, K; Breard, Y; Martin, C; Andre, G; Hardy, V; Simon, C; Maignan, A Author Full Names: Pachoud, E.; Singh, K.; Breard, Y.; Martin, C.; Andre, G.; Hardy, V.; Simon, Ch.; Maignan, A.
Source:
PHYSICAL REVIEW B, 86 (5):10.1103/PhysRevB.86.054437 AUG 21 2012
Abstract:
In order to get to the bottom of substitution effects reported in CuCrO2 delafossite, structural, magnetic, and electric properties of several CuCr1-xMxO2 series, where M3+ is a S = 0 cation (M3+ = Al3+, Ga3+, Sc3+, Rh3+), have been investigated. It is shown that the homogeneity of the substitution is element dependent and is particularly difficult to achieve for the smallest Al3+ cation. Ferroelectricity and dielectric properties are found to depend on the x value, but also on the nature of M: The largest substitution effects are observed for the larger elements, owing to the decrease of the Cr3+-Cr3+ interaction resulting from the enlargement of the in-plane lattice parameter. However, the magnetic structures of CuCr0.9Ga0.1O2 and CuCr0.9Rh0.1O2, revealed close to that of CuCrO2 by neutron diffraction, demonstrate the great stability of this antiferromagnetic incommensurate structure against the presence of {M3+, S = 0} cations. This emphasizes the very different nature of the magnetic ground state of CuCrO2, as compared to CuFeO2, despite their common structural characteristics.
Title:
Magnetoelectric properties in orthorhombic Nd1-xYxMnO3: Neutron diffraction experiments
Authors:
Landsgesell, S; Prokes, K; Ouladdiaf, B; Klemke, B; Prokhnenko, O; Hepp, B; Kiefer, K; Argyriou, DN Author Full Names: Landsgesell, S.; Prokes, K.; Ouladdiaf, B.; Klemke, B.; Prokhnenko, O.; Hepp, B.; Kiefer, K.; Argyriou, D. N.
Source:
PHYSICAL REVIEW B, 86 (5):10.1103/PhysRevB.86.054429 AUG 20 2012
Abstract:
In this paper we investigate the complex transformation of the magnetoelectric properties from the collinear A-type phase to the multiferroic noncollinear spin cycloid in the solid solution Nd1-xYxMnO3 from compositions of x = 0.3 to 0.55 in single crystal samples. Neutron diffraction experiments at the structural phase transition (x = 0.35 to 0.45) reveal the coexistence of the A-type order and several incommensurate orders, varying with composition and temperature.
Title:
Magnetic and electronic orderings in orthorhombic RMnO3 (R = Tm, Lu) studied by resonant soft x-ray powder diffraction
Authors:
Garganourakis, M; Bodenthin, Y; de Souza, RA; Scagnoli, V; Donni, A; Tachibana, M; Kitazawa, H; Takayama-Muromachi, E; Staub, U Author Full Names: Garganourakis, M.; Bodenthin, Y.; de Souza, R. A.; Scagnoli, V.; Doenni, A.; Tachibana, M.; Kitazawa, H.; Takayama-Muromachi, E.; Staub, U.
Source:
PHYSICAL REVIEW B, 86 (5):10.1103/PhysRevB.86.054425 AUG 17 2012
Abstract:
Resonant soft x-ray powder diffraction experiments on orthorhombic TmMnO3 and LuMnO3 are presented. Experiments were performed in the vicinity of the Tm M-5 and the Mn L-2,L-3 edges to study the Tm and Mn magnetic moments, respectively. These experiments show that for the heavy rare-earth perovskite with an E-type ordered ground state, the Tm magnetic moments order already in the nonferroelectric incommensurate magnetic phase. Additionally, deviations from the collinear E-type Mn magnetic structure at low temperatures are found for both compounds. These experiments show the power of resonant soft x-ray diffraction, extended to polycrystalline 4f materials.
Title:
Antiferrodistortive phase transition in EuTiO3
Authors:
Goian, V; Kamba, S; Pacherova, O; Drahokoupil, J; Palatinus, L; Dusek, M; Rohlicek, J; Savinov, M; Laufek, F; Schranz, W; Fuith, A; Kachlik, M; Maca, K; Shkabko, A; Sagarna, L; Weidenkaff, A; Belik, AA Author Full Names: Goian, V.; Kamba, S.; Pacherova, O.; Drahokoupil, J.; Palatinus, L.; Dusek, M.; Rohlicek, J.; Savinov, M.; Laufek, F.; Schranz, W.; Fuith, A.; Kachlik, M.; Maca, K.; Shkabko, A.; Sagarna, L.; Weidenkaff, A.; Belik, A. A.
Source:
PHYSICAL REVIEW B, 86 (5):10.1103/PhysRevB.86.054112 AUG 17 2012
Abstract:
X-ray diffraction, dynamical mechanical analysis, and infrared reflectivity studies revealed an antiferrodistortive phase transition in EuTiO3 ceramics. Near 300 K, the perovskite structure changes from cubic Pm (3) over barm to tetragonal I4/mcm due to antiphase tilting of oxygen octahedra along the c axis (a(0)a(0)c(-) in Glazer notation). The phase transition is analogous to SrTiO3. However, some ceramics as well as single crystals of EuTiO3 show different infrared reflectivity spectra bringing evidence of a different crystal structure. In such samples, electron diffraction revealed an incommensurate tetragonal structure with modulation wave vector q similar or equal to 0.38 a*. Extra phonons in samples with modulated structure are activated in the IR spectra due to folding of the Brillouin zone. We propose that defects such as Eu3+ and oxygen vacancies strongly influence the temperature of the phase transition to antiferrodistortive phase as well as the tendency to incommensurate modulation in EuTiO3.
Title:
Multiple magnetic structures of correlated Ce ions in intermetallic CeAu2Ge2
Authors:
Singh, DK; Thamizhavel, A; Lynn, JW; Dhar, SK; Hermann, T Author Full Names: Singh, D. K.; Thamizhavel, A.; Lynn, J. W.; Dhar, S. K.; Hermann, T.
Source:
PHYSICAL REVIEW B, 86 (6):10.1103/PhysRevB.86.060405 AUG 13 2012
Abstract:
Neutron diffraction measurements on a high quality single crystal of CeAu2Ge2 reveal two magnetic structures that coexist with commensurate long-range antiferromagnetic order below the Neel temperature T-N similar or equal to 14 K. The magnetic structures, which exhibit distinct temperature and field dependencies, are described by both commensurate and incommensurate magnetic structures and introduce a new region in the H-T phase diagram. These experimental observations provide important information for developing a universal understanding of the magnetic properties of this class of Ce-based CeX2M2 (X = Cu, Ag, Au; M = Ge, Si) compounds, which are prototypes for exploring quantum phase transitions, and their interplay with unconventional superconductivity.
Title:
QUASICRYSTALS: Tile at random
Authors:
Klopper, A Author Full Names: Klopper, Abigail
Source:
NATURE PHYSICS, 8 (8):582-582; AUG 2012
Title:
Nanosize icosahedral quasicrystal in Mg90Ca10 glass: An ab initio molecular dynamics study
Authors:
Durandurdu, M Author Full Names: Durandurdu, Murat
Source:
JOURNAL OF CHEMICAL PHYSICS, 137 (3):10.1063/1.4736581 JUL 21 2012
Abstract:
Rapid solidification of Mg90Ca10 from its liquid state is studied by means of an ab initio molecular dynamics technique, and its local structure is investigated by various analyzing methods. The liquid and amorphous states are found to have slightly different short range order even though the perfect and defective icosahedral bonding environments are major bonding elements of both liquid and amorphous states. Perfect icosahedrons with a small frequency exist in the liquid state, more develop during the cooling process and they become the leading building units in the glass state, indicating an icosahedral short range order in Mg90Ca10 glass. Also the linked icosahedrons lead to an icosahedral medium range order. Furthermore, an ordered arrangement of some icosahedrons in the hexagonal symmetry is observed in the glass model, representing a nanoscale icosahedral quasicrystalline phase in Mg90Ca10 glass. (C) 2012 American Institute of Physics. [http://dx.do! i.org/10.1063/1.4736581]
Title:
THERMAL STABILITY OF Al-Mn-Be MELT-SPUN RIBBONS
Authors:
Lojen, G; Boncina, T; Zupanic, F Author Full Names: Lojen, Gorazd; Boncina, Tonica; Zupanic, Franc
Source:
MATERIALI IN TEHNOLOGIJE, 46 (4):329-333; JUL-AUG 2012
Abstract:
As with other kinds of finely dispersed, small particles, icosahedral quasicrystals (IQCs) also have a distinct strengthening effect, which can be utilised to enhance the mechanical properties of aluminium alloys. In Al-Mn-Be alloys, IQCs already form at moderate cooling rates, which can be utilised when using some conventional casting processes, like mould or injection casting. In this case, however, crystalline intermetallic phases are also present and the mechanical properties are inferior to those of two-phase alpha(Al)-IQC alloys. Two-phase microstructures are feasible using rapid solidification techniques, e.g., melt spinning. Further processing often involves technologies (consolidation, extrusion etc.), which include the influence of heat. The alloy must not be overheated in order to preserve the strengthening effect of the metastable IQC-particles. In this investigation the Al-Mn-Be alloy was melt-spun using a free-jet melt spinner. Subsequently, the thermal stability of the IQCs was explored by annealing the ribbons for 24 h at different temperatures. The samples were examined in the as-cast and heat-treated conditions using a dual-beam, scanning electron microscope (SEM-FIB). X-ray diffraction (XRD) and differential scanning calorimetry (DSC). It was discovered that in the as-cast condition, the ribbons had a two-phase microstructure, consisting of an alpha(Al) matrix and finely dispersed IQCs. During annealing at temperatures up to 400 degrees C, the IQCs did not decompose and the phase composition remained unchanged. Annealing at 500 degrees C and at higher temperatures caused a decomposition of the IQCs, and only the crystalline intennetallic phases Al6Mn and Be4AlMn could be found in the alpha(Al) matrix.

Update: 12-Sep-2012

Title:
Structural Modulation in the High Capacity Battery Cathode Material LiFeBO3
Authors:
Janssen, Y; Middlemiss, DS; Bo, SH; Grey, CP; Khalifah, PG Author Full Names: Janssen, Yuri; Middlemiss, Derek S.; Bo, Shou-Hang; Grey, Clare P.; Khalifah, Peter G.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 134 (30):12516-12527; 10.1021/ja301881c AUG 1 2012
Abstract:
The crystal structure of the promising Li-ion battery cathode material LiFeBO3 has been redetermined based on the results of single crystal X-ray diffraction data. A commensurate modulation that doubles the periodicity of the lattice in the a-axis direction is observed. When the structure of LiFeBO3 is refined in the 4-dimensional superspace group C2/c(alpha 0 gamma)00, with alpha = 1/2 and gamma = 0 and with lattice parameters of a = 5.1681 angstrom, b = 8.8687 angstrom, c = 10.1656 angstrom, and beta = 91.514 degrees, all of the disorder present in the prior C2/c structural model is eliminated and a long-range ordering of 1D chains of corner-shared LiO4 is revealed to occur as a result of cooperative displacements of Li and O atoms in the c-axis direction. Solid-state hybrid density functional theory calculations find that the modulation stabilizes the LiFeBO3 structure by 1.2 kJ/mol (12 meV/f.u.), and that the modulation disappears after delithiation to form a structurally related FeBO3 phase. The band gaps of LiFeBO3 and FeBO3 are calculated to be 3.5 and 3.3 eV, respectively. Bond valence sum maps have been used to identify and characterize the important Li conduction pathways, and suggest that the activation energies for Li diffusion will be higher in the modulated structure of LiFeBO3 than in its unmodulated analogue.
Title:
Spontaneous formation of filamentary Cd whiskers and degradation of CdMgYb icosahedral quasicrystal under ambient conditions
Authors:
Lu, L; Wang, JB; Zheng, H; Zhao, DS; Wang, RH; Gui, JN Author Full Names: Lu, Lu; Wang, Jianbo; Zheng, He; Zhao, Dongshan; Wang, Renhui; Gui, Jianian
Source:
JOURNAL OF MATERIALS RESEARCH, 27 (14):1895-1904; 10.1557/jmr.2012.136 JUL 2012
Abstract:
The whiskers spontaneously grown in Cd-Mg-Yb alloy containing icosahedral quasicrystal as dominant phase have been investigated by electron microscopy. It is found that: (i) the whiskers are mainly composed of Cd with growth direction along, <<(2)over bar>110>(Cd). CdO particles are frequently observed on surfaces of whiskers and the alloy, indicating the importance of the oxidation process during the whisker growth; (ii) there exist four types of orientation relationship between Cd and CdO. The interfaces between them are shown to accommodate large lattice misfit, which is well explained by near coincidence site lattice model; (iii) nanosized Cd particles are observed to aggregate around the whisker root, providing a convincing experimental evidence for the long-range atomic diffusion. Our study offers a unique opportunity to unveil the relationship between unstability of quasicrystal structure and whisker formation and may have some implications for oxidation process of me! tals.

Update: 5-Sep-2012

Title:
Incommensurate Modulated Structures in the Ta2O5-Al2O3 System
Authors:
Schmid, S; Fung, V Author Full Names: Schmid, Siegbert; Fung, Veronica
Source:
AUSTRALIAN JOURNAL OF CHEMISTRY, 65 (7):851-859; 10.1071/CH12080 2012
Abstract:
Members of the (1 - x)Ta2O5 center dot xAl(2)O(3) series were synthesized, and the structures investigated using synchrotron X-ray powder diffraction and neutron powder diffraction data for the first time. Structural models were developed and refined using the Rietveld method and a [3 + 1] dimensional incommensurately modulated composite structure approach with a composition dependent modulation vector q, and superspace group Xmmm(0 beta 0)s00. Displacive atomic modulation functions across the (1 - x)Ta(2)O(5 center dot)xAl(2)O(3) series were found to be very similar, and strongly resemble those for the Ta2O5-WO3 system, in line with the notion that there are structure types in higher dimensional space just as there are in 3D space. Bond valence sum calculations and bond distance plots showed that the introduction of the modulation to the structural model generally led to more favourable bond valence sum values and bond distances. Fourier difference plots were examined, and the occupational modulation of aluminium refined to determine that the aluminium atoms preferentially occupy the octahedral sites.

Update: 29-Aug-2012

Title:
Effect of microalloying on the formation and stability of the Ti-Zr-Ni icosahedral quasicrystal
Authors:
Lee, GW; Gangopadhyay, AK; Kelton, KF Author Full Names: Lee, G. W.; Gangopadhyay, A. K.; Kelton, K. F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 537 171-174; 10.1016/j.jallcom.2012.05.040 OCT 5 2012
Abstract:
The influence of small additions of Cu, Ag, Au, Pt, Pb, and Si on the formation and stabilization of Ti-Zr-Ni icosahedral quasicrystal (i-phase) are discussed. Among these elements, only the addition of Ag improved the stability and formability of the i-phase, significantly. A small amount of supercooling and the nucleation and growth of only the i-phase from the liquid during levitation melting experiments signal the presence of well developed extended icosahedral short range order (ISRO) in the liquid. These results are explained in terms of a better atomic size ratio of Ag to Zr to form ISRO. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Electrochemical properties of Ti-based Quasicrystal and ZrV2 Laves phase alloy composite materials as negative electrode for Ni-MH secondly batteries
Authors:
Liu, WQ; Liang, F; Zhang, SS; Lin, J; Wang, XL; Wang, LM Author Full Names: Liu, Wanqiang; Liang, Fei; Zhang, Shanshan; Lin, Jing; Wang, Xinlu; Wang, Limin
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 358 (15):1846-1849; 10.1016/j.jnoncrysol.2012.05.035 AUG 1 2012
Abstract:
The Ti1.4V0.6Ni alloy ribbon is prepared by arc melting and subsequent melt-spinning technique. The ZrV2 alloy is prepared by arc melting and annealing at 1250k for 80 h. The structure and electrochemical properties of the Ti1.4V0.6Ni and their ball-milled composites with annealed ZrV2 are investigated. Phase structure investigations of the composites show that alloys mainly consist of the icosahedral quasicrystal (I-phase), C14 Laves phase with a hexagonal structure, C15 Laves phase with cubic structure, V-based solid solution phase with BCC structure and face centered cubic (FCC) phase with Ti2Ni-type structure. The negative electrode made by composite alloys has a maximum discharge capacity of 360.3 mAh/g at a current density of 30 mA/g and a high rate discharge ability of 82.7% at 240 mA/g. The cyclic stability of the negative electrode made of Ti1.4V0.6Ni and annealed ZrV2 composite is higher than that of Ti1.4V0.6Ni. The mechanism for the capacity loss of the alloy electrodes during charge and discharge cycling has been studied in this paper. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Multiferroic FeTe2O5Br: Alternating spin chains with frustrated interchain interactions
Authors:
Pregelj, M; Jeschke, HO; Feldner, H; Valenti, R; Honecker, A; Saha-Dasgupta, T; Das, H; Yoshii, S; Morioka, T; Nojiri, H; Berger, H; Zorko, A; Zaharko, O; Arcon, D Author Full Names: Pregelj, M.; Jeschke, H. O.; Feldner, H.; Valenti, R.; Honecker, A.; Saha-Dasgupta, T.; Das, H.; Yoshii, S.; Morioka, T.; Nojiri, H.; Berger, H.; Zorko, A.; Zaharko, O.; Arcon, D.
Source:
PHYSICAL REVIEW B, 86 (5):10.1103/PhysRevB.86.054402 AUG 1 2012
Abstract:
A combination of density functional theory calculations, many-body model considerations, and magnetization and electron-spin-resonance measurements shows that the multiferroic FeTe2O5Br should be described as a system of alternating antiferromagnetic S = 5/2 chains with strong Fe-O-Te-O-Fe bridges weakly coupled by two-dimensional frustrated interactions, rather than the previously reported tetramer model. The peculiar temperature dependence of the incommensurate magnetic vector can be explained in terms of interchain exchange striction being responsible for the emergent net electric polarization.

Update: 22-Aug-2012

Title:
Growth of large-grain Ag-In-Yb icosahedral quasicrystals and approximant crystals
Authors:
Cui, C; Tsai, AP Author Full Names: Cui, Can; Tsai, An Pang
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 536 91-93; 10.1016/j.jallcom.2012.05.031 SEP 25 2012
Abstract:
Large-grain quasicrystals and approximant crystals are desirable for the physical properties and surface properties study. In this letter, we present a study on the growth of large-grain icosahedral quasicrystals and 2/1 and 1/1 approximant crystals of Ag-In-Yb alloy using a facile self-flux method in indium-rich melt-solution. The as-grown samples show facets along 5-, 3- and 2-fold planes in the quasicrystal sample, whereas the 1/1 approximant crystal exhibits facets along {1 0 0} and {1 1 0} planes and the 2/1 approximant crystal along the {1 1 1} planes. The facets are considered to be thermodynamically favorite planes in the above crystals and they offer valuable information for understanding the surface stability in icosahedral quasicrystals. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Unified (3+1)-dimensional superspace description of the 2212-type stair-like [Bi2Sr3Fe2O9](m)[Bi4Sr6Fe2O16] family of compounds
Authors:
Elcoro, L; Perez, O; Perez-Mato, JM; Petricek, V Author Full Names: Elcoro, Luis; Perez, Olivier; Perez-Mato, J. M.; Petricek, Vaclav
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 68 341-355; 10.1107/S0108768112018095 Part 4 AUG 2012
Abstract:
The (3 + 1)-dimensional superspace approach is applied to describe and refine a series of sheared compounds related to layered high T-c superconducting oxides. Two commensurate members (m = 4, 5) of the 2212 stair-like [Bi2Sr3Fe2O9](m)-[ Bi4Sr6Fe2O16] family of compounds, previously studied using single-crystal diffraction data, are analyzed. A common average unit cell has been identified and a composition-dependent modulation wavevector is proposed. The model is built using only three independent atomic domains, one for the metal atoms and two for the O atoms. The three Sr, Bi and Fe species are described using close-connected crenel-like functions forming a continuous atomic domain along the internal space. The two oxygen domains are represented by crenel functions and the displacive modulation functions are built up by Legendre polynomials recently implemented in the program JANA2006. Surprisingly, the results of the refinements show a striking similarity of the displacive modulations for the two compounds analyzed, indicating that a unique model can be used to describe the correlations between the atomic displacements of the 2212 stair-like series. This final model is then applied to predict the structure of new members of the family.
Title:
Solitonic lattice and Yukawa forces in the rare-earth orthoferrite TbFeO3
Authors:
Artyukhin, S; Mostovoy, M; Jensen, NP; Le, D; Prokes, K; de Paula, VG; Bordallo, HN; Maljuk, A; Landsgesell, S; Ryll, H; Klemke, B; Paeckel, S; Kiefer, K; Lefmann, K; Kuhn, LT; Argyriou, DN Author Full Names: Artyukhin, Sergey; Mostovoy, Maxim; Jensen, Niels Paduraru; Le, Duc; Prokes, Karel; de Paula, Vincius G.; Bordallo, Heloisa N.; Maljuk, Andrey; Landsgesell, Sven; Ryll, Hanjo; Klemke, Bastian; Paeckel, Sebastian; Kiefer, Klaus; Lefmann, Kim; Kuhn, Luise Theil; Argyriou, Dimitri N.
Source:
NATURE MATERIALS, 11 (8):694-699; 10.1038/NMAT3358 AUG 2012
Abstract:
The random fluctuations of spins give rise to many interesting physical phenomena, such as the 'order-from-disorder' arising in frustrated magnets and unconventional Cooper pairing in magnetic superconductors. Here we show that the exchange of spin waves between extended topological defects, such as domain walls, can result in novel magnetic states. We report the discovery of an unusual incommensurate phase in the orthoferrite TbFeO3 using neutron diffraction under an applied magnetic field. The magnetic modulation has a very long period of 340 angstrom at 3 K and exhibits an anomalously large number of higher-order harmonics. These domain walls are formed by Ising-like Tb spins. They interact by exchanging magnons propagating through the Fe magnetic sublattice. The resulting force between the domain walls has a rather long range that determines the period of the incommensurate state and is analogous to the pion-mediated Yukawa interaction between protons and neutrons in nuclei.
Title:
Structure refinement and superspace description of the system Bi2(n+2)MonO6(n+1) (n=3, 4, 5 and 6)
Authors:
Bereciartua, PJ; Zuniga, FJ; Perez-Mato, JM; Petricek, V; Vila, E; Castro, A; Rodriguez-Carvajal, J; Doyle, S Author Full Names: Bereciartua, P. J.; Zuniga, F. J.; Perez-Mato, J. M.; Petricek, V.; Vila, E.; Castro, A.; Rodriguez-Carvajal, J.; Doyle, S.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 68 323-340; 10.1107/S0108768112017478 Part 4 AUG 2012
Abstract:
The system Bi(2(n + 2))MonO(6(n + 1)) is described within the superspace formalism. Two superspace models are proposed for the different members of this family, depending on the parity of the parameter n. The superspace model for the odd members is constructed through the embedding of the cationic distribution of the member with n = 3, and the modification of a superspace model previously proposed for the compound Bi2MoO6. However, this model cannot be applied to the even members of the family. Performing the appropriate transformations, a suitable superspace model for the even members is obtained. The atomic structure of the different compounds of the family have been refined through the Rietveld method combining synchrotron X-ray and neutron powder diffraction data.
Title:
Effect of Cu on rapidly solidified Al-Mn-Be alloy
Authors:
Zupanic, F; Lojen, G; Barba, L; Boncina, T Author Full Names: Zupanic, F.; Lojen, G.; Barba, L.; Boncina, T.
Source:
MATERIALS CHARACTERIZATION, 70 48-54; 10.1016/j.matchar.2012.05.002 AUG 2012
Abstract:
The microstructure of an Al-Mn-Be-Cu alloy was characterised after melt spinning and heat-treatment at different temperatures. The optimised melt-spinning parameters made it possible to obtain ribbons with thicknesses ranging from 30 to 200 mu m, having a microstructure composed of a supersaturated Al-rich solid solution, finely dispersed icosahedral quasicrystalline (IQC) particles, and a small fraction of Al2Cu. The finest dispersion of the IQC-particles, and consequently the highest microhardness, was obtained on the wheel-side. The initial microstructure started to decompose at temperatures around 400 degrees C. The IQC-phase was replaced by the intermetallic compounds tau(1)-Al29Mn6Cu4 and Be4Al(Mn,Cu). The maximum hardness of the ribbons, which was approximately 50% higher than in the as-cast state, was attained after heat treatment at 400 degrees C, and could be attributed to the fine dispersion of tau(1)-Al29Mn6Cu4 and IQC-particles. (C) 2012 Elsevier Inc. All rights reserved.
Title:
[Ni(MeCN)(H2O)(2)(NO3)(2)]center dot(15-crown-5)center dot MeCN: detailed study of a four-phase sequence that includes an intermediate modulated phase
Authors:
Siegler, MA; Parkin, S; Brock, CP Author Full Names: Siegler, Maxime A.; Parkin, Sean; Brock, Carolyn Pratt
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 68 389-400; 10.1107/S0108768112018319 Part 4 AUG 2012
Abstract:
A sequence of four phases has been found for an acetonitrile-solvated co-crystal with 15-crown-5 of the nickel complex [acetonitrilediaqua-kappa O-1-nitrato-kappa O-2-nitratonickel(II)]. The structure could be determined at intervals of ca 10 K in the range 90-273 K because crystals remain single through the three transitions. In phase (I) (T >= ca 240 K; P2(1)/m, Z' = 1/2), there is extensive disorder, which is mostly resolved in phase (III) (ca 230-145 K; P2(1)/c, Z' = 1). Phase (IV) (ca 145-90 K, and probably below; P (1) over bar, Z' = 2) is ordered. Phase (II) (ca 238-232 K) is modulated, but the satellite reflections are too weak to allow the structure to be determined within its stability range by standard methods. Most crystals that were flash-cooled from room temperature to 90 K have a metastable P2(1), Z' = 5 superstructure that (at least in a commensurate approximation) was identified as similar to the structure of phase (II) by comparison of reconstructed reciprocal-lattice slices and by analogy with the phase behavior of the very similar compound [Ni(H2O)(6)](NO3)(2)center dot(15-crown-5)center dot 2H2O [Siegler et al. (2011). Acta Cryst. B67, 486-498]. In the phase (II) structure slab-like regions that are like the disordered phase (I) structure alternate with regions of similar shape and size that are like the more ordered phase (III) structure.
Title:
Two types of adjacent dimer layers in the low-temperature phase of BaCuSi2O6
Authors:
Sheptyakov, DV; Pomjakushin, VY; Stern, R; Heinmaa, I; Nakamura, H; Kimura, T Author Full Names: Sheptyakov, D. V.; Pomjakushin, V. Yu.; Stern, R.; Heinmaa, I.; Nakamura, H.; Kimura, T.
Source:
PHYSICAL REVIEW B, 86 (1):10.1103/PhysRevB.86.014433 JUL 30 2012
Abstract:
The low-temperature crystal structure of BaCuSi2O6 has been investigated with high-resolution synchrotron x-ray and neutron powder diffraction techniques and has been found to be on average (ignoring the incommensurate modulation) orthorhombic, with the most probable space group Ibam. The Cu-Cu dimers in this material are forming two types of layerswith distinctly different interatomic distances. Subtle changes also modify the partially frustrated interlayer Cu-Cu exchange paths. The present results corroborate the interpretation of low-temperature nuclear magnetic resonance and inelastic neutron scattering data in terms of distinct dimer layers.
Title:
High CO2 and H-2 Uptake in an Anionic Porous Framework with Amino-Decorated Polyhedral Cages
Authors:
Zhai, QG; Lin, QP; Wu, T; Wang, L; Zheng, ST; Bu, XH; Feng, PY Author Full Names: Zhai, Quan-Guo; Lin, Qipu; Wu, Tao; Wang, Le; Zheng, Shou-Tian; Bu, Xianhui; Feng, Pingyun
Source:
CHEMISTRY OF MATERIALS, 24 (14):2624-2626; 10.1021/cm301322b JUL 24 2012
Title:
Phase stability of Ni-2(Mn1-xFex)Ga: A first-principles study
Authors:
Luo, HB; Hu, QM; Li, CM; Yang, R; Johansson, B; Vitos, L Author Full Names: Luo, Hu-Bin; Hu, Qing-Miao; Li, Chun-Mei; Yang, Rui; Johansson, Borje; Vitos, Levente
Source:
PHYSICAL REVIEW B, 86 (2):10.1103/PhysRevB.86.024427 JUL 23 2012
Abstract:
Ni-2(Mn1-xFex)Ga ferromagnetic shape memory alloy shows unusual composition-dependent martensitic transformation temperature (T-M), namely, T-M decreases with increasing e/a ratio. In hope of understanding this unusual behavior, we investigated the composition dependence of the heat of formation (H-f) and shear elastic modulus (C') of the cubic austenite as well as the stability of the five-layer modulated (5M) tetragonal martensite relative to the austenite, using first-principles exact muffin-tin orbital method in combination with coherent potential approximation. Our calculations demonstrated that H-f of the austenite increases with the Fe content x. C' increases slightly with x up to 0.05 but decreases thereafter. The composition dependence of both H-f and C' cannot fully account for the trend of T-M against x although such correlations have been proposed in literature for other Ni-Mn-Ga based alloys. The structure of 5M martensite phase of Ni-2(Mn1-xFex)Ga wit! h 0 < x < 0.2 is determined by optimizing both the shear (changing c/a) and wavelike shuffle of atoms in (110) planes along [1 (1) over bar0] direction adopting the experimentally determined modulation function. The energy difference Delta E-AM between the austenite and 5M phases decreases with increasing x up to 0.05, following the lower Delta E-AM corresponding to lower T-M rule. However, with x larger than 0.05, Delta E-AM increases, against the experimental T-M similar to x behavior. We propose that, if taking the temperature effect and the spin-orbital coupling into account, the Delta E-AM similar to x curve might be altered and may explain the unusual composition dependence of Ni-2(Mn1-xFex)Ga.
Title:
Effect of Trivalent Additions and Processing on Structural and Magnetic Transitions in Ni-Mn-Ga Ferromagnetic Shape Memory Alloys
Authors:
Mathur, RP; Singh, RK; Ray, S; Ghosal, P; Chandrasekaran, V Author Full Names: Mathur, R. P.; Singh, R. K.; Ray, S.; Ghosal, P.; Chandrasekaran, V.
Source:
DEFENCE SCIENCE JOURNAL, 62 (4):252-260; JUL 2012
Abstract:
Ferromagnetic shape memory Ni50Mn30Ga15Al5-xBx (x = 0, 1, and 4) alloys were prepared by vacuum arc melting and subsequent heat-treatment as well as by melt spinning to investigate the effect of trivalent element additions in ternary Ni-Mn-Ga alloys. The heat-treated alloys containing Al were reported to possess a modulated martensite structure, however alloy containing both Al and B showed a loss of modulated structure in martensite formed. The rapidly solidified alloys on the other hand showed the formation of a similar modulated structure without composition change in alloys containing Al and the alloys containing Al and B. In addition, the former showed a presence of an amorphous phase with latter showing crystalline boron rich phases. The magnetisation of the B containing alloys in both the processing technique was however very low, showing lower magnetic exchange interaction in such alloys.
Title:
Exchange coupling and helical spin order in the triangular lattice antiferromagnet CuCrO2 using first principles
Authors:
Jiang, XF; Liu, XF; Wu, YZ; Han, JR Author Full Names: Jiang Xue-Fan; Liu Xian-Feng; Wu Yin-Zhong; Han Jiu-Rong
Source:
CHINESE PHYSICS B, 21 (7):10.1088/1674-1056/21/7/077502 JUL 2012
Abstract:
The magnetic and electronic properties of the geometrically frustrated triangular antiferromagnet CuCrO2 are investigated by first principles through density functional theory calculations within the generalized gradient approximations (GGA)+U scheme. The spin exchange interactions up to the third nearest neighbours in the ab plane as well as the coupling between adjacent layers are calculated to examine the magnetism and spin frustration. It is found that CuCrO2 has a natural two-dimensional characteristic of the magnetic interaction. Using Monte-Carlo simulation, we obtain the Neel temperature to be 29.9 K, which accords well with the experimental value of 24 K. Based on non-collinear magnetic structure calculations, we verify that the incommensurate spiral-spin structure with (110) spiral plane is believable for the magnetic ground state, which is consistent with the experimental observations. Due to intra-layer geometric spin frustration, parallel helical-spin chains arise along the a, b, or a + b directions, each with a screw-rotation angle of about 120 degrees. Our calculations of the density of states show that the spin frustration plays an important role in the change of d-p hybridization, while the spin-orbit coupling has a very limited influence on the electronic structure.
Title:
Defect structure and electrical conductivity in the pseudo-binary system Bi3TaO7-Bi3NbO7
Authors:
Struzik, M; Liu, X; Abrahams, I; Krok, F; Malys, M; Dygas, JR Author Full Names: Struzik, M.; Liu, X.; Abrahams, I.; Krok, F.; Malys, M.; Dygas, J. R.
Source:
SOLID STATE IONICS, 218 25-30; 10.1016/j.ssi.2012.05.005 JUN 22 2012
Abstract:
A study of electrical and structural characteristics of compositions in the Bi3Ta1-xNbxO7 system, using X-ray and neutron powder diffraction and AC impedance spectroscopy, is presented. The electrical conductivity increases with increasing niobium content. A full solid solution is observed which adopts an incommensurately ordered pseudo-cubic fluorite structure (type II). Analysis of the defect structure of the x=0.50 composition shows chains of niobate/tantalate octahedra as a likely structural motif. A small degree of non-linearity in the thermal expansion of the cubic subcell lattice parameter is observed. (C) 2012 Elsevier B.V. All rights reserved.

Update: 8-Aug-2012

Title:
Dodecagonal tiling in mesoporous silica
Authors:
Xiao, CH; Fujita, N; Miyasaka, K; Sakamoto, Y; Terasaki, O Author Full Names: Xiao, Changhong; Fujita, Nobuhisa; Miyasaka, Keiichi; Sakamoto, Yasuhiro; Terasaki, Osamu
Source:
NATURE, 487 (7407):349-353; 10.1038/nature11230 JUL 19 2012
Abstract:
Recent advances in the fabrication of quasicrystals in soft matter systems have increased the length scales for quasicrystals (1) into the mesoscale range (20 to 500 angstroms). Thus far, dendritic liquid crystals (2), ABC-star polymers(3), colloids(4) and inorganic nanoparticles(5) have been reported to yield quasicrystals. These quasicrystals offer larger length scales than intermetallic quasicrystals (a few angstroms)(1,6), thus potentially leading to optical applications through the realization of a complete photonic bandgap induced via multiple scattering of light waves in virtually all directions(7-9). However, the materials remain far from structurally ideal, in contrast to their intermetallic counterparts, and fine control over the structure through a self-organization process has yet to be attained. Here we use the well-established self-assembly of surfactant micelles to produce a new class of mesoporous silicas, which exhibit 12-fold (dodecagonal) symmetry in both electron diffraction and morphology. Each particle reveals, in the 12-fold cross-section, an analogue of dodecagonal quasicrystals in the centre surrounded by 12 fans of crystalline domains in the peripheral part. The quasicrystallinity has been verified by selected-area electron diffraction and quantitative phason strain analyses on transmission electron microscope images obtained from the central region. We argue that the structure forms through a non-equilibrium growth process, wherein the competition between different micellar configurations has a central role in tuning the structure. A simple theoretical model successfully reproduces the observed features and thus establishes a link between the formation process and the resulting structure.
Title:
Field-induced incommensurate spin structure of TbNiAl4
Authors:
Hutchison, WD; Goossens, DJ; Whitfield, RE; Studer, AJ; Nishimura, K; Mizushima, T Author Full Names: Hutchison, W. D.; Goossens, D. J.; Whitfield, R. E.; Studer, A. J.; Nishimura, K.; Mizushima, T.
Source:
PHYSICAL REVIEW B, 86 (1):10.1103/PhysRevB.86.014412 JUL 13 2012
Abstract:
TbNiAl4 exhibits incommensurate and commensurate magnetic ordering as a function of temperature. As a function of applied field it undergoes a series of magnetic phase transitions. The first of these transitions, into an intermediate spin arrangement, is the source of a large inverse magnetocaloric effect, an unusual result given that an aligning field is being applied. This has potential uses in magnetic cooling. Here, single-crystal neutron diffraction with applied magnetic field is used to obtain the intermediate field spin arrangement in TbNiAl4. We find that not only does the applied field drive the system from commensurate to incommensurate ordering, but that the phase transition shows hysteresis such that a mixed state simultaneously showing commensurate and incommensurate antiferromagnetic ordering, along with ferromagnetism, can be obtained.
Title:
Structure of a new ternary compound with high magnesium content, so-called Gd13Ni9Mg78
Authors:
Couillaud, S; Gaudin, E; Weill, F; Gomez, S; Stan, C; Plante, D; Miraglia, S; Bobet, JL Author Full Names: Couillaud, S.; Gaudin, E.; Weill, F.; Gomez, S.; Stan, C.; Plante, D.; Miraglia, S.; Bobet, J. L.
Source:
ACTA MATERIALIA, 60 (10):4144-4151; 10.1016/j.actamat.2012.04.012 JUN 2012
Abstract:
The magnesium-rich composition Gd13Ni9Mg78 was synthesized from its constituent elements in sealed tantalum tubes in an induction furnace. X-ray diffraction, electron probe microanalysis and dark-field transmission electron microscopy (TEM) images revealed a new compound with a composition ranging from Gd10-15Ni8-12Mg72-78 and low crystallinity. In order to increase the crystallinity, different experimental conditions were investigated for numerous compounds with the initial composition Gd13Ni9Mg78. In addition, several heat treatments (from 573 to 823 K) and cooling rates (from room temperature quenched down to 2 K h(-1)) have been tested. The best crystallinity was obtained for the slower cooling rates ranging from 2 to 6 K h(-1). From the more crystallized compounds, the structure was partially deduced using TEM and an average cubic structure with lattice parameter a = 4.55 A could be assumed. A modulation along both a and b axis with vectors of modulation q1 = 0.42a* and q2 = 0.42b* was observed. This compound, so-called Gd13Ni9Mg78, absorbs around 3 wt.% of hydrogen at 603 K, 30 bars and a reasonable degree of reversibility is possible, because after the first hydrogenation, irreversible decomposition into MgH2, GdH2 and NiMg2H4 has been shown. The pathway of the reaction is described herein. The powder mixture after decomposition shows an interesting kinetics for magnesium without ball milling. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
ANALYSIS OF QUASICRYSTAL GENERATION IN CONVENTIONALLY SOLIDIFIED AL-CU-FE ALLOYS
Authors:
Varga, B; Fazakas, E; Varga, KL Author Full Names: Varga, Bela; Fazakas, Eva; Varga, K. Lalos
Source:
METALURGIA INTERNATIONAL, 17 (8):27-30; 2012
Abstract:
The paper analyzes the structure of Al-Cu-Fe alloys solidified by chill casting. The non-equilibrium structure that results after casting is transformed into a quasicrystal structure by grinding and heat treatment by annealing. Structural analyses were conducted by X-rays, optical microscopy and dilatometry. Dilatometric determinations revealed the peritectic reactions underlying the metastable to stable quasicrystal structure transformation. In the areas five of phase transformations the physical dilatation coefficient ranges between 13.10(-6) and 17.10(-6) K-1.

Update: 1-Aug-2012

Title:
Atomic structure of quasicrystals
Authors:
de Boissieu, M Author Full Names: de Boissieu, Marc
Source:
STRUCTURAL CHEMISTRY, 23 (4):965-976; 10.1007/s11224-012-0004-4 AUG 2012
Abstract:
The 2011 Nobel Prize in chemistry has been awarded to Dan Shechtman for his discovery of quasicrystals. The discovery has indeed been a breakthrough in crystallography and solid state physics and chemistry. After a brief introduction to the subject, we review some of the recent advances in the understanding of the atomic structure of icosahedral quasicrystals and in particular for the binary Cd-Yb type quasicrystal. Thanks to a combined analysis of periodic approximant, high quality synchrotron data, and the superspace approach, a detailed insight in the crystal chemistry of this binary quasicrystal has been achieved.
Title:
On non-Euclidean crystallography, some football manifolds
Authors:
Molnar, E Author Full Names: Molnar, Emil
Source:
STRUCTURAL CHEMISTRY, 23 (4):1057-1069; 10.1007/s11224-012-0041-z AUG 2012
Abstract:
In polyhedral crystallography, non-Euclidean possibilities come into considerations as well. The so-called football manifolds appearing in the Bolyai-Lobachevskian hyperbolic space (H (3)) can model "fullerens" very probably. This may give us the feeling that-in atomic measure-space can wear non-Euclidean structures, e.g., hyperbolic (H (3)), spherical (S (3)) and other ones, respectively. Such phenomena as pentagonal or decagonal symmetry and the discovery of quasicrystals might strengthen these impressions. We examine here some Archimedean solids: (4, 6, 6) in E (3) (the truncated octahedron in the classical Euclidean space, for analogue as motivation, Fig. 1); (5, 6, 6) the "real football" (now in H (3), Fig. 2, from Molnar in Proceedings of International Conference on Differential Geometry and Its Applications, 1988), (3, 10, 10) in H (3) (Fig. 3 from Molnar in the previous Proceedings); an extra solid (4, 6, 8) with two manifolds on it in H (3) (Figs. 4, 5), published first time in this paper. Furthermore (3, 8, 8) will be realized in the spherical space S (3) (Fig. 6). We can study this classical example as a simple non-Euclidean one also for motivation to our method (see also Molnar in Acta Cryst A61:542-552, 2005, as an introductory paper). Each of them will be a manifold, i.e., it can be endowed with an appropriate face pairing (topological glueing), so that every point has a ball-like neighborhood in the corresponding space, especially of constant curvature, but completely in the classical analogy. In addition, each manifold will be compact (bounded and closed) whose fundamental group can be generated by two screw motions.
Title:
Cluster packing from a higher dimensional perspective
Authors:
Steurer, W; Deloudi, S Author Full Names: Steurer, Walter; Deloudi, Sofia
Source:
STRUCTURAL CHEMISTRY, 23 (4):1115-1120; 10.1007/s11224-011-9864-2 AUG 2012
Abstract:
The way to find the optimum packing of quasicrystal-constituting clusters is discussed based on the projected-cell approach. We illustrate why the quasiperiodic arrangement of partially overlapping clusters with decagonal or icosahedral symmetry is the most efficient one, by relating it to the packing of unit cells in hypercubic lattices.
Title:
Phase diagram of the Dzyaloshinskii-Moriya helimagnet Ba2CuGe2O7 in canted magnetic fields
Authors:
Muhlbauer, S; Gvasaliya, S; Ressouche, E; Pomjakushina, E; Zheludev, A Author Full Names: Muehlbauer, S.; Gvasaliya, S.; Ressouche, E.; Pomjakushina, E.; Zheludev, A.
Source:
PHYSICAL REVIEW B, 86 (2):10.1103/PhysRevB.86.024417 JUL 13 2012
Abstract:
The evolution of different magnetic structures of noncentrosymmetric Ba2CuGe2O7 is systematically studied as a function of the orientation of the magnetic field H. Neutron diffraction in combination with measurements of magnetization and specific heat show a virtually identical behavior of the phase diagram of Ba2CuGe2O7 for H confined in both the (1,0,0) and (1,1,0) plane. The existence of a recently proposed incommensurate double-k AF-cone phase is confirmed in a narrow range for H close to the tetragonal c axis. For large angles enclosed by H and the c axis, a complexly distorted nonsinusoidal magnetic structure has recently been observed. We show that its critical field H-c systematically increases for larger canting. Measurements of magnetic susceptibility and specific heat finally indicate the existence of an incommensurate/commensurate transition for H approximate to 9T applied in the basal (a, b) plane and agree with a nonplanar, distort! ed cycloidal magnetic structure.
Title:
FMR determination of the period of an incommensurate magnetic structure in chiral organometallic crystals
Authors:
Mushenok, FB; Kirman, MV; Koplak, OV; Morgunov, RB Author Full Names: Mushenok, F. B.; Kirman, M. V.; Koplak, O. V.; Morgunov, R. B.
Source:
PHYSICS OF THE SOLID STATE, 54 (7):1358-1362; 10.1134/S1063783412070281 JUL 2012
Abstract:
A sequence of maxima of microwave absorption has been found in the ferromagnetic resonance (FMR) spectra of the chiral molecular ferrimagnet [Mn{(R/S)-pn}](2)[Mn{(R/S)-pn}(2)(H2O)][Cr(CN)(6)](2), which, as is shown, corresponds to the spin-soliton resonance. It has been established that this sequence corresponds to an incommensurate magnetic structure induced by the competition between the symmetric and antisymmetric exchange interactions. On the basis of the FMR spectra and their dependence on the temperature, the parameters of the modulated magnetic structure have been estimated.

Update: 25-Jul-2012

Title:
Tailoring martensitic transformation and martensite structure of NiMnIn alloy by Ga doping In
Authors:
Liu, ZH; Li, GT; Wu, ZG; Ma, XQ; Liu, Y; Wu, GH Author Full Names: Liu, Z. H.; Li, G. T.; Wu, Z. G.; Ma, X. Q.; Liu, Y.; Wu, G. H.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 535 120-123; 10.1016/j.jallcom.2012.04.088 SEP 15 2012
Abstract:
The martensitic transformation and the martensite crystal structure of alloys Ni50Mn34In16 xGax (x = 0, 2, 4, 6, 8, 10, 12, 14, 16) have been investigated in this study. The studied alloys, with cubic L2(1) phase (x = 0, 2), seven-layered modulated (14 M) martensite phase (x = 4, 6, 8), and non-modulated (NM) martensite phase (x = 10, 12, 14, 16), exhibit martensitic transformation with critical temperature increasing linearly from 238 K for x = 0 to 486 K for x = 16. The linearity coefficient is estimated to be similar to 15 K per at.% of Ga. With regards to the lattice parameters, a elongates, whereas b and c contract as the austenite phase transformed to 14 M martensite phase. While, it turns to c elongates, a and b contract as austenite transformed to NM martensite phase. It is found that the unit cell volume decreases with increasing Ga content, which contributes to the increase of transformation temperature with Ga content. A maximum strain of 12% is predicted through the lattice distortion in 14 M martensite. Magnetic measurement shows the Curie temperature for martensite increases with Ga content. (C) 2012 Elsevier B.V. All rights reserved.
Title:
The effect of nanoquasicrystals on mechanical properties of as-extruded Mg-Zn-Gd alloy
Authors:
Huang, H; Kato, H; Chen, CL; Wang, ZC; Yuan, GY Author Full Names: Huang, Hua; Kato, Hidemi; Chen, Chunlin; Wang, Zhongchang; Yuan, Guangyin
Source:
MATERIALS LETTERS, 79 281-283; 10.1016/j.matlet.2012.04.018 JUL 15 2012
Abstract:
The Mg-3.5Zn-0.6Gd (at. %) alloy was prepared and homogenized at 673 K for 8 h, and then extruded at 523 K with an extrusion ratio of 9:1. The rnicrostructure and mechanical properties of the extruded alloy have been investigated. lcosahedral quasicrystalline phase (I-phase) existed in extruded Mg-Zn-Gd-based alloys in two morphologies: (1) micron-scale I-phase formed in the solidification, (2) nano-scale ellipsoid-shape I-phase particles precipitated in the extrusion process. A definite orientation relationship and good atomic match between I-phase and alpha-Mg matrix were directly observed by conventional and high-resolution transmission electron microscopy (HRTEM), which contribute to the high tensile strength of 308 MPa and the large plasticity of 16.4%. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Ti1.4V0.6Ni quasicrystal and its composites with xV(18)Ti(15)Zr(18)Ni(29)Cr(5)Co(7)Mn alloy used as negative electrode materials for the nickel-metal hydride (Ni-MH) secondary batteries
Authors:
Liu, WQ; Zhang, SS; Wang, LM Author Full Names: Liu, Wanqiang; Zhang, ShanShan; Wang, Limin
Source:
MATERIALS LETTERS, 79 122-124; 10.1016/j.matlet.2012.04.040 JUL 15 2012
Abstract:
This study examined the structure and electrochemical hydrogen storage characteristics of the Ti1.4V0.6Ni quasicrystal and their ball-milled composites with V18Ti15Zr18Ni29Cr5Co7 alloy. It is found by XRD that composite material alloys consist of the icosahedral quasicrystal (I-phase), C14 Laves phase with a hexagonal structure and a V-based solid solution phase with a BCC structure and a face centered cubic (FCC) phase with a Ti2Ni-type structure. The maximum discharge capacity of the alloy electrodes increases with increasing V18Ti15Zr18Ni29Cr5Co7 in the Ti1.4V0.6Ni alloy when using such composite materials as Ni-MH battery anodes under the condition that the discharge current density is 30 mA g(-1) at 303 K. Also, composite materials lead to significant improvement in the high-rate dischargeability (HRD) as well as the cyclic stability. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Neutron scattering studies of spin excitations in superconducting Rb0.82Fe1.68Se2
Authors:
Wang, MY; Li, CH; Abernathy, DL; Song, Y; Carr, SV; Lu, XY; Li, SL; Yamani, Z; Hu, JP; Xiang, T; Dai, PC Author Full Names: Wang, Miaoyin; Li, Chunhong; Abernathy, D. L.; Song, Yu; Carr, Scott V.; Lu, Xingye; Li, Shiliang; Yamani, Zahra; Hu, Jiangping; Xiang, Tao; Dai, Pengcheng
Source:
PHYSICAL REVIEW B, 86 (2):10.1103/PhysRevB.86.024502 JUL 5 2012
Abstract:
We use inelastic neutron scattering to show that superconducting (SC) rubidium iron selenide Rb0.82Fe1.68Se2 exhibits antiferromagnetic (AF) spin excitations near the in-plane wave vector Q = (pi, 0) identical to that for iron arsenide superconductors. Moreover, we find that these excitations change from incommensurate to commensurate with increasing energy and occur at the expense of spin waves associated with the coexisting root 5 x root 5 block AF phase. Since these spin excitations cannot come from Fermi surface nesting based on angle resolved photoemission experiments, our results indicate the presence of local moments in SC Rb0.82Fe1.68Se2 that may have a similar origin as the hourglass-like spin excitations in copper oxide superconductors.
Title:
Magnetic order tuned by Cu substitution in Fe1.1-zCuzTe
Authors:
Wen, JS; Xu, ZJ; Xu, GY; Lumsden, MD; Valdivia, PN; Bourret-Courchesne, E; Gu, GD; Lee, DH; Tranquada, JM; Birgeneau, RJ Author Full Names: Wen, Jinsheng; Xu, Zhijun; Xu, Guangyong; Lumsden, M. D.; Valdivia, P. N.; Bourret-Courchesne, E.; Gu, Genda; Lee, Dung-Hai; Tranquada, J. M.; Birgeneau, R. J.
Source:
PHYSICAL REVIEW B, 86 (2):10.1103/PhysRevB.86.024401 JUL 2 2012
Abstract:
We study the effects of Cu substitution in Fe1.1Te, the nonsuperconducting parent compound of the iron-based superconductor, Fe1+yTe1-xSex, utilizing neutron scattering techniques. It is found that the structural and magnetic transitions, which occur at similar to 60 K without Cu, are monotonically depressed with increasing Cu content. By 10% Cu for Fe, the structural transition is hardly detectable, and the system becomes a spin glass below 22 K, with a slightly incommensurate orderingwave vector of (0.5 - delta, 0, 0.5) with delta being the incommensurability of 0.02, and correlation length of 12 angstrom along the a axis and 9 angstrom along the c axis. With 4% Cu, both transition temperatures are at 41 K, though short-range incommensurate order at (0.42, 0, 0.5) is present at 60K. With further cooling, the incommensurability decreases linearly with temperature down to 37 K, below which there is a first-order transition to a long-range almost-commensurate antiferromagnetic structure. A spin anisotropy gap of 4.5 meV is also observed in this compound. Our results show that the weakly magnetic Cu has a large effect on the magnetic correlations; it is suggested that this is caused by the frustration of the exchange interactions between the coupled Fe spins.

Update: 18-Jul-2012

Title:
A possible generalization of the phenomenological theory of phase transitions in type II ferroelectrics with incommensurate phase
Authors:
Korda, VY; Berezovsky, SV; Molev, AS; Korda, LP; Klepikov, VF Author Full Names: Korda, V. Yu.; Berezovsky, S. V.; Molev, A. S.; Korda, L. P.; Klepikov, V. F.
Source:
PHYSICA B-CONDENSED MATTER, 407 (17):3388-3393; 10.1016/j.physb.2012.04.043 SEP 1 2012
Abstract:
We develop a generalized phenomenological theory of the paraelectric - incommensurate - commensurate phase transitions in type II ferroelectrics. The linear temperature dependence of the sixth-power term coefficient in the thermodynamic potential expansion is proposed. Contrary to the pre-existing theoretical approaches, the developed model eliminates a number of long-standing problems in the theory of type II ferroelectrics and can provide a correct description of the experimental data on the temperature dependence of the properties of type II ferroelectrics in the incommensurate phase. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Magnetic properties and magnetic structures of the CeScSi-type RMgPb (R=Ce-Nd, Sm, Gd-Tm) compounds
Authors:
Lemoine, P; Verniere, A; Venturini, G; Mareche, JF; Capelli, S; Malaman, B Author Full Names: Lemoine, P.; Verniere, A.; Venturini, G.; Mareche, J. F.; Capelli, S.; Malaman, B.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 324 (19):2937-2952; 10.1016/j.jmmm.2012.03.037 SEP 2012
Abstract:
Investigations made by powder X-ray diffraction, magnetic measurements and neutron powder diffraction on the CeScSi-type ternary magnesium plumbides RMgPb (R=Ce-Nd, Sm, Gd-Tm) are reported. Macroscopic magnetic measurements performed in the 2-300 K temperature range show that these compounds follow a Curie-Weiss law in the paramagnetic state (except SmMgPb) and behave antiferromagnetically at low temperature (T-N <= 61 K). Field dependence of the magnetization performed at 5 K evidence metamagnetic-like behaviors (H-crit < 7 T). Neutron powder diffraction evidenced complex antiferromagnetic structures in fair agreement with the magnetic data. PrMgPb and NdMgPb compounds present a commensurate antiferromagnetic structure, while (Tb-Er)MgPb are characterized by incommensurate sine-wave modulated magnetic structure down to lower temperature or square-wave magnetic structure due to appearance of higher odd integer harmonics. CeMgPb and TmMgPb evidence more complex sine-wave modulated magnetic structures, never encountered with the CeScSi-type structure, characterized by two propagation vectors. These results are discussed and compared with those of the isotypic RMgSn compounds. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Modeling of Incommensurate omega Structure in the Zr-Nb Alloys
Authors:
Tang, B; Cui, YW; Chang, H; Kou, HC; Li, JS; Zhou, L Author Full Names: Tang, Bin; Cui, Y. -W.; Chang, Hui; Kou, Hongchao; Li, Jinshan; Zhou, Lian
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 43A (8):2581-2586; 10.1007/s11661-012-1214-5 AUG 2012
Abstract:
Kanzaki force induced by substitutional solutes was introduced as a composition-dependent oscillating defect field in the Ginzburg-Landau model to simulate the pre-transition structure preceding the beta-to-omega phase transformation. A three-dimensional (3-D) modulated incommensurate structure of the omega phase composed of alternating omega and beta phases was predicted to be present in the moderately concentrated Zr-Nb alloys. The modeling work suggests that the Kanzaki force acts as a resistance that generates and retains the incommensurate structure of the omega phase.
Title:
Enhanced microhardness of mechanically activated carbon-quasicrystal composite
Authors:
Yadav, TP; Singh, D; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Singh, Devinder; Tiwari, R. S.; Srivastava, O. N.
Source:
MATERIALS LETTERS, 80 5-8; 10.1016/j.matlet.2012.04.034 AUG 1 2012
Abstract:
In this work, Al65Cu20Fe15 icosahedral quasicrystal and mechanically activated carbon (graphite) composite have been investigated. The low intensity milling (100 rpm) of quasicrystalline phase with mechanically activated carbon (MAC) showed to conserve the quasicrystalline (QC) phase as well as the small amount of nano crystalline B2 phase. Mechanical behavior of the sintered samples (200 degrees C) showed an increase in the hardness of the composite materials up to 5 at.% of MAC. The hardness value is nearly 0.37 times higher than that for stable Al-Cu-Fe quasicrystal. The high hardness value may be attributed to the microstructural variation resulting due to 5 at.% MAC addition. This work has demonstrated the possibility of producing MAC-QC composite materials with acceptable and reliable properties. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Microstructure and properties of extruded rapidly solidified AlCr4.7Fe1.1Si0.3 (at.%) alloys
Authors:
Cavojsky, M; Balog, M; Dvorak, J; Illekova, E; Svec, P; Krizik, P; Janickovic, D; Simancik, F Author Full Names: Cavojsky, Miroslav; Balog, Martin; Dvorak, Jiri; Illekova, Emilia; Svec, Peter; Krizik, Peter; Janickovic, Dusan; Simancik, Frantisek
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 549 233-241; 10.1016/j.msea.2012.04.051 JUL 15 2012
Abstract:
The rapidly solidified AlCr4.7Fe1.1Si0.3 (at.%) alloy produced at large scale by direct extrusion of gas atomised powders was investigated. Hot-extrusion yielded sound compacts and did not create any major structural changes compared to the as-atomised state. Microstructural characterisation of the as-extruded material revealed submicron scale alpha-Al grains with an embedded Al7Cr crystalline phase and traces of a nano-scale quasicrystalline Al84.6Cr15.4 Phase. The long-term thermal stability up to 300 degrees C of compacts was proven. The thermal stability of compacts was accompanied by high mechanical properties, especially high strength and Young's modulus, and creep performance up to 300 degrees C. The same material was prepared by laboratory scale extrusion of cryo-chopped melt-spun ribbons as a reference material. No major differences in the structure or properties of the industrially prepared material were observed compared to the reference material. (c) 2012 Elsevier B.V. All rights reserved.
Title:
The microstructural evolution and superplastic behavior at low temperatures of Mg-5.00Zn-0.92Y-0.16Zr (wt.%) alloys after hot extrusion and ECAP process
Authors:
Xu, SW; Zheng, MY; Kamado, S; Wu, K Author Full Names: Xu, S. W.; Zheng, M. Y.; Kamado, S.; Wu, K.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 549 60-68; 10.1016/j.msea.2012.03.116 JUL 15 2012
Abstract:
In this study, equal channel angular pressing (ECAP) was applied to a hot-extruded Mg-5.00Zn-0.92Y-0.16Zr (wt.%) alloy to produce an ultrafine-grained a-Mg structure of 0.6 mu m with uniformly distributed fine quasicrystal Mg3YZn6 particles. The basal planes in the as-ECAPed alloy were inclined approximately 45 degrees to the ECAP direction (EPD); thus, a high Schmid factor of 0.36 for (0 0 0 1)< 1 1 (2) over bar 0 > basal slip along EPD was obtained. Then, the superplastic behavior at low temperatures of 150-250 degrees C and initial strain rates of 1.67 x 10(-3) s(-1)-1.67 x 10(-1) s(-1) of the as-ECAPed alloy was investigated and compared with that of the as-extruded alloy. The microstructural development, texture evolution and cracking behavior during tensile tests were systemically investigated by electron backscattered diffraction (EBSD) analysis. During the tensile test along the EPD, the basal planes in the as-ECAPed alloy specimen were tilted approximately 15 degrees away from the original position; thus, the basal planes were still in a position favorable for the basal slip along the EPD. As a result, a maximum elongation of 865% was obtained at 200 degrees C and a strain rate of 1.67 x 10(-3) s(-1), as a result of this favored basal texture and the excellent thermal stability of the ultrafine-grained structure. This optimum superplastic temperature of 200 degrees C is much lower than that obtained for other Mg-Zn-Y-(Zr) alloys. In contrast, for the as-extruded alloy specimen, superplastic behavior did not occur until the critical condition of 250 degrees C and a strain rate of 1.67 x 10(-3) s(-1). Below this temperature and strain rate, the strong extrusion basal texture was maintained, and the cracks in the hot-worked coarse region (or un-DRXed region) were observed nucleating mainly associated with the formation of a 38 degrees {1 0 (1) over bar 1}-{1 0 (1) over bar 2} double twin. At this temperature and strain rate, the hot-work! ed coarse regions were significantly refined by the dynamic re! covery a nd the following recrystallization process. In the case, the formation of a double twin was prevented and the facture was delayed. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.
Title:
The polarizability model for ferroelectricity in perovskite oxides
Authors:
Bussmann-Holder, A Author Full Names: Bussmann-Holder, Annette
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (27):10.1088/0953-8984/24/27/273202 JUL 11 2012
Abstract:
This article reviews the polarizability model and its applications to ferroelectric perovskite oxides. The motivation for the introduction of the model is discussed and nonlinear oxygen ion polarizability effects and their lattice dynamical implementation outlined. While a large part of this work is dedicated to results obtained within the self-consistent-phonon approximation, nonlinear solutions of the model are also handled, which are of interest to the physics of relaxor ferroelectrics, domain wall motions, and incommensurate phase transitions. The main emphasis is to compare the results of the model with experimental data and to predict novel phenomena.
Title:
Polarized IR and Raman spectra of Ca2MgSi2O7, Ca2ZnSi2O7 and Sr2MgSi2O7 single crystals: Temperature-dependent studies of commensurate to incommensurate and incommensurate to normal phase transitions
Authors:
Hanuza, J; Ptak, M; Maczka, M; Hermanowicz, K; Lorenc, J; Kaminskii, AA Author Full Names: Hanuza, J.; Ptak, M.; Maczka, M.; Hermanowicz, K.; Lorenc, J.; Kaminskii, A. A.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 191 90-101; 10.1016/j.jssc.2012.02.051 JUL 2012
Abstract:
IR and Raman spectra of Ca2MgSi2O7. Ca2ZnSi2O7 and Sr2MgSi2O7 oriented single crystals and powders have been measured. The temperature dependence of phonons has been established in the 4-650 K range. Discussion of the results has been performed on the basis of factor group approach for the tetragonal P (4) over bar2(1)m (D(2)(3)d) space group with Z=2. The assignment of the bands observed to the internal and external modes has been made on their polarization behaviour, phonon energy calculations and literature data. The evidences of the LO-TO splitting and commensurate (C) to incommensurate (IC) as well as incommensurate (IC) to normal (N) phase transitions have been found. As a representative example, the results obtained for the spontaneous Raman scattering have also been used in the discussion of the stimulated Raman spectra of Ca2ZnSi2O7. (C) 2012 Elsevier Inc. All rights reserved.
Title:
Nanoscale modulations in (KLa)(CaW)O-6 and (NaLa)(CaW)O-6
Authors:
Licurse, MW; Borisevich, AY; Davies, PK Author Full Names: Licurse, Mark W.; Borisevich, Albina Y.; Davies, Peter K.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 191 220-224; 10.1016/j.jssc.2012.03.026 JUL 2012
Abstract:
Complex nanoscale modulations are identified in two new A-site ordered perovskites, (KLa)(CaW)O-6 and (NaLa)(CaW)O-6. In (KLa)(CaW)O-6, selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM) show an incommensurate nanocheckerboard modulation with similar to 9.4 x 9.4a(p) periodicity (a(p) approximate to 4 angstrom for the cubic perovskite aristotype). For (NaLa)(CaW)O-6 a one-dimensional modulation is observed with a similar to 16(1 1 0)a(p) repeat; the < 1 1 0 > orientation of the nanostripes is different from the < 1 0 0 > stripes observed in other mixed A-site systems. Studies using high temperature x-ray diffraction suggest the formation of the complex modulations is associated with small deviations from the ideal 1:1:1:1 stoichiometry of the (A(+)La(3+))(CaW)O-6 phases. Z-contrast images acquired on an aberration-corrected microscope provide evidence for deviations from stoichiometry with a similar to 1:15 periodic arrangement of La-4/3(CaW)O-6:(NaLa)(CaW)O-6 nano-phases. (C) 2012 Elsevier Inc. All rights reserved.
Title:
The fluorite related modulated structures of the Gd-2(Zr2-xCex)O-7 solid solution: An analogue for Pu disposition
Authors:
Reid, DP; Stennett, MC; Hyatt, NC Author Full Names: Reid, D. P.; Stennett, M. C.; Hyatt, N. C.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 191 2-9; 10.1016/j.jssc.2011.12.039 JUL 2012
Abstract:
We present an overview of the Gd-2(Zr2-xCex)O-7 phase diagram, of interest as a model system for ceramic disposition of Pu (with Ce as a Pu surrogate). The fluorite related structures of this solid solution were determined using a modulated structure approach, to identify the underlying cation and vacancy ordering mechanisms from analysis of key satellite reflections in selected zone axis electron diffraction patterns. This revealed the formation of four structure types: pyrochlore for x < 0.25, defect fluorite for 0.5 < x < 0.75, an incommensurate C*-type structure for x=1.00, and a C-type structure for x > 1.50. X-ray absorption (XAS) and electron energy loss (EELS) spectra confirmed the presence of Ce4+ as the dominant species in compositions across this system, remaining analogous to Pu4+. (C) 2012 Elsevier Inc. All rights reserved.
Title:
Texture Modification by Addition of Ca in Mg-Zn-Y Alloy
Authors:
Kyeong, JS; Kim, JK; Lee, MJ; Park, YB; Kim, WT; Kim, DH Author Full Names: Kyeong, Joon Seok; Kim, Jeong Kyun; Lee, Myung Jae; Park, Yong Bum; Kim, Won Tae; Kim, Do Hyang
Source:
MATERIALS TRANSACTIONS, 53 (5):991-994; 10.2320/matertrans.M2011401 MAY 2012
Abstract:
The secondary solidification phase of icosahedral (I-) phase in rolled Mg-Zn-Y alloy is replaced with 1 + Ca2Mg6Zn3 phases by addition of Ca. Addition of Ca in Mg-Zn-Y alloy significantly accelerates dynamic and static recrystallization resulting in much fine grain size and more random texture. EBSD analysis indicates that the presence of Ca in the alpha-Mg solid solution matrix may play a role in weakening of basal texture rather than particle stimulation nucleation effect by the second solidification phases. [doi:10.2320/matertrans.M2011401]
Title:
Microstructural evolutions and hardness during heat treatment of Al64Cu20Fe12Si4 quasicrystal alloy
Authors:
Karakose, E; Keskin, M Author Full Names: Karakose, Ercan; Keskin, Mustafa
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 92 (7):314-326; 10.1080/09500839.2012.669056 2012
Abstract:
The microhardness and microstructural characteristics and subsequent heat treatment of conventionally solidified Al64Cu20Fe12Si4 quasicrystal were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM) together with energy dispersive spectroscopy (EDS), differential thermal analysis (DTA), and Vickers microhardness tester. XRD analysis indicated that the conventionally solidified samples showed a quasicrystalline icosahedral phase (i-phase) together with cubic beta-AlFe, tetragonal theta-Al2Cu, and monoclinic lambda-A(13)Fe(4) crystal phases. However, the i-phase together with cubic beta-AlFe and monoclinic lambda-A(13)Fe(4) phases observed heat threaded samples. As-cast and subsequently heat-treated quasicrystal samples were measured using a microhardness test device. Vickers microindentation tests were carried out on the heat-treated quasicrystal samples with the load ranging from 1 to 500 mN at room temperature. The melting point of the i-phase was determined as 900 degrees C by DTA examinations.

Update: 11-Jul-2012

Title:
The magnetoelectric effect due to local noncentrosymmetry
Authors:
Sakhnenko, VP; Ter-Oganessian, NV Author Full Names: Sakhnenko, V. P.; Ter-Oganessian, N. V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (26):10.1088/0953-8984/24/26/266002 JUL 4 2012
Abstract:
Magnetoelectrics often possess ions located in noncentrosymmetric surroundings. Based on this fact we suggest a microscopic model of magnetoelectric interaction and show that the spin-orbit coupling leads to spin-dependent electric dipole moments of the electron orbitals of these ions, which results in non-vanishing polarization for certain spin configurations. The approach accounts for the macroscopic symmetry of the unit cell and is valid for both commensurate and complex incommensurate magnetic structures. The model is illustrated by the examples of MnWO4, MnPS3 and LiNiPO4. Application to other magnetoelectrics is discussed.
Title:
Formation and rotation of skyrmion crystal in the chiral-lattice insulator Cu2OSeO3
Authors:
Seki, S; Kim, JH; Inosov, DS; Georgii, R; Keimer, B; Ishiwata, S; Tokura, Y Author Full Names: Seki, S.; Kim, J. -H.; Inosov, D. S.; Georgii, R.; Keimer, B.; Ishiwata, S.; Tokura, Y.
Source:
PHYSICAL REVIEW B, 85 (22):10.1103/PhysRevB.85.220406 JUN 22 2012
Abstract:
Small-angle neutron scattering experiments were performed on a bulk single crystal of chiral-lattice multiferroic insulator Cu2OSeO3. In the absence of an external magnetic field, helical spin order with magnetic modulation vector q parallel to < 001 > was identified. When a magnetic field is applied, a triple-q magnetic structure emerges normal to the field in the A phase just below the magnetic ordering temperature T-c, which suggests the formation of a triangular lattice of skyrmions. Notably, the favorable q direction in the A phase changes from q parallel to < 110 > to q parallel to < 001 > upon approaching T-c. Near the phase boundary between these two states, the external magnetic field induces a 30 degrees rotation of the skyrmion lattice. This suggests a delicate balance between the magnetic anisotropy and the spin texture near T-c, such that even a small perturbation significantly affects the ordering pattern of the skyrmions.
Title:
High-field NMR of the quasi-one-dimensional antiferromagnet LiCuVO4
Authors:
Buttgen, N; Kuhns, P; Prokofiev, A; Reyes, AP; Svistov, LE Author Full Names: Buettgen, N.; Kuhns, P.; Prokofiev, A.; Reyes, A. P.; Svistov, L. E.
Source:
PHYSICAL REVIEW B, 85 (21):10.1103/PhysRevB.85.214421 JUN 20 2012
Abstract:
We report on NMR studies of the quasi-one-dimensional (1D) frustrated S = 1/2 chain cuprate LiCuVO4 in magnetic fields H up to mu H-0 = 30 T (approximate to 70% of the saturation field H-sat). NMR spectra in fields higher than H-c2 (mu H-0(c2) approximate to 7.5 T) and temperatures T < T-N can be described within the model of a spin-modulated phase in which the magnetic moments are aligned parallel to the applied field H and their values alternate sinusoidally along the magnetic chains. Based on theoretical concepts about frustrated 1D S = 1/2 chains, the field dependence of the modulation strength of the magnetic structure is deduced from our experiments. Relaxation time T-2 measurements of the V-51 nuclei show that T-2 depends on the particular position of the probing V-51 nucleus with respect to the magnetic copper moments within the 1D chains: the largest T-2 value is observed for the vanadium nuclei which are right next to the magnetic Cu2+ ion with the largest ordered magnetic moment. This observation is in agreement with the expectation for the spin-modulated magnetic structure. The (H, T) magnetic phase diagram of LiCuVO4 is discussed.
Title:
Surface scaling properties of decagonal quasicrystals under nonequilibrium vertical growth
Authors:
Jeong, HC; Kim, JM Author Full Names: Jeong, Hyeong-Chai; Kim, Jin Min
Source:
PHYSICAL REVIEW E, 85 (6):10.1103/PhysRevE.85.061118 Part 1 JUN 20 2012
Abstract:
Restricted solid-on-solid (RSOS) growth models are studied on two different decagonal quasicrystal lattices, namely the Penrose tiling lattice and the random tiling lattice. There exist two types of growth blocks-fat and skinny tiles-which may have different sticking probabilities. We found that the RSOS growths on both lattices belong to the Kardar-Parisi-Zhang universality class when they have the same sticking probabilities in spite of the lack of periodicity in the substrates. However, when they have tile-type dependent sticking probabilities, the RSOS models on two lattices may produce different scaling behaviors. Growth on Penrose tiling shows that the roughness exponent is around 0.4 while that on random tiling is around 0.49. Our observation may provide an effective way to investigate the bulk structures of decagonal quasicrystals.
Title:
Conical antiferromagnetic order in the ferroelectric phase of Mn0.8Co0.2WO4 resulting from the competition between collinear and cycloidal structures
Authors:
Urcelay-Olabarria, I; Ressouche, E; Mukhin, AA; Ivanov, VY; Balbashov, AM; Garcia-Munoz, JL; Skumryev, V Author Full Names: Urcelay-Olabarria, I.; Ressouche, E.; Mukhin, A. A.; Ivanov, V. Yu.; Balbashov, A. M.; Garcia-Munoz, J. L.; Skumryev, V.
Source:
PHYSICAL REVIEW B, 85 (22):10.1103/PhysRevB.85.224419 JUN 19 2012
Abstract:
Evolution of competing commensurate collinear (AF4) and incommensurate cycloidal (AF2) magnetic structures in Mn0.8Co0.2WO4 multiferroic was studied by neutron diffraction, magnetic, and pyroelectric characterization measurements. In contrast to pure and slightly Co doped MnWO4, the antiferromagnetic AF4 collinear phase [k(1) = (1/2,0,0)] inherent to the pure CoWO4 was observed below N ' eel temperature T-N approximate to 20 K in Mn0.8Co0.2WO4. This collinear order survives down to the lowest temperature reached in the experiments (2 K) even after the appearance of the second (cycloidal AF2) spin order below T-FE approximate to 8.5 K [k(2) = (-0.211, 1/2, 0.452)]. Ferroelectric polarization along b axis was revealed below T-FE in the low temperature conical phase resulting from the superposition of the AF4 and AF2 spin structures. The arrangement of the spins after the two successive magnetic transitions are thoroughly described. In particular, we found that spins in the AF4 phase are aligned along the easy direction in the ac plane (similar to 142 degrees with respect to the c* axis), while the cycloidal AF2 spin order is developed in the magnetically hard directions, perpendicular to the easy one, and consequently the T-FE decreases compared to the pure MnWO4.
Title:
Large magneto (thermo) dielectric effect in multiferroic orthorhombic LuMnO3
Authors:
Wang, LJ; Chai, YS; Feng, SM; Zhu, JL; Manivannan, N; Jin, CQ; Gong, ZZ; Wang, XH; Li, LT Author Full Names: Wang, L. J.; Chai, Y. S.; Feng, S. M.; Zhu, J. L.; Manivannan, N.; Jin, C. Q.; Gong, Z. Z.; Wang, X. H.; Li, L. T.
Source:
JOURNAL OF APPLIED PHYSICS, 111 (11):10.1063/1.4722299 JUN 1 2012
Abstract:
We have investigated the relation between ferroelectric and magnetic orders of orthorhombic (o-) LuMnO3 ceramics. The increase of dielectric constant e exceeds 82% near incommensurate to commensurate E-type antiferromagnetic (AFM) spin ordering transition temperature T-L, reflecting a large magneto (thermo) dielectric response. Meanwhile, distinct anomalies and thermal hysteresis behavior are observed near this temperature in both temperature dependence of epsilon and specific heat C-p, indicating a strong coupling between FE and magnetic orders in o-LuMnO3. Comparing to o-HoMnO3, TmMnO3, and YbMnO3 with similar E-type AFM ground state, o-LuMnO3 has the largest magneto (thermo) dielectric effect (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4722299]
Title:
The story of Nobel-winning 'quasicrystals'
Authors:
Malhotra, R Author Full Names: Malhotra, Richa
Source:
CURRENT SCIENCE, 102 (10):1356-1357; MAY 25 2012

Update: 4-Jul-2012

Title:
In-situ investigation of the icosahedral Al-Cu-Fe phase formation in thin films
Authors:
Haidara, F; Duployer, B; Mangelinck, D; Record, MC Author Full Names: Haidara, F.; Duployer, B.; Mangelinck, D.; Record, M. -C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 534 47-51; 10.1016/j.jallcom.2012.04.036 SEP 5 2012
Abstract:
This work is an investigation of the formation by reactive diffusion at high temperatures of the icosahedral phase, i-Al62.5Cu25Fe12.5, in thin films. The samples were prepared by sputtering at room temperature. The elements Al, Cu and Fe were sequentially deposited onto oxidized silicon substrates. The two following stacking sequences, Al/Cu/Fe and Al/Fe/Cu, were investigated. The phase formation was studied using in situ resistivity, in situ X-ray Diffraction and Differential Scanning Calorimetry measurements. Whatever the stacking sequence, the sequences of phase formation evidenced during the heating treatment are similar. However the temperatures of formation for the first phases that are formed are different; they are higher in the case of the Al/Fe/Cu stacking sequence. (C) 2012 Elsevier B. V. All rights reserved.
Title:
Reactivity of metal-containing monomers 71. Synthesis of nanosized quasicrystals and related metallopolymer composites
Authors:
Aldoshin, SM; Dzhardimalieva, GI; Pomogailo, AD; Abuzin, YA Author Full Names: Aldoshin, S. M.; Dzhardimalieva, G. I.; Pomogailo, A. D.; Abuzin, Yu. A.
Source:
RUSSIAN CHEMICAL BULLETIN, 60 (9):1871-1879; 10.1007/s11172-011-0282-9 SEP 2012
Abstract:
The methods for the preparation of quasicrystalline intermetallic compounds in the protective matrix in the systems Al65Cu22Fe13 and Al54Cu9Mg37 were developed. They are formed both earlier and from elements during the formation of a metallopolymer composite material. Three methods of preparation are optimal: from low-dimensional powders of quasicrystals and film-forming polymers, by the in situ formation of quasicrystals during the thermal decomposition of the corresponding precursors, and via the thermal polymerization of metal-containing monomers (components of quasicrystals) followed by the controlled pyrolysis of the metallopolymers that formed. The metallopolymer composite obtained by the incorporation of Al63Cu22Fe13 into the high-density polyethylene or polyacrylamide matrix affords up to 10 wt.% cubic phase of beta-Al-50(Cu,Fe)(50). The products of thermal decomposition of the low-molecular-weight precursors are a mixture of the quasicrystalline (Al65Cu22Fe13) and crystalline (cubic beta-Al-50(Cu,Fe)(50) and tetragonal omega-Al7Cu2Fe, Al2Cu) phases. The thermolysis of the metallo-polymer composition yields a finely dispersed powder, whose main component is an alloy Al7Cu3Mg6 with an admixture of the Al2CuMg phase.
Title:
Multilayer thin film growth on crystalline and quasicrystalline surfaces: A phase-field crystal study
Authors:
Muralidharan, S; Khodadad, R; Sullivan, E; Haataja, M Author Full Names: Muralidharan, Srevatsan; Khodadad, Raika; Sullivan, Ethan; Haataja, Mikko
Source:
PHYSICAL REVIEW B, 85 (24):10.1103/PhysRevB.85.245428 JUN 14 2012
Abstract:
In this paper, we explore the effects of misfit strain fields on both heterogeneous nucleation behavior and anisotropic growth of islands at submonolayer coverages and compositional patterning at complete monolayer coverage via simulations of a phase-field crystal model. In particular, deposition on top of a herringbone structure and quasicrystalline (QC) substrate are considered, the former representing a system with spatially periodic misfit strain fields arising from the presence of surface dislocations, and the latter representing a system which inherently possesses a wide range of local, aperiodic misfit patterns. In the case of single-component systems, we demonstrate that misfit strain fields lead to heterogeneous nucleation behavior and anisotropic island growth. In the case of QC substrate, a wide range of morphologies, such as coexistence of locally hexagonally ordered atomic clusters within a larger scale arrangement with overall QC symmetry and so-called "starfish" aggregates, is observed in a pure system at submonolayer coverages when the adlayer-substrate interaction strength and lattice mismatch are tuned. In the case of bulk-immiscible binary systems at complete monolayer coverage, strain-stabilized compositional domains emerge at low line tension values for both substrates. Interestingly, the compositional domains on the QC substrate inherit their symmetries at sufficiently low line tension values, while at larger line tension values, the domain structure begins to resemble the classical spinodal microstructure. Such domain structures should be readily observable in colloidal systems in which attractive interparticle and particle-substrate interactions can be tuned.
Title:
Coexistence and Competition of the Short-Range Incommensurate Antiferromagnetic Order with the Superconducting State of BaFe2-xNixAs2
Authors:
Luo, HQ; Zhang, R; Laver, M; Yamani, Z; Wang, M; Lu, XY; Wang, MY; Chen, YC; Li, SL; Chang, S; Lynn, JW; Dai, PC Author Full Names: Luo, Huiqian; Zhang, Rui; Laver, Mark; Yamani, Zahra; Wang, Meng; Lu, Xingye; Wang, Miaoyin; Chen, Yanchao; Li, Shiliang; Chang, Sung; Lynn, Jeffrey W.; Dai, Pengcheng
Source:
PHYSICAL REVIEW LETTERS, 108 (24):10.1103/PhysRevLett.108.247002 JUN 12 2012
Abstract:
Superconductivity in the iron pnictides develops near antiferromagnetism, and the antiferromagnetic (AF) phase appears to overlap with the superconducting phase in some materials such as BaFe2-xTxAs2 (where T = Co or Ni). Here we use neutron scattering to demonstrate that genuine long-range AF order and superconductivity do not coexist in BaFe2-xNixAs2 near optimal superconductivity. In addition, we find a first-order-like AF-to-superconductivity phase transition with no evidence for a magnetic quantum critical point. Instead, the data reveal that incommensurate short-range AF order coexists and competes with superconductivity, where the AF spin correlation length is comparable to the superconducting coherence length.
Title:
Stable icosahedral phase in Mg44Zn44Gd12 alloy
Authors:
Wang, XD; Du, WB; Wang, ZH; Liu, K; Li, SB Author Full Names: Wang Xudong; Du Wenbo; Wang Zhaohui; Liu Ke; Li Shubo
Source:
JOURNAL OF RARE EARTHS, 30 (5):503-506; 10.1016/S1002-0721(12)60080-5 MAY 2012
Abstract:
The microstructure of the as-cast Mg44Zn44Gd12 alloy was investigated by using X-ray diffraction (XRD), differential scanning (DSC), scanning electron microscopy (SEM) and a detailed transmission electron microscope. The XRD, DSC and SEM results indicated that the as-cast Mg44Zn44Gd12 alloy were mainly composed of three types of phases: the primary solidification phase, the dendritic phase and the eutectic phase. The primary solidification phase had an icosahedral structure. The dendritic phase was the W-phase, and eutectic structure phase was the Mg7Zn3 phase. Microstructures of icosahedral phase (I-phase), W-phase and Mg7Zn3 phase in Mg44Zn44Gd12 alloy were investigated. The results indicated that the I-phase in Mg44Zn44Gd12 alloy was a face-centered icosahedral quasicrystal with stoichiometric composition of Mg42Zn50Gd8 which had an excellent thermal stability up to 420 degrees C. The solid solution of Gd Gradually decreased during solidification, which played an important role in activating the formation of Mg7Zn3 phase and W-phase from icosahedral phases.

Update: 27-Jun-2012

Title:
Dynamic mechanical relaxation and loss in the incommensurate phase of quartz
Authors:
Peng, Z; Chien, SY; Redfern, SAT Author Full Names: Peng, Z.; Chien, S-Y; Redfern, S. A. T.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (25):10.1088/0953-8984/24/25/255403 JUN 27 2012
Abstract:
The dynamic mechanical properties of quartz have been studied as a function of temperature across the alpha-beta phase transition and in the vicinity of the incommensurate (IC) phase on cooling from the beta phase. The mechanical response of the IC phase shows strong anelasticity for measurement of Young's modulus (closely related to C-11 in our geometry) with modulated stress driven at 1 Hz. The dynamic shear modulus does not show similar strong effects in its imaginary component, although a very weak anomaly is barely detectable in the real part of the modulus. Our results indicate that the incommensurate microstructures within the quartz transition interval are susceptible to dilatational stress with relaxation times around 1 s.
Title:
Soft-mode-driven lattice instabilities in Cs2HgCl4 crystal: phenomenological treatment and far-infrared spectroscopy of the structurally modulated phases
Authors:
Shchur, Y; Kamba, S; Parasyuk, OV; Kityk, AV Author Full Names: Shchur, Ya; Kamba, S.; Parasyuk, O. V.; Kityk, A. V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (24):10.1088/0953-8984/24/24/245901 JUN 20 2012
Abstract:
This paper reports a comprehensive phenomenological description and experimental infrared (IR) investigations of the soft-mode-driven lattice instabilities into various commensurately and incommensurately modulated phases of Cs2HgCl4 crystals. Our theoretical analysis shows that the lattice instabilities along the a and c crystallographic directions are related to low-frequency transverse optical (TO) phonon branches of Sigma(2) and Lambda(3) symmetry, respectively, which merge together in the center of the Brillouin zone at the point of B-3g symmetry. As the temperature decreases both branches fall down, leading first to the direct condensation of the soft TO Sigma(2) mode in the symmetric Sigma direction (k parallel to a*). On the other hand, coupling of the TO and transverse acoustic (TA) modes of Lambda(3) symmetry causes, at somewhat lower temperatures, a series of frozen modulated commensurate and incommensurate states developing along the symmetric 3 direction (k parallel to c*). Polarized far-infrared (FIR) reflectivity spectra (15-600 cm(-1)) of Cs2HgCl4 crystals were measured in a broad temperature region, 10-297 K. Despite a rich sequence of structurally modulated phases existing above 163 K we observed rather moderate temperature evolution of IR spectra where only a few new modes of different polarizations have been activated. However, the commensurately modulated phases occurring below 163 K made an essential impact on the spectra of all three polarizations. The process of activation of both the Raman- and the IR-active phonons in the structurally modulated phases is subjected to the phenomenological analysis.
Title:
Electronic properties of PrNi1-xCuxAl compounds
Authors:
Fikacek, J; Javorsky, P; Vejpravova, J; Prchal, J; Kastil, J; Nenert, G; Santava, E Author Full Names: Fikacek, J.; Javorsky, P.; Vejpravova, J.; Prchal, J.; Kastil, J.; Nenert, G.; Santava, E.
Source:
PHYSICAL REVIEW B, 85 (21):10.1103/PhysRevB.85.214410 JUN 8 2012
Abstract:
We report on the evolution of magnetic properties in the PrNi1-xCuxAl series investigated by measurements of magnetization, AC susceptibility, specific heat, and powder neutron diffraction. For compounds with a low Cu content, we observe antiferromagnetic incommensurate structures characterized by propagation vector k = (1/20q) having q = 0.416 +/- 0.002 and 0.428 +/- 0.006 in the case of x = 0.1 and 0.2, respectively. A commensurate antiferromagnetic structure with k = (1/20 1/2) then appears in compounds with x = 0.4 and 0.5, which is followed by a spin-glass state with short-range correlations in the Cu-rich part of the series. The short-range magnetic correlations have an antiferromagnetic character with a propagation vector close to the one observed in the magnetically ordered PrCuAl. Investigations of the spin relaxation phenomena by use of the frequency-dependent AC susceptibility revealed that a spin-glass-like state develops at low temperatures with evidence of collective clustering. A crystal-field energy scheme, deduced from specific heat data, is characterized by a quasidoublet ground state in the whole series.
Title:
Incommensurate spin density wave versus local magnetic inhomogeneities in Ba(Fe1-xNix)(2)As-2: a Fe-57 Mossbauer spectral study
Authors:
Olariu, A; Bonville, P; Rullier-Albenque, F; Colson, D; Forget, A Author Full Names: Olariu, A.; Bonville, P.; Rullier-Albenque, F.; Colson, D.; Forget, A.
Source:
NEW JOURNAL OF PHYSICS, 14 10.1088/1367-2630/14/5/053044 MAY 29 2012
Abstract:
We report Fe-57 Mossbauer spectral results in pure and doped Ba(Fe1-xNix)(2)As-2 with x = 0.01 and 0.03. We show that all these materials present a first-order magnetic transition towards a magnetically ordered state. In the doped compounds, a broad distribution of Fe hyperfine fields is present in the magnetic phase. We successfully fit the Mossbauer data in Ba(Fe1-xNix)(2)As-2 in the framework of two different models: (i) an incommensurate spin density wave (IC-SDW); (ii) a dopant-induced perturbation of the Fe polarization, recently proposed to interpret As-75 NMR data in Ba(Fe1-xNix)(2)As-2, which is valid only in the very dilute limit x = 0.01. Moreover, we show here that these NMR data can also be successfully analysed in terms of the 'incommensurate model' for all doping contents by using the parameters obtained from the Mossbauer spectral analysis. Therefore it is not possible to rule out the presence of an IC-SDW on the basis of the As-75 NMR data.
Title:
Structural studies of the P-T phase diagram of sodium niobate
Authors:
Jabarov, SG; Kozlenko, DP; Kichanov, SE; Belushkin, AV; Mammadov, AI; Savenko, BN; Mekhtieva, RZ; Lathe, C Author Full Names: Jabarov, S. G.; Kozlenko, D. P.; Kichanov, S. E.; Belushkin, A. V.; Mammadov, A. I.; Savenko, B. N.; Mekhtieva, R. Z.; Lathe, C.
Source:
JOURNAL OF SURFACE INVESTIGATION-X-RAY SYNCHROTRON AND NEUTRON TECHNIQUES, 6 (3):546-551; 10.1134/S1027451012060250 MAY 2012
Abstract:
The crystal structure of sodium niobate (NaNbO3) has been investigated by energy-dispersive X-ray diffraction at high pressures (up to 4.3 GPa) in the temperature range 300-1050 K. At normal conditions, NaNbO3 has an orthorhombic structure with Pbcm symmetry (antiferroelectric P phase). Upon heating, sodium niobate undergoes a series of consecutive transitions between structural modulated phases P-R-S-T(1)-T(2)-U; these transitions manifest themselves as anomalies in the temperature dependences of the positions and widths of diffraction peaks. Application of high pressure leads to a decrease in the temperatures of the structural transitions to the R, S, T(1), T(2), and U phases with different baric coefficients. A phase diagram for sodium niobate has been build in the pressure range 0-4.3 GPa and the temperature range 300-1050 K. The dependences of the unit-cell parameters and volume on pressure and temperature have been obtained. The bulk modulus and the volume coefficients of thermal expansion have been calculated for different structural modulated phases of sodium niobate. A phase transition (presumably, from the antiferroelectric orthorhombic P phase to the ferroelectric rhombohedral N phase) has been observed at high pressure (P = 1.6 GPa) and room temperature.
Title:
Deformation twinning in Ni2MnGa
Authors:
Pond, RC; Muntifering, B; Mullner, P Author Full Names: Pond, R. C.; Muntifering, B.; Muellner, P.
Source:
ACTA MATERIALIA, 60 (9):3976-3984; 10.1016/j.actamat.2012.03.045 MAY 2012
Abstract:
Deformation twinning is investigated in the martensitic phase of a Ni46.75Mn34Ga19.25 (at.%) alloy. X-ray and electron diffraction are used to establish the crystallography of the non-modulated tetragonal martensite, and transmission electron microscopy is employed to deduce the twinning parameters. It is convenient to define the twinning parameters with respect to a "monoclinic" unit cell, designated 2M: then K-1, eta(1), K-2, and eta(2) are (001), [100], (100), and [001] respectively. The Burgers vector of the active twinning disconnections is close to 1/6[100] and the disconnections are associated with steps of height d((002)). These defects are expected to be highly mobile since their motion does not require atomic shuffling. It is shown that periodic arrangements of two layer twins produce modulated crystal structures, such as 14M. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 20-Jun-2012

Title:
EDMA: a computer program for topological analysis of discrete electron densities
Authors:
Palatinus, L; Prathapa, SJ; van Smaalen, S Author Full Names: Palatinus, Lukas; Prathapa, Siriyara Jagannatha; van Smaalen, Sander
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 45 575-580; 10.1107/S0021889812016068 Part 3 JUN 2012
Abstract:
EDMA is a computer program for topological analysis of discrete electron densities according to Bader's theory of atoms in molecules. It locates critical points of the electron density and calculates their principal curvatures. Furthermore, it partitions the electron density into atomic basins and integrates the volume and charge of these atomic basins. EDMA can also assign the type of the chemical element to atomic basins based on their integrated charges. The latter feature can be used for interpretation of ab initio electron densities obtained in the process of structure solution. A particular feature of EDMA is that it can handle superspace electron densities of aperiodic crystals in arbitrary dimensions. EDMA first generates real-space sections at a selected set of phases of the modulation wave, and subsequently analyzes each section as an ordinary three-dimensional electron density. Applications of EDMA to model electron densities have shown that the relative accuracy of the positions of the critical points, the electron densities at the critical points and the Laplacian is of the order of 10(-4) or better.

Update: 13-Jun-2012

Title:
Microstructure and mechanical properties of a Mg-Zn4.3Y0.7 alloy powder reinforced by quasi-crystalline particles
Authors:
Chae, HJ; Kim, BS; Do Kim, Y; Kim, TS Author Full Names: Chae, Hong Jun; Kim, Bum-Sung; Do Kim, Young; Kim, Taek-Soo
Source:
MATERIALS LETTERS, 77 63-66; 10.1016/j.matlet.2012.02.074 JUN 15 2012
Abstract:
Rapidly solidified (RS) Mg-Zn4.3Y0.7 alloy powders were prepared by using a gas atomization device, followed by the warm extrusion. The microstructure and mechanical properties were analyzed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), and the constituent phases were characterized using X-ray diffraction (XRD). The microstructure of the powders indicated that the icosahedral Mg3YZn6 (I-Phase) quasi-crystals were distributed in the alpha-Mg matrix. I-phases on the order of 0.5 mu m were generally formed along the grain boundaries. The powders were extruded with an area reduction ratio to identify the extrusion behavior. As the extrusion ratio increased from 10:1 to 15:1 and 20:1, the microstructures had a more uniform distribution of the I-phase and showed increased mechanical properties, such as tensile strength and elongation. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Interaction between graphene and nickel(111) surfaces with commensurate and incommensurate orientational relationships
Authors:
Shibuta, Y; Elliott, JA Author Full Names: Shibuta, Yasushi; Elliott, James A.
Source:
CHEMICAL PHYSICS LETTERS, 538 112-117; 10.1016/j.cplett.2012.04.048 JUN 11 2012
Abstract:
The interaction energy between a rigid defect-free graphene sheet and a fixed Ni(111) surface with respect to rotational and translational displacements is examined using an empirical bond order potential. The Rosei (hollow site) structure, and others in which metal atoms are adjacent to hollow sites in graphene, give rise to global and local energy minima, respectively, whereas the interaction energy is almost constant for incommensurate structures. Only a few degrees rotation from the Rosei structure substantially diminishes the energy barrier for translational displacement. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Dy-0.64{Dy-5[Fe2C9]}: A complex carbide with a composite structure
Authors:
Davaasuren, B; Dashjav, E; Kniep, R; Kreiner, G; Schnelle, W; Akselrud, L; van Smaalen, S; Wolfel, A Author Full Names: Davaasuren, Bambar; Dashjav, Enkhtsetseg; Kniep, Ruediger; Kreiner, Guido; Schnelle, Walter; Akselrud, Lev; van Smaalen, Sander; Woelfel, Alexander
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 190 73-79; 10.1016/j.jssc.2012.02.008 JUN 2012
Abstract:
The ternary carbide Dy-5.64[Fe2C9] has been prepared by high temperature synthesis from the elements. The compound forms as a composite structure with two partial structures, {Dy-5[Fe2C9]} and (Dy-0.64) crystallizing in space groups Pnam and Pbam, respectively. The lattice parameters a=2934.63(9) pm and 6=1263.63(5) pm for the two partial structures are identical, whereas the c lattice parameters for {Dy-5[Fe2C9]} (c(H)=504.14(3) pm) and {Dy-0.64} (c(G)=1056.01(5) pm) are different. This gives rise to a modulated structure in the (3+1)D superspace group Pnam(00g) with q=c(H)/c(G)=0.4775. The refinement converged to R(F) values below 0.055 for each partial structure using harmonic and Crenel functions. The compound is a bad metallic conductor and represents a new structure type composed of Dy3+ species embedded in a matrix of discrete planar FeC(C-2)(2) units and edge-sharing Fe(C-2)(4) tetrahedra forming infinite chains Fe(C-2)(4/2) running along the c axis. (C) 2012 Elsevier Inc. All rights reserved.
Title:
Neutron diffraction and electrical transport studies on the incommensurate magnetic phase transition in holmium at high pressures
Authors:
Thomas, SA; Uhoya, WO; Tsoi, GM; Wenger, LE; Vohra, YK; Chesnut, GN; Weir, ST; Tulk, CA; dos Santos, AM Author Full Names: Thomas, Sarah A.; Uhoya, Walter O.; Tsoi, Georgiy M.; Wenger, Lowell E.; Vohra, Yogesh K.; Chesnut, Gary N.; Weir, Samuel T.; Tulk, Christopher A.; dos Santos, Antonio M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (21):10.1088/0953-8984/24/21/216003 MAY 30 2012
Abstract:
Neutron diffraction and electrical transport measurements have been made on the heavy rare earth metal holmium at high pressures and low temperatures in order to elucidate its transition from a paramagnetic (PM) to a helical antiferromagnetic (AFM) ordered phase as a function of pressure. The electrical resistance measurements show a change in the resistance slope as the temperature is lowered through the antiferromagnetic Neel temperature. The temperature of this antiferromagnetic transition decreases from approximately 122 K at ambient pressure at a rate of -4.9 K GPa(-1) up to a pressure of 9 GPa, whereupon the PM-to-AFM transition vanishes for higher pressures. Neutron diffraction measurements as a function of pressure at 89 and 110 K confirm the incommensurate nature of the phase transition associated with the antiferromagnetic ordering of the magnetic moments in a helical arrangement and that the ordering occurs at similar pressures as determined from the resistance results for these temperatures.
Title:
Neutron diffraction study of spin and charge ordering in SrFeO3-delta
Authors:
Reehuis, M; Ulrich, C; Maljuk, A; Niedermayer, C; Ouladdiaf, B; Hoser, A; Hofmann, T; Keimer, B Author Full Names: Reehuis, M.; Ulrich, C.; Maljuk, A.; Niedermayer, Ch.; Ouladdiaf, B.; Hoser, A.; Hofmann, T.; Keimer, B.
Source:
PHYSICAL REVIEW B, 85 (18):10.1103/PhysRevB.85.184109 MAY 22 2012
Abstract:
We report a comprehensive neutron diffraction study of the crystal structure and magnetic order in a series of single-crystal and powder samples of SrFeO3-delta in the vacancy range 0 <= delta <= 0.23. The data provide detailed insights into the interplay between the oxygen vacancy order and the magnetic structure of this system. In particular, a crystallographic analysis of data on Sr8Fe8O23 revealed a structural transition between the high-temperature tetragonal and a low-temperature monoclinic phase with a critical temperature T = 75 K, which originates from charge ordering on the Fe sublattice and is associated with a metal-insulator transition. Our experiments also revealed a total of seven different magnetic structures of SrFeO3-delta in this range of delta, only two of which namely an incommensurate helix state in SrFeO3 and a commensurate, collinear antiferromagnetic state in Sr4Fe4O11) had been identified previously. We present a detailed refinement of some of the magnetic ordering patterns and discuss the relationship between the magnetotransport properties of SrFeO3-delta samples and their phase composition and magnetic microstructure.
Title:
Crystal Chemistry of Melilite [CaLa](2)[Ga](2)[Ga2O7](2): a Five Dimensional Solid Electrolyte
Authors:
Wei, FX; Baikie, T; An, T; Kloc, C; Wei, J; White, T Author Full Names: Wei, Fengxia; Baikie, Tom; An, Tao; Kloc, Christian; Wei, Jun; White, Tim
Source:
INORGANIC CHEMISTRY, 51 (10):5941-5949; 10.1021/ic300585t MAY 21 2012
Abstract:
Melilite-type [A(2)](2)[B-I](2)[(B2O7)-O-II](2) gallates are promising ion conducting electrolytes for deployment in solid oxide fuel cells. Single crystals of [CaLa](2)[Ga](2)[Ga2O7](2), grown in an optical floating zone furnace, were investigated using a combination of transmission electron microscopy and single crystal X-ray diffraction. Strong anisotropic displacements of oxygen arise from the structural misfit between the interlayer Ca/La cations and the [Ga]-[Ga2O7] tetrahedral layers. A model employing two-dimensional modulation achieves bond lengths and bond angles that preserve satisfactory bond valence sums throughout the structure. The melilite belongs to the tetragonal superspace group P (4) over bar2(1)m(alpha, alpha, 0)00s((alpha) over bar, alpha, 0)000, alpha = 0.2160(5), with a subcell metric of a = 7.9383(2) angstrom, c = 5.2641(3) angstrom, onto which modulation vectors are superimposed: q(1) = alpha (a* + b*), q(2) = alpha (-a* + b*). Both displacive (cation and anion) and occupational (cation) modulations contribute to incommensuration. The analysis of structural adjustments that accompany changes in temperature and composition provides assurance that the crystal chemical model is correct. By better understanding the flexibility of this modulated structure a rational approach toward crystallochemical optimization of electrolyte performance by enhancing oxygen mobility becomes feasible.
Title:
Conductivity and incommensurate antiferromagnetism of Fe1.02Se0.10Te0.90 under pressure
Authors:
Katayama, N; Matsubayashi, K; Nomura, Y; Ji, S; Leao, J; Green, MA; Sato, TJ; Uwatoko, Y; Fujita, M; Yamada, K; Arita, R; Lee, SH Author Full Names: Katayama, N.; Matsubayashi, K.; Nomura, Y.; Ji, S.; Leao, J.; Green, M. A.; Sato, T. J.; Uwatoko, Y.; Fujita, M.; Yamada, K.; Arita, R.; Lee, S. -H.
Source:
EPL, 98 (3):10.1209/0295-5075/98/37002 MAY 2012
Abstract:
By performing resistivity, bulk susceptibility and neutron diffraction on single crystals of Fe1.02Se0.10Te0.90 under pressure, we show that an external pressure can enhance both conductivity and magnetism simultaneously. Surprisingly, the pressure-induced magnetic order is nearly three-dimensional, and incommensurate along both the c-axis and the a-axis, which is accompanied by a structural phase separation. Our powder neutron diffraction data show that the Fe(Se, Te)(4) tetrahedron becomes more regular under pressure, which is consistent with the enhancement of the metallicity but is counterintuitive to the three-dimensional magnetic order. Copyright (C) EPLA, 2012

Update: 6-Jun-2012

Title:
In-situ phase transformation studies of Ni48Mn39In13 melt-spun ribbons
Authors:
Kumar, DMR; Rao, DVS; Rao, NVR; Raja, MM; Singh, RK; Suresh, KG Author Full Names: Kumar, D. M. Raj; Rao, D. V. Sridhara; Rao, N. V. Rama; Raja, M. Manivel; Singh, R. K.; Suresh, K. G.
Source:
INTERMETALLICS, 25 126-130; 10.1016/j.intermet.2012.01.029 JUN 2012
Abstract:
The phase transformation in Ni48Mn39In13 melt-spun ribbons has been studied by employing in-situ transmission electron microscopy (TEM) techniques. At room temperature, the investigations showed the martensite phase consisting of plates with internal stacking faults. This phase exhibited the presence of 7M and 5M modulations. In addition, a small volume fraction of the austenite phase was observed. Upon in-situ heating from room temperature to 95 degrees C, the martensite phase transformed to austenite phase. However, in the subsequent cooling-heating cycles, the martensite phase was retained at high temperature. We discuss our experimental observations and the possible mechanisms for the stabilization of the martensite phase due to thermal cycling. (c) 2012 Elsevier Ltd. All rights reserved.
Title:
Structure of (Ga2O3)(2)(ZnO)(13) and a unified description of the homologous series (Ga2O3)(2)(ZnO)(2n+1)
Authors:
Michiue, Y; Kimizuka, N; Kanke, Y; Mori, T Author Full Names: Michiue, Yuichi; Kimizuka, Noboru; Kanke, Yasushi; Mori, Takao
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 68 250-260; 10.1107/S0108768112016084 Part 3 JUN 2012
Abstract:
The structure of (Ga2O3)(2)(ZnO)(13) has been determined by a single-crystal X-ray diffraction technique. In the monoclinic structure of the space group C2/m with cell parameters a = 19.66 (4), b = 3.2487 (5), c = 27.31 (2) angstrom, and beta = 105.9 (1)degrees, a unit cell is constructed by combining the halves of the unit cell of Ga2O3(ZnO)(6) and Ga2O3(ZnO)(7) in the homologous series Ga2O3(ZnO)(m). The homologous series (Ga2O3)(2)(ZnO)(2n+1) is derived and a unified description for structures in the series is presented using the (3 + 1)-dimensional superspace formalism. The phases are treated as compositely modulated structures consisting of two subsystems. One is constructed by metal ions and another is by O ions. In the (3 + 1)-dimensional model, displacive modulations of ions are described by the asymmetric zigzag function with large amplitudes, which was replaced by a combination of the sawtooth function in refinements. Similarities and differences between the two ho! mologous series (Ga2O3)(2)(ZnO)(2n+1) and Ga2O3(ZnO)(m) are clarified in (3 + 1)-dimensional superspace. The validity of the (3 + 1)-dimensional model is confirmed by the refinements of (Ga2O3)(2)(ZnO)(13), while a few complex phenomena in the real structure are taken into account by modifying the model.
Title:
Helical screw type magnetic structure of the multiferroic CaMn7O12 with low Cu-doping
Authors:
Slawinski, W; Przenioslo, R; Sosnowska, I; Petricek, V Author Full Names: Slawinski, W.; Przenioslo, R.; Sosnowska, I.; Petricek, V.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 68 240-249; 10.1107/S0108768112008038 Part 3 JUN 2012
Abstract:
The modulated crystal structure and modulated magnetic ordering of the multiferroic CaCuxMn7-xO12 is studied by analysing neutron and synchrotron-radiation (SR) powder diffraction data with a model based on the magnetic super-space group R31'(00 gamma)ts. Both atomic position modulations and magnetic modulations are described with the modulation vector (0, 0, q). The magnetic ordering is a screw-type circular helix where the magnetic moments are perpendicular to the c direction. The temperature dependence of the modulation vector length and the ordered magnetic moments of Mn3+ and Mn4+ ions is given between T = 50 K and the Neel temperature T-N similar or equal to 90 K. The atomic position modulation length L-p and the magnetic modulation length L-m fulfil the relation L-m = 2L(p) at all temperatures between 50 K and T-N.
Title:
Dodecagonal Quasicrystalline Morphology in a Poly(styrene-b-isoprene-b-styrene-b-ethylene oxide) Tetrablock Terpolymer
Authors:
Zhang, JW; Bates, FS Author Full Names: Zhang, Jingwen; Bates, Frank S.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 134 (18):7636-7639; 10.1021/ja301770v MAY 9 2012
Abstract:
A dodecagonal quasicrystalline (QC) morphology is identified in a poly(styrene-b-isoprene-bstyrene-b-ethylene oxide) (SISO) tetrablock terpolymer based on evidence provided by transmission electron microscopy (TEM), small-angle X-ray scattering, and dynamic mechanical spectroscopy measurements. The QC state occurs at temperatures between those associated with simple hexagonal order (HEX) and the sigma-phase (P4(2)/mnm), T-HEX < T-QC < T-sigma, where T-ODT, is the order-disorder transition temperature. All three morphologies are formed from spherical domains containing an 0 core surrounded by a shell of S that screens unfavorable segment segment interactions with an I-rich matrix. TEM analysis reveals a QC morphology with 12-fold rotational symmetry but devoid of long-range translational order, along with locally coordinated structures consistent with dodecagonal quasicrystalline approximants. The SISO molecular architecture decouples control over the domain shape and interdomain interactions, leading to a multiplicity of packing symmetries.
Title:
Na2/7Gd4/7MoO4: a Modulated Scheelite-Type Structure and Conductivity Properties
Authors:
Morozov, V; Arakcheeva, A; Redkin, B; Sinitsyn, V; Khasanov, S; Kudrenko, E; Raskina, M; Lebedev, O; Van Tendeloo, G Author Full Names: Morozov, V.; Arakcheeva, A.; Redkin, B.; Sinitsyn, V.; Khasanov, S.; Kudrenko, E.; Raskina, M.; Lebedev, O.; Van Tendeloo, G.
Source:
INORGANIC CHEMISTRY, 51 (9):5313-5324; 10.1021/ic300221m MAY 7 2012
Abstract:
Scheelite-type compounds with the general formula (A1,A2)(n)[(B1,B2)O-4](m) (2/3 <= n/m <= 3/2) are the subject of large interest owing to their stability, relatively simple preparation, and optical properties. The creation of cation vacancies (square) in the scheelite-type framework and the ordering of A cations and vacancies can be a new factor in controlling the scheelite-type structure and properties. For a long time, cation-deficient Nd3+:M2/7Gd4/7 square 1/7MoO4 (M = Li, Na) compounds were considered as potential lasers with diode pumping. They have a defect scheelite-type 3D structure (space group I4(1)/a) with a random distribution of Li+(Na+), Gd3+, and vacancies in the crystal. A Na2/7Gd4/7MoO4 single crystal with scheelite-type structure has been grown by the Czochralski method. Transmission electron microscopy revealed that Na2/7Gd4/7MoO4 has a (3 + 2)D incommensurately modulated structure. The (3 + 2)D incommensurately modulated scheelite-type cation-deficient structure of Na2/7Gd4/7MoO4 [super space group (I4) over bar (alpha-beta 0,beta alpha 0)00] has been solved from single-crystal diffraction data. The solution of the (3 + 2)D incommensurately modulated structure revealed the partially disordered distribution of vacancies and Na and Gd cations. High-temperature conductivity measurements performed along the [100] and [001] orientation of the single crystal revealed that the conductivity of Na2/7Gd4/7MoO4 at T = 973 K equals sigma = 1.13 X 10(-5) Omega(-1) cm(-1).
Title:
Influence of the Grain Size on the Magnetic Properties of TbMnO3
Authors:
Bazela, W; Dul, M; Dyakonov, V; Gondek, L; Hoser, A; Hoffmann, JU; Penc, B; Szytula, A; Kravchenko, Z; Nosalev, I; Zarzycki, A Author Full Names: Bazela, W.; Dul, M.; Dyakonov, V.; Gondek, L.; Hoser, A.; Hoffmann, J-U; Penc, B.; Szytula, A.; Kravchenko, Z.; Nosalev, I.; Zarzycki, A.
Source:
ACTA PHYSICA POLONICA A, 121 (4):785-788; APR 2012
Abstract:
The magnetic properties including magnetic structure of poly and nano samples of TbMnO3 are determined. All the samples investigated are antiferromagnets. In these samples the Mn ad Tb moments order antiferromagnetically at different temperatures and form modulated magnetic structure described by the propagation vector k=(k(x),0,0) with different value of k(x) for the Mn and Tb sublattices. Comparison of the data for poly and nano samples indicates the decrease of the moment and increase of the k(x) component of propagation vector in the nano specimens. The wide Bragg peak related to the Tb sublattice suggests that the magnetic order has the claster-like character. The magnetic moments value in both sublattices is smaller, whereas the k(x) values are larger for nano samples.
Title:
Electronic structure of two-dimensional hexagonal diselenides: Charge density waves and pseudogap behavior
Authors:
Kuchinskii, EZ; Nekrasov, IA; Sadovskii, MV Author Full Names: Kuchinskii, E. Z.; Nekrasov, I. A.; Sadovskii, M. V.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 114 (4):671-680; 10.1134/S1063776112020252 APR 2012
Abstract:
We theoretically study the electronic structure (spectral functions and Fermi surfaces) of incommensurate pseudogap and charge density wave (CDW) and commensurate CDW phases of quasi-two-dimensional diselenides 2H-TaSe2 and 2H-NbSe2. The incommensurate pseudogap regime is described within the scenario based on short-range-order CDW fluctuations, considered within the static Gaussian random field model. In contrast, e.g., to high- (c) cuprates, layered dichalcogenides have several different CDW scattering vectors and an electronic spectrum with two bands at the Fermi level. For this, we present a theoretical background for the description of multiple scattering processes within a multiple-band electronic spectrum. Theoretical spectral functions and Fermi surfaces thus obtained are compared with recent ARPES experimental data, demonstrating rather good qualitative agreement.
Title:
Residual stress in as-deposited Al-Cu-Fe-B quasicrystalline thin films
Authors:
Polishchuk, S; Boulet, P; Mezin, A; de Weerd, MC; Weber, S; Ledieu, J; Dubois, JM; Fournee, V Author Full Names: Polishchuk, Sergey; Boulet, Pascal; Mezin, Andre; de Weerd, Marie-Cecile; Weber, Sylvain; Ledieu, Julian; Dubois, Jean-Marie; Fournee, Vincent
Source:
JOURNAL OF MATERIALS RESEARCH, 27 (5):837-844; 10.1557/jmr.2011.415 MAR 2012
Abstract:
The residual stress in Al-Cu-Fe-B quasicrystalline thin films has been characterized by x-ray diffraction and the curvature method. Films with thicknesses in a range from 0.55 to 2.6 mu m were deposited using magnetron sputtering on Si(100) substrates maintained at a temperature of 560 degrees C. It is found that the tensile stress in uncracked films as determined by the curvature method is close to that measured by a modified sin(2)psi method using main diffraction peaks of the icosahedral structure and corresponds approximately to 1.1 GPa. This value is close to that of the thermal stress estimated from the mismatch between thermal expansion coefficients of the film and substrate, suggesting that thermal stress is the main source of residual stress. Increasing film thickness results in the development of cracks and partial delamination of the film, accompanied by the sudden decrease of the stress. The fracture toughness of the quasicrystalline films is estimated between 1.5 and 1.9 MPa root m.

Update: 30-May-2012

Title:
Observation of a possible charge-density-wave transition in cubic Ce3Co4Sn13
Authors:
Lue, CS; Liu, HF; Hsu, SL; Chu, MW; Liao, HY; Kuo, YK Author Full Names: Lue, C. S.; Liu, H. F.; Hsu, S. -L.; Chu, M. W.; Liao, H. Y.; Kuo, Y. K.
Source:
PHYSICAL REVIEW B, 85 (20):10.1103/PhysRevB.85.205120 MAY 11 2012
Abstract:
We report an observation of a first-order phase transition in Ce3Co4Sn13 by means of the specific heat, electrical resistivity, Seebeck coefficient, and thermal conductivity, as well as Co-59 nuclear magnetic resonance (NMR) measurements. The phase transition has been evidenced by marked features near T-o similar or equal to 155 K in all measured physical quantities except for magnetic susceptibility. This excludes a magnetic origin for the observed phase transition. In addition, x-ray diffraction results below and above T-o confirm the absence of a structural change, suggesting that the peculiar phase transition is possibly related to an electronic origin and/or electron-lattice coupling such as the formation of a charge density wave (CDW). As a matter of fact, the disappearance of the double-peak feature of 59Co NMR central lines below T-o can be realized as the spatial modulation of the electric field gradient due to incommensurate CDW superlattices. Also, a distinct peak found in the spin-lattice relaxation rate near T-o manifests a phase transition and its feature can be accounted for by the thermally driven normal modes of the CDW. From the NMR analyses, we obtained a consistent picture that the change of electronic structures below T-o is mainly due to the weakening of p-d hybridization. Such an effect could result in possible electron-lattice instability and, thus, the formation of a CDW state in Ce3Co4Sn13.
Title:
Tuning in magnetic modes in Tb(CoxNi1-x)(2)B2C: From longitudinal spin-density waves to simple ferromagnetism
Authors:
ElMassalami, M; Takeya, H; Ouladdiaf, B; Maia, R; Gomes, AM; Paiva, T; dos Santos, RR Author Full Names: ElMassalami, M.; Takeya, H.; Ouladdiaf, B.; Maia Filho, R.; Gomes, A. M.; Paiva, T.; dos Santos, R. R.
Source:
PHYSICAL REVIEW B, 85 (17):10.1103/PhysRevB.85.174412 MAY 9 2012
Abstract:
Neutron diffraction and thermodynamic techniques were used to probe the evolution of the magnetic properties of Tb(CoxNi1-x)(2)B2C. A succession of magnetic modes was observed as x is varied: the longitudinal modulated (k) over right arrow = (0.55,0,0) state at x = 0 is transformed into a collinear (k) over right arrow = (1/2,0,1/2) antiferromagnetic state at x = 0.2, 0.4 then into a transverse c-axis modulated (k) over right arrow = (0,0,1/3) mode at x = 0.6, and finally into a simple ferromagnetic structure at x = 0.8 and 1. Concomitantly, the low-temperature orthorhombic distortion of the tetragonal unit cell at x = 0 is reduced smoothly such that for x >= 0.4 only a tetragonal unit cell is manifested. Though predicted theoretically earlier, this is the first observation of the (k) over right arrow = (0,0,1/3) mode in borocarbides; our findings of a succession of magnetic modes upon increasing x also find support from a recently proposed theoretical model. The implication of these findings and their interpretation on the magnetic structure of the RM2B2 C series are also discussed.
Title:
Landau theory for the phase diagram of multiferroic Mn1-x(Fe,Zn,Mg)(x)WO4
Authors:
Matityahu, S; Aharony, A; Entin-Wohlman, O Author Full Names: Matityahu, Shlomi; Aharony, Amnon; Entin-Wohlman, Ora
Source:
PHYSICAL REVIEW B, 85 (17):10.1103/PhysRevB.85.174408 MAY 8 2012
Abstract:
We present a theoretical analysis of the temperature magnetic field concentration phase diagram of the multiferroic Mn1-xMxWO4 (M = Fe, Zn, Mg), which exhibits three ordered phases, with collinear and noncollinear incommensurate and with a commensurate magnetic order. The middle phase is also ferroelectric. The analysis uses a semiphenomenological Landau theory based on a Heisenberg Hamiltonian with a single-ion anisotropy. With a small number of adjustable parameters, the Landau theory gives an excellent fit to all three transition lines as well as the magnetic and the ferroelectric order parameters. The fit of the magnetic and ferroelectric order parameters is further improved by including the effect of fluctuations near the transitions. We demonstrate the highly frustrated nature of these materials and suggest a simple explanation for the dramatic effects of doping with different magnetic ions at the Mn sites. The model enables an examination of different sets of exchange couplings that were proposed by a number of groups. Small discrepancies are probably a consequence of small errors in the experimental magnetic parameters. In addition, using the Ginzburg criterion, we estimate the temperature range in which fluctuations of the order parameters become important.
Title:
Low temperature anomalous field effect in SrxBa1-xNb2O6 uniaxial relaxor ferroelectric seen via acoustic emission
Authors:
Dul'kin, E; Kojima, S; Roth, M Author Full Names: Dul'kin, E.; Kojima, S.; Roth, M.
Source:
JOURNAL OF APPLIED PHYSICS, 111 (8):10.1063/1.3702888 APR 15 2012
Abstract:
Sr0.75Ba0.25Nb2O6 [100]-oriented uniaxial tungsten bronze relaxor crystals have been studied by means of dedicated acoustic emission during their thermal cycling in 150-300K temperature range under dc electric field (E). A 1st order transition in a modulated incommensurate tetragonal phase has been successfully detected at T-m(i) = 198 K on heating and T-m(i) = 184 K on cooling, respectively. As field E enhances, a thermal hysteresis gradually narrows and vanishes in the critical point at E-th = 0.31 kV/cm, above which a phase transition becomes to 2nd order. The T-m(i)(E) dependence looks as a V-shape dip, not similar that previously has been looked as a smeared minimum between both the two polar and nonpolar tetragonal phases near T-m = 220 divided by 230K in the same crystals (Dul'kin et al., J Appl. Phys. 110, 044106 (2011)). Due to such a V-shape dip is characteristic for Pb-based multiaxial perovskite relaxor, a rhombohedral phase is waited to be induced by a field E in the critical point temperature range. The emergence of this rhombohedral phase as a crucial evidence of an orthorhombic phase presumably existing within the modulated incommensurate tetragonal phase in tungsten bronze SrxBa1-xNb2O6 relaxor is discussed. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3702888]
Title:
TEM microstructure of rapidly solidified Mg-6Zn-1Y-1Ce alloy
Authors:
Yang, WP; Guo, XF; Lu, ZX Author Full Names: Yang Wen-peng; Guo Xue-feng; Lu Zheng-xin
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 22 (4):786-792; 10.1016/S1003-6326(11)61246-6 APR 2012
Abstract:
Rapidly solidified (RS) Mg-6Zn-1Y-1Ce ribbons were prepared by single roller melt-spinning technique. Transmission electron microscopy and energy dispersive X-ray spectroscopy were employed to characterize the microstructure of RS ribbons. The results show that there is high density of particles distributed within grains and at grain boundaries in the region near wheel side. The particle density is decreased in the middle region and free surface region. The alloy is predominantly composed of supersaturated alpha-Mg solid solution, T phase and W phase; meanwhile, a few icosahedral quasicrystalline and Mg4Zn7 particles are also observed. The T phase is confirmed having a body-centered orthorhombic structure that is transformed from the body-centered tetragonal structure Mg12Ce phase due to the partial substitution of Mg atoms by Zn.
Title:
First-principles study on superconductivity of simple cubic, modulated and simple hexagonal phases in phosphorus
Authors:
Nakanishi, A; Ishikawa, T; Nagara, H; Shimizu, K; Katayama-Yoshida, H Author Full Names: Nakanishi, Akitaka; Ishikawa, Takahiro; Nagara, Hitose; Shimizu, Katsuya; Katayama-Yoshida, Hiroshi
Source:
HIGH PRESSURE RESEARCH, 32 (1):3-10; 10.1080/08957959.2011.644664 2012
Abstract:
Superconducting properties of simple cubic (sc), modulated, and simple hexagonal (sh) phases in phosphorus are investigated from first-principles. The superconducting transition temperature decreases through the phase transition from the sc phase to the modulated phase. The superconductivity survives in the modulated phase, which indicates the coexistence of the superconducting state and a charge density wave (CDW) if the modulated structure in phosphorus is caused by CDW. In the modulated phase, phonon modes which show strong electron-phonon coupling lie along the direction of a modulation wave vector. By further compression through phase transition from the modulated phase to the sh phase, the transition temperature increases again. The variation in the transition temperature can be correlated to the variation of the density of states at the Fermi level.

Update: 23-May-2012

Title:
Incommensurate SDW in cuprates
Authors:
Niksic, G; Kupcic, I; Sunko, DK; Barisic, S Author Full Names: Niksic, G.; Kupcic, I.; Sunko, D. K.; Barisic, S.
Source:
PHYSICA B-CONDENSED MATTER, 407 (11):1799-1802; 10.1016/j.physb.2012.01.033 JUN 1 2012
Abstract:
The incommensurate antiferromagnetism (AF) in metallic underdoped cuprates is interpreted with several complementary approaches, unified by a consistent disambiguation of the copper and oxygen degrees of freedom. Collinear (with respect to the copper lattice) peaks in the neutron response at low frequency are due to the oxygen-dominated arcs, while the diagonal peaks at high frequency or low doping come from the copper-dominated vH points. The latter switch from collinear to diagonal as the frequency increases. The direct O-O overlap induces an AF which is weaker and thermodynamically preferred to the AF of strongly localized copper sites, and which coexists with Fermi arcs. A theoretical understanding of the strongly k-dependent AF gap observed in ARPES and STM measurements is proposed. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Pinning and depinning process of an incommensurate CDW as revealed by coherent X-ray diffraction
Authors:
Pinsolle, E; Le Bolloc'h, D; Kirova, N; Jacques, VLR; Shinchenko, AA; Monceau, P Author Full Names: Pinsolle, E.; Le Bolloc'h, D.; Kirova, N.; Jacques, V. L. R.; Shinchenko, A. A.; Monceau, P.
Source:
PHYSICA B-CONDENSED MATTER, 407 (11):1848-1851; 10.1016/j.physb.2012.01.046 JUN 1 2012
Abstract:
Experiments on the coherent X-ray diffraction, and their modeling, have been performed on the Charge Density Wave (CDW) system NbSe3. The 2k(F) satellite reflection associated with the CDW has been measured with respect to external dc currents. Below the threshold current, reflection displays several fringes in the transverse direction which disappear when the threshold current is exceeded. In the sliding state, the transverse satellite profile has a form of two nonsymmetric peaks, one of them being centered at the same position as below the threshold and another one being shifted. The shift of the longitudinal peak position below the threshold current and the nonsymmetric peak in the transverse direction above the threshold one is interpreted as the influence of strong linear defect like a crystal step present on the sample surface, combined with induced arrays of dislocations. Coherent X-rays provide a new access to processes in a CDW driven by an external force in a random pinning potential. (C) 2012 Published by Elsevier B.V.
Title:
High-pressure X-ray diffraction study of 1T-TaS2
Authors:
Ravy, S; Laulhe, C; Itie, JP; Fertey, P; Corraze, B; Salmon, S; Cario, L Author Full Names: Ravy, Sylvain; Laulhe, Claire; Itie, Jean-Paul; Fertey, Pierre; Corraze, Benoit; Salmon, Sabrina; Cario, Laurent
Source:
PHYSICA B-CONDENSED MATTER, 407 (11):1704-1706; 10.1016/j.physb.2012.01.011 JUN 1 2012
Abstract:
We present a room temperature high-pressure X-ray diffraction study of the layered compound 1T-TaS2 up to 20 GPa. This material is known to exhibit a variety of structural phase transitions that are ascribed to the stabilization of charge density wave states. It has been recently shown that at pressures larger than 3 GPa and up to 25 GPa, 1T-TaS2 becomes superconductor below about 5 K. It was suggested that this superconductivity coexists with different CDW states, an hypothesis that can be tested by X-ray diffraction. Our first results at room temperature show that at around 1.9 GPa, the nearly-commensurate (NCCDW) phase transforms into a phase similar to the high temperature incommensurate phase (ICCDW). Above 9 GPa, we show the existence of another IC phase, still discernable up to 20 GPa despite the pressure-induced crystal damage above 13 GPa. These results are consistent with resistivity measurements, but call for a complete exploration of the P-T phase diagram of 1T-TaS2. (c) 2012 Elsevier B.V. All rights reserved.
Title:
"Quantization" of the q-vector in microcrystals of K0.3MoO3 and NbSe3
Authors:
Zybtsev, SG; Pokrovskii, VY; Zaitsev-Zotov, SV Author Full Names: Zybtsev, S. G.; Pokrovskii, V. Ya.; Zaitsev-Zotov, S. V.
Source:
PHYSICA B-CONDENSED MATTER, 407 (11):1810-1812; 10.1016/j.physb.2012.01.036 JUN 1 2012
Abstract:
We report steps of conductivity between discrete conducting states in microsamples of quasi-one-dimensional conductors K0.3MoO3 and NbSe3. The steps reveal single phase-slip events, and the discrete states reveal "quantization" of the wave vector q of the charge-density wave. The "quantization" is observed due to the coherence of the CDW within the sample volume and tight boundary conditions at the contacts. The distribution of steps in temperature gives the temperature dependences of the q-vectors, while the steps' height provides the carriers' mobilities. For the case of NbSe3 we give the 1st direct confirmation of the extremely high mobility of the "pocket" holes at low temperatures. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Microstructure and magnetocaloric effect of melt-spun Ni52Mn26Ga22 ribbon
Authors:
Li, ZB; Llamazares, JLS; Sanchez-Valdes, CF; Zhang, YD; Esling, C; Zhao, X; Zuo, L Author Full Names: Li, Z. B.; Sanchez Llamazares, J. L.; Sanchez-Valdes, C. F.; Zhang, Y. D.; Esling, C.; Zhao, X.; Zuo, L.
Source:
APPLIED PHYSICS LETTERS, 100 (17):10.1063/1.4704780 APR 23 2012
Abstract:
Microstructural features and magnetocaloric properties of Ni52Mn26Ga22 melt-spun ribbons were studied. Results show that there are four types of differently oriented variants of seven-layered modulated (7M) martensite at room temperature, being twin-related one another and clustered in colonies. Due to the coupled magnetic and structural transformations between parent austenite and 7M martensite, the melt-spun ribbons exhibit a significant magnetocaloric effect. At an applied magnetic field of 5 T, an absolute maximum value of the isothermal magnetic entropy change of 11.4 J kg(-1) K-1 is achieved with negligible hysteresis losses. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4704780]
Title:
Microstructure properties and microhardness of rapidly solidified Al64Cu20Fe12Si4 quasicrystal alloy
Authors:
Karakose, E; Keskin, M Author Full Names: Karakose, Ercan; Keskin, Mustafa
Source:
METALS AND MATERIALS INTERNATIONAL, 18 (2):257-263; 10.1007/s12540-012-2017-3 APR 2012
Abstract:
This paper presents differences in the microstructure and microhardness properties of conventional casting (ingot) and rapidly solidified Al64Cu20Fe12Si4 quasicrystal (QC) alloys. The phases present in the Al64Cu20Fe12Si4 ingot alloy were determined to be icosahedral quasicrystalline (IQC) Psi-Al65Cu20Fe15, cubic beta-AlFe, tetragonal theta-Al2Cu, and monoclinic lambda-A1(3)Fe(4) phases, whereas only IQC Psi-Al65Cu20Fe15 and cubic beta-AlFe phases were identified in the rapidly solidified alloy. The microhardness value of the melt spun alloy was measured to be approximately 790 kg/mm(2). Microhardness increases with increasing solidification rates.
Title:
Nanocrystalline Intermetallics in Al-Cu-Fe-Cr Decagonal Quasicrystalline Alloy
Authors:
Yadav, TP; Mukhopadhyay, NK; Srivastava, ON Author Full Names: Yadav, T. P.; Mukhopadhyay, N. K.; Srivastava, O. N.
Source:
MATERIALS AND MANUFACTURING PROCESSES, 27 (6):620-625; 10.1080/10426914.2011.593246 2012
Abstract:
In the present investigation, an Al-Cu-Fe-Cr decagonal quasicrystalline alloy synthesized by a slow-cooling technique was mechanically milled in a high-energy ball mill for various times ranging up to 100 hours under liquid hexane medium at the speed of 400 rpm with a ball to powder ratio of 40:1. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential thermal analysis (DTA), and energy-dispersive x-ray analysis (EDX) were employed to characterize the as-cast, milled, and annealed samples. Powders milled for more than 10 h contained predominantly the B2-type nano-crystalline phase with a lattice parameter of similar to 0.29 nm. The 100 h milled powder was annealed in air at 500 degrees C for 20-40 h. It was observed that 40 h annealed sample shows the best yield for the fabrication of nanospinel. The processing technique could be optimized to manufacture the composites of nano-quasicrystal, nano-B2, and nanospinels. These materials may be further investigated as a suitable material for pigment industries.

Update: 16-May-012

Title:
Preparation of Al-Cu-Fe-(Sn,Si) quasicrystalline bulks by laser multilayer cladding
Authors:
Feng, LP; Fleury, E; Zhang, GS Author Full Names: Feng, Li-ping; Fleury, Eric; Zhang, Guo-sheng
Source:
INTERNATIONAL JOURNAL OF MINERALS METALLURGY AND MATERIALS, 19 (5):434-440; 10.1007/s12613-012-0575-5 MAY 2012
Abstract:
(Al65Cu20Fe15)(100-x)Sn-x (x=0, 12, 20, 30) and Al57Si10Cu18Fe15 powders were cladded on a medium carbon steel (45# steel) substrate by laser multilayer cladding, respectively. The phases and properties of the produced quasicrystalline bulks were investigated. It was found that the main phases in the Al65Cu20Fe15 sample were crystalline lambda-Al13Fe4 and icosahedral quasicrystal together with a small volume fraction of theta-Al2Cu phase. The volume fraction of icosahedral phase decreased as the Sn content in the (Al65Cu20Fe15)(100-x)Sn-x samples increased owing to the formation of beta-CuSn phase. The increase of Sn content improved the brittleness of the quasicrystal samples. The morphology of the solidification microstructure in the Al57Si10Cu18Fe15 sample changed from elongated shape to spherical shape due to the addition of Si. The nanohardness of the laser multilayer cladded quasicrystal samples was equal to that of the as-cast sample prepared by vacuum quenching. In terms of hardness, the laser cladded Al57Si10Cu18Fe15 quasicrystalline alloy has the highest value among all the investigated samples.
Title:
Competition between commensurate and incommensurate magnetic ordering in Fe1+yTe
Authors:
Parshall, D; Chen, G; Pintschovius, L; Lamago, D; Wolf, T; Radzihovsky, L; Reznik, D Author Full Names: Parshall, D.; Chen, G.; Pintschovius, L.; Lamago, D.; Wolf, Th; Radzihovsky, L.; Reznik, D.
Source:
PHYSICAL REVIEW B, 85 (14):10.1103/PhysRevB.85.140515 APR 26 2012
Abstract:
The Fe1+yTe1-xSex compounds belong to the family of iron-based high-temperature superconductors, in which superconductivity often appears upon doping antiferromagnetic parent compounds. Unlike other Fe-based superconductors (in which the antiferromagnetic order is at the Fermi-surface nesting wave vector [1/2, 1/2, 1]), Fe1+yTe orders at a different wave vector, [1/2, 0, 1/2]. Furthermore, the ordering wave vector depends on y, the occupation of interstitial sites with excess iron; the origin of this behavior is controversial. Using inelastic neutron scattering on Fe1.08Te, we find incommensurate magnetic fluctuations above the Neel temperature, even though the ordered state is bicollinear and commensurate with gapped spin waves. This behavior can be understood in terms of a competition between commensurate and incommensurate order, which we explain as a lock-in transition caused by the magnetic anisotropy.
Title:
Structures and Magnetism of La1-xSrxMnO3-(0.5+x)/2 (0.67 <= x <= 1) Phases
Authors:
Dixon, E; Hadermann, J; Hayward, MA Author Full Names: Dixon, Edward; Hadermann, Joke; Hayward, Michael A.
Source:
CHEMISTRY OF MATERIALS, 24 (8):1486-1495; 10.1021/cm300199b APR 24 2012
Abstract:
Topotactic reduction of La1-xSrxMnO3 (0.67 <= x <= 1) phases with sodium hydride yields a series of isoelectronic materials of composition La1-xSrxMnO3-(0.5+x)/2. Lanthanum rich members of the series (0.67 <= x <= 0.83) adopt anion deficient perovskite structures with a 6-layer -OTOOT'O- stacking sequence of sheets of octahedra/square-based pyramids (O) and sheets of tetrahedra (T). The strontium rich members of the series (0.83 <= x <= 1) incorporate "step defects" into this 6-layer structure in which the OTOOT'O stacking sequence is converted into either OOTOOT' or TOOT'OO at a defect plane which runs perpendicular to the [201] lattice plane. The step defects appear to provide a mechanism to relieve lattice strain and accommodate additional anion deficiency in phases with x > 0.83. Magnetization and neutron diffraction data indicate La1-xSrxMnO3-(0.5+x)/2 phases adopt antiferromagnetically ordered states at low-temperature in which the ordered arrangement of magnetic spins is incommensurate with the crystallographic lattice.
Title:
Antiferromagnetic order in the quasicrystal approximant Cd6Tb studied by x-ray resonant magnetic scattering
Authors:
Kim, MG; Beutier, G; Kreyssig, A; Hiroto, T; Yamada, T; Kim, JW; de Boissieu, M; Tamura, R; Goldman, AI Author Full Names: Kim, M. G.; Beutier, G.; Kreyssig, A.; Hiroto, T.; Yamada, T.; Kim, J. W.; de Boissieu, M.; Tamura, R.; Goldman, A. I.
Source:
PHYSICAL REVIEW B, 85 (13):10.1103/PhysRevB.85.134442 APR 24 2012
Abstract:
We have used x-ray resonant magnetic scattering at the Tb L-2 edge to elucidate the nature of magnetic ordering in Cd6Tb, a 1/1 approximant closely related to the Cd-Mg-R ( R = rare earth) icosahedral alloys. Below T-N approximate to 24 K, the ordered moments associated with the icosahedral clusters at the corners and body center of the pseudocubic unit cell are antiferromagnetically correlated, and long-range magnetic order is realized.
Title:
Mullite and mullite-type crystal structures
Authors:
Fischer, RX; Gaede-Kohler, A; Birkenstock, J; Schneider, H Author Full Names: Fischer, Reinhard X.; Gaede-Koehler, Andrea; Birkenstock, Johannes; Schneider, Hartmut
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, 103 (4):402-407; 10.3139/146.110713 APR 2012
Abstract:
Synthetic mullites (Al4+2xSi2-2xO10-x) belong to one of the most important groups of ceramic materials. Their crystal structure consists of chains of edge-sharing AlO6 octahedra interconnected by tetrahedral double chains of TO4 (T = Al, Si) tetrahedra. The occurrence of oxygen vacancies is associated with the formation of triclusters of TO4 groups. The distribution of oxygen vacancies and the distribution of Al and Si on the tetrahedral sites are partially ordered yielding an incommensurately modulated crystal structure with satellite reflections in diffraction patterns. The number of symmetrically independent distribution patterns of oxygen vacancies is given for a 2 x 2 x 2 and a 3 x 3 x 2 superstructure model. Many other compounds have chain structures similar to mullite. These compounds are assigned to subgroups, all derived from a hypothetical tetragonal aristotype structure.
Title:
Incommensurate structures in a two-subsystem partially frustrated ferrimagnet
Authors:
Martynov, SN Author Full Names: Martynov, S. N.
Source:
JETP LETTERS, 95 (4):188-192; 10.1134/S0021364012040066 APR 2012
Abstract:
A new incommensurate magnetic structure with a locally triangular orientation of spins has been proposed for a two-subsystem magnet with frustrated intersystem exchange and competition between exchanges in one of the subsystems. When the temperature is lowered, this structure appears from the antiferromagnetic state after a first-order phase transition. It transfers to the Yafet-Kittel triangular structure when the threshold conditions for the exchange interactions are fulfilled. An increase in the length of the frustrated exchange bonds leads to the appearance of an incommensurate phase with the local antiferromagnetic orientation of the sublattices in each subsystem between the commensurate antiferromagnetic and Yafet-Kittel phases.
Title:
Shift and Broadening of Surface Polaritons of Sapphire upon Deposition of a Quasicrystalline Film
Authors:
Novikova, NN; Ol'shanskii, ED; Teplov, AA; Shaitura, DS; Yakovlev, VA Author Full Names: Novikova, N. N.; Ol'shanskii, E. D.; Teplov, A. A.; Shaitura, D. S.; Yakovlev, V. A.
Source:
PHYSICS OF THE SOLID STATE, 54 (3):573-577; 10.1134/S1063783412030213 MAR 2012
Abstract:
The influence of a quasicrystalline Al-Pd-Re film on the shift and broadening of surface polaritons of a substrate (sapphire) has been studied. Measurements have been performed both on a sample containing only the quasicrystalline phase and on a sample which, in addition to the quasicrystalline phase, contains the crystalline (metallic) phase. The complex dielectric function of the films in the mid-IR region (650-800 cm(-1)) has been estimated.
Title:
Dielectric Characteristics and Phase Transitions in Tl(InS2)(1-x)(FeSe2)(x) Solid Solutions
Authors:
Sheleg, AU; Hurtavy, VG; Mustafaeva, SN; Kerimova, EM; Shautsova, VV Author Full Names: Sheleg, A. U.; Hurtavy, V. G.; Mustafaeva, S. N.; Kerimova, E. M.; Shautsova, V. V.
Source:
PHYSICS OF THE SOLID STATE, 54 (3):607-610; 10.1134/S1063783412030304 MAR 2012
Abstract:
This paper reports on a study of the electrical conductivity and permittivity of Tl(InS2)(1 - x)(FeSe2)(x) crystals as functions of composition and temperature. It has been found that the permittivity decreases in magnitude, while the electrical conductivity increases with increasing x. Crystals Tl(InS2)(1 - x)(FeSe2)(x) have been observed to undergo a sequence of phase transitions characteristic of TlInS2, which manifests itself in formation of anomalies in the sigma = f(T) and epsilon = f(T) temperature dependences. It has been shown that as x increases, the phase transition temperatures decrease, while the temperature region within which the incommensurate phase persists broadens slightly.

Update: 10-May-2012

Title:
First-principles study of the atomic and electronic structures of misfit-layered calcium cobaltite (Ca2CoO3)(CoO2)(1.62) using rational approximants
Authors:
Rebola, A; Klie, R; Zapol, P; Ogut, S Author Full Names: Rebola, Alejandro; Klie, Robert; Zapol, Peter; Oeguet, Serdar
Source:
PHYSICAL REVIEW B, 85 (15):10.1103/PhysRevB.85.155132 APR 19 2012
Abstract:
The atomic and electronic structures of the misfit-layered thermoelectric oxide material Ca3Co4O9 are investigated using detailed first-principles computations performed within the framework of density functional theory (DFT) and its DFT + U extension to account for electron correlations. The structure of Ca3Co4O9, composed of two incommensurate subsystems-a distorted rocksalt-type Ca2CoO3 layer sandwiched between hexagonal CoO2 layers-is modeled by means of Fibonacci rational approximants with systematically increasing unit cells. We show that good agreement with photoemission and transport experiments can be obtained regarding the contribution of the two subsystems to states near the Fermi level, when electron correlations are taken into account with a Hubbard U. The size of the rational approximant plays a secondary role in the analysis; the relatively "small" structure of composition (Ca2CoO3)(6)(CoO2)(10) represents a good model for investigating the atomic and electron ic properties of Ca3Co4O9. Within the DFT + U formalism, the metallic conductivity of Ca3Co4O9 is shown to result from itinerant holes in the hexagonal CoO2 layers, in which the Co atoms are predicted to have a mixed valence of Co4+ with similar to 30% concentration and Co3+ with similar to 70% concentration, both in low-spin configurations. In most cases, the resulting electronic structures show very good agreement with available data from transport and magnetic measurements.
Title:
The Incommensurately Modulated Structures of the Perovskites NaCeMnWO6 and NaPrMnWO6
Authors:
Garcia-Martin, S; King, G; Nenert, G; Ritter, C; Woodward, PM Author Full Names: Garcia-Martin, Susana; King, Graham; Nenert, Gwilherm; Ritter, C.; Woodward, Patrick M.
Source:
INORGANIC CHEMISTRY, 51 (7):4007-4014; 10.1021/ic202071n APR 2 2012
Abstract:
The structures of the doubly ordered perovskites NaCeMnWO6 and NaPrMnWO6, with rock salt ordering of the Mn2+ and W6+ B-site cations and layered ordering of the Na+ and (Ce3+/Pr3+) A-site cations, have been studied by transmission electron microscopy, electron diffraction, neutron and synchrotron X-ray powder diffraction. Both compounds possess incommensurately modulated crystal structures. In NaCeMnWO6 the modulation vector (with reference to the ideal ABX(3) perovskite subcell) is q approximate to 0.067a* (similar to 58.7 angstrom) and in NaPrMnWO6 q approximate to 0.046a* (similar to 85.3 angstrom). In both compounds the superstructures are primarily the two-dimensional chessboard type, although some crystals of NaCeMnWO6 were found with one-dimensional stripes. In some crystals of NaPrMnWO6 there is a coexistence of chessboards and stripes. Modeling of neutron diffraction data shows that octahedral tilting plays an important role in the structural modulation.
Title:
Planar defects in the icosahedral phase in quasicrystal-forming AlCuFe alloys
Authors:
Shalaeva, EV; Prekul, AF; Nazarova, SZ; Khiller, VV Author Full Names: Shalaeva, E. V.; Prekul, A. F.; Nazarova, S. Z.; Khiller, V. V.
Source:
PHYSICS OF THE SOLID STATE, 54 (4):699-707; 10.1134/S1063783412040257 APR 2012
Abstract:
Electron microscopy has revealed that, upon the formation of a stable icosahedral (i) AlCuFe phase, there arise a large number of planar defects. The revealed defects are nanometer-sized coherent intergrowths of the P1-pentagonal approximant. It has been found that the formation of these defects is the result of a nonequilibrium intermediate transformation. The intergrowths are located in the planes with the fivefold symmetry axis and give rise to an elastic-strain state of the i-phase. Analysis of the diffraction contrast has revealed the presence of phason and phonon atomic displacements due to the mismatch between the quasiperiodic (i-phase) and periodic (P1-phase) lattices. The formed structure exhibits a higher electrical resistance as compared to the i-phase and has been considered as a model state of the imperfect icosahedral phase with preferred phonon displacements.
Title:
Theory of linear, nonlinear and dynamic fracture for quasicrystals
Authors:
Fan, TY; Tang, ZY; Chen, WQ Author Full Names: Fan, Tian-You; Tang, Zhi-Yi; Chen, Wei-Qiu
Source:
ENGINEERING FRACTURE MECHANICS, 82 185-194; 10.1016/j.engfracmech.2011.12.009 MAR 2012
Abstract:
In this paper, fracture theory of quasicrystalline material is presented, concerning with linear, nonlinear and dynamic fracture problems for different quasicrystal systems observed to date. Main attention is however paid to three-dimensional icosahedral quasicrystals and two-dimensional decagonal quasicrystals, which play the central role in the new kind of materials. Relevant experimental results are also discussed. (C) 2012 Elsevier Ltd. All rights reserved.

Update: 3-May-2012

Title:
Vacancy-like defects associated with icosahedral phase in Mg-Y-Nd-Zr alloys modified by the addition of Zn
Authors:
Cizek, J; Vlcek, M; Smola, B; Stulikova, I; Prochazka, I; Kuzel, R; Jager, A; Lejcek, P Author Full Names: Cizek, J.; Vlcek, M.; Smola, B.; Stulikova, I.; Prochazka, I.; Kuzel, R.; Jaeger, A.; Lejcek, P.
Source:
SCRIPTA MATERIALIA, 66 (9):630-633; 10.1016/j.scriptamat.2012.01.054 MAY 2012
Abstract:
Positron lifetime spectroscopy combined with other techniques was employed for the structural characterization of Mg-Y-Nd-Zr (WE43) alloy modified by the addition of Zn. A quasicrystalline icosahedral phase was formed in the alloy, thereby strengthening it. Vacancy-like defects characterized by a positron lifetime of similar to 300 ps were also found, although such defects are not present in WE43 alloy without Zn. This testifies that vacancy-like defects are associated with the quasicrystalline phase. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Structure of UMo4O14 oxide
Authors:
Zakharov, ND; Pippel, E; Hillebrand, R; Werner, P Author Full Names: Zakharov, N. D.; Pippel, E.; Hillebrand, R.; Werner, P.
Source:
PROGRESS IN NUCLEAR ENERGY, 57 150-154; SI 10.1016/j.pnucene.2011.10.012 MAY 2012
Abstract:
The structure and composition of UMo4O14 synthesized by solid state reaction method have been investigated by High Resolution Transmission Electron Microscopy (HRTEM), High Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF-STEM), Selected Area Electron Diffraction SAED, and energy Dispersive X-ray microanalysis (EDX). The unit cell is orthorhombic, Cccm (66), a = 0.732, b = 3.247, c = 0.81, alpha = 90.0, beta = 90.0, gamma = 90.0. It comprises 2 layers of U and Mo cations. Each following layer is shifted relatively to the previous one by vector a/2. The infinite layers of composition Mo2O7 running perpendicular to b direction can be easily distinguished in the image. These double MoO3 octahedra wide slabs are typical for U-Mo oxides. They are linked to each other by another MoO3 octahedra and infinite one octahedral wide slab, forming a two rows of hexagonal coordinated bi-pyramids occupied by...U-O-Mo-O... strings. One of characteristic features of the UMo4O14 phase is the incommensurate modulation observed in some crystals. The goal of this paper is to reveal three-dimensional atomic structure of U-Mo oxide and to clarify in what way it depends on U/Mo composition. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Magnetic superspace groups and symmetry constraints in incommensurate magnetic phases
Authors:
Perez-Mato, JM; Ribeiro, JL; Petricek, V; Aroyo, MI Author Full Names: Perez-Mato, J. M.; Ribeiro, J. L.; Petricek, V.; Aroyo, M. I.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (16):10.1088/0953-8984/24/16/163201 APR 25 2012
Abstract:
Superspace symmetry has been for many years the standard approach for the analysis of non-magnetic modulated crystals because of its robust and efficient treatment of the structural constraints present in incommensurate phases. For incommensurate magnetic phases, this generalized symmetry formalism can play a similar role. In this context we review from a practical viewpoint the superspace formalism particularized to magnetic incommensurate phases. We analyse in detail the relation between the description using superspace symmetry and the representation method. Important general rules on the symmetry of magnetic incommensurate modulations with a single propagation vector are derived. The power and efficiency of the method is illustrated with various examples, including some multiferroic materials. We show that the concept of superspace symmetry provides a simple, efficient and systematic way to characterize the symmetry and rationalize the structural and physical properties of incommensurate magnetic materials. This is especially relevant when the properties of incommensurate multiferroics are investigated.
Title:
Heat transport of the quasi-one-dimensional Ising-like antiferromagnet BaCo2V2O8 in longitudinal and transverse fields
Authors:
Zhao, ZY; Liu, XG; He, ZZ; Wang, XM; Fan, C; Ke, WP; Li, QJ; Chen, LM; Zhao, X; Sun, XF Author Full Names: Zhao, Z. Y.; Liu, X. G.; He, Z. Z.; Wang, X. M.; Fan, C.; Ke, W. P.; Li, Q. J.; Chen, L. M.; Zhao, X.; Sun, X. F.
Source:
PHYSICAL REVIEW B, 85 (13):10.1103/PhysRevB.85.134412 APR 5 2012
Abstract:
The very-low-temperature thermal conductivity (kappa) is studied for BaCo2V2O8, a quasi-one-dimensional Ising-like antiferromagnet exhibiting an unusual magnetic-field-induced order-to-disorder transition. The nearly isotropic transport in the longitudinal field indicates that the magnetic excitations scatter phonons rather than conduct heat. The field dependence of kappa shows a sudden drop at similar to 4 T, where the system undergoes the transition from the Neel order to the incommensurate state. Another dip at lower field of similar to 3 T indicates an unknown magnetic transition, which is likely due to the spin-flop transition. Moreover, the kappa(H) in the transverse field shows a very deep valleylike feature, which moves slightly to higher field and becomes sharper upon lowering the temperature. This indicates a magnetic transition induced by the transverse field, which however is not predicted by the present theories for this low-dimensional spin system.
Title:
Electrical and Magnetic Properties of Quasicrystal Approximants RCd6 (R: Rare Earth)
Authors:
Mori, A; Ota, H; Yoshiuchi, S; Iwakawa, K; Taga, Y; Hirose, Y; Takeuchi, T; Yamamoto, E; Haga, Y; Honda, F; Settai, R; Onuki, Y Author Full Names: Mori, Akinobu; Ota, Hisashi; Yoshiuchi, Shingo; Iwakawa, Ken; Taga, Yuki; Hirose, Yusuke; Takeuchi, Tetsuya; Yamamoto, Etsuji; Haga, Yoshinori; Honda, Fuminori; Settai, Rikio; Onuki, Yoshichika
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 81 (2):10.1143/JPSJ.81.024720 FEB 2012
Abstract:
We measured the electrical resistivity, magnetic susceptibility, magnetization, and specific heat of the quasicrystal approximants RCd6 (R: rare earth, Y-Lu) with a body-centered cubic (bcc) crystal structure. Single crystals were grown by the Cd-self flux method and annealing method. We confirmed that the structural order-disorder transition is realized at about 160K when the lattice constant a is larger than 15.481 angstrom in YCd6, namely, for R = Pr, Nd, Sm, Gd, Tb, Dy, and Yb. At lower temperatures, RCd6 compounds, except non-4f reference compounds YCd6 and LuCd6, and a divalent compound YbCd6, are found to order antiferromagnetically. We clarified that the structural order-disorder transition has a great influence on the magnetic ordering and transport properties. The Neel temperature of RCd6 (R: Nd, Sm, Tb, and Dy) with the structural order-disorder transition is appreciably higher than the de Gennes scaling normalized by the Neel temperature of GdCd6, while the the Neel temperature of RCd6 (R: Ho, Er, and Tm) without the structural transition approximately follows the de Gennes scaling. Moreover, the electrical resistivity of RCd6 with the structural transition decreases monotonically below the Neel temperature, while it increases below the Neel temperature and a large residual resistivity remains at low temperatures in RCd6 without the structural transition. The contribution of an Einstein oscillator to the phonon specific heat is also discussed in YCd6 and LuCd6.
Title:
Solidification of tin on quasicrystalline surfaces
Authors:
Singh, A; Somekawa, H; Matsushita, Y; Tsai, AP Author Full Names: Singh, Alok; Somekawa, H.; Matsushita, Y.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE, 92 (9):1106-1128; 10.1080/14786435.2011.640646 2012
Abstract:
A two-phase alloy of beta-Sn and Al63Cu25Fe12 quasicrystal produced by melt-spinning was annealed and aged to form various microstructures of tin in a quasicrystalline (QC) or microcrystalline (MC) matrix. The morphology and structure of the interfaces was studied by scanning and transmission electron microscopy and was related to melting and solidification behavior of tin studied by differential scanning calorimetry. In a MC matrix the tin phase occurred as nanoparticles and solidified with an undercooling of about 35 degrees C. In a QC matrix, tin formed intergranular layers on faceted matrix grains. Tin showed multiple solidification peaks in undercooling ranging from 8 degrees C to 43 degrees C, indicating several distinct nucleation sites which compete with each other and are selected kinetically. The interfacial energy (depending on the structural state of the matrix) had a more dominating effect on the solidification of tin than the size, shape and the distribution of the tin particles. It was also concluded that solidification of tin is easier on quasicrystalline surfaces than on aluminum.

Update: 26-Apr-2012

Title:
Fractal spectra in generalized Fibonacci one-dimensional magnonic quasicrystals
Authors:
Costa, CHO; Vasconcelos, MS; Barbosa, PHR; Barbosa, FF Author Full Names: Costa, C. H. O.; Vasconcelos, M. S.; Barbosa, P. H. R.; Barbosa Filho, F. F.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 324 (14):2315-2323; 10.1016/j.jmmm.2012.02.123 JUL 2012
Abstract:
In this work we carry out a theoretical analysis of the spectra of magnons in quasiperiodic magnonic crystals arranged in accordance with generalized Fibonacci sequences in the exchange regime, by using a model based on a transfer-matrix method together random-phase approximation (RPA). The generalized Fibonacci sequences are characterized by an irrational parameter sigma(p,q), which rules the physical properties of the system. We discussed the magnonic fractal spectra for first three generalizations, i.e., silver, bronze and nickel mean. By varying the generation number, we have found that the fragmentation process of allowed bands makes possible the emergence of new allowed magnonic bulk bands in spectra regions that were magnonic band gaps before, such as which occurs in doped semiconductor devices. This interesting property arises in one-dimensional magnonic quasicrystals fabricated in accordance to quasiperiodic sequences, without the need to introduce some de ferent atomic layer or defect in the system. We also make a qualitative and quantitative investigations on these magnonic spectra by analyzing the distribution and magnitude of allowed bulk bands in function of the generalized Fibonacci number F-n and as well as how they scale as a function of the number of generations of the sequences, respectively. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Study on phase stability and oxide ion conductivity in the BIAGVOX system
Authors:
Al-Areqi, NAS; Beg, S; Al-Alas, A Author Full Names: Al-Areqi, Niyazi A. S.; Beg, Saba; Al-Alas, Ahlam
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 73 (6):730-734; 10.1016/j.jpcs.2012.01.009 JUN 2012
Abstract:
A novel oxide ion conductor, BIAGVOX formulated as Bi4AgxV2-xO11-(2x)-delta is obtained by substituting a fraction (x) of V5+ by Ag+ in Bi4V2O11 samples of the BIAGVOX system in the composition range, 0.05 <= x <= 0.30 were synthesized using the standard solid-state reaction. XRPD, FT-IR, DTA and AC impedance spectroscopy were used for the investigation of the correlation between the structural phase stability and oxide ion performance of the BIAGVOX materials. It has been found that orthorhombic, beta, and incommensurate tetragonal, gamma' were stabilized at room temperature for compositions with x <= 0.15 and x >= 0.20, respectively. The enthalpy of beta ->gamma and gamma ->gamma transition exhibited a general drop with increasing Ag content and a minimum transition temperature was observed for x = 0.20. However, the oxide ion conductivity at lower temperatures remarkably increased in composition stability ranges of beta- and gamma-phase, while a maximum conductivity was reported for the high temperature gamma-phase at x = 0.15. However, the low temperature conductivity, sigma(300)degrees c measured for x = 0.30 was found to be comparable with the maximum ionic conductivity of the BICUVOX system reported for x = 0.20 at the same temperature. (C) 2012 Elsevier Ltd. All rights reserved.
Title:
Two-dimensional charge fluctuation in beta-Na0.33V2O5
Authors:
Ohwada, K; Yamauchi, T; Fujii, Y; Ueda, Y Author Full Names: Ohwada, Kenji; Yamauchi, Touru; Fujii, Yasuhiko; Ueda, Yutaka
Source:
PHYSICAL REVIEW B, 85 (13):10.1103/PhysRevB.85.134102 APR 6 2012
Abstract:
We have investigated the critical phenomena of the metal-to-insulator (MI) transition of beta-Na0.33V2O5. The critical exponent beta of 0.226(3) and anisotropic diffuse scattering suggest that the MI transition of beta-Na0.33V2O5 is two dimensional in nature and that the dimension of the order parameter is not Ising. The non-Ising-like order parameter indicates that the MI transition is not a simple order-disorder type such as that of alpha'-NaV2O5 but charge-density-wave like, where the valence at each V site is continuous and the arrangement is modulated. This closely corresponds to the situation predicted by neutron diffraction measurements [Nagai et al., J. Phys. Soc. Jpn. 74, 1297 (2005)] and NMR measurements [Itoh et al., Phys. Rev. B 74, 054434 (2006)].
Title:
Phase transitions and incommensurability in the layered semiconductor TlInS2-an NMR study
Authors:
Panich, AM; Mogilyansky, D; Sardarly, RM Author Full Names: Panich, A. M.; Mogilyansky, D.; Sardarly, R. M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (13):10.1088/0953-8984/24/13/135901 APR 4 2012
Abstract:
We report on the first NMR study of powder and single crystal samples of thallium indium sulfide, TlInS2. The crystal under study is a pure single-layer TlInS2 polytype. Our findings show that transformation from the high temperature paraelectric phase to the low temperature ferroelectric phase occurs via an incommensurate phase that exists in the temperature range from T-c = 192 K to T-i = 205 K. On approaching the phase transition at T-i from above, the crystal exhibits a soft mode behavior. A discrepancy in the literature data on the phase transitions in TlInS2 is discussed and ascribed to polytypism of the TlInS2 crystals.
Title:
Morphology of monolayer films on quasicrystalline surfaces from the phase field crystal model
Authors:
Rottler, J; Greenwood, M; Ziebarth, B Author Full Names: Rottler, Joerg; Greenwood, Michael; Ziebarth, Benedikt
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (13):10.1088/0953-8984/24/13/135002 APR 4 2012
Abstract:
We present a computational study of the morphology of adsorbed monolayers on quasicrystalline surfaces with five-and seven-fold symmetry. The phase field crystal model is employed to first simulate the growth of the quasicrystal surfaces and then to elastically couple a two-dimensional film to the substrate. We find several distinct pseudomorphic phases that depend on the position of adsorption sites as well as the strength of the monolayer/substrate interaction, and quantify them by computing local order parameters. In qualitative agreement with recent experiments using colloids in quasiperiodic light fields, we find that the formation of quasicrystalline order is greatly inhibited on seven-fold surfaces.
Title:
Unified minimum effective model of magnetic properties of iron-based superconductors
Authors:
Hu, JP; Xu, B; Liu, WM; Hao, NN; Wang, YP Author Full Names: Hu, Jiangping; Xu, Bao; Liu, Wuming; Hao, Ning-Ning; Wang, Yupeng
Source:
PHYSICAL REVIEW B, 85 (14):10.1103/PhysRevB.85.144403 APR 3 2012
Abstract:
Iron-based superconductors exhibit many different antiferromagnetically ordered ground states. We construct a minimum effective magnetic model that displays all magnetic phases. This model also captures three incommensurate magnetic phases as well, two of which have been observed experimentally. The model characterizes the nature of phase transitions between the different magnetic phases and explains a variety of magnetic properties, such as spin-wave spectra and electronic nematism. Most importantly, by unifying the understanding of magnetism, we cast insight on the key ingredients of magnetic interactions that are critical to the occurrence of superconductivity.
Title:
Incommensurate modulation of calcium barium niobate (CBN28 and Ce:CBN28)
Authors:
Graetsch, HA; Pandey, CS; Schreuer, J; Burianek, M; Muhlberg, M Author Full Names: Graetsch, Heribert A.; Pandey, Chandra Shekhar; Schreuer, Juergen; Burianek, Manfred; Muehlberg, Manfred
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 68 101-106; Part 2 10.1107/S0108768111054863 APR 2012
Abstract:
The incommensurately modulated crystal structures of Ca0.28Ba0.72Nb2O6 (CBN28) and Ce0.02Ca0.25Ba0.72Nb2O6 (Ce:CBN28) were refined in the supercentred setting X4bm(AA0,-AA0) of the 3 + 2-dimensional superspace group P4bm(aa(1/2),-aa(1/2)). Both compounds are isostructural with a tetragonal tungsten bronze-type structure. The modulation of CBN28 consists of a wavy distribution of Ba and Ca atoms as well as vacancies on the incompletely occupied Me2 site with 15-fold oxygen coordination. The occupational modulation is coupled with a modulation of the atomic displacement parameters and a very weak modulation of the positional parameters of Me2. The surrounding O atoms show strong displacive modulations with amplitudes up to ca 0.2 angstrom owing to the cooperative tilting of the rigid NbO6 octahedra. The Me1 site with 12-fold coordination and Nb atoms are hardly affected by the modulations. Only first-order satellites were observed and the modulations are described by first-order harmonics. In Ce:CBN28 cerium appears to be located on both the Me2 and Me1 sites. Wavevectors and structural modulations are only weakly modified upon substitutional incorporation of 0.02 cerium per formula unit of calcium.
Title:
Effective Electron Correlation and Spin Density Fluctuation in Iron-Based Fluorides SrFe1-xCoxAsF (x=0, 0.125)
Authors:
Wang, W; Sun, JF; Li, SW Author Full Names: Wang, Wei; Sun, Jiafa; Li, Suwen
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS, 167 (1-2):83-89; 10.1007/s10909-012-0597-4 APR 2012
Abstract:
Using first-principles calculation, we study effective electron correlation and spin density fluctuation in iron-based fluorides SrFe1-xCoxAsF (x = 0, 0.125). We obtain the observed magnetic moment of Fe atom with a strongly attractive electron correction. Whereas, different from the parent compound, the density of state of superconducting SrFe1-xCoxAsF (x = 0.125) near to the Fermi energy is reduced for both signs of effective electron correlation, and suggests strong instability there. In addition, spin density fluctuation resulted from the effective correlation exists in Co-doped compound, may propagate in the form of collective excitation and manifest as spin fluctuation with specific q-vector in momentum space.
Title:
Quasicrystal-polymer composites for selective laser sintering technology
Authors:
Kenzari, S; Bonina, D; Dubois, JM; Fournee, V Author Full Names: Kenzari, S.; Bonina, D.; Dubois, J. M.; Fournee, V.
Source:
MATERIALS & DESIGN, 35 691-695; 10.1016/j.matdes.2011.10.032 MAR 2012
Abstract:
Selective laser sintering (SLS) process is a layered manufacturing technique used for building functional parts from 3D computer-aided design. Materials compatible with SLS usually consist of polymer-based composites reinforced by metal or ceramic particles. We have investigated a new composite powder compatible with the SLS technology and containing AlCuFeB quasicrystalline filler particles. The processed parts show reduced friction and improved wear resistance compared to other composites used in SLS technology. In addition, the functional parts contain almost no porosity and are leak-tight allowing their direct use in many fluidic applications. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Effect of Zn/Er weight ratio on phase formation and mechanical properties of as-cast Mg-Zn-Er alloys
Authors:
Li, H; Du, WB; Li, SB; Wang, ZH Author Full Names: Li, Han; Du, Wenbo; Li, Shubo; Wang, Zhaohui
Source:
MATERIALS & DESIGN, 35 259-265; 10.1016/j.matdes.2011.10.002 MAR 2012
Abstract:
The results of X-ray diffraction (XRD), differential scanning calorimetry (DSC) and microstructure observations have shown that various Zn/Er weight ratio leads to different phase compositions in the investigated alloys. The composition range for the formation of icosahedral quasicrystalline (I-phase) and face-centered cubic phase (W-phase) in Mg-rich corner is obtained. The Zn/Er weight ratio adjusting from 10 to 6 results in the formation of I-phase exclusively as main secondary phase in the as-cast Mg-Zn-Er alloys. However, when the ratio is less than 0.8, it is mainly contributed to the precipitation of W-phase. When the ratio is in the range from 1 to 4, I-phase coexisting with W-phase is inclined to be formed. The results of tensile tests suggest that the as-cast Mg-5Zn-5.0Er alloy with I-phase and W-phase possesses the highest ultimate strength (UTS). It is concluded that UTS and elongation rate (ER) of as-cast Mg-Zn-Er alloys with I-phase as the main secondary phase are excellent. The UTS of the alloys with coexistence of I-phase and W-phase show the tendency of increasing firstly then decreasing with the increasing volume fraction of W-phase. The UTS declines when W-phase completely replaces I-phase in the alloy. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Magnetic enhancement across a ferroelectric-antiferroelectric phase boundary in Bi1-xNdxFeO3
Authors:
Wu, YJ; Chen, XK; Zhang, J; Chen, XJ Author Full Names: Wu, Yu-Jie; Chen, Xiao-Kun; Zhang, Jing; Chen, Xiao-Jia
Source:
JOURNAL OF APPLIED PHYSICS, 111 (5):10.1063/1.3693531 MAR 1 2012
Abstract:
The structural and magnetic properties of well-prepared Bi1-xNdxFeO3 (0 <= x <= 0.2) powders are investigated by combining x-ray diffraction, Raman scattering spectra, and magnetic measurements. Structural symmetric breaking from rhombohedral R3c to orthorhombic Pnma at the substituted Nd concentration of x = 0.125-0.15, accompanying a ferroelectric-antiferroelectric phase transition, is identified from x-ray diffraction patterns and Raman scattering spectra. The magnetization enhancement of Bi1-xNdxFeO3 is observed before approaching ferroelectric-antiferroelectric phase boundary conditions (0 <= x <= 0.15). We consider that such enhancement results from the destruction of the spin cycloid accompanying the structural transition. At x > 0.15, the magnetization decreases, which is probably attributable to further degradation of the space modulated spin structure, allowing a more perfect antiferromagnetic ordering. (C) 2012 American In! stitute of Physics. [http://dx.doi.org/10.1063/1.3693531]
Title:
Formation and properties of Zr-based bulk quasicrystalline alloys with high strength and good ductility (Retraction of vol 15, pg 2195, 2000)
Authors:
Inoue, A; Zhang, T; Saida, J; Matsushita, M Author Full Names: Inoue, Akihisa; Zhang, Tao; Saida, Junji; Matsushita, Mitsuhide
Source:
MATERIALS TRANSACTIONS, 53 (2):FEB 2012
Title:
Praphase Concept for the Phenomenological Description of Magnetoelectrics
Authors:
Sakhnenko, VP; Ter-Oganessian, NV Author Full Names: Sakhnenko, V. P.; Ter-Oganessian, N. V.
Source:
CRYSTALLOGRAPHY REPORTS, 57 (1):112-117; 10.1134/S1063774511060241 JAN 2012
Abstract:
Complex cascades of phase transitions with the alternation of antiferromagnetic, incommensurate, and magnetoelectric phases are observed in most crystals having magnetoelectric properties. The entire variety of observed phase transitions in numerous recent works is described by introducing several order parameters which are sequentially "condensed" with a decrease in temperature. The possibility of introducing the praphase concept into consideration to reduce the number of order parameters and interpret rich phase diagrams due to the smaller number of instabilities is demonstrated by the examples of MnWO4 and CuO magnetoelectrics. This approach is also used in the phenomenological description of the phase transitions in the BiFeO3 ferroelectromagnetic with the cubic phase of the perovskite structure as a starting point.

Update: 19-Apr-2012

Title:
Structural transformations in quasicrystals induced by higher dimensional lattice transitions
Authors:
Indelicato, G; Keef, T; Cermelli, P; Salthouse, DG; Twarock, R; Zanzotto, G Author Full Names: Indelicato, Giuliana; Keef, Tom; Cermelli, Paolo; Salthouse, David G.; Twarock, Reidun; Zanzotto, Giovanni
Source:
PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, 468 (2141):1452-1471; 10.1098/rspa.2011.0680 MAY 8 2012
Abstract:
We study the structural transformations induced, via the cut-and-project method, in quasicrystals and tilings by lattice transitions in higher dimensions, with a focus on transition paths preserving at least some symmetry in intermediate lattices. We discuss the effect of such transformations on planar aperiodic Penrose tilings, and on three-dimensional aperiodic Ammann tilings with icosahedral symmetry. We find that locally the transformations in the aperiodic structures occur through the mechanisms of tile splitting, tile flipping and tile merger, and we investigate the origin of these local transformation mechanisms within the projection framework.
Title:
Study of the structure and physical properties of quasicrystals using large scale facilities
Authors:
de Boissieu, M Author Full Names: de Boissieu, Marc
Source:
COMPTES RENDUS PHYSIQUE, 13 (3):207-217; 10.1016/j.crhy.2011.11.008 APR 2012
Abstract:
Quasicrystals have been puzzling scientists since their discovery. In this article we review some of the recent advances in this field and show how the use of large scale facilities has brought in decisive information for the understanding of their structure and physical properties. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Title:
Interplay between the magnetic and electric degrees of freedom in multiferroic Co3TeO6
Authors:
Li, WH; Wang, CW; Hsu, D; Lee, CH; Wu, CM; Chou, CC; Yang, HD; Zhao, Y; Chang, S; Lynn, JW; Berger, H Author Full Names: Li, Wen-Hsien; Wang, Chin-Wei; Hsu, Daniel; Lee, Chi-Hung; Wu, Chun-Ming; Chou, Chih-Chieh; Yang, Hung-Duen; Zhao, Yang; Chang, Sung; Lynn, Jeffrey W.; Berger, Helmuth
Source:
PHYSICAL REVIEW B, 85 (9):10.1103/PhysRevB.85.094431 MAR 28 2012
Abstract:
Neutron diffraction, magnetic susceptibility, specific heat, and dielectric constant measurements of single-crystal Co3TeO6 have been measured to study the interplay between the ferroelectricity and magnetic order. Long-range incommensurate magnetic order develops below T-M1 = 26 K, which is followed by three additional zero-field phase transitions at T-M2 = 19.5 K, T-M3 = 18 K, and T-M4 = 16 K where the incommensurate order changes and commensurate order develops. In magnetic fields up to 14 T we find that the magnetic intensities and incommensurate wave vector are dramatically altered as ferroelectricity develops, with a fifth abrupt transition around 10 T. The overall behavior characterizes Co3TeO6 as a type-II multiferroic.
Title:
Triangular-lattice anisotropic dimerized Heisenberg antiferromagnet: Stability and excitations of the quantum paramagnetic phase
Authors:
Doretto, RL; Vojta, M Author Full Names: Doretto, R. L.; Vojta, Matthias
Source:
PHYSICAL REVIEW B, 85 (10):10.1103/PhysRevB.85.104416 MAR 26 2012
Abstract:
Motivated by experiments on nonmagnetic triangular-lattice Mott insulators, we study one candidate paramagnetic phase, namely the columnar dimer (or valence-bond) phase. We apply variants of the bond-operator theory to a dimerized and spatially anisotropic spin-1/2 Heisenberg model and determine its zero-temperature phase diagram and the spectrum of elementary triplet excitations (triplons). Depending on model parameters, we find that the minimum of the triplon energy is located at either a commensurate or an incommensurate wave vector. Condensation of triplons at this commensurate-incommensurate transition defines a quantum Lifshitz point, with effective dimensional reduction that possibly leads to nontrivial paramagnetic (e.g., spin-liquid) states near the closing of the triplet gap. We also discuss the two-particle decay of high-energy triplons, and we comment on the relevance of our results for the organic Mott insulator (EtMeP)-P-3[Pd(dmit)(2)]! (2).
Title:
Commensurate-incommensurate magnetic phase transition induced in TbNi5 by an external magnetic field
Authors:
Bogdanov, SG; Gerasimov, EG; Skryabin, YN; Sherstobitova, EA; Sikolenko, VV; Schedler, R; Pirogov, AN Author Full Names: Bogdanov, S. G.; Gerasimov, E. G.; Skryabin, Yu N.; Sherstobitova, E. A.; Sikolenko, V. V.; Schedler, R.; Pirogov, A. N.
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 113 (3):228-232; 10.1134/S0031918X12030052 MAR 2012
Abstract:
Neutron-diffraction studies of a single crystal of TbNi5 have been performed. Temperature and field dependences of the intensities of the Bragg reflection (001) and magnetic satellites (001)(-) and (001)(+) have been determined. In the temperature range of 7-10 K, sharp changes in the intensities of both the Bragg reflection and its satellites have been revealed. A conclusion is made that these changes are due to the existence of a magnetic transition from an incommensurate into a lock-in structure. It has been found that at 11 K an external magnetic field mu(0) H = 0.1 T oriented along the [100] axis induces the same magnetic state of the crystal as its cooling to 7 K in the absence of a field. In an external magnetic field mu(0) H = 0.4 T, there occurs a magnetic transition from the incommensurate phase with a wave vector k = 2 pi/c (0, 0, 0.18) into a commensurate ferromagnetic phase with k = 0. In the ferromagnetic phase, an increase in the field from 0.4 to 0.6 T is accompanied by an increase in the intensity of the ferromagnetic reflection (001) by a factor of 1.6. This indicates the existence of strong fluctuations of the magnetization at 0.4 T.
Title:
Evolution of spin-modulated magnetic compound Bi(1-x)SrxFeO3
Authors:
Gippius, AA; Tkachev, AV; Gervits, NE; Pokatilov, VS; Konovalova, AO; Sigov, AS Author Full Names: Gippius, A. A.; Tkachev, A. V.; Gervits, N. E.; Pokatilov, V. S.; Konovalova, A. O.; Sigov, A. S.
Source:
SOLID STATE COMMUNICATIONS, 152 (6):552-556; 10.1016/j.ssc.2011.12.028 MAR 2012
Abstract:
BiFeO3 is a perovskite-like compound with magnetic and electrical long-range order with antiferromagnetic transition temperature about 670 K. It has space modulated magnetic structure of cycloidal type with the period lambda = 620 +/- 20 angstrom incommensurate with the lattice parameter leading to specific NMR line shape. Substitution of strontium for bismuth atoms destroys the space modulated structure. Several samples with substitution of strontium for bismuth Bi1-xSrxFeO3 were studied by means of zero field NMR and Mossbauer spectroscopy. A significant broadening of Fe-57 NMR spectrum was observed at x = 0.10 while Mossbauer spectroscopy demonstrates this effect at x = 0.07. This phenomena evidence for the destruction of the spatial modulated magnetic structure at x similar to 0.07-0.10 by the heterovalent substitution of strontium for bismuth without the destruction of crystal rhombohedral structure. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Morphotropic Phase Boundary, Weak Ferromagnetism, and Strong Piezoelectric Effect in Bi1-xCaxFeO3-x/2 Compounds
Authors:
Troyanchuk, IO; Karpinsky, DV; Bushinsky, MV; Kovetskaya, MI; Efimova, EA; Eremenko, VV Author Full Names: Troyanchuk, I. O.; Karpinsky, D. V.; Bushinsky, M. V.; Kovetskaya, M. I.; Efimova, E. A.; Eremenko, V. V.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 113 (6):1025-1031; 10.1134/S1063776111140196 DEC 2011
Abstract:
The crystal structure and magnetic and piezoelectric properties of the Bi1-xCaxFeO3-x/2 system (x <= 0.2) are studied. The crystal-structure transformations occur in the following sequence: rhombohedral (R3c) polar phase (x <= 0.06) -> modulated polar phase (0.07 <= x <= 0.1) -> modulated antipolar phase (0.11 <= x <= 0.14). The modulated polar and antipolar phases are weakly ferromagnetic with a spontaneous magnetization of 0.25 G cm(3)/g (x = 0.09). In the polar weak ferromagnet with x = 0.09, a uniform piezoelectric response 2.5 times stronger than in the initial BiFeO3 compound is detected by the piezoelectric force microscopy.

Update: 11-Apr-2012

Title:
Statistical mechanics of two dimensional tilings
Authors:
Kaatz, FH; Estrada, E; Bultheel, A; Sharrock, N Author Full Names: Kaatz, Forrest H.; Estrada, Ernesto; Bultheel, Adhemar; Sharrock, Noel
Source:
PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS, 391 (10):2957-2963; 10.1016/j.physa.2012.01.013 MAY 15 2012
Abstract:
Reduced dimensionality in two dimensions is a topic of current interest. We use model systems to investigate the statistical mechanics of ideal networks. The tilings have possible applications such as the 2D locations of pore sites in nanoporous arrays (quantum dots), in the 2D hexagonal structure of graphene, and as adsorbates on quasicrystalline crystal surfaces. We calculate the statistical mechanics of these networks, such as the partition function, free energy, entropy, and enthalpy. The plots of these functions versus the number of links in the finite networks result in power law regression. We also determine the degree distribution, which is a combination of power law and rational function behavior. In the large-scale limit, the degree of these 2D networks approaches 3, 4, and 6, in agreement with the degree of the regular tilings. In comparison, a Penrose tiling has a degree also equal to about 4. (C) 2012 Elsevier B.V. All rights reserved.
Title:
Imaging the coexistence of a superconducting phase and a charge-density modulation in the K0.73Fe1.67Se2 superconductor using a scanning tunneling microscope
Authors:
Cai, P; Ye, C; Ruan, W; Zhou, XD; Wang, AF; Zhang, M; Chen, XH; Wang, YY Author Full Names: Cai, Peng; Ye, Cun; Ruan, Wei; Zhou, Xiaodong; Wang, Aifeng; Zhang, Meng; Chen, Xianhui; Wang, Yayu
Source:
PHYSICAL REVIEW B, 85 (9):10.1103/PhysRevB.85.094512 MAR 23 2012
Abstract:
We report scanning tunneling microscopy studies of the local structural and electronic properties of the iron selenide superconductor K0.73Fe1.67Se2 with T-C = 32 K. On the atomically resolved FeSe surface, we observe a well-defined superconducting gap and the microscopic coexistence of a charge-density modulation with root 2 x root 2 periodicity with respect to the original Se lattice. We propose that a possible origin of the pattern is the electronic superstructure caused by the block-antiferromagnetic ordering of the iron moments. The widely expected iron vacancy ordering is not observed, indicating that it is not a necessary ingredient for superconductivity in the intercalated iron selenides.
Title:
A molecular "phase ordering" phase transition leading to a modulated aperiodic composite in n-heptane/urea
Authors:
Mariette, C; Huard, M; Rabiller, P; Nichols, SM; Ecolivet, C; Janssen, T; Alquist, KE; Hollingsworth, MD; Toudic, B Author Full Names: Mariette, C.; Huard, M.; Rabiller, P.; Nichols, Shane M.; Ecolivet, C.; Janssen, Ted; Alquist, Keith E., III; Hollingsworth, Mark D.; Toudic, B.
Source:
JOURNAL OF CHEMICAL PHYSICS, 136 (10):10.1063/1.3692329 MAR 14 2012
Abstract:
n-Heptane/urea is an aperiodic inclusion compound in which the ratio of host and guest repeats along the channel axis is very close to unity and is found to have a constant value (0.981) from 280 K to 90 K. Below 280 K, two phase transitions are observed. The first (T-c1 = 145 K) is a ferroelastic phase transition that generates superstructure reflections for the host while leaving the guest with 1D order. The second (T-c2 = 130 K) is a "phase ordering" transition to a four-dimensional structure (P2(1)11(0 beta gamma)) with pronounced host-guest intermodulation and a temperature dependent phase shift between guests in adjacent channels. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3692329]

Update: 5-Apr-2012

Title:
Fixed-point tile sets and their applications
Authors:
Durand, B; Romashchenko, A; Shen, A Author Full Names: Durand, Bruno; Romashchenko, Andrei; Shen, Alexander
Source:
JOURNAL OF COMPUTER AND SYSTEM SCIENCES, 78 (3):731-764; 10.1016/j.jcss.2011.11.001 MAY 2012
Abstract:
An aperiodic tile set was first constructed by R. Berger while proving the undecidability of the domino problem. It turned out that aperiodic tile sets appear in many fields, ranging from logic (the Entscheidungsproblem) to physics (quasicrystals). We present a new construction of an aperiodic tile set that is based on Kleene's fixed-point construction instead of geometric arguments. This construction is similar to J. von Neumann's self-reproducing automata: similar ideas were also used by P. Gacs in the context of error-correcting computations. This construction is rather flexible, so it can be used in many ways. We show how it can be used to implement substitution rules, to construct strongly aperiodic tile sets (in which any tiling is far from any periodic tiling), to give a new proof for the undecidability of the domino problem and related results, to characterize effectively closed one-dimensional subshifts in terms of two-dimensional subshifts of finite type (an ! improvement of a result by M. Hochman), to construct a tile set that has only complex tilings, and to construct a "robust" aperiodic tile set that does not have periodic (or close to periodic) tilings even if we allow some (sparse enough) tiling errors. For the latter, we develop a hierarchical classification of points in random sets into islands of different ranks. Finally, we combine and modify our tools to prove our main result: There exists a tile set such that all tilings have high Kolmogorov complexity even if (sparse enough) tiling errors are allowed. Some of these results were included in the DLT extended abstract (Durand et al., 2008 [9]) and in the ICALP extended abstract (Durand et al., 2009 [10]). (C) 2011 Elsevier Inc. All rights reserved.
Title:
Empirical oscillating potentials for alloys from ab initio fits and the prediction of quasicrystal-related structures in the Al-Cu-Sc system
Authors:
Mihalkovic, M; Henley, CL Author Full Names: Mihalkovic, Marek; Henley, C. L.
Source:
PHYSICAL REVIEW B, 85 (9):10.1103/PhysRevB.85.092102 MAR 19 2012
Abstract:
By fitting to a database of ab initio forces and energies, we can extract pair potentials for alloys with a simple six-parameter analytic form including Friedel oscillations, which give a remarkably faithful account of many complex intermetallic compounds. Furthermore, such potentials are combined with a method of discovering complex zero-temperature structures with hundreds of atoms per cell, given only the composition and the constraint of known lattice parameters, using molecular-dynamics quenches. We apply this approach to structure prediction in the Al-Cu-Sc quasicrystal-related system.
Title:
Magnetic Frustration in a Quantum Spin Chain: The Case of Linarite PbCuSO4(OH)(2)
Authors:
Willenberg, B; Schapers, M; Rule, KC; Sullow, S; Reehuis, M; Ryll, H; Klemke, B; Kiefer, K; Schottenhamel, W; Buchner, B; Ouladdiaf, B; Uhlarz, M; Beyer, R; Wosnitza, J; Wolter, AUB Author Full Names: Willenberg, B.; Schaepers, M.; Rule, K. C.; Suellow, S.; Reehuis, M.; Ryll, H.; Klemke, B.; Kiefer, K.; Schottenhamel, W.; Buechner, B.; Ouladdiaf, B.; Uhlarz, M.; Beyer, R.; Wosnitza, J.; Wolter, A. U. B.
Source:
PHYSICAL REVIEW LETTERS, 108 (11):10.1103/PhysRevLett.108.117202 MAR 16 2012
Abstract:
We present a combined neutron diffraction and bulk thermodynamic study of the natural mineral linarite PbCuSO4(OH)(2), this way establishing the nature of the ground-state magnetic order. An incommensurate magnetic ordering with a propagation vector k = (0, 0.186, 1/2) was found below T-N = 2.8 K in a zero magnetic field. The analysis of the neutron diffraction data yields an elliptical helical structure, where one component (0.638 mu(B)) is in the monoclinic ac plane forming an angle with the a axis of 27(2)degrees, while the other component (0.833 mu(B)) points along the b axis. From a detailed thermodynamic study of bulk linarite in magnetic fields up to 12 T, applied along the chain direction, a very rich magnetic phase diagram is established, with multiple field-induced phases, and possibly short-range-order effects occurring in high fields. Our data establish linarite as a model compound of the frustrated one-dimensional spin chain, with ferromagnetic nearest-neighbor ! and antiferromagnetic next-nearest-neighbor interactions. Long-range magnetic order is brought about by interchain coupling 1 order of magnitude smaller than the intrachain coupling.
Title:
Inelastic Neutron-Scattering Measurements of Incommensurate Magnetic Excitations on Superconducting LiFeAs Single Crystals
Authors:
Qureshi, N; Steffens, P; Drees, Y; Komarek, AC; Lamago, D; Sidis, Y; Harnagea, L; Grafe, HJ; Wurmehl, S; Buchner, B; Braden, M Author Full Names: Qureshi, N.; Steffens, P.; Drees, Y.; Komarek, A. C.; Lamago, D.; Sidis, Y.; Harnagea, L.; Grafe, H. -J.; Wurmehl, S.; Buechner, B.; Braden, M.
Source:
PHYSICAL REVIEW LETTERS, 108 (11):10.1103/PhysRevLett.108.117001 MAR 12 2012
Abstract:
Magnetic correlations in superconducting LiFeAs were studied by elastic and by inelastic neutron-scattering experiments. There is no indication for static magnetic ordering, but inelastic correlations appear at the incommensurate wave vector (0.5 +/- delta, 0.5 -/+ delta, 0) with delta similar to 0.07 slightly shifted from the commensurate ordering observed in other FeAs-based compounds. The incommensurate magnetic excitations respond to the opening of the superconducting gap by a transfer of spectral weight.
Title:
Fermi-edge polaritons in Bragg multiple-quantum-well structures
Authors:
Averkiev, NS; Glazov, MM; Voronov, MM Author Full Names: Averkiev, N. S.; Glazov, M. M.; Voronov, M. M.
Source:
SOLID STATE COMMUNICATIONS, 152 (5):395-398; 10.1016/j.ssc.2011.12.002 MAR 2012
Abstract:
The polariton propagation in one-dimensional photonic crystals and quasicrystals based on highly doped quantum-well structures has been theoretically studied. The superradiant and photonic crystal regimes have been considered and expressions for band gap edges for light waves in the Bragg structures have been obtained. The reflection and absorption spectra of such systems have been calculated and the so-called two-wave approximation to their study has been applied. The optical properties of the doped multiple-quantum-well structures are compared with those of undoped ones. (C) 2011 Elsevier Ltd. All rights reserved.

Update: 29_Mar_2012

Title:
Effect of yttrium addition on the formation and mechanical properties of Ti-Zr-Ni-Cu bulk quasicrystalline alloys
Authors:
Wang, XL (Wang, Xinlu); Zhang, SS (Zhang, Shanshan); Wang, LD (Wang, Lidong); Liu, WQ (Liu, Wanqiang); Wu, YM (Wu, Yaoming); Wang, LM (Wang, Limin) Author Full Names: Wang, XL (Wang, Xinlu); Zhang, SS (Zhang, Shanshan); Wang, LD (Wang, Lidong); Liu, WQ (Liu, Wanqiang); Wu, YM (Wu, Yaoming); Wang, LM (Wang, Limin)
Source:
JOURNAL OF ALLOYS AND COMPOUNDS Volume: 522 Pages: 96-100 DOI: 10.1016/j.jallcom.2012.01.096 Published: MAY 5 2012
Abstract:
The effect of yttrium (Y) on the structure and mechanical properties of the as-cast (Ti48Zr36Ni14Cu2)(1-x)Y-x (x = 0, 0.01 and 0.02) bulk quasicrystalline alloys was investigated. These alloys were mainly composed of icosahedral quasicrystalline phase (i-phase) accompanied by minor hexagonal C14 Laves phase and solid-solution. beta-(Ti/Zr) phase. The characterization on their mechanical properties had been carried out by means of microhardness indentation and compression tests at room temperature. The microhardness test showed that the toughness of them was much better than many other i-phase alloys because no obvious crack was detected even at the load of 4.9 N. The compressive fracture strengths first increased and then decreased with increasing x, and the highest strength was 1350 MPa when x = 0.01, it was 210 MPa higher than the without Y alloy. These results reveal that an appropriate amount of Y addition would enhance the mechanical properties of the bulk i-phase alloy. (C) 2012 Elsevier B. V. All rights reserved.
Title:
Kinetic control of structural and magnetic states in LuBaCo4O7
Authors:
Avci, S (Avci, S.); Chmaissem, O (Chmaissem, O.); Zheng, H (Zheng, H.); Huq, A (Huq, A.); Khalyavin, DD (Khalyavin, D. D.); Stephens, PW (Stephens, P. W.); Suchomel, MR (Suchomel, M. R.); Manuel, P (Manuel, P.); Mitchell, JF (Mitchell, J. F.) Author Full Names: Avci, S (Avci, S.); Chmaissem, O (Chmaissem, O.); Zheng, H (Zheng, H.); Huq, A (Huq, A.); Khalyavin, DD (Khalyavin, D. D.); Stephens, PW (Stephens, P. W.); Suchomel, MR (Suchomel, M. R.); Manuel, P (Manuel, P.); Mitchell, JF (Mitchell, J. F.)
Source:
PHYSICAL REVIEW B Volume: 85 Issue: 9 Article Number: 094414 DOI: 10.1103/PhysRevB.85.094414 Published: MAR 9 2012
Abstract:
The RBaCo4O7 (R = Ca, Y, Tb, Ho, Tm, Yb, Lu) compounds provide a novel topology for studying the competition between triangular geometry and magnetic order. Here, we report the structural and magnetic behavior of the Lu member of this series via neutron and synchrotron x-ray diffraction, magnetization, and resistivity measurements. We determined sequential phase transitions and a strong competition between a stable and a metastable low-temperature state that critically depends on controlled cooling rates and the associated heat removal kinetics. No evidence for long-range ordered magnetism was detected by neutron diffraction at any temperature. However, very slow spin dynamics are evidenced by time-dependent neutron diffraction measurements and can be explained by several competing magnetic phases with incommensurate short-range correlations coexisting in this material.
Title:
Coupling of replicate order-parameters in incommensurate multiferroics
Authors:
Mettout, B (Mettout, Bruno); Toledano, P (Toledano, Pierre) Author Full Names: Mettout, B (Mettout, Bruno); Toledano, P (Toledano, Pierre)
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER Volume: 24 Issue: 8 Article Number: 086002 DOI: 10.1088/0953-8984/24/8/086002 Published: FEB 29 2012
Abstract:
I The specific properties of incommensurate multiferroic phases resulting from the coupling of order-parameter replicates are worked out using the illustrative example of iron vanadate. The phase difference between the order-parameter copies induces an additional broken symmetry phase corresponding to the lowest symmetry of the system and varies critically at the transition to the multiferroic phase. It reflects the temperature dependence of the angle between paired spins in the antiferromagnetic spiral structure. Expressing the transition order-parameters in terms of spin-density waves allows us to show that isotropic exchange interactions contribute to the stabilization of the ferroelectric phase.
Title:
Commensurate-incommensurate transition of He-4 adsorbed on a single C-60 molecule
Authors:
Shin, H (Shin, Hyeondeok); Kwon, Y (Kwon, Yongkyung) Author Full Names: Shin, H (Shin, Hyeondeok); Kwon, Y (Kwon, Yongkyung)
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER Volume: 24 Issue: 8 Article Number: 086002 DOI: 10.1088/0953-8984/24/8/086002 Published: FEB 29 2012
Abstract:
The specific properties of incommensurate multiferroic phases resulting from the coupling of order-parameter replicates are worked out using the illustrative example of iron vanadate. The phase difference between the order-parameter copies induces an additional broken symmetry phase corresponding to the lowest symmetry of the system and varies critically at the transition to the multiferroic phase. It reflects the temperature dependence of the angle between paired spins in the antiferromagnetic spiral structure. Expressing the transition order-parameters in terms of spin-density waves allows us to show that isotropic exchange interactions contribute to the stabilization of the ferroelectric phase.

Update: 22-Mar-2012

Title:
Quasicrystal discovery-from NBS/NIST to Stockholm
Authors:
Hargittai, B; Hargittai, I Author Full Names: Hargittai, Balazs; Hargittai, Istvan
Source:
STRUCTURAL CHEMISTRY, 23 (2):301-306; 10.1007/s11224-012-9953-x APR 2012
Abstract:
There were ideal conditions in 1982 at the NBS/NIST for the kind of exploratory research that led Dan Shechtman to the quasicrystal discovery. Almost thirty years later, in 2011, Shechtman received the Nobel Prize for this achievement. What happened in between these two dates has been covered quite extensively elsewhere. But it is intriguing to learn more about the very beginning. Then, the festivities in Stockholm added to our seeing the story in a fuller perspective.
Title:
Structural aspects of the relaxation process in spin crossover solids: Phase separation, mapping of lattice strain, and domain wall structure
Authors:
Nicolazzi, W; Pillet, S Author Full Names: Nicolazzi, W.; Pillet, S.
Source:
PHYSICAL REVIEW B, 85 (9):10.1103/PhysRevB.85.094101 MAR 2 2012
Abstract:
We present a nonequilibrium study of the relaxation process in spin crossover solids using numerical simulations of a recently introduced two-variable elastic Ising-like model. We analyze the structural lattice distortions accompanying the relaxation from the metastable high-spin to the ground low-spin state as a function of cooperativity. In the highly cooperative case, a sigmoidal relaxation behavior of the high-spin fraction n(HS) is described, and it occurs jointly with a structural phase separation process. The mean lattice spacing follows a similar sigmoidal trend, owing to the interplay between electronic and lattice variables in the Hamiltonian. Weakly cooperative systems are characterized by single exponential relaxations of the high-spin fraction, the corresponding structural transformation proceeds homogeneously with a progressive relaxation of the mean lattice spacing. Long relaxation tail effects are also observed. We highlight the development of lattice strain accompanying the spin transition, and show that structural phase rebuilding proceeds in the late stage of the relaxation by releasing residual strain. Under specific conditions, a temporal decoupling between the electronic and lattice variables is observed, which may have direct applications for interpreting time-resolved spectroscopic or diffraction experiments and for elucidating unusual structural behaviors, such as the development of superstructures, modulated structures, or transient phases.
Title:
Similarity and Coincidence Isometries for Modules
Authors:
Glied, S Author Full Names: Glied, Svenja
Source:
CANADIAN MATHEMATICAL BULLETIN-BULLETIN CANADIEN DE MATHEMATIQUES, 55 (1):98-107; 10.4153/CMB-2011-076-x MAR 2012
Abstract:
The groups of (linear) similarity and coincidence isometries of certain modules Gamma in d-dimensional Euclidean space, which naturally occur in quasicrystallography, are considered. It is shown that the structure of the factor group of similarity modulo coincidence isometrics is the direct sum of cyclic groups of prime power orders that divide d. In particular, if the dimension d is a prime number p, the factor group is an elementary abelian p-group. This generalizes previous results obtained for lattices to situations relevant in quasicrystallography.
Title:
Pb3TeCo3V2O14: A Potential Multiferroic Co Bearing Member of the Dugganite Series
Authors:
Silverstein, HJ; Cruz-Kan, K; Hallas, AM; Zhou, HD; Donaberger, RL; Hernden, BC; Bieringer, M; Choi, ES; Hwang, JM; Wills, AS; Wiebe, CR Author Full Names: Silverstein, H. J.; Cruz-Kan, K.; Hallas, A. M.; Zhou, H. D.; Donaberger, R. L.; Hernden, B. C.; Bieringer, M.; Choi, E. S.; Hwang, J. M.; Wills, A. S.; Wiebe, C. R.
Source:
CHEMISTRY OF MATERIALS, 24 (4):664-670; 10.1021/cm202502p FEB 28 2012
Abstract:
Polycrystalline Pb3TeCo3V2O14, a structural analogue of the multiferroic Ba3NbFe3Si2O14, was synthesized and characterized using X-ray diffraction, magnetic susceptibility, specific heat, dielectric constant, and neutron diffraction. Magnetic susceptibility, specific heat capacity measurements, and bond valence analysis confirmed that the V5+ ion is nonmagnetic, while Co2+ is in its high spin state (S = 3/2). Two magnetic transitions were seen at T-N1 = 8.6 K and T-N2 = 6.0 K where the spins first adopt a magnetic structure with propagation vector (k) over right arrow = (0.752,0,1/2) and reorder into a commensurate structure with propagation vector (k) over right arrow = (5/6,5/6,1/2). Changes in the dielectric constant at both magnetic phase transitions suggest that magnetoelectric coupling exists in Pb3TeCo3V2O14.
Title:
Scanning-Tunneling Microscope Imaging of Single-Electron Solitons in a Material with Incommensurate Charge-Density Waves
Authors:
Brazovskii, S; Brun, C; Wang, ZZ; Monceau, P Author Full Names: Brazovskii, Serguei; Brun, Christophe; Wang, Zhao-Zhong; Monceau, Pierre
Source:
PHYSICAL REVIEW LETTERS, 108 (9):10.1103/PhysRevLett.108.096801 FEB 27 2012
Abstract:
We report on scanning-tunneling microscopy experiments in a charge-density wave (CDW) system allowing visually capturing and studying in detail the individual solitons corresponding to the self-trapping of just one electron. This "Amplitude Soliton'' is marked by vanishing of the CDW amplitude and by the pi shift of its phase. It might be the realization of the spinon-the long-sought particle (along with the holon) in the study of science of strongly correlated electronic systems. As a distinct feature we also observe one-dimensional Friedel oscillations superimposed on the CDW which develop independently of solitons.
Title:
THE DISCOVERY OF THE FIRST NATURAL QUASICRYSTAL A New Era for Mineralogy?
Authors:
Bindi, L; Steinhardt, PJ Author Full Names: Bindi, Luca; Steinhardt, Paul J.
Source:
ELEMENTS, 8 (1):13-14; 10.2113/gselements.8.1.13 FEB 2012
Abstract:
For nearly two centuries, a basic tenet of geology and solid state physics was that pure substances form crystals, periodic arrangements of atoms with a restricted set of possible symmetries. For example, the rigorous mathematical theorems of crystallography derived over 100 years ago strictly forbid solids with five-fold symmetry axes. Then, in 1984, Dan Shechtman, Ilan Blech, Denis Gratias, and John Cahn (Shechtman et al. 1984) reported the discovery of a puzzling man-made alloy of aluminum and manganese that produces a diffraction pattern of sharp spots like a crystal, but with the symmetry of an icosahedron.
Title:
Magnetic structure of the modulated martensite phase in Ni-Mn-Ga ferromagnetic shape memory alloys
Authors:
Singh, RK; Raja, MM; Mathur, RP; Shamsuddin, M Author Full Names: Singh, R. K.; Raja, M. Manivel; Mathur, R. P.; Shamsuddin, M.
Source:
MATERIALS CHEMISTRY AND PHYSICS, 132 (1):104-108; 10.1016/j.matchemphys.2011.11.003 JAN 16 2012
Abstract:
The magnetic structure of the seven layered (7 M) modulated martensite phases in Mn-rich Ni-Mn-Ga alloys was studied using Mossbauer spectroscopy. The Mossbauer results clearly demonstrate that in contrast to the non-modulated tetragonal structure two new magnetic sublattices exists for the 7M orthorhombic martensite phase. Based on the unit cell symmetry and atomic coordination, the additional magnetic sublattices have been assigned to the Ni site. The variation in the magnetic properties of the martensite phases has been related to the underlying magnetic structure. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Structural and Mechanical Characterization of Zr58.5Ti8.2Cu14.2Ni11.4Al7.7 Bulk Metallic Glass
Authors:
Prashanth, KG; Scudino, S; Khoshkhoo, MS; Surreddi, KB; Stoica, M; Vaughan, G; Eckert, J Author Full Names: Prashanth, Konda G.; Scudino, Sergio; Khoshkhoo, Mohsen Samadi; Surreddi, Kumar B.; Stoica, Mihai; Vaughan, Gavin; Eckert, Juergen
Source:
MATERIALS, 5 (1):1-11; 10.3390/ma5010001 JAN 2012
Abstract:
Thermal stability, structure and mechanical properties of the multi-component Zr58.5Ti8.2Cu14.2Ni11.4Al7.7 bulk metallic glass have been studied in detail. The glassy material displays good thermal stability against crystallization and a fairly large supercooled liquid region of 52 K. During heating, the alloy transforms into a metastable icosahedral quasicrystalline phase in the first stage of crystallization. At high temperatures, the quasicrystalline phase undergoes a transformation to form tetragonal and cubic NiZr2-type phases. Room-temperature compression tests of the as-cast sample show good mechanical properties, namely, high compressive strength of about 1,630 MPa and fracture strain of 3.3%. This is combined with a density of 6.32 g/cm(3) and values of Poisson's ratio and Young's modulus of 0.377 and 77 GPa, respectively. The mechanical properties of the glass can be further improved by cold rolling. The compressive strength rises to 1,780 MPa a! nd the fracture strain increases to 8.3% for the material cold-rolled to a diameter reduction of 10%.
Title:
Fabrication and Corrosion Resistance of Mg-Zn-Y-based Nano-quasicrystals Alloys
Authors:
Wang, ZF; Zhao, WM; Qin, CL; Cui, Y Author Full Names: Wang, Zhifeng; Zhao, Weimin; Qin, Chunling; Cui, Yan
Source:
MATERIALS RESEARCH-IBERO-AMERICAN JOURNAL OF MATERIALS, 15 (1):51-56; 10.1590/S1516-14392012005000004 JAN-FEB 2012
Abstract:
A wedge-shaped copper mold was used to fabricate micro quasicrystals (QCs). Stable Mg-Zn-Y-based nano-QCs were directly synthesized through this simple route instead of crystallization from metallic glasses or complicated forming processes at high temperature. The study showed that on the tips of the wedge-shaped ingots, the minimum diameter of nano-QCs approach to 4 similar to 6 nm. The main size of nano-QCs is about 10 similar to 30 nm. The maximum microhardness of QCs has been dramatically improved to about HV440 which increased by about 280% compared with that of the petal-like QCs fabricated under common cast iron mold cooling conditions. Possessing a certain negative enthalpy of mixing and existence of Frank-Kasper-type phases determined the formation of Mg-Zn-Y-based nano-QCs. The further electrochemical studies showed that Mg71Zn26Y2Cu1 nano-QC alloy possess high corrosion resistance in simulated seawater and its corrosion resistance is much better than those of the Mg72Zn26Y2 and Mg71Zn26Y2Cu0.5Ni0.5 nano-QC alloys.

Update: 7-Mar-2012

Title:
Continuous magnetic and structural phase transitions in Fe1+yTe
Authors:
Zaliznyak, IA; Xu, ZJ; Wen, JS; Tranquada, JM; Gu, GD; Solovyov, V; Glazkov, VN; Zheludev, AI; Garlea, VO; Stone, MB Author Full Names: Zaliznyak, I. A.; Xu, Z. J.; Wen, J. S.; Tranquada, J. M.; Gu, G. D.; Solovyov, V.; Glazkov, V. N.; Zheludev, A. I.; Garlea, V. O.; Stone, M. B.
Source:
PHYSICAL REVIEW B, 85 (8):10.1103/PhysRevB.85.085105 FEB 13 2012
Abstract:
We report a sequence of continuous phase transformations in iron telluride, Fe1+yTe with y = 0.10(1), which is observed by combining neutron diffraction, magnetic susceptibility, and specific-heat measurements on single-crystal samples. While a gradual increase of magnetic scattering near the wave vector (0.5,0,0.5) is seen below T approximate to 70 K, a temperature where the discontinuous first-order magnetostructural phase transition is found in systems with small y (less than or similar to 0.06), the reduction of the lattice symmetry in Fe1.1Te only occurs at T-s approximate to 63 K. Below T-N approximate to 57.5 K, the long-range magnetic order develops, the incommensurate wave vector Q(m) of which varies with temperature. Finally, at T-m less than or similar to 45 K, the system enters the low-T phase, where Q(m) is locked at approximate to (0.48,0,0.5). We conclude that these instabilities are weak compared to the strength of the underlying interactions, and we suggest that the impact of the Fe interstitials on the transitions can be treated with random-field models.
Title:
Defect-induced spin-glass magnetism in incommensurate spin-gap magnets
Authors:
Andrade, EC; Vojta, M Author Full Names: Andrade, E. C.; Vojta, M.
Source:
EPL, 97 (3):10.1209/0295-5075/97/37007 FEB 2012
Abstract:
We study magnetic order induced by non-magnetic impurities in quantum paramagnets with incommensurate host spin correlations. In contrast to the well-studied commensurate case where the defect-induced magnetism is spatially disordered but non-frustrated, the present problem combines strong disorder with frustration and, consequently, leads to spin-glass order. We discuss the crossover from strong randomness in the dilute limit to more conventional glass behavior at larger doping, and numerically characterize the robust short-range order inherent to the spin-glass phase. We relate our findings to magnetic order in both BiCu2PO6 and YBa2Cu3O6.6 induced by Zn substitution. Copyright (C) EPLA, 2012
Title:
QUASICRYSTALS Unearthly beauty
Authors:
Trabesinger, A Author Full Names: Trabesinger, Andreas
Source:
NATURE PHYSICS, 8 (2):112-112; FEB 2012

Update: 29-Feb-2012

Title:
Fermi surface reconstruction in CeTe2 induced by charge density waves investigated via angle resolved photoemission
Authors:
Kang, JS; Kim, DH; Lee, HJ; Hwang, J; Lee, HK; Kim, HD; Min, BH; Lee, KE; Kwon, YS; Kim, JW; Kim, K; Kim, BH; Min, BI Author Full Names: Kang, J-S.; Kim, D. H.; Lee, H. J.; Hwang, Jihoon; Lee, Han-Koo; Kim, H-D; Min, B. H.; Lee, K. E.; Kwon, Y. S.; Kim, J. W.; Kim, Kyoo; Kim, B. H.; Min, B. I.
Source:
PHYSICAL REVIEW B, 85 (8):10.1103/PhysRevB.85.085104 FEB 10 2012
Abstract:
Electronic structures of a charge-density wave (CDW) system CeTe2-xSbx (x = 0, 0.05) have been investigated by employing angle-resolved photoemission spectroscopy (ARPES) and the first-principles electronic and phonon band-structure methods. The observed Fermi surface (FS) agrees very well with the calculated FS for the undistorted CeTe2 both in shapes and sizes. The metallic states crossing the Fermi level (E-F) are observed in ARPES even in the CDW state. The carriers near E-F have mainly the Te(1) 5p character, with a negligible contribution from Ce 4f states. The supercell (shadow) bands and the corresponding very weak FSs are found to arise from band folding due to the interaction of Te(1) layers with Ce-Te(2) layers. We found that the CDW modulation vector is along Gamma-X (Q(CDW) approximate to X), which is not coincident with the most prominent FS nesting vector.
Title:
Examining the structure and bonding in complex oxides using aberration-corrected imaging and spectroscopy
Authors:
Klie, RF; Qiao, Q; Paulauskas, T; Ramasse, Q; Oxley, MP; Idrobo, JC Author Full Names: Klie, R. F.; Qiao, Q.; Paulauskas, T.; Ramasse, Q.; Oxley, M. P.; Idrobo, J. C.
Source:
PHYSICAL REVIEW B, 85 (5):10.1103/PhysRevB.85.054106 FEB 10 2012
Abstract:
Our ability to directly characterize the atomic and electronic structures is crucial to developing a fundamental understanding of structure-property relationships in complex-oxide materials. Here, we examine one specific example, the misfit-layered thermoelectric material Ca3Co4O9, which exhibits a high Seebeck coefficient governed by spin-entropy transport as well as hopping-mediated electron transport. However, the role of oxygen and its bonding with cobalt in thermoelectric transport remains unclear. We use atomic-resolution annular bright-field imaging to directly image the oxygen sublattice and to combine our experimental data with multislice image calculations to find that the oxygen atoms in the CoO2 subsystem are highly ordered, while the oxygen-atomic columns are displaced in the Ca2CoO3 subsystem. Atomic-column-resolved electron energy-loss spectroscopy and spectrum image calculations are used to quantify the bonding in the different subsystems of! incommensurate Ca3Co4O9. We find that the holes in the CoO2 subsystem are delocalized, which could be responsible for the p-type conductivity found in the CoO2 subsystem.
Title:
Giant Improper Ferroelectricity in the Ferroaxial Magnet CaMn7O12
Authors:
Johnson, RD; Chapon, LC; Khalyavin, DD; Manuel, P; Radaelli, PG; Martin, C Author Full Names: Johnson, R. D.; Chapon, L. C.; Khalyavin, D. D.; Manuel, P.; Radaelli, P. G.; Martin, C.
Source:
PHYSICAL REVIEW LETTERS, 108 (6):10.1103/PhysRevLett.108.067201 FEB 6 2012
Abstract:
In rhombohedral CaMn7O12, an improper ferroelectric polarization of magnitude 2870 mu Cm-2 is induced by an incommensurate helical magnetic structure that evolves below T-N1 = 90 K. The electric polarization was found to be constrained to the high symmetry threefold rotation axis of the crystal structure, perpendicular to the in-plane rotation of the magnetic moments. The multiferroicity is explained by the ferroaxial coupling mechanism, which in CaMn7O12 gives rise to the largest magnetically induced, electric polarization measured to date.
Title:
The effect of Li-substitution on the M-phases of AgNbO3
Authors:
Khan, HU; Sterianou, I; Miao, S; Pokorny, J; Reaney, IM Author Full Names: Khan, H. U.; Sterianou, I.; Miao, S.; Pokorny, J.; Reaney, I. M.
Source:
JOURNAL OF APPLIED PHYSICS, 111 (2):10.1063/1.3677871 JAN 15 2012
Abstract:
Ceramics in the solid solution, LixAg1-xNbO3 (LAN) with 0 <= x <= 0.20, have been synthesized by the mixed oxide method. X-ray diffraction (XRD) revealed that only compositions with x <= 0.05 were single phase which were indexed according to Pbcm symmetry with a unit cell, root 2a(p) x root 2a(p) x 4a(p) (where a(p) is the fundamental perovskite lattice parameter). For compositions with x >= 0.1, second phase peaks attributed to LiNbO3 were observed and the matrix phase transformed to a metrically rhombohedral structure according to XRD. A phase transition at 0.05 < x <= 0.1 was confirmed by Raman spectroscopy and electron diffraction but the latter technique revealed superstructure reflections for x >= 0.1 at +/- 1/6{00l} and 1/2{ooo} +/- 1/6{00l} (where o = odd). These support the premise that Li doping invokes a new complex modulated tilt system with a root 2a(p) x root 2a(p) x 6a(p) unit cell rather than root 2a(p) x root 2a(p) x 4a(p) (Pbcm). Reflections of the type +/- 1/6{00l} are, however, streaked along the inverted right perpendicular001inverted left perpendicular direction indicating that the structure may be incommensurate or only partially ordered. The appearance of the root 2a(p) x root 2a(p) x 6a(p) structure is associated with strong asymmetry in the peak in permittivity attributed to the M-3-M-2 and a decrease in intensity of the peak in permittivity associated with the M-2-M-1 transition. Slim polarization versus field curves characteristic of weak ferroelectricity were observed for compositions with x <= 0.05 but for higher values of x the loops were unsaturated albeit with larger remanent polarization. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3677871]
Title:
Structural phase transitions of FeCo and FeNi nanoparticles: A molecular dynamics study
Authors:
Meng, LJ; Peng, XY; Zhang, KW; Tang, C; Zhong, JX Author Full Names: Meng, L. J.; Peng, X. Y.; Zhang, K. W.; Tang, C.; Zhong, J. X.
Source:
JOURNAL OF APPLIED PHYSICS, 111 (2):10.1063/1.3675275 JAN 15 2012
Abstract:
We have investigated the structural phase transition of FeCo and FeNi nanoparticles by molecular dynamics (MD) simulation using the generalized embedded atom potential (GEAM). It is found that the phase varies with the atomic compositions and annealing processes. By using the Honeycutt and Andersen index (HA index), bond order parameters (BOP) and pair correlation function (PCF), we found that a BCC to defective icosahedra phase transition occurs in the FeCo nanoparticle when Co composition is increased to about 60 at %. In the FeNi nanoparticle, three phases have been identified, namely, the BCC phase, the mixed BCC/FCC phase, and the multilayer defective icosahedral phase, which correspond to the Ni compositions of 0-20 at %, 20-70 at %, and 70-100 at %, respectively. Our simulations have well reproduced the phase transition points and most of the phases observed in recent experiments. (C) 2012 American Institute of Physics. [doi:10.1063/1.3! 675275]
Title:
Effect of Thermal Fluctuations on Magnetic Phase Separation and on the Parameters of Spin-Spiral Waves
Authors:
Arzhnikov, AK; Groshev, AG Author Full Names: Arzhnikov, A. K.; Groshev, A. G.
Source:
JETP LETTERS, 94 (9):703-707; 10.1134/S002136401121003X JAN 2012
Abstract:
Effects of temperature on magnetic phase separation and on the parameters of spin-spiral waves are studied. The study is performed using the two-dimensional single-band Hubbard model and the Hubbard-Stratonovich transformation. Both commensurate (antiferromagnetic, ferromagnetic) and incommensurate (spiral) magnetic phases are considered. The problem is solved using the static approximation with allowance for transverse fluctuations of the magnetic moment. It is shown that the temperature significantly affects the collinear and spiral magnetic phases. With an increase in the temperature, the phase-separation region near the half-filling is sufficiently reduced and substituted by the antiferromagnetic phase. The results are used for the interpretation of the magnetic properties of cuprates.

Update: 23-Feb-2012

Title:
Evidence of oxygen-dependent modulation in LuFe2O4
Authors:
Bourgeois, J; Hervieu, M; Poienar, M; Abakumov, AM; Elkaim, E; Sougrati, MT; Porcher, F; Damay, F; Rouquette, J; Van Tendeloo, G; Maignan, A; Haines, J; Martin, C Author Full Names: Bourgeois, J.; Hervieu, M.; Poienar, M.; Abakumov, A. M.; Elkaim, E.; Sougrati, M. T.; Porcher, F.; Damay, F.; Rouquette, J.; Van Tendeloo, G.; Maignan, A.; Haines, J.; Martin, C.
Source:
PHYSICAL REVIEW B, 85 (6):10.1103/PhysRevB.85.064102 FEB 6 2012
Abstract:
A polycrystalline sample of LuFe2O4 has been investigated by means of powder synchrotron x-ray and neutron diffraction and transmission electron microscopy (TEM), along with Mossbauer spectroscopy and transport and magnetic properties. A monoclinic distortion is unambiguously evidenced, and the crystal structure is refined in the monoclinic C2/m space group [a(M) = 5.9563(1) angstrom, b(M) = 3.4372(1) angstrom, c(M) = 8.6431(1) angstrom, beta = 103.24(1)degrees]. Along with the previously reported modulations distinctive of the charge-ordering (CO) of the iron species, a new type of incommensurate order is observed, characterized by a vector (q) over right arrow (1) = alpha(1)(a) over right arrow (M)* + gamma(1)(c) over right arrow (M)* (with alpha(1) congruent to 0.55, gamma(1) congruent to 0.13). In situ heating TEM observations from 300 to 773 K confirm that the satellites associated with (q) over right arrow (1) vanish completely, only at a temperature significantly higher than the CO temperature. This incommensurate modulation has a displacive character and corresponds primarily to a transverse displacive modulation wave of the Lu cations position, as revealed by the high resolution, high angle annular dark field scanning TEM images and in agreement with synchrotron data refinements. Analyses of vacuum-annealed samples converge toward the hypothesis of a new ordering mechanism, associated with a tiny oxygen deviation from the O-4 stoichiometry.
Title:
Embedded atom method potentials for Al-Pd-Mn phases
Authors:
Schopf, D; Brommer, P; Frigan, B; Trebin, HR Author Full Names: Schopf, Daniel; Brommer, Peter; Frigan, Benjamin; Trebin, Hans-Rainer
Source:
PHYSICAL REVIEW B, 85 (5):10.1103/PhysRevB.85.054201 FEB 3 2012
Abstract:
A novel embedded atom method (EAM) potential for the Xi phases of Al-Pd-Mn has been determined with the force-matching method. Different combinations of analytic functions were tested for the pair and transfer part. The best results are obtained if one allows for oscillations on two different length scales. These potentials stabilize structure models of the Xi phases and describe their energy with high accuracy. Simulations at temperatures up to 1200 K show very good agreement with ab initio results with respect to stability and dynamics of the system.
Title:
Composition dependent elastic modulus and phase stability of Ni2MnGa based ferromagnetic shape memory alloys
Authors:
Hu, QM; Luo, HB; Li, CM; Vitos, L; Yang, R Author Full Names: Hu QingMiao; Luo HuBin; Li ChunMei; Vitos, Levente; Yang Rui
Source:
SCIENCE CHINA-TECHNOLOGICAL SCIENCES, 55 (2):295-305; 10.1007/s11431-011-4670-z FEB 2012
Abstract:
Ni2MnGa based ferromagnetic alloys are ideal candidates for applications such as actuators, magnetic refrigerators or magnetostrictive transducers due to their attractive properties such as magnetic field induced shape memory effect and large magnetocaloric effect. The properties of these alloys (e.g., the martensitic transformation temperature T (M) ) sensitively depend on the composition. Understanding the composition dependence of these properties so as to design the alloy as desired is one of the main research topics in this area. In recent years, we have investigated the composition dependent elastic modulus and phase stability of Ni2MnGa-based alloys by using a first-principles method, in hope of clarifying their connection to the properties of these alloys. In this article, we review the main results of our investigations. We show that the tetragonal shear modulus C' is a better predictor of the composition dependent T (M) than the number of valence electrons per atom! (e/a) since the general T (M) similar to C' correlation works for some of the alloys for which the T (M) similar to e/a correlation fails, although there exist several cases for which both the general T (M) similar to C' and T (M)similar to e/a correlations break down. Employing the experimentally determined modulation function, the complex 5-layer modulated (5M) structure of the martensite of Ni2MnGa and the Al-doping effect on it are studied. We find that the shuffle and shear of the 5M structure are linearly coupled. The relative stability of the austenite and the martensites is examined by comparing their total energies. The non-modulated martensite beta aEuro(3)aEuro(2) with the tetragonality of the unit cell c/a > 1 is shown to be globally stable whereas the 5M martensite with c/a < 1 is metastable. The critical Al atomic fraction over which the martensitic transformation between the 5M martensite and austenite cannot occur is predicted to be 0.26, in reasonable agreement with experimental findings.
Title:
Helical scattering signatures of strain and electronic textures in YbFe2O4 from three-dimensional reciprocal-space imaging
Authors:
Hearmon, AJ; Prabhakaran, D; Nowell, H; Fabrizi, F; Gutmann, MJ; Radaelli, PG Author Full Names: Hearmon, Alexander J.; Prabhakaran, Dharmalingam; Nowell, Harriott; Fabrizi, Federica; Gutmann, Matthias J.; Radaelli, Paolo G.
Source:
PHYSICAL REVIEW B, 85 (1):10.1103/PhysRevB.85.014115 JAN 27 2012
Abstract:
The insulating ternary oxide YbFe2O4 displays an unusual frustration-driven incommensurate charge-ordering (CO) transition, linked to possible ferroelectricity. Based on high-resolution synchrotron data, we report a detailed structural model showing that the CO phase is an incommensurate charge-density wave and cannot be ferroelectric, since the electrical dipole moments are also incommensurately modulated. The change between continuous and "spotty" helices of scattering at the CO transition is attributed to three-dimensional fluctuations of the direction of the ordering wave vector.
Title:
Atomic-Scale Imaging and Quantification of Electrical Polarisation in Incommensurate Antiferroelectric Lanthanum-Doped Lead Zirconate Titanate
Authors:
MacLaren, I; Villaurrutia, R; Schaffer, B; Houben, L; Pelaiz-Barranco, A Author Full Names: MacLaren, Ian; Villaurrutia, Rafael; Schaffer, Bernhard; Houben, Lothar; Pelaiz-Barranco, Aime
Source:
ADVANCED FUNCTIONAL MATERIALS, 22 (2):261-266; 10.1002/adfm.201101220 JAN 25 2012
Abstract:
Lanthanum doping of zirconium rich lead zirconate titanate gives rise to incommensurate, long-period antiferroelectric structures. The structure of two stacking sequences in this incommensurate phase is determined using quantitative analysis of high-resolution scanning transmission electron microscopy images, with the lead atom positions located with an exceptional precision of about 6 pm. This allows the estimation of local polarisation variations across the stacking units, and the polarisation varies in an approximately sinusoidal fashion along the stacking direction. The measured peak Pb atom displacements of about 28 pm and peak polarisation values of about 60 mu C cm-2 match extremely well to reported values for the commensurate antiferroelectric PbZrO3 phase.
Title:
Origin of the Large Polarization in Multiferroic YMnO3 Thin Films Revealed by Soft- and Hard-X-Ray Diffraction
Authors:
Wadati, H; Okamoto, J; Garganourakis, M; Scagnoli, V; Staub, U; Yamasaki, Y; Nakao, H; Murakami, Y; Mochizuki, M; Nakamura, M; Kawasaki, M; Tokura, Y Author Full Names: Wadati, H.; Okamoto, J.; Garganourakis, M.; Scagnoli, V.; Staub, U.; Yamasaki, Y.; Nakao, H.; Murakami, Y.; Mochizuki, M.; Nakamura, M.; Kawasaki, M.; Tokura, Y.
Source:
PHYSICAL REVIEW LETTERS, 108 (4):10.1103/PhysRevLett.108.047203 JAN 24 2012
Abstract:
We investigated the magnetic structure of an orthorhombic YMnO3 thin film by resonant soft x-ray and hard x-ray diffraction. We observed a temperature-dependent incommensurate magnetic reflection below 45 K and a commensurate lattice-distortion reflection below 35 K. These results demonstrate that the ground state is composed of coexisting E-type and cycloidal states. Their different ordering temperatures clarify the origin of the large polarization to be caused by the E-type antiferromagnetic states in the orthorhombic YMnO3 thin film.
Title:
Quasicrystals or - for What The Nobel Prize in Chemistry Was Awarded in 2011
Authors:
Michalcova, A Author Full Names: Michalcova, Alena
Source:
CHEMICKE LISTY, 106 (1):55-57; 2012
Abstract:
Quasicrystals are aperiodic objects in three dimensional space which exhibit 5-, 8-, 10 a 12- fold rotational symmetry forbidden in classical crystallography. They were discovered by Daniel Shechtman in rapidly solidified AlMn14 alloy in 1982. He managed to get over initial dislike of scientists community and for his significant work he was awarded The Nobel Prize in Chemistry 2011.
Title:
Magnetic phase transitions in the NdFe3(BO3)(4) multiferroic
Authors:
Zvyagina, GA; Zhekov, KR; Bilych, IV; Zvyagin, AA; Gudim, IA; Temerov, VL Author Full Names: Zvyagina, G. A.; Zhekov, K. R.; Bilych, I. V.; Zvyagin, A. A.; Gudim, I. A.; Temerov, V. L.
Source:
LOW TEMPERATURE PHYSICS, 37 (12):1010-1020; 10.1063/1.3674182 DEC 2011
Abstract:
Low-temperature studies of the behavior of the sound velocity and attenuation of acoustic modes have been performed on a single crystal NdFe3(BO3)(4) Transitions of the magnetic subsystem to the antiferromagnetically ordered state at T-N approximate to 30.6 K have been revealed in the temperature behavior of the elastic characteristics. The features in the temperature behavior of elastic characteristics of the neodymium ferroborate and its behavior in the external magnetic field, applied in the basic plane of the crystal, permit us to suppose that the transition to an incommensurate spiral phase is realized in the system. This phase transition behaves as the first order one. H-T phase diagrams for the cases H parallel to a and H parallel to b have been constructed. The phenomenological theory, which explains observed features, has been developed. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3674182]

Update: 15-Feb-2012

Title:
Evidence for the extraterrestrial origin of a natural quasicrystal
Authors:
Bindi, L; Eiler, JM; Guan, YB; Hollister, LS; MacPherson, G; Steinhardt, PJ; Yao, N Author Full Names: Bindi, Luca; Eiler, John M.; Guan, Yunbin; Hollister, Lincoln S.; MacPherson, Glenn; Steinhardt, Paul J.; Yao, Nan
Source:
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 109 (5):1396-1401; 10.1073/pnas.1111115109 JAN 31 2012
Abstract:
We present evidence that a rock sample found in the Koryak Mountains in Russia and containing icosahedrite, an icosahedral quasicrystalline phase with composition Al(63)Cu(24)Fe(13), is part of a meteorite, likely formed in the early solar system about 4.5 Gya. The quasicrystal grains are intergrown with diopside, forsterite, stishovite, and additional metallic phases [khatyrkite (CuAl(2)), cupalite (CuAl), and beta-phase (AlCuFe)]. This assemblage, in turn, is enclosed in a white rind consisting of diopside, hedenbergite, spinel (MgAl(2)O(4)), nepheline, and forsterite. Particularly notable is a grain of stishovite (from the interior), a tetragonal polymorph of silica that only occurs at ultrahigh pressures (>= 10 Gpa), that contains an inclusion of quasicrystal. An extraterrestrial origin is inferred from secondary ion mass spectrometry (18)O/(16)O and (17)O/(16)O measurements of the pyroxene and olivine intergrown with the metal that show them to have isotopic compositions unlike any terrestrial minerals and instead overlap those of anhydrous phases in carbonaceous chondrite meteorites. The spinel from the white rind has an isotopic composition suggesting that it was part of a calcium-aluminum-rich inclusion similar to those found in CV3 chondrites. The mechanism that produced this exotic assemblage is not yet understood. The assemblage (metallic copper-aluminum alloy) is extremely reduced, and the close association of aluminum (high temperature refractory lithophile) with copper (low temperature chalcophile) is unexpected. Nevertheless, our evidence indicates that quasicrystals can form naturally under astrophysical conditions and remain stable over cosmic timescales, giving unique insights on their existence in nature and stability.
Title:
Femtosecond Dynamics of the Collinear-to-Spiral Antiferromagnetic Phase Transition in CuO
Authors:
Johnson, SL; de Souza, RA; Staub, U; Beaud, P; Mohr-Vorobeva, E; Ingold, G; Caviezel, A; Scagnoli, V; Schlotter, WF; Turner, JJ; Krupin, O; Lee, WS; Chuang, YD; Patthey, L; Moore, RG; Lu, D; Yi, M; Kirchmann, PS; Trigo, M; Denes, P; Doering, D; Hussain, Z; Shen, ZX; Prabhakaran, D; Boothroyd, AT Author Full Names: Johnson, S. L.; de Souza, R. A.; Staub, U.; Beaud, P.; Moehr-Vorobeva, E.; Ingold, G.; Caviezel, A.; Scagnoli, V.; Schlotter, W. F.; Turner, J. J.; Krupin, O.; Lee, W. -S.; Chuang, Y. -D.; Patthey, L.; Moore, R. G.; Lu, D.; Yi, M.; Kirchmann, P. S.; Trigo, M.; Denes, P.; Doering, D.; Hussain, Z.; Shen, Z. -X.; Prabhakaran, D.; Boothroyd, A. T.
Source:
PHYSICAL REVIEW LETTERS, 108 (3):10.1103/PhysRevLett.108.037203 JAN 19 2012
Abstract:
We report on the ultrafast dynamics of magnetic order in a single crystal of CuO at a temperature of 207 K in response to strong optical excitation using femtosecond resonant x-ray diffraction. In the experiment, a femtosecond laser pulse induces a sudden, nonequilibrium increase in magnetic disorder. After a short delay ranging from 400 fs to 2 ps, we observe changes in the relative intensity of the magnetic ordering diffraction peaks that indicate a shift from a collinear commensurate phase to a spiral incommensurate phase. These results indicate that the ultimate speed for this antiferromagnetic reorientation transition in CuO is limited by the long-wavelength magnetic excitation connecting the two phases.
Title:
Chiral Quasicrystalline Order and Dodecahedral Geometry in Exceptional Families of Viruses
Authors:
Konevtsova, OV; Rochal, SB; Lorman, VL Author Full Names: Konevtsova, O. V.; Rochal, S. B.; Lorman, V. L.
Source:
PHYSICAL REVIEW LETTERS, 108 (3):10.1103/PhysRevLett.108.038102 JAN 19 2012
Abstract:
On the example of exceptional families of viruses we (i) show the existence of a completely new type of matter organization in nanoparticles, in which the regions with a chiral pentagonal quasicrystalline order of protein positions are arranged in a structure commensurate with the spherical topology and dodecahedral geometry, (ii) generalize the classical theory of quasicrystals (QCs) to explain this organization, and (iii) establish the relation between local chiral QC order and nonzero curvature of the dodecahedral capsid faces.
Title:
The success story of crystallography
Authors:
Schwarzenbach, D Author Full Names: Schwarzenbach, Dieter
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 227 (1):52-62; 10.1524/zkri.2012.1453 2012
Abstract:
Diffractionists usually place the birth of crystallography in 1912 with the first X-ray diffraction experiment of Friedrich, Knipping and Laue. This discovery propelled the mathematical branch of mineralogy to global importance and enabled crystal structure determination. Knowledge of the geometrical structure of matter at atomic resolution had revolutionary consequences for all branches of the natural sciences: physics, chemistry, biology, earth sciences and material science. It is scarcely possible for a single person in a single article to trace and appropriately value all of these developments. This article presents the limited, subjective view of its author and a limited selection of references. The bulk of the article covers the history of X-ray structure determination from the NaCl structure to aperiodic structures and macromolecular structures. The theoretical foundations were available by 1920. The subsequent success of crystallography was then due to the development of diffraction equipment, the theory of the solution of the phase problem, symmetry theory and computers. The many structures becoming known called for the development of crystal chemistry and of data banks. Diffuse scattering from disordered structures without and with partial long-range order allows determination of short-range order. Neutron and electron scattering and diffraction are also mentioned.
Title:
ELECTRONIC SPECTRA AND PHASE TRANSITIONS IN THIN [N(CH(3))(4)](2)CuCl(4) MICROCRYSTALS
Authors:
Shymkiv, RM; Sveleba, SA; Karpa, IV; Katerynchuk, IN; Kunyo, IM; Phitsych, EI Author Full Names: Shymkiv, R. M.; Sveleba, S. A.; Karpa, I. V.; Katerynchuk, I. N.; Kunyo, I. M.; Phitsych, E. I.
Source:
JOURNAL OF APPLIED SPECTROSCOPY, 78 (6):823-828; JAN 2012
Abstract:
Optical absorption spectra in thin [N(CH(3))(4)](2)CuCl(4) crystals in the thickness range 10 mu m <= d < 00 mu m have been studied. Strengthening of the crystal field has been found with a decrease in the [N(CH(3))(4)](2)CuCl(4) crystal size. The reasons for absorption band shifts in the visible region depending on the [N(CH(3))(4)](2)CuCl(4) crystal thickness and the manifestation of a size effect in crystals with an incommensurate superstructure are discussed.
Title:
Quasicrystal as a Reinforcement Material in Magnesium Alloys
Authors:
Chang, HJ; Kim, WT; Kim, DH Author Full Names: Chang, Hye Jung; Kim, Won Tae; Kim, Do Hyang
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1176-1184; SI 10.1002/ijch.201100133 DEC 2011
Abstract:
The existence of the two-phase region (icosahedral phase (I-phase) + a-Mg) in the Mg-rich corner of the Mg-Zn-Y system indicates that composites consisting of I-phase and ductile a-Mg can be fabricated by a simple solidification process. Alloys with a range of combined strength and ductility can be designed by changing the fraction of the I-phase. Strengthening in proportion with increasing the volume fraction of I-phase can be explained by the effect of dispersion hardening due to the presence of finely dispersed I-phase particles. When quasicrystals exist in the a-Mg matrix as a second phase in Mg-Zn-Y alloys, the quasicrystals are stable against coarsening during thermomechanical processes such as hot rolling and high-temperature forming, due to the low interfacial energy of the quasicrystals with the a-Mg crystalline matrix, which provides strong bonding properties at the I-phase/matrix interface. Therefore, quasicrystal-reinforced Mg-Zn-Y alloys exhibit a much better combination of mechanical properties and formability than commercially used alloys such as AZ31 and AZ 61.
Title:
A Cluster-Resonance Criterion for Al-TM Quasicrystal Compositions
Authors:
Chen, H; Qiang, JB; Wang, Q; Wang, YM; Dong, C Author Full Names: Chen, Hua; Qiang, Jianbing; Wang, Qing; Wang, Yingmin; Dong, Chuang
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1226-1234; SI 10.1002/ijch.201100139 DEC 2011
Abstract:
Compositions of binary Al-TM (TM=Cr to Ni) quasicrystals are interpreted with a unified cluster formula [icosahedron](glue)1 using the newly developed clusterresonance model and the e/a formalism. The icosahedra are chosen from the corresponding approximants by considering large radial atomic density, high degree of isolation, and narrow distribution of the shell atoms. Icosahedral quasicrystals are expressed by an icosahedron plus one averaged icosahedron atom as the glue atom [icosahedron](icosahedron/13)1, characterized by e/a similar to 1.831.85, while decagonal quasicrystals are expressed by an icosahedron plus one TM atom, with e/a similar to 1.711.78. The total electrons accommodated in unit cluster formulas of different Al-TM quasicrystals have the same value approaching 24, which implies that the cluster formulas are both chemical and electronic structural units.
Title:
Gas-Surface Interactions on Quasicrystals
Authors:
Curtarolo, S; Setyawan, W; Diehl, RD Author Full Names: Curtarolo, Stefano; Setyawan, Wahyu; Diehl, Renee D.
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1304-1313; SI 10.1002/ijch.201100129 DEC 2011
Abstract:
To commemorate the awarding of the Nobel Prize for Chemistry to Daniel Shechtman for his discovery of quasicrystals, this paper reviews our recent studies of the interaction of rare gases and hydrocarbon gases with the tenfold surface of quasicrystalline decagonal Al-Co-Ni.
Title:
Phonons and Phasons in Icosahedral Quasicrystals
Authors:
de Boissieu, M Author Full Names: de Boissieu, Marc
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1292-1303; SI 10.1002/ijch.201100131 DEC 2011
Abstract:
The discovery of quasicrystals not only has changed our view on long-range order, but was a breakthrough for solid state physics and chemistry, since the Bloch theorem can no longer be applied. We review some of the results obtained for icosahedral quasicrystals for lattice dynamics and phonons, as well as for phason modes, which are diffusive excitations characteristic of the quasicrystalline state.
Title:
Decagonal Quasicrystals and Approximants: Two-Dimensional or Three-Dimensional Solids?
Authors:
Dolinsek, J; Smontara, A Author Full Names: Dolinsek, Janez; Smontara, Ana
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1246-1256; SI 10.1002/ijch.201100132 DEC 2011
Abstract:
Crystallographic structures of decagonal quasicrystals (d-QCs) are traditionally described as a periodic stacking of atomic planes with quasiperiodic in-plane atomic order, so that d-QCs are considered to be two-dimensional (2D) quasicrystals, whereas they are periodic crystals in the third dimension. Similar stacked-layer structures are observed also in the periodic decagonal approximant phases. In this review paper, we consider the dimensionality of the chemical bonding network in the d-QCs and their approximants on the basis of electrical resistivity. By comparing the anisotropic resistivity along the stacking- and the in-plane directions of a series of decagonal approximants with different numbers of atomic layers within one periodicity unit (the two-layer Y-Al-Co-Ni, the four-layer o-Al13Co4, Al13Fe4 and Al13(Fe,Ni)4, and the six-layer Al4(Cr,Fe) and T-Al3(Mn,Fe)) and of a two-layer d-Al-Co-Ni decagonal quasicrystal, we show that universally, the stacking direction perpendicular to the atomic planes is always the most conducting one. Since the in-plane electrical resistivities are of the same order of magnitude as the resistivity along the stacking direction, this confirms the 3D character of the investigated solids. The stacked-layer description in terms of 2D atomic planes should therefore be regarded as a convenient geometrical approach to describe the complex structures of the d-QCs and their approximants, whereas their physical properties are those of true 3D solids.
Title:
So Useful, Those Quasicrystals
Authors:
Dubois, JM Author Full Names: Dubois, Jean-Marie
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1168-1175; SI 10.1002/ijch.201100149 DEC 2011
Abstract:
For years, the community working on quasicrystals in many countries in the world was expecting the ultimate recognition of its contribution to the advancement of crystal chemistry, solid-state physics, mathematics, and other fields. Nearly thirty years after the initial discovery, it was finally awarded in October 2011 to Prof. Danny Shechtman by the Nobel Committee for Physics and Chemistry. Many, most often independent, achievements contributed to this success. The purpose of this article is to chronicle the role played by the applications of quasicrystals and related compounds in the development of the field and its financing by governmental institutions as well as private companies. Those applications, potential or realized, have made the field of quasicrystals comprehensible to the general public and to decision makers all over the world, including in Stockholm, in spite of its rather complicated high-dimensional crystallographic background, and in spite of the absolute opposition that a great chemist manifested against it in its infancy.
Title:
Metadislocations in Complex Metallic Alloys and their Relation to Dislocations in Icosahedral Quasicrystals
Authors:
Feuerbacher, M; Heggen, M Author Full Names: Feuerbacher, Michael; Heggen, Marc
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1235-1245; SI 10.1002/ijch.201100142 DEC 2011
Abstract:
Complex metallic alloys and quasicrystals are closely related. Both possess icosahedral local order, but while in quasicrystals the long-range order and hence the macroscopic structure is also icosahedral, in complex metallic alloys a periodic structure with large lattice parameters is formed. Metadislocations are novel and highly complex structural defects in complex metallic alloys. Focusing on metadislocations in e-type phases, we will review the basic geometric concepts of metadislocations and the relation between the number of phason planes, Burgers vector, and the elastic energy. The properties of dislocations in icosahedral Al-Pd-Mn will briefly be recalled and discussed in relation to metadislocations.
Title:
Thin Film Growth on Quasicrystalline Surfaces
Authors:
Fournee, V; Ledieu, J; Shimoda, M; Krajci, M; Sharma, HR; McGrath, R Author Full Names: Fournee, Vincent; Ledieu, Julian; Shimoda, Masahiko; Krajci, Marian; Sharma, Hem-Raj; McGrath, Ronan
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1314-1325; SI 10.1002/ijch.201100141 DEC 2011
Abstract:
The surfaces of quasicrystals have proved to be a very interesting playground for thin film growth. They offer a complex potential energy surface where heterogeneous nucleation of islands at specific quasilattice sites is frequently observed. These islands tend to locally adopt the symmetry of the quasicrystalline substrate. For some specific adsorbates, a complete 2-dimensional quasiperiodic metal overlayer is even formed. Other interesting phenomena are also observed in the multilayer regime. This includes the formation of novel structures, like 1-dimensional quasiperiodic Cu films or Bi allotropes, the formation of nanoscale crystalline domains with 5-fold rotational epitaxy, or the occurrence of quantum size effects influencing the film morphology. This article presents a short review of some of the achievements in thin film growth on quasicrystalline surfaces that the discovery of quasicrystals by Dan Shechtman has enabled.
Title:
Electrons in Quasicrystals
Authors:
Grimm, U Author Full Names: Grimm, Uwe
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1257-1262; SI 10.1002/ijch.201100143 DEC 2011
Abstract:
Quasicrystals, discovered by Dan Shechtman in 1982, provide unique materials with long-range aperiodic order. Their electronic structure and the electronic transport in quasicrystalline alloys has been a focus of research, motivated by trying to understand the formation and stability of quasicrystals, and their pronounced transport anomalies. This brief review on the motion of electrons concentrates on one perspective of this problem. It focuses on results obtained for simple models which capture the essence of the aperiodic order, rather than on results which attempt a realistic description of quasicrystalline alloys by employing empirical interaction potentials.
Title:
Dan Shechtman's Quasicrystal Discovery in Perspective
Authors:
Hargittai, I Author Full Names: Hargittai, Istvan
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1144-1152; SI 10.1002/ijch.201100137 DEC 2011
Abstract:
Dan Shechtmans discovery of quasicrystals brought about a paradigm change in chemistry, physics, materials science, and other areas of science and engineering. Although superficially it could be looked at as a serendipitous event, Shechtmans curiosity and drive played equal parts with serendipity in this discovery. Shechtman was a lonely discoverer, again, seemingly detached from the main stream of generalized crystallography for which his contribution was a milestone. Generalized crystallography is the science of structures without restrictions structures beyond crystals.1 The discovery of quasicrystals can be seen as written into the history of ideas that have much extended our views about the tools of our scientific inquiry and the materials we aim at producing and utilizing. This review augments a recent Editorial in the August 2011 issue of Structural Chemistry about the lessons of the quasicrystal discovery2 and a book chapter about Dan Shechtmans traits as a discoverer and about his road to the discovery.3
Title:
Dodecagonal Quasicrystals Still in Progress
Authors:
Ishimasa, T Author Full Names: Ishimasa, Tsutomu
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1216-1225; SI 10.1002/ijch.201100134 DEC 2011
Abstract:
The dodecagonal quasiperiodic order is rather rare in the material world, but has been observed in various systems from alloys to aggregates of cylindrical polymers and in a wide range of dimensions. They exhibit uniaxial 12-fold diffraction symmetry, and have common structural properties originating from the arrangement of structural units on a squaretriangle tiling. All dodecagonal quasicrystals known so far were classified into the so-called random-tiling type and not into a mathematically ideal quasiperiodic type. The observed dodecagonal quasicrystals deviated from the ideal state with respect to the limited size of their quasicrystalline region and their structural inhomogeniety. This may be caused by the structural metastability that prevents synthesis of high quality quasicrystals. The effort toward an ideal dodecagonal quasicrystal, in particular in alloys, is reviewed here. There may be two key points: one is taking advantage of the entropy for stabilization, namely the tiling configurational entropy, and the other is taking advantage of so-called second generation tiles scaled up by a factor of 2+v3 as observed in Ta1.6Te quasicrystal and Mn-Si-(Cr, V) approximant systems.
Title:
Symmetry Breaking and Order in the Age of Quasicrystals
Authors:
Lifshitz, R Author Full Names: Lifshitz, Ron
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1156-1167; SI 10.1002/ijch.201100156 DEC 2011
Abstract:
The discovery of quasicrystals has changed our view of some of the most basic notions related to the condensed state of matter. Before the age of quasicrystals, it was believed that crystals break the continuous translation and rotation symmetries of the liquid-phase into a discrete lattice of translations, and a finite group of rotations. Quasicrystals, on the other hand, possess no such symmetriesthere are no translations, nor, in general, are there any rotations, leaving them invariant. Does this imply that no symmetry is left, or that the meaning of symmetry should be revised? We review this and other questions related to the liquid-to-crystal symmetry-breaking transition using the notion of indistinguishability. We characterize the order-parameter space, describe the different elementary excitations, phonons and phasons, and discuss the nature of dislocationskeeping in mind that we are now living in the age of quasicrystals.
Title:
Some Aspects of Stability and Nanophase Formation in Quasicrystals during Mechanical Milling
Authors:
Mukhopadhyay, NK; Yadav, TP Author Full Names: Mukhopadhyay, N. K.; Yadav, Thakur Prasad
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1185-1196; SI 10.1002/ijch.201100145 DEC 2011
Abstract:
Non-equilibrium processing and other related techniques can activate quasicrystalline structures to a higher energy level and enable them to attain various stable/metastable structures. During mechanical milling of quasicrystalline alloys, the stability of the complex structures is of immense importance from a scientific and technological point of view. The evolution of nanoquasicrystalline, nanocrystalline, and amorphous phases and their composites has been observed in the course of milling. The experimental results for mechanical alloying of elemental powders (required for the synthesis of quasicrystals) and mechanical milling of quasicrystals are discussed. The salient features observed in quasicrystals during other non-equilibrium processing are highlighted. Nanospinel formation from the Al-based quasicrystalline precursor is mentioned.
Title:
Chemical Bonding in Al5Co2: The Electron Localizability-Electron Density Approach
Authors:
Ormeci, A; Grin, Y Author Full Names: Ormeci, Alim; Grin, Yuri
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1349-1354; SI 10.1002/ijch.201100147 DEC 2011
Abstract:
Al5Co2 is an intermetallic compound which can be considered as an approximant of the quasicrystalline decagonal phases. Chemical bonding in Al5Co2 is investigated by using the electron localizabilityelectron density approach. The analysis reveals that two atomic clusters, one three dimensional, the other planar, can be identified on the basis of two-centre bonds that are formed around the shortest AlCo distances. These clusters and one of the Al types interact through multi-centre bonds, indicating that both covalent and metallic interactions coexist in Al5Co2.
Title:
Heat Transport in Aluminum-Based Quasicrystals i-AlPdMn, i-AlCuFe, and d-AlCoNi
Authors:
Popcevic, P; Stanic, D; Bihar, Z; Bilusic, A; Smontara, A Author Full Names: Popcevic, Petar; Stanic, Denis; Bihar, Zeljko; Bilusic, Ante; Smontara, Ana
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1340-1348; SI 10.1002/ijch.201100150 DEC 2011
Abstract:
We present a semi-quantitative model used to analyze thermal conductivity data of single-grain aluminum-based icosahedral i-AlPdMn and i-AlFeCu, and decagonal d-AlCoNi quasicrystals in the quasiperiodic plane. The analysis is based on the validity of the WiedemannFranz law and applicability of the Debye model of quasilattice thermal conductivity at low temperatures, where the main phonon scattering centers are assumed to be structural defects in the form of the stacking faults and phenomenological quasiumklapp. At high temperature, electron and quasilattice contributions underestimate the data. This has motivated us to consider two possible additional heat-carrying channels: the activation of localized lattice vibrations and modifications of the WiedemannFranz law.
Title:
Crystal Twins Revisited
Authors:
Senechal, MW Author Full Names: Senechal, Marjorie Wikler
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1153-1155; SI 10.1002/ijch.201100135 DEC 2011
Abstract:
Just as quasicrystals demanded a new definition of crystal, they demand that we redefine crystal twins.
Title:
The generalized Kahler geometry of N = (2,2) WZW-models
Authors:
Sevrin, A; Staessens, W; Terryn, D Author Full Names: Sevrin, Alexander; Staessens, Wieland; Terryn, Dimitri
Source:
JOURNAL OF HIGH ENERGY PHYSICS, (12):10.1007/JHEP12(2011)079 DEC 2011
Abstract:
N = (2, 2), d = 2 supersymmetric non-linear s-models provide a physical realization of Hitchin's and Gualtieri's generalized Kahler geometry. A large subclass of such models are comprised by WZW-models on even-dimensional reductive group manifolds. In the present paper we analyze the complex structures, type changing, the superfield content and the affine isometries compatible with the extra supersymmetry. The results are illustrated by an exhaustive discussion of the N = (2, 2) WZW-models on S(3) x S(1) and S(3) x S(3) where various aspects of generalized Kahler and Calabi-Yau geometry are verified and clarified. The examples illustrate a slightly weaker definition for an N = (2, 2) superconformal generalized Kahler geometry compared to that for a generalized Calabi-Yau geometry.
Title:
Properties of Cd-Based Binary Quasicrystals and Their 1/1 Approximants
Authors:
Tamura, R Author Full Names: Tamura, Ryuji
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1263-1274; SI 10.1002/ijch.201100138 DEC 2011
Abstract:
Electronic and structural properties of Cd-based binary quasicrystals (QCs) and their 1/1 approximants (APs) without chemical disorder are overviewed in terms of electronic states, electronic transport, and phase transitions. A pseudogap in the electronic density of states (DOS) as well as hybridization effect between sp and d states are discussed for both the QCs and their 1/1 APs in comparison with theoretical calculations. In contrast with the cases of ternary stable QCs, the resistivity of the Cd5.7Yb QC exhibits a positive temperature coefficient at low temperatures, which is regarded as an indication of an intrinsic metallic nature of the QC. A unique structural phase transition has been observed at low temperatures (LT) for a series of 1/1 Cd6M APs, which is interpreted as an orientational transition of a tetrahedron residing at the center of the Tsai-type icosahedral cluster. In most of the cases, the LT superstructure is understood as an antiferromagnetic ordering of the tetrahedra along a < 110 > direction of the high-temperature bcc phase. The transition is classified as a non-diffusive orderdisorder transition, which has not been observed in metallic alloys before.
Title:
Guest Editorial: Quasicrystals
Authors:
Thiel, PA Author Full Names: Thiel, Patricia A.
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1141-1142; SI 10.1002/ijch.201100127 DEC 2011
Title:
A Distinctive Feature of the Surface Structure of Quasicrystals: Intrinsic and Extrinsic Heterogeneity
Authors:
Thiel, PA; Unal, B; Jenks, CJ; Goldman, AI; Canfield, PC; Lograsso, TA; Evans, JW; Quiquandon, M; Gratias, D; Van Hove, MA Author Full Names: Thiel, Patricia A.; Uenal, Baris; Jenks, Cynthia J.; Goldman, Alan I.; Canfield, Paul C.; Lograsso, Thomas A.; Evans, James W.; Quiquandon, Marianne; Gratias, Denis; Van Hove, Michel A.
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1326-1339; SI 10.1002/ijch.201100148 DEC 2011
Abstract:
This paper reviews a feature of atomically-clean quasicrystal surfaces that distinguishes them from surfaces of crystalline materials. That feature is a high degree of heterogeneity among different terraces, and among structurally-identical adsorption sites. The heterogeneity can be both structural and chemical in origin. A large variability is expected even for a surface which is perfectly bulk-terminated, and we call this intrinsic heterogeneity. Additional variability can derive from the surface preparation process, which can yield metastable structures. We call this extrinsic heterogeneity. Experimental evidence is given for both cases. This heterogeneity can be an important factor in understanding and predicting surface phenomena such as chemisorption.
Title:
Liquid Quasicrystals
Authors:
Ungar, G; Percec, V; Zeng, XB; Leowanawat, P Author Full Names: Ungar, Goran; Percec, Virgil; Zeng, Xiangbing; Leowanawat, Pawaret
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1206-1215; SI 10.1002/ijch.201100151 DEC 2011
Abstract:
In the first part, this brief review discusses the discovery of the first example of supramolecular dendritic liquid quasicrystal, which represents also the first example of soft quasicrystal. In the second part, we show that soft quasicrystals generated from supramolecular spheres are scattered through libraries of self-assembling dendrons, dendrimers, and dendronized polymers. The supramolecular spheres forming soft quasicrystals are generated via at least two different mechanisms, and are chiral. Generation of quasicrystals from other organic building blocks is also discussed. Finally, potential applications in electronics, sensors, and as ionic liquid-based nanoreactors are also mentioned.
Title:
Quasicrystals: Substances with special Structures
Authors:
Welter, K Author Full Names: Welter, Kira
Source:
CHEMIE IN UNSERER ZEIT, 45 (6):366-367; 10.1002/ciuz.201190088 DEC 2011
Title:
Real Space Structure Factor for Different Quasicrystals
Authors:
Wolny, J; Kozakowski, B; Kuczera, P; Strzalka, R; Wnek, A Author Full Names: Wolny, Janusz; Kozakowski, Bartlomiej; Kuczera, Pawel; Strzalka, Radoslaw; Wnek, Anna
Source:
ISRAEL JOURNAL OF CHEMISTRY, 51 (11-12):1275-1291; SI 10.1002/ijch.201100144 DEC 2011
Abstract:
The statistical approach to the description of aperiodic structures using the concept of the so called Average Unit Cell (AUC) is presented. The use of this method is shown for 1D, 2D, and 3D structures. We start with the presentation of the basic ideas for 1D simple sinusoidal modulation (1q) and the Fibonacci chain (a 1D model of a quasicrystalline structure). Up to now the AUC concept has been most thoroughly studied for 2D decagonal quasicrystals. The idea of structure factor derivation for the decorated Penrose tiling, a quasilattice for the description of decagonal quasicrystals, is presented. Two examples of structure refinement of decagonal phases from the Al-Ni-Co system are discussed. The potential of the cluster description of decagonal structures is also presented. The AUC construction and structure factor derivation is shown for the 3D AmmanKramerNeri tiling, which is a model quasilattice for the description of icosahedral phases. The AUC concept can also be extended to structures with singular-continuous Fourier spectrum. An example for the 1D ThueMorse sequence is studied.
Title:
On finite symmetry groups of some models of three-dimensional quasicrystals
Authors:
Artamonov, VA; Sanchez, S Author Full Names: Artamonov, V. A.; Sanchez, S.
Source:
SIBERIAN MATHEMATICAL JOURNAL, 52 (6):969-979; 10.1134/S0037446611060024 NOV 2011
Abstract:
We give a full description of the finite symmetry groups of the cut-and-project model for three-dimensional quasicrystals under the assumption that the phase space dimension is at most 3.

Update: 9-Feb-2012

Title:
Structural and magnetic properties of Mn(3-x)Cd(x)TeO(6) (x=0, 1, 1.5 and 2)
Authors:
Ivanov, SA; Mathieu, R; Nordblad, P; Politova, E; Tellgren, R; Ritter, C; Proidakova, V Author Full Names: Ivanov, S. A.; Mathieu, R.; Nordblad, P.; Politova, E.; Tellgren, R.; Ritter, C.; Proidakova, V.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 324 (8):1637-1644; 10.1016/j.jmmm.2011.12.027 APR 2012
Abstract:
Mn(3)TeO(6) exhibits a corundum-related A(3)TeO(6) structure and a complex magnetic structure involving two magnetic orbits for the Mn atoms [Ivanov et al., 2011 [3]]. Mn(3-x)Cd(x)TeO(6) (x = 0, 1, 1.5, and 2) ceramics were synthesized by solid state reaction and investigated using X-ray powder diffraction, electron microscopy, and calorimetric and magnetic measurements. Cd(2+) replaces Mn(2+) cations without greatly affecting the structure of the compound. The Mn and Cd cations were found to be randomly distributed over the A-site. Magnetization measurements indicated that the samples order antiferromagnetically at low temperature with a transition temperature that decreases with increasing Cd doping. The nuclear and magnetic structure of one specially prepared (114)Cd containing sample: Mn(1.5) (114)Cd(1.5)TeO(6), was studied using neutron powder diffraction over the temperature range 2-295 K. Mn(1.5) (114)Cd(1.5)TeO(6) was found to order in an incommensurate helical magnetic structure, very similar to that of Mn(3)TeO(6) [Ivanov et al., 2011 [3]]. However, with a lower transition temperature and the extension of the ordered structure confined to order 240(10) angstrom. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Effect of Mn substitution on crystal structure and magnetic properties of Bi(1-x)Pr(x)FeO(3) multiferroics
Authors:
Khomchenko, VA; Troyanchuk, IO; Kovetskaya, MI; Kopcewicz, M; Paixao, JA Author Full Names: Khomchenko, V. A.; Troyanchuk, I. O.; Kovetskaya, M. I.; Kopcewicz, M.; Paixao, J. A.
Source:
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 45 (4):10.1088/0022-3727/45/4/045302 FEB 1 2012
Abstract:
Mn substitution-driven structural and magnetic phase evolution in the predominantly antiferromagnetic polar rhombohedral (space group R3c) and weak ferromagnetic antipolar orthorhombic (space group Pnam) phases of the Bi(1-x)Pr(x)FeO(3) perovskites was studied by x-ray diffraction, (57)Fe Mossbauer spectroscopy and magnetometry techniques at room temperature. Mn doping was found to effectively modify both the initial structures to stabilize a new phase demonstrating incommensurable modulation. Magnetic behaviour of the Mn-containing samples changes in correlation with the evolution of their structural state. Within the compositional range of the rhombohedrally distorted compounds, the manganese substitution gives rise to suppression of the dominant antiferromagnetic interaction. In the weak ferromagnetic doping-induced phase, a gradual decrease in room temperature spontaneous magnetization takes place with increasing Mn content.
Title:
Influence of Y on the phase composition and mechanical properties of as-extruded Mg-Zn-Y-Zr magnesium alloys
Authors:
Wang, JF; Song, PF; Gao, S; Wei, YY; Pan, FS Author Full Names: Wang, Jingfeng; Song, Pengfei; Gao, Shan; Wei, Yiyun; Pan, Fusheng
Source:
JOURNAL OF MATERIALS SCIENCE, 47 (4):2005-2010; 10.1007/s10853-011-5998-2 FEB 2012
Abstract:
The influence of Y on the microstructure, phase composition and mechanical properties of the extruded Mg-6Zn-xY-0.6Zr (x = 0, 1, 2, 3 and 4, in wt%) alloys has been investigated and compared by optical microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometer and tensile testing. The increase in Y content has shown grain refinement effects on the microstructure morphologies of the extruded alloys. However, when the content of Y exceeds 2.2 wt%, the grain refinement effect of the Y is not obvious any more with the increase of the Y content. The quasicrystal I-phase (Mg(3)YZn(6)), face-centred cubic structure W-phase (Mg(3)Y(2)Zn(3)) and a long period stacking ordered (LPSO) X-phase (Mg(12)YZn) can precipitate in different ranges of Y/Zn ratio (in at.%) when the Y content in the Mg-Zn-Y-Zr alloys is varied. Comparison of the mechanical properties of the alloys showed that the different ternary Mg-Zn-Y phases have different strengthening and toughening effects on the Mg-Zn-Y-Zr alloys in the following order: X-phase > I-phase > W-phase > MgZn(2).
Title:
Atomic ordering in Au-(42 to 50) at.% Pd: A diffuse scattering and first-principles investigation
Authors:
Schonfeld, B; Sax, CR; Ruban, AV Author Full Names: Schoenfeld, B.; Sax, C. R.; Ruban, A. V.
Source:
PHYSICAL REVIEW B, 85 (1):10.1103/PhysRevB.85.014204 JAN 24 2012
Abstract:
Atomic ordering in Au-Pd alloys was studied by diffuse x-ray scattering and first-principles methods. Diffuse scattering was done of a single crystal of Au-48 at.% Pd that was aged at 703 K for 24 days. The weakly modulated short-range-order scattering exhibits diffuse maxima with an incommensurate wave vector, which can be related to a Fermi-surface nesting mechanism. From effective pair interaction parameters determined by the inverse Monte Carlo method, a one-dimensional long-period superstructure of the CH structure, LPS1, was found for AuPd. Concurrent electronic-structure calculations of the effective cluster interaction (ECI) parameters indicated the presence of another closely related superstructure, LPS2, at 0 K. At the same time, direct first-principles calculations of the total energies of the CH structure and further one-dimensional long-period superstructures predicted the stabilization of LPS4. Although the energy differences between these structures are small and a complex behavior of the effective interactions is expected due to the Fermi-surface nesting, experimental data and theoretical results both support the stabilization of a long-period superstructure of the CH structure for AuPd at 0 K. The ECI parameters determined by the screened generalized perturbation method also predicted a ground-state structure different from Au(7)Pd(5), previously obtained from cluster expansion calculations. Its energetic preference was confirmed by direct total-energy calculations.
Title:
Intrinsic anisotropic magnetic, electrical, and thermal transport properties of d-Al-Co-Ni decagonal quasicrystals
Authors:
Bobnar, M; Jeglic, P; Klanjsek, M; Jaglicic, Z; Wencka, M; Popcevic, P; Ivkov, J; Stanic, D; Smontara, A; Gille, P; Dolinsek, J Author Full Names: Bobnar, M.; Jeglic, P.; Klanjsek, M.; Jaglicic, Z.; Wencka, M.; Popcevic, P.; Ivkov, J.; Stanic, D.; Smontara, A.; Gille, P.; Dolinsek, J.
Source:
PHYSICAL REVIEW B, 85 (2):10.1103/PhysRevB.85.024205 JAN 20 2012
Abstract:
To address the questions on the anisotropy of bulk physical properties of decagonal quasicrystals and the intrinsic physical properties of the d-Al-Co-Ni phase, we investigated the anisotropic magnetic susceptibility, the electrical resistivity, the thermoelectric power, the Hall coefficient, and the thermal conductivity of a d-Al-Co-Ni single crystal of exceptional structural quality. Superior structural order on the local scale of atomic clusters was confirmed by (27)Al nuclear magnetic resonance spectroscopy. The measurements were performed in the 10-fold periodic direction of the structure and in three specific crystallographic directions within the quasiperiodic plane, corresponding to the 2 and 2' twofold symmetry directions and their bisector. The specific heat, being a scalar quantity, was determined as well. The measurements of the second-rank bulk tensorial properties confirm the theoretical prediction that a solid of decagonal point group symmetry should exhibit isotropic physical properties within the quasiperiodic plane and anisotropy between the in-plane and the 10-fold directions. d-Al-Co-Ni is an anisotropic diamagnet with stronger diamagnetism for the magnetic field in the 10-fold direction. Electrical and thermal transport is strongly metallic in the 10-fold direction but largely suppressed within the quasiperiodic plane, the main reason being the lack of translational periodicity that hinders the propagation of electrons and phonons in a nonperiodic lattice. The third-rank Hall-coefficient tensor shows sign-reversal anisotropy related to the direction of the magnetic field when applied in the 10-fold direction or within the quasiperiodic plane. The observed anisotropy is not a peculiarity of quasicrystals but should be a general feature of solids with broken translational periodicity in two dimensions.
Title:
Structural and magnetic transitions in the crystalline approximant Cd(6)Sm
Authors:
Tamura, R; Muro, Y; Hiroto, T; Yaguchi, H; Beutier, G; Takabatake, T Author Full Names: Tamura, R.; Muro, Y.; Hiroto, T.; Yaguchi, H.; Beutier, G.; Takabatake, T.
Source:
PHYSICAL REVIEW B, 85 (1):10.1103/PhysRevB.85.014203 JAN 20 2012
Abstract:
Electrical resistivity, specific heat, magnetic susceptibility, and magnetization of the crystalline approximant Cd(6)Sm are investigated in a temperature range 1.8-300 K. Both structural and magnetic transitions are clearly evidenced. A sharp structural phase transition is observed at T(c) = 179 K in the electrical resistivity as well as in the specific heat, which is attributed to orientational ordering of the Cd(4) tetrahedron located at the center of the icosahedral cluster. In addition, three successive magnetic transitions are found at T(M1) = 12.5, T(M2) = 10.2, and T(M3) = 6.5 K. The anomaly at T(M1) is attributed to an antiferromagnetic transition, whereas those at T(M2) and T(M3) are to ferrimagnetic transitions. The observation of the ferrimagnetic orders indicates that (pseudo) icosahedra made of localized Sm spins have a nonzero net magnetic moment, and the moments of the magnetic clusters form a long-range magnetic order.
Title:
Zn-induced spin dynamics in overdoped La(2-x)Sr(x)Cu(1-y)Zn(y)O(4)
Authors:
Wilson, SD; Yamani, Z; Dhital, C; Freelon, B; Freeman, PG; Fernandez-Baca, JA; Yamada, K; Wakimoto, S; Buyers, WJL; Birgeneau, RJ Author Full Names: Wilson, Stephen D.; Yamani, Z.; Dhital, Chetan; Freelon, B.; Freeman, P. G.; Fernandez-Baca, J. A.; Yamada, K.; Wakimoto, S.; Buyers, W. J. L.; Birgeneau, R. J.
Source:
PHYSICAL REVIEW B, 85 (1):10.1103/PhysRevB.85.014507 JAN 17 2012
Abstract:
Spin fluctuations and the local spin susceptibility in isovalently Zn-substituted La(2-x)Sr(x)Cu(1-y)Zn(y)O(4) (x = 0.25, y approximate to 0.01) are measured via inelastic neutron-scattering techniques. As Zn(2+) is substituted onto the Cu(2+)-sites, an anomalous enhancement of the local spin susceptibility chi ''(omega) appears due to the emergence of a commensurate antiferromagnetic excitation centered at wave vector Q = (pi, pi, 0) that coexists with the known incommensurate spin-density wave excitations at Q(HK) = (pi +/- delta, pi),(pi, pi +/- delta). Our results support a picture of Zn-induced antiferromagnetic (AF) fluctuations appearing through a local staggered polarization of Cu(2+) spins, and the simultaneous suppression of T(c) as AF fluctuations are slowed in proximity to Zn impurities suggests the continued importance of high-energy AF fluctuations at the far overdoped edge of superconductivity in the cuprates.
Title:
Structural phase transitions in SrRh(2)As(2)
Authors:
Zinth, V; Petricek, V; Dusek, M; Johrendt, D Author Full Names: Zinth, V.; Petricek, V.; Dusek, M.; Johrendt, D.
Source:
PHYSICAL REVIEW B, 85 (1):10.1103/PhysRevB.85.014109 JAN 17 2012
Abstract:
SrRh(2)As(2) crystallizes with three polymorphs derived from the tetragonal ThCr(2)Si(2)-type structure and exhibits structural phase transitions comparable to those of BaFe(2)As(2), a parent compound of iron-based superconductors. The structure of alpha-SrRh(2)As(2) is monoclinic (a = 421.2(1) pm, b = 1105.6(2) pm, c = 843.0(1) pm, beta = 95 degrees) and was refined as a twin in the space group P2(1)/c with R1 = 0.0928. beta-SrRh(2)As(2) crystallizes with a modulated structure in the (3 + 1)-dimensional superspace group Fmmm(10 gamma)s00 (a = 1114.4(3) pm, b = 574.4(2) pm, and c = 611.5(2) pm) and an incommensurable modulation vector q = (1, 0, 0.3311(4)). High-temperature single-crystal diffraction experiments confirm the tetragonal ThCr(2)Si(2)-type structure for gamma-SrRh(2)As(2) at 623 K. Electronic band structure calculations indicate that the structural distortion in a-SrRh2As2 is caused by strong Rh-Rh bonding interactions within the layers and has therefore no magnetic origin as suggested for isotypic BaFe(2)As(2).
Title:
Quantum spin fluctuations for a distorted incommensurate spiral
Authors:
Fishman, RS Author Full Names: Fishman, Randy S.
Source:
PHYSICAL REVIEW B, 85 (2):10.1103/PhysRevB.85.024411 JAN 12 2012
Abstract:
Quantum spin fluctuations are investigated for the distorted incommensurate spiral state of a geometrically frustrated triangular-lattice antiferromagnet. With increasing easy axis anisotropy, the average reduction of the spin amplitude by quantum fluctuations is suppressed but the spiral also becomes more distorted. Quantum fluctuations enhance both the wave vector of the distorted spiral and the critical anisotropy above which it undergoes a first-order transition into a collinear state. An experimental technique is proposed to isolate the effects of quantum fluctuations from the classical distortion of the spiral. This analysis is applied to the elliptical spiral state of doped CuFeO(2).
Title:
Monte Carlo and variational calculations of the magnetic phase diagram of CuFeO(2)
Authors:
Fishman, RS; Brown, G; Haraldsen, JT Author Full Names: Fishman, Randy S.; Brown, Gregory; Haraldsen, Jason T.
Source:
PHYSICAL REVIEW B, 85 (2):10.1103/PhysRevB.85.020405 JAN 12 2012
Abstract:
Monte-Carlo and variational calculations are used to revise the phase diagram of the magnetically frustrated material CuFeO(2). For fields 50 < H < 65T, a new spin-flop phase is predicted between a canted 3-sublattice phase and the conventional conical spin-flop phase. With wave vector Q approximate to (0.8 pi, 0.43 pi), this phase is commensurate in the x direction but incommensurate in the y direction. A canted 5-sublattice phase is predicted between the multiferroic phase and either a collinear 5-sublattice phase for pure CuFeO(2) or a canted 3-sublattice phase for Al- or Ga-doped CuFeO(2).
Title:
Temperature-dependent multi-k magnetic structure in multiferroic Co(3)TeO(6)
Authors:
Ivanov, SA; Tellgren, R; Ritter, C; Nordblad, P; Mathieu, R; Andre, G; Golubko, NV; Politova, ED; Weil, M Author Full Names: Ivanov, S. A.; Tellgren, R.; Ritter, C.; Nordblad, P.; Mathieu, R.; Andre, G.; Golubko, N. V.; Politova, E. D.; Weil, M.
Source:
MATERIALS RESEARCH BULLETIN, 47 (1):63-72; 10.1016/j.materresbull.2011.10.003 JAN 2012
Abstract:
A complex magnetic order of the multiferroic compound Co(3)TeO(6) has been revealed by neutron powder diffraction studies on ceramics and crushed single crystals. The compound adopts a monoclinic structure (s.g. C2/c) in the studied temperature range 2-300 K but exhibits successive antiferromagnetic transitions at low temperature. Incommensurate antiferromagnetic order with the propagation vector k(1) = (0, 0.485, 0.055) sets in at 26 K. A transition to a second antiferromagnetic structure with k(2) = (0, 0, 0) takes place at 21.1 K. Moreover, a transition to a commensurate antiferromagnetic structure with k(3) = (0, 0.5, 0.25) occurs at 17.4 K. The magnetic structures have been determined by neutron powder diffraction using group theory analysis as a preliminary tool. Different coordinations of the Co(2+) ions involved in the low-symmetry C2/c structure of Co(3)TeO(6) render the exchange-interaction network very complex by itself. The observed magnetic phase transformations are interpreted as an evidence of competing magnetic interactions. The temperature dependent changes in the magnetic structure, derived from refinements of high-resolution neutron data, are discussed and possible mechanisms connected with the spin reorientations are described. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Mn substitution-driven structural and magnetic phase evolution in Bi(1-x)Sm(x)FeO(3) multiferroics
Authors:
Khomchenko, VA; Troyanchuk, IO; Kovetskaya, MI; Paixao, JA Author Full Names: Khomchenko, V. A.; Troyanchuk, I. O.; Kovetskaya, M. I.; Paixao, J. A.
Source:
JOURNAL OF APPLIED PHYSICS, 111 (1):10.1063/1.3676205 JAN 1 2012
Abstract:
X-ray diffraction and magnetization measurements of the Bi(0.9)Sm(0.1)Fe(1-y)Mn(y)O(3) and Bi(0.86)Sm(0.14)Fe(1-z)Mn(z)O(3) (y <= 0.4, z <= 0.3) series were carried out in order to follow the effect of Mn doping on the room temperature crystal structure and magnetic properties of Sm-substituted BiFeO(3). Initially polar rhombohedral Bi(0.9)Sm(0.1)FeO(3) compound (space group R3c) was shown to undergo the Mn-substitution driven structural transformation into the orthorhombic Pnam phase at y similar to 0.2. Further increasing of the Mn content stabilizes the modified structural phase demonstrating the features of incommensurability. In the Bi(0.86)Sm(0.14)Fe(1-z)Mn(z)O(3) series, the initially dominant antipolar orthorhombic Pnam phase transforms toward the nonpolar Pnma structure (z similar to 0.3). Changes of the main magnetic state (from mixed antiferromagnetic/weak ferromagnetic to weak ferromagnetic) were found to correlate with the rhombohedral-to-orthorhombic transition; however, within the compositional range of the orthorhombically distorted compounds, the room temperature spontaneous magnetization rapidly decreases with increasing Mn content. (C) 2012 American Institute of Physics. [doi:10.1063/1.3676205]
Title:
Structural Defects in Periodic and Quasicrystalline Binary Nanocrystal Superlattices
Authors:
Bodnarchuk, MI; Sheychenko, EV; Talapin, DV Author Full Names: Bodnarchuk, Maryna I.; Sheychenko, Elena V.; Talapin, Dmitri V.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133 (51):20837-20849; 10.1021/ja207154v DEC 28 2011
Abstract:
Binary nanocrystal superlattices (BNSLs) emerge as an important class of man-made materials where components and functionalities can be added, tuned, or combined in a predictable manner. These amazingly complex structures spontaneously self-assemble from colloidal solutions containing binary mixtures of functional (semiconducting, magnetic, plasmonic, etc.) nanocrystals. Further developments of the BNSL-based materials require a deep understanding and control over BNSL formation and structural perfection. Like any solid, BNSL can contain different kinds of structural defects. It is well-known that defects can have a tremendous effect on the material's behavior. Defect engineering is used to modify and improve many of the mechanical, electrical, magnetic, and optical properties of conventional solids. In this work, we provide the first systematic analysis of structural defects in various BNSL structures. We used BNSLs as a platform for studying structural defects in both periodic (crystalline) and aperiodic (quasicrystalline) lattices, as well as for direct imaging of the interfaces between crystalline and quasicrystalline domains. Such direct observation of local imperfections in complex multicomponent lattices provides a unique insight into the fundamental aspects of crystal formation.

Update: 1-Feb-2012

Title:
Neutron powder diffraction study of the ternary RMgSn (R=Ce-Nd, Tb-Tm, Yb) compounds
Authors:
Lemoine, P; Verniere, A; Venturini, G; Capelli, S; Malaman, B Author Full Names: Lemoine, P.; Verniere, A.; Venturini, G.; Capelli, S.; Malaman, B.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 324 (6):961-976; 10.1016/j.jmmm.2011.09.035 MAR 2012
Abstract:
The ternary intermetallic RMgSn compounds are studied by neutron powder diffraction. The CeScSi-type PrMgSn and NdMgSn compounds present a commensurate antiferromagnetic structure, while the (Tb-Tm)MgSn are characterized by an incommensurate sine-wave modulated magnetic structure, which can tend to a square-modulated arrangement at low temperature due to appearance of higher odd integer harmonics. The TiNiSi-type CeMgSn compound is also characterized by an incommensurate sine-wave modulated magnetic structure, while PrMgSn exhibits a ferromagnetic arrangement with a canting at low temperature. Finally, the ZrNiAl-type YbMgSn compound evidences no magnetic ordering. These results are discussed and compared with those published for the other CeScSi-type compounds. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Modeling of decagonal quasicrystal lattice
Authors:
Girzhon, VV; Kovalyova, VM; Smolyakov, OV; Zakharenko, MI Author Full Names: Girzhon, V. V.; Kovalyova, V. M.; Smolyakov, O. V.; Zakharenko, M. I.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 358 (2):137-144; 10.1016/j.jnoncrysol.2011.09.017 JAN 15 2012
Abstract:
The model of the reciprocal lattice of decagonal quasicrystal has been proposed. It is based on the multiplication of the basis sites' groups according to the proposed rules. This model was shown to provide the information not only on the reciprocal sites location, but also on the intensity of the appropriated diffraction reflections. The physical justification of the proposed model correctness has been provided on the base of projection of six-dimensional hyperlattice onto the three-dimensional space. The possibility of three-indices labeling of the diffraction reflections of decagonal quasicrystals has been exhibited. (C) 2011 Elsevier B.V. All rights reserved.
Title:
The luminescence of Na(x)Eu((2-x)/3)(3+)MoO(4) scheelites depends on the number of Eu-clusters occurring in their incommensurately modulated structure
Authors:
Arakcheeva, A; Logvinovich, D; Chapuis, G; Morozov, V; Eliseeva, SV; Bunzli, JCG; Pattison, P Author Full Names: Arakcheeva, Alla; Logvinovich, Dmitry; Chapuis, Gervais; Morozov, Vladimir; Eliseeva, Svetlana V.; Buenzli, Jean-Claude G.; Pattison, Philip
Source:
CHEMICAL SCIENCE, 3 (2):384-390; 10.1039/c1sc00289a 2012
Abstract:
Scheelite related compounds with general formula M(n)(XO(4))(m) are the subject of hefty interest owing to their optical properties, stability and relatively simple preparation. Eu(3+)-containing scheelites are considered as red-emitting phosphors and the main factors affecting their luminescence are thought to be chemical composition and particle size while the influence of their structure is generally ignored. Here we report eight compounds from the Na(x)Eu((2-x)/3)MoO(4) series prepared by conventional solid-state reaction and present a detailed analysis of their crystal structures. Six of them have modulated structures, a common feature of SRCs, in which dopant Eu(3+) ions are orderly distributed. Moreover, different amounts of Eu(3+) dimers are detected in the modulated structures, characterized by weak satellite reflections appearing in the lower angle part of the XRD patterns. These reflections are indexed and incorporated into Rietveld's refinement using superspace (3 + 1)-dimension symmetry. The remarkable feature of the compounds is that the characteristic luminescence parameters, overall (Q(L)(Eu)) and intrinsic (Q(Eu)(Eu)) quantum yields, Eu((5)D(0)) lifetimes, and sensitization efficiencies (eta(sens)), correlate with the number of Eu(3+) aggregates, but not directly with the composition x of the materials. This provides an efficient tool for understanding and controlling the luminescence properties of scheelite related compounds.
Title:
The success story of crystallography
Authors:
Schwarzenbach, D Author Full Names: Schwarzenbach, Dieter
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 68 57-67; Part 1 10.1107/S0108767311030303 JAN 2012
Abstract:
Diffractionists usually place the birth of crystallography in 1912 with the first X-ray diffraction experiment of Friedrich, Knipping and Laue. This discovery propelled the mathematical branch of mineralogy to global importance and enabled crystal structure determination. Knowledge of the geometrical structure of matter at atomic resolution had revolutionary consequences for all branches of the natural sciences: physics, chemistry, biology, earth sciences and material science. It is scarcely possible for a single person in a single article to trace and appropriately value all of these developments. This article presents the limited, subjective view of its author and a limited selection of references. The bulk of the article covers the history of X-ray structure determination from the NaCl structure to aperiodic structures and macromolecular structures. The theoretical foundations were available by 1920. The subsequent success of crystallography was then due to the development of diffraction equipment, the theory of the solution of the phase problem, symmetry theory and computers. The many structures becoming known called for the development of crystal chemistry and of data banks. Diffuse scattering from disordered structures without and with partial long-range order allows determination of short-range order. Neutron and electron scattering and diffraction are also mentioned.
Title:
Direct Preparation of Nano-Quasicrystals via a Water-Cooled Wedge-Shaped Copper Mould
Authors:
Wang, ZF; Zhao, WM; Qin, CL; Cui, Y; Fan, SL; Jia, JQ Author Full Names: Wang, Zhifeng; Zhao, Weimin; Qin, Chunling; Cui, Yan; Fan, Shenglei; Jia, Junqing
Source:
JOURNAL OF NANOMATERIALS, 10.1155/2012/708240 2012
Abstract:
We have successfully synthesized multicomponent Mg-based nano-quasicrystals (nano-QCs) through a simple route by using a water-cooled wedge-shaped copper mould. Nanoscale QCs are prepared directly on tip of wedge-shaped castings. The further study shows that nano-QCs in the Mg(71)Zn(26)Y(2)Cu(1) alloy show well microhardness of greater than HV450. Electrochemical properties of three kinds of quasicrystal alloys are investigated in simulated seawater. The Mg(71)Zn(26)Y(2)Cu(1) nano-QC alloy presents the best corrosion resistance in this study for the formation of well-distributed nano-QC phases (1 similar to 5 nm) and polygonal Mg(2)(Cu,Y) nanophases (40 similar to 50 nm).
Title:
Potts Model with the Simplest Modulated Phase
Authors:
Ganikhodjaev, N; Temir, S; Akin, H; Uguz, S Author Full Names: Ganikhodjaev, Nasir; Temir, Seyit; Akin, Hasan; Uguz, Selman
Source:
JOURNAL OF THE KOREAN PHYSICAL SOCIETY, 59 (5):2971-2979; 10.3938/jkps.59.2971 NOV 2011
Abstract:
We study the phase diagrams for the Potts model on the Bethe lattice with competing nearest-neighbor interactions J(1) and ternary interactions J(p) and J(t). At vanishing temperature, the phase diagram is fully determined for all values and signs of J(p)/J(1) and J(t)/J(1); in particular, we show that the phase diagrams contain ferromagnetic, paramagnetic and < 2 > phases only; i.e., the set of modulated phases consists of the < 2 > phase only for J(1) > 0 and J(p)/J(1) < 0. We verify that values of T/J(1) in the very narrow strip -0.11 < T/J(1) < 0 with -J(p)/J(1) < 0 favor the modulated phase, which is either a commensurate phase with a very large period or an incommensurate phase. The transition lines are obtained from stability conditions, and characteristic points in the phase diagram are analyzed by using numerical iterations. Also the wavevectors versus temperature are plotted for some critical points in the modulated phases.
Title:
Materials Researcher Dan Shechtman receives Nobel Prize for discovery of quasicrystals
Authors:
[Anonymous] Author Full Names: [Anonymous]
Source:
MRS BULLETIN, 36 (11):849-849; 10.1557/mrs.2011.284 NOV 2011

Update: 25-Jan-2012

Title:
Microstructure evolution of Zr(65)Al(7.5)Cu(12.5)Ni(10)Ag(5) bulk metallic glass due to rolling and its influence on the thermal stability
Authors:
Yan, ZJ; Yan, J; Hu, Y; Hao, WX Author Full Names: Yan, Z. J.; Yan, J.; Hu, Y.; Hao, W. X.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 513 75-79; 10.1016/j.jallcom.2011.09.083 FEB 5 2012
Abstract:
X-ray diffraction (XRD), differential scanning calorimetry (DSC) and high-resolution transmission electron microscopy (HRTEM) are employed to investigate the microstructure evolution of Zr(65)Al(7.5)Cu(12.5)Ni(10)Ag(5) bulk metallic glass subjected to rolling at room temperature. The strain rates are controlled to be 10(-4)-10(-3) s(-1). The results show that the plastic deformation during rolling behaves as an inhomogeneous mode with the characteristic of shear bands, which results in the two-state characteristic of atomic movement from competition between the ordering and disordering processes. The icosahedron-like clusters precipitate in the transition regions between the shear bands and the amorphous matrix, and they tend to aggregate into nano-sized orders. The results of DSC indicate that the onset precipitation temperature of I-phase during heating of the metallic glass obviously decreases due to rolling. However, the time window for the completion of amorphous-to-icosahedral phase transformation is evidently lengthened. The microstructure evolution during rolling and its influence on the thermal stability are discussed. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Incommensurate magnetic order in TbTe(3)
Authors:
Pfuner, F; Gvasaliya, SN; Zaharko, O; Keller, L; Mesot, J; Pomjakushin, V; Chu, JH; Fisher, IR; Degiorgi, L Author Full Names: Pfuner, F.; Gvasaliya, S. N.; Zaharko, O.; Keller, L.; Mesot, J.; Pomjakushin, V.; Chu, J-H; Fisher, I. R.; Degiorgi, L.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (3):10.1088/0953-8984/24/3/036001 JAN 25 2012
Abstract:
We report a neutron diffraction study of the magnetic phase transitions in the charge-density wave (CDW) TbTe(3) compound. We discover that in the paramagnetic phase there are strong 2D-like magnetic correlations, consistent with the pronounced anisotropy of the chemical structure. A long-range incommensurate magnetic order emerges in TbTe(3) at T(mag1) = 5.78 K as a result of continuous phase transitions. We observe that near the temperature T(mag1) the magnetic Bragg peaks appear around the position (0, 0, 0.24) (or its rational multiples), that is fairly close to the propagation vector. 0; 0; 0 : 29 associated with the CDW phase transition in TbTe(3). This suggests that correlations leading to the long-range magnetic order in TbTe(3) are linked to the modulations that occur in the CDW state.
Title:
Magnetic properties of sigma- and hexagonal-Mn(76)Si(18)Cr(6) approximant phases of a dodecagonal quasicrystal
Authors:
Kashimoto, S; Kocjan, A; Jaglicic, Z; Jazbec, S; Iga, H; Ishimasa, T; Dolinsek, J Author Full Names: Kashimoto, S.; Kocjan, A.; Jaglicic, Z.; Jazbec, S.; Iga, H.; Ishimasa, T.; Dolinsek, J.
Source:
PHYSICAL REVIEW B, 84 (22):10.1103/PhysRevB.84.224201 DEC 19 2011
Abstract:
The tetragonal sigma phase and the hexagonal (hex) phase in the Mn-Si-V(Cr) transition-metal-alloy systems are stable approximant phases of a dodecagonal (12-fold) quasicrystal that can be prepared in bulk quantities. We have synthesized samples of the sigma and hex phases of composition Mn(76)Si(18)Cr(6) and determined their magnetic properties. In the sigma-Mn(76)Si(18)Cr(6), a spin-freezing transition to a canonical spin-glass phase was detected below T(f) approximate to 8 K, characterized by a maximum in the zero-field-cooled susceptibility, a frequency-dependent cusp in the ac susceptibility, M(H) hysteresis, and ultraslow time decay of the thermoremanent magnetization. In contrast, no spin-glass transition was observed in the hex-Mn(76)Si(18)Cr(6) phase down to the lowest investigated temperature of 2 K. The analysis of the susceptibility has shown that the coupling of spins in both phases is antiferromagnetic (AFM), but the coupling strength is considerably stronger in the sigma phase. Since both phases are structurally described by the triangle-square tiling scheme related to that of the dodecagonal quasicrystal, which imposes geometric frustration of the AFM-coupled spins on triangles, the absence of spin-glass transition in the hex-Mn(76)Si(18)Cr(6) could be due to shifting of this transition below the lowest temperature of our experimental setup, as a consequence of weaker spin coupling and smaller moment sizes in the hex phase. In both investigated samples, tiny Mn(3)O(4) inclusions that undergo a transition to a ferrimagnetic phase at T(C) approximate to 42 K were detected in the magnetic signal. Geometric frustration of interactions between the AFM-coupled spins placed at the vertices of the triangle-square tiling should be a general feature of dodecagonal quasicrystals and their approximants, so that spin-glass-type ordering is expected to occur quite commonly in the dodecagonal phases.
Title:
Deformed triangular lattice antiferromagnets in a magnetic field: Role of spatial anisotropy and Dzyaloshinskii-Moriya interactions
Authors:
Griset, C; Head, S; Alicea, J; Starykh, OA Author Full Names: Griset, Christian; Head, Shane; Alicea, Jason; Starykh, Oleg A.
Source:
PHYSICAL REVIEW B, 84 (24):10.1103/PhysRevB.84.245108 DEC 12 2011
Abstract:
Recent experiments on the anisotropic spin-1/2 triangular antiferromagnet Cs(2)CuBr(4) have revealed a remarkably rich phase diagram in applied magnetic fields, consisting of an unexpectedly large number of ordered phases. Motivated by this finding, we study the role of three ingredients-spatial anisotropy, Dzyaloshinskii-Moriya interactions, and quantum fluctuations-on the magnetization process of a triangular antiferromagnet, coming from the semiclassical limit. The richness of the problem stems from two key facts: (1) the classical isotropic model with a magnetic field exhibits a large accidental ground-state degeneracy and (2) these three ingredients compete with one another and split this degeneracy in opposing ways. Using a variety of complementary approaches, including extensive Monte Carlo numerics, spin-wave theory, and an analysis of Bose-Einstein condensation of magnons at high fields, we find that their interplay gives rise to a complex phase diagram consisting of numerous incommensurate and commensurate phases. Our results shed light on the observed phase diagram for Cs(2)CuBr(4) and suggest a number of future theoretical and experimental directions that will be useful for obtaining a complete understanding of this material's interesting phenomenology.
Title:
Structure and Morphology of Induction-Melted Higher Manganese Silicide
Authors:
Zhou, AJ; Cui, HG; Li, JZ; Zhao, XB Author Full Names: Zhou Ai-Jun; Cui Heng-Guan; Li Jing-Ze; Zhao Xin-Bing
Source:
ACTA PHYSICO-CHIMICA SINICA, 27 (12):2915-2919; 10.3866/PKU.WHXB20112915 DEC 2011
Abstract:
Field emission scanning microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDXS) were used to study the morphology and composition of secondary phase precipitations in induction-melted higher manganese silicide (HMS). Striations of the secondary phase were observed in individual HMS crystals with an average interval of 5-30 pm and a thickness of similar to 30 nm. The chemical composition of the striations was examined and found to be MnSi, which was observed as an amorphous phase by high resolution transmission electron microscopy (HRTEM). The crystal structure of HMS was determined by selective area electron diffraction (SAED) and the results indicated a single Mn(4)Si(7) phase in the as-prepared material and no other incommensurate HMS phases were found. After ball milling and hot pressing many defects and stress fields were observed in the HMS by transmission electron microscope (TEM), which differentiated substantially from the morphology of the as-melted HMS.
Title:
Phase diagram of hard tetrahedra
Authors:
Haji-Akbari, A; Engel, M; Glotzer, SC Author Full Names: Haji-Akbari, Amir; Engel, Michael; Glotzer, Sharon C.
Source:
JOURNAL OF CHEMICAL PHYSICS, 135 (19):10.1063/1.3651370 NOV 21 2011
Abstract:
Advancements in the synthesis of faceted nanoparticles and colloids have spurred interest in the phase behavior of polyhedral shapes. Regular tetrahedra have attracted particular attention because they prefer local symmetries that are incompatible with periodicity. Two dense phases of regular tetrahedra have been reported recently. The densest known tetrahedron packing is achieved in a crystal of triangular bipyramids (dimers) with a packing density of 4000/4671 approximate to 85.63%. In simulation a dodecagonal quasicrystal is observed; its approximant, with periodic tiling (3.4.3(2).4), can be compressed to a packing fraction of 85.03%. Here, we show that the quasicrystal approximant is more stable than the dimer crystal for packing densities below 84% using Monte Carlo computer simulations and free energy calculations. To carry out the free energy calculations, we use a variation of the Frenkel-Ladd method for anisotropic shapes and thermodynamic integ ration. The enhanced stability of the approximant can be attributed to a network substructure, which maximizes the free volume (and hence the wiggle room) available to the particles and facilitates correlated motion of particles, which further contributes to entropy and leads to diffusion for packing densities below 65%. The existence of a solid-solid transition between structurally distinct phases not related by symmetry breaking - the approximant and the dimer crystal - is unusual for hard particle systems. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3651370]
Title:
Formation of Icosahedral Quasicrystals and 1/1 Crystal Approximants in Al-Pd-RE (RE: Rare Earth Metals) Systems
Authors:
So, YG; Yoshikawa, T; Saruhashi, F; Edagawa, K; Tamura, R Author Full Names: So, Yeong-Gi; Yoshikawa, Takuro; Saruhashi, Fukuaki; Edagawa, Keiichi; Tamura, Ryuji
Source:
MATERIALS TRANSACTIONS, 52 (11):2011-2015; 10.2320/matertrans.M2011162 NOV 2011
Abstract:
We have investigated the formation of an icosahedral quasicrystal (i-phase) and its 1/1-crystal approximant (1/1-phase) in the (Al, Ga)-Pd-RE (Rare earth metals) systems. Consequently, the Ga-Pd-Sc 1/1-phase, the Al-Pd-RE (RE = Yb, Tin and Er) 1/1-phase and the Al-Pd-Yb i-phase have been newly found by the substitution of Al for Ga, or Sc for other RE in the constituent elements of the Al(54)Pd(30)Sc(16) i-phase previously reported. For the i- and the 1/1-phases studied in this work, the number of valence electrons per atom (e/a) ratio is 2.10 and the atomic radius ratio of the rare earth element to that of the other base elements is in the range 1.15-1.24, which fulfilled the formation conditions previously reported for other Tsai-type i-phases. On the other hand, the stability of the i-phases becomes lower with increasing the atomic radii of the RE elements, which indicates that the atomic radius ratio plays important role in the formation of the Al-Pd-RE i- and 1/1-phases. [doi:10.2320/matertrans.M2011162]
Title:
Ti/Pr(0.7)Ca(0.3)MnO(3)/La(0.67)Sr(0.33)MnO(3)/Pt heterostructures
Authors:
Wang, ZW; Zhang, J; Li, HW; Dong, CY; Zhao, J; Zhao, X; Chen, W Author Full Names: Wang Zhong-Wei; Zhang Jian; Li Hong-Wei; Dong Chun-Ying; Zhao Jing; Zhao Xu; Chen Wei
Source:
ACTA PHYSICA SINICA, 60 (11):NOV 2011
Abstract:
Ti/Pr(0.7)Ca(0.3)MnO(3)/Pt and Ti/Pr(0.7)Ca(0.3)MnO(3)/La(0.67)Sr(0.33)MnO(3)/Pt heterostructures are prepared using a pulsed laser deposition (PLD) technique, and the resistive switching of the heterostructures is investigated. The Ti/Pr(0.7)Ca(0.3)MnO(3)/La(0.67)Sr(0.33)MnO(3)/Pt heterostructure, which has a La(0.67)Sro(0.33)MnO(3) modulation layer, shows superior characteristics of resistive switching. In particular, the switching ratio and the fatigue properties are improved greatly in this heterostructure. The mechanism of resistive switching in Ti/Pr(0.7)Ca(0.3)MnO(3)/La(0.67)Sr(0.33)MnO(3)/Pt heterostructure is also discussed in this paper.

Update: 19-Jan-2012

Title:
Evolution of the commensurate and incommensurate magnetic phases of the S=3/2 kagome staircase Co(3)V(2)O(8) in an applied field
Authors:
Helton, JS; Chen, Y; Bychkov, GL; Barilo, SN; Rogado, N; Cava, RJ; Lynn, JW Author Full Names: Helton, Joel S.; Chen, Ying; Bychkov, Georgii L.; Barilo, Sergei N.; Rogado, Nyrissa; Cava, Robert J.; Lynn, Jeffrey W.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (1):10.1088/0953-8984/24/1/016003 JAN 11 2012
Abstract:
Single crystal neutron diffraction studies have been performed on the S = 3/2 kagome staircase compound Co(3)V(2)O(8) with a magnetic field applied along the magnetization easy-axis ((H) over right arrow parallel to(a) over right arrow). Previous zero- field measurements (Chen Y et al 2006 Phys. Rev. B 74 014430) reported a rich variety of magnetic phases, with a ferromagnetic ground state as well as incommensurate, transversely polarized spin density wave (SDW) phases (with a propagation vector of (k) over right arrow = (0 delta 0)) interspersed with multiple commensurate lock-in transitions. The magnetic phase diagram with ((H) over right arrow parallel to(a) over right arrow) adds further complexity. For small applied fields, mu(0)H approximate to 0.05 T, the commensurate lock-in phases are destabilized in favor of the incommensurate SDW ones, while slightly larger applied fields restore the commensurate lock-in phase with delta = 1/2 and yield a new commensurate phase with delta = 2/5. For measurements in an applied field, higher-order scattering is observed that corresponds to the second harmonic.
Title:
Microstructures and mechanical properties of quasicrystal reinforced AZ31 matrix composites
Authors:
Wang, XD; Du, WB; Wang, ZH; Liu, K; Li, SB Author Full Names: Wang, Xudong; Du, Wenbo; Wang, Zhaohui; Liu, Ke; Li, Shubo
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 530 446-451; 10.1016/j.msea.2011.09.110 DEC 15 2011
Abstract:
In order to improve the mechanical properties of AZ31 alloys, the repeated plastic working process was employed to fabricate the AZ31-based composites reinforced with stable icosahedral quasicrystal particles. The microstructure of the composites has been investigated by XRD, SEM, TEM and HREM, and their mechanical properties have also been studied. The results showed that the RPW process reduced the grain size significantly, and the average grain size was only about 500 nm after 200 cycles of RPW. A good metallurgical bond interface between the quasicrystal particles and the Mg matrix was found in their crystallographic orientation relationship of (1 0 (1) over bar 0)(mg)//2-f. The composites exhibited the maximum yield tensile strength of 334 MPa and the maximum ultimate tensile strength of 372 MPa at room temperature, respectively. The enhanced mechanical properties were attributed to the strengthening effect of quasicrystal particles and the refined microstructure. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Effects of the commensurability and disorder on friction for the system Xe/Cu
Authors:
Franchini, A; Bortolani, V; Santoro, G; Xheka, K Author Full Names: Franchini, A.; Bortolani, V.; Santoro, G.; Xheka, K.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 23 (48):10.1088/0953-8984/23/48/484004 DEC 7 2011
Abstract:
We present molecular dynamics simulations of static friction for a monolayer of Xe deposited on a thick slab of Cu for two different geometries. The interaction potential between Xe and Cu has been derived from DFT calculations. The first geometry is the commensurate adsorption geometry (root 3 x root 3)R30 degrees suggested by LEED, corresponding to a coverage 1/3, where all Xe atoms are on top positions. The second one corresponds to a coverage 0.36 and is characterized by a large surface unit cell, containing 9 Xe atoms in different disordered positions. This large unit cell mimics an incommensurate case. Our analysis points out the effect of the order/disorder in tribological properties of a realistic three-dimensional system.
Title:
Resonant tunneling in GaAs/Al(x)Ga(1-x)As superlattices with aperiodic potential profiles
Authors:
Djelti, R; Aziz, Z; Bentata, S; Besbes, A Author Full Names: Djelti, R.; Aziz, Z.; Bentata, S.; Besbes, A.
Source:
SUPERLATTICES AND MICROSTRUCTURES, 50 (6):659-666; 10.1016/j.spmi.2011.09.007 DEC 2011
Abstract:
Using the exact Airy function formalism and the transfer-matrix technique, we have numerically investigated in this paper the effect of intentional correlations in spatial disorder on transmission properties of one-dimensional superlattices. Such systems consist of two different structures randomly distributed along the growth direction, with the additional constraint that barriers (wells) of one kind always appear in triply. It is shown that the intentional correlations in disorder and superlattices structural parameters are responsible to obtain resonant tunneling in aperiodic structure. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Structure, electrical and magnetic property investigations on dense Fe-doped hexagonal BaTiO(3)
Authors:
Wei, XK; Su, YT; Sui, Y; Zhang, QH; Yao, Y; Jin, CQ; Yu, RC Author Full Names: Wei, X. K.; Su, Y. T.; Sui, Y.; Zhang, Q. H.; Yao, Y.; Jin, C. Q.; Yu, R. C.
Source:
JOURNAL OF APPLIED PHYSICS, 110 (11):10.1063/1.3658813 DEC 1 2011
Abstract:
Hexagonal Ba(Ti(1-x)Fe(x))O(3-delta) (x = 1/6, 1/3) ceramics treated with post annealing are specifically synthesized to explore the origin mechanism of the unusual ferromagnetism in the doped system. X-ray diffraction refinements and transmission electron microscope experiments reveal that their structures are incommensurately modulated owing to simultaneous oxygen vacancies at both O1 and O2 sites. Consequently, coexisting weak ferrielectricity and weak ferromagnetism are presented at room temperature. Analysis on their leakage current plot reveals that their conduction follows trap-filled limit model. In combination with the magnetism studies on 5 mol% Fe-doped crystals [Phys. Rev. B 83, 144407 (2011)], the reduction of ferromagnetism with an increase of conductivity suggests that dynamic exchanges of trapped electrons among the bound magnetic polarons attribute to the intrinsic ferromagnetism. (C) 2011 American Institute of Physics. [doi:10.1063/1.3658813]
Title:
Analytic solutions to a finite width strip with a single edge crack of two-dimensional quasicrystals
Authors:
Li, W Author Full Names: Li Wu
Source:
CHINESE PHYSICS B, 20 (11):10.1088/1674-1056/20/11/116201 NOV 2011
Abstract:
In this paper, we investigate the well-known problem of a finite width strip with a single edge crack, which is useful in basic engineering and material science. By extending the configuration to a two-dimensional decagonal quasicrystal, we obtain the analytic solutions of modes I and II using the transcendental function conformal mapping technique. Our calculation results provide an accurate estimate of the stress intensity factors K(I) and K(II), which can be expressed in a quite simple form and are essential in the fracture theory of quasicrystals. Meanwhile, we suggest a generalized cohesive force model for the configuration to a two-dimensional decagonal quasicrystal. The results may provide theoretical guidance for the fracture theory of two-dimensional decagonal quasicrystals.
Title:
On a Realistic Growth Mechanism for Quasicrystals
Authors:
Steurer, W Author Full Names: Steurer, Walter
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 637 (13):1943-1947; SI 10.1002/zaac.201100210 NOV 2011
Abstract:
Simple rules are discussed that can guide under realistic conditions the growth of quasicrystals. We propose a two-step mechanism where the well-known overlap rules for the fundamental atomic clusters are complemented by the new layer-continuation rule. This rule demands that the sets of atomic layers, crisscrossing each atomic cluster according to its eigensymmetry, have to be continued across all other clusters formed during the growth process. On one hand, this combined growth rule is local because each fundamental cluster already defines the overlap rules as well as the basic set of atomic layers. On the other hand, it is global because the framework of atomic layers originating locally from each cluster extends infinitely. The layer-continuation rule guides the attachment of atoms to the growing quasicrystal and assists the overlap rules, which are at the high temperatures, where crystal growth takes place, only weakly supported by specific atomic arrangements in the shared cluster volumes.
Title:
Proton NMR study of the organic metal kappa-(BETS)(2)Mn[N(CN)(2)](3)
Authors:
Vyaselev, OM; Kushch, ND; Yagubskii, EB Author Full Names: Vyaselev, O. M.; Kushch, N. D.; Yagubskii, E. B.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 113 (5):835-841; 10.1134/S106377611114010X NOV 2011
Abstract:
Magnetic properties of the organic conductor kappa-(BETS)(2)Mn[N(CN)(2)](3) above and below the temperature of the metal-insulator transition that occurs at T (MI) a parts per thousand 25 K are studied by (1)H NMR. The proton spectrum is shown to be determined by the static dipolar fields from Mn(2+) localized moments, while the (1)H spin-lattice relaxation is dominated by fluctuating fields from Mn(2+) electrons. The NMR data, both static (the spectra) and dynamic (the spin-lattice relaxation), indicate the freezing of Mn(2+) moments into a short-range or an incommensurate long-range antiferromagnetic order below T (MI).
Title:
A Study of the Formation of Ln(2+x)Me(2-x)O(7-x/2) (Ln = Gd, Dy; Me = Zr, Hf) Nanocrystals
Authors:
Popov, VV; Zubavichus, YV; Petrunin, VF; Menushenkov, AP; Kashurnikova, OV; Korovin, SA; Chernikov, RV; Yaroslavtsev, AA Author Full Names: Popov, V. V.; Zubavichus, Ya. V.; Petrunin, V. F.; Menushenkov, A. P.; Kashurnikova, O. V.; Korovin, S. A.; Chernikov, R. V.; Yaroslavtsev, A. A.
Source:
GLASS PHYSICS AND CHEMISTRY, 37 (5):512-520; 10.1134/S1087659611050117 OCT 2011
Abstract:
It has been established that the process of producing the Ln(2+x)Me(2-x)O(7-x/2) (Ln = Gd, Dy; Me = Zr, Hf) nanocrystals by calcination of hydroxides, which, in turn, have been produced by coprecipitation of metal salts, includes several stages. At the beginning, the X-ray amorphous structure of the precursors remains unchanged during dehydration; during subsequent heating to 600-700 degrees C, nanocrystals with a disordered fluorite structure begin to be formed. An increase in the temperature above 700 degrees C leads to an increase in the size of crystallites (coherent scattering regions). This process is accompanied by changes occurring in their local structure. In the nanocrystalline powders of Cd(2)Hf(2)O(7) and Gd(2)Zr(2)O(7) synthesized at 1200 degrees C (6 h), the pyrochlore-type superstructure with the lattice parameters doubled relative to fluorite has been revealed. It has also been found that, possibly, the Dy(2)HfO(5) sample at 1600 degrees C (3 h) has a modulated structure.

Update: 11-Jan-2012

Title:
Ordered fluorite phases in the Bi(2)O(3)-Ta(2)O(5) system: A structural and electrical investigation
Authors:
Struzik, M; Malys, M; Wrobel, W; Abrahams, I; Krok, F; Dygas, JR Author Full Names: Struzik, M.; Malys, M.; Wrobel, W.; Abrahams, I.; Krok, F.; Dygas, J. R.
Source:
SOLID STATE IONICS, 202 (1):22-29; 10.1016/j.ssi.2011.08.009 NOV 2 2011
Abstract:
Structure and electrical behaviour are reported for the system Bi(1-x)Ta(x)O(1.5+x) (0.167 <= x <= 0.250). In the compositional range 0.200 < x <= 0.250 an incommensurately modulated pseudo-cubic phase (type II) is observed, with the appearance of a larger pseudo-cubic phase in the region 0.167 <= x <= 0.200. Structural analysis of the type II phases by neutron diffraction reveals subtle changes in the oxide ion distribution with temperature, associated with changes in the incommensurate modulation parameter. Analysis of the defect structure of the type II phase reveals chains of tantalate octahedra as a likely structural motif. It is proposed that these chains facilitate an electronic contribution to total conductivity at low temperatures through electron hopping along the chains. Changes in oxide ion vacancy ordering may explain the observed non-linear behaviour in the thermal expansion of lattice parameter and Arrhenius plots of total conductivity. (C) 2011 Elsevier B.V. A! ll rights reserved.

Update: 4-Jan-2012

Title:
Nobel Prize in Chemistry honors the discovery of quasicrystals
Authors:
Smart, AG Author Full Names: Smart, Ashley G.
Source:
PHYSICS TODAY, 64 (12):17-20; DEC 2011

Update: 29-Dec-2011

Title:
Microscopically derived Ginzburg-Landau theory for magnetic order in the iron pnictides
Authors:
Brydon, PMR; Schmiedt, J; Timm, C Author Full Names: Brydon, P. M. R.; Schmiedt, Jacob; Timm, Carsten
Source:
PHYSICAL REVIEW B, 84 (21):10.1103/PhysRevB.84.214510 DEC 7 2011
Abstract:
We examine the competition of the observed stripe spin density wave (SDW) with other commensurate and incommensurate SDW phases in a two-band model of the pnictides. Starting from this microscopic model, we rigorously derive an expansion of the free energy in terms of the different order parameters at the mean-field level. We show that three distinct commensurate SDW states are possible and study their appearance as a function of the doping and the electronic structure. We show that the stripe phase is generally present, but its extent in the phase diagram depends strongly upon the number of hole Fermi pockets that are nested with the electron Fermi pockets. Electron pockets competing for the same portion of a hole pocket play a crucial role. We discuss the relevance of our results for the antiferromagnetism of the pnictides.
Title:
(57)Fe Mossbauer spectroscopy studies of CaFe(4)As(3)
Authors:
Nowik, I; Felner, I; Karki, AB; Jin, R Author Full Names: Nowik, I.; Felner, I.; Karki, A. B.; Jin, R.
Source:
PHYSICAL REVIEW B, 84 (21):10.1103/PhysRevB.84.212402 DEC 7 2011
Abstract:
We report on the (57)Fe Mossbauer spectroscopy and direct-current magnetization studies of orthorhombic CaFe(4)As(3), which undergoes two magnetic transitions with the formation of spin density wave at T(N1) = 88 K (incommensurate) and T(N2) = 26 K (commensurate). The magnetic Mossbauer spectroscopy spectra below T(N1) are composed of four subspectra attributed to the four in-equivalent Fe crystallographic sites: three Fe ions in the divalent state (Fe(2+)) and one as Fe(1+). However, the magnetic lines are much broader than that below T(N2), indicating an incommensurate magnetic state. In the paramagnetic state, the Mossbauer spectroscopy spectra are composed of three doublets; one of them is related to Fe(1+). Evidence for spin fluctuations above T(N1) is observed.
Title:
Atomic dynamics and interatomic interaction in quasicrystals
Authors:
Parshin, PP; Zemlyanov, MG; Brand, RA Author Full Names: Parshin, P. P.; Zemlyanov, M. G.; Brand, R. A.
Source:
CRYSTALLOGRAPHY REPORTS, 56 (7):1145-1148; 10.1134/S1063774511070285 DEC 2011
Abstract:
The previous experimental data on the partial spectra of thermal atomic vibrations in icosahedral (Al(62)Cu(25.5)Fe(12.5)) and decagonal (Al(71.3)Ni(24)Fe(4.7)) quasicrystals have been used to perform a comparative analysis of the atomic dynamics features and determine the role that Al, Cu, Ni, and Fe atoms play in the formation of interatomic interaction in the alloys studied. A physical model of the decagonal quasicrystal structure is proposed.
Title:
Atomic packing and short-to-medium range order evolution of Zr-Pd metallic glass
Authors:
Qi, L; Liu, M; Zhang, SL; Zhang, XY; Tan, CL Author Full Names: Qi Li; Liu Mei; Zhang ShiLiang; Zhang XinYu; Tan ChunLin
Source:
CHINESE SCIENCE BULLETIN, 56 (36):3908-3911; 10.1007/s11434-011-4841-0 DEC 2011
Abstract:
A larger-scale Zr(70)Pd(30) alloy system has been simulated using molecular dynamics (MD) to investigate structure evolution in Zr(70)Pd(30) metallic glass. The simulated pair distribution function of Zr(70)Pd(30) metallic glass agrees well with the experimental results. Voronoi polyhedron analysis indicates that the icosahedra are not randomly distributed in space, but form characteristic intercrossed icosahedral clusters with medium-range order. Intercrossed icosahedral clusters are the dominant local configurations in Zr(70)Pd(30) metallic glass and probably cause the quasicrystalline phase discovered in Zr(70)Pd(30) metallic glass.
Title:
Highly mobile twinned interface in 10 M modulated Ni-Mn-Ga martensite: Analysis beyond the tetragonal approximation of lattice
Authors:
Straka, L; Heczko, O; Seiner, H; Lanska, N; Drahokoupil, J; Soroka, A; Fahler, S; Hanninen, H; Sozinov, A Author Full Names: Straka, L.; Heczko, O.; Seiner, H.; Lanska, N.; Drahokoupil, J.; Soroka, A.; Faehler, S.; Hanninen, H.; Sozinov, A.
Source:
ACTA MATERIALIA, 59 (20):7450-7463; 10.1016/j.actamat.2011.09.020 DEC 2011
Abstract:
The huge strains that Ni-Mn-Ga magnetic shape memory alloys can achieve are usually described in a tetragonal unit cell approximation of a five-layered modulated (10 M) crystal structure. Here we analyze the impact of a slight orthorhombic and monoclinic distortion of the 10 M structure in Ni(50.2)Mn(28.3)Ga(21.5)at(.%) single crystal. Combining dedicated experiments to probe the microstructure, structure and mechanical properties with calculation using elastic continuum theory, we prove the existence of fine a/b-laminates within modulation macrotwins of the order of 100 micrometers in size. This complex twin microstructure containing a Type II macrotwin interface is associated with an extraordinarily low twinning stress of between 0.05 and 0.3 MPa, while Type I twins exhibit twinning stress of about 1 MPa. The findings provide important guidelines for designing the martensitic microstructure for more efficient actuators. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Phase evolution and magnetic property of Bi(1-x)Ho(x)FeO(3) powders
Authors:
Wu, YJ; Zhang, J; Chen, XK; Chen, XJ Author Full Names: Wu, Yu-Jie; Zhang, Jing; Chen, Xiao-Kun; Chen, Xiao-Jia
Source:
SOLID STATE COMMUNICATIONS, 151 (24):1936-1940; 10.1016/j.ssc.2011.09.020 DEC 2011
Abstract:
The structural, vibrational, and magnetic properties of well prepared Bi(1-x)Ho(x)FeO(3) (x = 0-0.175) powders are investigated by combining X-ray diffraction, Raman scattering, and magnetometry measurements. A structural symmetry breaking from the rhombohedral R3c to orthorhombic Pnma between x = 0.10 and 0.125 is identified from the X-ray and Raman measurements, accompanying a ferroelectric-paraelectric phase transition. The remnant magnetization of Bi(1-x)Ho(x)FeO(3) is enhanced before approaching the ferroelectric-paraelectric phase boundary, and then it slightly decreases until x = 0.175. Such enhancement (0 <= x <= 0.10) is suggested to result from the destruction of the spin cycloid structure. The decrease in the remnant magnetization with higher substitution concentration is due to the further destruction in the space modulated spin structure allowing a more perfect antiferromagnetic ordering. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Incommensurate Antiferromagnetic Insulating State in (MDT-TS)(AuI(2))(x)
Authors:
Yoshioka, H; Seo, H; Otsuka, Y Author Full Names: Yoshioka, Hideo; Seo, Hitoshi; Otsuka, Yuichi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 80 (12):10.1143/JPSJ.80.123702 DEC 2011
Abstract:
We theoretically study the metal-insulator transition in a molecular conductor (MDT-TS)(AuI(2))(x) composed with an incommensurate ratio (x = 0.441), where the conduction band originated from the HOMO of donor MDT-TS molecules is incommensurately filled. We consider a two-dimensional Hubbard model taking account of anisotropic transfer integrals in the donor layer, under a periodic potential due to the anions (AuI(2))(-) which mismatches the donor lattice period, and investigate the ground state within mean-field approximation. An antiferromagnetic insulating state with induced charge disproportionation is obtained in the large U and delta region; the symmetry in the charge sector is unchanged from the paramagnetic metallic state realized at small U and delta, therefore this state corresponds to the incommensurate Mott insulating state predicted previously [H. Yoshioka et al.: J. Phys. Soc. Jpn. 74 (2005) 1922] based on a simplified one-dimensional model.
Title:
Complex magnetoelastic properties in the frustrated kagome-staircase compounds (Co(1-x)Ni(x))(3)V(2)O(8)
Authors:
Zhang, Q; Knafo, W; Adelmann, P; Schweiss, P; Grube, K; Qureshi, N; Wolf, T; von Lohneysen, HV; Meingast, C Author Full Names: Zhang, Q.; Knafo, W.; Adelmann, P.; Schweiss, P.; Grube, K.; Qureshi, N.; Wolf, Th.; v. Loehneysen, H.; Meingast, C.
Source:
PHYSICAL REVIEW B, 84 (18):10.1103/PhysRevB.84.184429 NOV 28 2011
Abstract:
High-resolution heat-capacity and thermal-expansion measurements on single crystals of the kagome-staircase compounds (Co(1-x)Ni(x))(3)V(2)O(8) are presented. The parent compounds Co(3)V(2)O(8) and Ni(3)V(2)O(8) undergo a sequence of first-and second-order magnetic phase transitions. The low-temperature (T <= 40 K) magnetic entropy evolves monotonically with the doping content x from the full value expected for Ni(2+) S = 1 magnetic moments in Ni(3)V(2)O(8) to only half the value expected for Co(2+) S = 3/2 moments in Co(3)V(2)O(8). The thermal-expansion coefficients alpha(i) (i = a, b, and c) show a strong anisotropy for all (Co(1-x)Ni(x))(3)V(2)O(8) compounds. The low temperature expansivities indicate that Co doping (Ni doping) yields changes similar to uniaxial pressures along a or b (c). Linear Gruneisen parameters Gamma(i) are extracted for the three main axes i and are found to exhibit a complex temperature and doping dependence. For each axis, Gamma(i) and alpha(i) exhibit a sign change at low temperature at the critical concentration x(c) similar or equal to 0.25 where the incommensurate magnetic propagation vector changes. Our study motivates further investigations to understand how the multiple and complex parameters such as magnetic frustration, magnetic anisotropy, and mixture of S = 1 and 3/2 ions affect the rich magnetoelastic properties of (Co(1-x)Ni(x))(3)V(2)O(8).
Title:
Investigation of the Formation of Quasicrystalline Al(70)-Pd(20)-Re(10) Phase in situ during Annealing
Authors:
Makhotkin, IA; Yakunin, SN; Seregin, AY; Shaitur, DS; Tsetlin, MB; Tereshchenko, EY Author Full Names: Makhotkin, I. A.; Yakunin, S. N.; Seregin, A. Yu.; Shaitur, D. S.; Tsetlin, M. B.; Tereshchenko, E. Yu.
Source:
CRYSTALLOGRAPHY REPORTS, 56 (5):871-874; 10.1134/S106377451105018X SEP 2011
Abstract:
The change in the phase composition of thin-film layered AlPdRe nanostructures during annealing, which led to the formation of a quasicrystalline layer, has been studied in situ. It is shown that the Al(3)Pd phase is formed at a temperature above 260 degrees C, which transforms into the AlPd phase at 580 degrees C, and the icosahedral quasicrystalline Al-Pd-Re phase is formed at 680 degrees C. DOI: 10.1134/S106377451105018X

Update: 22-Dec-2011

Title:
Determination of the orientation relationship between austenite and 5M modulated martensite in Ni-Mn-Ga alloys
Authors:
Li, ZB; Zhang, YD; Esling, C; Zhao, X; Zuo, L Author Full Names: Li, Zongbin; Zhang, Yudong; Esling, Claude; Zhao, Xiang; Zuo, Liang
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 44 1222-1226; Part 6 10.1107/S0021889811043366 DEC 2011
Abstract:
The microstructural and crystallographic characteristics of 5M martensite in an Ni(50)Mn(28)Ga(22) alloy were investigated by electron backscatter diffraction (EBSD) analysis. The microstructure of 5M martensite observed at room temperature can be characterized by broad plates with alternately distributed fine lamellae (variants). With the accurate EBSD orientation measurements and by application of monoclinic superstructure information, four twin-related variants in one broad plate were identified. On the basis of the correct orientation data of martensite variants acquired from the EBSD measurements, the more favourable orientation relationship between austenite and 5M martensite was revealed to be the Pitsch relation with (101)(A)//(1 (2) over bar(5) over bar)(5M) and [10 (1) over bar](A)//[(5) over bar(5) over bar1](5M) by detailed crystallographic calculation without residual austenite.
Title:
Mossbauer investigations of crystalline and quasicrystalline Al(3)(Mn, Fe) compounds
Authors:
Ali, K; Reissner, M; Steiner, W; Feuerbacher, M Author Full Names: Ali, K.; Reissner, M.; Steiner, W.; Feuerbacher, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 23 (47):10.1088/0953-8984/23/47/475501 NOV 30 2011
Abstract:
(57)Fe Mossbauer and magnetic measurements are reported on Taylor phase compounds T-Al(3)(Mn, Fe), which can be seen as complex metallic alloys. The orthorhombic unit cell contains 156 atoms. These investigations are further extended to Al(71)Mn(19)Fe(10) crystallizing as a decagonal quasicrystal. Common to both structures are layers, which are oriented perpendicular to the b axis in the crystalline or to the periodic axis in the quasicrystalline compound, allowing the formation of characteristic building blocks. At low temperatures for all samples spin glass behavior is observed with freezing temperatures T(f) increasing with Fe content. Above T(f) the (57)Fe Mossbauer spectra were analyzed by a superposition of two subspectra with intensity ratio around 75: 25, which can be allocated to Fe substituted on Mn sites surrounded either by Al and Mn or solely by Al with Mn only at the edge of the nearest neighbor shell. For both subspectra quadrupole splitting and center shift do not change significantly with Fe content and with structure. Below T(f) broad hyperfine field distributions with non-vanishing contributions at zero hyperfine field are present. Magnetic and electrostatic hyperfine interactions are governed by length scales which are determined by the very similar interatomic configurations forming the T-Al(3)Mn phase as well as the decagonal compound. The presence of long range atomic order is of less importance.
Title:
Coexistence of the long-range and short-range magnetic order components in SrEr(2)O(4)
Authors:
Hayes, TJ; Balakrishnan, G; Deen, PP; Manuel, P; Chapon, LC; Petrenko, OA Author Full Names: Hayes, T. J.; Balakrishnan, G.; Deen, P. P.; Manuel, P.; Chapon, L. C.; Petrenko, O. A.
Source:
PHYSICAL REVIEW B, 84 (17):10.1103/PhysRevB.84.174435 NOV 23 2011
Abstract:
Single-crystal neutron diffraction reveals two distinct components to the magnetic ordering in geometrically frustrated SrEr(2)O(4). One component is a long-range ordered k = 0 structure which appears below T(N) = 0.75 K. Another component is a short-range incommensurate structure which manifests itself by the presence of a strong diffuse scattering signal. On cooling from higher temperatures down to 0.06 K, the partially ordered component does not undergo a pronounced phase transition. The magnetic moments in the long-range commensurate and short-range incommensurate structures are predominantly pointing along the [001] and [100] axes, respectively. The unusual coexistence of two magnetic structures is probed using both unpolarized and XYZ-polarized neutron scattering techniques. The observed diffuse scattering pattern can be satisfactorily reproduced with a classical Monte Carlo simulation by using a simple model based on a ladder of triangles.

Update: 7-Dec-2011

Title:
Successive magnetic transitions and static magnetic order in RCoAsO (R = La, Ce, Pr, Nd, Sm, Gd) confirmed by muon-spin rotation and relaxation
Authors:
Sugiyama, J; Mansson, M; Ofer, O; Kamazawa, K; Harada, M; Andreica, D; Amato, A; Brewer, JH; Ansaldo, EJ; Ohta, H; Michioka, C; Yoshimura, K Author Full Names: Sugiyama, Jun; Mansson, Martin; Ofer, Oren; Kamazawa, Kazuya; Harada, Masashi; Andreica, Daniel; Amato, Alex; Brewer, Jess H.; Ansaldo, Eduardo J.; Ohta, Hiroto; Michioka, Chishiro; Yoshimura, Kazuyoshi
Source:
PHYSICAL REVIEW B 84 (18): 10.1103/PhysRevB.84.184421 NOV 16 2011
Abstract:
The presence of antiferromagnetic (AF) order seems to be a common feature for the parent compounds of cuprate as well as some pnictide high-temperature superconductors. In order to search for antiferromagnetic order in the closely related rare-earth cobalt arsenic oxides (RCoAsO), we have measured muon-spin rotation and relaxation (mu(+)SR) spectra on a series of powder samples with R = La, Ce, Pr, Nd, Sm, and Gd. It was found that, besides GdCoAsO, all the other five compounds enter into a static ferromagnetic ordered phase below around 70 K (=T(C)), while additional transitions into a static AF ordered phase were found for NdCoAsO and SmCoAsO. For GdCoAsO, a static ferrimagnetic phase appeared below 60.5 K and then an incommensurate spin-density-wave ordered phase followed below 3.2 K. The AF spin structure was also found to strongly depend on R.
Title:
Degenerate Quasicrystal of Hard Triangular Bipyramids
Authors:
Haji-Akbari, A; Engel, M; Glotzer, SC Author Full Names: Haji-Akbari, Amir; Engel, Michael; Glotzer, Sharon C.
Source:
PHYSICAL REVIEW LETTERS 107 (21): 10.1103/PhysRevLett.107.215702 NOV 15 2011
Abstract:
We report a degenerate quasicrystal in Monte Carlo simulations of hard triangular bipyramids each composed of two regular tetrahedra sharing a single face. The dodecagonal quasicrystal is similar to that recently reported for hard tetrahedra [Haji-Akbari et al., Nature (London) 462, 773 (2009)] but degenerate in the pairing of tetrahedra, and self-assembles at packing fractions above 54%. This notion of degeneracy differs from the degeneracy of a quasiperiodic random tiling arising through phason flips. Free energy calculations show that a triclinic crystal is preferred at high packing fractions.
Title:
Low-temperature structure of xi '-Al-Pd-Mn optimized by ab initio methods
Authors:
Frigan, B; Santana, A; Engel, M; Schopf, D; Trebin, HR; Mihalkovic, M Author Full Names: Frigan, Benjamin; Santana, Alejandro; Engel, Michael; Schopf, Daniel; Trebin, Hans-Rainer; Mihalkovic, Marek
Source:
PHYSICAL REVIEW B 84 (18): 10.1103/PhysRevB.84.184203 NOV 14 2011
Abstract:
We have studied and resolved occupancy correlations in the existing average structure model of the complex metallic alloy xi'-Al-Pd-Mn [Boudard et al., Philos. Mag. A 74, 939 (1996)], which has approximately 320 atoms in the unit cell and many fractionally occupied sites. Model variants were constructed systematically in a tiling-decoration approach and subjected to simulated annealing by use of both density functional theory and molecular dynamics with empirical potentials. To obtain a measure for thermodynamic stability, we reproduce the Al-Pd-Mn phase diagram at T = 0 K, and derive an enthalpy of formation for each structure. Our optimal structure resolves a cloud of fractionally occupied sites in pseudo-Mackay clusters. In particular, we demonstrate the presence of rotational degrees of freedom of an Al(9) inner shell, which is caged within two icosahedrally symmetric outer shells Al(30) and Pd(12). Outside these clusters, the chemical ordering on a chain of three nearby sites surprisingly breaks the inversion symmetry of the surrounding structure, and couples to an Al/vacancy site nearby. Our refined tiling-decoration model applies to any structure within the epsilon-phases family, including the metastable decagonal quasicrystalline phase.
Title:
Order in a spatially anisotropic triangular antiferromagnet
Authors:
Ghamari, S; Kallin, C; Lee, SS; Sorensen, ES Author Full Names: Ghamari, Sedigh; Kallin, Catherine; Lee, Sung-Sik; Sorensen, Erik S.
Source:
PHYSICAL REVIEW B 84 (17): 10.1103/PhysRevB.84.174415 NOV 14 2011
Abstract:
The phase diagram of the spin-1/2 Heisenberg antiferromagnet on an anisotropic triangular lattice of weakly coupled chains, a model relevant to Cs(2)CuCl(4), is investigated using a renormalization group analysis, which includes marginal couplings important for connecting to numerical studies of this model. In particular, the relative stability of incommensurate spiral spin-density order and collinear antiferromagnetic order is studied. While incommensurate spiral order is found to exist over most of the phase diagram in the presence of a Dzyaloshinskii-Moriya (DM) interaction, at small interchain and extremely weak DM couplings, collinear antiferromagnetic order can survive. Our results imply that Cs(2)CuCl(4) is well within the part of the phase diagram where spiral order is stable. The implications of the renormalization group analysis for numerical studies, many of which have found spin-liquidlike behavior, are discussed.
Title:
Mixed Acoustic Phonons and Phase Modes in an Aperiodic Composite Crystal
Authors:
Toudic, B; Lefort, R; Ecolivet, C; Guerin, L; Currat, R; Bourges, P; Breczewski, T Author Full Names: Toudic, B.; Lefort, R.; Ecolivet, C.; Guerin, L.; Currat, R.; Bourges, P.; Breczewski, T.
Source:
PHYSICAL REVIEW LETTERS 107 (20): 10.1103/PhysRevLett.107.205502 NOV 9 2011
Abstract:
Aperiodic crystals which are long range ordered materials present original dynamics features due to the lack of translational symmetry formally implying the nonvalidity of the Brillouin zone concept. This Letter reports the observation by neutron scattering of an overdamped acousticlike mode at a Bragg peak position in a n-alkane-urea inclusion crystal. This result implies the existence of a gap in the dispersion branch. The gap and anomalous damping of these collective modes are discussed in terms of specific dynamics and interaction in aperiodic materials.
Title:
Comment on "Origin of Friction Anisotropy on a Quasicrystal Surface" Reply
Authors:
Filippov, AE; Vanossi, A; Urbakh, M Author Full Names: Filippov, Aleksander E.; Vanossi, Andrea; Urbakh, Michael
Source:
PHYSICAL REVIEW LETTERS 107 (20): 10.1103/PhysRevLett.107.209402 NOV 8 2011
Title:
Comment on "Origin of Friction Anisotropy on a Quasicrystal Surface"
Authors:
McLaughlin, K; Rabson, D; Thiel, P Author Full Names: McLaughlin, K.; Rabson, D.; Thiel, P.
Source:
PHYSICAL REVIEW LETTERS 107 (20): 10.1103/PhysRevLett.107.209401 NOV 8 2011
Title:
Magnetic Structures of Pr(0.8)Lu(0.2)Mn(2)Ge(2) and Pr(0.6)Lu(0.4)Mn(2)Ge(2)
Authors:
Wang, JL; Studer, AJ; Campbell, SJ; Kennedy, SJ; Zeng, R; Dou, SX; Wu, GH Author Full Names: Wang, J. L.; Studer, A. J.; Campbell, S. J.; Kennedy, S. J.; Zeng, R.; Dou, S. X.; Wu, G. H.
Source:
IEEE TRANSACTIONS ON MAGNETICS 47 (10): 2893-2896 10.1109/TMAG.2011.2151180 OCT 2011
Abstract:
The magnetic structures of Pr(0.8)Lu(0.2)Mn(2)Ge(2) and Pr(0.6)Lu(0.4)Mn(2)Ge(2) have been determined by neutron powder diffraction over the temperature range 10-450 K. On cooling from the paramagnetic region the Mn sublattice of Pr(0.8)Lu(0.2)Mn(2)Ge(2) orders in a similar manner to PrMn(2)Ge(2) with first ab-plane intralayer antiferromagnetism (AFI) below T(N)(intra) similar to 397 K followed by canted ferromagnetism (Fmc) at T(C)(inter) similar to 330 K and then a conical (Fmi) spin structure below T(c/c) similar to 192 K. The transition at T(C)(Pr) = 35 K with related enhancement in magnetization, is assigned to the additional ferromagnetic contribution of the Pr sublattice leading to the combined (Fmc+F(Pr)). For Pr(0.6)Lu(0.4)Mn(2)Ge(2) the transition from PM to AFI occurs at T(N)(intra) similar to 375 K while the canted ferromagnetic (Fmc) state forms at T(C)(intra) similar to 321 K. The increased Lu concentration of Pr(0.6)Lu(0.4)Mn(2)Ge(2) destroys the incommensurate Fmi conical spin structure of Pr(0.8)Lu(0.4)Mn(2)Ge(2). Rather, in common with similar mixed RT(2)X(2) systems (e.g., La(1-x)Y(x)Mn(2)Si(2), La(1-x)Pr(x)Mn(2)Si(2)), the Pr(0.6)Lu(0.4)Mn(2)Ge(2) compound exhibits co-existence of the AFmc and Fmc phases on cooling from the pure Fmc state. Transformation to the combined ferromagnetic state (Fmc+F(Pr)) takes place on c-axis ordering of the Pr sublattice at T(C)(Pr) similar to 31 K. In the region of phase co-existence, the Fmc unit cell is larger than the AFmc unit cell indicating strong magneto-structural coupling with a change of the lattice inducing a change of the magnetic state.
Title:
Three-dimensional reconstruction of the atomic arrangement of icosahedral quasicrystals by binary discrete tomography
Authors:
Ishibashi, Y; Sugiura, H; Saitoh, K; Tanaka, N Author Full Names: Ishibashi, Y.; Sugiura, H.; Saitoh, K.; Tanaka, N.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2519-2527 SI 10.1080/14786435.2010.523717 2011
Abstract:
A three-dimensional reconstruction of the structure of icosahedral quasicrystals from high-resolution transmission electron microscope images observed along high-symmetry zone-axis projections is studied. As in discrete tomography, the quasicrystalline structure is treated as a discrete set of atoms arranged on the icosahedral lattice, including atom flip sites, which is a structural disorder originating from the degrees of freedom in the internal space. The occupancy of the atoms on each site of the lattice is determined using only the zone-axis projection images without any knowledge of the image intensity. Simulation studies using icosahedral model lattices composed of several thousands of atoms were carried out to test the present reconstruction method. In the case of the ideal icosahedral lattice, a reconstruction rate of 90% is achieved from 10 projection images and a reconstruction rate of 99% is achieved from 18 projections. The reconstruction rate degrades when the projection images are misaligned. Reconstruction of the three-dimensional distribution of the atom flips is discussed.

Update: 30-Nov-2011

Title:
Double-k phase of the Dzyaloshinskii-Moriya helimagnet Ba(2)CuGe(2)O(7)
Authors:
Muhlbauer, S; Gvasaliya, SN; Pomjakushina, E; Zheludev, A Author Full Names: Muehlbauer, S.; Gvasaliya, S. N.; Pomjakushina, E.; Zheludev, A.
Source:
PHYSICAL REVIEW B 84 (18): 10.1103/PhysRevB.84.180406 NOV 10 2011
Abstract:
Neutron diffraction is used to reinvestigate the magnetic phase diagram of the noncentrosymmetric tetragonal antiferromagnet Ba(2)CuGe(2)O(7). An incommensurate double-k magnetic phase is detected near the commensurate-incommensurate phase transition. This phase is stable only for field closely aligned with the fourfold symmetry axis. The results emphasize the inadequacy of existing theoretical models for this unique material, and points to additional terms in the Hamiltonian or lattice effects.
Title:
Conductivity of icosahedral AlPdRe
Authors:
Rapp, O; Poon, SJ Author Full Names: Rapp, O.; Poon, S. J.
Source:
PHYSICAL REVIEW B 84 (17): 10.1103/PhysRevB.84.174206 NOV 10 2011
Abstract:
The electrical conductivity sigma(T) of icosahedral (i) AlPdRe has been studied in order to address current problems and controversies. Two new approaches are presented. The temperature T(0) below which variable range hopping occurs was estimated directly from d sigma(T)/dT, avoiding the problem of the finite sigma(0) in i-AlPdRe. Secondly, sigma(T) is compared in detail for samples with radically different defects and morphologies. The temperature dependence of sigma(T) is found to be independent of these varying sample conditions. This finding rules out some proposed conduction mechanisms.
Title:
Symmetry and magnetic field driven transitions in the 2D triangular lattice compound RbFe(MoO(4))(2)
Authors:
Ribeiro, JL; Perez-Mato, JM Author Full Names: Ribeiro, J. L.; Perez-Mato, J. M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (44): 10.1088/0953-8984/23/44/446003 NOV 9 2011
Abstract:
The temperature versus magnetic field phase diagram of the 2D triangular lattice and multiferroic compound RbFe(MoO(4))(2) is analysed from the point of view of symmetry. The paramagnetic space group and its irreducible representations are used in order to obtain the magnetic symmetry of the possible modulated phases and characterize the restrictions imposed by this symmetry on the corresponding magnetic structures. Superspace symmetry is considered in the case of incommensurate phases. It is shown that the experimentally observed phases correspond to different isotropy subgroups originating in the same irreducible representation of the paramagnetic symmetry group. The relevant couplings between the primary transverse spin modulation and the electric polarization, the in-plane magnetization and the secondary longitudinal magnetic modulation are discussed. The mechanisms for the destabilization of the improper ferroelectric chiral phase and the origin of the different orienta! tion of the spins with respect to the external field in the two collinear phases are analysed from a symmetry based perspective.
Title:
Quasicrystals - Interfaces to Hyperspace
Authors:
Steurer, W Author Full Names: Steurer, Walter
Source:
NACHRICHTEN AUS DER CHEMIE 59 (11): 1035-1038 NOV 2011

Update: 23-Nov-2011

Title:
Microstructure development and properties of the AlCuFe quasicrystalline coating on near-alpha titanium alloy
Authors:
Moskalewicz, T; Kot, M; Wendler, B Author Full Names: Moskalewicz, T.; Kot, M.; Wendler, B.
Source:
APPLIED SURFACE SCIENCE 258 (2): 848-859 10.1016/j.apsusc.2011.09.013 NOV 1 2011
Abstract:
A protective quasicrystalline AlFeCu coating was deposited on TIMETAL 834 substrate by nonreactive magnetron sputtering in order to improve resistance of the alloy to oxidation. Microstructure characterisation of the substrate and the coating was performed by analytical scanning-and transmission electron microscopy as well as X-ray diffractometry. Depending on annealing temperature and time, the deposited coating (2.7 mu m thick) has a different microstructure. The coating in Specimen 1 (annealed 600 degrees C/4 h in vacuum) consisted of two zones: outer, composed of Al(5)Fe(2) and Al(2)Cu(3) phases and inner, in which only quasicrystalline psi phase was present. The coating in Specimen 2 (annealed 600 degrees C/4 h + 700 degrees C/2 h in vacuum) was fully quasicrystalline and consisted of icosahedral psi phase. Both coatings exhibit higher microhardness than the substrate material. It was established that the applied surface treatment essentially improves oxidation resistance of the alloy tested at 750 degrees C during 250 h in static air. Sample weight gain was 60% lower than in the case of uncoated sample. Oxide scale spallation occurred for uncoated alloy while the coated one did not show any spallation. It was found that the very brittle scale formed during oxidation on the uncoated alloy was consisting of TiO(2), while that on the coated one consisted mainly of alpha-Al(2)O(3). (C) 2011 Elsevier B. V. All rights reserved.
Title:
Lead adsorption on the Al(13)Co(4)(100) surface: heterogeneous nucleation and pseudomorphic growth
Authors:
Addou, R; Shukla, AK; Villaseca, SA; Gaudry, E; Deniozou, T; Heggen, M; Feuerbacher, M; Widmer, R; Groning, O; Fournee, V; Dubois, JM; Ledieu, J Author Full Names: Addou, R.; Shukla, A. K.; Villaseca, S. Alarcon; Gaudry, E.; Deniozou, Th; Heggen, M.; Feuerbacher, M.; Widmer, R.; Groening, O.; Fournee, V.; Dubois, J-M; Ledieu, J.
Source:
NEW JOURNAL OF PHYSICS 13 10.1088/1367-2630/13/10/103011 OCT 11 2011
Abstract:
We have investigated the adsorption of Pb atoms on the (100) surface of an orthorhombic Al(13)Co(4) crystal at 300 and 573K substrate temperatures. This complex metallic alloy is an approximant to the decagonal Al-Ni-Co quasicrystal. At submonolayer coverage and at 300 K, Pb adatoms remain highly mobile and adsorb preferentially within the hollow site situated in between adjacent Al pentagonal clusters present at the surface. These experimental findings are supported by ab initio calculations based on density functional theory (DFT). For both temperature regimes, Pb adsorption leads to the formation of pseudomorphic monolayers above which the high adsorbate mobility prohibits the growth of additional layers. For the high-temperature deposition, we propose a structural model for the Pb film and discuss its relationship with the underneath substrate.

Update: 16-Nov-2011

Title:
Magnetic and thermal properties of Er(75)Dy(25) single crystals
Authors:
Khan, M; Schlagel, DL; Lograsso, TA; Gschneidner, KA; Pecharsky, VK Author Full Names: Khan, Mahmud; Schlagel, D. L.; Lograsso, T. A.; Gschneidner, K. A., Jr.; Pecharsky, V. K.
Source:
PHYSICAL REVIEW B 84 (13): 10.1103/PhysRevB.84.134424 OCT 18 2011
Abstract:
We report on an experimental study of the thermal and magnetic properties of Er(75)Dy(25) single crystals with magnetic fields applied parallel to the [0001] and [10 (1) over bar0] directions. The [0001] direction is the easy axis of magnetization, while the [10 (1) over bar0] direction is the hard axis of magnetization. Three major transitions are observed in the heat capacity, magnetization, and alternating current magnetic susceptibility data. A first-order transition is observed at similar to 30 K, and two second-order transitions occur at similar to 45 and similar to 110 K. The H-T phase diagrams constructed from the experimental data reveal that several magnetic phases, including ferromagnetic cone, ferromagnetic fan, and c axis-modulated phases, exist in an Er(75)Dy(25) single crystal. Both similarities and dissimilarities are observed in the H-T phase diagrams of Er(75)Dy(25) when compared to the H-T phase diagrams of pure Er single crystals.

Update: 10-Nov-2011

Title:
Electrical transport and anomalous structural behavior of alpha-Eu(2) (MoO(4))(3) at high temperature
Authors:
Guzman-Afonso, C; Torres, ME; Gonzalez-Silgo, C; Sabalisck, N; Gonzalez-Platas, J; Matesanz, E; Mujica, A Author Full Names: Guzman-Afonso, C.; Torres, M. E.; Gonzalez-Silgo, C.; Sabalisck, N.; Gonzalez-Platas, J.; Matesanz, E.; Mujica, A.
Source:
SOLID STATE COMMUNICATIONS 151 (22): 1654-1658 10.1016/j.ssc.2011.08.009 NOV 2011
Abstract:
The study of XRD patterns of alpha-Eu(2)(MoO(4))(3) modulated scheelite reveals an anomalous behavior of its lattice parameter a in the range of temperatures from 473 to 973 K. We have analyzed the real part of the complex conductivity in the frequency range from 0.1 to 10,000 kHz and the temperature range from 550 to 900 K, and found that it follows a universal dielectric response. Detailed analysis of the temperature dependence of the adjusted parameters within this model shows that, in a temperature range, the dominant mechanism of electrical transport is due to the overlapping of large polarons. Rietveld refinements were performed using symmetry adapted modes at 523, 723 and 923 Kin order to study the thermal dependence of the distortion from the scheelite structure and to interpret the structural effects that favor the formation of polarons. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
New type of incommensurate magnetic ordering in Mn(3)TeO(6)
Authors:
Ivanov, SA; Nordblad, P; Mathieu, R; Tellgren, R; Ritter, C; Golubko, NV; Politova, ED; Weil, M Author Full Names: Ivanov, S. A.; Nordblad, P.; Mathieu, R.; Tellgren, R.; Ritter, C.; Golubko, N. V.; Politova, E. D.; Weil, M.
Source:
MATERIALS RESEARCH BULLETIN 46 (11): 1870-1877 10.1016/j.materresbull.2011.07.041 NOV 2011
Abstract:
The complex metal oxide Mn(3)TeO(6) exhibits a corundum related structure and has been prepared both in forms of single crystals by chemical transport reactions and of polycrystalline powders by a solid state reaction route. The crystal structure and magnetic properties have been investigated using a combination of X-ray and neutron powder diffraction, electron microscopy, calorimetric and magnetic measurements. At room temperature this compound adopts a trigonal structure, space group R (3) over bar with a = 8.8679(1) angstrom. c = 10.6727(2) angstrom. A long-range magnetically ordered state is identified below 23 K. An unexpected feature of this magnetic structure is several types of Mn-chains. Under the action of the incommensurate magnetic propagation vector k = [0, 0, 0.4302(1)] the unique Mn site is split into two magnetically different orbits. One orbit forms a perfect helix with the spiral axis along the c-axis while the other orbit has a sine wave character along the c-axis. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Structural stability and magnetic properties of Bi(1-x)La(Pr)(x)FeO(3) solid solutions
Authors:
Karpinsky, DV; Troyanchuk, IO; Mantytskaya, OS; Khomchenko, VA; Kholkin, AL Author Full Names: Karpinsky, D. V.; Troyanchuk, I. O.; Mantytskaya, O. S.; Khomchenko, V. A.; Kholkin, A. L.
Source:
SOLID STATE COMMUNICATIONS 151 (22): 1686-1689 10.1016/j.ssc.2011.08.002 NOV 2011
Abstract:
In this work, X-ray diffraction data taken on Bi(1-x)La(x)FeO(3) solid solutions are used to verify the following structural phase transitions: "polar rhombohedral-antipolar orthorhombic" at x approximate to 0.16 and "commensurate-incommensurate" within the orthorhombic phase at x approximate to 0.18. In contrast, in the Bi(1-x)Pr(x)FeO(3) series, the polar rhombohedral phase transforms into an antipolar orthorhombic one at x >= 0.13. The polar rhombohedral phase near the morphotropic phase boundary exhibits an isothermal transformation into an antipolar orthorhombic phase, though the transformation occurs much faster in the case of La-doped compounds. The incommensurate structural phase was not detected in Bi(1-x)Pr(x)FeO(3) solid solutions. The ternary structural phase diagram is constructed for (Bi, La, Pr)FeO(3) systems. In addition, the polar rhombohedral phase exhibits a magnetic field-induced transition from the modulated antiferromagnetic state into a homogeneous weak ferromagnetic state whereas the antipolar phase is a weak ferromagnetic state in the absence of an external field. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Seeing is Believing: Quasicrystals and the Demise of Perfect Order
Authors:
Balaram, P Author Full Names: Balaram, P.
Source:
CURRENT SCIENCE 101 (8): 981-982 OCT 25 2011
Title:
Electrical, magnetic, and thermal properties of the single-grain Ag(42)In(42)Yb(16) icosahedral quasicrystal: Experiment and modeling
Authors:
Bobnar, M; Vrtnik, S; Jaglicic, Z; Wencka, M; Cui, C; Tsai, AP; Dolinsek, J Author Full Names: Bobnar, M.; Vrtnik, S.; Jaglicic, Z.; Wencka, M.; Cui, Can; Tsai, An Pang; Dolinsek, J.
Source:
PHYSICAL REVIEW B 84 (13): 10.1103/PhysRevB.84.134205 OCT 17 2011
Abstract:
We have investigated the anisotropy of physical properties (themagnetic susceptibility, the electrical resistivity, the thermoelectric power, the Hall coefficient, and the thermal conductivity) of single-grain icosahedral i-Ag(42)In(42)Yb(16) quasicrystal along the two-, three-, and fivefold symmetry directions of the crystallographic structure. The specific heat, being a scalar quantity, was determined as well. The symmetry analysis predicts that the tensorial physical properties reduce to scalars for the ideal icosahedral symmetry. The experiments have shown that the anisotropy of the electronic transport coefficients of i-Ag(42)In(42)Yb(16) is either small enough to be considered within the range of the experimental uncertainty (the electrical resistivity and the thermal conductivity) or negligible (the Seebeck and the Hall coefficients). The anisotropy of the magnetization and magnetic susceptibility was also found small, originating from different Yb(3+) magnetic fractions (of the order 10(-3) of all Yb atoms) determined along the three symmetry directions. Our experimental results support the consideration that perfect icosahedral quasicrystals should be isotropic solids regarding their physical properties, unlike decagonal quasicrystals that are strongly anisotropic. Theoretical reproduction of the temperature-dependent electron transport coefficients of i-Ag(42)In(42)Yb(16) by a spectral conductivity model was another aim of this paper.
Title:
Structural evolution of one-dimensional spin-ladder compounds Sr(14-x)Ca(x)Cu(24)O(41) with Ca doping and related evidence of hole redistribution
Authors:
Deng, GC; Pomjakushin, V; Petricek, V; Pomjakushina, E; Kenzelmann, M; Conder, K Author Full Names: Deng, Guochu; Pomjakushin, Vladimir; Petricek, Vaclev; Pomjakushina, Ekaterina; Kenzelmann, Michel; Conder, Kazimierz
Source:
PHYSICAL REVIEW B 84 (14): 10.1103/PhysRevB.84.144111 OCT 17 2011
Abstract:
Incommensurate crystal structures of spin-ladder series Sr(14-x)Ca(x)Cu(24)O(41) (x = 3, 7, 11, and 12.2) were characterized by powder neutron scattering method and refined using the superspace group Xmmm(00 gamma)ss0 [ equivalent to superspace group Fmmm(0, 0, 1 + gamma)ss0; X stands for nonstandard centering (0, 0, 0, 0), (0, 1/2, 1/2, 1/2), (1/2, 1/2, 0, 0), (1/2, 0, 1/2, 1/2)] with a modulated structure model. The Ca doping effects on the lattice parameters, atomic displacement, Cu-O distances, Cu-O bond angles, and Cu bond valence sum were characterized. The refined results show that the CuO(4) planar units in both chain and ladder sublattices become closer to square shape with an increase of Ca doping. The Cu bond valence sum calculation provided new evidence for the charge transfer from the chains to ladders (approximately 0.16 holes per Cu from x = 0 to 12.2). The charge transfer was attributed to two different mechanisms: (a) the Cu-O bond distance shrinkage on the ladder and (b) increase of the interaction between two sublattices, resulting in Cu-O bonding between the chains and ladders. The low-temperature structural refinement resulted in the similar conclusion with a slight charge backflow to the chains.
Title:
Germanium Selenophosphates: The Incommensurately Modulated 1/infinity[Ge(4-x)P(x)Se(12)(4-)] and the Molecular [Ge(2)P(2)Se(14)](6-)
Authors:
Morris, CD; Malliakas, CD; Kanatzidis, MG Author Full Names: Morris, Collin D.; Malliakas, Christos D.; Kanatzidis, Mercouri G.
Source:
INORGANIC CHEMISTRY 50 (20): 10241-10248 10.1021/ic201249w OCT 17 2011
Abstract:
The new germanium selenophosphates K(4)Ge(4-x)P(x)Se(12) (1) and Rb(6)Ge(2)P(2)Se(14) (2) are reported. The former is a one-dimensional metastable compound synthesized using the polychalcogenide flux method that crystallizes in the monoclinic space group P2(1)/c with lattice parameters a = 6.7388(7) angstrom, b = 13.489(1) angstrom, c = 6.3904(6) angstrom, and beta = 91.025(8)degrees. At a glance, a mixed Ge(4+)/P(5+) tetrahedral site and disordered Se position are found among the corner sharing tetrahedra that make up the polymeric anion. After careful examination, the structure was found to be incommensurately modulated and a single q-vector of q = 0.4442(6)a* + 0.3407(6)c* was determined after annealing single crystals below their decomposition point for 30d. The latter compound contains the new discrete molecular anion [Ge(2)P(2)Se(14)](6-) and crystallizes in P (1) over bar with lattice parameters a = 7.2463(8) angstrom, b = 9.707(1)angstrom, c = 11.987(1)angstrom, alpha = 79.516(9)degrees, beta = 89.524(9)degrees, and gamma = 68.281(9)degrees. Both compounds are semiconductors with band gaps of 1 and 2 being 1.9 eV and 2.2 eV, respectively.
Title:
XRD and HREM studies from the decomposition of icosahedral AlCuFe single-phase by high-energy ball milling
Authors:
Patino-Carachure, C; Tellez-Vazquez, O; Rosas, G Author Full Names: Patino-Carachure, C.; Tellez-Vazquez, O.; Rosas, G.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (41): 10036-10039 10.1016/j.jallcom.2011.08.026 OCT 13 2011
Abstract:
In this investigation the Al(64)Cu(24)Fe(12) alloy was melted in an induction furnace and solidified under normal casting conditions. In order to obtain the icosahedral phase (i-phase) in a single-phase region, the as-cast sample was subject to a heat treatment at 700 degrees C under argon atmosphere. Subsequently, the i-phase was milled for different times in order to evaluate phase stability under heavy deformation. X-ray diffraction (XRD) and high-resolution electron microscopy (HREM) analysis were conducted to the structural characterization of ball-milled powders. XRD results indicated a reduction in quasicrystal size during mechanical ball milling to about 30 h. HREM analysis revealed the presence of aperiodic nanodomains, for example, with apparent fivefold symmetry axis. Therefore, the i-phase remains stable over the first 30 h of ball-milling time. However, among 30-50 h of mechanical milling the i-phase transforms progressively into beta-cubic phase. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Vacancies and atomic processes in intermetallics - From crystals to quasicrystals and bulk metallic glasses
Authors:
Schaefer, HE; Baier, F; Muller, MA; Reichle, KJ; Reimann, K; Rempel, AA; Sato, K; Ye, F; Zhang, XY; Sprengel, W Author Full Names: Schaefer, Hans-Eckhardt; Baier, Falko; Mueller, Markus A.; Reichle, Klaus J.; Reimann, Klaus; Rempel, Andrey A.; Sato, Kiminori; Ye, Feng; Zhang, Xiangyi; Sprengel, Wolfgang
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 248 (10): 2290-2299 10.1002/pssb.201147103 OCT 2011
Abstract:
A review is given on atomic vacancies in intermetallic compounds. The intermetallic compounds cover crystalline, quasicrystalline, and bulk metallic glass (BMG) structures. Vacancies can be specifically characterized by their positron lifetimes, by the coincident measurement of the Doppler broadening of the two quanta emitted by positron-electron annihilation, or by time-differential dilatometry. By these techniques, high concentrations and low mobilities of thermal vacancies were found in open-structured B2 intermetallics such as FeAl or NiAl, whereas the concentrations of vacancies are low and their mobilities high in close-packed structure as, e.g., L1(2)-Ni(3)Al. The activation volumes of vacancy formation and migration are determined by high-pressure experiments. The favorable sublattice for vacancy formation is found to be the majority sublattice in Fe(61)Al(39) and in MoSi(2). In the icosahedral quasicrystal Al(70)Pd(21)Mn(9) the thermal vacancy concentration is low, whereas in the BMG Zr(57)Cu(15.4)Ni(12).(6)Nb(3)Al(10) thermal vacancies are found in high concentrations with low mobilities. This may determine the basic mechanisms of the glass transition. Making use of the experimentally determined vacancy data, the main features of atomic diffusion studies in crystalline intermetallics, in quasicrystals, and in BMGs can be understood. Manfred Fahnle and his group have substantially contributed to the theoretical understanding of vacancies and diffusion mechanisms in intermetallics. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Title:
Grain size effect on the phase transformations of higher manganese silicide thermoelectric materials: An in situ energy dispersive x-ray diffraction study
Authors:
Zhou, AJ; Zhu, TJ; Zhao, XB; Mueller, E Author Full Names: Zhou, Aijun; Zhu, Tiejun; Zhao, Xinbing; Mueller, Eckhard
Source:
JOURNAL OF MATERIALS RESEARCH 26 (15): 1900-1906 10.1557/jmr.2011.80 AUG 2011
Abstract:
Phase structures of microscale and nanoscale higher manganese silicides (HMSs) were investigated using in situ energy dispersive x-ray diffraction at high temperatures or/and high pressure. A few phase transformations accompanied with the presence of MnSi phase were observed in different temperature regions, which were associated with the interevolution of several incommensurate HMS phases. It was found that in nanostructured HMS, the interevolution of HMS was remarkable and accelerated compared to that in the micropowders. Meanwhile, high pressure was able to influence these phase transformations due to giant strain in the materials. The phase transformations were discussed from thermodynamic aspects with respect to the different formation enthalpy of Mn-Si system and the large surface energy and structural instability of the nanopowders.
Title:
Surprising luminescent properties of the polyphosphates Ln(PO(3))(3): Eu (Ln = Y, Gd, Lu)
Authors:
Hoppe, HA; Kazmierczak, K; Kacprzak, S; Schellenberg, I; Pottgen, R Author Full Names: Hoeppe, Henning A.; Kazmierczak, Karolina; Kacprzak, Sylwia; Schellenberg, Inga; Poettgen, Rainer
Source:
DALTON TRANSACTIONS 40 (39): 9971-9976 10.1039/c1dt10043b 2011
Abstract:
The optical emission properties of the lanthanoid catena-polyphosphates Ln(PO(3))(3) (Ln = Y, Gd, Lu) doped with europium were investigated. Incommensurately modulated b-Y(PO(3))(3) : Eu (super space group Cc (0 vertical bar 0.364 vertical bar 0)0) and Gd(PO(3))(3) : Eu (space group I2/a) show the usual emission characteristics of Eu(3+), while in Lu(PO(3))(3) : Eu (space group Cc) the europium is unprecedentedly partially reduced to the divalent state, as proven by both a broad emission band at 406 nm excited at 279 nm and an EPR spectroscopic investigation. (151)Eu-Mossbauer spectroscopy showed that only a very small part of the europium is reduced in Lu(PO(3))(3) : Eu. An explanation for this unusual behaviour is given.

Update: 3-Nov-2011

Title:
Coexistence of superconductivity and incommensurate magnetic order
Authors:
Ptok, A; Maska, MM; Mierzejewski, M Author Full Names: Ptok, Andrzej; Maska, Maciej M.; Mierzejewski, Marcin
Source:
PHYSICAL REVIEW B 84 (9): 10.1103/PhysRevB.84.094526 SEP 26 2011
Abstract:
The influence of incommensurate spin-density waves (SDW) on superconductivity in unconventional superconductors is studied by means of the Bogolubov-de Gennes (BdG) equations. Exploiting translational symmetries of a magnetically ordered two-dimensional system, we propose an approach that allows to solve the BdG equations on much larger clusters than it is usually possible for inhomogeneous systems. Applying this approach, we demonstrate that the presence of incommensurate spin-density waves induces real-space inhomogeneity of the superconducting order parameter even in the absence of external magnetic field. In this case, a homogeneous order parameter of the Bardeen-Cooper-Schrieffer-type superconducting state is slightly modulated, or equivalently, a small fraction of the charge carriers form Cooper pairs with nonzero total momentum. However, when a sufficiently strong magnetic field is applied, the homogeneous component of the order parameter is suppressed and the system transits to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, where the order parameter oscillates changing sign. We show that for s-wave pairing, the presence of external magnetic field diminishes the destructive influence of the SDW order on superconductivity. A simple explanation of this effect is also proposed.
Title:
Spontaneous phase transitions in magnetic films with a modulated structure
Authors:
Arzamastseva, GV; Evtikhov, MG; Lisovskii, FV; Mansvetova, EG Author Full Names: Arzamastseva, G. V.; Evtikhov, M. G.; Lisovskii, F. V.; Mansvetova, E. G.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS 113 (3): 450-458 10.1134/S1063776111080024 SEP 2011
Abstract:
The influence of monoperiodic and biperiodic bias fields on the nucleation of domain structures in quasi-uniaxial magnetic films near the Curie point has been studied experimentally. The main types of observed nonuniform magnetic moment distributions have been established and chains of a devil's staircase phase transitions are shown to be realized when the films are slowly cooled.
Title:
Electrochemical properties of Ti(45)Zr(38-x)Ni(17+x) (0 <= x <= 8) quasicrystals produced by rapid-quenching
Authors:
Takasaki, A; Kuroda, C; Lee, SH; Kim, JY Author Full Names: Takasaki, Akito; Kuroda, Chihiro; Lee, Sang-Hwa; Kim, Jae-Yong
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 S782-S785 2 10.1016/j.jallcom.2010.11.042 SEP 2011
Abstract:
Discharge performances of Ti(45)Zr(38-x)Ni(17+x) (0 <= x <= 8) ribbons produced by rapid-quenching were measured by a three-electrode cell at room temperature, and the effect of substitution of Ni for Zr was investigated. All the ribbons after rapid-quenching were mostly the icosahedral (i) quasicrystal phase with a negligible amount of C14 Laves phase (hcp). The discharge capacity increased with increasing amount of Ni substituted for Zr. The maximum discharge capacity achieved was about 90 mAh/g from (Ti(45)Zr(30)Ni(25)) ribbon after substitution of Ni for Zr. The discharge performance was almost stable against the charge/discharge cycle (until 15 cycles) for all the ribbons, and the i-phase structure was also stable even after the 15th charge/discharge cycle. No metal hydride formation was observed. (C) 2010 Elsevier B.V. All rights reserved.

Update: 27-Oct-2011

Title:
Low-temperature evolution of the modulated magnetic structure in the ferroelectric antiferromagnet BiFeO(3)
Authors:
Sosnowska, I; Przenioslo, R Author Full Names: Sosnowska, I.; Przenioslo, R.
Source:
PHYSICAL REVIEW B 84 (14): 10.1103/PhysRevB.84.144404 OCT 3 2011
Abstract:
High-resolution time-of-flight neutron diffraction studies of the magnetic ordering in the multiferroic BiFeO(3) are presented. Our results show that the cycloidal modulated ordering proposed earlier [I. Sosnowska, T. Peterlin-Neumaier, and E. Steichele, J. Phys. C 15, 4835 (1982)] is stable between 10 and 295 K. The concept of the anharmonic character of the magnetic modulation in BiFeO(3) that was used for the interpretation of NMR, Raman, and THz spectroscopy studies of BiFeO(3) is discussed. The influence of the anharmonic modulation on the magnetic contributions to the BiFeO(3) neutron diffraction patterns is presented. Our experimental data can be described by assuming anharmonic effects with m < 0.25. We propose a method for the anharmonicity strength evaluation based on neutron diffraction data.
Title:
Five-Dimensional Incommensurate Structure of the Melilite Electrolyte [CaNd](2)[Ga](2)[Ga(2)O(7)](2)
Authors:
Wei, FX; Baikie, T; An, T; Schreyer, M; Kloc, C; White, TJ Author Full Names: Wei, Fengxia; Baikie, Tom; An, Tao; Schreyer, Martin; Kloc, Christian; White, Tim J.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 133 (38): 15200-15211 10.1021/ja206441x SEP 28 2011
Abstract:
Melilite-type gallium oxides are potential intermediate temperature electrolytes for solid oxide fuel cells. Single crystals of [CaNd](2)[Ga](2)[Ga(2)O(7)](2) grown using an optical floating zone furnace have been investigated using transmission electron microscopy and powder and single-crystal X-ray diffraction. The anion array topologically conforms to a [(3.5.4.5)(2), 3.5.3.5] network that contains distorted pentagonal tunnels. The distortion is necessary to achieve space filling and accommodate structural misfit between the layers. Satisfactory bond lengths and angles are obtained through two-dimensional modulation in the tetragonal based plane, leading to five-dimensional symmetry in the superspace group P (4) over bar2(1)m(alpha,alpha,0)00s((a) over bar ,a,0)000, alpha = 0.2319(2), with modulation vectors q(1) = alpha(a* + b*) and q(2) = alpha(-a* + b*). Both displacive and occupational modulations are found. Through this mechanism, melilites are primed to accommodate mobile oxygen interstitials, suggesting a rational approach to crystallochemical tailoring that will enhance ionic diffusion and optimize electrolyte performance.

Update: 20-Oct-2011

Title:
Damping properties in Mg-Zn-Y alloy with dispersion of quasicrystal phase particle
Authors:
Somekawa, H; Watanabe, H; Mukai, T Author Full Names: Somekawa, Hidetoshi; Watanabe, Hiroyuki; Mukai, Toshiji
Source:
MATERIALS LETTERS 65 (21-22): 3251-3253 10.1016/j.matlet.2011.07.001 NOV 2011
Abstract:
The effect of the interface structure between the matrix and the particle on the damping capacity was investigated using Mg-Zn and Mg-Zn-Y alloys in this study. The damping capacity was not affected by the interface structure at room temperature. However, the onset of temperature, which was higher in the Mg-Zn-Y alloy than in the Mg-Zn alloy despite their similar grain sizes, increased the damping capacity through grain boundary relaxation by grain boundary sliding. Compared to the Mg-Zn alloy, the existence of the quasicrystal phase particles, which had the coherent interface with low interface energy, was likely to have suppressed and delayed the grain boundary sliding in the Mg-Zn alloy. (C) 2011 Elsevier By. All rights reserved.
Title:
Ti-Doping to Reduce Conductivity in Bi(0.85)Nd(0.15)FeO(3) Ceramics
Authors:
Kalantari, K; Sterianou, I; Karimi, S; Ferrarelli, MC; Miao, S; Sinclair, DC; Reaney, IM Author Full Names: Kalantari, Kambiz; Sterianou, Iasmi; Karimi, Sarah; Ferrarelli, Matthew C.; Miao, Shu; Sinclair, Derek C.; Reaney, Ian M.
Source:
ADVANCED FUNCTIONAL MATERIALS 21 (19): 3737-3743 10.1002/adfm.201100191 OCT 7 2011
Abstract:
In 2009, Karimi et al. reported that Bi(1-x)Nd(x)FeO(3) 0.15 <= x <= 0.25 exhibited a PbZrO(3) (PZ)-like structure. These authors presented some preliminary electrical data for the PZ-like composition but noted that the conductivity was too high to obtain radio-frequency measurements representative of the intrinsic properties. In this study, Bi(0.85)Nd(0.15)Fe(1-y)Ti(y)O(3) (0 <= y <= 0.1) were investigated, in which Ti acted as a donor dopant on the B-site. In contrast to the original study of Karimi et al., X-ray diffraction (XRD) of Bi(0.85)Nd(0.15)FeO(3) revealed peaks which were attributed to a mixture of PZ-like and rhombohedral structures. However, as the Ti (0 < y <= 0.05) concentration increased, the rhombohedral peaks disappeared and all intensities were attributed to the PZ-like phase. For y = 0.1, broad XRD peaks indicated a significant decrease in effective diffracting volume. Electron diffraction confirmed that the PZ-like phase was dominant for y <= 0.05, but for y = 0.1, an incommensurate structure was present, consistent with the broadened XRD peaks. The substitution of Fe(3+) by Ti(4+) decreased the dielectric loss at room temperature from >0.3 to <0.04 for all doped compositions, with a minimum (0.015) observed for y = 0.03. The decrease in dielectric loss was accompanied by a decrease in the room temperature bulk conductivity from similar to 1 mS cm(-1) to < 1 mu S cm(-1) and an increase in bulk activation energy from 0.29 to >1 eV. Plots of permittivity (epsilon(r)) versus temperature for 0.01 <= y <= 0.05 revealed a step rather than a peak in epsilon(r) on heating at the same temperature determined for the antiferroelectric-paraelectric phase transition by differential scanning calorimetry. Finally, large electric fields were applied to all doped samples which resulted in a linear dependence of polarisation on the electric field similar to that obtained for PbZrO(3) ceramics under equivalent experimental conditions.
Title:
Detailed structure of the low-energy magnetic dispersion of the diagonal incommensurate phase in La(1.975)Sr(0.025)CuO(4)
Authors:
Matsuda, M; Fernandez-Baca, JA; Fujita, M; Yamada, K; Tranquada, JM Author Full Names: Matsuda, M.; Fernandez-Baca, J. A.; Fujita, M.; Yamada, K.; Tranquada, J. M.
Source:
PHYSICAL REVIEW B 84 (10): 10.1103/PhysRevB.84.104524 SEP 30 2011
Abstract:
Inelastic neutron scattering experiments have been performed on lightly doped La(1.975)Sr(0.025)CuO(4), which contains a hole concentration slightly higher than the critical concentration for three-dimensional long-range antiferromagnetic order. We previously found that the magnetic excitation spectrum in the insulating phase with a diagonal incommensurate spin modulation has similarities to that in the superconducting regime, where the spin modulation is bond parallel. In this study, we investigate the excitations in detail around Ecross, at which the excitations become most nearly commensurate. It is found that both the magnitude and the anisotropy of the momentum width of the excitations change abruptly at Ecross. Our experimental results suggest that the magnetic excitations rising from the pair of (diagonally) incommensurate wave vectors merge at Ecross into isotropic excitations.
Title:
Magnetic excitations in the geometric frustrated multiferroic CuCrO(2)
Authors:
Frontzek, M; Haraldsen, JT; Podlesnyak, A; Matsuda, M; Christianson, AD; Fishman, RS; Sefat, AS; Qiu, Y; Copley, JRD; Barilo, S; Shiryaev, SV; Ehlers, G Author Full Names: Frontzek, M.; Haraldsen, J. T.; Podlesnyak, A.; Matsuda, M.; Christianson, A. D.; Fishman, R. S.; Sefat, A. S.; Qiu, Y.; Copley, J. R. D.; Barilo, S.; Shiryaev, S. V.; Ehlers, G.
Source:
PHYSICAL REVIEW B 84 (9): 10.1103/PhysRevB.84.094448 SEP 28 2011
Abstract:
In this paper detailed neutron scattering measurements of the magnetic excitation spectrum of CuCrO(2) in the ordered state below T(N1) = 24.2 K are presented. The spectra are analyzed using a model Hamiltonian which includes intralayer exchange up to the next-next-nearest neighbor and interlayer exchange. We obtain a definite parameter set and show that exchange interaction terms beyond the next-nearest neighbor are important to describe the inelastic excitation spectrum. The magnetic ground state structure generated with our parameter set is in agreement with the structure proposed for CuCrO(2) from the results of single crystal diffraction experiments previously published. We argue that the role of the interlayer exchange is crucial to understand the incommensurability of the magnetic structure as well as the spin-charge coupling mechanism.
Title:
Effects of chemical doping and pressure on CaFe(4)As(3)
Authors:
Zhao, LL; Kim, SK; McCandless, GT; Torikachvili, MS; Canfield, PC; Chan, JY; Morosan, E Author Full Names: Zhao, Liang L.; Kim, S. K.; McCandless, Gregory T.; Torikachvili, Milton S.; Canfield, P. C.; Chan, Julia Y.; Morosan, E.
Source:
PHYSICAL REVIEW B 84 (10): 10.1103/PhysRevB.84.104444 SEP 28 2011
Abstract:
The effects of chemical doping by P, Yb, Co, and Cu, and hydrostatic pressure on CaFe(4)As(3), were studied on single-crystalline samples. While the former two dopants substitute the nonmagnetic ions, the latter two partially occupy the Fe sites within the magnetic sublattice. The incommensurate spin density wave (IC-SDW) ordering at T(N) similar to 88 K in CaFe(4)As(3) changes only by up to similar to 40% with doping and applied pressure. Thus the IC-SDW state appears more robust than in the layered Fe pnictides. The commensurate SDW (C-SDW) state below T(2) similar to 26 K is suppressed in the Co-doped series, while it moves up in temperature in the P-, Yb-, and Cu-doped compounds. A new magnetic phase transition is observed at an intermediate temperature T(3) in Ca(Fe(1-x)Co(x))(4)As(3). Resistivity and magnetization measurements on CaFe(4)As(3) were performed under hydrostatic pressure up to 5 GPa, showing a systematic decrease of T(N) and a domelike phase boundary at T(2) up to p(c) similar to 2.10 GPa. At higher pressures, a possible structural phase transition occurs, marked by a slowly increasing transition temperature. A phase diagram is shown to compare the effects of chemical doping and pressure.
Title:
Ordering and growth of Xe films on the 10-fold quasicrystalline approximant Al(13)Co(4)(100) surface
Authors:
Shin, H; Karimi, M; Setyawan, W; Curtarolo, S; Diehl, RD Author Full Names: Shin, Heekeun; Karimi, M.; Setyawan, W.; Curtarolo, S.; Diehl, R. D.
Source:
PHYSICAL REVIEW B 84 (11): 10.1103/PhysRevB.84.115454 SEP 27 2011
Abstract:
Xe adsorption on the (100) surface of the complex alloy Al(13)Co(4) has been carried out using low-energy electron diffraction (LEED) and grand canonical Monte Carlo (GCMC) simulations. This surface is an approximant to the 10-fold surface of decagonal Al-Ni-Co, on which Xe adsorption has been studied previously. The adsorption behavior on the periodic surface is largely similar to that on the quasicrystal (layer-by-layer growth, hexagonal ordering near the onset of the second-layer adsorption), but it also has some differences, such as the complete lack of registry of the Xe layer with the substrate structure in the hexagonal phase, and a high sensitivity of the Xe epitaxial direction to trace impurities. In the simulations, an ordering transition was observed between the low-density and high-density monolayer regimes that involves a uniaxial compression of the monolayer film.

Update: 13-Oct-2011

Title:
Quinary icosahedral quasicrystalline Ti-V-Ni-Mn-Cr alloy: A novel anode material for Ni-MH rechargeable batteries
Authors:
Hu, W; Wang, LD; Wang, LM Author Full Names: Hu, Wen; Wang, Lidong; Wang, Limin
Source:
MATERIALS LETTERS 65 (19-20): 2868-2871 10.1016/j.matlet.2011.06.059 OCT 2011
Abstract:
The substitution of manganese and chromium for 6 at.% nickel in Ti(1.6)V(0.4)Ni leads the rapid quenching synthesis of quinary icosahedral phase (i-phase) evidenced by the observations of 2-. 3- and 5-fold symmetries. As negative electrode in Ni-MH battery, the quinary Ti-V-Ni-Mn-Cr i-phase can deliver a maximum discharge capacity of 278 mAh g(-1) at 30 mA g(-1) larger than that of Ti(1.6)V(0.4)Ni master alloy anode owing to Mn and/or Cr doping. After a preliminary test of 30 consecutive cycles the cycling capacity retention rate (CR%) is 80%. The strong chemisorption of hydrogen shown in cyclic voltammetric (CV) response indicates that the electrocatalytic activity improvement for the i-phase negative electrode is highly demanded. (C) 2011 Elsevier B.V. All rights reserved.

Update: 6-Oct-2011

Title:
Modulated superconductivity due to vacancy and magnetic order in A(y)Fe(2-x/2)Se(2) [A = Cs, K, (Tl,Rb), (Tl,K)] iron-selenide superconductors
Authors:
Das, T; Balatsky, AV Author Full Names: Das, Tanmoy; Balatsky, A. V.
Source:
PHYSICAL REVIEW B 84 (11): 10.1103/PhysRevB.84.115117 SEP 19 2011
Abstract:
We present a calculation of a "modulated" superconducting state in iron-selenide superconductors. The zero-momentum d-wave pairing breaks the translational symmetry of the conventional BaFe(2)Se(2)-like crystal of the I4/mmm space group. This pairing state becomes compatible when the Fe vacancies form an ordered state and the crystal symmetry changes to a low-temperature I4/m one. For the specific case of an incommensurate vacancy order at Q(v) = (1/5, 3/5) in K(0.82(2))Fe(1.626(3))Se(2), we find that it induces a block checkerboard antiferromagnetic phase at wave vector Q(m) = 4Q(v). The coexistence of vacancy order and magnetic order leads to a reconstructed ground state which naturally couples to the d-wave superconductivity in a uniform phase in what we propose will be a general coupling for all iron-selenide superconductors. Our results agree with numerous experimental data available to date. We thus suggest that the incommensurability leads to a uniform coexistence of multiple phases as a viable alternative to a nanoscale phase separation in high-T(c) superconductors and play an important role in the enhancement of superconductivity.
Title:
Disordered polyhalide anion effect on the Fermi surface of the incommensurate organic superconductor (MDT-TSF)I(0.77)Br(0.52)
Authors:
Kawamoto, T; Mori, T; Enomoto, K; Konoike, T; Terashima, T; Uji, S; Kitagawa, H; Takimiya, K; Otsubo, T Author Full Names: Kawamoto, Tadashi; Mori, Takehiko; Enomoto, Kengo; Konoike, Takako; Terashima, Taichi; Uji, Shinya; Kitagawa, Hiroshi; Takimiya, Kazuo; Otsubo, Tetsuo
Source:
PHYSICAL REVIEW B 84 (9): 10.1103/PhysRevB.84.094518 SEP 19 2011
Abstract:
The effect of disorder in polyhalide anions is investigated in terms of the degree of charge transfer and the Fermi surface in the incommensurate organic superconductor (MDT-TSF)I(0.77)Br(0.52), where MDT-TSF is methylenedithio-tetraselenafulvalene. The Raman spectra suggest that the infinite polyhalide chains include the asymmetric trihalide anion I(2)Br(-) and that the degree of charge transfer from the donor molecule to the anion is 0.429, estimated from the lattice constants. The Shubnikov-de Haas (SdH) oscillation is in good agreement with this charge transfer degree. The beating behavior of the SdH oscillation gives a large interlayer transfer integral, which is consistent with a corrugated conducting sheet structure. The randomness of the disordered anions reduces the periodicity of the incommensurate anion potential; this destroys the Fermi surface reconstruction by the incommensurate anion potential. The factor dominating the superconducting transition temperature is not the randomness of the polyhalide anions but the effective cyclotron mass enhancement, i.e., the many-body effect.
Title:
Persistent multiferroicity without magnetoelectric effects in CuO
Authors:
Wang, F; Zou, T; Liu, Y; Yan, LQ; Sun, Y Author Full Names: Wang, Fen; Zou, Tao; Liu, Yi; Yan, Li-Qin; Sun, Young
Source:
JOURNAL OF APPLIED PHYSICS 110 (5): 10.1063/1.3636106 SEP 1 2011
Abstract:
Multiferroicity and magnetoelectric effects in CuO have been investigated by measurements of magnetization, dielectric constant, and electric polarization with and without magnetic fields. Dielectric anomalies which indicate ferroelectric transitions were observed at two magnetic transition temperatures. Ferroelectric polarization was well detected in the incommensurate spiral phase. However, both dielectric constant and polarization have little changes in a 7 T magnetic field. Our study suggests that although with a high multiferroic temperature, the spiral spin structure in CuO is very stable and the induced ferroelectricity sustains even in a high magnetic field, which results in little magnetoelectric effects. (C) 2011 American Institute of Physics. [doi:10.1063/1.3636106]

Update: 28-Sep-2011

Title:
Metamagnetism and soliton excitations in the modulated ferromagnetic Ising chain CoV(2)O(6)
Authors:
Kimber, SAJ; Mutka, H; Chatterji, T; Hofmann, T; Henry, PF; Bordallo, HN; Argyriou, DN; Attfield, JP Author Full Names: Kimber, Simon A. J.; Mutka, Hannu; Chatterji, Tapan; Hofmann, Tommy; Henry, Paul F.; Bordallo, Heloisa N.; Argyriou, Dimitri N.; Attfield, J. Paul
Source:
PHYSICAL REVIEW B 84 (10): 10.1103/PhysRevB.84.104425 SEP 15 2011
Abstract:
We report a combination of physical property and neutron scattering measurements for polycrystalline samples of the one-dimensional spin-chain compound CoV(2)O(6). Heat capacity measurements show that an effective S = 1/2 state is found at low temperatures and that magnetic fluctuations persist up to similar to 6T(N). Above T(N) = 6.3 K, measurements of the magnetic susceptibility as a function of T and H show that the nearest-neighbor exchange is ferromagnetic. In the ordered state, we have discovered a crossover from a metamagnet with strong fluctuations between 5 K and T(N) to a state with a 1/3 magnetization plateau at 2 < T < 5 K. We use neutron powder diffraction measurements to show that the antiferromagnetic state has incommensurate long-range order and inelastic time-of-flight neutron scattering to examine the magnetic fluctuations as a function of temperature. Above T(N), we find two broad bands between 3.5 and 5 meV and thermally activated low-energy features which correspond to transitions within these bands. These features show that the excitations are deconfined solitons rather than the static spin reversals predicted for a uniform ferromagnetic Ising spin chain. Below T(N), we find a ladder of states due to the confining effect of the internal field. A region of weak confinement below T(N), but above 5 K, is identified which may correspond to a crossover between two- and three-dimensional magnetic ordering.
Title:
Effect of dimension on charge order domain in Ruddlesden-Popper manganites
Authors:
Nagao, M; Nagai, T; Hara, T; Kimoto, K Author Full Names: Nagao, M.; Nagai, T.; Hara, T.; Kimoto, K.
Source:
PHYSICA B-CONDENSED MATTER 406 (17): 3192-3195 10.1016/j.physb.2011.05.024 SEP 1 2011
Abstract:
The charge order (CO) domains of dimensionally controlled manganites Pr(1-x)Ca(x)MnO(3) and Pr(1-x)Ca(1+x) MnO(4) (x=0.5, 0.6 and 0.67), which have three-dimensional (3D) and two-dimensional (2D) Mn-O networks, respectively, have been studied by transmission electron microscopy (TEM). Although the electron diffraction data show similar dependences of the modulation wave vector on hole doping x, there are distinctive differences between the 3D and 2D systems in terms of the CO domain sizes. In the 2D system, the TEM images show that the domain size is almost constant irrespective of hole doping x. On the other hand, in the 3D system, the domain size of the incommensurate CO for x=0.6 is much smaller than those of the commensurate CO for x=0.5 and 0.67. Namely, in the 3D system, the CO states are strongly influenced by the incommensurability for the parent lattice. This difference indicates that the dimension of the Mn-O network plays a crucial role in the CO domain and suggests that the electron-lattice coupling of the 3D system is stronger than that of the 2D system. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Effect of chemical composition on the microstructure and hardness of Al-Cu-Fe alloy
Authors:
Suarez, MA; Esquivel, R; Alcantara, J; Dorantes, H; Chavez, JF Author Full Names: Suarez, M. A.; Esquivel, R.; Alcantara, J.; Dorantes, H.; Chavez, J. F.
Source:
MATERIALS CHARACTERIZATION 62 (9): 917-923 10.1016/j.matchar.2011.06.009 SEP 2011
Abstract:
Four Al-Cu-Fe alloys with compositions; a) Al(65)Cu(20)Fe(15), b) Al(64)Cu(22.5)Fe(13.5), c) Al(61)Cu(26)Fe(13) and d) Al(62)Cu(25.5)Fe(12.5), where the icosahedral phase is present, have been experimentally studied in both as-cast and annealed conditions in order to investigate the effect of chemical composition on the percentage of icosahedral phase and the changes in hardness of the alloy and each phase. It was found that the a) Al(65)Cu(20)Fe(15) and b) Al(64)cu(22.5)Fe(13.5) alloys, which present the highest Fe content, showed the largest amount of lambda-Al(13)Fe(4) phase as well as the highest hardness in all phases. In contrast, the same alloys developed the lowest amount of icosahedral phase after heat treatment. The c) Al(61)Cu(26)Fe(13) and d) Al(62)Cu(25.5)Fe(12.5) alloys had a better response to heat treatment, reaching amounts of icosahedral phase up to 87% and 99% respectively. The hardness of phases after heat treatment increased with respect to alloys in as-! cast condition, the hardness of icosahedral phase increased between 20% and 25%, while the hardness of lambda-Al(13)Fe(4) phase increased 9%. The icosahedral phase of annealed a) Al(65)Cu(20)Fe(15) alloy was the toughest with a hardness value of 844HV. (c) 2011 Elsevier Inc. All rights reserved.
Title:
Fermi-surface reconstruction by stripe order in cuprate superconductors
Authors:
Laliberte, F; Chang, J; Doiron-Leyraud, N; Hassinger, E; Daou, R; Rondeau, M; Ramshaw, BJ; Liang, R; Bonn, DA; Hardy, WN; Pyon, S; Takayama, T; Takagi, H; Sheikin, I; Malone, L; Proust, C; Behnia, K; Taillefer, L Author Full Names: Laliberte, F.; Chang, J.; Doiron-Leyraud, N.; Hassinger, E.; Daou, R.; Rondeau, M.; Ramshaw, B. J.; Liang, R.; Bonn, D. A.; Hardy, W. N.; Pyon, S.; Takayama, T.; Takagi, H.; Sheikin, I.; Malone, L.; Proust, C.; Behnia, K.; Taillefer, Louis
Source:
NATURE COMMUNICATIONS 2 10.1038/ncomms1440 AUG 2011
Abstract:
The origin of pairing in a superconductor resides in the underlying normal state. In the cuprate high-temperature superconductor YBa(2)Cu(3)Oy (YBCO), application of a magnetic field to suppress superconductivity reveals a ground state that appears to break the translational symmetry of the lattice, pointing to some density-wave order. Here we use a comparative study of thermoelectric transport in the cuprates YBCO and La(1.8-x)Eu(0.2)Sr(x)CuO(4) (Eu-LSCO) to show that the two materials exhibit the same process of Fermi-surface reconstruction as a function of temperature and doping. The fact that in Eu-LSCO this reconstruction coexists with spin and charge modulations that break translational symmetry shows that stripe order is the generic non-superconducting ground state of hole-doped cuprates.
Title:
RELATIONSHIP BETWEEN CHEMICAL AND ICOSAHEDRAL LOCAL ORDERINGS IN Al-Ni-Fe MELTS
Authors:
Roik, AS; Samsonnikov, AV; Kazimirov, VP; Sokol'skii, VE Author Full Names: Roik, A. S.; Samsonnikov, A. V.; Kazimirov, V. P.; Sokol'skii, V. E.
Source:
JOURNAL OF STRUCTURAL CHEMISTRY 52 (2): 310-318 APR 2011
Abstract:
An X-ray diffraction study and simulation of the structure of ternary Al(81.6)Ni(14.9)Fe(3.5), Al(71.6)Ni(23)Fe(5.4), and Al(61.1)Ni(31.1)Fe(7.3) melts by the reverse Monte Carlo method are conducted. An analysis of the structural models of melts is performed by the Voronoi-Delaunay partition. It is shown that the prepeak on the structure factor curves in the diffraction vector range of 13 nm(-1) to 22 nm(-1) is due to two factors: chemical ordering of atoms and non-crystalline close packing. The origin of the icosahedral short-range order in the melts as one of the variants of ordering of atoms in non-crystalline close packed clusters is discussed.

Update: 22-Sep-2011

Title:
Spatial inhomogeneity and planar symmetry breaking of the lattice incommensurate supermodulation in the high-temperature superconductor Bi(2)Sr(2)CaCu(2)O(8+y)
Authors:
Poccia, N; Campi, G; Fratini, M; Ricci, A; Saini, NL; Bianconi, A Author Full Names: Poccia, Nicola; Campi, Gaetano; Fratini, Michela; Ricci, Alessandro; Saini, Naurang L.; Bianconi, Antonio
Source:
PHYSICAL REVIEW B 84 (10): 10.1103/PhysRevB.84.100504 SEP 12 2011
Abstract:
Using scanning micro-x-ray diffraction we report a mixed real and reciprocal space visualization of the spatial heterogeneity of the lattice incommensurate supermodulation in a single crystal of Bi(2)Sr(2)CaCu(2)O(8+y) with T(c) = 84 K. The mapping shows an amplitude distribution of the supermodulation with large lattice fluctuations at a microscale with similar to 50% amplitude variation. The angular distribution of the supermodulation amplitude in the a-b plane shows a lattice chiral symmetry, forming a left-handed oriented striped pattern. The spatial correlation of the supermodulation is well described by a compressed exponential with an exponent of 1.5 +/- 0.3 and a correlation length of similar to 50 mu m, showing intrinsic lattice disorder in high-temperature superconductors.
Title:
Magnetic structure and electric field effects in multiferroic YMn(2)O(5)
Authors:
de Souza, RA; Staub, U; Scagnoli, V; Garganourakis, M; Bodenthin, Y; Huang, SW; Garcia-Fernandez, M; Ji, S; Lee, SH; Park, S; Cheong, SW Author Full Names: de Souza, R. A.; Staub, U.; Scagnoli, V.; Garganourakis, M.; Bodenthin, Y.; Huang, S. -W.; Garcia-Fernandez, M.; Ji, S.; Lee, S. -H.; Park, S.; Cheong, S. -W.
Source:
PHYSICAL REVIEW B 84 (10): 10.1103/PhysRevB.84.104416 SEP 9 2011
Abstract:
The magnetic structure of multiferroic RMn(2)O(5) (R = Y, Er) has been investigated by means of resonant soft x-ray diffraction. Energy, temperature, and azimuthal angle scans were performed in addition to reciprocal space maps on the magnetic reflection in the different magnetic phases of YMn(2)O(5). We also investigated the orbital magnetic moment at the oxygen K-edge for RMn(2)O(5) with both, R = Y and R = Er compositions. These moments reflect the strong hybridization between Mn 3d and oxygen 2p states. Experiments with applied electric fields are additionally presented, showing that the helical component of the magnetic structure in the CM phase of YMn(2)O(5) can be reversed by the application of an electric field. However, the incommensurate magnetic reflection in the high-temperature phase is unaffected. Interestingly, this is observed only in the presence of a small electrical current, indicative of a current-induced/-enhanced switching of magnetic domains.

Update: 16-Sep-2011

Title:
Magnetoelectric Ordering of BiFeO(3) from the Perspective of Crystal Chemistry
Authors:
Volkova, LM; Marinin, DV Author Full Names: Volkova, L. M.; Marinin, D. V.
Source:
JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM 24 (7): 2161-2177 10.1007/s10948-011-1178-5 OCT 2011
Abstract:
In this paper we examine the role of crystal chemistry factors in creating conditions for formation of magnetoelectric ordering in BiFeO(3). It is generally accepted that the main reason of the ferroelectric distortion in BiFeO(3) is concerned with a stereochemical activity of the Bi lone pair. However, the lone pair is stereochemically active in the paraelectric orthorhombic -phase as well. We demonstrate that a crucial role in emerging of phase transitions of the metal-insulator, paraelectric-ferroelectric and magnetic disorder-order types belongs to the change of the degree of the lone pair stereochemical activity-its consecutive increase with the temperature decrease. Using the structural data, we calculated the sign and strength of magnetic couplings in BiFeO(3) in the range from 945 A degrees C down to 25 A degrees C and found the couplings, which undergo the antiferromagnetic -> aEuro parts per thousand ferromagnetic transition with the temperature decrease and give rise to the antiferromagnetic ordering and its delay in regard to temperature, as compared to the ferroelectric ordering. We discuss the reasons of emerging of the spatially modulated spin structure and its suppression by doping with La(3+).
Title:
Antiferromagnetic Order in Pauli-Limited Unconventional Superconductors
Authors:
Kato, Y; Batista, CD; Vekhter, I Author Full Names: Kato, Yasuyuki; Batista, C. D.; Vekhter, I.
Source:
PHYSICAL REVIEW LETTERS 107 (9): 10.1103/PhysRevLett.107.096401 AUG 26 2011
Abstract:
We develop a theory of the coexistence of superconductivity (SC) and antiferromagnetism (AFM) in CeCoIn(5). We show that in Pauli-limited nodal superconductors the nesting of the quasiparticle pockets induced by Zeeman pair breaking leads to incommensurate AFM with the magnetic moment normal to the field. We compute the phase diagram and find a first order transition to the normal state at low temperatures, the absence of normal state AFM, and the coexistence of SC and AFM at high fields, in agreement with experiments. We also predict the existence of a new double-Q magnetic phase.
Title:
PHOTOINDUCED CHANGES IN THE SPACE-MODULATED MAGNETIC ORDER OF A FeBO(3):Mg SINGLE CRYSTAL
Authors:
Dzhuraev, DR; Sokolov, BY; Faiziev, SS Author Full Names: Dzhuraev, D. R.; Sokolov, B. Yu.; Faiziev, Sh. Sh.
Source:
RUSSIAN PHYSICS JOURNAL 54 (3): 382-385 AUG 2011
Abstract:
An effect of nonpolarized white light on the modulated magnetic structure of a FeBO(3):Mg single crystal, which arises in this light-plane weak ferromagnet in the low temperature range during technical magnetization, has been revealed. It has been found that the degree of the light action on the magnetic state of FeBO(3):Mg depends both on its duration and on the orientation of the spontaneous magnetization vector M of the crystal during illumination. Interpretation of the results obtained has been performed in the context of the "magnetic ripple" theory on the assumption that the absorbed light induces additional uniaxial magnetic anisotropy in the easy plane of the crystal and that the anisotropy axis is collinear to the vector M during illumination.
Title:
Ordered and disordered states in NiAs/Ni(2)In-type Ni(1+delta)Sn: Crystallography and order formation
Authors:
Leineweber, A Author Full Names: Leineweber, Andreas
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH 102 (7): 861-873 10.3139/146.110540 JUL 2011
Abstract:
An overview on the occupational order disorder behaviour of NiAs/Ni(2)In-type Ni(1+delta)Sn alloys is given. This order disorder behaviour leads to the occurrence of one disordered high-temperature phase HT and three different low-temperature phases LT, LT' and LT". The low-temperature phases, forming in different compositional regimes, are characterised by long-range order of Ni atoms against vacancies on trigonal-bipyramidal sites formed by Sn, leading to a commensurate superstructure in LT whereas LT' and LT" are incommensurate. Different order disorder related phase transformation were monitored by X-ray powder diffraction. In particular during the formation of long-range order starting from disordered HT-Ni(1+delta)Sn, non-equilibrium crystal structures and microstructures evolve prior to formation of the ideally established equilibrium low-temperature phases. Quantitative analysis of the transformation kinetics including determination of activation energies was done by X-ray powder diffraction. The activation energies of the different processes can be related with the mobility of the Ni atoms in the crystal structure.

Update: 8-Sep-2011

Title:
First-principles investigations of the five-layer modulated martensitic structure in Ni(2)Mn(Al(x)Ga(1-x)) alloys
Authors:
Luo, HB; Li, CM; Hu, QM; Kulkova, SE; Johansson, B; Vitos, L; Yang, R Author Full Names: Luo, H. B.; Li, C. M.; Hu, Q. M.; Kulkova, S. E.; Johansson, B.; Vitos, L.; Yang, R.
Source:
ACTA MATERIALIA 59 (15): 5938-5945 10.1016/j.actamat.2011.06.002 SEP 2011
Abstract:
In this paper, the five-layer modulated (5M) martensitic structures of Ni(2)Mn(Al(x)Ga(1-x)), with x = 0, 0.1 and 0.2, are investigated by the use of the exact muffin-tin orbital method in combination with the coherent potential approximation. The 5M martensite is modeled by varying c/a (shear) and wave-like displacements of the atoms on (1 1 0) plane (shuffle) scaled by eta according to Martynov and Kokorin (J. Phys. III 2, 739 (1992)). For Ni(2)MnGa, we obtain 5M martensite with equilibrium c/a of 0.92 and eta of 0.08, in reasonable agreement with the experiment results (0.94 and 0.06, respectively). c/a and eta are linearly coupled to each other. Al-doping increases c/a and decreases eta, but the linear c/a similar to eta coupling remains. Comparing the total energies of the 5M martensite and L2(1) austenite, we find that the martensite is more stable than the austenite. Al-doping increases the relative stability of the austenite and finally becomes energetically degenerated with the 5M martensite at an Al atomic fraction (x) of about 0.26. The relative phase stability is analyzed based on the calculated density of states. The calculated total magnetic moments mu(0) as a function of c/a exhibit a maximum around the equilibrium c/a. Al-doping reduces mu(0) (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Unraveling the Perplexing Structure of the Zeolite SSZ-57
Authors:
Baerlocher, C; Weber, T; McCusker, LB; Palatinus, L; Zones, SI Author Full Names: Baerlocher, Christian; Weber, Thomas; McCusker, Lynne B.; Palatinus, Lukas; Zones, Stacey I.
Source:
SCIENCE 333 (6046): 1134-1137 10.1126/science.1207466 AUG 26 2011
Abstract:
Previous high-resolution x-ray powder diffraction and transmission electron microscopy studies of the zeolite SSZ-57 could not fully elucidate the structural basis for its puzzling adsorption behavior, which appears to be intermediate between that of a medium-(10-ring) and a large-pore (12-ring) zeolite. Now by applying advanced crystallographic techniques (structure solution in four-dimensional space and interpretation of three-dimensional diffuse scattering by Monte Carlo simulation) and crystal chemistry considerations to high-quality single-crystal x-ray diffraction data collected on a microcrystal (about 2 micrometers by 2 micrometers by 8 micrometers), we have been able to derive a comprehensive description of its silicate framework structure. The framework is related to that of ZSM-11 but is commensurately modulated along the c axis (P (4) over bar m2, a = b = 20.091 angstrom, c = 110.056 angstrom) to yield a structure with a 12-ring:10-ring ratio of 1:15. Disorder of the 12-rings results in a three-dimensional 10-ring channel system with large isolated pockets. The structure helps to clarify the material's catalytic activity.
Title:
GOVERNING EQUATIONS AND GENERAL SOLUTIONS OF PLANE ELASTICITY OF TWO-DIMENSIONAL DECAGONAL QUASICRYSTALS
Authors:
Gao, Y; Shang, LG Author Full Names: Gao, Yang; Shang, Lan-Ge
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B 25 (20): 2769-2778 10.1142/S0217979211101065 AUG 10 2011
Abstract:
Two-dimensional problem is systematically investigated for the coupled equations in two-dimensional decagonal quasicrystals, and three general solutions are presented by an operator method. To simplify governing equations, each general solution shall take three different forms expressed in terms of three displacement functions, which satisfy partial three differential equations of second order. To illustrate its utility, the closed-form solutions are obtained for problems of point phonon forces and phason force acting at the apex of a quasicrystal wedge, all in terms of the general solutions. Furthermore, these solutions can be degenerated to those of problems of point forces applied on the boundary of a quasicrystal half-plane.
Title:
Martensitic transformation in rapidly solidified Heusler Ni(49)Mn(39)Sn(12) ribbons
Authors:
Zheng, HX; Wu, DZ; Xue, SC; Frenzel, J; Eggeler, G; Zhai, QJ Author Full Names: Zheng, Hongxing; Wu, Dianzhen; Xue, Sichuang; Frenzel, Jan; Eggeler, Gunther; Zhai, Qijie
Source:
ACTA MATERIALIA 59 (14): 5692-5699 10.1016/j.actamat.2011.05.044 AUG 2011
Abstract:
In the present work, the microstructure evolution and kinetics of the martensitic transformation are investigated in as-spun and annealed ribbons of Heusler Ni(49)Mn(39)Sn(12) using electron microscopy, X-ray diffraction and differential scanning calorimetry. Both ribbons undergo a reversible martensitic transformation during thermal cycling and the low-temperature martensite is confirmed to be a modulated four-layered orthorhombic (4O) structure through in situ cooling transmission electronic microscopy investigation. The annealing effect on the martensitic transformation behavior is discussed from the viewpoints of electron concentration, Mn-Mn inter-atomic distance, atomic order degree and grain size. A strong cooling-rate dependence of phase transition kinetics is found and the mechanism is analyzed. The satisfactory reproducibility obtained during thermal cycling test of this alloy ribbons offers great potential for practical applications. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Antiferromagnet-Long-Period Structure Phase Transition in RMn(2)O(5) Oxides
Authors:
Men'shenin, VV; Nikolaev, VV; Dmitriev, AV Author Full Names: Men'shenin, V. V.; Nikolaev, V. V.; Dmitriev, A. V.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 112 (1): 25-35 10.1134/S0031918X11010315 JUL 2011
Abstract:
An analysis of the magnetic phase transition from an antiferromagnetic into an incommensurate phase in oxides RMn(2)O(5) has been performed. It has been shown that this is a second-order phase transition and that it can occur through one of complete irreducible representations of the space group Pbam, i.e., without a decrease in the symmetry of the crystal lattice. It has been established that the decrease in the electric polarization of the oxides in this transition is due to the development of long-period magnetic ordering.

Update: 31-Aug-2011

Title:
Magnetic correlation in the square-lattice spin system (CuBr)Sr(2)Nb(3)O(10): A neutron diffraction study
Authors:
Yusuf, SM; Bera, AK; Ritter, C; Tsujimoto, Y; Ajiro, Y; Kageyama, H Author Full Names: Yusuf, S. M.; Bera, A. K.; Ritter, C.; Tsujimoto, Yoshihiro; Ajiro, Yoshitami; Kageyama, Hiroshi
Source:
PHYSICAL REVIEW B 84 (6): 10.1103/PhysRevB.84.064407 AUG 18 2011
Abstract:
Magnetic correlation in the quantum S = 1/2 square-lattice system (CuBr) Sr(2)Nb(3)O(10) has been studied by neutron diffraction. A novel commensurate in-plane, helical antiferromagnetic (AFM) ordering, characterized by the propagation vector k = (0 3/8 1/2), has been confirmed from the appearance of magnetic Bragg peaks below T(N) similar to 7.5 K. The ordered moment at 2 K is found to be 0.79(7) mu B/Cu(2+)-ion. The observed helical AFM structure differs from the ground state predicted theoretically from the J(1)-J(2) model as well as from experimentally reported states for other quantum S = 1/2 square-lattice systems. However, the observed helical magnetic structure can be described in a J(1)-J(2)-J(3) model. Under a 4.5 T magnetic field, the spin-order changes drastically and is characterized by the propagation vector k(1) = (0 1/3 0.446) and a probable k(2) = (0 0 0) vector.
Title:
Mechanical properties of clusters in quasicrystal approximants: The example of the 1/1 Al-Cu-Fe approximant
Authors:
Jung, DY; Steurer, W Author Full Names: Jung, Daniel Y.; Steurer, Walter
Source:
PHYSICAL REVIEW B 84 (5): 10.1103/PhysRevB.84.054116 AUG 15 2011
Abstract:
Quantum-mechanical molecular dynamics have been used to investigate structural and physical properties of the 1/1 approximant of the icosahedral Al-Cu-Fe quasicrystal. Particular local structural arrangements of atoms, referred to here as clusters, have been analyzed with respect to their properties within the crystal structure. Artificial strain and cracks have been introduced to probe their mechanical properties, and artificial surfaces have been created to investigate their role for surface termination. From the energetics of the ab initio calculations results that flat surfaces cutting clusters are favored over puckered surfaces keeping clusters intact. The Vienna Ab-initio Simulation Package (VASP) was used for all calculations.
Title:
Pressure-induced formation of intermediate-valence quasicrystalline system in a Cd-Mg-Yb alloy
Authors:
Watanuki, T; Kawana, D; Machida, A; Tsai, A Author Full Names: Watanuki, Tetsu; Kawana, Daichi; Machida, Akihiko; Tsai, AnPang
Source:
PHYSICAL REVIEW B 84 (5): 10.1103/PhysRevB.84.054207 AUG 15 2011
Abstract:
A quasiperiodic intermediate-valence system was prepared by applying pressure to an icosahedral Cd-Mg-Yb quasicrystal. X-ray absorption spectroscopy near the Yb L(3) edge demonstrates that the Yb valence increases continuously upon compression from the divalent state (4f(14)) at ambient pressure and reaches a value of 2.71 at 57.6 GPa, which is close to the trivalent state (4f(13)). By following the trend of Yb-based intermediate-valence crystalline compounds, this large valence increase suggests the change of 4f character in the Cd-Mg-Yb quasicrystal from an itinerant state with weak electron correlations to an intermediate region between an itinerant and a localized state with strong correlations. The valence increases sensitively with pressure below similar to 30 GPa; however, the increase is significantly suppressed above similar to 30 GPa. The rate of valence increase with respect to pressure in the lower-pressure region is twice larger than that of a Cd-Yb quasicrystal in our previous study [Phys. Rev. B 81, 220202(R) (2010)]. This is mainly explained by the smaller bulk modulus of the Cd-Mg-Yb quasicrystal compared to the Cd-Yb system. The suppression of valence increase with respect to pressure in the higher-pressure region is most likely due to an increase of conduction-4f electron hybridization that counteracts 4f localization and reduces the Yb valence increase.
Title:
Effect of relaxation state on nucleation and grain growth of nanoscale quasicrystal in Zr-based bulk metallic glasses prepared under various cooling rates
Authors:
Saida, J; Setyawan, AD; Matsubara, E Author Full Names: Saida, Junji; Setyawan, Albertus Deny; Matsubara, Eiichiro
Source:
APPLIED PHYSICS LETTERS 99 (6): 10.1063/1.3622117 AUG 8 2011
Abstract:
Zr(65)Al(7.5)Ni(10)Cu(12.5)Pd(5) bulk metallic glasses (BMGs) in various relaxation states were prepared under different cooling rates. The grain growth rate of the primary quasicrystal was examined near the crystallization temperature. It was approximately 1 x 10(-9) m/s in less relaxed BMGs and approximately twice as large in relaxed BMGs. In contrast, the calculated homogeneous nucleation rate of the less relaxed samples was five to ten times higher (5 x 10(19)-1 x 10(20)/m(3)s) than those in the relaxed BMGs. The results indicate that the relaxation state of glassy alloys has a marked effect on nucleation and grain growth behaviors. (C) 2011 American Institute of Physics. [doi:10.1063/1.3622117]
Title:
Structural behavior and thermoelectric properties of the brownmillerite system Ca(2)(Zn(x)Fe(2-x))O(5)
Authors:
Asenath-Smith, E; Misture, ST; Edwards, DD Author Full Names: Asenath-Smith, Emily; Misture, Scott T.; Edwards, Doreen D.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 184 (8): 2167-2177 10.1016/j.jssc.2011.06.009 AUG 2011
Abstract:
The Ca(2)(Zn(x)Fe(2-x))O(5) series was synthesized and characterized to determine the influence of zinc dopant on the brownmillerite structure for thermoelectric applications. All single-phase compounds exhibited Pnma symmetry at room temperature up to the solubility limit at x=0.10. High-temperature X-ray powder diffraction was used to show that the nature of the Pnma-Imma(0 0 gamma)s00 transition in Ca(2)Fe(2)O(5) is modified by the presence of zinc. While the Zn-free composition transitions to an incommensurate phase, the Zn-containing phases transition instead to a commensurate phase, Imma(0 0 gamma)s00 with gamma=1/2. Both the Neel temperature and the onset temperature of the Pnma-Imma(0 0 gamma)s00 phase transition decreased with increasing zinc concentration. Rietveld analysis of the in situ diffraction pattern for the x=0 sample at 1300 degrees C demonstrates that the structure contains statistically disordered chain orientations as described by space group Imma. Thermoelectric properties were analyzed in air from 100 to 800 degrees C. The positive Seebeck coefficient revealed hole-type conduction for all compositions. Doped samples exhibited electrical conductivities up to 3.4 S/cm and thermal conductivity of 1.5 W/mK Transport analysis revealed thermally activated mobility consistent with polaron conduction behavior for all compositions. (C) 2011 Elsevier Inc. All rights reserved.
Title:
OPTICAL TRANSMISSION COEFFICIENT OF CRYSTALLINE [N(CH(3))(4)](2)MeCl(4) IN THE INCOMMENSURATE PHASE
Authors:
Sveleba, SA; Karpa, IV; Katerynchuk, IM; Semotyuk, OV; Shymkiv, RM; Kunyo, IM; Fitsych, OI Author Full Names: Sveleba, S. A.; Karpa, I. V.; Katerynchuk, I. M.; Semotyuk, O. V.; Shymkiv, R. M.; Kunyo, I. M.; Fitsych, O. I.
Source:
JOURNAL OF APPLIED SPECTROSCOPY 78 (2): 228-233 MAY 2011
Abstract:
This a study of the optical transmission of [N(CH(3))(4)](2)ZnCl(4) and [N(CH(3))(4)](2)CuCl(4) crystals in the incommensurate phase when a defect density wave is present. It is found that an anomalous reduction in the transmission coefficient is caused by scattering of light owing to a realignment of the superstructure during transitions between metastable states. When a defect density wave is present, the anomalous optical transmission of the crystal is related to the scattering of light on superstructure inhomogeneities produced by a superposition of existing modulation waves.

Update: 25-Aug-2011

Title: Magnetic phase diagrams of the CrB- and FeB-type HoSi compounds

Author(s): Schobinger-Papamantellos, P (Schobinger-Papamantellos, P.); Buschow, KHJ (Buschow, K. H. J.); Rodriguez-Carvajal, J (Rodriguez-Carvajal, J.)

Source: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Volume: 323 Issue: 21 Pages: 2592-2607 DOI: 10.1016/j.jmmm.2011.05.044 Published: NOV 2011

Abstract: The temperature magnetic phase diagrams of the dimorphic HoSi compound were studied by neutron diffraction. The sample comprises 35.5% CrB- (Cmcm) and 64.5% FeB-type (Pnma) of structure. Both phases order antiferromagnetically below T(N)=25 K and undergo first-order magnetic transitions at T(ic) = 16.5 K. Their T-phase diagrams comprise a low temperature (LT) 2.7 K - T(ic) and a high temperature (HT) range T(ic) - T(N) with distinct wave vectors. The LT magnetic ordering of the CrB-type HoSi with the wave vector q(1)=(1/2, 0, 1/2) corresponds to a uniaxial magnetic structure, with the Ho moments along the shortest axis c. At 2.7 K the ordered moment value is 8.6(2) mu(B)/Ho atom. The HT ordering, described by the wave vector q(2)=(q(2x), 0, q(2z)) with a T-variable length, corresponds to an amplitude modulated structure. The magnetic ordering of the FeB-type HoSi requires two symmetry independent vectors q(3)=(0, q(3y), q(3z)) for the LT- and q(4)=(q(4x), q(4y), 0) for the HT range. Both vectors correspond to sine wave modulated structures with the Ho magnetic moments confined along the shortest axis b. The q(3) vector has an almost invariable length vs. T close to approximate to (0, 9/17, 1/11). At 2.7 K the amplitude of the wave is 10.9(1) mu(B)/Ho atom. At T(ic) q(3) jumps to the wave vector q(4)=(q(4x), q(4y), 0) with a T-variable length. At 17 K q(4)=(0.092(1), 0.538(3), 0). Around T(ic) there is a narrow coexistence range of the q(3) and q(4) competing phases. Various models are discussed and compared with the isomorphic RSi (R=rare earth) compounds counterparts of HoSi, a comparison that has led us to briefly review the magnetic structures available in the literature for this interesting class of compounds. (C) 2011 Elsevier B.V. All rights reserved.

Title: Antiferromagnetic resonance in ferroborate NdFe(3)(BO(3))(4)

Author(s): Kobets, MI (Kobets, M. I.); Dergachev, KG (Dergachev, K. G.); Khatsko, EN (Khatsko, E. N.); Gnatchenko, SL (Gnatchenko, S. L.); Bezmaternykh, LN (Bezmaternykh, L. N.); Temerov, VL (Temerov, V. L.)

Source: PHYSICA B-CONDENSED MATTER Volume: 406 Issue: 18 Pages: 3430-3435 DOI: 10.1016/j.physb.2011.06.014 Published: SEP 15 2011

Abstract: The AFMR spectra of the NdFe(3)(BO(3))(4) crystal are measured in a wide range of frequencies and temperatures. It is found that by the type of its magnetic anisotropy the compound is an "easy-plane" antiferromagnet with a weak anisotropy in the basal plane. The effective magnetic parameters are determined: anisotropy fields H(a1) = 1.14 kOe and H(a2) = 60 kOe and magnetic excitation gaps Delta v(1) = 101.9 GHz and Delta v(2) = 23.8 GHz. It is shown that commensurate-incommensurate phase transition causes a shift in resonance field and a considerable change in absorption line width. At temperatures below 4.2 K nonlinear regimes of AFMR excitation at low microwave power levels are observed. (C) 2009 Elsevier B.V. All rights reserved.

Title: Incommensurate spin-density wave and a multiband superconducting phase in Na(x)FeAs revealed by nuclear magnetic resonance

Author(s): Klanjsek, M (Klanjsek, M.); Jeglic, P (Jeglic, P.); Lv, B (Lv, B.); Guloy, AM (Guloy, A. M.); Chu, CW (Chu, C. W.); Arcon, D (Arcon, D.)

Source: PHYSICAL REVIEW B Volume: 84 Issue: 5 Article Number: 054528 DOI: 10.1103/PhysRevB.84.054528 Published: AUG 11 2011

Abstract: We report a (23)Na and (75)As nuclear magnetic resonance (NMR) investigation of Na(x)FeAs series (x = 1, 0.9, 0.8) exhibiting a spin-density-wave (SDW) order below T(SDW) = 45, 50, and 43 K for x = 1, 0.9, 0.8, respectively, and a bulk superconductivity below T(c) approximate to 12 K for x = 0.9. Below T(SDW), a spin-lattice relaxation reveals the presence of gapless particle-hole excitations in the whole x range, meaning that a portion of the Fermi surface remains gapless. The superconducting fraction as deduced from the bulk susceptibility scales with this portion, while the SDW order parameter as deduced from the NMR linewidth scales inversely with it. The NMR line shape can only be reproduced assuming an incommensurate (IC) SDW. These findings qualitatively correspond to the mean-field models of competing interband magnetism and intraband superconductivity, which lead to an IC SDW order coexisting with superconductivity in part of the phase diagram.

Title: Effect of selective substitution of Co for Ni or Mn on the superstructure and microstructural properties of Ni(50)Mn(29)Ga(21)

Author(s): Kumar, AS (Kumar, A. Satish); Ramudu, M (Ramudu, M.); Seshubai, V (Seshubai, V.)

Source: JOURNAL OF ALLOYS AND COMPOUNDS Volume: 509 Issue: 32 Pages: 8215-8222 DOI: 10.1016/j.jallcom.2011.05.064 Published: AUG 11 2011

Abstract: Results from a systematic study of the effect of cobalt, selectively substituted for Ni and Mn, in the modulated orthorhombic (7 M) Ni(50)Mn(29)Ga(21) alloy are contrasted. Substitution of Co for Mn resulted in the stabilization of a non-modulated tetragonal (NM) phase at higher Co content. At lower Co contents, a mixture of 7 M and NM phases were found to co-exist. Increasing in Co content caused suppression of long-range twin deformation leading to sporadic islands within which twin variants were confined. These effects are attributed to the considerable stresses generated by an atomic volume change of 9.5% caused locally when Co is substituted for Mn. On the other hand, substitution of Co for Ni, which causes only 1.7% atomic volume change locally, was observed not to alter either the superstructural ordering or the long-range twin deformation. Our results show that the microstructures resultant on Co doping have a strong correlation to the structural ordering, which in turn depends on whether Co is substituted for Mn or for Ni, and also on the concentration of Co. (C) 2011 Elsevier B. V. All rights reserved.

Title: Thermal and electrical transport in the spin density wave antiferromagnet CaFe(4)As(3)

Author(s): Kim, MS (Kim, M. S.); Yin, ZP (Yin, Z. P.); Zhao, LL (Zhao, L. L.); Morosan, E (Morosan, E.); Kotliar, G (Kotliar, G.); Aronson, MC (Aronson, M. C.)

Source: PHYSICAL REVIEW B Volume: 84 Issue: 7 Article Number: 075112 DOI: 10.1103/PhysRevB.84.075112 Published: AUG 5 2011

Abstract: We present here measurements of the thermopower, thermal conductivity, and electrical resistivity of the newly reported compound CaFe(4)As(3). Evidence is presented from specific heat and electrical resistivity measurements that a substantial fraction of the Fermi surface survives the onset of spin density wave (SDW) order at the Neel temperature T(N) = 88 K and its subsequent commensurate lock-in transition at T(2) = 26.4 K. The specific heat below T(2) consists of a normal metallic component from the ungapped parts of the Fermi surface and a Bardeen-Cooper-Schrieffer (BCS) component that represents the SDW gapping of the Fermi surface. A large Kadowaki-Woods ratio is found at low temperatures, showing that the ground state of CaFe(4)As(3) is a strongly interacting Fermi liquid. The thermal conductivity kappa of CaFe(4)As(3) is an order of magnitude smaller than those of conventional metals at all temperatures, due to a strong phonon scattering. The thermoelectric power S displays a sign change from positive to negative indicating that a partial gap forms at the Fermi level with the onset of commensurate spin density wave order at T(2) = 26.4 K. The small value of the thermopower S and the enhancements of the resistivity due to gap formation and strong quasiparticle interactions offset the low value of the thermal conductivity kappa, yielding only a modest value for the thermoelectric figure of merit Z <= 5 x 10(-6) K(-1) in CaFe(4)As(3). The results of ab initio electronic structure calculations are reported, confirming that the sign change in the thermopower at T(2) is reflected by a sign change in the slope of the density of states at the Fermi level. Values for the quasiparticle renormalization Z are derived from measurements of the specific heat and thermopower, indicating that as T -> 0, CaFe(4)As(3) is among the most strongly correlated of the known Fe-based pnictide and chalcogenide systems.

Title: Switching behaviour of modulated ferroelectrics: the kinetics of the field induced lock-in transition in K(2)SeO(4)

Author(s): Leist, J (Leist, J.); Gibhardt, H (Gibhardt, H.); Hradil, K (Hradil, K.); Eckold, G (Eckold, G.)

Source: JOURNAL OF PHYSICS-CONDENSED MATTER Volume: 23 Issue: 30 Article Number: 305901 DOI: 10.1088/0953-8984/23/30/305901 Published: AUG 3 2011

Abstract: The field induced switching process across the ferroelectric lock-in transition in K(2)SeO(4) has been studied on a millisecond timescale using stroboscopic neutron diffraction. The time evolution of both the first and the third order satellites was examined. The time constants are found to vary with temperature between 0.2 and 1.2 ms. This is an order of magnitude faster than in the isostructural Rb(2)ZnCl(4). Moreover, the time dependence of the satellite's linewidth provides information about the evolution of the coherence of the modulated structure.

Title: Pressure-induced change in the magnetic ordering of TbMnO(3)

Author(s): Makarova, OL (Makarova, O. L.); Mirebeau, I (Mirebeau, I.); Kichanov, SE (Kichanov, S. E.); Rodriguez-Carvajal, J (Rodriguez-Carvajal, J.); Forget, A (Forget, A.)

Source: PHYSICAL REVIEW B Volume: 84 Issue: 2 Article Number: 020408 DOI: 10.1103/PhysRevB.84.020408 Published: JUL 20 2011

Abstract: We have studied TbMnO(3) by high-pressure neutron diffraction up to 3.6 GPa and down to 1.5 K. The incommensurate spin structures of the Mn and Tb moments are strongly suppressed under pressure, and an E-type commensurate spin structure with (0,1/2,0) propagation vector is stabilized for the Mn moments. The Mn and Tb incommensurate orders which persist at low pressures or low temperatures are also affected, with a change of phase of the modulation between neighboring Mn chains and a reorientation of the Mn moments along the a axis. The results suggest both a change of the balance of the different Mn-Mn interactions and a strengthening of the Tb-Tb (or Tb-Mn) interactions under pressure.

Title: Transverse and longitudinal lattice modulations in the charge-orbital-ordered manganite Sr(2-x)La(x)MnO(4) around x=0.5

Author(s): Arao, M (Arao, Masazumi); Inoue, Y (Inoue, Yasuhide); Toyoda, K (Toyoda, Kensei); Koyama, Y (Koyama, Yasumasa)

Source: PHYSICAL REVIEW B Volume: 84 Issue: 1 Article Number: 014102 DOI: 10.1103/PhysRevB.84.014102 Published: JUL 15 2011

Abstract: For Sr(2-x)La(x)MnO(4), having a nearly two-dimensional electronic system of e(g) electrons, we have examined the crystallographic features of the charge-orbital-ordered (COO) and charge-exchange (CE)-type magnetic states for 0.40 <= x <= 0.55 by transmission electron microscopy. Incommensurate and commensurate longitudinal lattice modulations were found below similar to 150 K for 0.47 <= x <= 0.51, while the cooling from the disordered tetragonal state resulted in the appearance of transverse modulations below T(COO) for 0.40 <= x <= 0.52. For 0.47 <= x <= 0.51, thus, the longitudinal and transverse modulations were present in both the lower-temperature region of the COO state and the CE-type magnetic state. In addition to these two states, the COO state for 0.40 <= x < 0.47 and 0.51 < x <= 0.52 accompanies only the transverse modulation and should be referred to as the orbital modulated state without a charge modulation.

Title: Neutron diffraction studies of RSn(1+x)Ge(1-x) (R=Tb-Er) compounds

Author(s): Gil, A (Gil, A.); Penc, B (Penc, B.); Baran, S (Baran, S.); Hoser, A (Hoser, A.); Szytula, A (Szytula, A.)

Source: JOURNAL OF SOLID STATE CHEMISTRY Volume: 184 Issue: 7 Pages: 1631-1637 DOI: 10.1016/j.jssc.2011.04.040 Published: JUL 2011

Abstract: The magnetic structures of RSn(1+x)Ge(1-x) (R=Tb, Dy, Ho and Er, x approximate to 0.1) compounds have been determined by neutron diffraction studies on polycrystalline samples. The data recorded in a paramagnetic state confirmed the orthorhombic crystal structure described by the space group Cmcm. These compounds are antiferromagnets at low temperatures. The magnetic ordering in TbSn(1.12)Ge(0.88) is sine-modulated described by the propagation vector k=(0.4257(2), 0, 0.5880(3)). Tb magnetic moment equals 9.0(1)mu(B) at 1.62 K. It lies in the b-c plane and form an angle theta=17.4(2)degrees with the c-axis. This structure is stable up to the Neel temperature equal to 31 K. The magnetic structures of RSn(1+x)Ge(1-x), where R are Dy, Ho and Er at low temperatures are described by the propagation vector k=(1/2, 1/2,0) with the sequence (++- +) of magnetic moments in the crystal unit cell. In DySn(1.09)Ge(0.91) and HoSn(1.1)Ge(0.9) magnetic moments equal 7.25(15) and 8.60(6)mu(B) at 1.55 K, respectively. The moments are parallel to the c-axis. For Ho-compound this ordering is stable up to T(N)=10.7 K. For ErSn(1.08)Ge(0.92), the Er magnetic moment equals 7.76(7)mu(B) at T=1.5 K and it is parallel to the b-axis. At T(t)=3.5 K it tunes into the modulated structure described by the k=(0.496(1), 0.446(4), 0). With the increase of temperature there is a slow decrease of k(x) component and a quick decrease of k(y) component. The Er magnetic moment is parallel to the b-axis up to 3.9 K while at 4 K and above it lies in the b-c plane and form an angle 48(3)degrees with the c-axis. In compounds with R=Tb, Ho and Er the magnetostriction effect at the Neel temperature is observed. (C) 2011 Elsevier Inc. All rights reserved.

Title: Microstructural features and domain formation in (Ba,Sr)(2)TiSi(2)O(8) fresnoites

Author(s): Wong, CL (Wong, Chui Ling); Ferraris, C (Ferraris, Cristiano); White, TJ (White, T. J.)

Source: JOURNAL OF SOLID STATE CHEMISTRY Volume: 184 Issue: 7 Pages: 1768-1776 DOI: 10.1016/j.jssc.2011.05.009 Published: JUL 2011

Abstract: The formation and co-existence of crystallographically modulated and non-modulated regions in (Ba,Sr)(2)TiSi(2)O(8) fresnoites is reviewed, particularly the dependence on local composition. It is shown that perturbations of the average fresnoite structure, determined from appreciable single crystals, are in some cases better described as nanometric domain intergrowths where departures from ideal stoichiometry are characteristics of incommensuration, while modulation is absent from volumes that are less perturbed chemically. Evidence for this differentiation is obtained from selected area electron diffraction (SAED) patterns and high-resolution transmission electron microscopy (HRTEM) images. The domains are readily distinguished by their unique contrast in bright field electron micrographs. Fourier reconstructions of HRTEM images collected from areas with darker contrast show that modulation can change within relatively small volumes. Nearby areas with lighter contrast were found by SAED to be free of structural disorder and incommensurate reflections. (C) 2011 Elsevier Inc. All rights reserved.

Title: Phase diagram studies of Ti-Zr-Ni alloys containing less than 40 at.% Ni and estimated critical cooling rate for icosahedral quasicrystal formation from the liquid

Author(s): Lee, GW (Lee, G. W.); Gangopadhyay, AK (Gangopadhyay, A. K.); Kelton, KF (Kelton, K. F.)

Source: ACTA MATERIALIA Volume: 59 Issue: 12 Pages: 4964-4973 DOI: 10.1016/j.actamat.2011.04.045 Published: JUL 2011

Abstract: A detailed phase diagram study of Ti-Zr-Ni alloys has been conducted using conventional X-ray scattering, microstructural and thermal annealing, and levitation techniques, to improve on the existing phase diagram. Various phases, such as simple crystalline, approximant, icosahedral quasicrystalline, and complex polytetrahedral phases, have been identified. A eutectic composition has been found near 21 at.% Ni for nearly equal Ti and Zr concentrations. From containerless processing studies, using electrostatic levitation, the phase boundary of the icosahedral quasicrystal (i-phase) is placed between 29 and 45 at.% Ti with 21 at.% Ni. A first-time estimate of the critical cooling rate for the formation of the i-phase directly from the liquid in alloys with 21 at.% Ni is less than 100 degrees C s(-1), which is much smaller than for most of the known metastable quasicrystals. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title: Mechanism of exchange striction of ferroelectricity in multiferroic orthorhombic oMnO(3) single crystals

Author(s): Lee, N (Lee, N.); Choi, YJ (Choi, Y. J.); Ramazanoglu, M (Ramazanoglu, M.); atcliff, W (Ratcliff, W., II); Kiryukhin, V (Kiryukhin, V.); Cheong, SW (Cheong, S. -W.)

Source: PHYSICAL REVIEW B Volume: 84 Issue: 2 Article Number: 020101 DOI: .1103/PhysRevB.84.020101 Published: JUL 1 2011

Abstract: E-type perovskite magnet HoMnO(3) is considered to be a prototype Mn-Mn change-striction driven multiferroic. We have grown orthorhombic HoMnO(3) single cryd studied the directional dependence of their electric polarization P. The direction of P is not ong the crystallographic a axis, as predicted, but along the c axis. The magnetic state is commensurate. The direction P along the c axis is primarily induced by Ho-Mn exchange riction, and Mn-Mn striction in the incommensurate spin state leads to an antiferroelecder along the a axis. We predict the rotation of P with temperature in commensurate E-tyMnO(3) (R denotes magnetic rare earth).

Title: Incommensurate Spin-Density Wave Order in Electron-Doped BaFe(2)As(2) uperconductors

Author(s): Pratt, DK (Pratt, D. K.); Kim, MG (Kim, M. G.); Kreyssig, A (Kreyssig, A.); Lee, B (Lee, Y. B.); Tucker, GS (Tucker, G. S.); Thaler, A (Thaler, A.); Tian, W (Tian, W.); arestky, JL (Zarestky, J. L.); Bud'ko, SL (Bud'ko, S. L.); Canfield, PC (Canfield, P. C.); armon, BN (Harmon, B. N.); Goldman, AI (Goldman, A. I.); McQueeney, RJ (McQueeney, R.)

Source: PHYSICAL REVIEW LETTERS Volume: 106 Issue: 25 Article Number: 57001 DOI: 10.1103/PhysRevLett.106.257001 Published: JUN 20 2011

Abstract: Neutron diffraction studies of Ba(Fe(1-x)Co(x-2))As(2) reveal that commensurate ntiferromagnetic order gives way to incommensurate magnetic order for Co compositions etween 0.056 < x < 0.06. The incommensurability has the form of a small transverse splitting , +/-epsilon, 0) from the commensurate antiferromagnetic propagation vector Q(AFM) = (1, 0, ) (in orthorhombic notation) where epsilon approximate to 0.02 - 0.03 and is composition ependent. The results are consistent with the formation of a spin-density wave driven by Ferface nesting of electron and hole pockets and confirm the itinerant nature of magnetise iron arsenide superconductors.

SN: 0031-9007

Title: Stability of the Sr(2)B(3)O(6.5-delta) Phases (B = Fe, Co, Ga): Existence Range, tructural and Physical Properties

Author(s): Desmoulins, H (Desmoulins, H.); Malo, S (Malo, S.); Perez, O (Perez, O.); elloquin, D (Pelloquin, D.); Maignan, A (Maignan, A.); Hervieu, M (Hervieu, M.)

Source: CHEMISTRY OF MATERIALS Volume: 23 Issue: 11 Pages: 2786-2794 DOI: 0.1021/cm103635g Published: JUN 14 2011

Abstract: A large solid solution Sr(2)(Fe(3-x)Co(x-y)Ga(y))O(6.5-delta)), isostructural with thodulated Fe-2201 and Co-2201-type structures, has been characterized using X-ray powdiffraction (XRPD), transmission electron microscopy (TEM), and energy dispersive pectroscopy (EDS) analyses. The disorder phenomena have been studied using High Rransmission Electron Microscopy (HREM). The evolution of the cell parameters, wavelength f the modulated structures, and transport properties are analyzed versus the three B (Fe, Co, o) cation contents, showing a violation of the Vegard law for a ratio Fe/(Fe + Co + Go) close o x approximate to 0.6. By decreasing the Fe content from that x value, an abrupt variation of esistivity of about 2 orders of magnitude is observed. This spectacular behavior is associated ith the creation of percolative - (Co-O-Co)- pathways. A double effect of the (Co/Ga) ubstitution for Fe is observed on the magnetic properties. First, the B-O-B magnetic nteractions (B = Fe, Co, Ga) are diluted because Ga(3+) is a d(10)s(0) cation and, second, the o(3+)-O-Co(3+) magnetic exchange in that structure is smaller than the Fe(3+)-O-Fe(3) ones. his explained why both the magnitude of the ferromagneto-like component and the T(N) vare reduced as compared to the Fe-2201's.

Title: Effect of Quasicrystal Phase Particle Dispersion on Mechanical Properties in Mg-Zn-Al lloys

Author(s): Somekawa, H (Somekawa, Hidetoshi); Osawa, Y (Osawa, Yoshiaki); Singh, A Singh, Alok); Mukai, T (Mukai, Toshiji)

Source: MATERIALS TRANSACTIONS Volume: 52 Issue: 6 Pages: 1111-1115 DOI: 0.2320/matertrans.MC201014 Published: JUN 11 2011

Abstract: Four kinds of Mg-x mass%Zn-y mass%Al (x = 6, 8, 10, 12 and y = 3, 4, 5, 6) alloys, ach with a grain size of 2 similar to 3 gm and containing quasicrystal phase particles, were uccessfully produced by casting and extrusion. These rare-earth free wrought processed agnesium alloys showed a reduction in mechanical asymmetry and a weak basal texture. lthough the yield strength improved, the elongation decreased with increasing volume fraction f quasicrystal phase particle. The decrease in ductility was related to the existence of coarse uasicrystal phase particles. The strength was affected by the interface strength mechanism; owever, the coherency strain in the quasicrystal phase was smaller than that in the cohase, due to the strong matching between the matrix and the quasicrystal phase. [doi: 0.2320/matertrans.MC201014]

Title: Medium-range icosahedral order in quasicrystal-forming Zr(2)Pd binary metallic glass

Author(s): Huang, L (Huang, Li); Fang, XW (Fang, X. W.); Wang, CZ (Wang, C. Z.); Kramer, MJ (Kramer, M. J.); Ding, ZJ (Ding, Z. J.); Ho, KM (Ho, K. M.)

Source: APPLIED PHYSICS LETTERS Volume: 98 Issue: 23 Article Number: 231906 DOI: 10.1063/1.3597302 Published: JUN 6 2011

Abstract: Medium-range order in Zr(2)Pd metallic glass was studied using a combination of x-ray diffraction experiment and atomistic simulations. We show that, in contrast to earlier experimental interpretations, the icosahedral-like polyhedron is centered around Pd, rather than Zr. Furthermore, we find that the ordered icosahedral packing around Pd extends to the third shell in the way similar to that in the Bergman-type clusters. The existence of Bergman-type clusters sheds interesting light into the formation of nanoquasicrystal phase during cprocess of Zr(2)Pd metallic glass. (C) 2011 American Institute of Physics. [doi:10.1063/1.3597302]

Title: Atomic structure of nanoscale quasicrystal-forming Zr-noble metal binary metallic glasses

Author(s): Saida, J (Saida, J.); Itoh, K (Itoh, K.); Sanada, T (Sanada, T.); Sato, S (Sato, S.); Imafuku, M (Imafuku, M.); Ohnuma, M (Ohnuma, M.); Inoue, A (Inoue, A.)

Source: JOURNAL OF ALLOYS AND COMPOUNDS Volume: 509 Pages: S27-S33 DOI: 10.1016/j.jallcom.2010.12.076 Supplement: 1 Published: JUN 2011

Abstract: We report the results of the local structural evaluation and mechanism of QC formation in the Zr(70)Pd(30) and Zr(80)Pt(20) glassy alloys. Voronoi analysis indicates the difference of local environment between two alloys. The perfect icosahedron frequently exists around Zr atom and major polyhedra have prism-like structure around Pd in Zr(70)Pd(30). In contrast, icosahedral-like distorted polyhedra formation is favorable around Pt as well as Zr in Zr(80)Pt(20). It is therefore, concluded that the quasicrystallization originates from the medium-range order based on the Zr-centered perfect icosahedron and the Pd-centered prism-like ones remain during the QC phase formation in Zr(70)Pd(30). Icosahedral-like local structure around Zr and Pt might contribute together to the nucleation of QC phase in Zr(80)Pt(20). This feature with a different mechanism of QC formation in the two alloys may correlate to the difference of solute concentration and the structure of stable crystalline phase after the decomposition of QC phase. (C) 2010 Elsevier B.V. All rights reserved.

Update: 15-Jul-2011

Title:
THE Al-Cr-Fe PHASE DIAGRAM. I. PHASE EQUILIBRIA AT SUBSOLIDUS TEMPERATURES OVER COMPOSITION RANGE 58-100 AT.% Al
Authors:
Khoruzha, VG; Kornienko, KE; Pavlyuchkov, DV; Grushko, B; Velikanova, TY Author Full Names: Khoruzha, V. G.; Kornienko, K. E.; Pavlyuchkov, D. V.; Grushko, B.; Velikanova, T. Ya
Source:
POWDER METALLURGY AND METAL CERAMICS 50 (1-2): 83-97 MAY 2011
Abstract:
Based on transmission and scanning electron microscopy, x-ray diffraction, electron microprobe and differential thermal analyses, the solidus surface of the ternary Al-Cr-Fe system is constructed for the first time on the concentration triangle over composition range 58-100 at.% Al. Four ternary compounds, D-3, O-1, H, and epsilon, with decagonal, orthorhombic base-centered, hexagonal, and orthorhombic primitive lattices participate in phase equilibria on the solidus surface. Solid solutions based on aluminum and binary compounds as well as ternary phases form 12 single-phase surfaces, 25 ruled surfaces of two-phase equilibria bounding two-phase regions, and 14 three-phase isothermal planes corresponding to invariant four-phase equilibria on the solidus surface.
Title:
Magnetic structure of azurite above the magnetization plateau at 1/3 of saturation
Authors:
Aimo, F; Kramer, S; Klanjsek, M; Horvatic, M; Berthier, C Author Full Names: Aimo, F.; Kraemer, S.; Klanjsek, M.; Horvatic, M.; Berthier, C.
Source:
PHYSICAL REVIEW B 84 (1): Art. No. 012401 JUL 1 2011
Abstract:
The transition from the 1/3 magnetization plateau toward saturation magnetization in azurite has been studied by low-temperature, high-magnetic-field, high-frequency proton nuclear magnetic resonance (NMR). The observed symmetrical splitting of the NMR spectra is incompatible with the longitudinal incommensurate order appearing when the longitudinal correlation function becomes dominant over the transverse one, which is the expected framework for the existence of the 2/3 magnetization plateau. The spectra are instead interpreted in terms of a more standard transverse antiferromagnetic (canted) order.
Title:
Mechanism of exchange striction of ferroelectricity in multiferroic orthorhombic HoMnO3 single crystals
Authors:
Lee, N; Choi, YJ; Ramazanoglu, M; Ratcliff, W; Kiryukhin, V; Cheong, SW Author Full Names: Lee, N.; Choi, Y. J.; Ramazanoglu, M.; Ratcliff, W., II; Kiryukhin, V.; Cheong, S. -W.
Source:
PHYSICAL REVIEW B 84 (2): Art. No. 020101 JUL 1 2011
Abstract:
E-type perovskite magnet HoMnO3 is considered to be a prototype Mn-Mn exchange-striction driven multiferroic. We have grown orthorhombic HoMnO3 single crystals and studied the directional dependence of their electric polarization P. The direction of P is not along the crystallographic a axis, as predicted, but along the c axis. The magnetic state is incommensurate. The direction P along the c axis is primarily induced by Ho-Mn exchange striction, and Mn-Mn striction in the incommensurate spin state leads to an antiferroelectric order along the a axis. We predict the rotation of P with temperature in commensurate E-type RMnO3 (R denotes magnetic rare earth).
Title:
First-order nature of the ferromagnetism in CeIn2 investigated using muon spin rotation and by systematic substitution of La for Ce
Authors:
Rojas, DP; Espeso, JI; Fernandez, JR; Sal, JCG; Rusu, C; Andreica, D; Dudric, R; Amato, A Author Full Names: Rojas, D. P.; Espeso, J. I.; Rodriguez Fernandez, J.; Gomez Sal, J. C.; Rusu, C.; Andreica, D.; Dudric, R.; Amato, A.
Source:
PHYSICAL REVIEW B 84 (2): Art. No. 024403 JUL 5 2011
Abstract:
The nature of the first-order ferromagnetic transition in binary CeIn2 alloy is investigated by muon spin rotation (mu SR) measurements and chemical substitution of Ce by La in the La1-xCexIn2 (0.9 <= x <= 1.0) series of alloys. Below 22 K, the analysis of mu SR spectra shows two spin precession frequencies associated with the local field at the muon site created by the surrounding ferromagnetic ordered magnetic moments. These frequencies abruptly disappear above T-C, indicating the first-order character of this transition, as previously reported. For temperatures between 22 and 24 K, the shape of the mu SR spectra indicates the existence of an additional magnetic phase with features of an incommensurate magnetic structure. The presence of this magnetic phase is supported by dc(ac)- magnetic susceptibility and specific-heat results obtained on chemical diluted samples, which also show a magnetic contribution above the ferromagnetic transition. The combined analysis of these results clarifies the first-order character of the ferromagnetic transition in CeIn2, based on the existence of an intermediate magnetic phase between the paramagnetic and ferromagnetic states.
Title:
Commensurate-incommensurate phase transition in bilayer graphene
Authors:
Popov, AM; Lebedeva, IV; Knizhnik, AA; Lozovik, YE; Potapkin, BV Author Full Names: Popov, Andrey M.; Lebedeva, Irina V.; Knizhnik, Andrey A.; Lozovik, Yurii E.; Potapkin, Boris V.
Source:
PHYSICAL REVIEW B 84 (4): Art. No. 045404 JUL 5 2011
Abstract:
A commensurate-incommensurate phase transition in bilayer graphene is investigated in the framework of the Frenkel-Kontorova model extended to the case of two interacting chains of particles. Analytic expressions are derived to estimate the critical unit elongation of one of the graphene layers at which the transition to the incommensurate phase takes place, the length and formation energy of incommensurability defects (IDs), and the threshold force required to start relative motion of the layers on the basis of dispersion-corrected density functional theory (DFT-D) calculations of the interlayer interaction energy as a function of the relative position of the layers. These estimates are confirmed by atomistic calculations using the DFT-D based classical potential. The possibility to measure the barrier for relative motion of graphene layers by the study of formation of IDs in bilayer graphene is discussed.
Title:
Enhanced piezoelectric and magnetic properties of Bi1-xCaxFe1-x/2Nbx/2O3 solid solutions
Authors:
Troyanchuk, IO; Tereshko, NV; Karpinsky, DV; Kholkin, AL; Kopcewicz, M; Barner, K Author Full Names: Troyanchuk, I. O.; Tereshko, N. V.; Karpinsky, D. V.; Kholkin, A. L.; Kopcewicz, M.; Baerner, K.
Source:
JOURNAL OF APPLIED PHYSICS 109 (11): Art. No. 114102 JUN 1 2011
Abstract:
An investigation of the crystal structure, the magnetic and the piezoelectric properties of polycrystalline Bi1-xCaxFe1-x/2Nbx/2O3 (I) and Bi1-xPbxFe1-x/2Nbx/2O3 (II) systems was performed by x-ray diffraction, Mossbauer spectroscopy, vibrating sample magnetometry, and piezoresponse force microscopy. It is shown that an increasing niobium content induces a polar-to-nonpolar morphotropic boundary near x = 0.19 (I) and x = 0.3 (II). Within the polar region of the system (I), (0.15 <= x <= 0.18), the solid solutions are homogeneous weak ferromagnets whereas compounds of the system (II) do not exhibit an appreciable spontaneous magnetization. It is assumed that chemical substitutions leading to a decrease of the initial volume of the unit cell favor the stabilization of the weak ferromagnetic state within the rhombohedral ferroelectric phase. The piezoresponse is significantly enhanced near the morphotropic boundary. The piezoelectric properties of the parent antiferromagnet BiFeO3, harboring a cycloidal spatially modulated spin structure, are compared with those of the polar weak ferromagnet Bi0.82Ca0.18Fe0.91Nb0.09O3. (C) 2011 American Institute of Physics. [doi:10.1063/1.3594251]

Update: 8-Jul-2011

Title:
Phase Transition and Mechanical Properties of Al-Based Composites Reinforced by Al72Ni12Co16 Decagonal Quasicrystalline Particles
Authors:
Zhu, M; Yang, GC; Cheng, SL; Yao, LJ; Zhou, YH Author Full Names: Zhu Man; Yang Gencang; Cheng Suling; Yao Lijuan; Zhou Yaohe
Source:
RARE METAL MATERIALS AND ENGINEERING 39 (9): 1604-1608 SEP 2010
Abstract:
Aluminum-based composites, using Al72Ni12Co16 decagonal quasicrystalline as reinforcing particles and pure Al and Al-5.5%Zn alloys (mass fraction) as base alloy, were fabricated. The microstructure and the particle distribution of the composite were analyzed by scanning electron microscopy (SEM) and energy dispersive spectrum (EDS). Results show that the phase transition occurs because the decagonal quaicrystalline particles are unstable in the melt. Regular polygon-like theta-phase distributes in the Al matrix, with particle sizes mainly ranging from 3.45-40 mu m. At the same time, fine strip-like gamma-phase with the size of 1.15-8.57 mu m are formed along the grain boundaries. Mechanical property testing results reveal that, due to the existence of the final crystallized phases, yield strength, ultimate tensile strength and Young's modulus of the composites are improved, but the elongation is decreased rapidly.
Title:
Lattice modulation induced by magnetic order in the magnetoelectric helimagnet Ba0.5Sr1.5Zn2Fe12O22
Authors:
Asaka, T; Yu, XZ; Hiraoka, Y; Kimoto, K; Hirayama, T; Kimura, T; Matsui, Y Author Full Names: Asaka, T.; Yu, X. Z.; Hiraoka, Y.; Kimoto, K.; Hirayama, T.; Kimura, T.; Matsui, Y.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 130401 APR 26 2011
Abstract:
By means of an electron diffraction technique, crystal-lattice modulations were investigated for a hexaferrite, Ba0.5Sr1.5Zn2Fe12O22, showing a helimagnetic order below T-N = 320 K. We observed a lattice modulation with a wave vector Q = (0,0,3 delta) below T-N. The value of delta varies between similar to 0.23 and 0.5 as a function of temperature and corresponds well to that of the magnetic modulation vector. By applying magnetic fields, Ba0.5Sr1.5Zn2Fe12O22 was found to exhibit successive changes in the lattice modulation, accompanied by the modifications of the helical magnetic order. We concluded that the observed lattice modulation is induced by the helical magnetic order via exchange magnetostriction.
Title:
Effects of pressure and temperature on the thermal conductivity of Sn2P2S6
Authors:
Andersson, O; Chobal, O; Rizak, I; Rizak, V; Sabadosh, V Author Full Names: Andersson, O.; Chobal, O.; Rizak, I.; Rizak, V.; Sabadosh, V.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 134121 APR 26 2011
Abstract:
The thermal conductivity kappa of the ferroelectric, paraelectric, and incommensurate phases of polycrystalline Sn2P2S6 has been measured in the 0.1-0.7 GPa range. The thermal conductivity kappa of the ferroelectric phase decreases with increasing pressure p. This unusual behavior, which is found in only a few other phases, is attributed to a negative Gruneisen parameter. The temperature T dependence of kappa for the ferroelectric phase (kappa similar to T-1) is well described by the Debye model for kappa, with three-phonon Umklapp scattering serving as the dominant scattering mechanism near and above the Debye temperature (similar to 100 K) up to a few tenths of degrees below the ferro- to paraelectric phase transition, where kappa(T) gradually changes and becomes temperature independent upon further heating. The thermal conductivity of the paraelectric and incommensurate phases was temperature independent and indistinguishable. Possible causes for the unu! sually weak T dependence at high temperatures and implications of the p dependence of kappa are discussed.
Title:
Noncollinear spin-density-wave antiferromagnetism in FeAs
Authors:
Rodriguez, EE; Stock, C; Krycka, KL; Majkrzak, CF; Zajdel, P; Kirshenbaum, K; Butch, NP; Saha, SR; Paglione, J; Green, MA Author Full Names: Rodriguez, E. E.; Stock, C.; Krycka, K. L.; Majkrzak, C. F.; Zajdel, P.; Kirshenbaum, K.; Butch, N. P.; Saha, S. R.; Paglione, J.; Green, M. A.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 134438 APR 28 2011
Abstract:
The nature of the magnetism in the simplest iron arsenide is of fundamental importance in understanding the interplay between localized and itinerant magnetism and superconductivity. We present the magnetic structure of the itinerant monoarsenide FeAs with the B31 structure. Powder neutron diffraction confirms incommensurate modulated magnetism with wave vector q = (0.395 +/- 0.001)c* at 4 K, but can not distinguish between a simple spiral and a collinear spin-density-wave structure. Polarized single-crystal diffraction confirms that the structure is best described as a noncollinear spin-density wave arising from a combination of itinerant and localized behavior with spin amplitude along the b-axis direction being (15 +/- 5)% larger than in the a direction. Furthermore, the propagation vector is temperature dependent, and the magnetization near the critical point indicates a two-dimensional Heisenberg system. The magnetic structures of closely related systems are discussed and compared to that of FeAs.
Title:
Stabilization of commensurate antiferromagnetism in CePt2In7 by pressure up to 2.4 GPa: In-115 NMR and NQR under zero field
Authors:
Sakai, H; Tokunaga, Y; Kambe, S; Lee, HO; Sidorov, VA; Tobash, PH; Ronning, F; Bauer, ED; Thompson, JD Author Full Names: Sakai, H.; Tokunaga, Y.; Kambe, S.; Lee, H. -O.; Sidorov, V. A.; Tobash, P. H.; Ronning, F.; Bauer, E. D.; Thompson, J. D.
Source:
PHYSICAL REVIEW B 83 (14): Art. No. 140408 APR 19 2011
Abstract:
Zero-field In-115-nuclear magnetic resonance (NMR) has been used to study single crystals of CePt2In7, a heavy-fermion antiferromagnet with a Neel temperature (T-N) of 5.2 K at ambient pressure. Narrow linewidths of In-115-nuclear quadrupolar resonance spectra are observed from each of three crystallographically inequivalent In(1), In(2), and In(3) sites. The NMR spectra under zero field near the 3 nu(Q) line of the orthorhombic In(3) sites are tracked by temperatures down to 1.6 K and by hydrostatic pressures up to 2.4 GPa. These data reveal the coexistence of commensurate and incommensurate antiferromagneic orders at ambient pressure and that the commensurate ordering is stabilized by increasing pressures where bulk superconductivity emerges.
Title:
Field-induced incommensurate-to-commensurate phase transition in the magnetoelectric hexaferrite Ba0.5Sr1.5Zn2(Fe1-xAlx)(12)O-22
Authors:
Lee, HB; Song, YS; Chung, JH; Chun, SH; Chai, YS; Kim, KH; Reehuis, M; Prokes, K; Mat'as, S Author Full Names: Lee, Hak Bong; Song, Young-Sang; Chung, Jae-Ho; Chun, Sae Hwan; Chai, Yi Sheng; Kim, Kee Hoon; Reehuis, M.; Prokes, K.; Mat'as, S.
Source:
PHYSICAL REVIEW B 83 (14): Art. No. 144425 APR 26 2011
Abstract:
Using neutron diffraction, we investigated the spin structures of magnetoelectric hexaferrite, Ba0.5Sr1.5Zn2(Fe1-xAlx)(12)O-22 (x = 0.08) under a magnetic field (H perpendicular to c). When the crystal was cooled in a zero field, longitudinal spin cones were observed at low temperatures. These incommensurate phases, however, were replaced by the commensurate phase [ k(1) = (0,0,3/2)] when the ferroelectricity was induced by an external field perpendicular to the c axis. Magnetic structure refinement confirms that this commensurate order is compatible with the spin-current polarization. We argue that planar magnetic anisotropy plays an important role in determining the magnetic structure that is responsible for its magnetoelectricity.
Title:
Electronically phase-separated charge-density waves in Lu2Ir3Si5
Authors:
Lee, MH; Chen, CH; Chu, MW; Lue, CS; Kuo, YK Author Full Names: Lee, M. H.; Chen, C. H.; Chu, M. -W.; Lue, C. S.; Kuo, Y. K.
Source:
PHYSICAL REVIEW B 83 (15): Art. No. 155121 APR 26 2011
Abstract:
We report the investigation of charge density waves (CDW's) in Lu2Ir3Si5 by electron diffraction and dark-field imaging in transmission electron microscopy using superlattice diffraction spots. The CDW state is confirmed by the presence of superlattice reflections. Most interestingly, the CDW state at low temperatures is found to be electronically phase separated, with the coexistence of CDW domains and low-temperature normal phase domains. With a change in temperature, unlike other typical incommensurate CDW systems in which commensurability varies with temperature, we find that commensurability remains unchanged in the present case and that the predominant change is in the redistribution of the area ratio of the two coexisting phases, which is clearly revealed in the dark-field images obtained from the CDW superlattice reflections. The electronic phase separation in the CDW state of Lu2Ir3Si5 is unprecedented in CDW systems, and its temperature dependence is also anomalous.
Title:
Emergent antiferromagnetism in a d-wave superconductor with strong paramagnetic pair-breaking
Authors:
Hatakeyama, Y; Ikeda, R Author Full Names: Hatakeyama, Yuhki; Ikeda, Ryusuke
Source:
PHYSICAL REVIEW B 83 (22): Art. No. 224518 JUN 28 2011
Abstract:
It is theoretically shown that, in the fourfold symmetric d-wave superconducting phase, a paramagnetic pair-breaking (PPB) enhanced sufficiently by increasing the applied magnetic field induces not only the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state but also an incommensurate antiferromagnetic (AFM) order with the Q vector parallel to a gap node. This AFM ordering tends to occur only below H-c2 at low temperatures, i.e., in the presence of a nonvanishing superconducting energy gap Delta rather than in the normal phase. Through a detailed study on the resulting AFM order and its interplay with the FFLO spatial modulation of Delta, it is argued that the strange high-field, low-temperature (HFLT) superconducting phase of CeCoIn5 is a coexisting phase of the FFLO and incommensurate AFM orders, and that this PPB mechanism of an AFM ordering is also the origin of the AFM quantum critical fluctuation which has occurred close to H-c2(0) in several unconventional superconductors including CeCoIn5.
Title:
Magnetic fluctuations and self-energy effects in two-dimensional itinerant systems with a van Hove singularity in the electronic spectrum
Authors:
Igoshev, PA; Irkhin, VY; Katanin, AA Author Full Names: Igoshev, P. A.; Irkhin, V. Yu.; Katanin, A. A.
Source:
PHYSICAL REVIEW B 83 (24): Art. No. 245118 JUN 22 2011
Abstract:
We investigate a competition of tendencies toward ferromagnetic and incommensurate order in two-dimensional fermionic systems within functional renormalization-group technique, accounting for the self-energy corrections and using temperature as a scale parameter. We assume that the Fermi surface (FS) is substantially curved and lies in the vicinity of van Hove singularity points. It is shown that the character of magnetic fluctuations is strongly asymmetric with respect to the Fermi level position relative to van Hove singularity (VHS). For the Fermi level above VHS, we find at low temperatures dominant incommensurate magnetic fluctuations, while below the VHS level, we find indications for the ferromagnetic ground state. In agreement with the Mermin-Wagner theorem, at finite temperatures and in small magnetic fields, we obtain small magnetization, which appears to be a power-law function of magnetic field. It is found that the FS curvature is slightly increased by correlation effects, and the renormalized bandwidth decreases at sufficiently low temperatures.
Title:
Modulated martensite: why it forms and why it deforms easily
Authors:
Kaufmann, S; Niemann, R; Thersleff, T; Rossler, UK; Heczko, O; Buschbeck, J; Holzapfel, B; Schultz, L; Fahler, S Author Full Names: Kaufmann, S.; Niemann, R.; Thersleff, T.; Roessler, U. K.; Heczko, O.; Buschbeck, J.; Holzapfel, B.; Schultz, L.; Faehler, S.
Source:
NEW JOURNAL OF PHYSICS 13: Art. No. 053029 MAY 16 2011
Abstract:
Diffusionless phase transitions are at the core of the multifunctionality of (magnetic) shape memory alloys, ferroelectrics and multiferroics. Giant strain effects under external fields are obtained in low symmetric modulated martensitic phases. We outline the origin of modulated phases, their connection with tetragonal martensite and consequences owing to their functional properties by analysing the martensitic microstructure of epitaxial Ni-Mn-Ga films from the atomic to the macroscale. Geometrical constraints at an austenite-martensite phase boundary act down to the atomic scale. Hence, a martensitic microstructure of nanotwinned tetragonal martensite can form. Coarsening of twin variants can reduce twin boundary energy, a process we could observe from the atomic to the millimetre scale. Coarsening is a fractal process, proceeding in discrete steps by doubling twin periodicity. The collective defect energy results in a substantial hysteresis, which allows the retention of modulated martensite as a metastable phase at room temperature. In this metastable state, elastic energy is released by the formation of a 'twins within twins' microstructure that can be observed from the nanometre to the millimetre scale. This hierarchical twinning results in mesoscopic twin boundaries. Our analysis indicates that mesoscopic boundaries are broad and diffuse, in contrast to the common atomically sharp twin boundaries of tetragonal martensite. We suggest that the observed extraordinarily high mobility of such mesoscopic twin boundaries originates from their diffuse nature that renders pinning by atomistic point defects ineffective.
Title:
Textures and mechanical properties in rare-earth free quasicrystal reinforced Mg-Zn-Zr alloys prepared by extrusion
Authors:
Ohhashi, S; Kato, A; Demura, M; Tsai, AP Author Full Names: Ohhashi, S.; Kato, A.; Demura, M.; Tsai, A. P.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 528 (18): 5871-5874 JUL 15 2011
Abstract:
Microstructure and mechanical properties of quasicrystals dispersed Mg alloys prepared by warm extrusion of the mixtures of Mg and Zn-Mg-Zr quasicrystalline (Qc) powders have been studied. Strong texture oriented along a [10 (1) over bar 0] direction observed in pure Mg was reduced in Qc-dispersed samples, as verified by pole figure method and electron back scattering diffraction. The ultimate tensile strengths at 150 degrees C for Qc-dispersed extrusions were much higher than 110 MPa for pure Mg, which drastically reached 156 MPa for 15 wt.% Qc by preventing the motion of dislocations. Elongation was improved by the randomization of grain orientation: from 5.7% for pure Mg to 12.9% for 10 wt.% Qc at room temperature; from 15% for pure Mg to 37.1% for 5 wt.% Qc at 150 degrees C. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Does the modulated magnetic structure of BiFeO3 change at low temperatures?, (vol 18, pg 2069, 2006)
Authors:
Przenioslo, R; Palewicz, A; Regulski, M; Sosnowska, I; Ibberson, RM; Knight, KS Author Full Names: Przenioslo, R.; Palewicz, A.; Regulski, M.; Sosnowska, I.; Ibberson, R. M.; Knight, K. S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (27): Art. No. 279501 JUL 11 2011
Title:
Kaleidoscopic morphologies from ABC star-shaped terpolymers
Authors:
Matsushita, Y; Hayashida, K; Dotera, T; Takano, A Author Full Names: Matsushita, Yushu; Hayashida, Kenichi; Dotera, Tomonari; Takano, Atsushi
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (28): Art. No. 284111 JUL 20 2011
Abstract:
Star-shaped terpolymers of the ABC type composed of incompatible polymer components give a variety of ordered structures with mesoscopic length scales depending on their composition ratio. Their peculiar features are summarized in this report. Polymer components adopted are polyisoprene (I), polystyrene (S) and poly(2-vinylpyridine) (P), and many monodisperse samples of the IXSY P-Z type were anionically prepared. Firstly our focus is on molecules of the I1.0S1.0Px1 type, where x(1) is only a variable. The complex but systematic morphology change was displayed within the range 0.2 <= x(1) <= 10, that is, their structures change from spherical plus lamellae structure for I1.0S1.0P0.2 to periodic tilings (0.4 <= x(1) <= 1.9), then to lamellae-in-lamella (3.0 <= x(1) <= 4.9) and lamellae-in-cylinder (7.9 <= x(1) <= 10) structures with increasing x(1). Here if we pay attention to the structural variation of the P domain inclusively, it transforms from sphere to cylinder, lamel! la and then to matrix, which is the same as that for linear polymers. Among them, several periodic Archimedean tiling patterns can be naturally formed when the relative lengths of the three chains are close to one another. Moreover, it has been found that the tiling zone is spread out widely. For example, the series I1.0S1.8Px2 (with 0.8 <= x(2) <= 2.9) and the other series I1.0SyP2.0 (with 1.1 <= y <= 2.7) show mostly Archimedean tilings. Additionally, block copolymer/homopolymer blends with a composition of I1.0S2.7P2.5 reveal a quasicrystalline tiling with dodecagonal symmetry. Furthermore, a zinc-blende-type four-branched network structure was created just a little outside of the tiling region for a block copolymer/homopolymer blend of I1.0S2.3P0.8. When some more asymmetry in chain length is introduced, hyperbolic tiling on a gyroid membrane has successfully been constructed for the sample I1.0S1.8P3.2 and it transforms into a hierarchical cylinders-in-lamella structure with further increase in P content to I1.0S1.8P6.4. Thus, kaleidoscopic morphologies have been generated from ABC star-shaped terpolymers and their structural change has turned out to be very sensitive to relative compositions.
Title:
Ductile quasicrystalline alloys (vol 76, pg 967, 2000)
Authors:
Inoue, A; Chen, MW; Sakurai, T; Zhang, T; Saida, J; Matsushita, M Author Full Names: Inoue, A.; Chen, M. W.; Sakurai, T.; Zhang, T.; Saida, J.; Matsushita, M.
Source:
APPLIED PHYSICS LETTERS 98 (25): Art. No. 259902 JUN 20 2011

Update: 1-Jul-2011

Title:
Organic molecular compounds with modulated crystal structures
Authors:
Schonleber, A Author Full Names: Schoenleber, Andreas
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 226 (6): 499-517 2011
Abstract:
Even though the higher-dimensional superspace approach is an established method to describe aperiodic crystal structures, it is not yet fully considered and applied by a larger community of scientists. In this contribution the structural description of incommensurately and commensurately modulated molecular compounds is discussed and it is shown, that the higher-dimensional superspace approach is an elegant way for an exact structural description and an exact crystal-chemical analysis of such structures. While discussing several modulated molecular compounds, the idea behind the higher-dimensional superspace approach is shown. On the examples treated in the discussion it is explained, how to understand and how to interprete modulated molecular compounds. Also a short introduction is given to the higher-dimensional superspace approach itself, to the basic principles and to the applied nomenclature.
Title:
Medium-range icosahedral order in quasicrystal-forming Zr2Pd binary metallic glass
Authors:
Huang, L; Fang, XW; Wang, CZ; Kramer, MJ; Ding, ZJ; Ho, KM Author Full Names: Huang, Li; Fang, X. W.; Wang, C. Z.; Kramer, M. J.; Ding, Z. J.; Ho, K. M.
Source:
APPLIED PHYSICS LETTERS 98 (23): Art. No. 231906 JUN 6 2011
Abstract:
Medium-range order in Zr2Pd metallic glass was studied using a combination of x-ray diffraction experiment and atomistic simulations. We show that, in contrast to earlier experimental interpretations, the icosahedral-like polyhedron is centered around Pd, rather than Zr. Furthermore, we find that the ordered icosahedral packing around Pd extends to the third shell in the way similar to that in the Bergman-type clusters. The existence of Bergman-type clusters sheds interesting light into the formation of nanoquasicrystal phase during crystallization process of Zr2Pd metallic glass. (C) 2011 American Institute of Physics. [doi:10.1063/1.3597302]

Update: 24-Jun-2011

Title:
THE FIBONACCI-PENROSE SEMIGROUP FORMALISM AND MORPHOGENETIC SYNTHESIS OF QUASICRYSTAL MOSAICS
Authors:
Yudin, VV; Startzev, ES; Permyakova, IG Author Full Names: Yudin, V. V.; Startzev, E. S.; Permyakova, I. G.
Source:
THEORETICAL AND MATHEMATICAL PHYSICS 167 (1): 517-537 APR 2011
Abstract:
We construct the group bundle for the inverse Fibonacci semigroups in the axiomatic approach framework. The proper Fibonacci semigroup is the corresponding group bundle for the Penrose semigroups, which can be interpreted as the generating grammar of the morphogenetic synthesis of the pentasymmetric Penrose parquet in the numbers of tiling by golden rhombuses. This morphogenetic synthesis of the Penrose parquet satisfies the scaling principle. Parquet plates are not absolutely rigid, and the relations between their metric characteristics are governed by the golden section and other magic numbers. The characteristic form factors of three-level dual alphabets are the corresponding invariants. We realize the morphogenetic synthesis in the examples of square-octagonal and bihexagonal lattices. We consider cumulative properties of magic series and the evolutionary aspects of semigroup orbits in the entropy representation.
Title:
Improvement of microstructure and mechanical properties of Mg-8Gd-3Y by adding Mg3Zn6Y icosahedral phase alloy
Authors:
Kang, HJ; Wu, SP; Li, XZ; Guo, JJ; Wang, Y Author Full Names: Kang, Huijun; Wu, Shiping; Li, Xinzhong; Guo, Jingjie; Wang, Ye
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 528 (16-17): 5585-5591 JUN 25 2011
Abstract:
Mg-Zn-Y quasicrystal alloy (QA) particles reinforced composite was prepared using an adscititious method, and characterized using scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and tensile testing technique at room temperature. Experimental results indicate that alpha-Mg columnar dendrite gradually becomes fine equiaxed dendrite and ellipsoidal cellular dendrite as more Mg-Zn-Y QA particles are added into the matrix alloy. Thread-like Mg-24(Gd,Y)(5) phases and rod-like Mg-5(Gd,Y) phases are replaced by lamellar Mg-24(Zn,Gd,Y)(5) compounds and granule Mg3Zn6(Y,Gd) quasicrystal l-phases. The ultimate tensile strength and yield strength of the composite increase by about 45 MPa and 20 MPa respectively when the amount of QA particles added increases from 3% to 15%. It can therefore be concluded that the microstructure and mechanical properties of Mg-8Gd-3Y alloy can be improved by adding QA particles. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Inelastic neutron and x-ray scattering from incommensurate magnetic systems
Authors:
Boni, P; Roessli, B; Hradil, K Author Full Names: Boeni, Peter; Roessli, Bertrand; Hradil, Klaudia
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (25): Art. No. 254209 JUN 29 2011
Abstract:
Neutrons and x-rays are powerful probes for studying magnetic and lattice excitations in strongly correlated materials over very wide ranges of momentum and energy transfers. In the focus of the present work are the incommensurate magnetic systems MnSi and Cr. Under application of a magnetic field, helically ordered MnSi transforms into a weak itinerant ferromagnet. Using polarized neutrons we demonstrate that the Stoner excitations are spin-flip excitations. The amplitude (longitudinal) fluctuations associated with the magnon modes are already strong far away from T-c. Interestingly, even the non-spin-flip excitations associated with the Stoner modes are observable. In Cr, we have observed Kohn anomalies in the phonon spectrum at those incommensurate positions in reciprocal space, where the spin density wave is observed. The corresponding phonon and magnon modes are not coupled. In addition, an anomalous softening of a transverse phonon branch along the N-H zone boundary line is observed that is caused by strong electron-phonon coupling. High resolution neutron scattering indicates that the low energy Fincher-Burke excitations may rather correspond to localized modes in momentum and energy and not to propagating collective modes. Finally, we demonstrate that in the near future it may become feasible to investigate excitations in very small samples, thus allowing us to measure the dynamics of strongly correlated materials under extreme conditions and in the vicinity of quantum phase transitions.
Title:
Fano line shape and anti-crossing of Raman active E-2g peaks in the charge density wave state of NbSe2
Authors:
Mialitsin, A Author Full Names: Mialitsin, Aleksej
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 72 (5): 568-571 Sp. Iss. SI MAY 2011
Abstract:
Low energy Raman scattering from the ab-plane of the 2H polytype single crystal NbSe2 has been investigated in the normal (N), incommensurate charge density wave (ICDW) and superconducting (SC) phases. The temperature dependence of the polarization resolved Raman response has been obtained for the excitation wavelength of 647 nm and fitted to phenomenological models for the E-2g and A(1g) symmetry channels. The A(1g) response can be fitted by a simple damped oscillator peak superimposed on continuous background. The E-2g response displays an anti-resonance interference pattern between the inter-layer phonon and the CDW-induced mode such that a hybridized configuration (Fano line shape [1]) is required for modelling. The polarization specific peak maxima positions and line widths as a function of temperature, deduced in this manner, are presented. Partial suppression of the electronic continuum scattering in the Raman shift range up to 110 cm(-1) in the A(1g) symmetry channel and beyond 300 cm(-1) in the E-2g symmetry channel is indicative of high energy electronic states far away from the Fermi surface participating in the ICDW formation. Published by Elsevier Ltd.
Title:
Atomic structure of nanoscale quasicrystal-forming Zr-noble metal binary metallic glasses
Authors:
Saida, J; Itoh, K; Sanada, T; Sato, S; Imafuku, M; Ohnuma, M; Inoue, A Author Full Names: Saida, J.; Itoh, K.; Sanada, T.; Sato, S.; Imafuku, M.; Ohnuma, M.; Inoue, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509: S27-S33 Suppl. 1 JUN 2011
Abstract:
We report the results of the local structural evaluation and mechanism of QC formation in the Zr70Pd30 and Zr80Pt20 glassy alloys. Voronoi analysis indicates the difference of local environment between two alloys. The perfect icosahedron frequently exists around Zr atom and major polyhedra have prism-like structure around Pd in Zr70Pd30. In contrast, icosahedral-like distorted polyhedra formation is favorable around Pt as well as Zr in Zr80Pt20. It is therefore, concluded that the quasicrystallization originates from the medium-range order based on the Zr-centered perfect icosahedron and the Pd-centered prism-like ones remain during the QC phase formation in Zr70Pd30. Icosahedral-like local structure around Zr and Pt might contribute together to the nucleation of QC phase in Zr80Pt20. This feature with a different mechanism of QC formation in the two alloys may correlate to the difference of solute concentration and the structure of stable crystalline phase after the decomposition of QC phase. (C) 2010 Elsevier B.V. All rights reserved.
Title:
The quasicrystalline phase formation in Al-Cu-Cr alloys produced by mechanical alloying
Authors:
Sviridova, TA; Shevchukov, AP; Shelekhov, EV; Diakonov, DL; Tcherdyntsev, VV; Kaloshkin, SD Author Full Names: Sviridova, T. A.; Shevchukov, A. P.; Shelekhov, E. V.; Diakonov, D. L.; Tcherdyntsev, V. V.; Kaloshkin, S. D.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509: S299-S303 Suppl. 1 JUN 2011
Abstract:
Almost single-phase decagonal quasicrystal with periodicity of 1.26 nm along 10-fold axis was produced in Al69Cu21Cr10 and Al72.5Cu16.5Cr11 alloys using combination of mechanical alloying (MA) and subsequent annealing. Phase transformations of as-milled powders depending on annealing temperature in the range of 200-800 degrees C are examined. Since the transformations can be explained based on kinetic and thermodynamic reasons it seems that applied technique (short preliminary MA followed by the annealing) permits to produce the equilibrium phases rather than metastable ones. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Microstructures and mechanical properties of conventionally solidified Al63Cu25Fe12 alloy
Authors:
Gogebakan, M; Avar, B; Tarakci, M Author Full Names: Gogebakan, M.; Avar, B.; Tarakci, M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509: S316-S319 Suppl. 1 JUN 2011
Abstract:
In this study, the microstructures and mechanical properties of conventionally solidified Al63Cu25Fe12 alloy after different heat-treatments were investigated. The microstructures of the as-cast and subsequently heat-treated samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analysis (DTA). The XRD results showed the presence of quasicrystalline icosahedral phase (i-phase) together with crystalline phases corresponding to beta-AlFe(Cu) solid solution phase (beta-phase) and tau-AlCu(Fe) solid solution phase (tau-phase). The SEM investigations clearly showed the formation of i-phase with pentagonal dodecahedra structure. However, the i-phase together with beta-phase was also observed in the heat-treated samples and the peak intensity of the beta-phase decreased with increasing heat-treatment temperature. From the DTA curves, the melting point of i-phase was determined as 890 degrees C for this alloy composition. Mechanical properties of the as-cast and subsequently heat-treated samples were measured by a Vickers indenter. Results showed that the microhardness (HV) and the elastic modulus (E) of the as-cast sample were around 598 kg fmm(-2) (5.86 GPa) and 104 GPa, respectively. In addition, the characteristic of material plasticity (delta(H)) value was calculated to be 0.54. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Stability of the Sr2B3O6.5-delta Phases (B = Fe, Co, Ga): Existence Range, Structural and Physical Properties
Authors:
Desmoulins, H; Malo, S; Perez, O; Pelloquin, D; Maignan, A; Hervieu, M Author Full Names: Desmoulins, H.; Malo, S.; Perez, O.; Pelloquin, D.; Maignan, A.; Hervieu, M.
Source:
CHEMISTRY OF MATERIALS 23 (11): 2786-2794 JUN 14 2011
Abstract:
A large solid solution Sr-2(Fe3-xCox-yGay)O6.5-delta), isostructural with the modulated Fe-2201 and Co-2201-type structures, has been characterized using X-ray powder diffraction (XRPD), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS) analyses. The disorder phenomena have been studied using High Resolution Transmission Electron Microscopy (HREM). The evolution of the cell parameters, wavelength of the modulated structures, and transport properties are analyzed versus the three B (Fe, Co, Go) cation contents, showing a violation of the Vegard law for a ratio Fe/(Fe + Co + Go) close to x approximate to 0.6. By decreasing the Fe content from that x value, an abrupt variation of resistivity of about 2 orders of magnitude is observed. This spectacular behavior is associated with the creation of percolative - (Co-O-Co)- pathways. A double effect of the (Co/Ga) substitution for Fe is observed on the magnetic properties. First, the B-O-B magnetic interactions (B = Fe, Co, Ga) are diluted because Ga3+ is a d(10)s(0) cation and, second, the Co3+-O-Co3+ magnetic exchange in that structure is smaller than the Fe3+-O-Fe-3 ones. This explained why both the magnitude of the ferromagneto-like component and the T-N values are reduced as compared to the Fe-2201's.

Update: 17-Jun-2011

Title:
Symmetry mode analysis of the phase transitions in Rb2ZnBr4
Authors:
Zuniga, FJ; Perez-Mato, JM; Orobengoa, D; Petricek, V; Breczewski, T Author Full Names: Javier Zuniga, Fco; Manuel Perez-Mato, J.; Orobengoa, Danel; Petricek, Vaclav; Breczewski, Tomasz
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 226 (5): 454-466 2011
Abstract:
Crystal structures of low temperature phases HI, IV and V of rubidium zinc bromide have been determined by single crystal X-ray diffraction at 90 K, 85 K, and 30 K, respectively. The analysis of the structures in terms of symmetry-adapted modes of the high temperature prototype phase permits the identification of the modes responsible for each phase and to assess its thermal evolution. The primary mode responsible for the incommensurate and lock-in phases remains dominant throughout the whole transition sequence, maintaining its structure and slightly increasing its amplitude as temperature decreases. The two monoclinic phases IV and V are presumably due to the instability of a second mode associated with a single active irreducible representation. However, the presence with similar weights of several symmetry-adapted distortions of different symmetry indicates a strong hybridization in phase permits the identification of the softer normal modes. A symmetry-mode description of the structures of phase IV and V fully consistent with a simple Landau model, can then only be obtained if phase III is taken as effective parent phase. Besides the insight on the microscopic origin of the different phases, the symmetry modes were used as crystallographic coordinates in the refinement of the structure of phase V. The result shows the advantages of using these non-conventional collective structural parameters instead of individual atomic coordinates. The refinable parameters can be reduced to the amplitudes of those symmetry modes with significant weight in the distortions.
Title:
Spiral ground state against ferroelectricity in the frustrated magnet BiMnFe2O6
Authors:
Abakumov, AM; Tsirlin, AA; Perez-Mato, JM; Petricek, V; Rosner, H; Yang, T; Greenblatt, M Author Full Names: Abakumov, Artem M.; Tsirlin, Alexander A.; Perez-Mato, Juan Manuel; Petricek, Vaclav; Rosner, Helge; Yang, Tao; Greenblatt, Martha
Source:
PHYSICAL REVIEW B 83 (21): Art. No. 214402 JUN 2 2011
Abstract:
The spiral magnetic structure and underlying spin lattice of BiMnFe2O6 are investigated by low-temperature neutron powder diffraction and density functional theory band structure calculations. In spite of the random distribution of the Mn3+ and Fe3+ cations, this centrosymmetric compound undergoes a transition into an incommensurate antiferromagnetically ordered state below T-N similar or equal to 220 K. The magnetic structure is characterized by the propagation vector k = [0, beta, 0] with beta similar or equal to 0.14 and the P22(1)2(1)1'(0 beta 0)0s0s magnetic superspace symmetry. It comprises antiferromagnetic helixes propagating along the b axis. The magnetic moments lie in the ac plane and rotate about pi(1 + beta) similar or equal to 204.8-deg angle between the adjacent magnetic atoms along b. The spiral magnetic structure arises from the peculiar frustrated arrangement of exchange couplings in the ab plane. The antiferromagnetic coupling along the c axis cancels the possible electric polarization and prevents ferroelectricity in BiMnFe2O6.
Title:
Vacancy and substitutional impurities in the spin-density wave state of Cr from first principles
Authors:
Soulairol, R; Fu, CC; Barreteau, C Author Full Names: Soulairol, R.; Fu, Chu-Chun; Barreteau, C.
Source:
PHYSICAL REVIEW B 83 (21): Art. No. 214103 JUN 3 2011
Abstract:
Density functional theory (DFT) calculations are carried out to study magnetic and energetic properties of vacancy, and magnetic and nonmagnetic substitutional impurities (respectively Fe and Cu) in the ground state of bcc Cr, i.e., spin-density wave (SDW). We find the lowest energy site for all the defects to be around a magnetic node, as compared with the high-spin SDW sites and (100)- layered antiferromagnetic (AF) and nonmagnetic (NM) phases. The corresponding differences for vacancy formation energy are 0.29, 0.32, and 0.23 eV, respectively. The migration of a vacancy is revealed to be highly anisotropic in the SDW state, mainly confined in the nodal and adjacent planes. The energy barrier for such a quasi-bidimensional motion is indeed 0.52 eV lower than that for migration in perpendicular directions. Regarding magnetic modifications of the SDW introduced by point defects, they are confirmed to be weak and rather local at low defect concentrations (0.27% and 0.55%). Cu behaves similarly to a vacancy-inducing magnetic moment enhancement on neighboring Cr atoms. On the other side, the presence of Fe atoms leads to multiple energy minima with different local magnetic arrangements, particularly around a node, due to competition between neighboring Fe-Cr, Cr-Cr, and Fe-Fe magnetic coupling tendencies. The present results strongly suggest that simple AF and NM phases may not allow an accurate description of defect properties in the ground state of Cr. Instead, an explicit SDW representation is required. In addition, we point out that the presence of vacancy and both Cu and Fe may promote a migration of SDW nodes, which may activate the SDW-to-AF phase transition through a node-annihilation mechanism as proposed in previous works.
Title:
Competing charge density waves and temperature-dependent nesting in 2H-TaSe2
Authors:
Leininger, P; Chernyshov, D; Bosak, A; Berger, H; Inosov, DS Author Full Names: Leininger, Ph; Chernyshov, D.; Bosak, A.; Berger, H.; Inosov, D. S.
Source:
PHYSICAL REVIEW B 83 (23): Art. No. 233101 JUN 2 2011
Abstract:
Multiple charge density wave (CDW) phases in 2H-TaSe2 are investigated by high-resolution synchrotron x-ray diffraction. In a narrow temperature range immediately above the commensurate CDW transition, we observe a multi-q superstructure with coexisting commensurate and incommensurate order parameters, clearly distinct from the fully incommensurate state at higher temperatures. This multi-q ordered phase, characterized by a temperature hysteresis, is found both during warming and cooling, in contrast to previous reports. In the normal state, the incommensurate superstructure reflection gives way to a broad diffuse peak that persists nearly up to room temperature. Its position provides a direct and accurate estimate of the Fermi surface nesting vector, which evolves nonmonotonically and starts approaching the commensurate position as the temperature is increased. This behavior agrees with our recent observations of the temperature-dependent Fermi surface in the same compound [D. S. Inosov, D. V. Evtushinsky, V. B. Zabolotnyy, A. A. Kordyuk, B. Buchner, R. Follath, H. Berger, and S. V. Borisenko, Phys. Rev. B 79, 125112 (2009).].
Title:
Elastic and antiferromagnetic anomalies in Pr0.48Ca0.52MnO3 as determined by resonant ultrasonic spectroscopy
Authors:
Salje, EKH; Carpenter, MA Author Full Names: Salje, E. K. H.; Carpenter, M. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (24): Art. No. 245401 JUN 22 2011
Abstract:
The Pnma incommensurate phase transition in the perovskite Pr0.48Ca0.52MnO3 at similar to 235 K is accompanied by shear strains of up to similar to 2.5% (from neutron diffraction) and changes in the shear modulus of up to similar to 40% (from resonant ultrasound spectroscopy, RUS), indicating strong coupling between the structural order parameter and strain. In contrast, the antiferromagnetic (AFM) ordering transition at similar to 180 K displays no detectable static strain, implying that there is either no coupling or only very weak coupling between the magnetic order parameter and strain. Conventional analysis of RUS data, based on measurements of resonance peak frequencies and peak widths, also failed to detect any anomaly in elastic or anelastic properties due to the AFM ordering. A new approach to the analysis the RUS data, based on autocorrelation and convolution of the entire spectra, however, has revealed that the AFM order does indeed affect the elastic behaviour in an unexpected manner. The new analysis shows, firstly, that dynamical fluctuations of the charge density ordering at T > T-c = 237 K lead to an increase of the RUS amplitude and of the spectral convolution function. Secondly, fluctuations and convolution effects peak at the transition point and decrease with decreasing temperatures. Below 180 K the stripe structure is essentially static. Finally, AFM ordering leads to an increase in the damping of the elastic resonances.
Title:
Helical magnetism and structural anomalies in triangular lattice alpha-SrCr2O4
Authors:
Dutton, SE; Climent-Pascual, E; Stephens, PW; Hodges, JP; Huq, A; Broholm, CL; Cava, RJ Author Full Names: Dutton, S. E.; Climent-Pascual, E.; Stephens, P. W.; Hodges, J. P.; Huq, A.; Broholm, C. L.; Cava, R. J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (24): Art. No. 246005 JUN 22 2011
Abstract:
alpha-SrCr2O4 has a triangular planar lattice of d(3) Cr3+ made from edge sharing CrO6 octahedra; the plane shows a very small orthorhombic distortion from hexagonal symmetry. With a Weiss temperature of -596 K and a three-dimensional magnetic ordering temperature of 43 K, the magnetic system is quasi-two-dimensional and frustrated. Neutron powder diffraction shows that the ordered state is an incommensurate helical magnet, with an in-plane propagation vector of k = (0, 0.3217(8), 0). Temperature dependent synchrotron powder diffraction characterization of the structure shows an increase in the inter-plane spacing on cooling below 100 K and an inflection in the cell parameters at the magnetic ordering temperature. These anomalies indicate the presence of a moderate degree of magnetostructural coupling.
Title:
Magnetic structure of the Mn5Si3-type Er5Si3 compound
Authors:
Morozkin, AV; Isnard, O; Granovsky, SA Author Full Names: Morozkin, A. V.; Isnard, O.; Granovsky, S. A.
Source:
INTERMETALLICS 19 (7): 871-875 JUL 2011
Abstract:
Neutron diffraction study has been performed on the Er5Si3 compound (hexagonal Mn5Si3-type, hP16, P6(3)/mcm) to understand its magnetic structure. The temperature dependent neutron diffraction results prove that this compound shows a complex antiferromagnetic ordering with sine modulated magnetic moments collinear to the c axis, presenting three subsequent changes in magnetization at similar to 29 K, 13 K and 10 K on cooling. The high-temperature magnetic component of Er5Si3 (C-3v, magnetic point group, P31m magnetic space group, K-1 = [0, 0, +/- 0.277(2)]) exists from 29 K to 10 K, whereas low-temperature magnetic component (symmetry C-1v, magnetic point group, Pm magnetic space group, K-2 = [0, +/- 1/4, 0]) exists from 13 K down to 1.5 K. The low-temperature and high-temperature magnetic components coexist between 13 K and 10 K. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Magnetocaloric properties of as-quenched Ni50.4Mn34.9In14.7 ferromagnetic shape memory alloy ribbons
Authors:
Llamazares, JL; Garcia, C; Hernando, B; Prida, VM; Baldomir, D; Serantes, D; Gonzalez, J Author Full Names: Sanchez Llamazares, J. L.; Garcia, C.; Hernando, B.; Prida, V. M.; Baldomir, D.; Serantes, D.; Gonzalez, J.
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 103 (4): 1125-1130 JUN 2011
Abstract:
The temperature dependences of magnetic entropy change and refrigerant capacity have been calculated for a maximum field change of Delta H = 30 kOe in as-quenched ribbons of the ferromagnetic shape memory alloy Ni50.4Mn34.9In14.7 around the structural reverse martensitic transformation and magnetic transition of austenite. The ribbons crystallize into a single-phase austenite with the L2(1)-type crystal structure and Curie point of 284 K. At 262 K austenite starts its transformation into a 10-layered structurally modulated monoclinic martensite. The first- and second-order character of the structural and magnetic transitions was confirmed by the Arrott plot method. Despite the superior absolute value of the maximum magnetic entropy change obtained in the temperature interval where the reverse martensitic transformation occurs (vertical bar Delta S-M(max)vertical bar = 7.2 J kg(-1) K-1) with respect to that obtained around the ferromagnetic transition of austenite (vertical bar Delta S-M(max)vertical bar = 2.6 J kg(-1) K-1), the large average hysteretic losses due to the effect of the magnetic field on the phase transformation as well as the narrow thermal dependence of the magnetic entropy change make the temperature interval around the ferromagnetic transition of austenite of a higher effective refrigerant capacity (RCeffmagn = 95 J kg(-1) versus RCeffstruct = 60 J kg(-1)).
Title:
Regenerating deuterium absorption of Ti36Zr40Ni20Pd4 icosahedral quasicrystal
Authors:
Huang, HG; Li, R; Liu, TW; Chen, L; Luo, DL Author Full Names: Huang, Huogen; Li, Rong; Liu, Tianwei; Chen, Liang; Luo, Deli
Source:
ACTA METALLURGICA SINICA-ENGLISH LETTERS 23 (6): 446-450 DEC 2010
Abstract:
Ti/Zr-based icosahedral quasicrystals are a kind of promising hydrogen storage materials, however their absorption regeneration after oxidation-poisoning has been scarcely studied. This work is intended to investigate the deuterium-storage regeneration of a suction-cast Ti36Zr40Ni20Pd4 quasicrystal. It was found that only through hot vacuuming the quasicrystal could be refreshed from air-flow poisoning to absorb deuterium in two cycles. During the first absorption course, a pregnancy period was observed before the real deuterium uptake while deuterium was loaded rapidly during the second one. The deuterium concentration in the alloy can reach 0.011 mol.D-2/(g.M) (corresponding to a hydrogen mass percent of 2.2%. D-2 and M denote molecular deuterium and the metallic alloy). But the loaded deuterium was very difficult to release completely even by eight-stage desorption at different temperatures. After the second desorption, the quasicrystal phase remained in a small! volume, as though the desorption temperature was beyond the crystallization temperature of the quasicrystal. This probably is attributed to the solution function of residual deuterium in the alloy.

Update: 10-Jun-2011

Title:
CHANGES OF STRUCTURE CHARACTERISTICS IN Ti41,5Zr41,5Ni17 AND Ti41,5Hf41,5Ni17 RAPIDLY QUENCHED RIBBONS UNDER RADIATION INFLUENCE
Authors:
Azhazha, VM; Lavrinenko, SD; Lonin, YF; Pylypenko, MM; Sereda, BV; Kryachko, SV; Malykhin, SV; Pugachov, AT; Reshetnyak, MV Author Full Names: Azhazha, V. M.; Lavrinenko, S. D.; Lonin, Yu. F.; Pylypenko, M. M.; Sereda, B. V.; Kryachko, S. V.; Malykhin, S. V.; Pugachov, A. T.; Reshetnyak, M. V.
Source:
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY (2): 33-38 2011
Abstract:
Influence of irradiation by X-ray fluxes with energies <= 1 MeV and doses up to 10(4) rad on phase and structural stability of the icosahedral quasicrystal phase (i-phase) and related crystals-approximant phases in Ti41,5Zr41,5Ni17 and Ti(41,5)Hf(41,5)Ni(17)ribbons prepared by rapid quenching was studied by the X-ray diffraction method.
Title:
Short-range and long-range incommensurate magnetic ordering in the frustrated antiferromagnets Ca3Co2-xFexO6: A neutron diffraction study
Authors:
Jain, A; Yusuf, SM Author Full Names: Jain, Anil; Yusuf, S. M.
Source:
PHYSICAL REVIEW B 83 (18): Art. No. 184425 MAY 25 2011
Abstract:
We present the results of a detailed neutron powder diffraction study on the spin-chain compounds Ca3Co2-xFexO6 (x = 0.2 and 0.4), crystallizing in the rhombohedral structure (space group R (3) over barc), in the temperature range of 1.5-20 K. At low temperature, these compounds show a long-range magnetic ordering (LRO) with an incommensurate structure having an amplitude modulation of the moments along the crystallographic c axis. Our analysis also shows that a short-ranged spin-spin correlation along the c axis (incommensurate type such as that of the LRO), however, with a long-range spin-spin correlation in the ab plane, coexists with the LRO below the LRO temperature of 20 and 17 K for x = 0.2 and 0.4 samples, respectively. The observed long-range as well as the short-range magnetic ordering can be described by a model of platelet-like-shaped magnetic crystallites, disorderly stacked along the crystallographic c direction. At 1.5 K, the LRO and short-range ordering (SRO) contribute in the magnetic phase in volume ratios of 13: 7 and 3: 2 for x = 0.2 and x = 0.4, respectively. The magnetic correlation lengths at 1.5 K for the LRO (xi(c)(I)) and SRO (xi(c)(II)) along the c axis are similar to 1027 and 60 angstrom for x = 0.2, and 1021 and 47 angstrom for x = 0.4, respectively. The relative contribution of the LRO and SRO in the magnetic phase remains constant down to 1.5 K (below transition temperature).
Title:
Homogeneous coexistence of superconducting and spin-density-wave states in CaFe1-xCoxAsF as seen via nuclear magnetic resonance
Authors:
Nakano, T; Tsutsumi, S; Fujiwara, N; Matsuishi, S; Hosono, H Author Full Names: Nakano, T.; Tsutsumi, S.; Fujiwara, N.; Matsuishi, S.; Hosono, H.
Source:
PHYSICAL REVIEW B 83 (18): Art. No. 180508 MAY 26 2011
Abstract:
We investigated the homogeneous coexistence of spin-density-wave (SDW) and superconducting (SC) states via As-75-nuclear magnetic resonance (NMR) in CaFe1-xCoxAsF and found that the electronic and magnetic properties of this compound are intermediate between those of LaFeAsO1-xFx and Ba(Fe1-xCox)(2)As-2. For 6% Co-doped samples, the paramagnetic spectral weight completely disappears in the crossover regime between the SDW and SC phases followed by anomalous behavior of relaxation rate (1/T-1), implying that the two phases are not segregated. Co-59-NMR spectra show that spin moments are not commensurate but spatially modulated. These experimental results suggest that incommensurate SDW (IC-SDW) and SC states are compatible in this compound.
Title:
Layered Perovskite-Like Pb2Fe2O5 Structure as a Parent Matrix for the Nucleation and Growth of Crystallographic Shear Planes
Authors:
Batuk, D; Hadermann, J; Abakumov, A; Vranken, T; Hardy, A; Van Bael, M; Van Tendeloo, G Author Full Names: Batuk, Dmitry; Hadermann, Joke; Abakumov, Artem; Vranken, Thomas; Hardy, An; Van Bael, Marlies; Van Tendeloo, Gustaaf
Source:
INORGANIC CHEMISTRY 50 (11): 4978-4986 JUN 6 2011
Abstract:
The Pb2Fe2O5 compound with a layered intergrowth structure has been prepared by a solid-state reaction at 700 degrees C. The incommensurate compound crystallizes in a tetragonal system with alpha = 3.9037(2) angstrom, c = 3.9996(4) angstrom, and q = 0.1186(4)c star, or when treated as a commensurate approximant, alpha = 3.9047(2) angstrom, c = 36.000(3) angstrom, space group I4/mmm. The crystal structure of Pb2Fe2O5 was resolved from transmission electron microscopy data. Atomic coordinates and occupancies of the cation positions were estimated from high-angle annular dark-field scanning transmission electron microscopy data. Direct visualization of the positions of the oxygen atoms was possible using annular bright-field scanning transmission electron microscopy. The structure can be represented as an intergrowth of perovskite blocks and partially disordered blocks with a structure similar to that of the Bi2O2 blocks in Aurivillius-type phases. The A-cation positions at the border of the perovskite block and the cation positions in the Aurivillius-type blocks are jointly occupied by Pb2+ and Fe3+ cations, resulting in a layer sequence along the c axis: -PbO-FeO2-PbO-FeO2-Phys(7/8)Fe(1/8)-O1-x-Fe-5/8/Pb-3/8-O-2-Fe5/8Pb3/8-. Upon heating, the layered Pb2Fe2O5 structure transforms into an anion-deficient perovskite modulated by periodically spaced crystallographic shear (CS) planes. Considering the layered Pb2Fe2O5 structure as a parent matrix for the nucleation and growth of CS planes allows an explanation of the specific microstructure observed for the CS structures in the Pb-Fe-O system.
Title:
Investigation of the thermal diffusion during the formation of a quasicrystalline phase in thin Al-Pd-Re films
Authors:
Seregin, AY; Makhotkin, IA; Yakunin, SN; Erko, AI; Tereshchenko, EY; Shaitura, DS; Chikina, EA; Tsetlin, MB; Mikheeva, MN; Ol'shanskii, ED Author Full Names: Seregin, A. Yu.; Makhotkin, I. A.; Yakunin, S. N.; Erko, A. I.; Tereshchenko, E. Yu.; Shaitura, D. S.; Chikina, E. A.; Tsetlin, M. B.; Mikheeva, M. N.; Ol'shanskii, E. D.
Source:
CRYSTALLOGRAPHY REPORTS 56 (3): 497-501 MAY 2011
Abstract:
The layer mixing during the formation of the Al70Pd20Re10 icosahedral quasicrystalline phase in thin (55 nm) Al-Pd-Re layered film systems subjected to vacuum annealing has been studied. It is shown that a combined layer of Pd and Al atoms (with the Al3Pd2 phase dominating) is formed in the first stage (at 350A degrees C), while the rhenium layer remains invariable. In the second annealing stage (at 450A degrees C), the beta'-AlPd phase is formed and the Re layer is diffused. In the third stage (700A degrees C), Pd and Re atoms are uniformly distributed throughout the film with the formation of a quasicrystalline phase.

Update: 3-Jun-2011

Title:
Stability of quasicrystals composed of soft isotropic particles
Authors:
Barkan, K; Diamant, H; Lifshitz, R Author Full Names: Barkan, Kobi; Diamant, Haim; Lifshitz, Ron
Source:
PHYSICAL REVIEW B 83 (17): Art. No. 172201 MAY 19 2011
Abstract:
Quasicrystals whose building blocks are of mesoscopic rather than atomic scale have recently been discovered in several soft-matter systems. Contrary to metallurgic quasicrystals whose source of stability remains a question of great debate to this day, we argue that the stability of certain soft-matter quasicrystals can be directly explained by examining a coarse-grained free energy for a system of soft isotropic particles. We show, both theoretically and numerically, that the stability can be attributed to the existence of two natural length scales in the pair potential, combined with effective three-body interactions arising from entropy. Our newly gained understanding of the stability of soft quasicrystals allows us to point at their region of stability in the phase diagram, and thereby may help control the self-assembly of quasicrystals and a variety of other desired structures in future experimental realizations.
Title:
Spin-Peierls transition in the S=1/2 compound TiPO4 featuring large intrachain coupling
Authors:
Law, JM; Hoch, C; Glaum, R; Heinmaa, I; Stern, R; Kang, J; Lee, C; Whangbo, MH; Kremer, RK Author Full Names: Law, J. M.; Hoch, C.; Glaum, R.; Heinmaa, I.; Stern, R.; Kang, J.; Lee, C.; Whangbo, M. -H.; Kremer, R. K.
Source:
PHYSICAL REVIEW B 83 (18): Art. No. 180414 MAY 23 2011
Abstract:
We investigated the magnetic and structural properties of the quasi-one-dimensional 3d(1) quantum chain system TiPO4 (J similar to 965 K) by magnetic susceptibility, heat capacity, electron spin resonance, x-ray diffraction, and nuclear magnetic resonance (NMR) measurements, and by density functional theory (DFT) calculations. TiPO4 undergoes two magnetostructural phase transitions, one at 111 K and the other at 74 K. Below 74 K, NMR detects two different P-31 signals and the magnetic susceptibility vanishes, while DFT calculations evidence a bond alternation of the Ti-Ti distances within each chain. Thus, the 74 K phase transition is a spin-Peierls transition which evolves from an incommensurate phase existing between 111 and 74 K.
Title:
Characteristic chemical shift of quasicrystalline alloy Al53Si27Mn20 studied by EELS and SXES
Authors:
Koshiya, S; Terauchi, M; Tsai, AP Author Full Names: Koshiya, S.; Terauchi, M.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE 91 (18): 2309-2316 2011
Abstract:
Chemical shifts of all constituent atoms for amorphous (Am), quasicrystalline (QC) and crystalline (Cryst) alloys of Al53Si27Mn20 were investigated for the first time by high energy-resolution electron energy-loss spectroscopy (EELS) and soft-X-ray emission spectroscopy (SXES). Among Al L-shell excitation EELS spectra of Am, QC and Cryst alloys, only QC alloy showed an apparent chemical shift to the larger binding energy side by 0.4 eV. In Al-K-alpha and Si-K-alpha emission SXES spectra of these alloys, only QC alloy showed a chemical shift to the larger binding energy side by 4 eV for Al-K-alpha and 6 eV for Si-K-alpha. These chemical shift values are comparable to those of corresponding metal oxides. This indicates a smaller amount of valence charge at Al and Si atomic sites in QC alloy. On the other hand, Mn-L SXES spectra did not show any chemical shift. Therefore, the decreased charge from Al and Si sites should be distributed between atomic sites, indicating the pres! ence of covalent bonding nature for QC ordered alloy.
Title:
The Eleventh International Conference on Quasicrystals
Authors:
Ishimasa, T; Ishii, Y Author Full Names: Ishimasa, Tsutomu; Ishii, Yasushi
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2419-2420 Sp. Iss. SI 2011
Title:
Once upon a time in Kamchatka: the search for natural quasicrystals
Authors:
Steinhardt, PJ; Bindi, L Author Full Names: Steinhardt, Paul J.; Bindi, Luca
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2421-2426 Sp. Iss. SI 2011
Abstract:
We present evidence for a naturally occurring quasicrystal consisting of micron-sized grains of Al63Cu24Fe13 with icosahedral symmetry embedded in a sample of khatyrkite (nominally, (Cu,Zn)Al2) obtained from the Khatyrka ultramafic zone of the Koryak Mountains in the northern half of the Kamchatka Peninsula.
Title:
High-energy X-ray diffraction studies of i-Sc12Zn88
Authors:
Goldman, AI; Kreyssig, A; Nandi, S; Kim, MG; Caudle, ML; Canfield, PC Author Full Names: Goldman, A. I.; Kreyssig, A.; Nandi, S.; Kim, M. G.; Caudle, M. L.; Canfield, P. C.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2427-2433 Sp. Iss. SI 2011
Abstract:
Although quasicrystals form in a wide variety of ternary and quaternary metallic alloys, examples of stable binary icosahedral quasicrystals are quite rare. Indeed, it has been a decade since the discovery of icosahedral phases in Yb-Cd and Ca-Cd. We have discovered millimeter-sized facetted grains of i-Sc12Zn88 with icosahedral (pentagonal dodecahedral and rhombic triacontahedral) morphologies in solution-grown samples. Structural characterization of the bulk icosahedral phase was accomplished through single-grain high-energy X-ray diffraction. For both growth morphologies, all diffraction peaks could be indexed by a primitive (P-type) icosahedral phase. The two types of morphology do, however, present interesting differences in their respective degrees of quasicrystalline order.
Title:
Solution growth of a decagonal quasicrystal and its related periodic crystals in the Al-Ni-Ru system
Authors:
Dasai, S; Takakura, H Author Full Names: Dasai, Shogo; Takakura, Hiroyuki
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2434-2442 Sp. Iss. SI 2011
Abstract:
Single crystals, with a typical size of several millimetres, of a decagonal phase with 1.6 nm periodicity in the Al-Ni-Ru system were grown successfully by the solution-growth method. The conditions for crystal growth were that the initial composition was Al80Ni16Ru4, the taking-out temperature 900-930 degrees C and the cooling rate 2 degrees C h-1. The lattice parameters were a = 0.2764(2) and c = 1.6523(5) nm, and the composition was in a small range around Al75.2Ni14.6Ru10.2. Single crystals of the orthorhombic Al13(Ni, Ru)4 phase and the monoclinic Al13(Ni, Ru)4 phase located at the high-Ni end also formed under slightly different conditions.
Title:
Synthesis of large single-grain 1/1 approximant crystals in the Ag-In-Eu system by the self-flux method
Authors:
Cui, C; Tsai, AP Author Full Names: Cui, Can; Tsai, An Pang
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2443-2449 Sp. Iss. SI 2011
Abstract:
In this work, we investigate single-grain 1/1 quasicrystal approximant crystals, grown via the self-flux method, in the Ag-In-Eu system, the structure of which is similar to the 1/1 approximant in the Cd-Eu system. Due to the similarities between the Cd-RE (RE = rare earth) and Ag-In-RE systems, Ag-In-RE can be regarded as a pseudo-binary phase, in which Ag and In replace Cd. Thus, based on the binary phase diagram of Cd-Eu, the growth conditions, including the nominal composition and decanting temperatures, for single-grain Ag-In-Eu 1/1 approximant crystal growth from indium-rich melt-solution were studied. A faceted, centimeter-sized single-grain 1/1 approximant crystal was obtained and characterized using powder X-ray diffraction, scanning electron microscopy and back-reflection Laue X-ray diffraction methods. The results are promising for the synthesis of single-grain approximant crystals in other Ag-In-RE systems.
Title:
Rapid synthesis and densification of single-phase Al-Cu-Fe quasicrystals by spark plasma sintering or microwave heating
Authors:
Nicula, R; Ishizaki, K; Stir, M; Shen, Z; Vaucher, S Author Full Names: Nicula, R.; Ishizaki, K.; Stir, M.; Shen, Z.; Vaucher, S.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2450-2457 Sp. Iss. SI 2011
Abstract:
Quasicrystalline (QC) phases are often stable only within narrow composition domains. For this reason, the synthesis of larger amounts of single-phase quasicrystalline powders is difficult. Powder metallurgical approaches, based on mechanical milling followed by conventional heating, have been explored in the recent past. The manufacturing process for single-phase quasicrystals - either in the form of powders or as bulk parts - can be accelerated by orders of magnitude using rapid heating methods that involve pulsed electric currents and/or high-frequency electromagnetic fields. Prior knowledge of the phase transformation sequence and transformation kinetics, as revealed by in situ time-resolved synchrotron radiation experiments, is crucial in obtaining single-phase quasicrystals. We report on the simultaneous synthesis and densification of bulk single-phase Al-Cu-Fe QCs by spark plasma sintering (SPS) within minutes and on the ultrafast synthesis of single-phase Al-Cu-Fe quasicrystalline powders by microwave heating within seconds. The effect of electric current application in the rapid processing of pre-alloyed powders is discussed in relation to the faster diffusion and enhanced phase transformation kinetics.
Title:
Growth morphology of single-crystal grains obtained by directional crystallisation of an Al-Cu-Fe alloy
Authors:
Surowiec, M; Bogdanowicz, W; Krawczyk, J; Formanek, B; Sozanska, M Author Full Names: Surowiec, Marian; Bogdanowicz, Wlodzimierz; Krawczyk, Jacek; Formanek, Boleslaw; Sozanska, Maria
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2458-2465 Sp. Iss. SI 2011
Abstract:
Quasicrystalline as well as crystalline faceted single grains of four phases were obtained during directional crystallisation of an Al-Cu-Fe alloy by the Bridgman technique. The monoclinic phase, Al13(Cu, Fe)4, dominating at high temperatures formed single-crystal lamellae 0.5 mm to 1 mm thick. A second type of attractive morphological form exhibiting flux dissolution terraces was observed on spherical single crystals of phase Al(Fe, Cu). Rectangular, hexagonal and octagonal shaped dissolution terraces were revealed at the positions of two-, three- and four-fold symmetry axes, respectively. A single quasicrystalline phase, Al6Cu2Fe, exhibited icosahedral symmetry with growth forms of a dodecahedron with pentagonal facets. The flux dissolution of the phase apparently plays an essential role in a peritectic reaction leading to quasicrystalline phase formation. Polygonal single grains of phase Al7Cu2Fe exhibiting tetragonal symmetry formed the fourth type of thermodynam ically stable growth forms. Single grains of the phase crystallised in the form of pellets with an octagonal cross-section. The growth morphology of the stable phases was investigated by scanning electron microscopy. The chemical composition of the growth forms described was confirmed by X-ray microanalysis using a scanning electron microscope, whereas the phase composition was determined using electron selected area diffraction and X-ray powder diffraction.
Title:
Synthesis of decagonal Zn-Mg-RE compounds
Authors:
Ors, T; Steurer, W Author Full Names: Oers, Taylan; Steurer, Walter
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2466-2473 Sp. Iss. SI 2011
Abstract:
In this study, the formation of decagonal (d-) quasicrystals in some Zn-Mg-RE systems (with RE = Dy, Er, Ho and Tm) was investigated. For samples with composition Zn58Mg40RE2 reported in literature, decagonal quasicrystals can be obtained as single phase after annealing the prealloys for 100 h at 350 degrees C. However, prolonged annealing at this temperature causes transformation of the d-phase into a hexagonal phase. The d-phase could also be obtained in systems with Er and Ho under different annealing conditions. For Dy- and Er-containing samples, slow cooling (instead of quenching) from higher temperatures also yields predominantly the d-phase.
Title:
Formation of quasicrystalline phase in Al70-xGaxPd17Mn13 alloys
Authors:
Yadav, TP; Singh, D; Shahi, RR; Shaz, MA; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Singh, Devinder; Shahi, Rohit R.; Shaz, M. A.; Tiwari, R. S.; Srivastava, O. N.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2474-2481 Sp. Iss. SI 2011
Abstract:
In the present investigation, the formation and stability of icosahedral phase in Al70-xGaxPd17Mn13 alloys has been explored using X-ray diffraction, scanning, transmission electron microscopy and energy dispersive X-ray analysis. Cast alloys and melt-spun ribbons with x = 2.5, 5, 7.5, 10, 12.5, 15 and 20 have been investigated. In both cases, the alloys up to 5 at% Ga exhibit the formation of pure icosahedral phase. However, for x epsilon 5 at% Ga content, the cast alloy exhibits the formation of multiphase material, consisting of an icosahedral phase along with AlPd-type B2 and ' crystalline (orthorhombic structure with unit cell a = 23.5 angstrom, b = 16.6 angstrom and c = 12.4 angstrom) phases. In the case of the melt spun ribbon for x = 5 at% Ga, only an icosahedral phase has been found, but for 15 x 5 at% Ga, an icosahedral phase is the majority phase with AlPd-type B2 phase being the minority component. For x = 15 at% Ga, a Al3Pd2-type hexagonal phase together with a small amount of quasicrystalline phase is formed. However, for x = 20, only a hexagonal Al3Pd2 phase results.
Title:
Strain-induced structural transformation of single-phase Al-Cu-Fe icosahedral quasicrystal during mechanical milling
Authors:
Mukhopadhyay, NK; Ali, F; Srivastava, VC; Yadav, TP; Sakaliyska, M; Surreddi, KB; Scudino, S; Uhlenwinkel, V; Eckert, J Author Full Names: Mukhopadhyay, N. K.; Ali, F.; Srivastava, V. C.; Yadav, T. P.; Sakaliyska, M.; Surreddi, K. B.; Scudino, S.; Uhlenwinkel, V.; Eckert, J.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2482-2490 Sp. Iss. SI 2011
Abstract:
A single-phase stable icosahedral quasicrystalline sample of high quality with the composition Al62.5Cu25Fe12.5 was produced by the spray forming technique. The material was further investigated by mechanical milling under an argon atmosphere to avoid oxidation during milling. At the initial stages of milling (within 5 h) a significant broadening of the diffraction peaks was observed, indicating a reduction of crystallite size and the introduction of lattice strain, which can be linked to phason strain of the quasilattice. Line broadening was noticed to increase with increasing milling time and in the material milled for longer time only a few broad diffraction peaks, which can be identified as a nanoscale bcc phase (i.e. disordered B2 phase, a 2.9 angstrom), were visible. At this stage the diffraction signals belonging to the quasicrystals were no longer observable, indicating a complete transformation of the quasicrystals into the bcc phase. Finally, the bcc phase formed during milling transformed back to the quasicrystalline phase during subsequent annealing treatment. The microhardness measured on the milled powders was found to decrease with increasing milling time, most likely as a consequence of the increased volume fraction of the ductile bcc phase. Attempts are made to rationalize the structural transformation.
Title:
Anisotropic local structure of decagonal quasicrystals by DAFS
Authors:
Abe, H; Saitoh, H; Nakao, H; Yamamoto, K Author Full Names: Abe, H.; Saitoh, H.; Nakao, H.; Yamamoto, K.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2491-2499 Sp. Iss. SI 2011
Abstract:
Diffraction anomalous fine structure (DAFS) analyses were performed on Al-Ni-Co (ANC) and Al-Ni-Fe (ANF) decagonal quasicrystals at the K-edges of Ni, Co and Fe. In ANC, an order-disorder phase transition with anisotropic atomic short-range order (SRO) is clearly recognizable at high temperature. During in situ observation, a zigzag correlation along the periodic direction developed during the early stage of ordering. Far above the phase transition temperature, this weak correlation along the periodic direction is independent of other correlations along the quasiperiodic one. In ANF, SRO of Fe developed along the quasiperiodic direction, although the local environment of Ni was almost random.
Title:
Structure refinement of decagonal Al-Ni-Co, superstructure type I
Authors:
Kuczera, P; Wolny, J; Fleischer, F; Steurer, W Author Full Names: Kuczera, P.; Wolny, J.; Fleischer, F.; Steurer, W.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2500-2509 Sp. Iss. SI 2011
Abstract:
The structure of decagonal Al-Ni-Co, superstructure type I (the so-called Edagawa phase), was refined in physical space. A statistical approach was used to calculate the structure factors based on a rhombic Penrose tiling, with tile edge length 12.1 angstrom, as reference frame. A total number of 691 parameters was refined against 6843 structure amplitudes, merged in Laue group 10/m.
Title:
Spectroscopic study of Ni-rich Al-Co-Ni quasicrystal
Authors:
Soda, K; Inukai, M; Kato, M; Yagi, S; So, YG; Edagawa, K Author Full Names: Soda, K.; Inukai, M.; Kato, M.; Yagi, S.; So, Y. -G.; Edagawa, K.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2510-2518 Sp. Iss. SI 2011
Abstract:
The valence-band electronic structure of a decagonal Ni-rich Al-Co-Ni quasicrystal, Al72Co8Ni20, was investigated using soft X-ray photoelectron spectroscopy. In particular, the energy distributions of the transition metal 3d bands were determined from the Co and Ni 2p-3d resonance photoemission and compared with those calculated by the discrete variational X method for a model cluster based on a proposed Ni-rich Al-Co-Ni approximant, as well as the 3d band observed in the Co-rich Al-Co-Ni quasicrystal, Al72Co16Ni12. In the Ni-rich Al-Co-Ni, the transition metal 3d band exhibits a peak at a binding energy, EB, of 2.3 eV, which is higher than that of the Co-rich Al-Co-Ni. The observed Ni 3d band has a single-peaked distribution around EB 2.4 eV, in contrast to the calculated bimodal and wide-spread distribution for the proposed Ni-rich Al-Co-Ni model cluster, whereas the Co 3d band is located at EB 1.7 eV, consistent with the model calculation.
Title:
Three-dimensional reconstruction of the atomic arrangement of icosahedral quasicrystals by binary discrete tomography
Authors:
Ishibashi, Y; Sugiura, H; Saitoh, K; Tanaka, N Author Full Names: Ishibashi, Y.; Sugiura, H.; Saitoh, K.; Tanaka, N.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2519-2527 Sp. Iss. SI 2011
Abstract:
A three-dimensional reconstruction of the structure of icosahedral quasicrystals from high-resolution transmission electron microscope images observed along high-symmetry zone-axis projections is studied. As in discrete tomography, the quasicrystalline structure is treated as a discrete set of atoms arranged on the icosahedral lattice, including atom flip sites, which is a structural disorder originating from the degrees of freedom in the internal space. The occupancy of the atoms on each site of the lattice is determined using only the zone-axis projection images without any knowledge of the image intensity. Simulation studies using icosahedral model lattices composed of several thousands of atoms were carried out to test the present reconstruction method. In the case of the ideal icosahedral lattice, a reconstruction rate of 90% is achieved from 10 projection images and a reconstruction rate of 99% is achieved from 18 projections. The reconstruction rate degrad es when the projection images are misaligned. Reconstruction of the three-dimensional distribution of the atom flips is discussed.
Title:
Multiple diffraction in an icosahedral Al-Cu-Fe quasicrystal
Authors:
Fan, CZ; Weber, T; Deloudi, S; Steurer, W Author Full Names: Fan, C. Z.; Weber, Th.; Deloudi, S.; Steurer, W.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2528-2535 Sp. Iss. SI 2011
Abstract:
In order to reveal its influence on quasicrystal structure analysis, multiple diffraction (MD) effects in an icosahedral Al-Cu-Fe quasicrystal have been investigated in-house on an Oxford Diffraction four-circle diffractometer equipped with an Onyx CCD area detector and MoK radiation. For that purpose, an automated approach for Renninger scans (-scans) has been developed. Two weak reflections were chosen as the main reflections (called P) in the present measurements. As is well known for periodic crystals, it is also observed for this quasicrystal that the intensity of the main reflection may significantly increase if the simultaneous (H) and the coupling (P-H) reflections are both strong, while there is no obvious MD effect if one of them is weak. The occurrence of MD events during -scans has been studied based on an ideal structure model and the kinematical MD theory. The reliability of the approach is revealed by the good agreement between simulation and experimen! t. It shows that the multiple diffraction effect is quite significant.
Title:
Hume-Rothery stabilisation mechanism and d-states-mediated Fermi surface-Brillouin zone interactions in structurally complex metallic alloys
Authors:
Mizutani, U; Inukai, M; Sato, H Author Full Names: Mizutani, U.; Inukai, M.; Sato, H.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2536-2542 Sp. Iss. SI 2011
Abstract:
The stability of Co2Zn11 and Al8V5 gamma-brasses, both of which are composed of a transition metal element and polyvalent elements Zn or Al, can be discussed in terms of d-states-mediated Fermi surface-Brillouin zone (FsBz) interactions in the context of first-principles full-potential linearised augmented plane wave (FLAPW) band calculations. A FsBz-induced pseudogap is revealed in the FLAPW-Fourier spectrum, though it is hidden behind a much larger d-band in the total density of states. The stability range of three families of complex metallic alloys (CMAs) that include gamma-brasses, RT-, MI- and Tsai-type 1/1-1/1-1/1 approximants and 2/1-2/1-2/1 approximant, each of which is characterised by [image omitted] = 18, 50 and 125, respectively, can be well scaled in terms of the number of electrons per unit cell (e/uc) given by the product of the number of atoms per unit cell and the e/a value determined by the Hume-Rothery plot on the basis of the FLAPW-Fourier method. This! is taken as the evidence for the justification of the Hume-Rothery stabilisation mechanism for all these CMAs having a pseudogap at the Fermi level.
Title:
Energetics and dynamics of caged Zn4 in i-ScZn
Authors:
Mihalkovic, M; Henley, CL Author Full Names: Mihalkovic, M.; Henley, C. L.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2548-2556 Sp. Iss. SI 2011
Abstract:
In i-ScZn, like other quasicrystals of the i-CaCd class, the innermost shell of the icosahedral cluster is a Zn4 tetrahedron, which thus breaks the symmetry of the outer cluster shells. We investigate theoretically the dynamics of individual tetrahedra, using interatomic pair potentials, fitted from an ab initio database, and molecular dynamics (MD). This includes the formulation of an effective Hamiltonian written in terms of a rigid-body rotation representing the state of each tetrahedron. We characterize the minimum-energy orientations of a tetrahedron, as well as the paths of the transitions between minima (reorientations). The velocity autocorrelations were evaluated for the tetrahedral atoms in the MD dynamics; the corresponding spectral density S() is fairly well fitted by a simplified model in which each atom hops in a double well.
Title:
Cell-constrained melt-quench simulation of d-AlCoNi: Ni-rich versus Co-rich structures
Authors:
Mihalkovic, M; Widom, M; Henley, CL Author Full Names: Mihalkovic, M.; Widom, M.; Henley, C. L.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2557-2566 Sp. Iss. SI 2011
Abstract:
Complex crystalline ground state structures may be obtained by direct (simulated) quenches from the melt for systems of up to a few hundred atoms, given the constraint of a fixed unit cell, coupled with use of (i) replica-exchange Monte Carlo, and (ii) realistic empirical interaction pair potentials. We applied this procedure to decagonal approximants of Al72Co8Ni20 and Al73Co27, obtaining the best energies seen to date for d-AlCoNi models (respectively +20 meV/atom and +9 meV/atom above the tie-plane of competing phases). We elucidated the reasons why different decagonal structures are associated with the Ni-rich and Co-rich compositions. We found a cell doubling to c = 8 angstrom due to layer puckering not only in the Co-rich structure, but (locally) in the nominally c = 4 angstrom Ni-rich structure.
Title:
Ab initio investigations on the stability of seven-fold approximants
Authors:
Orsini-Rosenberg, H; Steurer, W Author Full Names: Orsini-Rosenberg, Heinrich; Steurer, Walter
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2567-2578 Sp. Iss. SI 2011
Abstract:
The stability of theoretical heptagonal approximants was investigated. No approximant phase has yet been confirmed consisting of all three heptagonal rhomb prototiles. To solve this problem, two new approximant structures were constructed from supertiles taken from the ThB4 and YCrB4 structure types. In order to compare structural stability, the total energy convex hulls were calculated for the ternary systems B-Cr-RE (RE = Dy, Er, Ho, Y), as well as B-Mn-Dy and B-Mn-Y, by means of ab initio calculations, using density functional theory. This included all known stable monary, binary and ternary phases. Additionally, several layered boride structure types, which are not stable in the respective ternary systems but show four-, five-, six- or seven-fold local environments, were included by chemical substitution. In all ternary systems, the theoretical approximants were found to be mechanically stable, but chemically unstable by an amount of energy larger than the margin of error. A tendency towards the stabilization of structures showing five- or 10-fold local environments was observed. This is consistent with the findings of decagonal approximants in the systems B-Ti-Ru and B-Mg-Ru.
Title:
Eight different decagonal tilings derived from rhombic Penrose tiling
Authors:
Kato, K; Yamamoto, A Author Full Names: Kato, Kazuyuki; Yamamoto, Akiji
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2579-2586 Sp. Iss. SI 2011
Abstract:
We found 32 variations of dot tiling (DT) reported previously [J. Alloy. Comp. 342 (2002) p.206], which is similar to a tiling consisting of pentagon, hexagons, nonagon and decagons (PHND) [Phil. Mag. A l76 (1997) p.85] employed in the structure analysis of decagonal quasicrystals. They are its superstructures, with a five times larger unit cell in four-dimensional space. These tilings are built up by adding one dot in each fat rhombus in the rhombic Penrose tiling. Eight tilings among 32 DTs do not break the local symmetries of the eight types of vertices in the rhombic Penrose tiling. The eight tilings and their occupation domains are shown.
Title:
Low-temperature structural stability of Cd6M (M = Ho, Er, Tm and Lu) cubic crystalline approximants
Authors:
Nishimoto, K; Sato, T; Muraki, M; Tamura, R Author Full Names: Nishimoto, Kazue; Sato, Takeru; Muraki, Miki; Tamura, Ryuji
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2587-2593 Sp. Iss. SI 2011
Abstract:
TEM observations and electrical resistivity measurements have been performed to investigate the low temperature stability, e.g. the occurrence of a phase transition, in Cd6M (M = Ho, Er, Tm and Lu) approximants, which have the smallest M atomic radii among a series of Cd6M compounds. Unlike other Cd6M compounds, no changes or anomalies were observed in selected-area electron diffraction patterns or in electrical resistivity down to 20 and 15 K, respectively. Therefore, we conclude that a phase transition does not occur in Cd6M (M = Ho, Er, Tm and Lu) and orientational ordering of the Cd4 tetrahedron is kinetically suppressed when the space inside the icosahedral cluster is reduced to a certain level.
Title:
Crystal structure of 1/0-2/1-1/0 Cu-Al-Sc approximant
Authors:
Ishimasa, T; Hirao, A; Honma, T; Mihalkovic, M Author Full Names: Ishimasa, Tsutomu; Hirao, Arina; Honma, Takahiro; Mihalkovic, Marek
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2594-2602 Sp. Iss. SI 2011
Abstract:
The new crystal structure of an orthorhombic phase formed at the alloy composition Cu48.1Al36.4Sc15.5 was analyzed by means of the Rietveld method using synchrotron radiation diffraction data. The starting model for this analysis was constructed theoretically using the so-called 'cell constrained melt-quenching technique'. The space group of the final model is Cmmm, and the unit cell includes 49.0 Cu, 39.0 Al and 16.0 Sc atoms. The lattice parameters are a = 8.337(4) angstrom, b = 22.02(1) angstrom and c = 8.305(4) angstrom, which are related to the six-dimensional lattice parameter, a6D = 6.959 angstrom, of the corresponding Cu-Al-Sc icosahedral quasicrystal as 1/0, 2/1 and 1/0 approximations, respectively. The characteristics of the structure can be understood as a framework consisting of Sc atoms, which is regarded as a tiling of five local structural units; the largest is an icosahedron similar to that included in the Tsai-type quasicrystal. The second exhibits structural similarity to a Mg2Zn11-type crystal and the third is an octahedron.
Title:
Crystal structure of a new orthorhombic Al72Pd18Mn5Si5 approximant phase
Authors:
Simura, R; Kaji, N; Sugiyama, K; Hiraga, K Author Full Names: Simura, Rayko; Kaji, Nobutaka; Sugiyama, Kazumasa; Hiraga, Kenji
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2603-2609 Sp. Iss. SI 2011
Abstract:
The structure of an orthorhmbic Al72Pd18Mn5Si5 phase was determined by single crystal X-ray diffraction: space group Pnma (No.148), a = 1.4396(3) nm, b = 2.4003(2) nm, c = 0.7603(2) nm, V = 2.6272(9) nm3, atoms/cell = 168, F(000) = 3341, = 7.355 mm-1, Dcalc = 4.613 Mgm-3, R(F) = 0.0312 for observed 3919 reflections measured by Mo-K radiation ( = 0.071073 nm). The orthorhombic AlPdMnSi structure is well described by the stacking of a decagonal (0.72 nm) and pentagonal column (0.48 nm) along the b-axis. A new type of decagonal column structures with a periodicity of 1.2 nm (=0.48 + 0.72 nm) is proposed for the decagonal quasicrystals.
Title:
Structure of an approximant crystal in Ni-rich Al71Ni22Co7
Authors:
Abe, E; Yamamoto, A Author Full Names: Abe, E.; Yamamoto, A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2617-2623 Sp. Iss. SI 2011
Abstract:
A novel approximant crystalline structure formed in an Al71Ni22Co7 alloy annealed at 973 K is reported, for which the S1-type superlattice decagonal quasicrystal forms as a major phase. Electron diffraction and atomic-resolution Z-contrast scanning transmission electron microscope investigations successfully identified the approximant as having a monoclinic unit cell with a = c = 3.2 nm (b = 0.4 nm), = 108 degrees; the structure is constructed by the five-fold symmetric decagonal clusters 2 nm across, which are arrayed by inverting their pentagonal directions between the neighbours (antiferro order of the cluster sense). A plausible atomic model of the approximant is proposed by referring to a model structure of the S1-type decagonal quasicrystal, which is composed of the similar local linkages of the five-fold symmetry clusters. The present approximant is shown to share some structural characteristics with the PD3c-approximant reported for a Co-rich Al71.5Ni12.5Co16 alloy.
Title:
Approximant of dodecagonal quasicrystal formed in Mn-Si-V alloy
Authors:
Iga, H; Mihalkovic, M; Ishimasa, T Author Full Names: Iga, Hayato; Mihalkovic, Marek; Ishimasa, Tsutomu
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2624-2633 Sp. Iss. SI 2011
Abstract:
The crystal structure of a hexagonal phase formed in Mn70Si20V10 has been analyzed by the Rietveld method using synchrotron radiation diffraction data. Analysis was carried out by assuming an average metallic element Mn0.875V0.125 via high resolution electron microscopy. The space group of the refined model is P6/mmm (No. 191) and the unit cell includes 18.9 Si and 78.1 metallic atoms. The lattice parameters are a = 17.058(6) angstrom, c = 4.640(1) angstrom. This hexagonal phase is regarded as an approximant of a dodecagonal quasicrystal. The electron diffraction pattern along the c-axis exhibits pseudo 12-fold diffraction symmetry. In the c-projection, the structure is interpreted as the tiling of two types of local structural units, namely an equilateral triangle and square with the same edge length of 4.57 angstrom, which correspond to A15-type and Zr4Al3-type structures in the three dimensions, respectively. Both bond orientational order and scaling property, cha racteristic of a dodecagonal quasicrystal, are imitated in this periodic tiling.
Title:
Diffraction of limit periodic point sets
Authors:
Baake, M; Grimm, U Author Full Names: Baake, Michael; Grimm, Uwe
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2661-2670 Sp. Iss. SI 2011
Abstract:
Limit periodic point sets are aperiodic structures with pure point diffraction supported on a countably, but not finitely generated Fourier module that is based on a lattice and certain integer multiples of it. Examples are cut and project sets with p-adic internal spaces. We illustrate this by explicit results for the diffraction measures of two examples with 2-adic internal spaces. The first and well-known example is the period doubling sequence in one dimension, which is based on the period doubling substitution rule. The second example is a weighted planar point set that is derived from the classic chair tiling in the plane. It can be described as a fixed point of a block substitution rule.
Title:
Colourings of lattices and coincidence site lattices
Authors:
Loquias, MJC; Zeiner, P Author Full Names: Loquias, Manuel Joseph C.; Zeiner, Peter
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2680-2689 Sp. Iss. SI 2011
Abstract:
The relationship between the coincidence indices of a lattice 1 and a sublattice 2 of 1 is examined via the colouring of 1 that is obtained by assigning a unique colour to each coset of 2. In addition, the idea of colour symmetry, originally defined for symmetries of lattices, is extended to coincidence isometries of lattices. An example involving the Ammann-Beenker tiling is provided to illustrate the results in the quasicrystal setting.
Title:
Semi-perfect colourings of hyperbolic tilings
Authors:
de Las Penas, MLAN; Felix, RP; Gozo, BR; Laigo, GR Author Full Names: de Las Penas, Ma Louise Antonette N.; Felix, Rene P.; Gozo, Beaunonie R., Jr.; Laigo, Glenn R.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2700-2708 Sp. Iss. SI 2011
Abstract:
If G is the symmetry group of an uncoloured tiling, then a colouring of the tiling is semi-perfect if the associated colour group is a subgroup of G of index 2. Results are presented that show how to identify and construct semi-perfect colourings of symmetrical tilings. Semi-perfectly coloured tilings that emerge from the hyperbolic semi-regular tiling 8 center dot 10 center dot 16 are reported.
Title:
Determining quasicrystal structures on substitution tilings
Authors:
Akiyama, S; Lee, JY Author Full Names: Akiyama, Shigeki; Lee, Jeong-Yup
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2709-2717 Sp. Iss. SI 2011
Abstract:
Quasicrystals are characterized by the diffraction patterns which consist of pure bright peaks. Substitution tilings are commonly used to obtain geometrical models for quasicrystals. We consider certain substitution tilings and show how to determine a quasicrystalline structure for the substitution tilings computationally. In order to do this, it is important to have the Meyer property on the substitution tilings. We use the recent result of Lee and Solomyak, which determines the Meyer property on the substitution tilings from the expansion maps.
Title:
Aperiodic structures and notions of order and disorder
Authors:
Ben-Abraham, SI; Quandt, A Author Full Names: Ben-Abraham, S. I.; Quandt, A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2718-2727 Sp. Iss. SI 2011
Abstract:
The fabrication of artificial heterostructures is mainly based on substitution systems. We present simple ways to construct double-sided versions of the Fibonacci, Prouhet-Thue-Morse, paperfolding, period doubling and Golay-Rudin-Shapiro sequences. We also construct a generic instance of the two-dimensional Prouhet-Thue-Morse structure and explore its symbolic complexity. The complexity turns out to be polynomial and hence, the entropy goes to zero.
Title:
A long-range hierarchical clustering model for constructing perfect quasicrystalline formations
Authors:
Al Ajlouni, RA Author Full Names: Al Ajlouni, Rima A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2728-2738 Sp. Iss. SI 2011
Abstract:
Since their discovery, the unique structural signature of quasicrystals has posed a perplexing puzzle. Whereas significant progress has been made in determining their physical properties, a deeper understanding of the structure of quasicrystals remains an open question. Although available structural models provide important insights into understanding the quasiperiodic structural order, there is still significant information lacking concerning the determination of the long-range order of quasicrystals. A global multi-level hierarchical framework is presented that is able to describe the long-range translational and orientational order of the global empire pertaining to perfect Penrose tiling (PPT) models. In this order, the global empire is constructed of infinite levels of hierarchical clusters. Any cluster level, in this hierarchy, is composed of four smaller building clusters; two highly symmetrical clusters and their two fragments. Cluster configurations and the geometric arrangements of the multi-level clusters are determined entirely by a geometric progression of framework of nested decagrams. The proposed model suggests that the position of building units, locally and globally, is defined by one global framework, and not tiled based on local rules (matching or overlapping, etc). In this way, quasicrystal formations can grow rapidly ad infinitum without the need for any defects or mismatches.
Title:
Anisotropic Hall effect in Al13TM4 approximants
Authors:
Ivkov, J; Popcevic, P; Stanic, D; Bauer, B; Gille, P; Dolinsek, J; Smontara, A Author Full Names: Ivkov, J.; Popcevic, P.; Stanic, D.; Bauer, B.; Gille, P.; Dolinsek, J.; Smontara, A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2739-2745 Sp. Iss. SI 2011
Abstract:
The Hall coefficient, RH, in monoclinic Y-Al-Ni-Co, orthorhombic Al13Co4 and monoclinic Al13Fe4 and Al13(Fe,Ni)4 single crystals was investigated for all combinations of the electrical current and magnetic field directions and in the temperature interval from 90 to 370 K. In all three intermetallics, which belong to the Al13TM4 (TM = transition metal) class of approximants to the decagonal quasicrystals, the Hall coefficient exhibits well-defined anisotropy. RH is positive hole-like or zero for the magnetic field parallel to the plane that corresponds to the quasiperiodic plane in decagonal (d-) quasicrystals, and is negative electron-like or zero for the magnetic field perpendicular to this plane. The only exception is RH in Al13Fe4 for the field parallel to the stacking direction, which changes its sign from positive to negative value with an increase of temperature. The results for the anisotropy of RH are correlated to the anisotropy of RH in d-Al-Ni-Co and d-Al-Cu-Co quasicrystals and a brief overview of the theoretical results is presented.
Title:
Anisotropic transport properties of the Al13TM4 and T-Al-Mn-Fe complex metallic alloys
Authors:
Smontara, A; Popcevic, P; Stanic, D; Velebit, K; Dolinsek, J Author Full Names: Smontara, A.; Popcevic, P.; Stanic, D.; Velebit, K.; Dolinsek, J.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2746-2755 Sp. Iss. SI 2011
Abstract:
Anisotropy of the transport properties (electrical resistivity, (T), thermoelectric power, S(T), and thermal conductivity, (T)) of the Al76Co22Ni2 (Y-Al-Ni-Co), o-Al13Co4 and T-Al72.5Mn21.5Fe6.0 complex metallic alloys was investigated experimentally. These compounds belong to the class of approximants in decagonal quasicrystals phases with stacked-layer crystallographic structure and enabled us to study the evolution of transport properties with increasing structural complexity and the unit cell size. For Y-Al-Ni-Co and o-Al13Co4, the anisotropic electronic transport coefficients were analyzed theoretically by Boltzmann transport theory and ab initio calculated anisotropic Fermi surface. The non-metallic anisotropic electrical resistivity of the T-Al72.5Mn21.5Fe6.0 may be analyzed in a semi-quantitative way by the theory of quantum transport of slow charge carriers.
Title:
Novel properties of frustrated low-dimensional magnets with pentagonal symmetry
Authors:
Jagannathan, A; Motz, B; Vedmedenko, E Author Full Names: Jagannathan, A.; Motz, Benjamin; Vedmedenko, E.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2765-2772 Sp. Iss. SI 2011
Abstract:
We consider a new type of frustrated spin network with pentagonal loops and long-range quasiperiodic structural order. Five-fold loops can be expected to occur naturally in quasicrystals, and experimental studies of icosahedral alloys show manifestations of local five-fold symmetry in a variety of different physical contexts. Our model considers classical spins placed on the vertices of a subtiling of the two-dimensional Penrose tiling, and interacting with nearest neighbours via antiferromagnetic bonds. The ground state of this fractal system has a complex magnetic structure, and is studied analytically as well by Monte Carlo simulation on finite clusters.
Title:
Fermi surface effects in icosahedral quasicrystals
Authors:
Chernikov, MA; Vekilov, YK Author Full Names: Chernikov, M. A.; Vekilov, Yu. Kh.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2773-2777 Sp. Iss. SI 2011
Abstract:
In icosahedral quasicrystals, due to an interaction of the Fermi sphere with the boundaries of the pseudo-Brillouin zone associated with the strongest Fourier components of the pseudopotential, the Fermi surface consists of many small electron and hole pockets. Such a scenario can be described by the fractional multicomponent model of the Fermi surface. A discussion is provided of the electronic and thermal properties that follow from this model, in particular at high temperatures.
Title:
Breakdown of semi-classical conduction theory in approximants of the octagonal tiling
Authors:
de Laissardiere, GT; Oguey, C; Mayou, D Author Full Names: de Laissardiere, G. Trambly; Oguey, C.; Mayou, D.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2778-2786 Sp. Iss. SI 2011
Abstract:
We present numerical calculations of quantum transport in perfect octagonal approximants. These calculations include a Boltzmann (intra-band) contribution and a non-Boltzmann (inter-band) contribution. When the unit cell size of the approximant increases, the magnitude of the Boltzmann terms decreases, whereas the magnitude of the non-Boltzmann terms increases. This shows that, in large approximants, the non-Boltzmann contributions should dominate the transport properties of electrons. This confirms the breakdown of the Bloch-Boltzmann theory for understanding the transport properties in approximants with very large unit cells, and then in quasicrystals, as found in actual Al-based approximants.
Title:
Variable-range-hopping conductivity in polygrain samples of icosahedral Al-Re-Pd
Authors:
Vekilov, YK; Chernikov, MA Author Full Names: Vekilov, Yu. Kh.; Chernikov, M. A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2787-2791 Sp. Iss. SI 2011
Abstract:
We further develop a model, based on an analogy with granular electronic conductors, which explains the nature of the variable-range-hopping conductivity in polygrain samples of icosahedral Al-Re-Pd with resistivity ratios of [image omitted] in an excess of 13. The electrical conductivity of the model is determined by intergranular tunnelling and electrostatic energy. In polygrain icosahedral Al-Re-Pd, pores and precipitates of secondary phases create the barriers. Depending on the barrier height and electrostatic disorder, either an insulating variable-range-hopping regime of an Efros-Shklovskii or Mott type with elastic co-tunnelling or a metallic regime typical of homogeneously disordered conductors is possible.
Title:
Observation of log-periodic oscillations in the quantum dynamics of electrons on the one-dimensional Fibonacci quasicrystal
Authors:
Lifshitz, R; Mandel, SED Author Full Names: Lifshitz, Ron; Mandel, Shahar Even-Dar
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2792-2800 Sp. Iss. SI 2011
Abstract:
We revisit the question of quantum dynamics of electrons on the off-diagonal Fibonacci tight-binding model. We find that typical dynamical quantities, such as the probability of an electron to remain in its original position as a function of time, display log-periodic oscillations on top of the leading-order power-law decay. These periodic oscillations with the logarithm of time are similar to the oscillations that are known to exist with the logarithm of temperature in the specific heat of Fibonacci electrons, yet they offer new possibilities for the experimental observation of this unique phenomenon.
Title:
Negative refraction and localized states of a classical wave in high-symmetry quasicrystals
Authors:
Zhang, XD; Zhong, W; Feng, ZF; Wang, YQ; Li, ZY; Zhang, DZ Author Full Names: Zhang, Xiangdong; Zhong, Wei; Feng, Zhifang; Wang, Yiquan; Li, Zhi-Yuan; Zhang, Dao-Zhong
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2811-2819 Sp. Iss. SI 2011
Abstract:
Recently, negative refraction of electromagnetic waves in periodic photonic crystals has been demonstrated experimentally and sub-wavelength images observed. A theoretical and experimental investigation is reported of the electromagnetic wave transport in high-symmetry photonic quasicrystals (QCs). It is shown that negative refraction can appear in these transparent quasicrystalline photonic structures. It is interesting that highly symmetric two-dimensional photonic QCs possess a universal feature for non-near-field focus of two kinds of polarized waves (S wave and P wave). That is, the non-near-field focus for two kinds of polarized waves can be realized by using flat lenses, which consist of some high-symmetric two-dimensional photonic QCs with the same structures and parameters. In addition, some two-dimensional and three-dimensional localized states in defect-free photonic QCs have been found. It is evident that these unusual localized states can be explored by means of electron energy loss spectroscopy.
Title:
Internal friction of an Al-Cu-Fe icosahedral quasicrystal and its crystal approximant
Authors:
So, YG; Sato, S; Edagawa, K; Tamura, R Author Full Names: So, Yeong-Gi; Sato, Shun; Edagawa, Keiichi; Tamura, Ryuji
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2820-2827 Sp. Iss. SI 2011
Abstract:
The internal friction was measured for an Al-Cu-Fe icosahedral phase (i-phase) and an Al-Cu-Fe-Si 1/1 approximant phase (1/1-phase) by using a dynamical mechanical analyzer (DMA) in the frequency range 0.05-10 Hz and the temperature range 300-873 K. For the i-phase, four absorption peaks were observed at around 420, 580, 620 and 800 K, respectively. These were of the thermally activated relaxation type, and their activation parameters were evaluated. The parameters evaluated for the peak at 800 K indicate a relaxation process involving a collective atomic motion, which can be attributed to correlated phason jumps. This peak was absent for the 1/1-phase. These results are similar to the results of the internal friction measurements previously reported for an Al-Pd-Mn i-phase and its 1/1 approximant phase. Based on the phonon-phason dynamics model, the magnitudes of phason elastic constants were estimated for the Al-Cu-Fe i-phase.
Title:
On nature of the excess heat capacity in icosahedral quasicrystals
Authors:
Prekul, AF; Shchegolikhina, NI; Edagawa, K Author Full Names: Prekul, A. F.; Shchegolikhina, N. I.; Edagawa, K.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2828-2836 Sp. Iss. SI 2011
Abstract:
Experimental evidence is presented which indicates that the total heat capacity in the Al63Cu25Fe12 icosahedral phase contains a contribution associated with inconstancy of the charge carrier concentration. The contribution has an oscillating temperature dependence and is supposedly traceable to two Schottky-like heat anomalies.
Title:
Effect of Ti addition on the quasicrystalline phase formation and indentation characteristics of Zr69.5Al7.5Cu12Ni11 alloy
Authors:
Singh, D; Yadav, TP; Mandal, RK; Tiwari, RS; Srivastava, ON Author Full Names: Singh, Devinder; Yadav, T. P.; Mandal, R. K.; Tiwari, R. S.; Srivastava, O. N.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2837-2845 Sp. Iss. SI 2011
Abstract:
The crystallisation behaviour and indentation characteristics of melt-spun (Zr69.5Al7.5Cu12Ni11)100-xTix (x = 0-16 at. %) metallic glasses was investigated. Differential scanning calorimetry traces revealed changes in crystallisation behaviour with addition of Ti. Formation of a nanoquasicrystalline phase by annealing the glass was found up to x = 12. Further increase of Ti content gives rise to formation of a Zr2Ni-type crystalline phase. In addition to this, the size of nanoquasicrystals decreases with increasing addition of Ti. The load-dependent hardness behaviour of the metallic glasses and nanoquasicrystal-glass composites is reported in detail. The value of the yield strength of the materials was estimated with the help of hardness values based on the empirical correlations available in literature. The formation of shear bands around the indentation periphery was observed. It was found that microstructural and morphological changes alter the indentation characteristic! s of glasses as well as composites formed after controlled crystallisation.
Title:
Multi-cluster model of Al-Co-Ni Co-rich quasicrystal
Authors:
Yuhara, J; Sato, M; Matsui, T; Tsai, AP Author Full Names: Yuhara, J.; Sato, M.; Matsui, T.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2846-2853 Sp. Iss. SI 2011
Abstract:
We studied the surface modification of Al-Co-Ni Co-rich quasicrystals by Co or Ni deposition, using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). After depositing 0.2 monolayers (ML) of Co or Ni with post-annealing, no clear changes were observed in the spot intensity or pattern of LEED. Only the uppermost surface was successfully modified. Based on the STM images of the modified surface, we found that excess Co atoms modified the 2-nm Co clusters to form 0.47-nm clusters and that excess Ni atoms only formed 0.29-nm Ni clusters on the Al-Co-Ni Co-rich quasicrystal surface. Finally, based on the STM images of a clean Co-rich surface, the Al positions proposed by transmission electron microscopy has been modified to match the STM image. To account for the data, we propose a multi-cluster model - based in part on the Hiraga model - composed of three main clusters for both A and B stacking layers.
Title:
Asymmetric pentagonal cluster on an Al-Cu-Co quasicrystal surface
Authors:
Zenkyu, R; Matsui, T; Tsai, AP; Yuhara, J Author Full Names: Zenkyu, R.; Matsui, T.; Tsai, A. P.; Yuhara, J.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2854-2861 Sp. Iss. SI 2011
Abstract:
The 10-fold surface of a decagonal Al66Cu17Co17 quasicrystal has been studied by scanning tunneling microscopy (STM). Three kinds of characteristic pentagonal clusters are observed in the STM images. Clusters within a given terrace have the same orientation, while those in adjacent terraces have opposite orientations. We show that two of the pentagonal cluster types are part of the 2-nm cluster, which is considered to be the basic structural unit of the Al-Cu-Co quasicrystal. The local atomic arrangement in the 2-nm clusters is found to be asymmetric.
Title:
Step-terrace morphology and reactivity to C60 of the five-fold icosahedral Ag-In-Yb quasicrystal
Authors:
Nugent, PJ; Smerdon, JA; McGrath, R; Shimoda, M; Cui, C; Tsai, AP; Sharma, HR Author Full Names: Nugent, P. J.; Smerdon, J. A.; McGrath, R.; Shimoda, M.; Cui, C.; Tsai, A. P.; Sharma, H. R.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2862-2869 Sp. Iss. SI 2011
Abstract:
The surface of the icosahedral i-Ag-In-Yb quasicrystal provides one of the first non-Al-based aperiodic surfaces that is suitable for study under ultra-high vacuum conditions. We present a scanning tunnelling microscopy (STM) study of the five-fold surface of this new quasicrystal demonstrating detailed structure of the terraces and steps. The analysis of the autocorrelation functions of STM images at opposite bias polarities and of the in-plane structure of the bulk model of i-Cd-Yb, which is isostructural to i-Ag-In-Yb, reveals that the surface terminations occur at the centres of the rhombic triacontrahedral (RTH) clusters, which are the basic building blocks of this material. The study further confirms that the unoccupied electronic states are located on Yb sites. Step edges display a Fibonacci sequence of truncated clusters, which can also be explained in terms of the model structure. Occasionally, a single terrace is found to display different structures at negative bias, whereas the same terrace shows a uniform structure at positive bias. Depositing C60 creates a disordered overlayer on the surface with no resulting FFT or LEED patterns.
Title:
Influence of the substrate temperature and deposition flux in the growth of a Bi thin film on the ten-fold decagonal Al-Ni-Co surface
Authors:
Sharma, HR; Ledieu, J; Fournee, V; Gille, P Author Full Names: Sharma, H. R.; Ledieu, J.; Fournee, V.; Gille, P.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2870-2878 Sp. Iss. SI 2011
Abstract:
We compare the growth of a Bi thin film on the ten-fold surface of the decagonal Al-Ni-Co quasicrystal at different substrate temperatures and fluxes using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The growth at 29 K leads to the formation of a quasicrystalline monolayer, consistent with the results obtained at 300 K. Further deposition at low temperature produces pseudocubic islands with {100} surface orientation. The islands have two or four atomic layer heights. Both STM and LEED measurements reveal that there is a transition from the pseudocubic {100} film to the hexagonal {0001} surface orientation at coverage () 4 6 ML. The hexagonal domains are oriented along the high symmetry directions of the substrate. Growth at room temperature with different fluxes results in different island-height distributions. High flux predominantly produces islands of uniform four-layer high islands, whereas low flux yields islands of varying heig! hts, yielding a rough film morphology. The two-layer high islands are found to be more stable at low temperature than at room temperature.
Title:
Weak bonding of Zn in an Al-based approximant based on surface measurements
Authors:
Yuen, CD; Unal, B; Jing, DP; Thiel, PA Author Full Names: Yuen, Chad D.; Unal, Baris; Jing, Dapeng; Thiel, Patricia A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2879-2888 Sp. Iss. SI 2011
Abstract:
We have studied two surfaces of a new Al-Pd-Zn approximant using mass spectrometry, X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM). Zn is bonded weakly in this approximant, perhaps as weakly as in elemental Zn. This is based upon three observations: (1) the low vapor pressure of Zn above the approximant (detectable in the gas phase at 600 K), (2) preferential sputtering of Zn (contrary to the usual preferential sputtering of Al in Al-rich quasicrystals), and (3) preferential surface segregation of Zn. We further show that preferential segregation - and perhaps incipient evaporation - causes the surface to roughen, preventing it from forming a terrace-step morphology. Finally, our data show that at low O2 pressures, Al oxidizes. In air, Zn oxidizes as well. All results and conclusions are similar for the two-fold and pseudo-10-fold surfaces.
Title:
XPS study of adsorption and desorption of a Bi thin film on the five-fold icosahedral Al-Pd-Mn surface
Authors:
Young, KM; Cross, N; Smerdon, JA; Dhanak, VR; Sharma, HR; Lograsso, TA; Ross, AR; McGrath, R Author Full Names: Young, K. M.; Cross, N.; Smerdon, J. A.; Dhanak, V. R.; Sharma, H. R.; Lograsso, T. A.; Ross, A. R.; McGrath, R.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2889-2893 Sp. Iss. SI 2011
Abstract:
We have employed X-ray photoelectron spectroscopy to characterise the growth and thermal stability of a Bi thin film on the five-fold icosahedral Al-Pd-Mn surface. The growth can be characterised as Stranski-Krastanov, in agreement with previous STM studies. As a function of annealing temperature, the multilayer desorbs first and thereafter coverages of 1 ML and 0.5 ML are stable for significant temperature ranges.
Title:
Catalytic properties of Al13Co4 studied by ab initio methods
Authors:
Krajci, M; Hafner, J Author Full Names: Krajci, M.; Hafner, J.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2904-2912 Sp. Iss. SI 2011
Abstract:
While the surfaces of ordinary crystals provide only a few inequivalent adsorption sites, the complex landscape of the surfaces of quasicrystals and their approximants provides a rich variety of different adsorption sites. Recently, Armbruster et al. reported that Al13Co4, whose structure is closely related to decagonal Al-Ni-Co quasicrystals, is an efficient and selective hydrogenation catalyst for alkynes. In the present work, the hydrogenation of acetylene to ethylene on the (100) surface of Al13Co4 has been studied using ab initio density-functional simulations. Surprisingly, the stable cleavage surface of Al13Co4 is strongly corrugated. The surface is covered by zig-zag chains of edge-sharing Al pentagons, each centered on a Co atom and separated from neighboring chains by wide troughs. The binding energies for adsorption and co-adsorption of H2 and C2H2 molecules at various surface sites have been calculated. Surprisingly, in the energetically most favorable conf! iguration, acetylene is bound in a di-sigma configuration to two Al atoms, not to the Co atom. We have searched for the optimal reaction pathway for the dissociatible adsorption of hydrogen and for the hydrogenation of acetylene to vinyl, ethylene by a Langmuir-Hinshelwood mechanism. The energetic barriers for all reaction steps were calculated by the nudged-elastic-band method. It was found that the energetic barrier of any reaction step does not exceed 0.65 eV (63 kJ/mol). This value is lower than the activation energies for acetylene to ethylene hydrogenation over a Pd catalyst where barriers of 78 kJ/mol and 85 kJ/mol were reported for the rate-determining steps.
Title:
Theoretical studies on clean and adsorbed surfaces of Ag-In-Yb
Authors:
Nozawa, K; Ishii, Y Author Full Names: Nozawa, Kazuki; Ishii, Yasushi
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2913-2919 Sp. Iss. SI 2011
Abstract:
The adsorption structure of Pb atoms on the five-fold surface of a AgInYb quasicrystal is studied using a first-principles calculation. The aperiodic five-fold surface is replaced by a cluster model, following the quasicrystal model by Takakura et al. The potential energy surface (PES) for a single Pb adsorption reflects the five-fold symmetry of the substrate. The most preferred adsorbed site is a five-fold hollow site surrounded by three In and two Yb atoms, and the most preferred sites form a pentagon with edge length 9.9 angstrom. The PES for the second adsorbed atom is calculated to examine the effects of interadsorbate interaction. It turns out that the interadsorbate interaction is limited, and it does not change the PES essentially. Thus, at low coverage, the Pb atoms presumably adsorb onto the five-fold hollow sites, forming a Pb pentagon with edge length 9.9 angstrom around the cluster center. Possible adsorption structures at higher coverage are also discussed.
Title:
Synthesis of porous Cu from Al-Cu-Co decagonal quasicrystalline alloys
Authors:
Vani, VK; Kwon, OJ; Hong, SM; Fleury, E Author Full Names: Vani, V. Kalai; Kwon, O. J.; Hong, S. M.; Fleury, E.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2920-2928 Sp. Iss. SI 2011
Abstract:
The formation of a porous Cu structure from cast Al-Cu-Co decagonal quasicrystalline alloys has been studied using a selective corrosion technique. Two alkaline solutions were selected based on the electrochemical properties of the constituent elements. Selective corrosion of Al and Co was achieved by chemical immersion of the cast Al-Cu-Co alloy in both 5 M NaOH and 0.5 M Na2CO3 solutions; values for BET surface-to-weight ratio of up to 30 m2/g could be reached. Microstructural analyses indicated that the architecture of the resulting porous structures was composed of a needle-type phase, remaining from the decagonal phase, in addition to Cu and Cu-Co phases.
Title:
Preparation and wear resistance of Ti-Zr-Ni quasicrystal and polyamide composite materials
Authors:
Wang, XL; Li, XS; Zhang, ZJ; Zhang, SS; Liu, WQ; Wang, LM Author Full Names: Wang, Xinlu; Li, Xuesong; Zhang, Zhenjiang; Zhang, Shanshan; Liu, Wanqiang; Wang, Limin
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2929-2936 Sp. Iss. SI 2011
Abstract:
Ti-Zr-Ni icosahedral quasicrystal powders (Ti-QC), prepared by mechanical alloying and then annealing in a vacuum furnace, were used as a novel filler material in polyamide 12 (PA12). The melt processability of the composite was studied using a Haake torque rheometer. This indicates that PA12/Ti-QC composites can be melt-processed into a wear-resistant material. Further, these composites, fabricated by compression molding, were tested in sliding wear against a polished bearing steel counterface. The results from wear testing show that the addition of Ti-QC filler to PA12 enhances wear resistance and reduces volume loss by half compared with neat PA12. Furthermore, it is found that the hardness of the composite increases with increasing content of Ti-QC filler. In addition, PA12/Ti-QC composites exhibit a slightly higher crystallization temperature and better thermal stability than PA12. These combined results demonstrate that Ti-QC filler may be a desirable alternative when attempting to increase the wear resistance of PA12.
Title:
Pressure-composition-temperature curves and structure stability induced by hydrogen in TiZrNi quasicrystals
Authors:
Choi, SB; Lee, SH; Kim, JY Author Full Names: Choi, Soo-bin; Lee, Sang-hwa; Kim, Jae Yong
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2937-2943 Sp. Iss. SI 2011
Abstract:
To evaluate the potential applications of Ti-based quasicrystals as hydrogen storage materials, metastable Ti53-xZr27Ni20Pdx (x = 0, 2, 4, 6) quasicrystals were prepared by a rapid quenching method and equilibrium vapor pressures for hydrogen were measured. Pressure-composition-temperature curves measured in Pd-added TiZrNi quasicrystals revealed a significantly increased equilibrium vapor pressure for hydrogen with increasing Pd concentration, while hydrogen loading capacity decreased. After hydrogen absorption, no hydride phase was found for samples made with less than x = 4. The main peaks shifted to the lower angle of 2 in X-ray diffraction patterns, demonstrating that the quasi-lattice constants increased from 5.13 to 5.38 angstrom after hydrogenation. The quasi-lattice constants linearly expanded with increasing absorption amount of hydrogen. Interestingly, analyzing the full width at half maximum values of the main peaks in the X-ray diffraction patterns showed that the coherence lengths of the quasicrystals significantly increased from 120 to 240 angstrom after hydrogenation, presumably due to kinetic rather than thermal factors.
Title:
Novel HDPE-quasicrystal composite fabricated for wear resistance
Authors:
Kothalkar, A; Sharma, AS; Biswas, K; Basu, B Author Full Names: Kothalkar, Ankush; Sharma, Amit S.; Biswas, Krishanu; Basu, Bikramjit
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2944-2953 Sp. Iss. SI 2011
Abstract:
The present paper reports, for the first time, the processing, characterization and wear property of a novel HDPE-decagonal quasicrystal (QC) composite prepared by compression molding. The composites were prepared at 130 degrees C and an applied pressure of 0.735 MPa with different holding time to obtain a fully dense product. It was found that a holding time of 60 min is the optimum at the specified melting temperature and pressure. The second phase (QC) content was varied from 5 to 20 wt% to obtain optimum mechanical properties. SEM observations indicate well-dispersed QC particles within the HDPE matrix, with fine scale distribution for 20 wt% QC. Ball-on-disc wear tests revealed that the composites showed better wear resistance than pure HDPE samples. The results are discussed using the currently available literature.
Title:
Atomic pair distribution function (PDF) analysis of Raney Pd and Rh fine particles
Authors:
Murao, R; Sugiyama, K; Kashiwagi, Y; Kameoka, S; Tsai, AP Author Full Names: Murao, R.; Sugiyama, K.; Kashiwagi, Y.; Kameoka, S.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2954-2961 Sp. Iss. SI 2011
Abstract:
Raney Pd and Rh fine particles were prepared from decagonal Al75Pd25 and Al9Rh2 with an Al9Co2-type structure, respectively, by leaching with NaOH aqueous solution. The atomic pair distribution functions (PDFs) for the Raney Pd and Rh fine particles indicate structural features similar to an fcc structure, suggesting atomic rearrangement toward the closest packing of constituents during the leaching process. Transmission electron micrographs indicate that Raney Pd and Rh are aggregates of fcc-structured nano-crystallites with a diameter of 5-6 nm.
Title:
Quasicrystals: diversity and complexity
Authors:
Dubois, JM; Lifshitz, R Author Full Names: Dubois, Jean-Marie; Lifshitz, Ron
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2971-2982 Sp. Iss. SI 2011
Abstract:
Scientific presentations at ICQ11 the 11th International Conference on Quasicrystals, which took place in Sapporo, Japan, in June 2010 offered a variety of stimulating new experimental data and novel theoretical results. New aperiodic crystals were presented; new theoretical ideas were described; exciting experimental results were revealed; and potential applications of quasicrystals were reviewed, showing an unprecedented level of development. ICQ11 was a great success thanks to the high standard of its scientific content and to the efficiency of its organization. ICQ11 proved that quasicrystal research is sure to continue offering diverse challenges and profound insights into the complexity of matter.
Title:
Hydrothermal synthesis of compounds in the fresnoite mineral family (Ba2TiSi2O8)
Authors:
Abbott, EE; Mann, M; Kolis, JW Author Full Names: Abbott, Edward E.; Mann, Matthew; Kolis, Joseph W.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 184 (5): 1257-1262 MAY 2011
Abstract:
Crystals of Ba2TiSi2O8, Sr2TiSi2O8, and Ba2VSi2O8, all belonging to the fresnoite family were prepared by the hydrothermal method. Attempts to synthesize other members by substitution at the alkaline earth site, transition metal site, and tetrahedral site were not successful, but did lead to the formation of a variety of other mineral phases as well as the incommensurate structure, Ba2TiGe2O8. Structural studies on this compound and analysis of the other known fresnoite phases were performed to elucidate the nature of the incommensurate structure. (C) 2011 Elsevier Inc. All rights reserved.
Title:
Critical behaviour of optical birefringence near the normal-incommensurate phase transition in [N(CH3)(4)](2)ZnCl4 crystals under the influence of hydrostatic pressure
Authors:
Kushnir, OS; Kityk, AV; Dzyubanski, VS; Shopa, RY Author Full Names: Kushnir, O. S.; Kityk, A. V.; Dzyubanski, V. S.; Shopa, R. Y.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (22): Art. No. 225403 JUN 8 2011
Abstract:
We have estimated the Ginzburg number G governing crossover from the asymptotic to the classical critical behaviour near the normal-incommensurate phase transition in [N(CH3)(4)](2)ZnCl4 (TMAZC) crystals and the dependence of G on the hydrostatic pressure (0.1-330 MPa), following from the experimental data for the optical birefringence and the quantitative analysis of temperature derivatives of the birefringence in the framework of the approximation of weak Gaussian fluctuations. The Ginzburg number found experimentally for TMAZC is G similar to 8 x 10(-3) at the atmospheric pressure and a considerable part of it is assumed to refer to structural defects. It is shown that the G value for TMAZC decreases with increasing hydrostatic pressure and, based on analysis of the literature birefringence data for Cs2CdBr4 and Cs2HgBr4 crystals, this behaviour might be expected to be generally typical for all the A(2)BX(4) family. The results obtained are discussed using a phenomenological theory of second-order structural phase transitions. In particular, they provide a basis for estimating the limits of the asymptotic critical region in TMAZC and demonstrate that the major part of the incommensurate phase should belong to the crossover region.
Title:
The first find of dodecagonal quasiperiodic tiling in historical Islamic architecture
Authors:
Makovicky, E; Makovicky, NM Author Full Names: Makovicky, Emil; Makovicky, Nicolette M.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 44: 569-573 Part 3 JUN 2011
Abstract:
The tympanum of the entrance of the Zaouia Moulay Idriss II in Fez contains the only known example of a dodecagonal cartwheel quasiperiodic pattern in Islamic art, dating possibly from the Merinid epoch. This pattern, carved in a marble plate, is based on a type of Ammann quasilattice known also from modern mathematical literature. The central portions of this pattern were used as elements in a periodic pattern on the walls of the Saadian mausoleum in Marrakech.
Title:
Three-Dimensional Atomic Images of TlInSe2 Thermoelectric Material Obtained by X-ray Fluorescence Holography
Authors:
Hosokawa, S; Happo, N; Hayashi, K; Mimura, K; Wakita, K; Hu, W; Ishii, H; Yoshimura, M; Jeyakanthany, J; Mamedov, N Author Full Names: Hosokawa, Shinya; Happo, Naohisa; Hayashi, Kouichi; Mimura, Kojiro; Wakita, Kazuki; Hu, Wen; Ishii, Hirofumi; Yoshimura, Masato; Jeyakanthany, Jeyaraman; Mamedov, Nazim
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS 50 (5): Art. No. 05FC06 Part 3 Sp. Iss. SI MAY 2011
Abstract:
Three-dimensional (3D) atomic images around the Tl atoms in single-crystal TlInSe2 thermoelectric material in the incommensurate phase were reconstructed by Tl L-III X-ray fluorescence holography measured at room temperature. In the obtained 3D image, the In atoms are clearly visible at the proper positions in the normal phase. The Tl atomic images are also observed but very weakly. By comparing the experimental image with a theoretically calculated one, it is concluded that only the Tl atoms have large spatial fluctuations, which are related to the incommensurate phase of this material. (C) 2011 The Japan Society of Applied Physics
Title:
Charged Defects as an Origin of the Memory Effect in Incommensurate Phase of TlInS2 Ferroelectric-Semiconductors
Authors:
Seyidov, MY; Suleymanov, RA; Mammadov, TG; Fedotov, AK; Babayev, SS; Sharifov, GM Author Full Names: Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Mammadov, Tofig G.; Fedotov, Aleksandr K.; Babayev, Sardar S.; Sharifov, Galib M.
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS 50 (5): Art. No. 05FD07 Part 3 Sp. Iss. SI MAY 2011
Abstract:
The effects of annealing within the incommensurate phase and doping with the lanthanum impurity on the dielectric function epsilon of the TlInS2 single crystals have been investigated. It is shown that illumination and application of external electric field transform the epsilon(T) dependences for both the annealed and doped samples in the same manner. The inference is made that the correlation between observed effects is conditioned by the internal electric fields induced either by activation (polarization) of native defects during the annealing procedure or after the doping the crystals with active La centers. (C) 2011 The Japan Society of Applied Physics
Title:
An Incommensurately Modulated Structure of eta '-Phase of Cu3+xSi Determined by Quantitative Electron Diffraction Tomography
Authors:
Palatinus, L; Kementova, M; Drinek, V; Jarosova, M; Petricek, V Author Full Names: Palatinus, Lukas; Kementova, Mariana; Drinek, Vladislav; Jarosova, Marketa; Petricek, Vaclav
Source:
INORGANIC CHEMISTRY 50 (8): 3743-3751 APR 18 2011
Abstract:
The diffraction data of eta'-Cu3+x(Si,Ge) were collected by 3D quantitative electron diffraction tomography on a submicrometer-sized sample, and the structure was solved by the charge-flipping algorithm in superspace. It is shown that the structure is trigonal, and it is incommensurately modulated with two modulation vectors q(1) = (alpha, alpha, 1/3) and q(2) = (-2 alpha, alpha, 1/3), superspace group P (3) over bar 1m (alpha, alpha, 1/3)000(-2 alpha, alpha, 1/3)000. The modulation functions of some atoms are very complicated and reach amplitudes comparable with the unit cell dimensions. The modulated structure can be described as sheets of Cu clusters separated by honeycomb layers of mixed Si/Ge positions. The shape of the Cu clusters in the sheets strongly varies with the modulation phase, and the predominant form is an icosahedron. The striving of the Cu layers to form icosahedral clusters is deemed to be the main driving force of the modulation. The combination of methods used in this work can be applied to other structures that are difficult to crystallize in large crystals and opens new perspectives, especially for investigations of aperiodic or otherwise complex metallic alloys.
Title:
Icosahedrite, Al63Cu24Fe13, the first natural quasicrystal
Authors:
Bindi, L; Steinhardt, PJ; Yao, N; Lu, PJ Author Full Names: Bindi, Luca; Steinhardt, Paul J.; Yao, Nan; Lu, Peter J.
Source:
AMERICAN MINERALOGIST 96 (5-6): 928-931 MAY-JUN 2011
Abstract:
Icosahedrite, ideally Al63Cu24Fe13, is a new mineral from the Khatyrka River, southeastern Chukhotka, Russia. It occurs as dark gray-black anhedral to subhedral grains up to 100 mu m across, closely associated with spine!, diopside, forsterite, nepheline, sodalite, corundum, stishovite, khatyrkite, cupalite, and an unnamed phase of composition AlCuFe. Icosahedrite is opaque with a metallic luster, possesses a gray streak, and is brittle with an uneven fracture. The density could not be determined. For quasicrystals, by definition, the structure is not reducible to a single three-dimensional unit cell, so neither cell parameters nor Z can be given. In plane-polarized incident light, icosahedrite exhibits neither bireflectance nor pleochroism. Between crossed polars, it is isotropic. Reflectance percentages (R-min = R-max) for the four standard COM wavelengths are 62.3 (471.1 nm), 60.6 (548.3 nm), 58.1 (586.6 nm), and 56.0 (652.3 nm), respectively. The X-ray powder pattern was indexed on the basis of six integer indices, as conventionally used with quasicrystals, where the lattice parameter (in six-dimensional notation) is measured to be a(6D) = 12.64 angstrom, with probable space group Fm (3) over bar (5) over bar. The four strongest X-ray powder-diffraction lines [d in angstrom (I/I-0)(n(1),n(2),n(3),n(4),n(5),n(6))] are: 2.006 (100) (4 (2) over bar0 042), 2.108 (90) (42 (2) over bar (2) over bar 22), 1.238 (30) (60 (4) over bar 064), and 3.41 (25) (31 (1) over bar (1) over bar 11). Average results of 34 electron-microprobe analyses gave, on the basis of total atoms = 100, the formula Al63.11Cu24.02Fe12.78Si0.03Co0.01Ca0.01Zn0.01Cr0.02Cl0.01. The simplified formula is Al63Cu24Fe13, which requires the mass fractions Al 43.02, Cu 38.60, Fe 18.38, total 100.00 wt%. The new mineral is named for the icosahedral symmetry of its internal atomic structure, as observed in its diffraction pattern. Both the new mineral and mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification, IMA (2010-042).
Title:
Twin relationships of 5M modulated martensite in Ni-Mn-Ga alloy
Authors:
Li, ZB; Zhang, YD; Esling, C; Zhao, X; Zuo, L Author Full Names: Li, Zongbin; Zhang, Yudong; Esling, Claude; Zhao, Xiang; Zuo, Liang
Source:
ACTA MATERIALIA 59 (9): 3390-3397 MAY 2011
Abstract:
For Ni-Mn-Ga ferromagnetic shape memory alloys, the characteristic features of modulated martensite (including the number/shape of constituent variants, the inter-variant orientation relationship and the geometrical distribution of variant interfaces) determine the attainability of the shape memory effect. In the present work, a comprehensive microstructural and crystallographic investigation has been conducted on a bulk polycrystalline Ni50Mn28Ga22 alloy. As a first attempt, the orientation measurements by electron backscatter diffraction (EBSD) - using the precise information on the commensurate 5M modulated monoclinic superstructure (instead of the conventionally simplified non-modulated tetragonal structure) - were successfully performed to identify the crystallographic orientations on an individual basis. Consequently, the morphology of modulated martensite, the orientation relationships between adjacent variants and the characters of twin interfaces were unambiguously determined. With the thus-obtained full-featured image on the configuration of martensitic variants, the possibility of microstructural modification by proper mechanical "training" was further discussed. This new effort makes it feasible to explore the crystallographic/microstructural correlations in modulated martensite with high statistical reliability, which in turn provides useful guidance for optimizing the microstructure and shape memory performance. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Modulated anharmonic ADPs are intrinsic to aperiodic crystals: a case study on incommensurate Rb2ZnCl4
Authors:
Li, L; Wolfel, A; Schonleber, A; Mondal, S; Schreurs, AMM; Kroon-Batenburg, LMJ; van Smaalen, S Author Full Names: Li, Liang; Woelfel, Alexander; Schoenleber, Andreas; Mondal, Swastik; Schreurs, Antoine M. M.; Kroon-Batenburg, Loes M. J.; van Smaalen, Sander
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 67: 205-217 Part 3 JUN 2011
Abstract:
A combination of structure refinements, analysis of the superspace MEM density and interpretation of difference-Fourier maps has been used to characterize the incommensurate modulation of rubidium tetrachlorozincate, Rb2ZnCl4, at a temperature of T = 196 K, close to the lock-in transition at T (lock-in) = 192 K. The modulation is found to consist of a combination of displacement modulation functions, modulated atomic displacement parameters (ADPs) and modulated third-order anharmonic ADPs. Up to fifth-order Fourier coefficients could be refined against diffraction data containing up to fifth-order satellite reflections. The center-of-charge of the atomic basins of the MEM density and the displacive modulation functions of the structure model provide equivalent descriptions of the displacive modulation. Modulations of the ADPs and anharmonic ADPs are visible in the MEM density, but extracting quantitative information about these modulations appears to be difficult. In the structure refinements the modulation parameters of the ADPs form a dependent set, and ad hoc restrictions had to be introduced in the refinements. It is suggested that modulated harmonic ADPs and modulated third-order anharmonic ADPs form an intrinsic part, however small, of incommensurately modulated structures in general. Refinements of alternate models with and without parameters for modulated ADPs lead to significant differences between the parameters of the displacement modulation in these two types of models, thus showing the modulation of ADPs to be important for a correct description of the displacive modulation. The resulting functions do not provide evidence for an interpretation of the modulation by a soliton model.

Update: 27-May-2011

Title:
Spatially modulated antiferromagnetic structures in an easy-plane multiferroic
Authors:
Kulagin, NE; Popkov, AF; Zvezdin, AK Author Full Names: Kulagin, N. E.; Popkov, A. F.; Zvezdin, A. K.
Source:
PHYSICS OF THE SOLID STATE 53 (5): 970-977 MAY 2011
Abstract:
Possible types of spatially modulated periodic antiferromagnetic structures in a uniaxial rhombohedral multiferroic with BiFeO3 crystal symmetry have been studied depending on the ratio of the uniaxial anisotropy and magnetoelectric interaction parameters. It has been shown that, along with symmetric cycloid antiferromagnetic structures with zero transverse component of the antiferromagnetism vector, there are changes in the antiferromagnetism vector direction with both right and left nonzero components of the antiferromagnetic moment, which are branched from the high-symmetry spatially modulated distribution. These solutions degenerate into a homogeneous state at a critical value of the normalized easy-plane anisotropy parameter. The existence of the found spatially inhomogeneous antiferromagnetic states with an incommensurate period can lead to additional features in magnetoelectric properties in multiferroics of the type under consideration near magnetic phase transitions in electric and magnetic fields.
Title:
Short-range-order diffuse scattering in decagonal Ni-rich Al-Ni-Co quasicrystals
Authors:
Yamamoto, A Author Full Names: Yamamoto, Akiji
Source:
PHYSICAL REVIEW B 83 (18): Art. No. 184203 MAY 12 2011
Abstract:
An analytical expression of the diffuse scattering (DS) intensity due to short-range order derived in a recent paper [A. Yamamoto, Acta Crystallogr. Sect. A 66, 372 (2010)] is applied to analyze DS intensities of the S1 phase at 1120 K and the quenched basic Ni rich (b-Ni) phase in decagonal Al70Ni22Co8 (d-Al70Ni22Co8) quasicrystals. The analysis is based on a microdomain model consisting of 20 angstrom clusters. The S1 and b-Ni phases are low-and high-temperature phases of d-Al70Ni22Co8 so that microdomains with the S1 phase structure are assumed to be formed in the b-Ni phase and vice versa. The intercluster correlation of the 20 angstrom clusters within the microdomains is assumed to be the same as that in a corresponding completely ordered structure up to the third intercluster distance similar or equal to 32 angstrom. It is demonstrated that simulated DS intensity distributions reproduce characteristic features in the observed DS intensity in these phases. This sugg! ests that the analysis of DS intensity is efficient for understanding phase transition mechanisms of quasicrystals. It also shows the effectiveness of the theory and applicability of cluster-based DS intensity calculations to real quasicrystals, which reduce the number of short-range-order parameters drastically.
Title:
Microstructure of Rapidly Solidified Al-12Zn-3Mg-1.5Cu Alloy with Zr and Sc Additions
Authors:
Litynska-Dobrzynska, L; Dutkiewicz, J; Maziarz, W; Goral, A Author Full Names: Litynska-Dobrzynska, Lidia; Dutkiewicz, Jan; Maziarz, Wojciech; Goral, Anna
Source:
MATERIALS TRANSACTIONS 52 (3): 309-314 Sp. Iss. SI MAR 2011
Abstract:
The rapid solidification of Al-12 Mg-1.5 Cu (in mass%) alloy was investigated in order to determine structure changes and the effect of Zr or Sc+Zr additions. Rapidly solidified ribbons with the thickness of 30-50 pm were obtained by a melt spinning technique. The alloys cast into a copper mould were used as a reference material. The mould cast alloys as well as the melt spun ribbons revealed the dendritic microstructure of alpha(Al) solid solution and eta(MgZn2) phase in the interdendritic areas. Additionally the T-Mg-32(Zn. Al)(49) phase with icosahedral quasicrystalline symmetry was found in the form of small particles located mainly at the wheel side in the Zr or Zr+Sc containing ribbons. The refinement of the microstructure and the reduction of volume fraction of the eta phase was observed in the ribbons. Large Al3Zr primary precipitates were observed in the mould cast alloy containing zirconium, while almost whole Zr in the ribbons dissolved in the aluminium solid ! solution. Annealing of ribbons at 400 degrees C led to the precipitation of spherical L1(2)-Al3Zr or Al-3(Sc, Zr) particles, coherent with the matrix. They could be responsible for the improvement of properties of the aluminium alloys by the retardation of recrystallization and grain growth. Plate like precipitates of metastable eta' phase appeared after ageing at 120 degrees C and led to the increase of microhardness up to about 230 HV. [doi:10.2320/matertrans.MB201009]
Title:
Neutron Diffraction Investigations of Magnetism in BiFeO3 Epitaxial Films
Authors:
Ratcliff, W; Kan, D; Chen, WC; Watson, S; Chi, SX; Erwin, R; McIntyre, GJ; Capelli, SC; Takeuchi, I Author Full Names: Ratcliff, William, II; Kan, Daisuke; Chen, Wangchun; Watson, Shannon; Chi, Songxue; Erwin, Ross; McIntyre, Garry J.; Capelli, Sylvia C.; Takeuchi, Ichiro
Source:
ADVANCED FUNCTIONAL MATERIALS 21 (9): 1567-1574 MAY 10 2011
Abstract:
The recovery of a modulated magnetic structure in epitaxial BiFeO3 thin films as revealed by neutron diffraction is reported. The magnetic structure in thin films is found to strongly depend on substrate orientation. The substrate orientation causes different strain-relaxation processes resulting in different thin-film crystal structures. The (110) oriented film with a monoclinic structural phase has a single-domain modulated magnetic structure where the magnetic moment lies in the HHL plane. For the (111) oriented film that has a rhombohedral structure, a modulated structure superimposed on the G-type antiferromagnetic order is found. These results indicate that slight structural modifications in the BiFeO3 thin film cause drastic changes in the magnetic structure.

Update: 20-May-2011

Title:
Ground State of the Quasi-1D Compound BaVS3 Resolved by Resonant Magnetic X-Ray Scattering
Authors:
Leininger, P; Ilakovac, V; Joly, Y; Schierle, E; Weschke, E; Bunau, O; Berger, H; Pouget, JP; Foury-Leylekian, P Author Full Names: Leininger, Ph.; Ilakovac, V.; Joly, Y.; Schierle, E.; Weschke, E.; Bunau, O.; Berger, H.; Pouget, J. -P.; Foury-Leylekian, P.
Source:
PHYSICAL REVIEW LETTERS 106 (16): Art. No. 167203 APR 21 2011
Abstract:
Resonant magnetic x-ray scattering near the vanadium L-2,L-3-absorption edges has been used to investigate the low temperature magnetic structure of high quality BaVS3 single crystals. Below T-N = 31 K, the strong resonance revealed a triple-incommensurate magnetic ordering at the wave vector (0.226 0.226 xi) in hexagonal notation, with xi = 0.033. The azimuthal-angle dependence of the scattering signal and time-dependent density functional theory simulations indicate an antiferromagnetic order within the ab plane with the spins polarized along a in the monoclinic structure.
Title:
Non-nesting spin-density-wave antiferromagnetism in FeAs from first principles
Authors:
Parker, D; Mazin, II Author Full Names: Parker, David; Mazin, I. I.
Source:
PHYSICAL REVIEW B 83 (18): Art. No. 180403 MAY 2 2011
Abstract:
The antiferromagnetic (AFM) state of FeAs is very different from that of the FeAs-based superconductor parent compounds, and it is rather complicated, with the Fe spins forming an incommensurate magnetic spiral pattern with a wavelength of about 15 A. To model this, we perform first-principles calculations and find the nearest-neighbor AFM ordering to be energetically favorable, with the lowest-energy pattern reproducing the experimentally found nearest-neighbor correlations. Other AFM orderings are also very stable, although higher in energy. Unlike in the superconductor parent compounds, the Fermi-surface geometry thus plays a small role. We calculate the bare Lindhard susceptibility in the AFM state and find that the observed spin-density-wave ordering vector Q similar or equal to (0,0,0.4) is not that given by this calculation. This is again unlike the superconductor parent compounds, which generally show a magnetic pattern matching the Lindhard susceptibility maximum. Thus in FeAs, the observed pattern must be due to a subtler mechanism.
Title:
Fermionic Representation of Two-Dimensional Dimer Models
Authors:
Grande, HLC; Salinas, SR; da Costa, FA Author Full Names: Casa Grande, Helder L.; Salinas, S. R.; da Costa, F. A.
Source:
BRAZILIAN JOURNAL OF PHYSICS 41 (1): 86-93 MAY 2011
Abstract:
Dimer models in two dimensions give rise to well-known statistical lattice problems, which can be exactly solved by the same combinatorial techniques associated with the Ising model and which have been used to account for the phase transitions in a number of physically interesting systems. More recently, dimer models have been regarded as classical limits of the quantum ground state of some antiferromagnetic systems. We then revisit an early transfer-matrix calculation for the dimer model on the simple square lattice. We write a spin representation for the transfer matrix associated with the canonical partition function of two paradigmatic dimers models, on the 4-8 lattice, with an Ising-type transition, and on the brick lattice, with a peculiar commensurate-incommensurate transition. Using standard techniques, the problem is reduced to the calculation of the eigenvalues of a system of free fermions.

Update: 13-May-2011

Title:
Effects of Reciprocating Extrusion on Microstructures and Mechanical Properties of as-Cast Mg-0.85Zn-0.15Y-0.6Zr Alloys
Authors:
Li, AT; Wang, JC; Si, L; Lai, YT; Yang, GC Author Full Names: Li Antao; Wang Jincheng; Si Lin; Lai Yunting; Yang Gencang
Source:
RARE METAL MATERIALS AND ENGINEERING 40 (3): 515-518 MAR 2011
Abstract:
Effects of reciprocating extrusion on the microstructures and mechanical properties of as-cast Mg-0.85Zn-0.15Y-0.6Zr alloys enforced by quasicrystal particles were investigated by OM, SEM and XRD. The results show that the reciprocating extrusion can greatly refine the microstructure of as-cast Mg-0.85Zn-0.15Y-0.6Zr alloy, and make I phase relatively uniformly distribute in the alpha-Mg matrix. Compared with that of the as-cast alloy, the yield strength, tensile strength and elongation of the Mg-0.85Zn-0.15Y-0.6Zr magnesium alloys after reciprocating extrusion are increased by 75.8%, 43.2% and 35%, respectively.
Title:
Precipitation hardening through sacrificial phase in aluminum-quasicrystal metal matrix composites
Authors:
Kim, SD; Ko, DS; Jang, WK; Shin, KS; Kim, YW Author Full Names: Kim, Sung-Dae; Ko, Dong-Su; Jang, Woo Kil; Shin, Kwang Seon; Kim, Young-Woon
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 528 (13-14): 4845-4848 MAY 24 2011
Abstract:
Al65Cu20Fe15 quasi-crystalline phase worked as a donor of copper by phase dissociation to form Al-Cu-Mg precipitates in mechanically alloyed, Al-Mg-based composite. Fine precipitates played a major role in the improvement of the strength up to 1 GPa of compressive yield strength. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Temperature effects in ion-electron emission of graphite quasicrystal
Authors:
Avilkina, VS; Andrianova, NN; Borisov, AM; Virgiliev, YS; Kulikauskas, VS; Mashkova, ES; Pitirimova, EA Author Full Names: Avilkina, V. S.; Andrianova, N. N.; Borisov, A. M.; Virgiliev, Yu. S.; Kulikauskas, V. S.; Mashkova, E. S.; Pitirimova, E. A.
Source:
JOURNAL OF SURFACE INVESTIGATION-X-RAY SYNCHROTRON AND NEUTRON TECHNIQUES 5 (2): 221-224 APR 2011
Abstract:
Analysis of the comparative influence of complete amorphization of a polycrystalline graphite surface layer and radiation-induced disordering of highly oriented pyrolytic graphite UPV-1T on the character of temperature dependences of the ion-electron emission yield under high-dose (10(18)-10(19) ion/cm(2)) 30 keV Ar+ ion irradiation has been carried out.
Title:
Plastic analysis of the crack problem in two-dimensional decagonal Al-Ni-Co quasicrystalline materials of point group 10, (10)over-bar
Authors:
Li, W; Fan, TY Author Full Names: Li Wu; Fan Tian You
Source:
CHINESE PHYSICS B 20 (3): Art. No. 036101 MAR 2011
Abstract:
The fundamental plastic nature of the quasicrystalline materials remains an open problem due to its essential complicacy. By developing the proposed generalized cohesive force model, the plastic deformation of crack in point group 10, (10) over bar decagonal quasicrystals is analysed strictly and systematically. The crack tip opening displacement (CTOD) and the size of the plastic zone around the crack tip are determined exactly. The quantity of the crack tip opening displacement can be used as a parameter of nonlinear fracture mechanics of quasicrystalline material. In addition, the present work may provide a way for the plastic analysis of quasicrystals.
Title:
The relation between the generalised Eshelby integral and the generalised BCS and DB models
Authors:
Fan, TY; Fan, L Author Full Names: Fan Tian-You; Fan Lei
Source:
CHINESE PHYSICS B 20 (3): Art. No. 036102 MAR 2011
Abstract:
The generalised BCS dislocation group model and the generalised DB atomic cohesive force zone model have obtained the same results on nonlinear fracture study of some one-, two- and three-dimensional quasicrystals. This work reveals some inherent connection between the two models, and finds that their common basis is the generalised Eshelby integral based on the generalised Eshelby energy momentum tensor for quasicrystals. Further applications of the theory in solving nonlinear fracture problems of the materials are also discussed.

Update: 6-May-2011

Title:
Single crystal growth of Al-based intermetallic phases being approximants to quasicrystals
Authors:
Gille, P; Bauer, B; Hahne, M; Smontara, A; Dolinsek, J Author Full Names: Gille, Peter; Bauer, Birgitta; Hahne, Michael; Smontara, Ana; Dolinsek, Janez
Source:
JOURNAL OF CRYSTAL GROWTH 318 (1): 1016-1020 MAR 1 2011
Abstract:
Decagonal (d) quasicrystals are formed in a number of Al-based ternary systems with d-AlCoNi being the best studied decagonal phase. They are highly anisotropic showing unusual properties of e.g. electric and thermal transport when measured along the periodic or quasiperiodic directions. For a long time, this has been attributed to the lack of periodicity in certain crystallographic orientations. Some neighbouring phases in the Al-Co-Ni system as well as in related ternaries consist of the same type of large icosahedral clusters, but are periodic in all three directions, sometimes with very large unit cells. Therefore, they are called approximants to the decagonal quasicrystals. They allow comparative studies of these phases as to judge whether some unusual properties of quasicrystals arise from the lack of periodicity or from the common atomic arrangements. Additional to decagonal AlCoNi quasicrystals, various approximants (monoclinic Al-13(Co,Ni)(4), orthorhombic Al13CO4, orthorhombic Al-4(Cr,Fe), monoclinic Al13Fe4 and its ternary extensions Al-13(Fe,Cr)(4) and Al-13(Fe,Ni)(4)) were grown by the Czochralski method as large single crystals as to carry out transport orientation-dependent measurements. It could be found that transport properties show remarkably similar anisotropic features when comparing corresponding crystallographic directions in these phases that can be related to the periodic stacking of layers. (C) 2010 Elsevier B.V. All rights reserved.

Update: 29-Apr-2011

Title:
Evidence for Charge Orbital and Spin Stripe Order in an Overdoped Manganite
Authors:
Ulbrich, H; Senff, D; Steffens, P; Schumann, OJ; Sidis, Y; Reutler, P; Revcolevschi, A; Braden, M Author Full Names: Ulbrich, H.; Senff, D.; Steffens, P.; Schumann, O. J.; Sidis, Y.; Reutler, P.; Revcolevschi, A.; Braden, M.
Source:
PHYSICAL REVIEW LETTERS 106 (15): Art. No. 157201 APR 12 2011
Abstract:
Overdoped La0.42Sr1.58MnO4 exhibits a complex ordering of charges, orbitals, and spins. Neutron diffraction experiments reveal three incommensurate and one commensurate order parameters to be tightly coupled. The position and the shape of the distinct superstructure scattering as well as higher-order signals are inconsistent with a harmonic charge and spin-density-wave picture but point to a stripe arrangement in which ferromagnetic zigzag chains are disrupted by excess Mn4+.
Title:
Shape of spin density wave versus temperature in AFe(2)As(2) (A = Ca, Ba, Eu): A Mossbauer study
Authors:
Blachowski, A; Ruebenbauer, K; Zukrowski, J; Rogacki, K; Bukowski, Z; Karpinski, J Author Full Names: Blachowski, A.; Ruebenbauer, K.; Zukrowski, J.; Rogacki, K.; Bukowski, Z.; Karpinski, J.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 134410 APR 11 2011
Abstract:
Parent compounds AFe(2)As(2) (A = Ca, Ba, Eu) of the 122 family of the iron-based superconductors have been studied by 57Fe Mossbauer spectroscopy in the temperature range 4.2-similar to 300 K. Spin density waves (SDW) have been found with some confidence. They are either incommensurate with the lattice period or the ratio of the respective periods is far away from the ratio of small integers. SDW shape is very unconventional (i.e., differs from the sinusoidal shape). Magnetic order starts with lowered temperature as narrow sheets of the significant electron spin density separated by areas with very small spin density. Magnetic sheets are likely to be ordered in the alternate antiferromagnetic fashion as the material as a whole behaves similarly to the collinear antiferromagnet. A further lowering of temperature simply expands sheet thickness leading to the near triangular SDW. Finally, sheets fill the whole available space and the almost rectangular shape of the SDW is reached. The substantial maximum amplitude of SDW appears at the temperature just below the magnetic onset temperature, and this maximum amplitude increases slightly with lowering temperature. The square root from the mean squared hyperfine field behaves versus temperature according to the universality class (1,2) (i.e., with the electronic spin space having dimensionality equal to unity and the real space having dimensionality equal to 2). The more or less pronounced tail above transition temperature due to the development of incoherent SDW is seen.
Title:
Magnetic phase diagram of alpha-NdIr2Si2
Authors:
Mihalik, M; Pospisil, J; Hoser, A; Sechovsky, V Author Full Names: Mihalik, M.; Pospisil, J.; Hoser, A.; Sechovsky, V.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 134414 APR 12 2011
Abstract:
Magnetism in alpha-NdIr2Si2 single crystals has been probed through specific-heat, magnetization, magnetic susceptibility, and electrical resistivity measurements as a function of temperature, under an applied magnetic field, and for the magnetization curves under high hydrostatic pressures. Neutron diffraction experiments performed with powder and single-crystal samples were focused on microscopic aspects. Two collinear (Nd moments along the c axis) antiferromagnetic phases are found at low temperatures: a longitudinal sine-modulated structure with the magnetic propagation vector k = (0 0 5/6) at temperatures 18.2(2) K < T < 32.3(3) K (+T-N) and a simple AF1-type structure; k = (0 0 1/2) for T < 18.2(2) K (+T-t). Both of the magnetically ordered phases can be destabilized by applying a strong magnetic field along the c axis. The character of the unusual magnetic-field-induced phases is discussed, and the complex magnetic phase diagram is constructed. Applied hydrostatic pressure yields an increase of both TN and Tt. The determined physical properties of a-NdIr2Si2 are discussed in the context of behavior of alpha-PrIr2Si2.
Title:
Long-range magnetic interactions in the multiferroic antiferromagnet MnWO4
Authors:
Ye, F; Fishman, RS; Fernandez-Baca, JA; Podlesnyak, AA; Ehlers, G; Mook, HA; Wang, YQ; Lorenz, B; Chu, CW Author Full Names: Ye, Feng; Fishman, Randy S.; Fernandez-Baca, Jaime A.; Podlesnyak, Andrey A.; Ehlers, Georg; Mook, Herbert A.; Wang, Yaqi; Lorenz, Bernd; Chu, C. W.
Source:
PHYSICAL REVIEW B 83 (14): Art. No. 140401 APR 12 2011
Abstract:
The spin-wave excitations of the multiferroic MnWO4 have been measured in its low-temperature collinear commensurate phase using high-resolution inelastic neutron scattering. These excitations can be well described by a Heisenberg model with competing long-range exchange interactions and a single-ion anisotropy term. The magnetic interactions are strongly frustrated within the zigzag spin chain along the c axis and between chains along the a axis, while the coupling between spin along the b axis is much weaker. The balance of these interactions results in the noncollinear incommensurate spin structure associated with the magnetoelectric effect, and the perturbation of the magnetic interactions leads to the observed rich phase diagrams of the chemically doped materials. This delicate balance can also be tuned by the application of external electric or magnetic fields to achieve magnetoelectric control of this type of materials.
Title:
Dynamic microstructural changes during hot extrusion and mechanical properties of a Mg-5.0 Zn-0.9 Y-0.16 Zr (wt.%) alloy
Authors:
Xu, SW; Zheng, MY; Kamado, S; Wu, K; Wang, GJ; Lv, XY Author Full Names: Xu, S. W.; Zheng, M. Y.; Kamado, S.; Wu, K.; Wang, G. J.; Lv, X. Y.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 528 (12): 4055-4067 MAY 15 2011
Abstract:
In this study, firstly, dynamic microstructural changes of an as-cast Mg-5.0 Zn-0.9 Y-0.16 Zr (wt.%) alloy (designated ZWK510) during hot extrusion at 350 degrees C and a ram speed of 3.33 mm s(-1) was systematically investigated by electron backscattering diffraction (EBSD) analysis. The dynamic recrystallization (DRX) mechanism during hot extrusion was discussed. Then, the effect of microstructure and texture on the mechanical properties of the as-extruded alloy specimens at room temperature was discussed. The as-cast ZWK510 alloy consists of a-Mg and quasicrystalline I-phase. During hot extrusion at 350 degrees C, the main DRX mechanism is the continuous DRX near the original grain boundaries. The I-phase can accelerate the DRX behavior near these areas by obstructing the slip of dislocations. The deformation twins and massive blocky substructures formed in original grains can coordinate the DRX process near the original grain boundaries, however the DRX seldom occurs inside of these area. After further deformation, these deformation twins and massive blocky substructures are elongate I along the material flow and become so-called unDRXed area, then a bimodal "necklace structure" composed of fine DRXed grains of about 2.1 mu m and unrecrystallized coarse area is formed. The extruded ZWK510 alloy shows a DRX ratio of about 58% and a typical basal fiber texture of (0 0 0 1) < 1 0 (1) over bar 0 >(matrix)// extrusion direction (ED). In the DRXed area around the crushed eutectic I-phase a large number or fine I-phase precipitates are observed pinning at the newly formed DRXed grain boundaries. The 0.2% proof strength and the ultimate tensile strength of the extruded ZWK510 alloy specimen are 317 and 363 MPa, respectively, with an elongation to failure of 12%, which have been attributed to strong basal fiber texture, refined grain size as well as the existence of fine precipitates formed during the hot extrusion. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Change in local environment upon quasicrystallization of Zr-Cu glassy alloys by addition of Pd and Pt
Authors:
Saida, J; Sanada, T; Sato, S; Imafuku, M; Ohnuma, M; Ohkubo, T; Hono, K; Matsubara, E Author Full Names: Saida, Junji; Sanada, Takashi; Sato, Shigeo; Imafuku, Muneyuki; Ohnuma, Masato; Ohkubo, Tadakatsu; Hono, Kazuhiro; Matsubara, Eiichiro
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (17): Art. No. 175303 MAY 4 2011
Abstract:
The effects of Pd and Pt, which are known quasicrystal (QC)-forming elements, on the local atomic structure in Zr70Cu30 glassy alloys are investigated. A QC phase precipitates from a glassy phase above a certain temperature by a cooperative-like motion of icosahedral clusters. Quasicrystallization is accompanied by a significant change in the local environment around the Zr atoms and a slight change around the noble metal. However, the local environment around the Cu atoms remains almost the same during QC formation. It is suggested that two types of icosahedral polyhedra exist in the glassy state: one has a relatively perfect icosahedral structure formed around the Zr atoms. The other is in a distorted state around the Cu atoms. We speculate that the medium-range order (i.e. QC nucleus) has a Zr-centered icosahedral cluster as its core, and the QC grows via aggregation of possible clusters in the initial stage. Pd or Pt atoms stabilize and/or connect individual Zr-centered icosahedral clusters, facilitating the formation of the nucleus and growth of the QC phase.
Title:
Microstructure and properties of Ni-Mn-Ga alloys produced by rapid solidification and pulsed electric current sintering
Authors:
Soderberg, O; Brown, D; Aaltio, I; Oksanen, J; Syren, J; Pulkkinen, H; Hannula, SP Author Full Names: Soderberg, Outi; Brown, David; Aaltio, Ilkka; Oksanen, Jussi; Syren, Jesse; Pulkkinen, Heikki; Hannula, Simo-Pekka
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (20): 5981-5987 MAY 19 2011
Abstract:
Ni-Mn-Ga alloys were compacted using pulsed electric current sintering (PECS) at 850-875 degrees C (50 MPa, 8 min) of flake-like powders made from the rapidly quenched melt-spun ribbons. Two kinds of ribbons were used: one made with a relatively slow wheel speed (6 m/s; average grain size similar to 14 mu m), and another with a faster wheel speed (23 m/s; average grain size similar to 5 mu m). Both sets of flake-like powders consisted of a mixture of non-modulated martensite (NM) and seven-layered modulated martensite (7M) structure. The amount of NM was greater in the slower speed material, while the other one exhibited mostly the 7M structure. These crystal structures were inherited by the sintered samples. In the compacts having the NM structure the multi-step martensitic reaction overlapped with the magnetic transition, and the Curie temperatures during heating and cooling differed from each other. In the compacts having mainly 7M structure the Curie point was about 100 degrees C and the martensitic transition took place in the paramagnetic state, while the intermartensitic one occurred in the region of 60-85 degrees C. This material demonstrated good magnetic properties and saturation magnetization, at best similar to 50 emu/g. Mechanical properties of the compacts were good, and comparable to those of the polycrystalline Ni-Mn-Ga samples in compression. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Phase Transitions in Incommensurate Composites
Authors:
Janssen, T Author Full Names: Janssen, T.
Source:
FERROELECTRICS 412: 4-7 2011
Abstract:
Incommensurate phases show a rich variety of phase transitions. We discuss here two types of phase transitions in a class of aperiodic crystals, the incommensurate composites. A model is presented to understand a recently observed phase transition in nona-decane-urea.
Title:
Incommensurate Phases Induced by a Weak Electric Field
Authors:
Sannikov, DG Author Full Names: Sannikov, D. G.
Source:
FERROELECTRICS 412: 8-11 2011
Abstract:
It is shown that an external electric field E-3 (even if it is arbitrary weak) can induce an incommensurate phase in the crystal. The components M-1 and M-2 of the magnetic moment M-i are chosen as the order parameter components.
Title:
Growth temperature dependent graphene alignment on Ir(111)
Authors:
Hattab, H; N'Diaye, AT; Wall, D; Jnawali, G; Coraux, J; Busse, C; van Gastel, R; Poelsema, B; Michely, T; Heringdorf, FJMZ; Horn-von Hoegen, M Author Full Names: Hattab, H.; N'Diaye, A. T.; Wall, D.; Jnawali, G.; Coraux, J.; Busse, C.; van Gastel, R.; Poelsema, B.; Michely, T.; Heringdorf, F. -J. Meyer Zu; Horn-von Hoegen, M.
Source:
APPLIED PHYSICS LETTERS 98 (14): Art. No. 141903 APR 4 2011
Abstract:
The morphology of graphene monolayers on Ir(111) prepared by thermal decomposition of ethylene between 1000 and 1530 K was studied with high resolution low energy electron diffraction. In addition to a well-oriented epitaxial phase, randomly oriented domains are observed for growth temperatures between 1255 and 1460 K. For rotational angles of +/- 3 degrees around 30 degrees these domains lock-in in a 30 degrees oriented epitaxial phase. Below 1200 K the graphene layer exhibits high disorder and structural disintegrity. Above 1500 K the clear moire spots reflect graphene in a single orientation epitaxial incommensurate phase. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3548546]

Update: 22-Apr-2011

Title:
Lattice study of the incommensurate omega phase transition in Zr-Nb alloys
Authors:
Kubo, H; Farjami, S Author Full Names: Kubo, H.; Farjami, S.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 134302 APR 7 2011
Abstract:
The stability of the incommensurate omega phase has been studied in the scheme of the Landau-Lifshitz (L-L) free-energy model reformed for the weak first-order phase transition. It is revealed that the negative third-order term of the L-L expansion drives the transition and works, in competition with the second-harmonic term, to form the modulated omega phase; moreover, it functions to maintain soliton walls with constant width against temperature changes. The modulated omega phase is elucidated to have a microstructure with the sequence of subvariants-omega 1-omega 3-omega 2-separated by soliton walls of anti-omega structure. A series of primitive activation units of the modulated omega phase, which can be depicted in a phase diagram, is obtained in the Zr-20 wt% Nb-alloy system by analyzing the L-L free-energy function with the appropriate numerical calculations.
Title:
Anomalous vibrational dynamics in the Mg2Zn11 phase
Authors:
Euchner, H; Mihalkovic, M; Gahler, F; Johnson, MR; Schober, H; Rols, S; Suard, E; Bosak, A; Ohhashi, S; Tsai, AP; Lidin, S; Gomez, CP; Custers, J; Paschen, S; de Boissieu, M Author Full Names: Euchner, H.; Mihalkovic, M.; Gaehler, F.; Johnson, M. R.; Schober, H.; Rols, S.; Suard, E.; Bosak, A.; Ohhashi, S.; Tsai, A. -P.; Lidin, S.; Gomez, C. Pay; Custers, J.; Paschen, S.; de Boissieu, M.
Source:
PHYSICAL REVIEW B 83 (14): Art. No. 144202 APR 7 2011
Abstract:
We present a combined experimental and theoretical study of the structure and the lattice dynamics in the complex metallic alloy Mg2Zn11, by means of neutron and x-ray scattering, as well as ab initio and empirical potential calculations. Mg2Zn11 can be seen as an intermediate step in structural complexity between the simple Laves-phase MgZn2 on one side, and the complex 1/1 approximants and quasicrystals ZnMgAl and Zn(Mg)Sc on the other. The structure can be described as a cubic packing of a triacontahedron whose center is partially occupied by a Zn atom. This partially occupied site turned out to play a major role in understanding the lattice dynamics. Data from inelastic neutron scattering evidence a Van Hove singularity in the vibrational spectrum of Mg2Zn11 for an energy as low as 4.5 meV, which is a unique feature for a nearly-close-packed metallic alloy. This corresponds to a gap opening at the Brillouin zone boundary and an interaction between a low-lying optical branch and an acoustic one, as could be deduced from the dispersion relation measured by inelastic x-ray scattering. Second, the measured phonon density of states exhibits many maxima, indicating strong mode interactions across the whole energy range. The origin of the low-energy modes in Mg2Zn11 and other features of the vibrational spectra are studied, using both ab initio and empirical potential calculations. A detailed analysis of vibrational eigenmodes is presented, linking features in the vibrational spectrum to atomic motions within structural building blocks.
Title:
Effect of particle size and annealing on spin and phonon behavior in TbMnO3
Authors:
Das, R; Jaiswal, A; Adyanthaya, S; Poddar, P Author Full Names: Das, Raja; Jaiswal, Adhish; Adyanthaya, Suguna; Poddar, Pankaj
Source:
JOURNAL OF APPLIED PHYSICS 109 (6): Art. No. 064309 MAR 15 2011
Abstract:
Interest has grown to study TbMnO3 as it was recently reported to show a gigantic magnetoelectric effect. Here, we report the synthesis and detailed magnetic and Raman spectroscopy study on TbMnO3 particles of size similar to 25 nm and 2-3 mu m, respectively. The incommensurate-commensurate (lock-in) transition, usually observed at 27 K for bulk phase of TbMnO3 was not observed in susceptibility versus T curve but was seen at 30 K in the coercivity versus T curve in similar to 25 nm particles. This transition, which is due to the spin modulation length scale, gets weakened in nanosize due to the increased intrinsic lattice strain observed in 2-3 mu m particles, due to the effect of increased particle size. The increased value of magnetization in the 2-3 mu m sample was attributed to double exchange interactions between Mn+3 and Mn+4 spins. The role of annealing related effects on the fate of the Neel temperature for TbMnO3 was investigated. Raman spectroscopy indicated a decrease in the lattice distortion for similar to 25 nm particles. (c) 2011 American Institute of Physics. [doi:10.1063/1.3563571]
Title:
Crystallographic relationship of orthorhombic phi-Al5Mg11Zn4 phase to icosahedral quasicrystalline phase
Authors:
Singh, A; Rosalie, JM; Somekawa, H; Mukai, T Author Full Names: Singh, Alok; Rosalie, J. M.; Somekawa, H.; Mukai, T.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (14): 4676-4681 APR 7 2011
Abstract:
The orthorhombic phi-Al5Mg11Zn4 phase is known to be related to quasicrystalline phases, but the exact relationship has not been shown yet. In this study, the relationship of this phase to the icosahedral quasicrystalline phase is explored through analysis of the electron diffraction patterns. It is shown that icosahedral coordinations in three orientations occur in the unit cell - one with three mutually perpendicular twofold axes along (100) of the unit cell, and two with a twofold axis along [100] and a fivefold along [001]. In this, this phase is similar to aluminum and zinc based hexagonal phases which are related to quasicrystals. (C) 2011 Elsevier B.V. All rights reserved.

Update: 15-Apr-2011

Title:
Evolution of Paramagnetic Quasiparticle Excitations Emerged in the High-Field Superconducting Phase of CeCoIn5
Authors:
Kumagai, K; Shishido, H; Shibauchi, T; Matsuda, Y Author Full Names: Kumagai, K.; Shishido, H.; Shibauchi, T.; Matsuda, Y.
Source:
PHYSICAL REVIEW LETTERS 106 (13): Art. No. 137004 MAR 30 2011
Abstract:
We present In-115 NMR measurements in a novel thermodynamic phase of CeCoIn5 in a high magnetic field, where exotic superconductivity exists with the incommensurate spin-density wave order. We show that the NMR spectra in this phase provide direct evidence for the emergence of the spatially distributed normal quasiparticle regions. The quantitative analysis for the field evolution of the paramagnetic magnetization and newly emerged low-energy quasiparticle density of states is consistent with the nodal plane formation, which is characterized by an order parameter in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. The NMR spectra also suggest that the spatially uniform spin-density wave is induced in the FFLO phase.
Title:
Magnetic structure of epitaxial multiferroic BiFeO3 films with engineered ferroelectric domains
Authors:
Ke, X; Zhang, PP; Baek, SH; Zarestky, J; Tian, W; Eom, CB Author Full Names: Ke, X.; Zhang, P. P.; Baek, S. H.; Zarestky, J.; Tian, W.; Eom, C. B.
Source:
PHYSICAL REVIEW B 82 (13): Art. No. 134448 OCT 29 2010
Abstract:
We report on neutron scattering and piezoresponse force microscopy studies of multiferroic BiFeO3 films epitaxially grown on vicinal SrTiO3 substrates. We find that these BiFeO3 films exhibit a G-type antiferromagnetic structure modulated with cycloidal spiral magnetic ordering with the features of magnetic domains depending upon the ferroelectric domain states: a single antiferromagnetic domain for the films with a ferroelectric monodomain while two- or multiantiferromagnetic domains existing in the films displaying two- or four-ferroelectric variants, respectively. These results imply the correlation between ferroelectric and magnetic order parameters in the BiFeO3 films and the expected strong magnetoelectric coupling makes these multiferroic films promising candidates for device applications with the capability to tune the magnetism using an electric field.
Title:
Magnetic structure of epitaxial multiferroic BiFeO3 films with engineered ferroelectric domains
Authors:
Ke, X; Zhang, PP; Baek, SH; Zarestky, J; Tian, W; Eom, CB Author Full Names: Ke, X.; Zhang, P. P.; Baek, S. H.; Zarestky, J.; Tian, W.; Eom, C. B.
Source:
PHYSICAL REVIEW B 82 (13): Art. No. 134448 OCT 29 2010
Abstract:
We report on neutron scattering and piezoresponse force microscopy studies of multiferroic BiFeO3 films epitaxially grown on vicinal SrTiO3 substrates. We find that these BiFeO3 films exhibit a G-type antiferromagnetic structure modulated with cycloidal spiral magnetic ordering with the features of magnetic domains depending upon the ferroelectric domain states: a single antiferromagnetic domain for the films with a ferroelectric monodomain while two- or multiantiferromagnetic domains existing in the films displaying two- or four-ferroelectric variants, respectively. These results imply the correlation between ferroelectric and magnetic order parameters in the BiFeO3 films and the expected strong magnetoelectric coupling makes these multiferroic films promising candidates for device applications with the capability to tune the magnetism using an electric field.
Title:
Analysis and modelling of structural disorder by the use of the three-dimensional pair distribution function method exemplified by the disordered twofold superstructure of decagonal Al-Cu-Co
Authors:
Schaub, P; Weber, T; Steurer, W Author Full Names: Schaub, Philippe; Weber, Thomas; Steurer, Walter
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 44: 134-149 Part 1 FEB 2011
Abstract:
Theoretical concepts and the practical application of the three-dimensional pair distribution function (3D-PDF) method and its variant, the three-dimensional delta-pair distribution function (3D-delta PDF) method, are presented. In analogy to traditional Patterson function analysis, advantage is taken of the Fourier transformation either of the full three-dimensional diffraction pattern of a disordered crystal or just of the isolated diffuse scattering, respectively. By the use of three-dimensional information, analysis of disorder becomes straightforward, and it becomes possible to investigate far more complicated structures than is feasible with well established powder diffraction-based PDF analysis. Compared to more traditional modelling techniques, such as Monte Carlo simulation, the 3D-delta PDF provides direct access to disorder models and allows selective modelling of distinct structural features, which are, in contrast to reciprocal space, well localized in PDF space. The principles of the 3D-delta PDF approach are exemplified using an analysis of the twofold (similar to 8 A) periodic superstructure of a decagonal Al65Cu20Co15 quasicrystal. Although analysis of disorder in quasicrystals is far more demanding than in the case of periodic structures, details of the disordered structure could be elucidated. The superstructure is found to be built from columnar units, having a maximum diameter of similar to 14.5 A. The lateral correlation between these columns is weak. Internally, the columns consist of a long-range-ordered alternation of flat and puckered layers. The development of the model and the atomic structure of the columns are described in detail.
Title:
Zn2LiGaO4, Wurtzite- Derived Wide Band Gap Oxide
Authors:
Omata, T; Kita, M; Nose, K; Tachibana, K; Otsuka-Yao-Matsuo, S Author Full Names: Omata, Takahisa; Kita, Masao; Nose, Katsuhiro; Tachibana, Kosuke; Otsuka-Yao-Matsuo, Shinya
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS 50 (3): Art. No. 031102 MAR 2011
Abstract:
The phase that appeared in the pseudo-binary LiGaO2-ZnO system was investigated by powder X-ray diffraction (XRD), selected area electron diffraction by transmission electron microscopy (TEM-SAD) and Raman spectroscopy, especially focusing on the 0.5(LiGaO2)(1/2) - 0.5ZnO composition. A new quaternary wurtzite-derived Zn2LiGaO4 phase was found in this system. The TEM-SAD indicated that the phase possesses an incommensurately modulated ordering. The optical energy band gap of Zn2LiGaO4 was determined to be similar to 4: 0 eV from its diffuse reflectance and photoluminescence spectra; and it was suggested that the Zn2LiGaO4 was a direct semiconductor. (C) 2011 The Japan Society of Applied Physics
Title:
Three dimensional elastodynamics of 2D quasicrystals: The derivation of the time-dependent fundamental solution
Authors:
Yakhno, VG; Yaslan, HC Author Full Names: Yakhno, V. G.; Yaslan, H. Cerdik
Source:
APPLIED MATHEMATICAL MODELLING 35 (6): 3092-3110 JUN 2011
Abstract:
The time-dependent differential equations of elasticity for 20 quasicrystals with general structure of anisotropy (dodecagonal, octagonal, decagonal, pentagonal, hexagonal, triclinic) are considered in the paper. These equations are written in the form of a vector partial differential equation of the second order with symmetric matrix coefficients. The fundamental solution (matrix) is defined for this vector partial differential equation. A new method of the numerical computation of values of the fundamental solution is suggested. This method consists of the following: the Fourier transform with respect to space variables is applied to vector equation for the fundamental solution. The obtained vector ordinary differential equation has matrix coefficients depending on Fourier parameters. Using the matrix computations a solution of the vector ordinary differential equation is numerically computed. Finally, applying the inverse Fourier transform numerically we find the values of the fundamental solution. Computational examples confirm the robustness of the suggested method for 2D quasicrystals with arbitrary type of anisotropy. (C) 2010 Elsevier Inc. All rights reserved.
Title:
Determination of the orientation relationship between austenite and incommensurate 7M modulated martensite in Ni-Mn-Ga alloys
Authors:
Li, ZB; Zhang, YD; Esling, C; Zhao, X; Zuo, L Author Full Names: Li, Z. B.; Zhang, Y. D.; Esling, C.; Zhao, X.; Zuo, L.
Source:
ACTA MATERIALIA 59 (7): 2762-2772 APR 2011
Abstract:
For Ni-Mn-Ga ferromagnetic shape memory alloys, a large magnetic-field-induced strain could be reached through the reorientation of martensitic variants in the martensite state. Owing to the collective and displacive nature of the austenite to martensite transformation, a certain orientation relationship (OR) between the parent and the product phase is required to minimize the transformation strain and the strain energy generated, which brings about self-accommodating groups of martensitic variants with specific orientation correlations. In this work, the microstructural and crystallographic characteristics of martensitic variants in a polycrystalline Ni50Mn30Ga20 alloy were investigated by electron backscatter diffraction analysis. With accurate orientation measurement on inherited martensitic variants, the local orientations of parent austenite grains were predicted using four classical OR for the martensitic transformation. Furthermore, a specific OR, namely the Pitsch relation with (1 0 1)(A)//(1 (2) over bar (10) over bar)(7M) and [1 0 (1) over bar](A)//[(10) over bar (10) over bar 1](7M), was unambiguously determined by considering the magnitude of discontinuity between the lattices of the product and parent phases and the structural modulation of the incommensurate 7M modulated martensite. The present procedure to determine the OR, without recourse to the presence of retained austenite, is in general applicable to a variety of materials with modulated superstructure for insight into their martensitic transformation processes. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Elastic and viscoelastic properties of glassy, quasicrystalline and crystalline phases in Zr65Cu5Ni10Al7.5Pd12.5 alloys
Authors:
Pelletier, JM; Louzguine-Luzgin, DV; Li, S; Inoue, A Author Full Names: Pelletier, Jean-Marc; Louzguine-Luzgin, Dmitri V.; Li, Song; Inoue, Akihisa
Source:
ACTA MATERIALIA 59 (7): 2797-2806 APR 2011
Abstract:
The elastic and viscoelastic properties of Zr65Ni10Cu5Al7.5Pd12.5 bulk metallic glass have been studied over a wide temperature and frequency range. In the amorphous state the mechanical response of the alloy is simple, similar to that observed in other bulk metallic glasses. In contrast, the phase-transformation process which occurs during annealing at elevated temperature induces a complex evolution. This alloy transforms to a supercooled liquid and then primarily forms an icosahedral phase followed by the formation of a mixture of crystalline phases. The mechanical properties in the amorphous state are well described using a physical model based on the concept of defects in amorphous materials. Atomic mobility is then governed by two parameters: activation energy U-el (0.92 eV) and correlation factor chi (0.39). The influence of the phase composition on the properties is discussed. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Relation between icosahedral short-range ordering and plastic deformation in Zr-Nb-Cu-Ni-Al bulk metallic glasses
Authors:
Zhu, ZW; Gu, L; Xie, GQ; Zhang, W; Inoue, A; Zhang, HF; Hu, ZQ Author Full Names: Zhu, Z. W.; Gu, L.; Xie, G. Q.; Zhang, W.; Inoue, A.; Zhang, H. F.; Hu, Z. Q.
Source:
ACTA MATERIALIA 59 (7): 2814-2822 APR 2011
Abstract:
The relation between icosahedral short-range ordering (ISRO) and plastic deformation was investigated in Zr70-xNbxCu13.5Ni8.5Al8 (at.%, x = 0, 2, 4, 6, 7, 8, 10) bulk metallic glasses (BMG). The formation of icosahedral quasicrystal (I-phase) during the annealing process implies that ISRO widely exists in these materials. The degree of ISRO is thermodynamically evaluated to show that ISRO increases with increasing Nb content. Compression tests indicate that BMG with 0-7 at.% Nb possess similar unusual plastic deformability, which is attributed to ISRO-mediated local distribution of free volume (FV) and ISRO prompted deformation-induced crystallization. A proposed core shell model coupled with transmission electron microscopy analysis demonstrates that the FV is distributed more heterogeneously with increasing ISRO, which is beneficial for multiplying the shear bands. Deformation-induced crystallization is facilitated, owing to the low interfacial energy of the nucleation and growth of the crystals attributed to ISRO in the amorphous matrix, which improves plasticity by consuming energy and the product altering the stress field in the amorphous matrix. Design of new ductile BMG is discussed in these strategies. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 8-Apr-2011

Title:
Quantitative atom column position analysis at the incommensurate interfaces of a (PbS)(1.14)NbS2 misfit layered compound with aberration-corrected HRTEM
Authors:
Garbrecht, M; Spiecker, E; Tillmann, K; Jager, W Author Full Names: Garbrecht, M.; Spiecker, E.; Tillmann, K.; Jaeger, W.
Source:
ULTRAMICROSCOPY 111 (3): 245-250 FEB 2011
Abstract:
Aberration-corrected HRTEM is applied to explore the potential of NCSI contrast imaging to quantitatively analyse the complex atomic structure of misfit layered compounds and their incommensurate interfaces. Using the (PbS)(1.14)NbS2 misfit layered compound as a model system it is shown that atom column position analyses at the incommensurate interfaces can be performed with precisions reaching a statistical accuracy of +/- 6 pm. The procedure adopted for these studies compares experimental images taken from compound regions free of defects and interface modulations with a structure model derived from XRD experiments and with multi-slice image simulations for the corresponding NCSI contrast conditions used. The high precision achievable in such experiments is confirmed by a detailed quantitative analysis of the atom column positions at the incommensurate interfaces, proving a tetragonal distortion of the monochalcogenide sublattice. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Magnetic transitions in Mn3O4 and an anomaly at 38 K in magnetization and specific heat
Authors:
Guillou, F; Thota, S; Prellier, W; Kumar, J; Hardy, V Author Full Names: Guillou, F.; Thota, S.; Prellier, W.; Kumar, J.; Hardy, V.
Source:
PHYSICAL REVIEW B 83 (9): Art. No. 094423 MAR 23 2011
Abstract:
Mn3O4 is one of the archetypal examples of tetragonally distorted spinels. In this paper we reinvestigate its complex magnetic ordering process by using high-resolution magnetic and calorimetric measurements. The first-order transition to the ground state is found to exhibit a latent heat of similar or equal to 4 J mol(-1) and a thermal hysteresis of similar or equal to 0.6 K. Moreover, the peculiar field-induced broadening observed at this transition is shown to be consistent with general predictions about incommensurate-to-commensurate transition. In addition to the known sequence of transitions at T-N similar or equal to 43 K, T-1 similar or equal to 40 K, and T-2 similar or equal to 34 K, a new anomaly close to T* similar or equal to 38 K is observed in both *magnetization* and heat capacity data. A possible origin of this feature is discussed in terms of magnetic instability within the incommensurate spiral spin configuration.
Title:
Structural and magnetic properties of Sc1.1Fe3.9Al8 alloy
Authors:
Recko, K; Dobrzynski, L; Senyshyn, A; Fuess, H; Szymanski, K; Kotur, BY; Suski, W Author Full Names: Recko, K.; Dobrzynski, L.; Senyshyn, A.; Fuess, H.; Szymanski, K.; Kotur, B. Yu; Suski, W.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 323 (14): 1860-1867 JUL 2011
Abstract:
The crystallochemical and magnetic nature of ternary Sc1+delta Fe4-delta Al8 intermetallic with a small Sc excess delta = 0.1 was investigated by scanning electron microscope, X-ray powder diffraction, neutron diffraction, Mossbauer effect and superconducting quantum interference device techniques. The sample crystallizes in a tetragonal ThMn12 type structure. The excess of Sc atoms substitute Fe at the (8f) positions and have a pronounced effect on the magnetic properties. The experiments carried out in temperature range 4-320 K show that below 120 K the magnetic structure of the alloy forms a double cycloid with magnetic moments rotating according to the incommensurate in-plane wave vector, which is temperature independent upto 160 K. The value of Fe magnetic moment is close to 0.9 mu(B) atom(-1) at 4K. Temperature dependence of unit cell dimensions can be explained within the Debye-Gruneisen approximation. (c) 2011 Elsevier B.V. All rights reserved.
Title:
New high magnetic field phase of the frustrated S=1/2 chain compound LiCuVO4
Authors:
Svistov, LE; Fujita, T; Yamaguchi, H; Kimura, S; Omura, K; Prokofiev, A; Smirnov, AI; Honda, Z; Hagiwara, M Author Full Names: Svistov, L. E.; Fujita, T.; Yamaguchi, H.; Kimura, S.; Omura, K.; Prokofiev, A.; Smirnov, A. I.; Honda, Z.; Hagiwara, M.
Source:
JETP LETTERS 93 (1): 21-25 MAR 2011
Abstract:
Magnetization of the frustrated S = 1/2 chain compound LiCuVO4, focusing on high magnetic field phases, is reported. Besides a spin-flop transition and the transition from a planar spiral to a spin modulated structure observed recently, an additional transition was observed just below the saturation field. This newly observed magnetic phase is considered as a spin nematic phase, which was predicted theoretically but was not observed experimentally. The critical fields of this phase and its dM/dH curve are in good agreement with calculations performed in a microscopic model (M.E. Zhitomirsky and H. Tsunetsugu, Europhys. Lett. 92, 37001 (2010)).
Title:
TEMPERATURE AND SPECTRAL CHANGES IN THE REFRACTIVE INDICES OF LiKSO4 CRYSTALS UNDER UNIAXIAL PRESSURES
Authors:
Stadnyk, VI; Romanyuk, MO; Kushnir, OS; Brezvin, RS; Franiv, AV; Gaba, VM Author Full Names: Stadnyk, V. I.; Romanyuk, M. O.; Kushnir, O. S.; Brezvin, R. S.; Franiv, A. V.; Gaba, V. M.
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B 24 (32): 6219-6233 DEC 30 2010
Abstract:
We have studied spectral and temperature variations of the principal refractive indices of lithium potassium sulfate crystals, LiKSO4, subjected to uniaxial mechanical pressures. Notable baric increases in the refractive indices are found, which have been interpreted using classical single-oscillator dispersion Sellmeier equation and Lorentz-Lorenz formula. Significant pressure-induced shifts of low-temperature phase transitions in LiKSO4 are revealed and qualitatively explained in terms of modifications of crystalline structure imposed by the pressures. It is established that high enough pressures applied along the crystallographic axis c can generate a "triple point" on the phase diagram "temperature-uniaxial pressure". It is inferred that the temperature behavior of the refractive indices below the room temperature cannot be interpreted as a pure result of spontaneous strains and should possibly involve some other mechanisms, e.g., a hypothesis of incommensurately modulated phase existing about below 255 K.
Title:
Selective hydrogenation of Ti-Zr-Ni alloys
Authors:
Kocjan, A; Kovacic, S; Gradisek, A; Kovac, J; McGuiness, PJ; Apih, T; Dolinsek, J; Kobe, S Author Full Names: Kocjan, A.; Kovacic, S.; Gradisek, A.; Kovac, J.; McGuiness, P. J.; Apih, T.; Dolinsek, J.; Kobe, S.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 36 (4): 3056-3061 FEB 2011
Abstract:
We prepared series of Ti-Zr-Ni samples by melt-spinning and subsequent thermal treatment at 700 degrees C for 2 h in dynamic 10(-5) mbar vacuum in order to obtain mixture of crystalline C14 Laves and alpha,beta-(Tr,Zr) phases. These samples were exposed to hydrogen gas at 300 degrees C and 50 bar for 1000 min. The mass% of H was obtained gravimetrically and volumetrically. When approximately 1% of air was present in the Sievert device we found relatively narrow area in Ti-Zr-Ni phase diagram, so-called zero-zone, where hydrogen amounts in crystalline samples varied between 0 and 0.8 mass%. Surprisingly, icosahedral quasicrystalline (i-QC) samples showed no selective hydrogenation and absorbed more than 1.5 mass% H in the interval of compositions, where the i-phase is formed. XPS analysis revealed that the oxide layer thickness is similar after melt-spinning and thermal treatment for both type of samples, i.e. from inside and outside of the zero-zone. However, after hydrogenation the zero-zone samples had 5-times thicker surface oxide layer. In order to find, whether this is correlated to different electronic structure, DOS near E-F was examined by H-1 NMR. In parallel, thermal desorption of hydrogen was performed in order to reveal, if H-bonding sites are correlated to different hydrogenation behaviour of various samples. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
Title:
Polarization reversal by intramolecular disordering in organic ferroelectrics: trichloroacetamide
Authors:
Saito, K; Yamamura, Y; Kikuchi, N; Nakao, A; Yasuzuka, S; Akishige, Y; Murakami, Y Author Full Names: Saito, Kazuya; Yamamura, Yasuhisa; Kikuchi, Naoya; Nakao, Akiko; Yasuzuka, Syuma; Akishige, Yukikuni; Murakami, Youichi
Source:
CRYSTENGCOMM 13 (7): 2693-2698 2011
Abstract:
Mechanism of successive ferroelectric-paraelectric phase transitions exhibited by an organic ferroelectric, trichloroacetamide, is clarified through structural and calorimetric experiments. The transition mechanism, intramolecular disordering, reasonably explains the polarization reversal. This mechanism is only possible in molecular solids and is applicable to other compounds as a possible strategy to design new molecular ferroelectrics. Also revealed is the incommensurate nature of the intermediate phase, the origin of which is briefly discussed at phenomenological and molecular levels.

Update: 1-Apr-2011

Title:
Electronic structure of Mg-Zn-based compounds
Authors:
Ishii, Y; Dankhazi, Z; Belin-Ferre, E Author Full Names: Ishii, Yasushi; Dankhazi, Zoltan; Belin-Ferre, Esther
Source:
PHILOSOPHICAL MAGAZINE 91 (11): 1643-1652 2011
Abstract:
We present a comparison between calculated densities of states of the Laves phase MgZn2 and hexagonal Mg28Zn65Y7 and experimental results obtained using both X-ray emission and photoabsorption spectroscopy techniques. We show that there is general agreement between both sets of data for both alloys. We also point out that the two samples retain a metallic character, yet the hexagonal approximant of the Mg-Zn-Y quasicrystal family is less metallic than the Laves phase.
Title:
Structure of liquid Al-Cu-Co alloys near the quasicrystal-forming range
Authors:
Roik, OS; Galushko, SM; Samsonnikov, OV; Kazimirov, VP; Sokolskii, VE Author Full Names: Roik, O. S.; Galushko, S. M.; Samsonnikov, O. V.; Kazimirov, V. P.; Sokolskii, V. E.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 357 (3): 1147-1152 FEB 1 2011
Abstract:
A local short-to-intermediate range order in liquid Al63.9Cu19.4Co16.7. Al71Cu5Co23, and Al60Cu29Co11 alloys was investigated by X-ray diffraction technique and the reverse Monte Carlo modeling. A prepeak at Q similar to 17 nm(-1) originating from the unique bonding between the TM-TM pair (TM = Co, Cu) is observed in the structure factors of all investigated melts. The Voronoi-Delaunay analysis of RMC models indicates that a medium-range ordering of TM atoms in dense non-crystalline polytetrahedral clusters is associated with a chemical short-range order. The icosahedral short-range order is also closely related to the dense packing polytetrahedral clusters. A decrease of temperature leads to an enhancement of both chemical short-range order and icosahedral short-range order. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Raman study of lattice dynamics in quasicrystals
Authors:
Ponosov, YS; Shchegolikhina, NI; Prekul, AF Author Full Names: Ponosov, Yu. S.; Shchegolikhina, N. I.; Prekul, A. F.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 357 (3): 1235-1238 FEB 1 2011
Abstract:
We present the first Raman investigation of icosahedral quasicrystals. Broad structured bands in the energy range up to similar to 500 cm(-1) have been observed in a series of AlCuFe, AlPdMn and AlPdRe systems. Original information on the vibrational density of states g(omega) was obtained for AlPdRe; for AlCuFe and AlPdMn estimated g(omega) shows a good agreement with the previous neutron results, but demonstrates finer structure. Strong increase in the parameter of electron-vibrational coupling for the low-energy vibrations and its correlation with changes in electronic conductivity has been observed in the series from AlCuFe to AlPdRe. This suggests the increase of the degree of localization for these vibrational excitations and involved electronic states. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Magnetic properties of the 1/1 approximant Ag42In42Gd16 to the icosahedral quasicrystal Ag-In-Gd
Authors:
Wang, P; Stadnik, ZM; Przewoznik, J Author Full Names: Wang, P.; Stadnik, Z. M.; Przewoznik, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (8): 3435-3440 FEB 24 2011
Abstract:
The structural, magnetic, and Gd-155 Mossbauer spectral properties of the 1/1 approximant Ag42In42Gd16 to an icosahedral quasicrystal Ag-In-Gd are reported. Based on dc magnetic susceptibility measurements, it is shown that the studied compound develops no long-range magnetic order in the temperature range 1.8-300K. The dc zero-field-cooled and field-cooled susceptibility data indicate that the 1/1 approximant Ag42In42Gd16 is a spin glasss with freezing temperature T-f = 3.6(1)K. This is further confirmed by the analysis of the frequency dependence of T-f using the Vogel-Fulcher law and the dynamic scaling behavior near T-f. It is argued that the spin freezing process is a true equilibrium phase transition rather than a nonequilibrium phenomenon. The large frustration parameter of the studied compound indicates that it belongs to a category of strongly geometrically frustrated magnets. The Gd-155 Mossbauer spectra of the 1/1 approximant Ag42In42Gd16 confirm that the Gd spins are frozen at 1.5K and are fluctuating at 4.6 K. The Debye temperature of the 1/1 approximant Ag42In42Gd16 is 200(1) K. (c) 2010 Elsevier B.V. All rights reserved.
Title:
Planar Symmetry Incompatibility in Ru-Sn-Zn Pseudo-Decagonal Approximants Composed of Novel Pentagonal Antiprisms
Authors:
Xiong, DB; Okamoto, NL; Inui, H Author Full Names: Xiong, Ding-Bang; Okamoto, Norihiko L.; Inui, Haruyuki
Source:
INORGANIC CHEMISTRY 50 (3): 827-835 FEB 7 2011
Abstract:
Two new ternary compounds in the Ru-Sn-Zn system were synthesized by conventional high-temperature reactions, and their crystal structures were analyzed by means of the single crystal X-ray diffraction: Ru2Sn2Zn3 (orthorhombic, Pnma, Pearson symbol oP28, a = 8.2219(16), b = 4.1925(8), c = 13.625(3) angstrom, V=469.66(16) angstrom(3), Z = 4) and Ru4.15Sn4.96Zn5.85 (orthorhombic, Pnma, Pearson symbol oP60-delta, a = 8.3394(17), b = 4.2914(9), c = 28.864(6) angstrom, V = 1032.98(40) angstrom(3), Z = 4). With the increase in the Sn content, the half-decagon structure unit with a triangle center in Ru2Sn2Zn3 grows up to a symmetry incompatible decagonal unit with a central triangle in the common plane in Ru4.15Sn4.96Zn5.85. Both structures can be described by hexagonal arrays of Sn-centered novel pentagonal antiprisms. In light of their pseudodecagonal diffraction in the h0l section and point group mmm, both phases are considered as new quasicrystal approximants in the Ru-Zn Sn ternary system. The temperature dependences of the electrical resistivity for both compounds exhibit metallic behavior, but their Seebeck coefficients are of opposite sign.

Update: 25-Mar-2011

Title:
NdRhSn: A ferromagnet with an antiferromagnetic precursor
Authors:
Mihalik, M; Prokleska, J; Kamarad, J; Prokes, K; Isnard, O; McIntyre, GJ; Donni, A; Yoshii, S; Kitazawa, H; Sechovsky, V; de Boer, FR Author Full Names: Mihalik, M.; Prokleska, J.; Kamarad, J.; Prokes, K.; Isnard, O.; McIntyre, G. J.; Doenni, A.; Yoshii, S.; Kitazawa, H.; Sechovsky, V.; de Boer, F. R.
Source:
PHYSICAL REVIEW B 83 (10): Art. No. 104403 MAR 9 2011
Abstract:
NdRhSn has a ferromagnetic ground state [T-t = 7.6(1) K] with a magnetic moment equal to 2/3 of the free Nd3+-ion moment. Upon cooling from the paramagnetic state, the ferromagnetism is preceded by an incommensurate antiferromagnetic state between T-N = 9.8(1) K and T-t. In both magnetic phases the magnetic moments are locked along the c axis, which is the easy-magnetization axis of the system. We have investigated this unusual situation by measuring anomalies of several bulk physical properties characteristic for the magnetic phase transitions at T-N and T-t and the response of these properties to an applied magnetic field. Neutron-diffraction experiments have been also performed at low temperatures. Furthermore, in order to understand better the physical properties of NdRhSn, single crystals have been studied under external hydrostatic and uniaxial pressure and in high magnetic fields. An antiferromagnetic phase with a propagation vector (0 0 1/11) has been found between T-N and T-t. The magnetic-ordering temperatures T-N and T-t are sensitive to both hydrostatic and uniaxial pressures, but in a different manner. Application of hydrostatic pressure leads to a reduction of the ordering temperatures at rates Delta T-N/Delta p = -0.76(5) K/GPa and Delta T-t/Delta p = -0.9(2) K/GPa while uniaxial pressure applied along the c axis leads to an increase of the ordering temperatures at rates Delta T-N/Delta p = +1.2(5) K/GPa and Delta T-t/Delta p = +2.7(4) K/GPa. No considerable influence of pressure on the antiferromagnetic propagation vector has been found. The peculiar evolution of magnetism in NdRhSn with temperature indicates a complex hierarchy of exchange interactions.
Title:
Electronic structure of EuPtSi3 studied from the first principles calculation
Authors:
Pan, D; Wan, XG Author Full Names: Pan, D.; Wan, X. G.
Source:
PHYSICA B-CONDENSED MATTER 406 (5): 1129-1131 MAR 1 2011
Abstract:
We investigate the electronic structure of EuPtSi3 using full potential linearized augmented plane wave method within the generalized gradient approximation. We reproduce the observed easy axis of magnetization as well as magnetic moment and propose that the magnetic configuration for this compound is incommensurate or noncollinear. We find that the spin configuration has only negligible effect on the band around Fermi energy. EuPtSi3 and its isostructural superconductor BaPtSi3 have similar band structures. Despite the shorter Pt-Si bond, EuPtSi3 possesses larger density of state near the Fermi energy compared with BaPtSi3, thus the structural difference and the associated difference in band structure cannot explain the non-superconductivity of EuPtSi3. (C) 2010 Elsevier B.V. All rights reserved.
Title:
A general solution of elasto-hydrodynamics of two-dimensional quasicrystals
Authors:
Li, XF Author Full Names: Li, X-F
Source:
PHILOSOPHICAL MAGAZINE LETTERS 91 (4): 313-320 2011
Abstract:
Dynamic problems of quasicrystals are analysed within the framework of continuum mechanics. Phonon excitations yield wave propagation while phason excitations yield atomic diffusion. Phonon fields obey the equations of motion and phason fields obey the diffusion equations. Governing equations of elasto-hydrodynamics of decagonal quasicrystals combine characteristics of the equations of motion and diffusion. A general solution is derived in terms of two introduced auxiliary functions. It provides an easy-to-use approach to solve initial-boundary value problems encountered in elasticity problems for quasicrystals. Explicit expressions for displacements and stresses in the phonon and phason fields can be directly obtained. A derived general solution is also applicable to some planar quasicrystals such as pentagonal quasicrystals with fivefold symmetry.
Title:
Mechanical Property and Corrosion Resistance of Mg-Zn-Y Alloys Containing Icosahedral Phase
Authors:
Kim, DH; Kim, YK; Kim, WT; Kim, DH Author Full Names: Kim, Do Hyung; Kim, Young Kyun; Kim, Won Tae; Kim, Do Hyang
Source:
KOREAN JOURNAL OF METALS AND MATERIALS 49 (2): 145-152 FEB 2011
Abstract:
Mechanical and property corrosion resistance of Mg-Zn-Y alloys with an atomic ratio of Zn/Y of 6.8 are investigated using optical microscopy, scanning electron microscopy, transmission electron microscopy, uniaxial tensile test and corrosion test with immersion and dynamic potentiometric tests. The alloys showed an in-situ composite microstructure consisting of alpha-Mg and icosahedral phase (I-phase) as a strengthening phase. As the volume fraction of the I-phase increases, the yield and tensile strengths of the alloys increase while maintaining large elongation (26 similar to 30%), indicating that I-phase is effective for strengthening and forms a stable interface with surrounding alpha-Mg matrix. The presence of I-phase having higher corrosion potential than alpha-Mg, decreased the corrosion rate of the cast alloy up to I-phase volume fraction of 3.7%. However further increase in the volume fraction of the I-phase deteriorates the corrosion resistance due to enhanced internal galvanic corrosion cell between alpha-Mg and I-phase.
Title:
Hydrogen and Zr-based metallic glasses: Gas/solid absorption process and structure evolution
Authors:
Paillier, J; Rongeat, C; Gutfleisch, O; Gebert, A Author Full Names: Paillier, Jerome; Rongeat, Carine; Gutfleisch, Oliver; Gebert, Annett
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (5): 1636-1643 FEB 3 2011
Abstract:
The absorption of hydrogen by means of gas-solid reaction and its consequence on the structure have been studied for fully amorphous alloys as well as quasicrystals/glassy composite alloys based on the composition Zr59Ti3Cu20Al10Ni8. The process of hydrogen absorption has been performed and monitored under 20 bar of H-2 using high pressure-differential scanning calorimetry (HP-DSC). The structure evolution of the samples has been followed by X-ray diffractometry (XRD). Results show that the nature of the surface oxide layer strongly affects the process of hydrogen absorption, especially its starting temperature. The structure evolves nevertheless along the same basic sequence, regardless of the sample: (i) the alloys keep a global amorphous structure up to roughly H/M =0.8 and T= 350 degrees C; (ii) then ZrH2 and at higher temperature Cu2AlZr are formed. The stability of the glass is weakened and the formation of quasicrystals is inhibited under 20 bar of H-2. An heterogeneous distribution of hydrogen atoms inside the amorphous matrix has been inferred from the results. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Formation of nano quasicrystalline and crystalline phases by mechanical alloying
Authors:
Shamah, AM; Ibrahim, S; Hanna, FF Author Full Names: Shamah, A. M.; Ibrahim, S.; Hanna, F. F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (5): 2198-2202 FEB 3 2011
Abstract:
In the present work, the formation of nano quasicrystalline icosahedral phase in Al86Cr14, Al84Fe16 and Al62.5Cu25Fe12.5 alloys has been investigated by mechanical alloying. Mixtures of quasicrystalline and related crystalline phases have been observed under various milling conditions. The X-ray diffraction, differential thermal analysis and electrical resistivity techniques have been used for characterization and physical property measurements. The particle size was calculated by X-ray profile using Williamson-Hall plot method and it was found to be 25-50 nm size. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Effect of processing parameter on hydrogen storage characteristics of as quenched Ti45Zr38Ni17 quasicrystalline alloys
Authors:
Shahi, RR; Yadav, TP; Shaz, MA; Srivastava, ON; van Smaalen, S Author Full Names: Shahi, Rohit R.; Yadav, T. P.; Shaz, M. A.; Srivastava, O. N.; van Smaalen, S.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 36 (1): 592-599 JAN 2011
Abstract:
The present study deals with the microstructural changes with respect to the processing parameter (quenching rate) and their correlation with hydrogen storage characteristics of Ti45Zr38Ni17 quasicrystalline alloys. The ribbons of the alloy have been synthesized at different quenching rates obtained through different wheel speeds (35, 40, 45 and 50 m/s) and investigated for their hydrogen storage characteristics. The lower cooling rate obtained through low wheel speed (35 m/s) produces, i-phase grains whose size ranges from 300-350 nm, whereas higher cooling rates obtained through high wheel speed (45 and 50 m/s) promote the formation of grains with size ranges from 100-150 nm in Ti45Zr38Ni17 ribbons. It has been found that the ribbons synthesized at 35 m/s absorbed similar to 2.0 wt%, whereas ribbons synthesized at 50 m/s absorbed similar to 2.84 wt. % of hydrogen. Thus the hydrogen storage capacity of ribbon increases for the ribbons produced at higher quenching rate. One of the salient features of the present study is that the improvement of hydrogen storage capacity obtained through higher quenching rates (similar to 45 to 50 m/s wheel speed) leading to the formation of lower grain size. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
Title:
Electrochemical performance of TiVNi-Quasicrystal and AB(3)-Type hydrogen storage alloy composite materials
Authors:
Liu, WQ; Wang, XL; Hu, W; Kawabe, Y; Watada, M; Wang, LM Author Full Names: Liu, Wanqiang; Wang, Xinlu; Hu, Wen; Kawabe, Yoshiteru; Watada, Masaharu; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 36 (1): 616-620 JAN 2011
Abstract:
The Ti1.4V0.6Ni ribbon alloy and AB(3)-type (La0.65Nd0.12Mg0.23Ni2.9Al0.1) alloy ingot are prepared by melt-spinning technique and induction levitation melting technique, respectively. The Ti1.4V0.6Ni + 20 wt.% AB(3) mixture powders are synthesized by ball-milling the above prepared alloy ingots, and their structures and the electrochemical hydrogen storage properties are investigated. It is found that the icosahedral quasicrystal, Ti2Ni, BCC structural solid solution and AB3-type phases are all presented in the composite material. The maximum electrochemical discharge capacity of the composite electrode is 294.7 mAh/g at the discharge current density of 30 mA/g and 303 K. In addition, the electrode made of Ti1.4V0.6Ni and AB(3) composite holds better high-rate discharge ability than that of Ti1.4V0.6Ni. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
Title:
The formation of quasicrystals and their hydrides in Ti-Zr-Ni system
Authors:
Shekhtman, VS; Hakobyan, HG; Aleksanyan, AG; Dolukhanyan, SK; Ter-Galstyan, OP; Sakharov, MK Author Full Names: Shekhtman, V. Sh.; Hakobyan, H. G.; Aleksanyan, A. G.; Dolukhanyan, S. K.; Ter-Galstyan, O. P.; Sakharov, M. K.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 36 (1): 1206-1208 JAN 2011
Abstract:
In the present work, an essentially new approach to production of quasicrystals in Ti-Zr-Ni system is described. It consists in co-compaction and dehydrogenation-sintering of mixture of powders of Ni with two and more hydrides of transition metals of IV group (Ti, Zr). The interaction of some of received quasicrystals with hydrogen in combustion mode is studied, the hydrides of these quasicrystals are synthesized and investigated. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Update: 18-Mar-2011

Title:
Birefringence Properties of Mechanically Clamped K2ZnCl4 Crystals
Authors:
Stadnyk, VI; Gaba, VM; Andrievskii, BV; Kogut, ZO Author Full Names: Stadnyk, V. I.; Gaba, V. M.; Andrievskii, B. V.; Kogut, Z. O.
Source:
PHYSICS OF THE SOLID STATE 53 (1): 131-137 JAN 2011
Abstract:
The effect of uniaxial pressure applied along the principal crystallographic directions on the dispersion and temperature dependences of the birefringence Delta n(i) of K2ZnCl4 crystals has been studied. It has been established that the birefringence Delta n(i) is sensitive to uniaxial pressures and that the uniaxial stresses do not change the character of the dispersion and temperature dependences of Delta n(i). A new "pseudoisotropic" state of this crystal has been revealed. It has been found that the points of the paraphase-incommensurate phase-commensurate phase transitions can be significantly shifted under pressure toward different temperature ranges depending on the direction of the applied pressure due to the effect of uniaxial stresses on the structure of the K2ZnCl4 crystal.
Title:
Universal Hysteresis Scaling for Incommensurate Magnetic Order in Dysprosium
Authors:
Kobayashi, S Author Full Names: Kobayashi, Satoru
Source:
PHYSICAL REVIEW LETTERS 106 (5): Art. No. 057207 FEB 3 2011
Abstract:
We study the scaling properties of magnetic minor hysteresis loops in a polycrystalline dysprosium metal, varying temperature and magnetic-field amplitudes. We observe irreversibility-related hysteresis loss in the helical antiferromagnetic phase, which is related with remanent flux density as a power law with the same scaling exponent of 1.25 +/- 0.05 as that in ferromagnetic materials. In contrast to hysteresis scalings in ferromagnets associated with 180 degrees Bloch walls, the observed law is governed by spiral walls which separate helical domains with oppositely rotating spins.
Title:
Magnetic excitations in the metallic single-layer ruthenates Ca2-xSrxRuO4 studied by inelastic neutron scattering
Authors:
Steffens, P; Friedt, O; Sidis, Y; Link, P; Kulda, J; Schmalzl, K; Nakatsuji, S; Braden, M Author Full Names: Steffens, P.; Friedt, O.; Sidis, Y.; Link, P.; Kulda, J.; Schmalzl, K.; Nakatsuji, S.; Braden, M.
Source:
PHYSICAL REVIEW B 83 (5): Art. No. 054429 FEB 24 2011
Abstract:
By inelastic neutron scattering, we have analyzed the magnetic correlations in the paramagnetic metallic region of the series Ca2-xSrxRuO4, 0.2 <= x <= 0.62. We find different contributions that correspond to two-dimensional ferromagnetic fluctuations and to fluctuations at incommensurate wave vectors Q(1)(IC) = (0.11,0,0), Q(2)(IC) = (0.26,0,0), and Q(alpha beta)(IC) = (0.3,0.3,0). These components constitute the measured response as a function of the Sr concentration x, of the magnetic field, and of the temperature. A generic model is applicable to metallic Ca2-xSrxRuO4 close to the Mott transition, in spite of their strongly varying physical properties. The amplitude, characteristic energy, and width of the incommensurate components vary only slightly as functions of x, but the ferromagnetic component depends sensitively on concentration, temperature, and magnetic field. While ferromagnetic fluctuations are very strong in Ca1.38Sr0.62RuO4 with a low characteristic energy of 0.2 meV at T = 1.5 K, they are strongly suppressed in Ca1.8Sr0.2RuO4, but reappear upon the application of a magnetic field, and form a magnon mode above the metamagnetic transition. The inelastic neutron scattering results document how the competition between ferromagnetic and incommensurate antiferromagnetic instabilities governs the physics of this system.
Title:
Crossover from Commensurate to Incommensurate Antiferromagnetism in Stoichiometric NaFeAs Revealed by Single-Crystal Na-23,As-75-NMR Experiments
Authors:
Kitagawa, K; Mezaki, Y; Matsubayashi, K; Uwatoko, Y; Takigawa, M Author Full Names: Kitagawa, Kentaro; Mezaki, Yuji; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Takigawa, Masashi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 (3): Art. No. 033705 MAR 2011
Abstract:
We report the results of Na-23 and As-75 nuclear magnetic resonance (NMR) experiments on a self-flux grown high-quality single crystal of stoichiometric NaFeAs. The NMR spectra reveal a tetragonal to twinned-orthorhombic structural phase transition at T-O = 57K and an antiferromagnetic (AF) transition at T-AF = 45 K. The divergent behavior of nuclear relaxation rate near T-AF shows significant anisotropy, indicating that the critical slowing down of stripe-type AF fluctuations are strongly anisotropic in spin space. The NMR spectra at sufficiently low temperatures consist of sharp peaks showing a commensurate stripe AF order with a small moment of similar to 0.3 mu(B). However, the spectra just below T-AF exhibit a highly asymmetric broadening pointing to an incommensurate modulation. The commensurate-incommensurate crossover in NaFeAs shows a certain similarity to the behavior of SrFe2As2 under high pressure.
Title:
Incommensurate-to-Commensurate Magnetic Phase Transition in SmIn3 Observed by Muon Spin Relaxation
Authors:
Ito, TU; Higemoto, W; Ninomiya, K; Luetkens, H; Sugai, T; Haga, Y; Suzuki, HS Author Full Names: Ito, Takashi U.; Higemoto, Wataru; Ninomiya, Kazuhiko; Luetkens, Hubertus; Sugai, Takashi; Haga, Yoshinori; Suzuki, Hiroyuki S.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 (3): Art. No. 033710 MAR 2011
Abstract:
Magnetic susceptibility and muon spin relaxation (mu SR) measurements in the intermetallic cubic compound SmIn3 with a Gamma(8) crystalline-electric-field ground state are reported. Anomalies corresponding to successive phase transitions were observed in the magnetic susceptibility at T-I similar to 16.5 K, T-II similar to 15.1 K, and T-III similar to 14.7 K. A spontaneous local magnetic field was detected below T-I using the mu SR technique in zero applied field in contrast to the pure quadrupolar ordering scenario proposed in the phase between T-I and T-II. This result clearly indicates that the primary order parameters in all the ordered phases are magnetic. The local field distribution changes at around TII from a continuous broad one to a sharp one with decreasing temperature, suggesting that an incommensurate-to-commensurate magnetic phase transition takes place at this temperature. A possible magnetic structure in the ground state and the importance of multipolar interactions in the Gamma(8) subspace are discussed.
Title:
Incommensurate Magnetic Structure and Its Long-Time Variation in a Geometrically Frustrated Magnet Ca3Co2O6
Authors:
Moyoshi, T; Motoya, K Author Full Names: Moyoshi, Taketo; Motoya, Kiyoichiro
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 (3): Art. No. 034701 MAR 2011
Abstract:
Magnetization and neutron scattering measurements have been performed on a single crystal of the magnetically frustrated compound Ca3Co2O6. This compound has no random magnetic interactions, but has frustrating magnetic interactions arising from its crystal structure. In this material, a long-time variation in magnetic structure has been observed. After cooling the sample below the transition temperature T-c2 = 13 K, the magnetic Bragg peaks at (1, 0, +/-delta) corresponding to an incommensurate antiferromagnetic structure move toward (1,0,0) with time. The characteristic time for this variation follows the Arrhenius law with an activation energy E-a/k(B) similar to 53 K. A new magnetic structure model of this material is also presented.
Title:
The Al-rich region of the Al-Mn-Ni alloy system. Part II. Phase equilibria at 620-1000 degrees C
Authors:
Balanetskyy, S; Meisterernst, G; Grushko, B; Feuerbacher, M Author Full Names: Balanetskyy, S.; Meisterernst, G.; Grushko, B.; Feuerbacher, M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (9): 3795-3805 MAR 3 2011
Abstract:
Phase equilibria in the Al-rich region of the Al-Mn-Ni alloy system were studied at 1000, 950, 850, 750, 700, 645 and 620 degrees C. Three ternary thermodynamically stable intermetallics, the phi-phase (Al5Co2-type, hP26, P6(3)/mmc; a = 0.76632(16), c = 0.78296(15) nm), the kappa-phase (kappa-Al14.4Cr3.4Ni1.1-type, hP227, P6(3)/m; a = 1.7625(10), c = 1.2516(10) nm), and the O-phase (O-Al77Cr14Pd9-type, Pmmn, oP650,: a = 2.3316(16), b = 1.2424(15), c = 3.2648(14) nm), as well as three ternary metastable phases, the decagonal D-3-phase with periodicity about 1.25 nm, the Al-9(Mn,Ni)(2)-phase (Al9Co2-type, P112(1)/a, mP22; a = 0.8585(16), b = 0.6269(9), c = 0.6205(11) nm, beta = 95.34(10)degrees) and the O-1-phase (base-centered orthorhombic, a approximate to 23.8, b approximate to 12.4, c approximate to 32.2 nm) were revealed. Their physicochemical behaviour in the Al-Mn-Ni alloy system was studied. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Structural and hyperfine properties of Ti48Zr7Fe18 nano-compounds and its hydrides
Authors:
Zywczak, A; Gondek, L; Figiel, H; Zukrowski, J; Czub, J; Takasaki, A Author Full Names: Zywczak, A.; Gondek, L.; Figiel, H.; Zukrowski, J.; Czub, J.; Takasaki, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (9): 3952-3957 MAR 3 2011
Abstract:
It is well established that Ti-based nano-alloys are able to absorb hydrogen with relatively high hydrogen to metal ratio of 4/3. In this study the Ti48Zr7Fe18 nano-compound, prepared by mechanical alloying (MA), has been investigated. In its initial state the compound is amorphous, however upon thermal treatment it transforms to the quasicrystalline icosahedral structure (i-phase), which is based on the Mackay cluster type. Structural characterization of the sample was made by means of XRD measurements. Thermodynamic properties were studied by differential scanning calorimetry (DSC) and thermal desorption spectroscopy (TDS). To find the influence of hydrogen and structure type on hyperfine interactions the Mossbauer spectroscopy (MS) experiment was performed, as well. The amorphous sample after MA was hydrogenated in order to unveil hydrogen influence on crystal properties of the sample. Upon hydrogenation of the amorphous sample a decomposition into simple hydrides took place. (C) 2011 Elsevier B. V. All rights reserved.
Title:
Piezo-optic properties of incommensurately modulated K2ZnCl4 crystals
Authors:
Stadnyk, VI; Kogut, ZO; Brezvin, RS Author Full Names: Stadnyk, V. I.; Kogut, Z. O.; Brezvin, R. S.
Source:
CRYSTALLOGRAPHY REPORTS 56 (1): 84-88 JAN 2011
Abstract:
The effect that uniaxial pressures along the principal crystallophysical directions have on the dispersion and temperature dependences of the birefringence in incommensurate K2ZnCl4 crystals has been investigated in a wide temperature range. This parameter has been established to be fairly sensitive to uniaxial pressures. The spectral and temperature dependences of combined piezo-optic coefficients are analyzed. Significant anomalies of these coefficients are found at the incommensurate-commensurate phase transition. They are due to the change in the induced birefringence that results from spontaneous polarization and to the significant effect of uniaxial stress on the soliton structure of the crystal. The contributions that the electrooptic effect, the elasto-optic effect, and the order parameter make to the spontaneous changes in the piezooptic coefficients are separated.
Title:
Vibrational and thermodynamic properties and molecular motions in the incommensurate crystal of morpholinium tetrafluoroborate studied by H-1 NMR
Authors:
Owczarek, M; Jakubas, R; Bator, G; Pawlukojc, A; Baran, J; Przeslawski, J; Medycki, W Author Full Names: Owczarek, M.; Jakubas, R.; Bator, G.; Pawlukojc, A.; Baran, J.; Przeslawski, J.; Medycki, W.
Source:
CHEMICAL PHYSICS 381 (1-3): 11-20 MAR 18 2011
Abstract:
Dynamics of molecules in morpholinium tetrafluoroborate, [NH2(C2H4)(2)O][BF4], has been studied in a wide temperature range by means of AC calorimetry, H-1 NMR and infrared spectroscopy. Simultaneously, DFT (density functional theory) calculations of the molecular structure and normal vibration frequencies have been performed by using various functionals for initial structural data of the low temperature phase. Infrared spectra of polycrystalline [NH2(C2H4)(2)O][BF4] have been analyzed in a frequency range 4000-400 cm (1). Substantial changes in a temperature evolution of internal modes of both morpholinium cations and [BF4] anions are due to the freezing of these moieties motions below 117 K. A dynamic non-equivalence of protons involved in N-H center dot center dot center dot F and N-H center dot center dot center dot O hydrogen bonds has been detected. Heat capacity anomalies around structural phase transitions detected by AC calorimetry (117 and 153 K) have been evaluated and described. A molecular mechanism of the phase transitions is discussed on the basis of presented results. (C) 2011 Elsevier B. V. All rights reserved.
Title:
Unifying cluster-based structure models of decagonal Al-Co-Ni, Al-Co-Cu and Al-Fe-Ni
Authors:
Deloudi, S; Fleischer, F; Steurer, W Author Full Names: Deloudi, Sofia; Fleischer, Frank; Steurer, Walter
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 67: 1-17 Part 1 FEB 2011
Abstract:
The geometrical building principles of Al-based decagonal quasicrystals and their approximants are discussed from a cluster-based approach. Our investigations cover 11 modifications with two-or four-layer periodicity in the systems Al-Co-Ni, Al-Co-Cu and Al-Fe-Ni. We identified a cluster that leads to a unifying view of all these phases. This unit cluster has similar to 20 angstrom diameter, four-layer periodicity along its tenfold axis and rod symmetry group p (10) over bar 2m. The models obtained are in agreement with all the electron-density maps and electron-microscopy images available.
Title:
Modulated structure of nepheline
Authors:
Friese, K; Grzechnik, A; Petricek, V; Schonleber, A; van Smaalen, S; Morgenroth, W Author Full Names: Friese, Karen; Grzechnik, Andrzej; Petricek, Vaclav; Schoenleber, Andreas; van Smaalen, Sander; Morgenroth, Wolfgang
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 67: 18-29 Part 1 FEB 2011
Abstract:
The incommensurately modulated structure of a natural nepheline of composition K0.54Na3.24Ca0.03Al3.84Si4.16O16 has been determined in superspace. The compound crystallizes in the trigonal centered superspace group X3(00 gamma)0 with gamma = 0.2048 (10), X = (0, 0, 0, 0), (1/3, 2/3, 0, 2/3), (2/3, 1/3, 0, 1/3), a = 17.2889 (8) and c = 8.3622 (10) angstrom. The structure is characterized by a framework of corner-connected (Al,Si)O-4 tetrahedra. The additional cations are incorporated in two different types of channels of the framework. All atoms in the structure are displacively modulated with amplitudes below 0.1 angstrom. The modulation can be well described taking into account harmonics of first order only. Atomic positions in the smaller channels of the framework are fully occupied by Na+. Cationic positions in the larger channel are occupationally modulated, yet the variation of electron density as a function of the internal coordinate t is very small and indicates that the incorporation of different types of cations (K+, Na+, Ca2+) and vacancies is realised in a highly disordered way. Average T-O distances indicate a nearly complete Al/Si ordering in the tetrahedral framework. A large part of the O atoms are approximated by split-atom positions, which are additionally affected by occupational modulation resulting in a high degree of disorder in the modulated structure. Occupational probabilities for the split-atom positions are complementary. Occupational modulations of the cations in the larger channels and the O atoms of the tetrahedral framework are coupled and correlations between occupational and displacive modulations exist.

Update: 11-Mar-2011

Title:
Defect structure and electrical conductivity in the Bi3+xNb0.8W0.2O7.1+3x/2 system
Authors:
Borowska-Centkowska, A; Kario, A; Krok, F; Abrahams, I; Chan, SCM; Liu, X; Wrobel, W; Malys, M; Hull, S; Dygas, JR; Suard, E Author Full Names: Borowska-Centkowska, A.; Kario, A.; Krok, F.; Abrahams, I.; Chan, S. C. M.; Liu, X.; Wrobel, W.; Malys, M.; Hull, S.; Dygas, J. R.; Suard, E.
Source:
SOLID STATE IONICS 181 (39-40): 1750-1756 DEC 20 2010
Abstract:
An investigation of electrical conductivity and defect structure in the fluorite related system Bi3+xNb0.8W0.2O7.1+3x2 (0.0 <= x <= 2.0) using a.c. impedance spectroscopy and powder neutron diffraction is presented. All compositions exhibit incommensurate ordering of the cubic fluorite sublattice, with only the x = 2.0 composition showing evidence for an order-disorder transition above 650 degrees C. Non-linear behaviour in the thermal expansion of the cubic lattice parameter and the Arrhenius plot of total conductivity are discussed in terms of the defect structure. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Colloidal hard dumbbells under gravity: structure and crystallization
Authors:
Marechal, M; Dijkstra, M Author Full Names: Marechal, Matthieu; Dijkstra, Marjolein
Source:
SOFT MATTER 7 (4): 1397-1408 2011
Abstract:
We study the structure and phase behavior of hard dumbbells under gravity. The fluid shows layering near the wall, where subsequent layers of dumbbells align alternatingly parallel or perpendicular to the wall. We observe coexistence of a fluid with a plastic crystal (PC) and an aligned crystal (CP1) in a single sediment for short dumbbells. For longer dumbbells, we observe a direct fluid-CP1 coexistence, while for dumbbells of almost tangent spheres, the aperiodic crystal phase appears in between the fluid and CP1 phase. The locations of the coexistences between these phases are well described by a simple expression based on an approximation similar to the local density approximation, which has been successfully applied to hard spheres under gravity [M. Marechal and M. Dijkstra, Phys. Rev. E, 2007, 75, 061404]. The fluid-PC-CP1 coexistence could not be explained using this expression. We attribute this discrepancy to a lattice constant mismatch between the PC and CP1 phases. Finally, we show using direct simulations that the plastic crystal stacks preferably as the hexagonal close packed crystal for short dumbbells, as is the case for a bulk plastic crystal [M. Marechal and M. Dijkstra, Phys. Rev. E, 2008, 77, 061405].
Title:
Ultra-fine grain size and isotropic very high strength by direct extrusion of chill-cast Mg-Zn-Y alloys containing quasicrystal phase
Authors:
Singh, A; Osawa, Y; Somekawa, H; Mukai, T Author Full Names: Singh, Alok; Osawa, Yoshiaki; Somekawa, H.; Mukai, T.
Source:
SCRIPTA MATERIALIA 64 (7): 661-664 APR 2011
Abstract:
Very fine grain sizes up to similar to 1 mu m with yield strengths up to about 400 MPa in tension and compression, with elongations ranging from 12% to 18%, have been achieved by chill casting and direct extrusion of Mg93Zn6Y alloy containing a quasicrystalline phase. These alloys respond to ageing at 150 degrees C, showing two peaks. The hardness stabilizes at the level of the second peak. The effect of precipitation on the yield strength, ductility and yield asymmetry has been studied. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Structural studies of a mixed-valence state in the incommensurate composite crystal Sr1.261CoO3
Authors:
Isobe, M; Yoshida, H; Muromachi, ET; Ohoyama, K Author Full Names: Isobe, Masaaki; Yoshida, Hiroyuki; Muromachi, Eiji Takayama; Ohoyama, Kenji
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 11 (6): Art. No. 065004 DEC 2010
Abstract:
The incommensurate modulated crystal structure of the hexagonal cobalt oxide Sr1.261CoO3 has been studied using a four-dimensional (4D) superspace profile analysis of neutron powder diffraction data. Sr1.261CoO3 is a composite crystal that consists of the [CoO3] and [2Sr] subsystems. The [CoO3] subsystem forms 1D chains that run parallel to the c-axis and consist of face-sharing CoO6 polyhedra with octahedral (Oh) and trigonal prismatic (TP) coordinations. The structure analysis reveals that the [CoO3] chains contain 73.9% Oh and 26.1% TP sites, and that the TP sites have longer Co-O bonds than the Oh sites: d(av). = 2.039(4) angstrom (TP) and 1.895(3) angstrom (Oh). The averaged Co bond valences are Co3.56(3)+ in the Oh sites and Co2.45(3)+ in the TP sites, suggesting that a considerable amount of Co3+ ions are mixed with Co4+ ions in the Oh sites and with Co2+ ions in the TP sites. The observed magnetic susceptibility can be well explained assuming that the compound has the Co mixed-valence state with the spin configurations of S = 0 low-spin state for Co3+(d epsilon(6)), S = 1/2 low-spin state for Co4+(d epsilon(5)) and S = 3/2 high-spin state for Co2+(d epsilon(5)d gamma(2)). The Weiss temperature, approximately 0.8 K, implies that Sr1.261CoO3 naturally assumes a Curie paramagnetic state, probably owing to the obstruction of the intrachain magnetic interaction by the nonmagnetic Co3+ ions. These results suggest that the nonmagnetic Co3+ ions play an essential role in the magnetism of Sr2 gamma CoO3 systems.
Title:
MECHANICAL PROPERTIES OF Al-Cu-Fe ALLOYS SINTERED AT HIGH PRESSURE
Authors:
Mil'man, YV; Efimov, NA; Ul'shin, SV; Bykov, AI; Neikov, OD; Samelyuk, AV Author Full Names: Mil'man, Yu. V.; Efimov, N. A.; Ul'shin, S. V.; Bykov, A. I.; Neikov, O. D.; Samelyuk, A. V.
Source:
POWDER METALLURGY AND METAL CERAMICS 49 (5-6): 280-288 NOV 2010
Abstract:
The structure and mechanical behavior of bulk Al-Cu-Fe materials sintered at high hydrostatic pressure are studied at room temperature. Quasicrystalline Al63Cu25Fe12 and Al62.7Cu25Fe12Sc0.3 powders and Al66Cu18Fe8Cr8, powder, which is the quasicrystal approximant, are sintered at high pressure. The powders are obtained by high-pressure water atomization. At an optimal hot compaction pressure of 4.5 GPa, the porosity of the compact materials is lower than 2%. Sintering is conducted at 700 degrees C. The stress-strain curves of quasicrystals and their approximants that are brittle in standard test conditions are obtained using indentation method. It is shown that the crystalline approximants of quasicrystals are much closer in their mechanical behavior to quasicrystals than to crystalline solids.
Title:
Nuclear and incommensurate magnetic structure of NaFeGe2O6 between 5 K and 298 K and new data on multiferroic NaFeSi2O6
Authors:
Redhammer, GJ; Senyshyn, A; Meven, M; Roth, G; Prinz, S; Pachler, A; Tippelt, G; Pietzonka, C; Treutmann, W; Hoelzel, M; Pedersen, B; Amthauer, G Author Full Names: Redhammer, Guenther J.; Senyshyn, Anatoliy; Meven, Martin; Roth, Georg; Prinz, Sebastian; Pachler, Astrid; Tippelt, Gerold; Pietzonka, Clemens; Treutmann, Werner; Hoelzel, Markus; Pedersen, Bjoern; Amthauer, Georg
Source:
PHYSICS AND CHEMISTRY OF MINERALS 38 (2): 139-157 FEB 2011
Abstract:
The compound NaFeGe2O6 was grown synthetically as polycrystalline powder and as large single crystals suitable for X-ray and neutron-diffraction experiments to clarify the low temperature evolution of secondary structural parameters and to determine the low temperature magnetic spins structure. NaFeGe2O6 is isotypic to the clinopyroxene-type compound aegirine and adopts the typical HT-C2/c clinopyroxene structure down to 2.5 K. The Na-bearing M2 polyhedra were identified to show the largest volume expansion between 2.5 K and room temperature, while the GeO4 tetrahedra behave as stiff units. Magnetic susceptibility measurements show a broad maximum around 33 K, which marks the onset of low-dimensional magnetic ordering. Below 12 K NaFeGe2O6 transforms to an incommensurately modulated magnetic spin state, with k = [0.323, 1.0, 0.080] and a helical order of spins within the M1-chains of FeO6 octahedra. This is determined by neutron-diffraction experiments on a single crystal. Comparison of NaFeGe2O6 with NaFeSi2O6 is given and it is shown that the magnetic ordering in the latter compound, aegirine, also is complex and is best described by two different spin states, a commensurate one with C2'/c' symmetry and an incommensurate one, best being described by a spin density wave, oriented within the (1 0 1) plane.
Title:
Incommensurate Magnetism in FeAs Strips: Neutron Scattering from CaFe4As3
Authors:
Nambu, Y; Zhao, LL; Morosan, E; Kim, K; Kotliar, G; Zajdel, P; Green, MA; Ratcliff, W; Rodriguez-Rivera, JA; Broholm, C Author Full Names: Nambu, Yusuke; Zhao, Liang L.; Morosan, Emilia; Kim, Kyoo; Kotliar, Gabriel; Zajdel, Pawel; Green, Mark A.; Ratcliff, William; Rodriguez-Rivera, Jose A.; Broholm, Collin
Source:
PHYSICAL REVIEW LETTERS 106 (3): Art. No. 037201 JAN 18 2011
Abstract:
Magnetism in the orthorhombic metal CaFe4As3 was examined through neutron diffraction for powder and single crystalline samples. Incommensurate [q(m) approximate to (0.37-0.39) x b*] and predominantly longitudinally (parallel to b) modulated order develops through a 2nd order phase transition at T-N = 89.63(6) K with a 3D Heisenberg-like critical exponent beta = 0.365(6). A 1st order transition at T-2 = 25.6(9) K is associated with the development of a transverse component, locking q(m) to 0.375(2)b*, and increasing the moments from 2.1(1) to 2.2(3) mu(B) for Fe2+ and from 1.3(3) to 2.4(4) mu(B) for Fe+. The ab initio Fermi surface is consistent with a nesting instability in cross-linked FeAs strips.
Title:
Incommensurate Spin Fluctuations in Hole-Overdoped Superconductor KFe2As2
Authors:
Lee, CH; Kihou, K; Kawano-Furukawa, H; Saito, T; Iyo, A; Eisaki, H; Fukazawa, H; Kohori, Y; Suzuki, K; Usui, H; Kuroki, K; Yamada, K Author Full Names: Lee, C. H.; Kihou, K.; Kawano-Furukawa, H.; Saito, T.; Iyo, A.; Eisaki, H.; Fukazawa, H.; Kohori, Y.; Suzuki, K.; Usui, H.; Kuroki, K.; Yamada, K.
Source:
PHYSICAL REVIEW LETTERS 106 (6): Art. No. 067003 FEB 11 2011
Abstract:
A neutron scattering study of heavily hole-overdoped superconducting KFe2As2 revealed a well-defined low-energy incommensurate spin fluctuation at [pi(1 +/- 2 delta), 0] with delta = 0.16. The incommensurate structure differs from the previously observed commensurate peaks in electron-doped AFe(2)As(2) (A = Ba, Ca, or Sr) at low energies. The direction of the peak splitting is perpendicular to that observed in Fe(Te, Se) or in Ba(Fe, Co)(2)As-2 at high energies. A band structure calculation suggests interband scattering between bands around the Gamma and X points as an origin of this incommensurate peak. The perpendicular direction of the peak splitting can be understood within the framework of multiorbital band structure. The results suggest that spin fluctuation is more robust in hole-doped than in electron-doped samples, which can be responsible for the appearance of superconductivity in the heavily hole-doped samples.
Title:
Nanodomains due to Phason Defects at a Quasicrystal Surface
Authors:
Duguet, T; Unal, B; Ledieu, J; Dubois, JM; Fournee, V; Thiel, PA Author Full Names: Duguet, T.; Uenal, B.; Ledieu, J.; Dubois, J. -M.; Fournee, V.; Thiel, P. A.
Source:
PHYSICAL REVIEW LETTERS 106 (7): Art. No. 076101 FEB 16 2011
Abstract:
Among the three coexisting types of terraces found on the twofold surface of the d-Al-Cu-Co quasicrystal, nanodomains are essentially observed on the transition-metal rich ones, with a coherent interface boundary. Both clean surface and Ag growth analyses, demonstrate that nanodomain surfaces are structurally identical to one of the two other terraces, which contains 85 at.% Al. We provide evidence that the nanodomains are a manifestation of phason defects that extend downward toward the bulk, and state that nanodomains develop because the energetic cost of creating the phason is outweighed by the change in surface energy. Consequently, the formation of nanodomains involves more than just the surface layer, but is driven by surface energetics.
Title:
Variation of growth morphology with chemical composition of terraces: Ag on a twofold surface of a decagonal Al-Cu-Co quasicrystal
Authors:
Duguet, T; Unal, B; Han, Y; Evans, JW; Ledieu, J; Jenks, CJ; Dubois, JM; Fournee, V; Thiel, PA Author Full Names: Duguet, T.; Uenal, B.; Han, Y.; Evans, J. W.; Ledieu, J.; Jenks, C. J.; Dubois, J. M.; Fournee, V.; Thiel, P. A.
Source:
PHYSICAL REVIEW B 82 (22): Art. No. 224204 DEC 9 2010
Abstract:
Growth of Ag thin films on the twofold surface of a decagonal Al-Cu-Co quasicrystal is characterized by scanning tunneling microscopy, at different temperatures, and for coverages ranging from submonolayer to 11 monolayers. From prior work, three types of clean surface terraces are known to exist. By correlation with a bulk structural model, the major difference between them lies in their transition-metal (TM) content, two being aluminum-rich (0 and 15 at. % TM) and one being TM-rich (40-50 at. % TM). The present article focuses on understanding the difference between Ag film morphologies on these terminations, in terms of their chemical content. Growth is found to be smoother on the TM-rich terraces and rougher on the Al-rich ones. The first Ag atomic layer is even pseudomorphic on the TM-rich terraces. Roughness variation with temperature shows that the equilibrium morphology is two dimensional for TM-rich terraces and three dimensional for Al-rich terraces. The explanation of different growth modes in terms of different terrace compositions is supported by calculations of the adhesion energy of a Ag slab with Ag, Al, Cu, and Co slabs, using density-functional theory. For the Al-rich terraces, the roughness variation with temperature also indicates reentrant growth, i.e., anomalously smooth growth at low temperature due to kinetic effects.
Title:
High-pressure suppression of long-range magnetic order in the triangular-lattice antiferromagnet CuFeO2
Authors:
Terada, N; Osakabe, T; Kitazawa, H Author Full Names: Terada, N.; Osakabe, T.; Kitazawa, H.
Source:
PHYSICAL REVIEW B 83 (2): Art. No. 020403 JAN 10 2011
Abstract:
We succeeded in observing pressure-suppressed magnetic long-range ordering (LRO) in the triangular-lattice antiferromagnet CuFeO2, using neutron-diffraction experiments under an isotropic pressure. The magnetic LRO of the four-sublattice ground state under ambient pressure in CuFeO2 almost disappears at the high pressure of 7.9 GPa, and is replaced by an incommensurate order with temperature-independent wave number of (0.192 0.192 1.5). The incommensurate wave number observed at 7.9 GPa corresponds to that observed just above the temperature at which lattice distortion and magnetic LRO simultaneously occur under ambient pressure. Therefore, the long-range magnetic ordering disappears because the high pressure suppressed the lattice distortion that otherwise relieves spin frustration and leads the spin system to LRO.
Title:
Monte Carlo and Molecular Dynamics Simulation of Disorder in the Ag+ Fast Ion Conductors Pearceite and Polybasite
Authors:
Welberry, TR; Pasciak, M Author Full Names: Welberry, T. R.; Pasciak, M.
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE 42A (1): 6-13 JAN 2011
Abstract:
The pearceite-polybasite group of minerals (i.e., pearceite, antimonpearceite, arsenpolybasite, and polybasite) of general stoichiometry [(M6T2S7)-T-I-S-III][(Ag9CuS4)-Cu-I-S-I], with M = Ag+, Cu+ and T = As3+, Sb3+, occur relatively commonly in nature. All have recently been shown to exhibit Ag+ fast ion conduction at rather low temperatures (only slightly above or below room temperature([1])). The average crystal structure determination of these materials shows the positions of the Ag+ ions to be smeared out or delocalized within sheets in an ordered framework structure comprised of the other ions. At the same time, strong and highly structured diffuse scattering has been observed, which contains diffuse peaks that are incommensurate with the diffraction peaks of the framework structure. In order to try to understand the origins of the fast ion conduction properties of these materials, we have used computer simulation of a model system (Monte Carlo and molecular dynamics (MD)) to analyze this observed diffuse scattering.
Title:
Short range magnetic correlations induced by La substitution in Ho1-xLaxMn2O5
Authors:
Wang, CW; Wu, CM; Li, CY; Karna, SK; Hsu, CK; Li, CHC; Li, WH; Yu, CC; Wu, CP; Chou, H; Lynn, JW Author Full Names: Wang, Chin-Wei; Wu, Chun-Ming; Li, Chi-Yen; Karna, Sunil K.; Hsu, Chien-Kang; Li, Carissa H. C.; Li, Wen-Hsien; Yu, Chun-Chen; Wu, Chun-Pin; Chou, Hsiung; Lynn, Jeffrey W.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (24): Art. No. 246002 JUN 23 2010
Abstract:
Magnetic susceptibility, x-ray diffraction, neutron diffraction and Raman scattering measurements are employed to study the effects of La substitution on the magnetic properties of multiferroic HoMn2O5. 9% and 18% La-substituted compounds crystallize into the same orthorhombic Pbam symmetry as the parent compound. The magnetic responses to an ac driving magnetic field between 40 and 140 K are greatly enhanced by 18% La substitution. The neutron magnetic diffraction patterns reveal the development of short range magnetic correlations below 140 K. In addition, two Raman peaks and a series of new x-ray diffraction peaks suddenly develop below this temperature. Incommensurate long range antiferromagnetic order appears below 38 K. Magnetic frustration could be the main mechanism governing the present observations.
Title:
Evolution of microstructure induced by calcination in leached Al-Cu-Fe quasicrystal and its effects on catalytic activity
Authors:
Tanabe, T; Kameoka, S; Tsai, AP Author Full Names: Tanabe, Toyokazu; Kameoka, Satoshi; Tsai, An Pang
Source:
JOURNAL OF MATERIALS SCIENCE 46 (7): 2242-2250 APR 2011
Abstract:
Effects of calcination on catalytic activity for steam reforming of methanol (SRM) over an Al-Cu-Fe quasicrystal (QC) leached with NaOH aq. have been investigated in terms of microstructure with X-ray diffraction and transmission electron microscope (TEM). Calcination at 600 A degrees C in air drastically improved the catalytic activity of the leached QC. TEM observations on cross-section of the samples revealed that cubic Cu (x) Fe3-x-y Al (y) O-4 spinel was formed at the outermost layer of the leached QC after calcinations. Prior to the catalytic reaction, the Cu (x) Fe3-x-y Al (y) O-4 spinel decomposed to a composite where fine Cu nanoparticles dispersed in (Fe,Al)(3)O-4 matrix under H-2 treatment at 300 A degrees C. Drastic increase in catalytic activity is responsible for the fine Cu nanoparticles in the composite. The Cu nanoparticles sit along the same orientation with (Fe,Al)(3)O-4, e.g., Cu [013]//(Fe,Al)(3)O-4 [013] and Cu [200]//(Fe,Al)(3)O-4 [400]. This orientation relationship may stabilize the Cu nanoparticles through a bonding of Cu-O-Fe.
Title:
Modulated magnetic structure in quasi-one-dimensional clinopyroxene NaFeGe2O6
Authors:
Drokina, TV; Petrakovskii, GA; Keller, L; Schefer, J; Balaev, AD; Kartashev, AV; Ivanov, DA Author Full Names: Drokina, T. V.; Petrakovskii, G. A.; Keller, L.; Schefer, J.; Balaev, A. D.; Kartashev, A. V.; Ivanov, D. A.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS 112 (1): 121-126 JAN 2011
Abstract:
The magnetic structure of the NaFeGe2O6 monoclinic compound has been experimentally investigated using the elastic scattering of neutrons. At a temperature of 1.6 K, an incommensurate magnetic structure has been observed in the form of an antiferromagnetic helix formed by a pairs of the spins of the Fe3+ ions with helical modulation in the ac plane of the crystal lattice. The wave vector of the magnetic structure has been determined and its temperature behavior has been studied. The analysis of the temperature dependences of the specific heat and susceptibility, as well as the isotherms of the field dependence of the magnetization, has revealed the existence of not only the order-disorder magnetic phase transition at the point T (N) = 13 K, but also an additional magnetic phase transition at the point T (c) = 11.5 K, which is assumingly an orientation phase transition.
Title:
Highly repulsive interaction in novel inclusion D-2-N-2 compound at high pressure: Raman and x-ray evidence
Authors:
Kim, M; Yoo, CS Author Full Names: Kim, Minseob; Yoo, Choong-Shik
Source:
JOURNAL OF CHEMICAL PHYSICS 134 (4): Art. No. 044519 JAN 28 2011
Abstract:
We present spectral and structural evidences for the formation of a homogeneous cubic delta-N-2-like, noncrystalline solid and an incommensuratelike hexagonal (P6(3)22) inclusion compound (N-2)(12)D-2, formed by compressing a nitrogen-rich mixture to 5.5 and 10 GPa, respectively. A strong repulsive coupling in (N-2)(12)D-2 is evident from a blue shift, discontinuous changes, and the absence of turnover of the D-2 vibron to 70 GPa-all in sharp contrast to both pure D-2 and other inclusion compounds. This repulsive interaction is responsible to the observed incommensuratelike structure and large internal pressure. (C) 2011 American Institute of Physics. [doi:10.1063/1.3533957]
Title:
Ca14Au46Sn5: a "Colored" Gd14Ag51-Type Structure Containing Columns of Well-Differentiated Hexagonal Gold Stars
Authors:
Lin, QS; Corbett, JD Author Full Names: Lin, Qisheng; Corbett, John D.
Source:
INORGANIC CHEMISTRY 50 (5): 1808-1815 MAR 7 2011
Abstract:
A novel hexagonal phase discovered near the Ca15Au60Sn25 quasicrystal and its cubic approximants (ACs) was synthesized by means of high-temperature solid-state reactions. Single-crystal structural analyses show that this is a Gd14Ag51 isotype with composition within the range Ca14Au45.56(4)-46.67(4)Sn5.14(3)-4.14(3), space group P6/m (No. 175), and lattice parameters a =12.763(3)-12.879(3) angstrom and c = 9.326(3)-9.3815(4) angstrom. In this phase, Sn mixes with Au in two of seven anionic sites to give a strong coloring that generates a narrow honeycomb-like Au/Sn template, in which sizable columns of hexagonal Au stars are confined. This phase transforms into the cubic 211 AC phase through a peritectic reaction at similar to 678 degrees C. The valence electron count per atom (eta) of the present phase is in the range 1.41-1.45. However, it does not appear to follow a Hume-Rothery mechanism.

Update: 4-Mar-2011

Title:
Polar Nanodomains and Giant Converse Magnetoelectric Effect in Charge-Ordered Fe2OBO3
Authors:
Yang, HX; Tian, HF; Song, YJ; Qin, YB; Zhao, YG; Ma, C; Li, JQ Author Full Names: Yang, H. X.; Tian, H. F.; Song, Y. J.; Qin, Y. B.; Zhao, Y. G.; Ma, C.; Li, J. Q.
Source:
PHYSICAL REVIEW LETTERS 106 (1): Art. No. 016406 JAN 7 2011
Abstract:
The magnetoelectric coupling and polar nanodomains in the charge-ordered Fe2OBO3 have been extensively studied from room temperature down to 100 K. In situ TEM investigations demonstrate that the charge-ordering transition characterized by an incommensurate modulation could evidently result in remarkable polar nanodomains at low temperatures. This kind of nanodomain could play a critical role in triggering a high dielectric constant and notable dielectric dispersion as observed in Fe2OBO3. Moreover, measurements of the magnetoelectric coupling under electrical field demonstrate the existence of giant electrically induced changes in magnetization around the magnetic transition.
Title:
Fast diffusion of a graphene flake on a graphene layer
Authors:
Lebedeva, IV; Knizhnik, AA; Popov, AM; Ershova, OV; Lozovik, YE; Potapkin, BV Author Full Names: Lebedeva, Irina V.; Knizhnik, Andrey A.; Popov, Andrey M.; Ershova, Olga V.; Lozovik, Yurii E.; Potapkin, Boris V.
Source:
PHYSICAL REVIEW B 82 (15): Art. No. 155460 OCT 29 2010
Abstract:
Diffusion of a graphene flake on a graphene layer is analyzed and a diffusion mechanism is proposed for the system under consideration. According to this mechanism, rotational transition of the flake from commensurate to incommensurate states takes place with subsequent simultaneous rotation and translational motion until the commensurate state is reached again, and so on. The molecular dynamics simulations and analytic estimates based on ab initio and semiempirical calculations demonstrate that the proposed diffusion mechanism is dominant at temperatures T similar to(1-3)T-com, where T-com corresponds to the barrier for transitions of the flake between adjacent energy minima in the commensurate states. For example, for the flake consisting of similar to 40, 200, and 700 atoms the contribution of the proposed diffusion mechanism through rotation of the flake to the incommensurate states exceeds that for diffusion of the flake in the commensurate states by one to two orders of magnitude at temperatures 50-150 K, 200-600 K, and 800-2400 K, respectively. The possibility to experimentally measure the barriers to relative motion of graphene layers based on the study of diffusion of a graphene flake is considered. The results obtained are also relevant for understanding of dynamic behavior of polycyclic aromatic molecules on graphene and should be qualitatively valid for a set of commensurate adsorbate-adsorbent systems.
Title:
Chemical doping-induced flop of ferroelectric polarization in multiferroic Mn0.9Co0.1WO4
Authors:
Song, YS; Yan, LQ; Lee, B; Chun, SH; Kim, KH; Kim, SB; Nogami, A; Katsufuji, T; Schefer, J; Chung, JH Author Full Names: Song, Y. -S.; Yan, Li Qin; Lee, Bumsung; Chun, Sae Hwan; Kim, Kee Hoon; Kim, Sung Baek; Nogami, A.; Katsufuji, T.; Schefer, J.; Chung, J. -H.
Source:
PHYSICAL REVIEW B 82 (21): Art. No. 214418 DEC 15 2010
Abstract:
We studied the multiferroic properties of the incommensurate spiral phase of Mn1-xCoxWO4 using single-crystal neutron-diffraction and ferroelectric measurements. Whereas the rotational plane of the spin spiral is parallel to the b axis for x <= 0.05, it flops by 90 degrees for x=0.10. As a result, the direction of the ferroelectric polarization also flops from the b to the a axis. These results show that the orientation of the ferroelectric polarization in MnWO4 can be controlled via chemical doping.
Title:
Tuning the superconducting and magnetic properties of FeySe0.25Te0.75 by varying the iron content
Authors:
Bendele, M; Babkevich, P; Katrych, S; Gvasaliya, SN; Pomjakushina, E; Conder, K; Roessli, B; Boothroyd, AT; Khasanov, R; Keller, H Author Full Names: Bendele, M.; Babkevich, P.; Katrych, S.; Gvasaliya, S. N.; Pomjakushina, E.; Conder, K.; Roessli, B.; Boothroyd, A. T.; Khasanov, R.; Keller, H.
Source:
PHYSICAL REVIEW B 82 (21): Art. No. 212504 DEC 7 2010
Abstract:
The superconducting and magnetic properties of FeySe0.25Te0.75 single crystals (0.9 <= y <= 1.1) were studied by means of x-ray diffraction, superconducting quantum interference device magnetometry, muon-spin rotation, and elastic neutron diffraction. The samples with y < 1 exhibit coexistence of bulk superconductivity and incommensurate magnetism. The magnetic order remains incommensurate for y >= 1 but with increasing Fe content superconductivity is suppressed and the magnetic correlation length increases. The results show that the superconducting and the magnetic properties of the FeySe1-xTex can be tuned not only by varying the Se/Te ratio but also by changing the Fe content.
Title:
Selective adsorption and electronic interaction of F16CuPc on epitaxial graphene
Authors:
Wang, YL; Ren, J; Song, CL; Jiang, YP; Wang, LL; He, K; Chen, X; Jia, JF; Meng, S; Kaxiras, E; Xue, QK; Ma, XC Author Full Names: Wang, Yi-Lin; Ren, Jun; Song, Can-Li; Jiang, Ye-Ping; Wang, Li-Li; He, Ke; Chen, Xi; Jia, Jin-Feng; Meng, Sheng; Kaxiras, Efthimios; Xue, Qi-Kun; Ma, Xu-Cun
Source:
PHYSICAL REVIEW B 82 (24): Art. No. 245420 DEC 14 2010
Abstract:
We investigate the electronic coupling between copper hexadecafluoro-phthalocyanine (F16CuPc) and epitaxial graphene (EG) on 6H-SiC (0001) using a combined approach of low-temperature scanning tunneling spectroscopy and electronic structure calculations. The molecules are preferentially adsorbed on monolayer EG than bilayer EG. Competing molecule-surface and intermolecular van der Waals interactions result in two well-ordered incommensurate phases. We show that the amount of charge transfer from EG to F16CuPc can be tuned by applied voltage or the thickness of graphene layers. A characteristic feature at similar to 0.4 eV above the Dirac point is identified in bilayer EG, which indicates its electronic structure is modified via introducing extra unoccupied states upon adsorption.
Title:
Helical magnetic state in the distorted triangular lattice of alpha-CaCr2O4
Authors:
Chapon, LC; Manuel, P; Damay, F; Toledano, P; Hardy, V; Martin, C Author Full Names: Chapon, L. C.; Manuel, P.; Damay, F.; Toledano, P.; Hardy, V.; Martin, C.
Source:
PHYSICAL REVIEW B 83 (2): Art. No. 024409 JAN 24 2011
Abstract:
The magnetic properties of the high temperature a form of the CaCr2O4 compound have been investigated for the first time by magnetic susceptibility, specific heat, and powder neutron diffraction. The system undergoes a unique magnetic phase transition at 43 K to a long-range ordered incommensurate helical phase with magnetic propagation vector k = (0,0.3317(2),0). The magnetic model proposed from neutron diffraction data shows that the plane of rotation of the spins is perpendicular to the wave vector and that the magnetic modulation is consistent with two modes belonging to distinct irreducible representations of the group. The magnetic point group 2221 ' is not compatible with ferroelectricity unlike the CuCrO2 delafossite [Kimura et al., Phys. Rev. B, 78 140401 (2008)], but predicts the existence of quadratic magnetoelectric effects, discussed based on a Landau analysis.
Title:
Hysteretic behavior and magnetic ordering in CeRuSn
Authors:
Mydosh, JA; Strydom, AM; Baenitz, M; Chevalier, B; Hermes, W; Pottgen, R Author Full Names: Mydosh, J. A.; Strydom, A. M.; Baenitz, M.; Chevalier, B.; Hermes, W.; Poettgen, R.
Source:
PHYSICAL REVIEW B 83 (5): Art. No. 054411 FEB 9 2011
Abstract:
We report the thermodynamic and transport properties of the newly synthesized Ce-intermetallic compound CeRuSn. This ternary stannide possesses an unconventional structure with two Ce sites at room temperature which exhibit different valencies. Just below room temperature there are large thermal hysteretic effects in the magnetic susceptibility, in the specific heat, as well as in electronic and heat transport properties suggesting the formation of an incommensurate charge density wave modulation whose q vector changes as a function of temperature. Our measurements indicate that one site displays magnetic Ce3+ behavior while the other is a valence fluctuator. At 2.7 K antiferromagnetic long-range order occurs within one-half of the Ce sites, e.g., the magnetic entropy of the transition is 1/2R ln 2. Below T-N a series of metamagnetic transitions takes place in rather small fields (similar to 1-2 T), leaving a magnetically fluctuating background. Such behavior is unique among the many Ce-transition-metal compounds.
Title:
Misfit strain accommodation in epitaxial ABO(3) perovskites: Lattice rotations and lattice modulations
Authors:
Vailionis, A; Boschker, H; Siemons, W; Houwman, EP; Blank, DHA; Rijnders, G; Koster, G Author Full Names: Vailionis, A.; Boschker, H.; Siemons, W.; Houwman, E. P.; Blank, D. H. A.; Rijnders, G.; Koster, G.
Source:
PHYSICAL REVIEW B 83 (6): Art. No. 064101 FEB 11 2011
Abstract:
We present a study of the lattice response to the compressive and tensile biaxial stress in La0.67Sr0.33MnO3 (LSMO) and SrRuO3 (SRO) thin films grown on a variety of single-crystal substrates: SrTiO3, DyScO3, NdGaO3, and (La,Sr)(Al,Ta)O-3. The results show that, in thin films under misfit strain, both SRO and LSMO lattices, which in bulk form have orthorhombic (SRO) and rhombohedral (LSMO) structures, assume unit cells that are monoclinic under compressive stress and tetragonal under tensile stress. The applied stress effectively modifies the BO6 octahedra rotations, whose degree and direction can be controlled by the magnitude and sign of the misfit strain. Such lattice distortions change the B-O-B bond angles and therefore are expected to affect magnetic and electronic properties of the ABO(3) perovskites.
Title:
Strong magnetoelastic effect on the magnetoelectric phenomena of TbMn2O5
Authors:
Oh, YS; Jeon, BG; Haam, SY; Park, S; Correa, VF; Lacerda, AH; Cheong, SW; Jeon, GS; Kim, KH Author Full Names: Oh, Yoon Seok; Jeon, Byung-Gu; Haam, S. Y.; Park, S.; Correa, V. F.; Lacerda, A. H.; Cheong, S. -W.; Jeon, Gun Sang; Kim, Kee Hoon
Source:
PHYSICAL REVIEW B 83 (6): Art. No. 060405 FEB 17 2011
Abstract:
Comparative studies of magnetoelectric susceptibility (alpha), magnetization (M), and magnetostriction (u) in TbMn2O5 reveal that the increment of M owing to the field-induced Tb3+ spin alignment produces a field-asymmetric line shape in the alpha(H) curve, which is conspicuous in a low-temperature incommensurate phase but persistently subsists in the entire ferroelectric phase. Correlations among electric polarization, u, and M-2 variation represent linear relationships, unambiguously showing the significant role of Tb magnetoelastic effects on the low-field magnetoelectric phenomena of TbMn2O5. An effective free energy capturing the observed experimental features is also suggested.
Title:
Wood anomalies in resonant photonic quasicrystals
Authors:
Poddubny, AN Author Full Names: Poddubny, A. N.
Source:
PHYSICAL REVIEW B 83 (7): Art. No. 075106 FEB 8 2011
Abstract:
A theory of light diffraction from a planar quasicrystalline lattice with resonant scatterers is presented. Rich structure, absent in the periodic case, is found in specular reflection spectra, and interpreted as a specific kind of Wood anomaly, characteristic of quasicrystals. The theory is applied to semiconductor quantum dots arranged in Penrose tiling.
Title:
Resonant x-ray scattering investigation of magnetic ordering in NpAs1-xSex (x=0.05, 0.10)
Authors:
Rodrigues, VH; Paixao, JA; Costa, MMR; Mannix, D; Bombardi, A; Rebizant, J; Lander, GH Author Full Names: Rodrigues, V. H.; Paixao, J. A.; Costa, M. M. R.; Mannix, D.; Bombardi, A.; Rebizant, J.; Lander, G. H.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (2): Art. No. 026002 JAN 19 2011
Abstract:
A resonant x-ray scattering investigation of the NpAs1-xSex system with single crystals of 5 and 10% Se content is reported. The main features of the magnetic phase diagram previously studied by neutron scattering were confirmed. The coexistence within a single domain of ferro- and antiferro-components in the low-T ferrimagnetic phase was established, as well as the single-k character of the incommensurate phase and of the antiferromagnetic component of the ferrimagnetic phase. A tetragonal lattice distortion was found in the ferro-and ferrimagnetic phases which is not compatible with the proposed model for the ferromagnetic phase. The study of ferromagnetism was carried out using polarization analysis of the diffracted beam to separate the scattering intensities originating from magnetism and charge, which are superimposed in reciprocal space. The magnetic character of the ferromagnetic signal calculated from the measured intensities in the polarization analysis sigma pi and sigma sigma channels was confirmed by analysis of the corresponding temperature dependence.
Title:
A charge density wave in the hidden order state of URu2Si2
Authors:
Su, JJ; Dubi, Y; Wolfle, P; Balatsky, AV Author Full Names: Su, Jung-Jung; Dubi, Yonatan; Woelfle, Peter; Balatsky, Alexander V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (9): Art. No. 094214 Sp. Iss. SI MAR 9 2011
Abstract:
We argue that the hidden order (HO) state in URu2Si2 will induce a charge density wave. The modulation vector of the charge density wave will be twice that of the hidden order state, Q(CDW) = 2Q(HO). To illustrate how the charge density wave arises we use a Ginzburg-Landau theory that contains a coupling of the charge density wave amplitude to the square of the HO order parameter Delta(HO). This simple analysis allows us to predict the intensity and temperature dependence of the charge density wave order parameter in terms of the susceptibilities and coupling constants used in the Ginzburg-Landau analysis.
Title:
Temperature-pressure phase diagram of an aperiodic host guest compound
Authors:
Toudic, B; Rabiller, P; Bourgeois, L; Huard, M; Ecolivet, C; McIntyre, GJ; Bourges, P; Breczewski, T; Janssen, T Author Full Names: Toudic, B.; Rabiller, P.; Bourgeois, L.; Huard, M.; Ecolivet, C.; McIntyre, G. J.; Bourges, P.; Breczewski, T.; Janssen, T.
Source:
EPL 93 (1): Art. No. 16003 JAN 2011
Abstract:
This letter reports on the structural instabilities of an aperiodic composite crystal under pressure. The (P, T) phase diagram up to 0.55GPa of nonadecane-urea is reported showing various symmetry breakings in crystallographic superspaces, towards three different orthorhombic phases. These structural phase transitions are characterized by a change in the intermodulation and are described by increasing the rank of the crystallographic superspaces. Copyright (C) EPLA, 2011
Title:
Fabrication of quaternary Mg-Zn-Y-Ce quasicrystal alloys and their strengthening effects on AZ91 magnesium alloys
Authors:
Wang, ZF; Zhao, WM; Li, HP; Liang, CY Author Full Names: Wang Zhifeng; Zhao Weimin; Li Haipeng; Liang Chunyong
Source:
CHINA FOUNDRY 7 (4): 342-348 NOV 2010
Abstract:
Quaternary Mg-Zn-Y-Ce quasi-crystal-containing alloys were fabricated using a metal mold casting route. The microstructures of Mg-Zn-Y-Ce alloys and the distribution of the major elements were analyzed. The differences in morphology and micro-hardness between quaternary Mg-Zn-Y-Ce quasi-crystals and ternary M Zn-Y quasi-crystals were discussed. The result showed that the micro-hardness of Mg-Zn-Y-Ce quasi-crystals reached peak value when the content of Ce was 0.8at.%. Subsequently, various contents of Mg-Zn-Y-0.8Ce alloys were used to strengthen AZ91 magnesium alloys. The microstructural modification and mechanical properties of reinforced AZ91 alloys with and without solution as well as their aging treatments were also studied Further research showed that aging-treated AZ91-10wt.%(Mg-Zn-Y-0.8at.%Ce) alloys exhibited excellent mechanical properties: their Brinell hardness, tensile strength, and elongation were HV91, 252 MPa, and 4.1%, respectively. Through this study, the range of application of AZ91 alloys can further be extended.
Title:
Transmission electron microscopy investigation of Ag-free lillianite and heyrovskyite from Vulcano, Aeolian Islands, Italy
Authors:
Mitolo, D; Capitani, GC; Garavelli, A; Pinto, D Author Full Names: Mitolo, Donatella; Capitani, Gian Carlo; Garavelli, Anna; Pinto, Daniela
Source:
AMERICAN MINERALOGIST 96 (2-3): 288-300 FEB-MAR 2011
Abstract:
We present a transmission electron microscopy (TEM) investigation of lillianite (Pb3Bi2S6) and heyrovskyite (Pb6Bi2S9), from Vulcano, Aeolian Islands, Italy. The minerals investigated represent the only naturally occurring Ag- and Cu-free sulfosalts in the lillianite homologous series (LHS). Three methods (crushing, ion-milling, and ultramicrotomy) were used to prepare TEM specimens. Selected area electron diffraction (SAED) patterns and high-resolution TEM (HRTEM) images indicate well-ordered crystals with only minor stacking faults and, more rarely, nanoscale intergrowths of lillianite and heyrovskyite. The latter were sometimes found to form an incommensurate structural modulation with an angle of similar to 29 degrees relative to b* in the (hk0) plane and a wavelength of similar to 75 angstrom. This represents the first observation of such incommensurate modulations in heyrovskyite. Although considerable evidence points toward an artifact induced by the sample preparation technique (i.e., ion-milling), the possibility that the incommensurate modulation could be a primary feature of heyrovskyite itself cannot be completely ruled out. The modulation could derive from an ordering process of Pb and Bi cations over Me4 and Me5 sites within the PbS-like layer or from ordering of vacancies, naturally present or induced by Bi2S3 sublimation during ion-milling.
Title:
Infrared Reflectance Kramers--Kronig Analysis by Anchor-Window Technique
Authors:
Tumenas, S; Kasalynas, I; Karpus, V; Arwin, H Author Full Names: Tumenas, S.; Kasalynas, I.; Karpus, V.; Arwin, H.
Source:
ACTA PHYSICA POLONICA A 119 (2): 140-142 FEB 2011
Abstract:
An algorithm for the Kramers-Kronig analysis of the reflectivity spectra, based on an anchor-window technique is presented. The high-frequency asymptote, required for the Kramers-Kronig analysis, is determined by minimizing differences between the Kramers Kronig-deduced optical constants of a system under investigation and known optical constants measured in a small anchor-window. The algorithm is illustrated by applying it for a reconstruction of the optical conductivity sigma(omega) of the fci-ZnMgRE quasicrystals in the spectral range of 0.01-6.5 eV from the experimental IR Fourier-transform reflectivity data and the experimental spectral ellipsometry VIS-UV data. The reliability of the suggested Kramers-Kronig analysis technique is confirmed by independent infrared spectral ellipsometry sigma(omega) measurements for fci-ZnMgRE.
Title:
ON THE MECHANICAL MILLING OF AlCuCo QUASICRYSTALLINE PHASE.
Authors:
Tellez-Vazquez, JO; Patino-Carachure, C; Garcia-De Leon, E; Rosas, G Author Full Names: Tellez-Vazquez, J. O.; Patino-Carachure, C.; Garcia-De Leon, E.; Rosas, G.
Source:
ACTA MICROSCOPICA 19 (3): 322-327 2010
Abstract:
In the present work, the Al65Cu15Co20 alloy composition was processed by high-energy ball milled to systematically evaluate the phase transitions of the quasicrystalline prealloyed ingot. The quasicrystalline alloy was previously fabricated by conventional casting techniques. Subsequently, this alloy was milled for different times using an SPEX mixer mill. The microstructures were examined by high-resolution electron microscopy and the structural changes were also analyzed by X-ray diffraction patterns. The results indicate that the quasicrystalline alloy is stable after 5 h of milling, containing nano-quasicrystalline domains. However, the sample milled by 10 h shows a quasicrystal-to-amorphous phase transition. Subsequently, after 20 h of milling, the amorphous phase re-crystallizes to the B2 structure type.

Update: 26-Feb-2011

Title:
Structure of BiFeO3 ceramics treated with hot-pressing
Authors:
Su, WN; Wu, XL; Wu, XS; Wang, DH; Du, YW; Chu, PK Author Full Names: Su, W. N.; Wu, X. L.; Wu, X. S.; Wang, D. H.; Du, Y. W.; Chu, Paul K.
Source:
SOLID STATE COMMUNICATIONS 151 (1): 5-8 JAN 2011
Abstract:
BiFeO3 ceramics synthesized at high temperature and pressure is observed to possess large spontaneous polarization and magnetism The selected-area electron diffraction patterns indicate the coexistence of polycrystalline and nanocrystalline grains in the hot-pressed samples Raman spectroscopic studies reveal that the Bi-O bond strain and cations (Fe3+) away from the oxygen octahedral center Induce the polarization The Fe-O bond strain oxygen octahedral rotation around the [111] axis and electromagnons build a long-range interaction between electrical polarization and magnetic moment reorientation to form an Incommensurate spiral magnetic structure This work clearly shows that the hot-pressed treatment can modify the structure and properties of BiFeO3 ceramics (C) 2010 Elsevier Ltd All rights reserved
Title:
Effects of Calcium Addition on High Temperature Creep Resistance of Magnesium Alloys with High Zinc
Authors:
Wan, XF; Sun, YS; Xue, F; Bai, J; Tao, WJ Author Full Names: Wan Xiaofeng; Sun Yangshan; Xue Feng; Bai Jing; Tao Weijian
Source:
RARE METAL MATERIALS AND ENGINEERING 39 (12): 2112-2116 DEC 2010
Abstract:
The effects of trace Ca addition on microstructure and high-temperature creep resistance of as-cast Mg-12Zn-4Al-0.3Mn alloy were investigated. Results show that the as-cast microstructure of the base alloy consists of alpha-Mg matrix and block quasicrystalline phase at gain boundaries. The composition of this quasicrystalline phase is closed to that of the equilibrium tau phase (Mg-32(Al,Zn)(49)) in the Mg-Zn-Al ternary system. A small amount of Ca addition to the base alloy results in the formation of a lamellar eutectic phi(Al2Mg5Zn2) and the transformation of the quasicrystalline phase to the equilibrium tau phase in the as-cast microstructure of the alloy. The volume fraction of the phi phase increases with the increase of Ca addition. The creep resistance of the alloys is significantly improved by Ca addition. The optimum creep resistance of the alloy is obtained by 0.6% Ca addition under the creep condition of 175 degrees C, 70 MPa, whose steady state creep rate is approximately one order of magnitude lower than that of its base alloy.
Title:
Long-range magnetic order in the quasicrystalline approximant Cd6Tb
Authors:
Tamura, R; Muro, Y; Hiroto, T; Nishimoto, K; Takabatake, T Author Full Names: Tamura, R.; Muro, Y.; Hiroto, T.; Nishimoto, K.; Takabatake, T.
Source:
PHYSICAL REVIEW B 82 (22): Art. No. 220201 DEC 8 2010
Abstract:
We report the observation of a long-range magnetic order in a quasicrystalline approximant, i.e., Cd6Tb, demonstrating that a spin glass is not the ground state for the binary approximant but localized spins on the vertices of an icosahedron become antiferromagnetically ordered below 24 K. The result is in contrast to the spin-glasslike behaviors reported for Cd-Mg-R quasicrystals composed of same icosahedral clusters.
Title:
Single composite crystal structure analysis of incommensurate spin-ladder compound Sr2.5Ca11.5Cu24O41
Authors:
Gotoh, Y; Fujihisa, H; Takeya, S; Yamawaki, H; Akimitsu, J Author Full Names: Gotoh, Y.; Fujihisa, H.; Takeya, S.; Yamawaki, H.; Akimitsu, J.
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S219-S220 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
Single-crystal X-ray structure analysis of mutually incommensurate (Sr0.36Ca1.64Cu2O3)(0.706)CuO2, "Sr2.5Ca11.5Cu24O41" has been performed on the basis of superspace group approach. The lattice constants of (Sr0.36Ca1.64Cu2O3)(0.706)CuO2 are a = 1.1298(1), b = 1.2582(1), c(1) = 0.2750(1) nm for the CuO2 part and a = 1.1298(1), b = 1.2582(1), c(2) = 0.3897(1) nm for the (Sr0.36Ca1.64Cu2O3) one. From the average structure analysis, it has been expected that the formation of CuO5 with pyramidal coordination by O atoms occurs in the Cu2O3 ladder. The minimum distance between Cu atom in the Cu2O3 ladder and O atom in the CuO2 chain has clearly shown that O in the CuO2 acts as apical oxygen to form the CuO5 coordination. It has been concluded that (Sr0.36Ca1.54Cu2O3)(0.706)CuO2 bears a marked structural resemblance to the cuprate High T-c superconductors. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Phase diagram of the two-dimensional 16-band d-p model for iron-based superconductors
Authors:
Yanagi, Y; Yamakawa, Y; Ono, Y Author Full Names: Yanagi, Y.; Yamakawa, Y.; Ono, Y.
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S349-S350 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
The electronic state of the Fe2As2 plane in iron-based superconductors is investigated on the basis of the two-dimensional 16-band d-p model. Using the random phase approximation for the on-site Coulomb interaction between Fe d electrons, we obtain the phase diagram including the magnetic ordered states and the superconductivity. It is found that the s(+/-)-wave superconductivity, where the gap functions have different signs between the electron pockets and the hole pockets, is realized near the incommensurate magnetic ordered phase with q similar to (pi, pi). The absolute values of the gap functions on the Fermi surfaces are almost isotropic but largely depend on the energy bands. (C) 2009 Elsevier B.V. All rights reserved.
Title:
NMR studies of field induced magnetism in CeCoIn5
Authors:
Curro, NJ; Young, BL; Urbano, RR; Graf, MJ Author Full Names: Curro, Nicholas J.; Young, Ben-Li; Urbano, Ricardo R.; Graf, Matthias J.
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S521-S524 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
Recent Nuclear Magnetic Resonance and elastic neutron scattering experiments have revealed conclusively the presence of static incommensurate magnetism in the field-induced B phase of CeCoIn5. We analyze the NMR data assuming the hyperfine coupling to the In(2) nuclei is anisotropic and simulate the spectra for several different magnetic structures. The NMR data are consistent with ordered Ce moments along the [001] direction, but are relatively insensitive to the direction of the incommensurate wavevector. (C) 2009 Published by Elsevier B.V.
Title:
NMR study of magnetically-ordered state in a novel superconducting phase in CeCoIn5
Authors:
Kumagai, K; Kondoh, N; Shishido, H; Matsuda, Y Author Full Names: Kumagai, K.; Kondoh, N.; Shishido, H.; Matsuda, Y.
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S533-S535 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
The present NMR study indicates an appearance of finite hyperfine fields coupled to incommensurate antiferromagnetic order of the Ce moments in CeCoIn5. The magnetic order is never observed in the normal state and also in the BCS state, but appears only inside the novel superconducting phase. Strong field dependence of the ordered magnetic moments indicates the coexistence of the incommensurate SDW order and an modulated SC (FFLO) state. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Pairing symmetry reflected in vortex lattice structure of noncentrosymmetric superconductors
Authors:
Saiki, T; Hiasa, N; Ikeda, R Author Full Names: Saiki, Taro; Hiasa, Norihito; Ikeda, Ryusuke
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S581-S583 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
A novel type of modulated vortex states to be realized in Rashba noncentrosymmetric superconductors (NCSs) in parallel fields are studied by examining spatial distributions of the gauge-invariant phase of the order parameter Delta. It is found that a modulated structure reflecting a relative shift of the Fermi surfaces is not due to a single type of nodal lines but rather to rows of vortex-antivortex pairs, and that coalescence of these vortex pairs results in a square vortex lattice separated from the familiar triangular lattice via a first order structural transition. Such a structure supported by rows of vortex pairs is also the origin of striped structures in higher odd LL vortex lattices realizable in centrosymmetric systems with a strong paramagnetic depairing. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Se-77 NMR study of nonmagnetic-magnetic transition in (TMTSF)(2)X
Authors:
Mito, T; Nishiyama, K; Koyama, T; Ueda, K; Kohara, T; Takeuchi, K; Akutsu, H; Yamada, J; Kornilov, A; Pudalov, VM; Qualls, JS Author Full Names: Mito, T.; Nishiyama, K.; Koyama, T.; Ueda, K.; Kohara, T.; Takeuchi, K.; Akutsu, H.; Yamada, J.; Kornilov, A.; Pudalov, V. M.; Qualls, J. S.
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S592-S593 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
Se-77 NMR measurements have been carried out on (TMTSF)(2)X (X = PF6 and AsF6) single crystals. For both compounds, NMR lines split into double-peaked spectra in the SDW state, which is explained with sinusoidal internal field at Se nucleus positions having the same incommensurate wave number with that of the SDW order. No change in the lineshape was observed at T-x at which the spin-relaxation rate shows a kink, suggesting that this anomaly does not cause significant static changes in internal field at the Se-site. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Ca-for-Sr substitution in the thermoelectric [(Sr,Ca)(2)(O,OH)(2)](q)[CoO2] misfit-layered cobalt-oxide system
Authors:
Yamauchi, H; Karvonen, L; Egashira, T; Tanaka, Y; Karppinen, M Author Full Names: Yamauchi, Hisao; Karvonen, Lassi; Egashira, Takayuki; Tanaka, Yoshiaki; Karppinen, Maarit
Source:
JOURNAL OF SOLID STATE CHEMISTRY 184 (1): 64-69 JAN 2011
Abstract:
Calcium-for-strontium substituted samples of the misfit-layered cobalt-oxide system, [(Sr1-xCax)(2) (O,OH)(2)](q)[CoO2], were successfully synthesized up to x=0.2 with a sample-encapsulation technique originally developed for the x=0 end phase. While the x=0 sample has a commensurate match between the two layer blocks (i.e. q=0.5), isovalent Ca-for-Sr substitution induces lattice misfit (i.e. q > 0.5). At the same time the Seebeck coefficient gets increased, but the increase in resistivity results in suppressing the thermoelectric power factor. The magnetic anomaly in the x=0 sample gets released upon the Ca substitution for the x=0.2 sample to exhibit an almost Curie-Weiss behavior. It is concluded that with increasing x in [(Sr1-xCax)(2)(O,OH)(2)](q)[CoO2] the properties smoothly evolve towards those previously reported for the x=1.0 end member, [Ca1.7O2.1H2.4](0.58)[CoO2]. (C) 2010 Elsevier Inc. All rights reserved.
Title:
Crystal nucleation of colloidal hard dumbbells
Authors:
Ni, R; Dijkstra, M Author Full Names: Ni, Ran; Dijkstra, Marjolein
Source:
JOURNAL OF CHEMICAL PHYSICS 134 (3): Art. No. 034501 JAN 21 2011
Abstract:
Using computer simulations, we investigate the homogeneous crystal nucleation in suspensions of colloidal hard dumbbells. The free energy barriers are determined by Monte Carlo simulations using the umbrella sampling technique. We calculate the nucleation rates for the plastic crystal and the aperiodic crystal phase using the kinetic prefactor as determined from event driven molecular dynamics simulations. We find good agreement with the nucleation rates determined from spontaneous nucleation events observed in event driven molecular dynamics simulations within error bars of one order of magnitude. We study the effect of aspect ratio of the dumbbells on the nucleation of plastic and aperiodic crystal phases, and we also determine the structure of the critical nuclei. Moreover, we find that the nucleation of the aligned close-packed crystal structure is strongly suppressed by a high free energy barrier at low supersaturations and slow dynamics at high supersaturations. (C) 2011 American Institute of Physics. [doi:10.1063/1.3528222]
Title:
Correlation between primary phases and atomic clusters in a Zr-based metallic glass
Authors:
Liu, XJ; Chen, GL; Liu, CT Author Full Names: Liu, X. J.; Chen, G. L.; Liu, C. T.
Source:
JOURNAL OF APPLIED PHYSICS 108 (12): Art. No. 123516 DEC 15 2010
Abstract:
Atomic clusters exiting in the Zr65Ti10Ni25 metallic glass and primary phases generated during crystallization were studied by x-ray scattering and high-resolution transmission microscopy. An intrinsic correlation between the atomic clusters and the primary phases has been revealed. It is found that there are topological icosahedral short-range orders (ISROs) in the as-cast sample in addition to fcc-Zr2Ni-type chemical SROs. These topological ISRO and fcc-Zr2Ni-type chemical SRO can simultaneously quasicrystallize/crystallize into the corresponding nanoscaled icosahedral quasicrystalline phase (I-phase) and fcc-Zr2Ni crystal as primary products during crystallization. The synchronic precipitation of these two metastable phases can be understood in terms of their structural similarity between the fcc-Zr2Ni and I-phase in local atomic configuration. In comparison with fcc-Zr2Ni crystal, the I-phase has a smaller size and lower volume fraction due to its lower growth rate attributed to its more complex composition and higher structural symmetry. The competitive growth between these two phases results in the development of nanostructured materials in this alloy after annealing. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3525985]
Title:
Cold-sprayed Coatings based on High Strength Aluminium alloys Reinforced by Quasicrystalline Particles: Microstructure and Key Properties
Authors:
Byakova, AV; Kiz, MM; Sirko, AI; Yakovleva, MS; Milman, YV Author Full Names: Byakova, A. V.; Kiz, M. M.; Sirko, A. I.; Yakovleva, M. S.; Milman, Yu. V.
Source:
HIGH TEMPERATURE MATERIALS AND PROCESSES 29 (5-6): 325-337 Sp. Iss. SI 2010
Abstract:
This study presents significant advantages of cold-spraying in performance of coatings based on Al matrix reinforced by metastable nano- and submicrosized quasicrystalline particles as compared to those processed by thermal spraying and, in particular, by high velocity oxy-fuel (HVOF) spraying technique. Two kinds of feedstock powders with nominal compositions. Al94Fe3Cr3 and Al94Fe2.5Cr2.5Ti1 were employed in spraying the coatings on cold rolled steel substrate. Microstructure and key mechanical characteristics of feedstock powders and coatings performed by cold-spraying and HVOF process were studied and discussed. The main benefit of cold-spraying as opposed to HVOF spraying was that the composite quasicrystalline structure of initial feedstock powders is retained in the interior of flattened particles heavily deformed under impact in solid state. Strain hardening of coating and substrate is resulted from impact during cold-spraying. The results showed that unlike to HVOF sprayed coatings important advantage of cold-sprayed quasicrystalline coatings is referred to combination of increased hardness with ductility indicated by plasticity characteristic just about critical value delta(H) approximate to 0.9, which is quite enough for preventing brittle failure of material during particle impact onto substrate or previously deposited particles.
Title:
Interfaces between Lead and Amorphous Matrices in Immiscible Alloy Systems
Authors:
Singh, A; Tsai, AP Author Full Names: Singh, Alok; Tsai, A. P.
Source:
HIGH TEMPERATURE MATERIALS AND PROCESSES 29 (5-6): 523-530 Sp. Iss. SI 2010
Abstract:
Interfaces between solid lead and amorphous matrix are described, with experimental data from system of lead particles embedded into Al-Cu-V amorphous matrix. Since the structure of the amorphous matrix cannot be described with surety, it has been approached by taking known factors in account, such as the relative stability of various facets of lead and its interfaces with quasicrystals. Lead particles take a round shape in accordance with the amorphous matrix, and are often twinned to form more uniform facets (with uniform energy) on the surface/interface. Interface stability of the lead particle; is indicated by their melting and solidification behavior. Therefore melting and solidification behavior of the embedded particles in amorphous matrix has been compared with those in crystalline and quasicrystalline matrices.
Title:
Crystal structure of simple metals at high pressures
Authors:
Degtyareva, O Author Full Names: Degtyareva, Olga
Source:
HIGH PRESSURE RESEARCH 30 (3): 343-371 2010
Abstract:
The effects of pressure on the crystal structure of simple (or sp-) elements are analysed in terms of changes in coordination number, packing density, and interatomic distances, and general rules are established. In the polyvalent elements from groups 14-17, the covalently bonded structures tend to transform to metallic phases with a gradual increase in coordination number and packing density, a behaviour normally expected under pressure. Group 1 and 2 metallic elements, however, show a reverse trend towards structures with low packing density due to intricate changes in their electronic structure. Complex crystal structures such as host-guest and incommensurately modulated structures found in these elements are given special attention in this review in an attempt to determine their role in the observed phase-transition sequences.
Title:
Antiferroelectric (Pb,Bi)(1-x)Fe1+xO3-y Perovskites Modulated by Crystallographic Shear Planes
Authors:
Abakumov, AM; Batuk, D; Hadermann, J; Rozova, MG; Sheptyakov, DV; Tsirlin, AA; Niermann, D; Waschkowski, F; Hemberger, J; Van Tendeloo, G; Antipov, EV Author Full Names: Abakumov, Artem M.; Batuk, Dmitry; Hadermann, Joke; Rozova, Marina G.; Sheptyakov, Denis V.; Tsirlin, Alexander A.; Niermann, Daniel; Waschkowski, Florian; Hemberger, Joachim; Van Tendeloo, Gustaaf; Antipov, Evgeny V.
Source:
CHEMISTRY OF MATERIALS 23 (2): 255-265 JAN 25 2011
Abstract:
We demonstrate for the first time a possibility to vary the anion content in perovskites over a wide range through a long-range-ordered arrangement of crystallographic shear (CS) planes. Anion-deficient perovskites (Pb,Bi)(1-x)Fe1+xO3-y with incommensurately modulated structures were prepared as single phases in the compositional range from Pb0.857Bi0.094Fe1.049O2.572 to Pb0.409Bi0.567Fe1.025O2.796. Using a combination of electron diffraction and high-resolution scanning transmission electron microscopy, we constructed a superspace model describing a periodic arrangement of the CS planes. The model was verified by refinement of the Pb0.64Bi0.32Fe1.04O2.675 crystal structure from neutron powder diffraction data ((3 + 1)D S.G. X2/m(alpha 0 gamma), X = [1/2,1/2,1/2,1/2], a = 3.9082(1) angstrom, b = 3.90333(8) angstrom, c = 4.0900(1) angstrom, beta = 91.936(2)degrees, q = 0.05013(4)a* + 0.09170(3)c* at T = 700 K, R-P = 0.036, R-wP = 0.048). The (Pb,Bi)(1-x)Fe1+xO3-y structures consist of perovskite blocks separated by CS planes confined to nearly the (509)(p) perovskite plane. Along the CS planes, the perovskite blocks are shifted with respect to each other over the 1/2[110](p) vector that transforms the corner-sharing connectivity of the FeO6 octahedra in the perovskite framework to an edge-sharing connectivity of the FeO5 pyramids at the CS plane, thus reducing the oxygen content. Variation of the chemical composition in the (Pb,Bi)(1-x)Fe1+xO3-y series occurs mainly because of a changing thickness of the perovskite block between the interfaces, that can be expressed through the components of the q vector as Pb6 gamma+2 alpha Bi1-7 gamma-alpha Fe1+gamma-alpha O3-3 gamma-alpha. The Pb, Bi, and Fe atoms are subjected to strong displacements occurring in antiparallel directions on both sides of the perovskite blocks, resulting in an antiferroelectric-type structure. This is corroborated by the temperature-, frequency-, and field-dependent complex permittivity measurements . Pb0.64Bi0.32Fe1.04O2.675 demonstrates a remarkably high resistivity > 0.1 T Omega cm at room temperature and orders antiferromagnetically below T-N = 608(10) K.
Title:
Structural Evolution of the BiFeO3-LaFeO3 System
Authors:
Rusakov, DA; Abakumov, AM; Yamaura, K; Belik, AA; Van Tendeloo, G; Takayama-Muromachi, E Author Full Names: Rusakov, Dmitriy A.; Abakumov, Artem M.; Yamaura, Kazunari; Belik, Alexei A.; Van Tendeloo, Gustaaf; Takayama-Muromachi, Eiji
Source:
CHEMISTRY OF MATERIALS 23 (2): 285-292 JAN 25 2011
Abstract:
The (1 - x)BiFeO3-xLaFeO(3) system has been investigated and characterized by room-temperature and high-temperature laboratory and synchrotron powder X-ray diffraction, electron diffraction, high-resolution transmission electron microscopy, differential scanning calorimetry, and magnetization measurements. At room temperature, the ferroelectric R3c phase is observed for 0.0 <= x <= 0.10. The PbZrO3-related root 2a(p) x 2 root 2a(p) x 4a(p) superstructure (where a(p) is the parameter of the cubic perovskite subcell) is observed for Bi0.82La0.18FeO3, while an incommensurately modulated phase is formed for 0.19 <= x <= 0.30 with the root 2a(p) x 2a(p) x root 2a(p) basic unit cell. The GdFeO3-type phase with space group Pnma (root 2a(p) x 2a(p) x root 2a(p)) is stable at 0.50 <= x <= 1. Bi0.82La0.18FeO3 has no detectable homogeneity range (space group Pnma, a = 5.6004(1) angstrom, b = 11.2493(3) angstrom, c = 15.6179(3) angstrom). The incommensurately modulated Bi0.75La0.25FeO3 structure was solved from synchrotron X-ray powder diffraction data (Imma(00 gamma)s00 superspace group, a = 5.5956(1) angstrom, h = 7.8171(1) angstrom, c = 5.62055(8) angstrom; q = 0.4855(4)c*, R-P = 0.023, R-wP = 0.033). In this structure, cooperative displacements of the Bi and O atoms occur, which order within the (AO) (where A = Bi, La) layers, resulting in an antipolar structure. Local fluctuations of the intralayer antipolar ordering are compensated by an interaction with the neighboring (AO) layers. A coupling of the an tipolar displacements with the cooperative tilting distortion of the perovskite octahedral framework is proposed as the origin of the incommensurability. All the phases transform to the GdFeO3-type structure at high temperatures. Bi0.82La0.18FeO3 shows an intermediate PbZrO3-type phase with root 2a(p) x 2 root 2a(p) x 2a(p) (space group Pbam; a = 5.6154(2) angstrom, b = 11.2710(4) angstrom, and c = 7.8248(2) angstrom at 570 K). The compounds in the compositional range of 0.18 <= x <= 0.95 are canted antiferromagnets.
Title:
Observation of anomalous phonons in orthorhombic rare-earth manganites
Authors:
Gao, P; Chen, HY; Tyson, TA; Liu, ZX; Bai, JM; Wang, LP; Choi, YJ; Cheong, SW Author Full Names: Gao, P.; Chen, H. Y.; Tyson, T. A.; Liu, Z. X.; Bai, J. M.; Wang, L. P.; Choi, Y. J.; Cheong, S. -W.
Source:
APPLIED PHYSICS LETTERS 97 (26): Art. No. 262905 DEC 27 2010
Abstract:
We observe the appearance of a phonon near the lock-in temperature in orthorhombic REMnO3 (RE denotes rare earth) (RE: Lu and Ho) and anomalous phonon hardening in orthorhombic LuMnO3. The anomalous phonon occurs at the onset of spontaneous polarization. No such changes were found in incommensurate orthorhombic DyMnO3. These observations directly reveal different electric polarization mechanisms in the E-type and incommensurate-type orthorhombic REMnO3. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3533022]

Update: 18-Feb-2011

Title:
Direct methods beyond small-molecule crystallography
Authors:
Fan, HF Author Full Names: Fan, Hai-fu
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 207 (12): 2621-2638 DEC 2010
Abstract:
The development of direct methods outside their traditional field began since the middle 1960s. New applications were explored gradually in four directions. They are the transition of: (i) from single crystals to powder samples, (ii) from X-ray crystallography to electronmicroscopy (EM), (iii) from periodic structures to incommensurate structures and (iv) from small molecules to macromolecular structures. The research on methods of solving crystal structures at the Institute of Physics in Beijing has been focused on the last three directions. The transition of direct methods from X-ray crystallography to EM led to a two-step image processing technique in high-resolution electron microscopy (HREM). This technique combines information of EM and that of electron diffraction (ED) revealing the structure of minute crystals that are unsuitable for X-ray diffraction analysis. The transition of direct methods from periodic crystal structures to incommensurate structures led to the multi-dimensional direct methods enabling ab initio solution of incommensurate modulated structures and composite structures without relying on an assumed modulation model or even the known basic structure. Finally the combination of direct methods with traditional protein crystallographic methods has greatly enhanced the ability of solving protein structures. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Title:
Electronic properties of stable decagonal quasicrystals
Authors:
Zhang, DL Author Full Names: Zhang, Dianlin
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 207 (12): 2666-2673 DEC 2010
Abstract:
Selected topics of electronic properties of stable decagonal quasicrystals are reviewed. Phonon localization and enhanced electron-phonon interaction may play important roles in the transport properties of these materials. The electronic specific heat measurements support the picture that the Hume-Rothery instability is responsible for the formation of the phase. On the other hand, careful examination of the magnetoresistance on highly oriented quasicrystalline films does not support the applicability of the quantum interference effect to the phenomenon. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Title:
Magnetic Phase Transitions and Magnetic-Field-Induced Polarization Flops in Multiferroic YbMn2O5
Authors:
Fukunaga, M; Sakamoto, Y; Kimura, H; Noda, Y Author Full Names: Fukunaga, Mamoru; Sakamoto, Yuma; Kimura, Hiroyuki; Noda, Yukio
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 (1): Art. No. 014705 JAN 2011
Abstract:
We have measured the electric polarization along the b- and a-axes of multiferroic YbMn2O5 under a magnetic field along the c-axis up to 14.5 T. We found that the polarization along the b-axis disappears, while that along the a-axis appears below 5.5 K in 0 T, though the direction of the polarization switches again above 1.5 T at 4.3 K. Ferroelectric hysteresis loops along the both axes of YbMn2O5 were clearly observed by the double-wave method. This polarization-flop phenomenon is very similar to that previously found in TmMn2O5. We have also studied the magnetic phase transitions of YbMn2O5 by neutron diffraction, and compared the data with those of TmMn2O5. The low-temperature incommensurate magnetic phases relating to the polarization flop of YbMn2O5 and TmMn2O5 are similar, though YbMn2O5 lacks a commensurate magnetic and ferroelectric phase which exists in TmMn2O5 and typical similar compounds.
Title:
Magnetic properties of the Ag-In-rare-earth 1/1 approximants
Authors:
Ibuka, S; Iida, K; Sato, TJ Author Full Names: Ibuka, Soshi; Iida, Kazuki; Sato, Taku J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (5): Art. No. 056001 FEB 9 2011
Abstract:
We have performed magnetic susceptibility and neutron scattering measurements on polycrystalline Ag-In-RE (RE, rare-earth) 1/1 approximants. In the magnetic susceptibility measurements, for most of the RE elements, inverse susceptibility shows linear behaviour in a wide temperature range, confirming well localized isotropic moments for the RE3+ ions. Exceptionally for the light RE elements, such as Ce and Pr, nonlinear behaviour was observed, possibly due to significant crystalline field splitting or valence fluctuation. For RE = Tb, the susceptibility measurement clearly shows a bifurcation of the field-cooled and zero-field-cooled susceptibility at T-f = 3.7 K, suggesting a spin-glass-like freezing. On the other hand, neutron scattering measurements detect significant development of short-range antiferromagnetic spin correlations in the elastic channel, which is accompanied by a broad peak at (sic)omega = 4 meV in the inelastic scattering spectrum. These features have striking similarity to those in the Zn-Mg-Tb quasicrystals, suggesting that the short-range spin freezing behaviour is due to local high-symmetry clusters commonly seen in both systems.
Title:
Temperature and magnetic field induced multiple magnetic transitions in DyAg2
Authors:
Arora, P; Chattopadhyay, MK; Chandra, LSS; Sharma, VK; Roy, SB Author Full Names: Arora, Parul; Chattopadhyay, M. K.; Chandra, L. S. Sharath; Sharma, V. K.; Roy, S. B.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (5): Art. No. 056002 FEB 9 2011
Abstract:
The magnetic properties of the rare-earth intermetallic compound DyAg2 are studied in detail with the help of magnetization and heat capacity measurements. It is shown that the multiple magnetic phase transitions can be induced in DyAg2 both by temperature and magnetic field. The detailed magnetic phase diagram of DyAg2 is determined experimentally. It was already known that DyAg2 undergoes an incommensurate to commensurate antiferromagnetic phase transition close to 10 K. The present experimental results highlight the first order nature of this phase transition, and show that this transition can be induced by magnetic field as well. It is further shown that another isothermal magnetic field induced transition or metamagnetic transition exhibited by DyAg2 at still lower temperatures is also of first order nature. The multiple magnetic phase transitions in DyAg2 give rise to large peaks in the temperature dependence of the heat capacity below 17 K, which indicates its potential as a magnetic regenerator material for cryocooler related applications. In addition it is found that because of the presence of the temperature and field induced magnetic phase transitions, and because of short range magnetic correlations deep inside the paramagnetic regime, DyAg2 exhibits a fairly large magnetocaloric effect over a wide temperature window, e.g., between 10 and 60 K.
Title:
Effect of composition on the i-phase cell parameter of Ti-(Zr,Cu)-Ni alloys
Authors:
Kocjan, A; McGuiness, PJ; Recnik, A; Kovac, J; Kobe, S Author Full Names: Kocjan, A.; McGuiness, P. J.; Recnik, A.; Kovac, J.; Kobe, S.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 356 (50-51): 2769-2773 NOV 2010
Abstract:
Quasicrystalline (i-phase) Ti-Zr-Ni samples were obtained using the melt-spinning technique where the Ti/Zr ratio ranged from 1 to 3 while the Ni content remained nearly constant varying between 17 and 20 at % We replaced the Zr with 3 and 5 at % of Cu in order to test the i-phase-forming ability of the samples which were all subsequently hydrided from the gas phase at 45 bar and 300 C for 1000 min We then made XRD analyses of the as spun and loaded samples in order to determine the influence of the composition and the absorbed hydrogen content on the cell parameter of the i phase An almost linear decrease of this parameter with the ([Ti] + [Cu])/[Zr] ratio was found for the as-prepared and hydrided samples where the slope of the lineal fit is preserved after hydrogenation but with about 6% higher values due to the expansion of the quasi lattice XPS analyses of the melt-spun i-Ti45Zr35Ni17Cu3 revealed an oxide-layer thickness of 4 nm A TEM investigation revealed that the size of the i-phase grains on the wheel side of the ribbon was approximately five times smaller than on the bright side as a result of the higher cooling rate and the resulting faster nucleation rate (C) 2010 Elsevier BV All rights reserved
Title:
Magneto structural transition in the DySi CrB- and micro-structural changes in the FeB-type compounds by XRPD and neutron diffraction
Authors:
Schobinger-Papamantellos, P; Brunelli, M; Rodriguez-Carvajal, J; Buschow, KHJ; Ritter, C; Gramm, F Author Full Names: Schobinger-Papamantellos, P.; Brunelli, M.; Rodriguez-Carvajal, J.; Buschow, K. H. J.; Ritter, C.; Gramm, F.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 323 (7): 903-914 APR 2011
Abstract:
We present the magnetic temperature phase diagrams of the CrB- and FeB-type orthorhombic phases of the DySi compound, determined from high-quality powder XRPD and neutron diffraction, as well as the sample microstructure as determined by HRTEM. Both phase diagrams comprise a HT (T-c1, T-c2 - T-N) and a LT range (5K-T-c1, T-c2) separated by a monoclinic phase transition at T-c1 = T-c2 = 23.5 K well below the second-order Neel transition (T-N = 40 K). The transition paths are for CrB-type Cmcm (HT) T-c1 -> C-2/m11 (LT), and for FeB Pnma (HT) T-c2 -> P2(1)/n11 (LT). The transitions are related to non-monotonous changes of the lattice and structural parameters displaying anomalies at T-c1, T-c2 and slight volume changes. For the CrB-type the monoclinic angle decreases smoothly from T-c1 down to 5 K and the maximum strain experienced by the crystal lattice in the (0 2 1) direction was found at T-c1. In the FeB-type, in addition to the magneto-elastic transition at T-c2 = 23.5 K, minor anomalies are found at 13.5 K in the temperature dependence of the monoclinic angle and the maximum strain along (0 1 1). Both temperatures mark the sequence of changes in the magnetic domain microstructure observed in FeB: below T-2 = 23.5 K the incommensurate HT magnetic phase with q(3) approximate to (01/2 1/7) disproportionates into two LT phases q(3) approximate to (01/2 1/11) T-2 and q(2) approximate to (01/2 1/6) coexisting in the form of domains with portions varying with T going from T-2 down to 13.5 K(q(2) increasing at the cost of q(3)). This behaviour could be related to structural inhomogeneities below the first-order magneto-elastic transition T-c2, if one assumes a broad two phase range, where the HT (Pnma) phase coexists with(P2(1)/n) as a metastable phase at LT in the form of domains with different magnetic behaviour. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Helical Magnetic Structure in a Quasi-One-Dimensional LiCu2O2 Multiferroic Crystal According to Cu-63,Cu-65 NMR Studies
Authors:
Sadykov, AF; Gerashchenko, AP; Piskunov, YV; Ogloblichev, VV; Buzlukov, AL; Verkhovskii, SV; Yakubovskii, AY; Kumagai, K Author Full Names: Sadykov, A. F.; Gerashchenko, A. P.; Piskunov, Yu. V.; Ogloblichev, V. V.; Buzlukov, A. L.; Verkhovskii, S. V.; Yakubovskii, A. Yu.; Kumagai, K.
Source:
JETP LETTERS 92 (8): 527-531 OCT 2010
Abstract:
The NMR spectra of Cu-63 and Cu-65 natural copper isotopes in a LiCu2O2 multiferroic single crystal compound have been measured above and below the temperature of magnetic phase transition (T-c = 23 K) in zero magnetic field and in applied magnetic field H-0 = 94 kOe parallel to the c axis of the crystal. In LiCu(2O)2 below T-c, a complicated helical magnetic structure with the magnetic moment of copper ions Cu2+ varying along the chain according to the harmonic law with the wave vector being incommensurate to the crystal lattice constants has been revealed. The experimental results have been successfully interpreted using the model based on the planar helical magnetic structure. It has been found that the plane of rotation for Cu2+ magnetic moments in LiCu2O2 does not coincide at H-0 = 0 with the ab plane. The high magnetic field (H-0 = 94 kOe) applied along the c axis of the single crystal does not affect the spatial orientation of the plane of rotation.
Title:
Ab initio reconstruction of difference densities by charge flipping
Authors:
Palatinus, L; Fleischer, F; Pattison, P; Weber, T; Steurer, W Author Full Names: Palatinus, Lukas; Fleischer, Frank; Pattison, Phillip; Weber, Thomas; Steurer, Walter
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 67: 9-20 Part 1 JAN 2011
Abstract:
The charge-flipping algorithm in its band-flipping variant is capable of ab initio reconstructions of scattering densities with positive and negative values. It is shown that the method can be applied to reconstructions of difference electron densities of superstructures, i.e. densities obtained as a difference between the true scattering density and the average density over two or more subcells of the true structure. The amplitudes of reflections lying on the reciprocal lattice of the subcell are not required for the procedure. A series of examples shows applications of the method to the solution of superstructures in periodic crystals or quasicrystals as well as the application to ab initio solution of modulation of an incommensurately modulated structure from satellite reflections only and solution of a structure from a crystal twinned by reticular pseudomerohedry. The method is especially suited for solving pseudosymmetry problems occurring frequently in superstructures.
Title:
Generation of (3+d)-dimensional superspace groups for describing the symmetry of modulated crystalline structures
Authors:
Stokes, HT; Campbell, BJ; van Smaalen, S Author Full Names: Stokes, Harold T.; Campbell, Branton J.; van Smaalen, Sander
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 67: 45-55 Part 1 JAN 2011
Abstract:
A complete table of (3 + 1)D, (3 + 2)D and (3 + 3)D superspace groups (SSGs) has been enumerated that corrects omissions and duplicate entries in previous tables of superspace groups and Bravais classes. The theoretical methods employed are not new, though the implementation is both novel and robust. The paper also describes conventions for assigning a unique one-line symbol for each group in the table. Finally, a new online data repository is introduced that delivers more complete information about each SSG than has been presented previously.

Update: 4-Feb-2011

Title:
Investigation of thermodynamic properties and magnetic ordering in TmNiIn
Authors:
Baran, S; Kaczorowski, D; Arulraj, A; Penc, B; Szytula, A Author Full Names: Baran, S.; Kaczorowski, D.; Arulraj, A.; Penc, B.; Szytula, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 323 (6): 833-837 MAR 2011
Abstract:
The magnetic, electrical resistivity, specific heat and powder neutron diffraction measurements were performed on a polycrystalline sample of TmNiIn. The compound crystallizes in a hexagonal structure of the ZrNiAl-type. It orders antiferromagnetically below T-N = 2.5 K. The magnetic structure is an incommensurate one and may be described by the propagation vector (k) over right arrow = [k(x),k(x),1/2], where k(x)=0.281(2). The magnetic moments are confined within the basal hexagonal plane. The results are compared with those reported for isostructural thulium compounds like TmAgSi, TmAgGe and TmPtIn. (C) 2010 Elsevier B.V. All rights reserved.

Update: 28-Jan-2011

Title:
Bond orientational ordering in a metastable supercooled liquid: a shadow of crystallization and liquid-liquid transition
Authors:
Tanaka, H Author Full Names: Tanaka, Hajime
Source:
JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT : Art. No. P12001 DEC 2010
Abstract:
It is widely believed that a liquid state can be characterized by a single order parameter, density, and that a transition from a liquid to solid can be described by density ordering (translational ordering). For example, this type of theory has had great success in describing the phase behaviour of hard spheres. However, there are some features that cannot be captured by such theories. For example, hard spheres crystallize into either hcp or fcc structures, without a tendency of bcc ordering which is expected by the Alexander-McTague theory based on the Landau-type free energy of the density order parameter. We also found hcp-like bond orientational ordering in a metastable supercooled liquid, which promotes nucleation of hcp crystals. Furthermore, theories based on the single order parameter cannot explain water-like thermodynamic and kinetic anomalies of a liquid and liquid-liquid transition in a single-component liquid. Based on these facts, we argue that we need an additional order parameter to describe a liquid state. It is bond orientational order, which is induced by dense packing in hard spheres or by directional bonding in molecular and atomic liquids. Bond orientational order is intrinsically of local nature, unlike translational order which is of global nature. This feature plays a unique role in crystallization and quasicrystal formation. We also reveal that bond orientational ordering is a cause of dynamic heterogeneity near a glass transition and is linked to slow dynamics. In relation to this, we note that, for describing the structuring of a highly disordered liquid, we need a structural signature of low configurational entropy, which is more general than bond orientational order. Finally, the water-like anomaly and liquid-liquid transition can be explained by bond orientational ordering due to hydrogen or covalent bonding and its cooperativity, respectively. So we argue that bond orientational ordering is a key to the physical understanding of crystallization, quasicrystallization, glass transition, water-like anomaly and liquid-liquid transition. A unified description of these phenomena may be possible along this line.

Update: 21-Jan-2011

Title:
Effect of infrared illumination on the modulated magnetic structure of the weak ferromagnet FeBO3: Mg
Authors:
Sokolov, BY Author Full Names: Sokolov, B. Yu.
Source:
PHYSICS OF THE SOLID STATE 52 (12): 2527-2534 DEC 2010
Abstract:
The effect of unpolarized white light on the period and conditions of the existence of the modulated magnetic structure of the FeBO3: Mg single crystal, which is formed in this easy-plane weak ferromagnet in the low-temperature range during technical magnetization, has been investigated experimentally. It has been revealed that the degree of light action on the magnetic state of the crystal depends on both the irradiation duration and the orientation of the ferromagnetic vector during illumination. It has been established that light with wavelengths in the range 0.8 mu m < lambda < 0.9 mu m has a maximum effect on the parameters of the modulated magnetic structure formed in the FeBO3: Mg single crystal. The results obtained have been interpreted in the framework of the "magnetic ripple" theory using the model of photosensitivity of anisotropic magnetic centers associated with the presence of Mg impurity ions in the composition of the crystal.
Title:
Quasicrystal-like structure and its crystalline approximant in an Fe48Cr15Mo14C15B6Tm2 bulk metallic glass
Authors:
Hirata, A; Hirotsu, Y; Amiya, K; Inoue, A Author Full Names: Hirata, Akihiko; Hirotsu, Yoshihiko; Amiya, Kenji; Inoue, Akihisa
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 504: S186-S189 Suppl. 1 AUG 2010
Abstract:
Nanoscale quasicrystal-like structural states have been found in the course of crystallization in an Fe-based Fe48Cr15Mo14C15B6Tm2 bulk metallic glass. The quasicrystal-like structure is similar with the chi-FeCrMo structure exhibiting a deformed tenfold diffraction pattern due to projected pentagonal arrangements regarded as a Mo framework. We show the preliminary structural model for the quasicrystal-like structure and discuss the three-dimensional features based on the chi-FeCrMo crystalline approximant. (C) 2010 Elsevier B.V. All rights reserved.
Title:
TEM study of the cooling rate dependent crystallization behavior of (Zr65Al10Ni10Cu15)(98)Nb-2 metallic glass
Authors:
Wang, YM; Shek, CH; Wang, Q; Qiang, JB; Dong, CA Author Full Names: Wang, Yingmin; Shek, Chan Hung; Wang, Qing; Qiang, Jianbing; Dong, Chuang
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 504: S234-S238 Suppl. 1 AUG 2010
Abstract:
The crystallization of (Zr65Al10Ni10Cu15)(98)Nb-2 metallic glasses has been studied using transmission electron microscopy (TEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The ribbon glass and bulk metallic glass (BMG) of this alloy exhibit different crystallization behaviors. For ribbon glass in the first stage crystallization, icosahedral quasicrystal (I-phase) precipitated together with the eta-Zr2Ni (a = 1.226 nm) phase. The BMG alloy transforms into the I-phase and two coherently coexisted phases, namely, the Al2Zr3 phase and an unknown primitive cubic phase (a = 0.76 nm) in this stage. The experimental evidence indicates that the liquid cooling rate for sample preparation has a significant effect on its crystallization behavior of this alloy glass. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Decomposition of icosahedral phase in Ti52Zr28Ni20 powder during electro-discharge sintering
Authors:
Song, GA; Shin, JS; Kang, TJ; Choi, HS; Lee, JK; Lee, MH; Kim, TS; Fleury, E; Prima, F; Lee, WH; Kim, KB Author Full Names: Song, G. A.; Shin, J. S.; Kang, T. J.; Choi, H. S.; Lee, J. K.; Lee, M. H.; Kim, T. S.; Fleury, E.; Prima, F.; Lee, W. H.; Kim, K. B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 504: S302-S305 Suppl. 1 AUG 2010
Abstract:
A single pulse of 0.57-1.1 kJ/0.45 g-atomized spherical Ti52Zr28Ni20 powders in size range of 10-30 and 30-50 mu m consisting of a mixture of beta-(Ti, Zr) and icosahedral phases was applied to understand the structural evolution of icosahedral phase during electro-discharge sintering (EDS). The structural analysis revealed that high electrical input energies leaded to complete decomposition of icosahedral phase into C14 Laves and beta-(Ti, Zr) phases. Furthermore, the critical input energy inducing decomposition of icosahedral phase during EDS is dependent on the size of the powder. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Characterisation of an Al93Fe3Cr2Ti2 alloy obtained by spray forming
Authors:
Garcia-Escorial, A; Echevarria, M; Lieblich, M; Stone, I Author Full Names: Garcia-Escorial, A.; Echevarria, M.; Lieblich, M.; Stone, I.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 504: S519-S521 Suppl. 1 AUG 2010
Abstract:
Al93Fe3Cr2Ti2 is a highly promising alloy due to its capacity to form quasicrystals. In the present work bulk Al93Fe3Cr2Ti2 obtained by spray forming is microstructurally characterised. A microstructure gradient is observed, in which the external layer consists of an alpha-Al matrix with Al3Ti precipitates and fine quasicrystals while the internal core presents intermetallics of the equilibrium phases Al13Cr2 + Al13Fe4, with intermediate stages between both areas. The hardness ranges from the 140Hv of the external layer to the 90Hv of the core. Spray forming can therefore produce nanoquasicrystalline Al93Fe3Cr2Ti2 which evolves towards equilibrium as the process proceeds, due to the heating produced by the deposition of successive layers. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Composites reinforced by Al-Cu-Fe quasicrystalline particles with a copper matrix and their tribological properties
Authors:
Shaitura, DS; Teplov, AA; Chikina, EA; Klevachev, AM; Efimochkin, IY; Fedotov, SV; Petrzhik, MI; Levashov, EA; Abuzin, YA Author Full Names: Shaitura, D. S.; Teplov, A. A.; Chikina, E. A.; Klevachev, A. M.; Efimochkin, I. Yu.; Fedotov, S. V.; Petrzhik, M. I.; Levashov, E. A.; Abuzin, Yu. A.
Source:
JOURNAL OF SURFACE INVESTIGATION-X-RAY SYNCHROTRON AND NEUTRON TECHNIQUES 4 (6): 951-955 NOV 2010
Abstract:
Copper-based composite coatings with addition of 34 wt % of Al-Cu-Fe quasicrystalline powder of dispersity less than 20 fum, as well as 70 wt % of quasicrystalline powder of dispersity less than 40fum and less than 3 fum, were produced by the cold spray process. The phase composition during annealing of samples at various temperatures was studied by X-ray phase analysis. Tribological properties of each composite coating and pure copper were investigated. The experimental results showed a considerable improvement of the tribological properties of the material at the addition of quasicrystals. The least wear was observed in the composite sample containing quasicrystalline inclusions of less than 3 fum subjected to thermal treatment. In this case the counterbody wear was practically absent.

Update: 14-Jan-2011

Title:
DELONE MEASURES OF FINITE LOCAL COMPLEXITY AND APPLICATIONS TO SPECTRAL THEORY OF ONE-DIMENSIONAL CONTINUUM MODELS OF QUASICRYSTALS
Authors:
Klassert, S; Lenz, D; Stollmann, P Author Full Names: Klassert, Steffen; Lenz, Daniel; Stollmann, Peter
Source:
DISCRETE AND CONTINUOUS DYNAMICAL SYSTEMS 29 (4): 1553-1571 Sp. Iss. SI APR 2011
Abstract:
We study measures on the real line and present various versions of what it means for such a measure to take only finitely many values. We then study perturbations of the Laplacian by such measures. Using Kotani-Remling theory, we show that the resulting operators have empty absolutely continuous spectrum if the measures are not periodic. When combined with Gordon type arguments this allows us to prove purely singular continuous spectrum for some continuum models of quasicrystals.
Title:
X-ray topography study of deformed composites obtained by directional solidification of Al-Cu-Co alloy
Authors:
Krawczyk, J; Bogdanowicz, W; Goryczka, T Author Full Names: Krawczyk, J.; Bogdanowicz, W.; Goryczka, T.
Source:
CRYSTAL RESEARCH AND TECHNOLOGY 45 (12): 1321-1325 Sp. Iss. SI DEC 2010
Abstract:
Fibre-reinforced composites were produced by the modification of the static horizontal Bridgman method. The single-crystalline composite matrix consisted of the tetragonal T phase (Al72Cu27Co1). Decagonal quasi-crystal D phase (Al64Cu20Co16) was the reinforcement in the form of fibres parallel to the solidification direction. These fibres were surrounded by the tetragonal Theta phase (Al66Cu31Co3). The composite specimens in the shape of plates were studied by tensile tests and X-ray topography. The specimens deformed up to rupture and, from the X-ray topographs, the dependence of the composite structure defects on deformation was examined. It was found that the rupture of specimens is related to low-angle boundaries created during deformation. The influence of defects on the strength of the composites is discussed. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Update: 6-Jan-2011

Title:
QUINARY AXIS: AN ELEMENT OF SYMMETRY THAT OCCURS IN MOLECULES AND QUASICRYSTALS - A DIDACTIC EXPERIMENT OF CRYSTALLOGRAPHY.
Authors:
das Neves, PCP; de Freitas, DV; Baptista, LA Author Full Names: Pereira das Neves, Paulo Cesar; de Freitas, Dareson Vieira; Baptista, Luis Andre
Source:
QUIMICA NOVA 33 (9): 1977-1979 2010
Abstract:
QUINARY AXIS: AN ELEMENT OF SYMMETRY THAT OCCURS IN MOLECULES AND QUASICRYSTALS - A DIDACTIC EXPERIMENT OF CRYSTALLOGRAPHY. Axis of quinary symmetry occur in molecular symmetry, as in the case of fullerenes, and in crystalline symmetry, in the quasicrystals. Minerals with pentagonal faces do not have this element of symmetry, as the pyrite (FeS2) which shows a ridge that is different from the other ones, in any face of the crystal. The purpose of this paper is to demonstrate conceptual differences between pyritohedron and regular pentagonal dodecahedron symmetries, discussing students' difficulties to identify them. Also is proposed a didactic experiment with spatial models of the above-mentioned forms and the demonstration of its symmetries in clinographic projections.
Title:
Structural modulation and magnetic properties of hexagonal Ba(Ti1-xFex)O3-delta ceramics
Authors:
Wei, XK; Yao, LD; Shen, X; Yang, Y; You, SJ; Li, FY; Jin, CQ; Yu, RC Author Full Names: Wei, X. K.; Yao, L. D.; Shen, X.; Yang, Y.; You, S. J.; Li, F. Y.; Jin, C. Q.; Yu, R. C.
Source:
PHYSICA B-CONDENSED MATTER 405 (23): 4851-4854 DEC 1 2010
Abstract:
This paper investigates the structural and magnetic properties of hexagonal Ba(Ti1-xFex)O3-delta (x=0.3 and 0.7) ceramics, synthesized with solid-state reaction method. Transmission electron microscope investigations reveal that structural phase separation featured by non-modulated and modulated phases is identified by the electron diffraction patterns taken along [0 0 1] zone axis in x=0.3 sample (BTF30). While for x=0.7 sample (BTF70), a pure phase with commensurate and incommensurate modulations at different directions is identified. The superstructure peaks observed in their X-ray diffraction patterns are verified by their individual commensurate modulation, q(s)=1/2 (31-2) in the modulated phase of BTF30 and q(4,-1)=4/9(3 0 4)-(0 0 1) in BTF70. In addition to the room-temperature weak ferromagnetism of BTF30 and paramagnetism of BTF70, spin glass transitions with T-f=3.4 K for the former and T-f=33.6 K for the latter are observed. On the basis of the structural characteristics, the influence of O1 and O2 vacancies on magnetic and dielectric properties of the doped system is discussed. (C) 2010 Elsevier B.V. All rights reserved.
Title:
The Role of Strain Tensor in Formation of Incommensurate Phases in Quartz
Authors:
Sannikov, DG Author Full Names: Sannikov, D. G.
Source:
FERROELECTRICS 400: 8-11 2010
Abstract:
It is shown that the strain tensor components play a decisive role in the theory of formation of incommensurate phases in quartz.
Title:
Improper Ferroelectric Antiferromagnetics
Authors:
Sakhnenko, VP; Ter-Oganessian, NV Author Full Names: Sakhnenko, V. P.; Ter-Oganessian, N. V.
Source:
FERROELECTRICS 400: 12-18 2010
Abstract:
Experiments reveal that magnetoelectric crystals usually experience incommensurate magnetic ordering. In this work we present symmetry arguments for the intimate coupling between ferroelectric magnetically ordered phases and modulated magnetic order. The obtained results are applied to crystals belonging to the D-2h (mmm) crystallographic class and illustrated by two examples of rare-earth manganites RMn2O5 and MnWO4.
Title:
The modulated structure of the calcium aluminate Ca6AlO212 center dot Bi2O3
Authors:
Perez, O; Malo, S; Hervieu, M Author Full Names: Perez, O.; Malo, S.; Hervieu, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 585-593 Part 6 DEC 2010
Abstract:
Bismuth calcium aluminate, Bi2Ca6Al12O27, has been prepared as a ceramic and a single crystal. Analysis of reciprocal space using both electron and X-ray diffraction show an R-centred hexagonal unit cell: a = b = 17.3892 (4), c = 6.986 (1) A. Additional weak reflections are observed; they require the introduction of a modulation wavevector q = 0.0453 (2)c* for indexing. The modulated structure has been solved using the superspace formalism [superspace group X (3) over bar (00 gamma)0]. A frame-work of corner-sharing AlO4 tetrahedra forms corrugated sixfold rings and uncommon triple rings. The Ca2+ cations exhibit an eightfold coordination sphere; edge-sharing CaO8 polyhedra form intertwinned zigzagging rows along c creating a three-dimensional net. Bi atoms are located in large hexagonal tunnels parallel to c and form Bi2O3 pairs, which adopt a trigonal bipyramidal configuration. The 6s(2) loneelectron pairs (Lp) point along c, in the opposite direction to the three Bi-O strong bonds to form two BiO(3)Lp tetrahedra with a common base. Different orientations of the Bi(2)O(3)Lp(2) pairs, rotated by 60 degrees around c, are observed. Their stacking modes in each of the hexagonal tunnels are described. The sequence of the stacking varies along c in each of the tunnels.
Title:
Crystal chemistry of transition metal diarsenates M2As2O7 (M = Mn, Co, Ni, Zn): variants of the thortveitite structure
Authors:
Weil, M; Stoger, B Author Full Names: Weil, Matthias; Stoeger, Berthold
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 603-614 Part 6 DEC 2010
Abstract:
The structures of the 3d divalent transition-metal diarsenates M2As2O7 (M = Mn, Co, Ni, Zn) can be considered as variants of the monoclinic (C2/m) thortveitite [Sc2Si2O7] structure type with a similar or equal to 6.7, b similar or equal to 8.5, c similar or equal to 4.7 angstrom, alpha similar or equal to 90, beta similar or equal to 102, gamma similar or equal to 90 degrees and Z = 2. Co2As2O7 and Ni2As2O7 are dimorphic. Their high-temperature (beta) polymorphs adopt the thortveitite aristotype structure in C2/m, whereas their low-temperature (alpha) polymorphs are hettotypes and crystallize with larger unit cells in the triclinic crystal system in space groups P (1) over bar and P1, respectively. Mn2As2O7 undergoes no phase transition and likewise adopts the thortveitite structure type in C2/m. Zn2As2O7 has an incommensurately modulated crystal structure [C2/m(alpha,0,gamma) 0s] with q = [0.3190 (1), 0, 0.3717 (1)] at ambient conditions and transforms reversibly to a commensurately modulated structure with Z = 12 (I2/c) below 273 K. The Zn phase resembles the structures and phase transitions of Cr2P2O7. Besides descriptions of the low-temperature Co2As2O7, Ni2As2O7 and Zn2As2O7 structures as five-, three-and sixfold superstructures of the thortveitite-type basic structure, the superspace approach can also be applied to descriptions of all the commensurate structures. In addition to the ternary M2As2O7 phases, the quaternary phase (Ni,Co) 2As2O7 was prepared and structurally characterized. In contrast to the previously published crystal structure of the mineral petewilliamsite, which has the same idealized formula and has been described as a 15-fold superstructure of the thortveitite-type basic structure in space group C2, synthetic (Ni,Co)(2)As2O7 can be considered as a solid solution adopting the alpha-Ni2As2O7 structure type. Differences of the two structure models for (Ni,Co)(2)As2O7 are discussed.

Update: 31-Dec-2010

Title:
Modulation in Tl2SeO4 in the temperature range 298-90 K
Authors:
Fabry, J; Kopecky, M; Kub, J Author Full Names: Fabry, Jan; Kopecky, Milos; Kub, Jiri
Source:
PHASE TRANSITIONS 83 (10-11): 980-984 Sp. Iss. SI 2010
Abstract:
Synchrotron experiments have revealed a structural modulation in Thallium selenate, Tl2SeO4, in the temperature range 298-90 K. The modulation is manifested by the presence of the first-order satellites. In difference to the majority of -K2SO4 compounds where the modulation takes place along the axis a (Pnma setting), the incommensurate modulation in Tl2SeO4 takes place along the b setting emphasizing exceptionality of Tl2SeO4 in this structural family. The modulation vector q = (0.0, 0.397(9), 0.0); the space group Pnma(0b0)000.
Title:
Three-dimensional static vortex solitons in incommensurate magnetic crystals
Authors:
Borisov, AB; Rybakov, FN Author Full Names: Borisov, A. B.; Rybakov, F. N.
Source:
LOW TEMPERATURE PHYSICS 36 (8-9): 766-771 AUG 2010
Abstract:
A new type of three-dimensional magnetic soliton in easy-axis ferromagnets is predicted by taking simultaneous account of the Dzyaloshinsky-Moriya interaction and an external magnetic field. The numerically obtained static three-dimensional solitons with a finite energy are characterized by a Hopf topological index H=0 and have a vortex structure. The structure of these solitons and the dependence of their energy on the external field are determined. The asymptotic behavior of these solitons is investigated and a necessary condition for their existence is found. (c) 2010 American Institute of Physics. [doi:10.1063/1.3493376]
Title:
Atomic and magnetic order in the shape memory alloy Mn2NiGa
Authors:
Brown, PJ; Kanomata, T; Neumann, K; Neumann, KU; Ouladdiaf, B; Sheikh, A; Ziebeck, KRA Author Full Names: Brown, P. J.; Kanomata, T.; Neumann, K.; Neumann, K. U.; Ouladdiaf, B.; Sheikh, A.; Ziebeck, K. R. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (50): Art. No. 506001 DEC 22 2010
Abstract:
Magnetization and high resolution neutron powder diffraction measurements on the magnetic shape memory alloy Mn2NiGa have confirmed that it is ferromagnetic with a Curie temperature above 500 K. The compound undergoes a broad structural phase transformation Delta T similar to 90 K with a mean transition temperature T-M similar to 270 K. The high temperature parent phase is cubic (a = 5.937 angstrom) and has a modified L2(1) structure. At 500 K the ordered magnetic moment essentially all on the 4a site is 1.35 mu B/Mn. The low temperature martensite has space group I4/mmm and is related to the cubic phase through a Bain transformation a(tet) = (a(cub) + b(cub))/2, b(tet) = (a(cub) - b(cub)) and c(tet) = c(cub) in which the change in cell volume is <2.6%. In this structure at 5 K the ordered moment of approximate to 2.3 mu(B) is again found to be confined to the sites with full Mn occupation and is aligned parallel to c. Neutron diffraction patterns obtained at 5 K suggested the presence of a weak incommensurate antiferromagnetic phase characterized by either a (1/3 0 1/3) or (00 1/3) propagation vector.
Title:
REFRACTIVE INDICES OF K2ZnCl4 CRYSTALS IN AN INCOMMENSURATE PHASE UNDER UNIAXIAL STRESSES
Authors:
Gaba, VM; Stadnyk, VI; Kogut, ZO; Brezvin, RS Author Full Names: Gaba, V. M.; Stadnyk, V. I.; Kogut, Z. O.; Brezvin, R. S.
Source:
JOURNAL OF APPLIED SPECTROSCOPY 77 (5): 648-653 NOV 2010
Abstract:
The influence of uniaxial mechanical stresses directed along the principal crystallophysical axes on refractive-index temperature dependences in K2ZnCl4 crystals was studied. It is established that the refractive indices ni are quite sensitive to uniaxial stresses. Significant baric shifts of the paraphase-incommensurate-commensu-rate phase transition points to different temperature regions were observed, which is due to the effect of the uniaxial stress on the K2ZnCl4 crystal structure. It is found that applying uniaxial pressure increases the value of the temperature hysteresis of the commensurate-incommensurate phase transition.
Title:
Specific Heat and Linear Birefringence in Incommensurate Phase of NH4HSeO4 Crystal
Authors:
Przeslawski, J; Kosturek, B; Czapla, Z Author Full Names: Przeslawski, J.; Kosturek, B.; Czapla, Z.
Source:
FERROELECTRICS 401: 79-85 2010
Abstract:
Precise measurements of the specific heat and linear birefringence changes were performed for the NH4HSeO4 crystal. Phase transitions at about 100 K, 252 K and 260 K were confirmed. The continuous second order phase transition at 260 K to the incommensurate phase has been described by the 3D XY model. Thermal parameters (as the excess enthalpy H, and the excess entropy S) of the N-IC transition were estimated. The critical index [image omitted] approximate to 0.832 was determined below Ti from the linear birefringence increment. Hysteretic behaviour of the linear birefringence in the incommensurate phase was observed at various temperature rates.
Title:
Influence of the Chemical Composition of Alloys on the Ideal Local Order in Approximants of the Icosahedral Quasicrystals
Authors:
Chizhikov, VA; Dmitrienko, VE Author Full Names: Chizhikov, V. A.; Dmitrienko, V. E.
Source:
CRYSTALLOGRAPHY REPORTS 55 (6): 953-963 NOV 2010
Abstract:
Correlations between atomic displacements from ideal structural positions in the physical space and the atomic coordinates in the perpendicular space are revealed for approximants of icosahedral quasicrystals. On average, the displacement magnitude increases with an increase in the distance from the center of projection on the perpendicular space; this indicates that disordering in quasicrystals is concentrated at the periphery of atomic surfaces. It is found that the chemical composition of an alloy significantly affects the specific features of distortion of the ideal structure of quasicrystals and their approximants.
Title:
Scaling in the Optical Characteristics of Aperiodic Structures with Self-Similarity Symmetry
Authors:
Zotov, AM; Korolenko, PV; Mishin, AY Author Full Names: Zotov, A. M.; Korolenko, P. V.; Mishin, A. Yu
Source:
CRYSTALLOGRAPHY REPORTS 55 (6): 964-970 NOV 2010
Abstract:
The properties of diffraction gratings and multilayered systems constructed using 1D models of quasicrystals are considered based on numerical simulation. It is shown that there is a direct relationship between the self-similarity symmetry of quasicrystals and scaling in the characteristics of the above-mentioned optical devices. The degree of structural correspondence between the graphical representations of the geometric properties of crystals, light diffraction patterns of gratings, and the transmission spectra of multilayered systems is estimated. It is shown that certain types of self-similarity symmetry make the characteristics of aperiodic diffraction gratings highly stable to a change in the size ratio of forming elements.
Title:
Cluster self-organization of intermetallic systems: Quasi-spherical nanocluster precursors with internal Friauf polyhedra (A-172) and icosahedra (B-137) in the Li19Na8Ba15 (hP842) crystal structure
Authors:
Ilyushin, GD; Blatov, VA Author Full Names: Ilyushin, G. D.; Blatov, V. A.
Source:
CRYSTALLOGRAPHY REPORTS 55 (7): 1093-1099 DEC 2010
Abstract:
A combinatorial and topological analysis of Li19Na8Ba15 (hP842, a = 20 angstrom, c = 93 angstrom, V = 33552 angstrom(3), P (3) over bar) has been performed using computer methods ( the TOPOS program package). Two types of crystal-forming quasi-spherical nanoclusters about 20 angstrom in diameter with internal Friauf polyhedra (A-172) and icosahedra (B-137) have been established by the complete decomposition of the 3D factor graph of the structure into cluster substructures. Each type of nanoclusters forms close-packed 2D layers 3(6), which alternate along the c axis. The B-137 and A-172 nanoclusters are composed of three layers and have shell compositions (1 + 12 + 32 + 92) and (1 + 16 + 59 + 103) with local symmetries 3 and (3) over bar, respectively; they were revealed for the first time in crystal structures as cluster precursors. The icosahedral B-137 nanocluster contains a 104-atom quasicrystal approximant (Samson cluster).
Title:
A low temperature anomaly observed in off-stoichiometric Ni-Mn-Ga system studied by higher harmonic ac-susceptibility measurements
Authors:
Srivastava, SK; Srivastava, VK; Joshi, A; Kamasa, P; Varga, LK; Khovaylo, VV; Chatterjee, R Author Full Names: Srivastava, Saurabh Kumar; Srivastava, Vijay Kumar; Joshi, Anupam; Kamasa, Pawel; Varga, Lajos Karoly; Khovaylo, V. V.; Chatterjee, Ratnamala
Source:
APPLIED PHYSICS LETTERS 97 (12): Art. No. 122505 SEP 20 2010
Abstract:
Results of fundamental and third order ac susceptibility measurements in a Ni49Mn29Ga22 single crystal demonstrate that higher harmonics of ac-susceptibility measurement is an excellent tool to identify transitions/anomalies originating from different magnetic substructures that remain undetected by usual dc susceptibility measurements. Anomaly observed at low temperature (similar to 150 K) has also been explored by differential scanning calorimetry, temperature dependent x-ray diffraction, and transmission electron microscopy measurements. The results demonstrate that the magnetic subsystem in Ni-Mn-Ga is unstable at low temperatures not only for metastable modulated crystal structure but also for very stable nonmodulated tetragonal structure. (C) 2010 American Institute of Physics. [doi:10.1063/1.3486155]

Update: 24-Dec-2010

Title:
Ultrabroadband dielectric spectroscopy and phonons in (Pb1-x/2Lax)(Zr0.9Ti0.1)O-3
Authors:
Buixaderas, E; Bovtun, V; Veljko, S; Savinov, M; Kuzel, P; Gregora, I; Kamba, S; Reaney, I Author Full Names: Buixaderas, E.; Bovtun, V.; Veljko, S.; Savinov, M.; Kuzel, P.; Gregora, I.; Kamba, S.; Reaney, I.
Source:
JOURNAL OF APPLIED PHYSICS 108 (10): Art. No. 104101 NOV 15 2010
Abstract:
The dielectric behavior of (Pb1-x/2Lax) (Zr0.9Ti0.1)O-3 PLZT 100x/90/10 (0 <= 100x <= 1) was studied in the frequency range 10(2)-10(14) Hz using dielectric, time-domain terahertz (THz), far-infrared, and Raman spectroscopy in the temperature interval 10-900 K. PZT 90/10 and PLZT 2/90/10 undergo two phase transitions, from a cubic paraelectric to a rhombohedral untilted ferroelectric (FE) phase and on further cooling to a tilted FE phase. PLZT 4/90/10 and PLZT 10/90/10 are incommensurately modulated and composed of an intergrowth of polar and antipolar cation displacements. These samples consequently demonstrate a FE soft mode which exhibits minimal frequency several tens of degrees above the nominal antiferroelectric phase transition temperature. The dielectric response of PLZT 100x/90/10 is mainly governed by a gigahertz relaxation and a soft phonon component in the THz range. As in other PbO-based perovskites, the soft mode is split into a higher-frequency component (omega similar to 80 cm(-1)) and a highly damped THz component (omega similar to 30 cm(-1)), with larger dielectric strength already in the paraelectric phase. (C) 2010 American Institute of Physics. [doi:10.1063/1.3501105]

Update: 17-Dec-2010

Title:
Growth and superconductivity of 2H-Ni-0 02TaSe2 single crystals
Authors:
Li, LJ; Sun, YP; Zhu, XD; Wang, BS; Zhu, XB; Yang, ZR; Song, WH Author Full Names: Li, L. J.; Sun, Y. P.; Zhu, X. D.; Wang, B. S.; Zhu, X. B.; Yang, Z. R.; Song, W. H.
Source:
SOLID STATE COMMUNICATIONS 150 (45-46): 2248-2252 DEC 2010
Abstract:
2H-Ni-0 02TaSe2 single crystals were successfully grown via the iodine vapor transport technique The typical dimension of the crystal is about 3 x 2 x 0 5 mm(3) Compared with the parent compound 2H-TaSe2 with a superconducting transition temperature T-C = 0 14 K the electronic transport specific heat and magnetization results indicate that the superconductivity of the Ni-0 02TaSe2 single crystal is obviously enhanced (T-C = 2 79 K) In addition It is found that the incommensurate charge-density-wave (ICDW) disappears while the commensurate charge-density-wave (CCDW) shifts to about 96 2 K with the intercalation of a little of Ni It clearly indicates that there is a competition between superconductivity (SC) and charge-density-wave (CDW) order for 2H-TaSe2 system and that between SC and ICDW is more drastic (C) 2010 Elsevier Ltd All rights reserved
Title:
Charge-density waves arising from two electron bands
Authors:
Buker, DW Author Full Names: Buker, Donald W.
Source:
PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES 467 (2125): 166-173 JAN 8 2011
Abstract:
A theory for a quasi-one-dimensional incommensurate charge-density wave state arising from electron-phonon (el-phon) interaction connecting electron states in two different bands is presented. An expression for the fundamental component of the energy gap as a function of the effective el-phon coupling, valid for all coupling strengths, has been found. For a single band, the expression simplifies to a reciprocal hyperbolic-sine dependence on the reciprocal effective coupling. The effective coupling, although simply related to the n assumed phonon-band frequencies, is not generally expressible as a sum of independent functions of these frequencies. The theory is applied to tetrathiofulvalinium-tetracyanoquinodimethane and to potassium blue bronze.
Title:
Generalized dynamics of moving dislocations in quasicrystals
Authors:
Agiasofitou, E; Lazar, M; Kirchner, H Author Full Names: Agiasofitou, Eleni; Lazar, Markus; Kirchner, Helmut
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (49): Art. No. 495401 DEC 15 2010
Abstract:
A theoretical framework for dislocation dynamics in quasicrystals is provided according to the continuum theory of dislocations. Firstly, we present the fundamental theory for moving dislocations in quasicrystals giving the dislocation density tensors and introducing the dislocation current tensors for the phonon and phason fields, including the Bianchi identities. Next, we give the equations of motion for the incompatible elastodynamics as well as for the incompatible elasto-hydrodynamics of quasicrystals. We continue with the derivation of the balance law of pseudomomentum thereby obtaining the generalized forms of the Eshelby stress tensor, the pseudomomentum vector, the dynamical Peach-Koehler force density and the Cherepanov force density for quasicrystals. The form of the dynamical Peach-Koehler force for a straight dislocation is obtained as well. Moreover, we deduce the balance law of energy that gives rise to the generalized forms of the field intensity vector and the elastic power density of quasicrystals. The above balance laws are produced for both models. The differences between the two models and their consequences are revealed. The influences of the phason fields as well as of the dynamical terms are also discussed.
Title:
Indentation characteristics of metallic glass and nanoquasicrystal-glass composite in Zr-Al (Ga)-Cu-Ni alloys
Authors:
Singh, D; Yadav, TP; Mandal, RK; Tiwari, RS; Srivastava, ON Author Full Names: Singh, Devinder; Yadav, T. P.; Mandal, R. K.; Tiwari, R. S.; Srivastava, O. N.
Source:
INTERMETALLICS 18 (12): 2445-2452 DEC 2010
Abstract:
Indentation characteristics of melt-spun Zr69.5Al7.5-xGaxCu12Ni11 (x = 0-2.5; in at %) metallic glasses have been investigated. Formation of a nano-quasicrystalline phase by annealing the glass has been found only upto x = 1.5. The substitution of Ga changes the size and shape of this phase. The load dependent hardness behaviour of metallic glasses and nanoquasicrystal-glass composites are reported in detail. It has been observed that substitution of 1.5 at % Ga improved microhardness property of Zr-Al-Cu-Ni alloy. The value of yield strength of the materials was estimated with the help of hardness values based on the empirical correlations available in literature. It has been found that microstructural and morphological changes alter the Meyer exponent. Pile up parameters seems to be sensitive to structural and microstructural details. (C) 2010 Elsevier Ltd. All rights reserved.
Title:
Development of an Icosahedral Quasicrystal and Two Approximants in the Ca-Au-Sn System: Syntheses and Structural Analyses
Authors:
Lin, QL; Corbett, JD Author Full Names: Lin, Qisheng; Corbett, John D.
Source:
INORGANIC CHEMISTRY 49 (22): 10436-10444 NOV 15 2010
Abstract:
The realm of Tsai-type (YCd6-type) quasicrystals (QCs) and their approximants (ACs) continues to expand to the east in the Periodic table. The heavy tetrel Sn is now one of the major components in the new Ca15.0(5)Au60.0(4)Sn25.0(2) (atom %) icosahedral QC and in the corresponding 1/1 and 2/1 ACs. (The 2/1 AC with Yb is also established.) Single-crystal X-ray diffraction on a 1/1 AC gives the refined formula of Ca3Au14.36(3)Sn4.38(5) in space group Im (3) over bar, a = 15.131(1) angstrom, whereas a representative 2/1 AC gives Ca13Au47.2(1)Sn28.1(1), Pa (3) over bar and a = 24.444(1) angstrom. Both ACs contain five-shell multiply endohedral triacontahedral clusters as the common building blocks, as in the parent structure of YCd6. The 2/1 AC also contains four Ca-2-dimer-centered prolate rhombohedra (PRs) in the unit cell. The long-range order between triacontahedra and PRs in the 2/1 AC is the same as those in Bergman-type 2/1 ACs. A TB-LMTO-ASA calculation on an ideal 1/1 AC model reveals a shallow pseudogap in the total densities-of-states data around the Fermi energy, as expected. The depth of the pseudogap is considerably enhanced through interactions between the Ca 3d states and s and p states of Au and Sn.
Title:
Tuning macro-twinned domain sizes and the b-variants content of the adaptive 14-modulated martensite in epitaxial Ni-Mn-Ga films by co-sputtering
Authors:
Tillier, J; Bourgault, D; Odier, P; Ortega, L; Pairis, S; Fruchart, O; Caillault, N; Carbone, L Author Full Names: Tillier, Jeremy; Bourgault, Daniel; Odier, Philippe; Ortega, Luc; Pairis, Sebastien; Fruchart, Olivier; Caillault, Nathalie; Carbone, Laurent
Source:
ACTA MATERIALIA 59 (1): 75-81 JAN 2011
Abstract:
In order to obtain modulated martensite in our epitaxial Ni-Mn-Ga films, we tuned the composition by using a co-sputtering process Here we present how the composition affects the variant distribution of the 14-modulated martensite at room temperature The nature of such modulated martensites is still strongly debated for magnetic shape memory alloys It has been very recently demonstrated that the modulated martensites in Ni-Mn-Ga are adaptive phases The results presented here corroborate this theory for the first time, for three different compositions Moreover, we demonstrate with the help of the adaptive modulations theory that b variants of the 14-modulated martensite form close to the free surface of the film to release the stress induced by branching of macro-twinned domains during the martensitic transformation on a rigid substrate At room temperature, the content of such b-variants is found to strongly decrease when the macro-twinned domain sizes increase (C) 2010 Acta Materialia Inc Published by Elsevier Ltd All rights reserved

Update: 10-Dec-2010

Title:
Interplay between spin density wave and pi-phase-shifted superconductivity in the iron pnictide superconductors
Authors:
Lee, N; Choi, HY Author Full Names: Lee, Nayoung; Choi, Han-Yong
Source:
PHYSICAL REVIEW B 82 (17): Art. No. 174508 NOV 10 2010
Abstract:
We explore if the phase separation or coexistence of the spin density wave (SDW) and superconductivity (SC) states has any relation to the incommensurability of the SDW in the Fe pnictide superconductors. A systematic method of determining the phase separation or coexistence was employed by computing the anisotropy coefficient beta from the the fourth-order terms of the Ginzburg-Landau expansion of the free energy close to the tricritical/tetracritical point. It was complemented by the self-consistent numerical iterations of the gap equations to map out the boundaries between the phase separation and coexistence of the SDW and SC phases, and between commensurate (C) and incommensurate (IC) SDW in the temperature-doping plane. Our principal results for the sign reversed s-wave pairing SC, in terms of the multicritical temperature, T-c, the phase separation/coexistence boundary between the SDW and SC,T*, and the boundary between C/IC SDW, T*(M), are: (a) IC-SDW and SC coexist for T-c < T* and phase separate otherwise, (b) SDW takes the C form for T-c > T-M* and IC form for T-c < T-M*, and (c) the thermodynamic first-order phase transition intervenes in between the C-SDW and IC-SDW boundary for large TM 0, where T-M(0) is the SDW transition temperature at zero doping, T* = 0.35T(M)(0) and T-M* = 0.56T(M)(0). The intervention makes the phase diagram more complicated than previously reported. By contrast no coexistence was found for the equal sign pairing SC. These results will be compared with the experimental reports in the Fe pnictide superconductors.
Title:
Magnetic and multiferroic phases of single-crystalline Mn0.85Co0.15WO4
Authors:
Chaudhury, RP; Ye, F; Fernandez-Baca, JA; Wang, YQ; Sun, YY; Lorenz, B; Mook, HA; Chu, CW Author Full Names: Chaudhury, R. P.; Ye, F.; Fernandez-Baca, J. A.; Wang, Y. -Q.; Sun, Y. Y.; Lorenz, B.; Mook, H. A.; Chu, C. W.
Source:
PHYSICAL REVIEW B 82 (18): Art. No. 184422 NOV 17 2010
Abstract:
The magnetic and multiferroic phase diagram of Mn0.85Co0.15WO4 single crystals is investigated by means of magnetic, heat-capacity, dielectric, polarization, and neutron-scattering experiments. Three magnetic phase transitions are detected through distinct anomalies in all physical quantities. The ferroelectric polarization is observed only along the b axis below 10 K but not along the a axis as recently suggested. The magnetic phases studied by neutron scattering are very complex. Up to four different magnetic structures, partially coexisting at certain temperature ranges, have been identified. Upon decreasing temperature two commensurate phases (AF4, AF1) are followed by an incommensurate phase (AF5) and a second incommensurate phase (AF2) is detected as a minor phase. The ferroelectric polarization is possibly associated with both (AF2 and AF5) phases.
Title:
Two- and three-dimensional growth of Bi on i-Al-Pd-Mn studied using medium-energy ion scattering
Authors:
Noakes, TCQ; Bailey, P; McConville, CF; Draxler, M; Walker, M; Brown, MG; Hentz, A; Woodruff, DP; Lograsso, TA; Ross, AR; Smerdon, JA; Leung, L; McGrath, R Author Full Names: Noakes, T. C. Q.; Bailey, P.; McConville, C. F.; Draxler, M.; Walker, M.; Brown, M. G.; Hentz, A.; Woodruff, D. P.; Lograsso, T. A.; Ross, A. R.; Smerdon, J. A.; Leung, L.; McGrath, R.
Source:
PHYSICAL REVIEW B 82 (19): Art. No. 195418 NOV 9 2010
Abstract:
Recent work on the growth of thin metal films on quasicrystalline substrates has indicated the formation of so-called "magic height" islands with multiples of 4 atomic layers (AL) arising as a result of quantum size effects, which lead to enhanced stability. Here the results of a study are reported of Bi deposition on i-Al-Pd-Mn using medium-energy ion scattering to characterize the island thickness and the structural arrangement of Bi atoms within the islands. In addition, data were taken from annealed surfaces after Bi cluster desorption to leave a single aperiodic monolayer of Bi at the surface. Scattered-ion energy spectra from the Bi islands are consistent with a single Bi monolayer covered with mainly 4 AL islands for both 1.8 and 3.2 monolayer equivalent coverages but with some occupation of 2 and 8 Al islands as well. The angular dependence of the scattered-ion intensity ("blocking curve") from Bi has been compared with simulations for various models of both rhombohedral Bi and a distorted "black-phosphorus"-like structure. The data demonstrate bilayer formation within the Bi islands. In the case of the aperiodic Bi monolayer, the blocking curves from substrate scattering are found to be inconsistent with two high-symmetry sites on the quasicrystalline surface that theory indicates are energetically favorable but do not exclude the formation of pentagonal arrangements of Bi atoms as seen in other recent experimental work.
Title:
Martensitic transformation from incommensurate state with nano-scale domain structure in a Ti-42Ni-8Fe (at.%) alloy under a compressive stress
Authors:
Todai, M; Higaki, A; Fukuda, T; Kakeshita, T Author Full Names: Todai, Mitsuharu; Higaki, Akio; Fukuda, Takashi; Kakeshita, Tomoyuki
Source:
PHILOSOPHICAL MAGAZINE LETTERS 91 (1): 31-36 2010
Abstract:
This article reports a martensitic transformation from an incommensurate state with a nano-scale domain-like structure in a Ti-42Ni-8Fe alloy. The martensitic transformation is suppressed at a temperature above 4.2 K under zero stress, but occurs under a compressive stress. The product phase is most likely to be the R-phase, but there is a large temperature hysteresis of about 87 K.
Title:
Strain-induced dimensionality crossover and associated pseudoelasticity in the premartensitic phase of Ni2MnGa
Authors:
Nie, ZH; Ren, Y; Wang, YD; Liu, DM; Brown, DE; Wang, G; Zuo, L Author Full Names: Nie, Z. H.; Ren, Y.; Wang, Y. D.; Liu, D. M.; Brown, D. E.; Wang, G.; Zuo, L.
Source:
APPLIED PHYSICS LETTERS 97 (17): Art. No. 171905 OCT 25 2010
Abstract:
The in situ high-energy x-ray diffraction was used for revealing an atomic mechanism on the two-step pseudoelastic behavior found in the premartensitic phase of Ni2MnGa magnetic shape memory alloy. The applied stress first suppresses the three-dimensional modulated structure of the premartensitic phase to a two-dimensional modulated one, which is accompanied by a change in the modulation wave vector and accommodates a large lattice strain reaching similar to 1%. With further increasing stress, the two-dimensional modulated premartensite transforms to the five-layered modulated martensite. The observation of the stress-induced dimensionality crossover of atomic modulation has broad impacts in understanding not only the mechanical properties of advanced shape memory alloys but also the physical properties of condensed matter with heterogeneous structures. (C) 2010 American Institute of Physics. [doi:10.1063/1.3506508]

Update: 3-Dec-2010

Title:
Charge density waves in NbSe3: The models and the experimental evidence
Authors:
Prodan, A; van Midden, HJP; Zitko, R; Zupanic, E; Bennett, JC; Bohm, H Author Full Names: Prodan, A.; van Midden, H. J. P.; Zitko, R.; Zupanic, E.; Bennett, J. C.; Boehm, H.
Source:
SOLID STATE COMMUNICATIONS 150 (43-44): 2134-2137 NOV 2010
Abstract:
Charge density wave (CDW) ordering in the prototypical low-dimensional compound NbSe3 is reconsidered. It is shown that the model with two incommensurate modulations, q(1) = (0, 0.241, 0) and q(2) = (0.5, 0.260, 0.5), localized on type-III and type-I bi-capped trigonal prismatic columns, does not explain details, revealed by various microscopic methods. An alternative explanation, based on the existence of modulated layered nano-domains below both COW onset temperatures, is suggested. It accounts for the presence of the q(2) modulation in the STM images recorded above the T-2 CDW transition and for the absence of q(2) satellites in the corresponding diffraction patterns. The long periodic modulation, detected by LT STM, is attributed to a beating between the two CDWs, centered on adjacent columns of the same type. Such pairs of alternatively modulated columns represent the basic modulation units, ordered into nano-domains. (C) 2010 Elsevier Ltd. All rights reserved.
Title:
Effect of the pseudogap on suppressing high energy inelastic neutron scattering in superconducting YBa2Cu3O6.5
Authors:
Stock, C; Cowley, RA; Buyers, WJL; Frost, CD; Taylor, JW; Peets, D; Liang, R; Bonn, D; Hardy, WN Author Full Names: Stock, C.; Cowley, R. A.; Buyers, W. J. L.; Frost, C. D.; Taylor, J. W.; Peets, D.; Liang, R.; Bonn, D.; Hardy, W. N.
Source:
PHYSICAL REVIEW B 82 (17): Art. No. 174505 NOV 8 2010
Abstract:
We have measured the spin fluctuations in the YBa2Cu3O6.5 (YBCO6.5, T-c=59 K) superconductor at high-energy transfers above similar to 100 meV. Within experimental error, the momentum dependence is isotropic at high energies, similar to that measured in the insulator for two-dimensional spin waves, and the dispersion extrapolates back to the incommensurate wave vector at the elastic position. This result contrasts with previous expectations based on measurements around 50 meV which were suggestive of a softening of the spin-wave velocity with increased hole doping. Unlike the insulator, we observe a significant reduction in the intensity of the spin excitations for energy transfers above similar to 100 meV similar to that observed above similar to 200 meV in the YBCO6.35 (T-c=18 K) superconductor as the spin waves approach the zone boundary. We attribute this high-energy scale with a second gap and find agreement with measurements of the pseudogap in the cuprates associated with electronic anomalies along the antinodal positions. In addition, we observe a sharp peak at around 400 meV whose energy softens with increased hole doping. We discuss possible origins of this excitation including a hydrogen-related molecular excitation and a transition of electronic states between d levels.
Title:
Bose condensation in flat bands
Authors:
Huber, SD; Altman, E Author Full Names: Huber, Sebastian D.; Altman, Ehud
Source:
PHYSICAL REVIEW B 82 (18): Art. No. 184502 NOV 2 2010
Abstract:
We derive effective Hamiltonians for lattice bosons with strong geometrical frustration of the kinetic energy by projecting the interactions on the flat lowest Bloch band. Specifically, we consider the Bose Hubbard model on the one-dimensional sawtooth lattice and the two-dimensional kagome lattice. Starting from a strictly local interaction the projection gives rise to effective long-range terms stabilizing a supersolid phase at densities above nu(c) = 1/9 of the kagome lattice. In the sawtooth lattice on the other hand we show that the solid order, which exists at the magic filling nu(c) = 1/4, is unstable to further doping. The universal low-energy properties at filling 1/4 + delta nu are described by the well-known commensurate-incommensurate transition. We support the analytic results by detailed numerical calculations using the density-matrix renormalization group and exact diagonalization. Finally, we discuss possible realizations of the models using ultracold atoms as well as frustrated quantum magnets in high magnetic fields. We compute the momentum distribution and the noise correlations, that can be extracted from time of flight experiments or neutron scattering, and point to signatures of the unique supersolid phase of the kagome lattice.
Title:
Phase transformation above T-m in PbSc0.5Ta0.5O3 relaxor as seen via acoustic emission
Authors:
Dul'kin, E; Mihailova, B; Catalan, G; Gospodinov, M; Roth, M Author Full Names: Dul'kin, E.; Mihailova, B.; Catalan, G.; Gospodinov, M.; Roth, M.
Source:
PHYSICAL REVIEW B 82 (18): Art. No. 180101 NOV 3 2010
Abstract:
Chemically B-site disordered PbSc1/2Ta1/2O3 relaxor crystals have been studied by means of dielectric and acoustic emission methods in the vicinity of T-m approximate to 280 K. Along with the intrinsic cubic-to-rhombohedral phase transformation at T-c = 261 K, a phase transformation at T-n = 293 K is evidently detected by acoustic emission. Under an external dc electric field T-c gradually increases with increasing the field, whereas T-n exhibits nontrivial behavior, namely, initially decreases and then starts increasing, similarly to T-c. The characteristic temperature T-n is attributed to the occurrence of incommensurate modulated antiferroelectric regions, which have previously been suggested to coexist with both the cubic paraelectric and rhombohedral ferroelectric phases in the vicinity of T-m. The nontrivial behavior of T-n under an external dc electric field is also discussed.
Title:
Dielectric constant in the incommensurate SDW phase of (TMTTF)(2)Br
Authors:
Matsunaga, N; Akita, T; Ichimura, K; Nomura, K; Kawamoto, A Author Full Names: Matsunaga, Noriaki; Akita, Tomonori; Ichimura, Koichi; Nomura, Kazushige; Kawamoto, Atsushi
Source:
PHYSICA B-CONDENSED MATTER 405 (11): S108-S110 Suppl. S JUN 1 2010
Abstract:
The low-frequency dielectric constant was measured in the pressure induced incommensurate SDW phase of (TMTTF)(2)Br in order to investigate the dynamics of the SDW Under the pressure above 0 5 GPa the huge dielectric constant attributed to the motion of the SDW were observed The temperature dependence of the real part of the dielectric constant epsilon whose amplitudes grow with decreasing frequency shows the peak behavior in the Incommensurate SDW phase In contrast of the case of (TMTSF)(2)PF6 the peak temperature of epsilon ' is constant irrespective of the frequency These peak temperature T-P are scaled as T-P/T-SWD similar to 0 3 irrespective of pressure for the pressure larger than 08 GPa and is associated with the sub-phase transition in the incommensurate SOW proposed by the NMR measurement The dielectric properties are probably connected with the co-existence of the CDW component proposed for high temperature sub-phase (C) 2010 Elsevier B V All rights reserved
Title:
SDW phase of (EDT-TTF)(2)AuBr2
Authors:
Nomura, K; Shimohara, N; Denda, D; Matsunaga, N; Kawamoto, A Author Full Names: Nomura, K.; Shimohara, N.; Denda, D.; Matsunaga, N.; Kawamoto, A.
Source:
PHYSICA B-CONDENSED MATTER 405 (11): S116-S119 Suppl. S JUN 1 2010
Abstract:
The low temperature phase in (EDT-TTF)(2)AuBr2 was investigated by H-1 NMR and magnetic susceptibility measurements for protonated and partially deuterated single crystals Two sharp peaks were observed in the temperature dependence of T-1(-1) for both salts associated with the SOW transition T-SDW and the sub-phase transition T* common in the Incommensurate SDW phase The values of T-SDW determined as 15 and 19K for h- and d-salts respectively indicate the negative chemical pressure effect The obtained ratios T/T-SDW 0 37 and 0 43 for h- and d-salts respectively are slightly larger than the common value T*/T-SDW congruent to 0 3 observed in (TMTCF)(2)X The ratio T*/T-SDW increases for larger T-SDW and the low temperature sub-phase becomes more stable (C) 2009 Elsevier B V All rights reserved
Title:
First observation of superconductivity by uniaxial strain in (TMTTF)(2)X-salt
Authors:
Yokogawa, K; Yoshino, H; Nakamura, T; Brooks, JS; Murata, K Author Full Names: Yokogawa, Keiichi; Yoshino, Harukazu; Nakamura, Toshikazu; Brooks, James S.; Murata, Keizo
Source:
PHYSICA B-CONDENSED MATTER 405 (11): S291-S294 Suppl. S JUN 1 2010
Abstract:
We studied superconductivity and spin density wave by measuring temperature dependence of resistivity of (TMTTF)(2)Br under uniaxial strain up to 3 7 GPa (room temperature) The superconducting phase of (TMTTF)(2)Br under uniaxial strain was observed below 0 8 K at 37 GPa for the first time which was realized by the compression along the a-axis but not along other directions Superconductivity was found below a slight SDW-hump in resistance with the a-axis strain however with the b'- and c*-axis strain both superconductivity and SDW was suppressed The anomaly in d In rho(c)/d(1/T) was observed at T similar to 0 22T(SDW) under uniaxial strain along the a-axis This behavior suggests the existence of the sub-phase structure in incommensurate SDW phase under the a-axis compression This behavior reminds us of the same tendency in (TMTSF)(2)PF6 in the previous reports of Kondo et al where only the a-axis uniaxial strain favors superconductivity even though the SDW transition is not suppressed sufficiently in both samples (C) 2010 Elsevier B V All rights reserved
Title:
Structural evolution induced by acceptor doping into BaTiO3 ceramics
Authors:
Wei, XK; Zhang, QH; Li, FY; Jin, CQ; Yu, RC Author Full Names: Wei, X. K.; Zhang, Q. H.; Li, F. Y.; Jin, C. Q.; Yu, R. C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 508 (2): 486-493 OCT 22 2010
Abstract:
Solid state reaction method is used to synthesize Ba(Tii-xTMx)O3-delta (TM = Fe, Mn and Co) and (Ba1-ySry)(Ti1/3Fe2/3)O3-delta ceramics. The X-ray diffraction, scanning electron microscopy and transmission electron microscopy investigations reveal that structural evolutions from an orthorhombic BaTiO3 to a hexagonal Ba(Ti1-xTMx)O3-delta, a hexagonal to a rhombohedral in Ba(Ti1-xMnx)O3-delta, and a hexagonal to a pseudo-cubic transition in (Ba1-ySry)(Ti1/3Fe2/3)O3-delta are induced by increasing the doping concentration. Due to the oxygen vacancies derived from acceptor doping, nanoscale domains of incommensurate modulation (ICM) resultant are commonly observed in the hexagonal Ba(Ti1-xTMx)O3-delta compounds. The newly discovered rhombohedral Ba(Ti1/3Mn2/3)O3-delta having characteristic of face-sharing prism corner-connected by oxygen atoms is a typical example in searching for novel multiferroics. Discrepancies between the ionic radii of the B- and A-site dopants and that of Ti and Ba as a function of the doping concentrations, i.e., the effects of oxygen vacancies and the electronic configurations of the dopants, are concluded to be the driving forces for the structural transitions. (c) 2010 Elsevier B.V. All rights reserved.

Update: 19-Nov-2010

Title:
Structural Stability and Kinetics of Hydrogen in TiZrNi Quasicrystals
Authors:
Lee, SH; Choi, SB; Ito, E; Kim, JY Author Full Names: Lee, Sang-hwa; Choi, Soo-bin; Ito, Eisuke; Kim, Jae-yong
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 10 (11): 7680-7683 Sp. Iss. SI NOV 2010
Abstract:
When hydrogen atoms slowly diffuse into a metastable structure, a coherence length of thin TiZrNi quasicrystal metallic ribbons is increased. Improved atomic order with addition of hydrogen is an uncommon phenomenon in metals, and may reflect the unordinary structural property of quasicrystals. Metastable TiZrNi quasicrystals prepared by rapid quenching of molten ingots were hydrogenated in a low pressure of hydrogen (lower than 1000 Torr) at high temperature. After completion of the pressure-composition-temperature measurements between 200 to 300 degrees C, X-ray diffraction data revealed that the full width at half maximum values of the diffraction peaks were decreased suggesting that the quasicrystal phase may stabilized by hydrogen inclusion. Annealing of the same sample at 200 degrees C without hydrogen yields no change of the relative intensity of diffraction peaks.
Title:
Structural and Magnetic Properties of TiZrNi Thin Films Prepared by Magnetron Sputtering and Thermal Annealing
Authors:
Shin, H; Choi, SB; Lee, IJ; Yu, CJ; Kim, JY Author Full Names: Shin, Hyemin; Choi, Soo-bin; Lee, Ik-jae; Yu, Chung-jong; Kim, Jae-yong
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 10 (11): 7804-7807 Sp. Iss. SI NOV 2010
Abstract:
Distinctive thin layers of TiZr and Ni were deposited by using a magnetron sputtering method and a thermal annealing was applied to discover metallic films of quasicrystals. After a heat treatment in vacuum, 70 nm thick deposited layers were well mixed with nominal compositions of 49.7, 29.3 and 21.0 for Ti, Zr and Ni, respectively, which is very close with the one forming a quasicrystalline phase. The magnetization values were significantly decreased from 0.286 to 0.142 emu/mm(3) at 2000 Oe, after annealing, while a shape of magnetic hysteresis was maintained. It is believed that a different magnetic behavior after thermal annealing is due to the homogeneous mixing of atomic elements and possible existence of a metastable phase.
Title:
Simple tilings by polyhedra with five- and six-sided faces
Authors:
Delgado-Friedrichs, O; O'Keeffe, M Author Full Names: Delgado-Friedrichs, Olaf; O'Keeffe, Michael
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 66: 637-639 Part 6 NOV 2010
Abstract:
Thirteen tilings of space by simple polyhedra with five- and six-sided faces (`fullerenes') are reported in which there are up to 11 kinds of vertex (vertex 11-transitive). All tilings contain dodecahedra and one or more of nine other kinds of tile. The duals are tilings by tetrahedra and include the four simplest of the known Frank-Kasper intermetallic structure phases. A fifth structure involving just the Frank-Kasper coordination polyhedra has a higher average coordination number than any known or postulated Frank-Kasper phase.
Title:
Magnetic space and superspace groups, representation analysis: competing or friendly concepts?
Authors:
Petricek, V; Fuksa, J; Dusek, M Author Full Names: Petricek, Vaclav; Fuksa, Jiri; Dusek, Michal
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 66: 649-655 Part 6 NOV 2010
Abstract:
Although encoded in theoretical works, relationships between the diffraction symmetry of magnetic structures and magnetic space/superspace groups are often ignored in practical applications. It is shown that magnetic symmetry operations have a direct impact through the rotation parts in the diffraction symmetry of the crystal and can be used to simplify calculations of magnetic structure factors. Besides, the translation parts can introduce specific systematic extinctions of magnetic reflections. Another point is that the efficiency and stability of refinement of magnetic crystal structures, in analogy with the refinement of nuclear structures, depend on direct application of the magnetic symmetry in the structure-factor formula. Magnetic symmetry also allows diffractionally independent magnetic domains and their mutual spatial orientations to be recognized. The selection of one irreducible representation can provide extra relationships between magnetic moments which do not directly affect diffraction symmetry. Thus the combination of both methods seems to be the most effective way to analyze and refine magnetic structures.

Update: 12-Nov-2010

Title:
Elastic and anelastic relaxations associated with the incommensurate structure of Pr0.48Ca0.52MnO3
Authors:
Carpenter, MA; Howard, CJ; McKnight, REA; Migliori, A; Betts, JB; Fanelli, VR Author Full Names: Carpenter, Michael A.; Howard, Christopher J.; McKnight, Ruth E. A.; Migliori, Albert; Betts, Jon B.; Fanelli, Victor R.
Source:
PHYSICAL REVIEW B 82 (13): Art. No. 134123 OCT 27 2010
Abstract:
The elastic and anelastic properties of a polycrystalline sample of Pr0.48Ca0.52MnO3 have been investigated by resonant ultrasound spectroscopy, as a function of temperature (10-1130 K) and magnetic field strength (0-15 T). Marked softening of the shear modulus as the Pnma <-> incommensurate phase transition at similar to 235 K in zero field is approached from either side is consistent with pseudoproper ferroelastic character, driven by an order parameter with Gamma(+)(3) symmetry associated with Jahn-Teller ordering. This is accompanied by an increase in attenuation just below the transition point. The attenuation remains relatively high down to similar to 80 K, where there is a distinct Debye peak. It is attributed to coupling of shear strain with the Gamma(+)(3) order parameter which, in turn, controls the repeat distance of the incommensurate structure. Kinetic data extracted from the Debye peak suggest that the rate-controlling process could be related to migration of polarons. Elastic softening and stiffening as a function of magnetic field at constant temperatures between 177 and similar to 225 K closely resembles the behavior as a function of temperature at 0, 5, and 10 T and is consistent with thermodynamically continuous behavior for the phase transition in both cases. This overall pattern can be rationalized in terms of linear/quadratic coupling between the Gamma(+)(3) order parameter and an order parameter with Sigma(1) or Sigma(2) symmetry. It is also consistent with a dominant role for spontaneous strains in determining the strength of coupling, evolution of the incommensurate microstructure, and equilibrium evolution of the Jahn-Teller ordered structure through multicomponent order-parameter space.
Title:
Magnetic phase diagram of the multiferroic FeTe2O5Br
Authors:
Pregelj, M; Zorko, A; Zaharko, O; Kutnjak, Z; Jagodic, M; Jaglicic, Z; Berger, H; de Souza, M; Balz, C; Lang, M; Arcon, D Author Full Names: Pregelj, M.; Zorko, A.; Zaharko, O.; Kutnjak, Z.; Jagodic, M.; Jaglicic, Z.; Berger, H.; de Souza, M.; Balz, C.; Lang, M.; Arcon, D.
Source:
PHYSICAL REVIEW B 82 (14): Art. No. 144438 OCT 27 2010
Abstract:
The low-temperature magnetic phase diagram of the multiferroic system FeTe2O5Br down to 300 mK and up to 9 T is presented. Short-range magnetic correlations within the crystal layers start to develop already at similar to 50 K, i.e., far above T-N1 similar to 11.0 K, where the system undergoes a magnetic phase transition into the high-temperature incommensurate (HT-ICM) phase. Only 0.5 K lower, at T-N2, the system undergoes a second phase transition into the low-temperature incommensurately modulated (LT-ICM) phase accompanied by a spontaneous electric polarization. When the magnetic field is applied, the transition temperatures shift depending on the field orientation. In the case of B parallel to b and B > 4.5 T, the HT-ICM phase disappears along with the electric polarization in the LT-ICM phase. The field dependence of the magnetic transition temperatures is explained in the context of the magnetic susceptibility behavior. Similarities and differences between the novel well-established magnetoelectrics are discussed.
Title:
Spray Forming of Bulk Ultrafine-Grained Al-Fe-Cr-Ti
Authors:
Banjongprasert, C; Hogg, SC; Liotti, E; Kirk, CA; Thompson, SP; Mi, J; Grant, PS Author Full Names: Banjongprasert, C.; Hogg, S. C.; Liotti, E.; Kirk, C. A.; Thompson, S. P.; Mi, J.; Grant, P. S.
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE 41A (12): 3208-3215 DEC 2010
Abstract:
An Al-2.7Fe-1.9Cr-1.8Ti alloy has been spray formed in bulk and the microstructure and properties compared with those of similar alloys produced by casting, powder aomization (PA), and mechanical alloying (MA) routes. In PA and MA routes, a nanoscale metastable icosahedral phase is usually formed and is known to confer high tensile strength. Unlike previous studies of the spray forming of similar Al-based metastable phase containing alloys that were restricted to small billets with high porosity, standard spray forming conditions were used here to produce a similar to 98 pct dense 19-kg billet that was hot isostatically pressed ("HIPed"), forged, and/or extruded. The microstructure has been investigated at all stages of processing using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and synchrotron X-ray diffraction (XRD) at the Diamond Light Source. Consistent with the relatively low cooling rate in spray forming under standard conditions, the microstructure showed no compelling evidence for the formation of metastable icosahedral phases. Nonetheless, after downstream processing, the spray-formed mechanical properties as a function of temperature were very similar to both PA rapid solidification (RS) materials and those made by MA. These aspects have been rationalized in terms of the typical phases, defects, and residual strains produced in each process route.
Title:
Investigation of the Spin-Glass Regime between the Antiferromagnetic and Superconducting Phases in Fe1+ySexTe1-x
Authors:
Katayama, N; Ji, SD; Louca, D; Lee, S; Fujita, M; Sato, TJ; Wen, JS; Xu, ZJ; Gu, GD; Xu, GY; Lin, ZW; Enoki, M; Chang, S; Yamada, K; Tranquada, JM Author Full Names: Katayama, Naoyuki; Ji, Sungdae; Louca, Despina; Lee, Seunghun; Fujita, Masaki; Sato, Taku J.; Wen, Jinsheng; Xu, Zhijun; Gu, Genda; Xu, Guangyong; Lin, Ziwei; Enoki, Masanori; Chang, Sung; Yamada, Kazuyoshi; Tranquada, John M.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (11): Art. No. 113702 NOV 2010
Abstract:
Using bulk magnetization along with elastic and inelastic neutron scattering techniques, we have investigated the phase diagram of Fe1+ySexTe1-x and the nature of magnetic correlations in three nonsuperconducting samples of Fe1.01Se0.1Te0.9, Fe1.01Se0.15Te0.85, and Fe1.02Se0.3Te0.7. A cusp and hysteresis in the temperature dependence of the magnetization for the x = 0.15 and 0.3 samples indicates spin-glass (SG) ordering below T-sg = 23 K. Neutron scattering measurements indicate that the spin-glass behavior is associated with short-range spin density wave (SDW) ordering characterized by a static component and a low-energy dynamic component with a characteristic incommensurate wave vector of Q(m) = (0.46, 0, 0.50) and an anisotropy gap of similar to 2.5 meV. Our high Q-resolution data also show that the systems undergo a glassy structural distortion that coincides with the short-range SDW order.
Title:
Liquid to quasicrystal transition in bilayer water
Authors:
Johnston, JC; Kastelowitz, N; Molinero, V Author Full Names: Johnston, Jessica C.; Kastelowitz, Noah; Molinero, Valeria
Source:
JOURNAL OF CHEMICAL PHYSICS 133 (15): Art. No. 154516 OCT 21 2010
Abstract:
The phase behavior of con. fined water is a topic of intense and current interest due to its relevance in biology, geology, and materials science. Nevertheless, little is known about the phases that water forms even when confined in the simplest geometries, such as water confined between parallel surfaces. Here we use molecular dynamics simulations to compute the phase diagram of two layers of water confined between parallel non hydrogen bonding walls. This study shows that the water bilayer forms a dodecagonal quasicrystal, as well as two previously unreported bilayer crystals, one tiled exclusively by pentagonal rings. Quasicrystals, structures with long-range order but without periodicity, have never before been reported for water. The dodecagonal quasicrystal is obtained from the bilayer liquid through a reversible first-order phase transition and has diffusivity intermediate between that of the bilayer liquid and ice phases. The water quasicrystal and the ice polymorphs based on pentagons are stabilized by compression of the bilayer and are not templated by the confining surfaces, which are smooth. This demonstrates that these novel phases are intrinsically favored in bilayer water and suggests that these structures could be relevant not only for confined water but also for the wetting and properties of water at interfaces. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3499323]
Title:
Tendencies toward nematic order in YBa2Cu3O6+delta: Uniform distortion vs. incipient charge stripes
Authors:
Vojta, M Author Full Names: Vojta, M.
Source:
EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS 188 (1): 49-59 OCT 2010
Abstract:
Recent neutron scattering and transport data obtained on underdoped YBa2Cu3O6+delta, with strong signatures of rotation symmetry breaking at low temperatures, point toward electron-nematic order in the charge sector. Such order may originate from a uniform distortion with d-wave symmetry or as a precursor of a uni-directional stripe phase. Here, we discuss whether the neutron scattering data can be linked to incipient charge stripes. We employ and extend a phenomenological model for collective spin and charge fluctuations and analyze the resulting spin excitation spectrum under the influence of lattice anisotropies. Our results show that the experimentally observed temperature-dependent magnetic incommensurability is compatible with a scenario of incipient stripes, the temperature dependence being due to the temperature variation of both strength and correlation length of the charge stripes. Finally, we propose further experiments to distinguish the possible theoretical scenarios.
Title:
An ARPES view on the high-T-c problem: Phonons vs. spin-fluctuations
Authors:
Kordyuk, AA; Zabolotnyy, VB; Evtushinsky, DV; Inosov, DS; Kim, TK; Buchner, B; Borisenko, SV Author Full Names: Kordyuk, A. A.; Zabolotnyy, V. B.; Evtushinsky, D. V.; Inosov, D. S.; Kim, T. K.; Buechner, B.; Borisenko, S. V.
Source:
EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS 188 (1): 153-162 OCT 2010
Abstract:
We review the search for a mediator of high-T (c) superconductivity focusing on ARPES experiment. In case of HTSC cuprates, we summarize and discuss a consistent view of electronic interactions that provides natural explanation of both the origin of the pseudogap state and the mechanism for high temperature superconductivity. Within this scenario, the spin-fluctuations play a decisive role in formation of the fermionic excitation spectrum in the normal state and are sufficient to explain the high transition temperatures to the superconducting state while the pseudogap phenomenon is a consequence of a Peierls-type intrinsic instability of electronic system to formation of an incommensurate density wave. On the other hand, a similar analysis being applied to the iron pnictides reveals especially strong electron-phonon coupling that suggests important role of phonons for high-T (c) superconductivity in pnictides.

Update: 5-Nov-2010

Title:
Chiral Charge-Density Waves
Authors:
Ishioka, J; Liu, YH; Shimatake, K; Kurosawa, T; Ichimura, K; Toda, Y; Oda, M; Tanda, S Author Full Names: Ishioka, J.; Liu, Y. H.; Shimatake, K.; Kurosawa, T.; Ichimura, K.; Toda, Y.; Oda, M.; Tanda, S.
Source:
PHYSICAL REVIEW LETTERS 105 (17): - OCT 18 2010
Abstract:
We discovered the chirality of charge-density waves (CDW) in 1T-TiSe2 by using STM and time-domain optical polarimetry. We found that the CDW intensity becomes Ia(1):Ia(2):Ia(3) 1:0.7 +/- 0.1:0.5 +/- 0.1, where Ia(i) (i = 1, 2, 3) is the amplitude of the tunneling current contributed by the CDWs. There were two states, in which the three intensity peaks of the CDW decrease clockwise and anticlockwise. The chirality in CDW results in the threefold symmetry breaking. Macroscopically, twofold symmetry was indeed observed in optical measurement. We propose the new generalized CDW chirality H-CDW equivalent to q(1) . (q(2) x q(3)), where q(i) are the CDW q vectors, which is independent of the symmetry of components. The nonzero H-CDW-the triple-q vectors do not exist in an identical plane in the reciprocal space-should induce a real-space chirality in CDW system.
Title:
Density-wave instability in alpha-(BEDT-TTF)(2)KHg(SCN)(4) studied by x-ray diffuse scattering and by first-principles calculations
Authors:
Foury-Leylekian, P; Pouget, JP; Lee, YJ; Nieminen, RM; Ordejon, P; Canadell, E Author Full Names: Foury-Leylekian, Pascale; Pouget, Jean-Paul; Lee, Young-Joo; Nieminen, Risto M.; Ordejon, Pablo; Canadell, Enric
Source:
PHYSICAL REVIEW B 82 (13): Art. No. 134116 OCT 18 2010
Abstract:
alpha-(BEDT-TTF)(2)KHg(SCN)(4) develops a density wave ground state below 8 K whose origin is still debated. Here we report a combined x-ray diffuse scattering and first-principles density functional theory study supporting the charge density wave (CDW) scenario. In particular, we observe a triply incommensurate anharmonic lattice modulation with intralayer wave vector components which coincide within experimental errors to the maximum of the calculated Lindhard response function. A detailed study of the structural aspects of the modulation shows that the CDW instability in alpha-(BEDT-TTF)(2)KHg(SCN)(4) is considerably more involved than those following a standard Peierls mechanism. We thus propose a microscopic mechanism where the CDW instability of the BEDT- TTF layer is triggered by the anion sublattice. Our mechanism also emphasizes the key role of the coupling of the BEDT- TTF and anion layers via the hydrogen bond network to set the global modulation.
Title:
Possible magnetic order and suppression of superconductivity by V doping in Sr2VO3FeAs
Authors:
Tegel, M; Schmid, T; Sturzer, T; Egawa, M; Su, YX; Senyshyn, A; Johrendt, D Author Full Names: Tegel, Marcus; Schmid, Tanja; Stuerzer, Tobias; Egawa, Masamitsu; Su, Yixi; Senyshyn, Anatoliy; Johrendt, Dirk
Source:
PHYSICAL REVIEW B 82 (14): Art. No. 140507 OCT 21 2010
Abstract:
Superconductivity at 33 K in Sr2VO3FeAs is completely suppressed by small amounts of V doping in Sr2VO3(Fe0.93(+/- 0.01)V0.07(+/- 0.01))As. The crystal structures and exact stoichiometries are determined by combined neutron powder diffraction and x-ray powder diffraction. Sr2VO3FeAs is shown to be very sensitive to Fe/V mixing, which interferes with or even suppresses superconductivity. This inhomogeneity may be intrinsic and explains scattered reports regarding T-c and reduced superconducting phase fractions in Sr2VO3FeAs. Neutron-diffraction data collected at 4 K indicate incommensurate magnetic ordering of the V sublattice with a propagation vector q approximate to(0,0,0.306). This suggests strongly correlated vanadium, which does not contribute significantly to the Fermi surface of Sr2VO3FeAs.
Title:
Induction of charge density waves by spin density waves in iron-based superconductors
Authors:
Balatsky, AV; Basov, DN; Zhu, JX Author Full Names: Balatsky, A. V.; Basov, D. N.; Zhu, Jian-Xin
Source:
PHYSICAL REVIEW B 82 (14): Art. No. 144522 OCT 22 2010
Abstract:
We argue that spin density wave (SDW) phase in ferrous superconductors contains charge density wave (CDW) with the modulation momentum that is a double of characteristic momenta of SDW. We discuss symmetry constraints on allowed momenta of CDW generated by coupling to spin modulations. To be specific, we considered the CDW that could be realized in Fe-11 (e.g., FeTe) and Fe-122 (e.g., BaFe2As2) compounds. In case of commensurate SDW, the CDW modulation vector is at the Bragg-peak positions and could be revealed by local scanned probes. In case of incommensurate SDW, the CDW is incommensurate and can be seen also by x-ray and elastic neutron scattering. We also discuss observable charge modulation due to CDW formation near defects and twin boundaries.
Title:
Temperature-pressure phase diagram and electronic properties of the organic metal kappa-(BETS)(2)Mn[N(CN)(2)](3)
Authors:
Zverev, VN; Kartsovnik, MV; Biberacher, W; Khasanov, SS; Shibaeva, RP; Ouahab, L; Toupet, L; Kushch, ND; Yagubskii, EB; Canadell, E Author Full Names: Zverev, V. N.; Kartsovnik, M. V.; Biberacher, W.; Khasanov, S. S.; Shibaeva, R. P.; Ouahab, L.; Toupet, L.; Kushch, N. D.; Yagubskii, E. B.; Canadell, E.
Source:
PHYSICAL REVIEW B 82 (15): Art. No. 155123 OCT 18 2010
Abstract:
The crystal and electronic band structures as well as the transport properties of the recently synthesized layered radical cation salt kappa-(BETS)(2)Mn[N(CN)(2)](3) are investigated. It is shown that this salt is more anisotropic in the plane of conducting layers than other kappa phases, a feature which noticeably influences its physical behavior. A phase transition resulting in the formation of an incommensurate superstructure below 102 K has been found. At temperature below 30 K a metal-insulator transition is observed. We argue that the transition is associated with electronic interactions rather than with structural changes. The T-P phase diagram has been studied under He-4 gas pressure up to 2.5 kbar. At moderately high pressure P approximate to 0.5 kbar the metal-insulating transition is suppressed and the crystal becomes superconducting with T-c approximate to 5.7 K. In the pressurized metallic state, Shubnikov-de Haas oscillations have been found, revealing a very small closed Fermi surface with a high-effective cyclotron mass influenced by many-body interactions.
Title:
Green's functions for infinite planes and half-planes consisting of quasicrystal bi-materials
Authors:
Gao, Y Author Full Names: Gao, Yang
Source:
JOURNAL OF ZHEJIANG UNIVERSITY-SCIENCE A 11 (10): 835-840 Sp. Iss. SI OCT 2010
Abstract:
This paper deals with the combination of point phonon and phason forces applied in the interior of infinite planes and half-planes of 1D quasicrystal bi-materials. Based on the general solution of quasicrystals, a series of displacement functions are adopted to obtain Green's functions for infinite planes and bi-material planes composed of two half-planes in the closed form, when the two half-planes are supposed to be ideally bonded or to be in smooth contact. Since the physical quantities can be readily calculated without the need of performing any transform operations, Green's functions are very convenient to be used in the study of point defects and inhomogeneities in the quasicrystal materials.
Title:
Molecular dynamics simulations of laser induced surface melting in orthorhombic Al13Co4
Authors:
Sonntag, S; Roth, J; Trebin, HR Author Full Names: Sonntag, S.; Roth, J.; Trebin, H. -R.
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 101 (1): 77-80 OCT 2010
Abstract:
Laser induced surface melting of the aluminum-cobalt alloy Al13Co4 is investigated. For the simulations of the lattice ions we use molecular dynamics, while for the time evolution of the electron temperature a generalized heat-conduction equation is solved. Energy transfer between the sub-systems is allowed by an electron-phonon coupling term. This combined treatment of the electronic and atomic systems is an extension of the well-known two-temperature model [Anisimov et al. in JETP Lett. 39(2), 1974]. The alloy shows large structural affinity to decagonal quasicrystals, which have an in-plane five-fold symmetry,while in perpendicular direction the planes are stacked periodically. As a consequence we observe slight anisotropic melting behavior.

Update: 29-Oct-2010

Title:
Modulated monoclinic crystal structure and large shape memory effect in nickel-rich Ni53.5Mn26.0Ga20.5
Authors:
Ramudu, M; Kumar, AS; Seshubai, V; Muraleedharan, K; Prasad, KS; Rajasekharan, T Author Full Names: Ramudu, M.; Kumar, A. Satish; Seshubai, V.; Muraleedharan, K.; Prasad, K. S.; Rajasekharan, T.
Source:
SCRIPTA MATERIALIA 63 (11): 1073-1076 NOV 2010
Abstract:
We report a seven-layered modulated monoclinic crystal structure in the Ni-rich, Ga-poor Ni53.5Mn26.0Ga20.5 alloy. The present composition exhibits coupled magneto-structural transformation around 350 K. Multi-mode twinning with a predominance of crossing twins, indicative of low residual stresses, is observed. A significant shape memory effect of 1.6% and a high strain recovery ratio of 89% are achieved in the polycrystalline specimen at low stresses, owing to lower twinning energies arising from lattice modulation. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Second harmonic generation on incommensurate structures: The case of multiferroic MnWO4
Authors:
Meier, D; Leo, N; Yuan, G; Lottermoser, T; Fiebig, M; Becker, P; Bohaty, L Author Full Names: Meier, D.; Leo, N.; Yuan, G.; Lottermoser, Th.; Fiebig, M.; Becker, P.; Bohaty, L.
Source:
PHYSICAL REVIEW B 82 (15): Art. No. 155112 OCT 7 2010
Abstract:
A comprehensive analysis of optical second harmonic generation on an incommensurate (IC) magnetically ordered state is presented using multiferroic MnWO4 as model compound. Two fundamentally different SHG contributions coupling to the primary IC magnetic order or to secondary commensurate projections of the IC state, respectively, are distinguished. Whereas the latter can be described within the formalism of the 122 commensurate magnetic point groups the former involves a breakdown of the conventional macroscopic symmetry analysis because of its sensitivity to the lower symmetry of the local environment in a crystal lattice. Our analysis thus foreshadows the fusion of the hitherto disjunct fields of nonlinear optics and IC order in condensed-matter systems.
Title:
Phase Separation and Suppression of the Structural and Magnetic Transitions in Superconducting Doped Iron Tellurides, Fe1+xTe1-ySy
Authors:
Zajdel, P; Hsieh, PY; Rodriguez, EE; Butch, NP; Magill, JD; Paglione, J; Zavalij, P; Suchomel, MR; Green, MA Author Full Names: Zajdel, Pawel; Hsieh, Ping-Yen; Rodriguez, Efrain E.; Butch, Nicholas P.; Magill, Jeff D.; Paglione, Johnpierre; Zavalij, Peter; Suchomel, Matthew R.; Green, Mark A.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 132 (37): 13000-13007 SEP 22 2010
Abstract:
Single crystal and powder samples of the series of iron chalcogenide superconductors with nominal composition, Fe1.15Te1-ySy, are found to form for 0 <= y <= 0.15. They crystallize in the tetragonal anti-PbO structure, which is composed of layers of edge-shared Fe(Te, S)(4) tetrahedra. For y = 0, Fe1+xTe (x approximate to 0.12(1)) is nonsuperconducting and undergoes a tetragonal (P4/nmm) to monoclinic (P2(1)/m) structural transition at similar to 65 K, associated with the onset of commensurate antiferromagnetic order at q = (0.5 0 0.5). We show that on sulfur substitution, Fe1+xTe1-ySy becomes orthorhombic (Pmmn) at low temperature for 0 <= y <= 0.15, where the greatly suppressed magnetic scattering is now incommensurate at q = (0.5-delta 0 0.5) and possesses short ranged magnetic correlations that are well fitted with a two-dimensional Warren peak shape. At much higher concentrations of S (y >= 0.075), there is suppression of both the structural and magnetic transitions and a superconducting transition at 9 K is observed. Between these two composition regimes, there exists a region of phase separation (0.025 <= y <= 0.05), where the low temperature neutron diffraction data is best refined with a model containing both the tetragonal and orthorhombic phases. The increase in the amount of sulfur is found to be associated with a reduction in interstitial iron, x. Microprobe analysis of a single crystal of composition Fe1.123(5)Te0.948(4)S0.052(4) confirms the presence of compositional variation within the crystals, rationalizing the observed phase separation.
Title:
The various modes of growth of metals on quasicrystals
Authors:
Smerdon, JA Author Full Names: Smerdon, J. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (43): Art. No. 433002 NOV 3 2010
Abstract:
Quasicrystals are fascinating intermetallic compounds composed of two or more elements. They differ from conventional crystals in that they possess long-range order, but no translational symmetry-that is, they are aperiodic. Much effort has been expended on identifying routes towards exploiting and exploring the properties of such systems due to their aperiodic nature. One such route is concerned with the deposition of thin films, particularly of metals, to investigate how their growth progresses in this inherently frustrated scenario. This topical review will examine the various epitaxial relationships observed in quasicrystal research with particular emphasis on single-element metallic films deposited under ultrahigh-vacuum conditions.
Title:
Transport properties of electrons in fractal magnetic-barrier structures
Authors:
Sun, LF; Fang, C; Guo, Y Author Full Names: Sun, Lifeng; Fang, Chao; Guo, Yong
Source:
JOURNAL OF APPLIED PHYSICS 108 (6): Art. No. 063715 SEP 15 2010
Abstract:
Quantum transport properties in fractal magnetically modulated structures are studied by the transfer-matrix method. It is found that the transmission spectra depend sensitively not only on the incident energy and the direction of the wave vector but also on the stage of the fractal structures. Resonance splitting, enhancement, and position shift of the resonance peaks under different magnetic modulation are observed at four different fractal stages, and the relationship between the conductance in the fractal structure and magnetic modulation is also revealed. The results indicate the spectra of the transmission can be considered as fingerprints for the fractal structures, which show the subtle correspondence between magnetic structures and transport behaviors. (C) 2010 American Institute of Physics. [doi:10.1063/1.3488647]

Update: 22-Oct-2010

Title:
Dynamics of particle flips in two-dimensional quasicrystals
Authors:
Engel, M; Umezaki, M; Trebin, HR; Odagaki, T Author Full Names: Engel, Michael; Umezaki, Masahiro; Trebin, Hans-Rainer; Odagaki, Takashi
Source:
PHYSICAL REVIEW B 82 (13): Art. No. 134206 OCT 8 2010
Abstract:
The dynamics of quasicrystals is more complicated than the dynamics of periodic solids and difficult to study in experiments. Here, we investigate a decagonal and a dodecagonal quasicrystal using molecular dynamics simulations of the Lennard-Jones-Gauss interaction system. We observe that the short-time dynamics is dominated by stochastic particle motion, so-called phason flips, which can be either single-particle jumps or correlated ringlike multi-particle moves. Over long times, the flip mechanism is efficient in reordering the quasicrystals and can generate diffusion. The temperature dependence of diffusion is described by an Arrhenius law. We also study the spatial distribution and correlation of mobile particles by analyzing the dynamic propensity.
Title:
Electrical transport in charge-ordered Fe2OBO3: Resistive switching and pressure effects
Authors:
Akrap, A; Angst, M; Khalifah, P; Mandrus, D; Sales, BC; Forro, L Author Full Names: Akrap, Ana; Angst, Manuel; Khalifah, Peter; Mandrus, David; Sales, Brian C.; Forro, Laszlo
Source:
PHYSICAL REVIEW B 82 (16): Art. No. 165106 OCT 5 2010
Abstract:
The pressure-temperature-electric field phase diagram of Fe2OBO3 is studied under ambient and high pressure using resistivity and thermoelectric power measurements. The onset of the incommensurate charge order at T-CO=340 K does not depend on pressure up to at least 2 GPa. The temperature of the transition to the commensurate charge order is increased by similar to 10 K/GPa. High pressure stabilizes the commensurate phase. We find evidence for resistive switching in the incommensurate phase, which may be linked to the dynamics of the charge-order domain boundaries.
Title:
The magneto-dielectric properties of compounds and alloys in the systems of TlInS2-TlFeS2, TlInS2-TlFeSe2
Authors:
Veliyev, RG; Seyidov, MY; Gasanov, NZ; Seyidov, FM Author Full Names: Veliyev, R. G.; Seyidov, M. Yu.; Gasanov, N. Z.; Seyidov, F. M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 506 (2): 800-803 SEP 17 2010
Abstract:
The research of dielectric properties of TlInS2-layered compound shows that TlInS2 is extrinsic ferroelectric (T-c approximate to 202.4 K) with intermediate incommensurable phase (T-i approximate to 206.3 K). Analysis of publications was carried out by us on magnetic properties of TlFeS2 and TlFeSe2 compounds, having chained crystalline structure, allows to draw a conclusion that these compounds are highly anisotropic (quasione-dimensional) antiferromagnets with Neel temperatures equal to similar to 12 K and similar to 14 K respectively (long-range magnetic order). Moreover, on the temperature dependence of reverse magnetic susceptibility TlFeS2 and TlFeSe2 in paramagnetic area at 196 K and 290 K respectively, wide minimums exist, which characterize short-range magnetic order in these quasi-one-dimensional antiferromagnets. Using method of differential-thermal analysis were founded regions of homogenous and heterogeneous co-existence of ferroelectric and antiferromagnetic orderings in the systems of TlInS2-TlFeS2 and TlInS2-TlFeSe2. (C) 2010 Elsevier B.V. All rights reserved.

Update: 15-Oct-2010

Title:
Neutron diffraction investigation of the crystal and magnetic structures in KCrF3 perovskite
Authors:
Xiao, Y; Su, Y; Li, HF; Kumar, CMN; Mittal, R; Persson, J; Senyshyn, A; Gross, K; Brueckel, T Author Full Names: Xiao, Y.; Su, Y.; Li, H. -F.; Kumar, C. M. N.; Mittal, R.; Persson, J.; Senyshyn, A.; Gross, K.; Brueckel, Th.
Source:
PHYSICAL REVIEW B 82 (9): Art. No. 094437 SEP 23 2010
Abstract:
KCrF3 represents another prototypical orbital-ordered perovskite, where Cr2+ possesses the same electronic configuration of 3d(4) as that of strongly Jahn-Teller distorted Mn3+ in many colossal magnetoresistance manganites. The crystal and magnetic structures of KCrF3 compound are investigated by using polarized and unpolarized neutron powder-diffraction methods. The results show that the KCrF3 compound crystallizes in tetragonal structure at room temperature and undergoes a monoclinic distortion with the decrease in temperature. The distortion of the crystal structure indicates the presence of cooperative Jahn-Teller distortion which is driven by orbital ordering. With decreasing temperature, four magnetic phase transitions are observed at 79.5, 45.8, 9.5, and 3.2 K, which suggests a rich magnetic phase diagram. Below T-N = 79.5 K, the Cr2+ moment orders in an incommensurate antiferromagnetic arrangement, which can be defined by the magnetic propagation vector (1/2 + delta, 1/2 + delta, 0). The incommensurate-commensurate magnetic transition occurs at 45.8 K and the magnetic propagation vector locks into (1/2, 1/2, 0) with the Cr moment of 3.34(5) mu(B), aligned ferromagnetically in (220) plane, but antiferromagnetically along [110] direction. Below 9.5 K, the canted antiferromagnetic ordering and weak ferromagnetism arise from the collinear antiferromagnetic structure while the Dzyaloshinskii-Moriya interaction and tilted character of the single-ion anisotropy might give rise to the complex magnetic behaviors below 9.5 K.
Title:
The Behavior of Thermal Conductivity in the Chaotic Phase of [N(CH3)(4)](2)ZnCl4 Crystal
Authors:
Sveleba, SA; Karpa, IV; Kunyo, IM; Semotyuk, OV; Katerynchuk, IM; Phitsych, EI; Pankivskyi, YI Author Full Names: Sveleba, S. A.; Karpa, I. V.; Kunyo, I. M.; Semotyuk, O. V.; Katerynchuk, I. M.; Phitsych, E. I.; Pankivskyi, Yu. I.
Source:
CRYSTALLOGRAPHY REPORTS 55 (4): 652-656 JUL 2010
Abstract:
A thermal investigation of the modulated structure dynamics at the transition between metastable states in the incommensurate phase of [N(CH3)(4)](2)ZnCl4 crystal have been performed. It is established that the anomalous behavior of the thermal conductivity in the absence of a defect-density wave is due to the inelastic scattering of thermal phonons from critical phonons of the soft optical branch. In the presence of a defect-density wave, the anomalous increase in thermal conductivity is caused by the existence of a chaotic phase and is related to the contribution that soft optical phonons make to the heat transfer due to the increase in their group velocity.
Title:
2D quasi-periodic Rauzy tiling as a section of 3D periodic tiling
Authors:
Maleev, AV; Shutov, AV; Zhuravlev, VG Author Full Names: Maleev, A. V.; Shutov, A. V.; Zhuravlev, V. G.
Source:
CRYSTALLOGRAPHY REPORTS 55 (5): 723-733 SEP 2010
Abstract:
A method for constructing a 2D quasi-periodic Rauzy tiling Til as a section of some 3D periodic tiling Til (3D) is considered. The translation lattice of the tiling Til (3D) and its connectivity graph are constructed using the discrete modeling of packings. The calculation of the layer-by-layer growth polyhedron for the tiling Til (3D) made it possible to estimate from upper the shape of a growth polygon for the tiling Til. As a result, the growth shape in six out of eight growth sectors has been rigorously proven. A set of quasi-periodic tilings (locally indistinguishable from the Rauzy tiling Til), including seven centrosymmetric tilings, has been obtained.
Title:
Effect of the number of defect density waves on the dynamics of the soliton system in [N(CH3)(4)](2)CuCl4 and [N(CH3)(4)](2)Zn0.98Ni0.02Cl4 crystals
Authors:
Karpa, IV; Sveleba, SA; Kunyo, IM; Katerynchuk, IM; Semotyuk, OV; Blashko, OI Author Full Names: Karpa, I. V.; Sveleba, S. A.; Kunyo, I. M.; Katerynchuk, I. M.; Semotyuk, O. V.; Blashko, O. I.
Source:
CRYSTALLOGRAPHY REPORTS 55 (5): 815-820 SEP 2010
Abstract:
The time dependences of the birefringence and thermal conductivity of [N(CH3)(4)](2)CuCl4 and [N(CH3)(4)](2)Zn0.98Ni0.02Cl4 crystals in the incommensurate phase at a constant temperature have been studied. A multiwave state of modulated superstructure is found to be formed in the presence of defect density waves in the crystal. It is shown that, depending on the number of defect density waves in the crystal, either a superposition of existing modulation waves or a domainlike structure arise in it.
Title:
Magnetic properties of quasicrystalline Al65Cu22Fe13 powders synthesized by solid-phase diffusion
Authors:
Semenovskii, PV; Nikonov, AA; Teplov, AA; Ol'shanskii, ED; Bryazkalo, AM Author Full Names: Semenovskii, P. V.; Nikonov, A. A.; Teplov, A. A.; Ol'shanskii, E. D.; Bryazkalo, A. M.
Source:
CRYSTALLOGRAPHY REPORTS 55 (5): 833-836 SEP 2010
Abstract:
The magnetic properties of quasicrystalline Al65Cu22Fe13 powders synthesized by solid-phase diffusion as a result of thermal treatment in vacuum and in a hydrogen atmosphere have been studied. The magnetic properties of the samples synthesized in hydrogen were found to be much better than those of the samples synthesized in vacuum. It is shown that an increase in the treatment time in vacuum decreases the number of magnetic nanoclusters and elimninates the time instability of their magnetic properties (magnetic susceptibility and magnetization).
Title:
Incommensurately modulated lanthanide coinage-metal diarsenides. I. CeAu1-delta As2 [delta=0.015 (2)] - a new distortion variant of the HfCuSi2 type with irregularly stacked cis-trans chains of arsenic atoms
Authors:
Rutzinger, D; Doert, T; Ruck, M Author Full Names: Rutzinger, D.; Doert, Th.; Ruck, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 519-526 Part 5 OCT 2009
Abstract:
Rare-earth metal coinage-metal diarsenides LnTAs(2) (Ln = Y, La, Ce-Lu; T = Cu, Ag, Au) are known to crystallize in structures closely related to the HfCuSi2 type, which comprises a stacking sequence of puckered TAs layers and planar square As nets, separated by the Ln atoms. CeAu1-delta As2, with delta = 0.015 (2), shows an incommensurate positional modulation of the arsenic atoms in the planar As nets. Based on X-ray diffraction data on a twinned crystal, a structure model in the monoclinic superspace group P12(1)/m1(alpha 0 gamma)00 (No. 11.1) with basic unit-cell parameters of a = 5.804 (1), b = 5.814 (1), c = 10.179 (1) A and beta = 90.09 (8)degrees is presented. The components of the modulation wavevector q = alpha a* + 0b* + gamma c* are alpha = 0.08 (1) and gamma = 0.39 (1). The structure comprises cis-trans chains and rectangles of As atoms and displays an intricate stacking sequence of the modulated arsenic nets. Rod groups and layer groups of the respective arrangements are identified and the arrangement of different motifs of the modulated As net is discussed.
Title:
Incommensurately modulated lanthanide coinage-metal diarsenides. II. GdCuAs2, GdAu1-delta As2 and TbAu1-delta As2 - new distortion variants of the HfCuSi2 type with irregularly stacked zigzag chains of arsenic atoms
Authors:
Rutzinger, D; Bartsch, C; Doert, T; Ruck, M Author Full Names: Rutzinger, D.; Bartsch, C.; Doert, Th.; Ruck, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 527-534 Part 5 OCT 2009
Abstract:
GdCuAs2, GdAu1-delta As2 and TbAu1-delta As2 crystallize as incommensurately modulated variants of the HfCuSi2 type. Structure models have been developed in the monoclinic superspace group P12(1)/m1(alpha 0 gamma)00 (No. 11.1). The components of the modulation wavevectors q = alpha a* + 0b* + gamma c* are alpha = 0.04 (1) and gamma = 0.48 (1) for GdCuAs2, alpha = 0.03 (1) and gamma = 0.48 (1) for GdAu1-delta As2 and alpha = 0.02 (1) and gamma = 0.46 (1) for TbAu1-delta As2. The predominant effect of the positional modulation is the distortion of a square net of arsenic atoms, which results in planar zigzag chains. Rod groups and layer groups of the respective structure motifs are identified and discussed.
Title:
Modulation of atomic positions in CaCuxMn7-xO12 (x <= 0.1)
Authors:
Slawinski, W; Przenioslo, R; Sosnowska, I; Bieringer, M; Margiolaki, I; Suard, E Author Full Names: Slawinski, W.; Przenioslo, R.; Sosnowska, I.; Bieringer, M.; Margiolaki, I.; Suard, E.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 535-542 Part 5 OCT 2009
Abstract:
The modulation of atomic positions in CaCu (x) Mn7-x O-12 (x = 0 and 0.1) was studied using synchrotron radiation powder diffraction below 250 and 220 K, respectively. The copper-rich member CaCu (x) Mn7-x O-12 (x = 0.23) does not show any modulation of the atomic positions at temperatures as low as 10 K. Using low-temperature neutron powder diffraction the modulation of the magnetic moments of Mn ions in CaCu (x) Mn7-x O-12 (x = 0, 0.1 and 0.23) has been investigated. Long-range modulated magnetic ordering in CaCu (x) Mn7-x O-12 (x = 0, 0.1 and 0.23) is observed below 90.4, 89.2 and 78.1 K. (0,0,q (p)) and (0,0,q (m)) are the propagation vectors describing the modulations of the atomic positions and the magnetic moments. For CaCu (x) Mn7-x O-12 (x = 0 and 0.1) the magnetic modulation and atomic modulation lengths are related by a factor of 2 satisfying the relation (1 - q (p)) = 2(1 - q (m)).
Title:
Modulated crystal structure of incommensurate low tridymite
Authors:
Graetsch, HA Author Full Names: Graetsch, Heribert A.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 543-550 Part 5 OCT 2009
Abstract:
The incommensurately modulated crystal structure of low SiO2 tridymite was refined based on single-crystal X-ray diffraction data in the superspace group Cc(alpha 0 gamma)0. The data set consists of 885 main reflections, 1751 first-order, 924 second-order and 119 third-order satellite reflections with I > 3 Sigma(I). The modulation is mainly made up from cooperative twistings of the rigid SiO4 tetrahedra. Two orders of displacement waves are used to describe the modulation of the Si atoms and three orders for the O atoms. The maximal amplitudes are ca 0.6 A. O atoms bridging pairs of tetrahedra in cis and trans configurations show different positional modulation patterns. The anisotropic displacement parameters (ADPs) are also modulated. A correlation between ADP modulations and positional modulations was found.
Title:
Eu3Si15-xAl1+xOxN23-x(x similar or equal to 5/3) as a commensurate composite crystal
Authors:
Michiue, Y; Shioi, K; Hirosaki, N; Takeda, T; Xie, RJ; Sato, A; Onoda, M; Matsushita, Y Author Full Names: Michiue, Yuichi; Shioi, Kousuke; Hirosaki, Naoto; Takeda, Takashi; Xie, Rong-Jun; Sato, Akira; Onoda, Mitsuko; Matsushita, Yoshitaka
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 567-575 Part 5 OCT 2009
Abstract:
A new Eu-SiAlON crystal, Eu3Si15 - x Al1 + x O (x) N23 - x (x similar or equal to 5/3), was found and the structure was determined by an X-ray diffraction technique using a twinned sample. The structure consists of a host framework, which is constructed by the connection of MX (4) tetrahedra (M: Si or Al; X: O or N), and Eu ions as the guest ions. The structure is considered to be a commensurate composite crystal. The basic vectors are a (1) = a/3, b and c for the first substructure, and a (2) = a/5, b and c for the second substructure. The first substructure consists of part of the host framework and the Eu ions, while the remainder of the host structure is taken as the second substructure. Possible phases belonging to the series are proposed using the composite crystal model in (3 + 1)-dimensional superspace. Chemical composition, possible space groups, cell parameters, and the basic model for those phases are presented.
Title:
Ternary fluorides BaMF4 (M = Zn, Mg and Mn) at low temperatures
Authors:
Posse, JM; Grzechnik, A; Friese, K Author Full Names: Maria Posse, Jose; Grzechnik, Andrzej; Friese, Karen
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 576-586 Part 5 OCT 2009
Abstract:
Ternary fluorides BaMF4 (M = Zn, Mg, Mn) have been studied in the temperature range from 300 to 10 K using synchrotron and laboratory powder and single-crystal diffraction. The first two compounds are stable down to 10 K, while the third one undergoes a phase transition to an incommensurately modulated structure at approximately 250 K. The modulated phase is stable down to 10 K. The magnetic anomalies at 45 and 27 K observed previously in BaMnF4 are exclusively reflected in the behavior of the gamma component of the q vector, which assumes an irrational value of approximately 0.395 A-1 at the temperature corresponding to the onset of the magnetic ordering and then stays constant down to 10 K. Mn-Mn distances do not indicate any structural response to the magnetic ordering. The formation of the modulated phase can be explained on the basis of simple geometrical criteria. The incorporation of the large Mn cation in the octahedral sheets implies an increase of the cavity in which the Ba ion is incorporated. This leads to the formation of the modulated structure to adapt the coordination sphere around Ba in such a way that the bond-valence sums can be kept close to the ideal value of two. With further lowering of the temperature, the charge balance around the Ba ion requires an increasingly anharmonic character of the modulation function of Ba, until finally at 10 K a crenel-like shape is assumed for the modulation of this atom.
Title:
Modulated structure and phase transitions of Sr10Ga6O19
Authors:
Kruger, H; Lazic, B; Arroyabe, E; Kahlenberg, V Author Full Names: Krueger, Hannes; Lazic, Biljana; Arroyabe, Erik; Kahlenberg, Volker
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 587-592 Part 5 OCT 2009
Abstract:
The crystal structure of Sr10Ga6O19 was investigated by in situ single-crystal X-ray diffraction in the temperature range 298-673 K. At ambient conditions the compound shows a (3 + 1)-dimensional modulated structure in the superspace group C2/c(0 beta 0)s0 [a = 34.9145 (13), b = 7.9369 (2), c = 15.9150 (7) A and beta = 103.551 (3)degrees] with a modulation wavevector of q = 0.4288 (2)b*. Whereas the presented structural model uses first-order harmonic modulation functions only, some features of the modulations are discussed utilizing an electron density derived by the maximum entropy method. Furthermore, two phase transitions were identified: between 453 and 503 K the incommensurate superstructure is replaced by a doubling of the a and b lattice constants, and between 503 and 673 K a phase with the basic cell is formed, identical to alpha-Sr10Ga6O19. Under some cooling conditions crystals showing a combined diffraction pattern of bot! h superstructures can be obtained. The relation of these results to alpha-Sr10Ga6O19 [Kahlenberg (2001). J. Solid State Chem. 160, 421-429] is discussed.
Title:
Superspace description of the modulated structure of the metal-salt-hybrid Bi7-delta Ni2Br5-2 delta (delta = 1/9)
Authors:
Wahl, B; Ruck, M Author Full Names: Wahl, B.; Ruck, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 593-599 Part 5 OCT 2009
Abstract:
The compound Bi7 - delta Ni2Br5 - 2 delta = (Bi3Ni)(2)[Bi1 - delta Br4]Br1 -2 delta (delta = 1/9) is a sub-bromide of the intermetallic phase Bi3Ni. Its crystal structure contains metallic rods, (1)(infinity)[Bi3Ni], which are embedded in a salt-like matrix of bromido-bismuthate(III) and bromide anions. The non-stoichiometry originates from the variation of the number n of trans edge-sharing octahedra in the [Bi (n) Br4n + 2](n + 2)- oligomers (3 < n < 5), as well as from vacancies on the sites of the isolated Br atoms. The simplified structure is described in the orthorhombic space group Cmcm with a = 4.0660 (4), b = 23.305 (3), c = 17.130 (2) A. It shows a statistical distribution of vacancies and orientational disorder of the concatenated octahedra. By choosing the modulation vector q = a*/9 + b*/2, the additional weak reflections of the diffraction pattern can be indexed. In the [3 + 1]-dimensional superspace group Pmnm(alpha 1/20)000, an ordered structure model is achieved. The modulated crystal structure bears a strong resemblance to the somewhat higher oxidized sub-bromide Bi7 - delta Ni2Br5 (delta = 1/9).

Update: 8-Oct-2010

Title:
Second order incommensurate phase transition in 25L-Ta2O5
Authors:
Audier, M; Chenevier, B; Roussel, H; Salaun, AL Author Full Names: Audier, M.; Chenevier, B.; Roussel, H.; Salauen, A. Lintanf
Source:
JOURNAL OF SOLID STATE CHEMISTRY 183 (9): 2068-2076 SEP 2010
Abstract:
A new structural state 25L-Ta2O5, obtained from sintering and annealing treatments of a Ta2O5 powder, is identified both by electron diffraction and high resolution imaging on a transmission electron microscope (TEM). According to general rules for the different L-Ta2O5 structures proposed by Grey et al. (J. Solid State Chem. 178 (2005) 3308), a structural model is derived from their crystallographic data on 19L-Ta2O5. This model yields simulated images in agreement with high resolution TEM observations of the structure oriented along its [001] zone axis, but only for a very thin crystal thickness of less than 1.2 nm. Such a limitation is shown to be due to a modulation of the structure along its [001] axis. Actually, from an analysis of a diffuse scattering and of its evolution into satellites reflections as a function of the cooling rate, a second order incommensurate phase transition can be assumed to occur in this compound. The property of single phase samples observed by TEM is also verified by X-ray powder diffraction. In a discussion about studies performed by different authors on incommensurate structures in the system Ta2O5-WO3, it is noticed that TEM results, similar to ours, indicate that phase transitions could be expected in these structures. (C) 2010 Elsevier Inc. All rights reserved.
Title:
Magnetic structures of orthorhombic rare earth stannides LSn2 (L = Tb-Tm)
Authors:
Venturini, G; Lemoine, P; Malaman, B; Ouladdiaf, B Author Full Names: Venturini, G.; Lemoine, P.; Malaman, B.; Ouladdiaf, B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 505 (2): 404-415 SEP 3 2010
Abstract:
The magnetic structures of the orthorhombic compounds LSn2 (S.G.: Cmcm; L = Tb-Tm) have been determined from neutron diffraction studies. The compounds LSn2 (L = Tb, Dy, Ho Er) order below 26.7, 17.2, 7.8 and 4.5 K, respectively, in a sine-modulated structure characterized by the propagation vector k = approximate to 0.39, 0, approximate to 0.41). Below 12.7, 5, 4.8 and 2 K, respectively, these compounds undergo a transition towards a collinear antiferromagnetic structure characterized by the propagation vector k = (0, 0, 1/2) for Tb and Er, k = (1/2, 1/2, 0) for Ho and k = (1/2, 1/2, 1/2) for Dy. The compound TmSn2 orders below 4.0 K in a sine-modulated structure characterized by the propagation vector k = (0, 0.667, 0.380). The moment direction is close to [0 0 1] for L = Tb, Dy, Ho and aligned along [1 0 0] for L = Er, Tm. The results are discussed and a relative scale of the stability of the moment configuration in the (0 1 0) plane is proposed. (C) 2010 Elsevier BM. All rights reserved.
Title:
Microindentation of dispersed phases in an Al94Mn2Be2Cu2 alloy
Authors:
Boncina, T; Cekada, M; Markoli, B; Zupanic, F Author Full Names: Boncina, Tonica; Cekada, Miha; Markoli, Bostjan; Zupanic, Franc
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 505 (2): 486-491 SEP 3 2010
Abstract:
This paper investigated properties of dispersed phases in an Al94Mn2Be2Cu2 alloy using a microindentation hardness test. The focus was directed to the possible strengthening phases for aluminium alloys: an icosahedral quasicrystalline phase (i-phase), a hexagonal quasicrystalline approximant with a large unit cell (H-phase) and a ternary cubic Be4AlMn. A single grain mu-Al4Mn was also examined as a reference. The application of scanning electron microscopy and a focussed ion beam, significantly increased the reliability and reproducibility of the microindentation results. The i-phase was distinguished by the highest Vickers hardness and the highest fraction of elastic energy, while the elastic modulus was the highest for Be4AlMn, being close to that of pure Be. The striking resemblances of the indentation curves for the phases with cluster substructures: i-phase, H-phase and mu-Al4Mn, especially the presence of pop-ins, suggested related deformation mechanisms. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Stationary straight cracks in quasicrystals
Authors:
Radi, E; Mariano, PM Author Full Names: Radi, Enrico; Mariano, Paolo Maria
Source:
INTERNATIONAL JOURNAL OF FRACTURE 166 (1-2): 105-120 Sp. Iss. SI NOV 2010
Abstract:
Stationary straight cracks in quasicrystals in linear elastic setting are under scrutiny. The analysis is developed by using Stroh formalism which is modified to account for a totally degenerate eigenvalue problem: in fact, the fundamental matrix of the governing equations of motion admits a repeated eigenvalue corresponding to a single eigenvector. Cases of a semi-infinite rectilinear crack loaded along its margins and a crack of finite length under remote loading conditions are considered. Standard and phason stresses display square-root singularities at crack tip. The latter stresses represent peculiar microstructural inner actions occurring in quasicrystals and are determined by rearrangements assuring quasi-periodicity of the atomic tiling-modes described by a vector field, called phason field, collecting the local degrees of freedom exploited by the atoms within the material elements. Energy release rate increases with the coupling parameter between displacement ! and phason fields.

Update: 1-Oct-2010

Title:
Quasicrystals
Authors:
Vekilov, YK; Chernikov, MA Author Full Names: Vekilov, Yu Kh; Chernikov, M. A.
Source:
PHYSICS-USPEKHI 53 (6): 537-560 2010
Abstract:
We review the structure of quasicrystals and their electronic spectra, lattice excitation spectra, physical properties, and applications. The aperiodic filling of space according to certain rules with several structural units or overlapping atomic clusters is discussed. Perfect tiling, random tiling, and icosahedral glass models, as well as phason strain are considered. The effect that the aperiodic long-range order and local atomic structure have on electron and thermal transport and on the optical, magnetic, and other properties is examined.
Title:
Calorimetric investigation of electronic and lattice excitations of the icosahedral quasicrystal in the range of moderate temperatures
Authors:
Prekul, AF; Shalaeva, EV; Shchegolikhina, NI Author Full Names: Prekul, A. F.; Shalaeva, E. V.; Shchegolikhina, N. I.
Source:
PHYSICS OF THE SOLID STATE 52 (9): 1797-1802 SEP 2010
Abstract:
The precise measurements of the specific heat and the linear expansion coefficient of polygrain samples of the ordered icosahedral phase Al63Cu25Fe12 have been performed in the temperature range 1.8-400.0 K. The deviations from the Gruneisen law, according to which the temperature dependences of the lattice specific heat at constant volume and the linear expansion coefficient are identical to each other, have been analyzed. The proofs that the specific heat of the quasicrystals contains latent electronic and lattice contributions of the Schottky type have been obtained. The revealed contributions can be thermodynamic consequences of the fractal energy spectra.
Title:
Formation Kinetics of a Bi3Nb1-xTaxO7 Fluorite-Type Solid Solution and Thermodynamic Stability of the Bi3TaO7 End Member
Authors:
Pirnat, U; Valant, M; Radmilovic, V Author Full Names: Pirnat, Ursa; Valant, Matjaz; Radmilovic, Velimir
Source:
JOURNAL OF THE AMERICAN CERAMIC SOCIETY 93 (9): 2909-2914 SEP 2010
Abstract:
Analysis of kinetic characteristics of the incommensurate-commensurate transformation in the Bi3Nb1-xTaxO7 system with a fluorite-like crystal structure enabled us to define the compositional and thermal stability ranges of the commensurate tetragonal polymorph. We showed that the tetragonal polymorph across the entire homogeneity range is isostructural to the Bi3NbO7 end member. The kinetics of the transformation from the cubic incommensurate to the tetragonal commensurate phase decreases with an increase in Ta concentration within the Bi3Nb1-xTaxO7 system. The formation studies indicate that the tetragonal Bi3TaO7 is thermodynamically stable; however, its formation via the metastable incommensurate-cubic phase is suppressed.

Update: 24-Sep-2010

Title:
Kagome staircase compound Co3V2O8 in an applied magnetic field: Single-crystal neutron diffraction study
Authors:
Petrenko, OA; Wilson, NR; Balakrishnan, G; Paul, DM; McIntyre, GJ Author Full Names: Petrenko, O. A.; Wilson, N. R.; Balakrishnan, G.; Paul, D. Mck; McIntyre, G. J.
Source:
PHYSICAL REVIEW B 82 (10): Art. No. 104409 SEP 8 2010
Abstract:
The magnetic properties of Co3V2O8 have been studied by single-crystal neutron diffraction. In zero magnetic field, the observed broadening of the magnetic Bragg peaks suggests the presence of disorder both in the low-temperature ferromagnetic and in the higher temperature antiferromagnetic state. The field dependence of the intensity and position of the magnetic reflections in Co3V2O8 reveals a complex sequence of phase transitions in this Kagome staircase compound. For H parallel to a, a commensurate-incommensurate-commensurate transition is found in a field of 0.072 T in the antiferromagnetic phase at 7.5 K. For H parallel to c at low temperature, an applied field induces an unusual transformation from a ferromagnetic to an antiferromagnetic state at about 1 T accompanied by a sharp increase in magnetization.
Title:
Ab initio study of stabilization of the misfit layer compound (PbS)(1.14)TaS2
Authors:
Kabliman, E; Blaha, P; Schwarz, K Author Full Names: Kabliman, Evgeniya; Blaha, Peter; Schwarz, Karlheinz
Source:
PHYSICAL REVIEW B 82 (12): Art. No. 125308 SEP 8 2010
Abstract:
In the present work we perform ab initio electronic-structure calculations of the (PbS)(1.14)TaS2 misfit layer compound in order to understand the basic mechanism of its stabilization. Density-functional based calculations were carried out in commensurate unit cells containing 74 or 296 atoms using the WIEN2K code. The two experimentally predicted mechanisms of stabilization, namely, metal cross substitution (interchange of Pb and Ta atoms in the PbS and TaS2 layers) and nonstoichiometry (substitution of Pb by Ta), were investigated. The results show clearly that the nonstoichiometry mechanism plays the significant role. When Pb inside the PbS layer is substituted by Ta with concentrations around 0.13-0.19, a stabilization is found with respect to the parent PbS and TaS2 compounds. These results are explained by an analysis of partial densities of states. The calculated x-ray photoemission spectroscopy core-level shifts are in reasonable agreement with experiments.
Title:
Symmetry and strain analysis of structural phase transitions in Pr0.48Ca0.52MnO3
Authors:
Carpenter, MA; McKnight, REA; Howard, CJ; Knight, KS Author Full Names: Carpenter, Michael A.; McKnight, Ruth E. A.; Howard, Christopher J.; Knight, Kevin S.
Source:
PHYSICAL REVIEW B 82 (9): Art. No. 094101 SEP 7 2010
Abstract:
Structural evolution as a function of temperature through the Pnma <-> incommensurate (IC) phase transition in Pr0.48Ca0.52MnO3 perovskite has been analyzed from the perspectives of symmetry and strain. The structure and stability of both phases are shown to depend on combinations of order parameters which have symmetries associated with irreducible representations M-3(+), R-4(+), M-2(+), Gamma(+)(3) and Sigma(2) of space group Pm (3) over barm. The physical origin of these can be understood in terms of octahedral tilting, cooperative Jahn-Teller distortions and charge order/Zener polaron ordering. The M-2(+) order parameter describes the Jahn- Teller ordering scheme which develops in LaMnO3 while the Gamma(+)(3) order parameter relates to an ordering scheme in which the unique axes of the distorted octahedra are all aligned in the same direction. Irrep Sigma(2) contains two components with gradient coupling and provides the symmetry-breaking mechanism by which the IC transition can occur. Each order parameter couples with macroscopic spontaneous strains in a manner that depends strictly on symmetry and this leads to specific interactions between the order parameters through their coupling with common strains. In order to establish the extent and importance of this coupling, symmetry- adapted strains have been extracted from a new set of lattice parameters obtained by high-resolution powder neutron diffraction in the temperature interval 10-1373 K. It is found that the predominant strain of the incommensurate structure (up to similar to 2.5%) is a tetragonal shear strain which arises by bilinear coupling with the Gamma(+)(3) order parameter. This combination is probably responsible for most of the energy reduction accompanying the Pnma. IC transition and also gives it some characteristics typical of a pseudoproper ferroelastic transition. Strain coupling promotes mean-field behavior and the evolution of the symmetry-breaking order parameter can be described by a standard Landau tricritical solution, q(4)proportional to(T-c-T) with T-c = 237 +/- 2 K. Octahedral tilting at high temperatures is closely similar to tilting in the Pnma structure of other perovskites, such as SrZrO3. This is accompanied by a degree of Jahn- Teller ordering on the basis of the M-2(+) scheme below similar to 775 K but is replaced by the Gamma(+)(3) scheme below T-c. In contrast with the tilting and Jahn-Teller effects, magnetic ordering at the Neel temperature (similar to 180 K) is accompanied by only the slightest volume strain and is not likely to influence the evolution of the other order parameters to any significant extent, therefore. An additional change in the volume strain below similar to 85 K is perhaps related to changes in magnetic structure at lower temperatures. Line broadening in powder diffraction patterns collected in the temperature interval similar to 150-260 K appears to be related to the presence of ferroelastic twins arising from octahedral tilting and draws attention to the fact that the Pnma <-> IC transition takes place in a material which already contains heterogeneities. Finally, correlation of the repeat distance of the IC structure with Gamma(+)(3) distortions of MnO6 octahedra shows that the nature of the IC structure itself is also deermined essentially by geometrical factors and strain.
Title:
Magnetic structure of the zigzag chain family NaxCa1-xV2O4 determined by muon- spin rotation
Authors:
Ofer, O; Ikedo, Y; Goko, T; Mansson, M; Sugiyama, J; Ansaldo, EJ; Brewer, JH; Chow, KH; Sakurai, H Author Full Names: Ofer, Oren; Ikedo, Yutaka; Goko, Tatsuo; Mansson, Martin; Sugiyama, Jun; Ansaldo, Eduardo J.; Brewer, Jess H.; Chow, Kim H.; Sakurai, Hiroya
Source:
PHYSICAL REVIEW B 82 (9): Art. No. 094410 SEP 7 2010
Abstract:
We present muon-spin-rotation measurements on polycrystalline samples of the complete family of the antiferromagnetic (AF) zigzag chain compounds, NaxCa1-xV2O4. In this family, we explore the magnetic properties from the metallic NaV2O4 to the insulating CaV2O4. We find a critical x(c)(similar to 0.833) which separates the low and high Na-concentration-dependent transition temperature and its magnetic ground state. In the x < x(c) compounds, the magnetic ordered phase is characterized by a single homogenous phase and the formation of incommensurate spin-density-wave order. Whereas in the x > x(c) compounds, multiple subphases appear with temperature and x. Based on the muon data obtained in zero external magnetic field, a careful dipolar field simulation was able to reproduce the muon behavior and indicates a modulated helical incommensurate spin structure of the metallic AF phase. The incommensurate modulation period obtained by the simulation agrees with that determined by neutron diffraction.
Title:
Composition rule for Al-transition metal binary quasicrystals
Authors:
Chen, H; Wang, Q; Wang, YM; Qiang, JB; Dong, C Author Full Names: Chen, Hua; Wang, Qing; Wang, Yingmin; Qiang, Jianbing; Dong, Chuang
Source:
PHILOSOPHICAL MAGAZINE 90 (30): 3935-3946 2010
Abstract:
Compositions of Al-transition metal (TM) binary quasicrystals are revisited using the cluster-plus-glue-atom model. These compositions all conform to a unified cluster formula [icosahedron](glue)1, where the icosahedron is taken from a crystalline approximant. In a given binary system, icosahedral and decagonal quasicrystals are expressed by the same icosahedron but glued, respectively, by one Al and one TM, and their e/a ratios fall close to 1.86 and 1.71-1.79, respectively. Their relative stabilities are discussed by referring to compositions satisfying the fully filled TM-3d states according to Haussler's resonance model.
Title:
Microstructure of a composite with a quasicrystalline phase fraction obtained by directional solidification of Al61Cu27Fe12 alloy
Authors:
Krawczyk, J; Bogdanowicz, W; Goryczka, T Author Full Names: Krawczyk, Jacek; Bogdanowicz, Wodzimierz; Goryczka, Tomasz
Source:
PHILOSOPHICAL MAGAZINE 90 (30): 3987-3998 2010
Abstract:
The microstructure of a composite containing a quasicrystal phase, i.e. so-called crystal-quasicrystal (CQ) composite, was studied. The CQ composite was obtained by the Bridgman method via solidification of Al61Cu27Fe12 alloy (numbers indicate at%). The process was conducted at a pull out rate of v = 0.07 mm/min. The average temperature gradient in the heating zone was 43 K/cm. The composite matrix consisted of cubic phase Al(Fe, Cu), with reinforcement of -phase rod-shaped fibres surrounded by a quasicrystal icosahedral phase, which also existed in the fibre core. The fibres were rhomboidal in cross-section. The composite was studied using X-ray and electron diffraction, light-optical and scanning electron microscopy (SEM), X-ray topography and Laue diffraction.
Title:
Interplay of quantum criticality and geometric frustration in columbite
Authors:
Lee, S; Kaul, RK; Balents, L Author Full Names: Lee, SungBin; Kaul, Ribhu K.; Balents, Leon
Source:
NATURE PHYSICS 6 (9): 702-706 SEP 2010
Abstract:
CoNb2O6 is a material with remarkable properties that are determined by an exciting interplay of quantum mechanics and geometric frustration. On the one hand, weakly coupled ferromagnetic Ising chains of Co2+ ions can be tuned by an applied magnetic field through a quantum critical point to be paramagnetic; on the other hand, the Ising chains must contend with residual interactions on a frustrated triangular lattice in their choice of how to order. Motivated by the material, we theoretically study the phase diagram of quantum ferromagnetic Ising chains coupled antiferromagnetically on a triangular lattice in the plane perpendicular to the chain direction. We combine exact solutions of the quantum criticality in the isolated chains with perturbative approximations for the frustrated interchain couplings. When the triangular lattice has an isosceles distortion, which occurs in the real material, the phase diagram at absolute zero temperature is rich with five different states of matter: ferrimagnetic, Neel, antiferromagnetic, paramagnetic and incommensurate phases, separated by quantum phase transitions. Implications of our results on experiments in CoNb2O6 are discussed.
Title:
Quasicrystalline phase formation during heat treatment in mechanically alloyed Al65Cu20Fe15 alloy
Authors:
Gogebakan, M; Avar, B Author Full Names: Gogebakan, M.; Avar, B.
Source:
MATERIALS SCIENCE AND TECHNOLOGY 26 (8): 920-924 AUG 2010
Abstract:
Quasicrystalline phase formation during heat treatment in the mechanically alloyed Al65Cu20Fe15 powders was studied by X-ray diffraction (XRD) and differential scanning calorimeter (DSC). The mechanical alloying was performed at speed of 300 rev min(-1) for times up to 70 h. It was found that mechanical alloying of the Al65Cu20Fe15 powders did not result in the quasicrystalline (QC) icosahedral phase (i-phase) formation. The long time milling resulted in the formation of a cubic Al (Cu,Fe) solid solution phase (beta-phase). The cubic Al (Cu,Fe) solid solution identified as beta-phase was observed to be present as one of the major phases in the Al65Cu20Fe15 alloy. The formation of the quasicrystalline icosahedral phase (i-phase) was only observed for short time milled powders after additional annealing at temperature above 500 degrees C. The present investigation also showed that a tetragonal Al2Cu phase (theta-phase) forms with short time milling. The tetragonal Al7Cu2Fe1 phase (w-phase) was observed after heat treatment of the short time milled and unmilled powders. The present investigation indicated that an effective process to prepare the quasicrystalline materials was using a combination of short time milling and subsequent annealing.
Title:
Ab initio density-functional calculations in materials science: from quasicrystals over microporous catalysts to spintronics
Authors:
Hafner, J Author Full Names: Hafner, Juergen
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (38): Art. No. 384205 SEP 29 2010
Abstract:
During the last 20 years computer simulations based on a quantum-mechanical description of the interactions between electrons and atomic nuclei have developed an increasingly important impact on materials science, not only in promoting a deeper understanding of the fundamental physical phenomena, but also enabling the computer-assisted design of materials for future technologies. The backbone of atomic-scale computational materials science is density-functional theory (DFT) which allows us to cast the intractable complexity of electron-electron interactions into the form of an effective single-particle equation determined by the exchange-correlation functional. Progress in DFT-based calculations of the properties of materials and of simulations of processes in materials depends on: (1) the development of improved exchange-correlation functionals and advanced post-DFT methods and their implementation in highly efficient computer codes, (2) the development of methods allowing us to bridge the gaps in the temperature, pressure, time and length scales between the ab initio calculations and real-world experiments and (3) the extension of the functionality of these codes, permitting us to treat additional properties and new processes. In this paper we discuss the current status of techniques for performing quantum-based simulations on materials and present some illustrative examples of applications to complex quasiperiodic alloys, cluster-support interactions in microporous acid catalysts and magnetic nanostructures.
Title:
Dichalcogenide Bonding in Seven Alkali-Metal Actinide Chalcogenides of the KTh2Se6 Structure Type
Authors:
Bugaris, DE; Wells, DM; Yao, JY; Skanthakumar, S; Haire, RG; Soderholm, L; Ibers, JA Author Full Names: Bugaris, Daniel E.; Wells, Daniel M.; Yao, Jiyong; Skanthakumar, S.; Haire, Richard G.; Soderholm, L.; Ibers, James A.
Source:
INORGANIC CHEMISTRY 49 (18): 8381-8388 SEP 20 2010
Abstract:
The solid-state compounds CsTh2Se6, Rb0.85U1.74S6, RbU2Se6, TIU2Se6, Cs-0.88(La0.68U1.32)Se-6, KNP2Se6, and CsNp2Se6 of the AAn(2)Q(6) family (A = alkali metal or TI; An = Th, U, Np; Q = S, Se, Te) have been synthesized by high-temperature techniques. All seven crystallize in space group lmmm of the orthorhombic system in the KTh2Se6 structure type. Evidence of long-range order and modulation were found in the X-ray diffraction patterns of TIU2Se6 and CsNp2Se6. A 4a X 4b supercell was found for TIU2Se6 whereas a 5a x 5b x 5c supercell was found for CsNp2Se6. All seven compounds exhibit Q-Q interactions and, depending on the radius ratio R-An/R-A1 disorder of the A cation over two sites. The electrical conductivity of RbU2Se6, measured along [100], is 6 x 10(-5) S cm(-1) at 298 K. The interatomic distances, including those in the modulated structure of TIU2Se6, and physical properties suggest the compounds may be formulated as containing tetravalent Th or U, but the formal oxidation state of Np in the modulated structure of CsNp2Se6 is less certain. The actinide contraction from Th to U to Np is apparent in the interatomic distances.

Update: 17-Sep-2010

Title:
M-Al-M groups trapped in cages of Al13M4 (M=Co, Fe, Ni, Ru) complex intermetallic phases as seen via NMR
Authors:
Jeglic, P; Vrtnik, S; Bobnar, M; Klanjsek, M; Bauer, B; Gille, P; Grin, Y; Haarmann, F; Dolinsek, J Author Full Names: Jeglic, P.; Vrtnik, S.; Bobnar, M.; Klanjsek, M.; Bauer, B.; Gille, P.; Grin, Yu.; Haarmann, F.; Dolinsek, J.
Source:
PHYSICAL REVIEW B 82 (10): Art. No. 104201 SEP 3 2010
Abstract:
The crystallographic structures of decagonal quasicrystals and their periodic approximants are traditionally described as a periodic stacking of atomic planes. By performing a Al-27 NMR spectroscopic study of the Al13M4 (M=transition metal) family of four-layer decagonal approximants, including the orthorhombic o-Al13Co4, the monoclinic Al13Fe4, its ternary derivative Al-13 (Fe,Ni)(4), and the monoclinic Al13Ru4, we show that all these phases contain structural detail of a nearly linear M-Al-M atomic group trapped inside an elongated cage, resembling the three-dimensional (3D) "cage-compound" structure of the intermetallic clath-rates. We determined the electric-field-gradient- (EFG) and the magnetic-shielding tensors at the Al site of the M-Al-M groups. The asymmetry parameter of the EFG tensor was estimated theoretically by a point-charge model, taking into account the charges of both the M-Al-M atoms and the surrounding cage atoms. The calculations support ionic bonding of the M-Al-M group to the cage atoms and the existence of a 3D chemical bonding network in the Al13M4 phases. The above results show that the traditional description of the Al13M4 decagonal approximant phases in terms of two-dimensional (2D) atomic layers stacked along the pseudotenfold crystallographic direction is a convenient geometrical approach to describe their complex structures but is not appropriate for the description of their physical properties, which should be analyzed by taking into account the full 3D nature of the chemical bonding framework. This favors the 3D cage-compound structural description of the Al13M4 phases over the pseudo-2D stacked-layer description.
Title:
Evolution of the magnetic field-temperature phase diagram in UAs1-xSex
Authors:
Plackowski, T; Matusiak, M; Sznajd, J Author Full Names: Plackowski, Tomasz; Matusiak, Marcin; Sznajd, Jozef
Source:
PHYSICAL REVIEW B 82 (9): Art. No. 094408 SEP 3 2010
Abstract:
The evolution of the magnetic field-temperature phase diagram of UAs1-xSex with x in the range of 0-0.1 is studied by means of magnetocaloric and specific-heat measurements. Our interest is focused on the high-temperature phase transitions and especially on the point, where the paramagnetic (P) and two ordered phases meet. For undoped UAs these two ordered states are the ferrimagnetic (Fi) and the type-I antiferromagnetic phases. According to Sinha et al. [Phys. Rev. Lett. 45, 1028 (1980)] the antiferromagnetic phase transition is in the vicinity of a Lifshitz point. Furthermore, Kuznietz et al. [J. Magn. Magn. Mater. 61, 246 (1986)] showed that an incommensurate phase (IC) emerges between the type-I (or type-IA) antiferromagnetic and paramagnetic phases in the case of UAs1-xSex with 0 < x < 0.15 in zero magnetic field. The results reported in this paper show the existence of a T-Fi/IC(B) line that separates the ferrimagnetic region from a phase, which cannot be identified on the basis of our thermodynamic measurements. However, one may assume it is the IC phase, consistent with the above mentioned zero field results. The T-Fi/IC(B) line merges with the order-disorder line at point (B-p, T-p), where the critical line (IC/P) meets with two first order transitions lines: Fi/P and Fi/IC. This point can be considered as an analog of a Lifshitz point. A simple phenomenological description of the phase transitions near this special point is provided.
Title:
Plasticity of quasicrystals and of bulk metallic glasses: An analogy
Authors:
Guyot, P Author Full Names: Guyot, P.
Source:
INTERMETALLICS 18 (10): 1925-1929 Sp. Iss. SI OCT 2010
Abstract:
Despite their antinomic atomic structures, long range ordered but non-periodically for quasicrystals (QC), or disordered for met-glasses (MG), both materials share surprisingly a similar mechanical behaviour: brittleness at low temperature, plasticity at high temperature. Such a-priori surprising results are considered and analysed, focussing on the high temperature ductility. Due to the aperiodic order of the QC atomic structure, the dislocation motion creates a topological and chemical disorder from which a friction stress results. Combining the friction stress strain reduction with classical dynamic properties of dislocations allows to establish a constitutive equation of the deformation, which reproduces the essential characteristics of the experimental stress strain and creep curves [7]. In MG, the diffusion of the free volume flow defects [9] is at the origin of the high temperature plastic strain. Their flow equation, where time and strain variations of the flow carriers density are introduced, leads to a satisfactory description of experimental observations: scaling of the glass viscosity with strain-rate and temperature, transient regimes occurring during specimen loading/unloading or strain-rate changes. Common features underlying the constitutive equation of the high temperature deformation of both materials are emphasized and discussed. (C) 2010 Elsevier Ltd. All rights reserved.

Update: 10-Sep-2010

Title:
Commensurate charge-density wave with frustrated interchain coupling in SmNiC2
Authors:
Wolfel, A; Li, L; Shimomura, S; Onodera, H; van Smaalen, S Author Full Names: Woelfel, Alexander; Li, Liang; Shimomura, Susumu; Onodera, Hideya; van Smaalen, Sander
Source:
PHYSICAL REVIEW B 82 (5): Art. No. 054120 AUG 30 2010
Abstract:
Temperature-dependent x-ray diffraction on SmNiC2 has shown that the orthorhombic lattice symmetry of this compound persist down to a temperature of at least 9 K, i.e., into the charge-density-wave (CDW) state below T-CDW = 148 K and in the ferromagnetically ordered state below T-C = 17.7 K. The modulated crystal structure has been determined for the incommensurate CDW state with q(CDW) = (0.5,0.516,0) at T=60 K. The observed atomic modulation displacements indicate that the CDW should be considered as a commensurate CDW centered on chains of Ni atoms along a. Frustrated interchain coupling is responsible for the incommensurability of the three-dimensionally ordered CDW state.
Title:
Quasicrystals as alloys with short-range order
Authors:
Sulston, KW; Burrows, BL Author Full Names: Sulston, K. W.; Burrows, B. L.
Source:
PHYSICA B-CONDENSED MATTER 405 (18): 3885-3889 SEP 15 2010
Abstract:
The electronic structure of quasiperiodic lattices is studied. An alloy theory, including short-range order effects, is used to approximate Fibonacci and Thue-Morse lattices. Short-range order is treated by embedding small clusters in an alloy that itself incorporates a two-site approximation, and the probabilities of these clusters are used to construct an efficient procedure for the calculation of electronic properties. This approach allows easy identification of the contributions of particular clusters to the electronic density of states. As the short-range order is increased via the number of clusters, the density of states can be clearly seen to transition from that of an alloy to that of a quasicrystal. It is shown that the techniques may be applied to other lattices defined by substitution rules. (C) 2010 Elsevier B.V. All rights reserved.
Title:
A comparative scanning tunneling spectroscopy investigation of the (12110)-surface of decagonal Al-Ni-Co and the (100)-surface of its approximant Y-Al-Ni-Co
Authors:
Mader, R; Widmer, R; Groning, P; Ruffieux, P; Steurer, W; Groning, O Author Full Names: Maeder, Ruben; Widmer, Roland; Groening, Pierangelo; Ruffieux, Pascal; Steurer, Walter; Groening, Oliver
Source:
NEW JOURNAL OF PHYSICS 12: Art. No. 073043 JUL 30 2010
Abstract:
We present a low-temperature scanning tunneling spectroscopy study of the local density of states (LDOS) on the (12110)-surface of the decagonal quasicrystal d-Al-Ni-Co and the (100)-surface of its structurally closely related approximant Y-Al-Ni-Co in the range of +/- 1 eV around the Fermi energy. The LDOS of both surfaces are dominated by a large parabolic pseudogap centered at the Fermi energy, which can be attributed to the Hume-Rothery stabilization mechanism or to an orbital hybridization. Superimposed on this large pseudogap, a spatially varying fine structure is revealed, whose spatial distribution correlates with the structures of both of the surfaces. This fine structure shows narrow peaks and pseudogaps exhibiting typical energy widths between 50 and 150 meV. The spatial extent of these localized states is of the order of the width of the topographic features, which is about 0.45 nm. Our findings show that specific electronic states are localized on equivalent topographic features regardless of the presence of periodic or quasiperiodic long-range order. We interpret this result as an indication that the fine structure in the LDOS is dominated much more by the complex short-range order than by the presence of the quasiperiodic long-range order.
Title:
Mode crystallography of distorted structures
Authors:
Perez-Mato, JM; Orobengoa, D; Aroyo, MI Author Full Names: Perez-Mato, J. M.; Orobengoa, D.; Aroyo, M. I.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 66: 558-590 Part 5 SEP 2010
Abstract:
The description of displacive distorted structures in terms of symmetry-adapted modes is reviewed. A specific parameterization of the symmetry-mode decomposition of these pseudosymmetric structures defined on the setting of the experimental space group is proposed. This approach closely follows crystallographic conventions and permits a straightforward transformation between symmetry-mode and conventional descriptions of the structures. Multiple examples are presented showing the insight provided by the symmetry-mode approach. The methodology is shown at work, illustrating its various possibilities for improving the characterization of distorted structures, for example: detection of hidden structural correlations, identification of fundamental and marginal degrees of freedom, reduction of the effective number of atomic positional parameters, quantitative comparison of structures with the same or different space group, detection of false refinement minima, syste! matic characterization of thermal behavior, rationalization of phase diagrams and various symmetries in families of compounds etc. The close relation of the symmetry-mode description with the superspace formalism applied to commensurate superstructures is also discussed. Finally, the application of this methodology in the field of ab initio or first-principles calculations is outlined. At present, there are several freely available user-friendly computer tools for performing automatic symmetry-mode analyses. The use of these programs does not require a deep knowledge of group theory and can be applied either a posteriori to analyze a given distorted structure or a priori to parameterize the structure to be determined. It is hoped that this article will encourage the use of these tools. All the examples presented here have been worked out using the program AMPLIMODES [Orobengoa et al. (2009). J. Appl. Cryst. 42, 820-833].

Update: 27-Aug-2010

Title:
Effect of Mg-based spherical quasicrystal on microstructures and mechanical properties of ZA54 alloy
Authors:
Zhang, JS; Zhang, YQ; Zhang, Y; Xu, CX; Wang, XM; Yan, J Author Full Names: Zhang Jin-shan; Zhang Yong-qing; Zhang Yan; Xu Chun-xiang; Wang Xiao-ming; Yan Jie
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA 20 (7): 1199-1204 JUL 2010
Abstract:
To improve the strength, toughness and heat-resistance of magnesium alloy, the microstructure and mechanical properties of ZA54 alloy reinforced by icosahedral quasicrystal phase (I-phase) particles were studied. Except alpha-Mg, phi-phase and tau-phase, MgZnYMn I-phase particles can be obtained in ZA54-based composites by the addition of icosahedral quasicrystal-contained Mg-Zn-Y-Mn master alloy. The introduction of MgZnYMn I-phase into ZA54 alloy has great contribution to the refinement of matrix microstructures and the improvement of mechanical properties. When the addition of Mg-based spherical quasicrystal master alloy is up to 3.5% (mass fraction), the macro-hardness of ZA54-based composites is increased to HB 68. The impact toughness of composites reaches the peak value of 18.3 J/cm(2), which is about 29% higher than that of ZA54 mother alloy. The highest tensile properties at ambient and elevated temperatures with master alloy addition of 2.5% (473 K) are also obtained in ZA54-based composites with 3.5% (mass fraction) Mg-Zn-Y-Mn master alloy addition. The ultimate tensile strength of composites at ambient and elevated temperatures are 192.5 MPa and 174 MPa, which are 23.4% and 33.8% higher than that of ZA54 mother alloy, respectively. The improved mechanical properties are mainly attributed to the pinning effect of I-phase on grain boundaries.
Title:
Magnetic field and temperature dependence of the amplitude-modulated magnetic structure of PrNi2Si2 determined by single-crystal neutron diffraction
Authors:
Blanco, JA; Fak, B; Ressouche, E; Grenier, B; Rotter, M; Schmitt, D; Rodriguez-Velamazan, JA; Campo, J; Lejay, P Author Full Names: Blanco, J. A.; Fak, B.; Ressouche, E.; Grenier, B.; Rotter, M.; Schmitt, D.; Rodriguez-Velamazan, J. A.; Campo, J.; Lejay, P.
Source:
PHYSICAL REVIEW B 82 (5): Art. No. 054414 AUG 11 2010
Abstract:
The temperature and magnetic field dependence of the magnetic structure in the singlet crystal-field ground-state system PrNi2Si2 have been determined using single-crystal neutron diffraction. At the magnetic ordering temperature in zero field, T-N=20.0 +/- 0.5 K, an amplitude-modulated magnetic structure sets in with a propagation vector k=(0, 0, 0.87) and the magnetic moments of the Pr3+ ions parallel to the c axis of the body-centered tetragonal structure. The magnetic structure remains amplitude modulated down to low temperatures (T=1.6 K) with only a small tendency to squaring up, as signaled by the weak intensity of the third harmonic that develops below 16 K. With applied field along the easy axis, the modulated structure goes smoothly over into a ferromagnetic state. At the critical field of H-c=58 kOe, the first harmonic disappears and the field-induced ferromagnetic moment shows a kink, in agreement with magnetization measurements. Both the temperature and magnetic field dependence are well described by a periodic field Hamiltonian including magnetic exchange and the crystalline electric field.
Title:
Quasiperiodic Pb monolayer on the fivefold i-Al-Pd-Mn surface: Structure and electronic properties
Authors:
Krajci, M; Hafner, J; Ledieu, J; Fournee, V; McGrath, R Author Full Names: Krajci, M.; Hafner, J.; Ledieu, J.; Fournee, V.; McGrath, R.
Source:
PHYSICAL REVIEW B 82 (8): Art. No. 085417 AUG 11 2010
Abstract:
Lead is one of few elements that adopts a pseudomorphic structure when deposited on quasicrystalline substrates. We present a structural model of quasiperiodic Pb overlayers formed on the fivefold surface of an icosahedral A1-Pd-Mn quasicrystal at two different coverages close to saturation. The skeleton of the Pb monolayer is formed by a network of "starfish" (SF) clusters formed at the initial stages of Pb deposition, as studied in detail in our previous work [Ledieu et al., Phys. Rev. B 79, 165430 (2009)]. The atomic structure of the Pb monolayers can be represented as a decorated pentagonal Penrose P1 tiling. The structural models reproduce also the quasiperiodic superstructure of the layers observed in experimental scanning tunneling microscopy (STM) images which is described by the tau-scaled tau P1 tiling (tau is the golden mean). The atomic structure underlying the observed tau-scaled "white flower" motifs and the origin of irregular bright spots in STM! images are discussed. The bright spots appear in the centers of the SF clusters centered at substrate sites occupied by A1 atoms. The calculated electronic structure shows that the minimum in the density of states (pseudogap) at the Fermi level which is characteristic for the A1-Pd-Mn quasicrystals appears also in the local density of states of the adsorbed Pb monolayer. However, our analysis demonstrates that the formation of this pseudogap is not due to the quasiperiodic arrangement of the Pb atoms but to the strong hybridization of their orbitals with the substrate.
Title:
Structure and reactivity of Bi allotropes on the fivefold icosahedral Al-Pd-Mn quasicrystal surface
Authors:
Smerdon, JA; Cross, N; Dhanak, VR; Sharma, HR; Young, KM; Lograsso, TA; Ross, AR; McGrath, R Author Full Names: Smerdon, J. A.; Cross, N.; Dhanak, V. R.; Sharma, H. R.; Young, K. M.; Lograsso, T. A.; Ross, A. R.; McGrath, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (34): Art. No. 345002 SEP 1 2010
Abstract:
The growth of Bi on a pseudomorphic Bi monolayer on the fivefold surface of the icosahedral Al-Pd-Mn quasicrystal has been investigated using low energy electron diffraction and scanning tunnelling microscopy. Initially randomly oriented pseudocubic islands are formed with a preference for an even number of layers. Subsequently a morphological transformation takes place to hexagonal Bi islands, which align along high symmetry directions of the substrate. The Bi flux is found to have a strong effect on which island structure is preferred. When C-60 is adsorbed on the three different allotropes of Bi present in this system, hexagonal C-60 islands are formed in each case. On the pseudocubic and hexagonal islands, the C-60 islands are aligned with the substrate. We discuss the energetic, kinetic and geometrical factors which influence the morphological transformation referred to above.
Title:
Activated impurity states in the incommensurate phase of ferroelectric semiconductor TlInS2
Authors:
Seyidov, MY; Suleymanov, RA; Salehli, F Author Full Names: Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Salehli, Ferid
Source:
JOURNAL OF APPLIED PHYSICS 108 (2): Art. No. 024111 JUL 15 2010
Abstract:
The effect of annealing within the incommensurate phase on the dielectric function epsilon of the TlInS2 single crystals has been investigated. It is shown that the effect of annealing is very close to the effect of doping by electrically active impurity La. The inference is made that the correlation between observed effects in annealed and doped crystals is conditioned by the internal electric fields induced by the activation (polarization) of native defects during the annealing procedure. The investigations of the Second harmonic generation in undoped TlInS2 crystal and the pyrocurrent in TlInS2 : La confirms the proposed model. (C) 2010 American Institute of Physics. [doi:10.1063/1.3466764]
Title:
Magnetic ordering in PrT2Ge2 (T = Ni, Ru and Rh) compounds
Authors:
Szytula, A; Kaczorowski, D; Gondek, L; Pikul, A; Arulraj, A; Balanda, M; Baran, S; Penc, B Author Full Names: Szytula, A.; Kaczorowski, D.; Gondek, L.; Pikul, A.; Arulraj, A.; Balanda, M.; Baran, S.; Penc, B.
Source:
INTERMETALLICS 18 (9): 1766-1771 SEP 2010
Abstract:
X-ray and neutron diffraction, magnetization, magnetic susceptibility and electrical resistivity measurements were performed on polycrystalline samples of PrNi2Ge2, PrRu2Ge2 and PrRh2Ge2. All the investigated compounds crystallize with a tetragonal structure of the ThCr2Si2-type. All of them exhibit metallic-like electrical conductivity and order magnetically at low temperatures, namely PrNi2Ge2 and PrRh2Ge2 are antiferromagnetic below T-N = 23.5 and 45 K, respectively, while PrRu2Ge2 is a ferromagnet with T-C = 14.8 K. The neutron diffraction data indicated a modulated antiferromagnetic structure in PrNi2Ge2 in the entire ordered region. For PrRh2Ge2 a collinear antiferromagnetic ordering was derived below T-t = 30 K and a sine-modulated ordering above that temperature. The neutron diffraction corroborated a simple ferromagnetic structure in PrRu2Ge2. (C) 2010 Elsevier Ltd. All rights reserved.

Update: 20-Aug-2010

Title:
Sound behavior near the Lifshitz point in proper ferroelectrics
Authors:
Kohutych, A; Yevych, R; Perechinskii, S; Samulionis, V; Banys, J; Vysochanskii, Y Author Full Names: Kohutych, A.; Yevych, R.; Perechinskii, S.; Samulionis, V.; Banys, J.; Vysochanskii, Yu.
Source:
PHYSICAL REVIEW B 82 (5): Art. No. 054101 AUG 4 2010
Abstract:
The interaction between soft optic and acoustic phonons was investigated for Sn2P2(Se0.28S0.72)(6) proper uniaxial ferroelectrics by Brillouin-scattering and ultrasonic pulse-echo techniques. The elastic softening of hypersound velocity of transverse-acoustic phonons and for both longitudinal and transverse ultrasound waves which propagate near direction of the modulation wave vector (in the incommensurate phase at x > x(LP)) was found at cooling to the Lifshitz point in the paraelectric phase. The strong increase in the ultrasound attenuation has also been observed. Such phenomena are related to the linear interaction of the soft optic and acoustic branches in the region of relatively short-range hypersound waves and to the strongly developed long-range order-parameter fluctuations in the ultrasound frequency range. The hypersound velocity temperature dependence was described within the Landau-Khalatnikov approximation for the ferroelectric phase.
Title:
Time relaxation of permittivity in [(CH3)2NH2]3CuCl5 crystal under external electric field
Authors:
Eliyashevskyy, Y; Czapla, Z; Dacko, S Author Full Names: Eliyashevskyy, Yu.; Czapla, Z.; Dacko, S.
Source:
PHASE TRANSITIONS 83 (8): 564-571 2010
Abstract:
Continuation of our previous studies connected with dielectric properties of tris-dimethylammoniumpentachlorocuprate crystal [(CH3)2NH2]3CuCl5 crystal under the influence of electric field are presented in this article. We studied the time dependence of the permittivity under the influence of electric field at constant temperatures above Tc. In experiment, slow but significant decrease of permittivity was observed, which can be described with two main relaxation processes. The observed dielectric behavior can be related to the coexistence of phases and slow transition to ferroelectric one through long-time metastable states connected with the presence of incommensurate phase in the studied crystal. The coexistence of phases and slow transition was confirmed from the appearance of induced polarization under external electric field, measured as depolarization current.
Title:
The local structure and composition of Ba4Nb2O9-based oxycarbonates
Authors:
Bezjak, J; Abakumov, AM; Recnik, A; Krzmanc, MM; Jancar, B; Suvorov, D Author Full Names: Bezjak, Jana; Abakumov, Artem M.; Recnik, Aleksander; Krzmanc, Marjeta Macek; Jancar, Bostjan; Suvorov, Danilo
Source:
JOURNAL OF SOLID STATE CHEMISTRY 183 (8): 1823-1828 AUG 2010
Abstract:
X-ray powder-diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), infrared spectroscopy (IR), thermogravimetry (TG) and mass spectroscopy (MS) were performed to investigate the composition and the crystal structure of tetra-barium di-niobate (V) Ba4Nb2O9. The TG, MS and IR studies revealed that the compound is a hydrated oxycarbonate. Assuming that the carbonate stoichiometrically replaces oxygen, the composition of the low-temperature alpha-modification, obtained by slow cooling from 1100 degrees C, corresponds to Ba4Nb2O8.8(CO3)(0.2)center dot 0.1H(2)O, while the quenched high-temperature gamma-modification has the Ba4Nb2O8.42(CO3)(0.58)center dot 0.38H(2)O composition. The alpha-phase has a composite incommensurately modulated structure consisting of two mutually interacting [Ba](infinity) and the [(Nb, square)O-3](infinity) subsystems. The composite modulated crystal structure of the alpha-phase can be described with the lattice parameters a=10.2688(1) angstrom, c=2.82426(8) angstrom, q=0.66774(2)c* and a superspace group R (3) over barm(00 gamma)0s. The HRTEM analysis demonstrates the nanoscale twinning of the trigonal domains parallel to the {1 0 0} crystallographic planes. The twinning introduces a one-dimensional disorder into the [(Nb, square(3)](infinity) subsystem, which results in an average P (6) over bar 2c crystal structure of the alpha-phase. Possible places for the carbonate group in the structure are discussed using a comparison with other hexagonal perovskite-based oxycarbonates. (C) 2010 Elsevier Inc. All rights reserved.
Title:
Magnetic structure of ErCu2Ge2
Authors:
Penc, B; Baran, S; Kaczorowski, D; Hoser, A; Szytula, A Author Full Names: Penc, B.; Baran, S.; Kaczorowski, D.; Hoser, A.; Szytula, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 503 (1): L18-L20 JUL 30 2010
Abstract:
The compound ErCu2Ge2 which crystallizes in the tetragonal ThCr2Si2-type crystal structure orders antiferromagnetically at low temperatures. At 1.4 K, the Er magnetic moments are arranged in a commensurate structure described by the propagation vector (k) over right arrow = [1/2, 0, 1/2]. The magnetic moment is equal to 6.80(7) mu(B) and forms an angle of 27 degrees with the c-axis. At T-t = 2.6 K an additional incommensurate magnetic structure appears and at higher temperatures both structures coexist and concurrently disappear at T-N = 3.1 K. The magnetic phase transitions at T-t and T-N clearly manifest themselves in the heat capacity and thermal expansion data of the compound. (C) 2010 Elsevier B.V. All rights reserved.

Update: 13-Aug-2010

Title:
Coexistence and Competition of Magnetism and Superconductivity on the Nanometer Scale in Underdoped BaFe1.89Co0.11As2
Authors:
Marsik, P; Kim, KW; Dubroka, A; Roessle, M; Malik, VK; Schulz, L; Wang, CN; Niedermayer, C; Drew, AJ; Willis, M; Wolf, T; Bernhard, C Author Full Names: Marsik, P.; Kim, K. W.; Dubroka, A.; Roessle, M.; Malik, V. K.; Schulz, L.; Wang, C. N.; Niedermayer, Ch.; Drew, A. J.; Willis, M.; Wolf, T.; Bernhard, C.
Source:
PHYSICAL REVIEW LETTERS 105 (5): Art. No. 057001 JUL 27 2010
Abstract:
We report muon spin rotation (mu SR) and infrared spectroscopy experiments on underdoped BaFe1.89Co0.11As2 which show that bulk magnetism and superconductivity (SC) coexist and compete on the nanometer length scale. Our combined data reveal a bulk magnetic order, likely due to an incommensurate spin density wave (SDW), which develops below T-mag approximate to 32 K and becomes reduced in magnitude (but not in volume) below T-c = 21.7 K. A slowly fluctuating precursor of the SDW seems to develop already below the structural transition at T-s approximate to 50 K. The bulk nature of SC is established by the mu SR data which show a bulk SC vortex lattice and the IR data which reveal that the majority of low-energy states is gapped and participates in the condensate at T << T-c.
Title:
Synthesis of Ti-Zr-Ni amorphous and quasicrystal powders by mechanical alloying, and their electrochemical properties
Authors:
Takasaki, A; Okuyama, T; Szmyd, JS Author Full Names: Takasaki, Akito; Okuyama, Tetsuya; Szmyd, Janusz S.
Source:
JOURNAL OF MATERIALS RESEARCH 25 (8): 1575-1582 AUG 2010
Abstract:
Mechanical alloying of Ti45Zr38-xNi17+x and Ti45-xZr38Ni17+x (0 <= x <= 8) elemental powders produced an amorphous phase, but subsequent annealing converted the amorphous phase into an icosahedral quasicrystal phase, along with a Ti2Ni-type phase. The discharge capacities, measured in a three-electrode cell at room temperature for both the amorphous and quasicrystal electrodes, increased with increasing Ni substitution for Zr or Ti. The highest discharge capacities, which were about 60 mAh/g for the amorphous electrode and 100 mAh/g for the quasicrystal electrode, were obtained from (Ti45Zr30Ni25) after substitution of Ni for Zr. For the Ti45Zr30Ni25 composition, the discharge performance of the quasicrystal electrode was stable over charge/discharge cycling, but that of the amorphous electrode gradually decreased with cycling. The structure of the quasicrystal phase in the electrodes was stable, even after 15 charge/discharge cycles, but the amorphous phase converted to a (Ti, Zr)H-2 f.c.c. hydride.
Title:
Relation between glass and quasicrystal formation in the Zr-Nb-Cu-Ni-Al alloys upon solidification
Authors:
Zhu, ZW; Zhang, W; Xie, GQ; Inoue, A Author Full Names: Zhu, Zhengwang; Zhang, Wei; Xie, Guoqiang; Inoue, Akihisa
Source:
APPLIED PHYSICS LETTERS 97 (3): Art. No. 031919 JUL 19 2010
Abstract:
We reported the relationship among the icosahedral short-range order (ISRO), glass formation and quasicrystal formation in the Zr-Nb-Cu-Ni-Al alloys. The alloys with the Nb addition stabilized ISRO, making the alloys form the amorphous, quasicrystal and crystal with decreasing the cooling rate. Not only bulk glass but also bulk quasicrystal were found to form for these alloys. The structural evolution from the amorphous phase, to the quasicrystal and crystals with the variation in the Nb content or the cooling rate is present. These findings were related to the degree of ISRO, which are advantageous for understanding the glass formation phenomenon. (C) 2010 American Institute of Physics. [doi:10.1063/1.3467827]

Update: 6-Aug-2010

Title:
Phase separation and ferroelectric ordering in charge-frustrated LuFe2O4-delta
Authors:
Yang, HX; Tian, HF; Zhang, Y; Qin, YB; Zeng, LJ; Ma, C; Shi, HL; Lu, JB Author Full Names: Yang, H. X.; Tian, H. F.; Zhang, Y.; Qin, Y. B.; Zeng, L. J.; Ma, C.; Shi, H. L.; Lu, J. B.
Source:
SOLID STATE COMMUNICATIONS 150 (31-32): 1467-1472 AUG 2010
Abstract:
The transmission electron microscopy observations of the charge ordering (CO) which governs the electronic polarization in LuFe2O4-delta clearly show the presence of a remarkable phase separation at low temperatures. Two CO ground states are found to adopt the charge modulations of Q(1) = (1/3, 1/3, 0) and Q(2) = (1/3 + epsilon, 1/3 + epsilon, 3/2), respectively. Our structural study demonstrates that the incommensurately Q(2)- modulated state is chiefly stable in samples with relatively lower oxygen contents. Data from theoretical simulations of the diffraction suggest that both Q(1)- and Q(2)- modulated phases have ferroelectric ordering. The effects of oxygen concentration on the phase separation and electric polarization in this layered system are discussed. (C) 2010 Elsevier Ltd. All rights reserved.
Title:
Extreme sensitivity of a frustrated quantum magnet: Cs2CuCl4
Authors:
Starykh, OA; Katsura, H; Balents, L Author Full Names: Starykh, Oleg A.; Katsura, Hosho; Balents, Leon
Source:
PHYSICAL REVIEW B 82 (1): Art. No. 014421 JUL 20 2010
Abstract:
We report a thorough theoretical study of the low temperature phase diagram of Cs2CuCl4, a spatially anisotropic spin S = 1/2 triangular lattice antiferromagnet, in a magnetic field. Our results, obtained in a quasi-one-dimensional limit in which the system is regarded as a set of weakly coupled Heisenberg chains, are in excellent agreement with experiment. The analysis reveals some surprising physics. First, we find that when the magnetic field is oriented within the triangular layer, spins are actually most strongly correlated within planes perpendicular to the triangular layers. This is despite the fact that the interlayer exchange coupling in Cs2CuCl4 is about an order of magnitude smaller than the weakest (diagonal) exchange in the triangular planes themselves. Second, the phase diagram in such orientations is exquisitely sensitive to tiny interactions, heretofore neglected, of order a few percent or less of the largest exchange couplings. These interactions, which we describe in detail, induce entirely new phases, and a novel commensurate-incommensurate transition, the signatures of which are identified in NMR experiments. We discuss the differences between the behavior of Cs2CuCl4 and an ideal two-dimensional triangular model, and in particular, the occurrence of magnetization plateaux in the latter. These and other related results are presented here along with a thorough exposition of the theoretical methods, and a discussion of broader experimental consequences to Cs2CuCl4 and other materials.
Title:
Magnetic excitations in Dy/Y superlattices as seen via inelastic neutron scattering
Authors:
Grunwald, ATD; Wildes, AR; Schmidt, W; Tartakovskaya, EV; Kwo, J; Majkrzak, C; Ward, RCC; Schreyer, A Author Full Names: Gruenwald, A. T. D.; Wildes, A. R.; Schmidt, W.; Tartakovskaya, E. V.; Kwo, J.; Majkrzak, C.; Ward, R. C. C.; Schreyer, A.
Source:
PHYSICAL REVIEW B 82 (1): Art. No. 014426 JUL 23 2010
Abstract:
Measurements of the spin excitations propagating normal to the interfaces in Dy/Y superlattices using neutron inelastic scattering are presented. For a given magnon momentum, a neutron-scattering spectrum shows multiple peaks at different energies, which indicates discrete energy spectra. The results are compared with theoretical calculations developed here to describe magnetic excitations in rare-earth superlattices. The theory accounts for Ruderman-Kittel-Kasuya-Yosida (RKKY) and Dzyaloshinsky-Moriya interactions in incommensurate helicoidal structures and achieves a quantitative agreement with the experimental data. This work demonstrates that neutron inelastic scattering can be used for systematic studies of the exchange interactions and spin dynamics in nanomagnetic systems over wide areas of the Brillouin zone.
Title:
Spatial inhomogeneities in iron pnictide superconductors: The formation of charge stripes
Authors:
Gor'kov, LP; Teitel'baum, GB Author Full Names: Gor'kov, Lev P.; Teitel'baum, Gregory B.
Source:
PHYSICAL REVIEW B 82 (2): Art. No. 020510 JUL 21 2010
Abstract:
The heterogeneous coexistence of antiferromagnetism (spin-density wave (SDW)] and superconductivity on a mesoscopic scale was observed in iron pnictides in many recent experiments. We suggest and discuss the scenario in which the heterogeneity is caused by formation of domain walls inherent to the SDW state of pnictides at a proper doping or under applied pressure. Superconductivity would emerge from the modulated SDW structure. The phenomenon is akin to the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) phase in superconductors.
Title:
Light localization in photonic band gaps of quasiperiodic dielectric structures
Authors:
Wang, K Author Full Names: Wang, Kang
Source:
PHYSICAL REVIEW B 82 (4): Art. No. 045119 JUL 23 2010
Abstract:
Localized light wave states in the photonic band gaps in two-dimensional octagonal and decagonal quasiperiodic dielectric media are investigated by considering the corresponding approximant structures. The structure effects on the local resonances at high-symmetry centers are studied in terms of the interscatterer correlation and the coupling strength between neighbor scatterers is analyzed as a function of the local symmetry order, the structure dielectric contrast, and the scatterer size. It is shown that an interscatterer distance threshold can be defined for the light localization regime. The threshold is determined by the geometrical and dielectric properties of the scatterers and independent of the local symmetry. It is thus likely a universal parameter for light localization in dielectric structures containing high-symmetry centers.
Title:
Symmetry and magnetoelectric interactions in BaMnF4
Authors:
Zvezdin, AK; Pyatakov, AP Author Full Names: Zvezdin, A. K.; Pyatakov, A. P.
Source:
LOW TEMPERATURE PHYSICS 36 (6): 532-537 JUN 2010
Abstract:
Symmetry analysis is used to study magnetic anisotropy and magnetoelectric interactions in the ferroelectric antiferromagnet BaMnF4 theoretically. It is shown that symmetry admits the existence in this material of a nonuniform magnetoelectric interaction (flexomagnetoelectric type) with a specific dependence on the magnitude and orientation of the external magnetic field. With increasing magnetic field this interaction can cause a phase transition into a magnetic incommensurate phase with a characteristic jump of the electric polarization. The linear and quadratic magnetoelectric effects and the question of the relativistic canting of the sublattices, which is due to the magnetoelectric interaction, are examined. The proposed approach is a natural generalization of the method of constructing invariants from the magnetic modes of the crystal to the case of phase transitions with a doubled unit cell of the crystal and can be used for symmetry analysis of other ferroelectric magnetic compounds. (c) 2010 American Institute of Physics. [doi:10.1063/1.3455798]
Title:
Quasicrystalline Tenfold Symmetry Order in Boron Compounds
Authors:
Miyazaki, Y; Okada, J; Abe, E; Yokoyama, Y; Kimura, K Author Full Names: Miyazaki, Yoshinobu; Okada, Junpei; Abe, Eiji; Yokoyama, Yoshihiko; Kimura, Kaoru
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (7): Art. No. 073601 JUL 2010
Abstract:
We report the first quasicrystalline boride formed in a rapidly-solidified B40Ti12Ru48 alloy, whose diffraction pattern clearly reveals a tenfold rotation axis of decagonal symmetry. The local structure appears to be significantly deviated from an ideal quasicrystal, but the long-range bond-orientational-order restricted by linkages between the robust unit-clusters has successfully generated the apparent 10-fold-symmetric Bragg peaks. This may be attributed to an extreme case of random-tiling quasicrystals, which enable the occurrence of local tiling disorders to account for entropy.
Title:
High-Temperature Multiferroic State of RBaCuFeO5 (R = Y, Lu, and Tm)
Authors:
Kawamura, Y; Kai, T; Satomi, E; Yasui, Y; Kobayashi, Y; Sato, M; Kakurai, K Author Full Names: Kawamura, Yuji; Kai, Takahiro; Satomi, Erika; Yasui, Yukio; Kobayashi, Yoshiaki; Sato, Masatoshi; Kakurai, Kazuhisa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (7): Art. No. 073705 JUL 2010
Abstract:
Magnetic and/or dielectric/ferroelectric behaviors have been studied for YBaCuFeO5, LuBaCuFeO5, and TmBaCuFeO5, which are members of oxygen-deficient ordered perovskite systems RBaCuFeO5 (R = lanthanide Ln and other trivalent elements) and have two magnetic transitions. The magnetic structure of the high-temperature (T) ordered phase is basically antiferromagnetic, and in the low-T ordered phase, a modulated magnetic component is superposed on the antiferromagnetic moments. The results of the pyrocurrent measurements indicate that electric polarization is induced in all these systems by the ordering to the modulated magnetic structure. For TmBaCuFeO5, the transition to this low-T phase is found at a temperature as high as the melting point of ice.
Title:
Elastic constants and anisotropic internal frictions of decagonal Al72Ni18Co8 single quasicrystal at low temperatures
Authors:
Tarumi, R; Ledbetter, H; Shiomi, S; Ogi, H; Hirao, M; Tsai, AP Author Full Names: Tarumi, R.; Ledbetter, H.; Shiomi, S.; Ogi, H.; Hirao, M.; Tsai, A. P.
Source:
JOURNAL OF APPLIED PHYSICS 108 (1): Art. No. 013514 JUL 2010
Abstract:
We studied the complete set of elastic constants C-ij and internal frictions tensor Q(ij)(-1) of anisotropic decagonal Al72Ni18Co8 single quasicrystal by electromagnetic acoustic resonance at low temperatures, to 5 K. Most C-ij(T) showed usual stiffening upon cooling and their temperature behaviors are well characterized by an Einstein-lattice-vibration model. The average Gruumlneisen parameter estimated from the bulk modulus is 2.4, almost identical to crystalline Al. Ambient temperature Q(ij)(-1) show a linear relationship to the elastic-constants temperature derivatives vertical bar dC(ij)/dT vertical bar/C-ij with a slope of 1.28 K-1, suggesting that lattice anharmonicity plays a dominant role for Q(ij)(-1). The longitudinal modulus for the decagonal axis C-33 and corresponding internal friction Q(33)(-1), however, showed significant deviation from such ideal behavior, suggesting additional low-frequency phonon-excitation modes along the decagonal axis.
Title:
Layers of order - the past, present and future of superspace crystallography
Authors:
Christensen, J Author Full Names: Christensen, Jeppe
Source:
CRYSTALLOGRAPHY REVIEWS 16 (2): 105-114 2010
Abstract:
The importance of having correct structural descriptions is becoming ever clearer, not only in drug discovery research, but also in the development of new advanced materials. Here the key to optimizing properties lies in understanding the structure-property relationships. Without a correct description theoretical calculations will inevitably fail to describe and explain any experimental observations. With increasing complexity of developed materials, modulated structures are likely to make up an increasing proportion of the structures to be investigated in the future. To take up this challenge, a development is needed in three areas of crystallography: The way we teach and what we teach our students; how we think about, and perform our crystallographic investigations; what tools are available, and how we use them. These areas are strongly coupled and any development in one is dependent on progress in the other two.

Update: 30-Jul-2010

Title:
Atomic dynamics of the alpha-(Al,Si)CuFe alloy: A crystalline approximant of a quasicrystal...
Authors:
Parshin, PP; Zemlyanov, MG; Brand, RA; Pavlyuchkov, D; Ollivier, J Author Full Names: Parshin, P. P.; Zemlyanov, M. G.; Brand, R. A.; Pavlyuchkov, D.; Ollivier, J.
Source:
PHYSICS OF THE SOLID STATE 52 (7): 1492-1498 JUL 2010
Abstract:
The atomic dynamics of the Al0.550Si0.070Cu0.255Fe0.125 alloy with the structure that approximates the structure of an icosahedral quasicrystal with a similar chemical composition has been investigated using inelastic neutron scattering. The partial vibrational spectra of copper, iron, and aluminum atoms and the total spectrum of thermal vibrations of the compound have been directly reconstructed from the experimental data for the first time. A combined analysis of the results obtained and the data on the atomic dynamics of the i-AlCuFe icosahedral quasicrystal has been performed.
Title:
Incommensurate Magnetic Order and Dynamics Induced by Spinless Impurities in YBa2Cu3O6.6
Authors:
Suchaneck, A; Hinkov, V; Haug, D; Schulz, L; Bernhard, C; Ivanov, A; Hradil, K; Lin, CT; Bourges, P; Keimer, B; Sidis, Y Author Full Names: Suchaneck, A.; Hinkov, V.; Haug, D.; Schulz, L.; Bernhard, C.; Ivanov, A.; Hradil, K.; Lin, C. T.; Bourges, P.; Keimer, B.; Sidis, Y.
Source:
PHYSICAL REVIEW LETTERS 105 (3): Art. No. 037207 JUL 16 2010
Abstract:
We report an inelastic-neutron-scattering and muon-spin-relaxation study of the effect of 2% spinless (Zn) impurities on the magnetic order and dynamics of YBa2Cu3O6.6, an underdoped high-temperature superconductor that exhibits a prominent spin pseudogap in its normal state. Zn substitution induces static magnetic order at low temperatures and triggers a large-scale spectral-weight redistribution from the magnetic resonant mode at 38 meV into uniaxial, incommensurate spin excitations with energies well below the spin pseudogap. These observations indicate a competition between incommensurate magnetic order and superconductivity close to a quantum critical point. Comparison to prior data on La2-xSrxCuO4 suggests that this behavior is universal for the layered copper oxides and analogous to impurity-induced magnetic order in one-dimensional quantum magnets.
Title:
Neutron-Scattering Measurement of Incommensurate Short-Range Order in Single Crystals of the S=1 Triangular Antiferromagnet NiGa2S4
Authors:
Stock, C; Jonas, S; Broholm, C; Nakatsuji, S; Nambu, Y; Onuma, K; Maeno, Y; Chung, JH Author Full Names: Stock, C.; Jonas, S.; Broholm, C.; Nakatsuji, S.; Nambu, Y.; Onuma, K.; Maeno, Y.; Chung, J. -H.
Source:
PHYSICAL REVIEW LETTERS 105 (3): Art. No. 037402 JUL 16 2010
Abstract:
Neutron scattering is used to investigate spin correlations in ultrapure single crystals of the S = 1 triangular lattice NiGa2S4. Despite a Curie-Weiss temperature of Theta(CW) = -80(2) K, static (T > 1 ns) short-range (zeta(ab) = 26(3) angstrom) incommensurate order prevails for T > 1.5 K. The incommensurate modulation Q(0) = (0.155(3), 0.155(3), 0), Theta(CW), and the spin-wave velocity (c = 4400 m/s) can be accounted for by antiferromagnetic third-nearest-neighbor interactions J(3) = 2.8(6) meV and ferromagnetic nearest-neighbor coupling J(1) = -0.35(9) J(3). Interplane correlations are limited to nearest neighbors and weakened by an in-plane field. These observations show that the short-range ordered glassy phase that has been observed in a number of highly degenerate systems can persist near the clean limit.
Title:
Single-crystal neutron diffraction study of the magnetic structure of Er3Co
Authors:
Gubkin, AF; Podlesnyak, A; Baranov, NV Author Full Names: Gubkin, A. F.; Podlesnyak, A.; Baranov, N. V.
Source:
PHYSICAL REVIEW B 82 (1): Art. No. 012403 JUL 13 2010
Abstract:
The effect of the magnetic field applied along the main crystallographic directions on the magnetic structure of Er3Co has been studied by means of single-crystal neutron diffraction technique. At zero field the compound exhibits a noncoplanar commensurate magnetic structure with ferromagnetic alignment of the Er magnetic-moment projections along the b axis in an orthorhombic unit cell. The present measurements revealed that the application of the magnetic field along the c direction [c perpendicular to (ab)] leads to the pronounced metamagneticlike transition in the low-field region mu H-0<1.2 T, although, the magnetization curve does not exhibit any anomalies. Combining the present single-crystal diffraction and magnetization data with the results of the previous powder neutron diffraction study [Gignoux et al., Solid State Commun. 8, 391 (1970)], we conclude that the nature of the magnetic ion, whether Kramers or non-Kramers, has a decisive effect on the commensurability of the magnetic structure of R3Co. In particular, the commensurate magnetic structure observed in Er3Co originate from the Kramers character of Er3+ ion in contrast to the incommensurate structures found earlier in R3Co with R= Tb and Ho.
Title:
Transition from a phase-segregated state to single-phase incommensurate sodium ordering in gamma-NaxCoO2(x approximate to 0.53)
Authors:
Feyerherm, R; Dudzik, E; Valencia, S; Wolter, AUB; Milne, CJ; Landsgesell, S; Alber, D; Argyriou, DN Author Full Names: Feyerherm, R.; Dudzik, E.; Valencia, S.; Wolter, A. U. B.; Milne, C. J.; Landsgesell, S.; Alber, D.; Argyriou, D. N.
Source:
PHYSICAL REVIEW B 82 (2): Art. No. 024103 JUL 13 2010
Abstract:
Synchrotron x-ray diffraction investigations of two single crystals of sodium cobaltate NaxCoO2 from different batches with composition x=0.525-0.530 reveal homogeneous incommensurate sodium ordering with propagation vector (0.53 0.53 0) at room temperature. The incommensurate (qq0) superstructure exists between 220 and 430 K. The value of q varies between q=0.514 and 0.529, showing a broad plateau at the latter value between 260 and 360 K. On cooling, an unusual reversible phase segregation into two volume fractions is observed. Below 220 K, one volume fraction shows the well-known commensurate orthorhombic x=0.50 superstructure while a second volume fraction with x=0.55 exhibits another commensurate superstructure, presumably with a 6a x 6a x c hexagonal supercell. We argue that the commensurate-to-incommensurate transition is an intrinsic feature of samples with Na concentrations x=0.5+ delta with delta approximate to 0.03.

Update: 23-Jul-2010

Title:
Magnetic structure of the edge-sharing copper oxide chain compound NaCu2O2
Authors:
Capogna, L; Reehuis, M; Maljuk, A; Kremer, RK; Ouladdiaf, B; Jansen, M; Keimer, B Author Full Names: Capogna, L.; Reehuis, M.; Maljuk, A.; Kremer, R. K.; Ouladdiaf, B.; Jansen, M.; Keimer, B.
Source:
PHYSICAL REVIEW B 82 (1): Art. No. 014407 JUL 12 2010
Abstract:
Single-crystal neutron diffraction has been used to determine the incommensurate magnetic structure of NaCu2O2, a compound built up of chains of edge-sharing CuO4 plaquettes. Magnetic structures compatible with the lattice symmetry were identified by a group-theoretical analysis and their magnetic structure factors were compared to the experimentally observed Bragg intensities. In conjunction with other experimental data, this analysis yields an elliptical helix structure in which both the helicity and the polarization plane alternate among copper-oxide chains. This magnetic ground state is discussed in the context of the recently reported multiferroic properties of other copper-oxide chain compounds.
Title:
Surface oxidation of the icosahedral Ag-In-Yb quasicrystal
Authors:
Nugent, PJ; Simutis, G; Dhanak, VR; McGrath, R; Shimoda, M; Cui, C; Tsai, AP; Sharma, HR Author Full Names: Nugent, P. J.; Simutis, G.; Dhanak, V. R.; McGrath, R.; Shimoda, M.; Cui, C.; Tsai, A. P.; Sharma, H. R.
Source:
PHYSICAL REVIEW B 82 (1): Art. No. 014201 JUL 9 2010
Abstract:
The oxidation of the high-symmetry surfaces of a single grain icosahedral (i) Ag-In-Yb quasicrystal has been studied using x-ray photoemission spectroscopy. The oxidation was carried out in vacuum, air, and water. It is found that air exposure results in the same degree of oxidation as exposure to oxygen in vacuum. The oxidation in water is more effective. Among the three constituent elements, the core levels of Yb are most affected by oxidation, Ag core levels are unchanged, and In shows moderate effects as expected from heats of formation of bulk oxides of the three elements. The comparison of the results with pure elements also reveals that the oxidation of Ag, In, and Yb in the quasicrystal is very similar to that of pure elements in all three environments. Scanning tunneling microscopy and low-energy electron diffraction reveal that oxidation destroys the quasicrystalline order of the clean surface.
Title:
Structural study by X-ray diffraction and transmission electron microscopy of the misfit compound (SbS1-xSex)(1.16)(Nb1.036S2)(2)
Authors:
Kars, M; Fredrickson, DC; Gomez-Herrero, A; Lidin, S; Rebbah, A; Otero-Diaz, LC Author Full Names: Kars, Mohammed; Fredrickson, Daniel C.; Gomez-Herrero, A.; Lidin, Sven; Rebbah, Allaoua; Otero-Diaz, L. C.
Source:
MATERIALS RESEARCH BULLETIN 45 (8): 982-988 AUG 2010
Abstract:
In the Sb-Nb-S-Se system, a new misfit layer compound (MSL) has been synthesized and its structure was determined by combining single crystal X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. It presents a composite crystal structure formed by (SbS1-xSex)slabs stacking alternately with double NbS2 layers and both can be treated as separate monoclinic subsystems. The (SbS1-xSex) slabs comprise a distorted, two-atom-thick layer with NaCl-type structure formed by an array of (SbX5) square pyramids joined by edges (X: S, Se); the NbS2 layers consist of (SbX5) trigonal prisms linked through edge-sharing to form sheets, just as in the 2H-NbS2 structure type. Both sublattices have the same lattice parameters a = 5.7672(19) angstrom, c = 17.618(6) angstrom and beta = 96.18(3)degrees, with incommensurability occurring along the b direction: b(1) = 3.3442(13) angstrom for the NbS2 subsystem and b(2) = 2.8755(13) angstrom for the (SbS1-xSex) subsystem. The occurrence of diffuse scattering intensity streaked along c* indicates that the (SbS1-xSex) subsystem is subjected to extended defects along the stacking direction. Published by Elsevier Ltd.

Update: 16-Jul-2010

Title:
Magnetic ordering and low-temperature thermodynamic properties of ErFe2Ge2
Authors:
Szytula, A; Kaczorowski, D; Baran, S; Penc, B; Gil, A; Hoser, A Author Full Names: Szytula, A.; Kaczorowski, D.; Baran, S.; Penc, B.; Gil, A.; Hoser, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 (19): 2973-2977 OCT 2010
Abstract:
Polycrystalline sample of ErFe2Ge2 was investigated by means of magnetic susceptibility, heat capacity and electrical resistivity measurements, as well as by powder neutron diffraction. All these experiments yielded an evidence of magnetic ordering setting at about 3 K. The low-temperature neutron data revealed the formation of a sine-modulated commensurate antiferromagnetic structure characterized by the propagation vector k=(0, 0, 14). The erbium magnetic moment is aligned parallel to the crystallographic a-axis. At T=1.55 K it is equal to 7.06(5) mu(B). (C) 2010 Elsevier B. V. All rights reserved.
Title:
Pattern analysis and interpretation of scattering from short-range order stacking in the layered composite crystal 2H-NaxCoO2 center dot yD(2)O (x similar or equal to 0.35, y similar or equal to 1.3)
Authors:
Onoda, M; Takada, K; Sasaki, T Author Full Names: Onoda, Mitsuko; Takada, Kazunori; Sasaki, Takayoshi
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 677-685 Part 4 AUG 2010
Abstract:
Information about the features of Bragg reflections and/or diffuse streaks was obtained through simulation of a neutron powder diffraction pattern based on the model used in a successful analysis of the superconductor 2H-NaxCoO2 center dot yD(2)O (x similar or equal to 0.35, y similar or equal to 1.3). Intensity distributions were calculated based on a superstructure expression of a commensurate composite crystal model, where the structures of the CoO2 part (a(1) = b(1) = 2.82 angstrom) and the guest (a(2) = b(2) = 3.26 angstrom) with short-range order stacking are described on a cell of A = B = 2a(1) = 3(1/2) a(2) = 5.64 angstrom, and with alternate stacking based on c = 4.9 angstrom. It is shown that the most conspicuous diffuse reflection band corresponds to the main reflection scattering of the guest sheet, with local maxima at half-integer positions of zeta' based on the stacking distance 2c, and that the Bragg diffraction components of the host and gues! t are coherent in terms of the peak height at integer zeta '' based on 4c.
Title:
Influence of quasicrystalline phase on transport processes in Zr70Pd30 amorphous alloy
Authors:
Pekala, K; Antonowicz, J; Jaskiewicz, P; Drobiazg, T; Konupek, J Author Full Names: Pekala, Krystyna; Antonowicz, Jerzy; Jaskiewicz, Piotr; Drobiazg, Tomasz; Konupek, Jan
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 500 (2): 145-148 JUN 25 2010
Abstract:
Electron transport and structural properties of amorphous Zr75Pd30 alloy are investigated by electrical resistivity, thermoelectric power, differential scanning calorimetry and X-ray diffraction methods. It was found that appearance of the icosahedral quasicrystalline phase in the first crystallization stage contributes to an increase of the electrical resistivity and Seebeck coefficient. Temperature variation of transport properties in amorphous phase excludes a variable range hopping model, which supplies unreasonable values of hopping energy and hopping distance. A similar degree of agreement between experimental results and both the Ziman and weak localization models is found for the electrical resistivity. However, a relatively high content of early transition Zr atoms in the alloy points rather that the weak localization may play a role. (C) 2010 Elsevier B.V. All rights reserved.
Title:
o '-Al13Co4, a new quasicrystal approximant
Authors:
Fleischer, F; Weber, T; Jung, DY; Steurer, W Author Full Names: Fleischer, F.; Weber, T.; Jung, D. Y.; Steurer, W.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 500 (2): 153-160 JUN 25 2010
Abstract:
The crystal structure of o '-Al13Co4, a new Al13TM4 (TM = transition metal) modification was determined by single-crystal X-ray diffraction. The phase, with Pearson symbol oP204-x (x=6), crystallizes in the orthorhombic space group Pnma (No. 62) with lattice parameters a = 28.890(4) angstrom, b = 8.138(2) angstrom and c = 12.346(1) angstrom. The structure, which can be seen as a stacking of four flat and puckered atomic layers along the pseudo-tenfold b axis, is closely related to o-Al13Co4 and m-Al13Co4. First-principles total-energy calculations indicate that all these related Al13Co4 modifications, some of them stabilized by vacancies, seem to be slightly unstable at low temperatures. (C) 2010 Elsevier B.V. All rights reserved.
Title:
The magnetoelectric effects in weak ferromagnetic YMn2O5 modulated structure: a Landau theory approach
Authors:
Tehranchi, MM; Phirouznia, A Author Full Names: Tehranchi, M. M.; Phirouznia, A.
Source:
EUROPEAN PHYSICAL JOURNAL B 75 (4): 439-442 JUN 2010
Abstract:
According to the group theory approach, linear magnetoelectric effect (ME) can not be obtained for the spatial group of YMn2O5, which was known to be mmm. Regard to the magnetic structure of these type of materials, we propose a magnetic group structure for the YMn2O5 by considering spin orientation of the Mn3+ and Mn4+ ions. According to the landau theory of phase transition it can be shown, how symmetrical rules result in relationship between quantities such as magnetic order, polarization, and etc. This relation shows a weak ferromagnetic state, associated with spontaneous polarization, arisen by Dzyaloshinskii-Moriya type interaction and a field induced change in magnetoelectrical susceptibility.

Update: 9-Jul-2010

Title:
THE Al-Cu-Ir ISOTHERMAL SECTION AT 800 degrees C IN THE ALUMINUM-RICH RANGE
Authors:
Kapush, DO; Grushko, B; Velikanova, TY Author Full Names: Kapush, D. O.; Grushko, B.; Velikanova, T. Ya.
Source:
POWDER METALLURGY AND METAL CERAMICS 49 (1-2): 79-85 MAY 2010
Abstract:
The partial isothermal section at 800 degrees C is represented for the first time. The structure of the Al-Cu-Ir alloys in the Al70Ir30-Al40Cu60-Al range, which are quenched from 800 degrees C, is investigated by SEM/EDX and XRD methods. Three ternary phases (decagonal quasicrystalline D-1, orthorhombic epsilon(6), and cubic (fcc) C-2) are stable at this temperature. The (Al9Ir2), phi, epsilon(6), D-1, gamma(1), and epsilon(2) phases coexist with a liquid phase at 800 degrees C.
Title:
Surface Charge Density Wave Phase Transition in NbSe3
Authors:
Brun, C; Wang, ZZ; Monceau, P; Brazovskii, S Author Full Names: Brun, Christophe; Wang, Zhao-Zhong; Monceau, Pierre; Brazovskii, Serguei
Source:
PHYSICAL REVIEW LETTERS 104 (25): Art. No. 256403 JUN 24 2010
Abstract:
The two charge-density wave (CDW) transitions in NbSe3 were investigated by scanning tunneling microscopy (STM) on an in situ cleaved (b, c) plane. The temperature dependence of first-order CDW satellite spots, obtained from the Fourier transform of the STM images, was measured between 5 and 140 K to extract the surface critical temperatures (T-s). The low-T CDW transition occurs at T-2s = 70-75 K, more than 15 K above the bulk T-2b = 59 K while at exactly the same wave number. A plausible mechanism for such an unusually high surface enhancement is a softening of transverse phonon modes involved in the CDW formation. The regime of 2D fluctuations is analyzed according to a Berezinskii-Kosterlitz-Thouless type of surface transition, expected for this incommensurate 2D CDW, by extracting the temperature dependence of the order parameter correlation functions.
Title:
Domains and Domain Walls in Multiferroic Ferroelectric-Ferromagnet and Control of Its Modulation
Authors:
Lykah, VA Author Full Names: Lykah, V. A.
Source:
FERROELECTRICS 398: 71-76 2010
Abstract:
Ferroelectric-ferromagnet with inhomogeneous exchange-relativistic magneto-electric interaction (Dzyaloshinskii-Moriya) is studied theoretically in external electric field. The domain wall combines properties of usual 180 degrees. one in ferroelectric and unusual magnetic one, consisting of linear topological defects (Bloch lines), situated periodically with large density. It is shown that the external electric field changes both ferroelectric and ferromagnetic subsystems. It is found that the helicoids step is formed in each domain in the magnetic subsystem and Bloch lines period demonstrates incommensurate structure. Final solution for magnetic moment in Bloch lines and modulated helicoids period near domain wall can be expressed in Jacobian elliptic functions.
Title:
Tricritical Behavior of Sn2P2S6 Ferroelectrics at Hydrostatic Pressure
Authors:
Vysochanskii, YM; Kohutych, AA; Kityk, AV; Zadorozhna, AV; Khoma, MM; Grabar, AA Author Full Names: Vysochanskii, Yu. M.; Kohutych, A. A.; Kityk, A. V.; Zadorozhna, A. V.; Khoma, M. M.; Grabar, A. A.
Source:
FERROELECTRICS 399: 83-88 2010
Abstract:
For Sn2P2S6 ferroelectrics with three-well potential under hydrostatic compression the second order phase transition approaches tricritical point as expected according to Blume-Emery-Griffiths (BEG) model. Joint consideration of BEG model and known ANNNI model, describing the incommensurate phase appearing as a result of competitive interactions, allows one to draw conclusion about possibility of tricritical point presence on temperature-pressure diagram of Sn2P2S6 without incommensurate phase appearing. Investigations of temperature dependences of longitudinal ultrasound velocity at different pressures for Sn2P2S6 crystals confirm such conclusion.
Title:
Synthesis, Spectroscopic and Magnetic Properties of the Co-2(OH)(PO4)(1-x)-(AsO4)(x) [0 <= x <= 1] Solid Solution
Authors:
de Pedro, I; Rojo, JM; Fernandez, JR; Lezama, L; Rojo, T Author Full Names: de Pedro, Imanol; Maria Rojo, Jose; Rodriguez Fernandez, Jesus; Lezama, Luis; Rojo, Teofilo
Source:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY (17): 2514-2522 JUN 2010
Abstract:
The Co-2(OH)(PO4)(1-x)(AsO4)(x) [0 <= x <= 1] solid solution was prepared by hydrothermal synthesis and, polycrystalline samples characterized by X-ray powder diffraction and spectroscopic measurements. The cell parameters of the isostructural phosphate-arsenate phases follow Vegard's law in the whole range of composition. The IR spectra are characteristic of three distinct features corresponding principally to the vibrations of both the hydroxide and tetrahedral (XO4)(3-) (X = P, As) groups together with the evolution of the intensity of stretching [vas (X-O)] vibration modes corresponding to the PO4 and AsO4 tetrahedra in the solid solution. Diffuse reflectance data show bands belonging to the octahedral and trigonal bipyramidal geometries of the Co2+ ions with a high degree of covalence in the Co-O bonds of the arsenate phases. Magnetization measurements of Co-2(OH)(PO4)(1-x)(AsO4)(x) [0 <= x <= 1] show the existence of antiferromagnetic interactions with the presence of a ferromagnetic component below the ordering temperature. TN decreases from 71 to 19 K as the arsenate amount is increased. ZFC-FC curves show irreversibility just below T-N for Co-2(OH)(PO4)(1-x)(AsO4)(x) [x = 0.1-0.75]. The magnetic behavior of Co-2(OH)(PO4)(0.1)(AsO4)(0.9) is completely different from the rest of the hydroxyphosphate-arsenate members and similar to that observed in the undoped arsenate compound where an incommensurate magnetic phase is observed.
Title:
Incommensurate spin density wave in Co-doped BaFe2As2
Authors:
Bonville, P; Rullier-Albenque, F; Colson, D; Forget, A Author Full Names: Bonville, P.; Rullier-Albenque, F.; Colson, D.; Forget, A.
Source:
EPL 89 (6): Art. No. 67008 MAR 2010
Abstract:
Fe-57 Mossbauer spectroscopy measurements are presented in the underdoped Ba(Fe1-xCox)(2)As-2 series for x=0.014 (T-c < 1.4K) and x=0.03 and 0.045 (T-c similar or equal to 2 and 12K, respectively). The spectral shapes in the so-called spin density wave (SDW) phase are interpreted in terms of incommensurate modulation of the magnetic structure, and allow the shape of the modulation to be determined. In undoped BaFe(2)A(s)2, the magnetic structure is commensurate, and we. nd that incommensurability is present at the lowest doping level (x= 0.014). As Co doping increases, the low-temperature modulation progressively loses its " squaredness" and tends to a sine-wave. The same trend occurs for a given doping level, as temperature increases. We. nd that a magnetic hyper. ne component persists far above the SDW transition, its intensity being progressively tranferred to a paramagnetic component on heating. Copyright (C) EPLA, 2010 Resistivity
Title:
Mossbauer spectroscopy of spin dynamics in MnxFe1-xSe0.85 superconductors: Evidence for an incommensurate-spin-density-wave state
Authors:
Hamdeh, HH; El-Tabey, MM; Asmatulu, R; Ho, JC; Huang, TW; Yeh, KW; Wu, MK Author Full Names: Hamdeh, H. H.; El-Tabey, M. M.; Asmatulu, R.; Ho, J. C.; Huang, T. W.; Yeh, K. W.; Wu, M. K.
Source:
EPL 89 (6): Art. No. 67009 MAR 2010
Abstract:
In the tetragonal crystalline structure of MnxFe(1-x)Se(0.85), the magnetic state contains low-and high-spin Fe2+, with high-spin numbers equal to that of the combined Mn substitute and Se deficiency atoms. The state is pinned by " spin-hopping" around substitution centers via highspin. low-spin conversions. During the structural distortion from tetragonal to orthorhombic, from 90K to 70K, the rate of spin conversions increases and the iterant character of the magnetic state is enhanced. In the orthorhombic structure, the spin dynamics evolve into an incommensurate spin-density wave (ISDW). Excitations of the ISDW decrease with temperature and level out across the superconducting phase. The ISDW appears to have more than one oscillation mode and contributions from high-order harmonics. Copyright (C) EPLA, 2010
Title:
Large increase in perpendicular giant magnetoresistance of quasiperiodic magnetic multilayers
Authors:
Tao, YC Author Full Names: Tao, Y. C.
Source:
EPL 90 (2): Art. No. 27005 APR 2010
Abstract:
Combining the transfer matrix method with Landauer-Buticker formalism, we study the spin-polarized transport in the current-perpendicular-to-the plane (CPP) geometry of a quasiperiodic magnetic multilayered structure consisting of a ferromagnet (FM) and a nonmagnet (NM) arranged in a Fibonacci sequence. The CPP giant magnetoresistance (GMR) in the quasiperiodic structure is found to be largely enhanced compared with that in the periodic one. It is also shown that there are the same and different properties in the variations of the relative conductivities and of the GMR with the number of bilayers between the quasiperiodic and periodic structures, implying that there exist common and different physical origins in them. Copyright (C) EPLA, 2010

Update: 2-Jul-2010

Title:
Synthesis and brittle-to-ductile transition of the omega-Al0.7Cu0.2Fe0.1 tetragonal phase
Authors:
Laplanche, G; Joulain, A; Bonneville, J; Gauthier-Brunet, V; Dubois, S Author Full Names: Laplanche, G.; Joulain, A.; Bonneville, J.; Gauthier-Brunet, V.; Dubois, S.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 527 (16-17): 4515-4518 JUN 25 2010
Abstract:
Synthesis of omega-Al-Cu-Fe single phase material is reported. Microhardness tests performed over the temperature range 293-898 K indicate a brittle-to-ductile transition between 673 K and 823 K. Fracture toughness was determined from indentation cracks at 293 K. Both the hardness and fracture toughness are comparable to that of the icosahedral Al0.635Cu0.240Fe0.125 material. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Structural themes in approximant and decagonal quasicrystalline phases in Al based alloys
Authors:
Boudard, M Author Full Names: Boudard, M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 495 (2): 365-371 APR 16 2010
Abstract:
The structure of two periodic phases in the Al-Pd-Mn system showing the importance of chemical ordering in the formation of decagonal quasicrystalline and approximant crystalline structures is reviewed Different descriptions of the periodic phases in terms of clusters, dense planes and pentagonal chains of transition metals are presented. We also review a structural model for AlPdMn decagonal quasicrystals derived from the general schematic distribution of TM existing in the approximant phases This model is discussed in relation of an unique decagonal overlapping cluster in a Penrose pentagonal tiling. (C) 2009 Elsevier B V All rights reserved.
Title:
Nanoquasicrystalline Al-Fe-Cr-based alloys with high strength at elevated temperature
Authors:
Galano, M; Audebert, F; Escorial, AG; Stone, IC; Cantor, B Author Full Names: Galano, Marina; Audebert, Fernando; Garcia Escorial, Asuncion; Stone, Ian C.; Cantor, Brian
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 495 (2): 372-376 APR 16 2010
Abstract:
Nanoquasicrystalline Al-Fe-Cr-based alloys have a microstructure composed of nanoquasicrystalline particles embedded in an alpha-Al matrix, and have high strength at elevated temperatures. However, the metastability of the quasicrystalline phase can limit the use of these alloys at elevated temperatures The microstructure, stability and mechanical properties at different temperatures on melt-spun nanoquasicrystalline Al-Fe-Cr-based alloys containing Ti, V, Nb or Ta have been studied and summarized in the present work The structural characterisation was carried out by means of X-ray diffraction, hot-stage transmission electron microscopy and scanning-transmission electron microscopy The addition of a fourth element to the Al-93(Fe3Cr2)(7) alloy increases the thermal stability, in particular in the case of the Nb and Ta containing alloys, leading to the delay of the phase transformation towards the melting of the alloys. The mechanical properties at elevated temperatures were studied by tensile tests at different test temperatures with different pre-heat treatments. All the alloys showed a very high strength up to 350 C, more than five times the strength of the commercial Al alloys. These values and the enhanced thermal stability achieved in the quaternary nanoquasicrystalline Al-Fe-Cr-(Ti, V, Nb or Ta) alloys make these alloys very promising for industrial applications. (C) 2009 Elsevier B.V All rights reserved
Title:
Laser remelting of Al91Fe4Cr3Ti2 quasicrystalline phase former alloy
Authors:
Gargarella, P; Vilar, R; Almeida, A; Kiminami, CS; Rios, CT; Bolfarini, C; Botta, WJ Author Full Names: Gargarella, P.; Vilar, R.; Almeida, A.; Kiminami, C. S.; Rios, C. T.; Bolfarini, C.; Botta, W. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 495 (2): 646-649 APR 16 2010
Abstract:
In the present work, an Al-Fe-Cr-Ti alloy with adequate composition to form quasicrystalline phases has been surface remelted using laser processing techniques The surface of spray formed Al91Fe4Cr3Ti2 bulk samples was remelted using a 2 kW CW Nd:YAG laser. Two different laser beam powers were applied with the goal of studying its influence in the quasicrystalline phase formation in the remelted coating. After laser treatment, the samples were characterized by X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (FEG-SEM). The formation of quasicrystalline phases was observed in the X-ray diffractograms and their transformations were verified in DSC analyses. A greater formation of quasicrystalline phase was verified in the coating produced with smaller laser beam power, i.e. higher cooling rate, and its morphology was more close to the sphere. The results indicate the possibility of producing low density coatings conta! ining quasicrystalline phases by laser remelting of spray formed materials Crown Copyright (C) 2009 Published by Elsevier B V All rights reserved.
Title:
Interdependence between glass stability and phase formation sequence during crystallization of Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass
Authors:
Mechler, N; Wanderka, N; Macht, MP Author Full Names: Mechler, S.; Wanderka, N.; Macht, M. -P.
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH 101 (5): 601-610 MAY 2010
Abstract:
Knowledge of the crystallization sequence of metallic glasses can yield a deep insight into the origin of their thermal stability. Crystallization of metallic glasses often leads to the simultaneous formation of different metastable crystalline phases that makes their identification difficult. In order to separate formation of crystalline phases from each other, long term isothermal pre-annealing below the glass transition temperature of Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk metallic glass prior to crystallization was performed. It is found that this pre-annealing strongly influences the crystallization sequence and depending on the pre-annealing time leads to preferential formation of different phases. In addition to the well known intermetallic Be2Zr phase and a quasicrystalline phase, three further previously unknown crystalline phases are identified and described in terms of their structure and composition. The formation of the crystalline phases is discussed with respect to the glass forming ability and thermal stability of the glass phase.
Title:
Strong crystalline field at the Fe site and spin rotation in olivine LiNi0.99 Fe-57(0.01) PO4 material by Mossbauer spectroscopy
Authors:
Kim, W; Rhee, CH; Kim, HJ; Moon, SJ; Kim, CS Author Full Names: Kim, Woochul; Rhee, Chan Hyuk; Kim, Hyung Joon; Moon, Seung Je; Kim, Chul Sung
Source:
APPLIED PHYSICS LETTERS 96 (24): Art. No. 242505 JUN 14 2010
Abstract:
The crystal structure of LiNi0.99 Fe-57(0.01) PO4 compound has been determined to be orthorhombic by Rietveld refinement method. Temperature dependence of magnetization M shows an anomalous antiferromagnetic behavior. A sudden change in both the magnitude of magnetic hyperfine field and its slope below 11 K suggests that magnetic phase transition related to the spin ordering takes place abruptly. From the result of Moumlssbauer measurement, it is shown that a strong electric crystalline field of octahedral symmetry including the contribution of spin-orbit coupling and magnetic hyperfine field by space-modulated spin structure is acted to the sites of Fe2+ ions simultaneously at low temperature. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3455312]
Title:
Structure factor for decorated Penrose tiling in physical space
Authors:
Kozakowski, B; Wolny, J Author Full Names: Kozakowski, Bartlomiej; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 66: 489-498 Part 4 JUL 2010
Abstract:
The structure factor for an arbitrarily decorated Penrose tiling has been calculated in the average unit cell description. The obtained formula uses only the physical coordinates of the atoms decorating a structure. The final equation can be easily extended so that it can describe the other physical properties of a structure. Its usefulness is demonstrated by its use in the Al-Ni-Co alloy structure-refinement process. (c) 2010 International Union of Crystallography Printed in Singapore - all rights reserved

Update: 25-Jun-2010

Title:
Polychromatic Photonic Quasicrystal Cavities
Authors:
Thon, SM; Irvine, WTM; Kleckner, D; Bouwmeester, D Author Full Names: Thon, Susanna M.; Irvine, William T. M.; Kleckner, Dustin; Bouwmeester, Dirk
Source:
PHYSICAL REVIEW LETTERS 104 (24): Art. No. 243901 JUN 14 2010
Abstract:
Photonic crystal slabs provide unique opportunities for the manipulation of light on semiconductor chips. The patterns of holes in the slabs are typically designed to maximize the width, depth and symmetry of a single photonic band gap. Quasicrystalline patterns are ideal from this point of view; here, we show that, owing to the presence of multiple Bragg scattering length scales, they also have the desirable property of supporting multiple photonic band gaps in the same slab. This opens up the possibility of creating polychromatic cavities that could be used to extend the possibilities for single photons on optical chips, including on-chip frequency conversion in III-V semiconductors. We study several quasicrystalline structures which support high quality cavity modes at multiple resonant frequencies using 2D and 3D FDTD simulations.
Title:
Symmetry replication and toroidic effects in the multiferroic pyroxene NaFeSi2O6
Authors:
Mettout, B; Toledano, P; Fiebig, M Author Full Names: Mettout, Bruno; Toledano, Pierre; Fiebig, Manfred
Source:
PHYSICAL REVIEW B 81 (21): Art. No. 214417 JUN 11 2010
Abstract:
The magnetoelectric and toroidic effects occurring in NaFeSi2O6 are analyzed theoretically. The symmetry-breaking mechanism giving rise to the incommensurate antiferromagnetic-ferroelectric phase observed below 6 K is shown to be induced by replication of a single transition order parameter. It implies an effective-continuous symmetry of the system identified as the phason rotation of the incommensurate order parameter. The magnetic-field induced toroidal moment is expressed in terms of the macroscopic and spin variables. It shows that the toroidal susceptibility components vary critically as the electric polarization, denoting the inherently magnetoelectric nature of the scaling properties of the ferrotoroidic state. The toroidal moment arising under applied field in antiferromagnetic-ferroelectric structures is induced simultaneously with a spin wave which exhibits the same symmetry properties but spans different degrees of freedom. The difference between microscopic spins degrees of freedom and the electromagnetic macroscopic magnetization and toroidal fields is emphasized.
Title:
Zigzag ladders with staggered magnetic chirality in the S=3/2 compound beta-CaCr2O4
Authors:
Damay, F; Martin, C; Hardy, V; Maignan, A; Andre, G; Knight, K; Giblin, SR; Chapon, LC Author Full Names: Damay, Francoise; Martin, Christine; Hardy, Vincent; Maignan, Antoine; Andre, Gilles; Knight, Kevin; Giblin, Sean R.; Chapon, Laurent C.
Source:
PHYSICAL REVIEW B 81 (21): Art. No. 214405 JUN 7 2010
Abstract:
The crystal and magnetic structures of the S=3/2 antiferromagnet beta-CaCr2O4 have been investigated by means of specific heat, magnetization, muon relaxation, and neutron powder diffraction between 300 and 1.5 K. In this compound, in which the unusual topology of the Cr3+ magnetic lattice can be described as a network of triangular "zigzag" ladders with legs parallel to c, a complex antiferromagnetic ordering with an incommensurate propagation vector k=(0,0,q) (q similar to 0.477 at 1.5 K) is evidenced below T-N=21 K. This complex magnetic ordering can be described as a honeycomblike arrangement of cycloids, running along c, and presenting a unique pattern of staggered chirality. To understand the experimental observation of this staggered chirality, we propose to use antisymmetric Dzyaloshinskii-Moriya terms in the exchange Hamiltonian.
Title:
Transport between twisted graphene layers
Authors:
Bistritzer, R; MacDonald, AH Author Full Names: Bistritzer, R.; MacDonald, A. H.
Source:
PHYSICAL REVIEW B 81 (24): Art. No. 245412 JUN 8 2010
Abstract:
Commensurate- incommensurate transitions are ubiquitous in physics and are often accompanied by intriguing phenomena. In few-layer graphene (FLG) systems, commensurability between honeycomb lattices on adjacent layers is regulated by their relative orientation angle theta, which is in turn dependent on sample preparation procedures. Because incommensurability suppresses interlayer hybridization, it is often claimed that graphene layers can be electrically isolated by a relative twist, even though they are vertically separated by a fraction of a nanometer. We present a theory of interlayer transport in FLG systems which reveals a richer picture in which the specific conductance depends sensitively on theta, single-layer Bloch-state lifetime, in-plane magnetic field, and bias voltage. We find that linear and differential conductances are generally large and negative near commensurate values of theta, and small and positive otherwise. We show that accounting for interlayer coupling may be essential for describing transport in FLG despite its physically insignificant effect on the band structure of the system.
Title:
IDENTIFICATION OF A QUASICRYSTALLINE PHASE IN THE Al-Cu-Fe SYSTEM
Authors:
Kalmykov, KB; Zvereva, NL; Dunaev, SF; Kazennov, NV Author Full Names: Kalmykov, K. B.; Zvereva, N. L.; Dunaev, S. F.; Kazennov, N. V.
Source:
METAL SCIENCE AND HEAT TREATMENT 51 (9-10): 440-443 SEP 2009
Abstract:
The methods of scanning and transmission electron microscopy, x-ray phase analysis, and energy dispersive microanalysis are used to study alloys of the Al - Cu - Fe system in the aluminum-rich domain. The range of existence of a quasicrystalline i-phase with composition Al62.5Cu25Fe12.5 is determined.
Title:
Single-molecule probing of incommensurate biphenyl
Authors:
Pars, M; Palm, V; Kikas, J Author Full Names: Paers, M.; Palm, V.; Kikas, J.
Source:
LOW TEMPERATURE PHYSICS 36 (5): 448-450 MAY 2010
Abstract:
Our data on the distribution of purely electronic linewidths of single molecules of terrylene in incommensurate biphenyl crystals are compared with the data obtained by other groups for different low-temperature organic solid hosts and with results of numerical simulations. The first two moments of the distributions measured within a narrow temperature interval have been used to calculate a single dimensionless parameter characterizing each of the respective hosts-the variation coefficient. It appears that different amorphous hosts have similar values of this coefficient, but the value obtained for the incommensurate crystal of biphenyl is significantly different. One can conclude that the remarkable single-molecule line broadening in biphenyl at 1.8 K cannot be solely explained by the interaction with two-level systems, which is considered to cause the broadening in amorphous hosts. (C) 2010 American Institute of Physics.
Title:
Observation of twin-like composition modulation and phase separation with long-range order induced by oxygen deficiency in single crystal manganites
Authors:
Jia, RR; Feng, ZJ; Wang, SP; Liu, YS; Jing, C; Cao, SX; Zhang, JC Author Full Names: Jia, Rongrong; Feng, Zhenjie; Wang, Shipeng; Liu, Yongsheng; Jing, Chao; Cao, Shixun; Zhang, Jincang
Source:
JOURNAL OF CRYSTAL GROWTH 312 (12-13): 1963-1967 JUN 1 2010
Abstract:
Single crystal La2/3Sr1/3MnO3-delta manganite with an unusual structure was obtained by the optical-floating method with controlled growth in a flowing argon atmosphere. A modulated twin-like structure with phase separation characteristics in the long-range order is found. The energy-dispersive X-ray spectroscopy measurement reveals that there is a strong chemical fluctuation for different stripes, i.e. resulting from the nonstoichiometry due to oxygen deficiency. After annealing, the twin-like stripe phase disappears and the single crystal shows excellent properties. These results may be of great significance for controlled growth of oxide electronics materials with artificial superstructure-like technique. (C) 2010 Elsevier B.V. All rights reserved.

Update: 18-Jun-2010

Title:
Effects of Nd and high-valence Mn co-doping on the electrical and magnetic properties of multiferroic BiFeO3 ceramics
Authors:
Hu, ZQ; Li, MY; Yu, Y; Liu, J; Pei, L; Wang, J; Liu, XL; Yu, BF; Zhao, XZ Author Full Names: Hu, Zhongqiang; Li, Meiya; Yu, Yang; Liu, Jun; Pei, Ling; Wang, Jing; Liu, Xiaolian; Yu, Benfang; Zhao, Xingzhong
Source:
SOLID STATE COMMUNICATIONS 150 (23-24): 1088-1091 JUN 2010
Abstract:
Pure BiFeO3 (BFO), 15% Nd doped BFO (BNF), and 15% Nd and 2% high-valence Mn co-doped BFO (BNFM) multiferroic ceramics were prepared by a rapid liquid phase sintering technique. A structural transition from rhombohedral R3c to orthorhombic P4mm occurred in the BNF and BNFM ceramics. The co-doped BNFM ceramics exhibit the largest dielectric constant, the smallest dielectric loss and leakage current, and an improved rectangular-shaped polarization hysteresis loop with a remnant polarization as high as 31 mu C/cm(2), which could be attributed to the lower concentration of charge defects and the structural transition. Besides, enhanced ferromagnetism is confirmed in BNFM with a remnant magnetization of 0.075 emu/g and a coercive magnetic field of 5.8 kOe, which might be attributed to the effective suppression of the spatially modulated spin structure by the Nd and Mn co-doping. (C) 2010 Elsevier Ltd. All rights reserved.
Title:
Hydrogen in the approximant i-TiZrHf: The energy state, charge, and diffusion
Authors:
Belov, MP; Isaev, EI; Vekilov, YK Author Full Names: Belov, M. P.; Isaev, E. I.; Vekilov, Yu. Kh.
Source:
PHYSICS OF THE SOLID STATE 52 (6): 1111-1114 JUN 2010
Abstract:
The energy of hydrogen dissolution in different tetrahedral pores of a 1/1 approximant of the icosahedral TiZrHf quasicrystal has been determined in terms of the density functional theory and ab initio pseudopotentials. At low and high degrees of loading of TiZrHf with hydrogen, the charges of atoms involved in the system and the Mayer bond order have been calculated for all possible M-M and M-H pairs. The diffusion coefficient of a single hydrogen atom in the system under study has been estimated numerically.
Title:
Frustration of the stable Zr-Ti-Ni quasicrystal as the basis of glass formation
Authors:
Mechler, S; Macht, MP; Schumacher, G; Zizak, I; Wanderka, N Author Full Names: Mechler, S.; Macht, M. -P.; Schumacher, G.; Zizak, I.; Wanderka, N.
Source:
PHYSICAL REVIEW B 81 (18): Art. No. 180101 MAY 1 2010
Abstract:
The origin of glass formation and the systematics of quasicrystal formation in Zr-Ti-Ni-(Cu-Be)-based metallic glasses is unraveled. Both are found to rely on frustration of the stable Zr41.5Ti41.5Ni17 quasicrystal. A systematic change in composition of the stable Zr-Ti-Ni quasicrystal prevents icosahedral order from direct growth in the deeply undercooled liquid and induces the glass transition. Quasicrystals form in the amorphous phase to reduce frustration, i.e., to recover the ideal symmetry and composition of the stable Zr-Ti-Ni quasicrystal. This relation is established especially by the discovery of a new type of sequential phase transformations of icosahedral quasicrystalline phases involving chemical redistribution.
Title:
Anisotropic physical properties of the Al13Fe4 complex intermetallic and its ternary derivative Al-13(Fe, Ni)(4)
Authors:
Popcevic, P; Smontara, A; Ivkov, J; Wencka, M; Komelj, M; Jeglic, P; Vrtnik, S; Bobnar, M; Jaglicic, Z; Bauer, B; Gille, P; Borrmann, H; Burkhardt, U; Grin, Y; Dolinsek, J Author Full Names: Popcevic, P.; Smontara, A.; Ivkov, J.; Wencka, M.; Komelj, M.; Jeglic, P.; Vrtnik, S.; Bobnar, M.; Jaglicic, Z.; Bauer, B.; Gille, P.; Borrmann, H.; Burkhardt, U.; Grin, Yu; Dolinsek, J.
Source:
PHYSICAL REVIEW B 81 (18): Art. No. 184203 MAY 1 2010
Abstract:
We have investigated the magnetic susceptibility, the electrical resistivity, the specific heat, the thermoelectric power, the Hall coefficient, and the thermal conductivity of the Al13Fe4 and Al13(Fe, Ni)(4) monoclinic approximants to the decagonal quasicrystal. While the Al13Fe4 crystals are structurally well ordered, the ternary derivative Al-13(Fe, Ni)(4) contains substitutional disorder and is considered as a disordered version of the Al13Fe4. The crystallographic-direction-dependent measurements were performed along the a*, b, and c directions of the monoclinic unit cell, where the (a*, c) atomic planes are stacked along the b direction. The electronic transport and the magnetic properties exhibit significant anisotropy. The stacking b direction is the most conducting direction for the electricity and heat. The effect of substitutional disorder in Al-13(Fe, Ni)(4) is manifested in the large residual resistivity rho(T -> O) and significantly reduced thermal conductivity of this compound, as compared to the ordered Al13Fe4. Specific-heat measurements reveal that the electronic density of states at the Fermi level of both compounds is high. The anisotropic Hall coefficient R-H reflects complex structure of the anisotropic Fermi surface that contains electronlike and holelike contributions. Depending on the combination of directions of the current and the magnetic field, electronlike (R-H<0) or holelike (R-H>0) contributions may dominate, or the two contributions compensate each other (R-H approximate to 0). Similar complicated anisotropic behavior was observed also in the thermopower. The anisotropic Fermi surface was calculated ab initio using the atomic parameters of the refined Al13Fe4 structural model that is also presented in this work.
Title:
Anisotropic physical properties of the Taylor-phase T-Al72.5Mn21.5Fe6.0 complex intermetallic
Authors:
Heggen, M; Feuerbacher, M; Ivkov, J; Popcevic, P; Batistic, I; Smontara, A; Jagodic, M; Jaglicic, Z; Janovec, J; Wencka, M; Dolinsek, J Author Full Names: Heggen, M.; Feuerbacher, M.; Ivkov, J.; Popcevic, P.; Batistic, I.; Smontara, A.; Jagodic, M.; Jaglicic, Z.; Janovec, J.; Wencka, M.; Dolinsek, J.
Source:
PHYSICAL REVIEW B 81 (18): Art. No. 184204 MAY 1 2010
Abstract:
We have investigated anisotropic physical properties (the magnetic susceptibility, the electrical resistivity, the thermoelectric power, the Hall coefficient and the thermal conductivity) of the single-crystalline Taylor-phase T-Al72.5Mn21.5Fe6.0 complex intermetallic that is an orthorhombic approximant to the d-Al-Mn-Pd decagonal quasicrystal. The measurements were performed along the a, b, and c directions of the orthorhombic unit cell, where (a, c) atomic planes are stacked along the perpendicular b direction. The T-Al72.5Mn21.5Fe6.0 shows spin-glass behavior below the spin-freezing temperature T-f approximate to 29 K with a small anisotropy in the magnetic susceptibility. The anisotropic electrical resistivities are rather large and show negative temperature coefficient. The resistivity is lowest along the stacking direction, which appears to be a common property of the decagonal-approximant phases with a stacked-layer structure. The temperature-dependent resis! tivity was theoretically reproduced by the quantum transport theory of slow charge carriers. The thermopower is positive for all three crystallographic directions, indicating that holes are the majority charge carriers, and no anisotropy can be claimed within the experimental precision. The same conclusion on the holes being the dominant charge carriers follows from the Hall-coefficient measurements, which is a sum of the (positive) normal Hall coefficient and the anomalous term, originating from the magnetization. The anisotropy of the thermal conductivity is practically negligible. The T-Al72.5Mn21.5Fe6.0 Taylor phase can be considered as a "close-to-isotropic" complex intermetallic. The relation of the anisotropic physical properties of the Taylor phase to other families of decagonal-approximant phases with the stacked-layer structure is discussed.
Title:
Incommensurate spin-density wave and magnetic lock-in transition in CaFe4As3
Authors:
Manuel, P; Chapon, LC; Todorov, IS; Chung, DY; Castellan, JP; Rosenkranz, S; Osborn, R; Toledano, P; Kanatzidis, MG Author Full Names: Manuel, P.; Chapon, L. C.; Todorov, I. S.; Chung, D. Y.; Castellan, J. -P.; Rosenkranz, S.; Osborn, R.; Toledano, P.; Kanatzidis, M. G.
Source:
PHYSICAL REVIEW B 81 (18): Art. No. 184402 MAY 1 2010
Abstract:
The magnetic structure for the recently synthesized iron-arsenide compound CaFe4As3 has been studied by neutron-powder diffraction. Long-range magnetic order is detected below 85 K, with an incommensurate modulation described by the propagation vector k=(0, delta, 0), delta similar to 0.39. Below similar to 25 K, our measurements detect a first-order phase transition where delta locks into the commensurate value 3/8. A model of the magnetic structure is proposed for both temperature regimes, based on Rietveld refinements of the powder data and symmetry considerations. The structures correspond to longitudinal spin-density waves with magnetic moments directed along the b axis. A Landau analysis captures the change in thermodynamic quantities observed at the two magnetic transitions, in particular, the drop in resistivity at the lock-in transition.
Title:
H-T phase diagram of the two-dimensional Ising model with exchange and dipolar interactions
Authors:
Diaz-Mendez, R; Mulet, R Author Full Names: Diaz-Mendez, Rogelio; Mulet, Roberto
Source:
PHYSICAL REVIEW B 81 (18): Art. No. 184420 MAY 1 2010
Abstract:
We explore the equilibrium properties of a two-dimensional Ising spin model with short-range exchange and long-range dipolar interactions as a function of the applied magnetic field H. The model is studied through extensive Monte Carlo simulations that show the existence of many modulated phases with long-range orientational order for a wide range of fields. These phases are characterized by different wave vectors that change discontinuously with the magnetic field. In particular, the emergence of novel anharmonic phases that keep the orientational order but are characterized by several wave vectors is studied in detail. We provide numerical evidence supporting the existence of first-order transitions between modulated phases. At higher fields our results suggest a Kosterliz-Thouless scenario for the transition from a bubble to a ferromagnetic phase.
Title:
Synthesis of natural superlattice structure in the binary ZnO-Fe2O3 system by microwave irradiation
Authors:
Katayose, S; Miyazaki, T; Hayashi, Y; Takizawa, H Author Full Names: Katayose, Satomi; Miyazaki, Takamichi; Hayashi, Yamato; Takizawa, Hirotsugu
Source:
JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 118 (1377): 387-389 MAY 2010
Abstract:
Homologous compounds, Fe2O3(ZnO)(m), with the modulated natural superlattice structure were obtained within a short period by solid state reaction of component oxides under 2.45 GHz microwave irradiation. TEM observation revealed that two types of superlattice structures were observed in different Fe concentration; one is longitudinal superlattice structure in a rod shaped precipitation at high Fe concentration, and the other is modulated structure showing zigzag shape at low Fe concentration. It is conclude that the non-equilibrium nature of microwave selective heating, as well as rapid heating and quenching effects, plays a key role to form the superstructure. The obtained products exhibit ferromagnetic behavior with the Curie temperature above 300 K. (C) 2010 The Ceramic Society of Japan. All rights reserved.
Title:
Deformation-induced structural transformation leading to compressive plasticity in Zr65Al7.5Ni10Cu12.5M5 (M = Nb, Pd) glassy alloys
Authors:
Setyawan, AD; Saida, J; Kato, H; Matsushita, M; Inoue, A Author Full Names: Setyawan, Albertus D.; Saida, Junji; Kato, Hidemi; Matsushita, Mitsuhide; Inoue, Akihisa
Source:
JOURNAL OF MATERIALS RESEARCH 25 (6): 1149-1158 JUN 2010
Abstract:
Zr65Al7.5Ni10Cu12.5Nb5 glass was found to exhibit a large plastic compressive strain of over 10% and the property was suggested to be due to deformation-induced nanocrystallization. A transmission electron microscopic observation, however, only revealed obscure ordered clusters with a size of similar to 2 nm in the fracture surface of a deformed sample, instead of well-identified crystals as previously reported for the Zr-Al-Ni-Cu-Pd system. This phenomenon is suggested to correlate with the higher viscosity of supercooled liquid and the slower grain growth of icosahedral phase during primary crystallization in the Zr65Al7.5Ni10Cu12.5Nb5 compared to those in the Zr65Al7.5Ni10Cu12.5Pd5 alloy. The role of the deformation-induced nanoclusters on the enhanced compressive plasticity was discussed.
Title:
Structural and magnetic properties of magnetron sputtered Ni-Mn-Sn ferromagnetic shape memory alloy thin films
Authors:
Vishnoi, R; Kaur, D Author Full Names: Vishnoi, Ritu; Kaur, Davinder
Source:
JOURNAL OF APPLIED PHYSICS 107 (10): Art. No. 103907 MAY 15 2010
Abstract:
In the present study, structural and magnetic properties of Mn-rich, off-stoichiometric, nanocrystalline Ni-Mn-Sn ferromagnetic shape memory alloy thin films, grown on Si (100) substrates at 550 degrees C by dc magnetron sputtering have been systematically investigated. The crystallization, surface morphology, and structural features were studied using x-ray diffraction, atomic force microscopy, and field emission scanning electron microscopy. The structural transition from austenite to martensite was observed with an increase of Mn content. Austenitic phase with mixed L2(1)/A2+B2 structure has been observed at room temperature in Ni52.6Mn23.7Sn23.6 (S-1) and Ni51.5Mn26.1Sn22.2 (S-2) films, while those with composition of Ni58.9Mn28.0Sn13.0 (S-3) and Ni58.3Mn29.0Sn12.6 (S-4) show martensitic phase with 14M modulated monoclinic structures. Field induced martensite-austenite transformation has been observed in magnetization studies using superconducting quantum interference device magnetometer. Temperature dependent magnetization measurements demonstrate the influence of magnetic field on the structural phase transition temperature. The investigations reveal an increase of martensitic transformation temperature (T-M) with corresponding increase in substitution of Mn. The films exhibit ferromagnetic behavior at low temperatures below Curie temperature (T-C). The decrease in saturation moment with increasing Mn content, indicates the existence of antiferromagnetic correlations within ferromagnetic matrix. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3393961]

Update: 3-Jun-2010

Title:
Muon spin relaxation study of the layered magnetoelectric FeTe2O5Br with spin amplitude modulated magnetic structure
Authors:
Zorko, A; Pregelj, M; Berger, H; Arcon, D Author Full Names: Zorko, A.; Pregelj, M.; Berger, H.; Arcon, D.
Source:
JOURNAL OF APPLIED PHYSICS 107 (9): Art. No. 09D906 MAY 1 2010
Abstract:
Local-probe weak-transverse-field and zero-field mu SR measurements have been employed to investigate magnetic ordering in the new magnetoelectric compound FeTe2O5Br. Below the Neel transition temperature T-N=10.6 K a static local magnetic field starts to develop at the mu(+) sites. Fast mu(+) polarization decay below T-N speaks in favor of a broad distribution of internal magnetic fields, in agreement with the incommensurate magnetic structure suggested by neutron diffraction experiments. Above T-N the presence of short-range order is detected as high as at 2T(N), which suggests only weak interlayer magnetic coupling. On the other hand, strong Fe3+ spin fluctuations likely reflect geometrically frustrated structure of [Fe4O16](20-) spin clusters, which are the main building blocks of the layered FeTe2O5Br structure. (C) 2010 American Institute of Physics. [doi:10.1063/1.3362909]
Title:
Hall Coefficient of the Y-Al-Ni-Co Decagonal Approximant
Authors:
Stanic, D; Ivkov, J; Dolinsek, J; Gille, P Author Full Names: Stanic, Denis; Ivkov, Jovica; Dolinsek, Janez; Gille, Peter
Source:
CROATICA CHEMICA ACTA 83 (1): 7-10 Sp. Iss. SI APR 2010
Abstract:
We have investigated anisotropic Hall coefficient of Y-Al-Ni-Co decagonal approximant of the Al76Co22Ni2 composition. The crystalline-direction-dependent studies were performed along three orthogonal directions a*, b and c of the Y-Al-Ni-Co unit cell, where (a,c) monoclinic atomic planes are stacked along the perpendicular b direction. Hall coefficient R-H exhibits pronounced anisotropy, while at the same time the magnetic field in a given crystalline direction yields the same R-H for the current along the other two crystalline directions in the perpendicular plane. The observed anisotropy is studied in terms of the anisotropic structure of the Y-Al-Ni-Co phase and Fermi surface. The results are compared to the anisotropy of the Hall coefficient of the d-Al-Ni-Co decagonal quasicrystal reported in literature.
Title:
Anisotropic Transport Properties of the Orthorhombic Al13Co4 Approximant to the Decagonal Quasicrystal
Authors:
Lukatela, J; Stanic, D; Popcevic, P; Ivkov, J; Dolinsek, J; Gille, P Author Full Names: Lukatela, Jagoda; Stanic, Denis; Popcevic, Petar; Ivkov, Jovica; Dolinsek, Janez; Gille, Peter
Source:
CROATICA CHEMICA ACTA 83 (1): 27-32 Sp. Iss. SI APR 2010
Abstract:
Anisotropic transport properties (electrical resistivity, thermoelectric power, Hall coefficient and thermal conductivity) of the o-Al13Co4 orthorhombic approximant to the decagonal phase were investigated. The crystalline-direction-dependent measurements were performed along the a, b and c directions of the orthorhombic unit cell, where (b, c) atomic planes are stacked along the perpendicular a direction. Anisotropic electrical and thermal conductivities are the highest along the stacking a direction. The anisotropic thermoelectric power changes sign with the crystalline direction and so does the anisotropic Hall coefficient, which changes from the negative electron-like to the positive hole-like for different combinations of the electric current and magnetic field direction. The transport properties of the o-Al13Co4 phase were compared to the literature data on approximant to the decagonal quasicrystals, the Al76Co22Ni2 and the Al80Cr15Fe5, allowing for the study of evolution of transport properties with increasing structural complexity and unit cell size.
Title:
The Influence of Thermal Treatment on Magnetic Moments in i-Al-Pd-Mn Quasicrystals
Authors:
Jagodic, M; Jaglicic, Z; Grushko, B; Dolinsek, J Author Full Names: Jagodic, Marko; Jaglicic, Zvonko; Grushko, Benjamin; Dolinsek, Janez
Source:
CROATICA CHEMICA ACTA 83 (1): 39-42 Sp. Iss. SI APR 2010
Abstract:
The influence of cooling rate on thermal strains in the quasicrystalline icosahedral Al-Pd-Mn complex metallic alloy was investigated. In general, measurements of the electronic magnetization can be used as an indirect method for determining the short-scale disorder in the crystal structure as the magnetic moments at the Mn sites are highly dependent on their local environment. Excluding the contributions of thermal vacancies and second phase precipitates by proper selection of preannealing temperatures and durations, the changes in magnetization can be ascribed to the appearance or disappearance of thermal strains in the crystal structure. It was found that water-quenching increases thermal strains irrespective of previous thermal history.
Title:
The Solidification Path of the Complex Metallic Al-Mn-Be Alloy
Authors:
Markoli, B; Boncina, T; Zupanic, F Author Full Names: Markoli, Bostjan; Boncina, Tonica; Zupanic, Franc
Source:
CROATICA CHEMICA ACTA 83 (1): 49-54 Sp. Iss. SI APR 2010
Abstract:
The solidification paths of the Al86.1Mn2.5Be11.4 and Al84Mn5.1Be10.9 alloys, melt spun, cast into a copper mould and controlled cooled (during DSC) were investigated by means of light-optical microscopy (LOM), differential scanning calorimetry (DSC) combined with thermogravimetry (TG) or simultaneous thermal analysis (STA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Auger electron spectroscopy (AES) and the X-ray diffraction (XRD) line in Elletra Trieste, Italy. The constitutions of samples from both alloys were examined in all three states, i.e., after melt spinning, after casting into a copper mould and after differential scanning calorimetry. It was established that in the cast and controlled-cooled specimens the alloys consisted of an aluminium-rich alpha(Al)-matrix, and the Al4Mn and Be4AlMn phases. In the case of casting and DSC the primary crystallization began with the precipitation of the Be4AlMn phase, followed by what can most lik! ely be characterized as a uni-variant binary eutectic reaction L -> (Be4AlMn + Al4Mn). The solidification process continued with an invariant ternary eutectic reaction, where the remaining melt (L) formed the heterogeneous structure (alpha(Al) + Al4Mn + Be4AlMn) or a ternary eutectic. When extremely high cooling rates were employed, as is the case with melt-spinning, the constituting phases of both alloys were precipitated in a very small form and the Be4AlMn phase was completely absent in the form of primary polygonal particles and replaced by the icosahedral quasicrystalline phase or the i-phase. There was also no evidence of the Al4Mn phase. The distribution, size and shape of all the constituents in the melt-spun alloys also varied from the contact surface towards the free surface of the ribbons. The smallest constituents were established at the contact surface, measuring less than 0.1 mu m, to 0.5 mu m at the free surface. The grains of the aluminium-rich matrix had mean diameters of less than 20 mu m, close to the free surface, down to 1 mu m at the contact surface.
Title:
Open Theoretical Problems in the Physics of Aperiodic Systems
Authors:
Jagannathan, A Author Full Names: Jagannathan, Anuradha
Source:
CROATICA CHEMICA ACTA 83 (1): 59-63 Sp. Iss. SI APR 2010
Abstract:
Quasicrystals have intrigued and stimulated research in a large number of disciplines. Mathematicians, physicists, chemists, metallurgists and materials scientists have found in them a fertile ground for new insights and discoveries. In the quarter century that has ensued since the publication of the experimental observation of a quasiperiodic Al-Mn alloy,(1) many different kinds of quasiperiodic alloys have been manufactured and studied. The physical properties of quasicrystals are no less interesting than the unusual structural properties that led to their discovery in 1984. In this review, some of the properties that characterize quasicrystals are presented, several types of theories that have been put forward briefly discussed, and some new behaviors that might be investigated by experiment described.
Title:
Anisotropic Transport Properties of Complex Metallic Alloys
Authors:
Smontara, A; Dolinsek, J Author Full Names: Smontara, Ana; Dolinsek, Janez
Source:
CROATICA CHEMICA ACTA 83 (1): 75-80 Sp. Iss. SI APR 2010
Abstract:
Anisotropic transport properties (electrical resistivity, rho, and thermal conductivity, kappa) of the Y-phase Al-Ni-Co, o-Al13Co4 and Al-4(Cr,Fe) complex metallic alloys were investigated. They belong to the class of decagonal approximant phases with stacked-layer crystallographic structure and allowed us to study the evolution of anisotropic transport properties with increasing structural complexity and the unit cell size.
Title:
Anisotropic Transport Properties of the Al13Fe4 Decagonal Approximant
Authors:
Popcevic, P; Smontara, A; Dolinsek, J; Gille, P Author Full Names: Popcevic, Petar; Smontara, Ana; Dolinsek, Janez; Gille, Peter
Source:
CROATICA CHEMICA ACTA 83 (1): 101-105 Sp. Iss. SI APR 2010
Abstract:
We have investigated electrical resistivity, thermoelectric power and thermal conductivity of the Al13Fe4 monoclinic approximant to the decagonal quasicrystal. The crystallographic-direction-dependent measurements were performed along the a*, b and c directions of the monoclinic unit cell, where (a*,c) atomic planes are stacked along the perpendicular b direction. The electronic transport exhibit significant anisotropy. The stacking b direction is the most conducting direction for the electricity and heat. The anisotropic thermopower reflects complicated structure of the anisotropic Fermi surface that contains electron-like and hole-like contributions.
Title:
Hall Effect of the Al13Fe4 Decagonal Approximant and Its Ternary Extension Al-13(Fe,Ni)(4)
Authors:
Ivkov, J; Popcevic, P; Dolinsek, J; Gille, P Author Full Names: Ivkov, Jovica; Popcevic, Petar; Dolinsek, Janez; Gille, Peter
Source:
CROATICA CHEMICA ACTA 83 (1): 107-111 Sp. Iss. SI APR 2010
Abstract:
We have measured Hall coefficient and electrical resistivity of the Al13Fe4 and Al-13(Fe,Ni)(4) monoclinic approximants to the decagonal quasicrystal. While the Al13Fe4 crystals are structurally well ordered, the ternary extension Al-13(Fe,Ni)(4) contains quenched disorder and can be viewed as a disordered version of Al13Fe4. The crystallographic-direction-dependent Hall effect measurements were performed along the a*, b and c directions of the monoclinic unit cell, where (a*,c) atomic planes are stacked along the perpendicular b direction. The stacking b direction is the most conducting direction for the electricity. The effect of quenched disorder in Al-13(Fe,Ni)(4) is manifested in the large residual resistivity rho(T -> 0) as compared to the ordered Al13Fe4. The Hall coefficient, R-H, values for all combinations of directions, are typical metallic. The anisotropic Hall coefficient reflects complicated structure of the anisotropic Fermi surface that contains electron-like and hole-like parts. Depending on the combination of directions of the current and magnetic field electron-like (R-H < 0) or hole-like (R-H > 0) contributions may dominate, or the two contributions compensate each other (R-H approximate to 0).
Title:
Lattice dynamics and structural phase transitions
Authors:
Shapiro, SM Author Full Names: Shapiro, S. M.
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 99 (3): 543-548 Sp. Iss. SI JUN 2010
Abstract:
Results of lattice dynamics, or atomic motions in a solid, explain many of the thermodynamic properties of solids. Inelastic neutron scattering conveniently explores the atomic motions, quantized as phonons. Of particular interest are materials that undergo structural phase transitions. The soft mode theory has been successful in relating anomalous phonon behavior to structural changes in solids. One such example is the ferromagnetic shape memory alloy, Ni2MnGa, which undergoes a sequence of phase transitions leading to a magnetic, incommensurate modulated, tetragonal phase as the ground state. The experiments, coupled with first principles calculations, provide evidence that strong electron-phonon coupling is the driving mechanism of the phase transformation.
Title:
Comparing properties of substrate-constrained and freestanding epitaxial Ni-Mn-Ga films
Authors:
Backen, A; Yeduru, SR; Kohl, M; Baunack, S; Diestel, A; Holzapfel, B; Schultz, L; Fahler, S Author Full Names: Backen, Anja; Yeduru, Srinivasa R.; Kohl, Manfred; Baunack, Stefan; Diestel, Anett; Holzapfel, Bernhard; Schultz, Ludwig; Faehler, Sebastian
Source:
ACTA MATERIALIA 58 (9): 3415-3421 MAY 2010
Abstract:
In order to use the magnetic shape memory alloy Ni-Mn-Ga with its high achievable strain of up to 10% for microactuators, freestanding epitaxial films are required. Here we show that these conditions can be fulfilled when using chromium as a sacrificial layer. The low misfit towards Ni-Mn-Ga enables epitaxial growth. Furthermore, Cr can afterwards be removed selectively by wet-chemical etching and during deposition no significant interdiffusion is observed. The structure, microstructure and magnetic properties of micrometer thick films are not affected by the etching process. Films are ferromagnetic at room temperature and we observe the coexistence of non-modulated (NM) and seven layered modulated (14 M) martensite. Tensile stress-strain measurement of a freestanding bridge reveals a broad strain plateau of 12% at a twinning stress of 25 MPa, indicating reorientation of NM variants. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 27-May-2010

Title:
Phenomenological theory of phase transitions in multiferroic MnWO4: magnetoelectricity and modulated magnetic order
Authors:
Sakhnenko, VP; Ter-Oganessian, NV Author Full Names: Sakhnenko, V. P.; Ter-Oganessian, N. V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (22): Art. No. 226002 JUN 9 2010
Abstract:
The phenomenological theory of phase transitions in multiferroic MnWO4 is suggested. The theoretical model uses the assumption that the magnetic order is driven by the instability in the (1/4; 1/2; 1/2) point of the Brillouin zone, which is justified by the symmetry of the low-temperature magnetic phase. It is shown that the experimentally observed incommensurate magnetic order is due to the Lifshitz invariants allowed for the corresponding order parameters. Invariants responsible for the magnetoelectric interaction are found and a schematic phase diagram is calculated. The influence of the magnetic field on the phase transition sequence is also analyzed. It is suggested that the description of the phase transitions in MnWO4 starting from the orthorhombic praphase significantly simplifies the approach and allows us to draw important conclusions.
Title:
TEM-assisted dynamic scanning force microscope imaging of (001) antigorite: Surfaces and steps on a modulated silicate
Authors:
Palacios-Lidon, E; Grauby, O; Henry, C; Astier, JP; Barth, C; Baronnet, A Author Full Names: Palacios-Lidon, Elisa; Grauby, Olivier; Henry, Claude; Astier, Jean-Pierre; Barth, Clemens; Baronnet, Alain
Source:
AMERICAN MINERALOGIST 95 (5-6): 673-685 MAY-JUN 2010
Abstract:
Ultra-high vacuum dynamic scanning force microscopy (dynamic SFM) has been performed on in situ cleaved and as-grown (001) surfaces of low-T, m = 18 and m = 20, antigorite from the Kovdor Mine, Russia. The internal microstructure of the same crystal before cleavage has been checked by conventional TEM on FIB-cut cross-sections. The structural wave is imaged by dynamic SFM with a similar to 0.25 nm topographic amplitude (outcropping tetrahedral sheet) on cleaved and as-grown surfaces, and with a similar to 0.5 nm topographic amplitude (outcropping tetrahedral + octahedral sheets) mostly found on cleaved surfaces. Atomic resolution imaging was successfully applied on the cleavage surface through imaging individual atomic features on the outer hexagonal net of the emerging (Mg, O, OH) octahedra of the half-wave. The antigorite cleavage crack undulates through a single octahedral sheet, thereby avoiding rupture of strong Si-O bonds. The two tetrahedral reversals, which form the edges of the modulation repeat, are found to be strongly non-equivalent in structure: across < 010 >, one reversal is sharp as expected from the standard models of the antigorite structure, whereas the other reversal is unexpectedly "extended." The latter suggests some scheme of anti-polar positioning of silicate tetrahedra along < 010 > at the 6-membered ring reversal. High-resolution transmission electron microscopy (HRTEM) structure imaging of antigorite viewed down to < 010 > confirms spread out electron densities at this reversal. Numerous step height measurements on (001) surfaces show incremental results as integral multiples of 0.25 nm, the spacing between O,OH surfaces along c. Many of them differ in height from integral multiples of the unit cell repeat along c and could be explained from carving the bulk wave structure. For all surfaces and steps, local stoichiometry and global electro-neutrality of the surface are satisfied.

Update: 13-May-2010

Title:
Low-energy lattice excitations in the decagonal Al-Ni-Fe and icosahedral Al-Cu-Fe quasicrystals and the (Al,Si)-Cu-Fe cubic phase
Authors:
Panova, GK; Zemlyanov, MG; Parshin, PP; Shikov, AA; Brand, RA Author Full Names: Panova, G. Kh.; Zemlyanov, M. G.; Parshin, P. P.; Shikov, A. A.; Brand, R. A.
Source:
PHYSICS OF THE SOLID STATE 52 (4): 771-775 APR 2010
Abstract:
The specific heat of decagonal Al71.3Ni24.0Fe4.7 and icosahedral Al62Cu25.5Fe12.5 quasicrystals and the Al55.0Si7.0Cu25.5Fe12.5 cubic phase approximating the structure of the icosahedral alloy has been studied in the temperature range 4.2-40.0 K. All the three compounds exhibit low coefficients of the electronic heat capacity and pronounced deviations of the low-temperature lattice heat capacity from a cubic temperature law in the range 5-10 K. The results obtained by the thermodynamic method and inelastic neutron scattering have been compared and analyzed. It has been established that, at energies E > < 14 meV, the spectral density of thermal vibrations in the icosahedral quasicrystal is substantially higher than those in the cubic approximant and in decagonal quasicrystal.
Title:
Investigation of the structure of compacts and sheets of an Al-Cu-Li alloy strengthened by Al2CuLi (T-1) particles
Authors:
Shamrai, VF; Timofeev, VN; Grushko, OE Author Full Names: Shamrai, V. F.; Timofeev, V. N.; Grushko, O. E.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 109 (4): 383-391 APR 2010
Abstract:
X-ray diffraction and electron microscopy have been used to investigate structural states of the material of compacts and sheets of an aluminum-copper-lithium alloy with a lithium content corresponding to the field of equilibrium of a solid solution with the phase T (1) (Al2CuLi). In pressed strips, there arises a multicomponent texture (Bs "110"aOE (c) 112 >, Cu "211"aOE (c) 111 >, S "123"aOE (c) hkl >) typical of pressed articles of aluminum-lithium alloys. Their microstructure was characterized by the presence of slip bands oriented in the rolling direction. The formation of lamellar precipitates of the T (1) phase at slip-band boundaries in the process of deformation is supposedly stimulated by Shockley partial dislocations. In hot-rolled sheets, there arose an unusually intense nearly single-component texture of the Ex (1) "011"aEuro111aEuro parts per thousand type, whose appearance is mainly caused by the cross rolling of the sheets. The reduced strength characteristics of the sheets examined are connected with a sharply oriented character of the structure of both the matrix phase and the strengthening T (1) phase. A quasicrystalline phase T (2) present in the material and the precipitates of the delta' phase exert no marked effect on the level of mechanical properties.
Title:
Structural phase transformations in quasicrystal-forming Al-Cu-Fe alloys and defects of the icosahedral phase
Authors:
Shalaeva, EV; Prekul, AF Author Full Names: Shalaeva, E. V.; Prekul, A. F.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 109 (4): 392-401 APR 2010
Abstract:
Transmission electron microscopy was used to investigate structural and phase transformations and defects of the icosahedral (iota) phase that is formed upon isothermal annealings (T (ann) = 550-700A degrees C) of quenched quasicrystal-forming alloys Al61Cu26Fe13 and Al63Cu25Fe12 (beta solid solution + iota phase). It has been established that in the Al63Cu25Fe12 alloy there occurs a reversible iota-R-approximant transformation, whereas in the Al61Cu26Fe13 alloy there is formed a single-phase iota structure with regions with a high density of randomly distributed planar defects (T (ann) = 550A degrees C), which are partially annealed at 650A degrees C. The observed defects are, mainly, ultrathin interlayers ("intergrowths" to 3-5 nm in thickness) on quasicrystal planes with A5(iota) axes with an imperfect decagonal structure. As the basic mechanism, the growth mechanism of the formation of defects during the beta -> i transformation is proposed. The role of the alloy composition and low-temperature beta -> 3C-phase transformation in the realization of this mechanism is discussed.
Title:
Charge and spin ordering in the mixed-valence compound LuFe2O4
Authors:
Harris, AB; Yildirim, T Author Full Names: Harris, A. B.; Yildirim, T.
Source:
PHYSICAL REVIEW B 81 (13): Art. No. 134417 APR 1 2010
Abstract:
Landau theory and symmetry considerations lead us to propose an explanation for several seemingly paradoxical behaviors of charge ordering (CO) and spin ordering (SO) in the mixed valence compound LuFe2O4. Both SO and CO are highly frustrated. We analyze a lattice gas model of CO within mean-field theory and determine the magnitude of several of the phenomenological interactions. We show that the assumption of a continuous phase transitions at which CO or SO develops implies that both CO and SO are incommensurate. To explain how ferroelectric fluctuations in the charge-disordered phase can be consistent with an antiferroelectric-ordered phase, we invoke an electron-phonon interaction in which a low-energy (20 meV) zone-center transverse phonon plays a key role. The energies of all the zone center phonons are calculated from first principles. We give a Landau analysis which explains SO and we discuss a model of interactions which stabilizes the SO state, if it is assumed commensurate. However, we suggest a high-resolution experimental determination to see whether this phase is really commensurate, as believed up to now. The applicability of representation analysis is discussed. A tentative explanation for the sensitivity of the CO state to an applied magnetic field in field-cooled experiments is given.
Title:
Sinusoidal magnetic structure in a three-dimensional antiferromagnetic Co-2(OH)AsO4: Incommensurate-commensurate magnetic phase transition
Authors:
de Pedro, I; Rojo, JM; Fernandez, JR; Fernandez-Diaz, MT; Rojo, T Author Full Names: de Pedro, I.; Rojo, J. M.; Rodriguez Fernandez, J.; Fernandez-Diaz, M. T.; Rojo, T.
Source:
PHYSICAL REVIEW B 81 (13): Art. No. 134431 APR 1 2010
Abstract:
Co-2(OH)AsO4 has been prepared by hydrothermal synthesis and characterized from x-ray and neutron powder diffraction. The structure consists of a three-dimensional framework in which Co(1)O-5-trigonal bi-pyramid dimers and Co(2)O-6-octahedra chains are simultaneously present. The magnetic structure has been determined by neutron (D2B and D1B) powder-diffraction data. Below 22 K, the Co-2(OH)AsO4 phase shows an incommensurate antiferromagnetic structure along the b direction. The propagation vector (0, delta, 0) is temperature dependent with a value of delta=0.430 at the lowest temperature (1.8 K). Magnetization measurements of Co-2(OH)AsO4 show a complex magnetic behavior with the presence of three different signals. Between 6 and 21 K, a strong dependence of the magnetic field is observed with a shift of the inflexion point associated to the three-dimensional antiferromagnetic ordered from 18 K at 1 kOe to 20.1 K at 90 kOe. The small sp! litting observed in the zero-field-cooled-field-cooled curves at low temperatures is characteristic of ferromagnetic interactions but saturation is not reached even up to 90 kOe. Heat-capacity measurements show an unusual dependence on the magnetic field for antiferromagnetic transitions with a jump at the Neel temperature quite small (2 J/Kmol). The magnetic contribution exhibits a lambda-type anomaly associated to the three-dimensional antiferromagnetic ordering. Surprisingly, the lambda anomaly grows with the magnetic field and becomes better defined. Neutron powder diffraction in different fields shows a magnetic phase transition. The incommensurate magnetic structure evolves at low temperatures toward a collinear AF phase for fields higher than 35 kOe.
Title:
Magnetic order of multiferroic ErMn2O5 studied by resonant soft x-ray Bragg diffraction
Authors:
Staub, U; Bodenthin, Y; Garcia-Fernandez, M; de Souza, RA; Garganourakis, M; Golovenchits, EI; Sanina, VA; Lushnikov, SG Author Full Names: Staub, U.; Bodenthin, Y.; Garcia-Fernandez, M.; de Souza, R. A.; Garganourakis, M.; Golovenchits, E. I.; Sanina, V. A.; Lushnikov, S. G.
Source:
PHYSICAL REVIEW B 81 (14): Art. No. 144401 APR 1 2010
Abstract:
Resonant magnetic soft x-ray diffraction is used to study the magnetic order of the Mn sublattices in multiferroic ErMn2O5. Data were collected at the Mn L-2,L-3 edges as a function of temperature, incident polarization, including the analysis of scattered polarizations for selected azimuths. The energy dependence of the magnetic reflections depends on the azimuthal angle in the commensurate magnetic (CM) ferroelectric (FE) phase, indicating different contributions to the scattering. In the incommensurate magnetic [two-dimensional (2D)-ICM] phase, the two observed reflections (1/2 +/- delta(x) 0 1/4+delta(z)) have distinct energy dependences too. Different origins of these differences in spectral shape are discussed. The azimuthal angle dependence at the L-3 edge can only be qualitatively described by a generalized magnetic model. The observed discrepancies may indicate the importance of magnetoelectric multipole scattering to these reflections. Reciprocal mesh scans show diffuse scattering along q and perpendicular to q as well as along the (h 0 0) direction in the CM phase. Diffuse scattering is also observed along (h 0 0) in the one-dimensional-ICM phase. At higher temperatures, in the 2D-ICM phase, the diffuse magnetic scattering is almost isotropic.
Title:
V-51 NMR study of the kagome staircase compound Ni3V2O8
Authors:
Ogloblichev, V; Kumagai, K; Verkhovskii, S; Yakubovsky, A; Mikhalev, K; Furukawa, Y; Gerashenko, A; Smolnikov, A; Barilo, S; Bychkov, G; Shiryaev, S Author Full Names: Ogloblichev, V.; Kumagai, K.; Verkhovskii, S.; Yakubovsky, A.; Mikhalev, K.; Furukawa, Yu.; Gerashenko, A.; Smolnikov, A.; Barilo, S.; Bychkov, G.; Shiryaev, S.
Source:
PHYSICAL REVIEW B 81 (14): Art. No. 144404 APR 1 2010
Abstract:
We used V-51 NMR to study magnetic ordering in the Ni3V2O8 single crystal with a Kagome staircase structure of Ni atoms. The NMR spectra were measured in the temperature range T= (3-300) K and magnetic fields H= (2-9.4) T directed along the main a, b, c axes of the orthorhombic (Cmca) crystal. The local magnetic field at the V-51 NMR probe determines position and the shape of the corresponding NMR line. These parameters yield an unique information, respectively, on the uniform and the staggered spin components of the ordered Ni. The NMR data collected at H >= 2 T are considered in line with predictions of the representation theory [A. Harris, Phys. Rev. B 76, 054447 (2007)] with a result that incommensurate amplitude-modulated structure of the spine Ni-s spins acquires in the high-temperature incommensurate (HTI) phase two prominent nearly equal spin components S-a approximate to S-c >> S-b instead of the longitudinal incommensurate spin-density wave (SDW) order with S-a >> S-c, S-b as it was deduced from neutron-diffraction data [M. Kenzelmann et al., Phys. Rev. B 74, 014429 (2006)]. No noticeable variation of SDW polarization in the ab plane was detected below the HTI-low-temperature incommensurate (LTI) transition. In both the HTI and LTI phases two almost equal spin components of the Ni-s spins S-a approximate to S-c >> S-b exist at H < 4.7 T. Their phasing is still not determined. The bulk magnetization in these phases is explained by contribution of the cross-tie Ni-c spins which antiferromagnetic structure in the LTI phase is canted along H.
Title:
Magnetic properties of EuPtSi3 single crystals
Authors:
Kumar, N; Dhar, SK; Thamizhavel, A; Bonville, P; Manfrinetti, P Author Full Names: Kumar, Neeraj; Dhar, S. K.; Thamizhavel, A.; Bonville, P.; Manfrinetti, P.
Source:
PHYSICAL REVIEW B 81 (14): Art. No. 144414 APR 1 2010
Abstract:
Single crystals of EuPtSi3, which crystallize in the BaNiSn3-type crystal structure, have been grown by high-temperature solution growth method using molten Sn as the solvent. EuPtSi3 which lacks the inversion symmetry and has only one Eu site in the unit cell is found to be an antiferromagnet with two successive magnetic transitions at T-N1=17 K and T-N2=16 K, as inferred from magnetic susceptibility, heat capacity, and Eu-151 Mossbauer measurements. The isothermal magnetization data for H parallel to[001] reveal a metamagnetic transition at a critical field H-c=1 T. The magnetization saturates to a moment value of 6.43 mu(B)/Eu above 5.9 T (9.2 T) for H parallel to[001] ([100]), indicating that these fields are spin-flip fields for the divalent Eu moments along the two axes. The origin of this anisotropic behavior is discussed. A magnetic (H and T) phase diagram has been constructed from the temperature dependence of isothermal magnetization data. The reduced jump in the heat capacity at T-N1 indicates a transition to an incommensurate, amplitude modulated antiferromagnetic structure. The shape of the hyperfine field split Mossbauer spectrum at T-N1 provides additional support for the proposed nature of this magnetic transition.
Title:
Incommensurate spin correlations induced by magnetic Fe ions substituted into overdoped Bi1.75Pb0.35Sr1.90CuO6+z
Authors:
Hiraka, H; Hayashi, Y; Wakimoto, S; Takeda, M; Kakurai, K; Adachi, T; Koike, Y; Yamada, I; Miyazaki, M; Hiraishi, M; Takeshita, S; Kohda, A; Kadono, R; Tranquada, JM; Yamada, K Author Full Names: Hiraka, H.; Hayashi, Y.; Wakimoto, S.; Takeda, M.; Kakurai, K.; Adachi, T.; Koike, Y.; Yamada, I.; Miyazaki, M.; Hiraishi, M.; Takeshita, S.; Kohda, A.; Kadono, R.; Tranquada, J. M.; Yamada, K.
Source:
PHYSICAL REVIEW B 81 (14): Art. No. 144501 APR 1 2010
Abstract:
Spin correlations in the overdoped region of Bi1.75Pb0.35Sr1.90CuO6+z have been explored with Fe-doped single crystals characterized by neutron scattering, muon-spin-rotation spectroscopy, and magnetic-susceptibility measurements. Static incommensurate spin correlations induced by the Fe spins are revealed by elastic neutron scattering. The resultant incommensurability delta is unexpectedly large (similar to 0.2 r.l.u.), as compared with delta similar to 1/8 in overdoped superconductor La2-xSrxCuO4. Intriguingly, the large delta in this overdoped region is close to the hole concentration p. This result is reminiscent of the delta approximate to p trend observed in underdoped La2-xSrxCuO4; however, it is inconsistent with the saturation of delta in the latter compound in the overdoped regime. While our findings in Fe-doped Bi1.75Pb0.35Sr1.90CuO6+z support the commonality of incommensurate spin correlations in high-T-c cuprate superconductors, they also s! uggest that the magnetic response might be dominated by a distinct mechanism in the overdoped region.
Title:
Phase diagram of H-2 adsorbed on graphene
Authors:
Gordillo, MC; Boronat, J Author Full Names: Gordillo, M. C.; Boronat, J.
Source:
PHYSICAL REVIEW B 81 (15): Art. No. 155435 APR 15 2010
Abstract:
The phase diagram of the first layer of H-2 adsorbed on top of a single graphene sheet has been calculated by means of a series of diffusion Monte Carlo simulations. We have found that, as in the case of He-4, the ground state of molecular hydrogen is a root 3 x root 3 commensurate structure, followed, upon a pressure increase, by an incommensurate triangular solid. A striped phase of intermediate density was also considered and found lying on top of the equilibrium curve separating both commensurate and incommensurate solids.
Title:
Periodic step arrays on the aperiodic i-Al-Pd-Mn quasicrystal surface at high temperature
Authors:
Sato, Y; Unal, B; Lograsso, TA; Thiel, PA; Schmid, AK; Duden, T; Bartelt, NC; McCarty, KF Author Full Names: Sato, Y.; Unal, B.; Lograsso, T. A.; Thiel, P. A.; Schmid, A. K.; Duden, T.; Bartelt, N. C.; McCarty, K. F.
Source:
PHYSICAL REVIEW B 81 (16): Art. No. 161406 APR 15 2010
Abstract:
We have observed the configuration and motion of surface steps on the aperiodic icosahedral (i-) Al-Pd-Mn quasicrystal using low-energy electron microscopy and scanning tunneling microscopy. As the quasicrystal is cooled from high temperature, bulk vacancies migrate to the surface causing the surface to be etched. Surprisingly, this etching occurs by two types of steps with different heights moving in different directions with different velocities. The steady-state surface morphology is a uniformly spaced rhomboidal step network. This network requires that the layer stacking near the surface deviates from the bulk quasicrystal stacking.
Title:
Quantum critical behavior of antiferromagnetic itinerant systems with van Hove singularities
Authors:
Katanin, A Author Full Names: Katanin, A.
Source:
PHYSICAL REVIEW B 81 (16): Art. No. 165118 APR 15 2010
Abstract:
The interplay of magnetic and superconducting fluctuations in two-dimensional systems with van Hove singularities in the electronic spectrum is considered within the functional renormalization-group (fRG) approach. While the fRG flow has to be stopped at a certain minimal temperature T-RG(min), we study temperature dependence of magnetic and superconducting susceptibilities below T-RG(min) to obtain the crossover temperatures to the regime with strong magnetic and superconducting fluctuations. Near half filling we obtain the largest crossover temperature, corresponding to a regime with strong commensurate magnetic fluctuations, which is replaced by a regime with strong incommensurate fluctuations further away from half filling. With further decreasing density the system undergoes quantum phase transition from incommensurate to paramagnetic phase. Similarly to results of Hertz-Moriya-Millis approach, the temperature dependence of the inverse (in-commensurate) magnetic susceptibility at the magnetic quantum-critical point is found almost linear in temperature.
Title:
Classification and Interpretation of the Polarization of Multiferroic RMn2O5
Authors:
Fukunaga, M; Noda, Y Author Full Names: Fukunaga, Mamoru; Noda, Yukio
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (5): Art. No. 054705 MAY 2010
Abstract:
We have collected and compared temperature-dependent polarization data of multiferroic RMn2O5 for 11 kinds of rare earths (R) from the literature and our own measurements. Although the reported data are inconsistent, it was found that the maximum polarization values for R = Y, Dy, Ho, Er, and Tm are almost equal above 30 K except for the phase transition temperature where the polarization disappears. The findings suggest a standard polarization value for RMn2O5 of 100-120 nC/cm(2) at 30 K in a commensurate magnetic (CM) phase. We discuss the nature and issues of the measured polarization of RMn2O5 from the data and our detailed measurement results for YMn2O5. Temperature-dependent ferroelectric hysteresis loops of YMn2O5 by the double-wave method reveal that an antiferroelectric-like high-temperature incommensurate magnetic (ICM) phase and a ferroelectric low-temperature ICM phase, while the intermediate CM phase is ferrielectric.
Title:
Microstructural and mechanical study of an Al matrix composite reinforced by Al-Cu-Fe icosahedral particles
Authors:
Laplanche, G; Joulain, A; Bonneville, J; Gauthier-Brunet, V; Dubois, S; El Kabir, T Author Full Names: Laplanche, Guillaume; Joulain, Anne; Bonneville, Joel; Gauthier-Brunet, Veronique; Dubois, Sylvain; El Kabir, Tarik
Source:
JOURNAL OF MATERIALS RESEARCH 25 (5): 957-965 MAY 2010
Abstract:
In this study, we produced an Al matrix composite material reinforced by Al-Cu-Fe particles of the icosahedral phase. The composite material was prepared using a hot isostatic pressure technique at T = 673 K and P = 180 MPa. The mechanical properties were investigated by compression tests performed at constant strain rate over the temperature range 290-823 K. The results show a vigorous strengthening effect resulting from the reinforcement particles. Strengthening is attributed to two main contributions arising from load transfer between the Al matrix and the reinforcement particles and from plastic deformation of the Al grains. The present results are compared with those obtained in a previous work on an Al-based composite reinforced by Al-Cu-Fe particles of the omega-tetragonal phase.

Update: 6-May-2010

Title:
Structural and magnetic modulations in CaCuxMn7-xO12
Authors:
Slawinski, W; Przenioslo, R; Sosnowska, I; Bieringer, M Author Full Names: Slawinski, W.; Przenioslo, R.; Sosnowska, I.; Bieringer, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (18): Art. No. 186001 MAY 12 2010
Abstract:
Low temperature atomic position modulations and magnetic moment modulations are reported for CaCuxMn7-xO12 (x = 0.0, 0.1 and 0.23) using neutron powder diffraction. Both modulations are described with propagation vectors (0, 0, q) parallel to the c-axis in the hexagonal setting. The present neutron diffraction studies confirm the quantitative model describing the atomic position modulations in CaCuxMn(7-x)O(12) (x = 0.0 and 0.1) as derived from synchrotron based powder x-ray diffraction studies (Slawinski et al 2009 Acta Crystallogr. B 65 535). Neutron diffraction studies confirm the relation between the atomic position modulation length L-p and the magnetic modulation length L-m = 2L(p) between 50 K and the Neel temperature T-N. CaCuxMn(7-x)O(12) (x = 0.1 and 0.23) shows a magnetic phase transition near 50 K associated with considerable changes of the magnetic modulation length and the magnetic coherence length, similar to that observed in the parent CaMn7O12.
Title:
Magnetic properties of Bi(Fe1-x M (x) )O-3 (M = Mn, Ti)
Authors:
Troyanchuk, IO; Chobot, AN; Mantytskaya, OS; Tereshko, NV Author Full Names: Troyanchuk, I. O.; Chobot, A. N.; Mantytskaya, O. S.; Tereshko, N. V.
Source:
INORGANIC MATERIALS 46 (4): 424-428 APR 2010
Abstract:
The magnetic properties of Bi(Fe1 - x M (x) )O-3(M = Mn, Ti) solid solutions have been studied in magnetic fields of up to 11.2 x 10(3) kA/m, and the composition stability range of the R3c ferroelectric phase has been determined. The results indicate that partial Ti4+ substitution for Fe3+ leads to a transition from a modulated antiferromagnetic state to a homogeneous weakly ferromagnetic ferroelectric state (x = 0.08), whereas the Bi(Fe (1-x) (3+) Mn (x) (3+) )O-3 solid solutions do not exhibit weak ferromagnetism. Charge compensation in is assumed to be ensured by cation vacancies.
Title:
Short-range magnetic order, irreversibility and giant magnetoresistance near the triple points in the (x, T) magnetic phase diagram of ZrMn6Sn6-xGax
Authors:
Mazet, T; Ihou-Mouko, H; Mareche, JF; Malaman, B Author Full Names: Mazet, T.; Ihou-Mouko, H.; Mareche, J. -F.; Malaman, B.
Source:
EUROPEAN PHYSICAL JOURNAL B 74 (4): 487-497 APR 2010
Abstract:
We have studied pseudo-layered ZrMn6Sn6-xGax intermetallics (0.55 a parts per thousand currency sign x a parts per thousand currency sign 0.81) using magnetic, magnetoresistivity and powder neutron diffraction measurements. All the alloys studied have magnetic ordering temperatures in the 450-490 K temperature range. They present complex temperature-dependent partially disordered magnetic structures whose ferromagnetic component develops upon increasing the Ga content. ZrMn6Sn6-xGax alloys with x a parts per thousand currency sign 0.69 are essentially collinear antiferromagnets at high-temperature and adopt antifan-like arrangements at low temperature. For x a parts per thousand yen 0.75, the alloys order ferromagnetically and evolve to a fan-like structure upon cooling. The intermediate compositions (x = 0.71 and 0.73) present a canted fan-like order at high temperature and another kind of antifan-like arrangement at low temperature. The degree of short-range order tends to increase upon approaching the intermediate compositions. The (x, T) phase diagram contains two triple points (x similar to 0.70; T similar to 460 K and x similar to 0.74; T similar to 455 K), where the paramagnetic, an incommensurate and a commensurate phases meet, which possess some of the features of Lifshitz point. Irreversibilities manifest in the low-temperature magnetization curves at the antifan-fan or fan-ferromagnetic boundaries as well as inside the fan region. Giant magnetoresistance is observed, even above room temperature.
Title:
Elastic analysis of an elliptic notch in quasicrystals of point group 10 subjected to shear loading
Authors:
Li, LH Author Full Names: Li Lian-He
Source:
CHINESE PHYSICS B 19 (4): Art. No. 046101 APR 2010
Abstract:
Based on the stress potential and complex variable function method, this paper makes an elastic analysis of an elliptic notch subjected to uniform shear stress at infinity in quasicrystals with point group 10. With the aid of conformal transformation, an exact solution for the elliptic notch of the quasicrystals is obtained. The solution of the mode II Griffith crack as a special case is constructed. The stress intensity factor and energy release rate have been also obtained as a direct result of the crack solution.
Title:
Magnetization plateau and incommensurate spin modulation in Ca3Co2O6
Authors:
Zhao, Y; Gong, SS; Li, W; Su, G Author Full Names: Zhao, Yang; Gong, Shou-Shu; Li, Wei; Su, Gang
Source:
APPLIED PHYSICS LETTERS 96 (16): Art. No. 162503 APR 19 2010
Abstract:
The magnetic properties of a trigonal prism unit of the spin-2 frustrated compound Ca3Co2O6 are studied by means of the density-matrix renormalization group method. A magnetization plateau at m(s)/3 (m(s) is the saturation magnetization) with ferrimagnetic structure is observed. By fitting the experimental data of magnetic curve, an estimation of the couplings gives J(1)=-26.84 K, J(2)=0.39 K, and J(3)=0.52 K. The local magnetic moments are unveiled to exhibit an incommensurate sinusoidally modulation along the three chains of the trigonal prism, which gives a strong theoretical support to the experimentally observed incommensurate partially disordered antiferromagnetic state for Ca3Co2O6. The present result suggests that the modulation indeed originates from the competition of antiferromagnetic and ferromagnetic couplings. (C) 2010 American Institute of Physics. [doi:10.1063/1.3413931]
Title:
OXIDATION BEHAVIOR OF THE PHASE ICOSAEDRAL QUASICRISTAL Al-62,Al- 2 Cu-25,Cu-3 Fe-12,Fe-5
Authors:
Nascimento, L; Agostinho, LCL; Cavalcanti, BF Author Full Names: Nascimento, L.; Agostinho, L. C. L.; Cavalcanti, B. F.
Source:
ACTA MICROSCOPICA 18 (3): 295-303 2009
Abstract:
Oxidation behavior of the quasicrystalline alloy with nominal composition Al-62,Al- 2 Cu-25,Cu-3 Fe-12,Fe-5 was analyzed under different conditions of duration of thermal treatment. It was used X - Ray Diffratometry to follow the alloy phases evolution and Scanning Electron Microscopy (SEM) to analyze the quasicrystal morphology and oxidation. Below 750 degrees C the alloy shows intermetallic phases with associations of the alloy elements and above 675 degrees C the crystalline phase is stable. In icosahedral phase, aluminum oxidation forms a dense passivating layer at the outmost surface of the quasicrystal which causes depletion in both copper and iron. In the dense layer it was observed not only the presence of alumina, gamma - Al2O3, but also the formation of hematite.

Update: 15-Apr-2010

Title:
Microstructures and Phase Transformation of Al-Rased composite materials Reinforced by Al-Cu-Co Decagonal Quasicrystalline Particles
Authors:
Zhu, M; Yang, GC; Cheng, SL; Wang, BH; Zhou, YH Author Full Names: Zhu Man; Yang Gencang; Cheng Suling; Wang Binghui; Zhou Yaohe
Source:
RARE METAL MATERIALS AND ENGINEERING 38 (9): 1584-1588 SEP 2009
Abstract:
Al65Cu15Co20 decagonal quasicrystalline alloys were prepared by an arc-melting furnace. The aluminium-based composites were fabricated by using the Al65Cu15Co20 decagonal quasicrystalline particles as reinforcing phase and Al-4.5 wt%Cu alloy as matrix with mechanical stirring. The microstructures, the phase composition, and the distribution of Al65Cu15Co20 were characterisied by XRD, SEM, SEM and EDS for the Al65Cu15Co20 quasicrystalline alloys and the reinforced composites. And the morphology, chemical composition and structure changes of the quasicrystalline particles before and after adding to the melt were also analysised. As the interdiffusion occurs between the quasicrystalline particles and the melt, the quasicrystalline particles can not exist stably in the melt. The morphology of the particles turns from inregular polygons to block and lath-like in shape as following: D-Al62.10Cu17.46Co20.44 -> theta-Al79.55Cu1.10Co19.32 after adding the quasicrystalline particles into the melt. During the solidification process, the theta phase distributes uniformly along the grain boundaries because of the "interfacial pushing effect".
Title:
Evidence for a Magnetically Driven Superconducting Q Phase of CeCoIn5
Authors:
Kenzelmann, M; Gerber, S; Egetenmeyer, N; Gavilano, JL; Strassle, T; Bianchi, AD; Ressouche, E; Movshovich, R; Bauer, ED; Sarrao, JL; Thompson, JD Author Full Names: Kenzelmann, M.; Gerber, S.; Egetenmeyer, N.; Gavilano, J. L.; Straessle, Th; Bianchi, A. D.; Ressouche, E.; Movshovich, R.; Bauer, E. D.; Sarrao, J. L.; Thompson, J. D.
Source:
PHYSICAL REVIEW LETTERS 104 (12): Art. No. 127001 MAR 26 2010
Abstract:
We have studied the magnetic order inside the superconducting phase of CeCoIn5 for fields along the [1 0 0] crystallographic direction using neutron diffraction. We find a spin-density wave order with an incommensurate modulation Q = (q, q, 1/2) and q = 0.45(1), which within our experimental uncertainty is indistinguishable from the spin-density wave found for fields applied along [1 - 10]. The magnetic order is thus modulated along the lines of nodes of the d(x2-y2) superconducting order parameter, suggesting that it is driven by the electron nesting along the superconducting line nodes. We postulate that the onset of magnetic order leads to reconstruction of the superconducting gap function and a magnetically induced pair density wave.
Title:
Incommensurate spin-density-wave order in quasi-one-dimensional metallic antiferromagnet NaV2O4
Authors:
Nozaki, H; Sugiyama, J; Mansson, M; Harada, M; Pomjakushin, V; Sikolenko, V; Cervellino, A; Roessli, B; Sakurai, H Author Full Names: Nozaki, Hiroshi; Sugiyama, Jun; Mansson, Martin; Harada, Masashi; Pomjakushin, Vladimir; Sikolenko, Vadim; Cervellino, Antonio; Roessli, Bertrand; Sakurai, Hiroya
Source:
PHYSICAL REVIEW B 81 (10): Art. No. 100410 MAR 2010
Abstract:
To clarify the reason for the coexistence of long-range antiferromagnetic order and metallic conductivity for NaV2O4, in which the V ions form quasi-one-dimensional zigzag chains along the b axis, we have performed a neutron-scattering experiment using a powder sample down to 20 K. The analysis of the magnetic powder diffractogram below T-N=140 K demonstrates the formation of an incommensurate spin-density-wave order with k=(0,0.191,0); the ordered moment was estimated as (0,0,0.77 mu(B)) at 20 K.
Title:
Valence band structure of the icosahedral Ag-In-Yb quasicrystal
Authors:
Sharma, HR; Simutis, G; Dhanak, VR; Nugent, PJ; Cui, C; Shimoda, M; McGrath, R; Tsai, AP; Ishii, Y Author Full Names: Sharma, H. R.; Simutis, G.; Dhanak, V. R.; Nugent, P. J.; Cui, C.; Shimoda, M.; McGrath, R.; Tsai, A. P.; Ishii, Y.
Source:
PHYSICAL REVIEW B 81 (10): Art. No. 104205 MAR 2010
Abstract:
The valence band structure of the icosahedral (i) Ag-In-Yb quasicrystal, which is isostructural to the binary i-Cd-Yb system, is investigated by ultraviolet photoemission spectroscopy (UPS). Experimental results are compared with electronic-structure calculations of a cubic approximant of the same phase. UPS spectra from the fivefold, threefold, and twofold i-Ag-In-Yb surfaces reveal that the valence band near to the Fermi level is dominated by Yb 4f-derived states, in agreement with calculations. The spectra also exhibit peaks which are surface core level shifted, caused by changes in the electronic structure in surface layers. Calculations yield a pseudogap in the density of states due to a hybridization of the Yb 5d band with the Ag 5p and In 5p bands. Both experimental and calculated band features are very similar to those of Cd-Yb. The modification of the band structure after surface treatment by sputtering and by oxidation is also studied. Additionally, the work ! function of i-Ag-In-Yb measured from the width of UPS spectrum is found to be almost unaffected by surface orientation, but increases after sputtering or oxidation.
Title:
Static and dynamical susceptibility of LaO1-xFxFeAs
Authors:
Monni, M; Bernardini, F; Profeta, G; Sanna, A; Sharma, S; Dewhurst, JK; Bersier, C; Continenza, A; Gross, EKU; Massidda, S Author Full Names: Monni, M.; Bernardini, F.; Profeta, G.; Sanna, A.; Sharma, S.; Dewhurst, J. K.; Bersier, C.; Continenza, A.; Gross, E. K. U.; Massidda, S.
Source:
PHYSICAL REVIEW B 81 (10): Art. No. 104503 MAR 2010
Abstract:
The mechanism of superconductivity and magnetism and their possible interplay have recently been under debate in pnictides. A likely pairing mechanism includes an important role of spin fluctuations and can be expressed in terms of the magnetic susceptibility chi. The latter is therefore a key quantity in the determination of both the magnetic properties of the system in the normal state and of the contribution of spin fluctuations to the pairing potential. A basic ingredient to obtain chi is the independent-electron susceptibility chi(0). Using LaO1-xFxFeAs as a prototype material, in this report we present a detailed ab initio study of chi(0)(q, omega) as a function of doping and of the internal atomic positions. The resulting static chi(0)(q, 0) is consistent with both the observed M-point-related magnetic stripe phase in the parent compound and with the existence of incommensurate magnetic structures predicted by ab initio calculations upon doping.
Title:
Structure of the (010) surface of the orthorhombic complex metallic alloy T-Al-3(Mn,Pd)
Authors:
Deniozou, T; Addou, R; Shukla, AK; Heggen, M; Feuerbacher, M; Krajci, M; Hafner, J; Widmer, R; Groning, O; Fournee, V; Dubois, JM; Ledieu, J Author Full Names: Deniozou, Th.; Addou, R.; Shukla, A. K.; Heggen, M.; Feuerbacher, M.; Krajci, M.; Hafner, J.; Widmer, R.; Groening, O.; Fournee, V.; Dubois, J. -M.; Ledieu, J.
Source:
PHYSICAL REVIEW B 81 (12): Art. No. 125418 MAR 2010
Abstract:
The atomic and electronic structures of the (010) surface of the T-Al-3(Mn,Pd) complex metallic alloy is investigated by means of low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), x-ray photoelectron diffraction (XPD), and ab initio calculations. While structural imperfections are observed at the surface and out of the various possible terminations, the puckered P2 layer is identified as the only surface termination, thus pointing out the existence of a well-defined minimum in the surface energy landscape. The measured step heights correspond to distances between identical planes along the [010] direction in the bulk model, i.e., b/2. A bias dependency of the STM topography is found. The XPD and LEED patterns confirm the pseudotenfold symmetry of the sample. XPS and UPS show a more metallic signature of the T phase compared to Al-based quasicrystalline phases.
Title:
Incommensurate magnetic order and phase separation in the two-dimensional Hubbard model with nearest- and next-nearest-neighbor hopping
Authors:
Igoshev, PA; Timirgazin, MA; Katanin, AA; Arzhnikov, AK; Irkhin, VY Author Full Names: Igoshev, P. A.; Timirgazin, M. A.; Katanin, A. A.; Arzhnikov, A. K.; Irkhin, V. Yu.
Source:
PHYSICAL REVIEW B 81 (9): Art. No. 094407 MAR 1 2010
Abstract:
We consider the ground-state magnetic phase diagram of the two-dimensional Hubbard model with nearest- and next-nearest-neighbor hopping in terms of electronic density and interaction strength. We treat commensurate ferromagnetic and antiferromagnetic as well as incommensurate (spiral) magnetic phases. The first-order magnetic transitions with changing chemical potential, resulting in a phase separation (PS) in terms of density, are found between ferromagnetic, antiferromagnetic, and spiral magnetic phases. We argue that PS has a dramatic influence on the phase diagram in the vicinity of half-filling. The results imply possible interpretation of the unusual behavior of magnetic properties of single-layer cuprates in terms of PS between collinear and spiral magnetic phases. The relevance of our results to the magnetic properties of the ruthenates is also discussed.
Title:
Single magnetic chirality in the magnetoelectric NdFe3((BO3)-B-11)(4)
Authors:
Janoschek, M; Fischer, P; Schefer, J; Roessli, B; Pomjakushin, V; Meven, M; Petricek, V; Petrakovskii, G; Bezmaternikh, L Author Full Names: Janoschek, M.; Fischer, P.; Schefer, J.; Roessli, B.; Pomjakushin, V.; Meven, M.; Petricek, V.; Petrakovskii, G.; Bezmaternikh, L.
Source:
PHYSICAL REVIEW B 81 (9): Art. No. 094429 MAR 1 2010
Abstract:
We have performed an extensive study of single crystals of the magnetoelectric NdFe3 ((BO3)-B-11)(4) by means of a combination of single-crystal neutron diffraction and spherical neutron polarimetry. Our investigation did not detect significant deviations at low temperatures from space group R32 concerning the chemical structure. With respect to magnetic ordering our combined results demonstrate that in the commensurate magnetic phase below T-N approximate to 30 K all three magnetic Fe moments and the magnetic Nd moment are aligned ferromagnetically in the basal hexagonal plane but align antiferromagnetically between adjacent planes. The phase transition to the low-temperature incommensurate (IC) magnetic structure observed at T-IC approximate to 13.5 K appears to be continuous. By means of polarized neutron studies it could be shown that in the incommensurate magnetic phase the magnetic structure of NdFe3((BO3)-B-11)(4) is transformed into a long-period antiferromagnetic helix with single chirality. Close to the commensurate-incommensurate phase transition third-order harmonics were observed, which in addition indicate the formation of magnetic solitons.
Title:
Theoretical studies of the incommensurate magnetic structure of a heavy fermion system: CeRhIn5
Authors:
Bjorkman, T; Lizarraga, R; Bultmark, F; Eriksson, O; Wills, JM; Bergman, A; Andersson, PH; Nordstrom, L Author Full Names: Bjorkman, Torbjorn; Lizarraga, Raquel; Bultmark, Fredrik; Eriksson, Olle; Wills, John M.; Bergman, Anders; Andersson, Per H.; Nordstrom, Lars
Source:
PHYSICAL REVIEW B 81 (9): Art. No. 094433 MAR 1 2010
Abstract:
We have investigated the electronic structure and the incommensurate magnetic configuration of the pressure-induced superconductor CeRhIn5. Noncollinear first-principles calculations were performed in the local-density approximation plus U scheme. The observed magnetic configuration is described accurately in our calculations, especially considering the minute energy scale which is relevant (microelectron volt). The band structure and Fermi surfaces were investigated and nesting was found to be responsible for the complex noncollinear magnetic state of CeRhIn5.
Title:
Surface plasmon enhanced transmission through gold planar crystals with various aperture arrangements
Authors:
Xue, J; Dong, BQ; Wang, X; Yang, R; Xu, ZC; Chen, YF; Huq, E; Zeng, W; Qu, XP; Liu, R Author Full Names: Xue, Jing; Dong, Bi-Qin; Wang, Xu; Yang, Rong; Xu, Zhen-Cheng; Chen, Yifang; Huq, Ejaz; Zeng, Wei; Qu, Xin-Ping; Liu, Ran
Source:
MICROELECTRONIC ENGINEERING 87 (5-8): 1340-1343 MAY-AUG 2010
Abstract:
Various planar crystals in gold films are fabricated by focused ion beam (FIB) technique. We theoretically and experimentally show that the enhanced transmission through the planar crystals is dependent on the nanoaperture's arrangement and this extraordinary transmission can be attributed to the excitation of surface plasmon polaritons (SPPs) on the metal-air interface. In contrast to other crystals, the quasicrystal exhibits broadband plasmonic resonances. Near-field optical images provide direct evidence for surface plasmon-mediated enhanced transmission in a wide wavelength range through the gold quasicrystal. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Study of Biological Effect of MC3T3-E1 in vitro by A Novel 2.4GHz Radiofrequency Electromagnetic Field Exposure System
Authors:
Cherng, S; Teng, HC Author Full Names: Cherng, Shen; Teng, Hsien-Chiao
Source:
LIFE SCIENCE JOURNAL-ACTA ZHENGZHOU UNIVERSITY OVERSEAS EDITION 6 (4): 41-49 2009
Abstract:
A 2.4GHz mobile-phone/blue-tooth radiofrequency electromagnetic field (RF-EMF) exposure system for cellular experiment MC3T3-E1 in vitro was designed to study the biological effects and demonstrated in this report. Experimental results have illustrated the observation of signal at 14Hz through algorithm analysis of the measured near field magnetic fluctuation and the modulation of gap junction intercellular communication (GJIC) within mouse osteoblast cells (MC3T3-E1) under RF-EMF power density at 0.3mWatt/cm(2). [Life Science Journal. 2009; 6(4): 41 49] (ISSN: 1097-8135).
Title:
Influence of cooling rate and cerium addition on rapidly solidified Al-TM alloys
Authors:
Michalcova, A; Vojtech, D; Schumacher, G; Novak, P; Klementova, M; Serak, J; Mudrova, M; Valdaufova, J Author Full Names: Michalcova, A.; Vojtech, D.; Schumacher, G.; Novak, P.; Klementova, M.; Serak, J.; Mudrova, M.; Valdaufova, J.
Source:
KOVOVE MATERIALY-METALLIC MATERIALS 48 (1): 1-7 2010
Abstract:
Rapidly solidified alloys, based on an aluminium-transition metal (TM) system, are promising structural materials. They show good mechanical properties and excellent thermal stability, which is caused by the very fine nanostructure of these materials and by the presence of nonequilibrium intermetallic phases. Influence of the cooling rate and Ce addition on properties of Al-5.5Ce-3Fe-1.5Ti alloy that was prepared by the melt spinning method was studied in this work. It was shown that formation of the quasicrystalline phase depends on the cooling rate during melt spinning. The addition of a few weight percents of Ce modifies phase composition of the alloy and stabilizes quasicrystals at elevated temperatures. However, the influence of Ce addition on hardness was not observed.
Title:
Anisotropic Thermal Diffusivity and Conductivity of La-Doped Strontium Niobate Sr2Nb2O7
Authors:
Sparks, TD; Fuierer, PA; Clarke, DR Author Full Names: Sparks, Taylor D.; Fuierer, Paul A.; Clarke, David R.
Source:
JOURNAL OF THE AMERICAN CERAMIC SOCIETY 93 (4): 1136-1141 APR 2010
Abstract:
The thermal diffusivity of the La-doped layered perovskite Sr2Nb2O7 parallel and perpendicular to the perovskite layers is reported from room temperature up to 1000 degrees C. The anisotropy persists through an incommensurate-normal ferroelectric phase transformation at 215 degrees C and up to 1000 degrees C, the maximum temperature of our measurements. The thermal conductivity perpendicular to the perovskite layers, derived from the diffusivity in the same direction, calculated using the density and measured heat capacity, has a constant value of 1.05 +/- 0.05 W/mK up to 1000 degrees C. Possible explanations for the low thermal conductivity and anisotropy are described.
Title:
Structurally complex metallic coatings in the Al-Cu system and their orientation relationships with an icosahedral quasicrystal
Authors:
Duguet, T; Kenzari, S; Demange, V; Belmonte, T; Dubois, JM; Fournee, V Author Full Names: Duguet, Thomas; Kenzari, Samuel; Demange, Valerie; Belmonte, Thierry; Dubois, Jean-Marie; Fournee, Vincent
Source:
JOURNAL OF MATERIALS RESEARCH 25 (4): 764-772 APR 2010
Abstract:
Quasicrystals have been identified as alloys possessing unusually low surface energy. This results in poor adhesion properties of quasicrystalline coatings when deposited on metallic substrates, hindering the development of these new materials for technological applications. Here we investigate the possible use of complex Al-Cu metallic phases as interface layers to accommodate the structural and electronic mismatch between a quasicrystalline coating and a metallic substrate and improve adhesion. First, we show that all stable low-temperature phases of the Al-Cu system can be grown as thin films using DC magnetron sputtering. Among the various possible phases, we select the gamma-brass gamma-Al4Cu9 as a promising candidate for the interface layer. Then the gamma-Al4Cu9 phase is grown on the fivefold surface of an icosahedral (i-) Al-Pd-Mn quasicrystal. The interface is investigated by transmission electron microscopy and shows a clear texturing of the film. The gra! ins exhibit rotational epitaxy with the substrate. We find that the interface is mainly composed of a beta-phase of unknown chemical composition and sometimes exhibits gamma grains in direct contact with the quasicrystalline substrate. Occasionally, we observe a fourth phase at the beta/gamma interface, identified as beta(1), possessing a lattice parameter a(beta 1) equal to 2a(beta) and 2/3a(gamma).
Title:
The effect of thermal treatment on the magnetic state and cluster-related disorder of icosahedral Al-Pd-Mn quasicrystals
Authors:
Jaglicic, Z; Jagodic, M; Grushko, B; Zijlstra, ES; Weber, T; Steurer, W; Dolinsek, J Author Full Names: Jaglicic, Z.; Jagodic, M.; Grushko, B.; Zijlstra, E. S.; Weber, Th.; Steurer, W.; Dolinsek, J.
Source:
INTERMETALLICS 18 (4): 623-632 APR 2010
Abstract:
The evolution of the magnetic state and the cluster-related disorder upon thermal treatment of the icosahedral i-Al-Pd-Mn quasicrystals were studied on single-crystalline samples subjected to different thermal annealing sequences involving short and long annealing times and slow or fast cooling modes. In this way, thermal equilibration of the samples was systematically changed by varying the amount of vacancies and thermal strains. The results show that different thermal treatments can reduce or increase reversibly the paramagnetic magnetization of the i-Al-Pd-Mn samples of nominally the same composition by a factor up to 26. Magnetic susceptibility and magnetization measurements have demonstrated comparable importance of the vacancies and thermal strains on the size of the mean effective magnetic moment per Mn atom. While the reduced vacancy concentration reduces the mean effective moment, thermal strains induced by rapid cooling increase it. Theoretical ab-initio calculations of the effect of vacancies and thermal strains on the magnetic properties of a periodic approximant model to the i-Al-Pd-Mn phase predict that vacancies at specific Al sites introduce magnetic moments at the Mn sites, which are otherwise nonmagnetic in the perfect structure. Removal of thermal strains by relaxation of the structure containing vacancies acts in the opposite way by decreasing the moments. X-ray diffraction experiments with full reciprocal space sampling revealed that the cluster-related disorder cannot be improved noticeably by annealing at either 800 degrees C or 600 degrees C even for annealing times as long as three months, suggesting that this disorder may be intrinsic to the i-Al-Pd-Mn phase, needed for the electronic or entropic stabilization of the structure. (C) 2009 Elsevier Ltd. All rights reserved.
Title:
NEPHELINE: STRUCTURE OF THREE SAMPLES FROM THE BANCROFT AREA, ONTARIO, OBTAINED USING SYNCHROTRON HIGH-RESOLUTION POWDER X-RAY DIFFRACTION
Authors:
Antao, SM; Hassan, I Author Full Names: Antao, Sytle M.; Hassan, Ishmael
Source:
CANADIAN MINERALOGIST 48 (1): 69-80 FEB 2010
Abstract:
The crystal structure of three samples of nepheline (ideally, K2Na6[Al8Si8O32]) from the Bancroft area of Ontario (1a, b: Egan Chute, 2: Nephton, and 3: Davis Hill), each with different types of superstructure reflections, has been studied using synchrotron high-resolution powder X-ray diffraction (HRPXRD) data and Rietveld structure refinement. The samples have different origins. The structure was refined in space group P6(3). The R-F(2) index, number of unique observed reflections, pseudohexagonal subcell parameters, and site-occupancy factor (sof) for the K site are as follows: Sample 1b: R-F(2) = 0.0433, N-obs = 1399, a = 9.99567(1), c = 8.37777(1) angstrom, V = 724.907(2) angstrom(3), and K (sof) = 0.716(1). Sample 2: R-F(2) = 0.0669, N-obs = 1589, a = 10.00215(1), c = 8.38742(1) angstrom, V = 726.684(1) angstrom(3), and K (sof) = 0.920(1). Sample 3: R-F(2) = 0.0804, N-obs = 1615, a = 9.99567(1), c = 8.37873(1) angstrom, V = 724.991(1) angstrom(3), and K (sof) = 0.778(2). Sample 2 has the largest sof for K and the largest volume. The satellite reflections in the three nepheline samples were observed in the HRPXRD traces and give rise to different incommensurate superstructures. The Al and Si atoms in the T-3 and T-4 sites are ordered differently in the three samples, which may indicate the presence of a domain structure based on Al-Si order. The positions for the Al and Si atoms were interchanged in two samples because of the resulting < T-O > distances. The slight excess of Si over Al atoms, characteristically encountered in well-analyzed samples of nepheline, is reflected in the < T-O > distances.
Title:
The incommensurately modulated structures of natural natrite at 120 and 293 K from synchrotron X-ray data
Authors:
Arakcheeva, A; Bindi, L; Pattison, P; Meisser, N; Chapuis, G; Pekov, I Author Full Names: Arakcheeva, Alla; Bindi, Luca; Pattison, Philip; Meisser, Nicolas; Chapuis, Gervais; Pekov, Igor
Source:
AMERICAN MINERALOGIST 95 (4): 574-581 APR 2010
Abstract:
The incommensurately modulated structure of the mineral natrite has been refined for the first time. Two single-crystal grains, Lv and Kh, from two different occurrences [Mt. Karnasurt, Lovozero massif (Lv), Kola peninsula, Russia, and the pegmatite of Mt. Koashva, Khibiny massif (Kh)], have been investigated at 293 and 120 K using synchrotron X-ray data. The average structures of both minerals are identical and the basic features of the structural modulations are similar to the synthetic gamma-Na2CO3 phase previously published. The gamma (incommensurate) -> delta (lock-in) phase transition reported at low temperature for the synthetic compound was not observed down to 120 K in natural natrite. Crystal-chemical aspects, especially about the second coordination sphere for the carbon atoms, are examined to explain the different structural behaviors observed at low temperature. The possible role played by the minor isomorphous substitutions in natural na! trite specimens is also discussed.

Update: 8-Apr-2010

Title:
Structural investigation of composite phases Ba1+x[(NaxMn1-x)O-3] with x similar or equal to 2/7, 5/17 and 1/3; exotic Mn4.5+ valence
Authors:
Roussel, P; Perez, O; Quarez, E; Leligny, H; Mentre, O Author Full Names: Roussel, Pascal; Perez, Olivier; Quarez, Eric; Leligny, Henri; Mentre, Olivier
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 225 (1): 1-11 2010
Abstract:
Structural models are proposed for three composite compounds of chemical formula Ba1+x[(NaxMn1-x)O-3] (x similar or equal to 2/7, 5/17 and 1/3) by single crystal X-ray diffraction; superspace formalism is used to obtain an unified description of the three phases. The modulation affecting Ba atoms can be easily designed but the competition "occupational/displacive" modulations relating to the Mn/Na metallic columns were particularly difficult to modelize. However, the large amplitude of the displacive modulation affecting the oxygen atoms (similar or equal to +/- 0.7 angstrom) in comparison with that observed for related compounds (similar or equal to +/- 0.3 angstrom) makes it a direct consequence of the Na+ alkali insertion inside the trigonal prisms. Owing to this insertion, the Mn atoms exhibit, in the three phases, an "exotic" oxidation state of about +4.5. In addition, even if the sequence between face sharing MnO6 octahedra and NaO6 trigonal prisms can be analytically deduced from the x value, it is clear that the Na/Mn contrasts play in favour of its accurate determination through the XRD single crystal refinement.
Title:
Spin and Charge Order in the Doped Hubbard Model: Long-Wavelength Collective Modes
Authors:
Chang, CC; Zhang, SW Author Full Names: Chang, Chia-Chen; Zhang, Shiwei
Source:
PHYSICAL REVIEW LETTERS 104 (11): Art. No. 116402 MAR 19 2010
Abstract:
Determining the properties of the two-dimensional Hubbard model is an outstanding problem in physics. Applying recent advances in constrained path auxiliary-field quantum Monte Carlo techniques and simulating large rectangular supercells, we characterize the magnetic and charge properties in the ground state as a function of doping. At intermediate interaction strengths, an incommensurate spin density wave (SDW) state is found, with antiferromagnetic order and essentially homogeneous charge correlation. The wavelength of the collective mode decreases with doping, as does its magnitude. The SDW order vanishes beyond a critical doping. As the interaction is increased, the holes go from a wavelike (delocalized) to a particlelike (localized) state, and charge ordering develops which eventually evolves into stripelike states.
Title:
Quantum dislocations: the fate of multiple vacancies in two-dimensional solid He-4
Authors:
Rossi, M; Vitali, E; Galli, DE; Reatto, L Author Full Names: Rossi, M.; Vitali, E.; Galli, D. E.; Reatto, L.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (14): Art. No. 145401 APR 14 2010
Abstract:
Defects are believed to play a fundamental role in the supersolid state of He-4. We have studied solid He-4 in two dimensions (2D) as a function of the number of vacancies n(v), up to 30, inserted in the initial configuration at rho = 0.0765 angstrom(-2), close to the melting density, with the exact zero-temperature shadow path integral ground state method. The crystalline order is found to be stable also in the presence of many vacancies and we observe two completely different regimes. For small n(v), up to about 6, vacancies form a bound state and cause a decrease of the crystalline order. At larger n(v), the formation energy of an extra vacancy at fixed density decreases by one order of magnitude to about 0.6 K. It is no longer possible to recognize vacancies in the equilibrated state because they mainly transform into quantum dislocations and crystalline order is found almost independently of how many vacancies have been inserted in the initial configuration. The one-body density matrix in this latter regime shows a non-decaying large distance tail: dislocations, that in 2D are point defects, turn out to be mobile, their number is fluctuating, and they are able to induce exchanges of particles across the system mainly triggered by the dislocation cores. These results indicate that the notion of the incommensurate versus the commensurate state loses meaning for solid He-4 in 2D, because the number of lattice sites becomes ill defined when the system is not commensurate. Crystalline order is found to be stable also in 3D in the presence of up to 100 vacancies.
Title:
Characterization of microstructures obtained in wedge shaped Al-Zn-Mg ingots
Authors:
Suarez, MA; Alvarez, O; Alvarez, MA; Rodriguez, RA; Valdez, S; Juarez, JA Author Full Names: Suarez, M. A.; Alvarez, O.; Alvarez, M. A.; Rodriguez, R. A.; Valdez, S.; Juarez, J. A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 492 (1-2): 373-377 MAR 4 2010
Abstract:
The structure present in chill casting taper section of A1-5.3at.%Zn + Mg additions between 3 and 40at.%Mg have been studied by scanning electron microscopy, microanalysis and X-ray diffractometry in order to relate the impact of intermetallic phases such as the tau-Mg-32(Al,Zn)(49) obtained at low Mg-contents with an approximant phase related to quasicrystals at high Mg-contents on its electrochemical efficiency. After microstructural and electrochemical efficiency characterization, it was found that an alloy composition of A1-5.3at.%Zn-10at.%Mg showed a microstructure which consisted of alpha-Al dendrites with tau-phase precipitates showing an electrochemical efficiency of 90% fulfilling the needs for cathodic protection application of structural steels in sea water. (C) 2009 Elsevier B.V. All rights reserved.

Update: 1-Apr-2010

Title:
Transverse modulation and uniform period in Bi1-xSrxMnO3
Authors:
Nagao, M; Kimoto, K; Matsui, Y Author Full Names: Nagao, M.; Kimoto, K.; Matsui, Y.
Source:
PHYSICA B-CONDENSED MATTER 405 (7): 1686-1689 APR 1 2010
Abstract:
The crystal structures of the superstructure phases of the Bi-based manganite Bi1-xSrxMnO3 have been studied by transmission electron microscopy. On the basis of the selected area electron diffraction patterns, our crystallographic analysis revealed that the modulations of Bi1-xSrxMnO3 consist of only transverse modulation associated with the Pcnn-type symmetry, in contrast to the previously believed Ibmm-type symmetry. Moreover, our high-resolution transmission electron microscopy image indicated that a modulation with a noninteger-multiple period has a uniform period but not the mixed state of adjacent integer-multiple periods according to the lever rule. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Superspace description of the homologous series Ga2O3(ZnO)(m)
Authors:
Michiue, Y; Kimizuka, N Author Full Names: Michiue, Yuichi; Kimizuka, Noboru
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 117-129 Part 2 APR 2010
Abstract:
A unified description for the structures of the homologous series Ga2O3(ZnO)(m), gallium zinc oxide, is presented using the superspace formalism. The structures were treated as a compositely modulated structure consisting of two subsystems. One is constructed with metal ions and the other with O ions. The ideal model is given, in which the displacive modulations of ions are well described by the zigzag function with large amplitudes. Alternative settings are also proposed which are analogous to the so-called modular structures. The validity of the model has been confirmed by refinements for phases with m = 6 and m = 9 in the homologous series. A few complex phenomena in real structures are taken into account by modifying the ideal model.
Title:
Modulation functions of incommensurately modulated Cr2P2O7 studied by the maximum entropy method (MEM)
Authors:
Li, L; Schonleber, A; van Smaalen, S Author Full Names: Li, Liang; Schoenleber, Andreas; van Smaalen, Sander
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 130-140 Part 2 APR 2010
Abstract:
The maximum entropy method (MEM) has been used to determine electron density in superspace of incommensurately modulated chromium pyrophosphate from X-ray diffraction data measured by Palatinus et al. [(2006), Acta Cryst. B62, 556-566]. Chromium pyrophosphate, Cr2P2O7, contains ordered regions (83% of the volume) and regions with disorder. Analysis of the MEM density has allowed the determination of the displacive modulation functions within ordered regions. The disordered regions can be described as the alternate occupation of two conformations of the pyrophosphate group and two positions of the chromium atom, with occupational probabilities that depend continuously on the phase of modulation t. A structure model based on the interpretation of the MEM density provides a fit to the diffraction data of the same quality as the model given by Palatinus et al. (2006). The failure to find a model that better fits the data is attributed to the intrinsic inaccuracy of similar to 0.01 angstrom for positions derived from the MEM and to the difficulties in constructing an appropriate model for the anharmonic ADPs and their modulation functions from electron densities.

Update: 25-Mar-2010

Title:
Roles of Bond Alternation in Magnetic Phase Diagram of RMnO3
Authors:
Furukawa, N; Mochizuki, M Author Full Names: Furukawa, Nobuo; Mochizuki, Masahito
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (3): Art. No. 033708 MAR 2010
Abstract:
In order to investigate the nature of the antiferromagnetic structures in perovskite RMnO3, we study a Heisenberg J(1)-J(2) model with bond alternation using analytical and numerical approaches. The magnetic phase diagram which includes incommensurate spiral states and commensurate collinear states is reproduced. We discuss that the magnetic structure with spin up arrow up arrow down arrow down arrow configuration (E-type structure) and the ferroelectricity emerge cooperatively to stabilize this phase. Magnetoelastic couplings are crucial to understand the magnetic and electric phase diagram of RMnO3.
Title:
Theory of Unusual Superconducting Phase Transitions in Heavy Fermion Metals at High Magnetic Fields
Authors:
Zhuravlev, V; Maniv, T; Wosnitza, J Author Full Names: Zhuravlev, V.; Maniv, T.; Wosnitza, J.
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS 159 (1-2): 138-142 APR 2010
Abstract:
We present a non-perturbative theory of paramagnetically-driven superconducting (SC) phase transitions in heavy-fermion metals, which reliably determines their stable SC phases, treats properly the corresponding finite jumps of the order parameter, and can account for unusual features reported recently for this type of materials. It is found that for quasi-2D heavy-fermion metals, such as CeCoIn5, at high magnetic fields oriented perpendicular to the highly conducting planes, the effect of the Fulde-Ferrel (FF) modulation is too weak to prevent a direct first-order phase transition from the normal to the uniform SC state. For 3D heavy-fermion metals, such as URu2Si2, the FF modulation stabilizes, under a decreasing magnetic field, a non-uniform SC state via a second-order phase transition from the normal state. However, at a slightly lower field the modulated phase becomes unstable, transforming to a uniform SC state via a first-order transition.
Title:
Simulation of modulated reflections
Authors:
Lovelace, JJ; Winn, MD; Borgstahl, GEO Author Full Names: Lovelace, Jeffrey J.; Winn, Martyn D.; Borgstahl, Gloria E. O.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 285-292 Part 2 APR 2010
Abstract:
In a modulated crystal, the repeating unit is not periodic but contains a disorder of the molecules that can sometimes be described with a mathematical function. In the diffraction pattern from such a modulated crystal the standard periodic main reflections are flanked by satellite reflections. Generally, incommensurately modulated crystal diffraction cannot be simply described using integers along the reciprocal-lattice directions. However, in the special commensurate case where the satellite spacing is rational relative to the main reflections, a supercell can be used to describe the modulation. Using a supercell allows structural processing to proceed in a 'normal' fashion but with the downside of dealing with many more atoms. Not much is known about the relationship between a highly modulated macromolecular crystal and the resulting satellite intensities so in this study a modulated protein crystal was simulated using a supercell approach. The protein superstructure was modulated to varying degrees and the resultant diffraction patterns and electron-density maps were studied to understand better how a modulation may manifest itself in real protein data. In the case that was evaluated, relatively small structural modulation resulted in significant satellite intensities. Interesting cases were observed where extinguished main reflections had strong satellites.
Title:
The 5:7 Member of the Spin-Ladder Series in the Bi-Sr-Ca-Cu-O System
Authors:
Zaremba, O; Shcherban, O; Akselrud, L; Gladyshevskii, R; Banfi, F; Giannini, E Author Full Names: Zaremba, O.; Shcherban, O.; Akselrud, L.; Gladyshevskii, R.; Banfi, F.; Giannini, E.
Source:
ACTA PHYSICA POLONICA A 117 (1): 42-47 JAN 2010
Abstract:
The crystal structure of the (Bi0.02Sr0.39Ca0.59)(10)Cu17O29 spin-ladder compound was determined from single-crystal X-ray diffraction data. The precursor powder was prepared from stoichiometric amounts of SrCO3, CaCO3, CuO, and Bi2O3 by calcination at 820 degrees C for 20 h and pressed to form a rod used for the crystal growth. The travelling-solvent-floating-zone method was applied in an image furnace to grow large single crystals. The composite commensurate structure was solved and refined in space group F222, Pearson symbol oF224, a = 11.340(2), b = 12.829(2), c = 19.441(3) angstrom, Z = 4. The composite incommensurate structure of the (Bi0.02Sr0.39Ca0.59)(10)Cu17O29 compound was solved and refined in the (3 + 1)-space group F222(00 gamma), a = 11.340(2), b = 12.829(2), c(1) = 2.7773(4), c(2) = 3.8882(6) angstrom, q = 0.7143.

Update: 18-Mar-2010

Title:
Incommensurate 6M-modulated structure of Ni-Fe-Ga martensite
Authors:
Righi, L; Lazpita, P; Gutierrez, J; Barandiaran, JM; Chernenko, VA; Calestani, G Author Full Names: Righi, L.; Lazpita, P.; Gutierrez, J.; Barandiaran, J. M.; Chernenko, V. A.; Calestani, G.
Source:
SCRIPTA MATERIALIA 62 (6): 383-386 MAR 2010
Abstract:
The crystal structure of the modulated, low-temperature matensitic phase in Ni-2 41Fe0 59Ga ferromagnetic shape memory alloy (FSMA) has been determined by Rietveld refinement of neutron powder diffraction data The structure Shows an incommensurate modulated crystal lattice with some analogies with the 7 M modulated martensitic structure Found in Ni2Mn1 2Ga0 8 Heusler alloy The observed type of lattice modulation with q = 0 3521c* gives rise to a new type of martensitic crystal structure in the FSMAs (C) 2009 Acta Materialia Inc Published by Elsevier Ltd All rights reserved
Title:
NMR study of the high-field magnetic phase of LiCuVO4
Authors:
Buttgen, N; Kraetschmer, W; Svistov, LE; Prozorova, LA; Prokofiev, A Author Full Names: Buettgen, N.; Kraetschmer, W.; Svistov, L. E.; Prozorova, L. A.; Prokofiev, A.
Source:
PHYSICAL REVIEW B 81 (5): Art. No. 052403 FEB 2010
Abstract:
We report on NMR studies of the quasi-one-dimensional antiferromagnetic S= 1/2 chain cuprate LiCuVO4, focusing on the high-field spin-modulated phase observed recently in applied magnetic fields H > H-c2(mu H-0(c2) approximate to 7.5 T). The NMR spectra of Li-7 and V-51 around the transition from the ordered to the paramagnetic state were measured. It is shown that the spin-modulated magnetic structure forms with ferromagnetic interactions between spins of neighboring chains within the ab plane at low temperatures 0.6 K < T < T-N. The best fit provides evidence that the mutual orientation between spins of neighboring ab planes is random. For higher temperatures T-N < T less than or similar to 15 K, short-range magnetic order occurs at least on the characteristic time scale of the NMR experiment.
Title:
Revealing the atomic surface structure of the (100) Y-Al-Ni-Co approximant by low-energy electron diffraction and scanning tunneling microscopy
Authors:
Mader, R; Widmer, R; Bauer, B; Gille, P; Groning, P; Steurer, W; Groning, O Author Full Names: Maeder, R.; Widmer, R.; Bauer, B.; Gille, P.; Groening, P.; Steurer, W.; Groening, O.
Source:
PHYSICAL REVIEW B 81 (6): Art. No. 064201 FEB 2010
Abstract:
In this paper we present an investigation of the (100) Y-Al75.8Ni2.1Co22.1 surface, which is structurally and chemically related to the (10000) twofold symmetric surface of the decagonal Al-Ni-Co quasicrystal. The atomic surface structure was probed by low-energy electron diffraction (LEED) and by scanning tunneling microscopy (STM), revealing three different surface terminations and three different types of surface reconstructions. All three terminations were successfully assigned to the densest bulk layers and the origin of the surface reconstructions revealed by LEED could be identified locally by STM. The (100) Y-Al-Ni-Co surface shares with the related (10000) d-AlNiCo quasicrystal surface the strong tendency of reconstruction, which in the former case is occurring along the b axis and in the later along the periodic [00001] direction. Gaining a theoretical understanding of the reconstructions of the (100)Y-Al-Ni-Co surface might therefore help to understand the stability of bulk and surface atomic structures in decagonal quasicrystals. Furthermore, due to the strong relation to the quasicrystalline (10000) d-AlNiCo surface, the crystalline (100) Y-Al75.8Ni2.1Co22.1 surface is now a very promising candidate to study directional anisotropies in epitaxial thin film growth, friction, or the electronic structure, with the advantage of representing a much simpler structure (32 atoms/unit cell) which can be theoretically addressed with less effort compared to its quasicrystalline counter part.
Title:
Hydrodynamic structure factor of quasicrystals
Authors:
Chatzopoulos, A; Trebin, HR Author Full Names: Chatzopoulos, Andreas; Trebin, Hans-Rainer
Source:
PHYSICAL REVIEW B 81 (6): Art. No. 064205 FEB 2010
Abstract:
A theory of the hydrodynamic structure factor for quasicrystals is developed and exploited. Based on the hydrodynamic equations for icosahedral quasicrystals we introduce the terms of dynamic correlation and response. The phononic and phasonic diffuse part of the dynamic structure factor are examined in detail in frequency and time domain. We present a complete set of solutions for the hydrodynamic equations. Out of the diffusive modes we separately study the phasonic diffusion, the anisotropy of the phasonic diffusion constants, and the general solution for phason wall diffusion. All results include phonon-phason coupling.
Title:
Phason dynamics in one-dimensional lattices
Authors:
Lipp, H; Engel, M; Sonntag, S; Trebin, HR Author Full Names: Lipp, Hansjoerg; Engel, Michael; Sonntag, Steffen; Trebin, Hans-Rainer
Source:
PHYSICAL REVIEW B 81 (6): Art. No. 064302 FEB 2010
Abstract:
In quasicrystals, the phason degree of freedom and the inherent anharmonic potentials lead to complex dynamics, which cannot be described by the usual phonon modes of motion. We have constructed simple one-dimensional model systems, the dynamic Fibonacci chain, and approximants thereof. They allow us to study the dynamics of periodic and quasiperiodic structures with anharmonic double-well interactions both by analytical calculations and by molecular-dynamics simulations. We found soliton modes such as breathers and kink solitons and we were able to obtain closed analytical solutions for special cases, which are in good agreement with our simulations. Calculation of the specific heat shows an increase above the Dulong-Petit value, which is due to the anharmonicity of the potential and not caused by the phason degree of freedom.
Title:
Magnetic phase stability of monolayers: Fe on a TaxW1-x(001) random alloy as a case study
Authors:
Ondracek, M; Bengone, O; Kudrnovsky, J; Drchal, V; Maca, F; Turek, I Author Full Names: Ondracek, M.; Bengone, O.; Kudrnovsky, J.; Drchal, V.; Maca, F.; Turek, I.
Source:
PHYSICAL REVIEW B 81 (6): Art. No. 064410 FEB 2010
Abstract:
We present an approach to study the magnetic phase stability of magnetic overlayers on nonmagnetic substrates. The exchange integrals among magnetic atoms in the overlayer are estimated in the framework of the adiabatic approximation and used to construct the effective classical two-dimensional Heisenberg Hamiltonian. Its stability is then studied with respect to a large number of collinear and noncollinear magnetic arrangements which include, as special cases, not only ferromagnetic and various antiferromagnetic configurations but also possible incommensurate spin-spiral structures. This allows us to investigate a broader class of systems than a conventional total energy search based on few, subjectively chosen configurations. As a case study we consider the Fe monolayer on the random nonmagnetic bcc-TaxW1-x(001) surface which was studied recently by a conventional approach. We have found a crossover of the ground state of the Fe monolayer from the ferromagnet on the Ta surface to the c(2 x 2) antiferromagnet on the W surface and that at the composition with about 20% of Ta an incommensurate magnetic configuration might exist.
Title:
Stable and variable features of the magnetic structure of fcc Fe/Cu(001) films
Authors:
Sandratskii, LM Author Full Names: Sandratskii, L. M.
Source:
PHYSICAL REVIEW B 81 (6): Art. No. 064417 FEB 2010
Abstract:
After more than a decade of experimental and theoretical studies of the magnetic structure of the fcc Fe/Cu(001) films, most of the researchers agree that the atomic spins of two surface layers are ferromagnetically ordered whereas the magnetic structure of further layers is not ferromagnetic. The conclusions on the magnetic configuration of the nonferromagnetic part vary broadly from a simple collinear layer-by-layer antiferromagnet to complex incommensurate spin-density wave. We report detailed theoretical study of the fcc Fe/Cu(001) films with 6, 7, and 8 ML coverages. The study is based on the density-functional-theory calculations with the code allowing for the consideration of arbitrary noncollinear magnetic configurations. We suggest a view on the magnetism of the Fe/Cu(001) films that includes the grouping of the layers into blocks with robust collinear magnetic structure whereas the variation in the relative directions of the moments of different blocks is energetically relatively inexpensive. The robust magnetic structure of the three surface layers was found to be double down arrow double up arrow double up arrow. Further layers form the pairs with robust antiferromagnetic structure. We demonstrate that the formation of the robust magnetic blocks corresponds to a certain hierarchy of the interlayer exchange interactions. We suggest that the individual defect pattern of each fabricated film influences before all the relative orientation of the block magnetizations keeping the intrablock structure intact. The calculated inter-atomic exchange parameters are used to study magnetic thermodynamics of the films within mean-field approximation. In particular we focus on possible physical reasons of the appearance of the steplike features in the temperature dependence of the magnetization detected experimentally. We emphasize the important consequences of the inequivalence of the Fe atoms belonging to different layers of the film. This inequivalence makes the properties of the films to be essentially different from the properties of the corresponding bulk system. Using a rigid-band model we investigate the dependence of the exchange parameters on the electron number. We critically discuss the possibility of the formation of the incommensurate SDW in the thin Fe/Cu(001) films. The brief formulation of the idea of robust blocking and its experimental confirmation was recently published as a letter [H. L. Meyerheim, J.-M. Tonnerre, L. M. Sandratskii et al., Phys. Rev. Lett. 103, 267202 (2009)].
Title:
Electronic structure, magnetic, and dielectric properties of the edge-sharing copper oxide chain compound NaCu2O2
Authors:
Leininger, P; Rahlenbeck, M; Raichle, M; Bohnenbuck, B; Maljuk, A; Lin, CT; Keimer, B; Weschke, E; Schierle, E; Seki, S; Tokura, Y; Freeland, JW Author Full Names: Leininger, Ph.; Rahlenbeck, M.; Raichle, M.; Bohnenbuck, B.; Maljuk, A.; Lin, C. T.; Keimer, B.; Weschke, E.; Schierle, E.; Seki, S.; Tokura, Y.; Freeland, J. W.
Source:
PHYSICAL REVIEW B 81 (8): Art. No. 085111 FEB 2010
Abstract:
We report an experimental study of NaCu2O2, a Mott insulator containing chains of edge-sharing CuO4 plaquettes, by polarized x-ray absorption spectroscopy (XAS), resonant magnetic x-ray scattering (RMXS), magnetic susceptibility, and pyroelectric current measurements. The XAS data show that the valence holes reside exclusively on the Cu2+ sites within the copper-oxide spin chains and populate a d orbital polarized within the CuO4 plaquettes. The RMXS measurements confirm the presence of incommensurate magnetic order below a NEel temperature of T-N = 11.5 K, which was previously inferred from neutron powder-diffraction and nuclear-magnetic-resonance data. In conjunction with the magnetic-susceptibility and XAS data, they also demonstrate an "orbital" selection rule for RMXS that is of general relevance for magnetic-structure determinations by this technique. Dielectric property measurements reveal the absence of significant ferroelectric polarization below TN, which is in striking contrast to corresponding observations on the isostructural compound LiCu2O2. The results are discussed in the context of current theories of multiferroicity.
Title:
Ordered oxide layers on the pentagonal surface of AlPdMn quasicrystal
Authors:
Burkardt, S; Erbudak, M Author Full Names: Burkardt, S.; Erbudak, M.
Source:
PHYSICAL REVIEW B 81 (8): Art. No. 085417 FEB 2010
Abstract:
Recently, we reported the structural investigation of the oxide layers grown on the pentagonal surface of icosahedral Al70Pd20Mn10 quasicrystal based on low-energy electron diffraction. The oxide layer was described to consist of five twin domains rotated by 2 pi/5 with respect to each other in accordance with the symmetry of the quasicrystalline substrate each of which having one twofold-symmetry direction of the substrate as a mirror plane. Here, we discuss the oxidation process in more detail and report the growth of different oxide structures depending on the sample temperature and its pretreatment. At room temperature, amorphous oxide layers form. In contrast five distinct and few-nanometer-large domains possessing an internal hexagonal structure with substantial amount of contribution from antiphase domain boundaries grow at 700-800 K for small and large coverage. In an intermediate range, a mixture of antiphase domain-boundary contributions and fractional-order spots characteristic to a 2 root 3(1x1)R +/- 30 degrees S reconstruction of the surface oxide layer is found which additionally stabilized the interface. The previously reported twin-domain model, which was derived after an ion bombardment of the preoxidized surface with subsequent reoxidation, is identified as an oxide layer grown on the (110) surface of a crystalline Al-50(PdMn)(50) alloy as a result of the sputtering.
Title:
THE THERMAL CONDUCTIVITY OF Al73Mn27-xFex TAYLOR PHASES
Authors:
Stanic, D; Popcevic, P; Smiljanic, I; Bihar, Z; Lukatela, J; Leontic, B; Bilusic, A; Batistic, I; Smontara, A Author Full Names: Stanic, Denis; Popcevic, Petar; Smiljanic, Igor; Bihar, Zeljko; Lukatela, Jagoda; Leontic, Boran; Bilusic, Ante; Batistic, Ivo; Smontara, Ana
Source:
MATERIALI IN TEHNOLOGIJE 44 (1): 3-7 JAN-FEB 2010
Abstract:
The thermal conductivity (kappa) of Al73Mn27-xFex (x = 0, 2, 4, 6) complex metallic alloys has been measured in the temperature interval from 2 K to 300 K. All the alloys are Taylor (T) phases, except Al73Mn21Fe6, which is a decagonal (d) quasicrystal. The behaviours of kappa are typical for complex metallic alloys, i.e.. a relatively small magnitude, a Change of slope about 50 K and an increase of the conductivity above 100 K. At room temperature the magnitude of kappa for all the samples is between 2.7 W/mK and 3.3 W/mK. which is comparable to that of thermally insulating amorphous SiO2 and Zr/YO2 ceramics. The reason for such a low thermal conductivity is because both, the electronic and lattice conductivity are low. The electronic contribution to the thermal conductivity is low because of the large electrical resistivity of the samples. The lattice (hernial conductivity is greatly reduced because of the enhanced umklapp process of the phonon scattering (caused by (lie large lattice constant) and by the disorder in the structure.
Title:
HALL EFFECT IN THE CRYSTALLINE ORTHOROMBIC o-Al13Co4 APPROXIMANT TO THE DECAGONAL QUASICRYSTALS
Authors:
Ivkov, J; Stanic, D; Popcevic, P; Smontara, A; Dolinsek, J; Gille, P Author Full Names: Ivkov, Jovica; Stanic, Denis; Popcevic, Petar; Smontara, Ana; Dolinsek, Janez; Gille, Peter
Source:
MATERIALI IN TEHNOLOGIJE 44 (1): 9-12 JAN-FEB 2010
Abstract:
We have investigated the anisotropic Hall effect of the o-Al13Co4 orthorhombic approximant to the decagonal phase. The crystalline-direction-dependent measurements were Performed along the a, b and c direction of the orthorhombic Unit cell. The Hall all effect has been measured for all the combinations of the electrical current and magnetic field directions. The Hall coefficients RI, change with the crystallographic direction from negative electron-like or zero to positive hole-like for different combinations of the current and field directions. The results for the anisotropy of R-n is well correlated with the anisotropy of Rn in the d-Al-Ni-Co and d-Al-Cu-Co quasicrystals. The Hall coefficients of the o-Al13Co4 phase were compared to the literature data on single crystals of the Al76Co22Ni2 and the Al80Cr15Fe5 approximants to the decagonal quasicrystals. allowing I study of the evolution of the Hall coefficient with an increasing structural complexity and unit-cell size.

Update: 4-Mar-2010

Title:
STRUCTURE AND PROPERTIES FEATURES OF Ti-Zr-Ni-QUASICRYSTALS
Authors:
Azhazha, VM; Malykhin, SV; Merisov, BA; Pugachov, AT; Khadzhay, GY Author Full Names: Azhazha, V. M.; Malykhin, S. V.; Merisov, B. A.; Pugachov, A. T.; Khadzhay, G. Ya.
Source:
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY (6): 115-126 2009
Abstract:
For Ti-Zr-Ni ingots prepared by equilibrium crystallization, and 20 to 100 gm ribbons obtained by rapid quenching on the same disc, the dependence of phase composition on the super-pure components charge mixture composition and on the disc velocity has been studied. The technology parameters for synthesis of QC single-phase structures or ones with prevailing portion of icosahedral quasicrystalline structure were determined. The peculiarities of structure,. substructure and stress state of the ribbons were studied. Through the ribbon section, the gradient variations of phase composition, grain size, micro- and nano-hardness, Young modulus, structure and substructure parameters, and residual stress level were established. The gradient distributions depend on the quenching speed. The temperature behaviour of electrical resistivity without external magnetic field and under magnetic field was investigated. The transition to superconductivity state was found. The properties of! hydrogen accumulation and the parameters of its diffusion, as well as mechanical properties and deformation features, and thermo-physical properties of Ti-Zr-Ni quasicrystals were studied. The evolution of structure and stress state in quasicrystals as a result of thermal influence, hydrogen saturation, and irradiation was analyzed.
Title:
Origin of Friction Anisotropy on a Quasicrystal Surface
Authors:
Filippov, AE; Vanossi, A; Urbakh, M Author Full Names: Filippov, Aleksander E.; Vanossi, Andrea; Urbakh, Michael
Source:
PHYSICAL REVIEW LETTERS 104 (7): Art. No. 074302 FEB 19 2010
Abstract:
Wearless friction force experiments [Science 309, 1354 (2005)] have recently demonstrated that tribological response in quasicrystals could be related to the exotic atomic structure of the bulk material. Here, by numerical simulations, we address the origin of the experimentally observed friction anisotropy on a twofold decagonal quasicrystal surface. We predict the distinct stick-slip patterns in the lateral force along the periodic and quasiperiodic directions, specifically exploring the temperature dependence that rules the transitions between single and multiple-slip regimes of motion.
Title:
Geometrical property of the cluster model of the Yb-Cd icosahedral quasicrystal (vol 88, pg 1905, 2008)
Authors:
Takakura, H Author Full Names: Takakura, H.
Source:
PHILOSOPHICAL MAGAZINE 90 (5): 525-525 2010
Title:
The magnetic structure of clinopyroxene-type LiFeGe2O6 and revised data on multiferroic LiFeSi2O6
Authors:
Redhammer, GJ; Roth, G; Treutmann, W; Hoelzel, M; Paulus, W; Andre, G; Pietzonka, C; Amthauer, G Author Full Names: Redhammer, Guether J.; Roth, Georg; Treutmann, Werner; Hoelzel, Markus; Paulus, Werner; Andre, Gilles; Pietzonka, Clemens; Amthauer, Georg
Source:
JOURNAL OF SOLID STATE CHEMISTRY 182 (9): 2374-2384 SEP 2009
Abstract:
The clinopyroxene compounds LiFeSi2O6 and LiFeGe2O6 have been investigated by constant wavelength neutron diffraction at low temperatures and by bulk magnetic measurements. Both compounds are monoclinic, space group P2(1)/c and do not exhibit a change in nuclear symmetry down to 1.4 and 5 K respective. However, they transform to a magnetically ordered state below 20 K. LiFeSi2O6 shows a simple magnetic structure with no indication of an incommensurate modulation. The magnetic space group is P2(1)/c' and the structure is described by a ferromagnetic coupling of spins within the infinite M1 chains of edge-sharing octahedra, while the coupling between these M1 chains is antiferromagnetic. The magnetic phase transition is accompanied by magnetostriction of the lattice when passing through the magnetic phase transition. The magnetic structure of LiFeGe2O6 is different to the silicate: the space group is P2(1)'/c and the magnetic unit cell doubled along the a-direction. Within the M1 chains spins are coupled antiferromagnetically, while the chain to chain coupling is antiferromagnetic when coupling goes via the GeB tetrahedron and ferromagnetic when it goes via the GeA tetrahedron. (C) 2009 Elsevier Inc. All rights reserved.
Title:
Magnetic and structural properties of the magnetic shape memory compound Ni2Mn1.48Sb0.52
Authors:
Brown, PJ; Gandy, AP; Ishida, K; Ito, W; Kainuma, R; Kanomata, T; Neumann, KU; Oikawa, K; Ouladdiaf, B; Sheikh, A; Ziebeck, KRA Author Full Names: Brown, P. J.; Gandy, A. P.; Ishida, K.; Ito, W.; Kainuma, R.; Kanomata, T.; Neumann, K. U.; Oikawa, K.; Ouladdiaf, B.; Sheikh, A.; Ziebeck, K. R. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (9): Art. No. 096002 MAR 10 2010
Abstract:
Magnetization and high resolution neutron powder diffraction measurements on the magnetic shape memory compound Ni2Mn1.48Sb0.52 have confirmed that it is ferromagnetic below 350 K and undergoes a structural phase transition at T-M approximate to 310 K. The high temperature phase has the cubic L2(1) structure with a = 5.958 angstrom, with the excess manganese atoms occupying the 4(b) Sb sites. In the cubic phase above approximate to 310 K the manganese moments are ferromagnetically aligned. The magnetic moment at the 4(a) site is 1.57(12) mu(B) and it is almost zero (0.15(9) mu(B)) at the 4(b) site. The low temperature orthorhombic phase which is only fully established below 50 K has the space group Pmma with a cell related to the cubic one by a Bain transformation a(orth) = (a(cub) + b(cub))/2; b(orth) = c(cub) and c(orth) = (a(cub) - b(cub)). The change in cell volume is approximate to 2.5%. The spontaneous magnetization of samples cooled in fields less than 0.5 T decreases at temperatures below T-M and at 2 K the magnetic moment per formula unit in fields up to 5.5 T is 2.01(5) mu(B). Neutron diffraction patterns obtained below approximate to 132 K gave evidence for a weak incommensurate magnetic modulation with propagation vector (2/3, 1/3, 0).
Title:
Structures and Phase Transitions in (MoO2)(2)P2O7
Authors:
Lister, SE; Soleilhavoup, A; Withers, RL; Hodgkinson, P; Evans, JSO Author Full Names: Lister, Sarah E.; Soleilhavoup, Anne; Withers, Ray L.; Hodgkinson, Paul; Evans, John S. O.
Source:
INORGANIC CHEMISTRY 49 (5): 2290-2301 MAR 1 2010
Abstract:
We report structural investigations into (MoO2)(2)P2O7 using a combination of X-ray, neutron and electron diffraction, and solid-state NMR supported by first principles quantum chemical calculations. These reveal a series of phase transitions on cooling at temperatures of 377 and 325 K. The high temperature gamma-phase has connectivity consistent with that proposed by Kierkegaard at room temperature (but with improved bond length distribution), and contains 13 unique atoms in space group Pnma with lattice parameters a = 12.6577(1) angstrom, b = 6.3095(1) angstrom, c = 10.4161 (1) angstrom, and volume 831.87(1) angstrom(3) from synchrotron data at 423 K. The low temperature alpha-structure was indexed from electron diffraction data and contains 60 unique atoms in space group P2(1)/c with cell parameters a = 17.8161(3) angstrom, b = 10.3672(1) angstrom, c = 17.8089(3) angstrom, beta = 90.2009(2)degrees, and volume 3289.34(7) angstrom(3) at 250 K. First principles calculations of P-31 chemical shift and J couplings were used to establish correlation between local structure and observed NMR parameters, and 1D and 2D P-31 solid-state NMR used to validate the proposed crystal structures. The intermediate beta-phase is believed to adopt an incommensurately modulated structure; P-31 NMR suggests a smooth structural evolution in this region.

Update: 25-Feb-2010

Title:
Modulated Lanthanum Chains in the Crystal Structure of La-3.65[Ru(C-2)(3)]
Authors:
Davaasuren, B; Dashjav, E; Doert, T; Kreiner, G; Schnelle, W; Wagner, FR; Mihalkovic, M; Kniep, R Author Full Names: Davaasuren, Bambar; Dashjav, Enkhtsetseg; Doert, Thomas; Kreiner, Guido; Schnelle, Walter; Wagner, Frank R.; Mihalkovic, Marek; Kniep, Ruediger
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE 636 (1): 41-49 2010
Abstract:
Lanthanum ruthenium carbide La-3.65[Ru(C-2)(3)] crystallizes hexagonal (P6(3)/m with a 887.9(2) pm and c = 1606.8(6) pm, V = 1096.8(4).10(6) nm(3), and Z = 6. The crystal structure contains trigonal-planar Ru(C-2)(3) groups and lanthanum atoms, which form a partial structure of the chemical composition La3Ru(C-2)(3). Additional lanthanum atoms Occupy hexagonal channels built by those carbon atoms of the C-2 ligands, which are non-bonded to the central ruthenium atoms. The distribution of these lanthanum atoms along the c axis results ill a threefold superstructure, which was refined as a commensurate modulated structure (P6(3)/m (00g)s0, q = (0, 0, 1/3)). Harmonic occupational and displacive modulation functions Were used for the structure refinement. The structure converged to R-1 = 4.9 % for all data (R-1 = 2.6 % for the main reflections, R-1 = 11.1 % for the 1(st) order satellite reflections). A small homogeneity range for this phase is predicted by total energy calculations using the PAW-GGA method (VASP). Chemical bonding analysis reveals that file C-2 pairs are best described as acetylide C-2(2-) units.
Title:
SimulaTEM: Multislice simulations for general objects
Authors:
Gomez-Rodriguez, A; Beltran-del-Rio, LM; Herrera-Becerra, R Author Full Names: Gomez-Rodriguez, A.; Beltran-del-Rio, L. M.; Herrera-Becerra, R.
Source:
ULTRAMICROSCOPY 110 (2): 95-104 JAN 2010
Abstract:
In this work we present the program SimulaTEM for the simulation of high resolution micrographs and diffraction patterns. This is a program based on the multislice approach that does not assume a periodic object. It can calculate images from finite objects, from amorphous samples, from crystals, quasicrystals, grain boundaries, nanoparticles or arbitrary objects provided the coordinates of all the atoms can be supplied. (C) 2009 Elsevier B.V. All rights reserved.
Title:
A Tm-169-Mossbauer spectroscopy investigation of orthorhombic phase o-TmMnO3
Authors:
Salama, HA; Stewart, GA; Hutchison, WD; Nishimura, K; Scott, DR; O'Neill, HS Author Full Names: Salama, H. A.; Stewart, G. A.; Hutchison, W. D.; Nishimura, K.; Scott, D. R.; O'Neill, H. StC.
Source:
SOLID STATE COMMUNICATIONS 150 (5-6): 289-291 JAN 2010
Abstract:
AC susceptibility and specific heat measurements confirm that the Mn sub-lattice of o-TmMnO3 orders at T-N(Mn) approximate to 41 K with a weaker feature at T-C approximate to 32 K. Tm-169-Mossbauer spectra are interpreted in terms of a single, asymmetric, quadrupole-split doublet whose line width increases sharply at T-C. This suggests the presence of a weak induced Tm-site moment, consistent with claims that the Mn sub-lattice magnetism undergoes a transition from incommensurate to collinear antiferromagnetic order at this temperature. (C) 2009 Elsevier Ltd. All rights reserved.
Title:
Direction of modulation during twin boundary motion
Authors:
Chulist, R; Oertel, CG; Skrotzki, W; Lippmann, T Author Full Names: Chulist, R.; Oertel, C. -G.; Skrotzki, W.; Lippmann, T.
Source:
SCRIPTA MATERIALIA 62 (5): 235-237 MAR 2010
Abstract:
To study the change of modulation direction during deformation, two NiMnGa single crystals, one with a five-layered modulated tetragonal structure (5 M) and the other with a seven-layered modulated orthorhombic structure (7 M), were chosen. Synchrotron diffraction experiments show that the modulation takes place on the {1 1 0) plane along the < 1 1 0] directions. During deformation the c-axis orientation changes by twinning, and with this the direction of modulation obeying the twin relation also changes. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Geometrical property of the cluster model of the Yb-Cd icosahedral quasicrystal (vol 88, pg 1905, 2008)
Authors:
Takakura, H Author Full Names: Takakura, H.
Source:
PHILOSOPHICAL MAGAZINE 90 (1-4): 525-525 2010
Title:
LiZnNb4O11.5: A novel oxygen deficient compound in the Nb-rich part of the Li2O-ZnO-Nb2O5 system
Authors:
Morozov, VA; Arakcheeva, AV; Konovalova, VV; Pattison, P; Chapuis, G; Lebedev, OI; Fomichev, VV; Van Tendeloo, G Author Full Names: Morozov, Vladimir A.; Arakcheeva, Alla V.; Konovalova, Vera V.; Pattison, Philip; Chapuis, Gervais; Lebedev, Oleg I.; Fomichev, Valery V.; Van Tendeloo, Gustaaf
Source:
JOURNAL OF SOLID STATE CHEMISTRY 183 (2): 408-418 FEB 2010
Abstract:
A novel lithium zinc niobium oxide LiZnNb4O11.5 (LZNO) has been found in the Nb-rich part of Li2O-ZnO-Nb2O5 system. LZNO, with an original alpha-PbO2 related structure, has been synthesized by the routine ceramic technique and characterized by X-ray diffraction and transmission electron microscopy (TEM). Reflections belonging to the LZNO phase, observed in X-ray powder diffraction (XRPD) and electron diffraction, have been indexed as monoclinic with unit cell parameters a=17.8358(9)angstrom, b=15.2924(7)angstrom, c=5.0363(3)angstrom and gamma=96.607(5)degrees or as alpha-PbO2-like with lattice constants a=4.72420(3)angstrom, b=5.72780(3)angstrom, c=5.03320(3)angstrom, gamma=90.048(16)degrees and modulation vector q=0.3a*+1.1b* indicating a commensurately modulated alpha-PbO2 related structure. The monoclinic cell is a supercell related to the latter. Using synchrotron powder diffraction data, the structure has been solved and refined as a commensurate modulation (superspace group P112(1)/n(alpha beta 0)00) as well as a supercell (space group P2(1)/b). The superspace description allows us to consider the LZNO structure as a member of the proposed alpha-PbO2-Z (3 + 1)D structure type, which unifies both incommensurately and commensurately modulated structures. HRTEM reveals several types of defects in LZNO and structural models for these defects are proposed. Two new phases in Li2O-ZnO-Nb2O5 system are predicted on the basis of this detailed HRTEM analysis. (C) 2009 Elsevier Inc. All rights reserved.
Title:
Cooperative effect of monoclinic distortion and sinusoidal modulation in the martensitic structure of Ni2FeGa
Authors:
Lu, JB; Yang, HX; Tian, HF; Zeng, LJ; Ma, C; Feng, L; Wu, GH; Li, JQ; Jansen, J Author Full Names: Lu, J. B.; Yang, H. X.; Tian, H. F.; Zeng, L. J.; Ma, C.; Feng, L.; Wu, G. H.; Li, J. Q.; Jansen, J.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 183 (2): 425-430 FEB 2010
Abstract:
The structural features of the "5M" martensitic phase in Ni2FeGa alloys have been determined by electron diffraction using the multi-slice least-squares (MSLS) method. The results demonstrate that the "5M" phase contains an evident cooperative effect of monoclinic distortion and sinusoidal modulation along the [110](c) direction. Theoretical simulations based on Our refined data suggest that the "5M" martensitic phase observed in Ni-Fe-Ga and Ni-Mn-Ga has visible common behaviors in both stacking sequence and local structural distortion. Considering the cooperative effect of monoclinic distortion and sinusoidal modulation, we demonstrate that the "7M" martensitic phase could adopt two equivalent structural phases corresponding with the stacking sequences of (43). and (52)2, respectively. Crown Copyright (C) 2009 Published by Elsevier Inc. All rights reserved.
Title:
Advantages of aberration correction for HRTEM investigation of complex layer compounds
Authors:
Spiecker, E; Garbrecht, M; Jager, W; Tillmann, K Author Full Names: Spiecker, E.; Garbrecht, M.; Jaeger, W.; Tillmann, K.
Source:
JOURNAL OF MICROSCOPY-OXFORD 237 (3): 341-346 MAR 2010
Abstract:
Aberration-corrected high-resolution transmission electron microscopy (HRTEM) has been applied to resolve the atomic structure of a complex layered crystal, (PbS)(1.14)NbS2, which comprises a high density of incommensurate interfaces. The strong suppression of image delocalization and the favourable contrast transfer under negative C-s imaging (NCSI) conditions have been exploited for obtaining HRTEM images which directly reveal the projected crystal structure and allow to study lattice imperfections, like stacking disorder and layer undulations, with atomic scale resolution. The advantages of aberration-corrected HRTEM over conventional HRTEM are demonstrated by direct comparison of experimental images and computer simulations.
Title:
Microstructure of electrodeposited NiFe/Cu multilayers
Authors:
Tokarz, A; Wieczorek, P; Lis, AK; Morgiel, J Author Full Names: Tokarz, A.; Wieczorek, P.; Lis, A. K.; Morgiel, J.
Source:
JOURNAL OF MICROSCOPY-OXFORD 237 (3): 456-460 MAR 2010
Abstract:
NiFe/Cu multilayer films have been electrodeposited potentiostatically on (001)-oriented Si and polycrystalline Cu substrates by a single bath technique. Standard error of mean and energy dispersive X-ray studies of single NiFe(Cu) layers allow us to establish the right deposition parameters for NiFe and Cu sublayer. Standard error of mean results reveal the layered structure of deposits for relatively thick bilayer thickness (ca. similar to 200 nm). The modulated structure of NiFe/Cu multilayers with extremely thin bilayer thickness (nominal period Lambda = 8 nm) was investigated by transmission electron microscope techniques. A columnar structure of the deposit with column diameter in the range from 10 to 30 nm was observed. These results are comparable with X-ray diffraction measurements of crystallites size obtained by Scherer equation. The line scans acquired using EDS confirmed the layered structure of the deposit, but pointed towards possibility of intermixing! of species from alternating sublayers especially in case of those with finer period.
Title:
Effect of Titanium, Antimony, Cerium and Carbon Nanotubes on the Morphology and Microhardness of Mg-based Icosahedral Quasicrystal Phase
Authors:
Wang, ZF; Zhao, WM; Li, HP; Ding, J; Li, YY; Liang, CY Author Full Names: Wang, Zhifeng; Zhao, Weimin; Li, Haipeng; Ding, Jian; Li, Yongyan; Liang, Chunyong
Source:
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY 26 (1): 27-32 JAN 2010
Abstract:
For the first time, petal-like and spherical Mg-based icosahedral quasicrystal phase (I-phase) were obtained by introducing Ti, Sb, Ce and C nanotubes into Mg-Zn-Y alloy under normal casting conditions. The formation mechanism and stability criterion of spherical I-phase were discussed. The morphology and microhardness of I-phase and their determinants were studied in this paper. The results show that the different value of microhardness of I-phase could be attributed to the different kinds of the fourth component and its content, and its different innate characters. The final morphology of icosahedral quasicrystalline (IQC) is decided by the size of critical stable radius R-r, the content of the fourth component and degree of undercooling.
Title:
SUPERCONDUCTIVITY, SPIN AND CHARGE DENSITY STRUCTURES IN ONE AND TWO-DIMENSIONAL SELF-CONSISTENT MODELS
Authors:
Matveenko, SI Author Full Names: Matveenko, S. I.
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B 23 (20-21): 4297-4310 Sp. Iss. SI AUG 20 2009
Abstract:
We review some analytical results of our studies of the charge- and spin density modulations (CDW and SDW) in a one- and two-dimensional electron systems. Self-consistent solutions of Bogoliubov-de Gennes equations for spin-charge solitonic superstructure and superconducting state are obtained in the framework of one and two-dimensional extended Hubbard models. Possible correspondence of the theory with experimental data on stripe phase in high T-c cuprates is discussed. We found various solutions for the two-dimensional self-consistent model of superconductors with d(x2-y2) symmetry of the order parameter, taking into account spin and charge distributions. Analytical solutions for spin-charge density wave phases in the absence of the superconductivity("stripe" and "checkerboard" structures) are presented. Analytical solutions for coexisting superconductivity and stripe-phase modulations in the cores of the Abrikosov's vortices are also found.

Update: 18-Feb-2010

Title:
STUDY OF Al-Cu-Fe-Ti-Cr-Si POWDERS FOR THERMAL SPRAYING PRODUCED BY MECHANOCHEMICAL SYNTHESIS AND SUBSEQUENT ANNEALING
Authors:
Borisova, AL; Adeeva, LI; Tunik, AY; Karpets, MV; Rupchev, VL; Burlachenko, AN Author Full Names: Borisova, A. L.; Adeeva, L. I.; Tunik, A. Yu.; Karpets, M. V.; Rupchev, V. L.; Burlachenko, A. N.
Source:
POWDER METALLURGY AND METAL CERAMICS 48 (9-10): 514-521 SEP 2009
Abstract:
The paper examines the phase transformations of composite powders based on Al63Cu25Fe12 that contain alloying elements (Ti, Cr, Si in the ratio AlCuFe : TiCrSi = 75 : 25). The powders are produced by mechanochemical synthesis and subsequent thermal treatment. Amorphous and crystalline powder mixtures form during synthesis; their annealing results in multiphase structures consisting of alpha, beta(1), and beta(2) phases. High-temperature x-ray diffraction has revealed an alpha-phase between 700 and 900 degrees C. The new a-phase should be regarded as a 1/1 approximant of the nonequilibrium quasicrystalline phase. The maximum content of the approximant phase (68 wt.%) is observed after five-hour synthesis and subsequent annealing (T = 700 degrees C, tau = 2 h) of pressed powders, microhardness of the particles reaching 8900 MPa.
Title:
The surface science of quasicrystals
Authors:
McGrath, R; Smerdon, JA; Sharma, HR; Theis, W; Ledieu, J Author Full Names: McGrath, R.; Smerdon, J. A.; Sharma, H. R.; Theis, W.; Ledieu, J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (8): Art. No. 084022 MAR 3 2010
Abstract:
The surfaces of quasicrystals have been extensively studied since about 1990. In this paper we review work on the structure and morphology of clean surfaces, and their electronic and phonon structure. We also describe progress in adsorption and epitaxy studies. The paper is illustrated throughout with examples from the literature. We offer some reflections on the wider impact of this body of work and anticipate areas for future development.
Title:
Phase field simulation of microstructure evolution in Fe-Cr-Co alloy during thermal magnetic treatment and step aging
Authors:
Lv, LX; Zhen, L; Xu, CY; Sun, XY Author Full Names: Lv, L. X.; Zhen, L.; Xu, C. Y.; Sun, X. Y.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 (8): 987-995 APR 2010
Abstract:
The evolution of modulated structures in Fe-Cr-Co alloys during isothermal aging under an external magnetic field and multiple step aging was simulated based on a phase field method. In this simulation, the magnetic configuration during the decomposition was calculated by a micromagnetic method, and the chemical Gibbs energy function was calculated by the CALPHAD approach based on the experimental equilibrium phase diagram. The calculation results provide a quantitative microstructure change directly linked to the phase diagram and demonstrate obvious microstructure difference between isothermal aging and multiple aging. The ferromagnetic precipitates elongate along the direction of the external magnetic field. The simulated evolution and microstructure are in good agreement with the experimental results. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Desorption of hydrogen from Ti-Zr-Ni hydrides using a mass spectrometer
Authors:
Kocjan, A; McGuiness, PJ; Kobe, S Author Full Names: Kocjan, A.; McGuiness, P. J.; Kobe, S.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 35 (1): 259-265 JAN 2010
Abstract:
We have performed thermogravimetry (TG) and mass-spectrometry measurements of hydrogen desorbed from fully and partially hydrided ternary Ti-Zr-Ni amorphous, quasi-crystalline and crystalline alloys, with four different initial compositions, where the Ti/Zr ratio ranged from 1 to 2.4. The icosahedral, quasicrystalline Ti-Zr-Ni samples were obtained using the melt-spinning technique, and with subsequent annealing of these ribbons at 700 degrees C for 2 h in vacuum we were able to obtain a mixture of crystalline C14 Laves and alpha/beta solid-solution phases. in addition, using subsequent mechanical alloying we produced amorphous powders of Ti-Zr-Ni from the as-spun ribbons. These various samples were then hydrided and analyzed by TG and mass spectrometry. The TG measurements provided us with the mass% of desorbed hydrogen, whereas the mass-spectrometry revealed information about the hydrogen desorption temperatures in the material. Despite the fact that the amorphous and icosahedral. samples undergo some crystallization during the desorption measurements, the resulting mass spectra were different and were closely related to the alloy's structure. In contrast, the shapes of mass spectra were less affected by the composition, the total amount of desorbed hydrogen and the loading pressure. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
Title:
Crystal Structure and Optical and Magnetic Properties of Pr-2(MoO4)(3)
Authors:
Logvinovich, D; Arakcheeva, A; Pattison, P; Eliseeva, S; Tomes, P; Marozau, I; Chapuis, G Author Full Names: Logvinovich, D.; Arakcheeva, A.; Pattison, P.; Eliseeva, S.; Tomes, P.; Marozau, I.; Chapuis, G.
Source:
INORGANIC CHEMISTRY 49 (4): 1587-1594 FEB 15 2010
Abstract:
Praseodymium molybdate Pr-2(MoO4)(3) was synthesized using the standard ceramic route. The crystal structure of the material has been successfully solved in superspace group /2/b(alpha beta 0)00 with lattice constants a = 5.30284(4), b = 5.32699(3), c= 11.7935(1) angstrom, gamma = 90.163(1)degrees, and the modulation vector q = 2/3a* + 0.88810(2)b*. The deviation of the q vector from a rational value allows a description of the structure in terms of nanosize domains with the La-2(MoO4)(3)-like structure separated by stacking faults. Under 450 nm excitation, (P-3(0) level) Pr-2(MoO4)(3) exhibits the characteristic red emission, with the most intense band at 649 nm corresponding to a P-3(0) -> F-3(2) transition. Magnetic susceptibility measurements reveal Curie-Weiss paramagnetism with predominating antiferromagnetic interactions between PI-magnetic moments and no evidence of magnetic transitions down to T = 5 K.
Title:
Rational Synthesis and Characterization of a New Family of Low Thermal Conductivity Misfit Layer Compounds [(PbSe)(0.99)](m)(WSe2)(n)
Authors:
Lin, QY; Smeller, M; Heideman, CL; Zschack, P; Koyano, M; Anderson, MD; Kykyneshi, R; Keszler, DA; Anderson, IM; Johnson, DC Author Full Names: Lin, Qiyin; Smeller, Mary; Heideman, Colby L.; Zschack, Paul; Koyano, Mikio; Anderson, Michael D.; Kykyneshi, Robert; Keszler, Douglas A.; Anderson, Ian M.; Johnson, David C.
Source:
CHEMISTRY OF MATERIALS 22 (3): 1002-1009 FEB 9 2010
Abstract:
We describe here a general synthesis approach for the preparation of new families of misfit layer compounds and demonstrate its effectiveness through the preparation of the first 64 members of the [(PbSe)(0.99)](m) (WSe2)(n) family of compounds, where in and it are integers that were systematically varied from 1 to 8. The new Compounds [(PbSc)(1+y)](m) (WSe2)(n) were synthesized by annealing reactant precursors containing 177 layers of alternating elemental Pb and Se followed by it layers ofalternating elemental W and Se, in which the thickness of each pair of elemental layers was calibrated to yield a structural bilayer of rock salt structured PbSe and a trilayer of hexagonal WSe2. The compounds are kinetically trapped by the similarity of the composition profiles and modulation lengths in the precursor and the targeted compounds. The structural evolution from initial reactant of layer elements to crystalline misfit layer compounds was tracked using X-ray diffraction. The crystal structures of new compounds were probed using both analytical electron microscopy and X-ray diffraction. The c-axis of the misfit layer compound is perpendicular to the Substrate, with a c-axis lattice parameter that changes linearly with a slope of 0.612-0.615 nm as in is changed and n is held constant and with a slope of 0.654-0.656 nm as it is varied and m is held constant. The in-plane lattice parameters did not change as the individual layer thicknesses were increased and a misfit parameter of y = -0.01 was calculated, the first negative misfit parameter among known misfit layer compounds. Analytical electron microscopy images and X-ray diffraction data collected on mixed hkl reflections revealed rotational (turbostratic) disorder of the a-b planes.

Update: 11-Feb-2010

Title:
Phase separation in the CoO2 layer observed in thermoelectric layered cobalt dioxides
Authors:
Takami, T; Nanba, H; Umeshima, Y; Itoh, M; Nozaki, H; Itahara, H; Sugiyama, J Author Full Names: Takami, Tsuyoshi; Nanba, Hiroshi; Umeshima, Yasuhide; Itoh, Masayuki; Nozaki, Hiroshi; Itahara, Hiroshi; Sugiyama, Jun
Source:
PHYSICAL REVIEW B 81 (1): Art. No. 014401 JAN 2010
Abstract:
Co-59 nuclear magnetic resonance (NMR) measurements have been performed to study the local magnetic properties of the misfit layered cobalt dioxides (MLCO's) with the CoO2 and rock-salt layers, (Ca2CoO3)(0.62)CoO2 ( Ca3Co3.92O9.34) and Ca3Co3.92O9.34-delta with oxygen nonstoichiometry. The Co-59 NMR spectrum consists of mainly five lines at 4.2 K at which the samples are in a magnetically ordered state. Among the five NMR lines for Ca3Co3.92O9.34, three lines at higher frequencies (f's) satisfy the resonance condition with two branches indicating the presence of antiferromagnetic internal fields (H-int's). The other two lines exhibit one branch, and one of the two has a nonzero H-int under zero external field (ZF), which signifies the existence of ferromagnetic (FM) H-int's. The other has a zero H-int under ZF. By taking account of both the valence state of the Co ions in each layer and the lattice modulation due to the misfit between the CoO2 layer and the rock-salt layer, the NMR spectra at higher f's are attributed to the Co in the rock-salt layer, whereas those at lower f's to the Co in the CoO2 layer. Furthermore, a spin-density wave order appears to coexist with a FM order in the CoO2 layer for MLCO's. The magnetic and transport properties of these materials are discussed in terms of a separation between two phases.
Title:
Thermodynamics of multiferroic spin chains
Authors:
Sirker, J Author Full Names: Sirker, J.
Source:
PHYSICAL REVIEW B 81 (1): Art. No. 014419 JAN 2010
Abstract:
The minimal model to describe many spin-chain materials with ferroelectric properties is the Heisenberg model with ferromagnetic nearest-neighbor coupling J(1) and antiferromagnetic next-nearest-neighbor coupling J(2). Here we study the thermodynamics of this model using a density-matrix algorithm applied to transfer matrices. We find that the incommensurate spin-spin correlations-crucial for the ferroelectric properties and the analog of the classical spiral pitch angle-depend not only on the ratio J(2)vertical bar J(1)vertical bar but also strongly on temperature. We study small easy-plane anisotropies which can stabilize a vector chiral order as well as the finite-temperature signatures of multipolar phases, stable at finite magnetic field. Furthermore, we fit the susceptibilities of LiCuVO4, LiCu2O2, and Li2ZrCuO4. Contrary to the literature, we find that for LiCuVO4 the best fit is obtained with J(2) similar to 90 K and J(2)vertical bar J(1)vertical bar ! 0.5 and show that these values are consistent with the observed spin incommensurability. Finally, we discuss our findings concerning the incommensurate spin-spin correlations and multipolar orders in relation to future experiments on these compounds.
Title:
Anisotropic magnetic field responses of ferroelectric polarization in the trigonal multiferroic CuFe1-xAlxO2 (x=0.015)
Authors:
Nakajima, T; Mitsuda, S; Kanetsuki, S; Yamano, M; Iwamoto, S; Yoshida, Y; Mitamura, H; Sawai, Y; Tokunaga, M; Kindo, K; Prokes, K; Podlesnyak, A Author Full Names: Nakajima, Taro; Mitsuda, Setsuo; Kanetsuki, Shunsuke; Yamano, Motoyoshi; Iwamoto, Shunsuke; Yoshida, Yukihiko; Mitamura, Hiroyuki; Sawai, Yoshiki; Tokunaga, Masashi; Kindo, Koichi; Prokes, Karel; Podlesnyak, Andrey
Source:
PHYSICAL REVIEW B 81 (1): Art. No. 014422 JAN 2010
Abstract:
We have investigated magnetic field dependences of a ferroelectric incommensurate-helimagnetic order in a trigonal magnetoelectric multiferroic CuFe1-xAlxO2 with x=0.015, which exhibits the ferroelectric phase as a ground state, by means of neutron diffraction, magnetization, and dielectric polarization measurements under magnetic fields applied along various directions. From the present results, we have established the H-T magnetic phase diagrams for the three principal directions of magnetic fields; (i) parallel to the c axis, (ii) parallel to the helical axis, and (iii) perpendicular to the c and the helical axes. While the previous dielectric polarization (P) measurements on CuFe1-xGaxO2 with x=0.035 have demonstrated that the magnetic field dependence of the "magnetic domain structure" results in distinct magnetic field responses of P [S. Seki et al., Phys. Rev. Lett. 103, 237601 (2009)], the present study have revealed that the anisotropic! magnetic field dependence of the ferroelectric helimagnetic order "in each magnetic domain" can be also a source of a variety of magnetic field responses of P in CuFe(1-x)A(x)O(2) systems (A=Al, Ga).
Title:
Gutzwiller magnetic phase diagram of the undoped t-t '-U Hubbard model
Authors:
Markiewicz, RS; Lorenzana, J; Seibold, G Author Full Names: Markiewicz, R. S.; Lorenzana, J.; Seibold, G.
Source:
PHYSICAL REVIEW B 81 (1): Art. No. 014510 JAN 2010
Abstract:
We calculate the magnetic phase diagram of the half-filled t-t'-U Hubbard model as a function of t' and U, within the Gutzwiller approximation plus random-phase approximation. As U increases, the system first crosses over to one of a wide variety of incommensurate phases, whose origin is clarified in terms of double nesting. We evaluate the stability regime of the incommensurate phases by allowing for symmetry breaking with regard to the formation of spin spirals, and find a crossover to commensurate phases as U increases and a full gap opens. The results are compared with a variety of other recent calculations, and in general good agreement is found. For parameters appropriate to the cuprates, double occupancy should be only mildly suppressed in the absence of magnetic order, inconsistent with a strong-coupling scenario.
Title:
Charge-ordering transition and incommensurate antiphase structure of Fe2BO4 as seen via transmission electron microscopy
Authors:
Song, YJ; Yang, HX; Tian, HF; Ma, C; Qin, YB; Zeng, LJ; Shi, HL; Lu, JB; Li, JQ Author Full Names: Song, Y. J.; Yang, H. X.; Tian, H. F.; Ma, C.; Qin, Y. B.; Zeng, L. J.; Shi, H. L.; Lu, J. B.; Li, J. Q.
Source:
PHYSICAL REVIEW B 81 (2): Art. No. 020101 JAN 2010
Abstract:
The nature of the charge ordering (CO) in Fe2BO4 was carefully examined by in situ TEM observations from 360 K down to 20 K. An incommensurate structural modulation with the wave vector q = (1/2, 0, epsilon) becomes plainly visible in association with the CO transition at T-CO approximate to 340 K. Careful structural analysis suggests that this incommensurate structure originates from a well-defined Fe2+/Fe3+ ionic order along the FeO6 octahedral ribbons (in the a-axis direction) and from a discommensurate antiphase stripe order along the c-axis direction. The average periodicity of antiphase stripes changes notably with lowering temperature and, via certain intermediate states, toward a superstructure phase with modulation wave vector of q = (1/2, 0, 0) at similar to 150 K in association with a magnetic phase transition.
Title:
Solution growth of a binary icosahedral quasicrystal of Sc12Zn88
Authors:
Canfield, PC; Caudle, ML; Ho, CS; Kreyssig, A; Nandi, S; Kim, MG; Lin, X; Kracher, A; Dennis, KW; McCallum, RW; Goldman, AI Author Full Names: Canfield, P. C.; Caudle, M. L.; Ho, C-S.; Kreyssig, A.; Nandi, S.; Kim, M. G.; Lin, X.; Kracher, A.; Dennis, K. W.; McCallum, R. W.; Goldman, A. I.
Source:
PHYSICAL REVIEW B 81 (2): Art. No. 020201 JAN 2010
Abstract:
We report the discovery of a binary icosahedral phase in a Sc-Zn alloy obtained through solution-growth, producing millimeter-sized, facetted, single grain quasicrystals that exhibit different growth morphologies, pentagonal dodecahedra, and rhombic triacontahedra, under only marginally different growth conditions. These two morphologies manifest different degrees of quasicrystalline order. The discovery of i-Sc12Zn88 suggests that a re-examination of binary phase diagrams at compositions close to crystalline approximant structures may reveal other binary quasicrystalline phases.
Title:
Composition-dependent spin-phonon coupling in mixed crystals of the multiferroic manganite Eu1-xYxMnO3 (0 <= x <= 0.5) studied by Raman spectroscopy
Authors:
Issing, S; Pimenov, A; Ivanov, VY; Mukhin, AA; Geurts, J Author Full Names: Issing, S.; Pimenov, A.; Ivanov, V. Yu.; Mukhin, A. A.; Geurts, J.
Source:
PHYSICAL REVIEW B 81 (2): Art. No. 024304 JAN 2010
Abstract:
Yttrium substitution in Eu1-xYxMnO3 allows a quasicontinuous tuning of the lattice and magnetic properties of this multiferroic manganite without magnetic interference of rare-earth ions. In order to investigate the composition dependence of the spin-phonon coupling we employ polarized Raman scattering of orthorhombic mixed crystals of Eu1-xYxMnO3 (0 <= x <= 0.5) in the 10-300 K temperature range. Phonon frequency shifts and mode-mixing effects occur, depending on the average rare-earth ion radius determined by the concentration of Eu3+ and Y3+. Moreover, we observe a strong spin-phonon coupling with systematic composition dependence. It manifests itself as a mode-specific softening of the phonon modes in the temperature range of the magnetic ordered phases. The spin-phonon coupling is weakened for increasing Y contents but remains nonzero also in the incommensurate spiral magnetic phase, which occurs for 0.3 <= x <= 0.5. Thus for this class of manganites we report the observation of spin-phonon coupling in an ordered magnetic phase without ferromagnetic ordering within the MnO2 plane. Additionally for known sublattice magnetization quantitative values of the spin-phonon coupling constant are derived. Our results prove the suitability of phonons as a sensitive probe for the spin-spin correlation.
Title:
Critical properties of the unconventional spin-Peierls system TiOBr
Authors:
Clancy, JP; Gaulin, BD; Chou, FC Author Full Names: Clancy, J. P.; Gaulin, B. D.; Chou, F. C.
Source:
PHYSICAL REVIEW B 81 (2): Art. No. 024411 JAN 2010
Abstract:
We have performed detailed x-ray scattering measurements on single crystals of the spin-Peierls compound TiOBr in order to study the critical properties of the transition between the incommensurate spin-Peierls state and the paramagnetic state at T-C2 similar to 48 K. We have determined a value of the critical exponent beta which is consistent with the conventional three-dimensional universality classes, in contrast with earlier results reported for TiOBr and TiOCl. Using a simple power-law-fit function we demonstrate that the asymptotic critical regime in TiOBr is quite narrow, and obtain a value of beta(asy) = 0.32 +/- 0.03 in the asymptotic limit. A power-law-fit function which includes the first-order correction-to-scaling confluent singularity term can be used to account for data outside the asymptotic regime, yielding a more robust value of beta(avg) = 0.39 +/- 0.05. We observe no evidence of commensurate fluctuations above T-C1 in TiOBr, unlike its isostructural sister compound TiOCl. In addition, we find that the incommensurate structure between T-C1 and T-C2 is shifted in Q space relative to the commensurate structure below T-C1.
Title:
Tensile and creep behaviors of Mg-5Zn-2.5Er alloy improved by icosahedral quasicrystal
Authors:
Li, JH; Du, WB; Li, SB; Wang, ZH Author Full Names: Li, Jianhui; Du, Wenbo; Li, Shubo; Wang, Zhaohui
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 527 (4-5): 1255-1259 FEB 15 2010
Abstract:
The tensile and tensile creep properties of the as-cast Mg-5Zn-2.5Er (in wt.%) alloy strengthened by icosahedral quasicrystalline phase (1-phase) were studied. The Mg-5Zn-2.5Er alloy had better tensile properties both at room temperature and 175 degrees C than AE42 and Mg-5Zn alloys. Compared to AE42 alloy, the as-cast Mg-5Zn-2.5Er alloy had smaller steady-state creep rate and total creep strain under the creep conditions of 175 degrees C and 70 MPa for 100 h. The better creep resistance of the Mg-5Zn-2.5Er was mainly due to the formation of I-phase with high-thermal stability distributed along grain boundary. Moreover, microstructure analysis indicated that some fine precipitates in the alpha-Mg matrix can pin the dislocation effectively, improving the creep resistance of the alloy. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Directional magnetoelectric effects in MnWO4: magnetic sources of the electric polarization
Authors:
Toledano, P; Mettout, B; Schranz, W; Krexner, G Author Full Names: Toledano, P.; Mettout, B.; Schranz, W.; Krexner, G.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (6): Art. No. 065901 FEB 17 2010
Abstract:
The ferroelectric order and magnetic field induced effects observed in the spiral phase of MnWO4 are described theoretically. It is demonstrated explicitly that the Dzyaloshinskii-Moriya antisymmetric interactions contribute to the correlation between spins and electric dipoles in the incommensurate and commensurate ferroelectric phases of magnetic multiferroics. However, other single-site symmetric interactions are shown to be involved in the magnetoelectric process, suggesting the possible existence of an electric polarization originating from purely symmetric effects.
Title:
TEM study of a fluorite-type (1-x)Bi2O3 center dot xFe(2)O(3) superstructure in BiFeO3 ceramics synthesized by the rapid liquid-phase sintering method
Authors:
Guo, C; Pu, SZ; Chen, ZL; Li, MY; Cao, JF; Zou, HM Author Full Names: Guo, Chao; Pu, Shizhou; Chen, Zhenlian; Li, Meiya; Cao, Jiefeng; Zou, Huamin
Source:
CERAMICS INTERNATIONAL 36 (2): 507-512 MAR 2010
Abstract:
A commensurate modulated structure of (1 - x)Bi2O3 center dot xFe(2)O(3) is found in the BiFeO3 ceramics synthesized by the rapid liquid-phase sintering method. Transmission electron microscopy studies show that the superstructure is based on fluorite-type delta-Bi2O3 and modulated probably by oxygen vacancy ordering. The existence of such a superstructure may increase the leakage current of BiFeO3 ceramics. (C) 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Title:
Thermal hysteresis of ferroelectric transition in Sr4R2Ti4Nb6O30 (R=Sm and Eu) tetragonal tungsten bronzes
Authors:
Zhu, XL; Chen, XM Author Full Names: Zhu, X. L.; Chen, X. M.
Source:
APPLIED PHYSICS LETTERS 96 (3): Art. No. 032901 JAN 18 2010
Abstract:
Sr4R2Ti4Nb6O30 (R=Sm and Eu) tungsten bronze ceramics were prepared, and the dielectric properties and ferroelectric transition were investigated together with the crystal structure. A ferroelectric transition peak and a low temperature dielectric relaxation were observed from the curve of permittivity versus temperature during heating process for both ceramics. The ferroelectric transition indicated large thermal hysteresis during the heating and cooling cycles for both ceramics, where the ferroelectric transition peak disappeared during the cooling process, and the low temperature dielectric relaxation was obviously enhanced. Moreover, extremely large depression of the Curie-Weiss temperature (T-0) was observed in the present ceramics. These abnormal features were associated with the complex tetragonal tungsten bronze structure with two ferroelectrically active cations over two sets of sites and weak superstructure change from incommensurate to commensurate on cooling. The low temperature dielectric relaxation was due to the oxygen octahedron rotation in the ab plane and the possible compositional variations in the microscale.
Title:
A complicated quasicrystal approximant epsilon(16) predicted by the strong-reflections approach
Authors:
Li, MR; Sun, JL; Oleynikov, P; Hovmoller, S; Zou, XD; Grushko, B Author Full Names: Li, Mingrun; Sun, Junliang; Oleynikov, Peter; Hovmoller, Sven; Zou, Xiaodong; Grushko, Benjamin
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 17-26 Part 1 FEB 2010
Abstract:
The structure of a complicated quasicrystal approximant epsilon(16) was predicted from a known and related quasicrystal approximant epsilon(6) by the strong-reflections approach. Electron-diffraction studies show that in reciprocal space, the positions of the strongest reflections and their intensity distributions are similar for both approximants. By applying the strong-reflections approach, the structure factors of epsilon(16) were deduced from those of the known epsilon(6) structure. Owing to the different space groups of the two structures, a shift of the phase origin had to be applied in order to obtain the phases of epsilon(16). An electron-density map of epsilon(16) was calculated by inverse Fourier transformation of the structure factors of the 256 strongest reflections. Similar to that of epsilon(6), the predicted structure of epsilon(16) contains eight layers in each unit cell, stacked along the b axis. Along the b axis, epsilon(16) is built by banana-shaped tiles and pentagonal tiles; this structure is confirmed by high-resolution transmission electron microscopy (HRTEM). The simulated precession electron-diffraction (PED) patterns from the structure model are in good agreement with the experimental ones. epsilon(16) with 153 unique atoms in the unit cell is the most complicated approximant structure ever solved or predicted.
Title:
Structures of incommensurate and commensurate composite crystals Rb-x MnO2 (x=1.3711, 1.3636)
Authors:
Nuss, J; Pfeiffer, S; van Smaalen, S; Jansen, M Author Full Names: Nuss, Juergen; Pfeiffer, Steffen; van Smaalen, Sander; Jansen, Martin
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 27-33 Part 1 FEB 2010
Abstract:
Rb1.3711MnO2 (Rb11Mn8O16) has been synthesized via the azide/nitrate route from a stoichiometric mixture of the precursors Mn2O3, RbNO3 and RbN3. The structure of this extremely air- and moisture-sensitive compound can best be described in terms of an incommensurate composite structure, built up by a honeycomb-like framework of Rb ions, as one subsystem and by a second subsystem of chains, consisting of edge-sharing MnO4/2 tetrahedra. These two composite substructures interpenetrate in such a way that the manganate chain polyanions centre the channels of the Rb-honeycomb framework. Crystals transform by an aging process into Rb1.3636MnO2 (Rb15Mn11O22), which has a similar structure but a different commensurate modulation. Two reasons can be established for the origin of the modulations: the charge ordering of Mn2+/Mn3+ on one hand, and the incompatibility of the Mn-Mn and Rb-Rb separations on the other.

Update: 4-Feb-2010

Title:
Novel Geometrical Frustration Effects in the Two-Dimensional Triangular-Lattice Antiferromagnet NiGa2S4 and Related Compounds
Authors:
Nakatsuji, S; Nambu, Y; Onoda, S Author Full Names: Nakatsuji, Satoru; Nambu, Yusuke; Onoda, Shigeki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (1): Art. No. 011003 JAN 2010
Abstract:
Geometrical frustration may Suppress conventional magnetic long-range order and possibly promote a novel type of ordering associated with a higher order degree of freedom than spin dipolar-moment such as vector spin chirality and spin quadrupole moment. After a brief overview of such phenomena due to vector spin chirality, we focus on the two-dimensional (2D) frustrated magnetism in the layered chalcogenide Mott insulator NiGa2S4 and related compounds. NiGa2S4 provides the unique example of a S = 1 2D antiferromagnet on a regular exact triangular lattice. Extensive studies using high-purity samples of NiGa2S4 have revealed that Ni2+ S = 1 Heisenberg spins exhibit resonant critical slowing down at T* = 8.5 K without forming a magnetic long-range order, Signaling a viscous spin-liquid state. The critical spin-fluctuation regime extends over almost all order of magnitude in temperature both above and below T. Even well below T, the spin-spin correlation remains short-ranged at an incommensurate wave vector close to (1/6, 1/6,0), corresponding to a 120 degrees correlation with 2a period. Interestingly, however, a 2D linearly dispersive magnetic mode and a quasi-static spin component exist in the low temperature limit. Possibly relevant scenarios including topological phase transition associated with Z(2) vortex due to vector spin chirality, Spill quadrupolar nematic correlation, and C-3 bond-ordering are reviewed.
Title:
Sliding Friction of Kr Films Adsorbed on Graphite
Authors:
Kobayashi, H; Taniguchi, J; Suzuki, M; Miura, K; Arakawa, I Author Full Names: Kobayashi, Hajime; Taniguchi, Junko; Suzuki, Masaru; Miura, Kouji; Arakawa, Ichiro
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (1): Art. No. 014602 JAN 2010
Abstract:
We have carried Out quartz crystal microbalance (QCM) experiments for Kr films adsorbed on exfoliated graphite from a single crystal, and have examined the coverage dependence of the sliding friction and the depinning transition up to the bilayer film. For the monolayer film, the coupled mass density appears at the commensurate and fluid (C+F) phase. An increase of this density starts at the commensurate (C) phase and continues at the incommensurate (IC) phase after the C-IC transition. It was found that the monolayer film slides not uniformly but partly on the substrate, and that the slip time is 60 ns at the C phase. On the other hand, the film around the layer completion slides almost uniformly, and its slip time is about 10 ns. For the bilayer film, the experimental data are reasonably explained by a model in which the slip occurs at the boundary between the first and second atomic layers, in addition to the boundary between the film and the substrate. For the oscillation amplitude sweep at a constant coverage, a rapid change in frequency was observed for the monolayer and bilayer films, which is attributed to the depinning transition. This magnitude takes the minimum value around the layer completion.
Title:
Low temperature incommensurately modulated and noncollinear spin structure in FeCr2S4
Authors:
Kalvius, GM; Krimmel, A; Hartmann, O; Wappling, R; Wagner, FE; Litterst, FJ; Tsurkan, V; Loidl, A Author Full Names: Kalvius, G. M.; Krimmel, A.; Hartmann, O.; Wappling, R.; Wagner, F. E.; Litterst, F. J.; Tsurkan, V.; Loidl, A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (5): Art. No. 052205 FEB 10 2010
Abstract:
FeCr2S4 orders magnetically at T-N approximate to 170 K. According to neutron diffraction, the ordered state down to 4.2 K is a simple collinear ferrimagnet maintaining the cubic spinel structure. Later studies, however, claimed trigonal distortions below similar to 60 K coupled to the formation of a spin glass type ground state. To obtain further insight, muon spin rotation/relaxation (mu SR) spectroscopy was carried out between 5 and 200 K together with new Fe-57 Mossbauer measurements. Below similar to 50 K, our data point to the formation of an incommensurately modulated noncollinear spin arrangement like a helical spin structure. Above 50 K, the spectra are compatible with collinear ferrimagnetism, albeit with a substantial spin disorder on the scale of a few lattice constants. These spin lattice distortions become very large at 150 K and the magnetic state is now better characterized as consisting of rapidly fluctuating short-range ordered spins. The Neel transition is of second order, but ill defined, extending over a range of similar to 10 K. The Mossbauer data around 10 K confirm the onset of orbital freezing and are also compatible with the noncollinear order of iron. The absence of a major change in the quadrupole interaction around 50 K renders the distortion of crystal symmetry to be small.
Title:
EVAL15: a diffraction data integration method based on ab initio predicted profiles
Authors:
Schreurs, AMM; Xian, XY; Kroon-Batenburg, LMJ Author Full Names: Schreurs, Antoine M. M.; Xian, Xinyi; Kroon-Batenburg, Loes M. J.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 70-82 Part 1 FEB 2010
Abstract:
A novel diffraction data integration method is presented, EVAL15, based upon ab initio calculation of three-dimensional (x, y, omega) reflection profiles from a few physical crystal and instrument parameters. Net intensities are obtained by least-squares fitting the observed profile with the calculated standard using singular value decomposition. This paper shows that profiles can be predicted satisfactorily and that accurate intensities are obtained. The detailed profile analysis has the additional advantage that specific physical properties of the crystal are revealed. The EVAL15 method is particularly useful in circumstances where other programs fail, such as regions of reciprocal space with weak scattering, crystals with anisotropic shape or anisotropic mosaicity, K alpha(1)/K alpha(2) peak splitting, interference from close neighbours, twin lattices, or satellite reflections of modulated structures, all of which may frustrate the customary profile learning and fitting procedures. EVAL15 allows the deconvolution of overlapping reflections.
Title:
Ab initio structure solution by iterative phase-retrieval methods: performance tests on charge flipping and low-density elimination
Authors:
Fleischer, F; Weber, T; Deloudi, S; Palatinus, L; Steurer, W Author Full Names: Fleischer, Frank; Weber, Thomas; Deloudi, Sofia; Palatinus, Lukas; Steurer, Walter
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 89-100 Part 1 FEB 2010
Abstract:
Comprehensive tests on the density-modification methods charge flipping [Oszlanyi & Suto (2004). Acta Cryst. A60, 134-141] and low-density elimination [Shiono & Woolfson (1992). Acta Cryst. A48, 451-456] for solving crystal structures are performed on simulated diffraction data of periodic structures and quasicrystals. A novel model-independent figure of merit, which characterizes the reliability of the retrieved phase of each reflection, is introduced and tested. The results of the performance tests show that the quality of the phase retrieval highly depends on the presence or absence of an inversion center and on the algorithm used for solving the structure. Charge flipping has a higher success rate for solving structures, while low-density elimination leads to a higher accuracy in phase retrieval. The best results can be obtained by combining the two methods, i.e. by solving a structure with charge flipping followed by a few cycles of low-density elimination. It is shown that these additional cycles dramatically improve the phases not only of the weak reflections but also of the strong ones. The results can be improved further by averaging the results of several runs and by applying a correction term that compensates for a reduction of the structure-factor amplitudes by averaging of inconsistently observed reflections. It is further shown that in most cases the retrieved phases converge to the best solution obtainable with a given method.
Title:
An electron diffraction and Monte Carlo simulation study of an incommensurate antiferroelectric state in the relaxor ferroelectric Pb2ScTaO6
Authors:
Baba-Kishi, KZ; Pasciak, M Author Full Names: Baba-Kishi, K. Z.; Pasciak, M.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 140-150 Part 1 FEB 2010
Abstract:
Incommensurate satellite reflections modulating along the < 110 >* directions have been observed in the electron diffraction patterns of single crystals of the relaxor ferroelectric Pb2ScTaO6 (PST) recorded via transmission electron microscopy. The satellites occur characteristically within a specific temperature range and display differing or variable modulation vectors relative to their primary reflections. The satellites represent a weak frustrated antiferroelectric state in PST, termed the incommensurate antiferroelectric (IAFE) state. The observed IAFE state coexists with the ferroelectric and paraelectric states within a specific temperature regime and is dynamic in nature, meaning that the dispositions of the satellites can be altered by varying the temperature applied to the crystal, in-situ in the transmission electron microscope. The observed satellites are associated with thin, needle-shaped, closely packed striated domains of about 5-15 nm in width. The satellites appear exclusively in crystals of PST with an advanced degree of 1:1 chemical long-range order, exceeding 90%. The satellites and their domains are interpreted as originating from a displacive, antiferroelectric coupling of the ions, driven in particular by the Pb ions. The Monte Carlo (MC) method was used exhaustively to evaluate the structural regimes that lead to the occurrence of the IAFE state. In the MC simulations, the displacements were correlated with the ferroelectric and antiferroelectric couplings, resulting in the IAFE domains and their associated satellites of differing dispositions or modulation vectors. The results of the MC simulations agree well with the electron diffraction observations, supporting the model of an antiferroelectric displacement with an incommensurate modulation of the Pb ions in the < 110 >* directions.
Title:
EXTRAX: an ImageJ plug-in for electron diffraction intensity extraction
Authors:
Dorcet, V; Larose, X; Fermin, C; Bissey, M; Poullay, P Author Full Names: Dorcet, V.; Larose, X.; Fermin, C.; Bissey, M.; Poullay, P.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 191-195 Part 1 FEB 2010
Abstract:
A plug-in (EXTRAX) has been developed for ImageJ - a public domain Java-based program widely used for image processing and analysis in microscopy. This plug-in allows the extraction and measurement of intensities from electron diffraction spot patterns with a semi-automatic peak location based on a two-dimensional lattice given by the user. It is also possible to take into account supplementary spots originating from high-order Laue zones and/or the existence of a modulation vector.

Update: 29-Jan-2010

Title:
LaSe1.85, CeSe1.83, NdSe1.83 and SmSe1.84 - four new rare earth metal polyselenides with incommensurate site occupancy and displacive modulation
Authors:
Graf, C; Doert, T Author Full Names: Graf, Christian; Doert, Thomas
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 224 (12): 568-579 2009
Abstract:
Crystals of the four new binary rare earth metal polyselenides LaSe1.85, CeSe1.83, NdSe1.83 and SMSe1.84 were obtained by flux reactions. Their two-dimensionally incommensurately modulated structures were solved from X-ray diffraction data. Structure models were established in super space group X4/n(-alpha beta 0)(beta alpha 0)00 with modulation wave vectors q(1) = -alpha a* + beta b* and q(2) = beta a* + alpha b* and the centering vector (0, 0, 1/2, 1/2, 1/2). The unit cell parameters at T = 293 K are a = 4.216(1) angstrom and c = 17.048(2) angstrom for LaSe1.85, a = 4.178(1) angstrom and c = 16.942(3) angstrom for CeSe1.83, a = 4.123(1) angstrom and c = 16.792(2) angstrom for NdSe1.83 and a = 4.080(1) angstrom and c = 16.672(2) angstrom for SmSe1.84; the components of the modulation wave vectors are alpha = beta = 0.292(1) for LaSe1.85 and CeSe1.83, and alpha = beta = 0.293(1) for NdSe1.83 and SmSe1.84, respectively. The modulation originates from a site occupancy wave caused by defects in planar selenium layers coupled to a displacive modulation.
Title:
Interfacial reaction between Al72Ni12Co16 decagonal quasicrystalline particles and liquid aluminium
Authors:
Cheng, SL; Yang, GC; Wang, JC; Liu, F; Zhu, M; Zhou, YH Author Full Names: Cheng, Suling; Yang, Gencang; Wang, Jincheng; Liu, Feng; Zhu, Man; Zhou, Yaohe
Source:
JOURNAL OF MATERIALS SCIENCE 45 (6): 1438-1442 MAR 2010
Abstract:
The interfacial reaction between Al72Ni12Co16 quasicrystalline particles and pure Al melt at 670 A degrees C was investigated. For all the studied samples, only one interfacial reaction product was detected at the interface by scanning electron microscopy. The product was identified to be the Al-9(Co, Ni)(2) crystalline phase, which show an rod-like morphology. The growth rate of the Al-9(Co, Ni)(2) phase layer is very fast. Based on the microstructure analysis results, it is proposed that the layer growth is initially towards the liquid phase, but changes direction towards the quasicrystalline phase by the solid state reaction of diffusional Al with the quasicrystalline phase at the Al72Ni12Co16/Al-9(Co, Ni)(2) interface. A grain boundary grooving effect is deduced to have been involved during the reaction process.

Update: 22-Jan-2010

Title:
STRUCTURE AND PROPERTIES FEATURES OF Ti-Zr-Ni-QUASICRYSTALS
Authors:
Azhazha, VM; Malykhin, SV; Merisov, BA; Pugachov, AT; Khadzhay, GY Author Full Names: Azhazha, V. M.; Malykhin, S. V.; Merisov, B. A.; Pugachov, A. T.; Khadzhay, G. Ya
Source:
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY (6): 115-126 Part 3 2009
Abstract:
For Ti-Zr-Ni ingots prepared by equilibrium crystallization, and 20 to 100 mu m ribbons obtained by rapid quenching on the same disc, the dependence of phase composition on the super-pure components charge mixture composition and on the disc velocity has been studied. The technology parameters for synthesis of QC single-phase structures or ones with prevailing portion of icosahedral quasicrystalline structure were determined. The peculiarities of structure,. substructure and stress state of the ribbons were studied. Through the ribbon section, the gradient variations of phase composition, grain size, micro-and nano-hardness, Young modulus, structure and substructure parameters, and residual stress level were established. The gradient distributions depend on the quenching speed. The temperature behaviour of electrical resistivity without external magnetic field and under magnetic field was investigated. The transition to superconductivity state was found. The properties o! f hydrogen accumulation and the parameters of its diffusion, as well as mechanical properties and deformation features, and thermo-physical properties of Ti-Zr-Ni quasicrystals were studied. The evolution of structure and stress state in quasicrystals as a result of thermal influence, hydrogen saturation, and irradiation was analyzed.
Title:
A neutron powder diffraction study of the helimagnetic structure of TlCo2Se2-xSx
Authors:
Ronneteg, S; Berger, R; Andre, G Author Full Names: Ronneteg, Sabina; Berger, Rolf; Andre, Gilles
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 (6): 681-685 MAR 2010
Abstract:
The magneti clayer structure of TlCo2Se2-xSx has been thoroughly re-investigated with neutron powder diffraction. The cobalt magnetic moments are ferromagnetically arranged with in the layers, but the interlayer coupling differs profoundly with varying composition (x): the spins in TlCo2Se2 form a helix along the c-axis with a turning-angle of similar to 119 degrees at 1.4 K. This kind of helical structure prevails for 0 <= x <= 1.5 with a gradual decrease of the angle with increasing sulphur content, down to 34 degrees, showing an almost linear relationship with the interlayer distance of Co-Co. For x >= 1.75 the interlayer couplingchanges to ferromagnetic. Unexpectedly, two helices were found to coexist at x = 0.5 and x = 1.0. The interaction between adjacent cobalt layers is there characterized by an incommensurate angle (106 degrees, resp., 73 degrees) together with a commensurate angle of 90 degrees. The magnetic structures have been refined as two magnetic phases, each having a characteristic wave vector. A tentative model where the symmetry of the structure and the interlayer distance compete is considered for explaining the simultaneous occurrence of the two kinds of diffraction profile satellites. (C) 2009 Elsevier B. V. All rights reserved.

Update: 14-Jan-2010

Title:
Exploring low-energy landscape of quasi-one-dimensional conductors by heat relaxation and magnetic field
Authors:
Biljakovic, K; Lasjaunias, JC; Melin, R; Monceau, P; Remenyi, G; Sahling, S; Staresinic, D Author Full Names: Biljakovic, K.; Lasjaunias, J. C.; Melin, R.; Monceau, P.; Remenyi, G.; Sahling, S.; Staresinic, D.
Source:
SYNTHETIC METALS 159 (21-22): 2402-2405 Sp. Iss. SI NOV 2009
Abstract:
Modulated charge or spin superstructures of organic quasi-one-dimensional conductors exhibit specific low-energy excitations (LEE) at very low temperatures due to metastable states caused by strong pinning centers. These phase excitations (soliton-like topological defects) demonstrate rich and unexpected properties in a magnetic field, due to their magnetic moments. We discuss mainly on the dynamical aspects related to the non-equilibrium phenomena measured in heat relaxation below 1 K. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Magnetoelectric Response of Multiferroic BiFeO3 and Related Materials from First-Principles Calculations
Authors:
Wojdel, JC; Iniguez, J Author Full Names: Wojdel, Jacek C.; Iniguez, Jorge
Source:
PHYSICAL REVIEW LETTERS 103 (26): Art. No. 267205 DEC 31 2009
Abstract:
We present a first-principles scheme for computing the magnetoelectric response of multiferroics. We apply our method to BiFeO3 (BFO) and related compounds in which Fe is substituted by other magnetic species. We show that under certain relevant conditions-i.e., in the absence of incommensurate spin modulation, as in BFO thin films and some BFO-based solid solutions-these materials display a large linear magnetoelectric response. Our calculations reveal the atomistic origin of the coupling and allow us to identify the most promising strategies to enhance it.
Title:
Elastic behavior associated with phase transitions in incommensurate Ba2NaNb5O15
Authors:
Herrero-Albillos, J; Marchment, P; Salje, EKH; Carpenter, MA; Scott, JF Author Full Names: Herrero-Albillos, J.; Marchment, P.; Salje, E. K. H.; Carpenter, M. A.; Scott, J. F.
Source:
PHYSICAL REVIEW B 80 (21): Art. No. 214112 DEC 2009
Abstract:
The elastic behavior of barium sodium niobate (Ba2NaNb5O15) has been investigated by resonant ultrasound spectroscopy through six different structural phases, with emphasis on the five incommensurate phase transitions near 40, 110, 547, 565, and 582 K. Data near 40 K are at least consistent with the existence of a lock-in transition to P4nm at that temperature [Filipic , J. Phys.: Condens. Matter 19, 236206 (2007)], which has been controversial. A relaxation process occurs around the transition near 110 K and is assigned to a process involving movement of domain walls of the phase. Unusual behavior is observed through the high-temperature incommensurate transitions with large variations in frequency in the ultrasonic resonances, and a broad peak in the dissipation. No clear signature of the 1q-2q incommensurate-incommensurate transition at 565 K is observed. This is compatible with a model in which incommensurate-incommensurate transitions are not expected to manifest elastic anomalies.
Title:
Magnetism at surfaces and defects in icosahedral Al-Pd-Mn quasicrystals
Authors:
Krajci, M; Hafner, J Author Full Names: Krajci, M.; Hafner, J.
Source:
PHYSICAL REVIEW B 80 (21): Art. No. 214419 DEC 2009
Abstract:
In our recent work [Krajcciacute and Hafner, Phys. Rev. B 78, 224207 (2008)] we have demonstrated that the ground state of bulk i-Al-Pd-Mn quasicrystals is nonmagnetic. Mn atoms located at specific sites can acquire a large magnetic moment if they have at least two Pd neighbors in the first coordination shell. Such configurations can be created by substitutional Al/Pd defects which can be formed at low energetic cost because at these sites the overlap between the pseudo-Mackay and Bergman clusters building the quasicrystalline structure leads to conflicting assignments of the chemical decoration. Besides the large magnetic moments formed on these special Mn sites, we have found a broad diffuse background of smaller magnetic moments on many different Mn atoms induced by the large Mn moments. In the present work we extend these investigations to magnetism at the five-fold surface of the quasicrystal and at isolated point defects with particular attention to the formati! on of induced moments. For the stable five-fold surface we find that Mn atoms located in the surface layer carry indeed large magnetic moments of up to 3 mu(B) and that smaller magnetic moments (aligned both parallel and antiparallel to the surface moments) are induced at distances of up to 10 A degrees below the surface. We have considered three types of isolated point defects (and substitutional defects) around a Mn atom and investigated the formation of magnetic moments on the Mn atom and of induced moments on the surrounding sites. For both the magnetization induced below a magnetic surface and the magnetization induced around an Al/Pd substitutional defect, the induced moments show an irregular dependence on the distance from the inducing "source" moment, but a marked dependence on the location of the Mn atom in the occupation domain in six-dimensional hyperspace. Mn atoms with a large coordinate in perpendicular space show large induced moments. Based on the analysis of the local paramagnetic density of states we demonstrate that the formation of a large induced moment is caused by a large polarizability of these Mn atoms, which is related in turn to a rather loosely packed local environment. Per Mn atom, the sum of the source moment (created by a special substitutional defect in the bulk quasicrystal or by the reduced coordination of a Mn atom at the surface) and of the induced moments reaches values of 6 to 8 mu(B), i.e., much higher than the limit set by Hund's rule for the spin moment of a free Mn atom.
Title:
Multiferroicity and spiral magnetism in FeVO4 with quenched Fe orbital moments
Authors:
Daoud-Aladine, A; Kundys, B; Martin, C; Radaelli, PG; Brown, PJ; Simon, C; Chapon, LC Author Full Names: Daoud-Aladine, A.; Kundys, B.; Martin, C.; Radaelli, P. G.; Brown, P. J.; Simon, C.; Chapon, L. C.
Source:
PHYSICAL REVIEW B 80 (22): Art. No. 220402 DEC 2009
Abstract:
FeVO4 has been studied by heat capacity, magnetic susceptibility, electric polarization and single-crystal neutron-diffraction experiments. The triclinic crystal structure is made of S-shaped clusters of six Fe3+ ions, linked by VO43- groups. Two long-range magnetic ordering transitions occur at T-N1=22 K and T-N2=15 K. Both magnetic structures are incommensurate and below T-N2, FeVO4 becomes weakly ferroelectric coincidentally with the loss of the collinearity of the magnetic structure in a very similar fashion than in the classical TbMnO3 multiferroic material. However we argue that the symmetry considerations and the mechanisms invoked to explain these properties in TbMnO3 do not straightforwardly apply to FeVO4. First, the magnetic structures, even the collinear structure, are all acentric so that ferroelectricity in FeVO4 is not correlated with the fact magnetic ordering is breaking inversion symmetry. Regarding the mechanism, FeVO4 has quenched orbital moments that questions the exact role of the spin-orbit interactions.
Title:
Comparative study on internal friction in an Al-Pd-Mn icosahedral quasicrystal and its crystal approximants
Authors:
So, YG; Sato, S; Edagawa, K; Mori, T; Tamura, R Author Full Names: So, Yeong-Gi; Sato, Shun; Edagawa, Keiichi; Mori, Takahiro; Tamura, Ryuji
Source:
PHYSICAL REVIEW B 80 (22): Art. No. 224204 DEC 2009
Abstract:
The internal friction was measured for an Al-Pd-Mn icosahedral phase (i-phase) and its 1/1 and 2/1 approximant phases in an Al-Pd-Mn-Si system in a forced flexural-oscillation mode in a frequency range of 0.05-20 Hz and a temperature range of 300-873 K. For the i-phase, large and small absorption peaks were observed with Q(-1)approximate to 1.3x10(-2) and 8x10(-4), respectively. These two peaks were absent for the 1/1-phase, which showed two other peaks instead. The 2/1-phase exhibited the features of both the i and 1/1-phases; it showed two peaks of the i-phase and one of the two peaks of the 1/1-phase. All the observed peaks were of the thermally activated relaxation type, and their activation enthalpies and frequency factors were evaluated. The larger peak of the i-phase, which was absent for the 1/1-phase and present with a much reduced intensity for the 2/1-phase, was shown to result from a relaxation process involving collective atomic motion. Collective and correl! ated phason jumps were discussed as a possible mechanism for it. It was speculated that the other peaks observed only for the approximant phases are due to Zener relaxations by the reorientation of atom pairs involving Si.
Title:
Excitation spectrum and magnetic field effects in a quantum critical spin-orbital system: The case of FeSc2S4
Authors:
Chen, G; Schnyder, AP; Balents, L Author Full Names: Chen, Gang; Schnyder, Andreas P.; Balents, Leon
Source:
PHYSICAL REVIEW B 80 (22): Art. No. 224409 DEC 2009
Abstract:
The orbitally degenerate A-site spinel compound FeSc2S4 has been experimentally identified as a "spin-orbital liquid," with strong fluctuations of both spins and orbitals. Assuming that the second-neighbor spin-exchange J(2) is the dominant one, we argued in a recent theoretical study [G. Chen , Phys. Rev. Lett. 102, 096406 (2009)] that FeSc2S4 is in a local "spin-orbital singlet" state driven by spin-orbit coupling, close to a quantum critical point, which separates the spin-orbital singlet phase from a magnetically and orbitally ordered phase. In this paper, we refine further and develop this theory of FeSc2S4. First, we show that inclusion of a small first-neighbor exchange J(1) induces a narrow region of incommensurate phase near the quantum critical point. Next, we derive the phase diagram in the presence of an external magnetic field B, and show that the latter suppresses the ordered phase. Lastly, we compute the field-dependent dynamical magnetic susceptibility chi(k,omega;B), from which we extract a variety of physical quantities. Comparison with and suggestions for experiment are discussed.
Title:
Kinetic magnetism and orbital order in iron telluride
Authors:
Turner, AM; Wang, F; Vishwanath, A Author Full Names: Turner, Ari M.; Wang, Fa; Vishwanath, Ashvin
Source:
PHYSICAL REVIEW B 80 (22): Art. No. 224504 DEC 2009
Abstract:
Iron telluride (FeTe), a relative of the iron-based high-temperature superconductors, displays unusual magnetic order and structural transitions. Here, we explore the idea that strong correlations may play an important role in these materials. We argue that the unusual orders observed in FeTe can be understood from a picture of correlated local moments with orbital degeneracy, coupled to a small density of itinerant electrons. A component of the structural transition is attributed to orbital, rather than magnetic ordering, introducing a strongly anisotropic character to the system along the diagonal directions of the iron lattice. Double exchange interactions couple the diagonal chains leading to the observed ordering wave vector. The incommensurate order in samples with excess iron arises from electron doping in this scenario. The strong anisotropy of physical properties in the ordered phase should be detectable by transport in single domains. Predictions for ARPES, inelastic neutron scattering and hole/electron doping studies are also made.
Title:
Pokrovsky-Talapov model at finite temperature: A renormalization-group analysis
Authors:
Lazarides, A; Tieleman, O; Smith, CM Author Full Names: Lazarides, A.; Tieleman, O.; Smith, C. Morais
Source:
PHYSICAL REVIEW B 80 (24): Art. No. 245418 DEC 2009
Abstract:
We calculate the finite-temperature shift of the critical wave vector Q(c) of the Pokrovsky-Talapov model using a renormalization-group analysis. Separating the Hamiltonian into a part that is renormalized and one that is not, we obtain the flow equations for the stiffness and an arbitrary potential. We then specialize to the case of a cosine potential, and compare our results to well-known results for the sine-Gordon model, to which our model reduces in the limit of vanishing driving wave vector Q=0. Our results may be applied to describe the commensurate-incommensurate phase transition in several physical systems and allow for a more realistic comparison with experiments, which are always carried out at a finite temperature.
Title:
Hyperfine Fields and Magnetic Structure in the B Phase of CeCoIn5
Authors:
Curro, NJ; Young, BL; Urbano, RR; Graf, MJ Author Full Names: Curro, Nicholas J.; Young, Ben-Li; Urbano, Ricardo R.; Graf, Matthias J.
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS 158 (3-4): 635-646 FEB 2009
Abstract:
We re-analyze Nuclear Magnetic Resonance (NMR) spectra observed at low temperatures and high magnetic fields in the field-induced B phase of CeCoIn5. The NMR spectra are consistent with incommensurate antiferromagnetic order of the Ce magnetic moments. However, we find that the spectra of the In(2) sites depend critically on the direction of the ordered moments, the ordering wavevector and the symmetry of the hyperfine coupling to the Ce spins. Assuming isotropic hyperfine coupling, the NMR spectra observed for H parallel to [100] are consistent with magnetic order with wavevector Q = pi (1+delta/a, 1/a, 1/c) and Ce moments ordered antiferromagnetically along the [100] direction in real space. If the hyperfine coupling has dipolar symmetry, then the NMR spectra require Ce moments along the [ 001] direction. The dipolar scenario is also consistent with recent neutron scattering measurements that find an ordered moment of 0.15 mu(B) along [001] and Q(n) = pi(1+delta/a, 1+delta/a, 1/c) with in-commensuration delta = 0.12 for field H parallel to [1 (1) over bar0]. Using these parameters, we find that a hyperfine field with dipolar contribution is consistent with findings from both experiments. We speculate that the B phase of CeCoIn5 represents an intrinsic phase of modulated superconductivity and antiferromagnetism that can only emerge in a highly clean system.
Title:
Observation of two separate charge density wave transitions in Gd2Te5 via transmission electron microscopy and high-resolution X-ray diffraction
Authors:
Shin, KY; Ru, N; Fisher, IR; Condron, CL; Toney, MF; Wu, YQ; Kramer, MJ Author Full Names: Shin, K. Y.; Ru, N.; Fisher, I. R.; Condron, C. L.; Toney, M. F.; Wu, Y. Q.; Kramer, M. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 489 (2): 332-335 JAN 21 2010
Abstract:
Gd2Te5 is a layered material consisting of alternating single and double square planar Te sheets. At room temperature the material hosts a complex lattice modulation characterized by multiple in-plane wavevectors. Diffraction measurements performed via transmission electron microscopy and high-resolution X-ray scattering reveal two distinct transitions at T-c1 = 410(3) and T-c2 = 532(3) K, associated with an on-axis incommensurate lattice modulation and an off-axis commensurate lattice modulation respectively. Our results show that the two lattice modulations are separate in origin but that there is some coupling between them. (C) 2009 Elsevier B.V. All rights reserved.

Update: 7-Jan-2010

Title:
First-Principles Modeling of Multiferroic RMn2O5
Authors:
Cao, K; Guo, GC; Vanderbilt, D; He, LX Author Full Names: Cao, Kun; Guo, Guang-Can; Vanderbilt, David; He, Lixin
Source:
PHYSICAL REVIEW LETTERS 103 (25): Art. No. 257201 DEC 18 2009
Abstract:
We investigate the phase diagrams of RMn2O5 via a first-principles effective-Hamiltonian method. We are able to reproduce the most important features of the complicated magnetic and ferroelectric phase transitions. The calculated polarization as a function of temperature agrees very well with experiments. The dielectric-constant step at the commensurate-to-incommensurate magnetic phase transition is well reproduced. The microscopic mechanisms for the phase transitions are discussed.
Title:
Electric Control of Spin Helicity in Multiferroic Triangular Lattice Antiferromagnet CuCrO2 with Proper-Screw Order
Authors:
Soda, M; Kimura, K; Kimura, T; Matsuura, M; Hirota, K Author Full Names: Soda, Minoru; Kimura, Kenta; Kimura, Tsuyoshi; Matsuura, Masato; Hirota, Kazuma
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (12): Art. No. 124703 DEC 2009
Abstract:
We have carried out a spin-polarized-neutron study on multiferroic CuCrO2 to clarify the origin of the ferroelectricity. The neutron results demonstrate that an incommensurate proper-screw magnetic structure of CuCrO2 induces electric polarization. Not only the magnetic structure but also the oxygen location contributes to the ferroelectricity of CuCrO2. The electric polarization of CuCrO2 can be explained not by a conventional spin-current model but by a theoretical prediction proposed by Arima. The spin helicities of CuCrO2 can be reversed by the reversal of the electric field E in the multiferroic phase.
Title:
Coexistence of the antiferromagnetic and superconducting order and its effect on spin dynamics in electron-doped high-T-c cuprates
Authors:
Chen, CP; Jiang, HM; Li, JX Author Full Names: Chen, Cui-Ping; Jiang, Hong-Min; Li, Jian-Xin
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (3): Art. No. 035701 JAN 27 2010
Abstract:
In the framework of the slave-boson approach to the t-t'-t ''-J model, it is found that for electron-doped high-T-c cuprates, the staggered antiferromagnetic (AF) order coexists with the superconducting (SC) order in a wide doping level ranged from underdoped to nearly optimally doped at the mean-field level. In the coexisting phase, it is revealed that the spin response is commensurate in a substantial frequency range below a crossover frequency omega(c) for all dopings considered, and it switches to the incommensurate structure when the frequency is higher than omega(c). This result is in agreement with the experimental measurements. Comparison of the spin response between the coexisting phase and the pure SC phase with a d(x2-y2)-wave pairing plus a higher harmonics term (DP + HH) suggests that the inclusion of the two-band effect is important to consistently account for both the dispersion of the spin response and the non-monotonic gap behavior in the electron-doped cuprates.
Title:
The modulated structure and ferromagnetic insulating state in a nine-layer BaRuO3
Authors:
Du, CH; Yao, CH; Ling, DC; Tang, MT; Hsu, FC; Liu, HL; Hatton, PD; Ikeda, N Author Full Names: Du, Chao-Hung; Yao, Chang-Hung; Ling, Dah-Chin; Tang, Mau-Tsu; Hsu, Fon-Chi; Liu, Hsiang-Lin; Hatton, P. D.; Ikeda, Naoshi
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (3): Art. No. 036003 JAN 27 2010
Abstract:
We report the observation of a modulated structure and a ferromagnetic insulating state in a high quality single crystal of a nine-layer BaRuO3. Using x-ray scattering, the modulated satellites were observed to double the unit cell along the c-axis at low temperature. The ferromagnetic insulating state is confirmed by magnetic and resistivity measurements. Analyzing the peak profiles from the modulation and host structure respectively, showed a lattice distortion at T similar to 55 K. These findings elucidate the intimate relationship between ferromagnetism and lattice distortion in a nine-layer BaRuO3.
Title:
Evidence for a Self-bound Liquid State and the Commensurate-Incommensurate Coexistence in 2D He-3 on Graphite
Authors:
Sato, D; Tsuji, D; Takayoshi, S; Obata, K; Matsui, T; Fukuyama, H Author Full Names: Sato, D.; Tsuji, D.; Takayoshi, S.; Obata, K.; Matsui, T.; Fukuyama, Hiroshi
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS 158 (1-2): 201-206 Sp. Iss. SI JAN 2010
Abstract:
We made heat-capacity measurements of two dimensional (2D) He-3 adsorbed on graphite preplated with monolayer He-4 in a wide temperature range (0.1 <= T <= 80 mK) at densities higher than that for the 4/7 phase (= 6.8 nm(-2)). In the density range of 6.8 <= rho <= 8.1 nm(-2), the 4/7 phase is stable against additional 3He atoms up to 20% and they are promoted into the third layer. We found evidence that such promoted atoms form a self-bound 2D Fermi liquid with an approximate density of 1 nm(-2) from the measured density dependence of the gamma-coefficient of heat capacity. We also show evidence for the first-order transition between the commensurate 4/7 phase and the ferromagnetic incommensurate phase in the second layer in the density range of 8.1 <= rho <= 9.5 nm(-2).
Title:
Growth of large single-grain quasicrystals in the Ag-In-Yb system by Bridgman method
Authors:
Cui, C; Tsai, AP Author Full Names: Cui, Can; Tsai, An Pang
Source:
JOURNAL OF CRYSTAL GROWTH 312 (1): 131-135 DEC 15 2009
Abstract:
Well-defined single-grain Ag-In-Yb icosahedral quasicrystals of order of centimeter have been grown by the Bridgman method. The scanning electron microscopy (SEM) observation showed that the compositional distribution in the single-grain quasicrystals is uniform and Laue X-ray diffraction measurements verified the formation of single-grain icosahedral quasicrystals. The natural growth direction of the single-grain quasicrystals; is close to a direction parallel to a 2-fold axis. It turns out that the Yb content in the initial melt limited within 15-16 at.% is a critical factor determining the formation of single-grain quasicrystal. Based on the experimental result, the mechanism of the growth of single-grain quasicrystal and formation of intermediate zone between quasicrystal and approximant phases are discussed. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Dense quasicrystalline tilings by squares and equilateral triangles
Authors:
O'Keeffe, M; Treacy, MMJ Author Full Names: O'Keeffe, Michael; Treacy, Michael M. J.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 66: 5-9 Part 1 JAN 2010
Abstract:
Dense square-symmetry tilings of the plane by equilateral triangles and squares are described. Repeated substitution of a vertex of a tiling by groups of vertices leads asymptotically to a limiting density that is independent of the starting pattern and to a family of quasicrystalline patterns with 12-fold symmetry. Diffraction patterns were computed by treating the vertices as point scatterers. As the number of substitutions increases, and as the unit-cell size increases, the diffraction patterns from a single unit cell develop a near-perfect 12-fold symmetry. In addition, the low-intensity background scattering in the diffraction patterns exhibits fractal-like self-similar properties, with motifs of local intensity recursively decorating the more intense features as the number of substitutions progresses.

Update: 31-Dec-2009

Title:
Effect of the "negative chemical" pressure on the temperatures of phase transitions in the TlInS2 layered crystal
Authors:
Seyidov, MHY; Suleymanov, RA; Salehli, F Author Full Names: Seyidov, M. - H. Yu.; Suleymanov, R. A.; Salehli, F.
Source:
PHYSICS OF THE SOLID STATE 51 (12): 2513-2519 DEC 2009
Abstract:
The temperature dependences of the permittivity of TlInS2(1 -x)Se2x solid solutions have been experimentally investigated in the temperature range including the points of structural phase transitions in the solid solutions. It has been established that the isovalent substitution of selenium for sulfur in the anion sublattice of the TlInS2(1 - x)Se2x solid solutions shifts the phase transition temperatures T (i) and T (c) toward the low-temperature range with a simultaneous decrease in the temperature interval of the existence of the incommensurate phase. The T-x phase diagram is constructed for the solid solutions under study and the coordinates are determined for a critical point (of the Lifshitz type) at which the lines T (i) (x) and T (c) (x) converge in the phase diagram. The pattern of the T-x phase diagram for the TlInS2(1 - x)Se2x solid solutions has been analyzed within the phenomenological model of a virtual crystal.

Update: 24-Dec-2009

Title:
Hydriding of Ti45Zr38Ni17-xFex nanocompounds
Authors:
Zywczak, A; Shinya, D; Gondek, L; Takasaki, A; Figiel, H Author Full Names: Zywczak, A.; Shinya, Daigo; Gondek, L.; Takasaki, Akito; Figiel, H.
Source:
SOLID STATE COMMUNICATIONS 150 (1-2): 1-4 JAN 2010
Abstract:
Ti-based quasicrystals belong to the second largest group of the stable quasicrystals, showing attractive properties as hydrogen storage materials. The Ti45Zr38Ni17 intermetallic compound forms an icosahedral (i-phase) structure, in which Ti and Zr atoms possess very good chemical affinity for hydrogen absorption. We modified the Ti45Zr38Ni17 compounds by substituting 3d metals (iron) for Ni to obtain amorphous phase. The samples were produced by mechanical alloying. The 3d metal atoms are located in the same positions as nickel. The structural characterization was made by means of XRD measurements. Thermodynamic properties were studied by differential scanning calorimetry (DSC) and thermal desorption spectroscopy (TDS). The obtained amorphous phases Ti45Zr38Ni(9,13)Fe(8,4) transform to the i-phase at the similar temperature range as Ti45Zr38Ni17. The final concentration of absorbed hydrogen depends on the amount of Fe. When increasing the amount of iron, the hydrogen release temperature becomes lower. After hydriding, the samples decompose into simple metal hydrides. (C) 2009 Elsevier Ltd. All rights reserved.
Title:
MODULATED MAGNETIC STATE OF A NONUNIFORMLY STRAINED IRON BORATE SINGLE CRYSTAL INDUCED BY A MAGNETIC FIELD
Authors:
Boidedaev, SR; Sokolov, BY Author Full Names: Boidedaev, S. R.; Sokolov, B. Yu.
Source:
RUSSIAN PHYSICS JOURNAL 52 (7): 759-762 JUL 2009
Abstract:
A remarkable feature of technical magnetization of a nonuniformly strained iron borate (FeBO3) crystal is long-period spatial modulation of the magnetic order parameter for this weak ferromagnet observed in external magnetic field H-1 <= H <= H-2 [1]. Investigations performed in [1] have demonstrated that the modulated magnetic structure (MMS) of nonuniformly strained FeBO3 arises when the vector. is oriented near a certain reference crystal direction of the easy magnetization (basal) crystal plane. During magnetization in this direction, rotation of the ferromagnetism vector m (or of the antiferromagnetism vector l perpendicular to m by definition) in the basal plane occurs somewhat specifically: after the termination of displacements of the domain boundaries, the single domain structure is first formed in the crystal, and the local vectors m appear oriented along the easy magnetization direction (the uniform low-field phase); then at H = H-1! , the magnetic structure of the crystal changes from the uniform to spatially modulated structure stable for H-1 <= H <= H-2 (the sinusoidal phase); then at H = H-2, the crystal passes once again to the uniform magnetic state with m parallel to H (the uniform high-field phase). The sinusoidal phase has the form of a static transverse spin wave linearly polarized in the basal plane in which the azimuth of the local vector m oscillates about the average magnetization direction. Since the MMS is not observed in FeBO3 without mechanical stresses, the specific feature of magnetization of the examined crystal established in [1] was attributed to the occurrence in its basal plane of additional spatially nonuniform (random) magnetic anisotropy caused by local deformations of the crystal lattice at mechanical stresses. According to models of crystal transition from the uniform to modulated magnetic state suggested in [1], the spatial orientation of the vector m (l) in the sinusoidal magnetic phase is determined by competition between the orienting action of the exchange forces on the local sublattice magnetic moments and the disorienting action of the nonuniform magnetic anisotropy forces. Experimental investigations performed in [1] demonstrated that the MMS was observed at temperatures. T < T-s approximate to 140 K; in the examined temperature interval (90 <= T <= 140 K), the spatial MMS period D remained virtually independent of., but significantly decreased with increasing.. In this case, the direction along which modulation of the azimuth of the vector m (l) is observed is independent of. and.; the amplitude of deviation of the local vector m from the average crystal magnetization direction decreases with increasing. and/or.; the field strengths at which the MMS is observed Delta H = (H-2 - H-1) -> 0 when T -> T-s; transitions low-field uniform phase <-> sinusoidal phase <-> high-field uniform phase are the first-order magnetic phase transitions. The present work analyzes the above-listed main properties and conditions of existence of the MMS in a nonuniformly strained FeBO3 crystal using the model suggested in [1].

Update: 17-Dec-2009

Title:
Origin of the long-wavelength magnetic modulation in Ca3Co2O6
Authors:
Chapon, LC Author Full Names: Chapon, L. C.
Source:
PHYSICAL REVIEW B 80 (17): Art. No. 172405 NOV 2009
Abstract:
The origin of the long-wavelength incommensurate magnetic structure of Ca3Co2O6 is discussed considering possible interchains super-superexchange paths. The experimental value of the propagation vector k=(0,0,Delta) with Delta>1 can be reproduced only if one considers the next-nearest super-superexchange interaction. A spin-dimer analysis using the extended Huckel tight-binding method confirms that, despite longer interatomic Co-Co distances, the latter interaction is indeed much stronger. The stability of the observed structure with respect to certain commensurate states is discussed.
Title:
Magnetic and electronic properties of Eu1-xSrxMnO3 (0.3 < x < 0.7) single crystals
Authors:
Tomioka, Y; Kumai, R; Ito, T; Tokura, Y Author Full Names: Tomioka, Y.; Kumai, R.; Ito, T.; Tokura, Y.
Source:
PHYSICAL REVIEW B 80 (17): Art. No. 174414 NOV 2009
Abstract:
Among versatile perovskite manganites showing colossal magnetoresistance (CMR), Eu1-xSrxMnO3 around x similar to 0.4 shows the ferromagnetic metal with the lowest transition temperature (similar to 40 K) due to the narrowest one-electron bandwidth and hence is readily subject to the drastic phase changes with variations in temperature, magnetic field, and hole doping (x). We have investigated the variation in the electronic state with x with use of single crystals. As x increases, the ferromagnetic metal at 0.38 < x < 0.47 changes to a spin-glasslike insulator at 0.48 < x < 0.5, the layered antiferromagnetic (A-type) state at 0.51 < x < 0.6, and the chained antiferromagnetic (C-type) state at 0.6 < x, respectively. Due to the increased disorder upon alloying of Eu/Sr, the charge/orbital ordering with the modulation vector (0, q, 0) with q=1/2 in the orthorhombic Pbnm setting (a(0)similar to b(0)similar to c(0)/root 2 similar to root 2a(p), a(p) being the lattice parameter of the pseudocubic lattice) cannot be formed in a long range but remains short ranged. In the vicinity of x=0.5, an application of an external magnetic field removes such short-range charge/orbital ordering (q=1/2) to cause an insulator to metal transition or CMR. In a broad range of x (0.55 < x < 0.59), the critical temperature for the layered antiferromagnetic state is relatively lowered and alternatively the charge/orbital ordering with q similar to 1/3 becomes to be visible. It has also been found that the modulation is temperature dependent; commensurate with q similar to 1/3 upon the transition while incommensurate with q>1/3 at low temperatures.
Title:
Transition from spin-density-wave to layered antiferromagnetic state induced by hydrogen as a test for the origin of spin-density waves in chromium
Authors:
Uzdin, VM; Zabel, H; Remhof, A; Hjorvarsson, B Author Full Names: Uzdin, V. M.; Zabel, H.; Remhof, A.; Hjorvarsson, B.
Source:
PHYSICAL REVIEW B 80 (17): Art. No. 174418 NOV 2009
Abstract:
Neutron scattering experiments of Cr/V(001) superlattices are discussed, which show that the incommensurate spin-density-wave (SDW) in thick Cr layers becomes suppressed when the V spacer layers are loaded with hydrogen. The hydrogen loading triggers a transition from the incommensurate SDW state to a commensurate antiferromagnetic state. Model Hamiltonian calculations are presented, which show that this transition is not connected with the nesting property of the Cr Fermi surface. Instead, the transition is a manifestation of the antiferromagnetic ground state of Cr, which is separated from the incommensurate SDW state by an energy barrier. Hydrogen is identified as an effective trigger for reducing the activation barrier, enabling the system to relax to the ground state.
Title:
Mutual enhancement of magnetism and Fulde-Ferrell-Larkin-Ovchinnikov superconductivity in CeCoIn5
Authors:
Mierzejewski, M; Ptok, A; Maska, MM Author Full Names: Mierzejewski, Marcin; Ptok, Andrzej; Maska, Maciej M.
Source:
PHYSICAL REVIEW B 80 (17): Art. No. 174525 NOV 2009
Abstract:
Recent experiments on CeCoIn5 suggest an unusual interplay between superconducting and magnetic orders that gives rise to a multicomponent (magnetosuperconducting) phase. We demonstrate that characteristics of CeCoIn5 make this system particularly well suited for the onset of such a phase. Based on general considerations, we show that superconductivity with nonzero Cooper-pair momentum may lead to an enhancement of the spin-spin response function and, simultaneously, incommensurate spin-density wave may enhance the Cooper-pair susceptibility.
Title:
Incommensurate spin correlation driven by frustration in BiCu2PO6
Authors:
Mentre, O; Janod, E; Rabu, P; Hennion, M; Leclercq-Hugeux, F; Kang, J; Lee, C; Whangbo, MH; Petit, S Author Full Names: Mentre, O.; Janod, E.; Rabu, P.; Hennion, M.; Leclercq-Hugeux, F.; Kang, J.; Lee, C.; Whangbo, M. -H.; Petit, S.
Source:
PHYSICAL REVIEW B 80 (18): Art. No. 180413 NOV 2009
Abstract:
The magnetic properties of BiCu2PO6 have been analyzed by means of magnetic-susceptibility and inelastic neutron-scattering measurements on powder samples by evaluating the spin-exchange interactions on the basis of density-functional calculations and by simulating the inelastic neutron scattering in terms of spin-exchange parameters. BiCu2PO6 exhibits magnetic properties described by the two-leg spin ladder with strong spin frustration along each leg chain and has a gapped quantum singlet ground state with excited magnetic states, showing an incommensurate dispersion arising from frustration.
Title:
Basic Co-rich decagonal Al-Co-Ni: Average structure
Authors:
Strutz, A; Yamamoto, A; Steurer, W Author Full Names: Strutz, Angelica; Yamamoto, Akiji; Steurer, Walter
Source:
PHYSICAL REVIEW B 80 (18): Art. No. 184102 NOV 2009
Abstract:
The two-layer average structure of the high-temperature phase basic Co-rich decagonal Al72.5Co18.5Ni9 was determined based on single-crystal x-ray diffraction data. The five-dimensional (5D) structure model was refined in the noncentrosymmetric 5D space group P10m2 (112 parameters, wR=0.123 and R=0.156 for 957 reflections). The close relationship of the model structure with that of W-Al-Co-Ni, a << 3/2,2/1 >> approximant, is shown.
Title:
Magnetism in CeFeAsO1-xFx and LaFeAsO1-xFx from first principles
Authors:
Sharma, S; Shallcross, S; Dewhurst, JK; Sanna, A; Bersier, C; Massidda, S; Gross, EKU Author Full Names: Sharma, S.; Shallcross, S.; Dewhurst, J. K.; Sanna, A.; Bersier, C.; Massidda, S.; Gross, E. K. U.
Source:
PHYSICAL REVIEW B 80 (18): Art. No. 184502 NOV 2009
Abstract:
Using state-of-the-art first-principles calculations we study the magnetic behavior of CeOFeAs. We find the Ce layer moments oriented perpendicular to those of the Fe layers. An analysis of incommensurate magnetic structures reveals that the Ce-Ce magnetic coupling is rather weak with, however, a strong Fe-Fe and Fe-Ce coupling. Comparison of the origin of the tetragonal to orthorhombic structural distortion in CeOFeAs and LaOFeAs shows marked differences; in CeOFeAs the distortion is stabilized by a lowering of spectral weight at the Fermi level, while in LaOFeAs by increase in Fe spin moment. Finally, we investigate the impact of electron doping upon CeOFeAs and LaOFeAs and show that (a) while in CeOFeAs the ground-state Fe moment remains largely unchanged by doping, the stability of magnetic order goes to zero at a doping that corresponds well to the vanishing of the Neacuteel temperature and, (b) in contrast the LaOFeAs system remains magnetic wit! h a slowly vanishing moment as a function of doping.
Title:
Optimizing the thermoelectric efficiency of icosahedral quasicrystals and related complex alloys
Authors:
Macia, E Author Full Names: Macia, Enrique
Source:
PHYSICAL REVIEW B 80 (20): Art. No. 205103 NOV 2009
Abstract:
In this work we analyze the potential role of quasicrystals and related alloys in thermoelectric material research. Relatively large figure of merit values are expected for those samples exhibiting two properly located narrow features in the density of states close to the Fermi level. It is expected that optimized quasicrystals will perform better at relatively low temperatures, whereas the ZT curve of complex metallic alloys reaches its maximum at high temperatures. Among state-of-the-art quasicrystals most promising samples for thermoelectric applications are found in the AlPd (Mn,Re) system. Quasicrystalline and related approximants in the ScMgCuGa and CaAuIn systems, synthesized on the basis of pseudogap tuning concepts, appear as promising candidates as well.
Title:
Disordered, quasicrystalline and crystalline phases of densely packed tetrahedra
Authors:
Haji-Akbari, A; Engel, M; Keys, AS; Zheng, XY; Petschek, RG; Palffy-Muhoray, P; Glotzer, SC Author Full Names: Haji-Akbari, Amir; Engel, Michael; Keys, Aaron S.; Zheng, Xiaoyu; Petschek, Rolfe G.; Palffy-Muhoray, Peter; Glotzer, Sharon C.
Source:
NATURE 462 (7274): 773-U91 DEC 10 2009
Abstract:
All hard, convex shapes are conjectured by Ulam to pack more densely than spheres(1), which have a maximum packing fraction of phi = pi/root 18 approximate to 0.7405. Simple lattice packings of many shapes easily surpass this packing fraction(2,3). For regular tetrahedra, this conjecture was shown to be true only very recently; an ordered arrangement was obtained via geometric construction with phi = 0.7786 (ref. 4), which was subsequently compressed numerically to phi = 0.7820 (ref. 5), while compressing with different initial conditions led to phi = 0.8230 ( ref. 6). Here we show that tetrahedra pack even more densely, and in a completely unexpected way. Following a conceptually different approach, using thermodynamic computer simulations that allow the system to evolve naturally towards high-density states, we observe that a fluid of hard tetrahedra undergoes a first-order phase transition to a dodecagonal quasicrystal (7-10), which can be compressed to a packing fraction of phi = 0.8324. By compressing a crystalline approximant of the quasicrystal, the highest packing fraction we obtain is phi = 0.8503. If quasicrystal formation is suppressed, the system remains disordered, jams and compresses to phi = 0.7858. Jamming and crystallization are both preceded by an entropy-driven transition from a simple fluid of independent tetrahedra to a complex fluid characterized by tetrahedra arranged in densely packed local motifs of pentagonal dipyramids that form a percolating network at the transition. The quasicrystal that we report represents the first example of a quasicrystal formed from hard or non-spherical particles. Our results demonstrate that particle shape and entropy can produce highly complex, ordered structures.
Title:
Effects of the fourth component and undercooling on morphology of primary Mg-Zn-Y icosahedral quasicrystal phase under normal casting conditions
Authors:
Wang, ZF; Zhao, WM; Hur, BY; Huang, CY; Yu, CQ Author Full Names: Wang Zhifeng; Zhao Weimin; Hur, Bo-Young; Huang Chunying; Yu Chengquan
Source:
CHINA FOUNDRY 6 (4): 293-299 NOV 2009
Abstract:
The paper presents some results of the investigation on effects of the fourth component (Ti, C, Sb or Cu) and undercooling on the morphology, size and forming process of primary Mg-Zn-Y icosahedral quasicrystal phase (I-phase) under normal casting conditions. The result shows that the addition of certain amount of fourth component can transform I-phase morphology from petal-like to spherical. However, I-phase will grow up to petal-like if superfluous addition of the fourth component applied. It is also found that the solidified morphology of I-phase depends on the stability of spherical I-phase during the subsequent growth, and critical radius of maintaining the spherical I-phase interface relatively stable. Further, mini-sized spherical I-phase can be produced with high content of the fourth component by undercooling. Such findings are benefical for industrializing Mg-based quasicrystals.

Update: 11-Dec-2009

Title:
Influence of Boron Additions on Dissipative Properties of Quasicrystalline Al-Cu-Fe Coatings
Authors:
Ustinov, AI; Polishchuk, SS; Telychko, VA; Melnychenko, TV Author Full Names: Ustinov, A. I.; Polishchuk, S. S.; Telychko, V. A.; Melnychenko, T. V.
Source:
METALLOFIZIKA I NOVEISHIE TEKHNOLOGII 31 (6): 847-854 JUN 2009
Abstract:
Influence of boron on mechanical and dissipative properties of quasicrystalline Al-Cu-Fe coatings is studied. As shown, the hardness of coatings based on quasicrystalline Al-Cu-Fe phase under alloying with boron remains practically unchanged, while their fracture toughness slightly increases. At the same time, damping capacity of nanoquasicrystalline coating Al-Cu-Fe-B is found to be essentially lower as compared with that of similar coating without boron. Possible mechanisms of the change in dissipative properties are discussed.
Title:
The commensurate modulated structure of the metastable state in spin crossover complex [Fe(abpt)(2)(NCS)(2)]
Authors:
Sheu, CF; Chen, SM; Wang, SC; Lee, GH; Liu, YH; Wang, Y Author Full Names: Sheu, Chou-Fu; Chen, Szu-Miao; Wang, Shih-Chi; Lee, Gene-Hsiang; Liu, Yi-Hung; Wang, Yu
Source:
CHEMICAL COMMUNICATIONS (48): 7512-7514 2009
Abstract:
Two new polymorphs (C and D) of [t-Fe(abpt)(2)(NCS)(2)] are characterized, a commensurate modulated structure with the c axis tripled in the thermally quenched metastable high spin state at 25 K is found in polymorph C.
Title:
Superplastic Behavior in Mg-Zn-Y Alloy with Dispersed Quasicrystal Phase Particles
Authors:
Somekawa, H; Singh, A; Mukai, T Author Full Names: Somekawa, Hidetoshi; Singh, Alok; Mukai, Toshiji
Source:
ADVANCED ENGINEERING MATERIALS 11 (10): 782-787 OCT 2009

Update: 4-Dec-2009

Title:
Influence of polytypism on structural phase transformations in TlGaSe2 crystals
Authors:
Borovoi, NA; Gololobov, YP; Isaenko, GL; Stepanishchev, NB Author Full Names: Borovoi, N. A.; Gololobov, Yu. P.; Isaenko, G. L.; Stepanishchev, N. B.
Source:
PHYSICS OF THE SOLID STATE 51 (11): 2367-2370 NOV 2009
Abstract:
The polytypism is found to have a significant influence on the structural transformation of the crystal lattice of the TlGaSe2 ferroelectric with variations in temperature. In the 2C-polytype, unlike the C-polytype, a first-order structural phase transition, which leads to a change in the translational symmetry along the C axis, is not observed in the temperature range T = 90-300 K and a second-order phase transition due to the formation of an incommensurate phase occurs at a higher temperature.
Title:
Crossover Induced by Spin-Density-Wave Interference in the Coherence of Singlet Electron Pairs in Cr
Authors:
Robinson, JWA; Halasz, GB; Blamire, MG Author Full Names: Robinson, J. W. A.; Halasz, Gabor B.; Blamire, M. G.
Source:
PHYSICAL REVIEW LETTERS 103 (20): Art. No. 207002 NOV 13 2009
Abstract:
To study the interaction of s-wave superconductivity with spin-density waves (SDWs), we have measured a series of Nb/Cr/Nb Josephson junctions and determined the coherence length xi describing the decay of the critical current with Cr thickness, L. We observe a crossover in xi from approximately 14 nm to 4 nm as L increases to 10 nm, which is consistent with a transition from commensurate to incommensurate SDWs expected for this thickness range.
Title:
Ferroelastic crystals and their nonlinear elastic properties observed in frequency range from gigahertz to milihertz
Authors:
Wiesner, M Author Full Names: Wiesner, Maciej
Source:
PHASE TRANSITIONS 82 (10): 699-754 2009
Abstract:
The experiments reported in this article have been performed to unify the results of earlier and recent determinations of parameters describing the elastic properties of Rb4LiH3(SO4)4, LiCsSO4 (LCS) and KH2PO4 crystals measured by different experimental methods. The above crystals undergo a second-order phase transition, incommensurate phase transition (PT) and a first-order but close to second-order phase transition, respectively. To investigate the elastic properties of the crystals in the frequency range from 10-1 to 1010 Hz, five experimental methods were applied: dynamic mechanical analysis, piezoelectric resonance, composite oscillator bar, ultrasonic wave propagation and Brillouin light scattering. The results of the experiments allowed identification of the processes contributing to the elastic response of the crystals investigated. Moreover, for the LCS crystal a model of the incommensurate PT was presented.
Title:
Quasicrystalline phase formation in the conventionally solidified Al-Cu-Fe system
Authors:
Gogebakan, M; Avar, B; Uzun, O Author Full Names: Gogebakan, M.; Avar, B.; Uzun, O.
Source:
MATERIALS SCIENCE-POLAND 27 (3): 919-926 2009
Abstract:
Structural characteristics and thermal behaviour of the conventionally solidified Al-Cu-Fe alloys with nominal compositions of Al70Cu20Fe10, Al65Cu20Fe15 and Al63Cu25Fe12 were investigated by X-ray diffraction, scanning electron microscopy, and differential thermal analysis techniques. Results show that a single quasicrystalline phase forms in a conventionally solidified Al65Cu20Fe15 alloy, being thermodynamically stable without phase transition up to the melting point. A cubic AlFe(Cu) solid solution, identified as beta phase, and a cubic AlCu(Fe) solid solution, identified as tau phase, were observed with quasicrystalline phase for Al63Cu25Fe12 alloy. Conventional solidification of Al70Cu20Fe10 alloy does not result in quasicrystalline phase formation. However, the formation of quasicrystalline phase in conventionally solidified Al70Cu20Fe10 alloy was observed after additional annealing at elevated temperature. SEM micrographs for Al70Cu20Fe10 and Al63Cu25Fe12 alloys after annealing at 700 degrees C for 4 h revealed the formation of pentagonal dodecahedrons in the quasicrystalline phase, with an edge size of about 30 mu m.
Title:
Monte-Carlo investigation of an anisotropic Ising model
Authors:
Murtazaev, AK; Ibaev, ZG Author Full Names: Murtazaev, A. K.; Ibaev, Zh. G.
Source:
LOW TEMPERATURE PHYSICS 35 (10): 792-796 OCT 2009
Abstract:
The Monte Carlo method is used to study long-period modulated structures in an anisotropic Ising model with competing interactions (ANNNI model). The character, particularities, and dependence of the modulated structures on the temperature and ratio of the exchange interaction constants between the nearest and next-to-nearest neighbors are determined. The phase diagram is constructed. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3253402]
Title:
Lattice Distortion Coupled with Magnetic Ordering in a Triangular Lattice Antiferromagnet CuCrO2
Authors:
Kimura, K; Otani, T; Nakamura, H; Wakabayashi, Y; Kimura, T Author Full Names: Kimura, Kenta; Otani, Tsuyoshi; Nakamura, Hiroyuki; Wakabayashi, Yusuke; Kimura, Tsuyoshi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (11): Art. No. 113710 NOV 2009
Abstract:
We investigated magnetostrictive properties of a triangular lattice antiferromagnet CuCrO2 showing an incommensurate proper-screw spin order by means of x-ray diffraction and strain gauge measurements. A deformation of the triangular lattice plane leading to a lowered crystallographic symmetry was found upon the magnetic ordering, which demonstrates a strong spin-lattice coupling in this system. The resultant multiple structural domains can be successfully arranged by magnetic field cooling procedures. We discuss the relationship between the lattice distortion and incommensurability in CuCrO2.
Title:
Renormalization of Commensurate Magnetic Peak in Ni-Doped La1.85Sr0.15CuO4
Authors:
Matsuura, M; Kofu, M; Kimura, H; Hirota, K Author Full Names: Matsuura, Masato; Kofu, Maiko; Kimura, Hiroyuki; Hirota, Kazuma
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (11): Art. No. 114703 NOV 2009
Abstract:
We have studied magnetic excitations in impurity-doped La(1.85)Sr(0.15)Cu(1-y)A(y)O(4) (A = Ni or Zn) by neutron scattering. The dispersion for Zn:y = 0.017 is similar to that for the impurity-free sample: incommensurate peaks with incommensurability delta = 0.12 +/- 0.01 (rlu) do not change their positions up to 21 meV. On the other hand, for Ni:y = 0.029, two incommensurate peaks observed at low energies suddenly change into a single broad commensurate peak at E-cross = 15 meV. Compared with that for the impurity-free sample with a similar Sr concentration of x = 0.16, E-cross for Ni:y = 0.029 is decreased by nearly the same factor as the reduction in T-c. This is very similar to the shift of resonance energy (E-res) in Ni-doped YBa2Cu3O7. These common impurity effects on the shifts of E-cross and E-res suggest the same magnetic origin of the resonance peak in YBa2Cu3O6+x and that of the crossing point of upward and downward dispersions in La2-xSrxCuO4. We propose that the sudden change in the dispersions is better described by a crossover from incommensurate spin fluctuations to a gapped spin wave rather than an hourglass-like dispersion.
Title:
Antiferromagnetic Order and pi-Triplet Pairing in the Fulde-Ferrell-Larkin-Ovchinnikov State
Authors:
Yanase, Y; Sigrist, M Author Full Names: Yanase, Youichi; Sigrist, Manfred
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (11): Art. No. 114715 NOV 2009
Abstract:
The anti ferromagnetic Fulde-Ferrell-Larkin-Ovchinnikov (AFM-FFLO) state of coexisting d-wave FFLO superconductivity and incommensurate AFM order is studied on the basis of Bogoliubov-de Gennes (BdG) equations. We show that the incommensurate AFM order is stabilized in the FFLO state by the appearance of the Andreev bound state localized around the zeros of the FFLO order parameter. The AFM-FFLO state is further enhanced by the induced pi-triplet superconductivity (pair density wave). The AFM order occurs in the FFLO state even when it is neither stable in the normal state nor in the BCS state. The order parameters of the AFM order, d-wave superconductivity, and pi-triplet pairing are investigated by focusing on their spatial structures. Roles of the spin fluctuations beyond the BdG equations are discussed. Their relevance to the high-field superconducting phase of CeCoIn5 is discussed.
Title:
Atomic dynamics of a d-AlNiFe decagonal quasicrystal
Authors:
Parshin, PP; Zemlyanov, MG; Panova, GK; Shikov, AA; Brand, RA; Grushko, B Author Full Names: Parshin, P. P.; Zemlyanov, M. G.; Panova, G. Kh.; Shikov, A. A.; Brand, R. A.; Grushko, B.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS 109 (4): 645-651 OCT 2009
Abstract:
The atomic dynamics of an Al71.3Ni24Fe4.7 decagonal quasicrystal has been investigated using the isotopic contrast method for inelastic neutron scattering. The partial vibrational spectra of the Ni, Fe, and Al atoms and the spectrum of the thermal vibrations of the alloy have been reconstructed directly from the experimental data without any model assumptions. The cutoff energies and the positions of the main features of the spectra have been determined. It has been revealed that the average binding energy of the nickel atoms in the quasicrystal under investigation is lower than that of the iron atoms and the vibrational spectrum of the aluminum atoms is noticeably harder than the spectrum of the pure metal. The results obtained for the d-AlNiFe decagonal quasicrystal have been compared with the previously published data for an i-AlCuFe icosahedral quasicrystal.

Update: 26-Nov-2009

Title:
Long-period states of a crystal finite-size-particle system
Authors:
Dmitriev, SV; Potekaev, AI; Samsonov, AV Author Full Names: Dmitriev, S. V.; Potekaev, A. I.; Samsonov, A. V.
Source:
RUSSIAN PHYSICS JOURNAL 52 (6): 622-639 JUN 2009
Abstract:
A one-dimensional model is proposed, which ensures description of origination and main properties of longperiod and incommensurate phases of crystal having complex structure and consists of comparatively rigid "atomic clusters". In the case where reciprocal rotations of theses clusters are considerably large, not only translational but also rotational degrees of freedom have to be taken into account for the clusters. It is consideration of the rotational degrees of freedom which might provide for formation of long-period states and development of a number of physical effects, such as a variety of soliton solutions (of domain walls) and their non-trivial dynamics.
Title:
High-resolution electron microscopy for incommensurate structure of KxRhO2 crystal
Authors:
Yubuta, K; Shibasaki, S; Terasaki, I; Kajitani, T Author Full Names: Yubuta, Kunio; Shibasaki, Soichiro; Terasaki, Ichiro; Kajitani, Tsuyoshi
Source:
PHILOSOPHICAL MAGAZINE 89 (31): 2813-2822 2009
Abstract:
An incommensurate, (3 + 2)- dimensional structure is locally observed in a K0.49RhO2 crystal synthesized by the flux growth method. The averaged potassium to rhodium ratio of the grown crystals was determined as 0.49 using an electron probe microanalyzer operated in the wave dispersive spectroscopy mode. The potassium content of the incommensurate phase was determined as 0.25 by the transmission electron microscopy-energy dispersive spectroscopy method. Satellite reflections of an incommensurate phase having two modulation vectors, q(1)* = 0.15a(o)* + 0.21b(o)* and q(2)* = -0.21a(o)* + 0.36b(o)* (a(o) is the unit cell for a gamma-NaxCoO2-type structure), are indexed successfully. High-resolution electron microscopy (HREM) images show dark streaks running parallel in the a-b plane. The separations and directions of the dark streaks have a close relationship between the q-vector of satellite spots. A HREM image taken with the electron beam parallel to [100] direction shows planer clusters between CdI2-type RhO2 layers. These clusters correspond to the intercalated potassium ions.
Title:
Plastic analysis of crack problems in three-dimensional icosahedral quasicrystalline material
Authors:
Li, W; Fan, TY; Wu, YL Author Full Names: Li, Wu; Fan, Tian You; Wu, Yun Long
Source:
PHILOSOPHICAL MAGAZINE 89 (31): 2823-2831 2009
Abstract:
Due to their complexity, the basic plastic properties of all quasicrystalline materials are essentially unknown [M. Feuerbacher, C. Thomas, K. Urban, Plastic behaviour of quasicrystalline materials, in Quasicrystals: Structure and Physical Properties, H.R. Trebin, ed., Wiley/VCH, Berlin, 2003]. Plastic deformation of cracks in icosahedral quasicrystals have been analyzed in a strict and systematic form and the crack tip opening displacement (CTOD) and size of the plastic zone around the crack tip was determined exactly. CTOD is suggested as a parameter of plastic fracture for quasicrystalline materials. The present work may also provide a novel methodology for plastic analysis of quasicrystals.
Title:
Octahedral tilt twinning and compositional modulation in NaLaMgWO6
Authors:
King, G; Garcia-Martin, S; Woodward, PM Author Full Names: King, Graham; Garcia-Martin, Susana; Woodward, Patrick M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 676-683 Part 6 DEC 2009
Abstract:
A combination of selected-area electron diffraction (SAED), neutron powder diffraction (NPD) and high-resolution transmission electron microscopy (HRTEM) reveals a complex superstructure in the ordered perovskite NaLaMgWO6. Through indexing of SAED patterns the unit-cell dimensions are found to be 46.8 x 7.8 x 7.9 angstrom, which corresponds to a 12a(p) x 2a(p) x 2a(p) superstructure of the simple Pm (3) over barm perovskite unit cell. HRTEM images reveal the formation of an unmistakable stripe contrast that repeats with the same periodicity. Doubling of the b and c axes is brought about by a combination of layered ordering of Na and La, rock-salt ordering of Mg and W, and octahedral tilting. The a axis repeat distance results from a one-dimensional twinning of the octahedral tilts in combination with a compositional modulation. Modeling of the NPD pattern shows that the underlying tilt system is a(-)a(-)c(0) with tilt angles of similar to 8 degrees about the a and b axes. The octahedral tilt-twin boundaries run perpendicular to the a axis and are separated by 6a(p). Simulated HRTEM images show that octahedral tilt twinning alone cannot explain the stripes seen in the HRTEM images, rather a compositional modulation involving the A-site cations is necessary to explain the experimental images.

Update: 19-Nov-2009

Title:
A One-Dimensional Metal Embedded in Salt Matrices: Synthesis, Modulated Crystal Structures, Electrical Conductivity, and Chemical Bonding of (1)(infinity)[PdBi6][(Bi,Sn)(1-delta)Br5-delta,]
Authors:
Wahl, B; Kloo, L; Ruck, M Author Full Names: Wahl, Bernhard; Kloo, Lars; Ruck, Michael
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE 635 (12): 1979-1985 2009
Abstract:
The metal-rich compounds (1)(infinity)[PdBi6][(Bi,Sn)(1-delta)Br5-delta,] with delta(1) = 2/13, delta(1)' = 5/26, or delta(2) = delta(2)' = 2/12 were synthesized from Bi2Pd, BiBr3, and Sn at 300 degrees C. The crystal structures contain intermetallic rods (1)(infinity)[Pd@Bi2/1Bi8/2](2.5+) embedded in salt-like matrices, which consist of groups of bromido-bismuthate(III)-stannate(II) octahedra [(Bi,Sn)(n)Br4n+2](m-) (n = 2, 3) and isolated Br- ions. Metrical incompatibilities of the two subsystems in the crystalline metal-salt hybrid result in non-stoichiometry of the salt pan associated with complex superstructures. The average structure is described in the orthorhombic space group Pmmm with a approximate to 408 pm, b approximate to 2263 pm, c approximate to 849 pm. It feigns statistical distribution of vacancies and orientational disorder of the concatenated octahedra. By choosing the modulation vectors q(i) = 2/ta* + 1/2b* + 1/2c* with t(1) = 13 or t(2) = 12, the additional weak reflections of the diffraction patterns are indexed. Ordered structure models are achieved in the [3+1]-dimensional superspace group Pmmm(alpha 1/21/2)000. Metallic conductivity along [100], i.e. the direction of the (1)(infinity)[Pd@Bi2/1Bi8/2](2.5+) rods, was determined for a single-crystal. One-dimensional band structure calculations reveal Bi p-bands crossing the Fermi level for formula charges higher than 2+. The electron localization indicator (ELI) indicates two-center Bi-Bi bonds as well as multi-center bonds inside the metallic part, whereas the bismuth l one-pairs point towards the non-conducting part of the structure.
Title:
Quasiparticles of Spatially Anisotropic Triangular Antiferromagnets in a Magnetic Field
Authors:
Kohno, M Author Full Names: Kohno, Masanori
Source:
PHYSICAL REVIEW LETTERS 103 (19): Art. No. 197203 NOV 6 2009
Abstract:
The spectral properties of the spin-1/2 Heisenberg antiferromagnet on an anisotropic triangular lattice in a magnetic field are investigated using a weak-interchain-coupling approach combined with exact solutions of a chain. Dominant modes induced by interchain interactions in a magnetic field behave as quasiparticles which show distinctive features such as anomalous incommensurate ordering and high-energy modes. In terms of them, various unusual features observed in the anisotropic triangular antiferromagnet Cs2CuCl4 in a magnetic field are quantitatively explained in a unified manner.
Title:
The uniaxially aperiodic structure of a thin Cu film on fivefold i-Al-Pd-Mn
Authors:
Pussi, K; Gierer, M; Diehl, RD Author Full Names: Pussi, K.; Gierer, M.; Diehl, R. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (47): Art. No. 474213 NOV 25 2009
Abstract:
A thin film of copper on the fivefold surface of Al-Pd-Mn forms a structure that is uniaxially commensurate with the aperiodic structure of the substrate. This structure has been analyzed using low-energy electron diffraction and is found to consist of a vicinal surface of a body-centered tetragonal (bct) (100) structure. This bct(100) structure has lattice parameters of a = 2.88 angstrom, b = 2.55 angstrom and c = 2.88 angstrom, with the vicinal surface making an angle alpha of 13.28 degrees relative to the a-b plane. This structure provides an explanation for the delayed ordering observed during the growth of the film. Simple conditions are derived for which the growth of ordered one-dimensionally quasiperiodic thin films on quasicrystals may be favorable. This finding is relevant to the use of quasicrystals as a means of matching interfaces in thin film systems.
Title:
Synthesis of the quasi-crystalline phase in Al63Cu25Fe12 powders prepared by mechanical alloying
Authors:
Avar, B; Gogebakan, M Author Full Names: Avar, B.; Gogebakan, M.
Source:
JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS 11 (10): 1460-1463 OCT 2009
Abstract:
This work investigated the quasicrystalline phase formation during heat treatment in the Al63Cu25Fe12 alloy prepared via mechanical alloying, starting from pure elemental powders. The mechanical alloying process was performed at a speed of 300 rpm for times up to 70 hours. The structural evolution of the mechanically alloyed Al63Cu25Fe12 powders at different stages of milling was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The present results showed that mechanical alloying of the Al63Cu25Fe12 alloy did not result in the quasicrystalline icosahedral phase (i-phase). The long time milling resulted in the formation of an AlFe(Cu) solid solution identified as the beta-phase. In order to examine the structural changes with annealing temperature, the mechanically alloyed powders were heat treated at 600, 700 and 800 degrees C for 4 hours under vacuum. However, the formation of a quasicrystalline phase in the Al63Cu25Fe12 alloy was observed after additional annealing at elevated temperature. In the present work, quasicrystalline phase formation in both the as-milled and heat-treated powders is discussed in detail.
Title:
Minerals as advanced materials
Authors:
Depmeier, W Author Full Names: Depmeier, W.
Source:
CRYSTAL RESEARCH AND TECHNOLOGY 44 (10): 1122-1130 Sp. Iss. SI OCT 2009
Abstract:
A resume is given on relationships between minerals and materials. It is shown that Nature has many advantages over technology which can be profitably exploited for finding new materials with useful properties. However, Nature has also inherent limitations. Therefore, it seems advisable to use the knowledge of minerals as a treasure which can be tapped for getting inspired on the way to finding new materials. Several examples are given, including those of zorite/ETS-4/ETS-10, boracites, zircon, kesterite, a natural quasicrystal, opals, ultramarine and mayenite.

Update: 13-Nov-2009

Title:
AlCoNi quasicrystal sphere growth experiment from a metallic solution
Authors:
Meisterernst, G; Bauer, B; Gille, P Author Full Names: Meisterernst, Goetz; Bauer, Birgitta; Gille, Peter
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 224 (10): 471-477 2009
Abstract:
Crystal growth studies starting from spherical surfaces of single crystals can reveal morphological features that cannot be obtained in usual growth experiments. Especially, facets of a greater variety of crystallographic forms may occur that are otherwise hidden by the slowest growing faces which dominate the crystal's morphology. We did a sphere growth experiment with a decagonal Al72Co9Ni19 quasicrystal prepared from a large single-grain sample formerly grown using the Czochralski method from an off-stoichiometric melt. By heating the polished crystalline half-sphere to a temperature slightly higher than its own growth temperature a thin liquid layer of self-flux formed. A partial evaporation of Al being the solvent of this system caused re-crystallisation at the surface of the quasicrystalline sphere. After several times repeating this process at further increasing temperatures, tiny faces of four different crystallographic forms developed. By using an optical goniometer and electron scanning microscopy indexing of these facets was possible. With the only exception of the decagonal prism {10000} they had not been observed so far in contact to the melt. The results are discussed with respect to the inclined net plane concept established by Steurer and Cervellino [Acta Cryst. A57 (2001) 333-340]. The experimental approach is not specific to sphere growth studies of quasicrystals but can be applied to other high-temperature solution growth systems as well.
Title:
Atomic coexistence of superconductivity and incommensurate magnetic order in the pnictide Ba(Fe(1-x)Cox)(2)As-2
Authors:
Laplace, Y; Bobroff, J; Rullier-Albenque, F; Colson, D; Forget, A Author Full Names: Laplace, Y.; Bobroff, J.; Rullier-Albenque, F.; Colson, D.; Forget, A.
Source:
PHYSICAL REVIEW B 80 (14): Art. No. 140501 OCT 2009
Abstract:
As-75 nuclear magnetic resonance (NMR) and susceptiblity were measured in a Ba(Fe1-xCox)(2)As-2 single crystal for x=6%. NMR spectra and relaxation rates allow to show that all Fe sites experience an incommensurate magnetic ordering below T=31 K. Comparison with undoped compound allows to estimate a typical moment of 0.05 mu(B). Anisotropy of the NMR widths can be interpreted using a model of incommensurability with a wave vector (1/2-epsilon,0, l) with epsilon of the order of 0.04. Below T-C=21.8 K, a full volume superconductivity develops as shown by susceptibility and relaxation rate, and magnetic order remains unaffected, demonstrating coexistence of both states on each Fe site.
Title:
Coexistence of incommensurate magnetism and superconductivity in Fe(1+y)SexTe(1-x)
Authors:
Khasanov, R; Bendele, M; Amato, A; Babkevich, P; Boothroyd, AT; Cervellino, A; Conder, K; Gvasaliya, SN; Keller, H; Klauss, HH; Luetkens, H; Pomjakushin, V; Pomjakushina, E; Roessli, B Author Full Names: Khasanov, R.; Bendele, M.; Amato, A.; Babkevich, P.; Boothroyd, A. T.; Cervellino, A.; Conder, K.; Gvasaliya, S. N.; Keller, H.; Klauss, H. -H.; Luetkens, H.; Pomjakushin, V.; Pomjakushina, E.; Roessli, B.
Source:
PHYSICAL REVIEW B 80 (14): Art. No. 140511 OCT 2009
Abstract:
We have studied the superconducting and magnetic properties of Fe1+ySexTe1-x single crystals (0 <= x <= 0.5) by magnetic susceptibility, muon-spin rotation, and neutron diffraction. We find three regimes of behavior: (i) commensurate magnetic order for x less than or similar to 0.1, (ii) bulk superconductivity for x similar to 0.5, and (iii) a range x approximate to 0.25-0.45 in which superconductivity coexists with incommensurate magnetic order. The results are qualitatively consistent with two-band mean-field models in which itinerant magnetism and extended s-wave superconductivity are competing order parameters.
Title:
Transition from turbulent to nearly laminar vortex flow in superconductors with periodic pinning
Authors:
Gutierrez, J; Silhanek, AV; Van de Vondel, J; Gillijns, W; Moshchalkov, VV Author Full Names: Gutierrez, J.; Silhanek, A. V.; Van de Vondel, J.; Gillijns, W.; Moshchalkov, V. V.
Source:
PHYSICAL REVIEW B 80 (14): Art. No. 140514 OCT 2009
Abstract:
We revisit the vortex dynamics in Al thin films containing an artificial periodic array of antidots by means of electrical transport measurements. We clearly identify a turbulent to laminarlike vortex flow transition which manifests itself as a negative differential resistivity. This transition is accompanied by a strong irreversibility in the voltage-current characteristics. The dynamical phase diagrams obtained as a function of commensurability, temperature, and driving force are in good agreement with the early predictions by Reichhardt et al. [Phys. Rev. Lett. 78, 2648 (1997)] based on molecular dynamic simulations.
Title:
Lattice dynamics and external magnetic-field effects in Ni-Fe-Ga alloys
Authors:
Perez-Landazabal, JI; Recarte, V; Sanchez-Alarcos, V; Rodriguez-Velamazan, JA; Jimenez-Ruiz, M; Link, P; Cesari, E; Chumlyakov, YI Author Full Names: Perez-Landazabal, J. I.; Recarte, V.; Sanchez-Alarcos, V.; Rodriguez-Velamazan, J. A.; Jimenez-Ruiz, M.; Link, P.; Cesari, E.; Chumlyakov, Y. I.
Source:
PHYSICAL REVIEW B 80 (14): Art. No. 144301 OCT 2009
Abstract:
Precursor phenomena were investigated in a Ni-Fe-Ga alloy close to the stoichiometric Heusler composition Ni2FeGa. In particular, the phonon-dispersion curves, the diffuse scattering and the magnetic properties of a single crystalline Ni51.5Fe21.5Ga27 alloy were measured as a function of temperature. The TA(2) branch along the [110] direction of the L2(1) phase shows a significant phonon softening around xi = 0.35 resulting in a marked dip which becomes more pronounced as the temperature decreases. Diffuse neutron-scattering measurements performed along [(xi) over bar xi 0] direction around Bragg reflections also reveal the presence of small satellite peaks at xi = 0.33 whose intensity increases on approaching the martensitic transformation temperature. Both elastic and inelastic-scattering anomalies confirm the occurrence of premartensitic phenomena in Ni-Fe-Ga alloys. The influence of an external magnetic field (6 T) on the anomalous phonon is shown to be negli! gible and just a small shift of the transformation temperature takes place because of the magnetic field.
Title:
Thermal entanglement of spin chains with quantum critical behavior
Authors:
Zvyagin, AA Author Full Names: Zvyagin, A. A.
Source:
PHYSICAL REVIEW B 80 (14): Art. No. 144408 OCT 2009
Abstract:
Results for the characteristics of the macroscopic thermal entanglement for integrable spin-1/2 antiferro-magnetic chain models with multispin interactions in the thermodynamic limit are presented. Such interactions cause quantum-phase transitions to incommensurate phases with partial spontaneous magnetization. We have derived exact equations, which determine the thermal and magnetic field behavior of the concurrence of spin chains. The analysis of these equations shows that there exists a critical temperature, below which the thermal entanglement of considered spin chains is nonzero. We have shown that at those quantum-phase transitions, caused by multispin interactions, the thermal entanglement is reduced. Also, we have shown that the thermal entanglement is reduced due to nonzero magnetization of spin chains in the ground state, caused by multispin interactions.
Title:
Observation of strong magnetoelastic coupling in a first-order phase transition of CrOCl
Authors:
Angelkort, J; Wolfel, A; Schonleber, A; van Smaalen, S; Kremer, RK Author Full Names: Angelkort, Joachim; Woelfel, Alexander; Schoenleber, Andreas; van Smaalen, Sander; Kremer, Reinhard K.
Source:
PHYSICAL REVIEW B 80 (14): Art. No. 144416 OCT 2009
Abstract:
The phase transition of CrOCl toward a state of antiferromagnetic order below T-N=13.5 K has been identified as a first-order phase transition. The transition is accompanied by a lattice and structural distortion toward a twofold, 2b nuclear superstructure with a-axis unique monoclinic symmetry, as evidenced by temperature-dependent x-ray diffraction experiments. Magnetic-susceptibility and magnetization measurements indicate a transition with strong magnetoelastic coupling to a uniaxial antiferromagnet with ordered moments along c. A second transition is discovered at T-c approximate to 27.2 K that is presumably of purely magnetic origin and might indicate the formation of an incommensurate magnetic superstructure. The different behaviors of TiOCl, VOCl, and CrOCl are the result of the different symmetries of the filled 3d orbitals, which lead to different exchange interactions on the MO double layers of these isostructural compounds.
Title:
Formation of a well ordered ultrathin aluminum oxide film on icosahedral AlPdMn quasicrystal (vol 76, 094203, 2007)
Authors:
Longchamp, JN; Burkardt, S; Erbudak, M; Weisskopf, Y Author Full Names: Longchamp, J. -N.; Burkardt, S.; Erbudak, M.; Weisskopf, Y.
Source:
PHYSICAL REVIEW B 80 (14): Art. No. 149901 OCT 2009
Title:
Field suppression of the modulated phase of Ce2Pd2Sn
Authors:
Berisso, MG; Sereni, JG; Braghta, A; Schmerber, G; Chevalier, B; Kappler, JP Author Full Names: Gomez Berisso, M.; Sereni, J. G.; Braghta, A.; Schmerber, G.; Chevalier, B.; Kappler, J. P.
Source:
PHYSICA B-CONDENSED MATTER 404 (19): 2930-2933 OCT 15 2009
Abstract:
Low temperature magnetic (M) and thermal (C-p) properties of the intermetallic compound Ce2Pd2Sn have been investigated at zero and different magnetic fields. Two transitions were recognized at T-C = 2.1 K and T-M = 4.8 K, with latter nearly coinciding with the extrapolated Curie-Weiss temperature theta(p) = 4.5 K. The Curie factor evaluated from T >= T-M, is approximate to 2 mu(B) The positive value of theta(p), the triangular coordination of the magnetic (Ce) atoms and the weak effect of applied magnetic field, reveal that T-M cannot be considered as a canonic antiferromagnetic transition like claimed in the literature. M(T) measurements under moderate magnetic fields (0 <= B <= 2.5 kOe) show T-C(B) increasing while T-M(B) is practically not affected. Both transition merge in a critical point at T-cr = (4.3 +/- 0.3)K for B-cr = (2.1 +/- 0.3)kOe, where the intermediate phase is suppressed. At T-C = 2.2 K, the cusp of a first order transition is observed in C-p(T). According to the proposed ferromagnetic ground state, it is followed by a C-p(T)alpha T(3/2)exp(-E-g/T) dependence, with a gap of anisotropy E-g approximate to 7 K. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Antiferromagnetic structure in UNiAl at dilution temperatures
Authors:
Prokes, K; Bruck, E; Sechovsky, V Author Full Names: Prokes, K.; Bruck, E.; Sechovsky, V.
Source:
PHYSICA B-CONDENSED MATTER 404 (19): 3025-3027 OCT 15 2009
Abstract:
Neutron diffraction experiments in zero field reveals that the originally sine-wave-modulated antiferromagnetic structure in UNiAl starts to square-up at low temperatures. The squaring-up is, however, not completed even at 150 mK, most probably due to competing magnetic interactions. The fact that the magnetic moments are not equal at all the uranium atomic sites is responsible at least partially for the enhanced low-temperature-specific heat coefficient observed in UNiAl at low temperatures. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Resonant X-ray scattering study of Ca3Co2O6 ground state: Preliminary results of magnetic field effects
Authors:
Mazzoli, C; Bombardi, A; Agrestini, S; Lees, MR Author Full Names: Mazzoli, C.; Bombardi, A.; Agrestini, S.; Lees, M. R.
Source:
PHYSICA B-CONDENSED MATTER 404 (19): 3042-3044 OCT 15 2009
Abstract:
We present resonant magnetic X-ray scattering (RMXS) measurements in an applied magnetic field on a single crystal of Ca3Co2O6. We focus our attention on the transition from an incommensurate partially disordered antiferromagnetic state to a ferrimagnetic state: a lock-in and a divergence of the magnetic correlation length at the transition shed light on the nature of the ground state and on the c-axis vs. in-plane exchange couplings in this system. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Magnetic properties of the t-J model at low doping
Authors:
Falb, J; Neto, MBS; Muramatsu, A Author Full Names: Falb, J.; Silva Neto, M. B.; Muramatsu, A.
Source:
PHYSICA B-CONDENSED MATTER 404 (19): 3075-3078 OCT 15 2009
Abstract:
A path-integral for the t-J model in two dimensions is constructed based on Dirac quantization, with an action found originally by Wiegmann [Phys. Rev. Lett. 60 (1988) 821; Nucl. Phys. B 323 (1989) 311]. Concentrating on the low doping limit, we assume short range anti ferromagnetic order of the spin degrees of freedom. Going over to a local spin quantization axis of the dopant fermions that follows the spin degree of freedom, staggered CP1 fields result and the constraint against double occupancy can be resolved. The staggered CP1 fields are split into slow and fast modes, such that after a gradient expansion, and after integrating out the fast modes and the dopant fermions, a CP1 field-theory with a massive gauge field is obtained that describes generically incommensurate coplanar magnetic structures, as discussed previously in the context of frustrated quantum anti ferromagnets. The analysis of Landau damping shows that in this case, even in the presence of doping, the dynamical critical exponent z = 1. as a consequence of coupling of the dopant holes to a spin current, as opposed to a spin density. This result agrees with experimental observations in the underdoped region of high temperature superconductors, and departs from the one obtained by Hertz and Millis (z = 2) in the case of spin density waves in the Hubbard model. (C) 2009 Elsevier B.V. All rights reserved.
Title:
X-ray resonant scattering study of the magnetic phase diagram of multiferroic TbMnO3
Authors:
Walker, HC; Ewings, RA; Fabrizi, F; Mannix, D; Mazzoli, C; Wilkins, SB; Paolasini, L; Prabhakaran, D; Boothroyd, AT; McMorrow, DF Author Full Names: Walker, H. C.; Ewings, R. A.; Fabrizi, F.; Mannix, D.; Mazzoli, C.; Wilkins, S. B.; Paolasini, L.; Prabhakaran, D.; Boothroyd, A. T.; McMorrow, D. F.
Source:
PHYSICA B-CONDENSED MATTER 404 (19): 3264-3266 OCT 15 2009
Abstract:
We present the magnetic phase diagram of multiferroic TbMnO3 for H parallel to b determined using X-ray resonant scattering at the Tb L-3-edge. Investigations of two different magnetic domains, C-type and F-type, demonstrate very similar behaviour in high applied magnetic fields, with a low temperature incommensurate to commensurate transition at H similar or equal to 4.5T, concurrent with the polarisation flop observed in bulk magnetoelectric measurements. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Effect of Nonmagnetic Substituents Mg and Zn on the Phase Competition in the Multiferroic Antiferromagnet MnWO4
Authors:
Meddar, L; Josse, M; Deniard, P; La, C; Andre, G; Damay, F; Petricek, V; Jobic, S; Whangbo, MH; Maglione, M; Payen, C Author Full Names: Meddar, Lynda; Josse, Michael; Deniard, Philippe; La, Carole; Andre, Gilles; Damay, Francoise; Petricek, Vaclav; Jobic, Stephane; Whangbo, Myung-Hwan; Maglione, Mario; Payen, Christophe
Source:
CHEMISTRY OF MATERIALS 21 (21): 5203-5214 NOV 10 2009
Abstract:
The effects of substituting nonmagnetic Ma(2+) and Zn2+ ions for the Mn2+ (S = 5/2) ions oil the structural, magnetic, and dielectric properties of the multiferroic frustrated antiferromagnet MnWO4 were investigated Polycrystalline samples of Mn1-xMgxWO4 and Mn1-xZnxWO4 (0 <= x <= 0.3) solid Solutions were prepared via a solid-state route and characterized via X-ray and neutron diffraction, magnetization, and dielectric permittivity measurements. Mg and Zn substitutions result in very similar effects The Neel temperature (T-N), the AF3-to-AF2 magnetic phase-transition temperature (T-2), and the critical ferroelectric temperature (T-c = T-2) of MnWO4 are reduced upon nonmagnetic doping. At the lowest temperature (T = 1.5 K), the incommensurate magnetic Structure for x(Mg) = 0 15 and v(Zn) = 0.15 corresponds to either a sinusoidal spin arrangement or an elliptical spin-spiral phase similar to the polar AF2 structure observed in MnWO4 These findings were discussed by considering the effects of the Mg and Zn Substitutions oil the crystal lattice and on the spin exchange network of MnWO4.

Update: 5-Nov-2009

Title:
Crossover from incommensurate to commensurate magnetic orderings in CoCr2O4
Authors:
Chang, LJ; Huang, DJ; Li, WH; Cheong, SW; Ratcliff, W; Lynn, JW Author Full Names: Chang, L. J.; Huang, D. J.; Li, W-H; Cheong, S-W; Ratcliff, W.; Lynn, J. W.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (45): Art. No. 456008 NOV 11 2009
Abstract:
The conical spin order of multiferroic CoCr2O4 has been studied by a neutron diffraction to investigate its magnetic phase transitions at temperatures below 40 K. Magnetic order of a spiral spin component with an incommensurate propagation vector of (0.63, 0.63, 0) was observed at 26 K, while at 14.5 K, the incommensurate conical spin order showed a transition into the fixed commensurate propagation vector of (2/3, 2/3, 0). In addition, two satellite peaks with propagation vectors of (0.035, 0, 0) and (0, 0.035, 0) from the commensurate vector were observed. The widths of these peaks indicate a long-range magnetic order. This new magnetic configuration below 14.5 K may lead to a new model of multiferroic behavior differing from the well-known spin-current model for magnetic ferroelectricity.

Update: 29-Oct-2009

Title:
Electronic Self-Organization in the Single-Layer Manganite Pr1-xCa1+xMnO4
Authors:
Ye, F; Chi, SX; Fernandez-Baca, JA; Moreo, A; Dagotto, E; Lynn, JW; Mathieu, R; Kaneko, Y; Tokura, Y; Dai, PC Author Full Names: Ye, F.; Chi, Songxue; Fernandez-Baca, J. A.; Moreo, A.; Dagotto, E.; Lynn, J. W.; Mathieu, R.; Kaneko, Y.; Tokura, Y.; Dai, Pengcheng
Source:
PHYSICAL REVIEW LETTERS 103 (16): Art. No. 167202 OCT 16 2009
Abstract:
We use neutron scattering to investigate the doping evolution of the magnetic correlations in the single-layer manganite Pr1-xCa1-xMnO4, away from the x = 0.5 composition where the CE-type commensurate antiferromagnetic (AF) structure is stable. We find that short-range incommensurate spin correlations develop as the system is electron doped (x < 0.5), which coexist with the CE-type AF order. This suggests that electron doping in this system induces an inhomogeneous electronic self-organization, where commensurate AF patches with x = 0.5 are separated by electron-rich domain walls with short-range magnetic correlations. This behavior is strikingly different than for the perovskite Pr1-xCaxMnO3, where the long-range CE-type commensurate AF structure is stable over a wide range of electron or hole doping around x = 0.5.
Title:
Low temperature thermodynamical properties of ErCu2Si2
Authors:
Baran, S; Gondek, L; Szytula, A; Kaczorowski, D; Pikul, A; Penc, B; Piekarz, P; Hoser, A; Gerischer, S Author Full Names: Baran, S.; Gondek, L.; Szytula, A.; Kaczorowski, D.; Pikul, A.; Penc, B.; Piekarz, P.; Hoser, A.; Gerischer, S.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 (1): 12-18 JAN 2010
Abstract:
ErCu2Si2 crystallises in the tetragonal ThCr2Si2-type crystal structure. In this paper results of magnetometric, electrical transport, specific heat as well as neutron diffraction are reported. Results of electrical resistivity and specific heat measurements performed at low temperature yield existence of magnetic ordering roughly at 1.3 K. These results are in concert with neutron diffraction measurements, which reveal simple antiferromagnetic ordering between 0.47 and 1.00 K. At temperatures ranging from 1.00 up to 1.50K an additional incommensurate magnetic structure was observed. The propagation vector kappa = (0;0;0.074) was proposed to describe magnetic reflections within the amplitude modulated magnetic structure. Basing on specific heat studies the crystal field levels splitting scheme and magnetic entropy were calculated. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Competing magnetic structures in the DySi FeB-type phase diagram
Authors:
Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Ritter, C; Buschow, KHJ Author Full Names: Schobinger-Papamantellos, P.; Rodriguez-Carvajal, J.; Ritter, C.; Buschow, K. H. J.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 (1): 119-132 JAN 2010
Abstract:
The temperature magnetic phase diagrams, of the dimorphic DySi compound, have been studied in terms of wave vectors in the range 1.5-45 K, by neutron diffraction. The polycrystalline sample consists of 26% of CrB-type (Cmcm no. 63, all atoms at 4c site: (0, y, 1/4)) and of 74% of FeB-type (Pnma no. 62, all atoms at 4c site: (x, 1/4, z)). The CrB-ordering is described by the wave vector: q(1) = (0, 0, 1/2) over the entire magnetically ordered regime with a uniaxial magnetic structure along the shortest axis c. The FeB-type magnetic phase diagram reveals three distinct regions of magnetic ordering below T-N and one first order transition at T-2=23.5K (on heating). The ordering is described by two symmetry independent magnetic vectors q(2)=(0, 1/2,1/6) and q(3)=(0, q(3y), q(3z)) with a temperature variable length. At 1.5 K q(3y) approximate to 1/2 and q(3z) approximate to 1/11. The two phases coexist in the form of domains. They differ in the moment orientation of the q(3) phase that deviates by similar to 22 degrees from the b-axis in the (0, 0, 1) plane. The low temperature range (LT) 1.5 K-T-2 subdivides into two regions: (i) LT-1, between 1.5 K-T-1 where the relative amount of the two phases remains unchanged and in (ii) LT-2: T-1-T-2 where the amount of the incommensurate q3 phase increases at the cost of the commensurate q(2) amplitude modulated structure which remains unchanged but fully disappears at the first order transition at T-2=23.5 K. The q(3) phase undergoes minor changes until 22 K and gets destabilised at T-2 where the q(3z) component jumps from the LT value q(3z) approximate to 1/11 to the HT value approximate to 1/7 and the q(3y) component increases from 0.484(1) to 0.495(1). (iii) The high temperature (HT) range T-2-T-N (T-N=40 +/- 1 K) is described by a single wave vector q(3). The disproportionation of the HT magnetic phase q(3) below T-2 into two coexisting distinct phases q(2), q(3) down to 1.5 K is an unusual phenomenon, to our knowledge observed for the first time. Various mechanisms are discussed. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Self-similar transformation and quasi-unit cell construction of quasi-periodic structure with twelve-fold rotational symmetry
Authors:
Liao, LG; Fu, H; Fu, XJ Author Full Names: Liao Long-Guang; Fu Hong; Fu Xiu-Jun
Source:
ACTA PHYSICA SINICA 58 (10): 7088-7093 OCT 2009
Abstract:
The structural properties of a quasicrystal model with twelve-fold rotational symmetry are studied. We correct the errors in the self-similar transformation of the square-rhombus-hexagon tiling model proposed by Socolar. Based on the Stampfli-Gahler square-rhombus-triangle tiling model, the quasi-unit cell is successfully constructed, which can describe the dodecagonal quasiperiodic structure by the covering theory.
Title:
Measurement of anisotropy thermopower of decagonal AlCuCo quasicrystal
Authors:
Fan, ZJ; Geng, XW; Kong, WJ; Jin, YR Author Full Names: Fan Zhen-Jun; Geng Xue-Wen; Kong Wen-Jie; Jin Yi-Rong
Source:
ACTA PHYSICA SINICA 58 (10): 7119-7123 OCT 2009
Abstract:
The thermopower of decagonal AlCuCo quasicrystal was measured in the periodic and quasiperiodic direction by laser heating alternating current measurement method in the temperature range of from 300 K to 1200 K. We found that the thermopower is negative in the periodic direction and positive in the quasiperiodic direction. The thermopower hopps at 1123 K (850 degrees C) along the periodic direction. The change of the thermopower is not monotonic at high temperature. The measurement method we used is sensitive to the phase transition point.
Title:
Multiresolution of quasicrystal diffraction spectra
Authors:
Elkharrat, A; Gazeau, JP; Denoyer, F Author Full Names: Elkharrat, Avi; Gazeau, Jean-Pierre; Denoyer, Francoise
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 65: 466-489 Part 6 NOV 2009
Abstract:
A method for analyzing and classifying two-dimensional pure point diffraction spectra (i.e. a set of Bragg peaks) of certain self-similar structures with scaling factor beta > 1, such as quasicrystals, is presented. The two-dimensional pure point diffraction spectrum Pi is viewed as a point set in the complex plane in which each point is assigned a positive number, its Bragg intensity. Then, by using a nested sequence of self-similar subsets called beta-lattices, we implement a multiresolution analysis of the spectrum Pi. This analysis yields a partition of Pi simultaneously in geometry, in scale and in intensity (the 'fingerprint' of the spectrum, not of the diffracting structure itself). The method is tested through numerical explorations of pure point diffraction spectra of various mathematical structures and also with the diffraction pattern of a realistic model of a quasicrystal.

Update: 22-Oct-2009

Title:
Magnetic Properties of Multiferroics Bi(1-x)A(x)FeO(3-x/2) (A = Ca, Sr, Pb, Ba)
Authors:
Troyanchuk, IO; Mantytskaya, OS; Chobot, AN; Tereshko, NV Author Full Names: Troyanchuk, I. O.; Mantytskaya, O. S.; Chobot, A. N.; Tereshko, N. V.
Source:
PHYSICS OF THE SOLID STATE 51 (10): 2105-2108 OCT 2009
Abstract:
The magnetic properties of Bi(1-x)A(x)FeO(3-x/2) (A is an alkaline-earth ion) solid solutions have been studied in magnetic fields of up to 140 kOe. The ferroelectric phase (space group R3c) transforms into the nonpolar pseudocubic phase at x approximate to 0.2. It is demonstrated that the substitution of alkaline-earth ions for bismuth ions (x >= 0.1) leads to a complete destruction of the modulated antiferromagnetic structure and the appearance of a weakly ferromagnetic state within the R3c state. In the pseudocubic phase, the spontaneous magnetization is absent; however, the field dependence of the magnetization is nonlinear and depends on the magnetic prehistory.
Title:
MATERIALS SCIENCE Quasicrystals from nanocrystals
Authors:
van Blaaderen, A Author Full Names: van Blaaderen, Alfons
Source:
NATURE 461 (7266): 892-893 OCT 15 2009
Title:
Quasicrystalline order in self-assembled binary nanoparticle superlattices
Authors:
Talapin, DV; Shevchenko, EV; Bodnarchuk, MI; Ye, XC; Chen, J; Murray, CB Author Full Names: Talapin, Dmitri V.; Shevchenko, Elena V.; Bodnarchuk, Maryna I.; Ye, Xingchen; Chen, Jun; Murray, Christopher B.
Source:
NATURE 461 (7266): 964-967 OCT 15 2009
Abstract:
The discovery of quasicrystals in 1984 changed our view of ordered solids as periodic structures (1,2) and introduced new long-range-ordered phases lacking any translational symmetry(3-5). Quasi-crystals permit symmetry operations forbidden in classical crystallography, for example five-, eight-, ten-and 12-fold rotations, yet have sharp diffraction peaks. Intermetallic compounds have been observed to form both metastable and energetically stabilized quasicrystals (1,3,5); quasicrystalline order has also been reported for the tantalum telluride phase with an approximate Ta1.6Te composition(6). Later, quasicrystals were discovered in soft matter, namely supramolecular structures of organic dendrimers(7) and tri-block copolymers(8), and micrometre-sized colloidal spheres have been arranged into quasicrystalline arrays by using intense laser beams that create quasi-periodic optical standing-wave patterns(9). Here we show that colloidal inorganic nanoparticles can self-assemble into binary aperiodic superlattices. We observe formation of assemblies with dodecagonal quasicrystalline order in different binary nanoparticle systems: 13.4-nm Fe2O3 and 5-nm Au nanocrystals, 12.6-nm Fe3O4 and 4.7-nm Au nanocrystals, and 9-nm PbS and 3-nm Pd nanocrystals. Such compositional flexibility indicates that the formation of quasicrystalline nanoparticle assemblies does not require a unique combination of interparticle interactions, but is a general sphere-packing phenomenon governed by the entropy and simple interparticle potentials. We also find that dodecagonal quasicrystalline superlattices can form low-defect interfaces with ordinary crystalline binary superlattices, using fragments of (3(3).4(2)) Archimedean tiling as the 'wetting layer' between the periodic and aperiodic phases.
Title:
Magnetic structures of quaternary intermetallic borocarbides RCo2B2C (R = Dy, Ho, Er)
Authors:
ElMassalami, M; Moreno, R; Takeya, H; Ouladdiaf, B; Lynn, JW; Freitas, RS Author Full Names: ElMassalami, M.; Moreno, R.; Takeya, H.; Ouladdiaf, B.; Lynn, J. W.; Freitas, R. S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (43): Art. No. 436006 OCT 28 2009
Abstract:
The magnetic structures of the title compounds have been studied by neutron diffraction. In contrast to the isomorphous RNi2B2C compounds, wherein a variety of exotic incommensurate modulated structures has been observed, the magnetic structure of ErCo2B2C is found to be a collinear antiferromagnet with k = (12, 0, 12) while those of HoCo2B2C and DyCo2B2C are observed to be simple ferromagnets. For all studied compounds, the moments are found to be confined within the basal plane and their magnitudes are comparable to the values obtained from the low-temperature isothermal magnetization measurements. The absence of modulated magnetic structures in the RCo2B2C series (for ErCo2B2C, verified down to 50 mK) is attributed to the quenching of the Fermi surface nesting features.
Title:
A comparative study of the magnetic properties of the 1/1 approximant Ag50In36Gd14 and the icosahedral quasicrystal Ag50In36Gd14
Authors:
Wang, P; Stadnik, ZM; Al-Qadi, K; Przewoznik, J Author Full Names: Wang, P.; Stadnik, Z. M.; Al-Qadi, K.; Przewoznik, J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (43): Art. No. 436007 OCT 28 2009
Abstract:
We report on measurements of the dc and ac magnetic susceptibility, Gd-155 Mossbauer spectra, and specific heat of the 1/1 approximant Ag50In36Gd14, and of the ac magnetic susceptibility of the icosahedral quasicrystal Ag50In36Gd14. These alloys are shown to be spin glasses. For the icosahedral quasicrystal Ag50In36Gd14, spin freezing occurs at T-f = 4.3 K, and the frequency dependence of T-f is well accounted for by the Vogel-Fulcher and power laws. Spin freezing in the 1/1 approximant Ag50In36Gd14 occurs in two stages: at T-f1 = 3.7 K, Gd spins develop short-range correlations but continue to fluctuate, and then long-range freezing is achieved at T-f2 = 2.4 K. The frequency dependences of T-f1 and T-f2 can be accounted for by means of the Vogel-Fulcher law and the critical slowing down dynamics. It is shown that the spin freezing in both alloys is a nonequilibrium phenomenon rather than a true equilibrium phase transition. The Gd-155 Mossbauer spectra of the 1/1 approximant Ag50In36Gd14 confirm that the Gd spins are frozen at 1.5 K and are fluctuating at 4.6 K. The magnetic specific heat exhibits a maximum at a temperature that is 30% larger than T-f1, but the temperature derivative of the magnetic entropy peaks at T-f1. The Debye temperature of the 1/1 approximant Ag50In36Gd14 is 199(1) K as determined from the Mossbauer data, and 205(2) K as determined from the specific heat data.
Title:
Processing and characterization of rapidly quenched Ti-based alloys: Influence of solidification rate on the as-quenched structures
Authors:
Lefaix, H; Vermaut, P; Janickovic, D; Svec, P; Portier, R; Prima, F Author Full Names: Lefaix, H.; Vermaut, P.; Janickovic, D.; Svec, P.; Portier, R.; Prima, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 483 (1-2): 168-172 AUG 26 2009
Abstract:
>From technological viewpoint. icosahedral Ti-Zr-Ni phase may give challenging opportunities as novel hydrogen storage and hydride battery. Nevertheless. from the structural standpoint, the phase selection criterion as function of solidification route remains unclear. A series of Ti45Zr38Ni17 alloys, known to provide stable and well-ordered quasicrystals, was produced by planar flow casting using different processing parameters. From structural characterization, it appears that, at high cooling rate, i.e. high wheel speeds, or for the highest temperature of the melt, the as-quenched sample exhibits a mixture of nanoscale P and amorphous phases. The icosahedral phase precipitates when decreasing the wheel speed, from lower temperatures of the melt or after annealing a crystallized amorphous matrix. The reproducible formation of quasicrystals, observed in the amorphous matrix containing P particles, corroborates the competition between icosahedral and body-centered cubic (bcc) phases during the solidification process. These results are promising since it could be possible to control volume fractions of these two phases by choosing well-fitted thermal treatments so that quasicrystals mechanical properties should be improved by dispersion of a stable bcc phase. (C) 2008 Elsevier B.V. All rights reserved.
Title:
Multi-scaled polymer-based composite materials synthesized by mechanical alloying
Authors:
Kaloshkin, SD; Vandi, LJ; Tcherdyntsev, VV; Shelekhov, EV; Danilov, VD Author Full Names: Kaloshkin, S. D.; Vandi, L. -J.; Tcherdyntsev, V. V.; Shelekhov, E. V.; Danilov, V. D.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 483 (1-2): 195-199 AUG 26 2009
Abstract:
Multi-scaled composite materials are of great importance, because they exhibit higher mechanical properties than those attained using conventional fillers or polymer blends. In this work, multi-scaled composite materials based on ultra-high-molecular weight polyethylene (UHMWPE), quasicrystals, polyimide and bronze are investigated for use in the moving parts of machines, gears, bearings, and sliding elements. The main object is to investigate the process of fabricating such composite materials, and to check if these materials are reproducible and reliable to an industrial extent. The specimens were prepared using a high-energy planetary mill. When milled with bronze, the quasicrystalline phase was dissolved into an intermetallic solid solution: milling with polymers showed to conserve the quasicrystalline phase, whereas the crystallization of UHMWPE was achieved during the milling process. Tribological study of consolidated samples showed an increase in the wear resistance for the bronze-containing composite materials. in comparison with pure UHMWPE, the polyimide-based specimen exhibited higher strength and hardness. This work has demonstrated the possibility of producing composite materials with acceptable and reliable properties using the mechanical alloying technology. (C) 2008 Elsevier B.V. All rights reserved.
Title:
Nanostructure controlling in Zr-based metallic glasses using icosahedral local structure
Authors:
Saida, J; Kato, H; Setyawan, AD; Yoshimi, K; Inoue, A Author Full Names: Saida, J.; Kato, H.; Setyawan, A. D.; Yoshimi, K.; Inoue, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 483 (1-2): 231-234 AUG 26 2009
Abstract:
Glass-nano(quasi)crystal composite materials based on Zr-Al-Ni-Cu metallic glasses have been synthesized by controlling the nucleation and growth rates of the precipitated phase correlated with a unique icosahedral local structure. It is well known that the Zr65Al7.5Ni10Cu17.5 metallic glass has a high glass-forming ability (GFA), which enables us to produce the glassy sample with a bulky shape. Controlling a substitution of QC-forming elements such as noble metals with Cu and annealing condition, the nanoscale icosahedral quasicrystalline phase (I-phase) with various grain sizes and nucleus densities can be formed. Moreover, we have succeeded to control the nano-QC phase nucleation by changing the atmosphere pressure during casting, which results in the formation of new bulk metallic glasses (BMGs). These nanoscale structure and nucleation controlling techniques in BMGs bring a significant improvement of mechanical properties such as high strength and good ductility. (C) 2008 Elsevier B.V. All rights reserved.
Title:
Characterization of phases in complex metallic alloys Al73Mn27-xFex (x=2, 4 and 6)
Authors:
Priputen, P; Kusy, M; Kriska, M; Lipka, R; Illekova, E; Svec, P; Bursik, J; Svoboda, M; Dolinsek, J; Janovec, J Author Full Names: Priputen, P.; Kusy, M.; Kriska, M.; Lipka, R.; Illekova, E.; Svec, P.; Bursik, J.; Svoboda, M.; Dolinsek, J.; Janovec, J.
Source:
INTERMETALLICS 17 (12): 1047-1051 DEC 2009
Abstract:
The characterization of phases in Al73Mn27-xFex (x = 2, 4 and 6) alloys was performed using X-ray diffraction, differential thermal analysis, and scanning electron microscopy enabling energy dispersive X-ray spectroscopy. Both the annealed and the thermally cycled states were studied. In the annealed states the occurrence of T-phase was expected, however it was confirmed for alloys Al73Mn25Fe2 and Al73Mn23Fe4 only. The annealing of the Al73Mn21Fe6 alloy probably led to the formation of decagonal quasicrystal (D). The T- and D-phases were found to be unstable at low temperatures. In the states after DTA the low temperature Al-11(Mn,Fe)(4) and gamma(2) phases were observed in the Al73Mn25Fe2 and Al73Mn21Fe6 alloys, while only the former phase was observed in the Al73Mn23Fe4 alloy. (C) 2009 Elsevier Ltd. All rights reserved.
Title:
Structure Determination of Two Modulated gamma-Brass Structures in the Zn-Pd System through a (3+1)-Dimensional Space Description
Authors:
Gourdon, O; Izaola, Z; Elcoro, L; Petricek, V; Miller, GJ Author Full Names: Gourdon, Olivier; Izaola, Zunbeltz; Elcoro, Luis; Petricek, Vaclav; Miller, Gordon J.
Source:
INORGANIC CHEMISTRY 48 (20): 9715-9722 OCT 19 2009
Abstract:
The structure determination of two composite compounds in the Zn-Pd system with close relationships to the cubic gamma-brass structure Zn11-delta Pd2+delta is reported. Their structures have been solved from single crystal X-ray diffraction data within a (3 + 1)-dimensional [(3 + 1)D] formalism. Zn75.7(7)Pd24.3 and Zn78.8(7)Pd21.2 crystallize with orthorhombic symmetry, superspace group Xmmm(00 gamma)0s0 (X [(1/2,1/2,0,0); (0,1/2,1/2,1/2); (1/2,0,1/2,1/2)]), with the following lattice parameters, respectively: a(s) = 12.929(3) angstrom, b(s) = 9.112(4) angstrom, c(s) = 2.5631(7) angstrom, q = 8/13 c* and V-s = 302.1(3) angstrom(3) and a(s) = 12.909(3) angstrom, b(s) = 9.115(3) angstrom, c(s) = 2.6052(6) angstrom, q = 11/18 c* and V-s = 306.4(2) angstrom(3). Their structures may be considered as commensurate because they can be refined in the conventional 3D space groups (Cmce and Cmcm, respectively) using supercells, but they also refined within the (3 + 1)D formalism to residual factors R = 3.14% for 139 parameters and 1184 independent reflections for Zn75.7(7)Pd24.3 and R = 3.16% for 175 parameters and 1804 independent reflections for Zn78.8(7)Pd21.2. The use of the (3 + 1)D formalism improves the results of the refinement and leads to a better understanding of the complexity of the atomic arrangement through the various modulations (occupation waves and displacive waves). Our refinements emphasize a unique Pd/Zn occupancy modulation at the center of distorted icosahedra, a modulation which correlates with the distortion of these polyhedra.
Title:
Nanoquasicrystalline Al-Fe-Cr-based alloys. Part I: Phase transformations
Authors:
Galano, M; Audebert, F; Stone, IC; Cantor, B Author Full Names: Galano, M.; Audebert, F.; Stone, I. C.; Cantor, B.
Source:
ACTA MATERIALIA 57 (17): 5107-5119 OCT 2009
Abstract:
Nanoquasicrystalline Al-Fe-Cr-based alloys composed of sub-micro-sized icosahedral quasicrystalline particles embedded in alpha-Al matrix have a higher strength at elevated temperature compared with commercial Al alloys. However, further improvement of the microstructural stability is desirable in order to maximize the elevated temperature strength. A detailed study of the effect on the microstructure and the phase transformations by the addition of Ti, V, Nb or Ta to a ternary Al-93(Fe3Cr2)(7) alloy was carried out using heat treatment and microstructural characterization. The addition of the fourth element leads to a refined microstructure and can stabilize the icosahedral topology, delaying the quasicrystalline icosahedral phase decomposition until a higher temperature is reached. The addition of Nb or Ta enabled a greater stabilization effect than the addition of Ti or V, retaining a microstructure similar to the as-spun state after heat treatment between 450 and 550 degrees C and even retaining icosahedral particles up to 550 degrees C. The outstanding microstructural stabilization obtained with addition of Nb or Ta leads to very promising applications in the automotive and aeronautic industries. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 15-Oct-2009

Title:
Nonmetallic Nature of the Interrelation of Thermal, Magnetic, and Electrical Properties in Icosahedral Quasicrystals at High Temperatures
Authors:
Prekul, AF; Shchegolikhina, NI; Nazarova, SZ; Edagawa, K Author Full Names: Prekul, A. F.; Shchegolikhina, N. I.; Nazarova, S. Z.; Edagawa, K.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 108 (2): 120-124 AUG 2009
Abstract:
In the icosahedral phase of Al-Cu-Fe alloys in the temperature range above 300 K there has been found an interrelation between the heat capacity, magnetic susceptibility, and conductivity not characteristic of typical metals. It is supposed that these phases are systems whose properties at finite temperatures are predominantly determined by excited electrons rather than by electrons with a Fermi energy E-F.
Title:
Spin Amplitude Modulation Driven Magnetoelectric Coupling in the New Multiferroic FeTe2O5Br
Authors:
Pregelj, M; Zaharko, O; Zorko, A; Kutnjak, Z; Jeglic, P; Brown, PJ; Jagodic, M; Jaglicic, Z; Berger, H; Arcon, D Author Full Names: Pregelj, M.; Zaharko, O.; Zorko, A.; Kutnjak, Z.; Jeglic, P.; Brown, P. J.; Jagodic, M.; Jaglicic, Z.; Berger, H.; Arcon, D.
Source:
PHYSICAL REVIEW LETTERS 103 (14): Art. No. 147202 OCT 2 2009
Abstract:
The magnetic and ferroelectric properties of the layered geometrically frustrated cluster compound FeTe2O5Br were investigated with single-crystal neutron diffraction and dielectric measurements. An incommensurate transverse amplitude modulated magnetic order with the wave vector q = (1/2, 0.463, 0) develops below T-N = 10.6(2) K. Simultaneously, a ferroelectric order due to exchange striction involving polarizable Te4+ lone-pair electrons develops perpendicular to q and to Fe3+ magnetic moments. The observed magnetoelectric coupling is proposed to originate from the temperature dependent phase difference between neighboring amplitude modulation waves.
Title:
Magnetic structure and ferroelectric polarization of MnWO4 investigated by density functional calculations and classical spin analysis
Authors:
Tian, C; Lee, CH; Xiang, HJ; Zhang, YM; Payen, C; Jobic, S; Whangbo, MH Author Full Names: Tian, Chuan; Lee, Changhoon; Xiang, Hongjun; Zhang, Yuemei; Payen, Christophe; Jobic, Stephane; Whangbo, Myung-Hwan
Source:
PHYSICAL REVIEW B 80 (10): Art. No. 104426 SEP 2009
Abstract:
The ordered magnetic states of MnWO4 at low temperatures were examined by evaluating the spin exchange interactions between the Mn2+ ions of MnWO4 on the basis of first principles density functional calculations and by performing classical spin analysis with the resulting spin exchange parameters. Our work shows that the spin exchange interactions are frustrated within each zigzag chain of Mn2+ ions along the c direction and between such chains of Mn2+ ions along the a direction. This explains the occurrence of a spiral-spin order along the c and a directions in the incommensurate magnetic state AF2, and that of a up arrow up arrow down arrow down arrow spin order along the c and a directions in the commensurate magnetic state AF1. The ferroelectric polarization of MnWO4 in the spiral-spin state AF2 was examined by performing Berry phase calculations for a model superstructure to find that the ferroelectric polarization occurs along the b direction,! in agreement with experiment.
Title:
Magnetic and crystal structure of Ho-5(SixGe(1-x))(4) studied by neutron diffraction
Authors:
Ritter, C; Magen, C; Morellon, L; Algarabel, PA; Ibarra, MR; Pereira, AM; Araujo, JP; Sousa, JB Author Full Names: Ritter, C.; Magen, C.; Morellon, L.; Algarabel, P. A.; Ibarra, M. R.; Pereira, A. M.; Araujo, J. P.; Sousa, J. B.
Source:
PHYSICAL REVIEW B 80 (10): Art. No. 104427 SEP 2009
Abstract:
The magnetic and crystal structures of the magnetocaloric Ho-5(SixGe1-x)(4) (x= 1, 0.75, 0.5 and 0) have been studied by neutron powder diffraction experiments. The room-temperature crystal phases of the compositions x= 1, 0.75, and 0.5 are preserved in the whole temperature range 2-300 K, i.e. the Gd5Si4-type Pnma O(I) structure for Ho5Si4, the Gd5Si2Ge2-type P112(1)/a M state in x= 0.75, and the Sm5Ge4-type Pnma O(II) phase in x= 0.5. Ho5Si4 undergoes a second order ferromagnetic (FM) transition at T-C= 77 K into a noncollinear FM structure with the magnetization oriented mainly along the a axis and weak antiferromagnetic (AFM) coupling along b and c (magnetic space group Pnm'a'). Ho5Si3Ge becomes FM at T-C= 50 K (magnetic space group P112(1)'/a). At T-C'similar to 16 K an incipient second incommensurate magnetic phase appears which becomes commensurate below 8 K with a propagation vector k=(0 0 1/4). The magnetic structure of the main phase at 30 and 2 K shows the dominance of a FM coupling along the a axis with an AFM canting along c. Ho5Si2Ge2 stands out for the complexity of its low-temperature magnetic structure. In addition to the Neel transition of the O(II) phase at T-N similar to 30 K (magnetic space group Pn'm'a'), two additional magnetic phases with propagation vectors k=(0 0 1/4) and k=(1/2 0 0) appear at 15 and 12 K, respectively. In Ho5Ge4 the main O(II) structure orders AFM with k=(0 0 0) at T-N similar to 30 K in the same magnetic space group Pn'm'a'. Below 25 K a complete structural transition from high temperature O(II)Pnma to P2(1)/m takes place within the AFM state. The magnetic structure of this new nuclear phase stays AFM with k=(0 0 0), but sees two out of six independent Ho sites non magnetic. A second magnetic transition takes place at about 18 K characterized by the appearance of a second propagation vector k=(0 0 1/2) which magnetically couples the formerly non magnetic Ho sites. Magnetic- field dependent neutron diffractograms demonstrate that FM sets in in Ho5Ge4. The onset of ferromagnetism is associated with the previously reported nucleation of a new high field O(II) Pnma phase. Contrary to the intensity of the magnetic coupling with the propagation vector k=(0 0 0), which disappears quickly with the onset of FM, a progressive decrease of the intensity associated with the state k=(0 0 1/2) suggests a possible relationship between the extent of the magnetic coupling k=(0 0 1/2) and the percentage of remnant P2(1)/m phase.
Title:
Short-range incommensurate magnetic order near the superconducting phase boundary in Fe(1+delta)Te(1-x)Sex
Authors:
Wen, JS; Xu, GY; Xu, ZJ; Lin, ZW; Li, Q; Ratcliff, W; Gu, G; Tranquada, JM Author Full Names: Wen, Jinsheng; Xu, Guangyong; Xu, Zhijun; Lin, Zhi Wei; Li, Qiang; Ratcliff, W.; Gu, Genda; Tranquada, J. M.
Source:
PHYSICAL REVIEW B 80 (10): Art. No. 104506 SEP 2009
Abstract:
We performed elastic neutron-scattering and magnetization measurements on Fe1.07Te0.75Se0.25 and FeTe0.7Se0.3. Short-range incommensurate magnetic order is observed in both samples. In the former sample with higher Fe content, a broad magnetic peak appears around (0.46,0,0.5) at low temperature, while in FeTe0.7Se0.3, the broad magnetic peak is found to be closer to the antiferromagnetic (AFM) wave vector (0.5,0,0.5). The incommensurate peaks are only observed on one side of the AFM wave vector for both samples, which can be modeled in terms of an imbalance of ferromagnetic/antiferromagnetic correlations between nearest-neighbor spins. We also find that with higher Se (and lower Fe) concentration, the magnetic order becomes weaker while the superconducting temperature and volume increase.
Title:
Stability of nodal quasiparticles in underdoped YBa2Cu3O6+y probed by penetration depth and microwave spectroscopy
Authors:
Huttema, WA; Bobowski, JS; Turner, PJ; Liang, RX; Hardy, WN; Bonn, DA; Broun, DM Author Full Names: Huttema, W. A.; Bobowski, J. S.; Turner, P. J.; Liang, Ruixing; Hardy, W. N.; Bonn, D. A.; Broun, D. M.
Source:
PHYSICAL REVIEW B 80 (10): Art. No. 104509 SEP 2009
Abstract:
High-resolution measurements of superfluid density rho(s)(T) and broadband quasiparticle conductivity sigma(1)(Omega) have been used to probe the low-energy excitation spectrum of nodal quasiparticles in underdoped YBa2Cu3O6+y. Penetration depth lambda(T) is measured to temperatures as low as 0.05 K. sigma 1(Omega) is measured from 0.1 to 20 GHz and is a direct probe of zero-energy quasiparticles. The data are compared with predictions for a number of theoretical scenarios that compete with or otherwise modify pure d(x2-y2) superconductivity, in particular, commensurate and incommensurate spin and charge-density waves; d(x2-y2) + is and d(x2-y2) + id(xy) superconductivity; circulating current phases; and the BCS-BEC crossover. We conclude that the data are consistent with a pure d(x2-y2) state in the presence of a small amount of strong scattering disorder, and are able to rule out most candidate competing states either completely or to a level set by the energy scale of the disorder, T-d similar to 4 K. Commensurate spin and charge-density orders, however, are not expected to alter the nodal spectrum and therefore cannot be excluded.
Title:
Structure of the fivefold surface of the Ag-In-Yb icosahedral quasicrystal
Authors:
Sharma, HR; Shimoda, M; Sagisaka, K; Takakura, H; Smerdon, JA; Nugent, PJ; McGrath, R; Fujita, D; Ohhashi, S; Tsai, AP Author Full Names: Sharma, H. R.; Shimoda, M.; Sagisaka, K.; Takakura, H.; Smerdon, J. A.; Nugent, P. J.; McGrath, R.; Fujita, D.; Ohhashi, S.; Tsai, A. P.
Source:
PHYSICAL REVIEW B 80 (12): Art. No. 121401 SEP 2009
Abstract:
The surface structural study of an icosahedral (i) quasicrystal of the Cd-Yb family is presented. Comparison of bias-dependent scanning tunneling microscopy data from the fivefold surface of i-Ag-In-Yb with the refined bulk model of isostructural i-Cd-Yb indicates that surfaces are formed at bulk planes intersecting the center of the rhombic triacontahedral clusters, the building blocks of the Cd-Yb family quasicrystals. These observations open up the possibility of the use of this material as a template for epitaxial structures.
Title:
Electronic structure of RNiC2 (R = Sm, Gd, and Nd) intermetallic compounds
Authors:
Laverock, J; Haynes, TD; Utfeld, C; Dugdale, SB Author Full Names: Laverock, J.; Haynes, T. D.; Utfeld, C.; Dugdale, S. B.
Source:
PHYSICAL REVIEW B 80 (12): Art. No. 125111 SEP 2009
Abstract:
First-principles calculations of the electronic structure of members of the RNiC2 series are presented and their Fermi surfaces investigated for nesting propensities, which might be linked to the charge-density waves exhibited by certain members of the series (R=Sm, Gd, and Nd). Calculations of the generalized susceptibility, chi(0)(q, omega), show strong peaks at the same q vector in both the real and imaginary parts for these compounds. Moreover, this peak occurs at a wave vector which is very close to that experimentally observed in SmNiC2. In contrast, for LaNiC2 (which is a superconductor below 2.7 K) as well as for ferromagnetic SmNiC2, there is no such sharp peak. This could explain the absence of a charge-density wave transition in the former, and the destruction of the charge-density wave that has been observed to accompany the onset of ferromagnetic order in the latter.
Title:
Theoretical study of the magnetism in the incommensurate phase of TiOCl
Authors:
Mastrogiuseppe, DM; Torio, ME; Gazza, CJ; Dobry, AO Author Full Names: Mastrogiuseppe, D. M.; Torio, M. E.; Gazza, C. J.; Dobry, A. O.
Source:
PHYSICA B-CONDENSED MATTER 404 (18): 2805-2808 OCT 1 2009
Abstract:
Going beyond a recently proposed microscopic model [D. Mastrogiuseppe. A. Dobry, arXiv:0810.3018v] for the incommensurate transition in the spin-Peierls TiOX (X = Cl, Br) compounds, in the present work we start by studying the thermodynamics of the model with XY spins and adiabatic phonons. We find that the system enters an incommensurate phase by a first order transition at a low temperature T-c1. At a higher temperature T-C2 a continuous transition to a uniform phase is found. Furthermore, we study the magnetism in the incommensurate phase by density matrix renormalization group (DMRG) calculations on a one-dimensional Heisenberg model where the exchange is modulated by the incommensurate atomic position pattern. When the wave vector q of the modulation is near pi, we find local magnetized zones (LMZ) in which spins abandon their singlets as a result of the domain walls induced by the modulated distortion. When q moves far away enough from pi, the LMZ disappear and the system develops incommensurate magnetic correlations induced by the structure. We discuss the relevance of this result regarding previous and future experiments in TiOCl (C) 2009 Elsevier B.V. All rights reserved.
Title:
Frustration of Magnetic and Ferroelectric Long-Range Order in Bi2Mn4/3Ni2/3O6
Authors:
Claridge, JB; Hughes, H; Bridges, CA; Allix, M; Suchomel, MR; Niu, H; Kuang, X; Rosseinsky, MJ; Bellido, N; Grebille, D; Perez, O; Simon, C; Pelloquin, D; Blundell, SJ; Lancaster, T; Baker, PJ; Pratt, FL; Halasyamani, PS Author Full Names: Claridge, John B.; Hughes, Helen; Bridges, Craig A.; Allix, Mathieu; Suchomel, Matthew R.; Niu, Hongjun; Kuang, Xiaojun; Rosseinsky, Matthew J.; Bellido, Natalia; Grebille, Dominique; Perez, Olivier; Simon, Charles; Pelloquin, Denis; Blundell, Stephen J.; Lancaster, Tom; Baker, Peter J.; Pratt, Francis L.; Halasyamani, P. Shiv
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 131 (39): 14000-14017 OCT 7 2009
Abstract:
The slight incommensurate modulation of the structure of Bi2Mn4/3Ni2/3O6 is sufficient to suppress the electrical polarization which arises in commensurate treatments of the structure, due to antiferroelectric coupling of local polar units of over 900 angstrom(3). The incommensurate structure is produced by the competition between ferroelectric Bi lone pair-driven A site displacement, chemical order of Mn and Ni on the B site, and both charge and orbital order at these transition metals. The interplay between the frustrated polar Bi displacements and the frustrated spin order at the B site, induced by positional disorder, produces magnetodielectric coupling between the incommensurately modulated lattice and the spin-glass-like ground state with an unusual relationship between the magnetocapacitance and the applied field.
Title:
Molecular dewetting on insulators
Authors:
Burke, SA; Topple, JM; Grutter, P Author Full Names: Burke, S. A.; Topple, J. M.; Gruetter, P.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (42): Art. No. 423101 OCT 21 2009
Abstract:
Recent attention given to the growth and morphology of organic thin films with regard to organic electronics has led to the observation of dewetting (a transition from layer (s) to islands) of molecular deposits in many of these systems. Dewetting is a much studied phenomenon in the formation of polymer and liquid films, but its observation in thin films of the 'small' molecules typical of organic electronics requires additional consideration of the structure of the interface between the molecular film and the substrate. This review covers some key concepts related to dewetting and molecular film growth. In particular, the origins of different growth modes and the thickness dependent interactions which give rise to dewetting are discussed in terms of surface energies and the disjoining pressure. Characteristics of molecular systems which may lead to these conditions, including the formation of metastable interface structures and commensurate-incommensurate phase transitions, are also discussed. Brief descriptions of some experimental techniques which have been used to study molecular dewetting are given as well. Examples of molecule-on-insulator systems which undergo dewetting are described in some detail, specifically perylene derivatives on alkali halides, C-60 on alkali halides, and the technologically important system of pentacene on SiO2. These examples point to some possible predicting factors for the occurrence of dewetting, most importantly the formation of an interface layer which differs from the bulk crystal structure.

Update: 8-Oct-2009

Title:
Spin chirality and electric polarization in multiferroic compounds RMn2O5 (R = Ho, Er)
Authors:
Wakimoto, S; Kimura, H; Fukunaga, M; Nishihata, K; Takeda, M; Kakurai, K; Noda, Y; Tokura, Y Author Full Names: Wakimoto, Shuichi; Kimura, Hiroyuki; Fukunaga, Mamoru; Nishihata, Keisuke; Takeda, Masayasu; Kakurai, Kazuhisa; Noda, Yukio; Tokura, Yoshinori
Source:
PHYSICA B-CONDENSED MATTER 404 (17): 2513-2516 SEP 1 2009
Abstract:
Polarized neutron diffraction experiments have been performed on multiferroic materials RMn2O5 (R = Ho, Er) under electric fields in the ferroelectric commensurate (CM) and the low-temperature incommensurate (LT-ICM) phases, where the former has the highest electric polarization and the latter has reduced polarization. It is found that, after cooling in electric fields down to the CM phase, the magnetic chirality is proportional to the electric polarization. Also we confirmed that the magnetic chirality can be switched by the polarity of the electric polarization in both the CM and LT-ICM phases. These facts suggest an intimate coupling between the magnetic chirality and the electric polarization. However, upon the transition from the CM to LT-ICM phase, the reduction of the electric polarization is not accompanied by any reduction of the magnetic chirality, implying that the CM and LT-ICM phases contain different mechanisms of the magnetoelectric coupling. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Solid State Polyselenides and Polytellurides: A Large Variety of Se-Se and Te-Te Interactions
Authors:
Graf, C; Assoud, A; Mayasree, O; Kleinke, H Author Full Names: Graf, Christian; Assoud, Abdeljalil; Mayasree, Oottil; Kleinke, Holger
Source:
MOLECULES 14 (9): 3115-3131 SEP 2009
Abstract:
A large variety of different interactions between the chalcogen atoms, Q, occur in the solid state structures of polyselenides and polytellurides, including both molecular and infinite units. The simplest motifs are classical Q(2)(2-) dumbbells and nonlinear Qn(2-) chains (n = 3, 4, 5,..), e. g. found in alkali metal polychalcogenides. In addition, nonclassical so-called hypervalent motifs exist in the form of linear Q(3)(4-) units or within larger units such as Q(4)(4-) and Q(5)(4-). Infinitely extended Q units include zigzag, cis/trans and linear chains, as well as planar and slightly puckered layers. Several of those are susceptible to Peierls distortions, leading to the formation of both commensurate and incommensurate superstructures and anomalies in transport properties, including metal-nonmetal transitions.
Title:
Manganese adlayers on i-Al-Pd-Mn quasicrystal: growth and electronic structure
Authors:
Shukla, AK; Dhaka, RS; D'Souza, SW; Maniraj, M; Barman, SR; Horn, K; Ebert, P; Urban, K; Wu, D; Lograsso, TA Author Full Names: Shukla, A. K.; Dhaka, R. S.; D'Souza, S. W.; Maniraj, M.; Barman, S. R.; Horn, K.; Ebert, Ph; Urban, K.; Wu, D.; Lograsso, T. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (40): Art. No. 405005 OCT 7 2009
Abstract:
Pseudomorphic growth of thin elemental metal films is often observed on a variety of crystalline solids. On quasicrystalline surfaces with their complex structure and the absence of translational periodicity, the situation is different since elemental metals do not exhibit quasicrystalline order, and hence the specific interaction between overlayer and substrate is decisive. Here we study the growth of manganese films on an icosahedral i-Al-Pd-Mn alloy with a view to establishing the growth mode and electronic structure. Although we observe an exponential intensity variation of the adlayer and substrate related x-ray photoemission spectroscopy (XPS) peaks, low energy electron diffraction (LEED) shows that Mn adlayers do not exhibit quasicrystallinity. The detailed structure of the Mn 2p core level line reveals considerable electronic structure differences between the quasicrystalline and elemental metal environment. Evidence of a substantial local magnetic moment on the Mn atoms in the overlayer (about 2.8 mu(B)) is obtained from the Mn 3s exchange splitting.
Title:
Pressure-induced disorder in Rb2ZnCl4
Authors:
Machon, D; Grzechnik, A; Friese, K Author Full Names: Machon, Denis; Grzechnik, Andrzej; Friese, Karen
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (40): Art. No. 405405 OCT 7 2009
Abstract:
Rb2ZnCl4 in the normal phase (T = 308-313 K) has been studied under pressure by means of single-crystal x-ray diffraction up to 3.84 GPa and Raman spectroscopy up to 5.9 GPa. No pressure-induced phase transition has been observed but an orientational disorder of the tetrahedra is enhanced with the pressure. At the same time a partial one-dimensional correlation of some chlorine atoms might be favoured at high pressures. Raman spectra in the incommensurate phase (T = 293 K) were collected to higher pressure (24.2 GPa) varying the pressure-transmitting medium. The hydrostaticity during the compression is shown to affect drastically the broadness of the Raman peaks, leading to an amorphous-like spectrum in the least hydrostatic case.
Title:
Crystallographic and electrochemical characteristics of Ti-Zr-Ni-Pd quasicrystalline alloys
Authors:
Liu, BZ; Zhang, YD; Mi, GF; Zhang, Z; Wang, LM Author Full Names: Liu, Baozhong; Zhang, Yude; Mi, Guofa; Zhang, Zhi; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 34 (16): 6925-6929 Sp. Iss. SI AUG 2009
Abstract:
Ti45Zr35Ni20-xPdx (x = 0, 1, 3, 5 and 7, at%) alloys were prepared by melt-spinning. The phase structure and electrochemical hydrogen storage performances of melt-spun alloys were investigated. The melt-spun alloys were icosahedral quasicrystalline phase, and the quasi-lattice constant increased with increasing x value. The maximum discharge capacity of alloy electrodes increased from 79 mAh/g (x = 0) to 148 mAh/g (x = 7). High-rate dis-chargeability and cycling stability were also enhanced with the increase of Pd content. The improvement in the electrochemical hydrogen storage characteristics may be ascribed to better electrochemical activity and oxidation resistance of Pd than that of Ni. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Title:
Investigation of the New P ' 3-Na0.60VO2 Phase: Structural and Physical Properties
Authors:
Szajwaj, O; Gaudin, E; Weill, F; Darriet, J; Delmas, C Author Full Names: Szajwaj, Olivier; Gaudin, Etienne; Weill, Francois; Darriet, Jacques; Delmas, Claude
Source:
INORGANIC CHEMISTRY 48 (19): 9147-9154 OCT 5 2009
Abstract:
A new layered phase Na0.60VO2 was synthesized by chemical deintercalation of sodium from the pristine compound O3-NaVO2. The Na0.60VO2 compound exhibits a distorted P'3-type oxygen stacking (AABBCC) with an average monoclinic unit cell containing a = 4.9862(14) angstrom, b = 2.8708(8) angstrom, c = 5.917(2) angstrom, and beta = 104.36(3)degrees. A modulated structure was observed by transmission electron microscopy and X-ray diffraction (XRD) measurements. Indexation of the XRD pattern was achieved by using the q vector equal to 0.44b(star), and the 4D superspace group C2/m (0 beta 0) s0 was then deduced. The specific heat measurement showed a strong correlated system with a gamma value of around 20 mJ . mol(-1) . K-2. The electrical conductivity shows a semiconductor-like behavior with an activation energy of 0.52 eV. A paramagnetic behavior of the susceptibility is observed below room temperature with a Curie constant equal to C = 0.076 emu . K-1 . mol(-1) . Oe(-1). To explain this small value, a model of pseudotriangular clusters of vanadium with a random distribution of V3+ and V4+ was considered.
Title:
Phase formation and structures of quasicrystals and approximants in the Zn-Mg-(Ti, Zr, Hf) system
Authors:
Ohhashi, S; Abe, E; Tanaka, M; Tsai, AP Author Full Names: Ohhashi, S.; Abe, E.; Tanaka, M.; Tsai, A. P.
Source:
ACTA MATERIALIA 57 (16): 4727-4735 SEP 2009
Abstract:
The compositional regions for primitive (P) and face-centered (F) icosahedral quasicrystals (iQc) have been determined to be around Zn84Mg9Zr7 and Zn75Mg18Zr6, respectively. A 1/1 approximant of the F-type iQc was found to have a composition around Zn77Mg18Zr5. A similar tendency has been verified for the Zn-Mg-Hf system. No stable iQc was observed in the Zn-Mg-Ti system. High-resolution X-ray measurements performed with synchrotron radiation showed that the stable iQcs are highly ordered and contain less phason disorder. High-angle annular dark field (HAADF) scanning transmission electron microscopy observation of the 1/1 Zn-Mg-Hf approximant effectively revealed the Hf positions in the structure, whose local contrasts can be reasonably interpreted by a structural model where icosahedral and dodecahedral Hf clusters are mutually interpenetrated. Similar appearances of local contrasts were frequently observed in HAADF images of the F-type iQc, indicating that the iQc structure is also build up of icosahedral clusters that are almost identical to those in the 1/1 approximant. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 1-Oct-2009

Title:
Tailoring Thermally Induced Nano-Quasicrystallization and Deformation-Assisted Nanocrystallization for Mechanical Property Improvement in Zr-Al-Ni-Cu-Pd Bulk Metallic Glasses
Authors:
Saida, J; Setyawan, AD; Kato, H; Matsushita, M; Inoue, A Author Full Names: Saida, Junji; Setyawan, Albertus D.; Kato, Hidemi; Matsushita, Mitsuhide; Inoue, Akihisa
Source:
MATERIALS TRANSACTIONS 50 (8): 2079-2086 AUG 2009
Abstract:
The material design tailoring of a synergistic effect of an in-situ nano secondary phase formation and defomation-induced nanocrystallization for improving the mechanical strength and ductility, has been investigated in Zr65Al7.5Ni10Cu17.5-xPdx bulk metallic glasses (BMGs). As-cast Zr65Al7.5Ni10Cu17.5-xPdx (x = 5-17.5) BMGs have significant ductility in compressive deformation, which is attributed to deformation-induced dynamic nanocrystallization. The 10at% Pd-containing BMG with a low volume fraction of the quasicrystalline (QC) phase of less than 6% exhibits increases in strength and Young's modulus, in addition to a remaining plasticity of similar to 5%, compared with the monolithic glassy alloy. Such improvements in the mechanical properties originate from the combination of two effects of in-situ homogenous nano-QC formation and deformation-induced inhomogeneous nanocrystallization. The present method should be regarded as a new technique for the production of BMGs with high strength and good ductility. [doi:10.2320/matertrans.M2009135]

Update: 24-Sep-2009

Title:
Microstructure, surface composition and chemical stability of partly ordered LaTiO2N
Authors:
Logvinovich, D; Bocher, L; Sheptyakov, D; Figi, R; Ebbinghaus, SG; Aguiar, R; Aguirre, MH; Reller, A; Weidenkaff, A Author Full Names: Logvinovich, Dmitry; Bocher, Laura; Sheptyakov, Denis; Figi, Renato; Ebbinghaus, Stefan G.; Aguiar, Rosiana; Aguirre, Myriam H.; Reller, Armin; Weidenkaff, Anke
Source:
SOLID STATE SCIENCES 11 (8): 1513-1519 AUG 2009
Abstract:
LaTiO2N was synthesized in a thermal ammonolysis process of crystalline La2Ti2O7 prepared by conventional solid state reaction or by ammonolysis of a homogeneous amorphous precursor obtained from a soft-chemistry approach. At room temperature slowly cooled LaTiO2N prepared from either precursor crystallizes in space group I (1) over bar and shows a partially ordered anionic arrangement in contrast to a quenched reference sample. The material possesses a complex microstructure represented by twin domains of different types and orientations, as well as incommensurately modulated fragments. The presence of minor C- and N-containing phases such as carbonates, cyanides and nitrates as well as a small amount of a reoxidation intermediate was detected by infrared and Raman spectroscopy. These small amounts of secondary phases can generally influence the results of the O/N content determination of oxynitride compounds when using thermal analysis methods. The formation of such unwanted secondary phases can be avoided by quenching the oxynitride sample or by cooling in inert atmosphere. (C) 2009 Elsevier Masson SAS. All rights reserved.
Title:
Detailed Phase Analysis and Crystal Structure Investigation of a Bi1-xCaxFeO3-x/2 Perovskite-Related Solid Solution Phase and Selected Property Measurements Thereof
Authors:
Schiemer, J; Withers, R; Noren, L; Liu, Y; Bourgeois, L; Stewart, G Author Full Names: Schiemer, Jason; Withers, Ray; Noren, Lasse; Liu, Yun; Bourgeois, Laure; Stewart, Glen
Source:
CHEMISTRY OF MATERIALS 21 (18): 4223-4232 SEP 22 2009
Abstract:
A well-ordered, perovskite-related, (Bi1-xCaxFeO3-x/2)-O-III solid solution phase is synthesized via a rapid liquid phase sintering technique and shown to exist over the composition range similar to 0.20 < x < similar to 0.49. Two phase regions are shown to separate this phase from compositionally narrow end-member (Bi1-xCaxFeO3-x/2)-O-III solid solutions based on rhombohedral BiFeO3 and brownmillerite, Ca2Fe2O5, respectively. The wide range, non-stoichiometric phase is characterized by a well ordered, (in general) incommensurately modulated structure that varies systematically with composition. Mossbauer spectroscopy is used to verify the oxidation state of iron as (III), as well as showing the existence of three separate iron environments across the solid solution field. HRTEM imaging is used to develop a structural model for the phase at one particular composition. The magnetic, dielectric, and impedance properties of this solid solution phase are reported. Magnetic measurements show antiferromagnetic behavior. There is no change in either susceptibility or antiferromagnetic behavior with composition. Attempts at obtaining saturated ferroelectric loops failed due to high intrinsic conductivity. The phase is found to exhibit a low frequency impedance relaxation that is likely due to correlated oxygen vacancy hopping.
Title:
Differential geometry: a natural tool for describing symmetry operations
Authors:
Kocian, P; Schenk, K; Chapuis, G Author Full Names: Kocian, Philippe; Schenk, Kurt; Chapuis, Gervais
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 329-341 Part 5 OCT 2009
Abstract:
Differential geometry provides a useful mathematical framework for describing the fundamental concepts in crystallography. The notions of point and associated vector spaces correspond to those of manifold and tangent space at a given point. A space-group operation is a one-to-one map acting on the manifold, whereas a point-group operation is a linear map acting between two tangent spaces of the manifold. Manifold theory proves particularly powerful as a unified formalism describing symmetry operations of conventional as well as modulated crystals without requiring a higher-dimensional space. We show, in particular, that a modulated structure recovers a three-dimensional periodicity in any tangent space and that its point group consists of linear applications. (C) 2009 International Union of Crystallography Printed in Singapore - all rights reserved
Title:
Point substitution processes for decagonal quasi-periodic tilings
Authors:
Fujita, N Author Full Names: Fujita, Nobuhisa
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 342-351 Part 5 OCT 2009
Abstract:
A general construction principle for the inflation rules for decagonal quasiperiodic tilings is proposed. The prototiles are confined to be polygons with unit edges. An inflation rule for a tiling is the combination of expansion and division of the tiles, where the expanded tiles can be divided arbitrarily as long as the set of prototiles is maintained. A certain kind of point decoration process turns out to be useful for the identification of possible division rules. The method is capable of generating a broad range of decagonal tilings, many of which are chiral and have atomic surfaces with fractal boundaries. Two new families of decagonal tilings are presented; one is quaternary and the other ternary. The properties of the ternary tilings with rhombic, pentagonal and hexagonal prototiles are investigated in detail. (C) 2009 International Union of Crystallography Printed in Singapore - all rights reserved

Update: 17-Sep-2009

Title:
Symmetry Breaking in Dense Solid Hydrogen: Mechanisms for the Transitions to Phase II and Phase III
Authors:
Toledano, P; Katzke, H; Goncharov, AF; Hemley, RJ Author Full Names: Toledano, Pierre; Katzke, Hannelore; Goncharov, Alexander F.; Hemley, Russell J.
Source:
PHYSICAL REVIEW LETTERS 103 (10): Art. No. 105301 SEP 4 2009
Abstract:
Spectroscopic data for the high-pressure phases of hydrogen together with the topology of the phase diagram provide new insight on the behavior of the material at megabar pressure. Structural mechanisms are proposed for the transitions to phases II and III. These mechanisms include a partially ordered structure (possibly incommensurate) and an ordered isotranslational structure for the two phases, respectively. The analysis supports the existence of an additional phase, isostructural to phase III, with boundary that meets to form a second triple point with phases I and III.
Title:
Aperiodicity, structure, and dynamics in Ni(CN)(2)
Authors:
Goodwin, AL; Dove, MT; Chippindale, AM; Hibble, SJ; Pohl, AH; Hannon, AC Author Full Names: Goodwin, Andrew L.; Dove, Martin T.; Chippindale, Ann M.; Hibble, Simon J.; Pohl, Alexander H.; Hannon, Alex C.
Source:
PHYSICAL REVIEW B 80 (5): Art. No. 054101 AUG 2009
Abstract:
By combining the results of both x-ray diffraction and neutron total-scattering experiments, we show that Ni(CN)(2) exhibits long-range structural order only in two dimensions, with no true periodicity perpendicular to its gridlike layers. Reverse Monte Carlo analysis gives an experimental distinction between M-C and M-N bond lengths in a homometallic cyanide framework and identifies the vibrational modes responsible for anomalous positive and negative thermal expansion in the title compound.
Title:
Origin of Moireacute structures in C-60 on Pb(111) and their effect on molecular energy levels
Authors:
Li, HI; Franke, KJ; Pascual, JI; Bruch, LW; Diehl, RD Author Full Names: Li, H. I.; Franke, K. J.; Pascual, J. I.; Bruch, L. W.; Diehl, R. D.
Source:
PHYSICAL REVIEW B 80 (8): Art. No. 085415 AUG 2009
Abstract:
Low-energy electron diffraction (LEED) indicates that the monolayer structure of C-60 on Pb(111) comprises two coexisting incommensurate structures with nonsymmetry epitaxial rotations near 20 degrees relative to the Pb(111) lattice. These structures are observed in scanning tunneling microscopy (STM) as Moireacute superstructures having periods of about 46 A degrees and 34 A degrees. The Moireacute images and LEED patterns are consistent with two higher-order commensurate (HOC) structures that were identified using the hexagonal number sequence method. These structures are close to predictions from the Novaco-McTague theory of epitaxial rotation, assuming a weakly corrugated substrate potential. As a consequence of the fullerenes within the Moireacute structures having different local environments, the energetic alignment of the molecular resonances is also modulated, with shifts measured by tunneling spectroscopy of up to 20 meV.
Title:
Commensurate lock-in and incommensurate supersolid phases of hard-core bosons on anisotropic triangular lattices
Authors:
Isakov, SV; Chien, HC; Wu, JJ; Chen, YC; Chung, CH; Sengupta, K; Kim, YB Author Full Names: Isakov, Sergei V.; Chien, Hong-Chi; Wu, Jian-Jheng; Chen, Yung-Chung; Chung, Chung-Hou; Sengupta, Krishnendu; Kim, Yong Baek
Source:
EPL 87 (3): Art. No. 36002 AUG 2009
Abstract:
We investigate the interplay between commensurate lock-in and incommensurate supersolid phases of the hard-core bosons at half-filling with anisotropic nearest-neighbor hopping and repulsive interactions on triangular lattice. We use numerical quantum and variational Monte Carlo as well as analytical Schwinger boson mean-field analysis to establish the ground states and phase diagram. It is shown that, for finite-size systems, there exist a series of jumps between different supersolid phases as the anisotropy parameter is changed. The density ordering wave vectors are locked to commensurate values and jump between adjacent supersolids. In the thermodynamic limit, however, the magnitude of these jumps vanishes leading to a continuous set of novel incommensurate supersolid phases. Copyright (C) EPLA, 2009

Update: 10-Sep-2009

Title:
Coupled Magnetic and Ferroelectric Domains in Multiferroic Ni3V2O8
Authors:
Cabrera, I; Kenzelmann, M; Lawes, G; Chen, Y; Chen, WC; Erwin, R; Gentile, TR; Leao, JB; Lynn, JW; Rogado, N; Cava, RJ; Broholm, C Author Full Names: Cabrera, I.; Kenzelmann, M.; Lawes, G.; Chen, Y.; Chen, W. C.; Erwin, R.; Gentile, T. R.; Leao, J. B.; Lynn, J. W.; Rogado, N.; Cava, R. J.; Broholm, C.
Source:
PHYSICAL REVIEW LETTERS 103 (8): Art. No. 087201 AUG 21 2009
Abstract:
Electric control of multiferroic domains is demonstrated through polarized magnetic neutron diffraction. Cooling to the cycloidal multiferroic phase of Ni3V2O8 in an electric field E causes the incommensurate Bragg reflections to become neutron spin polarizing, the sense of neutron polarization reversing with E. Quantitative analysis indicates the E-treated sample has a handedness that can be reversed by E. We further show a close association between cycloidal and ferroelectric domains through E-driven spin and electric polarization hysteresis. We suggest that a definite cycloidal handedness is achieved through magnetoelastically induced Dzyaloshinskii-Moriya interactions.
Title:
Structural transformations and magnetic properties of Bi(1-x)Ln(x)FeO(3) (Ln = La, Nd, Eu) multiferroics
Authors:
Troyanchuk, IO; Bushinsky, MV; Karpinsky, DV; Mantytskaya, OS; Fedotova, VV; Prochnenko, OI Author Full Names: Troyanchuk, I. O.; Bushinsky, M. V.; Karpinsky, D. V.; Mantytskaya, O. S.; Fedotova, V. V.; Prochnenko, O. I.
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 246 (8): 1901-1907 AUG 2009
Abstract:
Crystal structures of Bi(1-x)Ln(x)FeO(3) systems (Ln = La, Nd, Eu) are studied using X-ray and neutron diffraction, magnetization measurements as well as electron microscopy. It was shown that the unit cell of the Bi1-xLaxFeO3 system is described with the R3c space group in the concentration interval 0 < x < 0.15, with the space group Imma (0.4 < x < 0.5) and with the Puma at x > 0.5. The mixed-phase state was observed in the range 0.15 < x < 0.4 independent of synthesis conditions. A similar sequence of the phase transformations was observed for Bi1-xNdxFeO3 system, In the case of qBi(1-x)Eu(x)FeO(3) series the unit cell is rhombohedral (R3c) at x 0.08 and orthorhombic (Pnma) at x > 0.20, whereas no evidence for Imma phase was found. The magnetization study has revealed the spontaneous magnetization to be associated with Prima and Imma phases that do not allow conventional ferroelectricity, The ferroelectric R3c phase exhibits meta-magnetic behavior due to transition from an incommensurately modulated antiferromagnetic state to a weak ferromagnetic state. Substitution of Bi3+ with Ln(3+) leads to a strong decrease of external magnetic field inducing a metamagnetic transition. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Title:
Resonant Magnetic X-ray Diffraction Study on the Triangular Lattice Antiferromagnet GdPd2Al3
Authors:
Inami, T; Terada, N; Kitazawa, H; Sakai, O Author Full Names: Inami, Toshiya; Terada, Noriki; Kitazawa, Hideaki; Sakai, Osamu
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (8): Art. No. 084713 AUG 2009
Abstract:
Resonant magnetic x-ray diffraction experiments were carried out on the stacked triangular lattice antiferromagnet GdPd2Al3. The experiments revealed an expected initial collinear c-axis order at T-N1 followed by an additional in-plane order at T-N2, while at the same time we found that the ground state is a helically ordered state of a very long incommensurate period of approximately 700 angstrom. The distribution of K-domains was highly anisotropic, and the domain with the modulation vector normal to the surface of the crystal was ascendant. Low-field magnetization is discussed on the basis of the observed incommensurate magnetic structure.
Title:
Studies of Multiferroic System of LiCu2O2: II. Magnetic Structures of Two Ordered Phases with Incommensurate Modulations
Authors:
Kobayashi, Y; Sato, K; Yasui, Y; Moyoshi, T; Sato, M; Kakurai, K Author Full Names: Kobayashi, Yoshiaki; Sato, Kenji; Yasui, Yukio; Moyoshi, Taketo; Sato, Masatoshi; Kakurai, Kazuhisa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (8): Art. No. 084721 AUG 2009
Abstract:
Neutron diffraction and Li-7-NMR have been applied to determine the three dimensional magnetic structures of the multiferroic system LiCu2O2, which has four chains (ribbon chains) of edge-sharing CuO4 square planes in a unit cell. First, we have confirmed that there are successive magnetic transitions at T-N1 = 24.5 K and T-N2 = 22.8 K. In the T region between T-N1 and T-N2, the quasi one-dimensional spins (S = 1/2) of Cu2+ ions within a chain have a collinear and sinusoidally modulated structure with Cu-moments parallel to the c-axis and with the modulation vector along the b-axis. At T < T-N2, an ellipsoidal helical spin structure with the incommensurate modulation has been found. We present detailed parameters, describing the modulation amplitudes, helical axis vectors as well as the relative phases of the modulations of four ribbon chains, which can well reproduce both the NMR and neutron results, in the two magnetically ordered phases. This finding of the rather precise magnetic structures enables us to discuss the relationship between the magnetic structure and the multiferroic nature of the present system in zero magnetic field, as presented in our companion paper (paper I), and open a way how to understand the reported electric polarization under the finite magnetic field.
Title:
Evaluation of the local environment for nanoscale quasicrystal formation in Zr80Pt20 glassy alloy using Voronoi analysis
Authors:
Saida, J; Itoh, K; Sato, S; Imafuku, M; Sanada, T; Inoue, A Author Full Names: Saida, Junji; Itoh, Keiji; Sato, Shigeo; Imafuku, Muneyuki; Sanada, Takashi; Inoue, Akihisa
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (37): Art. No. 375104 SEP 16 2009
Abstract:
The local atomic structure of nano-quasicrystal-forming Zr80Pt20 binary glassy alloy was investigated by reverse Monte Carlo modeling based on the results of x-ray diffraction. A prepeak at Q similar to 17 nm(-1) originating from the unique bonding between the Pt-Pt pair is observed in the structure factor. Voronoi analysis indicates that an icosahedral-like polyhedron is formed around Pt. It is also found that icosahedral-like polyhedra exist around Zr; however, the fraction of perfect icosahedra is considerably lower than that in the nano-quasicrystal-forming Zr70Pd30 glassy alloy. A difference in the local environment between the two binary quasicrystal-forming glassy alloys is suggested.
Title:
Direct observation of double-k lattice modulation in double-k magnetic structures. The case of CeAl2
Authors:
Stunault, A; Schweizer, J; Givord, F; Vettier, C; Detlefs, C; Boucherle, JX; Lejay, P Author Full Names: Stunault, A.; Schweizer, J.; Givord, F.; Vettier, C.; Detlefs, C.; Boucherle, J-X; Lejay, P.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 21 (37): Art. No. 376004 SEP 16 2009
Abstract:
Symmetry analysis is combined with x-ray scattering experiments to investigate the lattice modulation associated with the incommensurate magnetic structure in the case of a double-k structure. The expansion of the free energy shows that the components of the magnetic structure with propagation vectors k(1) and k(2) can couple via components of lattice modulations. It is shown that the classical diffraction peaks reflecting a 2k propagation vector, associated with magneto-elastic effects in single-k structures, will coexist with diffraction peaks with propagation vectors k(1) - k(2) or k(1) + k(2). The existence of these latter peaks can be considered as a signature of a double-k magnetic structure. In the case of the double-k modulated structure of CeAl2, group theory is applied directly to the study of the charge modulation. An x-ray scattering study of the 2k satellites shows that the lattice displacements of the two Ce sites of the structure are antiparallel to each other, and perpendicular to the direction of the magnetic modulation. We also confirm experimentally the existence of k(1) + k(2) satellites.
Title:
Formation of Nano-Quasicrystalline Decagonal Phase in the Al70Cu10Co5Ni15 System by High Energy Ball Milling
Authors:
Yadav, TP; Mukhopadhyay, NK; Shaz, MA; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Mukhopadhyay, N. K.; Shaz, M. A.; Tiwari, R. S.; Srivastava, O. N.
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 9 (9): 5527-5532 SEP 2009
Abstract:
A nano decagonal quasicrystalline phase in the Al70Cu10Co5Ni15 alloy has been synthesized by mechanical alloying of a mixture of elemental powders followed by annealing. A high-energy ball milling of the elemental mixture of Al, Cu, Co and Ni leads to the formation of B2 type quaternary intermetallic alloys. The X-ray diffraction and transmission electron microscopy techniques have been employed for characterization of the samples. It was observed that the dissolution of the individual elements into an alloy led to the formation of a nano B2 phase. This phase was found to be quite stable against milling and no other crystalline or amorphous phases could be detected. Milled powder after annealing at 700 degrees C for 60 h was found to transform to nano-decagonal phase. Attempts have been made to understand the evolution of the complex intermetallic nano phases and their relative stability during milling.
Title:
Two Variants of the 1/2[110](p)(203)(p) Crystallographic Shear Structures: The Phasoid Sr0.61Pb0.18(Fe0.75Mn0.25)O-2.29
Authors:
Lepoittevin, C; Hadermann, J; Malo, S; Perez, O; Van Tendeloo, G; Hervieut, M Author Full Names: Lepoittevin, Christophe; Hadermann, Joke; Malo, Sylvie; Perez, Olivier; Van Tendeloo, Gustaaf; Hervieut, Maryvonne
Source:
INORGANIC CHEMISTRY 48 (17): 8257-8262 SEP 7 2009
Abstract:
For the composition (Sr0.61Pb0.18)(Fe0.75Mn0.25)O-2.29, a new modulated crystallographic shear structure, related to perovskite, has been synthesized and structurally characterized by transmission electron microscopy. The structure can be described using a monoclinic supercell with cell parameters a(m) = 27.595(2) angstrom, b(m) = 3.8786(2) angstrom, c(m) = 13.3453(9) angstrom, and beta(m) = 100.126(5)degrees, refined from powder X-ray diffraction data. The incommensurate crystallographic shear phases require an alternative approach using the superspace formalism. This allows a unified description of the incommensurate phases from a monoclinically distorted perovskite unit cell and a modulation wave vector. The structure deduced from the high-resolution transmission electron microscopy and high-angle annular dark-field-scanning transmission electron microscopy images is that of a 1/2[110](p)(203)(p) crystallographic shear structure. The structure follows the concept of a phasoid, with two coexisting variants with the same unit cell. The difference is situated at the translational interface, with the local formation of double (phase 2) or single (phase 1) tunnels, where the Pb cations are likely located.
Title:
Spin density wave dislocation in chromium probed by coherent X-ray diffraction
Authors:
Jacques, VLR; Le Bolloc'h, D; Ravy, S; Giles, C; Livet, F; Wilkins, SB Author Full Names: Jacques, V. L. R.; Le Bolloc'h, D.; Ravy, S.; Giles, C.; Livet, F.; Wilkins, S. B.
Source:
EUROPEAN PHYSICAL JOURNAL B 70 (3): 317-325 AUG 2009
Abstract:
We report on the study of a magnetic dislocation in pure chromium. Coherent X-ray diffraction profiles obtained on the incommensurate Spin Density Wave (SDW) reflection are consistent with the presence of a dislocation of the magnetic order, embedded at a few micrometers from the surface of the sample. Beyond the specific case of magnetic dislocations in chromium, this work may open up a new method for the study of magnetic defects embedded in the bulk.
Title:
Field-dependent competing magnetic ordering in multiferroic Ni3V2O8
Authors:
Singh, AK; Jain, D; Ganesan, V; Nigam, AK; Patnaik, S Author Full Names: Singh, A. K.; Jain, D.; Ganesan, V.; Nigam, A. K.; Patnaik, S.
Source:
EPL 86 (5): Art. No. 57001 JUN 2009
Abstract:
The geometrically frustrated magnet Ni3V2O8 undergoes a series of competing magnetic ordering at low temperatures. Most importantly, one of the incommensurate phases has been reported to develop a ferroelectric correlation caused by spin frustration. Here we report an extensive thermodynamic, dielectric and magnetic study on clean polycrystalline samples of this novel multiferroic compound. Our low-temperature specific heat data at high fields up to 14 Tesla clearly identify the development of a new magnetic-field-induced phase transition below 2 K that shows signatures of simultaneous electric ordering. We also report temperature-and field-dependent dielectric constant that enables us to quantitatively estimate the strength of magnetoelectric coupling in this improper ferroelectric material. Copyright (C) EPLA, 2009
Title:
Theory of magnetic order in Fe1+yTe1-xSex
Authors:
Fang, C; Bernevig, BA; Hu, JP Author Full Names: Fang, Chen; Bernevig, B. Andrei; Hu, Jiangping
Source:
EPL 86 (6): Art. No. 67005 JUN 2009
Abstract:
We develop a local spin model to explain the rich magnetic structures in the ironbased superconductors Fe1+yTe1-xSex. We show that our model exhibits both commensurate antiferromagnetic and incommensurate magnetic order along the crystal a-axis. The transition from the commensurate to the incommensurate phase is induced when the concentration of excess Fe atoms is larger than a critical value. Experimentally measurable spin-wave features are calculated, and the mean-field phase diagram of the model is obtained. Our model also suggests the existence of a large quantum critical region due to strong spin frustration upon increasing Se concentration. Copyright (C) EPLA, 2009
Title:
A "checkerboard" orbital-stripe phase and charge ordering transitions in Pr(SrxCa2-x)Mn2O7 (0 <= x <= 0.45)
Authors:
Li, ZA; Li, X; Wang, Z; Tian, HF; Ma, C; Zeng, LJ; Yang, HX Author Full Names: Li, Z. A.; Li, X.; Wang, Z.; Tian, H. F.; Ma, C.; Zeng, L. J.; Yang, H. X.
Source:
EPL 86 (6): Art. No. 67010 JUN 2009
Abstract:
The charge/orbital ordering (COO) behaviors in the double-layered Pr(SrxCa2-x)Mn2O7 have been investigated by in situ transmission electron microscopy (TEM) observations. The experimental results reveal that two charge ordering (CO) phase transitions, so-called T-co1 and T-co2, commonly exist in the orthorhombic Pr(SrxCa2-x)Mn2O7 (0 <= x <= 0.45) samples. Moreover, a "checkerboard" orbital-stripe phase characterized by two orthogonal COO modulations, q(a) and q(b), is observed between T-co1 and T-co2 in all samples. Detailed TEM investigations on the x=0.2 sample, in which a visible electric polarization was found (Tokunaga Y. et al., Nat. Mater., 5 (2006) 937) demonstrate that the q(b) modulation only survives between T-co1 and T-co2, and the "checkerboard" phase transforms into the conventional one-dimensional COO stripe phase below T-co2. The reversal of in-plane optical anisotropy across the T-co2 transition (Tokunaga Y. et al., Nat. Mater., 5 (2006) 937) is also explained based on TEM result. Copyright (C) EPLA, 2009
Title:
Polygrain icosahedral Al-Pd-Re quasicrystal as a granular electronic conductor
Authors:
Vekilov, YK; Chernikov, MA Author Full Names: Vekilov, Yu. Kh.; Chernikov, M. A.
Source:
EPL 87 (1): Art. No. 17010 JUL 2009
Abstract:
The mechanism of low-temperature electronic transport in polygrain samples of icosahedral Al-Pd-Re is analyzed by analogy with granular electronic systems. The intergranular tunneling and electrostatic energy (Coulomb blockade) are responsible for a specific behaviour of the electrical conductivity in polygrain samples of icosahedral Al-Pd-Re at low temperatures. Depending on the structural state of the sample, both factors may be important and the variable-range hopping regime, of Efros-Shklovskii's type, takes place. For the strong-coupling state the tunneling prevails, and the low-temperature variation of the electrical conductivity is dominated by the Coulomb-interaction and weak-localization corrections. Copyright (C) EPLA, 2009
Title:
Suppression of the current leakage in charge ordered Lu2Fe2Fe1-xMnxO7 (0 < x < 0.86)
Authors:
Qin, YB; Yang, HX; Zhang, Y; Tian, HF; Ma, C; Zeng, LJ; Li, JQ Author Full Names: Qin, Y. B.; Yang, H. X.; Zhang, Y.; Tian, H. F.; Ma, C.; Zeng, L. J.; Li, J. Q.
Source:
APPLIED PHYSICS LETTERS 95 (7): Art. No. 072901 AUG 17 2009
Abstract:
The ferroelectricity, magnetic properties, and charge-ordering modulations in the layered Lu2Fe2Fe1-xMnxO7 have been investigated for x ranging from 0 to 0.86. Experimental measurements reveal that substitution of Mn for Fe could evidently influence the low temperature magnetic transition. Moreover, ferroelectric analysis suggests that introduction of Mn ions in this layered system can efficiently suppress the conducting leakage and result in clear hysteresis loops in the polarization-electric field switching curves. The charge ordering states in Lu2Fe2Fe1-xMnxO7 characterized by two incommensurate modulations has been observed and discussed in association with the local spontaneous polarizations.

Update: 3-Sep-2009

Title:
Rare-earth free wrought-processed magnesium alloy with dispersion of quasicrystal phase
Authors:
Somekawa, H; Osawa, Y; Singh, A; Mukai, T Author Full Names: Somekawa, Hidetoshi; Osawa, Yoshiaki; Singh, Alok; Mukai, Toshiji
Source:
SCRIPTA MATERIALIA 61 (7): 705-708 OCT 2009
Abstract:
Quasicrystal and related phase particles were successfully dispersed in wrought-processed Mg-7.6 wt.% Zn-3.9 wt.% Al alloy with homogeneous and fine-grained structures. This rare-earth-free alloy showed high strength and ductility balance, which was superior to that of the well-known quasicrystal phase dispersed in Mg-Zn-RE alloys, with a weak texture and a reduction of mechanical asymmetry in yield strength. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Microstructural characterization of a laser remelted coating of Al91Fe4Cr3Ti2 quasicrystalline alloy
Authors:
Gargarella, P; Almeida, A; Vilar, R; Afonso, CRM; Rios, CT; Bolfarini, C; Botta, WJ; Kiminami, CS Author Full Names: Gargarella, P.; Almeida, A.; Vilar, R.; Afonso, C. R. M.; Rios, C. T.; Bolfarini, C.; Botta, W. J.; Kiminami, C. S.
Source:
SCRIPTA MATERIALIA 61 (7): 709-712 OCT 2009
Abstract:
A bulk sample of Al-Fe-Cr-Ti alloy with adequate composition to form quasicrystalline phases has been surface remelted, using laser processing techniques, to produce a quasicrystalline surface coating. After the laser treatment,

Update: 31-Dec-2008

Title:
Lattice dynamical calculation of negative thermal expansion in ZrV2O7 and HfV2O7
Authors:
Mittal, R; Chaplot, SL Author Full Names: Mittal, R.; Chaplot, S. L.
Source:
PHYSICAL REVIEW B 78 (17): Art. No. 174303 NOV 2008
Abstract:
We report lattice dynamics calculations of negative thermal-expansion (NTE) behavior of ZrV2O7 family, extending our previous work on the ZrW2O8 family. The two families of compounds differ in terms of the oxygen coordination around the V/W atoms leading to differences in the nature of soft phonons under compression that are responsible for the NTE. Our calculations quantitatively reproduce the negative expansion over a range of temperatures. We also discuss the relation of the soft phonons with the phase transitions observed in the ZrV2O7 family. Especially, the calculations show a soft-phonon mode at a wave vector of 0.31 < 1,1,0 >, which is in excellent agreement with the known incommensurate modulation in ZrV2O7 below 375 K.
Title:
Infrared-active excitations related to Ho3+ ligand-field splitting at the commensurate-incommensurate magnetic phase transition in HoMn2O5
Authors:
Sirenko, AA; O'Malley, SM; Ahn, KH; Park, S; Carr, GL; Cheong, SW Author Full Names: Sirenko, A. A.; O'Malley, S. M.; Ahn, K. H.; Park, S.; Carr, G. L.; Cheong, S-W.
Source:
PHYSICAL REVIEW B 78 (17): Art. No. 174405 NOV 2008
Abstract:
Linearly polarized spectra of far-infrared (IR) transmission in HoMn2O5 multiferroic single crystals have been studied in the frequency range between 8.5 and 105 cm(-1) and for temperatures between 5 and 300 K. Polarization of IR-active excitations depends on the crystallographic directions in HoMn2O5 and is sensitive to the magnetic phase transitions. We attribute some of the infrared-active excitations to electric-dipole transitions between ligand-field (LF) split states of Ho3+ ions. For light polarization along crystalline b axis, the oscillator strength of electric dipoles at low frequencies (10.5, 13, and 18 cm(-1)) changes significantly at the commensurate-incommensurate antiferromagnetic phase transition at T-3=19 K. This effect shows a strong correlation with the pronounced steps of the b-directional static dielectric function. We propose that the LF on Ho3+ connects the magnetism and dielectric properties of this compound through coupling with the Mn spin structure. We comment on the possibility for composite excitations of magnons and excited LF states.
Title:
Doping-dependent charge and spin superstructures in layered cobalt perovskites
Authors:
Sakiyama, N; Zaliznyak, A; Lee, SH; Mitsui, Y; Yoshizawa, H Author Full Names: Sakiyama, N.; Zaliznyak, A.; Lee, S. -H.; Mitsui, Y.; Yoshizawa, H.
Source:
PHYSICAL REVIEW B 78 (18): Art. No. 180406 NOV 2008
Abstract:
We have investigated cobaltite relatives of the layered perovskite cuprates and nickelates, Pr2-xCaxCoO4 (0.39 <= x <= 0.73) and La2-xSrxCoO4 (x=0.4, 0.61), using elastic neutron scattering. We have discovered doping-dependent incommensurate short-range ordering of charges and magnetic moments, which in cobaltites occur in the nonitinerant polaron phase, for 0.5 <= x <= 0.75. The charge order exists already at room temperature and shows no change on cooling. The incommensurability of its propagation vector, Q(c)=(epsilon(c), 0, l), roughly scales with the concentration of Co2+ ions, epsilon(c) similar to (1-x). Magnetic order follows at low T less than or similar to 40 K and has twice larger periodicity, indicating a dominant antiferromagnetic correlation between the nearest Co2+ spins.
Title:
Magnetic switching and phase competition in the multiferroic antiferromagnet Mn1-xFexWO4
Authors:
Ye, F; Ren, Y; Fernandez-Baca, JA; Mook, HA; Lynn, JW; Chaudhury, RP; Wang, YQ; Lorenz, B; Chu, CW Author Full Names: Ye, F.; Ren, Y.; Fernandez-Baca, J. A.; Mook, H. A.; Lynn, J. W.; Chaudhury, R. P.; Wang, Y. -Q.; Lorenz, B.; Chu, C. W.
Source:
PHYSICAL REVIEW B 78 (19): Art. No. 193101 NOV 2008
Abstract:
Elastic neutron scattering is used to study the spin correlations in the multiferroic Mn1-xFexWO4 with x=0.035, 0.05, and 0.10. The noncollinear incommensurate (ICM) magnetic structure associated with the ferroelectric (FE) phase in pure MnWO4 is suppressed at x=0.035 and completely absent at x=0.10. The ICM spin order and FE phase can be restored by applying a magnetic field along the spin easy axis. The low-T commensurate magnetic structure extends in both H/T with increasing Fe concentration. The systematic evolution of the magnetic and electric properties indicates that the noncollinear ICM spin order results from competing magnetic interactions and its stabilization can be tuned by the internal (x) or external (magnetic-field) perturbations.
Title:
Microscopic model for transitions from Mott to spin-Peierls insulator in TiOCl
Authors:
Zhang, YZ; Jeschke, HO; Valenti, R Author Full Names: Zhang, Yu-Zhong; Jeschke, Harald O.; Valenti, Roser
Source:
PHYSICAL REVIEW B 78 (20): Art. No. 205104 NOV 2008
Abstract:
On the basis of ab initio density-functional-theory calculations, we derive the underlying microscopic model Hamiltonian for TiOCl, a unique system that shows two consecutive phase transitions from a Mott insulator to a spin-Peierls insulator through a structurally incommensurate phase. We show with our model that the presence of magnetic frustration in TiOCl leads to a competition with the spin-Peierls distortion, which results in the unusual incommensurate phase. In addition, our calculations indicate that the spin-Peierls state is triggered by adiabatic phonons, which is essential for understanding the nature of the phase transition.
Title:
Chimie Douce Route to Sodium Hydroxo Titanate Nanowires with Modulated Structure and Conversion to Highly Photoactive Titanium Dioxides
Authors:
Peng, CW; Richard-Plouet, M; Ke, TY; Lee, CY; Chiu, HT; Marhic, C; Puzenat, E; Lemoigno, F; Brohan, L Author Full Names: Peng, Chih-Wei; Richard-Plouet, Mireille; Ke, Tsung-Yin; Lee, Chi-Young; Chiu, Hsin-Tien; Marhic, Christiane; Puzenat, Eric; Lemoigno, Frederic; Brohan, Luc
Source:
CHEMISTRY OF MATERIALS 20 (23): 7228-7236 DEC 9 2008
Abstract:
Sodium hydroxo titanate nanowires with NaTi2O4(OH) formulation are fabricated by chimie-douce from TiO2 powders in a hot concentrated base solution. In the present work, we investigate, in detail, the structure and morphology of the titanate, acid-exchanged materials, and phases formed during dehydration of these compounds; we then discuss the relationship between the initial titanate structure and TiO2 formation. XRD, ED, HRTEM, EDS, density measurements, and TG/MS results suggest that the titanate and acid-exchanged structures were closely related to the pseudolepidocrocite arrangement ("Cs2Ti6O12" type). The average structure of NaTi2O4(OH) nanowires consists of noncorrugated Ti2O3(OH) and NaO layers stacked along the [0 10] direction and an energy minimization was further conducted by theoretical methods. From TEM study, we demonstrated that NaTi2O4(OH) exhibits a modulated structure (q wave vector equals to 1/7 [001]*), which originates from the misfit between the NaO and Ti2O3(OH) sublattices. NaTi2O4(OH) structure has a monoclinic distortion (I2/m space group) with refined unit cell a = 0.37000(6) nm, b = 1.7816(4) nm, c = 2.2077(3) nm, beta = 92.70(1)degrees. Proton exchange followed by heat treatment convert the sodium hydroxo titanate into highly photoactive TiO2 nanowires. The activity is attributed to the presence of preferentially exposed (001) surface plane which is explained by the topotactic phase transformation of TiO2(B) into anatase.
Title:
Activation of magnetic shape memory effect in Ni-Mn-Ga alloys by mechanical and magnetic treatment
Authors:
Straka, L; Heczko, O; Hanninen, H Author Full Names: Straka, Ladislav; Heczko, Oleg; Haenninen, Hannu
Source:
ACTA MATERIALIA 56 (19): 5492-5499 NOV 2008
Abstract:
Mechanical and magnetic training decreased considerably the twinning stress of five-layered modulated, approximately tetragonal martensite (5M) oh Ni-Mn-Ga and Ni-Mn-Ga doped with Fe, and of seven-layered modulated, approximately orthorhombic Ni-Mn-Ga martensite (7M). Repeated compressions along two perpendicular directions of single crystal specimens of 5M and 7M reduced the twinning stress approximately threefold. Further reduction of twinning stress of 7M was achieved by the rotation of the specimen in I T magnetic field several times. The training resulted in the appearance of the magnetic shape memory effect or giant magnetic-field-induced strain in agreement with a simple energy-based model of the effect. The origin of the decrease in twinning stress is discussed. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 19-Dec-2008

Title:
High-temperature heat capacity of the Al63Cu25Fe12 quasicrystal
Authors:
Prekul, AF; Kazantsev, VA; Shchegolikhina, NI; Gulyaeva, RI; Edagawa, K Author Full Names: Prekul, A. F.; Kazantsev, V. A.; Shchegolikhina, N. I.; Gulyaeva, R. I.; Edagawa, K.
Source:
PHYSICS OF THE SOLID STATE 50 (11): 2013-2015 NOV 2008
Abstract:
The mechanisms of energy absorption by metallic alloys with long-range aperiodic lattice order and electronic properties of marginal metals are studied. The heat capacity and linear expansion coefficient of the Al63Cu25Fe12 icosahedral phase in the temperature range 300-1000 K are measured for the first time. Disagreement between the measured heat capacity and predictions made from the Debye model is found and analyzed. It is shown that the excess heat capacity observed at the temperatures of the experiment is fitted by Einstein's function in the approximation T
Title:
Longitudinal Spin Density Wave Order in a Quasi-1D Ising-like Quantum Antiferromagnet
Authors:
Kimura, S; Matsuda, M; Masuda, T; Hondo, S; Kaneko, K; Metoki, N; Hagiwara, M; Takeuchi, T; Okunishi, K; He, Z; Kindo, K; Taniyama, T; Itoh, M Author Full Names: Kimura, S.; Matsuda, M.; Masuda, T.; Hondo, S.; Kaneko, K.; Metoki, N.; Hagiwara, M.; Takeuchi, T.; Okunishi, K.; He, Z.; Kindo, K.; Taniyama, T.; Itoh, M.
Source:
PHYSICAL REVIEW LETTERS 101 (20): Art. No. 207201 NOV 14 2008
Abstract:
>From neutron diffraction measurements on a quasi-1D Ising-like Co2+ spin compound BaCo2V2O8, we observed an appearance of a novel type of incommensurate ordering in magnetic fields. This ordering is essentially different from the Neel-type ordering, which is expected for the classical system, and the peculiar spin structure is caused by quantum fluctuation inherent in the quantum spin chain. A Tomonaga-Luttinger liquid nature characteristic of the gapless quantum 1D system is responsible for the realization of the incommensurate ordering.
Title:
Charge Order in LuFe2O4: Antiferroelectric Ground State and Coupling to Magnetism
Authors:
Angst, M; Hermann, RP; Christianson, AD; Lumsden, MD; Lee, C; Whangbo, MH; Kim, JW; Ryan, PJ; Nagler, SE; Tian, W; Jin, R; Sales, BC; Mandrus, D Author Full Names: Angst, M.; Hermann, R. P.; Christianson, A. D.; Lumsden, M. D.; Lee, C.; Whangbo, M. -H.; Kim, J. -W.; Ryan, P. J.; Nagler, S. E.; Tian, W.; Jin, R.; Sales, B. C.; Mandrus, D.
Source:
PHYSICAL REVIEW LETTERS 101 (22): Art. No. 227601 NOV 28 2008
Abstract:
X- ray scattering by multiferroic LuFe2O4 is reported. Below 320 K, superstructure reflections indicate an incommensurate charge order with propagation close to (1/3 1/3 3/2). The corresponding charge configuration, also found by electronic structure calculations as most stable, contains polar Fe= O double layers with antiferroelectric stacking. Diffuse scattering at 360 K, with (1/3 1/3 0) propagation, indicates ferroelectric short- range correlations between neighboring double layers. The temperature dependence of the incommensuration indicates that charge order and magnetism are coupled.

Update: 12-Dec-2008

Title:
Influence of Rolling on the Precipitation of Icosahedral Quasicrystalline Phase in Zr-Al-Ni-Cu-Ag Amorphous Alloy
Authors:
Dang, SE; Wang, XH; Lian, PX; Hu, Y; Yan, ZJ; Liang, W; Zhang, GQ Author Full Names: Dang Shu'e; Wang Xianghui; Lian Peixia; Hu Yong; Yan Zhijie; Liang Wei; Zhang Guoqing
Source:
RARE METAL MATERIALS AND ENGINEERING 37 (10): 1800-1803 OCT 2008
Abstract:
Influence of rolling on the precipitation of icosahedral quasicrystalline phase (I-phase) in Zr65Al7.5Ni10Cu12.5Ag5 amorphous alloy is investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results show that more I-phase precipitate in the rolled alloys than that in the as-cast one, and that the amount becomes the maximum when the deformation degree epsilon reaches 70 %. Furthermore, the thermal stability of the I-phase increases with the deformation degree increasing. The thermal stability of I-phase shows the maximum at epsilon=70 %, but subsequently decreases. It is attributed to the change of atomic configuration in the alloy during plastic deformation.
Title:
Magnetic Dispersion of the Diagonal Incommensurate Phase in Lightly Doped La2-xSrxCuO4
Authors:
Matsuda, M; Fujita, M; Wakimoto, S; Fernandez-Baca, JA; Tranquada, JM; Yamada, K Author Full Names: Matsuda, M.; Fujita, M.; Wakimoto, S.; Fernandez-Baca, J. A.; Tranquada, J. M.; Yamada, K.
Source:
PHYSICAL REVIEW LETTERS 101 (19): Art. No. 197001 NOV 7 2008
Abstract:
We present inelastic neutron scattering experiments on a single-domain crystal of lightly doped La1.96Sr0.04CuO4. We find that the magnetic excitation spectrum in this insulating phase with a diagonal incommensurate spin modulation is remarkably similar to that in the superconducting regime, where the spin modulation is bond parallel. In particular, we find that the dispersion slope at low energy is essentially independent of doping and temperature over a significant range. The energy at which the excitations cross the commensurate antiferromagnetic wave vector increases roughly linearly with doping through the underdoped regime.
Title:
Effect of the electric polarization on the modulation wave vector of the antiferromagnetic structure of TbMnO3
Authors:
Chupis, IE; Ushakova, IV Author Full Names: Chupis, I. E.; Ushakova, I. V.
Source:
LOW TEMPERATURE PHYSICS 34 (11): 898-900 NOV 2008
Abstract:
The effect of electric polarization on the temperature and field dependences of the modulation vector k of the antiferromagnetic structure in terbium manganite is analyzed. It is shown that in contrast to anharmonicity the electric polarization increases k, which could be why a nonmonotonic temperature dependence of the modulation vector is observed in TbMnO3.
Title:
Nuclear Magnetism in Two-Dimensional Solid Helium Three on Graphite
Authors:
Fukuyama, H Author Full Names: Fukuyama, Hiroshi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (11): Art. No. 111013 NOV 2008
Abstract:
Recent studies of nuclear magnetism of monolayer helium three (He-3) adsorbed on graphite are reviewed. This system provides us a fascinating testing ground for physics of highly frustrated quantum spins of two dimensions (2D) such as spin liquids. Particular emphasis is devoted to the gapless spin liquid state observed in the low-density commensurate phase (4/7 phase) in the second layer. Existing experiments on heat capacity in zero magnetic field and magnetization in low fields of this phase show unambiguously the gapless excitations down to three orders of magnitude lower temperatures than the relevant exchange interactions (approximate to 1 mK). This is a new class of spin liquid, and recently electronic counterparts are found in quasi-1D and -2D conductors. On the other hand, measured magnetic properties of the incommensurate phase at much higher densities can be described as a nearly ideal 2D S = 1/2 ferromagnet on a triangular lattice. We propose the existence of a new ferromagnetic commensurate phase at a density in between the 4/7 and incommensurate phases based on new heat capacity data. None of these phases show signatures of finite temperature phase transitions being consistent with the Mermin-Wagner theorem. The exchange interactions among He-3 nuclear spins originate from atom-atom tunnel exchanges due to the large zero-point motions. Because of the steric hindrance, higher order exchanges like three-, four-, five-, and six-spin ring exchanges are expected to compete each other in similar strengths (MSE model). The applicability of the MSE model to the experimental magnetic properties of this system including its density variation is discussed. It is satisfactory except the fact that the model does not reproduce the gapless nature of the 4/7 phase, which recently Stimulates different theoretical approaches such Lis the Hubbard model.
Title:
Symmetry determination following structure solution in P1
Authors:
Palatinus, L; van der Lee, A Author Full Names: Palatinus, L.; van der Lee, A.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 41: 975-984 Part 6 DEC 2008
Abstract:
A new method for space-group determination is described. It is based on a symmetry analysis of the structure-factor phases resulting from a structure solution in space group P1. The output of the symmetry analysis is a list of all symmetry operations compatible with the lattice. Each symmetry operation is assigned a symmetry agreement factor that is used to select the symmetry operations that are the elements of the space group of the structure. On the basis of the list of the selected operations the complete space group of the structure is constructed. The method is independent of the number of dimensions, and can also be used in solution of aperiodic structures. A number of cases are described where this method is particularly advantageous compared with the traditional symmetry analysis. (C) 2008 International Union of Crystallography Printed in Singapore - all rights reserved
Title:
>From space to superspace and back: Superspace Group Finder
Authors:
Orlov, I; Palatinus, L; Chapuis, G Author Full Names: Orlov, Ivan; Palatinus, Lukas; Chapuis, Gervais
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 41: 1182-1186 Part 6 DEC 2008
Abstract:
The symmetry of a commensurately modulated crystal structure can be described in two different ways: in terms of a conventional three-dimensional space group or using the superspace concept in (3 + d) dimensions. The three-dimensional space group is obtained as a real-space section of the (3 + d) superspace group. A complete network was constructed linking (3 + 1) superspace groups and the corresponding three-dimensional space groups derived from rational sections. A database has been established and is available at http:// superspace.epfl.ch/finder/. It is particularly useful for finding common superspace groups for various series of modular ('composition-flexible') structures and phase transitions. The use of the database is illustrated with examples from various fields of crystal chemistry.
Title:
Tetrahedral Chain Order in the Sr2Fe2O5 Brownmillerite
Authors:
D'Hondt, H; Abakumov, AM; Hadermann, J; Kalyuzhnaya, AS; Rozova, MG; Antipov, EV; Van Tendeloo, G Author Full Names: D'Hondt, Hans; Abakumov, Artem M.; Hadermann, Joke; Kalyuzhnaya, Anna S.; Rozova, Marina G.; Antipov, Evgeny V.; Van Tendeloo, Gustaaf
Source:
CHEMISTRY OF MATERIALS 20 (22): 7188-7194 NOV 25 2008
Abstract:
The crystal structure of the Sr2Fe2O5 browninillerite has been investigated using electron diffraction and high resolution electron microscopy. The Sr2Fe2O5 structure demonstrates two-dimensional order: the tetrahedral chains with two mirror-related configurations (L and k) are arranged within the tetrahedral layers according to the -L-R-L-R- sequence, and the layers themselves are displaced with respect to each other over 1/2[111] or 1/2[11 (1) over bar] vectors of the brownmillerite unit cell, resulting in different ordered stacking variants. A unified superspace model is constructed for ordered stacking sequences in brownmillerites based on the averacge brownmillerite structure with a = 5.5298(4)angstrom, b = 15.5875(12)angstrom, c = 5.6687(4)angstrom, and (3 + 1)-dimensional superspace group 12/m(0 beta gamma)0s, q = beta b* + gamma c*, 0 <= beta <= 1/2, 0 <= gamma <= 1.
Title:
Crystal structure of a synthetic tin-selenium representative of the cylindrite structure type
Authors:
Makovicky, E; Petricek, V; Dusek, M; Topa, D Author Full Names: Makovicky, E.; Petricek, V.; Dusek, M.; Topa, D.
Source:
AMERICAN MINERALOGIST 93 (11-12): 1787-1798 NOV-DEC 2008
Abstract:
The synthetic tin-selenium member of the cylindrite structural family, with the empirical formula Sn31.51Sb6.23Fe3.12S59.(12) based on electron-microprobe data, has a triclinic crystal structure composed of two alternating layer types, both with a pronounced one-dimensional modulation, and with a non-commensurate layer match in two dimensions. The pseudotetragonal (Q) layer is a MeSe layer two-atomic planes thick with lattice parameters a = 5.969(2) angstrom, b = 6.004(1) angstrom, and the layer-stacking vector c = 12.238(1) angstrom, alpha = 87.98(4)degrees, beta = 83.14(3)degrees, and gamma = 90.01(4)degrees. The pseudohexagonal (H) layer is a single-octahedral MeSe2 layer with a = 3.831(1) angstrom, b = 6.580(3) angstrom, c = 12.151(5) angstrom, alpha = 87.79(4)degrees, beta = 90.59(3)degrees, and gamma = 89.99(3)degrees; the a and b vectors of the two subsystems are parallel, the c vectors diverge. The transversal wave-like modulation has the wave-normal parallel to b, so that the modulation vector q is 0.0001(3) a* + 0.1921(4) b* - 0.0119(3) c* in terms of the pseudohexagonal subsystem. Superspace structure refinement in the superspace group X (1) over bar where X stands for non-primitive centering vectors (1/2,1/2,0,0,0), (0,0,0,0,1/2), (1/2,1/2,0,0,1/2) in five-dimensional superspace, and based on 2128 observed reflections, resulted in R-1 = 0.038 for all reflections. Composition of the H layer has been modeled as Sn2404+Fe542+Se588, that of the Q layer as Sn3062+Sb1083+Se414. The cation-anion distances in Q layer vary between 2.63 and 3.30 angstrom, indicating that the cations present are primarily Sn2+ (and Sb3+), whereas distances in the H layer lie between 2.665 and 2.721 angstrom and correspond to Sn4+ with admixture of Fe2+. The shortest cation-anion distance across the interlayer space is 3.24 angstrom. Relations between layer match and the modulation vector, divergence of layer stackings of the two components, and reasons for the modulation and for the pronounced disorder of the Q component, as well as the differences and similarities with levyclaudite, franckeite, and synthetic layer-misfit compounds are discussed in detail. In its structural principles, although not in numerical values, the Sn-Se cylindrite corresponds fully to the natural Pb-Sn-S cylindrite previously described.
Title:
Original disorder-order transition related to electronic and magnetic properties in the thermoelectric misfit phase [Ca2CoO3][CoO2](1.62)
Authors:
Muguerra, H; Grebille, D Author Full Names: Muguerra, Herve; Grebille, Dominique
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 676-683 Part 6 DEC 2008
Abstract:
A structural phase transition is shown around 400 K for the thermoelectric lamellar misfit cobalt oxide [Ca2CoO3][CoO2](1.62). This transition is related to a rearrangement of the central [CoO] layer of the [Ca2CoO3] slab of this structure, characterized by a commensurate intrinsic modulation q(2) = 2/3a* -1/3c*. The partial residual disorder related to split Co and O atomic sites along the misfit b direction disappears and one can describe this layer with its triple chains as a modulated configuration with a regular and not distorted periodicity along b. This phase transition is associated with small changes observed in the transport and magnetic properties as a function of temperature.
Title:
Modular crystals as modulated structures: the case of the lillianite homologous series
Authors:
Elcoro, L; Perez-Mato, JM; Friese, K; Petricek, V; Balic-Zunic, T; Olsen, LA Author Full Names: Elcoro, Luis; Perez-Mato, J. M.; Friese, Karen; Petricek, Vaclav; Balic-Zunic, Tonci; Olsen, Lars Arnskov
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 684-701 Part 6 DEC 2008
Abstract:
The use of the superspace formalism is extended to the description and refinement of the homologous series of modular structures with two symmetry-related modules with different orientations. The lillianite homologous series has been taken as a study case. Starting from a commensurate modulated composite description with two basic subsystems corresponding to the two different modules, it is shown how a more efficient description can be achieved using so-called zigzag modulation functions. These linear zigzag modulations, newly implemented in the program JANA2006, have very large fixed amplitudes and introduce in the starting model the two orientations of the underlying module sublattices. We show that a composite approach with this type of function, which treats the cations and anions as two separate subsystems forming a misfit compound, is the most appropriate and robust method for the refinements.

Update: 5-Dec-2008

Title:
Structural State of Surface Layers of Aluminum after Laser Alloying Using a Mixture of Copper and Iron Powders
Authors:
Girzhon, VV; Smolyakov, AV; Tantsyura, IV Author Full Names: Girzhon, V. V.; Smolyakov, A. V.; Tantsyura, I. V.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 106 (4): 384-388 OCT 2008
Abstract:
X-ray diffraction, metallographic, and electron-microscopic methods were used to study the regularities of the structure formation in the surface layers of aluminum upon pulse laser alloying using copper and iron powders taken in an atomic ratio of two to one. It is shown that, in the zone of laser alloying, a quasicrystalline phase can form, which leads to a considerable increase in microhardness. The effect of the thickness of the alloying layer on the structural and phase state of the laser-affected zone is analyzed.
Title:
Phase and Structural Transformations in the Alloy on the Basis of the Orthorhombic Titanium Aluminide
Authors:
Popov, AA; Illarionov, AG; Grib, SV; Demakov, SL; Karabanalov, MS; Elkina, OA Author Full Names: Popov, A. A.; Illarionov, A. G.; Grib, S. V.; Demakov, S. L.; Karabanalov, M. S.; Elkina, O. A.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 106 (4): 399-410 OCT 2008
Abstract:
Phase and structural transformations in the Ti-24.3 Al-24.8 Nb-1.0 Zr-1.4 V-0.6 Mo-0.3 Si (at %) alloy that take place during heating in the temperature range of 700-1050 degrees C have been investigated. The temperature ranges of existence of the O + beta, O + beta + alpha(2), beta + alpha(2), and beta phase fields have been established. A scheme of the relationships between the volume fractions of the O, beta, and alpha(2) phases depending on the temperature of heating of the alloy have been investigated. The formation of an ordered incommensurate omega (V (omega)) phase has been revealed in the alloy during quenching from 900 degrees C. The existence of a correlation between the hardness properties and changes in the phase composition and morphology of particles precipitating in the alloy has been shown.
Title:
Domain fluctuations near the field-induced incommensurate-commensurate phase transition of TbMnO3
Authors:
Barath, H; Kim, M; Cooper, SL; Abbamonte, P; Fradkin, E; Mahns, I; Rubhausen, M; Aliouane, N; Argyriou, DN Author Full Names: Barath, H.; Kim, M.; Cooper, S. L.; Abbamonte, P.; Fradkin, E.; Mahns, I.; Ruebhausen, M.; Aliouane, N.; Argyriou, D. N.
Source:
PHYSICAL REVIEW B 78 (13): Art. No. 134407 OCT 2008
Abstract:
We present temperature- and field-dependent inelastic light-scattering studies of multiferroic TbMnO3. By carefully examining the evolution of magneto-elastic modes in various phases of TbMnO3, our study reveals several features of the field-induced incommensurate-commensurate (IC-C) transition in TbMnO3. We find that, for fields applied along the b axis, there is a coexistence of distinct structural phases in the intermediate field regime (H=4-7 T) around the IC-C-phase transition. We present evidence for the existence of dynamical fluctuations of the C phase for fields lower than the critical field for H along the b axis, H < H-c(b). Furthermore, we present evidence for strong spin-lattice coupling effects in TbMnO3 in the form of zone-boundary phonon modes that strongly couple to the spins by modulating the exchange interaction in this material.
Title:
Raman scattering from the spin-gap mode in the Ni-doped spin-Peierls compound CuGeO3
Authors:
Sekine, T; Kaneko, T; Kuroe, H; Masuda, T Author Full Names: Sekine, Tomoyuki; Kaneko, Tomomi; Kuroe, Haruhiko; Masuda, Takatsugu
Source:
PHYSICAL REVIEW B 78 (13): Art. No. 134409 OCT 2008
Abstract:
By means of Raman scattering we have studied the spin-Peierls (SP) transition in Ni-doped CuGeO3 crystals. The folded-phonon peak extremely broadens and the two-magnetic-excitation mode disappears when the Ni concentration is above about 2.0%, indicating that the SP phase collapses. The spin-gap mode is activated in lightly Ni-doped samples. This peak neither splits nor shifts under magnetic fields in the SP phase, but its frequency increases in the incommensurate phase. The activation of the spin-gap mode is interpreted in terms of a mixing between the spin-singlet ground state and the S-z=0 triplet excited one by staggered fields around the doped impurities. Meanwhile, the two-magnetic-excitation mode gradually diminishes in intensity with increasing magnetic field in the incommensurate phase.
Title:
Fermi-surface-induced lattice modulation and charge-density wave in optimally doped YBa2Cu3O7-x
Authors:
Liu, X; Islam, Z; Sinha, SK; Moss, SC; McQueeney, RJ; Lang, JC; Welp, U Author Full Names: Liu, X.; Islam, Z.; Sinha, S. K.; Moss, S. C.; McQueeney, R. J.; Lang, J. C.; Welp, U.
Source:
PHYSICAL REVIEW B 78 (13): Art. No. 134526 OCT 2008
Abstract:
We have observed a Fermi-surface (FS) induced lattice modulation in a YBa2Cu3O7-x superconductor with a wave vector along CuO chains; i.e., q(1)=(0,delta,0). The value of delta similar to 0.21 is twice the Fermi wave vector (2k(F)) along b(*) connecting nearly nested FS "ridges." The q(1) modulation exists only within O-vacancy-ordered islands [characterized by q(0)=(1/4,0,0)] and persists well above and below T-c. Our results are consistent with the presence of a FS-induced charge-density wave.
Title:
Competing order, Fermi surface reconstruction, and quantum oscillations in underdoped high-temperature superconductors
Authors:
Dimov, I; Goswami, P; Jia, X; Chakravarty, S Author Full Names: Dimov, Ivailo; Goswami, Pallab; Jia, Xun; Chakravarty, Sudip
Source:
PHYSICAL REVIEW B 78 (13): Art. No. 134529 OCT 2008
Abstract:
We consider incommensurate order parameters for electrons on a square lattice which reduce to d-density wave order when the ordering wave vector Q is close to Q(0)=(pi/a,pi/a), a being the lattice spacing and describe the associated charge and current distributions within a single-harmonic approximation that conserves current to lowest order. Such incommensurate orders can arise at the mean-field level in extended Hubbard models, but the main goal here is to explore thoroughly the consequences within a Hartree-Fock approximation. We find that Fermi surface reconstruction in the underdoped regime can correctly capture the phenomenology of the recent quantum oscillation experiments that suggest incommensurate order, in particular the de Haas-van Alphen oscillations of the magnetization in high fields and very low temperatures in presumably the mixed state of these superconductors. For 10% hole doping in YBa2Cu3O6+delta, we find in addition to the main frequency around 530 T arising from the electron pocket and a hole frequency at around 1650 T, a new low frequency from a smaller hole pocket at 250 T for which there are some indications that require further investigations. The oscillation corresponding to the electron pocket will be further split due to bilayer coupling, but the splitting is sufficiently small to require more refined measurements. The truly incommensurate d-density wave breaks both time reversal and inversion, but the product of these two symmetry operations is preserved. The resulting Fermi surface splits into spin-up and spin-down sectors that are inversion conjugates. Each of the spin sectors results in a band structure that violates reflection symmetry, which can be determined in spin and angle-resolved photoemission spectroscopies. For those experiments such as the current photoemission experiments or the quantum oscillation measurements that cannot resolve the spin components, the bands will appear to be symmetric because of the equal mixture of the two spin sectors. There is some similarity of our results with the spiral spin-density wave order which, as pointed out by Overhauser, also breaks time reversal and inversion. Calculations corresponding to higher order commensuration produce results similar to antiphase spin stripes but appear to us to be an unlikely explanation of the experiments. The analysis of the Gorkov equation in the mixed state shows that the oscillation frequencies are unshifted from the putative normal state and the additional Dingle factor arising from the presence of the mixed state can provide a subtle distinction between the spiral spin-density wave and the d-density wave, although this is very difficult to establish precisely.
Title:
Static magnetic order in the triangular lattice of LixNiO2 (x <= 1): Muon-spin spectroscopy measurements
Authors:
Sugiyama, J; Mukai, K; Ikedo, Y; Russo, PL; Nozaki, H; Andreica, D; Amato, A; Ariyoshi, K; Ohzuku, T Author Full Names: Sugiyama, Jun; Mukai, Kazuhiko; Ikedo, Yutaka; Russo, Peter L.; Nozaki, Hiroshi; Andreica, Daniel; Amato, Alex; Ariyoshi, Kingo; Ohzuku, Tsutomu
Source:
PHYSICAL REVIEW B 78 (14): Art. No. 144412 OCT 2008
Abstract:
In spite of numerous experimental and theoretical reports on LiNiO2, no consistent picture has emerged of the nature of its ground state. We have investigated the LixNiO2 system (0.1 <= x <= 1) by means of muon-spin spectroscopy and susceptibility to gain further insight from the effects of varying the magnetic ion concentration. Static magnetic order, most likely to be incommensurate to the spatial lattice period, was found for x >= 0.6 at low temperatures (T), while disordered magnetism due to localized Ni moments appears for x=1/2-1/4 and, finally, Li0.1NiO2 exhibits almost fully nonmagnetic behavior down to the lowest T measured. The ground state of LiNiO2 is inferred to be a "static but short-range" A-type antiferromagnetic ordered system, in which the Ni3+ moments align ferromagnetically along the c axis in the NiO2 plane with an incommensurate modulation probably due to canting of the Ni3+ moments, but align antiferromagnetically between adjacent NiO2 planes.
Title:
Theory of the ordered phase in A-site antiferromagnetic spinels
Authors:
Lee, SB; Balents, L Author Full Names: Lee, SungBin; Balents, Leon
Source:
PHYSICAL REVIEW B 78 (14): Art. No. 144417 OCT 2008
Abstract:
Insulating spinel materials, with the chemical formula AB(2)X(4), behave as diamond lattice antiferromagnets when only the A-site atom is magnetic. Many exhibit classic signatures of frustration, induced not geometrically but by competing first- and second-neighbor exchange interactions. In this paper, we further develop a theory [D. Bergman , Nat. Phys. 3, 487 (2007)] of the magnetism of these materials, focusing on the physics observable within the ordered state. We derive a phenomenological Landau theory that predicts the orientation of the spins within incommensurate spiral ordered states. It also describes how the spins reorient in a magnetic field and how they may undergo a low-temperature "lock-in" transition to a commensurate state. We discuss microscopic mechanisms for these magnetic-anisotropy effects. The reduction in the ordered moment by quantum fluctuations is shown to be enhanced due to frustration. Our results are compared to experiments on MnSc2S4, the best characterized of such A-site spinels, and more general implications are discussed. One prediction is that magnetically induced ferroelectricity is generic in these materials, and a detailed description of the relation of the electric polarization to the magnetism is given.
Title:
Direct measurement of charge transfer in thermoelectric Ca3Co4O9
Authors:
Yang, G; Ramasse, Q; Klie, RF Author Full Names: Yang, G.; Ramasse, Q.; Klie, R. F.
Source:
PHYSICAL REVIEW B 78 (15): Art. No. 153109 OCT 2008
Abstract:
The misfit-layered cobalt oxide Ca3Co4O9 exhibits outstanding physical properties including high thermoelectric power, low thermal conductivity, low resistivity, and high thermal stability. We utilize atomic-resolution Z-contrast imaging in conjunction with electron energy-loss spectroscopy (EELS) in an aberration-corrected scanning transmission electron microscope (STEM) to characterize the local atomic and electronic structure of Ca3Co4O9. We will show that the position of the O atoms in the CoO2 layers can be directly imaged, and that the CoO columns in the rocksalt layer exhibit a strong modulation in the (010) direction. Further, we measure the local Co valence and find significant hole transfer from the rocksalt CoO to the hexagonal CoO2 layers. Our results are confirmed by self-consistent multiple-scattering calculations and we conclude that this hole transfer increases the mobile hole concentration and breaks the electron-hole symmetry in the CoO2 layers, thereby enabling the high thermoelectric power in the strongly correlated CoO2 subsystem.
Title:
Growth of Bi thin films on quasicrystal surfaces
Authors:
Sharma, HR; Fournee, V; Shimoda, M; Ross, AR; Lograsso, TA; Gille, P; Tsai, AP Author Full Names: Sharma, H. R.; Fournee, V.; Shimoda, M.; Ross, A. R.; Lograsso, T. A.; Gille, P.; Tsai, A. P.
Source:
PHYSICAL REVIEW B 78 (15): Art. No. 155416 OCT 2008
Abstract:
We present a comprehensive study of Bi thin-film growth on quasicrystal surfaces. The substrates used for the growth are the fivefold surface of icosahedral (i)-Al-Cu-Fe and i-Al-Pd-Mn and the tenfold surface of decagonal (d)-Al-Ni-Co quasicrystals. The growth is investigated at 300 and 525 K substrate temperatures and at different coverage (theta) ranging from submonolayer to ten monolayers. The film is characterized by scanning tunneling microscopy, reflection high-energy electron diffraction, and x-ray photoelectron spectroscopy. At 300 K, the deposited Bi yields a quasicrystalline film for theta <= 1. For 1
Title:
Effect of composition on the formability of quasicrystalline phase in mechanically alloyed Al-Cu-Fe powders
Authors:
Yin, SL; Li, CX; Blan, Q; Lu, M Author Full Names: Yin, Shilong; Li, Caixia; Blan, Qing; Lu, Min
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 496 (1-2): 362-365 NOV 25 2008
Abstract:
A systematic study has been carried out to investigate the effect of composition on the ability of mechanically alloyed Al-Cu-Fe powders to form quasicrystalline (QC)-phases. Their microstructures were measured by means of X-ray diffraction and transmission electron microscopy (TEM). The results show that the formation of Al-Cu-Fe QC-phases is sensitive to the starting ratio of the elements Al, Cu and Fe and that Al70Cu20Fe10 is the optimum composition among those studied. No single QC-phase was obtained, but a high volume fraction of the QC-phase can be obtained by a suitable choice of the milling time, annealing temperature and annealing time. The volume fraction of the QC-phase in Al70Cu20Fe10 powders milled for 2 h and annealed for 5 h at 750 degrees C is greater than 90%. (C) 2008 Elsevier B.V. All rights reserved.
Title:
Icosahedral quasicrystal phase in Mg-Zn-Nd ternary system
Authors:
Zhang, JS; Yan, J; Liang, W; Xu, CX; Zhou, CL Author Full Names: Zhang, J. S.; Yan, J.; Liang, W.; Xu, C. X.; Zhou, C. L.
Source:
MATERIALS LETTERS 62 (30): 4489-4491 DEC 15 2008
Abstract:
Mg-Zn-Nd master alloy containing icosahedral quasicrystal phase with an interesting macro-shape has been prepared under conventional casting conditions. The microstructures and phases of Mg-Zn-Nd ternary alloy have been investigated by using SEM, EDS and TEM. The results show that the spherical phase in Mg-Zn-Nd master alloy is a simple icosahedral quasicrystal with stoichiometric composition of Mg40Zn55Nd5 and quasilattice a(R) = 0.525 nm. In this research, when the content of Nd is 1.20 at.% and atom ratio value of Mg/Zn at the range of 2.4-2.7, the as-cast solidification microstructure mainly consists of primary I-phase and Mg7Zn3 single-phase matrix. (C) 2008 Elsevier B.V. All rights reserved.
Title:
Deuterium dynamics in the icosahedral and amorphous phases of the Ti40Zr40Ni20 hydrogen-absorbing alloy studied by H-2 NMR
Authors:
Gradisek, A; Kocjan, A; McGuiness, PJ; Apih, T; Kim, HJ; Dolinsek, J Author Full Names: Gradisek, A.; Kocjan, A.; McGuiness, P. J.; Apih, T.; Kim, Hae Jin; Dolinsek, J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (47): Art. No. 475209 NOV 26 2008
Abstract:
The Ti40Zr40Ni20 hydrogen-absorbing alloy was prepared in the icosahedral and amorphous phases by controlling the rotation speed of the melt-spinning method of sample preparation, and the deuterium dynamics was investigated by H-2 NMR dynamic lineshape and spin-lattice relaxation. The results were analysed by the lineshape and relaxation models that assume deuterium thermally activated hopping within a manifold of different chemical environments. The observed 8% larger activation energy for the deuterium hopping over the interstitial sites and the 10% larger static spectrum width of the amorphous phase, as compared to the icosahedral phase, can be accounted for by the larger deuterium content of the investigated amorphous sample. From the deuterium dynamics point of view, the icosahedral phase is not special with respect to the amorphous modification of the same material.
Title:
Noncentrosymmetric commensurate magnetic ordering of multiferroic ErMn2O5
Authors:
Roessli, B; Fischer, P; Brown, PJ; Janoschek, M; Sheptyakov, D; Gvasaliya, SN; Ouladdiaf, B; Zaharko, O; Golovenchits, E; Sanina, V Author Full Names: Roessli, B.; Fischer, P.; Brown, P. J.; Janoschek, M.; Sheptyakov, D.; Gvasaliya, S. N.; Ouladdiaf, B.; Zaharko, O.; Golovenchits, Eu; Sanina, V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (48): Art. No. 485216 DEC 3 2008
Abstract:
The noncentrosymmetric magnetic structure of ErMn2O5 has been shown to be very similar to that of HoMn2O5 (Vecchini et al 2008 Phys. Rev. B 77 134434). The magnetic modulation at 25 K has propagation vector (k) over right arrow = (1/2, 0, 1/4) and the symmetry imposes very few constraints on the magnetic configurations allowed. Only by combining the results of bulk magnetization measurements, powder and single crystal neutron diffraction and spherical neutron polarization analysis was it possible to distinguish clearly between different models. The susceptibility measurements show that the erbium magnetic moments are aligned parallel to the c-axis indicating strong single ion anisotropy. Spherical neutron polarimetry demonstrates the presence of two unequally populated chirality domains in ErMn2O5 single crystals. X-ray diffraction measurements on an ErMn2O5 powder using synchrotron radiation show that the buckling angles of the Mn-O-Mn bond change below the transition to the ferroelectric phase.
Title:
Possible mechanisms of formation of long-periodic magnetic structure in high-symmetry crystals
Authors:
Zavorotnev, YD; Medvedyeva, LI Author Full Names: Zavorotnev, Yu. D.; Medvedyeva, L. I.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 321 (3): 231-233 FEB 2009
Abstract:
On the example of a crystal with point symmetry group and based on the method of integral rational basis of invariants, linear and nonlinear invariants of first spatial derivatives with respect to the order parameters of the exchange origin have been calculated. It is shown the competition of what kind of parameters can initiate modulated magnetic structures in crystals of this symmetry. (C) 2008 Elsevier B.V. All rights reserved.
Title:
Nanoindentation studies on single crystals of Zn-Mg-Er and Zn-Mg-Ho icosahedral phases
Authors:
Mukhopadhyay, NK; Belger, A; Paufler, P; Uhrig, E; Bruhne, S; Assmus, W Author Full Names: Mukhopadhyay, N. K.; Belger, A.; Paufler, P.; Uhrig, E.; Bruehne, S.; Assmus, W.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 466 (1-2): 160-164 OCT 20 2008
Abstract:
Single crystals of Zn-Mg-Er and Zn-Mg-Ho icosahedral phases were grown from the melt using the liquid encapsulated top seeded solution growth technique. The fivefold planes of these as-grown single crystals were polished and used for the present nanoindentation studies using Hysitron triboscope attached to an atomic force microscope with a maximum load up to 16 mN. The reduced Young's modulus (E-r) and nanohardness (H) were found to be 135 +/- 10 GPa and 8.5 +/- 0.2 GPa for the F-type Zn65Mg25Er10 quasicrystal whereas for the P-type Zn74Mg15Ho11 quasicrystal (QC) these were 135 +/- 10 GPa and 7.8 +/- 0.2 GPa, respectively. Using the appropriate constants, the average E in both the quasicrystalline alloys was estimated as 140 10 GPa. The elastic and plastic deformation characteristics in load-displacement, F-h, curve appears to be identical in both the QC phases. The peculiarity in the load-displacement curves, in terms of pop-ins were observed frequently. AFM images showed the steps in the pile-up material which can be identified as shear bands and correlated with the pop-ins. The first pop-in was observed in the load range of 70 mu N in case Zn-Mg-Ho and 84 mu N in case of Zn-Mg-Er QC. The contact pressure, p, turns out to be 13 GPa for Zn-Mg-Ho and 18 GPa for Zn-Mg-Er QC. The maximum shear stress under the indent, TT,,c, is found to vary from 6 to 8 GPa, which is close to the theoretical shear strength of this material (similar to E/20). The energy required for the indentation was determined from the first pop-ins and it turned out to be 0.88 eV/atom, close to the thermal energy required for deformation of quasicrystals. Thus the 'pop-ins' are attributed to the elastic-plastic transition during indentation. (c) 2007 Elsevier B. V. All rights reserved.
Title:
On the Magnetically Driven Ferroelectric Phase in GdMnO3
Authors:
Ribeiro, JL Author Full Names: Ribeiro, J. L.
Source:
FERROELECTRICS 368: 352-357 2008
Abstract:
At room temperature, GdMnO3 is a paraelectric and paramagnetic with a distorted perovskite structure of orthorhombic symmetry (space group Pnma). On cooling, it undergoes a phase transition sequence to a magnetic incommensurate phase ([image omitted] = (T)[image omitted]*; Tc1 = 42 K) and a A-type antiferromagnetic phase (Tc2 = 27 K). At low temperatures (T 12 K), a magnetic field applied along the a-axis destabilizes the antiferromagnetic phase and induces a first order transition to a magnetic commensurate modulated phase ([image omitted] = 1/4[image omitted]*) that is also ferroelectric ([image omitted]//[image omitted]). This work analyses this field induced phase transition from the point of view of the symmetry and Landau theory.
Title:
Crystal Structures and Phase Transitions in A-Site Deficient Perovskites Ln(1/3)TaO(3)
Authors:
Zhou, QD; Saines, PJ; Sharma, N; Ting, J; Kennedy, BJ; Zhang, ZM; Withers, RL; Wallwork, KS Author Full Names: Zhou, Qingdi; Saines, Paul J.; Sharma, Neeraj; Ting, Jimmy; Kennedy, Brendan J.; Zhang, Zhaoming; Withers, Ray L.; Wallwork, Kia S.
Source:
CHEMISTRY OF MATERIALS 20 (21): 6666-6676 NOV 11 2008
Abstract:
The synthesis and structures of the perovskites Ln(1/3)TaO(3) are described. As the size of the Ln cation is reduced, the compounds display a sequence of structure: P4/mmm/La -> Cmmm/Ce-Gd -> Pmma/Tb, Dy -> Pmc2(1)/Ho. Er. Although apparently tetragonal in P4/mmm, electron diffraction patterns of Tm1/3TaO3 reveal this has a complex incommensurate structure. Likewise Gd1/3TaO3 appears metrically tetragonal. but electron diffraction and synchrotron X-ray powder diffraction demonstrate this is actually orthorhombic. The suppression of the spontaneous orthorhombic strain in Gd1/3TaO3 is thought to be due to the proximity to the first-order Cmmm-Pmma transition. Variable temperature studies show both Tb1/3TaO3 and Dy1/3TaO3 undergo a first-order Cmmm-Pmma transition upon heating.
Title:
Applications of Mossbauer Spectroscopy to Studies of Quasicrystals
Authors:
Stadnik, ZM Author Full Names: Stadnik, Z. M.
Source:
ACTA PHYSICA POLONICA A 114 (6): 1475-1482 DEC 2008
Abstract:
A review is presented of the application of the Mossbauer spectroscopy to the study of quasicrystals. The usefulness of the Mossbauer spectroscopy to solving the atomic structure of a complex icosahedral system is illustrated. The role of the Mossbauer spectroscopy in studies of magnetism of quasicrystals is discussed. The Mossbauer spectroscopy results on phason dynamics in quasicrystals are reviewed.

Update: 27-Nov-2008

Title:
Magnetization of Polycrystalline BiFeO3 in High Magnetic Fields
Authors:
Wardecki, D; Przenioslo, R; Sosnowska, I; Skourski, Y; Loewenhaupt, M Author Full Names: Wardecki, Dariusz; Przenioslo, Radoslaw
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (10): Art. No. 103709 OCT 2008
Abstract:
The magnetization of polycrystalline ceramic BiFeO3 has been studied with pulsed magnetic fields up to 58T. We observe a magnetic transition in both, increasing and decreasing magnetic fields. The critical field of the transition decreases with temperature. It is observed at 18.1 T at 80 K and 16.1 T at 235 K for increasing fields, whereas with decreasing fields the transition is observed at about 1.5 T below these values. The observed transition is the same as that reported in BiFeO3 single crystals at 10K [Kadomtseva et al.: JETP Lett. 79 (2004) 571]. It was attributed to the destruction of the modulated magnetic ordering in BiFeO3.
Title:
Evolution of an Unconventional Superconducting State inside the Antiferromagnetic Phase of CeNiGe3 under Pressure: A Ge-73-Nuclear-Quadrupole-Resonance Study
Authors:
Harada, A; Mukuda, H; Kitaoka, Y; Thamizhavel, A; Okuda, Y; Settai, R; Onuki, Y; Itoh, KM; Haller, EE; Harima, H Author Full Names: Harada, Atsushi; Mukuda, Hidekazu
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (10): Art. No. 103710 OCT 2008
Abstract:
We report a Ge-73 nuclear-quadrupole-resonance (NQR) Study on novel evolution of unconventional superconductivity in antiferromagnetic (AFM) CeNiGe3. The measurements of the Ge-73-NQR spectrum and the nuclear spin-lattice relaxation rate (1/T-1) have revealed that the unconventional superconductivity evolves inside a commensurate AFM phase around the pressure (P) where Neel temperature T-N exhibits its maximum at 8.5 K. The superconducting transition temperature T-SC has been found to be enhanced with increasing T-N, before reaching the quantum critical point at which the AFM order collapses. Above T-SC, the AFM structure transits from an incommensurate spin-density-wave order to a commensurate AFM order at T similar to 2 K. accompanied by a longitudinal spin-density fluctuation. With regard to heavy-fermion compounds, these novel phenomena have hitherto never been reported in the P-T phase diagram.
Title:
The roles of "ammonium" and "hydrogen-bond" protons in single crystals of the superionic conductor NH4HSeO4 by H-1 NMR relaxation
Authors:
Lim, AR; Jang, SW; Chang, JH Author Full Names: Lim, Ae Ran; Jang, Seo Won
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 69 (10): 2360-2365 OCT 2008
Abstract:
The variations with temperature of the line-shape, spin-lattice relaxation time, T-1, and spin-spin relaxation time, T-2, of the H-1 nuclei in NH4HSeO4 single crystals were investigated, and with these H-1 NMR results we were able to distinguish the crystals' "ammonium" and "hydrogen-bond" protons. The line width of the signal due to the ammonium protons abruptly narrows near the temperature of the superionic phase transition, T-si, which indicates that they play an important role in this phase transition. The H-1 T-1 for NH4+ and HSeO4- in NH4HSeO4 do not change significantly near the ferroelectric phase transition of T-c1 (= 250 K) and the incommensurate phase transition of T-i (= 261 K), whereas they change near the temperature of the superionic phase transition T-s1 (= 400 K). Our results indicate that the main contribution to the low-temperature phase transition below T-s1 is that of the molecular motion of ammonium and hydrogen-bond protons, and the main contribution to the conductivity at high temperatures above T-s1 is the breaking of the O-H...O bonds and the formation of new H- bonds in HSeO4-. In addition, we compare these results with those for the NH4HSO4 and (NH4)(3)H(SO4)(2) single crystals, which have similar hydrogen-bonded structure. (C) 2008 Elsevier Ltd. All rights reserved.
Title:
A Theory of General Solutions of Plane Problems in Two-Dimensional Octagonal Quasicrystals
Authors:
Gao, Y; Zhao, BS; Xu, SP Author Full Names: Gao, Yang; Zhao, Bao-Sheng
Source:
JOURNAL OF ELASTICITY 93 (3): 263-277 DEC 2008
Abstract:
A theory of general solutions of plane problems is developed for the coupled equations in plane elasticity of two-dimensional octagonal quasicrystals. In virtue of the operator method, the general solutions of the antiplane and inplane problems are given constructively with two displacement functions. The introduced displacement functions have to satisfy higher order partial differential equations, and therefore it is difficult to obtain rigorous analytic solutions directly and is not applicable in most cases. In this case, a decomposition and superposition procedure is employed to replace the higher order displacement functions with some lower order displacement functions, and accordingly the general solutions are further simplified in terms of these functions. In consideration of different cases of characteristic roots, the general solution of the antiplane problem involves two cases, and the general solution of the inplane problem takes three cases, but all are in simple forms that are convenient to be applied. Furthermore, it is noted that the general solutions obtained here are complete in x(3)-convex domains.
Title:
Thermoelectric properties of polygrained icosahedral Al71-xGaxPd20Mn9 (x=0,2,3,4) quasicrystals
Authors:
Takagiwa, Y; Kamimura, T; Hosoi, S; Okada, JT; Kimura, K Author Full Names: Takagiwa, Y.; Kamimura, T.
Source:
JOURNAL OF APPLIED PHYSICS 104 (7): Art. No. 073721 OCT 1 2008
Abstract:
The electrical and thermal transport properties of quaternary icosahedral Al71-xGaxPd20Mn9 (x=0,2,3,4) quasicrystals, obtained by replacing Al in icosahedral Al-Pd-Mn quasicrystal with Ga, have been measured in accordance with the guiding principle of "weakly bonded rigid heavy clusters" (WBRHCs). While the electrical conductivity and Seebeck coefficient were not dramatically changed, the thermal conductivity effectively decreased with increasing Ga concentration except for the sample with x=4. Although the thermoelectric properties do not obey the WBRHCs, the dimensionless figure of merit increased by a factor of 1.4 from 0.18 for Al71Pd20Mn9 to 0.26 for Al68Ga3Pd20Mn9 quasicrystal. (c) 2008 American Institute of Physics.
Title:
Fe-57 Mossbauer Effect Study of Zn-Sc-Fe Icosahedral Quasicrystal and Its 1/1 Crystal Approximant
Authors:
Edagawa, K; Tamura, R; Yamada, T; Oda, K Author Full Names: Edagawa, Keiichi; Tamura, Ryuji
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS 47 (5): 3581-3583 Part 1 MAY 2008
Abstract:
The Zn-Sc-Fe icosahedral quasicrystal and its 1/1 crystal approximant have been studied with Fe-57 Mossbauer spectroscopy at room temperature. The spectra for the two phases exhibit substantially different features, indicating largely different local atomic environments in the two phases. This is in contrast to the results previously reported for the Al-Cu-Fe(-Si) system, in which the icosahedral phase and its crystal approximants show similar features in Mossbauer spectra, indicating similar local atomic environments. Possible Fe sites in the Zn-Sc-Fe approximant phase are discussed on the basis of the crystal structure determined previously. [DOI: 10.1143/JJAP.47.3581]
Title:
A Layered Iron-Rich 2234-Type with a Mixed Valence of Iron: The Ferrimagnetic Tl-Doped Fe-2(Sr2-epsilon Tl epsilon)Sr(3)Fe(4)O14.65
Authors:
Lepoittevin, C; Malo, S; Nguyen, N; Hebert, S; Van Tendeloo, G; Hervieu, M Author Full Names: Lepoittevin, Christophe; Malo, Sylvie
Source:
CHEMISTRY OF MATERIALS 20 (20): 6468-6476 OCT 28 2008
Abstract:
A new Tl-doped strontium ferrite Fe-2(Sr2-epsilon Tl epsilon)Sr3Fe4O14.65, with an original structure, has been synthesized and structurally characterized by powder X-ray diffraction and transmission electron microscopy. The TGA and Mossbauer studies evidence a mixed valence of iron. The structure exhibits a commensurate modulation, with a F-type subcell a approximate to b approximate to 5.4 angstrom ( approximate to a(p)root/2), c approximate to 42 angstrom with a modulation vector (q) over right arrow = alpha(a) over right arrow* with alpha = 0.4. The supercell parameters have been refined as a= 27.1101(8) angstrom, b= 5.5187(2) angstrom and c= 42.0513(9) angstrom, in the space group Fmmm. The electron diffraction and electron microscopy data of this novel ferrite show that it can be described as a Fe-Tl-2234-type structure corresponding to the intergrowth of a quadruple perovskite slice [(SrFeO2.8)(4)] with a complex rock salt related slice Fe-2(Sr2-epsilon Tl epsilon)O-3.4](infinity), built up of one double iron layer [Fe2O2.4] sandwiched between two [SrO] layers. The HRTEM images show that the oxygen atoms and vacancies are randomly distributed in the perovskite layers while the HAADF STEM images evidence the absence of Tl segregation in the matrix. Fe-2(Sr2-epsilon Tl epsilon)Sr3Fe4O14.65 exhibits a very large value of chi (1 lemu/mol) at 5 K, which remains large at 400 K; the M(H) loop presents a shape characteristic of ferrimagnetism, with a large coercive field of 0.3 T. The value of magnetization saturates at 400 K at 0.68 mu(B)/17e. At 10 K. the value of magnetization reaches a maximum of 2 mu(B)/Fe. The resistivity presents a semiconducting-like behavior, with rho similar to 800 Omega.cm at 300 K.

Update: 14-Nov-2008

Title:
On the Ferroelectric Phase Transition in Polytypes of beta-TlInS2 Crystals
Authors:
Borovoi, NA; Gololobov, YP; Gorb, AN; Isaenko, GL Author Full Names: Borovoi, N. A.; Gololobov, Yu. P.
Source:
PHYSICS OF THE SOLID STATE 50 (10): 1946-1950 OCT 2008
Abstract:
Permittivity measurements and x-ray diffraction study were performed for polytypes c and 2c of beta-TlInS2 crystals in the temperature range T = 160-250 K. Substantial differences are revealed in the temperature, sequence, and character of the structural phase transitions associated with the formation of incommensurate modulated structures and the occurrence of a ferroelectric state in these polytypes.
Title:
Quasicrystals - The Silver Jubilee PREFACE
Authors:
Lifshitz, R Author Full Names: Lifshitz, Ron
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1879-1882 2008
Title:
Structures of quasicrystals: Where are the atoms?
Authors:
Gratias, D; Quiquandon, M Author Full Names: Gratias, D.; Quiquandon, M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1887-1903 2008
Abstract:
This paper is an attempt to present a chronological review of the structural concepts that have been developed to characterize quasicrystals, starting from the experimental discovery of D. Shechtman and the concomitant theoretical definition of quasicrystal as proposed by D. Levine and P. Steinhardt, up to the present research in the field. The largest part of the paper is a discussion of the specific points that make the atomic structure determination of quasicrystals an original and difficult scientific challenge. We finally discuss the soundness of our knowledge of the actual atomic structure in quasicrystals: we do have quite a solid idea of where the atoms are but we are not sure about the distribution of the chemical species.
Title:
Geometrical property of the cluster model of the Yb-Cd icosahedral quasicrystal
Authors:
Takakura, H Author Full Names: Takakura, H.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1905-1912 2008
Abstract:
The geometrical property of an atomic structure model of the Yb-Cd icosahedral quasicrystal is discussed from the higher-dimensional viewpoint. An occupation domain for the framework that specifies the arrangement of the three building units of the structure is presented based on a specific archetype occupation domain for the cluster centres. Different cluster configurations are enumerated and the numerical values of their frequencies are given.
Title:
Coordination and cluster packing in quasicrystals
Authors:
Fujita, N; Niizeki, K Author Full Names: Fujita, N.; Niizeki, K.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1913-1919 2008
Abstract:
We discuss some local and global characteristics of quasicrystalline structures. Firstly, we present an analysis of the coordination numbers in the Cd5.7Yb binary quasicrystal. A majority of the Cd and Yb atoms occupy 12- and 16-fold coordinated sites, respectively. It is argued that the coordination properties are closely related to the local stability of the quasicrystals. Secondly, a simple inflation algorithm is presented for generating an icosahedral quasilattice which has a dense packing of a given structural motif or cluster. The atomic surface of a P-type icosahedral quasilattice generated in this way has a fractal boundary.
Title:
Structure of quasicrystals described by statistical methods
Authors:
Kozakowski, B; Wolny, J; Kuczera, P Author Full Names: Kozakowski, B.; Wolny, J.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1921-1927 2008
Abstract:
The structure of quasicrystals can be described by using a statistical approach, which can be either in higher dimensions or in three-dimensional physical space only. In the multidimensional approach, complete statistical information is gathered in a so-called atomic surface. In the case of the physical approach, we use the idea of an average unit cell. These two approaches are linked by an oblique projection. For a full description of a diffraction pattern, two projections are required. Statistical methods have been used for the diffraction analysis of the model structures and the structure of real decagonal quasicrystals.
Title:
Structural vacancies in Al-Pd-Mn quasicrystal and its (1/1,2/1)-AlPdMnSi approximant crystals: Positron lifetime studies
Authors:
Takagiwa, Y; Okada, JT; Kimura, K; Kitahata, H; Matsushita, Y; Kanazawa, I Author Full Names: Takagiwa, Y.; Okada, J. T.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1929-1934 2008
Abstract:
Positron annihilation lifetimes of the stable icosahedral (i) Al-Pd-Mn quasicrystal and its (1/1, 2/1)-AlPdMnSi and 1/0-Al12Re approximant crystals were measured at ambient temperature. The observed single-lifetime of the i-Al-Pd-Mn quasicrystal is very close to that of the (1/1, 2/1)-AlPdMnSi approximant crystals, indicating that the same type of structural vacancies exists in all these specimens. On the other hand, the lifetime of 1/0-Al12Re approximant crystal, which has no structural vacancies, is significantly shorter than the above results. We discuss the relationship between the positron lifetimes and mean valence-electron density.
Title:
HAADF-STEM study of B-Mg-Ru approximant crystals
Authors:
Miyazaki, Y; Okada, JT; Abe, E; Kimura, K Author Full Names: Miyazaki, Y.; Okada, J. T.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1935-1940 2008
Abstract:
Two-dimensional structures of decagonal approximant crystals have been studied in a B-Mg-Ru system where decagonal quasicrystals have been predicted. High-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM) imaging confirms that four approximant phases, which form at high temperatures, can be described as tessellations of hexagon and boat subunits with the same atomic decorations as B11Mg5Ru13. The images also support the existence of bow-tie flip structures in the all four approximant crystals. Long periodicities in one direction up to 8.5 nm are interpreted to be caused by modulation of rows of boat tiles.
Title:
Simulations of high-resolution electron microscopy images of icosahedral quasicrystals
Authors:
Quiquandon, M; Beauchesne, JT; Gratias, D Author Full Names: Quiquandon, M.; Beauchesne, J. -T.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1941-1948 2008
Abstract:
We apply the scattering matrix formulation for calculating the images of high-resolution electron microscopy (HREM) images of quasiperiodic crystals and discuss their basic properties. The main feature in the image formation comes from the truncation effects of the q-basis, especially the perpendicular components which must be numerous enough for properly reproducing quasiperiodicity. A comparison between two types of atomic structural model is presented that illustrates the difficulties of differentiating the models from the HREM observations.
Title:
Highly-perfect decagonal quasicrystalline Al64Cu22Co14 with non-centrosymmetry
Authors:
Taniguchi, S; Abe, E Author Full Names: Taniguchi, S.; Abe, E.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1949-1958 2008
Abstract:
The structure of a decagonal quasicrystal of Al64Cu22Co14, which was a single-grain specimen (a few mm in size) grown by slow-cooling from a melt and subsequently annealed at 1073 K, was investigated using electron diffraction and scanning transmission electron microscopy (STEM). Electron diffraction patterns of the Al64Cu22Co14 revealed a large number of sharp reflections that indicate a good long-range quasiperiodic order, and convergent-beam electron diffraction (CBED) analysis identified the space group of the decagonal Al64Cu22Co14 as being non-centrosymmetric P (10) over bar m2. Atomic-resolution Z-contrast STEM imaging showed that the structure can be described based on a fivefold-symmetric decagonal cluster 2 nm across, most of which is found to be located at ideal positions in the pentagonal Penrose tiling with significantly less phason disorders. Therefore, to our knowledge, the present decagonal Al64Cu22Co14 provides one of the best quasiperiodic ordered structures among those belonging to non-centrosymmetric P (10) over bar m2. Further details of atomic configurations within the fivefold-symmetric cluster were also examined using ultrahigh-resolution Z-contrast STEM with an aberration-corrector for the objective lens. This clearly revealed both the Al and Cu/Co sites at resolution close to 1 . Atomic arrangements within the cluster are found to be fairly well described based on the fivefold-symmetry cluster that exists in the W-(AlCoNi) approximant crystal, except for the atomistic disorders localized around the cluster centres.
Title:
Stability of the decagonal quasicrystal in the Lennard-Jones-Gauss system
Authors:
Engel, M; Trebin, HR Author Full Names: Engel, M.; Trebin, H. -R.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1959-1965 2008
Abstract:
Although quasicrystals have been studied for 25 years, there are many open questions concerning their stability: What is the role of phason fluctuations? Do quasicrystals transform into periodic crystals at low temperature? If yes, by what mechanisms? We address these questions here for a simple two-dimensional model system, a monatomic decagonal quasicrystal, which is stabilized by the Lennard-Jones-Gauss potential in thermodynamic equilibrium. It is known to transform to the approximant Xi, when cooled below a critical temperature. We show that the decagonal phase is an entropically stabilized random tiling. By determining the average particle energy for a series of approximants, it is found that the approximant Xi is the one with lowest potential energy.
Title:
Ground-state configurations of decagonal and dodecagonal binary dipolar quasicrystals
Authors:
Roth, J Author Full Names: Roth, J.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1967-1976 2008
Abstract:
We search for ground states of binary decagonal dipolar quasicrystals increasing the parameter space step by step: first testing tiling types and small-scale approximants, then allowing continuous deformation of the tiles, and finally by simulated annealing through tile flips followed by local optimization. It turns out that the quasicrystals are not a true ground state but can be favoured in finite systems by the lack of costly defects. Similar studies for square-triangle binary dipolar quasicrystals show that there the energy reduces with the number of square pairs. Phase-separated crystals turn out to be more stable then quasicrystals.
Title:
Penrose matching rules from realistic potentials in a model system
Authors:
Lim, S; Mihalkovic, M; Henley, CL Author Full Names: Lim, S.; Mihalkovic, M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1977-1984 2008
Abstract:
We exhibit a toy model of a binary decagonal quasicrystal of composition Al80.1Co19.9 - closely related to actual structures - in which realistic pair potentials yield a ground state which appears to perfectly implement Penrose's matching rules, for Hexagon-Boat-Star (HBS) tiles of edge 2.45 angstrom. The second minimum of the potentials is crucial for this result.
Title:
Growth of facetted microvoids in Zn-Fe-Sc quasicrystal
Authors:
Ishimasa, T; Matsunagi, J Author Full Names: Ishimasa, T.; Matsunagi, J.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1985-1993 2008
Abstract:
Microvoids, the size of which ranges from 1 to 50 mu m in diameter, have been observed on the fracture surface of a millimeter-sized single icosahedral quasicrystal of stable Tsai-type Zn-Fe-Sc. The shape of the voids consists of planes related to the icosahedral symmetry, typically a dodecahedron with additional truncations by the planes perpendicular to the 2- and 3-fold axes. During controlled cooling from the melting point, approximately 824 degrees C, and additional annealing at 650 similar to 700 degrees C, the growth of the microvoids was observed. Corresponding to the increase of the size, the number density of voids is decreased so as to conserve the total volume of the voids, i.e. the porosity. This is the first direct evidence indicating that the growth process is essentially Ostwald ripening. The origin of the growth between 600 and 800 degrees C is considered to be not the supersaturated thermal vacancies, but vacancies coming from nearby shrinking voids. The growth is well explained by a thermally activated process with activation energy approximately 3.1 eV.
Title:
Formation and stability of icosahedral phase in Al65Ga5Pd17Mn13 alloy
Authors:
Yadav, TP; Shaz, MA; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Shaz, M. A.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 1995-2002 2008
Abstract:
The formation and characterization are described of a quaternary (pseudo-ternary) icosahedral quasicrystal in Al65Ga5Pd17Mn13 alloy. X-ray diffraction and transmission electron microscopy observations confirmed the formation of icosahedral, B2 type and xi' crystalline (orthorhombic structure with unit cell a = 23.5 angstrom, b = 16.6 angstrom and c = 12.4 angstrom) phases in as-cast alloy. The icosahedral phase is formed after annealing at 800 degrees C for 60 h. This is the first report of the formation of an icosahedral phase in an Al-Ga-Pd-Mn quaternary alloy by present technique. The energy dispersive X-ray analysis investigations suggest the presence of Ga (similar to 5 at.%) in the alloy. Icosahedral Al-Ga-Pd-Mn provides a new opportunity to investigate various characteristics, including surface characteristics. Attempts are made to discuss the micromechanisms for the formation of the quasicrystalline phase in Al-Ga-Pd-Mn alloys.
Title:
Mapping the aperiodic landscape, 1982-2007
Authors:
Senechal, M Author Full Names: Senechal, M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2003-2016 2008
Abstract:
The discovery of quasicrystals galvanized mathematics research in long-range aperiodic order, accelerating the dissolution of the the ancient periodic/non-periodic dichotomy begun by Penrose, Ammann, de Bruijn, and Mackay. What does the aperiodic landscape look like now, 25 years later, and what frontiers are still to be mapped?
Title:
Symmetry properties of Penrose type tilings
Authors:
Cotfas, N Author Full Names: Cotfas, N.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2017-2023 2008
Abstract:
The Penrose tiling is directly related to the atomic structure of certain decagonal quasicrystals and, despite its aperiodicity, is highly symmetric. It is known that the numbers 1, -tau , (-tau )(2), (-tau )(3),..., where tau = (1 + root 5)/2, are scaling factors of the Penrose tiling. We show that the set of scaling factors is much larger, and for most of them the number of the corresponding inflation centres is infinite.
Title:
Coincidences in four dimensions
Authors:
Baake, M; Zeiner, P Author Full Names: Baake, M.; Zeiner, P.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2025-2032 2008
Abstract:
The coincidence site lattices (CSLs) of prominent four-dimensional lattices are considered. CSLs in three dimensions have been used for decades to describe grain boundaries in crystals. Quasicrystals suggest also looking at CSLs in dimensions d > 3. Here, we discuss the CSLs of the root lattice A(4) and the hypercubic lattices, which are of particular interest both from the mathematical and the crystallographic viewpoints. Quaternion algebras are used to derive their coincidence rotations and the CSLs. We make use of the fact that the CSLs can be linked to certain ideals and compute their indices, their multiplicities and encapsulate all this in generating functions in terms of Dirichlet series. In addition, we sketch how these results can be generalized for four-dimensional Z-modules by discussing the icosian ring.
Title:
Aperiodic order and pure point diffraction
Authors:
Lenz, D Author Full Names: Lenz, D.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2059-2071 2008
Abstract:
The paper gives a leisurely introduction to mathematical diffraction theory with a focus on pure point diffraction. In particular, various characterizations of pure point diffraction and common models arising from cut and project schemes are discussed. It finishes with a list of open problems.
Title:
Ordering of adsorbed species on quasicrystal surfaces
Authors:
Smerdon, JA; Wearing, LH; Parle, JK; Leung, L; Sharma, HR; Ledieu, J; McGrath, R Author Full Names: Smerdon, J. A.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2073-2082 2008
Abstract:
We present an overview of experimental studies of the structure of adsorbed atomic and molecular species on quasicrystal surfaces with a particular focus on those systems where quasiperiodic ordering of the adsorbate structure occurs. Atomic adsorption is illustrated with examples from studies of Fe and Gd adsorption on the five-fold surface of i-Al-Pd-Mn. Overlayer structure is correlated with several physical parameters to identify trends. It is concluded that the chemical properties of the adsorbate (metallic radius, electronegativity, melting temperature) are important indicators of quasiperiodic structuring of the adsorbate system. These correlations allow predictions of those elements likely to yield pseudomorphic overlayers. Structural effects upon molecular adsorption on clean quasicrystal surfaces have been less successful. A new approach to ordered molecular adsorption is described and illustrated for C-60 adsorption on a Pb monolayer film on the ten-fold surface of d-Al-Ni-Co.
Title:
Testing bulk models of icosahedral quasicrystals with STM images of clean surfaces
Authors:
Papadopolos, Z; Widmer, R; Groning, O Author Full Names: Papadopolos, Z.; Widmer, R.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2083-2093 2008
Abstract:
In the case of icosahedral Al-Pd-Mn we compare the STM (scanning tunnelling microscopy) image of the real fivefold surface to the STM simulations on the candidates of the fivefold bulk terminations. We make the choice of which termination fits best to the real image. It leads us to some hints important either for the chemistry of the bulk-model or for the eventual correction of the model of atomic positions itself. We work in the frame of the particular model of atomic positions, based on the diffraction data for Al70Pd21Mn9 and Al62Cu25.5Fe12.5. We also discuss the possibilities beyond this model.
Title:
X-ray photoelectron diffraction on the 6-fold (001) mu-Al4Mn approximant surface
Authors:
Widmer, R; Maeder, R; Heggen, M; Feuerbacher, M; Groning, O Author Full Names: Widmer, R.; Maeder, R.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2095-2102 2008
Abstract:
In theoretical investigations, the study of the properties of quasicrystals via analysis of periodic approximant structures has proven to be very successful. We performed experimental surface structure studies on the mu-Al4Mn approximant, exhibiting a large unit cell of 563 atoms, to get on to the origin of the unusual physical properties of complex quasicrystalline systems. The 6-fold (001) mu-Al4Mn surface was investigated by surface-sensitive low energy electron diffraction and X-ray photoelectron diffraction. Detailed analysis of the experimental data using single scattering cluster calculations revealed a pure bulk truncated surface, which is cut at the z = c/2 and 3c/4 layers of the unit cell, with a slight preference for the z = 3c/4 termination. The possibility of preparing well ordered, bulk terminated surfaces of such a complex, yet periodic, crystal structure in the Al-Mn system allows the application of a wealth of surface analytical tool to obtain a greater understanding of the physical properties of complex metallic alloys in relation to quasicrystals.
Title:
Low-energy electron diffraction (LEED) study of an aperiodic thin film of Cu on 5-fold i-Al-Pd-Mn
Authors:
Pussi, K; Reid, DE; Ferralis, N; McGrath, R; Lograsso, TA; Ross, AR; Diehl, RD Author Full Names: Pussi, K.; Reid, D. E.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2103-2110 2008
Abstract:
Thin films of copper grown on five-fold i-AlPdMn at room temperature consist of domains that are rotationally aligned with the five primary symmetry directions of the substrate and which have one-dimensional aperiodic order. This aperiodic order is evident in scanning tunnelling microscopy images as wide and narrow rows that are spaced according to a Fibonacci sequence. A low-energy electron diffraction (LEED) study of this film indicates that the structure within the domains is periodic along the rows, with a repeat distance equal to the nearest-neighbour separation in bulk Cu. To determine the complete structure, a dynamical LEED experiment was performed for a five-layer Cu film at a sample temperature of 85 K. The analysis was performed using two different computational methods, one based on quasicrystalline slabs and the other on periodic approximants. Of the model structures tested, the film is found to be most consistent with a structure based on the Cu{100} surface structure, but having aperiodic displacements, both in-plane and out-of-plane, along a < 110 > direction.
Title:
Co nanocrystallites on an icosahedral Al-Pd-Mn quasicrystal
Authors:
Burkardt, S; Erbudak, M; Longchamp, JN; Weisskopf, Y Author Full Names: Burkardt, S.; Erbudak, M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2111-2116 2008
Abstract:
Recently, we reported that submonolayer deposits of Co onto the pentagonal surface of i-Al-Pd-Mn form a stable intermetallic compound of five CsCl-type AlCo domains rotated by 72 degrees with respect to each other. For multilayer deposition, Co was found to grow epitaxially on the AlCo domains in a body-centred cubic structure. Here we discuss this conclusion in more detail and report the formation of atomic rows at the surface for deposits larger than three monolayers. The details of the growth resulting in ordered nanostructures are extracted from low-energy electron diffraction investigations. Surface magneto-optical Kerr effect measurements confirm the decrease in the domain size for thicker films.
Title:
Alkaline-earth metal monolayers on 5-fold i-Al-Pd-Mn surface: Influence of adatom size on quasiperiodic ordering
Authors:
Krajci, M; Hafner, J Author Full Names: Krajci, M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2117-2122 2008
Abstract:
The structure and stability of a quasiperiodic alkaline-earth metal monolayer formed on a five-fold surface of an icosahedral Al-Pd-Mn quasicrystal have been investigated using ab initio density-functional methods. We study the influence of the size of the adatom on the regularity of the quasiperiodic ordering. It was found that Ca adatoms at a coverage 0.066 atoms/angstrom(2) (Theta = 0.5)form a highly regular quasiperiodic monolayer on the i-Al-Pd-Mn surface, with an ordering described by a decagonal DHBS tiling of decagons, hexagons, boats and pentagonal stars.
Title:
Discussion on the surface science of quasicrystals
Authors:
Thiel, PA Author Full Names: Thiel, P. A.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2123-2129 2008
Abstract:
This paper contains a short review of four aspects of the surface science of quasicrystals, together with a list of challenges for the scientific community in the near future. The first issue concerns the ability of surface science to shed light on bulk atomic structure. The second is the use of surfaces as quasiperiodic templates, particularly for films of periodic metals. Here, enforcing quasiperiodicity in the film may lead to unusual magnetic, tribological or adsorption properties. The third aspect concerns the effects of surface phasons and phonons on dynamical interactions with adsorbates, such as sticking coefficient, as well as on diffusion between the surface and near-surface region. The final area is tribology, where studies of quasicrystals have suggested that both adhesion and phononic friction may be important.
Title:
Electronic transport in AlMn(Si) and AlCuFe quasicrystals: Breakdown of the semiclassical model
Authors:
de Laissardiere, GT; Julien, JP; Mayou, D Author Full Names: de Laissardiere, G. Trambly; Julien, J. -P.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2131-2144 2008
Abstract:
The semiclassical Bloch-Boltzmann theory is at the heart of our understanding of conduction in solids, ranging from metals to semiconductors. Physical systems that are beyond the range of applicability of this theory are thus of fundamental interest. It appears that in quasicrystals and related complex metallic alloys, a new type of breakdown of this theory operates. This phenomenon is related to the specific propagation of electrons. We develop a theory of quantum transport that applies to a normal ballistic law, and also to these specific diffusion laws. As we show, phenomenological models based on this theory describe correctly the anomalous conductivity in quasicrystals. Ab initio calculations performed on approximants also confirm the validity of this anomalous quantum diffusion scheme. This provides us with an ab initio model of transport in approximants such as alpha-AlMnSi and AlCuFe 1/1 cubic approximant.
Title:
Anisotropic electrical, magnetic and thermal transport properties of the Al80Cr15Fe5 decagonal approximant
Authors:
Dolinsek, J; Vrtnik, S; Smontara, A; Jagodic, M; Jaglicic, Z; Bauer, B; Gille, P Author Full Names: Dolinsek, J.; Vrtnik, S.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2145-2153 2008
Abstract:
The anisotropic magnetic, electrical and thermal transport properties were studied of a single-crystalline Al80Cr15Fe5 approximant to the decagonal quasicrystal. The temperature-dependent electrical resistivity along the b and c crystalline directions shows non-metallic behaviour with a broad maximum, whereas it exhibits a metallic positive temperature coefficient along the a direction perpendicular to the (b, c) atomic planes. The resistivity can be treated with the model of slow charge carriers, where the increased electron-phonon scattering upon raising the temperature induces a transition from dominant Boltzmann (metallic) to dominant non-Boltzmann (insulating-like) regime. The magnetic susceptibility and thermal conductivity also reveal a small anisotropy.
Title:
Coupled quasicrystals
Authors:
Vekilov, YK; Isaev, EI Author Full Names: Vekilov, Yu. Kh.; Isaev, E. I.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2171-2173 2008
Abstract:
We predict that under certain experimental conditions external radiation with frequency half of that for the alternating Josephson effect can appear when a constant voltage is applied to a quasicrystal-quasicrystal tunnelling junction 1. The background for this possibility is the phase coherence of the wavefunctions across the barrier and the absence of scattering on the dynamical degrees of freedom (phonons).
Title:
Magnetism in quasicrystals
Authors:
Hippert, F; Prejean, JJ Author Full Names: Hippert, F.; Prejean, J. J.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2175-2190 2008
Abstract:
The present understanding of magnetic properties of quasicrystals (QCs) is reviewed. In AlMn and AlPdMn QCs, only a few Mn atoms, with concentrations from a few per cent down to 10(-4) carry a localized magnetic moment. These moments are coupled via RKKY interactions, leading to a canonical spin-glass ordering at low temperature. They also exhibit a Kondo effect and AlPdMn QCs turned out to be a model system for studying experimentally the competition between Kondo and RKKY interactions in the absence of long-range magnetic ordering. Besides, the presence of localized moments has very unusual consequences for the electronic transport in AlPdMn QCs. In RMgZn and RMgCd QCs ( R is a magnetic rare earth), with R concentration around 9%, a spin-glass like freezing is observed. However the short-range antiferromagnetic correlations detected above the freezing temperature are unusual and are certainly influenced by the quasiperiodicity.
Title:
Local environment and magnetism in icosahedral quasicrystals
Authors:
Godonyuk, AV; Isaev, EI; Vekilov, YK Author Full Names: Godonyuk, A. V.; Isaev, E. I.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2191-2196 2008
Abstract:
Based on density functional theory and all-electron projector-augmented wave (PAW) potentials, we studied the onset of local magnetic moments in the model icosahedral quasicrystal, Al46-xPd14Mn5Bx, where x is the number of boron (B) atoms with 0 <= x <= 3. We previously studied the dependence of local magnetic moment in Mn atoms on their atomic concentration [J. Magn. Magn. Mater. 300 567 (2006)]. In the current study, however, we have kept the number of Mn atoms constant. We have shown that the magnitude of local magnetic moment in a Mn atom depends significantly on the presence of Pd atoms inside the first coordination sphere. In qualitative agreement with experimental conclusion of Peng et al. [J. Magn. Magn. Mater. 184 319 (1998)], we also found that the average local magnetic moment in Mn depends on B concentration. The influence of B atoms is more pronounced if they are located inside the second coordination sphere.
Title:
In search of multipolar order on the Penrose tiling
Authors:
Vedmedenko, EY; Mandel, SED; Lifshitz, R Author Full Names: Vedmedenko, E. Y.; Mandel, S. Even-Dar
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2197-2207 2008
Abstract:
We use Monte Carlo calculations to analyse multipolar ordering on the Penrose tiling, relevant for two-dimensional molecular adsorbates on quasicrystalline surfaces and for nanomagnetic arrays. Our initial investigations are restricted to multipolar rotors of rank one through four-described by spherical harmonics Ylm with l = 1,....,4 and restricted to m = 0-positioned on the vertices of the rhombic Penrose tiling. At first sight, the ground states of odd-parity multipoles seem to exhibit long-range order, in agreement with previous investigations of dipolar systems. Yet, careful analysis performed here establishes that, despite earlier claims, long-range order is absent for all types of rotors, and only short-range order exists. Nevertheless, we show here that short-range order suffices to yield a superstructure in the form of the decagonal Hexagon-Boat-Star tiling. Our results should be taken as a warning for any future analysis of order in either real or simulated arrangements of multipoles on quasiperiodic templates.
Title:
Discussion of electronic properties of quasicrystals
Authors:
Mayou, D Author Full Names: Mayou, D.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2209-2215 2008
Abstract:
This article gives a short review of some important achievements in the field of electronic properties of quasicrystals. It focuses essentially on: the nature of quasicrystals as Hume-Rothery alloys, the energetics of quasicrystals and related phases, the magnetic properties, the localization of electronic states, and the transport properties. For each part we emphasize some promising directions of research. We end by listing some problems that are related to that of electrons in a quasiperiodic potential.
Title:
Quasicrystals and complex metallic alloys: Trends for potential applications
Authors:
Barthes-Labrousse, MG; Dubois, JM Author Full Names: Barthes-Labrousse, M. -G.; Dubois, J. -M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2217-2225 2008
Abstract:
Although the industrial development of complex metallic alloys (CMAs) and quasicrystals (QCs) has remained quite limited so far, these materials exhibit interesting and sometimes unexpected properties in terms of technological applications. A few selected examples of the most promising properties and trends for potential applications are presented.
Title:
Low-temperature synthesis of nanocrystalline spinel by mechanical milling and annealing of Al-Ni-Fe decagonal quasicrystals
Authors:
Yadav, TP; Mukhopadhyay, NK; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Mukhopadhyay, N. K.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2227-2236 2008
Abstract:
Attempts were made to synthesize a nanocrystalline spinel phase by mechanical milling and subsequent annealing of Al-Ni-Fe decagonal quasicrystalline alloy. The milling of the decagonal phase was carried out in an attritor ball mill at 400 rpm for 1-40 h with ball to powder ratio of 100:1 in hexane medium. Subsequently annealing was performed in vacuum as well as an air ambience for 10, 20, 40 and 80 h. The quasicrystal powders milled for 40 h showed the formation of B2-type nanocrystalline phase (a=2.91 angstrom). Annealing of 40 h milled powder in air at 500 degrees C resulted in the formation of spinel structure (a=8.15 angstrom). X-ray diffraction and transmission electron microscopy investigations confirmed the formation of spinel phase with an average grain size of similar to 60nm. The formation of nanospinels and the advantages of this synthesis route compared to the existing routes for the formation of spinels are discussed.
Title:
Correlation between charge state and diffusion of hydrogen in Ti-based quasicrystals
Authors:
Morozov, AY; Belov, MP; Barbin, NA; Isaev, EI; Vekilov, YK Author Full Names: Morozov, A. Y.; Belov, M. P.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2237-2243 2008
Abstract:
The dependence of the charge state of hydrogen as a function of H content in the 1/1 approximant to icosahedral Ti-based quasicrystals (QCs) was studied using a first-principles method based on the density functional theory and norm-conserving pseudopotentials. It was found that the dependence is strong and non-monotonic. Hydrogen diffusion is significantly hindered in QCs with a charged hydrogen atom.
Title:
Dodecagonal quasicrystal in a polymeric alloy II: specific heat
Authors:
Dotera, T Author Full Names: Dotera, T.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2245-2251 2008
Abstract:
In a previous paper, we reported the formation of a dodecagonal quasicrystal (DDQC) in a quasi-two-dimensional lattice Monte Carlo simulation of a star-shaped polymer. In this paper, we show a series of Archimedean and quasicrystalline phases (4.8(2)) -> (3(2).4.3.4) -> DDQC -> (4.6.12) with increase of one component of ABC star polymers. The phase behaviour can be regarded as a transition between square tiling and triangle tiling via square-triangle tiling. We compare the specific heat for the phases and find that the DDQC sample possesses higher specific heat at high temperatures, which may be attributed to phason dynamics.
Title:
Electronic energy spectra of square and cubic Fibonacci quasicrystals
Authors:
Mandel, SED; Lifshitz, R Author Full Names: Mandel, S. Even-Dar; Lifshitz, R.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2261-2273 2008
Abstract:
Understanding the electronic properties of quasicrystals, in particular the dependence of these properties on dimension, is among the interesting open problems in the field of quasicrystals. We investigate an off-diagonal tight-binding hamiltonian on the separable square and cubic Fibonacci quasicrystals. We use the well-studied Cantor-like energy spectrum of the one-dimensional Fibonacci quasicrystal to obtain exact results regarding the transitions between different spectral behaviours of the square and cubic quasicrystals. We use analytical results for the addition of one-dimensional spectra to obtain bounds on the range in which the higher-dimensional spectra contain an interval as a component. We also perform a direct numerical study of the spectra, obtaining good results for the square Fibonacci quasicrystal, and rough estimates for the cubic Fibonacci quasicrystal.
Title:
The square Thue-Morse tiling for photonic application
Authors:
Moretti, L; Mocella, V Author Full Names: Moretti, L.; Mocella, V.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2275-2284 2008
Abstract:
The photonic properties of a two-dimensional (2D) photonic aperiodic crystal based on the Thue-Morse (ThMo) substitutional sequence were investigated theoretically. In contrast to traditional photonic quasicrystals based on the Penrose tiling, these structures were obtained by removing the lattice points from a square arrangement, following the inflation rules emerging from the ThMo sequence. The resulting structure does not exhibit the typical translational symmetry of photonic crystals. In particular, it is well known that the ThMo sequence has a singular continuous Fourier transform. This property was transferred directly on the 2D ThMo photonic aperiodic crystal represented by an array of pillars in air. The electromagnetic field distribution can be described as a quasi-localized state, with characteristics lying between the localized states, corresponding to the defect state in a photonic crystal, and the Bloch states, as in the case of the eigenmode in a photonic crystal. The photonic bandgap formation was explored as a function of pillar radius. Furthermore, a preliminary investigation of the defect behaviour in square ThMo tiling was carried out. The electric field in the defect state was revealed to be strictly localized in the defect pillar. These structures provide interesting properties, which could be used to design novel optical devices.
Title:
Nonlinear photonic quasicrystals for novel optical devices
Authors:
Bahabad, A; Lifshitz, R; Voloch, N; Arie, A Author Full Names: Bahabad, A.; Lifshitz, R.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2285-2293 2008
Abstract:
Two well-known methods for the design of quasicrystal models are used to create novel nonlinear optical devices. These devices are useful for efficient three-wave mixing of several different processes, and therefore offer greater flexibility with respect to the more common periodic nonlinear photonic crystals. We demonstrate applications for polarization switching as well as multi-wavelength and multi-directional frequency doubling. The generalized dual grid method is proven to be efficient for designing photonic quasicrystals for one-dimensional collinear devices as well as elaborate two-dimensional multi-directional devices. The cut-and-project method is physically realized by sending finite-width optical beams at an irrational angle through a periodic two-dimensional nonlinear photonic crystal. This enables the creation of two simultaneous collinear optical processes that can be varied by changing the angle of the beams.
Title:
Phason modes in quasicrystals
Authors:
De Boissieu, M Author Full Names: De Boissieu, M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2295-2309 2008
Abstract:
Studies on phason modes in quasicrystals, but more generally in aperiodic phases, which encompass incommensurately modulated phases, composites and quasicrystals, are reviewed. After an introduction on phason modes in aperiodic phases, the hydrodynamic theory is presented. The case of incommensurately modulated phases is illustrated by results on ThBr4. Atomic models used to simulate phason modes in quasicrystals are then presented, followed by an overview of results obtained for icosahedral and decagonal phases.
Title:
Atomic dynamics of i-ScZnMg and its 1/1 approximant phase: Experiment and simulation
Authors:
Mihalkovic, M; Francoual, S; Shibata, K; De Boissieu, M; Baron, AQR; Sidis, Y; Ishimasa, T; Wu, D; Lograsso, T; Regnault, LP; Gahler, F; Tsutsui, S; Hennion, B; Bastie, P; Sato, TJ; Takakura, H; Currat, R; Tsai, AP Author Full Names: Mihalkovic, M.; Francoual, S.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2311-2318 2008
Abstract:
Quasicrystals are long-range ordered materials that lack translational invariance so that the study of their physical properties remains a challenging problem. In order to study the respective influence of the local order and of the long-range order (periodic or quasiperiodic) on lattice dynamics, we have carried out inelastic X-ray and neutron scattering experiments on single grain samples of the Zn-Mg-Sc icosahedral quasicrystal and of the Zn-Sc periodic cubic 1/1 approximant. Besides the overall similarities and the existence of a pseudo-gap in the transverse dispersion relation, marked differences are observed, the pseudo-gap being larger and better defined in the approximant than in the quasicrystal. This can be qualitatively explained using the concept of pseudo-Brillouin zone in the quasicrystal. These results are compared to simulations on atomic models and using oscillating pair potentials, which have been fitted against ab-initio data. The simulated response function reproduces both the dispersion relation but also the observed intensity distribution in the measured spectra. The partial vibrational density of states, projected on the cluster shells, is computed from this model.
Title:
High-temperature specific heat of icosahedral Al-Cu-Fe and decagonal Al-Ni-Co
Authors:
Shulyatev, DA; Nigmatulin, AS; Lobanova, AV; Gasparyan, TA Author Full Names: Shulyatev, D. A.; Nigmatulin, A. S.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2319-2323 2008
Abstract:
The high-temperature specific heat, c(p)(T), of icosahedral Al-Cu-Fe and decagonal Al-Ni-Co was measured at various temperature ranges between 420 and 1350 K. For both materials, the specific heat increases with increasing temperature, reaching the values that are substantially higher than the Dulong and Petit value. Comparisons are made with previously reported data for icosahedral and decagonal phases.
Title:
Quasicrystal plasticity in the framework of a constitutive model: Interaction of the microstructural parameters at high strain rates
Authors:
Heggen, M; Feuerbacher, M Author Full Names: Heggen, M.; Feuerbacher, M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2325-2331 2008
Abstract:
A unified description of quasicrystal plasticity in terms of a quantitative model using constitutive equations was presented by Feuerbacher and co-workers in 2001 [1]. In a later work, the model was successfully applied to a wide range of experimental parameters where various stress-strain behaviours were observed [2]. At high strain rates, for example, the occurrence of a low-strain work-hardening stage, the formation of a stress maximum at around 5%, and work softening at higher strains was observed. In the present work, the complex stress-strain behaviour of quasicrystals at high strain rates is analyzed in terms of the constitutive model. The evolution of the two microstructural parameters, the dislocation density and the order parameter, their interaction with other microstructural parameters and the influence on the macroscopic plastic deformation behaviour are analyzed and discussed.
Title:
Discussion of phasons in quasicrystals and their dynamics
Authors:
Widom, M Author Full Names: Widom, M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2339-2350 2008
Abstract:
Phasons are a type of excitation peculiar to quasicrystals and other incommensurate phases arising as a consequence of their spatial quasiperiodicity. Phason-related excitations are also observed in complex crystal structures known as approximants. This article briefly reviews the concepts of phasons with focus on current issues in their regard. We examine both continuum (hydrodynamic) and discrete (tiling) descriptions of phasons and review the state of experimental validation of the basic theoretical notions.
Title:
Twenty-five years of quasicrystals: Where are we now and what does the future hold? - A personal outlook
Authors:
Dubois, JM Author Full Names: Dubois, J. -M.
Source:
PHILOSOPHICAL MAGAZINE 88 (13-15): 2351-2356 2008
Abstract:
Twenty-five years after the historic discovery of a real material exhibiting fivefold symmetry, the scientific field opened as a result is still robust and active. On the experimental side, it has been strengthened in recent years by new inputs coming from studies of transport properties, surface physics, coating technology, catalysis, etc. Its future probably relies upon combining these very exotic, but now extremely well documented materials with more conventional materials in composites, or challenging the discovery of new, or more exciting properties in a systematic screening of intermetallics compounds with untried compositions. An effort towards making quasicrystals better understood outside our own community has become mandatory with a view to developing the field.
Title:
Transport properties of Ti-Zr-Ni quasicrystalline and glassy alloys
Authors:
Kuo, YK; Kaurav, N; Syu, WK; Sivakumar, KM; Shan, UT; Lin, ST; Wang, Q; Dong, C Author Full Names: Kuo, Y. K.; Kaurav, N.
Source:
JOURNAL OF APPLIED PHYSICS 104 (6): Art. No. 063705 SEP 15 2008
Abstract:
We report on measurements of the temperature dependence of the electrical resistivity (p), thermopower (S), and thermal conductivity (kappa) of Ti-Zr-Ni alloys between 10 and 300 K. A series of Ti-Zr-Ni quasicrystals (QCs) Ti40Zr40Ni20, Ti45Zr35Ni20, and Ti50Zr30Ni20 and metallic glasses Ti35Zr45Ni20 and Ti40Zr40Ni20 was prepared to systematically study the compositional and structural dependences of their transport properties. The resistivity of all these alloys was found to be very weakly temperature dependent with a negative temperature coefficient of resistance. Further, the observed increase in electrical resistivity with increasing Ti/Zr ratio is most likely due to the increase in disorder. The SIT against temperature curves exhibited a maximum between 20 and 50 K and a noticeable deviation from the expected linear behavior in S(T) at higher temperatures. Such observations in the thermopower of QCs have been attributed to the electron-phonon enhancement and phonon drag effect. The measured thermal conductivities were analyzed by separating the electronic and phonon contributions that provide a reasonable explanation for plateau-type feature in kappa(T) of QCs. Our present results suggest that the transport properties of glassy phase are influenced by the same mechanisms as those of quasicrystalline phase. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2977721]
Title:
Crystal structure of the 2/1 cubic approximant Ag42In42Yb16
Authors:
Li, MR; Hovmoller, S; Sun, JL; Zou, XD; Kuo, KH Author Full Names: Li, M. R.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 465 (1-2): 132-138 OCT 6 2008
Abstract:
The crystal structure of the 2/1 cubic approximant Ag42In42Yb16 was determined by single crystal X-ray diffraction. The structure model has the composition of Ag40.42In44.50Yb15.08 with a=24.8687 angstrom, space group Pa (3) over bar (No. 205). Among the 14 independent Ag, 13 In, and 5 Yb sites, 6 Ag sites and 6 In sites are icosahedrally coordinated, whereas two sites (In13, Yb1) are Frank-Kasper polyhedrally coordinated. Four Yb sites (Yb2-5) are double pentagonal antiprisms. The basic structural unit can be described as a 102-atom pseudo-Bergman cluster with three successive shells, of which the second shell consists of a dodecahedron and an only nine-atom polyhedron that breaks icosahedral symmetry. (C) 2007 Elsevier B.V. All rights reserved.
Title:
The effect of cooling rate on the microstructure and mechanical properties of Mg-Zn-Gd-based alloys
Authors:
Liu, Y; Yuan, GY; Yin, J; Lu, C; Ding, WJ; Jiang, JZ Author Full Names: Liu, Yong
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH 99 (9): 973-978 SEP 2008
Abstract:
The microstructure and mechanical properties of Mg3.5Zn0.6Gd and Mg3.5Zn0.6Gd1.5Cu alloys were investigated under different solidification conditions. The microstructure and phase constitutions of alloys were characterized using optical microscopy, scanning electron microscopy, X-ray diffraction and differential thermal analysis. The results indicate that the cooling rate plays an important role in grain refinement and phase constitutions of Mg-Zn-Gd alloys. In the cooling rate range from 4.8 K s(-1) to 18.5 K s(-1) for the Mg-Zn-Gd system, higher content of the icosahedral phase (I-phase) was obtained under the condition of higher cooling rate which accelerated the nucleation and growth of the I-phase. Under the cooling rate of 18.5 K s(-1), the mechanical properties of the Mg3.5Zn0.6Gd alloy were further improved by the high I-phase content due to its unique icosahedral structure, in addition to the contribution of grain refinement.
Title:
Computing with almost periodic functions
Authors:
Moody, RV; Nesterenko, M; Patera, J Author Full Names: Moody, R. V.; Nesterenko, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 64: 654-669 Part 6 NOV 2008
Abstract:
This paper develops a method for discrete computational Fourier analysis of functions defined on quasicrystals and other almost periodic sets. A key point is to build the analysis around the emerging theory of quasicrystals and diffraction in the setting on local hulls and dynamical systems. Numerically computed approximations arising in this way are built out of the Fourier module of the quasicrystal in question and approximate their target functions uniformly on the entire infinite space. The methods are entirely group theoretical, being based on finite groups and their duals, and they are practical and computable. Examples of functions based on the standard Fibonacci quasicrystal serve to illustrate the method (which is applicable to all quasicrystals modeled on the cut-and-project formalism). (C) 2008 International Union of Crystallography Printed in Singapore - all rights reserved

Update: 6-Nov-2008

Title:
Electron microscopy of an icosahedral phase in a rapidly solidified Al18Mg3Mn2 complex metallic alloy
Authors:
Mukhopadhyay, NK; Chang, HJ; Lee, JY; Kim, DH Author Full Names: Mukhopadhyay, N. K.; Chang, H. J.
Source:
SCRIPTA MATERIALIA 59 (10): 1119-1122 NOV 2008
Abstract:
The icosahedral quasicrystal (QC) has been found to form, along with a minor amount of alpha-Al, in the rapidly solidified Al18Mg3Mn2 complex metallic alloy. From the compositional analysis, the QC was found to be close to (AlMg)(82)Mn-18. The quasilattice constant (a(R) = 0.4604 nm) of the QC phase suggests that it is basically an Al-Mn type of Mackay quasicrystal, which conforms to the composition analysis. The rationale behind the formation of the Al-Mg-Mn ternary quasicrystal from the T-Al18Mg3Mn2 alloy is discussed. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Electronic structure of CePdAl experiment and calculations
Authors:
Glogowski, W; Goraus, J; Slebarski, A Author Full Names: Glogowski, W.; Goraus, J.
Source:
MATERIALS SCIENCE-POLAND 26 (3): 729-734 2008
Abstract:
CePdAl exhibits an antiferromagnetic phase below T-N = 2.7 K; its physical properties are typical of heavy fermion compounds (specific heat coefficient gamma = C/T = 270 mJ/(mol.K-2)). The triangular coordination symmetry of the magnetic Ce ions gives rise to geometrical frustration and leads to an incommensurate antiferromagnetic structure below T-N, showing a coexistence of ordered and frustrated Ce moments. The purpose of this work was to discuss electronic structure of CePdAl and its influence on the geometrical frustration in the Kagome-like lattice and the Kondo effect in CePdAl. We present the results of the X-ray diffraction analysis and the XPS Ce 3d core and valence band spectra. We also present the spin-polarized band structure calculations for CePdAl, using the LAPW method.
Title:
Crystallography and morphology of twins in equiatomic TiPt martensite
Authors:
Nishida, M; Matsuda, M; Yasumoto, Y; Yano, S; Yamabe-Mitarai, Y; Hara, T Author Full Names: Nishida, M.; Matsuda, M.
Source:
MATERIALS SCIENCE AND TECHNOLOGY 24 (8): 884-889 AUG 2008
Abstract:
Twins in the B19 (2H) martensite in Ti-Pt shape memory alloy have been investigated by transmission electron microscopy. There are three twinning modes evident, i.e. {111}(2H) Type I, < 121 >(2H) Type II and {101}(2H) compound twins. In addition to the 2H martensite, various long period stacking structures are observed such as 2112 stacking and incommensurate like modulated martensites. It is frequently observed that two martensite structures derived from the identical closed packed plane of the parent phase coexist in the same area, namely, 'two-in-one' morphology. The crystallographic aspects of the 'two-in-one' morphology are also discussed.
Title:
TEM investigation of intermediate phase transformation and micromodulation in Ni-Mn-Ga ferromagnetic shape memory alloys
Authors:
Tsuchiya, K; Todaka, Y; Umemoto, M Author Full Names: Tsuchiya, K.
Source:
MATERIALS SCIENCE AND TECHNOLOGY 24 (8): 920-926 AUG 2008
Abstract:
Intermediate phase transformation, martensitic transformations and modulated structures in Ni-Mn-Ga ferromagnetic shape memory alloys were investigated by TEM. The transformation from high temperature L2(1) phase to intermediate phase was characterised by the appearance of diffuse satellite spots at 0.167q(220) positions in electron diffraction patterns and intense fine striations in bright field images. These results are consistent with the reported results of neutron diffraction measurements related to the phonon anomaly. Also, high resolution TEM observations and fast Fourier transformation analysis on the near intermediate phase state in Ni-Mn-Ga-Gd were conducted. It was revealed that the coarse tweed contrast was associated with a long wavelength strain field while the fine striations are associated with the satellite spots and domains of micromodulation aligned parallel to {110}.
Title:
Some symmetry aspects of ferroics and single phase multiferroics
Authors:
Schmid, H Author Full Names: Schmid, Hans
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (43): Art. No. 434201 OCT 29 2008
Abstract:
The symmetry conditions for the occurrence in a same phase of one or more of the four primary ferroic properties, i.e., ferroelectricity, ferromagnetism, ferrotoroidicity and ferroelasticity, are discussed. Analogous conditions are outlined for the admission of so-called secondary and tertiary ferroic effects, such as magnetoelectric, piezoelectric, piezomagnetic, piezotoroidic, etc. Formerly postulated `magnetotoroidic' and 'electrotoroidic' effects are found to be describable as tertiary ferroic magnetoelectric effects. For understanding ferroic and multiferroic domains and their possibilities of switching, knowledge of the pairs of prototype point group/ferroic phase point group (so-called 'Aizu species') is decisive. A classification into ensembles of species with common properties, recently extended to ferrotoroidic crystals, allows distinguishing between full, partial or no coupling between order parameters and understanding domain patterns and poling procedures. The switching by reorientation with angles other than 180 degrees of ferromagnetic, antiferromagnetic and ferroelectric domains by magnetic fields, electric fields or by stress requires the ferroic phase to be ferroelastic. For ferromagnetic/ ferrotoroidic and antiferromagnetic/ ferrotoroidic phases, the ferrotoroidic domains are found to be identical with the ferromagnetic and antiferromagnetic ones, respectively. As a consequence and depending on symmetry, ferrotoroidic domains can be switched by crossed electric and magnetic fields, by collinear electric and magnetic fields or by a magnetic field alone. Examples of ferrotoroidic domains are discussed for Fe2-xGaxO3, Co3B7O13Br and LiCoPO4. Recent new results on symmetry and domains of the antiferromagnetic incommensurate phase of BiFeO3 are also discussed.
Title:
Magnetically induced ferroelectricity in the buckled Kagome antiferromagnet Ni3V2O8
Authors:
Lawes, G; Kenzelmann, M; Broholm, C Author Full Names: Lawes, G.; Kenzelmann, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (43): Art. No. 434205 OCT 29 2008
Abstract:
Ni3V2O8 is one of several recently identified multiferroic materials in which ferroelectricity is produced by long-range magnetic order. This staircase Kagome compound adopts a sequence of distinct low temperature magnetic phases, which exhibit different optical, dielectric, and transport properties, most notably ferroelectric order arising from a polar incommensurate magnetic structure. We give an overview of the experimental results from the existing literature on Ni3V2O8, and briefly discuss models that describe the coupling between magnetic and ferroelectric properties. We show that the temperature dependence of the dielectric constant provides evidence for spin-charge coupling in Ni3V2O8 away from the ferroelectric phase. An anomaly in the thermal conductivity at the incommensurate-commensurate phase transition suggests that spin scattering may limit thermal transport in the incommensurate phase. We associate each of the two incommensurate phase transitions with one magnetic order parameter, and we show that the temperature dependence of the ferroelectric polarization closely follows the product of these two magnetic order parameters-corroborating the validity of the phenomenological trilinear coupling model. Finally, we present inelastic powder neutron scattering measurements that provide evidence of several weakly dispersive magnetic modes that are typical for strongly frustrated antiferromagnets with large spin anisotropies.
Title:
Magnetic and ferroelectric properties of multiferroic RMn2O5
Authors:
Noda, Y; Kimura, H; Fukunaga, M; Kobayashi, S; Kagomiya, I; Kohn, K Author Full Names: Noda, Y.; Kimura, H.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (43): Art. No. 434206 OCT 29 2008
Abstract:
The magnetic and ferroelectric properties of multiferroic RMn2O5 (R = Y, Tb, Ho, Er, Tm) are reviewed based on recent neutron diffraction and dielectric measurements. Successive phase transitions of magnetic and dielectric ordering were found to occur simultaneously in this system. The characteristic magnetic ordering of the system exhibits an incommensurate-commensurate phase transition, and again transitions to an incommensurate phase. Special attention is given to the magnetic structure in order to discuss the mechanism for the introduction of ferroelectric polarization. For all the compounds examined, the spin configuration for Mn4+ and Mn3+ ions in the commensurate magnetic phase, where spontaneous electric polarization occurs, was determined to be a transverse spiral spin structure propagating along the c-axis. By contrast, the alignment of the induced 4f moment of R3+ ions showed variation, depending on the character of each of the elements. Corresponding responses to external fields such as a magnetic field, hydrostatic pressure etc at low temperature are strongly dependent on the rare earth element present in the RMn2O5 system. The so-called colossal magnetoelectric effect in this system can be easily interpreted by the phase transition from the magnetic incommensurate and weak ferroelectric phase to the commensurate and ferroelectric phase.
Title:
Phonons and magnetoelectric interactions in Ni3V2O8
Authors:
Yildirim, T; Vergara, LI; Iniguez, J; Musfeldt, JL; Harris, AB; Rogado, N; Cava, RJ; Yen, F; Chaudhury, RP; Lorenz, B Author Full Names: Yildirim, T.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (43): Art. No. 434214 OCT 29 2008
Abstract:
We present a detailed study of the zone-center phonons and magnetoelectric interactions in Ni3V2O8. Using combined neutron scattering, polarized infrared (IR) measurements and first-principles LDA + U calculations, we successfully assigned all IR-active modes, including eleven B-2u phonons which can induce the observed spontaneous electric polarization. We also calculated the Born-effective charges and the IR intensities which are in surprisingly good agreement with the experimental data. Among the eleven B2u phonons, we find that only a few of them can actually induce a significant dipole moment. The exchange interactions up to a cutoff of 6.5 A are also calculated within the LDA + U approach with different values of U for Ni, V and O atoms. We find that LSDA (i.e. U = 0) gives excellent results concerning the optimized atomic positions, bandgap and phonon energies. However, the magnitudes of the exchange constants are too large compared to the experimental Curie-Weiss constant, Theta. Including U for Ni corrects the magnitude of the superexchange constants but opens a too large electronic bandgap. We observe that including correlation at the O site is very important to get simultaneously the correct phonon energies, bandgap and exchange constants. In particular, the nearest and next-nearest exchange constants along the Ni-spine sites result in incommensurate spin ordering with a wavevector that is consistent with the experimental data. Our results also explain how the antiferromagnetic coupling between sublattices in the b and c directions is consistent with the relatively small observed value of Theta. We also find that, regardless of the values of U used, we always get the same five exchange constants that are significantly larger than the rest. Finally, we discuss how the B2u phonons and the spin structure combine to yield the observed spontaneous polarization. We present a simple phenomenological model which shows how trilinear (and quartic) couplings of one (or two) phonons to two spin operators perturbatively affects the magnon ( i.e. electromagnon) and phonon energies.
Title:
Laser deposition of a Cu-based metallic glass powder on a Zr-based glass substrate
Authors:
Sun, H; Flores, KM Author Full Names: Sun, H.; Flores, K. M.
Source:
JOURNAL OF MATERIALS RESEARCH 23 (10): 2692-2703 OCT 2008
Abstract:
Laser Engineered Net Shaping (LENS (TM)) is a laser-assisted manufacturing process that offers the possibility of producing metallic coatings and components with highly nonequilibrium microstructures. In this work, the microstructure developed by LENS deposition of Cu47Ti33Zr11Ni8Si1 powder on a bulk metallic glass substrate, with nominal composition Zr58.5Nb2.8Cu15.6Ni12.8Al10.3, is investigated. Single-layer deposition results in the formation of an inhomogeneous but partially amorphous layer above a crystalline heat-affected zone. Elemental analysis of the deposited layer indicates incomplete mixing of the powder with the melt pool. The as-deposited alloy exhibits a single glass transition event and its primary crystallization event is consistent with the first crystallization temperature of the Cu-based powder. Subsequent remelting of this layer results in a still partially amorphous deposit with a uniform composition of (Zr + Nb)(51.8)Cu24.7Ti3.4Ni16.4Al3.7. The remelted layer exhibits a structural rearrangement immediately prior to the primary crystallization event, possibly associated with the formation of a quasicrystalline phase.
Title:
The isostructural phase transition and frustrated magnetic ordering in TbPd0.9Ni0.1Al studied by neutron diffraction
Authors:
Donni, A; Keller, L; Kitazawa, H; Prchal, J; Fischer, P Author Full Names: Doenni, A.; Keller, L.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 464 (1-2): 67-74 SEP 22 2008
Abstract:
By using powder neutron diffraction we provide a detailed structural and magnetic investigation of the pseudo-ternary compound TbPd0.9Ni0.1Al with hexagonal ZrNiAl-type crystal structure and disorder of palladium and nickel atoms on two crystallographic sites, We provide experimental evidence for the Occurrence of an isostructural phase transition in TbPd0.9Ni0.1Al at 157 K, which is affected by structural disorder compared to that observed in TbPdAl. In TbPd0.9Ni0.1Al the step of the c/a ratio at the first-order phase transition appears about four times smaller than in TbPdAl. TbPd0.9Ni0.1Al undergoes two successive magnetic phase transitions at T-NI = 41 K and T-N2 approximate to 21.5 K. Two third of non-frustrated ordered Tb moments form commenstrate antiferromaganetic chains (k(1) = [1/2, 0, 1/2]) and coexist with one third of frustrated ordered Tb moments, which change from a commensurate structure (k(1) = [1/2. 0, 1/2]) between T-N2 and T-NI to an incommensurate structure (k(2i) = [0.50(1), 0.12(1). 1/21]) below T-N2. Due to the strong magneto-crystal line anisotropy all ordered Tb moments stay perpendicular to the ab-plane and reach at 1.5 K saturation values of 8.6 (2) mu(B) (non-frustrated) and 7.2 (2) mu(B) (frustrated). The symmetry of the magnetic structure of TbPd0.9Ni0.1Al is lower than that of TbNiAl. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Al-rich region of Al-Pd-Ru at 1000 to 1100 degrees C
Authors:
Pavyuchkov, D; Grushko, B; Velikanova, TY Author Full Names: Pavyuchkov, D.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 464 (1-2): 101-106 SEP 22 2008
Abstract:
Partial isothermal sections of the Al-Pd-Ru phase diagram at 1000, 1050 and 1100 degrees C are presented here. The Al-Pd orthorhombic epsilon-phases dissolve up to similar to 15.5 at.% Ru, Al13Ru4 < 2.5 at.% Pd and Al2Ru up to 1 at.% Pd. Between 66 and 75 at.% Al, ternary quasiperiodic icosahedral phase and three cubic phases: C (Pm (3) over bar, a = 0.7757 nm) C-1 (lm (3) over bar, a = 1.5532 nm) and C-2 (Fm (3) over bar, a = 1.5566 nm) were revealed. An additional complex cubic structure with a approximate to 3.96 nm was found to be formed at compositions close to those of the icosahedral phase. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Constitution of the high-Al region of Al-Cu-Rh
Authors:
Grushko, B; Kowalski, W; Przepiorzynski, B; Pavlyuchkov, D Author Full Names: Grushko, B.; Kowalski, W.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 464 (1-2): 227-233 SEP 22 2008
Abstract:
Phase equilibria between 540 and 1010 degrees C were studied in Al-Cu-Rh alloys containing more than 50 at.% Al. Congruent equiatomic AlRh dissolves more than 40 at.% Cu and extends up to 58 at.% Al at the high-Cu part of its compositional range. High-temperature cubic C-Al5Rh2 (C-phase) dissolves up to 13 at.% Cu, "Al3Rh" (epsilon(6)-phase) up to 15 at.% Cu and Al9Rh2 up to 1.5 at.% Cu. The solubility of the third element in other binary Al-Rh and Al-Cu phases is below 0.5 at.%. Close to the high-Cu limit of the C-phase region the fee C-2-phase structurally related to the C-phase is formed. Stable decagonal phase (D1-phase) is formed below 1005 degrees C in a compositional range extending from Al65Cu16Rh19 to Al62Cu23Rh15, which shifts to higher Cu concentrations with decreasing temperature. An additional ternary phase forming around the Al70Cu20Rh10 composition below 660 degrees C was revealed. Partial 1010, 990, 900, 800, 700, 600 and 540 degrees C isothermal sections were determined. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Microstructures and mechanical properties of quasicrystal reinforced Mg matrix composites
Authors:
Zhang, YB; Yu, SR; Song, YL; Zhu, XY Author Full Names: Zhang, Yingbo; Yu, Sirong
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 464 (1-2): 575-579 SEP 22 2008
Abstract:
Mg-based composites reinforced with stable in situ icosahedral quasicrystal phase (I-phase) were fabricated in this Study. The effects of Y content on the microstructures and mechanical properties of the composites were investigated. The results Show that the composites comprised dendrites of alpha-Mg matrix separated by interdendritic I-phase and lamellar (I-phase + alpha-Mg) eutectic. With the increase of Y content, the content of I-phase increases; the content and size of (I-phase + alpha-Mg) eutectic cell increase; the lamellar space between I-phase and alpha-Mg in eutectic cell also increases but the grain size of alpha-Mg matrix decreases. The failure mode of M-Zn-Y alloy matrix composites in tensile tests is quasi-cleavage fracture. With the increase of Y content, the tensile strengths of the composites increase, and (he elongation rates increase firstly and then decrease. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Hydrogenation study of suction-cast Ti40Zr40Ni20 quasicrystal
Authors:
Huang, HG; Li, R; Yin, C; Zheng, ST; Zhang, PC Author Full Names: Huang, Huogen; Li, Rong
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 33 (17): 4607-4611 SEP 2008
Abstract:
Suction casting was predicted to be an usable method for improving the hydriding kinetics of Ti/Zr-based icosahedral quasicrystals (IQCs) in our previous work. To further determine it, a suction-cast Ti40Zr40Ni20 IQC alloy was used for hydrogenation studies by Pressure Composition Isotherm (PCI) and Temperature Programmed Desorption (TPD) techniques. The results showed that, this alloy absorbed hydrogen rapidly with obvious hydrogen pressure plateau and some reversibility, however, displayed very limited hydrogen capacity (about 0.7 wt.%) and low equilibrium pressure. After several hydrogenation/dehydrogenation cycles, the IQC structure transformed into two hydride phases, ZrH2-x and one unknown, both of which decomposed at above 600 degrees C, suggesting high thermo-stability for them. On the whole, indeed the suction-casting method can increase the hydrogen absorption rate of Ti/Zr-based IQCs, however, the hydrogenation properties of the Ti40Zr40Ni20 IQC alloy still need a mighty advancement. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Title:
Crystal structure of 7M modulated Ni-Mn-Ga martensitic phase
Authors:
Righi, L; Albertini, F; Villa, E; Paoluzi, A; Calestani, G; Chernenko, V; Besseghini, S; Ritter, C; Passaretti, F Author Full Names: Righi, L.; Albertini, F.
Source:
ACTA MATERIALIA 56 (16): 4529-4535 SEP 2008
Abstract:
For the first time, the 7M modulated structure, frequently observed in ferromagnetic shape memory Ni-Mn-Ga martensitic phases, is solved by powder diffraction analysis. Two polycrystalline samples with composition Ni2Mn1.2Ga0.8 and Ni2.15Mn0.85Ga, respectively, showing a 7M martensitic state stable at room temperature, were studied. The determination of the modulated crystal structure of Ni2Mn1.2Ga0.8 martensite was achieved by refining the X-ray powder diffraction pattern by the Rietveld method. The basic structure belongs to monoclinic symmetry. The crystal structure, solved within the superspace approach, is found to show an incommensurate 7M modulation with q = 0.308c*. The Rietveld refinement for Ni2.15Mn0.85Ga martensite on the basis of neutron powder data surprisingly provides a very similar incommensurate 7M structure with the same periodicity and analogous modulation function. The incommensurate structure presents typical displacive modulation with several analogies with the Zhdanov (5,(2) over bar)(2) stacking sequence. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 31-Oct-2008

Title:
Tl-4(PO2NH)(4) center dot H2O - A commensurately modulated tetrametaphosphimate
Authors:
Sedlmaier, SJ; Oeckler, O; Schnick, W Author Full Names: Sedlmaier, Stefan J.; Oeckler, Oliver
Source:
SOLID STATE SCIENCES 10 (9): 1150-1158 SEP 2008
Abstract:
Tetrathallium(I) tetra-mu-imidocyclotetraphosphate monohydrate, Tl-4(PO2NH)(4)center dot H2O, was obtained by evaporation of combined aqueous solutions of K-4(PO2NH)(4)center dot 4H(2)O and TlOOCCH3 corresponding to the molar ratio of 1:4. The structure determination of Tl-4(PO2NH)(4)center dot H2O was performed by single-crystal X-ray diffraction methods. In addition to the basic structure (P (1) over bar, no. 2, a = 928.3(2), b = 974.6(2), c = 1018.0(2) pm, alpha = 74.47(3)degrees, beta = 64.68(3)degrees, gamma = 78.81(3)degrees, Z = 2), satellite reflections indicate a fourfold superstructure (AT, a = 928.0(2), b = 3897.1(8), c = 2035.4(4), a = 74.47(3)degrees, beta = 64.68(3)degrees, gamma = 78.81(3)degrees, Z = 16) that is described by an a x 4b x 2c, A-centered supercell which mainly concerns one thallium site of the basic structure. In order to reduce the number of parameters, this superstructure was handled as a commensurate occupancy modulation using the structural description in (3 + 1)-dimensional superspace (P (1) over bar(alpha beta gamma), q = 0.25b* + 0.50c*). The crystal structure of Tl-4(PO2NH)(4) center dot H2O consists of infinite columns of the cyclic [(PO2NH)(4)](4-) anions (saddle conformation) which are interconnected by four N-H center dot center dot center dot O hydrogen bonds. By coordination to the Tl+ ions the [(PO2NH)(4)](4-) columns form a three-dimensional network with channels along [100] wherein the thallium ions that are mainly affected by the modulation are located. The commensurate occupancy modulation of these Tl+ ions has been described with a single harmonic wave function. The modulation is verified by P-31 NMR spectroscopy. The thermal behavior of Tl-4(PO2NH)(4)center dot H2O and the IR data are discussed as well. (C) 2008 Elsevier Masson SAS. All rights reserved.
Title:
Characterization of atomized and extruded Al92Fe3Cr2Mn3 alloy
Authors:
Rios, CT; Fogagnolo, JB; Bolfarini, C; Botta, WJ; Kiminami, CS Author Full Names: Rios, C. Triveno; Fogagnolo, J. B.
Source:
REVIEWS ON ADVANCED MATERIALS SCIENCE 18 (4): 408-414 SEP 2008
Abstract:
Powders of the Al92Fe3Cr2Mn3 quaternary alloy were produced by spray atomization processing;, then they were processed by warm extrusion to obtain extruded ingots. The results revealed that in both the powder particles and the extruded bulk samples, alpha-Al, quasicrystalline and intermetallic phases coexist. The quasicrystalline phase was observed as aggregates and its decomposition to crystalline phase occurs above 500 degrees C. Microstructural changes after extrusion were not observed, indicating that the quasicrystalline phase and the intermetallic compounds are stable against coarsening during the time and temperature of extrusion. The presence of micro-porosities after the extrusion is attributed to the spherical form of the powders and mainly to the high volume of intermetallic faceted-particles.
Title:
Anisotropic magnetic, electrical, and thermal transport properties of the Y-Al-Ni-Co decagonal approximant
Authors:
Smontara, A; Smiljanic, I; Ivkov, J; Stanic, D; Barisic, OS; Jaglicic, Z; Gille, P; Komelj, M; Jeglic, P; Bobnar, M; Dolinsek, J Author Full Names: Smontara, Ana; Smiljanic, I.
Source:
PHYSICAL REVIEW B 78 (10): Art. No. 104204 SEP 2008
Abstract:
We have investigated anisotropic physical properties (magnetic susceptibility, electrical resistivity, thermoelectric power, Hall coefficient, and thermal conductivity) of Y-Al-Ni-Co decagonal approximant with composition Al76Co22Ni2. The crystalline-direction-dependent measurements were performed along three orthogonal directions a*,b, and c of the Y-Al-Ni-Co unit cell, where (a,c) monoclinic atomic planes are stacked along the perpendicular b direction. Anisotropic magnetic susceptibility of conduction electrons is paramagnetic for the field lying within the (a,c) atomic planes and diamagnetic for the field along the b direction. Anisotropic electrical resistivity is low in all crystalline directions, appearing in the order rho(a*)>rho(c)>>rho(b). Thermopower shows electron-phonon enhancement effect. Anisotropic bare thermopower (in the absence of electron-phonon interactions) was extracted, appearing in the same order as the resistivity, vertical bar S-a*(bare)/T vertical bar>S-c(bare)/T vertical bar>vertical bar S-b(bare)/T vertical bar. Anisotropic thermal conductivity appears in the order kappa(b)>kappa(c)>kappa(a*), so that b is the most conducting direction for both electricity and heat. Hall coefficient R-H exhibits pronounced anisotropy, where the magnetic field in a given crystalline direction yields the same R-H for the current along the other two crystalline directions in the perpendicular plane. These anisotropies are analyzed in terms of the anisotropic structure of the Y-Al-Ni-Co phase and the ab initio calculated anisotropic Fermi surface. The results are compared with the literature-reported anisotropy of the physical properties of the d-Al-Ni-Co decagonal quasicrystal.
Title:
Determination of magnetic order of the rare-earth ions in multiferroic TbMn2O5
Authors:
Johnson, RD; Bland, SR; Mazzoli, C; Beale, TAW; Du, CH; Detlefs, C; Wilkins, SB; Hatton, PD Author Full Names: Johnson, R. D.; Bland, S. R.
Source:
PHYSICAL REVIEW B 78 (10): Art. No. 104407 SEP 2008
Abstract:
We have employed resonant x-ray magnetic scattering to specifically probe the magnetic order of the rare-earth ions in multiferroic TbMn2O5. Two energy resonances were observed, one originated from the E1-E1 dipolar transition and the other from the E2-E2 quadrupolar transition. These resonances directly probe the valence 5d band and the partially occupied 4f band, respectively. First, full polarization analysis, which is a measurement of the scattered polarization as a function of incident polarization, confirmed a spin polarization of the terbium valence states (probed by the E1-E1 transition) by the Mn4+ spin density in the commensurate phase. Second, full polarization analysis data were collected in the low-temperature incommensurate and commensurate phases when tuned to the E2-E2 resonance. By employing a least-squares fitting procedure, the spin orientations of the terbium ion sublattice were refined.
Title:
Diagonal and collinear incommensurate spin structures in underdoped La2-xBaxCuO4
Authors:
Dunsiger, SR; Zhao, Y; Gaulin, BD; Qiu, Y; Bourges, P; Sidis, Y; Copley, JRD; Kallin, A; Mazurek, EM; Dabkowska, HA Author Full Names: Dunsiger, S. R.; Zhao, Y.
Source:
PHYSICAL REVIEW B 78 (9): Art. No. 092507 SEP 2008
Abstract:
We have studied incommensurate spin ordering in single-crystal underdoped La2-xBaxCuO4 with x similar to 0.08, 0.05, and 0.025 using neutron-scattering techniques. Static incommensurate magnetic order is observed in the La2-xBaxCuO4 (x = 0.05 and 0.025) compounds with ordering wave vectors which are rotated by 45 about the commensurate (0.5,0.5,0) position, with respect to that in the superconducting x = 0.08 material. These spin modulations are one dimensional in the x = 0.05 and 0.025 samples, with ordering wave vectors lying along the orthorhombic b* direction. Such a rotation in the orientation of the static spin ordering as a function of increasing Ba doping, from diagonal to collinear, is roughly coincident with the transition from an insulating to a superconducting ground state and is similar to that observed in the related La2-xSrxCuO4 system. This phenomenon is therefore a more generic property of underdoped La-214 cuprates.
Title:
Nonlocal Landau theory of the magnetic phase diagram of highly frustrated magnetoelectric CuFeO2
Authors:
Plumer, ML Author Full Names: Plumer, M. L.
Source:
PHYSICAL REVIEW B 78 (9): Art. No. 094402 SEP 2008
Abstract:
A nonlocal Landau-type free-energy functional of the spin density is developed to model the large variety of magnetic states, which occur in the magnetic-field-temperature phase diagram of magnetoelectric CuFeO2. Competition among long-range quadratic exchange, biquadratic antisymmetric exchange, and trigonal anisotropy terms, consistent with the high-temperature rhombohedral R (3) over barm crystal symmetry, are shown to all play important roles in stabilizing the unusual combination of commensurate and incommensurate spin structures in this highly frustrated triangular antiferromagnet. It is argued that strong magnetoelastic coupling is largely responsible for the nonlocal nature of the free energy. A key feature of the analysis is that an electric polarization is induced by a canting of the noncollinear incommensurate spin structure. Application of the model to ordered spin states in the triangular antiferromagnets MnBr2 and NaFeO2 is also discussed.
Title:
Differences between the R-phase and the commensurate phase in iron-doped Ti-Ni shape memory alloys
Authors:
Choi, MS; Yamamoto, T; Fukuda, T; Kakeshita, T; Taguchi, E; Mori, H Author Full Names: Choi, Mi-Seon; Yamamoto, Takuya
Source:
PHILOSOPHICAL MAGAZINE 88 (16): 2449-2460 2008
Abstract:
A Ti-44Ni-6Fe (at. %) alloy was recently reported to exhibit a second order-like incommensurate-commensurate transformation. Whether or not the commensurate (C) phase and the R-phase in Ti-Ni alloys are the same phase has now been investigated. Transformation behaviour was examined in a series of Ti-(50-x)Ni-Fe-x (at. %) alloys with x = 2.0, 4.0, 5.0, 5.5, 5.7, 6.0. Transformation temperature, entropy change and the transformation strain decrease continuously as x increases up to x = 5.7, where the product phase is apparently the R-phase. However, there is an obvious discontinuity in these values between x = 5.7 and x = 6.0. In addition, electron diffraction experiments have revealed that the intensity of satellite reflections of the C-phase is obviously weaker than that of the R-phase. These results strongly suggest that the C-phase is different from the R-phase.
Title:
Electric field induced anomalies in ferroelectric K2SeO4
Authors:
Leist, J; Gibhardt, H; Hradil, K; Eckold, G Author Full Names: Leist, J.; Gibhardt, H.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (41): Art. No. 415209 OCT 15 2008
Abstract:
The lock-in transition of K2SeO4 at 93.2 K was studied using high-resolution. gamma-ray diffraction, in situ dielectric measurements and neutron scattering. The phase transition shows a coexistence regime of 1.0 K with clearly resolved incommensurate and commensurate satellite reflections. Within a temperature interval of several K above the lock-in transition, strong third order satellites are observed, indicating a pronounced squaring of the modulation wave. Under the influence of high electric fields an intermediate phase is observed, which is characterized by a diffuse intensity distribution. In addition, the dielectric permittivity exhibits two maxima, indicating the existence of two separate phase transitions. This behaviour is attributed to distortions of the discommensuration lattice and pinning of the discommensurations by accumulated charged defects. It seems to be characteristic for modulated ferroelectrics of the A(2)BX(4) group, since a similar behaviour is also found in isostructural Rb2ZnCl4 and K2ZnCl4. The soft-mode dynamics close to T-c is found to be essentially independent of the electric field and not affected by the discommensuration lattice.
Title:
Increasing the structural complexity of chromium(IV) oxides by high-pressure and high-temperature reactions of CrO2
Authors:
Castillo-Martinez, E; Arevalo-Lopez, AM; Ruiz-Bustos, R; Alario-Franco, MA Author Full Names: Castillo-Martinez, E.; Arevalo-Lopez, A. M.
Source:
INORGANIC CHEMISTRY 47 (19): 8526-8542 OCT 6 2008
Abstract:
This work presents an overview of a series of increasingly complex oxides synthesized from CrO2, under high-pressure and high-temperature conditions, having C l in octahedral coordination. Although the emphasis is on the structure and microstructure of the compounds as obtained from X-ray diffraction and transmission electron microscopy and diffraction, attention is also given to their interesting electronic and magnetic properties. The study is complemented with an electron energy loss spectroscopic analysis of the different phases. These are the cubic perovskite SrCrO3, the orthorhombic perovskite CaCrO3, the solid solution Sr1-xCaxCrO3, the Ruddlesden-Popper-type Sr3Cr2O7, the family CrSr2RECu2O8 (RE = rare earth), a compositionally modulated perovskite "PbCrO3", and the misfit layer oxide SrO2[CrO2](1.85).
Title:
Transition-metal oxides with triangular lattices: Generation of new magnetic and electronic properties
Authors:
Maignan, A; Kobayashi, W; Hebert, S; Martinet, G; Pelloquin, D; Bellido, N; Simon, C Author Full Names: Maignan, A.; Kobayashi, W.
Source:
INORGANIC CHEMISTRY 47 (19): 8553-8561 OCT 6 2008
Abstract:
The search for multifunctional materials as multiferroics to be applied in microelectronic or for new, chemically stable and nontoxic, thermoelectric materials to recover waste heat is showing a common interest in the oxides whose structures contain a triangular network of transition-metal cations. To illustrate this point, two ternary systems, Ba-Co-O and Ca-Co-O, have been chosen. It is shown that new phases with a complex triangular structure can be discovered, for instance, by introduction of Ga3+ into the Ba-Co-O system to stabilize Ba6Ga2Co11O26 and Ba2GaCo8O14, which both belong to a large family of compounds with formula [Ba(Co,Ga)O3-delta](n)[BaCo8O11]. In the latter, both sublattices contain triangular networks derived from the hexagonal perovskite and the spinel structure. Among the hexagonal perovskite, the Ca3Co2O6 Crystals give clear evidence where the coupling of charges and spins is at the origin of a magnetocapacitance effect. In particular, the ferrimagnetic to ferromagnetic transition, with a one-third plateau on the M(M curve characteristic of triangular magnetism, is accompanied by a peak in the dielectric constant. A second class of cobaltites is the focus of much interest. Their 2D structure, containing CoO2 planes isostructural to a Cdl(2) slice that are stacked in an incommensurate way with rock salt type layers, is referred to misfit cobaltite. The 2D triangular network of edge-shared CoO6 octahedra is believed to be responsible for large values of the Seebeck coefficient and low electrical resistivity. A clear relationship between the structures-incommensurability ratios-and the electronic properties is evidenced, showing that the charge carrier concentration can be tuned via the control of the ionic radius of the cations in the separating layers.
Title:
Phase transitions in [N(CH3)(4)](2)ZnCl4 and [N(CH3)(4)](2)CuCl4 crystals related with the incommensurate modulation existence
Authors:
Sveleba, S; Semotyuk, O; Katerynchuk, I; Kunyo, I; Karpa, I; Pankivskyi, Y Author Full Names: Sveleba, S.; Semotyuk, O.
Source:
ACTA PHYSICA POLONICA A 114 (4): 791-806 OCT 2008
Abstract:
The continuous phase transitions are observed in the crystals with incommensurate phase. They are transitions of parent-incommensurate phases (T-i); transitions between metastable states; phases (T-i). It was set that phase transition between parent and incommensurate phase is a continuous second-order phase transition with a critical index beta = 0.5. The transition between metastable states is, a continuous phase transition through the intermediate temperature region - incommensurate phase. The wave vector changes with the temperature here and wave vector q* = q(1) - q(2) appears, where q(1), q(2) denote commensurate values of incommensurabilty wave vector of neighboring metastable states. It, was shown that the phase transition between incommensurate and commensurate phases is a continuous phase transition.

Update: 24-Oct-2008

Title:
Synthesis and crystal structure of commensurate polymorph of Ln(4)AlCu(2)B(9)O(23) (Ln=Lu,Ho) and refinement of Cu2Al6B4O17
Authors:
Plachinda, PA; Belokoneva, EL Author Full Names: Plachinda, P. A.; Belokoneva, E. L.
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE 634 (11): 1965-1970 2008
Abstract:
Single crystals of new Cu,Lu(Ho) - alumoborate and known Cu,Al-borate were synthesized through reaction between CuB2O4 and LnBO(3) on the Al2O3 surface by annealing at 1100 degrees C. Structure of commensurate modification of Ln(4)AlCu(2)B(9)O(23), (Ln = Lu,Ho), sp. gr. P (4) over bar2(1)m, was solved at room temperature. It was found that a low-temperature (110 K) modification possesses incommensurate modulations with modulation vector q =(0, 0, 0.132). The nonaborate block - [B9O23](19-)- 9[6T+3 Delta] forms an isolated unique dense closed anionic unit. This block is terminated by Al-tetrahedrons in the chessboard pattern, resulting in formation of complex alumoborate layer [AlB9O23](16-). Apical oxygen of central BO3 triangle of the nonaborate block seems to be the source of modulations observed in low temperature polymorph. Cationic layers with the Ln and Cu atoms are alternating along c axis with anionic layers. The structure Cu2Al6B4O17, previously studied by the Rietveld method, was corroborated by single crystal data and was compared with LiAl7B4O17.
Title:
Field-induced discommensuration in charge density waves in o-TaS3
Authors:
Inagaki, K; Tsubota, M; Higashiyama, K; Ichimura, K; Tanda, S; Yamamoto, K; Hanasaki, N; Ikeda, N; Nogami, Y; Ito, T; Toyokawa, H Author Full Names: Inagaki, Katsuhiko; Tsubota, Masakatsu
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (9): Art. No. 093708 SEP 2008
Abstract:
We report a synchrotron X-ray Study of charge density waves (CDWs) in an o-TaS3 crystal. We found that two independent CDWs coexist ill the temperature range of 130-50K. These waves are incommensurate and commensurate CDWs with longitudinal wave vectors q(c) = 0.252c* and 0.250c*, respectively. The temperature and electric current dependences of the intensity of the two CDW satellites were measured. We found that the commensurate CDW was converted to the incommensurate CDW at 80 K by inducing current flow. Our observation was interpreted in terms of the dynamics of topological defects. We determined the edge dislocation configuration from the electric Current dependence of the intensity of the two CDWs. The result implies Cor the first time that discommensurations are induced ill the commensurate CDW by applying an electric field.
Title:
Effect of quenched disorder on charge ordering structure in RE(1.67)AE(0.33)NiO(4) (RE = La, Pr, Nd, Sm; AE = Ca, Sr)
Authors:
Yu, XZ; Arima, TH; Seki, S; Asaka, T; Kimoto, K; Tokura, Y; Matsui, Y Author Full Names: Yu, Xiuzhen; Arima, Taka-hisa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (9): Art. No. 093709 SEP 2008
Abstract:
The structure feature of charge ordering (CO) has been investigated for the layered nickelates RE(1.67)AE(0.33)NiO(4) by transmission electron microscopy (TEM). A long-range commensurate CO is observed along the b-axis in Pr1.67Ca0.33NiO4 with minimal quenched disorder, while only a short-range incommensurate CO is observed in Sm1.67Sr0.33NiO4 with larger disorder. Increasing the quenched disorder, hence the number of stacking faults, leads, to an abrupt decrease in CO correlation length, indicating that the quenched disorder plays an important role in the CO collapse process.
Title:
Discovery of polarization flop transition and simultaneous measurements of magnetic ordering and dielectric properties of TmMn2O5
Authors:
Fukunaga, M; Nishihata, K; Kimura, H; Noda, Y; Kohn, K Author Full Names: Fukunaga, Mamoru; Nishihata, Keisuke
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (9): Art. No. 094711 SEP 2008
Abstract:
We have performed simultaneous measurements of magnetic neutron diffraction, ferroelectric D-E hysteresis loops and permittivity along the b- and a-axes of multiferroic TmMn(2)O(5)down to 2.5 K. It was confirmed that the permittivity peak coincides with an increase in both the polarization along the b-axis and a magnetic commensurate phase, which agrees with a previous similar experiment on ErMn2O5. We also discovered it polarization flop from the b-axis to the a-axis below 5 K coincident with a magnetic phase transition from one incommensurate phase to another incommensurate phase, which was confirmed by the simultaneous measurements. Although both phases are almost equivalent in the magnetic propagation wave vector, different magnetic structures induce it completely different ferroelectricity. Ferroelectric hysteresis loops along both the b- and a-axes were clearly observed by the double-wave method.
Title:
Full-field strain evolution during intermartensitic transformations in single-crystal NiFeGa
Authors:
Efstathiou, C; Sehitoglu, H; Carroll, J; Lambros, J; Maier, HJ Author Full Names: Efstathiou, C.; Sehitoglu, H.
Source:
ACTA MATERIALIA 56 (15): 3791-3799 SEP 2008
Abstract:
Using in situ digital image correlation to obtain full-field measurements, we study the intermartensitic transformations in single-crystal NiFeGa. Full-field strain measurements identify the coexistence of modulated martensite phases during the first plateau of the multistage stress-strain Curve at room temperature. At a higher temperature, the measurements indicate the bypassing of one of the modulated phases. Strain as high as 13% is measured as a result of the transformation to the intermediate monoclinic modulated and final tetragonal phase. Based on the full-field strain measurements, the phase fractions during the nucleation and the progression of the transformation are obtained. The evolution of the local strain and the phase fractions prove critical in explaining strain softening, hysteresis and other phenomena observed in the stress-strain curves. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Orientational ordering in the low-temperature stable phases of deuterated thiophene
Authors:
Damay, F; Rodriguez-Carvajal, J; Andre, D; Dunstetter, F; Szwarc, H Author Full Names: Damay, F.; Rodriguez-Carvajal, J.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 589-595 Part 5 OCT 2008
Abstract:
The stable structures of deuterated thiophene C4D4S were investigated at 155 (phase III), 115 (phase IV), 100 and 1.5 K (phase V) by neutron powder diffraction. At 155 K, thiophene is orthorhombic with space group Pbnm. Although there is some degree of in-plane orientational disorder, molecules begin to order along two symmetrically equivalent main orientations. At 115 K the structure is incommensurate, with a wavevector q similar or equal to 0.55a*. At 100 K and below, there is a doubling of the a cell parameter and the structure space group is P2(1). For the first time, it is shown that, unlike C4H4S, phase V of C4D4S is not an orientational glass: thiophene molecules are perfectly ordered and are oriented within the molecular plane along two alternating directions, corresponding to the two main orientations observed at 155 K. This ordering probably originates in the slowing down of the in-plane reorientational dynamics upon deuteration.

Update: 17-Oct-2008

Title:
Structural and magnetic properties of the ferroelectric magnet BaMn1-xZnxF4, a site diluted square-lattice two-dimensional Heisenberg antiferromagnet with S=5/2
Authors:
Veira, JR; Argyriou, DN; Kiefer, K; Wolter, AUB; Alber, D; Meissner, M; Almairac, R; Reehuis, M; Bordallo, HN Author Full Names: Veira, J. R.; Argyriou, D. N.; Kiefer, K.; Wolter, A. U. B.; Alber, D.; Meissner, M.; Almairac, R.; Reehuis, M.; Bordallo, H. N.
Source:
PHYSICAL REVIEW B 78 (5): Art. No. 054104 AUG 2008
Abstract:
The influence of Zn doping on the structural and magnetic properties of multiferroic BaMnF4 has been investigated using temperature dependent x-ray diffraction and magnetization measurements. With increasing Zn content the transition temperatures of the structural incommensurate phase transition as well as the AF ordering decrease. For x=0.75 no incommensurate phase is found anymore. The suppression of the structural transition can be explained due to the smaller size of Zn compared with Mn. The suppression of the antiferromagnetic ordering can be explained by a site dilution of the magnetic structure with nonmagnetic Zn. The percolation threshold is found to be x(p)=0.393(4). This is in agreement with predictions for a site-diluted square-lattice weak-anisotropy two-dimensional Heisenberg antiferromagnet with S = 5/2.
Title:
Origin of incommensurate modulations in the high-pressure phosphorus IV phase
Authors:
Marques, M; Ackland, GJ; Lundegaard, LF; Falconi, S; Hejny, C; McMahon, MI; Contreras-Garcia, J; Hanfland, M Author Full Names: Marques, M.; Ackland, G. J.; Lundegaard, L. F.; Falconi, S.; Hejny, C.; McMahon, M. I.; Contreras-Garcia, J.; Hanfland, M.
Source:
PHYSICAL REVIEW B 78 (5): Art. No. 054120 AUG 2008
Abstract:
We present results from x-ray diffraction experiments and density functional theory calculations which provide a fully consistent picture of the high-pressure phosphorus-IV phase (P-IV). P-IV has an incommensurately-modulated crystal structure described by the four-dimensional superspace group Cmmm(00 gamma)s00. Electronic structure calculations using a three-dimensional commensurate approximant to this structure give excellent agreement with experiment for the structural parameters and their variation with pressure. Density functional perturbation theory shows a phonon instability at the incommensurate wave vector, related to the opening of a pseudogap at the Fermi surface, showing that the atomic motions comprising the incommensuration occur to eliminate Fermi-surface nesting. Unusually, the pseudogap opens not at the incommensurate wave vector (00 gamma) itself, but at two larger wave vectors corresponding to strong reflections in the diffraction pattern.
Title:
Nucleation and growth of a quasicrystalline monolayer: Bi adsorption on the fivefold surface of i-Al70Pd21Mn9
Authors:
Smerdon, JA; Parle, JK; Wearing, LH; Lograsso, TA; Ross, AR; McGrath, R Author Full Names: Smerdon, J. A.; Parle, J. K.; Wearing, L. H.; Lograsso, T. A.; Ross, A. R.; McGrath, R.
Source:
PHYSICAL REVIEW B 78 (7): Art. No. 075407 AUG 2008
Abstract:
Scanning tunneling microscopy has been used to study the formation of a Bi monolayer deposited on the fivefold surface of i-Al70Pd21Mn9. Upon deposition of low submonolayer coverages, the nucleation of pentagonal clusters of Bi adatoms of edge length 4.9 angstrom is observed. The clusters have a, common orientation leading to a film with fivefold symmetry. By inspection of images where both the underlying surface and the Bi atoms are resolved, the pentagonal clusters are proposed to nucleate on pseudo-Mackay clusters truncated such that a Mn atom lies centrally in the surface plane. The density of these sites is sufficient to form a quasiperiodic framework, and subsequent adsorption of Bi atoms ultimately leads to the formation of a quasicrystalline monolayer. The suggested nucleation site is different from that proposed on the basis of recent density-functional theory calculations.
Title:
Neutron powder diffraction study of the magnetic and crystal structures of SrFe2(PO4)(2)
Authors:
Belik, AA; Huang, QZ; Takayama-Muromacchi, E; Lynn, JW Author Full Names: Belik, Alexei A.; Huang, Qingzhen; Takayama-Muromacchi, Eiji; Lynn, Jeffrey W.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 181 (9): 2292-2297 SEP 2008
Abstract:
The crystal and magnetic structures of SrFe22+(PO4)(2) have been determined by neutron powder diffraction data at low temperatures (space group P2(1)/c (no. 14); Z=4: a=9.35417(13)angstrom, b = 6.83808(10) angstrom, c = 10.51899(15) angstrom, and beta = 109.5147(7)degrees at 15 K). Two magnetic phase transitions were found at T-1 = 7.4 K (first-order phase transition) and T-2 = 11.4 K (second-order phase transition). The transition at T2 was hardly detectable by dc and ac magnetization measurements, and a small anomaly was observed by specific heat measurements. At T1, strong anomalies were found by dc and ac magnetization and specific heat. The structure of SrFe2(PO4)(2) consists of linear four-spin cluster units, Fe2-Fe1-Fe1-Fe2. Below T-1, the propagation vector of the magnetic structure is k [0,0,0]. The magnetic moments of the inner Fe1-Fe1 atoms of the four-spin cluster unit are ferromagnetically coupled. The magnetic moment of the outer Fe2 atom is also ferromagnetically Coupled with that of the Fe1 atom but with spin canting. The four-spin cluster units form ferromagnetic layers parallel to the [-101] plane, while these layers are stacked antiferromagnetically in the [-101] direction. Spill canting of the Outer Fe2 atoms provides a weak ferromagnetic moment of about 1 (mu B) along the b-axis. The refined magnetic moments at 3.5 K are 4.09 (mu B) for Fe1 and 4.07 (mu B) for Fe2. Between T-1 and T-2, a few weak magnetic reflections were observed probably due to incommensurate magnetic order. (C)2008 Elsevier Inc. All rights reserved.

Update: 10-Oct-2008

Title:
Devitrification of mechanically alloyed Zr-Ti-Nb-Cu-Ni-Al glassy powders studied by time-resolved X-ray diffraction
Authors:
Scudino, S; Sordelet, DJ; Eckert, J Author Full Names: Scudino, S.; Sordelet, D. J.; Eckert, J.
Source:
REVIEWS ON ADVANCED MATERIALS SCIENCE 18 (3): 221-224 AUG 2008
Abstract:
The crystallization of mechanically alloyed Zr67Ti6.14Nb1.92Cu10.67Ni8.52Al5.75 glassy powder is investigated by time-resolved X-ray diffraction. The powder displays a multi-step crystallization behavior characterized by the formation of a metastable nanoscale quasicrystalline phase during the first stage of the crystallization process. At higher temperatures, coinciding with the second crystallization event, the amorphous-to-quasicrystalline transformation is followed by the precipitation of the tetragonal Zr2Cu phase (space group 14/mmm) and the tetragonal Zr2Ni phase (space group 14/mcm). The transformations are gradual and the quasicrystals and the subsequent phases coexist over a temperature interval of about 25K.
Title:
Manipulating the magnetic structure of Co Core/CoO shell nanoparticles: Implications for controlling the exchange bias
Authors:
Inderhees, SE; Borchers, JA; Green, KS; Kim, MS; Sun, K; Strycker, GL; Aronson, MC Author Full Names: Inderhees, S. E.; Borchers, J. A.; Green, K. S.; Kim, M. S.; Sun, K.; Strycker, G. L.; Aronson, M. C.
Source:
PHYSICAL REVIEW LETTERS 101 (11): Art. No. 117202 SEP 12 2008
Abstract:
We present an experimental study of the effects of oxidation on the magnetic and crystal structures of exchange biased epsilon-Co/CoO core-shell nanoparticles. Transmission electron microscopy measurements reveal that oxidation creates a Co-CoO interface which is highly directional and epitaxial in quality. Neutron diffraction measurements find that below a Neel temperature T-N of similar to 235 K the magnetization of the CoO shell is modulated by two wave vectors, q(1)= (1/2 1/2 1/2)2 pi/alpha and q(2) = (100)2 pi/alpha. Oxidation affects the q(1) component of the magnetization very little, but hugely enhances the q(2) component, resulting in the magnetic decompensation of the core-shell interface. We propose that the large exchange bias effect results from the highly ordered interface between the Co core and CoO shell, and from enhanced core-shell coupling by the uncompensated interface moment.
Title:
Nature of the magnetic order in Ca3Co2O6
Authors:
Agrestini, S; Chapon, LC; Daoud-Aladine, A; Schefer, J; Gukasov, A; Mazzoli, C; Lees, MR; Petrenko, OA Author Full Names: Agrestini, S.; Chapon, L. C.; Daoud-Aladine, A.; Schefer, J.; Gukasov, A.; Mazzoli, C.; Lees, M. R.; Petrenko, O. A.
Source:
PHYSICAL REVIEW LETTERS 101 (9): Art. No. 097207 AUG 29 2008
Abstract:
We present a detailed powder and single-crystal neutron diffraction study of the spin chain compound Ca3Co2O6. Below 25 K, the system orders magnetically with a modulated partially disordered antiferromagnetic structure. We give a description of the magnetic interactions in the system which is consistent with this magnetic structure. Our study also reveals that the long-range magnetic order coexists with a shorter-range order with a correlation length scale of similar to 180 angstrom in the ab plane. Remarkably, on cooling, the volume of material exhibiting short-range order increases at the expense of the long-range order.
Title:
Frustration-induced quantum phases in mixed spin chain with frustrated side chains
Authors:
Hida, K; Takano, K Author Full Names: Hida, Kazuo; Takano, Ken'ichi
Source:
PHYSICAL REVIEW B 78 (6): Art. No. 064407 AUG 2008
Abstract:
A mixed Heisenberg spin chain with frustrated side chains is investigated by numerical and perturbational calculations. A frustration-induced quantum partially polarized ferrimagnetic phase and a nonmagnetic spin quadrupolar phase are found adjacent to the conventional Lieb-Mattis-type ferrimagnetic phase or the nonmagnetic singlet cluster solid phases. The partially polarized ferrimagnetic phase has an incommensurate spin structure. Similar structures are commonly found in other frustration-induced partially polarized ferrimagnetic phases. Numerical results also suggest a series of almost critical nonmagnetic ground states in a highly frustrated regime if the side chain spins weakly couple to the main chain.
Title:
Noncollinear magnetism in the high-pressure hcp phase of iron
Authors:
Lizarraga, R; Nordstrom, L; Eriksson, O; Wills, J Author Full Names: Lizarraga, Raquel; Nordstroem, Lars; Eriksson, Olle; Wills, John
Source:
PHYSICAL REVIEW B 78 (6): Art. No. 064410 AUG 2008
Abstract:
The magnetic structure of iron in its high-pressure hcp phase has been investigated with the full-potential augmented plane wave with local orbitals method that allows for noncollinear magnetism. In our study we consider different spin spiral structures and, three antiferromagnetic configurations that have been previously discussed in the literature. We found that some of the magnetic structures are only metastable, and that a nonsymmetric incommensurate spin spiral state with wave vector q = (0.56, 0.22, 0)2 pi/a and two different antiferromagnetic structures are the most stable ones being almost degenerate around the equilibrium volume. These magnetic structures ought to exist in the pressure range where hcp iron becomes stable.
Title:
Soft x-ray induced Ag diffusion in amorphous pulse laser deposited As50Se50 thin films: An x-ray photoelectron and secondary ion mass spectroscopy study
Authors:
Kalyva, M; Siokou, A; Yannopoulos, SN; Wagner, T; Krbal; Orava, J; Frumar, M Author Full Names: Kalyva, M.; Siokou, A.; Yannopoulos, S. N.; Wagner, T.; Krbal; Orava, J.; Frumar, M.
Source:
JOURNAL OF APPLIED PHYSICS 104 (4): Art. No. 043704 AUG 15 2008
Abstract:
In the present paper, x-ray photoelectron spectroscopy (XPS) is used to induce and study the Ag diffusion and dissolution in pulsed laser deposited As50Se50 amorphous chalcogenide films. Dynamic secondary ion mass spectroscopy (SIMS) is also employed to investigate the Ag atomic concentration in depth. Dynamic SIMS measurements reveal that even before x-ray irradiation a considerable percentage of the total silver amount diffuses into the matrix forming an similar to 70 nm mixed Ag-Se-As layer. XPS analysis shows that x-ray irradiation induces further diffusion of silver into the chalcogenide matrix. At the end of the procedure silver is found to be homogeneously dissolved into the matrix leaving only a 5-7 nm thick surface layer with excess silver concentration. In this surface layer stable Ag2Se clusters existing probably in quasicrystalline form prohibit further diffusion. The origin of the mechanism of the x-ray induced Ag diffusion and dissolution in amorphous chalcogenides is discussed in light of the present results. (c) 2008 American Institute of Physics.
Title:
Disordered structures of the TM-Mg-Zn 1/1 quasicrystal approximants (TM = Hf, Zr, or Ti) and chemical intergrowth
Authors:
Gomez, CP; Ohhashi, S; Yamamoto, A; Tsai, AP Author Full Names: Gomez, Cesar Pay; Ohhashi, Satoshi; Yamamoto, Akiji; Tsai, An Pang
Source:
INORGANIC CHEMISTRY 47 (18): 8258-8266 SEP 15 2008
Abstract:
The structures of three quasicrystal approximant phases in the TM-Mg-Zn (TM = Hf, Zr, Ti) systems with the analyzed compositions Hf5Mg18Zn77, Zr5Mg18Zn77, and Ti5.5Mg17.5Zn77 have been synthesized, and their structures have been analyzed by single-crystal X-ray diffraction. The structure analyses revealed that these cubic phases with the space group Pm contain two different rhombic-triacontahedral clusters. These clusters are so-called Bergman-type atomic clusters and previously known approximants of face-centered icosahedral (F-type) quasicrystals are composed only of Mackay-type clusters, thus these compounds are seen as new prototype structures. Electron density maps calculated by the maximum entropy method (MEM) show that one of the atomic clusters displays characteristic structural disorder. The disorder in these phases is related to the chemical intergrowth of different Friauf polyhedra, and the prospects of new guide lines for finding quasicrystals composed of such polyhedra are discussed.

Update: 3-Oct-2008

Title:
Structure and microstructure of the high pressure synthesised misfit layer compound [Sr2O2][CrO2](1.85)
Authors:
Castillo-Martinez, E; Schonleber, A; van Smaalen, S; Arevalo-Lopez, AM; Alario-Franco, MA Author Full Names: Castillo-Martinez, E.; Schoenleber, A.; van Smaalen, S.; Arevalo-Lopez, A. M.; Alario-Franco, M. A.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 181 (8): 1840-1847 AUG 2008
Abstract:
The strontium chromium oxide [Sr2O2][CrO2](1.85) misfit layer compound has been synthesised at high-pressure and high-temperature conditions. Electron diffraction patterns and high-resolution transmission electron microscopy images along [001] show the misfit character of the different layers composing the structure with a supercell along the incommensurate parameter b approximate to 7b(1)approximate to 13b(2). The modulated crystal structure has been refined within the superspace formalism against single-crystal X-ray diffraction data, employing the (3+1)-dimensional superspace group C'nrnb(0 sigma(2)0)0 0s. The compound has a composite structure with lattice parameters a(1) =5.182(1)angstrom, b(1) = 5.471(1)angstrom, c(1) = 18.194(3)angstrom for the first, SrO, subsystem and the same a and c, but with 152 = 2.925(1) angstrom for the second, CrO2, subsystem. The layer stacking is similar to that of orthorhombic PbS(TiS2)(1.18), but with a much stronger intersubsytem bonding in the case of the oxide. The intersubsystem lattice mismatch is mainly handled by displacement modulations of the Sr atoms, correlated with modulations of the valence, the coordination and the anisotropic displacement parameters. (C) 2008 Elsevier Inc. All rights reserved.
Title:
Single-crystal NMR for the layered semiconductor TlGaSe2
Authors:
Panich, AM; Kashida, S Author Full Names: Panich, A. M.; Kashida, S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (39): Art. No. 395211 OCT 1 2008
Abstract:
We report on a Ga-69 and Tl-205 NMR study of single-crystal thallium gallium selenide. Our findings show that transformation from the high temperature paraelectric phase to the low temperature ferroelectric phase occurs via an incommensurate phase that exists in the temperature range from T-c = 107.5 to T-i = 118 K. On approaching phase transition at Ti from above, the crystal exhibits soft mode behavior, which is somewhat different for thallium and gallium substructures. Redistribution of Ga-69 line intensities with temperature in the ferroelectric phase indicates a variation of the domain structure of this phase.

Update: 26-Sep-2008

Title:
Microstructure of Al-Mn-Be melt-spun ribbons
Authors:
Zupanic, F; Boncina, T; Sustarsic, B; Anzel, I; Markoli, B Author Full Names: Zupanic, Franc; Boncina, Tonica; Sustarsic, Borivoj; Anzel, Ivan; Markoli, Bostjan
Source:
MATERIALS CHARACTERIZATION 59 (9): 1245-1251 SEP 2008
Abstract:
Microstructures of two alloys with the nominal compositions of Al92Mn3Be5 and Al89Mn6Be5 were characterized in the initial as-cast condition (after vacuum induction melting and casting) and after melt spinning. In the initial conditions, both alloys consisted of an aluminum-rich solid solution and two metastable intermetallic phases: Be4AlMn and Al10Mn3(Be). Both alloys melted over a rather large temperature range (between 230 degrees C and 310 degrees C). This was the main reason for the presence of unmelted particles in the melt-spun ribbons. Nonetheless, with the use of optimized melt-spinning parameters a microstructure composed of the Al-rich solid solution and finely dispersed quasicrystalline particles in ribbons with thicknesses ranging from 30-200 mu m was achieved. The dispersion of quasicrystalline particles was finest on the wheel side of the thinnest ribbons, attaining microhardness values between 250 HV and 300 HV. (C) 2007 Elsevier Inc. All rights reserved.

Update: 19-Sep-2008

Title:
Synthesis and characterization of GaP nanochains with a twin-modulated quasi-periodic structure
Authors:
Liu, YK; Shan, YY; Wang, HB; Lee, CS; Lee, ST Author Full Names: Liu, Y. K.; Shan, Y. Y.; Wang, H. B.; Lee, Chun-Shen; Lee, Shu-Tong
Source:
SUPERLATTICES AND MICROSTRUCTURES 44 (2): 208-215 AUG 2008
Abstract:
GaP nanochains have been synthesized by hydrogen-assisted thermal evaporation, and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), and Raman spectroscopy. GaP nanochains possess a (111) twin crystal plane-modulated quasi-periodic structure, that gives a strong green photoluminescence at 618 nm. While the Raman spectrum of the nanochains is similar to that of the GaP crystal, the intensity of the longitudinal optical (LO) peak is stronger than that of the transverse optical (TO) peak, which is supposedly related to the nanochain microstructures. (C) 2008 Published by Elsevier Ltd.
Title:
Interaction between the chain and ladder subsystems in (Ca, Sr, La)(14)Cu24O41 compounds
Authors:
Schwingenschlogl, U; Schuster, C Author Full Names: Schwingenschloegl, U.; Schuster, C.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (38): Art. No. 382201 SEP 24 2008
Abstract:
We investigate the influence of structural modulations on the electronic properties of incommensurate (Ca, Sr, La)(14)Cu24O41 compounds by band structure calculations based on density functional theory and the local density approximation (LDA). Using a supercell approach with ten CuO2 chain and seven Cu2O3 ladder segments, we take into account the major effects of the structural incommensurability. We find that the LDA electronic states show very little response to these modulations. The coupling between the electronic and structural degrees of freedom, hence, can be well described in terms of two independent subsystems. The incommensurate charge density waves (CDWs) in the chains and the ladders are formed independently of each other.
Title:
Directional growth and characterizations of orthorhombic HoMnO3 films
Authors:
Lin, JG; Han, TC; Wu, CT; Chu, MW; Chen, CH Author Full Names: Lin, J. G.; Han, T. C.; Wu, C. T.; Chu, M. -W.; Chen, C. H.
Source:
JOURNAL OF CRYSTAL GROWTH 310 (16): 3878-3880 AUG 1 2008
Abstract:
In this work, we synthesize the orthorhombic HoMnO3 films on the SrTiO3(1 0 0) and LaAlO3(1 1 0) substrates by pulsed laser deposition and study their crystalline and magnetic properties. The orthorhombic HoMnO3 film with its b-axis perpendicular to the film surface is grown on the LaAlO3(1 1 0) substrate, and shows clearly three magnetic transitions at 45, 10 and 7K, which are attributed to the magnetization process of incommensurate spin structure of Mn3+ for 10K
Title:
Evolution of a nanocrystalline (Co,Ni)Al2O4 spinel phase from quasicrystalline precursor
Authors:
Yadav, TP; Tiwari, RS; Srivastava, ON; Mukhopadhyay, NK Author Full Names: Yadav, Thakur Prasad; Tiwari, Radhey Shyam; Srivastava, Onkar Nath; Mukhopadhyay, Nilay Krishna
Source:
INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY 5 (5): 449-457 2008
Abstract:
This work reports on the synthesis of a spinel phase from a thermodynamically stable decagonal quasicrystalline Al70Co15Ni15 alloy. The Al70Co15Ni15 alloy, synthesized through slow cooling of the molten alloy, was subjected to milling in an attritor ball mill at 400 rpm for 5, 10, 20, 30, and 40 h with a ball to powder ratio of 20:1 in the hexane medium. The differential thermal analysis, X-ray diffraction, scanning, and transmission electron microscopy techniques have been used for characterization of milled as well as annealed powders. The Voigt function analysis has been used for calculation of the effective crystallite size and relative strain of ball-milled samples. The crystallite size has been found to be similar to 14 nm after 40 h of milling along with a lattice strain of 8.1%. The annealing experiments have been carried out under two different conditions: (i) in vacuum and (ii) in air. The results of the present investigation clearly revealed that the nano-decagonal phase was stable in vacuum while annealing at 600 degrees C for 40 h. However, during annealing under a similar condition in air, the formation of a nanospinel of (Ni,Co)Al2O4 of size similar to 60 nm was identified. The possible structural evolution of the spinel from the quasicrystalline phase has been discussed.

Update: 12-Sep-2008

Title:
Temperature behavior of magnetic susceptibility and paramagnetism of the conduction electrons of an icosahedral quasicrystal Al63Cu25Fe12
Authors:
Prekul, AF; Shchegolikhina, NI; Shalaeva, EV Author Full Names: Prekul, A. F.; Shchegolikhina, N. I.; Shalaeva, E. V.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 106 (2): 157-163 AUG 2008
Abstract:
Problem of the origin of the enhanced paramagnetism of icosahedral phases below room temperature is studied experimentally. Temperature dependences of the magnetic susceptibility (chi(T)), Hall constant (R-H(T)), and conductivity (chi(T)) of the i phase of a nominal composition of Al63Cu25Fe12 are studied at temperatures of 4.2-400 K in magnetic fields of to 5 T. Temperature-dependent components of these quantities, namely, sigma (t) , chi(t) , and R-t were separated. The temperature-dependent component of the magnetic susceptibility chi(t) is approximately proportional to T-2. The number of thermally-induced charge carries n (t) and the ratio chi(t)/n (t) are approximately proportional to T-3 and T-1, respectively. Thus, we found two distinctive criteria indicating that temperature-induced changes in the conduction-electron paramagnetism play a substantial role in the magnetic properties of icosahedral phases at low temperatures. Earlier, these changes were considered to be substantial only at temperatures above the Debye temperature.
Title:
Local density of states of one-dimensional Mott insulators and charge-density wave states with a boundary
Authors:
Schuricht, D; Essler, FHL; Jaefari, A; Fradkin, E Author Full Names: Schuricht, Dirk; Essler, Fabian H. L.; Jaefari, Akbar; Fradkin, Eduardo
Source:
PHYSICAL REVIEW LETTERS 101 (8): Art. No. 086403 AUG 22 2008
Abstract:
We determine the local density of states of one-dimensional incommensurate charge-density wave states in the presence of a strong impurity potential, which is modeled by a boundary. We find that the charge-density wave gets pinned at the impurity, which results in a singularity in the Fourier transform of the local density of states at momentum 2k(F). At energies above the spin gap we observe dispersing features associated with the spin and charge degrees of freedom, respectively. In the presence of an impurity magnetic field we observe the formation of a bound state localized at the impurity. All of our results carry over to the case of 1D Mott insulators by exchanging the roles of spin and charge degrees of freedom. We discuss the implications of our result for scanning tunneling microscopy experiments on spin-gap systems such as two-leg ladder cuprates.
Title:
On the nature and stability of phases present in a rapidly solidified aluminium alloy 7010 containing scandium
Authors:
Prasad, KS; Mukhopadhyay, AK; Majumdar, B; Akhtar, D Author Full Names: Prasad, K. S.; Mukhopadhyay, A. K.; Majumdar, B.; Akhtar, D.
Source:
MATERIALS AND MANUFACTURING PROCESSES 23 (7): 658-664 2008
Abstract:
The influence of Sc on the nature and stability of phases present in rapidly solidified (RS) Al alloy 7010 (hereafter termed base alloy) produced by melt spinning were examined and compared with the phases present in the same alloys when produced by the conventional ingot metallurgical (IM) route. Transmission electron microscopy (TEM) revealed that the second phases present in the IM alloys have an HCP structure but with varying lattice parameters. On the other hand, the second phase particles present in the base alloy when produced by rapid solidification (RS) route always have a quasi-crystalline, icosahedral structure. In the rapidly solidified 7010+Sc alloy, however, the icosahedral phase is located only at the grain boundary triple point junctions, and the grain interfaces are populated by the second phase particles having an HCP structure. An analysis of the chemistry of the second phase particles revealed that the icosahedral phase is stabilized by certain minimum concentrations of Zn+Mg/Zn+Mg+Cu. The reason for the absence of the icosahedral phase at the grain interfaces of the rapidly solidified 7010+Sc alloy is the partitioning of relatively lower concentrations of the major alloying elements into the second phases formed at those sites. Micro-hardness measurements revealed higher hardness values for the RS 7010+Sc alloy in both as-melt spun as well as artificially aged conditions. These results are correlated with the microstructures developed in these materials.
Title:
Approximant phases and an icosahedral quasicrystal in the Ca-Au-Ga system: The influence of size of gallium versus indium
Authors:
Lin, QS; Corbett, JD Author Full Names: Lin, Qisheng; Corbett, John D.
Source:
INORGANIC CHEMISTRY 47 (17): 7651-7659 SEP 1 2008
Abstract:
Two crystalline approximants (ACs) and their corresponding icosahedral quasicrystal (i-QC) are obtained in the Ca-Au-Ga system through conventional solid-state exploratory syntheses. Single crystal structural analyses reveal that the 1/1 AC, Ca3AuxGa19-x (x = similar to 9.3-12.1) [Im3, a = 14.6941(6)-14.7594(6) angstrom], has the empty cubes in the prototypic YCd6 (= Y3Cd18) now fully occupied by Ga, resulting in a 3:19 stoichiometry. In parallel, the distorted cubes in the 2/1 AC, Ca13Au57.1Ga23.4 [Pa3, a = 23.9377(8) angstrom] are fully or fractionally occupied by Ga. The valence electron count per atom (e/a) for the 2/1 AC (1.64) is smaller than that over the 1/1 AC composition range (1.76-2.02), and the e/a of the Ca15.2Au50.3Ga34.5 i-QC, 1.84, is somewhat distant from typical values for Tsai-type i-QCs (similar to 2.0). Comparisons of the gallium results with the corresponding In phases suggest that the structural differences result mainly from size rather than electronic factors. The 1/1 and 2/1 appear to be thermodynamically stable on slow cooling, as usual, whereas the i-QC isolated by quenching decomposes on heating at similar to 660 degrees C, mainly into 2/1 AC and Ca-3(Au,Ga)(11). Calculations of the electronic structure of 1/1 AC suggest that the Fermi sphere-Brillouin zone interactions remain important for the Ca-Au-Ga i-QC.

Update: 5-Sep-2008

Title:
Incommensurate spin-density modulation in a copper oxide chain compound with commensurate charge order
Authors:
Raichle, M; Reehuis, M; Andre, G; Capogna, L; Sofin, M; Jansen, M; Keimer, B Author Full Names: Raichle, M.; Reehuis, M.; Andre, G.; Capogna, L.; Sofin, M.; Jansen, M.; Keimer, B.
Source:
PHYSICAL REVIEW LETTERS 101 (4): Art. No. 047202 JUL 25 2008
Abstract:
Neutron diffraction has been used to determine the magnetic structure of Na8Cu5O10, a stoichiometric compound containing chains based on edge-sharing CuO4 plaquettes. The chains are doped with 2/5 hole per Cu site and exhibit long-range commensurate charge order with an onset well above room temperature. Below T-N = 23 K, the neutron data indicate long-range collinear magnetic order with a spin-density modulation whose propagation vector is commensurate along, and incommensurate perpendicular to, the chains. Competing interchain exchange interactions are discussed as a possible origin of the incommensurate magnetic order.
Title:
Magnetic ground state and transition of a quantum multiferroic LiCu2O2
Authors:
Huang, SW; Huang, DJ; Okamoto, J; Mou, CY; Wu, WB; Yeh, KW; Chen, CL; Wu, MK; Hsu, HC; Chou, FC; Chen, CT Author Full Names: Huang, S. W.; Huang, D. J.; Okamoto, J.; Mou, C. Y.; Wu, W. B.; Yeh, K. W.; Chen, C. L.; Wu, M. K.; Hsu, H. C.; Chou, F. C.; Chen, C. T.
Source:
PHYSICAL REVIEW LETTERS 101 (7): Art. No. 077205 AUG 15 2008
Abstract:
Based on resonant soft x-ray magnetic scattering, we report that LiCu2O2 exhibits a large interchain coupling which suppresses quantum fluctuations along spin chains, and a quasi-2D short-range magnetic order prevails at temperatures above the magnetic transition. These observations unravel the fact that the ground state of LiCu2O2 possesses long-range 2D-like incommensurate magnetic order rather than being a gapped spin liquid as expected from the nature of quantum spin-1/2 chains. In addition, the spin coupling along the c axis is found to be essential for inducing electric polarization.
Title:
The synthesis and characterization of new [(BiSe)(1.10)](m)[NbSe2](n), [(PbSe)(1.10)](m)[NbSe2](n), [(CeSe)(1.14)](m)[NbSe2](n) and [(PbSe)(1.12)](m)[TaSe2](n) misfit layered compounds
Authors:
Heideman, C; Nyugen, N; Hanni, J; Lin, Q; Duncombe, S; Johnson, DC; Zschack, P Author Full Names: Heideman, Colby; Nyugen, Ngoc; Hanni, Jonathan; Lin, Qiyin; Duncombe, Scott; Johnson, David C.; Zschack, Paul
Source:
JOURNAL OF SOLID STATE CHEMISTRY 181 (7): 1701-1706 JUL 2008
Abstract:
Fifty-three new misfit layered compounds within the [(BiSe)(1.10)](m)[NbSe2](n), [(PbSe)(1.10)](m)[NbSe2](n), [(CeSe)(1.14)](m)[NbSe2](n) and [(PbSe)(1.12)](m)[TaSe2](n) families of compounds were successfully synthesized. This is the first report of compounds with n and m larger than 3, as self-assembly from designed precursors allows Compounds with particular n and m values to be selectively prepared. The compounds form as crystallographically aligned films, with the c-axis perpendicular to the Substrate, The Compounds are well ordered along the c-axis and in the ab plane, with shorter coherence lengths between the constituent layers. All 18 compounds that were measured were found to be metallic. (C) 2008 Elsevier Inc. All rights reserved.
Title:
The role of nanoquasicrystals on the ductility enhancement of as-extruded Mg-Zn-Gd alloy at elevated temperature
Authors:
Liu, Y; Yuan, GY; Lu, C; Ding, WJ; Jiang, JZ Author Full Names: Liu, Yong; Yuan, Guangyin; Lu, Chen; Ding, Wenjiang; Jiang, Jiangzhong
Source:
JOURNAL OF MATERIALS SCIENCE 43 (16): 5527-5533 AUG 2008
Abstract:
The microstructure and mechanical properties of Mg3.5Zn0.6Gd alloy containing quasicrystals was investigated after extrusion, the role of nanoquasicrystals on the ductility of alloy was analyzed. The results indicate that nanoquasicrystal was formed and distributed along grain boundary and in the matrix for Mg3.5Zn0.6Gd alloy after extrusion. As-extruded Mg3.5Zn0.6Gd alloy containing I-phase showed one relatively random and homogeneous texture due to the local lattice rotation during deformation. The Mg3.5Zn0.6Gd alloy extruded at 673 K exhibits larger elongation about 94% at 473 K, which could been ascribed to the combination of random texture and higher content of I-phase precipitated during extrusion at higher temperature. The a + c type dislocations can be effectively active due to the existence of nanoquasicrystals. The strengthening mechanism of Mg3.5Zn0.6Gd alloy can be explained as the dislocations annihilation effect. This annihilation of dislocations can play a role in the increase of flow strain during deformation.
Title:
Low thermal conductivity in nanoscale layered materials synthesized by the method of modulated elemental reactants
Authors:
Chiritescu, C; Cahill, DG; Heideman, C; Lin, QY; Mortensen, C; Nguyen, NT; Johnson, D; Rostek, R; Bottner, H Author Full Names: Chiritescu, Catalin; Cahill, David G.; Heideman, Colby; Lin, Qiyin; Mortensen, Clay; Nguyen, Ngoc T.; Johnson, David; Rostek, Raimar; Boettner, Harald
Source:
JOURNAL OF APPLIED PHYSICS 104 (3): Art. No. 033533 AUG 1 2008
Abstract:
We report the room-temperature, cross-plane thermal conductivities, and longitudinal speeds of sound of multilayer films [(TiTe2)(3)(Bi2Te3)(x)(TiTe2)(3)(Sb2Te3)(y)](i) (x=1-5, y=1-5) and misfit-layer dichalcogenide films [(PbSe)(m)(TSe2)(n)](i) (T=W or Mo, m=1-5, and n=1-5) synthesized by the modulated elemental reactants method. The thermal conductivities of these nanoscale layered materials fall below the predicted minimum thermal conductivity of the component compounds: two times lower than the minimum thermal conductivity of Bi2Te3 for multilayer [(TiTe2)(3)(Bi2Te3)(x)(TiTe2)(3)(Sb2Te3)(y)](i) films and five to six times lower than the minimum thermal conductivity of PbSe for misfit-layer dichalcogenides [(PbSe)(m)(TSe2)(n)](i). We attribute the low thermal conductivities to the anisotropic bonding of the layered crystals and orientational disorder in the stacking of layered crystals along the direction perpendicular to the surface. (C) 2008 American Institute of Physics.

Update: 29-Aug-2008

Title:
Reducing the positional modulation of NbO6-octahedra in SrxBa1-xNb2O6 by increasing the barium content: A single crystal neutron diffraction study at ambient temperature for x=0.61 and x=0.34
Authors:
Schefer, J; Schaniel, D; Petricek, V; Woike, T; Cousson, A; Wohlecke, M Author Full Names: Schefer, Juerg; Schaniel, Dominik; Petricek, Vaclav; Woike, Theo; Cousson, Alain; Woehlecke, Manfred
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 223 (6): 399-407 2008
Abstract:
We report on the influence of the barium content on the modulation amplitude in SrxBa1-xNb2O6 compounds by comparing Sr0.61Ba0.39Nb2O6 (SBN61) and Sr0.34Ba0.66Nb2O6 (SBN34). Our single crystal neutron diffraction results demonstrate that the amplitude of the positional modulation of the NbO6 octahedra is reduced with increasing barium content, indicating that the origin of the modulation is the partial occupation of the pentagonal channels by Sr and Ba atoms. By increasing the Sr content the bigger Ba atoms are replaced by the smaller Sr atoms, which leads to a larger deformation of the surrounding lattice and hence to a larger modulation amplitude. The more homogeneous the filling of these channels with one atomic type (Ba) the lower the modulation amplitude. Our results also show that the structure can be described with a two-dimensional incommensurate harmonic modulation. No second order modulation has been observed, both by single crystal diffraction measurements and q-scans. The positional modulation of the Nb atoms is much smaller than that of the oxygen atoms, such that the modulation can be seen as a rotational modulation of almost rigid NbO6-octahedra.
Title:
Icosahedral quasicrystal phase in Al15Mg50Zn35 ternary alloy by rapid quenching
Authors:
Zhu, M; Yang, GC; Liu, F; Wan, DQ; Cheng, SL; Zhou, YH Author Full Names: Zhu Man; Yang Gencang; Liu Feng; Wan Diqing; Cheng Suling; Zhou Yaohe
Source:
RARE METAL MATERIALS AND ENGINEERING 37 (7): 1179-1182 JUL 2008
Abstract:
Almost an icosahedral quasicrstyal phase is obtained in the Mg-riched region off the Bergman line by means of rapid quenching in a cool copper mould. The microstructures, chemical composition and atom cluster of the icosahedral phase are charactered by X-ray diffraction (XRD), scanning electron microscopy (SEM), field-emission scanning electron microscopy and transmission electron microscopy (TEM). It is found that the icosahedral quasicrystal phase is obtained with the composition of 39.76 at% Mg, 18.34 at% Al, and 41.90 at% Zn, which nucleates and grows directly from the melt with icosahedral symmetries. It exhibits a characteristic faceted dendritic growth with the fastest growth direction along a three-fold axes. At the same time, the regular hexagonal-polygon icosahedral quasicrystal grains with a size of 0.2 mu m can also be observed. The atomic cluster of icosahedral phase is pentagonal dodecahedron with icosahedral symmetries and micro-lobes on the each faceted pentagonal face.
Title:
Analytic study on specific heat of icosahedral Al-Mn-Pd quasicrystals
Authors:
Wang, J; Fan, TY Author Full Names: Wang, Jian; Fan, Tianyou
Source:
MODERN PHYSICS LETTERS B 22 (17): 1653-1659 JUL 10 2008
Abstract:
A simple and explicit formula for specific heat of icoschedral Al-Mn-Pd quasicrystals is obtained, theoretical predictions of which are in good agreement with that given by experiment.
Title:
Effect of icosahedral phase particles on the texture evolution in Mg-Zn-Y alloys
Authors:
Lee, JY; Lim, HK; Kim, DH; Kim, WT; Kim, DH Author Full Names: Lee, Ju Youn; Lim, Hyun Kyu; Kim, Do Hyung; Kim, Won Tae; Kim, Do Hyang
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 491 (1-2): 349-355 SEP 15 2008
Abstract:
In order to understand the role of the icosahedral phase (I-phase) particles on the improved mechanical properties of Mg-3Zn-0.6Y and Mg-6Zn-1.2Y alloys, the texture evolution has been investigated by the X-ray diffraction and electron back-scattered diffraction (EBSD) analyses. Mg-6Zn-1.2Y alloy exhibits higher strength than Mg-3Zn-0.6Y alloy due to the presence of larger amount of I-phase particles. However, Mg-6Zn-1.2Y alloy exhibits a larger elongation than Mg-3Zn-0.6Y alloy. With increasing the volume fraction of I-phase particles and rolling speeds, the relatively random texture is developed, which is attributed to local lattice rotations around I-phase particles during shear deformation. The relatively random texture plays an important role in enhancing the ductility when larger amount of I-phase particles are present in Mg-6Zn-1.2Y alloy. (C) 2008 Elsevier B.V. All rights reserved.
Title:
Distortion and charge density wave in the Ga square net coupled to the site occupancy wave in YCo0.88Ga3Ge
Authors:
Gray, DL; Francisco, MC; Kanatzidis, MG Author Full Names: Gray, Danielle L.; Francisco, Melanie C.; Kanatzidis, Mercouri G.
Source:
INORGANIC CHEMISTRY 47 (16): 7243-7248 AUG 18 2008
Abstract:
YCo0.88Ga3Ge has an incommensurately modulated structure that was solved with (3 + 1)D superspace techniques. YCo0.88Ga3Ge crystallizes in the orthorhombic superspace group Immm(alpha 00)00s with unit cell constants of a = 4.1639(4), b = 4.1639(4), c = 23.541(2) angstrom and a modulation vector of q = 0.3200(4)a* at 293 K. The incommensurate modulation, which creates a very large supercell (similar to 25 fold), arises from a charge density wave (CDW) in the square net of Ga atoms that is coupled with a site occupancy wave (SOW) of Co atoms. The distorted Ga net features polygallide ribbons, chains, as well as single atoms. Temperature dependent crystallographic studies of the structure from 100-500 K indicate that the CDW is "locked in". Electrical conductivity and thermopower measurements in the temperature range of 300-500 K show that YCo0.88Ga3Ge is a poor metal.
Title:
Formation and properties of quasicrystals
Authors:
Louzguine-Luzgin, DV; Inoue, A Author Full Names: Louzguine-Luzgin, D. V.; Inoue, A.
Source:
ANNUAL REVIEW OF MATERIALS RESEARCH 38: 403-423 2008
Abstract:
This article summarizes the general structural features and important properties of quasicrystals, a relatively new class of materials belonging to solid-state substances. Quasicrystals, which have a long-range quasiperiodic order but no three-dimensional translational periodicity, are structurally different from both conventional crystals and glassy solids. Although applications are still highly limited, quasicrystals are attracting significant attention as a structural constituent of mixed-phase materials exhibiting high strength together with certain ductility and can be applied as structural materials.

Update: 22-Aug-2008

Title:
Magnetic order of LiCu2O2 studied by resonant soft x-ray magnetic scattering
Authors:
Huang, SW; Huang, DJ; Okamoto, J; Wu, WB; Chen, CT; Yeh, KW; Chen, CL; Wu, MK; Hsu, HC; Chou, FC Author Full Names: Huang, S. W.; Huang, D. J.; Okamoto, J.; Wu, W. B.; Chen, C. T.; Yeh, K. W.; Chen, C. L.; Wu, M. K.; Hsu, H. C.; Chou, F. C.
Source:
SOLID STATE COMMUNICATIONS 147 (5-6): 234-237 AUG 2008
Abstract:
We present results of resonant soft x-ray magnetic scattering measurements on single crystals of LiCu2O2 to address the magnetic order. LiCu2O2 exhibits a long-range magnetic order incommensurate with the lattice, and the modulation vector is (0.5, zeta, 0) in reciprocal lattice units with zeta similar to 0.174, depending upon the temperature. The spin-spin correlation length along the spin chain deduced from the width of momentum scan is larger than 2100 angstrom. The inter-chain correlation length that lies within the ab plane was discovered to be substantial, similar to 690 angstrom. (c) 2008 Elsevier Ltd. All rights reserved.
Title:
Phase transformations induced by nitridation of quasicrystalline AlCuFeB powders
Authors:
Kenzari, S; Bonina, D; Dubois, JM; Fournee, V Author Full Names: Kenzari, S.; Bonina, D.; Dubois, J. M.; Fournee, V.
Source:
SCRIPTA MATERIALIA 59 (6): 583-586 SEP 2008
Abstract:
Nitridation is an important reaction which has never been investigated for Al-based quasicrystals. Here we show that AlCuFeB quasicrystalline particles undergo phase transformations upon annealing at high temperature in pure nitrogen. A thick nitride layer grows on the surface of the particles, and Al depletion in the bulk results in transformation of the quasicrystalline phase first into the cubic P-phase and then into the monoclinic X-phase. The kinetics of this transformation is much faster than that of oxidation. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Large-scale synthesis of Al-Cu-Fe submicron quasicrystals
Authors:
Li, LJ; Bi, QL; Yang, J; Fu, LC; Wang, LP; Wang, SC; Liu, WM Author Full Names: Li, Laijun; Bi, Qinling; Yang, Jun; Fu, Licai; Wang, Liping; Wang, Shuncai; Liu, Weimin
Source:
SCRIPTA MATERIALIA 59 (6): 587-590 SEP 2008
Abstract:
Al-Cu-Fe alloy with a nominal composition of Al62Cu25.5Fe12.5 (at.%) has been fabricated by a combination of pressure-assisted self-propagating high-temperature synthesis and rapid solidification. The as-synthesized Al-Cu-Fe alloy mainly consists of icosahedral quasicrystalline (IQC) Psi-Al65Cu20Fe15 and cubic beta-Al (Cu, Fe) solid solution phases, and exhibits finely equiaxed grains with a size ranging from 50 to 200 nm. The mechanism for the formation of the ultrafine-grained IQC phase has been explained. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Pressure-induced phase transitions in PrB6: Electrical resistivity measurements
Authors:
Iwakubo, H; Ikeda, S; Kishino, Y; Tanida, H; Sera, M; Iga, F Author Full Names: Iwakubo, H.; Ikeda, S.; Kishino, Y.; Tanida, H.; Sera, M.; Iga, F.
Source:
PHYSICAL REVIEW B 78 (1): Art. No. 012409 JUL 2008
Abstract:
We have studied the electrical resistivity of PrB6 under pressure up to P=0.8 GPa, with magnetic fields applied along the [001] and [111] directions. The commensurate (C) magnetic ordered phase is significantly stabilized by pressure, and another extra phase (denoted phase A) is observed under a low pressure of similar to 0.3 GPa. This phase appears above the transition temperature T-IC1=7 K at which the incommensurate magnetic order sets in at the ambient pressure. The magnetic phase diagram for H parallel to[111] changes drastically under pressure. Short-range interactions, which are strongly dependent on the Pr-Pr distances, are likely to play a dominant role in the relative stability of the different phases.
Title:
Signature of hidden order in heavy fermion superconductor URu2Si2: Resonance at the wave vector Q(0)=(1,0,0)
Authors:
Villaume, A; Bourdarot, F; Hassinger, E; Raymond, S; Taufour, V; Aoki, D; Flouquet, J Author Full Names: Villaume, A.; Bourdarot, F.; Hassinger, E.; Raymond, S.; Taufour, V.; Aoki, D.; Flouquet, J.
Source:
PHYSICAL REVIEW B 78 (1): Art. No. 012504 JUL 2008
Abstract:
Simultaneous neutron scattering and thermal expansion measurements on the heavy-fermion superconductor URu2Si2 under hydrostatic pressure of 0.67 GPa have been performed in order to detect the successive paramagnetic, hidden order, and large moment antiferromagnetic phases on cooling. The temperature dependence of the sharp low energy excitation at the wave vector Q(0)=(1,0,0) shows clearly that this resonance is a signature of the hidden order state. In the antiferromagnetic phase, this resonance disappears. The higher energy excitation at the incommensurate wave vector Q(1)=(1.4,0,0) persists in the antiferromagnetic phase but increases in energy.
Title:
Ga-substitution-induced single ferroelectric phase in multiferroic CuFeO2
Authors:
Terada, N; Nakajima, T; Mitsuda, S; Kitazawa, H; Kaneko, K; Metoki, N Author Full Names: Terada, N.; Nakajima, T.; Mitsuda, S.; Kitazawa, H.; Kaneko, K.; Metoki, N.
Source:
PHYSICAL REVIEW B 78 (1): Art. No. 014101 JUL 2008
Abstract:
We have succeeded in realizing a single ferroelectric phase in CuFe0.963Ga0.037O2 by substituting nonmagnetic Ga3+ for Fe3+ sites in CuFeO2. Ferroelectric polarization P in CuFe0.963Ga0.037O2 is observed below 7.5 K, and has the relatively large value of similar to 250 mu C/m(2), which is comparable to P=300 similar to 400 mu C/m(2) in the magnetic-field-induced ferroelectric phase of CuFeO2. In neutron-diffraction measurements, a single magnetic diffraction peak with an incommensurate wave number was observed below 7.5 K in CuFe0.963Ga0.037O2, indicating that the ferroelectric-incommensurate (FEIC) phase is realized as a single phase. Therefore, CuFe0.963Ga0.037O2 with a single FEIC phase is strongly expected to provide the best opportunity to investigate unresolved problems regarding the ferroelectric mechanism in CuFeO2. In this paper, we report measurements of magnetic susceptibility, specific heat, pyroelectric, dielectric constant, and neutron diffraction of a single crystal of CuFe0.963Ga0.037O2.
Title:
Effect of inversion symmetry on the incommensurate order in multiferroic RMn2O5 (R=rare earth)
Authors:
Harris, AB; Kenzelmann, M; Aharony, A; Entin-Wohlman, O Author Full Names: Harris, A. B.; Kenzelmann, M.; Aharony, Amnon; Entin-Wohlman, O.
Source:
PHYSICAL REVIEW B 78 (1): Art. No. 014407 JUL 2008
Abstract:
Starting from the irreducible representations of the group of the wave vector, we construct the spin-wave functions consistent with inversion symmetry, neglected in the usual representation analysis. We obtain the relation between the basis functions of different members of the star of the wave vector. We introduce order parameters and determine their transformation properties under the operations of the space group of the paramagnetic crystal. The results are applied to construct terms in the magnetoelectric interaction, which are quadratic and quartic in the magnetic order parameters. The higher-order magnetoelectric interactions can in principle induce components of the spontaneous polarization, which are not allowed by the lowest-order magnetoelectric interaction. We also obtain the relation between the spin-wave functions of the incommensurate phase and those of the commensurate phase, which lead to analogous relations between the order parameters of these two phases.
Title:
Magnetic order and multipole interactions in CexPr1-xB6 solid solutions
Authors:
Mignot, JM; Andre, G; Robert, J; Sera, M; Iga, F Author Full Names: Mignot, J. -M.; Andre, G.; Robert, J.; Sera, M.; Iga, F.
Source:
PHYSICAL REVIEW B 78 (1): Art. No. 014415 JUL 2008
Abstract:
Magnetic ordering phenomena in CexPr1-xB6 solid solutions have been studied using both powder and single-crystal neutron diffraction. A variety of magnetic structures are observed depending on temperature and Ce concentration. Over a broad composition range (x <= 0.7), Pr-Pr interactions play a dominant role, giving rise to incommensurate structures with wave vectors of the form k(IC1)=(1/4-delta,1/4,1/2) or k(IC2)=(1/4-delta,1/4-delta,1/2). The crossover to a CeB6-like regime takes place near x=0.7-0.8. For the latter composition, the antiferroquadrupolar phase transition observed in transport measurements precedes the onset, at lower temperature, of a commensurate magnetic order similar to that existing in CeB6. However, unlike in the pure compound, an incommensurate magnetic order is formed at even higher temperature and persists in the antiferroquadrupolar phase down to the lock-in transition. These results are shown to reflect the interplay between various type of dipole exchange and higher multipole interactions in this series of compounds.
Title:
Competing magnetic structures and magnetic transitions in Er2Ni2Pb: Powder neutron diffraction measurements
Authors:
Prokes, K; Munoz-Sandoval, E; Chinchure, AD; Mydosh, JA Author Full Names: Prokes, K.; Munoz-Sandoval, E.; Chinchure, Aravind D.; Mydosh, J. A.
Source:
PHYSICAL REVIEW B 78 (1): Art. No. 014425 JUL 2008
Abstract:
We have studied the magnetic structures of Er2Ni2Pb using a powder neutron diffraction technique in zero field. Previous bulk measurements suggested three distinct magnetic phase transitions. Our neutron diffraction experiments, which were made in the range 1.5-5 K, showed that magnetic Bragg reflections in Er2Ni2Pb can be indexed by several propagation vectors that coexist over an extensive temperature range. Rather than a homogeneous magnetic structure that is simultaneously described by all the existing propagation vectors, several spatially separated structures appear to exist in Er2Ni2Pb. The appearance/disappearance of representative reflections at T-N=3.5 K, T-m1=3.0 K, T-m2=2.3 K, and T-m3=1.8 K denote magnetic phase transitions. The only magnetic state that is determined by a single propagation vector exists just below T-N. In all other magnetic states, more than one propagation vectors are stable. Except for the lowest temperature state, which is commensurate, all other propagation vectors are incommensurate with respect to the crystal structure. Although the coexistence of several spatially separated magnetic structures can be explained by the competition of magnetic interactions along particular crystallographic directions, some of the details, e.g., the exact ground-state magnetic structure, are still unclear and need further study.
Title:
Magnetic ordering of weakly coupled frustrated quantum spin chains
Authors:
Zvyagin, AA; Drechsler, SL Author Full Names: Zvyagin, A. A.; Drechsler, S. -L.
Source:
PHYSICAL REVIEW B 78 (1): Art. No. 014429 JUL 2008
Abstract:
The ordering temperature of a quasi-one-dimensional system, consisting of weakly interacting quantum spin-1/2 chains with antiferromagnetic spin-frustrating couplings (or zigzag ladder), is calculated. The results show that a quantum critical point between two phases of the one-dimensional subsystem plays a crucial role. If the one-dimensional subsystem is in the antiferromagneticlike phase in the ground state, similar to the phase of a spin chain without frustration, weak couplings yield magnetic ordering of the Neel type. For intrachain spin-frustrating interactions larger than the critical one (at which the quantum phase transition takes place), the quasi-one-dimensional spin system manifests a spiral magnetic incommensurate ordering. The obtained results of our quantum theory are compared with the quasiclassical approximations. The calculated features of magnetic ordering are expected to be generic for weakly-coupled quantum spin chains with gapless excitations and spin-frustrating nearest- and next-nearest-neighbor interactions.
Title:
Identification of microscopic spin-polarization coupling in the ferroelectric phase of magnetoelectric multiferroic CuFe1-xAlxO2
Authors:
Nakajima, T; Mitsuda, S; Inami, T; Terada, N; Ohsumi, H; Prokes, K; Podlesnyak, A Author Full Names: Nakajima, Taro; Mitsuda, Setsuo; Inami, Toshiya; Terada, Noriki; Ohsumi, Hiroyuki; Prokes, Karel; Podlesnyak, Andrei
Source:
PHYSICAL REVIEW B 78 (2): Art. No. 024106 JUL 2008
Abstract:
We have performed synchrotron radiation x-ray and neutron diffraction measurements on magnetoelectric multiferroic CuFe1-xAlxO2 (x=0.0155), which has a proper helical magnetic structure with incommensurate propagation wave vector in the ferroelectric phase. The present measurements revealed that the ferroelectric phase is accompanied by lattice modulation with a wave number 2q, where q is the magnetic modulation wave number. We have calculated the Fourier spectrum of the spatial modulations in the local electric polarization using a microscopic model proposed by T. Arima [J. Phys. Soc. Jpn. 76, 073702 (2007)]. Comparing the experimental results with the calculation results, we found that the origin of the 2q-lattice modulation is not the conventional magnetostriction but the variation in the metal-ligand hybridization between the magnetic Fe3+ ions and ligand O2- ions. Combining the present results with the results of a previous polarized neutron diffraction study [Nakajima , Phys. Rev. B 77, 052401 (2008)], we conclude that the microscopic origin of the ferroelectricity in CuFe1-xAlxO2 is the variation in the metal-ligand hybridization with spin-orbit coupling.
Title:
Relaxor ferroelectric behavior in Ca-doped TbMnO3
Authors:
Mufti, N; Nugroho, AA; Blake, GR; Palstra, TTM Author Full Names: Mufti, N.; Nugroho, A. A.; Blake, G. R.; Palstra, T. T. M.
Source:
PHYSICAL REVIEW B 78 (2): Art. No. 024109 JUL 2008
Abstract:
We have studied the effect of Ca-doping in single-crystal Tb1-xCaxMnO3(x <= 0.1) on the crystal and magnetic structure, magnetocapacitance, and electric polarization. For low doping (x=0.05), the presence of Mn4+ ions gives rise to a state with behavior resembling that of a relaxor ferroelectric. The coherence length of the Mn magnetic spin spiral is reduced, while the Mn-modulation wave vector is unchanged. For doping larger than 5%, the ferroelectric state is suppressed, which we ascribe to breakdown of the spiral magnetic structure.
Title:
Magnetic-field-induced transitions in multiferroic TbMnO3 probed by resonant and nonresonant x-ray diffraction
Authors:
Strempfer, J; Bohnenbuck, B; Zegkinoglou, I; Aliouane, N; Landsgesell, S; Zimmermann, MV; Argyriou, DN Author Full Names: Strempfer, J.; Bohnenbuck, B.; Zegkinoglou, I.; Aliouane, N.; Landsgesell, S.; Zimmermann, M. V.; Argyriou, D. N.
Source:
PHYSICAL REVIEW B 78 (2): Art. No. 024429 JUL 2008
Abstract:
Multiferroic TbMnO3 is investigated using x-ray diffraction in high magnetic fields. Measurements on first- and second-harmonic structural reflections due to modulations induced by the Mn and Tb magnetic order are presented as function of temperature and field oriented along the a and b directions of the crystal. The relation to changes in ordering of the rare earth moments in applied field is discussed. Observations below T-N(Tb) without and with applied magnetic field point to a strong interaction of the rare earth order, the Mn moments, and the lattice. Also, the incommensurate to commensurate transition of the wave vector at the critical fields is discussed with respect to the Tb and Mn magnetic order, and a phase diagram on basis of these observations for magnetic fields H parallel to a and H parallel to b is presented. The observations point to a complicated and delicate magnetoelastic interaction as function of temperature and field.
Title:
Very weak electron-phonon coupling and strong strain coupling in manganites
Authors:
Cox, S; Loudon, JC; Williams, AJ; Attfield, JP; Singleton, J; Midgley, PA; Mathur, ND Author Full Names: Cox, S.; Loudon, J. C.; Williams, A. J.; Attfield, J. P.; Singleton, J.; Midgley, P. A.; Mathur, N. D.
Source:
PHYSICAL REVIEW B 78 (3): Art. No. 035129 JUL 2008
Abstract:
We describe transmission electron microscopy experiments that demonstrate the validity of the charge density wave (CDW) Landau theory in describing the so-called stripe phase of the manganites and that permit quantitative estimates of some of the theoretical parameters that describe this state. In polycrystalline Pr0.48Ca0.52MnO3 a lock-in to q/a(*)=0.5 in a sample with x>0.5 has been observed. Such a lock-in has been predicted as a key part of the Landau CDW theory of the stripe phase. Thus it is possible to constrain the size of the electron-phonon coupling in the CDW Landau theory to between 0.08% and 0.50% of the electron-electron coupling term. In the thin film samples, films of the same thickness grown on two different substrates exhibited different wave vectors. The different strains present in the films on the two substrates can be related to the wave vector observed via Landau theory. It is demonstrated that the elastic term, which favors an incommensurate modulation, has a similar size to the coupling between the strain and the wave vector, meaning that the coupling of strain to the superstructure is unexpectedly strong.
Title:
Incommensurability and atomic structure of c(2x2)N/Cu(100): A scanning tunneling microscopy study
Authors:
Choi, T; Ruggiero, CD; Gupta, JA Author Full Names: Choi, T.; Ruggiero, C. D.; Gupta, J. A.
Source:
PHYSICAL REVIEW B 78 (3): Art. No. 035430 JUL 2008
Abstract:
We use a scanning tunneling microscope operating in a low-temperature ultrahigh vacuum environment to study the atomic structure of single layer films of Cu2N grown on Cu(100). The c(2x2) lattice of Cu2N is incommensurate, with a lattice constant of 0.372 +/- 0.001 nm that is 3% larger than the bare Cu(100) surface. This finding suggests that the strain due to lattice mismatch contributes to self-assembly in this system. We find that the image contrast on Cu2N islands depends on bias voltage, which reconciles several interpretations in the literature. We assign features in these STM images to the Cu, N, and hollow sites in the Cu2N lattice with the aid of coadsorbed CO molecules. This atomic registry allows us to characterize four different defects on Cu2N, which influence the sticking coefficient and electronic coupling of adsorbates.
Title:
Structure of Al-Co-Ni pentagonal quasicrystal studied by HAADF-STEM and ab initio calculations
Authors:
Song, S; Wang, J; Wang, R; Xiong, D; Zhao, D; Gui, J; Liu, H; Yan, Y Author Full Names: Song, S.; Wang, J.; Wang, R.; Xiong, D.; Zhao, D.; Gui, J.; Liu, H.; Yan, Y.
Source:
PHILOSOPHICAL MAGAZINE LETTERS 88 (7): 519-531 2008
Abstract:
Using a combination of atomic-resolution high-angle annular dark-field (HAADF) Z-contrast imaging and ab initio calculations, atomic models of clusters 2 nm in diameter and 0.8 nm in height are proposed for the Al-Co-Ni pentagonal quasicrystal. This quasicrystal has 5-fold symmetry (the so-called 5f state) without superstructures, and is one of numerous modifications of the Al-Co-Ni decagonal quasicrystal. HAADF results reveal that the two-dimensional quasi-periodic lattice contains mainly Penrose pentagonal tiling. The centres within the decorated pentagonal tiles, i.e. the so-called pentagonal super-clusters, show structural characteristics having both a satellite-orbit shape and a pentagon-symmetry shape. The proposed atomic models, based directly on the HAADF images, are subjected to ab initio total energy calculations. After relaxation, the calculations demonstrate that the models with 5-fold symmetry are energetically more favourable than those with 10-fold symmetry.
Title:
Commensurate-incommensurate phase transition in muthmannite, AuAgTe2: first evidence of a modulated structure at low temperature
Authors:
Bindi, L Author Full Names: Bindi, Luca
Source:
PHILOSOPHICAL MAGAZINE LETTERS 88 (7): 533-541 2008
Abstract:
To study the temperature-dependent structural changes and to analyze the crystal chemical behavior of silver as a function of temperature, a crystal of muthmannite, AuAgTe2, has been investigated by X-ray single-crystal diffraction methods at 300 K and 110 K. At room temperature, muthmannite was confirmed as belonging to the space group P2/m, while at low temperature (110 K) it undergoes a reversible commensurate-incommensurate phase transition with a modulation wave vector q = 0.215(1)a* + 0.379(2)c*. Muthmannite reconverts to the commensurate type upon returning to room temperature, thus indicating that the phase transition is completely reversible in character. The average structure of the low-temperature muthmannite remains monoclinic, space group P2/m, and shows only normal thermal compression over the entire temperature range investigated. Crystal-chemical characteristics are compared with published data on the other members of the system Au-Ag-Te. Speculations on the possible origin of the modulated structure at low temperature are also given.
Title:
Dielectric, ferroelectric properties, and grain growth of CaxBa1-xNb2O6 ceramics with tungsten-bronzes structure
Authors:
Ke, SM; Fan, HQ; Huang, HT; Chan, HLW; Yu, SH Author Full Names: Ke, Shanming; Fan, Huiqing; Huang, Haitao; Chan, H. L. W.; Yu, Shuhui
Source:
JOURNAL OF APPLIED PHYSICS 104 (2): Art. No. 024101 JUL 15 2008
Abstract:
Dielectric properties, microstructures, and phase transition behaviors of alpha and beta phases of CaxBa1-xNb2O6 (x= 0.22, 0.30, and 0.38) ceramics were investigated. All the three compositions had partially filled tungsten-bronze structure (TTB) and relatively high Curie temperatures (up to 345 degrees C) compared with Sr1-xBaxNb2O6. The alpha phase exhibits unambiguously a diffused phase transition, while the beta phase is associated with an incommensurate phase and needs to be further studied. The dielectric and ferroelectric properties of CaxBa1-xNb2O6 ceramics were strongly processing-dependent. A mechanism was proposed to explain the grain growth behavior of TTB ceramic niobates. (c) 2008 American Institute of Physics.
Title:
Laves phases, gamma-brass, and 2x2x2 superstructures: A new class of quasicrystal approximants and the suggestion of a new quasicrystal
Authors:
Berger, RF; Lee, S; Johnson, J; Nebgen, B; So, ACY Author Full Names: Berger, Robert F.; Lee, Stephen; Johnson, Jeffreys; Nebgen, Ben; So, Adrian Chi-Yau
Source:
CHEMISTRY-A EUROPEAN JOURNAL 14 (22): 6627-6639 2008
Abstract:
Of the most common cubic intermetallic structure types, several (MgCU2, CU5Zn8, Ti2Ni, and alpha-Mn) have superstructures with unusual symmetry properties. These superstructures (Be5Au, Li21Si5, Sm11Cd45, and Mg44Ir7) have the unusual property of pairs of perpendicular pseudo fivefold axes, most apparent in their X-ray diffraction patterns. The current work shows that an 8D to 3D projection method cleanly describes most (and in one case, all) of the atomic positions in the four superstructures mentioned above. This type of projection, which maps the E-8 lattice (a mathematically simple 8D crystal) into 3D space, combines the desired higher dimensional point group's perpendicular fivefold rotations with 3D translational symmetry-exactly what we see in the experimental crystal structures. The projection method successfully accounts for all heavy atom positions in the four superstructures, and at least 60-70% of the light atom positions. The results suggest that all of these structures, previously known to be connected only by qualitative similarities in their atomic "clusters", are approximants of a single, as-yet unknown, class of quasicrystal.

Update: 15-Aug-2008

Title:
Mossbauer study of antiferromagnetic CuFeO2
Authors:
Choi, DH; Shim, IB; Kim, CS Author Full Names: Choi, Dong Hyeok; Shim, In-Bo; Kim, Chul Sung
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 320 (20): E575-E577 OCT 2008
Abstract:
We have studied the magnetic spin structure of antiferromagnetic CuFeO2 by X-ray diffraction (XRD) and Mossbauer spectroscopy. Its crystal structure determined by XRD analysis was a rhombohedral structure ( space group R-3m) and lattice constants a(0) and c(0) were 3.0333 and 17.1595 angstrom, respectively. In spite of 4-Fe sublattices in a delafossite CuFeO2, its Mossbauer spectra were analyzed with 1-set (6-Lorentzian lines) below 10K due to the collinear-commensurate spin structure, but the spectra were fitted with 4-sextet above 10K due to the incommensurate spin structure. This phenomenon was attributed to the spin-lattice relaxation effect. Magnetic Neel temperature was also determined at 18 K, which corresponded to the high-spin Fe3+ valance state. On the other hand, CuFe0.98Al0.02O2 powder with a noncollinear spin structure was fitted with 4-sextet at 4.2 K. (c) 2008 Elsevier B.V. All rights reserved.
Title:
Mechanical alloying and self-propagating high-temperature synthesis of stable icosahedral quasicrystals
Authors:
Bokhonov, BB Author Full Names: Bokhonov, B. B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 461 (1-2): 150-153 AUG 11 2008
Abstract:
The phase evolution of the mechanically alloyed ternary 63%Al + 25%Cu + 12%Fe and 65%Al + 20%Cu + 15%Fe powder mixtures with milling time has been studied by X-ray diffraction method. It was found that an icosahedral quasicrystalline phase was formed directly during high-energy ball milling of the Al-Cu-Fe mixtures. The X-ray and scanning electron microscopic investigations demonstrated the possibility to use self-propagating high-temperature synthesis (SHS) in combination with preliminary mechanical activation for the synthesis of stable icosahedral quasicrystals. The typical morphology of the Al63Cu25Fe12 icosahedral quasicrystals formed in the SHS process is a pentagonal dodecahedron with a size of 3-5 mm. The phase composition of the SHS products depends on the time of preliminary mechanical activation. The content of cubic intermetallic phase in SHS products increases with the time of preliminary mechanical activation of the 63%Al + 25%Cu + 12%Fe powder mixtures. (c) 2007 Elsevier B. V. All rights reserved.

Update: 8-Aug-2008

Title:
Quasicrystals at interfaces
Authors:
Fournee, V; Ledieu, J; Thiel, P Author Full Names: Fournee, Vincent; Ledieu, Julian; Thiel, Patricia
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 310301 AUG 6 2008
Title:
Microstructural evolution and the role of interfaces in Mg-Zn-Y alloys with high strength and formability
Authors:
Chang, HJ; Lee, JY; Kim, DH Author Full Names: Chang, H. J.; Lee, J. Y.; Kim, D. H.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314001 AUG 6 2008
Abstract:
Composites consisting of a quasicrystalline, icosahedral phase (I-phase) and ductile alpha-Mg can be fabricated by controlling the alloy composition in the Mg-Zn-Y alloy system. The I-phase in Mg-Zn-Y alloys shows a variation in structural order from a well-ordered icosahedral phase to a 1/1 rhombohedral approximant phase. The structural change in the icosahedral phase can be explained by microdomain formation due to compositional change during solidification. The characteristic of strong bonding between icosahedral particles and the alpha-Mg matrix indicates that the structural change from I-phase to crystalline phase is not discontinuous, but gradual. The interface layer of alpha-Mg with several nm thickness preserves an orientational relationship with the I-phase, although the remaining alpha-Mg shows a different orientation due to plastic deformation during deformation (rolling process). Such a strong interface can provide an excellent combination of high str ength and formability in Mg-based alloys, enabling application as lightweight structural parts.
Title:
Quasicrystal-crystal interfaces in bulk materials
Authors:
Singh, A; Tsai, AP Author Full Names: Singh, Alok; Tsai, A. P.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314002 AUG 6 2008
Abstract:
The formation of interfaces of simple crystals with icosahedral quasicrystals has been described. Crystals take on various orientation relationships (ORs) with the quasicrystals in order to make low energy interfaces by matching close packed planes across the interfaces. In the icosahedral phase the closest packed planes are fivefold and twofold. Among various possibilities, an OR will get selected by the surface on which nucleation of a phase occurs. Since one of the phases is quasicrystalline and the other is crystalline, even within the same OR there are variations of several degrees. The high symmetry of the icosahedral phase ensures many possible orientations for planar matching with another phase. The quasiperiodicity ensures an epitaxy with periodic planes of many possible spacings at the interface. Epitaxy can be observed as coincidence of spots in the reciprocal space and verified by imaging in high resolution electron microscopy. In this article examples of interfaces of Al-Cu-Fe icosahedral phases with lead, bismuth and tin, and Mg-Zn-Y icosahedral phases with magnesium are shown. The high symmetry of the icosahedral phase ensures that epitaxy is produced on nearly all interfaces in bulk. Slight misorientations across interfaces are accommodated by dislocations.
Title:
Models for quasicrystal-crystal epitaxy
Authors:
Widjaja, EJ; Marks, LD Author Full Names: Widjaja, E. J.; Marks, L. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314003 AUG 6 2008
Abstract:
Not long after the discovery of quasicrystals, a specific orientation relationship between crystalline and quasicrystalline structures was observed. The specific orientational relationships were discovered in many systems, for instance surface alterations of bulk quasicrystals, the growth of atomic overlayers on quasicrystalline substrates and quasicrystalline thin films on crystalline substrates. In this paper, we review various models described in the literature in explaining such quasicrystal-crystal epitaxy.
Title:
Epitaxial interfaces between half-crystals of quasicrystalline and periodic material
Authors:
Theis, W; Franke, KJ Author Full Names: Theis, W.; Franke, K. J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314004 AUG 6 2008
Abstract:
We recently demonstrated that epitaxial interfaces can be formed between periodic and quasiperiodic materials (Franke et al 2007 Phys. Rev. Lett. 99 036103). Such interfaces exhibit the same defining characteristic as epitaxial interfaces between commensurate periodic materials, namely the locking into registry of the two half-crystals' atomic structures. This real space characteristic is equivalent to the requirement of a coincidence of reciprocal lattice points. Here, we explore the characteristics of the potential interfaces within the class of quasicrystals exhibiting a periodic direction, including decagonal quasicrystals. We derive our results geometrically from a higher dimensional description, thus providing visual insight into the underlying concepts. Since the reciprocal lattice of quasicrystalline structures is generated by more basis vectors than their periodic counterparts', suitable quasicrystalline interlayers can be designed to epitaxially link incommensurate half-crystals. We give examples of selected model structures as illustrations.
Title:
Nucleation and growth of pseudomorphic monolayers on quasicrystal surfaces
Authors:
Smerdon, JA; Sharma, HR; Ledieu, J; McGrath, R Author Full Names: Smerdon, J. A.; Sharma, H. R.; Ledieu, J.; McGrath, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314005 AUG 6 2008
Abstract:
We present a review of experimental studies of adsorption systems where pseudomorphic growth on quasicrystal surfaces has been observed. From these studies, we correlate information on the known or suggested adsorption and nucleation sites. For fivefold surfaces of icosahedral quasicrystals, two favoured locations emerge: the centres of equatorially truncated pseudo-Mackay clusters, and the centres of pentagonal hollows. The information on adsorption sites on decagonal quasicrystals is less definitive. Nevertheless the correlation of known information leads to a simple picture of pseudomorphic growth, at least for the first monolayer. We also remark on the possibilities for studies using quantitative surface structural techniques.
Title:
Bulk and surface structure of the clean and adsorbate-covered decagonal Al-Co-Ni quasicrystal
Authors:
Burkardt, S; Deloudi, S; Erbudak, M; Kortan, AR; Mungan, M; Steurer, A Author Full Names: Burkardt, S.; Deloudi, S.; Erbudak, M.; Kortan, A. R.; Mungan, M.; Steurer, Andw
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314006 AUG 6 2008
Abstract:
We review our Al adsorption experiments on the tenfold-symmetry surface of the decagonal Al-Co-Ni quasicrystal and present computational simulations of adsorption on a structural model based on a fundamental Al-Co cluster with 20 angstrom diameter, symmetry (102) over barm, and 8 angstrom periodicity. This cluster is the building unit of tau(2)-Al13Co4, from which, by a sequence of minor changes, the structures of the phases in the stability region of decagonal Al-Co-Ni can be derived. The model used for the decagonal Al70Co15Ni15 is an idealized model with a two-layer periodicity (4 angstrom) and no chemical or structural disorder. We find that the bulk and surface properties of this model are in good agreement with experiments. Our molecular-dynamics simulations of Al adsorption reproduce the experimental results and show that by varying the thermal relaxation rates of the adsorbed layer, a variety of different surface morphologies can be achieved. We also present our recent experiments on dissociative adsorption of oxygen on the decagonal surface.
Title:
Gas adsorption on quasicrystalline surfaces
Authors:
Diehl, RD; Setyawan, W; Curtarolo, S Author Full Names: Diehl, R. D.; Setyawan, W.; Curtarolo, S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314007 AUG 6 2008
Abstract:
The low-friction properties of quasicrystal surfaces suggest their use as coatings on moving machine parts, including those in internal combustion engines. In such applications, additional lubricants are typically used. Since the low-friction properties of quasicrystals are thought to depend on their aperiodic structures, the interactions of lubricants on quasicrystalline surfaces may have an impact on their frictional properties. In this paper, we address the fundamental issues that affect the growth and structural properties of gases on a quasicrystal surface. Studies of the adsorption and growth of rare gases on quasicrystal surfaces are reviewed, and new results are presented for the modeling and simulation of hydrocarbons on quasicrystal surfaces. The calculated interaction parameters are presented for methane adsorption on ten-fold Al-Ni-Co. Methane is found to form aperiodically ordered structures, consistent with the rules established earlier for rare gases on Al-Ni-Co.
Title:
Sputter-induced crystalline layers and epitaxial overlayers on quasicrystal surfaces
Authors:
Shimoda, M; Sharma, HR Author Full Names: Shimoda, M.; Sharma, H. R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314008 AUG 6 2008
Abstract:
We present here an overview of surface and interface studies on various quasicrystals, focusing on areas where reflection high-energy electron diffraction plays an important role. Subjects included here are sputter-induced crystalline layers, surface alloying and epitaxial films. These phenomena are observed on the high symmetry surface of Al-based quasicrystals, such as decagonal Al-Ni-Co, icosahedral (i) Al-Cu-Fe and i-Al-Cu-Ru. For comparison, studies on i-Ag-In-Yb quasicrystal, an isostructure of the binary i-Cd-Yb quasicrystal, and. xi'-Al-Pd-Mn approximant are also included.
Title:
Surface alloys as interfacial layers between quasicrystalline and periodic materials
Authors:
Duguet, T; Ledieu, J; Dubois, JM; Fournee, V Author Full Names: Duguet, T.; Ledieu, J.; Dubois, J. M.; Fournee, V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314009 AUG 6 2008
Abstract:
Low adhesion with normal metals is an intrinsic property of many quasicrystalline surfaces. Although this property could be useful to develop low friction or non-stick coatings, it is also responsible for the poor adhesion of quasicrystalline coatings on metal substrates. Here we investigate the possibility of using complex metallic surface alloys as interface layers to enhance the adhesion between quasicrystals and simple metal substrates. We first review some examples where such complex phases are formed as an overlayer. Then we study the formation of such surface alloys in a controlled way by annealing a thin film deposited on a quasicrystalline substrate. We demonstrate that a coherent buffer layer consisting of the gamma-Al4Cu9 approximant can be grown between pure Al and the i-Al-Cu-Fe quasicrystal. The interfacial relationships between the different layers are defined by [111](A1) parallel to [110](Al4Cu9) parallel to [5f](i-Al-Cu-Fe).
Title:
Contact angles of liquid metals on quasicrystals
Authors:
Bergman, C; Girardeaux, C; Perrin-Pellegrino, C; Gas, P; Dubois, JM; Rivier, N Author Full Names: Bergman, Claire; Girardeaux, Christophe; Perrin-Pellegrino, Carine; Gas, Patrick; Dubois, Jean-Marie; Rivier, Nicolas
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314010 AUG 6 2008
Abstract:
Wetting with mu m-sized Pb droplets on thin polycrystalline films of decagonal Al13Co4 is reported. The films were prepared under high vacuum conditions in order to have Pb droplets lying on a clean surface. The method used is sequential deposition and annealing of specific stackings of Al and Co layers of nanometric thicknesses. A 300 nm thick Pb slab was then deposited on top of the films and dewetting experiments were followed in situ in a scanning Auger microprobe. The contact angle between the Pb droplet and the surface of the film is measured to be 49 degrees +/- 7 degrees. Further investigation performed by cross section transmission electron microscopy allows us to better characterize the interface. Taking into account the rugosity of the film, it is concluded that there is partial wetting of the film, which corresponds to a smaller contact angle. The comparison with other results obtained either with pure metals or with a cubic AlCo compound leads to the conclusion that the wetting behaviour of Pb on the surface of a decagonal compound is close to that of a metal with a high melting point and not significantly different from that of a crystalline compound with a small unit cell.
Title:
Measurements of contact angles of water on Al-based intermetallic surfaces
Authors:
Dubois, JM; Fournee, V; Thiel, PA; Belin-Ferre, E Author Full Names: Dubois, J. M.; Fournee, V.; Thiel, P. A.; Belin-Ferre, E.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314011 AUG 6 2008
Abstract:
A systematic study was performed of the contact angle of minute droplets of water deposited on various aluminium-based intermetallics in ambient conditions. The dataset was complemented by measurements of electronic partial densities of states and oxide layer thicknesses. We studied a broad variety of specimens, ranging from simple cubic, CsCl-type phases to quasicrystals and high-order approximants. The thickness of the oxide layer, that is always present in air, was varied between 2 and more than 10 nm. Within these limits, the contact angle varies considerably and, surprisingly, decreases with increasing thickness of the oxide dielectric. Furthermore, it is clearly the highest on samples that show the largest crystal complexity, i.e. quasicrystals. It follows that the reversible adhesion energy directly deduced from contact angle is essentially controlled by the (squared) density of states at Fermi energy in the bulk of the sample and the inverse of the (squared) thickness of the native oxide film at the surface of the material. We interpret these results in terms of electrostatic image forces developed in the conduction cloud by the dipoles of the water molecules.
Title:
Atomic scale friction and adhesion properties of quasicrystal surfaces
Authors:
Park, JY; Thiel, PA Author Full Names: Park, Jeong Young; Thiel, P. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314012 AUG 6 2008
Abstract:
In this paper, we highlight recent studies of the atomic scale friction and adhesion properties of quasicrystals. We review tribological studies carried out in different mechanical regimes (elastic and inelastic) and at different length scales (macroscale and nanoscale). We address the role of the surface oxide and the nature of mechanical contact in determining friction and adhesion properties. We discuss the relationship between the aperiodic atomic structure of quasicrystals and their low friction, for both elastic and inelastic regimes.
Title:
First-principles studies for structural transitions in ordered phase of cubic approximant Cd6Ca
Authors:
Nozawa, K; Ishii, Y Author Full Names: Nozawa, K.; Ishii, Y.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 315206 AUG 6 2008
Abstract:
Recently a low-temperature structural transition has been reported for complex cubic compounds Cd6M (M = Ca, Yb, Y, rare earth) and it is believed that the transition is due to orientational ordering of an atomic shell in the icosahedral cluster in Cd6M. The first-principles electronic structure calculations and structural relaxations are carried out to investigate structures and orientational ordering of the innermost tetrahedral shell of the icosahedral cluster in Cd6Ca. The very short interatomic distances in the experimental average structures are relaxed and the innermost tetrahedral shell of an almost regular shape is obtained. Three types of orientation for the tetrahedral shell and eight different combinations of them for the clusters at a vertex and body-centre of a cubic cell are obtained. A possible model describing the orientational ordering at low temperatures or high pressures is discussed.
Title:
Reciprocal-space imaging of a real quasicrystal. A feasibility study with PILATUS 6M
Authors:
Weber, T; Deloudi, S; Kobas, M; Yokoyama, Y; Inoue, A; Steurer, W Author Full Names: Weber, Thomas; Deloudi, Sofia; Kobas, Miroslav; Yokoyama, Yoshihiko; Inoue, Akihisa; Steurer, Walter
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 41: 669-674 Part 4 AUG 2008
Abstract:
How many of the theoretically densely distributed Bragg reflections of a quasicrystal can be observed employing an area detector and synchrotron radiation? How does the reflection density of a real quasicrystal change as a function of exposure time, and what is the minimum distance between reflections? What does the distribution of diffuse scattering look like? To answer these questions, the Bragg reflection density of a perfect icosahedral quasicrystal with composition Al64Cu23Fe13 was measured employing a novel type of single-photon-counting X-ray pixel detector, PILATUS 6M, which allows noise-free data collection with the extraordinarily large dynamic range of 20 bit. The reflection density was found to be two orders of magnitude lower than expected for a strictly quasiperiodic structure. Moreover, diffuse scattering reflects significant structural disorder, breaking six-dimensional F-lattice symmetry. These findings have some implications for the interpretation! of physical properties.
Title:
Anomalous small-angle scattering from nanoquasicrystalline precipitates in Zr80Pt20 ribbons
Authors:
Okuda, H; Fukumoto, T; Saida, J; Ochiai, S; Sasaki, S; Masunaga, H Author Full Names: Okuda, Hiroshi; Fukumoto, Takefumi; Saida, Junji; Ochiai, Shojiro; Sasaki, Sono; Masunaga, Hiroyasu
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 41: 675-679 Part 4 AUG 2008
Abstract:
Anomalous small-angle X-ray scattering (ASAXS) profiles of Zr80Pt20 ribbons have been measured at the Zr K absorption edge. By annealing the melt-spun ribbons at 800 K, well defined SAXS patterns from nanoquasicrystals were observed, although the compositions of the quasicrystals (QC) and the amorphous matrix have previously been reported to be the same. The SAXS intensities were found to show a small anomalous effect at the Zr K edge. Contrast analysis suggested that the origin of the small-angle scattering is a small compositional fluctuation coupled with a small density difference, which enhances SAXS intensity but reduces the anomalous effect. A constant ASAXS intensity ratio for QC microstructure suggests that the ratio of the composition difference to the density difference between QC and the amorphous matrix is almost constant for the ZrPt ribbons examined here.
Title:
Incommensurate structure of InAl1-xTixO3+x/2 [x=0.701 (1)]: comparison between modulated and composite models
Authors:
Bereciartua, PJ; Zuniga, FJ; Breczewski, T Author Full Names: Bereciartua, P. J.; Zuniga, F. J.; Breczewski, T.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 405-416 Part 4 AUG 2008
Abstract:
The structure of the monoclinic phase of the compound InAl1-xTixO3+x/2 with x = 0.701 (1) has been analyzed within the (3 + 1)-dimensional superspace formalism. Two different models were refined describing the structure as an incommensurate modulated layer and modulated composite, respectively. Both models include the same composition structure relation. In the composite approach it is derived from the mismatching between the two subsystems. In the incommensurate modulated system, it is derived from a closeness condition between O atomic domains. The distribution and coordination of the cations is discussed and compared with previously proposed models for similar compounds.
Title:
Incommensurate structure of Ca2Al2O5 at high temperatures - structure investigation and Raman spectroscopy
Authors:
Lazic, B; Kruger, H; Kahlenberg, V; Konzett, J; Kaindl, R Author Full Names: Lazic, Biljana; Krueger, Hannes; Kahlenberg, Volker; Konzett, Juergen; Kaindl, Reinhard
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 417-425 Part 4 AUG 2008
Abstract:
A high-temperature X-ray diffraction study revealed that brownmillerite-type Ca2Al2O5 transforms to an incommensurately modulated structure at elevated temperatures. Single crystals of Ca2Al2O5 were synthesized in an end-loaded piston cylinder press at 2.5 GPa and 1273 K. The diffraction pattern observed at 1090 (10) K by in situ single-crystal diffraction experiments can be indexed by an I-centred orthorhombic cell and a modulation wavevector of q = 0.595 (1) c*. A (3 + 1)-dimensional model in superspace group Imma(00 gamma)s00 was used to refine the modulated structure. The structure is assembled from two building units: (i) layers of corner-sharing [AlO6] octahedra, stacked along b alternate with (ii) layers of zweier single chains of [AlO4] tetrahedra running along a. The modulated structure arises from an aperiodic sequence of two different configurations of the chains within the tetrahedral layers. The modulated high-temperature phase of Ca2Al2O5 is isotypic to the modulated high-temperature modification of Ca2Fe2O5. A large hysteresis was found in the phase-transition temperature. On heating, the transition occurs at ca 1075 (10) K; on cooling, satellite reflections can be observed down to 975 (10) K. The characterization of Ca2Al2O5 is completed by Raman spectroscopy, including a partial interpretation of the spectra.
Title:
Order, disorder and structural modulations in Bi-Fe-W-O-Br Sillen-Aurivillius intergrowths
Authors:
Avila-Brande, D; Landa-Canovas, AR; Otero-Diaz, LC Author Full Names: Avila-Brande, David; Landa-Canovas, Angel R.; Otero-Diaz, L. Carlos
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 438-447 Part 4 AUG 2008
Abstract:
Transmission electron microscopy observations on a new complex oxybromide with nominal composition Bi4Fe1/3W2/3O8Br, heated at high temperature, reveal the transformation of its basic structure yielding two types of crystals. The first crystal type shows ordered and disordered extended defects leading to a new family of intergrowths between one Sillen block and n Aurivillius blocks and occasionally between one Aurivillius block and n Sillen blocks. The second type presents a compositionally modulated structure, determined by electron diffraction, with an average composition Bi4Fe1/2W1/2O8-delta Br and unit-cell parameters a = (1/gamma) 3.8, b = 3.8, c = 14.5 angstrom (gamma = 0.10-0.15) in the superspace group Immm[(1-gamma)00] no. 71.1.

Update: 1-Aug-2008

Title:
Ab initio calculations of the vibrational spectra of 1/1 approximant of i-AlCuFe quasicrystal
Authors:
Rudenko, AN; Mazurenko, VG Author Full Names: Rudenko, A. N.; Mazurenko, V. G.
Source:
PHYSICS OF THE SOLID STATE 50 (7): 1326-1332 JUL 2008
Abstract:
The partial and total densities of vibrational states of the 1/1 crystal approximant of the icosahedral i-AlCuFe quasicrystal are calculated using the method of pseudopotentials in the generalized gradient approximation (to describe the electronic states) and the frozen-phonon method (to determine the dynamic matrix). The results obtained agree well with experimental inelastic neutron scattering data, which indicates that the method of calculations is appropriate and could be used to calculate other crystal approximants.
Title:
Materials science - A tale of two tilings
Authors:
Glotzer, SC; Keys, AS Author Full Names: Glotzer, Sharon C.; Keys, Aaron S.
Source:
NATURE 454 (7203): 420-421 JUL 24 2008
Title:
Archimedean-like tiling on decagonal quasicrystalline surfaces
Authors:
Mikhael, J; Roth, J; Helden, L; Bechinger, C Author Full Names: Mikhael, Jules; Roth, Johannes; Helden, Laurent; Bechinger, Clemens
Source:
NATURE 454 (7203): 501-504 JUL 24 2008
Abstract:
Monolayers on crystalline surfaces often form complex structures with physical and chemical properties that differ strongly from those of their bulk phases (1). Such hetero-epitactic overlayers are currently used in nanotechnology and understanding their growth mechanism is important for the development of new materials and devices. In comparison with crystals, quasicrystalline surfaces exhibit much larger structural and chemical complexity leading, for example, to unusual frictional(2), catalytical(3) or optical properties(4,5). Deposition of thin films on such substrates can lead to structures that may have typical quasicrystalline properties. Recent experiments have indeed showed 5-fold symmetries in the diffraction pattern of metallic layers adsorbed on quasicrystals (6,7). Here we report a real-space investigation of the phase behaviour of a colloidal monolayer interacting with a quasicrystalline decagonal substrate created by interfering five laser beams. We find a pseudomorphic phase that shows both crystalline and quasicrystalline structural properties. It can be described by an archimedean-like tiling (8,9) consisting of alternating rows of square and triangular tiles. The calculated diffraction pattern of this phase is in agreement with recent observations of copper adsorbed on icosahedral Al70Pd21Mn9 surfaces(10). In addition to establishing a link between archimedean tilings and quasicrystals, our experiments allow us to investigate in real space how single-element monolayers can form commensurate structures on quasicrystalline surfaces.
Title:
Electronic properties and phase transitions in low-dimensional semiconductors
Authors:
Panich, AM Author Full Names: Panich, A. M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (29): Art. No. 293202 JUL 23 2008
Abstract:
We present the first review of the current state of the literature on electronic properties and phase transitions in T1X and T1MX2 (M = Ga, In; X = Se, S, Te) compounds. These chalcogenides belong to a family of the low-dimensional semiconductors possessing chain or layered structure. They are of significant interest because of their highly anisotropic properties, semi-and photoconductivity, nonlinear effects in their I-V characteristics (including a region of negative differential resistance), switching and memory effects, second harmonic optical generation, relaxor behavior and potential applications for optoelectronic devices. We review the crystal structure of T1X and T1MX2 compounds, their transport properties under ambient conditions, experimental and theoretical studies of the electronic structure, transport properties and semiconductor -metal phase transitions under high pressure, and sequences of temperature-induced structural phase transitions with intermediate incommensurate states. The electronic nature of the ferroelectric phase transitions in the above-mentioned compounds, as well as relaxor behavior, nanodomains and possible occurrence of quantum dots in doped and irradiated crystals is discussed.
Title:
Dynamic crack propagation in decagonal Al-Ni-Co quasicrystal
Authors:
Zhu, AY; Fan, TY Author Full Names: Zhu, Ai-Yu; Fan, Tian You
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (29): Art. No. 295217 JUL 23 2008
Abstract:
The appearance of unusual internal variables - phason degrees - in quasicrystals challenges the traditional theory of condensed matter in macro- as well as in microscopy, especially for a dynamic process. The elasto-/hydrodynamic model for quasicrystals is suggested and investigated. With this model and the finite difference method the wave propagation and diffusion and their interaction through a cracked sample are revealed in this study. Even though the phason degrees of freedom present the diffusion nature according to the present model, this influences the dynamic process greatly. The influences are different for dynamic initiation of crack growth and fast crack propagation; for the latter the nonlinear effect - moving boundary effect - is evident as well as the wave propagation effect, diffusion effect and phonon-phason coupling effect.
Title:
Effect of hot forging on the microstructure and mechanical properties of Mg-Zn-Y alloy
Authors:
Garces, G; Muller, A; Onorbe, E; Perez, P; Adeva, P Author Full Names: Garces, G.; Mueller, A.; Onorbe, E.; Perez, P.; Adeva, P.
Source:
JOURNAL OF MATERIALS PROCESSING TECHNOLOGY 206 (1-3): 99-105 SEP 12 2008
Abstract:
The use of hot forging as an alternative thermo-mechanical treatment to refine a quasicrystalline reinforced Mg-Zn-Y cast alloy has been explored. Hot forging refines the grain size of the cast Mg-Zn-Y alloy and induces a strong texture with the basal planes perpendicular. to the forging direction. However, forging is not effective to distribute the I-phase homogeneously through the magnesium matrix. At low temperature, grain refinement is the main strengthening mechanism and contributes to increasing the mechanical strength of the forged-Mg-Zn-Y alloy. Furthermore, the basal texture affords an additional strengthening contribution whose magnitude depends only on the texture intensity. (c) 2008 Published by Elsevier B.V.
Title:
Reaction efficiency of diffusion-controlled processes on finite, aperiodic planar arrays
Authors:
Garza-Lopez, RA; Kaufman, A; Patel, R; Chang, J; Brzezinski, J; Kozak, JJ Author Full Names: Garza-Lopez, Roberto A.; Kaufman, Aaron; Patel, Reena; Chang, Joseph; Brzezinski, Jack; Kozak, John J.
Source:
CHEMICAL PHYSICS LETTERS 459 (1-6): 137-140 JUN 27 2008
Abstract:
Using the theory of finite Markov processes, we show quantitatively that diffusion-limited, reactive events on two finite planar arrays having an aperiodic lattice structure are kinetically advantaged relative to processes on platelets having a regular, hexagonal [6(3)] structure. The possible relevance of the results obtained to catalytic processes on quasicrystals and zeolite 'rafts' is noted. (c) 2008 Elsevier B. V. All rights reserved.

Update: 25-Jul-2008

Title:
Main features and the driving force for the formation of the quasicrystalline phase in Al-Cu-Fe powders after mechanoactivation
Authors:
Cherdyntsev, VV; Kaloshkin, SD; Tomilin, IA; Principi, G Author Full Names: Cherdyntsev, V. V.; Kaloshkin, S. D.; Tomilin, I. A.; Principi, G.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 105 (6): 610-621 JUN 2008
Abstract:
The evolution of the phase and structural states during heating of a powder mixture of composition Al65Cu23Fe12 subjected to mechanoactivation has been investigated. The solid-state transformations have been studied using Mossbauer spectroscopy, X-ray diffraction, and differential scanning calorimetry. The sequence of phase formation during heating was compared with the data on the heat of formation of binary solutions and compounds in the system. The analysis performed showed that the nature of transformations in the process of the formation of the quasicrystalline phase was caused by the thermodynamic parameters of the system.
Title:
Metal-insulator transition and its relation to magnetic structure in (LaMnO3)(2n)/(SrMnO3)(n) superlattices
Authors:
Bhattacharya, A; May, SJ; Velthuis, SGET; Warusawithana, M; Zhai, X; Jiang, B; Zuo, JM; Fitzsimmons, MR; Bader, SD; Eckstein, JN Author Full Names: Bhattacharya, A.; May, S. J.; Velthuis, S. G. E. te; Warusawithana, M.; Zhai, X.; Jiang, Bin; Zuo, J. -M.; Fitzsimmons, M. R.; Bader, S. D.; Eckstein, J. N.
Source:
PHYSICAL REVIEW LETTERS 100 (25): Art. No. 257203 JUN 27 2008
Abstract:
Superlattices of (LaMnO3)(2n)/(SrMnO3)(n) (1 <= n <= 5), composed of the gapped insulators LaMnO3 and SrMnO3, undergo a metal-insulator transition as a function of n, being metallic for n <= 2 and insulating for n >= 3. Measurements of transport, magnetization, and polarized neutron reflectivity reveal that the ferromagnetism is relatively uniform in the metallic state, and is strongly modulated in the insulating state, being high in LaMnO3 and suppressed in SrMnO3. The modulation is consistent with a Mott transition driven by the proximity between the (LaMnO3)/(SrMnO3) interfaces. The insulating state for n >= 3 obeys variable range hopping at low temperatures. We suggest that this is due to states at the Fermi level that emerge at the (LaMnO3)/(SrMnO3) interfaces and are localized by disorder.
Title:
Martensitic transformation of Ni2FeGa ferromagnetic shape-memory alloy studied via transmission electron microscopy and electron energy-loss spectroscopy
Authors:
Zhang, HR; Ma, C; Tian, HF; Wu, GH; Li, JQ Author Full Names: Zhang, H. R.; Ma, C.; Tian, H. F.; Wu, G. H.; Li, J. Q.
Source:
PHYSICAL REVIEW B 77 (21): Art. No. 214106 JUN 2008
Abstract:
The structural properties of Ni2FeGa Heusler alloy synthesized by melt-spinning technique have been systematically studied by means of in situ heating and cooling transmission electron microscopy. It was found that the Ni2FeGa alloy was annealed into a well-defined L2(1) structure at around 980 K, and complex microstructural domains appeared along with lowering temperature. At room temperature (293 K), a rich variety of micromodulated domains were observed. The domain structures were aligned along the < 110 > or < 100 > directions resulting to complex tweed structures. Below martensitic transformation (MT) temperature (M-s,similar to 142 K), the cubic parent phase transformed into unmodulated martensitic variants and modulated martensitic variants. The variants were alternated along the < 100 > direction with various arrangements and steplike incommensurate boundaries. The modulated martensitic variants were composed of lamellar structures that have predominately a 5M modulation structure along the < 110 > directions. The electron energy-loss spectroscopy analysis of the low-loss region and the electron energy-loss near-edge fine structure revealed a visible change of the electronic structure along with MT, which can be well interpreted by means of intra-atomic or intraband charge redistribution due to spd orbital hybridization among the Ni-Fe-Ga atoms.
Title:
Ordered magnetic phases of the frustrated spin-dimer compound Ba3Mn2O8
Authors:
Samulon, EC; Jo, YJ; Sengupta, P; Batista, CD; Jaime, M; Balicas, L; Fisher, IR Author Full Names: Samulon, E. C.; Jo, Y. -J.; Sengupta, P.; Batista, C. D.; Jaime, M.; Balicas, L.; Fisher, I. R.
Source:
PHYSICAL REVIEW B 77 (21): Art. No. 214441 JUN 2008
Abstract:
Ba3Mn2O8 is a spin-dimer compound based on pairs of S=1, 3d(2), Mn5+ ions arranged on a triangular lattice. Antiferromagnetic intradimer exchange leads to a singlet ground state in zero field. Here we present the first results of thermodynamic measurements for single crystals probing the high-field ordered states of this material associated with closing the spin gap to the excited triplet states. Specific heat, magnetocaloric effect, and torque magnetometry measurements were performed in magnetic fields up to 32 T and temperatures down to 20 mK. For fields above H-c1 similar to 8.7 T, these measurements reveal a single magnetic phase for H parallel to c but two distinct phases (approximately symmetric about the center of the phase diagram) for H perpendicular to c. Analysis of the simplest possible spin Hamiltonian describing this system yields candidates for these ordered states corresponding to a simple spiral structure for H parallel to c and to two distinct modulated phases for H perpendicular to c. Both single-ion anisotropy and geometric frustration play crucial roles in defining the phase diagram.
Title:
Pressure-induced polarization reversal in multiferroic YMn2O5
Authors:
Chaudhury, RP; dela Cruz, CR; Lorenz, B; Sun, YY; Chu, CW; Park, S; Cheong, SW Author Full Names: Chaudhury, Rajit P.; dela Cruz, Clarina R.; Lorenz, Bernd; Sun, Yanyi; Chu, Ching-Wu; Park, S.; Cheong, Sang-W.
Source:
PHYSICAL REVIEW B 77 (22): Art. No. 220104 JUN 2008
Abstract:
The low-temperature ferroelectric polarization of multiferroic YMn2O5 is completely reversed at a critical pressure of 10 kbar and the phase transition from the incommensurate to the commensurate magnetic phase is induced by pressures above 14 kbar. The high-pressure data correlate with thermal-expansion measurements, indicating a significant lattice strain at the low-temperature transition into the incommensurate phase. The results support the exchange striction model for the ferroelectricity in multiferroic RMn2O5 compounds and they show the importance of magnetic frustration as well as the spin-lattice coupling.
Title:
Incommensurate spin ordering and fluctuations in underdoped La2-xBaxCuO4
Authors:
Dunsiger, SR; Zhao, Y; Yamani, Z; Buyers, WJL; Dabkowska, HA; Gaulin, BD Author Full Names: Dunsiger, S. R.; Zhao, Y.; Yamani, Z.; Buyers, W. J. L.; Dabkowska, H. A.; Gaulin, B. D.
Source:
PHYSICAL REVIEW B 77 (22): Art. No. 224410 JUN 2008
Abstract:
By using neutron scattering techniques, we have studied the incommensurate spin ordering as well as the low energy spin dynamics in single crystal underdoped La2-xBaxCuO4 with x similar to 0.095 and 0.08, which are high temperature superconductors with T-C similar to 27 and 29 K, respectively. Static two dimensional incommensurate magnetic order appears below T-N=39.5 +/- 0.3 K in La2-xBaxCuO4 (x=0.095) and a similar temperature for x=0.08 within the low temperature tetragonal phase. The spin order is unaffected by either the onset of superconductivity or the application of magnetic fields of up to 7 T applied along the c axis in the x=0.095 sample. Such a magnetic field independent behavior is in marked contrast to the field induced enhancement of the staggered magnetization observed in the related La2-xSrxCuO4 system, which indicates that this phenomenon is not a universal property of cuprate superconductors. Surprisingly, we find that the incommensurability delta is only weakly dependent on doping relative to La2-xSrxCuO4. Dispersive excitations in La2-xBaxCuO4 (x=0.095) at the same incommensurate wave vector persist up to at least 60 K. The dynamical spin susceptibility of the low energy spin excitations saturates below T-C in a similar manner to that seen in the superconducting state of La2CuO4+y.
Title:
Change of antiferromagnetic structure near a quantum critical point in CeRh1-xCoxIn5
Authors:
Yokoyama, M; Oyama, N; Amitsuka, H; Oinuma, S; Kawasaki, I; Tenya, K; Matsuura, M; Hirota, K; Sato, TJ Author Full Names: Yokoyama, M.; Oyama, N.; Amitsuka, H.; Oinuma, S.; Kawasaki, I.; Tenya, K.; Matsuura, M.; Hirota, K.; Sato, T. J.
Source:
PHYSICAL REVIEW B 77 (22): Art. No. 224501 JUN 2008
Abstract:
The elastic neutron-scattering experiments were carried out on the solid solutions CeRh1-xCoxIn5 to clarify the nature of the antiferromagnetic (AF) state in the vicinity of the quantum critical point: x(c)similar to 0.8. The incommensurate AF order with the wave vector of q(h)=(1/2,1/2,similar to 0.3) observed in pure CeRhIn5 is weakly suppressed upon doping with Co, and a commensurate q(c)=(1/2,1/2,1/2) and an incommensurate q(1)=(1/2,1/2,similar to 0.42) AF structures evolve at intermediate Co concentrations. The AF orders with q(c) and q(1) are enhanced at x=0.7, and furthermore, the q(h) AF order vanishes. These results suggest that the AF correlations with the q(c) and q(1) modulations are significantly enhanced in the intermediate x range, and may be connected with the evolution of the superconductivity observed above x similar to 0.3.
Title:
Effect of Al addition on the elevated temperature deformation behavior of Mg-Zn-Y alloy
Authors:
Kim, DH; Lee, JY; Lim, HK; Kim, WT; Kim, DH Author Full Names: Kim, Do Hyung; Lee, Ju Yeon; Lim, Hyun Kyu; Kim, Won Tae; Kim, Do Hyang
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 487 (1-2): 481-487 JUL 25 2008
Abstract:
The effect of the addition of Al on the high temperature deformation behavior of wrought Mg-4Zn-0.8Y alloy has been investigated. The addition of Al significantly improves the high temperature formability, i.e. increases elongation from 260% to 370% under a strain rate of 1 x 10(-4) s(-1) at 300 degrees C. Strain rate sensitivity measured at different strain rates shows that the addition of Al induces the transition of high temperature deformation mechanism from dislocation creep mode to grain boundary sliding mode. Effect of alloying elements and microstructural evolution including the role of icosahedral-phase during deformation are discussed. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Characterization of Ni-Mn-Ga alloy with Gd addition
Authors:
Zhang, ZY; Du, ZW; Shao, BL; Liu, AS; Sun, ZM Author Full Names: Zhang, Z. Y.; Du, Z. W.; Shao, B. L.; Liu, A. S.; Sun, Z. M.
Source:
MATERIALS CHARACTERIZATION 59 (8): 1041-1045 AUG 2008
Abstract:
The effect of rare earth element Gd additions in an Ni-Mn-Ga alloy on magnetocaloric effect has previously been investigated. In this paper, the microstructure of Ni53.4Mn20Ga25.6Gd1 was studied by TEM. The results show that Gd partly dissolves in the matrix and partly occurs as precipitates such as Gd and Ni-rich Ni-Mn-Ga-Gd quaternary phases. At room temperature, the alloy is mainly composed of non-modulated martensite with a small amount of seven-layered and ten-layered modulated martensite. The high-resolution electron microscopy (HREM) images also reveal that some layered structures in certain zones are microtwins in nature with a thickness of a few atomic planes as the stacking sequence is not periodic. (C) 2007 Elsevier Inc. All rights reserved.
Title:
Superspace description, crystal structures, and electric conductivity of the Ba4In6-xMgxO13-x/2 solid solutions
Authors:
Abakumov, AM; Rossell, MD; Gutnikova, OY; Drozhzhin, OA; Leonova, LS; Dobrovolsky, YA; Istomin, SY; Van Tendeloo, G; Antipovt, EV Author Full Names: Abakumov, Artem M.; Rossell, Marta D.; Gutnikova, Olga Yu.; Drozhzhin, Oleg A.; Leonova, Ludmila S.; Dobrovolsky, Yuri A.; Istomin, Sergey Ya.; Van Tendeloo, Gustaaf; Antipovt, Evgeny V.
Source:
CHEMISTRY OF MATERIALS 20 (13): 4457-4467 JUL 8 2008
Abstract:
Ba3In6-xMgxO13-x/2 solid solutions have been prepar for 0 <= x <= 0.4 and their crystal structures have been studied by transmission electron microscopy and X-ray powder diffraction. The compounds adopt a modulated structure with a face-centered orthorhombic average unit cell with a(0)approximate to a(p) root 2, b(0)approximate to 20.5 angstrom, c(0)approximate to a(p) root 2 (a(p) - parameter of the perovskite subcell) and modulation vector.q=alpha a(0)* , which is compositionally dependent according to the Ba4In4+4 alpha Mg2-4 alpha O12+2 alpha formula.The -superspace group Xmms(alpha 00)0s0 Xrnrn2(a00)0s0 with centering vectors (0,1/2,1/2,1/2), (1/2,0,1/2,0.(1/2,1/2,0 1/2) was propose ed from electron diffraction and structural considerations. A unified suoersoace model is" construtted'to describe the atomic arrangements and the variable oxygen content in the modulated (In, Mg)2Q2+a layers with rock-salt type structure. This model was used to refine the crystai structures of two x= 0 (R-I 0.040, R-p = 0.042) and x = 0.4 (R-I = 0.062, R-p = 0.040) limiting points of the solid solu tions. The cations in these layers adopt a five-fold coordination that can be virtually classified as strongly distorted trigonal bipyramids and tetragonal pyramids. The close similarity of the structural organization of the Ba4In6-xMgxO13-x/2 solid solutions, Sr4Fe6O13 and its anion-deficient derivatives is discussed. Electric conductivity of the Ba4In6-xMgxO13-x/2 was studied by impedance spectroscopy indicating mixed ionicelectronic type of conductivity. Electronic conductivity at different P(O-2) was compared for Ba4In6-xMgxO13-x/2 and Ba2In2O5 and discussed taking into account the peculiarities of their crystal structures.

Update: 18-Jul-2008

Title:
Software package for structure analysis of quasicrystals
Authors:
Yamamoto, A Author Full Names: Yamamoto, Akiji
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 9 (1): Art. No. 013001 JAN-MAR 2008
Abstract:
Recently a software package for the structure analysis of quasicrystals has been released, giving a better environment for determining quasicrystal structures. Therefore we can analyze their structures if we know data collection and indexing methods and a theory of structure analysis. For the use of the package, the structure analysis method and several techniques used in the package are shortly reviewed. How to treat key information in the input files of the programs is described in detail.
Title:
Icosahedral clusters, icosaheral order and stability of quasicrystals - a view of metallurgy
Authors:
Tsai, AP Author Full Names: Tsai, An Pang
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 9 (1): Art. No. 013008 JAN-MAR 2008
Abstract:
We review the stability of various icosahedral quasicrystals ( iQc) from a metallurgical viewpoint. The stability of stable iQcs is well interpreted in terms of Hume-Rothery rules, i.e. atomic size factor and valence electron concentration, e/a. For metastable iQcs, we discuss the role of phason disorder introduced by rapid solidification, in structural stability and its interplay with chemical order and composition.
Title:
Finite doping of a one-dimensional charge density wave: Solitons vs Luttinger liquid charge density
Authors:
Weiss, Y; Goldstein, M; Berkovits, R Author Full Names: Weiss, Yuval; Goldstein, Moshe; Berkovits, Richard
Source:
PHYSICAL REVIEW B 77 (20): Art. No. 205128 MAY 2008
Abstract:
The effects of doping on a one-dimensional wire in a charge density wave state are studied using the density-matrix renormalization group method. We show that for a finite number of extra electrons, the ground state becomes conducting but the particle density along the wire corresponds to a charge density wave with an incommensurate+ wave number determined by the filling. We find that the absence of the translational invariance can be discerned even in the thermodynamic limit is long as the number of doping electrons is finite. The Luttinger liquid behavior is reached only for a finite change in the electron filling factor, which for an infinite wire corresponds to the addition of an infinite number of electrons. In addition to the half filled insulating Mott state and the conducting states, we find evidence for subgap states at fillings different from half filling by a single electron or hole. Finally, we show that by coupling our system to a quantum dot, one ca! n have a discontinuous dependence of its population on the applied gate voltage in the thermodynamic limit, similar to the one predicted for a Luttinger liquid without umklapp processes.
Title:
Phase transformation behaviour in continuously cooled Zr65Al7.5Ni10Cu17.5-xPdx (x=0-17.5) glass-forming alloys and consequences for structure and property control
Authors:
Setyawan, AD; Kato, H; Saida, J; Inoue, A Author Full Names: Setyawan, A. D.; Kato, H.; Saida, J.; Inoue, A.
Source:
PHILOSOPHICAL MAGAZINE 88 (8): 1125-1136 2008
Abstract:
Continuous cooling transformation (CCT) diagrams were successfully constructed for Zr65Al7.5Ni10Cu17.5-xPdx (x=0-17.5) glass-forming alloys, comparing phase-transformation features in the alloy system to composition. While a low-Pd alloy (x=5) showed a single transformation curve, corresponding to the formation of a crystalline phase on the high-temperature side of the undercooled-liquid region, for a given time-scale, a high-Pd alloy (x=17.5) revealed an additional curve, corresponding to quasicrystalline phase formation on the lower temperature side. The result provides a clue to the structural and property control on the alloy system. Glassy specimens of the same size but with different intrinsic structure, evaluated by structural relaxation during continuous heating, could be fabricated for the low-Pd alloy (x=5). Plasticity was found to increase proportionally with the relaxation enthalpy. On the other hand, the critical size for glass formation could be improved considerably from 5 to 7 mm in diameter for the high-Pd alloy (x=17.5).
Title:
A multi-component Fermi surface in the vortex state of an underdoped high-T-c superconductor
Authors:
Sebastian, SE; Harrison, N; Palm, E; Murphy, TP; Mielke, CH; Liang, RX; Bonn, DA; Hardy, WN; Lonzarich, GG Author Full Names: Sebastian, Suchitra E.; Harrison, N.; Palm, E.; Murphy, T. P.; Mielke, C. H.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Lonzarich, G. G.
Source:
NATURE 454 (7201): 200-203 JUL 10 2008
Abstract:
To understand the origin of superconductivity, it is crucial to ascertain the nature and origin of the primary carriers available to participate in pairing(1-6). Recent quantum oscillation experiments on high- transition- temperature ( high- T-c) copper oxide superconductors(7-10) have revealed the existence of a Fermi surface akin to that in normal metals, comprising fermionic carriers that undergo orbital quantization(11). The unexpectedly small size of the observed carrier pocket, however, leaves open a variety of possibilities for the existence or form of any underlying magnetic order, and its relation to d- wave superconductivity(12-15). Here we report experiments on quantum oscillations in the magnetization ( the de Haas- van Alphen effect) in superconducting YBa2Cu3O6.51 that reveal more than one carrier pocket. In particular, we find evidence for the existence of a much larger pocket of heavier mass carriers playing a thermodynamically dominant role in this hole- doped superconductor. Importantly, characteristics of the multiple pockets within this more complete Fermi surface impose constraints on the wavevector of any underlying order and the location of the carriers in momentum space. These constraints enable us to construct a possible density- wave model with spiral or related modulated magnetic order, consistent with experimental observations.
Title:
Origins of superstructure ordering and incommensurability in stuffed CoSn-Type phases
Authors:
Fredrickson, DC; Lidin, S; Venturini, G; Malaman, B; Christensen, J Author Full Names: Fredrickson, Daniel C.; Lidin, Sven; Venturini, Gerard; Malaman, Bernard; Christensen, Jeppe
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 130 (26): 8195-8214 JUL 2 2008
Abstract:
The CoSn structure type contains large interstitial void spaces that frequently host electropositive guest atoms, such as rare earth elements. In this stuffing process, an intriguing ordering occurs between the neighboring void spaces leading to a family of long-period superstructures comprising intergrowths of the ScFe6Ge6 and ScFe6Ga6 structure types. This superstucture ordering culminates in incommensurability in the REFe6Ge6_delta Ga6 systems with RE = Sc, Tb, and Lu. In this work, we derive a 3 + 1 D superspace model encompassing this series of structures and investigate the origins of the structural trends in this family with electronic structure calculations, at both the LDA-DFT and extended Huckel levels. Using our 3 + 1 D model, we refine the structures of four new ErFe6Ge6-delta Ga delta (0 <= 6 <= 6) phases, two commensurate and two incommensurate, from powder X-ray diffraction data. The refinement results confirm trends observed in the Sc-, Tb -, and Lu-based series: a gradual lengthening and, eventually, turning of the q-vector as Ge is progressively exchanged for Ga. These trends, and the incommensurate ordering as a whole, are traced to a tension between two modes by which the host lattice responds to stuffing atom insertion: (1) an atomic charge modulation enhancing the anionic character of the cavity walls around the guest atoms, and (2) a positional modulation expanding the cavities occupied by guest atoms. These two modes direct the stuffing atom ordering pattern toward opposite ends of the ScFe6Ge6-ScFe6Ga6 intergrowth series. The full series of structures, complex and incommensurate, reflects various degrees of balance between these two factors.
Title:
Incommensurate strain-induced ordering of interstitial oxygen in Nb
Authors:
Kurta, RP; Bugaev, VN; Stierle, A; Dosch, H Author Full Names: Kurta, R. P.; Bugaev, V. N.; Stierle, A.; Dosch, H.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (27): Art. No. 275206 JUL 9 2008
Abstract:
We present a semi-phenomenological theory of the strain-induced interaction between interstitial oxygen dissolved in Nb and predict an incommensurate oxygen ordering wave which is mediated by the intrinsic bcc instability at kappa = 2/3(111). We discuss the stability range of this ordering phenomenon, which may play a role in the performance of Nb radio frequency (RF) cavities for high energy particle accelerators.
Title:
Effects of Nb on the formation of icosahedral quasicrystalline phase in Ti-rich Ti-Zr-Ni-Cu-Be glassy forming alloys
Authors:
Mei, JN; Li, JS; Kou, HC; Fu, HZ; Zhou, L Author Full Names: Mei, J. N.; Li, J. S.; Kou, H. C.; Fu, H. Z.; Zhou, L.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 354 (28): 3332-3335 JUN 15 2008
Abstract:
As-cast (Ti40Zr25Ni8Cu9Be18)(100-x)Nb-x (0 <= x <= 5) (Phi 3) glassy forming alloys were investigated in order to clarify the role of Nb on the formation of icosahedral quasicrystalline phase (I-phase) in Ti-rich Ti-Zr-Ni-Cu-Be glassy system. It is found that an I-phase is formed in Ti-Zr-Ni-Cu-Be glassy alloy by addition of Nb element; however, the nucleation rate of I-phase increases, whereas the grain growth rate decreases with increasing Nb content. Moreover, with increasing Nb content, the thermal stability against crystallization increases, while the temperature range of stability of the I-phase decreases. (C) 2008 Elsevier B.V. All rights reserved.
Title:
Thermal stability, microstructure and crystallization kinetics of melt-spun Zr-Ti-Cu-Ni metallic glass
Authors:
Scudino, S; Venkataraman, S; Eckert, J Author Full Names: Scudino, S.; Venkataraman, S.; Eckert, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 460 (1-2): 263-267 JUL 28 2008
Abstract:
Melt-spun Zr63.33Ti8.89Cu15.45Ni2.33 glassy ribbons display a double-step devitrification behavior characterized by the precipitation of a metastable quasicrystalline phase in the first stage of the crystallization process, followed by the formation of crystalline phases in the following crystallization event. Investigation of the crystallization kinetics reveal that the initial part of the glass-to-quasicrystalline transformation (x <= 55 vol.%) occurs by diffusion controlled growth with an increasing nucleation rate (Avrami exponent n >= 2.5), whereas the later stage of the transformation (x > 55 vol.%) is dominated by the growth of the formed nuclei rather than by the generation of new nuclei (2.0 <= n <= 2.5). The activation energy for quasicrystallization is 360 kJ/mol, which is comparable to the values reported for other quasicrystal-forming Zr-based metallic glasses. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Unusual devitrification behaviour in rapidly solidified Ti45Zr38Ni17 alloy
Authors:
Lefaix, H; Vermaut, P; Janickovic, D; Svec, P; Gloriant, T; Portier, R; Prima, F Author Full Names: Lefaix, H.; Vermaut, P.; Janickovic, D.; Svec, P.; Gloriant, T.; Portier, R.; Prima, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 460 (1-2): 392-399 JUL 28 2008
Abstract:
In this study, Ti45Zr38Ni17 ribbons have been elaborated using planar flow casting method (v(quenching) 106 K s(-1)). The rapidly quenched samples, displaying a dispersion of nanoscaled beta phase particles in an amorphous matrix, have been extensively characterised using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Devitrification behaviour, investigated by four-probe resistivity measurements and differential scanning calorimetry as well as high resolution TEM analysis, revealed the formation of nanometric quasicrystals (QC) during the first exothermic phase transformation as well as the precipitation of omega domains inside beta particles. On the basis of these data, it has been noticed that nanoscaled beta metastable particles had adopted the same temperature dependence as beta metastable bulk. Furthermore, particular orientation relationships have been observed for QCs in the vicinity of beta particles which have suggested probable influence of crystalline structure on the QCs growth, although the presence of such peculiar materials after annealing treatment could be mainly explained by an icosahedral short-range order prevailing in Ti-Zr-Ni melt and favouring their nucleation. (C) 2007 Elsevier B.V. All rights reserved.

Update: 11-Jul-2008

Title:
SEM study of quasi-crystallized Zr65Cu12.5Ni10Al7.5Ag5 amorphous alloy at initial stage
Authors:
Wu, HM; Sun, W; Zhang, Z; Liu, L; Zhang, T Author Full Names: Wu Huimin; Sun Wei; Zhang Ze; Liu Li; Zhang Tao
Source:
RARE METAL MATERIALS AND ENGINEERING 37 (5): 823-826 MAY 2008
Abstract:
Microstructure evolvement during crystallization process for the melt-spun Zr65Cu12.5Ni10Al7.5Ag5 amorphous alloy has been studied by DSC analysis and TEM. We monitor the crystallization process by DSC, and stop at given temperatures, following by cooling down from these temperatures in the DSC furnace to examine the corresponding microstructure evolvement by TEM. The results show that the crystallization of Zr65Cu12.5Ni10Al7.5Ag5 alloy can be divided into three stages. At the initial stage, an icosahedral quasi-crystal (I-phase) is formed as primary phase from the amorphous matrix without apparent compositional variation. In comparison with the amorphous matrix, the I-phase is Zr-rich and Cu-poor slightly with high nucleation and growth rates by consuming the amorphous matrix, leading to a microstructure with closed packed grains at the first stage of crystallization. However, the residual amorphous phase still exists at this stage.
Title:
Pressure dependence of the magnetic ordering in CeRhIn5
Authors:
Raymond, S; Knebel, G; Aoki, D; Flouquet, J Author Full Names: Raymond, S.; Knebel, G.; Aoki, D.; Flouquet, J.
Source:
PHYSICAL REVIEW B 77 (17): Art. No. 172502 MAY 2008
Abstract:
We determine by neutron diffraction the propagation vector of the magnetic structure of CeRhIn5 under pressures of 1.5 and 1.7 GPa down to 375 mK. For both pressures, an incommensurate propagation vector k(IC2)=(1/2,1/2,0.4) is found in contrast to the low pressure one k(ICI)=(1/2,1/2,0.298). At 1.7 GPa, no change is found in the propagation vector and the intensity of the magnetic peaks in the superconducting phase below 1 K.
Title:
Magnetically asymmetiric interfaces in a LaMnO3/SrMnG(3) superlattice due to structural asymmetries
Authors:
May, SJ; Shah, AB; Velthuis, SGET; Fitzsimmons, MR; Zuo, JM; Zhai, X; Eckstein, JN; Bader, SD; Bhattacharya, A Author Full Names: May, S. J.; Shah, A. B.; Velthuis, S. G. E. te; Fitzsimmons, M. R.; Zuo, J. M.; Zhai, X.; Eckstein, J. N.; Bader, S. D.; Bhattacharya, A.
Source:
PHYSICAL REVIEW B 77 (17): Art. No. 174409 MAY 2008
Abstract:
Polarized neutron reflectivity measurements of a ferromagnetic [(LaMnO3)(11.8)/(SrMnO3)(4.4)](6) superlattice reveal a modulated magnetic structure with an enhanced magnetization at the interfaces where LaMnO3 was deposited on SrMnO3 (LMO/SMO). However, the opposite interfaces (SMO/LMO) are found to have a reduced ferromagnetic moment. The magnetic asymmetry is accompanied by a corresponding asymmetry in the lateral structural roughness of the two interfaces observed via electron microscopy, with enhanced ferromagnetism present at the interfaces that are atomically smooth over tens of nanometers. This result demonstrates that atomic-scale roughness can destabilize interfacial phases in complex oxide heterostructures.
Title:
Spin polarization of the magnetic spiral in NaCu2O2 as seen by nuclear magnetic resonance spectroscopy
Authors:
Gippius, AA; Moskvin, AS; Drechsler, SL Author Full Names: Gippius, A. A.; Moskvin, A. S.; Drechsler, S. -L.
Source:
PHYSICAL REVIEW B 77 (18): Art. No. 180403 MAY 2008
Abstract:
The incommensurate (IC) spin ordering in quasi-one-dimensional edge-shared cuprate NaCu2O2 has been studied by Na-23 nuclear magnetic resonance spectroscopy in an external magnetic field near 6 T applied along the main crystallographic axes. The NMR line shape evolution above and below TN approximate to 12 K yields a clear signature of an IC static modulation of the local magnetic field consistent with a Cu2+ spin spiral polarized in the bc plane rather than in the ab plane, as reported from earlier neutron diffraction data.
Title:
Comparison between experimental surface data and bulk structure models for quasicrystalline A1PdMn: Average atomic densities and chemical compositions
Authors:
Unal, B; Jenks, CJ; Thiel, RA Author Full Names: Unal, Baris; Jenks, C. J.; Thiel, R. A.
Source:
PHYSICAL REVIEW B 77 (19): Art. No. 195419 MAY 2008
Abstract:
We have examined bulk structure models for icosahedral A1PdMn in terms of the densities, compositions, and interplanar spacings for the fivefold planes that might represent physical surface terminations. We focus on four models that contain no partial or mixed occupancies, but some comparison is made to a fifth model containing such sites. Each of the four models contains paired planes (layers) that can be separated into two main families on the basis of three features: the relative densities of the two planes, the gap separating the layer from the nearest atomic plane, and the Pd content in the topmost plane. The experimental data and other arguments lead to the conclusion that the family with no Pd in the top plane is favored. Finally, all models show that correlations should be expected between the heights of steps that delineate terraces and average compositional and/or structural features of the terraces.
Title:
Mechanical properties and microstructure of twin-roll cast Mg-Zn-Y alloy
Authors:
Kim, KH; Lee, JG; Bae, GT; Bae, JH; Kim, NJ Author Full Names: Kim, Kyung-Hun; Lee, Jung Gu; Bae, Geun Tae; Bae, Jun Ho; Kim, Nack J.
Source:
MATERIALS TRANSACTIONS 49 (5): 980-985 MAY 2008
Abstract:
Mg97.3Zn2.3Y0.4 alloy has been subjected to twin-roll casting (TRC) process. As-cast microstructure consists of alpha-Mg dendrite and icosahedral interdendritic phase. The icosahedral phase present in TRC alloy is found to be thermally unstable and transforms to H-phase and W-phase during subsequent thermo-mechanical treatment (TMT) at 400 degrees C. It shows that the pre-heating condition has a significant effect on the microstructural evolution during TMT. The specimen pre-heated at 400 degrees C for 30 min shows elongated microstructure after TMT, while the specimen pre-heated at 400 degrees C for 12 h shows equiaxed recrystallized structure after TMT. Such homogeneous microstructure of the specimen pre-heated at 400 degrees C for 12 h results in better combinations of strength and ductility than the specimen pre-heated at 400 degrees C for 30 min.
Title:
Pressure-induced commensurate magnetic order in multiferroic HoMn2O5
Authors:
Kimura, H; Nishihata, K; Noda, Y; Aso, N; Matsubayashi, K; Uwatoko, Y; Fujiwara, T Author Full Names: Kimura, Hiroyuki; Nishihata, Keisuke; Noda, Yukio; Aso, Naofumi; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Fujiwara, Tetsuya
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (6): Art. No. 063704 JUN 2008
Abstract:
The pressure-temperature (p-T) phase diagram for microscopic magnetism in the multiferroic compound HoMn2O5 was established using neutron diffraction measurements under a hydrostatic pressure up to 1.25 GPa. At ambient pressure, incommensurate-commensurate-incommensurate magnetic phase transitions occur successively with decreasing temperature. Upon applying pressure, the incommensurate phase at the lowest temperature almost decreases and the commensurate phase appears. The p-T phase diagram established shows excellent agreement with the recently reported p-T dielectric phase diagram, where ferroelectricity is induced by applying pressure. We also found that the p-T magnetic phase diagram is quite similar to the previously obtained magnetic field-temperature phase diagram.
Title:
Discommensurate structure in [(Ca0.90Sr0.10)(2)CoO3](0.61)CoO2
Authors:
Yubuta, K; Huang, XY; Miyazaki, Y; Kajitani, T Author Full Names: Yubuta, Kunio; Huang, Xiangyang; Miyazaki, Yuzuru; Kajitani, Tsuyoshi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (6): Art. No. 064604 JUN 2008
Abstract:
The crystal structure of partly Sr-substituted Co-121, i.e., "Ca3Co4Co9", single crystal is studied by means of the electron diffraction measurements and high-resolution transmission electron microscopy (HREM). The crystal structure consists of two interpenetrating subsystems of a CoO2 sheet and a distorted three-layered (Ca,Sr)(2)CoO3 rock-salt (RS)-type block layers, which belong to a triclinic system. Both subsystems have common a-, c-axes and alpha-, beta-, gamma-angle with a = 4.8267(1) angstrom, c = 10.9214(3) angstrom, alpha = 90.916(2)degrees, beta = 98.291(5)degrees, and gamma = 89.957(3)degrees. On the other hand, the crystal structure is modulated parallel to the b-axis, along which the CoO2 sheet has b(1) = 2.8346(1) angstrom and the (Ca,Sr)(2)CoO3 RS-type block layer has b(2) = 4.6391(2) angstrom, respectively. On the basis of the b(1)/b(2) ratio and analyzed chemical compositions, the structure analogue is formulated as [(Ca0.90Sr0.10)(2)CoO3](0.61)CoO2. In electron diffraction patterns, there are many new satellite reflections, namely 0101, 0202, 0204, and 0103, which are not present in the end member Co-121, i.e., (Ca2CoO3)(0.620)CoO2. Because of the new superlattice reflections, the crystal structure of the Sr-doped Compound is different from the end member. HREM images were taken with the incident electron beam parallel to the [0010] and [1000] directions. The basic crystal structure of the present system consists of 5-CoO2 and 3-RS subcells with b = 14 angstrom being connected discommensuratedly parallel to the a- and b-axes. Systematic introduction of stacking faults parallel to the a-b plane is also noticed.
Title:
Twin boundary structure of the modulated variants in a Ni-Mn-Ga alloy
Authors:
Han, M; Kong, FF Author Full Names: Han, M.; Kong, F. F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 458 (1-2): 218-222 JUN 30 2008
Abstract:
The micro structure of a Ni-Mn-Ga ferromagnetic shape memory alloy has been characterized by transmission electron microscopy. Electron diffraction reveals that the microstructure of the alloy predominately consists of seven-layer modulated martensite. There exists reflection-twinned relation between the martensitic variants. It is found that there are parallel and equidistant fringes at the boundary. The nature of these fringes is discussed and the results show that the boundary fringes are caused by the elastic strains associated with the coherent interface. (c) 2007 Elsevier B.V All rights reserved.
Title:
Bond stretching phonon anomalies due to incommensurate charge density wave instabilities in high-T-c cuprates
Authors:
Citro, R; Cojocaru, S; Marinaro, M Author Full Names: Citro, R.; Cojocaru, S.; Marinaro, M.
Source:
EUROPEAN PHYSICAL JOURNAL B 63 (2): 179-185 MAY 2008
Abstract:
Phonon anomalies observed in various high T-c cuprates are analyzed theoretically within the Hubbard-Holstein model in the limit of strong local electron correlations and in presence of long-range Coulomb interaction. The phonon self-energy is evaluated by taking into account the charge collective modes that become critical upon doping approaching an instability towards an incommensurate charge density wave (ICDW) driven by electron correlations. The doping dependence of phonon softening features and the highly distinctive phonon self-energy dependence on the wave vector agree with experiments. We discuss relevance of dynamical corrections to the density correlation function to achieve a sizeable bond-stretching phonon softening with a kink-like profile away from the zone boundary.
Title:
Reaction efficiency of diffusion-controlled processes on finite, aperiodic planar arrays
Authors:
Garza-Lopez, RA; Kaufman, A; Patel, R; Chang, J; Brzezinski, J; Kozak, JJ Author Full Names: Garza-Lopez, Roberto A.; Kaufman, Aaron; Patel, Reena; Chang, Joseph; Brzezinski, Jack; Kozak, John J.
Source:
CHEMICAL PHYSICS LETTERS 458 (1-6): 137-140 JUN 27 2008
Abstract:
Using the theory of finite Markov processes, we show quantitatively that diffusion-limited, reactive events on two finite planar arrays having an aperiodic lattice structure are kinetically advantaged relative to processes on platelets having a regular, hexagonal [ 63] structure. The possible relevance of the results obtained to catalytic processes on quasicrystals and zeolite 'rafts' is noted. (c) 2008 Elsevier B. V. All rights reserved.
Title:
Inter-martensite strain evolution in NiMnGa single crystals
Authors:
Hamilton, RF; Sehitoglu, H; Aslantas, K; Efstathiou, C; Maier, HJ Author Full Names: Hamilton, R. F.; Sehitoglu, H.; Aslantas, K.; Efstathiou, C.; Maier, H. J.
Source:
ACTA MATERIALIA 56 (10): 2231-2236 JUN 2008
Abstract:
Stress-induced martensitic transformations are clarified in classes of NiMnGa alloys which undergo the stress-free, thermal-induced inter-martensite transformation austenite (A) reversible arrow pre-martensite (PM) reversible arrow martensite. This study implements a comprehensive experimental approach, including analysis of the strain-temperature and stress-strain response, which discloses stress-induced inter-martensite transitions. The evolution of the transitions is elucidated using in situ digital image correlation (DIC) measurements of meso-scale strain fields. Under stress, this body of work unequivocally demonstrates that the transformation path becomes A reversible arrow PM reversible arrow I reversible arrow 10M. The I-phase is an intermediate stress-induced martensite with a modulation period between three and five-layers. Owing to the intermediate transition, the thermal hysteresis in the strain-temperature response is tiny (<10 degrees C) compared with the hysteresis (32 degrees C) for A reversible arrow 10M. The differential hysteresis levels are rationalized based on a thereto-mechanical formulation. Meso-scale DIC measurements quantify inter-martensite strain levels, which are indistinguishable from macro-scale stress-strain and strain-temperature responses. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Dislocation-climb plasticity: Modelling and comparison with the mechanical properties of icosahedral AlPdMn
Authors:
Mompiou, F; Caillard, D Author Full Names: Mompiou, F.; Caillard, D.
Source:
ACTA MATERIALIA 56 (10): 2262-2271 JUN 2008
Abstract:
A model of plasticity controlled by the pure climb motion of dislocations is proposed and compared with the mechanical properties of icosahedral AlPdMn. This model takes into account the chemical stress due to an out-of-equilibrium average concentration of vacancies, and the difficult nucleation of jog-pairs on climbing dislocations. It accounts for several unexplained properties of AlPdMn, namely a high strain-hardening at yield, a steady-state flow stress twice higher than the elastic limit, and two-stage relaxation curves. It also explains values of the stress-strain rate sensitivity larger than expected a priori, and activation energies larger than the self-diffusion one. The model may also be applicable to high-temperature deformation of crystals. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Elastic properties of two-dimensional quasicrystals
Authors:
Grimmer, H Author Full Names: Grimmer, Hans
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 64: 459-464 Part 4 JUL 2008
Abstract:
Quasicrystals (QC) with two-dimensional quasiperiodic and one-dimensional periodic structure are considered. Their symmetry can be described by embedding the three-dimensional physical space V-E in a five-dimensional superspace V, which is the direct sum of V-E and a two-dimensional internal space V-I. A displacement v in V can be written as v = u + w, where u is an element of V-E and w is an element of V-I. If the QC has a point group P in V-E that is crystallographic, it is assumed that w and a vector u' is an element of V-E lying in the plane in which the crystal is quasiperiodic transform under equivalent representations of P, inequivalent ones if the point group is 5-, 8-, 10-or 12-gonal. From the Neumann principle follow restrictions on the form of the phonon, phason and phonon-phason coupling contributions to the elastic stiffness matrix that can be determined by combining the restrictions obtained for a set of elements generating the point group of interest. For the phonon part, the restrictions obtained for the generating elements do not depend on the system to which the point group belongs. This remains true for the phason and coupling parts in the case of crystallographic point groups but, in general, breaks down for the non-crystallographic ones. The form of the symmetric 12 x 12 matrix giving the phonon, phason and phonon-phason coupling contributions to the elastic stiffness is presented in graphic notation.

Update: 4-Jul-2008

Title:
Single-crystalline B12As2 on m-plane (1(1)over-bar00) 15R-SiC
Authors:
Chen, H; Wang, G; Dudley, M; Xu, Z; Edgar, JH; Batten, T; Kuball, M; Zhang, LH; Zhu, YM Author Full Names: Chen, Hui; Wang, Guan; Dudley, Michael; Xu, Zhou; Edgar, J. H.; Batten, Tim; Kuball, Martin; Zhang, Lihua; Zhu, Yimei
Source:
APPLIED PHYSICS LETTERS 92 (23): Art. No. 231917 JUN 9 2008
Abstract:
Single crystal, heteroepitaxial growth of icosahedral B12As2 (IBA, a boride semiconductor) on m-plane 15R-SiC is demonstrated. Previous studies of IBA on other substrates, i.e., (111)Si and (0001)6H-SiC, produced polycrystalline and twinned epilayers. In contrast, single-crystalline and untwinned IBA was achieved on m-plane 15R-SiC. Synchrotron white beam x-ray topography, Raman spectroscopy, and high resolution transmission electron microscopy confirm the high quality of the films. High quality growth is shown to be mediated by ordered nucleation of IBA on (474) substrate facets. This work demonstrates that m-plane 15R-SiC is a good substrate choice to grow high-quality untwinned IBA epilayers for future device applications. (C) 2008 American Institute of Physics.

Update: 27-Jun-2008

Title:
Analytical solutions for some defect problems in 1D hexagonal and 2D octagonal quasicrystals
Authors:
Wang, X; Pan, E Author Full Names: Wang, X.; Pan, E.
Source:
PRAMANA-JOURNAL OF PHYSICS 70 (5): 911-933 MAY 2008
Abstract:
We study some typical defect problems in one-dimensional (ID) hexagonal and two-dimensional (2D) octagonal quasicrystals. The first part of this investigation addresses in detail a uniformly moving screw dislocation in a ID hexagonal piezoelectric quasicrystal with point group 6mm. A general solution is derived in terms of two functions phi(1), phi(2), which satisfy wave equations, and another harmonic function phi(3). Elementary expressions for the phonon and phason displacements, strains, stresses, electric potential, electric fields and electric displacements induced by the moving screw dislocation are then arrived at by employing the obtained general solution. The derived solution is verified by comparison with existing solutions. Also obtained in this part of the investigation is the total energy of the moving screw dislocation. The second part of this investigation is devoted to the study of the interaction of a straight dislocation with a semi-infinite crack in an octagonal quasicrystal. Here the crack penetrates through the solid along the period direction and the dislocation line is parallel to the period direction. We first derive a general solution in terms of four analytic functions for plane strain problem in octagonal quasicrystals by means of differential operator theory and the complex variable method. All the phonon and phason displacements and stresses can be expressed in terms of the four analytic functions. Then we derive the exact solution for a straight dislocation near a semi-infinite crack in an octagonal quasicrystal, and also present the phonon and phason stress intensity factors induced by the straight dislocation and remote loads.
Title:
Synthesis and stability of Ti-Zr-Ni quasicrystals
Authors:
Azhazha, VM; Bovda, AM; Lavrinenko, SD; Onischenko, LV; Malykhin, SV; Pugachov, AT; Reshetnyak, MV; Stetsenko, OM; Savitskiy, BA Author Full Names: Azhazha, V. M.; Bovda, A. M.; Lavrinenko, S. D.; Onischenko, L. V.; Malykhin, S. V.; Pugachov, A. T.; Reshetnyak, M. V.; Stetsenko, O. M.; Savitskiy, B. A.
Source:
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY (4): 82-87 2007
Abstract:
For the Ti-Zr-Ni ribbons prepared by melt spinning, phase composition, structure, substructure, state of stress and several physical properties were studied as functions of their element compositions; and optimum parameters for single-phase icosahedral quasicrystal synthesis have been found. The icosahedral structure perfection characteristics, namely quasicrystallinity parameter X-ray coherence length, and average micro-strain values were determined for different synthesis regimes. Transversal gradient-like distributions of grain size, micro-and nano-hardness, Young modulus, residual stress, and substructure parameters have been revealed in the ribbons.
Title:
Modulated magnetic structures of the antiferromagnetic hydride CeRuSiH
Authors:
Tence, S; Andre, G; Gaudin, E; Chevalier, B Author Full Names: Tence, S.; Andre, G.; Gaudin, E.; Chevalier, B.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (25): Art. No. 255239 JUN 25 2008
Abstract:
The hydride CeRuSiH is derived from the non-magnetic heavy-fermion ternary silicide CeRuSi that crystallizes in the tetragonal CeFeSi-type structure (P4/nmm space group). This hydride exhibits two antiferromagnetic transitions at T-N1 = 7.5( 2) K and T-N2 = 3.1(2) K, evidenced by magnetization and specific heat measurements. Crystal and magnetic structures of CeRuSiH have thus been investigated by means of neutron powder diffraction, which has shown firstly that H-atoms are fully inserted in the [Ce-4]- tetrahedra. Moreover, between T-N1 and T-N2, the Ce magnetic moments are ordered in a collinear antiferromagnetic sinusoidal structure associated with the propagation vector k = (k(x), k(x), 1/2) (k(x) < 1/3 and tends to 1/3 with decreasing temperature). At T-N2, the magnetic structure becomes square wave modulated and commensurate with k = (1/3, 1/3, 1/2) as propagation vector. At 1.5 K, the structure is antiphase with a Ce magnetic moment of 1.68(2) mu(B). These magnetic structures are compared with those previously reported on the substituted ternary silicides (Ce1-xLax)Ru2Si2 and CeRu2(Si1-xGex)(2), which also present an antiferromagnetic behaviour.
Title:
Designed synthesis of families of misfit-layered compounds
Authors:
Lin, Q; Heideman, CL; Nguyen, N; Zschack, P; Chiritescu, C; Cahill, DG; Johnson, DC Author Full Names: Lin, Qiyin; Heideman, Colby L.; Nguyen, Ngoc; Zschack, Paul; Chiritescu, Catalin; Cahill, David G.; Johnson, David C.
Source:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY (15): 2382-2385 MAY 2008
Abstract:
The synthesis of several new families of misfit-layered compounds is demonstrated. These compounds are crystalline along the c-axis and in the ab-plane, but show very short coherence lengths between ab-planes. This disorder leads to ultra-low and tunable thermal conductivity. Annealing iso-structural samples under a chalcogen vapour until equilibrium is reached results in reproducible Seebeck and resistivity values. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).
Title:
Quasicrystal mystery unraveled with computer simulation
Authors:
[Anon]
Source:
ADVANCED MATERIALS & PROCESSES 166 (6): 12-12 JUN 2008

Update: 20-Jun-2008

Title:
DFT studies on structure, mechanics and phase behavior of magnetic shape memory alloys: Ni2MnGa
Authors:
Kart, SO; Uludogan, M; Karaman, I; Cagin, T Author Full Names: Kart, S. Oezdemir; Uludogan, M.; Karaman, I.; Cagin, T.
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 205 (5): 1026-1035 MAY 2008
Abstract:
Magnetic shape memory alloys (MSMAs) are the smart materials which can undergo a reversible structural phase transition when a magnetic field is applied. The experimentally most studied MSMA, Ni2MnGa, undergoes a martensitic phase transition from a high temperature cubic phase to a low temperature tetragonal phase. In this work, a detailed study of structure, magnetic and mechanical properties of Ni2MnGa in these phases were performed using density functional theory (DFT). The predicted lattice constant, bulk modulus, magnetic moments and elastic constants of the initial L2(1) structure are in good agreement with experimental results and previous calculations. We report the martensitic phase at cla = 1.26 for non-modulated and cla = 0.93 for 5M modulated structures which are consistent with the experiments. Analysis of electronic density of states showed that the double minority spin peak appeared at the Fermi level is due to the hybridization of Ga 4p and Ni 3d states. The peaks in the minority spin in the cubic structure reverse their order during martensitic transformation. The elastic constants of martensitic phases were also calculated to encourage measurements of these quantities.
Title:
An effective model of magnetoelectricity in multiferroics RMn2O5
Authors:
Fang, C; Hu, JP Author Full Names: Fang, Chen; Hu, Jangping
Source:
EPL 82 (5): Art. No. 57005 JUN 2008
Abstract:
An effective model is developed to explain the phase diagram and the mechanism of magnetoelectric coupling in multiferroics, RMn2O5. We show that the nature of magnetoelectric coupling in RMn2O5 is a coupling between two Ising-type orders, namely, the ferroelectric order in the b-axis, and the. coupled magnetic order between two frustrated antiferromagnetic chains. The frustrated magnetic structure drives the system to a commensurate-incommensurate phase transition, which can be understood as a competition between a collinear order stemming from the "order by disorder" mechanism and a chiral symmetry order. The low-energy excitation is calculated and it quantitatively matches experimental results. Distinct features and the effects of external magnetic field in the electromagnon spectra in the incommensurate phase are predicted. Copyright (c) EPLA, 2008.

Update: 13-Jun-2008

Title:
Local structure of perovskite-based "Pb2Fe2O5"
Authors:
Hadermann, J; Abakumov, AM; Nikolaev, IV; Antipov, EV; Van Tendeloo, G Author Full Names: Hadermann, Joke; Abakumov, Artem M.; Nikolaev, Ivan V.; Antipov, Evgeny V.; Van Tendeloo, Gustaaf
Source:
SOLID STATE SCIENCES 10 (4): 382-389 APR 2008
Abstract:
The reciprocal lattice and defect structure of the crystallographic shear (CS) structures in perovskite-based "Pb2Fe2O5" are investigated using transmission electron microscopy. The reciprocal space for all observed 1/2[110](h0l)p CS structures can be described with the same average pseudocubic unit cell with a approximate to a(p) (a(p) - the parameter of the perovskite subcell), and modulation vector q approximate to alpha a* + gamma c* with alpha/y = h/l and superspace group X2/m(alpha 0 gamma) with a centering vector [1/2,1/2,1/2,1/2]. The defect structure is characterized by numerous mirror twins and coherent intergrowths of 1/2[110](h0l)p CS structures with different (h0l)p. There are no single CS planes in the perovskite matrix and there is no variation of the perovskite block thickness between the successive CS planes. The crystallographic similarity and the structural and chemical differences between the CS structures in "Pb2Fe2O5" and those in ReO3 and/or TiO2-type oxides are discussed. (C) 2007 Elsevier Masson SAS. All rights reserved.
Title:
Indentation creep study on a Zr-based bulk metallic glass containing nano-quasicrystals
Authors:
Lendvai, J; Fatay, D; Gubicza, J Author Full Names: Lendvai, J.; Fatay, D.; Gubicza, J.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 483: 607-610 Sp. Iss. SI JUN 15 2008
Abstract:
The effect of crystallization on the creep behavior of a Zr-based bulk metallic glass (BMG) with the composition of Zr44Ti11Cu10Ni10B25 (at.%) was studied by indentation technique. The crystallization process was studied by isothermal annealing in a differential scanning calorimeter at three different temperatures above the glass transition temperature (677, 682 and 687 K). Two exothermic peaks are detected, the first one corresponds to the formation of a quasicrystalline phase. Indentation creep tests were carried out isothermally at the same three temperatures for studying the correlation between the amount of quasicrystalline phase and the creep behavior. A simple relationship between the viscosity and the crystalline phase fraction was found and the activation energy was found to decrease with the progress of crystallization. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Model for the transformation of an icosahedral phase into a B2 crystalline phase
Authors:
Kraposhin, VS; Talis, AL; Lam, HT; Dubois, JM Author Full Names: Kraposhin, V. S.; Talis, A. L.; Lam, Ha Thanh; Dubois, J-M
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (23): Art. No. 235215 JUN 11 2008
Abstract:
A model for the transformation of an Al-Cu-Fe icosahedral quasicrystal into a crystal with a B2-type phase is proposed. The model is based on two assumptions: ( 1) the main building block for the quasicrystal structure is a hierarchical dodecahedron composed of two icosahedral clusters, coinciding with two different sections of the {3, 3, 5} polytope; ( 2) the transformation of the quasicrystal into a B2-type crystal phase can be described as the transition between 3D sections of two polytopes, namely {3, 3, 5} and {3, 4, 3}. In the framework of the proposed model, two experimental facts gain plausible explanations: the transformation of the Al-Cu-Fe quasicrystal into the BCC phase specifically and the orientational relationships observed between this BCC phase and the initial icosahedral quasicrystal.
Title:
Amorphous-to-quasicrystalline transformations in the Ti-Zr-Ni and Ti-Hf-Ni systems
Authors:
Kocjan, A; McGuiness, PJ; Linaric, MR; Kobe, S Author Full Names: Kocjan, A.; McGuiness, P. J.; Linaric, M. Rajic; Kobe, S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 457 (1-2): 144-149 JUN 12 2008
Abstract:
We have synthesized Ti-Zr-Ni- and Ti-Hf-Ni-based quasicrystals by the mechanical alloying of elementary powders with an average particle size of 35 mu m in a high-energy planetary ball mill followed by a vacuum heat treatment. The X-ray diffraction (XRD) spectra indicate that the mixture was to a large extent amorphous after mechanically alloying for more than 40 h. These largely amorphous precursors, after various times of mechanical alloying, were subsequently analysed by means of differential scanning calorimetry (DSC) in order to obtain the kinetic parameters of crystallization, such as the temperature and the activation energy. DSC was used in combination with XRD to identify the structural changes related to the peaks in the DSC scans. The morphologies and compositions were analysed using scanning electron microscopy with an energy-dispersive spectrometer. We observed agglomerates ranging in size from 5 to 50 mu m; these agglomerates consisted of smaller particles with sub-micrometer diameters. The composition of the agglomerates was not homogenous, since small areas (similar to 1 mu m) of Zr-rich secondary phase were observed inside them. Using a vibrating-sample magnetometer (VSM) we found that the saturation magnetization decreases with mechanical treatment, and is additionally decreased with the time and temperature of a subsequent vacuum heat treatment. The saturation magnetization (M-s) decreases fairly linearly, from the initial mixture of crystalline elements, which is ferromagnetic due to nickel, through to a largely amorphous phase, and then to the quasicrystalline phase, where the M-s value is the lowest. As a result, measuring the magnetic properties allows us to probe the structural transformations in the material. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Collinear second harmonic generations in a nonlinear photonic quasicrystal
Authors:
Sheng, Y; Koynov, K; Dou, JH; Ma, BQ; Li, JJ; Zhang, DZ Author Full Names: Sheng, Yan; Koynov, Kaloian; Dou, Junhong; Ma, Boqin; Li, Jingjuan; Zhang, Daozhong
Source:
APPLIED PHYSICS LETTERS 92 (20): Art. No. 201113 MAY 19 2008
Abstract:
LiNbO3 nonlinear photonic quasicrystal with octagonal symmetry was fabricated. The collinear quasiphase matched second harmonic generations at 22 wavelengths were observed. It is shown that not only the standard type quasiphase matching but also the recently proposed projection-based quasiphase matching plays an important role in these harmonic generations. (c) 2008 American Institute of Physics.

Update: 6-Jun-2008

Title:
Pseudogap and charge density waves in two dimensions
Authors:
Borisenko, SV; Kordyuk, AA; Yaresko, AN; Zabolotnyy, VB; Inosov, DS; Schuster, R; Buchner, B; Weber, R; Follath, R; Patthey, L; Berger, H Author Full Names: Borisenko, S. V.; Kordyuk, A. A.; Yaresko, A. N.; Zabolotnyy, V. B.; Inosov, D. S.; Schuster, R.; Buechner, B.; Weber, R.; Follath, R.; Patthey, L.; Berger, H.
Source:
PHYSICAL REVIEW LETTERS 100 (19): Art. No. 196402 MAY 16 2008
Abstract:
Using angle-resolved photoemission spectroscopy we demonstrate that a normal-state pseudogap exists above TN-IC in one of the most studied two-dimensional charge-density wave (CDW) dichalcogenides 2H-TaSe2. The initial formation of the incommensurate CDW is confirmed as being driven by a conventional nesting instability, which is marked by a pseudogap. The magnitude, character, and anisotropy of the 2D-CDW pseudogap bear considerable resemblance to those seen in superconducting cuprates.
Title:
Commensurate to incommensurate transition in the chiral helimagnet CuB2O4
Authors:
Fujta, T; Fujimoto, Y; Mitsudo, S; Idehara, T; Saito, T; Kousaka, Y; Yano, SI; Akimitsu, J; Kishine, JI; Inoue, K; Motokawa, M Author Full Names: Fujta, Toshiyuki; Fujimoto, Yoshikuni; Mitsudo, Seitaro; Idehara, Toshitaka; Saito, Teruo; Kousaka, Yusuke; Yano, Shin-ichiro; Akimitsu, Jun; Kishine, Jun-ichiro; Inoue, Katsuya; Motokawa, Mitsuhiro
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (5): Art. No. 053702 MAY 2008
Abstract:
We have studied a commensurate to incommensurate transition in the novel helimagnet CuB2O4 by means of high-frequency ESR. In the commensurate weak ferromagnetic (CWF) state, two ESR modes have been found at low temperatures, which are explained in terms of an electron paramagnetic resonance of the Cu2+ spins at 8d-sites and an antiferromagnetic resonance of the magnetically ordered Cu2+ spins at 4b-sites with the Dzyaloshinskii-Moriya (DM) interaction. The DM interaction among the Cu2+ spins at 4b-sites that carries the CWF state is evaluated quantitatively. The incommensurate helimagnetic state is discussed in terms of the magnetic frustration.
Title:
Field-induced incommensurate lattice modulations in the delafossite CuFeO2
Authors:
Terada, N; Mitsuda, S; Tanaka, Y; Tabata, Y; Katsumata, K; Kikkawa, A Author Full Names: Terada, Noriki; Mitsuda, Setsuo; Tanaka, Yoshikazu; Tabata, Yoshikazu; Katsumata, Koichi; Kikkawa, Akiko
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (5): Art. No. 054701 MAY 2008
Abstract:
The results of synchrotron X-ray diffraction measurements on a single crystal of the triangular lattice antiferromagnet CuFeO2 under zero and non-zero applied magnetic fields are reported. We find four satellite reflections at (0, 3+q, 1/2), (0,4 -q, 1/2), (0,4 -2q, 0), and (0, 3+2q, 0) with the incommensurate wave number q similar to 0.415 in the ferroelectric incommensurate (FEIC) phase which appears in the magnetic field, H, between 7 and 13 T at low temperatures. In the partially disordered (PD) phase which exists in the temperature, T, range between 11 and 14 K, we find two satellite reflections at (0, 4-q, 1/2) and (0, 4-2q, 0) with the incommensurate wave number q similar to 0.4. The T and H dependence of these satellite reflections are studied. We interpret that the reflections observed in the FEIC phase arise from incommensurate lattice modulations caused by a magnetoelastic coupling with the underlying magnetic structure. The observation of the reflection (0, 4-q, 1/2) in finite fields and the (0, 4-2q, 0) reflection at 0 <= H in the PD phase is also explained by the same model. A calculation of the X-ray diffraction intensity assuming the displacement of oxygen ions only successfully explains the observation. We discuss the relevance of these satellite reflections to the ferroelectricity.
Title:
Optical phonon characteristics of incommensurate and commensurate modulated phases of Bi3NbO7 ceramics
Authors:
Moreira, RL; Matinaga, FM; Pirnat, U; Suvorov, D; Dias, A Author Full Names: Moreira, Roberto L.; Matinaga, Franklin M.; Pirnat, Ursa; Suvorov, Danilo; Dias, Anderson
Source:
JOURNAL OF APPLIED PHYSICS 103 (9): Art. No. 094108 MAY 1 2008
Abstract:
Raman and infrared-reflectivity spectroscopies were used to investigate the optical phonon modes of the cubic-incommensurate and tetragonal-commensurate phases of Bi3NbO7 ceramic samples. For both structures, the observed features could be well described by applying the factor-group method to average oxygen-deficient fluorite subcells; i.e., it was possible to predict the correct number and the activities of the observed phonon modes. The spectra showed rather broad bands, which are mainly for the cubic-incommensurate phase, probably because of the disorder of the oxygen vacancies and the folding of the Brillouin zone due to the modulation of the atomic positions. This can partially explain the higher quality factor and the potential interest in the tetragonal phase of this material for applications in microwave devices. (C) 2008 American Institute of Physics.
Title:
Vacancy-ordering effects in AlB2-type ErGe2-x (0.4 < x <= 0.5)
Authors:
Christensen, J; Lidin, S; Malaman, B; Venturini, G Author Full Names: Christensen, Jeppe; Lidin, Sven; Malaman, Bernard; Venturini, Gerard
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 272-280 Part 3 JUN 2008
Abstract:
In the Er-Ge system, the compostion range ErGe2 to Er2Ge3 has been investigated. Eight samples were produced by arc melting of the elements, and analyzed using X-ray powder diffraction. Nine crystal structures were found to be present in the samples. The structures are described as a homologous series and presented within the superspace formalism using the superspace group X2/m(alpha 0 gamma)0s, X representing the centring vector (1/2, 1/2, 0, 1/2). In this description the modulation vector q = (alpha a+gamma c) is shown to be a direct measure of the Ge content as ErGe2-alpha (alpha falls in the range 1/3 to 1/2). The large composition range is achieved by extended vacancy ordering in the planar 6(3) net of Ge with subsequent relaxation.

Update: 30-May-2008

Title:
On the magnetic phase diagram of copper metaborate
Authors:
Popov, MA; Petrakovskii, GA; Bolsunovskaya, OA Author Full Names: Popov, M. A.; Petrakovskii, G. A.; Bolsunovskaya, O. A.
Source:
PHYSICS OF THE SOLID STATE 50 (5): 909-912 MAY 2008
Abstract:
A stepwise transition from one incommensurate state of the spin system of a copper metaborate crystal to another incommensurate state was previously revealed using neutron scattering in an applied magnetic field. In this paper, the new state is interpreted as a combination of a commensurate state of one spin subsystem and an incommensurate state of another spin subsystem of the crystal.
Title:
Plastic fracture of quasicrystals
Authors:
Fan, TY; Fan, L Author Full Names: Fan, T. Y.; Fan, L.
Source:
PHILOSOPHICAL MAGAZINE 88 (4): 523-535 FEB 1 2008
Abstract:
Elasto-plastic crack solutions for some one- and two-dimensional quasicrystals have been found based on the generalized Dugdale-Barenblatt model. The size of the plastic zone and crack tip opening displacement are determined, from which a plastic fracture criterion for the materials is suggested.
Title:
Crystallographic studies on the iron-containing intermetallic phases in the 319-type aluminium casting alloys
Authors:
Hwang, JY; Doty, HW; Kaufman, MJ Author Full Names: Hwang, J. Y.; Doty, H. W.; Kaufman, M. J.
Source:
PHILOSOPHICAL MAGAZINE 88 (4): 607-619 FEB 1 2008
Abstract:
The iron-containing intermetallic compounds in type 319 aluminium casting alloys were investigated using convergent beam electron diffraction (CBED) and electron backscatter diffraction (EBSD). The Chinese script U-phase was identified as having the cubic Im 3 space group consistent with the Al19Fe4MnSi2 phase reported in the literature. However, the atomic ordering of this phase results in complex Kikuchi lines in the CBED and EBSD patterns, which makes phase and orientation identification difficult. In fact, it is shown that the EBSD patterns in the scanning electron microscope and Kikuchi patterns in the transmission electron microscope from this phase are closely related to the structurally similar m (3) over bar (5) over bar icosahedral quasicrystals that form in numerous aluminium-transition metal alloys by both conventional and rapid solidification. The other iron-containing phase in these alloys was determined to be plate shaped and to have the orthorhombic Cmcm space group consistent with the beta-Al5FeSi phase, which has sometimes been confused with having a tetragonal or monoclinic structure. The nature of this structure is such that it frequently grows with a high density of faults that separate equivalent variants; these will be described and related to the previously incorrect interpretations of this being a tetragonal phase.
Title:
Inelastic neutron scattering of a Ti-44 at.%Ni-6 at.%Fe alloy exhibiting an incommensurate-commensurate transition
Authors:
Fukuda, T; Choi, MS; Kakeshita, T; Ohba, T Author Full Names: Fukuda, Takashi; Choi, Mi-Seon; Kakeshita, Tomoyuki; Ohba, Takuya
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 481: 235-238 Sp. Iss. SI MAY 25 2008
Abstract:
Inelastic neutron scattering has been made for a Ti-44 at.%Ni-6 at.%Fe alloy which exhibits a second-order like incommensurate-commensurate (IC-C) transformation [M.-S. Choi, T. Fukuda, T. Kakeshita, Philos. Mag. 86 (2006) 67] in order to understand the nature of the transformation. The phonon frequencies of the [zeta zeta 0]-TA(2) phonon branch near zeta = 1/3 decrease as temperature decreases, exhibit the lowest value at about 200 K and then increase on further cooling. This temperature (200 K) is near the temperature below which diffuse incommensurate scattering can be noticed, and it is by 20 K higher than the IC-C transition temperature. Presumably, the phonon softening is responsible for the formation of the incommensurate state, but not directly connected to the formation of the commensurate state. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Observation of phonon softening in a Ti-Ni-Fe alloy by inelastic X-ray scattering
Authors:
Ohba, T; Kitanosono, D; Morito, S; Fukuda, T; Kakeshita, T; Baron, AQR; Tsutsui, S Author Full Names: Ohba, T.; Kitanosono, D.; Morito, Shigekazu; Fukuda, T.; Kakeshita, T.; Baron, A. Q. R.; Tsutsui, Santoshi
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 481: 254-257 Sp. Iss. SI MAY 25 2008
Abstract:
Phonon softening of the martensitic transformation, which is a typical first-order transformation, is an interesting concept in connection with the transformation mechanism. Recently, Kakeshita and his group studied a wide range of Fe-substituted Ti-Ni alloys [Ti-(50 - x)Ni-xFe, at.%] and reported anomalies in electrical resistivity, magnetic susceptibility and specific heat. Furthermore, they observed electron diffraction patterns and reported second-order-like features in a Ti-44Ni-6Fe alloy with an incommensurate-commensurate phase transformation prior to the transformation to the R phase. Inelastic X-ray scattering experiments were performed in order to observe the phonon behavior in Ti-44Ni-6Fe. Since the energy of phonons is about six orders of magnitude lower than that of X-rays, precise experiments are necessary to observe phonons by X-ray inelastic scattering experiments. The beam-line BL35XU at the synchrotron radiation facility, SPring-8 was utilized f! or the experiments. [zeta zeta 0]TA(2) phonon modes were measured at various temperatures. The temperature at which the softest phonon is observed is at approximately 180 K, corresponding to the incommensurate-commensurate transformation temperature. Possible differences between results of neutron inelastic scattering and X-ray inelastic scattering experiments will be discussed in the text. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Temperature dependence of the damping properties of Ni-Mn-Ga alloys
Authors:
Aaltio, I; Lahelin, M; Soderberg, O; Heczko, O; Lofgren, B; Ge, Y; Seppala, J; Hannula, SP Author Full Names: Aaltio, I.; Lahelin, M.; Soderberg, O.; Heczko, O.; Lofgren, B.; Ge, Y.; Seppala, J.; Hannula, S. -P.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 481: 314-317 Sp. Iss. SI MAY 25 2008
Abstract:
Single-crystalline 5M (exhibiting magnetic shape memory effect) and non-modulated martensitic Ni-Mn-Ga alloys were studied by dynamic mechanical analysis (DMA) at different temperatures. The chemical compositions of the alloys were determined using energy-dispersive X-ray spectrometry in a scanning electron microscope. The crystal structures were confirmed with X-ray diffraction and the transformation temperatures were measured. DMA measurements showed that the mechanical modulus (stiffness) and damping capacity increased during heating and a clear peak of the loss angle, was detected which is related to the reverse phase transformation of martensite to austenite. During cooling, there is a corresponding peak related to the martensite reaction. Significant decrease of the damping capacity occurs during transformation to austenite. Enhanced damping in the martensitic phase can be attributed to the mobility of twin boundaries. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Competing multiple-q magnetic structures in HoGe3: II. Magnetic structures observed in HoGe3
Authors:
Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Tung, LD; Ritter, C; Buschow, KHJ Author Full Names: Schobinger-Papamantellos, P.; Rodriguez-Carvajal, J.; Tung, L. D.; Ritter, C.; Buschow, K. H. J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (19): Art. No. 195202 MAY 14 2008
Abstract:
The high temperature (HT) and the low temperature (LT) multiple-q vector magnetic structures of the antiferromagnetic HoGe3 compound (T-N = 11 K) are derived from refinements of high resolution neutron data in terms of Fourier analysis. Various models are discussed. Over the HT range T-2 -> T-N, T-2 = 8.1 K (on heating), the magnetic phase is described with the wavevectors (q(1), q(2)) where q(1) = (q(1x), 0, 0) and q(2) = (q(2x), 0, q(2z)), q(1x) = q(2x) approximate to 1 2 and q(2z) approximate to 1 3, with T dependent length. It corresponds to an amplitude modulated magnetic phase with the moments at an angle of 24 degrees (2) with the c axis within the plane (b, c). Surprisingly this structure does not square up to a constant moment structure with q1 = (1 2, 0, 0) and q2 = (1/2, 0, 1/3) or alternatively (2a, b, 3c). Instead of locking, the q(2) vector jumps at T-2 via a first-order transition to a long period structure with an almost 24-times larger cell approximate to (2a, 4b, 3c), or in terms of wavevectors to q(3) = (1/2, q(3y), 0) and q(4) = (1/2, q(4y), 1/3), which dominates the (LT) range 1.6 K -> T-2. The (LT) range subdivides into the lock-in LT1 range 1.6 K -> T-3 (T-3 = 4.8 K on heating) where the q(3y) = q(4y) = 1/4 components have a constant length and the LT2 range T-3 -> T-2 where q(3y) and q(4y) have a length variable with T. In the intermediate temperature range, around the first-order T-2 transition (on heating or cooling), the two structures described with the wavevectors (q(1), q(2)) and (q(3), q(4)) coexist in varying proportions. The most probable LT magnetic structure corresponds to a complex monoclinic multiaxial canted structure with four independent Ho sites as a result of geometric frustration related to the underlying trigonal prism arrangement of the magnetic atoms with antiferromagnetic interactions.
Title:
Protein crystals can be incommensurately modulated
Authors:
Lovelace, JJ; Murphy, CR; Daniels, L; Narayan, K; Schutt, CE; Lindberg, U; Svensson, C; Borgstahl, GEO Author Full Names: Lovelace, Jeffrey J.; Murphy, Cameron R.; Daniels, Lee; Narayan, Kartik; Schutt, Clarence E.; Lindberg, Uno; Svensson, Christer; Borgstahl, Gloria E. O.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 41: 600-605 Part 3 JUN 2008
Abstract:
For a normal periodic crystal, the X-ray diffraction pattern can be described by an orientation matrix and a set of three integers that indicate the reciprocal lattice points. Those integers determine the spacing along the reciprocal lattice directions. In aperiodic crystals, the diffraction pattern is modulated and the standard periodic main reflections are surrounded by satellite reflections. The successful indexing and refinement of the main unit cell and q vector using TWINSOLVE, developed by Svensson [(2003). Lund University, Sweden], are reported here for an incommensurately modulated, aperiodic crystal of a profilin: actin complex. The indexing showed that the modulation is along the b direction in the crystal, which corresponds to an 'actin ribbon' formed by the crystal lattice. Interestingly, the transition to the aperiodic state was shown to be reversible and the diffraction pattern returned to the periodic state during data collection. It is likely that the protein underwent a conformational change that affected the neighbouring profilin: actin molecules in such a way as to produce the observed modulation in the diffraction pattern. Future work will aim to trap the incommensurately modulated crystal state, for example using cryocooling or chemical crosslinking, thus allowing complete X-ray data to be collected.
Title:
Interpenetrating networks of three-dimensional Penrose tiles in CaAu3Ga, the structurally simplest cubic approximant of an lcosahedral quasicrystal
Authors:
Lin, Q; Corbett, JD Author Full Names: Lin, Qisheng; Corbett, John D.
Source:
INORGANIC CHEMISTRY 47 (9): 3462-3464 MAY 5 2008
Abstract:
Double-Friauf polyhedra (DFPs) which play important roles in quasicrystal (QC) models are the unique building blocks in the novel 1/0 AC, CaAu3+Delta Ga1-Delta (Delta approximate to 0-0.13) [Pa (3) over bar; a = 9.0875(3)-9.1107(5) angstrom]. The packing of DFPs generates interpenetrating networks of condensed three-dimensional Penrose tiles, the geometry of which is close to that assumed for QCs.
Title:
Quasicrystal surfaces
Authors:
Thiel, PA Author Full Names: Thiel, Patricia A.
Source:
ANNUAL REVIEW OF PHYSICAL CHEMISTRY 59: 129-152 2008
Abstract:
Studies of ordered, yet nonperiodic, metallic alloys known as quasicrystals have generated exciting questions and fundamental insights about the relationship between surface atomic structure and surface properties. In this review, I give examples from oxidation, friction, heterogeneous catalysis, and solid film growth, in which the Al-rich quasicrystals exhibit unusual properties, relative to crystalline materials of similar composition.

Update: 23-May-2008

Title:
Effect of nano-quasicrystals on viscosity of a Zr-based bulk metallic glass (vol 58, pg 291, 2008)
Authors:
Gubicza, J; Labar, JL; Agocs, E; Fatay, D; Lendvai, J Author Full Names: Gubicza, J.; Labar, J. L.; Agocs, E.; Fatay, D.; Lendvai, J.
Source:
SCRIPTA MATERIALIA 58 (11): 1038-1038 JUN 2008
Title:
Incommensurate magnetic ground state revealed by resonant x-ray scattering in the frustrated spin system Ca3Co2O6
Authors:
Agrestini, S; Mazzoli, C; Bombardi, A; Lees, MR Author Full Names: Agrestini, S.; Mazzoli, C.; Bombardi, A.; Lees, M. R.
Source:
PHYSICAL REVIEW B 77 (14): Art. No. 140403 APR 2008
Abstract:
We have performed a resonant x-ray scattering study at the Co pre-K edge on a single crystal of Ca3Co2O6. The measurements reveal an abrupt transition to a magnetically ordered state immediately below T-N=25 K, with a magnetic correlation length in excess of 5500 A along the c axis chains. There is no evidence for modifications to the Co3+ spin state. A temperature dependent modulation in the magnetic order along the c axis and an unusual decrease in the magnetic correlation lengths on cooling are observed. The results are compatible with the onset of a partially disordered antiferromagnetic structure in Ca3Co2O6.
Title:
Direct observation of charge-density waves in Ho5Ir4Si10
Authors:
Tseng, CM; Chen, CH; Yang, HD Author Full Names: Tseng, C. M.; Chen, C. H.; Yang, H. D.
Source:
PHYSICAL REVIEW B 77 (15): Art. No. 155131 APR 2008
Abstract:
We report the direct observation of charge-density waves in Ho5Ir4Si10 by dark-field imaging in transmission electron microscopy using superlattice diffraction spots. The incommensurate phase of charge-density wave is found to be discommensurate with small commensurate domains separated by domain walls (discommensurations). Configurations of charge-density wave dislocations convincingly show that the charge-density wave phase transition is accompanied by a concomitant cell-doubling crystallographic structural phase transition, an unprecedented phenomenon in other charge-density wave systems.
Title:
Theory of subgap interchain tunneling in quasi 1D conductors
Authors:
Brazovskii, S; Matveenko, SI Author Full Names: Brazovskii, S.; Matveenko, S. I.
Source:
PHYSICAL REVIEW B 77 (15): Art. No. 155432 APR 2008
Abstract:
We suggest a theory of internal coherent tunneling in the pseudogap region when the applied voltage U is below the free electron gap 2 Delta(0). We address quasi-one-dimensional (quasi 1D) systems, where the gap is originated by spontaneous lattice distortions of the incommensurate charge density wave type. The results can be adjusted also to quasi 1D superconductors. The instanton approach allows one to calculate the interchain tunneling current both in single electron (amplitude solitons, i.e., spinons) and bielectron (phase slips) channels. Transition rates are governed by a dissipative dynamics originated by the emission of gapless phase excitations in the course of the instanton process. We find that the single-electron tunneling is allowed down to the true pair-breaking threshold at U-c1=2W(as)< 2 Delta(0), where W-as=2/pi Delta(0) is the amplitude soliton energy. Most importantly, the bielectronic tunneling stretches down to U-c2=0 (in the 1D regime). In both cases, the threshold behavior is given by power laws J similar to(U-U-c)(beta), where the exponent beta similar to v(F)/u is as large as the ratio of the Fermi velocity v(F) and the phase u. In the two-dimensional or three-dimensional ordered phases, at temperature T < T-c, the one-electron tunneling current does not vanish at the threshold anymore, but saturates above it at U-U-c1 similar to T-c <
Title:
Fermi surface nesting and the origin of charge density waves in metals
Authors:
Johannes, MD; Mazin, II Author Full Names: Johannes, M. D.; Mazin, I. I.
Source:
PHYSICAL REVIEW B 77 (16): Art. No. 165135 APR 2008
Abstract:
The concept of a charge density wave (CDW), which is induced by Fermi-surface nesting, originated from the Peierls idea of electronic instabilities in purely one-dimensional metals and is now often applied to charge ordering in real low-dimensional materials. The idea is that if Fermi surface contours coincide when shifted along the observed CDW wave vector, then the CDW is considered to be nesting derived. We show that, in most cases, this procedure has no predictive power, since Fermi surfaces either do not nest at the right wave vector or nest more strongly at the wrong vector. We argue that only a tiny fraction, if any, of the observed charge ordering phase transitions are true analogs of the Peierls instability because electronic instabilities are easily destroyed by even small deviations from perfect nesting conditions. By using prototypical CDW materials NbSe2, TaSe2, and CeTe3, we show that such conditions are hardly ever fulfilled and that the CDW phases are actually structural phase transitions driven by the concerted action of electronic and ionic subsystems, i.e., a q-dependent electron-phonon coupling plays an indispensable part. We also mathematically show that the original Peierls construction is so fragile that it is unlikely to apply to real materials. We argue that no meaningful distinction between a CDW and an incommensurate lattice transition exists.
Title:
Computer simulation solves quasicrystal mystery
Authors:
[Anon]
Source:
MATERIALS WORLD 16 (5): 14-14 MAY 2008
Title:
Friction anisotropy: A unique and intrinsic property of decagonal quasicrystals
Authors:
Park, JY; Ogletree, DF; Salmeron, M; Jenks, CJ; Thiel, PA; Brenner, J; Dubois, JM Author Full Names: Park, Jeong Young; Ogletree, D. F.; Salmeron, M.; Jenks, C. J.; Thiel, P. A.; Brenner, J.; Dubois, J. M.
Source:
JOURNAL OF MATERIALS RESEARCH 23 (5): 1488-1493 MAY 2008
Abstract:
We show that friction anisotropy is an intrinsic property of the atomic structure of Al-Ni-Co decagonal quasicrystals and not only of clean and well-ordered surfaces that can be prepared in vacuum [J.Y. Park et al., Science 309, 1354 (2005)]. Friction anisotropy is manifested in both nanometer-size contacts obtained with sharp atomic force microscope tips and macroscopic contacts produced in pin-on-disk tribometers. We show that the friction anisotropy, which is not observed when an amorphous oxide film covers the surface, is recovered when the film is removed due to wear. Equally important is the loss of the friction anisotropy when the quasicrystalline order is destroyed due to cumulative wear. These results reveal the intimate connection between the mechanical properties of these materials and their peculiar atomic structure.
Title:
A study of the high-Al part of the Al-Pd-Re phase diagram
Authors:
Balanetskyy, S; Grushko, B Author Full Names: Balanetskyy, S.; Grushko, B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 456 (1-2): 105-112 MAY 29 2008
Abstract:
The Al-Pd-Re phase diagram was studied in the compositional range above 50 at.% Al at temperatures between 700 and 1100 degrees C. Apart from the Al-Pd epsilon-phases exhibiting ternary extension up to similar to 6 at.% Re, the binary phases in both Al-Pd and Al-Re dissolve only a little of the third element. In addition to the stable ternary icosahedral and decagonal phases reported earlier a new ternary hexagonal chi-phase (a approximate to 1.231, c approximate to 2.742 nm) was discovered in a compositional range from Al77.8Pd13.8Re8.4 to Al76.2Pd19.0Re4.8. The overall compositional range of the icosahedral phase was found to be between 8.3 and 10.4 at.% Re and between 68.5 and 71.9 at.% Al. This range shifts to lower Re at lower temperatures. Partial isothermal sections at 1100, 1000, 790 and 700 degrees C are presented. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Crystallization behavior and consolidation of ball milled Zr60Ti5Ag5Cu12.5Ni10Al7.5 glassy powders
Authors:
Scudino, S; Venkataraman, S; Sakahyska, M; Eckert, J Author Full Names: Scudino, S.; Venkataraman, S.; Sakahyska, M.; Eckert, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 456 (1-2): 159-162 MAY 29 2008
Abstract:
Zr60Ti5Ag5Cu12.5Ni10Al7.5 glassy powders produced by ball milling of crystalline compounds were consolidated by uniaxial hot pressing. The consolidation parameters were chosen in order to obtain partially crystallized bulk samples with a composite microstructure consisting of glassy, quasicrystalline and tetragonal CuZr2 phases. Hardness measurements reveal promising mechanical properties: Vickers hardness of 4.61 GPa and estimated yield strength of 1.53 GPa. These values are comparable to those reported for bulk Zr-based glassy alloys prepared by other techniques. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Recent topics in microstructure control by magnetic field in Ni2MnGa and CoPt and new transformation behavior in Ti-Ni-Fe alloys
Authors:
Kakeshita, T; Fukuda, T Author Full Names: Kakeshita, T.; Fukuda, T.
Source:
EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS 158: 73-78 MAY 2008
Abstract:
Three topics related to solid-solid phase transformations are presented. The first topic is related to ferromagnetic shape memory alloys. The general condition for rearrangement of martensite variants by magnetic field is discussed quantitatively. The second topic is related to microstructure control of CoPt (tetragonal L1(0)-type structure) during ordering heat-treatment under a magnetic field. We show that a single variant state is realized by magnetic field, and magnetic field is especially effective at the early stage of ordering. The third topic is related to the so-called precursor phenomena in Ti-Ni-Fe shape memory alloys. In the topic we will show the existence of a commensurate phase, which inherits the microstructure of the incommensurate phase and is probably different from the R-phase.
Title:
Crystal structure of martensite and intermediate phases in Ni2MnGa studied by neutron diffraction
Authors:
Kushida, H; Fukuda, K; Terai, T; Fukuda, T; Kakeshita, T; Ohba, T; Osakabe, T; Kakurai, K; Kato, K Author Full Names: Kushida, H.; Fukuda, K.; Terai, T.; Fukuda, T.; Kakeshita, T.; Ohba, T.; Osakabe, T.; Kakurai, K.; Kato, K.
Source:
EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS 158: 87-92 MAY 2008
Abstract:
We have investigated crystal structures of martensite and intermediate phases in stoichiometric Ni2MnGa. The neutron diffraction profile of the martensite phase measured at T = 4.2 K exhibits four satellites between [2 0 0](P)* and [0 2 0](P)* reflections (P stands for the parent phase) at incommensurate positions of [h 2 - h 0](P)* with h = 0.428, 0.863, 1.136 and 1.572. The pro. le of the intermediate phase measured at T = 210 K exhibits two satellites between [2 0 0](P)* and [0 2 0](P)* reflections at incommensurate positions of [h 2 - h 0](P)* with h = 0.343 and 1.657. Although each satellite of the martensite phase moves toward its nearest fundamental reflection as temperature increases, that of the intermediate phase does not move significantly. On the contrary, the intensity of each satellite decreases significantly in the intermediate phase as temperature increases while not in the martensite phase. A synchrotron X-ray diffraction and a Rietveld analysis of the result reveal that, for both the phases, the displacement of atoms from the parent phase are represented by a sine wave whose propagation vector is parallel to [1 1 0](P).

Update: 16-May-2008

Title:
Fivefold i-Al-Pd-Mn surface as template for growing monatomic quasiperiodic layers: First-principles simulations for adatoms from groups one to three
Authors:
Krajci, M; Hafner, J Author Full Names: Krajci, Marian; Hafner, J.
Source:
PHYSICAL REVIEW B 77 (13): Art. No. 134202 APR 2008
Abstract:
By using ab initio density-functional calculations, we have explored the conditions for the formation of quasiperiodic overlayers on top of a fivefold surface of an icosahedral Al-Pd-Mn quasicrystal. We calculate binding energies of single adatoms at special sites of the surface, with the aim to construct the potential-energy landscape of the quasiperiodic surface. We show that the energetically favorable adsorption sites are located at the vertices of a DHBS tiling [consisting of decagons (D), hexagons (H), boats (B), and stars (S)] describing the quasiperiodic ordering of the surface. An idealized structural model for the adlayer is constructed by decorating the interior of these tiles such that atoms are placed again in energetically favorable locations and that the local arrangement does not break the fivefold symmetry of the underlying substrate. The stability of this idealized structure is probed for elements from groups one to three of the Periodic Table by performing a conjugate-gradient relaxation under the action of the ab initio calculated forces. We demonstrate that in addition to a strong binding of the adatoms to the substrate, the size of the adatoms and the achievement of a dense surface coverage are the most important factors influencing the stability of quasiperiodic ordering in the adsorbed monolayer. From the analysis of the geometrical distribution of the adsorption sites, we conclude that a dense quasiperiodic overlayer with a density of 0.066 atoms/angstrom(2) (corresponding to a coverage Theta approximate to 0.50 monolayers) can be formed by adatoms with an atomic size of 3.7 angstrom +/- 0.4 angstrom. Atoms with this size are Na, Ca, Y, and La. We suggest that these elements and presumably also most rare-earth elements are good candidates for the formation of highly regular quasiperiodic adlayers with a structure described by a decagonal DHBS tiling consisting of decagons, hexagons, boats, and pen! tagonal stars.
Title:
Formation and properties of Al composites reinforced by quasicrystalline AlCuFeB particles
Authors:
Kenzari, S; Weisbecker, P; Curulla, M; Geandier, G; Fournee, V; Dubois, JM Author Full Names: Kenzari, S.; Weisbecker, P.; Curulla, M.; Geandier, G.; Fournee, V.; Dubois, J. M.
Source:
PHILOSOPHICAL MAGAZINE 88 (5): 755-766 2008
Abstract:
Al-based composites reinforced by icosahedral (i-) Al59Cu25.5Fe12.5B3 quasicrystalline particles were prepared by solid-state sintering. It was found that Al diffusion from the matrix to the quasicrystalline particles induces phase transformation into the omega-Al7Cu2Fe tetragonal phase. In order to preserve the i phase, we used an oxidation pre-treatment of the particles and studied its influence on the kinetics of the phase transformation (Al + i -> omega) as a function of temperature by high energy X-ray diffraction. The oxide layer acts as a barrier, reducing efficiently the diffusion of Al up to a sintering temperature of 823 K, allowing the control of the phases in the composites. The mechanical properties and the friction behaviour of the composites were investigated and show the negative influence of the oxide on the interface strength.
Title:
The influence of cooling rate on the microstructure of an Al-Mn-Be alloy
Authors:
Rozman, N; Boncina, T; Anzel, I; Zupanic, F Author Full Names: Rozman, Niko; Boncina, Tonica; Anzel, Ivan; Zupanic, Franc
Source:
MATERIALI IN TEHNOLOGIJE 42 (2): 65-68 MAR-APR 2008
Abstract:
In ternary Al-Mn-Be alloys a metastable quasicrystalline phase can form at relatively low cooling rates (approximate to 100 K/s); however, besides the quasicrystalline phase other phases can also be present. We found that the investigated alloy is very prone to the formation of metastable phases, which are also quasicrystalline. Using different investigation methods we determined the type of phases, their shape, morphology, chemical composition and distribution. Special attention was given to the micro- and nano-sized quasicrystalline particles. When using slow cooling, Al10Mn3 and Be4AlMn were present; however, with a faster cooling rate a quasicrystal approximant and a quasicrystalline phase were formed.
Title:
Effect of Ti addition on the crystallization behavior and glass-forming ability of Zr-Al-Cu alloys
Authors:
Qiang, JB; Zhang, W; Xie, GQ; Inoue, A Author Full Names: Qiang, J. B.; Zhang, W.; Xie, G. Q.; Inoue, A.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 354 (18): 2054-2059 APR 15 2008
Abstract:
The crystallization behavior of melt-spun (Zr65Al7.5Cu27.5)(100-x)Ti-x (x = 0- 15; in at.%) metallic glasses has been investigated by X-ray diffraction (XRD), transmission electron microscopy(TEM) and differential scanning calorimetry (DSC). The DSC traces showed an altered crystallization mode in the vicinity of 3 at.% Ti addition. A metastable icosahedral quasicrystal precipitated at the first crystallization stage of the Ti-bearing metallic glasses, which subsequently transformed to the stable Zr2Cu-type phase in the followed exothermic reaction. The glass-forming abilities (GFAs) of these metallic glasses were assessed by the recognized GFA indicators T-rg Delta T-x and gamma. BMGs were easily made in the compositions containing 3-7 at.% Ti by means of copper mold casting. The validity of these parameters was clarified using the critical BMG forming diameter evidence. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Electrical and optical properties of the mixed-valence misfit-layer compound (YbS)(1.25)CrS2
Authors:
Ohno, Y; Yamaguchi, T Author Full Names: Ohno, Y.; Yamaguchi, T.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 455 (1-2): 10-16 MAY 8 2008
Abstract:
The crystals of the new misfit-layer compound (YbS)(1.25)CrS2 were grown by chemical transport reaction in a closed silica ampoule. This compound is built up of alternately stacking of YbS and CrS2 layers. The dimensions of a unit cell are a(1) = 5.31 angstrom, b(1) = 5.75 angstrom, and c(1) = 10.63 angstrom for the YbS sublattice and a(2) = 3.32 angstrom, b(2) = 5.75 angstrom, and c(2) = 10.63 angstrom for the CrS2 sublattice. Both layers are incommensurate along the a-axis and the incommensurability parameter, which is defined by alpha = a(2)/a(1), is about 0.625. It is found from the comparison of lattice parameters among a series of lanthanide misfit-layer compounds and lanthanide monosulfides that Yb is in an intermediate valence state close to trivalency rather than divalency due to charge transfer to CrS2 layers. Temperature-dependent electrical resistivity shows that the compound is a semiconductor with the activation energy of about 0.31 eV. This activation energy almost agrees with that of the acceptor levels in nonstoichiometric YbS samples. A reflectivity spectrum reveals small peaks at 0.8 and 1.1 eV, whereas an absorption spectrum exhibits a large peak at 1.1 eV The results obtained suggest that valence fluctuation happens for Yb-like Eu in (EuS)(1.173)NbS2. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Formation of AlCuFe icosahedral quasicrystal by mechanical alloying: XAFS and XRD studies
Authors:
Yin, SL; Xie, Z; Bian, Q; He, B; Pan, ZY; Sun, ZH; Wei, Z; Qian, LY; Wei, SQ Author Full Names: Yin, Shilong; Xie, Zhi; Bian, Qing; He, Bo; Pan, Zhiyun; Sun, Zhihu; Wei, Zheng; Qian, Liying; Wei, Shiqiang
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 455 (1-2): 314-321 MAY 8 2008
Abstract:
The structural evolutions of the mechanically alloyed ternary Al70Cu20Fe10 powders with the milling times and the annealing treatment were studied by X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). It was found that during the milling process, only Cu can incorporate into the lattice of Al to form an Al2Cu compound or an AlCu solid solution, depending on the milling times. However, Fe remains the original structure of bcc alpha-Fe. Annealing treatment at 700 degrees C for 4 h can drive the alpha-Fe to react with the Al2Cu compounds and AlCu solid solution, and the main products of the annealed Al70Cu20Fe10, 0 (10 h) and the annealed Al70Cu20Fe10 0 (40 h) are the icosahedral Al65Cu20Fe15 quasicrystal and the Al(Cu, Fe) solid solution, respectively. The local structural disorders around Fe and Cu atoms in the icosahedral QC phase is about 50% larger than those of the Al(Cu, Fe) solid solution. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Multiferroicity due to nonstoichiometry in the chain cuprate LiVCuO4
Authors:
Moskvin, AS; Drechsler, SL Author Full Names: Moskvin, A. S.; Drechsler, S. -L.
Source:
EPL 81 (5): Art. No. 57004 MAR 2008
Abstract:
The recently observed multiferroic behavior in the s= 1/2 chain cuprate LiVCuO4 (equivalent to LiCuVO4) with edge-shared CuO4 plaquettes and helical spin ordering does not agree with the existing theories such as a spin-current scenario. We argue that the effect can be consistently explained, if the exchange-induced electric polarization on the out-of-chain Cu2+ centers substituting for Li ions in LiVCuO4 is taken into account. These substituent centers are proved to be an effective probe of the spin incommensurability and the magnetic-field effects. Copyright (c) EPLA, 2008.

Update: 9-May-2008

Title:
Thermoelectrical properties of a monocrystalline Al64Cu23Fe13 quasicrystal
Authors:
Smiljanic, I; Bilusic, A; Bihar, Z; Lukatela, J; Leontic, B; Dolinsek, J; Smontara, A Author Full Names: Smiljanic, Igor; Bilusic, Ante; Bihar, Zeljko; Lukatela, Jagoda; Leontic, Boran; Dolinsek, Janez; Smontara, Ana
Source:
MATERIALI IN TEHNOLOGIJE 41 (6): 265-270 NOV-DEC 2007
Abstract:
We performed investigations of the electrical resistivity, thermopower and thermal conductivity of a monocrystalline i-Al64Cu23Fe13 as well as a polycrystalline i-Al63Cu25Fe12 icosahedral quasicrystal, for comparison. The electrical resistivity of both samples, the monocrystalline i-Al64Cu23Fe13 and the polycrystalline i-Al63Cu25Fe12, exhibits a negative temperature coefficient with rho(4K) = 3950 mu Omega cm and rho(4K)= 4900 mu Omega cm, and the ratio rho(4K)/rho(300K) = 1-8, rho(4K)/rho(300K) = 1.7, respectively. The thermopowers are large and have a negative sign. In addition, the thermopower of the monocrystalline i-Al64Cu23Fe13 exhibits a sign reversal at T = 278 K. The thermal conductivity is anomalously low, of the order of 1 W/mK at room temperature, with a slightly different temperature variation at low temperatures. On the basis of these results, we concluded that there are no systematic differences between the high-quality monocrystalline and polycrystalline icosahedral i-Al-Cu-Fe quasicrystals. Moreover, the reported transport properties of i-Al-Cu-Fe appear to be intrinsic to this family of icosahedral quasicrystals.
Title:
Phases in a quasicrystalline alloy Al(64,4)Cu(23,5)Fe13,1
Authors:
Boncina, T; Markoli, B; Anzel, I; Zupanic, F Author Full Names: Boncina, Tonica; Markoli, Bogtjan; Anzel, Ivan; Zupanic, Franc
Source:
MATERIALI IN TEHNOLOGIJE 41 (6): 271-277 NOV-DEC 2007
Abstract:
In the ternary system Al-Cu-Fe an i-phase (icosahedral quasicrystal) is present. It is thermodynamically stable and a part of the equilibrium phase diagram. However, according to the chemical composition and conditions during the solidification and heat treatment, a considerable number of intermetallic phases can be in stabile or metastabile equilibrium with the i-phase. Consequently, synthesis of onephase quasicrystalline alloy is possible only in a narrow concentration range and after appropriate heat treatment. In the investigation, alloy Al64,4Cu22,5Fe13,1 was synthesized and heat treated to increase the fraction of the i-phase. The presence of phases and other microstructural characteristics were determined using appropriate metallographic preparation methods, light microscopy (LM), scanning electron microscopy (SEM), microchernical analyses (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and microhardness measurements. The presence of quasicrystalline phase i was clearly confirmed using XRD and TEM.
Title:
Hydrogen absorption by Ti-Zr-Ni-based alloys
Authors:
Skulj, I; Kocjan, A; McGuiness, PJ; Sustarsic, B Author Full Names: Skulj, Irena; Kocjan, Andraz; McGuiness, Paul J.; Sustarsic, Borivoj
Source:
MATERIALI IN TEHNOLOGIJE 41 (6): 279-282 NOV-DEC 2007
Abstract:
Some transition metals and their alloys have the ability to reversibly absorb considerable amounts of hydrogen. The amount of absorbed hydrogen and the absorption kinetics depend on interactions between the hydrogen atoms and the alloy. Titanium and zirconium show a high affinity for hydrogen, and Ti-Zr-Ni alloys with either amorphous or quasicrystalline structures have proved to be excellent absorbers of hydrogen. In this study we have focused on processing Ti-Zr-Ni ribbons with four different compositions and investigating their hydrogenation behaviour. A melt-spinning process was used as the alloy-preparation technique, and samples from each composition were examined before and after the hydrogenation process. The ribbons were analysed by X-ray diffraction (XRD) and examined with a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS). Only the sample with the lowest nickel concentration was found to absorb any significant quantity of hydrogen under the applied experimental conditions.
Title:
Structural and magnetic roughness in a Co/Ru multilayer patterned into a large scale hexagonal array
Authors:
Kinane, CJ; Porter, NA; Marrows, CH; Hickey, BJ; Arena, DA; Dvorak, J; Sirotkin, E; Ogrin, FY; Charlton, T; Langridge, S Author Full Names: Kinane, C. J.; Porter, N. A.; Marrows, C. H.; Hickey, B. J.; Arena, D. A.; Dvorak, J.; Sirotkin, E.; Ogrin, F. Y.; Charlton, T.; Langridge, S.
Source:
JOURNAL OF APPLIED PHYSICS 103 (7): Art. No. 07B513 APR 1 2008
Abstract:
Self-assembled arrays of nanospheres have been used to pattern a Co/Pt multilayer into nanopillars. On top of this has been deposited a Co/Ru multilayer, which is antiferromagnetically coupled. The nanopillars introduce a known structural and magnetic lateral modulation into the multilayer. Soft x-ray magnetic scattering was used to observe the interference patterned from the patterned substrate. This has allowed us to show how the magnetic roughness correlates with the structural roughness and obtain selective magnetometry of the various magnetic elements. (C) 2008 American Institute of Physics.
Title:
Formation of periodic magnetic structure by localized amorphization of crystalline Co2MnSi using femtosecond laser
Authors:
Baek, KH; Park, JH; Kim, JH; Kim, CK; Yoon, CS; Lee, GJ; Lee, YP Author Full Names: Baek, Kwang H.; Park, Jun H.; Kim, Jung H.; Kim, Chang K.; Yoon, Chong S.; Lee, Geon Joon; Lee, Young Pak
Source:
JOURNAL OF APPLIED PHYSICS 103 (7): Art. No. 07E701 APR 1 2008
Abstract:
Femtosecond laser-interference induced amorphization (FLIA) was used to form a spatially periodic magnetic structure by selectively amorphizing the surface of bulk Co2MnSi. Regularly spaced alternating lines with a periodicity of 2 mu m were produced by FLIA. Magnetic force microscopy of the samples clearly revealed one-dimensional periodic magnetic domains resulting from the modulated surface structure which was confirmed by transmission electron microscopy. The periodicity of the modulated structure can be further decreased or the process can be modified to write two-dimensional pattern so that the resulting magnetic structure can be potentially utilized for a permanent magnetic identification. (C) 2008 American Institute of Physics.
Title:
A superstructure modulation induced by La doping of the layered manganate LaxSr4-xMn3O10
Authors:
Yang, H; Tang, YK; Yao, LD; Zhang, W; Li, QA; Li, FY; Jin, CQ; Yu, RC Author Full Names: Yang, H.; Tang, Y. K.; Yao, L. D.; Zhang, W.; Li, Q. A.; Li, F. Y.; Jin, C. Q.; Yu, R. C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 454 (1-2): 1-4 APR 24 2008
Abstract:
In this paper, transmission electron microscopy (TEM) has been used for studying the slightly La-doped layered manganate LaxSr4-xMn3O10. Albeit the samples for x <= 0. 15 appear single phased from the powder X-ray diffraction (XRD) analysis, the presence of numerous modulated domains in them has been revealed by electron diffraction and high-resolution electron microscopy. Electron diffraction data indicate that the local superstructure modulation is two-dimensional, and the modulation plane lies in the ac plane. The two primary modulation vectors are q(1) = (1/4)a* and q(2) = (1/2)c*. High-resolution electron microscopy data suggest that the origin of the modulated structure is possibly attributable to an ordering of the La dopants. The locally modulated structure may have a correlation with the magnetic properties, typical of the ferromagnetic (FM) clusters, of the LaxSr4-xMn3O10 manganate. (C) 2006 Elsevier B.V. All rights reserved.
Title:
Phase equilibria of the Al-Fe-Ni system at 850 degrees C and 627 degrees C
Authors:
Zhang, LJ; Du, Y; Xu, HG; Tang, CY; Chen, HL; Zhang, WQ Author Full Names: Zhang, Lijun; Du, Yong; Xu, Honghui; Tang, Chengying; Chen, Hailin; Zhang, Wenqing
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 454 (1-2): 129-135 APR 24 2008
Abstract:
The phase equilibria at 850 degrees C and 627 degrees C in the Al-Fe-Ni system with Al content above 50 at.% are investigated by using 19 alloys. The annealed alloys are examined by means of X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) and election probe microanalysis (EPMA). It is confirmed that tau(2) phase (Al10Fe3Ni) with hexagonal structure and tau(3) phase (Al71Fe5Ni24) with the decagonal quasi-crystalline structure, exist at 850 degrees C. The homogeneity of tau(2) spans in the range of 5.7-13.1 at.% Ni and 14.4-22.2 at.% Fe. At 850 degrees C, the maximum solubilities of Ni in Al5Fe2 and Al2Fe are determined to be 1.3 at.% and 2.1 at.%, respectively, while the maximum solubility of Fe in Al3Ni2 is measured to be 4,9 at.%. At 627 degrees C, tau(1) (Al9FeNi) and tau(2) exist. At this temperature, the hornogeneity range for tau(1) is from 8.7 at.% to 14.3 at.% Ni and 4.5 at.% to 10.0 at.% Fe, and that for tau(2) is within the range of 7.2-12.4 at.% Ni and 15.6-22.5 at.% Fe. The maximum solubilities of Ni in Al13Fe4, Al5Fe2 and Al2Fe are determined to be 8.9, 1.5, and 2 at.%, respectively, while that of Fe in Al3Ni is measured to be 3.6 at.%. At 627 degrees C, the maximum solubilities of both Fe and Ni in (Al) phase are determined to be extremely small, about 0.58 at.% for both elements. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Comment on "Model of rotational tunneling in quasicrystals of the Cd6Yb parent compound"
Authors:
Coddens, G Author Full Names: Coddens, Gerrit
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 454 (1-2): 523-524 APR 24 2008
Abstract:
We show that in a recent model calculation on tunneling of Cd-4 "clusters" in CdYb quasicrystals (QC) and its approximants the assumption that the clusters would be rigid is not justified. (C) 2006 Elsevier B.V. All rights reserved.
Title:
Single-crystal X-ray study of Ba2Cu2Te4O11Br2 and its incommensurately modulated superstructure companion
Authors:
Takagi, RF; Johnsson, M; Lidin, S Author Full Names: Takagi, Rie Fredrickson; Johnsson, Mats; Lidin, Sven
Source:
CHEMISTRY-A EUROPEAN JOURNAL 14 (11): 3434-3441 2008
Abstract:
Compounds containing lone-pair elements such as Te-IV are very interesting from the structural point of view, as the lone-pair nonbonding regions create low-dimensional geometrical arrangements. We have synthesized two new compounds with these features-Ba2Cu2Te4O11Br2 (I) and Ba2Cu2Te4O11-delta(OH)(2 delta)Br-2 (II, delta approximate to 0.57) - as members of the AE-M-Te-O-X (AE=alkaline-earth metal, M = transition metal, X=halide) family of compounds by solid-state reactions. Preliminary single-crystal X-ray analysis indicated that compound I crystallizes in the orthorhombic system, but attempts at refinement proved unsatisfactory. Closer inspection of the reciprocal lattice revealed systematic, non-crystallographic absences that indicate twinning. The structure is in fact triclinic, space group C (1) over bar (equivalent to P (1) over bar), with unit cell parameters (at 120 K) of a = 10.9027(9), b = 15.0864(7), c = 9.379(2) angstrom, beta = 106.8947 degrees. It is layered and built from [TeO3E] tetrahedra, [TeO3+1E] trigonal bipyramids (where E is the lone pair of Te-IV), [CuO4] squares and irregular [BaO10Br] polyhedra. The crystal structure of 11 shows the same basic structure as I but contains additional oxygen, probably in the form of OH groups. The presence of satellites reveals that ordering on this 0 site creates an incommensurate modulation, primarily affecting Br and Te. The modulated structure of II was solved in the triclinic superspace group X (1) over bar(alpha beta gamma)0 with the vector q approximate to 1/16 c*.

Update: 2-May-2008

Title:
On the magnetic structure of quasi one dimensional spin 1/2 system of Li2ZrCuO4
Authors:
Tarui, Y; Kobayashi, Y; Sato, M Author Full Names: Tarui, Yasuko; Kobayashi, Yoshiaki; Sato, Masatoshi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (4): Art. No. 043703 APR 2008
Abstract:
Magnetization and Li-7-NMR measurements have been carried out for an a-axis-aligned sample of Li2ZrCuO4, which has quasi one-dimensional Cu2+ spins (s = 1/2) in chains of edge-sharing CuO4 square planes and exhibits the magnetic transition at temperature T-N similar to 7 K. The NMR results at similar to 2 K indicate that the system has an incommensurate helical order of Cu spins within the ac-plane. Although the feroelectricity is predicted in this ordered state by existing theories developed for a single chain, no anomalies have been observed in the dielectric susceptibility E and electric polarization P for polycrystalline samples.
Title:
Competition of magnetic and quadrupolar order parameters in HoB4
Authors:
Okuyama, D; Matsumura, T; Mouri, T; Ishikawa, N; Ohoyama, K; Hiraka, H; Nakao, H; Iwasa, K; Murakami, Y Author Full Names: Okuyama, Daisuke; Matsumura, Takeshi; Mouri, Takuya; Ishikawa, Naoko; Ohoyama, Kenji; Hiraka, Haruhiro; Nakao, Hironori; Iwasa, Kazuaki; Murakami, Youichi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (4): Art. No. 044709 APR 2008
Abstract:
The successive magnetic phase transitions of HoB4 with T-N1 = 7.1 K and T-N2 = 5.7 K have been investigated in detail by neutron and X-ray diffraction. Since Ho ions in the c-plane form a Shastry-Sutherland lattice, geometrical frustration has been expected in this compound. Below T-N1, HoB4 exhibits an incommensurate antiferromagnetic order with q = (delta, delta, delta ') (delta = 0.022, delta ' = 0.43), followed by a first-order transition at T-N2 into a commensurate order with q = (0, 0, 0), where four magnetic moments are antiferromagnetically coupled in a unit cell. After determining the magnetic structures of the two phases by neutron powder diffraction, we pay particular attention to diffuse scatterings responsible for the critical behavior. Very broad diffuse scatterings, extending almost to the zone boundary, are observed already in the paramagnetic phase at around q = (0, 0, 0) and (0, 0, 1/2) with magnetic correlation lengths of xi < 10 angstrom. Below T-N1, a strong diffuse scattering develops in a more concentrated region at around q = (0, 0, with 30 A, followed by the appearance of a Bragg peak at (delta, delta, delta '). Simultaneously, a sharp Bragg peak corresponding to q = (0, 0, 0) also develops at (1, 0, 1) upon diffuse scattering. This complex critical behavior is discussed from the viewpoint of competing order parameters of magnetic and quadrupolar origins. The striking resemblance of the critical behavior to that of HoB2C2 with a square lattice of Ho is interpreted as a manifestation of a universality for a three-dimensional system with competing magnetic and quadrupolar order parameters and a long-ranged RKKY interaction. It is considered that the microscopic difference in interionic interaction due to the difference in crystal structure becomes less prominent in the critical behavior as the correlation length becomes much larger than the lattice constant. On the other hand, the strong diffuse scattering in HoB4, which is hardly d etected in HoB2C2, might be ascribed to geometrical frustration. The softening of the elastic constant in HoB4 and HoB2C2 is also discussed.
Title:
Synthesis and structural properties of n=1 Ruddlesden-Popper manganites Nd1-xCa1+xMnO4
Authors:
Nagai, T; Yamazaki, A; Kimoto, K; Matsui, Y Author Full Names: Nagai, T.; Yamazaki, A.; Kimoto, K.; Matsui, Y.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 453 (1-2): 247-252 APR 3 2008
Abstract:
Polycrystalline samples of n = 1 Ruddlesden-Popper manganites Nd1-xCa1+xMnO4 (0.55 <= x <= 1.00) were synthesized by a solid-state reaction. X-ray diffraction (XRD) and electron diffraction (ED) measurements confirmed that the fundamental crystal structure at room temperature consists of three distorted K2NiF4-types: orthorhombic Bmab (64) phase in 0.55 <= x< 0.73, orthorhombic Acam (64) phase in 0.73 <= x<0.85 and tetragonal I4(1)/acd(142) phase in 0.85 <= x <= 1.00. Furthermore, in a whole range of 0.55 <= x <= 0.75, low-temperature magnetic and ED measurements revealed charge-orbital ordering (COO) states, which are accompanied by suppression of magnetization and structural modulations with q = (1 - x)a*. The COO transition temperatures are high with a maximum of similar to 330 K at x=0.67, and then higher than those in non-distorted n = I Ruddlesden-Popper manganites. The observations suggest that COO states are much stabilized by the distortion in the fundamental structures. (C) 2006 Elsevier B.V. All rights reserved.
Title:
Effect of Mg-based spherical quasicrystals on microstructure and mechanical properties of AZ91 alloys
Authors:
Zhang, JS; Pei, LX; Du, HW; Liang, W; Xu, CX; Lu, BF Author Full Names: Zhang, Jinshan; Pei, Lixia; Du, Hongwei; Liang, Wei; Xu, Chunxiang; Lu, Binfeng
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 453 (1-2): 309-315 APR 3 2008
Abstract:
To lay theoretical foundations for room and elevated temperature application of AZ91 magnesium alloys, microstructure and mechanical properties of AZ91 magnesium alloys strengthened by Mg-based spherical quasicrystalline phase have been investigated using XRD, SEM, TEM, hard-meter and impact testing machine. The experiment results show that macro-hardness and impact toughness of AZ91 magnesium alloys were improved a lot as the addition level of spherical quasicrystal containing Mg-Zn-Y-Mn master alloy increased; while adding 5.1 wt.% spherical quasicrystal containing master alloy, impact toughness of AZ91 matrix composites reached the peak value, 15.3 J cm(-2), which was about 252% as many as that of AZ91 master alloy. Majority of beta-Mg17Al12 phase dissolved when spherical quasicrystal particles remained stable after 28-h T4 solution treating. Small dimples on fracture surface by impact of AZ91 magnesium alloy strengthened by quasicrystal particles exhibited the feature of ductile fracture. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Quasiperiodic plane tilings based on stepped surfaces
Authors:
Shutov, AV; Maleev, AV Author Full Names: Shutov, A. V.; Maleev, A. V.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 64: 376-382 Part 3 MAY 2008
Abstract:
Static and dynamic characteristics of layerwise growth in two-dimensional quasiperiodic Ito-Ohtsuki tilings are studied. These tilings are the projections of three-dimensional stepped surfaces. It is proved that these tilings have hexagonal self-similar growth with bounded radius of neighborhood. A formula is given for the averaged coordination number. Deviations of coordination numbers from its average are quasiperiodic. Ito-Ohtsuki tiling can be decomposed into one-dimensional sector layers. These sector layers are one-dimensional quasiperiodic tilings with properties like Ito-Ohtsuki tilings.
Title:
A new simple tiling, with unusual properties, by a polyhedron with 14 faces
Authors:
Gabbrielli, R; O'Keeffe, M Author Full Names: Gabbrielli, Ruggero; O'Keeffe, Michael
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 64: 430-431 Part 3 MAY 2008
Abstract:
A monotypic simple tiling by a 14-face polyhedron that does not admit an isohedral tiling is described. The tiling is triclinic and contains four distinct, but combinatorially equivalent, kinds of tile.

Update: 25-Apr-2008

Title:
Structural properties of octagonal quasicrystal based on covering theory
Authors:
Liao, LG; Fu, XJ Author Full Names: Liao, Longguang; Fu, Xiujun
Source:
SOLID STATE COMMUNICATIONS 146 (1-2): 35-38 APR 2008
Abstract:
Cluster covering is a new approach to generate quasicrystal models, based on which a two-dimensional quasilattice can be described in terms of a single quasi-unit cell. We investigate the structural properties of a covering model of the octagonal quasicrystal. The pair covering rules, the nearest-neighbor configurations, and the configuration distributions are presented.(c) 2008 Elsevier Ltd. All rights reserved.
Title:
Magnetic properties and neutron diffraction study of two manganese sulfosalts: monoclinic MnSb2S4 and benavidesite (MnPb4Sb6S14)
Authors:
Leone, P; Doussier-Brochard, C; Andre, G; Moelo, Y Author Full Names: Leone, Philippe; Doussier-Brochard, Charlotte; Andre, Gilles; Moelo, Yves
Source:
PHYSICS AND CHEMISTRY OF MINERALS 35 (4): 201-206 MAY 2008
Abstract:
Mn2+Sb2S4, a monoclinic dimorph of clerite, and benavidesite (Mn2+Pb4Sb6S14) show well-individualized ingle chains of manganese atoms in octahedral coordination. Their magnetic structures are presented and compared with those of iron derivatives, berthierite (Fe2+Sb2S4) and jamesonite (Fe2+Pb4Sb6S14). Within chains, interactions are antiferromagnetic. Like berthierite, MnSb2S4 shows a spiral magnetic structure with an incommensurate 1D propagation vector [0, 0.369, 0], unchanged with temperature. In berthierite, the interactions between identical chains are antiferromagnetic, whereas in MnSb2S4 interactions between chains are ferromagnetic along c-axis. Below 6 K, jamesonite and benavidesite have commensurate magnetic structures with the same propagation vector [0.5, 0, 0]: jamesonite is a canted ferromagnet and iron magnetic moments are mainly oriented along the a-axis, whereas for benavidesite, no angle of canting is detected, and manganese magnetic moments are oriented along b-axis. Below 30 K, for both compounds, one-dimensional magnetic ordering or correlations are visible in the neutron diagrams and persist down to 1.4 K.
Title:
Polarized neutron scattering study on antiferromagnetic states in CeRh0.6Co0.4In5
Authors:
Yokoyama, M; Oyama, N; Amitsuka, H; Oinuma, S; Kawasaki, I; Tenya, K; Matsuura, M; Hirota, K Author Full Names: Yokoyama, M.; Oyama, N.; Amitsuka, H.; Oinuma, S.; Kawasaki, I.; Tenya, K.; Matsuura, M.; Hirota, K.
Source:
PHYSICA B-CONDENSED MATTER 403 (5-9): 812-814 APR 1 2008
Abstract:
Polarized neutron scattering experiments were performed on mixed compound CeRh0.6Co0.4In5 to clarify the nature of the low-temperature ordered states. Three nonequivalent Bragg peaks, characterized by the wave vectors of q(h)similar to(1/2,1/2,0.3), q(1)similar to(1/2,1/2,0.4) and q(c) = (1/2, 1/2, 1/2), were observed at 1.4K. These Bragg peaks are found to occur entirely in spin-flip channel. This indicates that these Bragg peaks originate from the magnetic scattering, i.e., the antiferromagnetic orders with three different modulations appear in this compound. (c) 2007 Elsevier B.V. All rights reserved.
Title:
How do holes get heavy and superconduct?
Authors:
Harrison, N; Sebastian, SE; Batista, CD; Trugman, SA Author Full Names: Harrison, N.; Sebastian, S. E.; Batista, C. D.; Trugman, S. A.
Source:
PHYSICA B-CONDENSED MATTER 403 (5-9): 977-981 APR 1 2008
Abstract:
We discuss the implications of recent de Haas-van Alphen effect (magnetic quantum oscillation) measurements on cubic CeIn3, which reveal pockets of f-electron holes centered at Q/2 in the Brillouin zone (where Q = [pi, pi, pi] is the antiferromagnetic modulation vector). This system had previously been identified as a local-moment magnet in which the f-electrons are completely localized. We discuss the Lifshitz Fermi surface topological changes in these pockets that takes place in strong magnetic fields and that is likely to take place as a function of pressure. We further discuss the implications for pressure-tuned superconductivity and the relevance of the experimental findings to CeRhIn5 and cuprate superconductors. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Intimate interplay between superconductivity and antiferromagnetism in CeNiGe3 : A(73) Ge-NQR study under pressure
Authors:
Harada, A; Mukuda, H; Kitaoka, Y; Thamizhavel, A; Okuda, Y; Settai, R; Onuki, Y; Itoh, KM; Haller, EE; Harima, H Author Full Names: Harada, A.; Mukuda, H.; Kitaoka, Y.; Thamizhavel, A.; Okuda, Y.; Settai, R.; Onuki, Y.; Itoh, K. M.; Haller, E. E.; Harima, H.
Source:
PHYSICA B-CONDENSED MATTER 403 (5-9): 1020-1022 APR 1 2008
Abstract:
We report the Ge-73-NQR studies on the antiferromagnetic (AFM) heavy-fermion compound CeNiGe3 which shows two domes like pressure-induced superconducting phases in the pressure (P) ranges of 1.7-3.7GPa and 5.9-7.3GPa denoted as SC1 and SC2, respectively [M. Nakashima, et al., J. Phys. Condens. Matter. 16 (2004) L255, H. Kotegawa, et al., J. Phys. Soc. Jpn. 75 (2006) 044713]. The NQR spectra have revealed a change from an incommensurate AFM structure at P = 0 and 2.0 GPa into a commensurate one at P = 2.8 GPa. The onset of the SCI may be relevant to an intimate evolution from the incommensurate into commensurate AFM-spin structure as P increases. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Occurrence of magnetism in CeMIn5-xHgx (M = Rh, Ir)
Authors:
Bauer, ED; Ronning, F; Maquilon, S; Pham, LD; Thompson, JD; Fisk, Z Author Full Names: Bauer, E. D.; Ronning, F.; Maquilon, S.; Pham, L. D.; Thompson, J. D.; Fisk, Z.
Source:
PHYSICA B-CONDENSED MATTER 403 (5-9): 1135-1137 APR 1 2008
Abstract:
The physical properties of CeM(In1-xHgx)(5) (M = Rh, Ir) including specific heat and magnetic susceptibility are reported. Two magnetic phases exist in CeRhIn(In1-xHgx)(5) with some evidence of a change from incommensurate magnetic order to a commensurate structure near 10% nominal Hg substitution. In CeIr(In1-xHgx)(5), an antiferromagnetic quantum critical point near x = 3% (followed by robust long-range antiferromagnetism for x > 5%) appears to be separated from superconductivity in CeIrIn5. The multitude of magnetic ground states observed in the CeM(In1-xHgx)(5) Materials is quite sensitive to doping and magnetic fields. (C) 2007 Published by Elsevier B.V.
Title:
The pressure effect on the magnetic commensurability and ferroelectricity in multiferroic HoMn2O5
Authors:
dela Cruz, CR; Lorenz, B; Ratcliff, W; Lynn, J; Gospodinov, MM; Chu, CW Author Full Names: dela Cruz, C. R.; Lorenz, B.; Ratcliff, W.; Lynn, J.; Gospodinov, M. M.; Chu, C. W.
Source:
PHYSICA B-CONDENSED MATTER 403 (5-9): 1359-1361 APR 1 2008
Abstract:
The multiferroic HoMn2O5 is a frustrated magnetic system with a non-collinear commensurate structure in its ferroelectric state. This work presents polarization measurements under isotropic pressure showing the stabilization of the high ferroelectric polarization state. This is associated with the pressure induced phase transition from an incommensurate magnetic structure to a commensurate one once the critical pressure is passed as shown by elastic powder neutron diffraction measurements. In addition, the small increase in the polarization upon spin reorientation in the commensurate magnetic state of HoMn2O5 is associated with a change in the magnetic structure without change in commensurability. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Specific heat of the Kagome mixed compounds (Co1-xNix)(3)V2O8
Authors:
Zhang, Q; Knafo, W; Grube, K; Lohneysen, HV; Meingast, C; Wolf, T Author Full Names: Zhang, Qin; Knafo, William; Grube, Kai; Loehneysen, Hilbert V.; Meingast, Christoph; Wolf, Thomas
Source:
PHYSICA B-CONDENSED MATTER 403 (5-9): 1404-1405 APR 1 2008
Abstract:
We present high-resolution specific heat data from 2 to 3 0 K of the mixed Kagome compounds (Co1-xNix)(3)V2O8 for x = 0, 0.12, 0.2, 0.5 and 1.0. We show that the specific heat at the first-order transitions of the end compounds (x = 0 and 1), obtained using relaxation calorimetry, is up to a factor of 10 larger than that previously reported in the literature. The mixed compounds exhibit only the highest temperature transition to an presumably, incommensurate magnetic structure. A slope change of T-N versus x at x = 0.2 indicates the transition from the Ni3V2O8- to Co3V2O8-type magnetic structures. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Influence of chemical substitutions on the charge instability of BaVS3
Authors:
Bernu, S; Foury-Leylekian, P; Pouget, JP; Akrap, A; Berger, H; Forro, L; Popov, G; Greenblatt, M Author Full Names: Bernu, S.; Foury-Leylekian, P.; Pouget, J. P.; Akrap, A.; Berger, H.; Forro, L.; Popov, G.; Greenblatt, M.
Source:
PHYSICA B-CONDENSED MATTER 403 (5-9): 1625-1627 APR 1 2008
Abstract:
We study the influence of Sr substitutions on the structural counterpart of the MI transition of BaVS3. When Sr content increases, the commensurate CDW modulation of pure BaVS3 is changed into an incommensurate short range modulation that we attribute to a charge ordering of the e(t(2g)) electrons. The same features are observed in S deficient samples. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Equilibrium and non-equilibrium microstructures of Mg-Zn-Y quasicrystal alloy
Authors:
Wan, DQ; Linlin, GYC; Feng, ZG Author Full Names: Wan, Diqing; Linlin, Gencang Yang; Feng, Zhigang
Source:
MATERIALS LETTERS 62 (10-11): 1711-1714 APR 15 2008
Abstract:
Applied SEM and TEM methods, an investigation on the difference between equilibrium and non-equilibrium microstructures of Mg-Zn-Y quasicrystal alloys have been carried out. lcosahedral quasicrystal (1-phase), W-phase, and Mg7Zn3 phase have been obtained in the as-cast alloy, while the non-equilibrium microstructure, which is mainly made up of amorphous composition and stable I-phase, is gained in the as-quenched Mg-Zn-Y alloy. The mechanism of formation of the non-equilibrium microstructure in as-quenched alloy is also discussed. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Theoretical calculations of phase transitions and optical properties of solid iodine under high pressures
Authors:
San, XJ; Wang, LC; Ma, YM; Liu, ZM; Cui, T; Liu, BB; Zou, GT Author Full Names: San, Xiaojiao; Wang, Liancheng; Ma, Yanming; Liu, Zhiming; Cui, Tian; Liu, Bingbing; Zou, Guangtian
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (17): Art. No. 175225 APR 30 2008
Abstract:
The structural stability and optical properties of solid iodine under pressure have been studied using the ab initio pseudopotential plane-wave method. The dependence of lattice parameters on pressure indicates that the first structural phase transition from phase I to phase V occurs at about 20 GPa. From the pressure dependence of our elastic constants for solid iodine in phase I, it is found that the first structural transformation from molecular phase I to the intermediate phase V occurs at about 20 GPa due to the softening of the elastic constant C-44, which is very close to the transition pressure of 20 GPa obtained by geometry optimizations and 23.2 GPa obtained by experimental measurements. The optimized structure for phase V is a face-centered orthorhombic (fco) phase with equal interatomic distances d(1) = d(2) = d(3), but this fco structure is mechanically unstable, with shear elastic stiffness coefficient C-44 < 0. To understand the modulated phase V, we use a periodic crystal structure to mimic the incommensurate phase V and obtain some quantitative information. In our calculation, the modulated phase is thermodynamically and mechanically stable. It is believed that phase V is not a monatomic phase but an intermediate state between a molecular and a monatomic state.

Update: 11-Apr-2008

Title:
X-ray resonant diffraction study of multiferroic DyMn2O5
Authors:
Ewings, RA; Boothroyd, AT; McMorrow, DF; Mannix, D; Walker, HC; Wanklyn, BMR Author Full Names: Ewings, R. A.; Boothroyd, A. T.; McMorrow, D. F.; Mannix, D.; Walker, H. C.; Wanklyn, B. M. R.
Source:
PHYSICAL REVIEW B 77 (10): Art. No. 104415 MAR 2008
Abstract:
X-ray resonant scattering has been used to measure the magnetic order of the Dy ions below 40 K in multiferroic DyMn2O5. The magnetic order has a complex behavior. There are several different ordering wave vectors, both incommensurate and commensurate, as the temperature is varied. In addition a nonmagnetic signal at twice the wave vector of one of the commensurate signals is observed, the maximum intensity of which occurs at the same temperature as a local maximum in the ferroelectric polarization. Some of the results, which bear resemblance to the behavior of other members of the RMn2O5 family of multiferroic materials, may be explained by a theory based on so-called acentric spin-density waves.
Title:
Spin dynamics near the critical doping in weakly superconducting underdoped YBa2Cu3O6.35 (T-c=18 K)
Authors:
Stock, C; Buyers, WJL; Yamani, Z; Tun, Z; Birgeneau, RJ; Liang, R; Bonn, D; Hardy, WN Author Full Names: Stock, C.; Buyers, W. J. L.; Yamani, Z.; Tun, Z.; Birgeneau, R. J.; Liang, R.; Bonn, D.; Hardy, W. N.
Source:
PHYSICAL REVIEW B 77 (10): Art. No. 104513 MAR 2008
Abstract:
>From neutron inelastic and elastic scattering we have determined the magnetic structure and fluctuations in the YBa2Cu3O6.35 (YBCO) superconductor (T-c = 18 K) near the boundary of the superconducting phase. The long-range ordered collinear spins of the insulating antiferromagnet are replaced by a commensurate central mode arising from slow, isotropically polarized, short-range spin correlations extending over four planar unit cells. The inelastic spectrum up to 30 meV is also broad in wave vector and commensurate. In contrast to the resonance peak of higher-T-c superconductors, the spins exhibit a single overdamped spectrum whose rate of relaxation Gamma decreases on cooling and saturates at 2 Gamma= 5 +/- 1 meV below similar to 50 K. As the relaxation rate saturates, the quasistatic spin correlations grow and become resolution limited in energy. The spin susceptibility above similar to 50 K follows the same omega/T scaling relation found for the monolayer La2-xSrxCuO4 system, indicating that the dominant energy scale is set by the temperature. Below 50 K the scale length is geometric and not linked by velocity to dynamic widths. Despite the large differences from an antiferromagnet, we show that integrated intensity conserves the total moment sum rule, and that on cooling the spectral weight transfers from the inelastic spin relaxation to the elastic central peak. There is no observable suppression of the spin fluctuations or central mode upon the onset of superconductivity. The spins respond not to coherent charge pairs but to hole doping, allowing coexistence of glassy short-range spin order with superconductivity. Since the physics of the weakly superconducting system YBCO6.35 must connect continuously with that in more strongly superconducting YBCO6.5, we find that neither incommensurate stripe-like spin modulations nor a well-defined neutron spin resonance are essential for the onset with doping of pairing in a high-temperature cuprate superconductor.
Title:
Investigation of defects in Al-Pd-Mn icosahedral quasicrystals by simulation of x-ray topography images
Authors:
Ma, JY; Wang, JB; Wang, RH Author Full Names: Ma, Jiayan; Wang, Jianbo; Wang, Renhui
Source:
JOURNAL OF PHYSICS D-APPLIED PHYSICS 41 (8): Art. No. 085413 APR 21 2008
Abstract:
The simulation of the diffraction contrast in x-ray topography has been extended from conventional crystals to quasicrystals (QCs). Case studies are presented for the investigation of two kinds of typical defects, i.e. spherical inclusions and straight dislocations, in an Al-Pd-Mn icosahedral QC using the extended program. The good agreement between the simulated and experimental images for spherical inclusions validates the extension. The systematic simulation for straight dislocations employing both phonon and phason strain fields illustrates not only the contrast dependences on various parameters, i.e. Burgers vector, diffraction vector, wavelength, deviation from exact Bragg diffraction, etc, but also the important contribution from the phason component, which is peculiar for QCs and normally makes the experimental analysis much more complex. The calculation can be applied to any defect in QCs in general and be of help in the defect characterization by matching with the experimental images, as in conventional crystals.
Title:
Band structure and localization of electronic states in a fivefold symmetric quasicrystal model
Authors:
Fu, XJ; Zhang, XW; Hou, ZL Author Full Names: Fu, Xiujun; Zhang, Xiaowei; Hou, Zhilin
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 354 (15-16): 1740-1743 MAR 15 2008
Abstract:
A fivefold symmetric quasilattice is constructed by the self-similar transformation on Gummelt two-color decagon and a single electron tight-binding model is proposed. We reduce the Hamiltonian to five identical subsets and analyze the spectral properties. By numerical calculation, three kinds of wave functions are found, which correspond to extended, localized and intermediate states, respectively. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Remarks on symmetries of 2D-quasicrystals
Authors:
Artamonov, V; Sanchez, S Author Full Names: Artamonov, V.; Sanchez, S.
Source:
INTERNATIONAL JOURNAL OF COMPUTER MATHEMATICS 85 (3-4): 319-328 2008
Abstract:
The paper presents a strict mathematical proof of the classifications of finite groups of symmetries of two-dimensional quasicrystals given by Hermisson, Richard and Baake in 1997.
Title:
Optical response of fci-ZnMgHo quasicrystal
Authors:
Karpus, V; Babonas, GJ; Reza, A; Suchodolskis, A; Tumenas, S; Hunderi, O; Assmus, W; Bruhne, S Author Full Names: Karpus, V.; Babonas, G. -J.; Reza, A.; Suchodolskis, A.; Tumenas, S.; Hunderi, O.; Assmus, W.; Bruehne, S.
Source:
ACTA PHYSICA POLONICA A 113 (3): 1005-1008 MAR 2008
Abstract:
The results of an optical spectroscopy study of the icosahedral fci-ZnMgHo quasicrystal are presented. The dielectric function of the quasicrystal was measured by the spectroscopic ellipsometry technique in the spectral range of 0.1-5.0 eV. The analysis of the dielectric function shows that an optical response of fci-ZnMgHo is a superposition of the free-electron Drude-type contribution and that of the interband transitions across the fci-ZnMgHo pseudogap.
Title:
Diffuse neutron scattering in the Mn0.4Cu0.6 alloy
Authors:
Jankowska-Kisielinska, J; Mikke, K; Fijal-Kirejczyk, I Author Full Names: Jankowska-Kisielinska, J.; Mikke, K.; Fijal-Kirejczyk, I.
Source:
ACTA PHYSICA POLONICA A 113 (4): 1171-1178 APR 2008
Abstract:
The diffuse neutron scattering in the Mn0.4Cu0.6 alloy was measured in the temperature range 15-390 K at the 3-axis neutron spectrometer at MARIA reactor in Swierk. The broad maxima of the neutron intensity were observed in the surrounding of the (0.5,1,0) reciprocal lattice point and other symmetry related points. The effect is similar to that observed in Mn-Cu alloys with lower Mn content at room temperature. Our results are in agreement with the earlier finding that the maxima of the short-range order incommensurate spin density wave scattering are placed at the (0.5 +/- delta,1,0) reciprocal lattice point with a linear dependence of delta on the Mn concentration. In addition, some commensurate antiferromagnetic short-range order was found.

Update: 4-Apr-2008

Title:
Role of smectite quasicrystal dynamics in adsorption of dinitrophenol
Authors:
Pereira, TR; Laird, DA; Thompson, ML; Johnston, CT; Teppen, BJ; Li, H; Boyd, SA Author Full Names: Pereira, Tanya R.; Laird, David A.; Thompson, Michael L.; Johnston, Cliff T.; Teppen, Brian J.; Li, Hui; Boyd, Stephen A.
Source:
SOIL SCIENCE SOCIETY OF AMERICA JOURNAL 72 (2): 347-354 MAR-APR 2008
Abstract:
Understanding sorption mechanisms and processes is critical for predicting the fate of organic pollutants in soils and for development of effective remediation strategies for contaminated soils. A novel suspension x-ray diffraction (XRD) technique was used to elucidate the influence of the size and swelling of K- and Ca-smectite quasicrystals in aqueous suspensions on adsorption of 4,6-dinitro-o-cresol (DNOC). X-ray diffraction patterns of randomly oriented smectite quasicrystals in aqueous suspensions were compared with diffraction patterns for air-dried and oven-dried oriented films of the same smectites. The XRD patterns reveal that the phenolate form of DNOC, which is predominant in solution with pH >= 4.4, is primarily adsorbed on external surfaces of K-smectite quasicrystals in aqueous suspensions and may enter the interlayers as a K-DNOC complex when K-smectite quasicrystals coalesce. In Ca-smectite suspensions with pH > 4.4, the phenolate form of DNOC is adsorbed only on external surfaces; however, DNOC may become entrapped between substacks within Ca-smectite quasicrystals as the smectite suspension dries to form an oriented film. The neutral form of DNOC (pH <= 4.4) was adsorbed in the interlayers of a low-charge-clensity Ca-smectite in aqueous suspension but not in the interlayers of the high-charge-density Ca-smectite, apparently due to steric restrictions. Clearly, XRD analysis is a valuable toot for gaining insight into interactions between smectites and organic molecules, but caution must be used in extrapolating data based on XRD patterns of air-dried and oven-dried smectite films to processes that may occur in aqueous smectite suspensions.
Title:
Theoretical sequence of s- and t-incommensurate phases in quartz
Authors:
Sannikov, DG Author Full Names: Sannikov, D. G.
Source:
PHYSICS OF THE SOLID STATE 50 (3): 507-510 MAR 2008
Abstract:
The sequence of s- and t-incommensurate phases observed with variations of the temperature in quartz is substantiated theoretically.
Title:
Effect of Nb on nanoquasicrystalline Al-based alloys
Authors:
Galano, M; Audebert, F; Stoney, IC; Cantor, B Author Full Names: Galano, M.; Audebert, F.; Stoney, I. C.; Cantor, B.
Source:
PHILOSOPHICAL MAGAZINE LETTERS 88 (4): 269-278 2008
Abstract:
Nanoquasicrystalline Al-based alloys, containing icosahedral particles in alpha-Al matrix, exhibit high strength at elevated temperature. The metastability of the quasicrystals can limit the use of these alloys. In the present work, the microstructural evolution of Al-93(Fe3Cr2)(7) and Al93Fe3Cr2Nb2 (at%) alloys was studied using heat treatments and structural characterization by XRD, TEM and STEM-EDX analysis. It was observed that the Nb is dissolved in the Al-Fe-Cr icosahedral phase. This provides higher thermal stability, retaining the fine nanoquasicrystalline microstructure for longer times at high temperature.
Title:
A new orthorhombic approximant of the icosahedral Al-Cu-Fe quasicrystal
Authors:
Lei, Y; Kenzari, S; Demange, V; Fournee, V; Dubois, JM Author Full Names: Lei, Y.; Kenzari, S.; Demange, V.; Fournee, V.; Dubois, J. M.
Source:
PHILOSOPHICAL MAGAZINE LETTERS 88 (4): 279-286 2008
Abstract:
We report on the formation of a new crystalline approximant phase of the icosahedral (i-)Al-Cu-Fe quasicrystal. This phase is formed during sintering of Al-based composites reinforced with i-AlCuFeB quasicrystalline particles. The structure of this phase has been characterized by transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). TEM revealed that it is a B-centred orthorhombic phase with lattice parameters a = 1.166 nm, b = 1.195 nm and c = 3.44 nm. Its chemical composition, as determined by electron energy loss spectroscopy (EELS), is close to Al76.9Cu2.7Fe20.4, with an average number of valence electrons per atom e/a of 1.92, similar to the value in all other approximants of the i-phase discovered thus far. Initial results on local atomic arrangements along one of its pseudo-5-fold axes are also presented.
Title:
Observation of beta phase particles in an isothermally aged Al-10 mass%Mg alloy with and without 0.5 mass%Ag
Authors:
Kubota, M Author Full Names: Kubota, Masahiro
Source:
MATERIALS TRANSACTIONS 49 (2): 235-241 FEB 2008
Abstract:
Characterization of the beta' and beta precipitate phases formed in the aged Al-10mass%Mg alloy with and without 0.5mass%Ag at 200 degrees C and 240 degrees C has been carried out using TEM. The plate-like precipitate particles were formed in binary alloys aged from 2 h at 200 degrees C. The plate-like particles had habit planes of {100}(alpha), and were identified as the beta' phase. Whereas the very fine scale, uniformly distributed precipitate particles with a spherical shape were formed as the dominant precipitate particle in ternary alloy aged at 200 degrees C for periods of 4 h and 6 h. These small spherical particles were identified to be icosahedral phase while no icosahedral phase was observed in the Ag-free alloys when samples were aged at 200 degrees C. Formation of a precipitate cluster consisting of two distinguishable parts has been observed in binary alloys aged 5 h at 240 degrees C, and these precipitate particles were identified as the equilibrium beta and metastable beta' phases. Whereas a higher volume fraction of dispersed precipitate phases which comprised a mixture of a coarse-scale, rod-like particles and blocky particles, was observed in ternary alloy aged 5 h at 240 degrees C. With further increase of ageing time up to 24 h at 240 degrees C, the microstructure contained a high volume fraction of coarse-scale, globular precipitate particles, together with a secondary distribution of fine-scale spheroidal precipitates, these coarse globular particles were identified to be the equilibrium beta phase.
Title:
Crystal and magnetic structures in the Tb(Pd, Ni) Al series
Authors:
Javorsky, P; Prokleska, J; Isnard, O; Prchal, J Author Full Names: Javorsky, P.; Prokleska, J.; Isnard, O.; Prchal, J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (10): Art. No. 104223 MAR 12 2008
Abstract:
We report on the magnetic structures in the TbPd1-xNixAl compounds as determined by powder neutron diffraction. The development of magnetic structures in the Tb(Pd, Ni) Al series is relatively simple. All the compounds show the existence of two magnetic phases with almost unchanged Neel temperature T-N similar or equal to 44 K and an additional magnetic phase transition temperature T-1 similar or equal to 23 K. The arrangement of the Tb moments between T-N and T-1 is identical for all the concentrations and is characterized by a (1/2, 0, 1/2) propagation vector with one-third of Tb moments frustrated to nearly zero. Certain concentration development occurs only below T-1. Magnetic moments that are frustrated between T-N and T-1 change their propagation below T-1 to commensurate (1/2, -1/2, 1/2) or incommensurate (1/2, -tau, 1/2), depending on the Ni concentration. The magnetic moments stay parallel to the hexagonal c axis for all concentrations and temperatures.
Title:
Magnetic phase diagram of Ho-Ag
Authors:
Paul-Boncour, V; Hoser, A; Hense, K; Gratz, E; Rotter, M; Stusser, N Author Full Names: Paul-Boncour, V.; Hoser, A.; Hense, K.; Gratz, E.; Rotter, M.; Stuesser, N.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (10): Art. No. 104225 MAR 12 2008
Abstract:
The magnetic phase diagram of Ho-Ag has been established using magnetoresistance, magnetostriction and neutron diffraction experiments versus applied field and temperature. Three different magnetic phases were observed: an incommensurate antiferromagnetic phase (IC) below T-N = 33 K, a commensurate antiferromagnetic phase (C) above 5 T and below T-1 (5-8 K) and a ferromagnetic component above 3 T. The IC phase undergoes spin reorientations around 5 T (IC') and 13 T (IC'').
Title:
Magnetic excitations in the ordered phases of praseodymium hexaboride
Authors:
Le, MD; McEwen, KA; Park, JG; Lee, S; Iga, F; Rule, KC Author Full Names: Le, M. D.; McEwen, K. A.; Park, J-G; Lee, S.; Iga, F.; Rule, K. C.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (10): Art. No. 104231 MAR 12 2008
Abstract:
We have made the first inelastic neutron scattering measurements on single crystal PrB6, studying the magnetic excitations in the ordered phases. The lowest energy mode has a minimum energy of approximate to 1.0 meV at the magnetic zone centre, with a significant dispersion along the [001] direction, but very little dispersion along [110]. Interactions out to fourth nearest neighbours are required to explain the [001] dispersion. Measurements of the temperature dependence of the excitations show a strong softening and broadening of the lowest energy mode at the magnetic zone centre between 2 K (commensurate phase) and 5 K (incommensurate phase).
Title:
Effects of oxygen deficiency on the magnetic ordering of Mn in (TbNa0.1MnO2.9)-Na-0.9
Authors:
Yang, CC; Wu, CM; Li, WH; Chan, TS; Liu, RS; Chen, YY; Avdeev, M Author Full Names: Yang, C. C.; Wu, C-M; Li, W-H; Chan, T. S.; Liu, R. S.; Chen, Y. Y.; Avdeev, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (10): Art. No. 104234 MAR 12 2008
Abstract:
Monovalent Na+ ions have been incorporated into a multiferroic TbMnO3 compound. Structural studies, using high-resolution neutron diffraction patterns, show that monovalent Na+-doping results in a noticeable oxygen deficiency in the compound. The alternations in crystalline and magnetic structures due to oxygen deficiency are investigated by neutron diffraction and magnetic susceptibility measurements. Na-doping turns the modulated incommensurate Mn spin structure, observed for the parent compound, into a simple commensurate one. The observed magnetic diffraction patterns agree very well with that calculated assuming a D-type arrangement for the Mn spins, with the moments pointing along the c-axis direction. No significant alternation in the ordering temperature of the Mn moments is found.
Title:
Charge ordering in CaCuxMn7-xO12 (x=0.0 and 0.1) compounds
Authors:
Slawinski, W; Przenioslo, R; Sosnowska, I; Bieringer, M; Margiolaki, I; Fitch, AN; Suard, E Author Full Names: Slawinski, W.; Przenioslo, R.; Sosnowska, I.; Bieringer, M.; Margiolaki, I.; Fitch, A. N.; Suard, E.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (10): Art. No. 104239 MAR 12 2008
Abstract:
The crystal structure of CaMn7O12 and CaCu0.1Mn6.9O12 has been studied by synchrotron radiation (SR) based powder x-ray diffraction and neutron powder diffraction in the temperature range from 10 K up to 290 K. The lattice parameter a exhibits a minimum at 45 K in CaMn7O12. The c lattice parameter in CaMn7O12 and CaCu0.1Mn6.9O12 has a maximum at the same temperature. Additional Bragg peaks have been found in the SR diffraction patterns in CaMn7O12 and CaCu0.1Mn6.9O12 below 250 K and 220 K, respectively. All diffraction peaks have been indexed as (h, k, l +/- k), where. was equal to 0.079(15) for CaMn7O12 and 0.093( 15) for CaCu0.1Mn6.9O12. The incommensurate low-temperature diffraction peaks are not observed in neutron diffraction patterns. This leads to the conclusion that the phase transition to the incommensurate structure is due to charge ordering rather than atomic position modulation. The charge ordering temperature coincides with dielectric constant changes of four orders of magnitude for CaMn7O12.
Title:
The structure model of a cubic aperiodic phase ('quasicrystal without forbidden symmetry axes')
Authors:
Kraposhin, VS; Talis, AL; Lam, HT Author Full Names: Kraposhin, V. S.; Talis, A. L.; Lam, Ha Thanh
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (11): Art. No. 114115 MAR 19 2008
Abstract:
A model structure of the aperiodic cubic phase (a cubic quasicrystal) has been constructed as a periodical packing of hierarchical octahedral clusters which were composed of truncated tetrahedra (Friauf-Laves polyhedra) and chains of Frank-Kasper polyhedra with 14 vertices. The construction of the hierarchical model for the cubic aperiodic phase became possible due to the discovery of a new space subdivision with equal edges and with vertices belonging to two orbits of the space group Fm3m. The subdivision is characterized by unique values and unique relations between the coordinates of the starting points of two orbits. Calculated x-ray diffraction patterns for the proposed hierarchical model are in qualitative agreement with published experimental x-ray patterns for aperiodical phases observed in melt-quenched Mg-Al and Fe-Nb-B-Si alloys.
Title:
Electronic and atomic disorder in icosahedral AlPdRe
Authors:
Rapp, O; Karkin, AA; Goshchitskii, BN; Voronin, VI; Srinivas, V; Poon, SJ Author Full Names: Rapp, O.; Karkin, A. A.; Goshchitskii, B. N.; Voronin, V. I.; Srinivas, V.; Poon, S. J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (11): Art. No. 114120 MAR 19 2008
Abstract:
Relations between electronic and atomic disorder of i-AlPdRe have been investigated by studies of neutron irradiated and annealed samples. The advantage with this technique is that a single sample can be monitored over a significant range of varying electronic properties, without concern for any influence of varying impurities. X-ray diffraction, the electrical resistivity and its temperature dependence, and the magnetoresistance are studied. The results show that annealings of an irradiated sample lead to improvement of the atomic order, as reflected in increased intensities of the x-ray diffraction peaks, while electronic properties change in the direction of increasing electronic disorder towards a metal-insulator transition. The observed relation in quasicrystals that improved atomic structure is associated with stronger anomalies in transport properties is thus also seen in i-AlPdRe. In particular, the variation of the diffusion constant in the region of small values of the resistivity is found to be similar for annealed polygrain samples and for single grain samples with varying Pd concentration, as evaluated from literature data, indicating a similar development of electronic disorder in both sets of samples. However, the problem remains as to why the resistivity is small in single grain samples which are atomically well-ordered. The possibility of a strong sensitivity to concentration differences is pointed out.
Title:
Thermodynamic properties of Al-Mn, Al-Cu, and Al-Fe-Cu melts and their relations to liquid and quasicrystal structure
Authors:
Zaitsev, AI; Zaitseva, NE; Shimko, RY; Arutyunyan, NA; Dunaev, SF; Kraposhin, VS; Lam, HT Author Full Names: Zaitsev, A. I.; Zaitseva, N. E.; Shimko, R. Yu; Arutyunyan, N. A.; Dunaev, S. F.; Kraposhin, V. S.; Lam, Ha Thanh
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (11): Art. No. 114121 MAR 19 2008
Abstract:
Thermodynamic properties of molten Al-Mn, Al-Cu and Al-Fe-Cu alloys in a wide temperature range of 1123-1878 K and the whole range of concentrations have been studied using the integral effusion method and Knudsen mass spectrometry. Thermodynamic functions of melts were described by the associated solution model. The possibility of icosahedral quasicrystal (i-QC) precipitation from liquid Al-Mn and Al-Cu-Fe alloys was found to be a consequence of the existence in liquid associates (clusters). A geometric model is suggested for the structure of associates in liquid.
Title:
(Ca0.37Sr0.63)TiO3 perovskite - an example of an unusual class of tilted perovskites
Authors:
Howard, CJ; Withers, RL; Knight, KS; Zhang, Z Author Full Names: Howard, C. J.; Withers, R. L.; Knight, K. S.; Zhang, Z.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (13): Art. No. 135202 APR 2 2008
Abstract:
The structure of Ca0.37Sr0.63TiO3 perovskite has been carefully investigated using electron and neutron diffraction. Electron diffraction supports the supercell and Pbcm space group previously proposed, while high resolution neutron powder diffraction data provide the basis for a new structure refinement. The distortions of the resultant structure relative to the ideal parent perovskite structure type have been decomposed into normal modes. It is found that the primary modes of distortion are octahedral tilting modes associated with the R point (k = [1/2, 1/2, 1/2]*) and the xi = 1/4 point on the T line of symmetry (k = [1/2, 1/2,xi]*). There is a smaller secondary, probably induced, mode of distortion involving antiferroelectric displacements of the Ti cations associated with the xi = 1/4 point on the Delta line of symmetry (k = [0, 0, xi]*). This compound provides one of the very few currently known examples of a tilted perovskite structure that shows tilting modes associated with the ubiquitous k = < 1/2, 1/2, xi > modulation wavevectors for a value of xi different from 0 and 1/2.
Title:
The accurate magnetic structure of CeAl2 at various temperatures in the ordered state
Authors:
Schweizer, J; Givord, F; Boucherle, JX; Bourdarot, F; Ressouche, E Author Full Names: Schweizer, J.; Givord, F.; Boucherle, J-X; Bourdarot, F.; Ressouche, E.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (13): Art. No. 135204 APR 2 2008
Abstract:
The magnetic structure of the cubic compound CeAl2 is incommensurate and double-k. The moments on the two Ce sites describe two elliptical helices of opposed chiralities and lie in the (1 (1) over bar0) plane, with their Fourier components m(k) close to the [111] direction. Recent symmetry considerations, including for the first time the inversion center of the crystal, have reduced the number of parameters of this structure and have underlined the existence of a phase difference between the projections m(x)(k), m(y)(k) and m(z)(k) of m(k). Up to now, although many neutron investigations have been carried out on CeAl2 single crystals, no set of magnetic intensities was available which was large and good enough to check whether this phase difference exists or not. We have measured such a set of data, taking great care of the instrumental resolution in order to avoid unwanted contributions to the intensities from other domains. As the magnetic form factor of the Gamma(7) ground state of CeAl2 depends very much on the direction of the applied field, it was necessary to go through a self-consistent determination of the magnetic form factor in the direction of the Fourier components m(k) to obtain good agreement between the refined magnetic structure and the experimental data. The resulting Fourier components are close but not exactly along the [111] direction and their departure from this direction at low temperature reduces the ellipticity of the helices. The phase difference between the projections m(x)(k), m(y)(k) and m(z)(k) is small but undoubtedly exists and is temperature dependent. It leads to a small distortion of the elliptical helices, with magnetic moments slightly out of the (1 (1) over bar0) plane.
Title:
Glass formation dependence on casting-atmosphere pressure in Zr65Al7.5Ni10Cu17.5-xPdx (x=0-17.5) alloy system: A resultant effect of quasicrystalline phase transformation and cooling mechanism during mold-casting process
Authors:
Setyawan, AD; Kato, H; Saida, J; Inoue, A Author Full Names: Setyawan, Albertus D.; Kato, Hidemi; Saida, Junji; Inoue, Akihisa
Source:
JOURNAL OF APPLIED PHYSICS 103 (4): Art. No. 044907 FEB 15 2008
Abstract:
A different dependence of apparent glass-forming ability (GFA) on casting-atmosphere pressure is observed in a Zr65Al7.5Ni10Cu17.5-xPdx (x = 0-17.5) alloy system. Low-Pd alloys (x < 12.5) reveal low GFA dependence, while high-Pd ones (x >= 12.5) show high GFA dependence on atmosphere pressure applied during casting. The phenomenon is suggested to originate from the fact that for the high-Pd alloys, the transformation region of supercooled-liquid to quasicrystalline phase is located at the low-temperature side of the undercooled-liquid region where the atmosphere-pressure dependence of cooling characteristic coincidently takes place. The on-cooling phase transformation in the alloy system and the cooling mechanism during mold-casting process are discussed comprehensively. (c) 2008 American Institute of Physics.
Title:
Quasicrystalline phase in melt-spun Al-Mn-Be ribbons
Authors:
Zupanic, F; Boncina, T; Krizman, A; Grogger, W; Gspan, C; Markoli, B; Spaic, S Author Full Names: Zupanic, Franc; Boncina, Tonica; Krizman, Alojz; Grogger, Werner; Gspan, Christian; Markoli, Bostjan; Spaic, Savo
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 452 (2): 343-347 MAR 20 2008
Abstract:
The quasicrystalline phase in melt-spun Al-Mn-Be alloys was investigated. In ribbons 40-60 mu m thick the phase was present in the form of small particles rather uniformly dispersed in an aluminium solid solution matrix. The quasicrystalline phase had a primitive icosahedral structure. It was confirmed that it contained a substantial amount of Be. Nonetheless, it seemed that the electron-to-atom ratio remained close to that of binary Al80Mn20 quasicrystal. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Formation of icosahedral phase in Zr65Al7.5Ni10Cu12.5Ag5 metallic glass
Authors:
Yan, ZJ; Dang, SE; Li, QS; Hao, WX; Hu, Y Author Full Names: Yan, Z. J.; Dang, S. E.; Li, Q. S.; Hao, W. X.; Hu, Y.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 452 (2): 359-366 MAR 20 2008
Abstract:
Two Zr65Al7.5Ni10Cu12.5Ag5 amorphous specimens were prepared from the mother ingots with different solidification microstructures. Observation by high-resolution electron microscopy (HREM) revealed that there existed numerous nano-sized short-range order regions (SRORs) in the as-cast specimens although their amorphous nature had been verified by X-ray diffraction (XRD). The average size of the SRORs decreased significantly as the solidification microstructure of the mother ingot became finer. The transformation from amorphous to icosahedral phase (I-phase) in the Zr65Al7.5Ni10Cu12.5Ag5 metallic glass was systematically investigated by differential scanning calorimetry (DSC) under isochronal and isothermal conditions. The results indicated that the transformation kinetics slightly changed, and that the formation of I-phase was triggered by the growth of those SRORs as the pre-existing embryos. It was strongly suggested that the atomic configuration of the unit structure in the metallic glasses showed an icosahedron-like one. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Quasicrystal derived catalyst for steam reforming of methanol
Authors:
Ngoc, BP; Geantet, C; Aouine, M; Bergeret, G; Raffy, S; Marlin, S Author Full Names: Ngoc, B. Phung; Geantet, C.; Aouine, M.; Bergeret, G.; Raffy, S.; Marlin, S.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 33 (3): 1000-1007 FEB 2008
Abstract:
Two alloys of composition Al(59)Cu(25.5)sFe(12.4)B(3) and Al71Cu9.7Fe8.7Cr10.6 were characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The latter forms a mixture of imperfect icosahedral phase and cubic phase upon rapid solidification from the liquid state. After heat treatment, this alloy transforms into a decagonal quasicrystalline phase. Both alloys can be used as catalysts precursors and transformed into active metallic phases after alkali leaching with a NaOH solution. These catalysts were used for hydrogen production by steam reforming of methanol between 473 and 773 K. The catalytic activities of these treated alloys were compared to that of a reference Cu/ZnO/Al2O3 catalyst. Quasicrystal derived catalysts showed a high catalytic activity for the production of hydrogen. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Update: 28-Mar-2008

Title:
Spin resonance in the d-wave superconductor CeCoIn5
Authors:
Stock, C; Broholm, C; Hudis, J; Kang, HJ; Petrovic, C Author Full Names: Stock, C.; Broholm, C.; Hudis, J.; Kang, H. J.; Petrovic, C.
Source:
PHYSICAL REVIEW LETTERS 1 (8): Art. No. 087001 FEB 29 2008
Abstract:
Neutron scattering is used to probe antiferromagnetic spin fluctuations in the d-wave heavy fermion superconductor CeCoIn5 (T-c=2.3 K). Superconductivity develops from a state with slow (h Gamma=0.3 +/- 0.15 meV) commensurate [Q(0)=(1/2,1/2,1/2)] antiferromagnetic spin fluctuations and nearly isotropic spin correlations. The characteristic wave vector in CeCoIn5 is the same as CeIn3 but differs from the incommensurate wave vector measured in antiferromagnetically ordered CeRhIn5. A sharp spin resonance (h Gamma < 0.07 meV) at h omega=0.60 +/- 0.03 meV develops in the superconducting state removing spectral weight from low-energy transfers. The presence of a resonance peak is indicative of strong coupling between f-electron magnetism and superconductivity and consistent with a d-wave gap order parameter satisfying Delta(q+Q(0))=-Delta(q).
Title:
Deposition of atoms on a quasicrystalline substrate: Molecular dynamics study in three dimensions
Authors:
Mungan, M; Weisskopf, Y; Erbudak, M Author Full Names: Mungan, Muhittin; Weisskopf, Yves; Erbudak, Mehmet
Source:
PHYSICAL REVIEW B 76 (19): Art. No. 195443 NOV 2007
Abstract:
We study the three-dimensional structure formation when atoms are deposited onto a substrate with a decagonal quasicrystalline order. Molecular dynamics calculations show that the adsorbate layer consists of ordered nanoscale domains with orientations determined by the underlying substrate symmetry. Depending on the relative strength of the interactions of adsorbate atoms with each other and with the substrate atoms, different morphologies are observed ranging from layer-by-layer growth to cluster formation. We also find that the film thickness likewise affects the overall structure of the growing film: Depending on the relative strength of the interaction between adsorbate atoms, a structural transition of the configuration of the adsorbate layers closest to the substrate can occur as the number of deposited layers increases. This is a simulation of three-dimensional crystal growth on a quasicrystal on a scale large enough to capture the formation of multiple domains.
Title:
Morphotropic phase-boundary-like characteristic in a lead-free and non-ferroelectric (1-x)NaNbO3-xCaTiO(3) system
Authors:
Tripathi, S; Pandey, D; Mishra, SK; Krishna, PSR Author Full Names: Tripathi, Saurabh; Pandey, Dhananjai; Mishra, Sanjay Kumar; Krishna, P. S. R.
Source:
PHYSICAL REVIEW B 77 (5): Art. No. 052104 FEB 2008
Abstract:
We report here an anomalous peak in the composition dependence of the dielectric permittivity of non-ferroelectric (1-x)NaNbO3-xCaTiO(3) ceramics for the composition range 0.10 < x < 0.20. This is reminiscent of a similar phenomenon in the ferroelectric morphotropic phase boundary ceramics. Rietveld analysis of the powder x-ray diffraction data for various compositions reveals that this peak is linked with a change of crystal structure from one orthorhombic phase in the Pbma space group for 0 <= x <= 0.10 to another orthorhombic phase in the Pbnm space group for x >= 0.20 through an intermediate long period modulated orthorhombic phase whose lattice parameter is similar to 14 times the lattice parameter of the Pbnm phase of CaTiO3 in the [010] direction (q similar to[0,1/14,0]).
Title:
Friedel oscillations of density of states in a one-dimensional Mott insulator and incommensurate charge-density wave or superconductor
Authors:
Tsvelik, AM Author Full Names: Tsvelik, A. M.
Source:
PHYSICAL REVIEW B 77 (7): Art. No. 073402 FEB 2008
Abstract:
Oscillations of local density of states generated by a single scalar impurity potential are calculated for one-dimensional systems with dynamically generated charge or spin gap. At zero temperature, the oscillations develop at finite wave vector (pi for the Mott insulator and 2k(F) for incommensurate charge-density wave or superconductor) and at frequencies larger than the soliton spectral gap m. Their amplitude has a broad maximum at omega approximate to 3m, where m is the gap magnitude.
Title:
Self-assembly, structure, and electronic properties of a quasiperiodic lead monolayer
Authors:
Ledieu, J; Leung, L; Wearing, LH; McGrath, R; Lograsso, TA; Wu, D; Fournee, V Author Full Names: Ledieu, J.; Leung, L.; Wearing, L. H.; McGrath, R.; Lograsso, T. A.; Wu, D.; Fournee, V.
Source:
PHYSICAL REVIEW B 77 (7): Art. No. 073409 FEB 2008
Abstract:
A quasiperiodic Pb monolayer has been formed on the fivefold surface of the Al-Pd-Mn quasicrystal. Growth of the monolayer proceeds via self-assembly of an interconnected network of pentagonal Pb stars, which are shown to be tau inflated compared to similar structural elements of the quasiperiodic substrate. Measurements of the electronic structure of the system using scanning tunneling spectroscopy and ultraviolet photoemission spectroscopy reveal that the Pb monolayer displays a pseudogap at the Fermi level which is directly related to its quasiperiodic structure.
Title:
Complex metallic alloys in the Ce-Au-Sn system: a study of the atomic and electronic structures
Authors:
Kenzari, S; Demange, V; Boulet, P; de Weerd, MC; Ledieu, J; Dubois, JM; Fournee, V Author Full Names: Kenzari, S.; Demange, V.; Boulet, P.; de Weerd, M. C.; Ledieu, J.; Dubois, J. M.; Fournee, V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (9): Art. No. 095218 MAR 5 2008
Abstract:
We report the formation of a new stable quasicrystal approximant in the Ce-Au-Sn system. The crystalline structure of the Ce15Au65Sn20 compound is investigated by x-ray diffraction and is found to be of similar structure type to the Zn17Sc3 1/1 approximant. Large clusters with icosahedral symmetry are located at the node of the body-centred cubic (bcc) unit cell (a = 1.5190 nm) containing 161 atoms. We have used transmission electron microscopy to emphasize the relationship of this new compound with the icosahedral space group. The valence band has been investigated by photoemission spectroscopy and shows an indication of Van Hove singularities in the density of states, characteristic of quasicrystalline and related approximant phases. We expect similar 1/1 approximant and possibly icosahedral phases to be discovered in the new RE-Au-Sn systems (where RE is rare earth). We also found a hexagonal phase with a large unit cell possessing local icosahedral order, co-existing as a minority phase.
Title:
The magnetic composition-temperature phase diagram of the kagome mixed system (CoxNi1-x)(3)V2O8
Authors:
Qureshi, N; Fuess, H; Ehrenberg, H; Hansen, TC; Ritter, C; Adelmann, P; Meingast, C; Wolf, T; Zhang, Q; Knafo, W Author Full Names: Qureshi, N.; Fuess, H.; Ehrenberg, H.; Hansen, T. C.; Ritter, C.; Adelmann, P.; Meingast, C.; Wolf, Th; Zhang, Q.; Knafo, W.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (9): Art. No. 095219 MAR 5 2008
Abstract:
The magnetic composition-temperature (x-T) phase diagram of the mixed kagome system (CoxNi1-x)(3)V2O8 (CNVO) deduced from neutron powder diffraction and single-crystal heat capacity experiments is presented. CNVO changes its magnetic structure twice below 5.5 K as a function of the compositional parameter x. A sample with x = 0.98 has been found to be of a critical composition where both ferromagnetic and antiferromagnetic reflections of the Co3V2O8 (CVO) type magnetic structure have been observed in the diffraction pattern. Below this composition the ferromagnetic phase is completely suppressed and antiferromagnetic short-range order is present, which is modulated by a propagation vector k(1) = (0, delta, 0) with delta being temperature and composition dependent. Below 4.2 K delta has a constant value of 0.4 for 0.76 < x < 0.92. In the region 0.71 < x < 0.76 a change of the magnetic structure into the long-range ordered Ni3V2O8 (NVO) type with k(2) = (delta, 0, 0), where delta is only dependent on x, takes place. Finally, for x < 0.035 the positions of the magnetic reflections become temperature dependent again.
Title:
A linked structural and electronic transition in Na0.63CoO2
Authors:
Zhou, T; Wright, AJ; Zhang, D; Button, TW; Greaves, C Author Full Names: Zhou, Tong; Wright, Adrian J.; Zhang, Dou; Button, Tim W.; Greaves, Colin
Source:
JOURNAL OF MATERIALS CHEMISTRY 18 (12): 1342-1346 2008
Abstract:
A structural transition at 158 degrees C in Na0.63CoO2 is associated with a resistivity anomaly. Raman spectroscopy suggests a change in Na ordering at the transition and, for the first time, we have identified the nature of this rearrangement using variable temperature neutron powder diffraction. On heating, some Na ions migrate to the thermodynamically less stable (Na1) site from Na2, consistent with loss of an incommensurate superstructure. It is suggested that the change in Na order is linked to a change in the electronic band structure, which is reflected in the resistivity anomaly.
Title:
Method on holomorphic vector functions and applications in two-dimensional quasicrystals
Authors:
Gao, Y; Xu, BX Author Full Names: Gao, Yang; Xu, Bai-Xiang
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B 22 (6): 635-643 MAR 10 2008
Abstract:
Generalization of the Stroh formalism to two-dimensional quasicrystal materials results in a ten-dimensional formalism for which there are five pairs of complex eigenvalues. By virtue of the generalized Stroh formalism, two-dimensional problems of quasicrystals elasticity are transferred into the boundary value problems of holomorphic vector functions in a given region. If the conformal mapping from an ellipse to a circle is known, a general method can be presented for solving the boundary value problems of holomorphic vector functions. Using the necessary and sufficient condition of boundary value problems of holomorphic vector functions, several basic two-dimensional problems in two-dimensional quasicrystals are solved.
Title:
Characterization and hydrogen absorption at low temperature of suction-cast Ti45Zr38Ni17 quasicrystalline alloy
Authors:
Huang, HG; Dong, P; Yin, C; Zhang, PC; Bai, B; Dong, C Author Full Names: Huang, Huogen; Dong, Ping; Yin, Chen; Zhang, Pencheng; Bai, Bin; Dong, Chuang
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 33 (2): 722-727 JAN 2008
Abstract:
The formation of surface oxide layer often brings an obstacle for the hydrogen absorption of Ti-based icosahedral quasicrystals (IQCs). This work is presented to investigate the hydrogenation properties of the Ti45Zr38Ni17 alloy which was produced by suction casting and then exposed to ambient air for about two months. XRD, SEM, EDS, TEM, XPS techniques were used to the characterization of the alloy. The results show that, a mixture of IQC, beta-Ti/Zr and C14 Laves phases was formed in the alloy which yielded a surface oxide layer, approximately 70 nm thick. By being crushed into particles, however, the alloy can absorb 1.5 wt% H with an induction time of about 500s at 30 degrees C and 2.88wt% H (correspondingly H/M approximate to 1.6) at 60 degrees C more rapidly, giving a preliminary evidence that suction casting may be a feasible approach to promote the hydrogenation properties of Ti-based IQC alloys. After several hydriding cycles, the primary phases were replaced by two hydride phases, tetragonal ZrH2 and hexagonal TiZrH1.68. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Title:
Disordered misfit [Ca2CoO3][CoO2](1.62) structure revisited via a new intrinsic modulation
Authors:
Muguerra, H; Grebille, D; Bouree, F Author Full Names: Muguerra, Herve; Grebille, Dominique; Bouree, Francoise
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 144-153 Part 2 APR 2008
Abstract:
The structure of the thermoelectric lamellar misfit cobalt oxide [Ca2CoO3][CoO2](1.62) was refined again using single-crystal X-ray diffraction data. A new commensurate intrinsic modulation was observed involving a modulation vector orthogonal to the misfit direction (2/3,0, -1/3). The five-dimensional superspace group is C2/m(1 delta 0)(alpha 0 gamma) gm and the structure was solved using a commensurate approximation. A new model is given involving an occupation modulation of the split sites of the [CoO] layer. This [CoO] layer can be described by triple chains running along b. The residual disorder along b can then be explained by the assumption of a local ordering with two types of clusters: CoO2 and Co5O4. A powder neutron diffraction experiment confirmed the ordering evidenced by the single-crystal X-ray diffraction study, but was not sufficient by itself to deal with this double modulated scheme. The new intrinsic modulation is destroyed by partial metal substitutions in the [CoO] layer. The structural modifications of this layer directly influence the physical properties which are related to the electronic structure of the [CoO2] layers.
Title:
KSm(MoO4)(2), an incommensurately modulated and partially disordered scheelite-like structure
Authors:
Arakcheeva, A; Pattison, P; Chapuis, G; Rossell, M; Filaretov, A; Morozov, V; Van Tendeloo, G Author Full Names: Arakcheeva, Alla; Pattison, Philip; Chapuis, Gervais; Rossell, Marta; Filaretov, Andrey; Morozov, Vladimir; Van Tendeloo, Gustaaf
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 160-171 Part 2 APR 2008
Abstract:
The incommensurately modulated scheelite-like KSm( MoO4)(2) structure has been refined in the monoclinic superspace group I2/b(alpha beta 0)00 by the Rietveld method on the basis of synchrotron radiation powder diffraction data. The systematic broadening of satellite reflections has been accounted for by applying anisotropic microstrain line-broadening. The microstructure has been studied by transmission electron microscopy (TEM). The partial disorder of the K and Sm cations in the A position is best approximated by a combination of harmonic and complex crenel functions with (0.952Sm + 0.048K) and (0.952K + 0.048Sm) atomic domains. This combination yields a compositional wave distribution from {KMoO4} to {SmMoO4} observed in the ab structure projection along q. The specific features of KSm(MoO4)(2) and degree of the A-cation ordering are discussed in comparison with the previously reported structure of KNd(MoO4)(2).

Update: 21-Mar-2008

Title:
Observation of correlations up to the micrometer scale in sliding charge-density waves
Authors:
Le Bolloc'h, D; Jacques, VLR; Kirova, N; Dumas, J; Ravy, S; Marcus, J; Livet, F Author Full Names: Le Bolloc'h, D.; Jacques, V. L. R.; Kirova, N.; Dumas, J.; Ravy, S.; Marcus, J.; Livet, F.
Source:
PHYSICAL REVIEW LETTERS 1 (9): Art. No. 096403 MAR 7 2008
Abstract:
A high resolution coherent x-ray diffraction experiment has been performed on the charge-density wave (CDW) system K0.3MoO3. The 2k(F) satellite reflection associated with the CDW has been measured with respect to external dc currents. In the sliding regime, the 2k(F) satellite reflection displays secondary satellites along the chain axis which corresponds to correlations up to the micrometer scale. This super long-range order is 1500 times larger than the CDW period itself. This new type of electronic correlation seems inherent to the collective dynamics of electrons in charge-density wave systems. Several scenarios are discussed.
Title:
Magnetic-field dependence of the ferroelectric polarization and spin-lattice coupling in multiferroic MnWO4
Authors:
Taniguchi, K; Abe, N; Sagayama, H; Ohtani, S; Takenobu, T; Iwasa, Y; Arima, T Author Full Names: Taniguchi, K.; Abe, N.; Sagayama, H.; Ohtani, S.; Takenobu, T.; Iwasa, Y.; Arima, T.
Source:
PHYSICAL REVIEW B 77 (6): Art. No. 064408 FEB 2008
Abstract:
The magnetic-field dependence of the ferroelectric polarization and the spin-lattice coupling in multiferroic MnWO4 have been investigated. The ferroelectric transition from the low temperature paraelectric phase occurs when the magnetic field is applied along the a, c, and the spin easy axes. The ferroelectric polarization in the magnetic field along the a and the c axis shows a contrasting behavior depending on the field direction, possibly reflecting the relative configuration between the crystallographic axis and the magnetic principal axis in the ac plane. Incommensurate lattice modulation observed in the ferroelectric spiral-spin phase confirms the existence of spin-lattice coupling in MnWO4. The lattice modulation indicates that the ferroelectric AF2 phase also takes the incommensurate magnetic structure in a magnetic field. In the high-field phase, which appears in high magnetic fields above 12 T along the easy axis, the magnetic-field-induced ferroelectric polarization disappeared.
Title:
Broken ergodicity, memory effect, and rejuvenation in Taylor-phase and decagonal Al-3(Mn,Pd,Fe) complex intermetallics
Authors:
Dolinsek, J; Slanovec, J; Jaglicic, Z; Heggen, M; Balanetskyy, S; Feuerbacher, M; Urban, K Author Full Names: Dolinsek, J.; Slanovec, J.; Jaglicic, Z.; Heggen, M.; Balanetskyy, S.; Feuerbacher, M.; Urban, K.
Source:
PHYSICAL REVIEW B 77 (6): Art. No. 064430 FEB 2008
Abstract:
The Taylor-phase complex intermetallic compound T-Al3Mn, its solid solutions with Pd and Fe, T-Al-3(Mn,Pd) and T-Al-3(Mn,Fe), and the related decagonal d-Al-Mn-Fe quasicrystal belong to the class of magnetically frustrated spin systems that exhibit rich out-of-equilibrium spin dynamics in the nonergodic phase below the spin-freezing temperature T-f. Performing large variety of magnetic experiments as a function of temperature, magnetic field, aging time t(w), and different thermal histories, we investigated broken-ergodicity phenomena of (i) a difference in the field-cooled and zero-field-cooled susceptibilities, (ii) the frequency-dependent freezing temperature, T-f(nu), (iii) hysteresis and remanence, (iv) ultraslow decay of the thermoremanent magnetization, (v) the memory effect (a state of the spin system reached upon isothermal aging can be retrieved after a negative temperature cycle), and (vi) "rejuvenation" (small positive temperature cycle within the nonergodic phase erases the effect of previous aging). We show that the phenomena involving isothermal aging periods (the memory effect, rejuvenation, and the ultraslow decay of the thermoremanent magnetization) get simple explanation by considering that during aging under steady external conditions, localized spin regions quasiequilibrate into more stable configurations, so that higher thermal energy is needed to destroy these regions by spin flipping, as compared to the thermal energy required to reverse a frustrated spin in a disordered spin-glass configuration that forms in the case of no aging. Common to all the investigated broken-ergodicity phenomena is the slow approach of a magnetically frustrated spin system toward a global equilibrium, which can never be reached on accessible experimental time scales due to macroscopic equilibration times.
Title:
Dynamical magnetic susceptibility in the lamellar cobaltate superconductor NaxCoO2 center dot yH(2)O
Authors:
Korshunov, MM; Eremin, I Author Full Names: Korshunov, M. M.; Eremin, I.
Source:
PHYSICAL REVIEW B 77 (6): Art. No. 064510 FEB 2008
Abstract:
We systematically analyze the influence of the superconducting gap symmetry and the electronic structure on the dynamical spin susceptibility in superconducting NaxCoO2 center dot yH(2)O within three different models: The single a(1g)-band model with nearest-neighbor hoppings, the realistic three-band t(2g) model with, and without e(g)' pockets present at the Fermi surface. We show that the magnetic response in the normal state is dominated by the incommensurate antiferromagnetic spin density wave fluctuations at large momenta in agreement with experimental temperature dependence of the spin-lattice relaxation rate. Also, we demonstrate that the presence or the absence of the e(g)' pockets at the Fermi surface does not significantly affect this conclusion. In the superconducting state our results for d(x)(2)-y(2)- or d(xy)-wave symmetries of the superconducting order parameter are consistent with experimental data and exclude nodeless d(x)(2)-y(2)+id(xy)-wave symmetry. We further point out that the spin-resonance peak proposed earlier is improbable for the realistic band structure of NaxCoO2 center dot yH(2)O. Moreover, even if present the resonance peak is confined to the antiferromagnetic wave vector and disappears away from it.
Title:
X-ray scattering study of charge density waves in La2-xBaxCuO4
Authors:
Kim, YJ; Gu, GD; Gog, T; Casa, D Author Full Names: Kim, Young-June; Gu, G. D.; Gog, T.; Casa, D.
Source:
PHYSICAL REVIEW B 77 (6): Art. No. 064520 FEB 2008
Abstract:
We report a comprehensive x-ray scattering study of charge density wave (stripe) ordering in La2-xBaxCuO4 (x approximate to 1/8), for which the bulk superconducting T-c is greatly suppressed. Strong superlattice reflections corresponding to static ordering of charge stripes were observed in this sample. The structural modulation at the lowest temperature was deduced based on the intensity of over 70 unique superlattice positions surveyed. We found that the charge order in this sample is described with one-dimensional charge density waves, which have incommensurate wave vectors (0.23, 0, 0.5) and (0, 0.23, 0.5), respectively, on neighboring CuO2 planes. The structural modulation due to the charge density wave order is simply sinusoidal, and no higher harmonics were observed. Just below the structural transition temperature, short-range charge density wave correlation appears, which develops into a large scale charge ordering around 40 K, close to the spin density wave ordering temperature. However, this charge ordering fails to grow into a true long range order, and its correlation length saturates at similar to 230 angstrom, and slightly decreases below about 15 K, which may be due to the onset of two-dimensional superconductivity.
Title:
Study on as-cast microstructures and solidification process of Mg-Zn-Y Alloys
Authors:
Zhang, YB; Yu, SR; Zhu, XY; Luo, YR Author Full Names: Zhang, Yingbo; Yu, Sirong; Zhu, Xianyong; Luo, Yanru
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 354 (14): 1564-1568 MAR 1 2008
Abstract:
The microstructures and phases of as-cast Mg-Zn-Y alloys were investigated by means of scanning electron microscopy (SEM), energy-dispersive spectrum (EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) in this study. Stable icosahedral Mg30Zn60Y10 quasicrystals were obtained using common casting technique. With increasing Y content, the contents of quasicrystals increased, the distribution of quasicrystals was improved, and the morphologies of quasicrystal and other microstructures of Mg-Zn-Y alloys showed different characteristics. In addition, the solidification process of Mg-Zn-Y alloys was analyzed. Icosahedral Mg30Zn60Y10 quasicrystalline phase is easy to nucleate in slow cooling. (C) 2007 Elsevier B.V. All rights reserved.

Update: 14-Mar-2008

Title:
Solid-state physics - How does your quasicrystal grow?
Authors:
Steinhardt, PJ Author Full Names: Steinhardt, Paul J.
Source:
NATURE 452 (7183): 43-44 MAR 6 2008
Title:
Efficient photocatalytic decomposition of acetaldehyde over a solid-solution perovskite (Ag0.75Sr0.25)(Nb0.75Ti0.25)O-3 under visible-light irradiation
Authors:
Wang, DF; Kako, T; Ye, JH Author Full Names: Wang, Defa; Kako, Tetsuya; Ye, Jinhua
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 130 (9): 2724-+ MAR 5 2008
Abstract:
A green chemistry process for environmental purification is realized on a novel visible-light-active photocatalyst (Ag0.75Sr0.25) (Nb0.75Ti0.25)O-3. This mixed valent solid-solution perovskite with a modulated electronic structure possesses a strong oxidative 4 potential for efficient photocatalytic decomposition of acetaldehyde into CO2 at ambient temperature.
Title:
Anomalous behavior of hardness and crystal structure in CeRh3Bx (x=0-1) phase
Authors:
Yubuta, K; Nomura, A; Yamamura, T; Shishido, T Author Full Names: Yubuta, K.; Nomura, A.; Yamamura, T.; Shishido, T.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 451 (1-2): 301-304 FEB 28 2008
Abstract:
We have examined the relationship between hardness and crystal structure of a Cu3Au-type compound CeRh3Bx (x = 0-1) by electron diffraction and high-resolution electron microscopy. The electron diffraction revealed 1/2 1/2 1/2-type superlattice reflections and fine satellite ones in B content range of 0.4 < x < 0.5, where anomalous decrease of hardness was observed. The observed high-resolution image taken with a diffraction pattern showing the satellite reflections along the [011] direction shows a domain structure with size of about 3 nm, and a lattice modulation and some edge dislocations have been observed at boundaries between the domains. Conclusively, ordering of B atoms and followed by the appearance of the long-ranged modulated structure could lead to the anomalous behavior of hardness in CeRh3Bx. (c) 2007 Elsevier B.V. All rights reserved.

Update: 7-Mar-2008

Title:
Phase separation and crystallization in a melt-spun Ti45Zr35Ni17Cu3 alloy
Authors:
Wang, LM; Liu, BZ; Ma, LQ; Ma, CL; Inoue, A Author Full Names: Wang, Limin; Liu, Baozhong; Ma, Liqun; Ma, Chaoli; Inoue, Akihisa
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 354 (10-11): 1010-1014 FEB 1 2008
Abstract:
Structure and crystallization behavior of amorphous and quasicrystalline Ti45Zr35Ni17Cu3 alloy have been studied. DSC trace of the amorphous alloy obtained during continuous heating to 1300 K shows distinctly an exothermic peak and two endothermic peaks. The amorphous alloy has different structures depending on annealing temperature. The first exothermic reaction at low temperature region from 400 K to 900 K is due to the precipitation of an icosahedral quasicrystalline phase, and the second endothermic reaction at higher temperature region from 950 K to 990 K results from the transformation of the I-phase to C14 Laves and alpha-(Ti, Zr) phases. (C) 2007 Published by Elsevier B.V.
Title:
On phase transformations in mechanically alloyed and subsequently annealed Al70Cu20Fe10
Authors:
Wang, Y; Tian, Y; Wang, Y; Geng, HR; Zhang, ZH Author Full Names: Wang, Yan; Tian, Ying; Wang, Yi; Geng, Haoran; Zhang, Zhonghua
Source:
INTERMETALLICS 16 (2): 121-129 FEB 2008
Abstract:
In the present work, phase transformations during mechanical alloying (MA) and post-MA annealing of Al70Cu20Fe10 have been investigated using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). No icosahedral quasicrystalline phase (i-phase) is observed during the milling process of Al70Cu20Fe10. A totally disordered beta-Al(Cu,Fe) phase firstly forms in the as-milled powders after 40 h of MA and thus transforms into the stable beta-phase with a B2 structure with increasing milling time up to 70 h. The i-phase appears in the as-annealed products and its amount increases with increasing milling time. In addition, the omega-Al7Cu2Fe phase only forms after heat treatment of the milled Al70Cu20Fe10 powders. Furthermore, the formation of both the i-phase and omega-phase depends upon the milling time and annealing temperature. (C) 2007 Elsevier Ltd. All rights reserved.
Title:
Higher-dimensional point groups in superspace crystallography
Authors:
Janner, A Author Full Names: Janner, A.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 64: 280-283 Part 2 MAR 2008
Abstract:
Crystallographic puzzles not covered by the present crystallography, like integral indexing and crystallographic scaling of axial-symmetric biomacromolecules and icosahedral viral capsids and/or integral lattices, can possibly be explained by extending (n, d)-dimensional superspace crystallography to include finite subgroups of the higher-dimensional orthogonal group O(n) and not only those of O(d), as restricted by the physical dimension d.

Update: 29-Feb-2008

Title:
Sound velocity and absorption measurements under high pressure using picosecond ultrasonics in a diamond anvil cell: Application to the stability study of AlPdMn
Authors:
Decremps, F; Belliard, L; Perrin, B; Gauthier, M Author Full Names: Decremps, F.; Belliard, L.; Perrin, B.; Gauthier, M.
Source:
PHYSICAL REVIEW LETTERS 1 (3): Art. No. 035502 JAN 25 2008
Abstract:
We report an innovative high pressure method combining the diamond anvil cell device with the technique of picosecond ultrasonics. Such an approach allows us to measure sound velocity and attenuation of solids and liquids under pressure of tens of GPa, overcoming all the drawbacks of traditional techniques. The power of this experimental technique is demonstrated in studies of lattice dynamics and relaxation processes in a metallic single grain of AlPdMn quasicrystal, and in rare gas solids neon and argon.
Title:
Strain amplification of the 4k(F) chain instability in Sr14Cu24O41
Authors:
Rusydi, A; Abbamonte, P; Eisaki, H; Fujimaki, Y; Smadici, S; Motoyama, N; Uchida, S; Kim, YJ; Rubhausen, M; Sawatzky, GA Author Full Names: Rusydi, A.; Abbamonte, P.; Eisaki, H.; Fujimaki, Y.; Smadici, S.; Motoyama, N.; Uchida, S.; Kim, Y. -J.; Ruebhausen, M.; Sawatzky, G. A.
Source:
PHYSICAL REVIEW LETTERS 1 (3): Art. No. 036403 JAN 25 2008
Abstract:
We used resonant soft x-ray scattering to study the chain ordering in Sr14Cu24O41 (SCO). We observed, for the first time, both the chain and ladder orders in SCO with the same probe. We found that the chain modulation in SCO is incommensurate with wave vector L-c=0.318, is strongly temperature (T) dependent, and is accompanied by a substantial hole modulation. By contrast, the chain modulation in a hole-depleted control sample La6Ca8Cu24O41 was commensurate (L-c=0.3), T independent, and purely structural. We conclude that the chain charge order in SCO is a 4k(F) charge density wave stabilized by the misfit strain between the ladder and chain substructures.
Title:
Optical coupling to spin waves in the cycloidal multiferroic BiFeO3
Authors:
de Sousa, R; Moore, JE Author Full Names: de Sousa, Rogerio; Moore, Joel E.
Source:
PHYSICAL REVIEW B 77 (1): Art. No. 012406 JAN 2008
Abstract:
The magnon and optical phonon spectrum of an incommensurate multiferroic such as BiFeO3 is considered in the framework of a phenomenological Landau theory. The resulting spin wave spectrum is quite distinct from commensurate substances due to soft mode anisotropy and magnon zone folding. The former allows electrical control of spin wave propagation via reorientation of the spontaneous ferroelectric moment. The latter gives rise to multiple magnetodielectric resonances due to the coupling of optical phonons at zero wave vector to magnons at integer multiples of the cycloid wave vector. These results show that the optical response of a multiferroic reveals much more about its magnetic excitations than previously anticipated on the basis of simpler models.
Title:
Neutron scattering study on spin correlations and fluctuations in the transition-metal-based magnetic quasicrystal Zn-Fe-Sc
Authors:
Sato, TJ; Kashimoto, S; Masuda, C; Onimaru, T; Nakanowatari, I; Iida, K; Morinaga, R; Ishimasa, T Author Full Names: Sato, Taku J.; Kashimoto, Shiro; Masuda, Chihiro; Onimaru, Takahiro; Nakanowatari, Isao; Iida, Kazuki; Morinaga, Rei; Ishimasa, Tsutomu
Source:
PHYSICAL REVIEW B 77 (1): Art. No. 014437 JAN 2008
Abstract:
Spin correlations and fluctuations in the 3d-transition-metal-based icosahedral quasicrystal Zn-Fe-Sc have been investigated by neutron scattering using polycrystalline samples. Magnetic diffuse scattering has been observed in the elastic experiment at low temperatures, indicating development of static short-range-spin correlations. In addition, the inelastic scattering experiment detects a Q-independent quasielastic signal ascribed to single-site relaxational spin fluctuations. Above the macroscopic freezing temperature T-f similar or equal to 7 K, the spin relaxation rate shows Arrhenius-type behavior, indicating thermally activated relaxation process. In contrast, the relaxation rate remains finite even at the lowest temperature, suggesting a certain quantum origin for the spin fluctuations below T-f.
Title:
Structural modulation and electronic structural features in the charge ordered state of La0.5Sr1.5MnO4
Authors:
Zeng, LJ; Ma, C; Yang, HX; Xiao, RJ; Li, JQ; Jansen, J Author Full Names: Zeng, L. J.; Ma, C.; Yang, H. X.; Xiao, R. J.; Li, J. Q.; Jansen, J.
Source:
PHYSICAL REVIEW B 77 (2): Art. No. 024107 JAN 2008
Abstract:
The structural changes associated with the charge ordering (CO) transition in layered La0.5Sr1.5MnO4 have been determined by electron diffraction using the multislice least-squares method. The results demonstrate that the structural deformations of the Mn3+O6 octahedra can be well characterized by a transverse modulation wave along the < 110 > direction. Based on these structural data, we have performed a theoretical calculation of the electronic structure by density functional theory plus the on-site Coulomb interaction U. The resultant density of states exhibits a clear band gap at the Fermi level for this low-temperature CO insulating state. It is also noted that the essential Jahn-Teller effects in this layered system can evidently affect the electronic structures and orbital hybridization appearing with the CO transition. Charge disproportionation and orbital ordering in La0.5Sr1.5MnO4 have been extensively discussed in comparison with the data obtained for the cubic perovskite La0.5Ca0.5MnO3.
Title:
Displacive mechanisms and order-parameter symmetries for the A7-incommensurate-bcc sequences of high-pressure reconstructive phase transitions in Group Va elements
Authors:
Katzke, H; Toledano, P Author Full Names: Katzke, Hannelore; Toledano, Pierre
Source:
PHYSICAL REVIEW B 77 (2): Art. No. 024109 JAN 2008
Abstract:
The high-pressure structural transitions observed in the Group Va elements P, As, Sb, and Bi are described by displacive atomic mechanisms. A theoretical analysis of the proposed mechanisms shows that two different structural paths are followed relating the low-pressure A7 structure to the highest-pressure bcc structure. One structural path gives rise to the host-guest structures found in As, Sb, and Bi, whereas another path yields the incommensurate P IV structure recently disclosed in P. The incommensurate character of the host-guest and P IV structures is shown to be imposed by the energetically most favorable path relating the A7 and bcc structures.
Title:
Weakly anisotropic frustrated zigzag spin chain
Authors:
Dmitriev, DV; Krivnov, VY Author Full Names: Dmitriev, D. V.; Krivnov, V. Ya.
Source:
PHYSICAL REVIEW B 77 (2): Art. No. 024401 JAN 2008
Abstract:
The frustrated spin-1/2 model with weakly anisotropic ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchanges is studied with use of variational mean-field approach, scaling estimates of the infrared divergencies in the perturbation theory and finite-size calculations. The ground-state phase diagram of this model contains three phases: the ferromagnetic phase, the commensurate spin-fluid phase, and the incommensurate phase. The nontrivial behavior of the boundaries between these phases and the character of the phase transitions in case of weak anisotropy are determined.
Title:
A study of an incommensurately modulated structure in Ca0.28Ba0.72Nb2O6 by electron microscopy
Authors:
Ge, BH; Wang, YM; Li, XM; Li, FH; Song, HL; Zhang, HJ Author Full Names: Ge, B. H.; Wang, Y. M.; Li, X. M.; Li, F. H.; Song, H. L.; Zhang, H. J.
Source:
PHILOSOPHICAL MAGAZINE LETTERS 88 (3): 213-217 2008
Abstract:
Two equivalent modulation wavevectors of the incommensurately modulated structure (IMS) observed in the tetragonal tungsten bronze Ca0.28Ba0.72Nb2O6 were determined by electron diffraction to be q(1) = 0.286(a* + b*) + 0.5c*and q(2) = 0.286(a - b) + 0.5c*. The projection of the IMS in the a + b direction has been obtained from a single high-resolution electron microscope image via image deconvolution. According to the high-dimensional space description of the IMS, a (1 + 1)-dimensional hypersection passing through the pentagonal channels has been obtained, showing both occupational and displacive modulations. The origin of the incommensurate modulation is discussed.
Title:
Formation of omega-Al7Cu2Fe phase during laser processing of quasicrystal-forming Al-Cu-Fe alloy
Authors:
Biswas, K; Chattopadhyay, K Author Full Names: Biswas, K.; Chattopadhyay, K.
Source:
PHILOSOPHICAL MAGAZINE LETTERS 88 (3): 219-230 2008
Abstract:
The formation of an omega-Al7Cu2Fe phase during laser cladding of quasicrystal-forming Al65Cu23.3Fe11.7 alloy on a pure aluminium substrate is reported. This phase is found to nucleate at the periphery of primary icosahedral-phase particles. A large number of omega-phase particles form an envelope around the icosahedral phase. On the outer side, they form an interface with an alpha-Al solid solution. Detailed transmission electron microscopic observations show that the omega phase exhibits an orientation relationship with the icosahedral phase. Analysis of experimental results suggests that the omega phase forms by precipitation on an icosahedral phase by heterogeneous nucleation and grows into the aluminium-rich melt until supersaturation is exhausted. The microstructural observations are explained in terms of available models of phase transformations.
Title:
Effects of extrusion on the microstructure and mechanical properties of Mg-Zn-Gd alloy reinforced with quasicrystalline particles
Authors:
Yuan, GY; Liu, Y; Ding, WJ; Lu, C Author Full Names: Yuan, Guangyin; Liu, Yong; Ding, Wenjiang; Lu, Chen
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 474 (1-2): 348-354 FEB 15 2008
Abstract:
The microstructure and mechanical properties of Mg95.9Zn3.5Gd0.6 alloy reinforced with icosahedral quasi-crystalline particles (I-phase) were investigated after extrusion at 573 K and 673 K. The effects of extrusion temperature and heat treatment on the microstructure and mechanical properties of the alloy were analyzed and the strengthening effect of I-phase was discussed. The results show that the I-phase is significantly refined upon extrusion. At room temperature, the alloy extruded at 573 K exhibits better tensile mechanical properties as compared to the alloy extruded at 673 K. At 473 K, the as-extruded alloy exhibits high elongation of about 94% due to the high cohesion of the I-phase with the matrix. As compared to the alloy extruded at 573 K, the alloy extruded at 673 K exhibits higher precipitate strengthening effect due to a higher density of I-phase precipitates, which results in not only a high ultimate tensile strength of 117 MPa, but also a high elongation of 82.5% at 473 K. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Iron deposition on the tenfold surface of the Al72Ni11Co17 decagonal quasicrystal
Authors:
Wearing, LH; Smerdon, JA; Leung, L; Dhesi, SS; Ledieu, J; Bencok, P; Fisher, I; Jenks, CJ; McGrath, R Author Full Names: Wearing, L. H.; Smerdon, J. A.; Leung, L.; Dhesi, S. S.; Ledieu, J.; Bencok, P.; Fisher, I.; Jenks, C. J.; McGrath, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 20 (1): Art. No. 015005 JAN 9 2008
Abstract:
The adsorption behaviour of Fe on the tenfold surface of the decagonal quasicrystal Al72.6Ni10.5Co16.9 has been studied using scanning tunnelling microscopy, low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and x-ray magnetic circular dichroism (XMCD). The results show the growth of a disordered film up to a coverage of 9 MLE (monolayer equivalent) after which polycrystalline island growth is observed. These islands are interconnected, and the LEED pattern indicates that they preferentially align along five directions. The AES results indicate that the film is composed of Fe intermixed with the substrate elements. The XMCD results point to an induced magnetic moment for Co and Ni in the intermixed layer/interface region.
Title:
Effect of Tb doping on electric and magnetic behavior of BiFeO3 thin films
Authors:
Wang, Y; Nan, CW Author Full Names: Wang, Yao; Nan, Ce-Wen
Source:
JOURNAL OF APPLIED PHYSICS 103 (2): Art. No. 024103 JAN 15 2008
Abstract:
The effect of Tb doping on crystal structure and electric and magnetic behavior of BiFeO3 thin films prepared via a solution processing on (111)Pt/Ti/SiO2/Si substrates was studied. The substitution of Bi ions by a small amount of Tb ions could stabilize the valence of Fe3+ in BiFeO3 thin films, and as indicated by transmission electron microscope images and largely reduced leakage current in comparison with pure BiFeO3 thin films, the quality of the films was improved by Tb doping. Electric and magnetic behavior of Tb-doped BiFeO3 films was investigated with employing La-doped BiFeO3 films as comparison. Large enhancement in both remnant and saturation polarization and the polarization switching were observed in Tb-doped BiFeO3 films, while the inhomogeneous spin-modulated magnetic structure of BiFeO3 was not modified through Tb substitution but by La substitution. (C) 2008 American Institute of Physics.

Update: 22-Feb-2008

Title:
New general solutions of plane elasticity of one-dimensional quasicrystals
Authors:
Gao, Y; Xu, BX; Zhao, BS; Chang, TC Author Full Names: Gao, Yang; Xu, Bai-Xiang; Zhao, Bao-Sheng; Chang, Tian-Chun
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 245 (1): 20-27 JAN 2008
Abstract:
A theory of general solutions of plane problems is developed for the coupled equations of plane elasticity of one-dimensional quasicrystals. By introducing a displacement function, very large numbers of complicated equations of the in-plane problem are simplified to a sixth-order partial differential governing equation, and then three general solutions are presented through an operator method. Since the displacement function is required to satisfy the sixth-order governing equation, it is still difficult to obtain rigorous analytic solutions from the higher-order equation directly and is not applicable in most cases. Therefore, a decomposition and superposition procedure is employed to replace the higher-order displacement function with three second-order displacement functions, and accordingly the general solutions are simplified in terms of these functions. In consideration of different cases of three characteristic toots, the general solutions involve three cases, but all are in simple forms that are conveniently applied. Furthermore, it is worth noting that the general solutions obtained here are complete in X-3-convex domains. To illustrate the application of the general solutions obtained, the closed form solutions are obtained for wedge problems subjected to point phonon force and phason force at the apex.
Title:
Wave models of non-crystallographic structures
Authors:
Losev, A Author Full Names: Losev, A.
Source:
PHILOSOPHICAL MAGAZINE 88 (2): 201-208 2008
Abstract:
Combinations of oscillations with incommensurate periods are utilized to generate discrete planar structures with non-crystallographic symmetries. Some previously known tilings and results are reconsidered in this context. A new kind of decagonal tiling, its relations with the Penrose tilings, and some experimental reports are discussed.
Title:
New sequences of phase transition in ni-mn-ga ferromagnetic shape memory nanoparticles
Authors:
Liu, DM; Nie, ZH; Wang, YD; Liu, YD; Wang, G; Ren, Y; Zuo, L Author Full Names: Liu, D. M.; Nie, Z. H.; Wang, Y. D.; Liu, Y. D.; Wang, G.; Ren, Y.; Zuo, L.
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE 39A (2): 466-469 FEB 2008
Abstract:
In-situ high-energy X-ray diffraction was used for tracing the structural transitions in Ni2MnGa and Ni47Mn25Ga22Co6 nanoparticles that were prepared by a ball-milling and subsequent annealing process. A decrease in martensitic transformation temperature was evidenced in all annealed nanoparticles. It was found that a three-layered modulated structure, usually observed as a metastable premartensitic phase in coarse-grained alloys, becomes a stable phase in the annealed Ni2MnGa nanoparticles up to 4 K.
Title:
Friction and wear behavior of as-cast Mg-Zn-Y quasicrystal materials
Authors:
Zhang, YB; Yu, SR; Luo, YR; Hu, HX Author Full Names: Zhang, Yingbo; Yu, Sirong; Luo, Yanru; Hu, Haixia
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 472 (1-2): 59-65 JAN 15 2008
Abstract:
Mg-Zn-Y quasicrystal materials were fabricated using casting method. The friction and wear behaviors of the quasicrystal materials were investigated under dry sliding condition. The results show that the friction coefficients decreased with increasing applied loads in all Mg-Zn-Y quasicrystal materials. High applied load brought about high plastic deformation on the worn surface of the Mg-Zn-Y quasicrystal materials. The friction coefficients and the wear mass losses of the Mg-Zn-Y quasicrystal materials decreased firstly and then increased with increasing Y content. When the Y content was 2at.%, the Mg-Zn-Y quasicrystal materials exhibited the lowest friction coefficients and the best wear resistance at all applied loads. There existed noncrystal phase in the wear debris of the Mg-25Zn-1.5Y quasicrystal material at the applied load of 70 N. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Effect of quasicrystal and Laves phases on strength and ductility of as-extruded and heat treated Mg-Zn-Gd-based alloys
Authors:
Yuan, GY; Liu, Y; Lu, C; Ding, WJ Author Full Names: Yuan, Guangyin; Liu, Yong; Lu, Chen; Ding, Wenjiang
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 472 (1-2): 75-82 JAN 15 2008
Abstract:
Microstructure and mechanical properties of Mg95.9Zn3.5Gd0.6 and Mg94.4Zn3.5Gd0.6Cu1.5 alloys reinforced by icosahedral quasicrystalline phase (I-phase) and Laves phase have been studied after extrusion at 573 K and 673 K. Extrusion significantly refined the I-phase and Laves phase, and made them exist as particles along the grain boundary and in the matrix. The strengthening effect of I-phase and Laves phase has been analyzed. The combination of I-phase and Laves phase has higher contribution to the improvement of yield strength, which made the Mg94.4Zn3.5Gd0.6CU1.5 alloy exhibits strong heat resistance. The results show that the two alloys have different heat treatment effect due to different fraction of I-phase and Laves phase. The Mg94.4Zn3.5Gd0.6 alloy after extrusion at 673 K has higher elongation about 94% at 473 K due to higher fraction of I-phase. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Optical transmission through generalized SML superlattices
Authors:
Yin, HL; Yang, XB; Guo, Q; Lan, S Author Full Names: Yin, Hailong; Yang, Xiangbo; Guo, Qi; Lan, Sheng
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (35): Art. No. 356221 SEP 5 2007
Abstract:
The SML model is a kind of one-dimensional (1D) quasiperiodic three-tile structure proposed by Liu et al (1991 Phys. Rev. B 43 13240; 1991 Chin. Phys. Lett. 8 533) based on the experimental results of Al-Si-Mn quasicrystals (Boissieu et al 1990 J. Phys.: Condens. Matter 2 2499). Generalized SML models (GSML(m, n)) are extensions of the SML one. In this paper, we study the transmission properties of light through GSML(m, n) aperiodic superlattices and use the transparent-component-decimation (TCD) method to analyze the relationship between the characteristics of structures and transmission coefficients. It is found that the propagation matrices (PMs) and transmission coefficients (TCs) for GSML(m, n) multilayers exhibit interesting properties: (1) when n is even, they are all constant; (2) when n is odd but m is even, the former exhibit a six-cycle property while the latter possess a three-cycle feature; (3) when n is odd and m = 1, they both possess a pseudo-seven-! cycle characteristic. The analytic results are confirmed by numerical evaluations.
Title:
Synthesis, structure, and bonding of Sc4MgxCu15-Ga-x similar to(7.5) (x=0, 0.5). Two incommensurately modulated scandium substitution derivatives of cubic Mg2Cu6Ga5
Authors:
Lin, QS; Lidin, S; Corbett, JD Author Full Names: Lin, Qisheng; Lidin, Sven; Corbett, John D.
Source:
INORGANIC CHEMISTRY 47 (3): 1020-1029 FEB 4 2008
Abstract:
The substitution of scandium for magnesium in Mg2Cu6Ga5 (Mg2Zn11-type) yields an irrational superstructure phase that includes the refined compositions, Sc4Mg0.50(2)Cu14.50(2)Ga7.61(2) and Sc4Cu14.76(2)Ga7.51(2)- These crystallize in Cmmm, a = similar to 8.31 angstrom, b = similar to 21.72 angstrom, c = -8.30 angstrom. The structures feature Sc-2 dimers, Cu-6 octahedra, a 3D CuGa (Cu12Ga2) framework, and arachno gallium-centered Cu4Ga6 icosahedra that are condensed into zigzag chains. The arrangement of these building blocks exhibits a topologic relationship to Mg2Cu6Ga5. Further studies reveal that the quaternary compound exhibits incommensurate modulations along a, with q = (0.694, 0, 0). Structure refinements with superspace group Xmmm(a00)000 led to saw-tooth modulations for two fractional or mixed sites that avoid short Cu-Ga distances. Band structure analyses reveal that the Fermi surface and bonding are sensitive to the incommensurately modulated atoms.
Title:
All the disorder mechanisms in the 13 : 58 phases come together. out of the modulated confusion rises the remarkable phase Ce12.60Cd58.68(2)
Authors:
Piao, SY; Palatinus, L; Lidin, S Author Full Names: Piao, Shu Ying; Palatinus, Lukas; Lidin, Sven
Source:
INORGANIC CHEMISTRY 47 (3): 1079-1086 FEB 4 2008
Abstract:
The compound Ce12.60Cd58.68(2) is a metrically commensurate representative of the incommensurately modulated phase Ce13Cd57+delta. It is most likely a lock-in phase. The structure, which was solved using seeding of the modulation from those positions most affected as well as direct solution by charge flipping, represents a rare case of ordering in a family of structures where disorder is the rule. The disorder mechanisms, known from other RE13Zn/Cd-58 phases, order in this phase to give rise to a remarkable interplay between interstitials and vacancies. The compound crystallizes in the super space group Ccmm(alpha 00)00s (standard setting Amma(00 gamma)s00) with cell parameters a 27.2789(14) angstrom, b = 15.7592(1) angstrom, and c = 15.5816(4) angstrom and a q vector close to 2/3.

Update: 15-Feb-2008

Title:
Solidification of Mg28Zn2Y and Icosahedral quasicrystal morphology evolution
Authors:
Wan, DQ; Yang, GC; Zhou, YH Author Full Names: Wan Diqing; Yang Gencang; Zhou Yaohe
Source:
RARE METAL MATERIALS AND ENGINEERING 36 (12): 2166-2168 DEC 2007
Abstract:
Applying XRD, OM, SEM and TEM techniques, an investigation on the solidification of Mg28Zn2Y quasicrystal alloy was carried out. It is found that alpha-Mg phase, Mg7Zn3 phase and icosahedral quasicrystal phase coexist in the as-solidified morphology. A perfect five-branch icosahedral quasicrystal morphology was observed. It is attributed to the icosahedral quasicrystal free growth with preferred growth direction of five-fold symmetry axes resulting in five-branch morphology. Furthermore, the effect of cooling rate on the quasi-crystal morphology was also studied. High cooling rate leads to rapid solidification, and in turn, petal-like quasi-crystal morphology is reserved. On the other hand, slow cooling rate favors coarsening and branching of the quasi-crystal, and subsequently, subjected to long curing time, the formation of polygonal quasi-crystals driven by the action of interface energy.
Title:
Pseudospin soliton in the nu=1 bilayer quantum Hall state
Authors:
Fukuda, A; Terasawa, D; Morino, M; Iwata, K; Kozumi, S; Kumada, N; Hirayama, Y; Ezawa, ZF; Sawada, A Author Full Names: Fukuda, A.; Terasawa, D.; Morino, M.; Iwata, K.; Kozumi, S.; Kumada, N.; Hirayama, Y.; Ezawa, Z. F.; Sawada, A.
Source:
PHYSICAL REVIEW LETTERS 1 (1): Art. No. 016801 JAN 11 2008
Abstract:
We investigate a domain structure of pseudospins, a soliton lattice in the bilayer quantum Hall state at total Landau level filling factor nu=1, in a tilted magnetic field, where the pseudospin represents the layer degree of freedom. An anomalous peak in the magnetoresistance R-xx appears at the transition point between the commensurate and incommensurate phases. The R-xx at the peak is highly anisotropic for the angle between the in-plain magnetic field B-parallel to and the current, and indicates a formation of the soliton lattice aligned parallel to B-parallel to. The temperature dependence of the R-xx peak reveals that the dissipation is caused by thermal fluctuations of pseudospin solitons. We also study a phase diagram of the bilayer nu=1 system, and the effects of density imbalance between the two layers.
Title:
Two-dimensional quasicrystals of decagonal order in one-component monolayer films - Comment
Authors:
Schmiedeberg, M; Stark, H Author Full Names: Schmiedeberg, Michael; Stark, Holger
Source:
PHYSICAL REVIEW LETTERS 1 (1): Art. No. 019601 JAN 11 2008
Abstract:
A Comment on the Letter by A. Patrykiejew and S. Sokolowski, Phys. Rev. Lett. 99, 156101 (2007). The authors of the Letter offer a Reply.
Title:
Two-dimensional quasicrystals of decagonal order in one-component monolayer films - Reply
Authors:
Patrykiejew, A; Sokolowski, S Author Full Names: Patrykiejew, A.; Sokolowski, S.
Source:
PHYSICAL REVIEW LETTERS 1 (1): Art. No. 019602 JAN 11 2008
Abstract:
A Reply to the Comment by Michael Schmiedeberg and Holger Stark.
Title:
Long- and short-range order in stuffed titanate pyrochlores
Authors:
Lau, GC; McQueen, TM; Huang, Q; Zandbergen, HW; Cava, RJ Author Full Names: Lau, G. C.; McQueen, T. M.; Huang, Q.; Zandbergen, H. W.; Cava, R. J.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 181 (1): 45-50 JAN 2008
Abstract:
We report a structural study of the stuffed pyrochlore series Ln(2)(Ti(2-x)Ln(x))O7-x/2 (Ln = Ho, Yb; 0 <= x <= 0.67). Electron microscopy and Rietveld refinements of neutron powder diffraction data for the x = 0.67 end members, HO2TiO5 and Yb2TiO5, reveal that small domains (similar to 50 angstrom, or less) exist where the Ln and Ti/Ln sublattices are pyrochlore like, while the average structure is fluorite like. Both the Ho and Yb stuffed pyrochlore series for 0.1 <= x <= 0.5 are shown to be a composite of long- and short-range-ordered pyrochlore phases. The relative fraction of long-range vs. short-range pyrochlore order decreases with increasing Ln doping. An additional complex structural modulation of the pyrochlore structure is observed in electron diffraction and high-resolution electron microscopy images. (c) 2007 Elsevier Inc. All rights reserved.
Title:
In situ synchrotron radiation monitoring of phase transitions during microwave heating of Al-Cu-Fe alloys
Authors:
Vaucher, S; Nicula, R; Catala-Civera, JM; Schmitt, B; Patterson, B Author Full Names: Vaucher, Sebastien; Nicula, Radu; Catala-Civera, Jos-Manuel; Schmitt, Bemd; Patterson, Bruce
Source:
JOURNAL OF MATERIALS RESEARCH 23 (1): 170-175 JAN 2008
Abstract:
The effect of rapid microwave heating has so far been evaluated mainly by comparing the state of materials before and after microwave exposure. Yet, further progress critically depends on the ability to follow the evolution of materials during ultrafast heating in real time. We describe the first in situ time-resolved monitoring of solid-state phase transitions during microwave heating of metallic powders using wide-angle synchrotron radiation diffraction. Single-phase Al-Cu-Fe quasicrystal powders were obtained by microwave heating of nanocrystalline alloy precursors at 650 degrees C in <20 s.
Title:
Martensitic phase transformation in rapidly solidified Mn50Ni40In10 alloy ribbons
Authors:
Llamazares, JLS; Sanchez, T; Santos, JD; Perez, MJ; Sanchez, ML; Hernando, B; Escoda, L; Sunol, JJ; Varga, R Author Full Names: Llamazares, J. L. Sanchez; Sanchez, T.; Santos, J. D.; Perez, M. J.; Sanchez, M. L.; Hernando, B.; Escoda, Ll.; Sunol, J. J.; Varga, R.
Source:
APPLIED PHYSICS LETTERS 92 (1): Art. No. 012513 JAN 7 2008
Abstract:
Heusler alloy Mn50Ni40In10 was produced as preferentially textured ribbon flakes by melt spinning, finding the existence of martensitic-austenic transformation with both phases exhibiting ferromagnetic ordering. A microcrystalline three-layered microstructure of ordered columnar grains grown perpendicularly to ribbon plane was formed between two thin layers of smaller grains. The characteristic temperatures of the martensitic transformation were M-S=213 K, M-f=173 K, A(S)=222 K, and A(f)=243 K. Austenite phase shows a cubic L2(1) structure (a=0.6013(3) nm at 298 K and a Curie point of 311 K), transforming into a modulated fourteen-layer modulation monoclinic martensite. (c) 2008 American Institute of Physics.
Title:
On twinning and microstructures in calcite and dolomite
Authors:
Larsson, AK; Christy, AG Author Full Names: Larsson, Ann-Kristin; Christy, Andrew G.
Source:
AMERICAN MINERALOGIST 93 (1): 103-113 JAN 2008
Abstract:
Apparent superlattice reflections obtained in electron diffraction patterns of modulated calcite and dolomite have been ascribed to local domains of various different metastable Ca-Mg ordering schemes that are not known as macroscopic phases. We show that the type "c" reflections in diffraction patterns of supposed superstructures can in fact be produced by superposition of diffraction from the host crystal and that from domains that are in an orientation related to the host by twinning on (104). From details of the additional reflections present, we deduce that the carbonate anions are orientationally disordered in the twin nanodomains, which have the R (3) over barm space group of high-temperature disordered calcite. This twinning can explain the diffraction ascribed to type "gamma"/"mu"/"v" superstructures, and resolves controversies over the occurrence of these purportedly different superstructures. The relationships between composition, orientational order of the carbonates, molar volume and known macroscopic structures, and the possibility of interfacial strain reduction by static disorder in the twin domain, are discussed. We stress the importance of checking for presence of twinned nanodomains using microdiffraction before attributing an apparent superstructure modulation to local cation ordering. High-resolution imaging may not be diagnostic, since overlap of small domains and host matrix can give Moire patterns that resemble superlattice fringes.
Title:
Synthesis and characterization of low-OH-fluor-chlorapatite: A single-crystal XRD and NMR spectroscopic study
Authors:
Mccubbin, FM; Mason, HE; Park, H; Phillips, BL; Parise, JB; Nekvasil, H; Lindsley, DH Author Full Names: Mccubbin, Francis M.; Mason, Harris E.; Park, Hyunsoo; Phillips, Brian L.; Parise, John B.; Nekvasil, Hanna; Lindsley, Donald H.
Source:
AMERICAN MINERALOGIST 93 (1): 210-216 JAN 2008
Abstract:
Low-OH apatite of the compositional rangeCa(4.99-5.06)(PO4)(2.98-3.00)F0.51-0.48Cl0.38-0.36OH0.14-0.1, was synthesized and characterized structurally by synchrotron-based single-crystal X-ray diffraction (XRD), and multiple nuclear magnetic resonance (NMR) spectroscopic techniques. The average structure is hexagonal with space group P6(3)/m. The presence of scattering in the single-crystal diffraction data set, which is incommensurate within the average hexagonal structure, suggests the presence of localized short-range monoclinic domains. Complex lineshapes in the P-31 and F-19 MAS NMR spectra are also consistent with the presence of an incommensurate phase. No evidence was detected for splitting of the Ca2 site into two distinct sites (as had been previously reported for hexagonal ternary apatites). Structure refinement and F-19 {Cl-35} TRAPDOR NMR experiments verified intercolumnal neighborine of F and Cl atoms (inter-column distance of 2.62 angstrom) within this low-OH- apatite suggesting that long-range neighboring of F and Cl within the apatite anion channels is feasible.
Title:
Capabilities and limitations of a (3+d)-dimensional incommensurately modulated structure as a model for the derivation of an extended family of compounds: example of the scheelite-like structures
Authors:
Arakcheeva, A; Chapuis, G Author Full Names: Arakcheeva, Alla; Chapuis, Gervais
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 12-25 Part 1 FEB 2008
Abstract:
The previously reported incommensurately modulated scheelite-like structure KNd(MoO4)(2) has been exploited as a natural (3 + 1)-dimensional superspace model to generate the scheelite-like three-dimensional structure family. Although each member differs in its space-group symmetry, unit-cell parameters and compositions, in ( 3 + 1)-dimensional space, they share a common superspace group, a common number of building units in the basic unit cell occupying Wyckoff sites with specific coordinates (x, y, z) and specific basic unit-cell axial ratios (c/a, a/b, b/c) and angles. Variations of the modulation vector q, occupation functions and t(0) are exploited for the derivation. Eight topologically and compositionally different known structures are compared with their models derived from the KNd(MoO4)(2) structure in order to evaluate the capabilities and limitations of the incommensurately modulated structure to act as a superspace generating model. Applications of the KNd(MoO4)(2) structure as a starting model for the refinement and prediction of some other modulated members of the family is also illustrated. The (3 + 1)dimensional presentation of the scheelite-like structures reveals new structural relations, which remain hidden if only conventional three-dimensional structure descriptions are applied.

Update: 8-Feb-2008

Title:
Structure and properties of mechanically alloyed composite materials Al/Al-Cu-Fe quasicrystal
Authors:
Cherdyntsev, VV; Kaloshkin, SD; Tomilin, IA; Shelekhov, EV; Laptev, AI; Stepashkin, AA; Danilov, VD Author Full Names: Cherdyntsev, V. V.; Kaloshkin, S. D.; Tomilin, I. A.; Shelekhov, E. V.; Laptev, A. I.; Stepashkin, A. A.; Danilov, V. D.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 104 (5): 497-504 NOV 2007
Abstract:
The structure and properties of metal-matrix Al/Al-Cu-Fe-quasicrystal composites produced by compacting mechanically alloyed powders have been studied. An increase in the time of mechanical alloying was found to lead to an increase in the microhardness. Compression tests showed that the failure of samples occurred via the intense formation of cracks along the direction parallel to the applied stresses; the ultimate strength increases with increasing time of mechanical alloying. As the compacting temperature increases, the ultimate strength remains unchanged to temperatures of 300-400 degrees C; at higher temperatures, a marked increase in the ultimate compression strength is observed. An increase in the compacting temperature leads to an improvement of frictional characteristic of samples.
Title:
Incommensurate charge order phase in Fe2OBO3 due to geometrical frustration
Authors:
Angst, M; Hermann, RP; Schweika, W; Kim, JW; Khalifah, P; Xiang, HJ; Whangbo, MH; Kim, DH; Sales, BC; Mandrus, D Author Full Names: Angst, M.; Hermann, R. P.; Schweika, W.; Kim, J. -W.; Khalifah, P.; Xiang, H. J.; Whangbo, M. -H.; Kim, D. -H.; Sales, B. C.; Mandrus, D.
Source:
PHYSICAL REVIEW LETTERS 99 (25): Art. No. 256402 DEC 21 2007
Abstract:
The temperature dependence of charge order in Fe2OBO3 was investigated by resistivity and differential scanning calorimetry measurements, Mossbauer spectroscopy, and synchrotron x-ray scattering, revealing an intermediate phase between room temperature and 340 K, characterized by coexisting mobile and immobile carriers, and by incommensurate superstructure modulations with temperature-dependent propagation vector (1/2, 0, tau) . The incommensurate modulations arise from specific antiphase boundaries with low energy cost due to geometrical charge frustration.
Title:
X-ray scattering study of the spin-Peierls transition and soft phonon behavior in TiOCl
Authors:
Abel, ET; Matan, K; Chou, FC; Isaacs, ED; Moncton, DE; Sinn, H; Alatas, A; Lee, YS Author Full Names: Abel, E. T.; Matan, K.; Chou, F. C.; Isaacs, E. D.; Moncton, D. E.; Sinn, H.; Alatas, A.; Lee, Y. S.
Source:
PHYSICAL REVIEW B 76 (21): Art. No. 214304 DEC 2007
Abstract:
We have studied the S=1/2 quasi-one-dimensional antiferromagnet TiOCl using single crystal x-ray diffraction and inelastic x-ray scattering techniques. The Ti ions form staggered spin chains which dimerize below T-c1=66 K and have an incommensurate lattice distortion between T-c1 and T-c2=92 K. Based on our measurements of the intensities, wave vectors, and harmonics of the incommensurate superlattice peaks, we construct a model for the incommensurate modulation. The results are in good agreement with a soliton lattice model, though some quantitative discrepancies exist near T-c2. The behavior of the phonons has been studied using inelastic x-ray scattering with similar to 2 meV energy resolution. For the first time, a zone-boundary phonon which softens at the spin-Peierls temperature T-SP has been observed. Our results show reasonably good quantitative agreement with the Cross-Fisher [Phys. Rev. B. 19, 402 (1979)] theory for the phonon dynamics at wave vectors near the zone boundary and temperatures near T-SP. However, not all aspects of the data can be described, such as the strong overdamping of the soft mode above T-SP. Overall, our results show that TiOCl is a good realization of a spin-Peierls system, where the phonon softening allows us to identify the transition temperature as T-SP=T-c2=92 K.
Title:
Comment on "Extrinsic origin of the insulating behavior of polygrain icosahedral Al-Pd-Re quasicrystals"
Authors:
Poon, SJ; Rapp, O Author Full Names: Poon, S. J.; Rapp, O.
Source:
PHYSICAL REVIEW B 76 (21): Art. No. 216201 DEC 2007
Abstract:
In a recent paper, Dolinsek et al. [Phys. Rev. B 74, 134201 (2006)] suggested that the insulating behavior of icosahedral (i) Al-Pd-Re is of extrinsic origin. Large resistivities and insulatinglike properties of high resistivity samples were conjectured to result from the porous structure and the observed enhanced oxygen concentration in between the quasicrystal grains in some i-Al-Pd-Re samples. We point out that these hypotheses are incompatible with published work on the structure and properties of i-Al-Pd-Re.
Title:
Reply to "Comment on 'Extrinsic origin of the insulating behavior of polygrain icosahedral Al-Pd-Re quasicrystals' "
Authors:
Dolinsek, J; McGuiness, PJ; Klanjsek, M; Smiljanic, I; Smontara, A; Zijlstra, ES; Bose, SK; Fisher, IR; Kramer, MJ; Canfield, PC Author Full Names: Dolinsek, J.; McGuiness, P. J.; Klanjsek, M.; Smiljanic, I.; Smontara, A.; Zijlstra, E. S.; Bose, S. K.; Fisher, I. R.; Kramer, M. J.; Canfield, P. C.
Source:
PHYSICAL REVIEW B 76 (21): Art. No. 216202 DEC 2007
Abstract:
We clarify issues raised in the preceding Comment regarding the viewpoint that the highly porous and oxidized arc-melted polygrain i-Al-Pd-Re samples could reveal intrinsic electrical transport properties of this icosahedral family. Flux-grown single-grain i-Al-Pd-Re samples of superior structural quality do not show insulatinglike behavior, and their transport properties are on common ground with all other Al-based icosahedral families.
Title:
Spin-density wave in polycrystalline Cr films from infrared reflectivity
Authors:
Boekelheide, Z; Helgren, E; Hellman, F Author Full Names: Boekelheide, Z.; Helgren, E.; Hellman, F.
Source:
PHYSICAL REVIEW B 76 (22): Art. No. 224429 DEC 2007
Abstract:
The spin-density wave properties of polycrystalline chromium thin films were determined by using infrared reflectivity to determine the gap energies. The incommensurate spin-density wave of bulk chromium is highly sensitive to perturbations from stress, disorder, and finite size effects, such as those found in polycrystalline films. Films prepared under various conditions display three different types of spin-density wave behavior: incommensurate, commensurate, and mixed. Unexpectedly, the mixed phase includes the incommensurate spin-density wave and two different forms of commensurate spin-density wave. A phenomenologically determined low-temperature phase diagram is created to describe the spin-density wave in chromium in the stress-disorder plane. The effects of stress and disorder on the spin-density wave of chromium films are analogous to the effects of dilute alloying in bulk chromium. In this case, tensile stress has a similar effect to Mn impurities, while disorder has a similar effect to Al.
Title:
Random walk analysis of the commensurate-incommensurate transition in the isotropic spin-1 chain
Authors:
Yarotsky, DA Author Full Names: Yarotsky, D. A.
Source:
JOURNAL OF STATISTICAL PHYSICS 130 (5): 957-981 MAR 2008
Abstract:
It has been observed that in the isotropic spin-1 chain a transition in the asymptotic properties of the correlation function (commensurate-incommensurate transition) occurs at the AKLT point. We propose a simple random-walk-type argument, explaining this transition. Also, we consider a modification of the AKLT model, for which this argument can be turned into a rigorous proof.

Update: 1-Feb-2008

Title:
Fascinating quasicrystals
Authors:
Steurer, W; Deloudi, S Author Full Names: Steurer, Walter; Deloudi, Sofia
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 64: 1-11 Part 1 JAN 2008
Abstract:
It took Dan Shechtman more than two years to get his discovery of an Al-Mn phase with icosahedral diffraction symmetry and sharp Bragg reflections published. A paradigm shift had to take place before this novel ordering state of matter - seemingly contradicting crystallographic laws - could be accepted. Today, more than 25 years later, the existence of quasicrystals is beyond doubt. However, not everything is settled yet. All the factors governing formation, growth, stability and structure of quasicrystals are still not fully understood, nor is it resolved whether their structures are strictly or only on average quasiperiodic, and it is still an open question why only quasicrystals with 5-, 8-, 10- and 12-fold rotational symmetry have been experimentally observed so far. These points will be addressed in this review article.
Title:
The charge flipping algorithm
Authors:
Oszlanyi, G; Suto, A Author Full Names: Oszlanyi, Gabor; Suto, Andras
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 64: 123-134 Part 1 JAN 2008
Abstract:
This paper summarizes the current state of charge flipping, a recently developed algorithm of ab initio structure determination. Its operation is based on the perturbation of large plateaus of low electron density but not directly on atomicity. Such a working principle radically differs from that of classical direct methods and offers complementary applications. The list of successful structure-solution cases includes periodic and aperiodic crystals using single-crystal and powder diffraction data measured with X-ray and neutron radiation. Apart from counting applications, the paper mainly deals with algorithmic issues: it describes and compares new variants of the iteration scheme, helps to identify and improve solutions, discusses the required data and the use of known information. Finally, it tries to foretell the future of such an alternative among well established direct methods.

Update: 25-Jan-2008

Title:
Effect of nano-quasicrystals on viscosity of a Zr-based bulk metallic glass
Authors:
Gubicza, J; Labar, JL; Agocs, E; Fatay, D; Lendvai, J Author Full Names: Gubicza, J.; Labar, J. L.; Agocs, E.; Fatay, D.; Lendvai, J.
Source:
SCRIPTA MATERIALIA 58 (4): 291-294 FEB 2008
Abstract:
The effect of formation of nano-quasicrystals on the creep behavior of a Zr44Ti11Cu10Ni10Be25 bulk metallic glass was studied by the indentation technique above the glass transition temperature. The apparent viscosity of the supercooled liquid-quasicrystal composite increases with increasing volume fraction of the quasicrystalline phase following a simple relationship derived previously for dilute suspensions. The formation of quasicrystalline particles is accompanied by the decrease of activation energy of creep. This was related to the increase of the Be/Ti ratio in the supercooled liquid phase. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Chiral magnetic ordering and commensurate-to-incommensurate transition in CuB2O4
Authors:
Kousaka, Y; Yano, SI; Kishine, JI; Yoshida, Y; Inoue, K; Kikuchi, K; Akimitsu, J Author Full Names: Kousaka, Yusuke; Yano, Shin-Ichiro; Kishine, Jun-Ichiro; Yoshida, Yusuke; Inoue, Katsuya; Kikuchi, Koichi; Akimitsu, Jun
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 (12): Art. No. 123709 DEC 2007
Abstract:
We measured the anisotropic magnetization processes of copper metaborate CuB2O4 in detail. We propose an interpretation of the magnetization anomaly observed under the magnetic field applied perpendicular to the tetragonal axis, based on the field- and temperature- induced commensurate-to-incommensurate (C-IC) transition (Freedericksz transition) accompanied by the chiral soliton lattice formation.
Title:
Very low temperature electronic transport in Al-Pd-Re quasicrystalline alloys
Authors:
Rosenbaum, R; Balanetskyy, S; Grushko, B; Przepiorzynski, B Author Full Names: Rosenbaum, Ralph; Balanetskyy, Sergiy; Grushko, Benjamin; Przepiorzynski, Bartosz
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS 150 (1-2): 82-100 JAN 2008
Abstract:
Electrical resistivities of two icosahedral (I) Al-Pd-Re alloys have been measured between room temperature and mK temperatures. One quasicrystalline (QC) polygrain Al-Pd-Re sample exhibited insulating behavior in its resistivities, increasing by a factor of r=R(4 K)/R(300 K)=7.76; its room temperature resistivity was 9,890 mu Omega cm. A "phenomenological" expression fitted the conductivity data well between 300 K to 0.5 K. Below 0.4 K a crossover to an activated variable-range hopping law was observed. Low temperature magnetoresistance ratio data and fits using the wave function shrinkage theory are presented. A second QC Al-Pd-Re sample had a small resistance temperature ratio r=2.12. The room temperature resistivity was extremely large, rho(300 K)approximate to 40,980 mu Omega cm. Its conductivity could be described well using a simple temperature power law between 300 K to 20 K. Below 20 K there was a crossover to a new behavior. Below 1 K, the conductivity could be fitted using a very weakly insulating power law where sigma(T)approximate to 11.37T(0.032) in (Omega cm)(-1), suggesting that this sample is located just below the metal-insulator transition. The magnetoconductivity data could not be fitted successfully using the 3D weak localization (WL) theory and inserting into it physical and realistic fitting magnitudes for the inelastic magnetic field B-in.
Title:
New potassium bismuth thiophosphates including the modulated K1.5Bi2.5(PS4)(3)
Authors:
Gave, MA; Weliky, DP; Kanatzidis, MG Author Full Names: Gave, Mafthew A.; Weliky, David P.; Kanatzidis, Mercouri G.
Source:
INORGANIC CHEMISTRY 46 (26): 11063-11074 DEC 24 2007
Abstract:
The compounds K3Bi3(PS4)(4) (I), K1.5Bi2.5(PS4)(3) (II), and KgBi(PS4)(4) (III) were synthesized, and their properties are described. Red needles of I crystallize in the tetragonal spacegroup P4/ncc with a = 21.0116(8) angstrom and c = 13.3454(10) angstrom and have a three-dimensional Bi/P/S framework structure with large channels occupied by K+ ions. Deep-red plates of 11 crystallize in the monoclinic super spacegroup P2/c(alpha(1/2 gamma))00 with a = 21.8034(12) angstrom, b = 8.8064(7) angstrom, c = 10.0333(6) angstrom, and beta = 90.004(5)degrees. This compound has an incommensurately modulated superstructure with the modulation vector q = 0.25a* + 0.5b* + 0.16c*. Bright-red irregularly shaped blocks of III crystallize in the orthorhombic space group P2(1)2(1)2 with a = 18.306(4) angstrom, b = 8.926(2) angstrom, and c = 9.710(2) angstrom and have a discrete molecular salt structure with mononuclear [Bi(PS4)(4)](9-) complexes. The structures reveal that as the relative amount of K3PS4 increases, there is a marked decrease in dimensionality of the framework. It was also possible to form a glass with the same stoichiometry as that of compound I. When annealed at 320 degrees C, the glass crystallized into compound II. The (31)p solid-state NMR spectra are reported, and they are consistent with the crystallographic results.
Title:
A water-based synthesis of octahedral, decahedral, and icosahedral Pd nanocrystals
Authors:
Lim, B; Xiong, YJ; Xia, YN Author Full Names: Lim, Byungkwon; Xiong, Yujie; Xia, Younan
Source:
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 46 (48): 9279-9282 2007

Update: 18-Jan-2008

Title:
Microstructure and mechanical properties of Mg-Zn-Gd-based alloys strengthened with quasicrystal and Laves phase
Authors:
Liu, Y; Yuan, GY; Lu, C; Ding, WJ Author Full Names: Liu Yong; Yuan Guang-yin; Lu Chen; Ding Wen-jiang
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA 17: S353-S357 Part A Sp. Iss. 1 NOV 2007
Abstract:
One kind of Mg3.5Zn0.6Gd-based alloy strengthened with quasicrystals was designed, and the effect of alloying elements on microstructure and mechanical properties of as-cast Mg-Zn-Gd alloy at room temperature and elevated temperatures were studied. The results indicate that MgZnCu Laves phase, which coexists with quasicrystal at grain boundary, emerges with the addition of copper element in Mg-Zn-Gd alloy. The strength of alloys exhibits the parabola curve with the increase of copper content. The alloy with 1.5% (mole fraction) Cu shows better mechanical properties at room temperature: tensile strength 176 MPa, yield strength 176 MPa and elongation 6.5%. The existence of MgZnCu Laves phase can effectively improve the heat resistance and elevated temperature properties of the alloy. The alloy with 1.5% Cu has better mechanical properties at 200 degrees C: tensile strength 130 MPa and elongation 18.5%. The creep test of the alloys at 200 degrees C and 50 MPa for 102 h indicates that Mg3.5Zn0.6Gd alloy reinforced with quasicrystal has better creep properties than AE42, which can be further improved with the introduction of Laves phase in the alloy.
Title:
Competition between local potentials and attractive particle-particle interactions in superlattices
Authors:
Lima, NA; Malvezzi, AL; Capelle, K Author Full Names: Lima, N. A.; Malvezzi, A. L.; Capelle, K.
Source:
SOLID STATE COMMUNICATIONS 144 (12): 557-560 DEC 2007
Abstract:
Naturally occuring or man-made systems displaying periodic spatial modulations of their properties on a nanoscale constitute superlattices. Such modulated structures are important both as prototypes of simple nanotechnological devices and as particular examples of emerging spatial inhomogeneity in interacting many-electron systems. Here we investigate the effect different types of modulation of the system parameters have on the ground-state energy and the charge-density distribution of the system. The superlattices are described by the inhomogeneous attractive Hubbard model, and the calculations are performed by density-functional and density-matrix renormalization group techniques. We find that modulations in local electric potentials are much more effective in shaping the system's properties than modulations in the attractive on-site interaction. This is the same conclusion we previously [M.F. Silva, N.A. Lima, A.L. Malvezzi, K. Capelle, Phys. Rev. B 71 (2005) 125130.] obtained for repulsive interactions, suggesting that it is not an artifact of a specific state, but a general property of modulated structures. (c) 2007 Elsevier Ltd. All rights reserved.
Title:
Phase diagram of hole doped two-leg Cu-O ladders
Authors:
Chudzinski, P; Gabay, M; Giamarchi, T Author Full Names: Chudzinski, P.; Gabay, M.; Giamarchi, T.
Source:
PHYSICAL REVIEW B 76 (16): Art. No. 161101 OCT 2007
Abstract:
In the weak coupling limit, we establish the phase diagram of a two-leg ladder with a unit cell containing both Cu and O atoms, as a function of doping. We use bosonization and design a specific renormalization group procedure to handle the additional degrees of freedom. Significant differences are found with the single orbital case; for purely repulsive interactions, a completely massless quantum critical region is obtained at intermediate carrier concentrations (well inside the bands) where the ground state consists of an incommensurate pattern of orbital currents plus a spin density wave structure.
Title:
Photonic band gaps in quasiperiodic photonic crystals with negative refractive index
Authors:
Vasconcelos, MS; Mauriz, PW; De Medeiros, FF; Albuquerque, EL Author Full Names: Vasconcelos, M. S.; Mauriz, P. W.; De Medeiros, F. F.; Albuquerque, E. L.
Source:
PHYSICAL REVIEW B 76 (16): Art. No. 165117 OCT 2007
Abstract:
We investigate the photonic band gaps in quasiperiodic photonic crystals made up of both positive (SiO2) and negative refractive index materials using a theoretical model based on a transfer matrix treatment. The quasiperiodic structures are characterized by the nature of their Fourier spectrum, which can be dense pure point (Fibonacci sequences) or singular continuous (Thue-Morse and double-period sequences). These substitutional sequences are described in terms of a series of generations that obey peculiar recursion relations. We discussed the photonic band gap spectra for both the ideal cases, where the negative refractive index material can be approximated as a constant in the frequency range considered, as well as the more realistic case, taking into account the frequency-dependent electric permittivity epsilon and magnetic permeability mu. We also present a quantitative analysis of the results, pointing out the distribution of the allowed photonic bandwidths for high generations, which gives a good insight about their localization and power laws.
Title:
Anomalous properties of the band-edge states in large two-dimensional photonic quasicrystals
Authors:
Lai, Y; Zhang, ZQ; Chan, CH; Tsang, L Author Full Names: Lai, Yun; Zhang, Zhao-Qing; Chan, Chi-Hou; Tsang, Leung
Source:
PHYSICAL REVIEW B 76 (16): Art. No. 165132 OCT 2007
Abstract:
By using the sparse-matrix canonical-grid method, we performed large-scale multiple-scattering calculations to study band-edge states in large-sized two-dimensional photonic quasicrystals. We find that the band-edge states evolve in an abrupt and irregular way when the sample size is increased. New states with reduced symmetries can emerge at the band edge in large samples. Strong multifractal behaviors in the wave functions are also observed. Our findings unveil important differences between quasiperiodic and periodic systems at band edges.
Title:
Scanning tunneling microscopy observation of Pb-induced superstructures on Si(557)
Authors:
Morikawa, H; Kim, KS; Jung, DY; Yeom, HW Author Full Names: Morikawa, Harumo; Kim, Keun Su; Jung, Duk Yong; Yeom, Han Woong
Source:
PHYSICAL REVIEW B 76 (16): Art. No. 165406 OCT 2007
Abstract:
Pb-induced superstructures on Si(557) are investigated by low-energy-electron diffraction (LEED) and scanning tunneling microscopy (STM). Using an indirect heating method, we have succeeded in obtaining almost perfect single-domain LEED patterns of one-dimensional wire (chain) structures, so called alpha x2 and beta x2 phases. Careful LEED analysis and STM investigation reveal that these phases are formed on the (223) and (112) facets, respectively. The alpha x2 phase has regular bundles of triple wires at low annealing temperature but wider bundles through step bunching after a higher temperature annealing. Along the wires of the alpha x2 phase, which was recently reported to exhibit a transition between one-dimensional (1D) metallic and 2D semiconducting conductance, a clear commensurate x2 modulation is observed at 78-120 K in contrast to the incommensurate and disordered structure reported previously. A tentative atomic structure model of the alpha x2 phase is proposed based on the dense Pb overlayers on (111) and (223) facets. The details of the STM images of the beta x2 phase are discussed.
Title:
Ferroelectric polarization and magnetic structure in Eu0.595Y0.405MnO3
Authors:
Kajimoto, R; Yokoo, T; Kofu, M; Noda, K; Kuwahara, H Author Full Names: Kajimoto, R.; Yokoo, T.; Kofu, M.; Noda, K.; Kuwahara, H.
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 68 (11): 2087-2090 Sp. Iss. SI NOV 2007
Abstract:
A neutron diffraction study was performed on a single crystal of 4f-moment-free perovskite manganite Eu0.595Y0.405MnO3 to elucidate the relation between the spontaneous ferroelectric polarization and the magnetic structure. Eu0.595Y0.405MnO3 shows an incommensurate magnetic ordering below T-N = 47 K. The ferroelectric polarization P along the c axis appears below 25 K, and it is replaced by P along the a axis below 23 K. We have observed the change of magnetic structure at temperatures where the ferroelectric polarization appears and changes its polarization direction. (c) 2007 Elsevier Ltd. All rights reserved.
Title:
Neutron and X-ray diffraction studies on the Tb2Ni3Si5 single crystal
Authors:
Hashimoto, Y; Kawano, S; Koyano, N; Takahashi, M Author Full Names: Hashimoto, Yuzo; Kawano, Shinji; Koyano, Nobumitu; Takahashi, Miwako
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 68 (11): 2095-2098 Sp. Iss. SI NOV 2007
Abstract:
Neutron and X-ray diffraction studies on the Tb2Ni3Si5 single crystal have been done to investigate its crystal modulation and magnetic properties. The modulated single crystal is constructed by the TbNiSi2 (CeNiSi2-type Cmcm) and the Tb2Ni3Si5 (U2Co3Si5-type Ibam) lattices. The relationship between the two lattices is described as direction of the b(1) (12)-axis coincides with the a(235)-axis. The crystal modulation gives significant effects on magnetism. Each of the two lattices takes complex antiferromagnetism with multiplex propagation vectors. (c) 2007 Elsevier Ltd. All rights reserved.
Title:
Antiferromagnetic spin structure in BaCoO3 below 15 K determined by neutron and mu+SR
Authors:
Nozaki, H; Janoschek, M; Roessli, B; Sugiyama, J; Keller, L; Brewer, JH; Ansaldo, E; Morris, GD; Takami, T; Ikuta, H Author Full Names: Nozaki, H.; Janoschek, M.; Roessli, B.; Sugiyama, J.; Keller, L.; Brewer, J. H.; Ansaldo, E. J.; Morris, G. D.; Takami, T.; Ikuta, H.
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 68 (11): 2162-2165 Sp. Iss. SI NOV 2007
Abstract:
The magnetic structure of the anti ferromagnetic (AF) hexagonal perovskite BaCoO3 was investigated by means of neutron powder diffraction in the temperature range between 60 and 1.5 K. AF diffraction peaks appear below the Neel temperature (T-N = 15 K). Although several possible spin arrangements fit the neutron diffraction pattern, when combined with the results of a muon spin spectroscopy experiment, the most reasonable description of the AF state in BaCoO3 is a modulated structure along the (110) direction, described as m(1) = m(0) cos(2 pi kl), where m(1) is the moment at the Co4+ site 1, m(0) = (0, 0, 0.53 mu(B)) at 1.5 K and k is the propagation vector(1/3, 1/3, 0). (c) 2007 Elsevier Ltd. All rights reserved.
Title:
Magnetic soliton lattice in CuB2O4 under an applied magnetic field
Authors:
Kousaka, Y; Yano, S; Nishi, M; Hirota, K; Akimitsu, J Author Full Names: Kousaka, Y.; Yano, S.; Nishi, M.; Hirota, K.; Akimitsu, J.
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 68 (11): 2170-2173 Sp. Iss. SI NOV 2007
Abstract:
We report here the formation of soliton lattice in copper metaborate CuB2O4,which is an candidate for a chiral magnetic structure. We performed the neutron diffraction experiments under an applied magnetic field perpendicular to the helical axis. In the temperature between 1.6 and 6K under the magnetic field, we found a new incommensurate magnetic phase, which was supposed to be a commensurate magnetic structure from the magnetization measurements. In the boundary just between the conventional incommensurate and the new incommensurate magnetic phases, we observed higher order magnetic satellite peaks, which can be an evidence of chiral soliton formation. (c) 2007 Elsevier Ltd. All rights reserved.
Title:
Detecting quasiperiodic structures with double diffraction
Authors:
Xu, J; Hubler, AW Author Full Names: Xu, J.; Huebler, A. W.
Source:
EPL 81 (1): Art. No. 16002 2008
Abstract:
We study interference patterns of double-diffraction systems with quasiperiodic structures. A quasiperiodic linear array of scatterers converts single delta pulses into a sequence of quasiperiodic pulses. This pulse train is diffracted from a second set of scatterers. We find that the interference pattern after the second diffraction has a pronounced peak if both sets of scatterers have similar quasiperiodic structures. We show that this method can be used for identifying the Fibonacci chain and related quasiperiodic sequences, if the number of scatterers in the first set is at least twice as large as the number of scatterers in the second set, and if the distances among the two sets of scatterers and the detector are all large compared to the size of the sets. This method may provide a methodology for identifying the structure of quasicrystals and quasiperiodic layered materials with a large signal-to-noise ratio. Copyright (C) EPLA, 2008.
Title:
Synthesis and characterization of new AA'BWO6 perovskites exhibiting simultaneous ordering of A-site and B-site cations
Authors:
King, G; Thimmaiah, S; Dwivedi, A; Woodward, PM Author Full Names: King, Graham; Thimmaiah, Srinivasa; Dwivedi, Akansha; Woodward, Patrick M.
Source:
CHEMISTRY OF MATERIALS 19 (26): 6451-6458 DEC 25 2007
Abstract:
Six new AA'BB'O-6 perovskites KLaMnWO6, NaLaMnWO6, NaNdMnWO6, NaTbMnWO6, NaNdCoWO6, and NaNdMgWO6 have been prepared. Each possesses the unusual combination of layered ordering of the A-site cations and rock-salt ordering of the B-site cations. The structure and properties of these samples have been characterized using monochromatic X-ray and neutron powder diffraction, UV-vis diffuse reflectance spectroscopy, and SQUID magnetometry. NaLaMnWO6, NaNdMnWO6, and NaTbMnWO6 adopt a structure with monoclinic P2(1) symmetry arising from the combination of cation ordering and a(-)a(-)c(+) octahedral tilting. The structures of the other three compounds are similar, but the presence of satellite reflections in the neutron diffraction data suggests a more complicated superstructure. Each of the four AA'MnWO6 samples shows a paramagnetic to antiferromagnetic transition with Neel temperatures ranging from 6 to 15 K. The NaTbMnWO6 compound shows a second magnetic transition at similar to 9 K. The origin of two magnetic phase transitions appears to arise from coupling between the Mn2+ sublattice and the Tb3+ sublattice.

Update: 11-Jan-2008

Title:
Hidden degrees of freedom in aperiodic materials
Authors:
Toudic, B; Garcia, P; Odin, C; Rabiller, P; Ecolivet, C; Collet, E; Bourges, P; McIntyre, GJ; Hollingsworth, MD; Breczewski, T Author Full Names: Toudic, Bertrand; Garcia, Pilar; Odin, Christophe; Rabiller, Philippe; Ecolivet, Claude; Collet, Eric; Bourges, Philippe; McIntyre, Garry J.; Hollingsworth, Mark D.; Breczewski, Tomasz
Source:
SCIENCE 319 (5859): 69-71 JAN 4 2008
Abstract:
Numerous crystalline materials, including those of bioorganic origin, comprise incommensurate sublattices whose mutual arrangement is described in a superspace framework exceeding three dimensions. We report direct observation by neutron diffraction of superspace symmetry breaking in a solid- solid phase transition of an incommensurate host- guest system: the channel inclusion compound of nonadecane/ urea. Strikingly, this phase transition generates a unit cell doubling that concerns only the modulation of one substructure by the other- an internal variable available only in superspace. This unanticipated pathway for degrees of freedom to rearrange leads to a second phase transition, which again is controlled by the higher dimensionality of superspace. These results reveal nature's capacity to explore the increased number of phases allowed in aperiodic crystals.
Title:
How do quasicrystals grow?
Authors:
Keys, AS; Glotzer, SC Author Full Names: Keys, Aaron S.; Glotzer, Sharon C.
Source:
PHYSICAL REVIEW LETTERS 99 (23): Art. No. 235503 DEC 7 2007
Abstract:
Using molecular simulations, we show that the aperiodic growth of quasicrystals is controlled by the ability of the growing quasicrystal nucleus to incorporate kinetically trapped atoms into the solid phase with minimal rearrangement. In the system under investigation, which forms a dodecagonal quasicrystal, we show that this process occurs through the assimilation of stable icosahedral clusters by the growing quasicrystal. Our results demonstrate how local atomic interactions give rise to the long-range aperiodicity of quasicrystals.
Title:
Valence changes and structural distortions in "Charge Ordered" manganites quantified by atomic-scale scanning transmission electron microscopy
Authors:
Loudon, JC; Kourkoutis, LF; Ahn, JS; Zhang, CL; Cheong, SW; Muller, DA Author Full Names: Loudon, J. C.; Kourkoutis, L. Fitting; Ahn, J. S.; Zhang, C. L.; Cheong, S. -W.; Muller, D. A.
Source:
PHYSICAL REVIEW LETTERS 99 (23): Art. No. 237205 DEC 7 2007
Abstract:
We investigate the microscopic nature of the "charge ordering" modulation in mixed-valent manganites in real space using scanning transmission electron microscopy. The modulation in Bi0.5Sr0.4Ca0.1MnO3 has a uniform periodicity appearing as stripes in high angle annular dark field images. Geometric phase analysis shows the modulation to be a displacement wave with transverse amplitude (0.008 +/- 0.001)a and longitudinal amplitude (0.003 +/- 0.001)a. Series of energy loss spectra taken across the stripes show no periodic changes and place an upper bound of +/- 0.04 on any valence changes of the Mn ions.
Title:
Competition between unconventional superconductivity and incommensurate antiferromagnetic order in CeRh1-xCoxIn5
Authors:
Ohira-Kawamura, S; Shishido, H; Yoshida, A; Okazaki, R; Kawano-Furukawa, H; Shibauchi, T; Harima, H; Matsuda, Y Author Full Names: Ohira-Kawamura, S.; Shishido, H.; Yoshida, A.; Okazaki, R.; Kawano-Furukawa, H.; Shibauchi, T.; Harima, H.; Matsuda, Y.
Source:
PHYSICAL REVIEW B 76 (13): Art. No. 132507 OCT 2007
Abstract:
Elastic neutron diffraction measurements were performed on the quasi-two-dimensional heavy-fermion system CeRh1-xCoxIn5, ranging from an incommensurate antiferromagnet for low Co composition x to an unconventional superconductor on the Co-rich end of the phase diagram. We found that the superconductivity competes with the incommensurate antiferromagnetic (AFM) order characterized by q(I)=(1/2,1/2,delta) with delta=0.298, while it coexists with the commensurate AFM order with q(c)=(1/2,1/2,1/2). This is in sharp contrast to the CeRh1-xIrxIn5 system, where both the commensurate and incommensurate magnetic orders coexist with the superconductivity. These results reveal that particular areas on the Fermi surface nested by q(I) play an active role in forming the superconducting state in CeCoIn5.
Title:
Biquadratic antisymmetric exchange and the magnetic phase diagram of magnetoelectric CuFeO2
Authors:
Plumer, ML Author Full Names: Plumer, M. L.
Source:
PHYSICAL REVIEW B 76 (14): Art. No. 144411 OCT 2007
Abstract:
Biquadratic antisymmetric exchange terms of the form -[C(ij)e(ij)(alpha)(s(i)xs(j))(z)](2), where e(ij) is the unit vector connecting sites i and j and alpha=x,y, due partially to magnetoelectric coupling effects, are shown to be responsible for the spin-flop helical phase in CuFeO2 at low magnetic field and temperature. Usual biquadratic symmetric exchange, likely due to magnetoelastic coupling, is found to support the stability of axial magnetic states at higher fields in this nearly-Heisenberg-like stacked triangular antiferromagnet. A model Hamiltonian which also includes substantial interplane and higher-neighbor intraplane exchange interactions reproduces the unique series of observed commensurate and incommensurate periodicity phases with increasing applied magnetic field in this highly frustrated system. The magnetic-field-temperature phase diagram is discussed in terms of a Landau-type free energy.
Title:
Symmetry and magnetically driven ferroelectricity in rare-earth manganites RMnO3 (R=Gd,Tb,Dy)
Authors:
Ribeiro, JL Author Full Names: Ribeiro, J. L.
Source:
PHYSICAL REVIEW B 76 (14): Art. No. 144417 OCT 2007
Abstract:
This work investigates the magnetically driven ferroelectricity in orthorhombic manganites RMnO3 (R=Gd, Dy, or Tb) from the point of view of the symmetry. The method adopted generalizes the one used to characterize the polar properties of displacive modulated structures to the case of an irreducible magnetic order parameter. The symmetry conditions for magnetically induced ferroelectricity are established, and the Landau-Devonshire free energy functionals are derived from general symmetry considerations. The ferroelectric polarization observed in DyMnO3 and TbMnO3 at zero magnetic field is explained in terms of the symmetry of a reducible magnetic order parameter. The polarization rotation induced in these compounds by external magnetic fields and the stabilization of a ferroelectric phase in GdMnO3 are accounted for by a mechanism in which magnetization and polarization are secondary order parameters that are not directly coupled but compete with each other through their coupling to competing primary modulated order parameters.
Title:
Coordination-induced structure of the Mg 2p core level in i-ZnMgR quasicrystals
Authors:
Karpus, V; Suchodolskis, A; Taulavicius, J; Karlsson, UO; Le Lay, G; Assmus, W; Bruhne, S Author Full Names: Karpus, V.; Suchodolskis, A.; Taulavicius, J.; Karlsson, U. O.; Le Lay, G.; Assmus, W.; Bruehne, S.
Source:
PHYSICAL REVIEW B 76 (15): Art. No. 155119 OCT 2007
Abstract:
We present a detailed analysis of Mg 2p photoemission (PE) spectra in icosahedral ZnMgR (R=Y, Ho, Er) quasicrystals and in the crystalline Zn2Mg Laves phase. Synchrotron-radiation PE measurements were performed on in situ cleaved single-grain samples at 10(-10) mbar pressure and low, 90-150 K, temperature. The analysis of Mg 2p PE spectra in Zn2Mg reveals a surface shift of the core level of -0.12 eV. The Mg 2p PE spectra in i-ZnMgR quasicrystals are essentially broadened as compared to spectra in Zn2Mg Laves phase. The effect is due to the coordination-induced structure of the Mg 2p levels. Different local surroundings of Mg atoms in quasicrystals induce both different shifts of the Mg 2p level and splittings of its spin-orbit components. The local coordination potential at different Mg sites in the quasicrystalline lattice is calculated on the basis of the face-centered icosahedral ZnMgY atomic structure data, recently determined from the pair distribution function analysis. The coordination shifts calculated are spread within an interval of about 0.3 eV, while the splittings of the 2p(3/2) component are of the order of 1-10 meV. The simulated theoretical Mg 2p PE spectra of fci-ZnMgR quasicrystals perfectly fit the experimental data.
Title:
Coupled In/Te and Ni/vacancy ordering and the modulated crystal structure of a B8 type, Ni3 +/- xIn1-yTe2+y solid solution phase
Authors:
Larsson, AK; Noren, L; Withers, RL; Rundlof, H Author Full Names: Larsson, A. -K.; Noren, L.; Withers, R. L.; Rundlof, H.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 180 (10): 2723-2733 OCT 2007
Abstract:
The commensurate superstructures of a NiAs/Ni2In type parent structure, Ni3.32InTe2 and Ni3.12In0.86Te2.14 (q = gamma[0 0 1]*, gamma = 2/3) as well as one dimensionally incommensurate structure of Ni31nTe2 (gamma = 0.71) were refined from neutron powder diffraction data (R-wp = 4.77%, 4.53% and 4.91 % for the three structures, respectively, at 298 K). The commensurate structures were refined in the P6(3)/mmc space group (c = 3c(NiAs)). The stacking sequence at the hcp array is -In/Te/Te/- and the trigonal bipyrainidal site within the In layer, Ni(2), is partially occupied while it is empty in the Te layers. The octahedral position in between the In and Te layers, Ni(1a), is fully occupied while the octahedral position in between two adjacent Te layers, Ni(1b), is partially occupied. With decreasing In and Ni content, the modulation wave vector,, was found to increase continuously until gamma = 1. From this, crenel functions to describe the whole homogeneity range of the solid solution were constructed with the length of the atomic domains Delta(Te) = gamma (and hence Delta(In) = Delta(Ni) = 1-gamma) and Delta(Ni(1b)) = gamma/2 (and hence Delta(Ni(1a)) = 1-gamma/2) which were then used for the refinement of the incommensurate structure of Ni3InTe2. The corresponding effect in real space is that the single In layers separating double layers of Te, occur less frequent when y in increasing until at gamma = 1 the CdI2 type structure of Ni1+xTe2 is reached. (C) 2007 Elsevier Inc. All rights reserved.
Title:
The influence of cobalt doping on photocatalytic nano-titania: Crystal chemistry and amorphicity
Authors:
Lim, SH; Ferraris, C; Schreyer, M; Shih, K; Leckie, JO; White, TJ Author Full Names: Lim, Suo Hon; Ferraris, Cristiano; Schreyer, Martin; Shih, Kalmin; Leckie, James O.; White, T. J.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 180 (10): 2905-2915 OCT 2007
Abstract:
Photocatalysts of nominal composition (Ti1-xCox)O2-delta with 0.001 <= x <= 0.05 were prepared via a sol-gel technique followed by air firing (200-1000 degrees C). The incorporation of cobalt inhibited crystal growth and slightly raised the anatase to rutile transformation temperature (similar to 700 degrees C). An amorphous component was invariably significant with the maxmum content (41-53wt%) appearing simultaneously with the removal of anatase, suggesting that rutile crystallizes via an aperiodic structure. While the introduction of cobalt shifted the apparent band gap to visible light energies this did not enhance performance as there was limited miscibility of cobalt in titania, non-catalytic secondary phases were present, and active Ti3+ sites were displaced by cobalt. (C) 2007 Elsevier Inc. All rights reserved.
Title:
Improvement of plasticity by tailoring combination of constituent elements in Ti-rich Ti-Zr-Be-Cu-Ni bulk metallic glasses
Authors:
Park, ES; Chang, HJ; Lee, JY; Kim, DH Author Full Names: Park, E. S.; Chang, H. J.; Lee, J. Y.; Kim, D. H.
Source:
JOURNAL OF MATERIALS RESEARCH 22 (12): 3440-3447 DEC 2007
Abstract:
The effect of replacement of Ti with Y or Nb in Ti-rich Ti-Zr-Be-Cu-Ni bulk metallic glasses (BMGs) has been investigated. The minor addition (MA) of Y (Y-Ti: +58 kJ/mol) induced phase separation into Y-rich crystalline particles and Ti-rich amorphous matrix, while the MA of Nb (Nb-Ti: +10 kJ/mol) led to nanocrystallization in Ti-rich BMGs with icosahedral nuclei. This result indicates that MA of elements having positive enthalpy of mixing can induce a different degree of instability in the single amorphous matrix depending on the amount of repulsive interaction energy. In particular, MA of Nb (up to 4 at.%) significantly increased the compressive fracture strain (is an element of(f)) up to similar to 9.35 +/- 0.2%, which indicates that the plasticity of BMGs can be enhanced by the size-modulated icosahedral phase embedded in the amorphous matrix.
Title:
Synthesis, crystal structure, and magnetic properties of Sr1.31Co0.63Mn0.37O3: A derivative of the incommensurate composite hexagonal perovskite structure
Authors:
Mandal, TK; Abakumov, AM; Hadermann, J; Van Tendeloo, G; Croft, M; Greenblatt, M Author Full Names: Mandal, Tapas Kumar; Abakumov, Artem M.; Hadermann, Joke; Van Tendeloo, Gustaaf; Croft, Mark; Greenblatt, Martha
Source:
CHEMISTRY OF MATERIALS 19 (25): 6158-6167 DEC 11 2007
Abstract:
We report the synthesis, structural investigation, and magnetic property studies of Sr1.31Co0.63Mn0.17O3 that adopts an incommensurate composite hexagonal perovskite-related structure. The crystal structure has been solved using a (3 + 1)-dimensional suRerspace approach from powder X-ray and neutron diffraction data (SSG R (3) over barm(00 gamma)0s, a = 9.5548(1) angstrom, q = 2.5599(l) A, q = 0.65581(4)c*, R-B = 0.041 R-P = 0.059). The structure consists of face-sharing chains of octahedra and trigonal prisms, wherein the trigonal prismatic sites are preferentially occupied by Co with some cation disorder. A combination of electron diffraction and high-resolution electron microscopic analysis has demonstrated that the compound possesses a complicated microstructure related to the formation of domains with slightly different lengths of the modulation vector. X-ray absorption near-edge spectroscopic (XAS) studies clearly indicate the presence of Mn in the 4+ and Co in the 3+ oxidation state. While the magnetic susceptibility data indicates the presence of anti ferro magnetic correlations in the system, the calculation of effective paramagnetic moment (mu(cal) = 3.561 mu(B)), assuming the metal oxidation states as obtained from XAS and the cation distribution as obtained from neutron refinement, is in agreement with the value obtained experimentally (mu(exp) = 3.676 mu(B)).

Update: 4-Jan-2008

Title:
Pressure-induced enhancement of ferroelectricity in multiferroic RMn2O5 (R=Tb,Dy,Ho)
Authors:
dela Cruz, CR; Lorenz, B; Sun, YY; Wang, Y; Park, S; Cheong, SW; Gospodinov, MM; Chu, CW Author Full Names: dela Cruz, C. R.; Lorenz, B.; Sun, Y. Y.; Wang, Y.; Park, S.; Cheong, S-W.; Gospodinov, M. M.; Chu, C. W.
Source:
PHYSICAL REVIEW B 76 (17): Art. No. 174106 NOV 2007
Abstract:
Measurements of ferroelectric polarization and dielectric constant were done on RMn2O5 (R=Tb,Dy,Ho) with applied hydrostatic pressures of up to 18 kbar. At ambient pressure, distinctive anomalies were observed in the temperature profile of both physical properties at critical temperatures marking the onset of long range antiferromegnetic order (T-N1) and ferroelectricity (T-C1), as well as at temperatures when anomalous changes in the polarization, dielectric constant, and spin wave commensurability have been previously reported. In particular, the step in the dielectric constant at low temperatures (T-C2), associated with both a drop in the ferroelectric polarization and an incommensurate magnetic structure, was shown to be suddenly quenched upon passing an R-dependent critical pressure. This was shown to correlate with the stabilization of the high ferroelectric polarization state, which is coincident with the commensurate magnetic structure. The observation is suggested to be due to a pressure-induced phase transition into a commensurate magnetic structure, as exemplified by the pressure-temperature (p-T) phase diagrams constructed in this work. The p-T phase diagrams are determined for all three compounds.
Title:
Origin of anisotropic nonmetallic transport in the Al80Cr15Fe5 decagonal approximant
Authors:
Dolinsek, J; Jeglic, P; Komelj, M; Vrtnik, S; Smontara, A; Smiljanic, I; Bilusic, A; Ivkov, J; Stanic, D; Zijlstra, ES; Bauer, B; Gille, P Author Full Names: Dolinsek, J.; Jeglic, P.; Komelj, M.; Vrtnik, S.; Smontara, Ana; Smiljanic, I.; Bilusic, A.; Ivkov, J.; Stanic, D.; Zijlstra, E. S.; Bauer, Birgitta; Gille, P.
Source:
PHYSICAL REVIEW B 76 (17): Art. No. 174207 NOV 2007
Abstract:
We present a study of the anisotropic transport properties (electrical resistivity, thermoelectric power, Hall coefficient, and thermal conductivity) of a single-crystalline Al80Cr15Fe5 complex metallic alloy that is an excellent approximant to the decagonal quasicrystal with six atomic layers in one periodic unit. Temperature-dependent electrical resistivity along the b and c crystalline directions shows a nonmetallic behavior with a broad maximum, whereas it shows a metallic positive temperature coefficient along the a direction perpendicular to the (b,c) atomic planes. Ab initio calculations of the electronic density of states reveal that the nonmetallic transport occurs in the presence of a high density of charge carriers. The very different temperature-dependent electrical resistivities along the three crystalline directions can all be treated within the same physical model of slow charge carriers due to weak dispersion of the electronic bands, where the increased electron-phonon scattering upon raising the temperature induces transition from dominant Boltzmann (metallic) to dominant non-Boltzmann (insulatinglike) regime. The temperature dependence of the resistivity is governed predominantly by the temperature dependence of the electronic diffusion constant D and the transition has no resemblance to the Anderson-type metal-to-insulator transition based on the gradual electron localization. Structural considerations of the Al80Cr15Fe5 phase show that the anisotropy of the transport properties is a consequence of anisotropic atomic order on the scale of nearest-neighbor atoms, suggesting that the role of quasiperiodicity in the anisotropic transport of decagonal quasicrystals is marginal. We also present a relaxed version of the Al-4(Cr,Fe) structural model by Deng et al.
Title:
Temperature-dependent photoemission spectra, spectral weight transfer, and chemical potential shift in Pr1-xCaxMnO3: Implications for charge-density modulation
Authors:
Ebata, K; Hashimoto, M; Tanaka, K; Fujimori, A; Tomioka, Y; Tokura, Y Author Full Names: Ebata, K.; Hashimoto, M.; Tanaka, K.; Fujimori, A.; Tomioka, Y.; Tokura, Y.
Source:
PHYSICAL REVIEW B 76 (17): Art. No. 174418 NOV 2007
Abstract:
We have studied the temperature dependence of the photoemission spectra of Pr1-xCaxMnO3 (PCMO) with x=0.25, 0.3, and 0.5. For x=0.3 and 0.5, we observed a gap in the low-temperature charge-exchange-type charge-ordered (CO) phase and a pseudogap with a finite intensity at the Fermi level (E-F) in the high-temperature paramagnetic insulating (PI) phase. Within the CO phase, the spectral intensity near E-F gradually increased with temperature. These observations are consistent with the results of Monte Carlo simulations on a model including charge ordering and ferromagnetic fluctuations [H. Aliaga , Phys. Rev. B 68, 104405 (2003)]. For x=0.25, on the other hand, little temperature dependence was observed within the low-temperature ferromagnetic insulating (FI) phase and the intensity at E-F remained low in the high-temperature PI phase. We attribute the difference in the temperature dependence near E-F between the CO and FI phases to the different correlation lengths of orbital order between both phases. Furthermore, we observed a chemical potential shift with temperature due to the opening of the gap in the FI and CO phases. The doping dependent chemical potential shift was recovered at low temperatures, corresponding to the disappearance of the doping dependent change of the modulation wave vector. Spectral weight transfer with hole concentration was clearly observed at high temperatures but was suppressed at low temperatures. We attribute this observation to the fixed periodicity with hole doping in PCMO at low temperatures.
Title:
Fincher-Burke spin excitations and omega/T scaling in insulating La1.95Sr0.05CuO4
Authors:
Bao, W; Chen, Y; Yamada, K; Savici, AT; Russo, PL; Lorenzo, JE; Chung, JH Author Full Names: Bao, Wei; Chen, Y.; Yamada, K.; Savici, A. T.; Russo, P. L.; Lorenzo, J. E.; Chung, J. -H.
Source:
PHYSICAL REVIEW B 76 (18): Art. No. 180406 NOV 2007
Abstract:
Insulating La1.95Sr0.05CuO4 shares with superconducting cuprates the same Fincher-Burke spin excitations, which usually are observed in itinerant antiferromagnets. The local spectral function satisfies omega/T scaling above similar to 16 K for this incommensurate insulating cuprate, together with previous results in commensurate insulating and incommensurate superconducting cuprates, further supporting the general prediction for square-lattice quantum spin S=1/2 systems. The width of incommensurate peaks in La1.95Sr0.05CuO4 scales to a similar finite value as at optimal doping, strongly suggesting that they are similarly distant from a quantum critical point. They might both be limited to a finite correlation length by partial spin-glass freezing.
Title:
Structure, charge ordering and physical properties of LuFe2O4
Authors:
Zhang, Y; Yang, HX; Guo, YQ; Ma, C; Tian, HF; Luo, JL; Li, JQ Author Full Names: Zhang, Y.; Yang, H. X.; Guo, Y. Q.; Ma, C.; Tian, H. F.; Luo, J. L.; Li, J. Q.
Source:
PHYSICAL REVIEW B 76 (18): Art. No. 184105 NOV 2007
Abstract:
Microstructural properties, phase transitions, and charge ordering of LuFe2O4 have been extensively investigated by means of transmission electron microscopy (TEM) in a large temperature range from 20 to 550 K. The experimental results demonstrate that the LuFe2O4 crystal is commonly modulated by charge ordering (CO), which is often recognizable by superstructure reflections. The (001) twinning domains as a common defect often appear in the LuFe2O4 crystals along the c-axis direction, with the crystals across each (001) boundary rotated by 180 degrees with respect to one another. The in situ cooling TEM observations from 300 K down to 20 K reveal remarkable alternations of the superstructures, suggesting a complex CO process in the present system. Careful analysis shows that the CO in the frustrated ground state is characterized by a modulation with a wave vector of q(1)=(1/3 1/3 2). In situ heating TEM observations from 300 to 550 K clearly reveal that the CO modulation in LuFe2O4 becomes invisible above a critical temperature of about T-C=530 K. These facts suggest that the CO should be the essential driving force for the structural transitions and ferroelectricity observed in this kind of layered material. Experimental measurements on the ferroelectricity show that the LuFe2O4 material, in general, has a large dielectric constant of about 10 000 at room temperature. In order to understand the properties of low-temperature phase transitions, the magnetization and specific heat from 300 to 4 K have been briefly discussed.
Title:
Ferroelectric phase transitions of 3d-spin origin in Eu1-xYxMnO3
Authors:
Yamasaki, Y; Miyasaka, S; Goto, T; Sagayama, H; Arima, T; Tokura, Y Author Full Names: Yamasaki, Y.; Miyasaka, S.; Goto, T.; Sagayama, H.; Arima, T.; Tokura, Y.
Source:
PHYSICAL REVIEW B 76 (18): Art. No. 184418 NOV 2007
Abstract:
Perovskite-type rare-earth manganites RMnO3 (R=Tb and Dy) undergo the ferroelectric transitions concomitantly with the collinear to noncollinear magnetic transitions of Mn 3d spins, in which the electric polarization direction can be controlled by an external magnetic field. To clarify how the magnetic transition of Mn 3d spins is correlated with the ferroelectric transition, we have investigated a mixed-crystal system of perovskite-type Eu1-xYxMnO3 (0 <= x <= 0.4) without the 4f magnetic moments of the rare earth ions. The choice of the present system has enabled us to systematically investigate the correlation between dielectric, magnetic (of Mn spin origin), and superlattice properties with varying the perovskite lattice distortion or equivalently the competing Mn spin superexchange interactions. The compounds with x=0.3 and 0.4 undergo the ferroelectric transitions with the spontaneous polarization along the a axis, which is associated with the formation of a ab-plane cycloidal spin structure with the modulation vector along the b axis. Among them, the x=0.4 compound was found to undergo the polarization flop from along the a axis to the c axis as induced not only thermally but also by a magnetic field applied along the a axis. The magnetic-field induced polarization flop and its mechanism for x=0.4 can be fully accounted for in terms of the rotation of the cycloidal spin plane from ab to bc stemming from the Mn spin flops. This is contrasted by the case of TbMnO3 and DyMnO3 with the rare-earth 4f Ising moments coupled to the Mn 3d spins, in which magnetic fields along the b axis and the a axis, but not along the c axis (up to 14 T), can flop the polarization from along the c axis to the a axis.
Title:
X-ray scattering study of the order parameters in multiferroic TbMnO3
Authors:
Mannix, D; McMorrow, DF; Ewings, RA; Boothroyd, AT; Prabhakaran, D; Joly, Y; Janousova, B; Mazzoli, C; Paolasini, L; Wilkins, SB Author Full Names: Mannix, D.; McMorrow, D. F.; Ewings, R. A.; Boothroyd, A. T.; Prabhakaran, D.; Joly, Y.; Janousova, B.; Mazzoli, C.; Paolasini, L.; Wilkins, S. B.
Source:
PHYSICAL REVIEW B 76 (18): Art. No. 184420 NOV 2007
Abstract:
We report on an extensive investigation of the multiferroic compound TbMnO3 using x-ray scattering techniques. Nonresonant x-ray magnetic scattering (NRXMS) was used to characterize the domain population of the single crystal used in our experiments. This revealed that the dominant domain is overwhelmingly A type. The temperature dependence of the intensity and wave vector associated with the incommensurate magnetic order was found to be in good agreement with neutron scattering data. X-ray resonant scattering experiments were performed in the vicinity of the Mn K and Tb L-3 edges in the high-temperature collinear phase, the intermediate temperature cycloidal and ferroelectric phase, and the low-temperature phase. In the collinear phase, where according to neutron diffraction only the Mn sublattice is ordered, resonant E1-E1 satellites were found at the Mn K edge associated with A-type but also F-type peaks. Detailed measurements of the azimuthal dependence of the F-type satellites (and their absence in the NRXMS experiments) leads us to conclude that they are most likely nonmagnetic in origin. We suggest instead that they may be associated with an induced charge multipole. At the Tb L-3 edge, resonant A- and F-type satellites were observed in the collinear phase again associated with E1-E1 events. We attribute these to a polarization of the Tb 5d states by the ordering of the Mn sublattice. On cooling into the cycloidal and ferroelectric phase, a new set of resonant satellites appear corresponding to C-type order. These appear at the Tb L-3 edge only. In addition to a dominant E1-E1 component in the sigma-pi' channel, a weaker component is found in the preedge with sigma-sigma' polarization and displaced by -7 eV with respect to the E1-E1 component. Comprehensive calculations of the x-ray scattering cross section were performed using the FDMNES code. These calculations show that the unrotated sigma-sigma' component of the Tb L-3 C-type peaks appearing in the ferroelectric phase contains a contribution from a multipole that is odd with respect to both space and time, known in various contexts as the anapole. Our experiments thus provide tentative evidence for the existence of a type of anapolar order parameter in the rare-earth manganite class of mulitferroic compounds.
Title:
Neutron scattering study of magnetic ordering and excitations in the ternary rare-earth diborocarbide (CeB2C2)-B-11
Authors:
Nakanowatari, I; Morinaga, R; Onimaru, T; Sato, TJ Author Full Names: Nakanowatari, Isao; Morinaga, Rei; Onimaru, Takahiro; Sato, Taku J.
Source:
PHYSICAL REVIEW B 76 (18): Art. No. 184427 NOV 2007
Abstract:
Neutron scattering experiments have been performed on the ternary rare-earth diborocarbide (CeB2C2)-B-11. The powder-diffraction experiment confirms formation of a long-range magnetic order at T-N=7.3 K, where a sinusoidally modulated structure is realized with the modulation vector q=[0.167(3),0.167(3),0.114(3)]. Inelastic excitation spectra in the paramagnetic phase comprise significantly broad quasielastic and inelastic peaks centered at h omega approximate to 0, 8, and 65 meV. Crystalline-electric-field (CEF) analysis satisfactorily reproduces the observed spectra, confirming their CEF origin. The broadness of the quasielastic peak indicates strong spin fluctuations due to coupling between localized 4f spins and conduction electrons in the paramagnetic phase. A prominent feature is suppression of the quasielastic fluctuations, and concomitant growth of a sharp inelastic peak in a low-energy region below T-N. This suggests dissociation of the conduction and localized 4f electrons on ordering, and contrasts the presently observed incommensurate phase with spin-density-wave order frequently seen in heavy fermion compounds, such as CexLa1-xRu2Si2.
Title:
Quasicrystals: Comparative dynamics
Authors:
Janssen, T Author Full Names: Janssen, Ted
Source:
NATURE MATERIALS 6 (12): 925-926 DEC 2007
Title:
Lattice dynamics of the Zn-Mg-Sc icosahedral quasicrystal and its Zn-Sc periodic 1/1 approximant
Authors:
De Boissieu, M; Francoual, S; Mihalkovic, M; Shibata, K; Baron, AQR; Sidis, Y; Ishimasa, T; Wu, D; Lograsso, T; Regnault, LP; Gahler, F; Tsutsui, S; Hennion, B; Bastie, P; Sato, TJ; Takakura, H; Currat, R; Tsai, AP Author Full Names: De Boissieu, Marc; Francoual, Sonia; Mihalkovic, Marek; Shibata, Kaoru; Baron, Alfred Q. R.; Sidis, Yvan; Ishimasa, Tsutomu; Wu, Dongmei; Lograsso, Thomas; Regnault, Louis-Pierre; Gaehler, Franz; Tsutsui, Satoshi; Hennion, Bernard; Bastie, Pierre; Sato, Taku J.; Takakura, Hiroyuki; Currat, Roland; Tsai, An-Pang
Source:
NATURE MATERIALS 6 (12): 977-984 DEC 2007
Abstract:
Quasicrystals are long-range-ordered materials that lack translational invariance, so the study of their physical properties remains a challenging problem. Here, we have carried out inelastic-X-ray- and neutron-scattering experiments on single-grain samples of the Zn-Mg-Sc icosahedral quasicrystal and of the Zn-Sc periodic cubic 1/1 approximant, with the aim of studying the respective influence of the local order and of the long-range order ( periodic or quasiperiodic) on lattice dynamics. Besides the overall similarities and the existence of a pseudo-gap in the transverse dispersion relation, marked differences are observed, the pseudo-gap being larger and better defined in the approximant than in the quasicrystal. This can be qualitatively explained using the concept of a pseudo-Brillouin-zone in the quasicrystal. These results are compared with simulations on atomic models and using oscillating pair potentials, and the simulations reproduce in detail the experimental results. This paves the way for a detailed understanding of the physics of quasicrystals.

Update: 28-Dec-2007

Title:
Quasicrystals: 25 years
Authors:
Hargittai, I Author Full Names: Hargittai, Istvan
Source:
STRUCTURAL CHEMISTRY 18 (5): 533-534 OCT 2007
Title:
Structure of the monoclinic-form misfit-layer compound, (Ca0.85OH)(2 alpha)CoO2 (alpha approximate to 0.57822)
Authors:
Isobe, M; Onoda, M; Shizuya, M; Tanaka, M; Takayama-Muromachi, E Author Full Names: Isobe, Masaaki; Onoda, Mitsuko; Shizuya, Mitsuyuki; Tanaka, Masahiko; Takayama-Muromachi, Eiji
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 129 (47): 14585-14596 NOV 28 2007
Abstract:
The incommensurate modulated crystal structure of the new misfit-layer calcium cobalt oxide (Ca0.85OH)(2 alpha) CoO2 was investigated using a superspace-group formalism with synchrotron X-ray diffraction data. The compound is a kind of composite crystal that consists of two interpenetrating subsystems, [CoO2](infinity) layers containing triangular lattices formed by edge-sharing CoO6 octahedra, separated from each other by [2Ca(0.85)OH](infinity) double-layered rock-salt-type slabs. Both the subsystems are monoclinic lattices with the unit cell parameters, a(1) = 2.8180(4) angstrom, b = 4.8938(6) angstrom, c = 8.810(1) angstrom, alpha(0) = 95.75(3)degrees, and alpha=vertical bar q vertical bar=a(1)/a(2)) = 0.57822(8), viz., a(2) = 4.8736 A, with Z = 2. A possible superspace group is C2/m(alpha 10)s0-C2(1)/m(alpha(-1) 10) for the respective subsystems. The atomic positions deviate from the average positions of the fundamental structure due to the incommensurable periodic interaction between the subsystems. A significant structural modulation was found in the [2Ca(0.85)OH] subsystem, whereas the modulation in the [CoO2 subsystem is less than in [2Ca(0.85)OH], due to the tight bonding of the close-packed CoO6 octahedra. The degree of modulation in the CoO2 layers, i.e., the potential modulation, is almost the same as those of other compounds of the misfit-layer cobalt oxides. Flattened CoO6 octahedra indicate hole doping into the CoO2 layers. The [2Ca(0.85)OH] blocks act as the charge reservoir layers, and the defect Ca ions are presumably the source of the holes.
Title:
Growth, structure and physical and Pb-doped Bi-based properties of single crystals of pure high T-c superconductors
Authors:
Giannini, E; Gladyshevskil, R; Clayton, N; Musolino, N; Garnier, V; Piriou, A; Flukiger, R Author Full Names: Giannini, E.; Gladyshevskil, R.; Clayton, N.; Musolino, N.; Garnier, V.; Piriou, A.; Fluekiger, R.
Source:
CURRENT APPLIED PHYSICS 8 (2): 115-119 MAR 2008
Abstract:
Single crystals of (Bi1-xPbx)(2)Sr2Ca2CU3O10+delta (x = 0 and 0.16) (sizes up to 3 x 2 x 0.1 mm(3)) have been grown by means of a newly developed "vapour-assisted travelling solvent floating zone" technique (VA-TSFZ). Post-annealing under high pressure of O-2 (up to 10 MPa at T = 500 degrees C) was applied to enhance T-c (up to 111 K) and improve the homogeneity of the crystals (Delta T-c <= 1 K). The structure of both Pb-free and Pb-doped Bi-2223 was refined for the first time from single crystal X-ray diffraction (XRD) data. The unit cell of the average structure is pseudo-tetragonal with a = 5.4210(7), b = 5.4133(6) and c = 37.010(7) angstrom, and a = 5.395(l), b = 5.413(l) and c = 37.042(11) angstrom, for the Pb-free and the Pb-doped phase, respectively. An incommensurate modulation in the direction of one of the short cell vectors has been defined (q similar to 0.21 a*), however, the structure can be conveniently described in a supercell with a fivefold volume (a = 27.105(4) angstrom). With respect to the "non-modulated" structure, one additional oxygen atom for ten initial O was found to be inserted into the BiO layers. The superconducting anisotropy of Bi-2223 was found to be similar to 50, from measurements of the lower critical field. The anisotropy of Bi-2223 is significantly reduced compared to that of Bi-2212, and this accounts for the enhanced irreversibility fields in Bi-2223. Furthermore, Bi-2223 has a higher critical current density, and a reduced magnetic relaxation rate compared to Bi-2212, which are both signatures of more effective pinning in Bi-2223 due to its reduced anisotropy. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Quasicrystals: Structure and properties
Authors:
Vekilov, YK; Isaev, EI Author Full Names: Vekilov, Yu. Kh.; Isaev, E. I.
Source:
CRYSTALLOGRAPHY REPORTS 52 (6): 932-937 NOV 2007
Abstract:
The structure and properties of quasicrystals are discussed. The short-and long-range atomic orders and the effect of these factors on the physical characteristics are considered. It is noted that investigations of the physical properties of quasicrystals at temperatures above room temperature should be performed. Promising applications are briefly outlined.
Title:
Growth of single crystals of quasicrystalline phases
Authors:
Shulyatev, DA Author Full Names: Shulyatev, D. A.
Source:
CRYSTALLOGRAPHY REPORTS 52 (6): 938-944 NOV 2007
Abstract:
To study the mechanical and physical properties of quasicrystals, single-crystal samples of large size (several centimeters) are necessary. However, obtainment of such single crystals meets a number of difficulties related to the peritectic character of melting of quasicrystalline compounds, high volatility and oxidizability of the initial components, low growth rate in aperiodic directions, and metastability of the most quasicrystalline structures. In this study, criteria for stable growth of quasicrystalline phases have been determined. The growth mechanisms of icosahedral and decahedral single crystals are described and experimental techniques of single-crystal growth are reviewed.
Title:
Fabrication of quasicrystalline coatings: A review
Authors:
Shaitura, DS; Enaleeva, AA Author Full Names: Shaitura, D. S.; Enaleeva, A. A.
Source:
CRYSTALLOGRAPHY REPORTS 52 (6): 945-952 NOV 2007
Abstract:
Unusual properties of quasicrystals-a low friction coefficient; high hardness, wear resistance, and oxidation; and low electrical and thermal conductivities-make quasicrystalline materials promising for practical applications. Methods of fabrication of quasicrystalline coatings and examples of their commercial application are considered.
Title:
Preparation of Al-Cu-Fe quasicrystalline powdered alloys and related materials by mechanical activation
Authors:
Kaloshkin, SD; Tcherdyntsev, VV; Danilov, VD Author Full Names: Kaloshkin, S. D.; Tcherdyntsev, V. V.; Danilov, V. D.
Source:
CRYSTALLOGRAPHY REPORTS 52 (6): 953-965 NOV 2007
Abstract:
A mechanochemical method is developed for preparing quasicrystalline powdered alloys in the Al-Cu-Fe system and related materials. Quasicrystals are designed and proposed for use in practice as filling materials for metal and polymer matrices. The structure and mechanical properties of the designed materials are described. The possible fields of application of the materials under consideration are discussed.
Title:
Modern methods for investigating functional surfaces of advanced materials by mechanical contact testing
Authors:
Petrzhik, MI; Levashov, EA Author Full Names: Petrzhik, M. I.; Levashov, E. A.
Source:
CRYSTALLOGRAPHY REPORTS 52 (6): 966-974 NOV 2007
Abstract:
Modern methods for determining the hardness, Young's modulus, elastic recovery, adhesive/cohesive strength, friction coefficient, and wear resistance of thin films, coatings, multilayer materials, and bulk materials are considered. The experimental data obtained in instrumented indentation, instrumented scratching, and tribological tests of nanostructured and quasicrystalline coatings and composite materials are analyzed. It is noted that the elastic recovery of a number of advanced materials is higher than the elastic recovery of metal alloys by a factor of 2-3. The coefficients of sliding friction of sintered samples and thin films containing Al-Cu-Fe quasicrystals are found to be relatively low. An increase in the fraction of quasicrystalline particles to 30% in composites with an aluminum matrix leads to an increase in the wear resistance.
Title:
Charge state and hydrogen diffusion in Ti-based alloys
Authors:
Morozov, AY; Isaev, EI; Vekilov, YK Author Full Names: Morozov, A. Yu.; Isaev, E. I.; Vekilov, Yu. Kh.
Source:
CRYSTALLOGRAPHY REPORTS 52 (6): 975-979 NOV 2007
Abstract:
The electronic structure, charge state, and hydrogen diffusion in icosahedral Ti-based alloys have been investigated by the methods based on the density-functional theory. The charge state of the hydrogen atom in Ti36Zr32Ni13 has been determined for different types of tetrahedral voids. The charge state of hydrogen atoms in Ti36Zr32Ni13, Ti36Hf32Ni13, and Ti48Zr8Fe18 is calculated for the ratio H/M = 1.7, where H is the number of hydrogen atoms and M is the number of metal atoms. It is established that hydrogen atoms in all objects studied are in an almost neutral state. The hydrogen diffusion coefficient is determined for Ti36Zr32Ni13.
Title:
Magnetic susceptibility of quasicrystalline Al65Cu22Fe13 powders
Authors:
Nikonov, AA; Semenovskii, PV; Teplov, AA; Shaitura, DS Author Full Names: Nikonov, A. A.; Semenovskii, P. V.; Teplov, A. A.; Shaitura, D. S.
Source:
CRYSTALLOGRAPHY REPORTS 52 (6): 980-983 NOV 2007
Abstract:
Magnetic properties of quasicrystalline Al65Cu22Fe13 powders synthesized by the solid-phase diffusion method via thermal treatment in vacuum or a hydrogen atmosphere have been studied. The powders synthesized in vacuum are found to contain a ferromagnetic fraction. The formation of iron oxide Fe3O4 is shown to be the most probable cause of the existence of this fraction. It is possible to avoid the formation of the ferromagnetic fraction in the powders synthesized or annealed in hydrogen. Removal of the ferromagnetic fraction from the powder by repeated magnetic separation made it possible to obtain a quasicrystalline fraction, for which the behavior of the magnetic susceptibility can be explained by the formation of nanoclusters. Such behavior is a general and integral property of quasicrystalline powders synthesized in both vacuum and hydrogen.
Title:
Gamma-resonance study of nanopowders with different dispersion and quasicrystalline phases in the Al-Cu-Fe system
Authors:
Frolov, KV; Mikheeva, MN; Lyubutin, IS; Nikonov, AA; Teplov, AA; Shaitura, DS; Abuzin, YA Author Full Names: Frolov, K. V.; Mikheeva, M. N.; Lyubutin, I. S.; Nikonov, A. A.; Teplov, A. A.; Shaitura, D. S.; Abuzin, Yu. A.
Source:
CRYSTALLOGRAPHY REPORTS 52 (6): 984-989 NOV 2007
Abstract:
Fe-57 Mossbauer spectroscopy has been used to monitor synthesis of quasicrystals in the Al-Cu-Fe system and study the influence of the size of quasicrystalline particles in powder samples of the Al63.1Cu25.6Fe11.3 alloy on the properties of synthesized materials. Quasicrystalline samples of different dispersion with particle sizes from 0.3 to 15 mu m have been studied in the temperature range 80-295 K. It is established that iron atoms in an Al63.1Cu25.6Fe11.3 quasicrystals occupy four types of structural positions, which differ in the atomic composition of the nearest environment. The results of the analysis suggest the dependence of the hyperfine-interaction parameters on the degree of sample dispersion. The components corresponding to iron atoms in both the surface layer and bulk of microparticles are isolated in the Mossbauer spectra. No magnetic hyperfine splitting has been found in the Mossbauer spectra in the entire temperature range. This fact suggests that a! localized magnetic moment is absent in iron atoms.
Title:
Study of melt-grown quasicrystalline samples in the Cd-Yb and Al-Cu-Fe systems
Authors:
Konoplev, DA; Kruglov, VS; Komarov, AO; Lobanova, AV Author Full Names: Konoplev, D. A.; Kruglov, V. S.; Komarov, A. O.; Lobanova, A. V.
Source:
CRYSTALLOGRAPHY REPORTS 52 (6): 990-995 NOV 2007
Abstract:
The regimes of preparation of bulk samples of the quasicrystalline phase in the Cd-Yb and Al-Cu-Fe systems have been investigated. A thermodynamically stable quasicrystalline phase Cd5.7Yb and its approximant Cd6Yb with a high degree of texture along the cooling axis have been obtained. X-ray diffraction analysis made it possible to reveal changes in the structure and phase composition of bulk samples with variation in the melting temperature and annealing for different methods of sample preparation. It is shown that the presence of a temperature gradient along the furnace axis significantly affects the volume of the quasicrystalline phase. It is established that, with a decrease in the volume of the quasicrystalline phase mixed with the crystalline phase, the character of the temperature dependence of resistivity changes from the semiconductor type to the metallic type and the microhardness decreases according to a linear law.
Title:
Correlations between electric, magnetic, and galvanomagnetic quantities in stable icosahedral phases based on aluminum
Authors:
Prekul, AF; Shchegolikhina, NI Author Full Names: Prekul, A. F.; Shchegolikhina, N. I.
Source:
CRYSTALLOGRAPHY REPORTS 52 (6): 996-1005 NOV 2007
Abstract:
On the basis of the results of the experimental investigation of the correlations between the electric, magnetic, and galvanomagnetic properties, the nature of the electronic phenomena leading to the difference of icosahedral quasicrystals from typical metals and insulators (low conductivity and negative temperature coefficient of resistance, diamagnetism of the ground state and its decrease with increasing temperature, and existence of residual and thermally induced charge carriers) is discussed.
Title:
EXAFS spectroscopy of quasicrystals
Authors:
Menushenkov, AP; Rakshun, YV Author Full Names: Menushenkov, A. P.; Rakshun, Ya. V.
Source:
CRYSTALLOGRAPHY REPORTS 52 (6): 1006-1013 NOV 2007
Abstract:
The results of the investigation of the features of the local structure of quasicrystalline materials by extended X-ray absorption fine structure (EXAFS) spectroscopy with the use of synchrotron radiation are analyzed. The advantages of this method from the point of view of deriving information about the local shifts of the atoms forming an icosahedral structure are demonstrated. The rearrangement of the local environment of copper and iron in Al-Fe-Cu ternary alloys at a transition from the crystalline to the quasicrystalline phase has been investigated. It is established that the nearest copper coordination retains the symmetry characteristic of the crystal; however, rotation and small displacements of copper matrix atoms lead to significant rearrangement of aluminum atoms around iron atoms. As a result, icosahedral clusters with pentagonal symmetry are formed around iron atoms and violation of the translational symmetry is accompanied by the transition of Al-Fe-Cu! to the quasicrystalline state.
Title:
Interatomic force interaction in an i-AlCuFe quasicrystal
Authors:
Parshin, PP; Zemlyanov, MG; Brand, RA Author Full Names: Parshin, P. P.; Zemlyanov, M. G.; Brand, R. A.
Source:
CRYSTALLOGRAPHY REPORTS 52 (6): 1020-1024 NOV 2007
Abstract:
Partial spectra of thermal vibrations of Al, Cu, and Fe atoms in an icosahedral quasicrystal have been obtained by the isotopic-contrast method in inelastic neutron scattering. Joint analysis of these results and the published data on the atomic and electronic structures of the icosahedral i-AlCuFe quasicrystal has been performed. A physical model of the quasicrystal structure is proposed that is in agreement with the existing experimental data and qualitatively describes the peculiarities of interatomic interaction.
Title:
Calculation of vibrational spectra of an icosahedral quasicrystal AlCuFe
Authors:
Rudenko, AN; Mazurenko, VG Author Full Names: Rudenko, A. N.; Mazurenko, V. G.
Source:
CRYSTALLOGRAPHY REPORTS 52 (6): 1025-1029 NOV 2007
Abstract:
Vibrational spectra of an icosahedral quasicrystal AlCuFe have been calculated on the basis of a crystalline 1/1 approximant by the recurrence method. To describe the interaction of atoms in a quasicrystal, the semiempirical EAM model was used. It is shown that the calculated spectra are in satisfactory agreement with the experimental neutron inelastic scattering data.
Title:
Local structure of binary alloys Zr70Pd30
Authors:
Menushenkov, AP; Kashurnikova, OV; Chernikov, RV; Panova, GK; Shikov, AA Author Full Names: Menushenkov, A. P.; Kashurnikova, O. V.; Chernikov, R. V.; Panova, G. Kh.; Shikov, A. A.
Source:
CRYSTALLOGRAPHY REPORTS 52 (6): 1030-1035 NOV 2007
Abstract:
The rearrangements of the local environment of zirconium and palladium atoms in the binary alloy Zr70Pd30 upon the transformation from the crystalline to the quasicrystalline and amorphous states were studied by extended X-ray absorption fine structure (EXAFS) analysis. In the quasicrystalline phase, the icosahedral environment was found to be formed only around the zirconium ions because of shifts of both the palladium and zirconium atoms to the center of the cluster; in addition, the structure of the icosahedral clusters is distorted. The transformation from the crystalline to the quasicrystalline phase is accompanied by the atomic rearrangement in the immediate environment of palladium, thus resulting in the partial displacement of palladium by zirconium. In the amorphous phase, the icosahedral short-range order is not observed. A model for the description of the structure of the quasicrystalline phase of Zr70Pd30 is proposed.
Title:
Distortions of the atomic structure of 2/1 approximants of icosahedral quasicrystals
Authors:
Dmitrienko, VE; Chizhikov, VA Author Full Names: Dmitrienko, V. E.; Chizhikov, V. A.
Source:
CRYSTALLOGRAPHY REPORTS 52 (6): 1040-1047 NOV 2007
Abstract:
Ideal structures of several 2/1 approximants of icosahedral quasicrystals with the sp. gr. Pm (3) over bar and Pa (3) over bar have been constructed. It is shown that most atoms have dodecahedral local coordination. The structural features of the crystals studied have been analyzed. It is found that displacements of atoms from ideal positions in real crystals tend to increase with an increase in the distance to the center of the approximant projection on the perpendicular space. Large displacements are generally related to the presence of very close neighbors in the ideal structure of the approximant. The importance of the investigation of approximants as a source of information about the structure of polyatomic nanoclusters is indicated.

Update: 21-Dec-2007

Title:
Structural characterization and stress-relaxation behavior of superlattice Cu5Zr
Authors:
Kim, KH; Ahn, JP; Kim, YM; Lee, BJ; Lee, JC Author Full Names: Kim, Kyou-Hyun; Ahn, Jae-Pyoung; Kim, Young-Min; Lee, Byeong-Joo; Lee, Jae-Chul
Source:
SCRIPTA MATERIALIA 58 (1): 5-8 JAN 2008
Abstract:
A self-organized superlattice containing modulated layers in Cu5Zr was manufactured by casting a Cu-Zr system. Substitutional Zr atoms caused compressive stress in the superlattice so that periodic stress fields were formed with a long-range order along the (110) directions on {111} for stress relaxation. On the other hand, it was demonstrated theoretically by atomistic simulations that a superlattice could form easily due to the large negative enthalpy of formation in the structure (-12.890 kJ/mol of atoms). (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Field-induced paramagnons at the metamagnetic transition of Ca1.8Sr0.2RuO4
Authors:
Steffens, P; Sidis, Y; Link, P; Schmalzl, K; Nakatsuji, S; Maeno, Y; Braden, M Author Full Names: Steffens, P.; Sidis, Y.; Link, P.; Schmalzl, K.; Nakatsuji, S.; Maeno, Y.; Braden, M.
Source:
PHYSICAL REVIEW LETTERS 99 (21): Art. No. 217402 NOV 23 2007
Abstract:
The magnetic excitations in Ca1.8Sr0.2RuO4 were studied across the metamagnetic transition and as a function of temperature using inelastic neutron scattering. At low temperature and low magnetic field the magnetic response is dominated by a complex superposition of incommensurate antiferromagnetic fluctuations. Upon increasing the magnetic field across the metamagnetic transition, paramagnon and finally well-defined magnon scattering is induced, partially suppressing the incommensurate signals. The high-field phase in Ca1.8Sr0.2RuO4, therefore, has to be considered as an intrinsically ferromagnetic state stabilized by the magnetic field.
Title:
Energy-based structure prediction for d(Al70Co20Ni10)
Authors:
Gu, N; Mihalkovic, M; Henley, CL Author Full Names: Gu, N.; Mihalkovic, M.; Henley, C. L.
Source:
PHILOSOPHICAL MAGAZINE LETTERS 87 (12): 923-933 2007
Abstract:
We use energy minimization principles to predict the structure of a decagonal quasicrystal - d(AlCoNi) - in the cobalt-rich phase. Monte Carlo methods are then used to explore configurations while relaxation and molecular dynamics are used to obtain a more realistic structure once a low-energy configuration has been found. We find five-fold symmetric decagons 12.8 angstrom in diameter as the characteristic formation of this composition, along with smaller pseudo-five-fold symmetric clusters filling the spaces between the decagons. We use our method to make comparisons with a recent experimental approximant structure model from Sugiyama et al.
Title:
Thermal stability of decagonal quasicrystal prepared from undercooled Al72Ni12Co16 alloy melt
Authors:
Liu, XB; Osawa, Y; Takamori, S; Yang, GC Author Full Names: Liu, Xinbao; Osawa, Yoshiaki; Takamori, Susumu; Yang, Gencang
Source:
MATERIALS LETTERS 61 (29): 5164-5168 DEC 2007
Abstract:
The thermal stability of the single-phase decagonal quasicrystal produced directly from the undercooled Al72Ni12CO16 alloy melt was investigated by different heat treatments. The optical microscopy, TEM, X-ray powder diffractometer (XRD) and differential thermal analyzer (DTA) techniques were adopted to observe the microstructure and to characterize the phase composition, respectively. Based on the analyses of the X-ray diffraction patterns and the DTA curves, two modifications of the decagonal quasicrystal existed in the annealed samples, which have a close structural relationship to the decagonal quasicrystal. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Magnetic properties and magnetic structures of CU3(OD)(4)XO4, X = Se or S: Cycloidal versus collinear antiferromagnetic structure
Authors:
Vilminot, S; Andre, G; Bouree-Vigneron, F; Richard-Plouet, M; Kurmoo, M Author Full Names: Vilminot, Serge; Andre, Gilles; Bouree-Vigneron, Francoise; Richard-Plouet, Mireille; Kurmoo, Mohamedally
Source:
INORGANIC CHEMISTRY 46 (24): 10079-10086 NOV 26 2007
Abstract:
We report a comparative study of the magnetic properties of synthetic Cu-3(OH)(4)(SO4)(x)(SeO4)(1-x) and the magnetic structures of the parent compounds. All compounds are isostructural and belong to the orthorhombic class of parent compounds. They consist of 3-legged ribbons of edge-sharing copper octahedra connected by mu(3)-OH and XO4 (X = S or Se). XO4 acts both as one-atom and three-atom bridges to connect seven Cu atoms (six Cu(2) and one Cu(1)) belonging to three neighboring ribbons. The two end members behave as low-dimensional AF with a long-range antiferromagnetic state below 5 (X = S) and 8 K (X = Se); the former shows evidence of a canting. Analyses of the neutron powder diffraction data for X = S were shown to display an ordered magnetic state (k = 0 0 0) where the moments of Cu(2) within the two outer legs are collinear and parallel within each leg but antiparallel from each other; the orientation of the moments of Cu(2) is the c axis, In contrast, for X = Se k = similar to 1/7 0 0 and the magnetic structure is cycloidal and transforms progressively from being incommensurate (T > 3 K) to commensurate (T <= 3 K). The moments of Cu(2) of each leg are oriented antiparallel as for X = S, but they rotate about the b axis while propagating along the a axis. In both cases the moments of Cu(1) of the inner leg remain random, The magnetic entropy of 15.2 +/- 1 J/kmol for the end members, estimated from integrating the heat capacity/temperature, is close to that expected (3R In 2) for three Cu2+ (S = 1/2).

Update: 15-Dec-2007

Title:
Study on solidification process, microstructures and the primary phase of peritectic reaction of Mg70Zn28Y2 alloy
Authors:
Wan, D; Yang, G; Zhu, M; Cheng, S; Zhou, Y Author Full Names: Wan Diqing; Yang Gencang; Zhu Man; Cheng Suling; Zhou Yaohe
Source:
RARE METAL MATERIALS AND ENGINEERING 36 (10): 1732-1735 OCT 2007
Abstract:
Adopting XRD, SEM, EDX, TEM, DTA and quenching techniques, an investigation on the solidification of Mg70Zn28Y2 quasicrystal alloy was carried out. The microstructure of as-solidified Mg70Zn28Y2 alloy consists of alpha-Mg dendrite, Mg7Zn3 phase and petal-like icosahedral quasicrystal phase. The equilibrium shape of quasicrystal in as-solidified Mg70Zn28Y2 alloy is of icosahedron. The peritectic reaction occurs in Mg70Zn28Y2 alloy solidification sequence, in which DTA analysis shows that the primary phase of peritectic reaction forms at 563 degrees C and then icosahedral quasicrystal phase forms at 416 degrees C. EDX analysis shows that the approximation composition of the primary phase precipitated before peritectic reaction is Mg22.94Zn55.73Y21.33. The, primary phase of peritectic reaction remained through quench process shows coarse dendrite shape, but its size is relatively small according to BSD image.
Title:
Non-resonant and resonant x-ray scattering studies on multiferroic TbMn2O5
Authors:
Koo, J; Song, C; Ji, S; Lee, JS; Park, J; Jang, TH; Yang, CH; Park, JH; Lee, KB; Koo, TY; Park, YJ; Kim, JY; Wermeille, D; Goldman, AI; Srajer, G; Park, S; Cheong, SW Author Full Names: Koo, J.; Song, C.; Ji, S.; Lee, J. -S.; Park, J.; Jang, T. -H.; Yang, C. -H.; Park, J. -H.; Lee, K. -B.; Koo, T. Y.; Park, Y. J.; Kim, J. -Y.; Wermeille, D.; Goldman, A. I.; Srajer, G.; Park, S.; Cheong, S. -W.
Source:
PHYSICAL REVIEW LETTERS 99 (19): Art. No. 197601 NOV 9 2007
Abstract:
Comprehensive x-ray scattering studies, including resonant scattering at Mn L, Tb L, and M edges, were performed on single crystals of TbMn2O5 for crystallographic data to elucidate the nature of its commensurate and incommensurate phases. The scattering results provide direct evidence of symmetry lowering to the ferroelectric phase driven by magnetically induced lattice modulations and show the presence of multiple magnetic orders. The competing orders under spin-frustrated geometry are believed to cause discommensuration and result in the commensurate-to-incommensurate phase transition around 24 K. It is proposed that the low temperature incommensurate phase consists of commensurate domains separated by antiphase domain walls which change both signs of spontaneous polarizations and x-ray scattering amplitudes for forbidden reflections.
Title:
Intergrowth and thermoelectric properties in the Bi-Ca-Co-O system
Authors:
Luo, XG; Jing, YC; Chen, H; Chen, XH Author Full Names: Luo, X. G.; Jing, Y. C.; Chen, H.; Chen, X. H.
Source:
JOURNAL OF CRYSTAL GROWTH 308 (2): 309-313 OCT 15 2007
Abstract:
Single crystals of the Bi-Ca-Co-O system have been grown using the flux method with cooling from 900 and 950 degrees C, respectively. The single crystals are characterized by transmission electron microscopy and X-ray diffraction. The misfit cobaltite [Ca2Bi1.4CO0.6O4](RS)[CoO2](1.69) single crystals with quadruple (n = 4) rocksalt (RS) layer are achieved with cooling from 900 degrees C. Such a crystal exhibits room-temperature thermoelectric power (TEP) of 180 mu V/K, much larger than that in Sr-based misfit cobaltites with quadruple RS layer. However, intergrowth of single crystals of quadruple (n = 4) and triple (n = 3) RS-type layer-based misfit cobaltites is observed with cooling from 950 degrees C. Both of TEP and resistivity were obviously enhanced by the intergrowth compared to [Ca2Bi1.4CO0.6O4](RS)[CoO2](1.69) single crystal, while the power factor at room temperature remains unchanged. (C) 2007 Published by Elsevier B.V.
Title:
Microstrain-like diffraction-line broadening as exhibited by incommensurate phases in powder diffraction patterns
Authors:
Leineweber, A; Petricek, V Author Full Names: Leineweber, Andreas; Petricek, Vaclav
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 40: 1027-1034 Part 6 DEC 2007
Abstract:
Variations of lattice and modulation parameters of an incommensurately modulated phase as well as the resulting line broadening arising in powder diffraction patterns were theoretically analysed. The resulting line broadening is in principle microstrain-like. For the case that only the modulation parameters vary, only the satellite reflections are broadened, and for constant-order satellite reflections, the line broadening can then be regarded as size-like.

Update: 7-Dec-2007

Title:
Structural studies of a Ti-Zr-Ni quasicrystal-forming liquid
Authors:
Kim, TH; Lee, GW; Gangopadhyay, AK; Hyers, RW; Rogers, JR; Goldman, AI; Kelton, KF Author Full Names: Kim, T. H.; Lee, G. W.; Gangopadhyay, A. K.; Hyers, R. W.; Rogers, J. R.; Goldman, A. I.; Kelton, K. F.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (45): Art. No. 455212 NOV 14 2007
Abstract:
Employing the technique of electrostatic levitation coupled with high-energy x-ray diffraction, Ti39.5Zr39.5Ni21 liquids were shown previously to develop significant short-range icosahedral order with supercooling. However, that conclusion was based on the assumption of a single dominant cluster type in the liquid and the observed evolution of the high-q shoulder on the second peak in the structure factor, S(q). Here, new diffraction data that were obtained using more rapid data acquisition methods are presented. These allow structural studies to be made down to and through recalescence to the icosahedral quasicrystal. The liquid structures obtained from a Reverse Monte Carlo analysis of these data are characterized by their bond-angle distributions, Honeycutt and Andersen indices and bond orientational order parameters. These analyses indicate that while there are several different types of local order, the icosahedral short-range order is dominant and increases gradually with supercooling.
Title:
Atomic short-range order in an Al72Ni18Fe10 decagonal quasicrystal studied by anomalous x-ray scattering
Authors:
Abe, H; Yamamoto, K; Matsuoka, S; Matsuo, Y Author Full Names: Abe, Hiroshi; Yamamoto, Kazuki; Matsuoka, Sayuri; Matsuo, Yoshie
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (46): Art. No. 466201 NOV 21 2007
Abstract:
Diffuse scattering around Bragg reflections was observed by anomalous x-ray scattering in a single decagonal quasicrystal of Al72Ni18Fe10. Intensity modulations of the diffuse scattering were measured for four incident x-ray beam energies. Quantitative analysis of the diffuse scattering data shows the presence of atomic short-range order ( SRO) in three kinds of pair-correlation functions: Al-Ni, Ni-Fe and Fe-Al. The SRO diffuse scattering is decomposed into each component by self-consistent calculation. Using Metropolis Monte Carlo simulations, the SRO diffuse scattering is calculated qualitatively using the SRO parameters. Asymmetric distributions of the diffuse scattering were seen along a longitudinal direction, even though the Al72Ni18Fe10 quasicrystal has quite small mosaicity.
Title:
Magnetic structure of Tm5Rh4Ge10
Authors:
Penc, B; Wawrzynska, E; Keller, L; Szytula, A Author Full Names: Penc, B.; Wawrzynska, E.; Keller, L.; Szytula, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 320 (1-2): L1-L4 JAN 2008
Abstract:
Neutron diffraction pattern recorded in the paramagnetic state confirmed that Tm5Rh4Ge10 exhibits tetragonal crystal structure of the Sc5Co4Si10 type. The Tb magnetic moments order below the Neel temperature of 6.9 K and form a sine-wave-modulated structure described by the propagation vector k = (k(x), k(x), 0). The value of k(x) changes from 0.216(1) at 1.5 K to 0.202(1) at 6.5 K. The T-m moments at three nonequivalent atomic positions are different but all are parallel to the c-axis. (C) 2007 Elsevier B.V. All rights reserved.

Update: 23-Nov-2007

Title:
Optical whispering gallery modes in dodecagonal zinc oxide microcrystals
Authors:
Nobis, T; Rahm, A; Czekalla, C; Lorenz, M; Grundmann, M Author Full Names: Nobis, Thomas; Rahm, Andreas; Czekalla, Christian; Lorenz, Michael; Grundmann, Marius
Source:
SUPERLATTICES AND MICROSTRUCTURES 42 (1-6): 333-336 JUL-DEC 2007
Abstract:
We have investigated optical modes in zinc oxide micropillars with dodecagonal cross section using polarization-resolved microphotoluminescence spectroscopy. Luminescence spectra of such pillars show series of resonance lines with characteristic line widths and spacings. The spectral positions of the observed lines can be explained assuming a circular two-dimensional dielectric resonator. Lowest radial mode numbers (n = 1, 2) indicate optical whispering gallery modes. (c) 2007 Elsevier Ltd. All rights reserved.
Title:
Dielectric anomalies in (BaxSr1-x)(4)Nd2Ti4Nb6O30 ceramics with various radius differences between A1-and A2-site ions
Authors:
Zhu, XL; Wu, SY; Chen, XM Author Full Names: Zhu, X. L.; Wu, S. Y.; Chen, X. M.
Source:
APPLIED PHYSICS LETTERS 91 (16): Art. No. 162906 OCT 15 2007
Abstract:
Dielectric response of tetragonal tungsten bronze dielectrics (BaxSr1-x) 4Nd2Ti4Nb6O30 was investigated over a broad temperature and frequency range, and the obvious composition- dependent dielectric anomalies with respect to x value were discussed in detail in association with the radius differences between A1- and A2- site ions. With decreasing the magnitude of radius difference between A1- and A2- site ions, the normal ferroelectric peak above 400 K became weaker, and two relaxor peaks at lower temperatures became obvious. The low- and high-temperature relaxor behaviors, which followed well the Vogel- Fulcher relationship, were associated with the polar clusters caused by the off-center Nb/Ti displacements and the incommensurate tilting modulation, respectively. (C) 2007 American Institute of Physics.

Update: 16-Nov-2007

Title:
Study of the electronic properties of a double-chain model for Al-rich-transition-metal quasicrystals, amorphous, and crystalline phases
Authors:
Landauro, CV; Janssen, T Author Full Names: Landauro, C. V.; Janssen, T.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 353 (32-40): 3192-3195 OCT 15 2007
Abstract:
The electronic properties of quasicrystals containing transition-metals are studied employing a simple double-chain model within the tight-binding approximation. We show that, under determined conditions, spectral fine structures are the result of competing localized-and extended-like states, which are not observed in traditional one-dimensional aperiodic models. These spectral features can explain the experimentally observed transport properties. From this point of view this double-chain model mimics the behavior of electrons in realistic icosahedral quasicrystals. Moreover, in view of the electronic transport, the relationsip between quasicrystals and related amorphous phases is explained in a natural way. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Electronic transport properties of amorphous and quasicrystals TMxAl100-x alloys
Authors:
Barzola-Quiquia, J; Haussler, P Author Full Names: Barzola-Quiquia, J.; Haeussler, P.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 353 (32-40): 3237-3242 OCT 15 2007
Abstract:
The electrical resistivity p(T) and the thermopower S(T), of amorphous films of (Mn,Fe)(x)Al100-x (15 <= x <= 50), as well Al-70.5 Pd21Mn8.5 and Al62.5CU25Fe12.5 have been measured in the temperature range between 5 K and 350 K. The amorphous films were prepared in situ by the sequential flash-evaporation technique at low temperature (T approximate to 10 K) and the quasicrystalline phases were obtained after annealing the samples to 900 K. The resistivity as well as the thermopower both show dependences on the TM-content and a pronounced non-metallic behaviour versus temperature. This behaviour can be explained in the frame of electronic stabilized amorphous systems, very similar to a Peierls effect in 1D-systems or Hume-Rothery alloys, where hybridisation effects of Al-(p), with TM-(d) electrons play an important rule. The electronic stabilization explanation is supported by resistivity and thermopower measurements, together with measurements of the static structure factor and the crystallisation behaviour of the amorphous samples. Finally, the resistivity and the thermopower both are fit to a model based on LMTO calculations, developed for TM-Al quasicrystalline materials, and supplies our description of the electronic density of states around the Fermi energy. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Formation of quasicrystals and metallic glasses in relation to icosahedral clusters
Authors:
Dong, C; Chen, WR; Wang, YG; Qiang, JB; Wang, Q; Lei, Y; Calvo-Dahlborg, M; Dubois, JM Author Full Names: Dong, Chuang; Chen, Weirong; Wang, Yingrain; Qiang, Jianbing; Wang, Qing; Lei, Yi; Calvo-Dahlborg, Monique; Dubois, Jean-Marie
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 353 (32-40): 3405-3411 OCT 15 2007
Abstract:
It has been widely accepted that quasicrystals and at least some metallic glasses are built up with icosahedral clusters. Information about the cluster structures can be obtained from crystalline counterparts. In this paper, we will describe the formation rules of bulk metallic glasses, originally developed for quasicrystals, by combining cluster structures with phase diagram features. We will introduce the e/a-constant and e/a-variant criteria for ternary systems, and e/a-constant and atomic size constant criteria for quaternary systems. We will show how the glass forming composition optimization is realized by applying these rules in the Zr-Al-Ni and Zr-Al-Ni-Cu systems. In both systems the optimized glass-forming composition is related to a common binary icosahedral cluster Zr9Ni4 derived from the fcc Zr2Ni phase. A novel route to reach amorphous forming composition is also attempted by mixing Al-based quasicrystal-forming compositions with Zr. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Formation of icosahedral quasicrystals in (Ag,Au)-based ternary systems
Authors:
Tamura, R; Katahoka, A; Nishimoto, K; Takeuchi, S Author Full Names: Tamura, R.; Katahoka, A.; Nishimoto, K.; Takeuchi, S.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 353 (32-40): 3412-3416 OCT 15 2007
Abstract:
We investigated the phase constitution of rapidly solidified (Ag,Au)-based ternary alloys at various compositions Of (M,X)(85.7)RE14.3 (M = Ag, Au, X = Al,Ga,In, RE = Er,Lu). It is found that an icosahedral phase is formed at an average electrons per atom ratio close to 2.0 as well as at the composition ratio Of (M,X)(6)RE, suggesting that these factors have crucial roles in the stability of the icosahedral phases. It is also found that the trend of the icosahedral phase formation in the Au-based alloys is quite different from that in the Ag-based alloys. (c) 2007 Published by Elsevier B.V.
Title:
Synthesis of single-phase Al-Cu-Fe quasicrystals using high-energy ball-milling
Authors:
Turquier, F; Coiocaru, VD; Stir, M; Nicula, R; Burkel, E Author Full Names: Turquier, F.; Coiocaru, V. D.; Stir, M.; Nicula, R.; Burkel, E.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 353 (32-40): 3417-3420 OCT 15 2007
Abstract:
Due to their unique combination of physical, thermal and mechanical properties, aluminium-based quasicrystals are of great interest for many applications such as low friction hard coatings. Nevertheless, as quasicrystalline phases are usually stable only within narrow composition domains, their production on an industrial scale meets some difficulties. Alloys with nominal composition Al67CU23Fe10 were prepared by high-energy ball-milling of elemental powders. The as-milled powder specimens consist of a nanocrystalline Al(Cu,Fe) solid solution. The structural phase transitions of the ball-milled Al-Cu-Fe nanopowders during constant rate heating were investigated by in situ X-ray diffraction at the B2 beamline at desy-hasylab (Hamburg, Germany). High-quality single-phase quasicrystalline (QC) powders were obtained from nanocrystalline precursors by slow heating to temperatures above 750 degrees C. The QC phase is preserved upon quenching and is stable during subsequent heating runs up to 800 degrees C. (c) 2007 Published by Elsevier B.V.
Title:
Amorphous and quasicrystalline Ti-Ni-Zr powders synthesized by mechanical alloying
Authors:
Zhernovenkova, YV; Sviridova, TA; Tcherdyntsev, VV; Kaloshkin, SD; Pomadchik, AL Author Full Names: Zhernovenkova, Yu. V.; Sviridova, T. A.; Tcherdyntsev, V. V.; Kaloshkin, S. D.; Pomadchik, A. L.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 353 (32-40): 3429-3433 OCT 15 2007
Abstract:
The formation of amorphous and quasicrystalline phases in the Ti45Zr38Ni17 system both directly by mechanical alloying and after subsequent annealing was studied. The presence of amorphous, icosahedral quasicrystalline and the Ti2Ni-type with a fee structure phases together with the initial metallic components was found in as-milled samples by X-ray diffraction. An increase of the milling time results in an increase of the amorphous phase content. Icosahedral quasicrystalline phases of Ti-Ni-Zr system were produced by mechanical alloying and subsequent annealing. Differential scanning calorimetry studies up to 520 degrees C showed an extended exothermal effect starting from 300 degrees C, which corresponds to the crystallization of the as-milled samples. The shape and size of the particles of the alloys were investigated by scanning electron microscopy and argon adsorption. The Specific area surface of the as-milled sample was rather small, in agreement with scanning electron microscopy data. The kinetics of the hydrogenation of the amorphous alloy Ti45Zr38Ni17 at different temperatures was studied. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Atomic structure and hydrogen storage properties of amorphous-quasicrystalline Zr-Cu-Ni-Al melt-spun ribbons
Authors:
Rud, AD; Schmidt, U; Zefinska, GM; Lalkhnik, AM; Kolbasov, GY; Danilov, MO Author Full Names: Rud, A. D.; Schmidt, U.; Zefinska, G. M.; Lalkhnik, A. M.; Kolbasov, G. Ya.; Danilov, M. O.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 353 (32-40): 3434-3438 OCT 15 2007
Abstract:
A structural state of the Zr-Cu-Ni-Al melt-spun ribbons has been investigated by means of X-ray diffraction analysis. It was established that conditions of ribbon production have a very strong effect on their structural state. The Zr69.3Cu9.7Ni15.1Al5.9 ribbons produced at the surface wheel velocity of 44 m/s have an amorphous state at the contact side and mixed amorphous-quasicrystalline state at the free side. At the same time the Zr67.5Cu12.5Ni12Al8 ribbons are fully amorphous in case of producing velocity of 44 m/s and have only small features of quasicrystalline peaks on the amorphous halo on the free side in case of producing velocity of 30 m/s in contrast to an amorphous structure on the contact side. The uncoated by Pd amorphous and amorphous-quasicrystalline Zr-Cu-Ni-Al ribbons have a property of absorbing a large amount of hydrogen. Parameters of the amorphous state were calculated for the ribbons as-prepared and hydrogenated. The temperature coefficient of resistivity for all ribbons is negative in range of 20-380 degrees C, what as well as the high resistivity values is typical to the Zr-Cu-Ni-Al based systems in amorphous and quasicrystalline states. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Metastable phase formation in rapidly quenched Zr80Pt20 alloys: Linkage to oxygen
Authors:
Sordelet, D; Yang, XY; Rozhkova, E; Besser, M; Kramer, M Author Full Names: Sordelet, Daniel; Yang, Xiaoyun; Rozhkova, Elena; Besser, Matthew; Kramer, Matthew
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 353 (32-40): 3439-3443 OCT 15 2007
Abstract:
Melt spun Zr80Pt20 ribbons having oxygen contents ranging from < 200 to approximate to 5000 mass ppm are shown to form various metastable phases during quenching. In the presence of sufficient oxygen, a big cube Zr6Pt3O phase forms, but this structure is de-stabilized towards an icosahedral quasicrystalline structure at lower oxygen levels. Further reduction of oxygen promotes increasingly stable Zr-Pt bonds, and a metastable beta-Zr(Pt) structure is formed. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Icosahedral ordering in Ti-Hf-Ni alloys?
Authors:
Sadoc, A; Huett, VT; Kelton, KF Author Full Names: Sadoc, Anne; Huett, V. T.; Kelton, K. F.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 353 (32-40): 3689-3692 OCT 15 2007
Abstract:
The local atomic structure of crystalline and amorphous Ti-Hf-Ni alloys has been probed by EXAFS. The local order is similar in the crystalline Ti-Hf-Ni alloy and in Ti-Zr-Ni crystalline and quasicrystalline phases, where icosahedral ordering exists around some nickel sites. The local atomic structure is different in the amorphous Ti-Hf-Ni alloys, in particular around the nickel atoms, where a new icosahedral atomic configuration that is similar to that in the Ti2Ni crystal phase is identified. (c) 2007 Elsevier B.V. All rights reserved.

Update: 9-Nov-2007

Title:
Preparation, characterization and crystal structure of the room temperature phase of [(CH3)(C6H5)(3)P](2)[ZnBr4]: A member of the A(2)BX(4) family
Authors:
Mostafa, MF; Youssef, AA; El-Dean, TS; Mostafa, AM; Farag, IS Author Full Names: Mostafa, Mohga F.; Youssef, Ahmed A.; El-Dean, Thanaa S.; Mostafa, Aisha M.; Farag, Ibrahim S.
Source:
ZEITSCHRIFT FUR NATURFORSCHUNG SECTION A-A JOURNAL OF PHYSICAL SCIENCES 62 (9): 549-554 SEP 2007
Abstract:
The compound bis(methyltriphenylphosphonium) tetrabromozincate(II), [C19H18P](2)[ZnBr4], M-r = 939.640, has a monoclinic unit cell, space group P2(1). The lattice parameters are a = 9.7693(4) angstrom, b = 12.5508(4) angstrom, c = 16.5372(6) angstrom, alpha = 90.00 degrees, beta = 105.2670(11)degrees, gamma = 90.00 degrees, V = 1956.11(11) angstrom(3), Z = 2, D-x = 1.595 mg m(-3) at T = 298 K. The structure consists of one distorted [ZnBr4](2-) tetrahedron and two [(CH3)(C6H5)(3)P](+) cations. Differential scanning calorimetry indicates a continuous second-order transition at (276 +/- 2) K that may be classified as a commensurate to incommensurate transformation. A first-order transition to a higher symmetry is associated with a four-fold rotation of the [ZnBr4](2-) ion and a change of entropy Delta S = 22.92 J/(K center dot mol) at T = (362 +/- 3) K. Dilatometric measurements showed a decrease of the lattice parameters in the temperature range 230-260 K, confirmed the transition at (276 +/- 2) K, and indicated the presence of a third transition at 282 K.
Title:
Field induced magnetic phase transition as a magnon Bose Einstein condensation
Authors:
Radu, T; Tokiwa, Y; Coldea, R; Gegenwart, P; Tylczynski, Z; Steglich, F Author Full Names: Radu, Teodora; Tokiwa, Yoshifurni; Coldea, Radu; Gegenwart, Philipp; Tylczynski, Z.; Steglich, Frank
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 8 (5): 406-409 JUL 2007
Abstract:
We report specific heat, magnetocaloric effect and magnetization measurements on single crystals of the frustrated quasi-2D spin -1/2 antiferromagnet CS2CUCl4 in the external magnetic field 0 <= B <= 12T along a-axis and in the temperature range 0.03K <= T <= 6K. Decreasing the applied magnetic field B from high fields leads to the closure of the field induced gap in the magnon spectrum at a critical field B-c similar or equal to 8.44T and a long-range incommensurate state below Bc. In the vicinity of Bc, the phase transition boundary is well described by the power law TN-(B, - B)1 0 with the measured critical exponent phi similar or equal to 1.5. These findings provide experimental evidence that the scaling law of the transition temperature T-N can be described by the universality class of 3D Bose-Einstein condensation (BEC) of magnons. (c) 2007 NIMS and Elsevier Ltd. All rights reserved.
Title:
Free energy calculation of quasicrystal phase Al6CuMg4 under electric field
Authors:
Zhang, J; Wang, Y; Chen, Z; Liu, B Author Full Names: Zhang Jianjun; Wang Yongxin; Chen Zheng; Liu Bing
Source:
RARE METAL MATERIALS AND ENGINEERING 36 (9): 1578-1583 SEP 2007
Abstract:
Based on Thomas-Fermi model, the change trend of free energy and Gibbs free energy of quasicrystal Al6CuMg4 against Al-Cu-Mg solid solution and compound Al2CuMg were calculated systematically and quantitatively. The main conclusion was following: free energy and Gibbs free energy of quasicrystal phase Al6CuMg4, Al2CuMg and Al-Cu-Mg solid solution increased with increasing of electric field. The effect of positive electric field was more intensive than the negative electric field, but their different was not big. The change trend of free energy and Gibbs free energy of quasicrystal Al6CuMg4 with the electric field was more sensitive than that of solid solution. With increasing of electric field, the differences of free energy and Gibbs free energy between Al6CuMg4 and solid solution increased quickly. The instability of quasicrytal increased under electric field. The stability of Al2CuMg under electric field was obviously higher than that of Al6CuMg4. For Al-Cu-Mg solid solution, the sensitivity increased with increasing of the Mg content, but the amplitude was far lower than those of the compound and quasicrystal.
Title:
Competition of charge-density waves and superconductivity in sulfur
Authors:
Degtyareva, O; Magnitskaya, MV; Kohanoff, J; Profeta, G; Scandolo, S; Hanfland, M; McMahon, MI; Gregoryanz, E Author Full Names: Degtyareva, O.; Magnitskaya, M. V.; Kohanoff, J.; Profeta, G.; Scandolo, S.; Hanfland, M.; McMahon, M. I.; Gregoryanz, E.
Source:
PHYSICAL REVIEW LETTERS 99 (15): Art. No. 155505 OCT 12 2007
Abstract:
A one-dimensional charge-density wave (CDW) instability is shown to be responsible for the formation of the incommensurate modulation of the atomic lattice in the high-pressure phase of sulfur. The coexistence of, and competition between, the CDW and the superconducting state leads to the previously observed increase of T-c up to 17 K, which we attribute to the suppression of the CDW instability, the same phenomenology found in doped layered dichalcogenides.
Title:
Magnetic interactions in the geometrically frustrated triangular lattice antiferromagnet CuFeO2
Authors:
Ye, F; Fernandez-Baca, JA; Fishman, RS; Ren, Y; Kang, HJ; Qiu, Y; Kimura, T Author Full Names: Ye, F.; Fernandez-Baca, J. A.; Fishman, R. S.; Ren, Y.; Kang, H. J.; Qiu, Y.; Kimura, T.
Source:
PHYSICAL REVIEW LETTERS 99 (15): Art. No. 157201 OCT 12 2007
Abstract:
The spin-wave excitations of the geometrically frustrated triangular lattice antiferromagnet CuFeO2 have been measured using high resolution inelastic neutron scattering. Antiferromagnetic interactions up to third nearest neighbors in the ab plane (J(1), J(2), J(3), with J(2)/J(1)approximate to 0.44 and J(3)/J(1)approximate to 0.57), as well as out-of-plane coupling (J(z), with J(z)/J(1)approximate to 0.29) are required to describe the spin-wave dispersion relations, indicating a three-dimensional character of the magnetic interactions. Two energy dips in the spin-wave dispersion occur at the incommensurate wave vectors associated with multiferroic phase and can be interpreted as dynamic precursors to the magnetoelectric behavior in this system.
Title:
The broken-symmetry phase of solid hydrogen: evidence from infrared and Raman active vibrons
Authors:
Zhang, LJ; Niu, YL; Cui, T; Li, Y; Ma, YM; He, Z; Zou, GT Author Full Names: Zhang, L. J.; Niu, Y. L.; Cui, T.; Li, Y.; Ma, Y. M.; He, Z.; Zou, G. T.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (42): Art. No. 425237 OCT 24 2007
Abstract:
The infrared (IR) and Raman-active vibrons (intramolecular stretching modes) of solid hydrogen in the broken-symmetry phase (phase II) are extensively studied using density-functional linear-response theory. We performed a group-theoretical analysis of allowed IR and Raman vibrons for proposed candidate structures to aid in determining the structure of phase II. From a comparison of the calculated intensities and frequencies of IR and Raman vibrons with available experimental results, some structures have been excluded. The current theory indicated that phase II of solid hydrogen might have the recently suggested incommensurate structure with Pa3-type local orientational order for solid deuterium, and that the energetically preferred P2(1)/c structure is also a better candidate.
Title:
Hydrogen absorption in Ti45Zr35Ni17Cu3 amorphous and quasicrystalline alloy powders
Authors:
Liu, BZ; Liu, DM; Wua, YM; Li, LQ; Wang, LM Author Full Names: Liu, Baozhong; Liu, Dongming; Wua, Yaoming; Li, Liquan; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 32 (13): 2429-2433 SEP 2007
Abstract:
Ti45Zr35Ni17Cu3 amorphous and icosahedral quasicrystal line (I-phase) powders were synthesized by mechanical alloying (MA) and subsequent annealing, the phase structure and hydrogen absorption properties of two powders were investigated. XRD analysis indicated that the MAed powder was an amorphous phase and annealed powder was an I-phase. Two alloy exhibited excellent hydrogen adsorption property and started to absorb hydrogen without induction time. PCT measurement showed that the plateau pressure of the amorphous powders was obviously higher than that of the I-phase powders. After the first hydrogen cycling, the partial amorphous phase changed to (Zr, Ti)H-2 phases, and the I-phase was steady. Similar hydride phases Ti2ZrH4 and (Zr, Ti)H-2 were also formed after the second hydrogen cycling for the amorphous and I-phase alloy powders. (C) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Title:
The piezoelectric effect of second order in stress or strain: its form for crystals and quasicrystals of any symmetry
Authors:
Grimmer, H Author Full Names: Grimmer, Hans
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 63: 441-446 Part 6 NOV 2007
Abstract:
The restrictions on the coefficients describing physical effects depend on the orientation of the symmetry elements of the crystal or quasicrystal with respect to the Cartesian coordinate system employed. They are given for the piezoelectric effect of second order in stress or strain for all the orientations that can be expressed by the sequence of elements in the Hermann-Mauguin symbol of the point group. In the literature, the restrictions are usually given only for a particular orientation, which sometimes is not specified.

Update: 2-Nov-2007

Title:
Dispersive collective charge modes in an incommensurately modulated cuprate Mott insulator
Authors:
Wray, L; Qian, D; Hsieh, D; Xia, Y; Eisaki, H; Hasan, MZ Author Full Names: Wray, L.; Qian, D.; Hsieh, D.; Xia, Y.; Eisaki, H.; Hasan, M. Z.
Source:
PHYSICAL REVIEW B 76 (10): Art. No. 100507 SEP 2007
Abstract:
We report measurement of collective charge modes of insulating Sr14Cu24O41 using inelastic resonant x-ray scattering over the complete Brillouin zone. Our results show that the intense excitation modes at the charge gap edge predominantly originate from ladder-containing planar substructures. The observed modes are found to be dispersive for momentum transfers along the "legs" (hQ parallel to c) but nearly localized along the "rungs" (hQ parallel to a). We show that the dispersion and peak width characteristics of the modes can be understood in the strong-coupling quantum limit (Hubbard U > t(ladder)>t(chain), where t is the hopping parameter). Quite generally, we demonstrate that the momentum tunability (Q resolution) of inelastic x-ray scattering can be utilized to resolve mode contributions in multicomponent incommensurate quantum electron systems.
Title:
Ab initio studies of solid bromine under high pressure
Authors:
Duan, DF; Liu, YH; Ma, YM; Liu, ZM; Cui, T; Liu, BB; Zou, GT Author Full Names: Duan, Defang; Liu, Yanhui; Ma, Yanming; Liu, Zhiming; Cui, Tian; Liu, Bingbing; Zou, Guangtian
Source:
PHYSICAL REVIEW B 76 (10): Art. No. 104113 SEP 2007
Abstract:
Crystal structures of bromine under high pressure have been studied by employing plane-wave pseudopotential method with the generalized gradient approximation. It is found that the band overlap in the molecular Cmca phase, which causes the pressure-induced insulator-to-metal transition, occurs at about 55 GPa. Geometry optimization shows that the bromine changes to a face-centered orthorhombic (fco) phase with equal interatomic distances d(1)=d(2)=d(3) at about 75 GPa, but this fco structure is mechanically unstable with shear elastic stiffness coefficient C-66 < 0. For understanding the structure of this phase, we have modeled an incommensurate structure by a rational approximation with modulation vector k=(0.25,0,0) according to the previous research results in solid iodine. Our results show that the enthalpy of this modulated phase is lower than that of the fco solid, and the elastic stiffness coefficients (C-ij) satisfy the Born stability criteria, indicating that the modulated structure is more thermodynamically stable and mechanically stable. In addition, through comparing the x-ray diffraction patterns of our structure with the experimental one, we conclude that the structure of bromine phase V is close to our modulated structure. It is clearly illustrated that the phase transition from Cmca phase to the incommensurate phase is associated with the instability of the shear elastic stiffness coefficient C-44 which is related to the softening of the long-wavelength part of the transverse branch near the center of the first Brillouin zone. With the increasing of pressure, the modulated phase transforms into the monatomic phase II with body-centered orthorhombic structure at about 100 GPa, which is in agreement with the experimental result.
Title:
Ferroelectricity in perovskite HoMnO3 and YMnO3
Authors:
Lorenz, B; Wang, YQ; Chu, CW Author Full Names: Lorenz, Bernd; Wang, Ya-Qi; Chu, Ching-Wu
Source:
PHYSICAL REVIEW B 76 (10): Art. No. 104405 SEP 2007
Abstract:
Ferroelectricity is observed in orthorhombic HoMnO3 and YMnO3 at the magnetic lock-in transitions into an E-type structure or an incommensurate phase with a temperature independent wave vector, respectively. In HoMnO3, the ferroelectric polarization strongly depends on the external magnetic field, indicating the involvement of the rare earth moment order in this compound. The results are discussed within the framework of recent theoretical models, in particular, the double exchange driven polar displacements predicted for E-type magnetic structures.
Title:
Formation of a well ordered ultrathin aluminum oxide film on icosahedral AlPdMn quasicrystal
Authors:
Longchamp, JN; Burkardt, S; Erbudak, M; Weisskopf, Y Author Full Names: Longchamp, J.-N.; Burkardt, S.; Erbudak, M.; Weisskopf, Y.
Source:
PHYSICAL REVIEW B 76 (9): Art. No. 094203 SEP 2007
Abstract:
We have exposed the pentagonal surface of icosahedral AlPdMn quasicrystal kept at 700 K to several hundred langmuirs of O-2, which results in the formation of a 5 A thick, well ordered aluminum oxide film. The local structure of the film resembles that of the oxide layers formed on ordered binary alloys of Al except that the quasicrystalline substrate makes the film consist of five pairs of nanometer-size aluminum oxide domains exposing their nominal (111) faces parallel to the substrate surface and rotated by 72 degrees with respect to each other. The orientational relationship between these domains and the substrate is a consequence of the affinity of the icosahedral structure of AlPdMn to the CsCl structure.
Title:
Multiband superconductivity in HoNi2B2C
Authors:
Muller, KH; Fuchs, G; Drechsler, SL; Opahle, I; Eschrig, H; Schultz, L; Behr, G; Loser, W; Souptel, D; Walte, A; Nenkov, K; Naidyuk, Y; Rosner, H Author Full Names: Mueller, Karl-Hartmut; Fuchs, Guenter; Drechsler, Stefan-Ludwig; Opahle, Ingo; Eschrig, Helmut; Schultz, Ludwig; Behr, Guenter; Loeser, Wolfgang; Souptel, Dmitri; Waelte, Andreas; Nenkov, Konstantin; Naidyuk, Yuri; Rosner, Helge
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 460: 99-102 Part 1 SEP 1 2007
Abstract:
HoNi2B2C single crystals prepared by the floating zone method were investigated by resistivity, magnetization, specific heat and point-contact measurements. The coexistence of superconductivity (SC) and antiferromagnetism (AFM) in HoNi2B2C is considered experimentally and theoretically for commensurate (C), incommensurate (IC) and metamagnetic magnetic structures within the multi-band picture of Fermi surface sheets (FSS) obtained within full potential FPLO-LDA calculations. Special attention is paid to the admixture of Ho 5d states which mediate the pair breaking exchange between the Ho 4f derived local moments and the conduction electrons bearing the superconductivity. Within the paramagnetic and the uniform IC spiral phases, anisotropic multiband SC coexists with magnetism. Within the C-phase (below T-N = 5.3 K) single band isotropic SC survives at a single FSS free of Ho 5d states in accord with isotropic standard WHH shaped upper critical fields H-c2(T). The superconducting energy gap obtained from point-contact data was found to disappear at a slightly higher temperature T-center dot = 5.6 K which is also observed in specific heat measurements. Using the experimental values for the energy gap Delta(0) and H-c2(T) at zero temperature, the characteristic phonon frequency, the electron-phonon coupling constant and the Fermi velocity of the residual superconducting phase were estimated from the standard isotropic single band model. (c) 2007 Published by Elsevier B.V.
Title:
STM studies on structural modulation and two-phase microstructures in Pb-doped Bi2201 single crystals
Authors:
Nishizaki, T; Kudo, K; Okumura, N; Kobayashi, N Author Full Names: Nishizaki, Terukazu; Kudo, Kazutaka; Okumura, Naoyuki; Kobayashi, Norio
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 460: 156-157 Part 1 SEP 1 2007
Abstract:
We have performed scanning tunneling microscopy studies on the structural modulation of Bi2.12-xPbxSr1.88CuOy (Pb-x-Bi2201, x = 0.18, 0.27, 0.32, 0.37) single crystals. The observed STM images show the clear atomic arrangement with the four-fold symmetry on the Bi(Pb)-O layer. The wavelength lambda of incommensurate structural modulations along the b-axis increases with Pb content (i.e., lambda similar to 43 angstrom for x = 0.18) and the modulations completely disappear for x similar to 0.37. In the intermediate content (x similar to 0.27, 0.32), we find two-phase microstructures which consist of the modulated region with lambda similar to 46 angstrom and the modulation-free region. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Structural and physical properties of a novel misfit-layered cobalt oxide (CaOH)(1.14)CoO2
Authors:
Isobe, M; Shizuya, M; Takayama-Muromachi, E Author Full Names: Isobe, Masaaki; Shizuya, Mitsuyuki; Takayama-Muromachi, Eiji
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 460: 477-478 Part 1 SEP 1 2007
Abstract:
We have studied crystal structure and physical properties of a new layered cobalt oxide (CaOH)(1.14)CoO2. The compound is a composite crystal which consists of two interpenetrating subsystems of the Cdl(2)-type CoO2 layer and the rock-salt-type double CaOH atomic layer. The two subsystems have incommensurate periodicity along the a-axis, resulting in modulated crystal structure due to the inter-subsystem interaction. We found that the observed physical properties originate in the electronic state with a "low-carrier-density limit" in the cobalt t(2g) band. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Commensurate and incommensurate "5M" modulated crystal structures in Ni-Mn-Ga martensitic phases
Authors:
Righi, L; Albertini, F; Pareti, L; Paoluzi, A; Calestani, G Author Full Names: Righi, L.; Albertini, F.; Pareti, L.; Paoluzi, A.; Calestani, G.
Source:
ACTA MATERIALIA 55 (15): 5237-5245 SEP 2007
Abstract:
It is well known that the composition of ferromagnetic shape memory Ni-Mn-Ga Heusler alloys determines both temperature of martensitic transformations and the structure type of the product phase. In the present work we focused our attention on the structural study of the so-called "5M" modulated structure. In particular, the structure of Ni1.95Mn1.19Ga0.86 martensitic phase is analysed by powder X-ray diffraction (PXRD) and compared with that of the stoichiometric Ni2MnGa martensite. The study of the diffraction data reveals the occurrence of commensurate (C) structural modulation in Ni1.95Mn1.19Ga0.86; this contrasts with Ni2MnGa, where an incommensurate (IQ structural modulation was evident. The two phases also differ in the symmetry of the fundamental martensitic lattice. In fact, the incommensurate modulation is related to an orthorhombic basic structure, while the commensurate variant presents a monoclinic symmetry. The commensurate modulated structure has been investigated by using the superspace approach already adopted to solve the structure of Ni2MnGa martensite. The structure has been determined by Rietveld refinement of PXRD data. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 26-Oct-2007

Title:
Vibrational and electronic characteristics of Zr70Pd30, Zr80Pt20 icosahedral quasicrystals and their amorphous counterparts
Authors:
Panova, GK; Chernoplekov, NA; Shikov, AA; Kemeny, T; Kiss, LF Author Full Names: Panova, G. Kh.; Chernoplekov, N. A.; Shikov, A. A.; Kemeny, T.; Kiss, L. F.
Source:
PHYSICS OF THE SOLID STATE 49 (9): 1617-1622 SEP 2007
Abstract:
The heat capacity of Zr70Pd30 and Zr80Pt20 icosahedral quasicrystals and their amorphous counterparts is studied in the temperature range 1.5-500 K in order to establish a correlation between the short-range atomic order and the physical properties of these compounds. A comparison of the data made it possible to reveal changes in the vibrational spectra within the low-and high-energy ranges, as well as in the density of states, superconducting characteristics, electron-phonon interaction, and anharmonicity of the lattice thermal vibrations and to calculate the main average frequencies (moments) characterizing the vibrational spectra. The lower superconducting transition temperature T (c) of the quasicrystals as compared to that of the amorphous counterparts can be associated with the decrease in the density of states on the Fermi surface, the hardening of the phonon spectrum, and the weakening of the electron-phonon coupling.
Title:
Incommensurate spin modulation in La2-xSrxCuO4 as a consequence of doped hole ordering
Authors:
Misen, K; Ivanenko, O Author Full Names: Misen, Kirill; Ivanenko, Olga
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 460: 1167-1168 Part 2 SEP 1 2007
Abstract:
A model explaining incommensurate spin modulation observed in La2-xSrxCuO4 without assuming stripe formation is proposed. In the frameworks model, all features of the observed spin textures in the entire doping range are associated only with the geometrical relations for the square lattice and with the competition between various forms of doped hole ordering. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Dielectric polarization measurements on the antiferromagnetic triangular lattice system CuFeO2 in pulsed high magnetic fields
Authors:
Mitamura, H; Mitsuda, S; Kanetsuki, S; Katori, HA; Sakakibara, T; Kindo, K Author Full Names: Mitamura, Hiroyuki; Mitsuda, Setsuo; Kanetsuki, Shunsuke; Katori, Hiroko Aruga; Sakakibara, Toshiro; Kindo, Koichi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 (9): Art. No. 094709 SEP 2007
Abstract:
Dielectric polarization parallel to the [110] direction of a single crystal of the triangular lattice antiferromagnet CuFeO2 has been measured by a pyroelectric method in pulsed high magnetic fields up to 43 T applied along the [00 1] direction. No distinct spontaneous dielectric polarization P is detected in the fourth field-induced phase with a noncollinear spin structure and 4-, 5-, and 3-sublattice phases with commensurate collinear spin structures. Among five magnetic phases that appear in magnetic fields, a finite P is observed only in the first field-induced phase with the incommensurate noncollinear spin structure. We also confirmed that P in the first field-induced phase is predominantly oriented within the (001) plane. A strong history dependence has been observed in P, and is interpreted in terms of the alignment and repopulation of magnetic Q-domains. The experimental technique for measuring P in pulsed high magnetic fields is described in detail.

Update: 19-Oct-2007

Title:
Modulated crystal structures and phase transitions - The compounds SrPt2As2 and EuPt2As2
Authors:
Irnre, A; Hellmann, A; Wenski, G; Grap, J; Johrendt, D; Mewis, A Author Full Names: Irnre, Anette; Hellmann, Andrea; Wenski, Guido; Grap, Juergen; Johrendt, Dirk; Mewis, Albrecht
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE 633 (11-12): 2037-2045 2007
Abstract:
The new compounds SrPt2As2 (a = 4.482(1), b = 4.525(1), c = 9.869(2) angstrom) and EuPt2As2 (a = 4.435(2), b = 4.467(2), c = 9.784(3) angstrom) have been prepared by reaction of the elements at 1050 degrees C. Satellite reflections observed in X-ray diffraction experiments on single crystals revealed that both compounds have modulated crystal structures at room temperature. The average structures can be derived from the CaBe2Ge2 type and described in the orthorhombic space group Pnimn (Z = 2) with splitted positions for half the Pt and As atoms. Based on the average structure of SrPt2As2, the modulated structure has been solved and refined using the (3+ I)-dimensional superspace group Pmmn(alpha 00)0s0 and a modulation vector q = 0,62 center dot a*. The modulation appears in the layers of the PtAs4 tetrahedra with occupational and displacive components. The other atoms are also slightly affected by the modulation. With increasing pressure, SrPt2As2 undergoes a phase transition at about 60 kbar. The crystal structure of the high pressure phase (HP-SrPt2As2: a = 9.752(2), b = 4.398(1), c = 8.727(2) angstrom, beta = 90.34(3)degrees; 66(5) kbar) is a monoclinic variant (P2(1)/c; Z = 4) of the tetragonal CaBe2Ge2 type known from EuPt2Ge2. Band structure calculations reveal that a Peierls-distortion within the Pt square nets is a reason for the structural instabilities in SrPt2As2. The satellite reflections of EuPt2As2 become weaker with increasing temperature and disappear above 200 degrees C. The high temperature phase (HT-EUPt2As2: a = 4.464(1), c = 9.832(1) angstrom; 350 degrees C crystallizes with the CaBe2Ge2 type (P4lnmm; Z = 2). High thermal displacement parameters of the Pt and As atoms of the PtAs4 tetrahedra cover the effects of the modulation at room temperature. Several analogous compounds were studied by X-ray diffraction resulting in the following lattice parameters: ! a = 4.5640(1), c = 10.021(2) angstrom for BaPt2As2, a = 4.603(2), c = 10.565(2) angstrom for SrPt2Sb2, a = 4.630(2), b 4.683(2), c = 10.389(3) angstrom for EuPt2Sb2, and a = 4.458(1), c 9.823(2) A for SrIr2As2.
Title:
TEM characterization of twinning in Co39Ni33Al28 alloy
Authors:
Wang, HY; Wang, K; Liu, ZH; Wang, YG; Wu, GH; Duan, XF Author Full Names: Wang, H. Y.; Wang, K.; Liu, Z. H.; Wang, Y. G.; Wu, G. H.; Duan, X. F.
Source:
MATERIALS TRANSACTIONS 48 (8): 2139-2142 AUG 2007
Abstract:
A body-centered tetragonal (bct) twin martensite has been found in Co39Ni33Al28 ferromagnetic shape memory alloy by transmission electron microscope (TEM) observation. The twin lamellae have Sigma = 25 (01 (1) over bar) twin boundaries and slip system [011] // (01 (1) over bar). Periodic appearance of the twin lamellae resulted in a modulated structure with a repeat periodicity of 56d01 (1) over bar perpendicular to the twin interface. The twinning mechanism during martensite transformation is discussed briefly.
Title:
Formation of Al70Cu20Fe10 icosahedral quasicrystal by mechanically alloyed method
Authors:
Yin, SL; Bian, Q; Qian, LY; Zhang, AM Author Full Names: Yin, Shilong; Bian, Qing; Qian, Liying; Zhang, Aimei
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 465 (1-2): 95-99 SEP 15 2007
Abstract:
The structural evolutions of the mechanically alloyed ternary Al70Cu20Fe10 powders with the milling time and the annealing treatment have been studied by X-ray diffraction (XRD), transmission electronic microscopy (TEM) and X-ray absorption fine-structure spectroscopy (XAFS) techniques. Results show that an Al2Cu compound forms with short-time milling, while a Cu9Al4 compound forms with long-time milling. Fe can react with Al-Cu alloy by annealing treatment. Al7Cu2Fe compound with tetragonal structure or Al (Cu, Fe) solid solution with cubic structure may form at lower temperature, while a quasicrystal phase of Al65Cu20Fe15 alloy may form at higher temperature. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Local structure characterization in quasicrystal-forming Zr80Pt20 binary amorphous alloy
Authors:
Saida, J; Sanada, T; Sato, S; Imafuku, M; Inoue, A Author Full Names: Saida, Junji; Sanada, Takashi; Sato, Shigeo; Imafuku, Muneyuki; Inoue, Akihisa
Source:
APPLIED PHYSICS LETTERS 91 (11): Art. No. 111901 SEP 10 2007
Abstract:
The local structure of melt-spun Zr80Pt20 alloy was investigated in the amorphous and icosahedral quasicrystal (QC)-formed states by x-ray diffraction and extended x-ray absorption fine structure measurements. While the local environment around the Zr atom in the amorphous state is considerably different from that in the QC-formed state, it remains during the quasicrystallization around the Pt atom. It is suggested that the stable icosahedral local structure is mainly formed in the center of the Pt atom in the amorphous state.
Title:
Revision of pyrrhotite structures within a common superspace model
Authors:
Izaola, Z; Gonzalez, S; Elcoro, L; Perez-Mato, JM; Madariaga, G; Garcia, A Author Full Names: Izaola, Zunbeltz; Gonzalez, Santiago; Elcoro, Luis; Perez-Mato, J. M.; Madariaga, Gotzon; Garcia, Alberto
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 63: 693-702 Part 5 OCT 2007
Abstract:
The structure of pyrrhotite ( Fe1-xS with 0.05 <= x <= 0.125) has been reinvestigated in the framework of the superspace formalism. A common model with a centrosymmetric superspace group is proposed for the whole family. The atomic domains in the internal space representing the Fe atoms are parametrized as crenel functions that fulfil the closeness condition. The proposed model explains the x-dependent space groups observed and the basic features of the structures reported up to now. Our model yields for any x value a well defined ordered distribution of Fe vacancies in contrast to some of the structural models proposed in the literature. A new ( 3 + 1)-dimensional refinement of Fe0.91S using the deposited dataset [Yamamoto & Nakazawa ( 1982). Acta Cryst. A38, 79-86] has been performed as a benchmark of the model. The consistency of the proposed superspace symmetry and its validity for other compositions has been further checked by means of ab initio calculations of both atomic forces and equilibrium atomic positions in non-relaxed and relaxed structures, respectively.
Title:
Hexagonal ferrites: a unified model of the (TS)(n)T series in superspace
Authors:
Orlov, I; Palatinus, L; Arakcheeva, A; Chapuis, G Author Full Names: Orlov, Ivan; Palatinus, Lukas; Arakcheeva, Alla; Chapuis, Gervais
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 63: 703-712 Part 5 OCT 2007
Abstract:
Hexagonal ferrites represent an extensive family of mixedlayer magnetic materials with periods up to 1500 A along the stacking direction, probably constituting the largest unit cells in the inorganic realm. The (TS)(n)T subfamily includes P (3) over bar m1 and R (3) over barm structures that can be derived from Y ferrite Ba2M2Fe12O22 ( M = Zn, Fe, Co, Mg, Mn) by introducing stacking faults. A unified ( 3 + 1)-dimensional superspace model is proposed for all members of the ( TS) nT family. The model belongs to the superspace group X (3) over bar m1(00 gamma) with X = {(1/3, 2/3, 0, 1/3), (2/3, 1/3, 0, 2/3)}, has a unit cell of the basic structure with a = 5.88, c = 4.84 angstrom and modulation vector q = 4n+3/ 9n+6 c*, where n is rational for periodic structures and irrational for the aperiodic ones. The model was tested on calculated data of one of the principal members of the (TS)(n)T family, the Y ferrite ( n = infinity). The fit obtained with the superspace model was excellent. The model allowed a reduction of refinable parameters by 19% with respect to the ordinary refinement without a significant increase of the refinement R values.

Update: 12-Oct-2007

Title:
Neutron powder diffraction experiments on the layered triangular-lattice antiferromagnets RbFe(MoO4)(2) and CsFe(SO4)(2)
Authors:
Inami, T Author Full Names: Inami, Toshiya
Source:
JOURNAL OF SOLID STATE CHEMISTRY 180 (7): 2075-2079 JUL 2007
Abstract:
Powder specimens of the layered triangular-lattice anti ferromagnets RbFe(MoO4)(2) and CsFe(SO4)(2) were prepared and neutron powder diffraction experiments were carried out in order to determine the magnetic structure. The magnetic structure of both compounds is the so-called 120 degrees structure in the triangular plane and is incommensurate between the planes. The ordered moments are confined in the basal ab-plane. It is also found that RbFe(MoO4)(2) exhibits structural phase transition at around 190 K from P $(3) over bar $ ml to P $(3) over bar $ (c) 2007 Elsevier Inc. All rights reserved.

Update: 5-Oct-2007

Title:
Magnetic phase transitions from the point of view of macroscopic and microscopic methods
Authors:
Szytula, A Author Full Names: Szytula, A.
Source:
MATERIALS SCIENCE-POLAND 25 (2): 313-320 2007
Abstract:
Magnetic phase transitions in some rare earth compounds are discussed from the point of view of different experimental methods. The discussion concentrates on the determination of phase transitions in magnetically ordered states. The data presented in this work suggest that the "classical" method, namely the specific heat method, does not yield information on phase transitions between commensurate and incommensurate magnetic structures.
Title:
Superplasticity of Mg-Zn-Y alloy containing quasicrystal phase processed by equal channel angular pressing
Authors:
Zheng, MY; Xu, SW; Wu, K; Kamado, S; Kojima, Y Author Full Names: Zheng, M. Y.; Xu, S. W.; Wu, K.; Kamado, S.; Kojima, Y.
Source:
MATERIALS LETTERS 61 (22): 4406-4408 SEP 2007
Abstract:
Equal channel angular pressing (ECAP) has been conducted on as-cast Mg-4-3 wt.%Zn-0.7 wt.%Y Mg alloy containing quasicrystal phase at a temperature of 623 K. After 8 ECAP passes, the grain size of the as-cast alloy is decreased from similar to 120 to similar to 3.5 mu m, and the coarse eutectic quasicrystal phases are broken and dispersed in the alloy. Tensile testing has been performed on the ECAPed Mg-Zn-Y alloy at temperatures of 523 K and 623 K with initial strain rates from 1.5 x 10(-3) to 1.5 x 10(-4) s(-1). The ECAPed alloy exhibits a maximum elongation of about 600% when testing at 623 K using an initial strain rate of 1.5 x 10(-4) s(-1). Grain boundary sliding is considered to be the dominant deformation mechanism of the Mg-Zn-Y alloy in the temperature and strain-rate range investigated. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Morphological characteristics of the rapidly and conventionally solidified alloys of the AlCuFe system
Authors:
Rosas, G; Reyes-Gasga, J; Perez, R Author Full Names: Rosas, G.; Reyes-Gasga, J.; Perez, R.
Source:
MATERIALS CHARACTERIZATION 58 (8-9): 765-770 Sp. Iss. SI AUG-SEP 2007
Abstract:
Different alloy compositions of AlCuFe in the composition range of Al (75-65), Cu (25-15) and Fe (15-7) at.% have been studied. Experimental results obtained in the Al70Cu20Fe10 and Al65Cu20Fe15 alloys prepared by conventional casting and Al74Cu18Fe8 and Al66Cu21Fe13 alloys produced by rapidly solidified techniques are presented. All these alloys were annealed at 600, 700, 850 and 950 degrees C and characterized using X-ray diffraction, scanning and transmission electron microscopy techniques. Several morphological aspects of the crystalline and the quasicrystalline phases as a function of the different solidification processes were observed. The experimental conditions where both crystalline and quasicrystalline phases coexist were analysed. The experimental results suggest the decomposition of ternary alloys such as: omega-Al7Cu2Fe, beta-Al-6(Cu,Fe) and psi-Al6Cu2Fe to binary compounds such as: theta-Al2Cu and Al13Fe4.
Title:
Chemical surface ageing in ambient conditions of an Al-Fe-Cr approximant phase
Authors:
Veys, D; Weisbecker, P; Domenichini, B; Weber, S; Fournee, V; Dubois, JM Author Full Names: Veys, D.; Weisbecker, P.; Domenichini, B.; Weber, S.; Fournee, V.; Dubois, J. M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (37): Art. No. 376207 SEP 19 2007
Abstract:
The gamma-Al65Cr27Fe8 phase is a complex metallic alloy with interesting electrochemical properties. Here we present a detailed study of the surface ageing of this alloy when exposed to ambient conditions for a long time. A combination of x-ray reflectivity, photoemission spectroscopy and secondary neutral mass spectroscopy measurements is used to provide a model of the modification of the surface structure and its composition as functions of ageing time. The near surface structure is described by the stacking of three layers. The first layer on top of the substrate corresponds to a mixed metal oxide and is amorphous. The intermediate layer consists of pure aluminum oxy-hydroxide while the outermost layer corresponds to carbonated contaminations. The total thickness of this near-surface region evolves with ageing time, reaching a stable state only after several days.
Title:
An in situ bulk Zr58Al9Ni9Cu14Nb10 quasicrystal-glass composite with superior room temperature mechanical properties
Authors:
Qiang, JB; Zhang, W; Xie, GQ; Kimura, H; Dong, C; Inoue, A Author Full Names: Qiang, J. B.; Zhang, W.; Xie, Guoqiang; Kimura, Hisamichi; Dong, C.; Inoue, A.
Source:
INTERMETALLICS 15 (9): 1197-1201 SEP 2007
Abstract:
An in situ bulk Zr58Al9Ni9Cu14Nb10 quasi crystal-glass composite has been fabricated by means of copper mould casting. The microstructure and constituent phases of the alloy composite have been analyzed by using X-ray diffraction, transmission electron microscopy and high-resolution transmission electron microscopy. Icosahedral quasicrystals were found to be the majority phase and the grain size is in half-mu m scale. In between the I-phase grains is a glassy phase. Optical microscopy and scanning electron microscopy revealed that the as-cast alloys were pore-free. The microhardness of the composite is about 5.90 +/- 0.30 GPa. The room temperature compression stress-true strain curve exhibits a 2% elastic deformation up to failure, and a maximum fracture stress of 1850 MPa at a quasi-static loading rate of 4.4 x 10(-4) s(-1). The mechanical property is superior to the early developed quasicrystal alloys, and is comparable to Zr-based bulk metallic glasses and their nanocomposites. The quasicrystal-glass composite exhibits basically a brittle fracture mode at room temperature. (c) 2007 Elsevier Ltd. All rights reserved.
Title:
Phase transitions in aperiodic crystals
Authors:
Janssen, T Author Full Names: Janssen, T.
Source:
FERROELECTRICS 354: 44-51 2007
Abstract:
We review phase transitions involving aperiodic crystals. Because the symmetry of aperiodic crystals is not a three-dimensional space group, but an n-dimensional superspace group, the usual procedure in the Landau theory has to be reconsidered. There are transitions where the dimension of the (super)space changes, and transitions where that is not the case. Moreover, different classes of aperiodic crystals pose specific problems. Phase transitions with modulated phases, incommensurate composites, quasicrystals, and incommensurate magnetic structures are discussed.

Update: 28-Sep-2007

Title:
Charge modulation driven fermi surface of Pb-Bi2201
Authors:
Dudy, L; Muller, B; Ziegler, B; Krapf, A; Dwelk, H; Lebben, O; Bluma, RP; Martovitsky, VP; Janowitz, C; Manzke, R Author Full Names: Dudy, L.; Mueller, B.; Ziegler, B.; Krapf, A.; Dwelk, H.; Luebben, O.; Bluma, R.-P.; Martovitsky, V. P.; Janowitz, C.; Manzke, R.
Source:
SOLID STATE COMMUNICATIONS 143 (8-9): 442-445 AUG 2007
Abstract:
It is well known that the (I x 5) superstructure of Bi cuprate superconductors will be suppressed due to doping with pb. Nevertheless, a surface map of Bi2-yPbySr2-xLaxCuO6+delta (y = 0.4 and x = 0.4) determined by angular resolved photoemission (ARPES) revealed Fermi surface features. Low-energy electron diffraction (LEED) and X-ray diffraction of this sample showed no sign of any Scanning tunneling microscopy (STM), on the other hand, revealed two distinct modulations of the charge density, one of (I x 32) and a of (6 x 6) periodicity. The wave vectors of both modulations have been extracted and used to simulate the corresponding Fermi surface, which compared with the experimental one. The origin of these modulations is discussed in terms of dopant ordering. 2007 Elsevier Ltd. All rights reserved.
Title:
Lattice dynamics of incommensurate composite Rb-IV and a realization of the monatomic linear chain model
Authors:
Loa, I; Lundegaard, LF; McMahon, MI; Evans, SR; Bossak, A; Krisch, M Author Full Names: Loa, I.; Lundegaard, L. F.; McMahon, M. I.; Evans, S. R.; Bossak, A.; Krisch, M.
Source:
PHYSICAL REVIEW LETTERS 99 (3): Art. No. 035501 JUL 20 2007
Abstract:
Longitudinal-acoustic (LA) phonons have been studied by inelastic x-ray scattering in the high-pressure incommensurate host-guest system Rb-IV in the pressure range of 16.3 to 18.4 GPa. Two LA-like phonon branches are observed along the direction of the incommensurate wave vector, which are attributed to separate lattice vibrations in the host and guest subsystems. The derived sound velocities for the host and the guest, nu(h) and nu(g), respectively, are similar in magnitude [nu(h)=nu(g)=3840(100) m/s at 18 GPa], but our results indicate rather different pressure dependences of dv(h)/dP=140(60) m/s GPa(-1) and d nu(g)/dP=280(80) m/s GPa(-1). The observations for the one-dimensional Rb guest chains are reproduced quantitatively on the basis of the monatomic linear chain model and the measured compressibility of the chains.
Title:
Achieving epitaxy between incommensurate materials by quasicrystalline interlayers
Authors:
Franke, KJ; Gille, P; Rieder, KH; Theis, W Author Full Names: Franke, K. J.; Gille, P.; Rieder, K.-H.; Theis, W.
Source:
PHYSICAL REVIEW LETTERS 99 (3): Art. No. 036103 JUL 20 2007
Abstract:
Epitaxial interfaces of commensurate periodic materials can be characterized by a locking into registry of their atomic structure. This characteristic is identified as a natural framework to capture the essence of epitaxy also for systems including quasicrystalline materials. The resulting general definition for epitaxy requires a matching of reciprocal lattice points. The consequences for the real space structure of an epitaxial interface between quasiperiodic and periodic materials are explored and an experimental realization of such an interface is presented. It is demonstrated that due to their higher number of reciprocal lattice basis vectors (exceeding three), quasicrystals can provide interlayers epitaxially linking incommensurate materials.
Title:
Entropic analysis of quantum phase transitions from uniform to spatially inhomogeneous phases
Authors:
Legeza, O; Solyom, J; Tincani, L; Noack, RM Author Full Names: Legeza, O.; Solyom, J.; Tincani, L.; Noack, R. M.
Source:
PHYSICAL REVIEW LETTERS 99 (8): Art. No. 087203 AUG 24 2007
Abstract:
We propose a new approach to study quantum phase transitions in low-dimensional fermionic or spin models that go from uniform to spatially inhomogeneous phases such as dimerized, trimerized, or incommensurate phases. It is based on studying the length dependence of the von Neumann entropy and its corresponding Fourier spectrum for finite segments in the ground state of finite chains. Peaks at a nonzero wave vector are indicators of oscillatory behavior in decaying correlation functions and also provide significant information about certain relevant features of the excitation spectrum; in particular, they can identify the wave vector of soft modes in critical models.
Title:
Neutron diffraction and mu SR study on the antiferromagnet BaCoO3
Authors:
Nozaki, H; Janoschek, M; Roessli, B; Sugiyama, J; Keller, L; Brewer, JH; Ansaldo, EJ; Morris, GD; Takami, T; Ikuta, H Author Full Names: Nozaki, H.; Janoschek, M.; Roessli, B.; Sugiyama, J.; Keller, L.; Brewer, J. H.; Ansaldo, E. J.; Morris, G. D.; Takami, T.; Ikuta, H.
Source:
PHYSICAL REVIEW B 76 (1): Art. No. 014402 JUL 2007
Abstract:
The magnetic structure of the antiferromagnetic (AF) hexagonal perovskite BaCoO3 was investigated by neutron diffraction using a powder sample in the temperature range between 60 and 1.5 K. It was found that AF diffraction peaks clearly appear below the Neel temperature (T-N=15 K), which are indexed with the propagation vector k=(1/3,1/3,0), indicating that the AF super unit cell is three times larger than the crystallographic unit cell. Data from a parallel muon-spin rotation/relaxation (mu+SR) measurement allowed the final selection of a unique AF spin structure from several possible spin arrangements compatible with the neutron diffraction pattern. The proposed AF structure is modulated along the (110) direction and described by m(l)=m(0) cos(2 pi kl), where m(l) is the moment at the Co4+ site l and m(0)=(0,0,0.53 mu(B)) at 1.5 K.
Title:
Spin-modulated quasi-one-dimensional antiferromagnet LiCuVO4
Authors:
Buttgen, N; von Nidda, HAK; Svistov, LE; Prozorova, LA; Prokofiev, A; ABmus, W Author Full Names: Buettgen, N.; von Nidda, H.-A. Krug; Svistov, L. E.; Prozorova, L. A.; Prokofiev, A.; Abmus, W.
Source:
PHYSICAL REVIEW B 76 (1): Art. No. 014440 JUL 2007
Abstract:
We report on magnetic resonance studies within the magnetically ordered phase of the quasi-one-dimensional antiferromagnet LiCuVO4. Our studies reveal a spin reorientational transition at a magnetic field H-c1 approximate to 25 kOe applied within the crystallographic ab plane in addition to the recently observed one at H-c2 approximate to 75 kOe [M. G. Banks , J. Phys.: Condens. Matter 19, 145227 (2007)]. Spectra of the antiferromagnetic resonance along low-frequency branches can be described in the framework of a macroscopic theory of exchange-rigid planar magnetic structures. These data allow us to obtain the parameter of the anisotropy of the exchange susceptibility together with a constant of the uniaxial anisotropy. Spectra of Li-7 nuclear magnetic resonance (NMR) show that, within the magnetically ordered phase of LiCuVO4 in the low-field range H < H-c1, a planar spiral spin structure is realized with the spins lying in the ab plane, in agreement with neutron-scattering studies of Gibson [Physica B 350, 253 (2004)]. Based on NMR spectra simulations, the transition at H-c1 can well be described as a spin-flop transition, where the spin plane of the magnetically ordered structure rotates to be perpendicular to the direction of the applied magnetic field. For H>H-c2 approximate to 75 kOe, our NMR spectra simulations show that the magnetically ordered structure exhibits a modulation of the spin projections along the direction of the applied magnetic field H.
Title:
Chiral plaquette polaron theory of cuprate superconductivity
Authors:
Tahir-Kheli, J; Goddard, WA Author Full Names: Tahir-Kheli, Jamil; Goddard, William A., III
Source:
PHYSICAL REVIEW B 76 (1): Art. No. 014514 JUL 2007
Abstract:
Ab initio density functional calculations on explicitly doped La2-xSrxCuO4 find that doping creates localized holes in out-of-plane orbitals. A model for cuprate superconductivity is developed based on the assumption that doping leads to the formation of holes on a four-site Cu plaquette composed of the out-of-plane A(1) orbitals apical O p(z), planar Cu d(3z)(2)-r(2), and planar O p(sigma). This is in contrast to the assumption of hole doping into planar Cu d(x)(2)-y(2) and O p(sigma) orbitals as in the t-J model. Allowing these holes to interact with the d(9) spin background leads to chiral polarons with either a clockwise or anticlockwise charge current. When the polaron plaquettes percolate through the crystal at x approximate to 0.05 for La2-xSrxCuO4, a Cu d(x)(2)-y(2) and planar O p(sigma) band is formed. The computed percolation doping of x approximate to 0.05 equals the observed transition to the "metallic" and superconducting phase for La2-xSrxCuO4. Spin exchange Coulomb repulsion with chiral polarons leads to d-wave superconducting pairing. The equivalent of the Debye energy in phonon superconductivity is the maximum energy separation between a chiral polaron and its time-reversed partner. This energy separation is on the order of the antiferromagnetic spin coupling energy, J(dd)similar to 0.1 eV, suggesting a higher critical temperature. An additive skew-scattering contribution to the Hall effect is induced by chiral polarons and leads to a temperature dependent Hall effect that fits the measured values for La2-xSrxCuO4. The integrated imaginary susceptibility, observed by neutron spin scattering, satisfies omega/T scaling due to chirality and spin-flip scattering of polarons along with a uniform distribution of polaron energy splittings. The derived functional form is compatible with experiments. The static spin structure factor for chiral spin coupling of the polarons to the undoped antiferromagnetic Cu d(9) spins is computed for classical spins on large two-dimensional lattices and is found to be incommensurate with a separation distance from (pi/a,pi/a) given by delta Q approximate to(2 pi/a)x, where x is the doping. When the perturbed x(2)-y(2) band energy in mean field is included, incommensurability along the Cu-O bond direction is favored. A resistivity similar to T mu+1 arises when the polaron energy separation density is of the form similar to Delta(mu) due to Coulomb scattering of the x(2)-y(2) band with polarons. A uniform density leads to linear resistivity. The coupling of the x(2)-y(2) band to the undoped Cu d(9) spins leads to the angle-resolved photoemission pseudogap and its qualitative doping and temperature dependence. The chiral plaquette polaron leads to an explanation of the evolution of the bilayer splitting in Bi-2212.
Title:
Search for magnetic order in superconducting RuSr2Eu1.2Ce0.8Cu2O10
Authors:
Lynn, JW; Chen, Y; Huang, Q; Goh, SK; Williams, GVM Author Full Names: Lynn, J. W.; Chen, Y.; Huang, Q.; Goh, S. K.; Williams, G. V. M.
Source:
PHYSICAL REVIEW B 76 (1): Art. No. 014519 JUL 2007
Abstract:
Neutron diffraction, polarized neutron transmission, and small angle neutron scattering have been used to investigate the crystal structure and nature of the magnetic order in a polycrystalline sample of RuSr2Eu1.2Ce0.8Cu2O10. The sample was made with the Eu-153 (98.8%) isotope to reduce the high neutron absorption for the naturally occurring element. Full refinements of the crystal structure, space group I4/mmm, are reported. At low temperatures only a single magnetic peak is clearly observed in a relatively wide angular range. A sharp spin reorientation transition (SRT) is observed around 35 K, close to the superconducting transition temperature (T-c similar to 40 K). Between the spin reorientation temperature and the Neel temperature of 59 K, additional magnetic reflections are observed. However, none of these can be simply indexed on the chemical unit cell, either as commensurate peaks or simple incommensurate magnetism, and the paucity of reflections at low T compels the conclusion that these magnetic Bragg peaks arise from an impurity phase. X-ray and neutron diffraction on the pressed pellet both show that the sample does not appear to contain substantial impurity phases, but it turns out that the magnetic impurity peaks exhibit strong preferred orientation with respect to the pellet orientation, while the primary phase does not. We have been unable to observe any magnetic order that can be identified with the ruthenate-cuprate system.
Title:
Intrinsic electrical, magnetic, and thermal properties of single-crystalline Al64Cu23Fe13 icosahedral quasicrystal: Experiment and modeling
Authors:
Dolinsek, J; Vrtnik, S; Klanjsek, M; Jaglicic, Z; Smontara, A; Smiljanic, I; Bilusic, A; Yokoyama, Y; Inoue, A; Landauro, CV Author Full Names: Dolinsek, J.; Vrtnik, S.; Klanjsek, M.; Jaglicic, Z.; Smontara, A.; Smiljanic, I.; Bilusic, A.; Yokoyama, Y.; Inoue, A.; Landauro, C. V.
Source:
PHYSICAL REVIEW B 76 (5): Art. No. 054201 AUG 2007
Abstract:
In order to test for the true intrinsic properties of icosahedral i-Al-Cu-Fe quasicrystals, we performed investigations of magnetism, electrical resistivity, thermoelectric power, and thermal conductivity on a single-crystalline Al64Cu23Fe13 quasicrystal grown by the Czochralski technique. This sample shows superior quasicrystallinity, an almost phason-free structure, and excellent thermal stability. Magnetic measurements revealed that the sample is best classified as a weak paramagnet. Electrical resistivity exhibits a negative temperature coefficient with rho(4 K)=3950 mu Omega cm and R=rho(4 K)/rho(300 K)=1.8, whereas the thermopower exhibits a sign reversal at T=278 K. Simultaneous analysis of the resistivity and thermopower using spectral-conductivity model showed that the Fermi energy is located at the minimum of the pseudogap in the spectral conductivity sigma(epsilon). Thermal conductivity is anomalously low for an alloy of metallic elements. Comparing the physical properties of the investigated single-crystalline Al64Cu23Fe13 quasicrystal to literature reports on polycrystalline i-Al-Cu-Fe material, we conclude that there are no systematic differences between the high-quality single-crystalline and polycrystalline i-Al-Cu-Fe quasicrystals, except for the hindering of long-range transport by grain boundaries in the polycrystalline material. The so far reported physical properties of i-Al-Cu-Fe appear to be intrinsic to this family of icosahedral quasicrystals, regardless of the form of the material.
Title:
Anomalous phonon behavior in the high-temperature shape-memory alloy Ti50Pd50-xCrx
Authors:
Shapiro, SM; Xu, GY; Winn, BL; Schlagel, DL; Lograsso, T; Erwin, R Author Full Names: Shapiro, S. M.; Xu, Guangyong; Winn, B. L.; Schlagel, D. L.; Lograsso, T.; Erwin, R.
Source:
PHYSICAL REVIEW B 76 (5): Art. No. 054305 AUG 2007
Abstract:
Ti50Pd50-xCrx is a high-temperature shape-memory alloy with a martensitic transformation temperature strongly dependent on the Cr composition. Prior to the transformation, a premartensitic phase is present with an incommensurate modulated cubic lattice with wave vector of q(0)=(0.22,0.22,0). The temperature dependence of the diffuse scattering in the cubic phase is measured as a function temperature for x=6.5, 8.5, and 10 at. %. The lattice dynamics has been studied and reveals anomalous temperature and q dependences of the [110]-TA(2) transverse phonon branch. The phonon linewidth is broad over the entire Brillouin zone and increases with decreasing temperature, contrary to the behavior expected for anharmonicity. No anomaly is observed at q(0). The results are compared with first principles calculation of the phonon structure.
Title:
Symmetry constraints on the electrical polarization in multiferroic materials
Authors:
Radaelli, PG; Chapon, LC Author Full Names: Radaelli, P. G.; Chapon, L. C.
Source:
PHYSICAL REVIEW B 76 (5): Art. No. 054428 AUG 2007
Abstract:
The symmetry conditions for the development of a macroscopic electrical polarization as a secondary order parameter to a magnetic ordering transition and the constraints on the direction of the polarization vector are determined by a nonconventional application of the theory of irreducible corepresentations. In our approach, which is suitable for both magnetic and structural modulations, antiunitary operators are employed to describe symmetry operations that exchange the propagation vector k with -k, rather than operations combined with time reversal as in classical corepresentation analysis. Unlike the conventional irreducible representations, corepresentations can capture the full symmetry properties of the system even if the propagation vector is in the interior of the Brillouin zone. It is shown that ferroelectricity can develop even for a completely collinear structure, and that helical and cycloidal magnetic structures are not always polar. In some cases, symmetry allows the development of polarization parallel to the magnetic propagation vector. Our analysis also highlights the unique importance of magnetic commensurability, enabling one to derive the different symmetry properties of equivalent commensurate and incommensurate phases even for a completely generic propagation vector.
Title:
Landau analysis of the symmetry of the magnetic structure and magnetoelectric interaction in multiferroics
Authors:
Harris, AB Author Full Names: Harris, A. B.
Source:
PHYSICAL REVIEW B 76 (5): Art. No. 054447 AUG 2007
Abstract:
This paper presents a detailed instruction manual for constructing the Landau expansion for magnetoelectric coupling in incommensurate ferroelectric magnets, including Ni3V2O8, TbMnO3, MnWO4, TbMn2O5, YMn2O5, CuFeO2, and RbFe(MO4)(2). The first step is to describe the magnetic ordering in terms of symmetry adapted coordinates which serve as complex-valued magnetic order parameters whose transformation properties are displayed. In so doing, we use the previously proposed technique to exploit inversion symmetry, since this symmetry has seemingly been universally overlooked. Inversion symmetry severely reduces the number of fitting parameters needed to describe the spin structure, usually by fixing the relative phases of the complex fitting parameters. By introducing order parameters of known symmetry to describe the magnetic ordering, we are able to construct the trilinear magnetoelectric interaction which couples incommensurate magnetic order to the uniform polarization, and thereby we treat many of the multiferroic systems so far investigated. In most cases, the symmetry of the magnetoelectric interaction determines the direction of the magnetically induced spontaneous polarization. We use the Landau description of the magnetoelectric phase transition to discuss the qualitative behavior of various susceptibilities near the phase transition. The consequences of symmetry for optical properties such as polarization induced mixing of Raman and infrared phonons and electromagnons are analyzed. The implication of this theory for microscopic models is discussed.
Title:
Commensurate-incommensurate transition and associated collective modes in the stripe state of cuprates near 1/8 hole-doping
Authors:
Kaneshita, E; Martin, I; Bishop, AR Author Full Names: Kaneshita, E.; Martin, I.; Bishop, A. R.
Source:
PHYSICAL REVIEW B 76 (5): Art. No. 054507 AUG 2007
Abstract:
We analyze the anomalous behavior in hole-doped cuprates near 1/8 doping in terms of the commensurate-incommensurate transition of a stripe phase. Based on an effective Ginzburg-Landau theory appropriate for weak pinning, we calculate the commensurate-incommensurate transition point and the energies of the phason and amplitudon collective modes. Using experimentally available parameters, we estimate the phason gap (pinning frequency), the conductivity, and the contribution of the phason mode to the dielectric function.
Title:
Incommensurate magnetic structure in the orthorhombic perovskite ErMnO3
Authors:
Ye, F; Lorenz, B; Huang, Q; Wang, YQ; Sun, YY; Chu, CW; Fernandez-Baca, JA; Dai, PC; Mook, HA Author Full Names: Ye, F.; Lorenz, B.; Huang, Q.; Wang, Y. Q.; Sun, Y. Y.; Chu, C. W.; Fernandez-Baca, J. A.; Dai, Pengcheng; Mook, H. A.
Source:
PHYSICAL REVIEW B 76 (6): Art. No. 060402 AUG 2007
Abstract:
By combining dielectric, specific heat, and magnetization measurements and high-resolution neutron powder diffraction, we have investigated the thermodynamic and magnetic and structural properties of the metastable orthorhombic perovskite ErMnO3 prepared by high-pressure synthesis. The system becomes antiferromagnetically correlated below 42 K and undergoes a lock-in transition at 28 K with propagation wave vector (0,k(b),0), which remains incommensurate at low temperature. The intercorrelation between the magnetic structure and electric properties and the role of the rare earth moment are discussed.
Title:
Thermodynamics of the up-up-down phase of the S=1/2 triangular-lattice antiferromagnet Cs2CuBr4
Authors:
Tsujii, H; Rotundu, CR; Ono, T; Tanaka, H; Andraka, B; Ingersent, K; Takano, Y Author Full Names: Tsujii, H.; Rotundu, C. R.; Ono, T.; Tanaka, H.; Andraka, B.; Ingersent, K.; Takano, Y.
Source:
PHYSICAL REVIEW B 76 (6): Art. No. 060406 AUG 2007
Abstract:
The specific heat and magnetocaloric effect are used to probe the field-induced up-up-down (UUD) phase of Cs2CuBr4, a quasi-two-dimensional spin-1/2 triangular antiferromagnet with near-maximal frustration. The transitions between the commensurate UUD phase and the incommensurate phases adjacent to it are clearly first order, at least at low temperatures. The shape of the magnetic phase diagram shows that the UUD phase is stabilized by quantum fluctuations, not by thermal fluctuations as in the corresponding phase of classical spins. The magnon gaps determined from the specific heat are considerably larger than those expected for a Heisenberg antiferromagnet.
Title:
Heisenberg antiferromagnet with anisotropic exchange on the kagome lattice: Description of the magnetic properties of volborthite
Authors:
Yavors'kii, T; Apel, W; Everts, HU Author Full Names: Yavors'kii, T.; Apel, W.; Everts, H.-U.
Source:
PHYSICAL REVIEW B 76 (6): Art. No. 064430 AUG 2007
Abstract:
We study the properties of the Heisenberg antiferromagnet with spatially anisotropic nearest-neighbor exchange couplings on the kagome net, i.e., with coupling J in one lattice direction and couplings J(') along the other two directions. For J/J(')greater than or similar to 1, this model is believed to describe the magnetic properties of the mineral volborthite. In the classical limit, it exhibits two kinds of ground state: a ferrimagnetic state for J/J(')< 1/2 and a large manifold of canted spin states for J/J(')>1/2. To include quantum effects self-consistently, we investigate the Sp(N) symmetric generalization of the original SU(2) symmetric model in the large-N limit. In addition to the dependence on the anisotropy, the Sp(N) symmetric model depends on a parameter kappa that measures the importance of quantum effects. Our numerical calculations reveal that, in the kappa-J/J(') plane, the system shows a rich phase diagram containing a ferrimagnetic phase, an incommensurate phase, and a decoupled chain phase, the latter two with short- and long-range order. We corroborate these results by showing that the boundaries between the various phases and several other features of the Sp(N) phase diagram can be determined by analytical calculations. Finally, the application of a block-spin perturbation expansion to the trimerized version of the original spin-1/2 model leads us to suggest that in the limit of strong anisotropy, J/J(')> 1, the ground state of the original model is a collinearly ordered antiferromagnet, which is separated from the incommensurate state by a quantum phase transition.
Title:
Incommensurate helical magnetic order in LiCu2O2 and NaCu2O2 quasi-one-dimensional compounds
Authors:
Gippius, AA; Moskvin, AS; Morozova, EN; Okhotnikov, KS Author Full Names: Gippius, A. A.; Moskvin, A. S.; Morozova, E. N.; Okhotnikov, K. S.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS 105 (1): 86-89 JUL 2007
Abstract:
The results of the measurements of the Li-6,Li- 7 and Na-23 nuclear magnetic resonance (NMR) and Cu-63,Cu- 65 nuclear quadrupole resonance in LiCu2O2 and NaCu2O2 quasi-one-dimensional compounds with a spin chains in the paramagnetic and magnetically ordered states are presented. The shape of the NMR line below T-c = 24 and 13 K for LiCu2O2 and NaCu2O2, respectively, is characteristic of the incommensurate static modulation of the local magnetic field matching with the incommensurate spiral modulation of the magnetic moments. The differences in the shape of the NMR spectra of Na-23 and Li-7 are discussed in terms of the features of the crystal structure of LiCu2O2 and NaCu2O2.
Title:
Frustration mechanism of formation of a helical magnetic structure in the CuB2O4 two-subsystem antiferromagnet
Authors:
Martynov, SN; Balaev, AD Author Full Names: Martynov, S. N.; Balaev, A. D.
Source:
JETP LETTERS 85 (12): 649-654 AUG 2007
Abstract:
A new mechanism is proposed for forming an incommensurate magnetic structure of the transverse helix type owing to the removal of frustration through intersubsystem exchange in a two-subsystem antiferromagnet. The symmetry analysis of the distribution of the Dzyaloshinskii-Moriya interaction and comparison with the experimental data on the field dependence of magnetization indicate that antisymmetric exchange and competition between symmetric exchanges cannot be responsible for forming a helical magnetic structure in CuB2O4.
Title:
Random tilings of compact Euclidean 3-manifolds
Authors:
Escudero, JG Author Full Names: Escudero, Juan Garcia
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 63: 391-399 Part 5 SEP 2007
Abstract:
Deterministic and random tilings for the ten compact Euclidean 3-manifolds are introduced. The main tools are substitution rules generating non-periodic planar patterns and a set of pre-axioms defined for each manifold. The sets of random tilings are obtained by suitable tile flips in the substitution atlas which allows us to compute their configurational entropies. The inflation rules in two dimensions together with one-dimensional substitutions in a perpendicular direction induce non-periodic three-dimensional tilings by triangular prisms which can be transformed into simplicial structures.

Update: 21-Sep-2007

Title:
Incommensurate modulations in a hollandite phase Ba-x(Al,Fe)(2x)Ti8-2xO16 intended for the storage of radioactive wastes: a (3+1) dimension structure determination
Authors:
Aubin-Chevaldonnet, V; Deniard, P; Evain, M; Leinekugel-Le-Cocq-Errien, AY; Jobic, S; Caurant, D; Petricek, V; Advocat, T Author Full Names: Aubin-Chevaldonnet, Virginie; Deniard, Philippe; Evain, Michel; Leinekugel-Le-Cocq-Errien, Aude Ysoline; Jobic, Stephane; Caurant, Daniel; Petricek, Vaclav; Advocat, Thierry
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 222 (8): 383-390 2007
Abstract:
Intensive researches on specific treatments of radioactive cesium, occurring in high level nuclear wastes, are in progress in France. Nowadays, a cesium immobilization in host matrices with a high chemical durability seems to be the favourite option. In that perspective, titanium based upon hollandite is a good candidate as a host matrix because of its high cesium incorporation ability, its excellent chemical stability, and its capacity to support charge compensation during the Cs+ into Ba2+ transmutation process. In this study we report the preparation and crystal growth in a BaF2-B2O3 flux melt of the BaxCsyMzTi8-zO16 hollandite phase and its characterization by single crystal X-ray diffraction. An attention was focused on materials with M = Al or Al + Fe and with barium only since single crystals including cesium could not be obtained from the flux method. An incommensurate modulation of the Ba cation site occupancy, with I4/m(00 gamma)00 as a superspace group, was observed for all the single crystals under study.
Title:
Solidification of Mg-28%Zn-2%Y alloy involving icosahedral quasicrystal phase
Authors:
Wan, D; Yang, G; Man, Z; Quan, X; Zhou, Y Author Full Names: Wan Di-qing; Yang Gen-cang; Man, Zhu; Quan, Xu; Zhou Yao-he
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA 17 (3): 586-589 JUN 2007
Abstract:
Applying XRD, DTA, SEM and TEM techniques, an investigation on the solidification microstructure and solidification sequence of Mg-rich Mg-28%Zn-2%Y (mole fraction) alloy was carried out. It is found that, a-Mg dendrites, Mg7Zn3 phase and icosahedral quasicrystal phase coexist in the as-solidified alloy, where the icosahedral quasicrystal, whose structure is indentified to be a face-centered type, originates from a peritectic reaction occurring at 416 degrees C. The primary phase of this peritectic reaction has the composition of Mg20Zn66Y14, which is coincident with the H phase reported by TSAI as (Zn, Mg)(5)Y. Furthermore, the single I-phase grain morphology was observed and its growth evolution was also discussed.
Title:
Phase transformations in the rapidly solidified Ti40Zr20Hf20Pd20 alloy
Authors:
Chen, N; Yao, K; Louzguine-Luzgin, DV; Qiu, SB; Ranganathan, S; Inoue, A Author Full Names: Chen, N.; Yao, Kefu; Louzguine-Luzgin, D. V.; Qiu, Shengbao; Ranganathan, S.; Inoue, A.
Source:
SCRIPTA MATERIALIA 57 (7): 631-634 OCT 2007
Abstract:
We report that an approximant phase was initially obtained in amorphous Ti40Zr20Hf20Pd20 alloy. In the initial stage of the devitrification process, the approximant phase transforms into an icosahedral (1) phase with a high thermal stability while the cF96 Zr2Ni-type (space group Fd (3) over barm with a = 1.25 nm and 96 atoms cell(-1)) particles precipitate from the amorphous matrix. Eventually the I phase grows to several hundred nanometers when annealed at about 1000 K and then transforms into the Zr2Ni-type phase with an endothermic reaction. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Medieval quasicrystals
Authors:
Min-Kel, JR Author Full Names: Min-Kel, J. R.
Source:
SCIENTIFIC AMERICAN 297 (3): 17-17 SEP 2007
Title:
STM studies of TbTe3: Evidence for a fully incommensurate charge density wave
Authors:
Fang, A; Ru, N; Fisher, IR; Kapitulnik, A Author Full Names: Fang, A.; Ru, N.; Fisher, I. R.; Kapitulnik, A.
Source:
PHYSICAL REVIEW LETTERS 99 (4): Art. No. 046401 JUL 27 2007
Abstract:
We observe unidirectional charge density wave (CDW) ordering on the quasi-2D material TbTe3 with a scanning tunneling microscope at similar to 6 K. Our analysis indicates that the CDW is fully incommensurate, with wave vector q(CDW)approximate to 0.71x2 pi/c. By imaging at various tip-sample voltages, we highlight effects of the subsurface layer and its effect on the CDW. We also observe an additional (possibly surface) dimerization and approximate to 0.68x2 pi/a ordering perpendicular to the CDW.
Title:
Persistence of high-frequency spin fluctuations in overdoped superconducting La2-xSrxCuO4 (x=0.22)
Authors:
Lipscombe, OJ; Hayden, SM; Vignolle, B; McMorrow, DF; Perring, TG Author Full Names: Lipscombe, O. J.; Hayden, S. M.; Vignolle, B.; McMorrow, D. F.; Perring, T. G.
Source:
PHYSICAL REVIEW LETTERS 99 (6): Art. No. 067002 AUG 10 2007
Abstract:
We report a detailed inelastic neutron scattering study of the collective magnetic excitations of overdoped superconducting La1.78Sr0.22CuO4 for the energy range 0-160 meV. Our measurements show that overdoping suppresses the strong response present for optimally doped La2-xSrxCuO4 which is peaked near 50 meV. The remaining response is peaked at incommensurate wave vectors for all energies investigated. We observe a strong high-frequency magnetic response for E greater than or similar to 80 meV suggesting that significant antiferromagnetic exchange couplings persist well into the overdoped part of the cuprate phase diagram.
Title:
Modeling the structural, dynamical, and magnetic properties of liquid Al1-xMnx (x=0.14, 0.2, and 0.4): A first-principles investigation
Authors:
Jakse, N; Pasturel, A Author Full Names: Jakse, N.; Pasturel, A.
Source:
PHYSICAL REVIEW B 76 (2): Art. No. 024207 JUL 2007
Abstract:
We report the results of first-principles molecular dynamics simulations of liquid Al1-xMnx alloys at three different compositions. The local structure as defined by the Bhatia-Thornton partial structure factors is found to display significant changes at x=0.4. In addition, a structural analysis using three-dimensional pair-analysis techniques evidences a fivefold symmetry around x=0.14, in agreement with the experimental quasicrystal-forming range, and an increasing complexity of the Frank-Kasper polytetrahedral symmetry around Mn atoms at x=0.4. We also examine the time evolution of the configurations at the three compositions in terms of the mean-square displacements and self-diffusion coefficients. Finally, we show a strong interplay between the structural changes and the evolution of the magnetic properties of the Mn atoms as a function of composition.
Title:
Magnetic structure and properties of the S=5/2 triangular antiferromagnet alpha-NaFeO2
Authors:
McQueen, T; Huang, Q; Lynn, JW; Berger, RF; Klimczuk, T; Ueland, BG; Schiffer, P; Cava, RJ Author Full Names: McQueen, T.; Huang, Q.; Lynn, J. W.; Berger, R. F.; Klimczuk, T.; Ueland, B. G.; Schiffer, P.; Cava, R. J.
Source:
PHYSICAL REVIEW B 76 (2): Art. No. 024420 JUL 2007
Abstract:
The magnetic properties of alpha-NaFeO2 are studied by neutron-diffraction and magnetization measurements. An ordered phase with spins aligned along the b(hex) axis exists at low temperatures (T < 4 K). At intermediate temperatures (4 K < T < 11 K), the system passes through an incommensurate ordered phase before transforming into a short-range-ordered state at higher temperatures that persists up to at least 50 K. Although the short-range ordering does not persist to room temperature according to neutron diffraction, the magnetic susceptibility does not follow the Curie-Weiss behavior, even up to 320 K. This rich magnetic behavior can be understood qualitatively as a competition between different magnetic exchange interactions that are similar in magnitude. The delicate balance between these interactions makes alpha-NaFeO2 a candidate for more detailed theoretical work to understand magnetic behavior in frustrated magnetic systems.
Title:
Onset of spin-density-wave antiferromagnetism in Cr/V multilayers
Authors:
Kravtsov, E; Brucas, R; Hjorvarsson, B; Hoser, A; Liebig, A; McIntyre, GJ; Milyaev, MA; Nefedov, A; Paolasini, L; Radu, F; Remhof, A; Ustinov, VV; Yakhou, F; Zabel, H Author Full Names: Kravtsov, E.; Brucas, R.; Hjoervarsson, B.; Hoser, A.; Liebig, A.; McIntyre, G. J.; Milyaev, M. A.; Nefedov, A.; Paolasini, L.; Radu, F.; Remhof, A.; Ustinov, V. V.; Yakhou, F.; Zabel, H.
Source:
PHYSICAL REVIEW B 76 (2): Art. No. 024421 JUL 2007
Abstract:
Spin-density-wave (SDW) magnetism in a series of Cr/V heterostructures with different Cr thicknesses was systematically investigated by combined resistivity, neutron, and synchrotron scattering measurements. We show that the onset of the bulklike SDW state comes through several necessary steps from a paramagnetic state through a commensurate SDW to an incommensurate SDW. The Neel temperature for the incommensurate SDW is found to scale with Cr thickness and reaches the bulk value at a Cr thickness of about 2000 angstrom. The proximity effect from Cr/V interfaces is found to lead to (i) the appearance of a 50-angstrom magnetically dead Cr layer near Cr/V interfaces and (ii) suppression of the spin-flip transition and stabilization of a single-domain SDW with out-of-plane spins and out-of-plane propagation wave vector. Finally, we show that the SDW period increases with decreasing Cr thickness and becomes temperature independent in sufficiently thin Cr layers.
Title:
Atomic structure and charge-density waves of blue bronze K0.3MoO3 (20(1)over-bar) by variable-temperature scanning tunneling microscopy
Authors:
Nikiforov, MP; Isakovic, AF; Bonnell, DA Author Full Names: Nikiforov, Maxim P.; Isakovic, Abdel F.; Bonnell, Dawn A.
Source:
PHYSICAL REVIEW B 76 (3): Art. No. 033104 JUL 2007
Abstract:
Blue bronze (K0.3MoO3) has been the focus of a number of scattering, transport, scanning tunneling microscopy (STM), and theoretical studies that have provided insight into the relation between atomic structure and charge-density wave (CDW) formation. However, the full extent of a relation of the CDWs to the atomic lattice and the microscopic origin of CDW pinning are still not completely resolved. In this study STM is used to distinguish the atomic structure and CDWs at the (20 (1) over bar) surface. Within the STM's spatial resolution, the CDWs are incommensurate with the lattice at midrange temperatures and approach commensurability at low temperatures. Incommensurate CDWs are present on the surface and the degree of the incommensurability between blue bronze lattice and CDW lattice agree well with those determined from bulk scattering techniques.
Title:
Interplay between indirect interaction and charge-density wave in Pb-adsorbed In(4x1)-Si(111)
Authors:
Hupalo, M; Chan, TL; Wang, CZ; Ho, KM; Tringides, MC Author Full Names: Hupalo, M.; Chan, T.-L.; Wang, C. Z.; Ho, K.-M.; Tringides, M. C.
Source:
PHYSICAL REVIEW B 76 (4): Art. No. 045415 JUL 2007
Abstract:
The response of the electronic structure of the quasi-one-dimensional In(4x1)-Si(111) surface to the adsorption of Pb atoms is investigated by scanning tunneling microscopy and first-principles calculations. Instead of a period of even multiples of the underlying In lattice spacing a along the In wire, as favored by the low temperature charge-density wave (CDW) modulation, the Pb adatoms are frequently found to occupy the odd adsorption sites separated by a distance 3a or 5a. These observations indicate a strong antiphase interference between the indirect interaction of adsorbed Pb atoms and the intrinsic CDW of the In(4x1)-Si(111) surface.
Title:
Magnetic structure of a frustrated antiferromagnetic spinel CdCr2O4 studied by spherical neutron polarimetry
Authors:
Matsuda, M Author Full Names: Matsuda, Masaaki
Source:
PHYSICA B-CONDENSED MATTER 397 (1-2): 7-10 JUL 15 2007
Abstract:
A review is given of a magnetic structure of the spinet CdCr2O4, in which geometrical frustration exists between the Cr3+ moments located at the corners of the tetrahedron. It shows an incommensurate antiferromagnetic ordering below T-N = 7.8 K with a characteristic wave vector of Q = (0, delta, 1) (delta similar to 0.09). We performed spherical neutron polarimetry analysis and determined that the magnetic structure is elliptical spiral in the ac plane with ellipse slightly elongated along the c-axis. An imbalance in chirality domains was also observed. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Chiral scattering in complex magnets
Authors:
Maleyev, SV Author Full Names: Maleyev, S. V.
Source:
PHYSICA B-CONDENSED MATTER 397 (1-2): 11-14 JUL 15 2007
Abstract:
General properties of the chiral scattering of polarized neutrons are considered for two possible axial vector interactions: Zeeman energy and non-alternating Dzyaloshinskii-Moriya interaction. Behavior in magnetic field of helical magnetic structures is discussed for MnSi and magneto-electric materials. The dynamical chiral fluctuations in magnetic field are considered briefly. The chiral fluctuations in materials with the Dzyaloshinskii-Moriya interaction are discussed and an assumption is made that above the transition temperature they have to be incommensurate. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Personal reflections on the history of aperiodic crystals from early days to the state of the art
Authors:
Janner, A Author Full Names: Janner, A.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2601-2611 2007
Abstract:
Aperiodic crystals occur as modulated, intergrowth and quasicrystal structures. Their characterization in terms of symmetries possibly requires not only a higherdimensional description, but also non-Euclidean transformations (like scaling). These crystallographic symmetries, observed in nature, have been investigated but only partially classified. Turning points in the structure determination of aperiodic crystals are presented in historical perspective up to the present time, together with methods and programs. The WEB allows us to get more information on all that, on additional tools and on databases. An attempt to present challenges towards lines of future research concludes the review.
Title:
Structure determination of quasicrystals
Authors:
De Boissieu, M; Takakura, H; Gomez, CP; Yamamoto, A; Tsai, AP Author Full Names: De Boissieu, M.; Takakura, H.; Gomez, C. Pay; Yamamoto, A.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2613-2633 2007
Abstract:
Structure determination of quasicrystals remains a complex and challenging problem. To date, the most successful approach has been the use of high dimensional crystallography. In this paper, we introduce the basic tools used in this method and illustrate it in the case of CdYb icosahedral phase determination. The relationship between the high dimensional description and the resulting 3D structure is presented. We briefly introduce the concept of phason modes and the effects on diffraction pattern.
Title:
Temperature dependence of the modulation wavelength in Co-akermanite
Authors:
Hagiya, K; Ohmasa, M; Kusaka, K Author Full Names: Hagiya, K.; Ohmasa, M.; Kusaka, K.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2635-2640 2007
Abstract:
Two-dimensional modulation in synthetic Co-akermanite, Ca2CoSi2O7, has been precisely studied using synchrotron X-ray diffraction methods in the temperature range between 180 and 523K to determine the temperature dependence of q (the magnitude of the primary wavevectors of modulation waves). Three kinds of plateau-like regions are observed for q similar to 2/7, 3/10 and 4/13 in addition to the low-temperature commensurate phase (q 1/3). Using a simulation method we were able to generate nearly commensurate structures. The most probable structure of incommensurate Co-akermanite is octagonal arrangements of the bundles along the c-axis, which are composed of four CaO6 arrays and a central array of CoO4 tetrahedra.
Title:
Modulated structure of the misfit-layered compound Bi2.12Ba2.00Rh1.95Ox
Authors:
Yubuta, K; Okada, S; Miyazaki, Y; Terasaki, I; Kajitani, T Author Full Names: Yubuta, K.; Okada, S.; Miyazaki, Y.; Terasaki, I.; Kajitani, T.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2641-2646 2007
Abstract:
The modulated crystal structure of Bi2.12Ba2.00Rh1.95Ox has been elucidated by electron diffraction measurements and high-resolution electron microscopy (HREM). The crystal structure consists of two interpenetrating subsystems of a CdI2-type RhO2 layer and a distorted four-layered rock-salt (RS)-type block. Both subsystems have common a- and c-axes and beta-angle with a = 5.38 angstrom, c = 15.15 angstrom and beta = 95.3 degrees. On the other hand, the crystal structure is incommensurate along the b-axes; b(1) = 3.05 angstrom for the RhO2 layer and b(2) = 5.45 angstrom for the RS-type block. The misfit ratio and the chemical composition ratio give a chemical formula of [(Bi1-xRhx)(2)(Ba1-yBiy)(2)O4+delta](0.56)RhO2 with x = 0.037, y = 0.047 and delta = 0.39. It is found that this compound has two modulation vectors, q(1) = a* + 0: 56b(1)* and q(2) = 0.11b(1)* + 0: 35c* and, thus, can be regarded as (3 + 2)-dimensional crystal. The vector q(1) is due to the misfit between the rock salt and RhO2 layers parallel to the b-axis. The modulation vector q(2) is unique for the Ba-Rh system relative to Bi1.91Sr2.0Rh1.77Ox and [Bi0.87SrO2](2)[CoO2](1.82). An additional modulation vector, q(3) = 0.12a* + 0.10b(1)*, is locally observed. High-resolution images, taken with the incident electron beam parallel to the a- and c-axes, clearly exhibit modulated atomic arrangements.
Title:
Modulated crystal structure of the composite crystal (CaOH)(1.14)CoO2
Authors:
Isobe, M; Onoda, M; Shizuya, M; Tanaka, M; Takayama-Muromachi, E Author Full Names: Isobe, M.; Onoda, M.; Shizuya, M.; Tanaka, M.; Takayama-Muromachi, E.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2647-2653 2007
Abstract:
The crystal structure of the new misfit-layer calcium cobaltite (CaOH)(1.14)CoO2 was determined by means of superspace-group formalism using synchrotron X-ray diffraction data. The compound belongs to the class of incommensurate composite crystals that are isostructural to an orthorhombic form of sulfide, (PbS)(1.18)TiS2. The structure of the present compound consists of two interpenetrating subsystems: (i) [CoO2]-containing triangular lattices formed by edge-sharing CoO6 octahedra and (ii) [CaOH] double-layered rock-salt-type slabs. The two subsystems have incommensurate periodicity along the a-axis (a(1)/a(2) = 0.576), resulting in a modulated crystal structure due to the inter-subsystem interaction. In this study, it was found that there is a significant structural modulation in the [CaOH] subsystem.
Title:
Superspace approach to crystallographic shear structures
Authors:
Michiue, Y; Yamamoto, A; Tanaka, M Author Full Names: Michiue, Y.; Yamamoto, A.; Tanaka, M.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2655-2661 2007
Abstract:
A systematic method for the superspace description of crystallographic shear (CS) structures is proposed. A (3 + 1)-dimensional [(3 + 1)D] superspace model for ideal CS structures is constructed in connection with the shear operation in 3D space, which is defined by a shear plane and a shear vector. All structural parameters in the model are related to those of the parent structures by this operation. This leads to inherently discontinuous and sawtooth-like modulation functions.
Title:
High-resolution electron microscopy study of misfit-layered Bi-based cobaltites
Authors:
Yubuta, K; Begum, S; Ono, Y; Miyazaki, Y; Kajitani, T Author Full Names: Yubuta, K.; Begum, S.; Ono, Y.; Miyazaki, Y.; Kajitani, T.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2663-2669 2007
Abstract:
The structural characteristics of Bi1.84Ca2.00Co1.88Ox and Bi2.49Sr2.00Co2.22Ox are studied by electron diffraction measurements and high-resolution electron microscopy. The crystal structures consist of two interpenetrating subsystems of a CdI2-type CoO2 sheet and a distorted four-layered rock-salt (RS)-type block. Both subsystems have common lattice constants a and c and a beta angle. The crystal structure is incommensurately modulated parallel to the b-axis. These compounds have modulation vectors, q(1) = a* + 0.58b(1)* and q(2) = 0.18b(1)* + 0.5c* for the Ca system, and q(1) = a* + 0.54b(1)* and q(2) = 0.05b(1)* for the Sr system. High-resolution images taken with the incident electron beam parallel to the a- and c-axes clearly exhibit modulated atomic arrangements. The local modulation mode is related to the shear deformation in the a-b plane.
Title:
Forms and origin of structure modulation in lazurites
Authors:
Bolotina, N Author Full Names: Bolotina, N.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2679-2685 2007
Abstract:
The crystal structure of lazurite, ideally Na6Ca2[Al6Si6O24](SO4,S)(2), has a flexible framework formed with four- and six-membered rings of the (Al,Si)O-4 tetrahedra shared by vertices. The framework cavities are occupied with Na,Ca cations and S-containing anionic groups. Six modulated lazurite polymorphs have been studied using X-ray diffraction techniques. General and special features of the structure modulation of lazurites are discussed for several different structures. A mechanism of commensurate modulation is revealed using the triclinic structure as an example. The 3D incommensurate modulation of the cubic framework is shown. The commensurate 1D-modulation of the triclinic structure is compared with the incommensurate 1D-modulation of the monoclinic structure. The S-containing groups are believed to play an important role in the formation of the structure modulations.
Title:
Nuclear magnetic resonance reveals 'forbidden' symmetries in quasicrystals and related metallic alloys with giant unit cells
Authors:
Jeglic, P; Klanjsek, M; Dolinsek, J Author Full Names: Jeglic, P.; Klanjsek, M.; Dolinsek, J.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2687-2692 2007
Abstract:
We report on measurements of angular dependences of the selectively excited NMR intensity in a decagonal AlNiCo quasicrystal, icosahedral AlPdMn quasicrystal and orthorhombic xi'-AlPdMn single crystal with approximately 258 atoms in the unit cell. In all three cases, we found 10-fold rotation patterns, in agreement with structural properties of the investigated samples. However, in the orthorhombic xi'-AlPdMn complex metallic alloy, a non-perfect 10-fold symmetry was observed, which is a consequence of periodicity that strictly forbids non-crystallographic rotational symmetries. These measurements represent a starting point for testing structural models of quasicrystals and related metallic alloys with giant unit cells by means of NMR.
Title:
Quasicrystal approximant Ho13Zn58+delta (delta approximate to 0.6): an incommensurate modulated tunnel structure
Authors:
Piao, SY; Lidin, S Author Full Names: Piao, S. Y.; Lidin, S.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2693-2699 2007
Abstract:
In a systematic study of the binary quasicrystal approximants RE13Zn similar to(58) (RE = rare earth elements) system, single crystals of Ho13Zn58+delta have been prepared. It is unique among family members of the RE13Zn similar to(58) system in that it shows a modulated superstructure ordering. Satellite reflections observed in single crystal X-ray diffraction pattern indicate the presence of a one-dimensional lattice distortion. The modulated structure has been solved and refined from X-ray data using the superspace group approach. The Ho13Zn58+delta structure can be described in the (3 +1)-dimensional superspace group Pc2(1)n(0 beta 0)s0s with lattice parameters a = 24.6481(7) angstrom, b = 14.2484(4) angstrom, c = 14.0153(3) angstrom and a modulation vector q = (0, 0.741, 0). The crystal structure is closely related to those of other RE13Zn similar to(58) compounds, comprising hexagon-shaped tunnels made up of rare earth-centred Zn polyhedra. All atoms in the structure are affected by a displacive modulation, but one set of Zn atoms are very strongly affected and display an almost composite behaviour with regard to the rest of the structure.
Title:
New approximant crystals of decagonal B-Mg-Ru quasicrystal
Authors:
Miyazaki, Y; Okada, JT; Kimura, K Author Full Names: Miyazaki, Y.; Okada, J. T.; Kimura, K.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2701-2706 2007
Abstract:
We have discovered four new approximant phases of the B-Mg-Ru decagonal quasicrystal. Six phases were observed in electron diffraction patterns of B-Mg-Ru alloys prepared at 1673K from B2xMg(1-x)Ru2(1-x) (x = 0.44-0.48). Two of them are known, B4Mg2Ru5 and B11Mg5Ru13, and the other four are new approximant phases. Their lattice parameters range from a 0.84 nm to 8.5 nm; some of them can be described with the Fibonacci sequence. We suggest tiling models of these approximants using two subunits of B4Mg2Ru5 and B11Mg5Ru13, 'hexagon' and 'boat'.
Title:
Boron-based quasicrystals with sevenfold symmetry
Authors:
Steurer, W Author Full Names: Steurer, W.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2707-2712 2007
Abstract:
It is not too surprising that 5-fold symmetry is the symmetry of quasicrystals since icosahedral coordination is the most frequent atomic environment type (AET) in intermetallic phases. What about AETs with 7-fold symmetry? Whereas no regular or semi-regular polyhedra (Platonic or Archimedean solids) exist with rotational symmetry larger than 5-fold, polyhedra with only axial n-fold symmetry (e.g. pyramids) are possible for arbitrary n. Indeed, (distorted) seven-membered rings are very common in ternary borides and borocarbides such as the YCrB4, ThB4, ThMoB4, Y2ReB6 structure types. The possibility to find heptagonal quasicrystals related to these phases will be discussed.
Title:
An interpenetrated cluster model of p-type Zn-Mg-Ho icosahedral quasicrystal
Authors:
Takakura, H; Yamamoto, A Author Full Names: Takakura, H.; Yamamoto, A.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2713-2720 2007
Abstract:
A six-dimensional (6D) cluster model of p-type Zn-Mg-Ho icosahedral quasicrystal has been proposed. The model consists of three large occupation domains centred at (0, 0, 0, 0, 0, 0), (1/2, 1/2, 1/2, 1/2, 1/2), and (1/2, 0, 0, 0, 0, 0) in the 6D primitive unit cell. The 3D structure is described by three building blocks: rhombic triacontahedron (RTH), obtuse rhombohedron (OR) and acute rhombohedron (AR). The RTH is an extended icosahedral cluster, which includes a Bergman-type cluster inside it. The RTH clusters are placed at a subset of 12-fold vertices of the three-dimensional Penrose tiling with an edge length of about 0.5 nm. A pair of neighbour RTH clusters shares a rhombus face or an OR along 2- or 3-fold connections, respectively. The interstices of the network of RTH clusters are described by combinations of ORs and ARs with atom decorations.
Title:
New icosahedral quasicrystals formed in Cu-based ternary alloys
Authors:
Honma, T; Ishimasa, T Author Full Names: Honma, T.; Ishimasa, T.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2721-2726 2007
Abstract:
New Cu-based P-type icosahedral quasicrystals have been observed in the ternary Cu-(Ga or Al)-Sc alloy systems. The Cu-Ga-Sc quasicrystal forms almost exclusively in a rapidly quenched Cu48Ga34Sc18 alloy, and has a six-dimensional lattice parameter a(6D) = 0.6930 nm. The as-cast alloy with the same composition contains no quasicrystal but has a 1/1 bcc approximant as its main phase. The Cu-Al-Sc quasicrystal forms at the alloy composition Cu46Al38Sc16 both in an as-cast alloy and in alloys aged at 776 and 873 K, and has a lattice parameter a(6D) = 0.6959 nm. Although electron diffraction patterns exhibit rather strong deviation from the ideal symmetric positions for weak reflections, the presence of the quasicrystal in the aged Cu-Al-Sc alloys indicates that this phase is a candidate of a stable phase in this ternary system.
Title:
Systematic cluster-based modelling of the phases in the stability region of decagonal Al-Co-Ni
Authors:
Deloudi, S; Steurer, W Author Full Names: Deloudi, S.; Steurer, W.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2727-2732 2007
Abstract:
Systematic cluster-based structural modelling of decagonal Al-Co-Ni is performed, based on a fundamental Al-Co cluster with 20 angstrom diameter, (102) over barm symmetry and 8 angstrom periodicity. This cluster is the building unit of tau(2)-Al13Co4, from which, via minor changes, the structures of the W-approximant, the basic Co-rich phase, the superstructures of type I, II, and S1, and the basic Ni-rich phase are derived. Good agreement with available experimental data based on X-ray-diffraction is achieved.
Title:
Structural disorder of the atom cluster in a highly-ordered decagonal quasicrystal of Al72Ni20Co8
Authors:
Saitoh, K; Tanaka, N; Tsai, AP; Ishizuka, K Author Full Names: Saitoh, K.; Tanaka, N.; Tsai, A. P.; Ishizuka, K.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2733-2739 2007
Abstract:
Spherical-aberration-corrected high-resolution transmission electron microscopy observation has been carried out for a highly ordered decagonal quasicrystal of water-quenched Al72Ni20Co8. Atom clusters with a 2 nm diameter, which are considered to be basic structural motifs of the present alloy, show triangular shaped atomic arrangements in the central part, as observed previously by high-angle annular dark-field scanning transmission electron microscopy. The triangular arrangement is not identical for all the atom clusters but varies from cluster to cluster, although the orientational order of the triangles agrees well with the quasiperiodic order. The present results indicate that decagonal Al72Ni20Co8 with a highly perfect quasiperiodic order contains a relatively large amount of structural disorder inside the atom cluster, which may be caused by a local relaxation to form the highly-ordered quasiperiodic arrangement of the atom-cluster.
Title:
ALCHEMI study of chemical order in Al-Cu-Co decagonal quasicrystals
Authors:
Saitoh, K; Tsai, AP Author Full Names: Saitoh, K.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2741-2746 2007
Abstract:
Electron channelling patterns were obtained for two types of Al-Cu-Co decagonal quasicrystals prepared by the Bridgman and water-quenching methods. In both alloys, it was found that the three constituent elements, Al, Cu and Co, occupied specific sublattice sites that are different from each other, i.e. they are mutually ordered. As the melt-quenched sample even showed chemical order between Cu and Co, a strong correlation between Cu and Co is assumed to be maintained near to the melting temperature in Al-Cu-Co quasicrystals. The present results suggest a particular stabilization mechanism in the Al-Cu-Co quasicrystals, which differs from the Al-Ni-Co system where the two transition metals, Ni and Co, are mutually disordered.
Title:
Structure solution of Co-rich decagonal Al-co-Ni
Authors:
Strutz, A; Steurer, W Author Full Names: Strutz, A.; Steurer, W.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2747-2752 2007
Abstract:
The structure of Co-rich decagonal Al72.5Co18.5Ni9 has been determined by single crystal X-ray diffraction methods. This is the only modification with four-layer periodicity showing sharp Bragg reflections in all reciprocal space layers. The quasilattice parameters are a(1-4) = 4.464(1) angstrom and a(5) = 8.137(3) angstrom; the Laue group is 10/mmm. Structure solution was performed by the 5D 'charge-flipping method'. Due to pseudosymmetry, only a structure model averaged over a two-layer period (4.068 angstrom) could be obtained.
Title:
Solution of the average structure of decagonal Al71.5Co14.6Ni13.9 by the 'charge-flipping method'
Authors:
Fleischer, F; Steurer, W Author Full Names: Fleischer, F.; Steurer, W.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2753-2758 2007
Abstract:
The average structure of the type-I modification of decagonal Al71.5Co14.6Ni13.9 was solved by the five-dimensional (5D) 'charge-flipping method' based on a synchrotron diffraction data set with Laue symmetry 10/mmm and quasilattice parameters a(1-4) = 18.826(2) angstrom and a(5) = 4.0816(5) angstrom. Although the superstructure reflections constitute 4692 of all 7660 unique reflections they contribute to only 5.1% of the total integrated intensity. Their weight seems not to be sufficient for the charge-flipping algorithm to fully reconstruct the superstructure. Consequently, only a kind of averaged model will be discussed, based on two fundamental clusters with approximate to 20 angstrom diameter.
Title:
Phonon-phason coupling in decagonal quasicrystals
Authors:
Edagawa, K Author Full Names: Edagawa, K.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2789-2798 2007
Abstract:
Phonon-phason coupling in decagonal quasicrystals has been discussed in terms of phonon strains induced in crystal approximants. Elastically, decagonal quasicrystals can be classified into two groups having different symmetries in the coupling constant tensor; one has only one independent coupling constant, K-4, and the other has two such constants, K-4 and K-5. It has been shown that the orthorhombic and monoclinic approximants formed in various alloy systems can be interpreted as resulting from the two different types of decagonal quasicrystals and that a slight distortion in the unit cell of the monoclinic phases is attributable to the effect of one of the coupling constants, K-5. Phonon strains induced in monoclinic approximants of the Al-Co system have been calculated from their lattice constants and the coupling constants K-4 and K-5 have been evaluated.
Title:
Modelling local disorder and diffuse scattering in quasicrystals
Authors:
Weber, T; Kobas, M; Steurer, W Author Full Names: Weber, T.; Kobas, M.; Steurer, W.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2799-2805 2007
Abstract:
Higher-dimensional and three-dimensional techniques are complementary approaches for modelling disorder and diffuse scattering in quasicrystals. The concept of phasonic disorder allows a higher-dimensional description of disorder and calculation of diffuse intensities without knowing the atomic structure of the quasicrystal. In three-dimensional space, disorder can be analyzed by application of Patterson techniques. Local order may be modelled quantitatively without considering medium or long-range order properties of the quasicrystal. Furthermore, a priori knowledge about the structure of clusters present in the crystal can be easily utilized with Patterson methods. Potential and limitations of the techniques are discussed and demonstrated by means of experimental data.
Title:
Defect-modulated structures in Al-Ni-Rh crystalline approximants
Authors:
Sun, W; Chen, YH; Zhang, Z Author Full Names: Sun, W.; Chen, Y. H.; Zhang, Z.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2815-2822 2007
Abstract:
Defect-modulated Al-Ni-Rh crystalline approximants, which are structurally related to a decagonal quasicrystal with 1.6 nm periodicity, have been found to form in an as- solidified Al75Ni15Rh10 alloy. Their structural features were studied by a combination of high- resolution electron microscopy (HREM) and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The results show that the prefect structures of Al-Ni-Rh crystalline approximants are characterized by periodic arrangements of hexogen units (H) constructed from atom columnar clusters. Defect-modulated structures were formed due to ordered arrangement of one- or two-dimensional structural defects of high density. The basic structural defect is associated with incorrect arrangements of atom columnar clusters which appear as polygons different from the H units. These polygons of atom columnar clusters represent a type of linear defect extending along the columnar axis direction, and they can array to form a planar defect. By means of the HAADF-STEM imaging technique, the structural nature of the core area for the linear defect, which usually exhibits dark contrast in HREM observations, has been clearly revealed.
Title:
Aperiodic packings of clusters obtained by projection
Authors:
Cotfas, N Author Full Names: Cotfas, N.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2823-2830 2007
Abstract:
Atomic-resolution electron microscope images show that a quasicrystal is a quasiperiodic packing of clusters. The outer atomic shells of multi-shell clusters occurring in quasicrystals are highly symmetric and rather robust, but some structural disorder may be present around the core. The models describing quasicrystal structure are quasiperiodic lattices containing two or more unit cells decorated by atomic clusters. We show that a modi. ed version of the strip projection method may become an alternative way to obtain useful models.
Title:
Pinwheel patterns and powder diffraction
Authors:
Baakey, M; Frettloh, D; Grimm, U Author Full Names: Baakey, M.; Frettloeh, D.; Grimm, U.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2831-2838 2007
Abstract:
Pinwheel patterns and their higher dimensional generalizations display continuous circular or spherical symmetries in spite of being perfectly ordered. The same symmetries show up in the corresponding diffraction images. Interestingly, they also arise from amorphous systems, and also from regular crystals when investigated by powder diffraction. We present. rst steps and results towards a general framework to investigate such systems, with emphasis on statistical properties that are helpful to understand and compare the diffraction images. We concentrate on properties that are accessible via an alternative substitution rule for the pinwheel tiling, based on two different prototiles. Due to striking similarities, we compare our results with a toy model for the powder diffraction of the square lattice.
Title:
Discrete tomography of Penrose model sets
Authors:
Baake, M; Huck, C Author Full Names: Baake, M.; Huck, C.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2839-2846 2007
Abstract:
Various theoretical and algorithmic aspects of inverse problems in discrete tomography of planar Penrose model sets are discussed. These are motivated by the demand of materials science for the reconstruction of quasicrystalline structures from a small number of images produced by quantitative high-resolution transmission electron microscopy.
Title:
Cut-and-project sets and their epsilon-duals
Authors:
Akama, Y; Iizuka, S Author Full Names: Akama, Y.; Iizuka, S.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2847-2854 2007
Abstract:
Motivated by approximation and real analysis, Meyer introduced model sets (also called cut- and- project sets), which are used as mathematical models of quasicrystals. In his study, a central role was played by the epsilon-dual. The epsilon-dual of a lattice is the reciprocal lattice, and that of a cut- and-project set is contained by the diffraction pattern. Let CP(L, W) be the cut-and-project set determined by locally compact Hausdor Abelian groups G, G(int), lattice L subset of G x G(int) and a window W subset of G(int). Then we prove CP(L, W)(epsilon) = CP(L-epsilon, W-epsilon) by using the Baake-Lenz-Schlottmann measure CP(L, W) by the symmetries of W.
Title:
A dodecagonal quasiperiodic tiling with a fractal window
Authors:
Niizeki, K Author Full Names: Niizeki, K.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2855-2861 2007
Abstract:
A dodecagonal quasiperiodic tiling is generated by a substitution rule (SR) for four kinds of tiles, namely, a triangle, a square, a trigonal hexagon and a dodecagon. The scaling factor of the SR is equal to 2 + root 3. The same tiling (exactly, quasilattice) is obtained with the projection method from a four-dimensional dodecagonal lattice and the relevant window has a fractal boundary. A set equation for the window is presented. It is emphasized that investigating quasiperiodic tilings of this type is a less explored but rich field in the crystallography of quasicrystals.
Title:
Local point symmetry of Bravais quasilattices
Authors:
Niizeki, K Author Full Names: Niizeki, K.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2863-2868 2007
Abstract:
Mutual-local-derivability (MLD) classifications of two-dimensional (2D) and 3D quasilattices were completed in previous papers. The MLD class to which a given quasicrystal belongs is, unfortunately, not determined by the diffraction experiment only. Furthermore, a quasilattice has several types of centres of local point symmetry and types of such centres are determined by the MLD class to which the QL belongs. I have completed lists of the types of local centres for all the MLD classes of 2D quasilattices. These lists together with real space probes like the STM will be used for the determination of the MLD class to which a given quasicrystal belongs.
Title:
Deformed Penrose tilings
Authors:
Welberry, TR; Sing, B Author Full Names: Welberry, T. R.; Sing, B.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2877-2886 2007
Abstract:
Monte Carlo (MC) simulation of a model quasicrystal (2D Penrose rhomb tiling) shows that the kinds of local distortions that result from size-effect-like relaxations are in fact very similar to mathematical constructions called deformed model sets. Of particular interest is the fact that these deformed model sets are pure point-diffractive, i. e. they give diffraction patterns that have sharp Bragg peaks and no diffuse scattering. Although the aforementioned MC simulations give diffraction patterns displaying some diffuse scattering, this can be attributed to the fact that the simulations include a certain amount of unavoidable randomness. Examples of simple deformed model sets have been constructed by simple prescription and hence contain no randomness. In this case the diffraction patterns show no diffuse scattering. It is demonstrated that simple deformed model sets can be constructed, based on the 2D Penrose rhomb tiling, by using deformations which are defined in terms of the local environment of each vertex. The resulting model sets are all topologically equivalent to the Penrose tiling (same connectedness), are perfectly quasicrystalline but show an enormous variation in the Bragg peak intensities. For the examples described, which are based on nearest-neighbour environments, 12 deformation parameters may be chosen independently. If more distant neighbours are taken into account further sets of parameters may be defined. One example of these simple deformed tilings, which shows great similarity to the size-effect-distorted tiling, is discussed in detail.
Title:
Low-temperature phase of the Zn-Sc approximant
Authors:
Ishimasa, T; Kasano, Y; Tachibana, A; Kashimoto, S; Osaka, K Author Full Names: Ishimasa, T.; Kasano, Y.; Tachibana, A.; Kashimoto, S.; Osaka, K.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2887-2897 2007
Abstract:
The low-temperature transition in the Zn-Sc 1/1 cubic approximant, reported by Tamura et al. [Phys. Rev. B 71 0902203 (2005)], has been confirmed by the following experimental evidence: (1) anomaly in temperature dependence of electrical resistivity at approximately 153 K, and (2) appearance of weak superlattice reflections both in electron and powder X-ray diffraction patterns. The low- temperature phase is monoclinic, belonging to the space group C2/c, with lattice parameters a = 1.947(5) nm, b = 1.379(3) nm, c = 1.955(5) nm and beta = 89.931(3) nm. The unit cell includes four unique Tsai-type clusters consisting of almost regular tetrahedron of Zn surrounded by triple shells. The first dodecahedral shell of Zn is highly distorted so as to avoid unrealistic short atomic distance to the Zn tetrahedron. Direct evidence of an orientational ordering of the clusters has been obtained by Reitveld analysis of the low-temperature phase. The occurrence of the transition is sensit! ive on alloy composition as well as heat treatment.
Title:
Occurrence of short-range-ordered incommensurate states in gamma-TiAl
Authors:
Kulkarni, UD Author Full Names: Kulkarni, U. D.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2899-2904 2007
Abstract:
This paper examines a lesser- known form of quasiperiodicity in alloys, namely, quasiperiodicity in superlattice structures. Unlike quasicrystals, a quasiperiodic superlattice (QPSL) structure has an underlying periodic lattice and it is the arrangement of the two atomic species on this lattice that makes the superlattice quasiperiodic. Central to the discussion will be a QPSL structure, comprising three different building blocks (tiles), whose approximants are the Al5Ti3 and Al11Ti7 structures in Al-rich gamma-TiAl. The three types of tiles represent unimolecular clusters of three different superlattice structures derived from gamma- iAl. Two different types of antiphase boundaries (APBs) occur in Al5Ti3. Their energies have been changed continuously in a Monte Carlo simulation to study transformations, either to the QPSL or to known periodic superlattice structures in Al- Ti. Some of the intermediate stages of transformation are short-range ordered states, which exhibit intensity maxima at incommensurate positions in the reciprocal space and different geometrical patterns of diffuse intensity. Very good agreement has been found in the simulation results, the results of a 4D to 2D projection scheme and TEM observations.
Title:
Development of a single-crystal X-ray diffraction system for hydrostatic-pressure and low-temperature structural measurement and its application to the phase study of quasicrystals
Authors:
Watanuki, T; Machida, A; Ikeda, T; Ohmura, A; Kaneko, H; Aoki, K; Sato, TJ; Tsai, AP Author Full Names: Watanuki, T.; Machida, A.; Ikeda, T.; Ohmura, A.; Kaneko, H.; Aoki, K.; Sato, T. J.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2905-2911 2007
Abstract:
We constructed a single-crystal synchrotron X-ray diffraction system to precisely study the structure under hydrostatic pressure conditions at low temperatures and applied it to a study on the phase transition phenomena of a Cd-Yb periodic approximant and a Cd-Yb quasicrystal. Four phases were newly observed for the 1/1 approximant crystal in a P-T range up to 5.2 GPa and down to 10 K. The innermost part of the atomic clusters of Cd-4 tetrahedra exhibited various orientational ordering sensitively depending on pressure and temperature. High pressure diffraction measurements using a highly parallel synchrotron X-ray beam and a hydrostatically compressed single crystal enabled us to detect the weak diffractions due to the subtle structural changes.
Title:
Structural transformations in quasicrystal-forming quenched alloys of Al61Cu26Fe13 subjected to isothermal annealing
Authors:
Shalaeva, EV; Prekul, AF Author Full Names: Shalaeva, E. V.; Prekul, A. F.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2913-2919 2007
Abstract:
Conventional transmission electron microscopy (TEM) was employed to investigate structural transformations on annealing of rapidly solidified Al61Cu26Fe13 alloys. In these alloys, beta(CsCl)- and iota-phases reveal close to basic orientation relationships ([101](beta) parallel to A5, [111](beta) parallel to A(2). The beta- phase is characterized by short-range order with tau(3)-type and omega-like displacements. On annealing at 450 degrees C, a solid-state transformation of the beta-phase ( which has a copper concentration of 40-50 at.%) takes place by homogeneous precipitation of cuboid particles of a phase with triple the unit cell parameter 3a(beta). This phase is regarded as close to beta- based phases and the vacancy-ordered tau-phases. On annealing at 550 degrees C, a single phase iota-structure is formed.
Title:
A high-pressure study of Co-rich decagonal Al-Co-Ni and its approximant, the W phase
Authors:
Krauss, G; Gu, QF; Katrych, S; Deloudi, S; Steurer, W Author Full Names: Krauss, G.; Gu, Q. F.; Katrych, S.; Deloudi, S.; Steurer, W.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2921-2927 2007
Abstract:
The stability of Co-rich decagonal Al-Co-Ni and its closely related approximant phase, W-Al-Co-Ni, was studied in situ using powder di. raction and synchrotron radiation at high pressures up to 61.4(1) GPa (d-Al-Co-Ni) and 50.6(2) GPa (d-Al-Co-Ni), respectively. Within the experimental errors, both compounds show comparable values of the bulk modulus, i. e. K-0 = 120(11) GPa for the quasicrystal and K-0 = 138(11) GPa for its approximant phase, respectively. Both phases were found to be stable within the framework of the experiment. The results indicate that the local structure dominates the bulk property and the type of long-range order has only a minor in. uence.
Title:
Formation and magnetic properties of p-type icosahedral quasicrystals in Zn-Fe-Sc-L (L = Ho, Er, Tm) alloys
Authors:
Kashimoto, S; Masuda, C; Motomura, S; Matsuo, S; Ishimasa, T Author Full Names: Kashimoto, S.; Masuda, C.; Motomura, S.; Matsuo, S.; Ishimasa, T.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2929-2937 2007
Abstract:
Icosahedral quasicrystals containing heavy lanthanoids L, namely Ho, Er or Tm, have been discovered in the Zn77Fe7Sc16-xLx alloy systems. The solubility limit of the lanthanoid is approximately half of the Sc atoms. All these quasicrystals belong to p-type and are stable at approximately 973 K. The temperature dependence of the magnetic susceptibility of the Zn77Fe7Sc8Tm8 quasicrystal follows the Curie-Weiss law and exhibits spin-glass-like behaviour with a freezing temperature of 9K. The Curie constants obtained by Curie-Weiss fit are larger than those calculated by the Lande g-factor of free Tm3+ ions based on Hund's rule, assuming all magnetization is caused by Tm atoms only. It is deduced that both Tm and Fe atoms exhibit magnetic moments. This is the first example of a stable icosahedral quasicrystal containing two types of magnetic atoms: Fe and the lanthanoids.
Title:
Magnetic excitations in the crystalline and quasicrystalline Zn-Mg-Ho phases
Authors:
Sato, TJ; Tsai, AP Author Full Names: Sato, T. J.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2939-2946 2007
Abstract:
A comparative study has been carried out on magnetic excitations in the primitive- (p-) and face-centred-(f-) icosahedral quasicrystalline phases, as well as crystalline phase, in the Zn-Mg-Ho system. The magnetic excitation spectrum in both the quasicrystalline phases has only a broad quasielastic peak centred at the elastic position; the signal for the positive energy-transfer (h omega) side is found to be almost temperature independent in a wide temperature range 1: 5 < T < 200 K. The magnetic excitation spectrum in the crystalline Zn65.2Mg27.9Ho6.9 phase is quite similar to that of the quasicrystalline phases at high temperatures; however, well-defined inelastic peaks due to crystalline-electric-field (CEF) splitting levels appear as the temperature is decreased. The appearance of the sharp CEF peaks confirms well-defined site symmetry around the rare-earth sites in the hexagonal phase, whereas the temperature-independent quasielastic signal suggests anomalous sp! in fluctuations in the quasicrystalline phases.
Title:
TEM spectroscopy study of electronic structures of quasicrystals and approximants
Authors:
Terauchi, M; Uemichi, Y; Ueda, H; Tsai, AP; Takeuchi, T; Mizutani, U Author Full Names: Terauchi, M.; Uemichi, Y.; Ueda, H.; Tsai, A. P.; Takeuchi, T.; Mizutani, U.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2947-2955 2007
Abstract:
The density of states ( DOS) of the conduction and valence bands of a single quasicrystal of Al72NI20Co8 were obtained using electron energy-loss spectroscopy and X-ray emission spectroscopy based on transmission electron microscopy. A complete DOS near the Fermi level, which shows a clear pseudo-gap structure compared to that of aluminium, is presented for the first time. The DOS distribution is non-symmetric about the Fermi level. Onset energies of Al L-shell excitation spectra of amorphous, quasicrystalline and crystalline Al75Cu15V10 are compared with that of aluminium. Only that of the quasicrystalline phase shows a shift to the higher energy side by 0.3 eV. Onset energies of Al L-shell excitation spectra of Al-based quasicrystals (Al73Co27, Al63Cu25Fe12, Al63Cu25Ru12 and Al70Pd20Mn10) and corresponding approximant crystals are compared with that of aluminium. The onset energies of these quasicrystals show chemical shifts to the high energy side, indicating a smaller amount of valence charge at Al atom sites in the quasicrystalline phase than that of aluminium. Onset energies of approximant crystals of tau 0,tau 2-Al73Co27, Al55Cu25Fe12Si8, Al55Cu25Ru12Si8 do not show a shift, and 1/1-Al67Pd11Mn14Si8 and 2/1-Al70Pd23Mn6Si1 show shifts compared with that of aluminium. An amount of the chemical shift of 2/1-Al70Pd23Mn6Si1 is larger than that of 1/1-Al67Pd11Mn14Si8. The results show that a decrese of valence charge at Al sites is characteristic for Al-based quasicrystalline materials. It may be attributed to an increase of covalency in the bonding of the quasicrystalline materials.
Title:
Electrical resistivity of crystal approximants in Sc-based alloys
Authors:
So, YG; Edagawa, K; Tamura, R Author Full Names: So, Y. G.; Edagawa, K.; Tamura, R.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2957-2963 2007
Abstract:
Electrical resistivity and specific heat have been investigated for MI-type 1/1 crystal approximant phases in binary Sc-M (M = Ru, Rh, Ir and Pt), and ternary Sc-Rh-Ti and Sc-Rh-Au alloys. The electrical resistivities of the binary phases are relatively low and show small positive temperature coefficients, in contrast to the MI-type ternary 1/1 phases which often exhibit large negative temperature coefficients. The electronic specific heat coefficients of the binary Sc-M phases are considerably large, consistent with the low electrical resistivity. The Debye temperature of the binary Sc-M phases increases with increasing atomic mass of the M element, which could be attributed to the increase in the covalent nature of the atomic bonds in the icosahedral clusters. In the ternary Sc-Rh-Ti system, the temperature coefficient of resistivity increases with increasing Ti concentration. On the other hand, the addition of Au decreases the temperature coefficient of resistivity and changes the sign to negative at 8 at% Au in the case of the Sc-Rh-Au system.
Title:
Thermophysical properties of the melts of AlPdMn icosahedral quasicrystal
Authors:
Ishikawa, R; Ishikawa, T; Okada, JT; Maski, T; Watanabe, Y; Nanao, S Author Full Names: Ishikawa, R.; Ishikawa, T.; Okada, J. T.; Maski, T.; Watanabe, Y.; Nanao, S.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2965-2971 2007
Abstract:
Thermophysical properties of Al72Pd20Mn8 icosahedral quasicrystal melts were measured using the electrostatic levitation ( ESL) technique. Viscosity increases substantially with decreasing temperature and increases rapidly just above the melting point. In the solidification process, an under-cooled state and a recalescence were not observed.
Title:
Ordering of rare gas films on a decagonal Al-Ni-Co quasicrystal
Authors:
Diehl, RD; Setyawan, W; Ferralis, N; Trasca, RA; Cole, MW; Curtarolo, S Author Full Names: Diehl, R. D.; Setyawan, W.; Ferralis, N.; Trasca, R. A.; Cole, M. W.; Curtarolo, S.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2973-2980 2007
Abstract:
This paper reviews recent progress in the study of rare gas films on quasicrystalline surfaces. The adsorption of Xe on the 10-fold surface of decagonal Al-Ni-Co was studied using low-energy electron diffraction (LEED). The results of these studies prompted the development of a theoretical model, which successfully reproduced the thermodynamic parameters found in the experiment. Grand canonical Monte Carlo (GCMC) simulations for Xe-produced structures that agreed with the experimental observations of the adsorption structures and provided a deeper insight into the nature of the ordering. A first-order commensurate-incommensurate transition, which involves a transition from a quasicrystalline five-fold structure to a periodic hexagonal structure, was discovered and characterized for the Xe monolayer. The five rotational domains of the hexagonal structure observed in the LEED study were shown in the GCMC study to be mediated by pentagonal defects, which are entropic in nature, and not by substrate defects. The GCMC study found an absence of any such transition for Kr, Ar and Ne on the same surface. A detailed analysis of this transition led to the conclusion that the formation of the hexagonal layer depends on matching the gas and substrate characteristic lengths.
Title:
Ab initio study of a quasiperiodic Na monolayer on a five-fold i-Al-Pd-Mn surface
Authors:
Krajci, M; Hafner, J Author Full Names: Krajci, M.; Hafner, J.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2981-2988 2007
Abstract:
The structure and stability of a quasiperiodic Na monolayer formed on a five-fold surface of an icosahedral Al-Pd-Mn quasicrystal have been investigated using ab initio density-functional methods. The structural model of the adsorbed monolayer has been constructed on the basis of a mapping of the potential-energy landscape of an isolated adatom on the five-fold surface of i-Al-Pd-Mn. Na atoms adsorbed on the surface arranged to a highly regular quasiperiodic monolayer. The quasiperiodic ordering can be described by a tiling of decagons, hexagons, boats and pentagonal stars (DHBS). The coverage density of the adsorbed monolayer is 0.067 atoms/angstrom(2).
Title:
First UHV surface studies of single-grain icosahedral Ag-In-Yb quasicrystal
Authors:
Sharma, HR; Shimoda, M; Ohhashi, S; Tsai, AP Author Full Names: Sharma, H. R.; Shimoda, M.; Ohhashi, S.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2989-2994 2007
Abstract:
We present the first ultrahigh vacuum (UHV) surface study of single-grain icosahedral Ag-In-Yb quasicrystal by using X-ray photoelectron spectroscopy (XPS), reflection high- energy electron diffraction (RHEED), and scanning tunnelling microscopy (STM). This new quasicrystal is found to exhibit surfaces with steps and terraces, upon suitable preparation conditions. The Fourier transform of high-resolution STM images and RHEED patterns reveal that the surface after annealing at appropriate temperatures retains quasicrystalline long-range order. The analysis of XPS data measured from this surface shows a near bulk chemical composition in the surface region.
Title:
Terrace-dependent nucleation of small Ag clusters on a five-fold icosahedral quasicrystal surface
Authors:
Unal, B; Evans, JW; Lograsso, TA; Ross, AR; Jenks, CJ; Thiel, PA Author Full Names: Unal, B.; Evans, J. W.; Lograsso, T. A.; Ross, A. R.; Jenks, C. J.; Thiel, P. A.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 2995-3001 2007
Abstract:
Nucleation of Ag islands on the five-fold surface of icosahedral Al-Pd-Mn is influenced strongly by trap sites. Submonolayers of Ag prepared by deposition at 365K and with a flux of 1 x 10(-3) monolayers/s exhibit a variation in Ag island densities across different terraces. Comparisons with previous work and with rate equation analysis indicate that trap sites are not saturated under these experimental conditions and that the difference in island densities is not necessarily due to variation in trap densities. While it could have a number of different origins, our results point to a terrace-dependent value of the effective diffusion barrier for Ag adatoms.
Title:
Energy distribution of Co and Ni 3d states of decagonal quasicrystal Al72Co16Ni12
Authors:
Inukai, M; Soda, K; Ota, S; Miyazaki, H; Suzuki, T; Kato, M; Yagi, S; Tezuka, Y; Yokoyama, Y Author Full Names: Inukai, M.; Soda, K.; Ota, S.; Miyazaki, H.; Suzuki, T.; Kato, M.; Yagi, S.; Tezuka, Y.; Yokoyama, Y.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 3003-3010 2007
Abstract:
The density of the Co and Ni 3d states of a decagonal quasicrystal Al72Co16Ni12 has been investigated by Co and Ni 2p-3d resonance photoemission spectroscopy (XPS) and soft X-ray emission spectroscopy (XES) with synchrotron radiation as an excitation source. The valence-band photoemission spectrum recorded at the high excitation photon energy shows a single 3d band at the binding energy of 2eV, which is higher than that obtained at the low excitation photon energy. This implies that the bulk 3d electronic states are different from the surface ones. The present resonance XPS and XES spectra also show that the Ni 3d-derived band is located at slightly higher binding energy than the Co 3d-derived one, in contrast with results reported so far. Comparison with the electronic structure calculated for a cluster simulating the local columnar atomic arrangement of the decagonal quasicrystal suggests rather random occupation of the transition metal sites by Co and Ni atoms.
Title:
Mean-field theory of Archimedean and quasicrystalline tilings
Authors:
Dotera, T Author Full Names: Dotera, T.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 3011-3019 2007
Abstract:
A simple Landau theory of three-component alloy systems under incompressible condition is investigated, which appears to give regions of the phase diagram in which Archimedean tiling phases are stable in two dimensions. Moreover, we find regions where dodecagonal and decagonal quasicrystals appear to be stable. The Alexander-MacTague and Mermin-Troian theories of weak crystallization are revisited.
Title:
Soft quasicrystals - Why are they stable?
Authors:
Lifshitz, R; Diamant, H Author Full Names: Lifshitz, R.; Diamant, H.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 3021-3030 2007
Abstract:
In the last two years we have witnessed the exciting experimental discovery of soft matter with nontrivial quasiperiodic long-range order - a new form of matter termed a soft quasicrystal. Two groups have independently discovered such order in soft matter: Zeng et al. in a system of dendrimer liquid crystals; and Takano et al. in a system of ABC star-shaped polymers. These newly discovered soft quasicrystals not only provide exciting platforms for the fundamental study of both quasicrystals and of soft matter, but also hold the promise for new applications based on self-assembled nanomaterials with unique physical properties that take advantage of the quasiperiodicity, such as complete and isotropic photonic band-gap materials. Here we provide a concise review of the emerging field of soft quasicrystals, suggesting that the existence of two natural length-scales, along with three-body interactions, may constitute the underlying source of their stability.
Title:
The aperiodic double chain model applied to composition. flexible compounds
Authors:
Janssen, T; Perez-Matoz, JM Author Full Names: Janssen, T.; Perez-Matoz, J.-M.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 3031-3041 2007
Abstract:
A simple model for composition flexible compounds is studied. A discussion is given of the coupling between structure and composition, and of the dynamics.
Title:
First-principles calculations of the geometry of a Zn-Sc cluster
Authors:
Mizuno, S; Ogasawara, M; Suzuki, S Author Full Names: Mizuno, S.; Ogasawara, M.; Suzuki, S.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 3043-3048 2007
Abstract:
A theoretical study is presented of the geometry of a Tsai-type cluster consisting of Zn and Sc. This cluster is a building block of both Zn-TM-Sc (TM=Mn, Fe, Co, Ni) quasicrystals and their approximants. First-principles structural optimizations are carried out and the stable structure of this cluster examined. Our results show that four Zn atoms inside the Tsai-type cluster form a distorted tetrahedron and the first shell of the cluster is also distorted.
Title:
The local controlled growth of a perfect Cartwheel-type tiling called the quasiperiodic succession
Authors:
Gaenshirt, U; Willsch, M Author Full Names: Gaenshirt, U.; Willsch, M.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 3055-3065 2007
Abstract:
Modelling of the growth of a decagonal Cartwheel-type tiling is not described well enough by the well known matching rules of Penrose tiles. This paper presents a deterministic algorithm which allows the calculation of a perfect Cartwheel-type tiling by the successive transfer of recursive values out of each cluster cell, Q, to its neighbour cells.
Title:
Modulation functions for quasicrystals
Authors:
Yamamoto, A Author Full Names: Yamamoto, A.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 3067-3072 2007
Abstract:
Modulation functions (MFs) are introduced for detailed descriptions of quasicrystals. As an example, the MFs for scalar properties, like the occupation probability, in dihedral quasicrystals are demonstrated. They are a linear combination of products of Chebyshev polynomials fulfilling the conditions imposed by the site symmetry and are orthogonal within polygonal occupation domains.
Title:
Super-coloured tilings: a novel class of two-dimensional limit-periodic structures
Authors:
Niizeki, K; Fujita, N Author Full Names: Niizeki, K.; Fujita, N.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 3073-3078 2007
Abstract:
A two-dimensional (2D) periodic coloured tiling has a colour symmetry if it is invariant against a symmetry operation involving the change of colours. The idea of colour symmetry may also be adopted for another type of symmetry, namely the inflation symmetry for self-similar structures. A general method for constructing substitution rules that generate a class of 2D aperiodic coloured tilings is presented, where we assume that there are only two colours and a single shape for the tiles. These structures are limit-periodic, and we will call them super-coloured tilings (SCTs). SCTs form an important class of aperiodic ordered structures with a perfect long-range order. Since their aperiodicity relies on the colours of the tiles, an SCT reduces to a periodic tiling if the colours of the tiles are disregarded.
Title:
In situ study of quasicrystal growth by synchrotron X-ray imaging
Authors:
Gastaldi, J; Reinhart, G; Nguyen-Thi, H; Mangelinck-Noel, N; Billia, B; Schenk, T; Hartwig, J; Grushko, B; Klein, H; Buffet, A; Baruchel, J; Jung, H; Pino, P; Przepiarzynskik, B Author Full Names: Gastaldi, J.; Reinhart, G.; Nguyen-Thi, H.; Mangelinck-Noel, N.; Billia, B.; Schenk, T.; Haertwig, J.; Grushko, B.; Klein, H.; Buffet, A.; Baruchel, J.; Jung, H.; Pino, P.; Przepiarzynskik, B.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 3079-3087 2007
Abstract:
One of the main challenges of quasicrystal science is to elucidate how the quasiperiodic order can extend so far, i.e. up to several centimetres according to the size of the single grains of various alloys routinely grown nowadays [ M. Boudard, E. Bourgeat-Lami, M. de Boissieu, et al., Phil. Mag. Lett. 71 11 (1995); Y. Yokoyama, R. Note, A. Kimura, et al., Mater. Trans. JIM 38 943 (1997); A. Langsdorf, and W. Assmus, J. Cryst. Growth 192 152 (1998)]. Noticing that most of the present knowledge on the growth of quasicrystal grains has been collected after their cooling at room temperature, we have carried out the first in situ and real time observation of this peculiar process, which has clearly disclosed both the shape of the growing interface and its defective state. Therefore we have studied the solidification of an AlPdMn alloy giving quasicrystal grains by synchrotron X-ray imaging, combining thereby radiography and X-ray topography techniques. Radiography allowed us to clearly evidence a facetted growth proceeding by lateral motion of ledges at the solid-melt interface and controlled by the interface kinetics, rather than by local heat flow as was widely thought. Thus, a realistic estimate of the kinetic coefficient was deduced from the solid-melt interface undercooling, which indicates that quasicrystal growth is more comparable with the growth of both semiconductors and oxides than with that of pure metals. X-ray topographs, recorded simultaneously with radiographs, revealed that a lot of strain and defects are generated in the quasicrystal grains during their growth, which could be related to the growth process itself and very informative on the origin of the stability of the quasicrystal lattice.
Title:
Crystal growth of quasicrystal and partial phase diagram involving quasicrystal in the Ag-In-Yb system
Authors:
Ohhashi, S; Hasegawa, J; Takeuchi, S; Tsai, AP Author Full Names: Ohhashi, S.; Hasegawa, J.; Takeuchi, S.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 3089-3094 2007
Abstract:
An isothermal section of the partial Ag-In-Yb phase diagram, involving the icosahedral quasicrystalline (i-QC) phase and its corresponding 2/1 and 1/1 approximants (AP) at 823 K, has been determined. The i-QC, 2/1 and 1/1 AP exist in the compositional region around Ag42In42Yb16, Ag41In44Yb15 and Ag40In46Yb14, respectively. In a way similar to the Cd-Yb system, the i-QC in the present system forms congruently from the melt at around 890 K. On the basis of the phase diagram, a large single grain of i-QC with a diameter of 10 mm was obtained by using the Bridgman method.
Title:
Periodic average structures in phononic quasicrystals
Authors:
Sutter-Widmer, D; Deloudi, S; Steurer, W Author Full Names: Sutter-Widmer, D.; Deloudi, S.; Steurer, W.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 3095-3102 2007
Abstract:
Periodic average structures for the pentagonal, heptagonal, octagonal and dodecagonal tilings were constructed and used for the interpretation of transmission spectra of corresponding two-dimensional phononic quasicrystals (QPNCs). In the hard scattering regime of steel rods in water, the transmission behaviour of QPNCs resembles that of disordered periodic phononic crystals. The average structures allow prediction of position and width of the first bandgap. Additionally, the type of deviation of the quasiperiodic from its periodic average structure is shown to support the understanding of the shape of the transmission spectra and may assist the choice of an optimal structure for specific phononic crystal applications.
Title:
Cross-section TEM investigation of quasicrystalline catalysts prepared by aqueous NaOH leaching
Authors:
Tanabe, T; Kameoka, S; Sato, F; Terauchi, M; Tsaizx, AP Author Full Names: Tanabe, T.; Kameoka, S.; Sato, F.; Terauchi, M.; Tsaizx, A. Pang
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 3103-3108 2007
Abstract:
The Al-Cu-Fe quasicrystal (QC) has been shown to reveal high catalytic activity and thermal stability for steam reforming of methanol (SRM: CH3OH+H2O -> 3H(2)+CO2), after leaching with NaOH aqueous solution. To investigate the origin of the high catalytic performance, cross-sectional transmission electron microscopy (TEM) observations of the catalyst particles were examined. By leaching with NaOH aq., a homogeneous composite structure, composed of Cu and Fe and/or their oxides or hydroxides, is formed at the outer layer of catalyst particles and the QC phase remains in the inner area. The homogeneous dispersion of Fe and/or the oxide/hydroxide in the composite suppresses sintering of Cu particles. In contrast, for the catalyst prepared from crystalline omega-phase (Al70Cu20Fe10), the original phase completely collapses and, instead, a complicated composite structure is formed. The inhomogeneity results in the formation of Cu-enriched regions at the rim of the catalyst particles. We suggest that the high catalytic performance of the Al-Cu-Fe QC catalyst prepared by leaching with NaOH aq. is due to the formation of a homogeneous composite region at the outer layer of the catalyst particles.
Title:
Nanoindentation studies on Ti-Zr-Ni bulk quasicrystalline intermetallics
Authors:
Mukhopadhyay, NK; Dong, C; Jianbing, Q; Sarma, VS Author Full Names: Mukhopadhyay, N. K.; Dong, C.; Jianbing, Q.; Sarma, V. S.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 3109-3115 2007
Abstract:
Polycrystalline Ti40Zr40Ni20 bulk quasicrystals are used for microindentation and nanoindentation studies. The microindentation test gives the Meyer's hardness as 6.22 +/- 0.16 GPa, but it does not exhibit any indentation size effect (ISE) nor any cracking, even at a higher 200g load. From nanoindentation tests, the reduced Young's modulus (Er) was found to vary from 115 to 124 GPa. Assuming suitable elastic constants of the indenter, the average Young's modulus (E) was determined to be 127 +/- 6 GPa. Nanohardness appears to vary from 8.5 to 11.2 GPa over a wide range of load, indicating an indentation size effect at a nanoscale. The discontinuities in the plot (known as pop-ins or strain bursts) of P-h data, obtained from nanoindentation tests, are observed frequently and these are correlated with shear bands, which are observed under atomic force microscopy (AFM). The first pop-ins, observed in the load range 50-100 mu N, led to the estimation of maximum shear stress as similar to 8 GPa, close to the theoretical shear strength (similar to E/25), and estimation of the energy as 0.67 eV/atom, which is required for elastic-plastic transition of this type of material. Thus, the pop-ins has been attributed to elastic-plastic transition during nanoindentation tests.
Title:
Studies on Al-Ni-Fe decagonal quasicrystalline alloy prepared by mechanical alloying
Authors:
Yadav, TP; Mukhopadhyay, NK; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Mukhopadhyay, N. K.; Tiwari, R. S.; Srivastava, O. N.
Source:
PHILOSOPHICAL MAGAZINE 87 (18-21): 3117-3125 2007
Abstract:
Decagonal quasicrystalline Al70Ni24Fe6 powder was produced by mechanical alloying of the elemental powders followed by annealing. A high-purity elemental powder mixture of 70 at.% Al, 24 at.% Ni and 6 at.% Fe was mechanically milled for various times up to 100 h and annealed at 750 degrees C for 40 h. The powders milled for 100 h upon annealing showed formation of 200-300nm size decagonal phase grains as the major component along with minor amounts of Al3Ni2 (tau 3) and B2-type phases. The formation of decagonal phase and related crystalline phases was confirmed using the X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray microanalysis techniques. It is interesting to note that the decagonal phase did not form directly after milling. Subsequent annealing is required for the formation of decagonal quasicrystalline phase.
Title:
Evolution of the premartensitic state in the NiAl phase of a NiCoCrAlY bond coat during thermal cycling
Authors:
Mendis, BG; Hemker, KJ Author Full Names: Mendis, B. G.; Hemker, K. J.
Source:
PHILOSOPHICAL MAGAZINE 87 (27): 4229-4251 2007
Abstract:
Transmission electron microscopy (TEM) is used to investigate the evolution of the premartensitic state in the NiAl-based beta- phase in NiCoCrAlY bond coats during thermal cycling. Bright-field imaging and diffraction analysis confirm that the lattice modulation is in the form of {110} < 1(1) over bar 0 > transverse displacement waves. High resolution electron microscopy (HREM) revealed an increase in modulation wavelength during thermal cycling due to the beta- phase becoming progressively richer in Ni through superalloy-bond coat interdiffusion. Transverse modulations extending over large regions of the crystal were observed in the HREM images, inconsistent with previous theories attributing the origin of the premartensitic state to point defects that couple to the dynamic instability of the lattice.
Title:
Phason mode of electromagnons in terbium manganite with sinusoidal antiferromagnetic structure
Authors:
Chupis, IE Author Full Names: Chupis, I. E.
Source:
LOW TEMPERATURE PHYSICS 33 (8): 715-717 AUG 2007
Abstract:
The interaction of light with electromagnons in a sinusoidally modulated antiferromagnetic phase of TbMnO3 is examined. It is predicted that the frequency dependence of the dielectric tensor epsilon(zz) changes substantially at the transition from a sinusoidal into a spiral magnetic phase with spontaneous electric polarization. The phason mode of such a transition is an electromagnon mode in which the magnetoelectric phase is due to modulation of the magnetic structure. (c) 2007 American Institute of Physics.
Title:
Ni-impurity effects on incommensurate spin correlations in the superconducting phase of La2-xSrxCuO4 near the spin-glass phase boundary
Authors:
Hiraka, H; Ohta, S; Wakimoto, S; Matsuda, M; Yamada, K Author Full Names: Hiraka, Haruhiro; Ohta, Soichi; Wakimoto, Shuich; Matsuda, Masaaki; Yamada, Kazuyoshi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 (7): Art. No. 074703 JUL 2007
Abstract:
Neutron scattering experiments were carried out to explore Ni-impurity effects on static spin correlations in La2-xSrxCuO4 in the vicinity of the superconductor-insulator boundary where both parallel and diagonal spin-density modulations (SDMs) coexist at low temperature. Dilute Ni substitution completely destroys the bulk superconductivity and alters well-defined incommensurate peaks of Ni-free SDMs into a single broad peak at (pi, pi). As the Ni concentration (y) reaches similar to x, the magnetic diffuse scattering is transformed to an intense sharp Bragg peak, corresponding to a three-dimensional antiferromagnetic (AF) order in bulk. T-N of such Ni-induced AF order depends on x and appears to disappear at x similar to 0. 1. A simplified cross section for the Q spectra taking into account the orthorhombic domain structure reproduces the Ni-impurity effect on the static spin correlations well, which results in a decreasing incommensurability of both types of SDMs. These effects are approximately ascribed by a reduction in the number of mobile holes, or by the effective hole number x(eff) = x - y, similarly to the case of diagonal SDMs in insulating spin-glasses.
Title:
Simultaneous measurements of magnetic neutron diffraction, electrical polarization and permittivity of multiferroic ErMn2O5
Authors:
Fukunaga, M; Nishihata, K; Kimura, H; Noda, Y; Kohn, K Author Full Names: Fukunaga, Mamoru; Nishihata, Keisuke; Kimura, Hiroyuki; Noda, Yukio; Kohn, Kay
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 (7): Art. No. 074710 JUL 2007
Abstract:
In order to determine an exact relationship between magnetic ordering and ferroelectricity in multiferroic rare-earth manganese oxides, we have performed simultaneous measurements of neutron diffraction, ferroelectric D-E hysteresis loops and the permittivity epsilon of ErMn2O5 down to 2.5 K. Special attention was paid to the area around the ferroelectric phase transition temperature. In contrast to previous expectations based on separate measurements, the peak of epsilon was found to coincide with a magnetic incommensurate-commensurate phase transition. However, it was confirmed that electrical polarization appears at the transition to a one-dimensionally incommensurate magnetic phase, which is higher than the peak of epsilon by 1.2 K. A previously unknown low-temperature incommensurate magnetic phase of ErMn2O5 below 8 K was found. The lowest-temperature phase appears to be paraelectric according to the D-E loops, while pyroelectric measurements show that the phase exhibits a small polarization.
Title:
Magnetic properties and Gd-155 Mossbauer spectroscopy of the icosahedral quasicrystal Ag50In36Gd14
Authors:
Stadnik, ZM; Al-Qadi, K; Wang, P Author Full Names: Stadnik, Zbigniew M.; Al-Qadi, Khalid; Wang, Pu
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (32): Art. No. 326208 AUG 15 2007
Abstract:
The results of x-ray diffraction, magnetic susceptibility, and Gd-155 Mossbauer spectroscopy studies of the recently discovered icosahedral quasicrystal Ag50In36Gd14 are reported. The studied quasicrystal has a simple six-dimensional Bravais lattice with the six-dimensional hypercubic lattice constant of 7.805(2) angstrom The observed broadening of the diffraction Bragg peaks reflects the presence of the topological/chemical disorder. The temperature dependence of the magnetic susceptibility follows the Curie-Weiss law with an effective magnetic moment of 8.15(1) mu B per Gd atom and the paramagnetic Curie temperature of -37.1(2) K. The studied quasicrystal is a spin glass with a freezing temperature of 4.25(5) K. The presence of a distribution of the electric quadrupole splitting in the Mossbauer spectra indicates the existence of a multiplicity of Gd sites. The values of the principal component of the electric field gradient tensor and the asymmetry parameter at these sites are, respectively, -4.91(10) x 10(21) V cm(-2) and. = 1.00( 20). The Debye temperature of Ag50In36Gd14 is 199(2) K. The hyperfine magnetic field sets in at a temperature higher than the freezing temperature.
Title:
High-field magnetization and magnetic structure of Tb3Co
Authors:
Baranov, NV; Gubkin, AF; Vokhmyanin, AP; Pirogov, AN; Podlesnyak, A; Keller, L; Mushnikov, NV; Bartashevich, MI Author Full Names: Baranov, N. V.; Gubkin, A. F.; Vokhmyanin, A. P.; Pirogov, A. N.; Podlesnyak, A.; Keller, L.; Mushnikov, N. V.; Bartashevich, M. I.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (32): Art. No. 326213 AUG 15 2007
Abstract:
The measurements of the magnetization in high steady and pulsed fields together with neutron diffraction measurements on a powder sample and on a single crystal have been performed to study the magnetic state of the Tb3Co compound. It has been shown that the modulated antiferromagnetic structure which exists in Tb3Co below TN = 82 K transforms to the incommensurate magnetic structure with a strong ferromagnetic component along the c-axis with further cooling below the critical temperature Tt approximate to 72 K. The phase transition from the high-temperature to the low-temperature magnetic state at Tt is of first order. The incommensurability of the low-temperature magnetic structure of Tb3Co is attributed to the non-Kramers character of the Tb3+ ion in combination with competition between the indirect exchange interaction and the low-symmetry crystal electric field.
Title:
>From clusters to phase diagrams: composition rules of quasicrystals and bulk metallic glasses
Authors:
Dong, C; Wang, Q; Qiang, JB; Wang, YM; Jiang, N; Han, G; Li, YH; Wu, J; Xia, JH Author Full Names: Dong, C.; Wang, Q.; Qiang, J. B.; Wang, Y. M.; Jiang, N.; Han, G.; Li, Y. H.; Wu, J.; Xia, J. H.
Source:
JOURNAL OF PHYSICS D-APPLIED PHYSICS 40 (15): R273-R291 AUG 7 2007
Abstract:
Metallic elements having negative enthalpies of mixing tend to form characteristic local atomic clusters. In this review, we use the structural information in the first nearest neighbour shell level, or first-shell atomic cluster, to derive the composition rules of two types of complex alloy phases, quasicrystals and bulk metallic glasses, both being composed of elements with negative enthalpies of mixing. We first show the composition phenomena in quasicrystal-forming systems, where major composition rules such as cluster line, electron concentration and atomic size criteria are derived. Then we analyse the composition rules of bulk metallic glasses using the very same approaches. Finally, we summarize their common composition rules into more general rules and basic theories.
Title:
Magnetic properties and structure of thin Ni-Mn-Sn films and alloys
Authors:
Dubowik, J; Goscianska, I; Kudryavtsev, YV; Szlaferek, A Author Full Names: Dubowik, J.; Goscianska, I.; Kudryavtsev, Y. V.; Szlaferek, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): 2773-2775 Part 3 MAR 2007
Abstract:
We report structural and magnetic properties of Ni-Mn-Sn films and compare them with those of the bulk Ni-Mn-Sn alloys. Bulk Ni50Mn50-Sn-x(x) (x approximate to 13-14) Heusler alloys show that at room temperature L2(1) (or B2) ordering for x = 14 and modulated martensitic structure for x = 13, and exhibit martensitic transformations typical of this system. The. ash- evaporated films (200 nm in thickness) deposited from the powders obtained from the same alloys show a X-ray diffraction (XRD) of almost the same lattice spacing but completely different peak intensities with the most intense (1 11) reflection, resulting either from a high (111) texture or the L1(0) ordering. Magnetic properties of the films are typical of soft magnetic films with M-s(0K)approximate to 650 Gs (4 pi M-eff 8000 Gs) with no sign of the martensitic transformation except for some anomalies in the FMR linewidth. (C) 2006 Elsevier B. V. All rights reserved.
Title:
Polarization study of non-resonant X-ray magnetic scattering from spin-density-wave modulation in chromium
Authors:
Ohsumi, H; Takata, M Author Full Names: Ohsumi, Hiroyuki; Takata, Masaki
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): E950-E952 Part 3 MAR 2007
Abstract:
We present a polarization study of non-resonant X-ray magnetic scattering in pure chromium. Satellite reflections are observed at +/- Q and +/- 2Q, where Q is the modulation wave vector of an itinerant spin-density-wave. The first and second harmonics are confirmed to have magnetic and charge origin, respectively, by means of polarimetry without using an analyzer crystal. This alternative technique eliminates intolerable intensity loss at an analyzer by utilizing the sample crystal also as an analyzer crystal. (C) 2006 Elsevier B. V. All rights reserved.
Title:
Single-crystal growth and structure determination of misfit layer oxide [Sr2TlO3][CoO2](1.77)
Authors:
Valkeapaa, M; Valldor, M; Lidin, S; Lada, T; Morawski, A; Eriksson, S Author Full Names: Valkeapaa, Markus; Valldor, Martin; Lidin, Sven; Lada, Tornasz; Morawski, Andrzej; Eriksson, Sten
Source:
JOURNAL OF CRYSTAL GROWTH 306 (1): 233-239 AUG 1 2007
Abstract:
We have synthesized single crystals of the misfit layer cobaltate [Sr,TIO3][CoO2](1.77) and determined its crystal structure by the means of X-ray single-crystal diffraction (XRSD) and transmission electron microscopy. The synthesis took place by spontaneous crystallization from an oxide melt at high gaseous pressure. The structure is described by two monoclinic subsystems, which share the unit cell parameters, a = 4.933(5),angstrom, c = 11.470(12) angstrom, and beta = 98.00(10)degrees, but are incommensurate in the direction of b-axes: b, = 5.009(8) A and b(2) = 2.830(8) angstrom, where b, is for the subsystem [Sr2TIO3] and b, for [CoO2]. The layer sequence in the structure consists of Cdl(2)-type structured (CoO2,)(infinity) and three puckered rock-salt (RS) layers, two of which are (SrO)(infinity) and one (TIO)(infinity). The solved structure confirms that the thermoelectric compounds [Ca2COO3][COO2](1.62) (Co-121) and [Sr2TlO3][CoO2](1.77) (TI-121) are isostructural. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Magnetic ordering in ZrNiA1-type crystal system
Authors:
Gondek, L; Szytula, A Author Full Names: Gondek, Lukasz; Szytula, Andrzej
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 442 (1-2): 111-113 SEP 13 2007
Abstract:
In this work, the theoretical studies, basing on the XY model, of possible magnetic ordering in ZrNiAl-type structure are presented. Our research are restricted to the ground state of XY Hamiltonian including interactions between nearest and next nearest magnetic moments. The influence of Dzialoshinsky-Moriya (DM) interaction is discussed as well. The results indicate several possible magnetic structures including simple ones of ferromagnetic or antiferromagnetic type. On the other hand, complicated magnetic structures described by commensurate as well as incommensurate propagation vectors were found as well. The resulting phase diagram of XY model is compared to experimentally determined magnetic structures of several compounds of ZrNiAl-type structure. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Grain refinement of Mg-Zn-Y alloy reinforced by an icosahedral quasicrystalline phase by severe hot rolling
Authors:
Muller, A; Garces, G; Perez, P; Adeva, P Author Full Names: Mueller, A.; Garces, G.; Perez, P.; Adeva, P.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 443 (1-2): L1-L5 SEP 27 2007
Abstract:
Severe plastic deformation allows obtaining fine grain sizes in a quasicrystalline reinforced Mg-Zn-Y alloy via hot rolling. The final grain size (similar to 1 mu m) is reached after two passes. The decreases in the grain size results in a strong increase in the yield stress. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Switching of spontaneous electric polarization in the DyMnO3 multiferroic
Authors:
Milov, EV; Kadomtseva, AM; Vorob'ev, GP; Popov, YF; Ivanov, Y; Mukhin, A; Balbashov, AM Author Full Names: Milov, E. V.; Kadomtseva, A. M.; Vorob'ev, G. P.; Popov, Yu. F.; Ivanov, Yu.; Mukhin, A.; Balbashov, A. M.
Source:
JETP LETTERS 85 (10): 503-506 JUL 2007
Abstract:
For the DyMnO3 multiferroic with a modulated magnetic structure, switching of its spontaneous electric polarization (P parallel to c axis) near the ferroelectric transition (T < T (FE) similar to 20 K) is revealed by measuring the dielectric hysteresis loops. It is found that the coercive field strongly increases as the temperature decreases (up to 2.6 kV/mm at 17.6 K). The values obtained for the spontaneous polarization are found to agree well with the data obtained from pyroelectric measurements. In addition, anomalies are observed in the temperature dependences of the spontaneous polarization P-c, dielectric constant epsilon(c), and magnetic susceptibility x (b) at T similar to 6 K; these anomalies are attributed to the antiferromagnetic ordering of the Dy3+ ions.
Title:
Occupation waves the way you have never seen them: the orthorhombic quasicrystal approximants RE13Zn58+delta (RE = Ho, Er, Tm, and Lu)
Authors:
Piao, SY; Lidin, S Author Full Names: Piao, ShuYing; Lidin, Sven
Source:
INORGANIC CHEMISTRY 46 (16): 6452-6463 AUG 6 2007
Abstract:
A series of binary quasicrystal approximants RE13Zn58+delta (RE = Ho, Er, Tm, and Lu) have been prepared, and structural studies were performed by means of single-crystal X-ray diffraction. All four compounds crystallize in the orthorhombic system, but while the Ho-containing compound crystallizes in space group Pcmn, the rest of the compounds crystallize in Pc2(1)n. This work is a continuation of the structural studies on RE13Zn similar to 58 (RE = Ce, Pr, Nd, Sm, Gd, Tb, and Dy), which all belong to the hexagonal system. The sequence of RE13Zn58+delta compounds exhibits a large variability in local ordering and composition, and therefore the crystal structures are generally rather more complex than those previously reported and exhibit a number of different ordering modes. These four compounds are structurally closely related to each other.
Title:
Complexity function and forcing in the 2D quasi-periodic rauzy tiling
Authors:
Zhuravlev, VG; Maleev, AV Author Full Names: Zhuravlev, V. G.; Maleev, A. V.
Source:
CRYSTALLOGRAPHY REPORTS 52 (4): 582-588 JUL-AUG 2007
Abstract:
The quantitative characteristics of the long-range translational order in the 2D quasi-periodic Rauzy tiling (complexity function and forcing depth) have been investigated. It is proved that the complexity function C(n) is equal to the number of figures in the n-corona grown from a seed composed of three figures of different types. The complexity function c(n) is found to be additive. A relationship between the jumps in the maximum forcing depth and large incomplete particular expansions in a chain fraction of irrational angles of rotation of a unit circle, which determine the growth of geodetic chains, is established.
Title:
X-ray diffraction analysis of modulated crystals: Review
Authors:
Bolotina, NB Author Full Names: Bolotina, N. B.
Source:
CRYSTALLOGRAPHY REPORTS 52 (4): 647-658 JUL-AUG 2007
Abstract:
The state of the art of X-ray diffraction analysis of modulated crystals is reviewed. The review begins with a brief historical overview followed by the consideration of the main concepts and notations used in this field. Then. methods of structural analysis of modulated crystals are considered with emphasis on recent achievements. The most interesting objects are listed, and the directions of investigation are outlined. Examples of analysis of both individual structures and families of modulated and incommensurate composite structures are L given in terms of superspace symmetry.
Title:
Materials simulations using VASP - a quantum perspective to materials science
Authors:
Hafner, J Author Full Names: Hafner, J.
Source:
COMPUTER PHYSICS COMMUNICATIONS 177 (1-2): 6-13 JUL 2007
Abstract:
The fundamental aspects of ab-initio simulations of materials properties and of processes in materials based on density-functional theory, and their implementation at various levels of theory in the Vienna ab-initio simulation package are reviewed. The state-of-the-art is illustrated at selected examples, chosen from nanostructured materials, quasicrystals, surface science and catalysis. Finally a brief outlook is given on current developments attempting to make post-DFT approaches applicable to materials-science problems. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Correlation between icosahedral short range order, glass forming ability, and thermal stability of Zr-Ti-Ni-Cu-(Be) glasses
Authors:
Mechler, S; Schumacher, G; Zizak, I; Macht, MP; Wanderka, N Author Full Names: Mechler, S.; Schumacher, G.; Zizak, I.; Macht, M.-P.; Wanderka, N.
Source:
APPLIED PHYSICS LETTERS 91 (2): Art. No. 021907 JUL 9 2007
Abstract:
The structure and the crystallization behavior of the bulk metallic glass Zr46.8Ti8.2Ni10Cu7.5Be27.5 and of its Be-free derivative Zr64.5Ti11.4Ni13.8Cu10.3 are analyzed by means of differential scanning calorimetry, transmission electron microscopy, and x-ray diffraction. These alloys reveal different glass forming abilities. Thermal stability and crystallization behavior of the glasses are also different. These differences are correlated with the different degrees of icosahedral short range order in the glasses. Results fit to the model of geometric frustration, which describes the structure of metallic glasses as "highly defective quasicrystals." In the present case Be degrades the ideal quasicrystalline structure. (C) 2007 American Institute of Physics.
Title:
Elastic behavior and pressure-induced structural evolution of nepheline: Implications for the nature of the modulated superstructure
Authors:
Gatta, GD; Angel, RJ Author Full Names: Gatta, G. Diego; Angel, Ross J.
Source:
AMERICAN MINERALOGIST 92 (8-9): 1446-1455 AUG-SEP 2007
Abstract:
The elastic behavior and the pressure-induced structural evolution of a natural nepheline(K0.54Na3.24Ca0.03Al4Si4O16) were investigated by in-situ single-crystal X-ray diffraction up to 7.5 GPa with a diamond anvil cell under hydrostatic conditions. As observed in previous studies, at room conditions the diffraction pattern of nepheline includes satellite reflections, whereas the structure refinement to the Bragg reflections confirms that the O1 site is displaced from the triad at (2/3, 1/3, z). The reflection conditions confirm that the space group of the average structure of nepheline remains as P6(3) through-out the pressure range investigated, and no significant compression of the T-O bonds was measured up to 7.5 GPa. As pressure was increased to around 1 GPa the integrated intensities of the satellites decreased slightly, and at 1.8 GPa no significant intensity of the satellites was detected. Over the same pressure range the O1 site moved toward the triad and thus the tilts of the T1and T2 tetrahedra decreased. The presence of the subsidiary non-Bragg reflections is therefore related to the split of the O1 site. When the satellites disappear at pressures above 2 GPa, the O1 site is on the triad at (2/3, 1/3, z), corresponding to a straight T1-O1-T2 bond. Below 2 GPa the structure responds to increased pressure by tilting of all four tetrahedra and above 2 GPa by tilting of the T3 and T4 tetrahedra alone. The change in compression mechanism arising from the changes in the O1 position is associated with changes in the compression of the unit-cell axes and the unit-cell volume. The volume can be described by fourth-order Birch-Murnaghan equation-of-state with parameters V-o = 723.57(4) angstrom(3), K-T0 = 47.32(26) GPa, K' = 2.77(24), and K''= 0.758(79) GPa (-1). The elastic behavior along the a- and c-axis can be described with a "linearized" fourth-order Birch-Murnaghan equations-of-state, with the following refined parameters:! a(0) = 9.9911(2) angstrom, K-T0(a) = 43.1(3) GPa, K'(a) = 2.5(3), and K''(a) = 0.68(8) GPa(-1) for the a-axis and c(0) = 8.3700(1) angstrom, K-T0(c) - 58.6(3) GPa, K'(c) = 4.0(3), and K''(c) = 0.85(l 1) GPa(-1) for the c-axis. The pressure-induced structural evolution in nepheline up to 7.5 GPa appears to be completely reversible. The recovery of the modulation upon complete pressure release points to the framework of nepheline having an instability corresponding to a rigid-unit mode with a wave vector corresponding to the observed positions of the satellite reflections.
Title:
Complex disorder in beta-NH4Fe2(PO4)(2): deciphering from a five-dimensional formalism
Authors:
Perez, O; Adam, L; Guesdon, A; Daturi, M; Raveau, B Author Full Names: Perez, Olivier; Adam, Laure; Guesdon, Anne; Daturi, M.; Raveau, Bernard
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 63: 521-531 Part 4 AUG 2007
Abstract:
A new mixed-valent iron ammonium phosphate, ss-NH4Fe2( PO4)(2), has been synthesized. The diffuse scattering observed on the diffraction patterns implies complex disorder phenomena and prevents a direct structure resolution. The latter can be solved by generating an artificially ordered orthorhombic structure, using a five-dimensional approach and performing partial integration of the diffuse streaks. In the artificially ordered structure, hexagonal tunnels, delimited by FeO6 octahedra, perpendicular to the directions [011] and [011] can then be seen; they are filled either by [FeP2O10]infinity zigzag ribbons or by NH4+ cations. It is shown that the disordering originates from the shifting of adjacent ( 100) tunnel slices of the structure with respect to each other along [011], allowing the formation of either new commensurate (superstructure) or incommensurate modulations, or even complete disorder along a. The close relationships with the ordered monoclinic form alpha-NH4Fe(2)(PO(4))2 are also explained by this description.

Update: 14-Sep-2007

Title:
Crystallization Behavior of Ti40Zr25Ni8Cu9Be18 amorphous alloy
Authors:
Mei, JN; Li, JS; Kou, HC; Xing, LQ; Fu, HZ; Zhou, L Author Full Names: Jinna, Mei; Li Jinshah; Kou Hongchao; Xing Liqian; Fu Hengzhil; Zhou Lian
Source:
RARE METAL MATERIALS AND ENGINEERING 36 (7): 1215-1218 JUL 2007
Abstract:
Ti-based bulk amorphous alloy with the composition of Ti(40)Zr(25)Ni(8)CugBe(18) of 3 rum in diameter was fabricated by suction casting method. The microstructure was investigated using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). In addition, the crystallization kinetics behavior and phase transition during crystallization process were studied by non-isothermal crystallization and isothermal anneal heat treatment, respectively. It is showed that the glass transition and crystallization behavior have the typical kinetic characteristics and better thermal stability with a supercooled liquid region Delta T-x of 54 K and a phase transformation E-p1 of 213.04 kJ/mol, respectively, for the amorphous alloy. On the other hand, the process of crystallization contained two stages: in the first stage, the crystallization reactions correspond to the precipitation of quasicrystalline phase I in the amorphous matrix; in the second stage, the quasicrystalline phase I was transformed to Laves phase which is directly precipitated from the remaining amorphous matrix.
Title:
Composite behavior and multidegeneracy in high-pressure phases of Cs and Rb
Authors:
Perez-Mato, JM; Elcoro, L; Petricek, V; Katzke, H; Blaha, P Author Full Names: Perez-Mato, J. M.; Elcoro, Luis; Petricek, Vaclav; Katzke, Hannelore; Blaha, Peter
Source:
PHYSICAL REVIEW LETTERS 99 (2): Art. No. 025502 JUL 13 2007
Abstract:
The pressure-driven phases Cs III and Rb III having large unit cells are shown to be peculiar examples of commensurate modulated composites with two monatomic subsystems of striking simplicity. The two subsystems are obverse-reverse layers, symmetry related but misfitted. Modulations are smooth and describable by a few parameters within a well-defined superspace symmetry. Ab initio density-functional theory calculations show that the composite character is reflected in their physical behavior. Cs III has a low-energy mode with phason character corresponding to the relative sliding of the neighboring misfitted layers, the energy barrier being lower than 0.01 meV/atom, which is most favorable for transforming to other configurations. These phases possess a quasidegenerate energy landscape, close to the signature of incommensurate systems and quasicrystals.
Title:
Origin of the effect of the gas atmosphere during mold-casting Zr65Al7.5Ni10Pd17.5 bulk glassy or nano-quasicrystal-forming alloy
Authors:
Setyawan, AD; Kato, H; Saida, J; Inoue, A Author Full Names: Setyawan, Albertus Deny; Kato, Hidemi; Saida, Junji; Inoue, Akihisa
Source:
MATERIALS TRANSACTIONS 48 (6): 1266-1271 JUN 2007
Abstract:
We provide a quantitative analysis of the importance of the gas species and pressure during mold-casting process on the apparent glass-forming ability (GFA) of Zr65Al7.5Ni10Pd17.5 alloy, recently reported by Kato et al. (e.g. Scripta Mater. 51 (2004) 13). The cooling characteristics are found to depend in remarkable detail on the g-as species and the pressure existing in the cavity between the melt and the mold presumably formed during the cooling process. This understanding has been successfully applied to significantly improve the critical diameter of the glassy rods to 7 mm in an atmosphere of helium environment from 5 mm in that of argon.
Title:
Local structure study in Zr-based metallic glasses
Authors:
Saida, J; Sanada, T; Sato, S; Imafuku, M; Matsubara, E; Inoue, A Author Full Names: Saida, Junji; Sanada, Takashi; Sato, Shigeo; Imafuku, Muneyuki; Matsubara, Eiichiro; Inoue, Akihisa
Source:
MATERIALS TRANSACTIONS 48 (7): 1703-1707 JUL 2007
Abstract:
The local structure in the glassy state is investigated in the Zr80Pt20 and Zr70Cu30 binary and Zr70Al10Ni20 ternary alloys in correlation with the quasicrystalline (QC) phase forniation. The Zr80Pt20 alloy has a high QC-forming ability. It is easily formed in the as-quenched state with a considerably low cooling rate or by annealing the glassy alloy. The radial distribution function (RDF) and extended X-ray absorption fine structure (EXAFS) analysis clearly indicate the existence of icosahedral local structure around Pt atom. The Zr70Cu30 binary and Zr70Al10Ni20 ternary metallic glasses have a QC-forming ability by the addition of a very small amount of noble metals such as Pd. We can also investigate the icosahedral local structure in these alloys. These results are realized that the icosahedral local structure can be applied as a dominant local atomic configuration in the supercooled liquid and/or glassy states in the QC-forming metallic glasses.
Title:
Cluster expansion approach for relative stability among different atomic structures in alloys: an approach from a dilute limit
Authors:
Asato, M; Takahashi, H; Inagaki, T; Fujima, N; Tamura, R; Hoshino, T Author Full Names: Asato, M.; Takahashi, H.; Inagaki, T.; Fujima, N.; Tamura, R.; Hoshino, T.
Source:
MATERIALS TRANSACTIONS 48 (7): 1711-1716 JUL 2007
Abstract:
We demonstrate the ability of our cluster expansion approach (CEA) for cohesive energies of alloys, which allows one to Study the chemical trends of the relative stability of different atomic structures of alloys. as an example, X dependence of the atomic structures of Al-rich AIX (X = Sc-Zn) alloys, including ordered structures (Ll(2)(Al3Sc), DO22 (Al3V)), a Mackay icosahedron (a local structure in the Al80Mn20 quasicrystal), and precipitate shapes in decomposition phases (Al1-c,Cu-c, Al1-cZnc; c < 0.05). All the terms in the CEA for Al-rich AIX alloy can be determined uniquely and successively from low-order to high-order by using the total energies of isolated Al and X atoms, pure Al and X metals, and X impurities in Al metal. The total energies of impurity systems are calculated accurately by using the all-electron full-potential Korringa-Kohn-Rostoker (FPKKR) Green's function method, combined with the density-functional theory in the generalized-gradient approximation! (GGA), we show: (1) the binding energies of X (X = Cu, Zn) impurities in Al are reproduced very well by the CEA including two- and three-bodv interaction energies of X impurities; (2) the chemical trends of Structural stability among ordered Structures (Ll(2), DO22, DO23) of Al3X (X = Sc, Ti, V), being determined by use of the screened-FPKKR and GGA band-structure calculations. are reproduced by the CEA including only two-body (X-X) interaction energies in Al.
Title:
Bulk glassy and quasicrystalline (Zr65Al7.5Cu27.5)(100-x)Ti-x alloys and their mechanical properties
Authors:
Qiang, JB; Zhang, W; Xie, GQ; Inoue, A Author Full Names: Qiang, J. B.; Zhang, W.; Xie, G. Q.; Inoue, A.
Source:
MATERIALS TRANSACTIONS 48 (7): 1789-1792 JUL 2007
Abstract:
The glass-forming ability (GFA) and thermal stability of (Zr65Al7.5Cu27.5)(100-x)Ti-x (x = 0 similar to 15; in at%) alloys have been investigated. It was revealed that a certain amount of Ti addition could improve the GFA of Zr65Al7.5Cu27.5 alloy effectively. The best bulk metallic glass (BMG) forming composition was found at (Zr65Al7.5Cu27.5)(93)Ti-7. Bulk glassy samples with diameter of 7 mm were made by means of copper mold casting. Further Ti additions deteriorated GFA and led to the precipitation of icosahedral phase, and 3 mm quasicrystalline cylinder was obtained at (Zr65Al7.5Cu27.5)(90)Ti-10. Room temperature compression testing showed that the quasicrystalline alloy had a fracture strength of 1875 MPa, being 300 MPa larger than that of the (Zr65Al7.5Cu27.5)(93)Ti-7 monolithic BMG.
Title:
Penrose structures described by different kite-clusters
Authors:
Duda, M; Kozakowski, B; Wolny, J Author Full Names: Duda, M.; Kozakowski, B.; Wolny, J.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 353 (24-25): 2500-2505 JUL 15 2007
Abstract:
The family of kite-clusters, i.e. K4, K7 and K17, obtained by applying inflation rules to the smallest, initial cluster (K4), were successfully used to cover the rhombic Penrose atomic structure. These clusters, especially the first two, namely four-atom K4 and seven-atom K7 clusters were thoroughly studied and compared with the previously described kite-like cluster K17 and the standard 33-atom Gummelt's cluster (G33). The first in series - monatomic K4 cluster - is probably too small for any real application. The next - K7 cluster is the simplest one that can be decorated by three different types of atoms. Their concentration is comparable to the concentration of atoms of the stable, decagonal quasicrystals Al-Ni-Co. This leads to the conclusion that the K7 could be also considered as a starting model for the structure refinement. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Quasicrystal-crystal structural transformation in Al-5 wt.% Mn alloy
Authors:
Saksl, K; Vojtech, D; Franz, H Author Full Names: Saksl, Karel; Vojtech, Dalibor; Franz, Hermann
Source:
JOURNAL OF MATERIALS SCIENCE 42 (17): 7198-7201 SEP 2007
Abstract:
The atomic structure of Al-5 wt.%Mn (Al-5Mn) alloy, prepared by rapid solidification, and pre-annealed at 623 and 773 K for 5 and 1 h, respectively, were characterized by X-ray powder diffraction (XRD) and extended X-ray absorption fine structure (XAFS) techniques. The sample in as-quenched stage was found crystalline, consisting of metastable alpha-Al (Al-Mn solid solution) and icosahedral quasicrystalline I-Al6Mn phases. Five hours annealing at 623 K proved thermal stability of both the phases. Pre-annealing at 773 K/1 h on the other hand leads to alpha-Al phase decomposition and structural transformation of metastable I-Al6Mn to stable orthorhombic Al6Mn phase. The EXAFS results indicate that Mn atoms are located preferably on the outer shell of icosahedrons. During the I-Al6Mn -> omicron-Al6Mn transformation the total Al atoms coordinating one Mn were found to be constant (similar to 10). Based on the results, only distance/symmetry changes in atomic arrangement around Mn atoms were suggested.
Title:
SUPERFLIP - a computer program for the solution of crystal structures by charge flipping in arbitrary dimensions
Authors:
Palatinus, L; Chapuis, G Author Full Names: Palatinus, Lukas; Chapuis, Gervais
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 40: 786-790 Part 4 AUG 2007
Abstract:
SUPERFLIP is a computer program that can solve crystal structures from diffraction data using the recently developed charge-flipping algorithm. It can solve periodic structures, incommensurately modulated structures and quasicrystals from X-ray and neutron diffraction data. Structure solution from powder diffraction data is supported by combining the charge-flipping algorithm with a histogram-matching procedure. SUPERFLIP is written in Fortran90 and is distributed as a source code and as precompiled binaries. It has been successfully compiled and tested on a variety of operating systems.
Title:
A single-crystal time-of-flight neutron diffractometer at a spallation neutron source
Authors:
Takahashi, M; Ohshima, KI; Arai, M Author Full Names: Takahashi, Miwako; Ohshima, Ken-ichi; Arai, Masatoshi
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 40: 799-807 Part 4 AUG 2007
Abstract:
A single-crystal diffractometer using the time-of-flight (TOF) Laue technique had been operated for studies of structural and magnetic disorder and phase transitions in alloys and magnetic materials at the pulsed spallation neutron source facility of the KEK Neutron Science Laboratory (KENS). In various sample environments, the diffractometer has demonstrated its usefulness in measurements of diffuse scattering for studying local structures, and in surveys of reciprocal space for studying phase transitions and incommensurate structures under the conditions of varying temperature and magnetic field. Particular emphasis is placed on the fact that though the instrument did not receive high-flux neutrons for long wavelengths suitable for the studies of magnetic scattering, it gave good results on the observations of magnetic diffuse scattering and superlattice reflections. Remarks and future tasks of the TOF Laue technique are discussed in relation to the asymmetric pulse shape, separation of the inelastic scattering, and dependence of data correction on the sample quality.
Title:
A mu SR magnetic study of UNiGe
Authors:
Kalvius, GM; Noakes, DR; El-Khatib, S; Ansaldo, EJ; Stronach, CE; Bruck, E; Nakotte, H Author Full Names: Kalvius, G. M.; Noakes, D. R.; El-Khatib, S.; Ansaldo, E. J.; Stronach, C. E.; Bruck, E.; Nakotte, H.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 441 (1-2): 11-18 AUG 30 2007
Abstract:
We have carried out mu SR spectroscopy on polycrystalline UNiGe between 2 K and 100 K. The existence of two magnetic transitions at T-N = 51 K and T-1 = 41.5 K is confirmed. The VSR spectra clearly reveal that the magnetic state between 51 K and 41.5 K is an incommensurate spin structure ruling out a spin-slip structure which had been considered an alternative. Below 41.5 K the spectra are compatible with simple antiferromagnetic order. The local field for T -> 0 is B-mu = 170 mT, a comparatively low value, indicating a rather small uranium ordered moment. When going from the commensurate to the incommensurate structures at T-1 a sudden reduction in local field by 23% occurs reflecting an equal change in ordered moment. The transition at T-1 is sharp, but TN extends over roughly 5 K. The antiferromagnetic spin structure exhibits persistent spin fluctuations in the limit T -> 0, implying the presence of some additional spin interactions which tries to suppress long-range magnetic order. (C) 2006 Elsevier B.V. All rights reserved.
Title:
Superspace crystal symmetry of thermoelectric misfit cobalt oxides and predicted structural models
Authors:
Grebille, D; Muguerra, H; Perez, O; Guilmeau, E; Rousseliere, H; Funahashi, R Author Full Names: Grebille, D.; Muguerra, H.; Perez, O.; Guilmeau, E.; Rousseliere, H.; Funahashi, R.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 63: 373-383 Part 3 JUN 2007
Abstract:
Single crystals of thermoelectric misfit lamellar cobalt oxide phases in the Bi-Ca-Co-O and I-Bi-Ca-Co-O systems were synthesized. They are characterized by aperiodic structures involving two partially independent sublattices: a CdI2-type pseudohexagonal CoO2 layer and a rocksalt-type BiCaO2 slab allowing the intercalation of iodine. The crystal symmetry of these structures is discussed using the four-dimensional superspace formalism. The superspace Lane classes of the iodine-free and the intercalated compounds are P2/m(0 delta 1/2) (a(1) = 4.901, b(1) = 4.730, b(2) = 2.80, c(1) = 14.66 angstrom, beta = 93.49 degrees) and A2/m(0 delta 1) (a(1)' = 4.903, b(1)' = 4.742, c(1)' = 36.51 angstrom, beta = 87.30 degrees), respectively. A comparison is given with the related Bi-SrCo-O misfit compounds. The present structures are compatible with the presence of an intrinsic modulation with a wavelength matching the misfit aperiodicity in the b direction. Preliminary partial structure refinements confirm the layer stacking of the structure and the intercalation of I between the Bi-O layers for the second phase. A comparison with other cobalt oxide phases, as well as symmetry and metric considerations allow us to predict average structures for these new phases and to describe the common structural features assumed for all these lamellar misfit cobalt oxides.
Title:
Three-periodic tilings and nets: face-transitive tilings and edge-transitive nets revisited
Authors:
Delgado-Friedrichs, O; O'Keeffe, M Author Full Names: Delgado-Friedrichs, Olaf; O'Keeffe, Michael
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 63: 344-347 Part 4 JUL 2007
Abstract:
Systematic generation of face-transitive tilings by size of Delaney-Dress symbol has recovered by dualization all the edge-transitive nets previously described and has led to the discovery of six new binodal edge-transitive nets which are described and illustrated.
Title:
Order parameters for phase transitions to structures with one-dimensional incommensurate modulations
Authors:
Stokes, HT; Campbell, BJ; Hatch, DM Author Full Names: Stokes, Harold T.; Campbell, Branton J.; Hatch, Dorian M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 63: 365-373 Part 4 JUL 2007
Abstract:
Phase transitions that result in incommensurate structural modulations are widely observed in crystalline solids and are relevant to a broad range of physical phenomena in magnetic, electronic, optical and structural materials. While the (3+1)-dimensional superspace-group symmetries associated with one-dimensional modulations have been tabulated, the order parameters that produce these modulations have not been explored in detail. Here, using group-theoretical methods, we present a unique and exhaustive enumeration of the isotropy subgroups (and their corresponding order-parameter directions) belonging to irreducible representations of the (3+1)-dimensional superspace extensions of the 230 crystallographic space groups at all incommensurate k points. The vast majority of experimentally observed incommensurately modulated structures have order parameters belonging to one of these subgroups.

Update: 7-Sep-2007

Title:
Absence of commensurate ordering at the polarization flop transition in multiferroic DyMnO3
Authors:
Strempfer, J; Bohnenbuck, B; Mostovoy, M; Aliouane, N; Argyriou, DN; Schrettle, F; Hemberger, J; Krimmel, A; von Zimmermann, M Author Full Names: Strempfer, J.; Bohnenbuck, B.; Mostovoy, M.; Aliouane, N.; Argyriou, D. N.; Schrettle, F.; Hemberger, J.; Krimmel, A.; von Zimmermann, M.
Source:
PHYSICAL REVIEW B 75 (21): Art. No. 212402 JUN 2007
Abstract:
Ferroelectric spiral magnets DyMnO3 and TbMnO3 show similar behavior of electric polarization in applied magnetic fields. Studies of the field dependence of lattice modulations on the contrary show a completely different picture. Whereas in TbMnO3 the polarization flop from P parallel to c to P parallel to a is accompanied by a sudden change from incommensurate to commensurate wave vector modulation, in DyMnO3 the wave vector varies continuously through the flop transition. This smooth behavior may be related to the giant magnetocapacitive effect observed in DyMnO3.
Title:
Penrose quantum antiferromagnet
Authors:
Jagannathan, A; Szallas, A; Wessel, S; Duneau, M Author Full Names: Jagannathan, A.; Szallas, A.; Wessel, Stefan; Duneau, Michel
Source:
PHYSICAL REVIEW B 75 (21): Art. No. 212407 JUN 2007
Abstract:
The Penrose tiling is a perfectly ordered two-dimensional structure with fivefold symmetry and scale invariance under site decimation. Quantum spin models on such a system can be expected to differ significantly from more conventional structures as a result of its special symmetries. In one dimension, for example, aperiodicity can result in distinctive quantum entanglement properties. In this work, we study ground-state properties of the spin-1/2 Heisenberg antiferromagnet on the Penrose tiling, a model that could also be pertinent for certain three-dimensional antiferromagnetic quasicrystals. We show, using spin-wave theory and quantum Monte Carlo simulation, that the local staggered magnetizations strongly depend on the local coordination number z and are minimized on some sites of fivefold symmetry. We present a simple explanation for this behavior in terms of Heisenberg stars. Finally, we show how best to represent this complex inhomogeneous ground state using the "perpendicular space" representation of the tiling.
Title:
Phase diagram and anisotropic physical properties of single crystal Bi1-xSrxMnO3 (0.35 <= x <= 0.64)
Authors:
Yamada, S; Matsunaga, T; Sugano, E; Sagayama, H; Konno, S; Nishiyama, S; Watanabe, Y; Arima, TH Author Full Names: Yamada, Shigeki; Matsunaga, Takuya; Sugano, Eri; Sagayama, Hajime; Konno, Shota; Nishiyama, Shinji; Watanabe, Yosuke; Arima, Taka-hisa
Source:
PHYSICAL REVIEW B 75 (21): Art. No. 214431 JUN 2007
Abstract:
Measurements of magnetization, electrical resistivity, and synchrotron x-ray diffraction were performed on single crystals of Bi1-xSrxMnO3 (0.35 <= x <= 0.64). The resistivity and magnetization curves show a kink near 570 K and an anomaly which is accompanied by a hysteresis at 400-500 K for all samples. Synchrotron x-ray diffraction of a sample with x=0.47 indicates that the kink and the anomaly are ascribed to an orbital- and a charge-ordering phase transition, respectively. Orbital ordering becomes incommensurate above the charge-ordering transition temperature, which is not reported in other perovskite manganese oxides. Magnetization measurements show an antiferromagnetic transition near 150 K. Below 40 K, a spin-glass-like behavior is observed for 0.35 <= x <= 0.53. We also investigated the anisotropic properties of a single-domain crystal with x=0.47. Magnetic anisotropy below the Neel temperature implies that the Mn spin moments orient themselves along the c axis. Anisotropic electrical conduction starts appearing below 570 K, which is the orbital-ordering transition temperature. This anisotropy is enhanced below charge-ordering temperature and is approximately rho(ab)/rho(c)similar or equal to 10 at room temperature, which indicates that e(g) electrons on excess Mn3+ ions move more easily along the c axis than in the ab plane.
Title:
Electrophysical and thermodynamic properties of shock compressed incommensurate phase Sc-II
Authors:
Molodets, AM; Shakhray, DV; Golyshev, AA; Fortov, VE Author Full Names: Molodets, A. M.; Shakhray, D. V.; Golyshev, A. A.; Fortov, V. E.
Source:
PHYSICAL REVIEW B 75 (22): Art. No. 224111 JUN 2007
Abstract:
The electric resistance of shock-compressed scandium has been studied up to pressures of 90 GPa. The low-pressure phase of scandium Sc-I undergoes polymorphic transformation in the high-pressure incommensurate phase Sc-II at a shock pressure of approximate to 16.5 GPa and a calculated shock temperature of approximate to 510 K. The equation of state of the incommensurate phase Sc-II is constructed.
Title:
Pseudomorphic quasiperiodic alkali metal monolayers on an i-Al-Pd-Mn surface
Authors:
Krajci, M; Hafner, J Author Full Names: Krajci, M.; Hafner, J.
Source:
PHYSICAL REVIEW B 75 (22): Art. No. 224205 JUN 2007
Abstract:
The structure and stability of quasiperiodic alkali metal monolayers and multilayer films formed on a fivefold surface of an icosahedral AlPdMn quasicrystal have been investigated using ab initio density-functional methods. A structural model of the adsorbed monolayer has been constructed on the basis of a mapping of the potential-energy landscape of a single adatom on the fivefold surface of i-Al-Pd-Mn. This model consists of a dense decoration of the P1 tiling describing the atomic arrangement on a fivefold surface of i-Al-Pd-Mn. Upon relaxation under action of ab initio calculated interatomic forces, a dense Na monolayer spontaneously transforms to another ordered quasiperiodic structure. The quasiperiodic ordering can be described by a decagonal DHBS tiling of decagons (D), hexagons (H), boats (B), and pentagonal stars (S). The internal decoration of these tiles, however, reduces the overall symmetry from decagonal to pentagonal. The saturation coverage of the adsorbed monolayer is Theta=0.50. K monolayers can adopt the same structure. Alkali layers with a lower coverage adopt a semiregular structure with part of the atoms forming a regular grid imposed by the strong binding of the alkali atoms to the quasiperiodically distributed charge-density minima. A stable quasiperiodic bilayer film can be formed by placing alkali atoms into the hollows of the adlayer. The coverage in the second layer is reduced to Theta=0.39. Films with three of more monolayers do not form a regular quasiperiodic pattern, upon relaxation they transform to a disordered amorphous arrangement.
Title:
Symmetry disquisition on the TiOX phase diagram (X=Br,Cl)
Authors:
Fausti, D; Lummen, TTA; Angelescu, C; Macovez, R; Luzon, J; Broer, R; Rudolf, P; van Loosdrecht, PHM; Tristan, N; Buchner, B; van Smaalen, S; Moller, A; Meyer, G; Taetz, T Author Full Names: Fausti, Daniele; Lummen, Tom T. A.; Angelescu, Cosmina; Macovez, Roberto; Luzon, Javier; Broer, Ria; Rudolf, Petra; van Loosdrecht, Paul H. M.; Tristan, Natalia; Buechner, Bernd; van Smaalen, Sander; Moeller, Angela; Meyer, Gerd; Taetz, Timo
Source:
PHYSICAL REVIEW B 75 (24): Art. No. 245114 JUN 2007
Abstract:
The sequence of phase transitions and the symmetry of, in particular, the low temperature incommensurate and spin-Peierls phases of the quasi-one-dimensional inorganic spin-Peierls system TiOX (X=Br and Cl) have been studied using inelastic light scattering experiments. The anomalous first-order character of the transition to the spin-Peierls phase is found to be a consequence of the different symmetries of the incommensurate and spin-Peierls (P2(1)/m) phases. The pressure dependence of the lowest transition temperature strongly suggests that magnetic interchain interactions play an important role in the formation of the spin-Peierls and the incommensurate phases. Finally, a comparison of Raman data on VOCl to the TiOX spectra shows that the high energy scattering previously observed has a phononic origin.
Title:
Band-insulator-metal-Mott-insulator transition in the half-filled t-t ' ionic Hubbard chain
Authors:
Japaridze, GI; Hayn, R; Lombardo, P; Muller-Hartmann, E Author Full Names: Japaridze, G. I.; Hayn, R.; Lombardo, P.; Mueller-Hartmann, E.
Source:
PHYSICAL REVIEW B 75 (24): Art. No. 245122 JUN 2007
Abstract:
We investigate the ground-state phase diagram of the half-filled t-t(') repulsive Hubbard model in the presence of a staggered ionic potential Delta using the continuum-limit bosonization approach. We find that with increasing on-site repulsion U, depending on the value of the next-nearest-neighbor hopping amplitude t('), the model shows three different versions of the ground-state phase diagram. For t '< t(c)(*'), the ground-state phase diagram consists of the following three insulating phases: band insulator at U < U-c, ferroelectric insulator at U-c < U < U-s, and correlated (Mott) insulator at U > U-c. For t(')>t(c ') there is only one transition from a spin-gapped metallic phase at U < U-c to a ferroelectric insulator at U > U-c. Finally, for intermediate values of the next-nearest-neighbor hopping amplitude t(c)(*')< t '< t(c)(') we find that with increasing on-site repulsion, at U-c1 the model undergoes a second-order commensurate-incommensurate-type transition from a band insulator into a metallic state and at larger U-c2 there is a Kosterlitz-Thouless-type transition from a metal to a ferroelectric insulator.
Title:
Incommensurate magnetic order in the pressure-induced superconductor CeRhSi3
Authors:
Aso, N; Miyano, H; Yoshizawa, H; Kimura, N; Komatsubara, T; Aoki, H Author Full Names: Aso, N.; Miyano, H.; Yoshizawa, H.; Kimura, N.; Komatsubara, T.; Aoki, H.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): 602-604 Part 1 MAR 2007
Abstract:
Neutron diffraction experiments were performed to investigate a nature of the antiferromagnetic ordered phase below T-N = 1.6K of the pressure-induced superconductor CeRhSi3. We observed incommensurate magnetic reflections characterized by the wave vector Q = (+/- delta,0,0.5) (delta similar to 0.215). The antiferromagnetic ordered state can be interpreted as a spin-density wave formation by taking account of the results on de Haas-van Alphen (dHvA) signals in CeRhSi3 where the 4f-electrons of CeRhSi3 are itinerant. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Pressure-induced antiferromagnetic superconductivity in CeNiGe3: A 73Ge-NQR study under pressure
Authors:
Harada, A; Kawasaki, S; Mukuda, H; Kitaoka, Y; Thamizhavel, A; Okuda, Y; Settai, R; Onuki, Y; Itoh, KM; Haller, EE; Harima, H Author Full Names: Harada, A.; Kawasaki, S.; Mukuda, H.; Kitaoka, Y.; Thamizhavel, A.; Okuda, Y.; Settai, R.; Onuki, Y.; Itoh, K. M.; Haller, E. E.; Harima, H.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): 614-616 Part 1 MAR 2007
Abstract:
We report on antiferromagnetic (AF) properties of pressure-induced superconductivity in CeNiGe3 via the Ge-73 nuclear-quadrupole-resonance (NQR) measurements under pressure (P). The NQR-spectrum measurements have revealed that the incommensurate antiferromagnetic ordering is robust against increasing P with the increase of ordered moment and ordering temperature. Nevertheless the measurements of nuclear spin-lattice relaxation rate (1/T-1) have pointed to the onset of superconductivity as a consequence of Ce-4f electrons delocalized by applying P. The emergence of superconductivity under the development of AF order suggests that a novel type of superconducting mechanism works in this compound. (c) 2006 Elsevier B. V. All rights reserved.
Title:
Resonant X-ray magnetic diffraction experiments on SmB2C2
Authors:
Inami, T; Honma, T; Tsutsui, S; Indoh, K; Onodera, H; Ishii, K; Ohwada, K; Kuzushita, K; Nakao, H; Murakami, Y Author Full Names: Inami, T.; Honma, T.; Tsutsui, S.; Indoh, K.; Onodera, H.; Ishii, K.; Ohwada, K.; Kuzushita, K.; Nakao, H.; Murakami, Y.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): 748-750 Part 1 MAR 2007
Abstract:
We investigated successive phase transitions in SmB2C2 at T-N1 = 51 and T-N2 = 37K by means of resonant X-ray diffraction. A strong resonant diffraction signal is observed at the 101 reflection below T-N2 at the Sm L-3 edge, whereas in the intermediate phase signals appear at incommensurate positions Q = (1 +/- delta, +/- delta, 1), where delta = 0.13. Accordingly, the transition at T-N2 is found to be a commensurate-to-incommensurate magnetic phase transition. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Magnetic excitations of charge-ordered La2NiO4.11
Authors:
Freeman, PG; Hayden, SM; Frost, CD; Prabhakaran, D; Boothroyd, AT Author Full Names: Freeman, P. G.; Hayden, S. M.; Frost, C. D.; Prabhakaran, D.; Boothroyd, A. T.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): 760-762 Part 1 MAR 2007
Abstract:
The incommensurate magnetic excitations of spin-charge ordered La2NiO4.11 were studied by inelastic neutron scattering. With increasing energy up to similar to 20meV the maximum intensity of the spin excitations is observed to shift slightly towards the 2D antiferromagnetic wave vector (1/2, 1/2). This asymmetry in the magnon dispersion about the incommensurate wave vector is a similar effect, though less marked, to what has been observed in the layered cuprate superconductors. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Anisotropic physical properties of the charge and orbital ordering phase in Bi0.53Sr0.47MnO3
Authors:
Yamada, S; Sugano, E; Nishiyama, S; Watanabe, Y; Arima, T Author Full Names: Yamada, S.; Sugano, E.; Nishiyama, S.; Watanabe, Y.; Arima, T.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): 771-773 Part 1 MAR 2007
Abstract:
Anisotropic properties of a single-domain crystal Bi1-xSrxMnO3 with x = 0: 47 were investigated. Temperature dependence of resistivity and magnetization show an anomaly which is accompanied by a hysteresis at 400-550K and a kink near 600 K. The hysteresis and the kink may be attributed to the charge order-disorder transition accompanied with orbital commensurate-incommensurate phenomenon, and to the orbital order-disorder transition, respectively. Magnetization measurements show an antiferromagnetic transition near 150 K. Below 150 K, the magnetization for a magnetic. field in the ab-plane is larger than that along the c-axis. This magnetic anisotropy indicates that the Mn spin moments direct to the c-axis. In the charge ordering phase, anisotropy of the resistivity is approximately rho(ab)/rho(c) similar or equal to 10. This indicates that e(g) electrons on excess Mn3+ ions can move more easily along the c-axis than in ab-plane. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Electronic band structures in LaRu4P12 and LaFe4P12 with modulated skutterudite structures
Authors:
Takegahara, K; Harima, H Author Full Names: Takegahara, Katsuhiko; Harima, Hisatomo
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): 861-863 Part 1 MAR 2007
Abstract:
The band structures are calculated for LaRu4P12 with a simple cubic Pm3- crystal structure and LaFe4P12 with a simple orthorhombic Pmmm crystal structure, by using an FLAPW method. The hybridization between La f-orbital and P p-state and Fermi surfaces are investigated. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Magnetic order of CePdAl under pressure - neutron diffraction study
Authors:
Prokes, K; Manuel, P; Adroja, DT; Kitazawa, H; Goto, T; Isikawa, Y Author Full Names: Prokes, K.; Manuel, P.; Adroja, D. T.; Kitazawa, H.; Goto, T.; Isikawa, Y.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): E28-E30 Part 1 MAR 2007
Abstract:
The heavy-fermion compound CePdAl adopting the hexagonal ZrNiAl type of structure (space group P-62m) orders at ambient pressure antiferromagnetically below 2.7K with an incommensurate propagation vector q = (0.50 tau), tau similar or equal to 0.35. Two, of the three Ce atoms in the hexagonal unit cell carry magnetic moment of about 1.6-1.8 mu(B), while the remaining one remains frustrated down to at least 35 mK. The application of hydrostatic pressure leads to a suppression of the long-range magnetic order above the critical pressure Pc. The results of neutron diffraction experiments under pressure suggest a value of P-c = 0.75 (5) GPa as compared with 0.95 GPa determined from the bulk measurements. At pressures lower than Pc, the magnetic structure of CePdAl seems to be quite robust with a very little temperature-dependent propagation vector and unusual dependence of the magnetic moment. The P-T phase diagram has been constructed. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Relation between superconductivity and superstructure in Ce2RhIn8
Authors:
Koeda, M; Fujiwara, T; Hedo, M; Uwatoko, Y; Sagayama, H; Wakabayashi, Y; Sawa, H Author Full Names: Koeda, Masahito; Fujiwara, Tetsuya; Hedo, Masato; Uwatoko, Yoshiya; Sagayama, Hajime; Wakabayashi, Yusuke; Sawa, Hiroshi
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): E31-E32 Part 1 MAR 2007
Abstract:
We have performed the electrical resistivity measurements on Ce2RhIn8 in the temperature range 0.3-300 K and observed zero-resistance state at ambient pressure on several samples. We have performed synchrotron X-ray diffraction experiment on single crystal of Ce2RhIn8 to investigate relation between superconductivity and crystal structure. Superlattice reflections were observed with modulation wave vector q similar to(0, 0, 1/8) on the superconducting samples at room temperature. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Crystal structure and physical properties of a misfit-layered cobaltite (CaOH)(1.14)CoO2
Authors:
Isobe, M; Shizuya, M; Takayama-Muromachi, E Author Full Names: Isobe, M.; Shizuya, M.; Takayama-Muromachi, E.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): E269-E271 Part 2 MAR 2007
Abstract:
We have studied the crystal structure and transport properties of the new cobalt oxide (CaOH)(1.14)CoO2. The compound has the layer structure, which consists of CdI2-type CoO2 layers and rock-salt-type double CaOH atomic layers. The two subcells have incommensurate periodicity along the a-axis, resulting in a modulated crystal structure due to the inter-subcell interaction. The structural modulation affects carrier conduction through the potential randomness. We found that the two-dimensional (2-D) variable-range-hopping-type hole conduction is dominant at low temperature. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Investigation of antiferromagnetic domains in Cr
Authors:
de Oliveira, AJA; de Souza, PEN; Giles, C; Mazzaro, I; de Camargo, PC Author Full Names: de Oliveira, A. J. A.; de Souza, P. E. N.; Giles, C.; Mazzaro, I.; de Camargo, P. C.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): E316-E318 Part 2 MAR 2007
Abstract:
Incommensurate spin-density wave (SDW) in chromium presents Q-domain configurations that can be studied through X-ray diffraction (XRD) due to charge-density wave satellites at (00 1) and (1 1 1) crystal faces. In the present work, we investigated superficial domains reorientation in the bulk multi-Q state, after the crystal had been maintained in the bulk single-Q state artificially prepared by field cooling under 90 kOe applied in (0 1 0)direction. Reciprocal lattice scans were performed along the three directions H, K and L to ensure proper CDW satellite measurements. Our results are in agreement with previous experiments where observed that the preferential orientation of CDW occurs naturally with Q perpendicular to the surface, parallel to (100). (c) 2006 Elsevier B.V. All rights reserved.
Title:
Possible chiral magnetism in CuB2O4
Authors:
Kousaka, Y; Kishine, J; Yana, S; Akimitsu, J Author Full Names: Kousaka, Y.; Kishine, J.; Yana, S.; Akimitsu, J.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): E463-E464 Part 2 MAR 2007
Abstract:
We reported here commensurate-to-incommensurate (C-IC) magnetic ordering in copper metaborate CuB2O4 on the basis of concomitant chiral soliton lattice formation. We measured the magnetization processes in detail under the applied magnetic fields parallel and perpendicular to the helical axis. We found the anomalous temperature and magnetic field dependence of the magnetization strongly anisotropic with respect to the applied magnetic fields. The experimental results were quite consistent with the theoretical prediction based on the lattice chiral XY model, which describes the C-IC transition as the chiral soliton picture. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Neutron diffraction investigation of NdNi2Si2 single crystal
Authors:
Hashimoto, Y; Kawano, S Author Full Names: Hashimoto, Yuzo; Kawano, Shinji
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): E547-E548 Part 2 MAR 2007
Abstract:
Neutron diffraction experiment was carried out on the single-crystal NdNi2Si2. Magnetic satellites reflections indicated that the magnetic structure is incommensurate with Q = (0.03, 0, 0.885). Numerical analysis of the experimental data determined that the magnetic structure exhibits a cycloidal modulation with Nd moment of 3.1 mu(B). (c) 2006 Elsevier B.V. All rights reserved.
Title:
NMR studies of single crystal chromium diboride
Authors:
Michioka, C; Itoh, Y; Yoshimura, K; Watabe, Y; Kousaka, Y; Ichikawa, H; Akimitsu, J Author Full Names: Michioka, C.; Itoh, Y.; Yoshimura, K.; Watabe, Y.; Kousaka, Y.; Ichikawa, H.; Akimitsu, J.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): E620-E622 Part 2 MAR 2007
Abstract:
We report B-11 NMR studies of a single crystal CrB2. From the temperature dependence of the Fourier-transformed NMR spectra in the paramagnetic state, the hyperfine coupling constants are estimated to be A(Cr)-(B) = -0.64,-0.74 and -0.71 kOe/mu(B) for H parallel to c, H parallel to a and H parallel to [210], respectively. In the magnetically ordered state, the spectra in H parallel to a and H parallel to [210] consist of superposition of abroad hump and five peaks, which correspond to the incommensurate and commensurate spin structures. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Te-125 NMR in the single crystal of CeTe3: Spin polarized CDW
Authors:
Chudo, H; Michioka, C; Itoh, Y; Yoshimura, K Author Full Names: Chudo, H.; Michioka, C.; Itoh, Y.; Yoshimura, K.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): 1105-1107 Part 2 MAR 2007
Abstract:
We report Tc-125 NMR studies for single crystals of CeTe3 between 22 and 307 K, under an applied field of H = 7.4847 T along a- or b-axis. The Te-125 NMR spectrum consists of superposition of broad and sharp peaks, which are assigned to the signals of Te-125(l) in Te(1) sheets and Te-125(2) in CeTe(2) bi-layers, respectively. The broad Te-125(1) NMR spectrum consists of three distinguishable lines, regarded as an evidence for the presence of the incommensurate charge-density wave (ICDW) modulation. The Knight shifts of 125Te(l) widely distribute from -0.16% to +0.58% at 110K and the temperature dependence of each Knight shift is proportional to the bulk susceptibility, indicating that the conduction electron spin density is polarized by the Cc local moments in the CDW state. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Uniaxial pressure dependencies of the phase transitions in GdMnO3
Authors:
Baier, J; Meier, D; Berggold, K; Hemberger, J; Balbashov, A; Mydosh, JA; Lorenz, T Author Full Names: Baier, J.; Meier, D.; Berggold, K.; Hemberger, J.; Balbashov, A.; Mydosh, J. A.; Lorenz, T.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): 1165-1167 Part 2 MAR 2007
Abstract:
GdMnO3 shows an incommensurate antiferromagnetic order below similar or equal to 42 K, transforms into a canted A-type antiferromagnet below 20 K, and for finite magnetic fields along the b-axis ferroelectric order occurs below similar or equal to 12 K. From high-resolution thermal expansion measurements along all three principal axes, we determine the uniaxial pressure dependencies of the various transition temperatures and discuss their correlation to changes of the magnetic exchange couplings in RMnO3 (R = La,..., Dy). (c) 2006 Elsevier B.V. All rights reserved.
Title:
Control of multiferroic phase in Tb1-x(Bi,La,Y)(x)MnO3
Authors:
Jang, TH; Muralidharan, R; Yang, CH; Koo, TY; Jeong, YH Author Full Names: Jang, T.-H.; Muralidharan, R.; Yang, C.-H.; Koo, T. Y.; Jeong, Y. H.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): 1171-1173 Part 2 MAR 2007
Abstract:
The effects of Bi-substitution in TbMnO3 on structural, magnetic, ferroelectric, and thermal properties were studied. Exotic enhancement of magnetism in Bi3+ substitution is distinguished from the simple dilution effect of magnetic Tb3+ ion with nonmagnetic Y3+ and La3+ replacement. From both structural and magnetic characterizations, we conjectured that the strong local anisotropic distortion around Bi3+ ion due to its 6s(2) tone pair modified neighboring Mn3+ spin configuration, from modulated antiferromagnetic to a ferromagnetic one and induced the formation of fierromagnetic cluster. Both the b-lattice parameter to which the modulation wave vector is parallel and the ferroelectric transition temperature turned out to be very susceptible to Bi-substitution. Controllability of both magnetic and ferroelectric phases suggests a possible route to the simultaneous occurrence of two phase transitions of different origins at the same temperature for the enhanced coupling between magnetism and ferroelectricity. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Classical antiferromagnet on the pyrochlore lattice
Authors:
Nakamura, T; Hirashima, D Author Full Names: Nakamura, Tota; Hirashima, Dai
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): 1297-1299 Part 2 MAR 2007
Abstract:
Classical Heisenberg antiferromagnet on the pyrochlore lattice is studied using the nonequilibrium relaxation method. Effects of farther neighbor interactions are investigated. We found two ordered phases stabilized by the second- and the third-neighbor interactions. One is a commensurate phase where both k = 0 mode and k = pi mode appear. It occurs when J(3) is more ferromagnetic than J(2). The other one is a double-incommensurate phase which is characterized by two incommensurate wave numbers. It occurs when J(2) is more ferromagnetic than J(3). No long range ordered state is realized when J(2) = J(3). (c) 2006 Elsevier B.V. All rights reserved.
Title:
Magnetic ordering in HoB12 below and above T-N
Authors:
Flachbart, K; Bauer, E; Gabani, S; Kaldarar, H; Lonkai, T; Mat'as, S; Pavlik, V; Priputen, P; Shitsevalova, N; Siemensmeyer, K; Sluchanko, N Author Full Names: Flachbart, K.; Bauer, E.; Gabani, S.; Kaldarar, H.; Lonkai, T.; Mat'as, S.; Pavlik, V.; Priputen, P.; Shitsevalova, N.; Siemensmeyer, K.; Sluchanko, N.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): 1727-1729 Part 2 MAR 2007
Abstract:
We present results of neutron scattering experiments on frustrated antiferromagnet HoB12 above and below Neel temperature T-N. Diffuse scattering patterns indicate that above T-N = 7.4 K pronounced correlations between neighboring magnetic moments of Ho-ions appear, similar to one-dimensional (1D) magnets. Moreover, the diffuse scattering patterns show a symmetry reduction from fee to simple cubic. Analogous behavior in three dimensional (3-D) systems is not known, although it was predicted by theory. Results below T-N and in applied magnetic field, on the other hand, reveal three amplitude-modulated incommensurate magnetic structures in this compound. The role of various interactions leading to this behavior (above and below T-N) is being discussed. Additional attention is paid also to rho(T) resistivity dependencies in various magnetic fields close to and above the quantum critical point. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Pressure induced helimagnetism in Fe-based (Y2Fe17, Lu2Fe17) intermetallic compounds
Authors:
Kamarad, J; Prokhnenko, O; Prokes, K; Arnold, Z; Andreev, AV Author Full Names: Kamarad, J.; Prokhnenko, O.; Prokes, K.; Arnold, Z.; Andreev, A. V.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (2): 1801-1803 Part 2 MAR 2007
Abstract:
The helimagnetic ground state was induced in the hexagonal Y2Fe17 and Lu2Fe17 intermetallics by hydrostatic pressure above 1.05 and 0.3 GPa, respectively. The observed incommensurate helical structure was characterized by a propagation vector (00 tau(z)) and by a metamagnetic transition at the critical field H-c. The new incommensurate magnetic structure has been revealed now in Lu2Fe17 at magnetic fields above Hc at low temperatures. A detailed pressure-temperature-field evolution of the magnetic structures in Y2Fe17 and Lu2Fe17 is presented. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Structural singularities in ferroelectric Sr2NaNb5O15
Authors:
Garcia-Gonzalez, E; Torres-Pardo, A; Jimenez, R; Gonzalez-Calbet, JM Author Full Names: Garcia-Gonzalez, E.; Torres-Pardo, A.; Jimenez, R.; Gonzalez-Calbet, J. M.
Source:
CHEMISTRY OF MATERIALS 19 (14): 3575-3580 JUL 10 2007
Abstract:
The structural features of the ferroelectric compound Sr2NaNb5O15 have been carefully studied. A detailed investigation has been performed by means of room temperature (RT) and high temperature (HT) powder X-ray diffraction (XRD), selected area electron diffraction (SAED), high resolution electron microscopy (HREM), and impedance spectroscopy. Comparison is done with the barium homologue compound and the two RT ferroelectric phases can be structurally distinguished. The use of electron diffraction in combination with HREM has revealed the formation of a superlattice structure of tetragonal tungsten bronze (TTB) at RT. While in Ba2NaNb5O15 the incommensurate nature of this RT phase seems to be doubtless, the Sr2NaNb5O15 ferroelectric phase displays a commensurate superstructure of the TTB structure-type. The RT XRD pattern can be indexed in the Im2a space group. The transition to the paraelectric phase occurs at 518 K, and the material can be indexed in the centrosymmetric P4/mbm space group. From the Rietveld refinement of this HT phase, disordered distribution of Na and Sr in the A positions of the structure seems to occur, as opposite to the barium compound where barium atoms show clear preference for the largest A2 sites.
Title:
Icosahedral quasicrystals by optical interference holography (vol 89, art no 251111, 2006)
Authors:
Tam, WY Author Full Names: Tam, Wing Yim
Source:
APPLIED PHYSICS LETTERS 90 (26): Art. No. 269902 JUN 25 2007

Update: 24-Aug-2007

Title:
Effect of the next-nearest neighbor hopping on the stability and band structure of the incommensurate phases in the cuprates
Authors:
Raczkowski, M; Fresard, R; Oles, AM Author Full Names: Raczkowski, Marcin; Fresard, Raymond; Oles, Andrzej M.
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 244 (7): 2521-2526 JUL 2007
Abstract:
Using a spin-rotation invariant version of the slave-boson approach we investigate the relative stability and band structure of various incommensurate phases in the cuprates. Our findings obtained in the Hubbard model with next-nearest neighbor hopping -t'/t similar or equal to 0. 15, as appropriate for the La2-xSrxCuO4 family, support the formation of diagonal (vertical) stripe phases in the doping regime x = 1/16 (x = 1/8), respectively. In contrast, based on the fact that a larger value -t'/t = 0.3 expected for YBa2Cu3O6+delta triggers a crossover to the diagonal (1, 1) spiral phase at increasing doping, we argue that it might explain why the static charge order has been detected in YBa2CU3O6+delta only in the highly underdoped regime. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Title:
Order-disorder transitions of t(2g)-orbitals of V3+ ions and incommensurate structural deformations in the metallic spinel CuV2S4
Authors:
Hidaka, M; Tokiwa, N; Wijesundera, RP; Awaka, J; Nagata, S; Park, YJ; Lee, KB Author Full Names: Hidaka, M.; Tokiwa, N.; Wijesundera, R. P.; Awaka, J.; Nagata, S.; Park, Young Jun; Lee, Ki Bong
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 244 (7): 2565-2575 JUL 2007
Abstract:
Structural transitions of the spinel CuV2S4 have been studied by means of X-ray diffraction using synchrotron radiation. The temperature dependence of reflections forbidden in a cubic spinel structure of Fd3m suggests that there are order-disorder transitions of 3d(2) (t(2g)) orbitals of V3+ ions at about 75 and 210 K. An incommensurate superlattice reflection of (2+3/4, 2, 2+3/4) shows the structural phase transition occurring at about 90 K, in addition to the superlattice structural modulation at about 30-35 and 55 K. A reduced wavevector q = (3/4-delta, 0, 3/4-delta) shows the temperature dependence of the delta value from 0.015 to -0.025. A lock-in of delta = 0.0 and a crossover of the delta value occur in the region of 40 to 50 K. The incommensurate structural modulation along [110], [011], and [101] directions appearing below about 90 K affects a paramagnetic spin order of V3+ ions at about 30-35 and 55 K, in addition to the 90 K structural transition. The paramagnetic behavior is interpreted mainly by the structural deformation and the (d(xy), d(yz), d(zx)) orbitals in the VS6 octahedral chains sited along [1101, [011], and [101] directions. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Wembeim.
Title:
Anomalous magnetic phase in an undistorted pyrochlore oxide Cd2Os2O7 induced by geometrical frustration
Authors:
Koda, A; Kadono, R; Ohishi, K; Saha, SR; Higemoto, W; Yonezawa, S; Muraoka, Y; Hiroi, Z Author Full Names: Koda, Akihiro; Kadono, Ryosuke; Ohishi, Kazuki; Saha, Shanta R.; Higemoto, Wataru; Yonezawa, Shigeki; Muraoka, Yuji; Hiroi, Zenji
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 (6): Art. No. 063703 JUN 2007
Abstract:
We report on the muon spin rotation/relaxation study of a pyrochlore oxide, Cd2Os2O7, which exhibits a metal-insulator (MI) transition at T-MI similar or equal to 225 K without structural phase transition. It reveals strong spin fluctuation (>= 10(8) s(-1)) below the MI transition, suggesting a predominant role of geometrical spin frustration amongst Os5+ ions. Meanwhile, upon further cooling, an incommensurate spin density wave discontinuously develops below T-SDW similar or equal to 150 K. These observations strongly suggest the occurrence of an anomalous magnetic transition and associated change in the local spin dynamics in undistorted pyrochlore antiferromagnet.
Title:
Ba0.9Sr0.1TiO3-based optical microcavities fabricated by chemical solution deposition
Authors:
Hong, XK; Hu, GJ; Shang, JL; Bao, J; Chu, JH; Dai, N Author Full Names: Hong, X. K.; Hu, G. J.; Shang, J. L.; Bao, J.; Chu, J. H.; Dai, N.
Source:
APPLIED PHYSICS LETTERS 90 (25): Art. No. 251911 JUN 18 2007
Abstract:
Single or coupled optical microcavities have been prepared by inserting one or two dense Ba0.9Sr0.1TiO3 layers, respectively, in the quasiperiodic Ba0.9Sr0.1TiO3 multilayers fabricated based on phase separation. The single microcavities exhibit well-defined resonant modes in the investigated wavelength range with a quality factor no less than 60. The resonant frequency of the mode can be tuned through varying the spinning rate during the spin-coating process to change the thickness of the inserted layer. The mode properties of the coupled microcavities strongly depend on the mismatch parameter of the inserted defect layers. The approach reported here offers a simple, inexpensive, and flexible route for fabricating high quality microcavities. (c) 2007 American Institute of Physics.

Update: 17-Aug-2007

Title:
The strengthening effect of icosahedral phase on as-extruded Mg-Li alloys
Authors:
Xu, DK; Liu, L; Xu, YB; Han, EH Author Full Names: Xu, D. K.; Liu, L.; Xu, Y. B.; Han, E. H.
Source:
SCRIPTA MATERIALIA 57 (3): 285-288 AUG 2007
Abstract:
Through investigating the mechanical properties of three kinds of Mg-Li-Zn-Y alloys, a strengthening method, i.e. introducing I-phase Mg(3)Zn(6)y, icosahedral quasicrystal structure) in the matrix of Mg-Li alloys, for as-extruded Mg-Li alloys has been demonstrated. The tensile results indicate that I-phase can effectively strengthen the alloys. The substantial enhancement of strength has been explained by microstructure changes. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
New phase transition of solid bromine under high pressure
Authors:
San-Miguel, A; Libotte, H; Gauthier, M; Aquilanti, G; Pascarelli, S; Gaspard, JP Author Full Names: San-Miguel, A.; Libotte, H.; Gauthier, M.; Aquilanti, G.; Pascarelli, S.; Gaspard, J.-P.
Source:
PHYSICAL REVIEW LETTERS 99 (1): Art. No. 015501 JUL 6 2007
Abstract:
Solid bromine has been studied by x-ray absorption spectroscopy experiments up to a maximum pressure of 75 GPa. The data analysis of the extended fine structure reveals that the intramolecular distance first increases, reaching its maximum value at 25 +/- 5 GPa. From this value the intramolecular distance abruptly begins to decrease evidencing a nonpreviously observed phase transformation taking place at 25 +/- 5 GPa. A maximum variation of 0.08 A is observed at 65 +/- 5 GPa where again a phase transition occurs. This last transformation could correspond with the recently observed change to an incommensurate modulated phase. We discuss the possible generalization of the observed new phase transition at 25 +/- 5 GPa to the case of the other halogens.
Title:
Coordination polymer with a staircase molecular architecture: connecting binuclear Zn(II) bis-chelate platforms with bridging 4,4 '-bipyridyl
Authors:
Soldatov, DV; Enright, GD; Sokolov, IE Author Full Names: Soldatov, D. V.; Enright, G. D.; Sokolov, I. E.
Source:
JOURNAL OF STRUCTURAL CHEMISTRY 48 (2): 325-331 MAR-APR 2007
Abstract:
A new tetraketone ligand with two separated beta-diketone functions was prepared, 1,3-[CO-CH2-CO-C(CH3)(2)OCH3](2)Ph (H2LiPrOMe). The title coordination polymer, [Zn-2(L-iPrOMe)(2)(DMSO)(2)(bipy)](n) (DMSO = dimethylsulfoxide; bipy = 4,4'-bipyridyl), formed as the only crystalline product upon interaction of Zn(II) acetate, H2LiPrOMe and bipy in 1 : 1 : 1 to 1 : 1 : 5 molar ratios in DMSO as a solvent. A single crystal XRD study of the compound revealed a staircase polymeric architecture of the complex. The architecture is based on binuclear 'Zn-2(L-iPrOMe)(2)' platforms where each Zn(II) cation is chelated by two beta-diketonate groups of two L-iPrOMe ligands in the equatorial plane, while each L-iPrOMe ligand chelates two Zn(II) cations. The coordination environment of each Zn(II) is completed to a distorted octahedron by an O atom of a terminal DMSO and an N atom of bridging bipy ligands. The resulting staircase polymeric ribbons are packed in a self-inclusion mode as would be expected for van der Waals interactions. Most fragments of the molecule were found to be disordered over two equally populated orientations, which was interpreted as evidence of a modulated structure. In addition, several fragments reveal additional minor disordering and high thermal motion.
Title:
Comparative NMR study of incommensurate helix magnetic order in quasi-1D chain cuprates LiCu2O2 and NaCu2O2
Authors:
Gippius, AA; Morozova, EN; Okhotnikov, KS; Moskvin, AS; Baenitz, M; Drechsler, S Author Full Names: Gippius, A. A.; Morozova, E. N.; Okhotnikov, K. S.; Moskvin, A. S.; Baenitz, M.; Drechsler, S.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 316 (2): 298-301 SEP 2007
Abstract:
NMR and NQR investigations on the complex magnetic structure in the ordered state as well as phase transitions in two isostructural quasi-1D edge-shared cuprates LiCu2O2 and NaCu2O2 have been performed. While LiCu2O2 exhibits a magnetic phase transition at T-c = 24 K, NaCu2O2 orders magnetically at around 13 K. Li-6,Li-7 and Na-23 NMR spectra in LiCu2O2 and NaCu2O2, respectively, provide an unambiguous experimental evidence that below T-c an incommensurate in-chain helical spin structure is established in both compounds. However, the features of the observed low-temperature NMR and NQR spectra are different pointing to different properties of the helical magnetic structure. (C) 2007 Elsevier B.V. All rights reserved.
Title:
The point-contact spectroscopy of DyMn6Ge6 and DyFe6Ge6
Authors:
Pristas, G; Sniadecki, Z; Kerschl, P; Reiffers, M; Idzikowski, B; Rossler, UK; Muller, KH Author Full Names: Pristas, Gabriel; Sniadecki, Zbigniew; Kerschl, Peter; Reiffers, Marian; Idzikowski, Bogdan; Roessler, Ulrich K.; Mueller, Karl-Hartmut
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 316 (2): E396-E399 SEP 2007
Abstract:
We have used point-contact (PC) spectroscopy to study two related 1:6:6 rare earth transition metal-metal with complex magnetic order. The compound DyMn6Ge6 with HfFe6Ge6-type structure is a ferromagnetic incommensurate helimagnet with local antiferromagnetic coupling of Mn- and Dy-sublattice. The compound DyFe6Ge6 with TbFe6Ge6-type structure shows antiferromagnetic order in the Fe-sublattice and an independent order of the Dy-sublattice at low temperature. Both homocontacts of meltspun ribbons from these compounds and heterocontacts with Cu or Pt have been obtained. We present a comparison of PC metallic and tunnelling characteristics measured on DyMn6Ge6, DyFe6Ge6. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Foldover, quasi-periodicity, spin-wave instabilities in ultra-thin films subject to RF fields
Authors:
d'Aquino, M; Bertotti, G; Serpico, C; Mayergoyz, ID; Bonin, R; Guida, G Author Full Names: d'Aquino, M.; Bertotti, G.; Serpico, C.; Mayergoyz, I. D.; Bonin, R.; Guida, G.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 316 (2): E523-E525 SEP 2007
Abstract:
We study magnetization dynamics in a uniaxial ultra-thin ferromagnetic disk subject to spatially uniform microwave external fields. The rotational invariance of the system is such that the only admissible spatially uniform steady states are periodic (P-modes) and quasiperiodic (Q-modes) modes. The stability of P-modes versus spatially uniform and nonuniform perturbations is studied by using spin-wave analysis and the instability diagram for all possible P-modes is computed. The predictions of the spin-wave analysis are compared with micromagnetic simulations. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Phase transitions in Ni-Mn-Ga alloys with the account of crystal lattice modulation
Authors:
Buchelnikov, VD; Taskaev, SV; Zagrebin, MA; Zayak, AT; Takagi, T Author Full Names: Buchelnikov, V. D.; Taskaev, S. V.; Zagrebin, M. A.; Zayak, A. T.; Takagi, T.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 316 (2): E591-E594 SEP 2007
Abstract:
Using the Ginzburg-Landau theory, phenomenological phase diagrams of Heusler alloys Ni-Mn-Ga are theoretically investigated. We take into account the magnetic, elastic and micro-modulation order parameters in order to understand their coupling in the real system. We focus on the aspect of crystal modulation which appears at c/a<1 only, and is never observed for tetragonal distortions characterized by c/a>1. The influences of the parameters are discussed on the basis of phase diagrams. From different phase diagrams we choose those corresponding to the experimental situation and draw a conclusion that two opposite tetragonal distortions, c/a<1 and c/a>1, must be driven by different instabilities having different microscopic origins. (c) 2007 Elsevier B.V. All rights reserved.
Title:
A simple method of determining the form of the phonon part of tensors describing quasicrystal properties
Authors:
Grimmer, H Author Full Names: Grimmer, Hans
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 63: 266-272 Part 3 MAY 2007
Abstract:
It is shown that the restrictions on the form of property tensors of rank < 5 that follow from the Neumann principle for the point groups describing quasicrystals can easily be deduced from the restrictions for the point groups describing ordinary crystals. For octagonal and dodecagonal point groups, this is true even for property tensors of rank < 8 and < 12, respectively. The results derived in a number of papers for various physical properties of quasicrystals with certain point-group symmetries are generalized to all quasicrystal point groups, and it is shown that the results become more lucid if the classification of quasicrystal point groups with a principal axis into pentagonal, decagonal, octagonal and dodecagonal ones is done appropriately. A comparison with other approaches shows that applying the Neumann principle for the point groups describing quasicrystals yields the form of the so-called phonon part of the tensor under consideration. Connections between the restrictions valid for property tensors of arbitrary rank are given for general Heesch-Shubnikov point groups in three dimensions. (c) 2007 International Union of Crystallography Printed in Singapore - all rights reserved.

Update: 10-Aug-2007

Title:
Comment on "friction between incommensurate crystals''
Authors:
Merkle, AP; Marks, LD Author Full Names: Merkle, A. P.; Marks, L. D.
Source:
PHILOSOPHICAL MAGAZINE LETTERS 87 (8): 527-532 2007
Abstract:
We present results from an independent analysis of friction that more generally addresses all crystalline materials by an extension of coincident site lattice theory and dislocation drag. Calculations for graphitic friction are carried out and agree in magnitude with experimental friction forces. More interestingly, static, dynamic and anisotropic friction forces, incommensurability effects and superlubricity are explained by a more rigorous analysis of the dislocation structure at a sliding interface.
Title:
Domain walls in systems with coupled order parameters
Authors:
Janssen, T Author Full Names: Janssen, T.
Source:
FERROELECTRICS 349: 64-70 2007
Abstract:
Domains meet on walls where the order parameter changes in a continuous or discontinuous way. For aperiodic crystals domain walls may be ordered (discommensurations) or disordered. The dynamics of these domain walls depends strongly on the character (continuous or discontinuous) of the order parameter change. The situation is still more complicated when coupled order parameters are present. A discussion is given of the dynamics in the different cases.

Update: 3-Aug-2007

Title:
Direct transition from a disordered to a multiferroic phase on a triangular lattice
Authors:
Kenzelmann, M; Lawes, G; Harris, AB; Gasparovic, G; Broholm, C; Ramirez, AP; Jorge, GA; Jaime, M; Park, S; Huang, Q; Shapiro, AY; Demianets, LA Author Full Names: Kenzelmann, M.; Lawes, G.; Harris, A. B.; Gasparovic, G.; Broholm, C.; Ramirez, A. P.; Jorge, G. A.; Jaime, M.; Park, S.; Huang, Q.; Shapiro, A. Ya.; Demianets, L. A.
Source:
PHYSICAL REVIEW LETTERS 98 (26): Art. No. 267205 JUN 29 2007
Abstract:
We report the first direct transition from a paramagnetic and paraelectric phase to an incommensurate multiferroic in the triangular lattice antiferromagnet RbFe(MoO4)(2). Ferroelectricity is observed only when the magnetic structure has chirality and breaks inversion symmetry. A Landau expansion of symmetry-allowed terms in the free energy demonstrates that chiral magnetic order can give rise to a pseudoelectric field, whose temperature dependence agrees with experiment.
Title:
Magnetic-order-induced ferroelectricity in orthorhombic perovskite manganites
Authors:
Hu, CD Author Full Names: Hu, C. D.
Source:
PHYSICAL REVIEW B 75 (17): Art. No. 172106 MAY 2007
Abstract:
We studied the ferroelectricity of magnetic oxides, in which its emergence coincides with the onset of a second incommensurate magnetic order. We solved for the wave function of e(g) electrons in the presence of magnetic orders. The coupling between the magnetic and electric orders is provided by the spin-orbit interaction. It was found that the net electric dipole moment of the system came from the bond between the transition metal and oxygen atoms. The anisotropy of d orbitals also played an important role. Finally, the form of the coupling leads us to the conclusion that it is an improper ferroelectricity.
Title:
Series of modulated structures in SrxCoO2 and the modulation rule
Authors:
Yao, LD; Guo, YQ; Luo, JL; Zhang, W; Li, FY; Jin, CQ; Yu, RC Author Full Names: Yao, L. D.; Guo, Y. Q.; Luo, J. L.; Zhang, W.; Li, F. Y.; Jin, C. Q.; Yu, R. C.
Source:
PHYSICAL REVIEW B 75 (17): Art. No. 174118 MAY 2007
Abstract:
The nominal composition of Sr0.39CoO2, prepared by a low-temperature ion exchange technique, has been systematically studied by transmission electron microscopy, energy dispersive x-ray spectroscopy (EDX), and electron-energy-loss spectroscopy (EELS). Besides a well-defined root 3 and a(p) x root 3a(p) modulated structure, a series of long periodic modulated structures (n root 3a(p) x 3a(p)) was revealed by high-resolution transmission electron microscopy (HRTEM) in some microzones, which are induced by alternate position ordering of strontium ions. The results of EDX analyses confirm the variation of Sr content in corresponding modulated phases. Moreover, the L-3/L-2 intensity ratio of Co-L-2,L-3 edges in the EELS spectra indicates the variation of Co ionic valence state induced by the different contents of Sr cations. Based on the root 3a(p) x 3a(p) superstructural model, we propose the possible corresponding structural models in this paper. The simulated HRTEM images, based on those models, are consistent with experimental ones. In addition, several phase separations and some structural defects were observed in the sample.
Title:
Multi-k magnetic structures in USb0.9Te0.1 and UAs0.8Se0.2 observed via resonant x-ray scattering at the U M-4 edge
Authors:
Detlefs, B; Wilkins, SB; Javorsky, P; Blackburn, E; Lander, GH Author Full Names: Detlefs, B.; Wilkins, S. B.; Javorsky, P.; Blackburn, E.; Lander, G. H.
Source:
PHYSICAL REVIEW B 75 (17): Art. No. 174403 MAY 2007
Abstract:
Experiments with resonant photons at the U M-4 edge have been performed on a sample of USb0.9Te0.1, which has an incommensurate magnetic structure with k=k=0.596(2) reciprocal lattice units. The reflections of the form < kkk >, as observed previously in a commensurate k=1/2 system [N. Bernhoeft , Phys. Rev. B 69, 174415 (2004)], are observed, removing any doubt that these occur because of multiple scattering or high-order contamination of the incident photon beam. They are clearly connected with the presence of a 3k configuration. Measurements of the < kkk > reflections from the sample UAs0.8Se0.2 in a magnetic field show that the transition at T-*similar to 50 K is between a low-temperature 2k and high-temperature 3k state and that this *transition* is sensitive to an applied *magnetic* field. These experiments stress the need for quantitative theory to explain the intensities of these < kkk > reflections.
Title:
Stripes in thin ferromagnetic films with out-of-plane anisotropy
Authors:
Clarke, D; Tretiakov, OA; Tchernyshyov, O Author Full Names: Clarke, David; Tretiakov, O. A.; Tchernyshyov, O.
Source:
PHYSICAL REVIEW B 75 (17): Art. No. 174433 MAY 2007
Abstract:
We examine the T=0 phase diagram of a thin ferromagnetic film with a strong out-of-plane anisotropy (e.g., Co/Pt multilayers) in the vicinity of the reorientation phase transition. The phase diagram in the anisotropy-applied-field plane is universal in the limit in which the film thickness is the shortest length scale. It contains uniform fully magnetized and canted phases, as well as periodically nonuniform states: weakly modulated spin-density waves and strongly modulated stripes. We determine the boundaries of metastability of these phases and point out the existence of a critical point at which the difference between the spin-density wave and striped phases vanishes. Out-of-plane magnetization curves exhibit hysteresis loops caused by the coexistence of one or more phases. Additionally, we study the effect of a system edge on the orientation of nearby stripes. We compare our results with recent experiments.
Title:
Variation of charge/orbital ordering in layered manganite Pr1-xCa1+xMnO4 investigated by transmission electron microscopy
Authors:
Yu, XZ; Mathieu, R; Arima, T; Kaneko, Y; He, JP; Uchida, M; Asaka, T; Nagai, T; Kimoto, K; Asamitsu, A; Matsui, Y; Tokura, Y Author Full Names: Yu, X. Z.; Mathieu, R.; Arima, T.; Kaneko, Y.; He, J. P.; Uchida, M.; Asaka, T.; Nagai, T.; Kimoto, K.; Asamitsu, A.; Matsui, Y.; Tokura, Y.
Source:
PHYSICAL REVIEW B 75 (17): Art. No. 174441 MAY 2007
Abstract:
Structural features of the charge/orbital ordering (CO/OO) in single-layered manganites Pr1-xCa1+xMnO4 (0.3 <= x <= 0.65) have been investigated systematically by transmission electron microscopy. Analyses of electron-diffraction patterns as well as dark-field images have revealed that the CO/OO shows a striking asymmetric behavior as the hole doping x deviates from x=0.5. The modulation wave number linearly decreases with increasing x in the over-hole-doped (x > 0.5) crystals, while much less dependent on x in the under-hole-doped (x < 0.5) crystals. A temperature-induced incommensurate-commensurate crossover is observed in 0.35 < x < 0.5 and x=0.65. The correlation length of CO/OO in x=0.3 was proven to become shorter than that in 0.35 <= x <= 0.65.
Title:
Incommensurate modulations of Bi-III and Sb-II
Authors:
McMahon, MI; Degtyareva, O; Nelmes, RJ Author Full Names: McMahon, M. I.; Degtyareva, O.; Nelmes, R. J.
Source:
PHYSICAL REVIEW B 75 (18): Art. No. 184114 MAY 2007
Abstract:
Single-crystal diffraction data from the incommensurate host-guest composite structure of Bi-III-stable between 2.8 and 7.7 GPa-are found to contain very weak satellite reflections arising from structural modulations attributed to interactions between the host and guest structures. The principal effects of the modulation are a quasipairing of the guest atoms along their chains and some reduction in the closest approach of the host and guest atoms. It is suggested that these modulations play a key role in the stability of the structure. A similar modulated structure fits powder-diffraction data from Sb-II.
Title:
Stripeless incommensurate magnetism in strongly correlated oxide La1.5Sr0.5CoO4
Authors:
Savici, AT; Zaliznyak, IA; Gu, GD; Erwin, R Author Full Names: Savici, A. T.; Zaliznyak, I. A.; Gu, G. D.; Erwin, R.
Source:
PHYSICAL REVIEW B 75 (18): Art. No. 184443 MAY 2007
Abstract:
We studied the nanoscale structure of the short-range incommensurate magnetic order in La1.5Sr0.5CoO4 by elastic neutron scattering. We find that magnetic diffuse scattering is isotropic in the a-b plane, in contrast with the naive expectation based on the popular stripe model. Indeed, charge segregation into lines favoring certain lattice direction(s) would facilitate linear stacking faults in an otherwise robust antiferromagnetism of undoped material, leading to anisotropic disorder with a characteristic symmetry pattern present in the neutron scattering data.
Title:
Photonic band structure calculations of two-dimensional Archimedean tiling patterns
Authors:
Ueda, K; Dotera, T; Gemma, T Author Full Names: Ueda, Kazunari; Dotera, Tomonari; Gemma, Tohru
Source:
PHYSICAL REVIEW B 75 (19): Art. No. 195122 MAY 2007
Abstract:
We present a study of photonic band structures of two-dimensional Archimedean tiling patterns. The tilings we have investigated are (4.8(2)), (6(3)), (4.6.12), and (3(2).4.3.4), which have been discovered computationally and experimentally in self-assembled microphase separation of ABC star block terpolymer systems. Using plane-wave method, we have calculated eigenvalue equations for various combinations of dielectric contrast on the complex patterns. We demonstrate the existence of complete photonic band gaps in the (4.6.12) structure. Furthermore, we find that complete photonic bands readily open in the (3(2).4.3.4) structures in the same way as in dodecagonal quasicrystals. Complex tilings open up a way to construct photonic crystals.
Title:
Structures and thermoelectric properties of the infinitely adaptive series (Bi-2)(m)(Bi2Te3)(n)
Authors:
Bos, JWG; Zandbergen, HW; Lee, MH; Ong, P; Cava, RJ Author Full Names: Bos, J. W. G.; Zandbergen, H. W.; Lee, M.-H.; Ong, P.; Cava, R. J.
Source:
PHYSICAL REVIEW B 75 (19): Art. No. 195203 MAY 2007
Abstract:
The structures and thermoelectric properties of the (Bi-2)(m)(Bi2Te3)(n) homologous series, derived from stacking hexagonal Bi-2 and Bi2Te3 blocks, are reported. The end members of this series are metallic Bi and semiconducting Bi2Te3; nine members of the series have been studied. The structures form an infinitely adaptive series and a unified structural description based on a modulated structure approach is presented. The as-synthesized samples have thermopowers (S) that vary from n type for Bi2Te3 to p type for phases rich in Bi-2 blocks but with some Bi2Te3 blocks present, to n type again for Bi metal. The thermoelectric power factor (S-2/rho) is highest for Bi metal (43 mu W/K-2 cm at 130 K), followed by Bi2Te3 (20 mu W/K-2 cm at 270 K), while Bi2Te (m:n=5:2) and Bi7Te3 (m:n=15:6) have 9 mu W/K-2 cm (at 240 K) and 11 mu W/K-2 cm (at 270 K), respectively. The results of doping studies with Sb and Se into Bi2Te are reported.
Title:
Magnetic and transport properties of a one-dimensional frustrated t-J model for vanadate nanotubes
Authors:
Costamagna, S; Riera, JA Author Full Names: Costamagna, S.; Riera, J. A.
Source:
PHYSICAL REVIEW B 75 (20): Art. No. 205104 MAY 2007
Abstract:
We propose a one-dimensional model consisting of a chain with a t-J Hamiltonian coupled to a Heisenberg chain in a frustrated geometry to describe the appearance of the ferromagnetic phase which has been experimentally observed in vanadate nanotubes. This model contains a mechanism of frustration suppressed by doping suggested by Krusin-Elbaum [Nature (London) 431, 672 (2004)]. We study, using numerical techniques in small clusters, the relation between magnetic order and transport properties in the proposed model, and we perform a detailed comparison of the physical properties of this model with those of the ferromagnetic Kondo lattice model. For this comparison, a number of results for the latter model, obtained using the same numerical techniques, will be provided to complement those results already available in the literature. We conclude that it does not appear to be a true ferromagnetic order in the proposed model, but rather an incommensurate ferrimagnetic one, and contrary to what happens in the ferromagnetic Kondo lattice model, electronic transport is somewhat suppressed by this ferrimagnetic order.
Title:
Raman spectra of (PbS)(1.18)(TiS2)(2) misfit compound
Authors:
Ovsyannikov, SV; Shchennikov, VV; Cantarero, A; Cros, A; Titov, AN Author Full Names: Ovsyannikov, Sergey V.; Shchennikov, Vladimir V.; Cantarero, Andres; Cros, Ana; Titov, Alexander N.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 462 (1-2): 422-426 Sp. Iss. SI JUL 25 2007
Abstract:
A Raman study on the (PbS)(1.18)(TiS2)(2) semiconductor structure with incommensurate layers (misfit) is reported. The different bands observed in the spectra are attributed to both the TiS2 host layers, at 219 (E-g) and 333 (A(1g)) cm(-1), and the intercalated PbS layers: the LO(Gamma), 2LO and 3LO phonons at 203, 412 and 634 cm(-1), respectively. A phonon peak probably related to the superposition of TiS2 and PbS vibrations, was observed near 286 cm(-1). The decrease of the phonon wave numbers (of the modes located at 203, 333, 412, and 634 cm(-1)) with increasing laser power pointed out negative temperature coefficients of these modes. A peak appearing with laser power near 151 cm(-1) is discussed. For higher laser powers the formation of oxides and oxysulfates complexes (PbO, TiO2, PbO2, PbSO4, "PbO center dot PbSO4") at the misfit's surface was observed from the Raman spectra. In the low-frequency region the peaks at 19, 73 and 95-96 cm(-1) have been revealed associated presumably with vibrations of the PbS layers. (C) 2006 Elsevier B.V. All rights reserved.
Title:
The multiple q-vector incommensurate magnetic structure of TbGe3
Authors:
Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Buschow, KHJ Author Full Names: Schobinger-Papamantellos, P.; Rodriguez-Carvajal, J.; Buschow, K. H. J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (23): Art. No. 236201 JUN 13 2007
Abstract:
The magnetic phase diagram of the antiferromagnetic compound TbGe3 ( space group Cmcm, T-N = 40 K) has been studied by neutron diffraction and magnetic measurements. It comprises three distinct ranges of magnetic ordering characterized by two symmetry-independent wavevectors q(1) = ( q(1x), 0, 0) and q(2) = ( q(2x), 0, q(2z)) in addition to the paramagnetic state: the high- temperature ( HT) range T-N down to T-ic = 24 K where q(1) and q(2) are incommensurate with the crystal lattice with variable length. In this range the magnetic structure corresponds to a planar ( 0, y, z) modulated structure with variable amplitude and direction. Below T-ic = 24 K q(1) and q(2) lock in to the commensurate values q(1x) = q(2x) = 1/2 and q(2z) = 1/ 3 corresponding to a sixfold cell enlargement ( 2a, b, 3c) and a twofold splitting of the atomic positions. The magnetic space group ( Shubnikov) is P(b)mma( Sh(51)(299)). The two Tb sublattices are coupled antiferromagnetically. Their different temperature dependence is discussed in terms of a Fourier analysis of the observed data. The magnetic structure corresponds to a uniaxial antiphase domain moment arrangement (+--) along c and (+-) along a. In the intermediate- temperature (IT) range T-ic down to 16 K, mu(Tb1)/mu(Tb2) increases continuously from 0.87 to 1. In this range, the magnetic structure described by two amplitudes squares up to a constantmoment phase with 8.1 mu B/Tb atomwhich persists in the low- temperature ( LT) range 16 - 8 K.
Title:
Low-temperature phase transitions in barium sodium niobate
Authors:
Filipic, C; Kutnjak, Z; Lortz, R; Torres-Pardo, A; Dawber, M; Scott, JF Author Full Names: Filipic, C.; Kutnjak, Z.; Lortz, R.; Torres-Pardo, A.; Dawber, M.; Scott, J. F.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (23): Art. No. 236206 JUN 13 2007
Abstract:
We present dielectric and specific heat data on barium sodium niobate ( Ba2Na1-xNb5O15) from 4 to 460 K with an emphasis on the low- temperature incommensurate phase transitions. This material is ferroelectric below T-c( x) = ca 830 K, and the reciprocal dielectric constant extrapolates to zero near this temperature throughout the low- temperature phases, which involve distortions within the non-polar plane and do not affect significantly the ferroelectric properties. The transition from orthorhombic to incommensurate near 113 K has highly frequency- dispersive dynamics, reminiscent of those in relaxors, and an activation energy of 0.42 eV. The 'lock- in' transition near 30 K to a tetragonal structure with an enlarged unit cell has been controversial, with studies in Japan ( 1996, 1997) and the Czech Republic ( 2004) not finding the P4nc phase predicted by Schneck ( 1982) and measured directly via spallation neutron scattering by Scott et al ( 1990); our new studies show that this transition is limited by kinetics and requires very slow cooling for detection.
Title:
Elastic field for a straight dislocation in an icosahedral quasicrystal
Authors:
Zhu, AY; Fan, TY; Guo, LH Author Full Names: Zhu, Ai-Yu; Fan, Tian-You; Guo, Li-Hui
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (23): Art. No. 236216 JUN 13 2007
Abstract:
A straight dislocation in a three- dimensional icosahedral quasicrystal is studied. A solution considering phonon - phason coupling is observed; the phonon phonon, phason - phason and phonon - phason interactions are revealed, in which a comparison between the present solution and other approximate solutions including the classic solution for crystals is given, and shows that the coupling effect is significant.
Title:
Magnetic structure of CeRhIn5 under magnetic field
Authors:
Raymond, S; Ressouche, E; Knebel, G; Aoki, D; Flouquet, J Author Full Names: Raymond, S.; Ressouche, E.; Knebel, G.; Aoki, D.; Flouquet, J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (24): Art. No. 242204 JUN 20 2007
Abstract:
The magnetically ordered ground state of CeRhIn5 at ambient pressure and zero magnetic field is an incommensurate helicoidal phase with the propagation vector k = (1/2, 1/2, 0.298) and the magnetic moment in the basal plane of the tetragonal structure. We determined by neutron diffraction the two different magnetically ordered phases of CeRhIn5 evidenced by bulk measurements under applied magnetic field in the basal plane. The low temperature high magnetic phase corresponds to a commensurate sine-wave structure of the magnetization with k = (1/2, 1/2, 1/4). At high temperature, the phase is incommensurate with k = (1/2, 1/2, 0.298) and a possible small ellipticity. The propagation vector of this phase is the same as that of the zero-field structure.
Title:
Improvement of thermoelectric properties of icosahedral AlPdRe quasicrystals by Fe substitution for Re
Authors:
Okada, JT; Hamamatsu, T; Hosoi, S; Nagata, T; Kimura, K; Kirihara, K Author Full Names: Okada, Junpei T.; Hamamatsu, Takehito; Hosoi, Shizuka; Nagata, Tomohiro; Kimura, Kaoru; Kirihara, Kazuhiro
Source:
JOURNAL OF APPLIED PHYSICS 101 (10): Art. No. 103702 MAY 15 2007
Abstract:
The thermoelectric properties of quaternary icosahedral AlPdReFe quasicrystals obtained by replacing Re with Fe in icosahedral AlPdRe quasicrystals have been studied according to the guiding principle of weakly bonded rigid heavy clusters (WBRHCs). Anisotropy in the microstructures of arc-melted and annealed samples was found, and the electrical and thermal conductivities are larger in the direction perpendicular to the bottom of the arc-melted button than in the parallel case. The dimensionless figure of merit (ZT) in the perpendicular direction was increased 2.6 times from 0.08 to 0.21 by Fe substitution for Re in the icosahedral AlPdRe quasicrystals, which was caused by the increase of the Seebeck coefficient and the decrease of the phonon thermal conductivity, and the increase of the electrical conductivity, expected and not for the WBRHCs, respectively. (c) 2007 American Institute of Physics.
Title:
Interfacial-layer modulation of domain switching current in ferroelectric thin films
Authors:
Jiang, AQ; Lin, YY; Tang, TA Author Full Names: Jiang, A. Q.; Lin, Y. Y.; Tang, T. A.
Source:
JOURNAL OF APPLIED PHYSICS 101 (10): Art. No. 104105 MAY 15 2007
Abstract:
It is found that the voltage drop across a 170-nm-thick Pb(Zr0.4Ti0.6)O-3 film keeps constantly at a well-defined coercive voltage during domain switching, irrespective of the applied voltage and frequency, and that the switching current of domains is reversely proportional to the resistance of loading resistors in the circuit. A simple formalism is derived for the speed of polarization reversal short into a few nanoseconds. The maximum speed of domain switching is limited by the time of compensation charge dissipation via loading resistors in the circuit, instead of reverse domain nucleation and growth. However, in most cases, the switching current decays with time and is thus peaked under different applied voltages, as observed in an 87-nm-thick film. This phenomenon is understood from our work due to the presence of interfacial passive layers that modulate switching current transient through the circuit RC-time constant, besides the consideration of a broad coercive-v! oltage distribution in a genuine thin film.
Title:
Dielectric and structural studies of Ba2MTi2Nb3O15 (BMTNO15, M=Bi3+,La3+,Nd3+,Sm3+,Gd3+) tetragonal tungsten bronze-structured ceramics
Authors:
Stennett, MC; Reaney, IM; Miles, GC; Woodward, DI; West, AR; Kirk, CA; Levin, I Author Full Names: Stennett, M. C.; Reaney, I. M.; Miles, G. C.; Woodward, D. I.; West, A. R.; Kirk, C. A.; Levin, I.
Source:
JOURNAL OF APPLIED PHYSICS 101 (10): Art. No. 104114 MAY 15 2007
Abstract:
The structure and dielectric properties of a new family of tetragonal tungsten bronze (TTB) ceramics with the general formula, Ba2MTi2Nb3O15 where M=Bi3+,La3+,Nd3+,Sm3+,Gd3+, have been investigated. Hereafter the compositions will be referred to by the abbreviation BMTNO15 where M=B(Bi3+), L(La3+), N(Nd3+), S(Sm3+) or G(Gd3+). BLTNO15 [permittivity maximum (T-m)similar to-80 degrees C] and BBTNO15 (T-m similar to-100 degrees C) exhibited relaxorlike dielectric behavior. In contrast, BNTNO15 (T-m similar to 165 degrees C), BSTNO15 (T-m similar to 250 degrees C), and BGTNO(15) (T-m similar to 320 degrees C) were classic ferroelectrics. T-m increased with decreasing radius of the M ion. Room temperature x-ray powder diffraction (XRD) patterns of all the compounds indexed on a prototype P4/mbm (or P4bm) space group with lattice parameters a approximate to 12.4 angstrom and c approximate to 4 angstrom. However, electron diffraction revealed that the relaxor phases, BLTNO15 and BBTNO15, exhibited an incommensurate modulation, whereas the classic ferroelectric BNTNO15, BSTNO15, and BGTNO(15) featured an orthorhombic superstructure with lattice parameters a approximate to b approximate to root 2a(TTB) and c approximate to 2c(TTB). (c) 2007 American Institute of Physics.
Title:
Electron density modulations in columnar banana phases
Authors:
Gorecka, E; Vaupotic, N; Pociecha, D Author Full Names: Gorecka, Ewa; Vaupotic, Natasa; Pociecha, Damian
Source:
CHEMISTRY OF MATERIALS 19 (12): 3027-3031 JUN 12 2007
Abstract:
The structure of columnar phases formed by bent-core mesogens is analyzed. The combination of the X-ray diffraction intensity data and the model predictions for the form factor phases allows for the construction of the electron density maps for these phases. Within the model, the smectic layer fragments are approximated by parallelograms placed in a body-centered crystallographic unit cell, the parallelogram size and orientation with respect to the unit cell sides being the free parameters. Obtained maps show that in the tilted columnar phase, the neighboring molecular blocks with opposite electric polarity are connected either through the walls or continuously by the less-ordered layer fragments. The type of connection between the blocks seems to be determined by the size of the crystallographic unit cell.
Title:
Polymeric quasicrystals
Authors:
Jacoby, M Author Full Names: Jacoby, Mitch
Source:
CHEMICAL & ENGINEERING NEWS 85 (21): 5-5 MAY 21 2007
Title:
Stable and metastable multicomponent alloys
Authors:
Cantor, B Author Full Names: Cantor, Brian
Source:
ANNALES DE CHIMIE-SCIENCE DES MATERIAUX 32 (3): 245-256 MAY-JUN 2007
Abstract:
This paper describes some underlying principles of stable and metastable multicomponent alloys and gives a variety of examples. Different types of muticomponent alloy and different methods for accessing multicomponent phase space are discussed. Particular examples include alloys in the CrMnFeCoNiNbGeVTi and the TiZrHfNbFeCoNiCuAgAl systems. The alloys have been manufactured by a variety of conventional and high speed solidification techniques, and their often nanoscale microstructures studied via optical, X-ray and electron microscope methods. The alloys exhibit a variety of amorphous, quasicrystalline, dendritic, eutectic and peritectic structures.
Title:
Quasicrystal surfaces: structure and growth of atomic overlayers
Authors:
Sharma, HR; Shimoda, M; Tsai, AP Author Full Names: Sharma, H. R.; Shimoda, M.; Tsai, A. P.
Source:
ADVANCES IN PHYSICS 56 (3): 403-464 2007
Abstract:
We review recent developments in surface studies of single- grain quasicrystals under ultra high-vacuum conditions, focusing on two di. erent topics: surface structure and growth of atomic overlayers on surfaces. Quasicrystalline phases are currently used for investigation of the. rst topic are icosahedral (i) Al-Pd-Mn, i-Al-Cu-Fe, i-Al-Cu-Ru, i-Ag- In-Yb and decagonal (d) Al-Ni-Co, and d-Al-Cu-Co. We report the progress made with all of these phases. The second topic covers the study of single-element overlayer growth by vapor deposition.

Update: 27-Jul-2007

Title:
Energy levels and their correlations in quasicrystals
Authors:
Jagannathan, A; Piechon, F Author Full Names: Jagannathan, A.; Piechon, F.
Source:
PHILOSOPHICAL MAGAZINE 87 (16-17): 2389-2415 2007
Abstract:
Quasicrystals can be considered, from the point of view of their electronic properties, as being intermediate between metals and insulators. For example, experiments show that quasicrystalline alloys such as AlCuFe or AlPdMn have conductivities far smaller than those of the metals that these alloys are composed from. Wavefunctions in a quasicrystal are typically intermediate in character between the extended states of a crystal and the exponentially localized states in the insulating phase, and this is also reflected in the energy spectrum and the density of states. In the theoretical studies we consider in this review, the quasicrystals are described by a pure hopping tight binding model on simple tilings. We focus on spectral properties, which we compare with those of other complex systems, in particular, the Anderson model of a disordered metal. We discuss 'strong' and 'weak' quasicrystals, which are described by different universal laws. We find similarities and universal behaviour, but also significant differences between quasiperiodic models and models with disorder. Like weakly disordered metals, the quasicrystal can be described by the universal level statistics that can be derived from random matrix theory. These level statistics are only one aspect of the energy spectrum, whose very large fluctuations can also be described by a level spacing distribution that is log-normal. An analysis of spectral rigidity shows that electrons diffuse with a bigger exponent (superdiffusion) than in a disordered metal. Adding disorder attenuates the singular properties of the perfect quasicrystal, and leads to improved transport. Spectral properties are also used in computing conductances of such systems, and to attempt to resolve the experimental enigmas such as whether quasicrystals are intrinsically conductors, and if so, how conductances depend on the structure.
Title:
Magnetic structures of the M2TbF6 (M = Li, K, Rb) fluorides: A complex behavior resulting from frustration
Authors:
Josse, M; El-Ghozzi, M; Avignant, D; Andre, G; Bouree, F Author Full Names: Josse, M.; El-Ghozzi, M.; Avignant, D.; Andre, G.; Bouree, F.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 180 (5): 1623-1635 MAY 2007
Abstract:
Neutron powder diffraction has been performed on Li2TbF6, K2TbF6 and Rb2TbF6 fluoroterbates. Incommensurate long-range magnetic order is observed below T-N = 2.02, 1.60 and 2.07 K. The square-modulating of the magnetic structures can be correlated with the geometric frustration induced by the pseudo-hexagonal packing of the [TbF6](2-) chains in these hexafluorides. This frustration and the magnetic interactions are discussed on the basis of experimental data and topological considerations. The magnetic structures encountered in this series, and the particular thermal evolution of the Li2TbF6 magnetic structure may result from the competition between the magnetic interactions taking place in the chains and the magnetic interactions coupling the chains. (c) 2007 Elsevier Inc. All rights reserved.
Title:
An investigation of the Al-Ni-Rh phase diagram between 50 and 100-at% Al
Authors:
Przepiorzynski, B; Mi, S; Grushko, B; Surowiec, M Author Full Names: Przepiorzynski, B.; Mi, S.; Grushko, B.; Surowiec, M.
Source:
INTERMETALLICS 15 (7): 918-928 JUL 2007
Abstract:
The Al-rich part of Al-Ni-Rh was studied between 800 and 1080 degrees C. The Al9Rh2 phase was found to contain up to 8 at% Ni. The orthorhombic Al-Rh epsilon(6)-phase extends up to 17.5 at% Ni, high-temperature cubic C-Al5Rh2 up to about 10 at% Ni while low-temperature hexagonal H-Al5Rh2 extends up to 4 at% Ni. The Al7Rh3 phases contained up to 3 at% Ni. The solubility of Rh in Al3Ni is up to 3 at% and in Al3Ni2 up to 5 at%. The isostructural binary AM and AlRh phases probably form a continuous beta-range of the CsCl-type solid solutions. A ternary hexagonal phase similar to Al28Ir9 (a = 1.213 and c = 2.626 nm) was found to be formed between Al76Ni4Rh20 and Al76Ni13Rh11. The formation of the high-temperature stable decagonal phase was confirmed. Another ternary phase, whose structure is not yet clarified, was revealed around Al70Ni11Rh19. Partial 1080, 1000, 900 and 800 degrees C isothermal sections of the Al-Ni-Rh phase diagram are presented. (C) 2006 Elsevier Ltd. All ri! ghts reserved.
Title:
Formation of quasiperiodic and related periodic intermetallics in alloy systems of aluminum with transition metals
Authors:
Grushko, B; Velikanova, T Author Full Names: Grushko, Benjamin; Velikanova, Tamara
Source:
CALPHAD-COMPUTER COUPLING OF PHASE DIAGRAMS AND THERMOCHEMISTRY 31 (2): 217-232 JUN 2007
Abstract:
Quasiperiodic phases (quasicrystals) have been found in numerous alloy systems of aluminum with transition metals (TM) between about 60 and 85 at.% Al. In binary Al-TM systems only metastable quasicrystals were observed, while in several ternary systems containing Cu, Ni or I'd the quasicrystals are stable. Many stable and metastable periodic phases formed in these compositional ranges exhibit structural relations to quasicrystals. Studies of these phenomenona have stimulated extensive investigation or revision of the high-Al regions of the ternary alloy systems belonging to theAl-Cu-TM, Al-Ni-TM and Al-Pd-TM groups. These studies are reviewed here. (C) 2007 Elsevier Ltd. All rights reserved.

Update: 20-Jul-2007

Title:
Charge-stripe order in the electronic ferroelectric LuFe2O4
Authors:
Zhang, Y; Yang, HX; Ma, C; Tian, HF; Li, JQ Author Full Names: Zhang, Y.; Yang, H. X.; Ma, C.; Tian, H. F.; Li, J. Q.
Source:
PHYSICAL REVIEW LETTERS 98 (24): Art. No. 247602 JUN 15 2007
Abstract:
The structural features of the charge ordering states in LuFe2O4 are characterized by in situ cooling transmission electron microscopy observations from 300 K down to 20 K. Two distinctive structural modulations, a major q(1)=(1/3,1/3,2) and a weak q(2)=q(1)/10+(0,0,3/2), have been well determined at the temperature of similar to 20 K. Systematic analysis demonstrates that the charges at low temperatures are well crystallized in a charge-stripe phase, in which the charge-density wave behavior in a nonsinusoidal fashion results in elemental electric dipoles for ferroelectricity. It is also noted that the charge ordering and ferroelectric domains often change markedly with lowering temperatures and yield a rich variety of structural phenomena.
Title:
Local order and phase selection in undercooled transition metal based systems: ab initio molecular dynamics study
Authors:
Jakse, N; Pasturel, A Author Full Names: Jakse, Noel; Pasturel, Alain
Source:
PHASE TRANSITIONS 80 (4-5): 369-384 2007
Abstract:
An overview of a recent series of ab initio molecular dynamics ( MD) simulations for pure liquid transition metals as well as for transition metals (TM) based liquid alloys is presented. The aim is to investigate the local structure of these systems and their evolution upon undercooling, and our results are analysed through a three-dimensional image of the short-ranger order (SRO) by means of the common-neighbour analysis. Recent diffraction experiments indicate that the structure of both pure metals and alloys in undercooled states is dominated by an icosahedral SRO. Such a SRO is predicted to influence the energy of the interface between the liquid and a solid nucleus, depending on the structure of the solid phase. This, in turn, decisively impacts the nucleation behaviour of solid phases from the undercooled melts. We find that the five-fold symmetry is already present in the liquid state of all the studied systems. However, our findings show that the five-fold symmetry in the liquid state as well as its evolution upon undercooling depends on the system under consideration. For Ni, Zr, and Ta, local configurations are more complex than that given by the simple icosahedron. For Al1-xMnx alloys, local configurations are the result of a strong competition between chemical and topological effects; more particularly, our results indicate the predominance of the fivefold symmetry around x = 0.14 in agreement with the experimental quasicrystal forming range.
Title:
Magnetic phase transitions in ScFe4Al8 by powder and single crystal neutron diffraction
Authors:
Recko, K; Dobrzynski, L; Goukassov, A; Biernacka, M; Brancewicz, M; Makal, A; Wozniak, K; Waliszewski, J; Talik, E; Kotur, B; Suskis, W Author Full Names: Recko, K.; Dobrzynski, L.; Goukassov, A.; Biernacka, M.; Brancewicz, M.; Makal, A.; Wozniak, K.; Waliszewski, J.; Talik, E.; Kotur, B.; Suskis, W.
Source:
PHASE TRANSITIONS 80 (6-7): 575-586 JUN-JUL 2007
Abstract:
Unpolarized neutron diffraction and magnetization experiments have been performed on single crystal of ScFe4Al8 intermetallic compound. In the single crystal both, neutron and high resolution X-ray diffraction measurements, indicate perfect crystallochemical order. The magnetic ordering was studied in the temperature range 8-250 K. LT neutron measurements show that the compound exhibits magnetic spiral structure. The scandium seems magnetically inactive while the iron site splits into two independent magnetic orbits. Below 115 K two sets of magnetic reflections were found. Each of them requires different wave vector representation i.e. (q) over right arrow (1) = (0.13, 0.13, 0) and (q) over right arrow (2) = (0. 18, 0.18, 0) and discloses different temperature behavior. In the basic elementary cell, the Fe moments of adjacent atoms along c axis are forming a constant angle while along the face diagonals the mutual orientation of magnetic moments is almost antiparallel. The iron moments rotate within the basal plane upon entering the neighboring cell. The magnetic structure with two modulation vectors is different from the one observed earlier by means of magnetic neutron powder diffraction, where only one modulation vector was observed. The reasons of this different magnetic behavior are discussed.
Title:
Development of the Ca-Au-In icosahedral quasicrystal and two crystalline approximants: Practice via pseudogap electronic tuning
Authors:
Lin, QS; Corbett, JD Author Full Names: Lin, Qisheng; Corbett, John D.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 129 (21): 6789-6797 MAY 30 2007
Abstract:
Electronic tuning and syntheses to gain the icosahedral quasicrystal (i-QC) (Ca14.1(2)Au44.2(8)In41.7(7), e/a = 1.98) and two approximant crystals (ACs) are reported. The tuning was derived from Na2Au6In5, another cubic Mg2Zn11-type structure, for which the Fermi level (e/a = 1.77) should tune to a calculated pseudogap (e/a = 2.02) under a rigid band assumption. The 1/1 AC, Ca3Au12.2(1)In6.3(2) (e/a = 1.73), crystallizes in space group Im (3) over bar, with a = 15.152(2) A, Z = 8, and the 2/1 AC, Ca12.6(1)Au37.0(2)In39.6(6) (e/a = 2.01), in Pa (3) over bar, with a = 24.632(3) A , Z = 8. Both have substantially fixed compositions according to lattice dimensions. Structure analyses reveal that both ACs contain triacontahedral clusters as the basic building blocks at the body-centered and primitive cubic unit cell levels, respectively. Densities-of-states (DOS) analyses for the 1/1 AC structure reveal a pseudogap at e/a = 2.00, close to the point at which the i-QC was predicted and experimentally tuned. Phase relationships of the ACs and the i-QC are reported according to DTA, XRD, and temperature-dependent XRD measurements. The QC is thermodynamically metastable below similar to 500 degrees C.
Title:
The (3+2)D structure of oxygen deficient LaSrCuO3.52
Authors:
Hadermann, J; Perez, O; Creon, N; Michel, C; Hervieu, M Author Full Names: Hadermann, Joke; Perez, Olivier; Creon, Nicolas; Michel, Claude; Hervieu, Maryvonne
Source:
JOURNAL OF MATERIALS CHEMISTRY 17 (22): 2344-2350 JUN 14 2007
Abstract:
The (3 + 2)D modulated structure of the oxygen deficient compound LaSrCuO3.52 was determined using a combination of electron diffraction and neutron diffraction. The cell parameters are a = b = 3.7587(3) angstrom, c = 13.0074(9) angstrom, alpha = beta = gamma = 90 degrees, superspace group I4/mmm (alpha alpha 0, alpha-alpha 0)00 mg, alpha = 0.2222(3), R-p = 4.5%, R-0 = 2.1%, R-1 = 4.9%. The oxygen vacancies are located in the CuO2-delta plane and are ordered with the oxygen atoms, creating three different oxygen environments for the Cu atoms: CuO4 squares, CuO5 pyramids and CuO6 octahedra.
Title:
A study of thermodynamic properties and association in the Al-Cu melt and their relation to quasicrystal formation conditions
Authors:
Zaitsev, AI; Shimko, RY; Arutyunyan, NA; Dunaev, SF Author Full Names: Zaitsev, A. I.; Shimko, R. Yu.; Arutyunyan, N. A.; Dunaev, S. F.
Source:
DOKLADY PHYSICAL CHEMISTRY 414: 115-119 Part 1 MAY 2007

Update: 13-Jul-2007

Title:
High-temperature phase transitions and intermediate incommensurate modulation of the tridymite form of AlPO4
Authors:
Graetsch, HA Author Full Names: Graetsch, Heribert A.
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 222 (5): 226-233 2007
Abstract:
Similar to silica tridymite, the corresponding AlPO4 analogue shows a sequence of displacive phase transitions at elevated temperatures. The transformation temperatures are lower than for SiO2 tridymite. The incommensurate structure of the tridymite form of AlPO4 between ca. 94 and 167 degrees C was refined in first harmonic approximation from X-ray powder diffraction data in the 3 + 1 dimensional superspace group P2(1)(alpha beta 0). The major components of the displacive modulation are wavy transversal shifts of the centers of the PO4/2 and AlO4/2 tetrahedra associated with additional tilting of the rigid tetrahedra. The wave vector varies continuously from q(1) = 0.068 a* + 0.006 b* at 165 degrees C to q(2) = 0.051 a* + 0.003 b* at 96 C. The amplitudes of the wave-like displacements increase with decreasing temperature to 0.2 angstrom at 96 degrees C for the Al and P atoms and up to ca. 0.6 angstrom for some of the oxygen atoms. The modulation is assumed to arise from the condensation of a rigid unit lattice vibration mode like in isostructural intermediate silica tridymite.
Title:
Crystal structure of the Aurivillius phases in the system Bi4Ti3O12-PbTiO3
Authors:
Tellier, J; Boullay, P; Mercurio, D Author Full Names: Tellier, Jenny; Boullay, Philippe; Mercurio, Daniele
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 222 (5): 234-243 2007
Abstract:
The crystal structure of four Aurivillius phases within the pseudo-binary system Bi4Ti3O12-PbTiO3 is examined using a 3 + 1D approach where these phases are treated as commensurately modulated layered structures. The structure of PbBi4Ti4O15, Pb2Bi4Ti5O18, Pb3Bi4Ti6O21 and PbBi8Ti7O27 are refined by the Rietveld method using XRPD data from single phased powders. The structure of Pb3Bi4Ti6O21 and PbBi8Ti7O27 is reported for the first time. When the lead content increases, the structure gets less distorted and approaches the prototype paraelectric phase in an apparent close relation with the onset of a "relaxor-like" ferroelectric behaviour. For these relaxor compounds, SAED investigation evidences the existence of a disorder in the form of micro-twinning.
Title:
Effect of Ca on crystallization of Mg-based master alloy containing spherical quasicrystal
Authors:
Zhang, JS; Du, HW; Lu, BF; Zhang, Y; Liang, W; Xu, CX; Lu, FL Author Full Names: Zhang Jin-shan; Du Hong-wei; Lu Bin-feng; Zhang Yan; Liang Wei; Xu Chun-xiang; Lu Feng-lei
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA 17 (2): 273-279 APR 2007
Abstract:
Spherical icosahedral quasicrystal line phase (I-phase) was obtained by introducing Ca into Mg-Zn-Y alloy under conventional casting conditions. Due to the addition of Ca, Mg45Zn50Y4.5Ca0.5 primary I-phase, which is thermodynamically stable and homogeneously distributed, was generated instead of decahedral quasicrystalline phase during the solidification process; the morphology of primary I-phase in the solidification microstructure changed from petal-like one (60-80 gm) to spherical one (<= 15 gm). When the mass fraction of Ca reaches 0.05%, spherical I-phase with the largest quantity, highest spheroidization rate and highest circular degree can be obtained. Meanwhile, due to the changed morphology and the decreased size of primary I-phase, the hardness of Mg-Zn-Y-Ca master alloy is reduced. The application of spherical I-phase as particulate reinforced phase provides great opportunities for the improvement of strength and toughness of magnesium alloys.
Title:
Compressive strength and yield asymmetry in extruded Mg-Zn-Ho alloys containing quasicrystal phase
Authors:
Singh, A; Somekawa, H; Mukai, T Author Full Names: Singh, Alok; Somekawa, H.; Mukai, T.
Source:
SCRIPTA MATERIALIA 56 (11): 935-938 JUN 2007
Abstract:
Two alloys, Mg96.9Zn2.7Ho0.4 and Mg93Zn6Ho, containing a quasicrystal phase were extruded at various temperatures to produce different grain sizes and tested at room temperature in tension and compression. For larger grains the strength of the Mg93Zn6Ho alloy was almost twice that of the Mg96.9Zn2.7Ho0.4 alloy. Yield stresses approached 300 MPa as the grain sizes decreased to 1 mu m. In the case of the Mg93Zn6Ho alloy, at grain sizes less than about 2 mu m, yield stresses in compression become higher than in tension. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
High fracture toughness of extruded Mg-Zn-Y alloy by the synergistic effect of grain refinement and dispersion of quasicrystalline phase
Authors:
Somekawa, H; Singh, A; Mukai, T Author Full Names: Somekawa, Hidetoshi; Singh, Alok; Mukai, Toshiji
Source:
SCRIPTA MATERIALIA 56 (12): 1091-1094 JUN 2007
Abstract:
The fracture toughness of an extruded Mg-2.6 at.% Zn-0.4 at.% Y alloy with a grain size of 1 mu m and containing quasicrystalline icosahedral phase was determined to be 32.5 MPa m(1/2), which is much higher than conventional wrought magnesium alloys. Microstructural observations showed that the quasicrystalline phase pinned many dislocation movements and prevented void nucleation because of its coherent interface with the matrix. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Effect of composition on the microstructure and mechanical properties of Mg-Zn-Al alloys
Authors:
Zhang, J; Guo, ZX; Pan, FS; Li, ZS; Luo, XD Author Full Names: Zhang, Jing; Guo, Z. X.; Pan, Fusheng; Li, Zhongsheng; Luo, Xiaodong
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 456 (1-2): 43-51 MAY 15 2007
Abstract:
Magnesium is receiving great attention for transport applications, particularly its cast alloys. This investigation focuses on the as-cast microstructure and mechanical properties of permanent-mould cast Mg-Zn-Al alloys with typical compositions within the high zinc castable domain. Three types of alloys were identified and characterized by Mg-32(Al, Zn)(49), also known as the tau phase; MgZn phase, also known as the epsilon phase; and a ternary icosahedral quasi-crystalline phase, denoted as the Q phase, respectively. A schematic phase diagram is proposed to show the change of microstructral constituents with element content and the Zn/Al ratio. The diagram reveals that the microstructral constituent is dominated by both the content of Zn or Al and the Zn/Al mass ratio; alloys with a high Zn/Al ratio and a low Al content fall into the epsilon-type; alloys with an intermediate Zn/Al ratio and an intermediate At content favour the T-type; and those with a low Zn/Al ratio and a high Al are dominated by the icosahedral quasi-crystalline phase. No Mg17Al12 (gamma) phase was found in those ZA series alloys. The solidification process and its effects on the phase constituents were discussed. Preliminary mechanical property testing showed that all the experimental alloys possess comparable ultimate strength and yield strength with the AZ91 alloy at ambient temperature, but show far superior creep resistance at elevated temperatures. Moreover, while ambient-temperature properties solely depend on the total element contents, the tau- and the Q-type alloys show greater potential than the e-type alloys on the improvement of elevated temperature properties. (C) 2006 Elsevier B.V. All rights reserved.
Title:
Structural investigation of oxygen non-stoichiometry and cation doping in misfit-layered thermoelectric (Ca2CoO3-x)(CoO2)(delta), delta approximate to 1.61
Authors:
Ling, CD; Aivazian, K; Schmid, S; Jensen, P Author Full Names: Ling, Chris D.; Aivazian, Karina; Schmid, Siegbert; Jensen, Paul
Source:
JOURNAL OF SOLID STATE CHEMISTRY 180 (4): 1446-1455 APR 2007
Abstract:
The chemical and crystallographic natures of oxygen non-stoichiometry and cation doping in the 'misfit-layered' cobaltate [Ca2CoO3-x][CoO2](delta), delta approximate to 1.16, were investigated. Single-phase polycrystalline samples were prepared with the help of a high-energy planetary ball mill, and single crystals grown from a K2CO3/KCl flux. Polycrystalline undoped, Ti4+-doped, and Nd3+-doped samples were annealed under both air and under argon in order to modify the oxygen non-stoichiometry. The incommensurately modulated composite crystal structures of undoped and Ti4+-doped single crystals were refined against X-ray diffraction data using the superspace group X2/m(0,delta,0)s0. For the as-made (air-annealed) undoped crystal, 14(2)% oxygen vacancies were found on the disordered O2 site in the central layer of the rock-salt-type subsystem, giving an overall stoichiometry [Ca2CoO2.86][CoO2](1.61). For the Ti4+ -doped crystal this site was found to be almost fully occupied, while Ti4+-dopant cations were located on the disordered Co1 site in the central layer of the rock-salt-type subsystem, giving an overall formula [Ca2Co0.74Ti0.26O1.98][CoO2](1.61). In both cases, the average cobalt oxidation state is 3.13+. The single-crystal refinements, thermogravimetric analyses and variations in the lattice parameters of polycrystalline samples refined against synchrotron X-ray diffraction (XRD) data indicate that for both undoped and Ti4+-doped samples, substantial numbers of additional oxygen vacancies (15-20%) can be introduced on this site by annealing under an inert atmosphere. Nd3+-doped samples have a much lower tolerance (< 5%) for oxygen vacancies. (c) 2007 Elsevier Inc. All rights reserved.
Title:
Direct observation of the bandwidth-disorder induced variation of charge/orbital ordering structure in RE0.5(Ca1-ySry)(1.5)MnO4
Authors:
Yu, XZ; Arima, T; Kaneko, Y; He, JP; Mathieu, R; Asaka, T; Hara, T; Kimoto, K; Matsui, Y; Tokura, Y Author Full Names: Yu, X. Z.; Arima, T.; Kaneko, Y.; He, J. P.; Mathieu, R.; Asaka, T.; Hara, T.; Kimoto, K.; Matsui, Y.; Tokura, Y.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (17): Art. No. 172203 MAY 2 2007
Abstract:
Changes in the charge/orbital ordering (CO/OO) structure with the bandwidth of the eg band and quenched disorder were investigated in doped manganites RE0.5(Ca1-ySry) 1.5MnO4 (RE=Pr, Eu) with a single-layer perovskite structure. A systematic study of the modulation structure associated with the CO/OO phase demonstrated that the long-range commensurate structure changes to a short-range incommensurate structure with increasing Sr content through the enhancement of the bandwidth and quenched disorder in these systems. At the same time, the transition temperature of CO/OO (TCO/OO) decreases. Changes in structure and TCO/OO with different A-site combinations reveal that the CO/OO phase is strongly suppressed by the widening of the eg band and the stronger quenched disorder in these layered manganites.
Title:
Modulated and unmodulated structures, and the transport mechanisms in the triangular lattice system NaxCoO2 with x similar or equal to 0.48, 0.58 and 0.65
Authors:
Onoda, M; Ikeda, T Author Full Names: Onoda, Masashige; Ikeda, Tomohiro
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (18): Art. No. 186213 MAY 9 2007
Abstract:
The crystal structures of the triangular lattice system. gamma-phase NaxCoO2 with compositions of x similar or equal to 0.48, 0.58 and 0.65 have been determined by means of x-ray four-circle diffraction. Na0.58CoO2 has lattice constants of a(h) = 2.8180(5) and c(h) = 11.005(9) angstrom with space group P6(3)/mmc and does not exhibit structural modulation. On the other hand, Na0.65CoO2 has a P6(3)/mmc-type superlattice with a doubled unit cell of ash = 5.6527(5) and C-sh = 10.9356(10) angstrom, and Na0.48CoO2 indicates a Pmmn-type superlattice with a(so) = 5.6261(5), b(so) = 11.1406(10) and c(so) = 4.8723(5) angstrom. The structural modulation for x similar or equal to 0.65 is attributed to the incomplete order of Na ions without an order for Co valence, while that for x similar or equal to 0.48 results in almost complete Na order and partial valence order for Co. For x similar or equal to 0.48, the metal-poor metal transition occurs at about 50 K. The electrical resistivities for x similar or equal to 0.58 and 0.65 follow a T-3/2 dependence below 200 and 80 K, respectively, which may be due to antiferromagnetic spin fluctuations in three dimensions. At higher temperatures, the resistivities for the CoO2 plane have a T-1 dependence, likely due to an enhancement of two dimensionality. For x similar or equal to 0.65, the resistivity maximum appears at about 250 K, which may be attributed to the renormalization effect of the Fermi surface by the fluctuations.
Title:
Effect of Co substitution for Ni on the Ti-Zr-(Ni, Co) pseudo-ternary quasicrystal formation
Authors:
Huang, HG; Qiang, JB; Bai, B; Dong, P; Zhang, PC Author Full Names: Huang, H. G.; Qiang, J. B.; Bai, B.; Dong, P.; Zhang, P. C.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 353 (16-17): 1670-1675 JUN 1 2007
Abstract:
A series of alloys designed along a Ti-9(Ni,Co)(4)-Zr e/a-variant line in the Ti-Zr-(Ni, Co) pseudo-ternary alloy system, are investigated by XRD and TEM. Experimental results show that bulk icosahedral quasicrystals (IQC) prepared by copper mold suction casting, can be obtained in a large region from Ti55Zr20(Ni,Co)(25) to Ti34.6Zr50(Ni,Co)(15.4) with Ni/Co ratio equal to 3/1, and in a sharply diminished region from Ti48Zr30(Ni,Co)(22) to Ti42Zr40(Ni,Co)(18) with decreased Ni/Co ratio equal to 2/2 or 1/3. Ti48Zr30Ni16.5Co5.5 is the optimal quasicrystal-forming composition, where a nearly pure bulk IQC phase is achieved. The stepwise substitutions of Co for Ni in this pseudo-ternary system contribute to the formation of Ti2Ni, fcc-Zr2Ni, C14-type Laves and beta-(Ti,Zr) solid solution phases. However, these substitutions greatly reduce the forming ability of the IQC phase. It is suggested that Co is essentially unfavorable to Ti/Zr-based quasicrystal formation. (C) 2007 Elsevier B.V. All rights reserved.
Title:
Stabilization of the pentagonal surface of the icosahedral AlPdMn quasicrystal by controlled Si absorption
Authors:
Longchamp, JN; Erbudak, M; Weisskopf, Y Author Full Names: Longchamp, J.-N.; Erbudak, M.; Weisskopf, Y.
Source:
APPLIED SURFACE SCIENCE 253 (14): 5947-5950 MAY 15 2007
Abstract:
The Debye-temperature of the pentagonal surface of the icosahedral AlPdMn quasicrystal (QC) is measured by means of low-energy electron diffraction after the absorption of different amounts of Si. We observe an increase of the surface Debye-temperature from 300 +/- 7 K for the freshly prepared surface to 330 +/- 7 K after the absorption of 60-angstrom Si. Because the quasicrystalline order persists at the surface in spite of the diffusion of Si into the substrate, we suggest that the diffusion is dominated by a vacancy-mediated process. (c) 2007 Elsevier B.V. All rights reserved.

Update: 6-Jul-2007

Title:
Self-assembly of monatomic complex crystals and quasicrystals with a double-well interaction potential
Authors:
Engel, M; Trebin, HR Author Full Names: Engel, Michael; Trebin, Hans-Rainer
Source:
PHYSICAL REVIEW LETTERS 98 (22): Art. No. 225505 JUN 1 2007
Abstract:
For the study of crystal formation and dynamics, we introduce a simple two-dimensional monatomic model system with a parametrized interaction potential. We find in molecular dynamics simulations that a surprising variety of crystals, a decagonal, and a dodecagonal quasicrystal are self-assembled. In the case of the quasicrystals, the particles reorder by phason flips at elevated temperatures. During annealing, the entropically stabilized decagonal quasicrystal undergoes a reversible phase transition at 65% of the melting temperature into an approximant, which is monitored by the rotation of the de Bruijn surface in hyperspace.
Title:
On the parameters of glass formation in metallic systems
Authors:
Azad, S; Mandal, A; Mandal, RK Author Full Names: Azad, Shankar; Mandal, Arnab; Mandal, R. K.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 458 (1-2): 348-354 JUN 15 2007
Abstract:
We have recently noted the structural similarities between the dominant clusters of bulk metallic glasses (BMGs) with those present in icosahedral phase and intermetallics with large unit cell volume based on the diffraction studies available in literature. Latter belongs to any one of the five space groups. These are I4/mcm (tl12), P6/m (hP68), Fddd (oF48), Fd3m (cF24) and an orthorhombic structure (Al11Sm3) whose space group is not known. We are unaware of such discussion in literature. We also present a Venn diagram based on compositionally dependent and independent parameters to classify the BMG alloy systems. It has been observed that there are two distinct categories of BMGs. One class displays Fermi surface-brillouin zone interaction whereas the other does not follow this criterion. We believe that such a classification will be helpful in knowing their characteristics with respect to some of their applications. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Formation of icosahedral phase in an Al93Fe3Cr2Ti2 bulk alloy
Authors:
Kim, KB; Xu, W; Tomut, M; Stoica, M; Calin, M; Yi, S; Lee, WH; Eckert, J Author Full Names: Kim, K. B.; Xu, W.; Tomut, M.; Stoica, M.; Calin, M.; Yi, S.; Lee, W. H.; Eckert, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 436 (1-2): L1-L4 JUN 14 2007
Abstract:
The microstructural investigation of a suction-cast Al93Fe3Cr2Ti2 bulk alloy reveals that an icosahedral phase forms together with monoclinic Al-13(Fe,Cr)(4) and tetragonal Al3Ti in an alpha-Al matrix. The icosahedral phase is often surrounded by Al3Ti particles indicating that the formation of the icosahedral phase strongly competes with the Al3Ti phase. Chemical analysis reveals that Ti has a strong influence to stabilize the Al3Ti phase. In contrast, both Cr and Fe are effective to stabilize the icosahedral phase. (C) 2006 Elsevier B.V. All rights reserved.

Update: 29-Jun-2007

Title:
Incommensurate structure of phosphorus phase IV
Authors:
Fujihisa, H; Akahama, Y; Kawamura, H; Ohishi, Y; Gotoh, Y; Yamawaki, H; Sakashita, M; Takeya, S; Honda, K Author Full Names: Fujihisa, Hiroshi; Akahama, Yuichi; Kawamura, Haruki; Ohishi, Yasuo; Gotoh, Yoshito; Yamawaki, Hiroshi; Sakashita, Mami; Takeya, Satoshi; Honda, Kazumasa
Source:
PHYSICAL REVIEW LETTERS 98 (17): Art. No. 175501 APR 27 2007
Abstract:
There are six known phases for phosphorus at room temperature under high pressure. Only the structure of phase IV, which exists from 107 GPa to 137 GPa, remains unsolved. We performed a powder x-ray diffraction experiment and a Rietveld analysis and successfully determined its structure to be an incommensurately modulated structure by only 1 site of atomic position. High-pressure phases of halogens and chalcogens have previously been shown to have a similar modulated structure; however, phosphorus phase IV is different from them and was shown to be the third case.
Title:
Quantum Lifshitz point in the infinite-dimensional Hubbard model
Authors:
Gunther, F; Seibold, G; Lorenzana, J Author Full Names: Guenther, F.; Seibold, G.; Lorenzana, J.
Source:
PHYSICAL REVIEW LETTERS 98 (17): Art. No. 176404 APR 27 2007
Abstract:
We show that the Gutzwiller variational wave function is very accurate for the computation of magnetic phase boundaries in the infinite-dimensional Hubbard model. This allows us to substantially extend known phase diagrams. For both the half-hypercubic and the hypercubic lattice, a large part of the phase diagram is occupied by an incommensurate phase, intermediate between the ferromagnetic and the paramagnetic phase. In case of the hypercubic lattice, the three phases join at a new quantum Lifshitz point at which the order parameter is critical and the stiffness vanishes.
Title:
Fluctuations and phase separation in a quasi-one-dimensional system
Authors:
Dona, E; Loerting, T; Penner, S; Minca, M; Menzel, A; Bertel, E; Schoiswohl, J; Berkebile, S; Netzer, FP; Zucca, R; Redinger, J Author Full Names: Dona, Enrico; Loerting, Thomas; Penner, Simon; Minca, Mariana; Menzel, Alexander; Bertel, Erminald; Schoiswohl, Johannes; Berkebile, Steven; Netzer, Falko P.; Zucca, Rinaldo; Redinger, Josef
Source:
PHYSICAL REVIEW LETTERS 98 (18): Art. No. 186101 MAY 4 2007
Abstract:
Phase transitions in a quasi-one-dimensional surface system on a metal substrate are investigated as a function of temperature. Upon cooling the system shows a loss of long-range order, fluctuations, and a transition into an inhomogeneous ground state due to competition of local adsorbate-adsorbate interactions with an incommensurate charge density wave. This agrees with a general phase diagram for correlated systems and high-temperature superconductors. The model surface system allows direct imaging of the fluctuations and the glassy inhomogeneous ground state by scanning tunneling microscopy.
Title:
Growth and vibrational spectroscopic studies of some incommensurate crystals
Authors:
Manonmani, N; Kesavamoorthy, R; Mahadevan, CK Author Full Names: Manonmani, N.; Kesavamoorthy, R.; Mahadevan, C. K.
Source:
PHYSICA B-CONDENSED MATTER 393 (1-2): 228-234 APR 30 2007
Abstract:
An attempt has been made to grow the single crystals of K3BaCl5 center dot 2H(2)O, K3CaCl5 center dot 2H(2)O and Na3CaCl5 center dot 2H(2)O from aqueous solutions by the slow evaporation of solution method. Atomic absorption spectroscopic (AAS) and X-ray diffraction (XRD) measurements have shown the incommensurate nature of the crystals grown. TG measurements have confirmed the presence of water of crystallization. Vibrational spectra were recorded and the observed Raman and infrared bands were assigned and discussed. (c) 2007 Published by Elsevier B.V.
Title:
Preparation and transport properties of a bulk icosahedral quasicrystalline Ti45Zr35Ni17Cu3 alloy
Authors:
Liu, BZ; Liu, N; Wu, YM; Wang, LM Author Full Names: Liu, Baozhong; Liu, Ning; Wu, Yaoming; Wang, Limin
Source:
PHYSICA B-CONDENSED MATTER 393 (1-2): 316-320 APR 30 2007
Abstract:
A bulk alloy which consists of the single icosahedral quasicrystalline phase (I-phase) in Ti45Zr35Ni17CU3 alloy has been fabricated by mechanical alloying and subsequent pulse discharge sintering technique. Crystallographic structure analyses show that the bulk alloy is an I-phase. The transport properties of the bulk alloy are examined, and the results show that the room-temperature thermal conductivity is 5.347 W K-(1) m(-1), and the electrical conductivity decreases with increasing the temperature from 300 to 450K. The Seebeck coefficient is negative at the temperature range from 300 to 360K, and changes to positive from 370 to 450K. Hall effect measurements indicate the bulk I-phase alloy has a high carrier concentration. The specific heat capacity increases when the temperature increases from 280 to 324 K. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Effects of ionizing radiation and thermal cycling on tensile properties of extruded Mg-Zn-Y-Zr alloys containing quasicrystalline phase
Authors:
Liu, ZH; Han, EH Author Full Names: Liu, Z. H.; Han, E. H.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 457 (1-2): 186-194 MAY 25 2007
Abstract:
Effects of ionizing radiation and thermal cycling simulated low-earth orbit (LEO) environments on tensile properties of three kinds of as-extruded Mg-Zn-Y-Zr alloys at room temperature have been studied for the first time. Results show that Alloy 2 containing 2.3% Y (wt.%) possesses the optimal tensile properties among the three kinds of alloys. Significant difference between the alloys performed ionizing radiation is in elongation which show increase after radiation in Alloy 3. This may result from combined effect of the grain growth and a possible transformation between W-phase and quasicrystalline phase during the radiation process. Similarly, there are possibly two kinds of opposing effects simultaneously operated on tensile properties of the alloys during the thermal cycling process. One is softening effect initiated at the interface between the second phases and alpha-Mg matrix. The other is strengthening effect of dislocations generated at the grain boundary and the precipitates and particles of the second phases. Therefore, there is a decrease in strength and ductility after 200 cycles but an increase after 500 cycles which could be due to an overriding effect of hardening during cycling over the softening effect. (C) 2006 Elsevier B.V. All rights reserved.
Title:
Thermal evolution of nanoquasicrystalline Al93Fe3Cr2Ti2 alloy
Authors:
Escorial, AG; Cremaschi, VF; Natale, E; Lieblich, M Author Full Names: Garcia Escorial, A.; Cremaschi, V. F.; Natale, E.; Lieblich, M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 434: 215-216 Sp. Iss. SI MAY 31 2007
Abstract:
In this work, thermal evolution of bulk nanoquasicrystalline Al93Fe3Cr2Ti2 material, obtained by consolidation of nanoquasicrystalline powder particles, is studied. The powder particles were obtained by gas atomization and the consolidation of the powders was achieved via warm extrusion [1,2]. The evolution of the microstructure during processing as well as with further thermal treatments was investigated. The consolidated material contains spherical particles of an icosahedral i-phase of around 200 nm in diameter. The quasicrystalline phase is detected even after 1 h at 500 degrees C, and afterwards, it evolves through a metastable Al6Fe phase to the equilibrium phases. (C) 2006 Elsevier B.V. All rights reserved.
Title:
Effect of Zr on the crystallization behavior of multi-component Zr-based metallic glasses
Authors:
Scudino, S; Eckert, J; Breitzke, H; Luders, K; Schultz, L Author Full Names: Scudino, Sergio; Eckert, Juergen; Breitzke, Hergen; Lueders, Klaus; Schultz, Ludwig
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 434: 217-220 Sp. Iss. SI MAY 31 2007
Abstract:
Melt-spun Zr-y(Ti0.186Nbu.058CU0.324Ni0.258Al0.174)(100-y) glassy ribbons with y=57 and 62 were investigated by differential scanning calorimetry, X-ray diffraction and transmission electron microscopy in order to clarify the role of Zr on the crystallization behavior. The devitrification of the ribbons is characterized by the formation of a metastable icosahedral quasicrystalline phase during the first stage of the crystallization process. With increasing amount of Zr the thermal stability against crystallization decreases whereas the temperature range of stability of the quasicrystalline phase increases. Furthermore, the grain size and the volume fraction of the quasicrystalline precipitates increases with increasing Zr content. Accordingly, appropriately adjusting the Zr content allows for tuning the thermal stability as well as the microstructure evolution upon heating. (C) 2006 Elsevier B.V. All rights reserved.
Title:
Amorphous and crystalline phases in rapidly solidified Al-Ta and Al-Ta-V alloys
Authors:
Donnadieu, P; Ochin, P Author Full Names: Donnadieu, Patricia; Ochin, Patrick
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 434: 255-258 Sp. Iss. SI MAY 31 2007
Abstract:
Al-Ta and Al-Ta-V alloys with composition corresponding to complex crystalline phases have been prepared by rapid solidification in order to examine the ability of these systems to form quasiperiodic or amorphous phases. According to transmission electron microscopy investigation, the rapidly solidified alloys show crystalline phases together with an amorphous phase having a high Ta content. TEM observations carried out on ground samples indicate that the crystalline phases transform into a nanocrystalline structure under mechanical grinding. (C) 2006 Elsevier B.V. All rights reserved.
Title:
Fabrication of Ti-Zr-Ni bulk quasicrystal by mechanical alloying and pulse current sintering
Authors:
Matsumoto, A; Kobayashi, K; Nishio, T; Ozaki, K Author Full Names: Matsumoto, Akihiro; Kobayashi, Keizo; Nishio, Toshiyuki; Ozaki, Kimihiro
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 434: 315-318 Sp. Iss. SI MAY 31 2007
Abstract:
Elementary powder mixtures with the composition of Ti-45 at.%Zr-38 at.%Ni and Y as an additive has been mechanically alloyed using a planetary ball mill. All of the obtained powders consisted of mainly an amorphous phase. With increasing content of Y, the quantity of icosahedral quasicrystal increased in heat-treated powders. The addition of 3 at.%Y led to almost fully quasicrystalline phase. Ti-Zr-Ni bulk quasicrystal was successfully prepared using a pulse current sintering method under an applied pressure of 500 MPa at 813 K. The obtained bulk quasicrystal material has a Vicker hardness of 6.9 GPa. (C) 2006 Published by Elsevier B.V.
Title:
Quasicrystal phase formation in Al-Cu-Fe nanopowders during field-activated sintering (FAST)
Authors:
Nicula, R; Turquier, F; Stir, M; Kodash, VY; Groza, JR; Burkel, E Author Full Names: Nicula, R.; Turquier, F.; Stir, M.; Kodash, V. Y.; Groza, J. R.; Burkel, E.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 434: 319-323 Sp. Iss. SI MAY 31 2007
Abstract:
The sequence of solid-state phase transformations in high-energy ball-milled Al-Cu-Fe alloy powders upon constant-rate heating were examined by in situ synchrotron radiation diffraction and thermal analysis (DSC/DTA) methods. The as-milled Al-Cu-Fe nanopowders were consolidated into disk-shape pellets using field-activated spark-plasma sintering (FAST/SPS). The chemical homogeneity and microstructure of the sintered bodies were investigated using scanning electron microscopy (SEM/EDX). The effect of electric field application on the formation of quasicrystalline phases from mechanically activated nanopowders during sintering by FAST/SPS is discussed. (C) 2006 Elsevier B.V. All rights reserved.
Title:
Medium-ranged interactions of transition-metal (3d and 4d) impurity pairs in Al and atomic structures of Al-rich Al-transition-metal alloys
Authors:
Hoshino, T; Fujima, N; Asato, M; Tamura, R Author Full Names: Hoshino, T.; Fujima, N.; Asato, M.; Tamura, R.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 434: 572-576 Sp. Iss. SI MAY 31 2007
Abstract:
We give systematic ab initio calculations for the interaction energies (from first to eighth neighbors) of impurity pairs X-X (X = Sc-Zn, Y-Cd) in At and discuss the micromechanism of the structural stability of Al-rich AIX alloys. The calculations are based on the generalized gradient approximation in the density-functional theory and employ the all-electron full-potential Korringa-Kohn-Rostoker Green's function method for point defects, which guarantees the correct embedding of the cluster of impurities and vacancies in an otherwise perfect crystal. We show: (1) the fundamental features of phase diagrams of these alloys, such as ordering and segregation, are understood by the sign of first-neighboring X-X interaction energies; (2) the structural stability of Al-rich AIX alloys such as LI, (Al3Sc and Al3Y), DO22 (Al3V and Al3Nb), and Mackay icosahedron in AlMn quasicrystal, are understood qualitatively by using the medium-ranged and oscillating X-X interactions, due to th! e strong sp-d (Al-X) hybridization; (3) the strength and oscillating behavior of the medium-ranged X-X interaction energies are specified very well by the d-electron numbers of X impurities. (C) 2006 Elsevier B.V. All rights reserved.
Title:
Hydrogen absorption in amorphous and quasicrystalline Ti45Ni17Zr38 powders synthesized by mechanical alloying
Authors:
Zhernovenkova, YV; Andreev, LA; Kaloshkin, SD; Sviridova, TA; Tcherdyntsev, VV; Tomilin, IA Author Full Names: Zhernovenkova, Yu. V.; Andreev, L. A.; Kaloshkin, S. D.; Sviridova, T. A.; Tcherdyntsev, V. V.; Tomilin, I. A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 434: 747-750 Sp. Iss. SI MAY 31 2007
Abstract:
Hydrogen absorption in amorphous and quasicrystalline Ti45Ni17Zr38 powders, obtained both directly by mechanical alloying (MA) and after subsequent annealing, was studied. MA was performed in a planetary ball mill under protective argon atmosphere. The powders were hydrogenated at 503 and 573 K under initial pressure of 2.9 kPa. Hydrogen absorption of the as-milled amorphous samples led to formation of TiH2, ZrH2 and (ZrTi)H-2 hydrides. Hydrogenation of quasicrystalline phase resulted in formation of hydrogen solution in quasicrystalline phase and ZrH2. The maximum registered concentration of H-2 in the samples was 1.38 H/M. Quasicrystalline phase disappeared after partial degassing up to 1.25 H/M. Activation energies of hydrogen absorption and hydrogen evolution were measured, these values were found as 40.4 +/- 0.2 and 25.2 +/- 0.1 kJ/mol correspondingly. (C) 2006 Elsevier B.V.. All rights reserved.
Title:
Magnetic structure of Er5Si3 at T >= 20 K
Authors:
Vokhmyanin, AP; Dorofeev, YA; Kurbakov, AI; Pirogov, AN; Skryabin, YN Author Full Names: Vokhmyanin, A. P.; Dorofeev, Yu. A.; Kurbakov, A. I.; Pirogov, A. N.; Skryabin, Yu. N.
Source:
CRYSTALLOGRAPHY REPORTS 52 (3): 420-423 MAY-JUN 2007
Abstract:
The symmetry analysis of magnetic structures of the Er5Si3 compound, possible at temperatures of 20 and 25 K, has been performed to interpret the experimental elastic neutron scattering data obtained at these temperatures. It was shown that the smallest dispersion factor R-m at these temperatures corresponds to the modulated magnetic structure in which the magnetic moments of Er atoms are directed along the a(3) axis of the unit cell and form an antiferromagnetic longitudinal spin wave characterized by the wave vector k = mu b(3), where mu is approximately 0.264 and 0.274 at 20 and 25 K, respectively. The analysis of the temperature behavior of the magnetic reflection intensities demonstrated that the Er5Si3 compound is paramagnetic at 30 K.
Title:
Investigation of the structure and properties of quartz in the alpha-beta transition range by neutron diffraction and mechanical spectroscopy
Authors:
Nikitin, AN; Markova, GV; Balagurov, AM; Vasin, RN; Alekseeva, OV Author Full Names: Nikitin, A. N.; Markova, G. V.; Balagurov, A. M.; Vasin, R. N.; Alekseeva, O. V.
Source:
CRYSTALLOGRAPHY REPORTS 52 (3): 428-435 MAY-JUN 2007
Abstract:
The paper reports on the results of complex investigations into the physical properties of synthetic quartz single crystals and quartz powders in the temperature range of the alpha-beta transition with the use of neutron diffraction and mechanical spectroscopy. The crystal structure of quartz powders with different average sizes of grains is determined in the temperature range up to 620 degrees C and in the alpha-beta transition temperature range. The temperature dependences of the internal friction and the resonant frequency for quartz samples in the vicinity of the phase transition temperature are obtained upon excitation of vibrations in the planes parallel and perpendicular to the Z axis of the quartz crystal. The temperatures at the maxima of the internal friction in the range 560-620 degrees C are determined. The assumptions regarding the possible reasons for the shift of the phase transition temperature are made. It is revealed that the internal friction is characteri! zed by a maximum that is observed in the vicinity of 350 degrees C and is not related to the structural transformations in quartz.
Title:
Structural correlations of the enhancement of dielectric permittivity in the (Ta2O5)(0.92)(TiO2)(0.08) system
Authors:
Liu, XQ; Han, XD; Zhang, Z; Ji, LF; Jiang, YJ Author Full Names: Liu, X. Q.; Han, X. D.; Zhang, Z.; Ji, L. F.; Jiang, Y. J.
Source:
APPLIED PHYSICS LETTERS 90 (21): Art. No. 211904 MAY 21 2007
Abstract:
A Ti-ion ordering which correlates to the significant enhancement of the dielectric constant was determined in the (Ta2O5)(0.92)(TiO2)(0.08) system by high resolution electron microscopy and the corresponding simulations. The alien Ti ions were determined to selectively sit on the octahedral locations in the Ta2O5 base structure in an average of 9-time period along the < 110 > direction. The authors suggest this Ti-ion ordering induces the directional enhancement of the dielectric permittivity of the (Ta2O5)(0.92)(TiO2)(0.08) system. The atomic mechanism of this modulated structure contributing to the enhancement of the dielectric constant was qualitatively interpreted using a one-dimensional chain model. The structural correlations of the dielectric enhancement revealed in this study suggest a way to search or design high-k materials. (c) 2007 American Institute of Physics.

Update: 22-Jun-2007

Title:
Unveiling quasiperiodicity through nonlinear wave mixing in periodic media
Authors:
Bahabad, A; Voloch, N; Arie, A Author Full Names: Bahabad, Alon; Voloch, Noa; Arie, Ady
Source:
PHYSICAL REVIEW LETTERS 98 (20): Art. No. 205501 MAY 18 2007
Abstract:
Quasiperiodicity is the concept of order without translation symmetry. The discovery of quasiperiodic order in natural materials transformed the way scientists examine and define ordered structure. We show and verify experimentally that quasiperiodicity can be observed by scattering processes from a periodic structure, provided the interaction area is of finite width. This is made through a momentum conservation condition, physically realizing a geometrical method used to model quasiperiodic structures by projecting a periodic structure of a higher dimension.
Title:
Prediction of band gaps in phononic quasicrystals based on single-rod resonances
Authors:
Sutter-Widmer, D; Steurer, W Author Full Names: Sutter-Widmer, Daniel; Steurer, Walter
Source:
PHYSICAL REVIEW B 75 (13): Art. No. 134303 APR 2007
Abstract:
Band-gap formation in two-dimensional quasiperiodic polymer/water heterostructures (with 4- to 14-fold Patterson symmetry in this study) is governed by strong acoustic resonances of the sound-soft single scatterers. Already with an eightfold-symmetric structure the first band gap is very isotropic. For isotropy of the higher gaps higher-symmetric structures are required. However, this can also be achieved by a smart tuning of the properties of the scatterers. Their symmetry (and therewith the symmetries of the scattered fields) has to better match the symmetry of a given structure. Polygon- and star-shaped prisms on quasiperiodic structures can yield smoother and more isotropic gaps in transmission spectra.
Title:
Origin of static friction and its relationship to adhesion at the atomic scale
Authors:
Zhang, Q; Qi, Y; Hector, LG; Cagin, T; Goddard, WA Author Full Names: Zhang, Qing; Qi, Yue; Hector, Louis G., Jr.; Cagin, Tahir; Goddard, William A., III
Source:
PHYSICAL REVIEW B 75 (14): Art. No. 144114 APR 2007
Abstract:
Using atomic scale interfaces consisting of slabs of the same materials, we study the relationship between adhesion and static friction. The work of separation, which is a measure of adhesion, and the spatial variation of the interface potential energy along the sliding direction are computed for both commensurate and incommensurate Al2O3/Al2O3 interfaces, and incommensurate smooth and rough Al/Al interfaces. These values are compared with the predicted static friction stress resulting from constant force and constant velocity molecular dynamics simulations. Simulation results show that static friction is not determined by the absolute value of adhesion. Rather, it is determined by the change of potential energy along the sliding direction.
Title:
Ab initio study of W-Al-Co-Ni: An approximant of the decagonal Al-Co-Ni quasicrystal
Authors:
Hassdenteufel, KH; Oganov, AR; Katrych, S; Steurer, W Author Full Names: Hassdenteufel, Kai H.; Oganov, Artem R.; Katrych, Sergiy; Steurer, Walter
Source:
PHYSICAL REVIEW B 75 (14): Art. No. 144115 APR 2007
Abstract:
We have performed ab initio simulations of binary and ternary periodic model structures based on the W phase in order to investigate chemical bonding, its response to pressure, and structural relaxations accompanying the substitution of Co by Ni. Our results support previous conclusions that the maximization of Al-Co and Ni-Ni interactions is favorable for reaching the lowest-energy state. The valence electron localization function (ELF) indicates partially covalent bonding supporting the formation of energetically favorable atomic clusters. The existence of a pseudogap in the calculated electronic density of states close to the Fermi level suggests electronic stabilization according to the Hume-Rothery-type mechanism. High-pressure simulations of binary W-(Al,Co) up to 90 GPa reveal increasing puckering of the atomic layers perpendicular to the pseudotenfold b axis. Furthermore, the basic pentagonal columnar clusters become distorted, leading to shorter distances between neighboring Co atoms. The structural changes in the vicinity of the distorted clusters point to local changes in the chemical bonding as reflected in the valence ELF.
Title:
Structure factors of harmonic and anharmonic Fibonacci chains by molecular dynamics simulations
Authors:
Engel, M; Sonntag, S; Lipp, H; Trebin, HR Author Full Names: Engel, Michael; Sonntag, Steffen; Lipp, Hansjoerg; Trebin, Hans-Rainer
Source:
PHYSICAL REVIEW B 75 (14): Art. No. 144203 APR 2007
Abstract:
The dynamics of quasicrystals is characterized by the existence of phason excitations in addition to the usual phonon modes. In order to investigate their interplay on an elementary level we resort to various one-dimensional model systems. The main observables are the static, the incoherent, and the coherent structure factor, which are extracted from molecular dynamics simulations. For the validation of the algorithms, results for the harmonic periodic chain are presented. We then study the Fibonacci chain with harmonic and anharmonic interaction potentials. In the dynamic Fibonacci chain neighboring atoms interact by double-well potentials allowing for phason flips. The difference between the structure factors of the dynamic and the harmonic Fibonacci chain lies in the temperature dependence of the phonon line width. If a bias is introduced in the well depth, dispersionless optic phonon bands split off.
Title:
Correlation of electronic structure and ordered charge and orbital patterns for single-layered manganites in a wide hole-doping range (0 <= x <= 1)
Authors:
Lee, YS; Arima, T; Onoda, S; Okimoto, Y; Tokunaga, Y; Mathieu, R; Yu, XZ; He, JP; Kaneko, Y; Matsui, Y; Nagaosa, N; Tokura, Y Author Full Names: Lee, Y. S.; Arima, T.; Onoda, S.; Okimoto, Y.; Tokunaga, Y.; Mathieu, R.; Yu, X. Z.; He, J. P.; Kaneko, Y.; Matsui, Y.; Nagaosa, N.; Tokura, Y.
Source:
PHYSICAL REVIEW B 75 (14): Art. No. 144407 APR 2007
Abstract:
We investigated the doping-dependent evolution of the charge-orbital ordering (CO-OO) phase using optical spectroscopy of a series of single-layer manganites, La1-xSr1+xMnO4 (x=0 and 1) and Pr1-xCa1+xMnO4 (0.3 <= x <= 0.7). We found that the electronic response of the CO-OO phase changes asymmetrically with respect to the addition or removal of e(g) electrons from x=1/2. Especially, low-energy optical spectra depend strongly on the modulation vector of striped phase in a higher doping region (x >= 1/2). This finding highlights the role of the nanoscale structure of e(g) ordering in the electronic property of the striped phase in the layered manganite.
Title:
Photonic band gaps and planar cavity of two-dimensional eightfold symmetric void-channel photonic quasicrystals
Authors:
Zhou, GY; Gu, M Author Full Names: Zhou, Guangyong; Gu, Min
Source:
APPLIED PHYSICS LETTERS 90 (20): Art. No. 201111 MAY 14 2007
Abstract:
By using the femtosecond laser induced microexplosion method, high-quality two-dimensional eightfold photonic quasicrystals have been fabricated in a solid transparent polymer material. Multiorder band gaps have been observed in a 25-layer structure with a suppression rate of up to 72% for the fundamental gap. Polarization measurements show that the photonic quasicrystal has a strong anisotropic effect, showing that the transverse electric is the favorite polarization. Fabry-Perot cavities have been fabricated by removing the central layer of channels. Based on the cavity mode position, the order of the mode and the effective cavity size have been determined. (C) 2007 American Institute of Physics.

Update: 15-Jun-2007

Title:
Growth and studies of the new crystal formed with NaCl and CaCl2
Authors:
Manonmani, N; Mahadevan, CK; Umayorubhagan, V Author Full Names: Manonmani, N.; Mahadevan, C. K.; Umayorubhagan, V.
Source:
MATERIALS AND MANUFACTURING PROCESSES 22 (3): 388-392 2007
Abstract:
We have attempted to grow the single crystals of Na3CaCl5 center dot 2H(2)O from aqueous solutions by the slow evaporation method. Crystals up to a size of 6 x 4 x 2mm(3) were obtained. Atomic absorption spectroscopic and X-ray diffraction (XRD) measurements have shown the incommensurate nature of the grown crystals. Thermogravimetric measurement has confirmed the presence of water of crystallization. Microhardness measurement showed the soft nature. DC conductivity measurements at various temperatures indicate that the crystal formed is an ionic conductor. Dielectric measurements were also carried out.
Title:
Crystal structures of incommensurately modulated Ln(PO3)(3) (Ln = Tb-Yb) and commensurate Gd(PO3)(3) and Lu(PO3)(3)
Authors:
Hoppe, HA; Sedlmaier, SJ Author Full Names: Hoeppe, Henning A.; Sedlmaier, Stefan J.
Source:
INORGANIC CHEMISTRY 46 (9): 3467-3474 APR 30 2007
Abstract:
The crystal structure of the late lanthanoids' catena-polyphosphates Ln(PO3)(3) (Ln = Tb-Yb) is incommensurately modulated (Dy(PO3)(3): space group Cc(0 beta 0)0; Z = 4; a = 1417.4(4), b = 670.96(14), c = 1009.5(3) pm; beta = 127.62(2)degrees, q= 0.364b*; R-all = 0.057, wR(all) = 0.071; 293 K) and consists of infinite chains of corner-sharing PO4 tetrahedra. The cations are coordinated 6-fold in an almost octahedral arrangement over the whole modulation period. All atoms comprise a sinoidal positional modulation. The basic structure can be derived from a fcc packing which explains the pseudo-face-centering observed in the diffraction patterns. The crystal structure of Lu(PO3)(3) is isotypic with C-type phosphates (Cc; Z = 12; a = 1397.2(1), b = 2001.8(2), c = 995.56(9) pm; beta = 127.351(6)degrees; R1 = 0.042, wR2 = 0.097, 293 K), and Gd(PO3)(3) crystallizes in a new structure type (I2/a; Z = 16; a = 2601.7(2), b = 1351.1(1), c = 1008.4(1) pm; beta = 119.311(6)degrees; R1 = 0.039, wR2 = 0.092; 293 K). Both can be described in terms of superstructures of the basic structure unit cell of the incommensurate phases, and thus, a consistent structural description of many polyphosphates is provided. Tb(PO3)(3) was obtained as single phase adopting a novel synthesis under reducing conditions. The absence of an inversion center in the incommensurate phases and Lu(PO3)(3) was proved by a SHG experiment. The vibrational spectra are also discussed.

Update: 8-Jun-2007

Title:
Medieval quasicrystals
Authors:
Minkel, JR Author Full Names: Minkel, J. R.
Source:
SCIENTIFIC AMERICAN 296 (5): 36-36 MAY 2007
Title:
Polymeric quasicrystal: Mesoscopic quasicrystalline tiling in ABC star polymers
Authors:
Hayashida, K; Dotera, T; Takano, A; Matsushita, Y Author Full Names: Hayashida, Kenichi; Dotera, Tomonari; Takano, Atsushi; Matsushita, Yushu
Source:
PHYSICAL REVIEW LETTERS 98 (19): Art. No. 195502 MAY 11 2007
Abstract:
A mesoscopic tiling pattern with 12-fold symmetry has been observed in a three-component polymer system composed of polyisoprene, polystyrene, and poly(2-vinylpyridine) which forms a star-shaped terpolymer, and a polystyrene homopolymer blend. Transmission electron microscopy images reveal a nonperiodic tiling pattern covered with equilateral triangles and squares, their triangle/square number ratio of 2.3 (approximate to 4/root 3), and a microbeam x-ray diffraction pattern shows dodecagonal symmetry. The same kind of quasicrystalline structures have been found for metal alloys (similar to 0.5 nm), chalcogenides (similar to 2 nm), and liquid crystals (similar to 10 nm). The present result (similar to 50 nm) confirms the universal nature of dodecagonal quasicrystals over several hierarchical length scales.
Title:
Nature of the magnetic order in the charge-ordered cuprate La1.48Nd0.4Sr0.12CuO4
Authors:
Christensen, NB; Ronnow, HM; Mesot, J; Ewings, RA; Momono, N; Oda, M; Ido, M; Enderle, M; McMorrow, DF; Boothroyd, AT Author Full Names: Christensen, N. B.; Ronnow, H. M.; Mesot, J.; Ewings, R. A.; Momono, N.; Oda, M.; Ido, M.; Enderle, M.; McMorrow, D. F.; Boothroyd, A. T.
Source:
PHYSICAL REVIEW LETTERS 98 (19): Art. No. 197003 MAY 11 2007
Abstract:
Using polarized neutron scattering we establish that the magnetic order in La1.48Nd0.4Sr0.12CuO4 is either (i) one dimensionally modulated and collinear, consistent with the stripe model or (ii) two dimensionally modulated with a novel noncollinear structure. The measurements rule out a number of alternative models characterized by 2D electronic order or 1D helical spin order. The low-energy spin excitations are found to be primarily transversely polarized relative to the stripe ordered state, consistent with conventional spin waves.
Title:
Manifestation of incommensurate structural modulations in the Ti-L-2,L-3 electron energy-loss near-edge structure of Sr2TiSi2O8
Authors:
Hoche, T; Grodzicki, M; Heyroth, F; Uecker, R; Van Aken, PA Author Full Names: Hoeche, T.; Grodzicki, M.; Heyroth, F.; Uecker, R.; Van Aken, P. A.
Source:
PHILOSOPHICAL MAGAZINE LETTERS 87 (6): 431-439 2007
Abstract:
Structural modulations hosted by complex oxides are - beyond relative orientation changes of 'rigid units' - accompanied by characteristic distortions of coordination polyhedra. Electronic structure calculations in the local density approximation, performed at model clusters derived from positionally modulated structures, proved that the molecular - orbital structure also sensitively reflects such distortions. The latter crystal-field splitting of unoccupied states is accessible by high-resolution electron energy-loss near-edge structure (ELNES) spectroscopy. However, since ELNES spectra average over many different individual target-ion environments, the resulting ELNES possesses significantly broadened spectral features. In this contribution, such broadening is shown to dramatically influence the spectral shape of the Ti-L-2,L-3 ELNES acquired at the strongly modulated fresnoite framework compound Sr2TiSi2O8.
Title:
Evolution of modulated structure in Fe-Cr-Co alloy during isothermal ageing with different external magnetic field conditions
Authors:
Sun, XY; Xu, CY; Zhen, L; Lv, LX; Yang, L Author Full Names: Sun, X. Y.; Xu, C. Y.; Zhen, L.; Lv, L. X.; Yang, L.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 312 (2): 342-346 MAY 11 2007
Abstract:
The evolution of modulated structure in Fe-Cr-Co alloy during isothermal ageing with and without external magnetic field was investigated by using transmission electron microscopy (TEM) and phase-field simulation. The isotropic modulated structure in Fe-Cr-Co alloy formed during isothermal ageing without external magnetic field could be converted to be anisotropy during further isothermal ageing under an 8 kOe external magnetic (thermo-magnetic treatment), and the formation of anisotropy was slower than the direct formation from spinodal decomposition under external magnetic field and is time dependent. The anisotropy characteristic of modulated structure in Fe-Cr-Co alloy subjected to thermo-magnetic treatment for I h remained during further isothermal ageing without external magnetic field for up to 20 h. Novel modulated structure could be obtained through specific thermo-magnetic treatment processes, which was confirmed by phase-field simulation. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Crystal structure of Sr0.35CoO2 compound studied by high-resolution electron microscopy
Authors:
Yubuta, K; Hasegawa, YK; Miyazaki, Y; Kajitani, T Author Full Names: Yubuta, Kunio; Hasegawa, Yuh-ki; Miyazaki, Yuzuru; Kajitani, Tsuyoshi
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 46 (2): 712-715 FEB 2007
Abstract:
The modulated crystal structure Of Sr0.35CoO2 is studied by electron diffraction measurement and high-resolution electron microscopy. Sr0.35CoO2 consists of two interpenetrating subsystems of CoO2 sheets and intercalated Sr layers. Both subsystems have common a- and c-axes with a = 4.80 angstrom and c = 11.33 angstrom. The two subsystems of Sr0.35CoO2 are mutually commensurated parallel to the b-axis, i.e., b(1) = 2.80 angstrom for the CoO2 sheets and b(2) = 8.41 angstrom for the intercalated Sr layers, showing that the axial b(1)/b(2) ratio is 1/3, i.e., rational. The high-resolution images taken with the incident electron beams parallel to the a-, b-. and c-axes clearly exhibit characteristic atomic arrangements.
Title:
Role and importance of nanoparticles in femtosecond pulsed laser ablation deposition of Al-Cu-Fe quasicrystal
Authors:
Teghil, R; De Bonis, A; Galasso, A; Santagata, A; Villani, P; Sordelet, DJ Author Full Names: Teghil, R.; De Bonis, A.; Galasso, A.; Santagata, A.; Villani, P.; Sordelet, D. J.
Source:
CHEMICAL PHYSICS LETTERS 438 (1-3): 85-88 APR 11 2007
Abstract:
In this Letter, the secondary plume produced by femtosecond laser ablation of an Al-Cu-Fe quasicrystal has been studied. The data evidence the presence of hot nanoparticles produced several microseconds after the laser shot. The cooling mechanisms of these particles have been analysed together with the evolution of their composition. The results indicate a clear relation between the final composition of the particles and the high temperature equilibrium vapour pressures of the different elements. The elemental analysis of the cross-section of films deposited by femtosecond laser ablation states the importance of nanoparticles in the film growth. (c) 2007 Elsevier B.V. All rights reserved.
Title:
Ferroelectric and optical properties of quasiperiodic PbZr0.5Ti0.5O3 multilayers grown on quartz wafers
Authors:
Hu, GJ; Hong, XK; Chu, JH; Dai, N Author Full Names: Hu, G. J.; Hong, X. K.; Chu, J. H.; Dai, N.
Source:
APPLIED PHYSICS LETTERS 90 (16): Art. No. 162902 APR 16 2007
Abstract:
PbZr0.5Ti0.5O3 (PZT) multilayers with total thickness of a few microns have been grown on quartz substrates by using sol gel technique. The PZT multilayer displays a well-defined polarization hysteresis loop with a nominally average remanent polarization of 36.5 mu C/cm(2) and an average coercive field of 66.5 kV/cm under a maximum applied voltage of 100 V. With 17 periods, 95% reflectivity and 62 nm stop-band width have been achieved at room temperature, indicating that the quasiperiodic PZT multilayer can be used as dielectric reflectors and filters. (C) 2007 American Institute of Physics.

Update: 1-Jun-2007

Title:
The conditions of formation and stability of quasi-crystalline phases in aluminum-manganese alloys
Authors:
Zaitsev, AI; Zaitseva, NE; Shakhpazov, EK; Arutyunyan, NA; Dunaev, SF Author Full Names: Zaitsev, A. I.; Zaitseva, N. E.; Shakhpazov, E. Kh.; Arutyunyan, N. A.; Dunaev, S. F.
Source:
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY 80 (6): 869-877 JUN 2006
Abstract:
The conditions of formation, stability, and thermodynamic properties of the icosahedral and decagonal quasi-crystalline phases in the Al-Mn system were studied experimentally. The thermodynamic properties of equilibrium crystalline Al-Mn compositions over the composition and temperature ranges 0-26 at % Mn and 628-1193 K, respectively, and of melts over wide temperature and composition ranges (1043-1670 K and 0-50.1 at % Mn) were determined. Measurements were made by the integral variant of the effusion method under the conditions of an ultrahigh oilless vacuum and Knudsen mass spectrometry. An original technique based on the initiation and study of equilibria in reactions of the alloys with special admixtures of sodium or magnesium fluorides with the formation of volatile products was used to extend the interval of measurements to low temperatures. Complete, reliable, and consistent data on the thermodynamic properties of icosahedral and decagonal quasi-crystalline and crystalline phases based on aluminum and Al-Mn melts were obtained for the first time. Al-Mn melts were shown to contain associates of three types, AlMn, Al2Mn, and Al5Mn. The contributions of covalent interactions to the Gibbs energy and enthalpy of mixing was found to be by far predominant. The thermodynamic properties of alloys of the same chemical composition in the quasi-crystalline and equilibrium crystalline states were compared. The decagonal phase was found to be more stable than icosahedral quasi-crystals. The difference of the Gibbs energies of quasi-crystals of the two types and crystalline compositions increased as the temperature lowered. Arguments in favor of the entropy nature of the stabilization of quasi-crystals were obtained. These phases, like metallic glasses, are only an intermediate state between liquids and crystals and cannot be ground stable alloy states. The conditions of obtaining quasi-crystalline phases from melts were found to be controlled by the appearance of a substantial fraction of icosahedral short-range order in liquids in the region of compositions where associates of a certain kind (Al5Mn) were formed in substantial amounts, x(Al5Mn) >= 0.11.
Title:
Effect of Mn on solidification microstructure morphology of quasicrystal phase in Mg-Zn-Y alloy
Authors:
Zhang, JS; Du, HW; Liang, W; Li, TB; Xu, CX; Wang, HX Author Full Names: Zhang Jinshan; Du Hongwei; Liang Wei; Li Tianbao; Xu Chunxiang; Wang Hongxia
Source:
RARE METAL MATERIALS AND ENGINEERING 36 (3): 381-385 MAR 2007
Abstract:
The effect of Mn on formation of three-dimension spherical icosahedral quasicrystal phase in Mg-based master alloy has been discussed. Experimental results show that in the solidification process under normal casting condition, the adding certain amount of Mn into the melt would surely change the formation process of Mg-Zn-Y quasicrystal containing master alloy, which avoided the appearance of decahedral quasicrystal phase, generated thermodynamically stable and homogeneously distributed Mg-Zn-Y-Mn Icosahedral quasicrystal, resulted in transformation of morphology of Icosahedral quasicrystal from petal-like one to spherical one. Moreover, because of the addition of Mn, icosahedral quasicrystal grain size changed from large petal-like (60 mu m similar to 80 mu m) to small spherical (<= 20 gm). The addition of Mn could lower the production cost of Mg-based quasicrystals containing master alloy, providing beneficial conditions for industrialization.
Title:
About structural changes in the YuNDK35T5AA alloy upon magnetic annealing
Authors:
Agapova, EV; Gundyrev, VM; Sidorov, EV Author Full Names: Agapova, E. V.; Gundyrev, V. M.; Sidorov, E. V.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 102 (2): 163-168 AUG 2006
Abstract:
The lattice parameters of alpha' and alpha phases with a "slightly tetragonal" structure, which are formed in YuNDK35T5AA single crystals grown from the melt, have been determined. Magnetic annealing of the single crystals was shown to result in an increase in the degree of tetragonality of both phases. The difference between the lattice parameters a of the phases increases substantially; the unit-cell volume of the alpha phase increases, whereas that of the alpha' phase decreases slightly. X-ray diffraction patterns obtained for the modulated structure formed in the YuNDK35T5AA single crystals in the as-grown state, after high-temperature annealing followed by cooling in air, and after magnetic annealing were compared; the modulation periods were determined.
Title:
Metastable phases of electron type in titanium alloys with 3d-metals
Authors:
Nosova, GI; Dlyakonova, NB; Lyasotskii, IV Author Full Names: Nosova, G. I.; Dlyakonova, N. B.; Lyasotskii, I. V.
Source:
METAL SCIENCE AND HEAT TREATMENT 48 (9-10): 427-432 SEP-OCT 2006
Abstract:
Conditions of formation and structural characteristics of metastable states forming due to changes in the concentration of alloying elements in titanium alloys with 3d-metals are considered. The states arising due to hardening from the range of solid solution and the states arising due to hardening from melt are studied. Growth in the concentration of alloying elements in all alloys of the type is accompanied by formation of a metastable omega-phase and an incommensurate w-phase; in alloys of the Ti - Fe and Ti - Mn systems the formed phases also include icosahedral quasi-crystals and their approximants. Effects of various factors on the formation of metastable phases are discussed. An incommensurate w-phase is considered as an example of specific nanocrystalline structure stabilized by electron interactions.
Title:
Surface properties of a nano-quasicrystalline forming Ti based system
Authors:
Lefaix, H; Prima, F; Zanna, S; Vermaut, P; Dubot, P; Marcus, P; Janickovic, D; Svec, P Author Full Names: Lefaix, Helene; Prima, Frederic; Zanna, Sandrine; Vermaut, Philippe; Dubot, Pierre; Marcus, Philippe; Janickovic, Dusan; Svec, Peter
Source:
MATERIALS TRANSACTIONS 48 (3): 278-286 MAR 2007
Abstract:
Two decades of intense research on quasicrystalline materials have suggested their potential use as surface coatings, considering their low coefficient of friction, high hardness, good corrosion and wear resistances and low surface energy. In that sense, quasicrystals could be introduced into the field of biomaterials since biomolecules are well known to be sensitive to solid surface properties. In this paper we report on investigations of the early stage of oxidation of the quasicrystals forming Ti45Zr38Ni17 alloy and its surface reactivity with respect to an amino-acid. After analysing the microstructure of as-quenched ribbons both by transmission electron microscopy and X-ray diffraction, surface oxide layers were characterized by X-ray Photoelectron Spectroscopy (XPS). Oxidation of Ti(45)Zr(3)gNi(17) results in the formation of a ZrO2/TiO2 barrier oxide layer, avoiding toxic Ni release. This latter is mainly present at the oxide/alloy interface. Thereafter, adsorption of L-glutamic acid has been investigated by infrared spectroscopy. Even if this biomolecule is found to adsorb to each substrate, it seems to display different adsorption mechanisms on quasicrystalline ribbons compared to that on pure titanium (CpTi) or on pure zirconium (Zr). leading to a weaker signal on Ti(45)Zr(3)sNi(17). We discuss these results along with the affinities of each alloying metal to oxygen and with the peculiar electronic properties of quasicrystals which could affect the surface properties of Ti(45)Zr(3)sNi(17.)
Title:
Transmission electron microscopy for precipitate phases in rapidly solidified Mg-2 at%Ce-1 at%Zn and Mg-2 at%Ce alloys
Authors:
Nishijima, M; Hiraga, K; Yamasaki, M; Kawamura, Y Author Full Names: Nishijima, Masahiko; Hiraga, Kenji; Yamasaki, Michiaki; Kawamura, Yoshihiko
Source:
MATERIALS TRANSACTIONS 48 (3): 476-480 MAR 2007
Abstract:
Precipitate phases in Mg-2 at%Ce-1 at%Zn (Mg97Ce2Zn1) and Mg-2 at%Ce (Mg98Ce2) alloys, prepared by a melt-quenching method, have been examined by high-resolution transmission electron microscopy (HRTEM) and high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). A precipitate phase formed at grain boundaries has an ordered structure with a hexagonal unit cell of root 13a(0) and c(0), in which a(0) and c(0) are lattice parameters of an h.c.p. structure of the Mg-matrix. On the other hand, a precipitate phase embedded in Mg-matrix grains has a long-period modulated structure formed by the appearance of two-dimensional anti-phase boundaries with a hexagonal symmetry in the fundamental hexagonal structure with lattice constants of root 3a(0) and c(0).
Title:
In situ study of icosahedral Zn-Mg-Dy and Co-rich decagonal Al-Co-Ni at high pressures and high temperatures
Authors:
Krauss, G; Gu, QF; Katrych, S; Steurer, W Author Full Names: Krauss, G.; Gu, Q. F.; Katrych, S.; Steurer, W.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (11): Art. No. 116203 MAR 21 2007
Abstract:
An in situ high- pressure high- temperature x- ray diffraction study on single-crystalline icosahedral Zn - Mg - Dy up to 12.5( 4) GPa at 873 K and powdered Co- rich decagonal Al - Co - Ni up to 12.3( 4) GPa at 973 K has been performed using a heatable diamond- anvil cell and synchrotron radiation. Quantitative reciprocal- space reconstruction from image plate data was used for evaluating the single- crystal data. The compressibility of the materials at ambient temperature was determined from x- ray powder diffraction up to 30.3( 2) GPa for icosahedral Zn - Mg - Dy and 61.4( 1) GPa for Co- rich decagonal Al - Co Ni. The bulk modulus at zero pressure and its pressure derivative were determined from fitting third- order Birch - Murnaghan equations of state as K-0 = 92( 4) GPa, K' = 3.1( 3) for icosahedral Zn - Mg - Dy and K-0 = 120(11) GPa, K' = 7.1( 7) for Co- rich decagonal Al - Co - Ni, respectively. The compressibilities of the quasicrystals are discussed with respect to their structure types and the available literature data. To a first approximation, a linear dependency of the squared electron density at the border of the Wigner Seitz atomic cell from the ratio of the bulk modulus and the molar volume was found. This behaviour is comparable to that of periodic alloys.
Title:
Zero-field random-field effect in diluted triangular lattice antiferromagnet CuFe1-xAlxO2
Authors:
Nakajima, T; Mitsuda, S; Kitagawa, K; Terada, N; Komiya, T; Noda, Y Author Full Names: Nakajima, T.; Mitsuda, S.; Kitagawa, K.; Terada, N.; Komiya, T.; Noda, Y.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (14): Art. No. 145216 APR 11 2007
Abstract:
We performed neutron scattering experiments on a diluted triangular lattice antiferromagnet (TLA), CuFe(1-x)AlxO(2) with x = 0.10. The detailed analysis of the scattering profiles revealed that the scattering function of magnetic reflection is described as the sum of a Lorentzian term and a Lorentzian-squared term with anisotropic width. The Lorentzian-squared term dominating at low temperature is indicative of the domain state in the prototypical random-field Ising model. Taking account of the sinusoidally amplitude-modulated magnetic structure with incommensurate wavenumber in CuFe1-xAlxO2 with x = 0.10, we conclude that the effective random field arises even at zero field, owing to the combination of site-random magnetic vacancies and the sinusoidal structure that is regarded as a partially disordered (PD) structure in a wide sense, as reported in the typical three-sublattice PD phase of a diluted Ising TLA, CsCo0.83Mg0.17Br3 (van Duijn et al 2004 Phys. Rev. Lett. 92 077202). While the previous study revealed the existence of a domain state in CsCo0.83Mg0.17Br3 by detecting magnetic reflections specific to the spin configuration near the domain walls, our present study revealed the existence of a domain state in CuFe1-xAlxO2 ( x = 0.10) by determination of the functional form of the scattering function.
Title:
Field-induced incommensurate order in frustrated spin ladder
Authors:
Sakai, T; Okamoto, K Author Full Names: Sakai, Toru; Okamoto, Kiyomi
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (14): Art. No. 145231 APR 11 2007
Abstract:
In the magnetization process of the S = 1/ 2 spin ladder system there are two critical magnetic fields H-c1 and H-c2. The spin gap vanishes at H-c1 and the magnetization is saturated at H-c2. Usually the commensurate antiferromagnetic spin correlation perpendicular to the external field H is dominant and the canted Neel order would be stabilized by interladder interaction for H-c1 H < H-c2. The present theoretical study based on numerical diagonalization indicated the following interesting results. In the presence of the next-nearest-neighbour interaction, the incommensurate spin correlation parallel to H would be possibly stronger than the commensurate one for some intermediate external field. As a result, with interladder interaction, another field- induced transition would occur from the usual canted N eel order to the incommensurate one. The new field- induced transition is based on the so- called.- inversion, namely a change from eta(z) > eta(x) to eta(z) < eta(x), where eta(z) and eta(x) are the critical exponents of the parallel and perpendicular spin correlation functions, respectively. Some phase diagrams including the eta-inversion and the magnetization plateau are presented.
Title:
Commensurate and incommensurate phases of the distorted triangular antiferromagnet Cs2CuBr4 studied using Cs-133 NMR
Authors:
Fujii, Y; Hashimoto, H; Yasuda, Y; Kikuchi, H; Chiba, M; Matsubara, S; Takigawa, M Author Full Names: Fujii, Y.; Hashimoto, H.; Yasuda, Y.; Kikuchi, H.; Chiba, M.; Matsubara, S.; Takigawa, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (14): Art. No. 145237 APR 11 2007
Abstract:
A quasi- two dimensional antiferromagnet Cs2CuBr4 is characterized as a frustrated spin system on a distorted triangular lattice with easy- plane type anisotropy. Cs-133 NMR experiments on Cs2CuBr4 have been performed in the range of magnetic field up to 15.9 T, applied along the b- axis, which covers the field range for the 1/3 magnetization plateau, in order to clarify the properties of the field- induced incommensurate - commensurate transition at both ends of the plateau. We found that the NMR spectrum shows hysteresis and two phase coexistence around the transition field. We also present a field dependence of T-1(-1) at 0.5 K showing a hysteresis around each end of the plateau, indicating a first order incommensurate - commensurate phase transition.
Title:
Field-induced ferroelectric state in frustrated magnet CuFe1-xAlxO2
Authors:
Kanetsuki, S; Mitsuda, S; Nakajima, T; Anazawa, D; Katori, HA; Prokes, K Author Full Names: Kanetsuki, S.; Mitsuda, S.; Nakajima, T.; Anazawa, D.; Katori, H. A.; Prokes, K.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (14): Art. No. 145244 APR 11 2007
Abstract:
By magnetization and neutron diffraction measurements in an applied magnetic field up to 15 T, we obtained the field ( H) versus temperature ( T) magnetic phase diagram of a geometrically frustrated triangular lattice antiferromagnet CuFe(1-x)AlxO(2) with x = 0.012, and found that the first-field-induced incommensurate noncollinear magnetic phase of CuFeO2 accompanying spontaneous electric polarization continuously connects, in the H - T phase diagram for x = 0.012, with the impurity- induced low- temperature ( LT) phase, in which the spontaneous polarization has recently been observed even in zero field. By pyroelectric measurements on the x = 0.012 sample in zero magnetic field, we also demonstrated that the thermal evolution of ferroelectric polarization corresponds to that of LT magnetic ordering.
Title:
Spatially anisotropic Heisenberg kagome antiferromagnet
Authors:
Apel, W; Yavors'kii, T; Everts, HU Author Full Names: Apel, W.; Yavors'kii, T.; Everts, H.-U.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (14): Art. No. 145255 APR 11 2007
Abstract:
In the search for spin-1/2 kagome antiferromagnets, the mineral volborthite has recently been the subject of experimental studies (Hiroi et al 2001 J. Phys. Soc. Japan 70 3377; Fukaya et al 2003 Phys. Rev. Lett. 91 207603; Bert et al 2004 J. Phys.: Condens. Matter 16 S829; Bert et al 2005 Phys. Rev. Lett. 95 087203). It has been suggested that the magnetic properties of this material are described by a spin-1/2 Heisenberg model on the kagome lattice with spatially anisotropic exchange couplings. We report on investigations of the Sp(N) symmetric generalization of this model in the large N limit. We obtain a detailed description of the dependence of possible ground states on the anisotropy and on the spin length S. A fairly rich phase diagram with a ferrimagnetic phase, incommensurate phases with and without long-range order and a decoupled chain phase emerges.
Title:
Magnetic phase diagrams of the Kagome staircase compounds Co3V2O8 and Ni3V2O8
Authors:
Wilson, NR; Petrenko, OA; Balakrishnan, G Author Full Names: Wilson, N. R.; Petrenko, O. A.; Balakrishnan, G.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (14): Art. No. 145257 APR 11 2007
Abstract:
An extensive low temperature magnetization study of high quality single crystals of the Kagome staircase compounds Ni3V2O8 and Co3V2O8 has been performed, and the H - T phase diagrams have been determined from these measurements. The magnetization and susceptibility curves for Co3V2O8 are analysed in terms of their compatibility with the different ferromagnetic and antiferromagnetic structures proposed for this compound. For Ni3V2O8, the phase diagram is extended to magnetic fields higher than previously reported; for a field applied along the a axis, the low temperature incommensurate phase is found to close at around 90 kOe.
Title:
Ill-behaved convergence of a model of the Gd3Ga5O12 garnet antiferromagnet with truncated magnetic dipole-dipole interactions
Authors:
Yavors'kii, T; Gingras, MJP; Enjalran, M Author Full Names: Yavors'kii, Taras; Gingras, Michel J. P.; Enjalran, Matthew
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (14): Art. No. 145274 APR 11 2007
Abstract:
Previous studies have found that calculations which consider long-range magnetic dipolar interactions truncated at a finite cut-off distance Rc predict spurious (unphysical) long-range ordered phases for Ising and Heisenberg systems on the pyrochlore lattice. In this paper we show that, similar to these two cases, calculations that use truncated dipolar interactions to model the Gd3Ga5O12 garnet antiferromagnet also predict unphysical phases with incommensurate ordering wavevector q(ord) that is very sensitive to the dipolar cut-off distance R-c.
Title:
B-11-NMR study of low-temperature phase transition in CuB2O4
Authors:
Yasuda, Y; Nakamura, H; Fujii, Y; Kikuchi, H; Chiba, M; Yamamoto, Y; Hori, H; Petrakovskii, G; Popov, M; Bezmaternikh, L Author Full Names: Yasuda, Y.; Nakamura, H.; Fujii, Y.; Kikuchi, H.; Chiba, M.; Yamamoto, Y.; Hori, H.; Petrakovskii, G.; Popov, M.; Bezmaternikh, L.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (14): Art. No. 145277 APR 11 2007
Abstract:
The material CuB2O4 presents a variety of phases in the B - T phase diagram, caused by the frustration and the Dzialoshinskii - Moriya interaction. In order to investigate the nature of the phase transitions, a B-11- NMR experiment on CuB2O4 has been performed under an applied magnetic field along the a- axis down to 0.4 K. A new incommensurate - incommensurate phase transition has been found at 0.8 K under a field of 0.5 T. Further, another phase transition has been observed at 4.7 K under a field of about 2 T, which is consistent with the transition reported by the neutron diffraction experiment.
Title:
The magnetic structure of beta-MnRu
Authors:
Stewart, JR; Wills, AS; Leavey, CJ; Rainford, BD; Ritter, C Author Full Names: Stewart, J. R.; Wills, A. S.; Leavey, C. J.; Rainford, B. D.; Ritter, C.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (14): Art. No. 145291 APR 11 2007
Abstract:
We have performed both conventional and polarized neutron scattering studies of a wide range of beta-Mn1-xRux alloy concentrations in the range 0.06 <= x <= 0.23. We find an incommensurate long-range ordered magnetic structure for Ru concentrations x >= 0.12, with a propagation vector of k = ( u, u, u) where u = 0.278. The magnetic structure is very complex - showing clear signs of the effect of geometrical frustration. Neutron polarization analysis investigations of the magnetic ground state reveal the persistence of a disordered component of the magnetic structure down to low temperatures.
Title:
Wave function behavior in a Fibonacci lattice with electronic correlation
Authors:
Navarro, O; Molina, S; Suarez, JR; Espinosa, JE Author Full Names: Navarro, O.; Molina, S.; Suarez, J. R.; Espinosa, J. E.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 353 (8-10): 996-998 APR 15 2007
Abstract:
The electronic correlation and the spatial symmetry in quasicrystals are by themselves two very complicated research topics since we cannot use the reciprocal space to study quasicrystals and the electronic correlation in many-body system has been solved exactly only for one and for infinite dimension. We should note that even in one-dimensional quasiperiodic structures, the interactions between electrons have often been neglected and only few results have been obtained. In this work, we solved the case of two interacting particles in a Fibonacci lattice using a real-space method and the Hubbard model. The real-space method is based on mapping the correlated many-body problem onto an equivalent site- and bond-impurity tight-binding one in a higher dimensional space. Within the Hubbard Hamiltonian we obtained the behavior of the wave function and the analysis of these eigen-functions in the Fibonacci lattice when correlation is off shows a critical behavior. (c) 2007 Elsevier B.V. All rights reserved.
Title:
On the crystal structure of the quasicrystalline approximant YbCd6 at low temperature
Authors:
Xia, SQ; Bobev, S Author Full Names: Xia, Shengqing; Bobev, Svilen
Source:
INTERMETALLICS 15 (4): 550-556 APR 2007
Abstract:
The body-centered cubic (space group Im (3) over bar, No. 204) crystal structure of the quasicrystalline approximant YbCd6 has been studied by means of single-crystal X-ray diffraction at low temperature. These studies suggest that below 120 K, the disorder in the innermost Cd-shell in YbCd6 is best modeled with a 1/3 occupied cube-octahedron representing Cd-4-tetrahedron in six possible orientations. The disordered cadmium atoms occupy the Wyckoff position 24g. Above this temperature, the disorder of the Cd-4-tetrahedra inside the Cd-20-dodecahedra in this "onion"-type structure becomes progressively larger and the Cd site can be further split as to occupy a general position with a Wyckoff letter 48f. These results are in agreement with the disorder model suggested previously from structure refinements of YbCd6 at room temperature. (c) 2006 Elsevier Ltd. All rights reserved.
Title:
Conditions for quasicrystal formation from mechanically alloyed Zr-based glassy powders
Authors:
Scudino, S; Eckert, J; Yang, XY; Sordelet, DJ; Schultz, L Author Full Names: Scudino, S.; Eckert, J.; Yang, X. Y.; Sordelet, D. J.; Schultz, L.
Source:
INTERMETALLICS 15 (4): 571-582 APR 2007
Abstract:
The absence of quasicrystalline phase formation in mechanically alloyed Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 glassy powders with respect to melt-spun ribbon having the same composition has been investigated by analyzing the influence of mechanical deformation, oxygen contamination and chemical composition on quasicrystal (QC) formation. The results suggest that oxygen affects the formation of QCs by selectively reacting with zirconium thus driving the chemical composition of the glassy phase out of the range suitable for QC formation. This hypothesis has been verified by appropriately adjusting the composition of the powders. The addition of an adequate amount of zirconium changes the crystallization behavior inducing the formation of the quasicrystalline phase as the first crystallization product. This implies that if a particular short-range order is necessary for the formation of QCs, it can be achieved also by solid-state processing and therefore the presence of a specific quenched-in short-range order is not a mandatory prerequisite for QC formation. (c) 2006 Elsevier Ltd. All rights reserved.
Title:
Dielectric and phase transitional properties of Cs2MnI4
Authors:
Shimizu, F; Takashige, M Author Full Names: Shimizu, Fuminao; Takashige, Masaaki
Source:
FERROELECTRICS 348: 484-490 2007
Abstract:
Crystals of Cs2MnI4 were grown by Bridgman method and differential thermal analysis and dielectric constant measurements were performed. Three phase transition points 240 K, 211 K and about 105 K were confirmed, which agrees with results already reported by X-ray diffraction study. Judging from the similarity in the temperature dependence of dielectric constant, it seems that phase transitions at around 240 K and 211 K correspond to normal-incommensurate and incommensurate-commensurate (lock-in) transition points.
Title:
Pyroelectric properties of novel protein amino acid-based single crystals
Authors:
Yarmarkin, VK; Shulman, SG; Lemanov, VV Author Full Names: Yarmarkin, V. K.; Shulman, S. G.; Lemanov, V. V.
Source:
FERROELECTRICS 348: 520-525 2007
Abstract:
A number of novel protein amino acid-based single crystals were grown from aqueous solutions and their dielectric and pyroelectric properties were studied in a temperature range 140-340 K. It was shown that some of the crystals such as L-His center dot(H3PO4)(2), L-Tyr center dot HCl, L-Ala(2)H(3)PO(3).H2O have pyroelectric figure-of-merit comparable to those of TGS. Anomalous dielectric properties of DL-Set(2)center dot H2SO4H2O single crystals were observed in a temperature range 260-270 K revealing a first-order phase transition to an incommensurate phase.

Update: 25-May-2007

Title:
Further notes on quasi-crystal tilings
Authors:
Lu, PJ; Steinhardt, PJ Author Full Names: Lu, Peter J.; Steinhardt, Paul J.
Source:
SCIENCE 316 (5827): 981-982 MAY 18 2007
Title:
Quasi-crystal conundrum opens a tiling can of worms (vol 315, pg 1066, 2007)
Authors:
Bohannon, J Author Full Names: Bohannon, J.
Source:
SCIENCE 316 (5827): 982-982 MAY 18 2007
Title:
Hydrogen permeation of the Zr65Al7.5Ni10Cu12.5Pd5 alloy in three different microstructures
Authors:
Yamaura, SI; Nakata, S; Kimura, H; Inoue, A Author Full Names: Yamaura, Shin-Ichi; Nakata, Shuhei; Kimura, Hisamichi; Inoue, Akihisa
Source:
JOURNAL OF MEMBRANE SCIENCE 291 (1-2): 126-130 MAR 15 2007
Abstract:
We have investigated the hydrogen permeation of the melt-spun Zr65Al7.5Ni10Cu12.5Pd5 alloy in the supercooled liquid, the quasi-crystalline particle-dispersed glassy and the crystalline states. The hydrogen permeability of this alloy is highest in the supercooled liquid state and is lowest in the crystalline state, compared among the three different structures. The hydrogen permeability of the melt-spun alloys consisting of quasi-crystalline particles-dispersed in the glassy state is intermediate between the single phase glassy, and the crystalline alloys. This is presumably because the Zr content in the residual glassy phase decreases after the primary precipitation of the icosahedral-phase (i-phase), resulting in a decrease in the hydrogen permeability. (c) 2007 Elsevier B.V. All rights reserved.

Update: 18-May-2007

Title:
Symmetry of multiferroicity in a frustrated magnet TbMn2O5
Authors:
Okamoto, J; Huang, DJ; Mou, CY; Chao, KS; Lin, HJ; Park, S; Cheong, SW; Chen, CT Author Full Names: Okamoto, J.; Huang, D. J.; Mou, C. -Y.; Chao, K. S.; Lin, H. -J.; Park, S.; Cheong, S-W.; Chen, C. T.
Source:
PHYSICAL REVIEW LETTERS 98 (15): Art. No. 157202 APR 13 2007
Abstract:
Based on measurements of soft-x-ray magnetic scattering and symmetry considerations, we demonstrate that the magnetoelectric effect in TbMn2O5 arises from an internal field determined by (S) over right arrow ((q) over right arrow) x (s) over right arrow (-(q) over right arrow) with (S) over right arrow ((q) over right arrow) being the magnetization at modulation vector (q) over right arrow, whereas the magnetoelastic effect in the exchange energy governs the response to external electric fields. Our results set fundamental symmetry constraints on the microscopic mechanism of multiferroicity in frustrated magnets.
Title:
Commensurate fluctuations in the pseudogap and incommensurate spin-Peierls phases of TiOCl
Authors:
Clancy, JP; Gaulin, BD; Rule, KC; Castellan, JP; Chou, FC Author Full Names: Clancy, J. P.; Gaulin, B. D.; Rule, K. C.; Castellan, J. P.; Chou, F. C.
Source:
PHYSICAL REVIEW B 75 (10): Art. No. 100401 MAR 2007
Abstract:
X-ray scattering measurements on single crystals of TiOCl reveal the presence of commensurate dimerization peaks within both the incommensurate spin-Peierls phase and the so-called pseudogap phase above T-C2. This scattering is relatively narrow in Q-space indicating long correlation lengths exceeding similar to 100 A below T-*similar to 130 K. It is also slightly shifted in Q relative to that of the commensurate long range ordered state at the lowest temperatures, and it coexists with the incommensurate Bragg peaks below T-C2. The integrated scattering over both commensurate and incommensurate positions evolves continuously with decreasing temperature for all temperatures below T-*similar to 130 K.
Title:
Structural studies of Ni2+xMn1-xGa by powder x-ray diffraction and total energy calculations
Authors:
Banik, S; Ranjan, R; Chakrabarti, A; Bhardwaj, S; Lalla, NP; Awasthi, AM; Sathe, V; Phase, DM; Mukhopadhyay, PK; Pandey, D; Barman, SR Author Full Names: Banik, S.; Ranjan, R.; Chakrabarti, A.; Bhardwaj, S.; Lalla, N. P.; Awasthi, A. M.; Sathe, V.; Phase, D. M.; Mukhopadhyay, P. K.; Pandey, D.; Barman, S. R.
Source:
PHYSICAL REVIEW B 75 (10): Art. No. 104107 MAR 2007
Abstract:
The crystal structure of Ni2+xMn1-xGa has been studied as a function of composition (x) by powder x-ray diffraction. For Ni2.24Mn0.75Ga, where one-fourth of the Mn atoms are replaced by Ni, the experimentally determined lattice constants are in good agreement with theoretical equilibrium lattice constants calculated by minimization of total energy using full potential linearized augmented plane-wave method. For 0.15 <= x <= 0.35, a nonmodulated tetragonal martensitic phase is obtained at room temperature, whose lattice constant c increases and a decreases linearly with increasing x following Vegard's law. A 7M modulated monoclinic phase is obtained for x=0.2 due to annealing. The small width of the hysteresis of the martensitic transition shows its thermoelastic nature that is the characteristic of a shape memory alloy. Phase coexistence is observed for 0.1 <= x <= 0.15 at room temperature, confirming the first-order nature of the martensitic transition.
Title:
Theoretical assessment on the validity of the Wiedemann-Franz law for icosahedral quasicrystals
Authors:
Macia, E; Rodriguez-Oliveros, R Author Full Names: Macia, Enrique; Rodriguez-Oliveros, Rogelio
Source:
PHYSICAL REVIEW B 75 (10): Art. No. 104210 MAR 2007
Abstract:
The validity of the Wiedemann-Franz law (WFL) for icosahedral quasicrystals belonging to the families AlCu(Fe,Ru) and AlPd(Mn,Re) is discussed. We exploit some characteristic features in the electronic structure in order to obtain closed analytical expressions for the transport coefficients in terms of the Hurwitz zeta function. Depending on the Fermi-level position, a systematic deviation from the ideal WFL is observed. The role of self-similar features in the electronic structure on the WFL is discussed. The obtained expression for the Lorenz function may be used in order to refine previous experimental results on the charge-carrier contribution to the thermal conductivity in these materials.
Title:
Spiral spin structure in the Heisenberg pyrochlore magnet CdCr2O4
Authors:
Matsuda, M; Takeda, M; Nakamura, M; Kakurai, K; Oosawa, A; Lelievre-Berna, E; Chung, JH; Ueda, H; Takagi, H; Lee, SH Author Full Names: Matsuda, M.; Takeda, M.; Nakamura, M.; Kakurai, K.; Oosawa, A.; Lelievre-Berna, E.; Chung, J. -H.; Ueda, H.; Takagi, H.; Lee, S. -H.
Source:
PHYSICAL REVIEW B 75 (10): Art. No. 104415 MAR 2007
Abstract:
A frustrated spinel CdCr2O4 undergoes a three-dimensional spin-Peierls transition at T-N=7.8 K from a cubic paramagnetic to a tetragonal Neel state. The Neel state has a spiral magnetic structure with a characteristic wave vector of (0, delta, 1) when the c axis is elongated [J.-H. Chung , Phys. Rev. Lett. 95, 247204 (2005)]. Here, we report our spherical neutron polarimetry experiments to investigate the spiral spin structure in detail. Our results indicate that the spins lie in the ac plane perpendicular to the direction of the spiral modulation. We also find that the spiral structure in the ac plane is elliptical with the c component larger by similar to 24% than the a component, suggesting a strong coupling between the magnetic structure and the structural distortion. Unpolarized neutron diffraction under an external magnetic field has also been performed. The magnetic-field dependence suggests the existence of magnetic anisotropy in the Neel state, which is consistent with our previous inelastic studies [J.-H. Chung , Phys. Rev. Lett. 95, 247204 (2005)].
Title:
Chiral magnetic ordering in two-dimensional ferromagnets with competing Dzyaloshinsky-Moriya interactions
Authors:
Vedmedenko, EY; Udvardi, L; Weinberger, P; Wiesendanger, R Author Full Names: Vedmedenko, E. Y.; Udvardi, L.; Weinberger, P.; Wiesendanger, R.
Source:
PHYSICAL REVIEW B 75 (10): Art. No. 104431 MAR 2007
Abstract:
Chiral magnetic ordering due to Dzyaloshinsky-Moriya interaction on two-dimensional lattices is studied theoretically. Several competing Dzyaloshinsky-Moriya vectors are introduced on the basis of symmetry arguments. The role of the exchange interaction, magnetic anisotropy, and dipolar coupling for the ordering in chiral nanomagnets is investigated. It is demonstrated that the periodicity of the modulated structure, which is determined by all interactions involved, is lattice dependent; the direction of spiral propagation and orientation of magnetization is determined by the competition between different Dzyaloshinsky-Moriya vectors and anisotropy; the anisotropy can induce a domain formation or destroy the chiral ordering depending on its orientation. We show that the Dzyaloshinsky-Moriya coupling is responsible for the chiral magnetic ordering in Fe/W(110).
Title:
Microstructural evolution in twin-roll strip cast Mg-Zn-Mn-Al alloy
Authors:
Park, SS; Oh, YS; Kang, DH; Kim, NJ Author Full Names: Park, Sung S.; Oh, Yoon S.; Kang, Dae H.; Kim, Nack J.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 449: 352-355 MAR 25 2007
Abstract:
A study has been made on the microstructural evolution in strip cast Mg-6 wt.% Zn-1 wt.% Mn-1 wt.% Al(ZMA611) alloy. The as-castZMA611 alloy strip shows equiaxed alpha-Mg dendritic structure throughout the thickness of the strip. Quasicrystalline phase and primary Al8Mn5 particles are formed in interdendritic region. During solution treatment at 330 degrees C, the interdendritic quasicrystal phase is rapidly replaced by equilibrium (D-phase (Mg-21(Al,Zn)(17)), which gradually disappears within a-Mg. In addition, fine secondary Al8Mn5 dispersoids precipitate from supersaturated as-strip cast alpha-Mg and these dispersoid particles act as effective nucleation sites for precipitation of MgZn2 phase during aging treatment. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Influence of oxygen on the devitrification of Zr-Ti-Nb-Cu-Ni-Al metallic glasses
Authors:
Scudino, S; Eckert, J; Breitzke, H; Luders, K; Schultz, L Author Full Names: Scudino, S.; Eckert, J.; Breitzke, H.; Lueders, K.; Schultz, L.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 449: 493-496 MAR 25 2007
Abstract:
The effect of oxygen on the crystallization behavior of melt-spun Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 (numbers indicate at.%) glassy ribbons has been investigated. With increasing oxygen content the size of the quasicrystals, the phase formed in the first stage of the crystallization process, decreases. In addition, with increasing amount of oxygen the glass transition and the crystallization temperature corresponding to the formation of the quasicrystals are shifted to higher values, indicating that oxygen has a positive effect on the thermal stability of the glass/supercooled liquid against (quasi)crystallization. A possible explanation for this behavior is linked with a variation in the crystallization behavior due to a change of the composition of the glassy phase. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Characterization of multiple crystallization steps in Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass
Authors:
Jun, HJ; Lee, KS; Chang, YW Author Full Names: Jun, Hyun-Joon; Lee, Kwang Seok; Chang, Young Won
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 449: 526-530 MAR 25 2007
Abstract:
The effects of crystallization on the thermal and mechanical properties of Zr41.2Ti13.8Cu12.5Ni10Be22.5 (number indicate at.%) bulk metallic glass (BMG) have been systematically studied by varying annealing times at 400 degrees C. An icosahedral quasicrystalline phase was identified in the specimen annealed for 30 min at 400 degrees C by using differential scanning calorimetry, X-ray diffraction, and (high-resolution) transmission electron microscopy. Embrittlement behavior due to nanocrystallization has also been examined by carrying out hardness and compression tests for specimens annealed for various times. The fracture strength at room temperature was found to decrease as the annealing time increased. The hardness was, on the other hand, observed to increase due to the increase in nanocrystalline volume fraction with the progress of annealing treatment. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Formation of e/a-constant phases in the Ti-Zr-Ni-Cu system
Authors:
Qiang, JB; Wang, Q; Wang, YM; Huang, H; Wu, J; Dong, C Author Full Names: Qiang, Jianbing; Wang, Qing; Wang, Yingmin; Huang, Huogen; Wu, Jiang; Dong, Chuang
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 449: 565-568 MAR 25 2007
Abstract:
Based on an optimized quasicrystal-forming composition Ti40Zr40Ni20 (numbers indicate at.%), e/a (valence electron per atom)-constant plane with ela value of 1.2 and R-a (average atomic size)-constant plane with R-a value of 0.1474 nm are constructed in the Ti-Zr-Ni-Cu system, and a series of Ti-Zr-Ni-Cu alloys are designed along the intersecting line of the two planes. The experimental results showed that the single-phase quasicrystals can be obtained by the casting method at the compositions of Ti40Zr40Ni20 and Ti33Zr44Ni18Cu5, and a bulk glassy alloy is formed at the composition of Ti12Zr55Ni13Cu20. In the Ti3Zr60Ni12Cu25 and Zr60Ni10Cu30 alloys, the tI-(Zr,Ti)(2)(Cu,Ni) tetragonal phase becomes the dominant phase. Theoretical analysis revealed that the above three types of phases belong to a group of e/a-constant electronic compounds, and there exists close relationship in their local atomic structure, which is supported by the crystallization event of the Ti12Zr55Ni13Cu20 bulk metallic glass. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Phase selection during solidification of undercooled Ti-Fe, Ti-Fe-O and Ti-Fe-Si-O melts-influence of oxygen and silicon
Authors:
Heinen, O; Holland-Moritz, D; Herlach, DM Author Full Names: Heinen, O.; Holland-Moritz, D.; Herlach, D. M.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 449: 662-665 MAR 25 2007
Abstract:
The alloy system Ti-Fe(-O, -Si) shows a great variety of stable and metastable solid phases including structurally complex phases such as quasicrystals and approximant phases. In this work the change in phase selection during solidification as a function of composition on going from lthe binary Ti72.3Fe27.7 over the ternary Ti69.4Fe26.6O4.0 to the quaternary Ti65.4Fe25.0Si5.7O3.9 alloy (numbers indicate at.%) is investigated. The liquid samples are processed and analyzed in situ using a combination of the electromagnetic levitation technique and energy-dispersive diffraction of synchrotron radiation. This allows us to directly determine the crystal structures of the solid phases formed during solidification. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Evidence for effect of hydrostatic pressure during casting on glass-forming ability in Zr65Al7.5Ni10Cu17.5-xPdx (x=0-17.5) alloys
Authors:
Setyawan, AD; Kato, H; Saida, J; Inoue, A Author Full Names: Setyawan, A. D.; Kato, H.; Saida, J.; Inoue, A.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 449: 903-906 MAR 25 2007
Abstract:
We have observed evidence for hydrostatic argon-pressure-dependence of glass-forming ability (GFA) in Zr65Al7.5Ni10Cu17.5-xPdx (numbers indicate at.% x = 0-17.5) alloys. The alloys containing low amount of Pd (x = 0-5) and those with higher Pd (x = 7.5-17.5) showed an opposite tendency in term of the GFA-dependence on pressure. This is supposed to be due to the positive or negative volume changes from the supercooled liquid, to the corresponding primary crystalline/quasicrystalline phase. The result also indicates that the glass-forming ability, in this alloy system may still be improved by controlling the atmosphere condition during casting, despite the previous results (e.g. [A. Inoue, T. Zhang, J. Saida, M. Matsushita, M.W. Chen, T. Sakurai, Mater. Trans. 40 (1999) 1181]) reporting that the substitution of small amount of Cu with noble metals (Pd, Pt, Ag) in Zr-Al-Ni-Cu-based alloys tends to facilitate the nucleation of crystalline or quasicrystalline phase within the glassy one. (c) 2006 Elsevier B.V. All rights reserved.
Title:
About the role of hybridization in wetting and friction on Al-based complex metallic compounds
Authors:
Belin-Ferre, E; Dubois, JM Author Full Names: Belin-Ferre, Esther; Dubois, Jean-Marie
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 449: 971-974 MAR 25 2007
Abstract:
The reversible adhesion energy of water was deduced for many Al-base conventional and complex intermetallics from contact angle measurements performed at the surface of the native oxide layer that always exists in air on top of such materials. Surprisingly, this quantity shows a direct correlation with the density of states at the Fermi level in the bulk material. Similarly, we obtained a straightforward assessment of the surface energy of Al-base complex intermetallics using pin-on-disk measurements performed in a vacuum chamber (using an adequate calibration procedure). For the two types of data, we stress in this article the important role played by the hybridization that occurs between Al p-d and transition metal (TM) d states in the bulk specimen, a mechanism that is also responsible for the specific stability of quasicrystals and high-rank approximants in Al(TM) systems. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Fabrication and mechanical properties of quasicrystal-reinforced Al-Mn-Mm alloys
Authors:
Jun, IH; Kim, JM; Kim, KT; Jung, WJ Author Full Names: Jun, Ioong-Hwan; Kim, Jeong-Min; Kim, Ki-Tae; Jung, Woon-Jae
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 449: 979-982 MAR 25 2007
Abstract:
Microstructures and room temperature mechanical properties of quasicrystal-reinforced Al(94-x)Mn(6)Mm(x) (Mm: misch metal, x = 0-6 at.%) alloys have been studied systematically. Cylindrical rod samples with 3 mm in diameter were synthesized by injection-casting into a Cu mould and analyzed by means of X-ray diffractometry, differential scanning calorimetry, optical microscopy and scanning electron microscopy with energy-dispersive X-ray spectrometry. Mechanical properties of the cylindrical rods were measured at room temperature by compression tests. The Al94Mn6 alloy contains hexagonal-shape particles and long needle-shape Al6Mn precipitates surrounded by alpha-Al matrix. An addition of Mm into the Al94Mn6 alloy generates icosahedral quasicrystalline phase (IQC) with an extinction of hexagonal and Al6Mn phases, and the fraction of IQC increases continuously with an increase in Mm content. Compressive yield strength (sigma(cys)) and ultimate compressive strength (sigma(ucs)) of the Al-Mn-Mm alloys are improved with Mm content up to 4%, whereas elongation is steeply deteriorated by the Mm addition. The Al(90)Mn(6)Mm(4) alloy exhibits the highest 570 and 783 MPa of sigma(cys) and sigma(ucs), respectively, both of which are comparable to those of Al90Mn6Ce4 alloy. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Devitrification of nano-scale icosahedral phase in multicomponent alloys
Authors:
Kim, KB; Warren, PJ; Cantor, B; Eckert, J Author Full Names: Kim, K. B.; Warren, P. J.; Cantor, B.; Eckert, J.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 449: 983-986 MAR 25 2007
Abstract:
A nano-scale icosahedral phase forms as first crystallization product upon devitrification of multicomponent amorphous (Ti33Zr33Hf33)50 (Ni50Cu50)(40)Al-10, (Ti33Zr33Hf33)(60)(Ni50Cu50)(30)Al-10 and (Ti33Zr33Hf33)(65)(Ni50Cu50)(27.5)Al-7.5 alloys (numbers indicate at.%). The onset temperatures and the values of the activation energy for the devitrification of the nano-scale icosahedral phase decrease with increasing (Ti33Zr33Hf33) content in these alloys. This indicates that the structural similarity between the amorphous and the icosahedral phases increases with increasing (Ti33Zr33Hf33) content. Furthermore, the devitrified nano-scale icosahedral quasicrystals form in a wide compositional range regardless of the (Ti33Zr33Hf33) content suggesting that the icosahedral phase in these novel multicomponent alloys, developed by equiatomic substitution may have an extensive solid solubility. After further heat treatment the devitrified nano-scale icosahedral phase fully decomposes into MgZn2-type crystals reflecting its metastability. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Effect of volume fraction of qusicrystal on the mechanical properties of quasicrystal-reinforced Mg-Zn-Y alloys
Authors:
Lee, JY; Lim, HK; Kim, DH; Kim, WT; Kim, DH Author Full Names: Lee, Ju Youn; Lim, Hyun Kyu; Kim, Do Hyung; Kim, Won Tae; Kim, Do Hyang
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 449: 987-990 MAR 25 2007
Abstract:
The dependence of the mechanical properties of Mg-Zn-Y alloys on the volume fraction of a reinforcing icosahedral phase (I-phase) has been investigated. The strength of Mg-Zn-Y alloys increases and the elongation to failure decreases with increasing I-phase volume fraction in the temperature range from 25 up to 200 degrees C. However, at a temperature of 300 degrees C, the strength of Mg-Zn-Y alloys decreases with the increase of the I-phase volume fraction, since the grain boundary sliding mechanism becomes dominant. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Stability and diffraction features of quasicrystal and 2/1 approximant phase in an Au42In42Yb16 alloy
Authors:
Singh, A; Guo, JQ; Tsai, AP Author Full Names: Singh, Alok; Guo, J. Q.; Tsai, A. P.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 449: 991-994 MAR 25 2007
Abstract:
An Au42In42Yb16 alloy has been studied by transmission electron microscopy in as-cast and melt-spun conditions. The as-cast alloy was found to contain a cubic 2/1 approximant phase (along with another crystalline phase) with lattice parameter 2.46 nm and space group Pa3. Electron diffraction features of this phase have been described. An icosahedral quasicrystal formed on melt-spinning. Differential thermal analysis indicates that the quasicrystalline phase is stable above 525 degrees C, until melting. Annealing at temperature 550 degrees C improves the quality of the quasicrystal, while annealing at 450 degrees C shows transformation to a microcrystalline state. At both temperatures, a 1/1 cubic approximant phase separates out. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Surface reactivity of rapidly quenched nano-quasicrystalline ribbons with respect to biomolecules
Authors:
Lefaix, H; Prima, F; Dubot, P; Janickovic, D; Svec, P Author Full Names: Lefaix, H.; Prima, F.; Dubot, P.; Janickovic, D.; Svec, P.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 449: 995-998 MAR 25 2007
Abstract:
In this paper, we report on preliminary investigations about surface reactivity of quasicrystalline-based alloys with respect to small biological molecules such as amino-acids. The main purpose is to study potential applications for these materials in biomedical fields since biomolecules are well known to be sensitive to solid surface wettability, surface energy and charge. In that sense, quasicrystals surfaces could be attractive considering their unusual symmetry, their low surface energy and their peculiar electronic properties. Our investigations were focussed on superficial reactivity of as-quenched Ti45Zr38Ni17 (numbers indicate at.%) ribbons, whose microstructure was analysed by transmission electron microscopy and X-ray diffraction. Surfaces were then carefully polished and immersed in a solution (C = 10(-2) mol l(-1), pH 6) Of L-glutamic acid or L-lysine for duration varying from 30 min to 6 days. Molecular vibrational modes and adsorption kinetics were investigated using infrared spectroscopy. The first results reveal that L-glutamic acid seems to display faster adsorption kinetic on quasicrystalline ribbons compared to that on pure titanium (cpTi) or on beta-metastable alloys (Ti-12 Mo-6 Zr-4.5 Sn), which is quite interesting since surface energy on quasicrystals is known to be low. (c) 2006 Elsevier B.V. All rights reserved.
Title:
On the evolution of quasicrystalline and crystalline phases in rapidly quenched Al-Co-Cu-Ni alloy
Authors:
Yadav, TP; Mukhopadhyay, NK; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Mukhopadhyay, N. K.; Tiwari, R. S.; Srivastava, O. N.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 449: 1052-1056 MAR 25 2007
Abstract:
The occurrence of stable decagonal quasicrystalline phase in Al-Co-Ni and Al-Cu-Co alloys through conventional solidification is well established. Earlier, we have studied the effect of Cu substitution in place of Co in the Al70Co15Ni15 alloy. Here we report the structural/microstructural changes with substitution of Cu for Ni in rapidly solidified Al-Co-Ni alloys. The melt spun ribbons have been characterized using X-ray diffractometry, scanning and transmission electron microscopy. With an increase in Cu content in the melt spun Al70Co15Cu,Ni15-x (x = 0-15 at.%) alloys, the relative amount of the decagonal phase decreased up to 10 at.% of Cu. At this composition, the quaternary alloy showed the co-existence of decagonal quasicrystal and superstructure of tau(3) vacancy ordered crystalline phases. The decagonal phase containing Cu showed more disordering than Al-Co-Ni alloys. The implication of the structural and microstructural changes due to Cu substitution instable decagonal quasicrystals will be discussed. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Rapidly solidified Al92Fe3Cr2Mn3 alloy
Authors:
Rios, CT; Bolfarini, C; Botta, WJ; Kiminami, CS Author Full Names: Rios, C. Triveno; Bolfarini, C.; Botta F, W. J.; Kiminami, C. S.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 449: 1057-1061 MAR 25 2007
Abstract:
The objective of the present work was to evaluate the possibilities to obtain quasicrystalline phases in bulk samples of the Al92Fe3Cr2Mn3 (at.%) alloy. Three process of rapid solidification were used to produce: (a) as-quenched ribbon, (b) wedge casting samples and (c) centrifugal force samples. The microstructures of the two bulk samples were compared with the as-quenched ribbon obtained by melt-spinning. The microstructures were evaluated by a combination of transmission and scanning electron microscopy, X-ray diffraction and differential scanning calorimetry. In both bulk samples we have observed the presence of quasicrystalline and polycrystalline aggregates with varied morphologies and also intermetallic phases radiating from quasicrystalline grains. In the wedge shape sample quasicrystalline microstructures has been observed for thickness up to 0.8 mm. Calorimetry and X-ray diffraction analysis indicated that the quasicrystalline phase is stable up to 450 degrees C and its transition for crystalline phases is completed above 520 degrees C. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Temperature-pressure phase diagram in TTF-TCNQ: Strong suppression of charge-density-wave state under extremely high pressure
Authors:
Yasuzuka, S; Murata, K; Arimoto, T; Kato, R Author Full Names: Yasuzuka, Syuma; Murata, Keizo; Arimoto, Taro; Kato, Reizo
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 (3): Art. No. 033701 MAR 2007
Abstract:
We have measured the resistivity of the organic conductor TTF-TCNQ under high pressure up to 8.0 GPa using a cubic anvil apparatus. Below 3 GPa, the pressure dependence of the charge-density-wave (CDW) transition temperature, T-CDW, is consistent with previous results, except for the observation of the "49 K-transition" at around I GPa. Above 3 GPa, TCDw decreases with increasing pressure but the CDW state survives even at 8.0 GPa. At 8.0 GPa, however, the resistivity shows metallic behavior below 25 K after the CDW transition with TCDW = 31 K. The origin of suppression is discussed in terms of the imperfect nesting originating from the increase in the interchain transfer integral, the significant deviation from the third-order commensurability, as well as the bandwidth broadening for both TTF and TCNQ stacks. The complete suppression of the CDW phase is expected near 9 GPa.
Title:
Evidence of the fine pseudogap at the fermi level in Al-based quasicrystals
Authors:
Okada, JT; Ekino, T; Yokoyama, Y; Takasaki, T; Watanabe, Y; Nanao, S Author Full Names: Okada, J. T.; Ekino, T.; Yokoyama, Y.; Takasaki, T.; Watanabe, Y.; Nanao, S.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 (3): Art. No. 033707 MAR 2007
Abstract:
Theoretical studies have predicted that quasicrystals (QCs) have conspicuously fine electronic structures near the Fermi level (E-F); the density of states (DOS) consists of sharp peaks and deep valleys with several 10 meV intervals. These fine electronic structures are believed to explain the unusual sensitivity of the electrical conductivity to slight changes in the chemical composition of QCs. We have investigated the DOS around the EF on single grains of icosahedral (i-)AlCuFe, i-AIPdMn, and decagonal (d-)AlCuCo QCs by break-junction tunneling spectroscopy at 4.2 K. Well-defined and reproducible pseudogaps at the EF are observed for these alloys. This is a direct experimental result that confirms the fine electronic structure existing in the vicinity of the EF.
Title:
Dynamic properties of Al-Ni-Co decagonal quasicrystals modelled by ab initio interatomic pair potentials
Authors:
Hiramatsu, S; Ishii, Y Author Full Names: Hiramatsu, Seiji; Ishii, Yasushi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 (3): Art. No. 034601 MAR 2007
Abstract:
Vibrational spectra of realistic structural models for ternary Al-Ni-Co decagonal quasicrystals are studied. A bunch of dispersion-less modes is obtained above a few meV, which is extremely low in comparison with usual optic modes. Analyzing the local vibrational density of states at an individual atomic site, we identify several Al sites where low- and high-frequency vibrations are localized. The localized vibrations are attributed to the strong Al-TM interaction and the local atomic arrangements realized in the complex structures. Low-frequency dispersion-less modes are of special interest in relation to the phason degrees of freedom in QC but no signature of large atomic motion causing the phasonic tile flip is obtained in the low-frequency localized vibrational modes.
Title:
Successive magnetic transitions of the kagome staircase compound Co3V2O8 studied in various magnetic fields
Authors:
Yasui, Y; Kobayashi, Y; Soda, M; Moyoshi, T; Sato, M; Igawa, N; Kakurai, K Author Full Names: Yasui, Yukio; Kobayashi, Yusuke; Soda, Minoru; Moyoshi, Taketo; Sato, Masatoshi; Igawa, Naoki; Kakurai, Kazuhisa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 (3): Art. No. 034706 MAR 2007
Abstract:
For the fictitious spin-1/2 kagome staircase system Co3V2O8, magnetic field-temperature (H-T) phase diagrams have been constructed for the fields along three principal directions up to 5 T, using results of various macroscopic measurements on single crystal samples and also using neutron diffraction data taken on both powder and single crystal samples under H along c. In zero magnetic field, the system exhibits three transitions at temperatures Tcl similar to 11.2K, T-c2 similar to 8.8K and T-c3 similar to (6.0-7.0)K. The single crystal data present clear evidence for the noncollinear nature of the magnetic structures in all magnetically ordered phases below Tl. The sinusoidal nature of the incommensurate modulation of the ordered moment reported in the former work has been confirmed between T-c1 and T-c2, that is, no higher harmonics of the modulation have been detected even for the present large single crystal. Even in the phase of commensurate modulation between T-c2 and T-c3, we have not detected any higher harmonics of the modulation. The phase diagrams show that the magnetically ordered phases sensitively change to other phases with H, indicating that the geometrical frustration inherent in this system is important for the determination of the phase diagram. No evidence for ferroelectric transitions has been observed in the measurements of the dielectric constant (s) applying the electric fields along three crystallographic axes, a, b, and c. Only small dielectric anomalies closely connected with the magnetic phase transitions have been found.
Title:
Phonon scattering in quasicrystalline i-Al72Pd19.5Mn8.5: A study of the low-temperature thermal conductivity
Authors:
Bilusic, A; Smontara, A; Dolimsek, J; McGuiness, P; Ott, HR Author Full Names: Bilusic, A.; Smontara, A.; Dolimsek, J.; McGuiness, P.; Ott, H. R.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 432 (1-2): 1-6 APR 25 2007
Abstract:
We measured the thermal conductivity of an icosahedral quasicrystal i-Al72Pd19.5Mn8.5 in the temperature range between 0.4 K and 300 K. The analysis of the low-temperature results was based on a Debye-type model. The results of the analysis for the two temperature regions of 0.4K < T < 40K and 0.4K < T < 1 K, are not consistent in the sense that a tunnelling-states contribution to phonon scattering is verified only for OAK < T < 1 K. The same fitting procedure indicates that structural defects of the stacking-fault type are an important source of phonon scattering. Their physical presence was clearly identified by a transmission electron microscopy experiment. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Intermetallic phases and phase reactions in Zn-Mg (< 40 at.%)-Y (< 20 at.%) region
Authors:
Li, MR; Kuo, KH Author Full Names: Li, M. R.; Kuo, K. H.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 432 (1-2): 81-89 APR 25 2007
Abstract:
Single phase regions of the icosahedral quasicrystal and the hexagonal (Zn, Mg)(58)Y-13, (Zn, Mg)(5)Y, and Z (a ternary phase containing 6-8 at.% Y) in the Zn-Mg (0-40 at.%)-Y (0-25 at.%) region have been determined. A tentative isothermal section at 600 degrees C was proposed. The (Zn, Mg)(5)Y and the icosahedral phase have wide ranges of Mg content and are the dominant phases in these alloys. The hexagonal (Zn, Mg)(5)Y is resulted from the substitution of Mg for Zn in the binary Zn5Y and therefore they are isostructural, so are also the hexagonal Zn58Y13 and (Zn, Mg)(58)Y-13 phases. Reactions among the intermetallic phases in this composition range during cooling were studied. Similar phase reactions have also been observed in the Zn-Mg-Ho/Er alloys. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Synthesis, structure and phase separation of a new 12R-type perovskite-related oxide Ba3NdMn2O9
Authors:
Yang, H; Tang, YK; Yao, LD; Zhang, W; Li, QA; Li, FY; Jin, CQ; Yu, RC Author Full Names: Yang, H.; Tang, Y. K.; Yao, L. D.; Zhang, W.; Li, Q. A.; Li, F. Y.; Jin, C. Q.; Yu, R. C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 432 (1-2): 283-288 APR 25 2007
Abstract:
A new 12R-type perovskite-related oxide, Ba3NdMn2O9, has been prepared by traditional solid-state reaction method and the presence of chemical phase separation phenomenon has been revealed by transmission electron microscopy. The perfect grains of the compound have an average chemical composition of Ba4NdMn3O12 (mainly for cationic ratio) according to the characterization by TEM-EDX. In this perfect 12R-type structure with composition Ba4NdMn3O12, the Nd cations are located in the corner-sharing octahedra, whereas the Mn cations are located in the face-sharing octahedra, leading to a remarkable cation ordering. Superstructure modulation was found to be a common phenomenon in the 12R polytype and the modulated areas were revealed by both EDX and EELS to be Nd rich compared to the perfect areas. This result together with the previous work [A.F. Fuentes, K. Boulahya, U. Amador, J. Solid State Chem. 177 (2004) 714] has shown that, for the rare-earth-containing Ba-RE-Mn-O systems (RE being rare-earth elements), the composition Ba4REMn3O12 (mainly for cationic ratio) is required for the formation of perfect 12R polytype. (c) 2006 Elsevier B.V. All rights reserved.

Update: 11-May-2007

Title:
Structure determination of the hexagonal quasicrystal approximant mu '-(Al,Si)(4)Cr by the strong reflections approach
Authors:
He, ZB; Zou, XD; Hovmoller, S; Oleynikov, P; Kuo, KH Author Full Names: He, Z. B.; Zou, X. D.; Hovmoller, S.; Oleynikov, P.; Kuo, K. H.
Source:
ULTRAMICROSCOPY 107 (6-7): 495-500 JUN-JUL 2007
Abstract:
A number of different crystalline phases have been found in At-rich Al-Cr-Si alloys by transmission electron microscopy (TEM). Among these, the new hexagonal phase mu'-(Al,Si)(4)Cr (a = 2.01 and c = 1.24 nm) often found coexisting with the hexagonal mu-(Al,Si)(4)Cr (a = 1.998 and c = 2.4673 nm, isostructural with mu-Al4Mn) and also with the hexagonal lambda-(Al,Si)(4)Cr (a = 2.839 and c = 1.239 nm, isostructural with lambda-Al4Mn). It is evident from their electron diffraction patterns that the structures of these three phases are related. The strong reflections in all three are distributed in a similar way. They all exhibit a pseudo-icosahedral symmetry. The structure factor amplitudes and phases for the strong reflections of the mu' phase could therefore be adopted from those of the lambda phase, according to the strong reflections approach. A structure model of the mu' phase is thus deduced from the known lambda-Al4Mn.u. mu' consists of chains of 3 + 3 or 4 + 2 interpenetrated icosahedra along the < 100 > directions. Similar to the lambda phase, there are two flat layers (F) and four puckered layers (P) in each unit cell of mu', stacked along the c-axis in a sequence of PFP(PFP)' where the (PFP)' block is related to the PFP block by a 63 screw. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Growing perfect decagonal quasicrystals by local rules
Authors:
Jeong, HC Author Full Names: Jeong, Hyeong-Chai
Source:
PHYSICAL REVIEW LETTERS 98 (13): Art. No. 135501 MAR 30 2007
Abstract:
A local growth algorithm for a decagonal quasicrystal is presented. We show that a perfect Penrose tiling (PPT) layer can be grown on a decapod tiling layer by a three dimensional (3D) local rule growth. Once a PPT layer begins to form on the upper layer, successive 2D PPT layers can be added on top resulting in a perfect decagonal quasicrystalline structure in bulk with a point defect only on the bottom surface layer. Our growth rule shows that an ideal quasicrystal structure can be constructed by a local growth algorithm in 3D, contrary to the necessity of nonlocal information for a 2D PPT growth.
Title:
Magnetic excitations in multiferroic TbMnO3: Evidence for a hybridized soft mode
Authors:
Senff, D; Link, P; Hradil, K; Hiess, A; Regnault, LP; Sidis, Y; Aliouane, N; Argyriou, DN; Braden, M Author Full Names: Senff, D.; Link, P.; Hradil, K.; Hiess, A.; Regnault, L. P.; Sidis, Y.; Aliouane, N.; Argyriou, D. N.; Braden, M.
Source:
PHYSICAL REVIEW LETTERS 98 (13): Art. No. 137206 MAR 30 2007
Abstract:
The magnetic excitations in multiferroic TbMnO3 have been studied by inelastic neutron scattering in the spiral and sinusoidally ordered phases. At the incommensurate magnetic zone center of the spiral phase, we find three low-lying magnons whose character has been fully determined using neutron-polarization analysis. The excitation at the lowest energy is the sliding mode of the spiral, and two modes at 1.1 and 2.5 meV correspond to rotations of the spiral rotation plane. These latter modes are expected to couple to the electric polarization. The 2.5 meV mode is in perfect agreement with recent infrared-spectroscopy data giving strong support to its interpretation as a hybridized phonon-magnon excitation.
Title:
Prediction of Bragg-scattering-induced band gaps in phononic quasicrystals
Authors:
Sutter-Widmer, D; Deloudi, S; Steurer, W Author Full Names: Sutter-Widmer, Daniel; Deloudi, Sofia; Steurer, Walter
Source:
PHYSICAL REVIEW B 75 (9): Art. No. 094304 MAR 2007
Abstract:
We have studied ultrasonic wave propagation in two-dimensional quasiperiodic steel/water heterostructures with 8-, 10-, 12-, and 14-fold Patterson symmetry. The formation of band gaps in this kind of quasiperiodic phononic crystal (QPNC) is mainly governed by multiple Bragg scattering. The particular role of the periodic average structure of the QPNC in prediction and understanding of their transmission spectra is shown. The smaller the deviations from average periodicity, the greater is the similarity of transmission spectra of the quasiperiodic and periodic heterostructures. Consequently, QPNC's with 8-fold symmetry (QPNC-8's) show much better defined transmittance bands and gaps than QPNC-10's and QPNC-14's, whose spectra resemble more those of disordered periodic systems. Smoother transmission spectra with clear gaps can be obtained by replacement of the cylinders of QPNC-10's by star-shaped prisms.
Title:
Magnetic phases in the Kagome staircase compound Co3V2O8 studied using powder neutron diffraction
Authors:
Wilson, NR; Petrenko, OA; Chapon, LC Author Full Names: Wilson, N. R.; Petrenko, O. A.; Chapon, L. C.
Source:
PHYSICAL REVIEW B 75 (9): Art. No. 094432 MAR 2007
Abstract:
The low temperature properties of the Kagome-type system Co3V2O8 have been studied by powder neutron diffraction both in zero field and in applied magnetic fields of up to 8 T. Below 6 K, the zero-field ground state is ferromagnetic with the magnetic moments aligned along the a axis. The size of the moment on one of the two Co sites, the so-called cross-tie site, is considerably reduced compared to the fully polarized state. The application of a magnetic field in this phase is found to rapidly enhance the cross-tie site magnetic moment, which reaches the expected value of similar to 3 mu(B) by the maximum applied field of 8 T. Different reorientation behaviors are found for the Co cross-tie and spine sites, suggesting a more pronounced easy-axis anisotropy for moments on the spine sites. Rietveld refinements reveal that a simple model, where the spins on both cross-tie and spine sites rotate in the ac plane in a magnetic field, reproduces the experimental diffraction patterns well. In addition, it is found that at higher temperatures and moderate magnetic fields, the incommensurate antiferromagnetic order, corresponding to a transverse sinusoidal modulation above 8 K, is suppressed to be replaced by ferromagnetic order.
Title:
X-ray photoelectron spectroscopy of ferroelectrics
Authors:
Grigas, J; Talik, E; Lazauskas, V Author Full Names: Grigas, Jonas; Talik, Ewa; Lazauskas, Valentinas
Source:
FERROELECTRICS 347: 86-100 2007
Abstract:
The paper presents the X-ray photoelectron spectra (XPS) of the valence band (VB) and of the principal core levels (CL) for SbSI-type and incommensurate TlInS2 single crystals. Form and electronic structure of the VB and CL splitting in the quasi-one-dimensional SbSI, SbSeI and BiSI, and in the incommensurate (IC) phase of TlInS2 crystals are discussed. Experimentally obtained energies were compared with the results of theoretical ab initio calculations. Large shifts (3 divided by 5 eV) in the CL binding energies in SbSI show a strong dependence on the surface crystallographic plane. The splitting of the CL was also obtained in the IC phase of TlInS2 crystals.
Title:
Layer-by-layer growth of quasi-periodic Rauzy tiling
Authors:
Zhuravlev, VG; Maleev, AV Author Full Names: Zhuravlev, V. G.; Maleev, A. V.
Source:
CRYSTALLOGRAPHY REPORTS 52 (2): 180-186 MAR-APR 2007
Abstract:
Some characteristics of the 2D quasi-periodic Rauzy tiling, which allows parametrization and is obtained from finite torus filings, have been investigated. The main characteristics of the layer-by-layer growth of this tiling were investigated theoretically and in a computer experiment. The polygonal character of self-simy ilar growth with a limited radius of deviation from the limiting polygon is demonstrated and formulas for both sectoral and global growth rates are obtained.

Update: 27-Apr-2007

Title:
Inhibition of Al grain coarsening by quasicrystalline icosahedral phase in the rapidly solidified powder metallurgy Al-Fe-Ti-Cr alloy
Authors:
Yamasaki, M; Nagaishi, Y; Kawamura, Y Author Full Names: Yamasaki, Michiaki; Nagaishi, Yusuke; Kawamura, Yoshihito
Source:
SCRIPTA MATERIALIA 56 (9): 785-788 MAY 2007
Abstract:
The quasicrystalline icosahedral phase prevents Al matrix grain coarsening in the rapidly solidified powder metallurgy Al92.5Fe2.5Ti2.5Cr2.5 alloy due to a thermally stable crystallographic orientation relationship between the icosahedral and Al phases. The 2-fold axis of the icosahedral phase is along the (112) axis of face centered cubic Al; this orientation relationship was observed in alloys annealed at 573 K for 1000 h. A highly dispersed intergranular icosahedral phase located on the Al matrix significantly enhances the heat resistance of the alloys. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
The effect of Ti, Nb, and Ta additions to ZrAlCu metallic glass on the crystallization and formation of the icosahedral phase
Authors:
Qiang, JB; Zhang, W; Xie, GQ; Inoue, A Author Full Names: Qiang, J. B.; Zhang, W.; Xie, G. Q.; Inoue, A.
Source:
JOURNAL OF MATERIALS RESEARCH 22 (4): 1093-1097 APR 2007
Abstract:
The addition of Ti, Nb, or Ta altered the crystallization behavior of the Zr65Al7.5Cu27.5 glass, and a metastable nanoscaled I-phase was obtained on primary crystallization of these quaternary glasses. The complete substitution of Al by Nb also led to the precipitation of I-phase upon crystallization. Negative heats of mixing between the addition metals and the transition metals of the mother alloy were demonstrated to be not a necessary condition for I-phase formation in the present alloy system.
Title:
Understanding modulated twin transition at the atomic level
Authors:
Han, M; Bennett, JC; Gharghouri, MA; Chen, J; Hyatt, CV Author Full Names: Han, M.; Bennett, J. C.; Gharghouri, M. A.; Chen, J.; Hyatt, C. V.
Source:
ACTA MATERIALIA 55 (5): 1731-1740 MAR 2007
Abstract:
The modulated martensitic variants in a Ni-Mn-Ga ferromagnetic shape memory alloy have been characterized in detail by transmission electron microscopy (TEM). Electron diffraction confirms that at room temperature most of the martensite in this alloy exhibits the 5-layer modulated structure. Trace analysis indicates that the self-accommodated variants have a coherent twinning plane of 112 31 relative to the martensitic phase. One of the twin relations was determined to be (1 (2) over bar(5) over bar)(A)//(1 (2) over bar(5) over bar)(C) with [(2) over bar(1) over bar0](A)//[210](C), revealing the presence of a reflection twin. Based on TEM experimental observations, a model describing the reorientation of the twinned variants on an atomic scale was developed to explain the reversible motion of the boundary. The twin transition between the variants with modulated structure is shown to involve deshuffle on the basal plane of the original variant, atomic displacement parallel to the twin boundary and shuffle again on the basal plane of the product variant. Crown Copyright (c) 2006 Published by Elsevier Ltd. All rights reserved.

Update: 20-Apr-2007

Title:
GdCo1-xGa3Ge: Charge density wave in a Ga square net
Authors:
Zhuravleva, MA; Evain, M; Petricek, V; Kanatzidis, MG Author Full Names: Zhuravleva, Marina A.; Evain, Michel; Petricek, Vaclav; Kanatzidis, Mercouri G.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 129 (11): 3082-+ MAR 21 2007
Abstract:
The intermetallic phase GdCo1-xGa3Ge exhibits a charge density wave distortion in the square nets of Ga which was elucidated with superspace crystallography. The distortion results in parallel infinite chains and ribbons with substantial interchain hypervalent interactions very similar to those observed in the charge density waves of RETe3 (RE = rare earth element).
Title:
Study of the microscopic structures in 0.72Pb(Mg1/3Nb2/3)O-3-0.28PbTiO(3) relaxor ferroelectrics by means of x-ray diffraction
Authors:
Guo, Z; Tai, RZ; Xu, HJ; Gao, C; Luo, HS; Pan, GQ; Hu, CS; Lin, D; Fan, R; Li, RP; Yan, R; Zhang, XZ; Namikawa, K Author Full Names: Guo, Zhi; Tai, Renzhong; Xu, Hongjie; Gao, Chen; Luo, Haosu; Pan, Guoqiang; Hu, Chuansheng; Lin, Di; Fan, Rong; Li, Ruipeng; Yan, Rui; Zhang, Xiangzhi; Namikawa, Kazumichi
Source:
JOURNAL OF APPLIED PHYSICS 101 (5): Art. No. 053505 MAR 1 2007
Abstract:
X-ray diffraction experiment has been conducted to study the microscopic-scale structures for 0.72PMN-0.28PT relaxor ferroelectrics in a high external dc field during phase transition. Clear quasiperiodic structures were observed along < 111 > and < 1-11 > directions near T-C. These structures are interpreted as originating from strong Coulomb interactions among adjacent polar clusters. The projected cluster size (correlation length) was estimated to be 17 nm. It was also found that the dominating cluster's orientation and their interaction direction (periodic direction) were changeable among < 111 > and < 1-11 > as temperature changed. (c) 2007 American Institute of Physics.
Title:
Superspace description of the crystal structures of Ca-n(Nb,Ti)(n)O3n+2 (n=5 and 6)
Authors:
Guevarra, J; Schonleber, A; van Smaalen, S; Lichtenberg, F Author Full Names: Guevarra, Jonathan; Schoenleber, Andreas; van Smaalen, Sander; Lichtenberg, Frank
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 63: 183-189 Part 2 APR 2007
Abstract:
The crystal structures of two members of the homologous series Ca-n(Nb, Ti)(n)O3n + 2, with n = 5 and 6, are presented within the superspace formalism. A common (3 + 1)-dimensional superspace model is used to describe the crystal structures of both compositions within a particular homologous series, where the primary modulation wavevector and the width of the atomic domains vary systematically with composition. The two crystal structures are characterized as commensurately modulated structures consisting of discontinuous atomic domains described by occupational crenel functions. The displacive modulation functions for the two compounds exhibit similarities, but they also show that the idea of a unified superspace model does not extend toward the precise atomic positions. For n = 6, the centrosymmetric (3 + 1)-dimensional superspace symmetry provides a natural explanation for the pseudo-symmetries that are present in the non-centrosymmetric (three-dimensional) superstructure of this compound. The efficiency of the superspace approach is demonstrated by structure refinements in (3 + 1)-dimensional superspace and by comparing these results with the refinements in their three-dimensional superstructures.

Update: 13-Apr-2007

Title:
Lanthanide contraction and magnetism in the heavy rare earth elements
Authors:
Hughes, ID; Dane, M; Ernst, A; Hergert, W; Luders, M; Poulter, J; Staunton, JB; Svane, A; Szotek, Z; Temmerman, WM Author Full Names: Hughes, I. D.; Daene, M.; Ernst, A.; Hergert, W.; Lueders, M.; Poulter, J.; Staunton, J. B.; Svane, A.; Szotek, Z.; Temmerman, W. M.
Source:
NATURE 446 (7136): 650-653 APR 5 2007
Abstract:
The heavy rare earth elements crystallize into hexagonally close packed ( h. c. p.) structures and share a common outer electronic configuration, differing only in the number of 4f electrons they have(1). These chemically inert 4f electrons set up localized magnetic moments, which are coupled via an indirect exchange interaction involving the conduction electrons. This leads to the formation of a wide variety of magnetic structures, the periodicities of which are often incommensurate with the underlying crystal lattice (2). Such incommensurate ordering is associated with a 'webbed' topology(3,4) of the momentum space surface separating the occupied and unoccupied electron states ( the Fermi surface). The shape of this surface - and hence the magnetic structure - for the heavy rare earth elements is known to depend on the ratio of the interplanar spacing c and the interatomic, intraplanar spacing a of the h. c. p. lattice (5). A theoretical understanding of this problem is, however, far from complete. Here, using gadolinium as a prototype for all the heavy rare earth elements, we generate a unified magnetic phase diagram, which unequivocally links the magnetic structures of the heavy rare earths to their lattice parameters. In addition to verifying the importance of the c/a ratio, we find that the atomic unit cell volume plays a separate, distinct role in determining the magnetic properties: we show that the trend from ferromagnetism to incommensurate ordering as atomic number increases is connected to the concomitant decrease in unit cell volume. This volume decrease occurs because of the so-called lanthanide contraction(6), where the addition of electrons to the poorly shielding 4f orbitals leads to an increase in effective nuclear charge and, correspondingly, a decrease in ionic radii.
Title:
Optical absorption in TlGaSe2 crystals near the two-phonon states zone
Authors:
Ibragimov, TD Author Full Names: Ibragimov, T. D.
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS 147 (1-2): 1-6 APR 2007
Abstract:
The temperature dependence of transmission spectra near the two-phonon states zone of TlGaSe2 crystals is investigated. The additional band at 142 K and a decrease of transmission at 257 K are observed. It is shown that the successive thermocycling processes between the commensurate and incommensurate phases lead to appreciable changes in these spectra. The experimental results are explained by revealing of phase transitions at indicated temperatures, the influence of semiconductor properties and layer disordering of the TlGaSe2 crystal.
Title:
Electrical, magnetic, thermal and thermoelectric properties of the "Bergman phase" Mg-32(Al,Zn)(49) complex metallic alloy
Authors:
Smontara, A; Smiljanic, I; Bilusic, A; Jaglicic, Z; Klanjsek, M; Roitsch, S; Dolinsek, J; Feuerbacher, M Author Full Names: Smontara, A.; Smiljanic, I.; Bilusic, A.; Jaglicic, Z.; Klanjsek, M.; Roitsch, S.; Dolinsek, J.; Feuerbacher, M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 430 (1-2): 29-38 MAR 14 2007
Abstract:
The Mg-Al-Zn system of intermetallics contains an exceptional crystalline phase Mg-32(Al,Zn)(49), named the Bergman phase, whose crystal structure is based on a periodic arrangement of icosahedral Bergman clusters within the giant-unit-cell, so that periodic and quasiperiodic atomic orders compete in determining the physical properties of the material. We have investigated electrical, magnetic, thermal and thermoelectric properties of a monocrystalline Bergman phase sample of composition Mg-29.4(Al,Zn)(51.6), grown by the Bridgman technique. Electrical resistivity is in the range rho approximate to 40 mu Omega cm and exhibits positive-temperature-coefficient with V dependence at low temperatures and T at higher temperatures, resembling non-magnetic amorphous alloys. Magnetic susceptibility x measurements revealed that the sample is a Pauli paramagnet with a significant Landau diamagnetic orbital contribution. The susceptibility exhibits a weak increase towards higher temperature. Combined analysis of the rho(T) and chi(T), together with the independent determination of the Pauli susceptibility via the NMR Knight shift suggests that the observed temperature dependence originates from the mean-free-path effect on the orbital susceptibility. The electronic density of states (DOS) at the Fermi energy E-F was estimated by NMR and was found to amount 72% of the DOS of the fee Al metal, with no evidence on the existence of a pseudogap. Thermal conductivity contains electronic, Debye and hopping of localized vibrations terms, whereas thermopower is small and negative. High structural complexity of the Bergman phase does not result in high complexity of its electronic structure. (c) 2006 Elsevier B.V. All rights reserved.

Update: 6-Apr-2007

Title:
Diffraction and modeling solve the structure of ytterbium-cadmium quasicrystals
Authors:
Wilson, M Author Full Names: Wilson, Mark
Source:
PHYSICS TODAY 60 (3): 23-25 MAR 2007
Title:
Enhanced ferroelectric polarization by induced Dy spin order in multiferroic DyMnO3
Authors:
Prokhnenko, O; Feyerherm, R; Dudzik, E; Landsgesell, S; Aliouane, N; Chapon, LC; Argyriou, DN Author Full Names: Prokhnenko, O.; Feyerherm, R.; Dudzik, E.; Landsgesell, S.; Aliouane, N.; Chapon, L. C.; Argyriou, D. N.
Source:
PHYSICAL REVIEW LETTERS 98 (5): Art. No. 057206 FEB 2 2007
Abstract:
Neutron powder diffraction and single crystal x-ray resonant magnetic scattering measurements suggest that Dy plays an active role in enhancing the ferroelectric polarization in multiferroic DyMnO3 above T-N(Dy) = 6.5 K. We observe the evolution of an incommensurate ordering of Dy moments with the same periodicity as the Mn spiral ordering. It closely tracks the evolution of the ferroelectric polarization. Below T-N(Dy) where Dy spins order commensurately, the polarization decreases to values similar for those of TbMnO3. The higher P-s found just above T-N(Dy) arises from the contribution of Dy spins so as to effectively increase the amplitude of the Mn spin spiral.
Title:
Transmission resonances through aperiodic arrays of subwavelength apertures
Authors:
Matsui, T; Agrawal, A; Nahata, A; Vardeny, ZV Author Full Names: Matsui, Tatsunosuke; Agrawal, Amit; Nahata, Ajay; Vardeny, Z. Valy
Source:
NATURE 446 (7135): 517-521 MAR 29 2007
Abstract:
Resonantly enhanced light transmission through periodic sub-wavelength aperture arrays perforated in metallic films(1) has generated significant interest because of potential applications in near-field microscopy, photolithography, displays, and thermal emission(2). The enhanced transmission was originally explained by a mechanism where surface plasmon polaritons ( collective electronic excitations in the metal surface) mediate light transmission through the grating(1,3). In this picture, structural periodicity is perceived to be crucial in forming the transmission resonances. Here we demonstrate experimentally that, in contrast to the conventional view, sharp transmission resonances can be obtained from aperiodic aperture arrays. Terahertz transmission resonances are observed from several arrays in metallic films that exhibit unusual local n-fold rotational symmetries, where n = 10, 12, 18, 40 and 120. This is accomplished by using quasicrystals with long-range order, as well as a new type of 'quasicrystal approximates' in which the long-range order is somewhat relaxed. We find that strong transmission resonances also form in these aperiodic structures, at frequencies that closely match the discrete Fourier transform vectors in the aperture array structure factor. The shape of these resonances arises from Fano interference(4) of the discrete resonances and the non-resonant transmission band continuum related to the individual holes(5). Our approach expands potential design parameters for aperture arrays that are aperiodic but contain discrete Fourier transform vectors, and opens new avenues for optoelectronic devices.

Update: 23-Mar-2007

Title:
(Al63Cu25Fe12)(p)/A356 aluminum alloy composites prepared by spray co-deposition
Authors:
Li, XP; Xu, Z Author Full Names: Li Xiao-ping; Xu Zhou
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA 16: S1362-S1365 Sp. Iss. 3 DEC 2006
Abstract:
A novel Al-based composite material (Al63Cu25Fe12)(p)/A356 was prepared by spray co-deposition. It is revealed that the reinforcement of Al63Cu25Fe12 quasicrystalline Particles disperses uniformly in the composite with small crystalline grain structure of about 10 mu m. The reaction between the Al63Cu25Fe12 quasicrystalline particle and the matrix metal is constrained or depressed because of the high cooling velocity in the process of spray co-deposition. Compared with the composite reinforced by non-continuous ceramics particle, the aging harden behavior of the composites of (Al63Cu25Fe12)(p)/A356 has outstanding characteristics with less time on aging peak happening and with higher hardening rate. The mechanical properties of the composites evidently enhance except plastic strain.
Title:
As-cast microstructure of Mg-Al-Zn magnesium alloys
Authors:
Zhang, J; Pan, FS; Yang, MB; Li, ZS Author Full Names: Zhang Jing; Pan Fu-sheng; Yang Ming-bo; Li Zhong-sheng
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA 16: S1655-S1659 Sp. Iss. 3 DEC 2006
Abstract:
The research achievements on as-cast microstructure in Mg-Al-Zn alloy were summarized. Under permanent mould cast condition, there are four kinds of primary compounds with distinct crystallographic morphology, Mg17Al12(gamma), Mg-32(Al,Zn)(49) (tau), MgZn (epsilon) and a ternary icosahedral quasi-crystalline compound (Q). Accordingly, Mg-Al-Zn alloy can be grouped into gamma-, tau-, epsilon- and Q-type alloy by each characteristic compound. The volume fraction Of gamma-Mg17Al12 in commercial gamma-type alloy increases with increasing Al content. MgZn and Mg chi Al gamma Znz ternary complex compounds emerge with the change of the element content Al and Zn and Zn/Al concentration ratio. A practical phase diagram showing microstructure constituent change with composition was proposed. The addition of micro-alloying elements Y and Sr results in not only obvious refinement of eutectic cluster but also eutectic morphological change from block to granule.
Title:
Effect of erbium on microstructure and thermal compressing flow behavior of Mg-6Zn-0.5Zr alloy
Authors:
Wang, ZJ; Zhang, CB; Shao, XH; Cui, JZ; Le, QC Author Full Names: Wang Zhong-jun; Zhang Cai-bei; Shao Xiao-hong; Cui Jian-zhong; Le Qi-chi
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA 16: S1774-S1778 Sp. Iss. 3 DEC 2006
Abstract:
A series of thermal compressing tests of Mg-6Zn-0.5Zr and Mg-6Zn-0.5Zr-1Er alloys were performed on a Gleeble-1500D thermal simulator. The microstructures of thermal compressed Mg-6Zn-0.5Zr and Mg-6Zn-0.5Zr-1Er alloys were determined by optical microscopy, transmission electron microscopy and X-ray diffractometry. The results show that Mg-6Zn-0.5Zr alloy mainly consists of alpha-Mg and MgZn(2)phase, while Mg-6Zn-0.5Zr-1Er alloy comprises a-Mg phase, coarse Mg3Zn4Er2 eutectic, rod-liked Mg3Zn4Er2 precipitated phase, fine I phase particle (Mg3Zn6Er, icosahedral quasicrystal structure). The peak flow stress becomes larger with increasing strain rate and erbium addition at the same temperature, and gets smaller with increasing deformation temperature at the same strain rate. The deformation activation energy increases with increasing temperature, strain rate and erbium addition. In addition, it is observed that the growth of dynamic recrystallization (DRX) grains of Mg-6Zn-0.5Zr-1Er alloy was markedly suppressed due to the pinning effect of fine I phase and Mg3Zn4Er2 phase during thermal compression.
Title:
Effect of Mg-Zn-Y quasicrystals on microstructure and mechanical properties of AZ91 alloy
Authors:
Zhang, JS; Pei, LX; Du, HW; Xu, CX; Lu, BF; Liang, W Author Full Names: Zhang Jin-shan; Pei Li-xia; Du Hong-wei; Xu Chun-xiang; Lu Bin-feng; Liang Wei
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA 16: S1884-S1887 Sp. Iss. 3 DEC 2006
Abstract:
The influence of the additions of Mg-Zn-Y quasicrystals-containing master alloy on the microstructures and mechanical properties of AZ91 alloy under conventional casting condition was studied using XRD, SEM equipped with energy dispersive spectrometer (EDS). The results show that the microstructure of Mg-Zn-Y quasicrystals reinforced AZ91 alloy consists of alpha-Mg supersaturating solid solution, beta-Mg17Al12 phase and quasicrystals phase. Quasicrystals particles with excellent elevated temperature stability are dispersively distributed in the a-Mg matrix or at grain boundaries. After the addition. of quasicrystals-containing master alloy, the matrix microstructure of AZ91 alloy is obviously grain-refined. The morphology of beta-Mg17Al12 phase changes from continuous nets to discrete nets. At room and elevated temperatures mechanical properties of AZ91 alloy are also improved dramatically. The utility of Mg-Zn-Y quasicrystals as a reinforced phase provides new theoretical basis and technical support for the composite strengthening of magnesium alloys.
Title:
Interfaces of bismuth with Al-Cu-Fe icosahedral quasicrystal
Authors:
Singh, A; Tsai, AP Author Full Names: Singh, A.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE LETTERS 87 (2): 85-94 FEB 2007
Abstract:
In a transmission electron microscopy study, it is shown that bismuth makes a better lattice match with an icosahedral quasilattice than with a crystalline lattice. A common orientation relationship is [0001]parallel to 2f (two-fold axis), {11 (2) over bar0}parallel to 5f (five-fold plane), in which a match of prominent planes and axes occurs. The match in the reciprocal-space and lattice images indicate epitaxy at the interfaces. In a variant of this orientation relationship, [0001]parallel to 2f, {01 (1) over bar2}parallel to 5f, where {0 (1) over bar 12} and five-fold are the closest-packed planes in bismuth and the icosahedral phase, respectively.
Title:
Al-Pd-Mn icosahedral quasicrystal: deformation mechanisms in the brittle domain
Authors:
Texier, M; Joulain, A; Bonneville, J; Thilly, L; Rabier, J Author Full Names: Texier, M.; Joulain, A.; Bonneville, J.; Thilly, L.; Rabier, J.
Source:
PHILOSOPHICAL MAGAZINE 87 (10): 1497-1511 APR 1 2007
Abstract:
The extreme brittleness of Al-Pd-Mn quasi-crystalline alloys over a wide range of temperatures drastically restricts investigation of their plastic deformation mechanisms over a small high-temperature regime. Recently, plastic deformation of Al-Pd-Mn quasicrystal has been achieved in the brittle domain (20 <= T <= 690 degrees C) using specific deformation devices, which combined a uniaxial compression deformation or a shear deformation with a hydrostatic pressure confinement (0.35-5GPa). Results of these experimental techniques, which provide various deformation conditions giving rise to a range of Al-Pd-Mn plastic features in the brittle domain, are discussed. On this basis, we propose that low and intermediate temperature plastic properties of Al-Pd-Mn are controlled by non-planar dislocation core extensions specific to the non-periodic Structure.
Title:
Ferroelectric transition induced by the incommensurate magnetic ordering in LiCuVO4
Authors:
Naito, Y; Sato, K; Yasui, Y; Kobayashi, Y; Kobayashi, Y; Sato, M Author Full Names: Naito, Yutaka; Sato, Kenji; Yasui, Yukio; Kobayashi, Yusuke; Kobayashi, Yoshiaki; Sato, Masatoshi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 (2): Art. No. 023708 FEB 2007
Abstract:
A ferroelectric transition occurring simultaneously with a helical spin order has been found in both the polycrystalline and single-crystal samples of LiCUVO4. The system has Cu2+ spins (s = 1/2) of the CuO2 chains formed of edge-sharing CuO4 squares. Possibly due to the frustrated nature caused by a competition between the nearest-neighbor and next-nearest-neighbor exchange interactions, Cu spins exhibit, as has been already reported, the helical magnetic order with the incommensurate modulation vector Q along the chain direction and with the helical axis e(3) perpendicular to the CuO4 squares. The electric polarization P can be understood by the recently predicted relation P proportional to Q x e(3). The transition temperature has been found to be gradually suppressed by the applied magnetic field.
Title:
Ferrimagnetic and long period antiferromagnetic phases in high spin Heisenberg chains with D-modulation
Authors:
Hida, K Author Full Names: Hida, Kazuo
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 (2): Art. No. 024714 FEB 2007
Abstract:
The ground state properties of the high spin Heisenberg chains with alternating single site anisotropy are investigated by means of the numerical exact daigonaization and DMRG method. It is found that the ferrimagnetic state appears between the Haldane phase and period doubled Neel phase for the integer spin chains. On the other hand, the transition from the Tomonaga-Luttinger liquid state into the ferrimagnetic state takes place for the half-odd-integer spin chains. In the ferrimagnetic phase, the spontaneous magnetization varies continuously with the modulation amplitude of the single site anisotropy. Eventually, the magnetization is locked to fractional values of the saturated magnetization. These fractional values satisfy the Oshikawa-Yamanaka-Affleck condition. The local spin profile is calculated to reveal the physical nature of each state. In contrast to the case of frustration induced ferrimagnetism, no incommensurate magnetic superstructure is found.
Title:
Role of cation demixing and quasicrystal formation and breakup on the stability of smectitic colloids
Authors:
Pils, JRV; Laird, DA; Evangelou, VP Author Full Names: Pils, Jutta R. V.; Laird, David A.; Evangelou, Vasilios P.
Source:
APPLIED CLAY SCIENCE 35 (3-4): 201-211 FEB 2007
Abstract:
The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory has been extensively used to explain colloid stability. This study investigated the effect of demixing of monovalent and divalent cations and crystalline swelling on the breakup and formation of smectite quasicrystals (QCs) and how these processes affect flocculation and dispersion of natural soil clay-humic complexes. The results indicated that in a Ca-dominated system the formation of large QCs enhanced flocculation and that increasing the concentration of Na+, K+, or NH4+ resulted in the breakup of large Ca-QCs, which enhanced dispersion. In low ionic strength systems, dispersion was caused by expanded double layers (DLVO) and the formation of small QCs. X-ray diffraction analyses showed that as large Ca-QCs breakup, monovalent cations resided primarily on the external surfaces and Ca2+ was preferentially retained in the interlayers. In high ionic strength systems increasing concentrations of monovalent cations also decreased the size of QCs but the effect was partially counteracted by compression of double layers between QCs. X-ray diffraction analyses indicated that monovalent cations were sorbed on both the external surfaces and in the interlayers in high ionic strength systems. (C) 2006 Elsevier B.V. All rights reserved.
Title:
Structures of incommensurate and commensurate composite crystals NaxCuO2 (x=1.58, 1.6, 1.62)
Authors:
van Smaalen, S; Dinnebier, R; Sofin, M; Jansen, M Author Full Names: van Smaalen, Sander; Dinnebier, Robert; Sofin, Mikhail; Jansen, Martin
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 63: 17-25 Part 1 FEB 2007
Abstract:
NaxCuO2 (x similar or equal to 1.6) has been synthesized for different compositions x, resulting in both commensurate and incommensurate composite crystals. The crystal structures are reported for two incommensurate compounds (x = 1.58 and 1.62) determined by Rietveld refinements against X-ray powder diffraction data. The incommensurate compounds and commensurate Na8Cu5O10 (X = 1.6) are found to possess similar structures, with valence fluctuations of Cu2+/Cu3+ as the origin of the modulations of the CuO2 subsystems; the displacive modulations of Na being defined by the closest Na - O contacts between the subsystems. A comparison of the structure models obtained from single-crystal X-ray diffraction, synchrotron-radiation X-ray powder diffraction and Xray powder diffraction with Cu K alpha(1) radiation indicates that single-crystal X-ray diffraction is by far the most accurate method, while powder diffraction with radiation from an Xray tube provides the least accurate structure model.

Update: 16-Mar-2007

Title:
The effect of the addition of Ta on the structure, crystallization and mechanical properties of Zr-Cu-Ni-Al-Ta bulk metallic glasses
Authors:
Liu, L; Chan, KC; Sun, M; Chen, Q Author Full Names: Liu, L.; Chan, K. C.; Sun, M.; Chen, Q.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 445: 697-706 FEB 15 2007
Abstract:
Zr-based bulk metallic glasses (BMGs) or bulk metallic glass matrix composites (BMGCs) have been prepared by using a copper-mold casting in the Zr65-xTaxCu17.5Al7.5Ni10 (where x = 1-10 at%) alloy system while varying the Ta content. A monolithic amorphous phase of BMG was achieved when Ta was less than 2 at%, while amorphous matrix composites reinforced by Ta-solid solutions were obtained when Ta is 5 at% or higher. The addition of Ta also affected significantly the crystallization of the amorphous phase. A multi-step process of crystallization with a preferential formation of quasicrystals occurred in the alloys containing 2-5 at% Ta, while a single-step pathway of crystallization with the formation of stable Zr-Cu intermetallic compounds took place when Ta was beyond this range. In addition, a quasi-static compression test revealed that both fracture strength and plasticity of the base BMG were remarkably enhanced as Ta content increased. The effect of the addition of Ta on the structure; crystallization process; and deformation behavior of the Zr-based alloys is discussed. (c) 2006 Elsevier B.V. All rights reserved.
Title:
The Pr2Se3-PrSe2 system: Studies of the phase relationships and the modulated crystal structure of PrSe1.85
Authors:
Doert, T; Graf, C; Schmidt, P; Vasilieva, IG; Simon, P; Carrillo-Cabrera, W Author Full Names: Doert, Thomas; Graf, Christian; Schmidt, Peer; Vasilieva, Inga G.; Simon, Paul; Carrillo-Cabrera, Wilder
Source:
JOURNAL OF SOLID STATE CHEMISTRY 180 (2): 496-509 FEB 2007
Abstract:
Thermochemical investigations have been carried out to elucidate the phase relationships in the system Pr2Se3-PrSe2 and to construct the p(Se)-T-x diagram. The result of the tensimetric and thermogravimetric studies showed the thermal decomposition of PrSe2 to be a step-wise process due to the formation of a sequence of discrete intermediate phases with the compositions PrSe1.9, PrSe1.85, PrSe1.8, and Pr2Se3. PrSe1.85 and PrSe1.8 have been previously considered as selenium-deficient non-stoichiometric phases. Conclusions derived from the thermodynamic study were verified by X-ray diffraction and electron microscopy studies on single crystals of PrSe1.85 which were obtained from reactions of praseodymium and selenium in stoichiometric amounts in a KCl flux at 1070K. A two-dimensional modulation could be observed for PrSe1.85 in X-ray and high-resolution transmission electron microscopy. The structure of PrSe1.85 was solved and refined in superspace group P4/n(alpha beta 1/2)(beta-alpha 1/2)00 with lattice parameters of a = 4.137(1) angstrom, c = 8.398(2) angstrom of the basic unit cell and alpha = beta = 0.293(1). The origin of the modulation can be attributed to a site occupancy wave and a charge density wave in its planar selenium layer. The experimentally determined magnetic moments indicate Pr3+ for the polyselenides PrSe2, PrSe1.9 and PrSe1.85. (c) 2006 Published by Elsevier Inc.
Title:
Electronic structure of spin-chain compounds: common features
Authors:
Schwingenschlogl, U; Schuster, C Author Full Names: Schwingenschloegl, U.; Schuster, C.
Source:
EUROPEAN PHYSICAL JOURNAL B 55 (1): 43-47 JAN 2007
Abstract:
The incommensurate composite systems M14Cu24O41 (M = Ca, Sr, La) are based on two fundamental structural units: CuO2 chains and Cu2O3 ladders. We present electronic structure calculations within density functional theory in order to address the interrelations between chains and ladders. The calculations account for the details of the crystal structure by means of a unit cell comprising 10 chain and 7 ladder units. It turns out that chains and ladders can be treated independently, which allows us to introduce a model system based on a reduced unit cell. For the CuO2 chains, we find two characteristic bands at the Fermi energy. Tight binding fits yield nearest and next-nearest neighbour interactions of the same order of magnitude.
Title:
Magnetic structures and crystal field in the heavy electron materials YbAgGe and YbPtIn
Authors:
Bonville, P; Rams, M; Krolas, K; Sanchez, JP; Canfield, PC; Trovarelli, O; Geibel, C Author Full Names: Bonville, P.; Rams, M.; Krolas, K.; Sanchez, J. -P.; Canfield, P. C.; Trovarelli, O.; Geibel, C.
Source:
EUROPEAN PHYSICAL JOURNAL B 55 (1): 77-84 JAN 2007
Abstract:
We have examined the magnetic properties of the heavy electron compounds YbAgGe and YbPtIn by Yb-170 Mossbauer spectroscopy down to 0.1 K, and the crystal field properties of YbAgGe by Perturbed Angular Correlations (PAC) measurements up to 900 K. In YbAgGe, we show that each of the two magnetically ordered phases below 0.8 K involves a specific incommensurate modulation of the Yb moment. An analysis of existing low temperature specific heat data suggests the persistence of fluctuations of the correlated Yb spins down to 0.1 K. The PAC data allow to discriminate among proposed Yb3+ crystal field level schemes. In YbPtIn, we show that the low temperature magnetic order phase has an antiferro-para structure, where zero moment Yb ions coexist with large moment ones, and that a 90 degrees moment reorientation occurs at 1.4 K.
Title:
The nanoblock structure of natural isoferroplatinum (Pt3Fe) and problem of quasicrystalline state of some platinum group minerals
Authors:
Distler, VV; Bityutskaya, LA; Kryachko, VV; Yudovskaya, MA; Grechkina, MV; Bogatikov, EV Author Full Names: Distler, V. V.; Bityutskaya, L. A.; Kryachko, V. V.; Yudovskaya, M. A.; Grechkina, M. V.; Bogatikov, E. V.
Source:
DOKLADY EARTH SCIENCES 407 (2): 335-338 FEB 2006
Title:
Pd0.213Cd0.787 and Pd0.235Cd0.765 structures: Their long c axis and composite crystals, chemical twinning, and atomic site preferences
Authors:
Schmidt, JT; Lee, S; Fredrickson, DC; Conrad, M; Sun, JL; Harbrecht, B Author Full Names: Schmidt, Joshua Teal; Lee, Stephen; Fredrickson, Daniel C.; Conrad, Matthias; Sun, Junliang; Harbrecht, Bernd
Source:
CHEMISTRY-A EUROPEAN JOURNAL 13 (5): 1394-1410 2007
Abstract:
We present single-crystal studies of Pd0.213Cd0.787 and Pd0.235Cd0.765, synchrotron powder studies of Pd1-xCd, 0.755 >= x >= 0.800, and LDA-DFT and extended Huckel (eH) calculations on these or related phases. The two single-crystal structures have a, b, and c axis lengths of 9.9013(7), 14.0033(10), 37.063(24) and 9.9251(3), 14.0212(7), 60.181(3) angstrom, respectively and they crystallize in the space groups Ccme and F2mm, respectively (solved as (3+1)-dimensional crystals their most convenient superspace group is Xmmm(00 gamma)s00). The structures have two different structural components each with their own separate axis parameters. Powder data shows that the ratio of these separate axes (S/L) varies from 1.615 to 1.64, values near the golden mean (1.618). For Pd0.213Cd0.787, different Pd and Cd site occupancies lead to variation in the R factor from 2.6-3.6%. The site occupancy pattern with the lowest R factor (among the 26820 variants studied) is the exact site occupancy pattern predicted by LDA-DFT parameterized eH Mulliken charge populations. The phases can be understood through a chemical twinning principle found in gamma-brass, the parent structure for the above phases (a relation with the MgCu2 Laves phase is also noted). This twinning principle can be used to account for Cd and Pd site preferences. At the same time there is a clean separation among the Cd and Pd atoms for the two separate chain types at height b=0 and 1/2. These results indicate that Cd:Pd stoichiometry plays a role in phase stability.
Title:
[SrF0.8(OH)(0.2)](2.526)[Mn6O12]: Columnar rock-salt fragments inside the todorokite-type tunnel structure
Authors:
Abakumov, AM; Hadermann, J; Van Tendeloo, G; Kovba, ML; Skolis, YY; Mudretsova, SN; Antipov, EV; Volkova, OS; Vasiliev, AN; Tristan, N; Klingeler, R; Buchner, B Author Full Names: Abakumov, Artem M.; Hadermann, Joke; Van Tendeloo, Gustaaf; Kovba, Maksim L.; Skolis, Yuri Ya.; Mudretsova, Svetlana N.; Antipov, Evgeny V.; Volkova, Olga S.; Vasiliev, Aleksandr N.; Tristan, Natalia; Klingeler, Ruediger; Buechner, Bernd
Source:
CHEMISTRY OF MATERIALS 19 (5): 1181-1189 MAR 6 2007
Abstract:
A new type of composite structure is described consisting of the todorokite-type [Mn6O12] framework with large square tunnels accommodating columnar fragments of the rock-salt structure. The crystal structure of the new todorokite-type [SrF0.8(OH)(0.2)](2.526)[Mn6O12] compound is solved from transmission electron microscopy, and the structure of its anhydrous form [SrF0.8O0.1](2.526)[Mn6O12] is refined from X-ray powder diffraction data. The [Mn6O12] framework consists of mutually perpendicular walls built of three edge-sharing rutile-type strings of MnO6 octahedra delimiting large square tunnels with the size of 3 x 3 octahedra. The interior space in the tunnels is filled with rock-salt type [Sr(F,OH)](4) columns. The structure can be interpreted as being an incommensurate composite structure with the modulation vector q(1) = gamma c(1)* (gamma = 0.63157(3)) parallel to the direction of tunnel propagation. The octahedral tunnel walls compose subsystem I with a [Mn6O12] composition and a periodicity c(1) = 2.84 angstrom, whereas the [Sr(F,OH)](4) columns belong to subsystem II with a periodicity c(1)/gamma = 4.49 angstrom, resulting in a [Sr(F,OH)](4 gamma)[Mn6O12] composition. [SrF0.8(OH)(0.2)](2.526)[Mn6O12] demonstrates a much larger number of cations inside the tunnels in comparison with the known synthetic and natural marine todorokites. The [SrF0.8(OH)(0.2)](2.526)[Mn6O12] compound shows a spin-glass behavior below T* approximate to 26 K with a dominant *antiferromagnetic* correlation.

Update: 9-Mar-2007

Title:
Hidden octupole order in URu2Si2
Authors:
Hanzawa, K Author Full Names: Hanzawa, Katsurou
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (7): doi:10.1088/0953-8984/19/7/072202 FEB 21 2007
Abstract:
We propose that the hidden order in URu2Si2 is an incommensurate octupole order, which is derived from a spin-1 XXZ model with XX octupole and Z dipole interactions based on the singlet - doublet crystal-field level scheme. The octupole moments break time-reversal invariance and give rise to finite hyperfine fields on the nuclei of the ligand Si and Ru ions. In order for the hyperfine fields to be observed as a nuclear magnetic resonance ( NMR) linewidth, the order must be incommensurate, with the ordering vector determined so as to account for the Si-29 NMR linewidth data quantitatively.
Title:
Diffraction with a coherent X-ray beam: dynamics and imaging
Authors:
Livet, F Author Full Names: Livet, Frederic
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 63: 87-107 Part 2 MAR 2007
Abstract:
Methods for carrying out coherent X-ray scattering experiments are reviewed. The brilliance of the available synchrotron sources, the characteristics of the existing optics, the various ways of obtaining a beam of controlled coherence properties and the detectors used are summarized. Applications in the study of the dynamics of speckle patterns are described. In the case of soft condensed matter, the movement of inclusions like fillers in polymers or colloidal particles can be observed and these can reflect polymer or liquid-crystal fluctuations. In hard condensed-matter problems, like phase transitions, charge-density waves or phasons in quasicrystals, the study of speckle fluctuations provides new time-resolved methods. In the domain of lensless imaging, the coherent beam gives the modulus of the sample Fourier transform. If oversampling conditions are fulfilled, the phase can be obtained and the image in the direct space can be reconstructed. The forthcoming improvements of all these techniques are discussed.
Title:
Hybrid quasiperiodic-periodic structures constructed by projection in two stages
Authors:
Ben-Abraham, SI; Quandt, A Author Full Names: Ben-Abraham, S. I.; Quandt, Alexander
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 63: 177-185 Part 2 MAR 2007
Abstract:
A two-stage variant of the cut-and-project method is presented, in which a periodic structure is cut and projected in a high-dimensional space onto three-dimensional physical space so that a second cut and projection onto a plane yields a quasiperiodic structure. The method is applied to the cases of octagonal, dodecagonal and pentagonal/decagonal symmetry. The focus is on the three-dimensional intermediate hybrid structures that are partly quasiperiodic and partly periodic. The method can be generalized to other symmetries as well as to include more intermediate steps.

Update: 2-Mar-2007

Title:
Pressure-temperature phase diagram of multiferroic Ni3V2O8
Authors:
Chaudhury, RP; Yen, F; dela Cruz, CR; Lorenz, B; Wang, YQ; Sun, YY; Chu, CW Author Full Names: Chaudhury, R. P.; Yen, F.; dela Cruz, C. R.; Lorenz, B.; Wang, Y. Q.; Sun, Y. Y.; Chu, C. W.
Source:
PHYSICAL REVIEW B 75 (1): Art. No. 012407 JAN 2007
Abstract:
The pressure-temperature phase diagram of multiferroic Ni3V2O8 is investigated for hydrostatic pressures up to 2 GPa. The stability range of the ferroelectric phase associated with the incommensurate helical spin order is reduced by pressure and ferroelectricity is completely suppressed at the critical pressure of 1.64 GPa at 6.2 K. Thermal expansion measurements at ambient pressure show strong steplike anomalies of the lattice parameters associated with the lock-in transition into the commensurate paraelectric phase. The expansion anomalies are highly anisotropic; the related volume change is consistent with the high-pressure phase diagram.
Title:
Interpretation of low-temperature nuclear quadrupole resonance spectra in La1.875Ba0.125CuO4 in terms of two-dimensional spin superstructure
Authors:
Fine, BV Author Full Names: Fine, Boris V.
Source:
PHYSICAL REVIEW B 75 (1): Art. No. 014205 JAN 2007
Abstract:
This paper reanalyzes the low temperature nuclear quadrupole resonance (NQR) experiments in La1.875Ba0.125CuO4 by Hunt [Phys. Rev. B 64, 134565 (2001)] in an attempt to determine the dimensionality of spin modulations in this and other compounds of the lanthanum family of high temperature cuprate superconductors. It is concluded that the shape of the NQR spectra obtained by Hunt favors the two-dimensional pattern of spin modulations known as "grid" or "checkerboard." The paper also contains the discussion of charge patterns, which can accompany the above spin modulation.
Title:
First-principles calculations of cohesive energies in the Al-Co binary alloy system
Authors:
Mihalkovic, M; Widom, M Author Full Names: Mihalkovic, M.; Widom, M.
Source:
PHYSICAL REVIEW B 75 (1): Art. No. 014207 JAN 2007
Abstract:
The phase diagram of the Al-Co binary alloy system is intensively studied because of its importance for understanding decagonal quasicrystals, but remains imprecisely known due to the occurrence of many competing complex structures with composition close to Al13Co4. We apply first-principles total energy calculations to compare the cohesive energies of known and hypothetical structures. Our results confirm the experimentally established phase diagram in every detail except near Al13Co4, where the reported phases (Pearson symbols mC102 and oP102, both well-known decagonal quasicrystal approximants) turn out to be unstable at low temperatures. They may be stabilized at high temperatures by the entropy of aluminum vacancy hopping and low frequency vibrational modes. Under molecular dynamics a subset of Al atoms displays nearly liquid diffusive motion.
Title:
Multiple ground state competition under pressure in beta-Sr0.33V2O5
Authors:
Yamauchi, T; Ueda, H; Yamaura, J; Ueda, Y Author Full Names: Yamauchi, Touru; Ueda, Hiroaki; Yamaura, Jun-Ichi; Ueda, Yutaka
Source:
PHYSICAL REVIEW B 75 (1): Art. No. 014437 JAN 2007
Abstract:
Magnetic susceptibility and resistivity of beta-Sr0.33V2O5 were precisely measured under pressure. With increasing pressure, the charge order transition is suppressed and furthermore anomalous behaviors are observed, indicating two or more phases in the charge ordered phase and two phases in the charge disordered phase. High-pressure x-ray oscillation photographs confirm different modulation vectors in these phases, which suggests the "devil's staircase"-type phase transition as observed in alpha'-NaV2O5. The obtained P-T phase diagram displays competition among multiple ground states under pressure.
Title:
Melting of incommensurate-ferroelectric phase with magnetic field in multiferroic TbMnO3
Authors:
Argyriou, DN; Aliouane, N; Strempfer, J; Zegkinoglou, I; Bohnenbuck, B; Habicht, K; Zimmermann, MV Author Full Names: Argyriou, D. N.; Aliouane, N.; Strempfer, J.; Zegkinoglou, I.; Bohnenbuck, B.; Habicht, K.; Zimmermann, M. V.
Source:
PHYSICAL REVIEW B 75 (2): Art. No. 020101 JAN 2007
Abstract:
We have investigated the reentrant ferroelectric behavior of TbMnO3 under a c-axis-aligned magnetic field (H parallel to c) using neutron and x-ray single-crystal diffraction. We find that below T-N=41 K and at high field the incommensurate ordering of Mn spins melts and coincides with the disappearance of ferroelectricity. The paraelectric phase which emerges is characterized by a simple commensurate antiferomagnetic ordering. We suggest that the reentrance of ferroelectricity at low temperatures and high magnetic field coincides with the development of incommensurate Mn- and Tb-spin ordering.
Title:
Topologically induced semiconductivity in icosahedral Al-Pd-Re and its approximants
Authors:
Krajci, M; Hafner, J Author Full Names: Krajci, M.; Hafner, J.
Source:
PHYSICAL REVIEW B 75 (2): Art. No. 024116 JAN 2007
Abstract:
We demonstrate that the opening of a semiconducting band-gap in the electronic spectrum of the i-Al-Pd-Re quasicrystal and its approximants is due to the formation of a topological band-gap, in analogy to the band-gap found in the FeSi (B20) structure. In both systems we have identified a network of linear chains of alternating Si(Al) and transition-metal (TM) atoms extending along twofold symmetry directions. In i-Al-Pd-Re the chains of alternating Al and TM atoms extend from a center of the pseudo-Mackay (M) cluster over the surface of the Bergman cluster to the center of another neighboring M cluster. Substitutional Al/Pd defects and a fragmentation of the chains by phason defects lead to the formation of localized states in the band-gap. The band-gap of the real i-Al-Pd-Re quasicrystal is filled by localized states. The i-Al-Pd-Re quasicrystal thus behaves as a disordered semiconductor.
Title:
Boson peak and hybridization of acoustic modes with vibrations of nanometric heterogeneities in glasses
Authors:
Duval, E; Mermet, A; Saviot, L Author Full Names: Duval, E.; Mermet, A.; Saviot, L.
Source:
PHYSICAL REVIEW B 75 (2): Art. No. 024201 JAN 2007
Abstract:
The low-frequency dynamics in glasses is compared with that in icosahedral quasicrystals. For both arrangements of matter, the existence of nanometric heterogeneities, implying the existence of a nanometric inhomogeneous elastic network, is expected to play a crucial role. Thanks to this comparison, mostly based on inelastic x-ray (neutron) scattering data, it is proposed that the excess of vibrational density of states observed in both materials is due to the hybridization of longitudinal and transverse acoustic modes with modes localized around the heterogeneities.
Title:
Universal non-near-field focus of acoustic waves through high-symmetry quasicrystals
Authors:
Zhang, XD Author Full Names: Zhang, Xiangdong
Source:
PHYSICAL REVIEW B 75 (2): Art. No. 024209 JAN 2007
Abstract:
The focus behaviors of acoustic waves through high-symmetry quasicrystals (QC) have been investigated by using exact multi-scattering numerical simulation. We have found that eightfold, tenfold, and twelvefold two-dimensional (2D) QC slabs possess some universal features for non-near-field focus of the acoustic wave. The non-near-field focus of the acoustic wave can be realized by these QC slabs from very low packing density (filling fraction beta = 10%) to close packing (filling fraction beta = 40%) at large ranges of the frequency. The physical origin for such a superior feature has also been analyzed. Thus, it is anticipated that such a phenomenon can be potentially applied to phononic devices.
Title:
Superfluid suppression in d-wave superconductors due to disordered magnetism
Authors:
Atkinson, WA Author Full Names: Atkinson, W. A.
Source:
PHYSICAL REVIEW B 75 (2): Art. No. 024510 JAN 2007
Abstract:
The influence of static magnetic correlations on the temperature-dependent superfluid density rho(s)(T) is calculated for d-wave superconductors. In self-consistent calculations, itinerant holes form incommensurate spin density waves (SDW) which coexist with superconductivity. In the clean limit, the density of states is gapped, and rho(s)(T < T-c) is exponentially activated. In inhomogeneously doped cases, the SDW are disordered and both the density of states and rho(s)(T) obtain forms indistinguishable from those in dirty but pure d-wave superconductors, in accordance with experiments. We conclude that the observed collapse of rho(s) at x approximate to 0.35 in underdoped YBa2Cu3O6+x may plausibly be attributed to the coexistence of SDW and superconductivity.
Title:
Te-125 NMR studies of single-crystal CeTe3
Authors:
Chudo, H; Michioka, C; Itoh, Y; Yoshimura, K Author Full Names: Chudo, H.; Michioka, C.; Itoh, Y.; Yoshimura, K.
Source:
PHYSICAL REVIEW B 75 (4): Art. No. 045113 JAN 2007
Abstract:
We report Te-125 NMR studies for single crystals of CeTe3 between 10 and 307 K, under an applied field of H=7.4847 T along the a or b axis H parallel to ab and the c axis H parallel to c, respectively. We observed that the Te-125 NMR spectra consist of a superposition of broad and sharp peaks, which we assign to the signals of Te-125(1) in double Te(1) sheets and Te-125(2) in CeTe(2) bilayers, respectively. For H parallel to ab, a broad Te-125(1) NMR spectrum shows a powder pattern with three split lines, which is evidence for an incommensurate charge-density wave modulation. The Te-125(1) NMR spectrum with three lines broadens with cooling. Knight shifts widely distributed from -0.16% to +0.58% at 110 K indicate that a spin density of conduction electron is polarized from Ce local moments. For H parallel to c, a spectrum has a fine structure with three lines, and the linewidth of the Te-125(1) NMR spectrum is narrow compared with that for H parallel to ab. On the other hand, the anisotropic Knight shift of the Te-125(2), which is located at the CeTe(2) bilayer, is positive with proportion to the anisotropic bulk susceptibility for H parallel to ab and H parallel to c. The hyperfine coupling constants of Te-125(2) are nearly isotropic but the nuclear spin-lattice relaxation rate is strongly anisotropic, indicating the anisotropic spin fluctuations in this system. The nuclear spin-lattice relaxation rate of the Te-125(2) diverges due to the slowing down of spin fluctuations.
Title:
Spin-dependent tunneling in modulated structures of (Ga,Mn)As
Authors:
Sankowski, P; Kacman, P; Majewski, JA; Dietl, T Author Full Names: Sankowski, P.; Kacman, P.; Majewski, J. A.; Dietl, T.
Source:
PHYSICAL REVIEW B 75 (4): Art. No. 045306 JAN 2007
Abstract:
A model of coherent tunneling, which combines multiorbital tight-binding approximation with Landauer-Buttiker formalism, is developed and applied to all-semiconductor heterostructures containing (Ga,Mn)As ferromagnetic layers. A comparison of theoretical predictions and experimental results on spin-dependent Zener tunneling, tunneling magnetoresistance, and anisotropic magnetoresistance is presented. The dependence of spin current on carrier density, magnetization orientation, strain, voltage bias, and spacer thickness is examined theoretically in order to optimize device design and performance.
Title:
Structure formation of a layer of adatoms on a quasicrystalline substrate: Molecular dynamics study
Authors:
Bilki, B; Erbudak, M; Mungan, M; Weisskopf, Y Author Full Names: Bilki, Burak; Erbudak, Mehmet; Mungan, Muhittin; Weisskopf, Yves
Source:
PHYSICAL REVIEW B 75 (4): Art. No. 045437 JAN 2007
Abstract:
We study the formation of structure when a layer of adatoms is deposited onto a substrate with quasicrystalline order. Molecular dynamics calculations with simulated annealing show that the adsorbate layer forms ordered domains whose orientation is determined by the underlying substrate symmetry. The domain size is found to depend on the relative strength of the adatom interactions with each other and the substrate, as well as the cooling rate of the growing film. These results are consistent with our earlier low-energy electron diffraction studies of Al grown on the decagonal surface of an Al-Co-Ni quasicrystal.
Title:
Ni7-delta SnTe2: Modulated crystal structure refinement, electronic structure and anisotropy of electroconductivity
Authors:
Isaeva, AA; Baranov, AI; Doert, T; Popovkin, BA; Kulbachinskii, VA; Gurin, PV; Kytin, VG; Shtanov, VI Author Full Names: Isaeva, A. A.; Baranov, A. I.; Doert, Th.; Popovkin, B. A.; Kulbachinskii, V. A.; Gurin, P. V.; Kytin, V. G.; Shtanov, V. I.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 180 (1): 221-232 JAN 2007
Abstract:
Single crystals of Ni7-delta SnTe2 were grown during re-crystallization of the presynthesized powder in a two zone furnace. The modulated structure was solved and refined in the (3+2)-dimensional superspace group I4/mmm(0-alpha 0, alpha 00)0.ss.mm with lattice parameters a = 3.759(1) and c = 19.410(2) angstrom (measured at 153 K) and Z = 2. Satellite reflections observed in the diffraction images can be assigned to the incommensurate modulation vectors q(1) = da* and q(2) = db* with d = 0.410(1). The composition resulting from X-ray structure refinement is Ni5.81SnTe2. The structure model has been also developed in the orthorhombic (3 + 1)-dimensional superspace group Immm(alpha 00)00s assuming twinning according to [110], giving thus the composition Ni5.79SnTe2. The origin of the modulation can be attributed to a variation of the occupancy of the Ni(3) site in Ni/Te slabs of the structure. Band structure calculations on a commensurate approximant and single crystal electrical resistivity measurements reveal anisotropic metallic conductivity for this compound. ((c) 2006 Elsevier Inc. All rights reserved.
Title:
New misfit-layered cobalt oxide (CaOH)(1.14)CoO2
Authors:
Shizuya, M; Isobe, M; Baba, Y; Nagai, T; Osada, M; Kosuda, K; Takenouchi, S; Matsui, Y; Takayama-Muromachi, E Author Full Names: Shizuya, Mitsuyuki; Isobe, Masaaki; Baba, Yuji; Nagai, Takuro; Osada, Minoru; Kosuda, Kosuke; Takenouchi, Satoshi; Matsui, Yoshio; Takayama-Muromachi, Eiji
Source:
JOURNAL OF SOLID STATE CHEMISTRY 180 (1): 249-259 JAN 2007
Abstract:
We synthesized a new cobalt oxide (CaOH)(1.14)CoO2 by utilizing a high-pressure technique. X-ray and electron diffraction studies revealed that the compound has a layered structure that consists of Cdl(2)-type CoO2 layers and rock-salt-type double CaOH atomic layers. The two subcells have incommensurate periodicity along the a-axis, resulting in a misfit-layered structure. From resistivity and Seebeck coefficient measurements, we have shown that the two-dimensional (2-D) variable-range hopping (VRH) regime with hole conduction is dominant at low temperature for this compound. As temperature increases, the conduction mechanism undergoes crossover from the 2-D VRH regime to a thermal activation-energy-type regime. (c) 2006 Elsevier Inc. All rights reserved.
Title:
Structural characterization of the hollandite host lattice for the confinement of radioactive cesium: Quantification of the amorphous phase taking into account the incommensurate modulated character of the crystallized part
Authors:
Leinekugel-Le-Cocq-Errien, AY; Deniard, P; Jobic, S; Gautier, E; Evain, M; Aubin, V; Bart, F Author Full Names: Leinekugel-le-Cocq-Errien, A. Y.; Deniard, P.; Jobic, S.; Gautier, E.; Evain, M.; Aubin, V.; Bart, F.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 180 (1): 322-330 JAN 2007
Abstract:
X-ray patterns of the Ba1Cs0.28Fe0.82Al1.46Ti5.72O16 compound evidence two wide peaks at low angle in addition to the well defined peaks of the I4/m hollandite structure type. Two hypotheses have been explored to account for these features: the coexistence of the hollandite phase with an amorphous phase and the appearance of a commensurate or incommensurate modulated structure associated with a cationic ordering, as proposed in the literature. Actually.. even if the amorphous phase quantification by the Rietveld method reveals about 15 wt% of non-crystalline phase in some of the powdered sample, the origin of the two wide peaks was found to stem from the incommensurate modulated character of the hollandite structure type (super space group I4/rn(00 gamma)00) with a distribution of the modulation wavevectors presumably related to slight chemical composition changes. (c) 2006 Elsevier Inc. All rights reserved.
Title:
Boundary conditions for plate bending in one-dimensional hexagonal quasicrystals
Authors:
Gao, Y; Xu, SP; Zhao, BS Author Full Names: Gao, Yang; Xu, Si-peng; Zhao, Bao-sheng
Source:
JOURNAL OF ELASTICITY 86 (3): 221-233 MAR 2007
Abstract:
For plate bending in one-dimensional (1D) hexagonal quasicrystals (QCs), the reciprocal theorem and the general solution for QCs media are applied in a novel way to obtain the appropriate stress and mixed boundary conditions accurate to all order for plates of general edge geometry and loadings. Through generalizing the method developed by Gregory and Wan, a set of necessary conditions on the edge-data for the existence of a rapidly decaying solution is established. The prescribed data must satisfy these conditions in order that they should generate a decaying state. When a set of stress edge-data or mixed edge-data is imposed on the plate edge, these decaying state conditions for the case of axisymmetric deformation of 1D hexagonal QC plates are derived explicitly. They are then used for the correct formulation of boundary conditions for the plate theory solution (or the interior solution). Furthermore, in the absence of phonon-phason fields coupling effect, corresponding necessary conditions for the case of transversely isotropic elastic plates are derived subsequently, and their isotropic elastic counterparts are also obtained.

Update: 23-Feb-2007

Title:
Structural changes in ab-plane of Zn doped Bi-2212HTSC single crystals
Authors:
Lovleena; Bidikin, IK; Kholkin, AL; Kumar, B Author Full Names: Lovleena; Bidikin, I. K.; Kholkin, A. L.; Kumar, Binay
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 451 (1): 44-48 JAN 1 2007
Abstract:
Single crystals of undoped and 1% Zn-doped Bi-2212 are grown by self-flux slow cooling method tinder similar growth conditions. T,(AT,) are found to be 84 K (2 K) and 82 K (8 K) for undoped and doped samples respectively. Effect of Zn doping on structure and modulation is studied. Different change in the value of a- and b-axes are observed resulting in a transformation of structure from tetragonal to orthorhombic one. However, no effective change in modulation is there. Distortions are compared in c- and b-axes for undoped and doped samples. The asymmetry in position and intensity of satellite peaks has been discussed. The value of a in excess of b has been reported for the first time. These results are discussed in terms of valancy, coordinates and position of occupancy of Zn ions vis-A-vis those of Cu- ions in Cu-O plane of the structure. (c) 2006 Published by Elsevier B.V.
Title:
Coupled negative magnetocapacitance and magnetic susceptibility in a Kagome staircase-like compound Co3V2O8
Authors:
Bellido, N; Martin, C; Simon, C; Maignan, A Author Full Names: Bellido, Natalia; Martin, Christine; Simon, Charles; Maignan, Antoine
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (5): Art. No. 056001 FEB 7 2007
Abstract:
The dielectric constant of the Kagome staircase-like Co3V2O8 polycrystalline compound has been measured as a function of temperature andmagnetic field up to 14 T. It is found that the application of an external magnetic field suppresses the anomaly for the dielectric constant beyond 6.1 K. Furthermore, its magnetic field dependence reveals a negative magnetocapacitance which is proportional to the magnetic susceptibility, suggesting a common magnetostrictive origin for the magnetic field dependence of the two quantities. This result is very different from that obtained from the isostructural compound Ni3V2O8 that presents a peak in the dielectric constant at the incommensurate magnetic phase transition coupled to a sign change of the magnetocapacitance.
Title:
Structural and thermal properties of Xe on the Pb(111) surface studied by low-energy electron diffraction
Authors:
Ferralis, N; Li, HI; Hanna, KJ; Stevens, J; Shin, H; Pan, FM; Diehl, RD Author Full Names: Ferralis, N.; Li, H. I.; Hanna, K. J.; Stevens, J.; Shin, H.; Pan, F. M.; Diehl, R. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (5): Art. No. 056011 FEB 7 2007
Abstract:
The growth, structures and thermodynamics of Xe adsorbed on Pb(111) were studied with low-energy electron diffraction (LEED). Measurements of equilibrium adsorption isobars indicate layer-by-layer growth for at least two layers in the temperature range 60-90 K, and an isosteric heat of adsorption of 191 +/- 10 meV for the first Xe layer and 158 +/- 20 meV for the second Xe layer. The monolayer has an incommensurate hexagonal structure with a lattice parameter similar to that found in bulk Xe, and its thermal expansion coefficient was measured to be 9 +/- 1 x 10(-4) K-1. The average overlayer substrate spacing was determined from a constant- momentum- transfer analysis of the LEED intensities to be 3.95 +/- 0.10 A. Vibrational information was obtained from measuring the decay of the diffraction intensities as a function of temperature. The perpendicular root mean square displacement of the Xe atoms at 50 K is 0.12 +/- 0.01 A, giving an effective Debye temperature for adsorbed Xe of 37 +/- 2 K. The corresponding vibrational energy for the perpendicular mode of Xe is 3.2 +/- 0.3 meV.
Title:
Deformation behavior of Mg-Zn-Gd-based alloys reinforced with quasicrystal and Laves phases at elevated temperatures
Authors:
Liu, Y; Yuan, GY; Ding, WJ; Cheng, L Author Full Names: Liu, Yong; Yuan, Guangyin; Ding, Wenjiang; Lu, Cheng
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 427 (1-2): 160-165 JAN 16 2007
Abstract:
Mg-Zn-Gd and Mg-Zn-Gd-Cu alloys, reinforced with quasicrystal (I-phase) and Laves phases, have been produced by extrusion process. The deformation behavior of these two alloys at room temperature and at elevated temperatures was investigated, respectively. The Mg-Zn-Gd alloy has high UTS of 305 MPa and elongation of 14.6% due to the strengthening effect of I-phase, while Mg-Zn-Gd-Cu alloy with Laves phases has higher yield stress of 217 MPa due to more strengthening particles and lower elongation of 11.9% resulting from the low content of I-phase and low symmetry of Laves phase due to which it cleaves easily (while the I-phase has a very high symmetry and therefore isotropic in nature). At high temperatures, Mg-Zn-Gd alloy shows large strain due to the excellent plastic compatibility coming from low interfacial energy of I-phase/matrix; Mg-Zn-Gd-Cu alloy has higher level of flow stress, strain exponent and more stable microstructure than Mg-Zn-Gd alloy due to better heat-resistance supplied by collaboration of Laves phases and quasicrystal phase, which can provide more effective pinning effect and suppress grain growth during deformation. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Effect of Mn on the formation of Mg-based spherical icosahedral quasicrystal phase
Authors:
Zhang, JS; Du, HW; Liang, W; Xu, CX; Lu, BF Author Full Names: Zhang, Jinshan; Du, Hongwei; Liang, Wei; Xu, Chunxiang; Lu, Binfeng
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 427 (1-2): 244-250 JAN 16 2007
Abstract:
Three-dimensional spherical icosahedral quasicrystalline phase (I-phase) has been obtained by introducing Mn into Mg-Zn-Y alloy under normal casting conditions. Due to the addition of Mn, Mg45Zn47Y5Mn3 primary I-phase,which is thermodynamically stable and homogeneously distributed, has been generated instead of decahedral quasicrystalline phase during the solidification process; morphology of primary I-phase in the solidification microstructure changed from petal-like one (60-80 mu m) to spherical one (<= 20 mu m). When the Mn content reached 2 wt.%, volume fraction Of Mg45Zn47Y5Mn3 spherical I-phase in as-cast Mg-Zn-Y-Mn master alloy was about 30-40%. Meanwhile, primary I-phase with highest spheroidization ratio and highest circular degree can be obtained; brittleness and hardness of as-cast Mg-Zn-Y-Mn master alloy reduced while density of as-cast Mg-Zn-Y-Mn master alloy increased. By analyzing spheroidization mechanism of Mg-based I-phase, spheroidization theory of Mg-based quasicrystals could be enriched a lot and a new way will be provided for the industrialization of Mg-based cluasicrystals. (c) 2006 Elsevier B.V. All rights reserved.
Title:
New stable decagonal quasicrystal in the system Al-Ir-Os
Authors:
Katrych, S; Weber, T; Kobas, A; Massuger, L; Palatinus, L; Chapuis, G; Steurer, W Author Full Names: Katrych, S.; Weber, Th.; Kobas, A.; Massueger, L.; Palatinus, L.; Chapuis, G.; Steurer, W.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 428 (1-2): 164-172 JAN 31 2007
Abstract:
A stable decagonal quasicrystal with nominal composition Al73Ir14.5Os12.5 has been grown from the aluminum-rich melt. It has an incongruent melting temperature of T-m = 1283 degrees C and does not transform into a periodic phase within the maximum applied annealing time of 8 weeks at 1000 degrees C. The phase equlibria in the aluminum-rich part of the system Al-Ir-Os have been explored. The X-ray diffraction patterns can be indexed by five reciprocal basis vectors with lengths a(i)(*) = 0.2588(2) angstrom(-1), i = 1,.., 4, and a(5)* = 0.05945(3) angstrom(-1). This corresponds to a quasilattice parameter (i.e. the edge length of the related Penrose tiling) of 2.501(2) angstrom and a translation period along the 10-fold axis of 16.821(8) A. The 5D space group is P10(5)mc. The structure of the decagonal phase has been solved by two different approaches, the 3D pseudo-approximant technique and the 5D charge-flipping method. It is closely related to those of decagonal Al-Os-Pd and Al-Ni-Ru and can be described as quasiperiodic packing of columnar clusters with 20.150 angstrom diameter. The clusters consist of eight quasiperiodic layers with stacking sequence...ABCDA'B'C'D'..., where the prime (') denotes the layers generated by a 10(5) operation. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Superspace group approach to the crystal structure of Na0.5CoO2
Authors:
Igarashi, D; Miyazaki, Y; Yubuta, K; Kajitani, T Author Full Names: Igarashi, Dai; Miyazaki, Yuzuru; Yubuta, Kunio; Kajitani, Tsuyoshi
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 46 (1): 304-310 JAN 2007
Abstract:
The crystal structure of layered cobalt oxide Na0.5CoO2 has been determined by means of the (3 + 1)-dimensional superspace group approach. Structural parameters have been refined with a superspace group of Ccmm(1p0)000 using powder neutron diffraction data collected below room temperature. The compound can be regarded as a misfit-layered cobalt oxide which consists of [Na] and [CoO2] subsystems, with a refined misfit parameter p = b(CoO2)/b(Na) = 0.5011(7) at 296 K. A parallel set of zigzag arrangements, i.e., the positional modulation, of Na ions has been revealed along the b-axis. The temperature-dependent alteration of Co-O distances shows discontinuous characteristics below the phase transition temperature around 80 K, which indicates the charge-separation of Co ions. On the basis of the bond valence sum calculation, a one-dimensional charge-separation pattern of Co ions with charges of +3.5 + delta and +3.5 - delta, perpendicular to the Na zigzag chains, is establis! hed.
Title:
Self-generated in-plane superlattice in relaxed epitaxial La0.67Sr0.33MnO3 films
Authors:
Zhou, TF; Li, G; Li, XG; Jin, SW; Wu, WB Author Full Names: Zhou, T. F.; Li, G.; Li, X. G.; Jin, S. W.; Wu, W. B.
Source:
APPLIED PHYSICS LETTERS 90 (4): Art. No. 042512 JAN 22 2007
Abstract:
The strain relaxation and its effect on the in-plane superlattice formation of epitaxial La0.67Sr0.33MnO3 (LSMO) thin films on the (LaAlO3)(0.3)(Sr2AlTaO6)(0.7) (001) [LSAT (001)] substrates were investigated as a function of film thickness by x-ray diffraction. Rocking curves and reciprocal space mappings around (002) and (103) reflections reveal that the film with a thickness above 27 nm is almost fully relaxed and has a modulated superlattice structure. The recovery of the pseudocubic angle of LSMO resulting from the relaxation of the shear strain introduced by the growth of rhombohedral LSMO on cubic LSAT was suggested to be the origin of the superlattice structure. (c) 2007 American Institute of Physics.

Update: 16-Feb-2007

Title:
Distortions of [Sb2Cl10](4-) bioctahedra and phase transitions in the chloroantimonate(III) (C3H5NH3)(2)[SbCl5] center dot (C3H5NH3)Cl
Authors:
Zarychta, B; Bujak, M; Zaleski, J Author Full Names: Zarychta, Bartosz; Bujak, Maciej; Zaleski, Jacek
Source:
ZEITSCHRIFT FUR NATURFORSCHUNG SECTION B-A JOURNAL OF CHEMICAL SCIENCES 62 (1): 44-50 JAN 2007
Abstract:
Bis(allylammonium)pentachloroantimonate(III)-allylammonium chloride, (C3H5NH3)(2)[SbCl5]center dot(C3H5NH3)Cl, belongs to the chloroantimonate(III) organic-inorganic salts family. The DSC studies of this compound showed two anomalies at 181 K and at 223 K. Both are associated with phase transitions, which mainly occur due to ordering-disordering processes of the organic cations. Between 181 and 223 K the structure is incommensurate. The crystal structure was determined at 298 and 86 K. At both temperatures the crystal structure consists of (C3H5NH3)(+) cations, anionic distorted [Sb2Cl10](4-) units and isolated Cl- ions. In the room-temperature phase two out of three, and in the low-temperature phase two out of six allylammonium cations were found to be disordered. The deformations of the [Sb2Cl10](4-) moieties in both phases are discussed and explained by the deviation of the Sb-III 5s electron tone pair from its spherical symmetry and the influence of N-H center dot center dot center dot Cl hydrogen bonds, which join together the organic and inorganic sublattices.
Title:
Pressure dependence of the charge-density-wave gap in rare-earth tritellurides
Authors:
Sacchetti, A; Arcangeletti, E; Perucchi, A; Baldassarre, L; Postorino, P; Lupi, S; Ru, N; Fisher, IR; Degiorgi, L Author Full Names: Sacchetti, A.; Arcangeletti, E.; Perucchi, A.; Baldassarre, L.; Postorino, P.; Lupi, S.; Ru, N.; Fisher, I. R.; Degiorgi, L.
Source:
PHYSICAL REVIEW LETTERS 98 (2): Art. No. 026401 JAN 12 2007
Abstract:
We investigate the pressure dependence of the optical properties of CeTe3, which exhibits an incommensurate charge-density-wave (CDW) state already at 300 K. Our data are collected in the midinfrared spectral range at room temperature and at pressures between 0 and 9 GPa. The energy for the single particle excitation across the CDW gap decreases upon increasing the applied pressure, similarly to the chemical pressure by rare-earth substitution. The broadening of the bands upon lattice compression removes the perfect nesting condition of the Fermi surface and therefore diminishes the impact of the CDW transition on the electronic properties of RTe3.
Title:
Electromagnons in multiferroic YMn2O5 and TbMn2O5
Authors:
Sushkov, AB; Aguilar, RV; Cheong, SW; Drew, HD Author Full Names: Sushkov, A. B.; Aguilar, R. Valdes; Cheong, S-W; Drew, H. D.
Source:
PHYSICAL REVIEW LETTERS 98 (2): Art. No. 027202 JAN 12 2007
Abstract:
Based on temperature dependent far infrared transmission spectra of YMn2O5 and TbMn2O5 single crystals, we report the observation of electric dipole-active magnetic excitations, or electromagnons, in these multiferroics. Electromagnons are found to be directly responsible for the steplike anomaly of the static dielectric constant at the commensurate-incommensurate magnetic transition and are the origin of the colossal magneto-dielectric effect reported in these multiferroics.
Title:
Modulated structure of the composite crystal [2CaOH](k)CoO2 (k=0.576)
Authors:
Isobe, M; Onoda, M; Shizuya, M; Tanaka, M; Takayama-Muromachi, E Author Full Names: Isobe, Masaaki; Onoda, Mitsuko; Shizuya, Mitsuyuki; Tanaka, Masahiko; Takayama-Muromachi, Eiji
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 (1): Art. No. 014602 JAN 2007
Abstract:
We have studied the crystal structure of the new misfit-layer calcium cobaltite [2CaOH](k)CoO2 (k = 0.576) by means of superspace-group formalism using synchrotron x-ray diffraction data. This compound is a kind of a composite crystal which consists of two interpenetrating subsystems: (a) [CoO2](infinity) containing triangular lattices formed by edge-sharing CoO6 octahedra and (b) [2CaOH]infinity double-layered rock-salt-type slabs. The two subsystems have incommensurate periodicity along the a-axis (a(1)/a(2) k = 0.576). resulting in a modulated crystal structure due to the inter-subsystem interaction. It was found that the significant structural modulation is realized in the [2CaOH] subsystem. Modulation in the [CoO2] subsystem is less marked than in the [2CaOH] ones owing to tight bonding of the closed-pack CoO6 octahedra. Thick CoO6 octahedra indicate insufficient hole-doping level in this compound.
Title:
Interfacial diffusion effect on phase transitions in Al/Mn multilayered thin films
Authors:
Srivastava, AK; Yu-Zhang, K; Kilian, L; Frigerio, JM; Rivory, J Author Full Names: Srivastava, A. K.; Yu-Zhang, K.; Kilian, L.; Frigerio, J. M.; Rivory, J.
Source:
JOURNAL OF MATERIALS SCIENCE 42 (1): 185-190 JAN 2007
Abstract:
Thin films of Al and Mn multilayers were synthesized using thermal evaporation under high vacuum conditions. The whole film thickness containing three bilayers of Al and Mn is about 120 nm. The global concentration of the samples was varied between 10 and 46.5 at.% Mn, by changing the thickness of the bilayer. The as-evaporated samples were heat treated at different temperatures (473, 623, 823 and 873 K) for 2 and 8 h to investigate the interfacial diffusion induced phase transformations in the multilayered thin films. Transmission electron microscopy (TEM) has been mainly used to characterize the crystalline structure of a variety of phases revealed on annealing, such as mu, lambda and phi phases up to 823 K, delta phase at 823 K and T6 phase at 873 K. The occurrence of a variety of structures on annealing has been attributed to the interfacial reactions at the Al-Mn bilayers, and, therefore, the global composition of the composite films is not significant during the process of phase transformations. The crystallographic relationships of Al-Mn approximant structures of the decagonal quasicrystal are discussed to understand the evolution and stability of the T6 phase at high temperature.
Title:
Quasicrystal structure solved
Authors:
Jacoby, M Author Full Names: Jacoby, Mitch
Source:
CHEMICAL & ENGINEERING NEWS 85 (3): 16-16 JAN 15 2007

Update: 9-Feb-2007

Title:
High-pressure Raman spectroscopy of antimony: As-type, incommensurate host-guest, and bcc phases
Authors:
Degtyareva, O; Struzhkin, VV; Hemley, RJ Author Full Names: Degtyareva, Olga; Struzhkin, Viktor V.; Hemley, Russell J.
Source:
SOLID STATE COMMUNICATIONS 141 (3): 164-167 JAN 2007
Abstract:
The vibrational dynamics of elemental solids that form incommensurate host-guest structures are of fundamental interest. High-pressure Raman scattering has been used to examine the vibrational spectrum of the group-V element Sb up to 33 GPa. A(1g) and E-g phonons of the ambient pressure rhombohedral A7 phase display a marked decrease with pressure, i.e., prior to the transition to the tetragonal host-guest Sb-II phase at 8.6 GPa, via the monoclinic host-guest Sb-IV phase. The Raman spectrum of the incommensurate host-guest Sb-II phase, has five bands between 80 cm(-1) and 200 cm(-1) that increase with pressure. For the bee structure stable above 28 GPa, we observe one weak disorder-induced band that increases with pressure. (C) 2006 Elsevier Ltd. All rights reserved.
Title:
Phase transitions in multiferroic BiFeO3 crystals, thin-layers, and ceramics: enduring potential for a single phase, room-temperature magnetoelectric 'holy grail'
Authors:
Kadomtseva, AM; Popov, YF; Pyatakov, AP; Vorob'ev, GP; Zvezdin, AK; Viehland, D Author Full Names: Kadomtseva, A. M.; Popov, Yu. F.; Pyatakov, A. P.; Vorob'ev, G. P.; Zvezdin, A. K.; Viehland, D.
Source:
PHASE TRANSITIONS 79 (12): 1019-1042 DEC 2006
Abstract:
Magnetic phase transitions in multiferroic bismuth ferrite (BiFeO3) induced by magnetic field, epitaxial strain, and composition modification are considered. These transitions from a spatially modulated spin spiral state to a homogenous anti ferromagnetic one are accompanied by tghe release of latent magnetization and a linear magnetoelectric effect that makes BiFeO3-based materials efficient room-temperature single phase multiferroics.
Title:
Strontium ordering, structural modulation in layered hexagonal SrxCoO2 and physical properties of Sr0.35CoO2
Authors:
Yang, HX; Shi, YG; Guo, YQ; Liu, X; Xiao, RJ; Luo, JL; Li, JQ Author Full Names: H. X. Yang; Y. G. Shi; Y. Q. Guo; X. Liu; R. J. Xiao; J. L. Luo; J. Q. Li
Source:
MATERIALS RESEARCH BULLETIN 42 (1): 94-101 JAN 18 2007
Abstract:
Layered Sr0.35CoO2 has been synthesized by means of an ion exchange reaction from Na0.7CoO2. Resistivity measurements show that this material can be either metallic or semiconducting depending on the annealing conditions. The magnetic susceptibility of the sample increases with decreasing temperature, showing a Curie-Weiss behavior in high temperatures. Transmission electron microscopy observations reveal the presence of two superstructures arising respectively from the intercalated Sr-ordering (a compositional modulation) with q(2) = a*/3 + b*/3 and a periodic *structural* distortion (a transverse structural modulation) with q(2) = a*/2. (C) 2006 Elsevier Ltd. All rights reserved.
Title:
Synthesis of nanocrystalline (Co, Ni)Al2O4 spinel powder by mechanical milling of quasicrystalline materials
Authors:
Yadav, TP; Mukhopadhyay, NK; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Mukhopadhyay, N. K.; Tiwari, R. S.; Srivastava, O. N.
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 7 (2): 575-579 FEB 2007
Abstract:
In the present study, attempts have been made to synthesize the nano-crystalline (Co, Ni)Al2O4 spinet powders by ball milling and subsequent annealing. An alloy of Al70Co15Ni15, exhibiting the formation of a complex intermetallic compound known as decagonal quasicrystal is selected as the starting material for mechanical milling. It is interesting to note that this alloy is close to the stoichiometry of aluminum and transition metal atoms required to form the aluminate spinet. The milling was carried out in an attritor mill at 400 rpm for 40 hours with ball to powder ratio of 20: 1 in hexane medium. Subsequent to this annealing was performed in an air ambience for 10, 20, and 40 h at 600 degrees C in side the furnace in order to oxidize the decagonal phase and finally to form the spinet structure. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the formation of nano-sized decagonal phase after milling and then (Co, Ni)Al2O4 spinet type phase after annealing. The XRD studies reveal the lattice parameter to be 8.075 angstrom and the lattice strain as 0.6%. The XRD and TEM explorations of spinet phase indicate the average grain size to be similar to 40 nm.
Title:
Icosahedral quasicrystals by optical interference holography
Authors:
Tam, WY Author Full Names: Tam, Wing Yim
Source:
APPLIED PHYSICS LETTERS 89 (25): Art. No. 251111 DEC 18 2006
Abstract:
Optical interference holography has been proven to be a useful technique in fabricating periodic photonic crystals in which electromagnetic waves are forbidden in certain frequency band gaps. Compared to periodic crystals, quasicrystals, having higher point group symmetry, are more favorable in achieving complete band gaps. In this letter, we propose two seven-beam optical interference configurations based on the reciprocal vector space representation to fabricate icosahedral quasicrystals. Interference simulations for the quasicrystals exhibit the full symmetry of an icosahedron. The result paves the way for the fabrication of photonic quasicrystals using holographic lithography. (c) 2006 American Institute of Physics.

Update: 2-Feb-2007

Title:
The new single crystal diffractometer RESI at FRM-II
Authors:
Pedersen, B; Frey, F; Scherer, W; Gille, P; Meisterernst, G Author Full Names: Pedersen, Bjorn; Frey, Friedrich; Scherer, Wolfgang; Gille, Peter; Meisterernst, Goetz
Source:
PHYSICA B-CONDENSED MATTER 385-86: 1046-1048 Part 2 NOV 15 2006
Abstract:
The new single crystal diffractometer RESI (REciprocal Space Investigator) at FRM-II has successfully passed the commissioning phase. With its unique setup of a kappa goniometer and a neutron sensitive imaging plate, it is very well suited for structure determination and the exploration of disorder phenomena. We will present first results from measurements on the new quasicrystalline phase of AlCoCu, showing the suitability of the instrument for fast collection of both Bragg and diffuse scattering data. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Quasicrystals - When all pieces fit together
Authors:
Thiel, P Author Full Names: Thiel, Patricia
Source:
NATURE MATERIALS 6 (1): 11-12 JAN 2007
Abstract:
The complete atomic distribution of a binary natural quasicrystal has been achieved by complementing X-ray diffraction patterns with the structure of closely related crystals. The result represents an essential starting point to find the atomic structure of more complex quasicrystals.
Title:
Atomic structure of the binary icosahedral Yb-Cd quasicrystal
Authors:
Takakura, H; Gomez, CP; Yamamoto, A; De Boissieu, M; Tsai, AP Author Full Names: Takakura, Hiroyuki; Gomez, Cesar Pay; Yamamoto, Akiji; De Boissieu, Marc; Tsai, An Pang
Source:
NATURE MATERIALS 6 (1): 58-63 JAN 2007
Abstract:
Icosahedral quasicrystals ( i-QCs) are long-range ordered solids that show non-crystallographic symmetries such as five-fold rotations. Their detailed atomic structures are still far from completely understood, because most stable i-QCs formas ternary alloys suffering from chemical disorder. Here, we present the first detailed structure solution of i-YbCd5.7, one of the very few stable binary i-QCs, by means of X-ray structure determination. Three building units with unique atomic decorations arrange quasiperiodically and fill the space. These also serve as building units in the periodic approximant crystals. The structure is not only chemically feasible, but also provides a seamless structural understanding of the i-YbCd5.7 phase and its series of related i-QCs and approximant crystals, revealing hierarchic features that are of considerable physical interest.
Title:
Microstructure characterisation of Al65Cr28Fe7 quasicrystalline approximant
Authors:
Janovec, J; Svoboda, M; Dolinsek, J; Godec, M; Bursik, J; Dusza, J Author Full Names: Janovec, J.; Svoboda, M.; Dolinsek, J.; Godec, M.; Bursik, J.; Dusza, J.
Source:
KOVOVE MATERIALY-METALLIC MATERIALS 44 (6): 313-320 2006
Abstract:
The microstructure characterisation of the quasicrystalline approximant Al65Cr28Fe7 was performed by transmission electron microscopy, electron diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and other methods. In the investigated sample, two phases were identified: the metallic matrix possessing hexagonal structure with lattice parameters a = 1.2728 nm and c = 0.7942 nrn (isostructural with the gamma-brass) and Al2O3 in the form of inclusions. The microstructure of the approximant was found to be formed by grains (their interior consists of plain and lamellate areas) surrounded by heterogeneous areas rich on the Al2O3 inclusions. The lamellate areas were found to be formed by parallel bands. Every other band showed the same orientation. In the band boundaries, the dislocation networks were found. It was shown that two sets of dislocations oriented nearly perpendicular to each other form dislocation networks also inside the bands.
Title:
Mechanisms at structural phase transitions
Authors:
Bohm, H Author Full Names: Boehm, H.
Source:
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 27 (2-3): 887-892 2007
Abstract:
Structural phase transitions in crystalline solids are accompanied with the change of symmetry. After EHRENFEST [Ehrenfest, P., Phasenumwandlungen im Oblichen und erweiterten Sinn, klassifiziert nach den entsprechenden Singularitdten des thermodynamischen Potentials. Proc. Kon., Amsterdam Acad., 1933, 36(Suppl 75b), 153-157] they can be distinguished between first and second order transitions. Two examples for first and second order transitions will be discussed in order two elaborate the characteristic features. The statements are verified by diffraction experiments; the second order transitions will be discussed on the basis of the LANDAU [Landau, L. and Lifshitz, E.M., Lehrbuch der Theoretischen Physik Band 3, Quantenmechanik. Akademie Verlag, Berlin, 1986] theory. The first example is the superstructure of Bi4Ti4O11, and the second example describes the sequence of modulated and non-modulated phases in melifite compounds e.g. Ca2COSi2O7. The sequence of phases in this compound exhibits both first and second order transitions. For both examples it will be shown, to what extent the characteristic criteria of first or second order transitions are valid. It will be pointed out that close to the transition point of second order transitions pronounced deviations are observed. From these features new concepts for the mechanism of the transition can be concluded. Precursors of the low symmetry structure are formed beyond the transition point in the high symmetry phase. For these precursors there is a continuous change from short range order to long range order, which is attained at the transition point. If the precursor domains adopt long range order an intermediate, incommensurately modulated structure may occur between the high symmetric structure and the structure/superstructure of low symmetry. (c) 2006 Published by Elsevier Ltd.
Title:
DRAWxtl, an open-source computer program to produce crystal structure drawings
Authors:
Finger, LW; Kroeker, M; Toby, BH Author Full Names: Finger, Larry W.; Kroeker, Martin; Toby, Brian H.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 40: 188-192 Part 1 FEB 2007
Abstract:
The computer program DRAWxtl produces crystal structure drawings in the form of an interactive screen representation, as well as VRML files for use on web pages and in classroom teaching, and creates input files for the popular Persistence of Vision Raytracer (POV-Ray) rendering program for publication-quality graphics, including generation of stereo pairs. DRAWxtl output produces the standard kinds of graphical representations: spheres, ellipsoids, bonds and polyhedra of any complexity. In addition, it can draw arrows to represent magnetic moments, show capped cones to indicate the location of lone-pair electrons and display Fourier contours in three dimensions. A unique feature of this program is the ability to plot incommensurately modulated and composite structures. This open-source program can be used with operating systems as diverse as Windows (9X, NT, 2000 and XP), Mac OS X, Linux and most other varieties of Unix.

Update: 26-Jan-2007

Title:
Quasiperiodic-periodic structures by projection in two stages: an illustrative example
Authors:
Quandt, A; Ben-Abraham, SI Author Full Names: Quandt, Alexander; Ben-Abraham, Shelomo I.
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 221 (12): 759-761 2006
Abstract:
Recently we have modified a two-stage variant of the cut-and-project method used to generate layered 8-fold (Ben-Abraham, 2004) and 12-fold (Ben-Abraham et al., 2004) quasiperiodic structures in three dimensions, and obtained 8-fold, 10-fold and 12-fold quasiperiodic structures via cut-and-project from various four dimensional lattices (Ben-Abraham and Quandt, 2006). However four dimensions are certainly not the most suitable playground to illustrate the basics of our general two-stage projection method. To this end we cut and project a periodic structure in three dimensions onto two-dimensional physical space, such that a second cut and projection onto a line yields a quasiperiodic structure. This simple example contains all of the basic elements of our two-stage projection method, but now the essential steps may directly be visualized.
Title:
Spin Hamiltonian, competing small energy scales, and incommensurate long-range order in the highly frustrated Gd3Ga5O12 garnet antiferromagnet
Authors:
Yavors'kii, T; Enjalran, M; Gingras, MJP Author Full Names: Yavors'kii, Taras; Enjalran, Matthew; Gingras, Michel J. P.
Source:
PHYSICAL REVIEW LETTERS 97 (26): Art. No. 267203 DEC 31 2006
Abstract:
Despite the availability of a spin Hamiltonian for the Gd3Ga5O12 garnet (GGG) for over 25 years, there has so far been little theoretical insight regarding the many unusual low temperature properties of GGG. Here we investigate GGG in zero magnetic field using mean-field theory. We reproduce the spin liquid-like correlations and, most importantly, explain the positions of the sharp peaks seen in powder neutron diffraction experiments. We show that it is crucial to treat accurately the long-range nature of the magnetic dipolar interactions to allow for a determination of the small exchange energy scales involved in the selection of the experimental ordering wave vector. Our results show that the incommensurate order in GGG is classical in nature, intrinsic to the microscopic spin Hamiltonian and not caused by weak disorder.
Title:
Unique six-dimensional structural model for Al-Pd-Mn and Al-Cu-Fe icosahedral phases
Authors:
Quiquandon, M; Gratias, D Author Full Names: Quiquandon, Marianne; Gratias, Denis
Source:
PHYSICAL REVIEW B 74 (21): Art. No. 214205 DEC 2006
Abstract:
A simple unique 6D atomic structural model for both i-AlPdMn and i-AlCuFe is proposed that is built with an unique and simple set of atomic surfaces and chemical subcells. The model has accurate compositions with respect to the best experimental estimates of both structures and fit reasonably well the experimental diffraction data of x-rays and neutrons spectra with no fitting parameters. It presents a surprisingly small number of chemical configurations for the basic B (Bergman) and M (Mackay) type clusters as compared to what could be expected for quasiperiodic ternary systems. Finally, because of its relative simplicity, the present model is well adapted for being used in discussing the physical properties of either i-AlPdMn or i-AlCuFe that are essentially dependent on the local atomic arrangements of the various chemical species.
Title:
Local atomic structure of martensitic Ni2+xMn1-xGa: An EXAFS study
Authors:
Bhobe, PA; Priolkar, KR; Sarode, PR Author Full Names: Bhobe, P. A.; Priolkar, K. R.; Sarode, P. R.
Source:
PHYSICAL REVIEW B 74 (22): Art. No. 224425 DEC 2006
Abstract:
The local atomic structure of Ni2+xMn1-xGa with 0 <= x <= 0.16 alloys was explored using Mn and Ga K-edge extended x-ray-absorption fine-structure (EXAFS) measurement. In order to study the atomic re-arrangements that occur upon martensitic transformation, room-temperature and low-temperature EXAFS were recorded. The changes occurring in the L2(1) unit cell and the bond lengths obtained from the analysis enables us to determine the modulation amplitudes over which the constituent atoms move giving rise to the shuffling of the atomic planes in the modulated structure. The EXAFS analysis also suggests the changes in hybridization of Ga-p and Ni-d orbitals associated with the local symmetry breaking upon undergoing martensitic transition.
Title:
Influence of structural modulations and the chain-ladder interaction in the Sr14-xCaxCu24O41 compounds
Authors:
Gelle, A; Lepetit, MB Author Full Names: Gelle, Alain; Lepetit, Marie-Bernadette
Source:
PHYSICAL REVIEW B 74 (23): Art. No. 235115 DEC 2006
Abstract:
We studied the effects of the incommensurate structural modulations on the ladder subsystem of the Sr14-xCaxCu24O41 family of compounds using ab initio explicitly correlated calculations. From these calculations we derived t-J model as a function of the fourth crystallographic coordinate tau describing the incommensurate modulations. It was found that in the highly calcium-doped system, the onsite orbital energies are strongly modulated along the ladder legs. On the contrary the two sites of the ladder rungs are isoenergetic and the holes are thus expected to be delocalized on the rungs. Chain-ladder interactions were also evaluated and found to be very negligible. The ladder superconductivity model for these systems is discussed in the light of the present results.
Title:
Unusual magnetic phase transitions of TbNi5
Authors:
Lee, S; Pirogov, AN; Podlesnyak, AA; Prokes, K; Dorofeef, YA; Teplykh, AE; Swainson, IP; Park, JG Author Full Names: Lee, Seongsu; Pirogov, A. N.; Podlesnyak, A. A.; Prokes, K.; Dorofeef, Yu. A.; Teplykh, A. E.; Swainson, I. P.; Park, J. -G.
Source:
PHYSICA B-CONDENSED MATTER 385: 349-352 Part 1 Sp. Iss. SI NOV 15 2006
Abstract:
In order to understand the nature of magnetic transitions in intermetallic TbNi5 compound, we have performed high resolution powder and single crystal neutron diffraction studies. Powder diffraction patterns can be described by a superposition of a ferromagnet (k(1) = 0) and a transverse spin wave (k(2) approximate to 2 pi/c(0, 0, 0.018)). The single crystal experiments reveal two spontaneous magnetic transitions: one is a second-order transition at 24 K from a paramagnetic state to an incommensurate structure and another a first-order transition at 10 K from the incommensurate structure to a lock-in structure. At the low-temperature transition a large (similar to 15 K) thermal hysteresis is observed in the temperature dependence of the intensity of magnetic peaks. External magnetic fields destroy the modulated structure and induce a ferromagnetic state, which remains stable even after magnetic fields are switched off. (c) 2006 Elsevier B.V. All rights reserved.
Title:
A neutron diffraction study on an Er7Rh3 single crystal
Authors:
Tsutaoka, T; Tanaka, A; Andoh, Y; Kawano, S; Kurisu, M; Nakamoto, G Author Full Names: Tsutaoka, T.; Tanaka, A.; Andoh, Y.; Kawano, S.; Kurisu, M.; Nakamoto, G.
Source:
PHYSICA B-CONDENSED MATTER 385: 353-355 Part 1 Sp. Iss. SI NOV 15 2006
Abstract:
Magnetic and neutron diffraction studies have been performed on an Er7Rh3 single crystal. The magnetic measurements show that there are two successive anti ferromagnetic transitions at T-N = 13.0 K and T-t1 = 6.2 K. A small magnetic anisotropy is observed in the paramagnetic susceptibility. Neutron diffraction also shows evidence of a commensurate to incommensurate magnetic transition at T-t2 = 4.5 K. The magnetic structure in the low temperature anti ferromagnetic phase below T-t2 is characterized by the two magnetic propagation vectors k(1) = (001/2) and k(2) = (000). With increasing temperature, the magnetic modulation characterized by k(2) disappears at T-t1 but the z-component is temperature independent. On the other hand, the magnetic modulation characterized by k(1) becomes incommensurate at T-t2 where k(1) = (000.42) and persists in the high temperature phase between T-t1 and T-N. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Investigation by spherical neutron polarimetry of magnetic properties in BaCo2(ASO(4))(2)
Authors:
Regnault, LP; Boullier, C; Henry, JY Author Full Names: Regnault, L. P.; Boullier, C.; Henry, J. Y.
Source:
PHYSICA B-CONDENSED MATTER 385: 425-427 Part 1 Sp. Iss. SI NOV 15 2006
Abstract:
The cobaltite BaCo2(ASO(4))(2) (BCAO) is a good realization of the quasi-2D system in which the Co2+ ions form a magnetically frustrated honeycomb lattice with magnetic moments mainly confined in the basal planes. Below T-N = 5.35 +/- 0.5 K, the ground state structure is described by an incommensurate propagation vector k approximate to (0.265, 0, -1.33) and the magnetic excitation spectrum displays a resolution-limited energy gap do P Delta(0) approximate to 1.45meV at q = 0. No magnetic excitations emerging from q = k could be detected, contrary to what would be expected for a simple helimagnetic ground state. In order to understand these puzzling results, we have recently re-investigated the magnetic structure and excitations in BCAO using spherical neutronpolarization analysis. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Noble gas films on a decagonal AlNiCo quasicrystal
Authors:
Setyawan, W; Diehl, RD; Ferralis, N; Cole, MW; Curtarolo, S Author Full Names: Setyawan, W.; Diehl, R. D.; Ferralis, N.; Cole, M. W.; Curtarolo, S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 19 (1): Art. No. 016007 JAN 10 2007
Abstract:
Thermodynamic properties of Ne, Ar, Kr, and Xe adsorbed on an Al-Ni-Co quasicrystalline (QC) surface are studied with the grand canonical Monte Carlo technique by employing Lennard-Jones interactions with parameter values derived from experiments and traditional combining rules. In all the gas/QC systems, a layer-by-layer film growth is observed at low temperature. The monolayers have regular epitaxial fivefold arrangements which evolve toward sixfold close-packed structures as the pressure is increased. The final states can contain either considerable or negligible amounts of defects. In the latter case, there occurs a structural transition from fivefold to sixfold symmetry which can be described by introducing an order parameter, whose evolution characterizes the transition to be continuous or discontinuous as in the case of Xe/QC (first-order transition with associated latent heat). By simulating fictitious noble gases, we find that the existence of the transition is correlated with the size mismatch between adsorbate and substrate characteristic lengths. A simple rule is proposed to predict the phenomenon.
Title:
Magnetic properties and electronic structure of the new HfFe6Ge6-type HfMn6Ge6 compound
Authors:
Ihou-Mouko, H; Mazet, T; Isnard, O; Malaman, B Author Full Names: Ihou-Mouko, Hilaire; Mazet, Thomas; Isnard, Olivier; Malaman, Bernard
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 426 (1-2): 26-30 DEC 21 2006
Abstract:
Magnetisation measurements, neutron diffraction experiments and electronic structure calculations have been performed on the new HfFe6Ge6-type (P6/mmm) HfMn6Ge6 compound. This compound orders antiferromagnetically below T-N = 650 K in a collimear easy-axis antiferromagnetic arrangement and undergoes a second transition at T, = 30 K into an incommensurate double-cone antiferromagnetic structure where the Mn moments (mm = 2.20 mu(B) at 2 K) slightly deviate from the c-axis. The computed electronic structure is characterised by a low density of states at the Fermi level and by a marked anisotropy in the band structure. The effect of partially substituting Ga for Ge on the magnetic properties is also investigated. The ordering temperature of the pseudo-temary HfMn6Ge6-xGax compounds (0 < x <= 1) is found to decrease upon Ga substitution while the antiferromagnetic order is preserved in the whole ordered temperature range. The results are compared with previously published data concerning other RMn6Ge6 and RMn6Ge6-xGax representatives. (c) 2006 Elsevier B.V. All rights reserved.
Title:
The influence of element Y on the mechanical properties of the as-extruded Mg-Zn-Y-Zr alloys
Authors:
Xu, DK; Liu, L; Xu, YB; Han, EH Author Full Names: Xu, D. K.; Liu, L.; Xu, Y. B.; Han, E. H.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 426 (1-2): 155-161 DEC 21 2006
Abstract:
This work mainly investigated the mechanical properties of the as-extruded Mg-Zn-Y-Zr Mg alloys with different Y contents. It showed that when Zn content was constant (5.65 wt.%), the alloys with Y content from 1.17 to 1.72 wt.% could have the highest strength. XRD analysis and the tensile testing results showed that the alloys with Y content in the range of 0 to 1.72 wt.% were composed of alpha-Mg matrix and icosahedral quasicrystal I-phase, and with the quantity of I-phase increasing, the strength of the alloys was improved. When Y content varied from 1.72 to 3.69 wt.%, w-phase would be detected. Through comparing with the mechanical properties of the alloys, it could be found that the occurrence of w-phase will degrade the strength of the alloys. Based on the Zn (wt.%)/Y (wt.%) ratios of I-phase and w-phase and compared with different Zn (wt.%)/Y (wt.%) ratios of the alloys, the occurrence of w-phase have been explained. Fracture observations revealed that with Y content increasing, the quantity of Mg-Zn-Y phase distributed on the fracture surfaces would gradually increase. (c) 2006 Elsevier B.V. All rights reserved.

Update: 19-Jan-2007

Title:
A general treatment of three-dimensional elasticity of quasicrystals by an operator method
Authors:
Gao, Y; Zhao, BS Author Full Names: Gao, Yang; Zhao, Bao-Sheng
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 243 (15): 4007-4019 DEC 2006
Abstract:
By an operator method the general solution of three-dimensional elasticity of quasicrystals is given constructively with some displacement functions, and its completeness is proved at the same time. Nonuniqueness and the scope of nonuniqueness of the general solution are also pointed out. The method used in the paper extends work from elasticity to quasicrystals elasticity. As two special cases, two-dimensional dodecagonal quasicrystal and one-dimensional hexagonal QCs are considered, and the general solutions based on the operator method are presented. (C) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Title:
Approximant phases, phason planes and domain-boundary networks in Al-Ni-Rh alloys
Authors:
Chen, YH; Sun, W; Zhang, Z Author Full Names: Chen, Y. H.; Sun, W.; Zhang, Z.
Source:
PHILOSOPHICAL MAGAZINE LETTERS 86 (12): 817-827 DEC 2006
Abstract:
Structurally complicated xi'- and xi-phases have been found, for the first time, in as-cast Al73Ni5Rh22 and Al75Ni15Rh10 alloys. The lattice parameters of these two phases were determined by means of electron diffraction and high-resolution transmission electron microscopy ( HREM). These two phases have similar orthorhombic structures but with different lattice parameters of a = 23.2 angstrom, b = 16.4 angstrom, c = 12.0 angstrom for the xi'-phase and a = 20.3 angstrom, b = 16.4 angstrom, c = 14.8 angstrom for the xi'-phase. A new two-dimensional domain-boundary network has also been observed in these two phases. Domain boundaries with normals closely parallel to the [001] direction are actually phason planes represented by a translation vector of r = (1/2)a + (1/2 tau)c in the xi'-phase and r = +/-(1/2 tau(2)) a + (tau/2)c in the xi'-phase, whereas the newly-found wide and zigzag boundaries perpendicular to the above set were attributed from the step-like boundary structures of domains related by a translation vector of r = (1/tau)((1/2)a + (1/2 tau)c). The structural difference between the two types of planar faults is discussed.
Title:
Stability of the B2-type structure and R-phase transformation behavior of Fe or Co doped Ti-Ni alloys
Authors:
Choi, MS; Ogawa, J; Fukuda, T; Kakeshita, T Author Full Names: Choi, Mi-Seon; Ogawa, Jumpei; Fukuda, Takashi; Kakeshita, Tomoyuki
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 438: 527-530 Sp. Iss. SI DEC 25 2006
Abstract:
We have investigated the R-phase transformation behavior in a series of Ti-(50-x)Ni-xFe (2 <= x <= 20) and Ti-(50-x)Ni-xCo (4 <= x <= 16) alloys. We found that the alloys with Fe/Co content of 6/14 at.% and more do not show a latent heat and surface relief although the alloys with Fe/Co content of 4/12 at.% and less show the R-phase transformation with an obvious latent heat and surface relief. However, some of the former alloys (6Fe, 8Fe, 10Fe, 14Co, 16Co) show anomalies in specific heat, such as the existence of broad peak and a low Debye temperature. Transmission electron microscope observation of the 6Fe alloy revealed the existence of an incommensurate-commensurate transition at 140 K. That is, diffuse scatterings continuously move to 1/3[110] position as temperature decreases and lock in to the exact position at 140 K. The commensurate phase inherits a nanoscale domain-like structure, which is introduced in the incommensurate phase beforehand. (c) 2! 006 Elsevier B.V. All rights reserved.
Title:
Low-temperature behaviour of Ni-Fe-Ga shape-memory alloys
Authors:
Segui, C; Pons, J; Cesari, E; Dutkiewicz, J Author Full Names: Segui, C.; Pons, J.; Cesari, E.; Dutkiewicz, J.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 438: 923-926 Sp. Iss. SI DEC 25 2006
Abstract:
Three polycrystalline alloys with compositions Ni53+xFe20-xGa27 (x = 0.5, 1, 2 at %) have been studied, paying particular attention to the low-temperature behaviour, between the martensite finish and liquid nitrogen temperature. In this respect, the dynamic mechanical analysis has proven to be a powerful tool in detecting structural and microstructural changes. The studied alloys display, on cooling in the above-mentioned temperature domain, a broad internal friction peak accompanied by a marked increase in the elastic modulus slope; on further cooling an additional modulus drop and concurrent internal friction jump take place. The internal friction and elastic modulus evolution is not strictly reversible on heating. Basing in the earlier results obtained for Ni-Mn-Ga alloys, the internal friction peak is attributed to the oscillating movement of twin boundaries in the layered martensites, while the lowest temperature anomaly suggests the occurrence of slight changes in the mixture of modulated martensite structures formed on cooling. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Crystal structure and macrotwin interface of five-layered martensite in Ni-Mn-Ga magnetic shape memory alloy
Authors:
Ge, Y; Jiang, H; Sozinov, A; Soderberg, O; Lanska, N; Keranen, J; Kauppinen, EI; Lindroos, VK; Hannula, SP Author Full Names: Ge, Y.; Jiang, H.; Sozinov, A.; Soderberg, O.; Lanska, N.; Keranen, J.; Kauppinen, E. I.; Lindroos, V. K.; Hannula, S. -P.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 438: 961-964 Sp. Iss. SI DEC 25 2006
Abstract:
The crystal structure of the five-layered (5M) martensite and the martensite to martensite interface in the alloys Ni48.9Mn30.8Ga20.3 and Ni49.5Mn28.6Ga21.9 (numbers indicate at.%) were investigated by the X-ray diffraction as well as by the conventional and by the high resolution transmission electron microscopy (FIRTEM). The martensite to martensite interface arises from meeting of growth fronts of two microtwin sequences with the twin planes (110) and (110), respectively. The interface was found to consist of two different configurations, the crossing and the step type. The HRTEM images reveal that the martensitic structure is not a perfect five-layered structure, but there are also other periodic structures (seven-layered and ten-layered), together with aperiodic structure and the irregular plane faults. (c) 2006 Elsevier B.V. All rights reserved.
Title:
New aspects of mechanical relaxation by hydrogen in metals
Authors:
Sinning, HR Author Full Names: Sinning, H. -R.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 442 (1-2): 99-105 Sp. Iss. SI DEC 20 2006
Abstract:
After an overview over the relevant relaxation mechanisms, divided into short- and long-range hydrogen motion and processes coupled with matrix defects, some recent work is reviewed with emphasis on two aspects: (i) comparison of similar relaxation effects in different amorphous, quasicrystalline and crystalline structures from the viewpoint of short-range order. The Snoek-type mechanism is discussed for the case of polytetrahedral order, and some conclusions are pointed out with respect to differences and similarities in short-range order between amorphous and quasicrystalline phases; (ii) observations of new effects based on known mechanisms. Stress gradients in the submicrometer range can produce high-frequency Gorsky effects, either by transverse H diffusion in nanomechanical resonators or by intercrystalline diffusion in ultrafine-grained polycrystals. The latter effect was studied simultaneously together with the Zener-type hydrogen relaxation in CuZr2, which was a! dvantageous for the identification, characterization and understanding of both effects. (c) 2006 Elsevier B.V. All rights reserved.
Title:
The high-temperature damping background in intermetallic alloys
Authors:
Weller, M; Clemens, H; Haneczok, G Author Full Names: Weller, M.; Clemens, H.; Haneczok, G.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 442 (1-2): 138-141 Sp. Iss. SI DEC 20 2006
Abstract:
The high-temperature damping background (HTDB) in various intermetallic compounds, such as gamma-TiAl based alloys, NiAl single crystals and quasicrystalline d-Ni-Al-Co exhibits viscoelastic behavior which can be observed as damping, increasing exponentially with temperature. The activation enthalpy H was determined from measurements of the HTDB at various frequencies. In gamma-TiAl based alloys with various chemical composition the activation enthalpies are in the range of H = 4.2-4.3 eV for Ti-46 at.%Al-9 at.%Nb, and H = 3.8-3.9 eV for Ti-46.5 at.%Al-4 at.% (Cr, Nb, Ta, B). For a Ni49.5Al50.5 single crystal an activation enthalpy of H = 3.3 eV was determined. The H-values in TiAl and NiAl agree well with activation enthalpies from creep and self-diffusion experiments. Therefore, the HTDB in TiAl and NiAl is assigned to diffusion-assisted climb of dislocations. Decagonal Al-Ni-Co quasicrystals show different behavior. The HTDB is only observed in polycrystalline material, but not in a single crystal. The activation enthalpies, H = 2.4-3 eV, agree with values obtained by tracer diffusion experiments. This indicates that the HTDB in decagonal Al-Ni-Co quasicrystals is due to an intragrain diffusion process which is equivalent to Nabarro-Herring creep. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Effect of microstructure and texture on the mechanical properties of the as-extruded Mg-Zn-Y-Zr alloys
Authors:
Xu, DK; Liu, L; Xu, YB; Han, EH Author Full Names: Xu, D. K.; Liu, L.; Xu, Y. B.; Han, E. H.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 443 (1-2): 248-256 JAN 15 2007
Abstract:
This work mainly studied the influence of the microstructure and crystallographic texture on the mechanical properties of the as-extruded Mg-Zn-Y-Zr alloys with different Y contents. The samples were machined from thick plates obtained by extrusion and the tensile tests were performed parallel to extrusion and transverse directions, respectively. Microstructure observation firmly indicated that the grain-refining effect of icosahedral quasicrystal phase (I-phase) was superior to that of the cubic W-phase. In addition, the tensile results indicated that I-phase could effectively improve the strength (yield strength and ultimate tensile strength) of alloys. However, strengthening effect of W-phase was lower. With the quantity of W-phase increasing, the strength of alloys was degraded. It also showed that the alloys were mechanically anisotropic, i.e. the longitudinal strength was higher than that of the transverse direction. However, the ductility of the transverse direction was superior. With the increase of Mg-Zn-Y phases, the anisotropy of the ultimate tensile strength (UTS) between the longitudinal and transverse directions increased remarkably. SEM fracture observations showed that the fractures of the TD samples were characterized by the typical "woody fracture", with a large amount of cracked Mg-Zn-Y particles (I-phase and W-phase) distributed at the bottom of dimples. With Y content increasing, the average spacing of the zonal distributed Ma-Zn-Y particles on the fracture surface became narrow, which influenced the transverse mechanical properties greatly. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Interpretation of selected structures of the bismuthinite-aikinite series as commensurately modulated structures
Authors:
Petricek, V; Makovicky, E Author Full Names: Petricek, Vaclav; Makovicky, Emil
Source:
CANADIAN MINERALOGIST 44: 189-206 Part 1 FEB 2006
Abstract:
The bismuthinite - aikinite (Bi2S3 - CuPbBiS3) series of ordered derivatives (superstructures) is based on the incremental Bi + vacancy --> - Pb + Cu substitution. Selected structures of this series, gladite, salzburgite, paarite and krupkaite, were refined as commensurately modulated structures using the superspace approach. The superspace group Pmcn(0 beta 0)00s was used for all these structures. beta assuming the value of 1/3. 1/4 1/5, and 2 in the above order. Two independent large-cation positions, one Cu position (in oversubstituted members, two) and three S positions were refined for the sequence of one or three to five subcells forming the above structures using the summation of sinusoidal functions for positional and displacement parameters. In this paper, we describe. in terms intended for non-specialists. our choice of the superspace group, its application to individual superstructures. the details of the structure refinement, and the structural interpretation of the results.

Update: 12_Jan_2007

Title:
Disordered commensurate structure of the 2212-related phase Fe-2(Bi0.69Sr2.31)Fe2O9.5 +/- 1/2 delta and structural mechanism
Authors:
Grebille, D; Lepoittevin, C; Malo, S; Perez, O; Nguyen, N; Hervieu, M Author Full Names: Grebille, Dominique; Lepoittevin, Christophe; Malo, Sylvie; Perez, Oliver; Nguyen, N.; Hervieu, Maryvonne
Source:
JOURNAL OF SOLID STATE CHEMISTRY 179 (12): 3849-3859 DEC 2006
Abstract:
The structure of the Fe-2(Bi0.69Sr2.31)Fe2O9.5-1/2 delta has been carried out by single crystal X-ray diffraction. Its structure can be considered as commensurately modulated with a basic structure of Fmmm symmetry and with a modulation vector (q) over right arrow = alpha(a) over right arrow* + gamma(c) over right arrow* whose alpha and gamma values are.. respectively, equal to 1/3 and 1. The ferrite is described as a three-fold superstructure with a approximate to 3 a(p)root 2, b approximate to a(p)root 2 and c approximate to 26 angstrom (space group Bbmb). It is described using a disorder model in agreement with diffuse scattering observations. The structure is built up from the intergrowth sequence between [(Bi, Sr)Fe2O3.5 +/- 1/2 delta](infinity). complex layers, related to the rock salt (RS)-type blocks, and double perovskite layers. Large analogies are found between the present structure and the so-called 2212 modulated structures related to the high T-c superconductor copper oxides or to the corresponding Fe or Co oxides; they are iscussed here. A statistical disorder characterizes the [Fe2O2.5 +/- 1/2 delta](infinity) double layer. Taking advantage of similar structural arrangements in related oxide compounds, a structural model is proposed. A description of this double layer is then given in terms of sequence of polyhedra (tetragonal pyramids, mono-caped tetrahedra and trigonal bi-pyramids), in comparison with other related modulated structures with different periodicities. The powder sample exhibits a statistical distribution of a around an average value of 0.35; the oxygen non-stoichiometry appears as the driving force for the a value, i.e. for the modulation, commensurate or incommensurate. The Mossbauer study has:been performed and interpreted on the basis of the refined structure. (c) 2006 Elsevier Inc. All rights reserved.
Title:
Coincidence-site lattices as rational approximants to irrational twins
Authors:
Ranganathan, S; Srivastava, AK; Lord, EA Author Full Names: Ranganathan, S.; Srivastava, A. K.; Lord, E. A.
Source:
JOURNAL OF MATERIALS SCIENCE 41 (23): 7696-7703 DEC 2006
Abstract:
It is well known that sequences of crystals with Mackay icosahedral motif and increasing lattice parameters exist converging to the icosahedral quasi-crystal in the limit. They are known as rational approximants. It has also been demonstrated that it is possible to create icosahedral symmetry by irrational twins involving five variants by 72 degrees rotations around an irrational axis [tau 10] or an irrational angle of 44.48 degrees around a rotation axis [1 1 1]. These twinned crystals do not share a coincidence site lattice. In this paper, it is demonstrated that the above twinning relationship arises in the limit of a sequence of coincidence site lattices starting with the cubic twins with Sigma = 3 and extending through Sigma = 7, 19, 49, 129, 337, ..., infinity created by rotation around [1 1 1] axis. It is also noted that the boundaries of higher CSL values (Sigma > 7) are composed of a combination of structural units from Sigma = 3 and Sigma = 7 boundaries.
Title:
Rare earth oxyfluorosulfides: A new class of compounds with modulated structure
Authors:
Pauwels, D; Weill, F; Tressaud, A; Demourgues, A Author Full Names: Pauwels, Damien; Weill, Francois; Tressaud, Alain; Demourgues, Alain
Source:
CHEMISTRY OF MATERIALS 18 (26): 6121-6131 DEC 26 2006
Abstract:
New rare earth oxyfluorosulfides with La4-xYxO2F2S3 (x = 0, 1, 2) composition have been prepared by solid-state reactions. The structures of these compounds vary according to the x value. La4O2F2S3 exhibits an incommensurately modulated structure that has been investigated by means of powder X-ray and electron diffraction. The modulated structure has an orthorhombic symmetry, space group Amam-(00 gamma)ss0 in (3 + 1) formalism with the following parameters a = 7.0250(4) angstrom, b = 7.2171(4) angstrom, c = 4.2696(3) angstrom, and q* = 0.26070(5) c*. A three-dimensional approximation of the *structure* can be proposed by considering a superstructure of the basic *cell* with c(1) = 23 c. La4-xYxO2F2S3 (x = 1, 2) compounds exhibit commensurate networks related to a Ce4O4S3 type structure and have been solved from X-ray powder diffraction data. These new phases exhibit ribbons and are closely related to the La2O2S type phases. The formation of these phases and the structural arrangements are explained by shearing mechanisms from the La2O2S structure. The origin of the modulation is discussed in terms of sheet arrangements and the local environment of the rare earth compound. Thus, it has been shown for the first time that the rare earth compound size, i.e., the nature, the number of neighbors, and the cation-anion bond distances, strongly influence the setting up of such modulations that occur to support constraints around the rare earth compound.
Title:
Structural and magnetic characterization of martensitic Ni-Mn-Ga thin films deposited on Mo foil
Authors:
Chernenko, VA; Anton, RL; Kohl, M; Barandiaran, JM; Ohtsuka, M; Orue, I; Besseghini, S Author Full Names: Chernenko, V. A.; Anton, R. Lopez; Kohl, M.; Barandiaran, J. M.; Ohtsuka, M.; Orue, I.; Besseghini, S.
Source:
ACTA MATERIALIA 54 (20): 5461-5467 DEC 2006
Abstract:
Three martensitic Ni51.4Mn28.3Ga20.3 thin films sputter-deposited on a Mo foil were investigated with regard to their crystal and magnetic domain structures, as well as their magnetic and magnetostrain properties. The film thicknesses, d, were 0.1, 0.4 and 10 mu m. X-ray and electron diffraction patterns revealed a tetragonal modulated martensitic phase (10 M) in the films. The surface topography and micromagnetic structure were studied by scanning probe microscopy. A maze magnetic domain structure featuring a large out-of-plane magnetization component was found in all films. The domain width, delta, depends on the film thickness as delta similar to root d. The thickness dependencies of the saturation magnetization, saturation magnetic field and magnetic anisotropy were clarified. Beam cantilever tests on the Ni-Mn-Ga/Mo composite as a function of magnetic field showed reversible strains, which are larger than ordinary magnetostriction. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
A symmetrical indexing scheme for decagonal quasicrystals analogous to Miller-Bravais indexing of hexagonal crystals
Authors:
Ranganathan, S; Lord, EA; Mukhopadhyay, NK; Singh, A Author Full Names: Ranganathan, S.; Lord, E. A.; Mukhopadhyay, N. K.; Singh, Alok
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 63: 1-10 Part 1 JAN 2007
Abstract:
The problems of redundancy and superfluous indices in indexing the planes and axes in a decagonal quasicrystal are considered, using a scheme of five coplanar vectors in the quasiperiodic plane and one perpendicular vector. Of all the indexing schemes in use, this scheme offers the maximum advantage. An analogy is drawn to the hexagonal system using Miller-Bravais indices. Based on this, a symmetry-based indexing system for decagonal phases is devised that follows a simplified approximate zone law analogous to the exact zone law for the hexagonal case. The indices based on this scheme will be designated as `Frank indices'. High-symmetry electron diffraction zone-axis patterns as well as powder X-ray diffraction patterns are indexed using Frank indices and compared with those of other indexing schemes.

Update: 5-Jan-2007

Title:
Spin incommensurability and two phase competition in cobaltites
Authors:
Phelan, D; Louca, D; Kamazawa, K; Lee, SH; Ancona, SN; Rosenkranz, S; Motome, Y; Hundley, MF; Mitchell, JF; Moritomo, Y Author Full Names: Phelan, D.; Louca, Despina; Kamazawa, K.; Lee, S. -H.; Ancona, S. N.; Rosenkranz, S.; Motome, Y.; Hundley, M. F.; Mitchell, J. F.; Moritomo, Y.
Source:
PHYSICAL REVIEW LETTERS 97 (23): Art. No. 235501 DEC 8 2006
Abstract:
The perovskite LaCoO3 evolves from a nonmagnetic Mott insulator to a spin cluster ferromagnet (FM) with the substitution of Sr2+ for La3+ in La1-xSrxCoO3. The clusters increase in size and number with x and the charge percolation through the clusters leads to a metallic state. Using elastic neutron scattering on La1-xSrxCoO3 single crystals, we show that an incommensurate spin superstructure coexists with the FM spin clusters. The incommensurability increases continuously with x, with the intensity rising in the insulating phase and dropping in the metallic phase as it directly competes with the commensurate FM, itinerant clusters. The spin incommensurability arises from local order of Co3+-Co4+ clusters but no long-range static or dynamic spin stripes develop. The coexistence and competition of the two magnetic phases explain the residual resistivity at low temperatures in samples with metalliclike transport.
Title:
Fractional charges and quantum phase transitions in imbalanced bilayer quantum Hall systems
Authors:
Ye, JW Author Full Names: Ye, Jinwu
Source:
PHYSICAL REVIEW LETTERS 97 (23): Art. No. 236803 DEC 8 2006
Abstract:
We extend the composite boson theory to study slightly imbalanced bilayer quantum Hall systems. In the global U(1) symmetry breaking excitonic superfluid side, as the imbalance increases, the system supports continuously changing fractional charges. In the translational symmetry breaking pseudospin density wave (PSDW) side, there are two quantum phase transitions from the commensurate PSDW to an incommensurate PSDW and then to the excitonic superfluid state. We compare our theory with experimental data and also the previous microscopic calculations.
Title:
Double symmetry breaking and magnetic transitions in ErFe4Ge2
Authors:
Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Buschow, KHJ Author Full Names: Schobinger-Papamantellos, P.; Rodriguez-Carvajal, J.; Buschow, K. H. J.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 (1): 63-75 MAR 2007
Abstract:
We have revised the T-magnetic phase diagram of the compound ErFe4Ge2 based on a recent X-ray powder diffraction study and software development enabling a new approach to this complex situation. Special emphasis is given to the intermediate temperature (IT) range 20 K-T-N, T-c below the double first-order magneto-elastic transition where the tetragonal high-temperature (HT) phase disproportionates into two distinct orthorhombic phases: P4(z)/mnm (HT phase) T-N,T-c = 44K -> Cmmm (majority low-temperature (LT) phase) q(1) = (0, 1/2, 0) + Pnnm (minority IT Phase) (q(2) = (0, q(y), 0), q(y) approximate to 2/11). The phase diagram comprises three distinct regions: the HT range T-N, T-c-293 K where the tetragonal phase P4(2)/mnm is stable, the IT range 20 K-TN, where the Cmmm and Pnnm phases coexist in strongly variable proportions and the LT range, 1.5-20K, where Cmmm prevails. The Pnnm phase reaches its highest concentration ( 33%) around 30 K. We report on the multi-axial amplitude modulated incommensurate magnetic structure of the Pnnm phase with a 2D-canted Fe moment arrangement q(2) = (0, q(y), 0) and on the coexisting Cmmm 3D-canted magnetic phase with q(1), = (0, 1/2, 0). The spin reorientation transitions occurring in the Cmmm phase relate to the various structural changes both arising from competing magnetoelastic mechanisms, involving the Er crystal field anisotropy the Er-Er, Er-Fe and Fe-Fe exchange interactions and their coupling to the lattice strain. The Er-Er and Er-Fe interactions are dominating in the LT Cmmm phase while the Fe-Fe and Er-Fe interactions prevail in the Pnnm phase. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Crystallographic and electrochemical properties of ball-milled quasicrystalline Ti45Zr35Ni17Cu3 alloy with 20 mass% Ni
Authors:
Liu, BZ; Wu, YM; Wang, LM Author Full Names: Liu, Baozhong; Wu, Yaoming; Wang, Limin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 425 (1-2): 296-301 NOV 30 2006
Abstract:
Icosahedral quasicrystalline Ti45Zr35Ni17Cu3 alloy powder was ball-milled with 20 mass% Ni, and the effect of the ball-milling time (t) on crystallographic and electrochemical characteristics were investigated. The amounts of icosahedral quasicrystalline and Ni phases decreased when ball-milling time increased from 30 to 180 min. The powder consisted of amorphous and (Ni and Ti) phases after 360 min of ball-milling. The maximum discharge capacity of the powder electrodes first increased from 89 (t = 0 min) to 192 mAh g(-1) (t = 180 min), and then decreased to 138 mAh g(-1) (t = 360 min). The high-rate dischargeability and the discharge capacity after 15 cycles increased with increasing ball-milling time. (c) 2006 Elsevier B.V. All rights reserved.
Title:
The possible origin of incommensurate spin textures in HTSC
Authors:
Mitsen, KV; Ivanenko, OM Author Full Names: Mitsen, K. V.; Ivanenko, O. M.
Source:
EUROPEAN PHYSICAL JOURNAL B 52 (2): 227-231 JUL 2006
Abstract:
An model of La2-xSrxCuO4 explaining the features of incommensurate spin textures without any assumption of stripe formation is proposed. The foundations of this model are the mechanism of negative-U center formation proposed earlier and the concept of specific ordering of doped ions. It is shown that within the framework of the proposed model the features of "stripe" textures of La2-xSrxCuO4 reflect exclusively the geometrical relations existing in a square lattice and the competition between different types of doped hole ordering.
Title:
Colossal magnetostriction effect in HoMn2O5
Authors:
Radulov, I; Nizhankovskii, VI; Lovchinov, V; Dimitrov, D; Apostolov, A Author Full Names: Radulov, I.; Nizhankovskii, V. I.; Lovchinov, V.; Dimitrov, D.; Apostolov, A.
Source:
EUROPEAN PHYSICAL JOURNAL B 52 (3): 361-364 AUG 2006
Abstract:
We have investigated the detailed field and temperature dependence of the dielectric constant, electric polarization, magnetization and magnetostriction in orthorhombic HoMn2O5 single crystals. HoMn2O5 displays incommensurate antiferromagnetic ordering below 39 K, becoming commensurate on further cooling. The commensurate-incommensurate transition takes place at low temperatures. The inherent magnetic frustration in this material is lifted by a small lattice distortion, primarily involving shifts of the Mn3+ cations and giving rise to a canted antiferroelectric phase. Colossal magnetostriction effect was observed and a novel phase transition diagram was build.
Title:
Investigation of whispering gallery mode dependence on cavity geometry of quasiperiodic photonic crystal microcavity lasers
Authors:
Lee, PT; Lu, TW; Tsai, FM; Lu, TC Author Full Names: Lee, Po-Tsung; Lu, Tsan-Wen; Tsai, Feng-Mao; Lu, Tien-Chang
Source:
APPLIED PHYSICS LETTERS 89 (23): Art. No. 231111 DEC 4 2006
Abstract:
Dodecagonal (12-fold) quasiperiodic photonic crystal (DQPC) microcavity lasers sustaining whispering gallery mode (WGM) are fabricated. Lasing characteristics of DQPC D2 microcavity lasers are obtained and compared with triangular lattice D2 photonic crystal (PC) lasers, and ultralow threshold is obtained. The strong WGM mode dependence on 12 nearest airholes of DQPC D2 microcavity and its fabrication tolerance is investigated and discussed by randomly varying the lattice of two separate regions. This mode dependence also indicates that one can enhance a WGM in different PC microcavities by modifying the cavity boundary to be circular. (c) 2006 American Institute of Physics.

Update: 29-Dec-2006

Title:
Incommensurate structural correlations in the disordered spin-dimer state induced by X-ray and electron irradiation in CuIr2S4
Authors:
Kiryukhin, V; Horibe, Y; Hor, YS; Noh, HJ; Cheong, SW; Chen, CH Author Full Names: Kiryukhin, V.; Horibe, Y.; Hor, Y. S.; Noh, H. J.; Cheong, S-W.; Chen, C. H.
Source:
PHYSICAL REVIEW LETTERS 97 (22): Art. No. 225503 DEC 1 2006
Abstract:
Irradiation with similar to 10 keV x rays or medium-energy electrons destroys long-range order of Ir spin dimers in CuIr2S4 while preserving the dimers locally. We find that as the order is destroyed, a new type of incommensurate structural correlations appears. This represents an intriguing example of order from disorder phenomenon, in which a previously unknown incommensurate order appears in the radiation-induced disordered state. These results suggest that two competing instabilities, one of which can be suppressed by radiation, are present in the system. Otherwise unrealized structural or electronic states can, therefore, be revealed in correlated systems by x-ray or electron irradiation.
Title:
Exchange bias as a probe of the incommensurate spin-density wave in epitaxial Fe/Cr(001)
Authors:
Parker, JS; Wang, L; Steiner, KA; Crowell, PA; Leighton, C Author Full Names: Parker, J. S.; Wang, L.; Steiner, K. A.; Crowell, P. A.; Leighton, C.
Source:
PHYSICAL REVIEW LETTERS 97 (22): Art. No. 227206 DEC 1 2006
Abstract:
We report clear multiple period oscillations in the temperature dependence of exchange bias in an Fe thin film exchange coupled to a neighboring Cr film. The oscillations arise due to an incommensurate spin-density wave in the Cr, with wave vector perpendicular to the Fe/Cr(001) interface. The exchange bias and coercivity allow for a determination of the extent of the thermally driven wavelength expansion, the (strain-suppressed) spin-flip transition temperature, and the Cr Neel temperature, which show a crossover from bulklike to finite-size behavior at a Cr thickness of similar to 1100 A. The data are consistent with a transition from a transverse to longitudinal wave on cooling.
Title:
Stress potential function formulation and complex variable function method for solving the elasticity of quasicrystals of point group 10 and the exact solution for the notch problem
Authors:
Li, LH; Fan, TY Author Full Names: Li, Lian He; Fan, Tian You
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 18 (47): 10631-10641 NOV 29 2006
Abstract:
The plane elasticity equations of two-dimensional quasicrystals of point group 10 are reduced to a single partial differential equation with eighth order by introducing a stress potential function. Further, we develop the complex variable function method for classical elasticity theory to that of the quasicrystals. The complex representations of stress and displacement components of phonon and phason fields in the quasicrystals are given. With the help of conformal transformation, an exact solution for the elliptic notch of the quasicrystals is presented. The solution of the Griffith crack problem as a special case of the results is also observed. This work shows that the stress potential and complex variable function methods are powerful for solving the complicated boundary value problems of higher order partial differential equations originating from quasicrystal elasticity.
Title:
Dynamics in the melt of an icosahedral Al72Pd20Mn8 quasicrystal
Authors:
Okada, JT; Inui, M; Ishikawa, D; Baron, AQR; Matsuda, K; Tsutsui, S; Watanabe, Y; Nanao, S; Ishikawa, T Author Full Names: Okada, J. T.; Inui, M.; Ishikawa, D.; Baron, A. Q. R.; Matsuda, K.; Tsutsui, S.; Watanabe, Y.; Nanao, S.; Ishikawa, T.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 18 (49): L613-L618 DEC 13 2006
Abstract:
The dynamic structure factor S(Q,.) of the melt of an icosahedral quasicrystal, Al72Pd20Mn8, was measured at 1223 K near the melting point, T-m = 1140 K, for momentum transfers, Q, from 1.5 to 27.15 nm(-1) by means of an inelastic x-ray scattering technique using synchrotron radiation at SPring-8. The composition of Al72Pd20Mn8 is a special one in AlPdMn ternary alloys, since an icosahedral AlPdMn quasicrystal is formed from the melt. The acoustic mode was observed in the low-Q region, and a substantial broadening of the longitudinal current current correlation function and the crossover of the effective sound velocity from hydrodynamic to viscoelastic regions were observed around 6 nm(-1), which hints at the existence of a cluster with a size of about 1 nm in the melt.
Title:
A case for local icosahedral order in undercooled metallic liquids and the influence on the nucleation barrier
Authors:
Kelton, KF; Gangopadhyay, AK; Kim, TH; Lee, GW Author Full Names: Kelton, K. F.; Gangopadhyay, A. K.; Kim, T. H.; Lee, G. W.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 352 (50-51): 5318-5324 DEC 1 2006
Abstract:
An overview of recent experimental and theoretical investigations on undercooled liquids is given, indicating developing short-range order with undercooling. Our in situ synchrotron X-ray diffraction studies of electrostatically levitated droplets of elemental Ti, Zr, and Ni liquids and coordinated undercooling and structural studies of a Ti-Zr-Ni liquid that forms an icosahedral quasicrystal are discussed in the context of these investigations. lcosahedral order is demonstrated to be a dominant component to the structures of all undercooled liquids studied, although it becomes significantly distorted with an increasing importance of the d-band bonding character. The liquid short-range order couples with the nucleation barrier, as predicted by Frank over a half-century ago. (c) 2006 Elsevier B.V. All rights reserved.
Title:
On the problem of the relation between phason elasticity and phason dynamics in quasicrystals
Authors:
Coddens, G Author Full Names: Coddens, G.
Source:
EUROPEAN PHYSICAL JOURNAL B 54 (1): 37-65 NOV 2006
Abstract:
It has recently been claimed that the dynamics of long-wavelength phason fluctuations has been observed in i-AlPdMn quasicrystals [S. Francoual et al. Phys. Rev. Lett. 91, 225501 (2003); A. Letoublon et al. 54, 753 (2001)]. We will show that the data reported call for a more detailed development of the elasticity theory of Jaric and Nelsson [M.V. Jaric and D.R. Nelsson, Phys. Rev. B 37, 4458 (1988)] in order to determine the nature of small phonon-like atomic displacements with a symmetry that follows the phason elastic constants. We also show that a simple model with a single diffusing tile is sufficient to produce a signal that (1) is situated at a "satellite position" at a distance q from each Bragg peak; that (2) has an intensity that scales with the intensity of the corresponding Bragg peak; (3) falls off as 1/q(2); and (4) has a time decay constant that is proportional to 1/Dq(2). It is thus superfluous to call for a picture of "phason waves" in order to explain such data, especially as such "waves" violate many physical principles.
Title:
Multicomponent alloys visualized as lower order alloys: Examples of quasicrystals and metallic glasses
Authors:
Biswas, T; Ranganathan, S Author Full Names: Biswas, Tripti; Ranganathan, Srinivasa
Source:
ANNALES DE CHIMIE-SCIENCE DES MATERIAUX 31 (6): 649-656 NOV-DEC 2006
Abstract:
Alloying is a powerful method by which metallurgical advances have been made. The possibility of multicomponent alloys opens up numerous possibilities. Three important themes solid solutions, quasicrystals and bulk metallic glasses - have emerged in recent years. However, an approach based on Structure Mapping pioneered by David Pettifor indicates that many higher order alloys can be visualized as pseudo-lower order alloys. Solid solutions can be seen to be pseudounary. Crystalline intermetallics are seen to be at the highest level pseudo-quaternary. It is also demonstrated that most quasicrystals and their rational approximants are pseudo-binary and that most metallic glasses are pseudo-ternary.

Update: 15-Dec-2006

Title:
The symmetry of the incommensurate magnetic phase of ErFe4Ge2
Authors:
Schobinger-Papamantellos, P; Janssen, T Author Full Names: Schobinger-Papamantellos, Penelope; Janssen, Ted
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 221 (11): 732-734 2006
Abstract:
ErFe4Ge2 has below the Neel temperature two phases in competition, one with a commensurate and one with an incommensurate spin wave. The symmetry of the latter may be analysed in terms of irreducible representations, superspace groups and magnetic superspace groups. In this paper we compare these approaches. The relation with the commensurate structure is discussed.
Title:
Search for new modulations in the BiFeO3 structure: SR diffraction and Mossbauer studies
Authors:
Palewicz, A; Szumiata, T; Przenioslo, R; Sosnowska, I; Margiolaki, I Author Full Names: Palewicz, A.; Szumiata, T.; Przenioslo, R.; Sosnowska, I.; Margiolaki, I.
Source:
SOLID STATE COMMUNICATIONS 140 (7-8): 359-363 NOV 2006
Abstract:
High resolution synchrotron radiation (SR) diffraction does not show any sign of charge ordering nor any crystal symmetry breaking in BiFeO3 at temperatures from 5 K up to 1000 K. The temperature dependence of the BiFeO3 lattice parameters shows a local minimum of the rhombohedral angle alpha(rh) around T-N suggesting a strong spin-lattice coupling. Mossbauer spectroscopy studies support the magnetic modulation of the hyperfine fields observed by NMR which are related to the modulated Fe3+ magnetic moments ordering observed by neutron diffraction. (c) 2006 Elsevier Ltd. All rights reserved.
Title:
Synchrotron X-ray diffractometry and imaging of strains and defects in icosahedral quasicrystal grains
Authors:
Gastaldi, J; Schenk, T; Mancini, L; Klein, H; Hartwig, J; Agliozzo, S; Baruchel, J; De Boissieu, M Author Full Names: Gastaldi, J.; Schenk, T.; Mancini, L.; Klein, H.; Hartwig, J.; Agliozzo, S.; Baruchel, J.; De Boissieu, M.
Source:
PHILOSOPHICAL MAGAZINE 86 (36): 5897-5908 DEC 21 2006
Abstract:
In order to better understand the long-range propagation of quasicrystalline order, as well as quasicrystal stability, it is important to know if defects are generated in the quasicrystal grains during their growth. Previously, we studied the degree of perfection of about ten icosahedral quasicrystal grains of various alloys (Al-Pd-Mn, Al-Cu-Fe, Zn-Mg-Y), as grown or annealed, and we disclosed that some of them were much more perfect than the others. In this work we have concentrated on another slice of such a grain of the Al-Pd-Mn alloy. Similarly, we have performed an extensive synchrotron X-ray topographic investigation of strain and defects in this grain, combined with phase-contrast radiography and high resolution X-ray diffraction examinations. Very few two-lobe contrasts associated with pores and no loop-shaped contrasts were observed on the X-ray topographs, but straight line segments and band contrasts have been identified. Line segments could be considered as the result of the climbing of polygonal dislocation loops, as observed by TEM by Caillard and coworkers. This would indicate that most strains and defects observed in quasicrystal grains, at room temperature, are the result of stresses (external and internal) acting after growth.
Title:
Elastic moduli of a Ti-Zr-Ni i-phase quasicrystal as a function of temperature
Authors:
Agosta, DS; Leisure, RG; Adams, JJ; Shen, YT; Kelton, KF Author Full Names: Agosta, D. S.; Leisure, R. G.; Adams, J. J.; Shen, Y. T.; Kelton, K. F.
Source:
PHILOSOPHICAL MAGAZINE 87 (1): 1-10 JAN 1 2007
Abstract:
The elastic constants of an icosahedral-phase (i-phase) quasicrystal of Ti39.5Zr39.5Ni21 were measured over the temperature range 3-292K using the technique of resonant ultrasound spectroscopy. Common elastic quantities were derived over this temperature range. Values at 290K are: bulk modulus 116.8 GPa; shear modulus 37.0 GPa; Young's modulus 100.5 GPa; Poisson's ratio 0.356. The internal friction was also studied. A Debye temperature of 316.7K was computed from the low-temperature elastic moduli. The present values for the elastic moduli and Poisson's ratio compare well with ultrasonically-derived values reported earlier for an i-phase Ti41.5Zr41.5Ni17 quasicrystal, but do not agree with recently reported results for i-phase forms of Ti40Zr40Ni20 and Ti52.8Zr26.2Ni21 obtained by pressure-volume measurements and conventional mechanical testing.
Title:
Friction between incommensurate crystals
Authors:
Friedel, J; de Gennes, PG Author Full Names: Friedel, J.; de Gennes, P. -G.
Source:
PHILOSOPHICAL MAGAZINE 87 (1): 39-49 JAN 1 2007
Abstract:
We present an overview of friction processes expected between two ideal crystals of strong layers (graphite, MoS2, etc.) when one crystal is rotated with respect to the other by a certain angle theta. We assume perfect conditions: no impurities; no preexisting dislocations in the bulk of the crystals; slow gliding velocities. Two regimes show up: (a) Weak coupling when theta > (U) over tilde (1)/U-L, where (U) over tilde (1) (U-L) are typical intra- (inter-) layer interactions. Here we expect weak friction, controlled by two-phonon processes, and analyzed by Sokolo. et al. However, we point out that surface waves at the interface also play a role. (b) Strong coupling (theta < (U) over tilde (1)/U-L) where two orthogonal sets of screw disclinations should build up in the contact plane, as shown long ago by F. C. Frank. Here (to a first approximation) the dislocations are arranged in ladders, and we expect solid friction with a Peierls-Nabarro threshold stress.
Title:
Experimental evaluation of phonon-phason coupling in icosahedral quasicrystals
Authors:
Edagawa, K; So, YG Author Full Names: Edagawa, K.; So, Y. Gi
Source:
PHILOSOPHICAL MAGAZINE 87 (1): 77-95 JAN 1 2007
Abstract:
By measuring phonon strain introduced in crystal approximants, the sign and magnitude of the phonon - phason coupling constant have been evaluated for icosahedral quasicrystals of Mg - Ga - Al - Zn and Al - Cu - Fe systems. The evaluated coupling constants are approximately -0.04 mu and 0.004 mu (mu = shear modulus) for the former and the latter, respectively. They are in good agreement with the results of a previously reported theoretical calculation. Possible effects of phonon - phason coupling on the onset of phasonic elastic instability in icosahedral quasicrystals are discussed.
Title:
The resonant X-ray diffraction in Co-akermanite: Theory and experiment
Authors:
Bindi, L; Dmitrienko, VE; Ovchinnikova, EN; Soedzhima, Y Author Full Names: Bindi, L.; Dmitrienko, V. E.; Ovchinnikova, E. N.; Soedzhima, Yu.
Source:
CRYSTALLOGRAPHY REPORTS 51 (6): 941-948 DEC 2006
Abstract:
The structural factors for X-ray resonant diffraction near the K - absorption edge of cobalt in Co-akermanite have been calculated with allowance for the known data about its incommensurate 2D modulation. It is shown that the local symmetry of Co atoms in the basic structure does not allow any pure resonant reflections in the dipole - dipole approximation. However, pure resonant reflections of the h00 ( h = 2 n + 1) type are possible owing to the dipole-quadrupole contribution. The 5D formalism is used for the incommensurately modulated structure. It is shown that the displacement terms in the anisotropic tensor atomic factors could mainly contribute to the first-order satellites, providing pure resonant satellite reflections of the hhlm0 (m = 2n + 1) or h00m (m) over bar (h = 2 n + 1) types.
Title:
Isotropic lazurite: A cubic single crystal with an incommensurate three-dimensional modulation of the structure
Authors:
Bolotina, NB Author Full Names: Bolotina, N. B.
Source:
CRYSTALLOGRAPHY REPORTS 51 (6): 968-976 DEC 2006
Abstract:
The incommensurately modulated structure of the isotropic lazurite Na6.41Ca1.36K0.04(Si6.09Al5.91)O-24(SO4)(1.73)Cl-0.17 from the Baikal region is solved in the (3 + 3)-dimensional symmetry group P23(gamma gamma 0) [where gamma = 0.2154(1)] with the basic unit cell parameter a = 9.077(1) angstrom. The structure is refined to R (0) = 0.04 for the main reflections and R-1 = 0.15 for the satellite reflections. Six modulation waves are directed along the side diagonals of the unit cell. The structural model under investigation is compared with the twin model previously proposed for the same crystal. The structural data obtained are used to construct fragments of the modulated structure. Considering the constructed fragments of the modulated structure, it has become possible for the first time to reproduce and describe the three-dimensional modulation of the framework and to reveal its relation to modulations of intraframework atoms.
Title:
Influence of layer charge on swelling of smectites
Authors:
Laird, DA Author Full Names: Laird, David A.
Source:
APPLIED CLAY SCIENCE 34 (1-4): 74-87 Sp. Iss. SI OCT 2006
Abstract:
Six separate processes control the swelling of smectites saturated with alkali and alkaline earth cations in aqueous systems. The basic mechanism and forces controlling each of the processes are different. Crystalline swelling occurs between smectite layers within quasicrystals and involves the intercalation of zero to four discrete layers of water molecules. A balance between strong electrostatic-attraction and hydration-repulsion forces controls crystalline swelling. The extent of crystalline swelling decreases with increasing layer charge. Double-layer swelling occurs between quasicrystals. An electrostatic repulsion force develops when the positively charged diffuse portions of double layers from two quasicrystals overlap in an aqueous suspension. Layer charge has little or no direct effect on double-layer swelling. The break up and formation of quasicrystals is a dynamic process that controls the average size of quasicrystals in an aqueous smectite suspension. As layer charge increases, quasicrystals tend to become larger and more stable. In smectite suspensions with more than one type of exchangeable cation, the cations can demix (e.g., Na and Ca may be segregated in different interlayer regions) due to a complex feed-back between cation exchange selectivity and crystalline swelling. Demixing influences the breakup and formation of quasicrystals because quasicrystals preferentially cleave along interlayers dominated by alkali cations. Increasing layer charge increases selectivity for alkaline earth cations relative to Na or Li, and hence reduces the breakup of quasicrystals. Co-volume swelling is an entropy driven process caused by restrictions on the rotational freedom of suspended quasicrystals. Brownian swelling is also an entropy driven process resulting from random thermal motion of suspended colloids. There is no reason to believe that layer charge directly influences either co-volume or Brownian swelling. Macro! scopic measures of swelling (e.g., change in total volume or w! ater con tent) necessarily measure the combined effect of all swelling processes occurring within the system. Published by Elsevier B.V.

Update: 8-Dec-2006

Title:
New class of compounds with unusual magnetic behaviour: Quasi-one-dimensional complex oxides of the A(3n) (+) (3m)A'(n) (+) O-n(9m) (+) (6n) family
Authors:
Bazuev, GV Author Full Names: Bazuev, G. V.
Source:
USPEKHI KHIMII 75 (9): 835-850 2006
Abstract:
The results of studies of the synthesis consitions, structure and magnetic properties of quasi-one-dimensional perovskite-like complex oxides of the A(3n+3m)A'nB3m+nO9m+6n family (A = Ca, Sr, Ba; A' = Cu, Ni, Co, Zn, Mg; B are platinum metals, Mn and other d- and p-elements) are generalised. It is shown that the low-dimensional structure of the compounds is determined by the presence of isolated chains consisting of octahedra with B-cations and trigonal prisms with A'-cations, which alternate in different ratios. The reasons for the formation of incommensurate compounds and the methods for refinement of their structures are considered. It is demonstrated that the presence of transition metals in A(3n+3m)A'(n)B(3m+n)O9(m+6n) and their quasi-one-dimensional structure are responsible for the high anisotropy of magnetic properties, in particular, retention of the intrachain exchange interactions at relatively high temperatures and low temperatures of three-dimensional magnetic ordering.
Title:
Magnetic excitations in metallic ferro- and antiferromagnets
Authors:
Endoh, Y; Boni, P Author Full Names: Endoh, Yasuo; Boeni, Peter
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 (11): Art. No. 111002 NOV 2006
Abstract:
The recent twenty years have witnessed significant progress in the basic understanding of the dynamical magnetic properties in metallic and strongly correlated materials, mainly due to the progress in inelastic neutron scattering (INS) techniques and polarization analysis. One of the major achievements in this discipline is, in fact, the finding that the magnetic scattering in ferromagnetic metals shows a universal behavior independent of the itinerancy of the magnetic moment. The dynamic susceptibility in the ordered state at low temperatures is well described by spin-wave excitation. In addition, the magnetic scattering function in the paramagnetic phase above the Curie temperature, T-C, follows a simple double Lorentzian behavior in both momentum and energy. Then, the energy scale of the spin fluctuations can be expressed in terms of the ratio of the strength of the magnetic correlations defined by the molecular field Curie temperature with respect to T-C. The magnetic fluctuations in incommensurate antiferromagnets, i.e., in metallic Cr or in the high temperature superconductors of doped La2CuO4 compounds, show, on the other hand, a rather complicated dynamical structure factor. In contrast to ferromagnetic metals and localized antiferromagnets, the longitudinal fluctuations seem to play an important role deep in the ordered state of Cr.
Title:
Collinear order in frustrated quantum antiferromagnet on square lattice (CuBr)LaNb2O7
Authors:
Oba, N; Kageyama, H; Kitano, T; Yasudai, J; Baba, Y; Nishi, M; Hirota, K; Narumi, Y; Hagiwara, M; Kindo, K; Saito, T; Ajiro, Y; Yoshimura, K Author Full Names: Oba, Noriaki; Kageyama, Hiroshi; Kitano, Taro; Yasudai, Jun; Baba, Yoichi; Nishi, Masakazu; Hirota, Kazuma; Narumi, Yasuo; Hagiwara, Masayuki; Kindo, Koichi; Saito, Takashi; Ajiro, Yoshitami; Yoshimura, Kazuyoshi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 (11): Art. No. 113601 NOV 2006
Abstract:
Magnetic susceptibility, heat capacity, high-field magnetization and neutron diffraction measurements have been performed on a two-dimensional S = 1/2 square-lattice system (CuBr)LaNb2O7, prepared by a topotactic ion-exchange reaction of a nonmagnetic double-layered perovskite RbLaNb2O7. (CuBr)LaNb2O7 exhibits a second-order magnetic transition at 32 K, in marked contrast to a spin-singlet nature for its Cl-based counterpart (CuCl)LaNb2O7, despite nearly identical structural parameters. The magnetic structure is a novel collinear antiferromagnetic (CAF) ordering characterized by a modulation vector q = (pi, 0, pi) with a reduced moment of 0.6 mu(B). Mixed ferromagnetic nearest-neighbor (J(1)) and anti ferromagnetic second-nearest-neighbor (J(2)) interactions are of comparable strength (J(1/)k(B) = -35.6 K and J(2)/k(B) = 41.3 K), placing the system in a more frustrated region of the CAF phase than ever reported.
Title:
Ferroelectricity induced by incommensurate-commensurate magnetic phase transition in multiferroic HoMn2O5
Authors:
Kimura, H; Kamada, Y; Noda, Y; Kaneko, K; Metokii, N; Kohn, K Author Full Names: Kimura, Hiroyuki; Kamada, Youichi; Noda, Yukio; Kaneko, Koji; Metokii, Naoto; Kohn, Key
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 (11): Art. No. 113701 NOV 2006
Abstract:
Neutron diffraction measurements under high magnetic fields in multiferroic HoMn2O5 have revealed a clear relationship between microscopic magnetism and field-induced ferroelectricity. The applied magnetic field induces a first-order phase transition from an incommensurate magnetic order to a commensurate magnetic order, where a spontaneous electric polarization occurs. The one-to-one correspondence between the magnetic phase diagram and the dielectric phase diagram under magnetic field clearly indicates that the electric polarization is magnetically induced and the commensurate magnetic structure is indispensable to the ferroelectricity in the multiferroic RMn2O5 system.
Title:
Spin dynamics in copper metaborate CuB2O4 studied by muon spin relaxation
Authors:
Fukaya, A; Watanabe, I; Yamada, K; Nagamine, K Author Full Names: Fukaya, Atsuko; Watanabe, Isao; Yamada, Kazuyoshi; Nagamine, Kanetada
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 (11): Art. No. 113705 NOV 2006
Abstract:
Copper metaborate CuB2O4 was studied by muon spin relaxation measurements in order to clarify its static and dynamic magnetic properties. The time spectra of muon spin depolarization suggest that the local fields at the muon site contain both static and fluctuating components in all ordered phases down to 0.3 K. In the weak ferromagnetic phase (20 > T > 9.3 K), the static component is dominant. On the other hand, upon cooling, the fluctuating component becomes dominant in the incommensurate helix phase (9.3 > T > 1.4 K). The dynamical fluctuations of the local fields persist down to 0.3 K, where a new incommensurate phase (T < 1.4 K) is suggested to appear. This result suggests that spins fluctuate even at T -> 0. We propose two possible origins of the remnant spin fluctuations: frustration of the exchange interactions and the dynamic behavior of the soliton lattice.

Update: 1-Dec-2006

Title:
Synthesis, crystal structure, phase relations and chemical bonding analysis of the new Nowotny chimney-ladder compound ZrBi1.62
Authors:
Bostrom, M; Lind, H; Lidin, S; Niewa, R; Grin, Y Author Full Names: Bostroem, Magnus; Lind, Hanna; Lidin, Sven; Niewa, Rainer; Grin, Yuri
Source:
SOLID STATE SCIENCES 8 (10): 1173-1180 OCT 2006
Abstract:
ZrBi1.62 is a new compound crystallising with an incommensurate Nowotny chimney-ladder structure, which was refined from single crystal X-ray diffraction data using a four-dimensional formalism. The tetragonal unit cell has the lattice parameters a = 6.958(7) angstrom, c = 3.460(3) angstrom and q = (0 0 0.382). The symmetry is described by the superspace group pair W:P4/nnc:q-1q1-P:I4(1)/amd:1-1ss. The full phase relations of ZrBi1.62 were established. with DTA and phase analysis by X-ray powder diffraction, showing that the compound is thermodynamically stable only in the limited temperature range of 740-820 degrees C. The chemical bonding in ZrBi1.62 was analyzed using the electron localization function (ELF) for the 5-fold and the 13-fold approximants of the incommensurate structure. The attractors of the ELF are located near the shortest Zr-Bi contacts, showing a covalent interaction between the zirconium and the bismuth atoms. No indication was found for direct bonding within the Zr and Bi networks, which usually is assumed in the crystal structure description of chimney-ladder phases. The calculated electron density of states (DOS) indicates metallic behavior. (c) 2006 Elsevier Masson SAS. All rights reserved.
Title:
HRTEM and SAED investigations of Cu-x MTe2 (M = V, Nb, Ta)
Authors:
Soergel, T; Kienle, L; Jansen, M Author Full Names: Soergel, Timo; Kienle, Lorenz; Jansen, Martin
Source:
SOLID STATE SCIENCES 8 (10): 1187-1192 OCT 2006
Abstract:
The copper intercalation compounds Cu0.87VTe2, CuNbTe2 and Cu0.89TaTe2 which were synthesised from the binary tellurides via topotactic low temperature intercalation reactions, were investigated by HRTEM and SAED. All the samples show microdomains with different types of order. Apart from the average structure which was revealed from Rietveld refinements earlier, also domains of commensurate superstructures with a fourfold b-axis and incommensurate modulations with q approximate to (0 1/4.2 0) are found. These domains show wave-like contrasts in the HRTEM micrographs. The "waves" have different propagation vectors, which can be related to the position of satellite reflections in SAED. For CuNbTe2, a large number of structure models was tested, which were based on the single crystal structure Of CU0.70NbTe2 (P2(1)/m (no. 11), a = 6.6872(9), b = 3.7018(5) and c = 7.324(1) angstrom, beta = 107.270(2)degrees). Finally, a structure model with a simple distortion is presented, which accounts for the superstructures seen in SAED, the wave-like contrast and the different propagation directions in the HRTEM micrographs. (c) 2006 Elsevier Masson SAS. All rights reserved.
Title:
Surface oxidation and thin film preparation of AlCuFe quasicrystals
Authors:
Rouxel, D; Pigeat, P Author Full Names: Rouxel, D.; Pigeat, P.
Source:
PROGRESS IN SURFACE SCIENCE 81 (10-11): 488-514 2006
Abstract:
This paper reviews the work carried out over the last decade by the Nancy team on surface oxidation and thin film preparation of AlCuFe icosahedral quasicrystals. After discussing the problems linked with the surfaces of these quasicrystals, this review addresses the issue of the preparation of quasicrystalline surfaces and the first steps of oxidation under very low pressure of oxygen. This paper compares the nucleation and growth of oxide on i-AlCuFe quasicrystal and on a classical crystalline phase of this alloy: omega-AlCuFe. Aluminium diffusion is studied through the aluminium segregation on the surface that occurs during exposure to oxygen. Some surface properties of quasicrystals are reviewed with regard to oxidation. The evolution of physical parameters such as surface energy, friction coefficient and optical emissivity is described. This review also deals with the preparation of i-AlCuFe thin films. Two protocols to make i-AlCuFe thin films with free surfaces are described and discussed. The mechanical resistance and the tribological behaviour of these thin films, the oxygen and carbon influence on the final crystalline structure, and the quasicrystallization kinetics are presented. (C) 2006 Elsevier Ltd. All rights reserved.
Title:
Effect of doping with iron on the charge ordering in La0.33Ca0.67Mn1-yFeyO3 (y=0, 0.05) manganites
Authors:
Orlova, TS; Laval, JY; Zakhvalinskii, VS; Stepanov, YP Author Full Names: Orlova, T. S.; Laval, J. -Y.; Zakhvalinskii, V. S.; Stepanov, Yu. P.
Source:
PHYSICS OF THE SOLID STATE 48 (11): 2115-2124 NOV 2006
Abstract:
The formation and specific features of the superstructure in La0.33Ca0.67Mn1-y Fe (y) O-3 (y = 0, 0.05) manganites doped with iron are investigated using transmission electron microscopy. The electron diffraction patterns of the manganites are studied in the temperature range 90-300 K, and the high-resolution electron microscope images recorded at temperatures of 91-92 K are analyzed. In both manganites, the structural transition that is accompanied by the formation of the superstructure and which is directly observed from the appearance of additional peaks in the electron diffraction patterns occurs at a temperature that is in close agreement with the charge ordering temperature T (CO) determined from the temperature dependences of the magnetization M(T). In the temperature range 90 < T < 200 K, the undoped compound has a commensurate superstructure characterized by the vector q = 1/3a* and triple the unit *cell* << 3a x b x c >> (where a approximate to b approximate to root 2a(p), c approximate to 2a(p) , and a(p)similar to 3.9 angstrom is the lattice parameter of a simple perovskite). The doping with iron (5 at. %) brings about a decrease in the charge ordering temperature T (CO) by 50 K and the formation of an incommensurate structure for which the magnitude of the vector q is smaller by approximately 15%. The unit cell of the superstructure in the iron-doped compound is not triple the unit cell but involves defects of ordering, such as quadrupling of the unit cell, numerous translations by a(p)root 2 along the a direction, and dislocation-type defects in the stripe structure of the charge ordering. These pseudoperiodic defects lead to a decrease in the magnitude of the vector q and are responsible for the incommensurability of the structure. A decrease in the charge ordering temperature T-CO due to the doping with iron and the incommensurability of the superstructure correlate with the change in the concentration of Mn3+ Jahn-Teller ions as a result of their replacement by Fe3+ non-Jahn-Teller ions.
Title:
New magnetic state in incommensurate magnetic phase of heavy-fermion superconductor CeRh0.6Co0.4In5
Authors:
Yokoyama, M; Amitsuka, H; Matsuda, K; Gawase, A; Oyama, N; Kawasaki, I; Tenya, K; Yoshizawa, H Author Full Names: Yokoyama, Makoto; Amitsuka, Hiroshi; Matsuda, Kei; Gawase, Akifumi; Oyama, Narumi; Kawasaki, Ikuto; Tenya, Kenichi; Yoshizawa, Hideki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 (10): Art. No. 103703 OCT 2006
Abstract:
We performed elastic neutron scattering experiments on solid solution CeRh1-xCoxIn5 with x = 0.4 to clarify the nature of the antiferromagnetic (AF) phase in the vicinity of the quantum critical point. We observed the incommensurate AF order below T-Nh = 3.5 K. The structure of the incommensurate AF order is basically unchanged from that for pure CeRhIn5. We further found the evolution of a new commensurate AF order with the modulation of q(c) = (1/2, 1/2, 1/2) below T-Nc, = 2.9 K. The volume-averaged moments for the incommensurate and commensurate AF phases are 0.38 mu(B)/Ce and 0.21 mu(B)/Ce, respectively, which are reduced from the incommensurate AF moment (0.75 mu(B)/Ce) for pure CeRhIn5. We suggest from these results that the commensurate magnetic correlation may be tightly coupled with the superconductivity observed below T-c = 1.4 K.
Title:
Transport properties of misfit-layered cobalt oxide [Sr2O2-delta](0.53)CoO2
Authors:
Ishiwata, S; Terasaki, I; Kusano, Y; Takano, M Author Full Names: Ishiwata, Shintaro; Terasaki, Ichiro; Kusano, Yoshihiro; Takano, Mikio
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 (10): Art. No. 104716 OCT 2006
Abstract:
We report on the measurements and analyses of resistivity, Hall coefficient, and thermopower of the misfit-layered compound, [Sr2O2-delta](p)CoO2, Using single-crystalline samples obtained by a high-pressure technique. Using a polycrystalline sample, magnetic susceptibilities are measured to roughly characterize the electronic states of the cobalt ions. The misfit ratio, p, was determined to be 0.53 from transmission electron microscopic analyses. [Sr2O2-delta](0.53)CoO2 shows metallic conduction down to 2K and Curie-Weiss-like susceptibility as Na0.75CoO2 does. In addition, the thermopower at room temperature is the smallest among the known misfit-layered cobalt oxides, though the carrier concentration is almost the same as that of the misfit-layered compound, Ca3Co4O9, which has a much larger thermopower. We discuss the room-temperature thermopower in misfit-layered cobalt oxides from the viewpoint of incommensurability-induced anisotropy which changes the density of states near the Fermi level.
Title:
Dielectric constant, loss factor and ac conductivity of Ni2+-doped K2ZnCl4 crystals in the ferroelectric-commensurate, incommensurate and normal phases
Authors:
Gaffar, MA; Abousehly, AM; Abu El-Fadl, A; Mostafa, MM Author Full Names: Gaffar, M. A.; Abousehly, A. M.; Abu El-Fadl, A.; Mostafa, M. M.
Source:
CRYSTAL RESEARCH AND TECHNOLOGY 41 (11): 1120-1130 NOV 2006
Abstract:
The dielectric constant (epsilon), dielectric loss (tan delta) and ac conductivity (sigma(ac)) of virgin and thermally cycled undoped and Ni2+-doped K2ZnCl4 (KZC) crystals in the ferroelectric-commensurate (FC), incommensurate (IC) and normal phases (N) have been studied Anomalous behaviour at the two-phase transition points was observed while measuring epsilon along the polar a-axis for the undoped sample. With increasing Ni2+-concentration a systematic shift of the phase transition temperature towards lower values and a continuous inhibition of the peak height were detected. epsilon changed linearly with lnf up to f=10(5) Hz. tan delta along the a-axis declared the phase transitions by peak changes, After Ni2+-doping this behaviour was preserved at the FC-IC phase transition point while the IC-N phase transition was manifested by a change in the slope of the straight line representing the tan delta-T dependence. The ac conductivity changed lineally with frequency according to a relation of the form sigma(ac) = sigma(o) f (beta) where 0>beta>1.9. sigma(ac) increased monotonically with increasing temperature and doping concentration in the low-temperature phases tending to merge in one straight-line with high activation energy that might be due to superionic dc conduction in the high temperature N-phase. Doping with Ni2+ pinned stripples, decreased the soliton-soliton interaction, weakened discommensuration effects, shortened the IC-phase and strongly affected the 'chaotic' behaviour at the TC-IC. (C) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Title:
Incommensurate modulation structure in ferroelectric Ca0.28Ba0.72Nb2O6 single crystals of tungsten bronze structure
Authors:
Lu, CJ; Qi, YJ; Li, JQ; Zhang, HJ; Wang, JY Author Full Names: Lu, C. J.; Qi, Y. J.; Li, J. Q.; Zhang, H. J.; Wang, J. Y.
Source:
APPLIED PHYSICS LETTERS 89 (19): Art. No. 191901 NOV 6 2006
Abstract:
Incommensurate modulation structure in uniaxial relaxor ferroelectric Ca0.28Ba0.72Nb2O6 single crystals was investigated using transmission electron microscopy (TEM). The wave-modulation vector can be expressed as q=(1/2)c(*)+(1+delta)(a(*)-b(*))/4, where the incommensurability parameter delta was determined to be about 0.09 from [110] diffraction pattern. High-resolution TEM observations along [110] zone provided direct evidence of the incommensurate superstructure. Structural modulation was also evident by high-resolution TEM images through [001] zone, where a sinusoidal variation along [110] and [1(1) over bar 0] was identified. The incommensurate superlattice structure is caused by the uniform mixing of slabs of two orthorhombic cells.
Title:
Improvement on the temperature coefficient of resonant frequency of hexagonal perovskites through intergrowth structures
Authors:
Zhao, F; Yue, ZX; Pei, J; Zhuang, H; Gui, ZL; Li, LT Author Full Names: Zhao, Fei; Yue, Zhenxing; Pei, Jing; Zhuang, Hao; Gui, Zhilun; Li, Longtu
Source:
APPLIED PHYSICS LETTERS 89 (20): Art. No. 202901 NOV 13 2006
Abstract:
Cation-deficient hexagonal perovskites Ba5Nb4O15, Ba6Nb4TiO18, and their intergrowth compounds were prepared by solid-state reaction method. Dielectric measurements showed that the intergrowth compounds had a relatively low temperature coefficient of resonant frequency (tau(f)) compared to that of the simple terms Ba5Nb4O15 and Ba6Nb4TiO18. On the basis of the structure data, the authors proposed a structural parameter d, the degree of atomic displacements, to evaluate the structural dependence of the temperature coefficient of resonant frequency. The reduced tau(f) value of intergrowths was considered to be resulted from the decreased degree of atomic displacements in the hexagonal perovskite structure. (c) 2006 American Institute of Physics.
Title:
Improvement of the thermoelectric characteristics of Fe-doped misfit-layered Ca3Co4-xFexO9+delta (x=0, 0.05, 0.1, and 0.2)
Authors:
Liu, CJ; Huang, LC; Wang, JS Author Full Names: Liu, Chia-Jyi; Huang, Li-Chen; Wang, Jung-Sheng
Source:
APPLIED PHYSICS LETTERS 89 (20): Art. No. 204102 NOV 13 2006
Abstract:
The authors report measurements of the electrical resistivity, Seebeck coefficient, and thermal conductivity for a series of misfit-layered oxides Ca3Co4-xFexO9+delta (x=0, 0.05, 0.1, 0.15, 0.2) prepared by solid state reaction. Structural parameters are refined with superspace group of X2/m(0b0)s0 using powder x-ray diffraction data. With partial substitution of Fe+2 for Co+3, the resistivity decreases, while the thermopower increases simultaneously. The x=0.05 sample exhibits a higher figure of merit (Z=3.01x10(-4) K-1) than that of Ca3Co4O9+delta (0.33x10(-4) K-1) at 300 K, indicating much improvement of thermoelectric characteristics via partial substitution of Fe for Co. (c) 2006 American Institute of Physics.
Title:
Superspace-symmetry determination and multidimensional refinement of the incommensurately modulated structure of natural fresnoite
Authors:
Bindi, L; Dusek, M; Petricek, V; Bonazzi, P Author Full Names: Bindi, Luca; Dusek, Michal; Petricek, Vaclav; Bonazzi, Paola
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 62: 1031-1037 Part 6 DEC 2006
Abstract:
The structure of natural fresnoite, Ba2TiSi2O8, from the sanbornite deposits of eastern Fresno County, California, has been solved and refined as an incommensurate structure in five- dimensional superspace. The structure is tetragonal, superspace group P4bm(alpha,alpha,1/2)(-alpha,alpha, 1/2)0gg, cell parameters a = 8.5353 (6), c = 10.4128 (7) A, modulation vectors q(1) = 0.3020 (3)(a* + b*), q(2) = 0.3020 (3)(a* + b*). Data collection was performed on an Xcalibur CCD diffractometer at 110 K. The structure was refined from 3452 reflections to final R = 0.0123. The model includes modulation of both atomic positions and displacement parameters. As a consequence of the Ba and O positional modulation, eight-, nine-and tenfold Ba coordinations occur throughout the structure. The change of coordination around the Ba atom is clearly represented by the deformation of the pentagonal rings, as seen from a projection along [001]. The deformed pentagonal rings correspond to Ba atoms with eight- and ninefold coordinations and form octagonal clusters closely resembling those observed in the incommensurate structure of melilite-type compounds.

Update: 24-Nov-2006

Title:
Structural properties of Sr0.61Ba0.39Nb2O6 in the temperature range 10-500 K investigated by high-resolution neutron powder diffraction and specific heat measurements
Authors:
Schefer, J; Schaniel, D; Pomjakushin, V; Stuhr, U; Petricek, V; Woike, T; Wohlecke, M; Imlau, M Author Full Names: Schefer, J.; Schaniel, D.; Pomjakushin, V.; Stuhr, U.; Petricek, V.; Woike, Th.; Woehlecke, M.; Imlau, M.
Source:
PHYSICAL REVIEW B 74 (13): Art. No. 134103 OCT 2006
Abstract:
We report high-resolution neutron powder diffraction on Sr0.61Ba0.39Nb2O6 in the temperature range 15-500 K. The results indicate that the low-temperature anomalies (T <= 100 K) observed in the dielectric dispersion are due to small changes in the incommensurate modulation of the NbO6 octahedra, as no structural phase transition of the average structure was observed. This interpretation is supported by specific heat measurements, which show no latent heat, but a glass-like behavior at low temperatures. Furthermore, we find that the structural changes connected with the ferroelectric phase transition at T-c similar or equal to 350 K start already at 200 K, explaining the anisotropic thermal expansion in the temperature range 200-300 K observed in a recent x-ray diffraction study.
Title:
Extrinsic origin of the insulating behavior of polygrain icosahedral Al-Pd-Re quasicrystals
Authors:
Dolinsek, J; McGuiness, PJ; Klanjsek, M; Smiljanic, I; Smontara, A; Zijlstra, ES; Bose, SK; Fisher, IR; Kramer, MJ; Canfield, PC Author Full Names: Dolinsek, J.; McGuiness, P. J.; Klanjsek, M.; Smiljanic, I.; Smontara, A.; Zijlstra, E. S.; Bose, S. K.; Fisher, I. R.; Kramer, M. J.; Canfield, P. C.
Source:
PHYSICAL REVIEW B 74 (13): Art. No. 1343201 OCT 2006
Abstract:
Polygrain icosahedral i-Al-Pd-Re quasicrystals are known to exhibit dramatically different electronic transport properties to other Al-based quasicrystals. By performing comparative experimental and theoretical studies of the electronic transport and electronic structure of polygrain and monocrystalline i-Al-Pd-Re samples, we show that the extraordinarily high electrical resistivity and the metal-to-insulator transition in the polygrain material are not intrinsic properties of the quasiperiodic lattice, but are of extrinsic origin due to the high porosity and the oxygen-rich weakly insulating regions in the material. We also compare theoretical electronic structures and experimental electrical resistivities of monocrystalline i-Al-Pd-Re and i-Al-Pd-Mn quasicrystals and show that there are no significant differences between these two isomorphous compounds, suggesting that i-Al-Pd-Re is on common ground with other Al-based quasicrystals. We present a structural model of i-Al-Pd-Re.
Title:
Theoretical analysis of the double-q magnetic structure of CeAl2
Authors:
Harris, AB; Schweizer, J Author Full Names: Harris, A. B.; Schweizer, J.
Source:
PHYSICAL REVIEW B 74 (13): Art. No. 134411 OCT 2006
Abstract:
A model involving competing short-range isotropic Heisenberg interactions is developed to explain the double-q magnetic structure of CeAl2 Theta. For suitably chosen interactions, terms in the Landau expansion quadratic in the order parameters explain the condensation of incommensurate order at wave vectors in the star of (1/2-delta,1/2+delta,1/2)(2 pi/a), where a is the cubic lattice constant. We show that the fourth-order terms in the Landau expansion lead to the formation of the so-called double-q magnetic structure in which long-range order develops simultaneously at two symmetry-related wave vectors, in striking agreement with the magnetic structure determinations. Based on the value of the ordering temperature and of the Curie-Weiss temperature Theta of the susceptibility, we estimate that the nearest-neighbor interaction K-0 is ferromagnetic with K-0/k=-11 +/- 1 K and the next-nearest neighbor interaction J is antiferromagnetic with J/k=6 +/- 2 K. We also briefly comment on the analogous phenomena seen in the similar system TmS.
Title:
Spin susceptibility of underdoped cuprates: The case of ortho-II YBa2Cu3O6.5
Authors:
Bascones, E; Rice, TM Author Full Names: Bascones, E.; Rice, T. M.
Source:
PHYSICAL REVIEW B 74 (13): Art. No. 134501 OCT 2006
Abstract:
We propose a model to explain the spin susceptibility of underdoped cuprates based on quasiparticle transitions between the arcs of a truncated Fermi surface. Such transitions are resonantly enhanced by scattering to the triplet spin resonance, which we view as the collective mode of a spin liquid. This model is able to explain the presence of magnetic scattering in the pseudogap state and its suppression at low energies on entering the superconducting state. We focus on recent inelastic neutron scattering measurements, which found that the spin susceptibility of detwinned and highly ordered ortho-II YBa2Cu3O6.5 exhibits, in both the normal and superconducting states, one-dimensional incommensurate modulations at low energies and which were interpreted as a signature of dynamic stripes. We show that the anisotropy in the experimental spin response is consistent with this model if the gap at the saddle points is anisotropic.
Title:
Composite incommensurate K-III and a commensurate form: Study of a high-pressure phase of potassium
Authors:
McMahon, MI; Nelmes, RJ; Schwarz, U; Syassen, K Author Full Names: McMahon, M. I.; Nelmes, R. J.; Schwarz, U.; Syassen, K.
Source:
PHYSICAL REVIEW B 74 (14): Art. No. 140102 OCT 2006
Abstract:
K-III, the high-pressure phase of potassium stable above 20 GPa, is reported to have a host-guest composite structure comprising the same 16-atom host structure as Rb-IV and a C-face-centered, rather than a body-centered, tetragonal, guest structure. At 22.0(2) GPa, the incommensurate ratio of the host and guest c-axis lattice parameters passes through the commensurate value of 8/5 but, within the experimental resolution of approximately 1 GPa, no lock-in to a commensurate structure is observed.
Title:
Electronic structure of charge-ordered Fe3O4 from calculated optical, magneto-optical Kerr effect, and OK-edge x-ray absorption spectra
Authors:
Leonov, I; Yaresko, AN; Antonov, VN; Anisimov, VI Author Full Names: Leonov, I.; Yaresko, A. N.; Antonov, V. N.; Anisimov, V. I.
Source:
PHYSICAL REVIEW B 74 (16): Art. No. 165117 OCT 2006
Abstract:
The electronic structure of the low-temperature (LT) monoclinic magnetite Fe3O4 is investigated using the local spin density approximation (LSDA) and the LSDA+U method. The self-consistent charge-ordered LSDA+U solution has a pronounced [001] charge density wave character. In addition, a minor [00 1/2] modulation in the phase of the charge order (CO) also occurs. While the existence of CO is evidenced by the large difference between the occupancies of the minority spin t(2g) states of "2+" and "3+" Fe-B cations, the total 3d charge disproportion is small, in accord with the valence-bond-sum analysis of structural data. Weak Fe orbital moments of similar to 0.07 mu(B) are obtained from relativistic calculations for the CO phase which is in good agreement with recent x-ray magnetic circular dichroism measurements. Optical, magneto-optical Kerr effect, and O K-edge x-ray absorption spectra calculated for the charge-ordered LSDA+U solution are compared to corresponding LSDA spectra and to available experimental data. The reasonably good agreement between the theoretical and experimental spectra supports the relevance of the CO solution obtained for the monoclinic LT phase. The results of calculations of effective exchange coupling constants between Fe spin magnetic moments are also presented.
Title:
Study of incommensurate modulation in V-doped La2Cu1-x(VO)(x)O4+delta by transmission electron microscopy
Authors:
Tang, CY; Liu, LH; Li, FH; Che, GC Author Full Names: Tang, C. Y.; Liu, L. H.; Li, F. H.; Che, G. C.
Source:
PHILOSOPHICAL MAGAZINE LETTERS 86 (10): 633-641 OCT 2006
Abstract:
Structural variations in a hole-rich grain of V-doped La2Cu1-x(VO)(x)O4+delta (x = 0.045, delta = 0.011) superconducting compound have been studied by electron diffraction and high-resolution transmission electron microscopy. Two types of one-dimensional (1-D) incommensurate modulation were observed one after the other when the specimen was exposed to electron beam irradiation. The features of these two modulated structures have been studied and are discussed.
Title:
Mechanical spectroscopy of quasicrystals
Authors:
Sinning, HR Author Full Names: Sinning, H. -R.
Source:
MECHANICAL SPECTROSCOPY III 115: 25-36 2006 Book series title: SOLID STATE PHENOMENA
Abstract:
The use of mechanical spectroscopy to characterize the quasicrystalline state of solid matter is reviewed. After a general, chronological survey of existing mechanical spectroscopy studies, which include elastic properties as well as various relaxation phenomena between low-temperature tunneling processes and high-temperature background damping, three subjects are considered in more detail: (i) the nature of intrinsic relaxation phenomena, including relaxation peaks in Al-Pd-Mn single quasicrystals, (ii) hydrogen-induced loss peaks in Zr/Ti-based quasicrystals and their use as a probe, and (iii) the study of nano-quasicrystalline structures and amorphous-quasicrystalline transitions. It is shown that by combined studies of different elastic and anelastic phenomena, mechanical spectroscopy can be a valuable tool to obtain information about the nature and motion of defects, about the type of local atomic order, and about phase transformations and different processes leading to the formation of quasicrystalline order.
Title:
Phenomenological theory of multiple spin density waves in fcc transition metals
Authors:
Uchida, T; Kakehashi, Y Author Full Names: Uchida, Takashi; Kakehashi, Yoshiro
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 (9): Art. No. 094703 SEP 2006
Abstract:
The relative stability among the multiple spin density wave (MSDW) states in fcc transition metals has been investigated on the basis of a Ginzburg-Landau type of free energy with terms up to the fourth order in magnetic moments. Obtained magnetic phase diagrams in the space of expansion coefficients indicate the possibility of various 3Q MSDW states in fee transition metals: the commensurate 30 state with Q = 2 pi/a (a being the lattice constant), the incommensurate linearly polarized 3Q state, and the incommensurate helically polarized 3Q state. It is shown that these 3Q states are always stabilized, when they are compared with the corresponding 2Q and 1Q states, and their magnetic moment amplitudes are the largest among those of the three states. The results are compared with previous results of the ground-state calculations, and possible scenarios to explain the experimental data of cubic gamma-Fe are proposed.
Title:
Properties of porous glasses with embedded ferroelectric materials
Authors:
Rysiakiewicz-Pasek, E; Poprawski, R; Polanska, J; Urbanowicz, A; Sieradzki, A Author Full Names: Rysiakiewicz-Pasek, E.; Poprawski, R.; Polanska, J.; Urbanowicz, A.; Sieradzki, A.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 352 (40-41): 4309-4314 NOV 1 2006
Abstract:
Methods of introducing two ferroelectric materials, viz. NaNO2 and (CH3NH3)(5)BiCl11 (PMACB), into porous glass matrices and the results of dielectric, pyroelectric, thermal expansion and SEM investigations are presented. The best filling degree was achieved for NaNO2 introduced from the melt, whereas a significantly worse filling effect was achieved for a water solution as the introducing agent. A splitting was observed in the temperature dependence of dielectric permittivity related to the incommensurate phase of NaNO2 embedded in porous glass from a water solution, whereas no incommensurate phase was observed in the case of glass filled with NaNO2 from the melt. The confined materials turned out to possess ferroelectric properties and exhibited phase transitions. The negative size effect was observed for porous glasses filled with NaNO2 and PMACB. The above conclusions are based on the anomaly of dielectric, pyroelectric and dilatometric properties observed in the phase transition regions. (c) 2006 Elsevier B.V. All rights reserved.

Update: 17-Nov-2006

Title:
Nonlinear transport in beta-Na0.33V2O5
Authors:
Sirbu, S; Yamauchi, T; Ueda, Y; van Loosdrecht, PHM Author Full Names: Sirbu, S.; Yamauchi, T.; Ueda, Y.; van Loosdrecht, P. H. M.
Source:
EUROPEAN PHYSICAL JOURNAL B 53 (3): 289-296 OCT 2006
Abstract:
Transport properties of the charge ordering compound beta-Na0.33V2O5 are studied in the temperature range from 30 K to 300 K using current driven DC conductivity experiments. It is found that below the metal-insulator transition temperature (T-MI = 136 K) this material shows a nonlinear charge density modulation behavior. The observed conductivity is discussed in terms of a classical domain model for charge density modulation transport.

Update: 10-Nov-2006

Title:
Modulated structures in Ni-Al-Cr alloy
Authors:
Jezierska, E; Pilawa, M
Source:
JOURNAL OF MICROSCOPY-OXFORD 223: 220-223 Part 3 SEP 2006
Abstract:
The crystal structures of the different modulated and layered martensites in Ni-Al-Cr alloy have been observed. The layered martensite can be well described by the L1(0) lattice with seven-layered or five-layered long-period stacking of {110} close-packed planes of the parent phase. Modulated martensite is considered as a lattice oscillation by shuffling of atoms.
Title:
A family of hexagonal and orthorhombic (Al,Si)(4)Cr approximants of quasicrystals
Authors:
He, ZB; Kuo, KH
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 424 (1-2): 164-170 NOV 9 2006
Abstract:
By means of transmission electron microscopy, four crystalline phases with compositions close to (Al,Si)(4)Cr have been found in Al-Cr-Si alloys. The hexagonal mu'-(Al4Si)(4)Cr has the same space group P6(3)/mmc as mu-(Al,Si)(4)Cr, but its c parameter is only one half of c mu. On the other hand, the orthorhombic epsilon-Al4Cr, epsilon'- and epsilon"-(Al,Si)(4)Cr have about the same lattice parameters but different space groups: Bbmm (or Cmcm), Pbnm and P2(1)2(1)2(1), respectively. The lattice parameters of these phases are closely related: a(epsilon,epsilon ',epsilon '') = root 3a(mu,mu ') congruent to 3.46 nm; = b(epsilon,epsilon ',epsilon '') = a(mu,mu ') = 2.00 nm; c(epsilon,epsilon ',epsilon '') = 1/2c(mu) = c(mu ') congruent to 1.24 nm. The symmetry of space group decreases from mu(mu '), epsilon, epsilon ' to epsilon '' and the space groups of any two neighboring phases have the minimal supergroup and the maximal subgroup relationship. Strong diffraction spots of all these phases exhibit pseudo icosahedral symmetry. In the (001) plane, icodahedra are linked by mutual penetration along the five-fold axis forming icosahedral chains in three directions at 120 degrees apart. These four (Al,Si)(4)Cr phases together with the epsilon-Al4Cr are not only structurally close related, but also are approximants of quasicrystals. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Double modulation and microstructure of the thermoelectric misfit compound [Ca(2-y)Ln(y)Cu(0.7+y)Co(1.3-y)O(4)][CoO2](b1/b2) (Ln = Pr, Y and 0 <= y <= 1/3)
Authors:
Creon, N; Perez, O; Hadermann, J; Klein, Y; Hebert, S; Hervieu, M; Raveau, B
Source:
CHEMISTRY OF MATERIALS 18 (22): 5355-5362 OCT 31 2006
Abstract:
In the present paper, we present one route for increasing the copper content in the misfit cobaltites by studying the [Ca(2-y)Ln(y)Cu(0.7+y)Co(1.3-y)O(4)][CoO2](b1/b2) (Ln = Pr, Y) series (Ln) magnetic Pr and nonmagnetic Y). We pay special attention to the modulated character of these compounds. The electron diffraction study shows a double modulation of the structure. The parameters of the two systems (rock salt and CdI2 types) are a(1) = a(2) = 4.805(9) angstrom, b(1) = 4.482(9) angstrom, b(2) = 2.804(9) angstrom, c(1) = c(2) = 12.75(3) angstrom, and, beta(1) = beta(2) = 93.7(2)degrees, v = b(1)/b(2)) 1.599(4). The first modulation vector q(1)* = 0.63b(1)* is associated with the misfit character of the compound, and the second one, q(2)* = 0.44a(1)* + 0.43c(1)*, is an intrinsic modulation of the rock salt layers. Accounting for this second modulation, the reconstruction of the reciprocal space leads the super-space group C2/m(1q0,alpha 0 gamma) mm, with q(1)* = 0.63b(1)* and q(2)* = 0.44a* + 0.43c*. The intrinsic *modulation* in the double [(Co,Cu)O](2) rock salt-type layer of a misfit cobaltite is shown for the first time by electron microscopy. Different twinning mechanisms are also characterized. The relationships with the strontium ferrites built up from four rock salt-related layers are discussed. An increase of the thermopower is obtained, as well with a magnetic (Pr) as a nonmagnetic (Y) cation, which shows that the enhancement is due to a valence effect rather than to a magnetic effect.
Title:
Limited quasicrystal formation in Zr-Ti-Cu-Ni-Al bulk metallic glasses
Authors:
Kuhn, U; Eymann, K; Mattern, N; Eckert, J; Gebert, A; Bartusch, B; Schultz, L
Source:
ACTA MATERIALIA 54 (18): 4685-4692 OCT 2006
Abstract:
Bulk amorphous Zr(62-x)Ti(x)Cu(20)Ni(8)AI(10) alloys with compositions of 0 <= x <= 7.5 were prepared by copper mold casting. Thermal stability and crystallization behavior of the specimens were characterized by differential scanning calorimetry. Structures were studied by X-ray diffraction and transmission electron microscopy. The mass density of the as-cast samples and of selected annealed states was determined. The difference in density changes, between as-cast glassy, relaxed and crystallized structures, depends on the Ti content of the alloys. The higher the packing density of the glassy state, the higher is the thermal stability of the bulk glass due to a decrease in atomic mobility. Small gradations of Ti in steps of 0.2 at.% reveal significant changes in the crystallization behavior of the alloys, concerning the size and the structure of the phases formed. Only compositions with 2 <= x < 4 form a metastable quasicrystalline phase during the first transformation step. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Discrete tomography of planar model sets
Authors:
Baake, M; Gritzmann, P; Huck, C; Langfeld, B; Lord, K
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 62: 419-433 Part 6 NOV 2006
Abstract:
Discrete tomography is a well-established method to investigate finite point sets, in particular finite subsets of periodic systems. Here, we start to develop an efficient approach for the treatment of finite subsets of mathematical quasicrystals. To this end, the class of cyclotomic model sets is introduced, and the corresponding consistency, reconstruction and uniqueness problems of the discrete tomography of these sets are discussed.

Update: 3-Nov-2006

Title:
Freezing and melting of a colloidal adsorbate on a 1D quasicrystalline substrate
Authors:
Schmiedeberg, M; Roth, J; Stark, H
Source:
PHYSICAL REVIEW LETTERS 97 (15): Art. No. 158304 OCT 13 2006
Abstract:
Using Monte Carlo simulations and an extended Landau-Alexander-McTague theory, we demonstrate that colloids in a one-dimensional quasicrystalline potential order in triangular and rhombic-alpha crystalline phases. Increasing the strength of the potential further, a new type of light-induced melting is discovered that has its origin in the nonperiodicity of the potential. In contrast to reentrant melting in periodic potentials, the quasicrystalline potential melts the crystalline phases even when they already exist at zero potential.
Title:
Glass transition on the development of a hydrogen-bond network in nano-channel ice, and subsequent phase transitions of the ordering of hydrogen atom positions within the network in [Co(H(2)bim)(3)](TMA)center dot 20H(2)O
Authors:
Watanabe, K; Oguni, M; Tadokoro, M; Oohata, Y; Nakamura, R
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 18 (37): 8427-8436 SEP 20 2006
Abstract:
Low-temperature thermal properties of crystalline [Co(H(2)bim)(3)](TMA)(.)20H(2)O were studied by adiabatic calorimetry, where H(2)bim is 2,2'-biimidazole, TMA is 1,3,5-benzene tricarboxylic acid, and 20H(2)O represents the water forming nano-channel in the crystal. A glass transition was observed at T-g = 107 K. It was discussed as a freezing-in phenomenon of a small number of water molecules remaining partially disordered in their positional arrangement. The possibility that some defects really remain in the hydrogen-bond network of channel water was mentioned. Two subsequent phase transitions were observed at 54.8 and 59 K. These were interpreted as being of a (super-structural commensurate)-incommensurate-(normal commensurate) type in the heating direction with respect to the hydrogen-atom positions as referred to the periodicity of the hydrogen-bond network. The transition entropy was evaluated to be 0.65 J K-1(H2O-mol)(-1) as a total of the two, indicating that the disorder of the hydrogen atoms is present only in part of the water molecules of the channel. Based on the fact that the excess heat capacity due to the equilibrium phase transition is observed down to 35-40 K, the relaxation time for the rearrangement of the hydrogen-atom positions was assumed at the longest to be 1 ks at 35 K. This indicates that the activation energy of the rearrangement amounts to at most 13 kJ mol(-1) and that the transfer of Bjerrum defects is attributed to the rearrangement.
Title:
Magnetization plateau in the S=1/2 spin ladder with alternating rung exchange
Authors:
Japaridze, GI; Pogosyan, E
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 18 (40): 9297-9306 OCT 11 2006
Abstract:
We have studied the ground-state phase diagram of a spin ladder with alternating rung exchange J(perpendicular to)(n) = J(perpendicular to)[1 + (-1)(n)delta] in a magnetic filed, in the limit where the rung coupling is dominant. In this limit the model is mapped onto an XXZ Heisenberg chain in uniform and staggered longitudinal magnetic fields, where the amplitude of the staggered field is similar to delta. We have shown that the magnetization curve of the system exhibits a plateau at magnetization equal to half of the saturation value. The width of a plateau scales as delta(nu), where. = 4/5 in the case of a ladder with isotropic antiferromagnetic legs and nu = 2 in the case of a ladder with isotropic ferromagnetic legs. We have calculated four critical fields (H-c1(+/-) and H-c2(+/-)) corresponding to transitions between different magnetic phases of the system. We have shown that these transitions belong to the universality class of the commensurate-incommensurate transition. The possibility for the realization of a new type of spin-Peierls instability, characterized by the spontaneous appearance of an alternating rung exchange in a uniform magnetic field and at a system magnetization equal to the half of its saturation value, is briefly discussed.

Update: 27-Oct-2006

Title:
Stable icosahedral phase in Mg-Zn-Gd alloy
Authors:
Liu, Y; Yuan, GY; Lu, C; Ding, WJ
Source:
SCRIPTA MATERIALIA 55 (10): 919-922 NOV 2006
Abstract:
Microstructural evolution including the stability of icosahedral phase (I-phase) in Mg95.9Zn3.5Gd0.6 alloy, before and after extrusion, has been investigated. The results indicate that the I-phase in Mg95.9Zn3.5Gd0.6 alloy is a face-centered icosahedral quasicrystal with stoichiometric composition Of Mg42Zn50Gd8 and that this I-phase has excellent thermal stability up to 713 K. The W-phase and W'-phase, which are considered approximate crystalline equivalents of I-phase, have also been observed in the as-extruded alloy. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Growth morphology and evolution of icosahedral quasicrystal in Mg-Zn-Y ternary alloys
Authors:
Wan, DQ; Yang, GC; Zhu, M; Zhou, YH
Source:
RARE METAL MATERIALS AND ENGINEERING 35 (9): 1404-1407 SEP 2006
Abstract:
A large volumetric fraction of icosahedral quasicrystal was gained through ordinary solidification technology in Mg-Zn-Y ternary alloys. The icosahedral quasicrystal in Mg-Zn-Y ternary alloys have two typical morphology features: petal-like, polygon-like. The different features of icosahedral quasicrystal are attributed to their morphology evolution. Alloying composition and cooling rate are major factors affecting the morphology of icosahedral quasicrystal. In the solidification process of quasicrystal alloys, the more the low-temperature phases and the less the cooling rate, the much more easily the changing into the polygon-like morphology from petal-like one takes place. Peritectic reaction occurs during the icosahedral quasicrystal formation which leads to element content difference in primary stage and in final stage of icosahedral quasicrystal evolution. The composition analyses show that Mg content is lower but Zn and Y contents are higher in the primary stage of quasicrystal growth.
Title:
Temperature dependence of atomic modulation in the incommensurate composite crystal structure of (Sr2Cu2O3)(0.70)CuO2 'Sr14Cu24O41'
Authors:
Gotoh, Y; Yamaguchi, I; Eisaki, H; Nagata, T; Akimitsu, J
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 445: 107-110 Sp. Iss. SI OCT 1 2006
Abstract:
Temperature dependence of atomic modulation in the incommensurate composite crystal structure of (Sr2Cu2O3)(0.70)CuO2, 'Sr14Cu24O41' with two-legged Cu2O3 ladder and edge-shared CuO2 chain has been investigated by single-crystal X-ray diffraction method using centrosymmetric (3 + 1)-dimensional superspace group. The displacive modulations of all constituent atoms at 150 K have been compared with those obtained at room temperature. The hole distribution between the Cu2O3 ladder plane and the one-dimensional CuO2 chain has been considered on the basis of the changes of lattice constants of incommensurate basic structure, the role of the atomic modulation and the interatomic distances between Cu atom in the Cu2O3 and O atom in the CuO2. It is indicated that the small amount of holes doped in the Cu2O3 ladder have been back-transferred to the CuO2 chain and that almost all of the holes in (Sr(2)Cu(2)O3)(0.70)CuO2 are localized in the CuO2 at low temperature. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Modulation in multiferroic BiFeO3: Cycloidal, elliptical or SDW?
Authors:
Przenioslo, R; Regulski, M; Sosnowska, I
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 (8): Art. No. 084718 AUG 2006
Abstract:
We present several modulated magnetic ordering models which all describe the high resolution neutron powder diffraction patterns of BiFeO3 with the same accuracy as the circular cycloid one proposed in [J. Phys. C 15 (1982) 4835]. These orderings are: the elliptical cycloid and the spin density wave (SDW). The ambiguity of the magnetic ordering in BiFeO3 is important in the context of recent models of the magnetoelectric coupling in perovskites.
Title:
The 1/1 and 2/1 approximants in the ScMgZn quasicrystal system: Triacontahedral clusters as fundamental building blocks
Authors:
Lin, QS; Corbett, JD
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 128 (40): 13268-13273 OCT 11 2006
Abstract:
Single-crystal structures are reported for Sc3Mg0.18(1)Zn17.73(3), the 1/1 approximant crystal (AC), and Sc11.18(9)Mg2.5(1)Zn73.6(2), the 2/1 AC, in the corresponding icosahedral quasicrystal (i-QC) system. The 1/1 AC crystallizes in space group Im (3) over bar, a = 13.863(2) angstrom, Z = 8, and the 2/1 AC, in Pa (3) over barh, a = 22.412 (2) angstrom, Z = 8. The latter, which is valuable in pointing the way to the QC structure, is the best ordered and refined 2/1 example to date. The fundamental building blocks in both ACs are triacontahedral clusters centered by smaller multiply endohedral Tsai-type arrays; the former are condensed through body-centered-cubic packing in the 1/ 1 and primitive cubic packing in the 2/1 AC. Novel prolate rhombohedra centered by Sc-Sc dimers are also generated between triacontahedra in the 2/1 AC.
Title:
Preparation and mechanical properties of a bulk icosahedral quasicrystalline Ti45Zr35Ni17Cu3 alloy
Authors:
Liu, BZ; Wu, YM; Wang, LM
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 352 (36-37): 3936-3941 OCT 1 2006
Abstract:
A bulk Ti45Zr35Ni17Cu3 alloy, which consisted of the icosahedral quasicrystalline phase, was prepared by mechanical alloying(MA) and subsequent pulse discharge sintering. Ti45Zr35Ni17Cu3 amorphous powders (with particle size < 50 mu m) were obtained after mechanical alloying for more than 150 h from the mixture of the elemental powder. The transformation temperature range from amorphous phase to the quasicrystalline phase was from 400 K to 900 K. The mechanical properties of the bulk quasicrystalline alloy have been examined at room temperature. The Vickers hardness and compressive fracture strength were 620 +/- 40 and 1030 +/- 60 MPa, respectively. The bulk quasicrystalline alloy exhibited the elastic deformation by the compressive test. The fracture mode was brittle cleavage fracture. (c) 2006 Elsevier B.V. All rights reserved.

Update: 20-Oct-2006

Title:
Deformed model sets and distorted Penrose tilings
Authors:
Sing, B; Welberry, TR
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 221 (9): 621-634 2006
Abstract:
In this article, we show how the mathematical concept of a deformed model set can be used to gain insight into the diffraction pattern of quasicrystalline structures. We explain what a deformed model set is, what its characteristic features are and how it relates to certain disorder phenomena in solids. We then apply this concept to distorted Penrose tilings, i.e., Penrose tilings where we apply size-effect-like distortions. While the size effect in crystals only operates on the diffuse scattering, there is also an intensity transfer on the Bragg peaks in distorted Penrose tilings. The persistence of pure point diffraction in distorted Penrose tilings can be explained by interpreting such tilings as deformed model sets.
Title:
Magnetic instability and oxygen deficiency in Na-doped TbMnO3
Authors:
Yang, CC; Chung, MK; Li, WH; Chan, TS; Liu, RS; Lien, YH; Huang, CY; Chan, YY; Yao, YD; Lynn, JW
Source:
PHYSICAL REVIEW B 74 (9): Art. No. 094409 SEP 2006
Abstract:
Oxygen vacancies in TbMnO3 were created by monovalent Na+ doping. The effects of the interruption of the superexchange paths on the spin orderings were investigated. Chemical doping resulted in a much higher ordering temperature, which is probably associated with enhanced Tb-Tb coupling because of a reduction in Tb-Tb interatomic distances. The oxygen vacancies turned the modulated Mn spin structure into a simple commensurate one, presumably due to interruptions of the in-plane (Mn-O)-(O-Mn) superexchange paths, which reduced the significance of the next nearest-neighbor interactions of the Mn ions. The modulated spin structure of the Mn moments was found to reappear in systems with high Na doping, indicating that the anisotropic magnetic couplings had reemerged.
Title:
Crystal and magnetic structure investigation of TbNi5-xCux (x=0,0.5,1.0,1.5,2.0): Experiment and theory
Authors:
Lizarraga, R; Bergman, A; Bjorkman, T; Liu, HP; Andersson, Y; Gustafsson, T; Kuchin, AG; Ermolenko, AS; Nordstrom, L; Eriksson, O
Source:
PHYSICAL REVIEW B 74 (9): Art. No. 094419 SEP 2006
Abstract:
The effect of Cu substitution on the structural and magnetic properties of TbNi5-xCux (x=0,0.5,1.0,1.5,2.0) have been investigated by x-ray diffraction, magnetization measurements and neutron powder and single crystal diffraction. The electronic and the magnetic structures of TbNi5 were studied using first principles theory. All samples were found to have the CaCu5-type structure, space group P6/mmm. The lattice parameters increase monotonically with increasing Cu concentration. The Curie temperature T-c has a maximum value of 29 K at x=1.0. The magnetic structure of TbNi5 at 10 K is incommensurate with a helimagnetic component [wave vector q similar to 2 pi/c(0,0,0.02)] perpendicular to a ferromagnetic one. In contrast, the substituted TbNi5-xCux alloy is ferromagnetic. All magnetic moments are observed to be located on the Tb atoms. The magnetocrystalline anisotropy in the ab plane is observed to be strongly increased by the Cu substitution, whereas the magnetization decreases with the Cu concentration. The observed magnetic structure of TbNi5 is consistent with first principles calculations regarding both the magnetic moments and the helimagnetic structure. The microscopical origin of the helimagnet is analyzed and correlated to the Fermi surface topology.
Title:
Coupling of phonons and electromagnons in GdMnO3
Authors:
Pimenov, A; Rudolf, T; Mayr, F; Loidl, A; Mukhin, AA; Balbashov, AM
Source:
PHYSICAL REVIEW B 74 (10): Art. No. 100403 SEP 2006
Abstract:
The infrared and terahertz properties of GdMnO3 have been investigated as functions of temperature and magnetic field, with special emphasis on the phase boundary between the incommensurate and the canted antiferromagnetic structures. The heterogeneous incommensurate phase reveals strong magnetodielectric effects, characterized by significant magnetoelectric contributions to the static dielectric permittivity and by the existence of electrically excited magnons (electromagnons). In the commensurate canted antiferromagnetic phase the magnetoelectric contributions to the dielectric constant and electromagnons are suppressed. The corresponding spectral weight is transferred to the lowest lattice vibration, demonstrating the strong coupling of phonons with electromagnons.
Title:
First-principles electronic structure study of Sc-II
Authors:
Ormeci, A; Koepernik, K; Rosner, H
Source:
PHYSICAL REVIEW B 74 (10): Art. No. 104119 SEP 2006
Abstract:
Sc crystallizes in the hcp structure at ambient pressure. The structure of the high-pressure phase Sc-II has been debated for a long time. Most recently, two different solutions for the Sc-II phase were proposed, both involving a composite incommensurate structure consisting of a host and a guest substructure. To explore the Sc-II crystal structure we perform first-principles total-energy calculations and find that the approximant modeling of the structure suggested by McMahon [Phys. Rev. B 73, 134102 (2006)] is the stable structure for pressures above the calculated transition pressure of 20 GPa. This theoretical value is in perfect agreement with the experimentally measured value of 23 GPa. Analyses of the band structures provide an explanation why the structure proposed by Fujihisa [Phys. Rev. B 72, 132103 (2005)] is not the correct Sc-II structure.
Title:
Spherical neutron polarimetry of the magnetic structure in HoNi2B2C: Interplay between magnetic phases and superconductivity
Authors:
Schneider, M; Zaharko, O; Gasser, U; Kreyssig, A; Brown, PJ; Canfield, PC
Source:
PHYSICAL REVIEW B 74 (10): Art. No. 104426 SEP 2006
Abstract:
Spherical neutron polarimetry has been used to answer open questions about different magnetic phases in HoNi2B2C, which are important in their interplay with superconductivity. We established that the incommensurate a(*) structure of k(3)=(0.585 0 0) at 5.4 K in a zero magnetic field is a transverse-amplitude modulated wave with the magnetic moment along the b direction of the tetragonal structure. The depolarization of a neutron beam scattered from the k(2)=(0 0 0.915) reflections reveals a multidomain state but does not allow an unambiguous determination of the spin configuration. Based on present knowledge of borocarbides and other rare-earth systems we give preference to a long-range incommensurate helical structure as the origin of the k(2)=(0 0 0.915) reflections.
Title:
Xe films on a decagonal Al-Ni-Co quasicrystalline surface
Authors:
Setyawan, W; Ferralis, N; Diehl, RD; Cole, MW; Curtarolo, S
Source:
PHYSICAL REVIEW B 74 (12): Art. No. 125425 SEP 2006
Abstract:
The grand canonical Monte Carlo method is employed to study the adsorption of Xe on a quasicrystalline Al-Ni-Co surface. The calculation uses a semiempirical gas-surface interaction, based on conventional combining rules and the usual Lennard-Jones Xe-Xe interaction. The resulting adsorption isotherms and calculated structures are consistent with the results of low energy electron diffraction experimental data. In this paper we focus on five features not discussed earlier [Phys. Rev. Lett. 95, 136104 (2005)]: the range of the average density of the adsorbate, the order of the transition, the orientational degeneracy of the ground state, the isosteric heat of adsorption of the system, and the effect of the vertical cell dimension.
Title:
Dielectric properties, conduction mechanism, and possibility of nanodomain state with quantum dot formation in impurity-doped gamma-irradiated incommensurate TlInS2
Authors:
Sardarly, RM; Mamedov, NT; Wakita, K; Shim, Y; Nadjafov, AI; Samedov, OA; Zeynalova, EA
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 203 (11): 2845-2851 SEP 2006
Abstract:
Temperature-dependent dielectric and conduction properties of the impurity-doped and gamma-irradiated samples of TlInS2 semiconductor-ferroelectric with incommensurate phase are presented. As found, in both cases a stable relaxor state is emerging in the material with temperature provided that the central ion in InS4 tetrahedron is replaced by an impurity atom such as Mn or Cr, or radiation dose exceeds 400 Mrad. Same as NMR-studies, the present work drives to a conclusion that In-displacements are among the components of the order parameter of the incommensurate phase transition. The origin of the non-activated conductivity observed in the relaxor state of TlInS2 is assumed to be resonance tunneling executed by charge carriers from electron levels in the band gap through potential barriers created by incommensurate superstructure. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Title:
The structural representation and properties of mutually incommensurate composite crystal (BiS)(x)TS2 (T = Ti, V, Nb and Ta)
Authors:
Gotoh, Y; Fujihisa, H; Takeya, S; Yamaguchi, I
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 203 (11): 2852-2855 SEP 2006
Abstract:
The structural representation of mutually incommensurate composite crystal, (BiS)(x)TS2 (T = Ti, V, Nb and Ta), with layered substructures has been described by superspace group approach. The incommensurate composite structures of (BiS)(x)TSx have been successfully characterized by the single-crystal X-ray-diffraction method. Temperature dependences of in-plane electrical resistivity of single composite crystals of (BiS)(x)TSx have been obtained by a standard d.c. four probe method in the range of 1.7-300 K. It has been found that the electronic transport properties of (BiS)(x)TSx compounds show metallic behavior below room temperature. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Title:
Features of the magnetoelectric behavior of the family of multiferroics RMn2O5 at high magnetic fields (Review)
Authors:
Kadomtseva, AM; Krotov, SS; Popov, YF; Vorob'ev, GP
Source:
LOW TEMPERATURE PHYSICS 32 (8-9): 709-724 AUG-SEP 2006
Abstract:
The family of multiferroics comprised of the orthorhombic manganates RMn2O5 (R=Eu,Gd,Er,Y), in which the coexistence of antiferromagnetism and ferroelectricity has been reported previously, is investigated at high magnetic fields. These compounds, unlike the members of the family RMnO3 (where R=Eu,Ge,Tb,Dy) have two subsystems of magnetic mixed-valence d ions Mn3+ and Mn4+, the direct and indirect interactions between which, being of the ferro- or antiferromagnetic type, depending on the particulars of the environment and properties of the rare-earth ions, enhance substantially the role of the frustrations observed in RMnO3 compounds. These systems, as a consequence of the specific combination of the additional magnetic degeneracy realized in them (due to competition between nearest- and next-nearest-neighbor interactions of nearly equal magnitude) and their strong magnetoelastic coupling, display a cascade of magnetic phase transitions, with the appearance/disappearance of incommensurate (modulated) magnetic structure independently along the a and c axes. The substantial magnetoelectric interactions observed in these systems provide the prerequisites not only for efficiently influencing the phase transitions by means of a magnetic field but also hold forth the possibility of magnetic control of electrical polarization effects.
Title:
Incommensurate modulated structure of the ferromagnetic shape-memory Ni2MnGa martensite
Authors:
Righi, L; Albertini, F; Calestani, G; Pareti, L; Paoluzi, A; Ritter, C; Algarabel, PA; Morellon, L; Ibarra, MR
Source:
JOURNAL OF SOLID STATE CHEMISTRY 179 (11): 3525-3533 NOV 2006
Abstract:
The ferromagnetic shape memory (NISM) alloy Ni2MnGa undergoes a martensitic transformation (NIT) at T = 220 K on cooling. The structure of this phase is studied by powder X-ray diffraction experiment. The analysis of the experimental data combined with the huge information reported in literature allowed to conclude that the Ni2MnGa martensite shows an incommensurate modulated structure closely related to a five-fold layered superstructure. The symmetry of the basic structure is found to be orthorhombic. The structure is refined by Rietveld method with superspace group Immm(00 gamma)s00 having a = 4.2187(1) angstrom, b = 5.5534(1), and c = 4.1899(1) angstrom and modulation vector q = 0.4248(3)c*. The results show that the modulation is mainly related to the periodic shuffling of the atomic *layers* perpendicular to the c-axis of the orthorhombic basic structure. (c) 2006 Elsevier Inc. All rights reserved.

Update: 13-Oct-2006

Title:
Progress in formation of the quasicrystalline phase in mechanically alloyed Al-Cu-Fe
Authors:
Yan, W; Zhang, ZH; Teng, XY; Geng, HR
Source:
RARE METAL MATERIALS AND ENGINEERING 35: 35-38 Suppl. 2 AUG 2006
Abstract:
Mechanical Alloying is a new method for material preparation and is widely used to process novel materials, such as amorphous alloys, quasicrystals, nanocrystals, intermetallics and supersaturated solid solutions, etc. As a thermodynamically stable icosahedral quasicrystalline phase, Al-Cu-Fe has received more attention due to its unique structure and physical properties. In the present paper, we review the research progress in the formation and thermodynamic stability of the quasicrystalline phase in mechanically alloyed Al-Cu-Fe system.
Title:
The precipitation sequence of Cu-Cr alloy materials
Authors:
Li, Q; Chen, JC; Sun, JL
Source:
RARE METAL MATERIALS AND ENGINEERING 35: 259-262 Suppl. 2 AUG 2006
Abstract:
Cu-1.56Cr alloy was prepared. Its structures in different aging stages were observed by TEM. In the initial stage, a modulated structure was found which is an ordered intermetallic phase named modulated structure I, and other modulated structure with DO3 type was found named modulated structure 11 upon aging at 500 degrees C for 45 min. The results show that the precipitation sequence of Cu-Cr alloy during aging does not to the traditional direct transformation form FCC structure to BCC, but to the sequence of gradual transformation a modulated structure to another modulated structure.
Title:
Apparently complex high-pressure phase of gallium as a simple modulated structure
Authors:
Perez-Mato, JM; Elcoro, L; Aroyo, MI; Katzke, H; Toledano, P; Izaola, Z
Source:
PHYSICAL REVIEW LETTERS 97 (11): Art. No. 115501 SEP 15 2006
Abstract:
The phase of gallium GaII, with symmetry C222(1) and 104 atoms per unit cell, has been recently reported as an example of structural complexity under high pressure. It is shown here that this phase is a simple modulated distortion of an average structure of Fddd symmetry with all atoms structurally equivalent. The modulation can be described with only 4 parameters and satisfies symmetry properties described by a centrosymmetric superspace group. The structural distortion is dominated by a frozen transversal mode associated with a single irreducible representation of Fddd, with a wave vector on the line Q, at an edge of the Brillouin zone. The average structure can be related with an hcp configuration through simple sliding of hcp layers, reminiscent of the hcp-bcc Burgers mechanism.
Title:
Electron localization or delocalization in incommensurate helical magnets
Authors:
Tanaka, S; Katsura, H; Nagaosa, N
Source:
PHYSICAL REVIEW LETTERS 97 (11): Art. No. 116404 SEP 15 2006
Abstract:
The electronic states in incommensurate helical magnets are studied theoretically from the viewpoint of the localization or delocalization. It is found that in the multiband system with a relativistic spin-orbit interaction, the electronic wave functions show both an extended and localized nature along the helical axis depending on the orbital, helical wave number, and the direction of the plane on which spins rotate. The possible realization of this localization is discussed.
Title:
Multiferroic properties of single-phase Bi0.85La0.15FeO3 lead-free ceramics
Authors:
Yuan, GL; Baba-Kishi, KZ; Liu, JM; Or, SW; Wang, YP; Liu, ZG
Source:
JOURNAL OF THE AMERICAN CERAMIC SOCIETY 89 (10): 3136-3139 OCT 2006
Abstract:
Single-phase and lead-free Bi0.85La0.15FeO3 multiferroic ceramics were prepared by a rapid liquid sintering method to study their crystal structure and multiferroic behaviors. Rietveld refinement of X-ray diffraction data showed a pseudo-cubic structure plus a small triclinic distortion. The absence of Fe2+ ions suggested few oxygen vacancies. Large polarizations of 20.3 mu C/cm(2) together with a piezoelectric d(33) coefficient of similar to 27.7 pC/N were achieved. This ferroelectricity originates from the stereochemical activity of the A-site Bi3+ lone electron pair. The remnant magnetizations of 0.0744-0.227 emu/g of Bi0.85La0.15FeO3 permitted by the canting angle of canted antiferromagnetic order was released as a result of the collapse of the space-modulated spin structure of BiFeO3. The observed dielectric anomalies proved the magnetoelectric couplings between ferroelectric order and canted antiferromagnetic order.
Title:
Preparation of AlRu intermetallic compounds by mechanical alloying
Authors:
de Medeiros, SN; Machado, FLA; Zampiere, RB; Santos, IA; Paesano, A
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 352 (32-35): 3718-3720 SEP 15 2006
Abstract:
The formation of Al6Ru intermetallic compounds using high-energy ball milling was investigated. High-purity Al and Ru crystalline powders, in the relative (molar) ratio of 6: 1, were milled for periods up to 30 h. Samples of the milled materials were annealed at different times and temperatures. The microstructures of the annealed samples were compared to those of the as-milled samples. It was found that the obtained alloys have compositions that are in accord with the Al-Ru phase diagram. However, the X-ray analysis of a 10 h milled sample, annealed at 873 K for 30 min, showed evidence of the formation of a quasicrystalline icosahedral alloy mixed with the crystalline Al6Ru. Scanning electron microscopy showed that the microstructures are similar to those obtained by other sample preparation techniques. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Spinodal decomposition in Fe-25Cr-12Co-1Si alloy under a 100 kOe magnetic field
Authors:
Sun, XY; Xu, CY; Zhen, L; Lu, LX; Qin, LC
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 306 (1): 69-72 NOV 1 2006
Abstract:
Spinodal decomposition in Fe-25Cr-12Co-1Si alloy subjected to thermo-magnetic treatment under a 100 kOe magnetic field was investigated by transmission electron microscopy (TEM) and Mossbauer spectrometry. The high magnetic field was found to accelerate spinodal decomposition in the early stage, but restrain the coarsening process, which led to the formation of very fine modulated structures with small aspect ratio for the ferromagnetic alpha(1) phase. The abnormal deterioration of magnetic properties was mainly attributed to the decrease of shape anisotropy of ferromagnetic alpha(1) phase for the step-aged Fe-25Cr-12Co-1Si alloy. (C) 2006 Elsevier B.V. All rights reserved.
Title:
The phase diagram and the structure of the charge-density-wave state in high magnetic field
Authors:
Grigoriev, PD; Lyubshin, DS
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS 142 (3-4): 167-172 FEB 2006
Abstract:
The properties of a charge-density wave (CDW) state in quasi-one-dimensional metals in magnetic field below the transition temperature are studied using the mean-field theory. We calculate the phase diagram and show that the CDW state with shifted wave vector in high magnetic field (CDWx phase) has at least double-cosine modulation on the most part of the phase diagram. The transition from CDW0 to CDWx state below the critical temperature is accompanied by a jump of the CDW order parameter and of the wave vector rather than by their continuous increase. This implies a first order transition between these CDW states and explains the strong hysteresis accompanying this transition in many experiments. We examine how the phase diagram changes in the case of imperfect nesting. The results are applicable to different families of organic metals.
Title:
Crystal growth and structure determination of oxygen-deficient Sr6Co5O15
Authors:
Sun, JL; Li, GB; Li, ZF; You, LP; Lin, JH
Source:
INORGANIC CHEMISTRY 45 (20): 8394-8402 OCT 2 2006
Abstract:
Large single crystals of oxygen-deficient Sr6Co5O15-delta compounds, i.e., Sr6Co5O14.70 and Sr6Co4.9Ni0.1O14.36, were obtained by using K2CO3 flux in the presence of additives of transition metal oxides. The single-crystal structure determination shows that the structures of Sr6Co5O14.70 and Sr6Co4.9Ni0.1O14.36 crystallize in the space group R (3) over bar and can be described as one-dimensional face-sharing CoO3 polyhedral chains and Sr cation chains. Unlike the other known 2H-perovskite-related oxides in which the polyhedral chains consist of octahedra (Oh) and trigonal prism (TP), the structure of Sr6Co5O14.70 and Sr6Co4.9Ni0.1O14.36 contain Oh and intermediate polyhedra (IP) and can be attributed to a general structure formula A(6)A'2B3O15-delta, which is closely related to the known A(6)A'B4O15 phases by shifting of a B atom and the O-3 triangle along the c axis. Further study on O3 reveals that this oxygen position splits into two independent positions, corresponding to polyhedral geometry of IP and TP, respectively. Therefore, the polyhedral chain in the structure should be more precisely described as a random composite of the 4Oh + TP and 3Oh + 2IP. This model is used to interpret the magnetic properties, although not quantitatively. The 4-D structure analysis was also conducted for both Sr6Co5O14.70 and Sr6Co4.9Ni0.1O14.36 with a commensurate modulated structure in a 4-D superspace group, R (3) over barm(00 gamma)0s, gamma = p/k = 3/5. By considering the same 4-D superspace group R (3) over barm(00 gamma)0s but different t-phases, one can understand the structure relationship between Sr6Co5O14.70 and Sr6Rh5O15.
Title:
High-pressure structures and phase transformations in elemental metals
Authors:
McMahon, MI; Nelmes, RJ
Source:
CHEMICAL SOCIETY REVIEWS 35 (10): 943-963 2006
Abstract:
At ambient conditions the great majority of the metallic elements have simple crystal structures, such as face-centred or body-centred cubic, or hexagonal close-packed. However, when subjected to very high pressures, many of the same elements undergo phase transitions to low-symmetry and surprisingly complex structures, an increasing number of which are being found to be incommensurate. The present critical review describes the high-pressure behaviour of each of the group 1 to 16 metallic elements in detail, summarising previous work and giving the best present understanding of the structures and transitions at ambient temperature. The principal results and emerging systematics are then summarised and discussed.
Title:
Coupling between octahedral tilting and ferroelectric order in tetragonal tungsten bronze-structured dielectrics
Authors:
Levin, I; Stennett, MC; Miles, GC; Woodward, DI; West, AR; Reaney, IM
Source:
APPLIED PHYSICS LETTERS 89 (12): Art. No. 122908 SEP 18 2006
Abstract:
Strong coupling between local polar displacements and a commensurate octahedral tilting is proposed to explain the onset of classic ferroelectric behavior in tetragonal tungsten bronzelike dielectrics Ba2LaxNd1-xNb3Ti2O15. The ferroelectric phase transition is associated with a discontinuous non-lock-in transformation of an incommensurate tilted structure to a commensurate superstructure. In a manner reminiscent of perovskitelike oxides, the driving force for commensurate tilting increases as the average ionic radius of the rare-earth ion decreases; no classical ferroelectric transition is observed for compositions with x > 0.75, which remain incommensurate and exhibit only relaxor behavior below room temperature. (c) 2006 American Institute of Physics.

Update: 6-Oct-2006

Title:
Spontaneous formation of the B2 phase from a decagonal quasicrystal under reduced constraint
Authors:
Kim, SH; Chattopadhyay, K; Inkson, BJ; Mobus, G; Kim, WT; Kim, DH
Source:
JOURNAL OF MATERIALS SCIENCE 41 (18): 6081-6086 AUG 2006
Title:
Modulated corrugations in the crystal structure of the superconductor CaAlSi
Authors:
Sparta, KM; Muller, R; Merz, M; Roth, G; Adelmann, P; Wolf, T
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 62: 710-718 Part 5 OCT 2006
Abstract:
We report the crystal structure analyses of CaAlSi from single-crystal and powder X-ray diffraction and the existence of two commensurately modulated phases, a sixfold and a fivefold modulated structure. This polymorphism seems to be correlated to the thermal history of the sample. We describe both modulated structures using a three-dimensional and a (3+1)-dimensional formalism.
Title:
Superspace description of the homologous series Ga4Tim-4O2m-2 with the crystallographic shear structure based on that of rutile
Authors:
Michiue, Y; Yamamoto, A; Tanaka, M
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 62: 737-744 Part 5 OCT 2006
Abstract:
A generalized approach is proposed for the structure description of the homologous series Ga4Tim-4O2m-2 with crystallographic shear ( CS) structures based on that of rutile. A (3+1)-dimensional model for an ideal CS structure is built up in connection with the CS operation in three-dimensional space. Its structural parameters are determined by m, the shear plane and the shear vector. The Rietveld fitting of the X-ray diffraction profile of Ga4Ti13O32 (m = 17) was successfully carried out using the ideal CS structure as an initial model, where modulation functions of atomic positions are inherently discontinuous and sawtooth-like. The deviation of a real structure from the ideal one was described by a few additional Fourier terms. This method was confirmed to be efficient for reducing the number of structural parameters required in the refinement in comparison to the conventional three-dimensional description.
Title:
First (3+2)-dimensional superspace approach to the structure of levyclaudite-(Sb), a member of the cylindrite-type minerals
Authors:
Evain, M; Petricek, V; Moelo, Y; Maurel, C
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 62: 775-789 Part 5 OCT 2006
Abstract:
The structure of synthetic levyclaudite-(Sb), approximately (Pb1-ySbyS)(1.357)[Sn1-x(Cu-2)(x)S-2], has been determined by single-crystal X-ray diffraction on the basis of the (3+2)-dimensional superspace approach. This misfit-layer compound, of the cylindrite type, results from the combination of two heavily modulated triclinic Q and H subsystems with a common q wavevector and only one shared reciprocal axis (stacking direction). The Q pseudo-tetragonal layer, similar to(Pb0.70Sb0.30S), derived from the NaCl archetype, is positively charged; the H pseudo-hexagonal layer, similar to(Sn0.85Cu0.30S2), derived from the CdI2 archetype, is negatively charged, owing to the replacement of Sn4+ in an octahedral coordination by Cu+ pairs in an opposite triangular coordination. The analysis shows a strong transverse displacive modulation of the two layers, referred to as a 'mondulation', correlated to a maximal Sb site occupation factor in the concavity of the Q layer undulation. The wavelength control of the 'mondulation' obeys the vernier principle (14c(Q) congruent to 13c(H)), which would correspond to an energy minimization through a charge transfer density modulation wave, common to all two-dimensional misfit-layer inorganic compounds.
Title:
Commensurate (C6H14N2)(2)[Mo8O26]center dot 4H(2)O and incommensurate (C6H14N2)(2)[Mo8O26]center dot 4.66H(2)O: a structural versatility linked to solvent content
Authors:
Evain, M; Petricek, V; Coue, V; Dessapt, R; Bujoli-Doeuff, M; Jobic, S
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 62: 790-797 Part 5 OCT 2006
Abstract:
The syntheses and structure determinations by means of single-crystal X-ray diffraction of commensurate (C6H14N2)(2)[Mo8O26]center dot 4H(2)O and incommensurate (C6H14N2)(2)[Mo8O26]center dot 4.66H2O, two new organic-inorganic hybrid compounds based on polyoxomolybdates and differing in their solvent content, are reported. Given the important disorder observed in the latter compound, only a combination of non-harmonic waves, crenel functions and TLS tensors offered a good modelling of the structure. (C6H14N2)(2)[Mo8O26]center dot nH(2)O results from the self-assembly of [Mo8O26](4-) anionic chains, C6H14N22+ (H(2)DABCO(2+)) cations and water molecules. The [Mo8O26](4-) chain is built from gamma-[Mo8O28](8)(-) octamolybdate clusters, connected to each other through corner sharing. In both compounds, the [Mo8O26](4-) chains are separated, in a similar way, by the H(2)DABCO(2+) subunits, acting as charge-compensating cations, and by the water molecules. The orientation of the H2DABCO(2+) cations is shown to be different from what has been observed previously in monoclinic (H(2)DABCO)(2)[Mo8O26]center dot 4H(2)O, and therefore to give a different network of hydrogen bonds.

Update: 29-Sep-2006

Title:
Charge state and diffusion of hydrogen in the TiZrNi icosahedral alloy
Authors:
Morozov, AY; Isaev, EI; Vekilov, YK
Source:
PHYSICS OF THE SOLID STATE 48 (9): 1625-1628 SEP 2006
Abstract:
The electronic structure of a hydrogen atom in a 1/1 approximant of the Ti-Zr-Ni icosahedral quasicrystal is investigated using ab initio methods based on the density functional theory. The charge state of the hydrogen atom in Ti36Zr32Ni13 with different types of tetrahedral pores, as well as the charge state of hydrogen at a ratio H/M approximate to 1.7, is determined. The hydrogen atom is found to be in a nearly neutral state. The coefficient of hydrogen diffusion in Ti36Zr32Ni13 is calculated.
Title:
A-site ordering versus electronic inhomogeneity in colossally magnetoresistive manganite films
Authors:
Moshnyaga, V; Sudheendra, L; Lebedev, OI; Koster, SA; Gehrke, K; Shapoval, O; Belenchuk, A; Damaschke, B; van Tendeloo, G; Samwer, K
Source:
PHYSICAL REVIEW LETTERS 97 (10): Art. No. 107205 SEP 8 2006
Abstract:
Epitaxial La3/4Ca1/4MnO3/MgO(100) (LCMO) thin film shows an unusual rhombohedral (R-3c) structure with a new perovskite superstructure at room temperature due to the CE-type ordering of La and Ca with modulation vector q=1/4[011]. A-site ordered film was found to be electronically homogeneous down to the 1 nm scale as revealed by scanning tunnelling microscopy/spectroscopy. In contrast, orthorhombic and A-site disordered LCMO demonstrate a mesoscopic phase separation far below the Curie temperature (T-C). Unique La/Ca ordering compensates the cation mismatch stress within one supercell, a(S)approximate to 1.55 nm, and enhances the electronic homogeneity. The phase separation does not seem to be a unique mechanism for the colossal magnetoresistance (CMR) as very large CMR approximate to 500% was also observed in A-site ordered films.
Title:
>From phason planes to superstructures in an Al-Pd-Mn alloy
Authors:
Tian, H; Sun, W; Zhang, Z
Source:
PHILOSOPHICAL MAGAZINE LETTERS 86 (9): 539-553 SEP 2006
Abstract:
The atomic structures of four structurally complex phases of an Al-Pd-Mn alloy, namely the Psi-, xi(1)-, xi(2)- and xi 3-phases, have been determined by means of high-resolution electron microscopy and by theoretical structure simulations based on the periodic stacking of two different types of phason planes. The structural characteristics of the Psi-phase appears as a thin slab of xi'-phase sandwiched between a pair of type-1 phason planes; in addition, three newly-found xi(i)-phases (i = 1-3) were constructed by periodic stacking of the type-2 phason planes with an adjacent stacking (xi(1)), centred by a flattened hexagon (xi(2)), which are sandwiched around a thin slab of xi-phase (xi(3)). High-resolution electron microscopy image simulations of the Psi-phase based on our structural model match very well with the experimental results and this agreement is also supported by electron diffraction and X-ray powder diffraction simulations based on the model. Our results show that structural models of periodic stacking of two types of phason planes can be used to construct the atomic structure of xi'- and xi-phase related superstructures in the Al-Pd-Mn alloy.
Title:
Effect of ionic strength and clay mineralogy on Na-Ca exchange and the SAR-ESP relationship
Authors:
Kopittke, PM; So, HB; Menzies, NW
Source:
EUROPEAN JOURNAL OF SOIL SCIENCE 57 (5): 626-633 OCT 2006
Abstract:
The relationship between sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) for all soils has traditionally been assumed to be similar to that developed by the United States Salinity Laboratory (USSL) in 1954. However, under certain conditions, this relationship has been shown not to be constant, but to vary with both ionic strength and clay mineralogy. We conducted a detailed experiment to determine the effect of ionic strength on the Na+-Ca2+ exchange of four clay minerals (kaolinite, illite, pyrophyllite, and montmorillonite), with results related to the diffuse double-layer (DDL) model. Clays in which external exchange sites dominated (kaolinite and pyrophyllite) tended to show an overall preference for Na+, with the magnitude of this preference increasing with decreasing ESP. For these external surfaces, increases in ionic strength were found to increase preference for Na+. Although illite (2:1 non-expanding mineral) was expected to be dominated by external surfaces, this clay displayed an overall preference for Ca2+, possibly indicating the opening of quasicrystals and the formation of internal exchange surfaces. For the expanding 2:1 clay, montmorillonite, Na+-Ca2+ exchange varied due to the formation of quasicrystals (and internal exchange surfaces) from individual clay platelets. At small ionic strength and large ESP, the clay platelets dispersed and were dominated by external exchange surfaces (displaying preference for Na+). However, as ionic strength increased and ESP decreased, quasicrystals (and internal exchange surfaces) formed, and preference for Ca2+ increased. Therefore, the relationship between SAR and ESP is not constant and should be determined directly for the soil of interest.
Title:
Pore-scale analysis of bulk volume change from crystalline interlayer swelling in Na+- and Ca2+-smectite
Authors:
Likos, WJ; Lu, N
Source:
CLAYS AND CLAY MINERALS 54 (4): 515-528 AUG 2006
Abstract:
Water-vapor sorption experiments were conducted to quantify bulk volume change of compacted expansive clay specimens resulting from interlayer hydration and dehydration in the crystalline swelling regime. Effects of interlayer cation type and pore fabric are examined by comparing results for natural Na+-smectite and Ca2+-smectite specimens compacted over a range of initial bulk densities. Transitions in interlayer hydration states are reflected in the general shape of the sorption isotherms and corresponding relationships between humidity and volume change. Hysteresis is observed in both the sorption and volume-change response. Volume change for Ca2+-smectite specimens is significantly greater than for Na+-smectite over the entire range of packing densities considered. Loosely compacted specimens result in less volume change for both clays. Results are interpreted in light of a conceptual framework based on previous SEM and TEM observations of particle and pore fabric for Na+ and Ca2+ smectite at high suctions. A pore-scale microstructural model is developed to quantitatively assess changes in interlayer and interparticle void volume during hydration. Modeling suggests that the relatively small volume changes observed for Na+-smectite are attributable to a reduction of interparticle void volume as expanding quasicrystals encroach into surrounding larger-scale pores. Volume change hysteresis is attributed to unrecovered alterations in interparticle fabric required to accommodate the swelling process. The results provide new insight to address volume change upscaling, hysteresis, and the general evolution of bi-modal pore fabric during crystalline swelling.
Title:
Identification of quasicrystalline particles in an isothermally aged Al-10Mg-0.5Ag alloy
Authors:
Kubota, M; Nie, JF; Muddle, BC
Source:
ALUMINIUM ALLOYS 2006, PTS 1 AND 2 519-521: 561-566 Part 1-2 2006 Book series title: MATERIALS SCIENCE FORUM
Abstract:
The trace additions of Ag to binary Al-Mg alloys promote precipitation of a phase in the under-aged condition. The structure of the phase in an Al-IOMg-0.5Ag (mass%) alloy have been characterised using transmission electron microscopy and electron microdiffraction. An icosahedral quasicrystal line phase, which is identified by the electron microdiffiraction patterns, has been found in the Al-10Mg-0.5Ag (mass%) alloy after solution treatment, water quenched and then aged during the time between 20 and 40 min. at 513K. The orientation relationship between the quasicrystalline phase and the alpha-Al matrix is as follows; i5 // < 011 >(alpha) and i3 // < 111 >(alpha). A uniform distribution of 14 finer-scale (typically 20 rim), faceted precipitate icosahedral quasicrystalline particles was observed within the core of the grains, but the precipitates became coarser (60-80 nm) approaching the grain boundary precipitate-free zone. The quasicrystalline particles contain elements of Al, Mg and Ag. The quasicrystalline precipitate particles, which are the metastable phase, appear to be the primary strengthening phase in the Al-10Mg-0.5Ag (mass%) alloy aged at 513K.
Title:
Spin-dependent phenomena in (Ga,Mn) As heterostructures
Authors:
Sankowski, P; Kacman, P
Source:
ACTA PHYSICA POLONICA A 110 (2): 139-150 AUG 2006
Abstract:
A model for spin-dependent tunneling in semiconductor heterostructures, which combines a multi-orbital empirical tight-binding approach with a Landauer-Buttiker formalism, is presented. Using this approach we explain several phenomena observed in modulated structures of (Ga,Mn)As, i.e., large values of the electron current spin polarization in magnetic Esaki-Zener diode and the high tunneling magnetoresistance ratio. Next, the relevance of this theory to assess the tunneling anisotropic magnetoresistance effect is studied. The results of applying the tight-binding model to describe the recently observed interlayer exchange coupling in (Ga,Mn)As-based superlattices are also shown.

Update: 22-Sep-2006

Title:
Commensurate and incommensurate ground states of Cs2CuCl4 in a magnetic field
Authors:
Veillette, MY; Chalker, JT
Source:
PHYSICAL REVIEW B 74 (5): Art. No. 052402 AUG 2006
Abstract:
We present calculations of the magnetic ground state of Cs2CuCl4 in an applied magnetic field, with the aim of understanding the commensurately ordered state that has been discovered in recent experiments. This layered material is a realization of a Heisenberg antiferromagnet on an anisotropic triangular lattice. Its behavior in a magnetic field depends on field orientation, because of weak Dzyaloshinskii-Moriya interactions. We study the system by mapping the spin-1/2 Heisenberg Hamiltonian onto a Bose gas with hardcore repulsion. This Bose gas is dilute, and calculations are controlled, close to the saturation field. We find a zero-temperature transition between incommensurate and commensurate phases as longitudinal field strength is varied, but only incommensurate order in a transverse field. Results for both field orientations are consistent with experiment.
Title:
Theory of hopping conductivity of a suspension of nanowires in an insulator
Authors:
Hu, T; Shklovskii, BI
Source:
PHYSICAL REVIEW B 74 (5): Art. No. 054205 AUG 2006
Abstract:
Thermal conductivity (kappa) of the Al-based Mackay-type 1/1-cubic approximants (alpha-phase) was investigated over a wide temperature range from 2 K to 300 K. Behaviors of kappa(T) observed for these 1/1-cubic approximants were essentially the same with those reported for the corresponding icosahedral quasicrystals; very small magnitude lower than 4.5 W/m K, small contribution of electrons, and possession of a local maximum and a local minimum around 30-50 K and 100-200 K, respectively. By analyzing measured lattice thermal conductivity kappa(lat)(T) in terms both of local atomic arrangements and phonon dispersions, we revealed that kappa(lat)(T) is greatly reduced by combination of the small group velocity of phonons and the enhanced umklapp process of phonon scattering. Those characteristics are brought about by the large lattice constant and vacancies in the structure.
Title:
Modulated magnetization depth profile in dipolarly coupled magnetic multilayers
Authors:
Bedanta, S; Kentzinger, E; Petracic, O; Kleemann, W; Rucker, U; Bruckel, T; Paul, A; Cardoso, S; Freitas, PP
Source:
PHYSICAL REVIEW B 74 (5): Art. No. 054426 AUG 2006
Abstract:
Polarized neutron reflectivity (PNR) and magnetometry studies have been performed on the metal-insulator multilayer [Co80Fe20(1.6 nm)/Al2O3(3 nm)](9) which exhibits dominant dipolar coupling between the ferromagnetic layers. Our PNR measurements at the coercive field reveal a novel and unexpected magnetization state of the sample, exhibiting an oscillating magnetization depth profile from CoFe layer to CoFe layer with a period of five bilayers along the multilayer stack. With the help of micromagnetic simulations we demonstrate that competition between long- and short-ranged dipolar interactions apparently gives rise to this unprecedented phenomenon.
Title:
Strain-amplified structural modulation of Bi-cuprate high-T-c superconductors
Authors:
Kaneko, S; Akiyama, K; Funakubo, H; Yoshimoto, M
Source:
PHYSICAL REVIEW B 74 (5): Art. No. 054503 AUG 2006
Abstract:
Two dimensional x-ray images of a multilayered bismuth high-temperature superconductor (HTS) together with reciprocal-space simulation have shown how unit cells are distorted to form "supercells," the structural modulation consisting of multiple unit cells with incommensurate modulation period in a HTS. Strain induced by the multilayered structure alters the lattice mismatch between bismuth and perovskite blocks, resulting in increased supercell distortion described by the amplitude in the modulation wave. While oxygen content affects the modulation period of the supercell, lattice mismatch dominates the displacement of each atom from its position in the perfect crystal to construct the distorted structure, the supercell.
Title:
Broken parity and a chiral ground state in the frustrated magnet CdCr2O4
Authors:
Chern, GW; Fennie, CJ; Tchernyshyov, O
Source:
PHYSICAL REVIEW B 74 (6): Art. No. 060405 AUG 2006
Abstract:
We present a model describing the lattice distortion and incommensurate magnetic order in the spinel CdCr2O4, a good realization of the Heisenberg "pyrochlore" antiferromagnet. The magnetic frustration is relieved through the spin-Peierls distortion of the lattice involving a phonon doublet with odd parity. The distortion stabilizes a collinear magnetic order with the propagation wave vector q=2 pi(0,0,1). The lack of inversion symmetry makes the crystal structure chiral. The handedness is transferred to magnetic order by the relativistic spin-orbit coupling: the collinear state is twisted into a long spiral with the spins in the ac plane and q shifted to 2 pi(0,delta,1).
Title:
Direct observation of an incommensurate multipolar order in CeB6 doped with Pr
Authors:
Tanaka, Y; Sera, M; Katsumata, K; Lovesey, SW; Tabata, Y; Shimomura, S; Kikkawa, A; Iga, F; Kishimoto, S
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 (7): Art. No. 073702 JUL 2006
Abstract:
Observations on an ordered alloy Ce0.7Pr0.3B6 by non-resonant X-ray diffraction are reported. We find incommensurate reflections (26, 1/2,0) (delta similar to 0.23) below about 3 K in zero applied magnetic field. The wave vector dependence of the intensity is compelling evidence for the first direct observation of an incommensurate multipolar ordering (MPO). The incommensurate MPO appears to coexist with a commensurate MPO with a wave vector (1/2, 1/2, 1/2), which is the ground state configuration. Additional insight to the properties is derived from extensive measurements made with the alloy placed in a magnetic field ranging up to 6T. We propose that a competition among RKKY-like exchange interactions between the Ce-Ce, Ce-Pr, and Pr-Pr multipoles is a main source for the appearance of the incommensurate MPO.
Title:
Thermodynamic study of an incommensurate organic superconductor (MDT-TSF)(AuI2)(0.436)
Authors:
Ishikawa, T; Nakazawa, Y; Yamashita, S; Oguni, M; Saito, K; Takimiya, K; Otsubo, T
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 (7): Art. No. 074606 JUL 2006
Abstract:
Low-temperature heat capacity measurements are performed on the organic superconductor (MDT-TSF)(AuI2)(0.436); its critical temperature determined by the transport measurement is 4.5 K. A broad but reproducible thermal anomaly related to the superconducting transition is observed during precise measurements of the heat capacity under magnetic fields of up to 6 T. An important finding is that almost 60% of the normal electron density of states remains even in the superconducting ground state. This phenomenon and the intrinsic broadening of the thermal anomaly are common to another organic superconductor kappa-(BEDT-TTF)(4)Hg2.89Br8, in which an incommensurate relationship exists between anion and donor lattices. However, it is emphasized that (MDT-TSF)(AuI2)(0.436) exhibits the superconducting transition at a relatively high temperature despite the small electronic heat capacity coefficient gamma and non-dimerized molecular arrangement in the donor layers.
Title:
Incommensurate lattice distortion in the high temperature tetragonal phase of La2-x(Sr,Ba)(x)CuO4
Authors:
Wakimoto, S; Kimura, H; Fujita, M; Yamada, K; Nodai, Y; Shirane, G; Gu, G; Kim, H; Birgeneau, RJ
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 (7): Art. No. 074714 JUL 2006
Abstract:
We report incommensurate diffuse (ICD) scattering appearing in the high-temperature-tetragonal (HTT) phase of La2-x(Sr,Ba)(x)CuO4 with 0.07 <= x <= 0.20 observed by the neutron diffraction technique. For all compositions, a sharp superlattice peak of the low-temperature-orthorhombic (LTO) structure is replaced by a pair of ICD peaks with the modulation vector parallel to the CuO6 octahedral tilting direction, that is, the diagonal Cu-Cu direction of the CuO2 plane, above the LTO-HTT transition temperature T-s. The temperature dependences of the incommensurability 6 for all samples scale approximately as T/T-s, while those of the integrated intensity of the ICD peaks scale as (T - T-s)(-1). These observations together with absence of ICD peaks in the non-superconducting x = 0.05 sample evince a universal incommensurate lattice instability of hole-doped 214 cuprates in the superconducting regime.
Title:
Magnetic structure of rare-earth dodecaborides
Authors:
Siemensmeyer, K; Flachbart, K; Gabani, S; Mat'as, S; Paderno, Y; Shitsevalova, N
Source:
JOURNAL OF SOLID STATE CHEMISTRY 179 (9): 2748-2750 Sp. Iss. SI SEP 2006
Abstract:
We have investigated the magnetic structure of HoB12, ErB12 and TmB12 by neutron diffraction on isotopically enriched single-crystalline samples. Results in zero field as well as in magnetic field up to 5 T reveal modulated incommensurate magnetic structures in these compounds. The basic reflections can be indexed with q = (1/2 +/- delta, 1/2 +/- delta, 1/2 +/- delta), where delta = 0.035 both for HoB12 and TmB12 and with q = (3/2 +/- delta, 1/2 +/- delta, 1/2 +/- delta), where delta = 0.035, for ErB12. In an applied magnetic field, new phases are observed. The complex magnetic structure of these materials seems to result from the interplay between the RKKY and dipole-dipole interaction. The role of frustration due to the fcc symmetry of dodecaborides and the crystalline electric field effect is also considered. (c) 2005 Elsevier Inc. All rights reserved.
Title:
Optical reflectivity as a simple diagnostic method for testing structural quality of icosahedral quasicrystals
Authors:
Brien, V; Dauscher, A; Machizaud, F
Source:
JOURNAL OF APPLIED PHYSICS 100 (4): Art. No. 043503 AUG 15 2006
Abstract:
The optical reflectivity of Al-based and Ti-based quasicrystalline and approximant samples were investigated versus the quality of their structural morphology using optical reflectometry, x-ray diffraction, and transmission electron microscopy. The different structural morphologies were obtained using three different preparation processes: sintering, pulsed laser deposition, and reactive cathodic magnetron sputtering. The work demonstrates that the canonical behavior of icosahedral state in specular reflectivity is extremely sensitive to different and very fine aspects of the microstructure: sizes of grains smaller than 50 nm, slight local diffuse disorder, and shifts away from the icosahedral crystallographic structure (approximants). The work explains why the optical properties of the same kind of quasicrystals found in literature sometimes reveal a different behavior from one author to another. The study then confirms the work of some authors and definitely shows that the canonical behavior of icosahedral state in specular reflectivity over the 30 000-50 000 cm(-1) domain is characterized by a decreasing function made of steps. It also shows that this behavior can be interpreted thanks to the cluster hierarchy of the model of Janot [Phys. Rev. B 53, 181 (1996)]. (c) 2006 American Institute of Physics.
Title:
Glass-forming ability and stability of ternary Ni-early transition metal (Ti/Zr/Hf) alloys
Authors:
Basu, J; Ranganathan, S
Source:
ACTA MATERIALIA 54 (14): 3637-3646 AUG 2006
Abstract:
Four Ni-bearing Ti, Zr and Hf ternary alloys of nominal composition Zr41.5Ti41.5Ni17, Zr25Ti25Ni50, Zr41.5Hf41.5Ni17 and Ti41.5Hf41.5Ni17 were rapidly solidified in order to produce ribbons. The Zr-Ti-Ni and Ti-Hf-Ni alloys become amorphous, whereas the Zr-Hf-Ni alloy shows precipitation of a cubic phase. The devitrification of all three alloys was followed and the relative tendency to form nanoquasicrystals and cF96 phases analysed. The relative glass-forming ability of the alloys can be explained by taking into account their atomic size difference. Addition of Ni often leads to quasicrystallisation or quasicrystal-related phases. This can be explained by the atomic radius and heat of mixing of the constituent elements. The phases precipitated at the initial stages of crystallisation indicate the possible presence of Frank-Kasper polyhedral structure in the amorphous alloys. Structural analysis reveals that the Laves and the anti-Laves phases have the same polyhedral structural unit, which is similar to the structural characteristics of glass. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
An application of Pettifor structure maps for the identification of pseudo-binary quasicrystalline intermetallics
Authors:
Ranganathan, S; Inoue, A
Source:
ACTA MATERIALIA 54 (14): 3647-3656 AUG 2006
Abstract:
Quasicrystal-forming ability is considered from the viewpoint of Pettifor maps, where a single phenomenological coordinate, the Mendeleev number, captures the bonding characteristics of elements in forming intermetallics. By considering the largest sized atom as the most important constituent, it is shown that most known ternary and quaternary quasicrystals can be treated as pseudo-binary intermetallics. This also results in a classification of quasicrystals into four structural classes based on the nature of the bond orbital - s, p, d or f - of the large atom with four associated related crystal structures. A colour scheme is introduced to indicate preferences for two types of sites. We propose a new classification of quasicrystals as centred on Li, Mg, Al, Ga, Ca, Sc, Y, Ti, Zr, Hf and rare earth elements, as they are the largest atoms in the constituent quasicrystals in contrast to the conventional classification based on majority species. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 15-Sep-2006

Title:
Formation of glassy and icosahedral phases in As-cast (Zr9Ni4)(75)(Al1-xTix)(25) alloys
Authors:
Qiang, JB; Zhang, W; Inoue, A
Source:
SCRIPTA MATERIALIA 55 (7): 617-620 OCT 2006
Abstract:
The icosahedral atomic cluster has been recognized as the building block of icosahedral quasicrystals (I-phase) and many bulk metallic glasses (BMGs). With this in mind, a series of (Zr9Ni4)(75)(Al1-xTix)(25) alloys were designed, and ribbons and rods of 3 mm in diameter were prepared. Structural analysis of these bulk samples revealed a pronounced alloying effect of Al and Ti on the formation of BMG and I-phase. BMGs were formed at low Ti compositions (x <= 0.20). As the Ti concentration increased, an I-phase began to form in the glassy matrix, and a nearly monolithic I-phase alloy was obtained in the Al-free alloy. The alloying effect is discussed by considering the different roles of Al and Ti in the stabilization of local icosahedral atomic structures. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Composition dependent ductility in the amorphous Zr-Ti-Ni-Cu-Be alloy system
Authors:
Conner, RD; Johnson, WL
Source:
SCRIPTA MATERIALIA 55 (7): 645-648 OCT 2006
Abstract:
This work maps the bending ductility versus composition of amorphous alloys in the Zr-Ti-Ni-Cu-Be system. Alloys with a Zr:Ti ratio of 5.67:1 show higher ductility and thermal stability over a wider composition range than those with a Zr:Ti ratio of 3:1. The loss of ductility occurs in alloys that have compositions near those of quasicrystal or intermetallic phases, which form in the amorphous matrix upon cooling. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Impurity effect in a novel spin-Peierls compound TiOBr
Authors:
Sasaki, T; Yamazawa, M; Takahashi, K; Nagai, T; Asaka, T; Matsui, Y; Akimitsu, J
Source:
PHYSICA B-CONDENSED MATTER 383 (1): 1-4 AUG 15 2006
Abstract:
We have performed magnetic susceptibility and electron diffraction measurements on impurity effect in a novel spin-Peierls system TiOBr, i.e. Ti1-xScxOBr.The impurity-induced antiferromagnetic long-range order found in Cu1-xZnxGeO3 could not be observed in this system. A number of unpaired spins induced by the impurities can be explained by a simple model that one Sc impurity creates one S = (1)/(2) spin up to the threshold concentration, x(c)similar to 0.025. The induced impurity suppresses the spin-Peierls transition temperature, T-c1 and the spin-Peierls phase disappears at x(1)similar to 0.028, although the incommensurate state still persists above x(1). Both values agree well with each other. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Incommensurate and commensurate quadrupole orders in Ce0.7Pr0.3B6
Authors:
Tanaka, Y; Sera, M; Tabata, Y; Shimomura, S; Kikkawa, A; Katsumata, K; Iga, F; Kishirnoto, S
Source:
PHYSICA B-CONDENSED MATTER 383 (1): 39-40 AUG 15 2006
Abstract:
Non-resonant X-ray diffraction experiments were performed on Ce0.7Pr0.3B6. We have found superlattice reflections for commensurate (n)/(2) (n)/(2) (n)/(2), where n are odd integers and incommensurate h +/- 26(k)/(2) l, where h and l are integers, and k are odd integers, at the low temperature phases in zero magnetic field. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Magnetic phase diagram of Ce0.70Pr0.30B6
Authors:
Mignot, JM; Sera, M; Iga, F
Source:
PHYSICA B-CONDENSED MATTER 383 (1): 41-42 AUG 15 2006
Abstract:
Low-temperature, high-field (H-[1 (1) over bar 0] <= 7.5 T), neutron diffraction experiments on single-crystal (Ce0.70Pr0.30B6)-B-11 are reported. Two successive incommensurate phases are found to exist in zero field. The appearance, for H >= 4.6 T at T = 2 K, of an antiferromagnetic structure with kAF = ((1)/(2), (1)/(2), (1)/(2)), most likely due to an underlying antiferroquadrupolar order, is discussed in connection with recent X-ray experiments. (c) 2006 Elsevier B.V. All rights reserved.

Update: 8-Sep-2006

Title:
Decagon covering model and equivalent HBS-tiling model
Authors:
Gummelt, P
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 221 (8): 582-588 2006
Abstract:
For decagonal Al-Co-Ni quasicrystals, coverings based on a single decagonally shaped columnar 20 angstrom-cluster as well as tilings of so-called hexagon-, boat-and star-tiles are used to model the atomic structure. We introduce geometrically defined local transformation rules which enable us to replace a covering of overlapping congruent decagons by an equivalent HBS-tiling at the same scale and vice versa. Starting from an obvious one-to-one correspondence in case of idealized, perfect Penrose order, we show that there is a very similar relation also for random decagon coverings with slightly relaxed structure. The proofs given here complete our statements announced in previous work.
Title:
LiBx (0.82 < x <= 1.0) - an incommensurate composite structure below 150 K
Authors:
Worle, M; Nesper, R; Chatterji, TK
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE 632 (10-11): 1737-1742 2006
Abstract:
The lithium boride LiBx (0.82 < X <= 1.0) contains linear boron chains isolelectronic to carbyne. The negatively charged boron chains are embedded in and stabilized by a lithium matrix. At room temperature they are disordered with respect to each other and also not commensurate with the Li matrix. Below about 150 K a phase transition takes place, where the boron chains successively order with respect to each other, but remaining still incommensurate with the Li substructure. The crystal structure of LiBx at 2 K was determined from neutron powder diffraction data and refined in the (3+1)-dimensional superspace group P (1) over bar(alpha beta gamma) The unit cell parameters are a = 4.012(1) angstrom, b = 4.012(1) angstrom, c = 2.794(1) angstrom, alpha = 90 degrees, beta = 90 degrees, gamma = 120 degrees for the lithium and a = 4.017(1) b = 4.019(1) angstrom, c = 1.578(1) angstrom, alpha = 93.35(1), beta = 92.83(1)degrees, gamma = 119.71(1)degrees for the boron substructure, respectively. The q-vector is (0.1267 0.1482 1.7707). The boron atoms within the linear chains are equidistant, suggesting a cumulated double bond system, similar to a cumulenic chain in the carbon case. Band structure calculations and the electron localization function give more insight into the unusual physical properties of LiBx.
Title:
Orthorhombic approximant phases and their relation to quasicrystals in mechanically alloyed Al-Cu-Fe-Si alloys
Authors:
Kim, SH; Chattopadhyay, K; Kim, KB; Kim, WT; Kim, DH
Source:
PHILOSOPHICAL MAGAZINE LETTERS 86 (7): 425-433 JUL 2006
Abstract:
The possibility of synthesis of quasicrystalline and associated approximant phases during mechanical alloying and subsequent heat treatment of Al65Cu20Fe10Si5 alloy powders has been investigated. It is shown that, in addition to the stable ordered quasicrystal and 1/1 cubic approximant, two more phases having orthorhombic symmetry coexist. The a and c parameters of both these phases are similar to the lattice parameters of the cubic approximant, whereas their b parameters are, respectively, three and four times larger than the c parameters. It is suggested that these phases evolve on account of local symmetry breaking of the cubic approximant phase, possibly due to ordering.
Title:
Structural features of the modulated BiCu2(P1-xVx)O-6 solid solution; 4-D treatment of x=0.87 compound and magnetic spin-gap to gapless transition in new Cu2+ two-leg ladder systems
Authors:
Mentre, O; Ketatni, EM; Colmont, M; Huve, M; Abraham, F; Petricek, V
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 128 (33): 10857-10867 AUG 23 2006
Abstract:
The BiCu2(P1-xVx)O-6 system shows the appearance of various phenomena that progressively change as a function of the average (P/V)O-4 groups size. Then, from x) 0 to x approximate to 0.7, a solid solution exists with respect to the basic orthorhombic unit cell of BiCu2PO6. For greater x values ( 0.7 < x < 0.96), structural modulations with incommensurate q vector that slightly change versus x appear. The 4-D treatment of single-crystal XRD data of the modulated phase corresponding to x = 0.87 at 100 K ( orthorhombic, a) 12.379(3) angstrom, b = 5.2344(9) angstrom, c = 7.8270(14) angstrom, q = 0.268(3) b*, super space group: Xbmm(0 gamma 0) s00, X stands for the nonprimitive centering vector (1/2,0,1/2,1/2), R(obs)(overall) = 5.27%, R(obs)(fundamental) = 4.48%, R(obs)( satellite)) = 6.58%) has evidenced strong positional modulated effects within the [BiCu2O2](3+) ribbons while three XO4 configurations compete along the x(4) fourth dimension. There is no P/V segregation along x(4) in good agreement with steric-only origins of the modulation. Finally for 0.96 < x < 1, two phases coexist, i.e., BiCu2VO6 ( X) 1) and a modulated phase of the previous domain. The BiCu2VO6 crystal structure shows a unit cell tripling associated with monoclinic symmetry lowering. The VO4 orientations between two ribbons proceed with respect to the interribbon distance. Then the full system shows flexible interactions between modulated Bi/M/O-based ribbons and surrounding tetrahedral groups, depending on the average XO4 size. Furthermore, between two ribbons the Cu2+ arrangement forms magnetically isolated zigzag copper two-leg ladders. Our preliminary results show a spin-gap behavior likely due to the existence of true S = 12 Heisenberg two-leg ladders. Modulated compositions are gapless, in good agreement with band-broadening toward a continuum in the magnetic excitation spectrum. The continuous distribution of Cu-Cu distances along the rungs and legs of the ladders should be mainly responsible for this magnetic change.
Title:
The {111}-modulated domains in tetragonal BaTiO3
Authors:
Wu, YC; Lu, HY; McCauley, DE; Chu, MSH
Source:
JOURNAL OF THE AMERICAN CERAMIC SOCIETY 89 (9): 2702-2709 SEP 2006
Abstract:
Barium titanate (BaTiO3) base-metal electrode multilayer ceramic capacitors of an X7R-formulation, sintered at 1200 degrees C under low oxygen partial pressures (of pO(2)approximate to 10(-9) and 10(-11) atm, respectively), followed by annealing at 1000 degrees C in an atmosphere containing a higher oxygen partial pressure (of pO(2)approximate to 10(-5)-10(-6) atm), have been analyzed for crystalline phases using X-ray diffractometry, for microstructure using transmission electron microscopy, and for microchemistry using energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy. The classical core-shell structure characterized by a core consisting of tetragonal ferroelectric {011} domains and featureless shell (designated type I) was observed only in sample A sintered in pO(2)approximate to 10(-9) atm. For sample B sintered in pO(2)approximate to 10(-11) atm, the core-shell structure is predominantly type II, consisting of a featureless shell similar to type I, but a core of modulated domains. The core of type II contained incommensurately modulated {111} superlattice domains along < 111 >. The superlattice can be described by a displacive modulation with incommensurate wave vectors k(1)=0.58a(*), k(2)=0.58b(*), and k(3)=0.58c(*). It is due to the ordering of defect associates (Ti'(Ti),V-O)(center dot) generated extrinsically from sintering in low pO(2). Shell thickness was determined by the lattice diffusion of Ca2+ solute cations into BaTiO3 grains during sintering. The core-shell interface became less distinguishable in type II because defect associates (Ti'(Ti),V-O)(center dot), unlike those in type I, were not completely eliminated by re-oxidizing in pO(2)approximate to 10(-5)-10(-6) atm, but became ordered along < 111 > and gave rise to structural modulation.
Title:
Simultaneous antiferromagnetic Fe3+ and Nd3+ ordering in NdFe3((BO3)-B-11)(4)
Authors:
Fischer, P; Pomjakushin, V; Sheptyakov, D; Keller, L; Janoschek, M; Roessli, B; Schefer, J; Petrakovskii, G; Bezmaternikh, L; Temerov, V; Velikanov, D
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 18 (34): 7975-7989 AUG 30 2006
Abstract:
By means of magnetic susceptibility and specific heat measurements, x-ray and unpolarized neutron diffraction investigations on powder and single-crystal samples, simultaneous long-range antiferromagnetic Fe and Nd ordering in NdFe3((BO3)-B-11)(4) with R32 chemical structure has been found at temperatures below T-N = 30.5(5) K down to 1.6 K. At temperatures down to 19 K the propagation vector is k(hex) = [0, 0, 3/2] and becomes slightly incommensurate at lower temperatures. Combined with symmetry analysis, best powder neutron profile fits are obtained with magnetic spiral configurations with the magnetic moments oriented parallel to the hexagonal basal plane according to the irreducible representations tau(3) in the commensurate case. This is in agreement with the easy directions of magnetization perpendicular to the c-axis as determined by magnetic susceptibility measurements. At 1.6 K the magnetic Fe moment amounts to 4.9 mu(B) B close to the free ion moment of Fe3+. The magnetic Nd3+ moment saturates presumably due to crystal-field effects at 2.7 mu(B).
Title:
Physical properties of the icosahedral quasicrystal Al60Cr19.9Fe0.1Ge20
Authors:
Stadnik, ZM; Wang, P
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 18 (35): 8383-8394 SEP 6 2006
Abstract:
The results of x-ray diffraction, Fe-57 M ossbauer spectroscopy, magnetic susceptibility, and electrical conductivity studies of the metastable icosahedral alloy Al60Cr19.9Fe0.1Ge20 are reported. The observed broadening of the diffraction Bragg peaks reflects the presence of the topological/chemical disorder. The distribution of the electric quadrupole splitting derived from M " ossbauer spectra indicates the existence of a multiplicity of Fe sites. The average quadrupole splitting decreases with temperature as T-3/2. The vibrations of the Fe atoms are well described by a Debye model, with the Debye temperature of 463( 15) K. The temperature dependence of the magnetic susceptibility follows the Curie-Weiss law with the effective magnetic moment of 0.312(3) mu(B) per Cr/Fe atom. The origin of the presence of the magnetic moment, and its absence in similar crystalline alloys, is discussed. The temperature dependence of the electrical conductivity can be successfully fitted with the use of theories of quantum interference effects, and values for spin orbit and inelastic scattering times are extracted from the fits. The scattering process in the studied quasicrystal is dominated by inelastic electron-electron scattering.
Title:
Ablative modification of graphite surfaces by single intense femtosecond pulses
Authors:
Kudryashov, SI
Source:
JOURNAL OF APPLIED PHYSICS 100 (3): Art. No. 036103 AUG 1 2006
Abstract:
Several types of center-symmetrical (elliptical) microstructures of multinanometer heights are fabricated on a surface of quasicrystalline graphite ablated by single femtosecond laser pulses with peak intensities in the range of 1-10(2) TW/cm(2). Potential underlying physical mechanisms for these high-intensity ablative micromodification phenomena are discussed. (c) 2006 American Institute of Physics.
Title:
Polar binary Zn/Cd-rich intermetallics: Synthesis, crystal and electronic structure of A(Zn/Cd)(13) (A = alkali/alkaline earth) and CS1.34Zn16
Authors:
Wendorff, M; Rohr, C
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 421 (1-2): 24-34 SEP 14 2006
Abstract:
The binary alkali/alkaline earth (A) zinc and cadmium (M) compounds that form the NaZn13 structure type (cubic, space group Fm (3) over barc), which were known only from indexed X-ray powder diagrams, have been synthesized from stoichiometric mixtures of the elements and have been structurally characterized using a combination of single crystal data and the Rietveld method. The alkali zinc phases A(l)Zn(13) are only formed with the lighter alkali elements sodium to rubidium (A(I) = Na: a=1227.3(2) pm, R1 = 0.0205; A(I) = K: a=1237.9(3) pm, R1 = 0.0154; A(I) = Rb: a=1245.19(1) pm, R-p = 0.0250), whereas the cadmium compounds A(I)Cd(13) are stable only for the heavier alkali metals potassium to cesium (A(I) = K: a=1379.2(4) pm, R1 = 0.0118; A(I) = Rb: a=1384.5(2) pm, R1 = 0.0139; A(I) = Cs: a=1392.0(3)pm, R1 = 0.0381). In the crystal structures M-centered M(2)M(1)(12) icosahedra are connected via strong exobonds (forming tetrahedral stars, stella quadrangula) to form a 3D net, in the interstices of which the alkali metals are located in a snub cube 24 coordination. In contrast, the alkaline earth (A) zinc compounds with calcium, strontium and barium (A(II)= Ca: a= 1215.4(1) pm, R1 = 0.0274; A(III)= Sr: a=1222.2(2) pm, R1 = 0.0154; A(II) = Ba: a=1235.8(2) pm, R1 = 0.0227) show statistical defects at the Zn(2) position centering the Zn(1) icosahedra. Both the geometric and the electronic stability of the NaZn13 structure type, which can be assessed from the pseudo-bandgap calculated using FP-LAPW-DFT methods, are discussed. In contrast to the aforementioned systems, the NaZn13 type ceases to exist in the binary system Cs-Zn. In this case a phase Cs1.36Zn16 with a new structure type but very similar stoichiometry emerges. This compound is the first and only known phase in the system Cs-Zn and crystallizes with a new incommensurably modulated structure: its average structure (orthorhombic, space group Imma, a = 264.2(5) pm, b = 720.8(14) pm, c = 1760(5) pm, R1 = 0.0198) already indicates the representative structural features: in a 3D net of Zn atoms tubular channels filled by the Cs atoms are formed. This Cs filling is, due to geometric requirements, not commensurate with the Zn host structure resulting in a modulated structure with satellite reflections that can be indexed with a (q) over right arrow vector of (0, 0, 0.2755). The final refinement in the superspace group (Pcn2(0 0 g)sso, a = 1760(5) pm, b = 720.8(14) pm, c = 264.2(5) pm, wR(main) = 0.0550, wR(satellites) = 0.140) shows a strong occupational and a weak positional modulation of Cs in the channels formed by the Zn partial structure. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Model of rotational tunneling in quasicrystals of the Cd6Yb parent compound
Authors:
Peternelj, J; Lakner, M; Dolinsek, J
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 421 (1-2): 72-79 SEP 14 2006
Abstract:
A microscopic theoretical model of rotational tunneling within the four-shell atomic clusters of the Cd6Yb structure, representing a 1/1 periodic approximant of the Cd-Yb and Cd-Ca quasicrystals, is presented, where the Cd-4 tetrahedral core undergoes reorientations around its three-fold symmetry axes in the crystal potential due to outer icosahedral atomic shells. The form of the effective hindering potential was derived from the symmetry of the four-shell cluster and was found to exhibit 12 equivalent double-well minima. These minima appear naturally from the details of the Cd6Yb atomic structure, providing link to the phenomenological tunneling-state model, where the existence of such double-well minima is assumed on the phenomenological grounds. The shape of the potential suggests two kinds of rotational tunneling processes, the Cd-4 reorientations for 120, which involve tunneling through barriers between adjacent double wells, and the reorientations for 44(degrees), which involve tunneling within the double wells. The low-temperature energy level scheme, representing the lowest rotational states of the Cd-4 tetrahedron undergoing rotational tunneling about its four three-fold symmetry axes, is obtained by a group-theoretical calculation. As the charge distribution within the Cd6Yb clusters is not known, the rotational tunneling frequencies were estimated for some trial values of the potential parameters. The estimated frequencies are slow, in accordance with the large mass of the tunneling particle, the Cd-4 tetrahedron. (c) 2005 Elsevier B.V All rights reserved.
Title:
Wetting of aluminium-based complex metallic alloys
Authors:
Belin-Ferre, E; Dubois, JM
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH 97 (7): 985-995 JUL 2006
Abstract:
Many complex metallic alloys are known to form in aluminium-based systems containing transition metals like Cu, Pd, Fe or Cr, the most famous one being the stable icosahedral quasicrystal discovered in the Al - Cu - Fe system. Although covered by a thin native oxide layer, adhesion of water onto the complex compounds is very different from that onto the oxide or onto oxidised aluminium. We show here how this atypical behaviour is related to the structural complexity of the compound. We then produce data that allows us to estimate the actual surface energy of the same compounds, a property that is also a fingerprint of structural complexity in Al-based intermetallics.
Title:
Annealing-induced phase transitions in a Zr-Ti-Nb-Cu-Ni-Albulkmetallic glass matrix composite containing quasicrystalline precipitates
Authors:
Kuhn, U; Eckert, J; Schultz, L
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH 97 (7): 996-1000 JUL 2006
Abstract:
The phase formation of a copper-mold-cast Zr60Ti2Nb6CU14 Ni9Al9 alloy has been investigated upon cooling from the melt as well as upon annealing of as-cast specimens. The different states of the samples are characterized by X-ray diffraction, optical and electron microscopy, and differential scanning calorimetry. The cooling rate as realized upon copper-mold casting leads to micrometer-sized quasicrystals, which are embedded in a glassy phase. The then-nal stability Delta T-x of the supercooled liquid state of the glassy phase that forms near to the wall of the copper mold, differs from that of the glassy matrix in the center of the rod due to different compositions of the glassy phase. This is a consequence of the change in local cooling conditions, which affects the phase formation upon solidification as well as the subsequent transformation behavior of the alloy upon constant-rate heating.
Title:
Isotropic and anisotropic physical properties of quasicrystals
Authors:
Gong, P; Hu, CZ; Zhou, X; Miao, L; Wang, X
Source:
EUROPEAN PHYSICAL JOURNAL B 52 (4): 477-481 AUG 2006
Abstract:
Since quasicrystals have positional and orientational long-range order, they are essentially anisotropic. However, the researches show that some physical properties of quasicrystals are isotropic. On the other hand, quasicrystals have additional phason degrees of freedom which can influence on their physical behaviours. To reveal the quasicrystal anisotropy, we investigate the quasicrystal elasticity and other physical properties, such as thermal expansion, piezoelectric and piezoresistance, for which one must consider the contributions of the phason field. The results indicate that: for the elastic properties, within linear phonon domain all quasicrystals are isotropic, and within nonlinear phonon domain the planar quasicrystals are still isotropic but the icosahedral quasicrystals are anisotropic. Moreover, the nonlinear elastic properties due to the coupling between phonons and phasons may reveal the anisotropic structure of QCs. For the other physical properties all quasicrystals behave like isotropic media except for piezoresistance properties of icosahedral quasicrystals due to the phason field.
Title:
Thermodynamic properties of crystalline Al-Fe alloys in the region of icosahedral phase precipitation
Authors:
Zaitsev, AI; Zaitseva, NE; Shakhpazov, EK; Arutyunyan, NA; Dunaev, SF
Source:
DOKLADY PHYSICAL CHEMISTRY 407: 98-101 Part 2 APR 2006
Title:
First molecular quasicrystal is designed
Authors:
[Anon]
Source:
CHEMICAL & ENGINEERING NEWS 84 (33): 49-49 AUG 14 2006

Update: 1-Sep-2006

Title:
KNd(MoO4)(2): A new incommensurate modulated structure in the scheelite family
Authors:
Morozov, VA; Arakcheeva, AV; Chapuis, G; Guiblin, N; Rossell, MD; Van Tendeloo, G
Source:
CHEMISTRY OF MATERIALS 18 (17): 4075-4082 AUG 22 2006
Abstract:
Potassium neodymium molybdenum oxide, KNd(MoO4)(2), has been synthesized by the solid-state method. The structure and microstructure have been studied by X-ray powder diffraction and transmission electron microscopy (TEM). TEM revealed that the KNd(MoO4)(2) structure is incommensurately modulated. The scheelite-like structure of KNd(MoO4)(2) has been refined from X-ray powder diffraction intensities in the (3 + 1) D superspace group I2/b(alpha,beta 0) 00 with a) 5.5202( 2) angstrom, b) 5.33376( 5) angstrom, c = 11.8977(3) angstrom, gamma = 90.9591(7)degrees, and modulation vector q = 0.57789( 4) a* - 0.14748( 6) b* (R-P = 3.09%, R-wP = 4.04%). The ordering of the K and Nd cations appears to be the primary parameter of the structure modulations. The compositional wave of the {KMoO4} and {NdMoO4} distribution is observed in the ab structure projection. The incommensurability of the compositional wave direction with respect to the a and b lattice constants is regarded as the origin of the incommensurate structure modulations.

Update: 18-Aug-2006

Title:
Complexity of hexagonal approximants in the RE13Zn similar to 58 system (RE = Ce, Pr, Nd, Sm, Gd, Tb and Dy)
Authors:
Piao, S; Gomez, CP; Lidin, S
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 221 (5-7): 391-401 2006
Abstract:
For the RE13Zn58 quasicrystal approximants (RE = Ce, Pr, Nd, Sm, Gd, Tb, Dy), single crystals were prepared from the elements and their structures were refined from single-crystal X-ray diffraction data. They are derived from the Gd13Cd58 type structure and crystallize in the space group P6(3)/mmc or its subgroups. The crystal structures of Ce and Pr compounds are identical to that of the archetype, in the Nd compound a pair exchange disorder changes the composition and for Sm a further, partially occupied interstitial position lowers the symmetry to P6(3)/mc. For the compounds with Gd, Tb and Dy, the occupancy may order, lowering the symmetry further. For the case of Tb13Zn59 high quality single crystals allowed Lis to refine the fully ordered orthorhombic super structure.
Title:
Reflections on symmetry and formation of axial quasicrystals
Authors:
Steurer, W
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 221 (5-7): 402-411 2006
Abstract:
Some ideas are presented on the geometrical factors governing structure and formation of axial quasi-crystals with 5- and 7-fold symmetry, respectively. First, the importance of thin atomic layers is discussed for the growth of decagonal quasicrystals. They are the only long-range ordered structural units carrying information on the local non-crystallographic symmetry of the constituent clusters. Second, the consequences of local polysynthetic twinning for the formation of pentagonal and heptagonal quasicrystals are demonstrated. Third, the special relationship of the beta-phase, (Co,Ni)(1-x)Al1+x, to the decagonal phase and its periodic average structure is discussed as well as its role as template for the formation and growth of decagonal Al-Co-Ni.
Title:
Mosaic-like tilings derivated from o-CO4Al13 and M-Co4Al13 crystal structures
Authors:
Burkhardt, U; Ellner, M
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 221 (5-7): 412-419 2006
Abstract:
Both well known crystal structures m-Co4Al13 and o-Co4Al13 are described in a simplified two-dimensional representation of regular pentagons and prolate rhombs. The dichromatic tilings differ in the periodic arrangements of prolate rhombs (brick-like and parquet-like, respectively) but show the same matching rules for the regular pentagons. The 2D scheme is used to show the variety in combination of these structural fragments that leads to related periodic as well as cyclical tilings. Starting from different initial nuclei, cyclical tilings with point group symmetry C-5v or C-10 are related to multiple twinned arrangements of the structure m-Co4Al13. Different decorations of these tilings are compared and characterised by their symmetry.
Title:
Compositional dependence on phase selection during devitrification of amorphous Zr-Pt alloys
Authors:
Lee, MH; Ott, RT; Besser, MF; Kramer, MJ; Sordelet, DJ
Source:
SCRIPTA MATERIALIA 55 (6): 505-508 SEP 2006
Abstract:
The devitrification pathways of alloys were determined using time-resolved synchrotron radiation. Amorphous Zr73Pt27 ribbons transformed directly to the stable Zr5Pt3 structure but ribbons with higher Zr contents first formed a metastable quasicrystalline phase before transforming to the Zr5Pt3 structure. Lower crystallization activation energies were observed for the higher Zr-content alloys. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
On the origin of nanocrystals in the shear band in a quasicrystal forming bulk metallic glass Ti40Zr29Cu9Ni8Be14
Authors:
Chang, HJ; Kim, DH; Kim, YM; Kim, YJ; Chattopadhyay, K
Source:
SCRIPTA MATERIALIA 55 (6): 509-512 SEP 2006
Abstract:
We report the formation of nanocrystals in the shear band of a Ti40Zr29Cu9Ni8Be14 bulk metallic glass which exhibits a large plastic strain. The nanocrystals in the shear band have the same crystal structure as the high temperature Laves phase which appears during crystallization by heating, strongly suggesting a temperature rise in the shear band. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Ordering phenomena in intermetallic CeMX (M = Ni, Cu and X = Si, Ge, Sn) upon hydrogenation
Authors:
Weill, F; Pasturel, M; Bobet, JL; Chevalier, B
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 67 (5-6): 1111-1116 Sp. Iss. SI MAY-JUN 2006
Abstract:
CeMX ternary compounds (M = Ni, Cu and X = Si, Ge, Sn) crystallize in derivative structures of the hexagonal AlB2-type which can be either the hexagonal ZrBeSi- or LiGaGe- type structure, either the orthorhombic TiNiSi-type structure or the tetragonal LaPtSi-type structure depending on M and X. Under hydrogenation, these ternary compounds form stable hydrides. Their crystallographic structure has been investigated by X-ray diffraction and electron transmission microscopy. The structural type of CeNiSiH0.8 remains that of the corresponding initial compound (i.e. the tetragonal LaPtSi-type structure). The hydrogenation only induces an anisotropic variation of the unit cell parameters (a decreases and c increases) without significant increase of the unit cell volume (+0.1%). The two other compounds based on nickel, CeNiGe and CeNiSn, undergo a structural transition during the absorption of hydrogen. The corresponding hydrides, CeNiGeH1.6 and CeNiSnH1.8 crystallize in the hexagonal ZrBeSi-type structure. For the compounds based on copper, no structural transitions are observed. Instead electron diffraction experiments point out the presence of superstructures forCeCuSiH1.3 andCeCuGeH(1.0) hydrides. These superstructures reveal the presence of an order between hydrogen and vacancies in the partially occupied (1/3 2/3 z approximate to 0.436 in the ZrBeSi-type structure) site. The volume of the cell corresponding to these superstructures is directly related to the amount of hydrogen atoms in the structure. The c parameter has to be multiplied by 5 for CeCuSiH1.35 compared with the ternary compound while it has only to be multiplied by 3 for the CeCuGeH1.0. The crystallographic evolution resulting from the hydrogenation of CeCuSn is more complex since incommensurate modulation was observed by electron diffraction and confirmed by single crystal X-ray diffraction. A short range ordering, leading to a displacement of heavy atoms takes place in this compound. (c) ! 2006 Elsevier Ltd. All rights reserved.
Title:
High- and low-temperature crystal and magnetic structures of epsilon-Fe2O3 and their correlation to its magnetic properties
Authors:
Gich, M; Frontera, C; Roig, A; Taboada, E; Molins, E; Rechenberg, HR; Ardisson, JD; Macedo, WAA; Ritter, C; Hardy, V; Sort, J; Skumryev, V; Nogues, J
Source:
CHEMISTRY OF MATERIALS 18 (16): 3889-3897 AUG 8 2006
Abstract:
The crystal and magnetic structures of orthorhombic epsilon-Fe2O3 have been studied by simultaneous Rietveld refinement of X-ray and neutron powder-diffraction data in combination with Mossbauer spectroscopy, as well as magnetization and heat-capacity measurements. It has been found that above 150 K, the epsilon-Fe2O3 polymorph is a collinear ferrimagnet with magnetic moments directed along the a axis, whereas the magnetic ordering below 80 K is characterized by a square-wave incommensurate structure. The transformation between these two states is a second-order phase transition and involves subtle structural changes mostly affecting the coordination of the tetrahedral and one of the octahedral Fe sites. The temperature dependence of the epsilon-Fe2O3 magnetic properties is discussed in light of these results.

Update: 11-Aug-2006

Title:
Synthesis and characterisation of quasicrystalline Al based composites
Authors:
Yong, XP; Chang, ITH; Jones, IP
Source:
POWDER METALLURGY 49 (2): 140-145 JUN 2006
Abstract:
Al matrix composites reinforced by Al-Cu-Fe quasicrystalline (QC) phase particles were produced from a mixture of Al and QC powders using electrical current heating and conventional sintering. A combination of X-ray diffractrometry, transmission and scanning electron microscopy was used to characterise the microstructure of consolidated specimens. The metallic bonding of the Al matrix and particles was improved by higher temperature sintering or electrical current heating. However, the dissolution of QC particles into the Al matrix was inevitable during heating and resulted in the formation of omega and/or beta phases. The dissolution of QC particles was effectively reduced using prealloyed Al powder containing 2 at. -% Cu. This had led to an increase in microhardness from 96 to 139 HV for specimens using pure Al to prealloyed Al powders. A homogeneous distribution of QC particles within the Al matrix could be achieved by mechanical milling followed by consolidation.
Title:
Types of defect ordering in undoped and lanthanum-doped Bi2201 single crystals
Authors:
Martovitsky, VP
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS 102 (6): 958-965 JUN 2006
Abstract:
Undoped and lanthanum-doped Bi2201 single crystals having a perfect average structure have been comparatively studied by x-ray diffraction. The undoped Bi2201 single crystals exhibit very narrow satellite reflections; their half-width is five to six times smaller than that of Bi2212 single crystals grown by the same technique. This narrowness indicates three-dimensional defect ordering in the former crystals. The lanthanum-doped Bi2201 single crystals with x = 0.7 and T-c = 8-10 K exhibit very broad satellite reflections consisting of two systems (modulations) misoriented with respect to each other. The modulation-vector components of these two modulations are found to be q(1) = 0.237b* + 0.277c* and q(2) = 0.238b* + 0.037c*. The single crystals having a perfect average structure and a homogeneous average distribution of doping lanthanum consist of 70- to 80-angstrom-thick layers that alternate along the c axis and have two different types of modulated superlattice. The crystals having a less perfect average structure also consist of alternating layers, but they have different lanthanum concentrations. The low value of T-c in the undoped Bi2201 single crystals (9.5 K) correlates with three-dimensional defect ordering in them, and an increase in T-c to 33 K upon lanthanum doping can be related to a thin-layer structure of these crystals and to partial substitution of lanthanum for the bismuth positions.
Title:
Dynamics of phason diffusion in icosahedral Al-Pd-Mn quasicrystals
Authors:
Feuerbacher, M; Caillard, D
Source:
ACTA MATERIALIA 54 (12): 3233-3240 JUL 2006
Abstract:
We present a direct experimental investigation of the dynamics of phason defects in an icosahedral quasicrystal. The activation parameters of the diffusion of phasons were determined as Delta H = 4.28 eV and t(d0)(-1) = 4 X 10(-1) s(-1). (c) 2006 Acta Materialia hic. Published by Elsevier Ltd. All rights reserved.

Update: 4-Aug-2006

Title:
Quantum transport of slow charge carriers in quasicrystals and correlated systems
Authors:
de Laissardiere, G; Julien, JP; Mayou, D
Source:
PHYSICAL REVIEW LETTERS 97 (2): Art. No. 026601 JUL 14 2006
Abstract:
We show that the semiclassical model of conduction breaks down if the mean free path of charge carriers is smaller than a typical extension of their wave function. This situation is realized for sufficiently slow charge carriers and leads to a transition from a metalliclike to an insulatinglike regime when scattering by defects increases. This explains the unconventional conduction properties of quasicrystals and related alloys. The conduction properties of some heavy fermions or polaronic systems, where charge carriers are also slow, present a deep analogy.
Title:
Physical space description of decorated 1D aperiodic sequences
Authors:
Buczek, P; Wolny, J
Source:
PHILOSOPHICAL MAGAZINE 86 (27): 4181-4194 SEP 21 2006
Abstract:
In this paper, a systematic method of dealing with the arbitrary decorations of quasicrystals is presented. The method is founded on the average unit cell formalism and operates in the physical space only, where each decorating atom manifests itself just as an additional component of the displacement density function in the average unit cell. This approach allows us to use almost all classical crystallography algorithms for structure refining based on experimental data and may meaningly decrease the number of parameters which have to be fit. Further help for structure analysis may be the use of proposed recently average Patterson function, here applied to decorated sets. As an example we present a description of class of decorated quasicrystals based on Sturmian sequence of two interatomic spacings: we calculate explicitly structure factor, the shape of average Patterson function and give an algorithm for pattern analysis.
Title:
Effect of Fe doping on structure, charge ordering, magnetic and transport properties of La0.33Ca0.67Mn1-yFeyO3 (0 <= y <= 0.06)
Authors:
Orlova, TS; Laval, JY; Monod, P; Noudem, J; Zahvalinskii, VS; Vikhnin, VS; Stepanov, YP
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 18 (29): 6729-6748 JUL 26 2006
Abstract:
The relationships between incommensurability, charge ordering and magnetic and electric transport properties were studied in La(0.33)Ca(0.67)Mn(1-y)FeyO(3) (0 <= y <= 0.06) polycrystalline samples. Incommensurability and charge ordering were directly observed by electron diffraction versus temperature and lattice imaging at low temperature in transmission electron microscopy. Both the charge ordering and the ferromagnetic Curie - Weiss temperature linearly decrease with increasing Fe concentration y. A mean field analysis yields an antiferromagnetic exchange J (Mn-Fe) = - 22 K. The undoped samples showed predominantly a commensurate charge ordering superstructure with q-vector 1/3a* over the whole temperature range < 200 K. For doped compositions, the q-vector (1/3-epsilon) a* is reduced by 12-15% for 5% Fe doping, as compared to the undoped composition. The low-temperature superstructure of the Fe-doped manganite does not correspond exactly to the threefold cell with lattice parameters 3a, b, c, and defects inducing shifts along the a direction create a disturbance in long-range charge ordering. Jahn-Teller effects on Mn3+ centres are proposed to play a crucial part in the superstructure formation as well as in the suppression of charge ordering temperature by doping with non-Jahn Teller impurity Fe3+ on Mn3+ sites.
Title:
Influence of lattice volume on magnetic states of Ce2Fe16MnDy compounds (y=0,1,2.3)
Authors:
Prokhnenko, O; Arnold, Z; Kuchin, A; Ritter, C; Isnard, O; Kamarad, J; Iwasieczko, W; Drulis, H
Source:
JOURNAL OF APPLIED PHYSICS 100 (1): Art. No. 013903 JUL 1 2006
Abstract:
The substitution of Mn for Fe in Ce2Fe17 suppresses its ferromagnetic ground state completely for Mn contents x >= 0.5 Mn/f.u. Ce2Fe16Mn has only an antiferromagnetic phase (incommensurate helix along c axis) below T-N=198 K. In this paper, we present and discuss the effects of deuterium insertion (that can be considered as an application of negative chemical pressure) on the magnetostructural properties of Ce2Fe16Mn. Application of (positive) high pressures up to 10 kbar on Ce2Fe16MnDy deuterides (y=1,2.3) allowed us to estimate the role of lattice volume and to divide it from the role of modified electronic band structure that both determines the magnetic states of the deuterated compounds. The results show that a ferromagnetic phase is stabilized by the insertion of D into the antiferromagnetic Ce2Fe16Mn. The Curie temperature T-C of Ce2Fe16MnDy deuterides increases with increasing D content reaching T-C=258 K for y=2.3 and remarkably decreases with pressure dT(C)/dP=-5.4 K/kbar and dT(C)/dP=-3.6 K/kbar for Ce2Fe16MnD1 and Ce2Fe16MnD2.3, respectively. Significant difference between the magnetization of Ce2Fe16MnD1 under pressure and the one of the parent compound at ambient pressure indicates that changes of the volume alone cannot determine the magnetic states upon the initial deuteration. However, the volume expansion becomes dominant when increasing the deuterium content up to 2.3 D/f.u. (c) 2006 American Institute of Physics.
Title:
Kinetic and electrochemical properties of icosahedral quasicrystalline Ti45Zr35Ni17Cu3 powder
Authors:
Liu, BZ; Wu, YM; Wang, LM
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 31 (10): 1394-1400 AUG 2006
Abstract:
Kinetic and electrochemical properties of icosahedral quasicrystalline Ti45Zr35Ni17Cu3 alloy powder as negative electrode material of Ni-MH battery have been investigated at different temperatures. The calculated results show that the apparent activation enthalpy of the charge-transfer reaction is 43.89 kJ mol(-1), and the activation energy of hydrogen diffusion is 21.03 kJ mol(-1). The exchange current density and the diffusion coefficient of hydrogen in the bulky electrode increase with increasing temperature, indicating that increasing temperature is beneficial to charge-transfer reaction and hydrogen diffusion. As a result, the maximum discharge capacity, activation property and high-rate dischargeability are greatly improved with increasing temperature. However, the charge retention and the cycling stability degrade with the increase of the temperature. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Title:
Approximants of icosahedral quasicrystals: Atomic structure, inherent defects, and superstructural ordering
Authors:
Dmitrienko, VE; Chizhikov, VA
Source:
CRYSTALLOGRAPHY REPORTS 51 (4): 552-558 JUL 2006
Abstract:
The structural features of approximants of icosahedral and decagonal quasicrystals and new unusual approximants (rhombohedral AlPd and cubic Al68Pd20Ru12) are considered. It is shown that most approximants can be described in terms of universal local ordering of atoms, in which the nearest neighbors of each atom occupy the vertices of an almost ideal dodecahedron: the so-called dodecahedral local ordering. A set of general atomic motifs in the approximants of different orders is found for quasicrystals of different types. It is shown that the dodecahedral local ordering can be easily described by the project method, in which the basis vectors directed along icosahedral threefold axes are used. Different types of defects inherent in dodecahedral local ordering are analyzed.
Title:
Average structure of incommensurately modulated monoclinic lazurite
Authors:
Bolotina, NB; Rastsvetaeva, RK; Sapozhnikov, AN
Source:
CRYSTALLOGRAPHY REPORTS 51 (4): 589-595 JUL 2006
Abstract:
The average structure of the monoclinic modification of lazurite Ca1.26Na6.63K0.04[Al6Si6O24](SO4)(1.53)S0.99Cl0.05 (discovered in the Lake Baikal region) incommensurately modulated along the c axis is solved by the single-crystal X-ray diffraction method. The unit-cell parameters are a = 9.069(1) angstrom, b = 12.868(1) angstrom, c = 12.872(1) angstrom, gamma = 90.19(1)degrees, sp. gr. Pa, R = 6.9%, 2057 reflections. The AlO4 and SiO4 tetrahedra form a partially ordered framework. The positions in the cavities of the framework are split and randomly occupied by Na and Ca atoms and the SO4, S-2, S-3, and SO2 anionic groups. The structure of the mineral is compared with the superstructure of triclinic lazurite. Conclusions are drawn about the causes of the incommensurate modulation in monoclinic and other lazurites.
Title:
Cancrinite: Crystal structure, phase transitions, and dehydration behavior with temperature
Authors:
Hassan, I; Antao, SM; Parise, JB
Source:
AMERICAN MINERALOGIST 91 (7): 1117-1124 JUL 2006
Abstract:
The structural behavior of a cancrinite, Na5.96Ca1.52[Al6Si6O24](CO3)(1.57)center dot 1.75H(2)O, was determined by using in situ synchrotron X-ray powder diffraction data [lambda = 0.91806(5) angstrom] at room pressure and from 25 to 982 degrees C. The sample was heated at a rate of about 9.5 degrees C/min, and X-ray traces were collected at about 15 degrees C intervals. The satellite reflections in cancrinite were lost at about 504 degrees C, where a phase transition occurs. All the unit-cell parameters for cancrinite also show a discontinuity at 504 degrees C. Initially, the [Ca.CO3] clusters and their vacancies are ordered in the channels, and this ordering is destroyed on heating to give rise to the phase transition. Cancrinite loses water continuously until about 625 degrees C; thereafter an anhydrous cancrinite phase exists. From 25 to 952 degrees C, a minimal amount of CO2 is lost from the structure. Over this temperature range, the average (Al-O-Si) bridging angle, which is an indication of the degree of rotation of the tetrahedra, increases from 143.7(4) to 147.7(5)degrees. Rotations of the tetrahedra are caused by expansion of the Na1-O2 bond lengths.
Title:
Structure and phase transitions in Ca2CoSi2O7-Ca2ZnSi2O7 solid-solution crystals
Authors:
Jia, ZH; Schaper, AK; Massa, W; Treutmann, W; Rager, H
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 62: 547-555 Part 4 AUG 2006
Abstract:
While the incommensurability in melilites is well documented, the underlying atomic configurations and the composition-dependent phase behavior are not yet clear. We have studied the transition from the incommensurate phase to the high-temperature normal phase (IC-N), and to the low-temperature commensurate phase (IC-C) of selected members of the Ca2Co1-xZnxSi2O7 system using X-ray and single-crystal electron diffraction, as well as calorimetric measurements. The space group of the unmodulated normal phase and of the basic structure of the incommensurate phase is P (4) over bar2(1)m; the commensurate lock-in superstructure was refined as a pseudomerohedral twin in the orthorhombic space group P2(1)2(1)2. We found that the commensurate modulation is mainly connected with a sawtooth-like periodicity of rotations of the T-1 tetrahedra in the 3 x 3 superstructure. In this structure, the clustering of the low-coordinated Ca2+ ions is not complete so that only imperfect octagons were detected. Generally, the effect of increasing substitution of Co by Zn was a continuous reduction of the IC-N and IC-C transition temperatures.
Title:
The incommensurately and commensurately modulated crystal structures of chromium(II) diphosphate
Authors:
Palatinus, L; Dusek, M; Glaum, R; El Bali, B
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 62: 556-566 Part 4 AUG 2006
Abstract:
Chromium(II) diphosphate, Cr2P2O7, has an incommensurately modulated structure at ambient conditions with a = 7.05, b = 8.41, c= 4.63 angstrom beta = 108.71 degrees and q = (-0.361, 0, 0.471). It undergoes a phase transition towards a commensurate structure with a commensurate q vector, q = ((3)/(1), 0, (2)/(1)), at T-c = 285 K. The incommensurate structure has been solved by the charge-flipping method, which yielded both the basic positions of the atoms and the shapes of their modulation functions. The structure model for the commensurate structure was derived directly from the incommensurate structure. The structure analysis shows that the modulation leads to a change of the coordination of the Cr2+ ions from distorted octahedra in the average structure towards a sixfold coordination in the form of a more regular octahedron and a fivefold coordination in the form of a square pyramid. The fivefold and sixfold coordination polyhedra alternate along the lattice direction a with the pattern 5-6-5 5-6-5 in the commensurate structure. In the incommensurate structure this pattern is occasionally disturbed by a 5-6-5-5 motif. Both structures can be described in superspace using the same superspace group and a similar modulated structure model. The same superspace model can also be used for the low-temperature phases of other metal diphosphates with the thortveitite stucture type at high temperature. Their low-temperature structures can be obtained from the superspace model by varying the q vector and the origin in the internal dimension t(0).

Update: 28-Jul-2006

Title:
Magnetic domains in the easy-plane ferromagnetic martensite
Authors:
Chernenko, VA; Lvov, VA; Besseghini, S; Murakami, Y
Source:
SCRIPTA MATERIALIA 55 (4): 307-309 AUG 2006
Abstract:
By Lorentz microscopy observations, the first evidence has been found that the one-to-one correspondence between the magnetic domains and crystallographic twins, which is well-known for the modulated tetragonal Ni-Mn-Ga martensite with c/a < 1, does not hold for the non-modulated Ni-Mn-Ga martensite with c/a > 1. This fact has been attributed to the easy-plane character of the magnetic anisotropy of the martensite with c/a > 1. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Quantum melting of the hole crystal in the spin ladder of Sr14-xCaxCu24O41
Authors:
Rusydi, A; Abbamonte, P; Eisaki, H; Fujimaki, Y; Blumberg, G; Uchida, S; Sawatzky, GA
Source:
PHYSICAL REVIEW LETTERS 97 (1): Art. No. 016403 JUL 7 2006
Abstract:
We have used resonant soft x-ray scattering to study the effects of discommensuration on the hole Wigner crystal (HC) in the spin ladder Sr14-xCaxCu24O41 (SCCO). As the hole density is varied the HC forms only with the commensurate wave vectors L-L=1/5 and L-L=1/3; for incommensurate values it "melts." A simple scaling between L-L and temperature is observed, tau(1/3)/tau(1/5)=5/3, indicating an inverse relationship between the interaction strength and wavelength. Our results suggest that SCCO contains hole pairs that are crystallized through an interplay between lattice commensuration and Coulomb repulsion, reminiscent of the "pair density wave" scenario.
Title:
Dominance of magnetic scattering in the electrical-transport of Al70.5Pd22Mn7.5 icosahedral quasicrystal
Authors:
Jaiswal, A; Rawat, R; Lalla, NP
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 352 (21-22): 2129-2136 JUL 1 2006
Abstract:
Conductivity vs. temperature (sigma-7) at zero and 8-T field, magneto-resistance (Delta rho/rho), magnetization vs. temperature (M-T) and magnetization vs. field (M-T) of Al70.5Pd22Mn7.5 quasicrystal have been studied in the temperature range of 1.4 K to 300 K. The sigma-T variations in both the field conditions show a sigma-T minima. In addition to this the sigma-T variation at 8 T shows a maxima also at similar to 6 K. Comparative analysis shows that the observed sigma-T minima arises due to competing inelastic scattering events in the presence of weak-localization effect. These events are e-ph scattering in the dirty-metallic limit (tau(i) proportional to T-2), and the Kondo-type spin-flip scattering (tau(tau sf)). The maxima observed for the sigma-T variation at 8 T, has been attributed to suppression of the spin-flip scattering in the presence of field. The magneto-resistance is found to be large and positive. It was properly accounted only when the Stoner-enhancement , found in the case of spin fluctuating systems, was taken into consideration. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Association in liquid Al-Fe alloys and its relation to quasicrystal formation
Authors:
Zaitsev, AI; Zaitseva, NE; Shakhpazov, EK; Arutyunyan, NA; Dunaev, SF
Source:
DOKLADY PHYSICAL CHEMISTRY 408: 145-148 Part 2 JUN 2006

Update: 21-Jul-2006

Title:
Effect of an electric field on ferroelastic phase transitions
Authors:
Sannikov, DG; Golovko, VA
Source:
PHYSICS OF THE SOLID STATE 48 (4): 753-758 APR 2006
Abstract:
The effect of an external electric field on the proper ferroelastic phase transitions described in a two-dimensional representation of the Dolt class is analyzed theoretically. The electric field induces a Lifshitz invariant. It is shown that this invariant does not lead to the formation of an incommensurate phase. The phase diagram for commensurate transitions occurring under the action of an electric field changes significantly. The second-order phase transition from the initial phase is split by an electric field of specific orientation into a sequence of two second-order phase transitions with close temperatures.
Title:
X-ray diffraction study of diffuse scattering in incommensurate rubidium-IV
Authors:
Falconi, S; McMahon, MI; Lundegaard, LF; Hejny, C; Nelmes, RJ; Hanfland, M
Source:
PHYSICAL REVIEW B 73 (21): Art. No. 214102 JUN 2006
Abstract:
X-ray diffraction data have been collected from single crystals of incommensurate Rb-IV in order to study the sheets of diffuse scattering arising from the one-dimensional (1D) guest chains. Discontinuities in both the relative intensity and width of the diffuse sheets are observed on pressure decrease below 16.7 GPa, the pressure at which the interchain correlations begin to decrease rapidly. These changes in the diffuse scattering are accompanied by the progressive disappearance of the Bragg peaks from the guest chains. By modeling the diffuse scattering as coming from either a perturbed 1D lattice or a 1D harmonic liquid, we have determined the pressure dependence of the intrachain spacing of the guest atoms and the root-mean-square (RMS) fluctuation of the guest atoms from their unperturbed sites. We have also made estimates of the sound velocity along the guest-atom chains, and their effective Debye temperature.
Title:
Experimental study of the competition between Kondo and RKKY interactions for Mn spins in a model alloy system
Authors:
Prejean, JJ; Lhotel, E; Sulpice, A; Hippert, F
Source:
PHYSICAL REVIEW B 73 (21): Art. No. 214205 JUN 2006
Abstract:
The quasicrystal Al-Pd-Mn is a model system for an experimental study of the competition between Ruderman-Kittel-Kasuya-Yoshida (RKKY) and Kondo interactions. First, specific of such alloys, only a few Mn atoms carry an effective spin and their concentration x is tunable over several orders of magnitude, even though the Mn amount is almost constant. Second, the characteristic energy scales for the interactions lie in the Kelvin range. Hence we could study the magnetization on both side of these energy scales, covering a range of temperatures (0.1-100 K) and magnetic fields (mu H-B/k(B)=0-5 K) for 22 samples and x varying over two decades. Using very general Kondo physics arguments, and thus carrying out the data analysis with no preconceived model, we found a very robust and simple result: The magnetization is a sum of pure Kondo (T-K=3.35 K) and pure RKKY contributions, whatever the moment concentration is and this surprisingly up to the concentration where the RKKY coupl! ings dominate fully and thus cannot be considered as a perturbation.
Title:
Spin-phonon coupling in orthorhombic RMnO3 (R=Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y): A Raman study
Authors:
Laverdiere, J; Jandl, S; Mukhin, AA; Ivanov, VY; Ivanov, VG; Iliev, MN
Source:
PHYSICAL REVIEW B 73 (21): Art. No. 214301 JUN 2006
Abstract:
The temperature-dependent Raman spectra of orthorhombic RMnO3 (R=Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Y) were studied in the 5-300 K temperature range. It was established that while the materials with large R3+ ionic radius r(R) and A-type antiferromagnetic order (R=Pr,Nd,Sm) exhibit significant phonon softening and other anomalies with decreasing temperature near and below T-N, the effect of magnetic ordering is much weaker or negligible in compounds with R=Eu, Gd, Tb, Dy, Ho, and Y, characterized by small r(R) and incommensurate magnetic structure. The results are discussed accounting for the variations with r(R) of the type of magnetic ordering and related spin-phonon interaction.
Title:
Structure of the incommensurate phase of the quantum magnet TiOCl
Authors:
Schonleber, A; van Smaalen, S; Palatinus, L
Source:
PHYSICAL REVIEW B 73 (21): Art. No. 214410 JUN 2006
Abstract:
The incommensurately modulated structure is reported for the low-dimensional spin-1/2 quantum magnet TiOCl. On the basis of an analysis of the structural distortions in the spin-Peierls state (stable below T-c1=67 K) and in the incommensurate phase (stable between T-c1 and T-c2=90 K), it is argued that both the incommensurability and the twofold superstructure at low temperatures are the result of frustration between a spin-Peierls pairing on chains of Ti atoms as driving force and elastic coupling between neighboring chains mediated by the oxygen atoms.
Title:
Incommensurability and edge states in the one-dimensional S=1 bilinear-biquadratic model
Authors:
Murashima, T; Nomura, K
Source:
PHYSICAL REVIEW B 73 (21): Art. No. 214431 JUN 2006
Abstract:
Commensurate-incommensurate change on the one-dimensional S=1 bilinear-biquadratic model [H(alpha)=Sigma(i){S-i center dot Si+1+alpha(S-i center dot Si+1)(2)}] is examined. The gapped Haldane phase has two subphases (the commensurate Haldane subphase and the incommensurate Haldane subphase) and the commensurate-incommensurate change point (the Affleck-Kennedy-Lieb-Tasaki point, alpha=1/3). There have been two different analytical predictions about the static structure factor in the neighborhood of this point. By using the Sorensen-Affleck prescription, these static structure factors are related to the Green functions, and also to the energy gap behaviors. Numerical calculations support one of the predictions. Accordingly, the commensurate-incommensurate change is recognized as a motion of a pair of poles in the complex plane.
Title:
Magnetic excitations and their anisotropy in YBa2Cu3O6+x: Slave-boson mean-field analysis of the bilayer t-J model
Authors:
Yamase, H; Metzner, W
Source:
PHYSICAL REVIEW B 73 (21): Art. No. 214517 JUN 2006
Abstract:
We perform a comprehensive analysis of the dynamical magnetic susceptibility chi(q,omega) in the slave-boson mean-field scheme of the bilayer t-J model. We use model parameters appropriate for YBa2Cu3O6+x (YBCO), a typical bilayer high-T-c cuprate compound well studied by neutron scattering experiments. In the d-wave pairing state, the strongest magnetic spectral weight appears at q=Q equivalent to(pi,pi) and omega=omega(res)(Q), and spreads into a diamond-shaped shell around Q in q space for omega omega(res)(Q) strong signals of Im chi(q,omega) tracing an upward dispersion are found and interpreted as an overdamped collective excitation near omega(res)(Q). In the normal state, Im chi(q,omega) has a broad peak at q=Q. That is, the IC and DIC signals appear only in the d-wave pairing state. We also study effects of a small orthorhombic anisotropy, which is intrinsic in untwinned YBCO crystals. Because of electron-electron correlations favoring d-wave shaped Fermi surface deformations, we expect an enhanced anisotropy of magnetic excitation spectra. This effect is particularly pronounced for low delta and at relatively high temperature. The present theory provides a rather detailed microscopic explanation of the most salient properties of magnetic excitations observed in YBCO.
Title:
Spontaneous spin-lattice coupling in the geometrically frustrated triangular lattice antiferromagnet CuFeO2
Authors:
Ye, F; Ren, Y; Huang, Q; Fernandez-Baca, JA; Dai, PC; Lynn, JW; Kimura, T
Source:
PHYSICAL REVIEW B 73 (22): Art. No. 220404 JUN 2006
Abstract:
We use high-resolution synchrotron x-ray and neutron diffraction to study the geometrically frustrated triangular lattice antiferromagnet CuFeO2. On cooling from room temperature, CuFeO2 undergoes two antiferromagnetic phase transitions with incommensurate and commensurate magnetic order at T-N1=14 K and T-N2=11 K, respectively. The occurrence of these two magnetic transitions is accompanied by second- and first-order structural phase transitions from hexagonal to monoclinic symmetry. Application of a 6.9 T magnetic field lowers both transition temperatures by similar to 1 K, and induces an additional incommensurate structural modulation in the temperature region where the field-driven ferroelectricity occurs. These results suggest that a strong magneto-elastic coupling is intimately related to the multiferroic effect.
Title:
Incommensurate magnetic order in Ag2NiO2 studied with muon-spin-rotation and relaxation spectroscopy
Authors:
Sugiyama, J; Ikedo, Y; Mukai, K; Brewer, JH; Ansaldo, EJ; Morris, GD; Chow, KH; Yoshida, H; Hiroi, Z
Source:
PHYSICAL REVIEW B 73 (22): Art. No. 224437 JUN 2006
Abstract:
The nature of the magnetic transition of the half-filled triangular antiferromagnet Ag2NiO2 with T-N=56 K was studied with positive muon-spin-rotation and relaxation (mu+SR) spectroscopy. Zero field mu+SR measurements indicate the existence of a static internal magnetic field at temperatures below T-N. Two components with slightly different precession frequencies and wide internal-field distributions suggest the formation of an incommensurate antiferromagnetic order below 56 K. This implies that the antiferromagnetic interaction is predominant in the NiO2 plane in contrast to the case of the related compound NaNiO2. An additional transition was found at similar to 22 K by both mu+SR and susceptibility measurements. It was also clarified that the transition at similar to 260 K observed in the susceptibility of Ag2NiO2 is induced by a purely structural transition.
Title:
Influence of a magnetic field on the spin susceptibility in high-T-c cuprates
Authors:
Jiang, HM; Li, JX
Source:
PHYSICAL REVIEW B 73 (22): Art. No. 224507 JUN 2006
Abstract:
In this paper, we investigate the effect of a magnetic field parallel to the CuO2 plane on spin dynamics in overdoped (clean) high-T-c cuprates. Starting from the slave-boson approach to the t-t(')-J model with a Zeeman field, we carry out the calculations based on the random-phase approximation. We find that the spin resonance (with energy E-r) is suppressed, broadened, and shifted toward lower frequencies by the field. The incommensurate peak is enhanced at low energies (< E-r) and suppressed at high energies (> E-r) with the inclusion of the field, and this contrasting feature holds in the whole temperature region below the superconducting transition temperature. We compare these results with experiments and give an explanation based on the topology of the Fermi surface and the d-wave superconducting gap, in which the effect of the magnetic field is to decrease the superconducting gap.
Title:
Magnetic excitations of stripes and checkerboards in the cuprates
Authors:
Yao, DX; Carlson, EW; Campbell, DK
Source:
PHYSICAL REVIEW B 73 (22): Art. No. 224525 JUN 2006
Abstract:
We discuss the magnetic excitations of well-ordered stripe and checkerboard phases, including the high energy magnetic excitations of recent interest and possible connections to the "resonance peak" in cuprate superconductors. Using a suitably parametrized Heisenberg model and spin wave theory, we study a variety of magnetically ordered configurations, including vertical and diagonal site- and bond-centered stripes and simple checkerboards. We calculate the expected neutron scattering intensities as a function of energy and momentum. At zero frequency, the satellite peaks of even square-wave stripes are suppressed by as much as a factor of 34 below the intensity of the main incommensurate peaks. We further find that at low energy, spin wave cones may not always be resolvable experimentally. Rather, the intensity as a function of position around the cone depends strongly on the coupling across the stripe domain walls. At intermediate energy, we find a saddle point at (pi,pi) for a range of couplings, and discuss its possible connection to the "resonance peak" observed in neutron scattering experiments on cuprate superconductors. At high energy, various structures are possible as a function of coupling strength and configuration, including a high energy square-shaped continuum originally attributed to the quantum excitations of spin ladders. On the other hand, we find that simple checkerboard patterns are inconsistent with experimental results from neutron scattering.
Title:
Decomposition and metastable phase formation in the bulk metallic glass matrix composite Zr56Ti14Nb5Cu7Ni6Be12
Authors:
Bracchi, A; Huang, YL; Seibt, M; Schneider, S; Thiyagarajan, P
Source:
JOURNAL OF APPLIED PHYSICS 99 (12): Art. No. 123519 JUN 15 2006
Abstract:
Decomposition in the undercooled liquid phase and crystallization during isothermal annealing in the glassy matrix of the bulk Zr56Ti14Nb5Cu7Ni6Be12 composite were investigated by x-ray diffraction, small angle neutron scattering (SANS), scanning electron microscopy, and transmission electron microscopy (TEM). Upon isothermal annealing near the glass transition temperature TEM images show the presence of quasicrystals, while SANS data exhibit an interference peak indicating a quasiperiodic arrangement of these metastable crystals. Samples annealed in the solid state show a transformation into the more stable Zr-2 TM-type (TM=Nb,Cu,Ni,Ti) phases. These results have been discussed on the basis of a phase separation process that determines the formation of the metastable quasicrystalline phase that is in good agreement with the behavior of other known bulk metallic glass-forming systems.
Title:
Exploratory synthesis of reduced rare-earth-metal halides, chalcogenides, intermetallics - New compounds, structures, and properties
Authors:
Corbett, JD
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 418 (1-2): 1-20 JUL 20 2006
Abstract:
A new direction in reduced rare-earth-metal (R) compounds opened up when tantalum (and niobium) were adapted to use as virtually faultless containers for these reactions, as these gave immediate access to many new metal-rich phases and structures. Examples are summarized for the new binary dihalides (e.g., Pr, Nd, Dy, Ho, Tm), metallic diodides (Sc, La, Ce, Gd), and metal-metal bonded chains (Sc, Y, Gd, Lu) that were so discovered. Furthermore, a large array of condensed metal cluster, chain, and sheet halides arise when a stoichiometric amount of a diverse variety of nonmetal or metal atoms is included to serve as an interstitial, the earliest examples originating with traces of common impurities. A change in anion charge type to telluride affords a whole new regime of condensed metal-rich cluster compounds and structures, including such remarkable examples as (Sc, Gd, Dy)(2)Te, Lu11Te4, Lu8Te, and Sc6PdTe2. Also, a number of novel Zintl phases, interstitial derivatives of the type R(5)Ge(3)Z, quasicrystals, and their approximants are generated in other intermetallic systems. Generalities in structures and bonding are described along the way. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Multi-walled nanotubes: Commensurate-incommensurate phase transition and NEMS applications
Authors:
Bichoutskaia, E; Heggie, MI; Lozovik, YE; Popov, AM
Source:
FULLERENES NANOTUBES AND CARBON NANOSTRUCTURES 14 (2-3): 131-140 APR-SEP 2006
Abstract:
Interaction of non-rigid walls of double-walled carbon nanotubes is studied within the Frenkel-Kontorova model. It reveals a clearly defined commensurate-incommensurate phase transition. Parameter which determines this phase is calculated for a set of double-walled nanotubes with non-chiral commensurate walls using ab initio interwall interaction energies and elastic properties. Possibility of formation of incommensurability defects in the commensurate phase is considered. The length of the defects and energy of their formation are calculated. Principal scheme of strain nanosensor based on the commensurate-incommensurate phase transition in double-walled nanotube is proposed.
Title:
Bi1-xCaxMnO3 (x=0.4 and 0.45): X-ray single-crystal and electron microscopy study
Authors:
Giot, M; Beran, P; Perez, O; Malo, S; Hervieu, M; Raveau, B; Nevriva, M; Knizek, K; Roussel, P
Source:
CHEMISTRY OF MATERIALS 18 (14): 3225-3236 JUL 11 2006
Abstract:
The superstructure of Bi1-xCaxMnO3 ( x = 0.4 or 0.45), which exhibits a charge/orbital-ordered state at room temperature ( T-CO approximate to 330 K), has been successfully determined at different temperatures using single-crystal X-ray diffraction data and the superspace formalism. This peculiar approach provides a very convenient way to analyze all possible 3D symmetry ( P2(1)/m, Pm, and Pnm2(1)) of the superstructure. The structural model of the ordered state has been confirmed thanks to complementary data from several other techniques ( electron diffraction, high-resolution electron microscopy ( HREM), and synchrotron high-resolution X-ray powder diffraction, all vs T). It is compatible with an orthorhombic cell ( a = 11.002( 2) angstrom, b = 7.588( 1) angstrom, c = 5.425( 4) angstrom at 150 K) and the space group Pnm2(1). The structural model is based on the alternation of one double band of Mn(1)O-6 octahedra and one double band of Mn(2)O-6 octahedra, the two octahedron types exhibiting almost similar distortion. HREM images were then simulated from the refined atomic positions; the good agreement with the experimental images confirms the model. Finally, the relationships between structural characterizations and magnetic properties have been investigated for these compounds.

Update: 14-Jul-2006

Title:
Low temperature SR-XRPD study of akermanite-gehlenite solid solution
Authors:
Merlini, M; Gemmi, M; Artioli, G
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE : 419-424 Part 2 Suppl. 23 2006
Abstract:
Low temperature thermal expansion coefficients of members of the solid solution gehlenite (ge)-akermanite (ak) were measured by synchrotron radiation X-Ray powder diffraction. The linear thermal expansion coefficient is maximum for a composition with about 50 % content of ak. In ak-rich compositions an incommensurate modulated structure is present. The ge-ak solid solution shows a non-ideal behaviour, with negative excess volume near the ge end-member.
Title:
Pressure effect on CeAl2 investigated by AC-Chi and Al-27-NQR measurements
Authors:
Tomisawa, S; Mito, T; Wada, S; Ohashi, M; Oomi, G
Source:
PHYSICA B-CONDENSED MATTER 378-80: 102-103 MAY 1 2006
Abstract:
To elucidate microscopically the transformation from the Fermi liquid to non-Fermi liquid states of an antiferromagnetic (AFM) Kondo compound CeAl2, we have carried out AC-chi and Al-27-NQR measurements at pressures up to P = 2.4 GPa. The AFM transition temperature T-N is suppressed from 3.8 (P = 0) to similar or equal to 2.6 K (2.4 GPa), and the NQR spectrum in the AFM ordered state varies in shape from a complex structure at P = 0 with large linewidth (Delta H similar to 400 kHz) to a Lorentzian-like structure with Delta H similar or equal to 200 kHz. This is ascribed to the transformation from a mixing-phase of the incommensurate and commensurate orderings at P = 0 to a single phase of commensurate above similar to 2 GPa. Variations in the spin-lattice relaxation behavior of Al-27 with pressure indicate the increase of the itinerant electron character and the density of states at the Fermi level. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Incommensurate spin dynamics in underdoped cuprate perovskites
Authors:
Sherman, A
Source:
PHYSICA B-CONDENSED MATTER 378-80: 558-560 MAY 1 2006
Abstract:
The incommensurate magnetic response observed in normal-state cuprate perovskites is interpreted based on Mori's projection operator formalism and the t-J model of Cu-O planes. In agreement with experiment, the calculated dispersion of maxima in the susceptibility has the shape of two parabolas with upward- and downward-directed branches which converge at the antiferromagnetic wave vector. The upper parabola reflects the dispersion of magnetic excitations of the localized Cu spins, while the lower parabola arises due to the weakness of the interaction between the spin excitations and holes near the hot spots. Also in conformity with experiment, the low-frequency incommensurability parameter delta grows with the hole concentration x for x less than or similar to 0.12 and then saturates. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Spin-charge-orbital ordering on triangle-based lattices
Authors:
Onishi, H; Hotta, T
Source:
PHYSICA B-CONDENSED MATTER 378-80: 589-591 MAY 1 2006
Abstract:
We investigate the ground-state property of an e(g)-orbital Hubbard model at quarter filling on a zigzag chain by exploiting the density matrix renormalization group method. When two orbitals are degenerate, the zigzag chain is decoupled to a double-chain spin system to suppress the spin frustration due to the spatial anisotropy of the occupied orbital. On the other hand, when the level splitting is increased and the orbital anisotropy disappears, a characteristic change in the spin incommensurability is observed due to the revival of the spin frustration. (c) 2006 Elsevier B.V. All rights reserved.
Title:
De Haas-van Alphen effect of PrB6 in commensurate and incommensurate phases
Authors:
Endo, M; Isshiki, T; Kimura, N; Aoki, H; Kunii, S
Source:
PHYSICA B-CONDENSED MATTER 378-80: 607-609 MAY 1 2006
Abstract:
We have studied the de Haas-van Alphen effect in the commensurate (C) and incommensurate (IC) phases of PrB6. It is found that the amplitudes and effective masses of the two oscillations alpha(1) and alpha(2) from the main Fermi surface are approximately the same in the C phase while they are considerably different in the IC phase. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Theory of the first order phase transition in the ferromagnetic phase of UGe2
Authors:
Hirohashi, K; Ueda, K
Source:
PHYSICA B-CONDENSED MATTER 378-80: 965-967 MAY 1 2006
Abstract:
The existence of the first order phase transition in the ferromagnetic phase is important for the occurrence of the superconductivity in UGe2. In order to clarify the mechanism of the first order phase transition, we have constructed a microscopic Hamiltonian of UGe2 taking account of the orbital degeneracy of the 54 electrons and investigated the ground state phase diagram of the Hamiltonian by the Hartree-Fock approximation. A rich ground state phase diagram which includes an SDW, a CDW, and a ferromagnetic phase modulated by an SDW component is obtained because of the orbital degeneracy. We have found two kinds of uniform ferromagnetic phases, which are separated by a first order phase transition, by adjusting the number of f electrons per uranium atom to be about 2.60. We discuss differences of the physical properties between the two ferromagnetism by comparing the Fermi surfaces and other properties. (c) 2006 Published by Elsevier B.V.
Title:
NMR studies of incommensurate quantum antiferromagnetic state of LiCuVO4
Authors:
Smith, R; Reyes, AP; Ashey, R; Caldwell, T; Prokofiev, A; Assmus, W; Teitel'baum, G
Source:
PHYSICA B-CONDENSED MATTER 378-80: 1060-1061 MAY 1 2006
Abstract:
Our V-51 NNIR measurements in the LiCUVO4 single crystal reveal that the classical quadrupole split signal transforms upon lowering temperature to the single line with the shape typical for the systems undergoing the phase transition to the incommensurate magnetic state. The angular dependence of such a lineshape together with the anomalies of the V-51 nuclear spin relaxation rates make it possible to conclude that the low-temperature magnetic order corresponds to the antiferromagnetic state with the incommensurate modulation along the b-axis of the crystal. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Incommensurate to commensurate phase transition in a new spin-Peierls system TiOBr
Authors:
Sasaki, T; Mizumaki, M; Nagai, T; Asaka, T; Kato, K; Takata, M; Matsui, Y; Akimitsu, J
Source:
PHYSICA B-CONDENSED MATTER 378-80: 1066-1067 MAY 1 2006
Abstract:
We report here on the observation of superlattice reflections in the new quasi-one-dimensional spin system TiOBr by electron and synchrotron radiation X-ray diffractions. We discussed on crystal symmetry and temperature dependence of superlattice reflections. Superlattice reflections can be observed at (h, k + 1/2, 0) below T-cl and (h +/- delta(h), k +/- delta k, 0) above Tcl; (h + k = 2n). We discussed the origin of two phase transitions, T-cl(= 27K) and T-c2(= 47K) in TiOBr. (c) 2006 Elsevier B.V. All rights reserved.
Title:
Structural instabilities in Nb, Ti and K substituted BaVS3
Authors:
Fagot, S; Foury-Leylekian, P; Pouget, JP; Popov, G; Lobanov, M; Greenblatt, M; Fertey, P
Source:
PHYSICA B-CONDENSED MATTER 378-80: 1068-1069 MAY 1 2006
Abstract:
The one-dimensional (1D) strongly correlated BaVS3 undergoes a series of unexplained phase transitions. Among them it undergoes a metal-insulator (MI) transition associated with a 2k(F) = c*/2 charge density wave (CDW) instability. We show that this CDW ground state is very sensitive to chemical substitutions and/or sulfur deficiency. Substitutions of V with approximate to 2% of Nb, Ti or Ba with approximate to 2% K in probably sulfur deficient samples leads to a completely different ground state. This ground state is characterized by a short range structural modulation with the incommensurate wave vector q(s) = (1/31/30.21)(H), which could be due to a CDW taking place in a differently filled d(z2) band. (c) 2006 Elsevier B.V.. All rights reserved.
Title:
Geometry of dislocations in icosahedral quasicrystals
Authors:
Gratias, D; Beauchesne, JT; Mompiou, F; Caillard, D
Source:
PHILOSOPHICAL MAGAZINE 86 (25-26): 4139-4151 SEP 1 2006
Abstract:
Quasicrystals are complex metallic alloys that are ductile at high temperatures close to their melting point. It has been early recognized that their plasticity is due to a flux of moving linear defects in all respects similar to dislocations in ordinary crystals. The present paper is an attempt to propose in a short didactic review a simple synthetic analysis of the basic underlying geometry of quasicrystalline dislocations exemplified with experimental and calculated images of electron microscopy in icosahedral phases.
Title:
Film growth arising from the deposition of Au onto an i-Al-Pd-Mn quasicrystal: a medium energy ion scattering study
Authors:
Noakes, TCQ; Bailey, P; Draxler, M; McConville, CF; Ross, AR; Lograsso, TA; Leung, L; Smerdon, JA; McGrath, R
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 18 (22): 5017-5027 JUN 7 2006
Abstract:
The room temperature deposition of 7 ML of Au onto the fivefold symmetric surface of icosahedral Al-Pd-Mn leads to the formation of a several monolayers thick Au-Al alloy film. An AlAu film with 1: 1 stoichiometry is formed, which shows no evidence of ordered structure, being either amorphous or polycrystalline. Annealing to 325 degrees C causes more Al to diffuse into the film, producing Al2Au but still with no indication of structure. Experiments using 0.5 ML of pre-deposited In demonstrated a surfactant effect as the In 'floated' on the surface during growth and produced a reduction in film roughness. However, contrary to previous findings the film was still either amorphous or polycrystalline, with no evidence of quasi-crystalline or aperiodic structure. Experiments were also conducted using smaller doses of Au to look for the formation of an epitaxial layer and, if formed, determine the registry with the substrate. However, no change in the Pd blocking curves for the surface could be seen, suggesting that the Au does not adsorb in well defined sites. This result is not surprising when considering that even for these low doses Al is drawn into the film, changing the composition and probably the structure of the topmost layers of the substrate, so that the potential adsorption sites on the clean surface may no longer exist.
Title:
Electronic structure of the charge-density-wave compound Er5Ir4Si10
Authors:
Bondino, F; Magnano, E; Carleschi, E; Zangrando, M; Galli, F; Mydosh, JA; Parmigiani, F
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 18 (24): 5773-5782 JUN 21 2006
Abstract:
Photoemission and x-ray absorption measurements have been performed on Er5Ir4Si10, a compound that exhibits an incommensurate charge-density-wave formation below 155 K. The resonant photoemission and x-ray absorption measurements performed across the Er N-54 and Er M-5 edge identify the Er 4f multiplet lines, the 4f occupancy and the character of the states close to the Fermi edge.
Title:
Complex antiferromagnetic order in Dy3Ag4Sn4
Authors:
Perry, LK; Cadogan, JM; Ryan, DH; Canepa, F; Napoletano, M; Mazzone, D; Riani, P
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 18 (24): 5783-5792 JUN 21 2006
Abstract:
We have studied the complex magnetic ordering of the Dy sublattices in orthorhombic Dy3Ag4Sn4 by high-resolution neutron diffraction and Sn-119 Mossbauer spectroscopy. Magnetic ordering in this compound occurs over two transitions. At 16 K the Dy( 2d) site orders in a doubled commensurate antiferromagnetic structure described by a propagation vector [ 0 1 2 0], with moments aligned along [ 100]. The Dy( 4e) site orders incommensurately with a propagation vector [ 0 0.628( 1) 0] and moments in the ( 001) plane. Below the second transition at 14 K both Dy site ordering modes are commensurate antiferromagnetic with the propagation vector [ 0 1 2 0] and unchanged ordering directions. The Sn-119 Mossbauer spectra comprise three magnetically split sextets in the area ratio 50%: 25%: 25% due to transferred hyperfine fields at the Sn-119 nuclei from the surrounding magnetic Dy neighbours. This spectral decomposition deviates from the area ratio 50%: 50% expected on the basis of the crystal structure and is in perfect agreement with the magnetic structure of Dy3Ag4Sn4 deduced from neutron diffraction data.
Title:
Mg 2p shallow core-level and local atomic structure of i-ZnMgRE quasicrystals
Authors:
Karpus, V; Suchodolskis, A; Karlsson, UO; Lay, G; Giovanelli, L; Assmus, W; Bruhne, S; Uhrig, E
Source:
APPLIED SURFACE SCIENCE 252 (15): 5411-5414 MAY 30 2006
Abstract:
We present a detailed analysis of the Mg 2p shallow core-levels measured on icosahedral single-grain ZnMgY, ZnMgHo, and ZnMgEr quasicrystals during a photoelectron microscopy study. The synchrotron radiation photoemission measurements were performed on in situ cleaved samples at a pressure of 10(-10) mbar and at low temperature, typically 90-150 K. The Mg 2p photoemission lines are essentially broadened as compared to those of the Mg 2p spin-orbit doublet recorded on the Zn2Mg crystalline Laves phase. The broadening is associated to the coordination shifts of the Mg 2p level due to the inequivalent magnesium sites in the quasicrystalline lattice. The coordination shifts are calculated on the basis of i-ZnMg(Ho, Y) atomic structure data, recently determined from the pair distribution function analysis. The coordination shifts obtained are up to 0.2 eV. The Mg 2p experimental spectral intensity is nicely reproduced by a superposition of coordination-shifted Mg 2p spin-or bit doublets. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Fabrication of two-dimensional metallodielectric quasicrystals by single-beam holography
Authors:
Yang, Y; Zhang, SH; Wang, GP
Source:
APPLIED PHYSICS LETTERS 88 (25): Art. No. 251104 JUN 19 2006
Abstract:
We experimentally demonstrate a single-beam holography for creating Ag nanoparticle-embedded eight-fold quasicrystals. By adjusting the phase relation of interference beams through an optical mask, we obtain eight-fold symmetry structures with three different profiles. The structure of quasicrystals is confirmed through scanning electron microscopy and optical diffraction pattern, respectively. Furthermore, we also numerically demonstrate that the method can encode even higher symmetric structures such as the most complex 14- and 18-fold quasicrystals as well by computer simulations. (c) 2006 American Institute of Physics.
Title:
The stochastic mode of the modulated structure in [N(CH3)(4)](2)MeCl4 dielectric crystals
Authors:
Sveleba, S; Semotyuk, O; Katerynchuk, I; Furgala, Y; Pankivskyi, Y
Source:
ACTA PHYSICA POLONICA A 109 (6): 695-700 JUN 2006
Abstract:
Temperature behavior of the optical birefringence in the transitional regions of the incommensurate phase of [N(CH3)]CUCl4 was studied. Temperature dependencies of the modulated structure wave vector and of the specific heat in these regions were analyzed. The stochastic mode of the incommensurate modulated structure in [N(CH3)]MeCl4 (Me = Cu, Fe) dielectric crystals was discovered.

Update: 7-Jul-2006

Title:
The Sr0.8Y0.2Co1-xFexO3-delta oxygen deficient perovskites: modulated structure, magnetic properties and magnetoresistance
Authors:
Breard, Y; Maignan, A; Lechevallier, L; Boulon, ME; Le Breton, JM
Source:
SOLID STATE SCIENCES 8 (6): 619-624 JUN 2006
Abstract:
A series of oxygen deficient perovskites Sr0.8Y0.2Co1-xO3-delta, has been prepared by solid state reaction in close ampoules. The structural study by transmission electron microscopy reveals the existence of extra reflection peaks resulting from ordering phenomenon of the oxygen anions. For x = 0.5 this implies a modulated structure characterized by a vector such as q = 0.45 in the Pm3m space group. Interestingly, the Fe introduction in Sr0.8Y0.2CoO3-delta broadens the ferromagnetic transition, increasing the T-C onset. Despite a lack of metallic-like behavior, the mixed "Co1-xFex" compounds exhibit negative magnetoresistance properties which magnitude increases as T decreases below TC to reach the best effect of -50% in 7 T for Sr0.8Y0.2Co0.5Fe0.5O3-delta. (C) 2006 Elsevier SAS. All rights reserved.
Title:
Spin dynamics in cuprate perovskites
Authors:
Sherman, A; Schreiber, M
Source:
LOW TEMPERATURE PHYSICS 32 (4-5): 375-379 APR-MAY 2006
Abstract:
Results obtained with the use of the t-J model of Cu-O planes and Mori's projection operator formalism are compared with data of neutron scattering experiments in lanthanum and yttrium cuprates. This comparison allows us to interpret the intensive peak at the anti ferromagnetic wave vector observed in yttrium cuprates as a manifestation of excitations of localized Cu spins. The high-frequency incommensurability detected both in lanthanum and yttrium cuprates is connected with the dispersion of these excitations, while the low-frequency incommensurability arises due to a dip in the spin-excitation damping at the antiferromagnetic wave vector. For moderate doping the dip sterns from the weakness of the interaction between the spin excitations and holes near hot spots. It is conjectured that the dissimilarity of the susceptibility frequency dependencies in yttrium and lanthanum cuprates may be connected with different values of the hole bandwidth and damping in th! ese crystals. (c) 2006 American Institute of Physics.
Title:
Microstructural and transport properties in substituted Bi2Sr2CaCu2O8+delta-modulated compounds
Authors:
Autret-Lambert, C; Pignon, B; Gervais, M; Monot-Laffez, I; Ruyter, A; Ammor, L; Gervais, F; Bassat, JM; Decourt, R
Source:
JOURNAL OF SOLID STATE CHEMISTRY 179 (6): 1698-1706 JUN 2006
Abstract:
X-ray powder diffraction and resistivity measurements were performed on Bi2Sr2CaCu2O8+delta ceramics substituted by Y and Zn for Ca and Cu sites, respectively. X-ray diffraction patterns show an incommensurate modulated structure along the b-axis. The structural refinements were carried out using the four-dimensional space group Bbmb(0 beta 1)000. From the X-ray peak profiles analysis, an anisotropic line-shape broadening was observed. The use of the "Williamson and Hall" method allows distinguishing the origin of broadening as mainly due to microstrains. A large transition from a metallic to semiconductor behaviour is observed on the resistivity curves at x approximate to 0.4 for Bi2Sr2Ca1-xYxCu2O8+delta and at x' approximate to 0.36 for Bi2Sr2Ca1-xYxCu1.94Zn0.06O8+delta, which can be also correlated to the defects. Oppositely to the metallic behaviour, which satisfies the Mathiessen's rule, the semiconducting one can be modelled by a variable range hopping process. (c) 2006 Elsevier Inc. All rights reserved.
Title:
A high-temperature structure for Ta(2)O(5)with modulations by TiO2 substitution
Authors:
Makovec, D; Zuo, HM; Twesten, R; Payne, DA
Source:
JOURNAL OF SOLID STATE CHEMISTRY 179 (6): 1782-1791 JUN 2006
Abstract:
Solid solutions in the series (1-x)Ta2O5-xTiO(2), with x = 0.0-0.1 were prepared by high-temperature ceramic processing methods, and the crystal structure was determined at room temperature by transmission electron microscopy, electron diffraction and high-resolution lattice imaging. A structural model is proposed for the oxygen-deficient tantalum oxide (Ta2O5) phase with high TiO2 doping level (x = 0.08). The model is based on edge sharing of an oxygen octahedron-hexagonal bi-pyramid-octahedron molecular building block unit that repeats four times per unit cell. Electron diffraction reveals a monoclinic distortion from a pseudo-tetragonal model structure that is modulated primarily along < 110 >. The modulation length varies with increasing TiO2 content. Furthermore, by quantitative HREM analysis and matching of lattice images by simulation, it is shown that the modulation is associated with small ionic displacements in specific lattice planes that coincide with Ta ions in the model structure coordinated by oxygen hexagonal bi-pyramids. Based on this evidence, it is suggested that the modulation comes from a replacement of Ta with Ti ions, and the loss of inversion symmetry in the modulated structure is related to the dielectric properties of the material. (c) 2006 Elsevier Inc. All rights reserved.
Title:
Crystal structure of the parent misfit-layered cobalt oxide [Sr2O2]qCoO(2)
Authors:
Nagai, T; Sakai, K; Karppinen, M; Asaka, T; Kimoto, K; Yamazaki, A; Yamauchi, H; Matsui, Y
Source:
JOURNAL OF SOLID STATE CHEMISTRY 179 (6): 1898-1903 JUN 2006
Abstract:
The crystal structure of our newly discovered Sr-Co-O phase is investigated in detail through high-resolution electron microscopy (HREM) techniques. Electron diffraction (ED) measurement together with energy dispersive X-ray spectroscopy (EDS) analysis show that an ampoule-synthesized sample contains an unknown Sr-Co-O ternary phase with monoclinic symmetry and the cation ratio of Sr/Co = 1. From HREM images a layered structure with a regular stacking of a CdI2-type CoO, sheet and a rock-salt-type Sr2O2 double-layered block is observed, which confirms that the phase is the parent of the more complex "misfit-layered (ML)" cobalt oxides of [M(m)A(2)O(m+2)],CoO2 with the formula of [Sr2O2](q)CoO2, i.e. m = 0. It is revealed that the misfit parameter q is 0.5, i.e. the two sublattices of the CoO2 sheet and the Sr2O2 block coexist to form a commensurate composite structure. We propose a structural model with monoclinic P2(1)/m symmetry, which is supported by simulations of ED patterns and HREM images based on dynamical diffraction theory. (c) 2006 Elsevier Inc. All rights reserved.
Title:
Pt29Zn49, a complex defective AlB2-type derivative structure
Authors:
Thimmaiah, S; Harbrecht, B
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 417 (1-2): 45-49 JUN 29 2006
Abstract:
The crystal structure of the title compound has been determined by X-ray diffraction means. Pt29Zn49 forms a complex superstructure of a defective AlB2-type derivative of the order 58: a=279.0(1)pm, b=11895.2(4)pm, c=698.0(1)pm, space group Amm2, Z=2. Ordering of vacancies is accompanied by a particular distortion of defective graphite-like 63 nets consisting exclusively of Zn atoms. The ordering induces a modulation of the structure along a(h) of an AlB2-type structure with a periodicity of nearly 12 nm. A mechanistic model is proposed elucidating how Pt29Zn49 evolves from the eutectoid decomposition of the inter-mediate high temperature precursor Pt7Zn12, (c) 2005 Elsevier B.V. All rights reserved.
Title:
An investigation of the Al-Cu-Cr phase diagram: Phase equilibria at 800-1000 degrees C
Authors:
Grushko, B; Kowalska-Strzeciwilk, E; Przepiorzynski, B; Surowiec, M
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 417 (1-2): 121-126 JUN 29 2006
Abstract:
The Al-Cu-Cr alloy system was investigated at 800-1000 degrees C. The Al-Cr gamma-range extends up to 18 at.% Cu, extensions of other binary phases are below 3 at.% of the third element. The stability of quasiperiodic decagonal phases reported in the literature was not confirmed at the temperatures studied. The formation of three ternary phases was observed: in addition to a hexagonal phase with a approximate to 1.77 and c approximate to 1.26 nm, and a cubic phase with a approximate to 1.82 nm reported earlier, also a primitive cubic phase with a approximate to 0.30 nm was revealed in the region of the Al46Cu36Cr18 composition. The latter phase only exists in a small temperature range around 900 degrees C. The isothermal section at 1000 degrees C and the partial isothermal sections at 900 and 800 degrees C were constructed. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Direct measurement of spatial distortions of charge density waves in K0.3MoO3
Authors:
Du, CH; Lee, YR; Lo, CY; Lin, HH; Chang, SL; Tang, MT; Stetsko, YP; Lee, JJ
Source:
APPLIED PHYSICS LETTERS 88 (24): Art. No. 241916 JUN 12 2006
Abstract:
Using x-ray scattering and multiple diffraction on a charge density wave (CDW) material, K0.3MoO3, under applied voltages, we demonstrate that the occurrence of nonlinear conductivity caused by the periodic media is through the internal deformation of the CDW lattice, i.e., a phase jump of 2 pi, as the applied voltage exceeds the threshold. From the evolution of the measured peak width of satellite reflections as a function of the field strength, we also report that the CDW lattice can be driven to move and undergo a dynamic phase transition from the disordered pinning state to ordered moving solid state and then to disordered moving liquid. (c) 2006 American Institute of Physics.

Update: 30-Jun-2006

Title:
Dynamics of the domain structure in ferroelectrics with an incommensurate phase
Authors:
Belonenko, MB; Sasov, AS
Source:
PHYSICS OF THE SOLID STATE 48 (6): 1134-1136 JUN 2006
Abstract:
The dynamics of the domain structure of ferroelectrics with an incommensurate phase (like sodium nitrite) is considered. The polarization properties of these ferroelectrics are described using the pseudospin formalism. The equation for the polarization is numerically solved together with the equation for acoustic waves. The obtained results are analyzed for various values of the parameters of the crystal and different initial conditions. It is shown that, after a sufficiently large time, the domain structure of the crystal becomes localized.
Title:
Local atomic structure and discommensurations in the charge density wave of CeTe3
Authors:
Kim, H; Malliakas, C; Tomic, A; Tessmer, S; Kanatzidis, M; Billinge, S
Source:
PHYSICAL REVIEW LETTERS 96 (22): Art. No. 226401 JUN 9 2006
Abstract:
The local structure of CeTe3 in the incommensurate charge density wave (IC-CDW) state has been obtained using atomic pair distribution function analysis of x-ray diffraction data. Local atomic distortions in the Te nets due to the CDW are larger than observed crystallographically, resulting in distinct short and long Te-Te bonds. Observation of different distortion amplitudes in the local and average structures is explained by the discommensurated nature of the CDW, since the pair distribution function is sensitive to the local displacements within the commensurate regions, whereas the crystallographic result averages over many discommensurated domains. The result is supported by STM data. This is the first quantitative local structural study within the commensurate domains in an IC-CDW system.
Title:
Fe-57 Mossbauer effect study of bannisterite: a modulated 2 : 1-type phyllosilicate
Authors:
Ferrow, EA
Source:
MINERALOGICAL MAGAZINE 70 (2): 187-199 APR 2006
Abstract:
Bannisterite is a modulated 2:1-type phyllosilicate having ten octahedral sites with hydroxyl groups in trans, cis and combined trans-cis configurations. Each octahedral site, depending on its proximity to the layer modulation, is exposed to a different degree of distortion. The electric field gradient at the Fe site and the site distortion are used to propose a model for the site assignment and oxidation mechanism in bannisterite. The results show that two models are compatible with the experimental results of fitting the spectrum of bannisterite. However, the model which allows for site distortion accounts better for the observed line overlap of the Fe-[6](2+) sites. Accordingly, the octahedral sites with a greater degree of distortion are assigned to the Fe-[6](2+) with lower electric quadrupole splitting, and the octahedral sites with lower site distortion are assigned to the Fe-[6](2+) with higher electric quadrupole splitting. Moreover, the ease of oxidation decreases in the order trans > trans-cis > cis.

Update: 2-Jun-2006

Title:
The molecular structure of 2-phenylbenzimidazole: a new example of incommensurate modulated intramolecular torsion
Authors:
Zuniga, FJ; Palatinus, L; Cabildo, P; Claramunt, RM; Elguero, J
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 221 (4): 281-287 2006
Abstract:
Molecular crystals of 2-phenylbenzimidazole, C13H10N2, exhibit a one-dimensional incommensurate structure. The Structure has been solved by charge flipping and refined using the superspace formalism in the (3 + 1) D superspace group C2/c(0b0) s0 with modulation wave-vector q = 0.368b*. The unit *cell* contains 8 *molecules*, each one disorderly occupying two configurations related by inversion center. The refinement based on a molecular model with two rigid-body parts per molecule includes up to second order Fourier amplitudes for the modulation. The displacive modulation involves a significant intra-molecular twist between the phenyl and the benzimidazole parts.
Title:
IR reflectance spectra and optical constants of Al-Cu-Fe quasicrystalline thin films
Authors:
Yakovlev, VA; Novikova, NN; Mattei, G; Teplov, AA; Shaitura, DS; Nazin, VG; Laskova, GV; Ol'shanskii, ED; Dolgii, DI
Source:
PHYSICS OF THE SOLID STATE 48 (5): 821-825 MAY 2006
Abstract:
The optical properties of Al-Cu-Fe quasicrystalline films and, for comparison, crystalline films of similar composition are studied using middle-and far-IR reflectance spectroscopy. Measurements are performed with 0.1-to 0.3-mu m-thick films on sapphire substrates. The complex dielectric function of the films is calculated from experimental data. It is found that the real part of the dielectric function is negative for the crystalline films but positive and weakly frequency dependent, except in the range near 245 cm(-1), for the quasicrystalline films. The optical conductivity of the quasicrystalline films does not feature the Drude peak observed for crystalline films and exhibits a peak at 245 cm(-1), which can be assigned to optical phonon excitations and is absent for crystalline films.
Title:
Quasi-one-dimensional Heisenberg antiferromagnetic model for an organic polymeric chain
Authors:
Wu, F; Wang, WZ
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 18 (15): 3837-3844 APR 19 2006
Abstract:
Using the exact diagonalization technique, we study the properties of the ground state of a spin-(1)/(2) antiferromagnetic Heisenberg model for a zigzag polymer chain with side radicals connected to the even sites. We consider the nearest-neighbour exchange J and the next-nearest-neighbour exchange alpha J along the main chain, and J(1) between the even site on the main chain and the radical site. For small alpha the ground state is ferrimagnetic. For alpha > alpha(c1), the ground state is a spiral phase, which is characterized by a peak of the static structure factor S(q) locating at an incommensurate value q(max). For alpha > alpha(c2), the ground state is antiferromagnetic. With increasing J(1), alpha(c1) decreases while alpha(c2) has a maximum at about J(1) = 0.5. For very small J(1) and alpha = 0.5, the spin configuration on the main chain is a product of nearest-neighbour singlets. In the antiferromagnetic phase, if J(1) is large enough the even site and the radical site form a singlet with exchange-decoupling from the odd site while the odd sites approximately form an antiferromagnetic chain.
Title:
Anisotropic 4f-spin dynamics across the B-T phase diagram of Ce7Ni3
Authors:
Schenck, A; Gygax, FN; Umeo, K; Takabatake, T; Andreica, D
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 18 (6): 1955-1966 FEB 15 2006
Abstract:
Longitudinal field mu SR measurements in applied fields parallel and perpendicular to the c-axis of the hexagonal heavy-fermion antiferromagnet Ce7Ni3 served to monitor the 4f-spin dynamics across the magnetic phase diagram in the B-T plane, which consists of an incommensurate/commensurate antiferromagnetic (AF) section below 1.9 K/0.7 K and below an applied field B of 0.25 T, and for B along the c-axis, of a field-induced magnetic (FIM) section for B >= 0.6 T and below 0.5 K. The observed mu(+)spin-lattice relaxation rates reveal persisting spin dynamics across the whole phase diagram, reflect the various phase boundaries and are interpreted to arise in the AF and FIM phases from the Ce3 sublattice (the Cc ions are located on three different sublattices) and in the intermediate phase, viewed as a short range ordered (SRO) state, also from the Ce1 and Ce2 sublattices with slower fluctuation rates. In the paramagnetic regime the Cel sublattice displays the slowest spin dynamics. In the FIM phase the fraction of relaxing mu(+) appears to shrink with rising B, evidencing a possible phase separation.
Title:
Does the modulated magnetic structure of BiFeO3 change at low temperatures?
Authors:
Przenioslo, R; Palewicz, A; Regulski, M; Sosnowska, I; Ibberson, RM; Knight, KS
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 18 (6): 2069-2075 FEB 15 2006
Abstract:
High resolution neutron powder diffraction has been applied to verify the model of distorted cycloidal magnetic modulation proposed on the basis of NMR studies of the multiferroic BiFeO3 in Zalesskii et al (2000 Europhys. Lett. 50 547). Our experimental results do not support the model of magnetic modulation given by Zalesskii et at for BiFeO3 at 4 K. Neutron diffraction patterns recorded at ambient temperature and 4 K agree with the cycloidal magnetic modulation model for BiFeO3 proposed by Sosnowska et al (1982 J. Phys. C: Solid State Phys. 15 4835). Present neutron diffraction results are compared with BiFeO3 NMR and Mossbauer literature data.
Title:
Ferroelectricity induced by incommensurate magnetism (invited)
Authors:
Harris, AB
Source:
JOURNAL OF APPLIED PHYSICS 99 (8): Art. No. 08E303 APR 15 2006
Abstract:
Ferroelectricity has been found to occur in several insulating systems, such as TbMnO3 and Ni3V2O8 which have more than one phase with incommensurately modulated long-range magnetic order. Here we give a phenomenological model which relates the symmetries of the magnetic structure as obtained from neutron diffraction to the development and orientation of a spontaneous ferroelectric moment induced by the magnetic ordering. This model leads directly to the formulation of a microscopic spin-phonon interaction which explains the observed phenomena. The results are given in terms of gradients of the exchange tensor with respect to generalized displacements for the specific example of NVO. It is assumed that these gradients will now be the target of first-principles calculations using the LDA+U or related schemes. (C) 2006 American Institute of Physics.
Title:
Evidence for strong spin-lattice coupling in multiferroic RMn2O5 (R=Tb,Dy,Ho) via thermal expansion anomalies
Authors:
dela Cruz, CR; Yen, F; Lorenz, B; Park, S; Cheong, SW; Gospodinov, MM; Ratcliff, W; Lynn, JW; Chu, CW
Source:
JOURNAL OF APPLIED PHYSICS 99 (8): Art. No. 08R103 APR 15 2006
Abstract:
Thermal expansion measurements were done on single-crystal RMn2O5 (R=Tb,Dy,Ho) along the principal crystallographic axes. Distinctive anomalies were observed in the linear thermal expansivities at critical temperatures marking the onset of long-range antiferromagnetic order (T-N1), ferroelectricity (T-C1), as well as at temperatures when anomalous changes in the polarization, dielectric constant, and spin wave incommensurability have been previously reported. These observations suggest that the coupling between the magnetic orders and the dielectric properties is mediated by the lattice distortion. In particular, a possible scenario as to how ferroelectricity arises and subsequently is altered as a result of the subtle changes in the highly frustrated magnetic order, is discussed in the light of the strong spin-lattice coupling observed in these materials. Neutron diffraction measurements on HoMn2O5 show a spin reorientation at 23 K corresponding to a step-like anomaly in the dielectric constant. (C) 2006 American Institute of Physics.
Title:
Minimal configurations for the Frenkel-Kontorova model on a quasicrystal
Authors:
Gambaudo, JM; Guiraud, P; Petite, S
Source:
COMMUNICATIONS IN MATHEMATICAL PHYSICS 265 (1): 165-188 JUL 2006
Abstract:
In this paper, we consider the Frenkel-Kontorova model of a one dimensional chain of atoms submitted to a potential. This potential splits into an interaction potential and a potential induced by an underlying substrate which is a quasicrystal. Under standard hypotheses, we show that every minimal configuration has a rotation number, that the rotation number varies continuously with the minimal configuration, and that every non negative real number is the rotation number of a minimal configuration. This generalizes well known results obtained by S. Aubry and P.Y. le Daeron in the case of a crystalline substrate.
Title:
Dislocation mechanisms and plasticity of quasicrystals: TEM observations in icosahedral AIPdMn
Authors:
Caillard, D
Source:
ADVANCED STRUCTURAL MATERIALS II 509: 49-56 2006 Book series title: MATERIALS SCIENCE FORUM
Abstract:
Quasicrystals can deform plastically at high temperatures by the movement of dislocations like in crystals. Little is known, however, on the mechanisms that control dislocation movements in these structures. In a first part, the crystallography of quasicrystals is introduced as the projection, in the physical space, of a periodic structure in a hyperspace with more than three dimensions (6 in the case of icosahedral structures). The main properties of dislocations are defined in the physical space and in the six-dimensional space. New results are then presented, showing that dislocation movements may have a large component of climb, in contrast with all existing models that are based on glide processes only. Dislocation movements in two-fold and five-fold planes are compared and discussed in connection with macroscopic mechanical properties.
Title:
Na2Si3O7: an incommensurate structure with crenel-type modulation functions, refined from a twinned crystal
Authors:
Kruger, H; Kahlenberg, V; Friese, K
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 62: 440-446 Part 3 JUN 2006
Abstract:
The structure of metastable, incommensurately modulated Na2Si3O7 has been determined from single-crystal X-ray diffraction data. In contrast to previous investigations which stated that the compound crystallizes in an orthorhombic space group, this study shows that the compound is monoclinic with a pseudo-orthorhombic cell and is affected by twinning. The structure is described in the (3 + 1)-dimensional superspace. Crenel-type modulation functions are used to account for an aperiodic sequence of right- and left- handed zweier single chains of silicate tetrahedra. The modulation mainly affects one of the two symmetrically independent tetrahedral chains, which are connected to build up [Si3O7](2-) layers. Sodium cations are coordinated by five oxygen ligands and provide linkage between adjacent tetrahedral sheets. Distortions of the silicate tetrahedra and crystal chemical relationships of the title compound to sodium and lithium di- and metasilicates are discussed in detail.
Title:
The incommensurately modulated structure of a tricyclic natural-product-like compound of empirical formula C22H20O3
Authors:
Guiblin, N; Fuhrer, CA; Haner, R; Stoeckli-Evans, H; Kurt, SA; Chapuis, G
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 62: 506-512 Part 3 JUN 2006
Abstract:
3,4-Diphenyl -2a, 5a, 6, 7, 8, 8a, 8b-heptahydro-furo[4, 3,2- de]-chromen-2- one (1) was prepared as part of a project aimed at the synthesis of polycyclic natural-product-like scaffolds. X-ray analysis of crystals grown from ethanol revealed an incommensurately modulated structure. Data include main and satellite reflections up to second order. The modulation vector was refined using the NADA program. The modulated character of the structure of the organic compound C22H20O3 is interpreted in terms of the intermolecular C-H . . .O hydrogen bonds and close-contact approximation.

Update: 21-Apr-2006

Title:
Transferred hyperfine field of Rb2CoCl4 single crystals in the ferroelectric-incommensurate-normal phase by Rb-87 NMR
Authors:
Lim, AR; Bong, PH; Jeong, SY
Source:
SOLID STATE COMMUNICATIONS 138 (1): 22-25 2006
Abstract:
The molecular susceptibility and paramagnetic shift of Rb2CoCl4 single crystals grown using the slow evaporation method were measured, and from these experimental results we obtained the transferred hyperfine interaction due to the transfer of spin density from Co2+ ions to Rb+ ions. The transferred hyperfine field was obtained for the ferroelectric, incommensurate, and normal phases. In the case of Rb(I), the transferred hyperfine interaction decreases with increasing temperature in the incommensurate phase, and increases with increasing temperature in the normal phase. The value of H-hf in the incommensurate and normal phases increases abruptly with increasing temperature in the case of Rb(II). These results indicate that the effects due to the transfer of spin density from Co2+ ions to the Rb(l) and Rb(II) ions are large above Ti. In particular, the effect due to the transfer of spin density to Rb(II) ions in the normal phase is very large; the variations with temperature of the transferred hyperfine interactions of the Rb(I) and Rb(II) nuclei are more or less continuous in T-c1 and T-i, and are not affected by the ferroelectric-incommensurate-normal phase transitions. (c) 2006 Elsevier Ltd. All rights reserved.
Title:
Phason and amplitudon in the charge-density-wave phase of one-dimensional charge stripes in La2-xSrxCuO4
Authors:
Sugai, S; Takayanagi, Y; Hayamizu, N
Source:
PHYSICAL REVIEW LETTERS 96 (13): Art. No. 137003 APR 7 2006
Abstract:
The present systematic Raman scattering experiments reveal the phason and amplitudon of the charge density wave (CDW) mode in the charge stripes of La2-xSrxCuO4. Only about 15% of the electronic density of states condenses into the CDW state. The symmetries of the CDW modes change by the rotation of the stripes at the insulator-metal transition. The energy of the phason is finite at 0.06 <= x <= 0.1 and zero at x=0.035 and 0.115 <= x <= 0.135, which suggests that the CDW is commensurate at 0.06 <= x <= 0.1 and incommensurate otherwise. The zero-energy phason seems to reduce T-c at x=1/8.
Title:
Comparative studies of positron annihilation lifetime and coincident Doppler broadening spectra for a binary Cd-based quasicrystal and 1/1-approximant crystal
Authors:
Takagiwa, Y; Kanazawa, I; Sato, K; Murakami, H; Kobayashi, Y; Tamura, R; Takeuchi, S
Source:
PHYSICAL REVIEW B 73 (9): Art. No. 092202 MAR 2006
Abstract:
We performed the positron annihilation lifetime and coincident Doppler broadening measurements for binary icosahedral quasicrystal Cd5.7Ca and its 1/1-cubic Cd6Ca and Cd6Yb approximants. Since the obtained positron lifetimes are quite similar to one another, it is likely that the same type of structural vacancies exists in quasicrystal Cd5.7Ca and 1/1-cubic Cd6Ca and Cd6Yb approximants. The vacancy-type defects are concluded to be surrounded mostly by Cd atoms in both quasicrystal Cd5.7Ca and its 1/1-cubic approximant Cd6Ca from the high-momentum Doppler broadening spectra. In addition, we studied the temperature dependence of the positron annihilation lifetime in the low temperature region from 10 to 300 K for 1/1-cubic approximant Cd6Ca and Cd6Yb crystals. As a whole, in both 1/1-cubic Cd6Ca and Cd6Yb approximants the positron lifetime tau(1) gradually increases with increasing temperature due to isotropic thermal expansion. However, the positron lifetime tau(1) does not change at the order-disorder transition temperature, namely, 100 and 110 K for 1/1-cubic Cd6Ca and Cd6Yb approximants, respectively. These results suggest that the size of the structural vacancies and local electron density do not change with the ordering.
Title:
Deuteron NMR and soliton density in incommensurate thiourea
Authors:
Blinc, R; Sustersic, J; Apih, T; Hlinka, J
Source:
PHYSICAL REVIEW B 73 (9): Art. No. 094119 MAR 2006
Abstract:
The deuteron nuclear magnetic resonance spectra of thiourea, SC(ND2)(2), show a gradual change of the incommensurate modulation wave from the plane wave to the soliton type. This demonstrates that even in type II incommensurate systems where there is no Lifshitz invariant and where it has been generally assumed until recently that the modulation wave is always of the plane wave type, a soliton regime can indeed take place. The behavior of type II incommensurate systems is in this sense thus not fundamentally different from that of type I systems with a nonzero Lifshitz term.
Title:
Role of the Dzyaloshinskii-Moriya interaction in multiferroic perovskites
Authors:
Sergienko, IA; Dagotto, E
Source:
PHYSICAL REVIEW B 73 (9): Art. No. 094434 MAR 2006
Abstract:
With the perovskite multiferroic RMnO3 (R=Gd,Tb,Dy) as guidance, we argue that the Dzyaloshinskii-Moriya interaction (DMI) provides the microscopic mechanism for the coexistence and strong coupling between ferroelectricity and incommensurate magnetism. We use Monte Carlo simulations and zero-temperature exact calculations to study a model incorporating the double-exchange, superexchange, Jahn-Teller, and DMI terms. The phase diagram contains a multiferroic phase between A and E antiferromagnetic phases, in excellent agreement with experiments.
Title:
Charge transfer degree and superconductivity of the incommensurate organic superconductor (MDT-TSF)(I-3)(0.422)
Authors:
Kawamoto, T; Mori, T; Konoike, T; Enomoto, K; Terashima, T; Uji, S; Kitagawa, H; Takimiya, K; Otsubo, T
Source:
PHYSICAL REVIEW B 73 (9): Art. No. 094513 MAR 2006
Abstract:
The influence of a small change of carrier number on the superconducting transition temperature T-c in the incommensurate organic superconductors is investigated for (MDT-TSF)(I-3)(0.422) (MDT-TSF: methylenedithio-tetraselenafulvalene, T-c=4.9 K) in comparison with (MDT-TSF)(AuI2)(0.436) (T-c=4.5 K). Careful estimation of the degree of charge transfer by means of the Raman spectra as well as the Shubnikov-de Haas (SdH) oscillations indicates that the charge-transfer degree 0.422 for the I-3 salt is obviously smaller than 0.436 in the AuI2 salt. According to the band calculation, the former salt has smaller density of states. However, the former salt exhibits higher T-c than the latter compounds, and this disagrees with the naive prediction of the BCS theory. The former salt shows considerably large effective cyclotron mass extracted from the SdH oscillations. These observations demonstrate that the strength of the many-body effect is the major factor that determines T-c in these organic superconductors.
Title:
Hysteresis effects in the phase diagram of multiferroic GdMnO3
Authors:
Baier, J; Meier, D; Berggold, K; Hemberger, J; Balbashov, A; Mydosh, JA; Lorenz, T
Source:
PHYSICAL REVIEW B 73 (10): Art. No. 100402 MAR 2006
Abstract:
We present high-resolution thermal expansion alpha(T) and magnetostriction Delta L(H)/L measurements of GdMnO3, which develops an incommensurate antiferromagnetic order (ICAFM) below T(N)similar or equal to 42 K and transforms into a canted A-type antiferromagnet (cAFM) below T(c)similar or equal to 20 K. In addition, a ferroelectric polarization P parallel to a is observed below T-FE for finite magnetic fields applied along the b direction. In zero-magnetic field, we find a strongly anisotropic thermal expansion with certain, rather broad anomalous features. In finite magnetic fields, however, very strong anomalies arise at T-c for fields applied along each of the orthorhombic axes and at T-FE for fields along the b axis. Both phase transitions are of first-order type and strongly hysteretic. We observe a downbending of the ICAFM-to-cAFM phase boundary T-c(H) for low magnetic fields and our data give evidence for coexisting phases in the low-field low-temperature range.
Title:
Low-temperature structural phase transition and incommensurate lattice modulation in the spin-gap compound BaCuSi2O6
Authors:
Samulon, EC; Islam, Z; Sebastian, SE; Brooks, PB; McCourt, MK; Ilavsky, J; Fisher, IR
Source:
PHYSICAL REVIEW B 73 (10): Art. No. 100407 MAR 2006
Abstract:
Results of high-resolution x-ray diffraction experiments are presented for single crystals of the spin-gap compound BaCuSi2O6 in the temperature range from 16 to 300 K. The data show clear evidence of a transition from the room-temperature tetragonal phase into an incommensurately modulated orthorhombic structure below similar to 100 K. This lattice modulation is characterized by a resolution-limited reduced wavevector q(IC)=(0,0.129 +/- 0.001,0) (reciprocal lattice units) referred to the orthorhombic lattice, and its second and third harmonics. The phase transition is first order and exhibits considerable hysteresis. This observation implies that the spin Hamiltonian representing the system is more complex than originally thought.
Title:
Multifunctional composite crystal CuxV4O11 (x approximate to 2.2)
Authors:
Onoda, M; Onoda, M
Source:
PHYSICAL REVIEW B 73 (10): Art. No. 104108 MAR 2006
Abstract:
The crystal structure of the incommensurately modulated system CuxV4O11 with x approximate to 2.2 has been determined in terms of a composite model of CuxV4O11 substructure and Cu subchain with different b constants for each monoclinic cell of Cm. The effective cation valences and the g factors obtained from the electron spin resonance suggest that the significantly modulated Cu chain in the CuxV4O11 substructure is mainly responsible for the Fermi-liquid-like transport between 120 and 340 K, while another Cu chain has an almost empty band. This composition indicates a large thermoelectric power due to the carrier mass enhancement, which might be regarded as a new candidate for thermoelectric devices. This system has also been known useful as a metallic cathode for high-capacity rechargeable batteries, which may be understood in the characteristic framework of composite structure.
Title:
Magnetoelectric interaction and magnetic field control of electric polarization in multiferroics
Authors:
Zvezdin, AK; Kadomtseva, AM; Krotov, SS; Pyatakov, AP; Popov, YF; Vorob'ev, GP
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 300 (1): 224-228 Sp. Iss. SI MAY 2006
Abstract:
Various aspects of magnetic field control of magnetoelectric (ME) and electric properties of multiferroics are considered: linear ME effect appearance at magnetic field-induced incommensurate-commensurate phase transition, polarization switching and reversal by magnetic field and magnetic field-induced polarization flop transition. The correlation between magnetic, electric, and magnetoelastic properties is shown. (c) 2005 Elsevier B.V. All rights reserved.
Title:
The spin-density waves in thin films of Cr in the Fe/Cr/Sn/Cr multilayers
Authors:
Arzhnikov, AK; Dobysheva, LV; Fedorov, DV
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 300 (1): 250-253 Sp. Iss. SI MAY 2006
Abstract:
Magnetism of Fe/Cr/Sn/Cr multilayers have been studied by the first-principles density-functional theory. Calculations by the full-potential linearized augmented plane waves (FPLAPW) and screened Korringa-Kohn-Rostoker (SKKR) methods have shown that two types of solutions may be found in these systems: a high-spin (HS) and a low-spin (LS) ones in accordance with the Cr magnetic moment magnitudes. In this work, we have concentrated our attention on the LS solution. The calculation has shown that the LS solution has a phase slip of antiferromagnetic ordering in Cr and is classified as an incommensurate spin density wave (ISDW). The dependence of the ISDW solution on the thickness of Cr, lattice parameter and boundary conditions has been investigated. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Electrical transport, magnetic and thermal properties of icosahedral Al-Pd-Mn quasicrystals
Authors:
Poddar, A; Das, S; Plachke, D; Carstanjen, HD
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 300 (2): 263-272 MAY 2006
Abstract:
We report measurements of electrical resistivity (rho), Hall coefficient (R-H), magnetization (M) and specific heat (C-p(T)) of high-quality icosahedral Al70.4Pd20.8Mn8.8 phases with different thermal treatment. An improvement in the quasi-crystallinity upon the annealing treatment caused a drastic increase in rho up to 7000 mu Omega cm accompanied by a very small electronic specific heat coefficient gamma. The low temperature rho(T) data has been analyzed in terms of weak localization and electron-electron interaction effects. The Hall resistivity (rho(H)) is found to be strongly temperature-dependent and varies linearly with the magnetization (M) for the same field and temperature. Magnetization measurement reveals that more conductive samples are more magnetic and vice versa. Magnetic susceptibility (chi) data of all the annealed samples agrees with the Curie-Weiss-like behavior implying the existence of localized moments. The negative Curie-Weiss temperature (theta) indicates strong antiferromagnetic coupling between individual Mn atoms. The magnetic Mn concentration is found to be small, ranging from 1.73 x 10(-4) for the less magnetic sample studied up to 3 x 10(-3) for the more magnetic one. The small electronic specific heat coefficient obtained for all the samples Suggests a significant reduction in the electronic density of states (DOS) at the Fermi level (E-F) upon thermal annealing treatment. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Magneto structural phase transitions of DyFe4Ge2: Part I - By XRPD
Authors:
Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Buschow, KHJ; Dooryhee, E; Fitch, AN
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 300 (2): 315-332 MAY 2006
Abstract:
We present the temperature phase diagram of the compound DyFe4Ge2 determined from high-quality powder XRPD for the entire magnetically ordered regime. DyFe4Ge2 undergoes at T-N, T-c = 55 K a simultaneous structural and magnetic transition of second-order P4(2)/mnm, T-N, T-c = 55 K -> Cmmm, followed by two subsequent isostructural first-order magnetic transitions at T-ic2 = 45 K and T-ic1 = 28 K. The structural transition at T-N, T-c is characterised by strong changes of the a/b ratio and of the shear strain while the T-ic1 = 28 K transition is related to a lattice expansion along c on cooling. Minor Fe parameter shifts and deformations (torsion angle and out-of plane Fe-Fe distances) of the Fe tetrahedra were found to accompany the two magnetic transitions. Using the XRPD instrumental resolution and modelling the anisotropic micro-strain enabled LIS to refine the observed anisotropic peak broadening associated with the presence of micro-structure effects. The maximum strain experienced by the crystal lattice during a sequence of subtle magnetic transitions was observed in the intermediate temperature interval T-ic1 = 28 K - T-ic2 = 45 K of incommensurate magnetic phases. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Magneto structural phase transitions of DyFe4Ge2: Part II - Neutron diffraction
Authors:
Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Andre, G; Buschow, KHJ
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 300 (2): 333-350 MAY 2006
Abstract:
We present the temperature magnetic phase diagram of the compound DyFe4Ge2 determined from neutron diffraction data for the entire magnetically ordered regime. DyFe4Ge2 undergoes at T-N, T-e = 55 K a simultaneous structural and magnetic transition of second order (or weakly first order) followed by two subsequent isostructural first-order magnetic transitions at T-ic2 = 45 K and T-ic1 = 28K: P4(2)/mnm, T-N, T-c = 55 K -> Cmmm, q(1) = (0 (1)/(2)0) T-ic2 = 45 K -> q(2) = (0 q(y) 0)T-ic1 = 28 K -> q(1). The re-entrant lock-in magnetic phase q(1) = (0 (1)/(2)0) is stable in the high-temperature range T-ic2-T-N and in the low- temperature range 1.5 K-T-ic1 while the incommensurately modulated q(2) = (0 q(y) 0) magnetic phase is sandwiched in the intermediate range T-ic1-T-ic2 between the two commensurate phases. The wave vector q(2) has it temperature-dependent length with a minimum in the middle of the incommensurate range and corresponds to a multiaxial amplitude modulated phase. Symmetry analysis leads for both propagation vectors in Cmmm to a twofold and fourfold splitting of the tetragonal Dy 2b site and the Fe 8i sites, respectively. The low temperature q(1) = (0 (1)/(2)0) and the q(2) = (0 q(y) 0) phases correspond to 3D canted magnetic structures described by the irredLicible representations (Irreps) Gamma(2) + Gamma(3) while the high-temperature q(1) phase to 2D canted magnetic structures described by a single Irrep Gamma(2). The T-ic2 transition is connected with reorientations of both Fe and Dy moments. (c) 2005 Elsevier B.V. All rights reserved.
Title:
A drop of hyperfine field at Sn in Fe/Cr/Sn/Cr multilayers
Authors:
Arzhnikov, AK; Dobysheva, LV; Fedorov, DV; Uzdin, VM
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 300 (2): 351-357 MAY 2006
Abstract:
The magnetism of the Fe/Cr/Sn/Cr multilayers was studied by the first-principle density functional theory. Possible reasons for an experimentally well-known drop of the hyperfine field (HFF) at Sri with a decrease of the Cr width (at 3 nm) are considered. The calculations by LAPW and SKKR methods showed that two solutions exist in the Fe-9/Cr-14/Sn/Cr-2 system. One of them originates from the antiferromagnetic order in the bulk Cr, and the other is connected to the incommensurate spin density wave (ISDW) in Cr, which is realized in our case in a Cr film thinner than the half-length period of commonly observed ISDW. The ISDW solution is investigated in more detail with respect to its dependence on temperature and the accuracy of the Fermi-surface description. In the Cr layers with width lower than a quarter of the wave (3 nm), the ISDW cannot exist and thus cannot be a cause of the sharp drop of the Sn HFF. It is shown by the calculation of the Fe-3/Cr-8/Sn/Cr-8 system that another possible reason for the HFF drop, connected to imperfections at the Fe/Cr interface, may cause a significant decrease in the HFF at Sri. This is shown For ail interfacial Fe/Cr mixing. (c) 2005 Elsevier B.V. All rights reserved.
Title:
In situ formation of a new Al-Pd-Mn-Si quasicrystalline phase on the pentagonal surface of the Al-Pd-Mn quasicrystal
Authors:
Longchamp, JN; Erbudak, M; Weisskopf, Y
Source:
JOURNAL DE PHYSIQUE IV 132: 117-120 MAR 2006
Abstract:
Growth of thin Si films deposited on the 5-fold symmetry surface of the icosahedral Al-Pd-Mn quasicrystal is monitored by low-energy electron diffraction, secondary-electron imaging. and Auger electron spectroscopy. We observe that below a sample temperature of 370 K, Si grows in an amorphous structure. Above 370K, a new Al-Pd-Mn-Si quasicrystalline phase, which exhibits the same icosahedral symmetry as the substrate, is formed at the surface by substitutionally replacing Al by absorbed Si.
Title:
Comparison of surface structure of icosahedral Al-Pd-Mn family quasi-crystals
Authors:
Sharma, HR; Shimoda, M; Tsai, AP
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 (3B): 2208-2211 MAR 2006
Abstract:
We present scanning tunneling microcopy (STM) studies of three different icosahedral (i) quasi-crystals of the same family, namely, i-Al-Cu-Fe, i-Al-Pd-Mn, and i-Al-Cu-Ru. STM images reveal that the fivefold surface of all three quasi-crystals is isostructural. Both step-height distribution and high-resolution images on terraces are consistent in all systems.
Title:
Structural transformation of mixed C-60 and C-70 fullerene monolayer on Ag(100)
Authors:
Sin, LYM; Tang, TB; Pai, WW
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 (3B): 2377-2381 MAR 2006
Abstract:
Fullerene C-60 and C-70 Mixture films oil Ag(100) have been Studied with scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). Ill contrast to the recently found aperiodic incommensurate "(111)" phase of C-60 oil Ag( 100), C-70 formed a commensurate c(6 x 4) Structure. Co-deposited C-60/C-70 mixture layers were examined as a function of controlled C-60/C-70 ratio. LEED showed that overall film symmetry evolved from "(111)" to c(6 x 4) as C-60 density increased. In contrast, STM revealed that C-60 and C-70 distributions were highly non-uniform, with many prominent unidirectional wavy bright lines due to local C-60 aggregation.
Title:
Thermodynamic study of crystalline and quasicrystalline Al-Mn alloys
Authors:
Zaitsev, AI; Zaitseva, NE; Arutyunyan, NA; Kalmykov, KB; Yazvitskii, MY
Source:
DOKLADY PHYSICAL CHEMISTRY 407: 67-71 Part 1 MAR 2006
Title:
Crystallization, mechanical and corrosion properties of Zr-Cu-Ni-Al-Nb bulk glassy alloys
Authors:
Lin, L; Sun, M; Chen, Q; Liu, B; Qiu, CL
Source:
ACTA PHYSICA SINICA 55 (4): 1930-1935 APR 2006
Abstract:
Zr65-xCu17.5Al7.5Ni10Nbx bulk metallic glasses (BMGs) with x = 0, 2 and 5 were prepared by water-cooled copper mold casting. X-ray diffraction and differential scanning calorimetry revealed that the addition of Nb changes crystallization pathway of the base alloy and promotes an initial formation of icosahedral quasicrystals. The mechanical properties of the BMGs prepared were measured with MTS in a mode of quasi-static compression. It was found that the addition of an appropriate amount of Nb significantly enhances the compression strength and plastic strain with the maximum value of sigma(b) = 1741 MPa and epsilon(p) = 5.0% for the BMG containing 5at% Nb. In addition, the corrosion behavior of the BMGs was investigated in 3 % NaCl aqueous solution by electrochemical measurements. It showed that the BMGs with different compositions are all spontaneously passivated with passive current density of 10(-6)-10(-5) A/cm(2), which is three order of magnitude lower than that of 1Cr18Ni9Ti stainless steel. The corrosion resistance of the BMGs can be further enhanced with the addition of Nb, as indicated by the increase in pitting potential with the increase of Nb content.

Update: 14-Apr-2006

Title:
Structural modulations in Sr14Cu24O41 and their relation to charge ordering
Authors:
Von Zimmermann, M; Geck, J; Kiele, S; Klingeler, R; Buchner, B
Source:
PHYSICAL REVIEW B 73 (11): Art. No. 115121 MAR 2006
Abstract:
Structural properties of the spin chain and ladder compound Sr14Cu24O41 have been studied using high energy x-ray diffraction. Strong incommensurate modulation reflections are observed due to the lattice mismatch of the chain and ladder structure, respectively. While modulation reflections of low orders display only a weak temperature dependence, higher orders dramatically increase in intensity when cooling the sample to 10 K. All observed modulation reflections are indexed within a super space group symmetry and no structural phase transition could be identified between 10 K and room temperature. We argue that these modulation reflections are not caused by a fivefold periodicity of the chain lattice, as claimed by Fukuda , Phys. Rev. B 66, 012104 (2002), but that holes localize in the potential given by the lattice modulation, which in turn gives rise to a further deformation of the lattice.
Title:
mu SR study of the triangular-lattice antiferromagnet CsNiBr3
Authors:
Gubbens, PCM; Visser, D; de Reotier, PD; Yaouanc, A; Amato, A; Cottrell, SP; King, PJC
Source:
PHYSICA B-CONDENSED MATTER 374: 160-162 MAR 31 2006
Abstract:
In the hexagonal compound CsNiBr3 the mu SR spin-lattice relaxation rate increases notably as the sample is cooled down towards T-NI, a conventional signature of the slowing down of the magnetic fluctuations. This is in contrast with earlier NMR measurements for which no critical magnetic fluctuations were observed. Zero-field spectra, recorded in the magnetically ordered phase exhibit Bessel-like oscillations. However, this does not allow to conclude for the incommensurability of the magnetic structures in the two magnetic phases of CsNiBr3. The damping of the oscillations, only found below the second phase transition T-N2, is a signature for the rotation of the canted spins around the c-axis. (c) 2005 Elsevier B.V. All rights reserved.
Title:
mu SR and neutron diffraction studies of U(NixCu1-x)(2)Si-2 magnetic structure
Authors:
Sikolenko, V; Pomjakushina, E; Zimmermann, U; Gribanov, A
Source:
PHYSICA B-CONDENSED MATTER 374: 171-173 MAR 31 2006
Abstract:
Neutron powder diffraction and zero-field mu SR studies of U(NixCu1-x)(2)Si-2 with x = 0 and 0.25 have been performed. These compounds have different types of AF ordering below T-N similar to 120K. Muon precession has been observed in both samples. Neutron diffraction together with pSR analysis have shown us changing between incommensurate phase and simple AF with the changes of temperature. Possible mechanisms of magnetic ordering are discussed. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Incommensurate spin density wave state in layered cobaltites
Authors:
Sugiyama, J; Itahara, H; Nozaki, H; Brewer, JH; Ansaldo, EJ; Morris, GD; Hebert, S; Maignan, A
Source:
PHYSICA B-CONDENSED MATTER 374: 282-285 MAR 31 2006
Abstract:
Magnetism of misfit layered cobaltites with a triple rocksalt-type subsystem, i.e., [A(M1-yCoy)O-3](x)(RS) [CoO2 (A = Ca and Sr, M = Ti, Hg, Tl and Pb, x = 0.5-0.7 and RS denotes the rocksalt-type subsystem) was investigated by mu+SR, using polycrystalline samples down to 1.8 K. Weak transverse-field measurements indicated the existence of a magnetic transition below similar to 150 K (= T-c(on)). A clear muon spin oscillation was however observed only in [Ca2Pb0.4Co0.6O3](0.62)(RS)[CoO2] below similar to 50K, indicating formation of an incommensurate spin density wave (IC-SDW) state. The oscillation frequency as T approaches at 0 K (f(SDW)(0 K)) was similar to 60 MHz which is comparable to that in the related compound [Ca2CoO3](0.62)(RS)[CoO2] (f(SDW)(0 K)similar to 54 MHz). Since the (Pb0.4Co0.6)O (or the Co-O) sheet is sandwiched by the two adjacent Ca-O sheets in the RS subsystem, the IC-SDW is most unlikely to form in the RS subsystem but in the CoO2 plane. Only a fast relaxation is apparent even at 1.8 K in both [Sr2Hg0.4Co0.6O3](0.57)(RS)[CoO2] and [Ca2Ti0.4Co0.6O3](0.57)(RS)[CoO2], although the Co content in the RS subsystem is equivalent to that for [Ca2Pb0.4Co0.6O3](0.62)(RS)[CoO2]. Assuming that the RS subsystem acts as a charge reservoir as in the high T-C cuprates, the present result suggests that the IC-SDW order is strongly affected by the carrier concentration in the [CoO2] plane. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Formation of the icosahedral quasicrystalline phase in a rapidly solidified Al52Cu25.5Fe12.5Si10 alloy
Authors:
Wang, Y; Zhang, ZH; Geng, HR; Yang, ZX
Source:
MATERIALS CHARACTERIZATION 56 (3): 200-207 APR 2006
Abstract:
In the present work, the effect of wheel speed (quenching rate) on the formation of the quasicrystalline phase in a rapidly solidified Al52Cu25.5Fe12.5Si10 alloy has been investigated using X-ray diffraction (XRD), differential thermal analysis (DTA), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The results show that rapid solidification has no effect on the phase constitution of the Al52Cu25.5Si10 alloy. The addition of Si decreases the stability of the quasicrystalline phase in the conventionally cast Al52Cu25.5Fe12.5S10 alloy. The thermal stability of the quasicrystalline phase in the melt-spun alloy depends upon the quenching rate. Moderate-rate rapid solidification can improve the thermal stability of the quasicrystalline phase in the melt-spun alloy. Higher quenching rate instigates the transformation of the quasicrystalline phase into the cubic approximant phase and decreases the stability of the quasicrystalline phase. Furthermore, the transformation temperature decreases with increasing Si addition into the Al(62-x)Cu25.5Fe12.5Six. (c) 2005 Elsevier Inc. All rights reserved.
Title:
Ag1/8Pr5/8MoO4: An incommensurately modulated scheelite-type structure
Authors:
Morozov, VA; Mironov, AV; Lazoryak, BI; Khaikina, EG; Basovich, OM; Rossell, MD; Van Tendeloo, G
Source:
JOURNAL OF SOLID STATE CHEMISTRY 179 (4): 1183-1191 APR 2006
Abstract:
The crystal structure of a complex molybdenum oxide Ag1/8Pr5/8MoO4 is reported. The Ag1/8Pr5/8MoO4 sub-structure can be described on the base of the scheelite (CaWO4) structure. Transmission electron microscopy reveals that the real structure is better described in a (3+1)D formalism. According to electron diffraction study the new scheelite-type complex oxide Ag1/8P5/8MoO4 crystallizes in the B2/b(alpha beta 0)00 (3+1)D super-space group with unit cell parameters a approximate to 7.50 angstrom, b approximate to 5.30 angstrom, c approximate to 11.74 angstrom and y approximate to 135 degrees (Z = 4) and modulation vector q = 0.56a* + 0.59b*. The *structure* of Ag1/8Pr5/8MoO4 is refined from X-ray powder data in the scheelite setting I2/b(alpha beta 0) with a = b = 5.3013(4) angstrom, c = 11.7407(11) angstrom, q = 1.14690(14)a* + 0.58921(12)b* with fixed gamma = 90 degrees angle (R-p = 0.033, R = 0.033, Rm = 0.029 R-1 = 0.047, S = 1.36). Displacement modulations apply for all atoms. The occupancy modulation shows that one-fourth of the Ag/Pr atoms are absent. The structure call be considered as a crystallographic shear structure with incommensurate ordering of vacancies and displacement modulations for all atoms. The arrangement of Ag/Pr atonis and vacancies is at the origin of the incommensurate modulation ill the cation-deficient Ag1/8Pr5/8MoO4 phase. (c) 2006 Elsevier Inc. All rights reserved.
Title:
Intergrowth compounds in the Zn-rich Zn-Pd system: Toward 1D quasicrystal approximants
Authors:
Gourdon, O; Miller, GJ
Source:
CHEMISTRY OF MATERIALS 18 (7): 1848-1856 APR 4 2006
Abstract:
A series of gamma-brass related structures in the Zn-rich portion of the Zn-Pd phase diagram (ca. 80 at % Zn) is investigated using single-crystal diffraction and tight-binding electronic-structure calculations. Earlier research identified regular arrays of inversion antiphase domains (IAPDs) over a narrow composition range but did not report any characteristic superstructure(s) over the same range. Single-crystal X-ray diffraction allowed for the identification of lattice constants for six "phases" in Zn1-xPdx (0.15 < x < 0.25), and refinements of two crystal structures indicate two important potential building blocks for the intermediate compositions, one of these being the cubic gamma-brass structure. A Farey tree construction is described that accounts for the observed long-period superlattice and provides a possible algorithm for targeting one-dimensional, quasiperiodic phases in this and related systems. Tight-binding electronic-structure calculations on the two limiting structures for this region of the Zn-Pd phase diagram suggest a relationship between structure and bonding in these complex intermetallic systems.

Update: 8-Apr-2006

Title:
On the evolution of a nanocrystalline phase from the Al-Cu-Fe quasicrystalline alloy during high energy ball milling
Authors:
Yadav, TP; Mukhopadhyay, NK; Tiwari, RS; Srivastava, ON
Source:
TRANSACTIONS OF THE INDIAN INSTITUTE OF METALS 58 (6): 1169-1176 DEC 2005
Abstract:
Mechanical milling of an Al-Cu-Fe quasicrystalline alloy was performed in a high energy ball mill (Szegvari attritor mill) at a constant speed of 400 rpm for various milling time (from 0.5 to 40 h) under liquid hexane medium with a ball to powder ratio of 40:1. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray diffraction (XRD) techniques were employed for characterizing the milled and unmilled samples. The evolution of nanocrystalline (NC) phase (bcc, a = 0.29 run) was observed from the quasicrystalline phase after 5h of milling. This nanocrystalline phase, which was quite stable up to 40h of milling, did not transform to amorphous or any other metastable phase. The size of crystalline particles was found to vary from 60nm to minimum 10nm for different milling durations. It is interesting to note that the strain induced in the milled samples tends to increase along with milling time. The possible mechanisms for the formation of nanocrystalline phase will be put forward based on the evolution of the structural and microstructural features.
Title:
Understanding nano quasicrystalline phase formation in Zr based alloys
Authors:
Murty, BS; Hono, K
Source:
TRANSACTIONS OF THE INDIAN INSTITUTE OF METALS 58 (6): 1213-1227 DEC 2005
Abstract:
Nano icosahedral phase formation was observed in a number of Zr-hased metallic glasses. This present paper reviews the present understanding on the nanoquasicrystal line phase formation in Zr-based alloys. The results indicate that oxygen stabilizes quasicrystalline phase. A large negative enthalpy of mixing and/or existence of Frank-Kasper-type phases.
Title:
Enhanced soliton transport in quasiperiodic lattices with introduced aperiodicity
Authors:
Sukhorukov, AA
Source:
PHYSICAL REVIEW LETTERS 96 (11): Art. No. 113902 MAR 24 2006
Abstract:
We study linear transmission and nonlinear soliton transport through quasiperiodic structures, where the lattice profiles are described by multiple modulation frequencies. We show that resonant scattering at mixed-frequency resonances limits transmission efficiency of localized wave packets, leading to radiation and possible trapping of solitons. We obtain an explicit analytical expression for optimal quasiperiodic lattice profiles, where additional aperiodic modulations suppress mixed-frequency resonances, resulting in dramatic enhancement of soliton mobility. Our results can be applied to the design of photonic waveguide structures, and arrays of magnetic micro-traps for atomic Bose-Einstein condensates.
Title:
Equal channel angular pressing of magnesium alloy containing quasicrystal phase
Authors:
Zheng, MY; Xu, SW; Qiao, XG; Gan, WM; Wu, K; Kamado, S; Kojima, Y; Brokmeier, HG
Source:
NANOMATERIALS BY SEVERE PLASTIC DEFORMATION 503-504: 527-532 2006 Book series title: MATERIALS SCIENCE FORUM
Abstract:
ZWK510 (Mg-5.0wt%Zn-0.9wt%Y-0.2wt%Zr) magnesium alloy containing Mg3YZn6 quasicrystal phase was prepared by conventional permanent mold casting. Part of the cast ingot was subjected to equal channel angular pressing (ECAP) directly; another part of the cast ingot was extruded initially, then ECAP was applied to the extruded alloy. After 4-pass ECAP, the fraction of coarse grains of the as-cast alloy was decreased to about 30%, and the grain size of fine grain was decreased to about 2 mu m. Both strength and ductility of the as-cast ZWK510 alloy were significantly improved with increasing ECAP passes, which was resulted from broken and dispersed I-phase, and fine grains formed due to recrystallization. The as-extruded ZWK510 had an initial grain size of about 2 mu m. and bands of quasicrystal phase parallel to the extrusion direction. After the extruded alloy was subjected to ECAP, the grain size of the extruded alloy was farther refined, the grain size was refined to below 0.5 mu m after 8-pass ECAP; and the quasicrystal phase was further broken and dispersed in the matrix. After ECAP, the elongation to failure of the extruded alloy was improved. However, both yield strength and ultimate tensile strength were decreased, which is considered to be resulted from the texture modification during ECAP.

Update: 1-Apr-2006

Title:
Successive phase transitions of [(PyO)(H/D)] [AuCl4] (PYO = C5H5NO)
Authors:
Asaji, T; Watanabe, J; Akiyama, E; Fujimori, H; Oguni, M
Source:
SOLID STATE COMMUNICATIONS 137 (9): 488-491 MAR 2006
Abstract:
Cl-35 NQR as well as heat capacity measurements of [(PyO)H][AuCl4] and its deuterated analog [(PyO)D][AuCl4] revealed successive phase transitions at 70.5 and 62.5 K, and at 71 and 63 K, respectively. The NQR frequency varied continuously through the upper transition point while discontinuously through the lower transition point. In the intermediate-temperature phase a remarkable decrease in the signal intensity was observed. These NQR observations as well as the feature of the heat capacity anomaly in which a broad peak is succeeded by a sharp peak with decreasing temperature suggest a possibility of normal-incommensurate-commensurate phase sequence. (c) 2006 Elsevier Ltd. All rights reserved.
Title:
Accurate equation of state of AlPdMn up to 35 GPa and pressure effect on the frozen-in phason strain
Authors:
Decremps, F; Gauthier, M; Ricquebourg, F
Source:
PHYSICAL REVIEW LETTERS 96 (10): Art. No. 105001 MAR 17 2006
Abstract:
Angle-dispersive monochromatic x-ray diffraction spectra from a perfect single-grain AlPdMn quasicrystal have been obtained under hydrostatic pressure in a diamond anvil cell up to 35 GPa. More than 50 Bragg peaks with sharpness comparable to that at ambient conditions were observed up to the maximum pressure, indexed and used to measure the hypercubic 6D lattice parameter, providing the most accurate determination of the equation of state in this pressure range to date. Within the instrumental resolution, the absence of broadening of the diffraction peaks indicates the absence of structural transition and/or unusual configurational entropy change expected from previous studies through pressure-induced amorphization or phason defects.
Title:
Pressure-induced phase transitions in the Cd-Yb periodic approximant to a quasicrystal
Authors:
Watanuki, T; Machida, A; Ikeda, T; Aoki, K; Kaneko, H; Shobu, T; Sato, TJ; Tsai, AP
Source:
PHYSICAL REVIEW LETTERS 96 (10): Art. No. 105702 MAR 17 2006
Abstract:
The phase study of a Cd-Yb 1/1 approximant crystal over a wide pressure and temperature range is crucial for the comparison study between periodic and quasiperiodic crystals. The Cd-4 tetrahedra, the most inner part of the atomic clusters, exhibited various structural ordering in the orientation sensitive to pressure and temperature. Five ordered phases appeared in a P-T span up to 5.2 GPa and down to 10 K. The propagation direction of ordering alternated from [110] to < 111 > at about 1.0 GPa and again to [110] at 3.5-4.3 GPa. The primarily ordered phases that appeared by cooling to 210-250 K between 1.0-5.2 GPa further transformed to finely ordered ones at 120-155 K. Besides the original short-range type interaction, a long-range type interaction was likely developed under pressure to lead to the primary ordering of Cd-4 tetrahedra. Coexistence of these interactions is responsible for the complicated phase behavior.
Title:
Ab initio study of L-edge X-ray resonant scattering from chromium in spin density wave state
Authors:
Takahashi, M; Igarashi, J
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 (1): Art. No. 013701 JAN 2006
Abstract:
We propose X-ray diffraction analyses exploiting the L-edge resonant scattering in the spin density wave (SDW) phase of Cr metal. We predict that strong signals could be detected on satellite spots corresponding to the charge density wave (CDW), by an ab initio band structure calculation. The sinusoidal modulation of spin moment makes the SDW exchange potential different from site to site, and accordingly the 3d density of states (DOS) locally varies. The signal detects this modulation in the unoccupied part of the local 3d DOS. This new mechanism predicts the signal detectable even in the absence of CDW ordering. Analyzing the energy profile, we demonstrate that the Ledge RXS is a sensitive probe for studying unoccupied 3d states.
Title:
Macroscopic properties in incommensurate magnetic ordered phases of PrB6 in magnetic field around the < 111 > direction
Authors:
Sera, M; Goto, S; Koshikawa, T; Kim, MS; Tou, H; Iga, F
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 (1): Art. No. 014706 JAN 2006
Abstract:
We measured the thermal expansion and magnetostriction of PrB6 under the longitudinal magnetic fields up to 15 T for three magnetic field directions. We found the following results in the IC1 and IC2 phases for H parallel to (111). The magnetostriction shows only a small magnetic field dependence in the IC1 phase but exhibits a large shrinkage with increasing magnetic field roughly proportional to -H-2 in the IC2 phase. The thermal expansion exhibits a small change in the IC1 phase but a large increase in the IC2 phase with decreasing temperature. These different behaviors between the IC1 and IC2 phases originate from the existence of both chi(parallel to) and chi perpendicular to components exist in the IC1 phase and only the chi perpendicular to component in the IC2 phase. The characteristic magnetic and magnetoelastic properties of the experimental results are reproduced by the simple calculation for the two sublattice model, although this model does not represent the incommensurate magnetic strucutres of PrB6. The important point is the weight of chi(parallel to) and chi perpendicular to components which determines the macroscopic properties such as the magnetization, magnetostriction and thermal expansion.
Title:
A novel high-temperature commensurate superstructure in a natural bariopyrochlore: A structural study by means of a multiphase crystal structure refinement
Authors:
Bindi, L; Petricek, V; Withers, RL; Zoppi, M; Bonazzi, P
Source:
JOURNAL OF SOLID STATE CHEMISTRY 179 (3): 729-738 MAR 2006
Abstract:
Additional X-ray diffraction effects yielding an eightfold commensurate superstructure [a = 20.974(5) angstrom] of the ideal pyrochlore structure were observed after annealing at 873 K of a thallium-doped bariopyrochlore single crystal. Electron diffraction indicated the coexistence of two cubic phases, the pyrochlore structure and a new F-centred, cubic phase. The superstructure was solved and refined in the space group F (4) over bar 3 m. The two phases were combined together and refined as independently diffracting to R = 0.0628. The resulting unit-cell content is (A, square)(20)Nb16Ti2O53 V = 8), with A = Ba, Tl, Ce, Th. For some atomic positions of the superstructure, third- and fourth-order anharmonic ADP's were used to account for the specific density shape having a continuous character as typical for ionic conductors. There are three distinct clusters in the superstructure, leading to a new structure type no longer strictly of pyrochlore-structure type. (C) 2005 Elsevier Inc. All rights reserved.
Title:
Hydrogen storage in Ti-based quasicrystal powders produced by mechanical alloying
Authors:
Takasaki, A; Kelton, KF
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 31 (2): 183-190 FEB 2006
Abstract:
Ti-based quasicrystals belong to the second largest group of the stable quasicrystals, showing attractive properties as hydrogen storage materials. This paper summarizes our recent research results on hydrogen absorption and desorption properties of the Ti-Zr-Ni and Ti-Hf-Ni quasicrystals and the related phases produced by a combination of mechanical alloying and subsequent annealing. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Title:
The effect of short-range and long-range orientational orders on the transmission properties of quasiperiodic photonic crystals
Authors:
Wang, YQ; Wang, YY; Feng, S; Li, ZY
Source:
EUROPHYSICS LETTERS 74 (1): 49-54 APR 2006
Abstract:
The effect of short-range and long-range orientational orders on the optical properties of 12-fold quasiperiodic photonic crystals is studied in this paper. We pick up a quasicrystalline supercell from the quasicrystal and construct two new periodic structures by arranging the supercell into square and triangular lattices. Numerical simulations show that the two periodic structures have very similar transmission properties to the quasiperiodic structure in regard to band and band gap positions, although these three structures have different long-range orientational orders, which are 4-fold, 6-fold, and 12-fold, respectively. In addition, their transmission properties are closely related with the propagation behavior of EM waves through the single building supercell. All these characteristics indicate that the optical properties of quasiperiodic photonic crystals are mainly determined by the local short-range geometric properties of the quasicrystal instead of the long-range orientational order.
Title:
Structure of barium in three phases under pressure
Authors:
Jona, F; Marcus, PM
Source:
EUROPHYSICS LETTERS 74 (1): 83-88 APR 2006
Abstract:
A first-principles calculation of the structure of barium under pressure was done with a procedure which finds the equilibrium structure by minimizing the Gibbs free energy at zero temperature with respect to structure at each pressure. The calculated structures agree with measurements at the 1% level in three phases, Ba I (body-centered cubic), Ba II and V ( hexagonal close-packed), over a range of pressure from 0 to 900 kbar. The fit to experiment is closer than that of two previous calculations, one of which used molecular dynamics under an applied stress to find equilibrium structure, and the other minimized the energy at constant volume. Hexagonal close-packed barium is shown to be metastable in the pressure range of the incommensurate Ba IV phase.
Title:
Description of Ba1+xNixRh1-xO3 with x=0.1170 (5) in superspace: modulated composite versus modulated-layer structure
Authors:
Schonleber, A; Zuniga, FJ; Perez-Mato, JM; Darriet, J; zur Loye, HC
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 62: 197-204 Part 2 APR 2006
Abstract:
The structure of the compound Ba1 + xNixRh1 (- x)O3 [x = 0.1170 (5)] has been analyzed at room temperature within the (3 + 1)-dimensional superspace approach using single-crystal X-ray diffraction data. Two different models are presented, the compound is refined as modulated composite as well as modulated-layer structure. In both models discontinuous atomic domains are applied to describe the structural modulations. While the first approach stresses the pseudo-one-dimensional constitution, the latter highlights the layered character of these structures.
Title:
Modulated structure of potassium sodium strontium barium niobates (KNSBN): harmonic solution
Authors:
Surmin, A; Fertey, P; Schaniel, D; Woike, T
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 62: 228-235 Part 2 APR 2006
Abstract:
The structures of two specimens of the (K-1 Na-- y(y))(2F) (- 2)(SrxBa1 - x)(2) - FNb2O6 family (KNSBN) have been solved and refined (x(I) = 0.6, y(I) = 0.45, F-I = 1.07 and x(II) = 0.72, y(II) = 0.45, F-II = 1.08). The KNSBN compounds appear to be incommensurately modulated, as described in a five-dimensional superspace approach with the tetragonal P4bm (pp1/2, p - p1/2) superspace group. Their modulation wavevectors are almost independent of the composition. The description of the modulation is restricted to first-order harmonics in order to limit the number of refined parameters. The modulation mainly affects the positions of the O atoms and their displacements depend on the Sr/Ba ratio. The structural models for the two compounds are not only almost identical, but also analoguous to the structural model of the SrxBa1 - xNb2O6 parent compound: doping with K+ and Na+ cations has no significant influence on the incommensurate modulation, contrary to the strong dependence observed for the physical properties.
Title:
(Z,2R,3R,4aR,7R,12aS)-2,3,7,8,12,12a-hexahydro-2,3-dimethoxy-2,3,7-trimethyl-4aH-[1,4]dioxino[2,3-c]oxecin-5(11H)-one: a commensurate occupationally modulated structure revealing a condition for diffraction symmetry enhancement for non-parent reflections
Authors:
Rae, AD; Willis, AC; Loong, DTJ; Banwell, MG
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 62: 262-267 Part 2 APR 2006
Abstract:
(Z, 2R, 3R, 4aR, 7R, 12aS)-2,3,7,8,12,12a-Hexahydro-2,3-dimethoxy-2,3,7-trimethyl-4aH-[1,4] dioxino[2,3-c] oxecin-5(11H)-one (C16H26O6) crystallizes in the space group P3(1) and approximates the conditions necessary for diffraction symmetry enhancement without twinning for the h - k not equal 3N reflections. The structure may be described as an occupancy modulation of a 1:1 disordered P3(1)21 parent structure with Z = 3 that would only contribute to the h - k = 3N reflections. The crystal studied was a 0.717 (2):0.283 twin, but also had a stacking fault that on average caused the (1-p(j)): p(j) population ratio for the alternative orientations of ordered columns along the three non-equivalent screw axes (j = 1, 2 or 3) of P3(1) to be describable by p(1) = 0.068 (3), p(2) = p(3) = 0.960 (3). The effect of these stacking faults could be simulated using global parameters that modify an ordered prototype structure. The structure reveals that the ten-membered lactone ring incorporates a Z-configured double bond and that the methoxy-substituted stereogenic centers created during a trans-diol protection step each possess the R-configuration.

Update: 24-Mar-2006

Title:
The effect of thermal annealing on impurity states in ferroelectric-semiconductor TlGaSe2 within the incommensurate phase
Authors:
Seyidov, MY; Coskun, E; Sahin, Y; Khamoev, R; Suleymanov, RA
Source:
SEMICONDUCTOR SCIENCE AND TECHNOLOGY 21 (2): 171-174 FEB 2006
Abstract:
The effect of thermal annealing on dark conductivity and thermally stimulated conductivity m ferroelectric-semiconductor TlGaSe2 within the incommensurate phase is investigated. It is shown that both types of conductivities are drastically changed after annealing of the crystal for some hours within the incommensurate phase. The results obtained lead to the conclusion that the main effect of annealing is a large decrease of impurity capture cross sections leading to the dramatic increasing of relaxation times.
Title:
Strengthening in magnesium alloys by icosahedral phase
Authors:
Singh, A; Watanabe, M; Kato, A; Tsai, AP
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 6 (8): 895-901 NOV 2005
Abstract:
Strengthening effects of quasicrystalline icosahedral phase has been studied in two alloys Mg95Zn4.2Y0.8 and Mg92.5Zn6.5Y extruded at 250 and 400 degrees C. The quasicrystal particles are facetted and show definite orientation relationships with the matrix. Due to its high symmetry and quasiperiodicity, the icosahedral phase can form strong interfaces with the matrix in various orientations. The icosahedral phase particles have a strong pinning effect on the grain boundaries, which stabilizes grain size. The icosahedral particles are resistant to coarsening, and remain hard at higher temperatures, imparting good strength with ductility at 200 degrees C. Very few deformation structures such as high dislocation density and twins are observed after extrusion or tensile tests. Dislocations commonly observed are c-type. Due to the stability of microstructure, various post-extrusion treatments are possible. In the (Mg92.5ZnY)-Y-6.5 alloy upon annealing at 400 degrees C the icosahedral phase transforms to a hexagonal Mg25Zn58Y17 phase. The icosahedral phase then reprecipitates on its interface, forming a nano-composite. Effects of microstructural features on the deformation behavior are described.
Title:
Determining the structure of phosphorus in phase IV
Authors:
Ishikawa, T; Nagara, H; Kusakabe, K; Suzuki, N
Source:
PHYSICAL REVIEW LETTERS 96 (9): Art. No. 095502 MAR 10 2006
Abstract:
We explore the unknown structure of phosphorus in phase IV (P-IV phase) based on first-principles calculations using the metadynamics simulation method. Starting from the simple cubic structure, we find a new modulated structure of the monoclinic lattice. The modulation is crucial to the stability of the structure. Through refining the structure further by changing the modulation period, we find the structure whose x-ray powder diffraction pattern is in best agreement with the experimental pattern. We expect that the modulation period of the structure in the P-IV phase is very close to that found in this study and probably incommensurate.
Title:
Collinear to spiral spin transformation without changing the modulation wavelength upon ferroelectric transition in Tb1-xDyxMnO3
Authors:
Arima, T; Tokunaga, A; Goto, T; Kimura, H; Noda, Y; Tokura, Y
Source:
PHYSICAL REVIEW LETTERS 96 (9): Art. No. 097202 MAR 10 2006
Abstract:
Lattice modulation and magnetic structures in magnetoelectric compounds Tb1-xDyxMnO3 have been studied around the ferroelectric (FE) Curie temperature T-C by x-ray and neutron diffraction. Temperature-independent modulation vectors through T-C are observed for the compounds with 0.50 <= x <= 0.68. This indicates that ferroelectricity with a polarization (P) along the c axis in the RMnO3 series cannot be ascribed to such an incommensurate-commensurate transition of an antiferromagnetic order as was previously anticipated. A neutron diffraction study with x=0.59 shows that the FE transition is accompanied by the transformation of the Mn-spin alignment from sinusoidal (collinear) antiferromagnetism into a transverse-spiral structure. The observed spiral structure below T-C is expected to produce P along the c axis with the "inverse" Dzialoshinski-Moriya interaction, which is consistent with observation.
Title:
Ferroelectricity induced by acentric spin-density waves in YMn2O5
Authors:
Chapon, LC; Radaelli, PG; Blake, GR; Park, S; Cheong, SW
Source:
PHYSICAL REVIEW LETTERS 96 (9): Art. No. 097601 MAR 10 2006
Abstract:
The commensurate and incommensurate magnetic structures of the magnetoelectric system YMn2O5, as determined from neutron diffraction, were found to be spin-density waves lacking a global center of symmetry. We propose a model, based on a simple magnetoelastic coupling to the lattice, which enables us to predict the polarization based entirely on the observed magnetic structure. Our data accurately reproduce the temperature dependence of the spontaneous polarization, particularly its sign reversal at the commensurate-incommensurate transition.
Title:
Intralayer molecular orientation in the B1 phase of a prototype bent-core molecule P-6-O-PIMB studied by X-ray microbeam diffraction
Authors:
Takanishi, Y; Takezoe, H; Watanabe, J; Takahashi, Y; Iida, A
Source:
JOURNAL OF MATERIALS CHEMISTRY 16 (9): 816-818 MAR 7 2006
Abstract:
The layer structure and intralayer molecular orientation in the B1 phase of a prototype bent-core molecule have been investigated using an X-ray microbeam. At small angles, in the absence of an electric field only one pair of diffraction spots was observed corresponding to a repeat distance of half the molecular length, whereas on applying a field, four spots were observed suggesting a modulated structure. At wide angles, four broad diffuse scattering peaks were observed without the electric field. These results indicate that the molecular bending plane is normal to the frustrated plane and this is different from the previous model of the B1 phase, but the same as the B1rev phase.
Title:
On the solidification microstructure of Mg-30Zn-2.5Y metal-intermetallic alloy
Authors:
Shao, G; Varsani, V; Wang, Y; Qian, M; Fan, Z
Source:
INTERMETALLICS 14 (6): 596-602 JUN 2006
Abstract:
The solidification microstructures of the Mg-30Zn-2.5Y alloy have been studied in detail using both optical and analytical electron microscopy. CALPHAD simulation has been carried out for in-depth understanding of the solidification process. The work clarifies phase equilibrium in the vicinity of the Mg corner of the Mg-Zn-Y ternary system, showing that a ternary icosahedral (I) quasicrystal phase is in equilibrium with the (Mg) solid solution phase. The suppression of the Z-phase during solidification is attributed to low thermodynamic driving force and sluggish transformation kinetics for ordering icosahedral clusters into the crystalline structure. The current work lays the foundation for developing (Mg)matrix composites with a ternary icosahedral phase as well as other intermetallic compounds. The work presents a case study of solidification process to demonstrate the feasibility to cast (Mg)-matrix composite containing the I-phase from the L + I semi-solid phase region, as long as the equilibrium volume fraction of the I-phase is not too high to guarantee practical slurry fluidity before casting. This would be useful for making use of primary I-phase particles as effective nucleation sites to improve structural refinement and thus maximize the benefit from the I-phase reinforcement. (c) 2005 Elsevier Ltd. All rights reserved.
Title:
High strength aluminum alloys reinforced by nanosize quasicrystalline particles for elevated temperature application
Authors:
Milman, YV; Sirko, AI; Iefimov, MO; Niekov, OD; Sharovsky, AO; Zacharova, NP
Source:
HIGH TEMPERATURE MATERIALS AND PROCESSES 25 (1-2): 19-29 2006
Abstract:
Powders and rods from 6 alloys of the group Al94FexCryTizZr6-x-y-z were produced and investigated. Powders were produced by a water atomization process and after degassing consolidated to rods by severe plastic deformation at 350 degrees C - 400 degrees C without sintering of the powders (by extrusion of powders in the preliminary evacuated and pressurized ampoules). Such a method of producing powders makes it possible to avoid liquation and other non-uniformities in chemical composition, to obtain the metastable quasicrystalline reinforcing particles in nanostructured aluminum matrix. The presence of the quasicrystalline icosahedral phase (the i-phase) in addition to alpha - Al matrix in the produced powders and rods of alloys Al94FexCryTizZr6-x-y-z is confirmed by X-ray diffraction analysis and TEM/SEM investigation. The high strength at 300 degrees C (up to 330 MPa) and sufficient plasticity at room temperature (5-8%) were obtained in investigated rods.
Title:
Structure and high-temperature properties of the alloyed quasicrystalline Al-Cu-Fe powders and thermal-sprayed coatings from them
Authors:
Iefimov, MO; Lotsko, DV; Milman, YV; Borisova, AL; Chugunova, SJ; Astakhov, YA; Neikov, OD
Source:
HIGH TEMPERATURE MATERIALS AND PROCESSES 25 (1-2): 31-38 2006
Abstract:
A structure and some properties of icosahedral quasicrystalline phase Al-Cu-Fe may be increased by directly alloying. Sc and Cr were selected as the alloying elements. The following composition were investigated: Al63Cu25Fe12, Al62.73Cu25Fe12Sc0.27, Al62.56Cu25Fe12Sc0.44, Al66Cu18Fe8Cr8. The powders were fabricated by melt atomization with high-pressure water. The thermal-sprayed coatings were manufactured from powders of the size fraction of (-63+40) mu m. It is established that alloying of the quasicrystalline Al-Cu-Fe alloy with scandium in the amount of 0.265 and 0.44 at. % increases the content of the quasicrystalline icosahedral psi-phase in powders and coatings. Thus, in the powder of (-63+40) pm size fraction the y-phase content increased to 60-65 wt. % compared to 55 wt. % in the non-alloyed powder. The thermal treatment of powders and coatings with scandium provided a reliable possibility to obtain a 100 % psi-phase content. In Al-Cu-Fe-Sc powders a single-phase psi-state was obtained by annealing for 1 h at 650 degrees C, whereas in the case of Al-Cu-Fe powders annealing at 700 degrees C was required. The annealing of Al-Cu-Fe-Cr powders at 600 degrees C results in formation of approximant phase (O-1-phase). The thermal-sprayed coating from Al-Cu-Fe powder has microhardness of about 6 GPa at room temperature, which hardly changes at 300 degrees C, whereas with further heating it gradually falls to a level of about 3 GPa at 600 T. Alloying with Sc and Cr did not essentially change the temperature dependence of the hardness of coatings from the non-alloyed alloy.

Update: 17-Mar-2006

Title:
Density-matrix renormalization-group study of the disorder line in the quantum axial next-nearest-neighbor Ising model
Authors:
Beccaria, M; Campostrini, M; Feo, A
Source:
PHYSICAL REVIEW B 73 (5): Art. No. 052402 FEB 2006
Abstract:
We apply density-matrix renormalization-group methods to study the phase diagram of the quantum axial next-nearest-neighbor Ising model in the region of low frustration where the ferromagnetic coupling is larger than the next-nearest-neighbor antiferromagnetic one. By finite-size scaling on lattices with up to 80 sites we locate precisely the transition line from the ferromagnetic phase to a paramagnetic phase without spatial modulation. We then measure and analyze the spin-spin correlation function in order to determine the disorder transition line where a modulation appears. We give strong numerical support to the conjecture that the Peschel-Emery one-dimensional line actually coincides with the disorder line. We also show that the critical exponent governing the vanishing of the modulation parameter at the disorder transition is beta(q)=1/2.
Title:
Magnetic excitations in the Zn-Mg-Tb icosahedral quasicrystal: An inelastic neutron scattering study
Authors:
Sato, TJ; Takakura, H; Tsai, AP; Shibata, K
Source:
PHYSICAL REVIEW B 73 (5): Art. No. 054417 FEB 2006
Abstract:
Low-temperature spin dynamics in the face-centered-icosahedral Zn-Mg-Tb quasicrystal has been investigated by inelastic neutron scattering around its spin-glass-like freezing temperature (T-f similar or equal to 5.8 K). A single broad inelastic peak, centered at h omega similar or equal to 2.5 meV, was observed in the inelastic scattering spectrum at temperatures ranging from the base temperature up to similar to 20 K. The inelastic peak energy is Q independent, whereas the peak intensity shows weak Q dependence, which is qualitatively similar to that observed for the elastic diffuse scattering. The inelasticity of spin excitations is hardly seen in canonical spin glasses and thus is a distinct feature of the Zn-Mg-Tb quasicrystal. We argue, with an aide of numerical simulation, that this broad inelastic peak can be interpreted as localized collective fluctuations of short-range-ordered spins in a dodecahedral spin cluster. In a much lower-energy region (h omega < 0.8 meV), we observed a strong quasielastic signal, appearing only above T-f; its peak width decreases as the temperature is lowered and vanishes at T-f. It is thus evident that the quasielastic signal corresponds to a slow spin dynamics that freezes at the macroscopic freezing temperature. The coexistence of the inelastic peak and quasielastic signal suggests that the short-range order in the single cluster is robustly formed but is dynamic for T-f < T < 20 K. The macroscopic freezing at T-f is, thus, attributed to a random freezing of spin-cluster fluctuations.
Title:
Growth and electronic structure of alkali-metal adlayers on icosahedral Al70.5Pd21Mn8.5
Authors:
Shukla, AK; Dhaka, RS; Biswas, C; Banik, S; Barman, SR; Horn, K; Ebert, P; Urban, K
Source:
PHYSICAL REVIEW B 73 (5): Art. No. 054432 FEB 2006
Abstract:
We report x-ray photoelectron spectroscopy (XPS) study of Na and K adlayers on icosahedral Al70.5Pd21Mn8.5 (i-Al-Pd-Mn) quasicrystal. The Na 1s core-level exhibits a continuous linear shift of 0.8 eV towards lower binding energies (BE) with increasing coverage up to one monolayer (ML) saturation coverage. In the case of K/i-Al-Pd-Mn, a similar linear shift in the K 2p spectra towards lower BE is observed. In both cases, the plasmon related loss features are observed only above 1 ML. The substrate core-level peaks, such as Al 2p, do not exhibit any shift with the adlayer deposition up to the highest coverage. Based on these experimental observations and previous studies of alkali metal growth on metals, we conclude that below 1 ML, both Na and K form a dispersed phase on i-Al-Pd-Mn and there is hardly any charge transfer to the substrate. The variation of the adlayer and substrate core-level intensities with coverage indicates layer by layer growth.
Title:
Distortion-dependent Raman spectra and mode mixing in RMnO3 perovskites (R=La,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Y)
Authors:
Iliev, MN; Abrashev, MV; Laverdiere, J; Jandl, S; Gospodinov, MM; Wang, YQ; Sun, YY
Source:
PHYSICAL REVIEW B 73 (6): Art. No. 064302 FEB 2006
Abstract:
The polarized Raman spectra of orthorhombic RMnO3 series (R=La,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Y) were studied at room temperature. The variation of phonon frequencies with R ionic radius r(R) as a whole confirms the commonly accepted Raman line assignments with two noticeable exceptions: (1) with decreasing r(R) the stretching A(g)(1) and bending A(g)(3) modes strongly mix for R=Sm to Tb, while for further decrease or r(R) (R=Dy,Ho,Y) the A(g)(3) mode is observed at higher frequency than A(g)(1) mode; (2) similar distortion-dependent mode mixing takes place for the rotational A(g)(2) and O1(x) [A(g)(7)] modes. The mode mixing is particularly strong for the RMnO3 compounds with r(R) values close to the transition from A type to incommensurate sinusoidal antiferromagnetic ordering at low temperatures. The frequency of rotational A(g)(2) and A(g)(4) modes scales to the angles of MnO6 [101] and [010] rotations, respectively, and could be used as a measure of their value.
Title:
Incommensurate magnetic ordering in Cu2Te2O5X2 (X=Cl,Br) studied by single crystal neutron diffraction
Authors:
Zaharko, O; Ronnow, H; Mesot, J; Crowe, SJ; Paul, DM; Brown, PJ; Daoud-Aladine, A; Meents, A; Wagner, A; Prester, M; Berger, H
Source:
PHYSICAL REVIEW B 73 (6): Art. No. 064422 FEB 2006
Abstract:
Polarized and unpolarized neutron-diffraction studies have been carried out on single crystals of the coupled spin tetrahedra systems Cu2Te2O5X2 (X=Cl, Br). A model of the magnetic structure associated with the propagation vectors k(') (Cl) approximate to (-0.150,0.422, (1)/(2)) and k'(Br) approximate to (-0.172,0.356, (1)/(2)) and stable below T-N = 18 K for X= Cl and T-N = 11 K for X = Br is proposed. A feature of the model, common to both the bromide and chloride, is a canted coplanar motif for the four Cu2+ spins on each tetrahedron which rotates on a helix from cell to cell following the propagation vector. The Cu2+ magnetic moment determined for X = Br, 0.395(5)mu(B), is significantly less than for X= Cl, 0.88 (1)mu(B) at 2 K. The magnetic structure of the chloride associated with the wave vector k' differs ;from that determined previously for the wave vector k approximate to (0.150,0.422, (1)/(2))
Title:
Local spin spirals in the Neel phase of La2-xSrxCuO4
Authors:
Luscher, A; Misguich, G; Milstein, AI; Sushkov, OP
Source:
PHYSICAL REVIEW B 73 (8): Art. No. 085122 FEB 2006
Abstract:
Experimental observations of lightly doped La2-xSrxCuO4, x < 0.02, revealed remarkable magnetic properties such as the incommensurate noncollinear ordering (additional to the Neel ordering) and a tremendous doping dependence of the uniform longitudinal susceptibility. We show that the spiral solution of the t-t'-t"-J model obtained by taking into account the Coulomb trapping of holes by Sr ions describes these puzzling data perfectly well. Our solution firstly explains why the incommensurate structure is directed along the orthorhombic b axis, and secondly allows a numerical calculation of the positions and shapes of the incommensurate neutron scattering peaks. Thirdly, we calculate the doping dependence of the spin-wave gap, and lastly, we study the longitudinal magnetic susceptibility and show that its doping dependence is due to the noncollinearity of the spin spiral.
Title:
Getting more out of an incommensurately modulated structure: the example of K5Yb(MoO4)(4)
Authors:
Arakcheeva, A; Chapuis, G
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 62: 52-59 Part 1 FEB 2006
Abstract:
A method based on the superspace approach is presented with the aim of generating a family of modular structures from a single incommensurately modulated structure. This approach based on the variation of the modulation vector q is applied to the generation of the K5Yb( MoO4) (4), potassium ytterbium tetramolybdate, family of modular structures. The beta coefficient of the modulation vector q = beta b* is a temperature-dependent variable which determines the modification. Our method gives a unified frame to describe and explain the three temperature- dependent phases of K5Yb( MoO4) (4). Phase beta can be represented as a polytypic modification with 1/ 2b* <= q <= 2/ 3b*; *phases* gamma ( q = 1/ 2b*) and alpha ( q = 1b*) are the lowest and the highest temperature members of the K5Yb( MoO4) 4 family, respectively.

Update: 10-Mar-2006

Title:
Effect of the electric field on "incommensurate-commensurate" magnetic phase transitions in BiFeO3-type multiferroics
Authors:
Zhdanov, AG; Zvezdin, AK; Pyatakov, AP; Kosykh, TB; Viehland, D
Source:
PHYSICS OF THE SOLID STATE 48 (1): 88-95 JAN 2006
Abstract:
The specific features of the "incommensurate-commensurate" phase transitions induced by a magnetic field in multiferroics (materials with coexisting magnetic and electric ordering) are considered. These materials are ferroelectromagnets, for example, bismuth ferrite BiFeO3 and BiFeO3-based compounds, which have spatially modulated spin structures. It is shown that the interaction between the electric and magnetic subsystems of the multiferroic material can lead to an electric-field-induced shift of the critical magnetic field corresponding to the transition from a spatially modulated state to a homogeneous antiferromagnetic state. According to the theoretical estimates obtained for material parameters characteristic of the bismuth ferrite, this shift is of the order of 0.5 T in an electric field of 50 kV/cm. The phase diagrams are constructed in the "electric field-magnetic field" coordinates. The results of calculations performed in the harmonic incommensurate structure approximation are compared with the exact soliton solution.
Title:
Lightly doped La2-xSrxCuO4 as a Lifshitz helimagnet
Authors:
Juricic, V; Neto, MBS; Smith, CM
Source:
PHYSICAL REVIEW LETTERS 96 (7): Art. No. 077004 FEB 24 2006
Abstract:
We study the static magnetic correlations in lightly doped La2-xSrxCuO4 within the framework of a dipolar frustration model for a canted antiferromagnet. We show that the stability of the canted Neel state for x < 2% is due to the Dzyaloshinskii-Moriya and XY anisotropies. For higher doping, the ground state is unstable towards a helicoidal magnetic phase, where the transverse components of the staggered magnetization rotate in a plane perpendicular to the orthorhombic b axis. Our theory reconciles, for the first time, the incommensurate peaks observed in elastic neutron scattering with Raman and magnetic susceptibility experiments in La2-xSrxCuO4.
Title:
Metastable and quasiperiodic phases in rapidly quenched Fe-B-Si-Nb(Cu) alloys
Authors:
Lyasotskii, IV; Dyakonova, NB; Vlasova, EN; Dyakonov, DL; Yazvitskii, MY
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 203 (2): 259-270 FEB 2006
Abstract:
The formation of metastable phases as a result of devitrification of amorphous iron-based alloys, in particular at the initial stages of the process, was investigated. Compositions with 4-14 at% B, 3-10 at% Nb, 13-15 at% Si, 0-1 at% Cu were studied by means of transmission electron microscopy, X-ray diffraction, and differential thermal analysis. The following metastable phases were observed: bcc phase with alpha-Mn-type structure; quasiperiodic structure with cubic symmetry; hexagonal phase (rhombohedral distortion of alpha-Mn structure); and Laves C14 phase. Some of these phases are also observed in "Finemet" alloys with 1% Cu: cubic quasiperiodic phase and a-Mn-type phase after laser annealing of amorphous phase, and the hexagonal phase at the late stages of crystallization.
Title:
The rhombohedral phase with incommensurate modulation in Na1/2Bi1/2TiO3
Authors:
Balagurov, AM; Koroleva, EY; Naberezhnov, AA; Sakhnenko, VP; Savenko, BN; Ter-Oganessian, NV; Vakhrushev, SB
Source:
PHASE TRANSITIONS 79 (1-2): 163-173 JAN-FEB 2006
Abstract:
The phase transition from tetragonal to rhombohedral phase in sodium bismuth titanate (NBT) is studied by means of neutron scattering. It is found that the rhombohedral phase has incommensurate modulation along the four-fold axis of the precursor tetragonal phase. The appearance of the incommensurate modulation is discussed on the symmetry grounds in the framework of the phenomenological theory of phase transitions.
Title:
Magnetoelectric coupling in epsilon-Fe2O3 nanoparticles
Authors:
Gich, M; Frontera, C; Roig, A; Fontcuberta, J; Molins, E; Bellido, N; Simon, C; Fleta, C
Source:
NANOTECHNOLOGY 17 (3): 687-691 FEB 14 2006
Abstract:
Nanoparticles of the ferrimagnetic epsilon-Fe2O3 oxide have been synthesized by the sol-gel method. Here we report on the measurement of the dielectric permittivity as a function of temperature, frequency and magnetic field. It is found that, coinciding with the transition from collinear ferrimagnetic ordering to an incommensurate magnetic state occurring at about 100 K, there is an abrupt change (about 30%) of permittivity, Suggesting the existence of magnetoelectric Coupling in this material. Indeed, magnetic field-dependent measurements at 100 K have revealed an increase in the permittivity of about 0.3% in 6 T. Possible advantages of epsilon-Fe2O3 as a magnetoelectric material are discussed.
Title:
Rare-earth intermetallic compounds at a magnetic instability
Authors:
Lohneysen, HV; Bartolf, H; Drotziger, S; Pfleiderer, C; Stockert, O; Souptel, D; Loser, W; Behr, G
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 408: 9-15 FEB 9 2006
Abstract:
Rare-earth intermetallic alloys and compounds, in particular those with Ce or Yb, are often close to a magnetic instability. In particular, CeCu6-xAux has become a prototype heavy-fermion (HF) system where, starting from not magnetically ordered CeCu6, An doping introduces long-range incommensurate antiferromagnetism for x > x(c) approximate to 0.1. At the critical concentration x, the system experiences a quantum phase transition (QPT). Here, the unusual magnetic fluctuations probed by inelastic neutron scattering lead to non-Fermi-liquid behavior, i.e. to anomalous low-temperature thermodynamic and transport properties. Hall-effect measurements delineate the "bandstructure" of heavy fermions across the critical concentration xc. While most rare-earth HF compounds have a tendency towards antiferromagnetic order, CeSi1.81 presents one of the comparatively few cases exhibiting ferromagnetic order below T-c = 9.5 K. In a search for a ferromagnetic QPT in HF metals, we have studied the pressure dependence of the magnetization and the spontaneously ordered magnetic moment, As, which vanishes around p approximate to 13 kbar. (c) 2005 Elsevier B.V. All rights reserved.
Title:
X-ray resonant magnetic study of CePtSn
Authors:
Janousova, B; Detlefs, C; Danis, S; Prchal, J; Komatsubara, T; Sechovsky, V
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 408: 33-36 FEB 9 2006
Abstract:
The antiferromagnetic ground state of the equiatomic ternary intermetallic compound CePtSn was studied by means of X-ray resonant magnetic scattering. The Cc L, edge signal shows that below the Neel temperature (similar to 7.5 K) an incommensurate magnetic structure with the propagation vector q(1) varying monotonously between (0 0.415 0) at T-N and (0 0.417 0) at 5.0 K is present. At T-M = 5 K, the magnetic propagation vector locks in, and an additional Fourier component develops at q(2) = (0 0.47 0). Polarization analysis was used to determine the direction of the ordered Cc moments. Near the Pt L-3 edge, only non-resonant scattering could be observed, suggesting the induced moment at the Pt site to be negligible, as also indicated by band structure calculations. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Neutron diffraction investigations of zero-field and field-induced magnetic structures of DyNiSn single crystal
Authors:
Murogaki, K; Kawano, S; Andoh, Y; Takahashi, M; Kurisu, M; Nakamoto, G; Anh, DTK; Tsutaoka, T
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 408: 136-139 FEB 9 2006
Abstract:
Single crystal neutron diffraction studies have been performed on the rare-earth ternary compound, DyNiSn. This crystal exhibits an incommensurate magnetic structure expressed by the propagation vector, Q = (0.662 0.3520) with its third harmonics at low temperatures. In an external magnetic field applied along the c-axis DyNiSn shows incommensurate modulation with Q = (10.3150) at 1.6 K, while along the easy magnetization direction of the b-axis a commensurate modulation with Q = (2/300) develops at 2 K. The results along the b-axis are fully consistent with the magnetization curve. (c) 2005 Published by Elsevier B.V.
Title:
Structure analysis of mutually incommensurate composite crystal (Ca0.5Y0.5)(0.80)CuO2
Authors:
Gotoh, Y; Yamaguchi, I; Takeya, S; Fujihisa, H; Honda, K; Ito, T; Oka, K; Yamaguchi, H
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 408: 1226-1229 FEB 9 2006
Abstract:
Single-crystal X-ray structure analysis of mutually incommensurate (Ca0.5Y0.5)(0.80)CuO2, "Ca2Y2Cu5O10" has been performed by the composite approach which leads to average substructures and their relative arrangement. The composite crystal structure of (Ca0.5Y0.5)(0.80)CuO2 has the CuO2 substructure and the Ca0.5Y0.5 substructure. The CuO2 substructure with a(1)=10.598(2) angstrom, b=6.189(2) angstrom, c(1) =2.825(2) angstrom, beta(1)=90.19(4)degrees, V-1=185.4(1) angstrom(3), Z=4 and space group F2/m has the plane of edge-shared one-dimensional CuO, chains along the c-axis. The Ca0.5Y0.5 substructure with a(2)=10.629(2) angstrom, b=6.189(2) angstrom, c(2)=3.517(1) angstrom beta(2) =94.36(3)degrees V-2=230.7(1) angstrom(3), Z=4 and space group F2/m forms the sheet of (Ca, Y) atoms in the ac-plane. By considering (3 + 1)-dimensional superspace group symmetry, it is concluded that the incommensurate composite crystal structure of (Ca0.5Y0.5)(0.80)CuO2 should be described by the combination of F2/m for the CuO2 substructure and F2/c for the Ca0.5Y0.5 substructure. The composite approach has made clear that the plane of CuO, chains and the sheet of (Ca, Y) atoms stack alternately to form a mutually incommensurate composite crystal with layered substructures. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Thermodynamic investigation of quasicrystal-forming Al-Mn melts
Authors:
Zaitsev, AI; Zaitseva, NE; Shakhpazov, EK; Arutyunyan, NA; Dunaev, SF
Source:
DOKLADY PHYSICAL CHEMISTRY 406: 5-8 Part 1 JAN 2006

Update: 3-Mar-2006

Title:
Possible evidence for electromagnons in multiferroic manganites
Authors:
Pimenov, A; Mukhin, AA; Ivanov, VY; Travkin, VD; Balbashov, AM; Loidl, A
Source:
NATURE PHYSICS 2 (2): 97-100 FEB 2006
Abstract:
Magnetodielectric materials are characterized by a strong coupling of the magnetic and dielectric properties and, in rare cases, simultaneously show both magnetic and polar order. Among other multiferroics, TbMnO3 and GdMnO3 reveal a strong magneto-dielectric coupling and as a consequence fundamentally different spin excitations exist: electro-active magnons (or electromagnons), spin waves that can be excited by a.c. electric fields. Here we provide evidence that these excitations appear in the phase with an incommensurate magnetic structure of the manganese spins. In external magnetic fields this incommensurate structure can be suppressed and the electromagnons wiped out, thereby inducing considerable changes in the index of refraction from d.c. up to terahertz frequencies. Hence, besides adding a creature to the zoo of fundamental excitations, the refractive index can be tuned by moderate magnetic fields, which enables the design of the next generation of opt! ical switches and optoelectronic devices.
Title:
Bulk metallic glass formation of Ti-based alloys from low purity elements
Authors:
Hao, GJ; Zhang, Y; Lin, JP; Wang, YL; Lin, Z; Chen, GL
Source:
MATERIALS LETTERS 60 (9-10): 1256-1260 MAY 2006
Abstract:
The effect of yttrium addition on the glass forming ability (GFA) of the alloy Ti40Zr25Be20Cu12Ni3 has been investigated. It is found that the GFA of alloy Ti40Zr25Be20Cu12Ni3 is sensitive to purity of the raw materials. With 0.5 at.% Y addition, the alloy exhibits improved GFA. The positive effect of yttrium addition on the glass formation is that 0.5 at.% of Y addition can suppress the precipitation of Laves phase, more addition leads to the precipitation of YCu phase and icosahedral phase (I-phase). The suppression effect is by removing impurities which will catalyses the Laves nucleation. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Nanoindentation-induced deformation in Al-Pd-Mn single quasicrystals
Authors:
Coupeau, C; Texier, M; Joulain, A; Bonneville, J
Source:
APPLIED PHYSICS LETTERS 88 (7): Art. No. 073103 FEB 13 2006
Abstract:
Nanoindentation experiments were performed at room temperature on Al-Pd-Mn single quasicrystals to induce plastic deformation in very localized areas and to examine microscopic mechanisms taking place in the bulk. Nanoindentation imprints investigated by transmission electron microscopy revealed the presence of grains and crystalline phases, but did not provide any evidence of dislocation activity. Pop-in events observed on the nanoindentation curves support the idea of grain formation and phase transformation just beneath the indenter, as shown by transmission electron microscopy.
Title:
The crystal structure of a second antigorite polysome (m=16), by single-crystal synchrotron diffraction
Authors:
Capitani, GC; Mellini, M
Source:
AMERICAN MINERALOGIST 91 (2-3): 394-399 FEB-MAR 2006
Abstract:
A model for the modulated crystal structure of all antigorite polysome with m = 16 (where in is related to the number of tetrahedra spanning a wavelength along a) was refined by single-crystal synchrotron diffraction data in C2/m, using crystals coexisting with the in = 17 polysome from Val Malenco, Italy, which was previously determined structurally. Lattice parameters [a = 81.664(10), b = 9.255(5), c = 7.261(5) angstrom, beta = 91.409(5)degrees] were determined using a single-crystal diffractometer equipped with an area detector at the Desy synchrotron (Hamburg). The structure was solved by direct methods, and the model refined using 19222 symmetry-related reflections. The final R-4 sigma factor was 0.0951, Calculated for 7246 reflections. The Structure of the m = 16 antigorite polysome strongly resembles that of the in = 17 polysome. A Continuous. wavy octahedral sheet is linked to a tetrahedral sheet, reversing its polarity through sixfold tetrahedral and eightfold tetrahedral rings. The half-wave has a Curvature radius of 80.1 angstrom. Polyhedral geometry, ditrigonalization angles, and interlayer O-O distances are similar in the two polysomes. The only differences concern the number of tetrahedra for the in = 16 polysome (an even number which leads to symmetric half-waves) and the periodic b/2 shift involving the eightfold rings (to produce file doubling of the a parameter and a C-centered cell).
Title:
Optical conductivity of decagonal quasicrystals
Authors:
Qiu, SD; Hu, CZ; Wang, AJ; Zhou, X
Source:
ACTA PHYSICA SINICA 55 (2): 743-747 FEB 2006
Abstract:
A disscussion is given of the optical conductivity of decagonal quasicrystals. With group theory it is proved that decagonal quasicrystals may have different optical conductivity in the periodic and quasiperiodic directions. The formula is derived for the optical conductivity. The optical conductivity of Al-65 Co-17 Cu-18 is calculated using this formula. The calculated results basically agree with the experimental data.

Update: 24-Feb-2006

Title:
Old friends in a new light: "SnSb" revisited
Authors:
Noren, L; Withers, RL; Schmid, S; Brink, FJ; Ting, V
Source:
JOURNAL OF SOLID STATE CHEMISTRY 179 (2): 404-412 FEB 2006
Abstract:
The binary pnictide 'SnSb' has been re-investigated using a combination of X-ray, synchrotron and electron diffraction as well as electron microprobe analysis. Its structure was found to be incommensurately modulated with an underlying rhombohedral parent structure of space group symmetry R(3) over barm (No. 166), unit cell parameters a(h) = b(h) = 4.3251(4) angstrom, c(h) = 5.3376(6) angstrom in the hexagonal setting. The incommensurate primary modulation wave vector q(h) = 1.3109(9)c(h)* and the superspace group symmetry is R(3) over barm, (0, 0, similar to 1.311) (No. 166.1). The refinement of the incommensurate structure indicates that the satellite reflections arise from displacive shifts of presumably essentially pure Sn and Sb layers along the hexagonal c-axis, with increasing distance between the Sn-layers and decreasing distance between the Sb layers. (C) 2005 Elsevier Inc. All rights reserved.
Title:
Magnetic study of two isotypic manganese chloro-sulfides: MnSbS2Cl and the new compound MnBiS2Cl
Authors:
Doussier, C; Andre, G; Leone, P; Janod, E; Moelo, Y
Source:
JOURNAL OF SOLID STATE CHEMISTRY 179 (2): 486-491 FEB 2006
Abstract:
Among the MnPnQ(2)X compounds (Pn: pnictide; Q: chalcogen; X. halogen), two isotypic chloro-sulfides, MnSbS2Cl and MnBiS2Cl, have been studied. MnBiS2Cl is a new compound synthesized by solid state reaction at 500 degrees C. It is orthorhombic, space group Pnma, with a=9.502(2), b=3.8802(8), c=12.305(3) angstrom, V=453.7(2) angstrom(3), Z=4. Its X-ray single crystal study shows (001) waved layers of MnS4Cl2 octahedra, opposite edge-sharing along b, and corner-sharing along a. Similar magnetic susceptibilities for both compounds have been recorded, indicating high spin Mn2+ with anti-ferro magnetic exchange. Correlatively, specific heat versus temperature shows a magnetic transition at T-N=35 K for the Sb-bearing compound, and a two-steps magnetic transition at 28 and 32 K for the Bi isotype. The magnetic structure of MnSbS2Cl has been determined by neutron diffraction, revealing a magnetic ordering at 1.5 K with an incommensurate wave-vector along b (k=[0, 0.3838, 0]). Two modulation models, sinusoidal and helicoidal, give quite equivalent reliability factors (R-mag=0.0573 and 0.0586, respectively). (C) 2005 Elsevier Inc. All rights reserved.
Title:
Crystal structure of misfit-layered compound [Bi1.94Bi1.83Oy](0.56)[RhO2]
Authors:
Yubuta, K; Okada, S; Miyazaki, Y; Terasaki, I; Kajitani, T
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 (1A): 179-185 JAN 2006
Abstract:
The modulated crystal structure of Bi2.12Ba2.00Rh1.95Ox has been studied by electron diffraction measurements and high-resolution electron microscopy. The crystal structure consists of two interpenetrating subsystems of a RhO2 sheet and a distorted four-layered rock-salt-type (Bi,Ba)O block. Both subsystems have common a- and c-axes and a P-angle with a = 5.38 angstrom, c = 15.15 angstrom and beta = 95.3 degrees. On the other hand, the crystal structure is incommensurate along the b-axes; b(1) = 3.05 angstrom for the RhO2 sheet and b(2) = 5.45 angstrom for the (Bi,Ba)O block. The misfit ratio and the analytical composition give the chemical formula of [Bi1.94Ba1.83Oy](0.56)[RhO2]. This compound has two modulation vectors, q(1) = -a* + 0.56b(1)* and q(2) = 0.11b(1)* + 0.35c*. and the superspace group is assigned as a C2/m(1 alpha 0,0 beta gamma)-type on the basis of the systematic absence of reciprocal lattice points shown in the electron diffraction patterns. This modulation vector q2 is different from the one in [Bi1.79Sr1.98Oy](0.63)[RhO2], which has recently been studied by the authors. An additional modulation vector, q(3) = 0.12a* + 0.10b(1)*, is locally observed. High-resolution images taken with the incident electron beam parallel to the a- and c-axes clearly exhibit modulated atomic arrangements. This compound is characterized by not only the displacement modulation but also the concentration modulation in the rock-salt subsystem.
Title:
Zn13Sb10: A structural and Landau theoretical analysis of its phase transitions
Authors:
Mozharivskyj, Y; Janssen, Y; Harringa, JL; Kracher, A; Tsokol, AO; Miller, GJ
Source:
CHEMISTRY OF MATERIALS 18 (3): 822-831 FEB 7 2006
Abstract:
Composition, crystal structures, polymorphic transformations, and stability of the thermoelectric material known in the literature as "Zn4Sb3" have been studied on a polycrystalline sample and Bi-flux-grown single crystals using X-ray diffraction techniques, resistance, and Seebeck coefficient measurements at various temperatures ranging from 4 to 773 K. Microprobe analysis yields the composition of the fluxgrown crystals to be close to Zn13Sb10, with minor Bi doping. High-temperature X-ray and Seebeck coefficient studies show that the phase is unstable at high temperatures in a vacuum because of Zn losses. Both X-ray diffraction and resistivity measurements indicate the presence of two consecutive symmetry-breaking transitions below room temperature, in agreement with our previous results on polycrystalline samples. Application of Landau theory suggests that the first R3c -> C2/c symmetry breaking may be second-order in nature. The second, low-temperature symmetry breaking may proceed along two routes. One of these pathways, a first-order C2/c - C1 symmetry reduction, may lead to an incommensurate structure and is consistent with our experimental observations.
Title:
Realization of optical periodic quasicrystals using holographic lithography
Authors:
Wang, X; Xu, J; Lee, JCW; Pang, YK; Tam, WY; Chan, CT; Sheng, P
Source:
APPLIED PHYSICS LETTERS 88 (5): Art. No. 051901 JAN 30 2006
Abstract:
We have fabricated three-dimensional periodic quasicrystals exhibiting quasiperiodicity of the Penrose structure in the x-y plane and periodic along the z axis using ten-beam visible light holographic lithography. The quasicrystals show photonic band gaps in the visible range. The band gaps are found to follow a simple relation as a function of periodicity and polymeric volume fraction, in accord with the Bragg's diffraction relation. (c) 2006 American Institute of Physics.

Update: 17-Feb-2006

Title:
Magnetic structure of MnO at 10 k from total neutron scattering data
Authors:
Goodwin, AL; Tucker, MG; Dove, MT; Keen, DA
Source:
PHYSICAL REVIEW LETTERS 96 (4): Art. No. 047209 FEB 3 2006
Abstract:
Total neutron scattering data from a powdered sample of MnO collected at 10 K have been analyzed using the reverse Monte Carlo method to refine the nuclear and magnetic structure. The results give the first unambiguous assignment of the average magnetic structure. The magnetic moments are aligned ferromagnetically within (111) sheets with the magnetization vectors of alternate sheets along axes parallel and antiparallel to the < 11 (2) over bar > directions, albeit with a small modulated out-of-plane component. Small displacements of Mn and O (modulated with the same periodicity) accompany the magnetic ordering and both atomic and magnetic structures may be described in the monoclinic space group C2.
Title:
Incommensurate magnetic ordering in Cu2Te2O5X2 X=Cl, Br studied by neutron diffraction (vol 93, pg 217206, 2004)
Authors:
Zaharko, O; Daoud-Aladine, A; Streule, S; Mesot, J; Brown, PJ; Berger, H
Source:
PHYSICAL REVIEW LETTERS 96 (4): Art. No. 049901 FEB 3 2006
Title:
Ordering of Si atoms on the fivefold Al-Pd-Mn quasicrystal surface
Authors:
Ledieu, J; Unsworth, P; Lograsso, TA; Ross, AR; McGrath, R
Source:
PHYSICAL REVIEW B 73 (1): Art. No. 012204 JAN 2006
Abstract:
Silicon atoms are found to form an ordered overlayer on the fivefold surface of the icosahedral Al-Pd-Mn quasicrystal. Using scanning tunneling microscopy, the adsorption site is identified as the center of truncated clusters which are building blocks of the bulk structure. Comparison with theoretical models suggests that this site is favored because of bonding to Mn atoms.
Title:
Incommensurate antiferromagnetism in FeAl2: Magnetic, Mossbauer, and neutron diffraction measurements
Authors:
Kaptas, D; Svab, E; Somogyvari, Z; Andre, G; Kiss, LF; Balogh, J; Bujdoso, L; Kemeny, T; Vincze, I
Source:
PHYSICAL REVIEW B 73 (1): Art. No. 012401 JAN 2006
Abstract:
Magnetic, Mossbauer, and neutron diffraction measurements were used to study the anomalous magnetic behavior of FeAl2. The magnetization is almost linear with the applied field up to 14 T at 5 K. The Fe-Al system Mossbauer measurement in the 7 T external magnetic field clearly shows the presence of canted, antiferromagnetically coupled Fe magnetic moments. Neutron diffraction indicates an incommensurate magnetic structure with a periodicity of about 1.1 nm.
Title:
Structural properties and cation ordering in layered hexagonal CaxCoO2
Authors:
Yang, HX; Shi, YG; Liu, X; Xiao, RJ; Tian, HF; Li, JQ
Source:
PHYSICAL REVIEW B 73 (1): Art. No. 014109 JAN 2006
Abstract:
A series of CaxCoO2 (0.15 <= x <= 0.40) materials have been prepared by means of an ion exchange reaction from NaxCoO2. Transmission electron microscopy (TEM) measurements revealed a rich variety of structural phenomena resulting from cation ordering, structural distortion, and twinning. Systematic structural analysis, in combination with the experimental data of NaxCoO2 (0.15 <= x <= 0.8) and SrxCoO2 (1.5 <= x <= 0.4) systems, suggests that there are two common well-defined cation ordered states corresponding, respectively, to the orthorhombic superstructure at around x=1/2 and the 3(1/2)ax3(1/2)a superstructure at around x=1/3 in this kind of system. Multiple ordered states, phase separation, and incommensurate structural modulations commonly appear in the materials with 0.33 < x < 0.5. The TEM observations also reveal an additional periodic structural distortion with q(2)=a(*)/2 in materials for x <= 0.35. This structural modulation also appears in the remarkable superconducting phase Na(0.33)CoO(2)center dot 1.3H(2)O.
Title:
Modulated structure of Rb2ZnCl4 in the soliton regime close to the lock-in phase transition
Authors:
Aramburu, I; Friese, K; Perez-Mato, JM; Morgenroth, W; Aroyo, M; Breczewski, T; Madariaga, G
Source:
PHYSICAL REVIEW B 73 (1): Art. No. 014112 JAN 2006
Abstract:
The structure of the incommensurate phase of Rb2ZnCl4 has been determined at 194 K (2 K above the lock-in transition) within the soliton regime using satellites up to fifth order. The rather anharmonic modulation functions agree with the expected steplike functions supported by theoretical arguments. In addition, the constancy of the ratio between the amplitudes of the fifth-order and first-order harmonics, a relation predicted by theory, indicate the correctness of the model and imply a value of 0.4 for the soliton density n(s). A symmetry mode analysis shows that the incommensurate structure is consistent with the one of the lock-in phase in the sense that the displacement pattern of every symmetry mode remains unaltered in the transition except for a global change in the amplitudes.
Title:
Impurity-induced orthogonal double sinusoidal magnetic structure in the triangular lattice antiferromagnet CuFe1-xAlxO2
Authors:
Terada, N; Mitsuda, S; Gukasov, A
Source:
PHYSICAL REVIEW B 73 (1): Art. No. 014419 JAN 2006
Abstract:
Magnetic ordering has been investigated in detail in the low-temperature (LT) phase of the triangular lattice antiferromagnet CuFe0.9845Al0.0155O2. The LT phase characterized by the original Heisenberg character of the orbital singlet Fe3+ (S=5/2, L=0) is induced from the quasi-Ising four-sublattice (up arrow up arrow down arrow down arrow) state in CuFeO2, by a small amount of nonmagnetic impurity; nevertheless, the magnetic structure was not identified in our previous neutron diffraction measurements with triple-axis spectrometer [J. Phys. Soc. Jpn. 74, 2604 (2005)]. In the present study, we could determine orthogonal double sinusoidal (ODS) structure in the LT phase, using a lifting-counter two-axis neutron diffractometer. The ODS structure consists of two sinusoidal spin modulations that are characterized by slightly different wave numbers and whose polarization axes are orthogonal to each other. Moreover, keeping the determined structure parameters of the ODS structure, we also discuss the stabilization of the four-sublattice state in CuFeO2.
Title:
Field-induced linear magnetoelastic coupling in multiferroic TbMnO3
Authors:
Aliouane, N; Argyriou, DN; Strempfer, J; Zegkinoglou, I; Landsgesell, S; Zimmermann, MV
Source:
PHYSICAL REVIEW B 73 (2): Art. No. 020102 JAN 2006
Abstract:
We have used in-field neutron and x-ray single-crystal diffraction to measure the incommensurability delta of the crystal and magnetic structures of multiferroic TbMnO3. We show that the flop in the electric polarization at the critical field H-C, for field H along the a and b axes, coincides with a first-order transition to a commensurate phase with propagation vector kappa= (0, 1/4,0). In- field x-ray diffraction measurements show that the quadratic magnetoelastic coupling breaks down with applied field as shown by the observation of the first harmonic lattice reflections above and below H-C. This indicates that magnetic field induces a linear magnetoelastic coupling.
Title:
Surface vacancies at the fivefold icosahedral Al-Pd-Mn quasicrystal surface: A comparison of ab initio calculated and experimental STM images
Authors:
Krajci, M; Hafner, J; Ledieu, J; McGrath, R
Source:
PHYSICAL REVIEW B 73 (2): Art. No. 024202 JAN 2006
Abstract:
Scanning tunneling microscopy (STM) images of the fivefold surface of the icosahedral (i) Al-Pd-Mn quasicrystal have been calculated using ab initio density functional methods. The STM signal is formed predominantly by the Al atoms in the surface plane. The Pd atoms are seen in the STM image as dark spots. The reason for their small contribution to the STM current is a small local density of states around the Fermi level and the localized d-character of the Pd states. On the other hand, the local paramagnetic density of states on Mn atoms is much higher than that on Pd atoms and therefore Mn atoms are seen in the STM images as bright spots. A direct comparison of the experimental images obtained from the STM with the ab initio calculated STM images reveals that the characteristic features of the images-the dark pentagonal holes-can also be created by surface vacancies and not only by truncated Bergman clusters as it has been supposed up to now.
Title:
Anomalous behavior of higher-harmonic spin density waves in Mn3Si
Authors:
Tomiyoshi, S; Cowley, ER; Onodera, H
Source:
PHYSICAL REVIEW B 73 (2): Art. No. 024416 JAN 2006
Abstract:
Higher-harmonic spin density waves (SDW's) in Mn3Si have been investigated by neutron diffraction, and the third-harmonic satellites have been found to exist at low temperatures at the 3Q positions expected from the propagation wave vector Q of the fundamental satellite. The magnitude of the magnetic moments of the third harmonics is about 1/40 that of the fundamental. The third-harmonic satellites did not follow the usual temperature variation of a magnetization curve, but disappeared abruptly above 9 K. This is far below the Neel temperature of 23 K, and the temperature dependence suggests a first-order-type phase transition. Associated with this transition the intensity of the fundamental satellites changed slightly and the presence of the third harmonics suppressed the amplitude of the fundamental SDW. This transition was confirmed by specific heat measurements showing a small hump at 8.5 K, which persists to high magnetic fields of more than 6 T. The possibility of the presence of second-harmonic satellites is suggested, but it is not as clear as that of third-harmonic satellites in the present experiment. The existence of the third-harmonic satellites suggests that a transverse sinusoidal structure with spins modulating in the (110) or (210) plane is the most probable spin structure of Mn3Si.
Title:
Phase diagram and incommensurate phases in undoped manganites
Authors:
Salafranca, J; Brey, L
Source:
PHYSICAL REVIEW B 73 (2): Art. No. 024422 JAN 2006
Abstract:
We study the existence of incommensurate phases in the phase diagram of the two orbital double exchange model coupled with Jahn-Teller phonons and with superexchange interactions. In agreement with experimental results, we find that undoped manganites RMnO3 (R being some rare earth element) show temperature induced commensurate-incommensurate phase transitions. In the incommensurate phase the magnetic wave vector varies with temperature. The incommensurate phase arises from the competition between the short range antiferromagnetic superexchange interaction and the long range ferromagnetic double exchange interaction.
Title:
Short-range charge ordering in Ho0.1Sr0.9CoO3-x (0.15 <= x <= 0.49)
Authors:
Streule, S; Medarde, M; Podlesnyak, A; Pomjakushina, E; Conder, K; Kazakov, S; Karpinski, J; Mesot, J
Source:
PHYSICAL REVIEW B 73 (2): Art. No. 024423 JAN 2006
Abstract:
We report the observation of Co3+/Co4+ short-range charge ordering in 10% Ho-doped SrCoO3-x by means of high resolution neutron powder diffraction. The associated one-dimensional commensurate modulation, which can be described with the propagation vector q(CO)=(0 0 1/2) with respect to the cubic perovskite cell Pm3m, occurs for compositions close to x=0.20, corresponding to a 1:1 Co3+/Co4+ ratio and extends over clusters of finite size (D similar to 250 A). The bond valence sums for the Co3+ and Co4+ sites are +3.07(7) and +3.95(11) (x=0.19), very close to their nominal values +3 and +4. We attribute this astonishing observation to the one-dimensional (1D) character of the associated distortion pattern, whose elastic stabilization is eased with respect to the 3D arrays reported for other charge-ordered perovskite oxides.
Title:
Core and valence level photoemission and photoabsorption study of icosahedral Al-Pd-Mn quasicrystals
Authors:
Horn, K; Theis, W; Paggel, JJ; Barman, SR; Rotenberg, E; Ebert, P; Urban, K
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 18 (2): 435-448 JAN 18 2006
Abstract:
The electronic structure of quasicrystalline Al-Pd-Mn is investigated by means of valence and core level photoelectron spectroscopy. Variations of the photoionization cross section in the constituents' valence electronic levels as a function of photon energy are used to identify contributions from the different atomic species, in particular near the Pd 4d Cooper minimum. Resonant photoemission at the Mn 2p absorption edge shows the contribution of the Mn 3d states to the density of states in a region near the Fermi level. The asymmetry of Pd 3d and Mn 2p core level photoemission lines, and its difference for emission from metallic and quasicrystalline phases, are utilized to infer the contributions of the different constituents to the density of states at the Fermi level.
Title:
Long-period, longitudinal spin density modulation in an itinerant 5f magnetic compound UCu2Si2
Authors:
Honda, F; Metoki, N; Matsuda, TD; Haga, Y; Onuki, Y
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 18 (2): 479-492 JAN 18 2006
Abstract:
The magnetic structure Of UCu2Si2 has been studied by means of neutron scattering. We have observed the first- and very weak third-order incommensurate satellite reflections for 100 K < T < 106 K with the propagation q = [0 0 delta], delta = 0.116 at T = 101 K, indicating nearly sinusoidal magnetic modulation with long periodicity of Lambda = 85.7 angstrom. The intensity of the first-order satellite reflections is consistent with a moment direction parallel to the c-axis. The second-order satellite due to lattice modulation accompanied by a charge density wave could not be detected within our experimental sensitivity. The long-period magnetic modulation in UCu2Si2 cannot be explained in terms of an ANNNI model based on frustrated antiferromagnetic short-range interactions. The nearly sinusoidal long-period modulation is evidence for a spin density wave state as a consequence of itinerant behaviour of the 5f electrons in UCu2Si2. The ferromagnetic ground state and the very weak upper critical field for the incommensurate phase are consistent with the long periodicity.
Title:
Structural modulation in bismuth cuprate superconductor observed by X-ray reciprocal space mapping
Authors:
Kaneko, S; Akiyama, K; Shimizu, Y; Hirabayashi, Y; Ohya, S; Funakubo, H; Yoshimoto, M
Source:
JOURNAL OF CRYSTAL GROWTH 287 (2): 483-485 JAN 25 2006
Abstract:
Reciprocal space mapping was performed on epitaxial bismuth cuprate superconducting film using X-ray diffraction methods with high-resolution diffractometer. Epitaxial film showed asymmetric intensity distribution of satellite peaks derived from structural modulation. A sawtooth function was applied as a modulation wave to give the crystal model, and reciprocal space mapping simulated on the crystal model showed good agreement with experimental results. (c) 2005 Elsevier B.V. All rights reserved.

Update: 10-Feb-2006

Title:
Comment on "Explanation of the glasslike anomaly in the low-temperature specific heat of incommensurate phases"
Authors:
Biljakovic, K
Source:
PHYSICAL REVIEW LETTERS 96 (3): Art. No. 039603 JAN 27 2006
Title:
New orthorhombic multiferroics R1-xYxMnO3 (R = Eu, Gd)
Authors:
Ivanov, VY; Mukhin, AA; Travkin, VD; Prokhorov, AS; Popov, YF; Kadomtseva, AM; Vorob'ev, GP; Kamilov, KI; Balbashov, AM
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 243 (1): 107-111 JAN 2006
Abstract:
A tendency to form multiferroic states with a spatially modulated antiferromagnetic structure and electric polarization in pure orthorhombic manganites RMnO3 upon decreasing of the rare-earth ionic radii has been realized in single crystals of substituted compounds Eu1-xYxMnO3 (0.2 <= x <= 0.5) and Gd1-yYyMnO3 (0 <= y <= 0.2). While the parent pure and slightly substituted (x <= 0.1) Compounds exhibited a spontaneous transition from the incommensurate (IC) to the canted anti ferromagnetic (CAF) state at T-CA < T-N = 45-50 K, the transitions from IC to commensurate ferroelectric (C/FE) phase were observed at T-lock < T-N for x >= 0.3 and y >= 0.05 accompanied by dielectric anomalies. Various phase transitions were observed in magnetic fields up to 250 kOe along the a-, b-, c-axes by magnetization, magnetostriction and electric polarization measurements. The latter indicate the existence of a spontaneous electric polarization below T-lock. (c) 2006 WILEY-VCH ! Verlag GmbH & Co. KGaA, Weinheim.
Title:
Effect of microstructural change on high-temperature deformation in pre-annealed Zr65Al10Ni10Cu15 bulk metallic glass
Authors:
Kobata, J; Tsuda, H; Takigawa, Y; Higashi, K
Source:
MATERIALS TRANSACTIONS 46 (12): 2864-2869 DEC 2005
Abstract:
The effect of the microstructural change on the high-temperature tensile deformation behavior in the supercooled liquid region is investigated in the pre-annealed Zr65Al10Ni10Cu15 bulk metallic glass. The microstructure before the tensile test on the specimen annealed at 673 K for 1.8 ks shows that a small amount of icosahedral phase precipitates and a large amount of amorphous phase still remains. On the contrary, the specimen annealed at 673 K for 2.7 ks shows that a large amount of icosahedral phase precipitates and the presence of amorphous phase is hardly noticeable. From the fact that flow stress of the specimen annealed at 673 K for 2.7 ks increases in comparison with that of as received specimen as well as the specimen annealed at 673 K for 1.8 ks in the tensile test, it seems that the deformation behavior in the tension tests is greatly influenced by the difference in the degree of the precipitation of icosahedral phase. Since the m value is about 0.5 and many grain boundaries of icosahedral phase are formed in the specimen annealed at 673 K for 2.7 ks, the interaction between the icosahedral phase particles must be the cause of increase in initial stress. Accordingly, the microstructure of the gage section after tensile test in the specimen annealed at 673 K for 1.8 ks shows that the large amount of icosahedaral phase precipitates in the amorphous matrix. The strain hardening must be caused by the interaction between the icosahedral phase particles whose precipitation and growth are enhanced by deformation.
Title:
Effect of trace additions of Ag on precipitation in Al-Mg alloys
Authors:
Kubota, M; Muddle, BC
Source:
MATERIALS TRANSACTIONS 46 (12): 2968-2974 DEC 2005
Abstract:
Effect of Ag additions on the precipitate microstructures of the Al-10Mg alloys has been investigated using transmission electron microscopy (TEM) and electron diffraction. In the Al-10Mg alloy aged at 240 degrees C, age-hardening response is attributable initially to an array of coarse-scale, sparsely distributed rodlike and/or plate-like beta' precipitate (particles). At the maximum hardness. the microstructure contained an increased volume fraction of coarse-scale beta' and beta precipitate particles. In a well over-aged condition, the microstructure exhibited very coarse-scale P precipitate particles. However, in the Al-10Mg-0.5Ag alloy aged at 240 degrees C, fine-scale and uniformly distributed icosahedral quasicrystalline precipitates were observed in the early stages of ageing, and it was to be replaced by the metastable crystalline T phase after the alloy is aged for 2 h at 240 degrees C. The T phase formed as faceted rods parallel to < 110 >(a) directions appeared to be the primary strengthening constitute exhibiting maximum hardness. The globular beta precipitate particles were observed to be replaced by the metastable rod-like T precipitate particles after the alloy was aged 72 h at 240 degrees C, and the beta phase is confirmed to be the equilibrium Constitute phase in the over-aged ternary Al-20Mg-0.5Ag alloy.
Title:
The effect of the Mn constituent on the electronic structures of Al70Pd22.5(Re1-xMnx)(7.5) quasicrystals studied by x-ray absorption and photoemission spectroscopy
Authors:
Pao, CW; Tsai, HM; Chiou, JW; Pong, WF; Tsai, MH; Pi, TW; Lin, HJ; Jang, LY; Lee, JF; Wang, CR; Lin, ST; Guo, JH
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 18 (1): 265-273 JAN 11 2005
Abstract:
X-ray absorption near-edge fine structure (XANES) and valence-band photoelectron spectroscopy (PES) measurements were performed to elucidate the effect of the Mn constituent on the electronic structures of icosahedral (i)-Al70Pd22.5(Re1-xMnx)(7.5) quasicrystals (QCs). Pd and Re L-3-edge and Al K-edge XANES spectra reveal that the unoccupied Pd 4d, Re 5d and Al 3p states are insensitive to the Mn doping. The valence-band PES and resonant photoemission analysis indicate a marked Mn 3d contribution within similar to 5 eV of the Fermi level, suggesting that the Mn doping increases the conductivity of i-Al-Pd-Re-Mn QCs.
Title:
Effect of Cu on the spinodal decomposition of AlZn alloy with symmetrical composition
Authors:
Hao, SM; Ren, YP; Li, HX; Wang, DP; Zhao, G
Source:
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY 21 (6): 836-840 NOV 2005
Abstract:
The effect of Cu addition on the spinodal decomposition of the Al-Zn alloy with symmetrical compositions has been investigated by X-ray diffraction analysis. It is found that the single fcc phase can be obtained in the AlZn alloy with the addition of 2 at. pct Cu after solution treatment at 400 degrees C and water quenching to room temperature. The modulation structure occurs in two types of alloys aged at room temperature for 30 min. The spinodal process remarkably slows down above or at the three phase equilibrium temperature, particularly at room temperature due to the addition of 2 at. pct Cu. The spinodal time increases by 20 times when aging at 300 degrees C and by more than 30 times when aging at room temperature.
Title:
Time-harmonic dynamic Green's functions for one-dimensional hexagonal quasicrystals
Authors:
Wang, X
Source:
ACTA MECHANICA SOLIDA SINICA 18 (4): 302-306 DEC 2005
Abstract:
Quasicrystals have additional phason degrees of freedom not found in conventional crystals. In this paper, we present; an exact solution for time-harmonic dynamic Green's function of one-dimensional hexagonal quasicrystals with the Lane classes 6/m(h) and 6/m(h)mm. Through the introduction of two new functions phi and psi, the original problem is reduced to the determination of Green's functions for two independent Helmholtz equations. The explicit expressions of displacement and stress fields are presented and their asymptotic behaviors are discussed. The static Green's function can be obtained by letting the circular frequency approach zero.

Update: 3-Feb-2006

Title:
Adhesion properties of decagonal quasicrystals in ultrahigh vacuum
Authors:
Park, JY; Ogletree, DF; Salmeron, M; Ribeiro, RA; Canfield, PC; Jenks, CJ; Thiel, PA
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 945-950 2006
Abstract:
The atomic scale adhesion properties of two high-symmetry surfaces of decagonal Al-Ni-Co quasicrystals have been investigated using atomic force microscopy (AFM) in ultrahigh vacuum. Imaging the surface allowed us to distinguish the plastic regime from the elastic (reversible) regime of tip-sample contact. The work of adhesion of the atomically clean quasicrystal surface in the plastic regime is smaller than that of single crystalline Pt(111) by a factor of 10, reflecting a lower surface energy for the quasicrystal surface. However, the adhesion force must be reduced even further, in order to make measurements outside of the plastic regime possible. We present a strategy for doing this that involves chemical modi. cation of the surface or the tip, together with appropriate choice of mechanical contact parameters.
Title:
Strengthening effects of icosahedral phase in magnesium alloys
Authors:
Singh, A; Watanabe, M; Kato, A; Tsai, AP
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 951-956 2006
Abstract:
Microstructure and strength of two alloys Mg95Zn4.2Y0.8 and Mg92.5Zn6.5Y containing icosahedral phase have been studied after extrusion at 250 degrees C and 400 degrees C. Due to its high symmetry and quasiperiodicity, the icosahedral phase can form strong interfaces with the matrix in various orientations. The icosahedral phase particles have a strong pinning effect on the grain boundaries that stabilizes grain size. They are resistant to coarsening, and remain hard at higher temperatures, imparting good strength with ductility at 200 degrees C. Very few deformation structures such as high dislocation density and twins are observed after extrusion or tensile tests. c-type dislocations are commonly observed, which has important implications for greater ductility. Due to the stability of microstructure, various post-extrusion treatments are possible.
Title:
Hydrogen storage in Ti-Zr and Ti-Hf-based quasicrystals
Authors:
Kelton, KF; Hartzell, JJ; Hennig, RG; Huett, VT; Takasaki, A
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 957-964 2006
Abstract:
The depletion of the world's petroleum reserves and the increased environmental impact of conventional combustion-engine-powered automobiles are leading to renewed interest in hydrogen storage materials. In the mid 1990s, Ti/Zr/Hf-based quasicrystals were demonstrated to store more hydrogen than competing crystal intermetallic phases. Unfortunately, recovery of the hydrogen required temperatures in excess of 400 degrees C, severely limiting the technological application of these materials. Here, the Ti/Zr-Hf-based quasicrystals and crystal approximants are reviewed and their hydrogenation properties are discussed. We also report the discovery of a relatively. at pressure plateau for hydrogenated TiZrNi quasicrystals at modest pressures (100-200 psi) that extends to hydrogen concentrations in excess of 4 wt.%. Approximately 2 wt.% of the hydrogen is easily recovered by heating at temperatures as low as 200 degrees C.
Title:
Cold welding and fretting tests on quasicrystals and related compounds
Authors:
Sales, M; Merstallinger, A; Brunet, P; De Weerd, MC; Khare, V; Traxler, G; Dubois, JM
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 965-970 2006
Abstract:
This paper reports a vacuum or space related effect, which is referred to as "cold welding'', "adhesion'' or "sticking''. This effect is studied for bulk quasicrystal (J.M. Dubois, Useful Quasicrystals (World Scientific, Singapore, 2005)) versus different kinds of counterparts (steel, aluminium, titanium, hard metals). Full series of samples, prepared either by crystal-pulling techniques (single crystals) or by sintering (multi-grain samples) were analysed by fretting tests. Four alloy systems were investigated: Al-Pd-Mn, Al-Cr-Fe-B, Al-Cu-B and Al-Cu-Fe-B, with different crystallographic structures and nominal compositions. These materials, especially icosahedral phases, exhibit the absence of cold-welding in vacuum versus certain steels.
Title:
Peculiarities of the structure and properties of quasicrystalline Al-Cu-Fe coatings produced by EBPVD process
Authors:
Ustinov, AI; Polishchuk, SS
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 971-977 2006
Abstract:
The effect of both composition and substrate temperature on the structure and properties of quasicrystalline Al-Cu-Fe coatings obtained by high-rate (similar to 100nm s(-1)) electron beam physical vapour deposition (EBPVD) was studied. An icosahedral phase has been observed in thick coatings in a much wider concentration range compared with in cast alloys. A lowering of substrate temperature results in a decrease of grain size of the quasicrystalline coating ( down to nanosized scale) and an increase of the concentration of vacancy-type defects in the quasicrystalline structure. The features of the quasicrystalline structure of the coatings are shown to have an influence on their mechanical behaviour at both static and alternate loadings.
Title:
Tiling models for metadislocations in AlPdMn approximants
Authors:
Engel, M; Trebin, HR
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 979-984 2006
Abstract:
The AlPdMn quasicrystal approximants xi, xi', and xi'(n) of the 1.6nm decagonal phase and R, T, and T-n of the 1.2nm decagonal phase can be viewed as arrangements of cluster columns on two-dimensional tilings. We substitute the tiles by Penrose rhombs and show that alternative tilings can be constructed by a simple cut and projection formalism in three-dimensional hyperspace. It follows that in the approximants there is a phasonic degree of freedom, whose excitation results in the reshuffling of the clusters. We apply the tiling model for metadislocations, which are special textures of partial dislocations.
Title:
Mechanical properties of dual-phase alloys of B2 and icosahedral phases in the Al-Cu-Fe system
Authors:
Kitaura, T; So, Y; Kamimura, Y; Edagawa, K
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 991-997 2006
Abstract:
Intermetallic alloys with B2 structure and dual-phase alloys of the B2 phase and an icosahedral (i-) phase have been produced, and their mechanical properties have been investigated. Vickers hardness measurements and compression experiments have shown that the dual-phase alloys have considerably higher strength than that of the B2 single-phase alloy up to a high temperature of around 750 K. The dual-phase alloys have also exhibited much better ductility than i- single-phase alloys. One possibility to be pointed out is that we can further design a high-strength and good-ductility alloy by tuning the volume fraction, size and morphology of the i-phase precipitates.
Title:
Nanomechanical characterization of Al-Co-Ni decagonal quasicrystals
Authors:
Mukhopadhyay, NK; Belger, A; Paufler, P; Gille, P
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 999-1005 2006
Abstract:
This paper addresses some issues related to the nanomechanical responses of decagonal quasicrystals using nanoindentation techniques. A Hysitron Triboscope with a Berkovich indenter was used to carry out the nanoindentation tests on single crystals of Al-Co-Ni decagonal phase. The anisotropy in terms of nanohardness at higher load was observed, whereas it was not possible to establish the same at lower loads. However, the Young's modulus was found to be indistinguishable in all these cases. Discontinuity in load displacement, which is known as a 'pop-in' effect, was observed frequently at various load regime. It was found that this discontinuity was not due to cracking or a phase transformation effect, but to a plastic yielding phenomena and nanodeformation of the material. Significant differences between the nanohardness and microhardness were noticed and are discussed based on various experimental parameters and the consequent mechanical response of materials.
Title:
Homologous temperature dependence of the yield stress of icosahedral quasicrystals and its implication
Authors:
Takeuchi, S
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 1007-1013 2006
Abstract:
Icosahedral quasicrystals are commonly plastically deformable at high temperatures, but the temperature ranges of the plastic deformation are largely different among different types of the quasicrystal. However, when we convert the upper yield stress vs. the temperature relations for various icosahedral quasicrystals into the non-dimensional stress normalised by Young's modulus E vs. the non-dimensional temperature normalised by E (a) over bar (3/)k(B) ((a) over bar: the average atomic diameter, k(B): the Boltzmann constant), the date fall around a universal curve. This homologous relation indicates that the deformation mechanism is common to all types of icosahedral quasicrystals. Assuming that the plasticity is carried by dislocation climb process, it is concluded that about a half of the activation enthalpy of the dislocation climb is due to the jog-pair enthalpy and the other half to the enthalpy of vacancy diffusion, both of which are a function of E (a) o! ver bar (3).
Title:
Fracture of complex metallic alloys: an atomistic study of model systems
Authors:
Rosch, F; Trebin, HR; Gumbsch, P
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 1015-1020 2006
Abstract:
Molecular dynamics simulations of crack propagation are performed for two extreme cases of complex metallic alloys. In a model quasicrystal the structure is determined by clusters of atoms, whereas the model C15 Laves phase is a simple periodic stacking of a unit cell. The simulations reveal that the basic building units of the structures also govern their fracture behaviour. Atoms in the Laves phase play a comparable role with the clusters in the quasicrystal. Although the latter are not rigid units, they have to be regarded as significant physical entities.
Title:
Investigation of phason statics and dynamics
Authors:
Trebin, HR; Koschella, U; Umezaki, M; Odagaki, T
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 1021-1028 2006
Abstract:
The experimental observation of phason fluctuations, both static and dynamic, is well established and has been interpreted within the framework of a hydrodynamic theory. Theoretically, it is still open in what temperature range a hydrodynamic description of phasons is applicable. It has been proposed in the literature that towards low temperatures the hydrodynamic regime is terminated because the form of the phason elastic energy changes from harmonic to non-analytical. Here we report two contributions to the field. Firstly, for a two-dimensional binary model quasicrystal at zero temperature we have investigated the relation between atomic two-body potentials and the phason elastic energy. It turns out that there are indeed certain potentials that can induce a non-analytical phason elastic energy, but these must have very peculiar features in their long-range part, rendering their existence highly unlikely. Secondly, one solution of the hydrodynamic equations is a phasonic excitation riding on a phonon. We have studied the atomistic counterpart via a nonlinear chain with double-well potentials, which resembles a dynamic Fibonacci sequence. We see correlated phason flips propagating with phonon excitations and the dynamic structure factor can separate phonon from phason dynamics.
Title:
Dynamics of long-wavelength phason fluctuations in the i-Al-Pd-Mn quasicrystal
Authors:
Francoual, S; Livet, F; de Boissieu, M; Yakhou, F; Bley, F; Letoublon, A; Caudron, R; Gastaldi, J; Currat, R
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 1029-1035 2006
Abstract:
We report on the dynamics of phason modes in the i-Al-Pd-Mn icosahedral quasicrystal, measured between room temperature and 650 degrees C, using the X-ray intensity fluctuation spectroscopy (XIFS) technique. Up to 500 degrees C, the autocorrelation function, F(q, t), displays almost no time evolution as expected for frozen-in phason fluctuations at low temperature. At higher temperatures, F( q, t) follows a single exponential time decay from which the characteristic time tau(C)(q) is extracted. These results are compared to the expected shape of F(q, t) as derived from the expressions of the eigenvalues and eigenvectors of the C-perpendicular to perpendicular to(q) phason dynamical matrix. In agreement with the hydrodynamic theory of quasicrystals, which predicts phasons with diffusive character, we find that tau(C)(q) varies linearly with q(-2) at 650 degrees C. The corresponding diffusion coefficient is 2.2(+/- 0.5) x 10(-18) m(2) s(-1) and the activation energy is e! stimated around 2.3(+/- 1) eV.
Title:
Thermal conductivity of the Al82.6-xMn17.4Six and Al82.6-xRe17.4Six 1/1-cubic approximants
Authors:
Takeuchi, T
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 1037-1042 2006
Abstract:
Thermal conductivity (k) of the Al82.6-xMn17.4Six and Al82.6-xRe17.4Six 1/1-cubic approximants was investigated with varying Si concentration x over a wide temperature range from 2K to 300 K. Behaviors in k observed for these 1/1-cubic approximants were essentially the same with those reported for the corresponding icosahedral quasicrystals; very small magnitude lower than 4.5W/mK, small contribution of electrons, and possession of a local maximum and a local minimum around 30 similar to 50K and 100 similar to 200 K, respectively. By analyzing measured k in terms of local atomic structure, we revealed that the lattice thermal conductivity is greatly reduced by combination of small group velocity of phonons and enhanced umklapp process of phonon-scattering. Those characteristics were caused by large lattice constant and vacancies in the structure.
Title:
Molecular dynamics simulation of aluminium diffusion in decagonal quasicrystals
Authors:
Hocker, S; Gahler, F; Brommer, P
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 1051-1057 2006
Abstract:
A1 diffusion in decagonal Al-Ni-Co and Al-Cu-Co quasicrystals is investigated by molecular dynamics simulations. Results obtained with newly developed embedded-atom method potentials are compared with our previous work with effective pair potentials. With both types of potential, strong aluminium diffusion is observed above two-thirds of the melting temperature, and the general behaviours of the system are quite similar. The diffusion constant is measured as a function of temperature and pressure, and the activation enthalpies and activation volumes are determined from the resulting Arrhenius plot. For a number of important diffusion processes, the energy barriers are determined with molecular statics simulations. The qualitative behaviour of the dynamics is also confirmed by ab-initio simulations.
Title:
Dislocation dynamics in a dodecagonal quasiperiodic structure
Authors:
Barak, G; Lifshitz, R
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 1059-1064 2006
Abstract:
We have developed a set of numerical tools for the quantitative analysis of defect dynamics in quasiperiodic structures. We have applied these tools to study dislocation motion in the dynamical equation given by Lifshitz and Petrich in 1997, the steady-state solutions of which include a quasiperiodic structure with dodecagonal symmetry. Arbitrary dislocations, parameterized by the homotopy group of the D-torus, are injected as initial conditions and quantitatively followed as the equation evolves in real time. We show that for strong diffusion the results for dislocation climb velocity are similar for the dodecagonal and the hexagonal patterns, but that for weak diffusion the dodecagonal pattern exhibits a unique pinning of the dislocation reflecting its quasiperiodic structure.
Title:
Dodecagonal quasicrystal in a polymeric alloy
Authors:
Dotera, T; Gemma, T
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 1085-1091 2006
Abstract:
We report the formation of an approximant of a dodecagonal quasicrystal in a quasi-two-dimensional lattice Monte Carlo simulation of a star-shaped three-component polymeric alloy. It is associated with the recent striking experimental manifestation of the complex Archimedean tiling (3(2).4.3.4) consisting of triangles and squares, related to the sigma phase in the Frank - Kasper family, but whose edge length is about 80 nm. The simulation box with periodic boundary conditions (128 x 128 x 10) can be regarded as the Stampfli inflation of the (3(2).4.3.4) tiling, an approximant of the dodecagonal quasicrystal. The corresponding edge length of deflated squares and triangles is thought to be about 300 nm. Furthermore, the phason dynamics of the deflated square - triangle tiling is observed at an elevated temperature.
Title:
Stable clusters in quasicrystals: fact or fiction?
Authors:
Steurer, W
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 1105-1113 2006
Abstract:
Undoubtedly, the cluster approach has been a very successful and useful tool for describing and modelling the structure of quasicrystals. However, a number of unanswered questions remain as to how stable these clusters are, in what way do they contribute to the stability of quasicrystals and what physical properties they have. In the following, the different ways in which the term cluster is used are summarised.
Title:
Stability of quasicrystals: energy, entropy and phason modes
Authors:
De Boissieu, M
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 1115-1122 2006
Abstract:
The energy and entropy contribution to the quasicrystal stability is an on-going matter of debate. In this respect, phason modes play a particular role since these excitations are characteristic of the quasicrystalline long-range order. We present some of the results and list open questions in the field.
Title:
Clusters, phason elasticity and entropic stabilization: a theoretical perspective
Authors:
Henley, CL
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 1123-1129 2006
Abstract:
Personal comments are made about the title subjects, including: the relation of Friedel oscillations of Hume-Rothery stabilization; how calculations may resolve the random-tiling versus ideal pictures of quasicrystals; and the role of entropics apart from tile-configurational.
Title:
Discussion on clusters, phasons and quasicrystal stabilisation
Authors:
Henley, CL; de Boissieu, M; Steurer, W
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 1131-1151 2006
Abstract:
This paper summarises a two-hour discussion at the Ninth International Conference on Quasicrystals, including nearly 20 written comments sent afterwards, concerning (i) the meaning [if any] of clusters in quasicrystals; (ii) phason elasticity, and (iii) thermodynamic stabilisation of quasicrystals.
Title:
Spin-wave spectrum of copper metaborate in the incommensurate phase T < 10 K
Authors:
Martynov, S; Petrakovskii, G; Boehm, M; Roessli, B; Kulda, J
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 299 (1): 75-81 APR 2006
Abstract:
The high-energy branch of the spin-wave spectrum of CuB2O4 in the incommensurate magnetic phase was investigated by means of a linear spin-wave theory. The influence of the intersubsystem interactions on the spectrum of the "strong" subsystem was taken into account as the effective field in the framework of the mean-field approach. The comparison with the inelastic neutron scattering experiment leads to the conclusion about the additional "spiral anisotropy" appearance due to the dynamical interaction through the "weak" subsystem fluctuations (the "order due to disorder" rnechanism) in the incommensurate phase. (C) 2005 Elsevier B.V. All rights reserved.
Title:
One-dimensional antiferromagnetism in the piezoelectric layered compound BaMnF4
Authors:
Yoshimura, M; Hidaka, M; Mizushima, T; Sakurai, J; Tsuboi, T; Kleemann, W
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 299 (2): 404-411 APR 2006
Abstract:
The magnetic properties of BaMnF4 have been studied by means of magnetic susceptibility using SQUID magnetometry and neutron diffraction. In the antiferromagnetic (AF) phase (AMP) below T-N approximate to 27 K, the Mn2+ spins are uniaxially aligned parallel to the b-axis. Under an applied magnetic field above a critical strength the spins are flopped and uniaxially aligned perpendicularly to the b-axis. In the intermediate magnetic phase (IMP) between TN, and T-A approximate to 45 K, the Mn2+ spins are easily aligned by an applied magnetic field B, 5 mT <= B <= 2T, although the spontaneous spin order is uniaxially AF. From neutron diffraction in zero applied magnetic field it is found that three-dimensional AF spin order (3-DAFS) of Mn2+ ions in the AMP occurs in a magnetic unit cell a x 2b x 2c, where a, b and c are the lattice constants of the room-temperature phase. Within T-N <= T <= T-A, plane-like magnetic diffuse scattering with a reduced wavenumber q(M) = (xi, xi, (1)/(2))(M); 0.0 <= xi <= 1.0 suggests that BaMnF4 has an one-dimensional AF spin order (1-DAFS) of the Mn2+ ions in the IMP. It arises from superexchange interaction between the Mn2+ spins within chains of MnF6 octahedra along the c-axis, but neither from intrachain superexchange interaction between neighboring spins in the zigzag-like (-Mn-F-Mn-F-Mn-) chains along the incommensurate a-axis nor from interplane AF interaction between pseudo two-dimensional MnF6 networks (folding screens), which are alternatively stacked along the b-axis.
Title:
Short-range order in undercooled and stable melts forming quasicrystals and approximants and its influence on nucleation
Authors:
Holland-Moritz, D; Schenk, T; Simonet, V; Bellissent, R
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 255-262 2006
Abstract:
An icosahedral short-range order has been predicted to prevail in undercooled metallic melts. For melts of pure metals, this hypothesis was recently experimentally confirmed by diffraction experiments. This paper presents results of neutron scattering experiments on the short-range order of stable and undercooled liquids of alloys forming quasicrystals and polytetrahedral crystals. The studies indicate that an icosahedral topological short-range order prevails in all of the investigated melts. The influence of this icosahedral short-range order on the nucleation behaviour of solid phases from the undercooled liquid is discussed.
Title:
Cluster-based composition rule for stable ternary quasicrystals in Al-(Cu, Pd, Ni)-TM systems
Authors:
Dong, C; Qiang, JB; Wang, YM; Jiang, N; Wu, J; Thiel, P
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 263-274 2006
Abstract:
Although hundreds of quasicrystals have been found, little is known about their quantitative composition rules that can help design new materials. In this paper we propose a cluster-based approach to decipher the composition rules. Our approach consists of the following steps: ( 1) selection of a known basic cluster in the constituent binary systems; ( 2) construction of a cluster line linking the binary cluster composition to a third element; and ( 3) the intersection of the two cluster lines points to a new quasicrystal composition if the e/a ratio falls in the appropriate range, typically from 1.8 to 2.0. The predicted compositions agree satisfactorily with experimental values.
Title:
Kinetics of the crystallization of icosahedral phase in ultra thin deposits of Al62Cu25.5Fe12.5 alloy
Authors:
Bonasso, N; Pigeat, P
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 275-280 2006
Abstract:
Made at room temperature, the deposition of the three elements Al, Cu, Fe in the atomic proportion 62/25.5/12.5 allows amorphous deposits to be obtained. The mixture becomes crystalline when subjected to heat treatment. Several deposits made on transmission electron microscopy (TEM) grids were heated up to different temperature thresholds. Only during annealing above 723K were nucleation and growth of i-AlCuFe observed. A Mehl-Johnson-Avrami model is proposed to describe this crystallization. This model fits the experimental data very well and allows mean activation energies for volume diffusion to be calculated. Assuming the time of the total transformation, a TTT curve is plotted. Nucleation density values and activation energy of the i-Al62Cu25.5Fe12.5 phase nucleation are estimated.
Title:
Structural evolution of nano-scale icosahedral phase in novel multicomponent amorphous
Authors:
Kim, KB; Warren, PJ; Cantor, B; Eckert, J
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 281-286 2006
Abstract:
Novel (Ti33Zr33Hf33)(70)(Ni50Cu50)(20)Al-10, (Ti25Zr25Hf25Nb25)(70)(Ni50Cu50)(20)Al-10, and (Ti33Zr33Hf33)(70)(Ni33Cu33Ag33)(20)Al-10 multicomponent amorphous alloys developed by equiatomic substitution transform into a nano-scale icosahedral phase upon devitrification. However, the decomposition sequence of the nano-scale icosahedral phase at higher temperatures is significantly different for each alloy. The occurrence of the Zr2Cu-type phase during the decomposition of the devitrified icosahedral phase can enhance the thermal stability of the icosahedral phase.
Title:
Influence of oxidation of i-AlCuFeB particles on the formation of Al-based composites prepared by solid state sintering
Authors:
Kenzari, S; Weisbecker, P; Geandier, G; Fournee, V; Dubois, JM
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 287-292 2006
Abstract:
We present new results concerning the formation of Al-based composites reinforced by icosahedral i-Al59Cu25.5Fe12.5B3 quasicrystalline particles. The issue is to limit the diffusion of Al from the matrix to the quasicrystalline particles during sintering in order to overcome the transformation of the i-phase into the omega-Al7Cu2Fe tetragonal phase. Here we have investigated the influence of an oxidation pre-treatment of the quasicrystalline particles onto the kinetics of this phase transformation by high energy X-ray diffraction. The quasicrystalline particles were annealed either in vacuum or in air, leading to a different thickness of the oxide layer. We show that the oxide barrier efficiently reduces the kinetics of Al diffusion, enabling the formation of composite materials with no phase transformation during the sintering process. The dependence of the tribological properties of these composites is investigated as a function of the volume fraction of i-AlCuFe B particles.
Title:
Quasicrystal formation in Zr-Cu-Ni-Al-Ta metallic glasses and composites
Authors:
Ott, RT; Kramer, MJ; Besser, MF; Hufnagel, TC; Sordelet, DJ
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 299-307 2006
Abstract:
We have examined the crystallisation behaviour of Zr-Cu-Ni-Al-Ta metallic glasses and metallic-glass-matrix composites. Monolithic and composite alloys were prepared by varying the amount of Ta added to a Zr-based glass-forming alloy. We find that additions as low as 2 at.% Ta promotes the formation of the icosahedral phase during devitrification, which in turn has a significant effect on the subsequent crystallisation behaviour. The DSC and time-resolved X-ray scattering results show that following the nucleation of the quasicrystals the alloys exhibit an exothermic event that does not correspond to any discernible structural change. We discuss the possible mechanisms for the second exotherm.
Title:
Quasicrystal formation in gas-atomized Zr80Pt20 powders
Authors:
Yang, XY; Rozhkova, EA; Sordelet, DJ
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 309-315 2006
Abstract:
Gas-atomized powders with a nominal composition of Zr80Pt20 have been investigated as a function of powder size range. Atomized powders were screened to the following sizes for examination: < 10 mm; +10, -20 mu m; +20, -45 mu m; +45, -75 mu m; +75, -106 mu m. For comparison of as-synthesized structure and crystallization behaviour, Zr80Pt20 melt-spun ribbons (MSRs) were also prepared. Results show that during atomization a metastable quasicrystalline (QC) phase is formed as the predominant phase independent of powder size; a small volume of amorphous phase and crystals were detected in finer and coarser sized powders, respectively. The QC grains formed during atomization are much larger than the nanosized quasicrystal obtained in the MSR, which is most likely attributed to the much slower cooling rates during gas atomization. Nucleation and growth occur during both rapid solidi. cation routes. The formation of an icosahedral quasicrystal during gas atomization and melt spinning is consistent with previous suggestions that icosahedral local structure exists in liquid and amorphous phases and facilitates nucleation of quasicrystal formation in Zr80Pt20 alloys.
Title:
Czochralski growth and X-ray topographic characterization of decagonal AlCoNi quasicrystals
Authors:
Bauer, B; Meisterernst, G; Hartwig, J; Schenkz, T; Gille, P
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 317-322 2006
Abstract:
Large single crystals of the decagonal AlCoNi phase were reproducibly grown by the Czochralski method from Al-rich melts. By using native seeds, it was possible to grow crystals with well-defined orientations, e. g. along the 10-fold periodic axis or parallel to one of the 2-fold axes. Quasicrystals, that had been pulled in periodic or quasiperiodic directions, were characterized by X-ray transmission topography at the synchrotron source (ESRF) and at laboratory sources using the Lang technique. Because of the metallurgical homogeneity of the grown quasicrystals, lattice parameter differences did not contribute to the topographic contrast, instead, orientation contrast dominated. A column-like substructure along the periodic direction could be revealed. From this it is concluded that crystal growth along a two-fold direction might be favourable with respect to minimizing defect spreading.
Title:
Understanding Czochralski growth of decagonal AlCoCu
Authors:
Meisterernst, G; Zhang, L; Dreier, P; Gille, P
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 323-328 2006
Abstract:
Czochralski growth of decagonal AlCoCu was investigated using spontaneous nucleation as well as AlCoNi seeds of different orientations. Contrary to all knowledge gained from the growth of large single crystals in the Al-Co-Ni system, growth of AlCoCu quasicrystals proved to be much more complicated. Second-phase inclusions were found to be the main problem, resulting in various features affecting regular crystal growth. Even at extremely low pulling rates, this could only be solved by growing along the two-fold [10000]-direction. Finally, large-grain Al67.5Co20.0Cu12.3 single crystals, having a rather homogeneous elemental distribution, were successfully grown from the initial melt of composition Al66Co10Cu24.
Title:
Phase transformations of icosahedral AlCuFe quasicrystals
Authors:
Zhang, LM; Luck, R
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 329-334 2006
Abstract:
Phase transformations with alloy compositions in the vicinity of the AlCuFe icosahedral quasicrystalline phase (i-phase) were studied. This phase forms via a ternary peritectic reaction at 882 degrees C from liquid and two primary solid phases termed lambda and beta. With decreasing temperature, the icosahedral phase is a reaction partner with liquid, lambda, beta and tetragonal omega in two different transition reactions. Furthermore, two solid-state phase transformations, involving the i-phase (a quasi-binary eutectoid beta -> i + phi at 640 degrees C and a ternary transition-type reaction i + beta -> phi at 616 degrees C), are reported. The conclusions are based on differential thermal analysis combined with powder X-ray diffraction investigations. A three-dimensional sketch of a wire model for the icosahedral phase was constructed, which demonstrates the shrinkage of the phase field of icosahedral phase with a decreasing temperature.
Title:
In situ observation of pore evolution during melting and solidification of Al-Pd-Mn quasicrystals by synchrotron X-ray radiography
Authors:
Gastaldi, J; Schenk, T; Reinhart, G; Klein, H; Hartwig, J; Mangelinck-Noel, N; Grushko, B; Thi, HN; Pino, P; Billia, B; Baruchel, J
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 335-340 2006
Abstract:
It is now generally admitted that pores are intriguing special features of quasicrystals. Therefore, we have performed an 'in situ' and real time observation of the pore evolution during directional solidi. cation and melting cycles of an icosahedral Al-Pd-Mn bi-grained sample, by synchrotron X-ray radiography. Rather surprisingly, no pore was observed to grow during the solidi. cation stages. Nucleation and growth of pores were first seen during melting. These pores were subsequently shrinking either just before being absorbed or during resumption of directional solidi. cation. It is concluded that the vacancy origin of pores is certainly valid whereas the vacancy supersaturation, needed thereby to explain their growth, would be more probably related to the peculiar structure of quasicrystal than to the destruction of the thermal equilibrium.
Title:
Heterogeneous nucleation of icosahedral phase from FCC phase in cast Al87Mn4Si2Be7 alloy
Authors:
Fleury, E; Chang, HJ; Kim, DH
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 349-354 2006
Abstract:
The formation of the icosahedral (i) quasicrystalline phase has been studied in the cast Al87Mn4Si2Be7 alloy. Under low cooling rates, i-phase particles of about 5 to 15 mm formed in the alpha(A1) matrix. A thorough examination of the microstructure revealed the existence of cubic crystalline phases embedded in the i-particles. Microstructural and thermal analyses indicated that the i-particles nucleated heterogeneously from the cubic AlMn(Si)Be-4 phases by a peritectic reaction, however with a slight misorientation.
Title:
Studies on low-temperature stability of decagonal Al-Co-Ni
Authors:
Hassdenteufel, KH; Steurer, W
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 355-359 2006
Abstract:
The stability of decagonal Al-Co-Ni (d-phase) has been investigated by in situ single-crystal X-ray diffraction, at temperatures between room (RT) and 20 K, as well as at 90 and 473 K, under a pressure of 2.8 GPa. Samples of the Ni-rich basic d-phase, as well as superstructure type I, have been studied. Besides a slight variation in reflection intensities, no phase transition could be observed under the given conditions. This is no proof, however, for the low-temperature (LT) stability of the d-phase, since high-energy ball-milling experiments at RT lead to a transition of the d-phase to the beta-phase, i.e. the disordered B2-type.
Title:
A metastable icosahedral quasicrystal in the Zn-Mg-Yb alloy system
Authors:
Mitani, T; Ishimasa, T
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 361-366 2006
Abstract:
The formation conditions for a Zn-Mg-Yb icosahedral quasicrystal, which is primitive (P) type and has a six-dimensional lattice parameter a(6D) = 7.371A, have been studied. This quasicrystal is formed only by quenching from a temperature higher than 650 degrees C in the narrow composition region between approximately Zn76Mg9Yb15 and Zn71Mg17Yb12. On annealing, this quasicrystal transforms to the Zn17Yb3-type cubic phase and the hexagonal Z phase, both of which are equilibrium phases in this alloy system. An annealing experiment, a morphological study of these phases and differential thermal analysis have revealed that this quasicrystal is a metastable phase.
Title:
Influence of ball milling on quasicrystal formation in melt-spun Zr-based glassy ribbons
Authors:
Scudino, S; Eckert, J; Breitzke, H; Luders, K; Schultz, L
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 367-371 2006
Abstract:
The effect of mechanical deformation on the formation of quasicrystals in Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 glassy ribbons has been investigated. The mechanical treatment drastically affects the crystallization behavior and, in particular, suppresses primary quasicrystal formation. However, quasicrystals can be formed by the addition of the appropriate amount of zirconium. This indicates that if a particular short-range order (e.g., icosahedral) is required for quasicrystal formation and if this short-range order is altered during milling, it can be restored by appropriately adjusting the chemical composition.
Title:
Formation of crystal approximants to icosahedral quasicrystal in Sc-based alloys
Authors:
So, YG; Shimizu, A; Edagawa, K; Takeuchi, S
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 373-379 2006
Abstract:
The composition range for the formation of a 1/1 cubic approximant phase to icosahedral quasicrystal has been investigated in various Sc based alloys of Sc-Rh-TM (TM:transition metal) type. The composition area of the approximant phase differs depending on the TM element and can be classified into three groups: in one group it extends roughly along a Rh constant line, in another it extends roughly along a Sc constant line and in the other it extends two-dimensionally in the diagram. The shape of the composition area correlates well with the position of the TM element in the periodic table, although it has no apparent correlation with the number of valence electrons per atom ratio (e/a ratio).
Title:
Synthesis and characterization of hexagonal Cd51Yb14 single crystals
Authors:
Wu, D; Ugurlu, O; Chumbley, LS; Kramer, MJ; Lograsso, TA
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 381-387 2006
Abstract:
Synthesis of large, bulk single grains of the hexagonal crystalline phase Cd51Yb14 has been accomplished using the Bridgman method. Growth was carried out under controlled solidi. cation conditions in sealed Ta crucibles, which maintain compositional integrity by eliminating evaporative losses of Cd and reaction with the containment material. Compositional analysis of the as-grown phase indicates no evidence of macrosegregation along the length of the crystal. High-resolution transmission electron microscopy (TEM) characterization of the hexagonal phase is hampered by the enhanced atmospheric reactivity of the higher Yb content of the hexagonal phase. Such a high sensitivity to ambient exposure was not observed during the recent synthesis and TEM studies of the quasicrystalline Cd5.7Yb or cubic approximate phase Cd6Yb. TEM and X-ray transmission diffraction results taken at the Advanced Photon Source at Argonne National Laboratory show the presence of a fine-structured second phase, which is randomly oriented throughout the matrix. The precipitates have been identified as pure Cd by d-spacing comparisons and likely form by selective atmospheric oxidation of Yb from the Cd51Yb14 phase.
Title:
Influence of Pd on formation of amorphous and quasicrystal phases in rapidly quenched Zr2Cu(1-x)Pdx
Authors:
Xu, M; Ye, Y; Morris, JR; Sordelet, DJ; Kramer, MJ
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 389-395 2006
Abstract:
The role of Pd in the transformation from an amorphous state to a metastable icosahedral quasicrystalline phase in Zr2Cu(1-x)Pdx(x = 0 to 1) metallic glasses was investigated using high-energy synchrotron X-rays and differential scanning calorimetry. The total scattering functions show an increasing development of the high-Q side of the second diffuse scattering peak at 5.09A(-1) with increasing Pd content. The reduced radial distribution functions reveals that the bonding distance of the Zr-(Pd/Cu) pairs increases from 2.76 to 2.82A when x increases from 0.00 to 1.00, while the distance for the Zr-Zr pairs remains almost constant at 3.10A. Thermal analysis and X-ray diffraction together show that an amorphous-to-quasicrystal phase transition is not observed in the Zr2Cu alloy, but partial or total substitution of Cu by Pd in Zr2Cu(1-x)Pdx alloys does lead to quasicrystal formation.
Title:
Phase transformations in Al70Ni24Fe6 decagonal system during high energy ball milling
Authors:
Yadav, TP; Mukhopadhyay, NK; Shaz, MA; Tiwari, RS; Srivastava, ON
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 397-404 2006
Abstract:
In the present investigation, the decagonal phase in Al70Ni24Fe6 alloy was used for studying the structural and microstructural stability during ball milling in an attritor mill for 1, 2, 4, 8, and 12 h under hexane medium with a powder to ball ratio of 1:100. The milled powder was annealed in an argon atmosphere for durations ranging from 1 to 40 h at 500 degrees C. The as-cast alloy was found to consist of micron size decagonal phase as a major one along with minor amount of Al3Ni and Al-13(Fe, Ni)(4) crystalline phases. Powders milled for more than 8h contained predominantly the B2 phase. The crystallite size of the B2 phase was estimated to be around 17 nm after 12 h of milling. A lamellar like microstructure exhibiting the presence of nano-phase embedded in the grain of B2 phase has been found to evolve after 8 h of ball milling. Subsequent annealing treatment at 500 degrees C for 10, 20 and 40 h of mechanically milled powder for 12 h has led to the transformation of B2 phase to the tau(3) type vacancy ordered phase. The implications of these phase transformations and the evolution of corresponding microstructures will be discussed.
Title:
Recent development in structure determinations for quasicrystals
Authors:
Yamamoto, A; Takakura, H
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 405-411 2006
Abstract:
This paper briefly reviews recently developed methods which are applicable to an accurate determination of quasicrystal structures on the basis of a higherdimensional cluster model. The structure analysis based on this model, which has been shown to be applicable to all quasicrystals, is demonstrated in the case of the basic Ni phase in decagonal Al-Ni-Co quasicrystals.
Title:
Modelling electric field gradients of icosahedral quasicrystals
Authors:
Klanjsek, M; Dolinsek, J
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 413-418 2006
Abstract:
A simple auxiliary model is presented that enables the extraction of general features of the electric field gradient (EFG) tensor distribution in icosahedral quasicrystals directly from the orientation dependence of the quadrupole-perturbed NMR spectrum. The only assumption of the model is a macroscopic icosahedral symmetry of the sample under study. It is shown that the model serves as a good filter since on the basis of the measured orientation-dependent NMR spectrum it can directly differentiate between qualitatively different icosahedral distributions of the EFG tensor orientations.
Title:
Zn1-xPdx (x=0.14-0.24): a missing link between intergrowth compounds and quasicrystal approximants
Authors:
Gourdon, O; Izaola, Z; Elcoro, L; Petricek, V; Miller, GJ
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 419-425 2006
Abstract:
Our investigations in the Zn-rich portion of the Zn-Pd system are related to the idea that a prototypic 1-dimensional (1D) quasicrystal, as defined by the Fibonacci sequence, can be regarded both as a quasicrystal and as an incommensurately modulated crystal. Consequently, there are two different ways to achieve the atomic structure. Six different new structures, closely related to the gamma-brass structure, in the Zn1-xPdx system have been synthesized and contain Pd-centred Zn icosahedra. A misfit character of all structures with two distinct main subsets and satellite reflections is clear from the diffraction patterns. Among these six structures, two specific examples, Zn10.65Pd2.35 (Zn0.819Pd0.181) and Zn212Pd64 (Zn0.768Pd0.232), have been refined by single crystal X-ray diffraction using traditional refinement methods but also using the (3+1) D formalism (superspace group Xmmm(00 gamma)0s0). Analogies with the Fibonacci sequence are possible if we identify dimers of Pd- centred Zn icosahedra (DI) as short segments, S, and trimers of Pd- centred Zn icosahedra (TI) as long segments, L. By de. ning these S and L segments, Zn11Pd2 and Zn212Pd64 correspond to the two first simplest approximants of a hypothetical 1D quasicrystal.
Title:
Formation condition of the icosahedral phase in rapidly quenched Ag-In-RE ( rare earth) alloys
Authors:
Iwano, S; Nishimoto, K; Tamura, R; Takeuchi, S
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 435-441 2006
Abstract:
Formation of icosahedral (i) phases in rapidly quenched Ag-In-RE (rare earth) (RE=Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) ternary alloys is investigated. It is found that the relative magnitude of the quasilattice constant is well explained by the atomic radius of the RE elements for Ag-In-RE alloys with trivalent RE elements, and the formation of the i phase is governed by the atomic radius of the RE element. Moreover, the i phase is found to be formed in a wide composition range for the Ag/In atomic ratio but in a very narrow range for the RE concentration, which suggests that the RE concentration plays a crucial role in the formation, i. e. the stability, of the i phase rather than the average electrons-per-atom ratio. Furthermore, it is suggested that the structural change caused by the variation of the Ag/In concentration ratio in the i phase cannot be understood as a consequence of simple mutual replacement between Ag and In.
Title:
Glass formation and crystallization in binary Zr-Pt systems
Authors:
Lee, MH; Yang, X; Kramer, MJ; Sordelet, DJ
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 443-449 2006
Abstract:
Previous rapid solidi. cation studies of Zr-Pt alloys have focused primarily on compositions very close to the Zr80Pt20 eutectic. In the current work, a wide range of alloys, ZrxPt100-(x) (69 <= x <= 81), were synthesized by melt spinning to examine their starting structures and devitrification behaviours. Similar to the frequently reported formation of a metastable quasicrystalline phase during heating of near-eutectic compositions, ribbons with Zr contents as low as 75 at.% show comparable transformations, but at higher temperatures, before transforming to the stable Zr5Pt3 structure. With the quench rate used in this study, a further decrease below 75 at.% Zr precludes the formation of the metastable quasicrystalline phase and instead results in crystallization directly to the stable Zr5Pt3 structure. Preliminary analysis of the transformation kinetics reveals a lower activation energy for the transformation of an amorphous Zr-Pt structure to the metastable quasicrystal phase in comparison to the stable Zr5Pt3 phase.
Title:
Structure of the pseudodecagonal Al-Co-Ni approximant PD4
Authors:
Oleynikov, P; Demchenko, L; Christensen, J; Hovmoller, S; Yokosawa, T; Doblinger, M; Grushko, B; Zou, XD
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 457-462 2006
Abstract:
A model for the pseudodecagonal approximant PD4 in the Al-Co-Ni system was deduced from single crystal X-ray diffraction data. The space group is Bbmm with a = 101.3, b = 32.1 and c = 4.1 angstrom. Atomic positions of 133 unique atoms in the unit cell with a reasonable geometry were found by direct methods and the difference Fourier syntheses. The obtained structure model is in good agreement with high-resolution electron microscopy images of PD4. Diffuse scattering observed along the a* direction in the hkl layers with l = 1/2, 3/2 etc. indicates a superstructure with a doubling of the periodicity along the c-axis and a lamellar disorder along the a-axis. If this diffuse scattering is taken into account, c = 8.2 angstrom.
Title:
Local atomic three-dimensional real-space structural analysis of icosahedral Mg-Zn-RE (RE = Y or Ho) alloys: Strategy, method and models
Authors:
Bruhne, S; Uhrig, E; Kreiner, G; Assmus, W
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 463-468 2006
Abstract:
The local structure of any condensed matter is accessible via an atomic pair distribution function (PDF) analysis. Here, the local atomic structure of the well-ordered face-centred icosahedral (fci)-Mg25Y11Zn64, fci-Ho9Mg26Zn65 and simple icosahedral Ho11Mg15Zn74 quasicrystals have been investigated by PDFs obtained from in-house X-ray and synchrotron powder data. Least-squares refinements using periodic 1/1 and 2/1 approximants as models for the local atomic structure have been performed. They reveal predominantly Frank Kasper-type coordination polyhedra. The basic building block is a Bergman cluster of about 100 atoms of 14 angstrom diameter. RE8 cubes of edge length 5.4 angstrom are part of the cluster occupying pentagon dodecahedral positions. The cluster connection scheme follows in general that of Henley's canonical cell tiling. However, according to our results, overlapping clusters are likely to be present in the quasicrystalline structure. Thus interpenetration seems to be a general feature for clusters in quasicrystals, which complicates the ongoing discussion on their nature.
Title:
Electron microscopy study of approximant phases in the Al-Cr-Fe system
Authors:
Demange, V; Ghanbaja, J; Dubois, JM
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 469-474 2006
Abstract:
We have characterized by transmission electron microscopy several new phases that we have discovered in bulk alloys of the Al-Cr-Fe system. These structures are an icosahedral compound and several approximants of the decagonal phase. According to the indexation of the electron diffraction patterns (EDPs), some of the approximants are not of Fibonacci type. These EDPs correspond to nanodomains, which are due to disorder introduced by quenching the alloys after melting the pure constituent metals. For these new types of approximant, we propose a crystallographic description related to the usual Fibonacci description. In addition, we suggest a construction of the corresponding tilings. The orientation relationships between these structures are described.
Title:
The formation of an Al-Cu-Co type decagonal quasicrystal in an [AlCuFe]-[AlCoNi] pseudo-binary alloy system
Authors:
Lei, Y; Dubois, JM; Calvo-Dahlborg, M; Dong, C; Zhang, Z
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 475-481 2006
Abstract:
Pseudo-binary IQC(100-x)DQC(x) alloys made from mixing Al62Cu25.5Fe12.5 icosahedral quasicrystal (IQC) and Al70Co15Ni15 decagonal quasicrystal (DQC) together in progressively increased proportions were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDAX). In this way the transition from IQC to DQC was manifested by the evolution of their constituent phases. The formation of these phases was found to follow the evolution of their valence electron concentration per atom (e/a) lines in the Al-(Cu,Ni)-(Fe,Co) pseudo-ternary phase diagram. An Al-Cu-Co type decagonal phase was found in the annealed IQC(80)DQC(20) alloy. This phase is characterized by transmission electron microscopy (TEM) and by high-resolution electron microscopy (HREM). The study proved that it is a superstructure of the DQC phase. The possible origin of its formation was discussed according to the variation of its DQC formation e/a-cons! tant line in the Al-(Cu,Ni)-(Fe,Co) alloy system.
Title:
Transition from quasicrystals to amorphous structures
Authors:
Orzechowski, D; Wolny, J
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 483-487 2006
Abstract:
For the model structure the smooth transition from perfect quasicrystalline to amorphous structure have been observed and changes in the diffraction patterns have been investigated. It turned out that all dependencies can be easily handled by the means of some well-defined probablility distributions. Given these distributions one can perform the appropriate calculations in the average unit cell method and describe the transition in a simple and consistent way.
Title:
Experimental investigations on the electronic structure and the low-temperature stability of Cd-based quasicrystals and their 1/1 cubic approximants
Authors:
Tamura, R; Minoda, K; Takeuchi, S; Takeuchi, T; Edagawa, K; Kiss, T; Yokoya, T; Shin, S
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 489-497 2006
Abstract:
Valence band spectra of icosahedral quasicrystals and their 1/1 cubic approximants in the Cd-Yb and Cd-Ca systems are investigated systematically. A sharp Fermi edge, indicative of sizable density of states at the Fermi level (EF), is clearly observed for all the compounds and EF is located not at the bottom of the pseudogap but at its shoulder. In addition, a peak structure appears just below E-F for the Cd-Ca system, which is also found for the Cd-Yb system when subtracting a Yb 4f derived doublet. Ca 2p-3d resonant photoemission spectroscopies on the Cd-Ca compounds reveal the existence of Ca 3d states at EF, indicating that the 3d states do contribute to the peak structure at EF, which is attributed to hybridization with the Cd sp states. The low-temperature structural properties of the Cd-based compounds are also reported. An occurrence of a structural phase transition at 110K and 100K for Cd6Yb and Cd6Ca, respectively, is well documented. The transitions are understood as a consequence of an orientational ordering of Cd-4 tetrahedron located at the center of the icosahedral clusters. It is suggested that two orientations of the Cd4 tetrahedron alternatively occur along the [110] direction of the high temperature bcc phase.
Title:
Low-temperature transmission electron microscopy studies of Cd-based 2/1 approximants and quasicrystals *
Authors:
Nishimoto, K; Tamura, R; Takeuchi, S; Edagawa, K; Ichihara, M
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 499-503 2006
Abstract:
Transmission electron microscopy (TEM) observations on Cd-based 2/1 cubic approximants and quasicrystals were performed at low temperatures down to 20 K. For 2/1 approximants, the appearance of superlattice spots was commonly observed at temperatures below 110 K, suggesting the occurrence of a phase transition. For quasicrystals, no appreciable change in diffraction pattern was recognized at temperatures down to 20 K, which may suggest that no phase transition occurred.
Title:
Stability of icosahedral Cd-Yb at low temperature
Authors:
Krauss, G; Steurer, W; Ross, AR; LoGrasso, TA
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 505-511 2006
Abstract:
The stability of i-Cd-Yb was studied between ambient temperature and 90K using single-crystal diffraction. To study the influence of mechanical stress at low temperatures, a modified grinding-jar housing was constructed and ball-milling experiments were carried out at 77 K. In neither case structural changes were observed. This indicates the thermodynamic stability of this binary quasicrystal.
Title:
The study of the binary quasicrystal Cd17Ca3 and its 1/1 approximant Cd6Ca by positron annihilation spectroscopy
Authors:
Takagiwa, Y; Akiyama, T; Kanazawa, I; Sato, K; Murakami, H; Kobayashi, Y; Tamura, R; Takeuchi, S
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 513-517 2006
Abstract:
The positron annihilation lifetime measurements for the Cd17Ca3 quasicrystal and its 1/1 Cd6Ca approximant were carried out at 300 K. The observed lifetime of the Cd17Ca3 quasicrystal is close to that of the 1/1 Cd6Ca approximant, implying the existence of the same type of structural vacancies. The temperature variations in the positron lifetime were investigated in the temperature region from 10 to 300K for the Cd17Ca3 quasicrystal annealed at 773K and the Cd17Ca3 quasicrystal cooled in the furnace. We found clear differences between both the absolute value and the temperature gradient of the positron lifetimes of the two quasicrystals. The results will be discussed in terms of the fluctuation in the four-Cd tetrahedron inside the 20-Cd dodecahedron between two quasicrystals.
Title:
Canonical cell model of cadmium-based icosahedral alloys
Authors:
Mihalkovic, M; Widom, M
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 519-527 2006
Abstract:
Cadmium-based quasicrystals (Cd-Ca and Cd-Yb) were the first binary alloys discovered to form thermodynamically stable quasicrystals. As binary alloys, and with a strong size difference between atomic species, they are ideal systems for structural and thermodynamic analysis. Observed quasicrystal approximants with crystallographically determined structures can be interpreted as decorations of Henley's canonical cells. We use first-principles total energy calculations to resolve details of the most favourable decorations.
Title:
Structure of type I and type II modifications of Al-Co-Ni decagonal quasicrystals studied by HAADF-STEM technique
Authors:
Song, S; Wang, R; Gui, J; Wang, J; Yan, Y
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 529-535 2006
Abstract:
The structure of type I and type II modi. cations of Al-Co-Ni decagonal quasicrystals was studied by using the high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM) technique. It was found that the quasi-unit-cell should be selected as columnar decagon of 3.2nm in diameter and 0.82nm in height, and its center consists of a bright circle with 0.76nm of the outer diameter, indicating that atomic distribution in the quasi-unit-cell is disordered. Lattices obtained by connecting the centers of the atom clusters in HAADF images reveal that the lattice of the type I modi. cation is rhombic Penrose tiling and the lattice of the type II is a mixture of the rhombic and pentagonal tilings. Namely, the lattice of the type II modi. cation is a mixture of the lattices of the type I and S1 modifications.
Title:
Phasonic disorder in decagonal Al-Co-Ni
Authors:
Weber, T; Kobas, M; Steurer, W
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 537-542 2006
Abstract:
Diffuse scattering from decagonal Al70Co12Ni18 (Edagawa phase) was investigated by means of Patterson methods. Basically two systems of diffuse intensities can be observed. The first system is found in quasiperiodic layers containing Bragg reflections. Model calculations show that underlying disorder can equally well be explained as phasonic disorder in a five dimensional approach, as well as fivefold orientational disorder of clusters in three dimensions. A second set of diffuse intensities is observed in layers halfway between the Bragg layers. Disorder associated thereto shows some correlation to phasonic/orientational disorder, but a different temperature dependency of the respective disorder phenomena suggests that these correlations are accidental.
Title:
Structure relations in real and reciprocal space of hexagonal phases related to i-ZnMgRE quasicrystals
Authors:
Zhang, H; Zou, XD; Oleynikov, P; Hovmoller, S
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 543-548 2006
Abstract:
The mu(3), mu(5) and mu(7) approximants in Mg-Zn-RE were related in real and reciprocal space. The structure factors of mu(3), mu(5) and mu(7) have quite similar intensity distributions and identical phases for the strongest corresponding reflections. Structure models of any of mu(3), mu(5) and mu(7) can be obtained from any of the others using the strong reflections approach.
Title:
Decorated quasicrystals and their diffraction patterns
Authors:
Kozakowski, B; Wolny, J
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 549-555 2006
Abstract:
The structure factor of two-dimensional quasicrystals obtained for decorated Penrose tilings was derived in statistical approach. Each atom can decorate the two rhombuses in an arbitrary fashion accompanied with an arbitrary occupation probability. The derived analytical formula was numerically checked for the refined model structure.
Title:
Tile decoration model of the W-(Al-Co-Ni) approximant
Authors:
Mihalkovic, M; Widom, M
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 557-565 2006
Abstract:
We use ab-initio total energy calculations to re. ne chemical ordering of the W-(Al-Co-Ni) approximant structure and calculate its stability relative to other ternary and binary competing compounds. This approximant structure has 8 angstrom stacking periodicity along its pseudofivefold axis and can be interpreted as stacking of two identical adjacent 4 angstrom slabs with stacking vector inclined relative to the pseudofivefold axis. We generalize this stacking motif to model the 8 angstrom quasicrystal. Starting with 4 angstrom slabs forming a 'binary' (three-level) decagonal tiling, we introduce tile flips between adjacent slabs analogous to the 'octagon' tile-reshuffling update move for binary Penrose tiling. These tile flips lower the total energy, implying 8 angstrom superorder for the quasicrystal at low temperatures, consistent with experiment.
Title:
Averaged coordination numbers of planar aperiodic tilings
Authors:
Baake, M; Grimm, U
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 567-572 2006
Abstract:
We consider averaged shelling and coordination numbers of aperiodic tilings. Shelling numbers count the vertices on radial shells around a vertex. Coordination numbers, in turn, count the vertices on coordination shells of a vertex, defined via the graph distance given by the tiling. For the Ammann-Beenker tiling, we find that coordination shells consist of complete shelling orbits, which enables us to calculate averaged coordination numbers for rather large distances explicitly. The relation to topological invariants of tilings is briefly discussed.
Title:
Chemical decoration in cubic approximant and quasicrystal in the Al-Cu-Fe system
Authors:
Simonet, V; Hippert, F; Brand, RA; Calvayrac, Y; Rodriguez-Carvajal, J; Sadoc, A
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 573-579 2006
Abstract:
The local order in the Al-Cu-Fe quasicrystal and in two of its approximants has been investigated by extended X-ray absorption. ne structure ( EXAFS) studies at the Cu and Fe K-edges. The chemical occupation of the crystallographic sites in the 1/1 cubic alpha-Al55Si7Cu25.5Fe12.5 phase is revisited. From these results, a model for the chemical short-range order in the Al62Cu25.5Fe12.5 quasicrystal is proposed.
Title:
5D modelling of decagonal Al-Co-Ni based on the W-approximant
Authors:
Deloudi, S; Kobas, M; Steurer, W
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 581-585 2006
Abstract:
A structure model for decagonal Al-Co-Ni with 8 angstrom periodicity along the decagonal axis is proposed. The model agrees well with available experimental information, such as electron microscopic images and three-dimensional ( 3D) Patterson maps calculated from X-ray-diffraction data. The model is based on a novel columnar cluster with 20 angstrom diameter and symmetry 5/mm building the W-approximant, Al72.5Co20Ni7.5. The proposed cluster also allows modelling of the various types of disorder and superstructures found in decagonal Al-Co-Ni.
Title:
Superquasicrystals with 8-, 10- and 12-fold point symmetries
Authors:
Fujita, N; Niizeki, K
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 587-592 2006
Abstract:
We present several limit-quasiperiodic structures with 8-, 10- and 12-fold point symmetries. These structures are generated with inflation procedures as in the case of the Penrose patterns. Yet they are the first structures ever known with limit-quasiperiodic order and non-crystallographic point symmetries, and we categorize them as superquasicrystals [ Niizeki and Fujita, J. Phys. A: Math: Gen. 38 L199 ( 2005)]. Their internal space structures are not as simple as quasicrystals, because the atomic-surfaces depend on the lattice points of the relevant hyperlattices. We numerically investigate such atomic-surfaces by mapping the real-space structure into the internal space. The structure factors are also calculated, in which successive generations of super-quasilattice reflections are clearly observed.
Title:
Co-rich decagonal Al-Co-Ni: predicting structure, orientational order and puckering
Authors:
Gu, N; Henley, CL; Mihalkovic, M
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 593-599 2006
Abstract:
We apply systematic methods previously used by Mihalkovic. et al. to predict the structure of the 'basic' Co-rich modi. cation of the decagonal Al70Co20Ni10 layered quasicrystal, based on known lattice constants and previously calculated pair potentials. The modelling is based on Penrose tile decoration and uses Monte Carlo annealing to discover the dominant motifs, which are converted into rules for another level of description. The result is a network of edge-sharing large decagons on a binary tilling of edge 10.5 angstrom. A detailed analysis is given of the instability of a four-layer structure towards c doubling and puckering of the atoms out of the layers, which is applied to explain the ( pentagonal) orientational order.
Title:
Distribution of electric field gradients in decagonal quasicrystals
Authors:
Jeglic, P; Dolinsek, J
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 601-606 2006
Abstract:
We measured the orientation-dependent (AlNMR)-Al-27 spectra of a decagonal Al-Ni-Co quasicrystal. In order to explain the experimental results, we had to introduce a model for electric field gradients ( EFGs) in decagonal quasicrystals. The EFGs reflect the structure of quasicrystals. Therefore, from the comparison between the NMR results and the model EFGs we can test the atomic structure models of quasicrystals.
Title:
Tuning icosahedral quasicrystals and their approximants from the Mg2Zn11 structure
Authors:
Lin, Q; Corbett, JD
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 607-613 2006
Abstract:
Electronic tuning of Sc-Mg-Zn icosahedral quasicrystal ( i-QC) and approximant ( AC) phases was achieved according to pseudogap predictions from an electronic band structure analysis of Mg2Zn11. The i-QC and two AC phases were obtained in the Mg2-xScxZn11 system. The QC compositions are Sc10.8(6)Mg3.2(6)Zn86.0(2) and Sc14.6(4)Mg3.3(4)Zn82.1(2) by EDX for x = 1.0 and 1.5, respectively. X-ray structure determination reveals that the 1/1 AC, Sc3Mg0.18(1)Zn17.73(1), crystallizes in space group Im3, with a = 13.863( 2) angstrom. Electronic structure calculations on the 1/1 AC reveal that the Fermi level is located in the centre of the pseudogap, which appears to be greatly enhanced by Zn 4p and Sc 3d orbital mixing.
Title:
First-principles studies on orientational ordering of atomic clusters in Cd6Ca
Authors:
Nozawa, K; Ishii, Y
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 615-620 2006
Abstract:
First-principles structural optimizations are carried out for 1/1 cubic approximant Cd6Ca. Newly proposed structure by Gomez and Lidin is used as the starting structure for the structural optimizations. The optimized structure is more stable than the non-optimized one by several eV. Two structures, which are almost degenerate before the structural optimizations, are split by about 100meV per unit cell after the structural optimizations. Clusters are deformed to relax interatomic distances and most of the neighbouring Cd-Cd distances close to that of hcp-Cd. Relaxed structures of clusters depend on the structure of the innermost shells of adjacent clusters.
Title:
Ab initio reconstruction of p-type icosahedral Zn-Mg-Ho quasicrystal structures
Authors:
Takakura, H; Yamamoto, A; Sato, TJ; Tsai, AP; Ozawa, Y; Yasuda, N; Toriumi, K
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 621-627 2006
Abstract:
The six-dimensional ( 6D) low density elimination method ( LDEM) has been applied to solve the p-type icosahedral Zn75Mg16Ho9 quasicrystal. The reconstructed electron density distribution by the LDEM exhibits three large occupation domains ( ODs) centred at ( 0, 0, 0, 0, 0, 0), ( 1/2, 1/2, 1/2, 1/2, 1/2, 1/2), and ( 1/2, 0, 0, 0, 0, 0) in the 6D primitive unit cell, and the OD at ( 1/2, 1/2, 1/2, 1/2, 1/2, 1/2) contains Ho atoms, which mainly distribute around the threefold directions. A geometrical analysis confirms that a rhombic triacontahedron cluster which includes a Bergman-type cluster is a basic building unit of the structure.
Title:
>From harmonically modulated structures to quasicrystals
Authors:
Urban, G; Wolny, J
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 629-635 2006
Abstract:
A statistical approach was used for the modulated structures and some universal behaviours of probability distributions and their autocorrelation functions ( average Patterson functions) were found. This method was also used for the analysis of the Fibonacci chain regarded as a multi-q modulated structure.
Title:
Decorated 2D quasicrystals: structure factor for clusters and average Patterson analysis
Authors:
Wolny, J; Kozakowski, B; Dabrowska, A
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 637-643 2006
Abstract:
Covering the two-dimensional Penrose atomic structure with different kite clusters consisting of four, seven and 17 atoms is discussed. These clusters are compared to the well-known 33-atom Gummelt's cluster. The number and concentrations of different atoms decorating the clusters were found. An analytical formula for the structure factor of decorated clusters was derived by a statistical approach.
Title:
Recent results at the metal-insulator transition of icosahedral AIPdRe
Authors:
Rapp, O; Srinivas, V; Poon, SJ
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 655-661 2006
Abstract:
The metal-insulator transition, MIT, in icosahedral AlPdRe has been studied from measurements of magnetoresistance and conductivity. Results for the localisation length xi, the characteristic hopping temperature To and their relations at the MIT are discussed. The results indicate important similarities between i-AlPdRe and doped semiconductors.
Title:
Numerical evidence of backscattering in approximants of quasicrystals
Authors:
De Laissardiere, GT; Julien, JP; Mayou, D
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 663-669 2006
Abstract:
We compute the velocity correlation function of electronic states close to the Fermi energy, in approximants of quasicrystals. As we show, the long time value of this correlation function is small. This means a small Fermi velocity, in agreement with previous band structure studies. Furthermore, the correlation function is negative on a large time interval, which means a phenomenon of backscattering. As shown in previous studies, the backscattering can explain unusual conduction properties observed in these alloys, such as the increase of conductivity with disorder.
Title:
Kondo-like magnetic scattering in electrical transport of Al70-x BxPd(20)Mn(10) (x=0, 0.5, 1, 2 and 4) quasicrystals
Authors:
Jaiswal, A; Rawat, R; Lalla, NP
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 679-685 2006
Abstract:
The electrical conductivity and magnetization behaviour of single-phase Al70-xBxPd20Mn10 ( x = 0, 0.5, 1, 2 and 4) quasicrystals have been measured. We observe that boron substitution for aluminium causes large changes in the sigma vs. T behaviours. sigma vs. ( lnT)(-1) plots shows linear behaviour. Scaling was achieved by plotting {(sigma(T) - sigma(min))/(sigma(4) - sigma(min))} vs. [ ln( T/T-min)](-1). These samples show large positive magnetoresistance with H-2 behaviour. In the Al-B-Pd-Mn and Al-Pd-Mn quasicrystals, the observed sigma( T) behaviour has been explained using the weak localization theory, including Kondo-type spin-flip scattering and not due to spin-orbit scattering.
Title:
Electronic structure of leached Al-Cu-Fe quasicrystals used as catalysts
Authors:
Belin-Ferre, E; Fontaine, MF; Thirion, J; Kameoka, S; Tsai, AP; Dubois, JM
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 687-692 2006
Abstract:
We used X-ray emission spectroscopy to investigate the electronic structure of various catalysts obtained by leaching a quasicrystalline Al-Cu-Fe compound in 5% Na2CO3 aqueous solution. The study of Al states confirmed that Al is almost totally oxidized in the catalysts. Fe is not as much oxidized probably because it is embedded in Cu-Al2O3 grains. Cu is only partly oxidized. However, it is not excluded that the catalytic activity could be due to a size effect that prevents the formation of a band as in metallic Cu, and gives to the electronic structure an atomic-like character. New measurements should be done from fresh specimens in order avoid further oxidation interference with the Cu spectral distributions.
Title:
Non-icosahedral ordering of transition elements in Zn-TM-Sc quasicrystals
Authors:
Ishii, Y; Nozawa, K; Fujiwara, T
Source:
PHILOSOPHICAL MAGAZINE 86 (3-5): 693-699 2006
Abstract:
Icosahedral quasicrystals ( QC) are obtained in ternary Zn-M-Sc alloys with various kinds of third element M which may be substituted for Zn. Electronic structures of cubic approximants Zn-M-Sc with M Fe substituted for Zn at several sites are studied theoretically. It is found that the binding energies in a range of 7-9 eV per atom are gained by substitution of Fe. However, the energy difference is not sufficiently large to conclude selectivity of atomic sites for Fe substitution. The spin-polarized calculations do not suggest any signature of strong magnetism observed in the experiment. When Fe atoms occupy a pair of the sites at a very short distance, formation of the Fe complex induces further stabilization of the system.
Title:
Insulator-like electrical transport in Al65-xSixCu20Ru15 (x=0.0, 0.5, 1.0, 1.5, 2.0) icosahedral quasicrystals
Authors:
Jaiswal, A; Lalla, NP
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 701-707 2006
Abstract:
Low-temperature resistivity and magneto-resistance have been measured from 2.8 to 300 K for stable icosahedral quasicrystals Al65-xSixCu20Ru15 (x = 0.0, 0.5, 1.0, 1.5, 2.0). The low-temperature sigma-T behavior, in the temperature range 2.8-15 K, for the Si-substituted samples are drastically different from undoped samples. The in-field sigma-T for the Si-undoped sample has been found to follow ln sigma vs. T-1/4 below 5K, indicating that this sample lies in the insulating side of the metal-insulator (MI) transition. The substitution of silicon at the aluminum site drives the Al-Cu-Ru quasicrystals to the metallic side of MI transition.
Title:
Atomic structure and electron transport properties of the Al-Pd-Mn-Re-Si 1/1-cubic approximant
Authors:
Takeuchi, T
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 709-716 2006
Abstract:
The formation area of the Al-Pd-Mn-Re-Si 1/1-cubic approximant (1/1-AC) was determined by partially substituting Re for Mn in the Al-Pd-Mn-Si 1/1-AC. It was found that the Al-Pd-Mn-Re-Si 1/1-AC is stabilized at compositions expressed by the formula Al67-0.125xPd11+0.375xMn14-1.25xRexSi8 with Re concentration x < 5 at. %. Synchrotron radiation Rietveld analysis was performed on the approximants to investigate the mechanism determining the formation range of the 1/1-AC. Re atoms were found not to be substituting for all Mn atoms but only those in limited sites. This selection rule for the Re substitution is caused by the 10% larger atomic radius of Re than that of Mn. The importance of the size effect of the constituent elements is strongly suggested for stabilizing quasicrystals and approximants.
Title:
Negative valence of Mn in i-Al-Pd-Mn quasicrystals
Authors:
Zijlstra, ES; Bose, SK
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 717-723 2006
Abstract:
The electronic structure of a modified version of the Quandt-Elser model of i-Al70.8Pd21.5Mn7.7 is studied by the full-potential linearized augmented plane wave method. Inspection of the electronic charge density and an analysis based on Bader's concept of atoms in a molecule reveal a charge transfer from the Al atoms to Mn. It is argued that this charge transfer is responsible for the negative valence of Mn in i-Al-Pd-Mn quasicrystals.
Title:
Systematic study of magnetic properties in Zn-based Tsai-type icosahedral quasicrystals and their approximant
Authors:
Kashimoto, S; Motomura, S; Francoual, S; Matsuo, S; Ishimasa, T
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 725-732 2006
Abstract:
We have investigated the magnetic properties of Zn-based Tsai-type icosahedral quasicrystals (i-QCs) and their approximants by measuring the field-and temperature-dependence of magnetization. The quasicrystals are formed by an addition of the third element M (M = Mg, Mn, Fe, Co, Ni, Cu, Pd, Ag, Pt or Au) to a Zn17Sc3 1/1 cubic approximant crystal. The remarkable feature of the Zn-M-Sc series is a variety of the additional M elements ranging from light metal Mg and 3d transition metals to noble metals. The experimental results obviously show that the i-QCs containing 3d transition metals (M = Mn, Fe, Co or Ni) have the local magnetic moment formation. We also confirmed appearance of Curie-Weiss paramagnetism for a Zn82Fe3Sc15 1/1 cubic approximant crystal. The present results indicate that the divalent Zn of major component in the present i-QCs and approximants may be favourable for the moment formation of iron group elements in contrast with the case of the trivale! nt Al-based i-QCs such as Al-Cu-Fe.
Title:
Interplay between magnetic and spatial order in quasicrystals
Authors:
Vedmedenko, EY; Grimm, U; Wiesendanger, R
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 733-739 2006
Abstract:
The stable magnetization configurations of antiferromagnets on quasiperiodic tilings are investigated theoretically. The exchange coupling is assumed to decrease exponentially with the distance between magnetic moments. It is demonstrated that the combination of geometric frustration and the quasiperiodic order of atoms leads to complicated non-collinear ground states. The structure can be divided into subtilings of different energies. The symmetry of the subtilings depends on the quasiperiodic order of magnetic moments. The subtilings are spatially ordered. However, the magnetic ordering of the subtilings in general does not correspond to their spatial arrangements. While subtilings of low energy are magnetically ordered, those of high energy can be completely disordered due to local magnetic frustration.
Title:
Electron localization and conduction mechanisms of metallic Al-Pd-Re quasicrystals
Authors:
Akiyama, T; Takagiwa, Y; Kanazawa, I
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 747-752 2006
Abstract:
We have analysed the electrical conductivities of metallic Al-Pd-Re quasicrystals in a low temperature region, taking into account the conducting mechanism of the quasicrystal-like system. The present analysis suggests that not only the weak localization and the electron-electron interaction contributions but also the conducting effect of the quasicrystal-like system should be considered.
Title:
Effective potentials for quasicrystals from ab-initio data
Authors:
Brommer, P; Gahler, F
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 753-758 2006
Abstract:
Classical effective potentials are indispensable for any large-scale atomistic simulations, and the relevance of simulation results crucially depends on the quality of the potentials used. For complex alloys such as quasicrystals, however, realistic effective potentials are almost non-existent. We report here our efforts to develop effective potentials especially for quasicrystalline alloy systems. We use the so-called force-matching method, in which the potential parameters are adapted so as to reproduce the forces and energies optimally in a set of suitably chosen reference configurations. These reference data are calculated with ab-initio methods. As a first application, embedded-atom method potentials for decagonal Al-Ni-Co, icosahedral Ca-Cd, and both icosahedral and decagonal Mg-Zn quasicrystals have been constructed. The influence of the potential range and degree of specialization on the accuracy and other properties is discussed and compared.
Title:
Electronic transport in multidimensional Fibonacci lattices
Authors:
Sanchez, V; Wang, C
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 765-771 2006
Abstract:
In this article, the Kubo-Greenwood formula is used to investigate the electronic transport behaviour in macroscopic systems by means of an exact renormalization method. The convolution technique is employed in the analysis of two-dimensional Fibonacci lattices. The dc electrical conductance spectra of multidimensional systems exhibit a quantized behaviour when the electric field is applied along a periodically arranged atomic direction, and it becomes a devil's stair if the perpendicular subspace of the system is quasiperiodic. The spectrally averaged conductance shows a power-law decay as the system length grows, neither constant as in periodic systems nor exponential decays occurred in randomly disordered lattices, revealing the critical localization nature of the eigenstates in quasicrystals. Finally, the ac conductance along periodic and quasiperiodic directions is compared with the optical conductivity measured in decagonal quasicrystals.
Title:
Scanning tunnelling microscopy with atomic resolution on the twofold surface of the icosahedral AlPdMn quasicrystal
Authors:
Groning, O; Widmer, R; Ruffieux, P; Groning, P
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 773-779 2006
Abstract:
We have investigated the 2-fold surface of an icosahedral Al70Pd21Mn9 quasicrystal by means of low-temperature scanning tunnelling microscopy (77 K). The sequence of the terrace step edge heights revealed a Fibonacci sequence with S = 2.40 angstrom and L = tau S 3.88 angstrom as fundamental terrace step heights. S and L can be related to the pentagon edge length of the below terrace Bergman polytope and the surface dissected Bergman polytope of the 5-fold surface. The atomic resolution STM images of the 2-fold surface have been compared to the M-model structure of the i-AlPdMn and the experimental STM surface structure of the 5-fold surface by analysis of the FFT spots. We could show that the positions of the FFT spots in the 2-fold surface are related to the FFT spots of the 5-fold surface by projections onto the fivefold axis and are in good correspondence to the model structure. We identified characteristic rectangular features on the 2-fold surface with edge length of 4.8, 7.7 and 12.6 angstrom corresponding to D2, tau D-2 and tau(2)D(2) with D-2 being the pentagon edge length of the surface dissected Bergman polytope. We interpret our results as being a strong indication for the bulk termination of the 2-fold surface of the i-AlPdMn quasicrystal.
Title:
Low-temperature scanning tunneling spectroscopy on the 5-fold surface of the icosahedral AlPdMn quasicrystal
Authors:
Widmer, R; Groning, O; Ruffieux, P; Groning, P
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 781-787 2006
Abstract:
We report on scanning tunneling spectroscopy investigations at low temperature (5.3 K) on a bare 5-fold surface of an icosahedral Al70Pd21Mn9 quasicrystal. By averaging tunneling spectra recorded over several nm(2) we could reproduce the typical line shape observed in point contact spectroscopy on oxidized surfaces. The averaged spectra show a large parabolic gap structure with a sharp dip of 20 meV FWHM at the Fermi energy. Whereas the averaged spectrum is relatively smooth and featureless, with exception of the sharp dip structure, the individual spectra show a rich structure of peaks and gaps. The distribution of the peak positions in energy shows a clear asymmetry between the occupied and the unoccupied states, in the sense that the peaks are mainly situated above the Fermi energy. The FWHM of these peaks is typically between 30 meV and 100 meV. The spectral features vary rapidly with tip position, where the spatial extent of a given peak in the spectrum is of the order of 0.5-1 nm. To the best of our knowledge, we will present for the first time LT-STS data in combination with high resolution STM images of a quasicrystalline surface to demonstrate the localization of electronic states and gaps and the asymmetry between the occupied and the unoccupied local density of states.
Title:
Tunneling spectroscopy and high electrical resistivity in quasicrystalline alloys
Authors:
Delahaye, J; Schaub, T; Berger, C
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 789-796 2006
Abstract:
We report on a scanning tunneling spectroscopy investigation at low temperature on oxidized surfaces of highly resistive icosahedral AlPdMn, AlCuFe and AlPdRe phases. The tunneling conductance is found to vary significantly as a function of the scanning tunneling microscope tip location on the surface. A common feature of our quasicrystalline samples is the presence of a zero bias dip, with square root voltage dependence from 5 mV to 300 mV. This is indicative that the one electron density of states has a square root singularity at the Fermi level. More generally, we discuss how tunneling spectroscopy can be used to determine the electronic density of states and its limitation for our quasicrystalline alloys.
Title:
Surface energy of complex - and simple - metallic compounds as derived from friction test in vacuum
Authors:
Dubois, JM; De Weerd, MC; Brenner, J; Sales, M; Mozdzen, G; Merstallinger, A; Belin-Ferre, E
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 797-805 2006
Abstract:
This article attempts to understand better the origin of low friction and zero solid-solid adhesion observed on quasicrystals placed in vacuum. We present an ensemble of experimental data that allows us on the one hand to estimate the true surface energy of unoxidized quasicrystals and approximants and on the other hand to point out a correlation with electronic densities of states.
Title:
Terrace-dependent morphology of thin Sn films deposited on the fivefold surface of the icosahedral Al-Cu-Fe quasicrystal
Authors:
Sharma, HR; Shimoda, M; Ross, AR; LoGrasso, TA; Tsai, AP
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 807-812 2006
Abstract:
We present an analysis of Sn film growth on the fivefold surface of the icosahedral Al-Cu-Fe quasicrystal at multilayer coverage. Scanning tunnelling microscopy of the Sn-deposited surface revealed that film morphology differed from terrace to terrace. Most terraces exhibited flat-topped clusters with preferential growth at the step edges, while a minority of terraces showed a smooth film. The height, lateral size and density of clusters also varied between terraces. Clusters have a preference for specific heights.
Title:
Local configurations on surfaces of icosahedral quasicrystals
Authors:
Kasner, G; Papadopolos, Z
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 813-818 2006
Abstract:
The surfaces of icosahedral quasicrystals of an F-phase, orthogonal to a fivefold symmetry axis have a terrace-like appearance. On highly resolved images of these terraces one observes different local configurations. We search for possible corresponding configurations in the bulk model of atomic positions. M based on the icosahedral tiling J*((2F)).
Title:
Voids and pits on sputter-annealed fivefold terraces of icosahedral Al-Pd-Mn quasicrystals
Authors:
Unal, B; LoGrasso, TA; Ross, AR; Jenks, CJ; Thiel, PA
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 819-824 2006
Abstract:
Our scanning tunneling microscope studies on clean surfaces of fivefold icosahedral Al70.2Pd20.7Mn9.1 reveal that, after annealing at 900 K, two types of. at depressions are visible on terraces: voids (small, shallow,. flat-bottomed depressions bordered by 2.5 angstrom steps) and pits (deeper, and often larger, depressions). They are different not only in their dimensions but in their behavior: voids preferentially nucleate on some of the terraces and, after annealing at 925 K, their coalescence and growth leads a new type of termination to be exposed. Pits, however, do not destroy the terraces on which they exist, under the experimental conditions. At the bottom of 4.1 angstrom-deep pits, 2.5 angstrom-deep voids nucleate, so that the total depth of the pit is 6.6 angstrom. We propose that 2.5 angstrom void-rich terraces are metastable terminations, and that these metastable terminations are also exposed at the bottom of the 4.1 angstrom-deep pits.
Title:
Ab-initio study of a quasiperiodic Bi monolayer on a fivefold icosahedral Al-Pd-Mn surface
Authors:
Krajci, M; Hafner, J
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 825-830 2006
Abstract:
The structure and stability of a quasiperiodic Bi monolayer formed on five-fold surface of an icosahedral Al-Pd-Mn quasicrystal have been investigated using ab-initio density-functional methods. The structural model of the adsorbed monolayer has been constructed on the basis of a mapping of the potential-energy landscape of an isolated adatom on the fivefold surface icosahedral Al-Pd-Mn. This leads to a structural model of the quasiperiodic adlayer with atoms at the vertices and midedge positions of the P1 tiling. The internal decoration of the tiles is enforced by the decoration of the circumference of the tiles.
Title:
Hydrogen interactions with quasicrystalline Al-Pd-Mn surfaces
Authors:
Bastasz, R; Whaley, JA; Lograsso, TA; Jenks, CJ
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 855-862 2006
Abstract:
In this work we examine the interaction of molecular and atomic deuterium with the fivefold surface of an icosahedral (i-) Al-Pd-Mn alloy using angle-resolved low-energy ion scattering under ultrahigh vacuum conditions. i-Al-Pd-Mn has been studied extensively and is known to form a laterally-bulk-terminated surface that is Al-rich. The density of Al atoms on the clean surface of fivefold i-Al-Pd-Mn is about that of Al(111) and hence we compare our results to studies of molecular and atomic hydrogen adsorbed on Al(111). We. nd that molecular deuterium does not adsorb or dissociate on i-Al-Pd-Mn, as on Al(111). Atomic D, however, readily adsorbs on both surfaces and on i-Al-Pd-Mn attenuates the scattering signals from Al, Pd and Mn substrate atoms. It thus appears that D chemisorbs on the outer layer of i-Al-Pd-Mn and bonds with Al atoms.
Title:
The ordering of a Xe monolayer on quasicrystalline Al-Ni-Co
Authors:
Diehl, RD; Ferralis, N; Pussi, K; Cole, MW; Setyawan, W; Curtarolo, S
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 863-868 2006
Abstract:
The ordering of physically adsorbed gases on quasicrystalline surfaces exemplifies the effects of competing interactions. In this study, grand canonical Monte Carlo simulations were performed to complement experimental measurements of the ordering of Xe adsorbed on the tenfold surface of decagonal Al-Ni-Co. The simulations employed a semi-empirical gas-surface interaction, based on conventional combining rules, and the Lennard-Jones Xe-Xe interaction. The simulation results are consistent with the experiment and provide a new insight into the ordering behavior. The film initially has a fivefold quasicrystalline symmetry, but it evolves into a close-packed structure during adsorption of the second layer. The presence of symmetry defects in the sixfold structure creates domains of Xe having different ( but equivalent) rotational epitaxy, suggesting that even in the absence of substrate defects, the annealed film has the five different rotational alignments observed in th! e experimental studies.
Title:
Adsorption of benzene on the five-fold surface of the i-Al70Pd21Mn9 quasicrystal
Authors:
Hoeft, JT; Ledieu, J; Haq, S; Lograsso, TA; Ross, AR; McGrath, R
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 869-874 2006
Abstract:
The adsorption behaviour of benzene (C6H6) on the five-fold surface of the icosahedral Al70Pd21Mn9 quasicrystal has been investigated. Reflection absorption infrared spectroscopy (RAIRS) data taken at a temperature of 92 K indicate molecular adsorption. The adsorption geometry of the molecules is found to change from parallel to the surface to oblique geometries as the dose is increased from monolayer to multilayer coverages. Scanning tunnelling microscopy (STM) images show that the molecules adsorb in a disordered fashion. The adsorbate layer is found to completely desorb at 153 K leaving the substrate unchanged.
Title:
Tilings, tiling spaces and topology
Authors:
Sadun, L
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 875-881 2006
Abstract:
To understand on aperiodic tiling (or a quasicrystal modeled on an aperiodic tiling), we construct a space of similar tilings, on which the group of translations acts naturally. This space is then an (abstract) dynamical system. Dynamical properties of the space (such as mixing, or the spectrum of the translation operator) are closely related to bulk properties of individual tilings ( such as the diffraction pattern). The topology of the space of tilings, particularly the Cech cohomology, gives information on how original tiling may be deformed. Tiling spaces can be constructed as inverse limits of branched manifolds.
Title:
Quantum dynamical properties of quasicrystals
Authors:
Damanik, D
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 883-888 2006
Abstract:
We discuss the dynamics of a quantum particle in quasi-crystalline environments. Detailed results are presented for the particular case of the Fibonacci sequence. This example exhibits anomalous transport at suffciently large coupling.
Title:
An extinction rule for a class of 1D quasicrystals
Authors:
Buczek, P; Wolny, J
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 889-894 2006
Abstract:
We study decorated one-dimensional quasicrystals obtained by a non-standard projection of a part of two-dimensional lattice. We focus on the impact of varying relative positions of decorated sites. First we give a general expression for the structure factor. Subsequently we analyse an example of an extinction rule.
Title:
Discrete quasiperiodic sets with predefined covering cluster
Authors:
Cotfas, N
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 895-900 2006
Abstract:
Some of the most remarkable tilings and discrete quasiperiodic sets used in quasicrystal physics can be obtained by using strip projection method in a superspace of dimension four, five or six, and the projection of a unit hypercube as a window of selection. We present some mathematical results which allow one to use this very elegant method in superspaces of dimension much higher, and to generate discrete quasiperiodic sets with a more complicated local structure by starting from the corresponding covering cluster. Hundreds of points of these sets can be obtained in only a few minutes by using our computer programs.
Title:
Substitutional structures in simply and multiconnected flat spaces, with astrophysical applications
Authors:
Escudero, JG
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 901-907 2006
Abstract:
Hexagonal, octagonal and dodecagonal tilings of both simply and multiconnected. at spaces in two dimensions are considered. The tessellations of the Euclidean plane have, in common, arrowed prototiles, which are used for the construction of fundamental polygons for the. at torus and the Klein bottle. Nondeterministic derivations in formal grammars, producing non-periodic ordered structures, have been introduced recently also for the analysis of variable stars with multiple periods, like the semiregular star UW Her and the delta-Scuti star V784 Cas. Observations of the V346 Ori light curve can be modelled with similar techniques.
Title:
Band structure, density waves and symmetries of aperiodic crystals
Authors:
Huesman, JF; Rabson, DA
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 909-914 2006
Abstract:
There are three types of invariants in crystals. The first two, corresponding to electronic degeneracies, are well known, but the third is novel, realized in incommensurate crystals of non-minimal rank. Since the first two invariants have consequences in band structure, it is natural to look there for the third type as well. Rather than developing an atomic or tiling model with the third type of symmetry, we introduce a tight-binding approach based on a density-wave pattern, which is easy to generate from the Rokhsar-Wright-Mermin phase functions.
Title:
Quasicrystals and model sets on substitution point sets
Authors:
Lee, JY
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 915-920 2006
Abstract:
The typical property of a quasicrystal is that it lacks periodic order but its diffraction pattern has a strong component of Bragg peaks. We consider the diffraction pattern consisting purely of Bragg peaks and call it pure point diffraction. It has been known that any regular model sets are pure point diffractive. But the converse has been a conjecture. Here we show that in substitution point sets, the sets are pure point diffractive if and only if they are model sets.
Title:
Limit-quasiperiodic Ammann bars and two-dimensional limit-quasiperiodic structures
Authors:
Niizeki, K
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 921-926 2006
Abstract:
Five octagonal limit-quasiperiodic tilings ( octagonal limit-quasiperiodic lattices) are constructed with the grid method on the basis of limit-quasiperiodic Ammann bar grids. They are self-similar with scaling ratio 2 + root 2. They belong to different locally-isomorphic classes but are mutually-locally derivable from each other. Each of them can be represented as a section of a four-dimensional limit-periodic structure with polygonal atomic surfaces.
Title:
Phenomenological study of quasicrystals as thermoelectric materials
Authors:
Macia, E
Source:
PHILOSOPHICAL MAGAZINE 86 (6-8): 927-933 2006
Abstract:
In this work we review the physical motivations, both experimental and theoretical, suggesting the possible use of quasicrystals as thermoelectric materials. Analytical expressions for the dimensionless thermoelectric figure of merit and the compatibility factor are discussed in order to optimize the thermoelectric performance of quasicrystals and their approximants. The potential of AlPd(Mn, Re) family is analysed within the context of current thermoelectric materials research.

Update: 28-Jan-2006

Title:
Nuclear-magnetic-resonance evidence for charge inhomogeneity in stripe ordered La1.8-xEu0.2SrxCuO4
Authors:
Grafe, HJ; Curro, NJ; Hucker, M; Buchner, B
Source:
PHYSICAL REVIEW LETTERS, 96 (1): Art. No. 017002 JAN 13 2006
Abstract:
We report O-17 nuclear-magnetic-resonance (NMR) results in the stripe ordered La1.8-xEu0.2SrxCuO4 system. Below a temperature T(q)similar to 80 K, the local electric field gradient and the absolute intensity of the NMR signal of the planar O site exhibit a dramatic decrease. We interpret these results as microscopic evidence for a spatially inhomogeneous charge distribution, where the NMR signal from O sites in the domain walls of the spin density modulation are wiped out due to large hyperfine fields, and the remaining signal arises from the intervening Mott insulating regions.
Title:
Structural characterization of electrodeposited nanophase Ni-Cu alloys
Authors:
Ghosh, SK; Grover, AK; Dey, GK; Kulkarni, UD; Dusane, RO; Suri, AK; Banerjee, S
Source:
JOURNAL OF MATERIALS RESEARCH, 21 (1): 45-61 JAN 2006
Abstract:
An investigation of Ni-Cu alloys electrodeposited from aqueous bath, using both direct current (dc) and pulsed current (pc) deposition techniques, has revealed many interesting features: A modulated structure with typical layer thickness of 90 and 75 nm of copper-rich and nickel-rich layers, respectively, is formed in dc plating. A surprising observation was that the modulation direction was parallel to the substrate, unlike in the case of artificial multilayers wherein it is along the growth direction. No such compositional modulations were observed in pc-plating in the present work. Spinodal phase separation, accompanied by L1(0) ordering, was found to have occurred in the as deposited samples in both the cases. The size of the deposited crystals in both the cases has been found to be in the range of 2.5-30 nm. Detailed high-resolution transmission electron microscopy has shown that the atomic arrangements are nearly perfect right upto the boundaries of the nanosiz! ed grains.
Title:
Magnetic, electrical and thermal transport properties of Al-Cr-Fe approximant phases
Authors:
Bihar, Z; Bilusic, A; Lukatela, J; Smontara, A; Jeglic, P; McGuiness, PJ; Dolinsek, J; Jaglicic, Z; Janovec, J; Demange, V; Dubois, JM
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 407 (1-2): 65-73 JAN 5 2006
Abstract:
Two stable approximant phases in the Al-Cr-Fe system - a gamma-brass phase (gamma-AlCrFe) and a mixture of two orthorhombic approximants of the decagonal phase (O-1/O-2-AlCrFe) - were investigated using magnetic susceptibility, electrical resistivity and thermal conductivity measurements, combined with structural investigations using X-ray diffraction, light microscopy (LM) and scanning electron microscopy (SEM). The investigated approximants exhibit physical properties that are in many respects between those of regular metals and quasicrystals (QCs); their electrical resistivities show very weak temperature dependences and the resistivity values are higher than for regular metals and lower than for Al-based QCs. The magnetic susceptibility results show the existence of a small fraction (of about 1% for the gamma-AlCrFe and about 10 times less for the O-1/O-2-AlCrFe) of localized magnetic moments with Curie-like temperature dependence. Thermal conductivity measurements show that the electronic and lattice contributions are of comparable size at room temperature. While the electronic contribution can be described by the Wiedemann-Franz law, the lattice contribution can be reproduced by the sum of the Debye term (long-wavelength phonons) and the term due to hopping of localized vibrations. At the lowest measured temperature (8 K), scattering of phonons on stacking-fault-like defects limits the heat transport, and this type of defect has also been observed in the LM and SEM structural investigations. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Trigonal Ir9Al28, a new structure type and approximant to decagonal quasicrystals
Authors:
Katrych, S; Gramlich, V; Steurer, W
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 407 (1-2): 132-140 JAN 5 2006
Abstract:
During an investigation of the binary system Al-Ir, a new phase with composition Ir9Al28 was identified. After annealing at 780 degrees C, its structure was determined by single-crystal X-ray diffraction. Trigonal Ir9Al28 is the first representative of a new structure type with Pearson symbol hP236-14, a = b = 12.2864(4) angstrom, c= 27.341(1) angstrom, gamma = 120 degrees, space group P31c, no. 159. The crystal structure can be described likewise as stacking of eight puckered and flat layers with a sequence... P(0)PFpp(0)p(i)F(i)P(i)... along [001], as a six-layer stacking sequence along [100], or as packing of pseudo-Mackay icosahedra. The Ir substructure with pseudosymmetry P6(3)/mmc resembles the V4Al23 Structure type. Pentagonal columnar clusters running along [001] show close resemblance to decagonal quasicrystals with six-layer period along the 10-fold axis. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Conduction and optical effects in the plastic charge-density waves
Authors:
Ogawa, N; Miyano, K; Brazovskii, S
Source:
JOURNAL DE PHYSIQUE IV, 131: 123-124 DEC 2005
Abstract:
The creep motion of the charge-density wave (CDW) and its modulation throught optical excitation in the low-temperature state of K0.3MoO3 are analyzed in terms of a local pinning-theory, in which local metastable states created by pinning-induced phase dislocations are considered. The nonlinear I-V curve below the sliding threshold field (V-s) can be well reproduced with a numerical calculation, and it is shown that photoexcitation increases the transition probability of phase slips, which promotes the creep motion, and also leads to it relaxation of the phase strain.
Title:
Effect of commensurability on the CDW deformation near a point contact
Authors:
Sinchenko, AA; Pokrovskii, VY
Source:
JOURNAL DE PHYSIQUE IV, 131: 227-229 DEC 2005
Abstract:
The results of investigation of normal metal(Cu, Au)-CDW (K0.3MoO3) point-contacts (CS) in a wide range of temperature are reported. At T > 80 K the contact characteristics are adequately described by the semiconducting model of CDW.At T < 70 K the l - V characteristics of PCs Cu-K0.3MoO3 demonstrate a strain-compress asymmetry of the CDW. The observed behavior is likely to reveal the lock-in transition (incommensurate commensurate) due to the elcctric-field induced strain of the CDW.
Title:
Origin of incommensurate spin modulation in La2-xSrxCuO4
Authors:
Mitsen, KV; Ivanenko, OM
Source:
JETP LETTERS, 82 (9): 580-585 2005
Abstract:
A model for explaining incommensurate spin modulation observed in La2 - xSrxCuO4 is proposed without assuming stripe formation. In this model, all features of the observed spin textures in the entire doping range are associated only with the geometrical relations for the square lattice and with the competition between various forms of ordering of Sr ions. (c) 2005 Pleiades Publishing, Inc.
Title:
Parent of misfit-layered cobalt oxides: [Sr2O2](q)CoO2
Authors:
Yamauchi, H; Sakai, K; Nagai, T; Matsui, Y; Karppinen, M
Source:
CHEMISTRY OF MATERIALS, 18 (1): 155-158 JAN 10 2006
Abstract:
Misfit-layered (ML) cobalt oxides of the general formula of [M(m)A(2)O(m+2)](q)CoO2 have been proven to be efficient thermoelectric materials because the structure is capable in accommodating the two seemingly contradictory characteristics of high electrical conductivity and large thermoelectric power. They are also potential hosts for other oxymoron-like functions. The known phases all contain one or two square-planar MO (M = Co, Bi, Pb, Tl, etc.) layers sandwiched together with two AO (A = Ca, Sr, Ba, etc.) planes of square symmetry between two adjacent CoO2 layers of hexagonal symmetry.. Here, we report the realization of the simplest (m = 0) ML phase forming in the Sr-Co-O system with the cation ratio Sr/Co = 1. Atomic-resolution transmission electron microscopy (TEM) imaging confirms for the new phase the parent three-layer crystal structure, SrO-SrO-CoO2, which is compatible with the formula of [Sr2O2](q)CoO2. Electron diffraction reveals that the phase is rather commensurate, i.e. the "misfit parameter" q is 0.5. Nevertheless, in terms of the transport-property characteristics, the new ML parent is comparable to its earlier-established and more-complex derivatives.

Update: 20-Jan-2006

Title:
Developments on methods of solving crystal structures
Authors:
Fan, HF
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 6 (7): 722-724 OCT 2005
Abstract:
Methods tackling the phase problem in diffraction analysis under various circumstances have been studied in the Institute of Physics in Beijing. Brief description on the development of phasing methods for solving aperiodic crystal structures, image processing in high-resolution electron microscopy and in high-throughput structure determination of proteins will be given. (c) 2005 Elsevier Ltd. All rights reserved.
Title:
Atomic occupancy preference of Ga and Ti and its effect on the Mn spin arrangements in YMn6Sn6: Evidence from Sn-119 Mossbauer spectroscopy
Authors:
Cheng, ZH; Kou, ZQ; Zhang, SY; Zhao, P; Di, NL; Shen, BG; Dunlap, RA; Yang, JB
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 6 (7): 778-783 OCT 2005
Abstract:
The effects of Ga and Ti substitutions for Sn on the Mn spin arrangements in the YMn6Sn6 compound have been investigated by means of X-ray diffraction (XRD), magnetization measurement and Mossbauer spectroscopy. XRD refinement indicates that Ga and Ti atoms prefer to occupy 2d and 2e sites, respectively. Mossbauer spectra indicate incommensurate magnetic structures for the YMn6Sn6, YMn6Sn5.4Ga0.6 and YMn6Sn5.4Ti0.6 compounds. The substitution of Ga for Sn at the 2d sites is found to significantly decrease the turn angle in the Mn-Sn-3-Sn-2-, Sn-3-Mn layer and to subsequently increase the net magnetization. On the other hand, the substitution of Ti for Sn at 2e sites increases the turn angles in the Mn-(Y,Sn-1)-Mn and Mn-Sn-3-Sn-2-Sn-3-Mn layers, and consequently decreases the exchange coupling of Mn-Mn between different layers. The resulting ferromagnetic and ferrimagnetic behavior, as has been observed for YMn6Sn5.4Ga0.6 and YMn6Sn5.4Ti0.6, respectively, can be explained in terms of these spin interactions. (c) 2005 Elsevier Ltd. All rights reserved.
Title:
Sr-87 NMR of phase transitions in (SrTiO3)-O-16 and (SrTiO3)-O-18
Authors:
Laguta, VV; Blinc, R; Itoh, M; Seliger, J; Zalar, B
Source:
PHYSICAL REVIEW B, 72 (21): Art. No. 214117 DEC 2005
Abstract:
Sr-87 quadrupole perturbed NMR data of SrTiO3 show that local symmetry breaking takes place also at the A site of the ABO(3) perovskite lattice in the cubic phase and not only at the B site as observed before. This is true for (SrTiO3)-O-16 (STO-16) and (SrTiO3)-O-18 (STO-18). The onset of the antiferrodistortive transition around T-a=105 K is accompanied by a huge splitting of the Sr-87 NMR line due to formation of macroscopic 90 degrees domains and an anomalous shortening of the spin-spin relaxation time T-2 of the quadrupole satellite transitions which persist in the tetragonal phase down to 30 K. This shows the presence of very low frequency fluctuations of the phase transition order parameter. Rhombohedral polar clusters appear in the tetragonal matrix both in STO-16 and STO-18 below 70 K and percolate in STO-18 below T approximate to 24 K leading to an inhomogeneous ferroelectric state. This is also supported by measurements of the field cooled Sr-87 ! NMR spectra.
Title:
Spin-dynamics simulation study of the field-induced phase transition for the spiral antiferromagnet Ba2CuGe2O7
Authors:
An, R; Wang, XP; Zhou, L
Source:
PHYSICAL REVIEW B, 72 (21): Art. No. 214422 DEC 2005
Abstract:
We perform spin-dynamics (SD) simulations to study the field induced incommensurate-to-commensurate phase transition for the spiral antiferromagnet Ba2CuGe2O7. Under an increasingly applied magnetic field, we find that the system undergoes a transition from a two-dimensional (2D) spiral state to a spin-flop state, passing through an intermediate phase. The simulations identify two order parameters to characterize this phase transition, of which one is the spiral period known previously, another is the root-mean-square value of a spin component. For the 2D spiral phase identified previously, our SD simulations yield essentially the same spin structures as previous continuum-field model studies when the applied field is very small, but quantitative differences exist when the field is not small. For the intermediate phase which was not fully understood by previous studies, our simulations reveal that its spin structure is a soliton-like state consisting of two spin-flop states connected by a three-dimensional spiral state.
Title:
Atomic scale coexistence of periodic and quasiperiodic order in a 2-fold Al-Ni-Co decagonal quasicrystal surface
Authors:
Park, JY; Ogletree, DF; Salmeron, M; Ribeiro, RA; Canfield, PC; Jenks, CJ; Thiel, PA
Source:
PHYSICAL REVIEW B, 72 (22): Art. No. 220201 DEC 2005
Abstract:
Decagonal quasicrystals are made of pairs of atomic planes with pentagonal symmetry periodically stacked along a 10-fold axis. We have investigated the atomic structure of the 2-fold surface of a decagonal Al-Ni-Co quasicrystal using scanning tunneling microscopy. The surface consists of terraces separated by steps of heights 1.9, 4.7, 7.8, and 12.6 angstrom containing rows of atoms parallel to the 10-fold direction with an internal periodicity of 4 angstrom. The rows are arranged aperiodically, with separations that follow a Fibonacci sequence and inflation symmetry. The results indicate that the surfaces are preferentially Al-terminated and in general agreement with bulk models.
Title:
Anticorrelation between ferromagnetism and ferroelectricity in perovskite manganites
Authors:
Goto, T; Yamasaki, Y; Watanabe, H; Kimura, T; Tokura, Y
Source:
PHYSICAL REVIEW B, 72 (22): Art. No. 220403 DEC 2005
Abstract:
Magnetic and dielectric properties have been investigated for a mixed-crystal system Tb1-xGdxMnO3 in between TbMnO3 with ferroelectric and incommensurate antiferromagnetic (AFM) orders and GdMnO3 with paraelectric and canted AFM (weakly ferromagnetic) states, as functions of x, temperature T, and magnetic field B applied along the c axis. A systematic study on the magnetic and electric phase diagrams in the x-T, B-T, and x-B planes has revealed important interplay between Mn d-electron spins and Gd f-electron moments. A clear anticorrelation between the (weak) ferromagnetism and the ferroelectricity is observed near the phase boundaries.
Title:
Transmission electron microscopy observations on Cu-Ti alloy systems
Authors:
Nishio, R; Konno, TJ; Semboshi, S
Source:
NEW FRONTIERS OF PROCESSING AND ENGINEERING IN ADVANCED MATERIALS, 502: 163-168 2005 Book series title: MATERIALS SCIENCE FORUM
Abstract:
Phase separation behaviors of a quenched Cu-3.0at%Ti alloy, as well as crystallographic structures of Cu-20.7at%Ti alloy have been studied using transmission electron microscopy. The furnace-cooled Cu-20.7at%Ti alloy are composed of alpha-Cu4Ti (Ni4Mo-type) and beta-Cu4Ti (Au4Zr-type) with the orientation relationship of (011)(alpha)//(110)(beta), [100](alpha)//[001](beta). As-quenched Cu-3.Oat%Ti alloy showed a modulated structure with the modulation length of about 4 nm. When aged at 723K for 8 hr, the alpha-Cu4Ti phase emerges within the modulated or tweed-like microstructure. Prolonged aging results in the growth of the alpha-Cu4Ti particles and the loss of coherency. It is likely that as-quenched Cu3.0at%Ti alloy decomposes spinodally at 723K, followed by polymorphous ordering; though the present study did not exclude, as an alternative path, a decomposition mechanism based on the catastrophic nucleation.
Title:
Light figure studies of optical anisotropy induced by nanoscale spatial modulation in TlInS2
Authors:
Shim, YG; Uneme, N; Abdullayeva, S; Mamedov, N; Yamamoto, N
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 66 (11): 2116-2118 NOV 2005
Abstract:
The incommensurate material, T1InS(2), with layer structure was studied by light figure spectroscopy techniques in spectral range 400-700 nm in temperature interval 80-350 K. Evolution of light figures with temperature in phase transition region was reliably established. The optic angle of T1InS(2) was found to be sample-dependent with essentially two types of critical behavior with temperature; peak-like behavior that was ascribed to a pure incommensurate phase and peak-free behavior that was attributed to the influence of the domains or defects. In latter case the samples showed symmetry forbidden rotation of optic plane with temperature. As a whole, the obtained results allow for a conclusion that incommensurate spatial modulation with correlation length at the nanoscale was contributing to biaxial anisotropy of T1InS(2) to a level of 10(-3) versus 10(-4) for basic lattice. (c) 2005 Elsevier Ltd. All rights reserved.
Title:
Distribution of Fe3+ in a synthetic (Ca,Na)(2)(Mg,Fe3+)Si2O7-melilite: Fe-57 Mossbauer and X-ray Rietveld studies
Authors:
Akasaka, M; Nagashima, M; Makino, K; Ohashi, H
Source:
JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES, 100 (6): 229-236 DEC 2005
Abstract:
Crystal structure and the Fe-57 Mossbauer spectrum of synthetic (Ca1.53Na0.47)(Mg0.52Fe0.493+)Si1.99O7-melilite have been investigated to confirm the location of Fe3+ at the T1 site, and to evaluate the effect of an incommensurate structure on Fe-57 Mossbauer hyperfine parameters. A conventional Rietveld refinement with occupancies of Ca(W), Na(W), Mg(T1), Fe3+(T1) and Si(T2) fixed to 0.765, 0.235, 0.515, 0.485 and 2.00, respectively, converged well with an R-wp (R-weighted pattern) of 13.14% and a goodness-of-fit of 1.337, indicating exclusive Fe3+ distribution at the T1 site. However, the Mossbauer spectrum consists of two doublets with an isomer shift of 0.19 mm/s and quadrupole splitting of 0.75 and 1.04 mm/s, which can be attributed to Fe3+ at the T1 site. There are two sorts of T1 site with distinguishable distortion in the synthetic Na-Fe3+-melilite, which might be attributed to the existence of an incommensurate phase at room temperature.
Title:
Helical ground state and weak ferromagnetism in the edge-shared chain cuprate NaCu2O2
Authors:
Drechsler, SL; Richter, J; Gippius, AA; Vasiliev, A; Bush, AA; Moskvin, AS; Malek, J; Prots, Y; Schnelle, W; Rosner, H
Source:
EUROPHYSICS LETTERS, 73 (1): 83-89 JAN 2006
Abstract:
We report on susceptibility, magnetization, Na-23 NMR, and specific heat data of the spin-chain material NaCu2O2 in the paramagnetic and ordered phases. Below 13 K, where a sharp field-dependent specific heat peak appears, the NMR lineshape points to an incommensurate static modulation of the local magnetic field consistent with a spiral state of the Cu magnetic moments. At 2 K weak ferromagnetism with an ordered moment of about 4.10(-3) mu B has been observed. LDA-based estimates of exchange integrals reveal a large inchain frustration leading to a magnetic spiral.

Update: 13-Jan-2006

Title:
Crystalline patterns and band structure dimensionality in a series of conducting hybrids associating amide-functionalized EDT-TTF pi-donors with the isosteric octahedral anions [FeNO(CN)(5)](2-) and [M(CN)(6)](3-) (M = Co, Fe)
Authors:
Zorina, LV; Khasanov, SS; Simonov, SV; Shibaeva, RP; Kushch, LA; Buravov, LI; Yagubskii, EB; Baudron, S; Meziere, C; Batail, P; Canadell, E; Auban-Senzier, P
Source:
SYNTHETIC METALS, 155 (3): 527-538 DEC 15 2005
Abstract:
Four new radical cation salts based on the amide functionalized EDT-TTF organic donors EDT-TTF-CONH2 (D1) and EDT-TTF-(CONH2)(2) (D2), alpha'-(D1)(4)[FeNO(CN)(5)] (1), alpha'-(D1)(4) [Co(CN)(6)] (2), beta-(D1)(6)[Fe(CN)(6)] (3) and (D2)(4)[FeNO(CN)(5)]NB (4), have been synthesized and characterized by X-ray single crystal diffraction experiments, band structure calculations and electrical resistivity measurements. Functionalized organic donors are remarkable for the ability to form cation...cation and cation...anion type hydrogen bonds which can effectively direct the crystal architecture of molecular conductors. The structural analysis reveals a well-developed hydrogen bond network in the crystals investigated. (D1)(2)-dimers or (D2)(n)-extended zigzag chains of donors connected through functional groups are found to be stable structural motifs in 1-4. Remarkably, salts 1 and 2 are isostructural despite the presence of anions of different charge (-2 and -3, respectively) and the inherent difference in the degree of charge transfer has a clear effect on the transport properties: sigma(RT)(2)/sigma(RT)(1)=300. Salt 3 differs from 1 and 2 both in the stoichiometry and packing of the conducting organic layer. Crystals of 4 exhibit a superstructure with the incommensurate vector q=+/-(0.5, 0.3, 0.2). (C) 2005 Elsevier B.V. All rights reserved.
Title:
Mechanical behavior of Ti-Zr-Ni quasicrystals during nanoindentation
Authors:
Azhazha, VM; Borisova, SS; Dub, SN; Malykhin, SV; Pugachov, AT; Merisov, BA; Khadzhay, GY
Source:
PHYSICS OF THE SOLID STATE, 47 (12): 2262-2267 2005
Abstract:
The parameters and mechanisms of deformation of a Ti41.5Zr41.5Ni17 quasicrystal and a W + 12 at. % Ta single crystal under nanoindentation conditions were studied and compared. It was found that, initially, the deformation of the quasicrystal is elastoplastic; however, beginning from a certain critical load, the deformation acquires a steplike character with alternating segments of slow elastoplastic deformation and rapid plastic deformation. A qualitative model is proposed for the plastic deformation of quasicrystals during nanoindentation. (c) 2005 Pleiades Publishing, Inc.
Title:
Modulation instability of magnetostatic waves in a magnetically coupled two-layer structure
Authors:
Shutyi, AM; Sementsov, DI
Source:
PHYSICS OF THE SOLID STATE, 47 (12): 2268-2273 2005
Abstract:
Modulation instability of direct bulk magnetostatic waves in structures consisting of two magnetically coupled planar films separated by a nonmagnetic layer is studied. It is found that, depending on the type of excitation of the waveguide modes, mode coupling can either change the characteristics of the modulation wave instability or ensure their stability with respect to the corresponding perturbations by affecting the dispersion properties of the structure.
Title:
Phonon modes at the 2H-NbSe2 surface observed by grazing incidence inelastic x-ray scattering
Authors:
Murphy, BM; Requardt, H; Stettner, J; Serrano, J; Krisch, M; Muller, M; Press, W
Source:
PHYSICAL REVIEW LETTERS, 95 (25): Art. No. 256104 DEC 16 2005
Abstract:
We have determined the dispersion of acoustic and optical surface phonon modes at the 2H-NbSe2 by inelastic x-ray scattering under grazing incidence conditions. Already, at room temperature, an anomaly is observed close to the charge density wave Q-vector position located at about one-third along the Gamma-M direction of the Brillouin zone. Our results indicate that the anomaly for the surface mode occurs at a lower energy than that measured in bulk sensitive geometry in the same experiment, showing evidence of a modified behavior in the uppermost layers. We demonstrate that inelastic x-ray scattering in grazing incidence conditions provides a unique tool to selectively study either surface or bulk lattice dynamics in a single experiment.
Title:
Nonicosahedral equilibrium overlayers of icosahedral quasicrystals
Authors:
Yurechko, M; Grushko, B; Ebert, P
Source:
PHYSICAL REVIEW LETTERS, 95 (25): Art. No. 256105 DEC 16 2005
Abstract:
We demonstrate that icosahedral Al-Pd-Mn quasicrystals can have nonicosahedrally ordered thermodynamic equilibrium overlayers. The formation of orthorhombic or decagonal equilibrium surface structures is determined by the phase equilibrium of the ternary alloy at given composition and temperature as well as by the surface acting as nucleation site. Nonequilibrium steady-state orthorhombic and hexagonal structures can also be derived with the same methodology when taking preferential evaporation into account. The results describe consistently all presently observed surface structures.
Title:
Incommensurate-commensurate transition and nanoscale domain-like structure in iron doped Ti-Ni shape memory alloys
Authors:
Choi, MS; Fukuda, T; Kakeshita, T; Mori, H
Source:
PHILOSOPHICAL MAGAZINE, 86 (1): 67-78 2006
Abstract:
Precursor phenomena of displacive transformation have been studied by optical and transmission electron microscope observation and X-ray diffraction of Ti-(50 - x)Ni - xFe (x = 2, 4, 6, 8 in at.%) alloys. We found that a Ti-44Ni-6Fe alloy exhibits a second-order-like incommensurate - commensurate transition without latent heat and discontinuity in lattice parameters. In other words, di. use scatterings appear in an electron di. raction pattern at an incommensurate position on cooling; they move gradually towards 1/3 < 110 > as the temperature decreases and lock into the commensurate position at 180 K. The commensurate phase is not expanded along one of the < 111 > directions, unlike the R-phase formed by a first- order transformation in Ti- 48Ni-2Fe and Ti- 46Ni-4Fe alloys. In addition, the commensurate phase shows a nanoscale domain-like structure, which is inherited from the incommensurate state of the parent phase. Thus, the anomalies in physical properties observed in the incommensurate state are most likely the precursor phenomena of the commensurate phase in the Ti- 44Ni-6Fe alloy. In the case of a Ti- 42Ni-8Fe alloy, the incommensurate state remains even at 19 K.
Title:
Pitting corrosion of zirconium-based bulk glass-matrix composites
Authors:
Gebert, A; Kuehn, U; Baunack, S; Mattern, N; Schultz, L
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 415 (1-2): 242-249 JAN 15 2006
Abstract:
The corrosion behaviour of two bulk glass-matrix composite alloys formed by copper mould casting was analysed: (i) Zr66.4Nb6.4Cu10.5Ni8.7Al8.0 with precipitated bcc dendrite phase and (ii) Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 with quasicrystalline phase, respectively. The electrochemical behaviour was tested on the cross-sectional areas of the composite rod samples in 0.5 M sulphuric acid solution with up to 0.5 M sodium chloride addition by potentiodynamic polarization measurements. The composition of anodically formed passive films was studied by means of Auger electron spectroscopy (AES). The morphology of local damages generated by a chloride-induced pitting process was examined with scanning electron microscopy. In result of those studies, a pitting mechanism is described. For both composites in chloride media, a pronounced selective dissolution of the glassy matrix phase occurs, whereas the crystalline phases are not attacked. Niobium and titanium components are beneficial in inhibiting the pitting initiation due to their participation in the passive film formation. The dissolution of the glassy matrix phase is explained by the principal higher chloride reactivity of metastable phases compared to that of stable crystalline phases and by the detected enrichment of copper in these phase regions. The chloride attack progressing along the matrix phase causes the formation of deep channels in the bulk composite material leading to an excavation and, finally, detachment of the bcc dendrites or quasicrystals, respectively. The re-passivation ability is very poor. (c) 2005 Elsevier B.V. All rights reserved.
Title:
In situ diffraction studies of the phase selection in undercooled Ti-Fe-Si-O melts
Authors:
Heinen, O; Holland-Moritz, D; Herlach, DM; Kelton, KF
Source:
JOURNAL OF CRYSTAL GROWTH, 286 (1): 146-151 JAN 1 2006
Abstract:
A time-resolved in situ determination of the phase formation sequence in undercooled Ti-Fe-Si-O melts was performed using the combination of electromagnetic levitation and energy-dispersive X-ray diffraction of synchrotron radiation. Ti-Fe-Si-O alloys are known to form a large variety of stable and metastable phases, including quasicrystals and approximant phases. Different solidification pathways are found as a function of undercooling, with the primary nucleation of the 1/1 crystal approximant phase from the liquid occurring at the largest undercoolings. The results on phase selection are discussed with respect to the influence of the short-range order in the undercooled liquid on the nucleation behavior of solid phases. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Current progress in the magnetism of rare-earth-hydrogen systems
Authors:
Vajda, P
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 404: 131-135 DEC 8 2005
Abstract:
We are reviewing recent progress obtained in the study of hydrogen interaction with magnetic structures in rare-earth metals, emphasizing the role of the ordering state of the H-sublattice. We shall present in particular: (1) the situation in the solid solutions of the heavy rare earths, alpha*-RHx, and the efforts to relate the special quasi-unidimensional configuration of this phase (charge-density waves) to their modulated magnetism (spin-density waves) via the Fermi surface; (2) an assembly of all magnetic structures determined up to now in the heavy-RE dihydrides, beta-RH(D)(2(+x)), for a tentative comparison of the observed commensurate and/or incommensurate configurations; special mention will be made of the remarkably stable short-range ordered (SRO) magnetism always present in these systems; (3) the need for further (thorough) neutron scattering work on the magnetism in the insulating R-trihydrides, gamma-RH(D)(3(-x)), in order to specify its mechanism in the absence of RKKY exchange interaction. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Crystal and magnetic structure of HoNiSnD0.67
Authors:
Szytula, A; Isnard, O; Yartys, VA; Riabov, AB
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 404: 200-203 DEC 8 2005
Abstract:
Crystal and magnetic structure and magnetic properties for deuteride HoNiSnD0.67 are provided on the basis of high-resolution powder X-ray and neutron diffraction and magnetometric data. This deuteride crystallises with the hexagonal ZrNiAl type related structure and is antiferromagnetic below the Neel temperature equal to 2.6(3) K. The deuterium atoms occupy the tetrahedral 4h Ho3Ni sites. At 2 K Ho magnetic moments form a sine-modulated magnetic structure described by the propagation vector K(= 0.34, 0.34, 0.117). The Ho magnetic moment, equal to 5.36 mu(B), lies in the basal plane (001). (c) 2005 Elsevier B.V. All rights reserved.
Title:
Hydrogen absorption in Ti-Zr-Ni quasicrystals and 1/1 approximants
Authors:
Kim, JY; Hennig, R; Huett, VT; Gibbons, PC; Kelton, KF
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 404: 388-391 DEC 8 2005
Abstract:
Ti/Zr-based quasicrystals and their approximants draw attention as new candidate materials for hydrogen storage applications based on recent discoveries that they absorb a large amount of hydrogen, reversibly, at low temperatures and pressures. In fact, Ti45Zr38Ni17 quasicrystals take hydrogen to a maximum value of hydrogen to host metal atom ratio (H/M) of nearly 2. To evaluate their technical usefulness and to probe the local structure of the quasicrystals, pressure-composition isotherms (p-c-T) were measured above 250 degrees C using a computer-controlled apparatus. In the Ti-Zr-Ni quasicrystal, the p-c-T curves do not exhibit a clear pressure plateau. Instead, the equilibrium vapor pressure remains low (< 5 Torr) below HIM; land increases sharply for increasing HIM. In the Ti-Zr-Ni 1/1 approximant phase, which is a large unit cell bcc structure (a = 13.13 angstrom), the p-c-T measurements show similar curves with a hint of pressure plateau consistent with a structural similarity between the phases. The quasicrystals desorb most of the absorbed hydrogen above 600 degrees C for 2 h in dynamical vacuum without phase transformation, and they do not become powder, even after a few absorption-desorption cycles. Interestingly, a small amount of Pd inhibits the growth of the (Ti,Zr)H-x hydride phase during hydrogenation. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Peculiarities of structural state and hydrogen storage properties of Ti-Zr-Ni based intermetallic compounds
Authors:
Rud, AD; Schmidt, U; Zelinska, GM; Lakhnik, AM; Perekos, AE; Kolbasov, GY; Danilov, MO
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 404: 515-518 DEC 8 2005
Abstract:
Structural states of the Ti-Zr-Ni based melt-spun ribbons have been investigated by means of the X-ray diffraction analysis. The ribbon structural state was found to be strongly affected by the production conditions. A small amount of Si (0.2-0.3 at.%) in the Ti-Zr-Ni alloy leads to the formation of an amorphous or a mixed amorphous-quasicrystalline state in the ribbons produced at the different hardening rates. The amorphous-quasicrystalline structural state of the ribbons is stable during annealing up to temperatures of 400 degrees C but some changes in its parameters take place. The uncoated by Pd amorphous and amorphous-quasicrystalline Ti-Zr-Ni ribbons have the property of absorbing a large amount of hydrogen. Changes in the amorphous and quasicrystalline subsystems have a reversible character: the structural states of the ribbons after natural dehydrogenation practically fully returns to the initial one. (c) 2005 Elsevier B.V. All rights reserved.
Title:
H-induced anelasticity as a probe: Application to nanoscale quasicrystals
Authors:
Sinning, HR; Golovin, IS
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 404: 519-522 DEC 8 2005
Abstract:
Anelastic relaxation peaks produced by hydrogen in icosahedral quasicrystals (at CH = 0.001 to 0.2 H/M) have been studied with the vibrating-reed technique in several rapidly quenched Ti/Zr-based alloys. Although a full quantitative theory of the expected Snoek-type mechanism is still missing, the properties of the relaxation peaks are considered as a probe of local atomic order on a more empirical level. Examples are presented which show the distinction between different icosahedral structure types (like Bergman or Mackay clusters), and the development of quasicrystalline order from amorphous and nano-quasicrystalline structures. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Crystal structure of thermoelectric compound [Bi1.79Sr1.98Oy](0.63)[RhO2]
Authors:
Yubuta, K; Okada, S; Miyazaki, Y; Terasaki, I; Kajitani, T
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 44 (12): 8557-8561 DEC 2005
Abstract:
We have studied the crystal structure of the misfit-layered crystal Bi1.91Sr2Rh1.77Ox by electron diffraction and high-resolution electron microscopy. This compound consists of two interpenetrating subsystems of a RhO2 sheet and a distorted four-layered rock-salt-type (Bi,Sr)O block. Both subsystems have common a-axes, c-axes. and beta-angles with a = 5.28 angstrom, c = 29.77 angstrom, and p = 93.7 degrees. On the other hand, the crystal structure is incommensurated parallel to the b-axis, b(1) = 3.07 angstrom for the RhO2 sheet and b(2) = 4.88 angstrom for the (Bi,Sr)O block. The axis ratio, b(1)/b(2) similar to 0.63. characterizes the structural analogue as [Bi1.79Sr1.98Oy](0.63) [RhO2]. This compound has two modulation vectors, q(1) = a* + 0.63b(1)* and q(2) = 0. 17b(1)* + c*. and the *superspace* group is assigned as the Cc(1 beta 0, 0 mu 1) type from electron diffraction patterns. High-resolution images taken with the incident electron beam parallel to the a- and c-axes clearly exhibit modulated displacive as well as compositional atomic arrangements. A tentative structure model has been proposed, and the calculated image reproduces observed characteristic features reasonably well.
Title:
Role of Ti in the formation of Zr-Ti-Cu-Ni-Al glasses
Authors:
Kim, TH; Gangopadhyay, AK; Xing, LQ; Lee, GW; Shen, YT; Kelton, KF; Goldman, AI; Hyers, RW; Rogers, JR
Source:
APPLIED PHYSICS LETTERS, 87 (25): Art. No. 251924 DEC 19 2005
Abstract:
It has been widely reported that glass formation improves in Zr62Cu20Ni8Al10 alloys when small amounts of Ti are substituted for Zr. Glasses containing greater than 3 at. % Ti crystallize to a metastable icosahedral phase, suggesting that Ti enhances icosahedral short-range order in the liquid/glass, making crystallization more difficult during cooling. However, based on containerless solidification and in situ high-energy synchrotron diffraction studies of electrostatically levitated supercooled liquids of these alloys, we demonstrate that Ti inhibits surface crystallization but neither increases the icosahedral short-range order nor improves glass formation. (c) 2005 American Institute of Physics.

Update: 6-Jan-2006

Title:
A new family of binary layered compounds of platinum with alkali metals (A = K, Rb, Cs)
Authors:
Karpov, A; Jansen, M
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 632 (1): 84-90 2006
Abstract:
By reacting platinum with alkali metals (A = K, Rb, Cs) a new family of binary alkali metal platinides has been synthesized and characterized by chemical analysis, X-ray powder diffraction, thermal analysis (DTA and DSC), and magnetic measurements. All three compounds exhibit similar XRD-patterns with strong reflections that can be indexed on the basis of a rhombohedral crystal system (KxPt: a = 2.6462(1), c = 17.123(1); RbxPt: a = 2.6415(1) angstrom, c = 17.871(1)angstrom; CsxPt: a = 2.6505(1) angstrom, c = 18.536(1) angstrom; x < 1/2). The a lattice constant is independent on the alkali metal used and of value close to the Pt-Pt distance in NaPt2 (2.645 angstrom). The c parameter increases monotonically with the growing atomic radius of the alkali metal. The average structure of the alloys consists of cubic close packed layers of platinum atoms with layers of disordered alkali metals in between. For all compounds besides the strong reflections small satellites are observed which cannot be indexed together with the rhombohedral peaks in any rational 3-dimensional lattice. However, these satellites can be indexed as incommensurate modulations within the ab plane (found propagation vectors k = (0.1011, 0.2506, 0) for CsxPt, and k = (0.0168, 0.2785, 0) for RbxPt).
Title:
Walk of a line defect in quasicrystals
Authors:
Mariano, PM
Source:
MECCANICA, 40 (4-6): 511-525 DEC 2005
Abstract:
Quasicrystalline alloys are quasiperiodic aggregates in which local atomic changes (phason activity) influence prominently the gross deformative behavior. The effects of these rearrangements on a line defect are analyzed here. Balances of standard and phason interactions are derived along the line together with the balance of actions driving eventually it the former are found to be covariant while the latter follows from a requirement of invariance with respect to the action of the group of isochoric diffeomorphisms. The results can be applied to the analysis of dislocations in quasicrystals.
Title:
Stability of the modulated structure of Baikal lazurite and its recrystallization at a temperature of 600 degrees C over a wide range of sulfur dioxide fugacities
Authors:
Tauson, VL; Sapozhnikov, AN
Source:
CRYSTALLOGRAPHY REPORTS, 50: S1-S9 Suppl. 1 2005
Abstract:
The stability of three-dimensional incommensurate modulation in cubic lazurite from the Baikal region is experimentally investigated at T = 600 degrees C. It is found that the X-ray photoelectron spectra of the annealed samples exhibit a peal, corresponding to sulfite and a split peak associated with the (Na,Ca)SO4 sulfate. It is assumed that the splitting is caused by the ordering of the complexes not involved in the framework. This assumption is confirmed by the presence of a similar split peak in the X-ray photoelectron spectra of triclinic lazurite. It is demonstrated that the initial modulation is retained at the fugacity f(SO2) = 8 X 10(-3) bar. The decisive factors responsible for the retention of the three-dimensional incommensurate modulation are the temperature and the fugacity of sulfur dioxide. The latter quantity should be close to the stability boundary of the basic lazurite structure. The growth and transformation mechanisms of the modulation formation are considered. (C) 2005 Pleiades Publishing, Inc.

Update: 30-Dec-2005

Title:
Bilbao crystallographic server: I. Databases and crystallographic computing programs
Authors:
Aroyo, MI; Perez-Mato, JM; Capillas, C; Kroumova, E; Ivantchev, S; Madariaga, G; Kirov, A; Wondratschek, H
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 221 (1): 15-27 2006
Abstract:
The Bilbao Crystallographic Server is a web site with crystallographic databases and programs available on-line at www. cryst.ehu.es. It has been operating for about six years and new applications are being added regularly. The programs available on the server do not need a local installation and can be used free of charge. The only requirement is an Internet connection and a web browser. The server is built on a core of databases, and contains different shells. The innermost one is formed by simple retrieval tools which serve as an interface to the databases and permit to obtain the stored symmetry information for space groups and layer groups. The k-vector database includes the Brillouin zones and the wave-vector types for all space groups. As a part of the server one can find also the database of incommensurate structures. The second shell contains applications which are essential for problems involving group-subgroup relations between space groups (e.g. subgroups and supergroups of space groups, splittings of Wyckoff positions), while the third shell contains more sophisticated programs for the computation of space-group representations and their correlations for group-subgroup related space groups. There are also programs for calculations focused on specific problems of solid-state physics. The aim of the article is to report on the current state of the server and to provide a brief description of the accessible databases and crystallographic computing programs. The use of the programs is demonstrated by illustrative examples.
Title:
The four-dimensional magnetic point and space groups
Authors:
Souvignier, B
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 221 (1): 77-82 2006
Abstract:
This paper describes the classification of magnetic point and space groups which are also referred to as antisymmetry groups or black-and-white groups. These groups play an important role in the description of discrete point sets in which the points are not only characterized by their spatial coordinates but also by an additional property taking one of two possible values (e.g. spin up or down). Each operation of a magnetic group may or may not switch the value of this additional property. In this paper, the methods for classifying magnetic groups in arbitrary dimensions are described in an algorithmic fashion. Results of the full classification in four-dimensional space are given and the application of the magnetic groups in this dimension to quasicrystals is indicated.
Title:
Statics and dynamics of incommensurate spin order in a geometrically frustrated antiferromagnet CdCr2O4
Authors:
Chung, JH; Matsuda, M; Lee, SH; Kakurai, K; Ueda, H; Sato, TJ; Takagi, H; Hong, KP; Park, S
Source:
PHYSICAL REVIEW LETTERS, 95 (24): Art. No. 247204 DEC 9 2005
Abstract:
Using elastic and inelastic neutron scattering we show that a cubic spinel, CdCr2O4, undergoes an elongation along the c axis (c > a=b) at its spin-Peierls-like phase transition at T-N=7.8 K. The Neel phase (T < T-N) has an incommensurate spin structure with a characteristic wave vector Q(M)=(0,delta,1) with delta similar to 0.09 and with spins lying on the ac plane. This is in stark contrast to another well-known Cr-based spinel, ZnCr2O4, that undergoes a c-axis contraction and a commensurate spin order. The magnetic excitation of the incommensurate Neel state has a weak anisotropy gap of 0.6 meV and it consists of at least three bands extending up to 5 meV.
Title:
Magnetic ordering in quasicrystals
Authors:
Vedmedenko, EY
Source:
MODERN PHYSICS LETTERS B, 19 (27): 1367-1385 NOV 30 2005
Abstract:
An overview of the theoretical advances in description of the magnetic ordering and its stability in two-dimensional quasiperiodic tilings with strongly localized magnetic moments is presented. It is demonstrated that combination of the magnetic frustration and the quasiperiodic order of atoms leads to noncollinear ground states. An experimental and theoretical evidence for the possibility of coexistence of stable, magnetically ordered subtilings with highly frustrated, glass-like phases in a single sample is given.
Title:
The decagonal quasicrystal Al65Co15Cu20 studied by the Mossbauer effect
Authors:
Stadnik, ZM; Zhang, G
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (42): 6599-6608 OCT 26 2005
Abstract:
A systematic Fe-57 Mossbauer effect study in a varying temperature range between 5.0 and 296.6 K and in an external magnetic field of 9.0 T on a highquality stable decagonal quasicrystal Al65Co15Cu19.9Fe0.1 is presented. It is shown that the iron atoms are located in two distinct classes of sites. The values of the principal component of the electric field gradient tensor and the asymmetry parameter at these sites are, respectively, -1.90(10) x 10(21) V m(-2), 0.97(15) and -3.95(12) x 10(21) V m(-2), 0.00(17). The average quadrupole splitting decreases with temperature as T-3/2. The vibrations of the Fe atoms are well described by a Debye model, with the Debye temperature of 546(7) K.
Title:
Calculations of the percolation thresholds of a three-dimensional (icosahedral) Penrose tiling by the cubic approximant method
Authors:
Zakalyukin, RM; Chizhikov, VA
Source:
CRYSTALLOGRAPHY REPORTS, 50 (6): 938-948 NOV-DEC 2005
Abstract:
The percolation thresholds of a three-dimensional Penrose tiling with icosahedral symmetry are determined using the cubic approximant method. The percolation thresholds of the three-dimensional Penrose tiling for the site problem and the bond problem are calculated with an accuracy of 0.001. (C) 2005 Pleiades Publishing, Inc.

Update: 23-Dec-2005

Title:
Effect of yttrium on microstructure and quasicrystal's formation in as-cast Mg-Zn-Y alloy
Authors:
Shi, F; Guo, XF; Zhang, ZM
Source:
RARE METAL MATERIALS AND ENGINEERING, 34 (11): 1726-1729 NOV 2005
Abstract:
Stable icosahedral Zn60Mg3O10 quasicrystals were prepared by as-cast method. On this base, the feasibility to prepare quasi crystalline reinforced low-density magnesium alloy was also discussed. The microstructure, the composition and the phases of the as-cast Mg-Zn-Y alloy were analyzed by optical microscope, SEM and EDS. The constituent phases were identified by XRD and quasi crystal structure was identified by TEM. Analyzing the different component of alloys, especially the mole fraction of yttrium, can lead quasi crystals that have different micro morphologies, amounts and distributing. Results show that the I-phases directly nucleate and grow from melt of cooling Mg-Zn-Y ternary alloys; the granularity, the circular-degree and the distributing-leveling of the quasi crystalline were improved with the increasing of yttrium's contents.
Title:
Defects in quasicrystals. Relation to symmetry
Authors:
Khannanov, SK
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 100 (5): 448-455 NOV 2005
Abstract:
In terms of a topological approach, a general classification of possible topological defects in quasi-C, crystals of any dimensionality and symmetry is given. According to this classification, different types of defects are associated with different elements of homotopy groups. From the general formulas derived, the earlier obtained concrete results follow as particular cases. Problems of constructing, linear defects in a quasilattice and of a topological description of physical processes involving defects are also considered.
Title:
High-temperature polymorphism in metastable BiMnO3
Authors:
Montanari, E; Calestani, G; Migliori, A; Dapiaggi, M; Bolzoni, F; Cabassi, R; Gilioli, E
Source:
CHEMISTRY OF MATERIALS, 17 (25): 6457-6467 DEC 13 2005
Abstract:
The multiferroic perovskite BiMnO3, synthesized under high-pressure conditions, decomposes if heated at room-pressure in the temperature range of 500-650 degrees C. Comparative studies by high-temperature X-ray diffraction, electron diffraction, thermal analysis, and magnetic investigation revealed the existence of a complex pathway to decomposition, depending on the heating rate, pressure, and atmosphere that involves different metastable phases. In particular the as-prepared monoclinic phase (I) transforms to a second monoclinic form (II) at 210 degrees C and then to an orthorhombic phase (III) at 490 degrees C. These phase transitions, fast and reversible, occur on heating with a drop in volume and are moved at higher temperatures when pressure is decreased. The transition from II to III, typically observed in inert atmosphere, can be detected also in air when the heating rate is kept sufficiently high. When III is heated in an oxygen-containing atmosphere a slow irreversible transition to variants IV and then V takes place with kinetics depending on temperature, heating rate, and oxygen partial pressure. Both IV and V are oxidized ferromagnetic phases containing Mn4+ characterized by a modulated structure based on fundamental triclinic perovskite cells. Their magnetic behavior shows a strong analogy with thin films of BiMnO3, suggesting for the latter an oxidized nature and for the former a possible multiferroic behavior.

Update: 16-Dec-2005

Title:
Synthesis and modulated crystal structure of KBaNbS4
Authors:
Wu, YD; Doert, T; Bensch, W
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 631 (15): 3019-3024 2005
Abstract:
Single crystals of KBaNbS4 have been prepared by the reaction of Nb with an in situ formed melt of K2S3, BaS, and S at 500 degrees C. Satellite reflections observed in X-ray diffraction experiments of these crystals indicate the presence of a one-dimensional lattice distortion. The modulated structure has been solved and refined from X-ray data using the superspace group approach. KBaNbS4 can be described in the (3 +1)-dimensional superspace group Pnma(alpha 00)0s0 with lattice parameters/a 9.187(1), b = 7.001 (1), and c = 12.494(1) angstrom and a modulation vector q (0, 0.629(1), 0). In the structure the NbS4 tetrahedra are stacked along the a axis and show a slight tilting against each other. The K+ and Ba2+ ions follow this tilting, both are slightly shifted from their positions in the average structure. The modulation does not lead to a significant change in the coordination spheres of the metal atoms. The small effects of the *mod! ulation* correspond to the relatively weak intensities of the *satellite* *reflections*. Results of temperature dependent *X*-*ray* investigations indicate that K+ librates at higher temperatures and the surrounding S2- anions follow this motion. With decreasing temperature the libration of K+ is reduced and the coordination geometry freezes under formation of an incommensurate modulation. The heavier Ba and Nb atoms are also affected by positional modulation of the substructure and accommodate to their environment.
Title:
Link between liquid structure and the nucleation barrier for icosahedral quasicrystal, polytetrahedral, and simple crystalline phases in Ti-Zr-Ni alloys: Verification of Frank's hypothesis
Authors:
Lee, GW; Gangopadhyay, AK; Croat, TK; Rathz, TJ; Hyers, RW; Rogers, JR; Kelton, KF
Source:
PHYSICAL REVIEW B, 72 (17): Art. No. 174107 NOV 2005
Abstract:
Comprehensive undercooling experiments on a large number of simple crystalline, polytetrahedral, and icosahedral quasicrystalline phase forming compositions in Ti-Zr-Ni alloys have been carried out using electrostatic levitation (ESL) techniques for containerless processing. Consistent with Frank's hypothesis, a direct correlation was found between the reduced undercooling [Delta T-r=(T-l-T-r)/T-l, where T-r and T-l are the nucleation and liquidus temperatures, respectively] and the icosahedral short-range order in the solid. The reduced undercooling is less for liquids that form the icosahedral quasicrystal (i phase) than for those that form the hcp C14 Laves polytetrahedral phase. For many compositions near 21 at. % Ni, the primary nucleation of a metastable i phase instead of a stable C14 Laves phase demonstrates that the interfacial free energy between the liquid and the i phase is smaller than between the liquid and the C14 Laves phase, indicating icosahedral local order in the undercooled liquid. This is in agreement with a classical-nucleation-theory-based estimate of the interfacial free energy and the work of formation of the critical cluster from the undercooling data. Taken together with high-energy x-ray diffraction studies of the undercooled liquid, these results demonstrate that the local structure of liquids in Ti-Zr-Ni alloys is icosahedral, as postulated by Frank over a half century ago.
Title:
Zone-axis x-ray diffraction of single-crystal Fe1-xO under pressure
Authors:
Ding, Y; Liu, HZ; Somayazulu, M; Meng, Y; Xu, J; Prewitt, CT; Hemley, RJ; Mao, H
Source:
PHYSICAL REVIEW B, 72 (17): Art. No. 174109 NOV 2005
Abstract:
Zone-axis synchrotron x-ray diffraction of single-crystal Fe1-xO to 25 GPa is used to study the effect of pressure on the defect cluster superstructure and to obtain further details on the cubic-to-rhombohedral phase transition in this material. Fe1-xO is found to exhibit a pressure-induced long-range order-disorder transition of defect clusters as the satellite reflections originating from an incommensurate defect superstructure disappear around 14.0 GPa. The wave vectors of the incommensurately modulated defect structure increase with pressure, while the intensity of incommensurate peaks decreases. In contrast to temperature-induced order-disorder transitions, the pressure-induced transition is not reversible. Additionally, twinning is unambiguously observed to accompany the transition from a cubic to a rhombohedral phase at 19.8 GPa.
Title:
Ab initio study of icosahedral Al-Pd-Mn quasicrystals: Structural model, electric field gradients, and negative valence of Mn
Authors:
Zijlstra, ES; Bose, SK; Klanjsek, M; Jeglic, P; Dolinsek, J
Source:
PHYSICAL REVIEW B, 72 (17): Art. No. 174206 NOV 2005
Abstract:
The atomic and electronic structures of the Quandt-Elser model of i-Al70.8Pd21.5Mn7.7 [A. Quandt and V. Elser, Phys. Rev. B 61, 9336 (2000)] are studied by pseudopotential and full-potential linear augmented plane-wave methods. A model with a lower total energy than the original Quandt-Elser model (Delta E=-0.03 eV/atom) is obtained by moving one of the Al atoms on a cube in the Mackay void away from its high symmetry position and by performing a subsequent structural relaxation. The electronic density of states of this modified Quandt-Elser model is found to be similar to that of the model of Katz and Gratias, but with a more pronounced pseudogap near the Fermi energy. Good agreement is obtained with an available photoemission spectrum, but calculated electric field gradients do not reproduce the angular dependence of a Al-27 nuclear magnetic resonance spectrum. By introducing vacancies at Mn sites and by comparing the filling of bands near the Fermi energy for the models with and without a vacancy, it is found that the Mn atoms have an apparent negative number of -3.2 valence electrons independent of the Mn site. It is argued that this apparent negative number of valence electrons is due to the filling of Mn-d states below the Fermi energy.
Title:
Modeling the spectral conductivity of Al-Mn-Si quasicrystalline approximants: A phenomenological approach
Authors:
Macia, E; Takeuchi, T; Otagiri, T
Source:
PHYSICAL REVIEW B, 72 (17): Art. No. 174208 NOV 2005
Abstract:
The electronic structure of a quasicrystalline approximant sample is analyzed by means of a combined study of different experimental transport curves within a phenomenological approach. The main features of the obtained spectral conductivity are discussed and compared to those corresponding to icosahedral quasicrystals. Such a comparison provides interesting clues about the role of quasiperiodic order and of local atomic arrangements in the origin of unusual behaviors in the electrical conductivity and thermopower observed in complex metallic alloys.
Title:
X-ray scattering study of temperature dependence of a structural incommensurability of the omega phase in Ti-V alloys
Authors:
Takesue, N
Source:
PHYSICAL REVIEW B, 72 (17): Art. No. 174210 NOV 2005
Abstract:
The incommensurate omega phase in titanium alloys has been revisited. A mechanism of the formation relevant to electron-lattice coupling has been re-investigated in terms of an x-ray-scattering technique on three kinds of single crystals, each containing 20, 24, and 27 mass % of vanadium respectively. The superlattice reflections of all systems observed for reduced wave vector q=(2/3+Delta,2/3+Delta,2/3+Delta) at temperature congruent to 30 K reveal the following three effects for their intensity distribution with increasing temperature, where Delta has a nonzero value giving the incommensurability: (1) decrease of the intensities, (2) increase of the distribution widths, and (3) reduction of the Delta values. The results suggest unstabilization of the lock-in state. A temperature region which indicates a notion of the transition is lowered with increasing concentration, implying excess of the valence electrons which prohibits lock-in nesting of the charge density wave. This idea was supported by molecular-orbital population analysis using cluster models of the two phases.
Title:
Group theoretical treatment of the low-temperature phase transition of the Cd6Ca 1/1-cubic approximant
Authors:
Tamura, R; Edagawa, K; Shibata, K; Nishimoto, K; Takeuchi, S; Saitoh, K; Isobe, M; Ueda, Y
Source:
PHYSICAL REVIEW B, 72 (17): Art. No. 174211 NOV 2005
Abstract:
An antiparallel orientational transition is reported for an intermetallic compound, i.e., Cd6Ca crystal, which is a 1/1-1/1-1/1 crystalline approximant to the icosahedral quasicrystal Cd5.7Ca. A group theoretical analysis based on the Landau theory predicts that the space group of the low-temperature phase is either C2/c or C2/m, in good agreement with the observations. Accordingly, two types of orientational orderings of Cd-4 tetrahedra, which are located in the center of icosahedral clusters, may occur below 100 K: In both cases, the Cd-4 tetrahedra are orientationally ordered in an antiparallel fashion along the [110] direction of the high temperature body-centered-cubic phase. Such a transition in a metal is reminiscent of orientational transitions in molecular solids.
Title:
Distinct order of Gd 4f and Fe 3d moments coexisting in GdFe4Al8
Authors:
Angst, M; Kreyssig, A; Janssen, Y; Kim, JW; Tan, L; Wermeille, D; Mozharivskyij, Y; Kracher, A; Goldman, AI; Canfield, PC
Source:
PHYSICAL REVIEW B, 72 (17): Art. No. 174407 NOV 2005
Abstract:
Single crystals of flux-grown tetragonal GdFe4Al8 were characterized by thermodynamic, transport, and x-ray resonant magnetic scattering measurements. In addition to antiferromagnetic order at T(N)approximate to 155 K, two low-temperature transitions at T(1)approximate to 21 K and T(2)approximate to 27 K were identified. The Fe moments order at T-N with an incommensurate propagation vector (tau,tau,0) with tau varying between 0.06 and 0.14 as a function of temperature, and maintain this order over the entire T < T-N range. The Gd 4f moments order below T-2 with a ferromagnetic component mainly out of plane. Below T-1, the ferromagnetic components are confined to the crystallographic plane. Remarkably, at low temperatures the Fe moments maintain the same modulation as at high temperatures, but the Gd 4f moments apparently do not follow this modulation. The magnetic phase diagrams for fields applied in [110] and [001] direction are presented and possible magnetic structures are discussed.
Title:
Three-wave vibrational mode broadening for Fibonacci one-dimensional quasicrystals
Authors:
Kats, EI; Muratov, AR
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (43): 6849-6869 NOV 2 2005
Abstract:
A one-dimensional Fibonacci chain is used to model vibrational mode broadening in icosahedral quasicrystals (i-QCs). All calculations are performed self-consistently for various finite size approximants at temperatures higher than the Debye temperature, T-D. This approach is extended to three-dimensional systems as well. It is shown that vibrational spectra depend crucially on the Fibonacci chain mass ratio m. For m = 3, which roughly mimics AlPdMn i-QC, there are three almost dispersionless optic modes separated from the acoustic mode by three large gaps, and for m = 1/3, which mimics ZnMgY i-QC, there is one dispersionless optic mode and one acoustic mode. For the first time we provide a qualitative model which predicts experimentally observed phonon spectrum broadening of i-QC. It is shown that three wave broadening for both one-dimensional and three-dimensional Fibonacci i-QCs is the leading mechanism of spectrum broadening. For the intermediate range of mode coupling constants, it scales with the mode frequency omega as c(1)omega + c(2)omega(2) (where c(1) and c(2) are some numerical constants). For smaller values of the coupling constant, phonon broadening is proportional to omega(3). We conclude that for a system with a non-simple elementary cell, vibrational spectrum broadening is always larger than for a system with a primitive cell (provided all other characteristics are the same).
Title:
Experimental study of the electronic density of states in aluminium-based intermetallics
Authors:
Belin-Ferre, E; Klanjsek, M; Jaglicic, Z; Dolinsek, J; Dubois, JM
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (43): 6911-6924 NOV 2 2005
Abstract:
We report on an experimental investigation of the electronic density of states (DOS) in aluminium-based interinetallics by three experimental techniques: electrical resistivity, NMR spin-lattice relaxation and soft x-ray emission spectroscopy (SXES). The investigated samples were alloys of Al with transition elements Cu, Fe, Cr, Pd and Mn and sometimes also a small amount of B. The samples were structurally very different and included (1) regular periodic intermetallic compounds, (2) large-unit-cell intermetallics that are translationally periodic on the scale of several nanometres and exhibit local polytetrahedral order (like quasicrystals) on the scale of interatomic distances and (3) quasicrystals. Correlation analysis between the DOS parameters determined independently by the three techniques employed showed that the order of samples with decreasing metallic character was the same in all experiments. Quantitative evaluation of the DOS at E-F has shown that in regular alloys the DOS is reduced to about 50% of the free-electron-like value in fcc Al metal, whereas the reduction becomes increasingly larger on going to large-unit-cell periodic solids and quasicrystals. Our results also demonstrate that low resistivities are accompanied by positive temperature coefficient (PTC) variation, whereas samples with large resistivity exhibit negative temperature coefficient (NTC). Samples with a resistivity of about 200 mu Omega cm appear to be at a crossover from PTC to NTC resistivity, resulting in a temperature-compensated resistivity with essentially zero temperature coefficient. Magnetic properties of the samples are also presented.
Title:
Nonlinear phenomena in A(2)MX(4) type crystals with incommensurate phases
Authors:
Kaluza, S; Suchanska, M; Belka, R
Source:
APPLIED MAGNETIC RESONANCE, 29 (2): 171-175 2005
Abstract:
Investigations of the nonlinear phenomena in A(2)MX(4) type crystals (A, organic cation or alkaline metal ion; M, metal ion; X, halogen ion) with incommensurate phases are very interesting from both a scientific and a practical point of view. In the crystals many interesting nonlinear phenomena are observed, e.g., thermal hysteresis of birefringence and absorption coefficient, piezooptic effect, electrooptic effect. Different anomalies (e.g., a discontinuity or change of sign of the birefringence coefficient, a distinct increase of the value of piezooptic and electrooptic coefficients) exist in the phase transition regions, They are especially distinct for a transition from the incommensurate phase to the commensurate phase. Some possibilities of detection and recognition of the existence of incommensurate phases by optical methods are suggested.

Update: 9-Dec-2005

Title:
The pressure influence on the incommensurate-commensurate ferroelectric phase transition in [4-NH2C5H4NH][SbCl4]
Authors:
Zdanowska-Fraczek, M; Jakubas, R
Source:
SOLID STATE COMMUNICATIONS, 136 (8): 470-474 NOV 2005
Abstract:
The dielectric properties of the [4-NH2C5H4NH] SbCl4 (abbreviated as 4-APCA) crystal were investigated under hydrostatic pressure up to 300Mpa. The pressure-temperature phase diagram was given. The paraelectric-ferroelectric phase transition (II -> III) temperature (T-c) increases linearly with increasing pressure with a slope dT(c)/dp=21X10(-) K-2/MPa. The pressure dependence of Curie-Weiss constants has been evaluated also. In the paraelectric phase (II) the Curie constant (C+) was pressure dependent whereas the C_ constant over the ferroelectric phase (III) was almost constant. The results are interpreted in terms of improper and displacive type phase transition model with a soft phonon at a zone boundary. (c) 2005 Elsevier Ltd. All rights reserved.
Title:
Novel coexistence of superconductivity with two distinct magnetic orders
Authors:
Christianson, AD; Llobet, A; Bao, W; Gardner, JS; Swainson, IP; Lynn, JW; Mignot, JM; Prokes, K; Pagliuso, PG; Moreno, NO; Sarrao, JL; Thompson, JD; Lacerda, AH
Source:
PHYSICAL REVIEW LETTERS, 95 (21): Art. No. 217002 NOV 18 2005
Abstract:
The heavy fermion CeRh1-xIrxIn5 system exhibits properties that range from an incommensurate antiferromagnet for small x to an exotic superconductor on the Ir-rich end of the phase diagram. At intermediate x where antiferromagnetism coexists with superconductivity, two types of magnetic order are observed: the incommensurate one of CeRhIn5 and a new, commensurate antiferromagnetism that orders separately. The coexistence of f-electron superconductivity with two distinct f-electron magnetic orders is unique among unconventional superconductors, adding a new variety to the usual coexistence found in magnetic superconductors.
Title:
Formation and crystallization of ZrCuTi metallic glasses
Authors:
Shen, YT; Xing, LQ; Kelton, KF
Source:
PHILOSOPHICAL MAGAZINE, 85 (31): 3673-3682 NOV 1 2005
Abstract:
We report the suction casting of Zr65Cu27Ti8 bulk metallic glasses with diameters up to 1 mm. While the substitution of Ti for Cu increases the glass forming ability significantly, the onset crystallization temperature and the width of the supercooled liquid region decrease. This decrease is due to the appearance of all icosahedral quasicrystal phase, which crystallises from the glass Lit a lower temperature than the Zr2Cu devitrification product ill the Zr65Cu35 glasses. Based on the results of recent structural studies of undercooled Ti/Zr-based alloys, this likely reflects the formation of icosahedral order in the undercooled liquid, which increases the nucleation barrier for the Zr2Cu phase during the quench, making glass formation easier.
Title:
Rapid suppression of the commensurate magnetic ordered phase of PrB6 by La doping
Authors:
Sera, M; Goto, S; Koshikawa, T; Kim, MS; Tou, H; Iga, F; Mitsukawa, Y; Kojima, K
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 74 (10): 2691-2694 OCT 2005
Abstract:
We have studied the magnetization, electrical resistivity and magnetic phase diagram of PrxLa1-xB6. The x dependence of the incommensurate (IC) magnetic ordering temperature, TIC,, is similar to that of NdxLa1-xB6. The noncollinear commensurate magnetic ordering is rapidly suppressed by La doping. These suggest that the IC magnetic ordering originates from the long-range RKKY-type exchange interaction and that the short-range O-xy-type AFQ interaction, which is easily affected by the local disturbance, is associated with the formation of the commensurate magnetic ordering in the C phase. The magnetic phase diagram of Pr0.8La0.2B6 is very different from those of PrB6 and Pr0.9La0.1B6. Although there exists the C and IC I phases at H = 0 in the latter two compounds, there exists only the IC I phase at H = 0 in Pr0.8La0.2B6. However, the C phase appears above 6T only for H parallel to < 111 >. The unusual magnetic phase diagram for H parallel to < 111 > is explained as a result of the competition between the exchange, quadrupolar and Zeeman interactions by taking into account the domain distribution, that depends on the applied magnetic field direction.
Title:
Structural determination of atomic substitution ratio in (K1-xRbx)(2)SeO4 mixed crystal system
Authors:
Sawae, S; Nakashima, T; Shigematsu, H; Kasano, H; Mashiyama, H
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 74 (10): 2748-2753 OCT 2005
Abstract:
In order to explain why Rb2SeO4 remains in normal phase down to 0 K while K2SeO4 transforms into the modulated phase at finite temperature, crystal structures of the mixed system have been refined at room temperature by X-ray single crystal analysis. Rb ion can be substituted for K ion with keeping the macroscopic symmetry of space group Pnam. Larger size of Rb ion occupies preferentially site 1, while smaller K ion prefers site 2. Here the atomic distance between an alkali ion and oxygen atoms is longer at site 1 than at site 2. The mean substitution ratio coincides with that from chemical analysis, however, the crystallographic structure analysis is only one method to determine the ratios at each site separately. A sublattice model is discussed to interpret the ion replacing effect on the phonon dispersion relation of the mixed crystal system. The hardening of the soft mode branch can be predicted by the change of interactions between the SeO4 tetrahe! drons if the alkali ions are replaced.
Title:
Magnetic property and pressure effect of a single crystal CeRhGe
Authors:
Ueda, T; Honda, D; Shiromoto, T; Metoki, N; Honda, F; Kaneko, K; Haga, Y; Matsuda, TD; Takeuchi, T; Thamizhavel, A; Sugiyama, K; Kindo, K; Settai, R; Onuki, Y
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 74 (10): 2836-2842 OCT 2005
Abstract:
We measured the electrical resistivity, specific heat, magnetic susceptibility, high-field magnetization, neutron scattering and electrical resistivity under pressure for CeRhGe. The anisotropy of the magnetic susceptibility and magnetization are very large, reflecting the orthorhombic crystal structure. The magnetic easy-axis is found to be oriented along the a-axis. From the neutron scattering experiment, the magnetic structure is, however, not simple, indicating an incommensurate antiferromagnetic structure. The magnetic susceptibility and magnetization were analyzed on the basis of the crystalline electric field scheme of localized-4f energy levels, indicating a very large splitting energy of the 4f levels.
Title:
Charge order and superconductivity in two-dimensional triangular lattice at n=2/3
Authors:
Watanabe, H; Ogata, M
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 74 (11): 2901-2904 NOV 2005
Abstract:
To investigate the possibility of charge order and superconductivity in a doped two-dimensional triangular lattice, we study an extended Hubbard model with the variational Monte Carlo method. At n = 2/3, a commensurate filling for a triangular lattice, it is shown that the nearest-neighbor Coulomb interaction V induces honeycomb-type charge order and antiferromagnetic spin order at U greater than or similar to 10t. We also discuss the possibility of superconductivity induced by charge fluctuation and the relation to the superconductivity in Na(0.35)CoO(2)center dot 1.3H(2)O and theta-type organic condoctors.
Title:
Possible coexistence of quadrupolar and magnetic ordering in Ce0.7Pr0.3B6
Authors:
Kishimoto, S; Kondo, A; Kim, MS; Tou, H; Sera, M; Iga, F
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 74 (11): 2913-2916 NOV 2005
Abstract:
We have investigated the physical properties of Ce0.7Pr0.3B6 in order to clarify the doping effect on the multipolar interactions in CeB6 and PrB6. As a result of the suppression of the antiferro-quadrupolar ordering temperature T-Q and the enhancement of T-N by Pr doping, six long-range ordered (LRO) phases appear. T-Q exhibits a smooth increase with increasing magnetic field as in CeB6. At a high magnetic field, above similar to 10 T, only phase II exists. As for the three LRO phases below similar to 10 T and below T-Q, there exists a possibility of incommensurate quadrupolar and magnetic ordering. A new question of how the quadrupolar ordering is compatible with the magnetic ordering appears in the present study. The coexistence of the magnetic and quadrupolar orderings in Ce0.7Pr0.3B6 indicates that the strong Ce-Pr interaction is different from the weak Ce-Nd interaction in CexNd1-xB6.

Update: 3-Dec-2005

Title:
Diffuse scattering and phason modes in the i-AlPdMn quasicrystalline phase
Authors:
de Boissieu, M; Francoual, S
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 220 (12): 1043-1051 2005
Abstract:
We review results obtained in the study of the diffuse scattering in the i-AlPdMn quasicrystal. Most of the diffuse scattering is the result of long wavelength phason modes. The shape and intensity distribution of the diffuse scattering is well reproduced using the generalised elasticity theory and two phason elastic constants. The temperature dependence of the diffuse scattering indicates a softening of the phason elastic constant as the temperature is lowered. Using coherent X-rays and photo-correlation X-ray spectroscopy, it is shown that phason modes are collective diffusive modes, in agreement with the hydrodynamic theory of long wavelength fluctuations in quasicrystals.
Title:
Thermodynamics of an incommensurate quantum crystal
Authors:
Anderson, PW; Brinkman, WF; Huse, DA
Source:
SCIENCE, 310 (5751): 1164-1166 NOV 18 2005
Abstract:
We present a theory of the thermodynamics of an incommensurate quantum solid. The ground state of the solid is assumed to. be an incommensurate crystal, with quantum zero-point vacancies and interstitials and thus a non-integer number of atoms per unit cell. We show that at low temperature T, the variation of the net vacancy concentration should be as T-4 and that the first correction to the specific heat due to this varies as T-7; these are quite consistent with experiments on solid helium-4. We also make some observations about the recent experimental reports of "supersolidity" in solid helium-4 that motivate a renewed interest in quantum crystals.
Title:
Finite-field ground state of an S=1 anisotropic antiferromagnetic chain
Authors:
Tonegawa, T; Okunishi, K; Sakai, T; Kaburagi, M
Source:
PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT, (159): 77-81 2005
Abstract:
We investigate, using numerical methods, the finite-field ground-state properties of an S = 1 anisotropic antiferromagnetic chain described by the Hamiltonian H=Sigma(l){S-l(x) S-l+1(x) + S-l(y) S-l+1(y) + Delta S-l(z) Sl+1} + d Sigma(l)(S-l(z)). It is found that the magnetization jump anomaly (a first-order phase transition) appears in the ground-state magnetization curve when Delta=5.0 and -1.50 less than or similar to D less than or similar to 1.05; in a certain region of D, the jump starts from a finite value of the magnetization m per spin. We also find that the a second-order phase transition between commensurate and incommensurate gapless phases takes place in the finite-field ground state. The critical point of this transition as well as the values of m at the onset and end of the magnetization jump is summarized in the m versus D phase diagram.
Title:
Field-induced phase transitions driven by quantum fluctuation in S=1/2 anisotropic triangular antiferromagnet Cs2CuBr4
Authors:
Ono, T; Tanaka, H; Kolomiyets, O; Mitamura, H; Ishikawa, F; Goto, T; Nakajima, K; Oosawa, A; Koike, Y; Kakurai, K; Klenke, J; Smeibidle, P; Meissner, M; Coldea, R; Tennant, AD; Ollivier, J
Source:
PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT, (159): 217-221 2005
Abstract:
The field induced magnetic phase transitions of Cs2CuBr4 were investigated by means of magnetization process and neutron scattering experiments. Cs2CuBr4 should be characterized as S = 1/2 two-dimensional triangular antiferromagnet. Below the ordering temperature T-N = 1.4 K, the spin structure is the helical incommensurate structure almost within the triangular lattice plane. In the field direction within the triangular lattice plane, Cs2CuBr4 exhibits the magnetization plateaux at one-third and two-thirds of the saturation magnetization. The spin structure in the one-third plateau phase is found to be almost collinear up-up-down structure which should be stabilized by quantum fluctuation as predicted by the theoretical studies.
Title:
Magnetization plateaus and magnetic excitations in the S=1/2 spin ladder antiferromagnet NH4CuCl3
Authors:
Harada, I; Miyazaki, H
Source:
PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT, (159): 246-250 2005
Abstract:
Field-induced magnetic phases are investigated in one-dimensional S = 1/2 generalized spin ladder systems having the lattice modulation along the leg with the wavevector pi/2a, a being the lattice constant, using numerical calculations. We point out that there exist cases where the 1/4- as well as the 3/4-magnetization plateaus appear but the 1/2-plateau does not, for an appropriate set of the parameters. Triplet excitations in the plateau regions are discussed in connection with the experimental result, which provides possible implications for the important role of the interaction between triplets.
Title:
NMR study of the successive phase transitions in CuB2O4
Authors:
Nakamura, H; Fujii, Y; Kikuchi, H; Chiba, M; Yamamoto, Y; Hori, H; Petrakovskii, G; Popov, M; Bezmaternikh, L
Source:
PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT, (159): 360-364 2005
Abstract:
Nuclear magnetic resonance (NMR) experiments on copper metaborate CuB2O4 are performed in order to study the successive phase transitions which includes the transition from the paramagnetic to the commensurate weak ferromagnetic phase at T-N = 21 K and further transition to the incommensurate helix phase at T* similar to 10 K. B-11-NMR spectra obtained for three crystal orientations (B parallel to [001], [110], [100]) were split into several lines below T-N and changed into more complicated line shapes below T*. The results of the angular dependence of the spectrum in the *commensurate* *phase* and the nuclear *spin*-*lattice* relaxation rate T-1(-1) are also discussed.
Title:
A new rhombic approximant in the Al-Pd-Fe system
Authors:
Balanets'kii, SO; Grushko, B; Urban, K; Velikanova, TY
Source:
POWDER METALLURGY AND METAL CERAMICS, 44 (5-6): 282-286 MAY-JUN 2005
Abstract:
Scanning and transmission electron microscopy have been used along with x-ray diffraction in the Al - Pd - Fe system to establish a new type of B-centered rhombic N phase. The lattice constants of the N phase are as follows: a = 2.31 nm, b = 1.60 nm, and c = 4.70 nm. Electron-probe microanalysis establishes the composition: Al76.6Pd10.0Fe13.4- Differential thermal analysis indicates that the N phase melts incongruently at a temperature close to 885 degrees C.
Title:
Effect of Nb content on the microstructure and mechanical properties of Zr-Cu-Ni-Al-Nb glass forming alloys
Authors:
Sun, YF; Shek, CH; Wei, BC; Li, WH; Wang, YR
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 403 (1-2): 239-244 NOV 10 2005
Abstract:
(Zr65Al10Ni10Cu15)(100-x) Nb-x glass forming alloys with Nb contents ranging from 0 to 15 at.% were prepared by water-cooled copper mould cast. The alloys with different Nb contents exhibited different microstructures and mechanical properties. Unlike the monolithic Zr65Al10Ni10Cu15 bulk metallic glass, only a few primary bee beta-Ti phase dendrites were found to distribute in the glassy matrix of the alloys with x = 5. For alloys with x = 10, more beta-phase dendrites forms, together with quasicrystalline particles densely distributed in the matrix of the alloys. For alloys with x = 15, the microstructure of the alloy is dominated by a high density of fully developed P-phase dendrites and the volume fraction of quasicrystalline particles significantly decreases. Room temperature compression tests showed that the alloys with x = 5 failed at 1793 MPa and exhibited an obvious plastic strain of 3.05%, while the other samples all failed in a brittle manner. The ultimate fracture strengths are 1793, 1975 and 1572 MPa for the alloys with x = 0, 10 and 15 at.% Nb, respectively. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Ferroelectric and ferroelastic phase transitions in molybdates and tungstates of monovalent and bivalent elements
Authors:
Isupov, VA
Source:
FERROELECTRICS, 322: 83-114 2005
Abstract:
Ferroelectric and ferroelastic phase transitions in molybdates and tungstates of monovalent and bivalent elements are reviewed. The nature and peculiarities of these transitions are briefly discussed. Most of interesting phase transitions are observed in compounds, containing monovalent ions, while among compounds of bivalent elements, only perovakites have properties of interest. Some molybdates and tungstates under consideration are improper ferroelectrics and ferroelastics, some of them have non-reversible, but reorienting, spontaneous polarization, some have modulated phases. There are indications on possibility of the ferroelectric state formation as a result of a reconstructive phase transition. Some crystal chemical problems are briefly discussed.
Title:
[M(H2O)(2)(15-crown-5)](NO3)(2): A system rich in polymorphic and modulated phases
Authors:
Hao, X; Siegler, MA; Parkin, S; Brock, CP
Source:
CRYSTAL GROWTH & DESIGN, 5 (6): 2225-2232 NOV-DEC 2005
Abstract:
The series of structurally related compounds [M(H2O)(2)(15-crown-5)1(NO3)(2), M = Cu, Mg, Zn, and Co (four phases) has been extended to include three new phases for M = Mn and two new phases for M = Fe. Two new structure types have been discovered, so nine phases of two basic types (two- or three-dimensional H-bonding pattern) are now known. For the 2-D H-bonded (or layered) structure type, four variants having different modulation patterns have been observed. All phases have more than one crystallographically independent formula unit (Z' > 1) The cation conformations of all the independent units in all the structures are essentially identical. Reversible phase transitions during which crystallinity is preserved link the two layered structures of the Mn compound and of the Fe compound. A reason for the existence of so many related phases has been identified.
Title:
Imaging antiferromagnetic domains in GdNi2Ge2 with x-ray resonant magnetic scattering
Authors:
Kim, JW; Kreyssig, A; Tan, L; Wermeille, D; Bud'ko, SL; Canfield, PC; Goldman, AI
Source:
APPLIED PHYSICS LETTERS, 87 (20): Art. No. 202505 NOV 14 2005
Abstract:
We describe investigations of antiferromagnetic domains by resonant magnetic diffraction using linearly polarized x rays at the L-2 edge of Gd in GdNi2Ge2. Studies of single domains and images of these domains provide details of the magnetic transition from a collinear antiferromagnetic structure for 16 K < T < 27.5 K to a spiral structure for T < 16 K. This technique may be used to discriminate between antiferromagnetic domains that differ in their modulation or moment direction, and between the ordering of different magnetic species. (C) 2005 American Institute of Physics.
Title:
Composition and structure of Cu-based nanoicosahedral phase in Cu-Zr-Ti-Pd alloy
Authors:
Louzguine-Luzgin, DV; Inoue, A; Nagahama, D; Hono, K
Source:
APPLIED PHYSICS LETTERS, 87 (21): Art. No. 211918 NOV 21 2005
Abstract:
The present work is devoted to an investigation of the composition of a nanoscale icosahedral phase in a Cu55Zr30Ti10Pd5 glassy alloy by three-dimensional atom probe analysis. The data indicate that the composition of the nanoicosahedral phase that precipitates from the Cu55Zr30Ti10Pd5 glassy alloy is not much different from that of the matrix, that is, the icosahedral phase is Cu-based containing more than 50 at. % Cu. The formation criteria for Cu- and Zr/Hf-based icosahedral phases are discussed based on quasi-lattice constant derived from average atomic diameter ratio. (c) 2005 American Institute of Physics.
Title:
Growth of Ag icosahedral nanocrystals on a SrTiO3(001) support
Authors:
Silly, F; Castell, MR
Source:
APPLIED PHYSICS LETTERS, 87 (21): Art. No. 213107 NOV 21 2005
Abstract:
We have investigated the structure and morphology of self-assembled silver nanocrystals supported on a SrTiO3(001)-(2x1) substrate using scanning tunneling microscopy. Ag forms nanocrystals with five-fold symmetry which have an icosahedral shape. Nanocrystals with point, edge, and face orientation (five-fold, two-fold, and three-fold symmetry, respectively) have been studied. The images of these nanocrystals allow a crystallographic identification of the supported shape of the icosahedral form. (c) 2005 American Institute of Physics.
Title:
A reinterpretation of the phase transitions in Na2CO3
Authors:
Arakcheeva, A; Chapuis, G
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 61: 601-607 Part 6 DEC 2005
Abstract:
Based on the structural data of phases alpha (hexagonal; 756-972 K), beta (monoclinic; 605-751 K), gamma (incommensurate, monoclinic; 295 K) and delta (lock-in, monoclinic; 110 K) of sodium carbonate, Na2CO3, we could draw a parallel between the phase transitions and the evolution of the second coordination sphere of the C atoms. The temperature-dependent structures observed in the beta phase are reproduced in the incommensurate gamma phase as a modulation wave, which relates to the content of the symmetrically equivalent {110} lattice planes in the alpha phase. By decreasing the temperature, the phase transitions are associated with a stepwise increase in the number of Na ions participating in the second coordination sphere of the C atoms. Over the full temperature range, this number increases from 3 to 7. The C-O distances and the mobility of the O atoms depends on the number of Na ions in the vicinity of the C atoms.
Title:
Tilt and acoustic instabilities in ABX(4), A(2)BX(4) and ABX(3) perovskite structure types: their role in the incommensurate phases of the organic-inorganic perovskites
Authors:
Swainson, IP
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 61: 616-626 Part 6 DEC 2005
Abstract:
An examination of the tilt modes and other low-frequency modes is made for an isolated, untilted perovskite layer, which maps very simply to the ABX(4) perovskites. A sheet of pure tilts exists at the Brillouin Zone boundary at {xi, 1/2, zeta}. An instability is also found at all wavevectors which can be described as continuously varying from pure tilts to pure layer displacements as a function of the wavevector. Analysis is extended by considering the stacking of layers in the I-centered A(2)BX(4)- layer perovskites. The effect of freezing in the commensurate tilt required to generate the Cmca tilt system, pertinent to the modulated phases of propylammonium salts, is examined. The zero-frequency modes are restricted to two planes in the Brillouin Zone. All of the observed wavevectors associated with modulated phases, and the commensurately tilted propylammonium tetrachlorocadmate, are consistent with this calculation. The effect of full three-dimensional connectivity is briefly reviewed for the true ABX(3) perovskites. While pure tilt incommensurates appear to be hypothetically possible, they do not appear to have been observed to date.
Title:
Incommensurately modulated ordering of tetrahedral chains in Ca2Fe2O5 at elevated temperatures
Authors:
Kruger, H; Kahlenberg, V
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 61: 656-662 Part 6 DEC 2005
Abstract:
The basic building units of brownmillerite-type A(2)B(2)O(5) structures are perovskite-like layers of corner-sharing BO6 octahedra and zweier single chains of BO4 tetrahedra. A three-dimensional framework is formed by alternate stacking of octahedral layers and sheets of tetrahedral chains. The compound Ca2Fe2O5 is known to have Pnma symmetry at ambient conditions. The space group Imma was reported to be evident above 963 K. New high-temperature single-crystal X-ray diffraction experiments at 1100 K revealed that Ca2Fe2O5 forms an incommensurately modulated structure adopting the superspace group Imma(00 gamma)s00, with gamma = 0.588 (2). The modulation affects the sequence of the enantiomorphic (right- and left-handed) oriented tetrahedral chains within the layer, breaking the lattice periodicity along c. This ordering can be modelled with crenel occupation modulation functions for the tetrahedrally coordinated Fe, as well as for the O atom interconnecting the tetrahedra.
Title:
Three modulation patterns in four related [M(H2O)(2)(15-crown-5)](NO3)(2) structures
Authors:
Hao, X; Parkin, S; Brock, CP
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 61: 675-688 Part 6 DEC 2005
Abstract:
The structures of [M(H2O)(2)(15-crown-5)](NO3)(2), M=Cu, Zn, Mg and Co, and 15-crown-5 = 1,4,7,10,13-pentaoxacyclopentadecane, have been redetermined at 294 and 90 K. The four structures, and a second form of the Cu structure, have been reported in the literature, but are all incorrect in some significant way. The structures, which all have at least two independent formula units (i.e. Z' >= 2), are related; each water ligand is hydrogen-bonded to two nitrate anions, while each nitrate anion is hydrogen bonded to the water ligands of two cations. In the tetragonal Co structure the hydrogen-bond pattern is three-dimensional; in the monoclinic Cu, Zn and Mg structures the hydrogen-bond patterns are two-dimensional. In the isostructural Zn and Mg structures Z' = 3, while in the Cu structure Z' = 5. The Cu, Zn and Mg structures are modulated variants of a basic structure, which was reported for Cu but which probably does not exist. The conformations of the 11 independent cations are remarkably similar; they all have approximate twofold symmetry and so exist as conformational enantiomers. The most important modulation is imperfect enantiomeric alternation of the cations along the longest cell axis; the independent cations are related by very good pseudotranslation and pseudoinversion operations. The diffraction patterns for all four structures have classes of weak, even very weak, reflections.
Title:
Isostructural phase transition in m-carboxyphenylammonium monohydrogenphosphite
Authors:
Bendeif, EE; Dahaoui, S; Francois, M; Benali-Cherif, N; Lecomte, C
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 61: 700-709 Part 6 DEC 2005
Abstract:
Crystals of m-carboxyphenylammonium monohydrogenphosphite, C(7)H(8)NO(2)(+)center dot H2PO3- (m-CPAMP), space group P2(1)/c, grown from aqueous solution undergo a reversible first-order single-crystal phase transition at T-c = 246 (2) K with a hysteresis of 3.6 K. The thermal behaviour of the sample was characterized by differential scanning calorimetry (DSC) experiments. Variations of the unit-cell parameters versus temperature between 100 and 320 K are reported. The transition from the higher-temperature phase (HTP) to the lower-temperature phase (LTP) is characterized by a unit-cell volume contraction of 1.77%. The average structure and unit-cell packing of m-CPAMP at lower temperature (100 K) are reported from accurate X-ray data sets and compared with those of the higher-temperature phase (293 K) in order to investigate the mechanism of the phase transition. The reciprocal lattice reconstruction showed a few very weak satellite reflections which will be discussed in a forthcoming paper.

Update: 25-Nov-2005

Title:
Phonon-phason coupling in a Mg-Ga-Al-Zn icosahedral quasicrystal
Authors:
Edagawa, K
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 85 (9): 455-462 SEP 2005
Abstract:
Precise X-ray diffraction measurements have revealed that phonon (conventional) strain is introduced at the phase transition from an icosahedral quasicrystal to its orthorhombic crystal approximant in a Mg-Ga-Al-Zn alloy. From the magnitude of the measured phonon strain, the phonon-phason coupling constant has been evaluated. This constant is approximately -0:03 mu (mu: shear modulus) and it is in good agreement with the result of a theoretical calculation reported previously (W.-J. Zhu and C. L. Henley, Europhys. Lett. 46 748 (1999)). This is the first study that experimentally evaluates the phonon-phason coupling constant in any existing quasicrystalline phase.
Title:
Features of interatomic force interaction in an i-AlCuFe quasicrystal
Authors:
Parshin, PP; Zemlyanov, MG; Brand, RA
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 101 (4): 676-679 2005
Abstract:
Earlier experimental results on partial thermal vibrational spectra and on the atomic and electronic structure of icosahedral i-AlCuFe quasicrystals are used for analyzing the role of Al, Cu, and Fe atoms in interatomic interactions in these quasicrystals. A physical model proposed for the structure of i-AlCuFe quasicrystals matches with the available experimental data and provides a qualitative description of the features of the interatomic interaction. (c) 2005 Pleiades Publishing, Inc.
Title:
Anomalous magnetoresistivity of the superconducting Zr80Pt20 system in quasicrystalline and amorphous states
Authors:
Panova, GK; Chernoplekov, NA; Shikov, AA
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 101 (4): 680-685 2005
Abstract:
The binary icosahedral Zr80Pt20 system has been synthesized during the crystallization of an initially amorphous alloy fabricated by melt quenching on the surface of a rotating copper wheel. The temperature and field dependences of the electrical resistivity and magnetoresistivity of the icosahedral and amorphous phases are studied and compared in a temperature range of 1.5-300 K and magnetic fields up to 8 T. Superconductivity has been detected for the first time in the icosahedral and amorphous phases of the Zr80Pt20 system. For both phases, the magnetoresistivity is positive and depends anomalously on the magnetic field. The anomalous behavior of magnetoresistivity is satisfactorily described by the theory of weak localization and electron-electron interaction in three-dimensional disordered systems, which takes into account electron scattering by superconducting fluctuations. The absolute values and temperature dependences of the electron-electron interaction constant and the times of inelastic scattering of conduction electrons are estimated for the icosahedral and amorphous phases of this binary system. (c) 2005 Pleiades Publishing, Inc.
Title:
Density wave and supersolid phases of correlated bosons in an optical lattice
Authors:
Kovrizhin, DL; Pai, GV; Sinha, S
Source:
EUROPHYSICS LETTERS, 72 (2): 162-168 OCT 2005
Abstract:
Motivated by the recent experiment on the Bose-Einstein condensation of Cr-52 atoms with long-range dipolar interactions (Werner J. et al., Phys. Rev. Lett., 94 (2005) 183201), we consider a system of bosons with repulsive nearest and next-nearest neighbor interactions in an optical lattice. The ground-state phase diagram, calculated using the Gutzwiller ansatz, shows, apart from the superfluid (SF) and the Mott insulator (MI), two modulated phases, i.e., the charge density wave (CDW) and the supersolid (SS). Excitation spectra are also calculated which show a gap in the insulators, gapless, phonon mode in the superfluid and the supersolid, and a mode softening of superfluid excitations in the vicinity of the modulated phases. We discuss the possibility of observing these phases in cold dipolar atoms and propose experiments to detect them.

Update: 19-Nov-2005

Title:
Recent breakthrough development of the magnetic shape memory effect in Ni-Mn-Ga alloys
Authors:
Soderberg, O; Ge, Y; Sozinov, A; Hannula, SP; Lindroos, VK
Source:
SMART MATERIALS & STRUCTURES, 14 (5): S223-S235 OCT 2005
Abstract:
Magnetic shape memory (MSM) alloys or ferromagnetic shape memory alloy (FSMA) materials discovered by Ullakko et al (1996 Appl. Phys. Lett. 69 1966-8) have received increasing interest, since they can produce a large strain with rather high frequencies without a change in the external temperature. These materials have potential for actuator and sensor applications. MSM materials exhibit giant magnetic field induced strain (MFIS) based on the rearrangements of the crystallographic domains (twin variants). The magnetization energy of the material is lowered when such twin variants that have the easy axis of magnetization along the field start to C grow due to twin boundary motion. Currently, the best working MSM materials are the near-stoichiometric Ni2MnGa Heusler alloys in which the properties are highly composition dependent. Their modulated martensitic structures, 5M and 7M, show 6% or 10% response respectively in a magnetic field less than 800 kA m(-1). The MSM service temperature of the 5M alloys is between 150 and 333 K, and the optimal frequency region is up to 500 Hz. The fatigue life of the MSM elements has been shown to be at least 50 x 10(6) shape change cycles. This paper reviews the research work carried out at Helsinki University of Technology on MSM materials since 1998.
Title:
Incommensurate composite crystal structure of scandium-II
Authors:
Fujihisa, H; Akahama, Y; Kawamura, H; Gotoh, Y; Yamawaki, H; Sakashita, M; Takeya, S; Honda, K
Source:
PHYSICAL REVIEW B, 72 (13): Art. No. 132103 OCT 2005
Abstract:
The long-unknown crystal structure of the high pressure phase scandium-II was solved by powder x-ray diffraction and was found to have tetragonal host channels along the c axis and guest chains that are incommensurate with the host, as well as the high pressure phases of Ba, Sr, Bi, and Sb. The pressure dependences of the lattice constants, the incommensurability, the atomic distances, and the atomic volume were investigated.
Title:
Anisotropy of incommensurate spin and charge fluctuations in detwinned YBa2Cu3O6+delta
Authors:
Zhou, T; Li, JX
Source:
PHYSICAL REVIEW B, 72 (13): Art. No. 134512 OCT 2005
Abstract:
Motivated by a recent neutron scattering experiment on a detwinned YBa2Cu3O6+delta superconductor, we examine the frequency and doping dependence of the anisotropy in the spin and charge fluctuation arising from the coupling between the plane and the chain (along the b axis). Starting from the two-dimensional t-t(')-J model and using the random-phase approximation (RPA), we find a pronounced anisotropy of the incommensurate (IC) peaks in the spin channel, namely the peak intensity at the (pi +/-delta,pi) direction is stronger than that at the (pi,pi +/-delta) direction in a wide frequency range from omega=0.2J to the resonance frequency omega(r)=0.35J. Above the resonance frequency, the IC peaks reemerge. Their intensities shift to the diagonal direction and no anisotropy exists along the two diagonal directions. We find that this anisotropy is robust with respect to the possible variation of the RPA correction factor and to the dopings. The charge fluctuation is also found to be incommensurate for all energies considered and peak at (0,delta) and (delta,0). An anisotropy in its IC peak intensity along the k(x) and the k(y) direction exists, but in sharp contrast to the spin channel, the maximum intensity of the IC peak is along the k(y) direction. Moreover, the IC peak in the charge channel exhibits an upward dispersion, in contrast to the downward dispersion below the spin resonance frequency for the spin IC peak. We explain these features based on the effect of the plane-chain coupling on the topology of the Fermi surface.
Title:
Formation of micrometer sized quasicrystals in slowly cooled Zr-Ti-Nb-Cu-Ni-Al alloys
Authors:
Kuhn, U; Eckert, J; Mattern, N; Schultz, L
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 202 (13): 2436-2441 OCT 2005
Abstract:
The solidification behavior of copper mold cast Zr60Ti6Nb2Cu14Ni9Al9 and Zr60Ti2Nb6Cu14Ni9Al9 alloys has been investigated. The phase formation of the alloy with a ratio of Ti: Nb = 3: 1 depends very sensitively on changes of the cooling conditions, exhibiting three competing phases: a glassy, an icosahedral quasicrystalline (i phase) and a crystalline phase, which are arranged very closely in the part of the sample with the highest cooling rate. Decreasing the cooling rate leads to a fully crystalline microstructure. In contrast, the alloy with a ratio of Ti: Nb = 1: 3 forms predominantly an i phase and presents only a low volume fraction of a residual glassy phase at the interfaces of the quasicrystals. Besides a specific cooling rate a content of Cu + Ni + Al of about 32 at% and a content of Ti + Nb of about 8 at% is required for the formation of an as-cast i phase in these Zr-based alloys, because of a decrease of their glass-forming ability linked with more pronounced icosahedral short-range ordering in the melt. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Title:
High pressure neutron diffraction investigation of CuO
Authors:
Chatterji, T; Brown, PJ; Forsyth, JB
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (40): S3057-S3062 Sp. Iss. SI OCT 12 2005
Abstract:
The dependence of the magnetic structure of CuO on hydrostatic pressure up to 18 kbar has been studied by means of neutron diffraction at low temperatures. The pressure dependences of both the Neel temperature T-N and the incommensurate-commensurate lock-in transition temperature T-L have been determined. The Neel temperature, which is 230 K at ambient pressure, increases to T-N = 235 K at P = 18 kbar, whereas the lock-in transition temperature, which is 213 K at ambient pressure, decreases continuously to TL = 207 K at P = 18 kbar. Since hydrostatic pressure increases the stability range of the incommensurate phase, it is likely that at very high pressures the incommensurate phase would be the only stable ordered magnetic phase of CuO and the commensurate antiferromagnetic phase would be completely suppressed.
Title:
Magnetization and neutron diffraction studies of LU2Fe17 under high pressure
Authors:
Kamarad, J; Prokhnenko, O; Prokes, K; Arnold, Z
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (40): S3069-S3075 Sp. Iss. SI OCT 12 2005
Abstract:
Combined magnetization and neutron diffraction measurements under high hydrostatic pressures up to 1 GPa were performed to study magnetic structures and their evolution in an LU2Fe17 single crystal. Pressures higher than 0.4 GPa suppress the collinear ferromagnetic ground state completely. The pressure induced magnetic structure can be described as a superposition of both incommensurate and commensurate magnetic components with propagation vectors tau(1) = (0; 0; tau(1z)) and tau(2) = 0. Mechanisms of the helimagnetic-ferromagnetic transitions induced by temperature and magnetic field in LU2Fe17 at ambient and high pressures are discussed.

Update: 13-Nov-2005

Title:
Five-dimensional model of the S1-superstructure phase in Al-Ni-Co quasicrystals
Authors:
Yamamoto, A; Takakura, H; Abe, E
Source:
PHYSICAL REVIEW B, 72 (14): Art. No. 144202 OCT 2005
Abstract:
A five-dimensional (5D) cluster model of the S1 superstructure phase of decagonal Al-Ni-Co quasicrystals is proposed based on the results of the structure refinement of the basic-Ni phase with the same chemical composition. This model leads to a structure composed of fivefold symmetric clusters at vertices of the Penrose pentagon tiling (PPT) with an edge length of about 20 angstrom. The clusters with two different orientations are located at the vertices of the PPT. The structure has the 5D color space group P10(5)/mc(')m(') which explains the satellite reflections characteristic of the S1 phase and forces to locate clusters with different orientations at most adjacent vertices of the PPT. The model is obtained from that for the basic-Ni phase by a small number of atom flips which can be regarded as interlayer phason flips. This suggests that the phase transition from the basic-Ni to S1 phases occurs by the interlayer phason flips without long-range atom diffusion.
Title:
Ab initio investigation of the magnetism of tetragonal Mn: Bulk, surface, ultrathin films, and multilayers
Authors:
Hafner, J; Spisak, D
Source:
PHYSICAL REVIEW B, 72 (14): Art. No. 144420 OCT 2005
Abstract:
The magnetic properties of the tetragonally distorted gamma and delta phases of Mn stabilized by epitaxial growth on metallic surfaces are still subject of a lively debate, but so far no consistent and generally accepted picture has emerged. We have performed detailed and comprehensive investigations of the geometric and magnetic properties of tetragonal Mn in the bulk, at a (100) surface, in ultrathin Mn/Fe(100) films, and in Mn/Fe multilayers using ab initio spin-density functional techniques. The cubic structures of both gamma (face-centered cubic) and delta (body-centered cubic) Mn are unstable against tetragonal distortion. Whereas for delta-Mn a structure contracted along the c axis and with c(2x2) in-plane (100) antiferromagnetism (AFM) is the unique ground state, for gamma-Mn a contracted tetragonal (c/a=0.945) phase with a layered (100) AFM, and an expanded (c/a=1.048) phase with in-plane (100) AFM are energetically almost degenerate. In addition we find that the antiferromagnetic phases of both delta and gamma Mn are susceptible to long-period helical modulations. At the (100) surface, the Mn moments are strongly enhanced, and the strong antiferromagnetic coupling between the high surface moments favors in-plane AFM in the surface layer even on top of the tetragonally compressed near-fcc phase stabilizing layered antiferromagnetism in the bulk. A similar result is found for ultrathin Mn/Fe(100) films with up to six monolayers. A strong ferromagnetic Mn/Fe coupling at the interface favors layered antiferromagnetism in the deeper layers, but the in-plane antiferromagnetic structure in the top layer is stable in any case. For the thinnest Mn films we have also examined noncollinear magnetic structures and found evidence for a perpendicular coupling between the Mn surface layer and the deeper layers of film and substrate. The strong ferromagnetic Mn/Fe interface coupling also determines the properties of Fe/Mn multilayers. The ferromagnetic interface coupling is not perturbed by Fe/Mn intermixing and stabilizes a layered antiferromagnetism in the Mn spacer. We discuss our results in the light of the available experimental data and of previous theoretical calculations.
Title:
Generation of tunable terahertz out-of-plane radiation using Josephson vortices in modulated layered superconductors
Authors:
Savel'ev, S; Yampol'skii, V; Rakhmanov, A; Nori, F
Source:
PHYSICAL REVIEW B, 72 (14): Art. No. 144515 OCT 2005
Abstract:
We show that a moving Josephson vortex in spatially modulated layered superconductors generates out-of-plane THz radiation. Remarkably, the magnetic and in-plane electric fields radiated are of the same order, which is very unusual for any good-conducting medium. Therefore, the out-of-plane radiation can be emitted to the vacuum without the standard impedance mismatch problem. Thus, the proposed tunable THz emitter for out-of-plane radiation can be more efficient than the standard one which radiates only along the ab-plane.
Title:
Stability of the modulated states in ErNi2B2C: A neutron diffraction study of chemically doped samples
Authors:
El Massalami, M; Galera, RM; Schmitt, D; Ouladdiaf, B; Takeya, H
Source:
PHYSICAL REVIEW B, 72 (14): Art. No. 144521 OCT 2005
Abstract:
Neutron-diffraction measurements on Er0.8R0.2Ni2B2C (R=Tb,Lu) and ErNi1.9Co0.1B2C have been carried out to investigate the influence of chemical doping on the stability of the modulated states in ErNi2B2C. Within the magnetically ordered phase and down to 1.6 K (the lowest measured temperature), the powder diffractograms of Lu and Tb doped compounds are consistent with a transverse sine-modulated (fundamental) mode. A neutron diffraction study on a single-crystal Er0.8Lu0.2Ni2B2C recorded at 1.8 K has confirmed the absence of higher order harmonics. In contrast, the low-temperature patterns of the Co doped compound reveal the presence of all the odd-order harmonics up to the fifth-order satellite, reminiscent of the structure of the undoped ErNi2B2C below the weak-ferromagnetic transition point T-WF=2.1 K: a squared-up, noncompensated long-period antiferromagnetic state. The above-mentioned findings are consistent with the conclusions drawn from our previous specific-heat and magnetization measurements on the same compounds: on lowering the temperature further below T-N, both ErNi2B2C and Co doped compounds undergo a spontaneous transition at T-WF. In contrast, for the Lu and Tb doped compounds, no such second magnetic phase transition was observed down to 1 K; eventually the squaring-up of these structures, as required by entropy arguments, should occur but at temperatures lower than 1 K.
Title:
Disclinations as a source of thermal resistance in icosahedral i-AlPdMn quasicrystals
Authors:
Krasavin, SE
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (39): 6173-6177 OCT 5 2005
Abstract:
We propose a model to analyse the experimental data for thermal conductivity of single-grain i-AlPdMn quasicrystals. The interpretation is based on the picture in which disclination pairs of wedge type are the main source of phonon scattering at low temperatures. The scattering of phonons due to strain fields of these dipoles is considered. Our numerical calculations show that experimentally observed thermal conductivity in a wide temperature range can be well fitted by a combination of wedge disclination dipole scattering and quasi-umklapp scattering processes.
Title:
New developments in experimental and analytical aspects of light figure spectroscopy
Authors:
Mamedov, N; Shim, Y; Yamamoto, N
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 44 (1B): 754-760 JAN 2005
Abstract:
Recent developments in light figure spectroscopy are reviewed with a purpose to promote their large-scale application to anisotropic materials and thin films. Both absolute and relative analytical approaches and the results of the experimental approval on the well-known uniaxial calcite, CaCO3, are given. Further generalization and extension onto optically active materials. are described with a stress on a shrinkage effect that was predicted and observed for the first time. The numbering of the interference curves in the presence of gyration is shown to be different in comparison with gyration-free case. A universal approach to the determination of the correct interference order is proposed and found to be in a good agreement with experimental data on CaCO3, TeO2 and AgGaS2. The effectiveness of the light figure method with regard to the nanomodulated structures is demonstrated by the recent application to the novel thallium-contained incommensurate materials, TlInS2 and TlGaSe2. Thin film applications are discussed in terms of the merits of homogeneously and non-homogeneously polarized testing beams and isotropic and anisotropic substrates. A preference is given. to anisotropic substrates which can provide creation of the optical vortexes with ellipsometric or higher sensitivity to film parameters and open a gateway to the light-figure-based characterization of the anisotropic films with vanishing thickness and optical anisotropy.
Title:
Diffuse scattering and ordering in the short-range modulated paraelectric phase of sodium nitrite, NaNO2
Authors:
Lukaszewicz, K; Pietraszko, A; Kucharska, M
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 61: 473-480 Part 5 OCT 2005
Abstract:
The incommensurately modulated antiferroelectric phase of sodium nitrite, NaNO2, transforms at T-N = 437.7 K to the short-range modulated paraelectric phase. The apparently discontinuous phase transition is accompanied by characteristic changes in the diffraction pattern. Contrary to the well known modulated structures with sharp satellite reflections, the diffraction pattern of a short-range modulated structure contains diffuse satellite reflections. The short-range modulated crystal structure of the paraelectric phase of sodium nitrite has been analysed by the Reverse Monte Carlo (RMC) simulation of X-ray diffuse scattering. The crystal structure of sodium nitrite may be regarded as consisting of [Na+NO2-]infinity rows running along the polar b axis. One can expect long fragments of rows with uniform polarity The assumption that single [Na+NO2-](infinity) rows are polar with uniform polarity proved to be a convenient approximation which is in good agreement with the observed diffraction pattern. The distribution of (+)- and (-)-[Na+NO2-] 1 polar rows crossing the (010) plane of short-range modulated NaNO2 revealed by RMC shows nanodomains consisting of distorted fragments of a sinusoidally modulated crystal structure. The size of the nanodomains and the degree of order in paraelectric NaNO2 decreases with temperature.

Update: 4-Nov-2005

Title:
Effects of air atomisation, spray deposition and melt overflow techniques on microstructural features of Al-Fe-V-Si alloy
Authors:
Kalkanli, A; Menekse, K; Ozyurda, HA
Source:
POWDER METALLURGY, 48 (3): 264-269 SEP 2005
Abstract:
Microstructural features of atomised powders, spray deposited preforms and melt overflow strips of 8009 series AlFeVSi alloy were investigated to reveal the microstructural evolution associated with the processing condition variations. X-ray diffraction (XRD), optical microscopy and scanning electron microscopy (SEM) techniques were used to identify the crystal structures of dispersoid phases in the specimens. The primary intermetallic phase was characterised as bee alpha-Al(Fe,V)Si having a lattice parameter in the range 12.51 - 12.53 angstrom, other phases are identified as icosahedral, Al3Fe and Al-13(Fe,V)(4) by XRD. SEM was used to examine the morphological changes and quantitative element analysis to reveal the chemical composition of these phases in specimens. Various phase morphologies such as starlike, band shape and needlelike intermetallics were observed in these products, whereas the primary phase crystal structure is cubic and stable.
Title:
Vortex core states in high-T-c superconductors with induced incommensurate spin and charge density waves
Authors:
Ichioka, M; Takigawa, M; Machida, K
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 426: 28-35 Part 1 OCT 1 2005
Abstract:
We investigate the change of the vortex structure in the presence of the induced stripe or checkerboard pattern modulation of the incommensurate spin density wave (SDW) and charge density wave (CDW) around the vortex core. The order parameter and the quasiparticle structure in the vortex lattice state are calculated by Bogoliubov-de Gennes theory on a two-dimensional Hubbard model with nearest-neighbor site pairing interaction. By the induced SDW and CDW, low-energy excitations around the vortex core are suppressed, producing "empty core" structure, as observed by the scanning tunneling microscopy. In the relation to these quasiparticle structures, we discuss the site-selective nuclear spin relaxation time T, and thermal conductivity in the vortex state. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Comparative study of anisotropic superconductivity in CaAlSi and CaGaSi
Authors:
Tamegai, T; Uozato, K; Kasahara, S; Nakagawa, T; Tokunaga, M
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 426: 208-212 Part 1 OCT 1 2005
Abstract:
In order to get some insight into the origin of the anomalous angular dependence of H-c2 in a layered intermetallic compound CaAlSi, electronic, superconducting, and structural properties are compared between CaAlSi and CaGaSi. The angular dependence of H-c2 in CaGaSi is well described by the anisotropic GL model. Parallel to this finding, the pronounced lattice modulation accompanying the superstructure along the e-axis in CaAlSi is absent in CaGaSi. A relatively large specific heat jump at the superconducting transition in CaAlSi compared with CaGaSi indicates the presence of strong electron-phonon coupling in CaAlSi, which may cause the superstructure and the anomalous angular dependence of H-c2. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Neutron scattering study on stripe correlations in La2-xBaxCuO4
Authors:
Fujita, M; Goka, H; Adachi, T; Koike, Y; Yamada, K
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 426: 257-261 Part 1 OCT 1 2005
Abstract:
We have performed neutron scattering experiment on the single crystals of La2-xBaxCuO4 (x = 0.10 and 0.125) in order to study the doping dependence of stripe correlations. At low temperatures, clear incommensurate (IC) peaks from spin-density-wave orders (SDW) were observed in both samples. The incommensurability (5) of the SDW in the x = 0.10 sample was found to be 0.110, which slightly deviates from the simple relation of 6 = x seen in La2-xSrx- CuO4, possibly due to the large stripe pinning effect in the low-temperature tetragonal (LTT) structure. The inelastic magnetic signal at the low-energy region below 6 meV drastically changes around the structural transition temperature between LTT and low-temperature orthorhombic (LTO) phases T-d2. Temperature dependences of the peak-width and the incommensurability also show an anomalous behavior at T-d2 rather than the spin ordering temperature, T-sp. These results suggest that spin correlations are well stabilized in the LTT phase as expected from the stripe model. With further increasing temperature in LTO phase, the incommensurability decreases and the peak-width grows due to the degradation of stripe correlations. However, the stiffness of stripe correlation seen in the low-energy IC spin fluctuations depends on the doping. In the x = 0.10 sample no well-defined magnetic excitation peak was observed below 6 meV at 200 K, while a flat top shaped single peak remains at 6 meV in the x = 0.125 sample. Deviation from the 1/8 doping more easily lose the spatial coherence of spin correlations above T-d2. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Correlation between modulation structure and electronic inhomogeneity on Pb-doped Bi-2212 single crystals
Authors:
Sugimoto, A; Kashiwaya, S; Eisaki, H; Yamaguchi, H; Oka, K; Kashiwaya, H; Tsuchiura, H; Tanaka, Y
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 426: 390-395 Part 1 OCT 1 2005
Abstract:
The correlation between nanometer-size electronic states and surface structure is investigated by scanning tunneling microscopy/spectroscopy (STM/S) on Pb-doped Bi(2-x)Pb(x)Sr(2)CaCu2O(8+x) (Pb-Bi-2212) single crystals. The advantage of the Pb-Bi-2212 samples is that the modulation structure can be totally or locally suppressed depending on the Pb contents and annealing conditions. The superconducting gap (Delta) distribution on modulated Pb-Bi-2212 samples showed the lack of correlation with modulation structure except a slight reduction of superconducting island size for the b-axis direction. On the other hand, the optimal doped Pb-Bi-2212 (x = 0.6) samples obtained by reduced-annealing showed totally non-modulated structure in topography, however, the spatial distribution of Delta still showed inhomogeneity of which features were quite similar to those of modulated samples. These results suggest that the modulation structure is not the dominant origin of inhomogeneity although it modifies the streaky Delta structure sub-dominantly. From the gap structure variation around the border of narrow gap and broad gap regions, a trend of the coexistence of two separated phases i.e., superconducting phase and pseudogap like phase, is detected. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Scanning tunneling microscopy and spectroscopy in lanthanide substituted Bi2Sr2CuOy
Authors:
Machida, T; Tsuji, N; Sakata, H
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 426: 407-410 Part 1 OCT 1 2005
Abstract:
We have performed scanning tunneling microscopy and spectroscopy experiments on Bi2Sr1.57La0.43CuOy and Bi2Sr1.52Nd0.48CuOy, The atomic images showing the incommensurate modulated structure and the tunneling spectra have been successfully obtained at 4.2 K. The observed superconducting gap values in both samples have evolved spatially on the length scale of about 20 nm. This length scale is much longer than that reported in Bi2Sr2CaCu2Oy. The distribution of the gap value seems to originate from the inhomogencous distribution of the lanthanide ions. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Role of atomic modulation in the incommensurate composite crystal structure of (Sr2Cu2O3)(0.70)CuO2, "Sr14Cu24O41" with two-legged ladder and one-dimensional chain
Authors:
Gotoh, Y; Yamaguchi, I; Eisaki, H; Fujino, H; Nagata, T; Akimitsu, J
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 426: 416-420 Part 1 OCT 1 2005
Abstract:
Role of atomic modulation in the incommensurate composite crystal structure of (Sr2Cu2O3)(0.70)CuO2, "Sr14Cu24O41" has been investigated by four-dimensional superspace group approach. It has become apparent that the displacive modulations of Sr and O atoms are effective for the stabilization of alternate stacking of the planes of the Cu2O3 ladder and the CuO2 chain. The Cu-O bonds in both of the modulated and unmodulated structures have been investigated to understand the origin of electronic and magnetic properties. In the average structure, it has been clarified that considerable amount of holes are generated in the CuO2 chain. In the course of the modulated structure analysis, the Cu-O bond in the CuO2, chain has become tilt toward the Cu2O3 ladder in order that the O atom in the chain acts as apical oxygen for the ladder plane. By the large modulation of the O atom in the CuO2 chain, the prepared holes are distributed to make the hole-ordered structure in the CuO2 plane. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Brittleness of Zr-based bulk metallic glass matrix composites containing ductile dendritic phase
Authors:
Sun, YF; Guan, SK; Wei, BC; Wang, YR; Shek, CH
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 406 (1-2): 57-62 OCT 15 2005
Abstract:
Zr63Al10Ni10Cu14Nb3 monolithic bulk metallic glass (BMG) and Zr55Al8.5Ni8.5Cu13Nb15 BMG matrix composite containing densely distributed bcc dendritic phase were prepared by copper mould casting. The ductility of the dendritic phase was verified by nanoindentation tests. However, the composite samples exhibit relatively lower yield strength and no plastic strain under room temperature compression test. Microstructural characterization and fractography studies reveal that the simultaneous formation of quasicrystalline phase on the outermost region of the composite results in the brittleness of the composites. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Combinatorial construction of tilings by barycentric simplex orbits (D symbols) and their realizations in Euclidean and other homogeneous spaces
Authors:
Molnar, E
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 61: 542-552 Part 6 NOV 2005
Abstract:
A new method, developed in previous works by the author (partly with coauthors), is presented which decides algorithmically, in principle by computer, whether a combinatorial space tiling (T, Gamma) is realizable in the d-dimensional Euclidean space E-d (think of d = 2, 3, 4) or in other homogeneous spaces, e. g. in Thurston's 3-geometries: E-3; S-3; H-3; S-2 x R, H-2 x R, (SL2R) over tilde, Nil, Sol. Then our group Gamma will be an isometry group of a projective metric 3-sphere PS3(R, (,)), acting discontinuously on its above tiling T. The method is illustrated by a plane example and by the well known rhombohedron tiling (T, Gamma), where Gamma = R(3) over bar m is the Euclidean space group No. 166 in International Tables for Crystallography.

Update: 29-Oct-2005

Title:
Linkage between oxygen content and metastable phase formation in melt spun Zr80Pt20 alloys
Authors:
Sordelet, D; Yang, XY
Source:
TRANSACTIONS OF THE INDIAN INSTITUTE OF METALS, 58 (4): 749-760 AUG 2005
Abstract:
This report continues previous studies that show melt spun Zr80Pt20 ribbons having oxygen contents ranging from < 200 to approximately 5000 mass ppm form various metastable phases during quenching, In the presence of sufficient oxygen, a big cube Zr6Pt30 phase forms, but this structure is destabilized towards an icosahedral quasicrystalline structure at lower oxygen levels. Further reduction of oxygen promotes increasingly stable Zr-Pt bonds, and a metastable beta-Zr(Pt) structure is formed.
Title:
Al-Mg- and Fe-based nanocomposites by rapid solidification processing
Authors:
Murty, BS; Hono, K
Source:
TRANSACTIONS OF THE INDIAN INSTITUTE OF METALS, 58 (4): 769-775 AUG 2005
Abstract:
Nanocomposites are new generation composites with ultrafine grained matrix and nanodispersions of reinforcement material. A variety of matrix materials in terms of their chemical nature (such as Al and Mg based) and structure (crystalline, quasicrystalline and amorphous matrices) and different reinforcements such as oxides, crystalline and quasicrystalline intermetallics are being considered worldwide.The present paper deals with the development of Al-, Mg- and Fe based nanocomposites by the Rapid solidification processing route. Al-Fe-V, Al-Ti-Cr, Mg-Cu-Y and Fe-Cu-B-Zr system are chosen for the work. A number of compositions have been made using arc melting of pure metals. These alloys were rapidly solidified using melt spinning at different wheel velocities in the range of 10-50 m/s. In all the cases, a variety of nanocomposite microstructures have been obtained depending on the composition and cooling rate during melt spinning. The microstructure of the melt spun nanocomposites has been analyzed using XRD and TEM. The microhardness of the nanocomposite ribbons have been studied and correlated to the microstructure,of the alloys.
Title:
Orientational phase transition into a modulated magnetic state in the weak ferromagnet FeBO3 : Mg
Authors:
Sokolov, BY
Source:
PHYSICS OF THE SOLID STATE, 47 (10): 1892-1899 2005
Abstract:
The transition from a homogeneous into a modulated magnetic state in the easy- plane weak ferromagnet FeBO3 : Mg is studied by a magnetooptic method. At T < 135 K, the application of a magnetic field in the basal plane of the crystal is shown to excite the modulation of its magnetic order parameter, which manifests itself in a periodic deviation of the local ferromagnetism vector from the magnetization direction. The conditions for the existence of a modulated magnetic superstructure in FeBO3 : Mg are studied, and its preferred orientation in the basal plane of the crystal is analyzed. A magnetic H - T phase diagram that shows the boundaries between the homogeneous and inhomogeneous magnetic states of this weak ferromagnet is constructed. The modulation period and the azimuthal angle specifying the local ferromagnetism vector direction in the structure are studied as a function of temperature and magnetic field. The results obtained are discussed in terms of the theory of magnetic ripple using the model of anisotropic magnetic centers appearing in a crystal doped by magnesium ions. (c) 2005 Pleiades Publishing, Inc.
Title:
Quantum size effects in metal thin films grown on quasicrystalline substrates
Authors:
Fournee, V; Sharma, HR; Shimoda, M; Tsai, AP; Unal, B; Ross, AR; Lograsso, TA; Thiel, PA
Source:
PHYSICAL REVIEW LETTERS, 95 (15): Art. No. 155504 OCT 7 2005
Abstract:
We have investigated by scanning tunneling microscopy the growth of Bi and Ag thin films on the fivefold surface of Al63Cu24Fe13 and Al72Pd19.5Mn8.5 quasicrystal, respectively. For both systems, we observe the formation of islands with magic height, corresponding to the stacking of a specific number of atomic layers. We interpret this unusual growth morphology in terms of quantum size effects, arising from the confinement of the electron within the film. The magic island heights are thus a direct manifestation of the electronic structure of the quasicrystalline substrates.
Title:
The impact of nanoindentation at room temperature upon the real structure of decagonal AlCoNi quasicrystals
Authors:
Reibold, M; Belger, A; Mukhopadhyay, NK; Gille, P; Paufler, P
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 202 (12): 2267-2276 SEP 2005
Abstract:
Plastic deformation of the quasicrystalline decagonal phase Al72Co9Ni19, which appears macroscopically brittle at room temperature, has been performed by nanoindentation. Employing high resolution transmission electron microscopy it could be shown that near indents regions of a nanocrystalline phase appeared, which was identified. as trigonal Al-3(Ni,Co)(2). So, for permanent deformation at room temperature no dislocation movement was needed. Instead, it seems reasonable to assume that the decagonal phase tends to decompose into a crystalline phase under stress. Values of nanohardness and elastic modulus determined during this work were found within the range of data reported so far by other authors. (c) 2005 WILEY-VCH Veriag GmbH & Co. KGaA, Weinheim.
Title:
Ordering in two-dimensional Ising models with competing interactions
Authors:
Chitov, GY; Gros, C
Source:
LOW TEMPERATURE PHYSICS, 31 (8-9): 722-734 AUG-SEP 2005
Abstract:
We study the 2D Ising model on a square lattice with additional non-equal diagonal next-nearest neighbor interactions. The cases of classical and quantum (transverse) models are considered. Possible phases and their locations in the space of three Ising couplings are analyzed. In particular, incommensurate phases occurring only at non-equal diagonal couplings, are predicted. We also analyze a spin-pseudospin model comprised of the quantum Ising model coupled to XY spin chains in a particular region of interactions, corresponding to the Ising sector's super-antiferromagnetic (SAF) ground state. The spin-SAF transition in the coupled Ising-XY model into a phase with co-existent SAF Ising (pseudospin) long-range order and a spin gap is considered. Along with destruction of the quantum critical point of the Ising sector, the phase diagram of the Ising-XY model can also demonstrate a re-entrance of the spin-SAF phase. A detailed study of the latter is presented. The mechanism of the re-entrance, due to interplay of interactions in the coupled model, and the conditions of its appearance are established. Applications of the spin-SAF theory for the transition in the quarter-filled ladder compound NaV2O5 are discussed. (C) 2005 American Institute of Physics.
Title:
Incommensurate magnetism in the coupled spin tetrahedra system Cu2Te2O5Cl2
Authors:
Zaharko, O; Ronnow, HM; Daoud-Aladine, A; Streule, S; Juranyi, F; Mesot, J; Berger, H; Brown, PJ
Source:
LOW TEMPERATURE PHYSICS, 31 (8-9): 814-818 AUG-SEP 2005
Abstract:
Neutron scattering studies on powder and single crystals have provided new evidence for unconventional magnetism in Cu2Te2O5Cl2. The compound is built from tetrahedral clusters of S=1/2 Cu2+ spins located on a tetragonal lattice. Magnetic ordering, emerging at T-N=18.2 K, leads to a very complex multi-domain, most likely degenerate, ground state, which is characterized by an incommensurate (ICM) wave vector k similar to[0.15,0.42,1/2]. The Cu2+ ions carry a magnetic moment of 0.67(1)mu(B)/Cu2+ at 1.5 K and form a four-helix spin arrangement with two canted pairs within the tetrahedra. A domain redistribution is observed when a magnetic field is applied in the tetragonal plane (H(c)approximate to 0.5 T), but not for H parallel to c up to 4 T. The excitation spectrum is characterized by two well-defined modes, one completely dispersionless at 6 meV, the other strongly dispersing to a gap of 2 meV. The reason for such complex ground state and spin excitations may be geometrical frustration of the Cu2+ spins within the tetrahedra, intra- and inter-tetrahedral couplings having similar strengths and strong Dzyaloshinski-Moriya anisotropy. Candidates for the dominant intra- and inter-tetrahedral interactions are proposed. (C) 2005 American Institute of Physics.
Title:
Inherent instabilities of some W5Si3-type binary phases with large electropositive metal atoms: Six examples in the Ba-Pb, Ca-Sn-Mg,Cu,Zn, and La-Ga-Al,Zn systems
Authors:
Ganguli, AK; Gupta, S; Zhao, JT; Leon-Escamilla, EA; Corbett, JD
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 178 (10): 2959-2972 OCT 2005
Abstract:
A particular pathology of certain W5Si3-type A(5)B(3) structures (I4/mcm) appears to arise because of unduly close approaches of the A1-type atoms on the cell faces at 1/2, 0, (1/4, 3/4) that occur with the larger and more electropositive A and/or in the presence of smaller B atoms. A structure refinement of binary Ba4.81Pb3 indicates such a marginal stability in that the Ba atoms in the facial Ba-0.81, chains exhibit an extreme displacement ellipsoid along (c) over right arrow. Although Ca5Sn3 and La5Ga3 binaries are unknown in this structure type, five stable ternary derivatives of these have been synthesized via substitution reactions and characterized by single crystal X-ray diffraction means: Ca4Sn3.223(4)Mg0.777, Ca4Sn3Cu1.30(4), Ca4.66(6)Sn3Zn0.704(4), La4.81(1)Ga1.38(2)Al1.62, and La4.762(5)Ga1.5(1)Zn1.5. Only the Ca-Sn-Zn phase exhibits lower symmetry, P4/mbm. The problematic A 1 sites exhibit diverse changes in these, whereas the surrounding B2 tetrahedra are largely unaltered. The Ca-Sn results are, respectively: direct Mg/Sn substitution at the Cal site; mixed fractional distribution of the smaller Cu at two sites around the A 1 position with an unresolved disorder; a pair of apparently independent modes, fractional Ca in the normal position and fractional Zn rectangles thereabout. The two La-Sn phases contain normal Ga,Al (Ga,Zn) tetrahedral chains with pairs of fractional disordered La atoms along 1/2, 0, z. Each can be rationalized in terms of a reasonable incommensurate structure. Electronic effects may also be operable. (c) 2005 Elsevier Inc. All rights reserved.
Title:
Compounds and subsolidus phase relations in the CaO-Co3O4-CuO system
Authors:
Miyazaki, Y; Huang, XY; Kajitani, T
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 178 (10): 2973-2979 OCT 2005
Abstract:
We have investigated the subsolidus phase relations in the system CaO-Co3O4-CuO at 920 degrees C under 1 atm of oxygen by means of powder X-ray diffraction method. Apart from the three known phases of Ca2CuO3, Ca3Co2O6 and (Co1-xCux)(3)O-4 spinel (0 <= x <= 0.06), two misfit-layered cobaltates have been identified. The first misfit is a solid solution, having a chemical formula [Ca-2(Co1-xCux)O-3](p)CoO2 with 0 <= x <= 0.12, while the other misfit has a pinpoint composition of [Ca-2(Co0.65Cu0.35)(2)O-4](p)CoO2. Both the phases have an incommensurate b-axes ratio, p similar to 0.62, due to the size difference between the two subsystems. Another phase is found in the Cu-rich quasi-one-dimensional composite crystal Ca-p(Cu1-xCox)O-2 (p similar to 0.83, 0.08 <= x <= 0.34), but the terminal compound Ca0.83CuO2 is not synthesized. The octahedral Co site in the Ca3Co2O6 phase can be partially substituted with Cu, up to 6%, to form the Ca-3(Co1-xCux)(2)O-6 (0 <= x <= 0.06) solid solution. (c) 2005 Elsevier Inc. All rights reserved.
Title:
High temperature phase transitions in barium sodium niobate: the wall roughening 1q-2q incommensurate transition and mean field tricritical behaviour in a disordered exclusion model
Authors:
Scott, JF; Hayward, SA; Miyake, M
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (37): 5911-5926 SEP 21 2005
Abstract:
Barium sodium niobate (Ba2NaNb5O15) is a tungsten bronze structure that exhibits a complicated sequence of six structural phase transitions, including three incommensurate (IC) phases. The phases are unusual in that all but the highest temperature P4/mbm structure are ferroelectric. Unlike the situation for most incommensurate insulators, in which ferroelectricity develops at low temperatures along the modulation direction, the polarization direction in barium sodium niobate is orthogonal to the modulation (s), permitting some unusual phenomena. In the present study we analyse the thermal and dielectric behaviour at the Curie temperature T-C near 830 K as well as that at the Ccm2(1)-IC(1q) transition near 543 K, the IC(1q)-IC(2q) transition near 565 K and the IC(2q)-P4bm transition at 582 K. The entropy change at 565 K is related to the wall roughening model of Rice et al (1981 Phys. Rev. B 24 275 1). Data near T-C = 830 K indicate close proximity to a tricritical point, and discussions of critical exponents are presented, all of which are found to be mean field. Because of Na vacancies, transition temperature variation is found among specimens Ba2Na1-xNb5O15 (830 K < T-C(x) < 865 K), and the system appears to be describable by the disordered exclusion model as a slightly first-order intrinsic system whose dynamics are suppressed by weak disorder. Near TC the specific heat C (T) is compared with the random bond prediction of Harris (1974 J. Phys. C: Solid State Phys. 7 1671): C(T) = C-0(T)/[1 + bx(2)C(0) (T)], where C-0 (T) is the intrinsic specific heat of the vacancy-free crystal varying as (T-C - T) (-1/2) and x is the sodium vacancy concentration. In agreement with Harris's model, the shifts in T-C(x) are to lower T with increasing x and scale as x; the broadening scales as x(2); and the effective critical exponent remains unchanged at alpha = 1/2.
Title:
Influence of the ingot solidification microstructure on the formation kinetics of icosahedral quasicrystalline phase during the crystallization of the corresponding amorphous alloy
Authors:
Tong, YQ; Shen, BC; Gan, YS; Yan, ZJ
Source:
ACTA PHYSICA SINICA, 54 (10): 4556-4561 OCT 2005
Abstract:
Zr65Al7.5 Cu-12.5 Ni-10 Ag-5 ingots with different solidification microstructures are obtained by repeated are melting of origin ingots. Under the same conditions, slices of amorphous alloys can be produced by suction casting in a copper mold. Differential scanning calorimetry (DSC) is employed to investigate the crystallization kinetics of the amorphous alloys. X-ray diffraction patterns (XRD) show that icosahedral quasicrystalline phase (I-phase) precipitates as primary phase during the crystallization of Zr65Al7.5Cu12.5Ni10Ag5 amorphous alloys. The results of Kissinger analyses suggest that the amorphous alloys made from the ingot with finer microstructure show better thermal stability, and that the I-phase precipitated becomes more stable against decomposition. Within the frame of structure heredity, the influence of ingot microstructure on the formation kinetics of I-phase during the crystallization of corresponding amorphous alloys is discussed.

Update: 22-Oct-2005

Title:
PDF from X-ray powder diffraction for nanometer-scale atomic structure analysis of quasicrystalline alloys
Authors:
Bruhne, S; Uhrig, E; Luther, KD; Assmus, W; Brunelli, M; Masadeh, AS; Billinge, SJL
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 220 (11): 962-967 2005
Abstract:
For three icosahedral alloys in the Mg-Zn-RE (RE = Ho, Y) systems, the atomic pair distribution functions (PDFs) have been obtained from sealed X-ray tube (in-house) and synchrotron (ESRF and APS) powder diffraction experiments. The PDFs are at least qualitatively comparable and are suitable for least squares r approximate to 2 nm local structure refinements. A recent local model for si-Ho-Mg-Zn from in-house data can be confirmed using the synchrotron data. Acquisition and the quality of the data from the different sources are discussed. The better resolved synchrotron data open perspectives for larger scale and thus more detailed models.
Title:
Non-linear transport in the incommensurate SDW phase of (TMTTF)(2)Br under pressure
Authors:
Nomura, K; Ishimura, K; Matsunaga, N; Nakamura, T; Takahashi, T; Saito, G
Source:
SYNTHETIC METALS, 153 (1-3): 433-436 Part 2 Sp. Iss. SI SEP 21 2005
Abstract:
The spin-density wave (SDW) phase with an incommensurate wave vector is induced as a ground state in the organic compound (TMTTF)(2)Br under the pressure above 0.5 GPa. We investigated the collective sliding motion of the SDW condensate with measuring the non-linear conductivity in this SDW phase. The measurement was done with dc and pulse methods. Below the SDW transition temperature T-SDW, the sharp increase of conductivity from the ohmic one was observed with the clearly defined threshold electric field E-T. This indicates the depinning of the SDW and the excess conductivity above E-T is associated with the sliding motion of the SDW. The absolute value of E-T is fairly larger than that observed in (TMTSF)(2)PF6, whose ground state is the incommensurate SDW at ambient pressure. With decreasing the temperature from T-SDW, E-T increases gradually and shows a relatively sharp drop after a peak around 0.3T(SDW). This temperature is supposed to be connected with the sub-phase transition proposed from the temperature dependence of NMR relaxation rate. In addition, the excess conductivity normalized to the ohmic one, which corresponds to the current carried by the SDW condensate, shows a dip at 0.3T(SDW) with decreasing the temperature. In the dc I-V characteristics, the hysteretic behavior near E-T appears only around 0.3T(SDW). These behaviors suggest that the sliding mechanism of the SDW condensate varies across 0.3T(SDW). We discuss the dynamics of the SDW in (TMTTF)(2)Br in comparison with that in (TMTSF)(2)X, considering the sub-phase transition.
Title:
Structural model and electronic structure of the icosahedral Al-Ga-Pd-Mn quasicrystal
Authors:
Zijlstra, ES; Bose, SK; Dolinsek, J
Source:
PHYSICAL REVIEW B, 72 (9): Art. No. 092203 SEP 2005
Abstract:
The structural model and the electronic structure of a newly discovered i-Al-Ga-Pd-Mn icosahedral quasicrystal with composition Al67Ga4Pd21Mn8 were studied by density functional methods. Calculations are based on the Quandt-Elser periodic approximant model of i-Al-Pd-Mn, which was fully relaxed. To determine which Al sites in the i-Al-Ga-Pd-Mn are occupied by Ga, total energies were compared, showing that Ga substitutes two of the aluminum glue atoms, Al-5 and Al-6, but no Al atoms that are part of a Bergman cluster. Since only specific Al sites are substituted by Ga, i-Al-Ga-Pd-Mn is predicted to be a true quaternary quasicrystal, structurally isomorphous with i-Al-Pd-Mn. Calculation of the electronic density of states of i-Al-Ga-Pd-Mn and its comparison to i-Al-Pd-Mn predicts that 4% Al -> Ga substitution in the i-Al-Pd-Mn lattice should have negligible influence on the electronic properties of this quasicrystal.
Title:
Thick atomic layers of maximum density as bulk terminations of quasicrystals
Authors:
Papadopolos, Z; Kasner, G
Source:
PHYSICAL REVIEW B, 72 (9): Art. No. 094206 SEP 2005
Abstract:
Clean surfaces of quasicrystals orthogonal to the directions of the main symmetry axes have a terracelike appearance. We extend Bravais' rule for crystals to some common quasicrystals by allowing thick layers of atomic planes, instead of single atomic planes/thin layers, to be candidates for terminations in bulk model.
Title:
Electronic structure of the topmost tenfold surface of decagonal Al-Ni-Co quasicrystal
Authors:
Suzuki, T; Sharma, HR; Nishimura, T; Shimoda, M; Yamauchi, Y; Tsai, AP
Source:
PHYSICAL REVIEW B, 72 (11): Art. No. 115427 SEP 2005
Abstract:
The electronic structure of the tenfold surface of a decagonal Al-Ni-Co quasicrystal was investigated using metastable He-*(2 S-3,1s2s) deexcitation spectroscopy, which is extremely sensitive to the topmost surface. It was found that the density of states at the Fermi level was remarkably reduced at the topmost surface. The deexcitation of He-* via a resonance transition followed by Auger neutralization observed on the quasicrystalline surface indicates the persistence of states within the pseudogap at the topmost surface. The similarity of the electronic structure between the topmost surface and the bulk is consistent with a bulk-terminated structure, as observed by low-energy ion scattering spectroscopy.
Title:
Field-induced incommensurate order in spin ladder with ring exchange
Authors:
Sakai, T; Okamoto, K
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 66 (8-9): 1450-1453 AUG-SEP 2005
Abstract:
The exact diagonalization study on the magnetization process of the S = 1/2 spin ladder system revealed that the incommensurate spin correlation parallel to H would be possibly dominant around half the saturation magnetization, with the ring exchange. In such a situation, an interladder coupling would yield the field-induced long-range incommensurate order. Several phase diagrams including the magnetization plateau are also presented. (c) 2005 Elsevier Ltd. All rights reserved.
Title:
Anisotropic magnetotransport around the v=1 bilayer quantum Hall state
Authors:
Iwata, K; Morino, M; Suzuki, M; Fukuda, A; Sawada, A; Ezawa, ZF; Kumada, N; Hirayama, Y
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 66 (8-9): 1556-1559 AUG-SEP 2005
Abstract:
An anisotropic magnetotransport that depends on a direction of an in-plane magnetic field was investigated in a bilayer quantum Hall system. We have found that the longitudinal resistance around the bilayer v = 1 quantum Hall state strongly varies when we changed the relative angle between the current and the in-plane field. Indeed, the anisotropy becomes remarkable at the phase transition point between the commensurate and incommensurate states. This result suggests that a unidirectional state appears around the transition. (c) 2005 Published by Elsevier Ltd.
Title:
Pseudospin domain of v=1 double-layer quantum Hall state near commensurate-incommensurate transition
Authors:
Terasawa, D; Kozumi, S; Fukuda, A; Sawada, A; Ezawa, ZF; Kumada, N; Hirayama, Y
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 66 (8-9): 1560-1562 AUG-SEP 2005
Abstract:
We investigate the quantum Hall (QH) state at the total Landau level filling factor v = 1 in double layer systems around the commensurate (C)- incommensurate (IC) transition point. We find a broad maximum in the magnetoresistance (R-xx) between the C and IC phases. The temperature dependence of R-xx shows that the maximum remains finite when the data are extrapolated down to 0 K. This fact suggests that there is a dissipative phase between the C and IC phases such as the theoretically predicted soliton lattice phase. (c) 2005 Elsevier Ltd. All rights reserved.
Title:
Growth of large single-grain decagonal quasicrystal by directional solidification of undercooled Al72Ni12Co16 alloy melt
Authors:
Liu, XB; Li, JG; Yang, GC
Source:
JOURNAL OF MATERIALS SCIENCE, 40 (19): 5255-5258 OCT 2005
Abstract:
The growth of decagonal quasicrystals was investigated by the directional solidification of highly undercooled Al72Ni12Co16 melts. The maximum single-grain decagonal quasicrystal contained in the grown crystals was about 0.5 mm in diameter and 6 mm in length. The quality of the grown crystals was examined by the X-ray powder diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). (c) 2005 Springer Science + Business Media, Inc.
Title:
Formation characteristics of the commensurate fluorite-type Bi2O3-Nb2O5 solid solution
Authors:
Pirnat, U; Valant, M; Jancar, B; Suvorov, D
Source:
CHEMISTRY OF MATERIALS, 17 (20): 5155-5160 OCT 4 2005
Abstract:
X-ray powder diffraction and transmission electron microscopy were used to investigate the formation characteristics and stability range of the tetragonal modification of a fluorite-type Bi2O3-Nb2O5 solid solution. The results showed that this tetragonal, commensurately modulated phase forms through the intermediate formation of the incommensurately modulated cubic fluorite phase followed by the incommensurate-commensurate transformation. This transformation can be described as a homogeneous nucleation with a temperature-dependent induction time and growth kinetics, which is determined by a growth rate of the tetragonal domains nucleated during the induction time. The homogeneity range of the tetragonal phase was found to extend between -0.2 <= y <= 0.04 for the general formula Bi3-yNb1+yO7+y. The tetragonal Bi3-yNb1+yO7+y phase is thermally stable up to the transition temperature where it transforms back to the cubic incommensurate phase. The transition temperature increases with Nb concentration from 750 degrees C for y = -0.2 to 920 degrees C for y = 0.04.
Title:
Twinning and the orientation relationships of icosahedral phase with the magnesium matrix
Authors:
Singh, A; Watanabe, M; Kato, A; Tsai, AP
Source:
ACTA MATERIALIA, 53 (17): 4733-4742 OCT 2005
Abstract:
Five possible orientation relationships OR1 to OR5 of icosahedral quasicrystal with magnesium matrix are derived and experimental evidences are shown. In three of these, an icosahedral twofold axis occurs along the hexagonal axis of magnesium, symmetrically in the case of OR1 and OR2 and asymmetrically in OR5. A fivefold axis occurs along the magnesium hexagonal axis in OR3. An icosahedral "mirror" zone axis occurs along the hexagonal axis in OR4. These orientation relationships are related by {102} twinning of magnesium or twinning of the icosahedral phase. OR2 and OR3 can form from the OR1 by a {102} twinning of the matrix. At the same time, twinning of an icosahedral phase which makes OR1 with magnesium can create OR3 with the same matrix. OR4 forms on a particular twinning of the icosahedral phase in OR1 and OR2 while OR5 can be derived by a twinning of the icosahedral phase in OR3. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reser! ved.

Update: 15-Oct-2005

Title:
Photonic quasicrystals for nonlinear optical frequency conversion
Authors:
Lifshitz, R; Arie, A; Bahabad, A
Source:
PHYSICAL REVIEW LETTERS, 95 (13): Art. No. 133901 SEP 23 2005
Abstract:
We present a general method for the design of 2-dimensional nonlinear photonic quasicrystals that can be utilized for the simultaneous phase matching of arbitrary optical frequency-conversion processes. The proposed scheme-based on the generalized dual-grid method that is used for constructing tiling models of quasicrystals-gives complete design flexibility, removing any constraints imposed by previous approaches. As an example we demonstrate the design of a color fan-a nonlinear photonic quasicrystal whose input is a single wave at frequency omega and whose output consists of the second, third, and fourth harmonics of omega, each in a different spatial direction.
Title:
Evolution of topological order in Xe films on a quasicrystal surface
Authors:
Curtarolo, S; Setyawan, W; Ferralis, N; Diehl, RD; Cole, MW
Source:
PHYSICAL REVIEW LETTERS, 95 (13): Art. No. 136104 SEP 23 2005
Abstract:
We report results of the first computer simulation studies of a physically adsorbed gas on a quasicrystalline surface Xe on decagonal Al-Ni-Co. The grand canonical Monte Carlo method is employed, using a semiempirical gas-surface interaction, based on conventional combining rules, and the usual Lennard-Jones Xe-Xe interaction. The resulting adsorption isotherms and calculated structures are consistent with the results of LEED experimental data. The evolution of the bulk film begins in the second layer, while the low coverage behavior is epitaxial. This transition from epitaxial fivefold to bulklike sixfold ordering is temperature dependent, occurring earlier (at lower coverage) for the higher temperatures.
Title:
Sensing dipole fields at atomic steps with combined scanning tunneling and force microscopy
Authors:
Park, JY; Sacha, GM; Enachescu, M; Ogletree, DF; Ribeiro, RA; Canfield, PC; Jenks, CJ; Thiel, PA; Saenz, JJ; Salmeron, M
Source:
PHYSICAL REVIEW LETTERS, 95 (13): Art. No. 136802 SEP 23 2005
Abstract:
The electric field of dipoles localized at the atomic steps of metal surfaces due to the Smoluchowski effect were measured from the electrostatic force exerted on the biased tip of a scanning tunneling microscope. By varying the tip-sample bias the contribution of the step dipole was separated from changes in the force due to van der Waals and polarization forces. Combined with electrostatic calculations, the method was used to determine the local dipole moment in steps of different heights on Au(111) and on the twofold surface of an Al-Ni-Co decagonal quasicrystal.
Title:
Epitactic growth of a decagonal phase in an Al-Ni-Co alloy film deposited on a (0001) sapphire substrate
Authors:
Saito, K; Ichioka, K; Sugawara, S
Source:
PHILOSOPHICAL MAGAZINE, 85 (30): 3629-3641 OCT 21 2005
Abstract:
Thin films of Al-Ni-Co alloy with an average thickness of 15 nm were produced by means of conventional vacuum deposition technique on ( 0001) sapphire substrates heated at various test temperatures. The microstructures and textures of the films obtained were thoroughly investigated by atomic force microscopy, X-ray diffraction and transmission electron diffraction and imaging techniques. The diffraction measurements have evidenced that the vacuum deposition of Al72Ni15Co13 alloy on the substrates heated above 400 degrees C allows a homogeneous poly-quasicrystalline film, consisting of the Ni-rich basic decagonal phase to grow. It has been further indicated by in-plane XRD analysis that the film deposited at 550 degrees C contains a considerable amount of the decagonal grains epitaxially grown on the sapphire substrate. Possible epitaxial relations occurring between the deposit and the substrate will be detailed on the basis of results obtained from electron diffraction measurements.
Title:
Magnetic phase diagram of the triangular lattice antiferromagnet CuFe1-xAlxO2
Authors:
Terada, N; Mitsuda, S; Fujii, T; Soejima, KI; Doi, I; Katori, HA; Noda, Y
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 74 (9): 2604-2611 SEP 2005
Abstract:
We have performed magnetic susceptibility, neutron diffraction and specific heat measurements on the triangular lattice antiferromagnet CuFe1-xAlxO2 for x <= 0.050. A magnetic phase diagram for temperature vs x was determined. The various magnetically ordered phases compete with each other on the x-T magnetic phase diagram, strongly suggesting that the quasi-Ising orderings are stabilized in CuFeO2 with delicate balance of competing interactions. In the ground state for 0.014 < x < 0.030 [low-temperature (LT) phase], the magnetic structure consists of two magnetic modulations with slightly different wave numbers. Moreover, we observed the change in magnetic diffraction patterns in the LT phase, which corresponds to a crystallographic distortion from "hexagonal" to "orthorhombic", suggesting that the Ising anisotropy in CuFeO2 is closely related to the crystallographic distortion.
Title:
Antiferromagnetism in the ordered subsystem of Cr ions intercalated into titanium diselenide
Authors:
Baranov, NV; Titov, AN; Maksimov, VI; Toporova, NV; Daoud-Aladine, A; Podlesnyak, A
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (34): 5255-5262 AUG 31 2005
Abstract:
The results of crystal structure, bulk magnetic properties and magnetic structure investigations are reported for the intercalated compound Cr0.5TiSe2. The Cr atoms are found to be ordered in the hexagonal TiSe2 matrix forming a superlattice a = a'root 3, b = a', c = 2c'. The first neutron diffraction measurements performed for this compound together with susceptibility and magnetization data have shown that this compound exhibits a complex incommensurate magnetic structure below T-N = 42 K. This structure is suggested to arise from the competition between the ferromagnetic exchange interaction dominating mainly within the Cr layers and antiferromagnetic interlayer exchange. Because of weakness of the interlayer exchange in comparison with intralayer one this compound exhibits metamagnetic properties.
Title:
Itinerancy and hidden order in URu2Si2
Authors:
Tripathi, V; Chandra, P; Coleman, P
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (34): 5285-5311 AUG 31 2005
Abstract:
We argue that key characteristics of the enigmatic transition at T-o = 17.5 K in URu2Si2 indicate that the hidden order is a density wave formed within a band of composite quasiparticles, whose detailed structure is determined by local physics. We expand on our proposal (with Mydosh) of the hidden order as incommensurate orbital antiferromagnetism and present experimental predictions to test our ideas. We then turn towards a microscopic description of orbital antiferromagnetism, exploring possible particle-hole pairings within the context of a simple one-band model. We end with a discussion of recent high-field and thermal transport experiments, and discuss their implications for the nature of the hidden order.
Title:
Thermal history and dielectric behavior in the incommensurate phase of TlGaSe2
Authors:
Mikailov, FA; Basaran, E; Tumbek, L; Senturk, E; Mammadov, TG
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 351 (33-36): 2809-2812 SEP 15 2005
Abstract:
The results of measurements of the dielectric constant of TlGaSe2 in the temperature range of successive phase transitions in various regimes, including the measurements after annealing the sample at a fixed temperature in the incommensurate phase are presented. A noticeable influence of the sample prehistory on the dielectric behavior of TlGaSe2 has been revealed. Peculiarities of the anomalies in the temperature dependence of the dielectric constant corresponding to structural phase transitions at the temperatures of 108 K and 115 K are discussed. It is suggested that these anomalies can be interpreted as successive lock-in commensurate transitions due to incommensurate structures appearing at 120 K and 242 K respectively. (c) 2005 Elsevier B.V. All rights reserved.

Update: 8-Oct-2005

Title:
A new orientation relationship OR4 of icosahedral phase with magnesium matrix in Mg-Zn-Y alloys
Authors:
Singh, A; Tsai, AP;
Source:
SCRIPTA MATERIALIA, 53 (9); 2005
Abstract:
A new orientation relationship OR4 between icosahedral phase and magnesium matrix is described. In this a -type zone axis is along the matrix hexagonal axis and a fivefold axis along hexagonal < 100 >. This orientation relationship can be derived from the most commonly observed OR1 by a twinning of the icosahedral phase. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Topological stripelike textures with inner incommensurability in 2D Heisenberg antiferromagnet
Authors:
Sinitsyn, EV; Bostrem, IG; Ovchinnikov, AS;
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 99 (3-4); 2005
Abstract:
We present an analysis of topological coreless excitations having a stripe form for two-dimensional Heisenberg antiferromagnet. These textures are characterized by singularities at the stripe boundaries. The structures may be observed as an occurrence of short-range incommensurate order in the antiferromagnetic environment.
Title:
Mean-field theory of the transition between incommensurate phases in the two-subsystem frustrated antiferromagnet CuB2O4
Authors:
Martynov, SN;
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 99 (3-4); 2005
Abstract:
Magnetic state of CuB2O4 was investigated in terms of the mean-field approach in the temperature ranae of 2K < T < 12 K. In the framework of a simple spiral model, a lone-periodic incommensurate magnetic structure at T > 10 K was determined. A transition between low- and high-temperature incommensurate structures occurs as a result of the competition of different contributions from the antisymmetric exchange interactions within and between the subsystems.
Title:
Magnetic excitations in incommensurate itinerant systems
Authors:
Boni, P; Roessli, B;
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 99 (3-4); 2005
Abstract:
Strongly correlated magnetic materials with incommensurate ordering like MnSi and Cr show a very interesting magnetic excitation spectrum. Because of the noncentrosymmetric crystal structure of MnSi, the antisymmetric Dzyaloshinskii-Moriya interaction leads to chiral spin waves in the ordered phase transforming to regular ferromagnetic spin waves when a large magnetic field is applied. Near T-C, critical scattering develops on the shell of a sphere coexisting with Bragg scattering from the magnetic satellites. In incommensurate Cr we show that the spin wave modes attain a larger velocity than the phason modes. Most interestingly, we find that despite the centrosymmetric bee structure of Cr, the low-energy fluctuations (Fincher-Burke modes) are not symmetric with respect to the propagation direction of the magnetic excitations, i.e., with respect to the commensurate position.
Title:
Energy relaxation in disordered charge and spin density waves
Authors:
Melin, R; Biljakovic, K; Lasjaunias, JC;
Source:
EUROPEAN PHYSICAL JOURNAL B, 43 (4); 2005
Abstract:
We investigate collective effects in the strong pinning model of disordered charge and spin density waves (CDWs and SDWs) in connection with heat relaxation experiments. We discuss the classical and quantum limits that contribute to two distinct contribution to the specific heat (a C-v similar to T-2 contribution and a C-v similar to T-alpha contribution respectively), with two different types of disorder ( strong pinning versus substitutional impurities). From the calculation of the two level system energy splitting distribution in the classical limit we find no slow relaxation in the commensurate case and a broad spectrum of relaxation times in the incommensurate case. In the commensurate case quantum effects restore a non vanishing energy relaxation, and generate stronger disorder effects in incommensurate systems. For substitutional disorder we obtain Friedel oscillations of bound states close to the Fermi energy. With negligible interchain couplings this explains the power-law specific heat C-v similar to T-alpha observed in experiments on CDWs and SDWs combined to the power-law susceptibility chi(T) similar to T-1+alpha observed in the CDW o-TaS3.
Title:
Charge stripe glasses in La2-xSrxNiO4 for 0.20 < x < 0.25
Authors:
Spencer, PD; Ghazi, ME; Wilkins, SB; Hatton, PD; Brown, SD; Prabhakaran, D; Boothroyd, AT;
Source:
EUROPEAN PHYSICAL JOURNAL B, 46 (1); 2005
Abstract:
We present high resolution X-ray measurements characterising the charge stripe order state in the La2-xSrxNiO4 system with x = 0.20, 0.225 and 0.25. We find that in the x = 0.20, 0.225 and 0.25 systems the charge stripe order exists in a charge stripe glass characterised by weak, poorly correlated incommensurate charge stripes in contrast to the strong well correlated charge stripes in the commensurate x = 1/3 system. No stabilisation of the charge order was observed at the next possible commensurate value of epsilon = 0.25. A comparison with high energy X-ray measurements suggested that the charge order may exist in a charge stripe glass in the bulk in the doping region x = 0.20-0.33. Finally at low temperature there was an initial increase in the intensity and correlation not observed with neutron measurements and it appears to be an effect that X-rays are sensitive to but neutrons are not.
Title:
Symmetry-dependent Mn-magnetism in Al69.8Pd12.1Mn18.1
Authors:
Rau, D; Gavilano, JL; Beeli, C; Hinderer, J; Felder, E; Wigger, GA; Ott, HR;
Source:
EUROPEAN PHYSICAL JOURNAL B, 46 (2); 2005
Abstract:
We investigated the stability of magnetic moments in Al69.8Pd12.1Mn18.1. This alloy exists in both, the icosahedral (i) and the decagonal (d) quasicrystalline form. The transition from the i- to the d-phase is achieved by a simple heat treatment. We present the results of measurements of the Al-27 NMR-response, the dc magnetic susceptibility, and the low-temperature specific heat of both phases. In the icosahedral compound, the majority of the Mn ions carries a magnetic moment. Their number is reduced by approximately a factor of two by transforming the alloy to its decagonal variety. For both compounds, we have indications for two different local environments of the Al nuclei. The first reflects a low density of states of conduction electrons and a weak coupling of the Al nuclei to the Mn-moments. The second type of environment implies a large d-electron density of states at the Fermi level and a strong coupling to the magnetic Mn moments. Spin-glass freezing transitions are observed at T-f(deca) = 12 K for the decagonal, and T-f(ico) = 19 K for the icosahedral phase.
Title:
Dielectric properties of thallium gallium diselenide layered crystal in the incommensurate phase
Authors:
Senturk, E; Tumbek, L; Mikailov, FA;
Source:
CRYSTAL RESEARCH AND TECHNOLOGY, 40 (9); 2005
Abstract:
The dielectric measurements of the layered crystal were studied in temperature range of successive phase transitions. The measurements revealed that the phase transition occurred in 242 K is an incommensurate phase transition. When the sample is annealed at a stabilized temperature in the incommensurate phase, a remarkable memory effect has been observed on cooling run. The mechanism of the memory effect in the incommensurate phase of the semiconducting ferroelectric TlGaSe2 can be interpreted in the frame of the theory of defect density waves. This theory claims that the memory effect is the result of pinning of the incommensurate structure by the lattice inhomogeneities. With decreasing the annealing temperature the phase transition temperature shifts to lower temperatures gradually. Moreover, the peak intensities also increase gradually. In addition to these effects, the phase transition temperature shifts to lower temperatures with increasing annealing time. (C) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Title:
Re-determining the Nowotny chimney-ladder structure VGe1.82 from powder diffraction data
Authors:
Lind, H; Bostrom, M;
Source:
POWDER DIFFRACTION, 20 (3); 2005
Abstract:
The Nowotny chimney-ladder compound VGe1.82 was redetermined from powder diffraction data and modelled with the incommensurately modulated composite approach. The dimensions of the tetragonal unit subcells are a = 5.9015(3) angstrom; c(Ge)=2.6916(2) angstrom, and c(V) = 4.9080(2) angstrom and the one-dimensional modulation vectors are q(Ge) = 0.45159(1)[001]* and q(V) = 0.17656(1)[001]*. Comparison is made with a previous reported commensurate approximation of the structure with a 31-fold C-Ge axis. (c) 2005 International Centre for Diffraction Data.
Title:
Solitonic phase in manganites
Authors:
Brey, L; Littlewood, PB;
Source:
PHYSICAL REVIEW LETTERS, 95 (11); 2005
Abstract:
Orbital order present in several transition metal compounds could give rise to topological defects. Here we argue that the topological defects in orbital ordered half doped manganites are orbital solitons that carry a charge of +/- e/2. When extra charge is added to the system an array of solitons is formed and an incommensurate solitonic phase occurs. The striking experimental asymmetry in the phase diagram as electrons or holes are added to half doped manganites is explained by the energy difference between positive and negative charged solitons. The presence of nanoscale inhomogeneities in manganites is naturally explained by the existence of solitonic phases.
Title:
High critical-current density and ultra high-voltage TEM study of filamentary 0.1 at% Zr-doped (Nd0.33Eu0.38Gd0.28)Ba2CU3Ox superconductors
Authors:
Goto, T; Sato, E; Watanabe, K; Nishijima, G; Matsui, Y; Nagai, T; Tsuruta, C;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 425 (3-4); 2005
Abstract:
We prepared filamentary 0.1 at% Zr-doped (Nd0.33Eu0.38Gd0.28)Ba2Cu3Ox superconductors by solution spinning and partial melting in flowing 0-1% O-2 + Ar gas. The transport critical-current density (J(c)) was measured at 77 K in applied magnetic fields up to 14 T by rotating the sample along a direction perpendicular to the filament length. Anisotropic behavior of the field dependence of J(c) was detected by applying a field of more than 4 T. The J(c) values for the Zr-doped sample were higher than those for the undoped sample on the application of fields of up to 11 T. The J(c) values measured at the optimized angle for the doped sample were more than 10(5) A/cm(2) at 77 K by applying fields of up to 6 T. Transmission electron microscopy (TEM) of the sample was performed using an ultra high-voltage TEM to clarify the pinning centers. Intergrowth of 124 phase and stacking faults in the oriented 123 matrix were observed both for the doped and undoped samples. Zr doping resulted in the fluctuation of the structure with a short disorder range of 10-30 nm. A modulated structure and fine twin planes crossing each other were partly observed for the doped sample. The presence of such small-scale disorder could improve flux pinning in the middle field region. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Electronic tuning of Mg2Cu6Ga5. A route to crystalline approximant and quasicrystalline phases
Authors:
Lin, QS; Corbett, JD;
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 127 (37); 2005
Abstract:
Title:
Modulated phases in NaNbO3: Raman scattering, synchrotron x-ray diffraction, and dielectric investigations
Authors:
Yuzyuk, YI; Simon, P; Gagarina, E; Hennet, L; Thiaudiere, D; Torgashev, VI; Raevskaya, SI; Raevskii, IP; Reznitchenko, LA; Sauvajol, JL;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (33); 2005
Abstract:
Raman spectra of sodium niobate (NaNbO3)were obtained in all phases and revealed a significant disorder in the high-temperature U, T2 and T1 phases and a complicated folding of the Brillouin zone at the transitions into modulated S, R, P and N phases associated with the competitive zone-boundary soft modes (in-phase and out-of phase octahedral tilts) along the M-T-R line. An extensive Raman study combined with x-ray diffraction (XRD) and dielectric measurements confirmed the presence of the incommensurate (INC) phase in sodium niobate. XRD experiments revealed the invar effect in the temperature interval 410-460 K corresponding to the INC phase associated with rotations of the NbO6 octahedra modulated along the b-direction. Our experiments suggest that the phase P consists of three phases: monoclinic (P-m )between 250 and 410 K, INC between 410 and 460 K, and orthorhombic (P-o) between 460 and 633 K. At the low-temperature transition to the ferroelectric rhombohedral N phase all folded modes originating from the M- and T-points of the Brillouin zone abruptly disappear, Raman spectra in the N phase become much simpler and all peaks were assigned.
Title:
Glassy and icosahedral phases in rapidly solidified Ti-Zr-Hf-(Fe, Co or Ni) alloys
Authors:
Chen, N; Louzguine-Luzgin, DV; Ranganathan, S; Inoue, A;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 351 (30-32); 2005
Abstract:
The icosahedral quasicrystalline, amorphous plus crystalline and glassy phases were formed in Ti40Zr20Hf20(3d-LTM)(20) alloys (3d-LTM = 3d late transition metals Fe, Co and Ni). The icosahedral phase formed in the melt-spun Ti40Zr20Hf20Fe20 alloy is metastable and the average size of the quasicrystalline icosahedral particles precipitated in the amorphous matrix is 5 nm. The metastable icosahedral phase transformed to a big-cubic fcc Hf2Fe phase with the grain size of about 20 nm after annealing for 1.8 ks at 841 K. The glassy phase was formed in the melt-spun Ti40Zr20Hf20Co20 alloy and no metastable phase was found to form during the transformation from glassy phase to a stable crystalline phase. Icosaheadral phase formed in the melt-spun Ti40Zr20Hf20Ni20 alloy transformed to a big-cubic fcc (Zr,Ti)(2)Ni solid solution phase by a solid state reaction. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Chemical and icosahedral short-range orders in liquid and undercooled Al80Mn20 and Al80Ni20 alloys: A first-principles-based approach
Authors:
Jakse, N; Le Bacq, O; Pasturel, A;
Source:
JOURNAL OF CHEMICAL PHYSICS, 123 (10); 2005
Abstract:
Atomic structures of stable liquid and undercooled liquid Al80Mn20 and Al80Ni20 alloys have been calculated by first-principles molecular-dynamics simulations. For both alloys, the local structure as defined by the Faber-Ziman pair-correlation functions is characterized by a strong Al-transition-metal affinity, which leads to a well-pronounced chemical short-range order which is more temperature dependent for Al80Mn20 than for Al80Ni20. In addition, a structural analysis using three-dimensional pair analysis techniques has been performed in details. More particularly, we find that the fivefold local symmetry around Mn atoms is predominant in both stable and undercooled Al80Mn20 alloys and displays no significant variation with temperatures. On the contrary, in Al80Ni20, a strong variation of the topological short-range order is observed since in the undercooled state, the local environment of Ni atoms is characterized by the predominance of the fivefold symmetry over the close-packed local symmetry which is opposed to what occurs in the stable liquid phase. (c) 2005 American Institute of Physics.
Title:
Microstructure of martensitic phase in the Co39Ni33Al28 shape memory alloys revealed by transmission electron microscopy
Authors:
Wang, HY; Liu, ZH; Wang, YG; Duan, XF; Wu, GH;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 400 (1-2); 2005
Abstract:
In the Co39Ni33Al28 alloy, the ferromagnetic shape memory effect was investigated. A martensitic transformation (MT) occurred in the Co39Ni33Al28 alloy when the temperature was lower than the martensitic start transformation temperature, M-S = 233 K. The morphologies and microstructures of the martensitic phase characterized by transmission electron microscope (TEM) showed a new 28-layered (28M) modulated martensite consisting of pinstripes and co-existing with the non-modulated martensite. Anomalies in magnetic properties and strain emerging around the MT have been briefly discussed. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Observations on the growth of Al-Ni-Co decagonal thin films by atomic force microscopy and transmission electron microscopy
Authors:
Saito, K; Ichioka, K; Sugawara, S;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 400 (1-2); 2005
Abstract:
Thin films of Al-Ni-Co alloy were produced by vacuum deposition technique using a substrate material of amorphous carbon thin-foil. Attempts were made to obtain a homogeneous decagonal quasicrystalline film, where the preparation technique was based on the direct evaporation of pre-alloyed ingot of Al72Ni15Co13 onto the heated substrates. In order to explore early stages of the decagonal film growth, the Al-Ni-Co films with different thicknesses ranging from 2 nm to 30 nm were deposited on either substrates heated at 500 degrees C or non-heated substrates. The film samples so obtained were examined mainly by atomic force microscopy in combination with transmission electron diffraction and imaging techniques. On the basis of these observations, deposition conditions necessary for the growth of decagonal phase in the resulting films as well as the growth mechanism of the decagonal film will be discussed. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Magnetic phase transitions in TbNi5 single crystal: Bulk properties and neutron diffraction studies
Authors:
Lee, S; Podlesnyak, AA; Prokes, K; Sikolenko, VE; Ermolenko, AS; Gerasimov, EG; Dorofeev, YA; Vokhmyanin, AP; Park, JG; Pirogov, AN;
Source:
JETP LETTERS, 82 (1); 2005
Abstract:
Magnetic susceptibility, heat capacity, and neutron diffraction measurements have been carried out in order to study the unusual magnetic ordering of TbNi5 using a single crystal over the temperature region of 2-30 K. Two spontaneous magnetic transitions have been observed: one is a second-order transition from a paramagnetic state to an incommensurate structure (T-p = 24 K), and the other, a first-order transition from the incommensurate structure to a lock-in phase (T-f(c) = 10 K). We also found an irreversible magnetic field-induced transition from the modulated structure to the ferromagnetic collinear one. (C) 2005 Pleiades Publishing, Inc.
Title:
Large enhancement of phononic gap in periodic and quasiperiodic elastic composites by using air inclusions
Authors:
Lai, Y; Zhang, ZQ;
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 220 (9-10); 2005
Abstract:
We find that a phononic gap in a periodic or quasiperiodic elastic composite can be significantly enhanced by inserting air inclusions into the systems. The positions of the insertion are chosen to suppress the shear potential energy of the acoustical branches and lower their frequencies. This is demonstrated in two dimensions. Gap positions and sizes as functions of the radii of the air cylinders for systems of aluminum cylinders in epoxy and steel cylinders in epoxy are presented for both triangular and 12-fold quasiperiodic lattices.
Title:
Effect of hot extrusion on microstructure and mechanical properties of quasicrystal-reinforced Mg-Zn-Y alloy
Authors:
Zheng, MY; Qiao, XG; Xu, SW; Gan, WM; Wu, K; Kamado, S; Kojima, Y; Brokmeier, HG;
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 15 (4); 2005
Abstract:
The microstructure and mechanical properties of as-cast and as-extruded Mg-Zn-Y alloy (Mg-11% Zn-0.9% Y, mass fraction) containing Mg-3 YZn6 quasicrystal were studied. The eutectic icosahedral quasicrystal phase (I-phase) is broken and almost distributes along the extrusion direction, and fine I-phase with nano-size is precipitated during the extrusion. The (alpha)-Mg matrix grains are refined due to recrystallization occuring during the hot extrusion. Some 1012 twins are observed in the extruded ZW1101 alloy. And (0002) 1010 fiber texture is formed in matrix alloys after hot extrusion. The extruded alloy exhibits high strength in combination with large elongation at room temperature. The strengthening mechanism of the as-extruded alloy was discussed.
Title:
Electronic structure and charge-density wave formation in LaTe1.95 and CeTe2.00
Authors:
Shin, KY; Brouet, V; Ru, N; Shen, ZX; Fisher, IR;
Source:
PHYSICAL REVIEW B, 72 (8); 2005
Abstract:
Results are presented of complementary measurements that probe the electronic structure and charge-density wave (CDW) modulation in the quasi-two-dimensional compounds LaTe1.95 and CeTe2. Transmission electron micrographs show that the modulation wave vectors associated with the CDW are different for the two materials, and in both cases are incommensurate with the underlying lattice. These wave vectors are shown to correspond to nesting features of a simplified model of the Fermi surface. Angle-resolved photoemission spectroscopy is used to reveal the electronic structure and Fermi-surface topology in the CDW state. The data indicate a large CDW gap that varies in magnitude around the Fermi surface somewhat differently for the two compounds. Differences in the volume of the original Fermi surface are related to the doping effect of Te vacancies. Heat-capacity measurements at low temperatures indicate a very small electronic density of states, consistent with the electrical resistivity, which appears to be semiconducting or semimetallic.
Title:
TEM observations of Al72Ni12CO16 decagonal quasicrystal subjected to high-temperature indentation
Authors:
Saito, K; Arakaki, Y; Sugawara, S; Shindo, R; Guo, JQ; Tsai, AP;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES, 403 (1-2); 2005
Abstract:
The effect of high-temperature indentation testing on the microstructural change of a single-grained Al72Ni12Co16 decagonal quasicrystal (d-QC) has been investigated by transmission electron diffraction and microscopy (TEM) technique. A definite surface normal to the 10-fold axis of the d-QC was subjected to Vickers indentation test at an elevated temperature of 800 degrees C with a load of 1 kgf. The TEM investigation of this sample has evidently shown that there are specific types of defects densely distributed in the indented-region, such as grain-boundaries, dislocations and phason-related defects. Furthermore, high-resolution electron microscopy observations have revealed the widespread distribution of nanocrystalline domains in the indented-region, where groups of decagonal atom clusters have a periodic arrangement to form a rhombic lattice. On the basis of these observations, possible deformation mechanisms of the d-QC during high-temperature indentation will be discussed. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Transmission electron microscopic study of the defect structure in Sr4Fe6O12+delta compounds with variable oxygen content
Authors:
Rossell, MD; Abakumov, AM; Van Tendeloo, G; Lomakov, MV; Istomin, SY; Antipov, EV;
Source:
CHEMISTRY OF MATERIALS, 17 (18); 2005
Abstract:
Sr4Fe6O12+delta (delta = 0.6, 0.8) compounds were prepared by a solid-state reaction in evacuated sealed silica tubes. The structure of these materials was studied by X-ray powder diffraction, electron diffraction, and high-resolution electron microscopy. The materials are characterized as a complicated superstructure appearing at three different levels: (a) modulations with q = alpha a* due to changing delta, so that delta = 2 alpha; (b) cooperative atomic displacements in the Fe2O2+delta layers resulting in the formation of distorted tetragonal pyramids and distorted trigonal bipyramids around the Fe cations; and (c) different stackings of neighboring Fe2O2+delta layers. Symmetry changes occurring at each of these three levels are discussed. A comparison is made between the Sr4Fe6O12+delta structures in bulk and in thin film.
Title:
Influence of superlattice and antiphase domain boundaries on dielectric loss in Ba[Mg-1/3(Nbx/4Ta(4-x)/4)(2/3)]O-3 ceramics
Authors:
Lin, CF; Lu, HH; Chang, TI; Huang, JL;
Source:
APPLIED PHYSICS LETTERS, 87 (10); 2005
Abstract:
The Ba[Mg-1/3(Nbx/4Ta(4-x)/4)(2/3)]O-3 ceramics (x=0, 1, 2, 3, and 4) synthesized by a solid reaction method were sintered at 1650 degrees C for 9 h. The quality factor (Q, similar to 1/tan delta,tan delta: dielectric loss) and superlattice structure were investigated by the cavity method and high-resolution electron microscopy. The excellent Q value of 17 600 obtained at appropriate Nb content (x=1). The disorder structure (superlattice modulation similar to 0.41 nm), 1:2 ordering structure (superlattice modulation similar to 0.71 nm) and antiphase domain boundary (APB) were revealed in Ba[Mg-1/3(Nbx/4Ta(4-x)/4)(2/3)]O-3 ceramics. The formation of extra ordering structure (superlattice modulation similar to 1.24 nm) on the APBs contributed to the improved Q value with the stabilization of ordering-induced domain boundaries. (c) 2005 American Institute of Physics.
Title:
Zero-field incommensurate spin-peierls phase with interchain frustration in TiOCl
Authors:
Ruckamp, R; Baier, J; Kriener, M; Haverkort, MW; Lorenz, T; Uhrig, GS; Jongen, L; Moller, A; Meyer, G; Gruninger, M;
Source:
PHYSICAL REVIEW LETTERS, 95 (9); 2005
Abstract:
We report on the magnetic, thermodynamic, and optical properties of the quasi-one-dimensional quantum antiferromagnets TiOCl and TiOBr, which have been discussed as spin-Peierls compounds. The observed deviations from canonical spin-Peierls behavior, e.g., the existence of two distinct phase transitions, have been attributed previously to strong orbital fluctuations. This can be ruled out by our optical data of the orbital excitations. We show that the frustration of the interchain interactions in the bilayer structure gives rise to incommensurate order with a subsequent lock-in transition to a commensurate dimerized state. In this way, a single driving force, the spin-Peierls mechanism, induces two separate transitions.
Title:
Diffuse scattering and phason fluctuations in the Zn-Mg-Sc icosahedral quasicrystal and its Zn-Sc periodic approximant
Authors:
de Boissieu, M; Francoual, S; Kaneko, Y; Ishimasa, T;
Source:
PHYSICAL REVIEW LETTERS, 95 (10); 2005
Abstract:
We report on the absolute scale measurement of the x-ray diffuse scattering in the ZnMgSc icosahedral quasicrystal and its periodic approximant. Whereas the diffuse scattering in the approximant is purely accounted for by thermal diffuse scattering, an additional signal is observed in the quasicrystal. It is related to phason fluctuations as indicated by its Q(per)(2) dependence. Moreover, when compared to previous measurements carried out on the i-AlPdMn phase, we find that the amount of diffuse scattering is smaller in the i-ZnMgSc phase, in agreement with larger phason elastic constants in this phase. This is confirmed by the observation of a large number of weak Bragg peaks having a high Q(per) reciprocal space component.
Title:
Anomalous thermal properties of the Heusler alloy Ni2+xMn1-xGa near the martensitic transition
Authors:
Kuo, YK; Sivakumar, KM; Chen, HC; Su, JH; Lue, CS;
Source:
PHYSICAL REVIEW B, 72 (5); 2005
Abstract:
We present the measurements of electrical resistivity (rho), specific heat (C-P), Seebeck coefficient (S), as well as thermal conductivity (kappa) of the Heusler compounds Ni2+xMn1-xGa from 10 to 400 K. A series of Ni2+xMn1-xGa alloys were prepared with x=0, 0.04, 0.06, 0.10, 0.14, 0.18, and 0.24 to systematically study the effect of substitution on the martensitic and ferromagnetic transitions. Unusual sharp peaks were observed in both S and kappa around the martensitic transition temperature (T-M), while a noticeable change of slope was seen in S and kappa at the ferromagnetic transition temperature (T-C) in Ni2+xMn1-xGa with x < 0.14. For x >= 0.14 the structural and magnetic phase transitions were found to merge together, as noticed from the sharp changes in all measured physical quantities. Existence of premartensitic transition (T-P) was unambiguously resolved in the stoichiometric compound Ni2MnGa by the C-P measurement, although such a feature becomes less pronounced with increasing x and completely disappears for the compositions x >= 0.10. Significant thermal hysteresis loops between heating and cooling cycles appear in the vicinity of T-M, which is associated with the presence of 7-layer and 5-layer modulated structures. In addition, huge peaks were observed in the thermal conductivity near T-M. We connected this observation to the nesting of the Fermi-level density of states, which is appropriate for the Peierls transition.
Title:
Thermal and electrical transport properties of Ag-In-Yb quasicrystals: An experimental study
Authors:
Kuo, YK; Sivakumar, KM; Lai, HH; Ku, CN; Lin, ST; Kaiser, AB;
Source:
PHYSICAL REVIEW B, 72 (5); 2005
Abstract:
The thermal and electrical transport properties, including electrical resistivity (rho), thermopower (S), and thermal conductivity (kappa) of Ag42In42Yb16, Ag42.25In42.25Yb15.5, and Ag42.5In42.5Yb15 icosahedral quasicrystals (QCs) are reported. Great similarities were found in measured transport properties between these ternary and their binary analogies Cd-Yb QC's. This finding indicates that the complete replacement of Cd by equal amount of Ag-In does not alter the electronic band structure significantly. Comparison between the previously reported binary Cd-Yb QC, Cd6Yb cubic approximant, and present ternary Ag-In-Yb QC suggests that the peculiar transport properties observed in the quasicrystalline Cd-Yb alloys may not be due to chemical disorder or quasiperiodicity. These findings provide valuable information for better understanding of the transport properties in quasicrystalline alloys.
Title:
Spectral and diffusive properties of silver-mean quasicrystals in one, two, and three dimensions
Authors:
Cerovski, VZ; Schreiber, M; Grimm, U;
Source:
PHYSICAL REVIEW B, 72 (5); 2005
Abstract:
Spectral properties and anomalous diffusion in the silver-mean (octonacci) quasicrystals in d=1,2,3 are investigated using numerical simulations of the return probability C(t) and the width of the wave packet w(t) for various values of the hopping strength v. In all dimensions we find C(t)similar to t(-delta), with results suggesting a crossover from delta < 1 to delta=1 when v is varied in d=2,3, which is compatible with the change of the spectral measure from singular continuous to absolute continuous; and we find w(t)similar to t(beta) with 0
Title:
Magnetic properties of Bi0.75Sr0.25MnO3 (x approximate to 2/8,T-CO=600 K): Ferromagnetism and charge order
Authors:
Garcia-Munoz, JL; Frontera, C; Respaud, M; Giot, M; Ritter, C; Capdevila, XG;
Source:
PHYSICAL REVIEW B, 72 (5); 2005
Abstract:
The possible coexistence of ferromagnetism and charge/orbital order in Bi3/4Sr1/4MnO3 has been investigated. The manganite Bi0.75Sr0.25MnO3, with commensurate charge balance, undergoes an electronic transition at T(CO)similar to 600 K that produces a long-range modulation with double periodicity along the a and c axes, and unusual anisotropic evolution of the lattice parameters. The magnetic properties of this new ordered phase were studied by neutron powder diffraction and high-magnetic fields. In zero field the magnetic structure is globally antiferromagnetic, ruling out the apparition of spontaneous ferromagnetism. However, the application of magnetic fields produces a continuous progressive canting of the moments, inducing a ferromagnetic phase even for relatively small fields (H << 1 T). Application of pulsed high fields produces a remarkable and reversible spin polarization (under 30 T, the ferromagnetic moment is similar to 3 mu(B)/Mn, without any sign of charge order melting). The coexistence of ferromagnetism and charge order at low and very-high fields is a remarkable property of this system.
Title:
Stability of inhomogeneous superstructures from renormalized mean-field theory of the t-J model
Authors:
Poilblanc, D;
Source:
PHYSICAL REVIEW B, 72 (6); 2005
Abstract:
Using the t-J model (which can also include Coulomb repulsion) and the "plain vanilla" renormalized mean-field theory of Zhang, [Supercond. Sci. Technol. 1, 36 (1988)], stability of inhomogeneous 4ax4a superstructures, such as those observed in cuprates superconductors around 1/8 hole doping is investigated. We find a nonuniform 4ax4a bond order wave involving simultaneously small (similar to 10(-2)t) inhomogeneous staggered plaquette currents as well as a small charge-density modulation similar to pair density wave order. On the other hand, no supersolid phase involving a decoupling in the superconducting particle-particle channel is found.
Title:
Magnetic, electrical, thermal transport, and thermoelectric properties of the xi ' and Psi complex metallic alloy phases in the Al-Pd-Mn system
Authors:
Dolinsek, J; Jeglic, P; McGuiness, PJ; Jaglicic, Z; Bilusic, A; Bihar, Z; Smontara, A; Landauro, CV; Feuerbacher, M; Grushko, B; Urban, K;
Source:
PHYSICAL REVIEW B, 72 (6); 2005
Abstract:
The Al-Pd-Mn system of intermetallics contains complex metallic alloy (CMA) phases, whose crystal structures are based on giant unit cells comprising up to more than a thousand atoms per cell. We performed investigation of the magnetic, electrical, and thermal transport and thermoelectric properties of the xi(') phase and the related Psi phase on single-crystalline samples grown by the Bridgman technique. The samples are diamagnets with a tiny paramagnetic Curie-like magnetization and an estimated fraction of magnetic Mn atoms about 100 ppm. The electrical resistivity between 300 and 4 K exhibits a temperature variation of less than 2%. The origin of this temperature-compensated resistivity is analyzed in terms of the spectral conductivity model. The thermal conductivity of the samples is small and can be described by the sum of the electronic and lattice contributions, which are of comparable size at room temperature. The lattice contribution can be reproduced by the sum of the Debye term (long-wavelength phonons) and the term due to hopping of localized vibrations. The thermoelectric power is small and negative, compatible with a low concentration of electrons as the majority charge carriers. The studied physical properties of the giant-unit-cell CMA phases in the Al-Pd-Mn system are in many respects intermediate between those of metals or simple intermetallics and quasicrystals, suggesting that both the polytetrahedral local atomic order and the large-scale periodicity influence the physical properties of the material.
Title:
Quantum phase transitions in low-dimensional quantum spin systems with incommensurate magnetic structures
Authors:
Zvyagin, AA;
Source:
PHYSICAL REVIEW B, 72 (6); 2005
Abstract:
Several exactly solvable quantum spin models with incommensurate magnetic structures, which manifest quantum phase transitions between incommensurate and commensurate phases, are proposed. The ground-state and thermodynamic characteristics of these quantum spin antiferromagnetic models with the Dzyaloshinsky-Moriya antisymmetric exchange interaction and spin-frustrating next-nearest-neighbor, three-spin, and four-spin (ring exchange) interactions are exactly studied. We investigated the ground state phases of the considered models, as function of the magnetic anisotropy, Dzyaloshinsky-Moriya interaction, next-nearest-neighbor coupling constants, and external magnetic field. Several quantum phase transitions between magnetically incommensurate phases and between incommensurate and ferromagnetic phases are predicted, and the behavior of thermodynamic characteristics of those models at phase transitions is studied. We have shown that for models with chiral three-spin interactions the Dzyaloshinsky-Moriya coupling yields the onset of the weak ferromagnetism, similar to three-dimensional ordered antiferromagnets, but not present in other quantum spin chains with the antisymmetric exchange. Considered models appeared to be important for several quasi-one-dimensional spin systems, studied in recent experiments.
Title:
Crystal and magnetic structural study of the La1-xCaxMnO3 compound (x=3/4)
Authors:
Pissas, M; Margiolaki, I; Prassides, K; Suard, E;
Source:
PHYSICAL REVIEW B, 72 (6); 2005
Abstract:
We studied the crystal and magnetic structure of the La1/4Ca3/4MnO3 compound using ultrahigh resolution synchrotron x-ray and neutron-diffraction techniques. The experimental results revealed that the particular compound undergoes a structural transition at T-CO=220 K. This transition results in an increase of the orthorhombic splitting and the appearance of superlattice diffraction peaks, which can be indexed assuming a supercell 4a (a is the unit cell parameter for T > T-CO). This transition is reminiscent of those observed for the x=1/2 and x=2/3 stoichiometries where superstructures with 2a and 3a, respectively, have been observed. At T-N=160 K the neutron-diffraction patterns exhibit additional diffraction peaks, corresponding to antiferromagnetic long-range order with propagation vectors k=[1/4,0,1/2] and k=[1/2,0,1/2]. In addition to the structural transition at T-CO the synchrotron high resolution x-ray diffraction patterns revealed a three phase coexistence.
Title:
Zn and Ni doping effects on the low-energy spin excitations in La1.85Sr0.15CuO4
Authors:
Kofu, M; Kimura, H; Hirota, K;
Source:
PHYSICAL REVIEW B, 72 (6); 2005
Abstract:
Impurity effects of Zn and Ni on the low-energy spin excitations were systematically studied in optimally doped La(1.85)Sr(0.15)Cu(1-y)A(y)O(4) (A=Zn,Ni) by neutron scattering. Impurity-free La1.85Sr0.15CuO4 shows a "spin gap" of omega=4 meV below T-c in the antiferromagnetic incommensurate spin excitation. In Zn:y=0.004, the spin excitation shows a spin gap of 3 meV below T-c. In Zn:y=0.008 and Zn:y=0.011, however, the dynamical susceptibility chi(") at omega=3 meV decreases below T-c and increases again at lower temperature, indicating an in-gap state. In Zn:y=0.017, the low-energy spin state remains unchanged with decreasing temperature, and elastic magnetic peaks appear below similar to 20 K and then exponentially grow. These results suggest that Zn induces a novel in-gap spin state, which becomes dominant and more static with increasing Zn. As for Ni:y=0.009 and Ni:y=0.018, the low-energy excitations below omega=3 meV and 2 meV disappear below T-c. The temperature dependence of chi(") at omega=3 meV, however, shows no upturn in contrast with Zn:y=0.008 and Zn:y=0.011, indicating the absence of an in-gap state. In Ni:y=0.029, though the magnetic signals were observed also at omega=0 meV, they showed no temperature dependence, implying that there is no static component. Furthermore, as omega increases, the magnetic peak width broadens and the peak position shifts toward the magnetic zone center (pi pi). We interpret the impurity effects as follows: Zn locally makes a nonsuperconducting island exhibiting the in-gap state in the superconducting sea with the spin gap. Zn reduces the superconducting volume fraction, thus suppressing T-c. On the other hand, Ni primarily affects the superconducting sea, and the spin excitations become more dispersive and broaden with increasing energy, which is recognized as a consequence of the reduction of energy scale of spin excitations. We believe that the reduction of energy scale is relevant to the suppression of T-c.
Title:
Stable quasicrystals and approximants in Zn-Mg-Zr and Zn-Mg-Hf alloys
Authors:
Hasegawa, J; Takeuchi, S; Tsai, AP;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 85 (6); 2005
Abstract:
Stable icosahedral quasicrystals and an approximant crystal have been found in Zn - Mg - Zr and Zn - Mg - Hf alloys. The formation of primitive (P-type) icosahedral quasicrystals with compositions around Zn85Mg7Zr8 and Zn85Mg7Hf8 has been observed in both the as-cast and the annealed states. A face-centred (F-type) icosahedral phase with a composition around Zn76Mg17Hf7 and its corresponding approximant crystal having a composition around Zn75Mg19Hf6 with a space group of Pm (3) over bar have been identified in a fully annealed Zn79Mg15Hf6 alloy. Chemical ordering between two distinctive icosahedral clusters, Zn54Mg12\ and Zn54Hf12 (or Zn54Zr12) are proposed to explain the low content of Hf (or Zr) and the occurrence of superlattice diffraction peaks observed for the F-type icosahedral quasicrystal and its 1/1 approximant. The two icosahedral clusters are equivalent in number in order to satisfy the criterion of an electron-to-atom ratio e/a equal to 2.15. They are randomly arranged for the P-type icosahedral phase and regularly arranged respectively at even- and odd-parity twelvefold vertices in the three-dimensional Penrose tiling for the F-type icosahedral phase.
Title:
Nuclear-magnetic-resonance interaction mechanism in Rb2CoCl4 single crystals with the electric magnetic type
Authors:
Lim, AR; Hong, KS;
Source:
JOURNAL OF APPLIED PHYSICS, 98 (4); 2005
Abstract:
The Rb-87 spin-lattice relaxation time of Rb2CoCl4 single crystals grown using the slow evaporation method was measured using nuclear magnetic resonance. The recovery trace for the central line of 87Rb with dominant magnetic relaxation cannot be represented with a single exponential function, but can be represented with a linear combination of two exponential functions. The change in the 87Rb spin-lattice relaxation rate near T-c1 corresponds to the ferroelectric to incommensurate phase transition. There is a weak anomalous contribution to T-1, and this seems to be the only detectable influence of a structural phase transition. The temperature dependence of T-1(-1) near T-i is more or less continuous and is not affected by the normal-incommensurate phase transition. For T > T-i, the spin-lattice relaxation rate is governed by molecular motion as described by the Bloembergen-Purcell-Pound theory. This behavior is different to that found for Rb in Rb2ZnCl4. The phase-transition temperatures of the Rb2CoCl4 and Rb2ZnCl4 single crystals are quite similar, but their phase-transition mechanisms are different. The nuclear-magnetic-resonance (NMR) interaction mechanism in Rb2ZnCl4 is well known to be of the electric quadrupolar type whereas in Rb2CoCl4 it is of magnetic origin. Therefore a completely different NMR behavior is obtained in the two crystals. (c) 2005 American Institute of Physics.
Title:
High frictional anisotropy of periodic and aperiodic directions on a quasicrystal surface
Authors:
Park, JY; Ogletree, DF; Salmeron, M; Ribeiro, RA; Canfield, PC; Jenks, CJ; Thiel, PA;
Source:
SCIENCE, 309 (5739); 2005
Abstract:
Strong friction anisotropy is found when the twofold surface of an atomically clean aluminum-nickel-cobalt quasicrystal slides against a thiol-passivated titanium-nitride tip. Friction along the aperiodic direction is one-eighth as much as that along the periodic direction. This anisotropy, which is about three times as large as the highest value observed in anisotropic crystalline surfaces, disappears after the surface is oxidized in air. These results reveal a strong connection between interface atomic structure and the mechanisms by which energy is dissipated, which likely include electronic or phononic contributions, or both.
Title:
Magnetic inversion symmetry breaking and ferroelectricity in TbMnO3
Authors:
Kenzelmann, M; Harris, AB; Jonas, S; Broholm, C; Schefer, J; Kim, SB; Zhang, CL; Cheong, SW; Vajk, OP; Lynn, JW;
Source:
PHYSICAL REVIEW LETTERS, 95 (8); 2005
Abstract:
TbMnO3 is an orthorhombic insulator where incommensurate spin order for temperature T-N< 41 K is accompanied by ferroelectric order for T < 28 K. To understand this, we establish the magnetic structure above and below the ferroelectric transition using neutron diffraction. In the paraelectric phase, the spin structure is incommensurate and longitudinally modulated. In the ferroelectric phase, however, there is a transverse incommensurate spiral. We show that the spiral breaks spatial inversion symmetry and can account for magnetoelectricity in TbMnO3.
Title:
Effect of Si on the formation and stability of the icosahedral quasicrystalline phase in Al-Fe-Cr-Ti alloys
Authors:
Sahoo, KL; Stone, IC;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 85 (5); 2005
Abstract:
The formation and stability of the quasicrystalline icosahedral (i) phase in melt-spun Al93-xFe3Cr2Ti2Six (x = 0-5) ribbons are reported. Samples were characterized by X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. Primitive (P-type) ordered i phase particles were found to be homogeneously distributed in an fcc alpha-Al matrix in the as-melt-spun ribbons. The size of the i phase particles decreased and their thermal stability increased with increasing substitution of Al by Si. The i phase had a decomposition temperature of approximately 480 degrees C in an Al93Fe3Cr2Ti2 ribbon whereas that in an Al92Fe3Cr2Ti2Si1 ribbon was approximately 500 degrees C. The i phase particles are resistant to coarsening prior to decomposition into crystalline phases. The presence of a small quantity of Si ( up to 1.0 at.%) is beneficial to both the thermal stability and the hardness of nanoquasicrystalline Al - Fe - Cr - Ti alloys.
Title:
Study of high-field magnetic phases of the low-carrier-system CeP by synchrotron radiation X-ray diffraction
Authors:
Hannan, A; Kawana, D; Kuwahara, K; Kohgi, M; Narumi, Y; Tabata, Y; Shimomura, S; Tanaka, Y; Katsumata, K;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 74 (8); 2005
Abstract:
The magnetic structures of the low-carrier-system CeP are investigated under magnetic fields up to 12.5 T with the field H parallel to [1 (1) over bar0] and up to 14 T with H II [001] by synchrotron X-ray diffraction utilizing the unique relationship between the magnetic structure and lattice modulation in this system. The magnetic phases corresponding to the modulation wave vectors k = 2/11, 2/10, 2/9 and 2/8 are observed at low temperatures, The magnetic phases with k = 2/8 (up arrow up arrow oooooo or up arrow up arrow --- - -), k = 2/9 (up arrow up arrow ooooooo or up arrow - - -- --) and k = 2/11 (up arrow up arrow ooooooooo) are the new phases under magnetic fields found in the present work. The result demonstrates that magnetic fields play a role similar to high pressure to realize the unique magnetic structure and its multistep change in CeP. This fact indicates the importance of the magnetic polaron effect mediated by the p-f mixing effect in the system.
Title:
Spatial order and diffraction in quasicrystals and beyond
Authors:
Gratias, D; Bresson, L; Quiquandon, M;
Source:
ANNUAL REVIEW OF MATERIALS RESEARCH, 35 (8); 2005
Abstract:
This review is an introduction to the problem of determining the nature of the diffraction spectra of ordered solids. After explicit computation examples of Bragg diffraction spectra of quasicrystals (bulk, surface) in kinematical and dynamical (high-resolution electron microscopy) situations, we show on simple toy models that long-range order does not necessarily lead to Bragg peaks which, in turn, are not necessarily the signature of the unique long-range periodic order.
Title:
Polarization anisotropy of X-ray atomic factors and 'forbidden' resonant reflections
Authors:
Dmitrienko, VE; Ishida, K; Kirfel, A; Ovchinnikova, EN;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 61 (7); 2005
Abstract:
Symmetry and physical aspects of 'forbidden' reflections excited by a local polarization anisotropy of the X-ray susceptibility are surveyed. Such reflections are observed near absorption edges where the anisotropy is caused by distortions of the atomic electronic states owing to interaction with neighbouring atoms. As a consequence, they allow for extracting nontrivial information about the resonant atom's local environment and their physical conditions. The unusual polarization properties of the considered reflections are helpful to distinguish them from other types of 'forbidden' reflections. When such reflections are excited, it is, for example, possible to determine not only the intrinsic anisotropy of an atomic form factor but also additional anisotropy induced by thermal motion, point defects and/or incommensurate modulations. Even the local 'chirality' of atoms in centrosymmetric crystals is accessible. Unsolved key problems and possible future developments are addressed.
Title:
Characterization and properties of nanocrystal-forming Zr-based bulk metallic glasses
Authors:
Saida, J; Kato, H; Setyawan, ADH; Inoue, A;
Source:
REVIEWS ON ADVANCED MATERIALS SCIENCE, 10 (1); 2005
Abstract:
The transformation behavior of Zr-Al-Ni-Cu-Pd metallic glasses is investigated. It is well known that the Zr65Al7.5Ni10Cu17.5 metallic glass has a high glass-forming ability, which is enable us to produce the glassy sample with a bulky shape. In the initial transformation stage of the alloy, the metastable fcc-Zr2Ni phase is precipitated. Since the fcc-Zr2Ni phase contains several icosahedral clusters in the unit cell, it is strongly correlated with the icosahedral local structure in the glassy state. By substitution of Pd with Cu, the primary phase changes into nanoscale icosahedral quasicrystalline phase. It is found that the nucleation frequency increases drastically with Pd addition, which results in the formation of nanostructured materials. These nanoscale structure control based on the glassy alloys is expected to exhibit unique mechanical properties such as a high strength and good ductility.
Title:
Elastic properties of icosahedral and decagonal quasicrystals
Authors:
Chernikov, MA;
Source:
PHYSICS-USPEKHI, 48 (4); 2005
Abstract:
Problems associated with determining the symmetry properties of the elastic constant tensor of icosahedral and decagonal quasicrystals are reviewed. Notions of elastic isotropy and anisotropy are considered, and their relation to the components of the elastic constant tensor is discussed. The question is addressed of how to determine experimentally whether a system under study is elastically isotropic. Experimental results produced by resonant ultrasound spectroscopy of icosahedral Al-Li-Cu and decagonal Al-Ni-Co single quasicrystals are discussed in detail.
Title:
Extended investigation of porosity in quasicrystals by synchrotron X-ray phase contrast radiography: Part II, in grains of other alloys and structures than AlPdMn
Authors:
Brunello, E; Agliozzo, S; Klein, H; Mancini, L; Hartwig, J; Baruchel, J; Gastaldi, J;
Source:
JOURNAL OF CRYSTAL GROWTH, 282 (1-2); 2005
Abstract:
The systematic study, by synchrotron X-ray phase sensitive radiography of the porosity in the bulk samples of the icosahedral Al-Pd-Mn quasicrystal (i-Al-Pd Mn) reported in the Part I of an emended investigation of porosity in quasicrystals (Part 1) has shown that the origin of this porosity is difficult to identify, As it is not clear if this type of porosity is characteristic of icosahedral quasicrystals in the present work. which is the Part II of the same investigation. we have studied the porosity in single grains of various alloys and structures (i-Al Pd Re, i-Zn Mg-Rare-Earth. d-Al-Co-Ni. xi'-Al-Pd-Mn) in order to attempt to elucidate this question. The results show that the presence of facetted micrometric pores is not restricted to icosahedral quasicrystals. Otherwise the part played by these pores to their actual existence and stability remains as questionable. The samples contain pores or not independently of the growth method, which does not seem to have an influence on the pores. Since pores were only observed in samples of the Al-rich phases this element could be an important ingredient for the formation of pores during the solidification process as it has been suggested in Part I. (c) 2005 Elsevier B.V. All rights reserved.

Update: 26-Aug-2005

Title:
Dynamic fracture of icosahedral model quasicrystals: A molecular dynamics study
Authors:
Rosch, F; Rudhart, C; Roth, J; Trebin, HR; Gumbsch, P
Source:
PHYSICAL REVIEW B, 72 (1): Art. No. 014128 JUL 2005
Abstract:
Ebert [Phys. Rev. Lett. 77, 3827 (1996)] have fractured icosahedral Al-Mn-Pd single crystals in ultrahigh vacuum and have investigated the cleavage planes in situ by scanning tunneling microscopy (STM). Globular patterns in the STM images were interpreted as clusters of atoms. These are significant structural units of quasicrystals. The experiments of Ebert imply that they are also stable physical entities, a property controversially discussed currently. For a clarification we performed the first large-scale fracture simulations on three-dimensional complex binary systems. We studied the propagation of mode-I cracks in an icosahedral model quasicrystal by molecular dynamics techniques at low temperature. In particular we examined how the shape of the cleavage plane is influenced by the clusters inherent in the model and how it depends on the plane structure. Brittle fracture with no indication of dislocation activity is observed. The crack surfaces are rough on the scale of the clusters, but exhibit constant average heights for orientations perpendicular to high-symmetry axes. From detailed analyses of the fractured samples we conclude that both the plane structure and the clusters strongly influence dynamic fracture in quasicrystals and that the clusters therefore have to be regarded as physical entities.
Title:
Experimental measurement of the photonic properties of icosahedral quasicrystals
Authors:
Man, WN; Megens, M; Steinhardt, PJ; Chaikin, PM
Source:
NATURE, 436 (7053): 993-996 AUG 18 2005
Abstract:
Quasicrystalline structures may have optical bandgap properties-frequency ranges in which the propagation of light is forbidden-that make them well-suited to the scientific and technological applications for which photonic crystals(1-3) are normally considered(4). Such quasicrystals can be constructed from two or more types of dielectric material arranged in a quasiperiodic pattern whose rotational symmetry is forbidden for periodic crystals (such as five-fold symmetry in the plane and icosahedral symmetry in three dimensions). Because quasicrystals have higher point group symmetry than ordinary crystals, their gap centre frequencies are closer and the gaps widths are more uniform-optimal conditions for forming a complete bandgap that is more closely spherically symmetric. Although previous studies have focused on one-dimensional and two-dimensional quasicrystals (4-7,) where exact (one-dimensional) or approximate (two-dimensional) band structures can be calculated numerically, analogous calculations for the three-dimensional case are computationally challenging and have not yet been performed. Here we circumvent the computational problem by doing an experiment. Using stereolithography, we construct a photonic quasicrystal with centimetre-scale cells and perform microwave transmission measurements. We show that three-dimensional icosahedral quasicrystals exhibit sizeable stop gaps and, despite their quasi-periodicity, yield uncomplicated spectra that allow us to experimentally determine the faces of their effective Brillouin zones. Our studies confirm that they are excellent candidates for photonic bandgap materials.
Title:
High mechanical properties of cast quasicrystal-reinforced Mg-alloys
Authors:
Yuan, GY; Ding, WJ; Amiya, K; Kato, H; Inoue, A
Source:
MAGNESIUM - SCIENCE, TECHNOLOGY AND APPLICATON, 488-489: 127-130 2005 Book series title: MATERIALS SCIENCE FORUM
Abstract:
Mg-8Zn-4Al-xY base alloys containing an icosahedral quasicrystal phase (i-phase) as a main strengthening phase were prepared by casting into a copper mould at moderate cooling rates. The Y addition was effective for decreasing the size of i-phase and the more homogeneousness of its dispersed state. The mechanical properties at room temperature were much superior to those of AZ91 alloy. The creep tests indicated a promising high temperature creep resistance of the quasicrystal-reinforced Mg-Zn-Al-Y cast alloy. The dislocation characteristic in crept specimens which containing i-phase and no i-phase was analyzed and strengthening mechanism was discussed.
Title:
Effect of equal channel angular extrusion on the microstructure and mechanical properties of magnesium alloy containing quasicrystallines
Authors:
Zheng, MY; Qiao, XG; Xu, SW; Wu, K; Kamado, S; Kojima, Y
Source:
MAGNESIUM - SCIENCE, TECHNOLOGY AND APPLICATON, 488-489: 589-592 2005 Book series title: MATERIALS SCIENCE FORUM
Abstract:
Equal channel angular extrusion (ECAE) was applied to an extruded ZW1101 (Mg - 11 wt%Zn - 0.9wt%Y) Mg alloy containing quasicrystallines. The as-extruded ZW1101 alloy had an initial grain size of about 12 mu m and bands of quasicrystalline phases parallel to the extrusion direction. After the extruded alloy was subjected to ECAE processing, the grain size was refined to about 0.5 mu m, and the quasicrystalline phases were further broken and dispersed in the matrix. After the ECAE processing, the micro-hardness and yield strength of the alloy were increased, however, the ultimate tensile strength and the ductility of the alloy were slightly decreased.
Title:
Dimethylammonium gallium sulfate hexahydrate and dimethylammonium aluminium sulfate hexahydrate - members of a crystal family with exceptional commensurate/incommensurate phase sequences
Authors:
Volkel, G; Bottcher, R; Michel, D; Czapla, Z; Banys, J
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (28): 4511-4529 JUL 20 2005
Abstract:
Dimethylammonium gallium sulfate hexahydrate (DMAGaS) and dimethylammonium aluminium sulfate hexahydrate (DMAAS) are isomorphous and ferroelastic at room temperature. But at lower temperatures their ordering behaviours are quite different. Whereas DMAAS shows only a single order-disorder-type transition into a ferroelectric phase, DMAGaS exhibits an exceptional sequence of commensurate and incommensurate phases with an antiferroelectric lock-in phase at low temperatures. The basic experimental findings from recent pressure and composition dependent dielectric investigations and from electron paramagnetic resonance studies are briefly reviewed. Experimental results are then discussed within the framework of the semimicroscopical extended discrete frustrated phi(4) (DIFFOUR) model. The frustrating nearest and next nearest neighbour interactions between the dimethylammonium (DMA) dipoles in the -DMA((i))-Ga/Al(H2O)(6(i))-DMA((i+1))-Ga/Al(H2O)(6(i+1))-chains give rise to the observed complex phase sequence. It will be shown that the phase sequence of DMAGaS, its variation under pressure and with DMAAS admixture, as well as the new pressure induced phases of DMAAS can be well interpreted by theory.
Title:
Extended investigation of porosity in quasicrystals by synchrotron X-ray phase contrast radiography - I: In icosahedral AlPdMn grains
Authors:
Agliozzo, S; Brunello, E; Klein, H; Mancini, L; Hartwig, J; Baruchel, J; Gastaldi, J
Source:
JOURNAL OF CRYSTAL GROWTH, 281 (2-4): 623-638 AUG 1 2005
Abstract:
The porosity was studied using coherent synchrotron X-ray radiography, firstly in several bulky icosahedral Al-Pd-Mn quasicrystals, grown in different laboratories by various techniques (Bridgman, Czochralski, Flux) and then in quasicrystal grains of many other alloys and structures (Part 11). In this part 1, we report a quantitative analysis which has been carried out in order to find some correlation of this porosity with some growth or after-growth cooling parameters (growth parameters). The size distribution of pores was observed to change drastically among samples grown with different growth parameters as well as in those extracted from the same ingot and no mode values were evidenced when we plotted the distribution of pores in all investigated as-grown samples. These changes point out the influence of the solidification process on the occurrence of porosity, especially the influence of the vacancy migration. These results are used to discuss the two main Current hypotheses on the origin of porosity. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Specific features of the magnetic field-induced orientational transition in EuMnO3
Authors:
Kadomtseva, AM; Popov, YF; Vorob'ev, GP; Ivanov, VY; Mukhin, AA; Balbashov, AM
Source:
JETP LETTERS, 81 (11): 590-593 2005
Abstract:
It is found that the spin-flop transition in EuMnO3 manganite induced by a magnetic field H parallel to the b axis is accompanied not only by a magnetization jump and magnetostriction anomalies but also by the appearance of electric polarization in the vicinity of the transition field H-cr similar to 200 kOe. This phenomenon can be associated with the occurrence of magnetically inhomogeneous (modulated) states in the vicinity of H-cr . In these states, the system loses the center of symmetry, which allows for the appearance of the polarization. The formation of such states in a magnetic field is caused by the general tendency of the occurrence of magnetically inhomogeneous (incommensurate) structures in the RMnO3 series due to the frustration of exchange interactions with decreasing ionic radius of the rare-earth ion R starting with R = Eu. (C) 2005 Pleiades Publishing, Inc.
Title:
Effect of oxygen pressure on structural modulation observed by X-ray reciprocal space mapping in epitaxial bismuth cuprate superconducting.
Authors:
Kaneko, S; Akiyama, K; Mitsuhashi, M; Hirabayashi, Y; Ohya, S; Seo, K; Funakubo, H; Matsuda, A; Yoshimoto, M
Source:
EUROPHYSICS LETTERS, 71 (4): 686-691 AUG 2005
Abstract:
Bi2Sr2Ca1Cu2Ox (Bi-2212) single layers were prepared on MgO(100) substrates in different conditions of oxygen pressure using a 266 nm laser generated by slower Q-switched YAG system. Several X-ray diffraction methods were employed to investigate the crystal structure of Bi-2212. X-ray diffraction (XRD) methods of theta-2 theta. and phi scan were used to verify the epitaxial growth of Bi-2212( 001), and reciprocal space mapping (RSM) of omega-2 theta was employed to investigate in-plane lattice constants and structural modulation. Satellite peaks generated by structural modulation on the RSM showed asymmetric distribution around the main peak. The periodicity of modulation was evaluated using satellite peaks on the RSM. With increasing oxygen pressure, the lattice constant expanded along the c-axis and contracted along the b-axis, while structural modulation expanded along both b- and c-axis directions.
Title:
Atomic structure in Zr70Cu29Pd1 metallic glass
Authors:
Yang, L; Jiang, JZ; Liu, T; Hu, TD; Uruga, T
Source:
APPLIED PHYSICS LETTERS, 87 (6): Art. No. 061918 AUG 8 2005
Abstract:
Local atomic structures of Pd, Cu, and Zr atoms in an as-prepared Zr70Cu29Pd1 glassy alloy and the annealed samples containing icosahedral quasicrystal have been investigated by Pd, Cu, and Zr K-edge extended x-ray absorption fine structure (EXAFS) measurements. It is found that Cu and Zr atoms have an icosahedral atomic surrounding. Cu atoms could locate at both center position and shell sites while Zr atoms most likely occupy the shell sites of icosahedron. Pd atoms neither substitute Zr atoms nor Cu atoms. They sit at octahedral interstices, which link up icosahedron and promote the growth of icosahedron into long-range-order icosahedral quasicrystal in the ternary Zr70Cu29Pd1 glassy alloy during annealing treatment. (c) 2005 American Institute of Physics.

Update: 19-Aug-2005

Title:
Specific heat and electrical resistivity of an icosahedral-structure Zr70Pd30 alloy and of its amorphous and crystalline analogs
Authors:
Panova, GK; Chernoplekov, NA; Shikov, AA
Source:
PHYSICS OF THE SOLID STATE, 47 (7): 1205-1210 2005
Abstract:
Binary icosahedral and crystalline phases of the Zr70Pd30 alloy were obtained in crystallization from the amorphous state during heat treatment. The specific heat and electrical resistivity of the icosahedral, amorphous, and crystalline phases were measured and compared. An increase in the electronic density of states on the Fermi surface, lattice softening, and an increase in the electron-phonon coupling constant were observed to occur with decreasing structural order. Despite the high valence electron density in the icosahedral phase, where the electronic densities of states are twice those in the crystal, the electrical resistivity of the icosahedral phase is similar to 50 times as high. Superconductivity was observed for the first time in the icosahedral phase of a binary system of transition metal atoms, Zr70Pd30. (c) 2005 Pleiades Publishing, Inc.
Title:
Incommensurate interactions and nonconventional spin-Peierls transition in TiOBr
Authors:
van Smaalen, S; Palatinus, L; Schonleber, A
Source:
PHYSICAL REVIEW B, 72 (2): Art. No. 020105 JUL 2005
Abstract:
Temperature-dependent x-ray diffraction of the low-dimensional spin-1/2 quantum magnet TiOBr shows that the phase transition at T-c2=47.1(4) K corresponds to the development of an incommensurate superstructure. Below T-c1=26.8 +/- 0.3 K the incommensurate modulation locks in into a twofold superstructure similar to the low-temperature spin-Peierls state of TiOCl. Frustration between intra- and interchain interations within the spin-Peierls scenario, and competition between the two-dimensional magnetic order and one-dimensional spin-Peierls order are discussed as possible sources of the incommensurability.
Title:
Electric-field-induced transformation of incommensurate modulations in antiferroelectric Pb0.99Nb0.02[(Zr1-xSnx)(1-y)Ti-y](0.98)O-3
Authors:
He, H; Tan, X
Source:
PHYSICAL REVIEW B, 72 (2): Art. No. 024102 JUL 2005
Abstract:
Most antiferroelectric ceramics are modified from the prototype PbZrO3 by adding Sn and Ti in conjunction with small amount of Nb or La to optimize their properties. These modifiers introduce unique nanoscale structural feature to the ceramics in the form of incommensurate modulations. It was shown previously that the modulation is strongly responsive to a change in chemical composition or temperature. However, its response to an electric field, the driving force in real applications, has not been explored before. In the present work the dynamic evolution of the incommensurate modulation during the electric field-induced antiferroelectric-to-ferroelectric transformation was observed with an in situ transmission electron microscopy (TEM) technique. The results indicate that the incommensurate modulation exists as a transverse Pb-cation displacement wave. The wavelength was found to be quite stable against external electrical stimuli, in sharp contrast to the dramatic change under thermal stimuli reported previously. It is suggested that the appeared incommensurate modulation is an average effect of a mixture of two commensurate modulations. The electric field-induced antiferroelectric-to-ferroelectric transformation proceeds with aligning the Pb-cation displacements, which resembles the process of 90 degrees reorientation and 180 degrees reversal in normal ferroelectrics.
Title:
Theory of the defect-free phason strain in quasicrystals
Authors:
Rochal, SB; Kozinkina, YA
Source:
PHYSICAL REVIEW B, 72 (2): Art. No. 024210 JUL 2005
Abstract:
A defect-free transformation of a perfect quasicrystalline order into a defect-free crystalline one by means of a linear phason strain (LPS) is under consideration. The structures based on octagonal, pentagonal, and Amman tilings are discussed. It is shown that the LPS induces a change of the shape of atomic surfaces (AS's). This change ensures a possibility to construct the deformed structure from the same tiles, which make up the initial quasicrystalline tiling. The LPS of any finite quasicrystalline sample can be performed in a discrete number of steps through a sequence of intermediate structures. The atomic positions in these structures either coincide, or differ in one of the orientationally equivalent vectors. The defect-free structure reconstruction is possible only in a bounded region of values of the LPS tensor components. In all the cases under consideration AS's become concave outside this region. A large number of real, periodic approximant structures correspond exactly to its boundary. For example, in the system Al-Co-Ni there are at least six periodic approximants of such a type.
Title:
Chemical order in 1/1 Al(Si)-Cu-Fe approximant phases
Authors:
Simonet, V; Hippert, F; Brand, RA; Calvayrac, Y; Rodriguez-Carvajal, J; Sadoc, A
Source:
PHYSICAL REVIEW B, 72 (2): Art. No. 024214 JUL 2005
Abstract:
The structures of the cubic alpha(')-Al71.7Si7Cu3.8Fe17.5 and alpha-Al55Si7Cu25.5Fe12.5 phases, 1/1 approximants of Al-Cu-Fe quasicrystals, are revisited. The chemical order in the alpha phase is inferred from joined x-ray and neutron powder diffraction data refinements and from extended x-ray absorption fine structure (EXAFS) studies at both Fe and Cu K-edges. The existence of crystallographic sites randomly occupied by both Al and Cu atoms, or by a combination of Al, Cu, and Fe atoms, allows the understanding of the chemical substitution mechanisms defining the existence domain of this approximant.
Title:
Ordering kinetics in the long-period superlattice alloy Cu0.79Pd0.21
Authors:
Wang, X; Mainville, J; Ludwig, K; Flament, X; Finel, A; Caudron, R
Source:
PHYSICAL REVIEW B, 72 (2): Art. No. 024215 JUL 2005
Abstract:
The kinetics of long-period superlattice (LPS) formation from the disordered state has been examined in a Cu0.79Pd0.21 alloy that exhibits a one-dimensional LPS ordered state. Time-resolved x-ray scattering shows that, following a rapid temperature quench from the disordered state into the LPS region of the phase diagram, the satellite peaks initially grow more quickly than do the central integer-order superlattice peaks. During this process, the satellite peak position, which is inversely related to the average modulation wavelength 2M, initially decreases rapidly, then reaches a minimum and relaxes slowly back toward its new equilibrium position. In the later stages of the LPS formation process, the satellite and central integer-order superlattice peaks narrow in a manner consistent with t(1/2) domain coarsening. A simple stochastic model of the partially ordered structure was developed to better understand the relationships between peak widths.
Title:
Antiferromagnetism in Pr3In
Authors:
Christianson, AD; Lawrence, JM; Zarestky, JL; Suzuki, HS; Thompson, JD; Hundley, MF; Sarrao, JL; Booth, CH; Antonio, D; Cornelius, AL
Source:
PHYSICAL REVIEW B, 72 (2): Art. No. 024402 JUL 2005
Abstract:
We present neutron diffraction, magnetic susceptibility and specific heat data for a single-crystal sample of the cubic (Cu3Au structure) compound Pr3In. Antiferromagnetic order occurs below T-N=12 K with propagation vector (0,0,0.5 +/-delta) where delta approximate to 1/12. The neutron diffraction results can be approximated with a model where the moments in each of the three Pr sublattices form ferromagnetic sheets perpendicular to and alternating in sign along the propagation direction, with a 12-unit-cell square-wave modulation. The very small specific heat anomaly that we observe at T-N=12 K may be a consequence of the fact that the ordered moment is induced in the Gamma(1) singlet when T < T-N. The magnetic susceptibility indicates that in addition to the antiferromagnetic transition at 12 K, there may be a transition near 70 K below which there is a very small remnant magnetization (0.005 mu(B)).
Title:
Anisotropic spin and charge excitations in superconductors: Signature of electronic nematic order
Authors:
Kao, YJ; Kee, HY
Source:
PHYSICAL REVIEW B, 72 (2): Art. No. 024502 JUL 2005
Abstract:
We study spin and charge susceptibilities in the d-wave superconducting state whose underlying electronic dispersion is anisotropic due to the formation of electronic nematic order. We show that the amplitude of the incommensurate peaks in the spin susceptibility near (pi,pi) reveals a pronounced anisotropy in momentum space. The relevance of our findings to the magnetic scattering pattern observed in recent neutron scattering measurements on untwinned YBa2Cu3O6+x is discussed. In the charge channel, we identify a well-defined collective mode at small momentum transfer with strong anisotropic amplitude depending on the direction of the momentum transfer, which is associated with the broken symmetry due to nematic ordering.
Title:
Optical conductivity and charge ordering in NaxCoO2
Authors:
Lupi, S; Ortolani, M; Baldassarre, L; Calvani, P; Prabhakaran, D; Boothroyd, AT
Source:
PHYSICAL REVIEW B, 72 (2): Art. No. 024550 JUL 2005
Abstract:
The infrared conductivity sigma(omega) of NaxCoO2 is studied as a function of doping and temperature for 0.5 <= x <= 1. A far-infrared peak (FIP) in sigma(omega), which coexists with a small Drude contribution, indicates charge localization in the CoO2 layers. Long-range ordering at x=0.5 is confirmed to create a far-infrared gap, in addition to the FIP. At low T and high incommensurate x values, in correspondence with the reported formation of a spin-density wave, the FIP abruptly shifts to higher energy, indicating a deepening of the localizing potential. An analysis of the in-plane E-1u phonon lifetime shows that Na+ ions lattice is "frozen in" at any T < 295 K for commensurate x and at T less than or similar to 150 K for incommensurate x. A comparison with the behavior of the FIP suggests that the Na+ "freezing" induces carrier localization only for low charge density and high Na+ concentration.
Title:
Spontaneous lateral modulation in short-period superlattices investigated by grazing-incidence X-ray diffraction
Authors:
Caha, O; Mikulik, P; Novak, J; Holy, V; Moss, SC; Norman, A; Mascarenhas, A; Reno, JL; Krause, B
Source:
PHYSICAL REVIEW B, 72 (3): Art. No. 035313 JUL 2005
Abstract:
The process of spontaneous lateral composition modulation in short-period InAs/AlAs superlattices has been investigated by grazing-incidence x-ray diffraction. We have developed a theoretical description of x-ray scattering from laterally modulated structures that makes it possible to determine the lateral composition modulation directly without assuming any structure model. From experimental intensity distributions in reciprocal space we have determined the amplitudes of the modulation and its degree of periodicity and their dependence on the number of superlattice periods. From the data it follows that the modulation process cannot be explained by bunching of monolayer steps and most likely, it is caused by stress-driven morphological instabilities of the growing surface.
Title:
Copper adsorption on the fivefold Al70Pd21Mn9 quasicrystal surface
Authors:
Ledieu, J; Hoeft, JT; Reid, DE; Smerdon, JA; Diehl, RD; Ferralis, N; Lograsso, TA; Ross, AR; McGrath, R
Source:
PHYSICAL REVIEW B, 72 (3): Art. No. 035420 JUL 2005
Abstract:
Recently we reported the formation of a quasiperiodic Cu thin film on the fivefold icosahedral Al-Pd-Mn quasicrystal using scanning tunneling microscopy, low energy electron diffraction, and Auger electron spectroscopy. Here we provide details pertaining to the growth, stability, and structure of this film. Structural information has been gained by LEED measurements carried out at 85 K. Cu atoms are organized periodically with a nearest-neighbor distance of 2.5 +/- 0.1 angstrom along the aperiodically spaced rows. Above 8 ML spontaneous mass transport resulting in island formation has been observed by STM. These observations point to ascending adatoms being responsible for the formation of 3D features. Finally, flashing the multilayer film to 570 K results in the desorption or diffusion of Cu into the bulk and the formation of five domains of a periodic structure.
Title:
Charge- and spin-density modulations in semiconductor quantum wires
Authors:
Lee, M; Bruder, C
Source:
PHYSICAL REVIEW B, 72 (4): Art. No. 045353 JUL 2005
Abstract:
We investigate static charge- and spin-density modulation patterns along a ferromagnet-semiconductor single-junction quantum wire in the presence of spin-orbit coupling. Coherent scattering theory is used to calculate the charge and spin densities in the ballistic regime. The observed oscillatory behavior is explained in terms of the symmetry of the charge and spin distributions of eigenstates in the semiconductor quantum wire. Also, we discuss the condition that these charge- and spin-density oscillations can be observed experimentally.
Title:
Real-space observation of quasicrystalline Sn monolayer formed on the fivefold surface of icosahedral Al-Cu-Fe quasicrystal
Authors:
Sharma, HR; Shimoda, M; Ross, AR; Lograsso, TA; Tsai, AP
Source:
PHYSICAL REVIEW B, 72 (4): Art. No. 045428 JUL 2005
Abstract:
We investigate a thin Sn film grown at elevated temperatures on the fivefold surface of an icosahedral Al-Cu-Fe quasicrystal by scanning tunneling microscopy (STM). At about one monolayer coverage, the deposited Sn is found to form a smooth film of height consistent with one-half of the lattice constant of the bulk Sn. Analysis based on the Fourier transform and autocorrelation function derived from high-resolution STM images reveals that Sn grows pseudomorphically and hence exhibits a quasicrystalline structure.
Title:
Structure and thermal stability of Mo/Al multilayers for soft x-ray mirrors
Authors:
Guo, QH; Shen, JJ; Du, HM; Jiang, EY; Bai, HL
Source:
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 38 (12): 1936-1942 JUN 21 2005
Abstract:
The structure and thermal stability of Mo/Al multilayers prepared by a four facing target sputtering system have been studied. Cross-sectional high-transmission electron microscopy reveals that Mo and Al layers are polycrystalline and that the thickness of the mixed layers at Mo-on-Al interfaces is larger than that at the Al-on-Mo interfaces. Annealing treatment up to 450 degrees C leads to the gradual period expansion and appearance of the 5th and 6th order Bragg peak, which can be attributed to grain growth and sharpness of the interfaces and/or improvement of the correlations of the roughness at different interfaces through annealing, respectively. Thermally induced interdiffusion or reaction at grain boundaries with high density restricts the further period expansion in spite of the increasing temperature. At 550 degrees C, the modulation structure is still well maintained though the amorphous Al-Mo alloy layer replaces the Al layer. On the base of effective heat of formation, Mo3Al8 is suggested to be the first phase formed at the interfaces. Further annealing to 600 degrees C would partly destroy the layered modulation structure.
Title:
The baric changes of the electron polarisability of LiRbSO4, LiKSO4 and (NH4)(2)BeF4 crystals
Authors:
Stadnyk, VY; Romanyuk, MO
Source:
FERROELECTRICS, 317: 255-260 2005
Abstract:
The effect of uniaxial mechanical stresses on the spectral and temperature dependences of principal refractive indices n(i) and birefringence Delta n(i) of LiRbSO4, LiKSO4 and (NH4)(2)BeF4 crystals have been studied in the wide spectral (250-800 nm) and temperature (100-800 K) ranges. Displacements of the PT points under the uniaxial stress action as well as both an extensition or narrowing of the temperature intervals of the incommensurate phase have been revealed. The baric increacement of the n; was observed.
Title:
Pressure effect on Sn2P2Se6 type incommensurate crystals
Authors:
Slivka, AG; Kedyulich, VM; Gerzanich, EI
Source:
FERROELECTRICS, 317: 281-285 2005
Abstract:
A theoretical analysis of pressure dependence of the incommensurate phase temperature interval and wavevector modulation in Sn2P2Se6 incommensurate ferroelectric is performed within the framework of phenomenological approach.

Update: 12-Aug-2005

Title:
Incommensurate modulation at 165 degrees C of intermediate tridymite
Authors:
Graetsch, HA; Brunelli, M
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 220 (7): 606-613 2005
Abstract:
The crystal structure of the incommensurate modification Of SiO2 tridymite existing between 150 and 200 degrees C was refined in the 3 + 1 dimensional superspace group P2(1)(alpha beta 0) from synchrotron powder diffraction data. The modulation consists of rotations and tiltings of rigid SiO4/2 tetrahedra with mainly transversal displacements of the atoms. At 165 degrees C the wave vector is r = 0.054a* + 0.004b*. The largest amplitude is ca. 0.4 angstrom for oxygen and ca. 0.2 angstrom for silicon. Si-O-Si intertetrahedral and O-Si (. . .) Si-O torsion angles vary by more than 10 degrees. The torsion rotations are larger for pairs of adjacent tetrahedra in trans-configuration than for those in cis-configuration. The shape of six-membered rings of tetrahedra change from almost hexagonal to ditrigonal along the modulation vector.
Title:
Few particles correlation in a one-dimensional quasiperiodic lattice
Authors:
Suarez, JR; Vallejo, E; Carvajal, E; Navarro, O
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 242 (9): 1759-1762 JUL 2005
Abstract:
During the last two decades, two of the most important discoveries in condensed matter physics have been the discovery of quasicrystals and the discovery of high-Tc ceramic superconductors. These topics have generated a large number of experimental and theoretical studies in the physics of low dimension. They have also modified some of the concepts in solid state physics. For instance, it was believed that the fivefold symmetry was incompatible with a long-range order and it was not expected that ceramic materials with a high-Tc and a short coherence length exhibit superconductivity. Therefore, it is important to revise both the spatial symmetry and the electronic correlation to identify how they affect the physical properties of materials. The study of these subjects is complex since we cannot use the reciprocal space to study quasicrystals and the electronic correlation in many-body systems has not entirely been solved. Even in one-dimensional quasiperiodic structures, the interactions between electrons have often been neglected and only few results have been obtained. In this work, we solved the cases of two and three interacting particles in a Fibonacci lattice using a real-space method, the Green function technique, the renormalized perturbation expansion method and the Hubbard model. For the case of two interacting particles an analytical solution for the pairing phase diagram was obtained using the extended Hubbard Hamiltonian. For the case of three interacting particles the binding energy was numerically calculated. The results present here are compared with those obtained for the periodic and binary lattices. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Title:
Thermal hysteresis and memory effects in TlGaSe2 crystal with incommensurate phase
Authors:
Mikailov, FA; Senturk, E; Tumbek, L; Mammadov, TG; Mammadov, TS
Source:
PHASE TRANSITIONS, 78 (5): 413-419 MAY 2005
Abstract:
Temperature dependencies of dielectric permittivity of TlGaSe2 have been measured under various thermal cycles. Peculiarities of anomalies in temperature dependencies of dielectric permittivity corresponding to structural phase transitions at 108 and 115K are discussed. The coexistence of two different incommensurate structures in TlGaSe2 was proposed. The phase transitions at 108 and 115K are considered as commensurate lock-in transitions. As a result a new model of the structural phase transitions in TlGaSe2 has been suggested.
Title:
Transmission electron microscopy study of dislocation motion in icosahedral Al-Pd-Mn
Authors:
Mompiou, F; Caillard, D
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 400: 283-293 JUL 25 2005
Abstract:
DPerfect and imperfect dislocations trailing phason faults in quasi-crystals are introduced using a simplified two-dimensional aperiodic structure. Then, on the basis of observations of deformed specimens as well as in situ experiments in a transmission electron microscope, the motion of dislocations in icosahedral Al-Pd-Mn is shown to take place exclusively by climb. Under such conditions, the very high brittleness of Al-Pd-Mn at low and medium temperatures is proposed to be a consequence of the difficulty of glide, which itself appears to be an intrinsic property of the quasi-crystalline structure. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Plastic deformation of Al-Cu-Fe quasicrystals embedded in Al2Cu at low temperatures
Authors:
Miyazaki, S; Kumai, S; Sato, A
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 400: 300-305 JUL 25 2005
Abstract:
Al-Cu-Fe icosahedral quasicrystals are known to be hardly deformable at temperatures lower than 0.8T(m). The microstructures of the quasicrystals deformed at such temperatures have not been examined in details. Although the quasicrystals are brittle at low temperature, there is a possibility that they can be deformed if they are protected by other ductile materials. In this study, a few methods are proposed to deform an Al-Cu-Fe quasicrystal. The purpose of this study is to reveal the deformation mechanism at low temperatures and compare the results with those reported for deformation at high temperature. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Dislocation processes in quasicrystals - Kink-pair formation control or jog-pair formation control
Authors:
Takeuchi, S
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 400: 306-310 JUL 25 2005
Abstract:
A computer simulation of dislocation in a model quasiperiodic lattice indicates that the dislocation feels a large Peierls potential when oriented in particular directions. For a dislocation with a high Peierls potential, the glide velocity and the climb velocity of the dislocation can be described almost in parallel in terms of the kink-pair formation followed by kink motion and the jog-pair formation followed by jog motion, respectively. The activation enthalpy of the kink-pair formation is the sum of the kink-pair formation enthalpy and the atomic jump activation enthalpy, while the activation enthalpy of thejog-pair formation involves thejog-pair enthalpy and the self-diffusion enthalpy. Since the kink-pair energy can be considerably larger than the jog-pair energy, the climb velocity can be faster than the glide velocity, so that the plastic deformation of quasicrystals can be brought not by dislocation glide but by dislocation climb at high temperatures. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Shear experiments under confining pressure conditions of Al-Pd-Mn single quasicrystals
Authors:
Texier, M; Thilly, L; Bonneville, J; Proult, A; Rabier, J
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 400: 311-314 JUL 25 2005
Abstract:
Icosahedral Al-Pd-Mn quasicrystalline alloys are known to be extremely brittle at low and intermediate temperatures when deformed with conventional tests. Using specific deformation conditions, such as high confining pressure techniques, allowed plastic deformation of this non-periodic structure at temperatures in the brittle domain. Surprisingly, low temperature deformation microstructures revealed the presence of dislocations, whose motion essentially implicates climb mechanisms. The aim of this study is to use a shear experiment technique, specially designed to favour glide processes, in order to check if glide may occur solely, without any climb component. The results confirm the difficulty to promote pure glide processes and support the idea that both glide and climb are activated. (c) 2004 Elsevier B.V. All rights reserved.
Title:
On the plasticity of Al-Cu-Fe quasicrystals
Authors:
Texier, M; Proult, A; Bonneville, J
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 400: 315-319 JUL 25 2005
Abstract:
A technique of repeated load relaxation tests (RLRT) has been used to evaluate microstructural evolutions and activation volumes of Al-Cu-Fe quasicrystals deformed in compression tests performed at constant strain-rate. The post-relaxation behaviour after reloading at constant strain-rate and the evolution of correction terms, measured by RLRT in order to account for microstructural evolution, confirm that Al-Cu-Fe plasticity is controlled by a strain-dependent thermally activated mechanism. Activation volumes measured in the hardening and softening stages of the yield point reveal that the same mechanism controls plastic deformation. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Kondo-like scaling of electrical conductivity of Al70-xBxPd20Mn10 (x=0.5, 1, 2, and 4) quasicrystalline alloys
Authors:
Jaiswal, A; Rawat, R; Lalla, NP
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 351 (24-25): 2057-2064 AUG 1 2005
Abstract:
The electrical-conductivity and magnetization behavior of single-phase Al70-xBxPd20Mn10 (x = 0, 0.5, 1, 2 and 4) quasicrystals have been studied. It has been observed that boron substitution brings drastic changes in the sigma-T behavior of Al-Pd-Mn quasicrystals. Even a 0.5 at.% replacement of aluminium by boron causes a drastic change in the sigma-T behavior. The sigma-T variation shows minima, which shifts rapidly towards high temperature with increasing boron concentration and goes even above the room temperature. Field cool and zero-field cool chi-T behavior shows the paramagnetic nature of the samples. The sigma-(ln(-1) T) plots show linear behavior and get scaled in a {(sigma(T) - sigma(min))/(sigma(4) - sigma(min))} vs (ln(-1) T/ln(-1) T-min) plot. These samples show large magnetoresistance with +H-2 behavior. Occurrences of these features very strongly indicate the dominating role of Kondo-scattering in electronic transport of this Al-B-Pd-Mn and in general for Al-Pd-Mn quasicrystalline system. The observed sigma(T) behavior has been accounted to the occurrence of Kondo-type spin-flip scattering in Al-B-Pd-Mn and Al-Pd-Mn quasicrystals in the presence of weak-localization. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Crystal structure of sulfur and selenium at pressures up to 160 GPa
Authors:
Degtyareva, O; Gregoryanz, E; Mao, HK; Hemley, RJ
Source:
HIGH PRESSURE RESEARCH, 25 (1): 17-33 MAR 2005
Abstract:
Using advanced in situ X-ray diffraction techniques at high pressures and temperatures, we have resolved the long-standing problem of the phase transition sequence of sulfur in its non-metallic state. Our data show that there are only two phases of sulfur stable between 1.5 GPa and pressure of metallization of 86GPa, S-II with triangular chain structure and S-III with novel squared chain structure. The same squared chain structure is formed in the heavier group-VI element Se at pressures of 20 GPa and temperatures of 450 K. Our X-ray diffraction data on metallic phases of sulfur above 83 GPa show that the S-IV phase has an incommensurately modulated monoclinic structure, the same as recently reported modulated structures of Te-III and Se-IV. S-IV is shown to transform to primitive rhombohedral beta-Po phase at 153(3) GPa, the same transition is found in Se at pressure of around 80 GPa.

Update: 5-Aug-2005

Title:
The effect of pressure on the spin density wave transition in the layered cobaltites [Ca2CoO3](0.62)[CoO2] and [Ca2Co4/3Cu2/3O4](0.62)[CoO2]
Authors:
Sugiyama, J; Andreica, D; Itahara, H; Tani, T
Source:
SOLID STATE COMMUNICATIONS, 135 (4): 263-267 JUL 2005
Abstract:
In order to investigate the pressure effect on the magnetism in the layered cobaltites, positive muon spin rotation and relaxation mu(+)SR experiments have been carried out up to 1.3 GPa using c-aligned polycrystalline samples of [Ca2CoO3](0.62) [CoO2] and [Ca2CO4/3Cu2/3O4](0.62)[CoO2]. A transverse field mu(+)SR experiment indicates that the transition temperature to an incommensurate spin density wave IC-SDW state is independent of hydrostatic pressure up to 1.3 GPa for the both compounds. Furthermore, there are no changes in the spontanious muon precession frequency in zero field at 5 K even under 1.3 GPa. These results strongly suggest that the IC-SDW exists not in the rocksalt-type block ([Ca2CoO3] and/or [Ca2CO4/3Cu2/3O4]) but in the CoO2 plane. (c) 2005 Elsevier Ltd. All rights reserved.
Title:
A new family of ferroelectric tetragonal tungsten bronze phases, Ba2MTi2X3O15
Authors:
Stennett, MC; Miles, GC; Sharman, J; Reaney, IM; West, AR
Source:
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 25 (12): 2471-2475 2005
Abstract:
The compositions Ba2MTi2X3O15: M = La, Pr, Nd, Sm, Eu, Gd, Dy, Bi; X = Nb, Ta form a new family of ferroelectric phases. With larger M cations, La, Bi, the materials exhibit relaxor behaviour with sub-ambient Tc. With decreasing M size, a sharp first order ferroelectric phase transition is observed and Tc rises to a maximum at similar to 330 degrees C for Gd. The phases are tetragonal tungsten bronzes with A-site order (BaM) and non-statistical B-site disorder (of Ti, Nb for M = La). All phases show a weak superstructure with doubled c and multiple periodicity parallel to [1 1 0] that is incommensurate for the relaxor ferroelectrics (M = La, Bi) but commensurate for the remainder. The phases exhibit complex non-stoichiometry with variable Ba:M and Ti:X ratios as well as variable oxygen content. (c) 2005 Elsevier Ltd. All rights reserved.
Title:
The order-disorder transition in Bi2O3-Nb2O5 fluorite-like dielectrics
Authors:
Valant, M; Jancar, B; Pirnat, U; Suvorov, D
Source:
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 25 (12): 2829-2834 2005
Abstract:
An analysis of the microwave dielectric properties showed that the cubic fluorite solid solutions (1-x)Bi(2)O(3)(.)xNb(2)O(5) (0.23 <= x <= 0.26), the so-called delta-BNSS Type II, exhibit a high permittivity of 100, but also high dielectric losses (Q x f = 300 GHz) and a high temperature dependence of resonant frequency (tau(f) = -200 ppm/K). Investigations using X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that the Cubic incommensurate phase undergoes an order-disorder phase transition into a commensurate tetragonal phase at temperatures below 900 degrees C (for x = 0.25). The higher degree of ordering in the tetragonal phase reduces the dielectric losses (Q x f = 1000 GHz) and changes the sign of the temperature coefficient of resonant frequency (tau(f) = 100 x 10(-6)/K). (c) 2005 Elsevier Ltd. All rights reserved.
Title:
Continuum elastic sphere vibrations as a model for low lying optical modes in icosahedral quasicrystals
Authors:
Duval, E; Saviot, L; Mermet, A; Murray, DB
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (23): 3559-3565 JUN 15 2005
Abstract:
The nearly dispersionless, so-called 'optical' vibrational modes observed by inelastic neutron scattering from icosahedral Al-Pd-Mn and Zn-Mg-Y quasicrystals are found to correspond well to modes of a continuum elastic sphere that has the same diameter as the corresponding icosahedral basic units of the quasicrystal. When the sphere is considered as free, most of the experimentally found modes can be accounted for, in both systems. Taking into account the mechanical connection between the clusters and the remainder of the quasicrystal allows a complete assignment of all optical modes in the case of Al-Pd-Mn. This approach provides support to the relevance of clusters in the vibrational properties of quasicrystals.
Title:
Ferromagnetism in quasicrystals: Symmetry aspects
Authors:
Vekilov, YK; Salikhov, SV; Isaev, EI; Johansson, B
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 100 (6): 1127-1128 2005
Abstract:
Magnetic-group analysis of the symmetries typical of quasicrystals shows that ferromagnetism is incompatible with the icosahedral symmetry. Depending on the magnetic field direction, the icosahedral symmetry in the magnetic field is reduced to pentagonal, trigonal or rhombic symmetries. (c) 2005 Pleiades Publishing, Inc.
Title:
Phase composition and transformation behavior of readily solidified Al-Ni-Fe alloys in alpha-Al-decagonal phase region
Authors:
Setyawan, AD; Louzguine, DV; Sasamori, K; Kimura, HM; Ranganathan, S; Inoue, A
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 399 (1-2): 132-138 AUG 16 2005
Abstract:
The structure and transformation behavior of two series of alloys located in the ternary concentration triangle in the Al-Ni-Fe system between aluminum and decagonal phases with two different periodicities have been investigated. The rapidly solidified alloys have the following compositions: Al100-x(T-2)(x) (x= 10-100) and Al100-x(T-8)(x) (x=30-100) in which T-2 and T-8 refer to the Al71.6Ni23.7Fe4.7 and Al75Ni10Fe15 single decagonal phase alloys, respectively. No evidence indicating the formation of coexistent decagonal and aluminum phases was found in low and medium decagonal-component contents (M-rich side), either in the as quenched or in the annealed state. As Fe and Ni increase, the decagonal phase forms. The increase in hardness with the transition-metal content of the decagonal component in different alloys is attributed to solution hardening, formation of the dispersed fcc-Al in amorphous matrix, and the dispersion of hard intermetallics including the decagonal phase. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Structure of KNbOB2O5 - a commensurately modulated structure
Authors:
Schmid, S; Wagner, T
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 61: 361-366 Part 4 AUG 2005
Abstract:
Members of the AMOB(2)O(5) (A = K, Rb, Cs, Tl; M = Nb, Ta) family of compounds can be described as modulated structures with a single superspace group and very similar modulation functions. Single-crystal X-ray diffraction data (Mo K alpha radiation) are used to solve and refine the structure of KNbOB2O5 in these terms for the first time. The average structure is solved and refined in the space group Pmn2(1). Subsequently, the atomic modulation functions are determined using JANA2000 and superspace-group symmetry Pmn2(1)(0,0.375,0) s. The commensurately modulated structure is finally refined as a superstructure in the space group Pbn2(1) using SHELXS97 converging to R-1 = 0.024.
Title:
The role of second coordination-sphere interactions in incommensurately modulated structures, using beta-K5Yb( MoO4)(4) as an example
Authors:
Arakcheeva, A; Chapuis, G; Petricek, C; Morozov, V
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 61: 400-406 Part 4 AUG 2005
Abstract:
The incommensurate palmierite-like structure of beta-K5Yb(MoO4)(4), potassium ytterbium tetramolydate, has been refined in the (3 + 1)- dimensional monoclinic superspace group X2/m(0 rho 0) 00, with X = [0 0 0 0; 1/2 1/2 0 0; 0 0 1/2 1/2; 1/2 1/2 1/2 1/2] and the unit-cell parameters a = 10.4054 (16), b = 6.1157 (12), c = 19.7751 (18) angstrom, beta = 136.625 (10)degrees; q = 0.6354 (30) b*. The occupations of the K and Yb atomic positions are described by crenel functions. The structure model reveals a balanced interaction between the atoms of the first and second coordination spheres. It is shown that the third coordination sphere should not be neglected in studies of modulated structures. The ordering of the K and Yb atoms appears to be the driving force for the modulation of all the other atoms.

Update: 29-Jul-2005

Title:
Electronic structure of complex Hume-Rothery phases and quasicrystals in transition metal aluminides
Authors:
de Laissardiere, GT; Nguyen-Manh, D; Mayou, D
Source:
PROGRESS IN MATERIALS SCIENCE, 50 (6): 679-788 AUG 2005
Abstract:
Aluminum based alloys which contain transition metal elements with concentrations up to 25% and additional small quantities of silicon, have a wide variety of atomic structures with unusual physical properties. Among these materials are the famous quasiperiodic alloys which were discovered in 1984 in Al-Mn by Shechtman et al. One find also numerous complex phases which atomic structures bear resemblance with medium-range structure of quasicrystalline phases. Some of these complex phases, but not all of them, are crystalline approximants of quasicrystals. This review focuses on the effect of the transition metal elements on the electronic structure of these alloys. The case of AI(Si)-Mn alloys is considered as a benchmarking one for the present study. But many of the results and concepts developed here can still be applied to other Al-rich alloys containing TM atom from the 3d, 4d, and 5d series. On the one hand, it is now well accepted that the Hume-Rothery stabilization of the valence electrons plays a crucial role in these materials. On the other hand, it has been shown that the TM atoms are also very important for their stability and their physical properties. But, until recently, there has been no model taking into account these two aspects together. We present a model that unifies the classical Hume-Rothery stabilization for sp electron metals with the virtual bound state model for TM atoms embedded in a metallic matrix. This new formalism for "spd electron phases" is applied successfully to Al(Si)-TM alloys and it gives a coherent conceptual picture of their stability and physical properties. It is compared to accurate first-principles calculations of the electronic structure for these alloys, and to the most important experimental and theoretical results in the literature. We also investigate the transition metal aluminide alloys with a non-metallic character. This can be due either to the creation of a gap or to the localization of electrons by some atomic clusters. Again in that case, the scattering of sp states by d orbitals of transition metal plays a central role. (c) 2005 Elsevier Ltd. All rights reserved.
Title:
Characterisation of quasicrystalline particles in an isothermally aged Al-10Mg-0.5Ag (mass%) alloy
Authors:
Kubota, M; Nie, JF; Muddle, BC
Source:
MATERIALS TRANSACTIONS, 46 (6): 1278-1287 JUN 2005
Abstract:
The quasicrystalline structure found in the isothermally aged microstructure in an Al-10Mg-0.5Ag (mass%) alloy after solution treated. water quenched and then aged during the time between 20 and 40 min at 240 C has been characterised using transmission electron microscopy. electron microdiffraction and energy dispersive x-ray spectroscopy The morphology of the quasicry stalline precipitate particles is rhombohe- dral in shape and those precipitate particles are homogeneously nucleated. and tinely and uniformly dispersed in the matrix. The orientation relationship between the quasicrystalline phase and the alpha-Al matrix is as follows: i5 parallel to < 011 >(sigma) and i3 parallel to < 111 >(sigma). The quasilattice constant d(R) of the icosahedral quasicrystalline phase is estimated to be 0.505 +/- 0.01 nm from the present 5-fold electron microdiffraction patterns. The lat tice parameter a(c) of the corresponding crystalline cubic approximant is thus calculated to he 1.390 +/- 0.028 nm. This is in good agreement with the lattice parameter of the crystalline T phase (Mg-32(Al.Ag)(49), a = 1.416 nm). The morphology of the quasierystalline precipitate particle is consistent with that predicted front the intersection point group (3) over bar, which was defined by symmetry elements common to the two lattices in the observed orientation relationship. The quasierystalline particles contain elements of Al, Mg and Ag. The quasierystalline precipitate particles, which are the metastable phase, appear to be the primary strengthening phase in the Al-10Mg-0.5Ag (mass%) alloy aged at 240 C.
Title:
Identification of metastable rod-like particles in an isothermally aged Al-10Mg-0.5Ag (mass%) alloy
Authors:
Kubota, M; Nie, JF; Muddle, BC
Source:
MATERIALS TRANSACTIONS, 46 (6): 1288-1294 JUN 2005
Abstract:
The structure and morphology of a precipitation product in an Al-10Mg-0.5Ag (mass%) alloy aged isothermally at 240 C have been characterised using transmission electron microscopy and microbeam electron diffraction. A metastable T phase (Mg32Al, Ag-49, b.c.c. a = 1.41 nm) which is identified by the electron microdiffraction patterns, has been found in the Al 10Mg 0.5Ag (mass%) alloy after solution treatment, water quenched and then aged for 2h at 240 C. The orientation relationship between the T phase and matrix alpha Al phase was of the form (010)(T) parallel to(111)(alpha) and [001](T) parallel to [110](alpha). Qualitative microanalysis suggested that the metastable crystalline T phase was a ternary compound that contained all three elements Al, Mg and Ag. The morphology of the metastable T phase is the (110)(alpha) rod like in shape and those precipitate particles are homogeneously nucleated, and tinely and uniformly dispersed in the Al matrix. The icosahedral quasicrystalline phase was observed in the early stages of ageing (0.5 h at 240 C), and it was to be replaced by the metastable crystalline T phase Mg32Al, Ag-49 after the alloy is aged for 2h at 240 C. The T phrase formed as faceted rods parallel to < 110 >(alpha) directions of the alpha.Al matrix appeared to be the primary strengthening constitute exhibiting maximum hardness in the Al-10Mg-0.5Ag (mass%) alloy at 240 C.
Title:
Magnetism of A(2)Cu(2)Mo(3)O(12) (A= Rb or Cs): Model compounds of a one-dimensional spin-1/2 Heisenberg system with ferromagnetic first-nearest-neighbor and antiferromagnetic second-nearest-neighbor interactions
Authors:
Hase, M; Ozawa, K; Suzuki, O; Kitazawa, H; Kido, G; Kuroe, H; Sekine, T
Source:
JOURNAL OF APPLIED PHYSICS, 97 (10): Art. No. 10B303 Part 2 MAY 15 2005
Abstract:
Magnetic susceptibility and magnetization showed that A(2)Cu(2)Mo(3)O(12) (A=Rb or Cs) includes a one-dimensional spin-1/2 Heisenberg system with ferromagnetic first-nearest-neighbor (INN) and antiferromagnetic second-nearest-neighbor (2NN) competing exchange interactions (competing system). Values of the INN and 2NN interactions are estimated as J(1)=-138 K and J(2)=51 K for A = Rb or J(1) = -93 K and J(2) = 33 K for A = Cs. Rb2Cu2Mo3O12 is a suitable compound to study the competing system with ferromagnetic J(1), because other interactions are small. The value Of J(2)/J(1) indicates that Rb2Cu2Mo3O12 has a spin-singlet incommensurate ground state. (c) 2005 American Institute of Physics.
Title:
Kinetic Monte Carlo study of Al-Mg precipitation
Authors:
Slabanja, M; Wahnstrom, G
Source:
ACTA MATERIALIA, 53 (13): 3721-3728 AUG 2005
Abstract:
We have performed a kinetic Monte Carlo study of the early stage of the precipitation process in supersaturated Al-Mg, using a model which describes both diffusion and equilibrium properties and is based solely upon first-principles density-functional theory calculations. We have found that the clustering process can be qualitatively affected by the temperature. At a low enough temperature a large abundance of small (on the atomic scale) clusters are quickly formed, while at higher temperatures, one or a few clusters dominate the system. The low temperature clustering could explain the existence of the initial phase, or modulated structure, seen experimentally at lower temperatures. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 22-Jul-2005

Title:
Spin dimer, electronic band structure and classical spin analyses of spin exchange interactions and ordered magnetic structures of magnetic solids
Authors:
Whangbo, MH; Dai, D; Koo, HJ
Source:
SOLID STATE SCIENCES, 7 (7): 827-852 JUL 2005
Abstract:
We reviewed briefly how spin dimer, electronic band structure and classical spin analyses are employed to describe spin exchange interactions and ordered magnetic structures of magnetic solids. It was shown that super-superexchange interactions are crucial in forming strongly interacting spin units of magnetic solids and hence in determining their magnetic properties, and that incommensurate magnetic superstructures are readily described by a Heisenberg spin Hamiltonian using the classical spin approximation. We probed the weak ferrimagnetism of monoclinic Fe-2(SO4)(3) in terms of spin dimer and mean-field-theory analyses to explain both the ordered magnetic structure and the sublattice magnetization. The classical spin and quantum mechanical descriptions of geometric spin frustration were compared to clarify their differences. (c) 2005 Elsevier SAS. All rights reserved.
Title:
Origin of modulated structures in YBa2Cu3O6.63: A first-principles approach
Authors:
de Fontaine, D; Ozolins, V; Islam, Z; Moss, SC
Source:
PHYSICAL REVIEW B, 71 (21): Art. No. 212504 JUN 2005
Abstract:
Recent diffraction studies have shown the existence of lattice modulations in yttrium barium cuprates (YBCO). We show that these modulations are caused by the ordering of O-Cu-O chains in the CuO planes according to a scheme of quasi-one-dimensional ordering developed previously. Remarkable agreement is illustrated in the case of underdoped YBCO between experimental diffraction patterns of diffuse intensity and calculated satellite intensity obtained from ab initio electronic structure calculations of atomic displacements in unit cells containing missing oxygen chains.
Title:
Crystal structure of the superconducting phases of S and Se
Authors:
Degtyareva, O; Gregoryanz, E; Somayazulu, M; Mao, HK; Hemley, RJ
Source:
PHYSICAL REVIEW B, 71 (21): Art. No. 214104 JUN 2005
Abstract:
Compressed S and Se are studied by x-ray diffraction with synchrotron radiation up to 160 GPa. Phase IV of S is shown to have a body-centered monoclinic structure and is stable between 83 and 153 GPa, where it transforms to S-V with a primitive rhombohedral beta-Po structure. Observation of the modulation reflections in S-IV up to 135 GPa shows that its crystal structure is incommensurately modulated, the same as known for Se and Te. Our study on the stability range of the modulated phase of Se (Se-IV) shows that Se-IV transforms to the beta-Po phase Se-V at around 80 GPa. Pressure dependence of the structural parameters of these high-pressure phases in S and Se are discussed in relation to their superconducting behavior.
Title:
Spin structure and magnetic frustration in multiferroic RMn2O5 (R=Tb,Ho,Dy)
Authors:
Blake, GR; Chapon, LC; Radaelli, PG; Park, S; Hur, N; Cheong, SW; Rodriguez-Carvajal, J
Source:
PHYSICAL REVIEW B, 71 (21): Art. No. 214402 JUN 2005
Abstract:
We have studied the crystal and magnetic structures of the magnetoelectric materials RMn2O5 (R=Tb,Ho,Dy) using neutron diffraction as a function of temperature. All three materials display incommensurate antiferromagnetic ordering below 40 K, becoming commensurate on further cooling. For R=Tb,Ho, a commensurate-incommensurate transition takes place at low temperatures. The commensurate magnetic structures have been solved and are discussed in terms of competing exchange interactions. The spin configuration within the ab plane is essentially the same for each system, and the radius of R determines the sign of the magnetic exchange between adjacent planes. The inherent magnetic frustration in these materials is lifted by a small lattice distortion, primarily involving shifts of the Mn3+ cations and giving rise to a canted antiferroelectric phase.
Title:
Multiple magnetic phase transitions in PrCoAl4 observed by muon spin rotation and relaxation measurements
Authors:
Schenck, A; Gygax, FN; Schobinger-Papamantellos, P; Tung, LD
Source:
PHYSICAL REVIEW B, 71 (21): Art. No. 214411 JUN 2005
Abstract:
Zero field muon spin rotation and relaxation (mu SR) measurements on a single crystal of orthorhombic PrCoAl4 revealed the presence of spontaneous static fields, extending above the well-known incommensurately modulated antiferromagnetic structure (T-N=17 K) up to at least 110 K. Two further transitions at 30 K and 84 K were clearly visible. The spontaneous fields above T-N are confined to the (b,c) plane and are tentatively ascribed to a spin density wave involving the Co 3d-band electrons.
Title:
Real-space imaging of coexisting charge-ordered and monoclinic phases in La1-xCaxMnO3 (x=0.67 and 0.71)
Authors:
Loudon, JC; Midgley, PA
Source:
PHYSICAL REVIEW B, 71 (22): Art. No. 220408 JUN 2005
Abstract:
Using transmission electron microscopy, we have observed the coexistence of two nonferromagnetic phases in La1-xCaxMnO3 (x=0.67 and 0.71) at 90 K: a modulated "charge-ordered" phase and a modulation-free region composed of monoclinic needle twins. Micron-sized regions containing these needle twins formed below 170 K over 30 s in La0.33Ca0.67MnO3 when cooled at a rate of similar to 0.2 K/min. A tweed microstructure was observed in the interface region between these two phases. We estimate that the needle twins occupied less than 10% of the volume of the manganites investigated here.
Title:
Field-induced transition between magnetically disordered and ordered phases in underdoped La2-xSrxCuO4
Authors:
Khaykovich, B; Wakimoto, S; Birgeneau, RJ; Kastner, MA; Lee, YS; Smeibidl, P; Vorderwisch, P; Yamada, K
Source:
PHYSICAL REVIEW B, 71 (22): Art. No. 220508 JUN 2005
Abstract:
We report the observation of a magnetic-field-induced transition between magnetically disordered and ordered phases in slightly underdoped La2-xSrxCuO4 with x=0.144. Static incommensurate spin-density-wave order is induced above a critical field of about 3 T, as measured by elastic neutron scattering. Our results allow us to constrain the location of a quantum critical point on the phase diagram.
Title:
RHEED and STM studies of the pseudo-tenfold surface of the xi(')-Al77.5Pd19Mn3.5 approximant crystal
Authors:
Sharma, HR; Shimoda, M; Fournee, V; Ross, AR; Lograsso, TA; Tsai, AP
Source:
PHYSICAL REVIEW B, 71 (22): Art. No. 224201 JUN 2005
Abstract:
The pseudo-tenfold surface of the xi'-Al77.5Pd19Mn3.5 crystal, an approximant of the icosahedral Al-Pd-Mn quasicrystal, is investigated by reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy. The observed RHEED patterns of the surface after sputtering are found to be consistent with those of a simple cubic lattice with (1(1) over bar 0) surface plane. The [001] and [110] axes of the surface plane are oriented along the principal low-index axes of the bulk. The RHEED patterns of the sputter-annealed surface consist of diffraction streaks with periodic spacings expected for the bulk truncated surface. The surface prepared under different preparation methods is found to exhibit different step-height distribution and terrace morphology. A longer annealing yields a high density of shallow pentagonal pits on terraces, separated predominantly by 0.80-nm high steps and occasionally by double steps. In contrast, the surface prepared with shorter annealing time exhibits highly perfect terraces with 0.80-nm-high steps and additional unusual steps of heights close to 0.40 nm. All step heights observed for both preparation methods are consistent with interlayer spacings of the bulk model.
Title:
Structural disorder in the decagonal Al-Co-Ni. I. Patterson analysis of diffuse x-ray scattering data
Authors:
Kobas, M; Weber, T; Steurer, W
Source:
PHYSICAL REVIEW B, 71 (22): Art. No. 224205 JUN 2005
Abstract:
The three-dimensional (3D) difference Patterson (autocorrelation) function of a disordered quasicrystal (Edagawa phase) has been analyzed. 3D diffuse x-ray diffraction data were collected in situ at 300, 1070, and 1120 K. A method, the punch-and-fill technique, has been developed for separating diffuse scattering and Bragg reflections. Its potential and limits are discussed in detail. The different Patterson maps are interpreted in terms of intercluster correlations as a function of temperature. Both at high and low temperatures, the clusters decorate the vertices of the same quasiperiodic covering. At low temperatures, for the disordered part of the structure, short-range intercluster correlations are present, whereas at higher temperatures, medium-range intercluster correlations are formed. This indicates disorder mainly inside clusters at low temperatures, whereas at higher temperatures disorder takes place inside larger superclusters. Qualitatively, the Patterson maps may be interpreted by intercluster correlations mainly inside pentagonal superclusters below 1120 K, and inside the larger decagonal superclusters at 1120 K. The results of our diffraction study are published in two parts. Part I focuses on the 3D Patterson analysis based on experimental data, Part II reports modeling of structural disorder in decagonal Al-Co-Ni.
Title:
Structural disorder in the decagonal Al-Co-Ni. II. Modeling
Authors:
Kobas, M; Weber, T; Steurer, W
Source:
PHYSICAL REVIEW B, 71 (22): Art. No. 224206 JUN 2005
Abstract:
The hydrodynamic theory of phasonic and phononic disorder is applied successfully to describe the short-range disordered structure of a decagonal Al71.5Co14.6Ni13.9 quasicrystal (Edagawa phase, superstructure type I). Moreover, model calculations demonstrate that the main features of diffuse scattering can be equally well described by phasonic disorder and fivefold orientational disorder of clusters. The calculations allow us to distinguish the different cluster types published so far and the best agreement with experimental data could be achieved with the mirror-symmetric Abe cluster. Modeling of phason diffuse scattering associated with the S1 and S2 superstructure reflections indicate disorder of superclusters. The former show basically intercluster correlations inside quasiperiodic layers, while the latter exhibit intra- and inter-cluster correlations, both between adjacent and inside quasiperiodic layers. The feasibility, potential, and limits of the Patterson method in combination with the punch-and-fill method employed is shown on the example of a phasonic disordered rhombic Penrose tiling. A variation of the elastic constants does not change qualitatively the way phasonic disorder is realized in the local quasicrystalline structure. For the same model system it is also shown that phasonic fluctuations of the atomic surfaces yield average clusters in the cut space, which correspond to fivefold orientationally disordered clusters.
Title:
Atomic surface occupancy of decagonal AlNiCo
Authors:
Naidu, S; Mihalkovic, M; Widom, M
Source:
PHYSICAL REVIEW B, 71 (22): Art. No. 224207 JUN 2005
Abstract:
We investigate the atomic surface structure of the high temperature decagonal quasicrystalline phase of Al72Ni20Co8 using a lattice gas Monte Carlo simulation. To avoid biasing towards a specific model we use an overdense site list with a large fraction of free sites, permitting the simulation to explore an extended region of perpendicular space. Representing the atomic surface occupancy in a basis of harmonic functions aids our analysis by directly revealing the fivefold symmetric component of our data. Patterns of occupancy are examined in both physical ("parallel") and perpendicular space, and compared with experiment in both cases. Additionally we compute the Patterson function representing correlations among atomic positions. Our results yield atomic surface structure with smooth variation of occupation and chemistry. Short distances in this model are avoided through correlations among partially occupied sites. The model naturally incorporates both an idealized average structure and intrinsic structural disorder, providing a more realistic description of the quasicrystal than is possible from an atomic surface model alone.
Title:
Field-induced magnetic order in the singlet-ground-state magnet CsFeCl3
Authors:
Toda, M; Fujii, Y; Kawano, S; Goto, T; Chiba, M; Ueda, S; Nakajima, K; Kakurai, K; Klenke, J; Feyerherm, R; Meschke, M; Graf, HA; Steiner, M
Source:
PHYSICAL REVIEW B, 71 (22): Art. No. 224426 JUN 2005
Abstract:
The field-induced magnetic order in the singlet-ground-state system CsFeCl3 (H parallel to c) has been studied by the measurements of the magnetization M-parallel to (the ferromagnetic component along the c axis) and the magnetic neutron scattering from M-perpendicular to (the antiferromagnetic component in the c plane). The field dependence of M-perpendicular to has clearly shown that the field-induced ordered phase is described by the order parameter < S-x> (M-perpendicular to=g(perpendicular to)mu(B)< S-x>). The development of the spin correlation and the incommensurate-commensurate phase transition have been observed in the field region of 5 T < H < 6 T, and the comparison has been made with the phase boundary at H similar to 10 T (H > H-c). Two possible magnetic configurations have been suggested for the commensurate three dimensional long-ranged order phase. The frustration and the magnetostriction effects have been discussed.
Title:
Magnetic structure of GdCo2Ge2
Authors:
Good, W; Kim, J; Goldman, AI; Wermeille, D; Canfield, PC; Cunningham, C; Islam, Z; Lang, JC; Srajer, G; Fisher, IR
Source:
PHYSICAL REVIEW B, 71 (22): Art. No. 224427 JUN 2005
Abstract:
Resonant and nonresonant magnetic x-ray scattering studies of GdCo2Ge2 were performed to determine its magnetic structure at low temperature. This compound orders in an incommensurate antiferromagnetic (AF) structure characterized by a propagation wave vector tau=(0 0 tau(z)). The value of tau(z) is temperature dependent and approaches 0.930 reciprocal lattice units well below T-N=33.25 K. A peak corresponding to 3 tau(z) was also observed, indicating either a squaring up of the magnetic structure or the presence of a noncollinear amplitude modulated structure below T-N. Fitting the angular dependence of the magnetic scattering integrated intensities to the relevant resonant and nonresonant scattering cross sections revealed that the moment direction lies primarily in the tetragonal basal plane. Scattering measurements at the Co K- edge failed to detect any resonant signal, consistent with the absence of a magnetic moment on the Co sites.
Title:
Neutron inelastic scattering investigation of the magnetic excitations in Cu2Te2O5X2 (X=Br,Cl)
Authors:
Crowe, SJ; Majumdar, S; Lees, MR; Paul, DM; Bewley, RI; Levett, SJ; Ritter, C
Source:
PHYSICAL REVIEW B, 71 (22): Art. No. 224430 JUN 2005
Abstract:
Neutron inelastic scattering investigations have been performed on the spin tetrahedral system Cu2Te2O5X2 (X=Cl, Br). We report the observation of magnetic excitations with a dispersive component in both compounds, associated with the three-dimensional incommensurate magnetic order that develops below T-N(Cl)=18.2 K and T-N(Br)=11.4 K. The excitation in Cu2Te2O5Cl2 softens as the temperature approaches T-N(Cl), leaving diffuse quasi-elastic scattering above the transition temperature. In the bromide, the excitations are present well above T-N(Br), which might be attributed to the presence of a degree of low dimensional correlations above T-N(Br) in this compound.
Title:
Surface pinning of fluctuating charge order: An extraordinary surface phase transition
Authors:
Brown, SE; Fradkin, E; Kivelson, SA
Source:
PHYSICAL REVIEW B, 71 (22): Art. No. 224512 JUN 2005
Abstract:
We study the mean-field theory of charge-density wave (CDW) order in a layered system, including the effect of the long-range Coulomb interaction and of screening by uncondensed electrons. We particularly focus on the conditions necessary for an "extraordinary" transition, in which the surface orders at a higher temperature, and is more likely to be commensurate, than the bulk. We interpret recent experiments on Ca2-xNaxCuO2Cl2 as indicating the presence of commensurate CDW at the surface that is not present in the bulk. More generally, we show that poor screening of the Coulomb interaction tends to stabilize incommensurate order, possibly explaining why the CDW order in La2-xSrxCuO4 and NbSe2 remains incommensurate to T -> 0, despite the small magnitude of the incommensurability.
Title:
Irreversible field-induced magnetic phase transitions and properties of Ho3CO
Authors:
Baranov, V; Goto, T; Hilscher, G; Markin, PE; Michor, H; Mushnikov, NV; Park, JG; Yermakov, AA
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (21): 3445-3462 JUN 1 2005
Abstract:
The results of magnetic susceptibility, magnetization, electrical resistivity and specific heat measurements performed on Ho3CO single crystals show that this compound exhibits two different antiferromagnetic structures: AF(II) at 8 K < T < 22 K and AF(I) below T-t approximate to 8K. Below the Neel temperature. T-N = 22 K the application of a magnetic field along the main crystallographic directions induces magnetic phase transitions which are accompanied by giant magnetoresistance. At T < Tt the field-induced phase transitions along the c- and b-axes are found to be irreversible, and a small ferromagnetic component is observed along the a-axis. These peculiarities are associated with the non-Kramers character of the Ho ion and with the presence of a complex incommensurate magnetic structure of Ho3Co below TN. The temperature coefficient of the electrical resistivity for Ho3Co above TN over a wide temperature range is found to differ from that observed for other R3CO compounds. Such a behaviour is attributed to the presence of an additional contribution to the conduction electron scattering by spin fluctuations induced by f-d exchange in the itinerant d-electron subsystem. The value of this extra contribution and its temperature range is suggested to depend on the spin value of the R ion. The excess of the effective magnetic moment per R ion, which is observed in Ho3CO and in other R3M type compounds, is also attributed to spin fluctuations induced by f-d exchange.
Title:
Investigation of the fracture toughness of radio frequency magnetron sputtered Al-Cu-Fe films via white-beam synchrotron radiography/topography
Authors:
French, BL; Daniels, MJ; Bilello, JC
Source:
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 38 (10A): A44-A49 Sp. Iss. SI MAY 21 2005
Abstract:
A novel white-beam synchrotron radiography/topography substrate curvature technique has been used to study stress development in situ during annealing of Al-Cu-Fe quasicrystalline and approximant coatings, as well as to image their failure modes in real time. Single crystal Si and sapphire substrates were coated with a 2.55 mu m precursor coating by RF sputtering from an Al65Cu23Fe12 powder composite target and subsequently annealed at 585 degrees C while stress and imaging data were acquired. After the initial ramp to the annealing temperature, a stress plateau was reached for coatings on both Si and sapphire substrates, although the magnitude of the stress plateau was different in each case. A tensile stress developed in the coatings during cooling due to differential thermal expansion between the coating and substrate, allowing for calculation of both the coefficient of thermal expansion and elastic modulus of the film. During cooling, the films exhibited different stress evolution above and below 470 degrees C, a temperature of interest in Al-Cu-Fe quasicrystal and approximant phase development. The Al-Cu-Fe coating on the Si substrate fractured at approximately 954 MPa, while the coating on the sapphire substrate fractured at approximately 431 MPa. From these values the fracture toughness was calculated to be 1.9 MPam(1/2) and 0.76MPam(1/2) for the coatings on Si and sapphire, respectively.
Title:
In situ transmission electron microscopy studies of electric-field-induced phenomena in ferroelectrics
Authors:
Tan, XL; He, H; Shang, JK
Source:
JOURNAL OF MATERIALS RESEARCH, 20 (7): 1641-1653 JUL 2005
Abstract:
High electric fields were delivered to specimens during imaging in the transmission electron microscopy (TEM) chamber to reveal details of electric field-induced phenomena in ferroelectric oxides. These include the polarization switching in nanometer-sized ferroelectric domains and the grain boundary cavitation in a commercial lead zirconate titanate (PZT) polycrystalline ceramic, the domain wall fracture in a Pb(Mg1/3Nb2/3)O-3-PbTiO3 single crystal, and the transformation of incommensurate modulations in Pb0.99Nb0.02[(Zr1-xSnx)(1-y)Ti-y](0.98)O-3 (PZST100x/ 100y/2) polycrystalline ceramics. In the PZT ceramic, a cavitation process was uncovered for the electric field-induced intergranular fracture. In the ferroelectric single crystal, a preexisting crack was observed to deflect and to follow a 90 degrees domain wall, indicating the presence of severe incompatible piezoelectric strains at the, domain wall. In the antiferroelectric PZST ceramics, the electric field-induced antiferroelectric-to-ferroelectric phase transformation was accompanied with the disappearance of incommensurate modulations.
Title:
Structural and magnetic properties of epitaxial ferromagnetic-antiferromagnetic manganite multilayers
Authors:
Moran, O; Gomez, ME; Ramirez, JG; Schwarz, T; Fuchs, D; Hott, R; Schneider, R
Source:
JOURNAL OF APPLIED PHYSICS, 97 (10): Art. No. 10K116 Part 3 MAY 15 2005
Abstract:
We have studied the exchange bias (EB) interaction in ferromagnetic La2/3Ca1/3MnO3/antiferromagnetic La1/3Ca2/3MnO3 superlattices fabricated on single crystal (001)-(LaAlO3)(0.3)(Sr2AlTaO6)(0.7) (LSAT) substrates using pulsed laser deposition. The as-grown multilayers were characterized with respect to their magnetic and structural properties by means of dc superconducting quantum interference device magnetometry and x-ray diffraction (XRD) measurements, respectively. The field cooling loop is shifted towards negative fields compared to the zero-field cooling measurement, indicating an EB effect. The XRD profile with clearly resolved superlattice Bragg peaks and multiple satellite peaks around (001) Bragg reflections of the LSAT substrate gives evidence of a well defined superlattice structure. (c) 2005 American Institute Of Physics.
Title:
Crystal-quasicrystal local structural transition in Al-Cu-Fe
Authors:
Menushenkov, AP; Rakshun, YV; Mikheeva, MN; Klementiev, KV; Teplov, AA; Bryazkalo, AM
Source:
JETP LETTERS, 81 (9): 479-483 2005
Abstract:
The rearrangement of the local environments of copper and iron in the ternary alloy Al65Cu22Fe13 in transition from a crystalline phase to a quasicrystalline phase has been studied by combined extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) analysis. It has been found that the nearest environment of copper retains symmetry characteristic of a crystal; however, a turn and small shifts of copper matrix atoms causes a considerable rearrangement of aluminum atoms around iron. As a result, icosahedral clusters with pentagonal symmetry are formed around iron atoms, and translational symmetry breaking is accompanied by the transition of Al65Cu22Fe13 to a quasicrystalline state. (C) 2005 Pleiades Publishing, Inc.
Title:
NMR studies on crystals with structurally incommensurately modulated phases
Authors:
Michel, D; Taye, A; Petersson, J
Source:
FERROELECTRICS, 314: 233-244 2005
Abstract:
The dynamics of the incommensurate (IC) modulation is investigated for several one dimensionally incommensurately modulated crystals near the transition to the normal high temperature phase at the temperature T-i. Using nuclei with nuclear quadrupole moments as local probe, nuclear magnetic resonance (NMR) line shape and spin-lattice relaxation have shown to be very sensitive to study the order parameter dynamics and slow elementary excitations in crystals with IC phases. All results can be described consistently in terms of a static modulation in the IC phase without any indication for "floating" or large scale fluctuations of the modulation wave. The critical exponents derived from the NMR line shape and the relaxation times T-l very nicely fit to the universality class of the 3d-XY model. Recently, the validity of this conclusion was also confirmed for the particular IC system of bis(4-chloi-ophenyl)sulphone ((ClC6H4)(2)SO2). For Rb2ZnBr4 and Rb2ZnCl4 crystals the characteristic frequency of the critical dynamics of the order parameter (OP) slows down to a frequency range which has been estimated to lie between 2...10 MHz. In this particular case one can derive the characteristic frequency of the critical dynamics of the OP above T-i and of the phason below T-i from the Larmor frequency dependence of Rb-87 NMR relaxation times T-1. The relatively broad temperature range where the critical dynamics was observed may be explained.

Update: 15-Jul-2005

Title:
Structural mechanisms and order-parameter symmetries for the high-pressure phase transitions in alkali metals
Authors:
Katzke, H; Toledano, P
Source:
PHYSICAL REVIEW B, 71 (18): Art. No. 184101 MAY 2005
Abstract:
The structural transitions occurring between the high-pressure phases of alkali metals are described by displacive mechanisms. The different structures are associated with critical instabilities of the ambient-pressure body-centered-cubic structure. Unifying mechanisms are found for the transitions occurring in (Li and Na) and (K, Rb and Cs), respectively. The RbIII-RbIV-RbV and CsIII-CsIV phase sequences are interpreted as reflecting the hybridization process of the s- and d-wave functions, which induces a deformation of the atomic shells, allowing a closer packing of the KIII, RbIV, and RbV structures. The RbIII and CsIII structures are proposed to represent commensurate approximations of incommensurately modulated structures locking in at the RbV and CsIV phases.
Title:
Local structure and vibrational properties of alpha-Pu, alpha-U, and the alpha-U charge-density wave
Authors:
Nelson, EJ; Allen, PG; Blobaum, KJM; Wall, MA; Booth, CH
Source:
PHYSICAL REVIEW B, 71 (18): Art. No. 184113 MAY 2005
Abstract:
The local atomic environment and vibrational properties of atoms in monoclinic pure a-plutonium as well as orthorhombic pure alpha-uranium and its low-temperature charge-density-wave (CDW) modulation are examined by extended x-ray absorption fine structure spectroscopy (EXAFS). Pu L-III-edge and U L-III-edge EXAFS data measured at low temperatures verify the crystal structures of alpha-U and alpha-Pu samples previously determined by x-ray diffraction and neutron scattering. Debye-Waller factors from temperature-dependent EXAFS measurements are fit with a correlated Debye model. The observed Pu-Pu bond correlated Debye temperature of theta(cD)(alpha-Pu)=162 +/- 5 K for the pure alpha-Pu phase agrees with our previous measurement of the correlated Debye temperature of the gallium-containing alpha'-Pu phase in a mixed phase 1.9 at. % Ga-doped alpha'-Pu/delta-Pu alloy. The temperature dependence of the U-U nearest neighbor Debye-Waller factor exhibits a sharp discontinuity in slope near T-CDW=43 K, the transition temperature at which the charge-density wave (CDW) in alpha-U condenses from a soft phonon mode along the (100) direction. Our measurement of the CDW using EXAFS is the first observation of the structure of the CDW in polycrystalline alpha-U. The different temperature dependence of the Debye-Waller factor for TT-CDW, the observed correlated Debye temperature of theta(cD)(alpha-U)=199 +/- 3 K is in good agreement with other measurements of the Debye temperature for polycrystalline alpha-U. CDW structural models fit to the alpha-U EXAFS data support a squared CDW at the lowest temperatures, with a displacement amplitude of epsilon=0.05 +/- 0.02 angstrom.
Title:
Ab initio study of quasiperiodic monolayers on a fivefold i-AlPdMn surface
Authors:
Krajci, M; Hafner, J
Source:
PHYSICAL REVIEW B, 71 (18): Art. No. 184207 MAY 2005
Abstract:
We present a structural model for quasiperiodic monolayers formed on the fivefold surface of an icosahedral AlPdMn quasicrystal, based on ab initio density functional calculations. As a starting point we have investigated the relative stability of unsupported triangular, square, and quasiperiodic monolayers. The unsupported quasiperiodic monolayers are shown to be unstable upon relaxation by interatomic forces. This result indicates the important role of the adsorbate/substrate interaction for the stabilization of a quasiperiodic layer. The structural model of a monolayer adsorbed on the fivefold surface has been constructed on the basis of a mapping of the potential-energy landscape of an isolated adatom on the i-AlPdMn substrate. The structure of a clean fivefold i-AlPdMn surface is well described by a P1 tiling, with the vertices of the tiling located in the centers of B (Bergman) clusters and occupied by Pd atoms. The potential-energy mapping emphasizes the important role of the P1 skeleton for the stabilization of a quasiperiodic adlayer: adsorption at the vertices of the P1 tiling leads to high binding energies of similar or equal to 4 eV/atom. The midedge positions of the P1 tiling and Mn atoms exposed at the surface are identified as further favorable adsorption sites. Altogether this leads to a structural model of the quasiperiodic adlayer with atoms at the vertices and midedge positions of the P1 tiling, centered pentagonal motifs decorating the pentagonal tiles, and one additional atom in the center of the pentagonal star and of the boat tile. For this structure we calculate a surface coverage of similar or equal to 0.09 atoms/angstrom(2) in perfect agreement with experiment. The diffraction pattern of the adlayer exhibits (pseudo) decagonal symmetry. The structural stability of a 2/1 approximant to this model has been tested for Sn, Bi, and Sb monolayers via relaxation by the Hellmann-Feynman forces from ab initio density function theory calculations. The skeleton of a dsorbed monolayers based on the P1 tiling was found. to be stable, although the atomic decoration inside the tiles is partially distorted, albeit without violating the overall symmetry.
Title:
Comparative study of local structure in Zr70Al10Ni20 and quasi-crystal-forming Zr70Al9Ni20Pd1 metallic glasses
Authors:
Saida, J; Imafuku, M; Sato, S; Sanada, T; Matsubara, E; Inoue, A
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 85 (3): 135-144 MAR 2005
Abstract:
The local structure of Zr70Al9Ni20Pd1 metallic glass, in which a nano-icosahedral quasi-crystalline phase (I-phase) is formed in the primary stage of crystallization, has been examined and compared with that of Zr70Al10Ni20, the supercooled liquid state of which has a high stability. Since the local environments around the Zr and Ni atoms do not change drastically by the addition of 1 at.% Pd to Zr70Al10Ni20, as evidenced by radial distribution function (RDF) and extended x-ray absorption. ne structure (EXAFS) studies, we deduce that the icosahedral phase formed in the Zr70Al9Ni20Pd1 metallic glass has a local structure similar to that in Zr70Al10Ni20. Although a very slight rearrangement of Zr-Zr atomic pairs occurs during quasi-crystallization, the I-phase formation is achieved without disturbing the dominant local structure in the glassy state of the Zr70Al9Ni20Pd1. An icosahedral local structure is proposed for Zr-Al-Ni metallic glass system as well as for primary quasi-crystal (QC)-forming Zr-based metallic glasses.
Title:
Solid and liquid thermal expansion and structural observations in the quasicrystalline Cd84Yb16 compound
Authors:
Kramer, MJ; Lograsso, TA; Sordelet, DJ
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 85 (3): 151-162 MAR 2005
Abstract:
The structure of single-grain Cd84Yb16 samples aligned along the twofold and fivefold axes has been followed from 300 to 1050 K using high-energy synchrotron X-rays. The quasicrystal phase is stable up to its melting temperature of 914 K and has a large linear thermal expansion of 37.1 ppm K-1 over this temperature range. The samples melt congruently over a temperature range of less than 1 K. The liquid is 7% less dense than the solid and, upon cooling from the melt, the quasicrystal phase directly solidifies within a 1 K interval. The amount of undercooling achieved, about 5-25 K, was dependent on the cooling rate. The total scattering function of the liquid is consistent with a dilute liquid Cd structure. These results agree with suggestions that the structure of the liquid must undergo reordering in order to form the solid phases. However, there is no compelling evidence for icosahedral short-range order in the liquid prior to the formation of the quasicrystalline structure.
Title:
Electrical and thermal transport properties of icosahedral Al70Pd22.5(Re1-xMnx)(7.5) quasicrystals
Authors:
Kuo, YK; Sivakumar, KM; Lin, CR; Lue, CS; Lin, ST
Source:
JOURNAL OF APPLIED PHYSICS, 97 (10): Art. No. 103717 Part 1 MAY 15 2005
Abstract:
This work presents measurements of the electrical resistivity (p), Seebeck coefficient, and thermal conductivity (K) of icosahedral Al70Pd22.5(Re1-xMnx)(7.5) quasicrystals from 10 to 300 K. A series of quasicrystals was prepared with x=0, 0.1, 0.2, 0.3, 0.5, 0.6, 0.8, and 1.0 to systematically study the effect of substitution. The electrical resistivity increases as the temperature decreases, suggesting a semiconductinglike behavior in these alloys. The room-temperature values of the Seebeck coefficient vary from -5 mu V/K to +65 mu V/K, showing a significant dependence on the value of x. However, K exhibits a rather weak composition dependence in the temperature range investigated. The room-temperature dimensionless thermoelectric figure of merit (ZT) of this system is optimized at x=0.1. With further appropriate heat treatments, high ZT is presumably available at elevated temperatures in the Al70Pd22.5(Re0.9Mn0.1)(7.5) sample. (c) 2005 American Institute of Physics.
Title:
Photonic band-gap engineering of quasiperiodic photonic crystals
Authors:
Wang, YQ; Jian, SS; Han, SZ; Feng, S; Feng, ZF; Cheng, BY; Zhang, DZ
Source:
JOURNAL OF APPLIED PHYSICS, 97 (10): Art. No. 106112 Part 1 MAY 15 2005
Abstract:
Band-gap engineering of quasiperiodic photonic crystals (QPC) is studied., Owing to the specific structural properties of the QPC, the distribution-especially its maximum position-of the electric field at different upper gap edge frequencies is quite varied. Therefore., by inserting metallic cylinders at different positions, the width of the gaps can be separately adjusted. This could hardly be realized in a periodic photonic crystal. (c) 2005 American Institute of Physics.
Title:
Defects and diffusion in d-AlNiCo-quasicrystals - Application of mechanical spectroscopy
Authors:
Weller, M; Damson, B; Feuerbacher, M
Source:
DIFFUSION IN MATERIALS: DIMAT 2004, PT 1AND 2, 237-240: 322-327 2005 Book series title: DEFECT AND DIFFUSION FORUM
Abstract:
Mechanical loss (internal friction) measurements were applied to polycrystalline d-AlNiCo quasicrystals for compositions ranging from Al72.8Ni7.5Co19.7 to Al71.1Ni18Co10.9 and to an Al71.3Ni13.4Co15.3 mono-quasicrystal The measurements were carried out in the temperature range from 290 K up to 1220 K for measuring frequencies between 0.1 Hz and 10 kHz. A loss maximum of Debye type is observed at approximate to 700 K (2Hz) for both the I-phase and the bCo-phase, which is attributed to local rearrangement of point defects. The activation enthalpy of the peak of H = 1.9 - 2.4 eV is in the range of values obtained from tracer diffusion experiments. This indicates that local defect rearrangement and self diffusion are governed by the same atomic diffusion process.. A high temperature viscoelastic damping background is only observed in polycrystalline samples with H = 2.4 - 3 eV. The background is assigned to viscolealastic relaxation based on intergranular diffusion.
Title:
Diffusion in decagonal and icosahedral quasicrystals and a related hexagonal phase
Authors:
Galler, R; Uhrig, E; Assmus, W; Flege, S; Mehrer, H
Source:
DIFFUSION IN MATERIALS: DIMAT 2004, PT 1AND 2, 237-240: 358-363 2005 Book series title: DEFECT AND DIFFUSION FORUM
Abstract:
We present investigations of gallium diffusion in decagonal AlNiCo quasicrystals in both principal directions and of gallium diffusion in icosahedral AlPdMn quasicrystals. Gallium was used to approximate aluminium self-diffusion, which cannot be measured using conventional tracer techniques. The depth-profiles of the stable isotopes were analysed by SIMS profiling. We compare our results in decagonal AlNiCo with experimental data on self-diffusion of cobalt and nickel and with MD-simulations of Al self-diffusion from literature. Our experiments and the MD simulations show that the diffusion parallel to the decagonal axis is faster than perpendicular to it. In addition we carried out diffusion studies of the major component zinc in icosahedral ZnMgY, icosahedral ZnMgHo (fci-phases) and a related hexagonal ZnMgY composition (Z-phase) along both principal directions. We report the Arrhenius parameters and compare the diffusion behaviour of the various materials.
Title:
Crystallization of amorphous In2O3-10 wt % ZnO thin films annealed in air
Authors:
Yaglioglu, B; Yeom, HY; Paine, DC
Source:
APPLIED PHYSICS LETTERS, 86 (26): Art. No. 261908 JUN 27 2005
Abstract:
We report on the crystallization of amorphous indium zinc oxide (a-IZO) with stoichiometry of In2Zn0.38O3.38 (In2O3-10 wt % ZnO) thin films deposited by dc magnetron sputtering. Transmission electron microscopy and glancing incidence x-ray diffraction were used to show that, when annealed in air at 500 degrees C, the product of a-IZO thin film crystallization is a compositionally modulated crystal of high-pressure corundum In2O3 phase. The composition, microstructure, resistivity, carrier density, and mobility of this new IZO phase are reported and are compared to the bixbyite ITO (In2O3-9.8 wt % SnO2) deposited and annealed under identical conditions.
Title:
Dynamics of domain inversion in LiNbO3 poled using topographic electrode geometries
Authors:
Johnston, BF; Withford, MJ
Source:
APPLIED PHYSICS LETTERS, 86 (26): Art. No. 262901 JUN 27 2005
Abstract:
We report results of an investigation studying the domain inversion kinetics of lithium niobate when electric field poling using laser-machined topographical electrodes. Inversion is shown to begin with a single nucleation spike and the domains evolve in a unique fashion governed by the topographical structure. We also demonstrate control of the resulting domain widths when poling using this technique. The results presented have implications for rapid prototyping of chirped and aperiodic domain structures in lithium niobate.

Update: 8-Jul-2005

Title:
Critical behavior of heat capacity in the vicinity of phase transitions in [NH2(CH3)(2)](5)Cd3Cl11
Authors:
Dekola, TI; Sheleg, AU; Tekhanovich, NP
Source:
PHYSICS OF THE SOLID STATE, 47 (6): 1161-1162 2005
Abstract:
The heat capacity of a [NH2(CH3)(2)](5)Cd3Cl11 crystal was studied calorimetrically in the temperature interval 100-300 K. The C-p(T) dependence indicates that, as the temperature is lowered, phase transitions occur at temperatures T-1 = 176.5 K and T-2 = 123.5 K. The thermodynamic characteristics of this crystal were determined. It is shown that the transition at T-2 = 123.5 K is an incommensurate-commensurate phase transformation and that the transition at T-1 = 176.5 K is a normal-incommensurate phase transition. (c) 2005 Pleiades Publishing, Inc.
Title:
Thermal expansion and phase transitions in akermanite and gehlenite
Authors:
Merlini, M; Gemmi, M; Artioli, G
Source:
PHYSICS AND CHEMISTRY OF MINERALS, 32 (3): 189-196 JUN 2005
Abstract:
Thermal expansion has been measured by laboratory and synchrotron X-ray powder diffraction for end-member (a) over circle kermanite (ak, Ca2MgSi2O7) and gehlenite (ge, Ca2Al2SiO7) in the range 20-1,500 K. In ak in the range 340-390 K, there is a negative linear thermal expansion in [001] direction. This is related to the phase transition from an incommensurate modulated structure (IC) to a normal one (N). The volumetric mean thermal expansion coefficients for ak and ge, obtained with a linear fit of the experimental data in the temperature range 298-1,400 K, are respectively 32.1x10(-6) and 28.3x10(-6) K-1. The variation of the c/a ratio with temperature, due to different thermal expansion along the crystallographic axes, can be related to the different behaviour of the tetrahedral layers in the N and IC phases. Analysis of the variation of the superstructure peaks intensity across the phase transition confirms the tricritical behaviour of the IC/N transition in ak.
Title:
Negative refraction and imaging using 12-fold-symmetry quasicrystals
Authors:
Feng, ZF; Zhang, XD; Wang, YQ; Li, ZY; Cheng, BY; Zhang, DZ
Source:
PHYSICAL REVIEW LETTERS, 94 (24): Art. No. 247402 JUN 24 2005
Abstract:
Recently, negative refraction of electromagnetic waves in photonic crystals was demonstrated experimentally and subwavelength images were observed. However, these investigations all focused on the periodic structure. Here, we report a new theoretical and experimental finding that negative refraction can appear in some transparent quasicrystalline photonic structures. The photonic quasicrystals (PQCs) exhibit an effective refractive index close to -1 in a certain frequency window. The index shows small spatial dispersion, consistent with the nearly homogeneous geometry of the quasicrystal. More interestingly, a superlens based on the 2D PQCs can form a non-near-field subwavelength image whose position varies with the source distance. These properties make PQCs promising for application in a range of optical devices.
Title:
Structural and transport properties of the incommensurate organic superconductor (MDT-ST)(I-3)(0.417)
Authors:
Kawamoto, T; Mori, T; Uji, S; Yamaura, JI; Kitagawa, H; Takamori, A; Takimiya, K; Otsubo, T
Source:
PHYSICAL REVIEW B, 71 (17): Art. No. 172503 MAY 2005
Abstract:
The incommensurate anion sublattice and transport properties of the organic superconductor (MDT-ST)I1+ delta [MDT-ST: 5H-2-(1,3-dithiol-2-ylidene)-1,3-diselena-4,6-dithiapentalene] are investigated. The Raman spectra as well as the incommensurate spots observed in the x-ray-oscillation photograph provide clear evidence that the polyiodide chain is composed of I-3(-) units. From these, the composition is determined to be (MDT-ST)(I-3)(0.417), and the degree of charge transfer is 0.417. The thermoelectric power shows large negative phonon drag at low temperatures in spite of the clean metallic resistive behavior. That the fundamental Raman line of the 13 chains is split into two lines below 150 K without any extra satellite reflections in the x-ray photographs suggests the possibility of a small structural change in the anion lattice.
Title:
Mn(2+)doping-induced-effects on commensuration and incommensuration of potassium zinc chloride crystal
Authors:
Gaffar, MA; Abousehly, AM; Abu El-Fadl, A; Mostafa, MM
Source:
PHASE TRANSITIONS, 78 (4): 295-315 APR 2005
Abstract:
Undoped and Mn2+-doped with different concentrations of potassium zinc chloride (KZC) crystals were grown from aqueous solutions by slow evaporation. The dielectric constant (epsilon), dielectric losses (tan delta) and ac conductivity (sigma(ac)) of the crystals in the ferroelectric-commensurate, incommensurate and normal phases have been measured as a function of frequency, in the range 1-100 kHz, and temperature, in the range 300-580 K. Virgin samples were subjected to measurements of the frequency dependence at selected temperatures and measurements of the temperature dependence was then followed using the same samples. The increase of epsilon with T could be due to a combination of conductivity, structural variations and discommensuration (DC) formation and pinning as well. The increase of tan delta with temperature was attributed to relaxation loss in addition to conduction loss, which increases more rapidly with temperature. The ac conductivity and tan delta along the polar axis of KZC increased significantly with increasing Mn2+ content while epsilon decreased. sigma(ac) changed with frequency according to a power law of the form sigma(ac) = f(s) where 0.15 < s < 1.27. A linear decrease of epsilon and tan delta with increasing the frequency was also found. The obtained results were treated by considering the effect of Mn2+-doping oil stripples nucleation, DC evolution/annihilation, DC-lattice formation and DCs pirming by the crystal lattice and/or structural defects for virgin and thermally treated samples.
Title:
Neutron and X-ray diffraction study of the broken symmetry phase transition in solid deuterium
Authors:
Goncharenko, I; Loubeyre, P
Source:
NATURE, 435 (7046): 1206-1209 JUN 30 2005
Abstract:
The solid hydrogen compounds D-2, HD and H-2 remain quantum molecular solids up to pressures in the 100 GPa range(1). A remarkable macroscopic consequence is the existence of a pressure-induced broken symmetry phase transition (2-4), in which the molecules go from a spherical rotational state to an anisotropic rotational state. Theoretical understanding of the broken symmetry phase structure remains controversial, despite numerous studies(5-10). Some open questions concern the existence of long- or short-range orientational order; whether a strong isotopic shift on the transition pressure should be assigned to the nuclear zero-point motion or to quantum localization; and whether the structures are cubic, hexagonal or orthorhombic. Here we present experimental data on the structure of the broken symmetry phase in solid D-2, obtained by a combination of neutron and X-ray diffraction up to 60 GPa. Our data are incompatible with orthorhombic structures predicted by recent theoretical works. We find that the broken symmetry phase structure is incommensurate with local orientational order, being similar to that found in metastable cubic para-D-2.
Title:
Laser cladding of quasi-crystal-forming Al-Cu-Fe-Bi on an Al-Si alloy substrate
Authors:
Biswas, K; Galun, R; Mordike, BL; Chattopadhyay, K
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 36A (7): 1947-1964 JUL 2005
Abstract:
We report here the results of an investigation aimed at producing coatings containing phases closely related to the quasi-crystalline phase with dispersions of soft Bi particles using an Al-Cu-Fe-Bi elemental powder mixture on Al-10.5 at. pct Si substrates. A two-step process of cladding followed by remelting is used to fine-tune the alloying, phase distribution, and microstructure. A powder mix of Al64CU22.3Fe11.7Bi2 has been used to form the clads. The basic reason for choosing Bi lies in the fact that it is immiscible with each of the constituent elements. Therefore, it is expected that Bi will solidify in the form of dispersoids during the rapid solidification. A detailed microstructural analysis has been carried out by using the backscattered imaging mode in a scanning electron microscope (SEM) and transmission electron microscope (TEM). The microstructural features are described in terms of layers of different phases. Contrary to our expectation, the quasi-crystalline phase could not form on the Al-Si substrate. The bottom of the clad and remelted layers shows the regrowth of aluminum. The formation of phases such as blocky hexagonal Al-Fe-Si and a ternary eutectic (Al + CuAl2 + Si) have been found in this layer. The middle layer shows the formation of long plate-shaped Al13Fe4 along with hexagonal Al-Fe-Si phase growing at the periphery of the former. The formation of metastable Al-Al6Fe eutectic has also been found in this layer. The top layer, in the case of the as-clad track, shows the presence of plate-shaped Al13Fe4 along with a 1/1 cubic rational approximant of a quasi-crystal. The top layer of the remelted track shows the presence of a significant amount of a 1/1 cubic rational approximant. In addition, the as-clad and remelted microstructures show a fine-scale dispersion of Bi particles of different sizes formed during monotectic solidification. The remelting is found to have a strong effect on the size and distribution of Bi particles. The dry-sliding wear properties of the samples show the i mprovement of wear properties for Bi-containing clads. The best tribological properties are observed in the as-clad state, and remelting deteriorates the wear properties. The low coefficient of friction of the as-clad and remelted track is due to the presence of approximant phases. There is evidence of severe subsurface deformation during the wear process leading to cracking of hard phases and a change in the size and shape of soft Bi particles. Using these observations, we have rationalized possible wear mechanisms in the Bi-containing surface-alloyed layers.
Title:
Effect of Zn/Y ratio on phase selection in Mg-Zn-Y alloys
Authors:
Lu, QL; Min, GH; Wang, CC; Yu, HS
Source:
METALLOFIZIKA I NOVEISHIE TEKHNOLOGII, 27 (1): 1-9 JAN 2005
Abstract:
In this work, several as-east Mg-Zn-Y alloys were fabricated by using the conventional casting method for the design of composition, and the effect of Y content on the phase selection is investigated in details. The result showed that the Mg-Zn-Y alloys containing icosahedral phase can be prepared when the content of Y is from 0.3 up to 2.0 at.% and the content of Zn is from 1.7 up to 6.0 at.%. The alpha-Mg was formed by the primary solidification of magnesium dendrites, and the most portion of Y remained in the liquid because of the presence of Zn that strongly decreased the Y solubility in solid magnesium. When the atoms' ratio of Zn/Y is about 6:1, the microstructure of as-east alloys is composed of both the a-Mg matrix and the grain-boundary phase. The detailed analysis showed that the as-east Mg95Zn4.3Y0.7 alloy contains the two-phase (alpha-Mg and icosahedral phase) microstructure in a grain boundary; no other phase was found. In other three alloys at issue, several crystalline phases are found in the alpha-Mg matrix. We can conclude that the phase selection in as-east Mg-Zn-Y alloys is determined by both the atoms' ratio of Zn/Y and the element content of Zn.
Title:
Effect of quasicrystalline phase on the deformation behavior of Zr62Al9.5Ni9.5Cu14Nb5 bulk metallic glass
Authors:
Sun, YF; Cheung, TL; Wang, YR; Shek, CH; Li, WH; Wei, BC
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 398 (1-2): 22-27 MAY 25 2005
Abstract:
Quasicrystalline phase with different volume fraction were formed by isothermally annealing the as-castZr(62)Al(9.5)Ni(9.5)Cu(14)Nb(5) bulk metallic glass at 723 K for different times. The effects of quasicrystals on the deformation behavior of the materials were studied by nanoindentation and compression test. It revealed that the alloys with homogeneous amorphous structure exhibit pronounced flow serrations during the nanoindentation loading, while no obvious flow serration is observed for the sample with quasicrystals more than 10 vol.%. However, further compression tests confirm that the no-serrated flows are formed due to different reasons. For annealed samples containing quasicrystals less than 35 vol.%, continuous plastic deformation occurs due to propagation of multiple shear bands. While the disappearance of serrated flow cannot be explained by the generation of multiple shear bands for samples containing quasicrystals more than 35 vol.%, which will fracture with a totally different fracture mode, namely, dimple fracture mode under loading instead of shear fracture mode. (c) 2005 Published by Elsevier B.V.
Title:
Electrical resistivity of Ti41.5Zr41.5Ni17 quasicrystals in the temperature region 0.3-300 K
Authors:
Azhazha, VM; Khadzhay, GY; Merisov, BA; Malikhin, SV; Pugachov, AT; Ott, HR; Sologubenko, AV
Source:
LOW TEMPERATURE PHYSICS, 31 (6): 477-480 JUN 2005
Abstract:
The electrical resistivity of icosahedral quasicrystals Ti41.5Zr41.5Ni17 is investigated in the temperature region between 0.3 and 300 K on samples of different quality. At temperatures between 0.3 and 2 K the influence of external magnetic fields up to 16 kOe on the superconducting transition of these materials is investigated. The temperature dependence of the resistivity in the region of the superconducting transition varies in a step-like manner. The data of the x-ray analysis imply the presence of several different quasicrystalline phases. Above the superconducting transition a resistivity minimum is observed. (C) 2005 American Institute of Physics.
Title:
Quasi-one-dimensional spin-density-wave states in presence of two commensurate potentials and interchain misfit
Authors:
Itakura, T
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 74 (6): 1777-1781 JUN 2005
Abstract:
The spin-density-wave (SDW) states of a quasi-one-dimensional system with an incommensurate wave vector perpendicular to the chain have been studied in the presence of two kinds of commensurate potential, which originate in a quarter-filled band and under dimerization along the chain. For the phase variance phase of the SDW order parameter, we classically treat a two-dimensional Hamiltonian, which includes both acoustic excitation with a long wavelength and a vortex excitation with a short wavelength. A phase diagram on the plane of temperature and chemical potential (where the latter corresponds to the deviation of the transverse wave vector from the commensurate one) exhibits a variety of states given by the commensurate SDW state without charge density, the commensurate SDW state with charge density, the incommensurate SDW state, and the disordered state.
Title:
Crystal structures of CeO2-ZrO2-Ta2O5 ternary system studied by Rietveld method
Authors:
Clemente, DA; Lucchini, E; Meriani, S; Furlan, N
Source:
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 25 (11): 1863-1876 JUL 2005
Abstract:
Solid solutions of the pseudo-ternary system Ce0.6/(1+x)Zr(Hf)((0.4-x)/(1+x))Ta2x/(1+x) (0.00 <= x <= 0.06), i.e. having molecular composition 1, 2, 3, 4, 5 and 6% in Ta2O5, have been prepared by traditional ceramic methods (1500 degrees C for 3 h). SEM observations and analysis of the X-ray diffraction powders allowed to establish that the solubility of Ta2O5 in the above mentioned system is 4 %mol. The Rietveld analysis of the powder X-ray diffraction data has shown that all the samples of the solid solution crystallize in tetragonal space group P4(2)/nmc (No. 137) but are nearly cubic, space group Fm (3) over barm (No. 225). The freshly prepared specimens (from I to 4 %mol of Ta2O5) show additional peaks due to a tetragonal supercell and also to a modulated structure. However, the modulated peaks disappear after 8 months. Compositions containing 5 and 6% of Ta2O5 show also additional peaks due to a small quantity of two crystalline phases having approximate composition: ZrO2-2CeO(2)-Ta2O5 and 2CeO(2)-Ta2O5 (later on identified as CeTaO4). (c) 2004 Elsevier Ltd. All rights reserved.
Title:
A universally applicable composite modulated structure approach to ordered BaxMyTi8-yO16 hollandite-type solid solutions
Authors:
Carter, ML; Withers, RL
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 178 (6): 1903-1914 JUN 2005
Abstract:
A wide range of barium titanate hollandites of the form Ba-x(2+) M-x(2+) Ti-8-x(4+) O-16 (M = Zn, Co, Mg, Fe and Mn) and Ba-x(2+) M-2x(3+) Ti-8-2x(4+) O-16 (M = Fe) with nominal x ranging from 1.0 to 1.4 have been synthesized and examined to investigate the solid solution range and the nature of the ordering of the Ba ions. Electron diffraction Studies confirm that the barium titanate hollandites are composite modulated single phase solid solutions made up of mutually incommensurable (along b) framework and Ba ion sub-structures. The overall superspace group symmetry was found to be I'2/m(0,x/2,0)1. The symbol I' here refers to the superspace centering operation {x(1) + 1/2, x(2) + 1/2, x(3) + 1/2, x(4) + 1/2} (see below). Both the framework and the Ba sub-structures have the same I2/m average structure space group symmetry. The solid solution ranges for the hollandites were calculated from the positions of well-defined superlattice peaks in X-ray diffraction patterns. The effect of cooling rate on Ba ion ordering is also examined. (c) 2005 Elsevier Inc. All rights reserved.
Title:
Where are the Sn atoms in LaSb2Snx, 0.1 <= x <= similar to 0.75?
Authors:
Noren, L; Withers, RL; Brink, FJ
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 178 (6): 2133-2143 JUN 2005
Abstract:
The composition range and (composite modulated) structure of compounds within the wide range non-stoichiometric LaSb2Snx, 0.1 <= x <= 0.75, solid solution is carefully investigated via a combined electron diffraction, XRD and electron probe microanalysis study. Evidence for metastability of the LaSb2Snx phase at the low x composition end of the solid solution is presented. Direct evidence is found for a reasonably (although by no means perfectly) well ordered Sn sub-structure which is, in general, mutually incommensurable with respect to a very well ordered underlying LaSb2 sub-structure along both a and c directions. The overall (3 + 2)-d superspace group symmetry is given along with a discussion of the consequences as regards the arrangement of the Sn atoms. The Sn sub-structure c-axis cell dimension shows very little variation with composition x providing direct experimental evidence of the importance of Sn-Sn metallic bonding (along one-dimensional [00 1] Sri strings) for the stability of the phase. (c) 2005 Elsevier Inc. All rights reserved.
Title:
The oxidation at 500 degrees C of AlCuFe quasicrystalline powders: A X-ray diffraction study
Authors:
Weisbecker, P; Bonhomme, G; Bott, G; Dubois, JM
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 351 (19-20): 1630-1638 JUL 1 2005
Abstract:
The oxidation behavior at 500 degrees C of AlCuFe icosahedral quasicrystalline powders was investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Powders have been characterized at room temperature before and after oxidation. Oxidation leads to a long-range diffusion of aluminum atoms, which form an amorphous oxide layer on top of the grains. When the loss of aluminum inside the grains is too high, the icosahedral phase transforms in cubic beta-phase (CsCl type). This transformation no longer occurs when the grain size is higher than a critical value. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Magnetic properties and the investigation of possible interstitial occupancy by small atoms in some R3Ni6X2 compounds (R = rare earth; X = Si and Al)
Authors:
Kalihari, V; Dhar, SK
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 294 (1): 40-48 JUN 2005
Abstract:
Polycrystalline samples of R3Ni6X2 compounds (R = Gd, Tb, Dy, Ho, Er and Y; X = Si and Al) were synthesized by arc melting followed by a long annealing at 800 degrees C. Powder X-ray diffraction spectra of these compounds showed that the R3Ni6X2 compounds crystallize in the cubic Ca3Ag8-type structure with a large unit cell parameter a similar to 8.9 angstrom as reported previously in the literature. Various physical properties like magnetization, electrical resistivity, and heat capacity of R3Ni6Al, and Gd3Ni6Si2 were measured. The aluminides order ferromagnetically and the Curie temperature, which is the highest (similar to 120K) in the Gd compound, decreases in the heavier analogs qualitatively, in accordance with the deGenness scaling. The data show evidence of two magnetic transitions in some compounds. We have also investigated the possibility of introducing small atoms like boron and carbon as interstitial atoms in these compounds by melting alloys with compositions R3Ni6X2Ty, (T = B and C; 0 < y <= 1.5). We find that while boron and carbon cannot be alloyed with R3Ni6Al2 compounds to form single-phase alloys, a limited solubility of carbon exists in Gd3Ni6Si2. Both Gd3Ni6Si2, and Gd3Ni6Si2C0.5 are anti ferromagnetic but the transition temperature of the carbide is enhanced compared to the parent compound. The resistivity of the carbide shows an upturn at the magnetic transition as the temperature is reduced, arising most probably due to the additional energy gaps introduced by incommensurate anti ferromagnetic order. (c) 2004 Elsevier B.V. All rights reserved.
Title:
Formation of the incommensurate ordered phase in TaCy carbide
Authors:
Lipatnikov, VN; Rempel, AA
Source:
JETP LETTERS, 81 (7): 326-330 2005
Abstract:
Structural neutron diffraction studies indicate that only one ordered phase arises after the disorder-order transition in nonstoichiometric cubic tantalum carbide TaCy . This phase arises in the composition range y = 0.79-0.89 due to long-term annealing with a decrease in temperature from 1600 to 300 K. It is incommensurate in the [1-11](B1) direction, but it is close to commensurate M6C5 structures (C2/m and P3(1) space groups) in mutual arrangement of atoms and vacancies in nonmetallic (1-11)(B1) planes. The disorder-order transition channel that is associated with the formation of the incommensurate superstructure in TaCy carbide includes two arms k(5)((6)) approximate to 0.473b(2) and k(5)((5)) = -k(5)((6)) of the {k(5)} star and arms of the {k(4)} and {k(3)} stars. The translation period of the incommensurate phase in the [1-11](B1) direction is 8.9-9.1 nm, which is larger than that in the commensurate phase M6C5 by a factor of about 18. (C) 2005 Pleiades Publishing, Inc.
Title:
Incommensurate spin dynamics in underdoped cuprate perovskites
Authors:
Sherman, A; Schreiber, M
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B, 19 (13): 2145-2159 MAY 20 2005
Abstract:
The incommensurate magnetic response observed in normal-state cuprate perovskites is interpreted based on the projection operator formalism and the t-J model of Cu-O planes. In agreement with experiment the calculated dispersion of maxima in the susceptibility has the shape of two parabolas with upward and downward branches which converge at the antiferromagnetic wave vector. The maxima are located at the momenta (1/2, 1/2 +/- delta), (1/2 +/- delta, 1/2) and at (1/2 +/- delta, 1/2 +/- delta), (1/2 +/- delta, 1/2 -/+ delta) in the lower and upper parabolas, respectively. The upper parabola reflects the dispersion of magnetic excitations of the localized Cu spins, while the lower parabola arises due to a dip in the spin-excitation damping at the antiferromagnetic wave vector. For moderate doping this dip stems from the weakness of the interaction between the spin excitations and holes near the hot spots. The frequency dependence of the susceptibility is shown to depend strongly on the hole bandwidth and damping and varies from the shape observed in YBa2Cu3O7-y to that inherent in La(2-x)Sr(x)uO(4).
Title:
Fingerprinting substitution sites in Pb, Dy-Bi2Sr2Ca1Cu2O8+delta using X-ray Photoelectron Diffraction
Authors:
Popovic, D; Bovet, M; Berger, H; Aebi, P
Source:
EUROPEAN PHYSICAL JOURNAL-APPLIED PHYSICS, 30 (3): 171-174 JUN 2005
Abstract:
The substitution sites of Pb and Dy dopants in the cuprate-type high temperature superconductor Bi2Sr2Ca1Cu2O8+delta are determined by a direct comparison of the angle-scanned X-ray photoelectron diffraction (XPD) patterns. We demonstrate the power of XPD as a fingerprinting tool and conclude that Pb occupies Bi sites and Dy the Ca sites. The presence of the incommensurate lattice modulation is not visible in XPD, probably due to a Pb-induced, reduced modulation amplitude.
Title:
Formation of Al4Cu9 on the 5 fold surface of icosahedral AlPdMn
Authors:
Bielmann, M; Barranco, A; Ruffieux, P; Groning, O; Fasel, R; Widmer, R; Groning, P
Source:
ADVANCED ENGINEERING MATERIALS, 7 (5): 392-396 MAY 2005
Title:
On the critical points of the structure amplitude for the case of one-dimensional displacive modulation
Authors:
Sliwinska, T; Gusin, P; Warczewski, J
Source:
ACTA PHYSICA POLONICA A, 107 (6): 917-931 JUN 2005
Abstract:
The behavior of the structure amplitude is analyzed in terms of the harmonics-of a modulation function for the case of one-dimensional longitudinal displacive modulation. This modulation function is given by a finite series of N sine functions. It turns out that: (1) for the large values of the amplitudes of the modulation function the structure amplitude tends to zero for the arbitrary values of the order m of the satellite reflections; (2) for certain values of the amplitudes of the modulation function the modulus of the structure amplitude assumes its maximum value and (3) for the latter case the intensity of an arbitrary satellite reflection is:a function of the intensities of both the closest main reflection and the intensities of the finite set of the neighbor satellite reflections.

Update: 1-Jul-2005

Title:
First-principle study of materials involved in incommensurate transitions
Authors:
Caracas, R; Gonze, X
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 220 (5-6): 511-520 2005
Abstract:
We discuss the applicability of the density functional theory to the study of incommensurate crystals. After a brief introduction to these aperiodic but ordered materials we present several types of ab initio methodologies that are adequate in the context of incommensurate transitions and phases. We also give a survey of the corresponding applications, while providing two case studies: Pb2MgTeO6 and K2SeO4.
Title:
Getting the hot structures
Authors:
Kelton, KF; Gangopadhyay, AK
Source:
POWDER DIFFRACTION, 20 (2): 87-93 JUN 2005
Abstract:
The recent advances in levitation methods for materials processing now enable structural, thermo-physical property, and phase transition studies to be made on high temperature solids and liquids without container contamination. These studies have led to new insights into the liquid state and have revealed how local order in the liquid can dictate phase formation. In this article, levitation techniques are briefly discussed, focusing most on electrostatic levitation. Recent synchrotron studies of electrostatically levitated undercooled Ti-Zr-Ni liquids are presented, which demonstrate that developing icosahedral short-range order in the liquid causes the nucleation of a metastable icosahedral quasicrystal instead of the stable tetrahedral Laves phase. In addition to providing the first experimental proof of a half-century-old hypothesis linking the order of the liquid with the nucleation barrier, these data raise new questions about the general applicability of the thermodynamic model assumed in the classical theory of nucleation. The combination of electrostatic levitation and synchrotron high-energy x-ray diffraction also allows rapid and accurate determinations of phase diagrams for high temperature materials. This is demonstrated using Ti-Fe-Si-O as a case study. This new technique, then, is of practical as well as basic importance. (c) 2005 International Centre for Diffraction Data.
Title:
Incommensurate-normal phase transition in natural melilite: an in situ high-temperature X-ray single-crystal study
Authors:
Bindi, L; Bonazzi, P
Source:
PHYSICS AND CHEMISTRY OF MINERALS, 32 (2): 89-96 JUN 2005
Abstract:
The structure of a natural melilite with chemical composition (Ca1.87Sr0.02Na0.10K0.02)(Sigma 2.01)(Mg0.96Al0.07)(Sigma 1.03)(Si1.98Al0.02)(Sigma 2.00)O-7 has been investigated by X-ray single-crystal diffraction methods within the temperature range 298-773 K. The values of the alpha coefficient of the modulation wave vector were determined at 298 K, 323 K, 348 K, and 358 K. These values show a continuous linear decrease from 0.2833(6) at 298 K to 0.2763(9) at 358 K. The incommensurate phase undergoes a phase transition to the normal phase at 359 K. The refinements of the structure, carried out at 298 K, 348 K, 359 K, 373 K, 413 K, 463 K, 513 K, 573 K, 673 K, and 773 K, showed that the normal phase (high-temperature phase) does not significantly differ from the basic structure (the average structure of the incommensurate structure). This study confirms that in natural melilites with chemical composition close to that of akermanite the wavelength of the incommensurate modulation increases when the temperature rises. The different behaviour of the q-vector as a function of temperature in natural and synthetic akermanite is discussed.
Title:
Raman scattering study on ferroelectric (Ba0.32Sr0.6)(2)M2O7 ceramics
Authors:
Hushur, A; Akishige, Y; Kojima, S
Source:
MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, 120 (1-3): 45-49 JUL 15 2005
Abstract:
Raman scattering technique was applied to examine the Ba-doping effect to the two low temperature phase transitions of Sr2Nb2O7 (SN) in the temperature range from -190 to 600 degrees C. The line shape of Raman spectra can be well fitted by multidamped harmonic oscillator model. We did not observe any soft mode related to the two low temperature phase transitions corresponding to those of the pure SN. It is correlated to the disappearance of the incommensurate phase in (Ba0.32Sr0.68)(2)Nb2O7 ceramics. However, the temperature dependence behavior of the three low frequency modes indicates another new structural phase transition around 270 degrees C. It is considered that the reduction of the interlayer interaction caused by partial replacement of Sr-site by Ba-site, whose ionic radius is larger than that of Sr, may be the reason for the disappearance of the incommensurate phase transition in (Ba0.32Sr0.68)(2)Nb2O7 ceramics. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Nucleation of crystals in deeply undercooled alloy melts
Authors:
Palumbo, M; Papandrea, C; Battezzati, L
Source:
JOURNAL OF MATERIALS SCIENCE, 40 (9-10): 2431-2435 MAY 2005
Abstract:
The CALPHAD approach coupled with modelling of solid-liquid interfacial energy has been used to calculate the driving force for nucleation in undercooled melts. Thermodynamic parameters needed in nucleation have been evaluated using simplified formulae or numerical methods from assessed phase diagrams. Various models for the interfacial energy and its temperature dependence have been used. Phase selection on solidification and devitrification of glasses as well as the range of amorphous phase formation have been predicted in the Al-Ce and Fe-B systems and compared with those experimentally determined. Furthermore, the formation of quasicrystals in the Al-Mn and the competition with other compounds has been investigated. (C) 2005 Springer Science + Business Media, Inc.
Title:
Helimagnetic order in the re-entrant ferromagnet Ce2Fe15.3Mn1.7
Authors:
Prokhnenko, O; Arnold, Z; Kamarad, J; Ritter, C; Isnard, O; Kuchin, A
Source:
JOURNAL OF APPLIED PHYSICS, 97 (11): Art. No. 113909 JUN 1 2005
Abstract:
Substitution of Mn for Fe in Ce2Fe17 strongly suppresses the ferromagnetic ground state, changing it into an antiferromagnetic one. However, a state of spontaneous magnetization is re-entered in the Ce2Fe17-xMnx compounds when the Mn content reaches x=1.3. Magnetic structures and magnetic interactions in the re-entrant ferromagnetic Ce2Fe15.3Mn1.7 compound have been studied using both microscopic (neutron powder diffraction in magnetic fields of up to 0.7 T) and macroscopic (ac susceptibility and magnetization measurements under high pressures of up to 8 kbar in magnetic fields of up to 5 T) techniques. A spiral magnetic structure distorted by the presence of an in-plane ferromagnetic component is found below T-N=182 K. Enhancement of the ferromagnetic interactions leads to a steep transformation of the magnetic spiral to a magnetic structure with nonzero spontaneous magnetization below Theta(T)=59 K. This structure is described by a distorted elliptical spiral model with an incommensurate propagation vector along the c axis. Magnetic field significantly expands the range of stability of this re-entrant ferromagnetic phase. In contrast to the magnetic field, application of pressure does not change Theta(T) within the achieved pressure range. It leads to a moderate reduction of the Neel temperature, dT(N)/dP=-2.3 K/kbar. The preferential placement of Mn on some crystallographic sites in Ce2Fe17-xMnx and the related changes of volume and internal magnetic field will be discussed as possible reasons of the peculiar magnetic behavior of this compound. (C) 2005 American Institute of Physics.
Title:
Critical behavior of the heat capacity in the region of the incommensurate phase transition of C(NH2)(2) crystals
Authors:
Kallaev, SN; Kamilov, IK; Aliev, AM; Abdulvagidov, SB; Amirova, AA; Batdalov, AB
Source:
INTERNATIONAL JOURNAL OF THERMOPHYSICS, 26 (2): 471-477 MAR 2005
Abstract:
The anomalous (nonclassical) behavior of the heat capacity in the region of the second-order phase transition "initial phase-incommensurate phase" was experimentally observed in the SC(NH2)(2) ferroelectric. Such a critical behavior of heat capacity above and below the temperature of incommensurate phase transition is shown to be qualitatively consistent with the fluctuation theory of XY-type systems.

Update: 24-Jun-2005

Title:
Ferromagnetism and metallicity in the modulated Sr1-xThxCoO3-delta oxygen deficient perovskites with x approximate to 0.1
Authors:
Hebert, S; Maignan, A; Caignaert, V; Pralong, V; Pelloquin, D; Raveau, B
Source:
SOLID STATE COMMUNICATIONS, 134 (12): 815-820 JUN 2005
Abstract:
The Th4+ for Sr2+ substitution in SrCoO3-delta is found to be an efficient way to stabilize an oxygen deficient perovskite. The structural study reveals a Th4+ solubility limited to similar to 10% so that the chemical formula, Sr0.9Th0.1CoO2.79, is obtained. The comparison to the Y3+ for Sr2+ substitution shows that a lower oxygen content is obtained for the former according to the Sr0.75Y0.25CoO2.55 formula. The higher oxygen content reached with Th4+ has a strong impact on the physical properties:Sr0.9Th0.1CoO2.79 is an itinerant ferromagnet(T(C)similar to 200 K, rho(5) K =2 m Omega cm) whereas Sr0.75Y0.25CoO2.55 is a robust insulating antiferromagnet (T-N similar to 320 K, rho(5) K = 10(5) Omega cm). Clearly, the substitution of a tetravalent cation for Sr2+ appears to be a promising route to synthesize SrCoO3-delta itinerant ferromagnets without the use of high oxygen pressure nor electrochemical oxidation. (c) 2005 Elsevier Ltd. All rights reserved.
Title:
Formation of amorphous and icosahedral phases in Ti-Zr-Hf-LTM (LTM = Ni, Pd or Pt) alloys
Authors:
Chen, N; Louzguine-Luzgin, DV; Kubota, T; Ranganathan, S; Inoue, A
Source:
SCRIPTA MATERIALIA, 53 (2): 213-216 JUL 2005
Abstract:
A nanoscale icosahedral (I) phase was formed in the melt-spun Ti40Zr20Hf20(LTM)(20) (LTM = Ni, Pd, or Pt) alloys. However, in Pd-bearing alloy it is presumed to be a distorted I-phase or a high-order approximation. I phase, Hf2Pt and beta-(Ti, Zr, Hf, Ni) solid solution phases are formed in the arc-melted Ti40Zr20Hf20Pt20 ingot. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Analysis of the crystallization of Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass using electrical resistivity measurement
Authors:
Chung, SJ; Hong, KT; Ok, MR; Yoon, JK; Kim, GH; Ji, YS; Seong, BS; Lee, KS
Source:
SCRIPTA MATERIALIA, 53 (2): 223-228 JUL 2005
Abstract:
The crystallization behavior of the Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass was investigated using the isothermal electrical resistivity measurements at 390 degrees C in the super-cooled liquid region. The crystallization process is completed through two sequential phase transformations. The first phase transformation was the formation of icosahedral phases, which is followed by the formation of intermetallic compounds. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Hall effect across the quantum phase transition of CeCu6-xAux
Authors:
Bartolf, H; Pfleiderer, C; Stockert, O; Vojta, M; von Lohneysen, H
Source:
PHYSICA B-CONDENSED MATTER, 359: 86-88 APR 30 2005
Abstract:
While CeCu6 is a Pauli-paramagnetic heavy-fermion (HF) system, An doping introduces long-range incommensurate antiferromagnetism for x > x(c) approximate to 0.1. At the critical concentration x(c), the system experiences a quantum phase transition (QPT). Here, both unusual magnetic fluctuations, studied by inelastic neutron scattering, and non-Fermi-liquid behavior, i.e. to anomalous low-temperature thermodynamic and transport properties have been observed. We report on Hall effect measurements that probe the electronic structure of heavy fermions across the critical concentration xc of the QPT. (c) 2005 Elsevier B.V. All rights reserved.
Title:
mu SR study of CeRu2(Ge1-xSix)(2) heavy fermion alloys
Authors:
Rainford, BD; Neville, AJ; Adroja, DT; Scott, CA
Source:
PHYSICA B-CONDENSED MATTER, 359: 166-168 APR 30 2005
Abstract:
Zero field mu SR measurements on CeRu2(Ge1-xSix)(2) for x = 0, 0.125, 0.25 and 0.5 show damped oscillations in the low-temperature-ordered phases. For x = 0.125, 0.25 two distinct regimes are found in the temperature dependence of the oscillation frequency, corresponding to sinusoidally modulated magnetic order and ferromagnetism. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Spin density wave and charge density wave in the Kondo-lattice compound Ce(Ru1-xRhx)(2)Si-2
Authors:
Tabata, Y; Taniguchi, T; Kawarazaki, S; Narumi, Y; Kimura, S; Tanaka, Y; Katsumata, K; Ishikawa, T; Staub, U; Kohgi, M; Iwasa, K
Source:
PHYSICA B-CONDENSED MATTER, 359: 260-262 APR 30 2005
Abstract:
We have performed an X-ray scattering experiment on the Kondo-lattice compound Ce(Ru1-xRhx)(2)Si-2 which shows an incommensurate spin density wave (IC-SDW) in the Rh-concentration range 0.03 < x < 0.35. We have discovered charge scattering due to the charge density wave (CDW) with a wave vector 2Q, where Q = (0 0 q) is the wave vector of IC-SDW. This is the first observation of the CDW associated with the IC-SDW in Kondo-lattice compounds. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Antiferromagnetism in CeCu2(Si1-xGex)(2): nature of the A phase
Authors:
Stockert, O; Deppe, M; Faulhaber, E; Jeevan, HS; Schneider, R; Stusser, N; Geibel, C; Loewenhaupt, M; Steglich, F
Source:
PHYSICA B-CONDENSED MATTER, 359: 349-356 APR 30 2005
Abstract:
We report on extensive neutron diffraction on single crystalline CeCu2(Si1-xGex)(2) to determine the antiferromagnetic order in the regime with low Ge content, initially called A phase due to the unknown origin of the magnetic order. Starting from the x = 0.45 alloy we followed the magnetic order to lower Ge concentrations and to pure CeCu2Si2. For all Ge concentrations x <= 1 an incommensurate magnetic order with a propagation vector close to tau = (0.25 0.25 0.5) is observed. The magnetic order is determined by the nesting properties of the Fermi surface. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Multipolar interactions in the Anderson lattice
Authors:
Sakurai, G; Kuramoto, Y
Source:
PHYSICA B-CONDENSED MATTER, 359: 720-722 APR 30 2005
Abstract:
The wave number dependence of RKKY multipolar interactions is derived for the Anderson-type model with orbital degeneracy in the simple cubic lattice. With the spherical Fermi surface and one conduction electron per cell, the Kohn anomaly arises in the magnetic interaction near the Gamma point of the Brillouin zone. This result may be relevant to the incommensurate magnetic structure observed in the quasi-cubic compound CeB2C2. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Modulated and localized structures in cubic helimagnets
Authors:
Bogdanov, AN; Rossler, UK; Pfleiderer, C
Source:
PHYSICA B-CONDENSED MATTER, 359: 1162-1164 APR 30 2005
Abstract:
Chiral modulated magnetic states in noncentrosymmetric crystals may theoretically arise as one-dimensional cycloids or conical helices or multidimensional textures, so called Skyrmions or vortex lattices. The micromagnetic equations for different modulated phases are derived and the main features in applied magnetic fields are discussed. The stability of these modulated states may be expressed in terms of the ratio of two experimentally meaningful parameters, the period of a helix and the classical width of a domain wall. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Charge order in the incommensurate compounds Sr14-xCaxCu24O41
Authors:
Lepetit, MB; Gelle, A
Source:
PHYSICA B-CONDENSED MATTER, 359: 1258-1260 APR 30 2005
Abstract:
The present paper studies, using ab initio calculations, the influence of the incommensurate structural modulations on the low-energy physics of the Sr14-xCaxCu24O41 oxides. On-site, nearest-neighbor and next-nearest-neighbor effective parameters were computed within a t - J + V model based on the copper oxide layers. The structural modulations appear to be the key degree of freedom, responsible for the low-energy properties such as the electron localization, the formation of dimers in the x = 0 compound or the anti-ferromagnetic order in the x = 13.6 compound. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Electron correlation in the two-dimensional triangular lattice of NaxCoO2 with x > 0.6
Authors:
Sugiyama, J; Brewer, JH; Ansaldo, EJ; Hitti, B; Mikami, M; Mori, Y; Sasaki, T
Source:
PHYSICA B-CONDENSED MATTER, 359: 1345-1347 APR 30 2005
Abstract:
Magnetism of layered cobaltites NaxCoO2 with x = 0.6 and 0.9 has been investigated by a positive muon spin rotation and relaxation (mu(+)SR) spectroscopy together with magnetic susceptibility and specific heat measurements, using single-crystal samples in the temperature range between 250 and 1.8 K. Zero-field mu(+)SR measurements on Na0.9CoO2 indicate a transition to an incommensurate spin density wave state at 19 K(= T-SDW). Since Na0.6CoO2 is paramagnetic down to 1.8 K, the magnitude of T-SDW is found to strongly depend on x. This behavior is explained using the Hubbard model within a mean field approximation on two-dimensional triangle lattice in the Coo, plane. Also, both the appearance of the IC-SDW state by the change in x and the magnitude of the electronic specific heat parameter of Na0.6CoO2 indicate that NaxCoO2 is unlikely to be a typical strongly correlated electron system. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Magnetic domain configurations in spark-eroded ferromagnetic shape memory Ni-Mn-Ga particles
Authors:
Solomon, VC; McCartney, MR; Smith, DJ; Tang, Y; Berkowitz, AE; O'Handley, RC
Source:
APPLIED PHYSICS LETTERS, 86 (19): Art. No. 192503 MAY 9 2005
Abstract:
Spherical particles of the ferromagnetic shape memory material Ni51Mn29Ga20 obtained by spark erosion transform during cooling from the high-temperature Heusler L2(1) cubic phase into tetragonal martensite. Using the Fresnel (i.e., Lorentz) imaging mode, magnetic domains with an average width of 100 nm are observed in the modulated martensitic phase in the absence of a magnetic field. The magnetization distribution within individual particles is determined using electron holography. The magnetic flux lines change direction when crossing boundaries between crystallographic twin variants. These boundaries, where the easy c-axis of the crystallographic variants rotate by 86.5 degrees, coincide with quasi-90 degrees magnetic domain walls, with thickness of approximately 17 nm. The magnetization saturation determined by electron holography is about 0.57 T. (c) 2005 American Institute of Physics.

Update: 17-Jun-2005

Title:
The ternary rare-earth polychalcogenides LaSeTe2, CeSeTe2, PrSeTe2, NdSeTe2, and SmSeTe2: Syntheses, crystal structures, electronic properties, and charge-density-wave-transitions
Authors:
Tsinde, BPF; Doert, T
Source:
SOLID STATE SCIENCES, 7 (5): 573-587 MAY 2005
Abstract:
Phase transitions have been observed for LaSeTe2, CeSeTe2, PrSeTe2, and NdSeTe2 during temperature dependent single-crystal structure determinations and measurements of the electrical transport properties. The high temperature structure of all compounds is an ordered ternary variant of the NdTe3 type and can be described in the space group Cmcm (no. 63). The low temperature structures are incommensurately modulated due to the occurrence of a charge density wave (CDW). The LT structures of LaSeTe2, PrSeTe2, and NdSeTe2 can be described in the (3 + 1)-dimensional superspace group Cmcm(00y)s00 with the following lattice parameters and translational parts gamma of the modulation vectors:.a = 4.295(1) angstrom, b = 25.371(4) angstrom, c = 4.306(1) angstrom, gamma = 0.29(1) for LaScTe2 (at T = 173 K); a = 4.262(1) angstrom, b = 25.034(4) angstrom, c = 4.272(1) angstrom, gamma = 0.29(1) for PrSeTe2 (at 120 K); a = 4.256(1) b = 24.993(3) angstrom, c = 4.258(1) angstrom, gamma = 0.30(1) for NdSeTe2 (at 173 K). The square tellurium nets of the basic structure are distorted at lower temperatures to give zigzag chains of tellurium atoms. SNED patterns show that CeSeTe2 exhibits a two-dimensional modulation with modulation vectors of q(1) = (-0.12(1), 0, 0.12(1)) and q(2) = (0. 12(1), 0, 0.12(1)), and can be described in the superspace group C2/c(s0q., r0p)00 with lattice parameters of a = 4.257(1) angstrom, b = 25.176(5) angstrom, c = 4.259(1) angstrom (at T = 120 K). Resistance measurements show that the non-modulated HT phases exhibit a metal-like temperature dependence of the resistance whereas the modulated LT phases behave like semiconductors. The transition temperatures T-CDW have been found to be 491(5) K for LaSeTe2, 226(3) K for PrSeTe2, and 207(3) K for NdSeTe2 by X-ray diffraction and 275(3) K for CeSeTe2 by measurements of the electrical resistance. (c) 2005 Elsevier SAS. All rights reserved.
Title:
Enhancement of plasticity in Ti-rich Ti-Zr-Be-Cu-Ni bulk metallic glasses
Authors:
Park, JM; Chang, HJ; Han, KH; Kim, WT; Kim, DH
Source:
SCRIPTA MATERIALIA, 53 (1): 1-6 JUL 2005
Abstract:
The plastic strain before failure in as-cast Ti-rich Ti-Zr-Be-Cu-Ni BMGs varies to a large degree depending on the alloy composition, i.e. when the first crystallization product is quasicrystalline phase, higher plastic strain is observed. A possible reason for the enhancement of plasticity is the existence of quenched-in icosahedral nuclei embedded in the amorphous matrix. © 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Crystallographic orientations quasicrystalline phase growing on and interfaces of icosahedral cubic W phase in Mg-Zn-Y alloys
Authors:
Singh, A; Watanabe, M; Kato, A; Tsai, AP
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 397 (1-2): 22-34 APR 25 2005
Abstract:
Formation of icosahedral quasicrystalline phase on the W cubic phase in alpha-Mg matrix has been studied in a Mg97Zn2.5Y0.5 alloy. The orientation relationship of the W phase with the matrix is determined to be [001]w vertical bar vertical bar[100](Mg), (001)(w)vertical bar vertical bar(001)(Mg), equivalent to Burgers orientation relationship. The icosahedral phase forms curved interfaces with the W phase, but planar interfaces on five-fold and two-fold planes with the matrix. The icosahedral phase shows its unique orientation relationship to the W phase, which results in two orientation relationships WOR1 and WOR2 with the matrix. WOR1 is a slight deviation of the orientation relation, OR1, of icosahedral phase precipitates in the matrix. In WOR2, one of the five-fold axes occur along the hexagonal axis. The resulting morphology and the interface structures are described here. It is shown that WOR1 and WOR2 are related to each other by twinning of the icosahedral phase. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Magnetic structures of Zr(6)CoAS(2)-type Ho6FeSb2, Ho6CoBi2, Ho6FeBi2 and Ho6MnBi2 compounds
Authors:
Morozkin, AV
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 395 (1-2): 7-16 MAY 31 2005
Abstract:
Investigations were made by neutron diffraction on Zr6CoAs2-type (space group P6b2m No 189) Ho6FeSb2, Ho6CoBi2, Ho6FeBi2 and Ho6MnBi2 compounds. The Ho6FeSb2, Ho6CoBi2, Ho6FeBi2 and Ho6MnBi2 compounds show seven magnetic ordering types: collinear ferromagnetic FC1 and FC2 type, and non-collinear ferromagnetic FNC1-FNC5 types. The Ho6FeSb2 compound has magnetic transitions at 52(4) K (FC1) 40(4) K (FC2) and 32(4) K (FNC4). Below 67(4) K the Ho6CoBi2 compound has a ferromagnetic collinear type of ordering (FC1) with the magnetic moments of the Ho atoms along the c-axis. Below 22(4) K the Ho6CoBi2 compound has an incommensurate kmagnetic structure (FNC1). The propagation vector is k = [0, 0, 1986(6)], the magnetic moments of the Ho atoms μ(Ho) = 7.5(8) μ(B)) form a cone with an angle β=20(3)&DEG; at 2 K (the cone axis coincides with c-axis). The Ho(6)FeB(i)2 compound has magnetic transitions at 48(4) K (FC1) 15(4) K (FNC2) and 9(4) K (FNC3). T! he Ho6MnBi2 compound displays magnetic transitions at 200(10) K (FCI), 78(4) K (FC2) and 58(4) K (FNC5).

Update: 11-Jun-2005

Title:
Reinvestigation of magnetic structures for the thermally induced states of CuFe1-xAlxO2 (x=0.00, 0.02 and 0.05) using a four-circle neutron diffractometer
Authors:
Terada, N; Kawasaki, T; Mitsuda, S; Kimura, H; Noda, Y
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 74 (5): 1561-1565 MAY 2005
Abstract:
We have reinvestigated the effect of non-magnetic impurity on thermally-induced magnetic orderings in geometrically frustrated triangular lattice antiferromagnets CuFe1-xAlxO2 with x = 0.00, 0.02 and 0.05, using a four-circle neutron diffractometer. Although we inferred in our previous work with a three-axis diffractometer that a proper screw type magnetic structure is realized in the intermediate-temperature (IM) phase of the samples with x = 0.02 and x = 0.05, in the present work we found that a sinusoidally amplitude-modulated magnetic structure with the magnetic moments canted by about 50 degrees from the c axis toward the hexagonal (1(1) over bar $0) direction is realized. These experimental findings suggest that the quasi-Ising magnetic orderings in CuFeO2 are stabilized not with the strong Ising anisotropy expected from the Ising-like successive magnetic phase transitions in CuFeO2 but with the small Ising anisotropy added to strongly competing exchange interactions.
Title:
New phenomena in epitaxial growth: solid films on quasicrystalline substrates
Authors:
Fournee, V; Thiel, PA
Source:
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 38 (6): R83-R106 MAR 21 2005
Abstract:
An overview is given of the research conducted in the field of solid film growth on quasiperiodic surfaces. An atomistic description of quasicrystalline surfaces is presented and discussed in relation to bulk structural models. The various systems for which thin film growth has been attempted so far are reviewed. Emphasis is placed on the nucleation mechanisms of the solid films, on their growth modes in relation to the nature of the deposited metals, on the possibility of intermixing or alloying at the interface and on the epitaxial relationships at the crystal-quasicrystal interfaces. We also describe situations where the deposited elements adopt a quasiperiodic structure, which opens up the possibility of extending our understanding of the relation between quasiperiodicity and the physical properties of such structurally and chemically complex solids.
Title:
Microstructure and chemistry of annealed Al-Cu-Fe-Cr quasicrystalline approximant coatings
Authors:
Daniels, MJ; Zabinski, JS; Wu, H; Grovenor, CRM; Bilello, JC
Source:
JOURNAL OF MATERIALS RESEARCH, 20 (1): 176-182 JAN 2005
Abstract:
An as-deposited Al-Cu-Fe-Cr film was annealed in flowing argon to study development of a quasicrystalline approximant microstructure. Sputter profile x-ray photoemission spectroscopy analysis showed oxygen incorporation reached approximately 70 at.% at the surface of the film, declined monotonically, and stabilized at similar to 10 at.% at a depth of 160 nm. Synchrotron grazing incidence x-ray scattering was used to probe the structure of the coating at various penetration depths by altering the angle of the incident x-ray beam. An amorphous structure was observed near the termination surface, which coexisted with a compressively strained crystalline aluminum. These phases were the dominant microstructure to a depth of 110 nm. Below 150 nm, the film was primarily O-1 decagonal approximant. Cross-section transmission electron microscopy elucidated a columnar growth morphology with associated porosity in the interstices between the columns. The resulting development of the Al-Cu-Fe-Cr decagonal approximant coatings from the precursor is reported.
Title:
Primary precipitation of icosahedral quasicrystal with rearrangement of constitutional elements in Zr65Al7.5Cu27.5 glassy alloy with low oxygen impurity
Authors:
Saida, J; Kato, H; Inoue, A
Source:
JOURNAL OF MATERIALS RESEARCH, 20 (2): 303-306 FEB 2005
Abstract:
The primary transformation reaction of the Zr65Al7.5Cu27.5 ternary glassy alloy with a low oxygen impurity of approximately 100 mass ppm was investigated. We have discovered the precipitation of the metastable icosahedral phase with a fine grain size of 50-100 nm in diameter accompanying with the formation of stable Zr2CU phase at the annealing temperatures ranging from 715 to 730 K. The lattice spacing of Zr2CU phase decreases at higher temperatures, which is attributed to the rearrangement of Zr and Cu in the decomposition of the icosahedral phase. It is suggested that the formation of the icosahedral phase in the primary stage originates from the existence of the quenched-in icosahedral local atomic configuration in the glassy state.
Title:
Excellent creep properties of Mg-Zn-Cu-Gd-based alloy strengthened by quasicrystals and Laves phases
Authors:
Yuan, GY; Kato, H; Amiya, K; Inoue, A
Source:
JOURNAL OF MATERIALS RESEARCH, 20 (5): 1278-1286 MAY 2005
Abstract:
A new type of Mg-Zn-Cu-Gd-based alloy strengthened by quasicrystal and Laves phase was developed. This alloy exhibits much better creep properties compared to AE42(Mg-4 wt% Al-2 wt% rare-earth) alloy, which is the benchmark creep-resistant magnesium die-casting alloy under the compressive creep condition of 180 degrees C and 80 MPa. The new alloy also exhibits high room-temperature mechanical properties close to that of AZ91 alloy. The good mechanical properties are attributed to the special microstructure; the thermally stable icosahedral quasicrystals phase (i-phase) and Laves phase distributed along the grain boundary as a hard skeleton, and some fine beta(1)' precipitates distributed homogenously on the matrix. The dislocation morphology after the creep test was studied, and the strengthening mechanism was proposed.

Update: 4-Jun-2005

Title:
Neutron diffraction studies of Tb2Rh3Si5 compound
Authors:
Gondek, L; Baran, S; Szytula, A; Hernandez-Velasco, J
Source:
SOLID STATE COMMUNICATIONS, 134 (7): 471-474 MAY 2005
Abstract:
In this work neutron diffraction studies of Tb2Rh3Si5 compound are reported. The compound crystallizes in the monoclinic crystal structure of Lu2CO3Si5-type. At 1.5 K an antiferrornagnetic ordering with a propagation vector k=(1/2;1/2;1/2) was observed. The Tb magnetic moments of 9.8(2) μ(B) form a non-collmear magnetic structure. In the vicinity of Neel temperature of 8 K a change of the magnetic ordering is evidenced. The change seems to be connected with phase transition from commensurate to incommensurate sine-wave modulation of the Tb magnetic moments. © 2005 Elsevier Ltd. All rights reserved.
Title:
Monte Carlo study of a frustrated Ising spin on a quasi-crystal
Authors:
Fujita, S; Niizeki, K
Source:
PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT, (157): 128-131 2005
Abstract:
We use Monte Carlo techniques to study an Ising spin system on the HBS tiling, i.e., a two-dimensional decagonal quasicrystal. The nearest- (or second-nearest-) neighbor interaction is assumed ferromagnetic (or antiferromagnetic). We found three phases for this system, namely, paramagnetic, ferromagnetic, and spin-glass-like.
Title:
Band gap formation and multiple scattering in photonic quasicrystals with a Penrose-type lattice
Authors:
Della Villa, A; Enoch, S; Tayeb, G; Pierro, V; Galdi, V; Capolino, F
Source:
PHYSICAL REVIEW LETTERS, 94 (18): Art. No. 183903 MAY 13 2005
Abstract:
This Letter presents a study of the local density of states (LDOS) in photonic quasicrystals. We show that the LDOS of a Penrose-type quasicrystal exhibits small additional band gaps. Among the band gaps, some exhibit a behavior similar to that typical of photonic crystals, while others do not. The development of certain band gaps requires large-size quasicrystals. It is explained by the long-range interactions involved in their formation. Moreover, the frequencies where the band gaps occur are not necessarily explained using single scattering and should therefore involve multiple scattering.
Title:
Observation of modulated quadrupolar structures in PrPb3
Authors:
Onimaru, T; Sakakibara, T; Aso, N; Yoshizawa, H; Suzuki, HS; Takeuchi, T
Source:
PHYSICAL REVIEW LETTERS, 94 (19): Art. No. 197201 MAY 20 2005
Abstract:
Neutron diffraction measurements have been performed on the cubic compound PrPb3 in a [001] magnetic field to examine the quadrupolar ordering. Antiferromagnetic components with q=(1/2 +/-delta 1/2 0), (1/2 1/2 +/-delta 0) (delta approximate to 1/8) are observed below the transition temperature T-Q (0.4 K at H=0) whose amplitudes vary linear with H and vanish at zero field, providing the first evidence for a modulated quadrupolar phase. For H < 1 T, a nonsquare modulated state persists even below 100 mK suggesting quadrupole moments associated with a Gamma(3) doublet ground state to be partially quenched by hybridization with conduction electrons.
Title:
Thickness effects on the magnetism of Ho thin films
Authors:
Herring, ADF; Nuttall, WJ; Thomas, MF; Goff, JP; Stunault, A; Ward, RCC; Wells, MR; Stirling, WG
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (17): 2543-2552 MAY 4 2005
Abstract:
This study was undertaken to probe any thickness dependence of the magnetic ordering in Ho film samples of thickness 1000 monolayers (ML), 100 ML and 50 ML. The study was carried out on the antiferromagnetic helical magnetic phase in the temperature range 65 -> 132 K (T-N). The magnetism was studied by x-ray magnetic scattering using the resonant process at the Ho L-III absorption edge, 8.071 keV. It was found that the magnetic modulation wavevector, tau, of the Ho helical structure changed systematically with temperature over the range 65 K -> TN. No evidence of a change in T with changing layer thickness was seen. The value of the Neel temperature TN decreased from 130 K for the 1000 ML sample to 110 K for the 50 ML sample. The critical exponent beta of the transition between the helical to paramagnetic state is measured as beta approximate to 0.5 for the 1000 and 100 ML samples compared to a literature value of beta = 0.39 for bulk. For the 50 ML film, beta = 0.28 +/- 0.05. The measured values of beta are discussed in terms of strain and reduced dimensionality.
Title:
Evidence of three types of short range ordered fluorite structure in the (1-x) Y0.15Zr0.85O1.93-x Y0.75Nb0.25O1.75 (0 <= x <= 1) system
Authors:
Garcia-Martin, S; Alario-Franco, MA; Fagg, DP; Irvine, JTS
Source:
JOURNAL OF MATERIALS CHEMISTRY, 15 (19): 1903-1907 2005
Abstract:
The microstructure of the high-temperature quenched oxides of the (1 - x) Y0.15Zr0.85O1.93 - x Y0.75Nb0.25O1.75 (0 &LE; x &LE; 1) system has been investigated by selected area electron diffraction and high resolution transmission electron microscopy. We have found three types of fluorite structure: the x 5 0 end member of the solid solution (Y0.15Zr0.85O1.93) shows evidence of tetragonal fluorite-type structure; we have also observed a modulated fluorite-type structure due to short-range ordering of the oxygen vacancies. The microdomain modulated structure gradually evolves from a distorted pyrochlore-type to a type intermediate between C-type and distorted pyrochlore as x decreases from 1 to 0.3.
Title:
Magnetic structure of the Zr6CoAs2-type Er6TX2 compounds (T = Mn, Fe, Co and X = Sb, Bi)
Authors:
Morozkin, AV; Nirmala, R; Malik, SK
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 394 (1-2): 75-79 MAY 17 2005
Abstract:
Investigations were made by neutron diffraction on the Zr6CoAs2-type (space group P(6)b2m, No. 189) Er6FeSb2, Er6MnSb2, Er6CoBi2, Er6FeBi2, Er6MnBi2 and Zr6MnBi2 compounds. The Er6FeSb2, Er6MnSb2, Er6CoBi2 and Er6MnBi2 compounds show a ferromagnetic type of ordering below 21(5), 110(5), 30(2) and 100(5) K, respectively. Below the ferromagnetic transition the magnetic structure of these compounds consist of Er ferromagnetic (100) layers. Below 33(25) K, the Er6MnBi2 compound has an incommensurate magnetic structure with constant propagation vectors [0.596(2), 0, 0]. The propagation vector coincides with the a-axis of the unit cell. The magnetic moments of the Er atoms make an angle with the c-axis (mu(Er) = 7.5(2)mu(B), beta(Er) = 6.7(4)degrees at 2 K). The Er6FeBi2 compound displays a ferromagnetic transition below 15(5) K. The magnetic structure of the Er6FeBi2 compound is not clear. In the Er6TX2 compounds, no local moment was detected on the transition metal site. Furthermore, no magnetic transition was detected in the Zr(6)CoAS(2)-type Zr6MnBi2 compound. Both, the type of transition metal and the distortion of the unit cell strongly influence the ferromagnetic type of ordering temperature and the magnetic structure in these compounds. (c) 2004 Elsevier B. V. All rights reserved.
Title:
Quasicrystalline phase formation in the mechanically alloyed Al-Cu-Fe system
Authors:
Tcherdyntsev, VV; Kaloshkin, SD; Shelekhov, EV; Salimon, AI; Sartori, S; Principi, G
Source:
INTERMETALLICS, 13 (8): 841-847 AUG 2005
Abstract:
Al-Cu-Fe samples were prepared by ball milling powders of elemental Al, Cu, Fe (first route) and of elemental At mixed with previously mechanically alloyed Cu-Fe solid solution (second route). Phase and structure transformations by annealing the as-milled powders were investigated by differential scanning calorimetry, X-ray diffraction and Mossbauer spectroscopy. The influence of the thermodynamic driving forces, namely the heat of mixing, positive for the Cu-Fe system and negative for the Al-Fe and Al-Cu systems, was discussed and correlated to the sequence of phase transformations during heating. (c) 2005 Elsevier Ltd. All rights reserved.
Title:
Phase equilibria in the system Al-Co-Si
Authors:
Richter, KW; Gutierrez, DT
Source:
INTERMETALLICS, 13 (8): 848-856 AUG 2005
Abstract:
The Al-Co-Si system was studied for three isothermal sections at 600 degrees C (equilibria with Si), 800 degrees C (alloys up to 50 at.% Co) and 900 degrees C (alloys with more than 50 at.% Co). A total number of seven ternary compounds were characterized in the ternary system and the homogeneity ranges of the various ternary solid solutions of binary Co-Al and Co-Si compounds were studied. X-ray powder diffraction and optical microscopy was used for initial sample characterization and electron probe microanalysis of the annealed samples was used to determine the phase compositions within the ternary system. Lattice parameters have been determined for all ternary compounds and the change of lattice parameters with the composition is given for the solid solution phases. (c) 2005 Elsevier Ltd. All rights reserved.
Title:
Preparation and characterisation of melt-spun Al-Cu-Fe quasicrystals
Authors:
Huttunen-Saarivirta, E; Vuorinen, J
Source:
INTERMETALLICS, 13 (8): 885-895 AUG 2005
Abstract:
Three Al-Cu-Fe alloys with compositions of Al60-65Cu20-27.5Fe12.5-15 were prepared by conventional casting and further processed by melt-spinning. The structures formed were examined to get an insight into the interrelated effects of synthesis, processing and microstructure of Al-Cu-Fe alloys. The study aimed at answering the questions such as whether the production of single-phase quasicrystalline ribbons is possible by the melt-spinning process and what is the role of the degree of undercooling in the development of microstructure in melt-spun ribbons. The icosahedral phi-Al65Cu20Fe15 phase forms by a peritectic reaction between the primary beta-AlFe phase and the liquid, as the temperature decreases. At the later stages of cooling, the monoclinic lambda-Al13Fe4 phase and the tetragonal theta-Al13Cu phase are formed in the cast alloys, as a result of peritectic reactions. In the rapidly solidified alloys, the formation of the tetragonal theta-A(12)Cu phase and, in the case of alloy Al60Cu25Fe15, the monoclinic lambda-Al13Fe4 phase is avoided, apparently due to high degree of undercooling. Thus, the production of single-phase quasicrystalline ribbons is not possible by the melt-spinning process, at least by using the cooling rate of 5-7 x 10(4) degrees C/s. In addition to phase selection, the degree on undercooling influences, for example, the composition of the phi-Al65Cu20Fe15 phase and the grain morphology in melt-spun ribbons. (c) 2005 Elsevier Ltd. All rights reserved.
Title:
Fabrication of ferroelectric PbZr0.4Ti0.6O3 multilayers by sol-gel process
Authors:
Hu, GJ; Chen, J; An, DL; Chu, JH; Dai, N
Source:
APPLIED PHYSICS LETTERS, 86 (16): Art. No. 162905 APR 18 2005
Abstract:
Quasiperiodic ferroelectric PbZr0.4Ti0.6O3 multilayers have been fabricated using the sol-gel technique based on one single precursor. The building block of the multilayer is the distinct PbZr0.4Ti0.6O3/porous-PbZr0.4Ti0.6O3 bilayer formed in a single spin-casting/annealing step and the formation of the bilayer is governed by phase segregation process. The quasiperiodic ferroelectric multilayer exhibits good performance as a Bragg reflector. With 11 periods, 90% reflectivity and 40-nm stop-band width have been achieved at room temperature. © 2005 American Institute of Physics.
Title:
Modulated one-dimensional structure of [Cd(NH3)(3)Ni(CN)(4)]
Authors:
Petricek, V; Dusek, M; Cernak, J
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 61: 280-286 Part 3 JUN 2005
Abstract:
The crystal structure of [Cd(NH3)(3)Ni(CN)(4)] has been solved and refined as an incommensurate structure in four-dimensional superspace. The Xcalibur point-detector diffractometer was used for data collection up to the third-order satellites. The structure was refined from 3496 observed reflections to a final R value of 0.0371. The modulation strongly affects all the atoms of the structure. The dominating feature of the modulation is the incommensurate alternation between octahedrally and tetrahedrally coordinated Cd atoms in the electroneutral chains [-Cd(NH3)(n)-NC-Ni(CN)(2)-CN-](&INFIN;) (n alternates between 2 and 4). The chain is propagated along the a axis, in which the [Cd(NH3)(n)](2+) cations are linked by square [Ni(CN)(4)](2-) anions. The atomic positional modulations, having mainly a transversal character in the c-direction, exhibit a switching character that can be described by the crenel and sawtooth functions. The effectively pentagonal coordinated cadmium positions were detected in the intermediate regions.

Update: 27-May-2005

Title:
Oxidation kinetics of the quasicrystalline i-AlCuFe phase compared with that of crystalline omega-AlCuFe and pure aluminum
Authors:
Rouxel, D; Gil-Gavatz, M; Pigeat, P; Weber, B
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 351 (10-11): 802-809 APR 15 2005
Abstract:
The oxidation of the quasicrystalline alloy i-AlCuFe has been compared with that of tetragonal ω-AlCuFe and that of pure aluminum. At 600 &DEG; C, for low exposure to oxygen in UHV conditions (up to 5000 L), much smaller thicknesses of oxide have been observed on i-AlCuFe by AES and depth profiling. After oxidations of 10(5) L, oxide crystallites are clearly observed by SEM on the surface of ω-AlCuFe and pure aluminum, in particular in the center of the grains. Such is not the case on i-AlCuFe grains. These oxide crystallites give rise after ion etching to cones structure on the surface of ω-AlCuFe and pure aluminum whereas the i-AlCuFe surface remains very smooth. However when oxidation is performed at 700 &DEG; C, oxide crystallites also appear on the whole icosahedral grains. These results show that the crystalline and the quasicrystalline phases have a different kinetics in the oxide growth, due to, in particular, a delay in the nucleation and growth rate of the oxide on the quasicrystalline phase. It is assumed that this difference is linked to the impossible epitaxial growth of the γ-Al-2-O-3 oxide on the aperiodic lattice of the i-AlCuFe phase. © 2005 Elsevier B.V. All rights reserved.
Title:
On the amorphous-to-quasicrystalline phase transformation in ball-milled and melt-spun Zr58.5Ti8.2Cu14.2Ni11.4Al7.7 glassy alloys
Authors:
Scudino, S; Eckert, J; Mickel, C; Schultz, L
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 351 (10-11): 856-862 APR 15 2005
Abstract:
The influence of the preparation technique on quasicrystal formation was investigated by comparing the devitrification of Zr58.5Ti8.2Cu14.2Ni11.4Al7.7 metallic glass produced by ball milling of crystalline intermetallic compounds with its corresponding rapidly quenched counterpart produced by melt spinning. Differently from the as-spun ribbon, which is fully amorphous, the as-milled powder displays the presence of a minor amount of a crystalline phase along with the glassy phase. However, the crystallization behavior of both the powder and the ribbon is characterized by the formation of a nanoscale quasicrystalline phase upon partial devitrification, demonstrating that quasicrystal-forming Zr-based alloys can also be produced by solid-state reaction. A possible explanation for the lack of quasicrystal formation reported in other ball-milled Zr-based alloys is proposed, suggesting that the formation of quasicrystals in ball-milled powders may be suppressed by the contamination of the starting material. © 2005 Elsevier B.V. All rights reserved.
Title:
In-situ TEM observations of the coarsening of a nanolamellar structure in a cobalt based magnetic alloy
Authors:
Li, HF; Foo, YL; Ramanujan, RV
Source:
JOURNAL OF MATERIALS SCIENCE, 40 (8): 1901-1907 APR 2005
Abstract:
The thermal stability and coarsening of nanostructures is of both scientific interest and of engineering significance in order to produce thermally stable nanomaterials. Real time observations were carried out using ultra high vacuum (UHV) in situ TEM to investigate the coarsening process of a highly modulated nanolamellar structure obtained by crystallization of a Co based Co65Si15B14Fe4Ni2 amorphous magnetic alloy. The coarsening process consisted of three steps: (a) precipitation of spherical fine precipitates; (b) continuous coarsening of the nanolamellar structure at the surface and precipitation at the grain boundaries; and (c) formation of a stable multiphase structure. Due to surface effects, continuous coarsening of nanolamellar structure was observed during in-situ annealing; this mechanism was different from that of the coarsening process found during conventional annealing. Discontinuous coarsening from grain boundaries, which dominates the coarsening process in the conventional annealing of bulk sample, also occurred in in-situ annealing of thin sample. The driving force for coarsening of the nanolamellar structure from interlamellar interfaces, grain boundaries and surfaces is discussed. (C) 2005 Springer Science + Business Media, Inc.
Title:
Determination of ordinary magnetic shape magnetostriction in Ni-Mn-Ga memory alloy
Authors:
Heczko, O
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 290: 846-849 Part 2 Sp. Iss. SI APR 2005
Abstract:
A saturation magnetostriction of five-layered modulated martensite (5 M) was determined from magnetization curves and by using direct measurements of the field-induced strain of strongly constrained single crystalline sample. The saturation magnetostriction of 5 M martensite was determined to be about 50 ppm. This is about five times smaller than previously reported. The error in determination of magneto stricti on due to magnetic shape memory effect and due to the presence of residual martensitic variants with different crystalographic orientation is discussed. © 2004 Elsevier B.V. All rights reserved.
Title:
A critical discussion of calculated modulated structures, Fermi surface nesting and phonon softening in magnetic shape memory alloys Ni2Mn(Ga, Ge, Al) and CO2Mn(Ga, Ge)
Authors:
Zayak, AT; Entel, P
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 290: 874-877 Part 2 Sp. Iss. SI APR 2005
Abstract:
A series of first-principle calculations have been carried out in order to discuss electronic structure, phonon dynamics, structural instabilities and the nature of martensitic transformations of the Heusler alloys Ni2Mn(Ga, Ge, Al) and Co2Mn(Ga, Ge). The calculations show that besides electronic peculiarities like Fermi-surface nesting, hybridizing optical and acoustic phonon modes are important for the stabilization of the modulated martensitic structures. © 2004 Published by Elsevier B.V.
Title:
Electron transport properties of the finite double-walled carbon nanotubes
Authors:
Chen, JW; Yang, LF
Source:
ACTA PHYSICA SINICA, 54 (5): 2183-2187 MAY 2005
Abstract:
Based upon the Landauer formula, we have studied electron transport properties of finite incommensurate and commensurate double-walled carbon nanotubes (DWNTs). The results obtained show that the geometrical structures of the tube may produce significant effects on their electron transport properties: Electron transport of the incommensurate DWNTs may be either ballistic or non-ballistic, depending on the energy region. The commensurate DWNTs formed by the armchair tubes may display quick and slow oscillation; however, those formed by the zigzag tubes have no regular slow oscillation.
Title:
Green functions for a decagonal quasicrystalline material with a parabolic boundary
Authors:
Wang, X
Source:
ACTA MECHANICA SOLIDA SINICA, 18 (1): 57-62 MAR 2005
Abstract:
This investigation presents the Green functions for a decagonal quasicrystalline material with a parabolic boundary subject to a line force and a line dislocation by means of the complex variable method. The surface Green functions are treated as a special case, and the explicit expressions of displacements and hoop stress at the parabolic boundary are also given. Finally, the stresses and displacements induced by a phonon line force acting at the origin of the lower half-space are presented.
Title:
The twofold superstructure of titanium(III) oxybromide at T = 17.5 K
Authors:
Palatinus, L; Schonleber, A; van Smaalen, S
Source:
ACTA CRYSTALLOGRAPHICA SECTION C-CRYSTAL STRUCTURE COMMUNICATIONS, 61: I47-I48 Part 5 MAY 2005
Abstract:
The low-temperature (T = 17.5 K) structure of titanium(III) oxybromide, TiOBr, is reported as a twofold superstructure of the crystal structure at room temperature. Weak superlattice reflections were measured with synchrotron radiation X-rays and were analyzed by structure refinements employing superspace techniques. Both the low-temperature and the room-temperature structures of TiOBr are isostructural with the corresponding structures of TiOCl. The results indicate that at low temperatures TiOBr is in a spin-Peierls state, similar to that of TiOCl, but with the modulations and relevant interactions smaller than in the latter compound.

Update: 20-May-2005

Title:
Structural phase transitions and sodium ordering in Na0.5CoO2: a combined electron diffraction and Raman spectroscopy study
Authors:
Yang, HX; Nie, CJ; Shi, YG; Yu, HC; Ding, S; Liu, YL; Wu, D; Wang, NL; Li, JQ
Source:
SOLID STATE COMMUNICATIONS, 134 (6): 403-408 MAY 2005
Abstract:
The nonstoichiometric NaxCoO2 system exhibits extraordinary physical properties that correlate with temperature and Na concentration in its layered lattice without evident long-range structure modification when conventional crystallographic techniques are applied. For instance, Na0.7CoO2, a thermodynamically stable phase, shows large thermoelectric power; water-intercalated Na(0.33)CoO(2)(.)1.3H(2)O is a newly discovered superconductor with T(c)similar to 4 K, and Na0.5CoO2 exhibits an unexpected charge ordering transition at around T(infinity)similar to 55 K. Recent studies suggest that the transport and magnetic properties in the NaxCoO2 system strongly depend on the charge carrier density and local structural properties. Here we report a combined variable temperature transmission electron microscopy and Raman scattering investigation on structural transformations in Na0.5CoO2 single crystals. A series of structural phase transitions in the temperature range from 80 to 1000 K are directly identified and the observed superstructures and modulated phases can be interpreted by Na-ordering. The Raman scattering measurements reveal phase separation and a systematic evolution of active modes along with phase transitions. Our work demonstrates that the high mobility and ordering of sodium cations among the CoO2 layers are a key factor for the presence of complex structural properties in NaxCoO2 materials, and also demonstrate that the combination of electron diffraction and Raman spectroscopy measurements is an efficient way for studying the cation ordering and phase transitions in related systems. (c) 2005 Elsevier Ltd. All rights reserved.
Title:
Ground state of a two-dimensional quasiperiodic quantum antiferromagnet
Authors:
Jagannathan, A
Source:
PHYSICAL REVIEW B, 71 (11): Art. No. 115101 MAR 2005
Abstract:
We consider the antiferromagnetic spin-1/2 Heisenberg model on a two-dimensional bipartite quasiperiodic tiling. The broken symmetry ground state in this model is inhomogeneous, reflecting the fact that there are a variety of local environments in such a structure. An important symmetry of the quasicrystal, namely that of invariance under discrete scale transformations is used to define an approximate real space renormalization scheme for the octagonal tiling. We solve for some of the fixed point properties of this quasiperiodic antiferromagnet. The ground state energy and local order parameters are calculated, and the results compare favorably with numerical values obtained by quantum Monte Carlo calculation. Despite the novel features of the ground state in this type of antiferromagnet, there are some interesting similarities with the well-known square lattice antiferromagnet. The most striking of these is the proximity of the values of the ground state energies of these two paradigms for two very dissimilar classes of solids.
Title:
Helicoidal magnetic order in the spin-chain compound NaCu2O2
Authors:
Capogna, L; Mayr, M; Horsch, P; Raichle, M; Kremer, RK; Sofin, M; Maljuk, A; Jansen, M; Keimer, B
Source:
PHYSICAL REVIEW B, 71 (14): Art. No. 140402 APR 2005
Abstract:
We report susceptibility, specific heat, and neutron diffraction measurements on NaCu2O2, a spin-1/2 chain compound isostructural to LiCu2O2, which has been extensively investigated. Below 12 K, we find a long-range ordered, incommensurate magnetic helix state with a propagation vector similar to that of LiCu2O2. In contrast to the Li analog, substitutional disorder is negligible in NaCu2O2. We can thus rule out that the helix is significantly influenced by impurities. A spin Hamiltonian with frustrated longer-range exchange interactions provides a good description of both the ordered state and the paramagnetic susceptibility.
Title:
Ab initio Ti-Zr-Ni phase diagram predicts stability of icosahedral TiZrNi quasicrystals
Authors:
Hennig, RG; Carlsson, AE; Kelton, KF; Henley, CL
Source:
PHYSICAL REVIEW B, 71 (14): Art. No. 144103 APR 2005
Abstract:
The ab initio phase diagram determines the energetic stability of the icosahedral TiZrNi quasicrystal. The complete ab initio zero-temperature ternary phase diagram is constructed from the calculated energies of the elemental, binary and ternary Ti-Zr-Ni phases. For this, the icosahedral i-TiZrNi quasicrystal is approximated by periodic structures of up to 123 atoms/unit cell, based on a decorated-tiling model [R. G. Hennig, K. F. Kelton, A. E. Carlsson, and C. L. Henley, Phys. Rev. B 67, 134202 (2003)]. The approximant structures containing the 45-atom Bergman cluster are nearly degenerate in energy, and are all energetically stable against the competing phases. It is concluded that i-TiZrNi is a ground-state quasicrystal, as it is experimentally the low-temperature phase for its composition.
Title:
Elastic and inelastic deformations of ethylene-passivated tenfold decagonal Al-Ni-Co quasicrystal surfaces
Authors:
Park, JY; Ogletree, DF; Salmeron, M; Ribeiro, RA; Canfield, PC; Jenks, CJ; Thiel, PA
Source:
PHYSICAL REVIEW B, 71 (14): Art. No. 144203 APR 2005
Abstract:
The adhesion and friction force properties between a tenfold Al-Ni-Co decagonal quasicrystal and a titanium nitride (TiN)-coated tip were investigated using an atomic force microscope in ultrahigh vacuum. To suppress the strong chemical adhesion found in the clean quasicrystal surfaces, the sample was exposed to ethylene that formed a protective passivating layer. We show that the deformation mechanism of the tip-substrate junction changes from elastic to inelastic at a threshold pressure of 3.8 to 4.0 GPa. Images of the indentation marks left above the threshold pressure indicate the absence of new steps, and indicate that surface damage is not accompanied by formation of slippage planes or dislocations, as found in plastically deforming crystalline materials. This is consistent with the lack of translational periodicity of quasicrystals. The work of adhesion in the inelastic regime is five times larger than in the elastic one, plausibly as a result of the displacement of the passivating layer. In the elastic regime, the friction dependence on load is accurately described by the Derjaguin-Muller-Toporov (DMT) model, consistent with the high hardness of both the TiN tip and the quasicrystal sample. Above the threshold pressure, the friction versus load curve deviates from the DMT model, indicating that chemical bond formation and rupture contribute to the energy dissipation.
Title:
Phason hierarchy and electronic stability of quasicrystals
Authors:
Naumis, GG
Source:
PHYSICAL REVIEW B, 71 (14): Art. No. 144204 APR 2005
Abstract:
We show that under a random phasonic field, there is a hierarchy in the probability of making a phason in real space. This effect divides the quasicrystal in a stable backbone plus an unstable part. The stable backbone and the unstable sites are obtained by the deflation rules of the corresponding quasicrystalline lattice, and thus analytical formulas to find the stable and unstable parts are provided. A discussion is made about how the electronic stabilization of a quasicrystal is affected by phason jumps in unstable sites. As a result, it is shown that phasons in unstable sites do not compromise the electronic stabilization of the structure, since they only affect low-amplitude diffraction spots of the quasicrystal.
Title:
Elastic and inelastic deformations of ethylene-passivated tenfold decagonal Al-Ni-Co quasicrystal surfaces (vol 71, art no 144203, 2005)
Authors:
Park, JY; Ogletree, DF; Salmeron, M; Ribeiro, RA; Canfield, PC; Jenks, CJ; Thiel, PA
Source:
PHYSICAL REVIEW B, 71 (14): Art. No. 149901 APR 2005
Title:
Terrace selection during equilibration at an icosahedral quasicrystal surface
Authors:
Unal, B; Lograsso, TA; Ross, A; Jenks, CJ; Thiel, PA
Source:
PHYSICAL REVIEW B, 71 (16): Art. No. 165411 APR 2005
Abstract:
We investigate the equilibration of a fivefold surface of the icosahedral Al-Pd-Mn quasicrystal at 900-915 and 925-950 K, using scanning tunneling microscopy. After annealing at the lower temperatures, there is a high density of shallow voids on some terraces but not on others; at 925-950 K, the void-rich terraces are much rarer. The terminations that are consumed by voids exhibit a distinctive local atomic configuration, called a "ring" by previous authors. Apparently, through growth and coalescence of the voids, a different termination becomes exposed on the host terraces, which also leads to a change in step heights at the edges of the terraces. We suggest that the shallow steps associated with the voids, and the ring configuration, signal a surface that is in an intermediate stage of structural equilibration.
Title:
About gamma-brass phases in the Al-Cr-Fe system and their relationships to quasicrystals and approximants
Authors:
Demange, V; Ghanbaja, J; Machizaud, F; Dubois, JM
Source:
PHILOSOPHICAL MAGAZINE, 85 (12): 1261-1272 APR 21 2005
Abstract:
We have identified two gamma-brass phases in the Al - Cr - Fe system by X-ray diffraction and transmission electron microscopy. These structures (rhombohedral and cubic) are closely related to each other and can co-exist in the same alloy together with approximants of quasicrystals. In particular, a long-period superlattice, typical of gamma-brass phases, was characterized in the cubic structure. This superstructure is constituted of inversion domains separated by boundaries lying at ((1) over bar 10) planes. The displacement vector between like domains was determined from high resolution microscopy data. This study deals also with a description of some structural links between gamma-brass phases and approximants of decagonal and icosahedral quasicrystals.
Title:
Electron states and the spin density wave phase diagram in Cr(110) films
Authors:
Rotenberg, E; Freelon, BK; Koh, H; Bostwick, A; Rossnagel, K; Schmid, A; Kevan, SD
Source:
NEW JOURNAL OF PHYSICS, 7: Art. No. 114 APR 29 2005
Abstract:
Chromium films offer an excellent system to study the impact of dimensional confinement on physical properties associated with the spin-density-wave (SDW) ground state observed in bulk materials. These properties are also of some technological importance since chromium is a common component of thin film magnetic structures. We prepared chromium ( 1 1 0) films of high crystalline quality on a W( 1 1 0) substrate with a wedge-shaped thickness profile so that the impact of confinement can be systematically studied. We have characterized these films using a combination of low-energy electron diffraction and microscopy as well as high-resolution angle-resolved photoemission spectroscopy. We have probed the Fermi surface and the nesting vectors therein that are relevant to the SDW ground state. We find these to predict accurately the observed bulk SDW periodicity. We have also characterized the SDW periodicity in the film directly by measuring the splitting between backfolded bands, and we find that this periodicity deviates markedly from the bulk periodicity for thinner films at higher temperatures. We have systematically mapped the SDW incommensurability and phase diagram as a function of both film thickness and temperature. We find commensurate and incommensurate phases that are separated by nearly continuous transitions. Our results suggest a simple model to explain the delicate interplay between commensurate and incommensurate phases that involves a balance between SDW stabilization energy and surface and interface energetics.
Title:
Devitrification of nano-scale icosahedral phase in (Ti0.33Zr0.33Hf0.33)(50)(Ni0.5Cu0.5)(40)Al-10 alloy with enlarging supercooled liquid region
Authors:
Kim, KB
Source:
MATERIALS LETTERS, 59 (14-15): 1771-1774 JUN 2005
Abstract:
This letter reports devitrification of novel multicomponent (Ti0.33Zr0.33Hf0.33)(50)(Ni0.5Cu0.5)(40)Al-10 alloy, developed by equiatomic substitution. The supercooled liquid region of the (Ti0.33Zr0.33Hf0.33)(50()Ni0.5Cu0.5)(40)Al-10 alloy increased with progress of the first exothemic reaction. The supercooled liquid region of 57 K in the as-quenched state was observed to increase to 108 K after heat treatment for 180 min at 743 K. The corresponding microstructure after heat treatment for 180 min at 743 K consisted of a homogeneous distribution of the nano-scale icosahedral phase embedded in the remaining amorphous matrix. Therefore, it is feasible to understand that the devitrification of the nanoscale icosahedral phase occurs in the (Ti0.33Zr0.33Hf0.33)(50)(Ni0.5Cu0.5)(40)Al-10 alloy by the primary crystallization. (c) 2005 Elsevier B.V. All rights reserved.
Title:
Magnetic structure of the Zr(6)CoAS(2)-type Tb6FeBi2 compound
Authors:
Morozkin, AV; Nikiforov, VN; Malaman, B
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 393 (1-2): L6-L9 MAY 3 2005
Abstract:
Investigations were made by neutron diffraction experiments on the Zr6CoAs2-type (space group P6b2m no. 189) Tb6FeBi2 compound. Below T-C1 = 250(5) Kthe magnetic structure of Tb6FeBi2 consists of Tb ferromagnetic (0 0 1) layers (mu(Tb) = 8.0(3) mu(B) at 70 K). Below T-C2 = 60(5) K the Tb6FeBi2 has an incommensurate magnetic structure with a constant propagation vector [0, 0, 0.350(1)]. The propagation vector coincides with the c axis. The magnetic moment of the Tb atoms makes an angle with the c axis (mu(Tb) = 8.9(3) mu(B), mu(Tb) = 6.2(4)degrees at 26 K). (c) 2004 Elsevier B.V. All rights reserved.
Title:
Magnetic structures of the CeScSi-type RZrSb compounds (R = Tb, Er)
Authors:
Morozkin, A; Halich, K; Welter, R; Ouladdiaf, B
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 393 (1-2): 34-40 MAY 3 2005
Abstract:
Investigations made by neutron diffraction experiments on the RZrSb compounds (R = Tb, Dy, Ho and Er) are reported. These compounds crystallize in the tetragonal CeScSi-type structure (space group I4/mmm, No. 139). Below T-C (65 and 45 K for the Tb and DyZrSb compounds, respectively), the magnetic structure of both TbZrSb and DyZrSb compounds consists of ferromagnetic, (0 0 1) layers staked along the c-axis (mu(Tb) = 5.6(5) mu(B) and mu(Dy) = 4.6(5) mu(B) at 2 K). Below T-C = 22(2) K, the magnetic structure of the HoZrSb compound consists of a canted ferromagnetic structure with M, = 1.02(5) mu(B) (an antiferromagnetic arrangement takes place in the a direction), M-z = 5.01(8) B and M-total = 5.11(8) mu(B) at 2 K. Below T-N = 13 K, the ErZrSb compound adopts an incommensurate magnetic structure (antiferromagnetic) with a propagation vectors Q [+/- 0.1580(6), 0, 0) and a total moment value Of mu(Er) = 3.58(6) mu(B) at 2 K. The results are discussed and compared with those obtained for the closely related RTGe (R = Tb, Er, T = Ti, Mn, Ru) CeFeSi-type and CeScSi-type compounds. (c) 2004 Elsevier B.V. All rights reserved.
Title:
Influence of Sr2+ doping, temperature and frequency on dielectric constant, dielectric loss factor and AC conductivity of ammonium zinc chloride crystal
Authors:
Gaffar, MA; Abu El-Fadl, AA; Bin Anooz, S
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 44 (4A): 1885-1893 APR 2005
Abstract:
Ammonium zinc chloride (AZC) crystals doped with different strontium concentrations have been grown by the slow evaporation technique. Detailed temperature (300-450 K) and frequency (400-10(5) Hz) study of the dielectric constant (epsilon), loss factor (tan delta) and the ac conductivity (sigma(ac)) of the grown crystals has been carried out. Along the polar b-axis epsilon increased gradually with increasing temperature showing clear peaks at the phase transitions. Thermal recycling decreased epsilon, inhibited the peak height, decreased its broadening but without shifting the transition points. However, Sr2+-doping causes a shift of the transition temperature towards lower values and a decrease in the E-peak broadening and height. Relation between 1/epsilon and T in the vicinity of the commensurate (C) to incommensurate (IC) phase transition revealed the validity of an equation similar to the Curie-Weiss law. Doping with Sr2+ in different concentrations causes a systematic change in the equation constants. Soliton pinning increased in the presence of Sr2+ leading to residual discommensurations (DC's) in the C-phase. The dielectric constant decreased continually with increasing frequency for the undoped and Sr2+-doped samples. Doping with 0.144 wt% Sr2+ destroyed 25% of the C-phase, which means the possibility of having AZC crystal with reduced C-phase. sigma(ac) increased with increasing frequency following a power law of the form sigma = sigma(o)f(s). Conduction by hopping was found to be dominant in all phases of AZC and after doping with Sr2+ in different concentrations. Mechanism for DC formation and annihilation was also discussed.
Title:
Effects of liquid quenching and subsequent heating on the structure of Co-Al alloys
Authors:
Portnoi, VK; Tret'yakov, KV; Filipova, SE; Latuch, J
Source:
INORGANIC MATERIALS, 41 (4): 350-355 APR 2005
Abstract:
The phase composition and structure of Co-Al alloys after liquid-quenching (LQ) and subsequent heating were determined by x-ray diffraction, differential thermal analysis, and differential scanning calorimetry. After LQ, the Co-19.5 at % Al alloy consisted of two phases: CoAl (B2 structure, a = 0.2852 nm) and an fcc Co1-xAlx solid solution (a = 0.3573 nm). The phase composition of the LQ alloy and the lattice parameters of the intermetallic phase CoAl and solid solution corresponded to a solidification temperature of 1100&DEG; C, rather than to the eutectic temperature (1400&DEG; C). Heating to 1000&DEG; C brought the alloy to the equilibrium state. In the range 25-28 at % Al, the LQ alloys were single-phase and consisted of Co-enriched CoAl (B2). Decomposition of this intermetallic phase during heating in the calorimeter gave rise to an exothermic peak at 680&DEG; C and led to precipitation of hcp Co, which converted to an fcc Co1-xAlx solid solution heating to 1000&DEG; C. The activation energy of the decomposition process, evaluated by the Kissinger method, was E-a = 125 &PLUSMN; 10 kJ/mol. The LQ Co-71.4 at % Al alloy consisted of three phases: metastable quasicrystalline phase (similar in structure to Al14CO3Ni3), CO2Al5, and CoAl. Heating brought the alloy to the equilibrium state (CO2Al5), With an exotherm near 690&DEG; C. The activation energy of this phase transformation was E, = 195 &PLUSMN; 15 kJ/mol. The LQ alloys containing 76.5 and 82 at % Al were single-phase and consisted of monoclinic CO4Al13 or CO2Al9 with reduced lattice parameters.

Update: 14-May-2005

Title:
Transition between incommensurate phases accompanied by reversal of the magnetic structure vector in CuB2O4
Authors:
Martynov, SN
Source:
PHYSICS OF THE SOLID STATE, 47 (4): 678-683 2005
Abstract:
The incommensurate magnetic state of copper metaborate CuB2O4 is studied in the temperature range 2 < T < 12 K. Competition between frustrated and non-frustrated antisymmetric exchange interactions is shown to cause the magnetic structure vector to reverse at T = 10 K. (C) 2005 Pleiades Publishing, Inc.
Title:
Redistribution of alloying elements in quasicrystallized Zr65Al7.5Ni10Cu7.5Ag10 bulk metallic glass
Authors:
Chen, MW; Inoue, A; Sakurai, T; Menon, ESK; Nagarajan, R; Dutta, I
Source:
PHYSICAL REVIEW B, 71 (9): Art. No. 092202 MAR 2005
Abstract:
We report experimental evidence on redistributions of alloying elements in a partially quasicrystallized Zr65Al7.5Ni10Cu7.5Ag10 bulk metallic glass. Energy-filtered elemental maps show that the partitioning of silver, zirconium, and aluminum occurs in the quasi crystallized glass. Silver is found to enrich into quasicrystals, but zirconium and aluminum are slightly depleted from the quasicrystals. These observations suggest that the amorphous-to-quasicrystal transformation in this alloy is not a simple polymorphous reaction and a long-range diffusion is involved in the devitrification, probably prior to the quasicrystallization.
Title:
Universal low-temperature phase transition in Zn- and Cd-based crystalline approximants
Authors:
Tamura, R; Nishimoto, K; Takeuchi, S; Edagawa, K; Isobe, M; Ueda, Y
Source:
PHYSICAL REVIEW B, 71 (9): Art. No. 092203 MAR 2005
Abstract:
Electron-diffraction studies have shown that a cubic crystal of Zn6SC (Im (3) over bar, alpha=1.383 11 nm), which is a 1/1-1/1-1/1 crystalline approximant to the icosahedral quasicrystal, undergoes a phase transition at a low temperature above 80 K. The transition accompanies breakdown of the cubic symmetry as well as a change of the periodicity in the [110] direction, resulting in a 2 alpha X 2 alpha X alpha-type superlattice at low temperatures. This finding has led us to the conclusion that Zn tetrahedra, which were recently found in the center of the icosahedral cluster, exhibit orientational ordering at a low temperature, resulting in the symmetry breaking of the lattice. Furthermore, such a low-temperature phase transition is found to be a universal phenomenon of the Cd- and Zn-based 1/1-cubic approximants, verifying that the cubic approximants (Im 3) are not in a ground state but are entropically stabilized.
Title:
In situ diffraction studies of the initial growth processes of textured icosahedral quasicrystalline thin films
Authors:
Willmott, PR; Schleputz, CM; Herger, R; Patterson, BD; Hassdenteufel, K; Steurer, W
Source:
PHYSICAL REVIEW B, 71 (9): Art. No. 094203 MAR 2005
Abstract:
The seeding and morphology of quasicrystalline TixNiyZr1-x-y thin films grown by pulsed-laser deposition on Al2O3(0001) have been investigated in situ, using in-plane x-ray diffraction and reflectivity. with synchrotron radiation. The crystallinity of the final films was further studied ex situ using a laboratory x-ray source. Local icosahedral order becomes established after a film thickness of 1.5 nm, which is followed by an abrupt change in the growth rate after a film thickness of approximately 5 nm, as long-range quasicrystalline order begins to become energetically favorable. The films grow two-dimensionally even up to thicknesses of over 100 nm and are highly textured, consisting of columnar grains with one of their fivefold symmetry axes perpendicular to the substrate surface.
Title:
Light-pulse propagation in Fibonacci quasicrystals
Authors:
Ghulinyan, M; Oton, CJ; Dal Negro, L; Pavesi, L; Sapienza, R; Colocci, M; Wiersma, DS
Source:
PHYSICAL REVIEW B, 71 (9): Art. No. 094204 MAR 2005
Abstract:
We report on an extensive study on light propagation in Fibonacci quasicrystals, with special focus on the optical states around the fundamental band gap of the structure. The samples are fabricated using free-standing porous silicon and experiments are performed using an ultrafast time-resolved transmission technique. Large pulse delays and pulse stretching are observed when exciting the band edge states of the Fibonacci structure. We carefully describe the various details concerning sample preparation and optical experiments. In particular, we highlight how optical path gradients related to technical limitations of the standard sample fabrication technique are responsible for a spatial confinement and intensity reduction of the narrow band edge states. However, band edge related pulse delay and stretching effects can still be observed experimentally in the time domain because the characteristic features originating from the quasiperiodic order are preserved. Experiment! s and numerical calculations are in good agreement.
Title:
Neutron scattering study on La1.9Ca1.1Cu2O6+delta and La1.85Sr0.15CaCu2O6+delta
Authors:
Hucker, M; Kim, YJ; Gu, GD; Tranquada, JM; Gaulin, BD; Lynn, JW
Source:
PHYSICAL REVIEW B, 71 (9): Art. No. 094510 MAR 2005
Abstract:
We present neutron scattering data on two single crystals of the high temperature superconductor La2-x(Ca,Sr)(x)CaCu2O6+delta. The Ca-0.1-doped crystal exhibits a long-range antiferromagnetically ordered ground state. In contrast, the Sr-0.15-doped crystal exhibits short-range antiferromagnetic order as well as weak superconductivity. In both crystals antiferromagnetic correlations are commensurate; however, some results on the Ca-0.1-doped crystal-resemble those on the spin-glass phase of La2-xSrxCuO4, where magnetic correlations became incommensurate. In addition, both crystals show a structural transition from tetragonal to orthorhombic symmetry. Quite remarkably, the temperature dependence and correlation length of the magnetic order is very similar to that of the orthorhombic distortion. We attribute this behavior to an orthorhombic strain-induced interbilayer magnetic coupling, which triggers the antiferromagnetic order. The large size of the crystals made it also possible to study the magnetic diffuse scattering along rods perpendicular to the CuO2 planes in more detail. For comparison we show x-ray diffraction and magnetization data. In particular, for the Ca-0.1-doped crystal these measurements reveal valuable information on the spin-glass transition as well as. a second anomaly associated with the Neel transition.
Title:
Total energy calculation for high pressure selenium: the origin of incommensurate modulations in SeIV and the instability of proposed SeII
Authors:
Ackland, GJ; Fox, H
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (12): 1851-1859 MAR 30 2005
Abstract:
We present calculations of the high pressure crystal structures in selenium, including rational approximants to the recently reported incommensurate phases. We show how the incommensurate phases can be intuitively explained in terms of imaginary phonon frequencies arising from Kohn anomalies in the putative undistorted phase. We also find inconsistencies between the calculated and experimental Se II phase-the calculations show it to be a metastable metal while the experiment finds a stable semiconductor. We propose that the experimentally reported structure is probably in error.
Title:
The effect of impurities on the phase transitions in the ferroelectric semiconductors T1InS(2) and T1GaSe(2)
Authors:
Babaev, SS; Basaran, E; Mammadov, TG; Mikailov, FA; Salehli, FM; Seyidov, MY; Suleymanov, RA
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (12): 1985-1993 MAR 30 2005
Abstract:
The temperature dependences of the dielectric constants of the ferroelectric semiconductors TlInS2 and TlGaSe2 have been studied following their annealing within the incommensurate phase. Unusual memory effects accompanied by both a remarkable inflection of the temperature dependence curves in the incommensurate phase and various shifts of the incommensurate (T-i) and commensurate (T-c) phase transition temperatures have been revealed in both crystals. The observed effects are explained on the basis of a defect density wave model taking into account the interaction of modulation waves with charge carriers localized at impurity states. The thermally activated population of these states during the heating or cooling processes is responsible for the changes of the phase transition temperatures.
Title:
Quasicrystal phase structural properties in the AlCuCo ternary system
Authors:
Rosas, G; Angeles-Chavez, C; Perez, R
Source:
JOURNAL OF NEW MATERIALS FOR ELECTROCHEMICAL SYSTEMS, 8 (2): 149-154 APR 2005
Abstract:
Different AlCuCo alloys, with composition values close to those values where the quasicrystalline decagonal phase was obtained in the past, have been prepared. The alloys were obtained using a rapid solidification technique and some of these alloys were subsequently annealed at different temperatures. The structural characteristics of the specimens were obtained using X-ray diffraction techniques (XRD) and transmission electron microscopy (TEM). The experimental results show different transformations between the decagonal phase and the crystalline phases. These results suggest that the formation and decomposition of the decagonal phase is closely related to a cubic phase (solid solution) transformation. Similar results have been reported in the past for the AlCuFe system.
Title:
Long-period martensitic structures of Ni-Mn-Ga alloys studied by high-resolution transmission electron microscopy
Authors:
Pons, J; Santamarta, R; Chernenko, VA; Cesari, E
Source:
JOURNAL OF APPLIED PHYSICS, 97 (8): Art. No. 083516 APR 15 2005
Abstract:
The layered martensitic structures formed in Ni-Mn-Ga alloys have been investigated by high-resolution transmission electron microscopy (including image simulations) in order to discern from two structural models reported in the literature. For the seven-layer martensite, the observations discard the model based on shuffling of the atomic positions (modulation) by a function with a period of seven planes and confirm its nanotwinned nature, which is inherent to the description as stacking of nearly close-packed planes derived from {110}(aust) with (5(2) over bar) sequence, that is, the so-called 14M structure. The observed stacking sequence, however, is notably distorted [the perfect (5(2) over bar) sequence is present only in small areas], although it preserves a predominant periodicity of seven planes. For another alloy composition, a nanotwinned martensite with periodicity of twelve planes and (7(5) over bar) average stacking sequence has also been observed. In case of the five-layer martensite, the image simulations and atom projections obtained from the two structural models fit well with the experimental images, which makes it very difficult to discern between them. (C) 2005 American Institute of Physics.
Title:
On finite-size effects in the simulation of high pressure, quartz-like structures
Authors:
Campana, C; Muser, MH
Source:
HIGH PRESSURE RESEARCH, 24 (4): 517-523 DEC 2004
Abstract:
The stability of two recently suggested crystalline structures arising from compressing quartz is investigated. One phase, called quartz II, is obtained by compressing a model of quartz to pressure P slightly above 22 GPa. The second phase is obtained by shock compressing the quartz II sample to P = 50 GPa. The new structure is a modulated structure of quartz II and the corresponding phase is called quartz IIm. We observe strong size effects or compatibility effects above 26 GPa. If the initial system consists of 360 or 720 SiO2 units, an 'ideal' quartz II structure remains stable up to 30 GPa, whereas a larger system of 864 SiO2 units shows modulations of the quartz II structure when compressed above 28 GPa. On decompression from the 50 GPa sample, the larger system appears to be more stable than the smaller system, for which the incompatibility of the intrinsic modulation with the box geometry apparently leads to large fluctuations of the cell geometry.
Title:
Modulated and disordered phases in the system LiCdVO4-LiCd4(VO4)(3)
Authors:
Gaudin, E; Ben Yahia, H; Zuniga, FJ; Perez-Mato, JM; Darriet, J
Source:
CHEMISTRY OF MATERIALS, 17 (9): 2436-2447 MAY 3 2005
Abstract:
A solid solution (1 - x)LiCdVO4 - xLi(1/3)Cd(1/3)square(1/3)CdVO(4) has been observed for 0 <= x <= 1. From the cell parameters evolution, two domains of the solid solution have been distinguished with a discontinuity at x approximate to 0.6. The first one for 0 <= x <= 0.6 corresponds to the LiCdVO4 substructure of the Na2CrO4-type. For 0.75 <= x <= 1 satellite peaks are observed which correspond to a modulated structure. The first end-member LiCdVO4 (x = 0) crystallizes in Cmcm space group with a = 5.911, b = 8.975, and c 6.513 A. The structure consists of infinite edge-sharing chains of [CdO6] octahedra linked together by [VO4] tetrahedra and [LiO4] tetrahedra. According to the general formula Li(1-2x/3)Cd(x/3)square(x/3)CdVO(4) of the solid solution, when x increases cadmium replaces lithium in the [LiO4] tetrahedra leading to [(Li/Cd/square)O-4] disordered tetrahedra. All the phases in the domain 0.7 <= x <= 1 are one-dimensionally modulated with wavevector q = gamma c* and gamma values of 0.75, 0.733, and 0.722 for x = 3/4, 6/7 and 9/10, respectively. The superspace group is Xmcm(00 gamma) where X stands for (1/2, 1/2, 0, 1/2) centering. The main structural result is a strong occupation modulation of lithium and cadmium in the tetrahedral site.

Update: 6-May-2005

Title:
Martensitic transformations of Ni54Mn25Ga21-xAlx shape memory alloys
Authors:
Xin, Y; Li, Y; Jiang, CB; Xu, HB
Source:
PRICM 5: THE FIFTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-5, 475-479: 1991-1994 Part 1-5 2005 Book series title: MATERIALS SCIENCE FORUM
Abstract:
The non-stoichiometric NiMnGa shape memory alloy with high Ni content has been developed as promising thermo-actuated materials applied at high temperature. A substitution of Al for Ga in the Ni54Mn25Ga21 alloys is performed. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements have been carried out to study the effects of the phase transformations and microstructures of the Ni54Mn25Ga21,Al-x shape memory alloys. The results show that the martensitic transformation temperatures almost linearly decrease with the increase of Al substitution for Ga, which can be explained considering the effect of the size factor, i.e. the lattice parameter. A structural transition from a non-modulated tetragonal type to a seven-layered 14M one has been found during the increase of Al substitution for Ga.
Title:
Nano atom clusters and their long-range quasiperiodic arrangements in the Al-Ni-Ru decagonal quasicrystal
Authors:
Sun, W; Zhang, Z; Hirage, K
Source:
PRICM 5: THE FIFTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-5, 475-479: 3351-3354 Part 1-5 2005 Book series title: MATERIALS SCIENCE FORUM
Abstract:
The structural features of nano-sized atom clusters and their long-rang arrangement in the Al-Ni-Ru decagonal quasicrystal with 1.6 nm periodicity have been studied and compared with those in the Al-Pd-Mn decagonal quasicrystal on the basis of electron microscopy. From the perpendicular-space analysis of the tiling obtained in a wide region, we conclude that long-range arrangement of atom clusters in the Al-Ni-Ru decagonal quasicrystal with 1.6 nm periodicity can form a Penrose-tiling-like quasiperiodic structure which is almost free of linear phase strain. In contrast, the tiling structure of the Al-Pd-Mn decagonal quasicrystal contains heavy phason strain. Our results clearly show that atom clusters formed in the Al-Ni-Ru decagonal quasicrystals and their linkage manner are completely different from those in the Al-Pd-Mn decagonal quasicrystal.
Title:
Synthesis and mechanical properties of conventionally cast icosahedral particle-reinforced Al-Mn(-Cu)-Be-Si alloys
Authors:
Fleury, E; Chang, HJ; Kim, DH; Kim, DH; Kim, WT
Source:
PRICM 5: THE FIFTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-5, 475-479: 3359-3362 Part 1-5 2005 Book series title: MATERIALS SCIENCE FORUM
Abstract:
The microstructure of the Al-Mn(-Cu)-Be-Si alloys analyzed by X-ray diffraction and TEM consisted of icosahedral (i) quasicrystal particles embedded in alpha(A1) matrix. The conjoint addition of Si and Be elements enabled the i-phase formation in circle divide 10 mm specimens prepared by conventional casting technique. The size, volume fraction and stability of the i-phase were found to be dependent on the Mn content. The addition of 2 at.% Cu did not affect the formation and stability of the i-phase but contributed significantly to the enhancement of the mechanical properties.
Title:
Enhancement of plasticity in Ti-based bulk metallic glass
Authors:
Chang, HJ; Kim, WT; Kim, DH
Source:
PRICM 5: THE FIFTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-5, 475-479: 3409-3414 Part 1-5 2005 Book series title: MATERIALS SCIENCE FORUM
Abstract:
The effects of structural relaxation and partial crystallization on the mechanical property of the Ti40Zr29Cu9Ni8Be14 bulk metallic glass (BMG) have been investigated. The atomic structure of the as-cast Ti40Zr29Cu9Ni8Be14 metallic glass transforms into a more relaxed state at the temperature region of 452-585 K, below the crystallization onset temperature of 631 K. Stable icosahedral phase forms in the amorphous matrix by growth of the pre-existing nuclei in the amorphous matrix during first crystallization step. The compressive plastic strain of the as-cast Ti40Zr29Cu9Ni8Be14 BMG is 6.7%, and decreases when the structural relaxation occurs. However, the plastic strain increases when a few nanometer size icosahedral phase particles form in the amorphous matrix by the partial crystallization treatment.
Title:
Quasicrystal formation in the system Zr75-xTixCu25-yNiy
Authors:
Soubeyroux, JL; Pelletier, JM
Source:
PRICM 5: THE FIFTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-5, 475-479: 3563-3566 Part 1-5 2005 Book series title: MATERIALS SCIENCE FORUM
Abstract:
During the crystallization study of the bulk metallic glass Zr46.8Ti8.2Cu7.5Ni10Be27.5 (Vit4) we have demonstrated that the primary crystals appearing during isothermal annealing in the glass region, above T-g and before T-x, were of quasicrystalline nature and beryllium free. The formula of the quasicrystalline phase so obtained and determined by electron techniques (EDX and EELS) was Zr63Ti14.4Ni12.4Cu10.2. We have synthesized phases in the system Zr75-xTixCu25-yNiy by melt spinning and obtained either amorphous or quasicrystalline phases. For the amorphous phases, we have studied the crystallization by in-situ neutron diffraction and obtained quasicrystals as primary crystals. Neutron and X-ray diffraction, DSC studies are presented.
Title:
Microstructure and tensile properties of magnesium alloy containing quasicrystallines processed by equal-channel-angular-extrusion
Authors:
Zheng, MY; Qiao, XG; Xu, SW; Wu, K; Kamado, S; Kojima, Y
Source:
PRICM 5: THE FIFTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-5, 475-479: 469-472 Part 1-5 2005 Book series title: MATERIALS SCIENCE FORUM
Abstract:
Equal channel angular extrusion (ECAE) was performed on as-cast ZW1101 (Mg-11wt%Zn-0.9wt%Y) Mg alloy containing quasicrystallines. The grain size of alpha-Mg was effectively refined, and coarse eutectic quasicrystalline phases were broken and dispersed in the alloy by ECAE. The alloy processed by ECAE exhibited a good combination of high strength and high ductility, which is due to the grain refinement and fine dispersed quasicrystallines in the alloy.
Title:
Precipitation behavior and phase stability of intermetallic phases in Fe-Cr-W-Co ferritic alloys
Authors:
Yamamoto, K; Kimura, Y; Mishima, Y
Source:
PRICM 5: THE FIFTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-5, 475-479: 845-848 Part 1-5 2005 Book series title: MATERIALS SCIENCE FORUM
Abstract:
Precipitation behavior of intermetallic phases in ferrite matrix is investigated by transmission electron microscopy (TEM) in Fe-10Cr-1.4W-4.5Co (at%) alloys with and without 0.3at%Si. It is intended to provide basic information for the alloy design of ferritic heat resistant alloys strengthened by intermetallic compounds. In the alloy containing Si, icosahedral quasicrytalline phase (I-phase) is found to precipitate during aging at 873K. It is confirmed that selected area diffraction (SAD) patterns of the precipitates exhibit two-, three- and five-fold symmetry and have diffraction spots in the positions related to the golden section. In the Si-free alloy, the R-phase precipitates instead of I-phase at 873K, and the Laves phase precipitates in both alloys during aging at higher temperature, 973K. The Laves phase formed at 973K transforms to the I-phase in the Si-added alloy but to the R-phase in the Si-free alloy during subsequent aging at 873K. The factors in controlling! the phase stability of I-phase, R-phase and Laves phase precipitates in Fe-based alloys are discussed by the atomic size ratio and electron concentration factor (e/a).
Title:
Origin of the opalescence at the alpha-beta transition of quartz: Role of the incommensurate phase studied by synchrotron radiation
Authors:
Dolino, G; Bastie, P; Capelle, B; Chamard, V; Hartwig, J; Guzzo, PL
Source:
PHYSICAL REVIEW LETTERS, 94 (15): Art. No. 155701 APR 22 2005
Abstract:
The origin of the light scattering observed at the alpha-beta transition of quartz is still a subject of controversy. We present structural studies performed during the coexistence of the alpha and the intermediate incommensurate (inc) phases using simultaneously synchrotron x-ray diffraction and optical techniques. The small and large angle light scatterings are due, respectively, to the orientation domains of the 3q inc phase and to the alpha phase twins revealed by diffuse x-ray scattering. In the vicinity of the interphase boundary, the two light scattering regions, both with perturbed properties, form a complex multiscale structure.
Title:
Mechanical behavior of nanostructured aluminum alloys containing quasicrystalline phase
Authors:
Milman, YV
Source:
MATERIALS STRUCTURE & MICROMECHANICS OF FRACTURE IV, 482: 77-82 2005 Book series title: MATERIALS SCIENCE FORUM
Abstract:
Aluminum-based alloys containing quasicrystalline particles of 50 - 600 nm in diameter as a reinforcing phase were produced in the form of powder or ribbons by water atomization or melt spinning techniques, respectively. Rods were compacted from powders and some ribbons by severe plastic deformation without sintering. Structure and mechanical behavior of alloys are discussed.
Title:
Cooperative displacements of Ba2+ ions in the incommensurate structural phase of piezoelectric layer compound BaMnF4
Authors:
Yoshimura, M; Hidaka, M
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 74 (4): 1181-1189 APR 2005
Abstract:
Structural properties of BaMnF4 has been studied in the incommensurate phase (ICP) below about 250 K by X-ray diffraction. The ICP structure has a unit cell of Na-p x 2b(p) x 2c(p); N similar to 5, where a(p), b(p) and c(p) mean lattice constants at room-temperature commensurate phase (CP). The structure is determined at about 200 K in addition to that at room temperature, by using a four-circle X-ray diffractometer. The large distortion of each MnF6 octahedron, which jointly owns two F- ions along the a-axis and a F- ion along the c-axis with a neighbor octahedron, is roughly similar in the ICP phase with those in the CP phase. In the ICP phase, the MnF6 octahedra show different tilting-scheme between nearest-neighboring two-dimensional MnF6 Octahedra networks (folding screens), which are stacked along the b-axis and alternatively displaced each other with a glide vector of (0, 1/4, 1/4) in the unit cell of the ICP phase. There are two types of folding screens which are stacked along the bp-axis alternately, and the MnF6 octahedra in the nearest-neighbor folding screens are mainly characterized by the tilts around the a(0)-, b(0)-, and c(0)-axes and around only the c(0) axis, respectively, where a(0), b(0) and c(0) means primitive axes of the MnF6 octahedron. It is interpreted that the structural incommensuration in the ICP phase arises from cooperative displacements of Ba2+ ions, largely correlated with the localized modulation of MnF6 zigzag chains along the a(p)-axis in BaMnF4.
Title:
Magnetic structures and (x, T) magnetic phase diagram of ZrMn6Sn6-xGax
Authors:
Mazet, T; Isnard, O; Malaman, B
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (10): 1547-1560 MAR 16 2005
Abstract:
ZrMn6Sn6-xGax (0.25 <= x <= 3.50) compounds of HfFe6Ge6-type structure (P6/mmm) have been studied using powder neutron diffraction experiments in the 2-600 K temperature range. Below their magnetic ordering temperatures, these phases adopt commensurate easy-plane magnetic arrangements: + - - + antiferromagnetic AF2 (x <= 0.60) or ferromagnetic (x >= 0.70). At low temperature, the Ga-poor compounds (x <= 0.80) exhibit a transition to concentration-dependent incommensurate configurations. Upon increasing the Ga content, this incommensurate state evolves from helimagnetic to fan-like through arrangements we termed antifan-like. The Mn moment value is close to m(Mn) approximate to 2.0 mu(B) for the Ga-rich and Ga-poor compounds and reaches a maximum amplitude of m(Mn) approximate to 3.0 mu(B) in the (anti)fan-like structures of intermediate concentrations. A tentative (x, T) magnetic phase diagram is presented. The occurrence of Lifshitz point(s) is forecast for 0.60 < x < 0.70.
Title:
The local atomic quasierystal structure of the icosahedral Mg25Y11Zn64 alloy
Authors:
Bruhne, S; Uhrig, E; Gross, C; Assmus, W; Masadeh, AS; Billinge, SJL
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (10): 1561-1572 MAR 16 2005
Abstract:
A local and medium range atomic structure model for the face centred icosahedral (fci) Mg25Y11Zn64 alloy has been established in a sphere of r = 27 angstrom. The model was refined by least squares techniques using the atomic pair distribution (PDF) function obtained from synchrotron powder diffraction. Three hierarchies of the atomic arrangement can be found: (i) five types of local coordination polyhedra for the single atoms, four of which are of Frank-Kasper type. In turn, they (ii) form a three-shell (Bergman) cluster containing 104 atoms, which is condensed sharing its outer shell with its neighbouring clusters, and (iii) a cluster connecting scheme corresponding to a three-dimensional tiling leaving space for a few glue atoms. Inside adjacent clusters; Y-8 cubes are tilted with respect to each, other and thus allow for overall icosahedral symmetry. It is shown that the title compound is essentially isomorphic to its holmium analogue. Therefore, fci-Mg-Y-Zn can be seen as the representative structure type for the other rare earth analogues fci-Mg-Zn-RE (RE = Dy, Er, Ho, Tb) reported in the literature.
Title:
Pressure dependence of the magnetic structure of the itinerant electron magnet MnSi
Authors:
Fak, B; Sadykov, RA; Flouquet, J; Lapertot, G
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (10): 1635-1644 MAR 16 2005
Abstract:
Elastic neutron scattering measurements have been performed under hydrostatic pressure on single-crystalline MnSi. The scaling between the staggered moment and the transition temperature. of the helical magnetic structure does not follow predictions from spin-fluctuation theories. For pressures below P* approximate to 12-13 kbar, where the transition is second order, the length of the helix decreases with increasing temperature. Such a behaviour is not expected for a ferromagnetic Dzyaloshinsky-Moriya instability. With increasing pressure, the length of the helix also decreases, but there is a lock-in to an incommensurate temperature-independent value above p*, where the phase transition is first order.
Title:
Soft x-ray diffraction study of magnetic ordering in holmium
Authors:
Spencer, PD; Wilkins, SB; Hatton, PD; Brown, SD; Hase, TPA; Purton, JA; Fort, D
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (10): 1725-1733 MAR 16 2005
Abstract:
We have conducted the first single-crystal resonant soft x-ray diffraction study of the magnetic order in holmium at the Ho M-V edge. Both the (0, 0, tau) and (0, 0, tau) satellite reflections can be accessed at the MV edge. Energy scans through these reflections display very different line shapes. The behaviour of the integrated intensity, and wavevector modulation was similar to that observed in earlier neutron and resonant x-ray diffraction studies at the L edges, which showed that valid qualitative results can be obtained using the soft x-ray diffraction technique. The,sample absorption at the MV edge is. considerable, reducing the penetration depth to approximately 100 angstrom.
Title:
Application of synchrotron X-ray imaging to the study of directional solidification of aluminium-based alloys
Authors:
Schenk, T; Thi, HN; Gastaldi, J; Reinhart, G; Cristiglio, V; Mangelinck-Noel, N; Klein, H; Hartwig, J; Grushko, B; Billia, B; Baruchel, J
Source:
JOURNAL OF CRYSTAL GROWTH, 275 (1-2): 201-208 FEB 15 2005
Abstract:
Third generation synchrotron X-ray sources like ESRF (European Synchrotron Radiation Facility) have enhanced the capabilities of in situ and real-time X-ray imaging so that it is possible to follow the solid-liquid interface dynamics on metallic alloys with improved spatial and time resolution. In this paper, we focus on the solidification patterns of Al-based alloys, visualised by absorption and phase contrast radiography at ESRF. Two metallic systems were selected for this study: (i) Al-3.5 wt% Ni (with and without refiners) for the analysis of columnar growth and equiaxed growth, and the influence of the refiners on the columnar to equiaxed transition (CET), which is a key point in solidification processing, (ii) Al72.4Pd20.5Mn7.1 for the analysis of interface shape of growing quasicrystals (QCs). For both alloys, striking features were observed and a preliminary discussion is presented. Those results demonstrate the high potential of ESRF Synchrotron source for the characterisation of the dynamical formation of the solid microstructure in materials processing. (c) 2004 Elsevier B.V. All rights reserved.
Title:
Inclined net plane faceting observed at Czochralski growth of decagonal AlCoNi quasicrystals
Authors:
Gille, P; Meisterernst, G; Faber, N
Source:
JOURNAL OF CRYSTAL GROWTH, 275 (1-2): 224-231 FEB 15 2005
Abstract:
In the ternary Al-Co Ni system, decagonal quasicrystals occur that have proved thermodynamically stable. Large single crystals can be grown using rather conventional crystal growth techniques from incongruent melts. Decagonal quasicrystals combine two different types of order, periodicity along the 10-fold rotational axis and non-periodic order perpendicular to it, which makes them particularly interesting for solid state physics. Based upon X-ray structure analysis data obtained from AlCoNi single crystals, the question has been discussed whether or not inclined net planes exist that intersect periodic as well as non-periodic directions in these quasicrystals. Several inclined net planes were proposed and ranked with respect to their structure amplitudes. We have studied single crystal growth of large decagonal Al72Co9Ni19 quasicrystals using the Czochralski method from Al-rich melts. The crystal surfaces show a remarkable faceting. Exact angle measurements by optical goniometry revealed that the observed morphological faceting perfectly corresponds to some of the theoretically predicted inclined net planes. Besides the two different decagonal prisms {10000} and {10 (1) over bar 00} and the pinacoid {00001} we have found the inclined planes of two decagonal dipyramids {00 (1) over bar(1) over bar1} and {10 (1) over bar 02}. (c) 2004 Elsevier B.V. All rights reserved.
Title:
Influence of striction on soliton interaction in crystals
Authors:
Minyukov, SA; Levanyuk, AP; Cano, A
Source:
CRYSTALLOGRAPHY REPORTS, 50 (2): 262-269 MAR-APR 2005
Abstract:
Striction-mediated attraction of domain walls, solitons in incommensurate phases, and Abrikosov vortices in superconductors are considered. It is shown (a) that it is this type of attraction that can be responsible for a soliton-density jump in lock-in transitions and (b) that the strain-induced vortex interaction in superconductors with a high Ginzburg-Landau parameter is higher by one or two orders of magnitude than was assumed earlier. (c) 2005 Pleiades Publishing, Inc.
Title:
Low-frequency phonon dynamics, spin-lattice relaxation, and sound attenuation in crystals with incommensurate phases
Authors:
Minyukov, SA; Levanyuk, AP
Source:
CRYSTALLOGRAPHY REPORTS, 50 (2): 270-277 MAR-APR 2005
Abstract:
Specific features of the low-frequency response of a phason and an amplitudon in the region of small wave vectors are considered in incommensurate displacive-type phases at high and low temperatures. The corresponding anomalies of spin-lattice relaxation (SLR) rate and attenuation of the longitudinal sound in the vicinity of the normal phase transformation into an incommensurate phase are analyzed. It is shown that the divergence of the amplitudon response at small wave vectors and low frequencies induced by the interaction with phasons clearly manifests itself only at low temperatures T and that the pronounced amplitudon contribution proportional to T-3 to the SLR rate is associated with this divergence. The phason-response divergence at low temperatures leads to the frequency-independent contribution proportional to T to the SLR rate. (c) 2005 Pleiades Publishing, Inc.
Title:
Mechanical properties of the single-phase Ti-Zr-Ni quasicrystalline alloy at room-temperature
Authors:
Qiang, JB; Yu, ZW; Huang, HG; Nan, J; Chuang, D
Source:
ACTA PHYSICA SINICA, 54 (4): 1909-1913 APR 2005
Abstract:
At the composition of Ti40Zr40Ni20 a single-phase cylindrical quasicrystalline alloy, 3 mm in diameter and 15 mm in length, can be fabricated by a copper-mold casting method. Its quasicrystalline nature and structural homogeneity were confirmed by x-ray diffraction and transmission electron microscopy. According to compression and indentation tests at room-temperature, the as-cast Ti40Zr40Ni20 quasicrystalline rod has a hardness of 5.5 CrPa and a fracture strength of 542 Wa. In particular, the Young's modulus (similar to 43 GPa) of Ti40Zr40Ni20 quasicrystals is coinsiderably low while they possess a high Poisson's ratio (similar to 0.48). Under monaxial compression, the Ti40Zr40Ni20 quasicrystalline alloy exhibits a highly elastic deformation capability of 1.25%. The cleavage fracture morphologies indicate a brittle fracture mechanism.
Title:
Statistical approach in cluster analysis of two-dimensional quasicrystals
Authors:
Dabrowska, A; Kozakowski, B; Wolny, J
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 61: 350-357 Part 3 MAY 2005
Abstract:
An analytical formula for the structure factor of Penrose tiling in the cluster approach was derived and tested. Probability distributions obtained for each Penrose position allow the number of different atoms that can decorate the cluster to be found. Calculations were performed in the average-unit-cell approach for Gummelt's cluster of 33 atoms, divided into three independent groups of atoms, and a kite cluster of 17 atoms, divided into seven independent groups.
Title:
Isohedral simple tilings: binodal and by tiles with <= 16 faces
Authors:
Delgado-Friedrichs, O; O'Keeffe, M
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 61: 358-362 Part 3 MAY 2005
Abstract:
All isohedral simple tilings of 3D Euclidian space by tiles with <= 16 faces have been determined. There are no such tilings by polyhedra with less than 14 faces. For simple polyhedra with 14, 15 and 16 faces, there are respectively 10, 65 and 434 that fill space and a total of 23, 136 and 710 distinct tilings. The tilings by 14-face polyhedra are described in detail as are binodal ( vertex 2-transitive) isohedral simple tilings.

Update: 29-Apr-2005

Title:
Effects of alloying elements on the crystallization behavior of Zr-base amorphous alloys
Authors:
Zhang, GY; Zhang, H; Hu, ZQ; Lin, R; Zhang, HF
Source:
RARE METAL MATERIALS AND ENGINEERING, 34 (3): 389-392 MAR 2005
Abstract:
The atom structure models of two kinds of quasicrystal in Zr-base amorphous alloys were set up by using the conjugate structure model of quasicrystals. The effects of alloying elements on the crystallization behavior of Zr-base amorphous alloys were investigated by recursion method. The results show that two kinds of quasicrystal -Zr6Ni, Ni6Zr clusters are exist in Zr-base amorphous alloys, and alloying elements (Ag, Pt, Pd, Au) occupy the sites of Ni ( or Cu) in the quasicrystal phase, and that increase the interaction of neighbor atoms, which explains the fact of alloying elements (Ag, Pd, Pt, Au) promoting the stable growth of the quasicrystal phase.
Title:
Helicoidal ordering in iron perovskites
Authors:
Mostovoy, M
Source:
PHYSICAL REVIEW LETTERS, 94 (13): Art. No. 137205 APR 8 2005
Abstract:
We study the double exchange in transition metal oxides with itinerant and localized electrons. We show that the charge transfer energy Delta and the oxygen-oxygen hopping amplitude t(pp) have a strong effect on magnetic ordering: while for Delta > 0 the ground state is ferromagnetic, for negative Delta and large t(pp) the double exchange gives rise to an incommensurate helicoidal ordering of local spins, observed, e.g., in the iron perovskites SrFeO3 and CaFeO3. For negative Delta, the metal-insulator transition into a charge-ordered state has little effect on magnetic ordering. This explains the difference in magnetic and transport properties of ferrates and manganites.
Title:
Lamellar phase separation and dynamic competition in La0.23Ca0.77MnO3
Authors:
Tao, J; Niebieskikwiat, D; Salamon, MB; Zuo, JM
Source:
PHYSICAL REVIEW LETTERS, 94 (14): Art. No. 147206 APR 15 2005
Abstract:
We report the coexistence of lamellar charge-ordered (CO) and charge-disordered (CD) domains, and their dynamical behavior, in La0.23Ca0.77MnO3. Using high-resolution transmission electron microscopy (TEM), we show that below T(CD)similar to 170 K a CD-monoclinic phase forms within the established CO-orthorhombic matrix. The CD phase has a sheetlike morphology, perpendicular to the q vector of the CO superlattice (a axis of the Pnma structure). For temperatures between 64 and 130 K, both the TEM and resistivity experiments show a dynamic competition between the two phases: at constant T, the CD phase slowly advances over the CO one. This slow dynamics appears to be linked to the magnetic transitions occurring in this compound, suggesting important magnetoelastic effects.
Title:
On the microstructure of the charge density wave observed in La1-xCaxMnO3
Authors:
Loudon, JC; Cox, S; Mathur, ND; Midgley, PA
Source:
PHILOSOPHICAL MAGAZINE, 85 (10): 999-1015 APR 1 2005
Abstract:
We have used low temperature (90 K) transmission electron microscopy to investigate the 'charge ordering' modulation in the mixed valent manganite, La1-xCaxMnO3. It has been stated that Mn3+ and Mn4+ ions order at low temperature to produce a structural modulation composed of supercells whose size is an integer multiple of the unmodulated unit cell. Here, we use convergent beam electron diffraction to show that the periodicity of the modulation need not be an integer multiple of the undistorted cell, even on the smallest scales. We therefore suggest that this modulation is a charge density wave with a uniform periodicity. We show that the modulation wavevector lies close to the a* axis of the crystal but need not be exactly collinear. A typical grain of size 0.5 mu m in La0.48Ca0.52MnO3 had a wavevector which varied on a scale of tens of nanometres with an average of (q)=0.450a* and a standard deviation Delta q=0.004a* in its magnitude and Delta theta=0.56 degrees in its direction at 90 K. The magnitude of the wavevector in this composition fell by 20% as the temperature was increased from 90 K to room temperature. This change occurred by nucleation and growth. Although weak, the modulation was still present at room temperature, some 30 K above the 'charge ordering temperature'.
Title:
Helicoidal magnetic ordering in double exchange systems
Authors:
Mostovoy, M
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (11): S753-S769 Sp. Iss. SI MAR 23 2005
Abstract:
We show that double exchange does not always favour the ferromagnetic spin state. In transition metal oxides with strongly hybridized dp bands, the energy of conduction electrons can be minimized by an incommensurate helicoidal ordering of local spins. This explains the magnetic order observed in the iron perovskites SrFeO3 and CaFeO3. This homogeneous helicoidal state is stable against phase separation in a wide interval of electron concentrations.
Title:
High strength potential of aluminium nanocomposites reinforced with nonperiodical phases
Authors:
Nagy, J; Balog, M; Izdinsky, K; Simancik, F
Source:
INTERNATIONAL JOURNAL OF MATERIALS & PRODUCT TECHNOLOGY, 23 (1-2): 79-90 2005
Abstract:
Extrusion of rapidly solidified Al94V4Fe2 ribbons and Al94V4Fe2/Al powder mixtures was studied. TEM studies revealed microstructural heterogeneity in as-received ribbons containing alpha-Al, quasicrystalline, nanoscale amorphous and Al10V intermetallic phases. Bulk profiles containing different amounts of cryo-milled Al94V4Fe2 particles and Al powders were prepared via hot extrusion. Temperature was found to play the decisive role in the extrusion process. The lack of plasticity led to insufficient material flow during extrusion and was found responsible for the formation of macroscopic voids. Al94V4Fe2 extruded bars exhibited quite satisfactory properties in compression tests, however preliminary failed in tensile tests due to insufficient consolidation. The addition of 1 mu m Al powder into the Al94V4Fe2 particles yielded extrusions at lower loads or at lower temperatures, resulting in composite samples with Al matrix reinforced with nanoscale nonperiodic phases. This approach appeared quite promising for the overall design of applicable technological routes inducing the non-periodic structures into bulk profiles.
Title:
Instability of Al-Cu-Co single quasicrystals at low temperature
Authors:
Bogdanowicz, W
Source:
CRYSTAL RESEARCH AND TECHNOLOGY, 40 (4-5): 482-487 APR 2005
Abstract:
Decomposition process of the Al-Cu-Co single quasicrystals (falling apart into small pieces) after annealing at 100 degrees C for 20 It was studied by X-ray topography, high-resolution electron microscopy, X-ray diffractometry and optical microscopy. It was found that the decomposition of the single quasicrystals is preceded by the creation of a large number of antiphase microdomains and the deformation of the clusters occurs in the two-fold directions of [01 $(1) over bar $ 00] type. The decomposition begins with the propagation of cracks in the directions of [01 $(1) over bar $ 00] type.
Title:
Study of Al-Cu-Co single quasierystals by X-ray topography
Authors:
Bogdanowicz, W
Source:
CRYSTAL RESEARCH AND TECHNOLOGY, 40 (4-5): 488-491 APR 2005
Abstract:
Al-Cu-Co single quasicrystals were studied by the reflective X-ray topography. It was found that on the surfaces of the single quasicrystals, which were parallel to (00001) decagonal plane, the contrast associated with screw dislocation occurs. In the topograms taken from other surfaces of the single quasicrystals the bands of contrast appear. This contrast comes from the antiphase domains and depends on the conditions of the single quasicrystals growth process.
Title:
Phase equilibrium of the In2O3-TiO2-MO (M = Ca, Sr) systems and the structure of In6Ti6CaO22
Authors:
Li, ZF; Sun, JL; You, LP; Jiao, H; Li, GB; Jing, XP; Liao, FH; Lin, JH
Source:
CHEMISTRY OF MATERIALS, 17 (8): 2186-2192 APR 19 2005
Abstract:
The phase relationships of the In2O3-TiO2-CaO and In2O3-TiO2-SrO systems have been studied at 1350 degrees C in air. The In2O3-TiO2-CaO system contains a ternary compound Ti6In6CaO22 crystallizing in an incommensurate structure. The In2O3-TiO2-SrO system, on the other hand, is a simple ternary phase diagram without any ternary phases. The structure of Ti6In6CaO22 can be expressed by an incommensurate composite model that consists of two subsystems: the first subsystem, containing the InO6 octahedral layer and the Ti atoms in the TiOx layer, is rather rigid and can be reasonably represented with the averaged structure within the main lattice, a = 5.951(1) angstrom, b(1) = 3.422(1) angstrom, c = 6.352(1) angstrom, and beta = 108.32(1)degrees; the second subsystem, consisting of only the O2 atoms in the TiOx layer, can be expressed with a smaller subcell, a = 5.951(1) angstrom, b(2) = 2.464(1) angstrom, c = 6.352(1) angstrom, and beta = 108.32(1)degrees. The overall structure was refined in the superspace group C2/m(0 beta 0)s0, beta = q/b* = 0.389(1) by using the program, JANA2000. The modulation of the structure is prominent in the second subsystem. Ti6In6-CaO22 is a semiconductor with a band gap of about 3.5 eV and its electrical conductivity depends strongly on the oxygen partial pressure with the activation energy of about 1.88, 1.76, and 1.48 eV respectively in the air, oxygen, and argon atmosphere.
Title:
Strain relaxation and oxygen superstructure modulation in epitaxial Sr4Fe6O13 +/-delta films
Authors:
Santiso, J; Pardo, JA; Solis, C; Garcia, G; Figueras, A; Rossell, MD; Van Tendeloo, G
Source:
APPLIED PHYSICS LETTERS, 86 (13): Art. No. 132105 MAR 28 2005
Abstract:
The compressive strain induced in epitaxial Sr4Fe6O13+/-delta (SFO) films of different thicknesses grown on SrTiO3 substrates is partially released by the modulation of the incommensurate oxygen superstructure along the a-axis parallel to the substrate [q=alpha a(m)* superspace group Xmmm(alpha 00)0s0]. The modulation alpha value varies proportionally to the in-plane a-parameter in a continuous range from 0.41, for fully strained thin films, of about 20-30 nm, to 0.44 for partially-relaxed thicker films of about 280 nm. This mechanism is responsible for the observed slow relaxation of the cell structure upon the film thickness increase in comparison with an equilibrium misfit dislocation-mediated relaxation. (C) 2005 American Institute of Physics.

Update: 22-Apr-2005

Title:
Formation of quasicrystalline particles in an isothermally aged Al-10Mg-0.5 Ag (mass%) alloy
Authors:
Kubota, M; Nie, JF; Muddle, BC
Source:
MATERIALS TRANSACTIONS, 46 (2): 365-368 FEB 2005
Abstract:
The trace additions of Ag to binary Al-Mg alloys promote precipitation of a phase in the tinder-aged condition. The structures of the phase in an Al-10 Mg45 Ag (mass%) alloy have been characterised using transmission electron microscopy and electron rnicrodiffraction. An icosahedral quasicrystalline phase. which is identified by the electron microdiffraction patterns, has been found in the Al-10 Mg-0.5 Ag (mass%) alloy after solution treatment. water quenched and then aged during the time between 20 and 40 min. at 240 degrees C. The orientation relationship between the quasicrystalline phase and the alpha-Al matrix is as follows; i5 // < 011 >(alpha) and i3 // < 111 >(alpha). A uniform distribution of finer-scale (typically 20 nm). faceted precipitate particles was observed within the core of the grains, but the precipitates became coarser (60-80 mn) approaching the grain boundary precipitate-free zone.
Title:
Plastic deformation of Mg-Zn-Y icosahedral quasicrystals under confining pressure
Authors:
Saito, T; Miyaki, K; Kamimura, Y; Edagawa, K; Takeuchi, S
Source:
MATERIALS TRANSACTIONS, 46 (2): 369-371 FEB 2005
Abstract:
Deformation experiments of Mg-Zn-Y icosahedral quasicrystals under a hydrostatic confining pressure have been performed to investigate their deformation mechanism in a low temperature range. The temperature dependence of the yield stress has been Successfully measured, for the first time down to room temperature. An irregular behavior has been found in the temperature dependence: the yield stress increases rapidly with lowering temperature down to 373 K and it becomes almost constant in the temperature region lower than 373 K. The origin of such ail irregular temperature dependence is discussed in terms of possible transition between two different dislocation processes: glide and climb.
Title:
Deformation of delone dynamieal systems and pure point diffraction
Authors:
Baake, M; Lenz, D
Source:
JOURNAL OF FOURIER ANALYSIS AND APPLICATIONS, 11 (2): 125-150 2005
Abstract:
This article deals with certain dynamical systems built from point sets and, more generally, measures on locally compact Abelian groups. These systems arise in the study of quasicrystals and aperiodic order and important subclasses of them exhibit pure point diffraction spectra. We discuss the relevant framework and recall fundamental results and examples. In particular, we show that pure point diffraction is stable under "equivariant" local perturbations and discuss various examples, including deformed model sets. A key step in the proof of stability consists in transforming the problem into a question on factors of dynamical systems.

Update: 15-Apr-2005

Title:
Martensitic transformation and electrical properties of a Ni2.14Mn0.81Fe0.05Ga alloy in its different structural states
Authors:
Imashev, RN; Mulyukov, KY; Sharipov, IZ; Shavrov, VG; Koledov, VV
Source:
PHYSICS OF THE SOLID STATE, 47 (3): 556-559 MAR 2005
Abstract:
Phase transformations in a Ni2.14Mn0.81Fe0.05Ga alloy in different structural states are studied from the temperature dependences of its electrical resistivity. The dependences obtained indicate that, in the coarse-grained state, this alloy undergoes two structural phase transformations: intermartensitic modulation transformation and martensite-austenite transformation. In the nanocrystalline state, these transformations are absent. The recrystallization of a nanocrystalline sample at 773 K for 30 min results in the martensite-austenite transformation; however, the phase transformation related to a change in the martensite modulation period does not occur in this state. The resistivity is shown to depend on the structural state of the alloy. (c) 2005 Pleiades Publishing, Inc.
Title:
Superconductivity competing with the incommensurate antiferromagnetic insulating state in the organic conductor (MDT-TS)(AuI2)(0.441)
Authors:
Kawamoto, T; Bando, Y; Mori, T; Takimiya, K; Otsubo, T
Source:
PHYSICAL REVIEW B, 71 (5): Art. No. 052501 FEB 2005
Abstract:
The organic conductor (MDT-TS)(AuI2)(0.441) undergoes a metal-insulator transition at T-MI=50 K, where MDT-TS is 5H-2-(1,3-diselenol-2-ylidene)-1,3,4,6-tetrathiapentalene. The static magnetic susceptibility demonstrates an antiferromagnetic ordering below this temperature. Hydrostatic pressure suppresses this insulating state, and a superconductivity appears at T-c=3.2 K above 10.5 kbar. The phase diagram demonstrates a transition from the incommensurate antiferromagnetic insulating state to a superconducting state in an organic conductor with a noninteger carrier number.
Title:
Structure, stability, and electronic properties of the i-AlPdMn quasicrystalline surface
Authors:
Krajci, M; Hafner, J
Source:
PHYSICAL REVIEW B, 71 (5): Art. No. 054202 FEB 2005
Abstract:
The structure, stability, and electronic properties of a fivefold surface of an icosahedral (i) Al-Pd-Mn alloy have been investigated using ab initio density-functional methods. Structural models for a series of rational approximants to the quasicrystalline structure of bulk i-AlPdMn have been constructed using the cut-and-projection technique with triacontahedral acceptance domains in the six-dimensional hyperspace according to the Katz-Gratias-Boudard model. This leads to a real-space structure describable in terms of interpenetrating Mackay and Bergman clusters. A fivefold surface has been prepared by cleaving the bulk structure along a plane perpendicular to a fivefold axis. The position of the cleavage plane has been chosen such as to produce a surface layer with a high atomic density. The atomic structure of these surfaces can be described by a PI tiling by pentagons, thin rhombi, pentagonal stars, and a "boat"-in terms of a cut-and-projection model the decagonal acceptance domain of the PI tiling corresponds to the maximal cross section of the triacontahedra defining the three-dimensional quasicrystal. The vertices of the P1 tiling are occupied by Pd atoms surrounded by pentagonal motifs of Al atoms. For the ab initio calculations we have prepared slab models of the surface based on the 3/2 and 2/1 approximants and containing up to 357 atoms in the computational cell. The analysis of the surface charge density shows flat minima at the vertices of the P1 tiling and strong charge depletion in some of the pentagonal tiles ("surface vacancies"). Both observations are in agreement with scanning tunneling microscopy studies of these surfaces. Structural relaxations have been performed only for the 2/1 models with up to 205 atoms/cell. The calculations demonstrate that the skeleton of the PI tiling fixed by the transition-metal atoms represents a stable,surface termination, but considerable rearrangement of the Al atoms and large relaxations of the interlayer distances. The analysis of the surf ace electronic structure shows that the deep structure-induced pseudogap just above the Fermi level is filled up at the surface as a consequence of the structural disorder in the arrangement of the Al atoms at the surface and of a shift of both the Pd and Mn d band to lower binding energy. The d band shift at the surface is in good agreement with observations based on photoelectron and Auger spectroscopies.
Title:
Magnetic structure of beta-ErD2: Long-range and short-range order from powder neutron diffraction
Authors:
Vajda, P; Andre, G; Udovic, TJ; Erwin, RW; Huang, Q
Source:
PHYSICAL REVIEW B, 71 (5): Art. No. 054419 FEB 2005
Abstract:
Two parallel neutron powder diffraction investigations were performed on different specimens of ErD2 at the LLB (CEN, Saclay) and at NIST for the determination of its magnetic structure. It comprises, below T-N=2.23 K, two coexisting sinusoidally modulated antiferromagnetic (AF) configurations, M' and M '', with the respective incommensurate propagation vectors, k'=(0.275,0.275,0.750), together with its third harmonic 3k', and k ''=(0.120,0.120,0.750). Contrary to other heavy rare-earth dideuterides, no commensurate AF configuration could be detected down to 120 mK. On the other hand, similar to earlier observations on HoD2 and TbD2, magnetic short-range order (SRO) shows up near 1.5 K in ErD2 after the disappearance of certain M '' lines. This SRO seems to correlate with the hexagonal gamma-phase of the trideuteride and suggests an electronic phase separation with. memory effects.
Title:
Magnetic interactions in a single-band model for the cuprates and ruthenates
Authors:
Monthoux, P; Lonzarich, GG
Source:
PHYSICAL REVIEW B, 71 (5): Art. No. 054504 FEB 2005
Abstract:
We consider the mean-field theory of superconductivity in quasi-two-dimensions assuming that a single tight-binding energy band is dominant. The effective interaction between quasiparticles is assumed to be of magnetic origin and built out of the Lindhard function of the single band together with a molecular field parameter, which is determined self-consistently. The tight-binding hopping matrix elements are chosen to be appropriate for the d(xy) band of Sr2RuO4, which is believed to be responsible for spin-triplet p-wave superconductivity below 1.5 K. As the band filling varies, the Lindhard function and hence the magnetic correlations display a surprisingly rich behavior even for our chosen simple tight-binding band. In particular, the Lindhard function displays both high-wave-vector and low-wave-vector peaks, which lead, respectively, to incommensurate anti ferromagnetic and incommensurate ferromagnetic correlations. Near half filling the Fermi surface has strong high-wave-vector nesting features that produce dominant antiferromagnetic correlations. When sufficiently enhanced by the molecular field, these correlations lead to robust spin-singlet d-wave pairing. As the band filling is increased, the Fermi surface expands and touches the zone boundary at the Van Hove singularity point. In this case, ferromagnetic correlations are dominant and even when enhanced strongly, only lead to surprisingly weak p-wave pairing, with a maximum superconducting transition temperature T-c more than two orders of magnitude lower than for d-wave pairing near half filling for the chosen model parameters. This p-wave pairing depends on a number of rather subtle aspects of the electronic structure and magnetic interaction and its weakness can be understood as the result of a near cancellation of large effects. Our findings can account in a natural way for the difficulty of finding superconducting analogs of spin-triplet p-wave superfluidity in He-3 such as Sr2RuO4. With the help of a symmetry tran sformation, the simple chosen tight-binding band can also describe systems with less than a half-filled band with Fermi surfaces similar to those of the cuprates. Our results therefore suggest that the dramatically different superconducting properties of the cuprates and of strontium ruthenate may be qualitatively understood, and naturally so, within the same framework.
Title:
Shock, waves in complex binary solids: Cubic Laves crystals, quasicrystals, and amorphous solids
Authors:
Roth, J
Source:
PHYSICAL REVIEW B, 71 (6): Art. No. 064102 FEB 2005
Abstract:
Shock waves have been simulated by molecular dynamics in the cubic Laves phase C15, in related Frank-Kasper-type (AlCu)Li quasicrystals, and in an amorphous solid of the same composition and potential parameters. The goal of this study was to generate shock waves in periodic and aperiodic structures and to compare their behavior. The expectation was that new types of defects would show up in aperiodic materials. Three regimes are observed in the Laves phase: at low shock wave intensity the system reacts elastically, at high intensities it turns disordered. In the intermediate region the velocity of the elastic wave saturates and an additional plastic wave appears. Extended defects are created which form a network of walls of finite width. The crystallites in between are rotated by the shock wave. If the samples are quenched a polycrystalline phase is obtained. The size of the grains decreases with increasing shock wave intensity until complete fragmentation occurs in the third regime. The behavior of the quasicrystal models is similar, except that there is a continuous transition from a quasielastic behavior to the plastic regime. Ring processes are observed which break up into open paths when the shock wave energy grows. The transition to a complete destruction of the structure is continuous. In the amorphous solid a linear u(s)-u(p) relation is found over the whole range of piston velocities. Two regimes are present, with unsteady plastic waves at weak shock strengths and steady waves in the range coinciding with the upper regime in the ordered structures.
Title:
Electronic inhomogeneity and competing phases in electron-doped superconducting Pr0.88LaCe0.12CuO4-delta
Authors:
Dai, PC; Kang, HJ; Mook, HA; Matsuura, M; Lynn, JW; Kurita, Y; Komiya, S; Ando, Y
Source:
PHYSICAL REVIEW B, 71 (10): Art. No. 100502 MAR 2005
Abstract:
We use neutron scattering to demonstrate that electron-doped superconducting Pr0.88LaCe0.12CuO4-delta in the underdoped regime is electronically phase separated in the ground state, showing the coexistence of a superconducting phase with a three-dimensional antiferromagnetically ordered phase and a quasi-two-dimensional spin-density wave modulation. The Neel temperature of both antiferromagnetic phases decreases linearly with increasing superconducting transition temperature (T-c) and vanishes when optimal superconductivity is achieved. These results indicate that the electron-doped copper oxides are close to a quantum critical point, where the delicate energetic balance between different competing states leads to microscopic heterogeneity.
Title:
Quantum fluctuations and excitations in antiferromagnetic quasicrystals
Authors:
Wessel, S; Milat, I
Source:
PHYSICAL REVIEW B, 71 (10): Art. No. 104427 MAR 2005

Update: 6-Jan-2006

Title:
A new family of binary layered compounds of platinum with alkali metals (A = K, Rb, Cs)
Authors:
Karpov, A; Jansen, M
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 632 (1): 84-90 2006
Abstract:
By reacting platinum with alkali metals (A = K, Rb, Cs) a new family of binary alkali metal platinides has been synthesized and characterized by chemical analysis, X-ray powder diffraction, thermal analysis (DTA and DSC), and magnetic measurements. All three compounds exhibit similar XRD-patterns with strong reflections that can be indexed on the basis of a rhombohedral crystal system (KxPt: a = 2.6462(1), c = 17.123(1); RbxPt: a = 2.6415(1) angstrom, c = 17.871(1)angstrom; CsxPt: a = 2.6505(1) angstrom, c = 18.536(1) angstrom; x < 1/2). The a lattice constant is independent on the alkali metal used and of value close to the Pt-Pt distance in NaPt2 (2.645 angstrom). The c parameter increases monotonically with the growing atomic radius of the alkali metal. The average structure of the alloys consists of cubic close packed layers of platinum atoms with layers of disordered alkali metals in between. For all compounds besides the strong reflections small satellites are observed which cannot be indexed together with the rhombohedral peaks in any rational 3-dimensional lattice. However, these satellites can be indexed as incommensurate modulations within the ab plane (found propagation vectors k = (0.1011, 0.2506, 0) for CsxPt, and k = (0.0168, 0.2785, 0) for RbxPt).
Title:
Walk of a line defect in quasicrystals
Authors:
Mariano, PM
Source:
MECCANICA, 40 (4-6): 511-525 DEC 2005
Abstract:
Quasicrystalline alloys are quasiperiodic aggregates in which local atomic changes (phason activity) influence prominently the gross deformative behavior. The effects of these rearrangements on a line defect are analyzed here. Balances of standard and phason interactions are derived along the line together with the balance of actions driving eventually it the former are found to be covariant while the latter follows from a requirement of invariance with respect to the action of the group of isochoric diffeomorphisms. The results can be applied to the analysis of dislocations in quasicrystals.
Title:
Stability of the modulated structure of Baikal lazurite and its recrystallization at a temperature of 600 degrees C over a wide range of sulfur dioxide fugacities
Authors:
Tauson, VL; Sapozhnikov, AN
Source:
CRYSTALLOGRAPHY REPORTS, 50: S1-S9 Suppl. 1 2005
Abstract:
The stability of three-dimensional incommensurate modulation in cubic lazurite from the Baikal region is experimentally investigated at T = 600 degrees C. It is found that the X-ray photoelectron spectra of the annealed samples exhibit a peal, corresponding to sulfite and a split peak associated with the (Na,Ca)SO4 sulfate. It is assumed that the splitting is caused by the ordering of the complexes not involved in the framework. This assumption is confirmed by the presence of a similar split peak in the X-ray photoelectron spectra of triclinic lazurite. It is demonstrated that the initial modulation is retained at the fugacity f(SO2) = 8 X 10(-3) bar. The decisive factors responsible for the retention of the three-dimensional incommensurate modulation are the temperature and the fugacity of sulfur dioxide. The latter quantity should be close to the stability boundary of the basic lazurite structure. The growth and transformation mechanisms of the modulation formation are considered. (C) 2005 Pleiades Publishing, Inc.

Update: 31-Dec-2004

Title:
Electrical properties of a stable icosahedral quasicrystal Zn-Fe-Sc
Authors:
Motomura, S; Kashimoto, S; Maezawa, R; Ishimasa, T; Matsuo, S
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73 (11): 3111-3114 NOV 2004
Abstract:
The electrical resistivity of a recently discovered stable icosahedral quasicrystal Zn77Fe7SC16 was found to have a T-1/2 dependence in low temperature region between 2 and 16 K, while it increased gradually by 6.8% with the decrease in temperature from 270 to 2 K. The increase is considered to arise from the weak localization of conduction electrons. Negative magnetoresistance was found below 32 K. The T-1/2 dependence of the resistivity and the negative magnetoresistance are interpreted on the basis of the short range magnetic order inferred from the spin-glass behavior.

Update: 24-Dec-2004

Title:
Crystal structure and thermoelectric properties of the misfit-layered cobalt oxides
Authors:
Miyazaki, Y
Source:
SOLID STATE IONICS, 172 (1-4): 463-467 Sp. Iss. SI AUG 31 2004
Abstract:
On the basis of the crystal chemistry and electronic structure of gamma-NaxCoO2, we explored many cobalt-based oxide systems and encountered the compound "Ca3Co4O9". Through the detailed structure analyses, the cobalt oxide has been revealed to be a misfit-layered compound, which consists of two interpenetrating monoclinic subsystems. The first subsystem [CoO2] has a Cdl2-type triangular lattice while the second subsystem [Ca2CoO3] is built up from an ordered three-layered NaCl-type (RS) block. The structure formula can be expressed as [Ca2CoO3](p)CoO2, where p stands for the b-axis ratio, b(CoO2)/b(RS) - 0.62. A typical polycrystalline sample of the compound exhibits reasonable thermoelectric (TE) performance with thermopower S = 130 muV K-1, resistivity = 15 mOmega cm and thermal conductivity kappa = 1 W m(-1) K-1 at 300 K. The resulting figure-of-merit Z (S-2/rhokappa) = 1.1 x 10(-4) K-1 is comparable to that of polycrystalline samples of the gamma-phase, indicating that the present misfit cobalt oxide is a potential candidate for a thermoelectric material. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Rietveld analysis of composite crystal with nominal composition Sr8/7TiS2.84 prepared in reductive atmosphere
Authors:
Onoda, M; Saeki, M
Source:
SOLID STATE IONICS, 172 (1-4): 481-484 Sp. Iss. SI AUG 31 2004
Abstract:
The structure of the incommensurate composite crystal with composition Sr8/7TiS2.84 prepared in reductive atmosphere has been analyzed on the basis of the four-dimensional superspace-group approach using the powder X-ray diffraction data and the Rietveld analysis process. The crystal is composed of interpenetrating two parts, columns of face-shared TiS3 polyhedra and Sr rows packed among TiS3 Columns. The details of the structures Of Sr8/7TiS2.84 and Sr8/7TiS3 are compared, and the variation of the structure with the S content is discussed. (C) 2004 Elsevier B.V All rights reserved.
Title:
Mossbauer effect study of the decagonal quasicrystal Al70Co15Ni15
Authors:
Stadnik, ZM; Zhang, GW
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (41): 7303-7312 OCT 20 2004
Abstract:
We present a systematic 57 Fe Mossbauer effect study in the temperature range between 5.3 and 298.2 K and in an external magnetic field of 9.0 T of a high-quality stable decagonal quasicrystal Al70Co15Ni14.9Fe0.1. The iron atoms are shown to be located in two distinct classes of sites. The values of the principal component of the electric field gradient tensor and the asymmetry parameter at these sites are, respectively, -1.901(61) x 10(21) V m(-2), 0.96(12) and -3.927(52) x 10(21) V m(-2), 0.27(9). The average quadrupole splitting decreases with temperature as T-3/2. The vibrations of the Fe atoms are well described by a Debye model, with the Debye temperature of 546(9) K.
Title:
The particle size effect of the spin-density wave in cubic gamma-Fe precipitates in Cu
Authors:
Naono, T; Tsunoda, Y
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (43): 7723-7732 NOV 3 2004
Abstract:
It is common knowledge that the magnetic structure of fcc Fe (gamma-Fe) can be described by means of an incommensurate spin-density wave (SDW). Previous experimental data, however, were mostly obtained for gamma-FeCo alloy precipitates in Cu in order to avoid the complexity of the structural phase transition. Since Fe is a fundamental element, reliable data on the SDW state for pure gamma-Fe are highly desired. We present here neutron scattering data for the SDW in pure gamma-Fe precipitates in Cu and discuss the particle size effect of the SDW.
Title:
A single-crystal high-pressure x-ray diffraction study of decagonal Al-Co-Cu up to 19.1 GPa
Authors:
Krauss, G; Steurer, W
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (43): 7769-7777 NOV 3 2004
Abstract:
An in situ single-crystal high-pressure x-ray diffraction study of decagonal Al-Co-Cu up to 19.1 GPa has been performed using diamond anvil cells and synchrotron radiation. Quantitative reciprocal space reconstruction from image plate data was used for data analysis. No significant variations with pressure were observed in Bragg as well as diffuse scattering, indicating the high stability of the quasiperiodic structure in the investigated pressure range. The bulk modulus at zero pressure was determined from fitting a second-order Birch-Murnaghan equation of state as K-0 = 131(8) GPa. The influence of different crystal orientations on the accessible amount of reciprocal space data is discussed.
Title:
Crystal and magnetic structures of RCuSb2 (R = Dy, Ho) compounds
Authors:
Szytula, A; Kolenda, A; Oles, A
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 383 (1-2): 224-227 NOV 30 2004
Abstract:
Powder neutron diffraction measurements have been carried out on RCuSb2 (R = Dy and Ho) compounds at low temperatures. These compounds crystallize in a tetragonal ZrCuSi2-type structure and are antiferromagnets with the Neel temperatures equal to 6.4 K (R = Dy) and 4.5 K (R = Ho). At 1.5 K the magnetic order of DyCuSb2 can be described by the propagation vector k = (0, 0.119, 0.521). At the same temperature the magnetic order in HoCuSb2 is described by three propagation vectors: k(1) = (0, 0.465, 0.260), k(2) = (0, 0.408, 0.770) and k(3) = (0, 0, 0.519). With increasing temperature the structure described by k(1) disappears about 3.5 K while the two other structures described by k(2) and k(3) are stable up to the Neel temperature. The Dy and Ho magnetic moments form a sine-wave modulated structure in the basal plane. (C) 2004 Elsevier B.V All rights reserved.

Update: 21-Dec-2004

Title:
X-ray diffraction study of decagonal Al-Co-Ni as a function of composition
Authors:
Katrych, S; Steurer, W
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 219 (10): 606-613 2004
Abstract:
The evolution was studied of structural order/disorder phenomena across the wide stability field of the decagonal phase in the system Al-Co-Ni. Full single-crystal X-ray diffraction data sets were collected of 31 samples annealed at 900 degreesC. Based on reciprocal space reconstructions of the imaging-plate-scanner data, the variation in Bragg as well as in diffuse scattering is discussed in detail. The samples were also characterized metallographically, by powder X-ray diffraction, differential thermal analysis and energy-dispersive X-ray spectroscopy. The (quasi)lattice parameters vary smoothly over the stability range of decagonal Al71.5CO28.5-xNix (8 less than or equal to x less than or equal to 20). A smooth variation is also observed for the diffuse scattering related to the approximate to 8 A superstructure. These observations indicate a continuous ordering process at 900 degreesC from the basic Co-rich phase via the type II and type I superstructures to the basic Ni-rich phase.
Title:
Structural complexity in gallium under high pressure: Relation to alkali elements
Authors:
Degtyareva, O; McMahon, MI; Allan, DR; Nelmes, RJ
Source:
PHYSICAL REVIEW LETTERS, 93 (20): Art. No. 205502 NOV 12 2004
Abstract:
Ga-II, the stable phase of Ga between 2 and 10 GPa at room temperature, is shown to have a complex 104-atom orthorhombic structure. A new phase, Ga-V, is found between 10 and 14 GPa, with a rhombohedral hR6 structure. Ga-II has a modulated layer structure like those recently reported for Rb-III and Cs-III, with similar 8- and 10-atom a-b layers stacked along the c axis in the sequence 8-10-8-8-10-8-8-10-8-8-10-8. The cI16 structure of Li and Na can be understood as a stacking of very similar 8-atom layers. It is suggested that a Hume-Rothery mechanism contributes to the occurrence of these complex structures in such different metals.
Title:
Charge modulation, spin response, and dual Hofstadter butterfly in high-T-c cuprates
Authors:
Tesanovic, Z
Source:
PHYSICAL REVIEW LETTERS, 93 (21): Art. No. 217004 NOV 19 2004
Abstract:
The modulated density of states observed in recent STM experiments in underdoped cuprates is argued to be a manifestation of the charge-density wave of Cooper pairs (CPCDW). CPCDW formation is due to superconducting phase fluctuations enhanced by Mott-Hubbard correlations near half-filling. The physics behind the CPCDW is related to a Hofstadter problem in a dual superconductor. It is shown that CPCDW does not impact nodal fermions at the leading order. An experiment is proposed to probe coupling of the CPCDW to the spin carried by nodal quasiparticles.
Title:
Incommensurate magnetic ordering in Cu2Te2O5X2 (X = Cl,Br) studied by neutron diffraction
Authors:
Zaharko, O; Daoud-Aladine, A; Streule, S; Mesot, J; Brown, PJ; Berger, H
Source:
PHYSICAL REVIEW LETTERS, 93 (21): Art. No. 217206 NOV 19 2004
Abstract:
We present the results of the first neutron powder and single crystal diffraction studies of the coupled spin tetrahedra systems Cu2Te2O5X2 (X=Cl,Br). Incommensurate antiferromagnetic order with the propagation vectors k(Cl)approximate to[0.150,0.422,1/2], k(Br)approximate to[0.158,0.354,1/2] sets in below T-N=18 K for X=Cl and 11 K for X=Br. No simple collinear antiferromagnetic or ferromagnetic spin arrangements within Cu2+ tetrahedra fit these observations. Fitting the diffraction data to more complex but physically reasonable models with multiple helices leads to a moment of 0.67(1)mu(B)/Cu2+ at 1.5 K for the Cl compound. The reason for such a complex ground state may be geometrical frustration of the spins due to the intratetrahedral and intertetrahedral couplings having similar strengths. In neither compound has any evidence for a structural transition accompanying the magnetic ordering been found.

Update: 10-Dec-2004

Title:
mu SR investigation of the magnetic ordering in EuAs3
Authors:
Chatterji, T; Henggeler, W
Source:
SOLID STATE COMMUNICATIONS, 132 (9): 617-622 DEC 2004
Abstract:
We have investigated the magnetic ordering and the incommensurate-commensurate phase transition in EuAs3 by zero-field (ZF) and longitudinal-field muSR. In the commensurate phase, stable at temperatures below T-L= 10.3 K, the ZF muon signal exhibits oscillations corresponding to four muon precession frequencies the lowest of which behaves anomalously. The muon signal shows no oscillation but exponential decay in the incommensurate phase stable in temperature range from T-L approximate to 10.3 K up to T-N approximate to 11 K. The temperature dependence of the fitted relaxation rate shows divergence-like behaviour at the ordering temperature TN approximate to 11 K and also at the lock-in transition T-L approximate to 10.3 K. The results are in qualitative agreement with those previously obtained by neutron and X-ray magnetic scattering investigations except for the anomalous temperature dependence of the lowest frequency in the commensurate phase. We propose a model for this anomalous behaviour. (C) 2004 Elsevier Ltd. All rights reserved.
Title:
Mechanical spectroscopy of decagonal Al-Cu-Fe-Cr quasicrystalline coatings
Authors:
Fikar, J; Schaller, R; Baluc, N
Source:
PHILOSOPHICAL MAGAZINE, 84 (33): 3571-3584 NOV 21 2004
Abstract:
Mechanical spectroscopy measurements were performed on decagonal quasicrystalline Al-Cu-Fe-Cr coatings of three different thicknesses deposited on a mild steel substrate. The mechanical loss spectra indicate that the internal friction is mostly caused by the quasicrystalline coating and that the contributions of both the steel substrate and the interface are small. The shear modulus measured in torsion increases with temperature, while the Young's modulus measured in flexion behaves normally. This shear modulus anomaly is interpreted as being due to solid friction between cracked segments of the quasicrystalline coating. This phenomenon also explains the broad athermal maximum found to occur in isochronal internal friction measurements. A quantitative model successfully reproducing the observed behaviour has been developed. Finally, the reversible high-temperature exponential background was interpreted as being due to the onset of the brittle-to-ductile transition in the quasicrystalline coating. The measured activation enthalpy is similar to the value that was deduced from compression tests performed at high temperatures on icosahedral Al-Cu-Fe bulk material.
Title:
Quasicrystal formation in mechanically alloyed Zr-Ti-Nb-Cu-Ni-Al glassy powders
Authors:
Scudino, S; Mickel, C; Schultz, L; Eckert, J; Yang, XY; Sordelet, DJ
Source:
APPLIED PHYSICS LETTERS, 85 (19): 4349-4351 NOV 8 2004
Abstract:
Different from the glassy Zr62Ti7.07Nb2.21Cu12.28Ni9.81Al6.62 melt-spun ribbon that forms a quasicrystalline phase upon devitrification, the corresponding alloy produced by mechanical alloying of elemental powder mixtures does not clearly show quasicrystal formation. However, the addition of an appropriate amount of elemental zirconium to the mechanically alloyed powder changes the crystallization behavior inducing the formation of an icosahedral quasicrystalline phase as the first crystallization product. This indicates that for this multicomponent metallic glass quasicrystal formation in the mechanically alloyed powder is crucially linked to the composition rather than to the question whether there is a special quenched-in short-range order. (C) 2004 American Institute of Physics.

Update: 3-Dec-2004

Title:
Section method for projected structures of icosahedral quasicrystals and its application to electron-microscopy-image and surface analyses
Authors:
Yamamoto, A
Source:
PHYSICAL REVIEW LETTERS, 93 (19): Art. No. 195505 NOV 5 2004
Abstract:
A section method for projected structures of icosahedral quasicrystals (IQCs) is given. A structure projected along a specified direction can be calculated directly from a six-dimensional periodic structure by this method. The method concludes that all peaks in high-resolution transmission electron-microscopy images of an IQC have different projected atom densities in general and leads to different chemical compositions and densities for all atom layers, suggesting that all surfaces of an IQC are different. Its application to icosahedral Al-Pd-Mn quasicrystals is shown.
Title:
Relationship between charge stripe order and structural phase transitions in La1.875Ba0.125-xSrxCuO4
Authors:
Kimura, H; Noda, Y; Goka, H; Fujita, M; Yamada, K; Mizumaki, M; Ikeda, N; Ohsumi, H
Source:
PHYSICAL REVIEW B, 70 (13): Art. No. 134512 OCT 2004
Abstract:
The nature of charge stripe order and its relationship with structural phase transitions were studied using synchrotron x-ray diffraction in La1.875Ba0.125-xSrxCuO4 (0.05less than or equal toxless than or equal to0.10). For x=0.05, as temperature increased, incommensurate superlattice peaks associated with the charge order disappeared just at the structural phase transition temperature, T-d2. However, for x=0.075 and 0.09, the superlattice peaks still existed as a short range correlation even above T-d2, indicating a precursor of charge ordering. Furthermore, temperature dependences of the superlattice peak intensity, correlation length, and incommensurability for x=0.05 are different from those for x=0.075 and 0.09. These results suggest that the transition process into the charge stripe order strongly correlates with the order of the structural phase transitions. A quantitative comparison of the structure factor associated with the charge order have been also made for all the samples.
Title:
Band-selective modification of the magnetic fluctuations in Sr2RuO4: A study of substitution effects
Authors:
Kikugawa, N; Bergemann, C; Mackenzie, AP; Maeno, Y
Source:
PHYSICAL REVIEW B, 70 (13): Art. No. 134520 OCT 2004
Abstract:
We report a study of magnetic, thermal, and transport properties of La3+ substituted Sr2RuO4, performed in order to investigate the effects of additional electron doping in this correlated metal. A gradual enhancement of the electronic part of specific heat and a more drastic increase of the static magnetic susceptibility were observed in Sr2-yLayRuO4 with increasing y. Furthermore, the quasi-two-dimensional Fermi-liquid behavior seen in pure Sr2RuO4 breaks down near the critical concentration y(c)similar to0.20. Combined with a realistic tight-binding model with rigid-band shift of Fermi level, the enhancement of the density of states can be ascribed to the elevation of the Fermi energy toward a van Hove singularity of the thermodynamically dominant gamma Fermi-surface sheet. On approaching the van Hove singularity, the effective nesting vector of the gamma band shrinks and further enhances the susceptibility near the wave vector qsimilar to0. We attribute the non-Fermi-liquid behavior to two-dimensional ferromagnetic fluctuations with short range correlations at the van Hove singularity. The observed behavior is in sharp contrast to that of Ti4+ substitution in Sr2RuO4 which enhances antiferromagnetic fluctuations and subsequently induces incommensurate magnetic ordering associated with the nesting between the other Fermi-surface sheets (alpha and beta). We thus establish that substitution of appropriate chemical dopants can band selectively modify the spin-fluctuation spectrum in the spin-triplet superconductor Sr2RuO4.
Title:
Thermoelectric properties of Al82.6-xRe17.4Six (7 <= x <= 12) 1/1-cubic approximants
Authors:
Takeuchi, T; Otagiri, T; Sakagami, H; Kondo, T; Mizutani, U; Sato, H
Source:
PHYSICAL REVIEW B, 70 (14): Art. No. 144202 OCT 2004
Abstract:
The thermoelectric power S(T) and thermal conductivity kappa(T) were systematically studied for a series of Al82.6-xRe17.4Six (7less than or equal toxless than or equal to12) 1/1-cubic approximants. We found that S(T) of these approximants is characterized by large magnitude, sign reversal with varying composition, and nonlinear temperature dependence, all of which are also known as characteristics of the corresponding quasicrystals. The calculated S(T) on the basis of the Boltzmann transport formula with accurately determined electronic structure showed extremely good agreement with the measured ones not only in their magnitude but also in the temperature and composition dependence. These results strongly indicate that these characteristic behaviors in S(T) of the approximants and the corresponding quasicrystals are brought about by their characteristic electronic structure, i.e., the presence of a pseudogap across the Fermi level.
Title:
Application of renormalization and convolution methods to the Kubo-Greenwood formula in multidimensional Fibonacci systems
Authors:
Sanchez, V; Wang, CM
Source:
PHYSICAL REVIEW B, 70 (14): Art. No. 144207 OCT 2004
Abstract:
Based on the Kubo formalism, electronic transport in macroscopic quasiperiodic systems is studied by means of an efficient renormalization method, and the convolution technique is used in the analysis of two- and three-dimensional lattices. For the bond problem, we found a transparent state located at a center of self-similarity and its ac conductivity is qualitatively different from that observed in mixing Fibonacci chains. The conductance spectra of multidimensional systems exhibit a quantized behavior when the electric field is applied along a periodically arranged atomic direction, and it becomes a devil's stair if the perpendicular subspace of the system is quasiperiodic. Furthermore, the dc conductance maintains a constant value for small imaginary parts (eta) of the energy and decays when eta>eta(c), where eta(c) is proportional to the inverse of the system length. Finally, the spectrally averaged conductance shows a power-law decay as the system length grows, neither constant as in periodic systems nor exponential decays occurred in randomly disordered lattices, revealing the critical localization nature of the eigenstates in quasicrystals.
Title:
Incommensurate charge stripe ordering in La2-xSrxNiO4 for x=(0.33,0.30,0.275)
Authors:
Ghazi, ME; Spencer, PD; Wilkins, SB; Hatton, PD; Mannix, D; Prabhakaran, D; Boothroyd, AT; Cheong, SW
Source:
PHYSICAL REVIEW B, 70 (14): Art. No. 144507 OCT 2004
Abstract:
In this paper we report studies of the charge stripe ordering using high resolution x-ray scattering in the nickelate system La2-xSrxNiO4 with doping levels of x=0.33, x=0.30, and x=0.275. The charge stripes for all doping levels were found to be two dimensional in nature with a high degree of correlation in the a-b plane. The in-plane inverse correlation length in the lower doped systems was greater than that in the x=0.33 system and is greatest for x=0.275, consistent with the stripes becoming less correlated as the doping level is decreased from x=0.33. However, the charge ordering in the x=0.33 system was observed to be more two dimensional in nature with a greater inverse correlation length between planes. The interaction between the lattice and charge order was observed to stabilize the charge ordering, even in the absence of spin ordering. In the x=0.30 and x=0.275 systems no long-range charge order could exist without the presence of the magnetic order. In both systems the charge stripes were incommensurate and on heating the incommensurability increased towards the stable epsilon=0.33 value as the stripes gained thermal energy to overcome the Coulombic repulsion. In all these systems the integrated intensity of the stripe reflections showed a clear difference in behavior from previous neutron studies with an initial increase in the integrated intensity as the temperature was increased, which was not found in the neutron studies.
Title:
Neutron scattering study of charge fluctuations and spin fluctuations in optimally doped YBa2Cu3O6.95
Authors:
Pintschovius, L; Endoh, Y; Reznik, D; Hiraka, H; Tranquada, J; Reichardt, W; Bourges, P; Sidis, Y; Uchiyama, H; Masui, T; Tajima, S
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 412-14: 70-75 Part 1 OCT 2004
Abstract:
Inelastic neutron scattering investigations on optimally doped YBCO revealed a very pronounced temperature dependence of the Cu-O in-plane bond-stretching vibrations along the (0 1 0)-direction: a downward shift of spectral weight with decreasing temperature by at least 10 meV in a narrow range of wave vectors halfway to the zone boundary. The temperature evolution starts around 200 K, well above the superconducting transition temperature. This phonon anomaly provides strong evidence for large electron-phonon coupling. It also indicates an incipient charge density wave instability within the CuO2 planes reminiscent of dynamical charge stripes. The magnetic fluctuations have been investigated in great detail on the same sample. Incommensurate spin fluctuations have been observed for energies both below and above the energy of the resonance peak at E = 41 meV. However, the dispersive nature of these fluctuations as well as their apparent isotropy in the basal plane speak against an interpretation of the spin fluctuation spectrum in the framework of the classical stripe phase picture. (C) 2004 Elsevier B.V. All rights reserved.
Title:
STM/STS observations of Pb-doped Bi-2212 single crystals
Authors:
Sugimoto, A; Kashiwaya, S; Eisaki, H; Oka, K; Tuchiura, H; Tanaka, Y
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 412-14: 270-274 Part 1 OCT 2004
Abstract:
The surface states of Bi2-xPbxSr2CaCu2O8+y (Pb-Bi-2212, x = 0.6) single crystals are investigated by scanning tunneling microscopy/spectroscopy in order to clarify the origin of inhomogeneous superconducting states. The topography obtained at a cleaved surface of Pb-Bi-2212 showed the coexistence of two (modulated and non-modulated) phases with domain structure of several tens of nanometers. The spatial distribution of gap amplitude observed on a modulated region showed the lack of the correlation between the gap distribution and the modulation structure. On the other hand, the weak correlation detected between the gap amplitude and bright spots on the topography obtained at 2 V bias implies the non-negligible influence of the local atomic distortion on the superconductivity. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Microstructure and strength of quasicrystal containing extruded Mg-Zn-Y alloys for elevated temperature application
Authors:
Singh, A; Watanabe, M; Kato, A; Tsai, AP
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 385 (1-2): 382-396 NOV 15 2004
Abstract:
Microstructural studies have been made on alloys Mg95Zn4.2Y0.8 and Mg92.5Zn6.5Y containing icosahedral quasicrystalline phase extruded at two different temperatures of 523 K and 673 K and correlated to room temperature and higher temperature tensile strength. Icosahedral phase occur-red as particles about half micron size at grain boundaries and as nano-sized precipitates in the matrix. Solutionizing at 673 K (1 h) was employed followed by annealing at 473 K for finer precipitation in the matrix. Solutionizing produced a fine precipitation of a ternary phase tau(1) in the matrix of the Mg95Zn4.2Y0.8 alloy, replaced by icosahedral precipitates on annealing. The Mg92.5Zn6.5Y alloy containing larger volume fraction of icosahedral phase showed higher strength. Solutionizing produced a composite of icosahedral and a H-Mg25Zn58Y17 hexagonal phase composite. Yield stresses of over 250 MPa at room temperature (elongation 15-20%) and 150 MPa at 473 K (UTS 240 MPa, elongation 40%) were obtained upon post extrusion annealing. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Synchrotron X-ray diffraction studies of the incommensurate phase of a spin-Peierls system CuGeO3 in strong magnetic fields
Authors:
Narumi, Y; Katsumata, K; Tabata, Y; Kimura, S; Tanaka, Y; Nakamura, T; Shimomura, S; Matsuda, M; Harada, I; Nishiyama, Y; Ishikawa, T; Kitamura, H; Hara, T; Tanaka, T; Tamasaku, K; Yabashi, M; Goto, S; Ohashi, H; Takeshita, K; Ohata, T; Matsushita, T; Bizen, T
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73 (10): 2650-2653 OCT 2004
Abstract:
Synchrotron X-ray diffraction measurements on a spin-Peierls material CuGeO3 in applied magnetic fields, H, up to 15 T are made. We find that the temperature, T, dependence of the incommensurate Bragg peak at a lower H is quite different from that at a higher H. At sufficiently high fields, we find that the lattice incommensurability, deltal, is almost independent of T, while at H slightly above the critical field = 12.25 T for the commensurate to incommensurate transition, deltal decreases with increasing T. We interpret that this finding is due to a stabilization of the incommensurate state by a strong magnetic field which suppresses thermal fluctuations.
Title:
Investigation of the surface terminations of icosahedral AlPdMn quasicrystal based on a modified non-spherical model
Authors:
Yu, FM; Zou, HM; Wang, JB; Wang, RH
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (39): 6821-6834 OCT 6 2004
Abstract:
The atomic positions are obtained from a modified non-spherical model of icosahedral AlPdMn quasicrystal (Fang et al 2003 J. Phys.: Condens. Matter 15 4947) by the cut method. The four-shell pseudo-Mackay clusters (PMCs) were searched for in a box of 400 Angstrom x 400 Angstrom x 400 Angstrom. The results show that the number of atoms in the fourth shell, an icosidodecahedron, of the pseudo-Mackay cluster can vary from 15 to 30 because of the cluster overlap, and about 99.96% of the total atoms are included in such incomplete pseudo-Mackay clusters. The characteristics of the atom distribution in the planes perpendicular to a fivefold axis indicate that the planes, which are 1.56 Angstrom apart from their neighbouring planes, are expected to be the terminal surfaces. If one such a plane and its closest neighbouring plane, between which the spacing is 0.48 Angstrom, are considered as a thin layer or a corrugated surface, these layers are also the layers with the maximum density. The pair of corrugated surfaces that are 1.56 Angstrom apart have almost identical chemical composition. These planes form terraces that follow the rule of the Fibonacci sequence with two step heights, 6.60 and 4.08 Angstrom. On the corrugated surfaces perpendicular to a fivefold axis the pentagonal holes arise from the interspaces of adjacent incomplete PMCs. For the atomic planes normal to a twofold axis, the planes with spacing of 1.48 Angstrom from their adjacent planes might be expected to be the terminal surfaces, which form terraces with step heights of 6.28 and 3.88 Angstrom following the rule of the Fibonacci sequence. For the atomic planes normal to a threefold axis, the planes with spacing of 0.86 Angstrom from their adjacent planes might be expected to be the terminal surfaces. No similar results were found for the atomic layers perpendicular to a pseudo-twofold axis.

Update: 27-Nov-2004

Title:
Orthorhombic epsilon-phases and transitional structures in Al-Pd-(Fe)
Authors:
Balanetskyy, S; Grushko, B; Velikanova, TY
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 219 (9): 548-553 2004
Abstract:
The results of an investigation of the structures formed in the range of about Al73Pd27 to Al76Pd14Fe10 by electron diffraction and high-resolution transmission microscopy are reported. The orthorhombic epsilon(6), epsilon(16), epsilon(22) and epsilon(28) phases were observed in specific compositional sub-ranges. Their lattice parameters aapproximate to2.34 and bapproximate to1.62 nm are essentially the same while the c parameters are approximate to1.23, 3.24, 4.49 and 5.70 nm, respectively. Apart from these regular structures, also structures aperiodic along the c-direction are revealed at intermediate compositions. Thus, inside the wide epsilon-phase range only slight continuous variations of the orthorhombic a and b cell parameters are accompanied by complicated modulations of the c cell parameter.
Title:
Monte Carlo simulation of Ising model on decagonal covering structure
Authors:
Ma, HH; Fu, XJ
Source:
SOLID STATE COMMUNICATIONS, 132 (6): 355-359 NOV 2004
Abstract:
We study the Ising model on a two-dimensional quasilattice developed from the decagonal covering structure. The periodic boundary conditions are applied to a patch of rhombus-like covering pattern. By means of the Monte Carlo simulation and the finite-size scaling analysis the critical temperature is estimated as 2.317 +/- 0.002. Two critical exponents are obtained being 1/v = 0.992 +/- 0.003 and eta = 0.247 +/- 0.002, which are close to the values of the two-dimensional regular lattices as well as the Penrose tilings. (C) 2004 Elsevier Ltd. All rights reserved.
Title:
Insights into oxygen-cation bonding in fresnoite-type structures from OK- and Ti L-23-electron energy-loss spectra and ab initio calculations of the electronic structure
Authors:
van Aken, PA; Hoche, T; Heyroth, F; Keding, R; Uecker, R
Source:
PHYSICS AND CHEMISTRY OF MINERALS, 31 (8): 543-552 OCT 2004
Abstract:
O K- and Ti L-23-core-loss spectra of fresnoite Ba2TiSi2O8 (BTS) and Sr2TiSi2O8 (STS), which is isotypic to BTS, have been measured by electron energy-loss spectroscopy (EELS). The energy-loss near-edge structures (ELNES) of the O K edge have been identified on the basis of theoretical simulations and interpretations of the X-ray absorption near-edge structures (XANES), which have been modelled in the framework of self-consistent full multiple-scattering (FMS) theory using FEFF8. Herewith, the K-absorption spectra of oxygen mu(E) and the local partial electron density of states (DOS) of all atoms have been calculated. For BTS, the observed spectral features in the O K-edge spectra are interpreted in terms of mixing between the central O p and neighbouring Ba 5d and 4f, Si 3p and 3d, and Ti 3d orbitals. The observed differences in the O K-edge spectra for STS and BTS can mainly be attributed to three properties: (1) The lack of high local partial Sr unoccupied DOS with 4f symmetry near the Fermi level compared to the high Ba 4f unoccupied DOS results in differences of overlapping O 2p cation orbitals. (2) The differences in the ionic radii of Sr and Ba result in a larger unit cell for BTS and, thus, in larger oxygen-cation bonding distances. (3) In comparison to STS, the strength of the incommensurate 2-D structural modulation is significantly weaker in BTS, i.e. distortions of coordination polyhedra occur to a much lesser extent. All these effects alter the oxygen-cation hybridization and, hence, result in a variation of the O 1s --> p transition and consequently of the O K-edge spectral shape. The observed peak broadening in Ti L-23 ELNES of STS compared to BTS is correlated with strong displacive modulations hosted in STS.
Title:
Quasicrystals as cluster aggregates
Authors:
Abe, E; Yan, YF; Pennycook, SJ
Source:
NATURE MATERIALS, 3 (11): 759-767 NOV 2004
Abstract:
Quasicrystals are solids that exhibit symmetries long thought forbidden in nature. Since their discovery in a rapidly solidified Al-Mn alloy in 1984, the central issue in the field has been to understand why they form. Are they energetically stable compounds or stabilized by entropy? In recent years, major strides have been made in determining atomic structure, largely by direct imaging using advanced electron microscopy. One system is now known to be energetically stabilized, and quasicrystals are therefore firmly established as a new physical state of matter. They represent a unique packing of atomic clusters some tens of atoms in size, with substantial localized fluctuations, referred to as phasons. Understanding phasons may in future allow their unique macroscopic properties to be tailored for useful materials applications.
Title:
On three-dimensional elastic problems of one-dimensional hexagonal quasicrystal bodies
Authors:
Chen, WQ; Ma, YL; Ding, HJ
Source:
MECHANICS RESEARCH COMMUNICATIONS, 31 (6): 633-641 NOV-DEC 2004
Abstract:
Based on rigorous operator theory, a general solution of the three-dimensional elasticity equations of equilibrium for 1D hexagonal quasicrystals is obtained. The solution is expressed in terms of four quasiharmonic functions, which is very simple and useful. The point phonon (phason) force solution of an infinite ID hexagonal quasicrystal body is derived, all in terms of elementary functions. They can play an important role in numerical simulations such as boundary element method. (C) 2004 Elsevier Ltd. All rights reserved.
Title:
Occurrence of Kondo-like behavior in electrical-conductivity of Al70Pd20+xMn10-x (x=0,1 and 2) icosahedral quasicrystals
Authors:
Jaiswal, A; Rawat, R; Lalla, NP
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 344 (3): 135-147 OCT 1 2004
Abstract:
Zero-field and in-field (at 8T) conductivity vs temperature (sigma-T), magneto-resistance (Deltarho/rho), magnetization vs temperature (M-T) and magnetization vs field (M-H) of unannealed Al70Pd20Mn10 and annealed Al70Pd20Mn10, Al70Pd21Mn9 and Al70Pd22Mn8 quasicrystalline alloys have been studied in the temperature range of 1.4-300 K. Room temperature resistivity and the low-temperature magneto-resistance show a correlation with the corresponding magnetization. The sigma-T for all the studied samples shows a pair of minima and maxima. The sigma-T maxima show a correlation with the total magnetization. The analysis shows that sigma-T is dominated by weak-localization effects. The minima are arising due to competing inelastic scattering times tau(i) (e-ph scattering in the dirty metallic limit, tau(i) proportional to T-2) and the Kondo-type spin-flip scattering time tau(sf) whereas the maxima has been attributed to 'Kondo-maxima', occurring due to maxima in the spin-flip rate tau(sf)(-1). The magneto-resistance of these samples shows a changeover from negative to positive where the negative component shows a correlation with the magnetization of the sample. The values of parameters derived from refinement give spin-flip scattering fields, which are found to be correlated with the total sample magnetization. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Synthesis of nanocrystalline/quasicrystalline Mg-32(Al,Zn)(49) by melt spinning and mechanical milling
Authors:
Mukhopadhyay, NK; Bhatt, J; Pramanick, AK; Murty, BS; Paufler, P
Source:
JOURNAL OF MATERIALS SCIENCE, 39 (16-17): 5155-5159 AUG-SEP 2004
Abstract:
In the present investigation we have made an attempt to synthesize T-Mg-32(Al,Zn)(49) Frank Kasper phase and investigate the mechanical properties of the T-Phase in micro and nano scale. Single T-Phase (bcc, a = 1.42 nm) has been prepared by conventional casting with a proper combination of flux in order to avoid the loss of magnesium from the melt. Chemical analysis by energy dispersive X-ray microanalysis system attached to scanning electron microscope has confirmed the desired composition for T-phase. The as-cast material was then rapidly solidified by melt spinning and mechanically milled using a high-energy ball mill. The samples were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction techniques. The rapidly solidified foils showed the presence of mostly nanoquasicrystalline phases coexisting with a minute amount of crystalline phases in the thin region where the cooling rate is expected to be high. The dark field imaging in electron microscopy clearly confirms the existence of nano phases. Mechanically milled powder exhibited the evolution of nanophases at higher milling time. Microhardness measurement at low load was carried out in both the as-cast and nanophase materials in order to understand the influence of nanophases on the mode of deformation and cracking at low load. (C) 2004 Kluwer Academic Publishers.
Title:
Structure and mechanical properties of mechanically alloyed Al/Al-Cu-Fe composites
Authors:
Kaloshkin, SD; Tcherdyntsev, VV; Laptev, AI; Stepashkin, AA; Afonina, EA; Pomadchik, AL; Bugakov, VI
Source:
JOURNAL OF MATERIALS SCIENCE, 39 (16-17): 5399-5402 AUG-SEP 2004
Abstract:
Quasicrystalline (QC) powder was prepared by mechanical alloying and subsequent annealing of Al65Cu23Fe12 composition. Obtained quasicrystals were milled together with pure aluminium in the ratios of Al-20 wt% QC and Al-10 wt% QC. A hot consolidation of samples was performed under pressure of 4.5 GPa at elevated temperatures. X-ray diffraction study of the as-consolidated samples shows that the quasicrystalline phase remained in the samples if consolidation temperature was lower than 500degreesC. Consolidation at higher temperatures results in disappearing of the QC and formation of crystalline phases, such as Al2Cu and Al7Cu2Fe by reaction between QC and aluminium matrix. SEM study of microstructure of the composite alloys shows an absence of open porosity in the consolidated bulk samples. Besides rather large particles of reinforcing phase of about 20 mum there are also very small particles of less than 1 mum. The uniformity of particles distribution in the matrix increases with increase in the milling duration. Microhadrness measurements and compression tests were performed, an effect of the treatment parameters on the compressive strength was studied. (C) 2004 Kluwer Academic Publishers.
Title:
Formation of quasicrystals in ball-milled amorphous Zr-Ti-Nb-Cu-Ni-Al alloys with different Nb content
Authors:
Scudino, S; Kuhn, U; Schultz, L; Breitzke, H; Luders, K; Eckert, J
Source:
JOURNAL OF MATERIALS SCIENCE, 39 (16-17): 5483-5486 AUG-SEP 2004
Abstract:
In order to investigate the effect of the preparation technique on quasicrystal formation, amorphous (Zr0.585Ti0.082Cu0.142Ni0.114Al0.077)(100-x)Nb-x alloys with x = 2.5 and 5 at.% were produced by melt spinning and by ball milling of crystalline intermetallic compounds. The calorimetric and microstructure investigations revealed striking similarities between the differently synthesized samples. All the samples are characterized by a two-step crystallization process in which the first crystallization product does not depend on the way of preparation. In fact, the same metastable nanoscale quasicrystalline phase has been obtained by partial devitrification of ball-milled powders as well as of melt-spun ribbons. This demonstrates that ball milling is an alternative processing route to rapid solidification techniques for the preparation of quasicrystal-forming Zr-based alloys. (C) 2004 Kluwer Academic Publishers.
Title:
X-ray diffraction on laterally modulated (InAs)(n)/(AlAs)(m) short-period superlattices
Authors:
Caha, O; Krapek, V; Holy, V; Moss, SC; Li, JH; Norman, AG; Mascarenhas, A; Reno, JL; Stangl, J; Meduna, M
Source:
JOURNAL OF APPLIED PHYSICS, 96 (9): 4833-4838 NOV 1 2004
Abstract:
Lateral composition modulation in InAs/AlAs short-period superlattices was investigated by x-ray grazing-incidence diffraction and coplanar x-ray diffraction at a "normal" wavelength and at an anomalous wavelength, for which diffraction from the (200) planes does not exhibit a chemical contrast. The experimental data were compared with theoretical simulations assuming that the interfaces consist of a periodic sequence of monoatomic steps. The displacement field in the superlattice was calculated by continuum elasticity and using a valence-force field method. From the fit of the experimental data to the theory, the lengths of individual atomic terraces were determined. (C) 2004 American Institute of Physics.
Title:
Modulated structure of misfit layered cobalt oxide [(Ca0.90Bi0.10)(2)(Co0.95Bi0.05)O-3]pCoO(2)
Authors:
Miyazaki, Y; Suzuki, Y; Onoda, M; Ishii, Y; Morii, Y; Kajitani, T
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 43 (9A): 6252-6258 SEP 2004
Abstract:
We have determined the crystal structure of Bi-substituted and Bi-free misfit layered cobalt oxides [Ca2CoO3](0.62)CoO2, by a (3+1)-dimensional superspace group approach. Structural parameters have been refined with a superspace group of C2/m(1p0)s0 using powder neutron diffraction data. Bismuth atoms are found to substitute for both Ca and Co atoms in the rock salt-type [Ca2CoO3] subsystem. The resulting structural formula is expressed as [(Ca0.90Bi0.10)(2)(Co0.95Bi0.05)O-3],CoO2 with a refined b-axis ratio of p = 0.6183. By Bi substitution, the modulation of the Co-O distances in the [Ca2CoO3] subsystem is markedly decreased relative to the Bi-free counterpart, whereas such a modulation in the [CoO2] subsystem is slightly increased. The observed increase in the Seebeck coefficient and electrical resistivity of the Bi-substituted phase can be explained in terms of the decrease in hole concentration in the CoO2 sheets.
Title:
Kinetic and structural study on amorphous-to-quasicrystalline transformation in ZrNiCuAlAg bulk metallic glass
Authors:
Liu, L; Chan, KC
Source:
INTERMETALLICS, 12 (10-11): 1143-1148 OCT-NOV 2004
Abstract:
Zr65Ni10Cu7.5Al7.5Ag10 bulk metallic glass was prepared by copper-mould casting. The kinetics and structure related to the phase transformation of the bulk metallic glass were studied by X-ray diffraction, differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). It was found that the Zr65Ni10Cu7.5Al7.5Ag10 bulk metallic glass exhibits a distinct glass transition followed by two exothermic reactions, with the first reaction being the amorphous-to-quasicrystalline transformation, and the second being the quasicrystalline-to-Zr2Cu intermetallic transformation. The isothermal kinetics for amorphous-to-quasicrystalline transformation was quantitatively analyzed in the framework of JMA equation. The parameter of local Avrami exponent was introduced to explain the details of nucleation and growth behaviour in the transformation. It was revealed that the local Avrami exponent for the transformation varied with an increase in the volume fraction transformed, indicating that multi-mechanisms were involved in the transformation. TEM observations demonstrated that the variation in transformation kinetics at different stages is most likely the result of the structural inhomogeneity in the as-cast bulk metallic glass caused by a temperature gradient along the radius direction during casting. (C) 2004 Elsevier Ltd. All rights reserved.
Title:
Influence of oxygen content in phase selection during quenching of Zr80Pt20 melt spun ribbons
Authors:
Sordelet, DJ; Yang, XY; Rozhkova, EA; Besser, MF; Kramer, MJ
Source:
INTERMETALLICS, 12 (10-11): 1211-1217 OCT-NOV 2004
Abstract:
Depending on processing conditions Zr80Pt20 alloys may form meta-stable quasicrystals either during devitrification of an amorphous phase or directly upon cooling from a liquid. This study reveals that oxygen content during melt spinning indeed strongly influences the formation of the as-quenched structure in this alloy system. At a wheel speed of 25 m/s, a critical amount of oxygen was found to be required to form amorphous ribbons. At lower oxygen levels (i.e. < 500 ppm mass), a fully crystallized structure forms that is composed mainly of meta-stable beta-Zr with a small fraction of a quasicrystals (QC) phase. At higher oxygen levels (similar to1000 ppm mass), the as-quenched structure transitions to an apparently amorphous structure, and with further oxygen additions forms a mixture of amorphous and either a QC phase (similar to1500 ppm mass) or a crystalline Zr6Pt3O phase (> 2500 ppm mass). Details regarding the structural similarity between the QC, beta-Zr and Zr6Pt30 phases are discussed. Published by Elsevier Ltd.
Title:
Decomposition and crystallization of Pd40Cu30Ni10P20 and Zr46.8Ti8.2Cu7.5Ni10Be27.5 metallic glasses
Authors:
Wollgarten, M; Mechler, S; Davidov, E; Wanderka, N; Macht, MP
Source:
INTERMETALLICS, 12 (10-11): 1251-1255 OCT-NOV 2004
Abstract:
The Pd40Cu30Ni10P20 and Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glasses exhibit extraordinary stability against crystallization. It is assumed, that this results from the complicate crystallization behavior, which requires strong decomposition of the glass in some cases already preceding to the crystallization. The crystallization behavior of both these glasses in its first stage is studied after different thermal treatments by means of differential scanning calorimetry, XRD, transmission electron microscopy, energy-filtered transmission electron microscopy and three-dimensional atom probe. During annealing for long times at temperatures above and below the calorimetric glass transition respectively both metallic glasses undergo decomposition. Nanometer-scaled amorphous regions are observed sporadic or homogeneously distributed in the respective glasses. They differ in composition from their amorphous environment. After extended annealing or short time heat treatment at higher temperatures nano-crystals form from these regions. The composition of these crystals resembles the compositions of the decomposed regions. In case of Pd-Cu-Ni-P the crystals accord with an intermetallic phase. In case of Zr-Ti-Cu-Ni-Be, they are quasicrystalline. Depending on the pre-annealing treatment of the Zr-Ti-Cu-Ni-Be glass three different types of quasicrystals are found. For both alloys long-range diffusion over a wide concentration range is one important factor which controls the decomposition kinetics. Thus diffusion contributes essentially to the stability of the glasses and effects the pathway of crystallization and the resulting microstructure. (C) 2004 Elsevier Ltd. All rights reserved.
Title:
In situ transmission electron microscopy study of the electric field-induced transformation of incommensurate modulations in a Sn-modified lead zirconate titanate ceramic
Authors:
He, H; Tan, X
Source:
APPLIED PHYSICS LETTERS, 85 (15): 3187-3189 OCT 11 2004
Abstract:
Electric field-induced transformation of incommensurate modulations in a Sn-modified lead zirconate titanate ceramic was investigated with an electric field in situ transmission electron microscopy technique. It is found that the spacing between the (1/x){110} satellite spots and the fundamental reflections do not change with external electric field, indicating that the modulation wavelength stays constant under applied field. The intensity of these satellites starts to decrease when the field level reaches a critical value. Further increase in the field strength eventually leads to the complete disappearance of the satellite reflections. In addition, the if 1/2{111}-type superlattice reflections showed no response to electrical stimuli. (C) 2004 American Institute of Physics.
Title:
Ab initio determination of incommensurately modulated structures by charge flipping in superspace
Authors:
Palatinus, L
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 60: 604-610 Part 6 NOV 2004
Abstract:
The charge flipping algorithm proposed by Oszlanyi & Suto [Acta Cryst. (2004), A60, 134-141] for ab initio reconstruction of crystal structures is generalized towards superspace. Its efficiency is demonstrated by successful reconstruction of eight known incommensurately modulated structures from experimental data. The output of the charge flipping algorithm is an electron density with symmetry P1. The symmetry of the structure is recovered by locating the positions of symmetry operators and averaging the density over the symmetry-related pixels. The reconstruction of a modulated structure by the charge flipping algorithm and the accuracy of the result is demonstrated in detail on the modulated structure of tetraphenylphosphonium hexabromotellurate(IV) bis{dibromoselenate(I)}.

Update: 19-Nov-2004

Title:
Structure of the fivefold surface of the icosahedral Al-Cu-Fe quasicrystal: Experimental evidence of bulk truncations at larger interlayer spacings
Authors:
Sharma, HR; Fournee, V; Shimoda, M; Ross, AR; Lograsso, TA; Tsai, AP; Yamamoto, A
Source:
PHYSICAL REVIEW LETTERS, 93 (16): Art. No. 165502 OCT 15 2004
Abstract:
Based on scanning tunneling microscopy of the fivefold surface of the icosahedral Al-Cu-Fe quasicrystal and the refined structure model of the isostructural i-Al-Pd-Mn, we present evidence that the surface corresponds to bulk truncations at the positions where blocks of atomic layers are separated by larger interlayer spacings (gaps). Both step-height distribution and high resolution scanning tunneling microscopy images on terraces reveal bulk truncations at larger gaps.
Title:
Resonant magnetic excitations at high energy in superconducting YBa2Cu3O6.85
Authors:
Pailhes, S; Sidis, Y; Bourges, P; Hinkov, V; Ivanov, A; Ulrich, C; Regnault, LP; Keimer, B
Source:
PHYSICAL REVIEW LETTERS, 93 (16): Art. No. 167001 OCT 15 2004
Abstract:
A detailed inelastic neutron scattering study of the high temperature superconductor YBa2Cu3O6.85 provides evidence of new resonant magnetic features, in addition to the well-known resonant mode at 41 meV: (i) a commensurate magnetic resonance peak at 53 meV with an even symmetry under exchange of two adjacent CuO2 layers, and (ii) high-energy incommensurate resonant spin excitations whose spectral weight is around 54 meV. The locus and the spectral weight of these modes provides unrevealed insight about the momentum shape of the electron-hole spin-flip continuum of d-wave superconductors.
Title:
Structural anomalies and multiferroic behavior in magnetically frustrated TbMn2O5
Authors:
Chapon, LC; Blake, GR; Gutmann, MJ; Park, S; Hur, N; Radaelli, PG; Cheong, SW
Source:
PHYSICAL REVIEW LETTERS, 93 (17): Art. No. 177402 OCT 22 2004
Abstract:
We have studied the magnetostructural phase diagram of multiferroic TbMn2O5 as a function of temperature and magnetic field by neutron diffraction. Dielectric and magnetic anomalies are found to be associated with steps in the magnetic propagation vector, including a rare example of a commensurate-incommensurate transition on cooling below 24 K, and in the structural parameters. The geometrically frustrated magnetic structure is stabilized by "canted antiferroelectric" displacements of the Mn3+ ions, an example of the magnetic Jahn-Teller effect. The Tb moments order ferromagnetically at low temperatures in an applied field, while the Mn magnetic structure is largely unchanged.
Title:
Electron energy-loss spectroscopy at incommensurately modulated crystalline and glassy Ba2TiGe2O8
Authors:
Hoche, T; van Aken, PA; Grodzicki, M; Heyroth, F; Keding, R; Uecker, R
Source:
PHILOSOPHICAL MAGAZINE, 84 (29): 3117-3132 OCT 11 2004
Abstract:
Based on cluster molecular orbital calculations, high-energy resolution (DeltaE similar to 0.4 eV) Ti-L-2,L-3 electron energy loss near-edge structures of single-crystalline and glassy Ba2TiGe2O8 are interpreted. The finding that the Ti-L-2,L-3 near-edge structure of the Ba2TiGe2O8 single crystal possesses less pronounced peaks than the glass under identical experimental conditions can be attributed to distinct distortions of the titanium environment caused by the very strong one-dimensional structural modulation hosted by the Ba2TiGe2O8 crystal lattice. As lattice periodicity is absent in the glass, the titanium environment is more regular in the vitreous surroundings. Moreover, the modulation in crystalline Ba2TiGe2O8 is responsible for the virtually indiscernible O-K near-edge structures of the glassy and crystalline samples.
Title:
A combined temperature-dependent electron and single-crystal X-ray diffraction study of the fresnoite compound Rb2V4+V25+O8
Authors:
Withers, RL; Hoche, T; Liu, Y; Esmaeilzadeh, S; Keding, R; Sales, B
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 177 (10): 3316-3323 OCT 2004
Abstract:
High-purity Rb2V3O8 has been grown and temperature-dependent electron and single-crystal X-ray diffraction used to carefully investigate its fresnoite-type reciprocal lattice. In contrast to other recently investigated representatives of the fresnoite family of compounds, Rb2V3O8 is not incommensurately modulated with an incommensurate basal plane primary modulation wave vector given by q similar to 0.3 <110>. A careful low-temperature electron diffraction study has, however, revealed the existence of weak incommensurate satellite reflections characterized by the primitive primary modulation wave vector q(1) similar to 0.16c. The reciprocal space positioning of these incommensurate satellite reflections, the overall (3 + 1)-d superspace group symmetry, as well as the shapes of the refined displacement ellipsoids determined from single-crystal XRD refinement, are all consistent with their arising from a distinct type of condensed rigid unit modes (RUMs) of distortion of the Rb2V3O8 parent structure. (C) 2004 Elsevier Inc. All rights reserved.
Title:
SrMn3O6: an incommensurate modulated tunnel structure
Authors:
Gillie, LJ; Hadermann, J; Perez, O; Martin, C; Hervieu, M; Suard, E
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 177 (10): 3383-3391 OCT 2004
Abstract:
The crystallographic structure of a mixed valent manganite SrMn3O6 with a 1D modulated structure is reported. The SrMn3O6 structure can be described with the basic subcell space group Pnma (a = 9.1334(5)Angstrom; b = 2.8219(2)Angstrom; c = 12.0959(7)Angstrom), but transmission electron microscopy revealed that the study of the real structure requires a 4D-formalism approach with superspace group P2(1)/a(alphabeta0)00 (unique axis c), with a modulation wave vector q having the approximate components (0.52a(*) + 0.31b(*)). The crystallographic structure is closely related to those of NaxFexTi2-xO4 and Pb1.5BaMn6Al2O16, comprising of unusual "figure-of-eight"-shaped tunnels, made up of strings of edge- and corner-sharing (Fe/Ti)O-6 or (Mn/Al)O-6 octahedra, with the other cations situated in the tunnel cavities. Structural refinement was performed on X-ray and neutron powder diffraction data using the 4D formalism. All atoms in the crystal are affected by a displacive modulation wave, and a saw tooth function is employed to model the displacement and occupancy of the Sr sites. Magnetic susceptibility measurements reveal a sharp antiferromagnetic transition with T-N similar to 46 K. (C) 2004 Elsevier Inc. All rights reserved.
Title:
2D metal slabs in new nickel-tin chalcogenides Ni(7-delta)SnQ(2) (Q=Se, Te): average crystal and electronic structures, chemical bonding and physical properties
Authors:
Baranov, AI; Isaeva, AA; Kloo, L; Kulbachinskii, VA; Lunin, RA; Nikiforov, VN; Popovkin, BA
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 177 (10): 3616-3625 OCT 2004
Abstract:
A systematic search for mixed low-valence, nickel-tin chalcogenides performed by establishing phase relations in the parts of Ni-Sn-Se and Ni-Sn-Te ternary systems resulted in the discovery of two new compounds, Ni5.62SnSe2 and Ni5.78SnTe2 Single crystals of both compounds were prepared by chemical transport with iodine and crystal structures were determined by single crystal X-ray investigation. The ED patterns for Ni5.78SnTe2 showed the presence of satellite reflections, which indicate a modulated structure with qapproximate to0.4a*. Average crystal structures of both compounds were determined to be of tetragonal symmetry (Sp.gr.I4/mmm, Z = 2) with a = 3.6890(8) Angstrom, c = 18.648(3) Angstrom, R-w = 0.0716 and a = 3.7680(5) Angstrom, c = 19.419(4) Angstrom, R-w, 0.0832, correspondingly, and are isostructural to known Ni5.72SbSe2 and Ni5.66SbTe2. Measurements were carried out for both compounds with respect to thermal, electrical and magnetic properties. Ab initio band structure calculations were also performed to take a first glance into the electronic structure of such type compounds. The anisotropy of their band structure was found. Physical property measurements showed both compounds to be the anisotropic metallic conductors and paramagnetics. Calculated difference charge density maps revealed pairwise covalent and multicenter metallic nature of the d-metal-chalcogen and d-metal-p-metal interactions, respectively. (C) 2004 Elsevier Inc. All rights reserved.
Title:
Preparation and thermoelectric properties of misfit-layered sulfide [Yb1.90S2](0.62)NbS2
Authors:
Miyazaki, Y; Ogawa, H; Kajitani, T
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS, 43 (9A-B): L1202-L1204 SEP 15 2004
Abstract:
We have prepared polycrystalline samples of Yb-Nb-S-based misfit-layered compound and measured their thermoelectric properties below 300 K. The compound consists of an alternate stacking of a trigonal prism (MoS2)-type [NbS2] layer and a two-layered rock-salt-type [Yb1.90S2] slab, being incommensurate parallel to the a-axis. Approximately 5% Yb deficiency is necessary to obtain single-phase samples. Metallic conductivity accompanied by a large Seebeck coefficient S has been observed down to 4.2 K for the single-phase samples. At 300 K, the sample exhibits S = 60 muV(.)K(-1) and resistivity of rho = 1.4mOmega(.)cm, with thermal conductivity of kappa = 0.80W(.)K(-1.)m(-1). The resulting figure-of-merit (Z = S-2/rhokappa) becomes 3.2 x 10(-4) K-1 at 300 K, yielding the dimensionless figure-of-merit of ZT similar to 0.1.
Title:
Eshelby's problem of an inclusion of arbitrary shape in a decagonal quasicrystalline plane or half-plane
Authors:
Wang, X
Source:
INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE, 42 (17-18): 1911-1930 OCT 2004
Abstract:
In this paper, a simple method based on analytical continuation and conformal mapping is presented to obtain an analytic solution for Eshelby's problem of a two-dimensional inclusion of arbitrary shape in a decagonal quasicrystalline plane or half-plane. The inclusion in this study refers to a subdomain which tends to undergo uniform stress-free phonon and phason eigenstrains without the constraint of the surrounding matrix. Furthermore, the inclusion penetrates through the solid along the period direction. The present method leads to elementary expressions for the internal phonon and phason fields within the inclusion in an entire decagonal quasicrystalline plane. Several examples are discussed to illustrate the method. (C) 2004 Published by Elsevier Ltd.
Title:
Magnetic ordering in iron tricyanomethanide
Authors:
Feyerherm, R; Loose, A; Landsgesell, S; Manson, JL
Source:
INORGANIC CHEMISTRY, 43 (21): 6633-6639 OCT 18 2004
Abstract:
Magnetic susceptibility, heat capacity, and neutron diffraction studies of Fe[C(CN)(3)](2) reveal the existence of two magnetic phase transitions at T-N,T-I = 2.45 K and T-N,T-II = 1.85 K. Between 1.85 and 2.45 K, the magnetic ordering is incommensurate with a temperature-dependent propagation vector (k(l,x) 0 0), k(l,x) = 0.525-0.540. In zero magnetic field, below 1.85 K the ordered structure is described by the propagation vector k(II) = ((1)/(2) 0 (1)/(2)), i.e., a doubling of the unit cell along the a and c directions of the orthorhombic lattice. The ordered moments of 3.4(1) and 3.2(1) /mu(B), respectively, are aligned approximately parallel to the principal axis of the elongated Fe coordination octahedron. At T < T-N,T-II, application of an external magnetic field of about 18 kOe destroys the commensurate phase and the incommensurate phase is established. The latter phase is stable in fields up to about 40 kOe. The magnetic ordering of Fe[C(CN)3]2 is discussed in terms of the 2D triangular topology of the lattice, producing partial frustration, and in comparison with the behavior of other compounds of the series M[C(CN)(3)](2), where M is a 3d transition metal.
Title:
Lattice dynamics and central-mode phenomena in the dielectric response of ferroelectrics and related materials
Authors:
Buixaderas, E; Kamba, S; Petzelt, J
Source:
FERROELECTRICS, 308: 131-192 2004
Abstract:
In this review we describe and discuss recent results on the linear dielectric response of high-permittivity dielectric crystals and ceramics in the wide frequency range 10(2)-10(14) Hz. Our attention is paid to materials which exhibit some interesting low-frequency polar-phonon anomalies in combination with some additional dielectric dispersion below the polar phonon region. The following compounds are discussed: microwave ceramics Bi1.5Zn1.0Nb1.5O7, antiferroelectric PbZrO3 ceramics and AgNbO3 crystals, ferroelectric LiNaGe4O9, LaBGeO5, Cd2Nb2O7 and SrBi2 Ta2O9 crystals, incommensurate ferroelectric Sr2Nb2O7, Ba2NaNb5O15 and BCCD crystals, dipolar-glass crystal of Rb-1/2(ND4)(1/2)D2PO4, relaxor ferroelectric Pb(Sc1/2Ta1/2)O-3 and PLZT ceramics and PMN crystals, antiferroelectric PUT 2/95/5 ceramics and relaxor-based PMN-PT PZN-PT and BiScO3-PT crystals and ceramics. For these materials the polar phonon spectra are discussed together with their flow-frequency dielectric response and dispersion regions in between, in the 10-300 K or higher temperature range, depending on the existing phase transitions of interest. Some universal features of the disorder and anharmonicities are pointed out: central-mode phenomena near displacive phase transitions and polar nano-clusters which appear at rather high temperatures and remain present down to low temperatures if the material remains structurally disordered. The manifestation of the latter in the dielectric spectra consists in extreme broadening of the relaxation region on cooling which at low temperatures results in constant loss spectra (1/f noise).
Title:
The microprocesses of the quasicrystalline transformation in Zr65Ni10Cu7.5Al7.5Ag10 bulk metallic glass
Authors:
Liu, L; Chan, KC; Pang, GKH
Source:
APPLIED PHYSICS LETTERS, 85 (14): 2788-2790 OCT 4 2004
Abstract:
The microprocesses of the amorphous-to-quasicrystalline transformation in Zr65Ni10Cu7.5Al7.5Ag10 bulk metallic glass were studied in detail by transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). It was found that the amorphous-to-quasicrystalline transformation in the present system undergoes a series of interprocesses and follows the sequence of the phase transformation of amorphous -->FCC Zr2Ni-->Tetragonal Zr2Ni-->Tetragonal Zr2Ni with a domain structure -->Quasicrystals. HRTEM indicated that a domain structure with a high density of stacking faults was formed in the sample at the stage just prior to the formation of quasicrystals. This special structure seems to possess the structural symmetries similar to those of icosahedral quasicrystals. Nanobeam energy dispersive x-ray spectrum revealed that atomic diffusion was involved in all interprocesses of the phase transformations. This suggests that the amorphous-to-quasicrystalline transformation in the present bulk metallic glass is a nonpolymorphous reaction. (C) 2004 American Institute of Physics.

Update: 12-Nov-2004

Title:
Steam and water lubrication of quasicrystalline films
Authors:
Phillips, BS; Zabinski, JS
Source:
TRIBOLOGY LETTERS, 17 (3): 429-434 OCT 2004
Abstract:
The present work reports on the comparison of tribological properties between quasicrystalline and approximant films under steam and water lubrication. These films have nearly the same stoichiometry, which allows evaluation of the quasicrystalline structure as compared with the crystalline structure of the approximant. The goal of this study is to determine the effects crystal structure has on tribological properties and to study the general tribological behavior of quasicrystals in a steam and water environment. AlCuFe quasicrystals coatings were deposited by unbalanced magnetron sputtering. The test films were 10 mum thick deposited on a 1 inch diameter Al2O3 disk and a 1/4 inch diameter Al2O3 ball. Data were collected under water and steam lubricated conditions. Friction coefficients and wear rates of quasicrystals and approximants were nearly indistinguishable. During water lubrication, quasicrystals act similar to ceramics where surface smoothing and hydrodynamic lift control the friction and wear properties. With steam-lubricated conditions, the friction and wear process is controlled by brittle fracture and third body abrasion. Generally, less than 5% difference in the friction and wear properties were observed between the icosahedral quasicrystal phase and the approximant phase.
Title:
Microstructure development and tribological behavior in AlCuFe quasicrystalline thin films
Authors:
Fehrenbacher, L; Zabinski, JS; Phillips, BS; Daniels, MJ; King, D; Ketola, KS; Bilello, JC
Source:
TRIBOLOGY LETTERS, 17 (3): 435-443 OCT 2004
Abstract:
A series of AlCuFe films were deposited by magnetron sputtering and subjected to X-ray diffraction and tribological testing to elucidate the correlation between quasicrystalline phase content and coefficient of friction. The sputter target was a pressed powder target comprised of a mixture of elemental powders combined in the ratio Al65Cu23Fe12 and pressed at 400 degreesC. This target was designed to produce film compositions within the single-phase icosohedral quasicrystalline regime. X-ray diffraction performed on the as-deposited coatings showed that they were comprised of a nanoscale/amorphous precursor phase with broad X-ray diffraction maxima. Anneals of the as-deposited films were performed at 450 or 500 degreesC in argon for various times to cause partial or full development of the quasicrystalline microstructure, and films were tribo-tested in two separate systems. The first of these was an oscillating pin-on-flat system, in which a coated 2 mm diameter pin was used to test as-deposited films at temperatures of up to 220 degreesC under vacuum and a 15 g load. The second system used a 0.25" diameter alumina ball and a load of 100 g to test films in air at temperatures of 25, 150, and 300 degreesC. Various anneal conditions were also tested. For an as-deposited coating, a coating annealed for 2 h at 450 degreesC, and a coating annealed for 1 h at 500 degreesC, the observed coefficients of friction were 0.45, 0.23, and 0.17, respectively. Correlation between quasicrystalline phase content, room temperature friction coefficient, and appearance of the wear track clearly showed that annealing to the fully developed quasicrystalline structure resulted in a harder film with a lower coefficient of friction.
Title:
Friction and adhesion properties of clean and oxidized Al-Ni-Co decagonal quasicrystals: a UHV atomic force microscopy/scanning tunneling microscopy study
Authors:
Park, JY; Ogletree, DF; Salmeron, M; Jenks, CJ; Thiel, PA
Source:
TRIBOLOGY LETTERS, 17 (3): 629-636 OCT 2004
Abstract:
The tribological properties of adhesion and friction between 10-fold Al-Ni-Co decagonal quasicrystals and conductive W2C and TiN coated tips were studied in ultrahigh vacuum (UHV) with an atomic force microscope. Contacts between the tip and clean quasicrystals are dominated by strong adhesion forces, which result in irreversible deformations and material transfer. The irreversible adhesion was suppressed following an oxygen exposure of 10 Langmuir, which also reduced the adhesion force by a factor of two. An additional 2/3 reduction in adhesion force occurred after several 100 Langmuir exposure. A much larger decrease (by a factor 10) occurred by air-oxidation. The friction force decreased also with oxygen exposure although not as dramatically. A linear decrease by a factor two, was observed between the clean surface and the surface exposed to 200 Langmuir of oxygen. After that the friction force remained constant. Air-oxidation reduced friction by roughly another factor of two. In contrast with the clean surface, contacts with the air oxide substrate are well described by the Derjaguin-Muller-Toporov (DMT) model, while contacts with oxygen chemisorbed substrates are in the transition regime between Johnson-Kendall-Roberts (JKR) and DMT models.
Title:
On the phase transformation of bulk as-cast Ti40Zr40Ni20 quasicrystal
Authors:
Qiang, JB; Wang, YM; Wang, DH; Dong, C
Source:
RARE METAL MATERIALS AND ENGINEERING, 33 (9): 949-952 SEP 2004
Abstract:
A pure quasicrystal with the composition Ti40Zr40Ni20 was obtained in bulk form by using conventional suction-casting. The quasi-lattice constant of the icosahedral phase (I-phase) is 0.523 nm. Differential scanning calorimetry (DSC) together with X-ray diffraction were used to study the temperature-induced phase transformation of the as-cast I-phase. Two endothermic reactions are identified in the DSC trace. The first endothermic reaction with an onset temperature of 964 K corresponds to eutectoid transformation from the I-phase to the C14-type Laves phase and beta-Zr(Ti) solid solution. The second one with an onset temperature of 1 107 K indicates the melting transformation of the eutectoid mixture.
Title:
Pure Al matrix composites produced by vacuum hot pressing: tensile properties and strengthening mechanisms
Authors:
Tang, F; Anderson, IE; Gnaupel-Herold, T; Prask, H
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 383 (2): 362-373 OCT 15 2004
Abstract:
Al matrix composites reinforced by spherical intermetallic particles, were consolidated from gas atomized elemental Al and Al-Cu-Fe alloy fine powders (< 10 mum) by a vacuum hot pressing technique. The composites were made from two types of powders including commercial inert gas atomized powder (99.7%) and high purity powder (99.99%) produced by a gas atomization reaction synthesis technique. The microstructures and tensile properties of the composites with three different volume fractions of the reinforcement particles (15, 20 and 30 vol.%) were characterized. Microstructural analysis of the samples demonstrated that the quasicrystalline phase in the Al-Cu-Fe particles transformed to a crystalline omega phase, which has similar elastic modulus, CTE, and hardness properties, but a reduced density. All the composites appear to be fully dense, with strong interparticle bonding, and exhibit elastic modulus values approaching upper bound predictions by rule of mixtures. Tensile test results and neutron diffraction measurements allowed an assessment of the relative influence of direct and secondary composite strengthening mechanisms on the yield strength of this model composite system. The results suggest that for elemental Al matrix composite samples without precipitation strengthening and severe strain hardening during consolidation, the direct and relevant secondary strengthening mechanisms can be combined to predict accurately the yield strength increase of the composites. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Minor dielectric anomalies in ANbO(3) (A-Li, Na,Kk) single crystals in the 100-300 degrees C temperature range
Authors:
Raevskaya, SI; Reznitchenko, LA; Semenchev, AF; Lisitsina, SO; Smotrakov, VG; Eremkin, VV; Dul'kin, EA
Source:
FERROELECTRICS, 307: 227-231 2004
Abstract:
In ANbO(3) (A-Li, Na, K) single crystals besides dielectric permittivity epsilon maxima, corresponding to the known ferroelectric and antiferroelectric phase transitions, minor epsilon(T) anomalies were observed in the 100-300degreesC temperature range. The temperature T of these anomalies does not depend on measuring frequency in the 10(2)-10(6) Hz range. Dilatometric studies showed that temperature dependences of relative dilatation DeltaL/L have an inflexion in the vicinity of T-a. Linear correlation between T-a and the temperature T-PE of the phase transition into the paraelectric phase was revealed. It is supposed that the minor epsilon(T) anomalies observed in ANbO(3) crystals in the 100-300degreesC temperature range are due to phase transitions to the incommensurate phase.
Title:
Microstructure of bonding interface in explosively-welded clads and bonding mechanism
Authors:
Chiba, A; Nishida, M; Morizono, Y
Source:
EXPLOSION, SHOCK WAVE AND HYPERVELOCITY PHENOMENA IN MATERIALS, 465-466: 465-473 2004 Book series title: MATERIALS SCIENCE FORUM
Abstract:
Microstructural aspects and bonding characteristics of the explosive welded Ti/Ti, Ti/steel and Ti/Ni clads were investigated mainly by TEM microscopy. It was found that the bonding interface was composed of layers of metastable phases such as amorphous phases, icosahedral quasicrystal and intermetallic compounds. These metastable phases are formed as a trace of melting followed by subsequent rapid solidification of thin layers of about 200 nm in thickness along the contact surface of both the component materials. It is concluded that the very thin melting layer is responsible for the bonding of explosively welded Ti base clads and especially amorphous phase formed in the bonding interface keeps high bonding strength.
Title:
Growth, structure, and superconducting properties of Bi2Sr2Ca2Cu3O10 and (Bi,Pb)(2)Sr2Ca2Cu3O10-y crystals
Authors:
Giannini, E; Garnier, V; Clayton, N; Musolino, N; Gladyshevskii, R; Flukiger, R
Source:
CRYSTAL RESEARCH AND TECHNOLOGY, 39 (10): 926-931 OCT 2004
Abstract:
Large and high-quality single crystals of both Pb-free and Pb-doped high temperature superconducting compounds (Bi1-xPbx)(2)Sr2Ca2Cu3O10-y (x = 0 and 0.3) were grown by means of a newly developed "Vapour-Assisted Travelling Floating Zone" technique (VA-TSFZ). This modified zone-melting technique was realised in an image furnace and allowed for the first time to grow Pb-doped crystals by compensating for the Pb losses occurring at high temperature. Crystals up to 3 x 2 x 0.1 mm(3) were successfully grown. Post-annealing under high pressure of O-2 (up to 10 MPa at T = 500degreesC) was undertaken to enhance T, and improve the homogeneity of the crystals. Structural characterisation was performed by single-crystal X-ray diffraction (XRD) and the structure. of the 3-layer Bi-based superconducting compound was refined for the first time. Structure refinement showed an incommensurate superlattice in the Pb-free crystals. The space group is orthorhombic, A2aa, with cell parameters a = 27.105(4) Angstrom, b=5.4133(6) Angstrom and c = 37.009(7) Angstrom. Superconducting studies were carried out by A.C. and D.C. magnetic measurements. Very sharp superconducting transitions were obtained in both kinds of crystals (DeltaT(c) less than or equal to 1 K). In optimally doped Pb-free crystals, critical temperatures up to 111 K were measured. Magnetic critical current densities of 2(.)10(5) A/cm(2) were measured at T = 30 K and mu(0)H = 0 T. A weak second peak in the magnetisation loops was observed in the temperature range 40-50 K above which the vortex lattice becomes entangled. We have measured a portion of the irreversibility line (0.1-5 Tesla) and fitted the expression for the melting of a vortex glass in a 2D fluctuation regime to the experimental data. Measurements of the lower critical field allowed to obtain the dependence of the penetration depth on temperature: the linear dependence of lambda(T) for T < 30 K is consistent with d-wave superconductivity in Bi-2223.
Title:
Chromate aluminate sodalite, Ca-8[Al12O24](CrO4)(2): Phase transitions and high-temperature structural evolution of the cubic phase
Authors:
Antao, SM; Hassan, I; Parise, JB
Source:
CANADIAN MINERALOGIST, 42: 1047-1056 Part 4 AUG 2004
Abstract:
The structural behavior of a chromate aluminate sodalite, Ca-8[Al12O24](CrO4)(2), at room pressure and on heating from 463 to 982degreesC was determined by using in situ synchrotron X-ray powder-diffraction data [lambda = 0.91997(4) Angstrom] and Rietveld refinements. The sample was heated at a rate of about 9.5degreesC/min., and X-ray traces were collected at intervals of about 17degreesC. The structure at 463degreesC is a modulated cubic phase, whereas above 512degreesC, the structure is cubic with space group I (4) over bar 3m. The a parameter increases linearly from 512 to 982degreesC, and the percent change in volume is 0.9(1)%. Between 463 and 982degreesC, the Al-O distance is nearly constant, the angle of rotation of the AlO4 tetrahedron, phi(Al), decreases by 0.6degrees and simultaneously, the Al-O-Al bridging angle increases by 0.8(2)degrees. Between 463 to 982degreesC, the Ca-O distances are nearly constant. The Ca atom is located nearly in the plane of the three O' framework atoms, so movement of the Ca atom out of this plane will cause longer Ca-O' bonds instead of shorter bonds that occur when the Ca atom is migrating toward this plane. The highly charged [Ca-4.CrO4](6+) clusters bond strongly to the framework oxygen atoms, which limits the rotation of the framework AlO4 tetrahedra; as a result, the expansion of the structure is small. We evaluate the differences between the thermal behavior of chromate aluminate sodalite and that of other structurally related phases (e.g., sodalite and danalite).

Update: 5-Nov-2004

Title:
Transport properties of Ti-Ni-Zr films grown by pulsed laser deposition
Authors:
Boffoue, O; Lenoir, B; Jacquot, A; Brien, V; Bellouard, C; Dauscher, A
Source:
SOLID STATE COMMUNICATIONS, 132 (3-4): 209-212 OCT 2004
Abstract:
Quasicrystalline Ti41.5Ni17Zr41.5 thin films have been synthesized at different temperatures by pulsed laser deposition (PLD) from a. Nd:YAG laser. Electrical resistivity, Hall coefficient, magnetoresistance and thermopower measurements have been conducted in the 4.4-300 K or 70-300 K temperature range. Ti41.5Ni17Zr41.5 quasicrystals are characterized by a high electrical conductivity, an order of magnitude higher than in other quasicrystals, independent of their morphology and microstructure. Hall measurements indicate that the films have a high carrier concentration. Thermoelectric powers in T41.5Ni17Zr41.5 have relatively small magnitudes and the values have been found to depend on the microstructure. (C) 2004 Elsevier Ltd. All rights reserved.
Title:
Four-unit-cell superstructure in the optimally doped YBa2Cu3O6.92 superconductor
Authors:
Islam, Z; Liu, X; Sinha, SK; Lang, JC; Moss, SC; Haskel, D; Srajer, G; Wochner, P; Lee, DR; Haeffner, DR; Welp, U
Source:
PHYSICAL REVIEW LETTERS, 93 (15): Art. No. 157008 OCT 8 2004
Abstract:
Diffuse x-ray scattering measurements reveal that the optimally doped YBa2Cu3O6.92 superconductor is intrinsically modulated due to the formation of a kinetically limited 4-unit-cell superlattice, q(0)=(1/4 ,0,0), along the shorter Cu-Cu bonds. The superlattice consists of large anisotropic displacements of Cu, Ba, and O atoms, respectively, which are correlated over similar to3-6 unit cells in the ab plane, and appears to be consistent with the presence of an O-ordered "ortho-IV" phase. Long-range strains emanating from these modulated regions generate an inhomogeneous lattice which may play a fundamentally important role in the electronic properties of yttrium-barium-copper-oxides.
Title:
Influence of boron content on the microstructure of sintered Al62.5-xCU25.3Fe12.2Bx alloys (x=0, 3, 5)
Authors:
Brien, V; Khare, V; Herbst, F; Weisbecker, P; Ledeuil, JB; de Weerd, MC; Machizaud, F; Dubois, JM
Source:
JOURNAL OF MATERIALS RESEARCH, 19 (10): 2974-2980 OCT 2004
Abstract:
Microstructures and morphological features of a series of sintered quasicrystalline Al62.5-xCU25.3Fe12.2Bx alloys, with x ranging from 0 to 5 at.% were studied using x-ray diffraction, scanning electron microscopy, x-ray mapping, and electron probe microanalysis. Electron backscattering diffraction (EBSD) was also used to get information about the structures of some phases and identify the crystalline relationship in-between phases. Increasing x results in the change of the nature of extra phases. These secondary phases are all less than 1% in volume of the total matter except for the beta phase at 5% of boron. Whatever the percentage of boron considered, boron seems to concentrate essentially in the parasite phases confirming doubts found in literature about the solubility of boron inside the face-centered-icosahedral Al-Cu-Fe phase. No special crystallographic relationship in between the tested phases could be spotted. EBSD is thus also confirmed as an excellent techni! que to get quasicrystalline grains orientations.
Title:
The effect of cation disorder on the structure of Sr2FeMoO6 double perovskite
Authors:
Klencsar, Z; Nemeth, Z; Vertes, A; Kotsis, I; Nagy, M; Cziraki, A; Ulhaq-Bouillet, C; Pierron-Bohnes, V; Vad, K; Meszarose, S; Hakl, J
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 281 (1): 115-123 OCT 1 2004
Abstract:
Double perovskite Sr2FeMoO6 with cation disorder was investigated by means of the X-ray diffractometry, atomic resolution transmission electron microscopy, AC susceptibility, and Fe-57 Mossbauer spectroscopy. Atomic resolution TEM measurements revealed the existence of domains with modulated crystal structure inside regions of the ideal double perovskite. Fe-57 Mbssbauer spectroscopy revealed that cation disorder leads to a suppression of delocalization of the 4d(1) electron of Mo5+, and consequently regions with cation disorder form insulating domains in the half-metallic matrix of the ordered double perovskite structure. (C) 2004 Elsevier B.V. All rights reserved.

Update: 29-Oct-2004

Title:
Strongly enhanced magnetic fluctuations in a large-mass layered ruthenate
Authors:
Friedt, O; Steffens, P; Braden, M; Sidis, Y; Nakatsuji, S; Maeno, Y
Source:
PHYSICAL REVIEW LETTERS, 93 (14): Art. No. 147404 OCT 1 2004
Abstract:
We have studied the magnetic excitations in Ca2-xSrxRuO4, x=0.52 and 0.62, which exhibit an anomalously high susceptibility and heavy mass Fermi liquid behavior. Our inelastic neutron scattering experiments reveal strongly enhanced magnetic fluctuations around an incommensurate wave-vector (0.22,0,0) pointing to a magnetic instability. The magnetic fluctuations show no correlation in the c direction and also along the RuO2 planes the signal is extremely broad, Deltaq=0.45 Angstrom(-1). These fluctuations can quantitatively account for the high specific heat coefficient and relate to the high macroscopic susceptibility. The magnetic scattering is attributed to the d(xy) band, the active band for spin triplet superconductivity in Sr2RuO4.
Title:
Temperature-dependent phason elasticity in a random tiling quasicrystal
Authors:
Mihalkovic, M; Henley, CL
Source:
PHYSICAL REVIEW B, 70 (9): Art. No. 092202 SEP 2004
Abstract:
Both phason elastic constants have been measured from Monte Carlo simulations of a random-tiling icosahedral quasicrystal model with a Hamiltonian. The low-temperature limit approximates the "canonical-cell" tiling used to describe several real quasicrystals. The elastic constant K-2 changes sign from positive to negative with decreasing temperature; in the "canonical-cell" limit, K-2/K-1 appears to approach -0.7, about the critical value for a phason-mode modulation instability. We compare to the experiments on i-AlPdMn and i-AlCuFe.
Title:
Comparative study of the binary icosahedral quasicrystal Cd5.7Yb and its crystalline 1/1-approximant Cd6Yb by positron annihilation spectroscopy
Authors:
Sato, K; Kobayashi, Y; Arinuma, K; Kanazawa, I; Tamura, R; Shibuya, T; Takeuchi, S
Source:
PHYSICAL REVIEW B, 70 (9): Art. No. 094107 SEP 2004
Abstract:
Previously, we showed that the icosahedral quasicrystal Cd5.7Yb possesses similar structural vacancies to those in its cubic 1/1-approximant Cd6Yb by positron lifetime measurements [K. Sato, H. Uchiyama, K. Arinuma, I. Kanazawa, R. Tamura, T. Shibuya, and S. Takeuchi, Phys. Rev. B 66, 052201 (2002)]. In the present paper, the local chemical environment around the structural vacancies is specifically investigated by two-detector coincident Doppler broadening spectroscopy. Essentially the same annihilation sites with Cd-rich chemical environments are identified for the two phases. This strongly suggests that the quasicrystal is composed of the same cluster as the approximant. The difference in the structural vacancy density between the two phases is examined by positron diffusion experiments using a slow positron beam. The structural vacancy density in the quasicrystal is found to be 20% lower than that in the approximant.
Title:
Bridgman-grown i-Al68.9Pd21.6Mn9.5 quasicrystal: Comparison of alpha, C-rho, sigma, and chi with those for flux-grown samples
Authors:
Swenson, CA; Lograsso, TA; Anderson, NE; Ross, AR
Source:
PHYSICAL REVIEW B, 70 (9): Art. No. 094201 SEP 2004
Abstract:
Thermal expansivity (alpha, 1-300 K), heat capacity (C-P, 1-108 K), electrical conductivity (sigma, 1-300 K) and magnetic susceptibility (chi, 1-300 K) data have been obtained for a Bridgman-grown single grain i-Al68.9Pd21.6Mn9.5 quasicrystal (BR) for direct comparison with data previously published for a flux-grown single grain sample [Phys. Rev. B 65, 184206 (2002); PRB], and present sigma, chi and C-P data for a second flux-grown sample described in an earlier publication [Philos. Mag. B 79, 1673 (1999); PM]. Fortuitously, comparative analyses show these samples to have essentially the same composition. At all temperatures, sigma and chi for BR are, respectively, approximately one-third and one-quarter those for PRB. The C-P's are the same (+/-1%) down to 30 K, below which the BR C-P decreases more rapidly to one-half that for PRB at 1 K. The alpha's agree to +/-2% from 300 to 40 K, with a more rapid decrease for BR below 30 K, eventually to 0.6 alpha(PRB) below 4 K. The total Gruneisen parameters are similar at all temperatures. The two methods for sample growth differ primarily in a quenching of the flux-grown sample to room temperature after growth, while the Bridgman-grown sample cools very slowly, resulting in slightly different phases, and magnetic properties which are associated with lattice defects. An attempt to convert the single grain flux-grown sample to the phase of the Bridgman sample using an 800degreesC anneal and a slow cool to room temperature was not successful, with the appearance of second phase inclusions. These inclusions are ascribed to slightly different compositions for the two phases [see Boissieu , Philos. Mag. A 78, 305 (1998)]. This suggests that a single grain flux-grown sample with an Mn composition near 9% cannot be converted by annealing and slow cooling into a single grain LT phase, and vice versa. These considerations may not apply to samples with Mn compositions closer to 8%.
Title:
Nonlinear elastic properties of decagonal quasicrystals
Authors:
Zhou, X; Hu, CZ; Gong, P; Qiu, SD
Source:
PHYSICAL REVIEW B, 70 (9): Art. No. 094202 SEP 2004
Abstract:
Quasicrystals have both positional and orientational long-range order. Thus, they are essentially anisotropic. However, both theory and experiment show that ordinary linear elastic property (linear phonon elasticity) is isotropic for quasicrystals. To detect the quasicrystal anisotropy the nonlinear elasticity should be discussed. In this paper the nonlinear elastic properties are analyzed for decagonal quasicrystals. All the third-order elastic constants (including phason strain) are determined for all symmetries of decagonal quasicrystals. The nonlinear elastic properties due to the coupling between phonons and phasons may reveal the anisotropic structure of decagonal quasicrystals by Hermann's theorem.
Title:
Compatibility factor of segmented thermoelectric generators based on quasicrystalline alloys
Authors:
Macia, E
Source:
PHYSICAL REVIEW B, 70 (10): Art. No. 100201 SEP 2004
Abstract:
In this work we present a prospective study on the possible use of certain quasicrystalline alloys in order to improve the efficiency of segmented thermoelectric generators. To this end, we obtain a closed analytical expression for their compatibility factor [G. J. Snyder and T. S. Ursell, Phys. Rev. Lett. 91, 148301 (2003)]. By comparing our analytical results with available experimental data we conclude that a promising high temperature material, compatible with benchmark thermoelectric materials, can be found among AlPdMn based icosahedral quasicrystals.
Title:
Evolution of the single-hole spectral function across a quantum phase transition in the anisotropic-triangular-lattice antiferromagnet
Authors:
Takei, S; Chung, CH; Kim, YB
Source:
PHYSICAL REVIEW B, 70 (10): Art. No. 104402 SEP 2004
Abstract:
We study the evolution of the single-hole spectral function when the ground state of the anisotropic-triangular-lattice antiferromagnet changes from the incommensurate magnetically ordered phase to the spin-liquid state. In order to describe both of the ground states on equal footing, we use the large-N approach where the transition between these two phases can be obtained by controlling the quantum fluctuations via an "effective" spin magnitude. Adding a hole into these ground states is described by a t-J-type model in the slave-fermion representation. Implications of our results to possible future angle-resolved photoelectron spectroscopy experiments on insulating frustrated magnets, especially Cs2CuCl4, are discussed.
Title:
Magnetic degradation of an FeCo/GaAs interface
Authors:
Park, S; Fitzsimmons, MR; Dong, XY; Schultz, BD; Palmstrom, CJ
Source:
PHYSICAL REVIEW B, 70 (10): Art. No. 104406 SEP 2004
Abstract:
Polarized neutron reflectometry was used to measure the magnetization depth profile of an epitaxial FeCo single crystal film grown on GaAs(100) (2x4)/c(2x8)beta2 at 95degreesC-a prototypical example of a ferromagnetic/semiconductor heterostructure. From a quantitative analysis of the neutron scattering data, we find the magnetic thickness of the FeCo layer to be 6 A thinner than its chemical thickness. Further, we show the chemical and magnetic structures of the FeCo film are incommensurate at the FeCo/GaAs interface, suggesting that the FeCo/GaAs interface region does not possess the magnetization of the FeCo film.
Title:
Magnetic structure of spin-density waves in Cr(001)/Sn multilayers with periodic monatomic spacer layers of nonmagnetic Sn
Authors:
Takeda, M; Mibu, K; Shinjo, T; Endoh, Y; Suzuki, J
Source:
PHYSICAL REVIEW B, 70 (10): Art. No. 104408 SEP 2004
Abstract:
Detailed magnetic structure of spin-density waves (SDWs) in epitaxial Cr(001)/Sn multilayers was investigated by neutron scattering combined with Mossbauer spectroscopic studies. Monatomic Sn layers were embedded in 240-nm-thick Cr(001) films with varying the periodic spacing from 4.2 to 16.2 nm. All samples were revealed to be a commensurate antiferromagnetic (CAF) phase at 300 K. The CAF structures changed to incommensurate SDW states with complex wave forms whose wavelength are controlled by the artificial periodicity at low temperatures although the CAF structure in the sample with the period of 4.2 nm persisted even at 10 K. The phase transition depends on the thickness of the Cr layers intervening between Sn monatomic layers. An appreciable phase slip in the SDW was observed during the phase transition in the sample with the period of 10.2 nm. The SDW structure is discussed by taking account of the competing forces between the nesting of Fermi surface and a pinning of antinodes at the Sn monatomic layers.
Title:
Magnetic properties of Rb2Cu2Mo3O12 including a one-dimensional spin-1/2 Heisenberg system with ferromagnetic first-nearest-neighbor and antiferromagnetic second-nearest-neighbor exchange interactions
Authors:
Hase, M; Kuroe, H; Ozawa, K; Suzuki, O; Kitazawa, H; Kido, G; Sekine, T
Source:
PHYSICAL REVIEW B, 70 (10): Art. No. 104426 SEP 2004
Abstract:
We have investigated magnetic properties of Rb2Cu2Mo3O12 powder. Temperature dependence of magnetic susceptibility and magnetic-field dependence of magnetization have shown that this cuprate can be considered as a compound of a one-dimensional spin-1/2 Heisenberg system with ferromagnetic first-nearest-neighbor (1NN) and antiferromagnetic second-nearest-neighbor (2NN) competing interactions (competing system). Values of the 1NN and 2NN exchange interactions are estimated as J(1)=-138 K and J(2)=51 K (alphaequivalent toJ(2)/J(1)=-0.37). This value of alpha suggests that the ground state is a spin-singlet incommensurate state. In spite of relatively large J(1) and J(2), no magnetic phase transition appears down to 2 K, while an antiferromagnetic transition occurs in other model compounds of the competing system with ferromagnetic 1NN interaction. For that reason, Rb2Cu2Mo3O12 is a suitable compound to study properties of the incommensurate ground state that are unconfirmed experimentally.
Title:
Stripe order, depinning, and fluctuations in La1.875Ba0.125CuO4 and La1.875Ba0.075Sr0.050CuO4
Authors:
Fujita, M; Goka, H; Yamada, K; Tranquada, JM; Regnault, LP
Source:
PHYSICAL REVIEW B, 70 (10): Art. No. 104517 SEP 2004
Abstract:
We present a neutron scattering study of stripe correlations measured on a single crystal of La1.875Ba0.125CuO4. Within the low-temperature-tetragonal (LTT) phase, superlattice peaks indicative of spin and charge stripe order are observed below 50 K. For excitation energies (h) over bar omegaless than or equal to12 meV, we have characterized the magnetic excitations that emerge from the incommensurate magnetic superlattice peaks. In the ordered state, these excitations are similar to spin waves. Following these excitations as a function of temperature, we find that there is relatively little change in the Q-integrated dynamical spin susceptibility for (h) over bar omegasimilar to10 meV as stripe order disappears and then as the structure transforms from LTT to the low-temperature-orthorhombic phase. The Q-integrated signal at lower energies changes more dramatically through these transitions, as it must in a transformation from an ordered to a disordered state. We argue that the continuous evolution through the transitions provides direct evidence that the incommensurate spin excitations in the disordered state are an indicator of dynamical charge stripes. An interesting feature of the thermal evolution is a variation in the incommensurability of the magnetic scattering. Similar behavior is observed in measurements on a single crystal of La1.875Ba0.075Sr0.050CuO4; maps of the scattered intensity in a region centered on the antiferromagnetic wave vector and measured at (h) over bar omega=4 meV are well reproduced by a model of disordered stripes with a temperature-dependent mixture of stripe spacings. We discuss the relevance of our results to understanding the magnetic excitations in cuprate superconductors.
Title:
Realization of a two-dimensional Ising system: Deuterium physisorbed on krypton-preplated graphite
Authors:
Wiechert, H; Kortmann, KD; Stusser, N
Source:
PHYSICAL REVIEW B, 70 (12): Art. No. 125410 SEP 2004
Abstract:
Volumetric adsorption isotherm, calorimetric, and neutron diffraction measurements were used to characterize the quantum system D-2 coadsorbed on graphite preplated by a monolayer of Kr. From the results obtained by these methods a detailed phase diagram of the complete submonolayer coverage range up to the initial stages of bilayer formation could be constructed. The dominant feature of the phase diagram is a commensurate (1x1)[1/2] structure, which was determined by neutron diffraction. Three phase transitions of this phase were studied: The order-disorder transition at the critical point which, according to the influence of the corrugation potential, occurs at a relatively high temperature (T-c=25.68 K), the order-disorder transition at the tricritical point (T-TC=17.88 K), and the commensurate-incommensurate (C-IC) transition at D-2 fillings above 1.2xroot3 monolayers. All these measurements gave convincing evidence that the system D-2/Kr/graphite can be regarded as realization of a two-dimensional (2D) Ising system. Critical exponents near the phase transitions were determined and good agreement with the theory obtained. Of particular interest was the investigation of the C-IC transition, which for a 2D Ising system could be studied. At this transition, the existence of a reentrant fluid was detected, which squeezes in between the C and IC phases down to at least 1.5 K, which is the lowest temperature to which a liquidlike phase of D-2 has ever been found. This observation confirms the Kosterlitz-Thouless criterion and the theory of the C-IC transition.
Title:
Defective structure in the high-T-c superconductor Hg-1234
Authors:
Luo, ZP; Li, Y; Hashimoto, H; Ihara, H; Iyo, A; Tokiwa, K; Cao, GH; Ross, JH; Larrea, JA; Baggio-Saltovitch, E
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 408-10: 50-51 AUG 2004
Abstract:
Samples with different fractions of structural modulation were synthesized in order to study the effect of a defective modulated structure on the critical temperature T-c of Hg-1234. Electron microscopy revealed the existence of modulated and unmodulated Hg-1234 structures in these samples. Measurements of critical temperature T-c on these samples revealed that the structural modulation significantly suppresses the T-c For the Hg-1234 sample without the structural modulation, the T-c was found to be close to the highest T-c for the Hg-1223 phase. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Magnetic phase diagram of ErNi2B2C
Authors:
Jensen, A; Toft, KN; Abrahamsen, AB; Andersen, NH; Jensen, J; Hedegard, P; Klenke, J; Prokes, K; Smeibidl, P; Danilkin, S; Sikolenko, V; Eskildsen, MR; Canfield, PC
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 408-10: 97-99 AUG 2004
Abstract:
The magnetic phase diagram of the superconductor ErNi2B2C (T-c = 11 K and T-N = 6 K) has been studied by neutron diffraction as a function of temperature and magnetic field applied along the symmetry directions [010], [110] and [001] of the tetragonal crystal structure. A series of commensurate magnetic structures, consistent with a transversely polarized spin-density wave with modulation vectors Q = n/ma* (0.55 less than or equal to n/m < 0.60) and the spins along b*, have been observed. The experimental data are compared with the results of a mean-field model that has been established from an analysis of bulk magnetization and zero-field neutron diffraction data. The model accounts for most of the observed features but fails to explain the occurrence of a small component Qdelta approximate to -0.005b* observed close to H-c2 when the field is applied along [110]. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Photoemission study of valence band dispersions in charge density wave material IT-TaS2
Authors:
Arita, M; Negishi, H; Shimada, K; Xu, FQ; Ino, A; Takeda, Y; Yamazaki, K; Kimura, A; Qiao, S; Negishi, S; Sasaki, M; Namatame, H; Taniguchi, M
Source:
PHYSICA B-CONDENSED MATTER, 351 (3-4): 265-267 SEP 15 2004
Abstract:
Angle-resolved photoemission spectra of 1T-TaS2 have been measured to reveal the electronic structure of valence bands in the incommensurate (IC) and commensurate (C) charge density wave (CDW) phases. In the ICCDW phase at 370 K. Ta 5d states are observed as a single branch along the Gamma-M direction over the binding energy range E-B = 0-1.2 eV. In the CCDW phase at 17 K, on the other hand, Ta 5d states are divided into three sub-band manifolds centered at E-B = 0.2, 0.5 and 1.0 eV. The former sub-band at E-B = 0.2 eV is less dispersive, while latter two show clear dispersive nature with the bandwidths of similar to0.5 and 0.3 eV. Furthermore, the spectral intensities are concentrated around the original Ta 5d band. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Gaseous hydrogen charging of Zr-Cu-Ni-Al glasses and quasicrystals
Authors:
Huett, VT; Zander, D; Jastrow, L; Majzoub, EH; Kelton, KF; Koster, U
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 379 (1-2): 16-22 OCT 6 2004
Abstract:
Metallic glasses as well as quasicrystalline alloys are new materials with very promising properties. Zr-based metallic glasses for example are used in a number of applications due to their superior mechanical properties, e.g. for golf clubs or penetrators. Zr-based glasses as well as quasicrystals, however, have been observed only recently to store hydrogen up to a content close to that of best crystalline materials, thus opening a promising new field for application. The objective point of our present research is to investigate in detail hydrogen absorption in amorphous and quasicrystalline Zr69.5Cu12Ni11Al7.5 from the gas phase and to study the influence of the microstructure on hydrogenation. However, as during hydrogenation concentration changes are expected to move the metastable materials out of their stability range, these processes might be accompanied by phase transformations. Therefore, special emphasis was also being given on the influence of hydrogenation on the microstructure and thermal stability, also in comparison with alloys hydrogenated electrochemically. Our results show that hydrogen in the amorphous alloy does change the phase evolution. Instead of forming first the quasicrystalline phase followed by the stable crystalline intermetallics at higher temperatures, these hydrogenated samples crystallize to Zr-hydrides. We were, however, not able to prove whether the amorphous samples were truly amorphous or nanocrystalline after hydrogenation. In (partially) quasicrystalline alloys the hydrogenation from the gas phase does not result in transformations into the approximants, or amorphization prior to the formation of crystalline hydrides as known from electrochemical charging. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Crystallographic excursion in superspace
Authors:
Chapuis, G
Source:
CRYSTAL ENGINEERING, 6 (4): 187-195 DEC 2003
Abstract:
After studying more than 100 different samples of calaverite Au1-pAgpTe2 (p < 0.15) three famous mineralogists declared in a well documented 1931 publication the invalidity of the law of rational indices. What could lead them to draw such an extreme conclusion from the observation law of Hauy dating from more than two centuries? Their observations remained unexplained for the next forty years. In the 1970's, the room temperature structure of gamma-Na2CO3 resisted any attempt for a precise structural analysis. The appearance of satellite reflections was noted on single crystal diffractograms which led to the generalisation of the concept of crystal. This generalisation consisted in using at least four integers to fully characterise each individual diffractions peaks. The theory of periodic crystals in space of higher dimension, i.e. the superspace was then developed to deal with the new experimental observations. Later, a new class of materials called composite crystals and still later, the discovery of quasicrystals only reinforced the validity of the superspace concept to describe any material requiring more than three integers to index their diffraction pattern. What is the essence of superspace to describe crystalline structures? Any crystal structure requesting more than three integers to index its diffraction pattern can be described as a periodic object in superspace with dimension equal to the number of required integer. The structure observed in our real word is a three dimensional cut of the superspace description. In general this cut is irrational and consequently the crystal is aperiodic. Calaverite and gamma-Na2CO3 are examples of aperiodic crystals which includes incommensurately modulated crystals, composite and quasi-crystals. Rational cuts are also possible. In this case, the structure is periodic and is usually called a superstructure. (C) 2004 Elsevier Ltd. All rights reserved.

Update: 22_Oct_2004

Title:
Conical second harmonic generation in a two-dimensional chi((2)) photonic crystal: A hexagonally poled LiTaO3 crystal
Authors:
Xu, P; Ji, SH; Zhu, SN; Yu, XQ; Sun, J; Wang, HT; He, JL; Zhu, YY; Ming, NB
Source:
PHYSICAL REVIEW LETTERS, 93 (13): Art. No. 133904 SEP 24 2004
Abstract:
A new type of conical second-harmonic generation was discovered in a 2D chi((2)) photonic crystal-a hexagonally poled LiTaO3 crystal. It reveals the presence of another type of nonlinear interaction-a scattering involved optical parametric generation in a nonlinear medium. Such a nonlinear interaction can be significantly enlarged in a modulated chi((2)) structure by a quasi-phase-matching process. The conical beam records the spatial distribution of the scattering signal and discloses the structure information and symmetry of the 2D chi((2)) photonic crystal.
Title:
Dislocations in basic-nickel decagonal Al-Ni-Co single quasicrystals
Authors:
Schall, P; Feuerbachery, M; Urban, K
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 84 (7): 471-481 JUL 2004
Abstract:
We present a study of dislocations in decagonal Al70Ni21Co9 quasicrystals by means of diffraction contrast analysis as well as convergent-beam electron diffraction in the transmission electron microscope. The nickel-rich Al-Ni-Co quasicrystals show diffraction patterns characteristic of the basic-nickel decagonal phase exhibiting almost no diffuse scattering. We succeeded in growing this phase in the form of large single quasicrystals. The two-beam bright-field images show a homogeneous background and no striation contrast as reported for other Al-Ni-Co decagonal phases. We have, for the first time in a two-dimensional quasicrystal, observed the weak contrast-extinction condition.
Title:
A new 2212-type stair like structure: Bi14Sr21Fe12O61, m=5 member of the generic [Bi2Sr3Fe2O9](m)[Bi4Sr6Fe2O16] family
Authors:
Allix, M; Perez, O; Pelloquin, D; Hervieu, M; Raveau, B
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 177 (9): 3187-3196 SEP 2004
Abstract:
A new oxide. Bi14Sr21Fe12O61, with a layered structure derived from the 2212 modulated type structure Bi2Sr3Fe2O9, was isolated. It crystallizes in the 12 space group, with the following parameters: a = 16.58(3) Angstrom, b = 5.496(1) Angstrom, c = 35.27(2) Angstrom and beta = 90.62degrees. The single crystal X-ray structure determination, coupled with electron microscopy, shows that this ferrite is the m = 5 member of the [Bi2Sr3Fe2O9](m)[Bi4Sr6Fe2O16] collapsed family. This new collapsed structure can be described as slices of 2212 structure of five bismuth polyhedra thick along a(-->), shifted with respect to each other and interconnected by means of [Bi4Sr6Fe2O16] slices. The latter are the place of numerous defects like iron or strontium for bismuth substitution; they can be correlated to intergrowth defects with other members of the family. (C) 2004 Elsevier Inc. All rights reserved.
Title:
Modulated magnetic structure of weak rhombohedral ferromagnets alpha-Fe2O3 : Ga and FeBO3 : Mg
Authors:
Sokolov, BY
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 99 (2): 417-426 AUG 2004
Abstract:
The effect of diamagnetic impurities on the stability of the homogeneous magnetic state of rhombohedral antiferromagnets with weak ferromagnetism (alpha-Fe2O3:Ga and FeBO3:Mg) is studied experimentally. It is shown that the application of an external magnetic field in the basal plane in the crystals under study in a certain temperature range induces a magnetic: superstructure along the hard magnetization axis, which can be presented in the form of a ripplon phase with the azimuth of the local ferromagnetism vector oscillating about the direction of the field. The preferred orientation of the discovered modulated structures relative to crystallographic directions in the basal plane of alpha-Fe2O3:Ga and FeBO3:Mg is studied, and the dependence of the spatial period of the superstructure on the applied magnetic field and temperature is analyzed. The magnetic-field-induced transition of the studied crystals from a homogeneous to an inhomogeneous magnetic state is described phenomenologically on the basis of the thermodynamic potential with gradient terms. In the discussion of physical reasons for magnetic order parameter modulation in weak ferromagnetic doped with diamagnetic ions, preference is given to the mechanism associated with the emergence of uniaxial magnetic centers with a random distribution of azimuths of easy axes in the nasal plane of the crystal in the vicinity of impurities. A model describing the formation of a modulated magnetic state in alpha-Fe2O3:Ga and FeBO3:Mg is proposed, according to which the competition between magnetoanisotropic and Zeeman interactions in the inhomogeneous magnetic phase of these crystals leads to periodic deviations in the direction of the local ferromagnetism vector from the direction of magnetization. (C) 2004 MAIK "Nauka/Interperiodica".
Title:
Al-Cu-Fe quasicrystals for steam reforming of methanol: a new form of copper catalysts
Authors:
Kameoka, S; Tanabe, T; Tsai, AP
Source:
CATALYSIS TODAY, 93-95: 23-26 SEP 1 2004
Abstract:
Alloy catalysts were prepared by leaching various structures of Al-Cu-(Fe) alloys (quasicrystal (QC), beta- or theta-phase) in NaOH and Na2CO3 aqueous solutions. Comparison of the catalytic properties for steam reforming of methanol (SRM) on different Al-Cu-(Fe) alloy phases (quasicrystalline versus crystalline phase) was made. At high temperatures (e.g., 360degreesC), the catalytic activity of the QC catalyst (5% Na2CO3-leached) for the SRM was much higher than that of other phase catalysts. No sintering of highly dispersed copper particles on QC catalyst was observed by XRD measurements even after the SRM reaction at 360degreesC. We propose that the high catalytic activity and the excellent thermal stability of copper particles on QC catalyst are due to the immiscibility of Fe with Cu and the interaction with QC surface. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Incommensurability imposed by the low-temperature phase transition at the (001) surface of SrTiO3
Authors:
Krainyukova, NV; Butskii, VV
Source:
APPLIED SURFACE SCIENCE, 235 (1-2): 43-48 JUL 31 2004
Abstract:
The reflection high-energy electron diffraction (RHEED) study of the SrTiO3 (0 0 1) surface structure in the temperature region from 6 to 300 K shows the "anomalous" growth of the surface lattice parameters under the temperature decrease. This behavior is ascribed to the specific character of the low-temperature phase transition connected with the rotation of the metal-centered oxygen octahedra around the normal to the (0 0 1) surface. RHEED intensities analysis based on R-factor minimization shows that the best-fit between the experiment and calculations is reached for oxygen octahedra rotations which are essentially different for two (0 0 1) surface terminations SrO and TiO2. Octahedra rotations were assumed to give rise to an increase of the surface lattice parameters resulting in the fact that incommensurability between the bulk and surface parameters inevitably arises. The histogram method applied to the set of lattice parameter values shows the discrete character of the distribution obtained. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Modulation derived satellite peaks in x-ray reciprocal mapping on bismuth cuprate superconductor film
Authors:
Kaneko, S; Shimizu, Y; Akiyama, K; Ito, T; Mitsuhashi, M; Ohya, S; Saito, K; Funakubo, H; Yoshimoto, M
Source:
APPLIED PHYSICS LETTERS, 85 (12): 2301-2303 SEP 20 2004
Abstract:
X-ray reciprocal space mapping (XRSM) was employed to investigate epitaxial Bi2Sr2Ca1Cu2Ox(Bi-2212) film. Ordinal cross section XRSM (omega-2theta) and plan view XRSM (omega-psi) clearly indicated asymmetric intensity distribution of four satellite peaks caused by supercell structure of Bi-2212 film. Modulation vector estimated by XRSM was q=0.2b(*)+0.9c(*). The XRSM image simulated by sawtooth wave vector showed good agreement with asymmetric satellite peaks observed on epitaxial film. (C) 2004 American Institute of Physics.

Update: 15_Oct_2004

Title:
Formation of a spin density wave in copper metaborate by a spin polaron
Authors:
Aplesnin, SS
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (32): 5907-5914 AUG 18 2004
Abstract:
Formation of incommensurate three-dimensional magnetic order below T* similar to 10 K in CuB2O4 is explained on the basis of strong correlation between the holes and localized spins. The Kondo lattice model is analysed for the case where spin polarons are the elementary excitations. The origin of the low-temperature specific heat maximum at T similar to 5 K is associated with a displacement of the polaron band bottom. A set of anomalies in the temperature dependence of the conductivity, shift of the optical conductivity maximum in the range of energies 0.02-0.12 eV and decreasing of the infrared absorption intensity is predicted.
Title:
Formation of icosahedral-hexagonal H phase nano-composites in Mg-Zn-Y alloys
Authors:
Singh, A; Watanabe, M; Kato, A; Tsai, AP
Source:
SCRIPTA MATERIALIA, 51 (10): 955-960 NOV 2004
Abstract:
A reaction is identified in formation of icosahedral phase in dilute Mg-Zn-Y alloys, involving a hexagonal phase H-Zn3MgY (a = 0.918, c = 0.95 nm). The crystallographic relationship and the interface between the H and the icosahedral phase are described. Formation of an icosahedral-H phase nano-composite in a Mg93Zn6Y alloy is shown. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Fermi surface reconstruction in the CDW state of CeTe3 observed by photoemission
Authors:
Brouet, V; Yang, WL; Zhou, XJ; Hussain, Z; Ru, N; Shin, KY; Fisher, IR; Shen, ZX
Source:
PHYSICAL REVIEW LETTERS, 93 (12): Art. No. 126405 SEP 17 2004
Abstract:
CeTe3 is a layered compound where an incommensurate charge density wave (CDW) opens a large gap (similar or equal to400 meV) in optimally nested regions of the Fermi surface (FS), whereas other sections with poorer nesting remain ungapped. Through angle-resolved photoemission, we identify bands backfolded according to the CDW periodicity. They define FS pockets formed by the intersection of the original FS and its CDW replica. Such pockets illustrate very directly the role of nesting in the CDW formation but they could not be detected so far in a CDW system. We address the reasons for the weak intensity of the folded bands, by comparing different foldings coexisting in CeTe3.
Title:
In-situ observation of dislocation motion in icosahedral Al-Pd-Mn quasicrystals
Authors:
Mompiou, F; Caillard, D; Feuerbacher, M
Source:
PHILOSOPHICAL MAGAZINE, 84 (25-26): 2777-2792 SEP 1 2004
Abstract:
Dislocation motion in icosahedral Al-Pd-Mn quasicrystals has been observed in situ in a transmission electron microscope between 700 and 750degreesC. Contrast analyses show that it takes place by pure climb in twofold, threefold and fivefold planes. Moving dislocations exhibit polygonal shapes with edges parallel to twofold directions, in agreement with a difficult jog-pair nucleation. Dislocation multiplication, annihilation and local pinning are described and discussed, as well as the role of the phason faults trailed in the wake of dislocations, at the lowest investigated temperatures.
Title:
Statistical approach to multiple-q modulated structures: average Patterson analysis
Authors:
Urban, G; Wolny, J
Source:
PHILOSOPHICAL MAGAZINE, 84 (27): 2905-2917 SEP 21 2004
Abstract:
Using a statistical approach, the average unit cells have been constructed for modulated structures with different types of modulation, from simple sinusoidal to square-wave functions. The obtained unit cells fully describe diffraction intensities of the main reflections and their satellites. A universal distribution, valid for different lengths of the modulation vector, has been found. Average Patterson functions have been constructed and used to distinguish between different types of modulation.
Title:
Orientation relationships of icosahedral quasicrystalline phase and laves phase precipitates in a ferritic alloy
Authors:
Yamamoto, K; Kimura, Y; Mishima, Y
Source:
MATERIALS TRANSACTIONS, 45 (8): 2598-2601 AUG 2004
Abstract:
The precipitation behavior and orientation relationships of icosahedral quasicrystal line phase (I-phase) and Laves phase precipitates in ferrite matrix have been investigated by transmission electron microscopy (TEM) in an Fe-10Cr-1.4W-4.5Co-0.3Si (at%) alloy. It is found that the precipitates of the alloy aged at 873 K are the I-phase but those of the alloy aged at 973 K are the Laves phase. Through a double aging experiment at both temperatures, it is shown that the transformation between the I-phase and the Laves phase occurs. Although a single orientation relationship is established between the I-phase and the ferrite matrix, three different types of the orientation relationships between the Laves phase and the ferrite matrix are obtained by the analysis of SAD patterns. The results can be explained by the coincidence between the five-fold symmetrical plane of the I-phase and the (1120) plane of the Laves phase on the phase transformation between them.
Title:
Quantification of micrometre-sized porosity in quasicrystals using coherent synchrotron radiation imaging
Authors:
Agliozzo, S; Cloetens, P
Source:
JOURNAL OF MICROSCOPY-OXFORD, 216: 62-69 Part 1 OCT 2004
Abstract:
Phase contrast radiography has been applied to investigate porosity in the bulk of quasicrystals. The pores act on X-rays as lenses, leading to drastic changes in the phase contrast images of pores. Depending on the recording conditions and pore features, different imaging regimes are accessed. The variation of the contrast makes the direct characterization of pores from image data, in terms of a precise determination of their size and volume, unreliable. The contrast in Fresnel diffraction images of pores was thus investigated with the support of numerical simulations. A phase retrieval procedure was carried out in order to obtain the correct information from the pore images.
Title:
Disordered quasicrystals: diffuse scattering in decagonal Al-Ni-Fe
Authors:
Weidner, E; Frey, F; Lei, JL; Pedersen, B; Paulmann, C; Morgenroth, W
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 37: 802-807 Part 5 OCT 2004
Abstract:
High-resolution synchrotron data of near-Bragg diffuse scattering from decagonal Al71.5Ni23.5Fe5 quasicrystals were recorded. A dominant phasonic origin is ruled out because of the absence of a significant G(perpendicular to) dependence. An analysis solely in the frame of thermal diffuse scattering (TDS) theory (phonon scattering) showed a good match between experimental and calculated data in the quasiperiodic layers, but with an improbable ratio of elastic constants, c(66)/c(11) = 4.0. In situ high-temperature measurements up to 1000 K revealed an increase of the intensity distribution perpendicular to the scattering vector G. Huang diffuse scattering (HDS) arising from quenched local defects has a general appearance that qualitatively reproduces the observed symmetry and anisotropy. An interpretation based on both TDS and HDS contributions is given.
Title:
Contribution of powder diffraction for structure refinements of aperiodic misfit cobalt oxides
Authors:
Grebille, D; Lambert, S; Bouree, F; Petricek, V
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 37: 823-831 Part 5 OCT 2004
Abstract:
Two families of misfit cobalt oxides have been reinvestigated using neutron and synchrotron powder diffraction data and Rietveld structure refinements in the four-dimensional formalism for aperiodic structures. In the first system [Ca2CoO3][CoO2](1.62), the structure-specific features of two complex polytypic phases previously described from single-crystal diffraction data have been confirmed for the main term of the series and are described with the C2/m(1,delta,0) s0 superspace symmetry (R-p = 0.026, R-wp = 0.031, R-B = 0.014). The high-resolution synchrotron diffraction experiments have been interpreted with a triclinic distortion of the structure, probably related to an intrinsic modulation of the [Ca2CoO3] sublattice in relation with Co and O split atomic sites. In the second system Ca-0.82(Cu0.65Co0.35O2), a new occupation modulation of the metallic site is shown with the Fmmm(alpha11) 0ss superspace symmetry (R-p = 0.031, R-wp = 0.039! , R-B = 0.027) and is interpreted in relation with the modulated interatomic distances of the square coordination of the cationic site. In both cases, recently developed tools for structure refinements of aperiodic systems using powder diffraction data ( in the JANA2000 package) have proved their efficiency, in particular as specific complements to previous single-crystal structure refinements.

Update: 8_Oct_2004

Title:
Crystal structure of the mixed Mn4+/Mn5+ 2H-perovskite-type Ba4Mn2NaO9 oxide
Authors:
Quarez, E; Roussel, P; Perez, O; Leligny, H; Bendraoua, A; Mentre, O
Source:
SOLID STATE SCIENCES, 6 (9): 931-938 SEP 2004
Abstract:
Single crystals of the new Ba4Mn2NaO9 have been prepared by electrosynthesis in molten NaOH. Its crystal structure has been solved from XRD data (a = 10.006(2), c = 8.210(3), space group P321, Z = 3, R = 3.21%, wR = 3.52%). It belongs to the wide family of 2H-related perovskite materials and shows columns of face-sharing MnO6 octahedra and NaO6 prisms according to the -(oct-oct-prism)sequence isolated by Ba2+ cations. The main characteristic of this new oxide is its mixed Mn4+/Mn5+ valence rarely reported up today. Help A to the superspace formalism, Ba4Mn2NaO9 (or Ba1+xNaMn1-xO3 with x = 1/3) can be regarded as composed of two interpenetrating sublattices [Ba1+x] and [Na1/3Mn2/3O3] with their own period along the c axis. The ratio gamma of these two periods is rational y = c(1)/c(2) = 2/3. This composite structure approach which allows us, help to established rules, to predict the crystal structure from the gamma-only knowledge has also been pointed out in this work. (C) 2004 Elsevier SAS. All rights reserved.
Title:
High-energy non-resonant X-ray magnetic scattering from EuAS(3)
Authors:
Chatterji, T; Liss, KD; Tschentscher, T; Janossy, B; Strempfer, J; Bruckel, T
Source:
SOLID STATE COMMUNICATIONS, 131 (11): 713-717 SEP 2004
Abstract:
We have investigated non-resonant high energy X-ray magnetic scattering from EuAs3 both in the antiferromagnetic and in the incommensurate phase by using an X-ray energy of 104 and 106 keV. In the antiferromagnetic phase, we obtained a signal to background ratio of about 10:1 for the magnetic Bragg peak at Q = (-1, 0, 1/2) and a maximum count rate of about 200 counts/s at T = 3.1 K. To our knowledge this is the first reported observation of the non-resonant magnetic signal from a rare-earth ion at X-ray energy as high as 106 keV. The temperature dependence of the integrated intensity of the (-1, 0, 1/2); magnetic reflection has been measured and compared with that obtained previously by neutron diffraction. We measured the integrated intensities of several magnetic reflections from the antiferromagnetic phase and have compared them with those calculated from the magnetic structure model derived from neutron diffraction. The intensities of the magnetic satellite reflections from the incommensurate phase have been measured and have been found to be very weak. We also investigated the temperature variation of the lattice spacing close to the magnetic ordering transition and have found a large magnetoelastic anomaly at the lock-in phase transition. (C) 2004 Elsevier Ltd. All rights reserved.
Title:
Structure and microstructure of colossal magnetoresistant materials
Authors:
Van Tendeloo, G; Lebedev, OI; Hervieu, M; Raveau, B
Source:
REPORTS ON PROGRESS IN PHYSICS, 67 (8): 1315-1365 AUG 2004
Abstract:
Most manganites exhibiting colossal magnetoresistant properties are structurally very simple. They are based on a perosvskite structure with the general formula (A(1-x)A'(x))MnO3. The electric and magnetic properties strongly depend on the composition (A, A', x) and eventually on the exact oxygen content. These changing properties are strongly related to structural and microstructural changes. Indeed, the structure has many degrees of freedom. The MnO6 octahedra can not only deform, they can also rotate along their fourfold or twofold axis, giving rise to different superstructures or modulated structures. This will lower the symmetry of the structure from cubic to orthorhombic, rhombohedral or monoclinic. A lowering in symmetry will of course introduce different orientation variants (twins) and translation variants (antiphase boundaries). These microstructural changes are reviewed here through a transmission electron microscopy study of bulk as well as thin film colossal magnetoresistance materials. For thin films grown on a single crystal substrate the misfit with the substrate is another very important parameter, which determines the structure and the microstructure. We review different methods of accommodating the stress induced by the substrate: elastically, through interface dislocations, through pseudo-periodic twinning, through formation of antiphase domains or through a phase transition in the film. (C) 2004 IOP Publishing Ltd.
Title:
Colossal magnetodielectric effects in DyMn2O5
Authors:
Hur, N; Park, S; Sharma, PA; Guha, S; Cheong, SW
Source:
PHYSICAL REVIEW LETTERS, 93 (10): Art. No. 107207 SEP 3 2004
Abstract:
We have investigated the detailed magnetic field dependence of the electric polarization and dielectric constant in (Tb,Dy,Ho)Mn2O5 where magnetic and ferroelectric transitions are intimately coupled. Our fundamental discovery is the unprecedented large change of the dielectric constant with magnetic field, particularly in DyMn2O5, associated with an unusual commensurate-incommensurate magnetic transition. This extraordinary effect appears to originate from the high sensitivity of the incommensurate state to external perturbation.

Update: 1-Oct-2004

Title:
Confirmation of the incommensurate nature of Se-IV at pressures below 70 GPa
Authors:
McMahon, MI; Hejny, C; Loveday, JS; Lundegaard, LF; Hanfland, M
Source:
PHYSICAL REVIEW B, 70 (5): Art. No. 054101 AUG 2004
Abstract:
Se-IV, the high-pressure phase of selenium stable above 28 GPa, is shown to have an incommensurately modulated structure to a least 70 GPa, the highest pressure reached in this study. Although the previously reported phase transition at 40-60 GPa to primitive rhombohedral Se-V is not observed, extrapolation of the Se-IV structural parameters suggests a continuous transition to Se-V would occur at 82 GPa. The incommensurate wave vector of Se-IV is significantly pressure dependent, varying from 0.314(1) at 28.9 GPa to 0.277(1) at 56 GPa.
Title:
First-principles calculation of defect-formation energies in the Y-2(Ti,Sn,Zr)(2)O-7 pyrochlore
Authors:
Panero, WR; Stixrude, L; Ewing, RC
Source:
PHYSICAL REVIEW B, 70 (5): Art. No. 054110 AUG 2004
Abstract:
Isometric pyrochlore, A(2)B(2)O(7), with compositions in the Y-2(Ti,Sn,Zr)(2)O-7 ternary system, are of particular interest because there are dramatic changes in properties, such as ionic conductivity, and response to radiation damage, as a function of disordering of the A- and B-site cations and oxygen vacancies. First-principles calculations using density functional theory and the plane-wave pseudopotential method, predict lattice constants (1.0049-1.0463 nm), atomic coordinates, and bulk moduli (176-205 GPa) that are linearly dependent on the B-site cation radius (0.062-0.072 nm). However, the energetics for the formation of cation-antisite (0-2 eV) and Frenkel-pair (4-11 eV) defects do not correlate with cation size, underscoring the importance of the specific electronic configuration of the B-site cation. The greater degree of covalent bonding between as compared with or results in defect formation energies otherwise unexpected solely due to the radius ratios of the cation species. Y2Sn2O7 shows 2-4 eV greater defect formation energies than otherwise predicted through mean B-site cation sizes. Relaxed calculations on coupled cation-antisite and Frenkel-pair defects show that cation-antisite reactions likely drive the oxygen-Frenkel pair defect formation process that ultimately leads to increased oxygen mobility and completely aperiodic structures. Total charge and partial density of states calculations show strikingly different behavior of oxygen on two different crystallographic positions, emphasizing the need for a full account of the electronic structure.
Title:
Incommensurate state in a quasi-one-dimensional S=1/2 bond-alternating antiferromagnet with frustration in magnetic fields
Authors:
Suzuki, T; Suga, S
Source:
PHYSICAL REVIEW B, 70 (5): Art. No. 054419 AUG 2004
Abstract:
We investigate the critical properties of the S=1/2 bond-alternating spin chain with a next-nearest-neighbor interaction in magnetic fields. By the numerical calculation and the exact solution based on the effective Hamiltonian, we show that there is a parameter region where the longitudinal incommensurate spin correlation becomes dominant around the half-magnetization of the saturation. Possible interpretations of our results are discussed. We next investigate the effects of the interchain interaction (J'). The staggered susceptibility and the uniform magnetization are calculated by combining the density-matrix renormalization group method with the interchain mean-field theory. For the parameters where the dominant longitudinal incommensurate spin correlation appears in the case J'=0, the staggered long-range order does not emerge up to a certain critical value of J' around the half-magnetization of the saturation. We calculate the static structure factor in such a parameter region. The size dependence of the static structure factor at k=2k(F) implies that the system has a tendency to form an incommensurate long-range order around the half-magnetization of the saturation. We discuss the recent experimental results for the NMR relaxation rate in magnetic fields performed for pentafluorophenyl nitronyl nitroxide.
Title:
Superconducting/ferromagnetic proximity effect mediated by Cr spacer layers
Authors:
Garifullin, IA; Tikhonov, DA; Garif'yanov, NN; Fattakhov, MZ; Tagirov, LR; Theis-Brohl, K; Westerholt, K; Zabel, H
Source:
PHYSICAL REVIEW B, 70 (5): Art. No. 054505 AUG 2004
Abstract:
We have studied the superconducting proximity effect in the thin film system Fe/Cr/V/Cr/Fe where the Cr layers play the role of screening layers between the superconducting V-layer and the strongly pair breaking Fe-layers. When keeping the thickness of the Fe-layers d(Fe) fixed and varying the thickness of the Cr-layers d(Cr), the superconducting transition temperature T-c first rises reaching a maximum at d(Cr)=40 Angstrom and then sharply drops for larger Cr-thickness. Keeping d(Cr) constant and varying d(Fe) the superconducting transition temperature becomes independent on d(Fe) for d(Cr)>40 Angstrom. The results demonstrate that the Cooper pairs penetrate into the Cr-layer to a depth of about 40 A. From our experimental results we suggest that the Cr-layer is nonmagnetic for d(Cr)<40 Angstrom and undergoes a transition to an incommensurate spin density wave state for d(Cr)>40 Angstrom.
Title:
Calorimetric investigation of successive phase transitions in Cd2Nb2O7
Authors:
Tachibana, M; Kawaji, H; Atake, T
Source:
PHYSICAL REVIEW B, 70 (6): Art. No. 064103 AUG 2004
Abstract:
We report the heat capacity (C-p) measurements on single crystals of pyrochlore Cd2Nb2O7 over the temperature range of 0.3 to 420 K. A peak in C-p appears at T-s=204 K, where a small anomaly is observed in the dielectric constant. Below T-s, there is a broad C-p anomaly that corresponds to the relaxor-like behavior in the dielectric constant. At lower temperatures, the shape of C-p anomalies around the continuous transition at 85 K and the first-order transition at 46 K is consistent with normal-incommensurate and incommensurate-commensurate transition, respectively, as suggested in previous Raman studies. In the lowest temperature region, C-p of Cd2Nb2O7 is compared with that of typical relaxor Pb(Mg1/3Nb2/3)O-3 (PMN). While the low-temperature C-p of PMN exhibits a glasslike behavior with the linear temperature-dependent coefficient of 1.6 muJ K-2 g(-1), C-p of Cd2Nb2O7 shows the crystalline behavior. This suggests that polar clusters associated with the relaxor-like behavior in Cd2Nb2O7 develop into normal ferroelectric domains below the incommensurate transitions.
Title:
Optical investigation of the origin of switching conduction in charge-density waves
Authors:
Ogawa, N; Miyano, K
Source:
PHYSICAL REVIEW B, 70 (7): Art. No. 075111 AUG 2004
Abstract:
Low-temperature dynamical properties of the sliding charge-density wave (CDW) in K0.3MoO3 was investigated using the optical modulation of the phase strain. An intimate relation between switching transition, size effects, and photoeffects was found, and discussed in terms of the plastic ground state of the CDW. Large evolution of the sliding threshold voltage and clear conduction delay were also observed, and manipulated through photoexcitation. Optical excitation is more effective in the plastic state, and it is confirmed that the switching occurs through the inhomogeneous breaking transition of the rigid but fragile CDW.
Title:
Room temperature study of a strain-induced electronic superstructure on a magnetite (111)surface
Authors:
Berdunov, N; Murphy, S; Mariotto, G; Shvets, IV
Source:
PHYSICAL REVIEW B, 70 (8): Art. No. 085404 AUG 2004
Abstract:
A magnetite (Fe3O4) single-crystal (111) surface has been studied at various oxygen-iron surface stoichiometries. The stoichiometry was modified by controlling the in situ sample anneal conditions. We have found the conditions that lead to the formation of an oxygen-rich surface that forms a quasihexagonal superstructure with a 42 A periodicity. The superstructure is highly regular and was observed by both low-energy election diffraction and scanning tunneling microscopy. The superstructure consists of three regions, two of which have identical atomic scale structures with a periodicity of 2.8 Angstrom, and a third having a periodicity that is about 10% larger (3.1 Angstrom). The subtle difference in the atomic periodicities between the three areas results from the modulation of intrinsic strain developed along the surface. The superstructure results from electronic effects rather than being a mosaic of different iron oxide terminations. The onset of the superstructure is sensitive to the surface stoichiometry. From our results we could estimate the critical density of defects leading to the disappearance of the superstructure. We have modeled the experimental results and calculated the electron density using density functional theory calculations. The model clearly shows the development of strain along the surface.
Title:
Real space renormalization group study of the S=1/2 XXZ chains with fibonacci exchange modulation
Authors:
Hida, K
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73 (8): 2296-2304 AUG 2004
Abstract:
Ground state properties of the S = 1/2 antiferromagnetic XXZ chain with Fibonacci exchange modulation are studied using the real space renormalization group method for strong modulation. The quantum dynamical critical behavior with a new universality class is predicted in the isotropic case. Combining our results with the weak coupling renormalization group results by Vidal et al., the ground state phase diagram is obtained.
Title:
The proximity effect in an Fe-Cr-V-Cr-Fe system
Authors:
Garifullin, IA; Tikhonov, DA; Garif'yanov, NN; Fattakhov, MZ; Tagirov, LR; Theiz-Brohl, K; Westerholt, K; Zabel, H
Source:
JETP LETTERS, 80 (1): 44-48 2004
Abstract:
The proximity effect was studied in a thin-film Fe-Cr-V-Cr-Fe layered system. As the chromium layer thickness (d(Cr)) increases at a fixed thickness of iron layers (d(Fe)), the dependence of the superconducting transition temperature (T-c) on d(Cr) exhibits a maximum at d(Cr) similar or equal to 40 Angstrom followed by a sharp decrease. Investigation of the dependence of T-c on d(Fe) at a fixed d(Cr) showed that the depth of penetration of the Cooper pairs into a chromium layer does not exceed 40 Angstrom. Analysis of the results obtained suggests that, at d(Cr) similar or equal to 40 Angstrom, chromium layers exhibit the transition from a nonmagnetic state to an incommensurate spin density wave state. (C) 2004 MAIK "Nauka / Interperiodica".
Title:
Splitting rules for the 2nd hierarchy structure of the electronic spectra of 2D FC(n) quasicrystals
Authors:
Li, F; Yang, XB
Source:
EUROPEAN PHYSICAL JOURNAL B, 39 (4): 475-481 JUN 2004
Abstract:
On the basis of our former work and by means of the decomposition-decimation method, we study the splitting rules for the second hierarchy of the electronic energy spectra for two-dimensional Fibonacci-class quasicrystals with one kind of atom and two bond lengths. It is found that every line of the sub-spectra for n x n and (n+1) x (n+1) clusters of FC(n)(ngreater than or equal to2) splits according to the type Y'((n-1)-2-1) and type Yn-2-1 respectively. The one for n x (n+1) clusters of FC(n) consists of three sub-subbands when nless than or equal to2, and five sub-subbranches when ngreater than or equal to3. The general formulae of the number of energy levels for the spectra of the second hierarchy are obtained. The analytical results are confirmed by numerical simulations.
Title:
Quasicrystal as a locally deformed crystal structure
Authors:
Chizhikov, VA
Source:
CRYSTALLOGRAPHY REPORTS, 49 (4): 537-546 JUL-AUG 2004
Abstract:
Lattice models for a two-dimensional octagonal quasicrystal and a three-dimensional icosahedral quasicrystal with the icosahedral-dodecahedral local order are introduced. It is shown that an octagonal quasicrystal may be obtained as a result of the local deformation of an ideal square atomic lattice. Possible paths of structural transformations between various phases of an AlPd crystal are determined. It is shown that icosahedral quasicrystals of aluminum alloys with transition metals can be considered to be a result of the local distortions of an ideal fcc lattice of elemental aluminum induced by a transition metal impurity. (C) 2004 MAIK "Nauka/Interperiodica".
Title:
Intensity and width of Bragg reflections from imperfect icosahedral quasicrystals obtained by simulating atomic growth
Authors:
Dmitrienko, VE; Chizhikov, VA; Astaf'ev, SB; Kleman, M
Source:
CRYSTALLOGRAPHY REPORTS, 49 (4): 547-552 JUL-AUG 2004
Abstract:
The Bragg reflections from icosahedral quasicrystals obtained in the course of a computer experiment on the simulation of crystal growth have been studied. The computer experiments based on the theory developed earlier allow one to "grow" in a computer the imperfect quasicrystals of nanometer dimensions. It is shown that the absolute value of the structure factor can be close to the maximum possible one for crystals, i.e., to the structure factor in the case where all the atoms scatter in phase. The spectral width of Bragg reflections is studied, and it is shown that the reflection width depends not only on the quasicrystal dimensions in the physical space but, also, on the perpendicular component of the reciprocal-lattice vectors. The data obtained are compared with the known experimental data. (C) 2004 MAIK "Nauka/Interpetiodica".

Update: 24-Sep-2004

Title:
First-principles prediction of a decagonal quasicrystal containing boron
Authors:
Mihalkovic, M; Widom, M
Source:
PHYSICAL REVIEW LETTERS, 93 (9): Art. No. 095507 AUG 27 2004
Abstract:
We interpret experimentally known B-Mg-Ru crystals as quasicrystal approximants whose deterministic decoration of tiles by atoms can be extended quasiperiodically. Experimentally observed disorder corresponds to phason fluctuations. First-principles total energy calculations find many distinct tilings close to stability and suggest a phase transition from a crystalline state at low temperatures to a high temperature state characterized by tile fluctuations. We predict B38Mg17Ru45 forms a metastable decagonal quasicrystal that may be thermodynamically stable at high temperatures.
Title:
Diffraction from one- and two-dimensional quasicrystalline gratings
Authors:
Ferralis, N; Szmodis, AW; Diehl, RD
Source:
AMERICAN JOURNAL OF PHYSICS, 72 (9): 1241-1246 SEP 2004
Abstract:
The diffraction from one- and two-dimensional aperiodic structures is studied by using Fibonacci and other aperiodic gratings produced by several methods. By examining the laser diffraction patterns obtained from these gratings, the effects of aperiodic order on the diffraction pattern was observed and compared to the diffraction from real quasicrystalline surfaces. The correspondence between diffraction patterns from two-dimensional gratings and from real surfaces is demonstrated. (C) 2004 American Association of Physics Teachers.

Update: 17-Sep-2004

Title:
An introduction to the surface science of quasicrystals
Authors:
Thiel, PA
Source:
PROGRESS IN SURFACE SCIENCE, 75 (3-8): 69-86 AUG 2004
Title:
Importance of bulk properties in the structure and evolution of cleavage surfaces of quasicrystals
Authors:
Ebert, P
Source:
PROGRESS IN SURFACE SCIENCE, 75 (3-8): 109-130 AUG 2004
Abstract:
The present work reviews the recent achievements in probing bulk properties of quasicrystals by using cleavage surfaces and surface sensitive techniques. In particular, it is shown that the cluster-subcluster-based structure of the cleavage surface of icosahedral Al-Pd-Mn quasicrystals can be related to the presence of stable atom clusters in the bulk, which force the crack front to circumvent them. Furthermore, by subjecting cleavage surfaces of differently pre-annealed Al-Pd-Mn quasicrystals to a post-cleavage heat treatment, we demonstrate that bulk vacancies migrate toward the surface, where they initiate structure and composition changes. These studies allow us to characterize Al-Pd-Mn quasicrystals with respect to their bulk vacancy concentration. As-grown Al-Pd-Mn quasicrystals are found to contain a supersaturation of all chemical species of vacancies in near stoichiometric composition, whereas long term pre-annealed material has a much lower, and predominantly Al, vacancy concentration. Analogous experiments for decagonal Al-Ni-Co quasicrystals show that as-grown Al-Ni-Co has a lower vacancy concentration than as-grown Al-Pd-Mn. (C) 2004 Elsevier Ltd. All rights reserved. Probing the surface structure of quasicrystals via angle-resolved low-energy ion scattering
Authors:
Jenks, CJ; Bastasz, R
Source:
PROGRESS IN SURFACE SCIENCE, 75 (3-8): 147-160 AUG 2004
Abstract:
Angle-resolved low-energy ion scattering is a valuable technique for examining the topmost surface layers of materials. Using this technique, information about both composition and structure can be obtained. We discuss the physical basis of this technique and present our findings for the fivefold surface of icosahedral (i-) Al-Pd-Mn. Our results clearly show that the exposed surface has a higher Al content than the bulk and can have fivefold periodicity. Information about frequently occurring interatomic distances on the surface can also be obtained by this technique. We discuss the results and compare them to recent scanning tunneling microscopy studies and to bulk structure models. (C) 2004 Published by Elsevier Ltd.
Title:
Crystal-quasicrystal interfaces on Al-Pd-Mn
Authors:
Erbudak, M; Fluckiger, T; Kortan, AR; Luscher, R
Source:
PROGRESS IN SURFACE SCIENCE, 75 (3-8): 161-175 AUG 2004
Abstract:
Two decades after their discovery, quasicrystals continue to fascinate our imagination. Even though there remain many outstanding questions about the basic structure, our focus has lately been shifting beyond the basic structural aspects, towards the search for interesting physical properties and technological applications. In this regard, undoubtedly, thin film growth on quasicrystal surfaces promises to be a very fertile ground. Despite their true long-range orientational order, quasicrystals possess forbidden fivefold or tenfold point-group symmetries and lack translational periodic order. Therefore, the interface between a quasicrystal and a crystal is of immense scientific interest, because it can metastabilize previously unknown structures with unique properties and potentially disclose structural mysteries of quasicrystalline surfaces. In our studies, we used various electron probes and observed that binary Al alloys exist as commensurate single crystals on the fivefold- and threefold-symmetry surfaces of the Al-Pd-Mn alloy. Thus, epitaxial growth conditions, like lattice and chemical matching observed in crystals are apparently satisfied on a local scale. We have also grown Al films at different temperatures on quasicrystal surfaces, and found that above RT Al readily diffuses into the bulk quasicrystal leading to a huge increase of its Debye temperature, implying that. the quasicrystalline structure contains vacancies, which are filled with the additional Al. For thin films grown at RT, epitaxy locks the Al atoms to a strained quasicrystalline lattice, whereas for thicker films, excess strain energy cannot be supported and the structure relaxes to the bulk-stable face-centered cubic phase by breaking into multi-twinned domains. The crystal-quasicrystal transformations also present an opportunity to investigate the electronic structure in a comparative way. We highlight a relevant result on the filling of the Mn 3d band in Al-Pd-Mn upon quasicrystal formation that gives rise t o the pseudo gap. (C) 2004 Elsevier Ltd. All rights reserved.
Title:
High resolution scanning tunneling microscopy studies of quasicrystal surfaces: an efficient tool to investigate quasiperiodic atomic structures
Authors:
Barbier, L; Gratias, D
Source:
PROGRESS IN SURFACE SCIENCE, 75 (3-8): 177-189 AUG 2004
Abstract:
High resolution scanning tunneling microscopy (HRSTM) images of i-Al-Pd-Mn reveal wide flat terraces along the 5-fold (5f) direction with quasiperiodic atomic arrangements that are consistent with the expected structure of the dense pure aluminum planes of the bulk material as defined by 6D-models. This makes encouraging the exploration by HRSTM of a QC surface to better understand its 3D real quasiperiodic atomic structure. (C) 2004 Published by Elsevier Ltd.
Title:
Structure and electronic structure of quasicrystal and approximant surfaces: a photoemission study
Authors:
Naumovic, D
Source:
PROGRESS IN SURFACE SCIENCE, 75 (3-8): 205-225 AUG 2004
Abstract:
The structure and electronic structure of different high-symmetry surfaces of either quasicrystalline or approximant Al-Pd-Mn were studied by means of photoemission-based techniques such as X-ray photoelectron diffraction (XPD) and ultraviolet photoelectron spectroscopy. We find that the twofold (2f), 3f and 5f surfaces of icosahedral Al-Pd-Mn exhibit all the symmetry elements of the icosahedral non-crystallographic group. These XPD experiments can be modeled by single-scattering cluster calculations. The bulk-terminated icosahedral or approximant surfaces are recovered after ion sputtering followed by annealing at T approximate to 500-600degreesC. A wealth of ordered surface phases (with different compositions) are found after sputtering and depending on the annealing temperature as, for example, a crystalline bcc multitwinned phase (for T < 400degreesC) or a stable decagonal quasicrystalline surface (for T > 650degreesC). The icosahedral surfaces are characterised by a lowering of the density of states close to the Fermi edge, compatible with the opening of a pseudogap, as expected for a quasicrystal. The crystalline overlayers are characterised by a sharp Fermi edge, while the approximant and decagonal quasicrystalline surfaces also have a lowered density of states. (C) 2004 Elsevier Ltd. All rights reserved.
Title:
Electronic structure investigations of quasicrystals
Authors:
Rotenberg, E; Theis, W; Horn, K
Source:
PROGRESS IN SURFACE SCIENCE, 75 (3-8): 237-253 AUG 2004
Abstract:
We present a review of the determination of density of states (DOS) of quasicrystals using valence band photoemission spectroscopy. The absence of fine or spiky structure in the angle-integrated DOS of quasicrystals suggests the possibility of delocalized electronic states. These were confirmed with angle-resolved photoemission studies, which clearly establish the presence of dispersing features attributed to momentum-dependent bandstructure. Such dispersing states are observed not only for deeper-lying sp states, but also for d-derived bands near the Fermi level. Data from three different high symmetry surfaces of decagonal Al-Ni-Co, an ideal model system, are presented. We find that only a few dominant reciprocal lattice vectors are sufficient to describe the quasiperiodic potential, and the implications for electronic properties are discussed. (C) 2004 Elsevier Ltd. All rights reserved.
Title:
Ti/Zr/Hf-based quasicrystals
Authors:
Kelton, KF
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 375-77: 31-37 Sp. Iss. SI JUL 15 2004
Abstract:
The formation, stability and structures of the icosahedral phase (i-phase) and related complex crystal and amorphous phases in Ti/Zr/Hf alloys are reviewed. Most attention is focused on the TiZrNi quasicrystal, demonstrating that this i-phase is a low-temperature stable quasicrystal, forming almost 300degreesC below the liquidus temperature. The persistence of the i-phase at low temperatures after very long duration anneals suggests it as the first realistic candidate for a ground-state quasicrystal. A structural model for i(TiZrNi) is presented, the first for any Ti/Zr/Hf-based quasicrystal; the energy is lower than for competing crystal phases, in agreement with the results of the annealing studies. With sufficient undercooling, metastable i(TiZrNi) nucleates in preference to a polytetrahedral C14 Laves phase, suggesting a local icosahedral order in the liquid. X-ray data are presented to support that conclusion. Hydrogen storage properties of these alloys are discussed briefly and pressure composition isotherm measurements are presented and analyzed. A new Ti-Hf-Ni crystal approximant that has superior hydrogen adsorption properties is discussed. Origins of quasicrystal nanostructures, formed by crystallizing Zr-based metallic glasses are proposed. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Defects in complex intermetallics and quasicrystals
Authors:
Feuerbacher, A; Heggen, A; Urban, K
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 375-77: 84-89 Sp. Iss. SI JUL 15 2004
Abstract:
In crystals with large unit cells, conventional plasticity mechanisms involving dislocations as carriers of plastic deformation tend to fail due to the occurrence of unfavorably large Burgers vectors or energetically costly stacking faults. In this paper, we discuss the structure of defects in a number of structurally complex alloy phases possessing large cell parameters. We show that different mechanisms to accommodate dislocations apply, ranging from rather conventional scenarios to highly exotic mechanisms involving completely novel types of defect. (C) 2003 Elsevier B.V. All rights reserved.
Title:
In situ resistometric investigation of phase transformations in rapidly solidified Al-based alloys containing dispersed nanoscale particles
Authors:
Prima, F; Tomut, M; Stone, I; Cantor, B; Janickonic, D; Vlasak, G; Svec, P
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 375-77: 772-775 Sp. Iss. SI JUL 15 2004
Abstract:
Structural studies and resistometric measurements have been correlated to investigate the microstructural evolution during annealing in a quasicrystal (QC) forming Al-based alloy, Al93Fe3Cr2Ti2 (at.%), containing nanoscale dispersed icosahedral particles in an fcc alpha-Al matrix. Isothermal and anisothermal resistometric runs have been carried out on as-quenched planar flow cast ribbons. Resistivity measurements have been shown to be a very sensitive method for comparing the quenched-in structures and the relative stability of the quasicrystalline phase as a function of the processing parameters, particularly with respect to the ordering kinetics and phase transformations. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Microstructure modification and quasicrystalline phase formation in Al-Mn-Si-Be cast alloys
Authors:
Chang, HJ; Fleury, E; Song, GS; Lee, MH; Kim, WT; Kim, DH
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 375-77: 992-997 Sp. Iss. SI JUL 15 2004
Abstract:
In this paper, we report the formation of the new quaternary icosahedral quasicrystal in the Al-Mn-Si-Be system, which has a primitive icosahedral structure and has a significant lower cooling rate at the time of its formation. The icosahedral quasicrystalline phase was found to form in the Al-rich composition of Al-Mn-Si-Be alloy by conventional casting technique as well as by rapid quenching technique, indicating that the addition of Be to Al-Mn-Si alloys improves the quasicrystal forming ability. The icosahedral phase in conventionally cast Al-Mn-Si-Be alloys forms as a dendritic phase in the under-cooled melt showing five well-developed branches indicating the five-fold symmetry structure. At the later stage of the growth of the icosahedral phase, 1/1 approximant phase forms heterogeneously from the icosahedral phase. The Al-Mn-Si-Be icosahedral phase is metastable, and transforms into the 1/1 cubic approximant phase at high temperature. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Magnetic properties of Cd-Mg-Tb quasicrystal
Authors:
Jaglicic, Z; Dolinsek, J; Trontelj, Z; Martinez-Agudo, JM
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 375-77: 998-1001 Sp. Iss. SI JUL 15 2004
Abstract:
The magnetic properties of an icosahedral Cd-Mg-Tb quasicrystal were studied by dc magnetization and thermoremanent magnetization time decay measurements. An unusual temperature dependence of the susceptibility below freezing temperature can be attributed to the inhomogeneous sample structure. In addition to the quasicrystalline portion which exhibits a spin-glass transition at 12.5 K a part of the sample behaves like a paramagnet. During aging of the sample in air the spin-glass part transforms into the paramagnetic one. The linear M proportional to H dependence of the thermoremanent magnetization time decay on magnetic field is quite different as compared to canonical spin glasses. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Electrical properties of the binary icosahedral quasicrystal and its approximant in the Cd-Yb system
Authors:
Tamura, R; Murao, Y; Kishino, S; Takeuchi, S; Tokiwa, K; Watanabe, T
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 375-77: 1002-1005 Sp. Iss. SI JUL 15 2004
Abstract:
Electrical resistivity, magnetoresistance, and specific heat measurements have been performed for the binary icosahedral Cd5.7Yb and its cubic approximant Cd6Yb. The resistivity of both the icosahedral phase (i-phase) and the approximant is found to show a rather metallic behavior with a large positive temperature coefficient of the resistivity (TCR) below 200-300 K followed by leveling-off at low temperatures below 10 K. For the approximant, we observe a stepwise change of the resistivity at 110 K which is due to a phase transition. Giant magnetoresistance as high as 200% at 9 T below 4.2 K is observed for the i-phase and the electronic specific heat coefficient gamma is found to be extraordinary large in both alloys, i.e., 2.87 mJ/(mole K-2) for the i-phase and 7.60 mJ/(mole K-2) for the approximant. Such large gamma values may be attributed to the Yb-derived states at the Fermi level. Furthermore, the Debye temperatures (Theta(D)) are very low and almost the same for both alloys, i.e., 142 and 144 K, respectively, which are indeed the lowest values ever reported in i-phases and approximants. The metallic character of the binary i-phase implies that the negative TCR is not necessarily a consequence of the quasiperiodicity. (C) 2003 Elsevier B.V. All rights reserved.
Title:
In situ transmission electron microscopy studies of directionally solidified Ni-Mn-Ga ferromagnetic shape memory alloys
Authors:
Bennett, JC; Hyatt, CV; Gharghouri, MA; Farrell, S; Robertson, M; Chen, J; Pirge, G
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 378 (1-2): 409-414 Sp. Iss. SI JUL 25 2004
Abstract:
Transmission electron microscopy has been used to examine the microstructure and transformation behaviour of four non-stoichiometric Ni-Mn-Ga oriented polycrystalline alloys grown by seedless Bridgman solidification. Despite similar average compositions, the observed microstructures and transformation temperatures of these alloys varied significantly. For alloy A with nominal composition Ni50.1Mn28.2Ga21.7 (at.%), the Heusler ordered (L2(1)) austenite phase was observed to exhibit characteristic "tweed" strain contrast at room temperature. On cooling, sharp satellite reflections associated with the formation of an intermediate phase appeared at similar to200 K, prior to a martensitic transformation at 190 K which generated a microstructure consisting predominately of seven-layer martensite with regions of five-layer martensite. For alloys B (nominal Ni49.3Mn28.6Ga22.1) and C (nominal Ni49.3Mn28.8Ga21.9), the martensitic transformation occurred slightly below room temperature and the TEM images revealed a fine-scale intermixture of austenite with five-layer, seven-layer and non-modulated martensite. The microstructure of alloy D (nominal Ni49.3Mn28.8Ga21.9), with a transformation temperature somewhat above room temperature was composed predominately of seven-layer martensite. The results indicate that small microscale variations in composition and/or parent phase grain size have a significant effect on the transformation behaviour of directionally solidified Ni-Mn-Ga alloys. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Magnetization plateaux of the S=1/2 two-dimensional frustrated antiferromagnet Cs2CuBr4
Authors:
Ono, T; Tanaka, H; Kolomiyets, O; Mitamura, H; Goto, T; Nakajima, K; Oosawa, A; Koike, Y; Kakurai, K; Klenke, J; Smeibidle, P; Meissner, M
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (11): S773-S778 Sp. Iss. SI MAR 24 2004
Abstract:
The field induced magnetic phase transitions of Cs2CuBr4 were investigated by means of a magnetization process and neutron scattering experiments. This system undergoes a magnetic phase transition at Neel temperature T-N = 1.4 K at zero field, and exhibits a magnetization plateau at approximately one third of the saturation magnetization for the field directions H parallel to b and H parallel to c. In the present study, an additional symptom of the two-third magnetization plateau was found in the field derivative of the magnetization process. The magnetic structure was found to be incommensurate with the ordering vector Q = (0, 0.575, 0) at zero field. With increasing magnetic field parallel to the c-axis, the ordering vector increases continuously and is locked at Q = (0, 0.662, 0) in the plateau field range 13.1 T < H < 14.4 T. This indicates that the collinear up-up-down spin structure is stabilized by quantum fluctuation at the magnetization plateau.
Title:
Effect of geometrical frustration on the magnetic properties of the triangular-layer system Tb2C2I2: a neutron diffraction investigation
Authors:
Ahn, K; Kremer, RK; Simon, A
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (11): S875-S881 Sp. Iss. SI MAR 24 2004
Abstract:
Powder neutron diffraction on Tb2C2I2 reveals strong resolution-limited magnetic Bragg reflections below 60 K due to commensurate antiferromagnetic (afm) long range ordering. Between 60 and 85 K the magnetic reflections broaden beyond instrumental resolution and the propagation vector becomes incommensurate. Above approximate to95 K magnetic scattering is only seen as a diffuse ridge which we ascribe to short-range correlations within the triangular Tb atom planes. With decreasing temperature an additional Lorentzian shaped reflection grows on top of the decaying edge of this diffuse ridge. We analyse the diffuse scattering by fitting a Warren-type lineshape and a Lorentzian shaped Bragg reflection. The results of the fits indicate that, with diverging intra-plane correlations, significant inter-plane afm correlations build up close to 85 K. Above 95 K inter-plane correlations are essentially limited to nearest-neighbour Tb atom double layers only.
Title:
The adsorption of Xe and Ar on quasicrystalline Al-Ni-Co
Authors:
Trasca, RA; Ferralis, N; Diehl, RD; Cole, MW
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (29): S2911-S2921 Sp. Iss. SI JUL 28 2004
Abstract:
An interaction potential energy between an adsorbate (Xe and Ar) and the ten-fold Al-Ni-Co quasicrystal is computed by summing over all adsorbate-substrate interatomic interactions. The quasicrystal atoms' coordinates are obtained from LEED experiments, and the Lennard-Jones parameters of Xe-Al, Xe-Ni and Xe-Co are found using semiempirical combining rules. The resulting potential energy function of position is highly corrugated. Monolayer adsorption of Xe and Ar on the quasicrystal surface is investigated in two cases: (1) in the limit of low coverage (Henry's law regime), and (2) at somewhat larger coverage, when interactions between adatoms are considered through the second virial coefficient, C-AAS. A comparison with adsorption on a flat surface indicates that the corrugation enhances the effect of the Xe-Xe (Ar-Ar) interactions. The theoretical results for the low coverage adsorption regime are compared to experimental (LEED isobar) data.
Title:
Neutron scattering studies on the vibrational excitations and the structure of ordered niobium hydrides: the lambda phases
Authors:
Hauer, B; Hempelmann, R; Udovic, TJ; Rush, JJ; Kockelmann, W; Schafer, W; Jansen, E; Richter, D
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (29): 5205-5228 Sp. Iss. SI JUL 28 2004
Abstract:
Neutron vibrational spectroscopy and neutron diffraction have been used to study the optical hydrogen vibrations in and the structure of ordered niobium hydrides NbHx and deuterides NbDx in the concentration range 0.73 < x < 1.0 and at temperatures between 13 and 250 K. The measurements performed at temperatures above 200 K confirm the established model of the beta phase. Neutron diffraction data collected in the regime of the. phases (T < 200 K, 0.73 < x < 1.0) show that the structure for x < 0.85 is made up of microdomains with beta phase structure. Neutron vibrational spectra display up to three families of peaks that can be assigned to three different hydrogen sites: an undisturbed tetrahedral site within the microdomains and two strongly disturbed tetrahedral sites within two different kinds of microdomain boundaries. Incommensurately modulated phases probably exist in this concentration range. For hydrogen concentrations around x approximate to 0.85 there is evidence for a change of symmetry of the basic cell as well as a change of the modulation at even higher concentrations. In the range of the gamma phase at x approximate to 0.9, strong isotopic effects occur. The results give new insights into the phase diagram.
Title:
Plastic flow coupled with a crack in some one- and two-dimensional quasicrystals
Authors:
Fan, T; Trebin, HR; Messerschmidt, U; Mai, YW
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (29): 5229-5240 Sp. Iss. SI JUL 28 2004
Abstract:
An analysis of a group of slip dislocations coupled with a crack dislocation group in some one- and two-dimensional quasicrystals is given. The extent of the plastic zone and the amount of the dislocation slip have been determined in a very explicit form.
Title:
A neutron diffraction and Rietveld analysis of cooperative Li motion in beta-eucryptite
Authors:
Sartbaeva, A; Redfern, SAT; Lee, WT
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (29): 5267-5278 Sp. Iss. SI JUL 28 2004
Abstract:
Li+ mobility and structural changes in the aluminosilicate beta-eucryptite have been studied by high-resolution powder neutron diffraction as a function of temperature from 573 to 873 K. A Li split-atom model was used to describe the disorder of Li+ ions in the structure. Analysis of the data shows two anomalies around 698 and 758 K. The first anomaly is attributed to an M-point zone boundary transition reported in the literature, which is connected to the appearance of the incommensurate structure. The second anomaly is attributed to a displacive phase transition of the framework and doubling in the a cell parameter.
Title:
Surface reconstruction of FeAl(110) studied by scanning tunnelling microscopy and angle-resolved photoemission spectroscopy
Authors:
Kizilkaya, O; Hite, DA; Zehner, DM; Sprunger, PT
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (30): 5395-5406 AUG 4 2004
Abstract:
The surface geometric and electronic structure of the FeAl(110) intermetallic alloy has been investigated by scanning tunnelling microscopy and angle-resolved photoemission spectroscopy (ARPES). Preferential sputtering results in depletion of Al in the surface region and subsequent annealing promotes surface segregation of Al and gives rise to new reconstructed phases. A bulk terminated surface structure is obtained after annealing the surface to 400 degreesC. However, an incommensurate phase develops above 800 degreesC with a stoichiometry consistent with an FeAl2 structure in the topmost layer. The ARPES measurements confirm the Al segregation with increased density of states (DOS) near the Fermi level. The increased DOS is believed to be due to hybridization between the Fe d and Al sp states. The increased intensity of the Al 2p core level for the incommensurate phase also confirms the higher Al surface concentration for this phase.
Title:
Piezoresistance properties of quasicrystals
Authors:
Zhou, X; Hu, CZ; Gong, P; Qiu, SD
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (30): 5419-5425 AUG 4 2004
Abstract:
Piezoresistance properties of quasicrystals due to both phonon and phason stresses are investigated. The classical formulae of the piezoresistance effect in crystals are generalized to the case of quasicrystals. The number of independent components of the piezoresistivity tensor and their matrix forms are determined for three-dimensional icosahedral quasicrystals and all two-dimensional quasicrystals with fivefold, eightfold, tenfold and twelvefold symmetries. Our results show that the piezoresistance effect may be related only to phonon stress in the case of dodecagonal quasicrystals or to both phonon and phason stresses in the other case.
Title:
Re-entrant magneto-elastic transition in HoFe4Ge2 a neutron diffraction study
Authors:
Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Andre, G; Ritter, C; Buschow, KHJ
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 280 (1): 119-142 SEP 1 2004
Abstract:
The re-entrant magneto-elastic transition of the antiferromagnetic HoFe4Ge2 compound has been studied by neutron powder diffraction as a function of temperature. The magnetic phase diagram comprises the wave vectors: (q(1o), q(2o), q(1t)) and three magnetic transitions, two of them occurring simultaneously with the structural changes at T-c, T-N = 52 and T-c', T-ic1 = 15 K, the third being purely magnetic at T-ic2 = 40 K. The first transition is of second order while the latter two of first order. The sequence of phases follows the path: P4(2)/mnm (HT), T-c, T-N = 52 K --> Cmmm (IT): (q(1o) = (0, 1/2, 0) T-ic2 = 40 K double right arrow q(2o) = (0, q(y), 0)), T-c', T-ic1 = 15 K double right arrow P4(2)/mnm (LT): q(1t) = (0, 1/2, 0). The magnetic structures described by the wave vectors (q(1o), q(2o) and q(1t)), where the components are referred to the reciprocal basis of the conventional Cmmm cell, correspond to canted multi-axial arrangements. The q(2o) wave vector length of the amplitude modulated phase varies non-monotonously, decreasing fast just below T-ic2,-slowly between 36K-T-c', T-ic1 and jumping to the q(1t) = (0, 1/2,0) lock-in value at T-c', T-ic1 simultaneously with the first order re-entrant transition to the (LT) tetragonal phase. In the coexisting meta-stable orthorhombic phase from T-c', T-ic1 down to 1.5 K the length of the wave vector q(2o) continues to decrease. To solve the magnetic structures of all the phases appearing in this complex situation, arising from competing ordering mechanisms and anisotropies of the underlying sublattices, we have used the simulated annealing method of global optimisation on high-resolution neutron powder diffraction data. (C) 2004 Published by Elsevier B.V.
Title:
Delone set models for quasicrystals
Authors:
Lagarias, JC
Source:
GROUP 24 : PHYSICAL AND MATHEMATICAL ASPECTS OF SYMMETRIES, 173: 99-101 2003 Book series title: INSTITUTE OF PHYSICS CONFERENCE SERIES
Abstract:
This work surveys recent mathematical developments motivated by quasicrystalline materials, i.e. materials whose atomic structure has (statistical) long-range translational order evidenced by X-ray diffraction patterns having sharp spots. which exhibit symmetries forbidden to crystals. Such materials cannot have a periodic arrangement of atoms.
Title:
Wavelet basis for quasicrystal diffraction
Authors:
Andrle, M; Elkharrat, A
Source:
GROUP 24 : PHYSICAL AND MATHEMATICAL ASPECTS OF SYMMETRIES, 173: 185-188 2003 Book series title: INSTITUTE OF PHYSICS CONFERENCE SERIES
Abstract:
In this article we present (1) a scale dependent partitioning procedure of the Fourier space based on beta-integers, with beta a quadratic Pisot number, for computing quasicrystals diffraction patterns, (2) a Haar wavelet analysis with beta-adic wavelets. These technics enhance the precision of numerical computation and analysis of the intensity function arising from diffraction patterns of one-dimensional model sets.
Title:
Haar wavelets for the quasiperiodic icosahedral Danzer tiling.
Authors:
Andrle, M; Kramer, P
Source:
GROUP 24 : PHYSICAL AND MATHEMATICAL ASPECTS OF SYMMETRIES, 173: 189-191 2003 Book series title: INSTITUTE OF PHYSICS CONFERENCE SERIES
Abstract:
Orthogonal wavelet bases on the quasiperiodic icosahedral Danzer tiling are constructed. The stone inflation is written in terms of discrete Euclidean operations on the prototiles. By geometric inflation we represent any fixed prototile as the union of scaled copies of prototiles. Application of the unitary representations of the Euclidean group for the inflation to the Haar characteristic functions on the prototiles yields a wavelet basis. This basis is constructed on any the of the tiling and orthogonalized in closed form.
Title:
Quasicrystalline combinatorics
Authors:
Baake, M; Grimm, U
Source:
GROUP 24 : PHYSICAL AND MATHEMATICAL ASPECTS OF SYMMETRIES, 173: 193-200 2003 Book series title: INSTITUTE OF PHYSICS CONFERENCE SERIES
Abstract:
Several combinatorial problems of (quasi)crystallography are reviewed with special emphasis on a unified approach, valid for both crystals and quasicrystals. In particular, we consider planar sublattices, similarity sublattices, coincidence sublattices and their module counterparts. The corresponding counting functions are encapsulated in Dirichlet series generating functions, with worked out results for the square lattice and the Tubingen triangle tiling. Finally, we discuss a novel approach to central and averaged shelling for these examples, also involving Dirichlet series.
Title:
Tilings and coverings embedded into the canonical decagonal tiling T*((A4))
Authors:
Papadopolos, Z; Kasner, G
Source:
GROUP 24 : PHYSICAL AND MATHEMATICAL ASPECTS OF SYMMETRIES, 173: 213-217 2003 Book series title: INSTITUTE OF PHYSICS CONFERENCE SERIES
Abstract:
This paper considers some tilings and coverings embedded in a quasilattice of the canonical tiling T*((A4)).
Title:
Superspace groups for incommensurate composite systems
Authors:
Zeiner, P; Janssen, T
Source:
GROUP 24 : PHYSICAL AND MATHEMATICAL ASPECTS OF SYMMETRIES, 173: 223-226 2003 Book series title: INSTITUTE OF PHYSICS CONFERENCE SERIES
Abstract:
We discuss the notion of superspace groups for incommensurate composite structures. We illustrate their main properties for the special case of a composite structure consisting of two subsystems.

Update: 11-Sep-2004

Title:
Short-wavelength atomic-displacement modulation preceding the B2 -> B19 ' martensitic transformation in a TiNi-based alloy
Authors:
Grishkov, VN; Lotkov, AI; Dubinin, SF; Teploukhov, SG; Parkhomenko, VD
Source:
PHYSICS OF THE SOLID STATE, 46 (8): 1386-1393 2004
Abstract:
Neutron diffraction studies of the fine structure of a Ti49Ni51 single crystal are performed before the onset of the B2 --> B19' martensitic transformation (temperature of the onset of the transformation M-s = 200 K). Upon cooling below 460 K, extra reflections are found to form; their positions in the B2-phase reciprocal lattice correspond to the full non-Lifshitz star of the wave vector q = 0.225<112>. At temperatures below 430 K, 0.45<110> extra reflections appear, corresponding to second-order diffraction effects. In the temperature range 300-460 K, reversible and nonhysteretic changes in the intensities and positions of both types of extra reflections are observed. Analysis of the intensities and spatial distribution of the extra reflections in the B2-phase reciprocal lattice indicates that a displacive superstructure dominated by longitudinally polarized atomic-displacement waves with q = 0.225<112> arises in the single crystal in the pretransition temperature range. (C) 2004 MAIK "Nauka / Interperiodica".
Title:
Aluminium diffusion in decagonal quasicrystals
Authors:
Hocker, S; Gahler, F
Source:
PHYSICAL REVIEW LETTERS, 93 (7): Art. No. 075901 AUG 13 2004
Abstract:
Aluminium is the majority element in many quasicrystals and expected to be the most mobile element, but its diffusion properties are hardly accessible to experiment. Here we investigate aluminum diffusion in decagonal Al-Ni-Co and Al-Cu-Co quasicrystals by molecular dynamics simulations, using classical effective pair potentials. Above two-thirds of the melting temperature, strong aluminum diffusion is observed. The diffusion constant is measured as a function of temperature and pressure, from which the activation enthalpies and activation volumes are determined. As there are no vacancies in the samples, the diffusion, which is anisotropic, must use a direct mechanism. The high mobility of aluminium is also relevant for structure determination, and will contribute to diffuse scattering. The qualitative behavior of the dynamics is confirmed by ab initio simulations.
Title:
Noncollinear magnetic order in quasicrystals
Authors:
Vedmedenko, EY; Grimm, U; Wiesendanger, R
Source:
PHYSICAL REVIEW LETTERS, 93 (7): Art. No. 076407 AUG 13 2004
Abstract:
Based on Monte Carlo simulations, the stable magnetization configurations of an antiferromagnet on a quasiperiodic tiling are derived theoretically. The exchange coupling is assumed to decrease exponentially with the distance between magnetic moments. It is demonstrated that the superposition of geometric frustration with the quasiperiodic ordering leads to a three-dimensional noncollinear antiferromagnetic spin structure. The structure can be divided into several ordered interpenetrating magnetic supertilings of different energy and characteristic wave vector. The number and the symmetry of subtilings depend on the quasiperiodic ordering of atoms.
Title:
Valence-bond crystal in a pyrochlore antiferromagnet with orbital degeneracy
Authors:
Di Matteo, S; Jackeli, G; Lacroix, C; Perkins, NB
Source:
PHYSICAL REVIEW LETTERS, 93 (7): Art. No. 077208 AUG 13 2004
Abstract:
We discuss the ground state of a pyrochlore lattice of threefold orbitally degenerate S=1/2 magnetic ions. We derive an effective spin-orbital Hamiltonian and show that the orbital degrees of freedom can modulate the spin exchange, removing the infinite spin-degeneracy characteristic of pyrochlore structures. The resulting state is a collection of spin-singlet dimers, with a residual degeneracy due to their relative orientation. This latter is lifted by a magnetoelastic interaction, induced in the spin-singlet phase space, that forces a tetragonal distortion. Such a theory provides an explanation for the helical spin-singlet pattern observed in the B spinel MgTi2O4.
Title:
Critical small-angle scattering of polarised neutrons in MnSi
Authors:
Georgii, R; Boni, P; Lamago, D; Stuber, S; Grigoriev, SV; Maleyev, SV; Okorokov, AI; Eckerlebe, H; Pranzas, PK; Roessli, B; Fischer, WE
Source:
PHYSICA B-CONDENSED MATTER, 350 (1-3): 45-47 JUL 15 2004
Abstract:
The chiral fluctuations in the weak itinerant magnet MnSi were studied by means of small-angle neutron scattering with polarized neutrons. Due to the lack of a centre of symmetry, the magnetic moments are arranged along a left-handed spiral due to the Dzyaloshinskii-Moriya (DM) interaction. The experiments show that the incommensurate magnetic peaks evolve with increasing temperature into diffuse scattering that is mainly concentrated in a ring with the radius q = 0.039 Angstrom(-1) centred at the position of the direct beam q = 0. The scattering is fully polarised for Q \\ P-0 and depolarised for Q perpendicular to P-0 proving that the scattering is chiral and that the spiral has a unique handiness. From the data, we have determined the critical exponents of the magnetisation, the susceptibility and the correlation lengths of the chiral fluctuations. The results are discussed in the framework of the renormalisation theory. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Charge and zener polaron order in Bi0.75Sr0.25MnO3: a comparison with Bi0.75Ca0.25MnO3
Authors:
Frontera, C; Garcia-Munoz, JL; Carrillo, AE; Hervieu, M; Calleja, A; Capdevila, XG; Casais, MT; Ritter, C
Source:
PHYSICA B-CONDENSED MATTER, 350 (1-3): 48-50 JUL 15 2004
Abstract:
We present a detailed magnetic and structural study of Bi0.75Sr0.25MnO3. With the aid of electron diffraction, neutron and synchrotron powder diffraction measurements we have found that at similar to 600 K the structure presents a considerable distortion of the cell parameters accompanied by a change in the space group and by the appearance of a modulation of the average structure. This modulation doubles the a and c lattice parameters (in the P bnm setting) of the high-temperature structure. Magnetic data reveal below this temperature that the paramagnetic units are not single Mn ions but a coexistence of Mn3+ and Mn-Mn pairs. This behavior strongly contrasts with that of Bi0.75Ca0.25MnO3 evidencing the strong differences between the Bi1-xSrxMnO3 and Bi1-xCaxMnO3 families. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Magnetism in Ce2Fe17 at pressures up to 70 kbar
Authors:
Prokhnenko, O; Goncharenko, I; Arnold, Z; Kamarad, J
Source:
PHYSICA B-CONDENSED MATTER, 350 (1-3): 63-65 JUL 15 2004
Abstract:
The magnetic phase diagram of Ce2Fe17 at ambient pressure shows a ferromagnetic (FM) phase transforming into an incommensurate helical antiferromagnetic (AFM) one above Theta(T)=97K, and becoming paramagnetic above T-N = 214 K. The FM ground state is highly unstable, dTheta(T)/dP = -24 K/kbar, whereas T-N only moderately decreases with pressure P, dT(N)/dP=-1.7K/kbar. Hence, pressures of the order of 100kbar are necessary to suppress the magnetic ordered state in Ce(2)Fe(1)7. The suppression of the FM phase under pressure is accompanied by the appearance of a new incommensurate anti ferromagnetic (AFM1) phase at low temperatures. To investigate the stability of the magnetic state and the behaviour of the new pressure-induced AFM1 phase, powder neutron diffraction measurements were performed with P less than or equal to 70 kbar. This completed the magnetic phase diagram of Ce2Fe17 in that region. The results clearly show that the pressure dependence of the Neel temperature is linear up to 25 kbar. The strong decrease in the intensity of the magnetic (000)(+) satellite with P gives clear evidence for the volume dependence of the Fe magnetic moments. Simultaneously, the incommensurate propagation vector tau = (0, 0, tau(z)) increases with pressure, reaching 0.72 r.l.u. at 4 K and 70 kbar. The results show the anisotropic behaviour of the exchange interactions between Fe moments in Ce2Fe17 and their complex dependence on volume changes. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Local Investigation of electronic structure modulation in BaPbxBi1-xO3 via highly spatially resolved low-loss electron energy loss spectroscopy
Authors:
Gutierrez-Sosa, A; Bangert, U; Flavell, WR
Source:
MICROSCOPY OF SEMICONDUCTING MATERIALS 2003, (180): 537-540 2003 Book series title: INSTITUTE OF PHYSICS CONFERENCE SERIES
Abstract:
BaPb1-xBixO3 (BPBO) samples with x=1, 0.25 and 0.5 have been studied using highly spatially resolved electron energy loss spectroscopy in the low loss energy range and energy dispersive X-ray (EDX) analysis. We have been able to identify crystallographic orientations and discover great inhomogeneities even within nanometre distances. We show the modulation of local electronic structure with local composition in BPBO phases with different nominal x. This enables us also to demonstrate the evolution of the metal-semiconductor transition as a function of x.
Title:
Precipitation hardening of Cu-Ti-Zr alloys
Authors:
Markandeya, R; Nagarjuna, S; Sarma, DS
Source:
MATERIALS SCIENCE AND TECHNOLOGY, 20 (7): 849-858 JUL 2004
Abstract:
The influence of age hardening temperature and time on the hardness, tensile properties, electrical conductivity, and microstructure of Cu-4Ti-0-1Zr and Cu-3Ti-0-1Zr alloys has been investigated. The resulting microstructure of these alloys suggests that zirconium addition prohibited the formation of compositional modulations in the solution treated condition. These alloys exhibited maximum hardness and strength on peak aging at 450degreesC for 24 h by the formation of a coherent and metastable Cu4Ti phase (beta') in modulated structure while overaging occurred by the formation of equilibrium phase beta-Cu3Ti. The electrical conductivity of both the alloys increased moderately on aging. Unlike in an earlier study of binary Cu-Ti and some ternary Cu-Ti-X alloys, overaging did not cause any discontinuous precipitation in the Cu-Ti-Zr alloys investigated. Modulated structure formed on peak aging persisted on prolonged aging at 450degreesC for 80 h or at 500degreesC for 8 h.
Title:
Incommensurate nature of the multilayered molecular ferromagnetic metals based on bis(ethylenedithio)tetrathiafulvalene and bimetallic oxalate complexes
Authors:
Coronado, E; Galan-Mascaros, JR; Gomez-Garcia, CJ; Martinez-Ferrero, E; van Smaalen, S
Source:
INORGANIC CHEMISTRY, 43 (16): 4808-4810 AUG 9 2004
Abstract:
The salt [ET](x)[MnRh(ox)(3)].CH2Cl2 (x = 2.526(1)) has been obtained and characterized. This paramagnetic metal is essentially isostructural to the ferromagnetic metal [ET](y)[MnCr(ox)(3)].CH2Cl2 (y approximate to 3) and provides a definite answer on the origin of the structural disorder present on such systems. As in the ferromagnetic analogue, this material shows high electrical conductivity at room temperature (13 S.cm(-1)) and metallic behavior.
Title:
Charge order and tilt modulation in multiferroic (KxMxM1-xF3)-M-II-F-III (0.4 < x < 0.6) transition metal fluorides with tetragonal tungsten bronze structure\
Authors:
Fabbrici, S; Montanari, E; Righi, L; Calestani, G; Migliori, A
Source:
CHEMISTRY OF MATERIALS, 16 (16): 3007-3019 AUG 10 2004
Abstract:
Transition metal fluorides with tetragonal tungsten bronze (TTB) structure, having general formula (KxMxM1-xF3)-M-II-F-III with 0.4 < x < 0.6 and M belonging to transition metals, have been studied over the past decades because of the frustrated magnetic ordering arising at low temperature. We investigated the structural properties of TTB fluorides by transmission electron microscopy (TEM). The results, coupled with an accurate structure analysis performed by single-crystal XRD on K0.53FeF3, revealed ferroelectricity and a unified structural description of these materials, where charge order and tilt modulations coexist, each one with its own periodicity differently commensurate to the conventional TTB cell. Whereas the charge order is peculiar of the mixed valence fluorides,the nature of the tilt modulation is clearly associable to the structural features of TTB niobates, suggesting also for the fluoride bronzes the existence of a generalized ferroelectric-ferroelastic behavior at room temperature.

Update: 3-Sep-2004

Title:
Structural studies of materials - Formation of quasicrystals and related structures in systems of aluminum with transition metals. I. Binary systems formed by aluminum with 3d metals
Authors:
Grushko, B; Velikanova, TY
Source:
POWDER METALLURGY AND METAL CERAMICS, 43 (1-2): 72-86 JAN-FEB 2004
Abstract:
Quasiperiodic phases (quasicrystals) with symmetries forbidden by classic crystallography have been observed in systems of aluminum with transition metals. In binary systems, these phases are metastable; they were obtained for the first time by rapid solidification of melts. We consider the formation of the quasicrystals and we refine the phase diagrams for binary systems A - 3d-M (from V to Ni) in which quasicrystals have been observed.
Title:
A 'checkerboard' electronic crystal state in lightly hole-doped Ca2-xNaxCuO2Cl2
Authors:
Hanaguri, T; Lupien, C; Kohsaka, Y; Lee, DH; Azuma, M; Takano, M; Takagi, H; Davis, JC
Source:
NATURE, 430 (7003): 1001-1005 AUG 26 2004
Abstract:
The phase diagram of hole-doped copper oxides shows four different electronic phases existing at zero temperature. Familiar among these are the Mott insulator, high-transition-temperature superconductor and metallic phases. A fourth phase, of unknown identity, occurs at light doping along the zero-temperature bound of the 'pseudogap' regime(1). This regime is rich in peculiar electronic phenomena(1), prompting numerous proposals that it contains some form of hidden electronic order. Here we present low-temperature electronic structure imaging studies of a lightly hole-doped copper oxide: Ca2-xNaxCuO2Cl2. Tunnelling spectroscopy (at energies \E\ > 100 meV) reveals electron extraction probabilities greatly exceeding those for injection, as anticipated for a doped Mott insulator. However, for \E\ < 100 meV, the spectrum exhibits a V-shaped energy gap centred on E = 0. States within this gap undergo intense spatial modulations, with the spatial correlations of a four CuO2-unit-cell square 'checkerboard', independent of energy. Intricate atomic-scale electronic structure variations also exist within the checkerboard. These data are consistent with an unanticipated crystalline electronic state, possibly the hidden electronic order, existing in the zero-temperature pseudogap regime of Ca2-xNaxCuO2Cl2.
Title:
Modulated structure of the composite crystal InCr1-xTixO3+x/2
Authors:
Michiue, Y; Onoda, M; Brown, F; Kimizuka, N
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 177 (8): 2644-2648 AUG 2004
Abstract:
Incommensurately modulated structure of the composite crystal InCr1-xTixO3+x/2 was refined by the profile fitting of powder X-ray diffraction based on the four-dimensional superspace group. The crystal consists of two monoclinic subsystems mutually incommensurate in b. The first subsystem is the alternate stacking of an edge-shared InO6 octahedral layer and a Cr/Ti triangle-lattice plane along c*. A sheet of oxygen atoms constructing the second subsystem is also extending on the Cr/Ti plane. The whole structure is the alternate stacking of an edge-shared InO6 octahedral layer and a Cr/Ti-O plane, where displacive modulation of O ions is prominent. Metal ions on the Cr/Ti-O plane are surrounded by three or four oxygen ions on the plane and, in addition, two axial ones. (C) 2004 Elsevier Inc. All rights reserved.
Title:
Possible influence of quenched-in nuclei on quasicrystal formation in mechanically alloyed Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 glassy powder
Authors:
Scudino, S; Eckert, J; Schultz, L
Source:
JOURNAL OF MATERIALS RESEARCH, 19 (8): 2211-2215 AUG 2004
Abstract:
The influence of quenched-in nuclei of icosahedral short range order, proposed as a possible explanation for quasicrystal formation, has been investigated by producing a melt-spun ribbon from previously mechanically alloyed Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 glassy powder. A ribbon prepared from highly pure materials forms a quasicrystalline phase during the first stage of the crystallization process, whereas no quasicrystal formation has been detected in the devitrification of the ribbon produced from the mechanically alloyed powder. This finding indicates that the absence of quenched-in nuclei may not be the only reason for the lack of quasicrystal formation in mechanically alloyed powders.
Title:
Study of decagonal approximant and gamma-brass-type compounds in Al-Cr-Fe thin films
Authors:
Demange, V; Ghanbaja, J; Beeli, C; Machizaud, F; Dubois, JM
Source:
JOURNAL OF MATERIALS RESEARCH, 19 (8): 2285-2297 AUG 2004
Abstract:
This paper reports the preparation conditions and structure characteristics of Al-Cr-Fe very thin films (10-30 nm) obtained by the flash evaporation technique. The films are either amorphous or crystallized, depending on the thickness of the sample and temperature of the substrate. Annealing of amorphous films leads to crystallization of intermetallic phases that are all linked with quasicrystals. In particular, we have identified by transmission electron microscopy the following structures: body-centered-cubic (bcc) gamma-brass phase, monoclinic lambda-Al-13(Cr,Fe)(4) phase, and orthorhombic O-1-phase, all of them already observed in this system, together with four new structures, i.e., a face-centered-cubic (fcc) gamma-brass phase (superstructure of the bcc phase), monoclinic lambda'-phase (related to the lambda-phase) and two orthorhombic phases (1/1/; 1/1) and (1/0; 2/1) approximants of the decagonal phase). In this study, we point out the occurrence of twin defects of the lambda-Al-13(Cr,Fe)(4) phase. Films prepared directly in the crystalline state comprise the O-1 approximant. Electron energy loss spectroscopy measurements show that all films are not oxidized except for the presence of a native oxide layer that forms in ambient atmosphere with a thickness that cannot exceed 0.3 nm. Optical properties were investigated and show that films need to be large enough (>30 nm) to reproduce the properties of bulk alloys. Finally, contact angle wetting measurements reveal that the presence of such films on a substrate, even at very low thickness, considerably decreases the wetting behavior by water.
Title:
Space-time parity violation and magnetoelectric interactions in antiferromagnets
Authors:
Kadomtseva, AM; Zvezdin, AK; Popov, YF; Pyatakov, AP; Vorob'ev, GP
Source:
JETP LETTERS, 79 (11): 571-581 2004
Abstract:
The properties of antiferromagnetic materials with violated space-time parity are considered. Particular attention is given to the bismuth ferrite BiFeO3 ferroelectric magnet. This material is distinguished from other antiferromagnets in that the inversion center is absent in its crystal and magnetic structures. This circumstance gives rise to diversified and unusual properties, namely, to the appearance of a spatially modulated spin structure and to the unique possibility of the linear magnetoelectric effect coexisting with a weak ferromagnetic moment. The magnetic-induced phase transitions accompanied by the suppression of the modulated spin structure and appearance of a number of new and unusual effects are considered. These are the linear magnetoelectric effect and the appearance of a toroidal moment and a weak ferromagnetic moment of the magnetoelectric nature. (C) 2004 MAIK "Nauka / Interperiodica".
Title:
Subgrain and domain structure of Al-Cu-Co single quasicrystals
Authors:
Bogdanowicz, W; Bojarski, Z
Source:
ARCHIVES OF METALLURGY AND MATERIALS, 49 (1): 29-36 2004
Abstract:
The influence of low-temperature (100degreesC) and high-temperature (900degreesC) thermal treatment on the subgrain and domain structure of two-subgrain single quasicrystals of Al-Cu-Co alloy was studied. The low-temperature treatment causes the fragmentation of the domains, and increases their boundaries density. The high-temperature thermal treatment causes some broadening of the domains which is connected with the partial disappearance of their boundaries. The treatment also causes the rotation of the subgrains in relation to one another.
Title:
Spin-dependent quantum transport in periodic magnetic modulations: Aharonov-Bohm ring structure as a spin filter
Authors:
Wu, MW; Zhou, J; Shi, QW
Source:
APPLIED PHYSICS LETTERS, 85 (6): 1012-1014 AUG 9 2004
Abstract:
Quantum interference in Aharonov-Bohm (AB) ring structure provides additional control of spin at mesoscopic scale. We propose a scheme for spin filter by studying the coherent transport through the AB structure with lateral magnetic modulation on both arms of ring structure. Large spin polarized current can be obtained with many energy channels. (C) 2004 American Institute of Physics.

Update: 27-Aug-2004

Title:
Effect of Be additions on the electronic density of states of icosahedral Al-Cu-Fe compounds
Authors:
Belin-Ferre, E; Kim, DH; Dankhazi, Z; Dubois, JM
Source:
FERROELECTRICS, 305: 229-233 2004
Abstract:
Using the Soft X-ray Emission Spectroscopy technique, we have investigated the electronic structure of a series of Al-Cu-Fe compounds in which Al atoms have been substituted by Be atoms. Changes in the shape of Al 3s,d spectral curves are clearly visible in the energy region extending over 2 e V below the Fermi level. Calculation of the moments of orders I and 2 of the partial electronic distributions show that there is a slight decrease of the contribution of Fe 3d states to the total energy of the system and that there are changes in Fe hybridisation that tend to enhance the localised character of the Al states in the vicinity of the Fermi level. Yet, the shape of the pseudo-gap does not change.
Title:
Electronic spectrum of the Amman-Kramer-Neri lattice
Authors:
Vekilov, YK; Isaev, EI; Godoniuk, AV
Source:
FERROELECTRICS, 305: 239-243 2004
Abstract:
Electronic spectrum of the Amman-Kramer-Neri (AKN) lattice with "central" decoration is investigated using the tight binding model. Inverse participation ratios, higher moments of the density probabilities, and fractal dimensions of the system are defined. The wave functions are "critical" and are multifractal measures leading to the whole spectrum of the exponents. The results show that the system is in the critical state of a metal-insulator transition.
Title:
Growth of Al on the faceted threefold-symmetry surface of the Al-Pd-Mn quasicrystal
Authors:
Luscher, R; Fluckiger, T; Erbudak, M
Source:
FERROELECTRICS, 305: 245-248 2004
Abstract:
We report on the deposition of thin Al films on the faceted threefold-symmetry surface of the icosahedral Al-Pd-Mn quasicrystal at and below room temperature. We find that twinned Al fcc nanocrystals grow with their [111] axes parallel to one of the threefold-symmetry axes of the icosahedral substrate. Moreover structural similarities of the growing film with the quasicrystalline substrate are observed.
Title:
Formation of nanoquasicrystalline Al-Cu-Fe coatings by EBPVD method
Authors:
Polishchuk, SS; Movchan, BA; Ustinov, AI
Source:
FERROELECTRICS, 305: 249-252 2004
Abstract:
Coatings with a quasicrystalline Al-Cu-Fe structure were formed during high rate (similar to100 nm/s) electron beam deposition of the vapour phase. The composition range of existence of icosahedral phase deposited as well as an effect of substrate temperatures in a range of 100...800degreesC on the coating structure were studied.
Title:
In-situ HREM observation of the structural change from a fundamental-lattice decagonal quasicrystal of Al72Ni20Co8 to the S1 type superlattice phase
Authors:
Saitoh, K; Tanaka, M; Yokosawa, T; Tsai, AP
Source:
FERROELECTRICS, 305: 253-256 2004
Abstract:
A structural change of an Al72Ni20Co8 decagonal quasicrystal into the S1-type superlattice ordered phase has been observed at about 400degreesC by in-situ high-resolution electron microscopy. It is considered that the formation of the SI-type superlattice order is attributed to the structural change of the atom cluster with 2 run diameter from mirror symmetric one to fivefold symmetric one and the disappearance of 1.2-nm intercluster bonds.
Title:
Re-refinement of the basic decagonal Al-Co-Ni phase
Authors:
Takakura, H; Yamamoto, A; Tsai, AP
Source:
FERROELECTRICS, 305: 257-260 2004
Abstract:
Structure refinements of two basic decagonal Al-Co-Ni quasicrystals have been performed using synchrotron radiation data. The refined structures of d-Al72Co8Ni20 and d-Al70.6Co6.7Ni22.7 are virtually identical. They have a small number of partially occupied atomic sites and are well chemically ordered in terms of Al and transition metals.
Title:
Fractal quantization of the electrical conductance in quasiperiodic systems
Authors:
Wang, C; Sanchez, V; Salazar, F
Source:
FERROELECTRICS, 305: 261-264 2004
Abstract:
In this work, the Kubo-Greenwood formula is used to investigate the electronic transport in multidimensional macroscopic quasiperiodic lattices within the tight-binding model. This investigation is carried out by means of a novel renormalization method and the convolution technique. The dc electrical conductance of two-dimensional (2D) periodic systems shows uniform steps in units of 2e(2)/h, as observed in 2D electron-gas experiments, and a fractal distribution of these steps is found when the atoms in perpendicular direction to the applied electricfield are quasiperiodically ordered. The spectral integral of these conductances presents a strong dependence on the imaginary part of energy in the Green's function, contrary to the case of density of states.

Update: ???

Title:
New Sr-substituted niobium-based misfit layer sulfides
Authors:
D'Yachenko, OG; Grippa, AY; Lidin, S; Rupasov, DP; Antipov, EV;
Source:
FERROELECTRICS, 305 (8): 3-6; 2004
Abstract:
Two series of [(Ln(1/3)Sr(2/3)S)(1.5)](1.15)NbS2 and (Ln(1-x)Sr(x)S)(1+y)NbS2 misfit layer sulfides have been synthesized and studied by X-ray powder and single crystal diffraction, electron diffraction, and EDX-analysis. The [(SM1/3Sr2/3S)(1.5)](1.15)NbS2 compound belongs to the 1.5Q/1H homologue type where the Sr-cations are mainly located at the exterior of the Q-slab whereas Sm preferably occupy the positions at its center The (Pr0.55Sr0.45S)(1.15)NbS2 sulfide is a member of the 1Q/1H homologue series where almost half of the Pr-atoms in the Q-slab are replaced by Sr ones with a statistical distribution of Pr and Sr over the cation positions.
Title:
Three years of developing JANA2000
Authors:
Dusek, M; Petricek, V
Source:
FERROELECTRICS, 305: 267-271 2004
Abstract:
We present the latest state of the computing system JANA2000. The main improvement comparing with the previous version JANA98 consists in the possibility to use powder diffraction data of one or more three-dimensional or modulated phases. The current development of JANA2000 comprises (1) generalization of the program from four to six dimensions, (2) improvement of the powder option, (3) developing of complex tools for transformations and (4) automatic determination of the (super)space symmetry.
Title:
Solving approximant structures using a "strong reflections" approach
Authors:
Christensen, J; Oleynikov, P; Hovmoller, S; Zou, XD
Source:
FERROELECTRICS, 305: 273-277 2004
Abstract:
A new general approach for solving tau-related approximants in an inflation series is derived. The strongest reflections from an approximant with known structure are used to deduce the structure of other approximants in the series. The structure model deduced in such a way is close enough to the true structure and a more accurate structure can be obtained from the refinement of such a model. The method is applied to m-Al13Co4, (C2/m, a = 15.173 Angstrom, b = 8.109 Angstrom, c = 12.349 Angstrom and beta = 107.84degrees) [1] and the inflation related tau(2) -Al13Co4 [2].
Title:
Refinement of i-Al-Cu-Fe and i-Al-Cu-Ru quasicrystal structures
Authors:
Yamamoto, A; Takakura, H; Tsai, AP
Source:
FERROELECTRICS, 305: 279-282 2004
Abstract:
The structure refinements of icosahedral Al-Cu-Fe (i-Al-Cu-Fe) and i-Al-CU-Ru quasicrystals were performed by using 6-dimensional cluster models and synchrotron radiation data. The structures were proved to be iso-structural to those of i-Al-Pd-Mn and i-Al-Pd-Re which were determined recently. They consist of two 20 Angstrom clusters, one of which is similar to the cluster in the Al-Pd-Mn-Si 2/1 approximant, and two Mackay-like clusters. This structure includes additional inter-penetrated Mackay-like clusters, which are parts of 20 Angstrom clusters.
Title:
Mathematical diffraction theory - A summary
Authors:
Baake, M
Source:
FERROELECTRICS, 305: 285-290 2004
Abstract:
Mathematical diffraction theory is concerned with the Fourier analysis of the autocorrelations of translation bounded measures on sigma-compact locally compact Abelian groups, with n-dimensional Euclidean space being the most important example. This mathematical approach provides new insight into the theory of kinematic diffraction, in particular into the distinction of pure Bragg versus diffuse scattering in X-ray diffraction. A number of unexpected properties can then be formulated and dealt with in a rigorous way.
Title:
Low-frequency structural dynamics in the incommensurate composite crystal Bi2Sr2CuO6+delta
Authors:
Etrillard, J; Bourgeois, L; Bourges, P; Liang, B; Lin, CT; Keimer, B
Source:
EUROPHYSICS LETTERS, 66 (2): 246-252 APR 2004
Abstract:
Inelastic coherent neutron scattering experiments have been performed to study the low-frequency structural excitations in single crystals of the incommensurate superconducting Bi2Sr2CuO6+delta (Bi-2201) system. As in the Bi-2212 family, the observation of two well-defined propagating "acoustic-like" branches around the main Bragg reflections reflects its composite nature. The two modes naturally correspond to the separate motions of the two sublattices. Constant-Q scans reveal a rapid evolution of the dynamical structure factor with the wave vector. Twenty years of structure research on quasicrystals. Part 1. Pentagonal, octagonal, decagonal and dodecagonal quasicrystals
Authors:
Steurer, W
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 219 (7): 391-446 2004
Abstract:
Is quasicrystal structure analysis a never-ending story? Why is still not a single quasicrystal structure known with the same precision and reliability as structures of regular periodic crystals? What is the state-of-the-art of structure analysis of axial quasicrystals? The present comprehensive review summarizes the results of almost twenty years of structure analysis of axial quasicrystals and tries to answer these questions as far as possible. More than 2000 references have been screened for the most reliable structural models of pentagonal, octagonal, decagonal and dodecagonal quasicrystals. These models, mainly based on diffraction data and/or on bulk and surface microscopic images are critically discussed together with the limits and potentialities of the respective methods employed.
Title:
Decagonal quasicrystals in Al-Ni-Co: generality and particulars
Authors:
Grushko, B; Doblinger, M
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 219 (7): 447-455 2004
Abstract:
A great number of stable and metastable structures associated with the Al-Ni-Co decagonal phase were observed in a continuous range from binary Al-Co to binary Al-Ni. Two independent basic binary compounds forming the continuous row of the decagonal solid solutions are argued for Al-Ni-Co. The formation of different quasiperiodic and periodic structures in this range is discussed. Our analysis leads to a significant simplification of the description of the decagonal range in the equilibrium Al-Ni-Co phase diagram.
Title:
Chain "melting" in the composite Rb-IV structure
Authors:
McMahon, MI; Nelmes, RJ
Source:
PHYSICAL REVIEW LETTERS, 93 (5): Art. No. 055501 JUL 30 2004
Abstract:
The Bragg peaks from the structure formed by the guest chains in the incommensurate composite structure of Rb-IV are all found to broaden strongly at pressures below 16.7(1) GPa. This signals a loss of the interchain correlation. At the lowest reachable pressure before the transition to Rb-III, 16.2 GPa, the correlation length is only similar to30 Angstrom, or 4 times the interchain distance. There is also evidence of a loss of long-range order within each chain. The chains thus exhibit the onset of the characteristics of an ordered 1D liquid.
Title:
Magnetic structure of TbMnO3 by neutron diffraction
Authors:
Kajimoto, R; Yoshizawa, H; Shintani, H; Kimura, T; Tokura, Y
Source:
PHYSICAL REVIEW B, 70 (1): Art. No. 012401 JUL 2004
Abstract:
Magnetic ordering in TbMnO3 was revisited by a neutron diffraction study. In addition to the previously reported A-type and G-type modulated structures with a propagation vector (0,q(Mn),0), we found C-type and F-type orderings of the Mn moments. All the components appear below T-N(Mn)=46 K, and the G-, C-, and F-type components are enhanced below T-lock=28 K, where q(Mn) ordering locks at its low temperature value. The locking of the propagation vector also yields the squaring up of the spin arrangement. The magnetic moments of Tb ions show a quasi-long-range ordering below T-N(Tb)=7 K. It drastically promotes the development of the G-, C-, and F-type components while suppressing the A-type components.
Title:
Ab initio calculations of structure and lattice dynamics in Ni-Mn-Al shape memory alloys
Authors:
Busgen, T; Feydt, J; Hassdorf, R; Thienhaus, S; Moske, M; Boese, M; Zayak, A; Entel, P
Source:
PHYSICAL REVIEW B, 70 (1): Art. No. 014111 JUL 2004
Abstract:
Ab initio calculations of the magnetic shape-memory alloy Ni50MnxAl50-x with 0less than or equal toxless than or equal to50 were carried out using density functional theory and PAW potentials. The alloy is ferromagnetic in the range from 14 to 31 at.% Mn. The magnetic moment and structural properties are discussed in terms of the density of states. Furthermore martensitic phases with long-periodic shuffling structure were calculated: 2M, 10M, and 14M. Their stability is discussed in respect to the electronic structure and the lattice dynamics, whereby phonon dispersion relations in [110] direction for the cubic L2(1) Heusler structure have been calculated. The transverse-acoustic phonon mode is shown to soften at the wave vector zeta=[1/3 1/3 0] which confirms the tendency of Ni2MnAl to form modulated structures at low temperatures. The theoretical results of the modulated martensitic phases correspond to experimental data, obtained from thin films near the stoichiometric composition.
Title:
NMR investigations of medium-range order and quasicrystal formation in Zr59Cu20Al10Ni8Ti3 metallic glass
Authors:
Breitzke, H; Luders, K; Scudino, S; Kuhn, U; Eckert, J
Source:
PHYSICAL REVIEW B, 70 (1): Art. No. 014201 JUL 2004
Abstract:
The structure and quasicrystal formation in bulk metallic glass-forming Zr59Cu20Al10Ni8Ti3 are studied by means of nuclear magnetic resonance (NMR). The samples are prepared by rapid solidification and annealed to induce primary quasicrystal formation. Al-27 and Cu-63 NMR spectra and relaxation curves are recorded before and after the annealing process. Structure estimation is done by simulations of the second moments of various binary Al and Cu compounds. The Al spin-lattice relaxation time (T-1) of the order of 500 ms indicates a pseudogap in the density of states (DOS) at the Fermi level at Al sites similar as predicted by band structure calculations for binary AlZr compounds. Simulations of the second moments of various Al and Cu structures also favor the existence of binary L-12 AlZr3 and C11(b) CuZr2 medium-range ordered regions in the metallic glass. The crystallization significantly changes the Cu-63 spectra and leaves the Al-27 spectra almost unchanged. The second moment of Cu-63 is strongly decreased after the crystallization accompanied by a strong increase in the Cu-63 spectral intensity. This indicates the formation of an icosahedral order involving CuX crystalline approximants.
Title:
Magnetic structures and spin-glass-like behavior in ordered and disordered Pt-rich Pt-Mn alloys
Authors:
Takahashi, M; Sembiring, T; Noda, Y; Shishido, T; Ohshima, K
Source:
PHYSICAL REVIEW B, 70 (1): Art. No. 014431 JUL 2004
Abstract:
The magnetism of Pt-rich Pt-Mn alloys was studied in single crystals with different Mn concentrations (12.5, 14.4, and 15.9 at.%) and different atomic arrangements of disordered, ABC(6) type and Cu3Au type structures by using neutron scattering and susceptibility measurements. The neutron scattering measurements showed drastic changes in the magnetic diffraction pattern with a slight difference in the atomic arrangement and Mn concentration. In disordered alloys, magnetic diffuse peaks were observed at 1/2, 0, 0 and equivalent symmetry positions of the fcc fundamental structure. In ordered alloys with the ABC(6) type structure, fourfold splitting along [011] and [0 (1) over bar1] with incommensurate maxima appeared in the 1/2, 0, 0 diffuse scattering in Pt-12.5 at.%Mn, while the 1/2, 0, 0 diffuse scattering completely disappeared, instead, commensurate superlattice peaks were newly observed at 1/2,+/-1/4,0 and 1/2,0,+/-1/4 in Pt-14.4 at.%Mn. Fourfold splitting and superlattice peaks were observed with the ABC(6) type symmetry. In ordered alloys with the Cu3Au type structure, ferromagnetic diffuse scattering was mainly observed at the zone center of the Cu3Au type structure. The origin of these magnetic scatterings is discussed in terms of three different magnetic interactions: a spin-density wave (SDW) originated by a nesting Fermi surface, an antiferromagnetic interaction on the ABC(6) type structure and a ferromagnetic interaction on the Cu3Au type structure. The dominant interaction largely depends on the atomic arrangement, indicating a strong coupling between the magnetic and atomic structures in the alloys. Susceptibility measurements showed a spin-glass-like behavior in all of the samples, which is attributed to the dynamics of the fluctuating SDW clusters, as observed in other Pd-M and Pt-M (M; 3d element) spin-glass alloys. The persistence of the SDW fluctuations indicates the instability of these magnetic structures.
Title:
Field-induced magnetic order in La2-xSrxCuO4 (x=0.10,0.115,0.13) studied by in-plane thermal conductivity measurements
Authors:
Kudo, K; Yamazaki, M; Kawamata, T; Adachi, T; Noji, T; Koike, Y; Nishizaki, T; Kobayashi, N
Source:
PHYSICAL REVIEW B, 70 (1): Art. No. 014503 JUL 2004
Abstract:
We have measured the thermal conductivity in the ab plane of La2-xSrxCuO4 (x=0.10,0.115,0.13) in magnetic fields up to 14 T parallel to the c axis and also parallel to the ab plane. By the application of magnetic fields parallel to the c axis, the thermal conductivity has been found to be suppressed at low temperatures below the temperature T-kappa which is located above the superconducting transition temperature and is almost independent of the magnitude of the magnetic field. The suppression is marked in x=0.10 and 0.13, while it is small in x=0.115. Furthermore, no suppression is observed in the 1% Zn-substituted La2-xSrxCu0.99Zn0.01O4 with x=0.115. Taking into account the experimental results that the temperature dependence of the relative reduction of the thermal conductivity is quite similar to the temperature dependence of the intensity of the incommensurate magnetic Bragg peak corresponding to the static stripe order and that the Zn substitution tends to stabilize the static order, it is concluded that the suppression of the thermal conductivity in magnetic fields is attributed to the development of the static stripe order. The present results suggest that the field-induced magnetic order in La2-xSrxCuO4 originates from the pinning of the dynamical stripes of spins and holes by vortex cores.
Title:
Quasiparticle dynamics and in-plane anisotropy in YBa2Cu3Oy near the onset of superconductivity
Authors:
Lee, YS; Segawa, K; Ando, Y; Basov, DN
Source:
PHYSICAL REVIEW B, 70 (1): Art. No. 014518 JUL 2004
Abstract:
We report on an infrared study of carrier dynamics within the CuO2 planes in heavily underdoped detwinned single crystals of YBa2Cu3Oy. In an effort to reveal the electronic structure near the onset of superconductivity, we investigate the strong anisotropy of the electromagnetic response due to an enhancement of the scattering rate along the a axis. We propose that the origin of this anisotropy is related to a modulation of the electron density within the CuO2 planes.
Title:
NMR and local-density-approximation evidence for spiral magnetic order in the chain cuprate LiCu2O2
Authors:
Gippius, AA; Morozova, EN; Moskvin, AS; Zalessky, AV; Bush, AA; Baenitz, M; Rosner, H; Drechsler, SL
Source:
PHYSICAL REVIEW B, 70 (2): Art. No. 020406 JUL 2004
Abstract:
We report on Li-6,Li-7 nuclear magnetic resonance measurements of the spin-chain compound LiCu2O2 in the paramagnetic and magnetically ordered states. Below 24 K the NMR line shape shows a clear signature of incommensurate (IC) static modulation of the local magnetic field consistent with an IC spiral modulation of the magnetic moments. Li-7 NMR reveals strong phason-like dynamical fluctuations extending well below 24 K. A series of phase transitions at 24.2, 22.5, and 9 K is observed. Local density approximation based calculations of exchange integrals reveal a large in-chain frustration leading to a magnetical spiral.
Title:
Origin of second-harmonic generation in the incommensurate phase of K2SeO4
Authors:
Aslanyan, TA
Source:
PHYSICAL REVIEW B, 70 (2): Art. No. 024102 JUL 2004
Abstract:
We show that a ferroelectric phase transition takes place in the incommensurate phase of the K2SeO4 crystal. The ferroelectric character of the incommensurate phase explains the second-harmonic generation observed in the corresponding temperature range.
Title:
Atomic structure of an Al-Co-Ni decagonal quasicrystalline surface
Authors:
Yuhara, J; Klikovits, J; Schmid, M; Varga, P; Yokoyama, Y; Shishido, T; Soda, K
Source:
PHYSICAL REVIEW B, 70 (2): Art. No. 024203 JUL 2004
Abstract:
We have analyzed the structure and composition of the first layer of an Al72Co16Ni12 tenfold surface by means of scanning tunneling microscopy (STM), ion scattering spectroscopy (ISS), and Auger electron spectroscopy (AES). High-resolution STM images reveal local structures that have decagonal symmetry in addition to the usual pentagonal symmetry of the surface. This quasicrystal surface resembles a random tiling instead of an ideal quasiperiodic tiling. After annealing at 1100 K, the total surface atomic density found by ISS is (9+/-1)x10(14) cm(-2). The surface densities of Al and TM (transition metal, i.e., Co and Ni) are determined as (8+/-1)x10(14) cm(-2) and (1.0+/-0.2)x10(14) cm(-2), respectively from ISS, indicating a similar density of Al and much lower density of the TM atoms in the surface layer than in a truncated bulk. The Al surface atomic density agrees well with the number of corrugation maxima in the STM images. A model of the arrangement of the Al atoms in the top layer is presented. Scanning tunneling spectroscopy (STS) is performed to study the local electronic structure. The STS spectrum at the corrugation maxima is similar to that at the corrugation minima. A few approximate to0.12 nm high protrusions in the STM images are attributed to local oxide clusters due to their STS spectra different from the corrugation maxima and through in situ STM observations during exposure to O-2 gas at 2x10(-6) Pa at RT.
Title:
Orbital hybridizations versus the Fermi surface-Brillouin zone interaction in strongly hybridizing Al-Li-Cu 1/1-1/1-1/1 approximant
Authors:
Sato, H; Takeuchi, T; Mizutani, U
Source:
PHYSICAL REVIEW B, 70 (2): Art. No. 024210 JUL 2004
Abstract:
The origin of a deep pseudogap existing at the Fermi level E-F in the Al52.5Li32.5Cu15 1/1-1/1-1/1 approximant was studied from two different points of view of orbital hybridizations and the Fermi surface-Brillouin zone interaction. The first-principle band calculations were performed in the framework of the linear muffin-tin orbital-atomic sphere approximation (LMTO-ASA) and the nearly free electron (NFE) model. The Al-3p/Al-3p orbital hybridization between the nearest neighbor Al atoms, on one hand, is shown to give rise to splitting into bonding and antibonding states across E-F. The Fermi surface-Brillouin zone interaction, on the other hand, is studied by calculating the local density of states (LDOS) in an element in the k space in the periodic zone scheme and subsequently by integrating them over a given zone plane. By examining carefully how the pseudogap develops on the zone plane, we are led to conclude that successive zones are not independent of each other but are strongly coupled to produce the pseudogap. The coupling of zones was studied in the 1061- and 1505-wave approximations in the NFE model, both being accurate enough to reproduce the electronic structure derived from LMTO-ASA. Encouraged by this success, we studied the effect of each zone on the pseudogap by deleting its form factor in the NFE model. We found the pseudogap to disappear almost completely in the following two cases: one, the elimination of (631), {(543),(710),(550)} zones, which is consistent with the prediction from the empirical Hume-Rothery matching rule, and the second all zones below Sigmah(2)less than or equal to16, where h represents the set of Miller indices (h,k,l) of the lattice planes. A localized charge density due to the Al-3p/Al-3p hybridizations between neighboring Al atoms is heavily destroyed, when these two sets of form factors are forced to zero.
Title:
Theoretical and experimental study of the magnetic structure of TlCo2Se2
Authors:
Lizarraga, R; Ronneteg, S; Berger, R; Bergman, A; Mohn, P; Eriksson, O; Nordstrom, L
Source:
PHYSICAL REVIEW B, 70 (2): Art. No. 024407 JUL 2004
Abstract:
The magnetic properties of TlCo2Se2 are investigated by means of single-crystal neutron diffraction experiments and first principles calculations. The previous suggestion of a noncollinear incommensurate magnetic structure based on powder neutron diffraction data is confirmed by single-crystal diffraction. Our theoretical calculations find that TlCo2Se2 adopts an antiferromagnetic ordering. The magnetism is dominated by the contribution from the Co atoms, where the magnetic moments are arranged ferromagnetically within the ab plane. The magnetic moments from experiments are reproduced very well by our theoretical calculations. The origin of the magnetic ordering is analyzed by a detailed inspection of the energy band structure and the Fermi surface. The small calculated energy difference (approximate to0.1 mRy) between the two magnetic arrangements, the experimental noncollinear and the antiferromagnetic, is viewed as the most likely origin of this discrepancy. The influence of nonstoichiometric samples on the magnetic state is also argued to be a possible source for the observed small discrepancy between experiment and theory.
Title:
Complex interplay of 3d and 4f magnetism in La1-xGdxMnO3
Authors:
Hemberger, J; Lobina, S; von Nidda, HAK; Tristan, N; Ivanov, VY; Mukhin, AA; Balbashov, AM; Loidl, A
Source:
PHYSICAL REVIEW B, 70 (2): Art. No. 024414 JUL 2004
Abstract:
We report on structural, magnetic, electrical, and thermodynamic properties of Gd-doped LaMnO3 single crystals for Gd doping levels 0less than or equal toxless than or equal to1. At room temperature, for all doping levels the orthorhombic O' phase is indicative of a strong Jahn-Teller distortion. All compositions are insulating. The magnetism of La1-xGdxMnO3 is dominated by the relatively strong Mn-O-Mn superexchange. For increasing Gd doping, the weakening of the nearest-neighbor exchange interactions due to the significant decrease of the Mn-O-Mn bond angles leads to the continuous suppression of the magnetic phase-transition temperature into the A-type antiferromagnetic low-temperature phase. The temperature dependence of the magnetization can only be explained assuming canting of the manganese spins. The magnetic moments of Gd are weakly antiferromagnetically coupled within the sublattice and are antiferromagnetically coupled to the Mn moments. For intermediate concentrations compensation points are found, below which the spontaneous magnetization becomes negative. In pure GdMnO3 the Mn spins undergo a transition into a complex, probably incommensurate magnetic structure at 41.5 K, followed by a further ordering transition at 18-20 K revealing weak ferromagnetism due to canting and finally by the onset of magnetic order in the Gd sublattice at 6.5 K. At the lowest temperatures and low external fields, both magnetic sublattices reveal a canted structure with antiparallel ferromagnetic components.
Title:
The incommensurably modulated structure of zeta-Zri(3-x)Sb(2)
Authors:
Bostrom, M; Lidin, S
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 376 (1-2): 49-57 AUG 11 2004
Abstract:
The incommensurately modulated structure of zeta-Zn3-xSb2 was solved and refined versus X-ray single crystal diffraction data using a 3 + 1 dimensional superspace formalism. The compound crystallizes in the orthorhombic system in the 3 + 1 dimensional superspace group Pnna(alpha0)0s0 with the cell parameters a = 7.283(3) Angstrom, b = 15.398(5) Angstrom, c = 25.06(1) Angstrom, q = (alpha, 0, 0), alpha approximate to 0.385. The structure features columns of intergrown icosahedra and columns of face sharing empty octahedra built up from Sb atoms. The Zn atoms are accommodated in tetrahedral interstices. The origin of the discommensuration and the relation between the modulation vector q and the chemical composition are explained. (C) 2004 Elsevier B.V. All rights reserved.
Title:
An investigation of the Al-Pd-Fe phase diagram between 50 and 100 at.% Al: phase equilibria at 750 degrees C
Authors:
Balanetskyy, S; Grushko, B; Velikanova, TY; Urban, K
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 376 (1-2): 158-164 AUG 11 2004
Abstract:
The isothermal 750degreesC section of Al-Pd-Fe was determined between 50 and 100 at.% Al. The range of the Al-Pd orthorhombic epsilon-phases extends up to similar to10 at.% Fe. Apart from the four specific structural variants epsilon6, epsilon16, epsilon22 and epsilon28, irregular structures were observed in this continuous range. In addition to the ternary cubic C-1, C-2 phases and orthorhombic O-Al-13(Fe,Pd)(4) observed at higher temperatures, a new stable orthorhombic N-phase was revealed. It exhibits a structural relation to the epsilon-phases and decagonal quasicrystals. (C) 2004 Elsevier B.V. All rights reserved.
Title:
An example of symmetry space-group for a quasicrystal
Authors:
Elkharrat, A; Frougny, C; Gazeau, JP; Verger-Gaugry, JL
Source:
FERROELECTRICS, 305: 9-13 2004
Abstract:
We present the construction of a symmetry plane-group for a quasiperiodic point-set in the plane named tau-lattice, tau being the golden-ratio. The tau-lattice generalizes the notion of periodic lattice to quasiperiodicity, The algebraic framework is issued from the counting system of tau-integers. The set of tau-integers can be equipped with an abelian group structure and an internal multiplicative law. These arithmetic structures lead to a freely generated symmetry plane-groupfor the tau-lattice, based on repetitions of discrete "tau-rotations" and "tau-translations" in the plane. Hence the tau-lattice; endowed with these adapted rotations and translations, can be viewed as a lattice with "rotational" symmetries.
Title:
Electrons and phonons on the square Fibonacci tiling
Authors:
Ilan, R; Liberty, E; Mandel, SED; Lifshitz, R
Source:
FERROELECTRICS, 305: 15-19 2004
Abstract:
We study the Schrodinger equation for an off-diagonal tight-binding hamiltonian, as well as the equations of motion for out-of-plane vibrations on the separable square Fibonacci quasicrystal. We discuss the nature of the spectra and wave functions of the solutions.
Title:
A maximum density rule for surfaces of quasicrystals
Authors:
Papadopolos, Z; Pleasants, P; Kasner, G
Source:
FERROELECTRICS, 305: 21-24 2004
Abstract:
Motivated by Bravais' rule, of wide validity for crystals, we introduce a maximum density rule for the surfaces of quasicrystals and use it to determine the 5-, 2- and 3-fold bulk terminations in a geometric icosahedral model of i-AlPdMn and i-AlCuFe that represent surfaces.
Title:
Group cohomology and quasicrystals II: The three crystallographic invariants in two and three dimensions
Authors:
Fisher, BN; Rabson, DA
Source:
FERROELECTRICS, 305: 25-28 2004
Abstract:
In Fourier-space crystallography, space groups are classified by their phase functions, Phi, and we can determine Phi (up to a gauge) by its invariants. Usually, the invariants imply necessary extinctions in diffraction, but among the 157 periodic non-symmorphic space groups, two are distinguished not by extinctions-they have none-but by a second type of invariant. We give a non-periodic example of a third type of invariant and assert that all invariants can be expressed as sums of just these three types.
Title:
Constructing an octagonal structure by projection in two stages
Authors:
Ben-Abraham, SI
Source:
FERROELECTRICS, 305: 29-32 2004
Abstract:
I projected a 4D simple cubic lattice into 3D so that a further projection to 2D yields an Octagonal structure. A 4D cube projects into a 3D hexagonal prism segment. The final result is a layer structure quasiperiodic in one direction and periodic in the perpendicular plane. The structure promises to be useful as a simple model of an aperiodic crystal.
Title:
Representations of the icosahedral group with application to quasicrystals
Authors:
Cotfas, N
Source:
FERROELECTRICS, 305: 33-36 2004
Abstract:
An icosahedral quasicrystal can be regarded as a packing of copies of a well-defined atomic cluster C. On the other hand, by starting from any cluster C with icosahedral symmetry we can define in terms of the strip projection method a quasiperiodic packing of copies of C. The dimension of the superspace we have to use in this definition can be reduced by using the notion of multi-component model set (a generalization of the notion of model set, proposed by Baake and Moody).
Title:
Group cohomology and quasicrystals I: Classification of two-dimensional space groups
Authors:
Fisher, BN; Rabson, DA
Source:
FERROELECTRICS, 305: 37-40 2004
Abstract:
In Fourier-space crystallography, the space group is defined in terms of the point group G, the inverse lattice (or Fourier module) L, and a phase function Phi. We classify the two-dimensional space groups (or plane groups), the major step being the classification of lattices, of all ranks, symmetric under the finite point group G. This step requires new ideas from integer representation theory. Given this classification, the remaining steps can be done easily using techniques of group cohomology.
Title:
Crenel functions and aperiodic structure determinations
Authors:
Evain, M; Petricek, V
Source:
FERROELECTRICS, 305: 43-48 2004
Abstract:
In the modeling of modulated or composite structures, crenel functions proved to be very efficient on many occasions. After a brief summary on the theory and practice of crenel functions, illustrations are provided from both modulated and composite structures. An example is also given where the use of crenel function, although apparently applicable, is not appropriate.
Title:
The ferroelectric phase transition and modulated valence electrons in the incommensurate phase of ammonium tetrafluoroberyllate
Authors:
Palatinus, L; Van Smaalen, S
Source:
FERROELECTRICS, 305: 49-52 2004
Abstract:
The incommensurate structure of (NH4)(2)BeF4 is determined from single-crystal x-ray diffraction at T = 175K. Comparison of this structure with the low-temperature structure shows the ferroelectric phase transition to correspond to the simultaneous development of local and global polarisations. The modulations of the electrons in the chemical bonds are made visible by the Maximum Entropy Method with the modulated structure as superspace prior.
Title:
A molecular dynamics study of an incommensurate modulation compound: 4,4 '-dichlorobiphenyl sulphone
Authors:
Pan, YS; Brown, D; Zuniga, FJ; Chapuis, G
Source:
FERROELECTRICS, 305: 53-56 2004
Abstract:
A molecular dynamics simulation of 4, 4'-dichlorobiphenyl sulfone was carried out in order to study the phase transition from a normal to incommensurate modulated phase observed experimentally. Agreements of simulated and experimental diffraction patterns and lattice constants indicates that the simulation is able to well reproduce the normal-incommensurate phase transition. The incommensurate modulation is found to originate from large-scale fluctuations in the displacements of the molecules.
Title:
Applications of the Maximum Entropy Method in superspace
Authors:
Van Smaalen, S; Palatinus, L
Source:
FERROELECTRICS, 305: 57-62 2004
Abstract:
The Maximum Entropy Method (MEM) can be used to derive the electron density in the superspace unit cell of aperiodic crystals from scattering data. Applications to (LaS)(1.14)NbS2, Bi-III and (NH4)(2)BeF4 show that the MEM provides a reliable, model-independent estimate of the true shapes of modulation functions, that go beyond the possibilities of structure refinements. Missing information on higher-order satellites might prevent higher-order harmonic contributions to the modulations functions to be determined.
Title:
Identification and characterization of modulated phases in A(2)BX(4) compounds
Authors:
Speziali, NL
Source:
FERROELECTRICS, 305: 63-68 2004
Abstract:
Three examples of compounds with virtually P6(3)/mmc symmetry at the high temperature phase are presented. Different experimental carefulness has been necessary in each case and it has been shown that conclusions can be biased by inadequate experimental procedures. The use of special scanning modes in X-ray diffraction experiments and particular thermal treatment has shown, in some cases, to be crucial for the conclusions about crystal symmetry and modulation in the crystal structure.
Title:
Constraints, 'order' and new types of modulated phases
Authors:
Withers, RL
Source:
FERROELECTRICS, 305: 69-74 2004
Abstract:
The strongest crystal chemical constraints are usually local and fix local parameters such as bond lengths, angles and even stoichiometries (although not necessarily orientations) in local co-ordination polyhedra. Surprisingly often, however, constraints of this sort are insufficiently severe or long range enough to lead to well-defined, conventional 3-d crystalline order Instead quite distinct new types of "modulated structure," commonly associated with the existence of sharp, highly structured, characteristic diffuse intensity distributions, can result.
Title:
Structural and dynamical aspects of structural phase transitions on incommensurate A(2)BX(4) compounds
Authors:
Jorio, A; Dantas, MSS; Speziali, NL; Pimenta, MA; Pinheiro, CB; Luk'Yanchuk, I; Saint-Gregoire, P
Source:
FERROELECTRICS, 305: 75-78 2004
Abstract:
At high temperature, the A(2)BX(4) crystals exhibit P6(3)/mmc structure. With temperature decreasing, a rich diagram of structural phases and phase transitions are observed, including different incommensurate phases. Ordering of the BX4 tetrahedra orientation in the unit cell drives the transitions, and they can be well described by an Ising model with competing interactions. Raman and infrared spectroscopy, differential scanning calorimetry (DSC) and thermogravimetry (TGA) are used to characterize the phase transitions in Cs2HgBr4 and Rb-2 WO4 crystals.
Title:
The high-temperature and intermediate phases of ferroelectric aurivillius compounds in superspace. A unified approach
Authors:
Elcoro, L; Perez-Mato, JM; Izaola, Z; Boullay, P; Mercurio, D
Source:
FERROELECTRICS, 305: 79-82 2004
Abstract:
The recently proposed superspace description of the Aurivillius compounds in their ferroelectric phase is here extended to their high-temperature phases. The probable existence of an intermediate phase between the tetragonal high-symmetry and the ferroelectric phases is stressed. The relevant superspace groups,for both the tetragonal and the intermediate phases are identified. Consequently, the 3D space groups for the intermediate phases as a function of composition are predicted.
Title:
Correlation between modulation and structural disorder in the 4,4 '-diethoxyazoxybenzene
Authors:
Pinheiro, CB; Gardon, M; Pattison, P; Chapuis, G
Source:
FERROELECTRICS, 305: 83-87 2004
Abstract:
The structural refinement of the modulated phase of 4,4'-Diethoxyazoxybenzene (DXB) indicates a correlation between the shifts on the DXB molecule (modulation) and the probability to find the azoxy (N --> O) group in different configurations (disorder). This study shows the correlation between disorder and modulation in order to optimize the crystal packing.
Title:
On the symmetry of optically isotropic modulated lazurites from the Baikal region
Authors:
Bolotina, NB; Rastsvetaeva, RK; Chapuis, R; Schonleber, A; Sapozhnikov, AN; Kashaev, AA
Source:
FERROELECTRICS, 305: 95-98 2004
Abstract:
The incommensurately modulated twinned crystal structure of lazurite from the Baikal region is presented for the first time. The orthorhombic structure was solved in a pseudo cubic unit cell, a(cub) = 9.077(1) Angstrom, and in the (3 + 2)D superspace group Pnn2(alphaalpha0, alpha - alpha0). The crystal is twinned with three components oriented along the [111] axis. In order to include all the measured satellites, the structure was also refined with trigonal symmetry R3, where the average structure refined to R = 3.6%. A 3D-modulated twinned trigonal structure will be further considered.
Title:
The structure of diaqua (15-crown-5) copper (II) dinitrate described in (3+1)-dimensional superspace
Authors:
Schonleber, A; Chapuis, G
Source:
FERROELECTRICS, 305: 99-102 2004
Abstract:
Diaqua (15-crown-5) copper (II) dinitrate is an organic salt presenting an one-dimensional commensurate modulation. The diffraction pattern is characterized by strong Bragg reflections and weaker superstructure reflections (satellites). The structure is described in the superspace formalism as a modulated structure in (3 + 1) dimensions with occupational and displacive modulation functions.
Title:
Incommensurately modulated phase of iodine under high pressure
Authors:
Takemura, K; Sato, K; Fujihisa, H; Onoda, M
Source:
FERROELECTRICS, 305: 103-106 2004
Abstract:
High-pressure powder x-ray diffraction experiments have been carried out on iodine at room temperature with a helium-pressure medium. A new high-pressure phase has been found in the pressure range 24-28 Gpa, in the close vicinity of the molecular dissociation. The structure is incommensurately modulated, which we interpret as a transient state between molecular and monatomic ones.
Title:
Multi-q modulated structures and their diffraction patterns
Authors:
Urban, G; Wolny, J
Source:
FERROELECTRICS, 305: 107-110 2004
Abstract:
Using a statistical approach, the average unit cells and the average Patterson functions have be constructed for modulated structures with different types of modulations. Universal probability distributions and autocorrelation functions for different lengths of the modulation vector have been found. Such universal behaviour allows to distinguish between differently modulated structures directly from the experimentally obtained average Patterson function.
Title:
Superspace description of NaCa4Nb5O17 as a modulated layered compound
Authors:
Zuniga, FJ; Elcoro, L; Perez-Mato, M
Source:
FERROELECTRICS, 305: 111-114 2004
Abstract:
Following the general model proposed for the series of compounds Sr-n(Nb, Ti)(n)O3n+2, the recently determined structure of the related compound NaCa4Nb5O17 has been re-analyzed in superspace and refined using a set of crenel occupational functions. The atomic positions in real space can be described using eight independent atomic domains with smooth modulations under the superpace monoclinic symmetry X112(1)/b(alphabeta0) (X standing for the centring translations generated from (3/4 1/2 0 1/4)), and with modulation wave vector q = 1/12 b* (alpha = 0, beta = 1/12). A refinement performed with the JANA2000 program using the same experimental data as the standard three-dimensional refinement gave indeed equivalent results. The superspace approach, however, reduced the number of structural variables.
Title:
Quasiperiodic magnetic order and geometrical frustration on the Penrose tiling
Authors:
Vedmedenko, EY
Source:
FERROELECTRICS, 305: 129-132 2004
Abstract:
The spatial variation of the coordination number on the Penrose tiling leads to suppression of the formation of macroscopic vortex configuration, usual to soft ferromagnetic films on periodic lattices, in favor of microscopic decagonal pattern. That state represents a new class of frustrated systems where the structure is aperiodic and consists of two parts: ordered, stable decagon chains and an unstable, spin-glass phase inside of the decagons. Virgin magnetizing is a two-step process in that system.
Title:
Optical phenomena in the region of incommensurate phases in quartz
Authors:
Bodnar, IT
Source:
FERROELECTRICS, 305: 133-136 2004
Abstract:
The temperature dependence of refractive indices of single quartz crystals was measured by the least deviation method. It was observed intricate behavior of mercury or laser lines in the region alpha-beta transition. On the ground of the obtained results it was concluded that the transition is accompanied coexistence of phase and diffraction and scattering of light.
Title:
Wave-function scaling exponents and the trace map of a Fibonacci chain
Authors:
Naumis, GG
Source:
FERROELECTRICS, 305: 137-140 2004
Abstract:
Approximate analytical expressions for the scaling exponents of the electronic wave-function of a Fibonacci chain are obtained from the trace map. This is done by relating the stability of the trace map with the localization nature of the system. A comparison is made with the only state for which an analytical expression of the scaling exponent is known.
Title:
Modulated structure and Superconducting Nano-Micromechanism in YBCO compounds
Authors:
Van Tri, N
Source:
FERROELECTRICS, 305: 141-145 2004
Abstract:
>From the ESR experimental results, a Modulated Structure with the twined Y-unit-cells in YBa2Cu3O7 (YBCO) ceramics have been revealed, in which appear two types of the [Cu-Y-Cu] Electron Spin Superexchange Coupled Pairs. On the basis of the particular behaviour of the quasi-free electrons in close connection with this Modulated Structure, some fundamental problems of the Superconducting Nano-Micromechanism in YBCO have been interpreted.
Title:
A way to estimate the true surface energy of complex metallic alloys
Authors:
Dubois, JM; De Weerd, MC; Brenner, J
Source:
FERROELECTRICS, 305: 159-162 2004
Abstract:
For the first time, to the best of our knowledge, a realistic approach for deriving an estimate by superior values of the surface energy of complex metallic alloys based on aluminium is proposed. It turns out that the surface energy of quasicrystals lies in the range 0.5-0.8 J/m(2), in contrast to pure aluminium (1.15 J/m(2)) or lambda-Al13Fe4 (2.0 J/m(2)) and omega-Al7Cu2Fe (2.2 J/m(2)) intermetallics.
Title:
Disorder in decagonal quasicrystals: Diffuse scattering in decagonal Al-Ni-Fe
Authors:
Frey, F; Weidner, E
Source:
FERROELECTRICS, 305: 163-166 2004
Abstract:
High resolution synchrotron x-ray data of near-Bragg diffuse scattering from decagonal Al71.5Ni23Fe5 quasicrystals was recorded. A significant dependence on Q(perpendicular to) was not observed, a dominant phasonic origin can thus be ruled out. An analysis in frame of a TDS theory gives an unlikely ratio of elastic constants c(66)/c(11) = 4.0. Moreover subsequent measurements up to 720 K do not reveal a pronounced intensity increase. Predictions of a theory of Huang diffuse scattering, however, nicely match the anisotropy of the measured data.
Title:
Atomic dynamics and diffusion in decagonal quasicrystals
Authors:
Gahler, F; Hocker, S
Source:
FERROELECTRICS, 305: 167-172 2004
Abstract:
The atomic dynamics of decagonal Al-Ni-Co and Al-Cu-Co quasicrystals is investigated by molecular dynamics simulations. Depending on the local environments, the mobility of the atoms varies greatly from site to site. Above two thirds of the melting temperature, a large fraction of the aluminium atoms become so mobile, that their diffusion can be measured directly in the simulation. As aluminium diffusion is hard to access experimentally, molecular dynamics simulations therefore provide a unique way to study aluminium diffusion in these complex systems.
Title:
Theory of phasons in aperiodic crystals
Authors:
Janssen, T; Radulescu, O
Source:
FERROELECTRICS, 305: 179-184 2004
Abstract:
The possibility of embedding a quasi-periodic structure into a higher-dimensional superspace gives rise to an interpretation of certain dynamical excitations as motions in the additional space. These excitations then are called phason excitations. There is always infinite degeneracy of the ground state of an aperiodic quasi-periodic system, but this degeneracy leads only to zero frequency modes if the atomic surfaces are smooth. If this is not the case, there is a phason gap. When the atomic surfaces are continuous, the linear phason excitations with low frequency may get an arbitrary amplitude. The excitations are almost frictionless when the velocity is below a threshold value. Above that value there is dissipation (i.e. energy transfer to phonons) even for smooth atomic surfaces.
Title:
Modelling disorder of decagonal Al-Co-Ni quasicrystals
Authors:
Kobas, M; Weber, T; Steurer, W
Source:
FERROELECTRICS, 305: 185-188 2004
Abstract:
The question whether quasicrystals exist only on global average or also on a local scale entails the question about their stabilization. A detailed model of the real structure and temperature dependent structural changes should provide insight into this problem. Simulations of disordered structures on different scales (ranging from sub-clusters to clusters with 6-20 Angstrom diameter) and in different dimensions (structural disorder in 3D and phasonic diffuse scattering (PDS) in 5D) were performed for decagonal Al70Co12Ni18. good reproduction of the experimental diffuse scattering has been achieved.
Title:
Semiconductivity in aluminum - Transition-metal quasicrystals induced by ordering in six dimensions
Authors:
Krajci, M; Hafner, J
Source:
FERROELECTRICS, 305: 189-192 2004
Abstract:
We report on a class of icosahedral aluminum-transition-metal (Al-TM) alloys with true semiconducting behavior The existence of a semiconducting gap is found to depend critically on a particular kind of Al-TM ordering defined by a simple rule in the 6-dimensional superspace. Any deviation from this 6D order leads to the formation of strongly localized defect states in the gap.
Title:
Low temperature magneto-transport properties of the I-AI(6)Ru quasicrystalline alloy
Authors:
De Medeiros, SN; Machado, FLA; Acioli, LH
Source:
FERROELECTRICS, 305: 193-198 2004
Abstract:
The magneto-transport properties of the I-Al6Ru alloy were investigated in a broad range of temperature (T), applied magnetic field (H), and the amplitude of the electrical current. Type II superconductivity was observed below 1.66 K with the transition to the superconducting state taking place in a broad range of T (deltaT(C) = 0.86 K). An Abrikosov to a vortex-liquid phase line was also observed and the data were nicely fitted to a de Almeida-Thouless line, H-C(T) = H-C(0)[1 - T-C (H)/T-C(0)](phi)/2, yielding phi = 3, H-C(0) = 140 mT and T-C (0) = 0.83 K. The influence of the DOS on deltaT(C) is also addressed in this work.
Title:
Phason coherency in real space
Authors:
Naumis, GG; Aragon, JL
Source:
FERROELECTRICS, 305: 199-202 2004
Abstract:
By considering fluctuations of a random phason field, we show that phasons defects are correlated in real space. This produces regions of the quasicrystal that are more stable than others against phason disorder. Analytical formulae for the stable and unstable parts of a quasilattice are provided, and a discussion about the physical consequences of this phenomenon is made.
Title:
Atomic dynamics of decagonal Zn58Mg40Y2
Authors:
Suck, JB; Scheffer, A; Sterzel, R
Source:
FERROELECTRICS, 305: 203-208 2004
Abstract:
Using cold and thermal neutron inelastic scattering at the Institut Laue-Langevin, Grenoble and at ISIS, UK, respectively, we determined the total dynamic structure factor S(Q,w) and the generalised vibrational density-of-states G(w) of decagonal Zn58Mg40Y2. We ompare these quantities with those determined earlier for the icosahedral phase in the same quasicrystal system of Frank-Kasper type. In spite of a considerably different intensity distribution in both quantities, the main bands in the angular averaged dispersion relations of both structures are surprisingly similar and two main bands even agree quite well with the main bands in the dispersion relation of glassy Zn30Mg70. This leads to the conclusion that the main bands are element specific and that the elements in this energy region vibrate largely independent of each other. This interpretation is supported by recent computer simulation of the dynamics of approximants to both aperiodic structures.
Title:
Ab initio structure solution of icosahedral Cd-Yb quasicrystals by a density modification method
Authors:
Takakura, H; Yamamoto, A; De Boissieu, M; Tsai, AP
Source:
FERROELECTRICS, 305: 209-212 2004
Abstract:
The six-dimensional (6D) low density elimination method has been applied to solve an icosahedral Cd-Yb quasicrystal. It shows that i-Cd-Yb is composed of similar atomic clusters that exist in the cubic approximant crystals, but the inner most shell is highly disordered. A construction of the 6D cluster model of i-Cd-Yb is outlined.
Title:
The disordered 8 angstrom superstructure of a decagonal Al70Co12Ni18 quasicrystal
Authors:
Weber, T; Kobas, M; Steurer, W
Source:
FERROELECTRICS, 305: 213-216 2004
Abstract:
Diffuse inter-layers from a decagonal quasicrystal with nominal composition Al70Co12Ni18 were investigated at 1120 K, 1070 K and 300 K. Patterson maps calculated from the inter-layers are interpreted such that the main units for correlated displacements along a(5) are structure motifs ('clusters') having a diameter of about 15 Angstrom. At 1120 K, displacements of the clusters are uncorrelated along quasiperiodic directions, while they form about 42 Angstrom-sized super-clusters at lower temperatures. The arrangement but not the inner structure of the super-clusters differs significantly at 1070 K and 300 K. Further, a first approach to the atomic structure of the 15 Angstrom cluster is presented.
Title:
Patterson analysis and average unit cell for quasicrystals
Authors:
Wolny, J; Kozakowski, B
Source:
FERROELECTRICS, 305: 217-221 2004
Abstract:
The average unit cells and the average Patterson functions have been constructed for 1D quasicrystals in statistical approach. A simple formula for the structure factor of decorated Fibonacci chain has been derived. Although the used method operates in the physical space only, its equivalence to the higher-dimensional analysis has been proved. Applications of the analysis to different decorated structures have been also discussed.
Title:
Structure refinement of quasicrystals
Authors:
Yamamoto, A; Takakura, H
Source:
FERROELECTRICS, 305: 223-227 2004
Abstract:
Recently, a structure refinement method based on higher-dimensional cluster models was successfully applied to several typical quasicrystals. This is equally applicable to the structures, which consists of clusters with the highest symmetry under the space group or with a lower symmetry. The refinement method and model building based on the higher-dimensional cluster model will be reviewed together with newly clarified quasicrystal structures.

Update: 20-Aug-2004

Title:
Electronic structure and bonding in antimony and its high pressure phases
Authors:
Ormeci, A; Rosner, H
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 219 (6): 370-375 2004
Abstract:
The effects of pressure on the electronic structure and on the bonding properties of Sb are studied by first-principles electronic structure methods. A commensurate approximate structure is used in the calculations for the modulated incommensurate Sb-II phase. It is found that the overlap of s and p bands increases with increasing pressure resulting in pressure-induced metallization of Sb. Analyses based on the electron localization function show that there is no chemical bond between the chain atoms of a previously suggested Sb-II structure. The high total energy of this structure with respect to other structures considered is a result of the absence of this binding.
Title:
Bravais quasilattices of icosahedral quasicrystals
Authors:
Niizeki, K
Source:
PHYSICAL REVIEW LETTERS, 93 (4): Art. No. 045501 JUL 23 2004
Abstract:
A classification of icosahedral quasicrystals based the mutual-local-derivability (MLD) concept is performed. There are eighteen MLD classes within the reservation that the faces of the hyperatoms (windows) are perpendicular to the two-, three-, or fivefold axes. Each MLD class has a representative member to be called the Bravais quasilattice from which the structure of each member of the class is derived by decorating it according to a local rule depending on the member.
Title:
Spectral and magnetic properties of the t-J model of cuprate perovskites
Authors:
Sherman, A
Source:
PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 241 (9): 2097-2108 JUL 2004
Abstract:
The use of the t-J model of Cu-O planes and projection operator technique for the Hubbard operators allows us to take proper account of strong electron correlations inherent in cuprate high-T, superconductors. A number of unusual properties of cuprates can be reproduced in this approach. Among them are the peculiarities of the temperature and concentration dependencies of the spin-lattice relaxation and spin-echo decay rates, the resonance peak and the incommensurate low-frequency magnetic response in neutron scattering. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Title:
H-bond effect on the phase transitions in [NH(4-n)(CH3)(n)](2)HgCl4 and related compounds
Authors:
Amami, M; Ben Salah, A
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73 (7): 1781-1785 JUL 2004
Abstract:
The structural instability of the [NH4-n(CH3)(n)](2)HgCl4 group have been investigated. Consideration of different crystals of this family shows that the H-bonds, obviously, hinder the appearance of incommensurately modulation. The dependence of phase transition sequence from the sizes of cation and anion may be obtained only for crystal with simple cation. The appearance of H-bonds complicates the situation and, leads to gradual disappearance of IC phase in the A(2)BX(4) family.
Title:
Formation of a superlattice order from a fundamental-lattice decagonal quasierystal of Al72Ni20Co8
Authors:
Saito, K; Yokosawa, T; Tanaka, M; Tsai, AP
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73 (7): 1786-1792 JUL 2004
Abstract:
A structural change of an Al72Ni2OCo8 decagonal quasicrystal into the S1-type superlattice ordered phase has been observed at about 450degreesC by in-situ high-resolution electron microscopy. The Al72Ni20Co8 alloy, prepared by water quenching from 900degreesC, is composed of mirror-symmetric atom-clusters (m-cluster) with a 2-nm diameter, which form the Penrose pentagon tiling with an edge length of 2.0 run. It has been found that above 400degreesC, most of the m-clusters transformed into fivefold-symmetric cluster (f-cluster) and the arrangement of the f-cluster formed the S1-type superlattice. It is considered that the formation of the S1 superlattice order is attributed to the disappearance of the 1.2-nm intercluster bond and to the preferential order of the sense of the f-cluster, which takes opposite senses between the neighboring clusters with a 2-nm intercluster distance. The phason flip of the positions of the 2-nm atom-clusters, which was first reported by Edagawa et al. [Phys. Rev. Lett. 85 (2000) 1674], has been observed with an atomic scale resolution. It has been found that the phason flip is caused by a flip between the fivefold-symmetry cluster and the mirror symmetric cluster. Structural models of the m- and f-clusters were reexamined.
Title:
Exotic properties of CeSb studied by x-ray diffraction
Authors:
Hannan, A; Iwasa, K; Kohgi, M; Osakabe, T; Kitazawa, H; Suzuki, T
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73 (7): 1881-1887 JUL 2004
Abstract:
Various properties of the strongly correlated electron system CeSb at ambient pressure as well as under high pressures have been investigated employing X-ray as a probe. The satellite peaks caused by the lattice modulation of CeSb in its AFP3 phase at ambient pressure have been analyzed successfully. The satellite peak intensity pattern was explained based on a model considering different effective ionic sizes and the scattering form factors for Gamma(7) and Gamma(8)-like Ce3+ ions which appear in the ordered phase. The wave function for the Gamma(8)-like Ce ion with larger moment was found almost the same as that of J(z) = 5/2, which is consistent with the neutron diffraction experiment. At high pressures above about 1.9 GPa, rapid decrease of lattice constant was found below a certain critical temperature T-L, below which a sudden increase of electrical resistivity appears. This phenomenon can be explained by the formation of magnetic polaron state below this temperature.
Title:
Multidataset refinement resonant diffraction, and magnetic structures
Authors:
Attfield, JP
Source:
JOURNAL OF RESEARCH OF THE NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, 109 (1): 99-106 JAN-FEB 2004
Abstract:
The scope of Rietveld and other powder diffraction refinements continues to expand, driven by improvements in instrumentation, methodology and software. This will be illustrated by examples from our research in recent years. Multidataset refinement is now commonplace; the datasets may be from different detectors, e. g., in a time-of-flight experiment, or from separate experiments, such as at several x-ray energies giving resonant information. The complementary use of x rays and neutrons is exemplified by a recent combined refinement of the monoclinic superstructure of magnetite, Fe3O4, below the 122 K Verwey transition, which reveals evidence for Fe2+/Fe3+ charge ordering. Powder neutron diffraction data continue to be used for the solution and Rietveld refinement of magnetic structures. Time-of-flight instruments on cold neutron sources can produce data that have a high intensity and good resolution at high d-spacings. Such profiles have been used to study incommensurate magnetic structures such as FeAsO4 and beta-CrPO4. A multiphase, multidataset refinement of the phase-separated perovskite (Pr0.35Y0.07Th0.04Ca0.04Sr0.5) MnO3 has been used to fit three components with different crystal and magnetic structures at low temperatures.
Title:
Magnetic and magnetoelectric dynamics in RMn2O5 (R = Gd and Eu)
Authors:
Golovenchits, E; Sanina, V
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (24): 4325-4334 JUN 23 2004
Abstract:
The dynamics of ferroelectromagnetic (multiferroic) crystals RMn2O5 (R = Eu and Gd), showing magnetic and ferroelectric phase transitions with close transition temperatures (40 and 30 K for R = Eu and Gd, respectively), was studied in the frequency and temperature ranges 20-300 GHz and 5-50 K, respectively. It was found that magnetic resonance spectra of GdMn2O5 are characteristic for the homogeneous long-range magnetic order both of the antiferomagnetic Mn-subsystem and Gd magnetic subsystem, possessing a large ferromagnetic moment. In other RMn2O5 crystals (with nonmagnetic or weakly magnetic rare-earth ions) incommensurate or space-modulated magnetic structures in Mn-subsystem are present. The strong Gd-Mn and Gd-Mn-Gd exchange interactions are responsible for the homogeneous magnetic state. A strong effect of the magnetic state on the ferroelectric state was discovered in GdMn2O5 crystal. The temperature of the ferroelectric phase transition in GdMn2O5 is shifted to the lower temperature as compared with other RMn2O5 crystals. Mixed magnetoelectric excitations in GdMn2O5 were observed for the first time.
Title:
Phase stability in the systems AeAl(2-x)Mg(x) (Ae = Ca, Sr, Ba): Electron concentration and size controlled variations on the laves phase structural
Authors:
Amerioun, S; Yokosawa, T; Lidin, S; Haussermann, U
Source:
INORGANIC CHEMISTRY, 43 (15): 4751-4760 JUL 26 2004
Abstract:
The systems AeAl(2-x)Mg(x) (Ae = Ca, Sr, Ba) display electron concentration induced Laves phase structural changes. However, the complete sequence MgCu2 --> MgNi2 --> MgZn2 with increasing x (decreasing electron count) is only observed for Ae = Ca. Compounds SrAl2-x,Mg-x, (0 < X less than or equal to 2) and BaAl2-x,Mg-x, (X = 0.85 and 2.0) were synthesized and structurally characterized by X-ray diffraction experiments. For the Sr system the structural sequence CeCu2 --> MgNi2 --> MgZn2 occurs with increasing Mg content x. Thus, larger Sr does not allow the realization of the MgCu2 structure at low x. For Ae = Ba a binary compound BaAl2 does not exist, but more Ba-rich Ba7Al13 forms. The reinvestigation of the crystal structure of Ba7Al13 by selected area and convergent beam electron diffraction in a transmission electron microscope revealed a superstructure, which subsequently could be refined from single X-ray diffraction data. The formula unit of the superstructure is Ba21Al40 (space group P31m, Z = 1, a = 10.568(l) Angstrom, c = 17.205(6) Angstrom). In Ba21Al40 a size match problem between Ba and Al present in Ba7Al13 is resolved. The structure of Ba7Al13 (Ba21Al40) can be considered as a Ba excess variant of the hexagonal MgNi2 Laves phase type structure. An incommensurately modulated variant of the MgNi2 structure is obtained for phases BaAl2-xMgx with x = 0.8-1. At even higher Mg concentrations a structural change to the proper MgZn2 type structure takes place.
Title:
Regular polytopes, root lattices, and quasicrystals
Authors:
King, RB
Source:
CROATICA CHEMICA ACTA, 77 (1-2): 133-140 MAY 2004
Abstract:
The icosahedral quasicrystals of five-fold symmetry in two, three, and, four dimensions are related to the corresponding regular polytopes exhibiting five-fold symmetry, namely the regular pentagon (H-2 reflection group), the regular icosahedron {3,5} (H-3 reflection group), and the regular four-dimensional polytope {3,3,5} (H-4 reflection group). These quasicrystals exhibiting five-fold symmetry can be generated by projections from indecomposable root lattices with twice the number of dimensions, namely A(4)-->H-2, D-6-->H-3, E-8-->H-4. Because of the subgroup relationships H-2 subset of H-3 subset of H-4, study of the projection E-8-->H-4 provides information on all of the possible icosahedral quasicrystals. Similar projections from other indecomposable root lattices can generate quasicrystals of other symmetries. Four-dimensional root lattices are sufficient for projections to two-dimensional quasicrystals of eight-fold and twelve-fold symmetries. However, root lattices of at least six-dimensions (e.g., the A(6) lattice) are required to generate two-dimensional quasicrystals of seven-fold symmetry. This might account for the absence of seven-fold symmetry in experimentally observed quasicrystals.
Title:
Structural phase transition of edge-sharing copper oxide Ca0.85CuO2 under high pressure
Authors:
Mai, WJ; Zhang, GM; Qin, XM; Chen, LC; Li, FY; Yu, RC; Liu, J; Jin, CQ
Source:
CHINESE SCIENCE BULLETIN, 49 (9): 872-874 MAY 2004
Abstract:
The perovskite-like structure compound Ca-0.85-CuCO2 has interesting structural properties: it has infinite one-dimensional edge-sharing copper-oxygen chains as well as partial occupancy of the Ca sites resulting in an incommensurate superstructure. In situ high-pressure energy dispersive X-ray diffraction measurements on polycrystalline powder Ca0.85CuO2 have been performed by using diamond anvil cell (DAC) instrument with synchrotron radiation. The results for the first time show that edge-sharing copper oxide Ca0.85CuO2 undergoes a structural transition at 14.5 GPa, and furthermore the structural transition is reversible.
Title:
Variation of large-scale regularity in modulated structures of Ca2CoSi2O7 studied by a simulation method
Authors:
Kusaka, K; Hagiya, K; Ohmasa, M; Iishi, K
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 60: 369-374 Part 4 AUG 2004
Abstract:
The period of two-dimensional modulation in Ca2CoSi2O7 varies with temperature (q = 0.285 - 1/3). The change in the modulated structure with the variation of q has been clarified by the construction of the structures using various q values and the modulation amplitudes determined at 293 K [ q = 0.2913 (1), tetragonal]. The features of the modulated structures are characterized by the formation of CaO6 polyhedra and the variable distribution of bundles along the c-axis, composed of four arrays of CaO6 polyhedra and an array of CoO4 tetrahedra. The formation of octagonal arrangements of the bundles is a typical feature of the structures in the incommensurate phase. Large-scale regularities with sizes much larger than the modulation wavelength are also formed in the structures.
Title:
Bis(1-chloro-2,2,4,4-tetramethyl-3-oxocyclobutan1-yl)pentasulfane: an occupancy modulated structure
Authors:
Rae, AD; Linden, A; Majchrzak, A; Mloston, G; Heimgartner, H
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 60: 416-423 Part 4 AUG 2004
Abstract:
The title compound crystallizes in the space group P2(1)/n and may be described by a partial ordering of a 1: 1 disordered P2(1)/a parent structure with the c axis halved. The pentasulfane chain completes a full turn of a helix, which gives molecules containing left- or right-handed helices similar spatial requirements and allows them to be interchanged. The structure can be redescribed as containing 0.732 (1) of an ordered P2(1)/n structure and 0.268 ( 1) of a 1: 1 disordered P2(1)/a structure, implying that 0.134 (1) of the molecule sites contain molecules of the opposite hand to that predicted by an ordered P2(1)/n structure. It is found that the average molecular position in the asymmetric unit is not the same for each component and that these structural differences must be recognized to obtain a satisfactory refinement.

Update: 13-Aug-2004

Title:
Quantum interference effects in the magnetopiezoresistance of InAs/AlGaSb quasi-one-dimensional electron systems
Authors:
Yamaguchi, H; Tokura, Y; Miyashia, S; Hirayama, Y
Source:
PHYSICAL REVIEW LETTERS, 93 (3): Art. No. 036603 JUL 16 2004
Abstract:
We measured the low temperature magnetopiezoresistance of a quasi-one-dimensional electron system by fabricating an InAs/AlGaSb micromechanical cantilever. The magnetopiezoresistance curve showed aperiodic but reproducible oscillation, which was similar to the differential magnetoresistance curve obtained for the same device. A detailed comparison with model calculations strongly suggests that the quantum interference effects that cause the conductance fluctuations in the magnetoresistance are responsible for the peculiar behavior of the magnetopiezoresistance.
Title:
New universality class in spin-one-half Fibonacci Heisenberg chains
Authors:
Hida, K
Source:
PHYSICAL REVIEW LETTERS, 93 (3): Art. No. 037205 JUL 16 2004
Abstract:
Low energy properties of the S=1/2 antiferromagnetic Heisenberg chains with Fibonacci exchange modulation are studied using the real space renormalization group method for strong exchange modulation. Using the analytical solution of the recursion equation, the true asymptotic behavoir is revealed, which was veiled by the finite size effect in the previous numerical works. It is found that the ground state of this model belongs to a new universality class with a logarithmically divergent dynamical exponent which is neither like Fibonacci XY chains nor like XY chains with relevant aperiodicity.
Title:
Difference in icosahedral short-range order in early and late transition metal liquids
Authors:
Lee, GW; Gangopadhyay, AK; Kelton, KF; Hyers, RW; Rathz, TJ; Rogers, JR; Robinson, DS
Source:
PHYSICAL REVIEW LETTERS, 93 (3): Art. No. 037802 JUL 16 2004
Abstract:
New short-range order data are presented for equilibrium and undercooled liquids of Ti and Ni. These were obtained from in situ synchrotron x-ray diffraction measurements of electrostatically levitated droplets. While the short-range order of liquid Ni is icosahedral, consistent with Frank's hypothesis, significantly distorted icosahedral order is observed in liquid Ti. This is the first experimental observation of distorted icosahedral short-range order in any liquid, although this has been predicted by theoretical studies on atomic clusters.
Title:
Superstructure of Eu4Cd25: A quasicrystal approximant
Authors:
Gomez, CP; Lidin, S
Source:
CHEMISTRY-A EUROPEAN JOURNAL, 10 (13): 3279-3285 JUL 5 2004
Abstract:
The quasicrystal approximant Eu4Cd25, formerly designated EuCd6, was synthesized and characterized by means of single-crystal X-ray diffraction. Superstructure reflections corresponding to an F-centered cubic unit cell with a doubled cell-parameter relative to the I-centered cubic sub-cell could be observed in the diffraction data. This gives the largest cubic unit cell reported to date among binary alloys. ne superstructure exhibits structural features that are found in all the RE-Cd-6 approximants as well as a further ordering between vacant/occupied Cd-8 cubes and oriented Cd-4 tetrahedra, which causes the superstructure. A reversible high-temperature phase-transition was observed at 782 K by means of DSC.
Title:
Plasticity of single-grain icosahedral Al-Pd-Mn quasi-crystals deformed at room temperature
Authors:
Mompiou, F; Caillard, D
Source:
ACTA MATERIALIA, 52 (12): 3613-3619 JUL 12 2004
Abstract:
Transmission electron microscopy observations have been performed on icosahedral Al-Pd-Mn quasi-crystal samples deformed at 20 degreesC under a high confining pressure. They reveal a large density of wavy walls from which several climbing dislocations are emitted. Near-screw dislocations have been found at the wall terminations with a Burgers vector contained in the wall plane. Careful plane determinations and dislocation analyses are not consistent with a glide and cross-slip mechanism. The results can be better interpreted as a deformation by cracks in mode III followed by a re-healing process. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 30-Jul-2004

Title:
Friction behavior of Al-Cu-Fe-B polycrystalline quasicrystals
Authors:
Zhou, XY; Li, PY; Luo, JM; Qian, SQ; Tong, JH
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 14 (3): 464-469 JUN 2004
Abstract:
Dry sliding friction between the polycrystalline Al59Cu25.5Fe12.5B3 quasicrystals (QCs) and coating of the diamond-like carbon(DLC) was carried out by self-made tribometer under different conditions. The influences of four parameters (temperature, sliding velocity, applied load, atmosphere) on friction of quasicrystal surface were studied. Microstructure of quasicrystal, morphology of worn surface, and wear debris were observed by scanning electron microscope (SEM). The results show that for QCs, the friction coefficient and the roughness of worn surface is influenced by the parameters, especially greatly by the temperature. With increasing the applied load and sliding velocity, the friction coefficient decreases. The dominant wear mechanism at 350 degreesC is delamination for QCs. The cracks forms on the worn surface during friction. Moreover, phase transformation is not observed on worn surface of QCs at 350 degreesC.
Title:
Ferroelectricity and giant magnetocapacitance in perovskite rare-earth manganites
Authors:
Goto, T; Kimura, T; Lawes, G; Ramirez, AP; Tokura, Y
Source:
PHYSICAL REVIEW LETTERS, 92 (25): Art. No. 257201 JUN 25 2004
Abstract:
The relationships among magnetism, lattice modulation, and dielectric properties have been investigated for RMnO3 (R=Eu, Gd, Tb, and Dy). These compounds show a transition to an incommensurate lattice structure below their Neel temperature, and subsequently undergo an incommensurate-commensurate (IC-C) phase transition. For TbMnO3 and DyMnO3 it was found that the IC-C transition is accompanied by a ferroelectric transition, associated with a lattice modulation in the C phase. DyMnO3 shows a gigantic magnetocapacitance with a change of dielectric constant up to Deltaepsilon/epsilonsimilar to500%.
Title:
Dependence of incommensurate phase formation on vacancy type in La-doped (Na1/2Ba1/2)TiO3
Authors:
Lee, JK; Yi, JY; Hong, KS
Source:
JOURNAL OF APPLIED PHYSICS, 96 (2): 1174-1177 JUL 15 2004
Abstract:
Changes in structure and phase transition behavior are investigated for two types of La-doped sodium bismuth titanate ceramics. When A-site vacancies are formed by La incorporation, the phase transition near 200 degreesC becomes pronounced. Hysteresis loop and epsilon(T) demonstrate that the structure above 200 degreesC is the incommensurate antiferroelectric phase. In contrast, B-site vacancies produced by La doping do not contribute to the incommensurate phase. The origin for the formation of the incommensurate antiferroelectric state between the rhombohedral ferroelectric phase and tetragonal paraelectric phase is discussed in a view of decoupling effects due to the A-site vacancies. (C) 2004 American Institute of Physics.

Update: 23-Jul-2004

Title:
Nonlinear dynamics of incommensurate surface layers
Authors:
Kovalev, AS; Gerasimchuk, IV; Maugin, GA
Source:
PHYSICAL REVIEW LETTERS, 92 (24): Art. No. 244101 JUN 18 2004
Abstract:
We describe analytically the nonlinear dynamics of the incommensurate surface layer ("self-modulated" system) with a spatially periodical structure. In the framework of the Frenkel-Kontorova model the nonlinear excitations of the periodic soliton lattice, such as moving additional kinks and gap solitons, are investigated.
Title:
Surface morphology and incommensurate modulation of self-flux grown Bi2Sr2CaCu2O8+x single crystals
Authors:
Kumar, P; Kumar, B; Bdikin, I; Kholkin, AL; Trigunayat, GC
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 406 (1-2): 72-78 JUL 1 2004
Abstract:
Structural studies have been carried out in large size superconducting single crystals of Bi2Sr2CaCu2O8+x grown by self-flux method. Surface morphology of the crystals in respect of growth steps, slip lines/bands and etch pits has been examined by scanning electron microscopy (SEM). A quantitative study of grain misorientation in the crystals has been conducted by X-ray diffraction, which has also revealed the existence of incommensurate modulation of the crystal structure. A detailed analysis of first and second order satellite reflections associated with the Bragg reflections 0 2 0 and 0 0 3 6, in terms of incommensurate b(*)-components and *modulation* wave vector q = 0.21b(*) + c(*), has been made. It is proposed that while the second order satellite reflections observed around 0 0 3 6 are linked with the existent neighboring Bragg reflections, the first order satellite reflections are correlated with a forbidden reflection. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Precipitation of a two-dimensional aperiodic approximant phase in Al-rich Al-Mn-Be alloy
Authors:
Chang, HJ; Fleury, E; Lee, YH; Kim, WT; Kim, DH
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 84 (5): 311-319 MAY 2004
Abstract:
The precipitation behaviour of a hexagonal two-dimensional aperiodic phase in Al-rich Al-Mn-Be alloy has been investigated. Upon heat treatment at temperatures above 450degreesC, the icosahedral phase formed in a conventionally cast Al-2.5 at.% Mn-3 at.% Be alloy transforms into the stable hexagonal H1 phase. The solute partitioning during transformation leads to the precipitation of a hexagonal two-dimensional aperiodic approximant phase (H' phase). The precipitates have an orientation relationship with the alpha-Al matrix. The similarity of the diffraction features indicates that the hexagonal two-dimensional aperiodic structure of the H' phase is an intermediate structure between the true sixfold quasiperiodic structure and the hexagonal structure of the crystalline counterpart H1 phase.
Title:
Disappearance of quasi-Ising character in triangular lattice antiferromagnet CuFeO2 by a small amount of substitution
Authors:
Terada, N; Mitsuda, S; Suzuki, S; Kawasaki, T; Fukuda, M; Nagao, T; Katori, HA
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73 (6): 1442-1445 JUN 2004
Abstract:
The effect of a small amount of substitution on magnetic ordering in a frustrated triangular lattice antiferromagnet CuFeO2 has been studied by neutron diffraction, magnetic susceptibility and specific heat measurements on CuFe1-xAlxO2 single-crystals with x = 0.02 and x = 0.05. With only a small amount of substitution, x = 0.02, the zero-field successive magnetic phase transitions with quasi-Ising character observed for x = 0.00 are entirely changed to successive phase transitions from a paramagnetic state to an incommensurate complex state through an incommensurate magnetic state, suggesting that the original Heisenberg spin character hidden in CuFeO2 is retrieved.
Title:
Reinvestigation of simultaneous magnetic and ferroelectric phase transitions in YMn2O5
Authors:
Kobayashi, S; Osawa, T; Kimura, H; Noda, Y; Kagomiya, I; Kohn, K
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73 (6): 1593-1596 JUN 2004
Abstract:
Magnetic ordering around the ferroelectric transition temperature T-C1 of weakly ferroelectric YMn2O5 has been reinvestigated by single-crystal neutron diffraction and dielectric measurements. Besides a two-dimensionally modulated incommensurate magnetic (2D-ICM) phase with the propagation vector q = (q(x), 0, q(z)) and a lock-in commensurate magnetic (CM) one with q = ((1)/(2), 0, (1)/(4)) reported previously, we observed a 1D-ICM phase characterized by q = (q(x), 0, (1)/(4)) with q(x) similar to 0.492 that appears in a narrow 4 temperature interval of similar to1 K and separates the 2D-ICM and CM phases. Corresponding to the 2D-ICM-to- 1D-ICM and 1D-ICM-to-CM phase transitions at T = 40.8 K and 40.0 K, a sharp peak and a shoulder in the dielectric constant along the b-axis were detected. These results suggest that the ferroelectricity appears simultaneously with the magnetic phase transition from the 2D-ICM to 1D-ICM phase in YMn2O5.
Title:
Subsolidus phase relations and crystal structure of compounds in the PrOx-CaO-CuO system
Authors:
Song, GB; Han, CQ; Chen, XL; Liang, JK; Liu, QL; Zhou, YQ; Liu, FS; Rao, GH
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 177 (7): 2394-2403 JUL 2004
Abstract:
The subsolidus phase relations of the PrOx-CaO-CuO pseudo-ternary system sintered at 950-1000degreesC have been investigated by X-ray powder diffraction. In this system, there exist one compound Ca10Pr4Cu24O41, one Ca2Pr2Cu5O10-bascd solid solution, seven three-phase regions and two two-phase regions. The crystal structures of Ca10Pr4Cu24O41, and Ca2Pr2Cu5O10-based solid solution have been determined. Compound Ca10Pr4Cu24O41 crystallizes in an orthorhombic cell with space group D-2h(20) - Cccm, Z = 4. Its lattice parameters are a = 11.278(2) Angstrom, b = 12.448(3) Angstrom and c = 27.486(8) Angstrom. The crystal structure of Ca2Pr2Cu5O10-based solid solution is an incommensurate phase based on the orthorhombic NaCuO2 type subcell. The lattice parameters of the subcell of the Ca2.4Pr1.6Cu5O10 are a(0) = 2.8246(7) Angstrom, b(0) = 6.3693(5) Angstrom, c(0) = 10.679(1) Angstrom, and those of the orthorhombic superstructure are with a = 5a(0), b = b(0), c = 5c(0). The Ca2.4Pr1.6Cu5O10 structure can also be determined by using a monoclinic supercell with space group C-2h(5) - P2(1)/c, Z = 4, a = 5a(0), b = b(0), c = c(0)/sin beta and beta = 104.79(1)degrees or 136.60(1)degrees, V = 5a(0)b(0)c(0). (C) 2004 Elsevier Inc. All rights reserved.
Title:
Structure and mechanical properties of cast quasicrystal-reinforced Mg-Zn-Al-Y base alloys
Authors:
Yuan, GY; Amiya, K; Kato, H; Inoue, A
Source:
JOURNAL OF MATERIALS RESEARCH, 19 (5): 1531-1538 MAY 2004
Abstract:
The structure and mechanical properties of Mg-Zn-Al-Y base cast alloys containing an icosahedral quasicrystal phase (i-phase) as a main strengthening phase were investigated. Mg-8Zn-4Al-xY base bulk alloys containing the i-phase were prepared by casting into a copper mold at moderate cooling rates. The Y addition was effective for decreasing the size of the i-phase and the increasing the homogeneity of its dispersed state. The mechanical properties examined by compression tests at room temperature were much superior to those of a conventional AZ91 Mg alloy. The creep tests at elevated temperatures indicated a promising high temperature creep resistance of the quasicrystal-reinforced Mg-Zn-Al-Y cast alloy. The strengthening mechanism was also discussed.
Title:
Interplay between magnetism and superconductivity in CeMIn5 heavy fermion
Authors:
Llobet, A; Bao, W; Moreno, NO; Pagliuso, PG; Sarrao, JL; Thompson, JD; Prokes, K; Mignot, JM
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 272-76: 175-176 Part 1 Sp. Iss. SI MAY 2004
Abstract:
We report a single-crystal magnetic neutron diffraction study on the antiferromagnetic and superconducting heavy-fermion compound CeRh0.65Ir0.35In5. Our experiments detect no change in the magnetic structure on cooling the single crystals below T-C indicating the coexistence of long-range magnetic order and superconductivity. We also show that an applied magnetic field converts the magnetic structure from incommensurate to commensurate. This work places new constraints on interpretations of the relationship between antiferromagnetism and unconventional superconductivity in this family of heavy-fermion superconductors. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Neutron scattering study of the magnetic structure and excitations of metallic (V1-xTix)(2)O-3
Authors:
Kikuchi, J; Tabaru, S; Motoya, K
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 272-76: 511-512 Part 1 Sp. Iss. SI MAY 2004
Abstract:
Neutron scattering patterns from metallic (V1-xTix)(2)O-3 reveal that the incommensurate spin-density-wave state with relatively small ordered moments exists for 0.05 less than or equal to x less than or equal to 0.4. The magnetic excitation spectrum consists of a broad lobe at each magnetic Bragg point for above and below the Neel temperature. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Magnetic properties of Tb-Mg-Zn and Tb-Mg-Cd quasicrystals in comparison with canonical spin glasses
Authors:
Jaglicic, Z; Dolinsek, J; Trontelj, Z
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 272-76: 597-598 Part 1 Sp. Iss. SI MAY 2004
Abstract:
The nature of spin-glass-like transition in icosahedral quasicrystals Tb-Mg-Zn and Tb-Mg-Cd was studied by the thermoremanent magnetization (TRM) decay as a function of magnetic field. The observed linear dependence of the TRM on the magnetic field in the low-field regime demonstrates difference to canonical spin glasses. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Modulated magnetic structure of ScFe4Al8 by X-ray, neutron powder diffraction and Mossbauer effect
Authors:
Recko, K; Hauback, BC; Dobrzynski, L; Szymanski, K; Satula, D; Kotur, BY; Suski, W
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 272-76: 764-766 Part 2 Sp. Iss. SI MAY 2004
Abstract:
ScFe4Al8 alloy belongs to the extensively investigated ThMn12-type family. The results of Mossbauer experiments are compared with the neutrons data. ScFe4Al8 alloy orders around 250 K by forming antiferromagnetic spiral iron sublattice, within the tetragonal basis plane ab and magnetic iron moments close to 1 mu(B) at 8 K. The spins are rotating in a plane parallel to the wave vector q = (q(x), q(x), 0). (C) 2004 Elsevier B.V. All rights reserved.
Title:
NMR study of S=1/2 quasi-two-dimensional antiferromagnet Cs2CuBr4
Authors:
Fujii, Y; Nakamura, T; Kikuchi, H; Chiba, M; Goto, T; Matsubara, S; Kodama, K; Takigawa, M
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 272-76: 861-862 Part 2 Sp. Iss. SI MAY 2004
Abstract:
Cs-133-NMR experiments on the S =, quasi-two-dimensional antiferromagnet Cs2CuBr4 have been performed up to magnetic fields of 15.9 T, which covers the field range for the 3 magnetization plateau. Outside the plateau region, the NMR spectrum at T = 0.5 K shows a double-horn type broad line shape characteristic of an incommensurate spin structure. On the other hand, discrete two peaks were observed in the plateau phase, indicating a commensurate up-up-down spin structure. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Magnetic properties of amorphous and quasicrystalline Al75Cu15V10
Authors:
Gavilano, JL; Rau, D; Beeli, C; Weller, M; Ott, HR; Tsai, AP
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 272-76: 1304-1305 Part 2 Sp. Iss. SI MAY 2004
Abstract:
We compare the magnetic susceptibilities chi(T) and electrical resistivities of well-characterized icosahedral and amorphous phases of Al75Cu15V10 between 2 and 350 K. The structure of both phases was confirmed by X-ray powder diffraction and TEM measurements. Above 100 K, the icosahedral phase exhibits a temperature-independent Pauli-type susceptibility, but below 100 K it decreases with decreasing temperature, hinting that there is a tiny gap in the electronic density of states at the Fermi level. The differences of chi between the amorphous and icosahedral phases suggest that the icosahedral structure does not favor the formation of localized V magnetic moments. No substantial changes are observed in the electrical resistivities of the two phases. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Inhomogeneous Mn-magnetism in Al-Pd-Mn quasicrystals
Authors:
Rau, D; Gavilano, JL; Mushkolaj, S; Beeli, C; Ott, HR
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 272-76: 1330-1331 Part 2 Sp. Iss. SI MAY 2004
Abstract:
We report the results of a comparative study of the Mn magnetism in decagonal and icosahedral quasicrystalline Al69.8Pd12.1Mn18.2. We made measurements of Al-27 NMR spectra, the Al-27 spin-lattice relaxation rate, and the DC magnetic susceptibility of the stable decagonal, as well as the metastable icosahedral alloy at varying temperatures. For the decagonal sample we found that at 300 K, less than half of all the Mn ions carry a magnetic moment and that this number decreases even further with decreasing temperatures below 100 K. A spin-glass type freezing transition occurs at T-f = 12 K. For the icosahedral alloy Al69.8Pd12.1Mn18.2 the effective Mn moment is significantly larger than for the decagonal case. The spin-glass freezing sets in at 18 K. The NMR-spectra of the two materials as well as the spin-lattice relaxation rates reveal further differences between the Mn-based magnetic features of icosahedral and decagonal Al69.8Pd12.1Mn18.2. (C) 2003 Elsevier B.V. All rights reserved.
Title:
A study of the incommensurate phase of Rb2ZnCl4 by ESR
Authors:
Agirtmis, M; Farach, HA; Creswick, RJ; Poole, CP
Source:
FERROELECTRICS, 300: 33-41 2004
Abstract:
The ESR absorption spectrum of Mn2+ ions at A positions has been studied in the incommensurate phase of Rb2ZnCl4. It is known that Rb2ZnCl4 crystals exhibit an incommensurate phase between temperatures T-i = 303 K and T-1 = 192 K. The form and the temperature dependence of ESR spectra are in good agreement with the predictions of the phase soliton theory. The parameters h(1) and h(2) determining the magnetic resonance field show, as expected, a power law as a function of the temperature. A modified superposition model was used to estimate the modulation amplitude of the incommensurate phase, and the principal axis of the zero field splitting D.
Title:
3D-incommensurate composite structures in (Rb-x(NH4)((1-x)))(2)SO4 crystals
Authors:
Shmyt'ko, IM; Afonikova, NS; Arnautova, EA
Source:
CRYSTALLOGRAPHY REPORTS, 49 (3): 370-378 MAY-JUN 2004
Abstract:
Detailed structural studies of (Rb-x(NH4)((1-x)))(2)SO4 Solid solutions have been performed. It is shown that the crystals consist of incommensurate composite phases. The newly discovered composite structures differ from the traditional composite phases-in the general case, the host and guest structures of these crystals are incommensurate along all the three crystallographic axes. (C) 2004 MAIK "Nauka/Interperiodica".
Title:
Structure and microstructure of epitaxial Sr4Fe6O13 +/-delta films on SrTiO3
Authors:
Rossell, MD; Abakumov, AM; Van Tendeloo, G; Pardo, JA; Santiso, J
Source:
CHEMISTRY OF MATERIALS, 16 (13): 2578-2584 JUN 29 2004
Abstract:
The crystal structure and the microstructure of epitaxial Sr4Fe6O13+/-delta thin films grown on a single-crystal SrTiO3 substrate by PLD have been investigated. A combination of electron diffraction and high-resolution microscopy allows us to refine the structure and to identify an incommensurate modulation in the Sr4Fe6O13+/-delta films. The incommensurate structure (q = alphaa(m)* approximate to 0.39alpha(m)*, *superspace* group Xmmm(alpha00)0s0) can be interpreted as an oxygen-deficient modification in the Fe2O2.5 double layers. Moreover, it is shown that the experimentally determined a component of the modulation can be used consistently to estimate the local oxygen content in the Sr4Fe6O13+/-delta films. The compound composition can therefore be described as Sr4Fe6O12+2alpha and the value alpha = 0.39 corresponds to a Sr4Fe6O12.78 composition. The misfit stress along the Sr4Fe6O13+/-delta/SrTiO3 interface is accommodated via both elastic deformation and inelastic mechanisms (misfit dislocations and 90degrees rotation twins). The present results also suggest the existence of SrFeO3 perovskite in the Sr4Fe6O13+/-delta films.
Title:
Comparative study of structural stability in [NH4-n(CH3)(n)](2)HgCl4 and in related compounds
Authors:
Amami, M; Ben Salah, A
Source:
CENTRAL EUROPEAN JOURNAL OF CHEMISTRY, 2 (2): 388-401 APR 2004
Abstract:
The structural instability of the [NH4-n(CH3)n](2)HgCl4 group has been investigated. Consideration of differerent crystals of this family shows that the H-bonds, obviously, hinder the appearance of incommensurate modulation. The dependence of phase transition sequence on the sizes of cation and anion may be obtained only for crystals with simple cation. The appearance of H-bonds complicates the situation and, leads to gradual disappearance of IC phase in the A(2)BX(4) family. (C) Central European Science Journals. All rights reserved.
Title:
Photon band gap properties and omnidirectional reflectance in Si/SiO2 Thue-Morse quasicrystals
Authors:
Dal Negro, L; Stolfi, M; Yi, Y; Michel, J; Duan, X; Kimerling, LC; LeBlanc, J; Haavisto, J
Source:
APPLIED PHYSICS LETTERS, 84 (25): 5186-5188 JUN 21 2004
Abstract:
Aperiodic one-dimensional Si/SiO2 Thue-Morse (T-M) multilayer structures have been fabricated in order to investigate both the band gap properties with respect to the system size (band gap scaling) and the omnidirectional reflectance at the fundamental optical band gap. Variable angle reflectance data have experimentally demonstrated a large reflectance band gap in the optical spectrum of a T-M quasicrystal, in agreement with transfer matrix simulations. We explain the physical origin of the T-M omnidirectional band gap as a result of periodic spatial correlations in the complex T-M structure. The unprecedented degree of structural flexibility of T-M systems can provide an attractive alternative to photonic crystals for the fabrication of photonic devices. (C) 2004 American Institute of Physics.
Title:
Polyhedral truncations as eutactic transformations
Authors:
Torres, M; Aragon, JL; Gomez-Rodriguez, A
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 60: 311-314 Part 4 JUL 2004
Abstract:
An eutactic star is a set of N vectors in R-n (N > n) that are projections of N orthogonal vectors in R-N. First introduced in the context of regular polytopes, eutactic stars are particularly useful in the field of quasicrystals where a method to generate quasiperiodic tilings is by projecting higher-dimensional lattices. Here are defined the concepts of eutactic transformations (as mappings that preserve eutacticity) and of vector radiations (vectors that stem from the vectors of an eutactic star), which are used to describe and parameterize polyhedral truncations. The polyhedral truncations preserve eutacticity, a result of relevance to the faceting and habit-forming characteristics of quasicrystals.

Update: 16-Jul-2004

Title:
Thermoelectric figure of merit of AlPdRe icosahedral quasicrystals: Composition-dependent effects
Authors:
Macia, E
Source:
PHYSICAL REVIEW B, 69 (18): Art. No. 184202 MAY 2004
Abstract:
In this work we present a theoretical study on the composition dependence of the thermoelectric figure of merit (ZT) of icosahedral AlPdRe quasicrystals. From our study we conclude that band-structure effects play a significant role in determining the thermoelectric performance of these alloys. By comparing our analytical results with available experimental data of transport coefficients we discuss the most appropriate stoichiometries for thermoelectric applications, concluding that (i) those samples whose Fermi level is located at the pseudogap's minimum exhibit very small ZT values, and (ii) relatively large ZT values are expected for those samples exhibiting narrow features in the density of states close to the Fermi level.
Title:
Quasiperiodic structures via atom-optical nanofabrication
Authors:
Jurdik, E; Myszkiewicz, G; Hohlfeld, J; Tsukamoto, A; Toonen, AJ; van Etteger, AF; Gerritsen, J; Hermsen, J; Goldbach-Aschemann, S; Meerts, WL; van Kempen, H; Rasing, T
Source:
PHYSICAL REVIEW B, 69 (20): Art. No. 201102 MAY 2004
Abstract:
We deposit a laser-collimated chromium beam onto a substrate through a quasiperiodic laser standing-wave (SW) tuned above the atomic resonance at the Cr-52 transition S-7(3)-->P-7(4)o at 425.55 nm. This SW is created by interference of five laser beams crossing in one point at mutual angles of 72degrees. The resulting chromium pattern on the substrate surface mimics the geometry of the SW and it is thus itself quasiperiodic. On a surface area of 0.2x0.2 mm(2) the spatial Fourier spectrum of the measured patterns is decagonal. Besides being of fundamental interest, this quasiperiodic nanofabrication via atom optics can find its applications in photonics.
Title:
Magnetic properties of the CeGe1-xSix series studied by powder neutron diffraction and mu SR-measurements
Authors:
Schobinger-Papamantellos, P; Kenzelmann, M; Schenck, A; Gygax, FN; Buschow, KHJ; Ritter, C
Source:
PHYSICA B-CONDENSED MATTER, 349 (1-4): 100-114 JUN 15 2004
Abstract:
The antiferromagnetic ordering in orthorhombic (Pnma) CeGe1-xSix pseudobinary series was studied by powder neutron diffraction and muSR measurements. The ordering temperature varies linearly between 10.4 K for CeGe and 6.1 K for CeSi. The magnetic phase diagram comprises two distinct regions of magnetic ordering as a function of Si concentration x, which are characterized by the wave vectors q(1) = (0, 1/2, 0) r.l.u., for 0 less than or equal to x less than or equal to 0.8 and q(2) = (0, 1/2, 1/16) r.l.u. for CeSi. Both structures correspond to collinear arrangements of the Ce moments within the (a, b) plane. The ordered Ce3+ moment value of 1.0(1)mu(B)/atom at 1.5 K of the commensurate q(1) phases as well as the amplitude of the wave of the modulated q(2) phase (1.56(4)mu(B)/atom) are strongly reduced compared to the free Ce3+ ion value gJmu(B) = 2.14mu(B). A harrow field distribution observed with muSR suggests that CeSi has a commensurate square wave magnetic structure, which possibility could not be tested in the neutron work due the unobservability of the expected weak higher harmonics. The temperature dependence of the internal field detected by muSR suggests that the spin interactions are long range in CeSi, but short ranged in CeGe. These results point towards a localized non-Kondo behavior for CeSi and strong hybridization of the 4f electrons with the conduction band for CeGe. (C) 2004 Elsevier.B.V. All rights reserved.
Title:
Magnetic behavior of (Al,Ge)(65)CuMn quaternary alloy quasicrystals
Authors:
Chatterjee, R; Kanjilal, A
Source:
JOURNAL OF APPLIED PHYSICS, 96 (1): 503-507 JUL 1 2004
Abstract:
We report the results of field and temperature dependent magnetization measurements on (Al,Ge)(65)CuMn quasicrystalline samples with similar to22 and 24 at. % Mn. The Ge content is also kept similar to25 at. %. The data for these samples are then compared with the data taken on samples with low Ge content (similar to10 and 0 at. %). Al40Ge25Cu10Mn25, a composition very close to one of the alloys studied here, is reported [Tsai , Jpn. J. Appl. Phys., 27, L2252 (1988)] in literature as a ferromagnetic, icosahedral QC with large T-C. The detailed magnetic studies described here prove that the magnetism observed in these quaternary alloys is highly disordered. The two important observations made in our studies are (i) observation of short-range ferromagnetism in samples with high Ge and high Mn content, up to very high fields (H=5 T) and (ii) oscillatory magnetization (or existence of multiple minima in the M-T curves) observed for the same samples for Hgreater than or equal to1 kOe. (C) 2004 American Institute of Physics.
Title:
Neutron diffraction study of the magnetic structures of one-dimensional M2TbF6 (M= Li, K, Rb) fluorides: frustration, incommensurability and magnetic interactions
Authors:
Josse, M; Dubois, M; El-Ghozzi, M; Avignant, D; Andre, G; Bouree, F; Guillot, M
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 374 (1-2): 207-212 JUL 14 2004
Abstract:
The three title compounds crystallize in the monoclinic system, with unit cell parameters (at 4.95 K): Li2TbF6: a = 7.5643(3) Angstrom, b = 4.9372(3) Angstrom, c = 11.0710(4) Angstrom, beta = 107.012(3)degrees, space group P2(1)/c (ndegrees 14), K2TbF6: a = 6.5909(2) Angstrom, b = 11.4135(4) Angstrom, c = 7.1235(2) Angstrom, beta = 90.502(2)degrees, space group C2/c (ndegrees 15), and Rb2TbF6: a = 6.8298(2) Angstrom, b = 11.8385(5) Angstrom, c = 7.2013(2) Angstrom, beta = 91.358(2)degrees, space group C2/c (ndegrees 15). Neutron diffraction study down to 1.4 K revealed an antiferromagnetic ordering for the three compounds, occurring at T-N = 2.02(1), 1.60(5) and 2.10(5) K for Li, K and Rb representatives, respectively. All the magnetic structures are incommensurate and square-modulated with extremely long periods at 1.40 K. While the magnetic structure of Li2TbF6 is characterized by a propagation vector k = (0, 0.01617(7), 0), those of the potassium and rubidium representatives exhibit propagation vectors k = (0.0073(2), 0, 0) and k = (0.01039(8), 0, 0), respectively, these three propagation vectors corresponding to the direction of the shortest interchain distances. This singular magnetic behaviour will be correlated with the nuclear structures and the potential competition between magnetic interactions occurring in these M2TbF6 compounds and will be discussed in the light of a fine topological analysis. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Investigation of the incommensurate and commensurate magnetic superstructures of LiCuVO4 and CuO on the basis of the isotropic spin exchange and classical spin approximations
Authors:
Dai, D; Koo, HJ; Whangbo, MH
Source:
INORGANIC CHEMISTRY, 43 (13): 4026-4035 JUN 28 2004
Abstract:
The spin lattices of magnetic oxides LiCuVO4 and CuO are made up of CuO2 ribbon chains. The incommensurate and commensurate magnetic superstructures of these oxides were examined by calculating the total spin exchange interaction energies of their long-range order spin arrangements on the basis of the isotropic spin exchange and classical spin approximations. The incommensurate superstructure (0, 0.532, 0) of LiCuVO4 was analyzed to find that the next-nearest-neighbor spin exchange interaction J(nnn) is more strongly antiferromagnetic than the nearest-neighbor spin exchange interaction J(nn) in the CuO2 chains. With this finding, we reassessed the relative strengths of the spin exchange interactions of LiCuVO4 and CuO and then analyzed the relative energies of their long-range order spin arrangements. The incommensurate superstructure (0, 0.532, 0) of LiCuVO4 is explained when the J(nn)/J(nnn) ratio is -0.40, Both the incommensurate superstructure (0.506, 0, -0.483) and the commensurate superstructure (0.5, 0, -0.5) of CuO, which occur at 231 and 212.5 K, respectively, are well explained in terms of the calculated total spin exchange interaction energies. The incommensurate superstructure of CuO becomes commensurate by a slight change in one interchain spin exchange interaction, which is due probably to a slight structure change brought about by the temperature lowering.

Update: 9-Jul-2004

Title:
Medium range real atomic structure of face-centred icosahedral Ho9Mg26Zn65
Authors:
Bruhne, S; Sterzel, R; Uhrig, E; Gross, C; Assmus, W
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 219 (5): 245-258; 2004
Abstract:
A complementary approach to quasicrystalline atomic structures in 3-dimensional (3D) real space is presented: The atomic pair distribution function (PDF) of face centred icosahedral Ho9Mg26Zn65 [a(6D) = 2 x 5.18(3) Angstrom] has been obtained from in-house powder X-ray diffraction data (MoKalpha(1)). For the first time, full profile PDF refinements of a quasicrystal were performed: Starting with rational approximant models, derived from 1/1- and 2/1-Al-Mg-Zn, its local and medium range structure was refined (r < 27 Angstrom; R = 12.9%) using the PDF data. 85% of all atoms show Frank-Kasper (FK) type coordinations. The basic structural unit is the 3-shell, 104-atom Bergman cluster (d approximate to 15 A) comprising a void at its center. The clusters are interconnected sharing common edges and hexagonal faces of the 3rd shells. The remaining space is filled by some glue atoms (9% of all atoms), yielding an almost tetrahedrally close packed structure. All Ho atoms are surrounded by 16 neighbours (FK-polyhedron "P"). Most of them (89%) are situated in the 2nd shell and form a Ho-8 cube (edge length 5.4 Angstrom); they are completed by 12 Mg atoms to a pentagon dodecahedron. Cubes in neighbouring clusters are tilted with respect to each other; their superposition generates diffraction symmetry 2/m35. The remaining Ho atoms act as glue atoms. As a result and as can be expected for real matter, local atomic coordinations in quasicrystals are similar when compared to common crystalline intermetallic compounds. From our results, the long range quasiperiodic structure of icosahedral Mg-Zn-RE (RE = Y and some rare earths) is anticipated to be a canonical cell tiling (CCT, after Henely) decorated with Bergman clusters.
Title:
Influence of the incommensurability in Sr14-xCaxCu24O41 family compounds
Authors:
Gelle, A; Lepetit, MB
Source:
PHYSICAL REVIEW LETTERS, 92 (23): -; JUN 11 2004
Abstract:
We study the influence of the structural modulation on the low energy physics of the Sr14-xCaxCu24O41 oxides, using ab initio determination of the on-site and nearest-neighbor effective parameters. The structural modulations appear to be the key degree of freedom responsible for the low energy properties, such as the electron localization, the formation of dimers in the x=0 compound, or the antiferromagnetic order in the x=13.6 compound.
Title:
Anisotropy in the incommensurate spin fluctuations of Sr2RuO4
Authors:
Nagata, T; Urata, M; Kawano-Furukawa, H; Yoshizawa, H; Kadowaki, H; Dai, PC
Source:
PHYSICAL REVIEW B, 69 (17): -; MAY 2004
Abstract:
It has been proposed that Sr2RuO4 exhibits spin-triplet superconductivity mediated by ferromagnetic fluctuations. So far neutron-scattering experiments have failed to detect any clear evidence of ferromagnetic spin fluctuations but, instead, this type of experiments has been successful in confirming the existence of incommensurate spin fluctuations near q=(1/3 1/3 0). For this reason there have been many efforts to associate the contributions of such incommensurate fluctuations to the mechanism of its superconductivity. Our unpolarized inelastic neutron-scattering measurements revealed that these incommensurate spin fluctuations possess c-axis anisotropy with an anisotropic factor chi(c)"/chi(a,b)" of similar to2.8. This result is consistent with theoretical ideas that the incommensurate spin fluctuations with a c-axis anisotropy may be the origin of p-wave superconductivity of this material.
Title:
Evidence for an incommensurate magnetic resonance in La2-xSrxCuO4
Authors:
Tranquada, JM; Lee, CH; Yamada, K; Lee, YS; Regnault, LP; Ronnow, HM
Source:
PHYSICAL REVIEW B, 69 (17): -; MAY 2004
Abstract:
We study the effect of a magnetic field (applied along the c axis) on the low-energy, incommensurate magnetic fluctuations in superconducting La1.82Sr0.18CuO4. The incommensurate peaks at 9 meV, which in zero field were previously shown to sharpen in q on cooling below T-c [T. E. Mason , Phys. Rev. Lett. 77, 1604 (1996)], are found to broaden in q when a field of 10 T is applied. The applied field also causes scattered intensity to shift into the spin gap. We point out that the response at 9 meV, though occurring at incommensurate wave vectors, is comparable to the commensurate magnetic resonance observed at higher energies in other cuprate superconductors.
Title:
A kinetics driven commensurate-incommensurate transition
Authors:
Chaudhuri, A; Sreeram, PA; Sengupta, S
Source:
PHASE TRANSITIONS, 77 (8-10): 691-701; AUG-OCT 2004
Abstract:
We study the steady-state structure of an interface in an Ising system on a square lattice with a nonuniform external field. This structure exhibits a commensurate-incommensurate transition driven by the velocity of the interface. The nonuniform field has a profile with a fixed shape which is designed to stabilize a flat interface, and is translated with velocity v,. For small velocities, the interface is stuck to the profile and is rippled with a periodicity which may be either commensurate or incommensurate with the lattice parameter of the square lattice. For a general orientation of the profile, the local slope of the interface locks into one of infinitely many rational directions, producing a devil's staircase structure. These lock-in or commensurate structures disappear as v, increases through a kinetics driven commensurate-incommensurate transition. For large v,, the interface becomes detached from the field profile and coarsens with Kardar-Parisi-Zhang (KPZ) exponents. The complete phase diagram and the multifractal spectrum corresponding to these structures have been obtained numerically together with several analytic results concerning the dynamics of the rippled phases. Our work has technological implications in crystal growth and the production of surfaces with desired surface morphologies.
Title:
Incommensurate phases induced in a crystal by external effects
Authors:
Sannikov, DG
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 98 (5): 997-1001; 2004
Abstract:
Lifshitz invariants emerging in the presence of external effects in a crystal are considered for 2D irreducible representations of the D-4h class. It is shown that, for a 2D irreducible vector representation, the electric field exceeding a critical value leads to the formation of an incommensurate phase on the phase diagram. (C) 2004 MAIK "Nauka/Interperiodica".
Title:
Governing equations and general solutions of plane elasticity of one-dimensional quasicrystals
Authors:
Liu, GT; Fan, TY; Guo, RP
Source:
INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 41 (14): 3949-3959; JUL 2004
Abstract:
Plane elasticity theory of one-dimensional quasicrystals dealing with all point groups is investigated systematically. The governing equations of elastic fields and their general solutions are derived by the complex variable functions method. As an example, the elastic fields of a straight dislocation along the quasiperiodic axis of an orthorhombic quasicystal are calculated. The relevant singularity of the stress field for the dislocation in the quasicrystals is also discussed. (C) 2004 Elsevier Ltd. All rights reserved.

Update: 3-Jul-2004

Title:
On the structure of icosahedral quasicrystals
Authors:
Cornwell, JF
Source:
PHYSICA SCRIPTA, 69 (5): 410-426; MAY 2004
Abstract:
For the 3-dimensional icosahedral quasicrystal structures that are obtained by projection from the 6-dimensional hypercubic lattice and its sublattices, the D6 root and scaled weight lattices, explicit general formulae are obtained for the precise distribution of atomic sites. The "invariants of the line" and both ordinary and generalized Fibonacci pseudo-invariants play significant roles.
Title:
Tensile behavior and cold workability of Ti-Mo alloys
Authors:
Takemoto, Y; Shimizu, I; Sakakibara, A; Hida, M; Mantani, Y
Source:
MATERIALS TRANSACTIONS, 45 (5): 1571-1576; MAY 2004
Abstract:
Three kinds of titanium-molybdenum alloy, Ti-8Mo, Ti-14Mo and Ti-20Mo (mass%), quenched from 1223 K were investigated to clarify the tensile behavior and the cold workability using tensile test and conical cup test. In the quenched state Ti-14Mo showed the superior workability. Ti-20Mo has poor ductility in tensile test, but has relatively good formability in conical cup test. Both Ti-8Mo and Ti-14Mo became brittle through a cold rolling of 50% reduction in thickness; however Ti-20Mo did not change in workability by the cold rolling at all. Hardness remarkably increased with rolling reduction in Ti-8Mo and Ti-14Mo, but was almost constant in Ti-20Mo, especially with Ti-20Mo containing high oxygen. Microstructure of Ti-8Mo and Ti-14Mo rolled until seventy-odd percentage exhibited very fine structure and changed to alpha' + beta and beta structure, respectively. On the other hand Ti-20Mo hardly changed in microstructure by a cold rolling besides the formation of some band-like products. The product was composed of single variant of commensurate omega-phase, whereas the matrix contained four variants of incommensurate omega-phase. It was suggested that the peculiar deformation mechanism of Ti-20Mo was concerned with stress induced transformation of the omega-phase.
Title:
Spin-glass like behavior in a new ternary uranium cobalt alummide, U3CO4+xAl12-x with x=0.55(2)
Authors:
Tougait, O; Noel, H; Troc, R
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 177 (6): 2053-2057; JUN 2004
Abstract:
The new compound U3Co4+xAl12-x, where x = 0.55(2), was prepared by arc-melting of the elemental components, followed by a prolonged annealing at elevated temperature. Scanning electron microscopy-energy-dispersive spectroscopy and powder X-ray diffraction were used to determine the deviation from the ideal stoichiometry. A small homogeneity range, that extends around the composition U3Co4+xAl12-x with 0.4(1) less than or equal to x less than or equal to 0.7(1), could be detected. Single-crystal diffraction experiments revealed that U3Co4.55Al11.45 crystallizes with the Gd3Ru4Al12 type-structure, (space group P6(3)/mmc, Z = 2) in a cell of dimensions at room temperature. a = 8.6518(2) Angstrom, c = 9.2620(2) Angstrom. The crystal structure can be viewed as an intergrowth of two distinct layers of Co and Al atoms. and U, Al and mixed Al/Co atoms that pile up along the hexagonal axis. The results of the DC magnetization suggest the occurrence of a spin glass state at low temperature (T-f = 8 K). The origin of freezing of the magnetic moments may arise from a topological frustration due to the location of the U atoms on the apexes of a distorted Kagome lattice. (C) 2004 Elsevier Inc. All rights reserved.
Title:
Structural state of melt-spun Ti-Zr-Ni ribbons with a small amount of Si
Authors:
Rud, AD; Schmidt, U; Slukhovskii, OI; Zelinska, GM
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 373 (1-2): 48-52; JUN 30 2004
Abstract:
A structural state of the melt spun Ti37.1Zr38.8Ni13.9Si0.2 ribbons produced at different cooling rates has been investigated. It was found by means of X-ray diffraction analysis that their structural states are affected very strongly by the ribbon production conditions. The small amount addition of Si (0.2-0.3 at.%) to the Ti-Zr-Ni alloy leads to the formation of an amorphous state on the both-contact and free-sides of the ribbons produced at the wheel surface velocity of 44 m/s. For the case of 30 m/s however we have detected an amorphous state for the contact side and a mixed amorphous-quasicrystalline state for the free side of the ribbon. Parameters of the amorphous state were calculated for the ribbons as prepared and annealed. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Magnetic property of stable icosahedral quasicrystal in Zn-Fe-Sc alloy
Authors:
Kashimoto, S; Motomura, S; Maezawa, R; Matsuo, S; Ishimasa, T
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS, 43 (4B): L526-L529; APR 15 2004
Abstract:
We report the observation on the magnetic property of the stable Zn77Fe7Sc16 icosahedral quasicrystal discovered recently. As a result of measurements of magnetization, it became clear that the new Zn-based icosahedral quasicrystal has large local magnetic moments and exhibits spin glass behavior. The magnetization curves show Curie-like paramagnetism, where the magnetization M is 4.45 cgsemu/g at 5 K under 70 kOe. The temperature dependence, of the magnetic susceptibility obeys the Curie-Weiss law between 76 and 300 K. On the assumption that all of the Fe atoms have the same magnitude of local magnetic moment, the effective number of Bohr magneton p of each Fe atom was estimated at 5.30 on average. Moreover, in the low-temperature region, the spin glasslike cusp of the magnetic susceptibility was observed with a freezing temperature T-f = 7.2 K

Update: 2-Jul-2004

Title:
Properties of incommensurate spin density waves in iron aluminides (invited)
Authors:
Noakes, DR; Arrott, AS; Belk, MG; Deevi, SC; Lynn, JW; Shull, RD; Wu, D;
Source:
JOURNAL OF APPLIED PHYSICS, 95 (11): 6574-6579; 2004
Abstract:
Neutron diffraction in Fe(Al) reveals incommensurate spin density waves (SDWs) in alloys known to be spin glasses. The wave vectors for crystals of Fe(34Al), Fe(40Al) and Fe(43Al) show n varying from 11 to 6 for q=2pi(h+/-1/n,k+/-1/n,l+/-1/n)/a(o), where (h,k,l) and a(o) characterize the parent bcc lattice of the CsCl structure. The magnetic reflections are present far above the spin-glass freezing temperatures. These SDWs keep the spins on nearest-neighbor Fe atoms close to parallel, in contrast with SDWs in Cr, which keep nearest-neighbor spins close to antiparallel. The competition between near-neighbor Fe-Fe ferromagnetism and 180degrees superexchange through the Al site has been used to explain the spin-glass behavior, but the appearance of the SDWs calls for a more fundamental source of the periodicity. The phase shift mechanism for SDW interactions with magnetic moments is invoked to explain the breadth of the peaks, which resemble the results for Cu(Mn), Pd(Mn), and Pd(Cr). The data are interpreted using cubic symmetry, but it has yet to be established whether the wave vectors all occur in a single domain or whether there are multiple domains. There are 48 wave vectors of magnitude almost equal to the {110} wave vectors of the bcc lattice, which could stabilize the SDWs by spanning the Fermi surface. These unanticipated results should have pervasive ramifications for the theory of metallic magnetism. (C) 2004 American Institute of Physics.
Title:
Universal features of charge and spin order in a half-doped layered perovskite
Authors:
Zaliznyak, IA; Tranquada, JM; Gu, G; Erwin, RW; Moritomo, Y; Shull, RD;
Source:
JOURNAL OF APPLIED PHYSICS, 95 (11): 7369-7371; 2004
Abstract:
We have investigated the peculiar structure of charge and spin ordering in the half-doped layered perovskite oxide La1.5Sr0.5CoO4 by elastic neutron scattering. Two samples with different preparation histories were studied. We find that the generic features of the ordered states, such as their short-range, glassy nature and the spin incommensurability, are sample-independent. At the same time, some subtle features of the ordered phases, such as the correlation lengths, differ. (C) 2004 American Institute of Physics.
Title:
Reversible phase changes of Ni-rich Al-Co-Ni decagonal quasicrystals studied by means of transmission electron microscopy and thermal analysis
Authors:
Saito, K; Ohsuna, T; Sun, W; Hiraga, K; Kipferl, W;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 372 (1-2): 169-175; 2004
Abstract:
In the stability region of the Ni-rich Al-Co-Ni decagonal quasicrystals, phase relationships among three different modulations, i.e. the so-called Ni-rich basic, S1-state and Type-I phases, and their phase changes have been thoroughly investigated by various transmission electron diffraction and imaging techniques in combination with thermal analysis. Electron diffraction experiments have clearly indicated that the S1-state phase formed in the Al70Co12N18 alloy, which is stable at 900degreesC, transforms into the Type-I phase by annealing at 650degreesC and that the Ni-rich basic phase formed in the Al71.5Co9Ni19.5 alloy, which is stable at 900degreesC, transforms into the S1-state phase by annealing at 650degreesC. In addition, differential scanning calorimetry measurements have evidenced for the first time that both phase changes occur reversibly at certain temperatures ranged between 700 and 800degreesC. The structural features of the modulations mentioned above have been distinguished and uniquely characterized by making the best use of high-angle annular detector dark-field scanning transmission electron microscopy as well as high-resolution transmission electron microscopy. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Commensurate-incommensurate magnetic phase transition in magnetoelectric single crystal LiNiPO4
Authors:
Vaknin, D; Zarestky, JL; Rivera, JP; Schmid, H; Kishi, Y;
Source:
PHYSICAL REVIEW LETTERS, 92 (20): 4620-4622; 2004
Abstract:
Neutron scattering studies of single crystal LiNiPO4 reveal a spontaneous first-order commensurate-incommensurate magnetic phase transition. Short- and long-range incommensurate phases are intermediate between the high temperature paramagnetic and the low temperature antiferromagnetic phases. The modulated structure has a predominant antiferromagnetic component, giving rise to satellite peaks in the vicinity of the fundamental antiferromagnetic Bragg reflection, and a ferromagnetic component, giving rise to peaks at small momentum transfers around the origin at (0,+/-Q,0). The wavelength of the modulated magnetic structure varies continuously with temperature. It is argued that the incommensurate short- and long-range phases are due to spin-dimensionality crossover from a continuous to the discrete Ising state.
Title:
In situ study of the annealing behavior of porosity in icosahedral Al-Pd-Mn quasicrystals using third generation x-ray synchrotron radiation imaging
Authors:
Agliozzo, S; Gastaldi, J; Klein, H; Hartwig, J; Baruchel, J; Brunello, E; Baenitz, M;
Source:
PHYSICAL REVIEW B, 69 (14): 561-574; 2004
Abstract:
The evolution of porosity in an icosahedral Al-Pd-Mn quasicrystal single grain has been studied in situ during an annealing at 800 degreesC. A drastic shrinkage of pores was observed and interpreted in the frame of a vacancy-mediated diffusion model.
Title:
Structure of the tenfold d-Al-Ni-Co quasicrystal surface
Authors:
Ferralis, N; Pussi, K; Cox, EJ; Gierer, M; Ledieu, J; Fisher, IR; Jenks, CJ; Lindroos, M; McGrath, R; Diehl, RD;
Source:
PHYSICAL REVIEW B, 69 (15): 561-574; 2004
Abstract:
The structure of the tenfold surface of decagonal Al-Ni-Co was studied using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). The surface region is a relaxed truncated bulk structure, having the same composition as the bulk. The outermost layer spacing is contracted by 10% relative to the bulk interlayer spacing, while the next layer spacing is expanded by 5%. A small degree of intralayer rumpling was observed within each layer. There is a one-to-one correspondence between protrusions observed in the STM images and a subset of atoms in the model structure, indicating that in-plane reconstruction is minimal.
Title:
Modeling the thermopower of icosahedral Al63Cu25Fe12 quasicrystals: Spectral fine structure
Authors:
Macia, E; Hsu, CL;
Source:
PHYSICAL REVIEW B, 69 (13): 922-926; 2004
Abstract:
On the basis of a realistic model for the spectral conductivity, obtained from a proper combination of tunneling spectroscopy [R. Escudero , J. Phys.: Condens. Matter 11, 383 (1999)] and transport measurements, we derive a closed analytical expression for the Seebeck coefficient, satisfactorily describing its temperature dependence over a wide temperature range. The relative importance of thermal broadening effects and the temperature dependence of chemical potential in the thermopower curve is quantitatively discussed. By comparing the obtained analytical results with the experimental S(T) curve evidence for band structure effects in the thermopower is reported.
Title:
Dislocations and dislocation reactions in decagonal Al-Ni-Co quasicrystals
Authors:
Schall, P; Feuerbacher, M; Urban, K; Menovsky, AA;
Source:
PHYSICAL REVIEW B, 69 (13): 922-926; 2004
Abstract:
Dislocations in decagonal Al70Ni15Co15 and Al73Ni10Co17 were studied by means of diffraction-contrast imaging and defocus convergent beam electron diffraction techniques in the transmission electron microscope. In addition to dislocations with Burgers vectors parallel to the periodic and quasiperiodic directions as first reported by Zhang and Urban [Z. Zhang and K. Urban, Philos. Mag. Lett. 60, 97 (1989)], a type of dislocation was found possessing a Burgers vector with components in the periodic as well as the quasiperiodic direction. The parallel-space component of this Burgers vector has a length of 2.5 Angstrom. The quasiperiodic Burgers vectors were found to have parallel-space lengths of 2.9 and 4.7 Angstrom. The Burgers vectors determined are correlated with interatomic vectors of the structure of decagonal Al-Ni-Co. In addition, dislocation reactions were identified by the determination of Burgers vectors of dislocations in triple-node arrangements. A model for the dislocation reaction is proposed which is in accordance with the results of the microstructural studies.
Title:
Atomic-scale structure of the fivefold surface of an AlPdMn quasicrystal: A quantitative x-ray photoelectron diffraction analysis
Authors:
Zheng, JC; Huan, CHA; Wee, ATS; Van Hove, MA; Fadley, CS; Shi, FJ; Rotenberg, E; Barman, SR; Paggel, JJ; Horn, K; Ebert, P; Urban, K;
Source:
PHYSICAL REVIEW B, 69 (13): 922-926; 2004
Abstract:
The atomic-scale structure of the fivefold symmetric surface of an AlPdMn quasicrystal is investigated quantitatively by comparing x-ray photoelectron diffraction simulations to experiment. The observed fivefold symmetry of the diffraction patterns indicates that the surface is quasicrystalline with no hint of a reconstruction from the bulk structure. In analyzing the experimental data, many possible bulk terminations have been tested. Those few that fit best to the data have in common that they contain an Al-rich surface layer followed by a dense mixed Al/Pd/Mn layer. These best terminations, while not identical to each other, are suggested to form terraces coexisting on a real surface. Structural relaxations of the quasicrystal surface are also analyzed: mixing several best-fit terminations gives average best-fit interlayer spacing changes of Deltad(12)=-0.057 Angstrom and Deltad(24)=+0.159 Angstrom. These results are in good agreement with a prior structure determination by low-energy electron diffraction on a sample that was prepared in a different manner.
Title:
Phase diagram of the three-dimensional asymmetric next-nearest-neighbor Ising model in an effective-field approximation
Authors:
Surda, A; Huan, CHA;
Source:
PHYSICAL REVIEW B, 69 (13): 922-926; 2004
Abstract:
An effective-field method for calculation of thermodynamic properties of three-dimensional lattice spin models is developed. It is applied to the axial next-nearest-neighbor Ising model on the simple-cubic lattice. The phase diagram of the model, consisting of a large number commensurate phases and of an incommensurate phase, is calculated, confirming the results of previous approaches. The phase transition lines for a number of commensurate structures are localized and a strong evidence for absence of the direct phase transition between commensurate phases and the disordered phase is found.
Title:
Bi1-xSbx under high pressure: Effect of alloying on the incommensurate Bi-III type composite structure
Authors:
Haussermann, U; Degtyareva, O; Mikhaylushkin, AS; Soderberg, K; Simak, SI; McMahon, MI; Nelmes, RJ; Norrestam, R; Paggel, JJ;
Source:
PHYSICAL REVIEW B, 69 (13): 922-926; 2004
Abstract:
The high-pressure structural behavior of alloys Bi1-xSbx was investigated experimentally and by means of first-principles calculations in order to study the effect of alloying on the incommensurate Bi-III type composite structure, which is adopted by the high-pressure phases Bi-III and Sb-II of the pure elements. High-pressure experiments of Bi0.75Sb0.25 and Bi0.50Sb0.50 resulted in a decomposition into Sb-rich phases with the ambient A7 structure and Bi-rich phases with the Bi-III structure. For Bi0.50Sb0.50 two composite phases were observed with different compositions. Bi0.25Sb0.75 transformed from A7 to Bi-III, such as elemental Sb, and did not show a phase separation under pressure. For the pure elements, the structural parameters of the high-pressure composite phase are similar and vary only very slightly with pressure. The parameters of the alloy composite phases distribute rather smoothly in between those for the elements. The incommensurate composite phases in alloys Bi1-xSbx appear to be site disordered. Importantly, the incommensuration of the Bi-III structure is virtually not influenced by either composition or pressure. Total energy calculations as a function of pressure yielded endothermic enthalpies of formation for alloys Bi1-xSbx in both the ground-state A7 structure and the high-pressure Bi-III structure. The formation enthalpy takes a maximum value at a pressure corresponding to the alloy A7-->Bi-III transition, which explains the experimentally observed phase separations.
Title:
Positron annihilation studies of icosahedral quasicrystals and their approximants in the Al-Cu-Ru-(Si) alloy systems
Authors:
Uchiyama, H; Takahashi, T; Arinuma, K; Sato, K; Kanazawa, I; Hamada, E; Suzuki, T; Kirihara, K; Kimura, K; Horn, K;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (10): 1899-1905; 2004
Abstract:
The positron lifetimes for the icosahedral quasicrystal Al62.4CU25.4RU12.2 and its cubic approximants (1/1-Al58Cu31.5Ru10.5, 1/1-Al68Cu7Ru17Si8, and 1/0-Al55Cu15Ru20Si10), two-detector coincident Doppler broadening for the icosahedral quasicrystal Al62.4aCu25.4Ru12.2 and its 1/1-Al68Cu7Ru17Si8 cubic approximant, and the Doppler broadening obtained by making use of a slow positron beam for the 1/1-Al58Cu31.5Ru10.5 cubic approximant have been measured. Structurally intrinsic trapping sites giving rise to saturation trapping were detected by lifetime measurements. The chemical environments of the trapping sites in the icosahedral quasicrystal Al62.4Cu25.4Ru12.2 and the 1/1-Al68Cu7Ru17Si8 cubic approximant were determined by coincident Doppler broadening techniques to be dominantly surrounded by A1 atoms. The positron diffusion length in the 1/1-Al58Cu31.5Ru10.5 cubic approximant derived from the measured S parameter measured by means of a slow positron beam was similar to180 Angstrom, which is clearly too short, probably due to the high concentration of trapping sites as described above. The atomic structures of the icosahedral quasicrystal Al62.4Cu25.4Ru12.2 and its variety of approximants are discussed and compared to the present proposed model.
Title:
Crystalline phases displaying pseudo-icosahedral symmetry in Ag42In42RE16 (RE = Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu)
Authors:
Ruan, JF; Kuo, KH; Guo, JQ; Tsai, AP; Asano, T;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 370 (1-2): L23-L27; 2004
Abstract:
A bcc phase (a = 1.510-1.519 nm), possibly isostructural with Cd6RE, exists in Ag42In42RE16 alloys, where RE = Gd, Tb, Dy, Ho, Er, Tm, and Lu. In Ag42In42Yb16, however, a C-centered monoclinic phase (a = 2.60 nm, b = 1.48 nm, c = 2.63 nm, beta similar to 108degrees) coexists with the icosahedral quasicrystal (IQC). All these crystalline phases show local pseudo-icosahedral symmetry. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Solidification study of Al-Co-Cu alloys using the Bridgman method
Authors:
Zhang, LM; Gille, P; Guo, JQ;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 370 (1-2): 198-205; 2004
Abstract:
The solidification of a series of Bridgman-grown Al-Co-Cu alloys with compositions in the vicinity of the quasicrystal was studied by powder X-ray diffraction (XRD), differential thermal analysis (DTA), electron microprobe analysis, and optical microscopy. The phase equilibria and microstructure of solidified alloys are presented; the temperatures of the involved solidification reactions were determined. These experimental data were used to construct a solidification phase diagram as to understand the crystallization path. The decagonal (D) AlCoCu quasicrystals form incongruently, but they can be primarily solidified from off-stoichiometric melts. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Experimental evidence for the p-d hybridization in the Cd-Ca quasicrystal: Origin of the pseudogap
Authors:
Tamura, R; Takeuchi, T; Aoki, C; Takeuchi, S; Kiss, T; Yokoya, T; Shin, S; Paulsen, C;
Source:
PHYSICAL REVIEW LETTERS, 92 (14): 3024-3030; 2004
Abstract:
Ca 2p-3d resonant photoemission spectroscopy of a Cd6Ca crystalline approximant unambiguously demonstrates that the low-lying unoccupied 3d levels of calcium are lowered below the Fermi energy by the formation of the approximant, as suggested from electronic structure calculations [Y Ishii and T Fujiwara, Phys. Rev. Lett. 87, 206408 (2001)]. Moreover, the Ca 3d partial density of states (DOS) obtained near the Fermi energy is in reasonable agreement with theoretical Ca 3d DOS. These results verify the unconventional Picture that the origin of the pseudogap in the Cd-based quasicrystals is due to hybridization of the Ca 3d band with the Cd 5p band.
Title:
Resonating valence bond wave function for the two-dimensional fractional spin liquid
Authors:
Yunoki, S; Sorella, S; Rech, J;
Source:
PHYSICAL REVIEW LETTERS, 92 (15): 3024-3030; 2004
Abstract:
The unconventional low-lying spin excitations, recently observed in neutron scattering experiments on Cs2CuCl4, are explained with a spin liquid wave function. The dispersion relation as well as the wave vector of the incommensurate spin correlations are well reproduced within a projected BCS wave function with gapless and fractionalized spin-1/2 excitations around the nodes of the BCS gap function. The proposed wave function is shown to be very accurate for one-dimensional spin-1/2 systems and remains similarly accurate in the two-dimensional model corresponding to Cs2CuCl4, thus representing a good ansatz for describing spin fractionalization in two dimensions.
Title:
Crystal structure of the orthorhombic Al-4(Cr, Fe) approximant of the Al-Cr-Fe decagonal quasicrystal
Authors:
Deng, DW; Mo, ZM; Kuo, KH; Takagi, T;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (13): 2283-2296; 2004
Abstract:
The crystal structure of the orthorhombic phase Al-4(Cr, Fe) with a composition of Al80.6Cr10.7Fe8.7 has been determined by single-crystal x-ray diffraction (table 2). There are 11 crystallographically independent Cr/Fe sites, of which 10 are icosahedrally coordinated. Of the 28 crystallographically independent Al sites 5 are icosahedrally coordinated. However, owing to the presence of many partial occupancies, caused by split atoms, some of these coordinations are only pseudo-icosahedral with effective coordination numbers C(eff)not equal12 (section 4.3). The icosahedral and pseudo-icosahedral clusters are oriented with a two-fold axis parallel to [100]. They are linked either by vertex-, edge-or face-sharing or by mutual interpenetration, thus forming large clusters of icosahedra in the (100) layers with one of the five-fold axes in the [0101 direction. Four of the 12 atoms defining the vertices of an icosahedral cluster lie in a mirror plane (F plane), while the other atoms are in puckered layers below and above the mirror plane. Thus, the icosahedral cluster consists of layers PFP' of three atoms thick. Two such layers stack within one lattice constant aapproximate to1.25 nm. The interconnection of icosahedra in the PFP' layer block forms large triangular and hexagonal structural motifs, though they have only two-fold rotational symmetry. Similar geometrical motifs but displaying three- or six-fold symmetry do exist in the structure of the hexagonal mu-Al4Mn, K-(AlCrNi), lambda-Al4Mn and v-Al12Cr2Fe phases.
Title:
Structural phase transition in two-dimensional kagome antiferromagnet m-N-methylpyridinium alpha-nitronyl nitroxide center dot BF4 center dot 1/3(Acetone)
Authors:
Kambe, T; Nogami, Y; Oshima, K; Fujita, W; Awaga, K; Sugiyama, K;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73 (4): 796-799; 2004
Abstract:
We found for the first time a structural phase transition in two-dimensional kagome antiferromagnet m-N-methylpyridinium alpha-nitronyl nitroxide (m-MPYNN)(.)BF(4)(.)1/3 (acetone). As, below T-s = 128.7 K, the intense satellite reflections are clearly observed at the modulation wave vector of q(s) = (1/3, 1/3, 0), the unit cell of the low-temperature phase is enlarged to root3a x root3a x c. In the low-temperature phase, the space group is determined to be P31c. The orientation of acetone molecules orders below T-s, leading to the lack of the three-fold axis. To confirm whether the low-temperature phase maintains a kagome-like network structure or not, we estimate the overlap integrals between the singly occupied molecular orbital wave functions of the MPYNN molecules by the extended Huckel method. The result is that all the overlap integrals are modified below T-s, suggesting that the system below T-s cannot be regarded as the uniform S = 1 kagome antiferromagnet.
Title:
Observation of structural change with possible charge disproportionation in copper vanadium oxide bronze beta '-Cu0.65V2O5
Authors:
Yamaura, JI; Yamauchi, T; Isobe, M; Yamada, H; Ueda, Y; Sugiyama, K;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73 (4): 914-920; 2004
Abstract:
We performed the X-ray diffraction measurements at low temperature under ambient pressure for the pressure-induced superconductor beta'-Cu0.65V2O5. Satellite reflections were observed with an incommensurate modulation and a successive commensurate state depending on the cooling rate. The X-ray structure analysis in the commensurate state indicates the structural deformation on the vanadium ladder. We suggest the occurrence of the charge disproportionation for the origin of the structural transition. Additionally, we reveal the structural and electronic character for beta (beta')-vanadium bronzes.
Title:
2D-to-1D modulated-to-lock in successive magnetic phase transitions associated with ferroelectricity in ErMn2O5
Authors:
Kobayashi, S; Osawa, T; Kimura, H; Noda, Y; Kagomiya, I; Kohn, K; Sato, M;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73 (4): 1031-1035; 2004
Abstract:
We report results of dielectric and neutron diffraction measurements in zero field on magnetic ordering of weakly ferroelectric ErMn2O5. Around the ferroelectric transition temperature of T-C1 similar to 38 K below T-N1 = 44K, we observed successive magnetic phase transitions from a two-dimensionally-modulated (2D) incommensurate magnetic (ICM) phase with the propagation vector q = (q(x), 0, q(z)) to another 1D-ICM one with q = (q(x), 0, 1/4) at T = 39.1 K, and then to a commensurate magnetic (CM) phase with q = 4 (1/2, 0, 1/4) at T = 37.7 K. These two magnetic phase transitions (39.1 K and 37.7 K) were found to be 2 4 associated with an anomaly in the dielectric constant along the b axis. In addition, we found that in the case of a rapid-cooling procedure a low-temperature ICM state characterized by q = (1 0, 0.265) shows 2 up and coexists with the CM phase below T-N2 = 11.5 K where evolution of magnetic order of the Er ions is inferred from measurements of the magnetoelectric effect. These observations indicate the strong coupling between ferroelectricity and magnetic ordering in this system.
Title:
Structural aspects of the spin-ladder compound Sr14Cu24O41
Authors:
Etrillard, J; Braden, M; Gukasov, A; Ammerahl, U; Revcolevschi, A; Cheng, CW;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 403 (4): 290-296; 2004
Abstract:
Single crystal neutron scattering measurements have been performed on the spin-ladder compound Sr14Cu24O41 at 7 K. The incommensurate composite structure has been determined using the superspace group formalism. The low-temperature structure does not show a significant shift of the CuO2 chains along the c direction. In addition to the main and satellite nuclear reflections compatible with the incommensurate composite structure, new weak super-structure peaks at Q = (hkL(c)), with L-c = n +/- 0.20 (+/-0.01) have been observed. Their origin is probably due to the charge ordering associated to a three-dimensional configuration of the spin dimers in the CuO2 chain. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Pressure effect on crystallization temperature in Zr70Pd30 metallic glass
Authors:
Jiang, JZ; Jeppesen, S; Saida, J; Lathe, C; Jiang, CP;
Source:
JOURNAL OF APPLIED PHYSICS, 95 (9): 4651-4654; 2004
Abstract:
The pressure effect on amorphous-to-quasicrystalline-to-intermetallic phase transformations in a Zr70Pd30 metallic glass has been investigated by in situ x-ray diffraction measurements using synchrotron radiation. It is found that the glass crystallizes in two steps: (1) amorphous-to-icosahedral quasicrystalline and (2) icosahedral quasicrystalline-to-intermetallic Zr2+xPd alloy. The intermetallic alloy has a tetragonal structure with lattice parameters, a=3.310(1) Angstrom and c=10.974(1) Angstrom, and a space group of I4/mmm. External pressure enhances the onset temperatures for the formation of quasicrystalline phase and intermetallic compound with rates of 11+/-3 and 9+/-4 K/GPa, respectively, while the temperature interval for the stability of quasicrystals remains almost unchanged in the pressure range of 0-3 GPa. External pressure does not affect the phase-selection sequence. The enhancement of the onset temperature for the formation of quasicrystals has been further discussed with the nucleation theory. (C) 2004 American Institute of Physics.
Title:
Spiral order induced by distortion in a frustrated square-lattice antiferromagnet
Authors:
Zaliznyak, IA; Chirita, V;
Source:
PHYSICAL REVIEW B, 69 (9): 4922-4927; 2004
Abstract:
In a strongly frustrated square-lattice antiferromagnet with diagonal coupling J('), for alpha=J/(2J('))less than or similar to1, an incommensurate spiral state with propagation vector Q=(pi+/-delta,pi+/-delta) near (pi,pi) competes closely with the Neel collinear antiferromagnetic ground state. For classical Heisenberg spins the energy of the spiral state can be lowered as it adapts to a distortion of the crystal lattice. As a result, a weak superstructural modulation such as exists in doped cuprates might stabilize an incommensurate spiral phase for some range of the parameter alpha close to 1.
Title:
Low-temperature superstructure and charge-ordering effect in eta-Na1.286V2O5
Authors:
Duc, F; Millet, P; Ravy, S; Thiollet, A; Chabre, F; Ghorayeb, AM; Mila, F; Stepanov, A; Zhou, HM;
Source:
PHYSICAL REVIEW B, 69 (9): 4922-4927; 2004
Abstract:
In this work, we report on x-ray diffraction, electron spin resonance, and magnetic susceptibility measurements performed on eta-Na1.286V2O5. The x-ray data clearly reveal the existence, around 100 K, of a structural second-order phase transition, stabilizing a superstructure associated with charge ordering. The complete superstructure is determined from x-ray scattering data measured at 15 and 40 K. The low-temperature structure remains centrosymmetric with space group P2/c but with a doubled b lattice parameter. An analysis using superspace symmetry shows that one of the vanadium atoms and its apical oxygen, namely the V7 and O7 atoms, are the most displaced. Two sites for V7 atoms are identified below the transition instead of one with the formal valence of V4.5+. We show that these two sites are occupied by V4+ and V5+, which corresponds to a charge ordering. We suggest that this transition is driven by electronic repulsions. The magnetic measurements give additional evidence for this transition and for the opening of a spin gap at low temperature. This is discussed in conjunction with superstructure formation.
Title:
Low-frequency incommensurate magnetic response in strongly correlated systems
Authors:
Sherman, A; Schreiber, M; Krajci, M;
Source:
PHYSICAL REVIEW B, 69 (10): 4922-4927; 2004
Abstract:
It is shown that in the t-J model of Cu-O planes at low frequencies the dynamic spin structure factor is peaked at incommensurate wave vectors (1/2 +/-delta, 1/2), (1/2,1/2+/-delta). The incommensurability is connected with the momentum dependencies of the magnon frequency and damping near the antiferromagnetic wave vector. The behavior of the incommensurate peaks is similar to that observed in La2-x(Ba,Sr)(x)CuO4+y and YBa2Cu3O7-y: for hole concentrations 0.020.12 it tends to saturation. The incommensurability disappears with increasing temperature. Generally the incommensurate magnetic response is not accompanied by an inhomogeneity of the carrier density.
Title:
La-induced conversion between the ferroelectric and antiferroelectric incommensurate phases in Pb1-xLax(Zr1-yTiy)O-3
Authors:
Asada, T; Koyama, Y; Krajci, M;
Source:
PHYSICAL REVIEW B, 69 (10): 4922-4927; 2004
Abstract:
In La-substituted Pb1-xLax(Zr0.95Ti0.05)O-3, an increase in the La content x served to convert the ferroelectric incommensurate (FI) phase into the antiferroelectric incommensurate (AI) phase around x=0.01. In order to elucidate the physical origin of the conversion between the FI and AI phases, the crystallographic features of the successive phase transitions related to these incommensurate phases have been investigated by transmission electron microscopy. It was found that the FI-to-AI transition actually occurred on cooling in the x=0.01 sample, and that in the x=0.03 sample, for instance, the AI phase basically consisted of four phases with commensurate modulations. The successive transitions among these four phases and the antiferroelectric commensurate (AC) phase were also suggested to proceed by the continuous change in a wave front of the modulation wave. In addition, the ferroelectric cluster (FS) state was found to exist in the paraelectric cubic (PC) phase above the AI phase. Because the M-3 and R-25 rotational displacements of the oxygen octahedra are, respectively, involved in the FI phase and the FS state, the conversion between the FI and AI phases should be associated with that between these rotational displacements.
Title:
Variation of the crystal structures of incommensurate LT '-Ni1+delta Sn (delta=0.35, 0.38, 0.41) and commensurate LT-Ni1+delta Sn (delta=0.47, 0.50) with composition and annealing temperature
Authors:
Leineweber, A; Nagasawa, K;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 177 (4-5): 1197-1212; 2004
Abstract:
The variation of the crystal structures of two Ni1+deltaSn phases (ordered NiAs/Ni(2)ln-type structures) as a function of the annealing temperature and composition was studied on the basis of X-ray powder patterns evaluated by Rietveld refinement. In both phases-incommensurate LT' (delta = 0.35, 0.38, 0.41; Cmcm(alpha00)0s0, alpha < 1/2) and commensurate LT (delta = 0.47, 0.50; Pbnm)-thc occupation modulations of Ni atoms in these phases cause strong displacements of all atoms from their ideal sites. The artificial description of the LT phase (for which 'conventional' structural parameters have been reported previously) as a commensurately modulated structure (Pbnm section of Cmcm(alpha00)0s0 with alpha = 1/2) allows a common analysis of the concentration and annealing-temperature-dependent modulation parameters of both phases, which reveals their close structural similarities. This confirms that the LT phase can be regarded as a commensurate special case (lock-in phase) of the LT' phase. (C) 2003 Elsevier Inc. All rights reserved.
Title:
Site occupancy wave and charge density wave in the modulated structure of Nd0.6Gd0.4Se1.85
Authors:
Doert, T; Tsinde, BPF; Lidin, S; Garcia, FJG; Landwehr, G;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 177 (4-5): 1598-1606; 2004
Abstract:
Single crystals of Nd0.6Gd0.4Se1.85 have been prepared by chemical transport reactions starting from pre-annealed powder samples. Satellite reflections observed in X-ray and electron diffraction experiments indicate the presence of a two-dimensional lattice distortion. The origin of this is a site occupancy wave and, coupled to this, a charge density wave in the planar selenium layer of this compound. The modulated structure has been solved and refined from X-ray data using the superspace approach. Nd0.6Gd0.4Se1.85 can be described in the (3 + 2)-dimensional superspace group P4/n(alphabeta1/2) (beta - alpha1/2)00 with lattice parameters of a = 4.088 (1) Angstrom, c 8.336 (1) Angstrom. Diffuse scattering contributions have been observed around the satellite reflections which can be understood by the formation of domains with slightly different ordering patterns of Se atonts. Thus, the incommensurate translational parts of the modulation vectors are not constant over the whole crystal and can be described as alpha = 0.29 + k and beta - 0.29 - k with -0.05 less than or equal to k less than or equal to 0.05. (C) 2004 Elsevier Inc. All rights reserved.
Title:
Application of mechanical alloying and self-propagating synthesis for preparation of stable decagonal quasicrystals
Authors:
Bokhonov, B; Korchagin, A; Lidin, S;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 368 (1-2): 152-156; 2004
Abstract:
The X-ray and electron microscopic investigations demonstrated principal possibility to use self-propagation high-temperature synthesis (SHS) in combination with preliminary mechanical activation for the synthesis of stable decagonal quasicrystals. The decagonal quasicrystals formed in SHS process look like faceted decaprisms with a length of 300-400 mum and a thickness of 30-40 mum. SAD patterns are characterized by the presence of the axes of 10- and 2-fold symmetry. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Pseudomorphic growth of a single element quasiperiodic ultrathin film on a quasicrystal substrate
Authors:
Ledieu, J; Hoeft, JT; Reid, DE; Smerdon, JA; Diehl, RD; Lograsso, TA; Ross, AR; McGrath, R; Klenke, J;
Source:
PHYSICAL REVIEW LETTERS, 92 (13): 152-156; 2004
Abstract:
An ultrathin film with a periodic interlayer spacing was grown by the deposition of Cu atoms on the fivefold surface of the icosahedral Al70Pd21Mn9 quasicrystal. For coverages from 5 to 25 monolayers, a distinctive quasiperiodic low-energy electron diffraction pattern is observed. Scanning tunneling microscopy images show that the in-plane structure comprises rows having separations of S=4.5+/-0.2 Angstrom and L=7.3+/-0.3 Angstrom, whose ratio equals tau=1.618... within experimental error. The sequences of such row separations form segments of terms of the Fibonacci sequence, indicative of the formation of a pseudomorphic Cu film.
Title:
Nature of the A phase in CeCu2Si2
Authors:
Stockert, O; Faulhaber, E; Zwicknagl, G; Stusser, N; Jeevan, HS; Deppe, M; Borth, R; Kuchler, R; Loewenhaupt, M; Geibel, C; Steglich, F; Sikolenko, V;
Source:
PHYSICAL REVIEW LETTERS, 92 (13): 152-156; 2004
Abstract:
Neutron diffraction experiments have been performed on a magnetically ordered CeCu2Si2 single crystal exhibiting A-phase anomalies in specific heat and thermal expansion. Below T(N)approximate to0.8 K antiferromagnetic superstructure peaks have been detected. The propagation vector of the magnetic order appears to be determined by the topology of the Fermi surface of heavy quasiparticles as indicated by renormalized band-structure calculations. The observation of long-range incommensurate antiferromagnetic order as the nature of the A phase in CeCu2Si2 suggests that a spin-density-wave instability is the origin of the quantum critical point in CeCu2Si2.
Title:
A TEM study of Ni ordering in the Ni6Se5-xTex, 0 < x < similar to 1.7, system
Authors:
Withers, RL; Liu, Y; Noren, L; Gerald, JDF; Jeevan, HS;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 177 (3): 972-978; 2004
Abstract:
The Ni6Se5-xTex, 0
Title:
High temperature vacancy studies of icosahedral Zn65Mg25Er10 quasicrystal
Authors:
Ye, F; Sprengel, W; Zhang, XY; Uhrig, E; Assmus, W; Schaefer, HE; Borth, R;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (9): 1531-1537; 2004
Abstract:
Formation of thermal vacancies in icosahedral Zn65Mg25Er10 quasicrystals has been specifically studied from room temperature to about 720 K by positron annihilation spectroscopy employing two-detector coincident Doppler broadening techniques. Significant vacancy formation was observed for temperatures higher than 0.6T(m). An apparent vacancy formation enthalpy of 1.2 eV was determined. The results are discussed in comparison with high temperature vacancy processes in quasicrystals as well as in other complex solids.
Title:
Continuous charge modulated diagonal phase in manganites
Authors:
Brey, L; Verhoeven, GS;
Source:
PHYSICAL REVIEW LETTERS, 92 (12): 2614-2616; 2004
Abstract:
We present a novel ground state that explains the continuous charge modulated diagonal order recently observed in manganese oxides, at hole concentrations x larger than one-half. In this diagonal phase the charge is modulated with a predominant Fourier component inversely proportional to 1-x. Magnetically this state consists of antiferromagnetically coupled zigzag chains. For a wide range of physical parameters such as electron-phonon coupling, antiferromagnetic interaction between Mn ions, and on-site Coulomb repulsion, the diagonal phase is the ground state of the system. Also we find that the diagonal modulation of the electron density is only a small fraction of the average charge, a much smaller modulation than the one obtained by distributing Mn+3 and Mn+4 ions. We discuss also the spin and orbital structure properties of this new diagonal phase.
Title:
Study of an order-disorder phase transition on an atomic scale: The example of decagonal Al-Ni-Co quasicrystals
Authors:
Sato, K; Baier, F; Sprengel, W; Wurschum, R; Schaefer, HE; Zandbergen, HW;
Source:
PHYSICAL REVIEW LETTERS, 92 (12): 2614-2616; 2004
Abstract:
In the present paper we succeeded in studying structural phase transitions from an atomistic point of view by positron annihilation Doppler broadening. This differs and is complementary to conventionally used diffraction experiments with large coherence lengths. In the exemplary case of the 1140 K order-disorder transition in decagonal Al71.5Ni14Co14.5 quasicrystals the importance of this atomistic approach and its wide scope of application is demonstrated.
Title:
Spatial dispersion in incommensurately modulated insulators
Authors:
Kushnir, OS; Baier, F;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (8): 1245-1267; 2004
Abstract:
Peculiarities of the non-local responses of spatially inhomogeneous insulating media to electromagnetic waves are considered within a phenomenological approach. In the case of a weak spatial dispersion (SD), a 'quasi-local' constitutive equation is derived, which allows one to isolate the effects of SD in relation to non-uniformities of the wavefield and the material properties of the medium. The symmetry of the material tensors is clarified. The material contribution to the SD suggests a novel mechanism for optical activity. The SD in crystalline media is described in terms of dielectric permittivity dependent upon a single argument which is a specific combination of the light wavevector and the reciprocal lattice vectors. The conditions and materials for which the relevant effects can be notable are pointed out. The character of the normal light wave polarization in dielectric crystals of the A(2)BX(4) group with incommensurately modulated superstructure is analysed and the effective crystal optical parameters are derived. It is shown that the first-order material SD effects associated with the bulk macroscopic properties of these crystals could be of practical importance.
Title:
Growth and physical properties of the decagonal Al-Cu-Co quasicrystal grown from the ternary melt
Authors:
Ribeiro, RA; Bud'ko, SL; Laabs, FC; Kramer, MJ; Canfield, PC; Cross, AW;
Source:
PHILOSOPHICAL MAGAZINE, 84 (12): 1291-1302; 2004
Abstract:
Large faceted single-grain quasicrystals of the approximate composition Al63.2Cu19.5Co17.3 and with a high degree of structural perfection are obtained through the slow cooling of a ternary melt with initial composition Al65Cu29Co6. X-ray diffraction patterns of crushed single-grain samples are exceptionally sharp, indicating a high degree of structural order, with no evidence of secondary phases. Transmission electron micrographs also reveal sharp diffraction patterns in the even-n layers but diffuse scattering in the odd-n layers. Temperature-dependent magnetization, electrical resistivity and specific heat are measured using bars cut perpendicular and parallel to the c axis and show diamagnetic behaviour: gamma approximate to 0.5 mJ mol(-1) K-2, rho(c)(2 K) approximate to 52 muOhm cm and rho(q)(2 K) approximate to 283 muOhm cm.
Title:
Microstructure evolution upon devitrification and crystallization kinetics of Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 melt-spun glassy ribbon
Authors:
Scudino, S; Kuhn, U; Schultz, L; Nagahama, D; Hono, K; Eckert, J; Ronald, K;
Source:
JOURNAL OF APPLIED PHYSICS, 95 (7): 3397-3403; 2004
Abstract:
The crystallization behavior of glassy Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 produced by melt spinning was investigated by differential scanning calorimetry, x-ray diffraction, electron microscopy, and atom probe investigations. The devitrification of the as-spun ribbon occurs by primary crystallization of a metastable nanoscale quasicrystalline phase during the first stage of the crystallization process, followed by successive transformation into intermetallic compounds at higher temperatures. The kinetics investigation reveals that quasicrystal formation is characterized by two overlapping processes: the first step probably linked with the redistribution of one or more elements, most likely Al and Zr, between the quasicrystalline phase and the remaining amorphous matrix, and the second step corresponding to the crystallization itself. Furthermore, a higher value of the activation energy for quasicrystal formation compared to other quasicrystal-forming alloys suggests an increased complexity of the crystallization mechanism. (C) 2004 American Institute of Physics.
Title:
A comparative study of the Al-Co-Pd and Al-Co-Ni alloy systems
Authors:
Yurechko, M; Grushko, B; Velikanova, TY; Urban, K; Hono, K;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 367 (1-2): 20-24; 2004
Abstract:
The Al-Pd-Co and Al-Ni-Co alloy systems are compared with respect to the formation of quasicrystals. Their structures, as expected, have some similarities due to the similarities of Ni and Pd, which belong to the same column of the Periodic Table. However, a metastable binary Al-Co decagonal quasicrystal is stabilized by Ni and not stabilized by Pd. A number of periodic phases are formed in Al-Pd-Co in the compositional range corresponding to the decagonal phase in Al-Ni-Co. Similar orthorhombic decagonal-like structures are formed in both systems with the same compositions as the (meta) stable quasicrystals at lower temperatures. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Stable and metastable quasicrystals in Al-based alloy systems with transition metals
Authors:
Grushko, B; Velikanova, TY; Velikanova, TY;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 367 (1-2): 58-63; 2004
Abstract:
Quasiperiodic phases or quasicrystals (QC) with symmetries 5 and 10 have been found in numerous alloy systems of Al with d-transition metals (TM). Apart from QCs, related periodic phases with complicated structures were also discovered in these systems. QCs are usually formed in the Al-rich regions between 60 and 85 at. % Al. In binary Al-TM systems (TM = V, Cr, Mn, Fe, Co, Ni; Mo, Ru, Rh, Pd; W, Re, Os, Ir, Pt), they are metastable and can be produced by rapid solidification. Binary QCs can be stabilized in a number of ternary alloy systems such as Al-Ni-(Fe, Co, Ru, Rh), Al-Cu-(Fe, Co, Ru, Rh) and Al-Pd-(Mn, Re). Some aspects of the systematics of their formation are discussed. (C) 2003 Elsevier B.V. All rights reserved.
Title:
The structures of mercury chalcogenhalogenides Hg(3)X(2)Hal(2)
Authors:
Minets, YV; Voroshilov, YV; Pan'ko, VV; Urban, K;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 367 (1-2): 109-114; 2004
Abstract:
The crystal structures of the four-component chalcogenhalogenide phases Hg(3)Te(2)Brl (I) and Hg3S2(Br0.67I0.33)(2) (II) were determined by the single crystal method. Compound I is monoclinic (space group: C2, a = 18.376(5) Angstrom, b = 9.587(2) Angstrom, c = 10.575(2) Angstrom, beta = 100.11(2)degrees), II has a commensurately modulated structure (super space group: Pp42(1)2, a = 13.32(1) Angstrom, c = 4.465 (5) Angstrom, modulation vector [001/2]). A classification of the structures of mercury chalcogenhalogenides Hg(3)X(2)Hal(2) is also given. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Synthesis and structure of five Sc3CuyZn18-y-type compositions (0 <= y <= similar to 2.2), 1/1 crystalline approximants of a new icosahedral quasicrystal. Direct example of tuning on the basis of size effects and hume-rothery concepts
Authors:
Lin, QS; Corbett, JD; Semina, VK;
Source:
INORGANIC CHEMISTRY, 43 (6): 1912-1919; 2004
Abstract:
The newly reported icosahedral quasicrystalline phase similar toSc(3)Cu(2.1)Zn(12.9) was approached through four synthetic, structural, and EDX analyses of the range of approximants formed by systematic substitutions of 0-4 Zn by Cu in the reported Sc3Zn17 as well as for the corrected Sc3Zn18 (ScZn6) composition. Structures of high yield products of the 0, 1, 2, 3 Cu atom steps all refined as isotypiC Sc3CuyZn18-y phases (lm (3) over bar, Z = 8, a = 13.8311(5) to 13.7528(5) Angstrom for 0 less than or equal to y less than or equal to2.2), basically isostructural with RCd6 phases known for many rare-earth elements. The present phases all exhibit the novel feature of disordered zinc tetrahedra in the center of four concentric polyhedral clusters: pentagonal dodecahedron (Zn/Cu), icosahedron (Sc), icosidodecahedron (Zn), and triacontahedron (Zn). The Cu tuning process reduces both the average electron count per atom (e/a) to 2.04 and the average atom size until major amounts of the zinc-poorer quasicrystal separate along with the present normal crystalline phase near four added Cu. The Cu is an important neighbor to the disordered Zn atoms. The approximant structure repeatedly exhibits components with pseudo-icosahedral symmetry.
Title:
Magnetic properties of copper metaborate: Two-parameter phenomenological model
Authors:
Popov, MA; Petrakovskii, GA; Zinenko, VI; Skakov, YA;
Source:
PHYSICS OF THE SOLID STATE, 46 (3): 491-497; 2004
Abstract:
Symmetry analysis is performed for the magnetic subsystem of copper metaborate, and a phenomenological model is proposed with two two-component order parameters that correspond to ferromagnetism and antiferromagnetism vectors lying in the tetragonal plane of this crystal. Owing to the I (4) over bar 2d space group of symmetry of this crystal, the thermodynamic potential contains the Lifshitz invariant having the form of an antisymmetric product of the order parameters and their spatial derivatives. Analysis of this model shows that the temperatures of ordering in the magnetic subsystem and of the formation of a spiral structure in it can be different. This fact allows numerical calculation of the temperature dependences of the spiral wave vector, magnetization, and intensities of first- and third-order magnetic satellites in the incommensurate phase that arise in neutron elastic scattering, as well as the field dependence of the magnetization. The experimental data, including a magnetic-field-temperature phase diagram, are satisfactorily described. The parameters of the phenomenological thermodynamic potential of the magnetic subsystem of copper metaborate are estimated. (C) 2004 MAIK "Nauka / Interperiodica".
Title:
Atomic dynamics of an Al0.62Cu0.255Fe0.125 icosahedral quasicrystal
Authors:
Parshin, PP; Zemlyanov, MG; Mashkov, AV; Brand, RA; Dianoux, AJ; Calvayrac, Y; Ronald, K;
Source:
PHYSICS OF THE SOLID STATE, 46 (3): 526-531; 2004
Abstract:
The atomic dynamics of an Al0.62Cu0.255Fe0.125 icosahedral quasicrystal is investigated using inelastic neutron scattering (the isotopic contrast method). The partial vibrational spectra of copper, iron, and aluminum atoms in the icosahedral quasicrystal and the total spectrum of thermal vibrations of the compound are directly reconstructed from the experimental data for the first time. It is found that the vibrational energies of copper and iron atoms fall in relatively narrow ranges near 16 and 30 meV, respectively, whereas the vibrational energies of aluminum atoms lie in a wide range (up to 60 meV). (C) 2004 MAIK "Nauka / Interperiodica".
Title:
Structure and peculiarities of nanodeformation in Ti-Zr-Ni quasi-crystals
Authors:
Azhazha, V; Dub, S; Khadzhay, G; Merisov, B; Malykhin, S; Pugachov, A; Ronald, K;
Source:
PHILOSOPHICAL MAGAZINE, 84 (10): 983-990; 2004
Abstract:
Ti - Zr - Ni samples with a substantial predominance of icosahedral quasicrystalline phase were produced by the melt-spinning technique. Their structure and mechanical properties were studied by X-ray diffraction and nanoindentation methods. The quasicrystalline phase was found to have a primitive lattice with the quasicrystallinity parameter a(q) = 0.5200 - 0.5210 nm. Quasicrystalline deformation behaviour under nanoindentation versus phase composition and structure is discussed in comparison with single crystal W 12wt% Ta. The estimated elastic modulus E of the quasicrystalline phase shows no correlation with the element composition. The nanohardness was shown to increase with increasing quasicrystalline-phase perfection. Load displacement curves of Ti - Zr - Ni quasicrystals (QCs) show stepwise character with alternation of elastic and plastic sections. Such non-uniform plastic flow in QCs might be caused by the localization of plastic deformation in shear bands. The non-uniformity of the plastic deformation increases with the increasing quasicrystalline phase perfection.
Title:
Dissolution patterns caused by chemical etching of Al-Co-Cu and Al-Co-Ni decagonal quasicrystals with a HF-HNO3-H2O solution
Authors:
Saito, K; Saito, Y; Sugawara, S; Shindo, R; Guo, JQ; Tsai, AP; Ronald, K;
Source:
PHILOSOPHICAL MAGAZINE, 84 (10): 1011-1020; 2004
Abstract:
Dissolution patterns essential for Al - Co - Cu and Al - Co - Ni decagonal quasicrystals (d-QCs) have been investigated in detail by chemical etching using a HF - HNO3 - H2O solution followed by scanning electron microscopy (SEM) observations. The chemical etching of definite surface areas of the samples, which are either normal or parallel to the tenfold axes, using a solution with HF - HNO3 - H2O (1 : 5 : 4 in volume ratio; 0 degreesC; 5 - 10 min), produces a large number of microfacet pits of decagonal prismatic shape. In addition, the same etching test in combination with SEM observations was carried out on a deformed sample of the Al - Co - Ni d-QC, which had been subjected to concentrated mechanical stress at an elevated temperature of 850 degreesC by means of the Vickers indentation technique. The morphological features of the resulting micropits and their possible origins are discussed on the basis of results obtained by SEM observations.
Title:
Magnetic properties of single grain r-mg-cd primitive icosahedral quasicrystals (R = Y, Gd, Tb or Dy)
Authors:
Sebastian, SE; Huie, T; Fisher, IR; Dennis, KW; Kramer, MJ; Tsai, AP;
Source:
PHILOSOPHICAL MAGAZINE, 84 (10): 1029-1037; 2004
Abstract:
The growth and characterization of single grains of the primitive icosahedral quasicrystal R - Mg - Cd ( R = Y, Gd, Tb or Dy) are described. From the thermodynamic properties, it is confirmed that the system is a spin glass exhibiting the characteristic spin-freezing transition of such systems. There is no evidence for two distinct freezing transitions previously observed for polygrain samples. The bulk magnetic properties and the effect of crystalline electric fields on the spin-freezing temperature are found to be very similar to those of the face-centred icosahedral quasicrystal R - Mg - Zn.
Title:
Imaging modulated reflections from a semi-crystalline state of profilin : actin crystals
Authors:
Lovelace, JJ; Narayan, K; Chik, JK; Bellamy, HD; Snell, EH; Lindberg, U; Schutt, CE; Borgstahl, GEO; Yin, H;
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 37 (4): 327-330; 2004
Abstract:
Modulated protein crystals remain terra incognita for most crystallographers. While small-molecule crystallographers have successfully wrestled with and conquered this type of structure determination, to date no modulated macromolecular structures have been reported. Profilin: beta-actin in a modulated semi-crystalline state presents a challenge of sufficient biological significance to motivate the development of methods for the accurate collection of data on the complex diffraction pattern and, ultimately, the solution of its structure. In the present work, fine phi-sliced data collection was used to resolve the closely spaced satellite reflections from these polymorphic crystals. Image-processing methods were used to visualize these data for comparison with the original precession data. These preliminary data demonstrate the feasibility of using fine phi-slicing to collect accurately the intensities and positions of the main and satellite reflections from these modulated protein crystals.
Title:
Structure of incommensurate ammonium tetrafluoroberyllate studied by structure refinements and the maximum entropy method
Authors:
Palatinus, L; Amami, M; van Smaalen, S; Gleeson, AJ;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 60 (12): 127-137; 2004
Abstract:
Incommensurately modulated ammonium tetrafluoroberyllate (AFB) occurs in a narrow temperature interval between the paraelectric room-temperature phase with space group Pnma (T-i = 178 K) and the ferroelectric low-temperature phase with space group Pna2(1) (T-c = 173 K). The structure is determined from accurate single-crystal X-ray diffraction data collected with synchrotron radiation at 175 K. The superspace group of the structure is Pnma(alpha00) 0ss with alpha = 0.4796 (4). Both structure refinements and the maximum entropy method lead to the same structure model, which involves only single harmonic modulations. The building units of the structure are BeF42- and NH4+ complex ions with approximately tetrahedral point symmetry. They are relatively rigid and the modulations consist mainly of translations of the tetrahedra and their rotations around a fixed axis. The modulation is related to changes in the network of the hydrogen bonds. The low-temperature superstructure can be described as a commensurately modulated structure with the same superspace symmetry. The first harmonic modulations of the low-temperature and incommensurate phases are related by a scale factor with a value of approximately two. In addition, the low-temperature phase exhibits a second harmonic modulation that is responsible for shifts along c and the ferroelectricity in this phase. The experimental data of the incommensurate phase do not contain any evidence for the presence of a second harmonic in the modulation functions. This suggests that the development of the second harmonic, i.e. the development of the spontaneous polarization, is responsible for the lock-in transition.
Title:
Model for the crystal packing and conformational changes of biphenyl in incommensurate phase transitions
Authors:
Dzyabchenko, A; Scheraga, HA; van Smaalen, S;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 60 (12): 228-237; 2004
Abstract:
Standard atom - atom potentials for hydrocarbons and a torsional potential to account for the pi-electron conjugation energy were used to model the crystal structures and phase transitions of biphenyl. The model describes the high-temperature phase ( I) with its planar molecule as a stationary point of the energy hypersurface. Phase I represents a low-energy barrier between the symmetry minima of the ground state ( phase III), in which the molecule is twisted with torsion angles of opposite sign. Global-energy minimization was carried out by considering both regular structures, with one or two independent molecules, and quasi-one-dimensional superstructures built of N cells (N up to 16) of the high-temperature structure. The various energy-minimized biphenyl structures demonstrate remarkable similarity in their crystal packing; in particular, there are characteristic rows of cooperatively twisted molecules parallel to the superstructure dimension b. The structures built of centrosymmetric rows (P (1) over bar 1, Z = 4 and 8) are almost as low in energy as the basic structure ( an N = 2 superstructure, Pa, Z = 4); moreover, one of them is isostructural with the low-temperature p-quaterphenyl structure. With N > 8, structures of lower energy than that of the basic structure ( N = 2) were found; their common feature is an M-fold modulation of the twist angle over the supercell period, with M smaller than N and generally not a simple fraction of it. The global minimum was found to conform to the ratio k = M/ N = 6/14, which is close to the experimentally observed k = 6/13 in the incommensurate phase III. Enthalpy minimization showed an overall decrease in the magnitude of the twist angle down to tau similar or equal to 0degrees, as well as the evolution of the modulated structures towards the high-temperature structure with increasing pressure, in agreement with evidence for the high-pressure limit of the incommensurate biphenyl phases.
Title:
Magnetic-field-induced phase transition in BiFeO3 observed by high-field electron spin resonance: Cycloidal to homogeneous spin order
Authors:
Ruette, B; Zvyagin, S; Pyatakov, AP; Bush, A; Li, JF; Belotelov, VI; Zvezdin, AK; Viehland, D; Yin, H;
Source:
PHYSICAL REVIEW B, 69 (6): 228-237; 2004
Abstract:
Bismuth ferrite is a magnetoelectric material, which simultaneously has polarization and spin orders. We have used electron spin resonance (ESR) as a local probe of the magnetic order in the magnetic-field range of 0-25 T, in the frequency domain of 115-360 GHz, and at a temperature of 4.2 K. The data reveal significant changes in the ESR spectra with increasing field, which have been analyzed by taking into account the magnetic anisotropy of the crystal and a magnetoelectric Dzyaloshinsky-Moria-like interaction. The results demonstrate an induced phase transition from an incommensurately cycloidal modulated state to one with homogeneous spin order.
Title:
Low-energy electron diffraction study of Xe adsorption on the ten-fold decagonal Al-Ni-Co quasicrystal surface
Authors:
Ferralis, N; Diehl, RD; Pussi, K; Lindroos, M; Fisher, I; Jenks, CJ; Hey, R;
Source:
PHYSICAL REVIEW B, 69 (7): 228-237; 2004
Abstract:
The adsorption of Xe onto the tenfold surface of decagonal Al-Ni-Co was studied using low-energy electron diffraction (LEED). LEED isobar measurements indicate that Xe grows in a layer-by-layer mode for at least the first two layers in the temperature range 60-80 K. The half-monolayer isosteric heat of adsorption was measured to be 250+/-10 meV. No superlattice was observed for the first layer of Xe, which is therefore presumed either to have a quasicrystalline structure or to be disordered. Upon adsorption of the second layer, an ordered Xe bilayer forms, which has a structure consistent with domains of bilayer Xe(111) aligned along substrate symmetry directions. At higher Xe coverages (several Xe layers), the LEED pattern becomes more distinct and remains consistent with that from a Xe(111) surface.
Title:
Icosahedral quasicrystals in Zn-T-Sc (T = Mn, Fe, Co or Ni) alloys
Authors:
Maezawa, R; Kashimoto, S; Ishimasa, T; Lindroos, M;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 84 (4): 215-223; 2004
Abstract:
Starting from the Zn17Sc3 cubic approximant, new quasicrystal alloys were sought by replacement of Zn with transition elements T. In the cases when T = Mn, Fe, Co and Ni, new icosahedral quasicrystals are formed in as-cast alloys as major phases at alloy compositions of Zn75T10Sc15. All these quasicrystals belong to a primitive type and have six-dimensional lattice parameters a(6D) ranging from 7.044 to 7.107 Angstrom. They have valence electron concentrations e/a ranging from 2.01 to 2.14, and almost the same ratios between the edge length a(R) of the Penrose tile and the averaged atomic diameter (d) over bar :a(R)/d approximate to 1.76. Moreover other Zn- and Cd-based quasicrystals, including the same type of atomic Tsai-type cluster, have the same values of e/a approximate to 2.1 and a(R)/(d) over bar approximate to 1.75 The equality in e/a indicates that the Hume-Rothery mechanism plays an important role for the formation of these quasicrystals.
Title:
Compositions of different phases appearing during devitrification of Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glass
Authors:
Van de Moortele, B; Epicier, T; Soubeyroux, JL; Pelletier, JM; Fisher, I;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 84 (4): 245-256; 2004
Abstract:
The devitrification process of Zr46.75Ti8.25Cu7.5Ni10Be27.5 metallic glass during annealing in the supercooled liquid region has been studied by conventional, high-resolution and analytical transmission electron microscopy (TEM). Two kinds of particle appear during devitrification: quasicrystals and crystalline precipitates. Nanoanalysis with energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy reveal that quasicrystals are Be free, while the crystallites have the ZrBe2 hexagonal structure. These experiments confirm the key role of Be during devitrification. They also indicate that quasicrystals can form in the system Zr-Ti-Cu-Ni ( without Be), as further evidenced by direct synthesis and an in situ neutron diffraction investigation, according to the chemical composition deduced from the TEM analysis.
Title:
Electronic transport in insulating AlPdRe quasicrystals
Authors:
Rosenbaum, R; Murphy, T; Brandt, B; Wang, CR; Zhong, YL; Wu, SW; Lin, ST; Lin, JJ; Yin, H;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (6): 821-831; 2004
Abstract:
Resistivity and magnetoresistance measurements have been performed on insulating icosahedral AlPdRe quasicrystal (QC) bar samples. At temperatures in the range 300 K greater than or equal to T greater than or equal to 50 K, the resistivities follow a simple inverse temperature law: rho(T) rho(0)/T(1.0+/-0.1). Below 1 K, the resistivity of a weakly insulating sample exhibited a simple inverse temperature law where rho(T) = rho0/T-0.33 and not an activated variable-range hopping (VRH) law. Strongly insulating samples exhibit saturation of their resistivities to finite values as T --> 0 K. These saturation resistivity values are believed to arise from the presence of a second metallic phase located within the quasicrystal's structure. By extrapolating the measured resistivities at 22 mK to absolute zero, the saturation conductivity values were estimated at T = 0 K and subtracted from the conductivity data points. These 'corrected' data, corresponding only to the QC phase, were found to follow activated VRH laws, having hopping exponents y that vary in the range 0.18 less than or equal to y less than or equal to 0.43. The activated VRH behaviours are observed only below 1 K. The magnetoresistances (MRs) of these samples are also anomalous. The MRs can be explained by including contributions from both the saturation conductivity values and from the QC MR ratios, estimated using the wavefunction shrinkage model.
Title:
A pressure and magnetotransport study of binary quasicrystal YbCd5.7
Authors:
Dhar, SK; Della Mea, M; Bauer, E; Manfrinetti, P; Palenzona, A; Wu, SW;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (6): 935-939; 2004
Abstract:
We have probed the quasicrystalline state in binary YbCd5.7 by monitoring its electrical resistivity between 1.5 and 300 K in externally applied hydrostatic pressure up to 16 kbar and measuring its magnetoresistivity up to 12 T from 0.5 to 20 K. The thermal variation of the resistivity is practically unaffected by pressure, indicating the stability of the quasicrystalline state in this pressure regime. A positive magnetoresistance, Deltarho/rho, of similar to0.8% is observed at 0.65 K, which reduces to similar to0.4% at 20 K in the maximum applied field of 12 T. Though the magnetoresistance of the sample investigated is about an order of magnitude larger than expected on the basis of the empirically derived relationship Deltarho/rho similar to p(1.3) observed for a large number of quasicrystals, it is much below the unusually large anomalous magnetoresistance (20-200%) reported earlier in the literature. We believe that the intrinsic magnetoresistivity of YbCd5.7 in different samples may be primarily masked by the presence of traces of free Cd which is known to have a giant magnetoresistivity at low temperatures.
Title:
Phonon activity and intermediate glassy phase of YVO3
Authors:
Massa, NE; Piamonteze, C; Tolentino, HCN; Alonso, JA; Martinez-Lope, MJ; Casais, MT; Lin, ST;
Source:
PHYSICAL REVIEW B, 69 (5): 813-821; 2004
Abstract:
We show that in YVO3 additional hard phonons gradually become zone center infrared active below similar to210 K, verifying that a lattice phase transition takes place at about that temperature. Their gradual increment in intensity between similar to210 and similar to77 K is associated with a "glassy" behavior found in the temperature-dependent V K edge pseudoradial distribution. This translates into an increase in the Debye-Waller factors ascribed to the appearance of V local structural disorder below similar to150 K. Conflicts between various ordering mechanisms in YVO3 bring up similarities of the intermediate phase to known results in dielectric incommensurate systems, suggesting the formation of commensurate domains below 116 K, the onset temperature of G-type antiferromagnetism. We propose that similar to210 and similar to77 K be understood as the temperatures where the commensurate-incommensurate and incommensurate-commensurate "lock-in" phase transitions take place. We found support for this interpretation in the inverted lambda shapes of the measured heat capacity and in the overall temperature dependence of the hard phonons.
Title:
Local densities of states for some embedded structures
Authors:
Losev, A; Moore, JE;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (4): 605-611; 2004
Abstract:
Recently we proposed and demonstrated a convolution method for the calculation of the local density of states (LDOS) [1, 2]. It has been shown to be applicable to relatively simple structures including some quasicrystals and other cases of disorder. Our efforts overlap with earlier work by Schwalm and Schwalm [3] even if we proceed along different lines. Here we investigate the case of embedded structures which are a particular case of heterogeneity. Over the years there has been a sustained interest about such objects and particularly the effect of localization observed in them, which is reflected in a wealth of papers and ideas [4-10]. There are indeed six simple embedded structures which we will consider: a pointlike impurity in a chain, a lattice or a solid (a crystal); a chain embedded in a lattice or a solid and a lattice embedded in a solid. The last three cases will be referred to as 'extended' impurities while the first three are naturally called 'pointlike'. They have been drawn schematically in figure 1. It will be shown that the characteristics of the former derive from the latter and also that some more complicated structures can be seen as variations of these simple cases. We construct the LDOS for the six basic cases starting with a one-dimensional solution. The convolution method provides analytic results even if they might be rather awkward to write explicitly. Implemented as a computational scheme it has the advantages of simplicity and speed, which stand out when compared with other numerical approaches. However, the method is shown to have some severe limitations. Nevertheless it offers some new insight into the constitution of already known results.
Title:
On the criteria for the formation of nanoquasicrystalline phase
Authors:
Murty, BS; Hono, K; Senthil, T;
Source:
APPLIED PHYSICS LETTERS, 84 (10): 1674-1676; 2004
Abstract:
The formation of nanoquasicrystalline phase is reported directly from the liquid on melt spinning over a wide range of wheel velocities of 10-30 m/s in Zr-Pd system at the eutectic composition (Zr75Pd25 alloy). The earlier studies in the Zr-Pd system (Zr70Pd30 and Zr65Pd35 alloys) showed nanoquasicrystallization on annealing of the amorphous phase obtained by melt spinning. Based on the existing results in various systems, a large negative enthalpy of mixing and/or existence of Frank-Kasper-type phases appear to be the crucial criteria for the formation of nanoquasicrystalline phase in any system. (C) 2004 American Institute of Physics.
Title:
Quasiparticle structure in antiferromagnetism around the vortex and nuclear magnetic relaxation time
Authors:
Takigawa, M; Ichioka, M; Machida, K; Ellenbogen, JC;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73 (2): 450-458; 2004
Abstract:
On the basis of the Bogoliubov-de Gennes theory for the two-dimensional extended Hubbard model, the vortex structure in d-wave superconductors is investigated including the contribution of the induced incommensurate antiferromagnetism around the vortex core. As the on-site repulsive interaction U increases, the spatial structure of charge and spin changes from the antiferromagnetic state with checkerboard modulation to that with the stripe modulation. By the effect of the induced antiferromagnetic moment, the zero-energy density of states is suppressed, and the vortex core radius increases. We also study the effect of the local density of states (LDOS) change on the site-dependent nuclear relaxation rate T-1(-1)(r). These results are compared with a variety of experiments performed on high T-c cuprates.
Title:
Anomalous states of the structure of [Rb-0.7(NH4)(0.3)](2)SO4 crystals in the temperature range 4.2-300 K
Authors:
Shmyt'ko, IM; Afonikova, NS; Arnautova, EA; Revkevich, GP;
Source:
PHYSICS OF THE SOLID STATE, 46 (2): 339-344; 2004
Abstract:
Crystals of [Rb-0.7(NH4)(0.3)](2)SO4 solid solutions are studied using x-ray diffractometry in the temperature range 4.2-300 K. No anomalies are revealed in the temperature dependences of the lattice parameters and the volume of the host unit cell. A series of superstructure reflections observed along the basis axes corresponds to the guest lattice formed in the matrix of the host structure. From analyzing the axial ratio of these structures and their temperature dependences, it is concluded that the structure of the crystal has the form of an incommensurate composite. The guest structure of the composite at room temperature can be considered a set of chains that are not correlated along the b direction. In the plane perpendicular to the chain axes, these chains form a regular framework that is also incommensurate to the host lattice. (C) 2004 MAIK "Nauka / Interperiodica".
Title:
Magnetic structure of CeRhIn5 as a function of pressure and temperature
Authors:
Llobet, A; Gardner, JS; Moshopoulou, EG; Mignot, JM; Nicklas, M; Bao, W; Moreno, NO; Pagliuso, PG; Goncharenko, IN; Sarrao, JL; Thompson, JD; Sikolenko, V;
Source:
PHYSICAL REVIEW B, 69 (2): 339-344; 2004
Abstract:
We report magnetic neutron-diffraction and electrical resistivity studies on single crystals of the heavy-fermion antiferromagnet CeRhIn5 at pressures up to 2.3 GPa. These experiments show that the staggered moment of Ce and the incommensurate magnetic structure change weakly with applied pressure up to 1.63 GPa, where resistivity, specific heat and nuclear quadrupole resonance measurements confirm the presence of bulk superconductivity. This work places important constraints on an interpretation of the relationship between antiferromagnetism and unconventional superconductivity in CeRhIn5.
Title:
Incommensurate magnetic structure of beta-MnO2 (vol 68, art no 172401, 2003)
Authors:
Regulski, M; Przenioslo, R; Sosnowska, I; Hoffmann, JU; Blugel, S;
Source:
PHYSICAL REVIEW B, 69 (2): 339-344; 2004
Abstract:
A detailed numerical study of the real-space configuration of vortices in disordered superconductors using two-dimensional London-Langevin model is presented. The magnetic field B is varied between 0 and B-c2 for various pinning strengths Delta. For weak pinning, an inhomogeneous disordered vortex matter is observed, in which the topologically ordered vortex lattice survives in large domains. The majority of the dislocations in this state are confined to the grain boundaries/domain walls. Such quasiordered configurations are observed in the intermediate fields, and we refer it as the domain regime (DR). The DR is distinct from the low-field and the high-fields amorphous regimes which are characterized by a homogeneous distribution of defects over the entire system. Analysis of the real-space configuration suggests domain-wall roughening as a possible mechanism for the crossover from the DR to the high-field amorphous regime. The DR also shows a sharp crossover to the high-temperature vortex liquid phase. The domain size distribution and the roughness exponent of the lattice in the DR are also calculated. The results are compared with some of the recent Bitter decoration experiments.
Title:
Geometric structure of Bergman clusters related to bulk amorphous alloys and quasicrystals
Authors:
Wang, XD; Qi, M; Thiel, PA; Dong, C; Hondou, K;
Source:
PHILOSOPHICAL MAGAZINE, 84 (8): 825-834; 2004
Abstract:
The fee Zr2Ni- and MgCu2-type phases, being primary crystalline products of certain amorphous alloys with high glass-forming ability, should provide local structural information about the related amorphous alloys. The present paper gives a detailed analysis of the common structural features of these two fee phases. They are both built from a similar building block consisting of tetrahedrally packed icosahedra. They also have shelled local structures similar to the first two shells of the Bergman-type clusters found in many icosahedral quasicrystals. Therefore the Bergman-type clusters probably play an important role in amorphous phase formation. Because of topological close packing inside dual-intergrown icosahedra, characteristic of Bergman clusters, the atomic radius ratios of the first- and second-shell atoms with respect to the central atom are nearly equal and fall in the range 1.1-1.2.
Title:
A common behaviour of thermoelectric layered cobaltites: incommensurate spin density wave states in [Ca2Co4/3Cu2/3O4](0.62)[CoO2] and [Ca2CoO3](0.62)[CoO2]
Authors:
Sugiyama, J; Brewer, JH; Ansaldo, EJ; Itahara, H; Dohmae, K; Xia, C; Seno, Y; Hitti, B; Tani, T; Sarrao, JL;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (49): 8619-8630; 2003
Abstract:
Magnetism of a misfit layered cobaltite [Ca2Co4/3Cu2/3O4](x)(RS)[CoO2] (x similar to 0.62, RS denotes a rocksalt-type block) was investigated by a positive muon spin rotation and relaxation (mu(+)SR) experiment. A transition to an incommensurate (IQ spin density wave (SDW) state was found below 180 K (=T-C(on)); and a clear oscillation due to a static internal magnetic field was observed below 140 K (=T-C). Furthermore, an anisotropic behaviour of the zero-field mu(+)SR experiment indicated that the IC-SDW lies in the a-b plane, with oscillating moments directed along the c axis. These results were quite similar to those for the related compound [Ca2CoO3](0.62)(RS)[CoO2], i.e., Ca3Co4O9. Since the]RS IC-SDW field in [Ca2Co4/3Cu2/3O4](0.62)(RS)[CoO2] was approximately the same]RS as those in pure and doped [Ca2CoO3](0.62)(RS)[CoO2], it was concluded that the IC-SDW exists in the [CoO2] planes.
Title:
The 2/1 cubic approximant of the Ag42In42Ca16 icosahedral quasicrystal
Authors:
Deng, BB; Kuo, KH; Ansaldo, EJ;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 366 (1-2): L1-L5; 2004
Abstract:
Using equal amounts of Ag and In to replace Cd in the stable Cd85Ca15 icosahedral quasicrystal, Guo and Tsai obtained the stable Ag42In42Ca16 icosahedral quasicrystal. However, the crystalline approximant of this quasicrystal is still not known yet. In the present study, the simple cubic Ag42In45Ca13 (Pa (3) over bar, a = 2.496 nm), displaying pseudo-icosahedral symmetry, has been found as the dominant phase in the ternary Ag3In3Ca alloy by electron and X-ray diffraction. Since the cubic Cd6Ca (Im (3) over bar, a = 1.564 nm) and Cd76Ca13 (Pa (3) over bar, a = 2.5339 nm), respectively, are known to be the 1/1 and 2/1 cubic approximants of the Cd85Ca15 icosahedral quasicrystal, this cubic Ag42In45Ca13 may be considered the 2/1 approximant of the Ag42In42Ca16 icosahedral quasicrystal. (C) 2003 Elsevier B.V. All rights reserved.
Title:
A five-dimensional model of dodecagonal Ta-Te quasicrystals with fractal occupation domains
Authors:
Yamamoto, A; Kim, YC;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 60 (8): 142-145; 2004
Abstract:
The consideration of two approximants of the first stable dodecagonal Ta - Te quasicrystal shows that the five-dimensional (5D) space group of the dodecagonal phase is P (12) over bar m2(12(5)mm) and the structure consists of five layers within a 10 Angstrom period. A 5D quasicrystal model leading to the two approximant structures by the introduction of appropriate linear phason strains is derived by the section method. The model shows 20 Angstrom dodecagonal clusters (DDC) arranged at each vertex of the square-triangle dodecagonal pattern and has fractal occupation domains, suggesting that the quasicrystal has either a deterministic or a random square-triangle packing of the DDC.
Title:
Magnetically ordered quasicrystals: enumeration of spin groups and calculation of magnetic selection rules
Authors:
Lifshitz, R; Mandel, SED; Cho, SH;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 60 (8): 167-178; 2004
Abstract:
Details are given of the theory of magnetic symmetry in quasicrystals, which has previously only been outlined. A practical formalism is developed for the enumeration of spin point groups and spin space groups, and for the calculation of selection rules for neutron scattering experiments. The formalism is demonstrated using the simple, yet non-trivial, example of magnetically ordered octagonal quasicrystals in two dimensions. In a companion paper [Even-Dar Mandel & Lifshitz ( 2004). Acta Cryst. A60, 179 - 194], complete results are provided for octagonal quasicrystals in three dimensions.
Title:
Symmetry of magnetically ordered three-dimensional octagonal quasicrystals
Authors:
Mandel, SED; Lifshitz, R; Cho, SH;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 60 (8): 179-194; 2004
Abstract:
The theory of magnetic symmetry in quasicrystals, described in a companion paper [Lifshitz & Even-Dar Mandel ( 2004). Acta Cryst. A60, 167 - 178], is used to enumerate all three-dimensional octagonal spin point groups and spin-space-group types and calculate the resulting selection rules for neutron diffraction experiments.
Title:
Multiple charge-density waves in R5Ir4Si10 (R=Ho, Er, Tm, and Lu)
Authors:
van Smaalen, S; Shaz, M; Palatinus, L; Daniels, P; Galli, F; Nieuwenhuys, GJ; Mydosh, JA; Hitti, B;
Source:
PHYSICAL REVIEW B, 69 (1): 104-108; 2004
Abstract:
The charge-density-wave (CDW) transitions in compounds R5Ir4Si10 (R=rare-earth element) have been studied by x-ray-diffraction and electrical conductivity experiments for temperatures between 20 and 300 K. At T-CDW incommensurate CDW's [(q) over right arrow=(+/-0.25+/-delta)(c) over right arrow* with deltaapproximate to0.03] develop in compounds with R=Ho, Er, Tm, and (Lu0.16Er0.84), while commensurate CDW's [(q) over right arrow=(n/7)(c) over right arrow*] develop in compounds with R=Lu and (Lu0.34Er0.66). T-CDW varies between 83 K in R=Lu and 161.4 K in R=Ho. The compounds with an incommensurate CDW exhibit a second transition at Tlock-in
Title:
Dynamic stripes and resonance in the superconducting and normal phases of YBa2Cu3O6.5 ortho-II superconductor
Authors:
Stock, C; Buyers, WJL; Liang, R; Peets, D; Tun, Z; Bonn, D; Hardy, WN; Birgeneau, RJ; Tani, T;
Source:
PHYSICAL REVIEW B, 69 (1): 104-108; 2004
Abstract:
We describe the relation between spin fluctuations and superconductivity in a highly ordered sample of YBa2Cu3O6.5 using both polarized and unpolarized neutron inelastic scattering. The spin susceptibility in the superconducting phase exhibits one-dimensional incommensurate modulations at low energies, consistent with hydrodynamic stripes. With increasing energy the susceptibility curves upward to a commensurate, intense, well-defined, and asymmetric resonance at 33 meV with a precipitous high-energy cutoff. In the normal phase, which we show is gapless, the resonance remains surprisingly strong and persists clearly in Q scans and energy scans. Its similar asymmetric spectral form above T-c=59 K suggests that incoherent superconducting pairing fluctuations are present in the normal state. On cooling, the resonance and the stripe modulations grow in well above T-c below a temperature that is comparable to the pseudogap temperature where suppression occurs in local and low-momentum properties. The spectral weight that accrues to the resonance is largely acquired by transfer from suppressed low-energy fluctuations. We find the resonance to be isotropically polarized, consistent with a triplet carrying similar to2.6% of the total spectral weight of the Cu spins in the planes.
Title:
Plastic deformation of decagonal Al73Ni10Co17 single quasicrystals
Authors:
Schall, P; Feuerbacher, M; Urban, K; Davies, JH;
Source:
PHILOSOPHICAL MAGAZINE, 84 (7): 705-718; 2004
Abstract:
Uniaxial compression tests were performed on decagonal Al73Ni10Co17 single quasicrystals at a constant strain rate of 10(-5) s(-1) in the temperature range between 800 and 890degreesC. The compression axis was chosen in three different orientations: parallel to, inclined by 45degrees to and perpendicular to the tenfold symmetry axis. During the deformation experiments stress relaxation tests and temperature changes were carried out to determine the strain-rate and temperature sensitivities of the flow stress. Highly anisotropic plastic behaviour is observed in both the flow stress and its strain and temperature dependences. Additionally, repeated stress relaxations were performed during the deformations, giving evidence that only minor microstructural changes take place during the relaxation tests.
Title:
Lifshitz-point instabilities and re-entrant incommensurability in LixV2O5
Authors:
Katzke, H; Czank, M; Toledano, P; Bellissent, R;
Source:
EUROPHYSICS LETTERS, 65 (3): 358-364; 2004
Abstract:
The concentration-induced sequence of three incommensurate phases (epsilon, epsilon'(1), epsilon'(2)) previously disclosed in LixV2O5 are interpreted as resulting from distinct Lifshitz-invariant and Lifshitz-points instabilities. When varying the temperature, the epsilon phase displays a re-entrant behavior, which is described as a folding of the high-temperature region triggered by the ordering of the lithium ions.
Title:
Quantum spins and quasiperiodicity: A real space renormalization group approach
Authors:
Jagannathan, A; Burnell, G;
Source:
PHYSICAL REVIEW LETTERS, 92 (4): 1153-1155; 2004
Abstract:
We study the antiferromagnetic spin-1/2 Heisenberg model on a two-dimensional bipartite quasiperiodic structure, the octagonal tiling, the aperiodic equivalent of the square lattice for periodic systems. An approximate block spin renormalization scheme is described for this problem. The ground state energy and local staggered magnetizations for this system are calculated and compared with the results of a recent quantum Monte Carlo calculation for the tiling. It is conjectured that the ground state energy is exactly equal to that of the quantum antiferromagnet on the square lattice.
Title:
Thermoelectric properties of binary Cd-Yb quasicrystals and Cd6Yb
Authors:
Kuo, YK; Lai, JR; Huang, CH; Ku, WC; Lue, CS; Lin, ST; You, LP;
Source:
JOURNAL OF APPLIED PHYSICS, 95 (4): 1900-1905; 2004
Abstract:
The thermoelectric properties, including electrical resistivity (rho), Seebeck coefficient (S), and thermal conductivity (kappa) on binary icosahedral Cd-Yb quasicrystals and Cd6Yb are investigated. The Cd-Yb quasicrystals have a room-temperature (RT) resistivity value of about 200 (muOmega cm), however, the temperature-dependent resistivity is sensitive to a small composition change in these compounds. For all studied samples, Seebeck coefficients are positive and small (similar to10 muV/K at RT). Upon cooling, S decreases quasilinearly, indicative of a metallic diffusion behavior, and then develops a broad phonon drag peak at around 40 K. The temperature characteristic of thermal conductivity kappa of Cd-Yb quasicrystals shows a most peculiar feature in all measured thermoelectric properties. The RT kappa value similar to6 (W/m K) of Cd-Yb quasicrystals is considerably larger than that of conventional ternary counterparts. Such an observation is attributed to the substantial electrical contribution kappa(e) (similar to50%) to their total thermal conductivity, as deduced from the Wiedemann-Franz's law, and larger lattice thermal conductivity kappa(P) due to less chemical disorder present in the binary Cd-Yb quasicrystalline structure. In addition kappa decreases with decreasing temperature and shows a distinct maximum, a broad maximum, or a plateau at low temperatures, depending on the sample composition. The dimensionless thermoelectric figure of merit (ZT) for Cd-Yb quasicrystals is estimated to be small, on the order of 0.005 at RT. (C) 2004 American Institute of Physics.
Title:
Aperiodic incommensurate phase of a C-60 monolayer on Ag(100)
Authors:
Hsu, CL; Pai, WW; Richardson, SL;
Source:
PHYSICAL REVIEW B, 68 (24): M76-M78; 2003
Abstract:
Detailed combined scanning tunneling microscopy and low-energy electron diffraction measurements reveal that the structure of a C-60 monolayer on Ag(100) is not the previously accepted commensurate c(6x4) phase but rather an incommensurate (111) close-packed phase. The film exhibits a characteristic molecular contrast pattern with merely short-range order, and room-temperature fluctuations of the contrast show that a thermal equilibrium state is reached. The nature of this controversial bright-dim C-60 contrast is clarified as a topographic feature due to C-60-induced reconstruction underneath the dim C-60 molecules. Due to interactions between the incommensurate C-60 adlayer and the reconstructed substrate, the (111) phase is distorted laterally, forming a novel "tetramer" configuration of specific contrast order. The spatial distribution of these tetramers is aperiodic; this has crucial implications for the peculiar short-range contrast order observed experimentally. A lattice gas model with anisotropic nearest-neighbor interactions and a configuration energy of the tetramer is developed. Quantitative agreements between observation and modeling are achieved with reasonable phenomenological parameters derived within experimental constraints.
Title:
Structure of dislocations and stacking faults in the complex intermetallic xi '-(Al-Pd-Mn) phase
Authors:
Klein, H; Feuerbacher, M; Richardson, SL;
Source:
PHILOSOPHICAL MAGAZINE, 83 (36): 4103-4122; 2003
Abstract:
We present the results of an electron microscopy study of defects in plastically deformed single crystals of the intermetallic xi'-(Al-Pd-Mn) phase. Pure edge dislocations with two different Burgers vector directions and four different Burgers vector magnitudes were found. All Burgers vector magnitudes observed can be described in terms of irrational fractions of the unit-cell parameters, and we have observed Burgers vector directions that can be indexed using irrational indices. The stacking faults observed have displacement vectors whose magnitudes and directions are incompatible with the unit cell of the xi' phase. A comparison of the Burgers vectors observed in this study with those reported for the corresponding icosahedral quasicrystal shows that they are equivalent with respect to their directions and lengths. This leads to the conclusion that local order rather than long-range periodic (or quasiperiodic) order governs the structure of defects in these materials.
Title:
Structural modulation, hole distribution, and hole-ordered structure of the incommensurate composite crystal (Sr2Cu2O3)(0.70)CuO2
Authors:
Gotoh, Y; Yamaguchi, I; Takahashi, Y; Akimoto, J; Goto, M; Onoda, M; Fujino, H; Nagata, T; Akimitsu, J; Shayegan, M;
Source:
PHYSICAL REVIEW B, 68 (22): 2549-2553; 2003
Abstract:
Modulated structure of incommensurate composite crystal (Sr2Cu2O3)(0.70)CuO2, "Sr14Cu24O41," has been investigated by single-crystal x-ray-diffraction method using centrosymmetric (3+1)-dimensional superspace group. In (Sr2Cu2O3)(0.70)CuO2, displacive modulation of O atom in the CuO2 chain is fairly large. Considering the modulation of bond angles, it has been found that the Cu-O bond in the CuO2 chain is tilting toward the Cu2O3 ladder in order that the O atom in the chain plays as apical oxygen for the CuO4 square in the ladder. The bond-valence sum (BVS) method has been applied to investigate the hole distribution in the modulated structure of (Sr2Cu2O3)(0.70)CuO2. It is indicated that the valence of Cu atom in the Cu2O3 ladder is +2.04, where about 0.03 holes are certainly transferred from the CuO2 chain through the modulated O atom in the CuO2. The BVS calculation has demonstrated that almost all of the holes are prepared in the CuO2 chain by the large modulation of the Cu-O bond. Cu atoms in the modulated CuO2 chain have been proved to form hole-ordered structure with next-nearest-neighbor Cu2+ ions separated by Cu3+ ion on the Zhang-Rice singlet site. The periodicity of the hole-ordered structure is five times of the average CuO2 lattice along the crystallographic c axis, which is compatible with the spin-dimerized state at low temperature. The new model of the two-dimensional hole-ordered structure in the CuO2 plane has been obtained by the BVS calculation. Furthermore, the two-dimensional configuration of the spin dimers has been successfully derived from the hole-ordered structure in the CuO2 plane. It has been concluded that the valences of Cu atoms both in the Cu2O3 ladder and in the CuO2 chain are well controlled by the modulated O atom in the CuO2 chain.
Title:
Width of the critical region at incommensurate phase transitions
Authors:
Wesselinowa, JM; Michel, D; Braeter, H; Plakida, NM; Petersson, J; Volkel, G; Fujino, H;
Source:
PHYSICAL REVIEW B, 68 (22): 2549-2553; 2003
Abstract:
Using the self-consistent phonon theory and the renormalization-group theory we have studied the critical behavior of systems with incommensurately modulated structure and especially the width of the critical region near structural phase transitions, where nonclassical critical exponents are valid. The critical region can be large if the dispersion of the soft mode is small (very "soft" mode) and/or if the anharmonic interaction constant is large. Taking parameters appropriate to rubidium tetrachloro zincate, rubidium tetrabromo zincate, and bis(4-chlorophenyl)sulfone we obtain results which are in good agreement with the experimental data.
Title:
New stable icosahedral quasicrystalline phase in the Sc-Cu-Zn system
Authors:
Lin, QS; Corbett, JD; Vos, M;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 83 (12): 755-762; 2003
Abstract:
Stable icosahedral quasicrystals have been synthesized in the Sc-Cu-Zn system by quench-and-anneal or in - situ filtration methods. These have a composition near Sc-16.2(3) Cu-12.3(3) Zn 71.5(6) at 480degreesC with a quasilattice constant of 4.995 6(7) Angstrom determined by the Elser method from a single-phase Guinier pattern. An electron diffraction study confirms that the icosahedral quasicrystals have a primitive lattice. Cuboctahedral single crystals with dimensions up to 100 mum have been grown by melt-spinning techniques. A cubic approximant phase Sc14.2Cu10.3Zn75.5 (ScCu0.73Zn5.33) with a concordant lattice constant lies nearby.
Title:
Superspace description of NaCa4Nb5O17 (a perovskite-related compound of the type A(n)B(n)O(3n+2)) as a modulated layered structure
Authors:
Elcoro, L; Zuniga, FJ; Perez-Mato, JM; Domagala, J;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 60 (3): 21-31; 2004
Abstract:
The recently determined structure of NaCa4Nb5O17 is reanalyzed within the superspace framework. The material follows the general features of the superspace model proposed for the perovskite-related compounds of the general formula A(n)B(n)O(3n+2) [Elcoro et al. (2001). Acta Cryst. B57, 471-484]. It can be described as a commensurate modulated structure with discontinuous atomic domains given by occupational crenel functions. These atomic domains automatically introduce the layered configuration of the actual structure in real space. However, the displacive modulations follow a quite different pattern from that observed in the Sr-n(Nb,Ti)(n)O3n+2 series, discussed in the above-mentioned reference. The superspace group relevant in this new case has been identified through a systematic search of all the possible groups and a comparison of the resulting superspace embeddings of the experimental three-dimensional structure. Being a commensurate structure, the fundamental ambiguity of the superspace description was broken by choosing the highest possible symmetry that yields smooth displacive atomic modulations and hence minimizes the number of parameters. The efficiency of the proposed superspace model is demonstrated with a new refinement of the structure. Assuming the model's general relevance, symmetry properties for the whole [Ca,Na](n)NbnO3n+2 series are predicted.
Title:
Quininium (R)-mandelate, a structure with large Z ' described as an incommensurately modulated structure in (3+1)-dimensional superspace
Authors:
Schonleber, A; Chapuis, G; Perez-Mato, JM;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 60 (3): 108-120; 2004
Abstract:
Quininium (R)-mandelate, C20H25N2O2+.C8H7O3-, is an organic salt with an incommensurately modulated structure. The superspace approach is required for a precise description of the structure at room temperature. In addition to the main reflections, the diffraction pattern also exhibits higher-order satellite reflections. The large number of first- and second-order satellite reflections with relatively strong intensities indicates a significant modulation. No average structure solution could be obtained on the basis of the main reflections only and hence the structure solution was performed in two suitable superstructure approximations, including satellite intensities. Positional modulation functions and modulation functions for the anisotropic atomic displacement parameters were introduced. The modulation originates from a competition between intramolecular and intermolecular forces, which is reflected, in the superspace formalism, in the modification of hydrogen bonds along the internal space variable t.
Title:
Hydrogen diffusion in partially quasicrystalline Zr69.5Cu12Ni11Al7.5
Authors:
Apih, T; Khare, V; Klanjsek, M; Jeglic, P; Dolinsek, J; Mikami, M;
Source:
PHYSICAL REVIEW B, 68 (21): 71-73; 2003
Abstract:
We report on the direct determination of the hydrogen diffusion constant D in the hydrogen-storage quasicrystalline alloy ZrCuNiAl using the technique of nuclear magnetic resonance diffusion in a static fringe field of a superconducting magnet. The diffusion constant of partially quasicrystalline Zr69.5Cu12Ni11Al7.5 exhibits a significant decrease with increasing hydrogen-to-metal ratio H/M, owing to creation of defects in the lattice during hydrogen loading, whereas the actual alloy structure-the amorphous, icosahedral, or approximant-appears to be less important in the hydrogen diffusivity.
Title:
Evidence for surface compaction in Al-incorporated Al-Pd-Mn quasicrystals
Authors:
Luscher, R; Fluckiger, T; Erbudak, M; Kortan, AR; Dolinsek, J;
Source:
PHYSICAL REVIEW B, 68 (21): 71-73; 2003
Abstract:
The quasicrystalline order at the pentagonal surface of the icosahedral Al-Pd-Mn is monitored by low-energy electron diffraction during the vacuum deposition of aluminum. We find that thick Al layers can readily be diffused into the bulk if the substrate is kept at 770 K, with no measurable changes in the surface quasicrystalline order. In the process, the surface Debye temperature (298 K) increases by more than 100 K suggesting the filling of the vacancy-rich, open-structured pentagonal surface of the Al-Pd-Mn quasicrystal with Al.
Title:
Cluster model of decagonal tilings
Authors:
Reichert, M; Gahler, F; Erbudak, M;
Source:
PHYSICAL REVIEW B, 68 (21): 71-73; 2003
Abstract:
A relaxed version of Gummelt's covering rules for the aperiodic decagon is considered, which produces certain random-tiling-type structures. These structures are precisely characterized, along with their relationships to various other random-tiling ensembles. The relaxed covering rule has a natural realization in terms of a vertex cluster in the Penrose pentagon tiling. Using Monte Carlo simulations, it is shown that the structures obtained by maximizing the density of this cluster are the same as those produced by the corresponding covering rules. The entropy density of the covering ensemble is determined using the entropic sampling algorithm. If the model is extended by an additional coupling between neighboring clusters, perfectly ordered structures are obtained, such as those produced by Gummelt's perfect covering rules.
Title:
Observation of high-temperature thermal vacancies in Al70Pd21Mn9 quasicrystals
Authors:
Sato, K; Baier, F; Rempel, AA; Sprengel, W; Schaefer, HE; Mikami, M;
Source:
PHYSICAL REVIEW B, 68 (21): 71-73; 2003
Abstract:
In quasicrystalline Al70Pd21Mn9, atomic processes as, e.g., thermal vacancy formation are studied specifically by a combination of positron lifetime and two-detector coincident Doppler broadening measurements. Two types of vacancies are detected: structural vacancies with an Al-rich surrounding at relatively low temperatures and thermal vacancies with an Al and transition metal surrounding. The present data of vacancy formation in quasicrystalline Al70Pd21Mn9 are correlated to studies of atomic diffusion and plastic deformation.
Title:
Comment on "Atomic jumps in quasiperiodic Al72.6Ni10.5Co16.9 and related crystalline material"
Authors:
Coddens, G; Musfeldt, JL;
Source:
PHYSICAL REVIEW B, 68 (21): 71-73; 2003
Abstract:
We disagree with a number of statements by Dolinsek [Phys. Rev. B 65, 212203 (2002)] about the specificity of phason dynamics in quasicrystals.
Title:
Reply to "Comment on 'Atomic jumps in quasiperiodic Al72.6Ni10.5Co16.9 and related crystalline material' "
Authors:
Dolinsek, J; Dubois, JM; Olejniczak, I;
Source:
PHYSICAL REVIEW B, 68 (21): 71-73; 2003
Abstract:
We clarify the issues raised in the preceding Comment [Phys. Rev. B 68, 216201 (2003)] on the NMR-observed atomic dynamics in quasicrystals and related crystalline material.
Title:
Spin freezing in icosahedral Tb-Mg-Zn and Tb-Mg-Cd quasicrystals
Authors:
Dolinsek, J; Jaglicic, Z; Sato, TJ; Guo, JQ; Tsai, AP; Hu, A;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (46): 7981-7996; 2003
Abstract:
The nature of spin freezing in geometrically frustrated icosahedral quasicrystals Tb-Mg-Zn and Tb-Mg-Cd was studied by thermoremanent dc magnetization (TRM) decay as a function of aging time and magnetic field. At low temperatures the magnetization exhibits typical broken-ergodicity phenomena, as characteristic of spin glasses (SGs). However, the observed linear dependence of the TRM on the magnetic field in the low-field regime is incompatible with the aging of a nonergodic system in an ultrametrically organized free energy of a SG, but compatible with a single-global minimum free energy of a superparamagnet below the blocking temperature. The Tb-Mg-Zn(Cd) quasicrystals are, from this point of view, different from site-disordered SGs, but similar to geometrically frustrated pure (site-ordered) systems, like the kagome and pyrochlore antiferromagnets, which also exhibit a superparamagnetic component in the magnetization below the spin freezing temperature and clustering of spins. The Tb-Mg-Zn(Cd) quasicrystals show features associated with both the site-disordered SGs and the superparamagnets. This duality is not a specific feature of spins in a quasiperiodic structure, but is found quite commonly in nonrandom (site-ordered) geometrically frustrated magnetic systems.
Title:
Evidence for positronium formation at incommensurate monolayers of argon on graphite
Authors:
Morton, RS; van der Werf, DP; Rice-Evans, P; Guo, JQ;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (50): L771-L776; 2003
Abstract:
Positronium formation has been studied at a graphite surface in the presence of a physisorbed monolayer of argon. In addition to the expected formation when a partial fluid monolayer is present, it is observed that formation is increased when the monolayer becomes an incommensurate solid.
Title:
Thouless and critical regimes in insulating icosahedral AlPdRe ribbons
Authors:
Delahaye, J; Berger, C; Fourcaudot, G; Guo, JQ;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (50): 8753-8766; 2003
Abstract:
We present conductivity measurements of quasicrystalline AlPdRe ribbons in a wide range of temperature (20 mK-300 K), for icosahedral samples spanning a broad resistivity range (R = rho(4) (K) /rho(300) (K) from 2 to 209). We focus here on a detailed analysis of the temperature dependence of the conductivity a (T) for the insulating samples (R > 16). Three successive regimes are revealed as the temperature is increased to 300 K: a low temperature variable range hopping like behaviour, followed by a Thouless regime and a high temperature critical regime. The temperature dependence of the inelastic scattering time found elsewhere by magnetoresi stance data analysis accounts well for the change of curvature in sigma (T) and the trends observed as R varies. The present results point to a similar behaviour between quasicrystalline AlPdRe samples and disordered systems close to the metal-insulator transition, in accordance with our previous analysis of the very low temperature insulating regime and of the finding of conductivity scaling laws.
Title:
Microstructure, fabrication and properties of quasicrystalline Al-Cu-Fe alloys: a review
Authors:
Huttunen-Saarivirta, E; Touboul, M;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 363 (1-2): 150-174; 2004
Abstract:
Quasicrystalline materials constitute a new materials group with certain crystalline structural characteristics, such as the generation of Bragg peaks in the X-ray data and points in the electron diffraction pattern, but translational symmetry is forbidden for crystalline materials. Thus, there exists aperiodicity in the structure of quasicrystalline materials. Besides being theoretically interesting due to their complicated atomic structure, the unique properties of quasicrystalline materials-low electrical and thermal conductivity, unusual optical properties, low surface energy and coefficient of friction, oxidation resistance, biocompatibility and high hardness, to name a few-also make them interesting for many practical purposes. Quasicrystalline phases are today encountered in over 100 alloy systems, of which the majority are aluminium based. Few of the alloying elements used to form aluminium-based quasicrystals are reasonable in price, easily available and non-toxic. However, quasicrystalline Al-Cu-Fe ternary alloys fulfill all these alloying-element criteria. In this paper, the microstructure, fabrication and properties of quasicrystalline Al-Cu-Fe alloys are reviewed from the perspective of materials engineer. The paper discusses the microstructure and metallurgy of quasicrystalline Al-Cu-Fe alloys. The preparation methods of quasicrystals in general and their application to the fabrication of Al-Cu-Fe quasicrystalline alloys are considered. The characteristics of different production methods, including both conventional methods yielding stable phases and more advanced methods introducing metastable phases, are compared in this paper. The properties of Al-Cu-Fe quasicrystals are also reviewed, aiming at a better understanding of the basic differences between crystalline and quasicrystalline materials with respect to structure and properties. Finally current and possible future applications of Al-Cu-Fe quasicrystals are discussed in the light of their pro
Title:
Amorphous-to-quasicrystalline transformation in Zr65Ni10Cu7.5Al7.5Ag10 bulk metallic glass
Authors:
Liu, L; Chan, KC; Nowogrocki, G;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 364 (1-2): 146-155; 2004
Abstract:
Two Zr65Ni10Cu7.5Al7.5Ag10 cast alloys, one fully amorphous and the other partially amorphous, were prepared by copper-mould casting. The phase transformations in the two alloys were investigated by using X-ray diffraction (XRD), differential canning calorimetry (DSC), optical microscopy and scanning electron microscopy (SEM). The DSC trace obtained during continuous heating shows two distinct exothermic reactions in each alloy. The first one corresponds to the formation of a quasicrystalline phase from the amorphous matrix, while the second reaction results from the formation of a supersaturated Zr2Cu-like phase from the previously formed quasicrystals. A shrinkage of the quasicrystal lattice during annealing was observed, which is possibly caused by the relaxation of pre-formed quasicrystals and primarily formation of a little amount of Zr2Cu-like phase along the grain-boundaries of the quasicrystals. The amorphous-to-quasicrystalline transformation kinetics of the two Zr65Ni10Cu7.5Al7.5Ag10 cast alloys was studied by differential scanning calorimetry in the mode of continuous heating and isothermal annealing. The details of the nucleation and growth behaviors during quasicrystallization are discussed in terms of local Avrami exponent. (C) 2003 Elsevier B.V. All rights reserved.
Title:
A study of the phase Mg2Cu6Ga5, isotypic with Mg2Zn11. A route to an icosahedral quasicrystal approximant
Authors:
Lin, QS; Corbett, JD; Nowogrocki, G;
Source:
INORGANIC CHEMISTRY, 42 (26): 8762-8767; 2003
Abstract:
The new title compound was synthesized by high-temperature means and its X-ray structure refined in the cubic space group Pm3, Z = 3, a = 8.278(1) Angstrom. The structure exhibits a 3-D framework made from a Ga-14 and Mg network within which large and small cavities are occupied by centered GaCu12 icosahedral and Cu-6 octahedral clusters, respectively. The clusters are well bonded within the network. Electronic structure calculations show that a pseudogap exists just above the Fermi energy, and nearly all pairwise covalent interactions remain bonding over a range of energy above that point. Analysis suggests that the compound is hypoelectronic with a four-electron deficiency per unit cell, and such a derivative with Sc substituting for Mg is an appropriate quasicrystal approximant (Im3). Such characteristics seem to be key factors in the formation of icosahedral quasicrystals.
Title:
Nanostructure diffusion and aggregation on desorbing rare-gas solids: Slip on an incommensurate lattice
Authors:
Antonov, VN; Palmer, JS; Bhatti, AS; Weaver, JH; Melloch, MR;
Source:
PHYSICAL REVIEW B, 68 (20): 178-188; 2003
Abstract:
Physical vapor deposition of a wide range of materials on rare-gas solids leads to spontaneous cluster formation. Desorption of the rare-gas buffer causes the clusters to aggregate, a process known as buffer-layer-assisted growth. We have studied the extent of aggregation and the size distribution of Au nanostructures as a function of the buffer composition (Xe, Kr, and Ar) and thickness, using transmission electron microscopy to image them after buffer desorption and delivery to amorphous carbon substrates. For small compact Au nanostructures (less than similar to5 nm mean radius, less than or equal to3x10(4) atoms), the diffusivity varies strongly with size and even increases with average size in a limited range. This enhanced diffusion phenomenon is attributed to self-heating during coalescence. It is most important for small particles and is more evident on Kr than on Xe because of weaker interface coupling. In the limit of large ramified Au nanostructures (exceeding similar to10 nm mean radius, greater than or equal to2x10(5) atoms), the diffusivity scales as the inverse of the contact area, in agreement with molecular dynamics simulations of fast slip diffusion of nanocrystals on incommensurate surfaces. Motion is driven by phonons of the cluster and substrate, and is controlled by friction between a cluster facet and the buffer surface. A simple model is proposed that explains the observed exponential dependence of cluster size on buffer thickness. In this model, the growth kinetics are controlled by competition between the rate of cluster diffusion and the rate of buffer depletion.
Title:
Transport properties of icosahedral Al70Pd22.5Re7.5 quasicrystals
Authors:
Kuo, YK; Lai, JR; Huang, CH; Lue, CS; Lin, ST; Kulda, J;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (44): 7555-7561; 2003
Abstract:
We report the electrical and thermal transport properties, including electric resistivity (rho), Seebeck coefficient (S) and thermal conductivity (kappa) Of icosahedral Al70Pd22.5Re7.5 quasicrystals in the temperature range between 10 and 300 K. Four Al70Pd22.5Re7.5 samples with a resistivity ratio R = rho4.2 K/rho300 K ranging from 10.2 to 84.4 were studied. The temperature-dependent resistivities increase with decreasing temperature for all samples, exhibiting a semiconductor-like behaviour. The Seebeck coefficients are positive for the large-R samples (R = 26.3 and 84.4) in the entire temperature range, while S-values become negative for the small-R samples (T = 10.2 and 19.4) below about 120 K. The significant dependence on 91 of the Seebeck coefficient can be qualitatively understood in the pseudogap scenario. The temperature variation of the thermal conductivity for these materials is quite similar, with values less than 2.5 W m(-1) K-1 in the temperature range we investigated. The dimensionless thermoelectric figure of merit (ZT) of this system is estimated to be two orders of magnitude smaller than that of conventional thermoelectric materials.
Title:
Charge density determination in icosahedral AlPdMn quasicrystal using quantitative convergent beam electron diffraction
Authors:
Yu, F; Zou, HM; Wang, JB; Wang, RH;
Source:
MICRON, 35 (6): 411-418; 2004
Abstract:
Charge density distribution in icosahedral AlPdMn quasicrystal has been studied on a single-crystal specimen by using quantitative convergent beam electron diffraction (QCBED) technique. The QCBED systematic row method was used in the refinement of structure factors. To refine the low-order structure factors, the wave-mechanical formulation of electron diffraction dynamical theory was used in the calculation of electron diffraction intensities for the quasicrystal in fitting the experimental intensity line scan profiles. The shapes of atomic surfaces (occupation domains) were described with symmetry-adapted series of surface harmonics. An iterative procedure was used in determination of structure factors of the quasicrystal. The structure factors of nine strongest symmetry inequivalent reflections according to X-ray diffraction experiment were refined with QCBED technique. The average of refinement results for a given reflection performed on several CBED patterns, which were slightly different in orientation and sample thickness, and on different line scans, was taken as the value of structure factor for the reflection. The obtained structure factors for electrons were transformed into X-ray structure factors with Mott formula. The bonding charge density map for the quasicrystal was constructed with the obtained nine structure factors. Assuming that the atoms are spheres, the gain or loss of electrons for different atoms were calculated. It shows that identical atoms can have different valences at different kinds of positions. The bonding charge is localized along certain directions. (C) 2004 Elsevier Ltd. All rights reserved.
Title:
Composition dependence on the martensitic structures of the Mn-rich NiMnGa alloys
Authors:
Jiang, CB; Muhammad, Y; Deng, LF; Wu, W; Xu, HB; Clausen, KN;
Source:
ACTA MATERIALIA, 52 (9): 2779-2785; 2004
Abstract:
The Mn-rich Ni50Mn25-xGa25-x (x = 0-5) alloys were developed to investigate the structural transitions and magnetic properties. Structural transitions from austenite to 5M, 7M, and non-modulated martensite were observed with the increase of Mn content. The lattice parameter a elongates, as where b and c contract, and the unit cell volume reduces with increasing Mn content. The martensitic transformation start temperatures M-s increase monotonically from 10.7 degreesC for x = 2 to 102.7 degreesC for x = 5. The saturation magnetization was measured at 5 K. where all the samples exhibit a martensitic structure. The average magnetic moments per Mn atom vary from 4.38 mu(B) to 2.93 mu(B) for x = 0 to x = 5. The negative effect of excess Mn atoms changes from -3.00 mu(B) for x = 2 to -7.25 mu(B) for x = 5. The excess Mn atoms modify the electronic structures of the unsubstituted Mn atoms, resulting ill the sharp decrease of the magnetic moments of the unsubstituted Mn atoms with increasing Mn content. Structural incommensurability was observed with TM for powder and non-modulated for bulk samper in a specific range of compositions and proved to be reversible when performing martensitic transformation. The 7M and non-modulated martensites Ni50Mn30Ga20 possess similar saturation magnetizations and Curie temperatures. The non-modulated martensite was estimated to have a lower free energy than 7M, and should be more stable for a reverse martensitic transformation, leading to a higher austenite start temperature A,, which is consistent with the experimental result. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
NMR line shape analysis in the incommensurate phase of bis(4-chlorophenyl)sulfone
Authors:
Taye, A; Michel, D; Deng, LF;
Source:
PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 241 (6): 1333-1342; 2004
Abstract:
High quality single BCPS crystals were used to study the influence of a structurally incommensurate (IC) modulation on the line shape in Cl-35 NMR spectra where the phase transition from the normal into the IC phase at ca. 150 K is clearly reflected in the appearance of an asymmetric frequency distribution with edge singularities. The line shape calculations are performed in a temperature range where the validity of the plane wave limit may be assumed. In nice agreement with an X-ray analysis of the rotational symmetry modes in the IC phase by Zuniga et al., the evaluation of the Cl-35 NMR frequency distributions is based on the IC modulation of the Euler angles which describe the orientation of Cl-35 NMR quadrupole coupling tensor in the crystal frame. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Title:
Defectiveness of two-subgrain Al-Cu-Co single quasicrystals in vicinity of subgrain boundary
Authors:
Bogdanowicz, W; Michel, D;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 372 (1-2): 91-97; 2004
Abstract:
Two-subgrain single quasicrystals of a decagonal phase of the Al-Cu-Co alloy were studied by means of X-ray diffractometry and X-ray topography. The full width at half maximum (FWHM) of the 00002 X-ray reflection, in vicinity of the subgrain boundary, was determined. The measurements were carried out at different distances from the boundary. The relation of the FWHM versus the distance from the subgrain boundary was called the FWHM linear distribution. These distributions were determined for the "as grown" single quasicrystals, after their thermal treatment at 100degreesC and after the subsequent treatment at 900degreesC. From the distribution analysis it was concluded that the annealing at 100degreesC causes certain defects to spread from the subgrain boundary towards the subgrain inner areas. The direction of the defect spreading tallied with the direction of the 10-fold symmetry axis. Change of the linear distributions after the treatment at 900degreesC were discussed in the relation to the change of the domain structure and rotation of the subgrains in relation to one another. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Corrosion behaviour of Al-Cu-Fe alloys containing a quasicrystalline phase
Authors:
Huttunen-Saarivirta, E; Tiainen, T; Deng, LF;
Source:
MATERIALS CHEMISTRY AND PHYSICS, 85 (2-3): 383-395; 2004
Abstract:
Corrosion of quasicrystalline and related crystalline phases coexisting in Al-Cu-Fe alloys with the compositions of Al60Cu27.5Fe12.5, Al62.5Cu25Fe12.5, Al65Cu20Fe15 and Al67.5Cu20Fe12.5 was studied in saline, acidic, neutral and basic solutions. The corrosion behaviour of the alloys was explored by potentiodynamic polarisation experiments, while the microstructural studies by X-ray diffraction and scanning electron microscopy yielded information on the phase structure and its changes as a result of the polarisation experiments. The results of the study indicated that the composition and relative amount of phases present in Al-Cu-Fe alloys are the key parameters defining the corrosion behaviour of the alloy. In saline solutions, the corrosion potentials were in the range where a homogeneous dissolution of the alloy, followed by a redeposition of Cu, took place, the corrosion rate being mainly determined by the amount of Cu-rich phases present in the structure. In acidic solutions, the Cu-rich phases remained untouched by corrosion, whereas phases containing less Cu were susceptible to corrosion. In neutral and basic solutions, oxidation was the primary surface reaction. However, Cu was found to introduce pores into the oxide layer and Fe to inhibit the oxidation process. Therefore, in neutral and basic solutions, the quasicrystalline phase, with intermittent Cu and Fe contents with respect to other phases present in the AI-Cu-Fe alloys studied, showed the best corrosion performance. (C) 2004 Elsevier B.V. All rights reserved.
Title:
NMR study of S=1/2 quasi-two-dimensional antiferromagnet Cs2CuBr4
Authors:
Fujii, Y; Nakamura, T; Kikuchi, H; Chiba, M; Goto, T; Matsubara, S; Kodama, K; Takigawa, M; McMorrow, DF;
Source:
PHYSICA B-CONDENSED MATTER, 346 (2-3): 45-49; 2004
Abstract:
(113) Cs-NMR experiments on the S = 1/2 quasi-two-dimensional antiferromagnet CS2CuBr4 have been performed up to magnetic fields of 15.9 T, which covers the field range for the 1/3 magnetization plateau. Outside the plateau region, the 3 NMR spectrum at T = 0.5 K shows a double-horn type broad line shape characteristic of an incommensurate spin structure. On the other hand, discrete two peaks were observed in the plateau phase, indicating a commensurate up-up-down spin structure. The nuclear spin-lattice relaxation rate T-1(-1) for commensurate phase decreases much more steeply with decreasing temperature than that for incommensurate phase, which indicates the different low lying excitations of the two phases. Experimental results in the paramagnetic phase are also discussed. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Study of the conductivity of thin quasicrystalline films and its relation with the electronic friction
Authors:
Landauro, CV; Janssen, T; Kikuchi, H;
Source:
PHYSICA B-CONDENSED MATTER, 348 (1-4): 459-464; 2004
Abstract:
In the present work, we study the conductivity of thin quasi crystalline films employing a modeled spectral conductivity that contains generic properties of the quasicrystal. The variation of the conductivity with the thickness of the sample is also discussed. We investigate possible consequences for the electronic contribution to the friction coefficient. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Synchrotron X-ray studies of phason and phonon strains in a Co-rich Al-Ni-Co decagonal quasicrystal
Authors:
Yamamoto, K; Yang, W; Nishimura, Y; Ikeda, N; Matsuo, Y; Shek, CH;
Source:
MATERIALS TRANSACTIONS, 45 (4): 1255-1260; 2004
Abstract:
Peak broadening and peak shifts of Bragg reflections were studied with the synchrotron single-crystal X-ray diffraction method for an Al72.7Ni8.5Co18.8 decagonal quasicrystal classified as the 5f state. From the Q(perpendicular to) and Q(parallel to) dependences of the full width of half maximum (FWHM) of the Bragg reflections along the longitudinal direction, the coexistence of random phason strains with phonon strains was observed. High-resolution synchrotron X-ray measurements Could present quantitative estimations of these strains. The value of the random phason strain component is 0.0054 similar to tau(-11). The asymmetrical broadening due to the phonon strain shows that the single crystal may be constructed with two kinds of grains that have A(5D) values of 0.6273 and 0.6265 nm.
Title:
Internal friction studies by resonant ultrasound spectroscopy
Authors:
Leisure, RG; Foster, K; Hightower, JE; Agosta, DS; Matsuo, Y;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 370 (1-2): 34-40; 2004
Abstract:
A description is given of the use of resonant ultrasound spectroscopy (RUS) to study internal friction in solids. The technique is applicable to a wide range of sample sizes and shapes. A method to extract the internal friction from the RUS spectrum in the presence of a coherent background signal is discussed. RUS has been used to study the internal friction due to hydrogen motion in hydrogen-metal materials. A comparison is made of internal friction due to hydrogen motion in a C15 Laves-phase intermetallic compound with that in a quasicrystalline material. The internal friction peak in the quasicrystalline material is much broader, probably reflecting a distribution of local environments for the hydrogen in this material. A low-temperature, internal friction peak due to deuterium motion in TaV2D0.17 is discussed. This peak was shown previously to result from a rapid local motion of D on a hexagon of interstitial g sites. A novel explanation is proposed for the temperature dependence of this peak. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Mechanical spectroscopy of hydrogen-absorbing quasicrystals
Authors:
Sinning, HR; Scarfone, R; Golovin, IS; Agosta, DS;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 370 (1-2): 78-82; 2004
Abstract:
The H-induced damping peak in icosahedral quasicrystals, generally attributed to a Snoek-type reorientation mechanism, was studied in comparison between Zr69.5Cu12Ni11Al7.5 and Ti53Zr27Ni20 using the vibrating-reed technique. Whereas the peak in ZT(69.5)CU(12)Ni(12)Al(7.5) is practically the same as in the amorphous phase (in accordance with icosahedral short-range order in metallic glasses), significant differences in shape and position of the peak are found between the two quasicrystalline alloys. These might possibly be used as a probe to distinguish between icosahedral structure types. Another interesting result is a higher intrinsic damping of quasicrystalline Zr69.5Cu12Ni11Al7.5, compared to the amorphous phase, between 450 and 650 K. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Mechanical spectroscopy of Al-Cu-Fe quasicrystalline coatings
Authors:
Fikar, J; Schaller, R; Baluc, N; Agosta, DS;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 370 (1-2): 524-530; 2004
Abstract:
Since the bulk Al-Cu-Fe quasicrystals are extremely brittle below 700 K, a quasicrystalline coating deposited on a steel substrate by thermal spraying was used for mechanical spectroscopy measurements at temperatures in the range of 300-800 K. The internal friction of this composite was measured in a forced torsion pendulum and the internal friction of the quasicrystalline coating itself was calculated. An internal friction maximum was observed around 600 K in isochronal measurements at 1 Hz, which is not present in isothermal measurements. This maximum may be associated with the relaxation of the thermal stresses built at the interface between the substrate and the coating. These stresses are also responsible for an anomalous increase of the shear modulus with temperature. The high temperature exponential background is interpreted as the brittle-to-ductile transition in the quasicrystalline coating. (C) 2003 Published by Elsevier B.V.
Title:
Incommensurate structure and the superconducting properties of the organic superconductor (MDT-ST)(I-3)(0.417)
Authors:
Kawamoto, T; Mori, T; Terashima, T; Uji, S; Kitagawa, H; Takimiya, K; Takamori, A; Otsubo, T; McMorrow, DF;
Source:
JOURNAL DE PHYSIQUE IV, 114 (3-4): 517-519; 2004
Abstract:
The charge-transfer degree and the superconducting properties of the organic superconductor (MDT-ST)I1+delta have been studied [MDT-ST: 5H-2-(1,3-dithiol-2-ylidene)-1,3-diselena-4,6-dithiapentalene]. The Raman spectrum and the x-ray oscillation photograph show that the polyiodide chain is composed of I-3(.), which is incommensurate to the donor lattice. The chemical composition is determined to be (MDT-ST)(I-3)(0.417). The upper critical fields are within the Clogston-Chandrasekhar paramagnetic limit in all directions, and the coherence lengths are longer than the thickness of the conducting sheet.
Title:
Low-temperature paramagnetism of AlCuFe quasicrystals
Authors:
Shchegolikhina, NI; Kuz'min, NY; Prekul, AF; Hawthorne, FC;
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 97 (4): 352-357; 2004
Abstract:
The magnetic properties of the Al62Cu25.5Fe12.5 alloy in different structural states (from asquenched disordered state to single-phase quasicrystalline state) that were obtained by various heat treatments have been studied. The concentrations of magnetically active-paramagnetic and magnetically ordered-iron atoms were determined from the Curie constant (C-CW) and spontaneous magnetization (I-s) curves, respectively. The Curie constant was determined from the temperature dependences of the magnetic susceptibility that follows the Curie-Weiss law. It was shown that changes in the concentration of iron atoms correlate with changes in the residual electrical conductivity sigma(0), which is determined by the concentration of free charge carriers. The strong dependence of the low-temperature paramagnetism of the Al-Cu-Fe alloys on the lattice perfection is due to the fact that the unpaired spins of iron atoms are formed only in the presence of local lattice distortions of the icosahedral phase.
Title:
Simulation studies of atomic resolution X-ray holography
Authors:
Kashyap, Y; Sarkar, PS; Sinha, A; Godwal, BK; Bassereau, P;
Source:
BULLETIN OF MATERIALS SCIENCE, 27 (1): 79-84; 2004
Abstract:
X-ray holography is a new method of structure determination based on measurement of interference of a known reference wave with an unknown object wave (containing information on atomic sites scattering the reference wave) so that phase information is preserved. Unlike X-ray diffraction, it does not demand for translational periodicity in the material. It is based on the idea similar to that of optical holography and has been tested on crystals, quasicrystals, thin films and doped semiconductors for their structure determination. In order to analyse potentials and limitations of this technique, we have carried out theoretical simulation studies on simple structures. In this paper we describe the basic algorithm of hologram generation and reconstruction of atomic positions from generated data. We illustrate this technique using Fe (bcc) single crystal as sample case to demonstrate its capabilities and limitations. Simulations were carried out on the Cu (fcc) structure and on complex structure such as the Al-Pd-Mn quasicrystal. Technical issues such as low signal to noise ratio, twin image problem etc have been discussed briefly to emphasize the need for high intensity X-ray source such as synchrotron for experiments and proper reconstruction algorithm. Finally the scope and potential of this technique have been discussed.
Title:
Synthesis of nano-quasierystalline decagonal phase
Authors:
Yadav, TP; Mukhopadhyay, NK; Srivastava, ON; Potekaev, AI;
Source:
INDIAN JOURNAL OF PHYSICS AND PROCEEDINGS OF THE INDIAN ASSOCIATION FOR THE CULTIVATION OF SCIENCE-PART A, 78A (2): 189-191; 2004
Abstract:
Al-Co-Ni system exhibits the existence of a stable decagonal phase with various degrees of order in periodic and quasiperiodic planes. Now it is a routine technique to grow macron to cm size rods of the decagonal phase by slow cooling technique. There are attempts to develop nano scale microstructure by various non-equilibrium processing techniques. The aim of the present investigation is to employ mechanical milling (MM) technique for the synthesis of the nano decagonals phases. The alloy ingots have been prepared by melting the constituent pure metals in the induction furnace, and then crushed to around 200 mesh size, as a starting material in the attritor. The milling was performed at 400 rpm under hexane medium with a ball : charge ratio as 20 : 1. During the course of milling, the disordering has been noticed from the broadening of the peaks and lowering of the peak height in the X-ray diffraction patterns. Milled powder after 40 h showed the diffraction peaks confirming the evolution of nano-D phase. The size aspects and the phase constituents has further been confirmed by the transmission electron microscopic investigation. The composition of the as-cast ingot and the milled powder has been analyzed by EDX.
Title:
Microstructure of tensile fracture in nanoicosahedral quasicrystal dispersed Zr80Pt20 amorphous alloy
Authors:
Saida, J; Inoue, A; Mao, BW;
Source:
SCRIPTA MATERIALIA, 50 (10): 1297-1301; 2004
Abstract:
The tensile fracture structure in the as-quenched Zr80Pt20 alloy hardened by the homogeneously precipitation of nanoicosahedral phase is investigated by high-resolution transmission electron microscopic observation. The evidence which indicates that the tensile fracture occurs in the residual amorphous phase in the intergranular region, is obtained in the nanocomposite alloy consisting of icosahedral and amorphous phases. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
The evolution of the antiferromagnetic structure of the terbium titanium oxysulfide Tb2Ti2S2O5 between 5K and 1.4K
Authors:
Lafond, A; Leynaud, O; Andre, G; Bouree, F; Caldes, M; Meerschaut, A; Takamori, A;
Source:
EUROPEAN POWDER DIFFRACTION EPDIC 8, 443-4 (2): 387-390; 2004
Abstract:
The Tb2Ti2S2O5 compound belongs to the lanthanide titanium oxysulfides family Ln(2)Ti(2)S(2)O(5). The 3D-structure can be schematically described as a 2D-stacking of [Tb2S2] layers alternating with [Ti2O5] ones. The magnetic structure of this compound was determined from neutron diffraction experiments on a powder sample in the 1.4 K - 15 K temperature range. An incommensurate antiferromagnetic long-range order (LRO) occurs at temperatures ranging from 4.1 K to 2.9 K, which turns to a commensurate state below 2.4 K. The evolution of the propagation vector from (k) over right arrow (i)(k(x)0,0), k(x) approximate to 0.46 to (k) over right arrow (c)(1/2,0,1/2) is quite unusual. The origin of this unusual change in direction of the propagation vector is not yet explained. On the other hand, a quite large part of the total magnetic moment is involved in a short range ordering (SRO). The refinement procedure taking into account the different coexisting magnetic phases leads to a smooth variation of the total magnetic moment versus temperature.
Title:
Temperature dependence of lattice parameters in martensite and effect of the external magnetic field on martensite structure in Ni2MnGa studied in situ with neutron diffraction
Authors:
Glavatska, N; Mogylnyy, G; Danilkin, S; Hohlwein, D; Caldes, M;
Source:
EUROPEAN POWDER DIFFRACTION EPDIC 8, 443-4 (2): 397-400; 2004
Abstract:
The crystal structure of Ni1.99Mn1.14Ga0.87 single-crystal that exhibits large magnetic field induced strain in the martensitic phase is studied by neutron diffraction within temperature range 300K-4K. The 5-layered modulated structure is observed within the whole temperature interval and no another martensitic transformations occur. The anisotropic change of the martensite lattice parameters during cooling from 300K down to 4K is found. The combined change in the a- and clattice parameters affects change of the (c/a) ratio in martensite with cooling down by 2.32%. Redistribution of twin martensitic variants in the external magnetic field is studied in-situ at temperatures 98K-296K.
Title:
Interpretation of the Hume-Rothery rule in complex electron compounds: gamma-phase Cu5Zn8 alloy, FK-type Al30Mg40Zn30 and MI-type Al68Cu7Ru17Si8 1/1-1/1-1/1 approximants
Authors:
Mizutani, U; Takeuchi, T; Sato, H; Hohlwein, D;
Source:
PROGRESS IN MATERIALS SCIENCE, 49 (3-4): 227-261; 2004
Abstract:
The Hume-Rothery matching rule 2k(F)=K-hktl has been theoretically investigated by performing the LMTO-ASA (Linear Muffin-Tin Orbital-Atomic Sphere Approximation) band calculations for the three electron compounds: the gamma-phase Cu5Zn8 compound or gamma-brass, the nearly-free-electron-like Frank-Kasper-type Al30Mg40Zn30 1/1-1/1-1/1 approximant and the Mackay-Icosahedral-type Al68Cu7Ru17Si8 1/1-1/1-1/1 approximant. The zone planes responsible for the formation of the pseudogap across the Fermi level are identified. In the free-electron-like Al-Mg-Zn approximant, the Fermi surface-Brillouin zone interaction participating in the Hume-Rothery matching rule solely gives rise to a sizable pseudogap at the Fermi level. In the case of the gamma-brass and the Al-Cu-Ru-Si approximant, where d-states are involved in the middle of the valence band, we could demonstrate that the particular Fermi surface-Brillouin zone interactions are strongly coupled with the sp-d hybridization to produce a deep pseudogap across the Fermi level. (C) 2003 Elsevier Ltd. All rights reserved.
Title:
The study of ZnMgSc quasicrystal and Zn17SC3 approximant by positron annihilation lifetime
Authors:
Arinuma, K; Takagiwa, Y; Kanazawa, I; Tamura, R; Takeuchi, S; Meerschaut, A;
Source:
POSITRON ANNIHILATION, ICPA-13, PROCEEDINGS, 445-4 (3-4): 39-41; 2004
Abstract:
We have measured positron annihilation lifetime spectra and discuss the first shell of atomic cluster in quasicrystal Zn-Mg-Sc and the approximant crystal Zn17Sc3 by comparing with Cd-Yb icosahedral quasicrystals and the approximant crystal Cd6Yb. These measurements suggested that vacancy-like open space might exist around the first shell of atomic cluster.
Title:
Precipitation of the icosahedral quasicrystalline phase, R-phase and Laves phase in ferritic alloys
Authors:
Yamamoto, K; Kimura, Y; Mishima, Y; Tamura, R;
Source:
MATERIALS TRANSACTIONS, 45 (2): 357-360; 2004
Abstract:
Precipitation behavior of intermetallic phases in ferrite matrix is investigated by transmission electron microscopy (TEM) in Fe-10Cr-1.4W-4.5Co (at%) alloys with and without 0.3 at%Si. It is intended to provide basic information for the alloy design of ferritic heat resistant alloys strengthened by intermetallic compounds. In the alloy containing Si, icosahedral quasicrytalline phase (I-phase) is found to precipitate during aging at 873 K. It is confirmed that selected area diffraction (SAD) patterns of the precipitates exhibit two-, three- and five-fold symmetry and have diffraction spots in the positions related to the golden section. In the Si-free alloy, the R-phase precipitates instead of I-phase at 873 K, and the Laves phase precipitates in both alloys during aging at higher temperature, 973 K. The Laves phase formed at 973 K transforms to the I-phase in the alloy containing Si but to the R-phase in the Si-free alloy during subsequent aging at 873 K. It is found that the structures among icosahedral quasicrystalline and crystalline R- and Laves phases are closely similar by comparing the orientation relationship, precipitate morphology and stability of I-phase with those of R- and Laves phases.
Title:
Estimation of thermal expansion properties of quasicrystalline alloys
Authors:
Qi, YH; Zhang, ZP; Hei, ZK; Sakakibara, A;
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 14 (1): 152-155; 2004
Abstract:
By investigating the thermal expansion properties of three quasi crystalline alloys Al65Cu20Cr15 quenched, Al65Cu20Cr15 cast and Al65Cu20Fe15 cast particles reinforced Al matrix composites from 25degreesC to 500degreesC, the thermal expansion coefficients of three quasicrystalline alloys were theoretically estimated. The results show that the thermal expansion coefficients of the composites are much lower than that of pure At, and the thermal expansion coefficients of the composites reinforced by Al-Cu-Cr quasicrystalline particles are lower than those of the composites reinforced by Al-Cu-Fe quasicrystalline particles. According to estimating, quasicrystalline alloys have negative thermal expansion coefficients 9 and the thermal expansion coefficients of Al-Cu-Cr quasicrystalline alloys are tower than those of Al-Cu-Fe quasicrystalline alloys. In the alloys, the more the qusicrystalline content, the lower the thermal expansion coefficient.
Title:
Nonadditivity of properties and the possibility of formation of ensembles of incommensurate structures in the GaSe-Ga2Se3 system
Authors:
Zavrazhnov, AY; Turchen, DN; Dobrokhotova, ZV; Volkov, VV; Makhonina, EV; Pervov, VS; Takamori, A;
Source:
INORGANIC MATERIALS, 40 (2): 107-114; 2004
Abstract:
The GaSe-Ga2Se3 system is studied by x-ray diffraction, electron microscopy, and differential scanning. calorimetry. The results demonstrate that the nonadditivity of heat capacity observed near the eutectic composition after quenching is similar to the nonadditivity of properties in misfit layer compounds, which con tain incommensurate structural components. The origin of this similarity is discussed in terms of the self-organization of interacting incommensurate elements in the melt and the formation of unstable suprastructural ensembles.
Title:
Unconventional superconductivity and magnetism in Sr2RuO4 and related materials
Authors:
Eremin, I; Manske, D; Ovchinnikov, SG; Annett, JF; Makhonina, EV;
Source:
ANNALEN DER PHYSIK, 13 (3): 149-174; 2004
Abstract:
We review the normal and superconducting state properties of the unconventional triplet superconductor Sr2RuO4 with an emphasis on the analysis of the magnetic susceptibility and the role played by strong electronic correlations. In particular, we show that the magnetic activity arises from the itinerant electrons in the Ru d-orbitals and a strong magnetic anisotropy occurs (chi(+-) < chi(zz)) due to spin-orbit coupling. The latter results mainly from different values of the g-factor for the transverse and longitudinal components of the spin susceptibility (i.e. the matrix elements differ). Most importantly, this anisotropy and the presence of incommensurate antiferromagnetic and ferromagnetic fluctuations have strong consequences for the symmetry of the superconducting order parameter. In particular, reviewing spin fluctuation-induced Cooper-pairing scenario in application to Sr2RuO4 we show how p-wave Cooper-pairing with line nodes between neighboring RuO2-planes may occur. We also discuss the open issues in Sr2RuO4 like the influence of magnetic and non-magnetic impurities on the superconducting and normal state of Sr2Ru4. It is clear that the physics of triplet superconductivity in Sr2RuO4 is still far from being understood completely and remains to be analyzed more in more detail. It is of interest to apply the theory also to superconductivity in heavy-fermion systems exhibiting spin fluctuations. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Title:
New group of stable icosahedral quasicrystals: structural properties and formation conditions
Authors:
Ishimasa, T; Kaneko, Y; Kaneko, H; Wittke, O;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 1-7; 2004
Abstract:
Structural studies on the icosahedral quasicrystals in Zn-Mg-Sc, Cu-Ga-Mg-Sc, and Zn-Mg-Ti alloys as well as their corresponding 1/1 cubic approximants, have revealed that these quasicrystals belong to a new structural group similar to Cd-based quasicrystals. This group is characterized by a triple-shell icosahedral cluster different from both Mackay- and Bergman-types. The presence of the atomic cluster has been deduced from the structure model of the approximant crystal, Zn17SC3, in which the clusters are embedded in a periodic network of so-called 'glue atoms'. Density measurement suggested the presence of at least 2.7 Zn atoms in the first shell of the cluster in this approximant. The substitutional relationship in these three quasicrystals indicates the important role of Hume-Rothery rule for the formation of this type of quasicrystal. The occurrence of a P-type icosahedral quasicrystal in Zn-Mg-Yb alloy is also reported. (C) 2004 Elsevier B.V. All rights reserved.
Title:
The formation condition of a stable Cu-Ga-Mg-Sc icosahedral quasicrystal
Authors:
Kaneko, Y; Maezawa, R; Ishimasa, T; Wittke, O;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 8-11; 2004
Abstract:
The formation condition and the stability of the Cu-Ga-Mg-Sc icosahedral quasicrystal have been investigated in terms of the effects of Mg concentration and long time annealing. An addition of a few percent of Mg to the Cu3.7Ga2.3Sc-type cubic approximant causes the formation of an icosahedral quasicrystal. This quasicrystal is formed near the alloy composition of Cu48Ga34Mg3Sc15, and is regarded as a thermodynamically stable phase since the amount of the icosahedral quasicrystal in the alloy increased by annealing at 770 degreesC. The structural quality of the quasicrystal was also improved by this annealing, and this improvement is related to the elimination or the reduction of quenched-in phason strains. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Formation of quasicrystalline phases in Al-rich Al-Mn-Be alloys
Authors:
Chang, HJ; Fleury, E; Song, GS; Kim, WT; Kim, DH; Aliev, VP;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 12-16; 2004
Abstract:
The effect of Be addition on the formation of quasicrystalline phases in Al-rich Al-Mn(-Be) alloys has been investigated. A metastable icosahedral quasicrystalline phase was found to form in a 93.5Al-5Mn-1.5Be (in wt%) alloy prepared by a conventional casting technique, indicating that the addition of Be to Al-Mn alloys improves the quasicrystal forming ability. The icosahedral phase in conventionally cast Al-Mn-Be alloys forms in the undercooled melt with the equilibrium growth morphology of the pentagonal dodecahedron. Heat treatment at 540 degreesC for 100 h results in the precipitation of small platelets of a two-dimensional quasiperiodic phase in the alpha-Al matrix. These precipitates have an orientation relationship with the a-Al. matrix. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Hume-Rothery controlled formation of structurally complex alloy phases in the ternary Ga-Mg-Pd system
Authors:
Kreiner, G; Moguilnikov, Y; Burkhardt, U; Schapers, M; Kim, DH;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 17-22; 2004
Abstract:
The Hume-Rothery rule has been used as a guide to search for new approximants of the Mackay icosahedron and Bergman cluster type in the Ga-Mg-Pd system. Ternary alloys with target compositions close to the e/a ratios 1.67 and 2.09 were synthesized by melting the elements and subsequent annealing in sealed tantalum ampoules. Six new intermetallic phases have been characterized: a cubic face-centered Mackay icosahedron approximant Gal(15-x-y)Mg(38+y)Pd(13+x) a rhombohedral Mackay icosahedron approximant Ga30-xMg32+xPd21, a cubic Bergman cluster approximant Ga12+x+yMg11-yPd6-x, a cubic phase with interpenetrating I3 and Frank-Kasper networks Ga32.6Mg43.4Pd29, an ordered ternary variant of the NiTi2 structure type GaMg3Pd2 and a ternary Laves phase. The e/a ratios for the approximants with Mackay icosahedra or Bergman clusters show a strong experimental correlation indicating that the valence electron concentration is an important factor concerning the stability of the phases. The approximant phases exist over a wide range of composition. The structure of the rhombohedral phase is based on the geometry of the canonical cell tiling CB2C. The results support the proposal by Henley and Mihalkovic on the geometrical structures of Mackay icosahedron-type quasicrystals in ternary systems with one transition and two main group metals. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Influence of alloying on the formation of Zr-based quasicrystals
Authors:
Khare, V; Janlewing, R; Zander, D; Jastrow, L; Lyubenova, L; Koster, U; Takamori, A;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 23-28; 2004
Abstract:
Glassy Zr-Cu-Ni-Al precursor alloys exhibit quasicrystal forming ability in a narrow concentration range via isothermal heating. The formation of quasicrystals has been explained by various arguments. Often, they are considered as Hume-Rothery phases, atomic size or bond strength dependent structures, or a hybrid structure built from Al2Cu- and MoSi2-type structural units. The aim of the present investigation is to find out the influence of alloying on quasicrystal formation using transmission electron microscopy and X-ray diffraction. Small addition of elements such as Sit or Mo was found to change the phase selection during the early stages of crystallization significantly. Substitution with Sri, having the same oxidation state, leads to the formation of the icosahedral phase. On the other hand, substitution with Mo, having a higher oxidation state, leads to the formation of the fcc big cube phase. However, in the present investigation substitution of atoms bigger than Zr such as Y or Ce leads to very easy formation of quasicrystals even at lower temperatures. Si, on the other hand, which is smaller than Zr leads to the formation of the tetragonal Zr2Ni phase. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Effect of Cu substitution in Al-Co-Ni decagonal quasicrystals
Authors:
Yadav, TP; Tiwari, RS; Srivastava, ON; Jastrow, L;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 39-43; 2004
Abstract:
A stable decagonal phase has been observed in both as-cast and rapidly solidified Al-Co-Ni and AI-Co-Cu alloys, which form in the composition range of 15-20 at.% Co and 10-15 at.% Ni or 15-20 at.% Cu. In the present investigation, copper was substituted for Co and Ni in Al70Co15Ni15. Compositions corresponding to Al70Co15-xCuxNi15 and Al70Co15CuxNi15-x were investigated. It is found that when the copper concentration reaches a value of 5 at.%, the disorder marker, i.e. the streaking along the 111, 113 rows becomes predominant. For Al70Co15-xCuxNi15, when all of the Co is replaced by Cu, the decagonal phase disappears and the only phase observed is the vacancy ordered phase. In Al70Co15CuxNi15-x when the Cu concentration reaches a value of 10 at.%, the decagonal and crystalline phases coexist. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Synthesis of (Al65Cu20Fe15)(100-x)Si-x quasicrystalline alloys by mechanical alloying
Authors:
Murty, BS; Barua, P; Srinivas, V; Schurack, F; Eckert, J; Koster, U;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 44-47; 2004
Abstract:
The effect of Si on the quasicrystalline phase formation in (Al65Cu20Fe15)(100-x)Si-x alloys by mechanical alloying has been investigated. The study indicates that mechanical alloying improves the quasicrystalline phase forming ability in comparison to rapid solidification processing by widening the range of e/a ratio over which the icosahedral phase can be obtained. This range can further be enhanced by the addition of Si. In addition, Si improves the thermal stability of the quasicrystalline phase. The quasi-crystals observed in the present study are in the nanocrystalline state. No amorphization has been observed even up to 15 at.% Si. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Stability of quasicrystalline phase in Al-Cu-Fe, Al-Cu-Co and Al-Pd-Mn systems by high energy ball milling
Authors:
Murty, BS; Rao, RVK; Mukhopadhyay, NK; Schurack, F;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 48-51; 2004
Abstract:
The stability of the quasicrystalline phase present in as-cast Al65Cu20Fe15, Al65Cu20Co15 and Al72Pd19.5Mn8.5 alloys during high energy ball milling and on subsequent annealing has been studied. The synthesis and stability of the quasicrystalline phase prepared by mechanical alloying of Al65Cu20Fe15, Al70Cu20Fe10 and Al65Cu20Co15 alloys has also been studied. In all the cases, the quasicrystalline phase is unstable with long hours of milling and transforms to the beta-phase (bcc phase), which is stable on further milling and on subsequent annealing up to 1073 K. The quasicrystalline to P-phase transformation appears to occur for grain sizes below 20 nm. (C) 2004 Elsevier B.V. All rights reserved.
Title:
High energy ball milling of a Al65Cu20Fe15 quasicrystalline alloy
Authors:
Mukhopadhyay, NK; Kurup, V; Srivastava, VC; Joshi, PB; Mandal, RK; Koster, U;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 52-56; 2004
Abstract:
The phase transformations of the quasicrystals and related crystalline phases present in an Al65Cu20Fe15 alloy were studied by high energy ball milling. The milling was carried out in an attritor mill at speeds of 200 and 400 rpm for 5, 10, 20 and 40 h with a ball to charge ratio of 20:1, using hexane as a process control agent. As-cast and milled samples were annealed at 500 degreesC for 7 days. All of the specimens were characterized by optical, scanning, X-ray diffraction and differential thermal analysis. The sample compositions were determined by energy dispersive X-ray analysis and electron spectroscopy for chemical analysis. The results of the present investigation are discussed in light of the current understanding of the phase stability in complex systems. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Synthesis of nano-quasicrystalline Al70Ni15Co15 decagonal phase through high energy ball milling
Authors:
Yadav, TP; Mukhopadhyay, NK; Srivastava, ON; Joshi, PB;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 57-61; 2004
Abstract:
In the present investigation we have synthesized the nano-decagonal phase by mechanical milling of a pre-alloyed Al70Co15Ni15 decagonal phase. The milling was performed at a speed of 400 rpm for 5, 10, 20 and 40 h under a hexane medium with a ball: charge ratio 20:1. The nano-phase constituents were confirmed by X-ray diffraction and transmission electron microscopy techniques. The stability of the nano-D phase in the milled powder was also investigated under various annealing treatments. After 10 h milling, the evolution of the nano-decagonal phase was observed. This nano-phase was found to be stable up to 40 It of milling. The milled powder after 40 h of milling confirms the existence of a nano-decagonal phase. The particle size of the milled powder was similar to10-15 nm. An isothermal heat treatment of the milled sample at 500 degreesC for 10 h still shows the existence of the nano-decagonal phase, although a coarsening of the nano-domain has been observed. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Random cluster covering model
Authors:
Gummelt, P; Mukhopadhyay, NK;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 62-67; 2004
Abstract:
The unit-cluster approach describing quasicrystalline structures by a single unit with possible 'fat' overlaps has mainly been worked out for the ideal case of perfect order. A general concept for corresponding random covering ensembles is still missing. As a natural framework, we introduce an 'overlap-version' of the well-known random tiling model in terms of relaxed cluster matching rules. We illustrate our method by a relaxed decagon determining a covering ensemble with positive configurational entropy. We characterize this coverings using equivalent underlying Penrose-type tilings, which form Hexagon-Boat-Star (HBS)-supertilings. Given an HBS-supertiling, we describe the effect of so-called bow-tie flips on corresponding decagon coverings. (C) 2004 Elsevier B.V. All rights reserved.
Title:
'Cluster-disordered glue' model for icosahedral quasicrystals
Authors:
Chidambaram, R; Mukhopadhyay, NK;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 68-70; 2004
Abstract:
A model for icosahedral quasicrystals is proposed, in which clusters become nearly perfect in the sense of having fivefold symmetry and the atoms in the glue region tend to become disordered. There is only a subtle rearrangement of atoms between the quasicrystalline phase and the related - existing or possible - crystalline phase. This model is consistent not only with diffraction data, but also with the results of positron annihilation and other non-diffraction experiments. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Constructing a dodecagonal structure by projection in two stages
Authors:
Ben-Abraham, SI; Lerer, Y; Snapir, Y; Joshi, PB;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 71-76; 2004
Abstract:
Decagonal and octagonal tilings can be covered by a single cluster but two clusters are needed to guarantee a quasiperiodic dodecagonal structure. This might be due to the extra freedom when projecting from 6D to 2D. To elucidate this issue, we projected a 6D simple cubic lattice into 3D so that further projection to 2D might yield a dodecagonal structure. A 6D cube projects into a 3D (non-Keplerian) triacontahedron with symmetry 3m. The final result is a layer structure quasiperiodic in the basal plane and periodic in the perpendicular direction. The point symmetry of the structure is only 3m but it does show characteristic dodecagonal features. The plane pattern has symmetry 6m. It supports some well-known dodecagonal tilings, such as the square-triangle tiling. Some tilings appear to be periodic, the quasiperiodicity being hidden in the changing decoration. Physically the structure should be interpreted as a packing of dodecagonal prisms. Mathematically it is best to consider the point set as such. The structure has many surprising features that call for further study. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Tile Hamiltonians for decagonal phases
Authors:
Widom, M; Al-Lehyani, I; Mihalkovic, M; Joshi, PB;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 86-90; 2004
Abstract:
A tile Hamiltonian (TH) replaces the actual atomic interactions in a quasicrystal with effective interactions between and within tiles. We study Al-Co-Ni and Al-Co-Cu decagonal quasicrystals described as decorated hexagon-boat-star (HBS) tiles using ab initio methods. A dominant term in the TH counts the number of H, B and S tiles, favoring tilings of H and B only. In our model for Al-Co-Cu, chemical ordering of Cu and Co along tile edges defines tile edge arrowing. Unlike the edge arrowing of Penrose matching rules, however, the energetics for Al-Co Cu do not force quasiperiodicity. Energetically favored structures resemble crystalline approximants to which the actual quasicrystalline compounds transform at low temperature. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Anomalous quantum diffusion in two- and three-dimensional generalized Rauzy tilings
Authors:
Triozon, F; Vidal, J; Mosseri, R; Mayou, D; Mandal, RK;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 91-95; 2004
Abstract:
We compute the quantum diffusion of electron wavepackets in two- and three-dimensional quasiperiodic structures: the generalized Rauzy tilings. The algorithm allows us to treat systems of more than one million sites, and to consider energy-filtered wavepackets. We show that the anomalous diffusion exponent, beta, depends on the energy, and that the propagation is almost ballistic at band edges (beta similar or equal to 1). This study is completed by exact diagonalizations of small clusters. The results strongly suggest that band-edge eigenstates are extended, which is consistent with their ballistic propagation. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Average unit cell of a square Fibonacci tiling
Authors:
Urban, G; Wolny, J; Mosseri, R;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 105-109; 2004
Abstract:
Square Fibonacci tiling is an example of a quasicrystalline structure with classical crystallographic 4-fold symmetry. Using a probabilistic approach, an average unit cell has been constructed in physical space. This allows one to calculate the diffraction patterns in different directions. The projected structure into different directions can be also regarded as decorated Fibonacci chain. The diffraction pattern of the square Fibonacci chain has been fully analyzed in the average unit cell approach. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Two-dimensional quasicrystals and their unit cells (elliptical or Gaussian approximations)
Authors:
Wolny, J; Kozakowski, B; Mosseri, R;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 110-113; 2004
Abstract:
In this paper the average unit cell was constructed by a statistical approach and approximated either by elliptically shaped or Gaussian distributions. These approximations were successfully applied to diffraction analysis of the imperfect structures based on Penrose tiling. In the Gaussian approximation the simple analytical expressions for the structure factor were also derived. Elliptical and Gaussian approximations describe well the diffraction patterns of 2D quasicrystals. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Cluster-disordered glue model and role of glue atoms in the icosahedral quasicrystalline structure
Authors:
Godwal, BK; Rao, RS; Chidambaram, R; Mayou, D;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 117-120; 2004
Abstract:
We adopt first principles methods for Zn-Mg clusters (related to AI-Zn-Mg quasicrystals) to estimate the energy cost for disorder in the glue region by giving small displacements to only the glue atoms, while keeping the atoms in the icosahedral cages frozen at the ideal icosahedral positions. We compare these estimates of cluster calculations with the energy changes for a structural transition in solids, and find that the glue region disorder costs at least an order of magnitude less energy. These results support the proposition of the cluster-disordered glue model, that the glue region in a quasicrystal may be disordered. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Electronic structure of the octagonal tiling
Authors:
Zijlstra, ES; Rao, RS;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 126-129; 2004
Abstract:
An s-band model on the octagonal tiling is studied. The matching rules, the inflation rules, and the standard approximants are reviewed. It is shown that in the approximants the matching rules are only slightly violated. Therefore electronic properties, e.g., the density of states (DOS), converge very fast w.r.t. the approximant size N, e.g., Delta(DOS) proportional to N-2. In the low kinetic-energy limit the electronic properties of the model are dominated by a one-dimensional aperiodic substitution chain. The Hamiltonian of this chain is given and spectral and transport properties are studied. It is shown that the support of the measure decreases as a power of the approximant size N. The conductance through a macroscopic cell (l similar to 0.2 mm) is shown to be finite. In the presence of a small random on-site potential (W = 0.01) the system becomes insulating. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Quasiperiodic tilings in a magnetic field
Authors:
Vidal, J; Mosseri, R; Chidambaram, R;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 130-136; 2004
Abstract:
We study the electronic properties of a two-dimensional quasiperiodic tiling, the isometric generalized Rauzy tiling, embedded in a magnetic field. Its energy spectrum is computed in a tight-binding approach using the recursion method. As for the square lattice, a rich band structure is obtained when the magnetic flux per elementary plaquette is varied. Then, we study the quantum dynamics of wave packets and discuss the influence of the magnetic field on the diffusion and spectral exponents. We show that contrary to the zero field case where the propagation is faster in a periodic structure than in a quasiperiodic one, the diffusion exponent may be larger in the Rauzy tiling than in the square lattice for some incommensurate fluxes. Finally, we consider a quasiperiodic superconducting wire network with the same geometry and we determine the critical temperature as a function of the magnetic field. A non-trivial cusp-like structure arises that reveals the real importance of the quasiperiodic order. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Quasicrystal structure analysis, a never-ending story?
Authors:
Steurer, W; Mosseri, R;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 137-142; 2004
Abstract:
Quasicrystal structure analysis comprises the determination on an atomic scale of both the short-range order (SRO) and long-range-order (LRO). SRO mainly refers to the atomic arrangement inside a cluster (i.e. a recurrent structural building unit), LRO to the ordering of the clusters themselves. The LRO of periodic structures can definitely be described by one of the 14 Bravais lattice types. In the case of quasicrystals, there is a choice of infinitely many different strictly quasiperiodic atomic arrangements, not to mention other types of aperiodic structures. Consequently, due to limited experimental information quasicrystal structures can only be solved approximately. In the case of a few decagonal and icosahedral phases the combined effort of mainly electron microscopic and diffraction methods conveyed an idea about the structure of clusters and their way of long-range ordering. However, we are still far away from the type of quantitative structure analysis as a function of temperature and pressure needed to answer the fundamental questions about the formation, structure and stability of quasicrystals. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Structure refinement of i-Al-Pd-Re quasicrystals by synchrotron radiation data
Authors:
Yamamoto, A; Takakura, H; Ozeki, T; Tsai, AP; Ohashi, Y; Koster, U;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 151-155; 2004
Abstract:
A structure of an icosahedral Al-Pd-Re (i-Al-Pd-Re) quasicrystal analyzed by using an imaging plate Weissenberg camera and synchrotron radiation is reported for the first time. An initial model for the refinement has been determined by the low-density elimination method (LDEM). The electron density in six-dimensional space showed that this phase is isostructural to i-Al-Pd-Mn, and its Re sites correspond to the Mn sites in the latter. The structure refinement gave an R-factor of 0.076 for 1312 independent reflections. Some atoms are shifted significantly from their ideal positions and some atom sites in i-Al-Pd-Mn are unoccupied. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Crystal structure of a 2/1 cubic approximant in an Al-Rh-Si alloy
Authors:
Sugiyama, K; Sun, W; Hiraga, K; Tsai, AP;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 156-160; 2004
Abstract:
The structure of a cubic Al66.5Rh26.1 Si-7.3 phase, which is referred as a 2/1 approximant for an icosahedral phase, was determined by means of single crystal X-ray structural analysis: space group Pm3, a = 19.935(2) Angstrom, Mo Kalpha (lambda = 0.71069 Angstrom); refined as Al70.4Rh29.6, R(wR2) = 0.087(0.194) for 1391 reflections with I > 2.0sigma (I). A dodecahedral atom cluster is located at the origin of a unit cell, and the corresponding atomic arrangement can be described as nine shells with a local icosahedral symmetry, by suggesting a close similarity to the dodecahedral atomic cluster of the 2/1-AlPdMnSi approximant. The 2/1-AlRhSi approximant is a second example of a simple cubic arrangement of dodecahedral atom clusters that are 20 Angstrom in diameter. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Structure of the Al65Rh27Si8 2/1-2/1-2/1 approximant
Authors:
Takeuchi, T; Koshikawa, N; Abe, E; Kato, K; Mizutani, U; Koster, U;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 161-166; 2004
Abstract:
Atomic arrangements in the thermodynamically stable Al65Rh27Si8 2/1-2/1-2/1 approximant were determined by means of synchrotron radiation Rietveld analysis. It was found that the Al65Rh27Si8 2/1-2/1-2/1 approximant possesses a cubic unit cell containing 564 atoms. We found that the atomic structure of this approximant is characterized by a CsCl-type structure with a large icosahedral atomic cluster of 19.76 Angstrom and a small icosahedral cluster of 6.8 Angstrom in diameter. The presence of chemical and structure disordering between (Al, Si) and Rh was also found in the structure as well as in the Mackay-type 1/1-1/1-1/1 approximants. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Structure analysis of Zn-Mg-Ho icosahedral quasicrystal by modified Rietveld method using ellipsoid and sphere windows
Authors:
Ishimasa, T; Oyamada, K; Arichika, Y; Nishibori, E; Takata, M; Sakata, M; Kato, K; Otsubo, T;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 167-172; 2004
Abstract:
A structure analysis of the Zn-Mg-Ho icosahedral quasicrystal was carried out by the powder X-ray diffraction method using synchrotron radiation (lambda = 0.73490 Angstrom) at SPring-8. The intensity distribution was analyzed by the Rietveld method modified for an icosahedral quasicrystal, in which simplified models were assumed: ellipsoid and spherical windows were assumed at five crystallographic sites in a F-type hypercubic unit cell. The analysis revealed the presence of an almost perfect Penrose tiling with edge length 5.20 Angstrom. The vertices are occupied alternatively by Zn and Mg, and almost all of the edge centers of the Penrose rhombohedra are occupied by 0.8Zn and 0.2Mg. Ho and Mg atoms tend to be present on the body diagonal of the prolate rhombobedra. Good agreement between the measured and calculated intensity distribution using the simplified model suggests the applicability and the limitation of the structure analysis using the powder X-ray diffraction method. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Combined energy-diffraction data refinement of decagonal AlNiCo
Authors:
Mihalkovic, M; Henley, CL; Widom, M; Nishibori, E;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 177-183; 2004
Abstract:
We incorporate realistic pair-potential energies directly into a non-linear least-square fit of diffraction data to quantitatively compare structure models with experimental data for the Ni-rich d(AlNiCo) quasicrystal. The initial structure models are derived from a few a priori assumptions (gross features of the Patterson function) and the pair-potentials. In place of the common hyperspace approach to the structure refinement of quasicrystals, we use a real-space tile-decoration scheme, which does not rely on strict quasiperiodicity, and makes it easy to enforce sensible local arrangements of the atoms. Inclusion of the energies provides information complementary to the diffraction data and protects the fit procedure from converging on spurious solutions. The method pinpoints sites that are likely to break the symmetry of their local environment. (C) 2004 Elsevier B.V. All rights reserved.
Title:
A new basis for the classification of quasicrystals
Authors:
Jeevan, HS; Ranganathan, S; Widom, M;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 184-189; 2004
Abstract:
The traditional basis for the classification of quasicrystals has been the majority constituent element, and thus Al-, Ga-, Ti-, Zr-, Hf-, Zn-, Cd- and Cu-based quasicrystals have been analyzed in the literature. Occasionally, when two elements are present in comparable proportions, they have been termed as Ti-Zr-, Zn-Mg-, Cd-Mg- and Ag-In-based quasicrystals. We propose a new classification of quasicrystals on the basis of atomic size to recognize the dominant role of the large size atoms in forming the icosahedral phases. We propose a classification of quasicrystals as centered on Li-, Mg-, Al-, Ga-, Ca-, Sc-, Y-, Ti-, Zr-, Hf- and rare-earth elements, as they are the largest atoms in the constituent quasicrystals. The term centered is used to indicate the central importance of this element, even though compositionwise it may not be the majority constituent. The usefulness of Pettifor maps in this context will be illustrated and extended by treating several ternary and quaternary quasicrystals as pseudo-binaries. (C) 2004 Published by Elsevier B.V.
Title:
Direct imaging of icosahedral clusters in a cubic Cd6Ca approximant crystal
Authors:
Abe, E; Tsai, AP; Widom, M;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 190-193; 2004
Abstract:
The structure of a cubic Cd6Ca crystal, which is constructed by a bee packing of multiple-shell icosahedral atomic clusters and regarded as a 1/1 approximant to a binary Cd5.7Ca icosahedral quasicrystal, has been investigated using atomic-resolution annular dark-field scanning transmission electron microscopy (ADF-STEM). Direct imaging of the projected icosahedral clusters reveals no significant ADF-contrast around the cluster center, suggesting that the Cd atoms at the core of the cluster are not located at definite position such as the cubic atomic sites proposed by X-ray analysis, but distributed in a significantly disordered manner. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Al-Ni-Ru icosahedral quasicrystal and coexisting decagonal quasicrystals with 0.4 nm periodicity, studied by atomic-resolution electron microscopy observations
Authors:
Sun, W; Hiraga, K; Widom, M;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 194-197; 2004
Abstract:
As-cast and rapidly solidified alloys with compositions of Al70-xNi25+xRu5 (x = 0, 5, 10 and 15) and Al70+yNi20-yRu10 (y = 0 and 5) were examined by transmission electron microscopy. The results show that the Al-Ni-Ru icosahedral quasicrystal, which belongs to the F-type class, and the decagonal quasicrystal with a 0.4 nm periodicity can coexist in both the as-cast and rapidly solidified states. By means of high-resolution electron microscopy observations, the structural features of the as-cast Al-Ni-Ru icosahedral quasicrystal and the coexisting decagonal quasicrystal, with basic quasiperiodic order, were revealed. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Decagonal structure of Al72Ni20Co8 studied by atomic-resolution electron microscopy
Authors:
Abe, E; Tsai, AP; Widom, M;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 198-201; 2004
Abstract:
We study the atomic structure of an Al72Ni20Co8 decagonal quasicrystal by a complementary use of conventional high-resolution transmission electron microscopy (HRTEM) and annular dark-field scanning transmission electron microscopy (ADF-STEM). The chemical ordering of the structure is derived from atomic-resolution ADF-STEM with Z-contrast (Z is the atomic number), highlighting the heavy atom positions. Details on the total atomic arrangements, including the relatively light constituent elements, are examined by HRTEM with phase contrast. The present results demonstrate that a combination of HAADF-STEM and HRTEM is quite powerful for complicated intermetallic structures, enabling a reliable structural analysis to be made based on electron microscopy. (C) 2004 Elsevier B.V. All rights reserved.
Title:
ALCHEMI study of an S1-type superlattice-ordered decagonal quasicrystal of Al70Ni18Co12
Authors:
Saitoh, K; Tanaka, M; Tsai, AP; Nishibori, E;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 202-206; 2004
Abstract:
Electron channeling patterns, which display the intensity variation of characteristic X-ray emission as a function of incident beam orientation, have been taken from an S1-type superlattice-ordered decagonal quasicrystal of Al70Ni18Co12, which shows diffuse streaks on and halfway between Bragg spot layers perpendicular to the decagonal direction in the electron diffraction patterns. The channeling patterns show that Al atoms and transition metals occupy different sublattice sites, and that both Ni and Co atoms randomly occupy the same sublattice sites, that is, they are disordered. This indicates that the origin of the diffuse streaks is not related to a chemical order between Ni and Co, but is caused only by a topological order, such as a small displacement of atoms. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Phase equilibrium in the vicinity of the Al-Ni-Ru decagonal phase
Authors:
Mi, S; Grushko, B; Dong, C; Urban, K; Takata, M;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 214-217; 2004
Abstract:
The Al-rich part of the Al-Ni-Ru phase diagram was re-investigated with respect to the existence of stable quasicrystalline phases. The thermodynamic stability of the ternary decagonal phase with a 1.6 nm periodicity was confirmed in a small compositional range around Al73.1Ni15.7Ru11.2 and at temperatures below 1050degreesC. The partial 900degreesC isothermal section of Al-Ni-Ru is presented. Apart from the decagonal phase, two ternary crystalline compounds are stable at this temperature. The results are compared to those in Al-Ni-Fe. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Structural changes of Ni-rich Al-Co-Ni decagonal quasicrystals
Authors:
Saito, K; Sun, W; Ohsuna, T; Hiraga, K; Takata, M;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 218-222; 2004
Abstract:
The phase relationship among three Al-Co-Ni decagonal quasicrystals in a Ni-rich decagonal phase, and their phase changes, have been studied by electron diffraction and high-resolution transmission electron microscopy, as well as thermal analysis. At 1173 K, the so-called Ni-rich basic decagonal quasicrystal exists in a Ni-rich region from Al72Co8Ni20 to Al70Co10Ni20, and transforms into the S1-type ordered decagonal quasicrystal in Al71Co10Ni19. The Ni-rich basic decagonal quasicrystal at 1173 K in Al72Co8Ni20 transforms into the S1-type decagonal quasicrystal by annealing at 923 K, whereas the S1-type quasicrystal at 1173 K in Al71Co10Ni19 alloy transforms into the type-I ordered decagonal quasicrystal by annealing at 923 K. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Quasicrystals in the Ti-Zr-Ni alloy system
Authors:
Qiang, JB; Wang, YM; Wang, DH; Kramer, M; Thiel, P; Dong, C; Kato, K;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 223-227; 2004
Abstract:
The empirical compositional criteria for ternary quasicrystals (QCs) based on the QCs' phase diagram features are applied in the Ti-Zr-Ni alloy system. The ideal quasicrystals-forming composition Ti40Zr40Ni20 has been identified, which lies at the crossing point of the two specific lines, termed as e/a-constant and e/a-variant lines. Bulk quasicrystalline Ti/Zr-based alloys are obtained in region of (TixZr100-y)(100-y)Ni-y (43.75 less than or equal to x less than or equal to 81.25, y = 17, 20 in at.%) by copper mold casting. It was confirmed that Ti40Zr40Ni20 is the optimal QC-forming composition, where a nearly pure bulk quasicrystal rod, 6 mm in diameter, can be formed. With a small deviation from this ideal composition, the Ti(Zr) solid solution phases and/or C14-type Laves phase, though as minority phases, are found coexisting with the majority icosahedral phase. At the same time, the explanation of the e/a-variant line is explored. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Phase stability of Cd-Y-Yb quasicrystal and 1/1-1/1-1/1 approximant
Authors:
Takahashi, H; Takeuchi, T; Mizutani, U; Guo, JQ; Tsai, AP; Dong, C;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 228-233; 2004
Abstract:
The formation range of the Cd-Y-Yb 1/1-1/1-1/1 approximant was determined and its atomic structure was investigated in detail by applying the Rietveld analysis to the powder X-ray diffraction data. The ternary Cd-Y-Yb 1/1-1/1-1/1 approximant is found to be formed only along a unique composition line connecting Cd85.7Yb14.3 and Cd84Y16, where a decrease in the Cd concentration from 85.7 to 84 at.% accompanies an increase in the Y concentration from 0 to 16 at.% and, in turn, an increase in nominal electron concentration e/a from 2.0 to 2.16. This is seemingly at variance with the Hume-Rothery rule which states that the approximant tends to be stabilized along a constant e/a line. However, the present structure analysis clearly showed an increase in the number of vacancies per unit cell with increasing e/a. As a result, the number of valence electrons per unit cell N-u is found to be kept constant at 338.0 +/- 2.0. From this we conclude that the ternary Cd-Y-Yb 1/1-1/1-1/1 approximant is formed in accordance with the Hume-Rothery matching rule, which must be restated such that N-u should be employed in place of e/a when the number of vacancies changes with composition. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Role of planar defects and their energies in periodic to quasiperiodic transformations - a Monte Carlo simulation
Authors:
Kulkarni, UD; Takeuchi, T;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 238-242; 2004
Abstract:
The initial stages of continuous periodic to quasiperiodic transitions are often characterized by the occurrence of two-dimensional defects (faults or antiphase boundaries) in the periodic structures. Considerable experimental as well as theoretical support exists in favor of such transitions in the cases of the beta-Mn to octagonal quasicrystal, the sigma-phase to dodecagonal quasicrystal, and the Al5Ti3 or Al11Ti7 phase to a quasiperiodic superlattice structure. The energy of the relevant planar defects is thus expected to play a vital role in these transitions. Monte Carlo simulations involving a continuous change in the antiphase boundary energy were carried out here to probe the atomic structures of the intermediate stages of the periodic to quasiperiodic superlattice transition observed in Al-rich TiAl intermetallics. The results of the simulation explain the observed changes in the electron diffraction patterns and bring out the salient features of the atomic arrangements in the imperfectly ordered near quasiperiodic structures encountered in the transition. (C) 2004 Elsevier B.V. All rights reserved.
Title:
High pressure Mossbauer studies of stable quasicrystal Al63.5Cu24Fe12.5
Authors:
Gupta, A; Paul, N; Vijaykumar, V; Godwal, BK; Tsai, AP;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 243-246; 2004
Abstract:
The effect of high pressure on the short-range order in the stable Al63.5Cu24Fe12.5 quasicrystal has been studied using Mossbauer spectroscopy. In agreement with the earlier studies, the system shows no structural transition up to the highest pressure of 24.2 GPa used in the present study. Variations in both the isomer shift (IS) and the quadrupole splitting (QS) of two non-equivalent iron sites with pressure suggest changes in the short-range order in the system. A linear variation of IS with pressure can be understood in terms of the compressibility of the structure around the Fe atoms. An increase in the quadrupole splitting with pressure suggests that in addition to the compression, a distortion of the local arrangement of Al atoms around an Fe atom also takes place. At 24.2 GPa, the Mossbauer lines exhibit significant broadening, indicating an increase in the static disorder in the system with pressure. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Hydrogen induced transformations in Zr-Cu-Ni-Al quasicrystals
Authors:
Zander, D; Koster, U; Khare, V; Godwal, BK;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 247-252; 2004
Abstract:
Zr-based quasicrystalline alloys can store hydrogen up to a content close to the highest value known for crystalline materials, but there are questions regarding their structural stability during hydrogen charging. Hydrogenation of Zr69.5Cu12Ni11Al7.5 quasicrystals was observed to increase the (quasi-)lattice constant, but at higher contents also to cause microstructural changes, as indicated by the weakening of the contrast of the quasicrystals in transmission electron microscopy as well as a disappearance of the weak diffraction spots in the corresponding diffraction pattern. A more detailed investigation reveals the formation of approximants at hydrogen contents above H/M = 0.4 and a variation in the order of approximants from lower to higher order with increasing amount of hydrogen. In addition, amorphization was observed starting with the nucleation and growth of amorphous hydrides at the interfaces between approximants and the amorphous matrix. The reason for arnorphization might be the change in the ratio e/a and/or the expansion of the quasilattice above a critical value. Pd coating can hinder the formation of ZrO2 layers, thus allowing not only faster hydrogen absorption, but also hydrogen desorption. However, only partial desorption occurred prior to the decomposition of the quasicrystalline phase. Only hydrogenation up to about H/M = 0.4, probably below the content necessary for the formation of approximants, seems to be fully reversible. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Crystallization of liquids and glasses to quasicrystals
Authors:
Kelton, KF; Koster, U;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 253-258; 2004
Abstract:
The local structures of metallic glasses and undercooled liquid metal alloys are presumed to contain a high degree of icosahedral short-range order, incompatible with translational periodicity and creating a barrier to the nucleation of crystal phases. The barrier should be lower for the nucleation of icosahedral quasicrystals (i-phase). A brief overview is provided of studies in liquids and glasses that support this conclusion. Recent X-ray diffraction and undercooling results in a TiZrNi alloy that forms an i-phase are presented, correlating an icosahedral local order in the liquid with a lower nucleation barrier for the i-phase. For a growing number of alloys that can be prepared as glasses, a nanosized i-phase microstructure forms upon glass crystallization (devitrification), consistent with the expected low nucleation barrier. However, since glasses that do not form quasicrystals have similar devitrification nanostructures, other crystallization mechanisms must also be operative. These are reviewed. A new model for homogeneous nucleation that couples the interfacial and the long-range diffusion fluxes, is advanced as one way to explain nanostructure formation in these metallic glasses. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Meta-stable quasicrystal formation in vitrified and solid state synthesized amorphous Zr-based alloys
Authors:
Sordelet, DJ; Rozhkova, E; Besser, MF; Kramer, MJ; Tsai, AP;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 263-269; 2004
Abstract:
Amorphous Zr70Pd30, Zr70Pd20Cu10, Zr80Pt20, Zr70Pt20Cu10, and Zr57Ti8Nb2.5Cu3.9Ni1.1Al7.5 alloys were prepared by melt spinning and mechanical milling to compare their devitrification behaviors. The melt-spun ribbons transform from an amorphous structure to a meta-stable quasicrystalline phase. This amorphous-to-quasicrystalline transition is not observed in amorphous powders obtained by mechanical milling. Since the mechanical milling process does not involve direct liquid phase formation of an amorphous structure, it is inferred that in the absence of the short-range order obtained directly from the liquid, meta-stable quasicrystalline phase formation is not energetically favored in these Zr-based metallic glasses. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Phason-elastic energy in a model quasicrystal
Authors:
Koschella, U; Gahler, F; Roth, J; Trebin, HR; Tsai, AP;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 276-279; 2004
Abstract:
The standard two-dimensional decagonal binary tiling quasicrystal with Lennard-Jones potentials is metastable at zero temperature with respect to one phason strain mode. By calculating the frequencies of local environments as a function of phason strain, a correction for the potentials is predicted, which stabilizes the quasicrystal. (C) 2004 Elsevier B.V. All rights reserved.
Title:
NMR methods for detection of slow atomic motions in quasicrystals
Authors:
Dolinsek, J; Apih, T; Jeglic, P; Klanjsek, M; Tsai, AP;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 280-286; 2004
Abstract:
We present NMR techniques for the detection of slow, low-activation-energy, diffusive atomic motion in quasicrystals, within the frequency window from several 10 kHz down to the milli-Hz region. The techniques involve two-dimensional exchange NMR experiments, the diffusion-induced decay of the Hahn spin echo in an inhomogeneous electric field gradient and the Carr-Purcell echo-train experiment. These techniques were applied to the icosahedral AlPdRe and decagonal AlNiCo quasicrystals and to the,vacancy-ordered' periodic AlCuNi phase. In all compounds we detected slow, low-activation-energy, diffusive atomic jumps that persist down to low and very low temperatures. Identical motions were detected also in the periodic AlCuNi alloy, suggesting that the observed atomic dynamics are not quasicrystal-specific. (C) 2004 Elsevier B.V. All rights reserved.
Title:
A comparative study of the atomic dynamics of icosahedral and decagonal ZnMgY
Authors:
Suck, JB; Scheffer, M; Sterzel, R; Klanjsek, M;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 291-294; 2004
Abstract:
A comparative investigation of the atomic dynamics of an icosahedral and a decagonal quasicrystal from the same alloy family, here the ZnMgRE/Y Frank-Kasper type of quasicrystals, has been performed for the first time. The i- and d-alloy were studied at 296 and 200 K, respectively at the ISIS neutron spallation source (UK) in a large region of energy and momentum transfers using neutron inelastic scattering (NIS). The quantitative comparisons of the single particle dynamics of the two ZnMgY samples via the generalized vibrational density of states shows a considerable difference in the intensity of the sub-bands constituting the main energy bands, but only small shifts of these bands and subbands in energy. We attribute the differences observed in the single particle dynamics more to differences in the short range structure of decagonal and icosahedral ZnMgY, leading to a stronger grouping of the local density of the states in the case of the decagonal alloy, than to their different aperiodic long range order. (C) 2004 Published by Elsevier B.V.
Title:
Thermal phason fluctuation in an Al-Cu-Co decagonal quasicrystal
Authors:
Edagawa, K; Suzuki, K; Mandal, P; Takeuchi, S; Tsai, AP;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 298-302; 2004
Abstract:
In situ high-temperature, high-resolution transmission electron microscopy (HRTEM) has been performed on an Al-Cu-Co decagonal quasicrystal, to investigate thermal phason fluctuations. The changing tiling pattern with elapsed time in the HRTEM image has been analyzed, and the spatial and temporal variations of the phason field have been deduced. In the temporal variation, abrupt and discrete changes have been observed in addition to smooth and continuous ones. The degrees of the spatial and temporal correlations of the phason fluctuation have been evaluated, both of which decrease continuously with increasing distance and time, respectively. The results have been discussed in light of the random tiling model of the quasicrystal. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Atomic dynamics in decagonal Al-Ni-Co quasicrystals
Authors:
Gahler, F; Hocker, S; Mandal, P;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 308-311; 2004
Abstract:
The atomic dynamics of decagonal Al-Ni-Co quasicrystals are investigated by molecular dynamics simulations. The model structures used consist of an alternating stacking of two layers, which are decorations of a hexagon-boat-star tiling. Apart from small relaxations, these model structures are essentially stable up to the melting point. Above two thirds of the melting temperature, a large fraction of the aluminium atoms becomes mobile, and long-range atomic diffusion sets in, without destroying the overall structure. The diffusion of aluminium is analyzed as a function of temperature and pressure, and the microscopic diffusion processes are discussed. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Micro-surface and bulk thermal behavior of a single-grain decagonal Al-Ni-Co quasicrystal
Authors:
Barrow, JA; Lemieux, MC; Cook, BA; Ross, AR; Tsukruk, VV; Canfield, PC; Sordelet, DJ; Otsubo, T;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 312-316; 2004
Abstract:
Scanning thermal microscopy is used to examine the thermal behavior of specific surfaces of a similar to0.8 cm(3) single-grain Al74Ni10Co16 decagonal quasicrystal. The response of a micro-thermal probe in contact with aperiodic and periodic surfaces in air reveals the anisotropic heat flow of the decagonal structure. Heat dissipation with the probe on the aperiodic surface is higher than when the probe is on the periodic surface. While the SThM technique is generally considered to be constrained to the surface region below the nominally 2-5 mum probe tip radius, the heat flow data obtained are clearly comprised of contributions from both the lateral surface around the probe tip and a volume normal to the surface in contact. Heat flow in the decagonal Al74Ni10Co16 quasicrystal can be modeled by an elliptical distribution of thermal diffusion. Parameters for the model used in this study were obtained by making bulk thermal diflusivity measurements using the laser flash method on specimens along the 2- and 10-fold directions. The model was applied to a surface oriented 45degrees to the major axes and verified from bulk measurements obtained from a sample cut along this orientation. (C) 2004 Elsevier B.V. All rights reserved.
Title:
A test of Hume-Rothery rules for stable quasicrystals
Authors:
Tsai, AP; Lemieux, MC;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 317-322; 2004
Abstract:
The stability of the icosahedral quasicrystals has been studied in terms of Hume-Rothery rules i.e., atomic size factor, electronegativity and valence electron concentration. It has been confirmed that most of the stable quasicrystals can be understood within the frame work of the Hurne-Rothery rules. Even more interestingly, it is found that stable quasicrystals are strict electron compounds, which only form at sharp valence electron concentration. All of the stable quasicrystals commonly have the corresponding valence electron concentration, but the dependence of stability on the atomic size factor is different among the groups. Qualitatively, the most relevant criterion for the formation of stable quasicrystals is that the alloy should have a definite valence electron concentration. On top of this, a high stability of the quasicrystal is observed when the atomic size factor is favored. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Electronic structure of quasicrystalline compounds
Authors:
Belin-Ferre, E; Lemieux, MC;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 323-330; 2004
Abstract:
Theoretical as well as many experimental means have been used to investigate the electronic structures of quasicrystalline compounds. In icosahedral quasicrystalline compounds a pseudo-gap at the Fermi level exists that is also present even at the surface. Its formation involves a Hume-Rothery stabilization mechanism and also Al-transition metal hybridization effects. The specific atomic arrangement in a hierarchy of interpenetrating clusters may also be invoked to participate in the formation of this pseudogap. For Al based decagonal quasicrystals containing transition metals, the d-d interaction is such that there is no pseudo-gap in the total density of states whereas it still exists in the Al sub-bands. The electronic states in the quasicrystals and their close approximants are of more localized-like character on both sides of the pseudo-gap than in regular intermetallics that signs a clear tendency to weak electron localization. Extended states are found more than 2 eV above and deep below the Fermi level. The pseudo-gap at the Fermi level is not a genuine characteristic of quasicrystalline compounds as it exists also in related crystalline alloys, but in conventional alloys of the same phase diagram it is less pronounced than in the quasicrystal. The Al 3p pseudo-gap is connected to the metallic character of the specimen since the larger and deeper the pseudo-gap, the less metallic is the sample. This may allow one to tune the metallic character through a series of compounds. (C) 2004 Published by Elsevier B.V.
Title:
Interpretation of the Hume-Rothery rule in quasicrystals and their approximants
Authors:
Mizutani, U; Takeuchi, T; Sato, H; Ross, AR;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 331-335; 2004
Abstract:
We have performed the LMTO-ASA band calculations for the gamma-phase Cu5Zn8 compound, the Frank-Kasper type Al30Mg40Zn30 and Al52.5Li32.5Cu15 1/1-1/1-1/1 approximants. In gamma-brass, where d-states exist in the middle of the valence band and the sp-d hybridization effect is significant near the Fermi level E-F, we show that it is critically important that the {3 3 0} and {4 1 1} zones satisfy the Hume-Rothery matching rule and that they are strongly coupled with the sp-d hybridization to produce a deep pseudogap across E-F . In the nearly-free-electron-like Al-Mg-Zn approximant, it is shown that the {5 4 3}, {7 1 0} and {5 5 0} zone planes are essentially responsible for a pseudogap at E-F. In the AI-Li-Cu approximant, the deep pseudogap at E-F is proven to arise mainly from the Al-3p/Al-3p hybridization effect, but that the {6 3 1} zone effect is still significantly important. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Ab initio studies on chemical bonding in Cd- and Zn-based quasicrystals
Authors:
Ishii, Y; Fujiwara, T; Sato, H;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 336-341; 2004
Abstract:
Large clusters with successive atomic shells of icosahedral symmetry are believed to be basic structural units of the newly discovered binary Cd-M (M = Yb and Ca) and ternary Zn-Mg-Sc quasicrystals. The electronic structures of approximants Cd6M (M = Ca) and Zn17Sc3 have been analyzed from a viewpoint of chemical bonding between atoms and clusters. It is found that the bonding nature changes from bonding to anti-bonding near the Fermi level for pairs of Cd/Zn atoms in the different atomic shells of a cluster. The Fermi level is located at the most optimal position for divalent M = Ca and substitution of a trivalent element for Ca causes partial occupation of the anti-bonding states. Consequently the substitution weakens the chemical bonding which favors the shell structure and linkage of the clusters. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Covalent bonding and semiconducting bandgap formation in Al-transition-metal quasicrystalline approximants
Authors:
Krajci, M; Hafner, J; Sato, H;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 342-346; 2004
Abstract:
We demonstrate that in some quasiperiodic transition-metal aluminides a special bonding between the Al(s,p) and transition-metal (TM) d-orbitals is responsible for the formation of a semiconducting gap in the electronic spectrum. We analyzed the electronic charge distribution and have observed an enhanced charge density along the Al-TM bonds that is characteristic for covalent bonding. The semiconducting gap is found in three lowest approximants of the hierarchy of approximants, which converges to the icosahedral quasicrystals of the fei class, to which also i-AlPdRe belongs. We predict the existence of novel truly semiconducting quasicrystalline 1/1-approximants with composition e.g. Al88Pd24Ir16, Al88Pd36W4, or Al88Au12Ir28 with the bandgap at the Fermi level up to 0.7 eV. These results allow us to predict the existence of semiconducting quasicrystals of a similar Al-TM composition. The possibility of the existence of a narrow semiconducting bandgap suggests an explanation of the anomalously high resistivity of the icosahedral AlPdRe quasicrystals. However, the observed bandgap formation and covalent bonding is not specific to quasicrystals, and has been observed also in crystalline Al-TM compounds. We conclude that it is not the quasicrystallinity but the unusual Al-TM bonding that is responsible for a substantial part of anomalies observed in the transport properties of Al TM quasicrystals. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Effective medium-range Mn-Mn pair interaction induces pseudogap in the density of states of Al(Si)-Mn approximants
Authors:
de Laissardiere, GT; Nguyen-Manh, D; Mayou, D; Ross, AR;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 347-351; 2004
Abstract:
The effect on the electronic structure of an effective medium-range Mn Mn interaction mediated by the valence states and the sp-d hybridization is presented. In Al(rich)-Mn phases related to quasicrystals (Al12Mn, o-Al6Mn, alpha-Al9Mn2Si), this effective interaction creates a Hume-Rothery pseudogap in the density of states together with a minimization of the band energy. It is shown that the Mn-Mn interaction up to the distance around 10-20 Angstrom plays an essential role in stabilizing related quasicrystal structures. (C) 2004 Published by Elsevier B.V.
Title:
Studies of icosahedral AlPdRe quasicrystals across the metal-insulator transition
Authors:
Rapp, O; Srinivas, V; Nordblad, P; Poon, SJ; Tsukruk, VV;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 356-362; 2004
Abstract:
The metal-insulator transition (MIT) in icosahedral AlPdRe quasicrystals is investigated by studying changes in sample properties across the transition. The magnetoresistance (MR) the conductivity sigma(T), and the magnetic susceptibility chi(T) have been studied. The MR results show that an MIT occurs for resistance ratios R [ = rho(4.2 K)/rho(295 K)] of about 20-30. sigma(0 K) is finite, and decreases over four orders of magnitude with increasing R. Besides the MR, the most prominent change in a studied property across the MIT is a change of slope of log sigma(0) vs R. In contrast, no features in the resistivity from 1.5 to 300 K reveals an MIT. New results for chi(T, R) are presented. The diamagnetic Z decreases from the metallic to the insulating side, while on the insulating side chi(T,R) is almost independent of R. Although the MR indicates a disorder driven MIT, there is no support for this picture from the results for Z. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Electronic conductivity of quasiperiodic approximants to decagonal aluminum
Authors:
Krajci, M; Hafner, J; Mihalkovic, M; Poon, SJ;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 363-367; 2004
Abstract:
We present ab initio calculations of the electronic transport properties of a hypothetical monoatomic quasiperiodic system, decagonal aluminum (d-Al). Our aim is to study the influence of quasiperiodicity on the transport properties in an example system that is sufficiently realistic to represent real Al-based quasicrystals, but does not involve the additional complexity of a strong s,p-d hybridization, which determines the properties of many crystalline and quasicrystalline Al-transition metal alloys. The investigation of the transport properties of a series of quasiperiodic approximants with increasing linear dimensions is based on a calculation of the electronic eigenstates and the Kubo-Greenwood formula. A scaling analysis demonstrates small deviations of the eigenstates from extended behavior and shows that the transport properties belong to the sub-ballistic regime, with a scaling exponent of the electronic diffusivity of beta similar to 0.66 that is somewhat larger than the quantum-diffusion limit (beta = 0.5), but distinctly smaller than for ballistic transport (beta = 1). In this sub-ballistic or over-diffusive regime the conductivity diverges in the thermodynamic limit, leading to metallic behavior. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Electronic transport of the icosahedral Zn-Mg-Sc quasicrystal and its 2/1 and 1/1 cubic approximants
Authors:
Hasegawa, J; Tamura, R; Takeuchi, S; Tokiwa, K; Watanabe, T; Canfield, PC;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 368-371; 2004
Abstract:
Comparisons of the electrical resistivity and the electronic contribution to the specific heat have been made among the P-type icosahedral Zn81Mg6Sc13, and their crystalline approximants 2/1-Zn82Mg5Sc13 and 1/1-Zn85Sc15. The temperature dependence of the resistivity, rho(T), is nearly the same for the quasicrystal and the 2/1-cubic approximant, with a negative coefficient and similar resistivity values, i.e., rho(4.2K) = 350 and 300 muOmegacm, respectively. On the other hand, rho(T) shows a metallic character with apositive coefficient and a rather low resistivity value of rho(4.2K) = 150 muOmegacm for the 1/1-cubic approximant. Electronic specific heat coefficients, 7, are small as in other i-phases and approximants; 0. 50, 0.42 and 0. 71 mJ/(mol K-2) for the quasicrystal, the 2/1- and the 1/1-approximants, respectively. The present result suggests that the electronic transport is essentially determined by the length scale of 22 Angstrom in the P-type i-phase. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Electrical resistivity of the Al65Rh27Si8 2/1 cubic approximant
Authors:
Koshikawa, N; Yoda, S; Edagawa, K; Minoda, K; Tamura, R; Takeuchi, S; Sordelet, DJ;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 372-375; 2004
Abstract:
Electrical resistivity measurements of the newly discovered 2/1 cubic approximants in the Al-Rh-Si system and the 1/0 cubic approximant in the Al-Rh system have been performed in order to gain insight into the role of the local atomic structure on electric transport in quasicrystals (QCs). The Al73Rh27 1/0 cubic approximant phase exhibits a distinctive metallic behavior with a low resistivity value of 350 muOmegacm at room temperature, while the Al64Rh27Si9 2/1 cubic approximant shows a QC-like behavior with a high resistivity value of around 2000 muOmegacm at room temperature. The ratio rho 15 K/rho300 K of the 2/1 approximant reaches 1.44, which is reminiscent of the behavior observed in highly resistive icosahedral phases. This indicates that electronic transport in the 2/1 cubic approximant is essentially the same as that of quasicrystals. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Evidence for a marginally conducting state in AlCuFe and AlPdMn quasicrystals
Authors:
Triozon, F; Mayou, D; Edagawa, K;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 376-379; 2004
Abstract:
In a quasiperiodic system without defects the dissipative part of the conductivity is expected to vary as Re sigma(0) (omega) proportional to omega(1-2beta) at low frequency omega (0 < beta < 1). beta is the diffusion exponent in the perfect structure such that the spreading of wavepackets is L(t) proportional to t(beta) at large time t. Under certain conditions disorder induces a current relaxation in a time tau and we express the conductivity, with defects, in terms of tau and of the conductivity without defects, Re sigma(0) (omega). For AlCuFe and AlPdMn quasicrystals a coherent interpretation of the conduction properties is obtained. We extract the values of tau and get beta similar or equal to 0. It means that quantum diffusion is slow or marginal in the perfect systems. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Structure defects of icosahedral quasicrystals as electrically active centres
Authors:
Prekul, AF; Kuzmin, NY; Shchegolikhina, NI; Minoda, K;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 380-383; 2004
Abstract:
By dilatometric experiments on rapidly quenched quasicrystalline Al-Cu-Fe, in the course of their annealing it is proposed that icosahedral (I-) phases with free carriers of different signs (either electrons or holes) have different senses of the volume changes upon ordering. The effect discovered serves as a direct experimental support that the structural defects in I-quasicrystals are electrically active centers. This circumstance allows the identification of intrinsic and extrinsic properties of I-phases and opens novel opportunities for understanding the physical properties of real quasicrystals. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Thermoelectric properties of Al-based icosahedral quasicrystals
Authors:
Nagata, T; Kirihara, K; Kimura, K; Minoda, K;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 384-387; 2004
Abstract:
Icosahedral AlPdRe quasicrystals show primarily semiconductor-like electronic properties and low thermal conductivity. We present the composition dependence of the electrical conductivity and Seebeck coefficient for icosahedral AlPdRe. The strong composition dependence is considered to be related to the pseudogap structure in the electron density of states at the Fermi energy, and to the variation in the bonding nature between Al and transition metals. The temperature dependence of the electrical properties has been analyzed using a two-band model. The results obtained suggest that the effective mass plays an important role in the improvement of thermoelectric properties. The dimensionless thermoelectric figure of merit, ZT, has a maximum value of approximately 0.1 in the temperature range from 600 to 700 K and reveals a strong composition dependence. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Observation of pseudo-gap and Kondo behaviour in Al70Pd30-xMnx quasicrystals
Authors:
Banerjee, GN; Banerjee, S; Goswami, R; Minoda, K;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 388-392; 2004
Abstract:
We report here the electrical and magnetic properties of Al70Pd30-xMnx quasicrystals (x = 9 and 11), from resistivity and point contact spectroscopy measurements. Electrical resistivity shows a resistivity maximum for both of these compositions. The positive TCR at lower temperature is attributed to spin-orbit scattering. For x = 11, we observe an upturn in the resistivity below 20 K, which follows a In T dependence indicating Kondo-like behaviour. In the point contact spectroscopy studies we observe two regimes showing a V-2 dependence at low bias voltages (for V < 10 meV) crossing over to the V-0.5 dependence at higher voltages. This is attributed to the signature of a pseudo-gap in the density of states at zero bias. We suggest that this V-2 dependence can also arise due to magnetic scattering effects, which are signatures of the Kondo-like behaviour. (C) 2004 Published by Elsevier B.V.
Title:
Magnetic and electrical properties of a new type Zn-Mg-Sc icosahedral quasicrystal
Authors:
Motomura, S; Kaneko, Y; Kashimoto, S; Nakano, H; Ishimasa, T; Matsuo, S; Sordelet, DJ;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 393-397; 2004
Abstract:
The magnetic susceptibility of the Zn-Mg-Sc icosahedral quasicrystals, which have a new type of atomic cluster structure, was found to increase with a rise in temperature from 100 to 300 K. The increase of the susceptibility was accounted for by the temperature dependent term of the Pauli paramagnetism, which indicated a pseudogap, in the electronic density of states (DOS) near the Fermi energy. This new type quasicrystal may be stabilized by the pseudogap in the DOS, as in various stable icosahedral quasicrystals discovered to date. We measured the temperature dependence of the electrical resistivity. In the temperature range between 2 and 300 K, the resistivity increased by 0.08% with a decrease in temperature. These measurements were analyzed on the basis of the weak localization theory of electrons in quasicrystals. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Magnetic and electrical properties of a Cu-Ga-Mg-Sc icosahedral quasicrystal
Authors:
Yamada, H; Motomura, S; Maezawa, R; Kaneko, Y; Ishimasa, T; Nakano, H; Matsuo, S; Otsubo, T;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 398-402; 2004
Abstract:
We have investigated the magnetic susceptibility and the electrical resistivity of a new P-type icosahedral quasicrystal Cu48.2Ga33.8Mg3Sc15 and a cubic phase Cu49Ga36Sc15, interpreted as a 1/1 approximant crystal of the quasicrystal. The magnetic susceptibility of the Cu48.2Ga33.8Mg3Sc15 quasicrystal showed an increase from -3.51 x 10(-4) to -2.78 x 10(-4) m(3) kg(-1) with a rise in temperature from 120 to 300 K. The Cu49Ga36Sc15 cubic phase showed also a rise from -6.18 x 10(-4) to -4.50 x 10(-4) m(3) kg(-1) between 100 and 300 K. The increase in the susceptibility was accounted for by the temperature dependence of the Pauli paramagnetism. The experimental results strongly suggest the existence of a pseudogap in the electronic density of states at Fermi energy for the Cu48.2Ga33.8Mg3Sc15 quasicrystal and the Cu49Ga36Sc15 approximant, which has been observed in various stable icosahedral quasicrystals. The electrical resistivity of the Cu47.1Ga32.9Mg5Sc15 quasicrystal showed a negative temperature coefficient in the temperature region between 2 and 270 K. The Cu49Ga33.8Sc15.2 cubic phase showed a positive temperature coefficient in the temperature region. The tendency of the quasicrystal was qualitatively accounted for by the weak localization theory. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Universal magnetic behavior of icosahedral F, F-2 and F-2M Al-Pd-Mn quasicrystals
Authors:
Hippert, F; Audier, M; Prejean, JJ; Sulpice, A; Simonet, V; Calvayrac, Y; Matsuo, S;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 403-407; 2004
Abstract:
Magnetic properties of a large set of icosahedral. Al-Pd-Mn single crystals were investigated in order to study parameters influencing the moment formation on Mn atoms. Whatever the structural state (F, F-2 or F-2M), the temperature dependence of the magnetic susceptibility exhibits a universal behavior, which can be explained by a Kondo effect gradually affected by magnetic interactions as the concentration of magnetic Mn increases. The magnetic Mn concentration remains small in all studied samples varying from 3.8 x 10(-3) up to 0.2 at.%. Thermal treatments affect the magnetism in a reversible way: slowly cooled samples are systematically found less magnetic than rapidly cooled ones, whatever the composition and structural states. Magnetic properties are so sensitive to composition that they reveal small concentration variations along the growth direction of a single grain obtained by the Czochralski technique. Therefore, magnetism in Al-Pd-Mn quasicrystalline phases is an extremely sensitive probe of atomic arrangement. (C) 2004 Elsevier B.V. All rights reserved.
Title:
A local approach of magnetism in icosahedral Al-Pd-Mn quasicrystals through nuclear magnetic resonance studies
Authors:
Simonet, V; Hippert, F; Berger, C; Calvayrac, Y; Simonet, V;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 408-411; 2004
Abstract:
Magnetism in icosahedral Al-Pd-Mn phases was investigated on a local scale through Al-27 and Mn-55 nuclear magnetic resonance experiments on polycrystalline ribbons of various compositions. In all samples, a Mn-55 resonance line is detected, which reveals the existence of non-magnetic Mn atoms. The presence of magnetic Mn atoms is detected through their influence on the width of the Al-27 resonance central line, which increases continuously from 300 to 5 K. Therefore, Al-Pd-Mn icosahedral phases are characterized by a coexistence of magnetic and non-magnetic Mn atoms. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Magnetoresistance studies in Al70Pd20+xMn10-x (x=0, 1) icosahedral quasicrystals
Authors:
Jaiswal, A; Rawat, R; Lalla, NP; Calvayrac, Y;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 412-416; 2004
Abstract:
Zero-field and in-field (at 8 T) conductivity vs. temperature (sigma-T) and magnetoresistance (Deltarho/rho) of as-prepared and unannealed Al70Pd20Mn10, annealed Al70Pd20Mn10, and annealed Al70Pd21Mn9 quasicrystalline (qc) alloys have been studied in the temperature range of 1.4-300 K. From room temperature to 30 K, sigma-T appears to be dominated by weak-localization effects including electron-phonon (e-ph) scattering as the inelastic process. sigma-T minima are possibly due to the dephasing arising from temperature dependent spin-spin scattering, resulting from a cluster-glass-like transition as indicated by the chi-T and M-H measurements. The U-T maxima at similar to9 K and the negative Deltarho/rho at 1.4 K originate probably from some ferromagnetic type magnetic interaction in the sample, which quenches the spin-spin scattering effects. (C) 2004 Elsevier B.V. All rights reserved.
Title:
A crossover from Mott to Efros-Shklovskii hopping conduction - In insulating Al70Pd22.5Re7.5 quasicrystals - a magnetoresistance study
Authors:
Fang, HC; Su, TI; Lin, ST; Calvayrac, Y;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 417-420; 2004
Abstract:
Combining the conductivity and the magnetoresistance (MR) data with MR theories, we found that there is a crossover from the Mott to Efros-Shklovskii variable-range hopping conduction in insulating Al70Pd22.5Re7.5 quasicrystals (QCs) with the resistivity ratio 93 = p(4.2 K)/rho(300 K) equal to 118 and 81. The crossover temperature is seen to decrease with decreasing 91 value. At low temperature the rapid decrease in the magnitude of the negative MR in highly resistive QCs might be correlated with the conduction via the states in the Coulomb gap as observed in CdTe semiconductors. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Magnetoresistance of highly resistive AlPdRe quasicrystals
Authors:
Srinivas, V; Rapp, O; Poon, SJ; Calvayrac, Y;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 427-430; 2004
Abstract:
The temperature dependence of the conductivity, sigma(T), and the magnetoresistance (MR), Deltarho(B)/rho, have been studied from below 0.05-300 K for two i-AlPdRe samples on the insulating side of the metal insulator transition. The temperature dependence of resistivity and MR show that there is a definite change in transport mechanism below 20 K. The MR is positive below I K. At intermediate temperatures a negative component develops and at temperatures above similar to40 K the MR is small. The magnetoresistance results are discussed in the framework of Efros-Shklovsksii (ES) variable range hopping. With decreasing temperature the characteristic field regions that describe ES hopping are successively depressed towards smaller magnetic fields and vanish. These results support an insulating ground state in samples with large resistance ratios. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Swift-heavy-ion irradiation on Al62CU25.5Fe12.5 quasicrystals
Authors:
Chatterjee, R; Kanjilal, A; Poon, SJ;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 431-435; 2004
Abstract:
The effect of swift-heavy-ion irradiation on a very stable and well-studied Al62Cu25.5Fe12.5 icosahedral quasicrystalline system is discussed here. The experiments are performed in the pure electronic excitation regime, where various ranges of energy (1.2 to similar to2.5 keV/Angstrom) are systematically deposited in to the system, causing electronic excitations in them. The choice of ions was generally dependent on calculations based on Monte-Carlo simulations and some existing literature studies on metals/metallic alloys. Samples were irradiated at fluences of 10(11) to a few 10(13) ions/cm(2), and a homogeneous irradiation was ensured. The effect of these electronic excitations on the electronic structure of the quasicrystals is analyzed by doing in situ resistivity vs. fluence and ex situ resistivity vs. temperature measurements, made on the irradiated pieces. (C) 2004 Published by Elsevier B.V.
Title:
Plastic deformation of a binary Cd-Yb icosahedral quasicrystal
Authors:
Imai, Y; Shibuya, T; Tamura, R; Takeuchi, S; Simonet, V;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 444-448; 2004
Abstract:
Polycrystalline icosahedral quasicrystals in a binary Cd-Yb alloy have been compressed at high temperatures for the first time. As-grown specimens were plastically deformable only above 698 K with the yield stress rapidly decreasing with increasing temperature. The true stress vs. true strain relation revealed continuous work softening to a large strain; the decrease of the true stress reaches 85% of the yield stress at 698 K and it is 20-50% at 773 K. Temperature change tests showed that the flow stress is sensitive to the deformation history; once a specimen has been initially deformed to a large strain at 773 K, it is plastically deformable even at 600 K. The activation analysis showed that the activation enthalpy decreases to two-third of that at the yielding stage as the strain increases, which is the cause of the work softening. (C) 2004 Elsevier B.V. All rights reserved.
Title:
The toughening of Al-Cu-Fe(-B) quasicrystals by Sn particles
Authors:
Fleury, E; Kim, YC; Kim, DH; Kim, DH; Kim, WT; Calvayrac, Y;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 449-452; 2004
Abstract:
The effect of soft Sn particles on the room temperature mechanical properties of as-cast Al-Cu-Fe(-B) quasicrystalline (QC) matrix composites has been studied by compression and three-point bending tests on notched specimens. Microstructural investigations indicated that the Sn particle size in the as-cast composites increased linearly with the volume fraction. The addition of about 10 vol.% Sn enabled a twofold increase of the strength for the cast Al-Cu-Fe and a threefold increase of the fracture toughness for the cast Al-Cu-Fe-B composites. The enhancement of the strength was attributed to micro-crack impediment and crack bridging mechanisms in the as-cast QC matrix composites with small and large Sn particle sizes, respectively. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Crack propagation in perfectly ordered and random tiling quasicrystals
Authors:
Rudhart, C; Trebin, HR; Gumbsch, P; Kim, DH;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 453-456; 2004
Abstract:
Numerical experiments have been performed on the propagation of mode-I cracks in both ordered and randomized two-dimensional decagonal model quasicrystals. In particular, the dependence on temperature, applied load and underlying structure has been investigated. The samples are endowed with an atomically sharp crack and subsequently loaded by linear scaling of the displacement field. The response of the system is followed by molecular dynamics simulations. For temperatures below 30% of the melting temperature T-m the crack velocity grows monotonically with the applied load and the model quasicrystal shows brittle fracture. For large overloads the crack becomes unstable and branches. In this low temperature regime crack tip velocities are in the range of 20-50% of the shear wave velocity v(s). For temperatures above 30% of T-m the crack does not remain atomically sharp but blunts spontaneously. To circumvent this and to nevertheless study a sharp crack a linear temperature gradient is established along a strip. From the low temperature regime, where a sharp tip can be stabilized, the crack is driven into a region of elevated temperature. In the range of 70-80% T-m the failure mode of the quasicrystal changes to a void formation process. Thus at low temperatures the crack propagates along crystallographic planes just like in periodic crystals, whereas a glass-like behavior is dominant at high temperatures. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Hydrogenation of Ti-Zr-Ni quasicrystals synthesized by mechanical alloying
Authors:
Takasaki, A; Huett, VT; Kelton, KF; Kim, DH;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 457-460; 2004
Abstract:
Mechanical alloying of a Ti45Zr38Ni17 powder mixture formed an amorphous phase, but subsequent annealing caused the formation of an icosahedral (i) quasicrystal phase with a small amount of the Ti2Ni-type crystal phase. After high-pressure hydrogenation at 573 K at a hydrogen pressure of 3.8 MPa, the amorphous phase transformed to a TiH2-type hydride, while the i-phase was structurally stable even after the hydrogenation. The maximum hydrogen concentration for the high-pressure hydrogenation was the same (hydrogen-to-metal atom ratio approximate to1.5) for the i-phase and amorphous powders, suggesting structural similarities between the i-phase and the amorphous phase. Pressure-composition isotherms (PCTs), measured under low-pressure hydrogenation at a temperature of 423 K, showed sloping plateau-like features at equilibrium hydrogen pressures lower than 1 kPa for both the i-phase and amorphous powders. The plateau-like region for the i-phase powder was steeper and narrower than that for the amorphous powder, indicating a slight difference in site energy distribution of hydrogen in the i-phase and the amorphous phase. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Ti-Zr-Ni and Ti-Hf-Ni quasicrystals and approximants as hydrogen storage alloys
Authors:
Gibbons, PC; Hennig, RG; Huett, VT; Kelton, KF; Kim, WT;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 461-465; 2004
Abstract:
X-ray and neutron powder diffraction data previously collected from the Ti-Zr-Ni quasicrystal have been analyzed. The data were modeled by an 8/5 rational approximant (RA) that was constructed using the known structure of the 1/1 RA and then refined. Ab initio total energy calculations were made for small structures with between 81 and 123 atoms, in which atomic positions were allowed to vary while minimizing the energy. The final structure is in good agreement with that obtained from the scattering data. Interstitial sites in which H is stable in the 1/1 model, and the H binding energies, were identified. An excellent fit to existing pressure-composition isotherms was obtained, but those data cannot be inverted to obtain experimental site binding energies. At 250 degreesC the Ti-Hf-Ni alloy can be loaded with H without the formation of any detectable crystal hydride phase, which is always found in similarly loaded Ti-Zr-Ni alloys. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Sliding on a quasiperiodic substrate
Authors:
Janssen, T; Hennig, RG;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 471-474; 2004
Abstract:
Unlike incommensurate modulated and composite systems, quasicrystals do not show propagating modes which can be considered as oscillations in internal space. However, sliding of a crystal over a quasiperiodic surface may have the character of a motion in superspace. It is argued that such motions may have a very low friction coefficient. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Friction and fretting on quasicrystals under vacuum
Authors:
Dubois, JM; Brunet, P; Costin, W; Merstallinger, A; Kim, WT;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 475-480; 2004
Abstract:
In order to investigate friction and fretting on quasicrystals at room temperature in a reliable manner, we have subjected sintered samples to tests in a vacuum chamber evacuated to a residual pressure lower than 10(-5) mbar. Pin-on-disc tests and fretting tests were ran using hard steel spherical counterparts. Experiments in vacuum reveal that the variation of the coefficient of friction with cumulated sliding distance is very different when one considers Cr-hard steel riding on alumina, on a (true) quasicrystal or on a high-carbon steel. Sharp minima in friction coefficients and adhesive forces occur when the quasicrystalline surface is loaded in contact with a metallic surface. The characteristic friction values measured in high vacuum are smaller than in ambient atmosphere by at least a factor 2, thus indicating that the oxide layer is involved to a significant extent in determining the tribological mechanisms. The discussion focuses on an interpretation of the differences observed between samples, based on their chemical composition and possible bonding to steel. For the first time, an estimate of the true surface energy of a quasicrystal is derived from measurements. (C) 2004 Elsevier B.V. All rights reserved.
Title:
A model of wetting on quasicrystals in ambient air
Authors:
Dubois, JM; Brunet, P;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 481-485; 2004
Abstract:
Water does not wet well-polished quasicrystal surfaces, in strong contrast to the behavior observed on aluminum metal in ambient atmosphere. Contact angle measurements combined with a determination of the electronic partial density of states and of oxide layer thicknesses demonstrate that this unexpected wetting property is related to the electronic density of states within the bulk material, underneath the oxide layer, and to the thickness of the oxide layer. A model is derived in this paper that aims at an interpretation of these results in terms of electrostatic image forces developed in the conduction electron cloud by the dipoles of the water molecules. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Experimental evidence of the stability of net planes in decagonal quasicrystals
Authors:
Jenks, CJ; Bjergaard, J; Canfield, P; Ross, AR; Steurer, W; Thiel, PA; Matsuo, S;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 486-490; 2004
Abstract:
Because of the aperiodic nature of quasicrystals, lattice planes, in the traditional sense, do not exist for quasicrystals. For decagonal quasicrystals, it has been proposed, however, that one can link the aperiodic and periodic directions using what are termed net planes [Acta Crystallogr. A 57 (2001) 333]. These net planes are thought to play a critical role in the stability and growth of decagonal quasicrystals. To explore their potential role during growth and to shed light on their structural stability, we have studied single-grain surfaces of decagonal Al-Ni-Co by low energy electron diffraction and scanning tunneling microscopy. Our results suggest that these planes do indeed have special stability. Published by Elsevier B.V.
Title:
Cleaved surfaces of d-AlNiCo and xi '-AlPdMn
Authors:
Cecco, C; Barth, C; Gille, P; Feuerbacher, M; Krausch, G; Reichling, M; Matsuo, S;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 491-494; 2004
Abstract:
Decagonal Al-Ni-Co quasicrystals were cleaved in ultrahigh-vacuum and the resulting surfaces were investigated by dynamic scanning force microscopy. The samples were cleaved perpendicular to the tenfold axis and perpendicular to one of the twofold axes. Both surfaces show a rough structure with lateral features on the nanometer scale and height differences of angstroms to nanometers. While the corrugation of the tenfold surface does not show any correlation to the quasiperiodic bulk structure, the twofold surface exhibits row-like corrugations, which indicate the existence of columnar structure motifs along the direction of the tenfold axis as expected from structure models. Images from surface regions tilted with respect to the twofold plane strongly indicate the existence of inclined netplanes. In addition, we studied surfaces of xi'-(Al-Pd-Mn) quasicrystal approximant, which was cleaved perpendicular to the pseudo-tenfold b-axis. These surfaces show a corrugated structure as well, similar to the results obtained from the decagonal Al-Ni-Co surfaces. There is no indication of a correlation to the periodicity or other structural features of this orthorhombic, crystalline material. (C) 2004 Elsevier B.V. All rights reserved.
Title:
SEM and AFM studies of a 5-fold surface of icosahedral AlPdMn
Authors:
Yu, FX; Bischoff, M; Ross, AR; Lograsso, TA; van Kempen, H; Janssen, T; Matsuo, S;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 495-499; 2004
Abstract:
A 5-fold surface of the icosahedral AlPdMn (i-AlPdMn) quasicrystal (QC) was studied by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM) under ambient conditions. We show that a very complicated inhomogeneous surface morphology may develop on the 5-fold surface prepared by ion sputtering and annealing cycles in UHV. Sputtering and sublimation both contribute to material removal on the surface. The sublimation takes place at the annealing temperature at sites of surface defects induced by mechanical polishing and sputtering in UHV. The surface is characterized by nano-sized clusters of about 40 nm in size which form terraces. Results give further evidence for the cluster-based structure of the i-AlPdMn QC. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Laser cladding of quasicrystal forming Al-Cu-Fe on aluminum
Authors:
Biswas, K; Galun, R; Mordike, BL; Chattopadhyay, K; Xia, YL;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 517-523; 2004
Abstract:
Composite quasicrystalline coatings are developed by laser cladding of an elemental powder mixture of aluminum, copper and iron on an aluminum substrate. Some of the tracks are remelted to see the effect of phase formation and related changes in hardness during remelting. The clad layers start growing with a cellular morphology from the substrate. The icosahedral phase forms in all the tracks along with some aluminides. It has also been found that the icosahedral phase forms both by a peritectic reaction between the liquid and Al13Fe4 and by direct nucleation from the liquid. This is a clear indication of a different levels of undercooling that the liquid undergoes before the nucleation of the primary phase inside the clad layers during laser processing. The formation of Al13Fe4 with a ten-pointed star like morphology has also been found at the bottom of the clad. The remelting of the clad tracks leads to a change in microstructure as far as phase formation is concerned. The formation of long lath-shaped Al13Fe4 can be observed in the remelted layer. The hardness profiles of the clad and remelted layers reveal a hardness (HV0.025) around 600. (C) 2004 Published by Elsevier B.V.
Title:
Initial oxidation of quasicrystals - an investigation by high-resolution RBS and ERDA
Authors:
Plachke, D; Khellaf, A; Kurth, M; Szokefalvi-Nagy, A; Carstanjen, HD; Dong, C;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 524-531; 2004
Abstract:
Surfaces of icosahedral AlPdMn with 5-fold orientation can be prepared either to be fully icosahedral or to form a cubic overlayer. When decagonal AlNiCo is cut perpendicular to the 10-fold axis, a fully quasicrystalline surface is obtained, however a 'mixed-type' (quasicrystalline-periodic) surface is obtained, when cut parallel to this axis. A comparison of the oxidation behavior of these different surfaces should therefore shed light on the suggestion by Rivier [N. Rivier, New Horizons in Quasicrystals: Research and Applications, in: A.I. Goldman, D.J. Sordelet, P.A. Thiel, and J.M. Dubois (Eds.), World Scientific, Singapore, 1997, p. 188] that quasicrystals are more corrosion resistant than their crystalline counterparts. The initial oxidation of the surfaces was studied by measuring oxygen depth profiles with high-resolution ERDA. The paper also reports about the preparation of the surfaces and the measurement of highly resolved depth profiles of the metallic components by RBS during the preparation. In both cases a high-resolution electrostatic spectrometer was used for the energy analysis. The results are in favor of an enhanced oxidation resistance of quasicrystalline surfaces. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Oxidation kinetics of an AlCuFeCr approximant compound: an ellipsometric study
Authors:
Bonhomme, G; LeMieux, A; Weisbecker, P; Tsukruk, VV; Dubois, JM; Dong, C;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 334 (1): 532-539; 2004
Abstract:
Using single wavelength laser ellipsometry (lambda = 634 nm), we have studied the oxidation kinetics of bulk polycrystalline samples of an AlCuFeCr orthorhombic approximant compound of the decagonal phase. Up to 300 degreesC in dry air, nearly no evolution of the ellipsometric characteristics was detected, which can be explained assuming that the growth of the oxide layer stops shortly after beginning the exposure to temperature and air. Above this temperature, the changes of the ellipsometric characteristics pointed out a higher oxidation rate and a continuous growth of the oxide layer. In boiling water, we found that the kinetics of oxidation were as fast as when above 300 degreesC in dry air. Taking also into account atomic force microscopy measurements of the surface roughness, plausible scenarios for the oxidation process are inferred from our data. (C) 2004 Elsevier B.V. All rights reserved.
Title:
Synchrotron X-ray diffraction measurements in applied magnetic fields
Authors:
Katsumata, K; Matsuda, M;
Source:
PHYSICA B-CONDENSED MATTER, 345 (1-4): 49-54; 2004
Abstract:
After a brief description of the experimental setup at the RIKEN's beam line BL19LXU in SPring-8, we report the recent results of non-resonant X-ray magnetic and charge scattering measurements on some anti ferromagnets in the applied magnetic fields: (1) observation of a spin-flop transition in a prototypical uniaxial antiferromagnet MnF2 and (2) the temperature dependence of incommensurability in the high field phase of a spin-Peierls compound CuGeO3. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Microscopic calculations of displacive (elpasolite family) and order-disorder (potassium selenate family) structural phase transitions
Authors:
Zinenko, VI; Zamkova, NG; Solis, C;
Source:
CRYSTALLOGRAPHY REPORTS, 49 (1): 29-39; 2004
Abstract:
The critical temperatures and thermodynamic characteristics for the displacive phase transition O-h(7) --> O-4h(5) in crystals of the elpasolite family Rb2KBF6 (B = Sc, In, Lu) and for the successive phase transitions D-6h(4) --> D-2h(16) --> I --> C-2h(5) (I is the incommensurate phase) in crystals of the selenate potassium family have been calculated. The calculations were carried out using the effective Hamiltonian method. The Hamiltonian parameters for the elpasolite-like crystals were determined from ab initio calculations, and those for the crystals of the selenate potassium family were found using a small number of fitting parameters. (C) 2004 MAIK "Nauka/Interperiodica".
Title:
Crystal structure and phase transitions in the new crystals of [(CH3)(2)NH2](2)CuCl4[(CH3)(2)NH2]Cl
Authors:
Kirpichnikova, LF; Pietraszko, A; Bednarski, W; Waplak, S; Sheleg, AU; Rossell, MD;
Source:
CRYSTALLOGRAPHY REPORTS, 49 (1): 86-93; 2004
Abstract:
Crystals grown from a solution of dimethylammonium and copper chlorides are studied using electron paramagnetic resonance (EPR) and X-ray diffraction. The dielectric properties of the crystals grown are measured. It is established that the crystals have the composition [(CH3)(2)NH2](2)CUCl4[(CH3)(2)NH2]Cl and, in phase I at room temperature, are described by the orthorhombic space group Pna2(1) with the unit cell parameters a = 11.338 Angstrom, b = 9.981 Angstrom, and c = 15.675 Angstrom. At temperatures of 279 K and 253 K, the crystals undergo jump-wise phase transitions into the incommensurate modulated ferroelectric phase 11 and commensurate modulated phase III, respectively. (C) 2004 MAIK "Nauka/Interperiodica".
Title:
Growth morphology of solidified GaMgZn alloys
Authors:
Jelen, P; Surowiec, M; Helbing, J;
Source:
JOURNAL OF CRYSTAL GROWTH, 261 (4): 581-589; 2004
Abstract:
The aim of the present investigations was to analyse the phase composition of Ga-Mg-Zn alloys of compositions in the vicinity of the quasicrystalline phase existence. Slow solidification from the melt was performed using home-made apparatus. The sample composition was different for alloys with Ga content varying from 16 at% to 31 at%, Mg from 26 at% to 38 at% and Zn content varying between 40 at% and 52 at%. During the solidification process of the alloys, several types of single crystals were obtained. Polygonal forms of MgZn2 (Laves phase) single crystals crystallised in the shrinkage cavities, single crystals of Ga28Mg42Zn30 and faceted forms of Ga14Mg27Zn59 single crystals were observed in our experiment for the first time. Apart from that relatively large (2 mm x 2 mm) polygonal Mg single crystals crystallised in shrinkage cavities. For some compositions colonies of Zn whiskers were formed throughout the whole volume of sample. The only quasiperiodic phase was found in alloys obtained for composition of Ga24Mg36Zn40, In the case when the original composition differed from that of the icosahedral phase three new phases were found: Ga14Mg19Zn67 and Ga14Mg27Zn59 with symmetry 6/mmm and Ga28Mg42Zn30 with 4/mmm symmetry. All phases coexisted in the whole volume of alloy. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Interaction between a semi-infinite crack and a straight dislocation in a decagonal quasicrystal
Authors:
Wang, X; Zhong, Z; Helbing, J;
Source:
INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE, 42 (5-6): 521-538; 2004
Abstract:
The interaction between a semi-infinite crack and a line dislocation in a decagonal quasicrystalline solid is investigated in detail by employing the complex variable method. The local stress intensity factors and energy release rate at the crack tip as well as the Peach-Koehler force acting on the line dislocation are presented. The crack tip shielding effect due to the line dislocation can be easily observed from the expressions of the local stress intensity factors. It is found that all the four components of the Burgers vector of the line dislocation can affect the local phonon and phason stress intensity factors. Besides, the problem of a line dislocation in a decagonal quasicrystalline half-space in which the boundary of the half-space is traction-free is also investigated and the Peach-Koehler force on the dislocation due to the presence of the free surface is derived. (C) 2003 Elsevier Ltd. All rights reserved.
Title:
Crystal growth and structure determination of barium rhodates: Stepping stones toward 2H-BaRhO3
Authors:
Stitzer, KE; El Abed, A; Darriet, J; zur Loye, HC; Weber, HP;
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126 (3): 856-864; 2004
Abstract:
Single crystals of two new barium rhodates were grown from a molten potassium carbonate flux. The new rhodates, Ba11Rh10O30 and Ba32Rh29O87, are structurally related to the 2H-hexagonal perovskite structure and are characterized by pseudo one-dimensional chains of alternating face-sharing trigonal prisms and octahedra. The structures of Ba11Rh10O30 and Ba32Rh29O87 were solved using the 4D superspace group approach in Jana2000. Ba11Rh10O30, with a repeat of nine RhO6 octahedra followed by one RhO6 trigonal prism, contains the longest chain sequence of face-sharing octahedra known for this 2H-perovskite related family of oxides. A structural analysis of these two compounds revealed clear trends in metal-metal distances and octahedral heights not previously identified for this family of oxides. The application of these trends toward the structure of the all-octahedra-containing end member of the structural series, the hypothetical 2H-BaRhO3, enabled a prediction of its rhodium-rhodium distance, octahedral height, and lattice parameters.
Title:
The modulated crystal structure of antigorite: The m=17 polysome
Authors:
Capitani, G; Mellini, M; Buseck, PR;
Source:
AMERICAN MINERALOGIST, 89 (1): 147-158; 2004
Abstract:
The modulated crystal structure of an antigorite polysome with m = 17 was refined by single crystal X-ray diffraction in the Pm space group, using highly ordered single crystals from Val Malenco, Italy. The chemical composition is (Mg2.673Fe0.0982+Fe0.0153+Al0.035Cr0.007Ni0.003Mn0.002)(Sigma=2.823)(Si1.997Al0.003)(Sigma=2)O-5(OH)(3.639).Lattice parameters [a = 43.505(6), b = 9.251(l), c = 7.263(1) Angstrom, beta = 91.32(1)degrees] were determined using a single-crystal diffractometer equipped with an area detector. The structure was refined using 9242 independent reflections, obtaining a final R-4sigma factor of 0.0577. A continuous, wavy octahedral sheet is linked to a tetrahedral sheet with tetrahedral apices alternatively pointing +c and-c. This sheet is located on the concave side of the octahedral-sheet wave. The octahedral sheet shows normal thickness for a serpentine of this composition, and does not have any internal offset. The tetrahedral sheet inverts its polarity through six- and eight-membered tetrahedral rings (6- and 8-reversals). Between reversals, 6-membered rings are distorted toward ditrigonal configuration, with tetrahedral rotation, (X values, ranging along the wave from 4 to 13.6degrees. The two half-waves have curvature radii of 99.4 and 110.9 Angstrom. Variable interlayer O-O distances occur, indicating the absence of homogeneous, continuous hydrogen bonding. The bond geometry, very similar to that of lizardite, suggests common crystal chemical and geochemical properties. The larger stability field of antigorite compared to lizardite is interpreted to arise from the occurrence of three-dimensionally connected chemical bonds.
Title:
Approximants in annealed IQC(Icosahedral Quasicrystal)-DQC(Decagonal quasicrystal) pseudo-binary alloys
Authors:
Lei, Y; Dubois, JM; Calvo-Dahlborg, M; Hei, ZK; Weisbecker, P; Dong, C; Van Tendeloo, G;
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 13 (6): 1360-1366; 2003
Abstract:
The structure and microstructure of constituent phases in annealed ICQ(100-x), DQC(x) alloys, made from mixtures of Al-62 Cu-25. s Fe-12.5 icosahedral quasicrystal (IQC) and Al-70 Co-15 Ni-15 decagonal quasicrystal (DQC), were studied by X-ray diffractometry(XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDAX). These constituent phases are mostly approximants: lambda, beta, and tau3. In addition, an Al-Cu-Co DQC phase is observed in IQC(80) DQC(20) alloy. The nature of these approximants and their relationship with the quasicrystals(QCs) are discussed; and the evolution of these phases is interpreted by the shifting of their e/a-constant lines in the Al-(Cu, Ni)-(Fe, Co) pseudo-ternary phase diagrams.
Title:
Microstructural evolution of decagonal quasicrystal in the undercooled Al72Ni12Co16 alloy melts
Authors:
Liu, XB; Li, JG; Yang, GC; Xue, QZ;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 333 (1): 95-100; 2004
Abstract:
The microstructure evolution of decagonal quasicrystals in Al72Ni12Co16 alloy was investigated by the electromagnetic melting and cyclic superheating method. Single-phase decagonal quasicrystals have been obtained when the undercoolings were larger than 60 K. The decagonal quasicrystals formed at various undercoolings show different microstructural morphologies. Furthermore, grain refinement was found near the undercooling of 120 K. Based on current thermodynamic and dendrite growth theories, a dimensionless superheating parameter was adopted to explain the effect of processing conditions on the microstructure of Al72Ni12Co16 alloy. The result indicate that the fine equiaxied microstructure of decagonal quasicrystal (D-phase) formed near on undercooling of 120 K originates from the break-up of dendrites. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Aperiodic order and quasicrystals: Spectral properties
Authors:
Lenz, D; Stollmann, P; Balic-Zunic, T;
Source:
ANNALES HENRI POINCARE, 4 (1): S933-S942; 2003
Abstract:
We present spectral theoretic results for Hamiltonians associated with Delone sets. For a family of discrete models we characterize the appearance of jumps in the integrated density of states. For a family of continuum models on the set of all Delone sets with suitable parameters we prove that generically purely singular continuous spectrum occurs.
Title:
Structural studies on the Fresnoite type compound Ba2VSi2O8
Authors:
Hoche, T; Esmaeilzadeh, S; Withers, RL; Schirmer, H; Zhao, JT;
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 218 (12): 788-794; 2003
Abstract:
Single crystals of Ba2VSi2O8 have successftilly been grown from a high-temperature solution and single crystal X-ray diffraction used to refine its fresnoite type average crystal structure. In contrast to other recently investigated representatives of the fresnoite family of compounds, Ba2VSi2O8 did not at first appear to be incommensurately modulated. Neither single crystal X-ray diffraction nor powder neutron diffraction gave any indication for the existence of satellite reflections in addition to the strong average structure Bragg reflections. A careful electron diffraction study, however, has revealed the existence of weak incommensurate satellite reflections characterized by the primitive primary modulation wave-vectors q(1) = 0.297 [110]*+ 1/2c* and q(2) = 0.297 [1 $(1) over bar $0]* + 1/2 c*. The reciprocal space positioning of these incommensurate primary modulation wave-vectors, the overall (3 + 2)-d superspace group symmetry, as well as the shapes of the refined displacement ellipsoids determined from the single crystal XRD refinement are all consistent with their arising from condensed Rigid Unit Mode (RUM) modes of distortion of the Ba2VSi2O8 parent structure. The weakness of the satellite reflections in Ba2VSi2O8 relative to, for example, Ba2TiGe2O8 or Sr2TiSi2O8 arises from the significantly smaller amplitude of the condensed RUM mode as is clear from the magnitudes of the refined average structure anistropic displacement ellipsoids.
Title:
Modulated structure of misfit-layered cobalt oxide [Ca-2(Co0.65Cu0.35)(2)O-4](0.6)CoO2
Authors:
Miyazaki, Y; Miura, T; Onoda, M; Uchida, M; Ishii, Y; Ono, Y; Morii, Y; Kajitani, T; Baran, M;
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 42 (12): 7467-7473; 2003
Abstract:
We have determined the crystal structure of novel thermoelectric compound [Ca-2(Co0.65Cu0.35)(2)O-4](0.63)CoO2 by a superspace group approach. Structural parameters have been refined with a superspace group of C2/m(l p 0)s0 using powder neutron diffraction data collected at 293 K. The compound consists of mutually interpenetrating triangular CoO2 layers and distorted four-layered rock salt-type Ca-2(Co0.65Cu0.35)(2)O-4 slabs, which are incommensurate parallel to the b-axis. The CoO2 layer is composed of the CdI2-type edge-shared CoO6 octahedra. Both the subsystems have common a- and c-axes, and beta-angle with a = 4.8212(4) Angstrom, c 12.7671(8) Angstrom and beta = 93.93(1)degrees. The b-axis lengths are b(1) = 2.8103(3) Angstrom for the [CoO2] subsystem and b(2) = 4.4915(3) Angstrom for the [Ca-2(Co0.65Cu0.35)(2)O-4] subsystem. A marked displacive modulation of the (Co, Cu) and O sites in the [Ca-2(Co0.65Cu0.35)(2)O-4] subsystem has been observed, yielding a large fluctuation of the (Co, Cu)-O distances in the range from 1.8 Angstrom to 2.7 Angstrom. Cu2+ ions appear to play an important role in stabilizing such a four-atom thick subsystem in this compound.
Title:
Local 3D real space atomic structure of the simple icosahedral Ho11Mg15Zn74 quasicrystal from PDF data
Authors:
Bruhne, S; Uhrig, E; Gross, C; Assmus, W; Ishii, Y;
Source:
CRYSTAL RESEARCH AND TECHNOLOGY, 38 (12): 1023-1036; 2003
Abstract:
We present a new complementary strategy to quasicrystalline structure determination: The local atomic structure of simple icosahedral (si) Ho11Mg15Zn74 [a(6D) = 5.144(3)Angstrom] in a sphere of up to r = 17Angstrom was refined using the atomic pair distribution function (PDF) from in-house X-ray powder diffraction data (MoKalpha(1), Q(max) = 13.5Angstrom(-1); R = 20.4%). The basic building block is a 105-atom Bergman-Cluster {Ho8Mg12Zn85}. Its center is occupied by a Zn atom - in contrast to a void in face centred icosahedral (fci) Ho9Mg26Zn65. The center is then surrounded by another 12 Zn atoms, forming an icosahedron (1st shell). The 2nd shell is made up of 8 Ho atoms arranged on the vertices of a cube which in turn is completed to a pentagon dodecahedron by 12 Mg atoms, the dodecahedron then being capped by 12 Zn atoms. The 3rd shell is a distorted soccer ball. of 60 Zn atoms, reflecting the higher Zn content of the si phase compared to the fci phase. In our model, 7% of all atoms are situated in between the clusters. The model corresponds to a hypothetical 1/1-approximant of the icosahedral (i) phase. The local coordinations of the single atoms are of a much distorted Frank-Kasper type and call to mind those present in 0/1-Mg2Zn11. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Title:
New complex oxides of the A3n+3mA ' nB3m+nO9m+6n family: Ba(6)A ' Mn4O15 (A ' = Mg, Ni)
Authors:
Bazuev, GV; Zaitseva, NA; Kellerman, DG; Assmus, W;
Source:
SOLID STATE SCIENCES, 5 (11-12): 1465-1470; 2003
Abstract:
Complex oxides Ba(6)AMn(4)O(15), where A = Mg (I) and Ni (II), belonging to the homologous series A(3n+3m)A'nB3m+nO9m+6n (n = 1, m = 1) were obtained by solid state reaction method from Ba carbonate and oxides MgO, NiO, MnO2. Both new oxides are incommensurate. Their crystal structures were interpreted as composite ones with two subcells: a = 10.042(3) Angstrom, c(1) = 4.318(2) Angstrom, c(2) = 2.565(1) Angstrom, C-1/c(2) = 1.6834 for (I) and a = 10.044(3) Angstrom, c(1) = 4.308(2) Angstrom, c(2) = 2.551(1) Angstrom, c(1)/c(2) = 1.6887 for (II). Magnetic susceptibility measurements in the range 2-850 K revealed antiferromagnetic correlations in Ba6MgMn4O15 (TN = 7 K) and a pseudo-square-planar environment of some Ni2+ cations in Ba6NiMn4O15. (C) 2003 Elsevier SAS. All rights reserved.
Title:
LaSeTe2-temperature dependent structure investigation and electron holography on a charge-density-wave-hosting compound
Authors:
Doert, T; Fokwa, BPT; Simon, P; Lidin, S; Sohnel, T; Ono, Y;
Source:
CHEMISTRY-A EUROPEAN JOURNAL, 9 (23): 5865-5872; 2003
Abstract:
Single crystals of LaSeTe2 have been prepared by reaction of the elements in a LiCl/RbCl flux at 970 K for seven days. Satellite reflections observed in diffraction experiments indicate the presence of an incommensurate lattice distortion, which is of the charge-density-wave (CDW) type. The modulated structure has been solved from X-ray data at 173, 293, and 373 K. LaSeTe2 crystallizes in the 3+1-dimensional orthorhombic superspace group Cmcm(00gamma)s00 (No. 63.2) with lattice parameters of a=4.295(1), b=25.37.1(4), c=4.306(1)Angstrom (173K), a= 4.297(1), b=25.408(4), c=4.309(1)A (293 K), and a= 4.309(1), b = 25.481(6), c=4.321(1) Angstrom (373 K). The modulation vector q = (0, 0, 0.288) does not change over the temperature interval. Electron holographic investigations confirm the existence of the modulation and help to visualize the charge-density wave.
Title:
TEM study of superstructure in a perovskite lead lanthanum zirconate stannate titanate ceramic
Authors:
Cai, Y; Phillipp, F; Zimmermann, A; Zhou, L; Aldinger, F; Ruhle, A; Morii, Y;
Source:
ACTA MATERIALIA, 51 (20): 6429-6436; 2003
Abstract:
The superstructure of an antiferroelectric Pb0.97La0.02(Zr0.66Sn0.25Ti0.09)O-3 phase, whose composition is near the morphotropic-phase boundary, was characterized. Systematic selected-area diffraction revealed that there were two kinds of superlattice reflections in the pseudocubic reciprocal lattice, i.e. 1/2{hkl} superlattice reflections (h, k, l all odd), and g +/- 1/7.24(a* + b*) one-dimensional incommensurate superlattice reflections, where g denotes the vectors of fundamental or 1/2{hkl} supertattice reflections. Convergent-beam electron diffraction disclosed that the average structure of the phase was rhombohedral with space group of R (3) over barm. Based on the rhombohedral reciprocal lattice, the 1/2{hkl} reflections were no longer superlattice but fundamental reflections, and the reciprocal vector of the one-dimensional incommensurate reflections was re-expressed as H = ha* + kb* + lc* +/- 1/7.24(a* + b*), where h, k, l are integers and (-h + k + l) = 3n. In the light of the average structure and the reflection condition, the superspace Bravais class of the phase with one-dimensional incommensurate structure was determined to be P-11 (B (3) over barm) in a (3 + 1)-dimensional space. In addition, the origins of the superlattice reflections were also examined and discussed. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Update: 31-Dec-2003

Title:
Two-dimensionally modulated structure of the rare-earth polysulfide GdS2-x (x=0.18 similar or equal to 13/72)
Authors:
Tamazyan, R; van Smaalen, S; Vasilyeva, IG; Arnold, H; Marcus, CM;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 59 (22): 709-719; 2003
Abstract:
The crystal structure of GdS2-x is determined by single-crystal X-ray diffraction as a 144-fold superstructure of the ZrSSi structure type. The superstructure is described as a two-dimensional, commensurately modulated structure with the superspace group P4/n(alphabeta1/2)(00)(ss) and with alpha = 1/4 and beta = 1/3. Structure refinements within the classical approach, employing the 144-fold supercell, fail because most of the superlattice reflections have zero intensities within the experimental resolution. Within the superspace approach the absent superlattice reflections are systematically classified as higher-order satellite reflections. Accordingly, the superspace approach has been used to refine the structure model comprising the basic structure positions and the amplitudes of the modulation functions of the three crystallographically independent atoms. The quality of fit to the diffraction data and the values of the refined parameters are independent of the assumption on the true symmetry ( incommensurate or a 12 x 12 x 2, I-centred superlattice with different symmetries). Arguments of structural plausibility then suggest that the true structure is a superstructure with space group I (4) over bar ,corresponding to sections of superspace given by (t(1), t(2)) equal to [(4n-1)/48, (4m-3)/48] or [(4n-3)/48, (4m-1)/48] (n and m are integers). Analysis of the structure, employing both superspace techniques (t plots) and the supercell structure model all show that the superstructure corresponds to an ordering of vacancies and an orientational ordering of S-2(2-) dimers within the square layers of the S2 atoms.
Title:
Structure of delta(1)-CoZn7.8, an example of a phason pinning-unpinning transformation?
Authors:
Lind, H; Bostrom, M; Petricek, V; Lidin, S; Marcus, CM;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 59 (22): 720-729; 2003
Abstract:
The novel structure of the delta(1) phase in the cobalt - zinc system was determined by single-crystal X-ray diffraction. The structure features fused double icosahedra linked by edge- and face-sharing. The delta(1)-CoZn7.8 structure is incommensurately modulated along the columnar b direction. The extent of the linear pentagonal antiprismatic intergrowth is limited to a maximum of two overlapping icosahedra because of geometric demands and radii relations. Even this limited fusion of icosahedra leads to strain that is believed to be the origin of the structural modulation. The compound was synthesized using a centrifugation-aided filtration method which yielded single crystals grown on cobalt pieces in a zinc-rich melt. The (3 + 1)-dimensional superspace group is F2/m(0beta0)s0 and the modulation wavevector was determined to q = 0.234b*. The partial amorphization of the sample when subjected to mechanical grinding is an indication of a metastable structure. The incommensurability of the structure may be seen as an ordered pinning of phasons.
Title:
Discontinuities of the integrated density of states for random operators on delone sets
Authors:
Klassert, S; Lenz, D; Stollmann, P; Hagn, E;
Source:
COMMUNICATIONS IN MATHEMATICAL PHYSICS, 241 (2-3): 235-243; 2003
Abstract:
Despite all the analogies with "usual random" models, tight binding operators for quasicrystals exhibit a feature that clearly distinguishes them from the former: the integrated density of states may be discontinuous. This phenomenon is identified as a local effect, due to the occurrence of eigenfunctions with bounded support.
Title:
Evidence of short-range antiferroelectric local states in lanthanum- and titanium-modified Sr0.3Ba0.7Nb2O6 ferroelectric ceramics
Authors:
Amorin, H; Perez, J; Fundora, A; Portelles, J; Guerrero, F; Soares, MR; Martinez, E; Siqueiros, JM;
Source:
APPLIED PHYSICS LETTERS, 83 (21): 4390-4392; 2003
Abstract:
Structural and electrical measurements were performed on lanthanum- and titanium-modified Sr0.3Ba0.7Nb2O6 ferroelectric (FE) ceramics. Dielectric properties show a well-defined relaxor anomaly around -50 degreesC with double-loop hysteresis curves from this point to the transition temperature. The thesis of short-range antiferroelectric (AFE) local states having incommensurate (INC) structure embedded in the FE polar matrix is proposed to explain the observed behavior. Structural lattice parameters show negative expansion coefficients and INC superlattice diffraction spots were observed through the selected-area diffraction patterns in the [110] zone for this minority local states. The titanium modification of this system seems to be the key fact in the coupling of the INC structure to the AFE local states in the FE-AFE coexistence region. (C) 2003 American Institute of Physics.
Title:
Structural chemistry and magnetic properties of incommensurate Sr1+x(CoxMn1-x)O-3
Authors:
Jordan, NA; Battle, PD; van Smaalen, S; Wunschel, M; Enichlmair, H;
Source:
CHEMISTRY OF MATERIALS, 15 (22): 4262-4267; 2003
Abstract:
The incommensurate, modulated crystal structures of Sr1+x(CoxMn1-x)O-3 (x approximate to 0.266 and 0.280) have been refined by a (3+1)D superspace profile analysis of neutron powder diffraction data. The structures are related to the 2H perovskite structure and consist of two subsystems, [CoxMn1-xO3](infinity) chains containing face-sharing MnO6 octahedra and CoO6 trigonal prisms (albeit with some cation site inversion), separated from each other by [Sr](infinity) chains. The observed structures are closely related to those expected for the idealized compositions Sr14Co3Mn8O33 and Sr9Co2Mn5O21. Both of the compositions investigated show hysteresis in their magnetic behavior below 13 K.
Title:
Evidence of icosahedral short-range order in Zr70Cu30 and Zr70Cu29Pd1 metallic glasses
Authors:
Saksl, K; Franz, H; Jovari, P; Klementiev, K; Welter, E; Ehnes, A; Saida, J; Inoue, A; Jiang, JZ;
Source:
APPLIED PHYSICS LETTERS, 83 (19): 3924-3926; 2003
Abstract:
Change in local atomic environment during crystallization of Zr-based glassy alloys was studied by extended x-ray absorption fine structure (EXAFS) spectroscopy. The formation of icosahedral quasicrystalline phase followed by crystallization of tetragonal CuZr2 has been observed in the Zr70Cu29Pd1 glassy alloy during annealing up to 850 K. On the other hand, the binary Zr70Cu30 alloy shows a single glassy to crystalline CuZr2 phase transformation. The local atomic environment of as-quenched Zr70Cu30 alloy is matched to an icosahedral local atomic configuration, which is similar to that of the as-quenched Zr70Cu29Pd1 alloy and the alloy annealed at 593 K containing icosahedral phase. Considering that the supercooled liquid region appears prior to crystallization in the Zr70Cu30 glassy alloy, the observed results support the theory claiming a strong correlation between the existence of local icosahedral short-range order and stability of the supercooled liquid state. (C) 2003 American Institute of Physics.
Title:
Effect of Ru substitution for Re on the thermoelectric properties of AlPdRe icosahedral quasicrystals
Authors:
Nagata, T; Kirihara, K; Kimura, K; Guo, GC;
Source:
JOURNAL OF APPLIED PHYSICS, 94 (10): 6560-6565; 2003
Abstract:
The thermoelectric properties of the quaternary AlPdReRu icosahedral quasicrystals (i-AlPdReRu) obtained by replacing Re with Ru in AlPdRe icosahedral quasicrystals have been studied. In the middle of the substitution of Ru for Re, the electrical conductivity increases and the peak of Seebeck coefficient shifts to a higher temperature side. By Ru substitution for the AlPdRe quasicrystal, the dimensionless figure of merit (ZT) increases 1.5 times from 0.1 to 0.15. According to the result of two-band analysis, the effective mass has peaks at both the compositions of i-AlPdRe and i-AlPdReRu which reveal the peak ZT values. We ascribe the behavior of effective mass to the change in the bond strength of intra- and inter-Mackay icosahedral clusters. (C) 2003 American Institute of Physics.
Title:
Three-dimensional reconstruction of the nu-AlCrFe phase by electron crystallography
Authors:
Zou, XD; Mo, ZM; Hovmoller, S; Li, XZ; Kuo, KH; Raffy, H;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 59 (18): 526-539; 2003
Abstract:
The three-dimensional (3D) structure of the huge quasicrystal approximant nu-AlFeCr (space group P6(3)/m, a = 40.687 and c = 12.546 Angstrom) was solved by electron crystallography. High-resolution transmission-electron-microscopy (HREM) images and selected-area electron diffraction patterns from 13 different zone axes were combined to give a 3D potential map. 124 out of 129 unique atoms were found in the 3D map. Procedures for ab initio structure determination by 3D reconstruction are given. It is demonstrated that 3D reconstruction from HREM images is very powerful for solving structures - even very complicated ones. There is no limit in terms of the number of unique atoms in a structure that can be solved by 3D reconstruction.
Title:
Modulated and ordered defect structures in electrically degraded Ni-BaTiO3 multilayer ceramic capacitors
Authors:
Yang, GY; Dickey, EC; Randall, CA; Randall, MS; Mann, LA; Raffy, H;
Source:
JOURNAL OF APPLIED PHYSICS, 94 (9): 5990-5996; 2003
Abstract:
Structural defects formed on {111} planes of BaTiO3 during the degradation of high performance multilayer Ni-BaTiO3 X7R ceramic capacitors are studied using transmission electron microscopy and electron energy loss spectroscopy (EELS). Regular pseudocubic barium titanate grains are present in as-produced (virginal) base-metal electrode capacitors. However, there is a coexistence of regular, modulated, and long-range ordered structures in intentionally electrically degraded devices. The EELS analysis demonstrates that the concentration of oxygen vacancies in barium titanate with modulated or ordered structures is higher than that in the regular perovskite grains. The clustering or accumulation of oxygen vacancies in the structural framework of BaTiO3 gives rise to the formation of new metastable structures. These observations are consistent with earlier models for degradation, but demonstrate that the details of the process may be more complex than originally assumed. Here we introduce new details on the nature of the reduction process and the manner in which the lattice accommodates the enhanced oxygen vacancy concentration towards the failed regions of the capacitors and in the vicinity of the "blocking" cathodic electrodes. (C) 2003 American Institute of Physics.
Title:
Structural disorder in Ti-Fe-Si icosahedral quasicrystal
Authors:
Mandal, P; Dickey, EC;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 361 (1-2): 96-101; 2003
Abstract:
A systematic structural investigation on rapidly solidified Ti-Fe-Si alloy system with various compositions and processing conditions has been carried out. Transmission electron microscopic studies on as-quenched alloys reveal the presence of various kinds of structural disorder. Different kinds of disorder and the resulting deviation from the icosahedral symmetry have been reported. This appears to be the first report of these results on a Ti-Fe-Si system. Anisotropy in the shape of diffraction spots, strong arcs of diffuse scattering of icosahedral phase in melt-quenched alloys have been observed. The microstructure of the icosahedral Ti-Fe-Si alloys has been characterized. Results have been compared with other known Ti based quasicrystalline alloys and analyzed on the basis of current understanding. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Gold as an alloying element promoting formation of a nanoicosahedral phase in a Cu-based alloy
Authors:
Louzguine, DV; Inoue, A; Randall, CA;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 361 (1-2): 153-156; 2003
Abstract:
The present paper presents a new application field of Au as an alloying element in Cu-based glassy alloys with a tendency to form nanoscale icosahedral particles having quasicrystalline symmetry upon devitrification. Nanoicosahedral particles with a size below 10 nm are formed in the amorphous matrix of Cu55Zr30Ti10Au5 glassy alloy in the initial stage of the devitrification process. The paper also illustrates structure changes on heating studied by X-ray diffraction, transmission electron microscopy, differential scanning and isothermal calorimetry methods. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Formations of amorphous and quasicrystal phases in Ti-Zr-Ni-Cu alloys
Authors:
Wang, LM; Ma, LQ; Ma, CL; Inoue, A; Mann, LA;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 361 (1-2): 234-240; 2003
Abstract:
The structure of melt-spun Ti45Zr35Ni20-x Cu-x (x=0, 1, 3, 5 and 7) alloys and a cast Ti45Zr35Ni17Cu3 bulk alloy have been studied. The melt-spun alloys have different structures depending on the thickness of the melt-spun ribbons. When the thickness is 86+/-5 mum, icosahedral quasicrystal (I) and Laves (L) phases are formed for x = 0 and 7, and a single I phase is formed for x = 1, 3 and 5. When the thickness decreases to 20 +/- 2 mum, I and amorphous phases are formed for x = 0 and 1, and a single amorphous phase is formed for x = 3, 5 and 7. The thickness of 15 +/- 1 mum for x = 0 and 1 also causes the formation of a single amorphous phase. The cast alloy also has different structures depending on the size of the bulk samples. The structure of the cast rod sample with a diameter (D) of I mm consists mainly of I and amorphous phases. The I phase is homogenously distributed and its particle size is less than 5 mum. I and C14 L phases are formed in the cast rod sample with D of 2 mm. The particle size of the I phase is less than 10 mum. The volume fraction (V-f) of the I phase is about 67% for D of 1 mm rod and 55% for D of 2 mm rod. Three phases of I phase, C14 L and beta-(Ti,Zr) are formed in the cast rod sample with D of 3 mm. EDS measurement indicates that the I phase has an approximate composition of Ti49Zr36Ni13CU2. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Magnetic properties of FePt nanoparticles
Authors:
Rellinghaus, B; Stappert, S; Acet, M; Wassermann, EF; Mann, LA;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 266 (1-2): 142-154; 2003
Abstract:
We have prepared FePt nanoparticles with concentrations in the vicinity of the stoichiometric Fe50Pt50 composition by means of a gas-phase-based process. The preparation technique employed allows to anneal ('sinter') the particles in the gas-phase prior to their deposition. Depending on the gas-pressure during preparation, the structure of the unsintered particles is icosahedral or polycrystalline face-centered cubic (FCC). Temperature-dependent magnetization measurements reveal that these particles are superparamagnetic at room temperature. Gas-phase sintering of polycrystalline FCC FePt nanoparticles results in the formation of predominantly single crystal particles which are face-centered tetragonal due to an increased degree of L1(0) order at elevated sintering temperatures T-S. Concurrently, we observe an increase of both the blocking temperature T-B and the coercivity H-C with increasing T-S. This enhancement of T-B and H-C is more pronounced in iron-rich off-stoichiometric samples, for which the concentrations are still within the L1(0) stability range of the FePt phase diagram. FC62Pt38 particles, which are sintered at T-S = 1273 K, reach T-B = 530 K and H-C0 = H-C(T = 0) = 4.7 kOe. Whereas the elevated blocking temperature is mainly due a somewhat increased particle size at elevated sintering temperatures, the higher coercivity is attributed to the enhanced degree of L1(0) order in the gas-phase sintered particles. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Role of nanometer-scale quasicrystals in improving the mechanical behavior of Ti-based bulk metallic glasses
Authors:
Kim, YC; Na, JH; Park, JM; Kim, DH; Lee, JK; Kim, WT; Li, ZZ;
Source:
APPLIED PHYSICS LETTERS, 83 (15): 3093-3095; 2003
Abstract:
The effect of the precipitation of nanosized quasicrystals on the mechanical properties of Ti-Zr-Cu-Ni-Be bulk metallic glasses (BMG) has been investigated. The Ti40Zr29Cu8Ni7Be16 BMG crystallizes by forming a few nanometer-size quasicrystals in the amorphous matrix, enabling the fabrication of quasicrystal-reinforced BMG matrix composites. Simultaneous improvement of strength and ductility can be obtained when 3-5-nm-size quasicrystals are isolated and homogeneously distributed in an amorphous matrix. The fracture strength and global strain, respectively, increase from 1921 MPa and 5.1% for as-cast BMG to 2084 MPa and 6.2% for partially crystallized BMG with the volume fraction of similar to7% quasicrystals. These improvements may be attributed to the structural similarity between quasicrystalline and amorphous phases. Stable low-energy interface between two phases may act as a source for multiple-shear-band formation. (C) 2003 American Institute of Physics.
Title:
REMGa3Ge and RE3Ni3Ga8Ge3 (M = Ni, Co; RE = rare-earth element): New intermetallics synthesized in liquid gallium. X-ray, electron, and neutron structure determination and magnetism
Authors:
Zhuravleva, MA; Pcionek, RJ; Wang, XP; Schultz, AJ; Kanatzidis, MG; Zhang, ZP;
Source:
INORGANIC CHEMISTRY, 42 (20): 6412-6424; 2003
Abstract:
New quaternary intermetallic phases REMGa3Ge (1) (RE = Y, Sm, Tb, Gd, Er, Tm; M = Ni, Co) and RE3Ni3Ga8Ge3 (2) (RE = Sm, Gd) were obtained from exploratory reactions involving rare-earth elements (RE), transition metal (M), Ge, and excess liquid Ga the reactive solvent. The crystal structures were solved with single-crystal X-ray and electron diffraction. The crystals of 1 and 2 are tetragonal. Single-crystal X-ray data: YNiGa3Ge, a = 4.1748(10) Angstrom, c = 23.710(8) Angstrom, V = 413.24(2) Angstrom(3), 14/mmm, Z = 4; Gd3Ni3Ga8Ge3, a = 4.1809(18) Angstrom, c = 17.035(11) Angstrom, V = 297.8(3) Angstrom(,)(3) P4/mmm, Z = 1. Both compounds feature square nets of Ga atoms. The distribution of Ga and Ge atoms in the REMGa3Ge was determined with neutron diffraction. The neutron experiments revealed that in 1 the Ge atoms are specifically located at the 4e crystallographic site, while Ga atoms are at 4d and 8g. The crystal structures of these compounds are related and could, be derived from the consecutive stacking of disordered [MGa](2) puckered layers, monatomic RE-Ge planes and [MGa4Ge2] slabs. Complex superstructures with modulations occurring in the ab-plane and believed to be associated with the square nets of Ga atoms were found by electron diffraction. The magnetic measurements show antiferromagnetic ordering of the moments located on the RE atoms at low temperature, and Curie-Weiss behavior at higher temperatures with the values of mu(eff) close to those expected for RE3+ free ions.
Title:
Dynamical dielectric properties of [4-NH2C5H4NH][SbCl4] in the incommensurate phase
Authors:
Bator, G; Jakubas, R; Tokizaki, T;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 72 (9): 2369-2371; 2003
Abstract:
Dielectric dispersion is shown to occur at radio-frequencies in single crystals of [4-NH2C5H4NH][SbCl4] in the frequency range of 200 Hz-1 MHz. It is found that dielectric dispersion, measured in the incommensurate phase (270.5-304 K) along the [102] direction of the monoclinic symmetry, is monodispersive, except for the close vicinity of T-c = 270.5 K, for T < T-c + 1 K. In the incommensurate phase (for T > T-c) the apparent critical slowing down is found with tau approximate to 1 X 10(-4) s just above T-c.
Title:
Microstructural evolution and macroscopic property relationship in antiferroelectric lead lanthanum stannate zirconate titanate ceramics
Authors:
Chan, WH; Xu, Z; Zhang, Y; Hung, TF; Chen, HD; Weston, JL;
Source:
JOURNAL OF APPLIED PHYSICS, 94 (7): 4563-4565; 2003
Abstract:
The antiferroelectric (AFE) Pb0.97La0.02(Zr0.60Sn0.30Ti0.10)O-3 ceramic has a composition near the morphotropic phase boundary that separates the AFE from the ferroelectric (FE) phase. Its structural changes as well as macroscopic properties were investigated over a temperature range of -180-300 degreesC using transmission electron microscopy, dielectric spectroscopy, and Sawyer-Tower polarization measurements. The previously reported tetragonal AFE phase is shown to be an incommensurate orthorhombic phase and it exhibits a sequence of phase transformations on heating from the incommensurate AFE to a multicell cubic, then to a simple cubic phase. This microstructural evolution with temperature is consistent with the corresponding macroscopic dielectric and AFE behaviors. The temperature dependence of the AFE-FE switching field is closely associated with the corresponding temperature dependence of the incommensurate modulation wavelength. (C) 2003 American Institute of Physics.
Title:
Initial stages of the decomposition of the decagonal phase in the system Al-Ni-Fe
Authors:
Doblinger, M; Wittmann, R; Grushko, B; Mensch, A;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 360 (1-2): 162-167; 2003
Abstract:
The decomposition of the Al-Ni-Fe decagonal quasicrystalline phase was studied in situ and ex situ by transmission electron microscopy. In contrast to many known transformations of quasicrystals, no long-range ordered transition states closely related to the quasicrystal were observed during its decomposition to three neighbouring periodic phases. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Isothermal sections of the Al-rich part of the Al-Ni-Ru phase diagram
Authors:
Mi, S; Grushko, B; Dong, C; Urban, K; Zheng, LX;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 359 (13): 193-197; 2003
Abstract:
The Al-rich part of the Al-Ni-Ru phase diagram was investigated by scanning electron microscopy and powder X-ray diffraction. The system contains four stable ternary crystalline phases and a stable ternary decagonal quasicrystalline phase with 1.6 nm periodicity. Partial isothermal 700, 800, 900, 1000 and 1100 degreesC sections were determined. The monoclinic Al13Ru4 phase was found to dissolve up to 7.0 at.% Ni at 1100 degreesC. The ternary extensions of Al3Ni, Al3Ni2, Al2Ru and Al6Ru are below 1.0 at.%. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Formation of quasicrystals by partial devitrification of ball-milled amorphous Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5
Authors:
Scudino, S; Eckert, J; Kuhn, U; Schultz, L; Zheng, LX;
Source:
APPLIED PHYSICS LETTERS, 83 (12): 2345-2347; 2003
Abstract:
Amorphous Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 powder with low oxygen contamination was prepared by ball milling of crystalline intermetallic compounds. The comparison with the corresponding alloy produced by melt spinning shows that the first crystallization phase does not depend on the way of preparation. In fact, devitrification of both powder and ribbon is characterized by the formation of a metastable nanoscale quasicrystalline phase during the first stage of the crystallization process. This suggests that both the amorphous ball-milled powder and the melt-spun ribbon have the same short-range order and that if this short-range order is icosahedral, it can be achieved also by solid-state processing. (C) 2003 American Institute of Physics.
Title:
Incommensurate magnetic ordering in NdNiSn
Authors:
Szytula, A; Penc, B; Stusser, N; Kim, G;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 265 (1): 94-97; 2003
Abstract:
Polycrystalline sample of NdNiSn compound has been prepared and studied by powder neutron diffraction measurements. NdNiSn crystallizes in the orthorhombic TiNiSi-type structure (space group Pnma). Below the Neel temperature equal to 3.0 K the Nd magnetic moments form an incommensurate sine-wave modulated structure described by the propagation vector k=(0, 0.482(1), 0.248(3)). Magnetic moments equal 2.42(9) mu(B) lie in the a-b plane and form the angle of 39degrees with the b-axis. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
The conical magnetic structure of Dy5Si3
Authors:
Semitelou, JP; Yakinthos, JK; Stusser, N;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 265 (2): 152-155; 2003
Abstract:
At 2 K the magnetic propagation vector has a k(z) = 0.2593(4) c* component and the dysprosium magnetic moments directions form a cone with its axis making an angle of 35degrees with the c-axis of the crystal. Their amplitudes are 7.9 and 4.5mu(B) for the 4d and 6 g sites, respectively. Neutron diffraction and susceptibility measurements on a powdered Dy5Si3 compound, crystallizing in space group P6(3)/mcm, indicate an incommensurate magnetic structure with Neel temperature equal to 125 K. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Determination of nanoparticle structure type, size and strain distribution from X-ray data for monatomic f.c.c.-derived non-crystallographic nanoclusters
Authors:
Cervellino, A; Giannini, C; Guagliardi, A; Kim, G;
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 36 (2): 1148-1158; 2003
Abstract:
Whole-profile-fitting least-squares techniques are applied to simulated and experimental X-ray diffraction patterns of monatomic face-centred cubic (f.c. c.)derived non-crystallographic nanoclusters to extract structure and size information. Three main structure types have been considered (cuboctahedral, icosahedral and decahedral). Nanocluster structure models have been generated within an original mathematical approach so as to be independent of a specific material. For each structure type, a log-normal size distribution is assumed and a phenomenological function is introduced to model possible additional size-related strain effects. The Debye function method (modified to increase computational efficiency) has been used to obtain the diffracted intensities of the nanocluster. Tests revealed the effectiveness of the method to recognize the structure types correctly and to estimate with good accuracy structure concentrations and size distributions. Application to a thiol-passivated gold nanoparticle sample is presented.
Title:
Anomalous Debye-Waller factor associated with an order-disorder transformation in an Al72Ni20Co8 decagonal quasicrystal
Authors:
Abe, H; Saitoh, H; Ueno, T; Nakao, H; Matsuo, Y; Ohshima, K; Matsumoto, H; Kao, YH;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 72 (8): 1828-1831; 2003
Abstract:
order-disorder transformation in a single decagonal quasicrystal of Al72Ni2OCo8 is studied in detail. In X-ray diffraction, the anomalous attenuation of intensities of Bragg reflections was found around the transformation temperature, T-c. The intensity attenuation at high temperature is explained by the anomalous Debye-Waller factor in thermal lattice dynamics. In particular, the intensity ratio above T-c and below T-c depends on \G(parallel to)\(2) values. In addition, the intensity ratio between room temperature and high temperature shows \G(perpendicular to)\(2) dependence. The results correspond to the in situ observation of a local vibrational anomaly related to an atomic flip by electron microscopy [Abe et al.: Nature 421 (2003) 347]. By X-ray diffraction, dynamic fluctuations as observed in electron microscopy are also realized even on a macroscopic scale at high temperature.
Title:
Localized electron nature of the antiferromagnetism of (CePd3)(8)Ge: Response to hydrostatic pressure and neutron diffraction
Authors:
Tabata, Y; Watanabe, K; Ohoyama, K; Yamaguch, Y; Ishizuka, M; Okada, K; Taniguchi, T; Takeuchi, T; Ramakrishnan, S; Kawarazaki, S; Furdyna, JK;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 72 (8): 2091-2096; 2003
Abstract:
The magnetic properties of the compound (CePd3)(8)Ge have been studied by means of neutron diffraction and specific heat measurement at ambient pressure and also of measurements of susceptibility and electrical resistivity under hydrostatic pressure. The magnetic modulation vector, q, of the antiferromagnetic phase is {001} and the spin polarization is parallel to q. With increasing the applied pressure up to 6 GPa, the Neel temperature keeps increasing, which indicates a strongly localized nature of the 4f-electrons of the compound.
Title:
Molecular dynamics simulation for the stability of structural incommensurability in K-hollandite
Authors:
Michiue, Y; Watanabe, M; Ohoyama, K;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 72 (8): 2122-2123; 2003
Abstract:
The magnetic properties of the compound (CePd3)(8)Ge have been studied by means of neutron diffraction and specific heat measurement at ambient pressure and also of measurements of susceptibility and electrical resistivity under hydrostatic pressure. The magnetic modulation vector, q, of the antiferromagnetic phase is {001} and the spin polarization is parallel to q. With increasing the applied pressure up to 6 GPa, the Neel temperature keeps increasing, which indicates a strongly localized nature of the 4f-electrons of the compound.
Title:
The maximum-entropy method in superspace
Authors:
van Smaalen, S; Palatinus, L; Schneider, M; Xiao, M;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 59 (9): 459-469; 2003
Abstract:
One of the applications of the maximum-entropy method (MEM) in crystallography is the reconstruction of the electron density from phased structure factors. Here the application of the MEM to incommensurately modulated crystals and incommensurate composite crystals is considered. The MEM is computed directly in superspace, where the electron density in the (3+d)-dimensional unit cell (d > 0) is determined from the scattering data of aperiodic crystals. Periodic crystals (d = 0) are treated as a special case of the general formalism. The use of symmetry in the MEM is discussed and an efficient algorithm is proposed for handling crystal symmetry. The method has been implemented into a computer program BayMEM and applications are presented to the electron density of the periodic crystal NaV2O5 and the electron density of the incommensurate composite crystal (LaS)(1.14)NbS2. The MEM in superspace is shown to provide a model-independent estimate of the shapes of the modulation functions of incommensurate crystals. The discrete character of the electron density is found to be the major source of error, limiting the accuracy of the reconstructed modulation functions to approximately 10% of the sizes of the pixels. MaxEnt optimization using the Cambridge and Sakata-Sato algorithms are compared. The Cambridge algorithm is found to perform better than the Sakata-Sato algorithm, being faster, always reaching convergence, and leading to more reliable density maps. Nevertheless, the Sakata-Sato algorithm leads to similar density maps, even in cases where it does not reach complete convergence.
Title:
New organic superconductors with an incommensurate anion lattice consisting of polyhalide chains (MDT-TSF)X-y (MDT-TSF = methylenedithiotetraselenafulvalene; X = halogen; y=1.27-1.29)
Authors:
Takimiya, K; Kodani, M; Kataoka, Y; Aso, Y; Otsubo, T; Kawamoto, T; Mori, T; Kissel, H;
Source:
CHEMISTRY OF MATERIALS, 15 (17): 3250-3255; 2003
Abstract:
The title radical cation salts of MDT-TSF (methylenedithiotetraselenafulvalene) with polyhalide anions prepared by electrocrystallization in the presence of various tetrabutylammonium trihalides show high conductivity at room temperature (>10(3) S cm(-1)) and become superconductors at below 4.0-5.5 K under ambient pressure. Their crystal structures elucidated by X-ray structural analysis are characterized by quasi two-dimensional conducting sheets consisting of uniform donor stacks. Their X-ray oscillation photographs reveal the existence of an incommensurate anion lattice originating from the infinite polyhalide chains. The chemical composition of these salts, as determined on the basis of the X-ray photographs together with the combustion elemental analyses, is (MDT-TSF)X1.27-1.29 (X = halogen). Considering that the most probable charged unit in the polyhalide chain is the trihalide (X-3(-)), the charge-transfer degree on each donor molecule is estimated to be nonstoichiometric, 0.42-0.43.
Title:
The magnetic phase diagram of the HoCo2X2 (X = Ge, Si) and DyCo2Ge2 compounds by neutron diffraction
Authors:
Schobinger-Papamantellos, P; Buschow, KHJ; Ritter, C; Keller, L; Swanekamp, SB;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 264 (2-3): 130-141; 2003
Abstract:
The magnetic ordering of the tetragonal (14/mmm) HoCo2X2 (X=Ge, Si) and DyCo2Ge2 compounds with the ThCr2Si2 type of structure has been reinvestigated by neutron powder diffraction. The HoCo2Si2 compound orders exclusively with the type-I antiferromagnetic structure with the wave vector q = (0, 0, 1) and the moments confined to the c-axis, while the magnetic-phase diagrams of the DyCo2Ge2 and HoCo2Ge2 compounds comprise three distinct regions of magnetic ordering: a low-temperature structure also of type-I (q, = (0, 0, 1)), stable in the range between 2 K and T-1C, a high-temperature longitudinal sine wave modulated structure with the wave vector q(2) = (0,0, 1 - q(z)), stable in the range T-IC-T-N and a coexistence region of q(1) and q(2) around T-IC. The wave vector component q(z) has a temperature-dependent length and locks-in by a first-order transition to the value q(z) = 0 at T-IC. In the case of the DyCo2Ge2 compound a spin reorientation transition was detected in the low-temperature range. The ordered moment values at 1.5 K are 7.8(1) mu(B)/Dy and 9.33(1) mu(B)/Ho for the RCo2Ge2 compounds and 8.8(1) mu(B)/Ho atom for the HoCo2Si2 compound at 3 K. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Magnetic structures of R3Cu4Ge4 (R = Tb, Dy, Ho, Er)
Authors:
Wawrzynska, E; Hernandez-Velasco, J; Penc, B; Szytula, A; Zygmunt, A; Belenky, G;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 264 (2-3): 192-201; 2003
Abstract:
Neutron diffraction studies of polycrystalline R3Cu4Ge4 (R = Tb; Dy, Ho, Er) intermetallic compounds with the orthorhombic Gd3Cu4Ge4-type crystal structure indicate complex magnetic structures. In these compounds the rare earth atoms occupy two nonequivalent 2d and 4c sublattices. For R=Tb and Er with decreasing temperature the magnetic moments in the 2d sublattice order first; the 4e sublattice magnetic moments order at lower temperatures. For R = Dy, Ho both sublattices order simultaneously although the magnetic moment values are different for each of them. In the compounds with R = Tb and Er a change of the magnetic structure, connected with the 2d sublattice, is observed near the Neel temperature. This is a transition from the commensurate structure, described by the propagation vector k = (0, 1/2, 0) at low temperatures to the incommensurate structure with k = (0, 1/2 + delta, 0) at higher temperatures (still below the Neel temperature). (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Local structure in hydrogenated Ti-Zr-Ni quasicrystals and approximants
Authors:
Sadoc, A; Majzoub, EH; Huett, VT; Kelton, KF; Zygmunt, A;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 356 (2-3): 96-99; 2003
Abstract:
We have investigated the influence of hydrogen on the local structure of Ti-Zr-Ni alloys, icosahedral quasicrystals or crystalline approximants, using extended X-ray absorption fine structure (EXAFS). With an increasing hydrogen-to-metal ratio from 0 to 1.7, a general increase of all the mean first distances was found except for the Zr-Ni (Ni-Zr) ones. The perturbation of the (quasi)lattice, induced by hydrogenation, is a maximum around the Ti and Zr atoms, which suggests that hydrogen atoms sit preferentially near titanium and zirconium atoms. (C) 2002 Elsevier B.V. All rights reserved.
Title:
Lithium and vacancy ordering in T(#)2-LixCoO2 derived from O2-type LiCoO2
Authors:
Shao-Horn, Y; Weill, F; Croguennec, L; Carlier, D; Menetrier, M; Delmas, C; Kawarazaki, S;
Source:
CHEMISTRY OF MATERIALS, 15 (15): 2977-2983; 2003
Abstract:
Electron diffraction revealed evidence of commensurate and incommensurate superstructures in an unusual phase, T(#)2, derived from O2-type layered LiCoO2 upon lithium deintercalation. 2a(orth.) x 2b(orth.) x 2c(orth.), 2a(orth.) x b(orth.) x C-orth., and incommensurate with q = gammaa(orth)* (gamma = 0.23 and 0.36) superstructures were found. It is believed that lithium and vacancy ordering is the most probable cause for the presence of these superstructures. Lithium ordering configurations were discussed in detail with respect to the superstructures observed. It is believed that the presence of various lithium and vacancy ordering configurations improves the stability of the T(#)2 structure over a range of lithium compositions. Nevertheless, it should be mentioned that the nature of superstructures present and possible lithium ordering configurations in T(#)2-LixCoO2 were complex and further investigations are needed. In addition, it is of significance to point out that a combination of transmission electron microscopy and electron diffraction showed that three T(#)2 variants could coexist in different regions within one T(#)2 crystal, which led to the development of a domain (mazed) microstructure.
Title:
In situ high-temperature powder diffraction study of reversible phase transitions in decagonal Al71.2Co12.8Ni16
Authors:
Soltmann, C; Beeli, C; Luck, R; Gander, W; Fukui, T;
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 36 (4): 1030-1039; 2003
Abstract:
This experimental work is aimed at confirming and broadening findings of former investigations into the type I <-> S1 phase transition in Al - Co - Ni quasicrystals. In situ high-temperature synchrotron radiation measurements were carried out on Al71.2Co12.8Ni16 powder samples. The cell parameters were precisely determined at various temperatures in the range 290 - 1110 K. The data provided a new extended insight into the thermal expansion of Al71.2Co12.8Ni16 and into fundamental properties of the phase transition.
Title:
Inflation rule for Gummelt coverings with decorated decagons and its implication for quasi-unit-cell models
Authors:
Jeong, HC; Beeli, C;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 59 (4): 361-366; 2003
Abstract:
The equivalence between quasi-unit-cell models and Penrose-tile models on the level of decorations is proved using inflation rules for Gummelt coverings with decorated decagons. Owing to overlaps, Gummelt arrangement of decorated decagons gives rise to nine different (context-dependent) decagon decorations in the covering. The inflation rules for decagons for each of nine types are presented and it is shown that inflations from differently typed decagons always produce different decorations of inflated decagons. However, if the original decagon region is divided into 'equivalent' rhombus Penrose tiles, typed-decagon arrangements in the tiles (of the same shape) become identical for the fourfold inflated decagons. This implies that a decagonal quasi-unit-cell model can be reinterpreted as a Penrose-tile model with fourfold deflated supertiles.
Title:
Modulated uric acid crystal growth in the presence of acridine dyes
Authors:
Fink, DA; Sours, RE; Swift, JA; Gander, W;
Source:
CHEMISTRY OF MATERIALS, 15 (14): 2718-2723; 2003
Abstract:
Single crystals of anhydrous uric acid (UA) and uric acid dihydrate (UAD) were grown from supersaturated aqueous solutions containing the fluorescent dye acriflavine neutral (AN), a two-component commercial mixture of proflavine (P), and its 10-methylated analogue acriflavine (A). During UA crystal growth at 37 degreesC, small quantities of AN, P, and A dye probes are found to be selectively included in {001} and {201} growth sectors. Increasing concentrations of dye in solution show a general retardation in the growth of (121) faces, resulting in an overall change from a rectangular to a prismatic habit. For UAD growth at 25 degreesC, AN, P, and A inclusion does not appear to favor any particular growth sector, and no discernible habit changes are observed under even the most concentrated dye solutions examined. The average orientation of dye molecules trapped in the UA and UAD matrixes was determined from polarization data obtained from a home-built microspectrometer. Dye-surface recognition events can be discerned on the basis of the calculated dye orientation. The difference in the interlayer distance between uric acid layers in UA and UAD and the resultant surface perturbations caused by dye recognition and inclusion can be used to rationalize the observed habit modification in the anhydrous form.
Title:
Semiconductivity in aluminum-transition-metal quasicrystalline alloys induced by ordering in six dimensions
Authors:
Krajci, M; Hafner, J; Hesse, D;
Source:
EUROPHYSICS LETTERS, 63 (1): 63-68; 2003
Abstract:
We report on a class of icosahedral aluminum-transition-metal (Al-TM) alloys with true semiconducting behavior. The existence of a semiconducting gap is found to depend critically on a particular kind of Al-TM ordering defined by a simple rule in the 6-dimensional superspace. Any deviation from this 6D order leads to the formation of strongly localized defect states in the gap. We show that by a judicious selection of transition metals to be alloyed with Al, we can find alloys with a semiconducting gap at the Fermi level for a hierarchy of approximants to a quasicrystal. As the electron/atom ratio placing the Fermi level into the gap is slightly different for each approximant, this suggests that the gap persists also in the quasiperiodic limit. Icosahedral Al-Pd-Re turns out to be a semiconductor with a band gap filled by the localized states.
Title:
Oxygen-stabilized glass formation in Zr80Pt20 melt-spun ribbons
Authors:
Sordelet, DJ; Yang, XY; Rozhkova, EA; Besser, MF; Kramer, MJ; Dong, ZL;
Source:
APPLIED PHYSICS LETTERS, 83 (1): 69-71; 2003
Abstract:
The as-quenched structure of Zr80Pt20 melt-spun ribbons containing measured oxygen contents ranging from 184 to 4737 ppm mass was studied. Ribbons containing less than 500 ppm mass oxygen are fully crystallized and consist predominantly of a metastable ordered beta-Zr phase with significant solution of Pt. Increasing oxygen content to 1053 and 1547 ppm mass produces a transition to fully amorphous and to mixed amorphous and quasicrystalline structures, respectively. Samples containing 4737 ppm mass consist of quasicrystalline and crystalline phases in an amorphous matrix. The results from this study suggest a critical level of oxygen is required to promote glass formation in Zr80Pt20 melt-spun ribbons produced at a specific quench rate. (C) 2003 American Institute of Physics.
Title:
Vortex structure and periodicity of disturbances in the wake of a rotationally oscillating cylinder
Authors:
Furukawa, H; Sasakawa, T;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 72 (5): 1092-1097; 2003
Abstract:
The onset of periodic behavior in a two-dimensional unsteady flow past a rotationally oscillating circular cylinder is examined numerically by the finite-element method. The main emphasis is placed on the wake-cylinder response for the high oscillation frequency. The frequency responses are examined by measuring the power spectra of the lift coefficient. It is shown that rotary oscillations produce a coupled wake-cylinder response. The power spectra of the lift coefficient associated with these coupled motions have dominant peaks which are combinations of multiples of the shedding frequency and the forcing frequency. Instantaneous vorticity contours are also displayed to show the near-wake flow structure subjected to the controlled forcing.
Title:
Non-stripe charge order in the theta-phase organic conductors
Authors:
Mori, T; Mashiyama, H;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 72 (6): 1469-1475; 2003
Abstract:
Phase diagrams of charge order patterns of the theta-phase organic conductors are investigated on the basis of the static-limit extended Hubbard model including the second nearest Coulomb repulsion V. Since the theta-phase is close to the triangular lattice rather than the square lattice, a 3-fold non-stripe charge order is stable in a considerably large region between the stripe phases and the uniform phase. At finite temperatures, such unevenly ordered patterns as the 3-fold phase D+D21/4+ become more stable than the evenly ordered stripes, (D+D0), and it is unlikely that the stripe phase directly transforms to the uniform phase. These results suggest the existence of an unevenly ordered pattern in the metallic state of theta-(BEDT-TTF)(2)RbM(SCN)(4) [BEDT-TTF: bis(ethyleneditho)tetrathiafulvalene, M = Zn and Co] above T-MI = 190 K, accounting for the observation of modulated structures in the X-ray measurement, broadening of the NMR line, flat temperature dependence of the resistivity, and the first-order character of the 190 K transition.
Title:
First-principle predictions of magnetic properties for a complex and strongly related to quasicrystalline phase: mu-Al4Mn
Authors:
Nguyen-Manh, D; de Laissardiere, GT; Morcrette, M;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 262 (3): 496-501; 2003
Abstract:
First-principle spin-polarized electronic structure calculations have been performed in the structure of mu-Al4Mn, a crystalline phase of 568 atoms per cell, considered to be closely related to the icosahedral quasicrystalline i-AlMn. It is found that the ferromagnetic state in this structure is more stable than corresponding paramagnetic one, being only about 156 meV/cell lower in energy. The average magnetic moment is predicted of 0.432 mu(B) per Mn atom and we show that its formation is governed by a local Stoner criterion. A creation of Hume-Rothery pseudogap nearby the Fermi level due to strong Al-sp-Mn-d hybridization in crystalline intermetallic compound is the origin of partially suppressed magnetic moment on all inequivalent Mn sites. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Sodium carbonate revisited
Authors:
Dusek, M; Chapuis, G; Meyer, M; Petricek, V; Grinevitch, V;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 59 (22): 337-352; 2003
Abstract:
We present the structure of anhydrous sodium carbonate at room temperature ( phase gamma) and 110 K ( phase delta) based on single-crystal X-ray diffraction data. The incommensurate phase gamma was determined almost 30 years ago in the harmonic approximation using one modulation wave and first-order satellites. In our work we use satellites up to fifth order and additional harmonic waves to model the anharmonic features of the structure. The commensurate phase delta is presented for the first time. Using the superspace approach, both phases are compared in order to find common trends in the whole range of the sodium carbonate phases. We present arguments supporting the hypothesis that the driving force of the phase transitions may originate in the unsaturated bonding potential of one of the Na ions.
Title:
Structural changes of hexamethylenetetramine and undecanedioic acid co-crystal (HMT-C11) as a function of the temperature
Authors:
Pinheiro, CB; Gardon, M; Chapuis, G; Lukaszewicz, K;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 59 (22): 416-427; 2003
Abstract:
HMT-C11 belongs to the family of adducts formed by the cocrystallization of N-4(CH2)(6) molecules ( hexamethylenetetramine or HMT) and aliphatic dicarboxylic acids HOOC(CH2)(n-2)COOH with 5 less than or equal to n less than or equal to 13 (Cn). The adducts exhibit a layered structure in which the packing between HMT and Cn is determined by strong hydrogen bonds. The compounds in this family studied so far present thermotropic structural phase transitions and, depending on the chain length, disordered, twinned and modulated phases. The structure refinement of HMT-C11 based on X-ray diffraction experiments indicates three distinct phases from the melting point down to liquid nitrogen temperature: phase I is not crystalline; phase II is disordered ( stacking fault) and its average structure is described in space group Bmmb; phase III is partially disordered and its symmetry is P2(1)/c. The systematic study of the structure evolution of phase III upon cooling revealed that the disorder has a dynamic character (anharmonicity). The main structural change observed from 293 K down to 93 K is the increase of the tilting angle of the C11 chains relative to the layer plane and the rotation of the HMT molecules. Both HMT and C11 behave like rigid bodies in the temperature range investigated. The quality of the refinements leads to a conclusive model for the O-H...N hydrogen bonds linking HMT and C11.
Title:
Unusual magnetic effects in an itinerant electron antiferromagnetic Cr-Pt alloy single crystal
Authors:
Venter, AM; Alberts, HL; Prinsloo, ARE; Dawe, AM; Kohno, H;
Source:
JOURNAL OF APPLIED PHYSICS, 93 (10): 7269-7271; 2003
Abstract:
Thermal expansion and neutron diffraction measurements are reported on a Cr+0.16 at. % Pt alloy single crystal. Anomalous hysteresis behavior is observed in the temperature dependence of the magnetovolume (Deltaomega) and of the magnitude of the spin-density-wave (SDW) wave vector (Q) below the incommensurate-commensurate SDW phase transition temperature. The hysteresis effects in Deltaomega and Q seem to be related, but are not linked in theoretical models. (C) 2003 American Institute of Physics.
Title:
Magnetic anisotropy in Ni-Mn-Ga martensites
Authors:
Straka, L; Heczko, O; Krivorotov, IN;
Source:
JOURNAL OF APPLIED PHYSICS, 93 (10): 8636-8638; 2003
Abstract:
We study the temperature dependence of the magnetic anisotropy of three different martensites known to exist in the Ni-Mn-Ga alloys. The anisotropy constants were determined from magnetization curves measured at different temperatures. The anisotropy of five-layered modulated tetragonal martensite is uniaxial with easy magnetization direction along short crystallographic axis. At room temperature K-1(rt)=1.65x10(5) J m(-3) and K-2 is negligible. Seven-layered modulated orthorhombic martensite exhibits easy magnetization direction along the shortest crystallographic axis. K-1(rt)=1.7x10(5) J m(-3) and K-2(rt)=0.9x10(5) J m(-3) referring to hard and mid-hard magnetization axes. Nonmodulated tetragonal martensite possesses a uniaxial anisotropy with easy plane and hard magnetization direction along the long crystallographic axis with K-1(rt)=-2.3x10(5) J m(-3) and K-2(rt)=0.55x10(5) J m(-3). The temperature dependence of K-1(T) of five-layered martensite follows magnetization power law with exponent n=3 suggesting a single ion origin of the magnetic anisotropy in Ni-Mn-Ga martensite. (C) 2003 American Institute of Physics.
Title:
Microstructural characterisation of thermally sprayed quasicrystalline Al-Co-Fe-Cr coatings
Authors:
Huttunen-Saarivirta, E; Turunen, E; Kallio, M; Urban, K;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 354 (1-2): 269-280; 2003
Abstract:
A microstructural characterisation was carded out for Al-Co-Fe-Cr feed powder and the coatings sprayed with a high velocity oxy-fuel method using different operation conditions. The aims of the study were to explore the structural development of thick Al-Co-Fe-Cr coatings and the influence of the spraying parameters on the microstructure of produced Al-Co-Fe-Cr coatings. X-ray diffractometry. scanning electron microscopy and analytical transmission electron microscopy were the techniques used in the phase identification and in the microstructural exploration of the study. The results show that Al-Co-Fe-Cr feed powder and the coatings sprayed with low and high operation temperature are composed of a dodecagonal quasicrystalline phase. The composition of this new dodecagonal phase approximately corresponds to that of the feed powder, being Al70.6Co12.5Fe9.4Cr7.5. The dodecagonal phase does not decompose during the spraying process. Instead, it orientates to form a lamellar coating structure. When a lower spraying temperature is used. the incomplete melting of powder particles introduces a partly orientated coating structure. Due to this incomplete melting of powder particles. porosity is also involved in these coatings. Higher spraying temperature, in turn, promotes oxidation, leading to the incorporation of an oxygen-containing film on the splat boundaries. While the feed powder and the coating deposited with a lower spraying temperature are one-phase quasicrystalline structures, the coating sprayed with a higher operation temperature is comprised of a dodecagonal phase and an oxygen-containing phase. This oxygen-containing phase is not pure aluminium oxide but contains all the elements present in the alloy. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Change in the nano-structure of Al-base alloy ribbons in response to tensile stress - a small-angle X-ray scattering study
Authors:
Kamiyama, T; Kimura, H; Sasamori, K; Inoue, A; Zhu, SN;
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 36 (9): 464-468; 2003
Abstract:
The microstructure of aluminum-base alloys consists of icosahedral or amorphous particles 3 to 10 nm in size distributed in the face centered Al-rich matrix. These particles are considered to cause high mechanical strength. Structural changes due to the deformation were detected for some Al-base alloys by small-angle X-ray scattering, even after very weak plastic deformation. An increase in the scattering intensities parallel to the uniaxial tensile stress was detected for scattering vectors near 0.02 Angstrom(-1), and can be attributed to the increase in the structure factor for the correlation between particles. This indicates that the degree of particle ordering is increased in the direction of the uniaxial tension with the motion of dislocations under tensile stress.
Title:
New magnetic structure study of TbNi5: Evidence of incommensurate structure
Authors:
Lee, S; Pirogov, AN; Park, JG; Swainson, IP; Dorofeev, YA; Teplykh, AE; Ermolenko, AS; Gerasimov, EG; Podlesnyak, AA; Yanusova, LG;
Source:
EUROPHYSICS LETTERS, 62 (3): 350-356; 2003
Abstract:
We have investigated the magnetic structure of TbNi5 using neutron diffraction from 2.2 to 30 K to find new magnetic satellites below T-C = 23 K, which have never been reported before. These satellites can be indexed as (0, 0, 1 +/- tau), (1, 0, 1 +/- tau), (0, 0, 2 +/- tau), and (1, 0, 2 +/- tau), where tau is equal to 0.0194 r. l. u. (reciprocal lattice units). We have observed these new peaks in addition to magnetic peaks seen in previous measurements. We can understand this long-period incommensurate structure in terms of two propagation vectors: k(1) = ( 0, 0, 0) and k(2) = (0, 0, tau). From the temperature dependence of the intensity of the commensurate and incommensurate peaks as well as our heat capacity data, we suggest that TbNi5 should have a modulated magnetic structure over the whole temperature range from 23 to 2 K, in contradiction to the long held view that TbNi5 is a collinear ferromagnet below T-C = 23 K.
Title:
Commensurate and incommensurate phases in Ho5Sn3 compound
Authors:
Semitelou, JP; Yakinthos, JK; Park, JG;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 261 (3): 392-398; 2003
Abstract:
Neutron diffraction has been performed on the intermetallic Ho5Sn3 crystallizing in the Mn5Si3-type structure with space group P-63/mcm. Ho5Sn3 has a Neel temperature equal to 22 K, two transition temperatures at 16 and 12 K and a metamagnetic behavior with a critical field H-c = 1.4 T. Between 22 and 16 K it presents an incommensurate magnetic propagation vector, while in the temperature ranges (16-12 K) and (12-1.5 K) two and three propagation vectors (commensurate and incommensurate) respectively. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Te for two: ordering phenomena in doped Ni1+xMyTe2 (M=Ag, Cu, In)
Authors:
Noren, L; Withers, RL; Brink, FJ; Swainson, IP;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 353 (1-2): 133-142; 2003
Abstract:
A detailed TEM and XRD study has been carried out on 138 related ternary solid solution phases in the Ni1+xMyTe2 (M = Ag, Cu, In) systems. Despite previous reports of a large 138 ternary compositional homogeneity range in the Ni1+xMyTe2 (M = Ag) system, no evidence for incorporation of Ag into Ni1+xTe2 could be found. In the case of M = Cu, several Ni1+xMyTe2 (M = Cu) compositions were found to be single-phase and part of a genuine ternary solid solution, but only if the Cu content was at much lower concentrations than previously suggested. In the case of M = In, two roughly determined solid solution fields were observed, an expected one based on the Ni1+xTe2 solid solution (SS1) and a second unexpected, quite distinct and compositionally broad solid solution (SS2) centred on the nominal composition Ni2.80In0.80Te2. The latter SS2 solid solution was shown to be incommensurately modulated with a composition-dependent primary modulation wavevector. The superspace group symmetry of the latter is determined and the observed B8 parent cell dimensions used to discuss possible substitution mechanisms. The origin of the incommensurate modulation in the case of the SS2 solid solution is attributed to the regular alternation of In-rich and Te-rich layers along the c direction. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Magnetic phases in Mn1-xFeWO4 studied by neutron powder diffraction
Authors:
Garcia-Matres, E; Stusser, N; Hofmann, M; Reehuis, M; Dorofeev, YA;
Source:
EUROPEAN PHYSICAL JOURNAL B, 32 (1): 35-42; 2003
Abstract:
The magnetic structures of Mn1-xFexWO4 with x = 0.0, 0.16, 0.21, 0.225, 0.232, 0.24, 0.27, 0.29, and 1.0 were refined from neutron powder diffraction data. The magnetic phase diagram could be completed in the coexistence range of different magnetic structures up to x = 0.29. For the magnetic state at 1.5 K a commensurate antiferromagnetic structure with a propagation vector k = (+/-1/4,1/2,1/2) was found for x less than or equal to 0.22 while the magnetic spins order with k = (1/2, 0, 0) for x greater than or equal to 0.22. In the latter phase, additionally, weak magnetic reflections indexed to an incommensurate ordering with k = (-0.214, 1/2, 0.457) occur in the diffraction pattern up to x = 0.29 indicating the occurence of a reentrant phase. For 0.12 less than or equal to x less than or equal to 0.29 the low temperature phases are separated from a magnetic high temperature phase showing only magnetic reflections indexed to a spin arrangement with k = (1/2, 0, 0). The magnetic phase diagram is discussed qualitatively considering random superexchange between the statistically distributed Mn2+- and Fe2+-ions in the coexistence range 0.12 less than or equal to x less than or equal to 0.29 of different magnetic structures related to those of pure MnWO4 and FeWO4.
Title:
(3+1)-dimensional structure refinement of the fresnoite framework-structure type compound Ba2TiGe2O8
Authors:
Hoche, T; Esmaeilzadeh, S; Uecker, R; Lidin, S; Neumann, W; Grein, C;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 59 (1): 209-216; 2003
Abstract:
The incommensurately modulated structure of the fresnoite framework-structure type compound Ba2TiGe2O8 has been solved using a (3 + 1)-dimensional superspace approach. The structure is orthorhombic and adopts the superspace group Cmm2(0,beta,1/2)s00 with beta similar or equal to 0.635 at room temperature. The refinement was based on neutron powder diffraction data obtained from a powdered single crystal grown by Czochralski pulling. The modulation parameters that were obtained support the idea that frozen-in rigid-unit modes cause the modulation. The modulation is mainly manifested by positional displacements of O atoms. Barium ions are either eightfold, ninefold or tenfold coordinated in the one-dimensional modulated structure. A significant improvement of the bond-valence sum for both barium positions is achieved by the introduction of the positional modulation. This finding strongly suggests that underbonded barium positions are critically involved in provoking the incommensurate modulation in Ba2TiGe2O8.
Title:
Superspace description of trigonal and ortho-rhombic A(1+x)A(x)' B1-xO3 compounds as modulated layered structures; application to the refinement of trigonal Sr6Rh5O15
Authors:
Elcoro, L; Perez-Mato, JM; Darriet, J; El Abed, A; Neumann, W;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 59 (1): 217-233; 2003
Abstract:
The structures of the trigonal compounds A(1+x)A(x)'B1-xO3 are described, to a first approximation, as a hexagonal close-packed stacking of A(3)O(9) and A(3)A'O-6 layers. However, quantitative analyses are usually performed in superspace, with the structures considered as modulated composites made of two subsystems: chains of A cations, and columns of trigonal prisms, A'O-6, and octahedra, BO6. It is demonstrated that an alternative superspace description as a single modulated structure can be found in terms of the aforementioned layers, with a composition-dependent modulation parameter and discontinuous atomic domains. In this approach, these compounds fulfill layer-stacking rules analogous to those observed in other layered compounds. These rules translate into a so-called closeness condition for the discontinuous atomic domains in superspace; this condition is analogous to that postulated in quasicrystals. Both superspace models, the composite and the layered model, when considered without displacive modulations, can be taken as two limiting idealized paradigms and can be used as the starting point of a structure refinement. As an example, the structure of the trigonal phase Sr6Rh5O15, which was previously refined as a modulated composite [Stitzer, El Abed et al. ( 2001), J. Am. Chem. Soc. 123, 8790-8796], has been refined anew, with equivalent results, as a single modulated structure taking as reference the ideal layered structure. A similar superspace layer description is applied to the recently reported orthorhombic family A(4m+4n) A'(n) B4m+2nO12m+9n. This description allows the a priori derivation of a refineable superspace model that includes the superspace symmetry and crenel functions and is valid for the whole family. This model has been successfully applied to the refinement of the compound Ba12Co11O33 [Darriet et al. (2002), Chem. Mater. 14, 3349-3363].
Title:
Neutron diffraction study of Lu2Fe17 under high pressure
Authors:
Prokhnenko, O; Ritter, C; Medvedeva, I; Arnold, Z; Kamarad, J; Kuchin, A; Janossy, A;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 258 (3): 564-566; 2003
Abstract:
Neutron diffraction techniques were used to study the evolution of the magnetic states of Lu2Fe17 under hydrostatic pressure up to 5 kbar in the temperature range 2-300 K. The ferromagnetic phase gets suppressed by pressure and an incommensurate antiferromagnetic phase is found to exist down to 2 K under a pressure of 5 kbar. The complex thermal evolution of the magnetic structures of Lu2Fe17 at ambient and high pressures is presented and discussed. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Observation of metal-insulator transition in Al-Pd-Re quasicrystals by x-ray absorption and photoemission spectroscopy
Authors:
Lay, YY; Jan, JC; Chiou, JW; Tsai, HM; Pong, WF; Tsai, MH; Pi, TW; Lee, JF; Ma, CI; Tseng, KL; Wang, CR; Lin, ST;
Source:
APPLIED PHYSICS LETTERS, 82 (13): 2035-2037; 2003
Abstract:
Using x-ray absorption and valence-band photoelectron spectroscopy (PES) we investigated the electronic structures of icosahedral (i)-Al70Pd22.5Re7.5 quasicrystals (QCs) with a 4.2 K/300 K resistivity ratio, r, ranging from 8.3 to 107 obtained under various annealing conditions. Our Al K- and Pd L-3-edge x-ray absorption results show that the density of states, N(E), near the Fermi level, E-F, jumps to a larger value when r decreases down to below about 20.6. The valence-band PES results show that N(E) near E-F is greatly reduced in i-Al70Pd22.5Re7.5 QCs relative to that of the pure metal, which confirms the existence of the pseudogap. The PES spectrum has a sharp cutoff at E-F for r=8.3 QC, while it decreases smoothly down to zero at E-F for larger r's. The combined results suggest the occurrence of metal-insulator transition at an r between 13 and 20.6. (C) 2003 American Institute of Physics.
Title:
An intensity evaluation method: EVAL-14
Authors:
Duisenberg, AJM; Kroon-Batenburg, LMJ; Schreurs, AMM; Tsai, HM;
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 36 (13): 220-229; 2003
Abstract:
A reflection intensity integration method is presented based upon ab initio calculation of three-dimensional (x, y, omega) reflection boundaries from a few physical crystal and instrument parameters. It is especially useful in challenging circumstances, such as the case of a crystal that is far from spherical, anisotropic mosaicity, alpha(1)alpha(2) peak splitting, interference from close neighbours, twin lattices or satellite reflections, and the case of streaks from modulated structures, all of which may frustrate the customary profile-learning and -fitting procedures. The method, called EVAL-14, has been implemented and extensively tested on a Bruker Nonius KappaCCD diffractometer.
Title:
Phasons and the plastic deformation of quasicrystals
Authors:
Kleman, M; Kroon-Batenburg, LMJ;
Source:
EUROPEAN PHYSICAL JOURNAL B, 31 (3): 315-325; 2003
Abstract:
The plastic deformation of quasicrystals (QC) is ruled by two types of singularities of the QC order, singularities of the 'phonon' strain field, and singularities of the 'phason' strain field. In the framework of the general topological theory of defects, in which the QC is defined as an irrational subset of a crystal of higher dimension, both types of defects appear as distinct components of the same entity; called a disvection [2]. Each of them can also be given a description in terms of more classical concepts, within a detailed analysis of the Volterra process: it can be shown that (a) the phonon singularity breaks some symmetry of translation, represented by its Burgers vector b(parallel to) projected from a high dimensional crystalline lattice onto the physical space; it is therefore akin to a perfect dislocation; (b) the phason singularities (there are many attached to each b(parallel to)-dislocation), that we call matching faults, are dipoles of dislocations whose Burgers vectors are of a special type; they do break not only a particular symmetry of translation but also the class of local isomorphism (in the jargon of QCs) of the QC. In fact, such dipoles, if they open up into loops, bound stacking faults - thus a phason singularity is an imperfect dislocation. A mismatch is nothing else than an elementary matching fault. It is suggested that it is the simultaneous presence of perfect dislocations and of phason singularities, and their interplay, that are at the origin of the peculiar characters of the plastic deformation of quasicrystals, namely the brittle-ductile transition followed by a stage of work softening; in particular the brittle-ductile transition could be related to a cooperative transition of the Kosterlitz-Thouless type which affects the dipoles and turn them into (imperfect) dislocation loops.
Title:
Synthesis and magnetic properties of incommensurate phases A(4)CuMn(2)O(9) (A=Ca, Sr)
Authors:
Bazuev, GV; Krasil'nikov, V; Kellerman, DG; Pietsch, U;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 352 (1-2): 190-196; 2003
Abstract:
New complex oxides A(4)CuMn(2)O(9) (A=Ca and Sr) belonging to the family of quasi-one-dimensional compounds A(3n + 3m) A(n)(')B(3m + n)O(9m + 6n) (n=3, m=1) have been obtained by solid-phase synthesis from Ca and Sr carbonates and oxides CuO and MnO2. It was established that both oxides are incommensurate and can be characterized by two sublattices with the same a, but different c (c, and c(2)) parameters. Their lattice parameters are a 9.195(2), c(1) 3.744(1), c(2) 2.580(1) Angstrom for Ca4CuMn2O9 and a 9.602(2), c(1) 3.940(1), c(2) 2.593(1) Angstrom for Sr4CuMn2O9. Magnetic susceptibility (chi) measurement results were interpreted with allowance for exchange-bound dimers Mn4+-Mn4+ and paramagnetic centers Cu2+. Magnetic measurements revealed the presence of calcium manganate CaMnO3 in Ca4CuMn2O9. The maxima on chi = f(T) dependences at 7.5 K (Sr4CuMn2O9) and 3.5 K (Ca4CuMn2O9) allowed us to surmise that the compounds in question have antiferromagnetic correlations. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Nanocrystal reinforced Hf60Ti15Ni15Cu10 metallic glass by melt-spinning
Authors:
Wang, LM; Ma, LQ; Inoue, A; Pietsch, U;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 352 (1-2): 265-269; 2003
Abstract:
A nanocrystal reinforced Hf60Ti15Ni15Cu10 alloy was prepared by melt-spinning. The thermal stability and mechanical properties of this alloy were studied. The microstructure of the alloy depends on the cooling rate, which is controlled by the circumferential velocity of copper roller. At the circumferential velocities of 25, 30 and 35 m/s, a mixed structure of nanoscale icosahedral quasicrystalline (I-phase), crystal (mainly alpha-Hf/Ti) and glass phases is formed. At a circumferential velocity of 40 m/s, a single glass phase is formed. The Vickers microhardness (H-v) increases with decreasing cooling rate. The tensile fracture strengths (sigma(f)) are 1650 and 1780 MPa for the samples with a single glass phase and mixed structure of I-phase, crystal and glass. The maximum sigma(f) can be obtained when the volume fraction (V-f) is about 22% and the size is smaller than 25 nm for the crystalline phase and I-phase particles. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Mn similar to 2.4Mo6O9: First example of empty twin chains of edge-sharing M-6 octahedra in transition metal cluster chemistry
Authors:
Barrier, N; Gougeon, P; Retoux, R; Leligny, H; Rochon, PL;
Source:
INORGANIC CHEMISTRY, 42 (5): 1734-1738; 2003
Abstract:
The novel ternary reduced molybdenum oxide Mnsimilar to2.4Mo6O9 has been synthesized by solid-state reaction at 1400 degreesC for 96 h in sealed molybdenum crucibles. Electron diffraction studies showed that Mnsimilar to2.4Mo6O9 presents a complex crystal structure with a 3d incommensurate modulation. The average crystal structure was determined on a single-crystal by X-ray diffraction in the orthorhombic space group Pnma with the following lattice parameters: a = 16,4824(2) Angstrom, b = 2.8273(2) Angstrom, c = 17.3283(2) Angstrom, Z = 4. The Mo network consists of empty twin chains of trans-edge-sharing octahedra that occur for the first time in a solid-state compound. The Mo-Mo distances within the chains range from 2.62 to 2.92 Angstrom, and the Mo-O distances from 1.99 to 2.17 Angstrom as usually observed in the reduced molybdenum oxides. Single-crystal resistivity measurements show that Mnsimilar to2.4Mo6O9 is metallic between 4.2 and 300 K. The magnetic susceptibility data indicate paramagnetic behavior due to the Mn2+ moment at high temperatures with a weak ferromagnetic behavior below 80 K.
Title:
The partition function and state equation of the point group 12mm two-dimensional dodecagonal quasicrystal
Authors:
Fan, TY; Mai, YW; Tachi, Y;
Source:
EUROPEAN PHYSICAL JOURNAL B, 31 (1): 25-27; 2003
Abstract:
This study extends the analysis of the vibrational spectrum of the one-dimensional hexagonal quasicrystal to the two-dimensional quasicrystal with the 12mm point group. Several thermodynamic functions and the state equation of the material are shown.
Title:
Mixed-valence state of europium in the misfit layer compound (EuS)(1.173)NbS2
Authors:
Cario, L; Palvadeau, P; Lafond, A; Deudon, C; Moelo, Y; Corraze, B; Meerschaut, A; Zheng, YD;
Source:
CHEMISTRY OF MATERIALS, 15 (4): 943-950; 2003
Abstract:
A new misfit layer compound (EuS)(1.173)NbS2 was synthesized, and its structure was solved :in a (3+1)D superspace using the superspace group Xm2m(alpha00) with X referring to a pseudo F centering. The cell parameters are a(s) = 3.3251(9) Angstrom, bs = 5.7432(9) Angstrom, and c(s) = 22.939(5) Angstrom (V-s = 438.1(3) Angstrom) with a modulation vector q = 0.5867(2) a(s)*. This compound is built from a regularly alternated stacking of [EuS] slabs (NaCl structure type with two atomic layers) and [NbS2] slabs (NbS2 structure type). Mossbauer and XPS spectroscopies as well as magnetic measurements clearly indicate a mixed-valence state for europium with a ratio EU2+/EU3+ close to 40:60. Bond valence calculations taking into account the modulation of the Eu-S distances ascertain the mixed valence state of europium and indicate that Eu2+ and Eu3+ ions occupy the same crystallographic site. Moreover, Mossbauer spectra demonstrate that a charge hopping between Eu2+ and Eu3+ takes place above room temperature. The misfit layer (EuS)(1.173)NbS2 can be considered as an inhomogeneous mixed-valence compound. Resistivity measurements show that (EuS)(1.173)NbS2 behaves as a metal and at 3.5 K a strong decrease of the resistivity is observed conjointly with a ferromagnetic transition.
Title:
X-ray study of modulated structure in [N(CH3)(4)](2)CuCl4 under high pressure
Authors:
Asahi, T; Izutsu, K; Osawa, T;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 72 (2): 330-334; 2003
Abstract:
Pressure-temperature dependence of modulation wavenumber of [N(CH3)(4)](2)CuCl4 was measured with X-ray diffraction method in the region of 22 less than or equal to T less than or equal to 160degreesC, 0.25 less than or equal to p less than or equal to 0.95 GPa. Two commensurate phases with modulation wavenumber q = 3/8 and 2/5 were found within the pressure-induced incommensurate phase. The phase q = 3/8 is identified as the high-pressure ferroelectric phase F-2 found by Gesi.
Title:
The incommensurate structure of K3In(PO4)(2)
Authors:
Arakcheeva, A; Chapuis, G; Petricek, V; Dusek, M; Schonleber, A; Martindale, SJ;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 59 (5): 17-27; 2003
Abstract:
The incommensurately modulated structure of K3In(PO4)(2) has been solved and refined. The origin of the modulation relates to the ordering of K cations within the hexagonal close packing of the PO4 anions. The driving forces for the modulation of the other cations are In-P and K-P interactions. The modulation of O atoms of rigid PO4 units follows the cations in order to stabilize the InO6 octahedron. It is shown that the previously published three-dimensional structure rerned from powder diffraction data obtained at room temperature is an average structure. Therefore the incommensurately modulated phase of K3In(PO4)(2) is the only one that has been unequivocally identired at room temperature. The origin of the modulation is discussed in comparison with the structures of Na3InP2, alpha- and beta-Na3In(PO4)(2), Na3Fe(PO4)(2) and Rb3In(PO4)(2).
Title:
The modulated structure of Ba0.39Sr0.61Nb2O6. I. Harmonic solution
Authors:
Woike, T; Petricek, V; Dusek, M; Hansen, NK; Fertey, P; Lecomte, C; Arakcheeva, A; Chapuis, G; Imlau, M; Pankrath, R; Arakawa, Y;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 59 (5): 28-35; 2003
Abstract:
The structure of a crystal of Sr0.61Ba0.39Nb2O6 has been solved and refined as an incommensurate structure in five-dimensional superspace. The structure is tetragonal, superspace group P4bm(pp1/2; p-p1/2), unit-cell parameters a = 12.4566 (9), c = 7.8698 (6) Angstrom, modulation vectors q(1) = 0.3075 (6) (a* +b*), q(2) = 0.3075 (6) (a - b). The data collection was performed on a KUMA-CCD diffractometer and allowed the integration of weak first-order satellite reflections. The structure was refined from 2569 reflections to a final value of R = 0.0479. The modulation affects mainly the positions of the O atoms, which are displaced by as much as 0.5 Angstrom, and the site 4c that is occupied by Sr and Ba atoms. Only a simplified model, in which this atomic position is occupied by an effective atom Sr/Ba, could be refined from the data set. The modulation of displacement parameters has been used to account for the modulated distribution of Sr and Ba. The whole refinement uses only first-order modulation waves, but there are strong indications that for a complete solution the use of higher-order satellites and a more complicated model is necessary.
Title:
Twinning in natural melilite simulating a fivefold superstructure
Authors:
Bindi, L; Rees, LH; Bonazzi, P; Gardon, M;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 59 (5): 156-158; 2003
Abstract:
Additional reflections seemingly leading to a tetragonal fivefold supercell have been observed in a number of melilites. A careful examination of the collected intensity data reveals that this feature is due to the coexistence of two twin domains related by a (1 (2) over bar0) twin plane. Reflections of the first domain (I) with h(b)(2) + k(b)(2) = 5n overlap those of the second domain (II) when both the following additional conditions are verified: -h(b) + 2k(b) = 5n and 2h(b) + k(b) = 5n. Indices of the superimposed reflections are h(b,I) k(b,I) l(b,I) for the first domain, and h(b,II) = 3/5 h(b,I) + 4/5 k(b,I), k(b,II) = 4/5 h(b,I) - 3/5 k(b,I), l(b,II) = l(b,I) for the second domain. The non-crystallographic pseudosymmetry in the melilite structure is discussed.
Title:
New type of charge/orbital ordering above room temperature in the perovskite Bi2/3Sr1/3MnO3
Authors:
Hervieu, M; Malo, S; Perez, O; Beran, P; Martin, C; Baldinozzi, G; Raveau, B; Ogle, CA;
Source:
CHEMISTRY OF MATERIALS, 15 (2): 523-527; 2003
Abstract:
A new type of charge ordering stable up to T-1 approximate to 500 K has been evidenced by electron microscopy in the Mn3+-rich perovskite Bi2/3Sr1/3MnO3. This new superstructure, based on a Imma-type subcell is characterized by a double modulation with a = 2a(p)root2, b = 4a(p), c = a(p)root2. X-ray powder diffraction evidences a second structural transition at T-2 approximate to 580 K and suggests a displacive modulation of the oxygen atoms below T-2. These results are interpreted as the correlated coexistence of charge-orbital ordering and modulated displacive ordering of oxygen atoms, in the form of double Mn stripes, below 500 K.
Title:
Magnetic and martensitic phase transitions in ferromagnetic Ni-Ga-Fe shape memory alloys
Authors:
Oikawa, K; Ota, T; Ohmori, T; Tanaka, Y; Morito, H; Fujita, A; Kainuma, R; Fukamichi, K; Ishida, K; Pankrath, R;
Source:
APPLIED PHYSICS LETTERS, 81 (27): 5201-5203; 2002
Abstract:
Ferromagnetic shape memory alloys with a body-centered-cubic ordered structure in a Ni-Ga-Fe system have been developed. The alloys with the composition range of Ni 27 at. % Ga (20-22 at. %)Fe exhibit a thermoelastic martensitic transformation from a B2 and/or an L2(1) parent to a martensite phase, with a seven-layer modulated (14M) and a five-layer modulated (10M) structure, in the ferromagnetic state. The parent phase transforms from the B2 to the L2(1) structure at about 970 K during cooling, and the degree of the L2(1) order in the parent phase is increased by annealing at 773 K, resulting in the increase of both the martensite starting and the Curie temperatures. The. ductility of these alloys is improved by introducing of a small amount of gamma-phase solid solution. Consequently, We can conclude that the present alloys are promising for ferromagnetic shape memory alloys. (C) 2002 American Institute of Physics. [DOI: 10.1063/1.1532105].
Title:
Lateral composition modulation in InAs/GaSb superlattices
Authors:
Stokes, DW; Forrest, RL; Li, JH; Moss, SC; Nosho, BZ; Bennett, BR; Whitman, LJ; Goldenberg, M; Ishida, K;
Source:
JOURNAL OF APPLIED PHYSICS, 93 (1): 311-315; 2003
Abstract:
We report the analysis of lateral composition modulation in (InAs)(m)/(GaSb)(m) superlattices by x-ray diffraction. Vertical and lateral satellite peaks for a 140 period structure were observed. The lateral modulation wavelength, average superlattice composition, and vertical superlattice wavelength were determined. The lateral modulation was observed only along one in-plane direction resulting in quantum wire-like structures along the [1 (1) over bar0] direction. The unconventional structure of the lateral composition modulation, in which the stacking of the layers leads to a doubling of the vertical superlattice period, is discussed. (C) 2003 American Institute of Physics.
Title:
Thermoelectric properties of icosahedral quasicrystals: A phenomenological approach
Authors:
Macia, E; Buixaderas, E;
Source:
JOURNAL OF APPLIED PHYSICS, 93 (2): 1014-1022; 2003
Abstract:
In this work, we introduce a phenomenological model describing the thermoelectric power of icosahedral quasicrystals. On the basis of a realistic model for the spectral conductivity, obtained from ab initio band-structure calculations [C. Landauro and H. Solbrig, Physica B 301, 267 (2000)], we derive a closed analytical expression for the Seebeck coefficient, satisfactorily describing its temperature dependence S(T) over a wide temperature range. We introduce four phenomenological coefficients relating the electronic structure to characteristic features of the experimental S(T) curves. By comparing our analytical results with available experimental data we relate the sensitivity of the thermopower curve to minor variations in the chemical composition to a systematic shift of the Fermi-level position. (C) 2003 American Institute of Physics.
Title:
A 4D composite description for Ca-0.82(Cu0.65Co0.35O2)
Authors:
Lambert, S; Grebille, D; Petzelt, J;
Source:
CHEMISTRY OF MATERIALS, 14 (12): 4904-4909; 2002
Abstract:
A misfit layer compound has been isolated in the Ca-Cu-Co-O system. It is constituted of two interpenetrating orthorhombic F sublattices exhibiting incommensurate periods along the [100] direction. The structure, determined by single-crystal X-ray diffraction using the 4D superspace formalism, is closely related to other oxide structures already depicted in the literature and corresponds to an alternate stacking along [001] of one-dimensional [MO2] chains (M == Cu or Co) and of Ca layers. A displacive modulation allows a satisfying bonding scheme for the Ca-O intersystem distances.
Title:
X-ray study of Rb2ZnBr4 under high pressure
Authors:
Asahi, T; Hasebe, K; Sun, HP;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 71 (12): 2925-2929; 2002
Abstract:
Pressure-temperature dependence of modulation wavenumber was measured by X-ray diffraction in the region of 295 less than or equal to T less than or equal to 400 K, 0 less than or equal to p less than or equal to 1.3 GPa. Contour map and phase diagram were drawn on p-T plane. Crystal structure of the high pressure phase with modulation wavenumber q = 0 was analyzed using X-ray diffraction data at p congruent to 1 GPa and T = 295 K.
Title:
Dielectric study of the pressure effect on the phase transitions in deuterated crystal [N(CD3)(4)](2)CuCl4
Authors:
Gesi, K; Hasebe, K;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 71 (12): 3047-3051; 2002
Abstract:
Effect of hydrostatic pressure on the phase transitions in deuterated crystal [N(CD3)(4)](2)CuCl4 have been studied by dielectric measurements. The pressure-temperature (p-T) phase diagram was obtained and compared with that of the hydrogen compound. By deuteration the boundary region between the atomspheric-pressure incommensurate phase (phase II: q < (1/3)c(0)*) and the presssure-induced incommensurate phase (phase II: q > (1/3)c(0)*) shifts toward lower pressure side. (q: the modulation wave vector, c(0)*: the reciprocal unit cell vector in the normal phase) Deuteration shifts the pressure- induced ferroelectric phase to lower pressure by about 40 MPa. The result shows that the effect of deuteration on the phase stability in [N(CH3)(4)](2)CuCl4 is equivalent to application of hydrostatic pressure. This deuteration effect is opposite tendency to that of other [N(CH3)(4)](2)XCl4-type crystals.
Title:
Three-periodic nets and tilings: regular and quasiregular nets
Authors:
Friedrichs, OD; O'Keeffe, M; Yaghi, OM; Kennedy, SJ;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 59 (1): 22-27; 2003
Abstract:
Regular nets are defined as those with symmetry that requires the coordination figure to be a regular polygon or polyhedron. It is shown that this definition leads to five regular 3-periodic nets. There is also one quasiregular net with a quasiregular coordination figure. The natural tiling of a net and its associated essential rings are also defined, and it is shown that the natural tilings of the regular nets have the property that there is just one kind of vertex, one kind of edge, one kind of ring and one kind of tile, i.e. transitivity 1111. The quasiregular net has two kinds of natural tile and transitivity 1112.
Title:
Average unit cell for Penrose tiling and its Gaussian approximation
Authors:
Wolny, J; Kozakowski, B; Yaghi, OM;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 59 (1): 54-59; 2003
Abstract:
In this paper, the average unit cell for a quasicrystal is constructed by a statistical approach. For the Penrose tiling, it is shown that such a unit cell is fully equivalent to the oblique projection of the atomic surface onto physical space. The obtained statistical distributions can be easily extended to imperfect structures by using a Gaussian approximation. This leads to simple analytical expressions for diffraction intensities, which can be very useful in structure refinement.
Title:
Hysteretic spin-density-wave ordering in confined geometries
Authors:
Fullerton, EE; Robertson, JL; Prinsloo, ARE; Alberts, HL; Bader, SD;
Source:
PHYSICAL REVIEW LETTERS, 91 (23); 2003
Abstract:
We have measured the antiferromagnetic spin-density-wave (SDW) order in Cr/Cr97.5Mn2.5(001) superlattices. The Mn doping creates a high Neel temperature layer that confines the incommensurate SDW order within the Cr layers. With temperature cycling we observe a transition from commensurate to incommensurate SDW order and discrete changes in the SDW period. We find that these transitions show significant hysteresis (up to 75 K) when the number of SDW nodes within the Cr layer changes by an odd number, while there is no hysteresis for changes of an even number of nodes. This results from the competition between maintaining the spin structure at the interfaces and introducing a spin slip at the nodes of the Cr SDW.
Title:
Dynamics of phason fluctuations in the i-AlPdMn quasicrystal
Authors:
Francoual, S; Livet, F; de Boissieu, M; Yakhou, F; Bley, F; Letoublon, A; Caudron, R; Gastaldi, J;
Source:
PHYSICAL REVIEW LETTERS, 91 (22); 2003
Abstract:
We report on the study of the dynamics of long wavelength phason fluctuations in the i-AlPdMn icosahedral phase using coherent x-ray scattering. When measured with a coherent x-ray beam, the diffuse intensity due to phasons presents strong fluctuations or speckles pattern. From room temperature to 500 degreesC the speckle pattern is time independent. At 650 degreesC the time correlation of the speckle pattern exhibits an exponential time decay, from which a characteristic time tau is extracted. We find that tau is proportional to the square of the phason wavelength, which demonstrates that phasons are collective diffusive modes in quasicrystals, in agreement with theoretical predictions.
Title:
Phase transitions and twin lamellae in the (Bi,Pb)2223 phase: in situ high temperature electron diffraction studies
Authors:
Zhigadlo, ND; Czank, M; Depmeier, W; Krupin, O;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 400 (1-2): 19-24; 2003
Abstract:
Phase transitions and twin lamellae of the (Bi,Pb)2223 phase have been studied by in situ heating experiments in a transmission electron microscope over a range of temperatures 293-800 K. In some crystal grains of the (Bi,Pb)2223 phase a modulation with the modulation wave vector q congruent to 0.137b(*) (Pb-type) was observed with 1st order satellites associated with the [0 0 1] zone. Furthermore, a monoclinic distortion was observed, as indicated by splitting of the reflections in the b(*) direction. The monoclinicity was confirmed by dark-field images, which showed (10 0) twin lamellae. Diffuse streaks along < h h 0 > are present in some crystals already at room temperature, but appear in others at temperatures below 365 K. Their intensities sharpen with increasing temperature, and at 630 K a 2a x 2b superstructure appears. At the same temperature the monoclinic distortion and the twin lamellae disappear gradually. The new 2a x 2b superstructure and Pb-type modulations coexist until the phase starts to decompose. The change of these structural modulations and twin transformations are discussed in connection with oxygen ordering within the different structural layers. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Structures of three polymorphs of the complex oxide K5Yb(MoO4)(4)
Authors:
Morozov, VA; Lazoryak, BI; Lebedev, OI; Amelinckx, S; Van Tendeloo, G; Matthias, E;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 176 (1): 76-87; 2003
Abstract:
Polymorphous modifications ( gamma-, beta- and alpha-) of the double potassium ytterbium molybdenum oxide K5Yb(MoO4)(4) were synthesized by the solid-state method and their structures were studied by X-ray powder diffraction, electron diffraction and high-resolution electron microscopy. DSC analysis shows that the gamma --> beta <----> alpha a phase transitions are not accompanied with a significant reconstruction of the palmierite-type structure. All modifications of K5Yb(MoO4)(4) are related to the mineral palmierite-K2Pb(SO4)(2). The palmierite-type structure is made up of isolated AO(4) tetrahedra, which connect the MOn polyhedra into a 3-D framework via common vertices. Cations occupy two crystallographic positions M1 and M2. The gamma-phase crystallizes in a monoclinic system (space group C2/c) with unit-cell parameters: a = 14.8236(1) Angstrom, b = 12.1293(1) Angstrom, c = 10.5151(1) Angstrom, beta = 114.559(1)degrees, Z = 4. The alpha-phase has space group R (3) over barm with unit-cell parameters: a = 6.0372(1) Angstrom, c = 20.4045(2) Angstrom. The structures of the gamma- and alpha-modification were refined by the Rietveld method (R-wp = 6.25%, R-1 = 2.16% and R-wp = 9.09%, R-1 = 5.80% for gamma- and alpha-, respectively). In K5Yb(MoO4)(4) ytterbium cations occupy M1 while K+ cations occupy M2 and M1 positions of the palmierite-type structure. In the high-temperature (alpha-) modification the Yb3+ and K+ occupy the M1 site in a statistical manner (M1 = 0.5Yb(3+) + 0.5K(+)) while in the low-temperature (gamma-) modification these cations occupy this site in an ordered way. The intermediate beta-phase shows an incommensurate modulated structure. (C) 2003 Elsevier Inc. All rights reserved.
Title:
Double (n=2) and triple (n=3) [M4Bi2n-2O2n](x+) polycationic ribbons in the new Bi similar to 3Cd similar to 3.72M similar to 1.28O5(PO4)(3) oxyphosphate (M = Co, Cu, Zn)
Authors:
Colmont, M; Huve, M; Ketatni, E; Abraham, F; Mentre, O; Matthias, E;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 176 (1): 221-233; 2003
Abstract:
The crystal structure of the new Bisimilar to3Cdsimilar to3.72Cosimilar to1.28O5(PO4)(3) has been refined from single crystal XRD data, R-1 = 5.37%, space group Abmm, a = 11.5322(28) Angstrom, b = 5.4760(13) Angstrom, c = 23.2446(56) Angstrom, Z = 4. Compared to Bisimilar to1.2Msimilar to1.2O1.5(PO4) and Bisimilar to6.2Cusimilar to6.2O8(PO4)(5), this compound is an additional example of disordered Bi3+/M2+ oxyphosphate and is well described from the arrangement of double [Bi4Cd4O6](8+) (= D) and triple [Bi2Cd3.44Co0.56O4](6+) (= T) polycationic ribbons formed of edge-sharing O(Bi,M)(4) tetrahedra surrounded by PO4 groups. According to the nomenclature defined in this work, the sequence is TT/DtDt, where t stands for the tunnels created by PO4 between two subsequent double ribbons and occupied by Co2+. The HREM study allows a clear visualization of the announced sequence by comparison with the refined crystal structure. The Bi3+/M2+ statistic disorder at the edges of T and D entities is responsible for the PO4 multi-configuration disorder around a central P atom. Infrared spectroscopy and neutron diffraction of similar compounds (without the highly absorbing Cadmium) even suggests the long range ordering loss for phosphates. Therefore, electron diffraction shows the existence of a modulation vector q* = 1/2a* + (1/3 + epsilon)b* which pictures cationic ordering in the (001) plane, at the crystallite scale. This ordering is largely lost at the single crystal scale. The existence of mixed Bi3+/M2+ positions also enables a partial filling of the tunnels by Co2+ and yields a composition range checked by solid state reaction. The title compound can be prepared as a single phase and also the M = Zn2+ term can be obtained in a biphasic mixture. For M = Cu2+, a monoclinic distortion has been evidenced from XRD and HREM patterns but surprisingly, the orthorhombic ideal form can also be obtained in similar conditions. (C) 2003 Elsevier Inc. All rights reserved.
Title:
Specific heat and linear birefringence behaviour of 4-aminopyridinium tetrachloroantimonate(III), [4-NH2C5H4NH][SbCl4]
Authors:
Przeslawski, J; Kosturek, B; Jakubas, R; Beere, HE;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (43): L643-L648; 2003
Abstract:
Thermal (specific heat) and optical (linear birefringence) studies were performed for a new ferroelectric crystal [4-NH2C5H4NH] [SbCl4]. Four phase transitions were confirmed and described. Thermal parameters (DeltaH, DeltaS) of the normal-incommensurate, N-IC, and incommensurate-ferroelectric commensurate, IC-F(C), phase transitions are given. The order-disorder mechanism of the N-IC phase transition is proved but the displacive one for the IC-F(C) transition can be proposed. The critical index value (2beta = 0.68+/-0.02) estimated from the linear birefringence measurements indicates that the N-IC phase transition can be described in terms of the 3d XY model.
Title:
Spin flop transition in doped antiferromagnets
Authors:
Peres, NMR; Kosturek, B;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (43): 7271-7286; 2003
Abstract:
In this paper we compute the mean field phase diagram of a doped anti-ferromagnet, in a magnetic field and with anisotropic exchange. We show that at zero temperature there is a metamagnetic transition from the antiferromagnetic configuration along the z direction to a spin flop (SF) state. In the spin flop phase the system prefers a commensurate magnetic order, at low doping, whereas at larger doping the incommensurate phase is favourable. Contrary to the pure Heisenberg case, the spin flop region does not span an infinite area in the (A, h) plane, where A is the exchange anisotropy and h is the external magnetic field. We characterize the magnetic and charge-tran sport properties of the SF phase, computing the magnetic susceptibility and the Drude weight. This latter quantity presents a sudden variation as the SF to paramagnet phase transition line is crossed. This effect could be used as a possible source of large magneto-resistance. Our findings may have some relevance for doped La2-deltaSrdeltaCuO4 in a magnetic field.
Title:
Large structural modulations in incommensurate Te-III and Se-IV
Authors:
Hejny, C; McMahon, MI; Jakubas, R;
Source:
PHYSICAL REVIEW LETTERS, 91 (21): 7271-7286; 2003
Abstract:
The high-pressure phase of tellurium, Te-III, is found to have an incommensurate monoclinic structure, superspace group I(')2/m(0q0)s0, of a type previously unknown in the elements. Te-III is stable from 4.5(2) to 29.2(7) GPa; the previously reported transition to a distinct Te-IV phase at 10.6 GPa is not observed. The incommensurate wave vector of Te-III is strongly pressure dependent and varies in a strongly nonlinear way. Se-IV is found to be isostructural with Te-III.
Title:
Incommensurate spin density waves in iron aluminides
Authors:
Noakes, DR; Arrott, AS; Belk, MG; Deevi, SC; Huang, QZ; Lynn, JW; Shull, RD; Wu, D;
Source:
PHYSICAL REVIEW LETTERS, 91 (21): 7271-7286; 2003
Abstract:
Neutron diffraction in Fe(Al) reveals incommensurate spin density waves (SDWs) in alloys known to be spin glasses. The wave vectors for crystals of Fe(34Al), Fe(40Al), and Fe(43Al) show n varying from 11 to 6 for (q) over right arrow =2pi(h+/-1/n,k+/-1/n,l+/-1/n)/a(0), where (h,k,l) and a(0) characterize the parent bcc lattice of the CsCl structure. The magnetic reflections are present far above the spin-glass freezing temperatures. These SDWs keep the spins on nearest-neighbor Fe atoms close to parallel, in contrast with SDWs in Cr, which keep nearest-neighbor spins close to antiparallel.
Title:
Inhomogeneous states of a thin-film incommensurate ferroelectric
Authors:
Ktitorov, SA; Pogorelova, OS; Charnaya, EV; Demidov, VV;
Source:
PHYSICS OF THE SOLID STATE, 45 (11): 2166-2170; 2003
Abstract:
Nonuniform distributions of the order parameter in a film of an incommensurate ferroelectric whose free energy expansion does not contain Lifshitz invariants are considered. An equation describing the order parameter distribution over the film thickness is derived in the approximation of slowly varying amplitudes. The effect of film thickness and surface properties on the temperature of transition to the incommensurate phase is analyzed. (C) 2003 MAIK "Nauka/Interperiodica".
Title:
Nanostructured quasiperiodic surfaces: the origin of pentagonal hollows and their role in adsorption and nucleation processes
Authors:
Ledieu, J; McGrath, R; Vysochanskii, YM;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (42): S3113-S3125; 2003
Abstract:
Pentagonal hollows, which are imaged as dark five-fold stars, form the dominant structural motif in scanning tunnelling microscopy (STM) measurements of the five-fold surfaces of icosahedral quasicrystals. Recent progress in the understanding of these surfaces has led to a thorough understanding of these entities; we illustrate how they may be considered as truncations of the basic building blocks (i.e. Bergman clusters) of the bulk structure. The use of these pentagonal hollows as adsorption and nucleation sites is demonstrated using STM images of their filling during scanning of the clean Al-Pd-Mn surface and in the adsorption Of C-60 molecules and copper atoms on Al-Pd-Mn and of aluminium atoms on Al-Cu-Fe.
Title:
Zn-doping effects on low-energy spin excitations in La1.85Sr0.15CuO4
Authors:
Kimura, H; McGrath, R;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 392 (42): 34-41; 2003
Abstract:
A review is given on neutron scattering study of Zn-doping effects on low-energy spin excitations in optimally hole-doped La2-xSrxCuO4. As Zn-impurities increase, energy spectra of incommensurate spin excitations show a dramatic change from a well defined "spin gap" state to a gap-less excitation with static antiferromagnetic (AF) spin correlations. This modification of the gap structure can be understood as not simply reduction of the gap energy but a development of the Zn-induced in-gap excitation, which becomes more static with increasing Zn. An inhomogeneous mixed state of the in-gap spin excitation and the superconductivity is discussed with referring to the swiss cheese model. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Lattice distortions and spin-charge inhomogeneity in the underdoped superconductivity of high-T-c cuprates
Authors:
Yanagisawa, T; Miyazaki, M; Yamaji, K; Cajipe, VB;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 392 (42): 42-47; 2003
Abstract:
Striped superconductivity (SC) with lattice distortions is investigated based on the 3-band (d-p) Hubbard model for high-T-c cuprates. A stable inhomogeneous striped state is investigated in the low-temperature tetragonal (LTT) phase and low-temperature orthogonal (LTO) phase using a quantum variational Monte Carlo method. The ground state has vertical or horizontal hole-rich arrays coexisting with incommensurate magnetism and SC induced by several percents of lattice deformations in the LTT phase. The diagonal stripes are stabilized in the lightly doped LTO phase. The SC order parameter oscillates according to the inhomogeneity in the antiferromagnetic background with its maximums in the hole-rich regions, and the SC condensation energy is reduced as the doping rate decreases. (C) 2003 Elsevier B.V. All rights reserved.
Title:
High-resolution transmission electron microscopy study of modulation structures in Bi2Sr2(RE1-xCex)(2)Cu2O10+y (RE: Y, Nd, Sm and Gd)
Authors:
Asaka, T; Yoshida, K; Anan, Y; Tsutsumi, S; Takayama-Muromachi, E; Kimoto, K; Matsui, Y; Cheng, P;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 392 (42): 105-109; 2003
Abstract:
Modulation structures of Bi2Sr2(RE1-xCex)(2)Cu2O10+y (RE: Y, Nd, Sm and Gd) were investigated by means of high-resolution electron microscopy and electron diffraction. We proved that this system's modulation structure is characterized by the displacement of atomic positions, as in other Bi-system high-T-C superconductors. Superlattice spots due to the modulation structures in electron diffraction showed that the incommensurate modulation wave vector was q = (0, 2/(9 - epsilon), 1/2). The a changed with the average ionic radii of rare earth ions, Ce substitution (x), and excess oxygen content (y). (C) 2003 Elsevier B.V. All rights reserved.
Title:
Indexing schemes for quasilattices
Authors:
Lord, EA; Costa, FM;
Source:
PHILOSOPHICAL MAGAZINE, 83 (29): 3283-3307; 2003
Abstract:
Various schemes have been proposed and employed, which extend the method of indexing lattice vectors and reciprocal-lattice vectors, so that it can be used in the context of quasicrystals. The concept of the generalized inverse of a matrix provides an elegant unified approach to the vectors and reciprocal vectors of quasilattices, and their associated zone laws and inflation rules. We present a survey, from the viewpoint provided by the concept of the Moore-Penrose inverse, of the indexing problem for quasicrystals.
Title:
Molecular probing of low-temperature incommensurate phases
Authors:
Kikas, J; Suisalu, A; Laisaar, A; Kuznetsov, A; Arima, T;
Source:
LOW TEMPERATURE PHYSICS, 29 (9-10): 801-804; 2003
Abstract:
Two-dimensional (2D) excitation-emission spectra of biphenyl doped with free-base chlorin are measured at 5 K under various pressures up to 350 MPa. Besides the features related to zero-phonon lines and their phonon sidebands, a broad spectral band amounting to 80% of the total intensity at 5 K is revealed in the 2D spectra. The inhomogeneous distribution function obtained shows drastic changes with increasing pressure-the triplet structure observable at normal pressure in the incommensurate phase ICIII of biphenyl converges to a singlet in the high-pressure commensurate phase CI. These observations are assumed to reflect a relaxation specific to incommensurate phases after optical excitation of the probe molecules and their interaction with the incommensurate modulation wave. (C) 2003 American Institute of Physics.
Title:
Structural, Mossbauer, and transport studies of the icosahedral quasicrystals A1(55)Si(7)CU(25.5)Fe(12.5), A1(62.5)CU(24.5)Fe(13) and the crystalline 1/1 approximant A1(55)Si(7)CU(25.5)Fe(12.5)
Authors:
Stadnik, ZM; Takeuchi, T; Tanaka, N; Mizutani, U; Jones, TS;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (37): 6365-6380; 2003
Abstract:
As-quenched icosahedral Al55Si7Cu25.5Fe12.5, its 1/1 approximant of the same composition, and icosahedral Al62.5Cu24.5Fe13 alloys have been studied using x-ray diffraction, scanning transmission electron microscopy and the high-angle annular dark field technique, zero-field and in-field Fe-57 Mossbauer spectroscopy, and electrical resistivity. The crystal structure of the 1/1 approximant Al55Si7Cu25.5Fe12.5 has been refined with the Rietveld method and shown to be compatible with the measured high-angle annular dark field images. The distribution of the principal component of the electric field gradient tensor has a bimodal character with a dominant negative sign in the icosahedral Al-Cu-Fe system. The local order of the Fe structural environment is compared in icosahedral Al55Si7Cu25.5Fe12.5, it 1/1 approximant, and icosahedral Al62.5Cu24.5Fe13. The average quadrupole splitting decreases with temperature as T-3/2 for all alloys studied, and its value is significantly larger for the icosahedral alloys. The vibrations of the Fe atoms in the alloys studied are well described by a Debye model, with characteristic Mossbauer temperatures of 468(25), 487(19), and 455(6) K for icosahedral Al55Si7Cu25.5Fe12.5, its 1/1 approximant, and icosahedral Al62.5Cu24.5Fe13, respectively. The electrical resistivity is discussed in terms of quantum interference effects and structural disorder.
Title:
Dislocation climb and low-temperature plasticity of an Al-Pd-Mn quasicrystal
Authors:
Mompiou, F; Bresson, L; Cordier, P; Caillard, D; Tamosauskas, G;
Source:
PHILOSOPHICAL MAGAZINE, 83 (27): 3133-3157; 2003
Abstract:
Dislocations and phason faults have been studied by transmission electron microscopy in an Al - Pd - Mn sample deformed at 300 degreesC under a high pressure. All dislocation movements have occurred by climb, in contrast with the usual interpretations of dislocation motion in quasicrystals. Several modes of dissociation and decomposition of dislocations have been observed, allowing for estimations of phason fault and antiphase-boundary energies. Work softening is tentatively explained in terms of a varying chemical stress.
Title:
The stability of the renormalization group as a diagnostic tool for localization and its application to the Fibonacci case
Authors:
Naumis, GG; Bresson, L;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (35): 5969-5978; 2003
Abstract:
A discussion of the investigation of electronic localization at the thermodynamical limit is given; we show that the usual methods involve practical difficulties, especially for quasicrystals. A method based on the scaling of bands of a supercrystal is proposed. Then, the nature of the localization is related to the stability of the renormalization group around the fixed points of a trace map. For quasiperiodic systems, the scaling exponents are obtained using modified Lyapunov exponents and a Thouless formula. The case of the Fibonacci chain is considered as an example, and analytical expressions for the scaling exponents are found.
Title:
Structure refinement of the icosahedral AlPdMn quasicrystal using quantitative convergent beam electron diffraction and symmetry-adapted parameters
Authors:
Fang, AH; Zou, HM; Yu, FM; Wang, RH; Duan, XF; Valiulis, G;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (29): 4947-4960; 2003
Abstract:
The atomic structure of the perfect AlPdMn icosahedral phase has been studied on a single-crystal specimen using the quantitative convergent beam electron diffraction (QCBED) technique combined with a description of the shapes of atomic surfaces using a symmetry-adapted series of surface harmonics. The spherical model (Boudard et al 1992 J. Phys.: Condens. Matter 4 10149) was used as a starting point for the refinement. By fitting the calculated electron diffraction intensities in the CBED line profile to the experimental electron diffraction intensities, the coefficients in the surface harmonic expansion of the atomic surfaces' boundaries are refined. The refined parameters show that the fluctuations of the external boundary of atomic surface for Pd at n(0) can be as large as 0.2 nm. The boundaries of the atomic surfaces for Mn show little fluctuation. Compared to the spherical model, in the present model the number of unphysically short interatomic distances is reduced significantly. The three-dimensional atomic clusters with centres located successively at the six-dimensional lattice nodes n(0), n(1) and bc(1) are generated by means of the cut method.
Title:
Diffusion of hydrogen in Ti-Zr-Ni quasicrystals
Authors:
Azhazha, V; Grib, A; Khadzhay, G; Malikhin, S; Merisov, B; Pugachov, A; Dubietis, A;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (29): 5001-5008; 2003
Abstract:
We report the first straightforward measurements of the diffusion coefficient of hydrogen migrating in icosahedral (i-) quasicrystal ribbons of Ti45Zr38Ni17 and in two-phase bulk samples containing both the i-phase and the Laves phase. It is found that at 273-353 K diffusion obeys Arrhenius's law with activation energy 0.24 eV and that the ratio of the volumes of the phases changes at hydrogenization.
Title:
Ordering of tetrahedral chains in the Sr2MnGaO5 brownmillerite
Authors:
Abakumov, AM; Alekseeva, AM; Rozova, MG; Antipov, EV; Lebedev, OI; Van Tendeloo, G; Dubietis, A;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 174 (2): 319-328; 2003
Abstract:
Tetrahedral chain ordering in the Sr2MnGaO5 structure is studied using electron diffraction (ED) and high-resolution electron microscopy. The ED patterns show the presence of satellite reflections, which indicate a commensurately modulated structure with a = 5.4056(8) Angstrom b 16.171(3) Angstrom, c = 5.5592(7) Angstrom, q - 1/2c*, superspace group Immma(00gamma,)s00. The Superstructure arises due to ordering of the two types of symmetry related tetrahedral chains (L and R) according to a ... LRLR ... sequence, where L and R chains alternate along the c-axis within the same (GaO) layer. Numerous defects at different structural levels were observed, comprising interleaving L and R chains, violation of the ... LRLR ... chain sequence within one layer, different stacking modes of the ... LRLR ... ordered layers with subsequent alternation of blocks of different width along the h-axis of the brownmillerite subcell and island fragmentation of the modulated superstructure. By in situ heating ED experiments it is found that the long-range ordering of the tetrahedral chains is stable tip to 665degreesC and is completely suppressed at 905degreesC. (C) 2003 Elsevier Inc. All rights reserved.
Title:
Spin- and charge-modulated trilayer magnetic junctions: La0.7Ca0.3MnO3/La0.45Ca0.55MnO3/La0.7Ca0.3MnO3
Authors:
Jo, MH; Blamire, MG; Ozkaya, D; Petford-Long, AK; Lebedev, OI;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (30): 5243-5251; 2003
Abstract:
We report on magnetic tunnel junctions entirely made up of mixed-valence manganites, La0.7Ca0.3MnO3/La0.45Ca0.55/La0.45Ca0.55MnO3/La0.7Ca0.3MnO3. In heteroepitaxial junctions, the different Mn3+/Mn4+ mixed-valence ratios can modulate the ground states throughout the trilayer, i.e. ferromagnetic metal/antiferromagnetic insulator/ferromagnetic metal. Interestingly, the tunnel magnetoresistance (TMR) of the device persists up to a higher temperature (T/T-C less than or equal to 0.75, where T-C is the Curie temperature) as compared to the case for equivalent non-manganite barrier junctions. The enhanced TMR at high temperatures in the present junction is discussed in relation to the properties of the unique interface between the metallic ferromagnet and the antiferromagnetic tunnel barrier, such as the interfacial bonding coherence and a magnetic interlayer coupling.
Title:
Roles of local icosahedral chemical ordering in glass and quasicrystal formation in metallic glass formers
Authors:
Tanaka, H; Blamire, MG;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (31): L491-L498; 2003
Abstract:
It is well known that bulk metallic glass formers have a tendency to show local icosahedral chemical ordering. We argue that the frustration between this short-range bond ordering and the long-range crystalline ordering controls the fragility and the glass-forming ability of these liquids. Our model suggests that a system having a stronger tendency to show local icosahedral ordering should be less fragile and a better glass former. This scenario also naturally explains the close relationship among the degree of local icosahedral ordering in liquid, glass formability, and quasicrystal formability.
Title:
Anisotropic electromagnetic response of lightly doped La2-xSrxCuO4 within the CuO2 planes
Authors:
Dumm, M; Komiya, S; Ando, Y; Basov, DN; Shayegan, M;
Source:
PHYSICAL REVIEW LETTERS, 91 (7): 691-696; 2003
Abstract:
Using infrared spectroscopy, we show that spin self-organization in untwinned La2-xSrxCuO4 (LSCO) crystals has profound consequences for the dynamical conductivity sigma(omega). The electronic response of CuO2 planes acquires significant anisotropy in the spin ordered state with enhancement of the conductivity along the direction of the diagonal spin stripes by up to a factor of 2. An examination of the anisotropic response indicates that the diagonal spin texture in weakly doped LSCO is also accompanied by the modulation of charge density. The electronic response of the charge stripes is found to be gapless consistent with the hypothesis of the metallic ground state. Our experiments directly show that the striped ordered systems reveal new degrees of freedom not present in ordinary one-dimensional conductors.
Title:
Comment on "Quasicrystal-crystal transformation in Zn-Mg-rare-earth alloys"
Authors:
Uhrig, E; Sterzel, R; Bruhne, S; Assmus, W; Shayegan, M;
Source:
PHYSICAL REVIEW LETTERS, 91 (8): 691-696; 2003
Abstract:
---
Title:
Comment on "Quasicrystal-crystal transformation in Zn-Mg-rare-earth alloys" - Reply
Authors:
Tsai, AP; Abe, E; Bruhne, S;
Source:
PHYSICAL REVIEW LETTERS, 91 (8): 691-696; 2003
Abstract:
---
Title:
Nanoprecipitates of icosahedral phase in quasicrystal-strengthened Mg-Zn-Y alloys
Authors:
Singh, A; Tsai, AP; Nakamura, M; Watanabe, M; Kato, A; Van Tendeloo, G;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 83 (9): 543-551; 2003
Abstract:
Extensive microstructural studies have been performed with respect to the formation of the icosahedral quasicrystalline phase and its relationship to other phases in Mg95Zn4.2Y0.8 alloy. The icosahedral phase forms as an intergranular eutectic phase as well as precipitates in the matrix. The precipitates are nanosized (typically 50 nm) with a definite orientation relationship with the matrix, sharply faceted on twofold planes which are on the basal and prismatic planes of the matrix. The detailed crystallographic relationship with the matrix is described. The icosahedral phase is occasionally found to coexist with the cubic W-Zn3Mg2Y3 phase with a definite crystallographic relationship.
Title:
Novel in-gap spin state in Zn-doped La1.85Sr0.15CuO4
Authors:
Kimura, H; Kofu, M; Matsumoto, Y; Hirota, K; Kato, A;
Source:
PHYSICAL REVIEW LETTERS, 91 (6): 1500-1503; 2003
Abstract:
Low-energy spin excitations of La1.85Sr0.15Cu1-yZnyO4 were studied by neutron scattering. In y=0.004, the incommensurate magnetic peaks show a well-defined "spin gap" below T-c. The magnetic signals at omega=3 meV decrease below T-c=27 K for y=0.008, also suggesting the gap opening. At lower temperatures, however, the signal increases again, implying a novel in-gap spin state. In y=0.017, the spin gap vanishes and elastic magnetic peaks appear. These results clarify that doped Zn impurities induce the novel in-gap state, which becomes larger and more static with increasing Zn.
Title:
Huge enhancement of electromechanical responses in compositionally modulated Pb(Zr1-x Ti-x)O-3
Authors:
Huang, ND; Liu, ZR; Wu, ZQ; Wu, J; Duan, WH; Gu, BL; Zhang, XW; Caironi, D;
Source:
PHYSICAL REVIEW LETTERS, 91 (6): 1500-1503; 2003
Abstract:
Monte Carlo simulations based on a first-principles-derived Hamiltonian are conducted to study the properties of Pb(Zr1-xTix)O-3 alloys compositionally modulated along the [100] pseudocubic direction near the morphotropic phase boundary. It is shown that compositional modulation causes the polarization to continuously rotate away from the modulation direction, resulting in the unexpected triclinic and C-type monoclinic ground states and huge enhancement of electromechanical responses (the peak of piezoelectric coefficient is as high as 30 000 pC/N). The orientation dependence of dipole-dipole interaction in modulated structure is revealed as the microscopic mechanism to be responsible for these anomalies.
Title:
Synthesis and structural characterization of Ba14Pd3Ir8O33
Authors:
Burley, JC; Battle, PD; Jordan, NA; Sloan, J; Weill, F; Gu, BL;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 174 (1): 96-103; 2003
Abstract:
Ba14Pd3Ir8O33 has been prepared in polycrystalline form and characterized by X-ray, neutron and electron diffraction, lattice imaging and magnetometry. The structure can be described as the n = 5, m = 9 member of the (A(3)O(9))(n)(A(3)A'O-6)(m) series which derives from the n = infinity, m = 0 2H perovskite structure. Ir and Pd cations occupy chains of octahedral and trigonal-prismatic sites in a disordered manner. An alternative description of the structure in (3 + 1)-dimensional superspace is also presented. No magnetic phase transitions were observed above 5 K. (C) 2003 Elsevier Science (USA). All rights reserved.
Title:
Atomic ordering in the doped rare earth cobaltates Ln(0.33)Sr(0.67)CoO(3-delta) (Ln = Y3+, Ho3+ and Dy3+)
Authors:
Withers, RL; James, M; Goossens, DJ; Sloan, J;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 174 (1): 198-208; 2003
Abstract:
The perovskite-based rare earth cobaltates (Ln(0.33)Sr(0.67)CoO(3-delta)) (Ln = Y3+, Ho3+ and Dy3+) have been synthesized at 1100degreesC under 1 atm oxygen. A thermogravimetric study has determined the overall oxygen content in each case while a combined electron diffraction (ED) and synchrotron X-ray diffraction study has revealed the presence of a complex, previously unreported, perovskite-related superstructure phase. ED gave a resultant C1c1 but most probably Cmcm (a = 2a(p) - 2c(p), b = 4b(p), c = 2a(p) + 2c(p)) perovskite-related superstructure, describable as a modulated I4/mmm intermediate parent structure. Synchrotron X-ray data has been used to refine the intermediate parent structures of all three compounds. Coupled Ln/Sr and O/vacancy ordering and associated structural relaxation is shown to be responsible for the observed superstructure. (C) 2003 Elsevier Science (USA). All rights reserved.
Title:
Superspace description of the hexagonal perovskites in the system Ba5Nb4O15-BaTiO3 as modulated layered structures
Authors:
Boullay, P; Teneze, N; Trolliard, G; Mercurio, D; Perez-Mato, JM; Gu, BL;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 174 (1): 209-220; 2003
Abstract:
A general structural model of B-site deficient hexagonal layer perovskites AB(1-x)X(3) having no tilting of anion octahedra in consecutive layers is presented. They are described as modulated layered structures using a (3 + 1)-dimensional superspace approach. The presence or not of a given atom along the stacking direction is described in superspace through step-like (crenel) occupational modulation functions. Being essentially composition independent, the model is applicable to any compounds related to this structural type. The component of the primary modulation vector q = gammac* is connected to the chemical composition by the relation gamma = (1 + x)/3. The model is confirmed and the efficiency of the superspace approach is demonstrated by the structural analysis of some of the hexagonal perovskite found in the system Ba5Nb4O15-BaTiO3, where long-period intergrowth compounds have been recently identified. (C) 2003 Elsevier Science (USA) All rights reserved.
Title:
Reciprocal-space imaging and the use of a diamond-anvil cell: a single-crystal high-pressure study of a quasicrystal up to 10.7 GPa
Authors:
Krauss, G; Miletich, R; Steurer, W; Mercurio, D;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 83 (8): 525-531; 2003
Abstract:
A comparative in-situ high-pressure single-crystal X-ray diffraction study of decagonal Al70Co12Ni18 (Edagawa phase) up to 10.7 GPa has been performed using a diamond-anvil cell with Mo Kalpha(1) X-rays as well as synchrotron radiation. A method of quantitative reciprocal-space reconstruction from image plate frames was used for data analysis. Although a diamond-anvil cell was used for pressure generation, very clear low-background images, comparable with those without a diamond-anvil cell were obtained. Neither Bragg scattering nor diffuse scattering show any variation with pressure, indicating the high stability of the decagonal quasicrystal structure. The compression behaviour was found to be quasiisotropic in the investigated pressure range. The bulk modulus at zero pressure was determined as 121(8) GPa.
Title:
Weak ferromagnetism and an intermediate incommensurate antiferromagnetic phase in LiNiPO4
Authors:
Kharchenko, YN; Kharcheno, NF; Baran, M; Szymczak, R; Perez-Mato, JM;
Source:
LOW TEMPERATURE PHYSICS, 29 (7): 579-583; 2003
Abstract:
The temperature dependence of the magnetization of single-crystal LiNiPO4 is measured for magnetic-field orientations along the a, b, and c crystallographic axes. It is found that the value of the magnetization depends on the magnetic prehistory of the sample. The magnetic behavior of the antiferromagnetic sample is explained by the presence of weak ferromagnetism in LiNiPO4. At a temperature of 5 K the value of the spontaneous magnetic moment along the c axis is around 0.005 G. When the sample is heated to 20.8 K the magnetic moment decreases monotonically to zero. All of the magnetic susceptibility curves M(T)/H exhibit two features: a jump and a kink at temperatures T-1 and T-2, respectively. At a magnetic field of 10 kOe these temperatures are close to 20.84 and 21.86 K. The observed features indicate that in the establishment of the main antiferromagnetic order in the LiNiPO4 crystal, an intermediate antiferromagnetic phase is spontaneously formed in the temperature interval from T-N1=20.8(5) K to T-N2=21.8(5). The sequence of continuous and abrupt transitions at the boundary temperatures of its existence region indicate that the intermediate phase is most likely an incommensurate antiferromagnetic state. (C) 2003 American Institute of Physics.
Title:
Successive phase transitions in a Kagome-like heavy-fermion compound, CePdAl
Authors:
Nishiyama, M; Oyamada, A; Maegawa, S; Goto, T; Kitazawa, H; Yamaguchi, Y;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (28): S2267-S2270; 2003
Abstract:
The heavy-fermion compound CePdAl exhibits an antiferromagnetic phase transition at 2.7 K (T-N). Cc atoms in CePdAl form a distorted Kagome lattice in the c-planes. The ordered spin structure in the Kagome plane is of a partially disordered type, which has a third paramagnetic spins. The kappa-vector is (1/2, 0, tau approximate to 0.35), which is incommensurate along the c-axis. Frustration effects in the Kagome plane are responsible for this partially disordered structure, although the origin of the incommensurability is not clear at present. Whether or not a magnetic phase transition occurs at lower temperatures is a question of considerable interest. Al-27 nuclear magnetic resonance measurements have been performed at low temperatures to investigate the transition below T-N. There is no remarkable change in the spin-echo spectra below T-N down to 0.5K. On the other hand, the spin-lattice relaxation rate shows a small anomaly around 1 K. This strongly suggests that there is another phase transition below T-N. Some possible origins of successive transitions are discussed.
Title:
Effects of ball milling and annealing of an alloy in the Al-Fe-Cu system: implications for phase equilibria
Authors:
Mukhopadhyay, NK; Yadav, TP; Srivastava, ON; Khor, HCK;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 83 (7): 423-432; 2003
Abstract:
An icosahedral quasicrystalline alloy in the Al-Fe-Cu system has been mechanically milled in a high-energy ball mill (Szegvari attritor) for 1, 3, 6 and 10 h. Samples were characterized by X-ray diffraction and transmission electron microscopy. The evolution of nanosize crystallites of the disordered B2 phase (bcc; a = 0.29 nm), coexisting with either the parent icosahedral phase or an amorphous phase, occurs during milling. Isothermal heat treatment of milled powder at various temperatures (200, 500, 600, 700, 800 and 850degreesC) leads in all cases, except at 200degreesC, to the transformation from disordered B2 and amorphous phases to an ordered B2 phase with a high degree of long-range ordering. The maximum degree of superlattice ordering was found after isothermal treatment at 800degreesC. The implications of these results are discussed with reference to phase equilibria existing between crystalline and quasicrystalline phases in the Al-Fe-Cu system.
Title:
Ti-Zr-Ni bulk quasicrystals prepared by casting
Authors:
Qiang, JB; Wang, YM; Wang, DH; Kramer, M; Dong, CA; Bishop, AR;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 83 (7): 467-472; 2003
Abstract:
A broad bulk-quasicrystal-forming region, (TixZr100-x)(100-y)Ni-y (43.75 less than or equal to x less than or equal to 81.25, 17 less than or equal to y less than or equal to 23), has been identified in the Ti-Zr-Ni system, and quasicrystals can be obtained by using a conventional suction-casting method. The quasilattice constant of the icosahedral (i) phase is within the range 0.505-0.530 nm. Ti40Zr40Ni20 is the optimal composition, where nearly pure bulk quasicrystals can be obtained. With a slight deviation from this composition, Ti-Zr solid-solution phases and/or C14-type Laves phase, although minority phases, coexist with the majority i phase. Differential thermal analysis reveals that the i phase in the bulk as-cast Ti40Zr40Ni20 alloy is stable below 953 K and transforms to the C14-type Laves phase and beta-Ti-Zr solid solution at higher temperatures.
Title:
Phonon- and phason-type spherical inclusions in icosahedral quasicrystals
Authors:
Wang, JB; Mancini, L; Wang, RH; Gastaldi, J; Dong, CA;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (24): L363-L370; 2003
Abstract:
Analytical expressions are derived as a first-order approximation for the elastic displacement fields, including both phonon- and phason-type components, induced by spherical inclusions in icosahedral quasicrystals (IQCs). The phonon-type component obtained is the same as that for a spherical inclusion in conventional elastically isotropic crystals, while the expression for the phasontype displacement, which decreases with increasing distance r to the sphere centre as r(-1), is derived for the first time. Three concrete cases are discussed. The phonon part of the analytical expressions has been used to simulate the black-white double-lobe contrasts in the x-ray topograph (XRT) images of the strain field around the pores in the AlPdMn IQCs. The analytical expression for the phason-type displacement is used to simulate the XRT images of the strain field around spherical inclusions having isomorphic structures. The striking resemblance between experimental and simulated images suggests that such inclusions are surrounded by antiphase boundaries with a phason-type displacement vector, being particular structural defects in IQCs.
Title:
Hopping transport in an insulating quasicrystal bar of Al70Pd22.5Re7.5 near the metal-insulator transition
Authors:
Rosenbaum, R; Lin, ST; Su, TI; Gastaldi, J;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (24): 4169-4180; 2003
Abstract:
We have observed that the conductivity or(T) for the Al70Pd22.5Re7.5 quasicrystal, with a resistivity ratio r = R(4.2 K)/R(300 K) = 13.2, obeys the variable-range hopping law, sigma (T) = sigma(0)/exp[(T-0/T)](mu), in the temperature range between 64 mK and 1.6 K. The hopping exponent mu is extracted to be 0.23, close to the Mott exponent of 1/4, and T-0 is 3.5 K. This insulating behaviour is consistent with the prediction of a previously determined scaling law that bulk Al70Pd22.5Re7.5 samples having r greater than or equal to 12.8 will be insulating. Large positive magnetoresistances (MRs) were observed in this sample. The percentage change in the MR = DeltaR(B, T)/R(0, T), as high as 185% at T = 0.11 K and B = 17 T, is the largest value ever reported in Al-Pd-Re QCs, to our knowledge. The difficulties using existing MR theories to explain the MR data for this insulating sample near the metal-insulator transition are discussed.
Title:
Solidification microstructure of as-cast Mg-Zn-Y alloys
Authors:
Ok, JB; Kim, IJ; Yi, S; Kim, WT; Kim, DH; Ward, RCC;
Source:
PHILOSOPHICAL MAGAZINE, 83 (20): 2359-2369; 2003
Abstract:
Composites consisting of icosahedral (i) phase and ductile alpha-Mg can be fabricated by controlling the alloy composition. With increasing Mg content, the primary solidification phase changed from the i phase to the alpha-Mg phase and single eutectic structure can be obtained at a composition Of Mg72Zn23.5Y3.5. The i phase showed a variation in structural order from the well-ordered icosahedral phase to the 1/1 rhombohedral approximant with lattice constants a = 27.2 Angstrom and a = 63.43degrees. The structural change in the i phase can be explained by microdomain formation due to compositional change during solidification. Annealing treatment improves the structural order of the i phase by homogenization. By controlling the alloy composition, a single eutectic structure consisting of a hard i phase and a ductile alpha-Mg phase could be obtained.
Title:
Dislocation motion in icosahedral quasicrystals at elevated temperatures: numerical simulation
Authors:
Schaaf, GD; Roth, J; Trebin, HR; Kim, WT;
Source:
PHILOSOPHICAL MAGAZINE, 83 (21): 2449-2465; 2003
Abstract:
We have simulated shear deformation of an icosahedral model quasicrystal at elevated temperatures with molecular dynamics. The generation of a dislocation loop was studied with a new visualization technique and a critical stress almost as large as the theoretical shear strength was measured. Built-in dislocations started to move at a temperature-dependent critical stress lower by one order of magnitude. While at zero temperature the dislocation propagated intermittently by large jumps, its motion became viscous as temperature increased. The dislocation cores bulged considerably owing to pinning at obstacles inherent in the structure. A calculation of the energy of a Peierls-Nabarro dislocation moving rigidly through the sample allowed us to determine the dominant obstacles. The results are considered in relation to two different models of quasicrystalline plasticity.
Title:
Effects of Pb-ion irradiation on the vortex pinning in melt-textured YBa2Cu3Ox
Authors:
Goeckner, HP; Olson, RJ; Kwok, WK; Claus, H; Kouvel, JS; Eidelman, Y;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 390 (4): 291-295; 2003
Abstract:
Melt-textured YBa2Cu3Ox quasicrystalline samples were studied for the effects of Pb-ion irradiation on the vortex pinning. The strength of the pinning was monitored by measurements of the saturation remanent magnetization (MR) as a detailed function of temperature from 4.2 K up to T-c (approximate to92 K). Our results show that M-R is greatly enhanced by the Pb-ion irradiation at all temperatures below T,. Specifically, when compared to a similar but nonirradiated sample, the MR of an optimally irradiated sample is raised by a factor of 3.4 at 4.2 K and, more strikingly, by 12.7 at 77 K. Contrastingly, in an earlier study of a gamma-ray irradiated Bi1.6Pb0.4Sr2Ca2Cu3O10 sample, the vortex pinning was seen to be enhanced but mainly near 4.2 K, suggesting that the gamma-ray irradiation produces highly localized pinning sites. Hence, our present results imply conversely that the Pb-ion irradiation creates extended structural defects that are effective as vortex pinning sites up to relatively high temperatures, including that of liquid nitrogen. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
About specific features of the structure modulation in the Bi-ferrate compounds isostructural with Bi2Sr2CaCu2O8
Authors:
Sedykh, V; Shekhtman, VS; Smirnova, IS; Bagautdinov, BS; Suvorov, EV; Dubovitskii, AV; Hirose, T;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 390 (4): 311-320; 2003
Abstract:
The single-crystalline specimens of the Fe-doped (5% Fe-57) Bi2Sr2CaCu2O8 (2212Cu) compound have been synthesized to compare the behavior of the structure modulation in Bi-cuprate and Bi-ferrate compounds. According to the Mossbauer data obtained, one can conclude that extra oxygen, related to the presence of Cu3+ in 2212Cu, is most probably arranged in the Ca layer rather than in the Bi layer, as was supposed in the model of extra oxygen. Based on the analysis of the experimental data we propose the explanation of the structure modulation in Bi compounds. Due to the mismatch between the internal perovskite block and the external BiO layers the structure of the Bi compounds is distorted. The Sr layer being boundary between these blocks probably is most distorted and stressed. We suppose that the different changes related to the modulation can occur just in this layer. The Bi excess, which is always present in Bi compounds (especially in single crystals), can be just the necessary condition at which the modulation appears. Extra oxygen in principle can be present in modulated structures. However, in our opinion, it only complements the influence of other factors and is not the driving force in the structure modulation. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Is the negative temperature coefficient of the resistivity of the quasicrystals due to chemical disorder?
Authors:
Tamura, R; Araki, T; Takeuchi, S; Manier, M;
Source:
PHYSICAL REVIEW LETTERS, 90 (22): 236-243; 2003
Abstract:
We have found that the electronic transport of the binary icosahedral (i) Cd-Yb is extremely sensitive to a minute substitution of Mg for Cd atoms; the positive temperature coefficient of the resistivity (TCR) at low temperatures seen in the binary i Cd-Yb disappears by addition of only 0.1 at. % Mg and, moreover, the TCR stays negative well up to 60 at. % Mg. Such sensitiveness of the resistivity in the very dilute Mg concentration region, which is a consequence of the long coherence length (>28 angle) of the conduction electrons in the quasiperiodic lattice, has led us to an unexpected conclusion: The negative TCR in the ternary i phase is due to partial chemical disorder; i.e., it is not a consequence of the quasiperiodicity.
Title:
Inhomogeneous d-wave state and lattice distortions in the three-band Hubbard model of high-T-c cuprates
Authors:
Yanagisawa, T; Miyazaki, M; Koikegami, S; Yamaji, K; Mercurio, D;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 388 (22): 72-73; 2003
Abstract:
Striped superconductivity (SC) with lattice distortions is investigated based on the three-band Hubbard model of high-T-c cuprates. A stable inhomogeneous striped state is determined in the low-temperature tetragonal phase using a quantum variational Monte Carlo method. The ground state has vertical or horizontal hole-rich arrays coexisting with incommensurate magnetism and SC. The SC order parameter oscillates according to the inhomogeneity in the antiferromagnetic background with its maximum in the hole-rich region. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Inhomogeneous superconductivity coexisting with SDW stripes in the two-dimensional Hubbard model
Authors:
Miyazaki, M; Yamaji, K; Yanagisawa, T; Yamaji, K;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 388 (22): 82-83; 2003
Abstract:
The condensation energy of a spatially inhomogeneous d-wave superconducting state coexisting with spin-density wave stripes is studied by using the variational Monte Carlo method. We calculate its hole-density dependence in the two-dimensional Hubbard model. With U = 8t, it turns out that the coexistent state is the most stable state among other ordered states in the under-doped region. The obtained hole-density dependence of the incommensurability of the coexisting state is in good agreement with the neutron scattering data for La2-x-yNdySrxCuO4 in a wide region. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Incommensurate properties of high-T-c superconductor YBa2Cu3O6.93
Authors:
Yokoo, T; Arai, M; Shiohara, Y; Tajima, S; Frost, CD; Endoh, Y; de Groot, PAJ;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 388 (22): 223-224; 2003
Abstract:
The resonance and incommensurate (IC) peaks in optimally doped high-T-c superconductor YBa2Cu3O6.93 are observed by means of TOF neutron scattering technique in a wide q-E space. The overall dynamical properties around (pi,pi) suggest that the incommensurability delta congruent to 0.1 (at E 36 meV) corresponds to the previous triple-axis measurement. The obtained delta = 0.1 is smaller than that expected from stripe like charge segregation. In the high frequency region, we found the same type of resonance and IC peaks at E = 53 meV. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
LT-STM observation of YBa2(Cu1-xZnx)(3)O7-delta single crystals
Authors:
Maki, M; Nishizaki, T; Kobayashi, N; Adachi, S;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 388 (22): 279-280; 2003
Abstract:
Low-temperature scanning tunneling microscopy on the BaO layer of cold-cleaved YBa2(Cu1-xZnx)(3)O7-delta single crystals reveals the one-dimensional charge modulations at lower bias voltage. These charge modulations have various lengths and are distributed randomly in space. The spatially inhomogeneous electronic state is regarded to be induced by Zn impurities in the CuO2 plane just under the BaO layer, because there are no charge modulations on Zn-free samples. The one-dimensional character possibly reflects the interaction between the CuO2 and the CuO-chain layers. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Spectral properties of incommensurate CDW scattering in cuprates
Authors:
Seibold, G; Varlamov, S; Sakai, N;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 388 (22): 309-310; 2003
Abstract:
Motivated by the observation of periodic charge modulations in Bi2Sr2CaCu2O8+delta by recent STM experiments we show that the associated collective charge dynamics can also account for the peculiar features as seen in ARPES experiments. Especially the famous peak-dip-hump structure of the line shape and the related kink in the dispersion can be well described by the coupling of the charge carriers to dynamical incommensurate CDW fluctuations. From a comparison with ARPES data we obtain a mode frequency which decreases towards optimal doping thus strongly supporting the existence of a quantum critical point around this concentration. Finally we extract the temperature dependence of the CDW mode from ARPES experiments and extend this approach in order to include the recently observed bilayer splitting. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Electronic and structural properties of organic superconductor kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]I
Authors:
Yefanov, VS; Kagoshima, S; Tanatar, MA; Ishiguro, T; Bondarenko, VA; Kushch, ND; Yagubskii, EB; Kikugawa, N;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 388 (22): 589-590; 2003
Abstract:
The thermopower, resistance under the uniaxial compression and X-ray diffuse scattering were measured on single crystals of kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]I. Diffuse X-ray studies revealed a two stage superstructural transformation, leading to a formation of an incommensurate superstructure in the ground state. Thermopower measurements show close relation between the SST and the formation of the insulating state in the salt at ambient pressure. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Modulated structure of solid iodine during its molecular dissociation under high pressure
Authors:
Kenichi, T; Kyoko, S; Hiroshi, F; Mitsuko, O; Bondarenko, VA;
Source:
NATURE, 423 (6943): 971-974; 2003
Abstract:
The application of pressure to solid iodine forces the molecules in the crystal to approach each other until intermolecular distances become comparable to the bond length of iodine; at this point, the molecules lose their identity and are essentially dissociated. According to room-temperature X-ray diffraction studies(1), this process involves direct dissociation of iodine molecules at about 21 GPa, whereas spectroscopic observations(2,3) have identified intermediate molecular phases at pressures ranging from 15 to 30 GPa. Here we present quasi-hydrostatic powder X-ray diffraction measurements that clearly reveal an intermediate phase during the pressure-induced dissociation of solid iodine. We find that, similar to the behaviour seen in uranium(4), the structure of this intermediate phase is incommensurately modulated, with the nearest interatomic distances continuously distributed over the range 2.86 - 3.11 Angstrom. The shortest of these interatomic distances falls between the bond length of iodine in the molecular crystal (2.75 Angstrom) and the nearest interatomic distance in the fully dissociated monatomic crystal (2.89 Angstrom), implying that the intermediate phase is a transient state during molecular dissociation. We expect that further measurements at different temperatures will help to elucidate the origin and stability of the incommensurate structure, which might lead to a better understanding of the molecular-level mechanism of the pressure-induced dissociation seen here and in the molecular crystals of hydrogen(5), oxygen(6) and nitrogen(7).
Title:
Diffraction on icosahedral Danzer tilings
Authors:
Escudero, JG; Garcia, JG; Tsai, L;
Source:
MODERN PHYSICS LETTERS B, 17 (8): 303-309; 2003
Abstract:
An interpretation of Icosahedral Danzer tilings in terms of algebraic substitutions is used in order to study the Fourier transform of suitable mass distributions. Numerical results axe obtained for a mass distribution placed on vertex positions.
Title:
The composite structure of Cu2.33-xV4O11
Authors:
Rozier, P; Lidin, S; Tsai, L;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 172 (2): 319-326; 2003
Abstract:
The copper vanadium oxide bronze Cu2.33-xV4O11, exhibits a three part composite structure refined on the basis of XRD low-temperature studies. It crystallizes in the triclinic system with the non-centric superspace group XI and cell parameters a = 15.280(3) Angstrom; b(1) = 3.616(1) Angstrom; c = 14.674(3) Angstrom; alpha = 90.0degrees; beta = 101.95(3)degrees; gamma = 90.0degrees with a modulation q-vector equal to (0,0.11,0). The three different parts of this composite structure differ by their b-unit cell repeat defined as b(1); b(2) = 2.964(1) Angstrom (b(2)* = b(1)* + 2q) and b(3) = 3.257(1) Angstrom (b(3)* = b(1)* + 1q). These parts are respectively associated to the V4O11 substructure and to each of the two different copper sites. Such refinement allows us to describe the structure using only one and fully occupied crystallographic site for each of the Cu ions. The maximum composition (x = 0) is then achieved. Bond valence sum calculations on the basis of such composite structure is in agreement with electronic structure calculation made using the average one and allows us to attribute the proper valence state to each Cu ions. Then, the calculated ratio appears, contrary to the average structure, in prefect agreement with the one deduced from XPS experiment. (C) 2003 Elsevier Science (USA). All rights reserved.
Title:
Point contact spectroscopy of Al70Pd30-xMnx quasicrystals
Authors:
Banerjee, GN; Banerjee, S; Goswami, R; Liu, CS;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (14): 2317-2326; 2003
Abstract:
We report here the electrical resistivity and point contact spectroscopy (PCS) of Al70Pd30-x Mn, quasicrystals (x = 7, 9 and 11). All samples show a negative temperature coefficient of resistivity (TCR) at room temperature and a positive TCR below 100 K giving rise to resistivity maxima. The positive TCR at lower temperature is attributed to spin-orbit scattering. For x = 11, we observe an upturn with a sharp rise in the resistivity below 20 K and In T dependence of resistivity is observed below 10 K indicating Kondo-like behaviour. In the PCS we are able to see evolution of the point contact regime to the tunnelling-like regime as a function of contact resistance. We see the signature of the Kondo effect in the PCS. In this spectroscopy we observe three regimes showing a V-n dependence where n similar to 1.7 at low bias voltages (for V < 10 meV) crossing over to n similar to 0.5 at higher voltages and to n similar to 2 above 60 meV.
Title:
The order parameter-entropy relation in some universal classes: experimental evidence
Authors:
Martin-Olalla, JM; Romero, FJ; Ramos, S; Gallardo, MC; Perez-Mato, JM; Salje, EKH; Robinson, MB;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (14): 2423-2434; 2003
Abstract:
Asymptotic behaviour near phase transitions can be suitably characterized by the scaling of Deltas / Q(2) with is an element of = 1 - T/T-c, where Deltas is the excess entropy and Q is the order parameter. As As is obtained by integration of the experimental excess specific heat of the transition Deltac, it displays little experimental noise so that the curve log(Deltas /Q(2)) versus log is an element of is better constrained than, say, log Deltac versus log is an element of. The behaviour of Deltas / Q(2) for different universality classes is presented and compared. In all cases, it clearly deviates from being a constant. The determination of this function can then be an effective method to distinguish asymptotic critical behaviour. For comparison, experimental data for three very different systems, Rb2CoF4, Rb2ZnCl4 and SrTiO3, are analysed under this approach. In SrTiO3, the function Deltas / Q(2) does not deviate within experimental resolution from a straight line so that, although Q can be fitted with a non mean-field exponent, the data can be explained by a classical Landau meanfield behaviour. In contrast, the behaviour of Deltas / Q(2) for the antiferromagnetic transition in Rb2CoF4 and the normal-incommensurate phase transition in Rb2ZnCl4 is fully consistent with the asymptotic critical behaviour of the universality class corresponding to each case. This analysis therefore supports the claim that incommensurate phase transitions in general, and the A(2)B(2)X(4) compounds in particular, in contrast with most structural phase transitions, have critical regions large enough to be observable.
Title:
Formation of decagonal and approximant phases in the Al-Ni-Ru system
Authors:
Mandal, P; Hashimoto, T; Suzuki, K; Hosono, K; Kamimura, Y; Edagawa, K; Finkelstein, KD;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 83 (5): 315-323; 2003
Abstract:
Al-Ni-Ru alloys with a wide composition range have been synthesized and examined by X-ray and electron diffraction experiments. In this system, two types of decagonal (d) phases are formed, namely basic-type and superlattice-type d phases. Annealing experiments have shown that the basic-type d phase is stable at high temperatures and that its single-phase region is located in a small composition range around Al75Ni15Ru10. On the other hand, the superlattice-type d phase is metastable and has been found to form only in the samples before annealing. Besides the d phases, a high-order crystal approximant phase with lattice parameters a = 99.5 Angstrom and b = 84.6 Angstrom has been found. The structural relation between the approximant phase and the d phase is discussed in terms of a phason tensor.
Title:
Specific heat of the [NH2(CH3)(2)](2)ZnCl4 crystal in the temperature region 80-300 K
Authors:
Sheleg, AU; Dekola, TI; Tekhanovich, NP; Mamedov, S;
Source:
PHYSICS OF THE SOLID STATE, 45 (5): 946-947; 2003
Abstract:
The specific heat of [NH2(CH3)(2)](2)ZnCl4 was measured calorimetrically in the temperature region 80-300 K. As the temperature T decreases, the C-p(T) dependence indicates a phase transition sequence, with the phase transition at T-6=151 K observed for the first time. The thermodynamic characteristics of the crystal were refined. The transformation occurring at T-2=298.3 K is shown to be an incommensurate-commensurate phase transition. (C) 2003 MAIK "Nauka/Interperiodica".
Title:
Quantum antiferromagnetism in quasicrystals
Authors:
Wessel, S; Jagannathan, A; Haas, S; Takeuchi, T;
Source:
PHYSICAL REVIEW LETTERS, 90 (17): 946-947; 2003
Abstract:
The antiferromagnetic Heisenberg model is studied on a two-dimensional bipartite quasiperiodic lattice. Using the stochastic series expansion quantum Monte Carlo method, the distribution of local staggered magnetic moments is determined on finite square approximants with up to 1393 sites, and a nontrivial inhomogeneous ground state is found. A hierarchical structure in the values of the moments is observed which arises from the self-similarity of the quasiperiodic lattice. The computed spin structure factor shows antiferromagnetic modulations that can be measured in neutron scattering and nuclear magnetic resonance experiments. This generic model is a first step towards understanding magnetic quasicrystals such as the recently discovered Zn-Mg-Ho icosahedral structure.
Title:
Oscillatory exchange bias due to an antiferromagnet with incommensurate spin-density waves
Authors:
Yang, FY; Chien, CL; Pu, H;
Source:
PHYSICAL REVIEW LETTERS, 90 (14): 697-702; 2003
Abstract:
Oscillatory exchange bias in both magnitude and in sign has been observed in epitaxial (100)Cr/Ni81Fe19 bilayers due to the incommensurate spin-density waves in antiferromagnetic (100)Cr layers. Salient effects due to the spin-flip transition between longitudinal and transverse spin-density waves as well as that of expanding wavelength have been observed.
Title:
High-energy spin dynamics in La1.69Sr0.31NiO4
Authors:
Bourges, P; Sidis, Y; Braden, M; Nakajima, K; Tranquada, JM; Berger, H;
Source:
PHYSICAL REVIEW LETTERS, 90 (14): 697-702; 2003
Abstract:
To test the prediction that the dispersion of the magnetic resonance in superconducting YBa2Cu3O6+x is similar to magnons in an incommensurate antiferromagnet, we have mapped out the spin dynamics in a stripe-ordered nickelate, La2-xSrxNiO4, with x similar or equal to 0.31, using inelastic neutron scattering. We observe spin-wave excitations up to 80 meV emerging from the incommensurate magnetic peaks with a surprisingly large and almost isotropic spin velocity: (h) over barc(s)similar to0.32 eV Angstrom. A comparison indicates that the inferred spin-excitation spectrum is not, by itself, an adequate model for the magnetic resonance feature of the superconductor.
Title:
Decagonal quasiferromagnetic microstructure on the penrose tiling
Authors:
Vedmedenko, EY; Oepen, HP; Kirschner, J; Fujita, M;
Source:
PHYSICAL REVIEW LETTERS, 90 (13): S1139-S1148; 2003
Abstract:
The stable magnetization configurations of a ferromagnet on a quasiperiodic tiling have been derived theoretically. The magnetization configuration is investigated as a function of the ratio of the exchange to the dipolar energy. The exchange coupling is assumed to decrease exponentially with the distance between magnetic moments. It is demonstrated that for a weak exchange interaction the new structure, the quasiferromagnetic decagonal configuration, corresponds to the minimum of the free energy. The decagonal state represents a new class of frustrated systems where the degenerated ground state is aperiodic and consists of two parts: ordered decagon rings and disordered spin-glass-like phase inside the decagons.
Title:
Atomic image of Bi2Sr2CaCu2O8+x cleaved surface
Authors:
Susla, B; Giersig, M; Czajka, R; Kaminski, A; Park, S;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 387 (1-2): 221-224; 2003
Abstract:
The results of the scanning tunneling microscopy/spectroscopy as well as transmission electron microscopy measurements on the bismuth cuprate superconductors Bi2Sr2CaCu2O8+x in the ab-plane are reported. STM high-resolution images of cleaved single crystal reveal an atomic lattice and a superimposed incommensurate superstructure. We have also clearly seen this superstructure in high-resolution electron micrographs. Scanning tunneling microscopy of the deposited clusters yield information on the cluster shape. Scanning tunneling spectroscopy at low temperature allows identifying quantum size effect in individual Ni clusters. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Atomic model of anti-phase boundaries in a face-centred icosahedral Zn-Mg-Dy quasicrystal
Authors:
Wang, JB; Yang, WG; Wang, RH; Kaminski, A;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (10): 1599-1611; 2003
Abstract:
An atomic model in the physical space for an anti-phase boundary (APB) in the ordered face-centred icosahedral Zn-Mg-Dy quasicrystal phase is presented, based on a six-dimensional model suggested by Ishimasa and Shimizu (2000 Mater. Sci. Eng. A 294-296 232, Ishimasa 2001 private communication). The physical space atomic positions of the defected structure were used for the calculation of the corresponding exit-plane wavefunction and high-resolution transmission electron microscopy images. The analysis of the defect by inverse Fourier transformation reveals that when superstructure reflection spots are used for back-transformation, then at the APB, bright lattice fringes are found to turn into dark ones, and vice versa. When fundamental reflections are used, the APB is not visible. This phenomenon is the same as the corresponding experimental study recently published by Heggen et al (2001a Phys. Rev. B 64 014202). Based on this atomic model it is found that the APB perpendicular to a fivefold axis A5 (APB-A5) is a non-conservative boundary, while the APB perpendicular to a pseudo-twofold axis A2P (APB-A2P) is a conservative one. This fact is consistent with the experimental observation (Heggen et al 2002 J. Alloys Compounds 342 330) that the frequency of occurrence of APB-A5 Is 90% in the heat-treated samples compared with that in the deformed samples (45%), while the frequency of occurrence of APB-A2P is 34% in the deformed samples compared with that in the heat-treated samples.
Title:
Diffuse scattering from an Al72Ni20Co8 decagonal quasicrystal on an order-disorder transformation
Authors:
Abe, H; Saitoh, H; Ueno, T; Nakao, H; Matsuo, Y; Ohshima, K; Matsumoto, H; Liu, XM;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (10): 1665-1676; 2003
Abstract:
Non-uniform distortion induced by superstructure domains has been observed during the ordering process of an order-disorder transformation in a single decagonal quasicrystal of Al72Ni20Co8. The full width At half maximum (FWHM) of the fundamental reflections increased below the transformation temperature, T-c. At the same time, the integrated intensity of the fundamental reflections varied drastically at T-c. A small hysteresis was also observed in the temperature dependences of both the FWHM and the integrated intensity of the fundamental reflections. Peak broadening of the fundamental reflections is predominantly dependent on \G(parallel to)\ below T-c. In addition, the weak dependence of the peak broadening with \G(perpendicular to)\ is extracted from the observed FWHM of the fundamental reflections. After deconvolution, the FWHM of the fundamental reflections appears to be a linear combination of \G(parallel to)\ and \G(perpendicular to)\. Coexistence of the non-uniform distortion and of the random phason strain contributes to the ordering process below T-c. The diffuse scattering from atomic short-range order (SRO) was distributed around the ideal positions of the superstructure reflections. The SRO diffuse scattering disappeared completely above T-c + 10 K. In addition, a small hysteresis of the SRO diffuse scattering was found in the temperature cycle.
Title:
Magnetic phase transitions in TbFe2Al10, HoFe2Al10 and ErFe2Al10
Authors:
Reehuis, M; Wolff, MW; Krimmel, A; Scheidt, EW; Stusser, N; Loidl, A; Jeitschko, W; Liu, XM;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (10): 1773-1782; 2003
Abstract:
The magnetic order of the orthorhombic aluminides TbFe2Al10, HoFe2Al10 and ErFe2Al10 (space group Cmcm) has been studied by specific heat and magnetic measurements, as well as by neutron powder diffraction down to 100 mK and in external fields up to 5 T. Only the rare-earth ions carry a magnetic moment. At T = 1.5 K the terbium moments in TbFe2Al10 show a square-wave modulated magnetic order with wavevector k = (0, 0.7977, 0) and a moment direction parallel to the a-axis. At a critical field of H-cl = 0.9 T one of ten spins is forced to flip, going into an intermediate ferrimagnetic phase that is stable up to the critical field H-c2 = 1. 8 T. Above this field finally all the rest of the spins flip, resulting in a ferromagnetic order of the terbium moments. ErFe2Al10 orders antiferromagnetically below T-N = 1.77(7) K with a similar magnetic structure characterized by a wavevector k = (0, similar to0.8, 0). In contrast, no signs of long range magnetic order could be observed for HoFe2Al10 down to 100 mK.
Title:
Growth of simple icosahedral single quasicrystals in the Zn-Mg-Ho system
Authors:
Uhrig, E; Bruhne, S; Sterzel, R; Schropfer, L; Assmus, W; Loidl, A;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 83 (4): 265-272; 2003
Abstract:
Single crystals of the simple icosahedral phase Zn76Mg14Ho10 have been grown from the melt. The composition of the melt was selected by differential thermal analysis in combination with scanning electron microscopy and wavelength-dispersive X-ray analysis. The quasicrystals have been characterized by single-crystal and powder X-ray diffraction. The quasilattice constant of the primitive six-dimensional hypercubic lattice is a = 0.5143(2) nm. There is no indication of atomic disorder. Holmium on a primitive icosahedral lattice presents a promising probe for possible quasiperiodic long-range magnetic order.
Title:
Synthesis and mechanical properties of mechanically alloyed Al-Cu-Fe quasicrystalline composites
Authors:
Schurack, F; Eckert, J; Schultz, L; Schropfer, L;
Source:
PHILOSOPHICAL MAGAZINE, 83 (11): 1287-1305; 2003
Abstract:
Al-Cu-Fe alloys were prepared by mechanical alloying starting from elemental powders in a high-energy planetary ball mill. Three different alloy compositions with the same c(Cu) : c(Fe) ratio of 2: 1 but different aluminium contents, that is Al55Cu30Fe15, Al63Cu25Fe12 and Al70Cu20Fe10, were investigated. A sequence of solid-state reactions resulting in quasicrystalline phase formation in Al63Cu25Fe12 proceeds during milling and during annealing of the as-milled powder. These reactions were studied by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. In order to form an aluminium-matrix composite, Al63Cu15Fe12 single-phase quasicrystalline powders were blended with different amounts of aluminium. In an intermediate milling step the powder blend was homogenized. The powders were consolidated by hot extrusion. The bulk samples revealed a homogeneous dispersion of the particles in the matrix but a rather heterogeneous size distribution. The mechanical properties at room temperature were tested by constant-rate compression tests. A rule-of-mixtures dependence of the ultimate strength and the yield strength on the volume fraction of the quasicrystalline particles was found.
Title:
The metastable Ni7 +/- xS6, and mixed Ni-6 +/- x(S1-ySey)(5), phases
Authors:
Liu, Y; Noren, L; Withers, RL; Hadermann, J; Van Tendeloo, G; Garcia-Garcia, FJ; Uchida, S;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 170 (2): 351-360; 2003
Abstract:
The closely related, narrowly non-stoichiometric, metastable as well as thermodynamically stable "phases" in the metal-rich part of the Ni-S phase diagram near the nominal composition Ni7+/-xS6 have been carefully re-investigated via electron diffraction and transmission electron microscope imaging. Two quite distinct polymorphs have been identified, a minority incommensurate interface-modulated polymorph and a (heavily twinned) majority Ila1, a = 2a(p), b = 2b(p), c = -a(p) + c(p) superstructure (of an underlying Bmmb, a(p) similar to 3.3, b(p) similar to 16.4, c(p) similar to 11.3 Angstrom parent structure) polymorph. The incommensurate polymorph is shown to be very closely related to the only known polymorph of Ni6+/-xSe5 and is rapidly stabilized to room temperature upon doping of the sulfide compounds with selenium. (C) 2002 Elsevier Science (USA). All rights reserved.
Title:
Quasiperiodic Bloch-like states in a surface-wave experiment
Authors:
Torres, M; Adrados, JP; Aragon, JL; Cobo, P; Tehuacanero, S; Li, ZQ;
Source:
PHYSICAL REVIEW LETTERS, 90 (11): 1267-1275; 2003
Abstract:
Bloch-like surface waves associated with a quasiperiodic structure are observed in a classic wave propagation experiment which consists of pulse propagation with a shallow fluid covering a quasiperiodically drilled bottom. We show that a transversal pulse propagates as a plane wave with quasiperiodic modulation, displaying the characteristic undulatory propagation in this quasiperiodic system and reinforcing the idea that analogous concepts to Bloch functions can be applied to quasicrystals under certain circumstances.
Title:
Degree of structural perfection of icosahedral quasicrystalline grains investigated by synchrotron X-ray diffractometry and imaging techniques
Authors:
Gastaldi, J; Agliozzo, S; Letoublon, A; Wang, J; Mancini, L; Klein, H; Hartwig, J; Baruchel, J; Fisher, IR; Sato, T; Tsai, AP; de Boissieu, AM;
Source:
PHILOSOPHICAL MAGAZINE, 83 (1): 1-29; 2003
Abstract:
A study of the structural perfection of icosahedral quasicrystalline grains of various alloys (Al-Pd-Mn, Zn-Mg-RE (RE equivalent to rare earth) and Al-Cu-Fe), grown by different slow solidification techniques (Czochralski, Bridgman, flux and annealing) was performed using high-resolution diffraction, including recording rocking curves combined with X-ray topography and phase contrast radiography, at a third-generation synchrotron radiation source (European Synchrotron Radiation Facility, Grenoble, France). For Al-Pd-Mn, additional coherent diffraction and diffuse scattering measurements were also carried out. After evaluating the potentialities of the techniques used, in the light of the criteria defined for crystals, it is shown that the structural perfection of icosahedral quasicrystals is quite comparable with that of metallic crystals but is considerably influenced by either uniform phason strains which can destroy the quasiperiodic long-range order, or by long-wavelength phason fluctuations leading to diffuse scattering. The structural perfection was also found to be extremely variable across the as-grown quasicrystalline grains and to be dependent on the presence and characteristics of inhomogeneities (pores and precipitates) often included in the quasicrystalline matrix. Regarding the grains that we used, it has been impossible to distinguish a clear influence of either the type of alloy or the growth method. It has, however, been noticed that Al-Pd-Mn and Al-Cu-Fe grains appeared less defective than Zn-Mg-RE grains and that the.. microstructure of these latter grains looks like that of crystals grown by the same technique. Annealing and mechanical polishing effects have also been analysed in the case of Al-Pd-Mn grains. It appeared that annealing improves the quasicrystalline lattice perfection by lowering phason strains insofar as no precipitates are nucleated. Mechanical polishing can introduce defects, located at the external surfaces, having the shape
Title:
Undissociated screw dislocations in silicon: calculations of core structure and energy
Authors:
Pizzagalli, L; Beauchamp, P; Rabier, J; Wang, J;
Source:
PHILOSOPHICAL MAGAZINE, 83 (10): 1191-1204; 2003
Abstract:
The stability of the perfect screw dislocation in silicon has been investigated using both classical potentials and first-principles calculations. Although a recent study by Koizumi et al. stated that the stable screw dislocation was located in both the 'shuffle' and the 'glide' sets of {111} planes, it is shown that this result depends on the classical potential used, and that the most stable configuration belongs to the 'shuffle' set only, in the centre of one (101) hexagon. We also investigated the stability of an sp(2) hybridization in the core of the dislocation, obtained for one metastable configuration in the 'glide' set. The core structures are characterized in several ways, with a description of the three-dimensional structure, differential displacement maps and derivatives of the disregistry.
Title:
Vacancy ordered phases in Al-Cu-Ni as quasiperiodic superlattice approximants
Authors:
Subramaniam, A; Beauchamp, P;
Source:
PHILOSOPHICAL MAGAZINE, 83 (6): 667-675; 2003
Abstract:
Vacancy ordered phases in the Al-Cu-Ni system have an arrangement of vacant and filled sites in the truncated Fibonacci sequence along the [111] direction. The length scales involved are commensurate and in the limit a quasiperiodic superlattice is obtained. The implication of having commensurate length scales and quasiperiodicity in conjunction is studied using the concept of average lattices and projection formalism.
Title:
Al-Mn-Ce quasicrystalline composites: phase formation and mechanical properties
Authors:
Schurack, F; Eckert, J; Schultz, L; Wang, J;
Source:
PHILOSOPHICAL MAGAZINE, 83 (7): 807-825; 2003
Abstract:
Aluminium-based composites with quasicrystalline particles as reinforcements were synthesized via the powder metallurgy processing route. In order to obtain bulk samples with a nanoscale microstructure most equivalent to that resulting from rapid solidification, powders of Al-Mn-Ce alloys were prepared by pulverization of melt-spun ribbons using a planetary ball mill. Significant differences in the phase formation upon quenching, composite microstructure and thermal stability of the microstructure were found for different alloy compositions. Severe grain growth during the subsequent consolidation by hot extrusion caused the formation of a micrometre-scale composite instead of the nanoscale phase mixture initially existing after rapid solidification. After hot extrusion, the specimens were deformed by compression at a constant compression rate at room temperature. With an ultimate strength of up to 975 MPa and a ductility of more than 4% the material yields excellent properties compared with conventionally produced aluminium-based alloys.
Title:
Intermediate stages of a transformation between a quasicrystal and an approximant including nanodomain structures in the Al-Ni-Co system
Authors:
Doblinger, M; Wittmann, R; Gerthsen, D; Grushko, B; Mancini, L;
Source:
PHILOSOPHICAL MAGAZINE, 83 (9): 1059-1074; 2003
Abstract:
Transition states between decagonal quasicrystal and periodic approximants are studied in the Al-Ni-Co system at a measured composition of Al71.3Ni11.3Co17.4 by high-resolution transmission electron microscopy and electron diffraction. The nanodomain structures appearing after annealing at 1270 K show periodic fluctuations coherently embedded in domains with the coarse order of a one-dimensional quasicrystal. Further annealing at lower temperatures changes the features of nanodomain structures and results in an increase in more periodic structures. These can be strongly disordered and full of defects but tiling analysis and electron diffraction patterns show that they correspond to locked phason strain values of two closely related periodic approximants. We conclude that the periodic approximants do not result from a continuous increase in phason strain but from the growth of seeds with a locked phason strain.
Title:
Magnetic structures of R3Mn4Sn4 (R = La, Pr and Nd)
Authors:
Wawrzynska, E; Baran, S; Leciejewicz, J; Sikora, W; Stusser, N; Szytula, A; Hartwig, J;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (6): 803-814; 2003
Abstract:
Neutron diffraction studies of polycrystalline R3Mn4Sn4 (R = La, Pr, Nd) intermetallic compounds with the orthorhombic Gd3Cu4Ge4-type crystal structure indicate the existence of different magnetic structures. The magnetic structures were studied with the support of group theoretical considerations. For R = La a sine wave modulated structure described by the propagation vector k = (k(x), 0, 0) is observed below T-N = 300 K. This ordering is stable down to 1.5 K. For the Pr3Mn4Sn4 and Nd3Mn4Sn4 compounds the Mn moments form a non-collinear anti ferromagnetic structure below the Neel temperatures of 230 and 210 K, respectively. Below T-l = 25 and 60 K for R = Pr and Nd, respectively, the rare earth Pr and Nd moments also order and form collinear magnetic structures while the magnetic order of the Mn moments remains unchanged.
Title:
On the structure of axial quasicrystals
Authors:
Cornwell, JF; Soibel, A;
Source:
PHYSICA SCRIPTA, 67 (2): 127-135; 2003
Abstract:
A unified treatment. valid for all the axial quasicrystals exhibiting 5-, 8-, 10-, and 12-fold symmetries. is presented for the linear distribution of atomic sites. The starting point is a cyclotomic integer basis that employs non-crystallographic roots involving Pisot-Vijayaraghavan algebraic integers. The general solution is expressed in the form of a theorem. An explicit method is given for determining the basis vectors that are involved. Both two- and three-dimensional quasicrystals with these axial symmetries are considered.
Title:
Low-energy electron diffraction from quasicrystal surfaces
Authors:
Diehl, RD; Ledieu, J; Ferralis, N; Szmodis, AW; McGrath, R; Menghini, M;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (3): R63-R81; 2003
Abstract:
The discovery of ordered but aperiodic quasicrystal structures has required the development of new diffraction methods to determine their structures. The purpose of this review is to highlight the challenges posed by the aperiodicity of quasicrystals to the study of their surface structures by low-energy electron diffraction (LEED). This paper describes how the LEED technique has been thus far adapted to study several quasiperiodic surface structures, and summarizes the results of those studies. It also presents new spot-profile-analysis LEED results from the fivefold surface of Al-Pd-Mn. An x-ray diffraction experiment and a He-atom diffraction experiment, both on Al-Pd-Mn, are also described for comparison.
Title:
Unusual magnetic-field dependence of partially frustrated triangular ordering in manganese tricyanomethanide
Authors:
Feyerherm, R; Loose, A; Manson, JL; Huang, XF;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (4): 663-673; 2003
Abstract:
Manganese tricyanomethanide, Mn[C(CN)(3)](2), crystallizes in an orthorhombic lattice consisting of two interpenetrating three-dimensional rutile-like networks. In each network, the tridentate C(CN)3 anion gives rise to superexchange interactions between the Mn2+, ions (S = 5/2) that can be mapped onto the 'row model' for partially frustrated triangular magnets. We present heat capacity measurements that reveal a phase transition at T-N = 1.18 K, indicative of magnetic ordering. From magnetic-field dependent heat capacity data a saturation field H-sat = 42 kOe is estimated. The zero-field magnetically ordered structure was solved from neutron powder diffraction data taken between 0.04 and 1.2 K. It consists of an incommensurate spiral with a temperature independent propagation vector Q = [2Q 0 0] = [+/-0.622 0 0], where different signs relate to the two different networks. This corresponds to [+/-0.311 +/-0.311 0] in a quasi-hexagonal representation. The ordered moment mu = 3.3 mu(B) is about two-thirds of the full Mn2+ moment. From the values of TN and Q, the exchange parameters J/k(B) = 0.15 K and J'/J = 0.749 are estimated. The magnetic-field dependence of the intensity of the (2Q00) Bragg reflection, measured for external fields H 11 Q, indicates the presence of three different magnetic phases. We associate them with the incommensurate spiral (H < 13.5 kOe), an intermediate 'up-up-down' phase (115 kOe < H < 16 kOe) and the '2-l' spin-flop-like magnetic structure (H > 16kOe) proposed for related compounds. For increasing fields, Q continuously approaches the value 1/3, corresponding to the commensurate magnetic structure of the fully frustrated triangular lattice. This value is reached at H* = 19 kOe. At this point, the field dependence reverses and Q adopts a value of 0.327 at 26 kOe, the highest field applied in the experiment. Except for H*, the magnetic ordering is incommensurate in all three field dependent magnetic phases of Mn [C(CN)(3)](2).
Title:
Light transport through the band-edge states of Fibonacci quasicrystals
Authors:
Dal Negro, L; Oton, CJ; Gaburro, Z; Pavesi, L; Johnson, P; Lagendijk, A; Righini, R; Colocci, M; Wiersma, DS; Konczykowski, M;
Source:
PHYSICAL REVIEW LETTERS, 90 (5): 352-357; 2003
Abstract:
The propagation of light in nonperiodic quasicrystals is studied by ultrashort pulse interferometry. Samples consist of multilayer dielectric structures of the Fibonacci type and are realized from porous silicon. We observe mode beating and strong pulse stretching in the light transport through these systems, and a strongly suppressed group velocity for frequencies close to a Fibonacci band gap. A theoretical description based on transfer matrix theory allows us to interpret the results in terms of Fibonacci band-edge resonances.
Title:
Incommensurate and commensurate magnetic structures of the ternary germanide CeNiGe3
Authors:
Durivault, L; Bouree, F; Chevalier, B; Andre, G; Weill, F; Etourneau, J; Martinez-Samper, P; Rodrigo, JG; Suderow, H; Vieira, S; Tamegai, T;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 15 (2): 77-90; 2003
Abstract:
The structural properties of CeNiGe3 have been investigated via electron diffraction and neutron powder diffraction (NPD). This ternary germanide crystallizes in the orthorhombic SmNiGe3-type structure (Cmmm space group). Electrical resistivity, ac- and dc-magnetization measurements show that CeNiGe3 orders antiferromagnetically below T-N = 5.5(2) K and exclude the occurrence at low temperatures of a spin-glass state for CeNiGe3 as previously reported. Specific heat measurements and NPD both reveal two magnetic transitions, observed at T-N1 = 5.9(2) K and T-N2 = 5.0(2) K. Between T-N1 and T-N2, the Ce magnetic moments in CeNiGe3 are ordered in a collinear antiferromagnetic structure associated with the k(1) = (100) wavevector and showing a relationship with the magnetic structure of the Ce3Ni2Ge7 ternary germanide. Below T-N2, this k(1) = (100) commensurate magnetic structure coexists with an incommensurate helicoidal magnetic structure associated with k(2) = (0 0.409(1) 1/2). This last magnetic structure is highly preponderant below T-N2 (93(5)% in volume). At 1.5 K, the Ce atoms in CeNiGe3 carry a reduced ordered magnetic moment (0.8(2) mu(B)). This value, smaller than that obtained in Ce3Ni2Ge7, results from an important hybridization of the 4f(Ce) orbitals with those of the Ni and Ge ligands.
Title:
New icosahedral and approximant phases in the Al-Rh-Si system
Authors:
Koshikawa, N; Yoda, S; Edagawa, K; Ohtsuki, M; Takeuchi, S; Bud'ko, SL;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 83 (3): 205-216; 2003
Abstract:
An icosahedral phase (i phase) and its crystal approximant of the 2/1 cubic type (a = 1.993 nm) have been found to form in the Al-Rh-Si system, in addition to a 1/0 cubic approximant phase (a = 0.767 nm) previously reported. X-ray and electron diffraction patterns of the i phase and approximant phases have been analysed in terms of the hyperspace structural description in quasicrystallography. While the i phase is metastable, the 2/1 cubic approximant phase is found to be stable. Single crystals of the 2/1 cubic phase of about 0.3 mm(3) in size have been grown by solidification following arc melting. The single crystals have cubic morphology with at facets.
Title:
Discrete change of spin-density-wave modulation in Cr(100)/Sn multilayers as a function of Cr layer thickness
Authors:
Mibu, K; Takeda, M; Suzuki, J; Nakanishi, A; Kobayashi, T; Endoh, Y; Shinjo, T; Rodrigo, JG;
Source:
PHYSICAL REVIEW LETTERS, 89 (28): 141-145; 2002
Abstract:
Magnetic structures of epitaxial Cr(001)/Sn multilayers, where monatomic Sn layers are periodically embedded in a Cr(001) film, were studied using neutron diffraction and Mossbauer spectroscopy. It was found that spin-density-wave (SDW) antiferromagnetic structures with the modulation along the perpendicular direction to the film plane are stabilized at low temperatures. The wavelength of the SDW discretely changes as a function of the superlattice period. The enhanced magnetic moments of Cr at the Cr/Sn interfaces are thought to pin the antimode of the SDW modulation at the interface, resulting in the SDW with the modulation harmonic to the superlattice period.
Title:
Epitaxial decagonal thin films on crystalline substrates
Authors:
Widjaja, EJ; Marks, LD; Gu, GD;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 83 (1): 47-55; 2003
Abstract:
Al-Cu-Fe-Cr quasicrystalline thin films were grown on atomically flat Al2O3 sapphire (0001) substrates by single-target magnetron sputtering followed by annealing. A decagonal phase with the tenfold axis A(10) parallel to the substrate surface normal was observed. The epitaxial decagonal film had two different unique orientations: a twofold P axis A(2P) and a twofold D axis A(2D) parallel to [10 (1) over bar0] of the substrate. These two configurations were explained using a coincidence reciprocal lattice planes model for the interface energy. We show that this classic approach for crystal-crystal epitaxy can be applied to quasicrystal-crystal systems.
Title:
Effect of impurities on the successive phase transitions in (Cs1-xRbx)(2)ZnI4 compounds
Authors:
Aleksandrova, IP; Bartolome, J; Falvello, LR; Torres, JM; Sukhovskii, AA; Pimenta, MA;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (49): 13623-13634; 2002
Abstract:
The heat capacity, nuclear quadrupole resonance (NQR) and x-ray diffraction of (Cs1-xRbx)(2)ZnI4 single crystals have been measured, for x = 0, 0.001, 0.005, 0.01, 0.025 and 0.05. The normal to incommensurate (N-Inc) phase transition at T-I, the incommensurate to commensurate (Inc-C) lock-in transition at T-L and the structural commensurate monoclinic to triclinic transition at T-LT, observed in the parent compound (x = 0), takes place for x = 0, 0.001, 0.005 and 0.01. For x = 0.025 only T-I and T-L are detected, while for x = 0.05 no transitions were observable. The values of T-I and T-L increase with x while T-LT decreases and disappears at the concentration x = 0.025. The effect of defects, besides modifying the transition temperatures, is that of broadening and lowering the heat capacity anomaly at the lock-in transition until its total quenching for x = 0.05. No observable hysteresis is detected in this transition. NQR and x-ray diffraction data show the Inc-C transition up to the highest concentration. We conclude that this phenomenology is caused by weak interaction of the incommensurate modulation with point defects even in the region close to the Inc-C transition.
Title:
The X-ray characterization of Bi2Sr2CaCu2O8+x single crystals grown by different methods
Authors:
Bdikin, IK; Maljuk, AN; Kulakov, AB; Lin, CT; Kumar, P; Kumar, B; Trigunayat, GC; Emel'chenko, GA; Suderow, H;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 383 (4): 431-437; 2003
Abstract:
We report on results of systematic X-ray investigations of the Bi2Sr2CaCU2O8+x (2212) single crystals grown by slow cooling, top seeded solution growth and travelling solvent floating zone (TSFZ) methods. The typical concentrations of dislocations in the Bi-2212 crystals are estimated from width of peaks. According to the obtained X-ray topography and diffractometry data, these crystals demonstrate misorientation anisotropy around different crystallographic axes, which is a consequence of incommensurate modulation in this compound. The highly perfect crystals grown by TSFZ method are found to demonstrate the abnormal transmission X-ray diffraction effect (Borrman effect). (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Direct observation of a local thermal vibration anomaly in a quasicrystal
Authors:
Abe, E; Pennycook, SJ; Tsai, AP; Awane, T;
Source:
NATURE, 421 (6921): 347-350; 2003
Abstract:
Quasicrystals have long-range order with symmetries that are incompatible with periodicity, and are often described with reference to a higher-dimensional analogue of a periodic lattice(1-3). Within the context of this 'hyperspace' crystallography, lattice dynamics of quasicrystals can be described by a combination of lattice vibrations and atomic fluctuations-phonons and phasons(1,4). However, it is difficult to see localized fluctuations in a real-space quasicrystal structure, and so the nature of phason-related fluctuations and their contribution to thermodynamic stability are still not fully understood. Here we use atomic-resolution annular dark-field scanning transmission electron microscopy to map directly the change in thermal diffuse scattering intensity distribution in the quasicrystal, through in situ high-temperature observation of decagonal Al72Ni20Co8. We find that, at 1,100 K, a local anomaly of atomic vibrations becomes significant at specific atomic sites in the structure. The distribution of these localized vibrations is not random but well-correlated, with a quasiperiodic length scale of 2 nm. We are able to explain this feature by an anomalous temperature (Debye-Waller) factor for the Al atoms that sit at the phason-related sites defined within the framework of hyperspace crystallography. The present results therefore provide a direct observation of local thermal vibration anomalies in a solid.
Title:
Incommensurate crystal growth behavior in strontium titanate glass ceramic system
Authors:
Thakur, OP; Kumar, D; Parkash, OM; Pandey, L; Fukuyo, A;
Source:
MODERN PHYSICS LETTERS B, 16 (27): 1037-1047; 2002
Abstract:
Crystals with different faceting behavior were observed in the strontium titanate borosilicate glass ceramic system with a small amount of bismuth oxide addition and proper heat treatment schedule. These types of faceting morphology were generally observed in phase-separated glasses followed by heterogeneous nucleation. X-ray diffraction and electron microscopic techniques were used to characterize these samples. X-ray diffraction patterns for bulk and pulverized samples were observed to be readily different from each other. Peaks in the X-ray diffraction pattern for bulk samples can be indexed for icosahedral symmetry.
Title:
Phonons and internal friction in incommensurate composites
Authors:
Janssen, T; Lee, CS;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (47): 12411-12422; 2002
Abstract:
The non-linear dynamics involved in sliding modes in an incommensurate composite is studied in the double chain model. The coupling between the chains leads to phonons in which the two chains participate in various ways. For displacements beyond the harmonic approximation it is shown that, for a coupling small enough to leave the modulation functions continuous, there is a dynamic transition from a practically frictionless regime to a regime with strong dissipation. In the cross-over region resonances lead to an oscillatory motion of the subsystems with respect to each other. In the regime of discontinuous modulation functions there is strong dissipation and a transition from a pinned to an unpinned state. The unpinned motion is a non-linear wave in superspace.
Title:
The first mixed valence radical cation salts of BEDT-TTF with the photochromic metal mononitrosyl complexes [RuNOX5](2-) (X=Br, Cl) as counterions
Authors:
Shevyakova, IY; Zorina, LV; Khasanov, SS; Buravov, LI; Tkacheva, VA; Shibaeva, RP; Yagubskii, EB; Canadell, E; Togano, K;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 168 (2): 514-523; 2002
Abstract:
New bis(ethylenedithio)tetrathiafulvalene BEDT-TTF radical cation salts with the [RuNOX5](2-) (X = Br, Cl) anions have been synthesized. The crystal structures of kappa-(BEDT-TTF)(4) [RuNOBr5] . C6H5CN (1): a = 8.747(2), b = 12.088(l), c = 17.300(2) Angstrom, alpha = 95.63(l), beta = 91.93(2), gamma = 94.79(2)degrees, V = 1812.3(5) Angstrom(3), P (1) over bar, Z = 1 and delta-(BEDT-TTF)(4)[RuNOCl5](1.33) (2): a = 6.721(l), b = 15.016(2), c = 35.386(3) Angstrom, alpha = 92.804(8), V=3567.0(8) Angstrom(3), I2/c, Z=2 have been determined. Their electronic band structures and transport properties have been studied. The radical cation salts kappa-(BEDT-TTF)(4) [RuNOCl5] . C6H5CN (3) and delta-(BEDT-TTF)(4)[RuNOBr5] (4) have also been found to exist and are isostructural to 1 and 2, respectively. Evidence for commensurate and incommensurate structural modulations was found for 2 and 4, respectively. The crystals of 1 and 3 are semiconductors while those of 2 and 4 exhibit an M-I transition at 50 and 80K, respectively. (C) 2002 Elsevier Science (USA).
Title:
Microstructure of icosahedral Al-Pd-Mn quasicrystals deformed at room temperature in an anisotropic confining medium
Authors:
Texier, M; Proult, A; Bonneville, J; Rabier, J; Baluc, N; Cordier, P; Kaminska, E;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 82 (12): 659-669; 2002
Abstract:
Plastic deformation of Al-Pd-Mn icosahedral quasicrystals has been achieved at room temperature using a high-confining-pressure medium. The deformation microstructure, investigated by transmission electron microscopy, is characterized by long straight bands of dislocations. A detailed analysis of the dislocation configurations indicates that the plastic deformation is controlled by dislocation glide.
Title:
Structural aspects of the dielectric anomaly in SC(NH2)(2) crystals at 161 K
Authors:
Bagautdinov, BS; Novikova, MS; Bonneville, J;
Source:
PHYSICS OF THE SOLID STATE, 44 (12): 2293-2297; 2002
Abstract:
The residual incommensurate modulations in the ferroelectric phase of the SC(NH2)(2) thiourea are investigated using single-crystal x-ray diffractometry. It is found that the structural states of the ferroelectric phase (T < 169 K) depend on the thermal prehistory of the crystal in the temperature range of existence of the incommensurate phase (202-169 K). The dielectric anomaly observed at T-x = 161 K is justified structurally. (C) 2002 MAIK "Nauka/Interperiodica".
Title:
Anomalous states of the structure of (NH4)(2)SO4 crystals in the temperature range 4.2-300 K
Authors:
Shmyt'ko, IM; Afonikova, NS; Torgashev, VI; Rabier, J;
Source:
PHYSICS OF THE SOLID STATE, 44 (12): 2309-2317; 2002
Abstract:
Crystals of the (NH4)(2)SO4 ammonium sulfate are studied using x-ray diffractometry. It is revealed that the temperature dependence of the lattice parameters exhibits an anomalous behavior, namely, a global hysteresis, and an anomalous increase in the lattice parameter a and the unit cell volume at temperatures below the ferroelectric phase transition point (T-c = 223 K). The series of superstructure reflections observed corresponds to an incommensurate composite structure. Analysis of the temperature behavior of the mismatch parameters for the matrix (host) and superstructure (guest) lattices demonstrates that the (NH4)(2)SO4 compound undergoes a number of phase transitions, including a transition to a three-dimensionally incommensurate composite phase and transitions to commensurate (along one of the crystallographic directions) composite phases. (C) 2002 MAIK "Nauka/Interperiodica".
Title:
Incommensurate phases in the improper ferroelastic MgGeF6 center dot 6H(2)O : Mn2+ studied by means of EPR
Authors:
Skrylnik, PG; Ziatdinov, AM; Torgashev, VI;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (45): 11671-11686; 2002
Abstract:
The results of an EPR study of the inhomogeneous phases existing in the temperature interval T-C = 311.0+/-0.3 K < T < T-il = 403+/-0.3 K in improper ferroelastic crystals of MgGeF6.6H(2)O:Mn2+ are presented. On-the basis of the analysis of the temperature and angle dependences of the experimental parameters and numerical calculations, the conclusion has been drawn that at T-il the crystals considered undergo a transition to a structurally modulated phase and the order parameter of this transition may be the angle of the Mg[H2O](6)(2+) octahedra rotation around the crystal C-3-axis. From T-il to T-C the modes of the modulated phase follow according to a completely classical scenario for incommensurate crystals: the origin of the incommensurate structure with plane-wave modulation at Til, the appearance of structural phase solitons below T-i2 = 380 +/- 0.3 K and decrease of the soliton density to values of approximate to0.85 as the temperature decreases to T 3 60 K. Below that temperature the soliton density is almost unchanged down to TC and, to successfully describe the experimental spectra, the effect of variation of the spin-lattice relaxation rate over the spectrum has also been taken into account within the temperature interval considered. At T-C the crystals investigated undergo a first-order improper ferroelastic phase transition into a monoclinic phase with unit-cell doubling. A comparison with results on MgSiF6.6H(2)O from a previous investigation and a theoretical analysis of the structure evolution in these crystals are also presented.
Title:
Evolution of the magnetic order in the Ho(Mn, Al)(2) system; neutron diffraction study
Authors:
Golosovsky, IV; Mirebeau, I; Markosyan, AS; Rodriguez-Carvajal, J; Roisnel, R; Cordier, P;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (45): 11737-11745; 2002
Abstract:
The neutron diffraction study of Ho(Mn1-xAlx)(2) shows the coexistence of two cubic Laves phases with different unit-cell parameters and substantially different magnetic behaviours. The first phase combines ordered ferrimagnetic and disordered antiferromagnetic components of the magnetic moments. With increasing Al content, starting from the long-range ferrimagnetic order with the induced Mn moment in HoMn2, the progressive formation of spontaneous Mn moments yields short-range order, which in turn transforms to ferromagnetic order in HoAl2. The second phase with incommensurate magnetic structure is driven by the spontaneous Mn moments and exists only over limited ranges of Al content and unit-cell parameter. It has a finite correlation length and appears from a second-order transition without a magneto-volume effect.
Title:
Nanoepitaxy: Size selection in self-assembled and oriented Al nanocrystals grown on a quasicrystal surface
Authors:
Fluckiger, T; Weisskopf, Y; Erbudak, M; Luscher, R; Kortan, AR;
Source:
NANO LETTERS, 3 (12): 1717-1721; 2003
Abstract:
The unusual interfacial lattice-mismatch properties of a periodic film and a quasiperiodic substrate are investigated in the Al films grown on an Al-Co-Ni decagonal substrate. The resulting mismatch causes the formation of well-oriented nanometric single crystals of At, satisfying the epitaxial conditions on a local scale. Total-energy calculations based on a rigid-lattice atomic model for the interface between a cubic and the decagonal surface reproduce the low-energy electron diffraction results concerning the size of the clusters, their distribution, and the details of the orientational alignment of aluminum islands. Such systems can be used in self-size-selecting growth of nanocrystals.
Title:
A method for predicting formation of quasicrystalline alloys
Authors:
Wang, LL; Huang, WQ; Deng, HQ; Li, XF; Tang, LM; Zhao, LH;
Source:
RARE METAL MATERIALS AND ENGINEERING, 32 (11): 889-892; 2003
Abstract:
The regularities of formation of quasicrystalline alloys have been studied successfully by the Miedema coordinates DeltaPhi(*) similar to Deltan(ws)(-1/3). The experimental data of 31 binary and 48 ternary quasicrystalline alloys were analyzed. The results were compared with 47 amorphous and 32 crystalline state alloys of binary, 54 amorphous and 12 crystalline state alloys of ternary systems prepared by electroless and electrodeposition. It is shown that the accuracy is larger than 93.5%, 87. 2%, 72.7% in quasicrystalline, amorphous, crystalline state of binary and larger than 97.9%, 87.0%, 75.0% in quasicrystalline, amorphous, crystalline state of ternary alloys, respectively. This criterion develops a new approach for qualitative studying and searching new quasicrystalline alloys. So it possesses an important meaning for the theoretical guidance in materials research field.
Title:
Phase transitions and metastable states in TIGaSe2
Authors:
Mikailov, FA; Basaran, E; Senturk, E; Tumbek, L; Mammadov, TG; Aliev, VP;
Source:
PHASE TRANSITIONS, 76 (12): 1057-1064; 2003
Abstract:
The results of measurements of the dielectric constant of TlGaSe2 in temperature range of successive phase transitions are presented. An anomaly in the temperature dependence of the real part of dielectric constant in TlGaSe2 has been observed at about 242K in addition to anomalies at 115, 108, and also near 65K as reported in previous publications. The presence of temperature hysteresis effects in temperature interval between 115 and 242K allowed making a conclusion about possible existence of an incommensurate phase in the mentioned temperature range. A model of succession of the structural phase transitions in TlGaSe2 has been suggested.
Title:
A new series of icosahedral quasierystals in Zn-M-Sc (M = Ag, An, Pd, Pt) alloys
Authors:
Kashimoto, S; Maezawa, R; Kasano, Y; Mitani, T; Ishimasa, T; Aliev, VP;
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 42 (10B): L1268-L1271; 2003
Abstract:
A new series of icosahedral quasicrystals has been found in Zn75M10Sc15 (M = Ag, Au, Pd and Pt) as-cast alloys. Electron and powder X-ray diffraction analyses indicated that these quasicrystals are of the P-type (primitive type) and have six-dimensional lattice parameters a(6D) = 0.7112-0.7151 nm. The quasicrystals are formed as main phases in these alloys. In the Zn80Ag5Sc15 alloy annealed at 981 K for 24h, a Zn85Sc15-type cubic phase is formed exclusively, which has the lattice parameter a = 1.3867 nm. The cubic phase is interpreted as a 1/1 approximant of Zn75Ag10Sc15. This observation, as well as intensity similarity in the X-ray diffraction patterns, suggests that Zn(75)M10Sc(15) quasicrystals belong to the same group as the Zn80Mg5Sc15 quasicrystal from the viewpoint of a local atomic configuration.
Title:
Microstructures and mechanical properties of pure Al matrix composites reinforced by Al-Cu-Fe alloy particles
Authors:
Tang, F; Anderson, IE; Biner, SB; Butskii, VD;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 363 (1-2): 20-29; 2003
Abstract:
A new type of composite material was produced from elemental Al matrix powders and 30 vol.% Al-Cu-Fe quasicrystal particles by a powder metallurgy technique. SEM examination shows that reinforcement particle cracking perpendicular to the loading axis is the dominant failure mechanism for the composites. Because of the fine (diameter < 10 mum) matrix and reinforcement particle sizes that match closely and a homogenous spatial distribution, the ultimate tensile strength (UTS) and yield strength (Y.S.) of this model composite material were improved over the matrix properties by 111 and 220%, respectively, for the commercial purity composite sample. Remarkably, the UTS and Y.S. of the composite were improved over the matrix properties by 201 and 328%, respectively, for a high purity version of the composite material. The elastic modulus of the composite, in both versions, is very close to the theoretical upper bound value from the rule of mixtures estimation. This highly effective composite strengthening is also consistent with the good interface bonding between the spherical reinforcement particles and Al matrix that was revealed by fracture surface examination. Diffusion layer measurements at the Al/reinforcement interface by an Auger method verified the good bonding condition, as well. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Synthesis and magnetic properties of crystalline and amorphous CuB2O4
Authors:
Udod, LV; Sablina, KA; Pankrats, AI; Vorotynov, AM; Velikanova, DA; Petrakovskii, GA; Bovina, AF;
Source:
INORGANIC MATERIALS, 39 (11): 1172-1180; 2003
Abstract:
Single-crystal and amorphous CuB2O4 samples are prepared, and their magnetic properties (temperature-dependent susceptibility and magnetic resonance) are compared. Crystalline CuB2O4 has a small magnetic moment in the basal plane in the temperature range 10-21 K and an incommensurate magnetic structure below 10 K. The effective exchange interaction is found to be stronger in amorphous CuB2O4.
Title:
Evaluation of fracture toughness of Al-Cu-Fe-B quasicrystal
Authors:
Zhou, XY; Li, PY; Qian, SQ; Farnan, I;
Source:
JOURNAL OF WUHAN UNIVERSITY OF TECHNOLOGY-MATERIALS SCIENCE EDITION, 18 (3): 46-49; 2003
Abstract:
Vickers indentation test, a simple method for the toughness determination, is used to test the fracture toughness of Al59Cu25.5Fe12.5B3 polycrystalline quasicrystal. According to the profiles of the indentation, the radial crack size and related equation, the microhardness Hv, Young's modulus E, cracking threshold, and future toughness have been evaluated. The results show that the Young's modulus of Al-Cu-Fe-B polycrystalline quasicrystal is evaluated as 134 GPa, and the fracture toughness is about 1.36 MPa . m - 1/2. For the Vickers indenter, the cracking threshold is in the range of 250 MN - 500 MN. Moreover, the surface morphology of the indentations and the cracks are observed by means of Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The relationship between the microstructure of quasicrystal and crack initiation and propagation is discussed in detail.
Title:
Structure and morphology of [icosahedral Al62Cu25.5Fe12.5](100-x)[decagonal Al70Co15Ni15](x) alloys, for x=10*(O-3 and 5-10)
Authors:
Lei, Y; Calvo-Dahlborg, M; Dubois, JM; Hei, Z; Weisbecker, P; Dong, C; Bovina, AF;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 330 (1-3): 39-49; 2003
Abstract:
Alloys made from mixtures of Al62Cu25Fe12.5 icosahedral quasicrystal (IQC) and Al70Co15Ni15 decagonal quasicrystal (DQC) were studied by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The transition from IQC to DQC was thus discussed by studying the evolution of their constituent phases in each alloy. Three approximant phases were found as common phases in most of the pseudo-binary alloys: lambda-Al13Fe4, beta-AlFe and tau3-Al3Ni2. It is found that, with the increment of the DQC content in the alloy, the lambda phase changes from Al13Fe4 to Al13Co4 and the tau3 phase changes from Al3Cu2 to Al3Ni2. The formation of these phases were found also to follow the evolution of their corresponding e/a-constant lines in the Al-(Cu,Ni)-(Fe,Co) pseudo-ternary phase diagram. Under this framework, the roles played by the related approximants in the transition process are briefly discussed. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Studies of the R-phase transformation in a Ti-51at.%Ni alloy by transmission electron microscopy
Authors:
Stroz, D; Calvo-Dahlborg, M;
Source:
JOURNAL DE PHYSIQUE IV, 112 (1-3): 689-692; 2003
Abstract:
The R-phase transformation in a Ti-51 at.%Ni shape memory alloy was studied by transmission electron microscopy (TEM) including high resolution microscopy and in situ observations at cooling. The incommensurability of the superlattice reflections was examined by recording the diffraction patterns with the use of a CCD slowscan camera and analysing the reflection positions by DigitalMicrograph program. It is shown that the incommensurability exists in this alloy within a wide temperature range and its is neither regular nor periodic. It decreases with decreasing temperature reaching finally the commensurate R-phase state.
Title:
Two-step martensitic transformation in Ni-Mn-Ga alloys
Authors:
Segui, C; Chernenko, VA; Pons, J; Cesari, E; Weisbecker, P;
Source:
JOURNAL DE PHYSIQUE IV, 112 (1-3): 903-906; 2003
Abstract:
The Ni-Mn-Ga L2(1) ordered alloys undergo a martensitic transformation (MT) which characteristics have been extensively analysed in relation to the electron to atom ratio (e/a). In that sense, alloys with e/a<7.60 are known to exhibit soft mode condensation into a premartensitic phase prior to the NIT itself, manifested as a weakly first order transformation, while alloys with e/a>7.70 do not undergo any premartensitic transformation but they show instead a first order intermartensitic transformation during cooling. Alloys with intermediate e/a do not show such defined behaviours, but they are highly sensitive to the external applied fields. In the present work, three single crystalline Ni-Mn-Ga alloys with e/a between 7.60 and 7.70 are studied. The obtained results indicate that, even though the transformation temperatures are quite similar and the martensitic structures are in all cases modulated crystal lattices of 5 or 7 layer period, the transformation behaviour is different for each alloy, as revealed by the DSC and, especially, by the internal friction (IF) and modulus (E) evolution during cooling and heating these alloys. Particularly, one of them show a two step MT which is mainly attributed to inhomogeneous storage of elastic energy during the transformation.
Title:
Study of austenite-martensite transformation in Ni-Mn-Ga magnetic shape memory alloy
Authors:
Straka, L; Heczko, O; Novak, V; Lanska, N; Weisbecker, P;
Source:
JOURNAL DE PHYSIQUE IV, 112 (1-3): 911-915; 2003
Abstract:
Ni49.7Mn29.1Ga21.2 magnetic shape memory sample showing magnefic-field-induced strain of 5.7 % in the magnetic field 0.5 T was studied at different conditions during austenite-martensite and martensite-austenite transformations. Transformation temperatures T-A = 317 K, T-M = 308 K were determined by AC susceptibility measurement. Structure parameters obtained from X-ray measurement are a(A) = 0.584 nm for austenite and a(M) = b(M) = 0.595 c(M), cm = 0.561 nm for martensite which has five-layered modulated structure. Mechanical stress up to 4 MPa and magnetic field up to I T were applied in order to study their influence on the transformations. Totally 39 transformation cycles were measured. The thermoelastic strains during transformations vary from -3.6 % to +1.8 %. Simultaneous change of magnetization and strain has been observed. Thermomechanical and magnetic history of the sample seems to have no or only very weak influence on the character of austenite-martensite transformation and no clear trend emerges in our experiments.
Title:
Martensitic transformation in Ti50Pd50-xFex alloy
Authors:
Li, S; Nishida, M; Murakami, Y; Shindo, D; Weisbecker, P;
Source:
JOURNAL DE PHYSIQUE IV, 112 (1-3): 1035-1038; 2003
Abstract:
In order to clarify the transformation sequence in Ti50.0Pd50.0XFeX alloy in detail, in-situ heating TEM observations and electron diffraction experiments were carried out in JEM-2010 microscope equipped with omega type energy-filter. Mf temperature of Ti50.0Pd43.0Fe7.0 alloy is about 520 K and martensite of 2H and 9R structures are observed at room temperature. The 9R martensite directly reverts to the B2 parent phase via no intermediate state. Only incommensurate (IC) phase is confirmed at room temperature in Ti50.0Pd40.0Fe10.0 and Ti50.0Pd36.0Fe14.0 alloys, although Mf temperatures of these alloys are above room temperature. The IC phase transforms to the B2 parent phase without any shift of intensity maximum position of IC reflections with heating. Therefore, the low temperature phase in the alloys with more than 8.0 at% of Fe is the IC phase. Based on these results, systematical transformation phase diagram is proposed.
Title:
2D vortices in incommensurate (Stripe-Domain) magnetic structures
Authors:
Kiselev, VV; Grzanka, E;
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 95 (22-24): S28-S34; 2003
Abstract:
A wide class of two-dimensional vortex-type defects characteristic of stripe-domain structures of ferro- and antiferromagnets have been studied by inverse scattering transform within the framework of the universal integrable nonlinear model. Essentially nonlinear 2D defects similar to Bloch lines in domain walls of the stripe-domain structure and various string configurations consisting of domain-wall segments against the background of the stripe-domain structure have been predicted and analytically described. The physical properties of soliton-like vortices are discussed.
Title:
Low-temperature study of natural melilite (Ca1.89Sr0.01Na0.08K0.02) (Mg0.92Al0.08)(Si1.97Al0.03)O-7: towards a commensurate value of the q vector
Authors:
Bindi, L; Bonazzi, P; Stel'makh, S;
Source:
PHYSICS AND CHEMISTRY OF MINERALS, 30 (9): 523-526; 2003
Abstract:
As is usual for peculiar chemical compositions, melilite-type compounds exhibit a two-dimensional incommensurately modulated structure which can be described with two wave vectors: q(1) = alpha(a* + b*) and q(2) = alpha(-a* + b*), where a and b are the tetragonal reciprocal axes of the basic cell. The low-temperature dependence of the modulation wave vector of a natural melilite crystal with chemical composition (Ca1.89Sr0.01 Na0.08K0.02)(Mg0.92Al0.08)(Si1.97Al0.03)O-7 has been studied by X-ray single-crystal diffraction methods in the temperature range 298-100 K. The value of the a coefficient shows a continuous linear increase, ranging from 0.281(1) at 298 K to 0.299(1) at 100 K. No plateau-like temperature dependence was observed throughout the temperature studied, thus indicating that no independent phase with a specific q stabilizes in this natural crystal. A comparison with the low-temperature behaviour of synthetic Ca2MgSi2O7 is given.
Title:
Nanoquasicrystallization in metallic glasses
Authors:
Saida, J; Matsubara, E; Inoue, A; Gierlotka, S;
Source:
MATERIALS TRANSACTIONS, 44 (10): 1971-1977; 2003
Abstract:
Nanoquasicrystallization in Zr-based glassy alloys was investigated. It is found that the nano scale icosahedral quasicrystalline phase (I-phase) is formed by addition of the elements, which obstruct the glass-forming ability (GFA) in the glassy alloy. The primary phase of fee Zr2Ni phase in the Zr65Al7.5Ni10Cu17.5 glassy alloy with high GFA changes to the fee Zr2Ni plus I-phases by substitution of noble metals or Zr for only 1 at% Cu. Since each phase is precipitated independently and the icosahedral local atomic configuration exits in the fcc Zr2Ni and I-phases, they are originated from the same local structure in the Zr-based glassy alloy with high GFA. We found that the icosahedral local structure is strongly correlated with the stability of the supercooled liquid state. The origin of the icosahedral local structure is combination of Zr + Cu and Zr + Al + Ni elements. In these alloy systems, the I-phase is easy to precipitate as a primary phase by addition of a very small amount of appropriate element. From the present results, it is concluded that the icosahedral local structure stabilizes the supercooled liquid state. We suggest that the high GFA for the preparation of bulk glassy alloy is attributed to the stability of icosahedral local structure.
Title:
Microstructure of rapidly solidified high strength Al94V4Fe2 alloy
Authors:
Murty, BS; Ping, DH; Hon, K; Kimura, H; Inoue, A; Bismayer, U;
Source:
MATERIALS TRANSACTIONS, 44 (10): 1993-1998; 2003
Abstract:
Al94V4Fe2 alloy melt-spun at different wheel velocities in the range of 20-50 m/s has been studied. The microstructure of the alloy consists of a nanoquasicrystalline phase in an Al matrix at slow cooling rates, while at higher cooling rates it shows nanodomains of an amorphous phase embedded in the Al matrix. The tensile fracture strength of the alloy reaches a maximum when it exhibits a nanocomposite microstructure consisting of quasicrystalline phase and Al. The composition of the quasicrystalline and amorphous phases has been identified using three dimensional atom probe field ion microscopy.
Title:
Atomic-scale characterization of nanostructured metallic materials by HAADF/Z-contrast STEM
Authors:
Abe, E; Ping, DH;
Source:
MATERIALS TRANSACTIONS, 44 (10): 2035-2041; 2003
Abstract:
We demonstrate that high-angle annular-dark-field scanning transmission electron microscopy (HAADF-STEM) with a finely-focused electron probe (similar to0.15 nm) is very powerful technique to provide direct information on a local chemistry of nano-materials at atomic scale. This is due to an atomic-number (Z) sensitive nature of the HAADF contrast (Z-contrast). We describe the microstructures of some crystalline, quasicrystalline and amorphous metallic materials with focusing on their local chemical environments. Not only the chemical Z-contrast, HAADF-STEM possesses more substantial advantages compared to the conventional phase-contrast high-resolution imaging, so that it would be one of the most powerful methods for total characterization of nano-structured materials.
Title:
Structural and chemical characterization of the decagonal quasicrystalline phase of an Al62Cu20Co15Si3 alloy obtained in an elliptical furnace
Authors:
Martinez-Mondragon, MM; Lara, JA; Riveros, RH; Reyes-Gasga, J; Inoue, A;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 329 (1-3): 27-30; 2003
Abstract:
A decagonal quasicrystalline phase and some approximant quasicrystalline phases were found in decaprisms of a spherical sample of an Al62Cu20Co15Si3 alloy obtained in a elliptical mirror furnace. In this work we present scanning and transmission electron microscopies, and X-ray energy dispersion spectroscopy analysis of these structures. The composition of the decagonal phase was Al60Cu23Co15Si2. Therefore, it was found that Si does play a role in the nucleation and growth of this phase and in the special properties that this decagonal phase presents. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Analytical solution for pairing of two-particles in a quasiperiodic lattice within the Hubbard model
Authors:
Vallejo, E; Navarro, O; Riveros, RH;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 329 (1-3): 131-133; 2003
Abstract:
In this work we solve the generalized Hubbard model for two-interacting particles in a Fibonacci infinite one-dimensional lattice, using a real-space mapping method, the renormalized perturbation expansion and the Green function technique. The real-space method is based on mapping the correlated many-body problem onto an equivalent site- and bond-impurity tight-binding problem in a higher dimensional space. Analyzing the quasiperiodic lattice in this new space we obtained an approximate analytical solution for the binding condition at the ground state. Our results reproduce the limit case, that is, the periodic lattice. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Kubo conductivity in two-dimensional Fibonacci lattices
Authors:
Sanchez, V; Wang, CM; Riveros, RH;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 329 (1-3): 151-154; 2003
Abstract:
The electronic transport at zero degrees in quasiperiodic systems is investigated by using the Kubo-Greenwood formula and a novel renormalization method, which allows an evaluation in an exact way of the products of the Green's function in macroscopic Fibonacci chains. The analysis of transport properties in two-dimensional Fibonacci super-lattices and in double quasiperiodic lattices is carried out by means of the convolution technique. The spectrally averaged conductance shows a linear dependence with the width of the system and a power-law decay as its length increases along the applied electric field. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Phonon localization in quasiperiodic systems
Authors:
Salazar, F; Wang, C; Gelover-Santiago, A; Zentella-Dehesa, A; Naumis, GG; Talamantes, J; Weber, HP;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 329 (1-3): 167-170; 2003
Abstract:
The effects of anharmonic interactions on the localization of phonons in quasiperiodic systems are studied by looking at the transmittance, Lyapunov exponent, participation ratio and energy-level-spacing distribution, within the rotating-wave approximation and first-order perturbation theory. For Fibonacci chains, a power-law distribution is found in the small-spacing region, since the eigenstates are critical. Even within first perturbation stages, anharmonic contributions do clearly manifest, weakening the level clustering behavior, contrary to the periodic case where the distribution is insensitive to weak anharmonic interactions. These results suggest a structural instability of the self-similar vibrational spectrum in quasiperiodic systems. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Aging behavior of Cu-Ni-Si alloy
Authors:
Zhao, DM; Dong, QM; Liu, P; Kang, BX; Huang, JL; Jin, ZH; Weber, HP;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 361 (1-2): 93-99; 2003
Abstract:
Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HREM) were employed to study the microstructure and transformation of Cu-Ni-Si alloy. In Cu-1.0Ni-0.25Si-0.1Zn (wt.%) alloy, the precipitate responsible for the age-hardening effect was the delta-Ni2Si originating in nucleation process. On aging at the temperature below similar to773 K in Cu-3.2Ni-0.75Si-0.3Zn (wt.%) alloy, there were three different transformation products: a modulated structure resulting from spinodal decomposition, a (Cu, Ni)(3)Si with DO22 ordering structure nucleating from the modulated structure, and a delta-Ni2Si phase with disc-like structure appearing in (Ni, Si)-rich regions. On aging at the temperature above similar to773 K, the transformation products were grain boundary and intragranular precipitations of delta-Ni2Si. The free energy versus composition curves were employed to further explain the experimental observations. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Effect of molecular dynamics and modulated structure on H-2 NMR spectrum studied in [Mg(H2O)(6)][SiF6]
Authors:
Iijima, T; Mizuno, M; Ogasawara, Y;
Source:
CHEMICAL PHYSICS LETTERS, 380 (5-6): 736-741; 2003
Abstract:
The spectrum of magnetic resonance is typically affected by a modulated structure in an incommensurate phase, resulting in the broadened spectrum characterized by 'edge singularities'. We demonstrate that the modulated structure in the crystal where molecular motion exists is responsible for the narrowing of the spectrum in the fast motional region by means of the simulation of H-2 NMR spectrum of [Mg(H2O)(6)][SiF6]. The program developed by combining the theories of phase solitons in the incommensurate phase and motional change of H-2 NMR spectrum was used for the simulation. We obtained a good agreement between the theoretical H-2 NMR spectrum and experimental one for [Mg(H2O)(6)][SiF6]. (C) 2003 Published by Elsevier B.V.
Title:
Studies of the electrical properties of nearly perfect K2ZnCl4 single crystals as measured during commensurate incommensurate-paraelectric phase transitions
Authors:
El-Korashy, A; Roberts, KJ; Nakamuta, Y;
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 64 (11): 2133-2139; 2003
Abstract:
Electrical conductivity and dielectric measurements were carried in the temperature range covering the commensurate ferroelectric-incommensurate-paraelectric normal phases (300-600 K) for the three main crystallographic axes of K2ZnCl4 single crystals. The values of activation energies in the three phases were calculated and discussed. A thermal hysteresis of about 12 K is observed which deduce the presence of first order transition for the lock-in ferroelectric transition at T-c = 404 K. Conductivity anomalies were observed in both ferroelectric and paraelectric phases. The conduction mechanism was discussed. The suggested occurrence of discommensuration in K2ZnCl4 crystals upon the lock-in transition in contrast with conductivity and dielectric results explains the anomalous behavior for the b-axis measurements. The orientation of these discommensuration was discussed on a view of projection in the three standard crystallographic directions. (C) 2003 Elsevier Ltd. All rights reserved.
Title:
Incommensurate and commensurate density-wave in the two-dimensional lattice
Authors:
Gebarowski, M; Mierzejewski, M; Thomson, M;
Source:
JOURNAL OF SUPERCONDUCTIVITY, 16 (6): 931-935; 2003
Abstract:
We have investigated anisotropic density-wave phase with arbitrary ordering wave vector (Q) and estimated the value of Q that corresponds to the minimum of the free energy. We have found that for a wide range of model parameters the commensurate d-density-wave (DDW) is actually the most stable density-wave state. However, for moderate doping the commensurate DDW state is stable only at finite temperatures and disappears when the temperature is sufficiently low. These features may assist in clarification of the mechanism of the pseudogap.
Title:
Quasicrystals: A matter of definition
Authors:
Lifshitz, R; Wagner, T;
Source:
FOUNDATIONS OF PHYSICS, 33 (12): 1703-1711; 2003
Abstract:
It is argued that the prevailing definition of quasicrystals, requiring them to contain an axis of symmetry that is forbidden in periodic crystals, is inadequate. This definition is too restrictive in that it excludes an important and interesting collection of structures that exhibit all the well-known properties of quasicrystals without possessing any forbidden symmetries.
Title:
Incommensurately modulated structure of isotropic lazurite as a product of twinning of two-dimensionally modulated domains
Authors:
Bolotina, NB; Rastsvetaeva, RK; Sapozhnikov, AN; Kashaev, AA; Shonleber, A; Chapuis, G; Weber, HP;
Source:
CRYSTALLOGRAPHY REPORTS, 48 (5): 721-727; 2003
Abstract:
The incommensurately modulated structure of isotropic lazurite (the Baikal region) was established for the first time. The structure was solved within a pseudocubic unit cell with the parameter a = 9.077(l) Angstrom and the (3 + 2)-dimensional superspace group Pnn2(gammagamma0, gamma-gamma0) based on a twin model consisting of three two-dimensionally modulated orthorhombic components related by a threefold axis along the [I I I] direction. The structure was refined with isotropic thermal parameters to wR(0) = 1.98% and wR(1) = 7.5% using 257 main reflections and 2392 first-order satellite reflections, respectively. (C) 2003 MAIK "Nauka/Interperiodica".
Title:
HRTEM study of the microstructure of TiC0.6/NiAl composite
Authors:
Hua, WS; Wu, XF; Shen, DH; Lu, H; Polak, M; Chapuis, G;
Source:
INTERMETALLICS, 11 (10): 981-985; 2003
Abstract:
Intermetallic NiAl bonded sub-stoichiometric titanium carbide based composite of TiC0.6/NiAl was fabricated by a two-step melt infiltration processing method, and its microstructure was characterized with scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Ordered Ni2AlTi precipitated in NiAl matrix and a new long period modulated structure as a transition layer appeared at the phase boundary. (C) 2003 Elsevier Ltd. All rights reserved.
Title:
Incommensurate phase in the kosmochlor-diopside join: A new polymorph of clinopyroxene
Authors:
Sakamoto, S; Shimobayashi, N; Kitamura, M; Lu, H;
Source:
AMERICAN MINERALOGIST, 88 (10): 1605-1607; 2003
Abstract:
Electron-diffraction patterns of clinopyroxene with an intermediate composition between kosmochlor and diopside show the presence of satellite reflections in diffuse streaks running perpendicular to (111) planes of the C2/c structure. The position of these satellite reflections indicates the existence of an incommensurate (INC) phase. Based on the characteristics of the diffraction patterns, it is suggested that the INC phase consists of a regular arrangement of kosmochlor-rich and diopside-rich slabs with a periodicity 2.6 to 6.0 times the (111) spacing in the C2/c structure. This is a new ordering scheme in clinopyroxenes.
Title:
Fabrication and wear resistance of Al-Cu-Fe quasicrystal-epoxy composite materials
Authors:
Bloom, PD; Baikerikar, KG; Anderegg, JW; Sheares, VV; Polak, M;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 360 (1-2): 46-57; 2003
Abstract:
Wear resistant polymer composites are prepared using a novel filler material, Al-Cu-Fe quasicrystals (QC). Novolac epoxy filled with Al-Cu-Fe quasicrystalline powder are evaluated by pin-on-disk testing using a 52100 steel counterface. Epoxy samples filled with aluminum, copper, iron, aluminum oxide, and silicon carbide are tested for comparison. The use of Al-Cu-Fe QC powder, as a filler in epoxy, maximizes the composite wear resistance while minimizing abrasion of the 52100 steel counterface. Wear mechanisms of the Al-Cu-Fe composites were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. The fabrication and wear properties of these unique materials will be described. (C) 2003 Elsevier B.V. All rights reserved.
Title:
The role of the Phi phase in the solidification process of Al-Cu-Fe icosahedral quasicrystal
Authors:
Zhao, DS; Wang, RH; Wang, JB; Qu, WB; Shen, NF; Gui, JI; Weber, HP;
Source:
MATERIALS LETTERS, 57 (29): 4493-4500; 2003
Abstract:
Several Al-Cui-Fe alloys with compositions of Al48-60Cu33-50Fe0-10 was prepared and the phase constituents of these alloys quenched from various temperatures were identified by using X-ray diffraction (XRD), differential thermal analysis (DTA), SEM with dispersive X-ray spectrometer (EDXS) attached to, and transmission electron microscopy (TEM) (including HRTEM). The present investigation confirmed again the existence of the Phi phase with a chemical composition of Al10Cu10Fe, having two variants. The high temperature variant (designated as Phi(1) phase) is stable when temperature is higher than nearly 600 degreesC and has a structure Of tau(3) phase, which is a three-time modulation structure along a <111>(B2) direction. The low temperature variant (designated as Phi(2) phase) is stable when temperature is lower than nearly 500 degreesC and has a 10-time modulation structure along a <011>(B2) direction. We show the preferred polythermal projection and reaction scheme. Compared with the suggestion proposed by Gayle et al. [Metal]. Trans., A 23A (1992) 2409.], Faudot [Ann. Chim. Fr. 18 (1993) 445.], and Zhang and Lueck [J. Alloys Compd. 343 (2002) 53.], the main amendment is to divide the previous beta region into beta + Phi two regions. The important reactions of the Phi phase involving the icosahedral quasicrystal (IQC) are (1) quasiperitectic at U-8: L + beta --> IQC; (2) quasiperitectic at U-5: L + IQC --> Phi + omega; (3) peritectic (between U-8 and U-5): L + IQC --> Phi. (C) 2003 Elsevier Science B.V All rights reserved.
Title:
New results on old problems: The use of single-crystals in high-pressure structural studies
Authors:
McMahon, MI; Degtyareva, O; Hejny, C; Nelmes, RJ; Shen, NF;
Source:
HIGH PRESSURE RESEARCH, 23 (3): 289-299; 2003
Abstract:
Single-crystal X-ray diffraction techniques have been applied to a number of outstanding structural problems in elemental metals. Cs-III, Rb-III and Ga-II are shown to be members of a new class of modulated elemental structure containing different stackings of 8- and 10-atom layers; the interaction of the host and guest components in the incommensurate composite structure of Bi-III is found to induce modulations of the basic host and guest structures; and Te-III is shown to have a body-centred monoclinic structure modulated by an incommensurate displacement wave.
Title:
Orthorhombic rational approximants for decagonal quasicrystals
Authors:
Ranganathan, S; Subramaniam, A; Hejny, C;
Source:
BULLETIN OF MATERIALS SCIENCE, 26 (6): 627-631; 2003
Abstract:
An important exercise in the study of rational approximants is to derive their metric, especially in relation to the corresponding quasicrystal or the underlying clusters. Kuo's model has been the widely accepted model to calculate the metric of the decagonal approximants. Using an alternate model, the metric of the approximants and other complex structures with the icosahedral cluster are explained elsewhere. In this work a comparison is made between the two models bringing out their equivalence. Further, using the concept of average lattices, a modified model is proposed.
Title:
Rational approximants to 5, 8 and 7-fold two-dimensional tilings
Authors:
Subramaniam, A; Ramakrishnan, K; Hejny, C;
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 218 (9): 590-596; 2003
Abstract:
The strip projection method is used to generate rational approximants to Penrose, octagonal and 7-fold tilings. Two types of approximants to the Penrose tiling are considered, wherein-the basis vectors of the approximants are either orthogonal or are 72degrees apart. Various types of approximants including those with partially retained quasiperiodicity are generated and the pseudosymmetries arising therein analyzed. A simplified approach based on uniform distortions of perpendicular space is put forth for the analyses.
Title:
Precipitates in a Mg-Zn-Y alloy reinforced by an icosahedral quasicrystalline phase
Authors:
Kim, IJ; Bae, DH; Kim, DH; Nelmes, RJ;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 359 (1-2): 313-318; 2003
Abstract:
The precipitation behavior under various heat treatment conditions in the as-cast and hot-rolled Mg-Zn-Y alloy has been investigated. While MgZn2 precipitates are distributed in the alpha-Mg matrix at 190 degreesC, in the temperature range of 350-420 degreesC, polygon-shaped icosahedral phase (I-phase) precipitates are mainly formed. The precipitated I-phase is mostly found to be localized near the eutectic region in the as-cast ingot, but it is randomly distributed throughout the refined alpha-Mg grains formed by dynamic recrystallization during the hot-rolling processes in the sheet. The I-phase precipitates have no specific orientation relationship with the alpha-Mg matrix and do not coarsen at high temperatures. An increase of the hardness value by I-phase precipitates is less significant than that by MgZn2 precipitates due to their relatively low number density and near-spherical morphology. (C) 2003 Elsevier B.V. All rights reserved.
Title:
Investigation of the elastic properties of UNi2Si2 a function of temperature, magnetic field, and pressure
Authors:
Quirion, G; Kelly, A; Newbury, S; Razavi, FS; Garrett, JD; Gui, JI;
Source:
CANADIAN JOURNAL OF PHYSICS, 81 (6): 797-804; 2003
Abstract:
It is now well-established that the strong anisotropy in the magnetic properties of the intermetallic compounds UT(2)S(i)2, where T stands for a transition metal, is responsible for their rich magnetic phase diagram. However, within that series of compounds, UNi2Si2 is one that shows an unusual sequence of magnetically ordered states. Thus, to better understand its unusual properties, we have investigated the elastic properties of UNi2Si2 as a function of temperature, magnetic field, and pressure. In all three magnetic phases, our measurements indicate that the sound-velocity temperature dependence is dominated by the magnetoelastic coupling. Moreover, the analysis of the temperature dependence for the incommensurate longitudinal spin-density wave phase is consistent with a critical exponent beta = 0.38 +/- 0.01. We also present the magnetic phase diagram for UNi2Si2 obtained at 0 and 8 kbar. Our investigation reveals that the triple-point coordinates (T-p, H-p) decrease with pressure at a rate of dT(p)/dP = -0.1 K/kbar and dH(p)/dP = -0.1 T/kbar, respectively.
Title:
Processing of nickel-quasicrystal composite coating produced by pulse reverse current plating
Authors:
Qu, NS; Chan, KC; Zhu, D; Mao, XY;
Source:
TRANSACTIONS OF THE INSTITUTE OF METAL FINISHING, 81 (10): 103-105; 2003
Abstract:
A new, composite coating, nickel-quasicrystal, was recently produced by pulse current electrodeposition. However. the surface finish vas not sufficiently smooth. In this paper, pulse reverse current, as all alternative to the use of levelling additives. was employed in the electrochemical deposition of nickel-quasicrystal composite coating. The effect of anodic lime on volume percentage of embedded quasicrystal particles, surface finish, and microhardness of the composite coating was examined With a rise in anodic time, an improved surface finish was obtained the volume percentage reduced, and microhardness decreased.
Title:
Memory effect in ferroelectric-semiconductor with incommensurate phase TlGaSe2
Authors:
Aliyev, VP; Babayev, SS; Mammadov, TG; Seyidov, MHY; Suleymanov, RA; Chen, XB;
Source:
SOLID STATE COMMUNICATIONS, 128 (1): 25-28; 2003
Abstract:
The paper is devoted to the investigations of the non-equilibrium properties of the incommensurate (INC) phase of the improper ferroelectric-semiconductor TlGaSe2. The influence of the prehistory of the heat treating of the crystal, i.e. annealing at a fixed, stabilized temperature in the region of INC-phase on the dielectric constant (epsilon) in the vicinity of the phase transition (PT)-INC phase (the commensurate (C) ferroelectric phase) was studied. The peculiar case of the memory effect leading to the temperature range change of the INC-phase existence is observed for the first time in TlGaSe2. (C) 2003 Elsevier Ltd. All rights reserved.
Title:
Relationship between Penrose vertices and decagonal covering configurations
Authors:
Fu, XJ; Hou, ZL; Liu, YY; Seyidov, MHY;
Source:
SOLID STATE COMMUNICATIONS, 128 (2-3): 75-78; 2003
Abstract:
Two-dimensional quasicrystals are generally described by the Penrose tiling model. An alternative is the cluster covering approach developed recently. There exists a correspondence between the two schemes. The distributions of rhombus vertices in Penrose tilings and the nearest neighbor configurations in the decagonal covering structures are studied. Their occurrence probabilities are expressed in terms of the powers of the golden mean tau and their relationship is obtained. (C) 2003 Elsevier Ltd. All rights reserved.
Title:
High-resistive anomalies of metallic alloys and chemical bond
Authors:
Prekul, AF; Kuz'min, NY; Shchegolikhina, NI; Seyidov, MHY;
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 96 (2): 160-169; 2003
Abstract:
Results of long-term investigations on the problem of so-called high-resistive anomalies in the alloys whose components are typical metals are systematized. This has become possible due to advances in studying stable icosahedral crystals. The results of experimental investigations of the electrical, magnetic, and galvanomagnetic properties at different stages of structural relaxation of quasicrystals of the Al-Cu-Fe system are presented in detail. Based on these results, we have shown for the first time that it is the polar type ofchemical bond that is responsible for the "elimination" of valence electrons of the metals melted together from conductivity. The dilatometric experiments on quasicrystalline Al-Cu-V, Al-Cu-Fe, and Al-Pd-Re alloys, which confirmed this assumption, are described.
Title:
Dynamical upper bounds on wavepacket spreading
Authors:
Killip, R; Kiselev, A; Last, Y; Sakai, S;
Source:
AMERICAN JOURNAL OF MATHEMATICS, 125 (5): 1165-1198; 2003
Abstract:
We derive a general upper bound on the spreading rate of wavepackets in the framework of Schrodinger time evolution. Our result consists of showing that a portion of the wavepacket cannot escape outside a ball whose size grows dynamically in time, where the rate of this growth is determined by properties of the spectral measure and by spatial properties of solutions of an associated time-independent Schrodinger equation. We also derive a new lower bound on the spreading rate, which is strongly connected with our upper bound. We apply these new bounds to the Fibonacci Hamiltonian-the most studied one-dimensional model of quasicrystals. As a result, we obtain for this model upper and lower dynamical bounds establishing wavepacket spreading rates which are intermediate between ballistic transport and localization. The bounds have the same qualitative behavior in the limit of large coupling.
Title:
On the character of the incommensurate modulation near transition to the triple-period phase
Authors:
Aslanyan, TA; Bastie, P;
Source:
FERROELECTRICS, 290 (8): 47-50; 2003
Abstract:
The character of the incommensurate modulation is discussed for the structures with the incommensurate modulation vector k approaching the vector b /3 ( b is the reciprocal lattice vector), i.e., near the lock-in transitions, when k = b /3 + kappa, with kappa tending to zero. It is shown that such IC wave can induce second and third order modulation harmonics with amplitudes larger than that of the first harmonic.
Title:
Formation of a new FCC tau 2 phase in rapidly quenched Al55Cu35V10 alloy
Authors:
Misra, DK; Tiwari, RS; Srivastava, ON; Aliouane, N;
Source:
CRYSTAL RESEARCH AND TECHNOLOGY, 38 (9): 755-759; 2003
Abstract:
X-ray diffraction and transmission electron microscopy experiments were carried out to study the structure of rapidly solidified as-cast and annealed Al55Cu35V10 alloy. The as-east Al55Cu35V10 alloy shows the presence of a new f.c.c. tau2 phase (a=0.58nm) along with a b.c.c. (a=0.89nm) phase which after subsequent annealing transforms into single f.c.c. phase (a=0.58nm). In this paper, it is also reported that these phases are crystalline approximants to an icosahedral phase on the basis of e/a (valence electron per atom) constant line.
Title:
Synthesis and structural investigations on the new Sr1.32Mn0.83CU0.17O3 compound
Authors:
Abakumov, AM; Mironov, AV; Govorov, VA; Lobanov, MV; Rozova, MG; Antipov, EV; Lebedev, OI; Van Tendeloo, G; Palosz, W;
Source:
SOLID STATE SCIENCES, 5 (8): 1117-1125; 2003
Abstract:
The Sr1.32Mn0.83Cu0.17O3 compound has been prepared by solid state reaction in an evacuated sealed silica tube at 1000degreesC. The crystal structure of Sr1.32Mn0.83Cu0.17O3 was studied by means of electron diffraction, high resolution electron microscopy and was refined from X-ray powder diffraction data (R-I = 0.042, R-P = 0.016). The compound belongs to the A(3m+3n)A(n)'B3m+nO9m+6n, family of hexagonal perovskites. Its incommensurate composite structure (a = 9.5964(1) Angstrom, c = 2.6001(1) Angstrom, q = 0.66159(3)c*, superspace group R (3) over barm(00gamma)0s) consists of the modulated [(Mn,Cu)O-3](infinity) and [Sr](infinity) subsystems. The repeat period along the [(Mn,Cu)O-3](infinity) chains of the BO6 octahedra and the A'O-6 trigonal prisms is equal to 99 polyhedra and can be represented as a sequence of 1 x (3 oct + 1 prism) and 9 x (2 oct + 1 prism) or 10 x (2 oct + 1 prism). Mn is located at the octahedral sites, whereas the trigonal prismatic sites are randomly occupied by Mn and Cu. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.
Title:
Coincident lattice sites between cubic beta-Zr(Pt) and an isochemical icosahedral phase in rapidly solidified Zr80Pt20 alloys
Authors:
Yang, XY; Kramer, MJ; Rozhkova, EA; Sordelet, DJ; Litvin, LV;
Source:
SCRIPTA MATERIALIA, 49 (9): 885-890; 2003
Abstract:
Epitaxial growth of a bcc hyperstoichiometric beta-Zr(Pt) (Im3m) superstructure on an icosahedral phase has been studied in rapidly solidified Zr80Pt20 alloys. Icosahedral twofold axes coincide with <110>, <111>, <112> and <113> axes in beta-Zr(Pt). The beta-Zr(Pt) has a close crystallographic match and nearly identical stoichiometry to the i phase, but, it is not an approximant. Both the beta-Zr(Pt) and the i phase are distorted. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Structure factor for quasicrystals - 1D case
Authors:
Kozakowski, B; Wolny, J; Parras, M;
Source:
ACTA PHYSICA POLONICA A, 104 (1): 55-66; 2003
Abstract:
Using a statistical approach a simple formula for the structure factor of decorated Fibonacci chain was derived. Although the used method operates in the physical space only, its equivalence to the higher-dimensional analysis was proved. Applications of the analysis to different decorated structures were also discussed.
Title:
Rietveld refinement of incommensurate low tridymite
Authors:
Graetsch, HA; Gao, QY;
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 218 (8): 531-535; 2003
Abstract:
The incommensurate modification of SiO2 low-tridymite was refined in the 3 + 1 dimensional superspace group Cc(alpha0gamma) 0 at 295 and 325 K from X-ray powder diffraction data. The displacive modulation mainly consists of tiltings of rigid SiO4/2 tetrahedra with the wave vector r = 0.656a* - 0.496c* (dimensions of the average cell: a = 5.005 Angstrom, b = 8.598 Angstrom, c = 8.213 Angstrom and beta = 91.50degrees). The largest amplitude is ca. 0.6 Angstrom for oxygen and ca. 0.3 Angstrom for silicon. Wave vector and amplitudes of the displacive modulation functions vary only very little with increasing temperature.
Title:
High temperature-high pressure synthesis and crystal structure of the incommensurately modulated, alpha-PbO2 related, compound MnTa2O6
Authors:
Tarakina, NV; Tyutyunnik, AP; Zubkov, VG; D'Yachkova, TV; Zainulin, YG; Hannerz, H; Svensson, G; Aseev, AL;
Source:
SOLID STATE SCIENCES, 5 (7): 983-994; 2003
Abstract:
A new high pressure-high temperature modification of MnTa2O6 has been prepared at T = 1400degreesC, P = 8 GPa. Electron and X-ray powder diffraction (XRPD) studies showed it to have a modulated alpha-PbO2 structure. It crystallises in the four-dimensional space group P: P112(1)/n (alphabeta0). The structure model could be refined by the Rietveld technique, using XRPD data. An incommensurate ordering of the Mn and Ta atoms gives rise to a modulation of the oxygen and metal atoms' positions. The occupational modulation is described by a combination of a Crenel and a sinusoidal function, whereas the positional modulations can be described purely by sinusoidal functions. The unit cell parameters are a = 4.7472(2) Angstrom, b = 5.7453(3) Angstrom, c = 5.1496(3) Angstrom, gamma = 90.023(9)degrees, and the modulation vector is q = -0. 1038(4) (.) a* + 0.6910(7) (.) b*. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.
Title:
Effect of composition and cooling rate on structures and properties of quenched or cast Al-V-Fe alloys
Authors:
Shek, CH; He, G; Bian, Z; Chen, GL; Lai, JKL; Hannerz, H;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 357 (1-2): 20-26; 2003
Abstract:
Rapidly solidified Al-V-Fe alloys are promising structural materials because of the high tensile strength of up to 1400 MPa combined with the light weight. In this investigation, the authors prepared Al-V-Fe alloys of various V and Fe contents by melt-spinning and water-cooled copper mould casting. The alloy samples were characterized with X-ray diffraction (XRD), SEM, TEM, nanoindention, and tensile test. It was shown that the V and Fe contents strongly affect the microstructure and hence the mechanical properties. Increasing V and Fe content causes an increase of the volume fraction of the quasicrystalline phase which gives rise to the strengthening of the alloy. The amount of quasicrystals depends also on the cooling rate during solidification. At very high cooling rate, dispersions of quasicrystals and amorphous nanoscale clusters are favored while at low cooling rate, a stable Al10V crystalline phase form instead in the alpha-Al matrix. A gradual transition between these two extremes is observed at intermediate cooling rates. (C) 2002 Elsevier B.V. All rights reserved.
Title:
Pressure induced non-collinear magnetic structures in Fe-rich intermetallics
Authors:
Arnold, Z; Kamarad, J; Prokhnenko, O; Thoss, M;
Source:
HIGH PRESSURE RESEARCH, 23 (1-2): 143-148; 2003
Abstract:
The results of a complementary study of magnetic properties, magnetovolume effects and neutron diffraction studies under pressure in R2Fe17 compounds with non-magnetic R (R - Y, Ce, Lu) are presented. The collinear ferromagnetic phase existing at low temperature in all three compounds is suppressed at high pressures. The critical pressure P-C depends on the compound studied (P-C congruent to 2.5 kbar for Ce2Fe17, P-C congruent to 3.5 kbar for Lu2Fe17, P-C congruent to 12 kbar for Y2Fe17). Incommensurate non-collinear magnetic structures that replace the ferromagnetic ones under high pressures have similar features - magnetic moments in each layer of atoms (perpendicular to z-axis) are parallel each other, their direction helically changes from layer to layer. A generalised phase diagram of the studied R2Fe17 compounds was determined with use of the recent compressibility data.
Title:
Pressure induced anisotropic magnetovolume phenomena in Lu2Fe17 intermetallics
Authors:
Machatova, Z; Kamarad, J; Andreev, AV; Arnold, Z; Prokhnenko, O; Hannerz, H;
Source:
HIGH PRESSURE RESEARCH, 23 (1-2): 165-169; 2003
Abstract:
Magnetisation and magnetic susceptibility of a Lu2Fe17 single crystal have been studied under hydrostatic pressure up to 1.2 GPa at temperatures down to 5 K using a SQUID magnetometer. The ferromagnetic phase of Lu2Fe17 is suppressed rapidly above a critical pressure P-C = 0.4 GPa in the whole temperature range below the critical temperature T-C. A magnetic phase diagram of Lu2Fe17 has been constructed using results of the magnetic susceptibility measurements under pressure. A pressure induced incommensurate antiferromagnetic phase exhibits metamagnetic transitions with the increasing critical magnetic field H-C under pressure. Taking into account recent neutron diffraction data, the pressure induced anisotropic changes of the lattice parameters of the Lu2Fe17 are discussed.
Title:
TEM study of incommensurate phases in minerals: implication for materials science
Authors:
Stenina, N; Gutakovskii, A; Andreev, AV;
Source:
MATERIALS CHEMISTRY AND PHYSICS, 81 (2-3): 237-240; 2003
Abstract:
Incommensurate (INC) phases as a special, one-dimensional case of quasi-crystals were found in natural minerals of plagioclase and pyroxene solid solutions, as well as in quartz and in telluriumantimony (Sb2Te3). A relationship between the chemical composition of the mineral and its ability to be in the metastable state of INC was justified based on the transmission electron microscopic (conventional and high-resolution) data. Namely, the amphoteric elements adjacent to the large diagonal of amphoters of the Mendeleev table favor the formation and prolonged life-time of INC. Telluriumantimony proved to display the most pronounced INC state. Its features suggest that the red/ox transition provides the generation of energy in chemical systems. (C) 2003 Elsevier Science B.V All rights reserved.
Title:
Generation of dislocations during plastic deformation
Authors:
Messerschmidt, U; Bartsch, M; Andreev, AV;
Source:
MATERIALS CHEMISTRY AND PHYSICS, 81 (2-3): 518-523; 2003
Abstract:
The models of dislocation generation during plastic deformation are reviewed. The different types of dislocation generation, i.e. localized Frank-Read sources and multiplication by the double-cross slip mechanism, are observed in ceramic single crystals, semiconductors, metals, intermetallics and quasicrystals during in situ deformation in a high-voltage electron microscope. The results are discussed with respect to the ability of cross slip in different materials. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
High-temperature oxidation of Al-Cu-Fe-Be quasicrystalline powders
Authors:
Fleury, E; Kim, JS; Kim, DH; Kim, WT; Prokhnenko, O;
Source:
JOURNAL OF MATERIALS RESEARCH, 18 (8): 1837-1841; 2003
Abstract:
The oxidation behavior in air of gas atomized Al-Cu-Fe-Be powders was investigated during isothermal exposures at 750, 800, and 830 degreesC. Oxidation data obtained at 750 degreesC for Al-Cu-Fe and Al-Cu-Fe-Cr powders are also presented and used as references. Thermogravimetric analyses showed that Be significantly improved the oxidation resistance of the icosahedral phase at 750 degreesC. At this temperature the i-phase in Al-Cu-Fe-Be powders was found to be stable even after oxidation for 300 h, while oxidation at and beyond 800 degreesC led to the formation of a cubic beta'-phase. Auger analyses suggested that, in addition to its role on the stability of the icosahedral phase, the presence of Be in the oxide layer provided efficient protection against air oxidation at high temperature.
Title:
Transversal growth microstructures of quasicrystalline Ti-Zr-Ni films
Authors:
Brien, V; Dauscher, A; Weisbecker, P; Ghanbaja, J; Machizaud, F; Hannerz, H;
Source:
JOURNAL OF CRYSTAL GROWTH, 256 (3-4): 407-415; 2003
Abstract:
Pulsed laser deposition from a Nd:YAG laser was employed in the production of hundreds of nanometer thick quasicrystalline Ti-Zr Ni films on glass substrate. The influence of deposition temperature T., on the structure, morphology and microstructure of the films across their thickness was investigated. The morphology and microstructure features were evaluated by X-ray diffraction and transmission electron microscopy techniques. The low deposition temperatures were found to produce films with nanometer sized grains embedded in an amorphous matrix. The Grains exhibit quasicrystalline order. The higher deposition temperatures lead to films whose structure is not uniform all along the growth direction. The layer in contact with the substrate is a very thin amorphous layer. The main part of the film consists of crystallized columns. The columns have grown from a nanocrystallized layer where the size of crystallites increases with increasing thickness. (C) 2003 Elsevier B.V. All rights reserved.
Title:
A construction of inflation rules for pisot octagonal tilings
Authors:
Escudero, JG; Dmitriev, SV;
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B, 17 (15): 2925-2931; 2003
Abstract:
A construction for the generation of eight-fold symmetry planar patterns is introduced. The basic building blocks are four triangle prototiles with six edge lengths. Subpatterns with three prototile shapes and two edge lengths can also be derived.
Title:
ZnS nanowires with wurtzite polytype modulated structure
Authors:
Jiang, Y; Meng, XM; Liu, J; Hong, ZR; Lee, CS; Lee, ST; Jezequel, G;
Source:
ADVANCED MATERIALS, 15 (14): 1195-+; 2003
Abstract:
A novel polytype modulated ID structure has been grown in ZnS nanowires via intermittent laser ablation-catalytic growth. The polytype modulated ZnS nanowires show a strong blue-shifted bandgap emission centered at 338.2 nm due to quantum size effects. The Figure shows a dark-field image of one of the nanowires (top) and the corresponding electron diffraction patterns (bottom).
Title:
Etol systems for composite dodecagonal quasicrystal patterns (vol 15, pg 1165, 2001)
Authors:
Escudero, JG; Dove, MT;
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B, 17 (14): 2789-2790; 2003
Abstract:
Infrared and Raman spectra of cristobalite are presented as a function of temperature through the phase transition. The modes are assigned and the assignments compared to those of earlier workers. The compatibility of modes at the Gamma-point of the alpha-phase with the X and Gamma-points of the beta-phase is given. In the transition region of ca. 500-550 K, smooth changes in intensity, frequency and linewidths are seen in many modes, indicative of coexistence of alpha- and beta-forms.
Title:
Thermal properties of thiourea studied using photopyroelectric technique
Authors:
Menon, CP; Philip, J; Palmer, DC;
Source:
FERROELECTRICS, 287 (7): 63-70; 2003
Abstract:
Thiourea undergoes successive phase transitions at 169K (T-1), 176K (T-2), 180K (T-3) and 202 K (T-4). The phase I below T-1 is ferroelectric having spontaneous polarization along the b-axis. Photopyroelectric study of the thermal properties of thiourea single crystal along the three principal directions have been carried out across the above transitions including the commensurate-incommensurate phase transition at T-4. The thermal parameters-thermal conductivity (k) and heat capacity (c(p))-of thiourea single crystals cut along the a-, b- and c-axis are measured and reported. The successive phase transitions get clearly reflected in these thermal parameters as clear anomalies at the transition points. Our results show that the photopyroelectric technique is sensitive to measure the thermal parameters across transition temperatures.
Title:
Repetitive Delone sets and quasicrystals
Authors:
Lagarias, JC; Pleasants, PAB; Palmer, DC;
Source:
ERGODIC THEORY AND DYNAMICAL SYSTEMS, 23 (7): 831-867; 2003
Abstract:
This paper studies the problem of characterizing the simplest aperiodic discrete point sets, using invariants based on topological dynamics. A Delone set of finite type is a Delone set X such that X - X is locally finite. Such sets are characterized by their patch-counting function N-X(T) of radius T being finite for all T. We formulate conjectures relating slow growth of the patch-counting function N-X(T) to the set X having a nontrivial translation symmetry.A Delone set X of finite type is repetitive if there is a function M-X (T) such that every closed ball of radius M-X(T) + T contains a complete copy of each kind of patch of radius T that occurs in X. This is equivalent to the minimality of an associated topological dynamical system with R-n-action. There is a lower bound for M-X(T) in terms of N-X(T), namely MX (T) greater than or equal to M-X(T))(1/n) for some positive constant c depending on the Delone set constants r, R, but there is no general upper bound for M-X(T) purely in terms of NX(T). The complexity of a repetitive Delone set X is measured by the growth rate of its repetitivity function M-X(T). For example, the function M-X(T) is bounded if and only if X is a periodic crystal. A set X is linearly repetitive if M-X(T)) = O(T) as T --> infinity and is densely repetitive if M-X(T) = O (N-X(T))(1/n) as T --> infinity. We show that linearly repetitive sets and densely repetitive sets have strict uniform patch frequencies, i.e. the associated topological dynamical system is strictly ergodic. It follows that such sets are diffractive, in the sense of having a well-defined diffraction measure. In the reverse direction, we construct a repetitive Delone set X in R-n which has M-X(T) = O (T (log T)(2/n) (log log log T)(4/n)), but does not have uniform patch frequencies. Aperiodic linearly repetitive sets have many claims to be the simplest class of aperiodic sets and we propose considering them as a notion of `perfectly ordered quasicrystals'.
Title:
The (3+1)-dimensional superspace description of the commensurately modulated structure of p-chlorobenzamide (alpha-form) and its relation to the gamma-form
Authors:
Schonleber, A; Pattison, P; Chapuis, G; Hong, ZR;
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 218 (7): 507-513; 2003
Abstract:
The room temperature structure (a-form) of the organic compound p-chlorobenzamide, C7H6ClNO, can be described as a classical three-dimensional periodic superstructure (alpha(s)) and also as a commensurately modulated structure (alpha(m)) in (3 + 1)-dimensional superspace. The diffraction pattern is characterized by a clear difference in intensity between main and satellite reflections. All reflections can be indexed with four indices hklm in a triclinic unit cell and one modulation vector in the superspace group P (1) over bar(alphabetagamma) with the modulation vector (q) over right arrow = 1/3 . (d) over right arrow*. The structure undergoes a phase transition at higher temperature. In this phase transition the modulation vanishes as indicated by the disappearance of the satellite reflections. The resulting high temperature phase (gamma-form) contains one molecule in the asymmetric unit, the space group is P (1) over bar. The high temperature structure (gamma) is very close to the reference structure of the modulated model at room temperature. The phase transition can therefore be understood as a loss of the modulation at high temperature.
Title:
Temperature dependence of optical activity and circular dichroism in alpha-ZnP2 crystals
Authors:
Kushnir, OS; Bevz, OA; Polovinko, II; Sveleba, SA; Lee, CS;
Source:
PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 238 (1): 92-101; 2003
Abstract:
The circular birefringence related to the gyration components along and perpendicular to the optical axis and the circular dichroism of tetragonal alpha-ZnP2 single crystals are determined in the temperature range 290-450 K, using universal null-polarimetric techniques. The oscillatory temperature behaviour of the optical rotatory power and the ellipticity of light passed through the crystal in the (001) direction is quantitatively well explained by the influence of multiple reflections of light. The observed thermal hysteresis and dependence of the gyration on sample prehistory testify indirectly the availability of incommensurately modulated structure in alpha-ZnP2.
Title:
Morphological features of the crystalline or quasicrystalline silicides observed in the quaternary Al-Fe-Mo-Si alloys
Authors:
De Macedo, MCS; Michot, G; Polovinko, II;
Source:
JOURNAL OF MATERIALS SCIENCE, 38 (14): 3143-3153; 2003
Abstract:
Rapidly solidified Al-Fe-Mo-Si powders were produced by centrifugal atomization and then consolidated by hot extrusion. Five compositions were chosen in order to obtain a theoretical constant volume fraction of ( silicide + Al12Mo) of 20%, with different relative fractions of [silicide]/[alpha-matrix] and different ratios of [Fe]/[Mo] within the silicide. This paper presents the microstructures observed in both as-atomized and consolidated states. The only phase detected by X-Ray Diffraction, the non equilibrium ternary Al12-13(Fe, Mo)(3)Si, exhibits different sizes and morphologies and is inhomogeneously distributed within the matrix. Accurate electron microscopy observations indicate that this silicide may grow from a quasicrystalline precursor. Grains within the polycrystalline silicide often exhibit orientation relationships ( micro twinning) giving rise to quasicrystalline-like patterns. (C) 2003 Kluwer Academic Publishers.
Title:
Analytic expressions for the vertex coordinates of quasiperiodic lattices
Authors:
Naumis, GG; Aragon, JL; Polovinko, II;
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 218 (6): 397-402; 2003
Abstract:
Using the generalized dual method, closed analytical expressions for the coordinates of quasiperiodic lattices, derived from periodic or quasiperiodic grids, are given. The obtained formulae constitute a useful and practical tool to generate and perform calculations in quasiperiodic structures.
Title:
Polarization leakage and asymmetric Raman line broadening in microwave dielectric ZrTiO4
Authors:
Kim, YK; Jang, HM; Krejcar, R;
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 64 (8): 1271-1278; 2003
Abstract:
Nano-scale structural characteristics and broken symmetry associated with the formation of incommensurately ordered phase from the high-temperature disordered phase of ZrTiO4 were studied using Raman scattering method. For this purpose, the Raman peak at 815 cm(-1) caused by the A(g)-symmetry normal mode was employed as a nano-structural probe. A polarization leakage was observed in the polarized Raman spectra of single-crystal ZrTiO4. The observed leakage was attributed to the random orientation of the short-range ordered domains in the beginning stage of the normal-to-incommensurate transformation. The computational result based on the phonon-confinement model indicated that the asymmetric Raman line broadening in the incommensurately ordered ZrTiO4 single-crystal was directly related to the existence of the faulted boundary having the average periodicity of 3.9 nm along the a-axis. (C) 2003 Elsevier Science Ltd. All rights reserved.
Title:
Coexistence of superconducting and spiral spin orders: Models of ruthenate
Authors:
Ovchinnikova, MY; Jang, HM;
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 96 (6): 1131-1139; 2003
Abstract:
The effect of a spiral spin structure on superconducting (SC) pairing in a three-band Hubbard model related to Sr2RuO4 is analyzed in the mean-field approximation. Such a structure with incommensurate vector Q = 2pi(1/3, 1/3) is the simplest one that removes the nesting instability of alpha and beta bands. It is assumed that there is an intralayer pairing interaction between two types of neighbor sites, those with attraction in a singlet channel and with attraction in both two-singlet and triplet channels. In both cases, a mixed singlet-triplet SC order is observed in the gamma band: a d-wave singlet order is accompanied by the formation of p-wave triplet pairs (k, -k - Q)(up arrowup arrow) and (k, -k + Q)(down arrowdown arrow) with large total momenta -/+Q and the spin projections +/-1 onto an axis perpendicular to the spin rotation plane of the spiral spin structure. Both the SC and normal states are states with broken time-reversal symmetry. In contradiction to the experiment, the models give different scales of T-c for the gamma band and for alpha and beta bands. This fact shows that the models with intralayer interactions or with the spin structure assumed are insufficient. (C) 2003 MAIK "Nauka/Interperiodica".
Title:
Quasicrystal strengthened Mg-Zn-Y alloys by extrusion
Authors:
Singh, A; Nakamura, M; Wantanabe, M; Kato, A; Tsai, AP; Theisinger, H;
Source:
SCRIPTA MATERIALIA, 49 (5): 417-422; 2003
Abstract:
Superior mechanical properties with high ductility at room and higher temperatures have been achieved by extruding Mg95Zn4.2Y0.S and Mg92.5Zn6.4Y alloys at 523 K. The strengthening phases are the icosahedral quasicrystal, finely distributed nano-sized precipitates of a ternary phase tau(1) and thin beta(1)('), phase rods several hundreds of nanometers long. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
Complex method of the plane elasticity in 2D quasicrystal with point group 10 mm tenfold rotational symmetry and holey problems
Authors:
Liu, GT; Fan, TY; Wantanabe, M;
Source:
SCIENCE IN CHINA SERIES E-TECHNOLOGICAL SCIENCES, 46 (3): 326-336; 2003
Abstract:
The complex method of the plane elasticity in 2D quasicrystal with point group 10 mm tenfold rotational symmetry is established. First displacement potential function. in the quasicrystal is represented by four analytic functions. Then by utilizing the properties of analytic function and through a great deal of derivation, the complex representations of stresses and displacements components of phonon fields and phason fields in the quasicrystal are given, which are theoretical foundation, for this method. From this theory, and by the help of conformal transformations. in the theory of complex function, the problems of elliptic hole in the quasicrystal are solved. Its special cases are the solutions of well-known crack problem. Meanwhile, the results show that even if under the self-counterbalance force in the quasicrystal plane with elliptic hole, the stress components of phonon fields are also related to material constants of the quasicrystal, when the phonon fields and phason fields are coupled, which is another distinctive difference from the properties of classical elastic theory. Besides, the present work is generalization and application of the complex method in the classical elastic. theory established by Muskhelishvili to 2D quasicrystal. As in the classical elastic theory, if only conformal transformation from the quasicrystal plane to unit circle is found, any holey and crack problem in the quasicrystal plane could be solved.
Title:
X-ray study of modulated structures of beta '-CuxV2O5 (x=0.29,0.39)
Authors:
Nagao, N; Nogami, Y; Oshima, K; Yamada, H; Ueda, Y; Theisinger, H;
Source:
PHYSICA B-CONDENSED MATTER, 329 (3): 713-714; 2003
Abstract:
High resolution X-ray study reveals the wave vector change in the modulated structure of the quasi-one-dimensional compound beta'-Cu vanadium bronze. Structural modulation of the reduced wave vector q(0) = (0, 0.305, 0) emerges below 220 K in beta'-Cu0.29V2O5. For beta'-Cu0.39V2O5, not the single q modulation but two kinds of modulations were observed. A three-fold superlattice structure with q(1) = (0, 0.333, 0) appears below 210 K. An incommensurate modulated structure with q(2) = (0, 0.26-0.29, 0) coexists below 175 K, whose satellite intensity and b* component Q(b) have temperature and passing-time dependencies between 140 and 175 K. The competition between q(1) and q(2) modulations was also observed. It seems that the q(2) is deeply related to the physical property change between 140 and 180 K confirmed by the decrease in the magnetic susceptibility and the increase in the resistivity. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Induced by magnetic field spin reorientation in YMn2O5
Authors:
Kadomtseva, AM; Popov, YF; Vorob'ev, GP; Kamilov, KI; Makhov, PN; Tehranchi, MM; Phirouznia, A; Aseev, AL;
Source:
PHYSICA B-CONDENSED MATTER, 329 (3): 856-857; 2003
Abstract:
In ferroelectric YMn2O5 weak ferromagnetism was found along a-axis of rhombic crystal. It was shown that the nature of ferromagnetic sublattices cant is determined by magnetoelectric ordering. Reorientation of magnetic moment was observed under strong magnetic field applied along b-axis of crystal, that was accompanied by sharp increase of magnetostriction and jumps of electric polarization. In EuMn2O5, as in YMn2O5, spontaneous and magnetic field induced phase transitions from incommensurate to commensurate phase were observed, accompanied by cardinal changing of magnetoelectrical properties. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
mu+SR studies on thermoelectric oxides
Authors:
Sugiyama, J; Brewer, JH; Ansaldo, EJ; Itahara, H; Hirano, S; Tani, T; Phirouznia, A;
Source:
PHYSICA B-CONDENSED MATTER, 329 (3): 902-903; 2003
Abstract:
To investigate the role of magnetism on transport properties of thermoelectric oxides, mu(+)SR spectroscopy has been used for polycrystalline Ca3Co4O9, Na0.7CoO2 and Sr0.92-yCayGd0.08MnO3 samples in the temperature range between 300 and 2.5 K. It was found that Ca3Co4O9 exhibits an incommensurate spin density wave transition around 100 K, though similar measurements on Na0.7CoO2 indicated no magnetic transitions below 250 K. The Sr0.92-yCayGd0.08MnO3 samples showed a ferro- or an antiferromagnetic transition below 250 K, while a muon precession was not observed even at 2.5 K probably due to an inhomogeneity of an internal magnetic field. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Superspace group description of single composite crystal (Ca0.5Y0.5)(0.80)CuO2
Authors:
Gotoh, Y; Takahashi, Y; Akimoto, J; Yamaguchi, I; Ito, T; Oka, K; Yamaguchi, H; Aseev, AL;
Source:
PHYSICA B-CONDENSED MATTER, 329 (3): 985-987; 2003
Abstract:
Symmetry and structural properties of single state of composite crystal (Ca0.5Y0.5)(0.80)CuO2, "Ca2Y2Cu5O10" with one-dimensional CuO2 chain have been investigated by means of the X-ray diffraction method and (3 + 1)-dimensional superspace group approach. By considering the satellite reflections, centrosymmetric superspace groups of (Ca0.5Y0.5)(0.80)CuO2 have been determined. It has become apparent that "Ca2+xY2-xCu5O10" phase should be generally described as (Ca0.5+xY0.5-x)(gamma)CuO2, "Ca5gamma(0.5+x)Y5gamma(0.5-x)Cu5O10". (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Spin-hole order in the 1-D chain cuprate Ca0.824CuO2
Authors:
Isobe, M; Kimoto, K; Takayama-Muromachi, E; Yamaguchi, I;
Source:
PHYSICA B-CONDENSED MATTER, 329 (3): 1012-1013; 2003
Abstract:
We have studied the magnetic state from a viewpoint of crystallographic features of the I-D chain compound Ca0.824CuO2, and determined a possible spin-hole arrangement in the coexisting state by precisely analyzing the local structural distortion in the CuO2 chain using a modulated-crystal-structure analysis technique. The essential periodic sequence expected is ... up arrowOdown arrowdown arrowOup arrow ... (up arrow down arrow : up- and down-spin, O : hole) along the chain. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Magnetism of decagonal Al69.8Pd12.1Mn18.1
Authors:
Rau, D; Gavilano, JL; Mushkolaj, S; Beeli, C; Ott, HR; Oka, K;
Source:
PHYSICA B-CONDENSED MATTER, 329 (3): 1103-1104; 2003
Abstract:
We report the results of measurements of Al-27 NMR spectra and the DC susceptibility of polycrystalline decagonal quasicrystalline Al69.8Pd12.1Mn18.1. The temperature variation of the magnetic susceptibility chi(T) and the Al-27 NMR-spectra imply that a fraction of the order of 20% of the Mn-atoms carry a magnetic moment, and that a spin-glass-type freezing of these Mn moments occurs at T-f = 12 K. The NMR spectra reveal two partially resolved lines for the Al-27 nuclei, indicating that there are two different sets of local environments for the Al-sites. Below 100 K and upon decreasing temperatures, the Al-27-NMR line width Delta increases with a progressively increasing negative slope dDelta/dt, as it is often observed in relation with spin-glass freezing processes. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Magnetic form factor of the heavy fermion compounds CeCu2Ge2 and CeCu1.9Ni0.1Ge2
Authors:
Krimmel, A; Zobkalo, I; Schweizer, J; Loidl, A; Ott, HR;
Source:
PHYSICA B-CONDENSED MATTER, 335 (1-4): 11-14; 2003
Abstract:
CeCu2Ge2 and CeCu1.9Ni0.1Ge2 are heavy fermion compounds that order in incommensurate magnetic structures at low temperatures. The neutron magnetic form factor of single crystalline samples has been established by polarized neutron diffraction in the paramagnetic, as well as within the magnetically ordered state. For both compounds the neutron magnetic form factor could be reasonably well described within the dipole approximation but is also in accord with a Gamma(7)-ground state as proposed on the basis of inelastic neutron scattering experiments. The present polarized neutron diffraction study shows that the ordered magnetic moment of CeCu2Ge2 is extremely stable against any change of temperature or magnetic field and further remains almost unaltered by alloying of 5% Ni. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Amorphous alloy composition with high glass-formation ability in the pseudoternary Zr-[IQC-Al62Cu25.5Fe12.5]- [DQC-Al70Co15Ni15] alloy system
Authors:
Lei, Y; Calvo-Dahlborg, M; Dubois, JM; Hei, ZK; Weisbecker, P; Dong, C; Yamaguchi, H;
Source:
JOURNAL OF MATERIALS RESEARCH, 18 (7): 1588-1593; 2003
Abstract:
A pseudoternary alloy system was constructed by combining icosahedral quasicrystal (IQC), decagonal quasicrystal (DQC), and Zr into one alloy system. Different proportions of Zr were added into pseudobinary alloy IQC(80)DQC(20) (in wt.%). The structural evolution in these alloys is discussed. An amorphous alloy composition was found in this system. Melt-spinning amorphous alloy was produced in this composition. Through differential scanning calorimetry experiments, the amorphous alloy exhibited a high glass-forming ability comparable to that of the Inoue alloy Zr65Al7.5Cu17.5Ni10.
Title:
Structural transitions at the surface of the decagonal quasicrystal Al-Co-Ni
Authors:
Fluckiger, T; Michlmayr, T; Biely, C; Luscher, R; Erbudak, A; Dong, C;
Source:
APPLIED SURFACE SCIENCE, 212 (3): 43-46; 2003
Abstract:
At the 2- and 10-fold-symmetry surfaces of the two-dimensional quasicrystal Al-Co-Ni an epitaxial cubic layer is induced by preferential sputtering of Al using Al+ ions. Annealing the sample at 760 K restores the Al concentration at the surface and, thereby, the quasicrystalline structure. Simultaneous observations of the surface chemistry by Auger electron spectroscopy and of its atomic structure by secondary-electron imaging reveal that the transition is a two-step process. The replenishment of Al at the surface is limited by high-temperature mediated diffusion of Al from bulk, while the assembly kinetics of the quasicrystalline structure proceeds at lower temperatures. Thus, the underlying bulk Al-Co-Ni quasicrystal acts as an Al reservoir and as a structural template for the recovery of the quasicrystal. The paper also presents a discussion of different cubic orientations of the surface phase formed by different sputtering conditions. (C) 2003 Published by Elsevier Science B.V.
Title:
Pseudogap structure in icosahedral ZnMgY and ZnMgHo quasicrystals
Authors:
Suchodolskis, A; Assmus, W; Cechavicius, B; Dalmas, J; Giovanelli, L; Gothelid, M; Karlsson, UO; Karpus, V; Le Lay, G; Sterzel, R; Uhrig, E;
Source:
APPLIED SURFACE SCIENCE, 212 (3): 485-490; 2003
Abstract:
The results of a photoemission study of icosahedral single-grain ZnMg(Y, Ho) quasicrystals and their crystalline approximant Zn2Mg are presented. Synchrotron radiation photoemission measurements have been performed on in situ cleaved samples at low temperature of approximate to90 K and 10(-10) mbar pressure. The spectra obtained indicate simple metal-type valence bands (VB) with distinct Fermi edge cutoff. Analysis of the Fermi edge spectra reveals the presence of a pseudogap in i-ZnMg(Y, Ho) quasicrystals. The pseudogap corresponds to a rather sharp DOS dip at the Fermi level with th approximate to50% (of the normal DOS) depth and the approximate to0.8 eV width. The values of i-ZnMg(Y, Ho) pseudogap parameters are comparable with those of other quasicrystals. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Discovery of critical oxygen content for glass formation in Zr80Pt20 melt spun ribbons
Authors:
Sordelet, DJ; Rozhkova, EA; Yang, XY; Kramer, MJ; Yamaguchi, M;
Source:
THERMEC'2003, PTS 1-5, 426-4 (9): 1903-1908; 2003
Abstract:
Zr80Pt20 alloys may form meta-stable quasicrystals either during devitrification of an amorphous phase or directly upon cooling from a liquid depending on processing conditions. To date, little attention has been given to the role of oxygen on the glass formation or devitrification behavior of Zr-Pt and similar alloys. This study reveals that oxygen content during melt spinning indeed strongly influences the formation of the as-quenched structure. A critical amount of oxygen was found to be required to form amorphous ribbons at a fixed quench rate. At lower oxygen levels (i.e., <500 ppm mass), a fully crystallized is formed; the structure is composed mainly of meta-stable beta-Zr with a small fraction of a quasicrystal line phase. At higher oxygen levels, the as-quenched structure transitions to a fully amorphous structure (similar to1000 ppm mass), and with further oxygen addition forms a mixture of amorphous and quasicrystalline (similar to1500 ppm mass) or crystalline phases (>2500 ppm mass). Details regarding the structure of the meta-stable beta-Zr phase in the low-oxygen ribbons are provided along with a discussion of the structural similarity between this phase and the quasicrystal structure that formed in this alloy.
Title:
A study on the improvement of the toughness in Al-Cu-Fe quasi-crystals
Authors:
Koo, JM; Hur, SK; Shin, K; Bae, JS; Yamaguchi, M;
Source:
THERMEC'2003, PTS 1-5, 426-4 (9): 2113-2118; 2003
Abstract:
Two approaches were made for improving the toughness of Al-Cu-Fe quasicrystals(QC), i.e., addition of Sn to the Al-Cu-Fe QC(Al-Cu-Fe-Sn), and composite fabrication of Al-Cu-Fe quasi-crystals with various content of pure aluminium. Powders of quasi-crystals were made by atomizer. They were sintered as a disk by PAS (Plasma Activated Sintering) process which shows some particular advantages during sintering. Composites of pure aluminium and Al-Cu-Fe quasi-crystal were also fabricated by PAS. The PASintered bulk specimens were examined by various methods. The experimental results represent that both sintered bulk specimens of Al-Cu-Fe-Sn QC and the composites have shown considerable improvement in toughness comparing with bulk specimen of Al-Cu-Fe quasi-crystals, if not applicable right away.
Title:
Bulk nanostructured aluminium alloy Al93Fe3Cr2Ti2: Processing and characterisation
Authors:
Chlup, Z; Todd, I; Garcia-Escorial, A; Lieblich, M; Chlupova, A; O'Dwyer, JG; Obara, H;
Source:
THERMEC'2003, PTS 1-5, 426-4 (9): 2417-2422; 2003
Abstract:
The ability to control the mechanical properties of bulk nanostructured aluminium alloys through judicious selection of processing parameters offers the potential for optimised performance together with the prospect of producing materials based on fitness-for-purpose criteria. In this investigation, nano-quasicrystalline powders of aluminium alloy Al93Fe3Cr2Ti2 (at. %) were consolidated using extrusion. This paper describes the influence of process variables on the tensile properties of the resultant bulk nanostructured alloy at room and at elevated temperatures. Lower extrusion temperatures provided an increase in strength without any significant reduction in ductility. The effect of extrusion ratio was negligible within the range investigated. The stress-strain characteristics were strongly influenced by test temperature, a significant increase in ductility being evident at higher temperatures. Fractographic and microstructural analyses enabled the scatter in ductility data to be rationalised on the basis of differences in the characteristics of the fracture surfaces.
Title:
Structural instabilities, incommensurate modulations and P and Q phases in sodium niobate in the temperature range 300-500 K
Authors:
Reznichenko, LA; Shilkina, LA; Gagarina, ES; Raevskii, IP; Dul'kin, EA; Kuznetsova, EM; Akhnazarova, VV; Karpus, V;
Source:
CRYSTALLOGRAPHY REPORTS, 48 (3): 448-456; 2003
Abstract:
The relation between the phase transition in the vicinity of 420 K discovered earlier and the formation of an incommensurate phase in the temperature range 410-460 K is established based on the X-ray, dielectric, and dilatometric studies of sodium niobate (NaNbO3) single crystals and ceramics. It is also established that this phase is characterized by temperature and temporal instabilities. Anomalies in some physical characteristics in the vicinity of 350 K are revealed. It is also shown that the thermodynamic history of the samples is important for the coexistence of the regions of the ferroelectric Q and anti ferroelectric P phases in NaNbO3. (C) 2003 MAIK "Nauka/Interperiodica".
Title:
Splitting of X-ray photoelectron spectra in incommensurate ferroelectric TlInS2 crystals
Authors:
Grigas, J; Tolik, E; Gagarina, ES;
Source:
PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 237 (2): 494-499; 2003
Abstract:
This paper presents the first observation of the resolved splitting of X-ray photoclectron spectra (XPS) in the incommensurate phase of the ferroelectric semiconductor TlInS2 single crystal. The XPS were measured with monochromatised Al K-alpha radiation in the energy range 0-1400 eV and the temperature range 195-300 K. At room temperature, the valence band is located 1-9 eV below the Fermi level. The chemical shifts in the TlInS2 crystal for the Tl, In and S states are obtained. The mechanism of the XPS splitting in the incommensurate phase is discussed.
Title:
Displacement function and simplifying of plane elasticity problems of two-dimensional quasicrystals with noncrystal rotational symmetry
Authors:
Liu, GT; Fan, TY; Guo, RP; Raevskii, IP;
Source:
MECHANICS RESEARCH COMMUNICATIONS, 30 (4): 335-344; 2003
Abstract:
The paper systematically investigates the plane elasticity problems of two-dimensional quasicrystals with noncrystal rotational symmetry. First, applying their independent elastic constants, the equilibrium differential equations of the problems in terms of displacements are derived and it is found that the plane elasticity of pentagonal quasicrystals is the same as that of decagonal. Then by introducing displacement functions, huge numbers of complicated partial differential equations of the problems are simplified to a single or a pair of partial differential equations of higher order, which is called governing equations, such that the problems can be easily solved. Finally, some solving methods of these governing equations obtained are introduced briefly. (C) 2003 Elsevier Science Ltd. All rights reserved.
Title:
Stable modulated and homogeneous structures of quartz (SiO2): Analysis of eigen-modes near phase transition points
Authors:
Semagin, DA; Dmitriev, SV; Abe, K; Shigenari, T; Dul'kin, EA;
Source:
FERROELECTRICS, 283 (4): 141-147; 2003
Abstract:
We obtain a variety of modulated and homogeneous phases of quartz, stable at zero-temperature, by means of relaxational and lattice dynamics calculation. The interatomic interaction is given by the Tsuneyuki pairwise potential. The order of appearance of the phases resembles the experimentally observed order. The essential role of the potential profile is obviated. The kinetics of phase transformations in quartz is illustrated by the analysis of dispersion curves and eigenvectors, which show some peculiarities near transition points.
Title:
Tribological properties of a B2-type Al-Pd-Mn quasicrystal approximant
Authors:
Mancinelli, C; Jenks, CJ; Thiel, PA; Gellman, AJ; Hock, R;
Source:
JOURNAL OF MATERIALS RESEARCH, 18 (6): 1447-1456; 2003
Abstract:
The tribological properties of a B2-type Al-Pd-Mn quasicrystal approximant were investigated and compared with those of an Al-Pd-Mn icosahedral quasicrystal. The approximant was of the P phase, having a crystalline CsCl-type structure and nominal composition Al48Pd42Mn10. Friction coefficients measured in ultrahigh vacuum between a pair of Al48Pd42Mn10 samples having truly clean surfaces were found to be twice as high as those reported for the Al70Pd21Mn9 quasicrystal. When the surfaces were oxidized by exposure to O-2 or H2O, the friction coefficients decreased by roughly a factor of two for both materials but the friction coefficient for the approximant remained roughly twice that of the quasicrystal. The rate of oxidation of the approximant was found to be one order of magnitude higher than that of the quasicrystal. This corroborates findings that suggest that quasicrystals exhibit an inherent resistance to oxidation and corrosion. Vickers hardness measurements show that the quasicrystal is roughly three times as hard as the approximant.
Title:
Formation of a decagonal quasicrystalline phase upon mechanical alloying and subsequent heating of the Al67Cu22Cr11 alloy
Authors:
Cherdyntsev, VV; Leonova, EA; Kaloshkin, SD; Gellman, AJ;
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 95 (5): 478-485; 2003
Abstract:
X-ray diffraction and differential scanning calorimetry were used to study the structure evolution in the Al67Cu22Cr11 alloy upon mechanical alloying and subsequent annealing. Mechanical alloying leads to the formation of aluminum- and copper-based solid solutions and aluminum-based binary intermetallic compounds. Heating of mechanically alloyed compositions is accompanied by a gradual homogenization of the chemical composition of the phases formed and finally leads to the formation of a decagonal quasicrystalline phase.
Title:
Dielectric susceptibility behaviour in the incommensurate phase of TlInS2
Authors:
Mikailov, FA; Basaran, E; Mammadov, TG; Seyidov, MY; Senturk, E; Currat, R;
Source:
PHYSICA B-CONDENSED MATTER, 334 (1-2): 13-20; 2003
Abstract:
Peculiarities of the temperature behaviour of the dielectric susceptibility of TlInS2 in the temperature interval of incommensurate (IC) phase have been theoretically investigated on the basis of recently suggested two-sublattice model of the phase transitions in TlInS2, which is based on the hypothesis about the coexistence of improper and proper ferroelectricity and also the presence of type I and type II incommensurations in the same compound. The temperature dependence of the dielectric constant of TlInS2 in the IC phase was calculated. An agreement between theoretical and experimental results has been obtained. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Photonic band gaps in 12-fold symmetric quasicrystals
Authors:
Hiett, BP; Beckett, DH; Cox, SJ; Generowicz, JM; Molinari, M; Thomas, KS; Wiersma, DS;
Source:
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 14 (5-7): 413-416; 2003
Abstract:
The 12-fold symmetric quasicrystal shows great potential as a novel photonic band gap (PBG) structure exhibiting a band gap for relatively low filling fractions and dielectric contrasts. The band gaps are highly homogeneous with respect to the angle of incidence of the incoming light due to the crystal's high degree of rotational symmetry. These crystals have been analyzed using a finite element method developed specifically for modelling PBG structures. We present and discuss quasicrystal structures and their optical properties. (C) 2003 Kluwer Academic Publishers.
Title:
A decagonal quasicrystal with an arc-shaped crack
Authors:
Wang, X; Zheng, Z; Cox, SJ;
Source:
ACTA MECHANICA SOLIDA SINICA, 16 (1): 8-15; 2003
Abstract:
A decagonal quasicrystal, which is weakened by an arc-shaped crack penetrating through the solid in the period direction, and which is subjected to remote uniform phonon stresses, is investigated by applying the complex variable method which is just developed by the authors. It is found that the phonon and phason stresses near the crack tips exhibit inverse square root singularities. The four complex stress functions characterizing the phonon and phason fields are derived. Explicit expressions for the phonon and phason stress intensity factors, crack opening displacements and energy release rate are also presented.
Title:
Magnetic structure of Tb3Cu4Si4
Authors:
Wawrzynska, E; Penc, B; Stusser, N; Szytula, A; Tomkowicz, Z; Thomas, KS;
Source:
SOLID STATE COMMUNICATIONS, 126 (9): 527-530; 2003
Abstract:
Polycrystalline sample of Tb3Cu4Si4 compound was prepared and studied by magnetic and powder neutron diffraction measurements. Tb3Cu4Si4 crystallizes in the orthorhombic Gd3Cu4Ge4-type structure (space group Immm). In this structure the Tb atoms occupy two non-equivalent crystallographic positions: 2d and 4e. Below T-N equal to 50 K the Tb moment in the 2d site orders and forms a collinear magnetic structure. At the temperature of T-t1 = 38 K a transition from the commensurate magnetic structure, described by the propagation vector k(2) = (0, 1/2, 0) to an incommensurate one, described by the propagation 2 vector k(1) = (0, 0.515, 0), is observed. Below T-t2 equal to 7 K the Tb moment in the 4e site forms a sine-wave modulated structure described by the propagation vector k(3) = (0.23, 1/2, 1/2). (C) 2003 Elsevier Science Ltd. All rights reserved.
Title:
Preface to the viewpoint set on: mechanical properties of quasicrystals
Authors:
Guyot, P; Penc, B;
Source:
SCRIPTA MATERIALIA, 49 (1): 1-3; 2003
Abstract:
The transposition of plastic deformation from crystals to quasicrystals raises different types of questions: at the microscopic scale where defect descriptions must be adapted, at the macroscopic scale where unusual stress-strain curves and a sharp intrinsic brittle-to-ductile transition are observed. Some problems ripe for development are outlined. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
Prolegomena to the plastic deformation of quasicrystals
Authors:
Kleman, M; Penc, B;
Source:
SCRIPTA MATERIALIA, 49 (1): 5-9; 2003
Abstract:
The plastic deformation of quasicrystals (QC) is ruled by two types of singularities of the QC order: 'perfect' dislocations, which are singularities of the 'phonon' strain field, and stacking faults (here called matching faults) which are singularities of the 'phason' strain field. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
Dislocation climb in icosahedral quasicrystals
Authors:
Caillard, D; Mompiou, F; Bresson, L; Gratias, D; Tomkowicz, Z;
Source:
SCRIPTA MATERIALIA, 49 (1): 11-17; 2003
Abstract:
We discuss here some arguments in favor of climb being the dominant mode of dislocation motion responsible for the plastic deformation of icosahedral quasicrystals. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
What is the elementary process of dislocation glide in quasicrystals?
Authors:
Takeuchi, S; Mompiou, F;
Source:
SCRIPTA MATERIALIA, 49 (1): 19-24; 2003
Abstract:
It is now well established that the plasticity of quasicrystals at high temperatures is governed largely by thermally activated dislocation glide. Discussion is made of the elementary process of the thermally activated dislocation motion overcoming a quasiperiodic Peierls potential, accompanied by a phason strain relaxation. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
Plastic behaviour of decagonal Al-Ni-Co single quasicrystals
Authors:
Feuerbacher, A; Schall, P; Bresson, L;
Source:
SCRIPTA MATERIALIA, 49 (1): 25-31; 2003
Abstract:
An overview on the plastic deformation behaviour of decagonal Al-Ni-Co quasicrystals is presented. These materials possess a high structural anisotropy comprising periodic as well as quasiperiodic directions. We present results on the microstructural. and macroscopic deformation properties and give a discussion in terms of the salient structure. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
Mechanisms of plastic deformation of icosahedral quasicrystals
Authors:
Messerschmidt, U; Bartsch, M; Bresson, L;
Source:
SCRIPTA MATERIALIA, 49 (1): 33-39; 2003
Abstract:
Icosahedral quasicrystals deform plastically by dislocation motion. The deformation behaviour can be modelled by simple equations of dislocation mobility, the damage of the quasicrystal structure and the kinetics of dislocation evolution, but fundamental questions are still discussed, like the mode of dislocation motion (glide or climb) and the role of phason defects. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
On the yield point of icosahedral AlCuFe quasicrystals
Authors:
Texier, M; Bonneville, J; Proult, A; Rabier, J; Baluc, N; Guyot, P; Wiersma, DS;
Source:
SCRIPTA MATERIALIA, 49 (1): 41-46; 2003
Abstract:
Transient creep (1) tests have been performed at the yield point of icosahedral AlCuFe poly-quasicrystalline specimens in order to investigate the actual causes of this phenomenon. The experimental results strongly suggest that the yield point occurrence is essentially related to the lack of dislocation mobility and that a competition does exist between dislocation velocity and short range recovery. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
On the cubic W phase and its relationship to the icosahedral phase in Mg-Zn-Y alloys
Authors:
Singh, A; Tsai, AP; Proult, A;
Source:
SCRIPTA MATERIALIA, 49 (2): 143-148; 2003
Abstract:
Crystallographic relationship is determined between cubic W-Mg2Zn3Y3 and icosahedral phase in Mg-Zn-Y alloys. The W phase coexists with three <111> axes along three of icosahedral twofold axes, and three <110> axes along fivefold axes. The orientation relationship implies that this cubic phase is not an approximant to the icosahedral phase. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
Phase transformation and mechanical properties of Zr-base bulk glass-forming alloys
Authors:
He, G; Loser, W; Eckert, J; Schultz, L; Baluc, N;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 352 (1-2): 179-185; 2003
Abstract:
Zr60Ti5Cu15Ni10Al10 and Zr57Ti4.75CU14.15Ni9.5Al9.5Ta5 glass-forming alloys are investigated regarding their phase formation, as-cast microstructure, thermal stability and transformation behavior, mechanical properties and fracture features. Zr60Ti5Cu15Ni10Al10 exhibits a glass transition temperature 7, of 635 K and a supercooled liquid region AT, of 64 K. The melt-spun glassy phase presents a two stage phase transformation sequence corresponding to glass-to-quasicrystal transformation at about 699 K and quasicrvstal-to-Zr2Cu + Zr4Al3 + Zr2Ni (tetragonal) transformation at about 753 K. With addition of 5 at.% Ta, T-g increases to 663 K and AT, is reduced to 52 K. The melt-spun glassy ribbons primarily precipitates cubic-Zr2Ni upon heating to about 715-755 K. The residual glassy phase transforms into Zr3Al and Zr2Ni (tetragonal) at about 798-873 K. As-cast Zr60Ti5Cu15Ni10Al10 3 mm diameter cylinders exhibit an ultimate compression stress sigma(f) of 1752 MPa and Young's modulus E of 100 GPa. The 5 at.% Ta addition leads to a reduction of of to 1534 MPa. None of the alloys exhibits yielding behavior or plastic deformation. Rock-layers and deformation bands are found on the fracture surface for Zr60Ti5Cu15Ni10Al10. A honeycomb-like morphology and deformation bands are also exhibited on the fracture surface of Zr57Ti4.75Cu14.25Ni9.5Al9.5Ta5. The remelting phenomenon observed for both alloys is attributed to the high strength, large elastic energy and low melting temperature of the alloys. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Melting behaviour of lead and bismuth nano-particles in quasicrystalline matrix - The role of interfaces
Authors:
Singh, A; Tsai, AP; Matalon, M;
Source:
SADHANA-ACADEMY PROCEEDINGS IN ENGINEERING SCIENCES, 28 (2): 63-80; 2003
Abstract:
Nanomaterials are playing an increasingly important role in modern technologies. Interfaces are crucial in nanotechnology. In this study, we have examined the stability of nanoparticles. Major emphasis is on understanding the effect of interfaces on melting. Melting behaviour of nanocrystalline interfaces, created by embedding lead and bismuth nanoparticles in quasicrystalline matrices, was studied. Sharply faceted and coherent interfaces can be related to sharper melting transitions, while irregularly shaped and incoherent interfaces can be directly correlated with lowering of melting temperatures. It is shown here that solid lead forms a high energy interface with phason strain-free quasicrystal (resulting in a lowering of the melting temperature) while bismuth forms a low energy interface with the quasicrystal (resulting in superheating, unusual for bismuth).
Title:
Microstructures and tensile properties of Mg-Zn-Y alloys containing quasicrystals
Authors:
Taniuchi, H; Watanabe, H; Okumura, H; Kamado, S; Kojima, Y; Kawamura, Y; Wiersma, DS;
Source:
MAGNESIUM ALLOYS 2003, PTS 1 AND 2, 419-4 (2): 255-260; 2003
Abstract:
An attempt has been made to obtain high tensile strength and ductility by grain refinement and the homogeneous dispersion of quasicrystals and intermetallic compounds through plastic forming of Mg-Zn-Y alloys. The alloys were hot rolled at 5 % per pass for a total reduction ratio of 80 %. Though cracks are observed around intermetallic compounds in hot rolled specimens, the specimens exhibit increased ultimate tensile strength, proof stress and elongation at room temperature compared to as-cast specimens. To prevent the occurrence of these cracks, the specimens were subjected to homogenization treatment at a higher temperature of 400 degreesC in order to dissolve the compounds that generate cracks during hot rolling. This makes it possible to carry out hot rolling at a high specimen temperature of 400 degreesC without cracking around the compounds. As a result, the elongation increases remarkably compared to the specimen that was hot rolled at 315 degreesC. However, the tensile strength is not significantly affected due to higher hot rolling temperature.
Title:
Polarized transmission intensity studies of off-zone-center incommensurate semiconductors-ferroelectrics TlMeX2
Authors:
Mamedov, N; Shim, Y; Yamamoto, N; Park, YK;
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 41 (11B): 7254-7259; 2002
Abstract:
Temperature dependent polarized transmission intensity studies in strongly converging and parallel light beams had been accomplished for off-zone-center incommensurate semiconductors-ferroelectrics TlInS2, TlGaSe2 and TlGaS2 having a layered structure and reportedly a C-2h(6) space group, of symmetry at room temperature. All above materials were biaxial. TlInS2, as compared to TlGaS2 and TlGaSe2, displayed a stronger wavelength dispersion of the normal-to-layer-plane optical anisotropy due to the strong polarization of the excitonic transitions near the absorption edge. Temperature dispersion of the dielectric axes of TlInS2 and TlGaSe2 Was shown to include forbidden rotation that might be associated with a lower than monoclinic symmetry or spatially dispersed microscopic domains., Macroscopic, spatially ordered domain structure was found in TlGaS2, for which, however, above-like rotation was not observed. Unusual effect with temperature behavior encountered in soliton-like incommensurate phases was observed for TlInS2. The optical anisotropy of the incommensurate phase was estimated at similar to10(-3) with the background value of similar to10(-4) for basic lattice.
Title:
Deformation of decagonal Al-Cu-Co single quasicrystals
Authors:
Bogdanowicz, W; Shim, Y;
Source:
CRYSTAL RESEARCH AND TECHNOLOGY, 38 (3-5): 307-312; 2003
Abstract:
Deformation process of decagonal single quasicrystals of Al-Cu-Co alloy was studied by X-ray topography and optical microscopy. The deformation was performed at elevated temperature (550degreesC) not higher than the temperature of disordering transformation of clusters inside anti-phase domains (600degreesC). It was found that at a deformation of about 3-5% glide occurs only in the direction of ten-fold symmetry axis in which the boundaries of anti-phase domains are arranged. At a deformation of about 7-9% the samples cracked.
Title:
Electron crystallography of aluminum alloy phases
Authors:
Gjonnes, J; Hansen, V; Andersen, SJ; Marioara, CD; Li, XZ; Lee, WM;
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 218 (4): 293-307; 2003
Abstract:
A series of structure analyses during 19942001 by electron crystallographic techniques applied to phases in aluminum alloys are reviewed. Methods for structure solution employ electron diffraction intensity data collected by the precession technique, by selected area micro-diffraction and by the convergent-beam technique. High-resolution electron microscope images (HRTEM) are treated by a different kind of processing, including exit wave reconstruction. Crystallographic calculations are performed either by direct method or Patterson and Fourier procedures, assuming kinematical scattering, or by refinement from models derived from HRTEM images. Dynamical scattering calculations can be introduced in the refinement stage or as a correction procedure applied to part of the intensity data. The phases studied include primary Al-Fe-(Si) particles, Al-Mn-Si dispersoids, Al-Co quasicrystals and two types of precipitate phases in age-hardening Al-Mg-Si and Al-Zn-Mg alloys.
Title:
Visual computing in electron crystallography
Authors:
Wan, ZH; Liu, YD; Fu, ZQ; Li, Y; Cheng, TZ; Li, FH; Fan, HF; Smit, B;
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 218 (4): 308-315; 2003
Abstract:
VEC is a program package for Visual computing in Electron Crystallography. The program is written mainly in C++ and Fortran and is for running under MS Windows 95, 98, NT and 2000. Apart from its user-friendly interface, sophisticated text-sensitive online helps and tutorials, VEC includes some unique crystallographic methods. They are direct-method image-processing techniques, ab-initio solution of incommensurate crystal structures and algorithms for searching one-dimensionally modulated atoms in 4-dimensional Fourier maps.
Title:
Investigation of X-ray diffuse scattering in theta-(BEDT-TTF)(2)RbM '(SCN)(4)
Authors:
Watanabe, M; Noda, Y; Nogami, Y; Mori, H; Cheng, TZ;
Source:
SYNTHETIC METALS, 135 (1-3): 665-666; 2003
Abstract:
The modulated structure of theta-(BEDT-TTF)(2)RbM'(SCN)(4); (M'=Zn, Co) were investigated by X-ray diffraction method. theta-(BEDTTTF)(2)RbM'(SCN)(4) are two-dimensional organic conductors which exhibit metal-insulator transition at 210 K. The insulating phase is known as a charge ordered state. Above T-MI = 210 K, diffuse rod of q=(1/3 k 1/4) was found. Below T-MI, there are some differences depending on the sample cooling speed. In the slow-cooled-state (0.2 K/min), the diffuse rod of q=(1/3 k 1/4) disappears and is replaced by superlattice of c*/2. In the rapid-cooled-state (5-6 K/min), the structural phase transition at T-MI becomes imperfect. The diffuse rod of q remains below T-MI and the lattice modulation of c*/2 is disordered in the direction of inter-conducting-layer.
Title:
A general structure model for Bi-Se phases using a superspace formalism
Authors:
Lind, H; Lidin, S; Nogami, Y;
Source:
SOLID STATE SCIENCES, 5 (1): 47-57; 2003
Abstract:
Solid-state synthesis in the Bi-Se system produced both commensurate and incommensurate phases of compositions ranging from Bi2Se3 to Bi4Se3, all crystallising in rhombohedral or trigonal layer structures. The a parameters are very similar for all phases but the c parameters vary irregularly between 10 and 100 Angstrom. A general model for all these phases was developed, using single crystal X-ray diffraction and a four-dimensional superspace formalism. The 4D superspace group is P: R (3) over bar :m (1) over bar1, with approximate cell parameters of a approximate to 4.2 Angstrom and c approximate to 5.7 Angstrom valid for all phases. The q vector value in this model, ranging from 1.70[001]* to 1.80[001]1* is the only parameter that varies with the composition. Two different modelling options were developed for the structures. One of them was a single-atom refinement model consisting of harmonic modulation waves and the other was a two-atom model based on a displacive sawtooth modulation of the Se atom. Both models converged to low R-values (R-all < 0.07) and small residual electron density values for all phases. The q vector may be physically interpreted as arising from the average distance between homoatomic layers in the structures. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.
Title:
(3+1)D superspace structural determination of two new modulated composite phases: Sr1+x(CuxMn1-x)O-3; x=3/11 and x=0.3244
Authors:
El Abed, A; Gaudin, E; zur Loye, HC; Darriet, J; Cheng, TZ;
Source:
SOLID STATE SCIENCES, 5 (1): 59-71; 2003
Abstract:
We report the structure determination of two new phases belonging to the A(1+x)(A'x B1-x)O-3 family of oxides with A = Sr, A' = Cu, and B = Mn, where x = 3/11 and x = 0.3244, corresponding to a commensurate and incommensurate composite structure, respectively. These two compounds are the first examples of oxides belonging to the Sr1+x(CuxMn1-x)O-3 family. Their structures were solved in the (3 + 1) dimensional superspace formalism as modulated composite structure's with two subsystems [(Cu,Mn)03] and [Sr]. The superspace group used to solve the structures is R (3) over barm(00gamma)0s. The first phase (x = 3/11), corresponding to the chemical formula Sr14Cu3Mn8O33, was obtained as a single crystal with unit cell parameters of a = 9.6025(3) Angstrom and c(1) = 2.5660(8) Angstrom (q = 7/11c(1)*, Z = 3), where c(1) is the lattice parameter corresponding to the c-axis of the trigonal subsystem [(Cu,Mn)O-3]. The second phase (x = 0.3244(1)), is a polycrystalline sample with unit cell parameters of a = 9.5933(7) and c(1) = 2,5933(3) (q = 0.6622c(1)*, Z = 3). In both structures, one dimensional chains run along the c-axis which, contain octahedra and trigonal prisms occupied by manganese and copper atoms, respectively. The refinement results show that in both cases copper occupies the rectangular faces of the trigonal prism while manganese occupies the octahedral sites. The magnetic measurements of the polycrystalline phase (Sr1+x(CuxMn1-x)O-3, x = 0.3244(2)) and the Curie constant obtained from the high temperature susceptibility are in agreement with a spin state configuration of S = 3/2 for Mn4+ and S = 1/2 for Cu2+. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.
Title:
The commensurately modulated structure of K2TeOF4
Authors:
Kessler, U; Friese, K; Paulmann, C; Jansen, M; Cheng, TZ;
Source:
SOLID STATE SCIENCES, 5 (1): 249-255; 2003
Abstract:
K2TeOF4 was prepared by solid state reaction of stoichiometric amounts of KF, TeO2 and KTeF5. Single crystal investigations were performed using combined data from a conventional X-ray source and synchrotron radiation data. The compound can be described as a commensurately modulated structure, superspace group Xmcm(alpha00)00s with X = (1/2, 1/2, 0, 1/2). Lattice parameters for the basic structure are a = 6.3002(6) Angstrom, b = 13.9886(14) Angstrom, c = 6.5170(6) Angstrom, the q vector is given by q = 1/6a* Angstrom(-1). A comparison with the closely related Cs2TeOF4 shows a stronger distortion of the TeOF42- anions and a change in the. coordination sphere of the monovalent cations in K2TeOF4. Calculated bond valence sums for the average structure of K2TeOF4 show 'under-' and 'overbonding' for the cations; they are significantly improved when one takes into account the modulation of the atoms. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.
Title:
Differences in quasicrystals of smectite-cationic surfactant complexes due to head group structure
Authors:
Imai, Y; Nishimura, S; Inukai, Y; Tateyama, H; Eyubova, NA;
Source:
CLAYS AND CLAY MINERALS, 51 (2): 162-167; 2003
Abstract:
The organoclay quasicrystals formed by exchange reactions of fluoromagnesian smectite (FMS) and two kinds of cationic surfactants were investigated by X-ray diffraction (XRD) of both aqueous suspensions and dried powders. potential measurements were also carried out. The two cationic surfactants employed in this study, dodecyltriphenylphosphonium bromide (C12PBr) and dodecyltrimethylammonium bromide (C12NBr), have the same alkyl chain length but different head group structures. In aqueous suspensions Of C12N/FMS, regular stacking with a basal spacing of 2.28 nm was observed within the range 0.4 to 1.0 of the cation exchange capacity (CEC) of the C12N/FMS ratios. The basal spacing was constant in this range. The most intense diffraction for the C12N/FMS suspension was observed at 0.6 CEC, and a further increase in the C12N/FMS ratio resulted in a decline of the diffraction intensity and a slight increase in the peak width. On the other hand, in C12P/FMS suspensions with the surfactant/FMS ratios <0.6 CEC, only weak, broad XRD peaks were observed. With higher C12P/FMS ratios (0.8 and 1.0 CEC), strong diffraction peaks appeared with a basal spacing of 3.20 nm. The difference in the observed basal spacings of C12N/FMS and C12P/FMS tactoids was &SIM;0.9 nm, which did not agree with the difference in the estimated height of the two surfactants (&SIM;0.1 nm). These differences of the tactoid structures between C12N/FMS and C12P/FMS suspensions could be explained in terms of the difference in the adsorption manner of the surfactants on the silicate surface and in the size of the surfactant head groups.
Title:
Frictional characteristics of quasicrystals at high temperatures
Authors:
Phillips, BS; Zabinski, JS; Inukai, Y;
Source:
TRIBOLOGY LETTERS, 15 (1): 57-64; 2003
Abstract:
AlCuFe quasicrystal coatings were deposited by unbalanced magnetron sputtering for study of their friction and wear properties at high temperatures. It has been shown that growth and annealing conditions can be controlled to produce icosahedral quasicrystal or the approximant cubic phase. The comparison of friction and wear properties between quasicrystal and an approximant with nearly the same stoichiometry permits assessment of the unique quasicrystalline structure for tribological applications. The goals of this study are to determine how crystal structure influences tribological properties and to study the general friction and wear behavior of quasicrystals. Tribological properties were evaluated using a pin-on-disk tribometer and crystal structure was characterized using an X-ray diffractometer. The tests specimens were 10 mum thick films deposited on a 1" diameter steel disk and a 1/4" diameter steel ball. Data was collected over a range of temperatures from room to 600 degreesC. Friction coefficients and wear rates of quasicrystals and approximants were nearly identical for room temperature tests. The wear process generated Al, Cu, Fe, and oxide debris on the side of the track, but overall wear was mild. The friction coefficient of the icosahedral phase was 25% lower than the cubic phase at 150 thru 450 degreesC. Generally, only moderate differences in the friction and wear properties were observed between the icosahedral quasicrystal phase and the cubic phase.
Title:
Structural modulation induced by the incommensurate antiferromagnetic phase transition in ZnCr2Se4
Authors:
Hidaka, M; Yoshimura, M; Tokiwa, N; Akimitsu, J; Park, YJ; Park, JH; Ji, SD; Lee, KB; Le Lay, G;
Source:
PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 236 (3): 570-577; 2003
Abstract:
The structural properties of normal-type spinel ZnCr2Se4 have been studied as a function of temperature by means of X-ray diffraction using synchrotron radiation. It is found that a structural phase transition from cubic to orthorhombic symmetry occurs at 22.5 K (T-c). It is also found that, below T-c, Se ions are cooperatively displaced in a pseudo-tetragonal (001) plane. Since the Cr3+ ion has no orbital angular momentum, a CrSe6 octahedron is not distorted by a crystal field produced by surrounding Se2- anions. It is interpreted that the pseudo-tetragonal displacements of Se ions are induced by magnetostriction among Cr3+ ions in CrSe2 chains, in which Cr ions share two Se2- with each other along <110>.
Title:
Polyhedral, and chemical orders in icosahedral Al-Pd-Mn quasicrystals
Authors:
Loreto, L; Farinato, R; Catallo, S; Janot, C; Gerbasi, G; De Angelis, G; Ji, SD;
Source:
PHYSICA B-CONDENSED MATTER, 328 (3-4): 193-203; 2003
Abstract:
Diffraction data and quasicrystallography provide average quasiperiodic structures for real quasicrystals. In the present paper it is reported a detailed analysis of one of these quasiperiodic structures, with the emphasis on complementarity of Mackay- and Bergman-like polyhedra as well as on chemical order aspects. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Preparation of Al-Cu-Fe ultra-thin quasicrystalline films without protective coatings by MBE: influence of processing
Authors:
Bonasso, N; Pigeat, P; Catallo, S;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 349 (1-2): 224-229; 2003
Abstract:
This study presents a process for making ultra thin films of icosahedral Al-Cu-Fe alloy with a free surface. Three independent evaporation guns were chosen for each of the three elements and were operated under ultra-high vacuum. Thick films (100 nm) made by the classical successive deposition method followed by annealing yield a significant roughness. Thus, it is impossible to study the physico-chemical and optical properties of the surface of this type of deposit. This study shows that the simultaneous deposition of the three elements results in homogeneous quasicrystalline deposits with a roughness ten times lower than with the successive deposition method. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Picosecond and femtosecond pulsed laser ablation and deposition of quasicrystals
Authors:
Teghil, R; D'Alessio, L; Santagata, A; Zaccagnino, M; Ferro, D; Sordelet, DJ; Ji, SD;
Source:
APPLIED SURFACE SCIENCE, 210 (3-4): 307-317; 2003
Abstract:
A Nd:glass laser with pulse duration of 250 fs and 1.3 ps has been used to evaporate a Al65Cu23Fe12 quasicrystalline target. The gaseous phase obtained from the ablation process has been characterised by several techniques such as emission spectroscopy, quadrupole mass spectrometry and ICCD imaging, used to study the plume composition, energy and morphology. The results show that the ablation processes in the short-pulse regimes are very different to the nanosecond one. In particular the plume angular distribution shows a characteristic high cosine exponent and the composition is completely stoichiometric and independent from the laser fluence. Furthermore the mass spectra indicate the presence of clusters, both neutral and ionised and the emission from the target suggest a rapid thermalisation leading to the melting of the surface. To clarify the ablation process some films have been deposited, on oriented silicon, at different experimental conditions and analysed by scanning electron microscopy, atomic force microscopy, energy dispersive X-ray analysis and X-ray diffraction. The analyses show the presence of nanostructured films retaining the target stoichiometry but consisting of different crystalline and non crystalline phases. In particular the nanostructure supports the hypothesis of the melting of the target during the ablation and a mechanism of material ejection is proposed for both picosecond and femtosecond regimes. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Retrieving modulation parameters from HRTEM images of modulated structures
Authors:
Hoche, T; Neumann, W; Santagata, A;
Source:
ULTRAMICROSCOPY, 96 (2): 181-190; 2003
Abstract:
Quantitative high-resolution transmission electron microscopy (qHRTEM) is methodologically extended towards the assessment of occupationally and positionally modulated structures. For this purpose, iterative digital image matching has been combined with data processing within the Rietveld refinement code JANA2000. In this approach, the number of free parameters is kept low and rather complicated modulated structures become assessable by qHRTEM. The feasibility of the improved methodology is demonstrated for the 1D modulated structure of Ba2TiGe2O8. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Phenomenological theory of new multiple spin density waves in fcc transition metals
Authors:
Uchida, T; Kakehashi, Y; Santagata, A;
Source:
PHYSICA STATUS SOLIDI A-APPLIED RESEARCH, 196 (1): 193-196; 2003
Abstract:
The relative stability among the helical and the multiple spin density wave states in fcc transition metals is investigated on the basis of the Ginzburg-Landau free energy. Taking into account the terms up to the fourth order in magnetic moments, we have obtained the magnetic phase diagram in the space of the Landau parameters. Our diagram shows up that the phase change NM --> AF --> 3-(Q) over cap --> 3-Q with increasing volume is possible, in addition to the change NM --> AF --> Helical. Here NM, AF, 3-Q, and 3-(Q) over cap denote the nonmagnetic, the first-kind antiferromagnetic, the incommensurate 3-Q, and the commensurate 3-(Q) over cap with (Q) over cap = 2pi/a (where a denotes the lattice constant) states, respectively. The result is consistent with the prediction of the recent molecular-dynamics and the first-principles band structure calculations of gamma-Fe.
Title:
Observation of spin modulated magnetic structure at Bi- and Fe-sites in BiFeO3 by nuclear magnetic resonance
Authors:
Gippius, AA; Khozeev, DF; Morozova, EN; Zalessky, AV; Ferro, D;
Source:
PHYSICA STATUS SOLIDI A-APPLIED RESEARCH, 196 (1): 221-224; 2003
Abstract:
NMR spectra were measured in Fe-57 enriched ferroelectric-antiferromagnet BiFeO3 with space modulated magnetic structure of cycloidal type, which has large period lambda = 620 +/- 20 Angstrom incommensurate with the lattice parameter. This structure leads to space modulation of local field on Fe-57 nuclei as well as space periodic spin-spin relaxation and specific NMR line shape with frequency variable local width. Space modulated magnetic structure induces also an appearence of hyperfine magnetic field H-hf of 11-12 T at Bi position which has been observed by zero-field Bi-209 NMR. Complicated Bi-209 spectrum consists of various lines with asymmetric line shape. It was simulated assuming that Hhf rotates in space following cycloidal magnetic structure with the same period as at Fe-site and anharmonic parameter 0.95.
Title:
Mechanical properties of decagonal quasicrystal formed from undercooled Al72Ni12Co16 alloy
Authors:
Liu, XB; Yang, GC; Fan, P; Sajko, DS;
Source:
JOURNAL OF MATERIALS SCIENCE LETTERS, 22 (8): 611-613; 2003
Abstract:
A classification of grain boundaries for arbitrary misorientations of contacting crystals and orientations of boundary planes is considered using the notions of incommensurate systems. The geometrical representations of linear (dislocations, steps) and point (vacancies and interstitials) defects on grain and interphase boundaries of a general type are developed. The representations of thermal excitations of grain boundaries are proposed. Various kinetic processes in grain boundaries of a general type, such as atomic structural relaxation and emission of vacancies are carefully considered. This allowed us to derive analytical expressions for the characteristics of grain boundary sliding and for the low-temperature and the high-temperature grain boundary internal friction peaks.
Title:
High-pressure structural trends of group 15 elements: Simple packed structures versus complex host-guest arrangements
Authors:
Haussermann, U; Cao, G;
Source:
CHEMISTRY-A EUROPEAN JOURNAL, 9 (7): 1472-1478; 2003
Abstract:
The Group 15 elements P, As, Sb, and Bi all have layered structures consisting of six-membered rings under ambient conditions and attain the body-centered cubic (bcc) structure at the highest pressures applied. In the intermediate pressure region, however, phosphorus and its heavier congeners behave profoundly differently. In this region P first attains the open packed simple cubic (sc) structure for a wide range of pressures and then transforms into the rarely observed simple hexagonal (sh) structure. For the heavier congeners complex, incommensurately modulated host-guest structures emerge as intermediate pressure structures. We investigated the high-pressure behavior of P and As by ab initio density functional calculations in which pseudopotentials and a plane wave basis set were employed. The incommensurately modulated high-pressure structure of As was approximated by a supercell. Our calculations reproduced the experimentally established pressure stability ranges of the sc and sh structures for P and the host-guest structure for As very well. We found that the sc and especially the sh structure are decisively stabilized by the admixture of d states in the occupied levels of the electronic structure. This admixture releases s-s antibonding states above the Fermi level (s-d mixing). With pressure, s - d mixing increases rapidly for P, whereas it remains at a low level for As. As a consequence, the band energy contribution to the total energy determines the structural stability for P in the intermediate pressure region, giving rise to simple packed structures. On the other hand, in the intermediate pressure region of the heavier Group 15 elements, a delicate interplay between the electrostatic Madelung energy and the band energy leads to the formation of complex structures.
Title:
'Weird' crystal structures of elements at high pressure
Authors:
Kolobyanina, TN; Rosov, NK;
Source:
PHYSICS-USPEKHI, 45 (12): 1203-1211; 2002
Abstract:
New crystal structures, in particular incommensurate composite crystals, discovered in the high-pressure phases of Group I, II, IV, and V elements are described, and their intermetallic and other binary structural analogs are discussed.
Title:
H-1 NMR in spin density wave phase of (TMTSF)(2)PF6
Authors:
Nomura, K; Kubota, H; Kotomizu, M; Hanajiri, T; Nakatsuji, S; Yamada, J; Ji, SD;
Source:
SYNTHETIC METALS, 133 (2): 19-21; 2003
Abstract:
We have investigated the multi-phase structure in the incommensurate spin density wave (SDW) phase in (TMTSF)(2)PF6 with H-1 NMR measurement. The temperature dependence of spin lattice relaxation rate T-1(-1) was measured at ambient pressure with varying the magnetic field up to 2.0 T. The divergent peak of T-1(-1) was observed at the temperature T* well below the SDW transition temperature T-SDW in each field. The peak height decreases with increasing the magnetic field, suggesting the divergent increase of low frequency fluctuation of local field at T*. These behaviors indicate that the phase transition with the magnetic fluctuation, which divides the incommensurate SDW phase into two. sub-phases, occurs at T*. With increasing the magnetic field, the peak temperature T* increases from 3 K at 0.3 T to 3.7 K at 1.2 T and shows a saturation behavior above 1.2 T. This indicates that the low temperature SDW sub-phase is stabilized more under the magnetic field around 1 T. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Study of C-I-CCDW phase transition in TTF-TCNQ with STM
Authors:
Wang, ZZ; Girard, JC; Pasquier, C; Jerome, D; Nakatsuji, S;
Source:
SYNTHETIC METALS, 133 (2): 23-26; 2003
Abstract:
TTF-TCNQ is a one-dimensional charge transfer compound. Charge density wave (CDW) transition occurs at 54 K in TTF-TCNQ, and CDW presents three phases: high temperature commensurate phase (T > 49 K; 2a x 3.39b); inter-mediated incommensurate phase (T = 38-49 K; mua x 3.39b) and low temperature commensurate phase (T < 38 K; 4a x 3.39b). In this report, we present our experimental result on cleaved (0 0 1) surfaces of TTF-TCNQ with UHV-LT-STM (Omicron LTSTM). For a broad temperature range (33-100 K), molecular resolution of TTF-TCNQ has been obtained. Below 54 K an additional two-dimensional superstructure of CDW appears in our images. The ordering of CDW modulation both along a and b direction are first revealed by our STM measurement. Our result shows that, on (0 0 1) surface of TTF-TCNQ, C-I-C CDW phase transition persists in nanometer scale and C-I-C transition is homogeneous. The determination of local CDW phase shift will be presented in this report too. At high temperature (60-280 K), we observed a v-shape pseudogap. The pseudo-gap and Peierls-gap co-exist at low temperature. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Commensurate-incommensurate transition in a one-dimensional dimerized electron system close to quarter-filling
Authors:
Yoshioka, H; Tsuchiizu, M; Suzumura, Y; Jerome, D;
Source:
SYNTHETIC METALS, 133 (2): 49-50; 2003
Abstract:
We investigate electronic states upon doping (i.e., by varying the chemical potential) for a quarter-filled one-dimensional electron system with a dimerization, on-site and nearest-neighbor repulsive interaction. By applying the renormalization group method to the bosonized Hamiltonian, the metal-insulator transition followed by commensurate-incommensurate transition is obtained for Mott insulating region as well as charge ordered insulating regime. We discuss the phase diagram on the plane of the chemical potential and the interaction. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Magnetic field dependence of incommensurate SDW transition in (TMTTF)(2)Br
Authors:
Ishikawa, A; Matsunaga, N; Nomura, K; Nakamura, T; Takahashi, T; Saito, G; Ji, SD;
Source:
SYNTHETIC METALS, 133 (2): 65-66; 2003
Abstract:
Resistivity measurements were performed on (TMTTF)(2)Br under pressure. Magnetic field was applied along c*-axis up to 16 T. Above 0.5 GPa, (TMTTF)(2)Br exhibits incommensurate spin density wave (ISDW) transition at low temperature. With increasing pressure, spin density wave (SDW) transition temperature T-SDW decreases from 19.5 K at 0.5 GPa to 12.5 K at 2.1 GPa. In the incommensurate SDW phase, with increasing magnetic field, T-SDW increases quadratically and the coefficient of quadratic term increases with increasing pressure. These results are qualitatively consistent with the prediction of the mean-field theory based on the imperfection of the nesting of Fermi surface. The relation between the coefficient of the quadratic term and T-SDW at zero magnetic field can be explained by the mean-field theory with taking into account the reduction of the coupling constant N(0)I by pressure. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Self-doping effect on the Mott transition accompanied with threefold charge ordering in (DCNQI)(2)Cu
Authors:
Kuwabara, M; Yonemitsu, K; Ohta, H; Nakamura, T;
Source:
SYNTHETIC METALS, 133 (2): 295-297; 2003
Abstract:
The commensurate state with threefold lattice distortion in the insulating phase of (DCNQI)(2)Cu is studied based on a two-band Peierls-Hubbard model by using the density-matrix renormalization-group method. With strong electron correlation among the d electrons, self-consistent lattice modulation strongly blocks the charge transfer between the pi and d orbitals in order to keep the commensurability condition even when the pi-d level difference is widely varied. A transition to an incommensurate phase requires a large deviation of the pi-d level difference from the optimal case. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
EXAFS study of the Fe local environment in icosahedral AlCuFe and its relation to magnetism of quasicrystals (vol 123, pg 527, 2002)
Authors:
Gomilsek, JP; Arcon, I; Kodre, A; Dolinsek, J; Takahashi, T;
Source:
SOLID STATE COMMUNICATIONS, 126 (3): 167-167; 2003
Abstract:
The commensurate state with threefold lattice distortion in the insulating phase of (DCNQI)(2)Cu is studied based on a two-band Peierls-Hubbard model by using the density-matrix renormalization-group method. With strong electron correlation among the d electrons, self-consistent lattice modulation strongly blocks the charge transfer between the pi and d orbitals in order to keep the commensurability condition even when the pi-d level difference is widely varied. A transition to an incommensurate phase requires a large deviation of the pi-d level difference from the optimal case. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Change in primary phase from icosahedral quasicrystal to fcc Zr2Ni by mechanical disordering in Zr-Al-Ni-Cu-Pd glassy alloy
Authors:
Saida, J; El-Eskandarany, MS; Inoue, A; Dolinsek, J;
Source:
SCRIPTA MATERIALIA, 48 (9): 1397-1401; 2003
Abstract:
Change in the primary crystallization from a single icosahedral quasicrystalline phase into the fcc Zr2Ni phase by mechanical disordering was investigated in a melt-spun Zr65Al7.5Ni10Cu12.5Pd5 glassy alloy. The transition of the primary phase is attributed to the mechanical strain induced in the icosahedral local structure in the glassy state. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
Stroboscopic neutron diffraction from spatially modulated systems
Authors:
Eckold, G; Gibhardt, H; Caspary, D; Elter, P; Elisbihani, K; Saito, G;
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 218 (2): 144-153; 2003
Abstract:
The combination of stroboscopic techniques and neutron diffraction can be used to study the kinetics of structural changes in condensed matter on a microscopic level. Transient states may be identified and characterized on time-scales down to the microsecond regime. Hence, valuable information about the underlying mechanisms can be obtained from time-resolved experiments. Particularly interesting subjects for this type of investigation are spatially modulated systems which undergo phase transitions or phase separation. The potential of stroboscopic neutron diffraction is demonstrated using three different examples in which samples are periodically perturbed by the variation of temperature, mechanical stress or electric field and their structural response is characterized by time-resolved diffraction. Spinodal decomposition in ionic crystals of the silver-alkali halide type is shown to be dominated by two different processes on different time-scales. The stress-induced phase transition into the incommensurate phase of quartz involves relaxation processes which are reflected by different kinetic behaviours of Bragg peaks and satellite reflections, respectively. Finally, metastable transient states are observed during the field induced lock-in transition in ferroelectric Rb2ZnCl4 which are most probably due to strain fields and pinning effects.
Title:
Disorder in decagonal quasicrystals
Authors:
Frey, F; Weidner, E; Caspary, D;
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 218 (2): 160-169; 2003
Abstract:
Complementary neutron and x-ray diffuse scattering may provide insight into structural super-ordering and disordering of decagonal quasicrystals (d-phases), and, in consequence, into the formation and stability of aperiodically ordered alloys. Neutron diffraction makes a contrasting almost isoelectronic atomic species possible, as well as a separation of elastic and inelastic diffuse intensity contributions. Experimental work at high temperatures is comparatively unproblematic. The method suffers, however, from the difficulty in obtaining sufficiently sized mono-grain samples and a lack of dedicated neutron diffraction instruments. Recent results, with a main focus on high-temperature (<1000 degreesC) investigations of disordered decagonal Al-Ni-Co phases are reported and some tentative models are discussed.
Title:
Pentagonal and trigonal quasilattices and their approximants
Authors:
Subramaniam, A; Lord, EA; Caspary, D;
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 218 (3): 182-186; 2003
Abstract:
The Strip Projection Method is used to generate pentagonal and trigonal 2-dimensional quasilattices as rational approximants to the icosahedral quasilattice. Further, 3-dimensionally periodic structures are generated as rational approximants to these 2-dimensional quasilattices. A simplified approach based on uniform distortions of perpendicular space is put forth for the analyses.
Title:
The transport property and the quasigap in the quasicrystal-like system
Authors:
Kanazawa, I; Lord, EA;
Source:
PHYSICA B-CONDENSED MATTER, 328 (1-2): 111-113; 2003
Abstract:
We have considered the transport property and the origin of the quasigap in the randomly distributed system of the aggregation that corresponds to the correlated unit cell configurations, in which the nearest distance between each configuration is similar to2pi/2k(F). (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Structure and magnetism of the composite crystal Ca0.824CuO2
Authors:
Isobe, M; Kimoto, K; Takayama-Muromachi, E; Tajima, S;
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS, 131 (3-4): 737-741; 2003
Abstract:
We have studied the magnetic state from a viewpoint of crystallographic features of the 1-D chain compound Ca0.824CuO2. A possible spin-hole arrangement in the magnetically coexisting state was determined by analyzing the local structural distortion in the CuO2 chain by means of a modulated-crystal-structure analysis. The essential periodic sequence expected is...up arrowcircledown arrowdown arrowcircleup arrow... (up arrowdown arrow: up- and down-spin, circle: hole), which can be regarded as a kind of spin-1/2 ferromagnetic-antiferromagnetic alternating Heisenberg chain.
Title:
Neutron diffraction study of the magnetism in single- crystalline CeCu2(Si1-xGex)(2)
Authors:
Stockert, O; Deppe, M; Geibel, C; Steglich, F; Hohlwein, D; Schneider, R; Ji, SD;
Source:
ACTA PHYSICA POLONICA B, 34 (2): 963-966; 2003
Abstract:
We have studied single-crystalline CeCu2(Si1-xGex)(2) using neutron diffraction to determine the antiferromagnetic order in the regime with low Ge content, x less than or equal to 0.5. The system orders in an incommensurate magnetic structure with a propagation vector close, to tau = (0.25 0.25 0.5). Up to two additional phase transitions were observed below the Neel temperature characterized by a spin reorientation and a lock-in to a probably commensurate structure.
Title:
Search for novel order in URu2Si2 by neutron scattering
Authors:
Bull, MJ; Fak, B; McEwen, KA; Mydosh, JA; Hohlwein, D;
Source:
ACTA PHYSICA POLONICA B, 34 (2): 1265-1268; 2003
Abstract:
We have made extensive reciprocal space maps in the heavy-fermion superconductor URu2Si2 using high-resolution time-of-flight single-crystal neutron diffraction to search for signs of a hidden order parameter related to the 17.5 K phase transition. Within the present sensitivity of the experiment (0.007 mu(B)/U-ion for sharp peaks), no additional features such as incommensurate structures or short-range order have been found in the (hOl) or (hhl) scattering planes. The only additional low-temperature scattering observed was the well-known tiny antiferromagnetic moment of 0.03 mu(B)/U-ion.
Title:
Chiral fluctuations in MnSi above the Curie temperature measured with polarized inelastic neutron scattering
Authors:
Roessli, B; Boni, P; Fischer, WE; Endoh, Y; Hohlwein, D;
Source:
ACTA PHYSICA POLONICA B, 34 (2): 1557-1560; 2003
Abstract:
Using polarized inelastic neutron scattering the antisymmetric part of the dynamical susceptibility in non-centrosymmetric MnSi is determined. The paramagnetic fluctuations are found to be incommensurate with the chemical lattice and to have a chiral character. We show that antisymmetric interactions must be taken into account to properly describe the critical dynamics in MnSi above the Curie temperature. The inelastic neutron data is interpreted within the framework of the SCR-theory, taking into account the Dzyaloshinskii-Moriya interaction.
Title:
Theory of elementary excitations in quasiperiodic structures
Authors:
Albuquerque, EL; Cottam, MG; Fischer, WE;
Source:
PHYSICS REPORTS-REVIEW SECTION OF PHYSICS LETTERS, 376 (4-5): 225-337; 2003
Abstract:
The aim of this work is to present a comprehensive and up-to-date review of the main physical properties (such as energy profiles, localization, scale laws, multifractal analysis, transmission spectra, transmission fingerprints, electronic structures, magnetization curves and thermodynamic properties) of the elementary excitations that can propagate in multilayered structures with constituents arranged in a quasiperiodic fashion. These excitations include plasmon-polaritons, spin waves, light waves and electrons, among others. A complex fractal or multifractal profile of the energy spectra is the common feature among these excitations. The quasiperiodic property is formed by the incommensurate arrangement of periodic unit cells and can. be of the type referred to as deterministic (or controlled) disorder. The resulting excitations are characterized by the nature of their Fourier spectrum, which can be dense pure point (as for the Fibonacci sequence) or singular continuous (as for the Thue-Morse and double-period sequences). These sequences are described in terms of a series of generations that obey particular recursion relations, and they can be considered as intermediate systems between a periodic crystal and the random amorphous solids, thus defining a novel, description of disorder. A discussion is also included of some spectroscopic techniques used to probe the excitations, emphasizing Raman and Brillouin light scattering. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Magnetic and transport properties of Ho7Rh3
Authors:
Tsutaoka, T; Nishiume, Y; Tokunaga, T; Nakamori, Y; Andoh, Y; Kawano, S; Nakamoto, G; Kurisu, M; Le Lay, G;
Source:
PHYSICA B-CONDENSED MATTER, 327 (2-4): 352-356; 2003
Abstract:
Magnetic and transport properties of Ho7Rh3 Single crystals have been studied by measuring magnetization, magnetic susceptibility, electrical resistivity and by performing neutron-diffraction experiments. Ho7Rh3 has two magnetic transitions from paramagnetic to antiferromagnetic at T-N = 34K and from antiferromagnetic to ferrimagnetic at T-C = 22K. In the ferrimagnetic phase, a small spontaneous magnetization in the c-plane is observed. It is found by neutron-diffraction measurements that Ho7Rh3 has a modulated incommensurate helical magnetic structure with the propagation vector Q = (0, 0, 0.38) at 1.5 K. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Spark plasma sintering of Al-Si-Cu-Fe quasi-crystalline powder
Authors:
Fleury, E; Lee, JH; Kim, SH; Kim, WT; Kim, JS; Kim, DH; Nakamoto, G;
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 34A (3): 841-849; 2003
Abstract:
This article presents the results of a study on the microstructure and mechanical properties of Al-Si-Cu-Fe specimens produced by the spark plasma sintering (SPS) technique. The microstructure of the starting powder and bulk specimens was analyzed by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The formation of the icosahedral and decagonal quasi-crystalline phases in the as-gas-atomized powders is described for the first time. It is then shown that these metastable phases transformed into the 1/1 cubic-approximant phase upon heating at about 600 degreesC. Second, the effects of SPS process parameters such as the temperature and time have been investigated. Owing to the generation of a spark discharge between neighboring powder particles, dense cylindrical samples were obtained after a short sintering time of 30 minutes at the temperature of 650 degreesC. The highest values of the Vickers microhardness, about 8.9 GPa, were obtained when the powders were sintered in the temperature range of 600 degreesC to 650 degreesC for a holding time of 30 minutes, while the fracture toughness was found to be inversely proportional to the sintering temperature. However, at the sintering temperature of 650 degreesC, the fracture toughness increased from about 1.40 to 1.52 MPa rootm as the holding time increased from 10 to 60 minutes. As compared to cast specimens, the enhanced mechanical properties are explained by the refined microstructure resulting from the low temperature and short sintering time applied during SPS processing.
Title:
Molecular and electron-spin dynamics in [M(H2O)(6)][AB(6)] as studied by solid state NMR
Authors:
Iijima, T; Mizuno, M; Suhara, M; Endo, K; Pervov, VS;
Source:
BUNSEKI KAGAKU, 52 (3): 157-163; 2003
Abstract:
A method using the H-2-NMR spectra was shown to be useful to study the solid state physics in diamagnetic and paramagnetic compounds and in crystals having a modulated structure. The spectra and T-1 of NMR in solids were measured for [M(H2O)(6)] [AB(6)] crystals to investigate the static and dynamic structure of H2O and [M(H2O)(6)](2+) as well as the dynamics of the electron spin in the paramagnetic M2+ ion. The physical properties of [M(H2O)(6)] [AB(6)] were found to be as follows: (1) The spin-lattice relaxations of the electron spin of M2+ in [M(H2O)(6)] [SiF6] (M2+ = Fe2+, Co2+, Ni2+) are dominated by the Orbach process, the Orbach process, and the Raman process, respectively. The spin-lattice relaxation of the electron spin Of Cu2+ in [Cu (H2O)(6)] [PtCl6] is caused by jumping between the Jahn-Teller configurations. (2) In [Cu(H2O)(6)] [PtCl6], H2O and [Cu(H2O)(6)](2+) undergo 180degrees flips and jumping between the different Jahn-Teller configurations, respectively. A weakening of the hydrogen bond O-H...Cl upon deuteration results in a lowering of the transition temperature. (3) In [M(H2O)(6)] [SiF6], H2O and [M(H2O)(6)](2+) undergo 180degrees flips and reorientation about the C-3 axis, respectively. The order-disorder transition is closely related to a freezing of this reorientation. (4) By elongation of [M(H2O)(6)](2)+ along the C-3 axis, the mobility becomes higher. (5) The disorder of [Fe(H2O)(6)](2+) in the high-temperature phase of [Fe(H2O)(6)] [SiF6] is dynamic. Rotational modulation of [Mg(H2O)(6)](2+) along the C-3 axis exists in the incommensurate phase of [Mg(H2O)(6)] [SiF6].
Title:
Spectroscopic ellipsometric characterization of approximant thin films of Al-Cr-Fe
Authors:
Johann, L; Naciri, AE; Broch, L; Demange, V; Ghambaja, J; Machizaud, F; Dubois, JM; Kurisu, M;
Source:
APPLIED SURFACE SCIENCE, 207 (1-4): 300-305; 2003
Abstract:
The reflection spectroscopic ellipsometric study of optical properties of thin films of Al-Cr-Fe is presented. Glass substrates were used for the optical characterization of Al-Cr-Fe thin films. Polarizer, rotating polarizer spectroscopic ellipsometer (PRPSE) equipped with an achromatic quarter wave was used for thin films/glasses analysis. Al-Cr-Fe approximant thin films were deposited from the vapor phase on the glass substrates. The optical constants were determined at room temperature in the spectral range from 500 to 800 nm. The best glass/layer/Al2O3 model using for the regression procedure is validated by the transmittance technique. The refractive index and extinction coefficient vary with the wavelength from 3.8 to 5.3 and 4.3 to 3.5, respectively. Surface layer on the glass substrates was treated as a mixture of air and Al-Cr-Fe compound by using the Bruggeman effective medium approximation. The oxide thickness derived as an independent parameter in the best model is in agreement with the oxide thickness derived from X-ray photoelectron spectroscopy measurements. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Modulated structure formation in demixing paraffin blends
Authors:
Gilbert, EP; Naciri, AE;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1-4): S339-S341; 2002
Abstract:
Small angle scattering (SANS and SAXS) and differential scanning calorimetry have been measured from C-28 : C-36 normal paraffin mixtures of varying composition quenched from the melt. Satellite peaks are observed in the SAXS whose offset in Q, relative to Bragg diffraction peaks associated with the average structure, are composition dependent. The offset is close to the position of the most intense peak observed in SANS. Scattering from the quenched structures is consistent with a correlated displacement and substitutional disorder model yielding modulations that are incommensurate with the average lattice. DSC shows an additional endotherm in the mixtures that is not present in the pure components and is associated with this superstructure formation.
Title:
Effect of pressure on magnetic structure in heavy-fermion CeRhIn5
Authors:
Bao, W; Trevino, SF; Lynn, JW; Pagliuso, PG; Sarrao, JL; Thompson, JD; Fisk, Z; Kurisu, M;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1-4): S557-S558; 2002
Abstract:
The effect of hydrostatic pressure on the incommensurate antiferromagnetic structure of CeRhIn5 is investigated with neutron diffraction using a He pressure cell. At 3.8 kbar, the staggered magnetic moment is 0.37(4) mu(B) per Ce ion at 1.6 K, which is the same as the ambient-pressure value. The Neel temperature T-N = 3.8(l) K is also the same as the ambient-pressure one, although the curve of the order parameter has changed with pressure. The incommensurability delta of the magnetic wave vector q(M) = (1/2, 1/2, delta) has reduced from delta = 0.297 at ambient pressure to delta = 0.294(l) at 3.8 kbar.
Title:
Magnetic field induced phase transition in Ce2Fe17-xMnx compounds
Authors:
Teplykh, A; Pirogov, A; Kuchin, A; Prokhnenko, O; Ritter, C; Arnold, Z; Isnard, O; Kurisu, M;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1-4): S577-S579; 2002
Abstract:
The atomic and magnetic structures of Ce2Fe17-xMnx compounds with x = 0.5 and 1.0 were investigated using neutron diffraction under magnetic fields up to 5.0 T over the temperature range 2 - 300 K. The magnetic reflexes observed at temperatures 2 - 208 K and mu(0)H = 0T correspond to an incommensurate antiferromagnetic structure with wave vector [0, 0, 0 +/- tau] at 2 K. This structure is suppressed in an external magnetic field and a ferromagnetic phase is induced in fields higher than 0.6 T. The complex transformation of the magnetic structures under magnetic field and temperature is analyzed and discussed.
Title:
Magnetic order in CeI2
Authors:
Kramer, KW; Gudel, HU; Fischer, P; Keller, L; Ritter, C;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1-4): S595-S597; 2002
Abstract:
CeI2 is a halide with metallic conductivity according to the formula (Ce3+)(I-)(2)(e(-)). Magnetic interactions are mediated by the conduction electrons and are significantly stronger than for insulating rare-earth halides. CeI2 crystallizes in the MoSi2 layer-type structure with space group I4/mmm and lattice parameters a = 3.87212(5) Angstrom and c = 13.8646(2) Angstrom at 15 K. At T-N = 10.0(2) K, a phase transition to a 3D antiferromagnetically ordered state occurs with an incommensurate k vector of (0, 0.2761(l), 1) at 1.5 K. The k vector is temperature-dependent and, as the sublattice magnetization, reaches saturation below 4 K. CeI2 has one magnetic sublattice with moments parallel to the a axis. The amplitude is sine-modulated along the b axis and amounts to 1.87(l) mu(B) per Cc(3+) ion. The crystal-field splitting reduces the ordered moment slightly below the F-2(5/2) free-ion value of g . J = 15/7 for Ce3+.
Title:
Effect of pressure and Mn substitution on magnetic ordering of Ce2Fe17-xMnx (x=0, 1)
Authors:
Prokhnenko, O; Ritter, C; Arnold, Z; Isnard, O; Teplykh, A; Kamarad, J; Pirogov, A; Kuchin, A; Le Lay, G;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1-4): S610-S612; 2002
Abstract:
The magnetic ordering of Ce2Fe17 and Ce2Fe16Mn at ambient and under high pressures up to 5 kbar was studied by neutron diffraction in the temperature range 2-300 K. The existence of collinear ferromagnetic (below 94 K) and incommensurate helical antiferromagnetic structures with a propagation vector tau(1) = (0, 0, tau(1z)) was found at ambient pressure in Ce2Fe17. A helical structure with tau(2) = (0, 0, tau(2z)) exists below 200 K down to low temperatures in Ce2Fe16Mn. Application of pressure results in the suppression of the ferromagnetic phase in Ce2Fe17 by P > 3 kbar. A new pressure-induced incommensurate antiferromagnetic phase appears at T < 80 K. This phase is characterized by an additional satellite with tau(3) = 0.078 Angstrom(-1) at 5 kbar. The helical structure of Ce2Fe16Mn significantly changes under pressure. Below 70-80 K at P > 3 kbar it transforms to a non-collinear phase, which can be described using a distorted elliptical spiral model.
Title:
Static spin correlations induced by Zn doping in La1.79Sr0.21Cu1-yZnyO4 (y=0, 0.01)
Authors:
Kimura, H; Hirota, K; Aoyama, M; Koike, Y; Yamada, K; Endoh, Y; Aso, N; Takeuchi, T; Le Lay, G;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1-4): S649-S651; 2002
Abstract:
Static antiferromagnetic (AF) spin correlations of overdoped La2-xSrxCuO4 (LSCO) with and without Zn doping have been studied by neutron scattering. In a single crystal of Zn-free LSCO for x = 0.21, no elastic magnetic signals were observed even at 80 mK. However, elastic signals appear below 22 K in 1% Zn-doped LSCO for x = 0.21, indicating that Zn stabilizes the static AF spin correlations even in the overdoped LSCO. The present study confirmed that the AF propagation wave vector is incommensurate with the lattice, characterized as Q(AF) = (1/2 not equivalent toeta 1/2 +/- epsilonO) with eta = 0.005 (2) and epsilon = 0.135 (2). The appearance temperature (T-m) of the elastic signal degrades under higher-energy resolution, suggesting that the static correlations induced by Zn have a spinglass-like nature.
Title:
Geometrical frustration and incommensurate magnetic ordering in CePdAl: a low-temperature neutron-diffraction study
Authors:
Keller, L; Donni, A; Kitazawa, H; van den Brandt, B; Yamada, K;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1-4): S686-S688; 2002
Abstract:
The ordering of the Ce3+ magnetic moments in the heavy-fermion compound CePdA1 was investigated by means of neutron powder diffraction measurements of high-quality polycrystalline samples at temperatures down to 180 mK. The triangular coordination symmetry of the magnetic ions gives rise to geometrical frustration and leads to an incommensurate antiferromagnefic structure, exhibiting a coexistence of ordered and frustrated disordered Ce moments. The magnetic propagation vector shows a pronounced temperature dependence below T-N and locks in to k = [1/2, 0, tau], r = 0.351, 2 below 1.9K. The magnetic structure at 180 mK could unambiguously be determined and the coexistence of ordered and disordered Ce moments is observed even at the lowest temperatures. A second magnetic phase transition can be excluded.
Title:
Magnetic order of TmCu2
Authors:
Kreyssig, A; Ritter, C; Schneider, H; Schneidewind, A; Isnard, O; Behr, G; Loewenhaupt, M; Takeuchi, T;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1-4): S701-S703; 2002
Abstract:
Neutron diffraction experiments on two different polycrystalline TMCu2 samples were carried out on D1B (ILL, Grenoble) to determine the dependence of the magnetic order on temperature and on annealing state. In zero field at least three different magnetic phases are found: one commensurate antiferromagnetic structure with the propagation vector Q 0 0) and two types of magnetic order with the incommensurate propagation vectors (0.633 0 0.018) and (0.645 0.127 0). The sample preparation strongly influences the magnetic order in the temperature region, where the squared-up commensurate and the incommensurate antiferromagnetic structures compete.
Title:
Incommensurate-commensurate phase transition in the frustrated antiferromagnet CsCuCl3 studied by neutron diffraction
Authors:
Hoser, A; Stusser, N; Schotte, U; Meissner, M; Isnard, O;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1-4): S707-S709; 2002
Abstract:
A diffraction study has been performed in order to study the incommensurate-commensurate phase transition expected in the magnetically frustrated system CsCuCl3 in a transverse field, H perpendicular to c axis. The phase transition was followed throughout the phase diagram. We will describe here the results near 16 T at a temperature of 2 K. In this region the transition to the commensurate phase is believed to be driven by quantum fluctuations. The field dependence of the propagation vector has been determined. No field hysteresis could be identified across the transition but a narrow two phase region was observed. Possibilities and limitations of neutron-diffraction studies at high fields using a Dy booster to enhance the field strength of superconducting magnets are addressed.
Title:
Neutron-diffraction study of CePtSn
Authors:
Janousova, B; Svoboda, P; Sechovsky, V; Prokes, K; Komatsubara, T; Nakotte, H; Chang, S; Ouladdiaf, B; Cisarova, I; Sterzel, R;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1-4): S731-S733; 2002
Abstract:
We report a neutron- and X-ray-diffraction study of single crystals of CePtSn. As for the crystallographic structure, we have determined that the space group is centrosymmetric Pnma, contrary to the previously reported noncentrosymmetric epsilon-TiNiSi-type structure. At low temperatures two magnetic phase transitions have been observed at T-N approximate to 7.5 K and T-M approximate to 5.2 K. Our neutron-diffraction data support the previously proposed 'spin-slip' magnetic structures with the basic propagation vector q = (0, 1/2, 0) and sample-dependent spin-slips resulting in various observed incommensurate propagation vectors. Two separately prepared CePtSn single crystals were studied. In one of them we have found coexistence of the propagation vectors q(1) = (0, 0.470, 0) and q(2) = (0, 0.422, 0) below T-M, while only q(2) exists between T-N and T-M. In the other sample the propagation vector q(2) also exists for the whole range T < T-N and coexists with q(1) below T-M, but the intensity of q(2)-related reflections is strongly suppressed with decreasing temperature.
Title:
Field-induced magnetic structures in UNiGe
Authors:
Prokes, K; Nakotte, H; Bruck, E; de Chatel, PF; Sechovsky, V; Nakotte, H;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1-4): S757-S759; 2002
Abstract:
Below T-N = 50 K, UNiGe exhibits incommensurate (INC) antiferromagnetic (AF) order with an additional order-order (AF) phase transition at T-M = 42.5 K. The ground-state AF structure is characterized by a propagation vector (0, 1/2, 1/2). At 4.2 K, there are two field-induced transitions at 17 and 25 T for the b-axis and at 3 and 10 T for fields along c. No transitions are observed for the a parallel to B orientation up to 38 T. While the intermediate field-induced phases for both b parallel to B and c parallel to B geometries have propagation vector (0, 1/3, 1/3), the INC structure is characterized by a propagation vector (0, delta(1), delta(2)). All phases have a non-collinear arrangement of U moments with all three components, i.e. also along the a-axis, which is the hard-magnetization direction. The field-forced ferromagnetic phase, which is established for c parallel to B above 10 T still exhibits a significant a-axis component. This suggests that the magnetic ordering in UNiGe is governed by anisotropic exchange interactions.
Title:
Magnetic structures of RPd2Ge (R = Tb-Er) compound0s
Authors:
Kolenda, M; Balanda, M; Hofmann, M; Penc, B; Szytula, A; Nakotte, H;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1-4): S775-S777; 2002
Abstract:
Crystal and magnetic structures of RPd2Ge (R = Tb - Er) compounds are determined on the basis of neutron-diffraction data. They crystallize in the orthorhombic Fe3C-type structure (space group Pnma). All the compounds are antiferromagnets. The Neel temperatures are 19 K, 13.5 K, 4.4 K and 3 K for the compounds with Tb, Dy, Ho and Er, respectively. TbPd2Ge and DyPd2Ge undergo a further phase transition in the ordered state and at 1.5 K they exhibit a collinear magnetic structure described by the propagation vector k = (0, 0, 1/2). With increasing temperature the structure changes into a sine-wave-modulated one (at 10 K and 5.5 K for R = Tb and Dy, respectively). HoPd2Ge has a sine-wave-modulated structure and ErPd2Ge is a collinear antiferromagnet at 1.5 K. In both cases the magnetic moments are parallel to the c axis.
Title:
Low-temperature incommensurate magnetic order in R2BaCoO5 [R = rare earth]
Authors:
Hernandez-Velasco, J; Saez-Puche, R; Hoser, A; Rodriguez-Carvajal, J; Szytula, A;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1-4): S781-S783; 2002
Abstract:
R2BaCoO5 oxides, with R = Er, Tm, Lu and Y, show incommensurate (I) magnetic order below T-N = 3.5 K. The Er compound remains as an I-magnetic structure down to T = 40 mK and the Y one shows the coexistence of both commensurate (C) and I structures in the vicinity of a Lifshitz point. Both facts are quite uncommon. A devil's staircase behaviour in helimagnetic Tm2BaCoO5 is observed at 1.4 K < T < 2.5 K. A sudden collapse of a sine-wave modulation of Co moments to a C-magnetic structure is evidenced in Lu2BaCoO5 at T = 2.5 K with Co magnetic moments mu similar to 3.9 mu(B) lying in the xy plane.
Title:
Pressure-induced antiferromagnetism in TbPt and TbPt0.6Cu0.4: a neutron-diffraction study
Authors:
Senas, A; Fernandez, JR; Sal, JCG; Goncharenko, I; Szytula, A;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1-4): S786-S788; 2002
Abstract:
We present the evolution of the magnetic structures of TbPt and TbPt0.6Cu0.4 under pressures up to 65 kbar. The first compound is ferromagnetic non-collinear -CxFz, while in the Cu-diluted one an almost antiferromagnetic (AF) behaviour appears, corresponding to a complex structure in which the -CxFz phase coexists with an incommensurate one. We have found that pressure favours a general AF behaviour, which manifests as a clear increasing of the AF component in the non-collinear phase, and in the evolution to a pure AF arrangement of the moments in the unit cell for the incommensurate one.
Title:
Neutron-diffraction studies of a Cr+0.88 at. % Ga alloy
Authors:
Venter, AM; Prinsloo, ARE; Alberts, HL; Goncharenko, I;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1-4): S850-S852; 2002
Abstract:
A neutron-diffraction study has been performed on a Cr-Ga alloy single crystal containing 0.88 at. % Ga. Well-defined anomalies were observed in the integrated neutron intensities at the spin-flip as well as at the incommensurate-commensurate spin-density-wave magnetic phase-transition temperatures T-sf and T-IC, respectively. Unusually strong spin-fluctuation effects persist in the crystal to temperatures well above the Neel point. The neutron-diffraction results enhance previous arguments to solve a reported discrepancy between the calculated and directly measured signs of the pressure derivative of T-IC.
Title:
Correlation between the structural and antiferromagnetic phase transitions in ZnCr2Se4
Authors:
Hidaka, M; Tokiwa, N; Fujii, M; Watanabe, S; Akimitsu, J; Nakotte, H;
Source:
PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 236 (1): 9-18; 2003
Abstract:
Structural properties of normal-type spinel ZnCr2Se4 have been studied as a function of temperature by means of neutron diffraction. It is found that the structural phase transition (T-C) from a cubic to orthorhombic symmetry simultaneously occurs at the antiferromagnetic phase transition temperature (T-N similar to 21 K), where the cubic and orthorhombic symmetry is O-7(h)-Fd3m and D-24(2h)-Fddd, respectively. The structural phase transition is mainly characterized by the cooperative displacements of Se2- ions, which are induced by a magnetostriction resulting from the magnetic interaction of Cr3+ ions in CrSe4 chains along [110]. The antiferromagnetic magnetic structure below TN is made by a spiral magnetic coupling between the ferromagnetic CrSe4 chains around crystallographic screw axes, which are parallel to an orthorhombic C axis. The spiral long-range order of the spins of Cr3+ is incommensurate and its periodicity of q along a reciprocal lattice axis C* shows temperature dependence from about 0.47 (2.5 K) to 0.43 (18 K). The spiral periodicity of the spin order along the C axis shows a first order transition at about 21 K.
Title:
Composition rule of bulk metallic glasses and quasicrystals using electron concentration criterion
Authors:
Wang, YM; Qiang, JB; Wong, CH; Shek, CH; Dong, C; Nakotte, H;
Source:
JOURNAL OF MATERIALS RESEARCH, 18 (3): 642-648; 2003
Abstract:
This paper aims at establishing a number of electrons/atom (e/a)-based criterion for searching bulk metallic glasses (BMGs) and quasicrystals with large forming abilities in the Zr-based multicomponent alloy systems. After discussions on the diffraction characteristics corresponding to the Fermi surfaces-Brillouin zone interaction in the Zr-based Hume-Rothery phases, the Hume-Rothery matching rule is well explained when the effective e/a value of the matrix element Zr is taken as 1.5. The BMG- and quasicrystal-related phases are pointed out to be a family of nearly e/a-constant phases in a given alloy system. An e/a-constant criterion is then used to predict the ideal composition of the quasicrystals and BMGs in the Zr-Ti-Ni, Zr-Al-Ni, and Zr-Al-Ni-Cu systems, respectively. Nearly pure bulk Zr-Ti-Ni quasicrystals and a series of BMGs with glass-forming abilities greater than that of the known Zr65Al7.5Ni10Cu17.5 alloy are found.
Title:
Characteristic crystal growth from amorphous WO3 film by vacuum heating
Authors:
Kimura, Y; Kaito, C; Wong, CH;
Source:
JOURNAL OF CRYSTAL GROWTH, 250 (3-4): 450-457; 2003
Abstract:
Selective growth of WO2, W and WO3-x crystals from amorphous WO3 film by vacuum heating at 400-900degreesC was clarified. The grown WO3-x crystals were incommensurate structure based on crystallographic share structure. The growth process of WO2 crystal in the amorphous film was directly observed at high temperature in the electron microscope. The growth front of the WO2 crystal consumes WO3 microcrystallites with various orientations. The growth speed of the WO2 depended on WO3 microcrystallites orientation. The origin of the wavy growth front of WO2 was due to an orientation dependence of the WO3 microcrystallites. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Investigation of transition from decagonal to vacancy ordered phase on replacement of Co by Cu in Al70Co15-xCuxNi15
Authors:
Yadav, TP; Shaz, MA; Tiwari, RS; Srivastava, ON; Dong, C;
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 218 (1): 12-16; 2003
Abstract:
The alloy with composition Al70Co15Ni15 forms one of the important quasicrystalline phase exhibiting formation of decagonal variants [1, 2]. In the present investigation, copper has been substituted in place of cobalt i.e. the phases corresponding to Al70Co15-xCuxNi15, have been investigated. It is found that when copper concentration reaches to a value of 10 atomic percent with the composition corresponding to Al70Cu15Ni15, the decagonal phase starts yielding to give rise to vacancy ordered phase. When all cobalt is replaced by copper i.e. when the composition corresponds to Al70Cu15Ni15, the decagonal phase disappears and the only phase observed is the vacancy ordered phase. It can thus be said that copper substitution brings in decagonal to vacancy ordered (VOP) phase transition. It has also been observed that gradual increase in concentration of Cu in Al70Co15-xCuxNi15 leads to cellular to dendritic transition in morphology.
Title:
Chemical localization
Authors:
Gantmakher, VF; Reck, G;
Source:
PHYSICS-USPEKHI, 45 (11): 1165-1174; 2002
Abstract:
The possibility that, in spite of high valence electron concentrations, metal-insulator transitions can in principle occur in materials composed of atoms of only metallic elements is demonstrated based on the analysis of experimental data. For such a transition to occur, stable atomic configurations forming deep potential wells capable of trapping dozens of valence electrons should appear in the system. This means, in essence, that bulk metallic medium transforms into an assembly of identical quantum dots. Depending on the parameters, such a material either does contain delocatized electrons (metal) or does not contain such electrons (insulator). The degree of disorder is one of these parameters. Two types of substances with such properties are discussed: liquid binary alloys with both components being metallic, and thermodynamically stable quasicrystals.
Title:
Dynamics of the incommensurate phase of the fully deuterated diacetylene 2,4-hexadiynylene bis(p-toluene sulfonate)
Authors:
Even, J; Bertault, M; Toudic, B; Cailleau, H; Girard, A; Delugeard, Y; Moussa, F; Ouladdiaf, B;
Source:
PHASE TRANSITIONS, 76 (3): 229-237; 2003
Abstract:
Inelastic coherent neutron and Raman scattering is used to make a dynamical study of the disubstituted and fully deuterated diacetylene 2,4-hexadiynylene bis(p-toluenesulfonate) (pTS-D) in a partially polymerized state (x= 1.5%). The aim of this study is to investigate the dynamics of the incommensurate phase and to make a comparison with the dynamics of the same monocrystal in the high-temperature phase [Even et al., Phys. Rev., 1352, 7142.] and the dynamics of the pure monomer pTS-D crystal [Bertault et al., Adv. Mat. for Optics and Electronics, 6, 317.]. The phason and amplitudon modes are observed as very damped phonon-like excitations. The effect of polymerization on the critical dynamics in pTS-D is discussed.
Title:
Devitrification studies of Zr-Pd and Zr-Pd-Cu metallic glasses
Authors:
Kramer, MJ; Besser, MF; Yang, N; Rozhkova, E; Sordelet, DJ; Zhang, Y; Lee, PL; Ouladdiaf, B;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 317 (1-2): 62-70; 2003
Abstract:
High temperature X-ray diffraction (HTXRD) is used to investigate the devitrification pathway for two related Zr-based metallic glasses, Zr70Pd30 and Zr70Pd20Cu10. Both alloys have similar as-quenched structures and initially devitrify to form a meta-stable quasicrystalline phase. The HTXRD data for the Zr70Pd30 alloy shows the coexistence of the quasicrystalline and the Zr2Pd (I4/mmm) crystalline phases over a range of 25 K. Conversely, the Zr70Pd20Cu10 alloy shows an additional transformation of the quasicrystalline phase to a meta-stable Zr-2(PdCu) intermetallic (Zr2Si type structure, I4/mcm) that polymorphically transforms to the Zr2Ni type structure (I4/mmm) over a very narrow temperature range. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
Quasicrystals from glass devitrification
Authors:
Saida, J; Inoue, A; Yang, N;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 317 (1-2): 97-105; 2003
Abstract:
It was found that the nano-icosahedral phase was formed in the devitrification stage of Zr- and Hf-based glassy alloys. The primary phases are metastable fcc Zr2Ni and fcc Hf2Ni phases in the Zr65Al7.5Ni10Cu17.5 and Hf65Al7.5Ni10Cu17.5 glassy alloys, respectively. By substitution of 5 at.% Pd for Cu, the primary phase changes to an icosahedral quasicrystalline phase in both alloys. The addition of elements, that have a positive or weak chemical affinity with one of the constitutional elements in the Zr-Al-Ni-Cu and Hf-Al-Ni-Cu glassy alloys is effective for the precipitation of the icosahedral phase. The icosahedral phase also precipitated with a slight deviation from the composition with a high glass-forming ability. Since an icosahedron is contained as a structure unit in the icosahedral, fcc Zr2Ni and fcc Hf2Ni phases, it is concluded that these phases are correlated with the local icosahedral order of the-glass. The high-resolution transmission electron microscopy images of the as-spun Zr65Al7.5Ni10Cu7.5Pd10, Zr70Al7.5Ni10Cu12.5 and Hf65Al7.5Ni10Cu12.5Pd5 alloys reveal a possibility of the existence of the icosahedral ordered regions. It is, therefore, concluded that the existence of icosahedral short- or medium-range order stabilizes the glassy state in the Zr- and Hf-based multicomponent alloys. (C) 2003 Elsevier Science B.V. All rights reserved.
Title:
An atomistic simulation study of a solid monolayer and trilayer of n-hexane on graphite
Authors:
Krishnan, M; Balasubramanian, S; Clarke, S; Rozhkova, E;
Source:
JOURNAL OF CHEMICAL PHYSICS, 118 (11): 5082-5086; 2003
Abstract:
We present all-atom molecular dynamics simulations of n-hexane on the basal plane of graphite at monolayer and trilayer coverages. In keeping with experimental data, we find the presence of ordered adsorbed layers at both coverages. Using a simulation method that does not impose any particular periodicity on the adsorbed layer, we quantitatively compare our results to the results of neutron diffraction experiments and find a structural transition from a uniaxially incommensurate lattice to a fully commensurate structure on increasing the coverage from a monolayer to a trilayer. The zig-zag backbone planes of all the alkane molecules lie parallel to the graphite surface at the trilayer coverage, while a few molecules are observed to attain the perpendicular orientation at monolayer coverage. (C) 2003 American Institute of Physics.
Title:
Three-dimensionally modulated incommensurate crystal structure of lazurite from the Baikal region
Authors:
Bolotina, NB; Rastsvetaeva, RK; Sapozhnikov, AN; Kashaev, AA; Schoenleber, A; Chapuis, G; Lee, PL;
Source:
CRYSTALLOGRAPHY REPORTS, 48 (1): 8-11; 2003
Abstract:
The three-dimensionally modulated incommensurate crystal structure of lazurite from the Baikal region was determined for the first time. The structure was solved within the cubic system with the unit-cell parameter a(cub) = 9.077(1) Angstrom and the (3+2)-dimensional superspace group Pnn2(q(1), q(2)) under the assumption of a twin model consisting of three orthorhombic components related by a threefold axis along the [111] direction. The structure was refined using 257 main reflections and 2392 first-order satellite reflections with the isotropic thermal parameters to wR(0) = 1.98% and wR(1) = 7.50% respectively. (C) 2003 MAIK "Nauka/Interperiodica".
Title:
Superspace approach applied to a neutron-diffraction study of the holographic data storage material Sr0.61Ba0.39Nb2O6
Authors:
Schaniel, D; Schefer, J; Petricek, V; Imlau, M; Pankrath, R; Granzow, T; Woike, T; Ouladdiaf, B;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1): S963-S965; 2002
Abstract:
We investigated the incommensurately modulated structure of Sr0.61Ba0.39Nb2O6 by means of single-crystal neutron diffraction. With the measured 620 satellite reflections we could verify the two modulation vectors Q(1,2) = (0.3075, +/-0.3075, 0.5) known from X-ray-diffraction experiments. As neutrons are much more sensitive to oxygen atoms than X-rays, we performed structural refinement of the oxygen atoms using the superspace approach. The largest amplitude for positional modulation was found for those oxygen atoms lying in the same plane (z = const.) as the Sr and Ba atoms. The final R values for main and satellite reflections are 0.063 and 0.153, respectively.
Title:
Diffuse neutron scattering study of disordered Al72Co16Ni12 quasicrystals up to 1000 degrees C
Authors:
Frey, F; Hradil, K; Weidner, E; de Boissieu, M; McIntyre, G; Currat, R; Tsai, AP; Ouladdiaf, B;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1): S998-S1000; 2002
Abstract:
Disordered decagonal Al72Co16Ni12 quasicrystals were investigated by recording diffuse neutron scattering at instruments D10 and IN8/ILL up to 1000degreesC. This neutron work supplements X-ray-diffraction investigations, which do not provide a scattering contrast of the transition metals. Moreover, diffuse scattering of inelastic origin could be suppressed, within the resolution limits, by using an analyser. The temperature dependence of the diffuse scattering in the quasiperiodic plane indicates complex re-ordering processes. A one-dimensional superorder along the unique axis, reflected by diffuse layers perpendicular to it, dissolves at 950 degreesC; short-range-order maxima remain visible at 980 degreesC.
Title:
Atomic-partial vibrational density of states of i-AlCuFe quasicrystals
Authors:
Parshin, PP; Zemlyanov, M; Brand, RA; Dianoux, AJ; Calvayrac, Y; Currat, R;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 74 (1): S1657-S1659; 2002
Abstract:
We present new results on the separation of the atomic-partial vibrational density of states for the ternary quasicrystal i-Al62Cu25.5Fe12.5. The decomposition into three atomic-partial functions, Al-, Cu- and Fe-g(E), has been performed self-consistently with the calculation of the multi-phonon contributions. The results show the surprising result that both Cu- and Fe-g(E) are strongly peaked. The low-energy regions of Al- and Cu-g(E) show strong deviations from Debye behaviour due to the presence of non-propagating low-energy vibrational states.
Title:
Transient spinodal decomposition during annealing of rapidly solidified Al-10Sr alloy
Authors:
Wang, Y; Liu, GD; Bian, XF; Sun, Y; Zhang, ZH; Staub, U;
Source:
JOURNAL OF UNIVERSITY OF SCIENCE AND TECHNOLOGY BEIJING, 10 (1): 58-60; 2003
Abstract:
Rapidly solidified Al-10Sr alloy ribbons were prepared using a single roller melt spinning technique. The annealing process of the rapidly solidified Al-10Sr alloy has been carried out using differential scanning calorimetry (DSC). The microstructure of as-annealed Al-10Sr alloy has been characterized by transmission electron microscopy (TEM). The equilibrium Al4Sr phase is dominant in the as-annealed alloy. Besides the Al4Sr phase, an AlSr phase is also found in the alloy isothermally annealed at 873 K for 90 min. Furthermore, a modulated nanostructure was observed in the alloy isothermally annealed at 873 K for 90 min. With further prolonged annealing time, however, the AlSr phase disappears in the as-annealed alloy. The dependence of particle size and growth rate on annealing time as well as the modulated structure shows that the occurrence of the AlSr phase may be due to the spinodal decomposition.
Title:
Pressure effects on the spectra of dye molecules in incommensurate and commensurate phases of biphenyl
Authors:
Zazubovich, V; Suisalu, A; Leiger, K; Laisaar, A; Kuznetsov, A; Kikas, J; Tsai, AP;
Source:
CHEMICAL PHYSICS, 288 (1): 57-68; 2003
Abstract:
Low-pressure tuning of spectral holes, burned in the spectra of chlorin molecules doped into polycrystalline biphenyl, as studied for the incommensurate phase III of biphenyl at T = 2 K and P = 0.1 to 2.5 MPa. A blue pressure shift of holes burned in the outermost red line of an inhomogeneous spectral triplet was found, in contrast to the red pressure shifts of the other two lines. Extrapolation of these shifts to higher pressures shows the convergence of that triplet at a pressure above 200 MPa. Such behaviour was confirmed by high-pressure measurements of two-dimensional (2D) excitation-emission spectra, from which the inhomogeneous distribution function (IDF) was extracted. At 5 K the low-pressure triplet shape of IDF converges to a high-pressure singlet at 170 MPa, close to the critical pressure for the incommensurate-commensurate transition. The results support a view that the optical spectra reflect interaction of the impurity molecule with the incommensurate modulation wave in biphenyl host matrix disappearing at transition to the commensurate phase. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Solidification behavior of decagonal quasicrystal in the undercooled Al72Ni12Co16 alloy melt
Authors:
Liu, XB; Yang, GC; Fan, P; Laisaar, A;
Source:
JOURNAL OF MATERIALS SCIENCE, 38 (5): 885-889; 2003
Abstract:
The microstructural evolution of Al72Ni12Co16 alloy at various undercoolings was investigated in this paper. A single-phase decagonal quasicrystal (D-phase) was obtained in the undercooled Al72Ni12Co16 alloy melts. Different microstructure morphologies of the D-phase were formed with increasing undercoolings. Based on Toner's model of the step growth of quasicrystals, the growth mechanisms of the D-phase under various undercoolings were discussed. The D-phases formed at various undercoolings in the undercooled melts show different microstructures owing to the change of preferential growth direction from the quasiperiodic to periodic direction. (C) 2003 Kluwer Academic Publishers.
Title:
Spin dynamics in the quantum spin system KCu5V3O13
Authors:
Klauss, HH; Lemmens, P; Birke, M; Baabe, D; Mienert, D; Litterst, FJ; Amato, A; Pommer, J; Ionescu, A; Choi, KY; Guntherodt, G; Kageyama, H; Hiroi, Z; Takigawa, M;
Source:
PHYSICA B-CONDENSED MATTER, 326 (1-4): 436-439; 2003
Abstract:
The complex Oxo-Cu-vanadate KCu5V3O13 with 5 independent Cu-sites (s = 1/2) per unit cell has an exchange topology described as a ladder of spin tetrahedra or triangles. Magnetic susceptibility measurements on single crystals show a steplike anomaly at 213 K and an antiferrornagnetic transition at 7.5 K. ZF muSR reveals only nuclear relaxation above 10 K and two spontaneous precession signals in the long range ordered regime. Below 3.7 K, a spin reorientation leads to a broad frequency distribution typical for an incommensurate spin structure. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Magnetic properties of geometrically frustrated ZnxLi1-xV2O4
Authors:
Kalvius, GM; Noakes, DR; Wappling, R; Buttgen, N; Krimmel, A; Klemm, M; Horn, S; Loidl, A; Ionescu, A;
Source:
PHYSICA B-CONDENSED MATTER, 326 (1-4): 470-474; 2003
Abstract:
muSR spectroscopy on ZnV2O4 shows paramagnetism for T > 40K. For 12K less than or equal to T less than or equal to 40K, the paramagnetic state coexists with a dynamically correlated spin-glass-like state whose volume fraction increases as temperature is reduced, reaching 100% around 12K. Cooling further leads to a highly damped Bessel-type oscillatory pattern which indicates an incommensurate spin-density-wave structure. The high transverse relaxation rate means large local spin disorder, probably preventing true long-range order, which would explain the absence of magnetic Bragg peaks in neutron diffraction. Furthermore, persistent slow spin fluctuations are observed. These features are indicators of frustration and it is concluded that the structural distortion around 50 K removes only some of the frustration. For Zn0.2Li0.8V2O4 no structural phase transition occurs and full frustration is expected. The muSR data show paramagnetic response above similar to 12 K. The relaxation rate follows a critical law on approaching 12 K from above, as does the T-1 relaxation in NMR. Below 12K a fast relaxing dynamic Gaussian Kubo-Toyabe signal appears, which is the signature of a dynamic disordered magnetic state. Spin freezing is not observed down to 2 K. The formation of this dynamic spin-glass-like state is consistent with a spin-glass transition temperature of similar to10 K deduced from specific heat and magnetisation measurements. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Quasicrystal-forming ability of the icosahedral phase in Al-Cu-Fe-Be alloys
Authors:
Song, GS; Fleury, E; Lee, SM; Kim, WT; Kim, DH; Klemm, M;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 346 (1-2): 42-49; 2003
Abstract:
The effect of Be (beryllium) addition and the influence of cooling rate on the solidification path of the icosahedral (i) phase in conventional casting Al62-x Be-x Cu25.5Fe12.5 (x = 0, 1, 3, 5, 7 at.%) alloys were investigated by means of X-ray diffraction, differential thermal analysis, SEM and EDX analyses. The addition of Be has been found to modify the i-phase formation mechanism from peritectic reaction to primary solidification. The volume fraction of the i-phase has been observed to increase from 45% for x = 0 to 90% for x = 7. These results suggested that the substitution of Al by Be is favorable for the increase of the quasicrystal-forming ability (QFA) of the i-phase. Two parameters have been proposed for defining and assessing the QFA for i-phase formed by peritectic reaction. These parameters can be expressed by the reduced quasicrystal transition temperature T-rq = T-p/T-l and the reduced undercooling DeltaT(r) = DeltaT(lp)/T-l, respectively, (T-l: liquidus temperature, T-p: peritectic peak temperature, and DeltaT(lp) = T-l - T-p: freezing range of primary phase). (C) 2002 Published by Elsevier Science B.V.
Title:
Influence of thermal treatment on the subgrain parameters and microstructure of two-subgrain Al-Cu-Co single quasicrystals
Authors:
Bogdanowicz, W; Fleury, E;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 346 (1-2): 328-335; 2003
Abstract:
The influence of low-temperature (100 degreesC) and high-temperature (900 degreesC) thermal treatment on the subgrain parameters i.e. misorientation angle, strain field, and microstructure of two-subgrain single quasicrystals of Al-Cu-Co alloy was studied. A banded microstructure was discovered in the single quasicrystals. The direction of the bands was found to be parallel to the tenfold symmetry axis. Low-temperature treatment induces a homogeneous strain field of macroscopic scale in the whole sample, causes fragmentation of the bands, and increases the boundaries' density. High-temperature thermal treatment at 900 degreesC carried out afterwards on the same samples causes some broadening of the bands which is connected with the partial disappearance of the boundaries. The treatment also causes disappearance of the homogeneous strain field and rotation of the subgrains in relation to one another about the tenfold symmetry axis. These observations are interpreted by describing the bands as anti-phase domains of the decagonal Al-Cu-Co alloy. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Domain variance and superstructure across the antiferroelectric/ferroelectric phase boundary in Pb1-1.5xLax(Zr0.9Ti0.1)O-3
Authors:
Knudsen, J; Woodward, DI; Reaney, IM; Kim, WT;
Source:
JOURNAL OF MATERIALS RESEARCH, 18 (2): 262-271; 2003
Abstract:
Transmission electron microscopy, x-ray diffraction, relative permittivity as a function of temperature, and polarization versus field loops were used to study the antiferroelectric/ferroelectric (AFE/FE) phase boundary in Pb1-1.5xLaxZr0.9Ti0.1O3 (PLZT, 100x/90/10) ceramics. X-ray diffraction and electrical measurements indicated a FE rhombohedral (R) to AFE tetragonal (T) phase transition between PLZT 2/90/10 and 4/90/10. Both phases exhibited superstructure reflections in electron-diffraction patterns at 1/2{hkl} positions consistent with rotations of the octahedra in antiphase. Previously, neutron diffraction suggested that the FER has an a(-)a(-)a(-) tilt system (Glazer notation), in agreement with its macroscopic symmetry. By analogy, it is proposed that the AFE(T) phase has an a(0)a(0)c(-) tilt system. The AFE phase was also characterized by incommensurate superstructure along pseudocubic <110>(p) directions, whereas the FE phase had extra commensurate superlattice reflections at 1/2{hk0}(p) positions. 1/2{hk0}(p) reflections are forbidden in both tilt systems, but their presence is explained by Pb ion displacements averaged along <111> but with short coherence antiparallel components along <110> directions. The antiparallel Pb displacements are coupled to an a(-)b(-)b(-) (a approximate to b) monoclinic tilt system in the vicinity of the AFE/FE boundary.
Title:
The charge ordered state and the possible 2k(F)-CDW state with Fermi surface nesting in organic conductor 0-(BEDT-TTF)(2)MM'(SCN)(4) (MM '= RbZn, CsCo)
Authors:
Watanabe, M; Noda, Y; Nogami, Y; Oshima, K; Mori, H; Klemm, M;
Source:
JOURNAL DE PHYSIQUE IV, 12 (PR9): 231-232; 2002
Abstract:
Two-dmensional organic conductor theta-(BEDT-TTF)(2)RbZn(SCN)(4) and theta-(BEDT-TTF)(2)CsCo(SCN)(4) were investigated by X-ray diffraction measurements. Both salts exhibit an isostructural crystal structure at room temperature (RT). However, the RbZn salt undergoes a metal-insulator transition associated with superlattice formation of 2c. The charge ordered state below T-Ml, was observed by crystal structure analysis taking into account of the superlattice. This modulation of 2c has no relation to the topology of the calculated Fermi surface nesting vector at all. Below T-Ml, the systematic deformations of BEDT-TTF molecular shape indicated charge disproportionation between BEDT-TTFs possibly caused by the electron correlation effect. On the other hand, in the CsCo salt, another incommensurate lattice modulation was found under high pressure of 1GPa. This incommensurate modulation vector of (2/3 0 0.29) is in agreement with the nesting vector of Fermi surface under high pressure. In this system, it seems that small change caused by chemical substitution can vary the electronic state from the charge ordered state to the CDW state.
Title:
Charge-density waves in Er(5)lr(4)Si(10) type compounds
Authors:
van Smaalen, S; Daniels, P; Galli, F; Feyerherm, R; Dudzik, E; Nieuwenhuys, GJ; Mydosh, JA; Loidl, A;
Source:
JOURNAL DE PHYSIQUE IV, 12 (PR9): 347-350; 2002
Abstract:
X-ray diffraction with synchrotron radiation has been used to study the phase transitions in compounds M5Ir4Si10 with M a rare-earth metal. For M = Er, Ho and Er0.84Lu0.16 phase transitions have been found towards a combined commensurate/ incommensurate state, that locks into a commensurate state at lower temperatures. For M = Lu and Er0.66LU0.34 there is a single transition towards a commensurate state. The results are interpreted in terms of commensurate structural transitions that induce incommensurate CDWs.
Title:
The significance of valence electron concentration on the formation mechanism of some ternary aluminum-based quasicrystals
Authors:
Athanasiou, NS; Politis, C; Spirlet, JC; Baskoutas, S; Kapaklis, V; Goze-Bac, C;
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B, 16 (31): 4665-4683; 2002
Abstract:
In the present study we report on the formation mechanism of some binary Al-TM and ternary Al-Cu-TM (TM = transition metal) quasicrystals. We have found that the formation mechanism of quasicrystalline phases in the binaxy Al-TM system takes place at extremely high solidification rates, is linked to the location of the transition metal in the periodic table, depends upon the atomic radius ratio of the constituents, is composition sensitive, and as a result is strongly affected by the effective atomic radius ratio (a(eff)). Applying empirical criteria on the formation of ternary Al-Cu-TM quasicrystals we were able to calculate the composition range at which the formation tendency and stability of quasicrystalline phases is enhanced. The method presented can be viewed as an empirical criterion to find new and high quality quasicrystalline materials and to optimize the quasicrystalline material composition. Furthermore, it was observed that the stabilization mechanism of the quasicrystalline Al-Cu-(Fe, Co, Ru, Rh, Os, Ir) phases takes place when the atomic ratio (TM+Cu)/Al ranges from 0.46 to 0.69 and for a(eff) values between 4.10 and 7.30. At the same valence electron concentration, metastable icosahedral Al-Cu-(Cr, Mn) phases are formed at relatively smaller atomic ratios (TM+Cu)/Al and having higher aeff values in comparison to those of the stable D- and I-phases.
Title:
Molecular dynamics simulations of the effect of icosahedral quasicrystal on the formation of amorphous
Authors:
Zhou, GR; Wu, YS; Zhang, CJ; Zhao, F; Kapaklis, V;
Source:
ACTA PHYSICO-CHIMICA SINICA, 19 (1): 13-16; 2003
Abstract:
By means of molecular dynamics simulation technique, the solidification process of Ni under different cooling rates has been studied. The variation of potential energy with temperature and the relationship between the energy and the structure of molecular-cluster have also been studied. With pair distribution function and pairs analysis method, the local symmetry of molecular-cluster has been analyzed. From the view of pairs analysis, the conclusion has been discussed.
Title:
"Back to the future" - An account discovery of stable ouasicrystals
Authors:
Tsai, AP; Wu, YS;
Source:
ACCOUNTS OF CHEMICAL RESEARCH, 36 (1): 31-38; 2003
Abstract:
In this Account, I will describe the discoveries of a series of stable quasicrystals in which I participated during the past 15 years. These discoveries led to a paradigm shift in the field of quasicrystals. The story started when I was a graduate student, has continued into the present, and may continue into the future. Of these discoveries, some were made independently by myself and some in collaboration with my colleagues. As it happens, I am the only one related to all of these discoveries, and so it seems appropriate that I tell the stories.
Title:
Synthesis and average and incommensurately modulated crystal structure of 2D-K3Ce2P3S12
Authors:
Gauthier, G; Evain, M; Jobic, S; Brec, R; Kapaklis, V;
Source:
SOLID STATE SCIENCES, 4 (11-12): 1361-1366; 2002
Abstract:
K3Ce2P3S12, a new thiophosphate of cerium and potassium, has been synthesized for the first time and its average structure solved from single crystal data. A tentative solution for its weakly modulated, incommensurate structure has also been found within a (3+1)D formalism. The average structure of this new, yellow material has monoclinic symmetry, space group C2/c with the following cell parameters a=20.595(3) Angstrom, b=9.6453(10) Angstrom, c=22.161(4) Angstrom, beta=97.360(13) and V=4366.0(19) Angstrom(3) (Z=8). Its crystal refinement yielded the residual factor R=4.77% for 187 parameters and 3117 independent reflections at a 2sigma(I) level. The two-dimensional structure can be viewed as built upon infinite (1)(infinity)[Ce2P2S12](8-) chains connected to each other by [PS4] tetrahedra to form (2)(infinity)[Ce2P3S12](3-) layers. These corrugated slabs are electrostatically linked-by potassium ions. K3Ce2P3S12 can be considered as a new member of the (K-4(I)(P-2)(VIII)Q(6)(-II))(l)(K(3)(I)P(V)Q(4)(-II))(m)(Ln(4)(III)(P-2)(3)S-VIII(18)-II)(n)(Ln(III)P(V)Q(4)(-II)) family (Ln=La, Ce; Q=S, Se) with l=0, m=1, n=0 and o=2 ((K3Ce2P3S12-II)-Ce-I-P-III-S-V) The crystal refinement of the true modulated structure within the (3+1)D formalism (wavevector: q = -0.559(2)a* + 0.589(3)c*) yielded the residual factor R=5.66% for 296 parameters and 3583 independent reflections (3117 main reflections and 466 first order satellites). In the aperiodic crystal, the modulation results. from the rotation of the [PS4] tetrahedra and the bicapped [CeS8] trigonal prisms around the alkali metals. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.
Title:
4,4 '-bipyMnF(3), a modulated hybrid layer structure with 1D magnetic properties
Authors:
Darriet, J; Massa, W; Pebler, J; Stief, R; Kapaklis, V;
Source:
SOLID STATE SCIENCES, 4 (11-12): 1499-1508; 2002
Abstract:
4,4'-bipyMnF(3) (bipy = bipyridine) has been crystallized from the system Mn-III/4,4'-bipy/HF/H2O/methanol/acetone and its crystal structure was determined by single crystal X-ray diffraction at different temperatures: at 295 K the structure is orthorhombic, space group 1222, Z = 2, a = 10.704(1), b = 11.384(2) Angstrom, c = 3.9413(4) Angstrom, wR(2) = 0.0637, R = 0.0244. Mn-III is octahedrally coordinated by four F and two N ligands. In the c direction an inorganic F-Mn-F-Mn- trans-chain is formed, along the b axis bridging by the organic bipy ligands takes place, thus the structure can be classified as a 2D hybrid coordination polymer. The 180degrees Mn-F-Mn bridge angle is symmetry-imposed. but larger, anisotropic displacement ellipsoids for the F ligands indicate dynamical disorder of an angular chain. At 240 K and 153 K 1D incommensurate modulated structures (space group 1222(00gamma)00s) are observed with large variation of the bridge angle down to 149degrees. Below 100 K the structure can be described as "lock-in phase" with doubled c-axis in the orthorhombic space group P2(1)2(1)2(1) and a bridge angle of 156.4degrees. 4,4/-bipyMnF(3) shows 1D antiferromagnetic properties with an exchange energy along the Mn-F-Mn chain of J/k = -11.5 K. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.
Title:
Energy-filtering transmission electron microscopy (EF-TEM) study of a modulated structure in metakaolinite, represented by a 14 angstrom modulation
Authors:
Lee, S; Kim, YJ; Moon, HS; Wade, AP;
Source:
JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 86 (1): 174-176; 2003
Abstract:
For the first time, a periodicity of 14 Angstrom is recognized as a typical modulation period in metakaolinite. Energy-filtered electron diffraction data confirm that dehydroxylation does not occur abruptly in kaolinite. The degree of ordering becomes much lower during the progression of dehydroxylation in metakaolinite than in kaolinite. However, different types of modulations, with periods in the range from similar to1.4d(001) (9.47 Angstrom) to 2.9d(001) (19.89 Angstrom), form along the c*-axis in metakaolinite. Modules (14.2 Angstrom = 2.1d(001)) that have a length that is approximately twice as long as the metakaolinite layer (6.86 Angstrom) are the most common. Presumably, the remnant oxygens and vacant anion sites rearrange to acquire stability in the layer structure, which builds modulations along the c*-axis in the metakaolinite.
Title:
Decagonal quasicrystal formed directly from the rapidly solidified Al66Cu17Co17 alloy
Authors:
Liu, XB; Yang, GC; Fan, JF; Song, GS; Dennison, S;
Source:
JOURNAL OF MATERIALS SCIENCE LETTERS, 22 (2): 103-105; 2003
Abstract:
For the first time, a periodicity of 14 Angstrom is recognized as a typical modulation period in metakaolinite. Energy-filtered electron diffraction data confirm that dehydroxylation does not occur abruptly in kaolinite. The degree of ordering becomes much lower during the progression of dehydroxylation in metakaolinite than in kaolinite. However, different types of modulations, with periods in the range from similar to1.4d(001) (9.47 Angstrom) to 2.9d(001) (19.89 Angstrom), form along the c*-axis in metakaolinite. Modules (14.2 Angstrom = 2.1d(001)) that have a length that is approximately twice as long as the metakaolinite layer (6.86 Angstrom) are the most common. Presumably, the remnant oxygens and vacant anion sites rearrange to acquire stability in the layer structure, which builds modulations along the c*-axis in the metakaolinite.
Title:
The formation of Sr silicates at low temperature and the solubility product of tobermoritelike Sr5Si6O16(OH)(2)center dot 5H(2)O
Authors:
Felmy, AR; Mason, MJ; Gassman, PL; McCready, DE; Pottgen, R;
Source:
AMERICAN MINERALOGIST, 88 (1): 73-79; 2003
Abstract:
The aqueous phase interaction of divalent Sr with silicate-containing solutions was studied over a range of pH values, dissolved silica, and Sr concentrations, and extending to basic solution (0.2 M NaOH) at room temperature (22-23 degreesC). Formation of an amorphous Sr silicate phase of variable composition was observed, beginning at approximately pH 10. The precipitate became quasi-crystalline at higher base concentrations and with aging time. The phase that formed at high base concentration (beginning at pH 11.5-12.0) was identified by total chemical analysis, X-ray diffraction, and thermogravimetric analysis to have a chemical formula of Sr5Si6O16(OH)(2).5H(2)O, with a tobermorite-like structure. The Sr5Si6O16(OH)(2).5H(2)O phase has not been previously reported. Scanning electron microscopy (SEM) analysis of alcohol-washed precipitates showed a fine granular structure similar to Ca silicate hydrates. De-ionized water washing of the precipitates resulted in dissolution and growth of surface phases with the classical "sheaf of wheat" nucleation structure previously identified only for Ca silicate hydrates. Solubility studies of the precipitates, which extended to 286 days of equilibration, yielded an estimate of the solubility product of quasicrystalline, tobermorite-like Sr silicate of Log K = -38.0 +/- 0.7 for the overall reaction, 5H(2)O + Sr5Si6O16(OH)(2).5H(2)O = 5Sr(2+) + 6H(3)SiO(4)(-) + 4OH(-). The first estimate of the association constant for the species SrH2SiO4(aq) of Log K = 2.86 was also made.
Title:
Fabrication of graded nickel-quasicrystal composite by electrodeposition
Authors:
Chan, KC; Qu, NS; Zhu, D; McCready, DE;
Source:
TRANSACTIONS OF THE INSTITUTE OF METAL FINISHING, 80 (1): 210-213; 2002
Abstract:
Functionally graded coatings with a gradual change in composition and microstructure can perforin specific functions and meet stringent performance requirements. A new graded composite coating, nickel-quasicrystal, it,as examined in this paper It was found that the volume percentage of embedded quasicrystal particles in the composite increased with an increase in current density up to 10 A dm(-2). A maximum volume percentage quasicrystal particles of 48.2% was obtained at the current density of 10 A dm(-2) an electrolyte particle content of 50 g dm(-3), agitation speed of 400 rpm, and particle size of 5 mum. Graded Ni-quasicrystal composite coatings were produced by manipulating the current density and the deposition time. and their hardness and composition were evaluated.
Title:
Phase diagram of lithium-doped copper oxide, Cu1-xLixO
Authors:
Saito, K; Ikeuchi, S; Nakazawa, Y; Zheng, XG; Maple, MB; Sorai, M; Anderson, MW;
Source:
SOLID STATE COMMUNICATIONS, 125 (1): 23-26; 2003
Abstract:
Heat capacities of lithium-doped samples of CuO have been measured below room temperature by adiabatic calorimetry. The antiferromagnetic ordering transition to incommensurately modulated state was detected as a step in the heat capacity. Its concentration dependence was compatible with existing reports based on Li-NMR. The incommensurate-commensurate transition of lithium-doped copper oxide was clearly detected. The magnetic phase diagram of Cu1-xLixO was thus constructed. The decrease of both transition temperatures with the Li doping is nearly twice as strong as that expected from mean-field and percolation theories. (C) 2002 Elsevier Science Ltd. All rights reserved.
Title:
Al-Cu-Fe quasicrystalline phase formation by mechanical alloying
Authors:
Tcherdyntsev, VV; Kaloshkin, SD; Salimon, AI; Leonova, EA; Tomilin, IA; Eckert, J; Schurack, F; Rogozin, VD; Pisarev, SP; Trykov, YP; Guntherodt, G;
Source:
MATERIALS AND MANUFACTURING PROCESSES, 17 (6): 825-841; 2002
Abstract:
Al-Cu-Fe alloys were prepared from elemental powders in a high-energy planetary ball mill. A sequence of solid state reactions resulting in quasicrystal (QC) phase formation takes place during heating of the as-milled powder. These reactions were studied by both differential scanning calorimetry and x-ray diffraction methods. Mechanically alloyed powders were consolidated by cold and hot pressing, as well as by explosive compaction. After annealing at sufficiently high temperatures, the consolidated samples are single-phase QC, except the ones consolidated by explosion. The high reactivity of the as-milled alloys causes the appearance of high porosity of the consolidated samples after the annealing.
Title:
Plane decagonal quasicrystals with 3-coordinated atoms
Authors:
Chizhikov, VA; Fowler, AD;
Source:
CRYSTALLOGRAPHY REPORTS, 47 (6): 897-900; 2002
Abstract:
A plane decagonal tiling with 3-connected nodes, which is obtained by decorating the Penrose tiling, is proposed as the structure of a two-dimensional covalent quasicrystal. The mean energy of the atoms in the given structure, calculated using the model Tersoff potential for carbon, is found to be close to the energy of the atoms in fullerene. An octagonal tiling containing 3-connected nodes and even cycles only is also proposed. (C) 2002 MAIK "Nauka/Interperiodica".
Title:
Characteristics of irreducible vectors rotating in superstructures with two one-component order parameters
Authors:
Zavorotnev, YD; Medvedeva, LI; Grieve, RAF;
Source:
CRYSTALLOGRAPHY REPORTS, 47 (6): 1003-1006; 2002
Abstract:
It is shown that incommensurate long-period structures formed by two synchronously rotating irreducible magnetic vectors are unstable and split into two interacting superstrucures. The behavior of such states away from and close to the phase-transition line is considered. (C) 2002 MAIK "Nauka/Interperiodica".
Title:
Growth morphologies of decagonal quasicrystal in highly undercooled Al72Ni12Co16 alloy melt
Authors:
Liu, XB; Yang, GC; Fan, JF; Wang, JC; Song, GS; Eckert, J;
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 12 (6): 1131-1134; 2002
Abstract:
The electromagnetic melting and cyclic superheating method was applied to undercool the Al72Ni12Co16 alloy melt, and a maximum undercooling, 180 K was obtained. Growth morphologies were characterized by using optical, microscopy, scanning electron microscope(SEM) and transmission microscopy(TEM),. The microstructural morphologies indicate that a continuous growth mode of D-phase along the periodic orientation of ten-fold axis is preferred at large undercoolings. According to the Toner's step growth mode of quasicrystal, the preferred continuous growth along the periodic orientation of ten-fold axis is caused by the loss of potential barrier for nucleating steps along this direction.
Title:
Long-range tiling structures in a highly ordered Al-Ni-Ru decagonal quasicrystal with 1.6nm periodicity and its closely related approximant
Authors:
Sun, W; Hiraga, K; Armstrong, T;
Source:
PHYSICA B-CONDENSED MATTER, 324 (1-4): 352-359; 2002
Abstract:
By means of high-resolution electron microscopy, tiling structures constructed by arrangements of atom clusters in a wide region (> 100 x 100 nm(2)) have been directly determined for the Al-Ni-Ru decagonal quasicrystal with 1.6 nm periodicity formed in the Al75Ni15Ru10 alloy annealed at 800degreesC and for its closely related approximant in the as-cast Al70Ni20Ru10 alloy, respectively. It has been found that the Al-Ni-Ru decagonal quasicrystal with 1.6 nm periodicity is a highly ordered quasicrystal and its structure is characterized by an aperiodic pentagonal tiling without any detectable linear phason strain. The approximant, which exhibits both periodic and quasiperiodic features in its electron diffraction pattern, is characterized by a pentagonal tiling containing a series of long chains of pentagons. The observed tilings for the Al-Ni-Ru decagonal quasicrystal and the approximant are compared with the theoretical tiling in the perpendicular space. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Comparative study of the high-pressure behavior of As, Sb, and Bi
Authors:
Haussermann, U; Soderberg, K; Norrestarrit, R; Wang, JC;
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 124 (51): 15359-15367; 2002
Abstract:
The high-pressure behavior of the heavier group 15 elements As, Sb, and Bi was investigated by means of ab initio density functional calculations employing pseudopotentials and a plane wave basis set. The high-pressure structural sequence of these elements is distinguished by the occurrence of the Bi-III structure, which is a complex, incommensurately modulated, host-guest structure. We approximated this structure by a supercell which reproduced the experimentally established pressure stability ranges of the host-guest structure for the different elements extremely well. With pressure we find an increasing admixture of d states (s-d hybridization) in the occupied levels of the electronic structure of As, Sb, and Bi. However, the s-d mixing remains at a low level. Thus, the emergence of a complex intermediate pressure structure cannot be explained by a pressure-induced altered valence state for these elements. Instead, it is argued that the Bi-III structure is a consequence of a delicate interplay between the electrostatic and the band energy contribution to the total energy. In the intermediate pressure range of heavier group 15 elements, both important parts of the total energy account equally for structural stability.
Title:
Origin of the superlattice reflections in Pb(Fe2/3W1/3)O-3
Authors:
Lin, MH; Lu, HY; Norrestarrit, R;
Source:
JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 85 (12): 3065-3070; 2002
Abstract:
Two types of superlattice reflections have been observed in pressureless-sintered Pb(Fe2/3W1/3)O-3 perovskite ceramics from selected-area electron diffraction patterns (SADPs). The presence of commensurate superlattice reflections of the {1/2 1/2 1/2} type found in as-sintered samples persisted after prolonged postsintering annealing at 800degreesC for 300 h. These reflections, conventionally termed the F-spots, represent the existence of the nanoscale cation-ordered domains of cubic perovskite Pb1-x(Fe1/2W1/2)O-3. However, the satellite-type incommensurate superlattice reflections, appearing as sideband spots to the fundamental reflections and occurring only along (111), (110), and (100), have gradually reduced their intensities and finally disappeared on postsintering annealing at 800degreesC. Observations via transmission electron microscopy (TEM) suggested that the "black dots" revealed in bright-field (BF) images have given rise to the incommensurate superlattice sideband spots. These dots of similar to5-10 mn are in fact a different type of nanocrystalline domain whose structure (and chemical composition) differs from those of the disordered Pb(Fe2/3W1/3)O-3 matrix and the ordered nanoscale Pb1-x(Fe1/2W1/2)O-3 domains. The nanocrystalline precipitates containing the paracrystalline phase are pyrochlore (Pb-2(Fe,W)O-6.5) formed during powder preparation via the solid-state mixed-oxide route. They become dispersed in the Pb(Fe2/3W1/3)O-3 perovskite matrix grain and have also undergone phase transformation to perovskite progressively during sintering and postsintering annealing. It is suggested that the nanocrystalline pyrochlore precipitates are metastable and disappear when chemical composition within the perovskite grains becomes homogenized from solid-state diffusion on postsintering annealing.
Title:
Nano icosahedral quasicrystals in Zr-based glassy alloys
Authors:
Saida, J; Matsushita, M; Inoue, A; Wang, JC;
Source:
INTERMETALLICS, 10 (11-12): 1089-1098; 2002
Abstract:
A nanoscale icosahedral quasicrystalline phase formation was found by the slight deviation from the three-component rule for high glass-forming ability in a Zr65Al7.5Ni10Cu17.5 glassy alloy. Since the primary phase consists of fee Zr2Ni and I-phases in the Zr65Al7.5Ni10Cu16.5(Ag, Pd, An or Pt)(1) glassy alloys, where an icosahedron is contained in both the phases, it is suggested that the local icosahedral atomic configuration exists in the glassy state and it stabilizes the supercooled liquid state. We also clarified that an I-phase precipitates in the Zr70Cu29Pd1 and Zr70Ni20Al9Pd1 glassy alloys and no I-phase formation is observed in the Zr70Ni29Pd1 amorphous alloy. Since the supercooled liquid region is confirmed in the Zr70Cu30 and Zr70Ni20Al10 glassy alloys and is not observed in the Zr70Ni30 amorphous alloy, it is concluded that the stability of the supercooled liquid state is strongly correlated with the existence of the local icosahedral order. (C) 2002 Elsevier Science Ltd. All rights reserved.
Title:
Formation of quasicrystals in Zr-Pd-(Cu) melt spun ribbons and mechanically milled powders
Authors:
Sordelet, DJ; Rozhkova, E; Besser, MF; Kramer, MJ; Eckert, J;
Source:
INTERMETALLICS, 10 (11-12): 1233-1240; 2002
Abstract:
Amorphous Zr70Pd30 and Zr70Pd20Cu10 alloys were prepared by mechanical milling and melt spinnng to compare their devitrification behaviors. The devitrification of mechanically milled Zr70Pd30 and Zr70Pd20Cu10 powders occurs via a single-step, first-order transformation to a stable Zr2Pd tetragonal structure. This is in sharp contrast to the devitrification of the same amorphous alloys prepared by melt spinning, in which a primary meta-stable quasicrystalline phase forms. Since the mechanical milling process does not involve direct liquid phase formation of an amorphous structure, it is inferred that the short-range order in the solid state derived amorphous powder is different from that in the melt spun ribbon. During mechanical milling of an amorphous melt spun ribbon, crystallization of the quasicrystalline phase appears to precede disordering into an amorphous structure having an different short range order. Deformation of an amorphous melt spun ribbon by repetitive rolling at ambient temperature crystallizes the meta-stable quasicrystalline phase. Published by Elsevier Science Ltd.
Title:
Effect of incommensurate charge-density wave scattering on the electronic structure of high-T-c cuprates
Authors:
Seibold, G; Varlamov, S; Besser, MF;
Source:
JOURNAL OF SUPERCONDUCTIVITY, 15 (5): 387-388; 2002
Abstract:
We argue that the collective mode as observed in angle resolved photoemission spectroscopy (ARPES) on a large class of cuprates can be associated with dynamic incommensurate CDW fluctuations present in these materials. This scenario is substantiated by a comparison of calculated spectra with experimental ARPES data where we obtain a mode frequency which decreases towards optimal doping thus strongly supporting the existence of a quantum. critical point around this concentration. Moreover we extract the temperature dependence of the associated bosonic spectrum from ARPES data where it turns out that there is a continuous evolution from mode-type behavior below T-c to a marginal Fermi liquid structure well above T-c.
Title:
Phase diagram for stripes in YBa2Cu3O6+x superconductors
Authors:
Mook, HA; Dogan, F; Besser, MF;
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 63 (12): 2163-2166; 2002
Abstract:
Neutron scattering has been used to measure the charge and spin structure in the YBa2Cu3O6+x, superconductors. Incommensurate static charge ordering is found at low doping levels while only charge fluctuations are found at higher doping. The spin structure is complex with both a commensurate resonance and incommensurate structure observed at low temperatures. The scattering results are used to construct a phase diagram for stripes in the YBa2Cu3O6+, system. (C) 2002 Published by Elsevier Science Ltd.
Title:
Millimeter-sized single Icosahedral quasicrystal of Zn-Mg-Sc alloy
Authors:
Kaneko, Y; Ishimasa, T; Besser, MF;
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 41 (10A): L1112-L1115; 2002
Abstract:
Millimeter-sized single icosahedral quasicrystals were produced by slow cooling from melt in Zn0.5Mg4.2Sc15.3 alloy. The alloy ingots were melted at 835degreesC for 1 h and then slowly cooled to an annealing temperature of 750degreesC at the cooling rates of 28 K/h and 60 K/h. Scanning electron microscopy, electron back-scattered diffraction. and selected-area electron diffraction and powder X-ray diffraction experiments repealed that the single quasicrystal has a P-type (primitive-type) structure with a six-dimensional lattice parameter of 0.7110 nm, and that the structural quality of the quasicrystal is high.
Title:
Modulated structures of Fe-10Mn-2Cr-1.5C alloy
Authors:
He, L; Jin, ZH; Lu, JD; Tang, J; Gonzalez-Calbet, JM;
Source:
MATERIALS & DESIGN, 23 (8): 717-720; 2002
Abstract:
In Fe-10Mn-2Cr-1.5C alloy the superlattice diffraction spots and satellite reflections have been observed by transmission electron microscopy, these results show that the ordering structure and modulated structure have taken place in this alloy. X-ray diffraction proved that austenitic steel in this alloy is more stable than in traditional austenitic manganese steel. Based on this investigation, we consider that the C-Mn ordering clusters were existing in austenitic manganese steel and the chromium could strengthen this effect by linking the weaker C-Mn couples together. These structures may play an important role in the work hardening of austenitic manganese steel. (C) 2002 Elsevier Science Ltd. All rights reserved.
Title:
Growth of a textured quasicrystalline phase in Ti-Ni-Zr films prepared by pulsed laser deposition
Authors:
Brien, V; Dauscher, A; Weisbecker, P; Machizaud, F; Gonzalez-Calbet, JM;
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 76 (2): 187-195; 2003
Abstract:
The preparation in thin film form of the known icosahedral phase in Ti-Ni-Zr bulk alloys has been investigate as a function of substrate temperature. Films were deposited by pulsed laser deposition on sapphire substrates at temperatures ranging from room temperature to 350 degreesC. Morphological and structural modifications have been followed by grazing-incidence and theta-2theta X-ray diffraction, transmission electron diffraction and imaging. Chemical composition has been analyzed by electron probe microanalysis. The in-depth variation of composition has been studied by secondary neutral mass spectroscopy. We show that pulsed laser deposition at 275 degreesC makes the formation of a 1-mum-thick film of Ti-Ni-Zr quasicrystalline textured nanocrystallites possible.
Title:
Quantum dynamics in high codimension tilings: From quasiperiodicity to disorder
Authors:
Vidal, J; Destainville, N; Mosseri, R;
Source:
PHYSICAL REVIEW B, 68 (17); 2003
Abstract:
We analyze the spreading of wave packets in two-dimensional quasiperiodic and random tilings as a function of their codimension, i.e., of their topological complexity. In the quasiperiodic case, we show that the diffusion exponent that characterizes the propagation decreases when the codimension increases and goes to 1/2 in the high codimension limit. By contrast, the exponent for the random tilings is independent of their codimension and also equals 1/2. This shows that, in high codimension, the quasiperiodicity is irrelevant and that the topological disorder leads in every case, to a diffusive regime, at least in the time scale investigated here.
Title:
Incommensurate magnetic structure of beta-MnO2
Authors:
Regulski, M; Przenioslo, R; Sosnowska, I; Hoffmann, JU;
Source:
PHYSICAL REVIEW B, 68 (17); 2003
Abstract:
beta-MnO2 has a well-known screw type magnetic structure. According to Yoshimori [J. Phys. Soc. Jpn. 14, 807 (1959)] the pitch of this screw is exactly 7/2c. We performed neutron powder diffraction measurements which show that the pitch of the screw is about 4% shorter than <7/2c so β-MnO2 has an incommensurate magnetic ordering. This result has important consequences on the calculation of the values of the exchange integrals in β-MnO2 by Yoshimori, and Ohama and Hamaguchi [J. Phys. Soc. Jpn. 30, 1311 (1971)]. The present results are compared with the neutron powder diffraction data measured on β-MnO2 by Gonzalo and Cox [An. Fis. 66, 407 (1970)] and recent magnetic x-ray diffraction by Sato [J. Phys. Soc. Jpn. 70, 37 (2001)]. The values of the magnetic moments of Mn+4 ions are estimated.
Title:
Low-temperature structural phase transition in a Cd6Y 1/1 approximant
Authors:
Tamura, R; Edagawa, K; Aoki, C; Takeuchi, S; Suzuki, K;
Source:
PHYSICAL REVIEW B, 68 (17); 2003
Abstract:
Electron and x-ray-diffraction studies have revealed that a Cd6Y 1/1 crystalline approximant (Im (3) over bar, a=1.5482 nm) undergoes a phase transition at some temperature around 160 K. The transition accompanies a change of the lattice period as well as an extremely small tetragonal distortion (c/a=0.9992+/-0.0002). Differential scanning calorimetry experiment also exhibits an anomaly around 175 K and the transition entropy suggests that the transition is of the order-disorder type with respect to the orientation of the Cd tetrahedron situated inside the icosahedral cluster. The phenomenon is discussed within the formalism of the Landau theory and it is suggested that the transition is attributed to an irreducible representation at the zone-boundary (N point) and the low-temperature phase possesses an orthorhombic 2ax2axa superlattice.
Title:
Structure and charge transfer driven by the controlled amount of additional oxygen in cation-stoichiometric Bi2Sr2CuO6+delta
Authors:
Jean, F; Colson, D; Collin, G; Blanchard, N; Konstantinovic, Z; Le Bras, G; Forget, A; Andrieux, M;
Source:
PHYSICAL REVIEW B, 68 (17); 2003
Abstract:
Polycrystalline Bi-2201 with stoichiometric cationic ratios has been prepared, and an extensive study for the determination and control of the oxygen content was carried out. The extra-oxygen amount per formula unit, delta in Bi2Sr2CuO6+delta, ranged from 0.18 down to 0.10 under appropriate annealing conditions. The evolution of the lattice parameters with the oxygen concentration, featuring a switch in the modulation wave-vector components, is presented. In this range of compositions, T-c varies from 3 K (overdoped) to 10 K (underdoped) through a maximum at 16.5 K, showing that, by fine tuning the oxygen excess, most doping levels are accessible in the nominal, substitution-free, Bi-2201.
Title:
Ferroquadrupole ordering and Gamma(5) rattling motion in the clathrate compound Ce3Pd20Ge6
Authors:
Nemoto, Y; Yamaguchi, T; Horino, T; Akatsu, M; Yanagisawa, T; Goto, T; Suzuki, O; Donni, A; Komatsubara, T;
Source:
PHYSICAL REVIEW B, 68 (18); 2003
Abstract:
Lattice effects in a cerium based clathrate compound Ce3Pd20Ge6 with a cubic Cr23C6-type structure have been investigated by ultrasonic and thermal expansion measurements. Elastic softenings of (C-11-C-12)/2 and C-44 proportional to the reciprocal temperature 1/T above T-Q1=1.25 K are well described in terms of the quadrupole susceptibility for the ground state Gamma(8) quartet. A huge softening of 50% in (C-11-C-12)/2 and a spontaneous expansion DeltaL/L=1.9x10(-4) along the [001] direction in particular indicate the ferroquadrupole ordering of O-2(0) below T-Q1. The elastic anomalies associated with the antiferromagnetic ordering at T-N2=0.75 K and the incommensurate antiferromagnetic ordering are also found. Notable frequency dependence of C-44 around 10 K is accounted for by the Debye-type dispersion indicating a Gamma(5) rattling motion of an off-center Ce ion along the [111] direction with eight fractionally occupied positions around the 4a site in a cage. The thermally activated Gamma(5) rattling motion obeying a relaxation time tau=tau(0) exp (E/k(B)T) with an attempt time tau(0)=3.1x10(-11) sec and an activation energy E=70 K dies out with decreasing temperature, and then the off-center tunneling state of Ce ion in the 4a-site cage will appear at low temperatures.
Title:
Contribution of local atomic arrangements and electronic structure to high electrical resistivity in the Al82.6-xRe17.4Six (7 <= x <= 12) 1/1-1/1-1/1 approximant
Authors:
Takeuchi, T; Onogi, T; Otagiri, T; Mizutani, U; Sato, H; Kato, K; Kamiyama, T; Donni, A;
Source:
PHYSICAL REVIEW B, 68 (18); 2003
Abstract:
Electrical resistivity of Al82.6-xRe17.4Six (7less than or equal toxless than or equal to12) 1/1-1/1-1/1 approximants was discussed in terms of their electronic structure near the Fermi level and the local atomic arrangements. Strong composition dependence of the electrical resistivity was observed for these 1/1-1/1/-1/1 approximants; samples with x=7, 9, and 12 show the Boltzmann-type electrical resistivity, while the others possess behaviors expected for system under the weak-localization. We found that the weak localization effect in the electrical resistivity, which is one of the characteristics of the corresponding Al-based quasicrystals, appears only when a condition of very low density of states with imperfections in the periodicity is satisfied. The Boltzmann-type behavior, on the other hand, takes place when one of the two factors, the very low density of states or the imperfection in the periodicity, is absent from the structure of the 1/1-1/1-1/1 approximant.
Title:
Semiconducting Al-transition-metal quasicrystals
Authors:
Krajci , M; Hafner, J; Otagiri, T;
Source:
PHYSICAL REVIEW B, 68 (16); 2003
Abstract:
We report on a class of icosahedral aluminum-transition-metal (Al-TM) alloys with true semiconducting behavior. Our description of the structure of these icosahedral quasicrystals is based on the six-dimensional Katz-Gratias-Boudard (KGB) model of the face-centered-icosahedral (fci) quasicrystal and its rational approximants. The shell structure of the atomic surfaces in perpendicular space defines the chemical order of aluminum and transition-metal (TM) atoms leading to semiconducting transport properties. In transition-metal aluminides the hybridization between the Al(s,p) and transition-metal d orbitals is responsible for the formation of a semiconducting gap in the electronic spectrum. We have analyzed the electronic charge distribution and observed an enhanced charge density along the Al-TM bonds that is characteristic of covalent bonding. The existence of an energy gap in the electronic spectrum at or in the vicinity of the Fermi level is explicitly demonstrated for several low-order approximants in the hierarchy of Fibonacci approximants which converges to the icosahedral quasicrystals of the fci class, to which also the i-AlPdRe belongs. We predict existence of truly semiconducting quasicrystalline 1/1-approximants. Our results also lead to the prediction of the existence of new semiconducting quasicrystals with specified Al-TM compositions. The possibility of the existence of a semiconducting band gap suggests an explanation for the anomalously high resistivity of the icosahedral AlPdRe quasicrystals. We demonstrate that substitutional defects violating the ideal Al-TM ordering predicted by the KGB model lead to the formation of localized states in the band gap. A real sample of i-AlPdRe thus seems to be a semiconductor with a band gap filled by the localized states.
Title:
Relations between the six-dimensional structure of icosahedral Al-Pd-Mn and its 1/1 crystal approximants
Authors:
Yamamoto, A; Takakura, H; Manolescu, A;
Source:
PHYSICAL REVIEW B, 68 (13); 2003
Abstract:
A six-dimensional (6D) structure of i-Al-Pd-Mn quasicrystal determined recently [Yamamoto , J. Alloys Compd. 342, 159 (2002)] leads to two 1/1 approximant structures of i-Al-Pd-Mn and i-Al-Cu-Ru with the space group Pm (3) over bar (alpha Al-Pd-Mn-Si and alpha Al-Ru-Cu) by the introduction of appropriate uniform (linear) phason strains. The different clusters in the 1/1 approximants are obtained from the different 3D hyperplane passing through (1,1,1,1,1,1)/4 and (1,0,0,0,0,0)/2 in the 6D icosahedral lattice. It is shown that for all cubic approximant represented by consecutive Fibonacci numbers Fn+1/F-n, two different structures can be obtained in the same manner.
Title:
Electron momentum distribution of icosahedral Cd84Yb16 studied by Compton scattering
Authors:
Okada, JT; Watanabe, Y; Nanao, S; Tamura, R; Takeuchi, S; Yokoyama, Y; Hiraoka, N; Itou, M; Sakurai, Y;
Source:
PHYSICAL REVIEW B, 68 (13); 2003
Abstract:
The electron momentum distribution in icosahedral Cd84Yb16 has been studied using the high-resolution Compton scattering technique with a momentum resolution of 0.16 a.u. The experimental valence-electron Compton profile is decomposed into two components: an inverted parabolalike one and a broad Gaussian-like one. We have found that the Fermi sphere, deduced from the number of electrons under the inverted parabolalike component, just coincides with the quasi-Brillouin zones constructed from the intense (211111) and (221001) reciprocal points. The Gaussian-like part is attributed to the electron occupation of the Yb 5d states. These facts are taken as signature that both the Hume-Rothery mechanism and the sp-d hybridization mechanism contribute to the formation of the pseudogap, stabilizing the icosahedral phase of Cd84Yb16.
Title:
Anomalous magnetism in decagonal Al69.8Pd12.1Mn18.1
Authors:
Rau, D; Gavilano, JL; Mushkolaj, S; Beeli, C; Chernikov, MA; Ott, HR; Hiraoka, N;
Source:
PHYSICAL REVIEW B, 68 (13); 2003
Abstract:
We report the results of measurements of Al-27 and Mn-55 NMR spectra, the related spin-lattice relaxation rates, and the dc magnetic susceptibility of the stable decagonal quasicrystal Al69.8Pd12.1Mn18.2. The temperature variation of the magnetic susceptibility chi(T) reveals that the Mn ions carry only an effective magnetic moment of approximately 2mu(B), and confirms a spin-glass-type freezing of the Mn moments at T-f=12 K. The NMR spectra reveal two partially resolved lines for the Al-27-nuclei, indicating that there are two different sets of environments for the Al-sites. The integrated intensity of the Mn line in the spectra suggests that about half of the Mn ions carry no magnetic moment. Below 50 K, and upon decreasing the temperature, the Al-27 NMR linewidth w and the spin-lattice relaxation rate T-1(-1) both grow with an increasingly negative slope, as it is often observed and interpreted as a critical "slowing down" of magnetic moments in systems approaching a spin-glass transition. Various features, such as a broad maximum in T-1(-1)(T) and a slope change in the w(chi) plot, both around 120 K, suggest a gradual reduction of the number of Mn moments with decreasing temperature below 120 K.
Title:
Structural perfection and the electrical and magnetic responses of icosahedral AlPdMn quasicrystals
Authors:
Klanjsek, M; Jeglic, P; McGuiness, P; Feuerbacher, M; Zijlstra, ES; Dubois, JM; Dolinsek, J; Itou, M;
Source:
PHYSICAL REVIEW B, 68 (13); 2003
Abstract:
According to reports in the literature, icosahedral i-AlPdMn quasicrystalline samples of a similar composition can exhibit very different magnetic and electrical properties, for example, the spin-glass state, the Kondo compensation of Mn magnetic moments, diamagnetism, and the maximum and minimum in the electrical resistivity. In order to shed light on the origin of these differences, we performed x-ray diffraction (XRD), electrical resistivity, magnetic susceptibility, and nuclear magnetic resonance (NMR) relaxation studies on three i-AlPdMn samples with high structural quasiperiodic order that were grown by two different techniques-the Czochralski and the self-flux. The measured parameters-the resistivity with its negative temperature coefficient, the fraction of magnetic Mn atoms, and the partial s-state electronic density of states (s-DOS)-of the investigated samples were found to be quite different, despite their comparable XRD-determined structural qualities. The Czochralski-grown samples were found to be less magnetic and more resistive than the self-flux-grown sample. The amount of magnetic Mn atoms increases with the increased metallic character of the samples. The NMR-determined s-DOS at the Fermi energy was compared to a theoretical ab initio calculation for an Al71Pd21Mn8 approximant, and good agreement was found. Our results are in qualitative agreement with the previously observed empirical trend that high resistivity is associated with high structural quality of the i-AlPdMn quasicrystals, but the observed small differences in the structural perfection of the investigated samples do not give convincing support to the hypothesis that this could be the main origin of the large differences in the electrical and magnetic response between the samples.
Title:
Coincidence of reciprocal lattice planes model for quasicrystal-crystal epitaxy
Authors:
Widjaja, EJ; Marks, LD; McGuiness, P;
Source:
PHYSICAL REVIEW B, 68 (13); 2003
Abstract:
A coincidence of reciprocal lattice planes model was developed to calculate the interfacial energy in quasicrystal-crystal epitaxy. This model allows a quantitative description of the interface as opposed to previously employed qualitative models that consider symmetry relations and alignment of rotation axes. Computations were carried out on several types of quasicrystal-crystal systems, namely, the crystalline structures on various surfaces of single quasicrystals (Al-Cu-Fe, Al-Ni-Co, and Al-Cu-Co) caused by ion bombardment, the crystalline thin films grown on quasicrystal substrates, and the quasicrystalline thin films grown on crystalline substrates. This model can also be extended to include quasicrystal-quasicrystal epitaxy.
Title:
Magnetic properties of icosahedral Al-Pd-Mn quasicrystals
Authors:
Hippert, F; Audier, M; Prejean, JJ; Sulpice, A; Lhotel, E; Simonet, V; Calvayrac, Y; Itou, M;
Source:
PHYSICAL REVIEW B, 68 (13); 2003
Abstract:
The magnetic properties of icosahedral Al-Pd-Mn phases have been investigated by studying a large set of samples, including single crystals and polycrystalline ribbons. The composition and structure (F, F-2, or F-2M) of each sample have been determined. Composition changes and thermal treatments lead to a wide range of magnetic susceptibility variations (by a factor around 55). The comparison of susceptibility data for all studied samples, as well as for literature samples, shows that the temperature dependence of the magnetic susceptibility exhibits a universal behavior, whatever the structural state, composition, and thermal treatment. It can be accounted for by a Kondo effect gradually affected by magnetic RKKY-type interactions as the concentration of magnetic Mn atoms increases. The magnetic Mn atom concentration is small, ranging from 3.8x10(-5) for the less magnetic sample studied up to 2x10(-3) for the more magnetic one-i.e., much less than the Mn concentration in the icosahredral phase (similar to8x10(-2)). It varies with thermal treatments and depends strongly on the composition of the icosahedral phase. In particular, the magnetic properties are found to evolve along the growth direction of a large single grain obtained by the Czochralski technique in relation with composition variations.
Title:
Hidden magnetic transitions in the thermoelectric layered cobaltite [Ca2CoO3](0.62)[CoO2]
Authors:
Sugiyama, J; Brewer, JH; Ansaldo, EJ; Itahara, H; Dohmae, K; Seno, Y; Xia, C; Tani, T; Sakurai, Y;
Source:
PHYSICAL REVIEW B, 68 (13); 2003
Abstract:
A positive muon spin rotation and relaxation (mu(+)SR) experiment on [Ca2CoO3](0.62)[CoO2] (i.e., Ca3Co4O9, a layered thermoelectric cobaltite) indicates the existence of two magnetic transitions at similar to100 K and 400-600 K; the former is a transition from a paramagnetic state to an incommensurate (IC) spin-density wave (SDW) state. The anisotropic behavior of zero-field mu(+)SR spectra at 5 K suggests that the IC-SDW propagates in the a-b plane, with oscillating moments directed along the c axis; also the IC-SDW is found to exist not in the [Ca2CoO3] subsystem but in the [CoO2] subsystem. In addition, it is found that the long-range IC-SDW order completes below similar to30 K, whereas the short-range order appears below 100 K. The latter transition is interpreted as a gradual change in the spin state of Co ions above 400 K. These two magnetic transitions detected by mu(+)SR are found to correlate closely with the transport properties of [Ca2CoO3](0.62)[CoO2].
Title:
Extended scattering continua characteristic of spin fractionalization in the two-dimensional frustrated quantum magnet Cs2CuCl4 observed by neutron scattering
Authors:
Coldea, R; Tennant, DA; Tylczynski, Z; Itahara, H;
Source:
PHYSICAL REVIEW B, 68 (13); 2003
Abstract:
The magnetic excitations of the quasi-2D spin-1/2 frustrated Heisenberg antiferromagnet Cs2CuCl4 are explored throughout the 2D Brillouin zone using high-resolution time-of-flight inelastic neutron scattering. Measurements are made both in the magnetically ordered phase, stabilized at low temperatures by the weak interlayer couplings, as well as in the spin liquid phase above the ordering temperature T-N, when the 2D magnetic layers are decoupled. In the spin liquid phase the dynamical correlations are dominated by highly dispersive excitation continua, a characteristic signature of fractionalization of S=1 spin waves into pairs of deconfined S=1/2 spinons and the hallmark of a resonating-valence-bond (RVB) state. The boundaries of the excitation continua have strong 2D-modulated incommensurate dispersion relations. Upon cooling below T-N magnetic order in an incommensurate spiral forms due to the 2D frustrated couplings. In this phase sharp magnons carrying a small part of the total scattering weight are observed at low energies, but the dominant continuum scattering which occurs at medium to high energies is essentially unchanged compared to the spin liquid phase. Linear spin-wave theory including one- and two-magnon processes can describe the sharp magnon excitation, but not the dominant continuum scattering, which instead is well described by a parametrized two-spinon cross section. Those results suggest a crossover in the nature of the excitations from S=1 spin waves at low energies to deconfined S=1/2 spinons at medium to high energies, which could be understood if Cs2CuCl4 was in the close proximity of transition between a fractional RVB spin liquid and a magnetically ordered state. A large renormalization factor of the excitation energies [R=1.63(5)], indicating strong quantum fluctuations in the ground state, is obtained using the exchange couplings determined from saturation-field measurements. We provide an independent consistency check of this quantum
Title:
Spin fluctuations and non-Fermi-liquid behavior of CeNi2Ge2
Authors:
Kadowaki, H; Fak, B; Fukuhara, T; Maezawa, K; Nakajima, K; Adams, MA; Raymond, S; Flouquet, J; Sakurai, Y;
Source:
PHYSICAL REVIEW B, 68 (14); 2003
Abstract:
Neutron scattering shows that non-Fermi-liquid behavior of the heavy-fermion compound CeNi2Ge2 is brought about by the development of low-energy spin fluctuations with an energy scale of 0.6 meV. They appear around the antiferromagnetic wave vectors (1/21/20) and (003/4) at low temperatures, and coexist with high-energy spin fluctuations with an energy scale of 4 meV and a modulation vector (0.23,0.23,1/2). This unusual energy dependent structure of Imchi(Q,E) in Q space suggests that quasiparticle bands are important.
Title:
Continuous defect-free structural transformation of long-range order from quasiperiodic to translational
Authors:
Rochal, SB; Lorman, VL; Fukuhara, T;
Source:
PHYSICAL REVIEW B, 68 (14); 2003
Abstract:
We show that the perfect (defect-free) quasicrystalline order can be transformed continuously into a perfect crystalline one through a sequence of intermediate structures. The example of the pentagonal Penrose tiling is analyzed. The atomic positions in neighboring structures of the sequence either coincide or differ by one of 10 orientationally equivalent atomic jump vectors. Defect-free reconstruction is possible provided the linear phason strain is accompanied by a simultaneous shape variation of the atomic surface (AS). Two-step quasicrystal-to-crystal transformation is considered. In such a case the final crystalline state is obtained by two mutually orthogonal continuous phason distortions. The distortion of the first type results in a one-dimensional defect-free quasicrystal.
Title:
Superstructures and coincidences of a thin oxide film on a metallic substrate: A STM study
Authors:
Maroutian, T; Degen, S; Becker, C; Wandelt, K; Berndt, R; Adams, MA;
Source:
PHYSICAL REVIEW B, 68 (15); 2003
Abstract:
An alumina thin film, grown at 1000 K on a Ni3Al(111) substrate, is investigated using low-temperature scanning tunneling microscopy. Depending on the (positive) voltage applied to the sample, two superstructures are imaged. Using tunneling spectroscopy, this effect is traced back to a lateral variation of the local density of states within the apparent unit cell of the oxide thin film. In the vicinity of the conduction-band edge, the density of empty states for tunneling electrons is locally enhanced over characteristic points of the unit cell. A coincidence lattice between film and metallic substrate, with a unit cell of same size and symmetry, is proposed as the origin of this modulation of the oxide electronic structure.
Title:
Ordering of an incommensurate molecular layer with adsorbate-induced reconstruction: C-60/Ag(100)
Authors:
Pai, WW; Hsu, CL; Reutt-Robey, JE;
Source:
PHYSICAL REVIEW B, 68 (12); 2003
Abstract:
The nature of distinct bright-dim C-60 contrast and its intricate ordering on Ag(100) is clarified with scanning tunneling microscopy. The C-60 film is (111) close-packed with locally distorted rhombic units of specific contrast order, forming an incommensurate aperiodic phase. We relate the C-60 contrast to an interfacial restructuring beneath each dim C-60, with its ordering determined by competing interactions in the reconstructed interface and of the rhombus configuration.
Title:
Possible presence of a charge-orbital density wave in layered manganites Nd1-xCa1+xMnO4
Authors:
Nagai, T; Kimura, T; Yamazaki, A; Tomioka, Y; Kimoto, K; Tokura, Y; Matsui, Y; Flouquet, J;
Source:
PHYSICAL REVIEW B, 68 (9); 2003
Abstract:
We have studied the structural modifications related to the charge-orbital ordering for single-layered manganites Nd1-xCa1+xMnO4 with both commensurate and incommensurate doping levels (0.55less than or equal toxless than or equal to0.75). High-resolution electron microscopy (HREM) revealed transverse and sinusoidal structural modulations with a doping-level-dependent period of d(s)=a/(1-x) in the charge-orbital ordered phases. We discuss the possibility of an orbital-density wave as well as a charge-density wave based on the HREM observation of the single-layered manganites.
Title:
Six-dimensional model of icosahedral Al-Pd-Mn quasicrystals
Authors:
Yamamoto, A; Takakura, H; Tsai, AP; Tomioka, Y;
Source:
PHYSICAL REVIEW B, 68 (9); 2003
Abstract:
A six-dimensional cluster model of icosahedral Al-Pd-Mn (i-Al-Pd-Mn) quasicrystals used in the recent structure refinement is described in detail. This model is based on five kinds of clusters located at vertices, edge centers of the inflated three-dimensional Penrose pattern (3DPP) with an edge length of about 20 Angstrom, and two body-diagonal positions of each acute rhombohedron. Two kinds of 20 Angstrom clusters, one of which is seen in beta-Al-Pd-Mn-Si, are located at even- and odd-parity 12-fold vertices of the inflated 3DPP. This is proved to give small R factors (R-w=0.055, R=0.049) for 493 independent reflections and leads to the 1/1 and 2/1 approximant structures of i-Al-Pd-Mn (alpha- and beta-Al-Pd-Mn-Si) by introducing appropriate cubic phason strains and taking a three-dimensional cut.
Title:
Spin freezing in the decagonal phase of the Al-Mn-Pd alloy system
Authors:
Chernikov, MA; Beeli, C; Felder, E; Buchi, S; Ott, HR; Tokura, Y;
Source:
PHYSICAL REVIEW B, 68 (9); 2003
Abstract:
We report the results of measurements of the low-temperature specific heat C-p(T) of annealed samples of decagonal Al69.8Mn18.1Pd12.1. A comparison with similar data, previously obtained for decagonal Al-Cu-Co quasicrystals, indicate a substantial excess specific heat C-ex(T) in the Al-Mn-Pd material, most likely due to magnetic degrees of freedom. The temperature dependence of C-ex(T) suggests a spin freezing phenomenon at T-f=12 K, which is confirmed by the temperature dependence of the third-order magnetic susceptibility chi(3)(T) and the time dependence of the remanent magnetization well below T-f.
Title:
High-temperature thermal transport properties of a single-grain decagonal Al74Ni10Co16 quasicrystal
Authors:
Barrow, JA; Cook, BA; Canfield, PC; Sordelet, DJ; Ott, HR;
Source:
PHYSICAL REVIEW B, 68 (10); 2003
Abstract:
Thermal transport properties have been determined for a decagonal Al74Ni10Co16 quasicrystal in the temperature range 373-873 K. Differential scanning calorimetry and a laser flash method were employed in the determination of heat capacity and thermal diffusivity, respectively. Thermal conductivity was determined from the product of diffusivity, heat capacity, and density. A high degree of anisotropy was observed between the aperiodic and periodic axes. The anisotropic heat flow is described using the thermal ellipsoid model. The model was applied to a surface oriented 45degrees to the major axes and substantiated from bulk measurements obtained from a sample cut along this orientation. Within this temperature range, the thermal transport of this two-dimensional quasicrystal may be described in a manner similar to anisotropic metallic single crystals.
Title:
Electronic valence bands in decagonal Al-Ni-Co
Authors:
Theis, W; Rotenberg, E; Franke, KJ; Gille, P; Horn, K; Tokura, Y;
Source:
PHYSICAL REVIEW B, 68 (10); 2003
Abstract:
Valence-band photoemission from the s-p region of the tenfold and the two inequivalent twofold surfaces of quasicrystalline decagonal Al71.8Ni14.8Co13.4 reveals strongly dispersing bands. These exhibit a free-electron-like dispersion along quasiperiodic and periodic directions of the decagonal quasicrystal. The experimental photoemission maps are reproduced in detail by a model in which parabolic bands emanate from a set of reciprocal lattice vectors. A parity rule for the principal zone centers is observed.
Title:
High-temperature magnetic order and coexisting spin dynamics in PrCu2: Manifestations of multipolar effects
Authors:
Schenck, A; Gygax, FN; Onuki, Y; Gille, P;
Source:
PHYSICAL REVIEW B, 68 (10); 2003
Abstract:
We present a comprehensive muon-spin-rotation/relaxation (muSR) study of the high-temperature magnetic order (T(N)similar or equal to65 K) in PrCu2, first observed quite unexpectedly in 1998 [A. Schenck , Phys. Rev. B 58, 5205 (1998)]. Measurements in zero and longitudinal fields as a function of temperature, orientation of the single-crystal sample, and strength of applied magnetic field H-ext confirmed the previous findings and allowed us to determine the properties of the internal spontaneous fields B in detail. It is found that B is strictly confined to the crystallographic (a,c) plane and encloses on average an angle theta of 30degrees-45degrees with the a axis, depending on temperature. Both parallel toBparallel to and theta display a large variation. This is consistent with, but does not unambiguously prove, the incommensurately modulated antiferromagnetic structure observed below similar to50 mK by neutron scattering [S. Kawarazaki and J. Arthur, J. Phys. Soc. Jpn. 57, 1077 (1988)]. The estimated ordered electronic moment of similar to0.29 mu(B) is smaller than the value quoted by Kawarazaki (0.54 mu(B)). The temperature dependence of parallel toBparallel to is highly unusual and scales perfectly with the temperature dependence of the elastic constant C-66 [R. Settai , J. Phys. Soc. Jpn 67, 636 (1998)], implying that the ordered moment is proportional to the strain susceptibility involving the O-xy quadrupole moment. mu(+) is also found to be exposed to fluctuating field components inducing spin-lattice relaxation. The relaxation rate lambda consists of a field-independent but rather anisotropic term and an essentially isotropic but field-dependent term. The first term reflects the Jahn-Teller transition at 7.5 K by a cusplike anomaly. Transverse-field measurements at 6 kOe and above 100 K allowed us to determine the anisotropic Knight shift, or the dipolar coupling tensor, from which it follows that mu(+) are located at 4e sites. At lower temperatures, w
Title:
Theory of spin response in underdoped cuprates as strongly fluctuating d-wave superconductors
Authors:
Herbut, IF; Lee, DJ; Onuki, Y;
Source:
PHYSICAL REVIEW B, 68 (10); 2003
Abstract:
We study the spin dynamics in underdoped cuprates at low temperatures by considering them as quasi-two-dimensional d-wave superconductors with strong quantum phase fluctuations. An effective theory of spin degrees of freedom of nodal quasiparticles coupled to vortex defects in the phase of the superconducting order parameter is formulated. It represents the minimal extension of the three-dimensional QED theory of the pseudogap phase into the superconducting region. The theory predicts a single superconductor-spin-density wave (SC-SDW) phase transition, without coexistence between the two phases. At the transition, which may be fluctuation-induced first order, vortices condense (and SC is lost) and the chiral symmetry for fermions simultaneously breaks (and SDW is formed). We compute the spin-spin correlation function in the fluctuating superconducting state and explain the evolution of the spin response with energy in underdoped YBa2Cu3O6+x observed in neutron-scattering experiments. In particular, we predict that at very low frequencies omegasimilar to(1/10)omega(res), with omega(res) being the energy of the "resonance" at Q=(pi,pi), (weak) spin response should become narrowly peaked at four diagonally incommensurate wave vectors that span between the nodes of the superconducting order parameter. These peaks represent the inherent collective mode of the phase fluctuating d-wave superconductor, the condensation of which would bring about the SDW order in the pseudogap phase. Our interpretation of the resonance suggests that it should become more elusive in the superconductors with lower T-c, in accord with its conspicuous absence in La2-xSrxCuO4.
Title:
Comparative structural study of the disordered MCd6 quasicrystal approximants
Authors:
Gomez, CP; Lidin, S; Depmeier, W;
Source:
PHYSICAL REVIEW B, 68 (2); 2003
Abstract:
Several of the MCd6 approximants (M = Pr, Nd, Sm, Eu, Gd, Dy, Yb, Y, and Ca) to the MCd5.7 quasicrystals (M = Yb and Ca) have been synthesized and their structures have been refined from single-crystal x-ray-diffraction data; the different types of disorder of the central Cd-4 tetrahedra located in the dodecahedral cavities of these closely related compounds have been examined and mutually compared. A model that describes this disorder and can be applied to all the examined MCd6 phases has been elaborated. The refinements made on these phases differ from what is found in previous reports.
Title:
Complex magnetic ground state of CuB2O4
Authors:
Boehm, M; Roessli, B; Schefer, J; Wills, AS; Ouladdiaf, B; Lelievre-Berna, E; Staub, U; Petrakovskii, GA; Sakurai, Y;
Source:
PHYSICAL REVIEW B, 68 (2); 2003
Abstract:
The magnetic ground-state of copper metaborate CuB2O4 was investigated with unpolarized and polarized neutron scattering. A phase transition was found at T-N = 21 K to a commensurate weakly ferromagnetic state followed by a second transition at T* = 10 K to an incommensurate magnetic structure. Neutron diffraction revealed a continuously changing magnetic propagation vector below T*, and unusually asymmetric magnetic satellite reflections. Additionally, diffuse scattering is observed in the temperature range 1.5 K less than or equal to Tless than or equal to 30 K. The magnetic structure determined in both phases are shown to be consistent with results of symmetry analysis. In particular, we find that only one of the two inequivalent Cu2+ sublattice fully orders down to the lowest temperature. Our results show that the complex magnetic behavior of copper metaborate is a consequence of mutual interaction between the two Cu2+ sublattices with different ordering temperatures.
Title:
Influence of quasicrystal bulk structure on oxidized AlPdMn surface properties probed by electronic and vibrational spectroscopies
Authors:
Dubot, P; Cenedese, P; Gratias, D; Uchinokura, K;
Source:
PHYSICAL REVIEW B, 68 (3); 2003
Abstract:
High-resolution electron energy-loss spectroscopy and x-ray photoemission are used to probe the fivefold AlPdMn oxidized surface. The vibrational spectrum reveals a strong increase of the Al-O stretching mode wave number while the oxygen Auger transition and photoelectron spectra prove the high ionicity of the thin alumina layer. These observations are markedly different from those made with oxidized aluminum and can be related to the low reactivity of the quasicrystal surface. The influence of the quasicrystal bulk structure on the oxidized surface vibrational mode and ionicity can be well understood by image forces theory and the static dielectric constant behavior between the pure free-electron metal and the quasicrystalline alloy.
Title:
Interplay between electronic structure and medium-range atomic order in hexagonal beta-Al9Mn3Si and phi-Al10Mn3 crystals
Authors:
de Laissardiere, GT; Fratini, S;
Source:
PHYSICAL REVIEW B, 68 (4); 2003
Abstract:
The electronic structures of the hexagonal beta-Al9Mn3Si and phi-Al10Mn3 phases are calculated from first-principles using the TB-LMTO method. These ab initio results are analyzed with a simplified model for Al-based alloys containing transition metal atoms. The results show a strong effect on the atomic structure stabilization by an effective Mn-Mn interaction mediated by conduction electrons over medium-range distances (5 Angstrom and more). The origin of large vacancies which characterize such atomic structures is explained. The position and the effect of Si atoms in stabilizing are also discussed. The atomic structures of beta-Al9Mn3Si and phi-Al10Mn3 bear resemblance with the atomic medium-range structures of approximants of quasicrystals. Consequently, the present work gives arguments on the interplay between the medium-range atomic order and an minimization of the band energy in quasicrystals and related phases.
Title:
Low-temperature phases of Xe on Pd(111)
Authors:
Zhu, JF; Ellmer, H; Malissa, H; Brandstetter, T; Semrad, D; Zeppenfeld, P; Canfield, RC;
Source:
PHYSICAL REVIEW B, 68 (4); 2003
Abstract:
Low-energy electron diffraction (LEED) and temperature-programmed desorption (TPD) were used to determine the adsorption properties and the structural phase diagram of Xe on the clean Pd(111) surface. The binding energy of a Xe atom to the substrate is found to be quite strong (320 +/- 10 meV), whereas the effective Xe-Xe lateral interaction is extremely weak (V-lat much less than10 meV) and most likely attractive on the clean Pd(111) surface. Within the monolayer regime, a phase transition sequence from a commensurate (root3 x root3)R30degrees phase to a hexagonal incommensurate phase (HI) and, finally, to a hexagonal incommensurate rotated phase (HIR) is observed. The resulting phase diagram is compared to theoretical predictions and other rare-gas adsorption systems. The Xe adlayer structure turns out to be extremely sensitive to the presence of impurities, such as H and CO. This sensitivity can be rationalized by the weak Xe-Xe lateral interaction.
Title:
First-principles studies of structures and stabilities of Pb/Si(111)
Authors:
Chan, TL; Wang, CZ; Hupalo, M; Tringides, MC; Lu, ZY; Ho, KM; Canfield, RC;
Source:
PHYSICAL REVIEW B, 68 (4); 2003
Abstract:
Various structures of Pb/Si(111) from 1/6 ML to 4/3 ML are investigated using first-principles calculations. Our calculations for the 1/6-ML mosaic phase and 1/3-ML beta-phase yield good agreement with the experimental results. The higher coverage range 1/3 < θ < 4/3 ML has been controversial experimentally, especially close to 4/3 ML with several different phases being observed (root3 x root7, hexagonal incommensurate, striped incommensurate, etc.). We compare the unit cell energies of different structures to deduce the energetically favorable ones. Structures consisting of very flat Pb overlayers have lower energy than missing-top-layer structures or structures with stacking faults. This is in very good agreement with experiments which measure high Pb mobility on the a phase.
Title:
Molecular and lattice dynamical study on modulated structures in quartz
Authors:
Dmitriev, SV; Semagin, DA; Shigenari, T; Abe, K; Nagamine, M; Aslanyan, TA; Canfield, RC;
Source:
PHYSICAL REVIEW B, 68 (5); 2003
Abstract:
It is shown that atomistic simulations using the Tsuneyuki potential for silica (SiO2) correctly reproduce the major experimentally observed properties of the incommensurate (INC) phases in quartz, such as the phase sequence, the direction of the modulation, the coupling of the soft optic with the TA modes, the dispersion surface anisotropy, the stress dependence of the transition temperature, etc. The obtained phase diagram is topologically equivalent to those predicted from general INC phase theories. At high temperature, our results give a short period modulation with kapproximate tob/3 as predicted by the new model for the origin of INC phase in quartz [Aslanyan , J. Phys.; Condens. Matter 10, 4565 (1998); 10, 4577 (1998)].
Title:
Low-energy surface phonons of decagonal and icosahedral quasicrystals by inelastic He-atom scattering
Authors:
Sharma, HR; Franke, KJ; Theis, W; Gille, P; Ebert, P; Rieder, KH; Ando, Y;
Source:
PHYSICAL REVIEW B, 68 (5); 2003
Abstract:
Low-energy surface phonons (Rayleigh mode) on quasicrystals were investigated by inelastic He-atom scattering. The tenfold surface of decagonal Al71.8Ni14.8Co13.4 and the fivefold surface of icosahedral Al70.5Pd21Mn8.5 are found to possess well-defined Rayleigh modes with isotropic sound velocities of about 3840 m/s and 3470 m/s, respectively. The observed sound velocities are in good agreement with calculations based on the respective bulk data. The experimental phonon dispersions exhibit quasi-Brillouin-zone centers located at strong Bragg peaks.
Title:
Indication of van Hove singularities in the density of states of ZnMg(Y,Ho) quasicrystals
Authors:
Suchodolskis, A; Assmus, W; Giovanelli, L; Karlsson, UO; Karpus, V; Le Lay, G; Sterzel, R; Uhrig, E; Goldman, AI;
Source:
PHYSICAL REVIEW B, 68 (5); 2003
Abstract:
We present a low-temperature synchrotron-radiation photoelectron microspectroscopy study of the valence bands of single-grain icosahedral ZnMgY and ZnMgHo quasicrystals. Their valence band photoemission spectra reveal in both cases a simple metal-type behavior with a clear metallic Fermi edge and a sharp pseudogap feature: the spectral intensity exhibits a maximum at approximate to0.7 eV below the chemical potential and a subsequent decrease as the Fermi level is approached. The analysis of the pseudogap feature, based on the band-structure hypothesis, shows that it corresponds to the van Hove singularities in the density of states (DOS), which originate from the intersections of the isoenergetic surface with the 222100 and 311111 Bragg planes. The reconstructed density of states agrees in general trends with the theoretical first-principles DOS of hexagonal ZnMgY approximants, and correctly reproduces the experimental value of i-ZnMgY electronic specific-heat coefficient.
Title:
Rules for computing symmetry, density, and stoichiometry in a quasi-unit-cell model of quasicrystals
Authors:
Jeong, HC; Steinhardt, PJ; Giovanelli, L;
Source:
PHYSICAL REVIEW B, 68 (6); 2003
Abstract:
The quasi-unit-cell picture describes the atomic structure of quasicrystals in terms of a single, repeating cluster that overlaps neighbors according to specific overlap rules. In this paper, we discuss the precise relationship between a general atomic decoration in the quasi-unit-cell picture of atomic decorations in the Penrose tiling and in related tiling pictures. Using these relations, we obtain a simple, practical method for determining the density, stoichiometry, and symmetry of a quasicrystal based on the atomic decoration of the quasi-unit-cell taking proper account of the sharing of atoms between clusters.
Title:
Conductivity and superlattice ordering in an icosahedral Al-Pd-Mn phase
Authors:
Capitan, MJ; Alvarez, J; Prejean, JJ; Berger, C; Karpus, V;
Source:
PHYSICAL REVIEW B, 68 (6); 2003
Abstract:
"In situ" conductivity measurements on Al-Pd-Mn quasicrystals have been combined with synchrotron x-ray-diffraction experiments for studying its behavior during phase transformations. In order to confidently reduce the possible contribution to the conductivity of defects and grain boundaries, single-crystal samples have been annealed in situ under UHV conditions. This combined experiment allows us to affirm unambiguously that the structural state of the i-Al-Pd-Mn single crystal influences the electrical conductivity.
Title:
Evidence for the coupling between gamma-band carriers and the incommensurate spin fluctuations in Sr2RuO4
Authors:
Lou, P; Chang, MC; Wu, WC; Auwarter, W;
Source:
PHYSICAL REVIEW B, 68 (1); 2003
Abstract:
The normal-state transport properties are investigated for Sr2RuO4 both in and out of the RuO2 plane. It is shown that a quantitatively consistent explanation of rho(ab) and rho(c) can be obtained by assuming that, in addition to the normal scattering of electrons by impurities and the electron-electron scattering, there is a strong coupling between the carriers of gamma band and the incommensurate spin fluctuations peaked at Q(i)=(+/-0.6,+/-0.6)pi/a. In order to test this model, we suggest a pressure-dependent resistivity measurement to be performed.
Title:
Covalent bonds and their crucial effects on pseudogap formation in alpha-Al(Mn,Re)Si icosahedral quasicrystalline approximant
Authors:
Kirihara, K; Nagata, T; Kimura, K; Kato, K; Takata, M; Nishibori, E; Sakata, M; Davies, G;
Source:
PHYSICAL REVIEW B, 68 (1); 2003
Abstract:
X-ray charge densities of Al-based icosahedral quasicrystalline approximant crystals alpha-AlReSi, alpha-AlMnSi, and Al12Re were observed by a combination of the maximum entropy method with the Rietveld method. We successfully obtained the clear images of interatomic covalent bonds between Al and transition metals (Mn, Re) and those in the Al (or Si) icosahedron in Mackay icosahedral clusters of both alpha-AlReSi and alpha-AlMnSi approximant crystals. The bonding nature of the three kinds of glue atom sites connecting Mackay icosahedral clusters was also clarified. This covalent bonding nature should strongly relate with the enhancement of the electron density-of-states pseudogap near the Fermi level. In addition, the interatomic covalent bonds of alpha-AlReSi are stronger than those of alpha-AlMnSi. This fact leads to the low effective carrier density of alpha-AlReSi in comparison with that of alpha-AlMnSi. Unlike the covalent bonding nature of an icosahedron in alpha-AlReSi and alpha-AlMnSi crystals, the Al icosahedron with an Re center atom exhibits no Al-Al interatomic covalent bonds in the Al12Re crystal. The tendency for metallic-covalent bonding conversion in the Al icosahedron, which is related to the atom site occupancy of the icosahedral cluster center, is also strongly supported.
Title:
Shift of incommensurate antiferromagnetic peaks in La2-xSrxCuO4
Authors:
Yamase, H; Kohno, H; Martinez, G;
Source:
PHYSICAL REVIEW B, 68 (1); 2003
Abstract:
Neutron scattering experiments on La2-xSrxCuO4 (LSCO) have revealed that the incommensurate antiferromagnetic peaks do not lie exactly on the symmetry axes (q(x)=+/-pi or q(y)=+/-pi), but are slightly shifted from them. In this paper, a scenario for such a "shift" is presented in terms of the anisotropy of t(') (diagonal hopping integral on the square lattice) in the slave-boson scheme of the two-dimensional t-J model. The predictions of the present theory based on fermiology are found to be different from those based on the "spin-charge stripes" hypothesis. This difference will serve to clarify a factor responsible for incommensurate antiferromagnetic correlations in LSCO systems.
Title:
Field-induced structural evolution in the spin-Peierls compound CuGeO3: High-field ESR study
Authors:
Zvyagin, SA; Krzystek, J; van Loosdrecht, PHM; Dhalenne, G; Revcolevschi, A; Nishibori, E;
Source:
PHYSICAL REVIEW B, 67 (21); 2003
Abstract:
The dimerized-incommensurate phase transition in the spin-Peierls compound CuGeO3 is probed using the tunable-frequency high-resolution electron spin resonance technique in magnetic fields up to 17 T. A field-induced development of the soliton like incommensurate superstructure is clearly indicated as a pronounced increase of the magnon spin resonance linewidth DeltaB, with a DeltaB(max) at B(c)similar to13.8 T. The anomaly is explained in terms of the magnon-soliton scattering and suggests that the solitonlike phase exists close to the boundary of the dimerized-incommensurate phase transition. In addition, magnetic excitation spectra in 0.8% Si-doped CuGeO3 are studied. Suppression of the DeltaB anomaly observed in the doped samples suggests a collapse of the long-range-ordered soliton states upon doping, which is consistent with high-field neutron experiments.
Title:
Electron correlation and two dimensionality in the spin-density-wave phase of (TMTTF)(2)Br under pressure
Authors:
Ishikawa, A; Matsunaga, N; Nomura, K; Sasaki, T; Nakamura, T; Takahashi, T; Saito, G; Davies, G;
Source:
PHYSICAL REVIEW B, 67 (21); 2003
Abstract:
The incommensurate spin-density-wave (SDW) phase in (TMTTF)(2)Br was investigated through transport measurements under pressure and magnetic fields parallel to the c(*) axis. For the incommensurate SDW phase of (TMTTF)(2)Br stabilized above 0.5 GPa, the SDW transition temperature T-SDW increases with the applied magnetic field. The field dependence of T-SDW is described by a quadratic behavior and the coefficient of the quadratic term increases with increasing pressure. These results are consistent with the prediction of the mean-field theory based on the suppression of the SDW transition by two dimensionality. From the relation between the coefficient of the quadratic term and T-SDW at zero magnetic field, we determined the role of electron correlation and two dimensionality in the SDW phase of (TMTTF)(2)Br under pressure and found that the SDW transition in (TMTTF)(2)Br can be well explained within the mean-field theory by taking into account the reduction of the coupling constant N(0)I by pressure.
Title:
Superconductivity in magnetically ordered CeTe1.82
Authors:
Jung, MH; Alsmadi, A; Kim, HC; Bang, YY; Ahn, KH; Umeo, K; Lacerda, AH; Nakotte, H; Ri, HC; Takabatake, T;
Source:
PHYSICAL REVIEW B, 67 (21); 2003
Abstract:
We report the discovery of pressure-induced superconductivity in a semimetallic magnetic material CeTe1.82. The superconducting transition temperature T-c=2.7 K (well below the magnetic ordering temperatures) under pressure (>2 kbar) is remarkably high, considering the relatively low carrier density due to a charge-density-wave transition associated with lattice modulation. The mixed magnetic structure of antiferromagnetism coexisting with ferromagnetism can provide a clue for this high T-c. We discuss a possible theoretical model for the superconducting pairing mechanism.
Title:
Structure and stability of the modulated phase Sb-II
Authors:
Schwarz, U; Akselrud, L; Rosner, H; Ormeci, A; Grin, Y; Hanfland, M; Lacerda, AH;
Source:
PHYSICAL REVIEW B, 67 (21); 2003
Abstract:
The crystal structure of Sb-II has been determined using angle-dispersive x-ray diffraction of synchrotron radiation. The crystal structure comprises an interpenetrating assembly of a tetragonal host sublattice with symmetry I422 and a tetragonal guest sublattice of symmetry I422, which realize common a axes but different c axes. Weak extra peaks that are also reported in recent investigations performed independently are attributed to modulation waves of the atomic positions in both sublattices. A refinement using full profiles of powder-diffraction data was performed in the four-dimensional superspace group L--111(I422):L--111(I422). The structural investigation is accompanied by ab initio full-potential band-structure calculations confirming the experimentally determined modification sequence. Fitting equations of state to the results of these computations generates pressure-volume relations which are in excellent agreement with the experimental data. On the basis of total-energy calculations, an earlier proposed crystal structure of the tetragonal phase has to be reconsidered in the light of the composite arrangement in Sb-II.
Title:
Scanning tunneling spectroscopy on oxidized surfaces of highly resistive quasicrystalline alloys
Authors:
Delahaye, J; Schaub, T; Berger, C; Calvayrac, Y; Grin, Y;
Source:
PHYSICAL REVIEW B, 67 (21); 2003
Abstract:
We report on a detailed investigation of the one-electron density of states on oxidized surfaces of highly resistive quasicrystalline alloys. Scanning tunneling spectroscopy measurements were performed at low temperatures (resolution around 5 meV) on icosahedral (i-)AlPdMn, i-AlCuFe, and i-AlPdRe. The tunneling spectra depend largely on the scanning tunneling microscope tip location on the oxidized surfaces. Beside spectra characteristic for the Coulomb blockade, we have identified a zero bias dip intrinsic to our quasicrystalline samples. This single feature increases as a square root of the bias voltage up to similar or equal to100 mV. A natural explanation comes from the combined effects of electron-electron interactions and disorder on the one-electron density of states. In this respect, highly resistive icosahedral alloys behave similar to disordered systems, for which such singularity has been predicted and widely observed. We have found no evidence for the quasicrystal specific energy dependence which was expected from anomalous diffusion laws predicted by quasiperiodic models. The predicted multiple gap structure has not been found either. We discuss which density of states is actually measured in tunneling spectroscopy to help clarify the controversial results obtained in this field.
Title:
Evolution of normal-state magnetic fluctuations by Ca and Ti substitutions in Sr2RuO4: Sr-87-NMR study
Authors:
Ishida, K; Minami, Y; Kitaoka, Y; Nakatsuji, S; Kikugawa, N; Maeno, Y; Lacerda, AH;
Source:
PHYSICAL REVIEW B, 67 (21); 2003
Abstract:
We report magnetic properties of (Sr2-xCax)RuO4 and Sr-2(Ru1-yTiy)O-4 investigated by Sr-87 nuclear magnetic resonance NMR to shed light on the effect of multibands on the magnetic character in the spin-triplet superconductor Sr2RuO4. In (Sr2-xCax)RuO4, the Knight shift (K-87) at 1.4 K increases progressively up to x=1.5. The Korringa relation between K and the nuclear-spin-lattice-relaxation rate 1/T-1 divided by temperature (1/T1T) reveals that ferromagnetic (FM) fluctuations develop with the increasing Ca content. In Sr-2(Ru1-yTiy)O-4, in contrast, it is found that anisotropic incommensurate (IC) antiferromagnetic (AFM) fluctuations present in the y=0 material are enhanced by a small amount of Ti substitution: 1/T1T is enhanced with the magnetic field parallel to the RuO2 plane, whereas it is unchanged for the field along the c axis in 3% Ti-doped Sr2RuO4. We demonstrate that Ca substitution affects the two-dimensional (2D) gamma band by enhancing the FM fluctuations, and that the Ti-substitution affects the 1D alpha and beta bands by enhancing the IC-AFM fluctuations. The unique substitution effects would relate with the multiband character in Sr2RuO4.
Title:
Detailed ab initio electronic structure study of two approximants to Al-Mn based icosahedral quasicrystals
Authors:
Zijlstra, ES; Bose, SK; Kitaoka, Y;
Source:
PHYSICAL REVIEW B, 67 (22); 2003
Abstract:
The electronic structure of three available models of alpha-AlMnSi and of three models of a hypothetical approximant in the Al-Pd-Mn system are studied by means of the linear muffin-tin orbital method in the atomic sphere approximation. The effect of the atomic sphere approximation is investigated. The energy resolution of our best calculation is estimated to be 50-100 meV. By comparing the available models the importance of accurate atomic positions for the electronic structure is demonstrated. In the density of states of alpha-AlMnSi and the AlPdMn approximant a wide pseudogap (similar to1 eV) is found near the Fermi energy. Total energies for various possible positions of the Si atoms in alpha-AlMnSi are compared. It is found to be favorable for the Si atoms to partially occupy three of the classes of inequivalent Al atoms. The full charge density of alpha-AlMnSi is calculated and compared with available experimental results. In contrast to the experimental results the strongest bonding is found to be between Si and Mn atoms.
Title:
Ab initio calculations of incommensurate antiferromagnetic spin fluctuations in hcp iron under pressure
Authors:
Thakor, V; Staunton, JB; Poulter, J; Ostanin, S; Ginatempo, B; Bruno, E; Prabhakaran, D;
Source:
PHYSICAL REVIEW B, 67 (18); 2003
Abstract:
We present ab initio calculations of the static paramagnetic spin susceptibility for hcp iron at finite temperatures and for a range of pressures. The dominant magnetic fluctuations in hcp Fe are found to be incommensurate antiferromagnetic, characterized by the wave vector q(inc) = (0.56,0.22,0). We show that q(inc) is linked to a Fermi-surface nesting feature. For the lowest pressure similar to16 GPa at which hcp Fe forms, we find that these modes become unstable below a Neel temperature (T-N) of 69 K. T-N rapidly diminishes with increasing pressure. We therefore predict that hcp Fe will be found to have an incommensurate spin-density-wave-ordered state over a small pressure range starting with the onset of hcp phase. We note the coincidence with the superconductivity recently found in this material.
Title:
Enhanced diffraction pattern from a Fibonacci chain
Authors:
Xu, J; Hubler, A; Poulter, J;
Source:
PHYSICAL REVIEW B, 67 (18); 2003
Abstract:
We study the diffraction patterns of a one-dimensional Fibonacci chain from quasiperiodic pulse trains. We find a single prominent peak when the dynamics of the incident wave matches the arrangement of the scatterers, that is, when the pulse train and the scatterers are in resonance. The maximum diffraction angle and the resonant pulse train determine the positions of the scatterers. These results may provide a methodology for the quality control of Fibonacci multilayers, and may have further impact when extended to higher dimensions.
Title:
Timescales of crystallization and viscous flow of the bulk glass-forming Zr-Ti-Ni-Cu-Be alloys
Authors:
Waniuk, T; Schroers, J; Johnson, WL; Ostanin, S;
Source:
PHYSICAL REVIEW B, 67 (18); 2003
Abstract:
Crystallization behavior and equilibrium viscosity of a series of alloys in the Zr-Ti-Cu-Ni-Be system are studied using multiple techniques to determine the various contributions to glass-forming ability. Low-temperature time-temperature-transformation diagrams of alloys whose compositions lie at equally spaced points along the tie line from Zr38.5Ti16.5Cu15.25Ni9.75Be20 to Zr46.25Ti8.25Cu7.5Ni10Be27.5 are measured during isothermal annealing of initially amorphous specimens. Surprisingly, for all investigated alloys, a primary quasicrystalline phase forms at a rate which varies substantially with alloy composition. Subsequent constant heating measurements, x-ray-diffraction patterns obtained after various states of annealing, beam bending viscosity results, and previous thermal analysis are all used to describe the influences on crystallization in this series. The description of both the kinetic and thermodynamic aspects of crystallization allows for an explanation of the crystallization mechanism. In addition, it explains why, in this series, thermal stability is greatest in those alloys with the poorest glass-forming ability. Overall, the investigations reveal that simple criteria like thermal stability or high viscosity fail to predict the glass-forming ability in complex bulk glass-forming systems.
Title:
Analytical expressions for the transport coefficients of icosahedral quasicrystals
Authors:
Landauro, CV; Macia, E; Solbrig, H; Ostanin, S;
Source:
PHYSICAL REVIEW B, 67 (18); 2003
Abstract:
We investigate by analytical means the electronic transport properties of approximants and quasicrystals. The spectral resistivity is modeled by Lorentz functions in agreement with realistic ab initio calculations (linear muffin-tin orbital basis, Kubo-Greenwood formula) for low-order approximants. The analytical expressions for the transport coefficients compare well with both numerical calculations and experiments. Thus, the temperature-dependent conductivity, thermopower, electronic thermal conductivity, and Lorenz number of certain approximants and quasicrystals can be consistently explained.
Title:
Effect of a magnetic field on the spin- and charge-density-wave order in La1.45Nd0.4Sr0.15CuO4
Authors:
Wakimoto, S; Birgeneau, RJ; Fujimaki, Y; Ichikawa, N; Kasuga, T; Kim, YJ; Kojima, KM; Lee, SH; Niko, H; Tranquada, JM; Uchida, S; Von Zimmermann, M;
Source:
PHYSICAL REVIEW B, 67 (18); 2003
Abstract:
The spin-density wave (SDW) and charge-density wave (CDW) order in superconducting La1.45Nd0.4Sr0.15CuO4 were studied under an applied magnetic field, using neutron and x-ray diffraction techniques. In zero field, incommensurate (IC) SDW order appears below similar to40 K, which is characterized by neutron diffraction peaks at (1/2+/-0.134,1/2+/-0.134,0). The intensity of these IC peaks increases rapidly below T(Nd)similar to8 K due to an ordering of the Nd3+ spins. The application of a 1 T magnetic field parallel to the c axis markedly diminishes the intensity below T-Nd, while only a slight decrease in intensity is observed at higher temperatures for fields up to 7 T. Our interpretation is that the c-axis field suppresses the parasitic Nd3+ spin order at the incommensurate wave vector without disturbing the stripe order of Cu2+ spins. Consistent with this picture, the CDW order, which appears below 60 K, shows no change for magnetic fields up to 4 T. These results stand in contrast to the significant field-induced enhancement of the SDW order observed in superconducting La2-xSrxCuO4 with xsimilar to0.12 and stage-4 La2CuO4+y. The differences can be understood in terms of the relative volume fraction exhibiting stripe order in zero field, and the collective results are consistent with the idea that suppression of superconductivity by vortices nucleates local patches of stripe order.
Title:
Two-dimensional alloy of immiscible metals: Single and binary monolayer films of Pb and Sn on Rh(111)
Authors:
Yuhara, J; Schmid, M; Varga, P; Ichikawa, N;
Source:
PHYSICAL REVIEW B, 67 (19); 2003
Abstract:
The single and binary metal films of Pb and Sn on Rh(111) have been studied at room temperature by scanning tunneling microscopy (STM), low-energy electron diffraction, and Auger electron spectroscopy. Both Pb and Sn are mobile at low coverage and form commensurate overlayers of (4x4)-Pb and c(2x4)-Sn, respectively. From atomically resolved STM images, the atomic arrangements of (4x4)-Pb and c(2x4)-Sn have been identified to be hexagonal and rectangular structures, respectively. With increasing coverage, both commensurate phases change into incommensurate phases followed by island formation (Stranski-Krastanov growth). This shows that Rh(111) is static and inert enough to support two-dimensional (2D) phases of Pb and/or Sn without alloying at room temperature. The Pb-Sn bimetallic film on Rh(111) forms an ordered 2D alloy of PbSn3 with an incommensurate structure close to (7x7), contrary to the immiscibility of Pb and Sn in the bulk. From atomically resolved STM images, the atomic arrangement of this (7x7)-(Pb,Sn) structure has been determined.
Title:
Field-induced magnetic transition in the heavy-fermion antiferromagnet Ce7Ni3
Authors:
Umeo, K; Echizen, Y; Jung, MH; Takabatake, T; Sakakibara, T; Terashima, T; Terakura, C; Pfleiderer, C; Uhlarz, M; von Lohneysen, H; Uchida, S;
Source:
PHYSICAL REVIEW B, 67 (14); 2003
Abstract:
We present a detailed study of the field (B) - temperature (T) phase diagram of the heavy-fermion antiferromagnet Ce7Ni3 that crystallizes in the hexagonal Th7Fe3-type structure with three nonequivalent Ce sites (Ce (I), Ce (II), and Ce (III)). This compound undergoes two magnetic transitions at T-N1=1.9 K and T-N2=0.7 K in zero field. Below T-N1, an incommensurate spin density wave (SDW) develops, and below T-N2 a commensurate SDW appears independently. By applying fields along the c axis, both T-N1 and T-N2, are suppressed and vanish at 0.3 T. For Bparallel toc>0.7 T, however, another magnetic phase appears below 0.5 K, which was found by magnetoresistance, specific heat, and magnetization measurements. The separation of the field induced phase from the SDW phase is attributed to large spin fluctuations of Ce (III), which originate from a geometrical frustration in the quasiregular tetrahedron made of Ce (I) and Ce (III).
Title:
Monte Carlo simulations of surface phase transitions in a modulated layered structure
Authors:
Gao, D; Jaszczak, JA; Baddorf, AP;
Source:
PHYSICAL REVIEW B, 67 (15); 2003
Abstract:
A solid-on-solid model of a layered crystal, which has five layers per repeat period in the direction normal to the surface and with only nearest-neighbor interactions, is studied using Monte Carlo simulation to investigate the relationship between crystal structure and the corresponding surface phases. Equilibrium properties, such as the surface specific heat, interface width, and autocorrelation times, are studied as a function of temperature and system size. Results indicate three distinct surface phases exist in this model: a low-temperature flat phase, an intermediate-temperature disordered but flat phase, and a high-temperature rough phase. We suggest the possibility of introducing several intermediate phases, as well as a rough phase, in a single system by appropriate modulation of the periodicity of the crystal structure normal to the surface. At the same time, growth simulations show an interesting growth-induced smoothing in the intermediate phase where, at low supersaturations, the growing intermediate phase has a smaller interface width than it does in equilibrium.
Title:
Lattice distortions, incommensurability, and stripes in the electronic model for high-T-c cuprates
Authors:
Yanagisawa, T; Miyazaki, M; Koikegami, S; Koike, S; Yamaji, K; Terashima, T;
Source:
PHYSICAL REVIEW B, 67 (13); 2003
Abstract:
Striped superconductivity (SC) with lattice distortions is investigated based on the three-band Hubbard model for high-T-c cuprates. A stable inhomogeneous striped state is determined in the low-temperature tetragonal phase with lattice distortions using a quantum variational Monte Carlo method. The ground state has vertical or horizontal hole-rich arrays coexisting with incommensurate magnetism and SC induced by several percents of lattice deformations. The SC order parameter oscillates according to the inhomogeneity in the antiferromagnetic background with its maxima in the hole-rich regions, and the SC condensation energy is reduced as the doping rate decreases.
Title:
Structure of the icosahedral Ti-Zr-Ni quasicrystal
Authors:
Hennig, RG; Kelton, KF; Carlsson, AE; Henley, CL; Yamaji, K;
Source:
PHYSICAL REVIEW B, 67 (13); 2003
Abstract:
The atomic structure of the icosahedral Ti-Zr-Ni quasicrystal is determined by invoking similarities to periodic crystalline phases, diffraction data, and the results from ab initio calculations. The structure is modeled by decorations of the canonical-cell tiling geometry. The initial decoration model is based on the structure of the Frank-Kasper phase W-TiZrNi, the 1/1-approximant structure of the quasicrystal. The decoration model is optimized using a method of structural analysis combining a least-squares refinement of diffraction data with results from ab initio calculations. The resulting structural model of icosahedral Ti-Zr-Ni is interpreted as a simple decoration rule and structural details are discussed.
Title:
Scanning tunneling microscopy in TTF-TCNQ: Phase and amplitude modulated charge density waves
Authors:
Wang, ZZ; Girard, JC; Pasquier, C; Jerome, D; Bechgaard, K; Rainford, BD;
Source:
PHYSICAL REVIEW B, 67 (12); 2003
Abstract:
Charge density waves (CDWs) have been studied at the surface of a cleaved tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) single crystal using a low temperature scanning tunneling microscope (STM) under ultrahigh-vacuum conditions, between 300 and 33 K with molecular resolution. All CDW phase transitions of TTF-TCNQ have been identified. The measurement of the modulation wave vector along the a direction provides evidence of the existence of domains comprising single plane wave modulated structures in the temperature regime where the transverse wave vector of the CDW is temperature dependent, as hinted by the theory more than 20 years ago.
Title:
Energy dependence of commensurate neutron scattering peak in the doped two-leg ladder antiferromagnet Sr14-xCaxCu24O41
Authors:
He, JH; Feng, SP; Chen, WY; Udron, D;
Source:
PHYSICAL REVIEW B, 67 (9); 2003
Abstract:
The dynamical spin response of doped two-leg ladder antiferromagnets is investigated based on the fermion-spin approach. Our calculations clearly demonstrate a crossover from incommensurate antiferromagnetism in the weak-interchain-coupling regime to commensurate spin fluctuation in the strong-interchain-coupling regime. In particular, the nuclear spin-lattice relaxation rate extracted from the commensurate spin fluctuation decreases exponentially with decreasing temperatures. The behaviors of the spin dynamics in the strong-coupling regime are quantitatively close to the experimental results of Sr14-xCaxCu24O41.
Title:
Incommensurate magnetic structure of CeRhIn5 (vol 62, art no 14621, 2000)
Authors:
Bao, W; Pagliuso, PG; Sarrao, JL; Thompson, JD; Fisk, Z; Lynn, JW; Erwin, RW; Morrison, TI;
Source:
PHYSICAL REVIEW B, 67 (9); 2003
Abstract:
Motivated by recent scanning tuneling microscopy (STM) experiments on Bi2Sr2CaCu2O8+delta [J. E. Hoffman , Science 295, 466 (2002); C. Howald , cond-mat/0201546 (unpublished); J. E. Hoffman , Science 297, 1149 (2002): K. McElroy (unpublished); C. Howald , cond-mat/0208442 (unpublished)], we study the effects of weak translational symmetry breaking on the quasiparticle spectrum of a d-wave superconductor. We develop a general formalism to discuss periodic charge order, as well as quasiparticle scattering off localized defects. We argue that the STM experiments in Bi2Sr2CaCu2O8+delta cannot be explained using a simple charge density wave order parameter, but are consistent with the presence of a periodic modulation in the electron hopping or pairing amplitude. We review the effects of randomness and pinning of the charge order and compare it to the impurity scattering of quasiparticles. We also discuss implications of weak translational symmetry breaking for angle resolved photoemission spectroscopy experiments.
Title:
Charge density wave in La0.84Sr0.16MnO3 revealed by Mn-55 nuclear magnetic resonance
Authors:
Savosta, MM; Novak, P; Jirak, Z; Thompson, JD;
Source:
PHYSICAL REVIEW B, 67 (10); 2003
Abstract:
Using Mn-55 nuclear magnetic resonance (NMR) in La0.84Sr0.16MnO3 single crystal we find evidence of the charge modulated ferromagnetic state below the metal-insulator transition. The NMR line shape reveals two inequivalent Mn positions with a ratio close to 3:1, which could be attributed to the hole-poor and hole-rich sites, respectively. The difference of the hyperfine fields for two positions is about 2.3 T at 22 K, corresponding to a charge disproportionation of similar to0.25 electron. An additional weak contribution to the NMR spectra is detected below 90 K, which may indicate a further ordering within the hole-rich site subsystem. The NMR spectra at low-temperature phase remain motionally narrowed, i.e., the hopping time of carriers is shorter than the period of the Larmor precession of the Mn nuclear spins.
Title:
Anisotropic magnetic properties of Ca3Co4O9: Evidence for a spin-density-wave transition at 27 K
Authors:
Sugiyama, J; Xia, CT; Tani, T; Thompson, JD;
Source:
PHYSICAL REVIEW B, 67 (10); 2003
Abstract:
The dc susceptibility chi of single crystal platelets of Ca3Co4O9 was measured in applied magnetic fields H below 55 kOe. At temperatures below 400 K, the crystals exhibited three magnetic transitions successively at T(SS)similar to380 K, T-SDW=27 K, and T-ferri=19 K. The highest spin state (SS) transition was found to be discontinuous with the appearance of a thermal hysteresis loop about 20 K wide. At 27 K, a small shoulder in the chi(T) curve was observed only for Hperpendicular toab, indicating the formation of an incommensurate spin-density-wave (SDW) state, which was also confirmed by independent muon spin rotation and relaxation experiments. The lowest of T-ferri is a transition to a ferrimagnetic state, for which also a ferrimagnetic hysteresis loop was observed for Hperpendicular toab, but not for Hparallel toab. This anisotropic behavior indicated that the ferrimagnetic interaction is parallel to the c axis. Considering the alternating stacking structure of Ca3Co4O9 along the c axis, the ferrimagnetism is most likely caused by interlayer coupling between the [Ca2CoO3] and [CoO2] subsystems.
Title:
Reinvestigation of magnetic excitations in the spin density wave of chromium
Authors:
Hiraka, H; Endoh, Y; Boni, P; Fujita, M; Yamada, K; Shirane, G; Winter, RW;
Source:
PHYSICAL REVIEW B, 67 (6); 2003
Abstract:
Low-energy magnetic excitations of chromium have been reinvestigated with a single-Q(+/-) crystal using neutron scattering techniques. In the transverse spin-density-wave phase a well-defined magnetic excitation is found around (0,0,1) with a weak dispersion perpendicular to the wave vector of the incommensurate structure. The magnetic excitation has an energy gap of omegasimilar or equal to4 meV at (0,0,1), which exactly corresponds to the Fincher excitation previously studied only along the incommensurate wave vector.
Title:
Prediction of insulating quasicrystalline approximants using ab initio electronic structure calculations
Authors:
Krajci, M; Hafner, J; Kasai, C;
Source:
PHYSICAL REVIEW B, 67 (5); 2003
Abstract:
Ab initio density-functional calculations have been used to search for icosahedral Al-transition-metal alloys with insulating behavior. We predict that low-order approximants to icosahedral AlPdTM, TM=Co, Rh, Ir are narrow-gap semiconductors. The stability of the gap suggests that it will survive in the quasicrystalline limit at least as a very deep pseudogap. We show that gap formation results from strong orbital hybridization and metallocovalent bonding, in analogy to many crystalline aluminides.
Title:
Effect of a magnetic field on long-range magnetic order in stage-4 and stage-6 superconducting La2CuO4+y
Authors:
Khaykovich, B; Birgeneau, RJ; Chou, FC; Erwin, RW; Kastner, MA; Lee, SH; Lee, YS; Smeibidl, P; Vorderwisch, P; Wakimoto, S; Kop'ev, PS;
Source:
PHYSICAL REVIEW B, 67 (5); 2003
Abstract:
We have measured the enhancement of the static incommensurate spin-density wave (SDW) order by an applied magnetic field in stage-4 and stage-6 samples of superconducting La2CuO4+y. We show that the stage-6 La2CuO4+y (T-c=32 K) forms static long-range SDW order with the same wave vector as that in the previously studied stage-4 material. We have measured the field dependence of the SDW magnetic Bragg peaks in both stage-4 and stage-6 materials at fields up to 14.5 T. A recent model of competing SDW order and superconductivity describes these data well.
Title:
Observation of two-dimensional spin fluctuations in the bilayer ruthenate Sr3Ru2O7 by inelastic neutron scattering
Authors:
Capogna, L; Forgan, EM; Hayden, SM; Wildes, A; Duffy, JA; Mackenzie, AP; Perry, RS; Ikeda, S; Maeno, Y; Brown, SP; Kop'ev, PS;
Source:
PHYSICAL REVIEW B, 67 (1); 2003
Abstract:
We report an observation of two-dimensional incommensurate magnetic fluctuations in the layered metallic perovskite Sr3Ru2O7. The wave vectors where the magnetic fluctuations are strongest are different from those observed in the superconducting single layer ruthenate Sr2RuO4 and appear to be determined by Fermi surface nesting. No antiferromagnetic ordering is observed for temperatures down to 1.5 K. For temperatures Tgreater than or similar to20 K, the fluctuations become predominately ferromagnetic. Our inelastic neutron scattering measurements provide concrete evidence of the coexistence of competing interactions in Sr3Ru2O7 and of the low-energy scale of the fluctuations.
Title:
Tile Hamiltonian for decagonal AlCoCu derived from first principles
Authors:
Al-Lehyani, I; Widom, M; Hayden, SM;
Source:
PHYSICAL REVIEW B, 67 (1); 2003
Abstract:
A tile Hamiltonian (TH) replaces the actual atomic interactions in a quasicrystal with effective interactions, between and within tiles. We studied Al-Co-Cu decagonal quasicrystals described as decorated hexagon-boat-star (HBS) tiles using ab initio methods. The dominant term in the TH counts the number of H, B, and S tiles. The phason flips that replace an HS pair with a BB pair lower the energy. In Penrose tilings, quasiperiodicity is forced by arrow matching rules on the tile edges. The edge arrow orientation in our model of AlCoCu is due to Co/Cu chemical ordering. The tile edges meet in vertices with 72degrees or 144degrees angles. We find strong interactions between edge orientations at 72degrees vertices that force a type of matching rule. Interactions at 144degrees vertices are somewhat weaker.
Title:
Quantum melting of incommensurate domain walls in two dimensions
Authors:
Momoi, T; Ishizaka, K;
Source:
PHYSICAL REVIEW B, 67 (1); 2003
Abstract:
Quantum fluctuations of periodic domain-wall arrays in two-dimensional incommensurate states at zero temperature are investigated using the elastic theory in the vicinity of the commensurate-incommensurate transition point. Both stripe and honeycomb structures of domain walls with short-range interactions are considered. It is revealed that the stripes melt and become a stripe liquid in a large-wall-spacing (low-density) region due to dislocations created by quantum fluctuations. This quantum melting transition is of second order and characterized by the three-dimensional XY universality class. Zero-point energies of the stripe and honeycomb structures are calculated. As a consequence of these results, phase diagrams of the domain-wall solid and liquid phases in adsorbed atoms on graphite are discussed for various domain-wall masses. Quantum melting of stripes in the presence of long-range interactions that fall off as power laws is also studied. These results are applied to incommensurate domain walls in two-dimensional adsorbed atoms on substrates and in doped antiferromagnets, e.g., cuprates and nickelates.
Title:
Zn-induced one-dimensional electronic modulation in YBa2Cu3O7-delta
Authors:
Maki, M; Nishizaki, T; Kobayashi, N; Greven, M;
Source:
PHYSICAL REVIEW B, 67 (1); 2003
Abstract:
Low-temperature scanning tunneling microscopy measurements have been performed on cold-cleaved YBa2(Cu1-xZnx)(3)O7-delta single crystals. We find one-dimensional charge-density modulations on the BaO layer at lower bias voltage, whereas such modulations were never observed on Zn-free samples. These modulations are closely related to the electronic local density of states in the CuO2 plane just under the BaO layer and are attributed to the spatial electronic inhomogeneity induced by Zn substitution. The one-dimensional character of the charge-density modulations suggests that the electronic state of the CuO2 plane is affected by the CuO-chain layer.
Title:
Interfaces and quasicrystals as competing crystal lattices: Towards a crystallographic theory of interfaces
Authors:
Romeu, D; Bottcher, R;
Source:
PHYSICAL REVIEW B, 67 (2); 2003
Abstract:
This paper shows that in a higher-dimensional approach, quasicrystals and interfaces are formally equivalent. Interfaces and quasicrystals are interpreted here as a region in space where the atoms of interpenetrated crystal lattices compete for space. Based on this paradigm, a method derived from the strip-projection method developed for the study of quasicrystals has been introduced. The method is completely general, independent of the parent crystal lattice type, relative orientation, and translation and of the position and orientation of the boundary plane. In this approach the perpendicular space coincides with Bollmanns' displacement space, while the parallel space contains a physical structure characterized by a minimum local strain that includes both the interface and adjacent crystal lattices. A classification of interfaces in a finite number of well-defined equivalence classes (local isomorphisms) that include orientational and translational degrees of freedom has been introduced. This classification is based on the symmetry of the hyperlattice and the position and shape of the strip and incorporates concepts from previous structural units and symmetry breaking approaches. It is suggested that such classes can be related to physical properties of interfaces. The formalism defines ideal (minimum strain) structures assumed to play an analogous role in grain boundaries (GB's) to those played by the perfect crystal and quasicrystal concepts in the study of crystals and quasiperiodic structures. Also, a lattice, called the phason lattice, is introduced to account for the dislocation content of nonsingular interfaces. Accordingly, the properties of any GB are seen to be determined by the periodicity of isosymmetrical regions related to the O and phason lattices and not by the ill-defined and pathologically discontinuous index number Sigma.
Title:
Surface structure of Al-Pd-Mn quasicrystals: Existence of supersaturated bulk vacancy concentrations
Authors:
Ebert, P; Yurechko, M; Kluge, F; Cai, T; Grushko, B; Thiel, PA; Urban, K; Otsubo, T;
Source:
PHYSICAL REVIEW B, 67 (2); 2003
Abstract:
We identified the presence and chemical nature of bulk vacancies in Al-Pd-Mn quasicrystals by measuring the structure and composition of two- and fivefold cleavage surfaces of different preannealed quasicrystals subjected to postcleavage heat treatments using scanning electron microscopy and Auger electron spectroscopy. A strong dependence of the surface structure from the preannealing is observed and explained by varying concentrations of bulk vacancies. The analysis of the data shows that as-grown Al-Pd-Mn quasicrystals contain Al, Pd, and Mn vacancies in supersaturated but near stoichiometric concentrations, while long-term preannealed samples contain a much lower vacancy concentration, with a tendency to have excess Al vacancies. We found that Al and Mn vacancies are more mobile at lower temperatures than Pd vacancies, and that the diffusion of Mn vacancies is directly coupled to the mobility of Al vacancies. The results demonstrate that the evolution of the surface structure is primarily affected by bulk vacancies migrating toward the surface during heat treatments and provide a new methodology to characterize the vacancies in intermetallic alloys.
Title:
Competition between composite and modulated configurations in Bi2Sr2CaCu2O8+delta and its relation to oxygen stoichiometry
Authors:
Perez-Mato, JM; Etrillard, J; Kiat, JM; Liang, B; Lin, CT; Thiel, PA;
Source:
PHYSICAL REVIEW B, 67 (2); 2003
Abstract:
The possible interpretation of the compound Bi2Sr2CaCu2O8+delta as a composite or a single modulated incommensurate structure is deeply interconnected with the existence of discontinuous atomic domains in the superspace description of the structure. Single-crystal neutron diffraction data have been used to obtain Fourier maps within the superspace description, which show that some atomic domains are indeed either discontinuous, like that of the atoms in the BiO layers, or strongly anharmonic. This contrasts with the structural models of this material, which usually consider a single modulated incommensurate structure with continuous modulations containing a few harmonics. The results demonstrate that these models are bound to yield unrealistic configurations for the so-called bridging zones in the BiO layers. The intrinsic discontinuous features of the atomic modulations, especially the longitudinal sawtooth modulations of the oxygens in the Bi2O2 slabs, are shown to be the signature of two competing length scales corresponding to the Bi2O2 slabs and the perovskite blocks Sr2CaCu2O6. In principle, this feature can be naturally included in a modulated composite description with occupational steplike modulations. An ideal composite configuration can be also proposed as a reference structure for describing the effects of the strong coupling between the Bi2O2 slabs and the perovskite blocks Sr2CaCu2O6, including its effect on the compound stoichiometry, in particular its oxygen content.
Title:
Nucleation and growth of Ag films on a quasicrystalline AlPdMn surface
Authors:
Fournee, V; Cai, TC; Ross, AR; Lograsso, TA; Evans, JW; Thiel, PA; Urban, K;
Source:
PHYSICAL REVIEW B, 67 (3); 2003
Abstract:
Nucleation and growth of thin films of Ag on the fivefold surface of an Al72Pd19.5Mn8.5 icosahedral quasicrystal is studied with scanning-tunneling microscopy. For low coverages, flux-independent island nucleation is observed involving adatom capture at "traps." With increasing coverage, islands start growing vertically, but then spread, and ultimately form hexagonal nanocrystals. These have fcc symmetry and pyramidlike multilayer stacking along the [111] direction. The constituent hexagonal islands have five different orientations, rotated by 2pi/5, thus reflecting the symmetry of the substrate.
Title:
Spin reorientation transition in the incommensurate stripe-ordered phase of La3/2Sr1/2NiO4
Authors:
Freeman, PG; Boothroyd, AT; Prabhakaran, D; Gonzalez, D; Enderle, M; Ali, MR;
Source:
PHYSICAL REVIEW B, 66 (21); 2002
Abstract:
The spin ordering of La3/2Sr1/2NiO4 was investigated by magnetization measurements and by unpolarized- and polarized-neutron diffraction. Spin ordering with an incommensurability epsilonapproximate to0.445 is observed below T(SO)similar to80 K. On cooling, a spin reorientation is observed at 57+/-1 K, with the spin axes rotating from 52degrees+/-4degrees to 78degrees+/-3degrees.
Title:
Pressure-induced change in the magnetic modulation of CeRhIn5
Authors:
Majumdar, S; Balakrishnan, G; Lees, MR; Paul, DM; McIntyre, GJ; Ali, MR;
Source:
PHYSICAL REVIEW B, 66 (21); 2002
Abstract:
We report the results of a high-pressure neutron-diffraction study of the heavy-fermion compound CeRhIn5 down to 1.8 K. CeRhIn5 is known to order magnetically below 3.8 K with an incommensurate structure. The application of hydrostatic pressure up to 8.6 kbar produces no change in the magnetic wave vector q(m). At 10 kbar of pressure, however, a sudden change in the magnetic structure occurs. Although the magnetic transition temperature remains the same, q(m) increases from (0.5, 0.5, 0.298) to (0.5, 0.5, 0.396). This change in the magnetic modulation may be the outcome of a change in the electronic character of this material at 9 kbar.
Title:
Experimental evidence for the high-temperature incommensurate structure in LiKSO4
Authors:
Ventura, DR; Pimenta, MA; Speziali, NL; Paul, DM;
Source:
PHYSICAL REVIEW B, 66 (21); 2002
Abstract:
A detailed x-ray diffraction study of the intermediate phase II of LiKSO4 was performed in the temperature range 730-830 K. Three-dimensional maps of the diffraction peaks were obtained by scanning the neighborhood of (h,k,l) reflections, which can be characterized as the main ones-those present in phase I and III-and a new set of secondary ones. It was observed that the main reflections are split in three different peaks, each one associated with one ferroelastic domain. The secondary reflections are composed by two peaks whose separation Delta depends on temperature. The structure of phase II is interpreted in terms of three incommensurate domains, described by the wave vector q=(Delta/2)a(ort)*, with average orthorhombic symmetry.
Title:
Limited conductivity in an octagonal quasicrystal
Authors:
Zijlstra, ES; Pimenta, MA;
Source:
PHYSICAL REVIEW B, 66 (21); 2002
Abstract:
Conductivity of an s-band model on the octagonal tiling is studied. Using perturbation theory it is shown that there is only one channel available for electronic transport, when the kinetic term in the Hamiltonian is small. This feature is independent of the size of the approximant and reveals a microscopic mechanism that is capable of severely limiting conduction processes in a quasicrystal. Numerical evidence indicates that the same result is valid even in case of realistic kinetic energies at some values of the Fermi energy.
Title:
Magnetic structures and reorientation transitions in noncentrosymmetric uniaxial antiferromagnets
Authors:
Bogdanov, AN; Rossler, UK; Wolf, M; Muller, KH; Kojima, KM;
Source:
PHYSICAL REVIEW B, 66 (21); 2002
Abstract:
A phenomenological theory of magnetic states in noncentrosymmetric tetragonal antiferromagnets is developed, which has to include homogeneous and inhomogeneous terms (Lifshitz invariants) derived from Dzyaloshinskii-Moriya couplings. Magnetic properties of this class of antiferromagnets with low crystal symmetry are discussed in relation to the recently detected compounds Ba2CuGe2O7 and K2V3O8. Crystallographic symmetry and magnetic ordering in these systems allow the simultaneous occurrence of chiral inhomogeneous magnetic structures and weak ferromagnetism. Incommensurate magnetic structures, chiral helices, with a rotation of the staggered magnetization accompanied by oscillations of the total magnetization, are possible. Field-induced reorientation transitions into modulated states have been studied and corresponding phase diagrams are constructed. Structures of magnetic defects (domain-walls and vortices) are discussed. In particular, vortices, i.e., localized nonsingular line defects, are stabilized by inhomogeneous Dzyaloshinskii-Moriya interactions in uniaxial noncentrosymmetric antiferromagnets.
Title:
Linear thermal expansivity (1-300 K), specific heat (1-108 K), and electrical resistivity of the icosahedral quasicrystal i-Al61.4Cu25.4Fe13.2
Authors:
Swenson, CA; Lograsso, TA; Ross, AR; Anderson, NE; Lee, SK;
Source:
PHYSICAL REVIEW B, 66 (18); 2002
Abstract:
Linear thermal expansivity (alpha, 1-300 K), heat capacity (C-p, 1-108 K), and electrical resistivity (rho, 1-300 K) measurements are reported for single grain i-Al61.4Cu25.4Fe13.2 quasicrystals as a function of sample processing. While rho(T) is sensitive to sample treatment, both C-p and alpha are relatively insensitive (to a few percent) except at the lowest temperatures (below 4 K), where an inverse correlation between rho and the electronic C-p coefficient gamma appears to exist. Dispersion effects (deviations from Debye-like behavior) in both C-p and the lattice Gruneisen parameter Gamma are large and comparable with those for single grain i-Al71Pd21Mn08 quasicrystal and its Al72Pd25Mn03 approximant [Phys. Rev. B 65, 184206 (2002)]. Since the 0-K Debye temperature [Theta(0)=536(2) K] is in reasonable agreement with that from 4-K elastic constants [548(8) K], a previous postulate for AlPdMn that these large dispersion effects are associated with high dispersion lattice modes in off-symmetry directions also appears to apply to i-Al-Cu-Fe. A comparison with other C-p data suggests that the major effects of sample treatment (and composition) are reflected, with a few exceptions, in the values of gamma, with remarkably similar lattice contributions.
Title:
Bulk termination of the quasicrystalline fivefold surface of Al70Pd21Mn9
Authors:
Papadopolos, Z; Kasner, G; Ledieu, J; Cox, EJ; Richardson, NV; Chen, Q; Diehl, RD; Lograsso, TA; Ross, AR; McGrath, R; Lee, SK;
Source:
PHYSICAL REVIEW B, 66 (18); 2002
Abstract:
The structure of the Al70Pd21Mn9 surface has been investigated using high-resolution scanning tunneling microscopy. From two large fivefold terraces on the surface in a short decorated Fibonacci sequence, atomically resolved surface images have been obtained. One of these terraces carries a rare local configuration in the form of a ring. The location of the corresponding sequence of terminations in the bulk model M of icosahedral i-AlPdMn based on the three-dimensional tiling T-*(2F) of an F phase has been estimated using this ring configuration and the requirement from low-energy electron diffraction work of Gierer that the average atomic density of the terminations is 0.136 atoms per Angstrom(2). A termination contains two atomic plane layers separated by a vertical distance of 0.48 Angstrom. The position of the bulk terminations is fixed within the layers of Bergman polytopes in the model M: they are 4.08 Angstrom in the direction of the bulk from a surface of the most dense Bergman layers. From the coding windows of the top planes in terminations in M we conclude that a Penrose (P1) tiling is possible on almost all fivefold terraces. The shortest edge of the tiling P1 is either 4.8 or 7.8 Angstrom. The experimentally derived tiling of the surface with the ring configuration has an edge length of 8.0+/-0.3 Angstrom and hence matches the minimal edge length expected from the model.
Title:
Anisotropic CE-type orbital correlations in the ferromagnetic metallic phase of Nd1/2Sr1/2MnO3
Authors:
Geck, J; Bruns, D; Hess, C; Klingeler, R; Reutler, P; von Zimmermann, M; Cheong, SW; Buchner, B; Ross, AR;
Source:
PHYSICAL REVIEW B, 66 (18); 2002
Abstract:
We present hard x-ray scattering studies of the charge and orbital ordering in Nd1/2Sr1/2MnO3 together with magnetization and thermal expansion measurements as a function of temperature and magnetic field. Superstructure reflections corresponding to the orbital ordering below T(CO)similar or equal to160 K are observed in the ferromagnetic metallic phase up to 200 K. The correlation length of the observed structural modulations is found to be highly anisotropic; i.e., the correlations exist predominantly in the ab planes. Moreover, the periodicity of the superstructure modulations is the same above and below T-CO. As a consequence, the modulations found in the ferromagnetic metallic phase are incommensurate to the average lattice structure. The results from hard x-ray scattering, thermal expansion, and magnetization studies can be consistently interpreted in terms of short-range orbital ordering in the ferromagnetic metallic phase of Nd1/2Sr1/2MnO3 .
Title:
Searching for sharp features in the pseudogap of icosahedral quasicrystals by NMR (vol 63, pg 8862, 2000)
Authors:
Dolinsek, J; Klanjsek, M; Apih, T; Smontara, A; Lasjaunias, JC; Dubois, JM; Poon, SJ; Buchner, B;
Source:
PHYSICAL REVIEW B, 66 (18); 2002
Abstract:
Although La2Cu1-xLixO4 (Li-LCO) differs from La2-xSrxCuO4 (Sr-LCO) in many ways (e.g., the absence of metallic transport, high-T-c superconductivity, and incommensurate antiferromagnetic correlations), it has been known that certain magnetic properties are remarkably similar. The present work establishes the detailed bulk magnetic phase diagram of Li-LCO (0less than or equal toxless than or equal to0.07), which is found to be nearly identical to that of lightly-doped Sr-LCO, and therefore extends the universality of the phase diagram to hole-doped but nonsuperconducting cuprates.
Title:
Commensurate-incommensurate transitions of quantum Hall stripe states in double quantum well systems
Authors:
Cote, R; Fertig, HA; Bourassa, J; Bouchiha, D; Plotnikov, AE;
Source:
PHYSICAL REVIEW B, 66 (20); 2002
Abstract:
In higher Landau levels (N>0) and around filling factors nu=4N+1, a two-dimensional electron gas in a double quantum well system supports a stripe ground state in which the electron density in each well is spatially modulated. When a parallel magnetic field is added in the plane of the wells, tunneling between the wells acts as a spatially rotating effective Zeeman field coupled to the "pseudospins" describing the well index of the electron states. For small parallel fields, these pseudospins follow this rotation, but at larger fields they do not, and a commensurate-incommensurate transition results. Working in the Hartree-Fock approximation, we show that the combination of stripes and commensuration in this system leads to a very rich phase diagram. The parallel magnetic field is responsible for oscillations in the tunneling matrix element that induce a complex sequence of transitions between commensurate and incommensurate liquid or stripe states. The homogeneous and stripe states we find can be distinguished by their collective excitations and tunneling I-V, which we compute within the time-dependent Hartree-Fock approximation.

Update: 31-Dec-2002

Title:
Magnetic ordering in Ce3Cu4Sn4 and Ce3Cu4Ge4
Authors:
Zaharko, O; Keller, L; Ritter, C; Lightfoot, P;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 253 (3): 130-139; 2002
Abstract:
Specific heat, magnetic susceptibility, magnetization and neutron diffraction measurements were carried out on Ce3Cu4Sn4 and Ce3Cu4Ge4 compounds (structure type Gd3Cu4Ge4, Immm, 2 Ce sites). The linear coefficient of specific heat is gamma = 330 mJ/mol(Ce) K-2 for the stannide and gamma = 225 mJ/mol(Ce) K-2 for the germanide, indicative for heavy fermion behaviour. The Ruderman-Kittel-Kasuya-Yosida exchange interactions in the presence of the magnetocrystalline anisotropy induce magnetic ordering, which is complex and proceeds in several steps. For both compounds below the Neel temperature T-N = 10.3 K incommensurate magnetic arrangements are favoured. They lock into a commensurate structure with the wave vector q(3) = (0 0 0) at T-2 (T-2 = 7.3 K for stannide and T-2' = 7.8 K for germanide). Due to a strong anisotropy the Ce magnetic moments are aligned along the x-axis in the T-2-T-3 interval, but at T-3 = T-3' = 2.6 K a reorientation of the moments into the xy-plane occurs. The evolution of the magnetic order and the moment values differ for the two inequivalent crystallographic Ce sites. The ordered Ce magnetic moment is 2.05(2) mu(B) at the 2d site and 1.10(2) mu(B) at the 4e site for germanide. For stannide the corresponding values are 0.75(1)mu(B) and 1.94(2)mu(B). Two different magnetic arrangements are possible for Ce3Cu4Sn4 at low temperatures. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Genetic algorithms as a tool in the study of aperiodic order, with application to the case of X-ray diffraction spectra of GaAs-AlAs multilayer heterostructures
Authors:
Leblanc, B; Lutton, E; Axel, F; Clarke, G;
Source:
EUROPEAN PHYSICAL JOURNAL B, 29 (4): 619-628; 2002
Abstract:
We present the first application of Genetic Algorithms to the analysis of data from an aperiodically ordered system, high resolution X-Ray diffraction spectra from multilayer heterostructures arranged according to a deterministic or random scheme. This method paves the way to the solution of the "inverse problem", that is the retrieval of the generating disorder from the investigation of the spectra of an unknown sample having non crystallographic, non quasi-crystallographic order.
Title:
The incommensurate modulation of the structure of Sr2Nb2O7
Authors:
Daniels, P; Tamazyan, R; Kuntscher, CA; Dressel, M; Lichtenberg, F; van Smaalen, S;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 58 (4): 970-976; 2002
Abstract:
The incommensurately modulated structure of Sr2Nb2O7 at room temperature is reported, as determined by single-crystal X-ray diffraction. The crystal structure of Sr2Nb2O7 comprises slabs with a perovskite-type structure that are separated by planes of additional O atoms. The driving force for the modulation is shown to be internal strain around the Sr atoms that lie at the interface between the slabs. At room temperature, Sr2Nb2O7 crystallizes in the superspace group Cmc2(1)(alpha00)0s0, with lattice parameters a=3.9544 (7), b=26.767 (6) and c=5.6961 (8) Angstrom. The modulation wave vector is determined as q=0.488 (3) a*. X-ray diffraction data were collected at a synchrotron using a CCD area detector. A total of 3626 unique main reflections and 1262 unique first-order satellites with I>3sigma(I) were obtained. Refinements using a single harmonic modulation wave converged at R=0.057 (R=0.051 for the main reflections and R=0.121 for the satellite reflections). The modulated structure is interpreted in terms of rotations of NbO6 octahedra and displacements of the Sr atoms.
Title:
Commensurate and incommensurate structures of the hexabromotellurate(IV) bis {dibromodiselenate(I)} ion - [(C2H5)(n)(C6H5)(4-n)P](2)[TeBr6(Se2Br2)(2)], n=0,1
Authors:
Janickis, V; Necas, M; Novosad, J; Dusek, M; Petricek, V; van Smaalen, S;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 58 (4): 977-985; 2002
Abstract:
Structure analysis of [(C2H5)(n)(C6H5)(4-n)P](2)[TeBr6(Se2Br2)(2)] is presented for n=1 and 0 [ hereafter (I) and (II)]. Crystal (I) has been synthesized from elemental selenium, tellurium tetrabromide, ethyltriphenylphosphonium bromide and bromine. It has a standard monoclinic structure, space group P2(1)/c, and has been solved and refined to R=0.0357 for 4803 observed X-ray reflections by traditional techniques. Crystal (II), which has been prepared from elemental selenium, tellurium tetrabromide, tetraphenylphosphonium bromide and bromine, is an incommensurately one-dimensionally modulated structure with planar monoclinic superspace group. (II) has been refined to R=0.0501 for 4247 observed reflections. The modulation of the atoms that belong to the anion switches between two different basic positions, which are described by the crenel function algorithm. The modulation of the phenyl groups is much weaker and it could be refined within the rigid-body approximation. The TeBr6 octahedron is nearly regular in both structures. The two Br atoms of the octahedron have a bond to one of the Se atoms in an Se2Br2 molecule. For (I) both bonded Br atoms are trans positioned, while for (II) they can be either trans or cis positioned. The alternations of those arrangements are caused by modulation. The point group of the anion is -1 for crystal (I) and 2/m for the average structure of crystal (II).
Title:
Structural study of an Al-Co approximant by high-angle annular dark-field scanning transmission electron microscopy
Authors:
Yokosawa, T; Saitoh, K; Tsai, AP; Tanaka, M; Petricek, V;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 71 (11): 2601-2604; 2002
Abstract:
It has been discovered by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) that a melt-quenched Al73Co27 alloy forms a new approximant. The approximant is composed of the Penrose skinny and fat rhombi with a 2 nm edge length, which are arranged periodically in one direction but disordered in the direction perpendicular to the periodic direction. It has been clarified that rocket- and butterfly-shaped tiles, which are constructed by the basic structural units of tau(2)- Al13Co4 (the 1-nm column pairs) [K. Saitoh et al.: J. Phys. Soc. Jpn. 68 (1999) 2886], appear at the skinny tile and over the skinny and fat tiles, respectively. The structural relationship between the skinny and fat tiles and the 1-nm column pairs has been clarified for the first time. It has been revealed that the tiling of the skinny and fat rhombi in the present approximant, including the disordered feature of the tiling, is formed by a network of the 1-nm column pairs.
Title:
A new icosahedral quasicrystal coexisting with decagonal quasicrystals in the Al-Ni-Ru system
Authors:
Sun, W; Hiraga, K; Treis, PA;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 347 (1-2): 110-114; 2002
Abstract:
We have found a new icosahedral quasicrystal which can coexist with a superlattice or basic decagonal quasicrystals with 0.4 nm periodicity in the Al-Ni-Ru system. This Al-Ni-Ru icosahedral quasicrystal is confirmed to belong to the F-type and its quasiperiodic structure is directly examined by high-resolution electron microscopy. Energy dispersive X-ray spectroscopy analysis and electron diffraction examinations show that the Al-Ni-Ru icosahedral quasicrystal and the coexisting decagonal quasicrystals with 0.4 nm periodicity are formed with different compositions and that they have a definite orientational relationship between them. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
High-pressure hydrogen loading in Ti45Zr38Ni17 amorphous and quasicrystal powders synthesized by mechanical alloying
Authors:
Takasaki, A; Kelton, KF; Treis, PA;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 347 (1-2): 295-300; 2002
Abstract:
Amorphous and icosahedral phase (i-phase) powders, synthesized directly by mechanical alloying (MA) and after subsequent annealing, respectively, are hydrogenated at a temperature of 573 K and an initial pressure of 3.8 MPa. The i-phase powder contains a Ti2Ni-type phase (fcc structure, lattice parameter, a=1.23 nm) as a minor phase. Hydrogen cycling for the i-phase powder decreases the coherence length and enhances the formation of an fcc hydride phase, namely (Ti, Zr)H-2. The amorphous powder, which transforms to the fcc hydride after hydrogenation, is transformed primarily into a Ti2Ni-type crystal phase and a small amount of the i-phase after hydrogen desorption. Hydrogen cycling and mechanical alloying in a hydrogen gas atmosphere dramatically reduces the loading time of hydrogen for both the i-phase and the amorphous powders. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Incommensurate magnetic structure in TmCuAl at low temperatures
Authors:
Javorsky, P; Gubbens, PCM; Mulders, AM; Prokes, K; Stusser, N; Gortenmulder, TJ; Hendrikx, RWA;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 251 (2): 123-128; 2002
Abstract:
We present a neutron powder diffraction study on TmCuAl, crystallizing in the ZrNiAl-type hexagonal structure. Our data confirm magnetic ordering below T-c = 1.9 K. The magnetic structure is a longitudinal spin wave described by a propagation vector k = (1/2 0 q) with Tm magnetic moments along the c-axis. In addition to that, a commensurate antiferromagnetic component within the basal plane with k = (1/2 0 1/2) develops below the magnetic phase transition at T-1 congruent to 1.2 K. It leads to a rather complex magnetic structure mow T-1. One-third of the thulium moments has a considerably reduced magnitude compared to the remaining ones. No further phase transitions were observed down to 50 mK. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Magnetic phase transitions in the ternary carbides Ln(2)Cr(2)C(3) (Ln = Tb, Ho, Er)
Authors:
Reehuis, M; Zeppenfeld, K; Jeitschko, W; Stusser, N; Ouladdiaf, B; Loidl, A; Hendrikx, RWA;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 251 (3): 260-270; 2002
Abstract:
The magnetic structures of the monoclinic carbides Tb2Cr2C3, Ho2Cr2C3 and Er2Cr2C3 (space group C2/m) have been investigated by neutron powder diffraction. Below the Neel temperatures T-N = 49(1), 14.0(5) and 6.8(5) K the magnetic moments of the terbium, holmium and erbium atoms order antiferromagnetically within the monoclinic ac-plane, respectively. In the case of Tb2Cr2C3 the magnetic structure can be described with the propagation vector k = (0 1 0) and it is stable up to the Neel temperature. The magnetic ordering in Ho2Cr2C3 and Er2Cr2C3 is more complex requiring different sets of coexisting wave vectors pertaining to distinct domains and comprising incommensurate regions and lock-in phase transitions. For the erbium compound the low-temperature ordering is described by the coexisting wave vectors k(1) = (0 0 1/2) and k(2) = (0 1 0) and both are stable up to T-t = 5.5(3) K. Between 4.5(3) K and T-N = 6.8(5) K a sine-wave modulated structure with k(3) = (tau(x), 0, 1/2 - tau(z),) appears, where the vector components vary with the temperature. At 5.3 K one obtains tau(x) = 0.055(1) and tau(z) = 0.070(1). For Ho2Cr2C3 the ordering associated with k(1) = (0 1 1/2) is stable between 1.6 K and T-t = 12.7(3) K. A second type of ordering appears below T-N = 14.0(5) K and corresponds to a sine-wave modulated structure with k(2) = (tau(x), 0, -tau(z),). The length of k(2) varies from (0.8856, 0, -0.1395) at 13 K to (0.9935, 0, -0.1075) at T-t = 10.2(2), where the modulated structure undergoes a transition to a square-wave one manifested by the presence of higher harmonics. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Effect of surface pretreatment on the electrochemical activity of a glass-forming Zr-Ti-Al-Cu-Ni alloy
Authors:
Wolff, U; Gebert, A; Eckert, J; Schultz, L; Aida, T;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 346 (1-2): 222-229; 2002
Abstract:
Zr59Ti3Al10Cu20Ni8 glassy ribbons were prepared by melt-spinning in an argon atmosphere. The samples were characterized concerning their microstructure and thermal stability by X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) at a constant heating rate. The crystallisation of the metallic glass from the undercooled liquid proceeds via primary formation of a large fraction of a nanoquasicrystalline phase. By controlled annealing a mainly quasicrystalline and a multiphase crystalline ribbon state was adjusted. The samples were pretreated by chemical etching in HF solutions and by cathodic reduction at -2 V/SCE. The resulting surface state was characterized by means of BET measurements, atomic force microscopy (AFM) and Auger electron spectroscopy (AES). Electrochemical measurements in 0.1 N NaOH were conducted to evaluate the activity for the cathodic hydrogen reduction reaction. The results of capacity measurements and potentiodynamic polarisation at a scan rate of 0.1 mV/s were compared to those obtained for untreated samples. Optimum pretreatment, i.e. etching in 1% HF solution for 5 min, generates high surface roughness and Cu- and Ni-enrichment in surface near regions causing significantly increased electrocatalytic activity. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
The Al-Pd-Mn quasicrystalline approximant xi '-phase revisited
Authors:
Shramchenko, N; Denoyer, F; Morell, G;
Source:
EUROPEAN PHYSICAL JOURNAL B, 29 (1): 51-59; 2002
Abstract:
A detailed investigation of the Fourier space of several Al-Pd-Mn samples with composition Al-72.6 at. %, Pd-22.9 at. %, Mn-4.5 at. % is reported. In the phase diagram of the Al-Pd-Mn ternary alloy, this composition corresponds to the so-called xi phase which was described as an icosahedral quasicrystalline approximant. By re-examining the Fourier space by means of X-ray diffraction (powder patterns and single crystal precession patterns), complex structures in close relation with the xi-phase have been observed. These long-range order complex structures are described as resulting from a periodic perturbation of the xi structure along the c direction. Two states with periodicities c(xi) (3 + tau) and c(xi) (5 + tau) have been observed in this study (tau golden mean). Structural models based on periodic arrangements of "defects" layers separating layers of xi phase are proposed. These two states are certainly intermediate states between the xi phase and the metastable decagonal quasicrystalline phase.
Title:
Phasons, sliding modes and friction
Authors:
Janssen, T; Radulescu, O; Rubtsov, AN; Petrakovskii, G;
Source:
EUROPEAN PHYSICAL JOURNAL B, 29 (1): 85-95; 2002
Abstract:
Aperiodic crystals may have additional low frequency modes related to the possibility to describe them in a higher-dimensional space. Dynamics associated with these degrees of freedom is called phasonic, but there are very different phenomena of this type. A discussion is given of the use of the term. The relation between phason modes, the crystal structure, and the modulation and sliding modes is discussed. Finally a relation with frictionless motion is studied.
Title:
Report of a Subcommittee on the Nomenclature of n-Dimensional Crystallography. II. Symbols for arithmetic crystal classes, Bravais classes and space groups
Authors:
Janssen, T; Birman, JL; Denoyer, F; Koptsik, VA; Verger-Gaugry, JL; Weigel, D; Yamamoto, A; Abrahams, SC; Kopsky, V;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 58 (1): 605-621; 2002
Abstract:
The Second Report of the Subcommittee on the Nomenclature of n-Dimensional Crystallography recommends specific symbols for R-irreducible groups in 4 and higher dimensions (nD), for centrings, for Bravais classes, for arithmetic crystal classes and for space groups (space-group types). The relation with higher-dimensional crystallographic groups used for the description of aperiodic crystals is briefly discussed. The Introduction discusses the general definitions used in the Report.
Title:
Long-period incommensurate structures in crystals with a triangular arrangement of magnetic ions
Authors:
Zavorotnev, YD; Medvedyeva, LI; Correa, JS;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 248 (3): 402-412; 2002
Abstract:
A possibility of origination of long-period structures in a crystal with the triangular arrangement of magnetic atoms is considered. It is shown that such superstructures as spiral, cycloidal, mixed and skew spiral can be realized. The vector of propagation of those superstructures is in the plane XOY, its direction is arbitrary when there occurs a structure in which one of the two components of the order parameter is zero. It is shown that cycloidal and spiral superstructures can pass one into another by a turn of the plane of rotation of the irreducible vectors and this is accompanied by an "anticentrifugal" effect. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Fabrication and transport properties of thin films of quasicrystals
Authors:
Grenet, T; Giroud, F; Loubet, K; Bergman, A; Safran, G; Labar, J; Barna, P; Joulaud, JL; Capitan, M; Watanabe, Y;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 2-6; 2002
Abstract:
We present a brief overview of the preparation of quasicrystalline thin films, emphasising the constraints and methods used to prepare stable ternary quasicrystal films. As an example, we present the preparation of thin i-Al-Cu-Fe and i-Al-Pd-Re films and the study of dimensionality effects in the electrical conductivity.(C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Growth of decagonal AlCoCu quasicrystals onto AlCoNi seeds
Authors:
Gille, P; Dreier, P; Barz, RU; Bergman, A;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 7-12; 2002
Abstract:
Crystal growth of Al68Co19Cu13 by the Czochralski method was investigated using a [00001]-oriented AlCoNi seed instead of native material or spontaneous nucleation on an alumina tip. Liquidus data of the Al66CoxCu34-x isopleth were determined so as to make sure to grow from starting melts with compositions within the primary crystallization field of the decagonal phase. Axially homogeneous AlCoCu crystals were obtained but the single-phase AlCoNi seed decomposed into decagonal needles and P-phase. The decay is discussed as the result of interdiffusion during the long-lasting growth process. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
A Zn-based icosahedral quasicrystal classified into the same structure type as Cd-based icosahedral quasicrystals?
Authors:
Ishimasa, T; Kaneko, Y; Kaneko, H; Bergman, A;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 13-17; 2002
Abstract:
New icosahedral quasicrystals have been discovered in Zn-Mg-Sc and Zn-Mg-Ti alloy systems. The former forms at the alloy composition of Zn80Mg5Sc15, and belongs to P-type (a(p) = 0.7111 nm) showing high degree of structural perfection. The icosahedral atomic cluster included in 1/1 approximant crystal, Zn17Sc3, suggests that the Zn-Mg-Sc icosahedral quasicrystal has structural similarity to the Cd-based icosahedral quasicrystals recently reported. Preliminary study of Zn-Mg-Ti alloys has revealed that two types of icosahedral quasicrystals form near the alloy composition of Zn84Mg8Ti8; namely P-type icosahedral quasicrystal with a(p) = 0.7023 nm, and F-type icosahedral quasicrystal exhibiting very weak superlattice reflections. The Zn-Mg-Sc and Zn-Mg-Ti quasicrystals have common features on diffraction intensity, stoichiometric composition, and average concentration of valence electrons. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Nano icosahedral phase in Zr-Pd and Zr-Pt binary alloys
Authors:
Saida, J; Matsushita, M; Inoue, A; Bergman, A;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 18-23; 2002
Abstract:
It was found that a nano icosahedral phase with a diameter less than 20 nm is formed as a primary crystalline phase in the melt-spun Zr70Pd30 and Zr80Pt20 binary amorphous alloys. The nano icosahedral phase is also formed in the as-quenched state in the Zr80Pt20 binary alloy by controlling the quenching rate. A slight redistribution of approximately 3 at% is observed during the quasicrystallization in the Zr70Pd30 alloy. In contrast, no significant compositional change between the nano icosahedral and residual amorphous phases is observed in the Zr80Pt20 alloy. The icosahedral medium-range order in the diameter range less than approximately 3 nm is observed in the high-resolution electron micrograph of the Zr70Pd30 amorphous alloy. It is suggested that the icosahedral quasicrystalline phase grows with assimilating the icosahedral medium-range order due to a slight redistribution of constitutional elements during quasicrystallization. The formation of the nano icosahedral phase in the Zr70Pd30 and Zr80Pt20 binary alloys seems to be attributed to the existence of the icosahedral medium-range order in the amorphous and/or liquid states. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
New approximants in the Al-Cr-Fe system and their oxidation resistance
Authors:
Demange, V; Machizaud, F; Dubois, JM; Anderegg, JW; Thiel, PA; Sordelet, DJ; Barna, P;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 24-29; 2002
Abstract:
Two new orthorhombic approximants of the decagonal phase as well as a gamma-brass type phase are pointed out in the Al-Cr-Fe system. Analysis of diffraction data shows that they are isotypic with compounds already known in the Al-Cu-Fe-Cr and Al-Cr alloys, respectively. Resistance to oxidation in water as well as at high temperature is significantly enhanced thanks to the addition of Cr. (C) 2002 Published by Elsevier Science B.V.
Title:
A study of high-Co Al-Ni-Co decagonal phase
Authors:
Grushko, B; Doblinger, M; Wittmann, R; Holland-Moritz, D; Thiel, PA;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 30-34; 2002
Abstract:
The stability and transformation behavior of the decagonal phase was studied at the composition Al72Co15.5Ni12.5. Similarly to the decagonal phase at high Ni-contents, it can transform with partitioning. The transformation requires significantly longer annealing times (up to several thousands of hours) and for the studied compositions results in the formation of the X-phase and the decagonal phase with higher-Ni composition than the initial decagonal phase. For shorter times, formation of a series of intermediate metastable states is observed. Some of them are identified with the structures reported earlier, to be specific variants of the high-Co decagonal phase. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Periodic approximants of quasicrystals in the Al-Rh-Si ternary system
Authors:
Koshikawa, N; Ohtsuki, M; Edagawa, K; Yoda, S; Tamura, R; Takeuchi, S; Barna, P;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 35-37; 2002
Abstract:
A 2/1 cubic type periodic approximant of a Mackey icosahedron type (MI-type) quasicrystal was found to form in conventionally solidified and annealed samples of Al65Rh27Si8. An almost single 2/1 cubic approximant phase is formed in the compositional range of 26-28 at.% Rh and 7-9 at.% Si. In the compositions with lower Si concentration, the 1/0 cubic approximant phase is formed. No phase transformation from the 2/1 cubic approximant was observed by long time annealing (48 h) of Al65Rh27Si8 at 1273 K, suggesting that the 2/1 cubic approximant phase is a thermodynamically stable phase at this temperature. The 1/0 cubic approximant phase is found to form also in Al-Rh-Pd and Al-Ru-Si systems in a comparative investigation with Al-Rh-Si system. (C) 2002 Published by Elsevier Science B.V.
Title:
An investigation on the transformation of the decagonal phase to a B2 phase in Al-Cu-Co alloy during mechanical milling
Authors:
Mukhopadhyay, NK; Murthy, GVS; Murty, BS; Weatherly, GC; Tamura, R;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 38-41; 2002
Abstract:
Al65Cu20Co15 decagonal phase, synthesized by a slow cooling technique, were mechanically milled in a high energy planetary ball mill for 10, 20 and 30 h. X-ray diffraction, scanning electron microscopy and transmission electron microscopy techniques were used for characterization of phases. The phase transformation from the decagonal phase to a B2-crystalline phase (ordered CsCl type phase) during mechanical milling is reported here for the first time. Powders milled for more than 10 It contained predominantly the B2 type crystalline phase with a lattice parameter of 0.29 nm. This crystalline phase was found to be quite stable after 30 h of milling and also on subsequent annealing at 600 degreesC. These experimental results lend support to an earlier suggestion that the decagonal phase in Al-Cu-Co is actually less stable than the B2 phase at low temperatures. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Icosahedral quasicrystal in the Al-Rh-Si ternary system
Authors:
Ohtsuki, M; Koshikawa, N; Yoda, S; Edagawa, RTK; Takeuchi, S; Takeuchi, S;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 42-44; 2002
Abstract:
A Mackey icosahedron type (MI-type) icosahedral (i-) quasicrystal was found to form in a melt-quenched sample of Al68Rh26Si6. Powder X-ray diffraction measurements showed that the i-phase has a F-type ordered structure and that the quasilattice constant is 4.48 Angstrom. Differential thermal analysis (DTA) studies indicated that the i-phase has a high stability. The i-phase and its cubic approximant phases of 1/0 and 2/1 types are found to form in the compositions with electron-per-atom ratio of about 1.85. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Dissolution patterns caused by etching of low-indexed surfaces of Al-Pd-Mn icosahedral and Al-Cu-Co decagonal quasicrystals
Authors:
Saito, K; Saito, Y; Sugawara, S; Guo, JQ; Tsai, AP; Kamimura, Y; Edagawa, K; Joulaud, JL;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 45-48; 2002
Abstract:
Dissolution patterns caused by anodic etching of an Al-Pd-Mn icosahedral quasicrystal and chemical etching of an Al-Cu-Co decagonal quasicrystal were examined by optical and electron microscopy as well as by atomic force microscopy. Appropriate etching treatments of these quasicrystals, i.e. the anodic etching of the Al-Pd-Mn quasicrystal in a solution of CH3OH-HNO3, and the chemical etching of the Al-Cu-Co quasicrystal in a solution of HF-HNO3-H2O resulted in occurrence of dissolution patterns composed of a number of well-facetted micropits (and hillocks for the Al-Cu-Co alloy as well) on low-indexed surfaces of the specimens. The morphological features of these etch-figures are discussed in relation to the internal structural symmetries. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Synthesis and microhardness measurement of Ti-Zr-Ni nanoquasicrystalline phase
Authors:
Shaz, MA; Mukhopadhyay, NK; Mandal, RK; Srivastava, ON; Tsai, AP;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 49-52; 2002
Abstract:
The Ti-Zr-Ni forms one of the interesting systems of quasicrystals and related structures. It is the only system in Ti-based quasicrystalline phases which belongs to Bergman class and at the same time gives rise to a stable quasicrystalline structure. We report the formation of nanoquasicrystalline phase directly from melt spinning of molten Ti53Zr27Ni20 alloy. Such a phase has been obtained at an optimum copper wheel speed (40 m/s) and jet pressure of 90 atm. We have also measured the mechanical response of this material by the microhardness technique. It shows much better ductility, strength and fracture toughness than the usual alloy having micron-sized quasicrystalline phase. Even at higher load (200 g) no crack seems to appear. We do observe shear bands suggesting the better toughness of bulk material containing nanoquasicrystalline/nanocrystalline phase. (C) 2002 Published by Elsevier Science B.V.
Title:
Phase equilibria of the icosahedral Al-Cu-Fe phase
Authors:
Zhang, LM; Luck, R; Mandal, RK;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 53-56; 2002
Abstract:
The phase equilibria of alloys in the vicinity of icosahedral phase region of the ternary Al-Cu-Fe system were investigated by thermal and magnetothermal analysis, metallographical methods and X-ray diffraction. It was reconfirmed that the icosahedral phase forms by a ternary peritectic reaction as L + lambda + betadouble left right arrowi. Its temperature was found at 882+/-2 degreesC. The liquidus projection was established. (C) 2002 Published by Elsevier Science B.V.
Title:
Temperature dependence of the 8-angstrom superstructure in decagonal Al-Co-Ni
Authors:
Frey, F; Weidner, E; Hradil, K; de Boissieu, M; Letoublon, A; McIntyre, G; Currat, R; Tsai, AP; Capitan, M;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 57-64; 2002
Abstract:
Diffuse layers corresponding to an 8 Angstrom superperiod along the 'periodic' axis of decagonal Al-Ni-Co phases were investigated by in situ X-ray and neutron diffraction at temperatures up to 980 degreesC. The diffuse layers consist of an unstructured diffuse background, diffuse bands, and diffuse maxima which (almost) all vanish above 900 degreesC, but show a different temperature dependence in detail. A tentative scenario of the related structural ordering process during cooling from high temperature is developed. A ID-columnar cluster model is compared to the experimental results. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Structure of a W-(AlCoNi) crystalline phase related to Al-Co-Ni decagonal quasicrystals, studied by single crystal X-ray diffraction
Authors:
Sugiyama, K; Nishimura, S; Hiraga, K; de Boissieu, M;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 65-71; 2002
Abstract:
The crystal structure of a W-(AlCoNi) phase, which is closely related to Al-Co-Ni decagonal quasicrystals, has been studied by the single crystal X-ray diffraction. The W-(AlCoNi) phase was obtained from an Al(72.5)Co(20)Ni(7.)5 alloy sample annealed at 950 degreesC and its structure indicates the space group On (No. 8) with lattice parameters a = 39.668(3) Angstrom, b = 8.158(1) Angstrom, c = 23392(1) Angstrom and beta = 90.05(1)degrees. A structural model with R(F) less than 0.087 for the observed 16 200 reflections can reproduce contrasts of atomic scale images obtained by high-angle annular detector dark-field scanning transmission electron microscopy together with high-resolution electron microscopy. The structure of the W-(AlCoNi) phase provides a fundamental atomic arrangement for the columnar atom cluster observed commonly in the Al-Co-Ni decagonal quasicrystals, and makes it possible to derive a structural model for the structures of the Al-Co-Ni decagonal quasicrystals. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Ab initio structure determination of quasicrystals by density modification method
Authors:
Takakura, H; Yamamoto, A; Shiono, M; Sato, TJ; Tsai, AP; McIntyre, G;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 72-76; 2002
Abstract:
A novel density modification method has been applied to phase reconstruction of X-ray single crystal data of quasicrystals. This is based on the low electron density elimination (LDE) method that is an ab initio structure determination method for crystal in the real space. The location, size and shape of the occupation domains for quasicrystals in the n-dimensional (nD) unit cell are obtained without any model structure. Therefore, the LDE method can be a substitute for the direct method for quasicrystals as nD crystals. The structure solution can easily be found in the trial sets (normally 100 sets) and is confirmed by the subsequent analysis. The result is used as a crude starting model for constructing a detailed structure model of quasicrystals. The solutions of several quasicrystals (i-AlPdMn, i-ZnMgHo and i-CdYb) are exemplified. The reliability and limitations of the algorithm to retrieve the quasicrystalline structures will also be discussed. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Short-range order in undercooled melts forming quasicrystals and approximants
Authors:
Holland-Moritz, D; Schenk, T; Simonet, V; Bellissent, R; Convert, P; Hansen, T; Currat, R;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 77-81; 2002
Abstract:
For the first time, the short-range order of deeply undercooled liquids of alloys fort-ning quasicrystalline and polytetrahedral phases (Al13Fe4 and Al74Co26) is investigated by combining the containerless processing technique of electromagnetic levitation with elastic neutron scattering. The experimentally determined structure factor, S(Q), was simulated by assuming that clusters with different structures exist in the liquid. The best fit of the experimental data is obtained under the assumption of an icosahedral short-range order. This supports the nearly 50 year-old prediction of Frank that an icosahedral short-range order prevails in undercooled metallic liquids. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
The local atomic structure of R-Mg-Zn (R=Y, Gd, Dy and Tb)
Authors:
Kramer, MJ; Hong, ST; Canfield, PC; Fisher, IR; Corbett, JD; Zhu, Y; Goldman, AI; Tsai, AP;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 82-86; 2002
Abstract:
The rare earth element in the R-Mg-Zn system provides a unique probe of the atomic structure of a face-centered icosahedral (fci) quasicrystal (qc). Unlike many of the other ternary and higher component qc systems, the compound around R8Mg42Zn50 allows for the substitution of one of its main components (R = Y, Er, Ho, Dy and Th) without any appreciable change in its qc structure (space group or quasi-unit cell dimension). The large atomic number difference between Y and the heavy rare earth elements affords large differences in the scattering cross-sections for electrons, neutrons and X-rays. Using high quality flux grown single grains with resolution limited diffraction peaks, the local atomic structure was probed with a variety of complimentary techniques. The differences in the pair distribution function (PDF) due to loss of the anti-ferromagnetic ordering of the Th between 4.2 and 30 K was used to probe the R site. High resolution TEM and single grain XRD have been used to determine the cluster structures. Results of this work suggest that there are local clusters in this fci compound consisting of five concentric polyhedra with 124 atoms: an icosahedron, dodecahedron, icosahedron, bucky-ball and a dodecahedron, similar to previous work. However, the HRTEM results indicate that the local structure consists only of these five shells which may edge share with the next cluster. Based on this atomic arrangement, the PDF results are consistent with R atoms partially occupying the vertices of the outer icosahedron and dodecahedron. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Structural study of an Al-Ni-Ru decagonal quasicrystal with 1.6 nm periodicity and a related approximant phase
Authors:
Sun, W; Ohsuna, T; Hiraga, K; Fisher, IR;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 87-91; 2002
Abstract:
The coexistence of a decagonal quasicrystal (D-phase) with 1.6 nm periodicity and its approximant phase was observed in as-east Al-Ni-Ru alloys. The structural characteristics of the Al-Ni-Ru D-phase and its approximant phase, and structural relationship between them have been clearly revealed by high-resolution electron microscopy (HREM) and high-angle annular detector dark-field (HAADF) scanning transmission electron microscopy (STM). The results show that the structure of the Al-Ni-Ru D-phase is characterized by an aperiodic pentagonal tiling of atom clusters with long-range quasiperiodic correlations, while that of the approximant phase by a rhombic tiling of atom clusters with crystalline correlations. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Transient ordering states in decagonal Al-Co-Ni at temperatures up to 1000 degrees C
Authors:
Weidner, E; Frey, F; Hradil, K; de Boissieu, M; McIntyre, G; Tsai, AP; Goldman, AI;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 92-95; 2002
Abstract:
Disordered decagonal quasicrystals with the nominal compositions Al72Ni12Co16 and Al72.5Ni11Co16.5 were investigated by comparative diffuse neutron (N) and X-ray (X) synchrotron studies, respectively, at temperatures up to 1000 degreesC. High resolution X-ray measurements reveal peak splitting consistent with a domain structure of 2D qp and 1D qp lamellae. At higher temperatures the strain fluctuations decrease, giving rise to larger areas of the 2D qp and ID qp domains. In summary, this disordered Al-Co-Ni phase is governed by complex transient ordering states, i.e. twinned lamellar domains of true 2D qc sequences, 1D and periodic domains accompanied by phason straining and phason fluctuations. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Structure of a metastable Al3Ni decagonal quasicrystal: comparison with a highly perfect Al72Ni20Co8
Authors:
Abe, E; Tsai, AP; Hradil, K;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 96-100; 2002
Abstract:
We study the structure of a decagonal quasicrystalline phase formed in a rapidly-solidified Al3Ni alloy, by using electron diffraction and atomic-resolution Z (atomic number)-contrast scanning transmission electron microscopy (STEM). Electron diffraction patterns of the metastable Al3Ni phase reveal features quite similar to those of the stable Al72Ni20Co8 phase; a large number of reflections in the tenfold symmetry plane and no significant diffuse streaks in the twofold patterns, indicating a good quasiperiodic order of the phase. Z-contrast STEM imaging shows that the structure of the Al3Ni phase can be interpreted based on a decagonal atomic cluster column with broken tenfold symmetry, being basically isostructural with that of the Al72Ni20Co8 phase, Structural disorders are found to be significant at the core of the decagonal atomic clusters in the metastable Al3Ni decagonal phase. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Crystal structure of the b.c.o. Al-4(Cr, Ni) decagonal approximant
Authors:
Deng, DW; Kuo, KH; Hradil, K;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 101-104; 2002
Abstract:
The crystal structure of the orthorhombic Al-4(Cr,Ni) coexisting with the decagonal quasicrystal in the Al-Cr-Ni system was determined by single crystal X-ray structure analysis: Immm (No. 71), a = 1.2505 nm, b = 1.2619 nm, c = 3.0660 nm, V = 4.8382 nm(3). Pearson symbol oI366-58.16, D-x = 3.451 g/cm(3), R-1= 0.0728 for 2257 reflections, goodness of fit S = 0,954. There are 39 (28Al + 11Cr/Ni) independent atoms in a unit cell, of which four Al and nine (Cr/Ni) atoms have icosahedral coordination. As in many Al-TM (transition metal) intermetallic phases, a number of Al sites in Al,(Cr,Ni) have a partial occupancy of only 0.5-0.67. The base-centered orthorhombic Al,(Cr,Ni) consists of six layers alone, the a-axis, two flat ones each sandwiched between two puckered layers in mirror reflection. The interconnection of icosahedral clusters in this structure also exists in the hexagonal mu-Al4Mn, kappa-AlCrNi, lambda-Al4Mn and nu-Al12Cr2Fe phases. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Diffraction by domains in decagonal Al-Co-Ni quasicrystals
Authors:
Frey, F; Weidner, E; Hradil, K;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 105-109; 2002
Abstract:
In the literature the formation of domains in d-phases is well documented by direct electron microscopy observations. Compared to this 'local' method, diffraction investigations provide a more 'global' structural insight. Various kinds of domains in decagonal quasicrystals are discussed by extending the theory of domain scattering of conventional crystals. Peculiar diffraction phenomena in decagonal Al-Ni-Co phases are compared to theoretical predictions of the domain scattering theory. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
The structural characteristics of Al-Co-Ni decagonal quasicrystals and crystalline approximants
Authors:
Hiraga, K; Ohsuna, T; Sun, W; Sugiyama, K; McIntyre, G;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 110-114; 2002
Abstract:
The structural characteristics of four modulations of Al-Co-Ni decagonal quasicrystals, called SI-type and type-l superstructures, Co-rich basic structure and 5-fold superstructure, and crystalline approximants, W-(AlCoNi) and PD3c phases, all of which are found in and around an Al-Co-Ni decagonal phase with a wide compositional range, are systematically discussed on the basis of results obtained from high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM) observations. All the structures of the modulations of decagonal quasicrystals and crystalline approximants are described as arrangements of columnar atom clusters, which have a decagonal section of 2.0 nm, in diameter and pentagonal symmetry. The structures of the S1-type and type-l superstructures can be characterized as ordered arrangements of two types of the atom clusters with two orientations of pentagonal symmetry in pentagonal and rhombic quasiperiodic lattices, respectively. On the other hand, the structures of the Co-rich basic state and 5-fold superstructure are described as arrangements of the atom clusters with one orientation of pentagonal symmetry. The PD3c and W-(AlCoNi) crystalline phases can be concluded to be approximants of the type-l and pentagonal superstructure, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Tiling models for decagonal quasicrystals with quasiperiodic potentials
Authors:
Jeong, HT; Kim, WT; Kim, DH; Jeong, HC; McIntyre, G;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 115-119; 2002
Abstract:
We study the thermal equilibrium properties of tiling models for decagonal quasicrystals using Monte Carlo simulations. Two-dimensional (2D) rhombus tilings with a ten-fold quasiperiodic potential are used to model the layers in the decagonal quasicrystals where the potential mimics interlayer interactions from the neighboring layers. When the long wavelength density wave with the ten-fold symmetry is used for the potential, the ground state becomes Penrose tiling. At high temperature, equilibrium configurations are locally similar to the maximal random tiling indicating almost free proliferation of phasons as in the unlocked phason phase. However, their phason-space fluctuations seem to remain finite indicating the long-range quasiperiodic ordering, whereas the logarithmic divergence of phason-space fluctuations is expected in an unlocked phase 2D tiling. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Structural relationship between an icosahedral phase and a 1/1 cubic crystalline approximant in an Al-Li-Cu alloy system, studied by atomic-scale observations of electron microscopy
Authors:
Konno, TJ; Ohsuna, T; Hiraga, K; Jeong, HC;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 120-125; 2002
Abstract:
We observed cubic R-phase and icosahedral I-phases in the Al-Li-Cu system by high-resolution transmission electron microscopy (HREM). The images of both the phases taken from three-fold axes showed the presence of the same kind of atom clusters, which are most likely to be the small triacontahedra. The R-phase was found to contain stacking faults along the {101} plane. This stacking fault is created by the insertion of extra atom units, which destroys the symmetry of the lattice, yet the symmetrical configuration of the facing clusters is well preserved. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Local structures appearing in an intermediate state of transformation from Al-Pd decagonal to Al3Pd crystalline phases
Authors:
Saito, K; Hiraga, K; Hiraga, K;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 126-129; 2002
Abstract:
The structures of an Al-Pd decagonal quasicrystal and an Al3Pd crystal are characterized as two-dimensionally quasiperiodic and periodic arrangements of the same columnar clusters of atoms, respectively. In order to study the transformation process from quasiperiodic to periodic arrangements of the atom clusters, melt-quenched Al3Pd alloys, annealed at various temperatures, have been examined by electron diffraction and high-resolution electron microscopy. In the intermediate state of the transformation, we have found locally periodic arrangements with special intervals, some of which are not in the Al3Pd crystal. Based on the periodic arrangements in the intermediate state of the transformation, metastable structures between the quasiperiodic to periodic arrangements of the atomic clusters have been discussed. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Stacking sequences of atom-clusters in decagonal quasicrystals and their approximants
Authors:
Saitoh, K; Tanaka, M; Hiraga, K;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 130-133; 2002
Abstract:
It has been shown that three types of structures of monoctinic Al13Fe4, decagonal Al72Ni20Co8 with 2-nm mirror-symmetric cluster-column and decagonal Al70Ni15Fe15 with 2-nm 5-fold-symmettic cluster-column, have pentagonal columns, which are composed of common atom-clusters with different stacking sequences. The Al13Fe4 structure and structural models of the two decagonal quasicrystals are summarized. The structural relation among them is discussed. (C) 2002 Elsevier Science BV All rights reserved.
Title:
On mutual transformations of icosahedral phase and beta-solid solution with participation of ordered omega-like displacements in quenched alloys of Al61Cu26Fe13
Authors:
Shalaeva, E; Tanaka, M;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 134-138; 2002
Abstract:
In the rapidly-quenched alloys of Al61Cu26Fe13 characteristic orientation relationships were found between the lattice of the icosahedral phase (L-phase) and that of the beta(CsCl)-solid solution (where P-solid solution contains fine regions of omega-like displacements): [1 1 1](beta) parallel to A2, [1 1 0](beta) parallel to A5. It was established that at the iota-phase (dendrite)/beta-solid solution (interdendritic layers) boundary areas there was a state formed with a modulated structure of the iota-phase. It is assumed that the fine regions of ordered w-like displacements are involved in the continuous transformations (direct and reverse) iota-phase-->modulated iota-Structure-->heterogencous beta-solid solution, going on in the boundary areas due to the strained state of quenched alloys. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Crystal structure of a cubic Al17Zn37Mg46; a 2/1 rational approximant structure for the AI-Zn-Mg icosahedral phase
Authors:
Sugiyama, K; Sun, W; Hiraga, K; Jeong, HC;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 139-142; 2002
Abstract:
The crystalline structure of a 2/1 cubic approximant phase Al17Zn37Mg46 (Pa3, a=23.1 Angstrom) for the AI-Zn-Mg icosahedral phase has been determined by the single crystal X-ray diffraction. The structure of the present 2/1 approximant is characterized by the packing of Bergman clusters and the atomic arrangements for six successive shells are similar to those found in the 1/1 cubic approximant. However, the fourth rhombicosidodecahedral shell of the 2/1 cubic approximant indicates a rather distorted figure together with the chemical disorder. This reflects the unique packing motif of the Bergman clusters in the 2/1 cubic approximant. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Diffuse scattering in decagonal Al-Ni-Fe
Authors:
Weidner, E; Lei, JL; Frey, F; Wang, R; Grushko, B; Suzuki, T;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 156-158; 2002
Abstract:
Significant diffuse scattering close to Bragg reflections was observed in decagonal Al71.5Ni23.5Fe5 phase which is otherwise free of disorder phenomena. As found by synchrotron measurements (DESY, RASYLAB) this diffuse scattering is anisotropically distributed and dumb-bell shaped with a major extension parallel to the scattering vector Q and a typical 1/q(2) fall-off of the diffuse wings. The diffuse data were tentatively interpreted in frame of a TDS theory [Phys. Rev. B 59 (1999) 8221 using only 2 (out of 5) phonon elastic constants, c(11) and c(66). A remarkable matching of observed and calculated diffuse data could be achieved, however, with an unusual (?) c(66)/c(11) ratio equal to 4.0. An alternative interpretation is based on strain fields caused by static lattice distortions [Phys. Rev. B 37 (1988) 4458]. Possibly there is a superposition of both contributions. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Structure refinement of i-Al-Pd-Mn quasicrystals by IP-Weissenberg camera data
Authors:
Yamamoto, A; Takakura, H; Tsai, AP; Wang, R;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 159-163; 2002
Abstract:
The structure refinement of i-Al-Pd-Mn quasicrystals using an IP-Weissenberg camera is reported. A 6D model proposed previously [Mater. Sci. Forum 150-151 (1944) 211] was used as an initial model for the refinement and was modified during the refinement. The final model includes 91 structural parameters and gave R-factors of R-w=0.053 and R=0.054 for 377 independent reflections. This suggests that an IP-Weissenberg camera gives a reliable data set for quasicrystals which includes many weak reflections. The structure includes two 20 Angstrom clusters, one of which is similar to that of the 2/1 approximant and the other two smaller clusters are the Mackay cluster and its variant. (C) 2002 Published by Elsevier Science B.V.
Title:
Cluster structure and low-energy planes in icosahedral Al-Pd-Mn quasicrystals
Authors:
Yang, WG; Feuerbacher, M; Urban, K; Wang, R;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 164-168; 2002
Abstract:
The structure of icosahedral Al-Pd-Mn phase has been examined with special emphasis on the arrangement of clusters at different hierarchical levels. A box of atomic positions calculated according to Boudard's model has been searched for clusters and superclusters (clusters of clusters on a higher inflation level). The arrangements of clusters and superclusters are very similar to those of the atomic positions, but scaled by inflation factors Of tau(3) and tau(6), respectively. Considering two-dimensional planes cutting through a model Al-Pd-Mn icosahedral quasicrystal, we discuss the energy of such planes, defining that the intersection area of a plane with the clusters determines its energy cost. Planes perpendicular to fivefold, twofold and pseudo twofold directions are investigated. The results show that the positions of the local energy minima of fivefold and twofold planes follows a Fibonacci sequence, whereas an almost constant energy cost was found for pseudo twofold planes. We found that the fivefold and twofold cut planes possess a chemical order showing a limited number of compositions, which we have termed H-, M-, L- and Hl-, H2-, Ll-, L2-plancs, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Structural variations in local areas of an Al70Ni15Fe15 decagonal quasicrystal and the interpretation by the 1-nm column-pair scheme
Authors:
Yokosawa, T; Saitoh, K; Tanaka, M; Tsai, AP; Grushko, B;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 169-173; 2002
Abstract:
Structural variations in local areas such as the star-shaped and butterfly-shaped tiles of a noncentrosymmetric decagonal quasicrystal of Al70Ni15Fe15 have been investigated by using the high-angle annular dark-field scanning transmission electron microscope method. It has been demonstrated that the variations of the star-shaped and butterfly-shaped tiles in Al70Ni13Fe15 are uniquely decomposed into the 1-nm column-pairs [Saitoh et al., J. Phys. Soc. Jpn. 68 (1999) 2886], which is the basic structural unit of the tau(2)-inflated Al13Co4 approximant. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Hierarchic multishell structures with icosahedral symmetry
Authors:
Kuo, KH; Deng, DW; Tanaka, M;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 174-179; 2002
Abstract:
Icosahedral quasicrystals are generally divided into the Mackay icosahedron (MI) type and the Frank-Kasper (F-K) type based on the multishell icosahedral structural motifs in their related crystalline phases. Their different hierarchic icosahedral structures have been discussed separately in the past. It is shown here that they both are faulted icosahedral shell structure of Mackay with the f.c.c. ABCA... sequence [Acta Crystallogr. 15 (1962) 916]: a h.c.p. fault in the ABCB sequence yields the MI type whereas an ABA sequence the F-K type hierarchic structure. This can also result from the different connections of the core and outer icosahedra in the hierarchic icosahedral structures: inversely oriented icosahedra yield the MI type while similarly oriented icosahedra. yield the F-K type hierarchic structure. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Cluster models of decagonal tilings and quasicrystals
Authors:
Gahler, F; Reichert, M; Tanaka, M;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 180-185; 2002
Abstract:
Two different relaxed versions of Gummelt's aperiodic cluster covering rules are considered. These relaxed covering rules produce certain random tiling type structures, which are precisely characterized, along with their relationships to various other random tiling ensembles. One variant of the relaxed covering rules allows for a natural realization in terms of a vertex cluster. It is shown with Monte Carlo simulations that the structures with maximal density of this cluster are the same as those produced by the corresponding covering rules. The entropy density of this covering ensemble is determined by Monte Carlo simulations, using entropic sampling techniques, Perfectly ordered structures, like those produced by Gummelt's perfect covering rules, can be obtained in our model if a coupling between neighboring clusters is introduced. This coupling can order the random tiling type structures to perfectly ordered quasicrystals. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
The square Fibonacci tiling
Authors:
Lifshitz, R; Reichert, M;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 186-190; 2002
Abstract:
We introduce the 2-dimensional square Fibonacci tiling and its generalization to higher dimensions as models for quasicrystals without 'forbidden' symmetries. We derive some of the basic mathematical properties of the tiling as well as calculate its diffraction pattern. We discuss the relevance of the Fibonacci tiling for quasicrystal research and for applications in other fields. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Comparison of quasi-unit-cell models to Penrose-tile models for decagonal quasicrystals
Authors:
Jeong, HC; Reichert, M;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 191-194; 2002
Abstract:
The structures of decagonal quasicrystals have been described as periodic stacks of decagonal quasicrystalline planes. Decagonal covering and Penrose tiling have been used to model the lattice structure of the quasicrystalline plane. We compare quasi-unit-cell models (decagon covering with decorated decagon) to Penrose-tile models (Penrose tiling with decorated rhombus tiles) and show that a quasi-unit-cell model can be interpreted as a Penrose-tile model with inflated rhombus tiles. For any given decagonal quasi-unit-cell model, there is a systematic way to generate the equivalent rhombus decorations of Penrose tiling. In general, the edge of the unit rhombus tiles in an equivalent Penrose decoration is shown to be tau(4) times longer than the edge of the quasi-unit decagon. This equivalence can be used in computing atomic densities of quasi-unit-cell models. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Colourings of planar quasicrystals
Authors:
Baake, M; Grimm, U; Scheffer, M; Tsai, AP;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 195-197; 2002
Abstract:
The investigation of colour symmetries for periodic and aperiodic systems consists of two steps. The first concerns the computation of the possible numbers of colours and is mainly combinatorial in nature. The second is algebraic and determines the actual colour symmetry groups. Continuing previous work, we present the results of the combinatorial part for planar patterns with it-fold symmetry, where n = 7, 9, 15, 16, 20, 24. This completes the cases with phi(n) less than or equal to 8, where phi is Euler's totient function. (C) 2002 Michael Baake. Published by Elsevier Science B.V. All rights reserved.
Title:
Construction of average unit cell for Penrose tiling
Authors:
Wolny, J; Kozakowski, B; Repetowiez, P; Tsai, AP;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 198-202; 2002
Abstract:
Two appropriate reference lattices, oriented in different directions, have been used to construct the average unit cell for Penrose tiling. The obtained unit cell consists of four pentagons arranged in the physical plane. It has been shown that the pentagons are just the projections of the atomic surface from the 3D perpendicular space. For the two scattering vectors (corresponding to the reference lattices) an appropriate 2D plane embedded in 5D space has been constructed. The atomic surface is then projected perpendicularly to this plane. The trace of such projection on physical space gives the average unit cell, which can be used for calculation of peak intensities of the diffraction pattern for Penrose tiling. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Hierarchies of quasicrystal substitutional patterns
Authors:
Escudero, JG; Garcia, JG; Repetowiez, P;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 203-205; 2002
Abstract:
Several species of quasicrystal tilings with symmetries significant from an experimental point of view can be obtained by superimposing structures with less allowed orientations. In the octagonal case two hierarchy levels can be reached and in some cases the structures can be converted into face-to-face tilings. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Structure model for icosahedral quasicrystals which consists of three types of unit cells without glue atoms
Authors:
Kato, K; Ninomiya, T; Repetowiez, P;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 206-209; 2002
Abstract:
By using new decoration for the two-dimensional Penrose tiling, we construct a tau(4)-scaling three-dimensional icosahedral structure consisting of three types of zonohedra; a triacontahedron, a star-like sixty-face rhombohedron and a rhombic icosahedron. The present 3D model extends only in a layer perpendicular to the five-fold axis of icosahedral symmetry with a finite thickness along the axis and there are few overlaps between the zonohedra. We calculate the electron diffraction pattern for the present model by putting atoms at all the vertices of the three types of zonohedral units. Reasonable agreement with the experimental results for i-AlMn phase is obtained. (C) 2002 Published by Elsevier Science B.V.
Title:
Average lattice and the long-wave length behavior of quasicrystals
Authors:
Naumis, GG; Aragon, JL; Torres, M; Tsai, AP;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 210-212; 2002
Abstract:
Using the generalized dual method, close analytical expressions for the coordinates of the quasiperiodic lattice are given. This allows to define the lattice as an average plus a fluctuation part. The average is a superposition of crystalline lattices, and the dynamical structure factor or the diffraction pattern of the quasiperiodic structure can be expressed in terms of the average plus the fluctuation part. The average lattice dominates the response for long-wave modes of a probe particle or field, which is relevant in some recent application of quasiperiodic structures. The method can be extended for quasiperiodic grids, and is a very efficient algorithm to perform calculations in quasicrystals. Finally, the present approach can be used to define a Brillouin zone without ambiguities in the reciprocal space. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Classification of quasilattices in two dimensions into mutual local-derivability classes
Authors:
Niizeki, K; Aragon, JL;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 213-216; 2002
Abstract:
Octagonal and decagonal quasilattices in two dimensions are classified into symmetry-preserving mutual-local-derivability (SMLD) classes. Our consideration is restricted to quasilattices with windows whose shapes are regular octagons or decagons being oriented appropriately in the internal spaces (i.e. the perp, space); moreover, the widths of the regular polygons are assumed to be 'rational' with respect to the relevant quadratic field, i.e. Q[root2] or Q[root5]. These quasilattices are self-similar in a strong sense. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Diffraction analysis of decorated aperiodic structure; decorated Thue-Morse sequence
Authors:
Wnek, A; Wolny, J; Torres, M;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 217-220; 2002
Abstract:
As an alternative to the Patterson analysis of quasicrystals and aperiodic structures, the reference lattice approach was applied to describe the diffraction pattern of the decorated Thue-Morse sequence. The Thue-Morse sequence is known as an aperiodic structure with a singular continuous Fourier transform. Such a sequence was decorated by combining every letter in the Thue-Morse sequence with a new expression. By using the reference lattice concept it was possible to find the envelope function, that gives the intensity of peaks in the diffraction patterns for main reflections and their satellites. (C) 2002 Published by Elsevier Science B.V.
Title:
Total-energy-based structure prediction for d(AlNiCo)
Authors:
Henley, CL; Mihalkovic, M; Widom, M; Tsai, AP;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 221-227; 2002
Abstract:
One may predict a quasicrystal structure starting from electrons and quantum mechanics, as approximated by interatomic pair potentials calibrated with ab initio total-energy calculations, combined with the experimentally known composition and lattice constants. Here we report our progress on the 'basic Ni' decagonal phase d(Al70Ni21Co9). Atomic configurations are represented as decorations of (possibly) random tilings. Our method was Monte Carlo simulation using both lattice-gas hops by atoms and tile-flip rearrangements, eventually followed by molecular dynamics and relaxation of the atom positions. Initially allowing the greatest freedom of atom positions, we observed nearly deterministic structural rules and enforced these as constraints involving larger tiles; this procedure was repeated at the next level of modeling. In crude and preliminary form, the effective Hamiltonian for tile-tile interactions is known, which is needed for further simulations to infer the long-range order. Our atomic arrangements in the 20-Angstrom decagonal cluster are compared with three structure models based on recent experiments. (C) 2002 Published by Elsevier Science B.V.
Title:
On the formation of quasicrystals and the evolution of transport anomalies
Authors:
Haussler, P; Haberkern, R; Madel, C; Barzola-Quiquia, J; Lang, M; Suzuki, T;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 228-231; 2002
Abstract:
We report on a (quasi) continuous structural evolution of the amorphous to the quasicrystalline state and the accompanied evolution of electronic transport anomalies. Both phases are known to be Hume-Rothery-stabilized. The amorphous phase shows, in the mean around any ad-atom, spherical-periodic short- and medium-range order causing a broad pseudogap at E, and relatively small deviations of electronic transport to the free-electron behaviour. During annealing, already in the amorphous state, angular correlation and planar order arises. This tau-related order matches the spherical periodic order and improves it. The planary order causes, additional to the broad, a sharp pseudogap at E-F Both pseudogaps together, their concentration and T-dependences, as well as their evolution during annealing, are able to explain all the unusual electronic transport properties of the conductivity, the thermopower and the Hall-coefficient for 50 K
Title:
The successive phase transformation in a Co-rich Al-Ni-Co decagonal phase
Authors:
Yamamoto, K; Yang, W; Nishimura, Y; Matsuo, Y; Takeuchi, S;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 237-240; 2002
Abstract:
Peak broadening and the peak positions of Bragg reflections were studied with the high-resolution X-ray diffraction method for decagonal Al72.7Ni8.5Co18.8 quasicrystals. From the Q(perpendicular to) dependences of the full-width at half-maximum (FWHM) of the Bragg reflections and the peak shifts from ideal Bragg peak positions along the longitudinal direction, these decagonal quasicrystals were classified into three groups with different phason strains. These three group, were identified as the random phason strain, the one-dimensional linear phason strain and the two-dimensional linear phason strain, respectively. This means that the Al72.7Ni8.5Co18.8 decagonal phase undergoes a successive phase transformation from a decagonal quasicrystal through a one-dimensional quasicrystal to an approximant crystal. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
An order-disorder transformation in Al72Ni20Co8 decagonal quasicrystals
Authors:
Abe, H; Saitoh, H; Kusawake, T; Nakao, H; Matsuo, Y; Ohshima, K; Morikawa, Y; Matsumoto, H; Kimura, K;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 241-245; 2002
Abstract:
The diffuse scattering from atomic short-range order (SRO) associated with an order-disorder transformation was observed in single decagonal quasicrystals of Al72Ni20Co8. The diffuse scattering was distributed around the superstructure reflections. The correlation length of the diffuse scattering was estimated to be 2.8 nm at room temperature and developed into more than 11.0 nm on the superstructure phase at high temperature. Full width at half maximum of Bragg reflections increased monotonically above the transformation temperature, T-c2. On the other hand, SRO diffuse intensities decreased gradually in the same temperature region. Moreover, hysteresis of SRO diffuse scattering appeared above T-c2. These behaviors at high temperature originate in the thermally activated fluctuations. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
On the phase transitions of the quasicrystalline phases in the Al-Cu-Fe-Co alloy
Authors:
Kim, SH; Kim, BH; Lee, SM; Kim, WT; Kim, DH; Ohshima, K;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 246-250; 2002
Abstract:
Microstructural change with Co content together with heat treatment was studied in rapidly solidified Al-Cu-Fe-Co alloys using X-ray diffractometry and transmission electron microscopy. With an increase in Co content in the as-cast Al65Cu20Fe15-xCox alloys, the relative amount of the icosahedral phase drastically decreased and that of the decagonal phase increased. In the as-melt spun alloys, effects of Co content are critically changed at around 5 at% Co. For the less Co containing alloys (below 5 at%), the icosahedral phase proved to be the major phase, while the 5 at% Co containing alloy showed the coexistence of the icosahedral and decagonal phases. The 8 at% containing alloy showed the monolithic decagonal phase in the as-melt spun state. Unlike as-cast alloys, all the as-melt spun alloys showed no trace of the lambda-phase. However, after heat treatment of ribbons, X-phase newly appeared in the Al65Cu20Fe10Co3 and Al65Cu20Fe10Co5 alloys. The lambda-phase showed orientation relationships with surrounding icosahedral or decagonal phases. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Enhancement of the quasicrystal-forming ability in Al-based alloys by Be-addition
Authors:
Song, GS; Fleury, E; Kim, SH; Kim, WT; Kim, DH; Ohshima, K;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 251-255; 2002
Abstract:
The influence of beryllium (Be) addition on the quasicrystal-forming ability (QFA) in Al-Cu-Fe and Al-Mn systems has been investigated using conventional solidification technique, For a series of as-east (Al62-xBex)Cu25.5Fe12.5 (x=0,1,3,5,7) alloys, the Be addition modified the icosahedral phase formation mechanism from peritectic reaction to primary solidification and resulted in the increase in the volume fraction of the i-phase from 40% for x=0 to 90% for x=7. Such an enhancement of the QFA with the increase of Be content can be represented by using the reduced quasicrystal transition temperature proposed in the present paper. In Al-Mn alloy system, microstructural changes due to the addition of Be were examined in detail by comparing as-cast Al90Mn2.5Be7.5 alloy with Al97.5Mn2.5 bulk ingot. For this alloy system, the substitution of Al by Be was found to reduce substantially the critical Mn-content and cooling rate necessary for the formation of the i-phase. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Evidence of phase transition and measurement of thermal expansion in decagonal Al-Co-Ni at low temperatures
Authors:
Kupsch, A; Meyer, DC; Gille, P; Paufler, P; Kim, DH;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 256-260; 2002
Abstract:
Powder samples of decagonal Al70.7Co13.3Ni16.0 were investigated by X-ray diffraction (XRD) in the temperature range 15-300 K, We evaluated the temperature dependence of lattice parameters a and c, along and perpendicular to the quasiperiodic plane, and observed indications of a phase transition. Temperature dependences were modelled best by second order polynomials leading to linear thermal coefficients whose anisotropy ratio gamma(T)/alpha(T) was found to decrease with increasing temperature from 1.60 (at 15 K) to 1.05 (at 300 K). At T = 150 K the occurrence of an intermediate phase is indicated by at least three additional reflections, which cannot be indexed using integers of reflections of the decagonal lattice. Furthermore, near this temperature the lattice parameters of the decagonal phase showed deviations from a smooth polynomial fit. We will solely describe the experimental facts as they are and make the suggestion that this transition is due to a periodic superorder of the decagonal lattice. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Nano-quasicrystalline phase formation in Mg-Cd-Yb alloys
Authors:
Singh, A; Divakar, R; Raghunathan, VS; Guo, JQ; Tsai, AP; Ohshima, K;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 261-264; 2002
Abstract:
The microstructure of Mg60+xCd25-xYb15, x=0, 5, 10, Mg50Cd30Yb20 and Mg25Cd65Yb10 as-cast alloys has been examined by transmission electron microscopy. While the Mg60Cd25Yb15 alloy showed only an icosahedral quasicrystalline phase, the magnesium rich alloys also showed a Zn2Mg type (Mg,Cd)(2)Yb Laves phase. The alloys showed nanosized particles of icosahedral phase. Eutectic microstructures involving the icosahedral phase were observed. A lamellar (50 nm) structure of icosahedral phase and Mg was observed, exhibiting a definite orientation relationship with the hexagonal axis along one of the twofold axes of the icosahedral phase. In the Cd-rich alloys the cubic Cd6Yb approximant phase occurred, along with the icosahedral phase and intermediate structures in nanocrystalline form. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
HRTEM observation of phason flips in Al-Cu-Co decagonal quasicrystal
Authors:
Edagawa, K; Suzuki, K; Takeuchi, S; Guo, JQ;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 271-277; 2002
Abstract:
In-situ high-temperature, high-resolution transmission electron microscopy (HRTEM) has been performed on an Al-Cu-Co decagonal quasicrystal, to investigate thermal fluctuation of phasons. A tiling pattern with the edge length of 2 tun was constructed by connecting white spots in the HRTEM image. Local tile-rearrangements, which can be interpreted as phason flips, have been observed at temperatures above 1073 K. The frequency of the phason flip is higher at thin areas near the edge of the sample than at thick areas. The origin of such a sample-thickness dependence of the frequency of the phason flip is discussed using a simple model calculation. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Atomic dynamics of icosahedral Zn63Mg26.3Y10.7 studied by neutron inelastic scattering
Authors:
Rouijaa, M; Suck, JB; Sterzel, R; Guo, JQ;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 283-286; 2002
Abstract:
The dynamic structure factor of ZnMgY has been determined using neutron inelastic scattering techniques. From the time-of-flight spectra also the generalized vibrational density of states (GVDOS) was determined, which was used to calculate the temperature dependence of some of the thermodynamic properties like the vibrational heat capacity. The GVDOS of icosahedral ZnMgY consists of two main bands. The main dominant band at lower energies is composed of three subbands. This is characteristically different from the GVDOS of the Mackay type of icosahedral alloys investigated so far. The more pronounced separation of the subbands seems to be characteristic for the GVDOS of Frank-Kasper type of icosahedral quasicrystals. (C) 2002 Published by Elsevier Science B.V.
Title:
Phason elastic constants of a binary tiling quasicrystal
Authors:
Koschella, U; Gahler, F; Roth, J; Trebin, HR; Tsai, AP;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 287-290; 2002
Abstract:
For a two-dimensional binary tiling model quasicrystal, the full set of (zero temperature) elastic constants is determined. It is found that the elastic energy is a perfect quadratic form in the phonon and phason strains. One of the phason elastic constants turns out to be negative, implying that the quasicrystal is only metastable at zero temperature. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Icosahedral Al-Pd-Mn, a melting pot for diffusion mechanisms
Authors:
Frank, W; Bluher, R; Schmich, I; Trebin, HR;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 291-295; 2002
Abstract:
The diffusion of Ge-71, Au-195, Pd-103, and Fe-59 in icosahedral (i-)Al-Pd-Mn was studied by means of a radiotracer technique. In addition, for Au-195 and Pd-103, the effect of proton irradiation during diffusion annealing was investigated. Based on the large body of diffusion data available for i-Al-Pd-Mn, a comprehensive discussion of the diffusion mechanisms operating in this quasicrystal is presented, (C) 2002 Published by Elsevier Science B.V.
Title:
Vacancy-mediated diffusion in quasicrystalline alloys
Authors:
Mehrer, H; Galler, R; Schmich, I;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 296-301; 2002
Abstract:
In this paper we summarize recent diffusion studies from our laboratory. Diffusion of the following elements has been studied in icosahedral quasicrystals: Mn, Fe, Ga, In and Zn in AlPdMn and Zn in ZnMgRE (RE=rare earth metal). The diffusivities follow Arrhenius-like temperature dependencies. In addition, for Mn and Zn in icosahedral AlPdMn we have studied the dependence of the diffusivities on hydrostatic pressure. Signs and values of the activation volumes around 0.7 atomic volumes are strongly in favour of a vacancy-type diffusion mechanism. Diffusion of Co and Ni has been studied in both principal directions of decagonal AlNiCo quasicrystals. The small diffusion anisotropy is a strong argument in favour of vacancy-mediated diffusion. Significant contributions of phason flips to diffusion should result in faster diffusion within the layers perpendicular to the decagonal axis, which is not observed. (C) 2002 Published by Elsevier Science B.V.
Title:
Heat capacity and thermal expansion of a decagonal Al-Co-Ni quasicrystal
Authors:
Inaba, A; Lortz, R; Meingast, C; Guo, JQ; Tsai, AP; Ohshima, K;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 302-305; 2002
Abstract:
Heat capacities and thermal expansion coefficients for a decagonal Al72Co16Ni12 single-grain quasicrystal were determined in the temperature range 5-300 K. The linear thermal expansion coefficient obtained at 300 K parallel to the ten-fold axis is approximately 10% larger than that perpendicular to the axis. This anisotropy becomes more prominent at low temperatures, resulting in quite anisotropic Gruneisen parameters. The measurements were also made for comparison for an icosahedral (isotropic) Al71.7Pd19.4Re8.9 single-grain quasicrystal. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Positron-trapping property in Al-Mg-Zn alloy system
Authors:
Sato, K; Uchiyama, H; Kanazawa, I; Hamada, E; Suzuki, T; Takeuchi, T; Mizutani, U; Matsumoto, H;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 306-309; 2002
Abstract:
Rhombic triacontahedral-type icosahedral quasicrystal and its 1/1- and 2/1-approximants in an Al-Mg-Zn alloy system were systematically studied by means of positron-annihilation measurements. The structural vacancy densities, average positron diffusion length, average positron diffusion length in the vacancy-free region, positron diffusion coefficient, and positron mobility were successfully derived. The results indicated that the thermarized positrons in the vacancy-free region tend to localize as the order of the approximant increases. (C) 2002 Published by Elsevier Science B.V.
Title:
Inelastic neutron scattering study of the dynamics of Al74Pd22Mn4 (xi ')
Authors:
Scheffer, M; Suck, JB; Kanazawa, I;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 310-313; 2002
Abstract:
The generalised vibrational density of states (GVDOS) of polycrystalline Al74Pd22Mn4 (xi') has been investigated by inelastic neutron scattering at the temperatures 296, 600, 800 and 1000 K. The GVDOS shows two broad main maxima near 14 and 32 meV, which are shifted to lower energies with increasing temperature. The data are compared to the GVDOS of the icosahedral phase [J. Non-Cryst. Solids 156-158 (1993) 872; Mater. Sci. Eng. A 226-228 (1997) 479; J. Non-Cryst. Solids 250-252 (1999) 855] in this system, the structure of which is strongly related to this crystalline phase [Philos. Mag. B 68 (1993) 607; Philos. Mag. A 74 (1996) 939]. At energies below 9 meV, the GVDOS of the xi'-phase shows higher densities and a much more harmonic behaviour than that of the icosahedral phase. Thermodynamic quantities like the heat capacity are calculated and compared to measured values. (C) 2002 Published by Elsevier Science B.V.
Title:
A comparative study of the atomic dynamics of icosahedral ZnMgHo and ZnMgEr by neutron inelastic scattering
Authors:
Rouijaa, M; Suck, JB; Sterzel, R; Petrenko, OA; Suzuki, T;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 314-317; 2002
Abstract:
The atomic dynamics of the Frank-Kasper type of FI icosahedral alloys ZnMgHo and ZnNIgEr have been determined at 200 K using thermal neutron energy loss scattering. From the sum of all double differential scattering cross-sections d(2)sigma/(dOmega dE) weighted with sin(theta) the generalised vibrational density of states (GVDOS) was calculated. The calculated GVDOS consists of two bands, a dominant one centered around 20 meV, which is composed of several subbands, and a rather weak one centered around 50 meV. Both alloys show very much the same atomic dynamics with small differences near 15, 22 and 38 meV. (C) 2002 Published by Elsevier Science B.V.
Title:
Atomic vacancies in quasicrystals - a study by positron annihilation spectroscopy
Authors:
Baier, F; Schaefer, HE; Sterzel, R;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 318-320; 2002
Abstract:
For studying atomic vacancies in quasicrystals the specific technique of positron annihilation spectroscopy has been employed. In quasicrystals and approximants of the Al-Pd-Mn and the Zn-Mg-Ho systems structural vacancies in the concentration range of 10(-1) have been observed. We perform the first in-situ measurements of the positron lifetime at high temperatures, where the formation of thermal vacancies in i-Al70.2Pd21.3Mn8.5 can be observed directly. The annealing behavior of quenched-in vacancies, which coincide with the data from earlier time differential dilatometry studies after fast temperature changes, gives access to the vacancy migration properties and kinetics in quasicrystals. From the coincident measurement of the Doppler broadening of the positron-electron annihilation photon line at ambient temperatures, we deduce that the vacancies observed in i-Al70.2Pd21.3Mn8.5 are predominantly located in an Al rich environment. Since high-temperature processes such as diffusion, plasticity and structural phase transformations, are strongly influenced by thermal vacancies and their kinetics, the present experiments can provide information on these processes. (C) 2002 Elsevier Science BY All lights reserved.
Title:
Comparative study of the tribological behavior of thermal sprayed quasicrystalline coating layers
Authors:
Fleury, E; Kim, YC; Kim, JS; Kim, DH; Kim, WT; Ahn, HS; Lee, SM; Matsumoto, H;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 321-325; 2002
Abstract:
To investigate the role of tribological reactions on the friction and wear of quasicrystalline materials, coatings with two alloy compositions have been prepared by plasma and HVOF spraying techniques. The tribolayers were characterized by the formation of a transfer film on the counterface and densification of the coating subsurfaces. It was observed that the thickness of the transfer film and pore-free region were dependent on the composition and process used for the deposition of the coatings as well as the sliding velocity. As the sliding velocity increased, the growth rate of the transfer film decreased, resulting in a decrease of the coefficient of friction. On the other hand, the wear rate appeared to be controlled by the thickness of the pore-free region formed within the coating surface zone. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Diffuse electron scattering determination of elastic constants of Al-Pd-Mn icosahedral quasicrystal
Authors:
Lei, JL; Wang, RH; Yin, JH; Duan, XF; Kim, WT;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 326-329; 2002
Abstract:
Quantitative diffuse electron scattering in the vicinity of some Bragg reflections has been measured for the first time on a single Al70.3Pd21.5Mn8.2 icosahedral quasicrystal in order to obtain information about elastic constants. The main contribution to the diffuse scattering comes from the phason disorder. The shape and the quantitative intensity distribution of diffuse scattering can be accounted for by considering only two phason elastic constants K-1 and K-2 with a ratio of K-2/K-1 = 0.50. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Microstructural analysis of plastically deformed icosahedral Zn-Mg-Dy single quasicrystals
Authors:
Heggen, M; Feuerbacher, M; Lange, T; Urban, K; Kim, WT;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 330-336; 2002
Abstract:
We present a detailed study of the microstructure of plastically deformed Zn-Mg-Dy single quasicrystals. Single quasicrystals grown using the self-flux technique were uniaxially deformed at strain rates of 10(-5) and 10(-6) s(-1) in the temperature range between 490 and 530 degreesC. Dislocations and planar defects in differently treated samples were analyzed using transmission electron microscopy. Antiphase boundaries (APBs) of the face-centered icosahedral structure were shown to be generated as a result of plastic deformation by moving partial dislocations. The determination of the APB planes, i.e. the planes of dislocation motion, along with an analysis of the Burgers vectors and the line directions of the dislocations attached to the APBs, allowed a detailed microstructural characterization on the mode of plastic deformation. Dislocations of 60degrees mixed-type were most frequently found. Slip occurs preferentially on planes that are inclined by an angle of almost 45degrees to the compression direction, i.e. planes of highest resolved shear-stress. It was shown that the mode of dislocation movement is mainly pure glide, though in some cases motion by climb was observed as well. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Theoretical and experimental investigation of the electronic structure of Ti-Zr-Ni and Ti-Zr-Ni : H alloys
Authors:
Belin-Ferre, E; Hennig, RG; Dankhazi, Z; Sadoc, A; Kim, JY; Kelton, KF; Lee, SM;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 337-342; 2002
Abstract:
We have calculated the band structure of a model 1/1 approximant of cubic Frank-Kasper type structure of the icosahedral Ti-Zr-Ni quasicrystal. We have shown that the electronic structure is dominated by the metals d bands with a complete mixing of Ti and Zr states. With respect to the pure metal, Ni d states appear to be strongly modified upon alloying. The experimental investigation of the icosahedral alloy shows good agreement with the theoretical calculations for the approximant. We have shown experimentally that dramatic modifications of both occupied and unoccupied states occur in the hydrogenated quasicrystal, due to bonding to H. We have asserted preferential Zr-H rather than Ni-H bonding. We have suggested that Ti-H bonding should also be significant. We interpret the high H/metal ratio by the fact that H bonds to each of the elements in the quasicrystal. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Electronic structures of Cd-based quasicrystals and approximants
Authors:
Ishii, Y; Fujiwara, T; Dankhazi, Z;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 343-347; 2002
Abstract:
Electronic structures of cubic Cd6M (M=Yb, Mg and Y), which are approximant crystals of newly discovered Cd-based quasicrystals, are studied theoretically. It is found that stabilization due to alloying is obtained if M is an element with low-lying unoccupied d states. This leads to the conclusion that the cohesion of the Cd-based compounds is certainly due to the hybridization of the d states with a wide sp band. Cd6M is composed of clusters of icosahedral shape, as are most approximant crystals, but a core of the cluster is of non-icosahedral symmetry. It is found that the atoms in the non-icosahedral core are rather weakly bound and do not play an important role in stabilizing the cluster and its packing. Stability of Zn17Sc3, which has a similar structure to Cd6M but has no non-icosahedral core, is understood in the same context as Cd6M. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Model simulations of momentum-resolved photoemission from quasicrystals
Authors:
Rotenberg, E; Theis, W; Horn, K; Sadoc, A;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 348-351; 2002
Abstract:
Recent experiments have demonstrated that valence band dispersion may be observed on suitably prepared surfaces of quasicrystals. We present model calculations for optical transitions for one-dimensional aperiodic lattices, and show that these calculations are consistent with the experimental photoemission results. We estimate the total number of bands which can be observed in such an experiment is reduced from infinite, to just two to three bands in a typical experiment. (C) 2002 Elsevier Science BY All rights reserved.
Title:
Anomalous Hall effect in the hopping regime of the insulating Al70Pd22.5Re7.5 quasicrystal
Authors:
Chen, KH; Su, TI; Fang, HC; Lee, SC; Lin, ST; Kelton, KF;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 352-354; 2002
Abstract:
The Hall coefficient R-H is seen to rise rapidly with decreasing temperature in the hopping regime of the insulating Al70Pd22.5Re7.5 quasicrystal with a resistivity ratio r = rho(4.2 K)/rho(300 K) equal to 24 and to exhibit the variable-range hopping behavior i.e. R-H = R-0(T-0H/T)(1/4). The obtained value of T-0H is much larger than the Mott's temperature T-0 extracted from the conductivity in the hopping regime. This is contrary to the prediction of Gruenewald et al. [Solid State Commum. 64 (1987) 11] for disordered systems. No existing theories can account for this anomalous effect. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Investigation of the Hume-Rothery stabilization mechanism from ab initio band calculations for different electron compounds: Cu5Zn8 and Al-Mg-Zn, Al-Cu-Ru-Si approximants
Authors:
Takeuchi, T; Sato, H; Mizutani, U; Lee, SC;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 355-359; 2002
Abstract:
The origin of the pseudogap formed across the Fermi level has been studied in relation to the Fermi surface-Brillouin zone interaction and the sp-d hybridization effect by performing the LMTO-ASA (Linear Muffin-Tin Orbital-Atomic Sphere Approximation) band calculations for the three electron compounds: the gamma-phase Cu5Zn8 alloy, the free-electron-like Al30Mg40Zn30 Frank-Kasper-type 1/1-1/1-1/1 approximant and the Al68Cu7Ru17Si8 Mackay-Icosahedral-type 1/1-1/1-1/1 approximant. We revealed that, in the free-electron-like Al-Mg-Zn approximant, the Fermi surface-Brillouin zone interaction is solely responsible for the formation of the pseudogap at the Fermi level. In the case of the gamma-phase and the Al-Cu-Ru-Si approximant, where d-states are involved across the Fermi level, we have demonstrated that the Fermi surface-Brillouin zone interaction is still strong enough to produce the pseudogap near the Fermi level but that its depth and width are substantially enhanced by the sp-d hybridization effect which splits the d-states into the bonding and antibonding states across the Fermi level. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Ten-fold-like magnetic anisotropy in electrical conductivity of Al-Pd-Mn icosahedral quasicrystal
Authors:
Mizutani, T; Nakano, H; Kashimoto, S; Takatani, Y; Mori, M; Ishimasa, T; Matsuo, S; Matsumoto, H;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 360-364; 2002
Abstract:
Ten-fold-like magnetic anisotropy is reproducibly observed in electrical conductivity of Al71Pd21Mn8 icosahedral quasicrystal. The voltage V is measured, where the current I is along a five-fold axis of the sample and is perpendicular to the magnetic field H. The voltage difference DeltaV=V(+I)+V(-I) has angle dependences at H=30similar to80 kOe and the temperature T=2similar to8 K. DeltaV is about 3000 times smaller than V and its 10-fold-like anisotropy comes from small non-linearity of I-V characteristics. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Magnetic correlations in the Cd-Mg-Tb icosahedral quasicrystal
Authors:
Sato, TJ; Takakura, H; Guo, JQ; Tsai, AP; Ohoyama, K; Ishimasa, T;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 365-368; 2002
Abstract:
We have carried out powder neutron diffraction experiments on the recently discovered Cd-Mg-Tb quasicrystal. Magnetic long-range order was not detected down to 2.5 K. Instead, short-range correlations develop continuously as temperature is decreased below the spin freezing temperature T-11 = 12.5 K; no discontinuous change was observed at T-12 = 5.6 K, where an additional anomaly was found in magnetic susceptibility. The short-range order is mostly identical to that observed in the Zn-Mg-Ho quasicrystal. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Pulsed and modulated photoconduction of icosahedral Al-Cu-Fe quasicrystalline thin film
Authors:
Soga, K; Suzuki, Y; Kojima, Y; Takeda, M; Kimura, K; Ishimasa, T;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 369-373; 2002
Abstract:
Pulsed and modulated photoconduction was measured on an icosahedral Al-Cu-Fe quasicrystalline film. This study is the first report of a pulsed photoconduction of a quasicrystal. By applying both the pulsed and modulated methods, photoconduction with a wide range of carrier relaxation times, 10(-8) to 10(0) s, are observed. The analysis of pulsed and modulated measurements reveals that photoconduction with recombination times longer than 10(-3) s is suppressed by increasing temperature, while that in the shorter one is almost temperature-independent. For the analysis of the modulated photoconduction, models with or without indirect excitation through a localized state are assumed to simulate the dependence of the current and phase on frequency. The calculated results fit the observed ones only when indirect excitation is included. The analysis of temperature dependence of the modulated photoconduction shows that the release of the carrier from the localized state is a thermally deactivated process. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Transport properties of the three-dimensional Penrose lattice
Authors:
Arai, Y; Ishii, Y; Kojima, Y;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 374-376; 2002
Abstract:
Transport properties of the three-dimensional (3-D) quasiperiodic systems have been studied for the 3-D Penrose lattice at zero temperature. The linear scaling with respect to the sample width (cross-section) is observed, With increasing sample width, the conductance fluctuation as a function of the Fermi energy is suppressed and a smooth energy dependence is obtained for larger samples. This suggests that the transport properties of the 3-D quasiperiodic systems are less anomalous than those of the low-dimensional quasiperiodic systems. The sample-length dependence of the conductance is, on the other hand, not that expected for extended Bloch waves and the conductance decreases with increasing sample length. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Slow relaxation of the thermoremanent magnetization and aging in icosahedral Tb-Mg-Zn quasicrystals
Authors:
Dolinsek, J; Jaglicic, Z; Kojima, Y;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 377-380; 2002
Abstract:
The nature of the spin state below spin freezing temperature was studied in an icosahedral Tb-Mg-Zn quasicrystal by the thermoremanent d.c. magnetization (TRM) time-decay as a function of aging time and magnetic field. The system does not exhibit a highly degenerate free energy landscape with an ultrametric organization of metastable states, which makes it essentially different from canonical spin glasses, (C) 2002 Elsevier Science BY All rights reserved.
Title:
Magnetic property of a Zn-Mg-Sc icosahedral quasicrystal
Authors:
Kashimoto, S; Motomura, S; Nakano, H; Kaneko, Y; Ishimasa, T; Matsuo, S; Matsuo, S;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 384-388; 2002
Abstract:
We have investigated the magnetism of a new Zn80Mg5Sc15 P-type icosahedral quasicrystal and a Zn85.5Sc14.5 cubic phase, which is interpreted to be a 1/1 approximant of the new icosahedral quasicrystal, in the temperature region between 2 and 700 K. The magnetic susceptibility of the Zn80Mg5Sc15 icosahedral quasicrystal shows an increase from -1.3x10(-7) to -0.8x10(-7) cgsemu/g with a rise in temperature from 90 to 700 K. The Zn85.5Sc14.5 cubic phase shows also a rise from -1.8x10(-7) to -1.0x1.0(-7) cgsemu/g between 120 and 700 K. The increase in the susceptibility with a rise in temperature is accounted for by a temperature dependence of the Pauli paramagnetism. The experimental results strongly suggest a pseudogap in the electronic density of states at Fermi energy for the Zn80Mg5Sc15 quasicrystal and the Zn85.5Sc14.5, approximant, which has been observed in various stable icosahedral quasicrystals. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Temperature dependence of the magnetoresistance of an insulating Al70Pd22.5Re7.5 quasicrystal
Authors:
Su, TI; Wang, CR; Lee, SC; Lin, ST; Rosenbaum, R; Matsuo, S;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 389-392; 2002
Abstract:
Using theories of the magnetoresistance in the variable-range hopping regime, we are able to interpret the low magnetic field magnetoresistance data taken at liquid helium temperatures of an insulating Al70Pd22.5Re7.5 quasicrystal having a resistivity ratio H = rho(4.2 K)/rho(300 K) equal to 77. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Magnetic properties of F2M-type Al-Pd-Mn quasicrystals
Authors:
Motomura, S; Ishimasa, T; Hirai, I; Kashimoto, S; Nakano, H; Matsuo, S; Matsuo, S;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 393-396; 2002
Abstract:
We measured temperature dependence of the susceptibility of the F2M-type Al-Pd-Mn quasicrystals in the range of temperature T between 2 and 600 K. In the range 2 K
Title:
Atomic and electronic structure determination for a series of Al-Re-Si MI-type 1/1-cubic approximants
Authors:
Onogi, T; Takeuchi, T; Sato, H; Mizutani, U; Nakano, H;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 397-401; 2002
Abstract:
The crystalline structure of the Mackay-Icosahedral type Al-Re-Si 1/1-cubic approximants was determined by Rietveld analysis on the powder diffraction spectra taken with synchrotron radiation. The electronic structure of this approximant was calculated by the LMTO-ASA method with the experimentally determined atomic structure. One of the Al-Re-Si 1/1-cubic approximants, Al73.6Re17.4Si9, was found to have a disorder-free structure in sharp contrast with other 1/1-approximants. This disorder-free structure leads to a positive temperature coefficient of the electrical resistivity and a relatively low residual resistivity. We evaluated the mean free path by substituting the electronic density of states at the Fermi level, the averaged Fermi velocity and the measured resistivity into the Boltzmann transport equation. The resulting mean free paths of 58 Angstrom at 5 K and 21 Angstrom at room temperature show a good consistency with the Boltzmann transport mechanism for this disorder-free complex compound. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Electronic structures of large approximants of Zn-Mg-Y
Authors:
Oshio, K; Ishii, Y; Sato, H;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 402-404; 2002
Abstract:
Zn-Mg-RE (RE=Y or rare-earth elements) alloys form a series of unique hexagonal crystals (approximants) in a composition range close to icosahedral quasicrystals. We studied the electronic structures of the hexagonal Zn-Mg-Y alloy with lattice parameters a = 14.6 Angstrom and a = 23.5 Angstrom. It was found that a pseudogap is formed in the electronic density of states at the Fermi energy. Localization of the valence electron density is found between Zn atoms at particular sites. We speculate that such bonding states between Zn-atom pairs is responsible for stabilizing quasicrystals. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Electronic structure of icosahedral quasicrystals: role of defects
Authors:
Prekul, AF; Kuz'min, NY; Shchegolikhina, NI; Mizutani, U;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 405-409; 2002
Abstract:
The results of the experimental investigation the purpose of which was to determine the thermodynamic coefficients of quasicrystalline alloy in the limit of zero residual conductivity are presented. The experimental picture of properties is obtained which is in concordance with critical character of localized electron states. (C) 2002 Elsevier Science BY All rights reserved.
Title:
Transport properties of icosahedral quasicrystal Al72Pd19.5Mn8.5
Authors:
Bilusic, A; Budrovic, Z; Smontara, A; Dolinsek, J; Canfield, PC; Fisher, IR; Matsuo, S;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 413-415; 2002
Abstract:
We present measurements of the thermoelectrical properties of polygrain icosahedral quasicrystal Al72Pd19.5Mn8.5 in the temperature range 10-300 K. Electrical resistivity has a relatively low room temperature value, rho(K.T) = 1.2 mOmega cm, by lowering the temperature it shows an increase with a maximum value at 120 K. Thermoelectric power is positive in the whole temperature ranges with a quite high room temperature value, S-R.T. = 70 muV/K. Thermal conductivity shows a maximum at 30 K, and a broad minimum around 125 K. The room temperature value is K-R.T. = 3.4 W/mK. The appearance of the maximum in thermal conductivity at 30 K comes mainly from structural scattering, while at temperatures above 120 K from the contribution of the localized phonon state. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Interpretation of high electrical resistivity behavior based on the structure determination of the Al-Cu-(Fe,Ru)-Si 1/1-cubic approximants
Authors:
Takeuchi, T; Mizutani, U; Smontara, A;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 416-421; 2002
Abstract:
The local atomic structure of Mackay icosahedral-type Al-Cu-(Fe,Ru)-Si 1/1-cubic approximants was determined by applying the Rietveld method to the powder diffraction spectra taken with synchrotron radiation. We found that these 1/1-cubic approximants involve chemical and structural disorders and that the difference in the magnitude of their electrical resistivities can be explained by taking into account the difference in the degree of chemical and structural disorder. The electrical resistivity of the Al54Cu25.5Ru12.5Si8 1/1-cubic approximant characterized by the possession of the strongest disorder is found to be the largest among the samples studied and to be comparable to that of the corresponding Al63Cu25Ru12 quasicrystal. We conclude that the degree of disorder involved in the atomic arrangements plays a more crucial role than the quasi-periodicity in determining the magnitude of the electrical resistivity in both quasicrystals and their 1/1-cubic approximants. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Resonant fluorescence emission of MnK beta in quasicrystals
Authors:
Watanabe, Y; Okada, JT; Shoji, H; Nanao, S; Canfield, PC;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 422-426; 2002
Abstract:
Resonant X-ray emission spectra of Mn Kbeta(1,3) (3p - 1s) were measured near the Mn K absorption edge for quasicrystalline icosahedral Al-Pd-Mn, icosahedral Al-Pd-Mn-B, icosahedral Al-Mn-Si, decagonal Al-Mn-Fe-Ge and crystalline alpha-Al-Mn-Si. Except for the Raman scattering energy region, the peak energy of Kbeta(1,3) is independent of incident photon energy for all the samples. The shape was also unchanged. A Kbeta' subpeak, which is caused by the splitting between the density of states of the high spin and the low spin in the 3p band, appeared in all the quasicrystal samples with lower intensity than those of the Mn oxides in spite of the fact that Mn atoms in the decagonal Al-Mn-Fe-Ge and the icosahedral Al-Pd-Mn-B are in a ferromagnetic state. In the profile of the icosahedral Al-Pd-Mn, alpha-Al-Mn-Si and decagonal Al-Mn-Fe-Ge, a clear hump was observed at the energy between Kbeta(1,3) and Kbeta'. In the emission spectra of Mn Kbeta(5) (3d --> 1s), peak positions were 1.5 eV lower for the ferromagnetic quasicrystals than those of the other quasicrystals. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Low-energy ion scattering measurements of quasicrystal surfaces
Authors:
Bastasz, R; Okada, JT;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 427-431; 2002
Abstract:
The technique of low-energy ion scattering spectroscopy is useful for determining the composition and structure of ordered surfaces. It can identify atoms in the topmost layer of a solid and provide real-space data about surface atom arrangement. This technique and its application to the study of quasicrystal surfaces is described using examples of the types of information that can be obtained from the ternary icosahedral alloy Al-Pd-Mn. These include surface layer and subsurface layer compositions, surface layer symmetry, interlayer spacings, and neighboring atom distances. In the case of annealed quasicrystalline Al-Pd-Mn, the surface is found to be composed primarily of Al atoms, a Pd-rich layer appears to exist just below the Al layer, and the top layers are deficient in Mn. The Al atoms at the surface exhibit local 5-fold symmetry. (C) 2002 Published by Elsevier Science B.V.
Title:
Quasicrystal surfaces: potential as templates for molecular adsorption
Authors:
McGrath, R; Ledieu, J; Cox, EJ; Haq, S; Diehl, RD; Jenks, CJ; Fisher, I; Ross, AR; Lograsso, TA; Watanabe, Y;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 432-436; 2002
Abstract:
We report on investigations of the potential for using quasicrystal surfaces as templates for molecular adsorption. The quasicrystalline surfaces of the i-Al-Pd-Mn and the d-Al-Ni-Co quasicrystals have been dosed with various molecules and the surface reactivity characterised by Fourier transform infrared spectroscopy (FTIR). The reflected signal intensities obtained are much weaker than those obtained from other crystals such as metals. Although both quasicrystals are Al-based their surface reactivities are seen to differ. For the Al-Pd-Mn surface, NO and HCOOH both dissociate at the surface and CO does not adsorb. CD4O adsorption leads to multilayers as in other crystals. C,H, molecules stick at low coverages and at low temperatures whilst not affecting the LEED pattern. For the Al-Ni-Co surface, CO molecules stick via activated adsorption to atop sites with vibrational frequencies very similar to CO adsorption on Ni. HCOOH forms multilayers at low temperatures which is reduced to a monolayer upon heating to 173 K; changes in the symmetry of the bonding are observed, which is also seen for HCOOH on Ni surfaces. NO and CD4O showed no characteristic spectra, which may be due to dissociation or a very low sticking probability. We summarise these observations and draw some conclusions as to the most favourable route for molecular overlayer formation. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Surface structure induced by Ar+-bombardment of decagonal AlNiCo
Authors:
Cecco, C; Albrecht, M; Wider, H; Maier, A; Schatz, G; Krausch, G; Gille, P; Ross, AR;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 437-440; 2002
Abstract:
We have investigated the surfaces of decagonal AlNiCo single quasicrystals in UHV by Reflection High Energy Electron Diffraction (RHEED), Atomic Force Microscopy (AFM) and Auger Electron Spectroscopy (AES). The surfaces were prepared by Ar+-sputtering and annealing. We observe well-defined RHEED patterns directly after sputtering at room temperature, revealing a ten-fold symmetry with respect to the azimuthal angle of the incident beam. Two patterns occur, alternating every 18degrees. This symmetry behaviour is probably caused by a bee overlayer consisting of multiple domains in different orientations. The RHEED patterns show a strong temperature dependence. A spontaneous phase transition into a quasiperiodic structure is observed upon annealing to about 350 degreesC. RHEED patterns of a flat, quasicrystalline surface of good structural quality are observed after sputtering at 400 degreesC. As indicated by AES, the influence of oxygen on the structural behaviour seems to be important. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Epitaxial film growth on quasiperiodic surfaces
Authors:
Shimoda, M; Sato, TJ; Tsai, AP; Guo, JQ; Schatz, G;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 441-444; 2002
Abstract:
We performed depositions of noble metals, such as Pt and Ag, onto quasicrystalline surfaces in order to investigate the nature of film growth on quasipcriodic surfaces. Pt depositions onto the ten-fold quasiperiodic surface of decagonal Al-Ni-Co quasicrystal yielded an epitaxial layer of multiply twinned PtAl2 crystals with the aid of predeposited In, which acted as a surfactant. This is quite similar to the case of Au depositions on the ten-fold surface, where an epitaxial layer of multiply twinned AuAl2 crystals was formed. In the case of Ag deposition, no epitaxial films were formed by similar procedures even under the existence of an In layer. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Application of quasicrystalline particles as a strengthening phase in Mg-Zn-Y alloys
Authors:
Bae, DH; Lee, MH; Kim, KT; Kim, WT; Kim, DH; Krausch, G;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 445-450; 2002
Abstract:
Fine-grained magnesium alloys reinforced by quasicrystalline particles were easily developed by thermomechanical processes for as-cast Mg-rich Mg-Zn-Y and Mg-Zn-Y-Zr alloys. The deformation behaviour of the alloys at room and high temperatures was investigated and compared with that of commercial AZ31, AZ61 and AZ91 alloys. The yield strength of the Mg-Zn-Y alloys, increasing with an increase of the volume fraction of the quasicrystalline phase, is relatively high due to the strengthening effect of the quasicrystalline particles. At high temperatures, the level of flow stress of the Mg-Zn-Y alloys is lower than that of commercial magnesium alloys due to the softness of the eutectic region, but the alloys exhibit much higher elongation since the large number of quasicrystalline particles in the Mg-Zn-Y alloys can effectively prohibit microstructural evolution of the alpha-Mg matrix during deformation. Icosahedral particles in the alloy are also stable against coarsening during deformation near the melting temperature of the eutectic due to their low interfacial energy, thereby forming a stable quasicrystalline particle/matrix interface. The stability of both the quasicrystalline particles and the microstructure of the Mg-Zn-Y alloys provides a large elongation with no void opening at the interface between the quasicrystalline particle and the alpha-Mg matrix. (C) 2002 Elsevier Science BM All rights reserved.
Title:
Quasicrystal application on catalyst
Authors:
Yoshimura, M; Tsai, AP; Kim, KT;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 451-454; 2002
Abstract:
Steam reforming of methanol (CH(3)OH4H(2)O-->3H(2)+CO2) has been performed on a stable AlCuFe quasicrystal. The AlCuFe quasicrystal reveals excellent activity after leaching treatment. The production rate of H-2 reaches 235 1/kg.min at 553 K. The quasicrystals have two advantages: one is their brittle nature, which allows them to be crushed efficiently; the other is thermal stability as a catalyst support, which make their high temperature application possible. Catalysts prepared from Al-Cu-Fe alloys with various compositions were also evaluated. Al63Cu25Fe12 was shown to have the highest activity per unit area among Al-Cu-Fe alloys. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Optical transmission spectra of two-dimensional quasiperiodic photonic crystals based on Penrose-tiling and octagonal-tiling systems
Authors:
Hase, M; Egashira, M; Shinya, N; Miyazaki, H; Kojima, KM; Uchida, S; Gille, P;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 455-459; 2002
Abstract:
We measured and calculated optical transmission spectra of two-dimensional quasiperiodic photonic crystals based on 5- and 8-fold symmetric patterns (Penrose and octagonal patterns). In our photonic crystals, dielectric cylindrical rods stood perpendicular to a basal plane on vertices of tiles in the patterns in air. In the TM mode, where electric fields of incident light are parallel to the rods, we found an isotropic photonic band gap even when the dielectric constant is as small as 2.4. Besides, we observed several dips depending on the incident direction of the light, which may be due to long-range multiple scattering. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Quasicrystals as thermoelectric materials: a theoretical prospective
Authors:
Macia, E; Egashira, M;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 460-463; 2002
Abstract:
In this work, we present a theoretical study on the possible use of quasicrystals as potential thermoelectric materials. By considering a suitable model for the spectral conductivity, we show that high values of the thermoelectric figure of merit, well beyond the practical upper limit ZT = 1, may be expected for certain quasicrystalline alloys. We compare our analytical results with available experimental data on the transport coefficients of these materials, and suggest the icosahedral Cd-Yb and the dodecagonal Ta-Te phases as two promising candidates for further research. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Growth and electrical and optical properties of Al(Pd,Mn) alloy thin films produced by simultaneous vapor deposition of the components
Authors:
Anton, R; Kreutzer, P; Shinya, N;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 464-468; 2002
Abstract:
Thin films of binary and ternary alloys in the system Al-Pd-Mn were deposited by simultaneous evaporation of the metals from separate sources on carbon substrates (a-C, HOPG), or on glass plates at temperatures up to 500 degreesC. Film structure and composition were characterized by TEM, electron diffraction, and EDX. In the binary system Al-Mn, the homogeneous icosahedral phase nucleated for Mn concentrations around 14 at.%, at rather low deposition rates, Crystalline phases precipitated at lower and higher Mn contents, as well as at higher deposition rates and/or higher substrate temperatures. Only crystalline phases were identified in Al-Pd deposits. For the ternary system Al-Pd-Mn, icosahedral order was observed for Al contents above 75 at.%, while crystalline Al-Pd phases segregated at lower Al contents. For films with icosahedral order, the electrical resistance revealed negative temperature coefficients down to 10 K. Optical reflectivity and absorption showed only little variation from the visible to the near IR. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Thermoelectric properties of AlPdRe icosahedral alloys
Authors:
Kirihara, K; Nagata, T; Kimura, K; Miyazaki, H;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 469-472; 2002
Abstract:
Seebeck coefficient, S, electrical conductivity, sigma, and thermal conductivity, kappa, of AlPdRe icosahedral alloys are investigated. As concentration of transition metal (either Pd or Re) is increased, S increases. The strong composition dependences of S and sigma relate to the spikiness in electronic density of states at Fermi energy, and to the variation in bonding nature between Al and TM. The thermoelectric figure of merit also reveals strong composition dependence and thus gives a possibility of good thermoelectric performance. Effect of Ru addition for the thermoelectric property is also presented. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Oxidation behavior of quasicrystalline Al63Cu25Fe12 alloys with additional elements
Authors:
Yamasaki, M; Tsai, AP; Kimura, K;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 473-476; 2002
Abstract:
dHigh temperature oxidation behavior of (Al63Cu25Fe12)(100-x)Ce-x (Y = 1, 2, 3, 4), and Al62CU24Fe12Zn2 powders were studied. Al62Cu24Fe12Zn2 alloy has a quasicrystalline structure, and shows high oxidation resistance in comparison with zinc-free Al63Cu25Fe12 alloy at 773 K. On the other hand, the (Al63Cu25Fe12)(100-x)Ce-x alloys consist of quasicrystalline phase and crystalline phases. The mass gain in the air oxidation at 773 and 1073 K increases with increasing cerium content. Our results show that the addition of zinc suppresses air oxidation, whereas the addition of cerium promotes air oxidation. Both cerium- and zinc-containing alloy powders oxidize to FeAI(2)O(4). Surface areas of the zinc-containing powder oxidized at 773 and 1073 K are lower than those of oxidized ternary alloy powder. On the other hand, surface areas of cerium-containing powders oxidized at 1073 K increase with increasing cerium content. (C) 2002 Elsevier Science BY All rights reserved.
Title:
Concluding remarks to Quasicrystals 2001
Authors:
Thiel, PA; Tsai, AP;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 342 (1-2): 477-479; 2002
Abstract:
dHigh temperature oxidation behavior of (Al63Cu25Fe12)(100-x)Ce-x (Y = 1, 2, 3, 4), and Al62CU24Fe12Zn2 powders were studied. Al62Cu24Fe12Zn2 alloy has a quasicrystalline structure, and shows high oxidation resistance in comparison with zinc-free Al63Cu25Fe12 alloy at 773 K. On the other hand, the (Al63Cu25Fe12)(100-x)Ce-x alloys consist of quasicrystalline phase and crystalline phases. The mass gain in the air oxidation at 773 and 1073 K increases with increasing cerium content. Our results show that the addition of zinc suppresses air oxidation, whereas the addition of cerium promotes air oxidation. Both cerium- and zinc-containing alloy powders oxidize to FeAI(2)O(4). Surface areas of the zinc-containing powder oxidized at 773 and 1073 K are lower than those of oxidized ternary alloy powder. On the other hand, surface areas of cerium-containing powders oxidized at 1073 K increase with increasing cerium content. (C) 2002 Elsevier Science BY All rights reserved.
Title:
Crystal structure of Ba12Co11O33. Reinvestigation using the superspace group approach of orthorhombic oxides A(1+x)(A'B-x(1-x))O-3 based on [A(8)O(24)] and [A(8)A'O-2(18)] layers
Authors:
Darriet, J; Elcoro, L; El Abed, A; Gaudin, E; Perez-Mato, JM; Kouvetakis, J;
Source:
CHEMISTRY OF MATERIALS, 14 (8): 3349-3363; 2002
Abstract:
We report the structure determination on a single crystal of Ba12Co11O33, which belongs to the family of 1-dimensional structures related to the 2H hexagonal perovskite. The structure can be derived from the hcp stacking of [Ba8Co2O18] and [Ba8O24] layers. Assuming a similitude in the building principle with that present in the homologue rhombohedral series based on [A(3)A'O-6] and [A(3)O(9)] layers, a generic model within the superspace formalism of the whole family is proposed and used successfully for Ba12Co11O33. Two different strategies are presented. The first one considers the structure as a commensurate modulated composite containing two subsystems [CoO3] and [Ba]. With the [CoO3] subsystem chosen as the reference, the superspace group is Fddd(00gammac)0s0 with a = 11.4129(2) Angstrom, b = 19.7677(2) Angstrom, c, = 2.4722(1) Angstrom, and q = (6/11)c(1)* (Z = 8 for the formula Ba12/11CoO3). The final global R value is 4.46% for 4625 independent reflections (at a I/sigma(I) > 3 level) and only 123 refineable parameters. The second model follows the natural description of the structure as formed by the uniform hcp stacking of the two types of layers [Ba8Co2O18] and [Ba8O24]. The structure is formulated as BaCo11/12O33/12 (Z = 16) and considered to be a commensurate modulated phase with crenel occupational modulations. The superspace group can be denoted as Xdcd(00gamma(L))qqO with a = 11.4129(2) Angstrom, b = 19.7677(2) Angstrom, c = 4.5324(1) Angstrom, and q = (1/6)c*. The final global R value is 4.36% for the same number of independent reflections and 151 refineable parameters. Both approaches yield similar results, demonstrating for the first time the feasibility of refining these structures as layerlike modulated structures, instead of composites. The chains consist of polyhedra sharing faces formed by 10 consecutive CoO6 octahedra followed by one trigonal prism. Previous models based on simulated and highresolution electron microscopy images are refute
Title:
Least path criterion (LPC) for unique indexing in a two-dimensional decagonal quasilattice
Authors:
Mukhopadhyay, NK; Lord, EA; Kurz, H;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 58 (9): 424-428; 2002
Abstract:
The least path criterion or least path length in the context of redundant basis vector systems is discussed and a mathematical proof is presented of the uniqueness of indices obtained by applying the least path criterion. Though the method has greater generality, this paper concentrates on the two-dimensional decagonal lattice. The order of redundancy is also discussed; this will help eventually to correlate with other redundant but desirable indexing sets.
Title:
A multigrid approach to the average lattices of quasicrystals (vol A58, pg 352, 2002)
Authors:
Aragon, JL; Naumis, GG; Torres, M; Scholl, E;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 58 (9): 507-507; 2002
Abstract:
The least path criterion or least path length in the context of redundant basis vector systems is discussed and a mathematical proof is presented of the uniqueness of indices obtained by applying the least path criterion. Though the method has greater generality, this paper concentrates on the two-dimensional decagonal lattice. The order of redundancy is also discussed; this will help eventually to correlate with other redundant but desirable indexing sets.
Title:
Aubry transition studied by direct evaluation of the modulation functions of infinite incommensurate systems
Authors:
van Erp, TS; Fasolino, A; Zhu, YY;
Source:
EUROPHYSICS LETTERS, 59 (3): 330-336; 2002
Abstract:
Incommensurate structures can be described by the Frenkel-Kontorova model. Aubry has shown that, at a critical value K c of the coupling of the harmonic chain to an incommensurate periodic potential, the system displays the analyticity-breaking transition between a sliding and pinned state. The ground-state equations coincide with the standard map in non-linear dynamics, with smooth or chaotic orbits below and above K-c, respectively. For the standard map, Greene and MacKay have calculated the value K-c = 0.971635. Conversely, evaluations based on the analyticity breaking of the modulation function have been performed for high commensurate approximants. Here we show how the modulation function of the infinite system can be calculated without using approximants but by Taylor expansions of increasing order. This approach leads to a value K'(c) = 0.97978, implying the existence of a golden invariant circle up to K-c' > K-c.
Title:
Structural properties of Ni/Tb multilayers
Authors:
Schmidt, T; Hoffmann, H; Zhang, HH;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 248 (2): 181-189; 2002
Abstract:
Thin multilayer films of alternating Ni and Tb layers (Ni = 5-80 Angstrom, t(Tb) = 30 Angstrom, 15 periods, top layer: 100 Angstrom Al) were sputter-deposited at room temperature and structurally characterised by XRD, AES depth profiling, TEM and XFA. Below a critical thickness of the Ni layers, t(Ni) approximate to 26 Angstrom, an inhomogeneous amorphous NiTb alloy phase was found due to the existence of intermixed interfaces between Ni layers deposited onto Tb layers. Comparatively smooth interfaces between Ni layers deposited onto Tb layers result in a compositionally modulated structure. At larger Ni thicknesses, t(Ni) greater than or equal to 26 Angstrom, a previously absent spatially separated fcc-Ni phase is observed in addition to the NiTb alloy phase. The corresponding results of magnetic investigations will be given elsewhere.(C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Formation and crystallization of Ti-Hf-Ni metallic glasses
Authors:
Huett, VT; Kelton, KF; Lee, HH;
Source:
APPLIED PHYSICS LETTERS, 81 (6): 1026-1028; 2002
Abstract:
The formation of a Ti25Hf50Ni25 metallic glass and the phase evolution upon crystallization (devitrification) are reported. The glass is strongly metastable, with a 65 degreesC separation between the glass transition temperature, T-g=335 degreesC, and the onset temperature for primary crystallization to a nanoscale microstructure consisting of an icosahedrally symmetric ordered phase, that can not be reported as the icosahedral phase (i-phase). There is no distinction between an i-phase and a high-order crystal rational approximant for such small grains, since the unit cell size of a reasonable high-order approximant is of the order of the grain size. Upon annealing at higher temperatures, the metastable icosahedrally symmetric phase transforms to a stable Ti2Ni-type crystal phase. (C) 2002 American Institute of Physics.
Title:
Diffuse X-ray scattering and reverse Monte Carlo simulation of the short-range order in ytterbium iodine phthalocyanine [YbPc2]I-2
Authors:
Krawczyk, J; Pietraszko, A; Lukaszewicz, K; Wardell, SMSV;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 58 (6): 622-626; 2002
Abstract:
Iodine-doped ytterbium phthalocyanine, C64H32N16YbI2, [YbPc2]I-2 (YPI), presents an example of a disordered modulated crystal structure of the intergrowth type. The short-range order in YPI has been studied at ambient temperature by the diffuse X-ray scattering technique. Both Yb and I atoms are disordered. In a unit cell of the average structure, the Yb atoms occupy two positions, 1/2, 1/2, 1/4 or 1/2, 1/2, 3/4, with occupancy 0.5. In the neighbouring unit cells in the (001) plane there is, however, a strong tendency towards an alternating distribution of ytterbium in positions shifted by Deltaz = 1/2. The crystal structure of YPI consists of one-dimensional columnar stacks of [YbPc22/3+](n) and of linear iodine chains [I-3(-)](n). The modulation is commensurate since the period c(I) of iodine chains [I-3(-)](n) in the [001] direction is equal to one-half of the period c of the [YbPc22/3+](n) stacks. In the crystal structure, each stack of [YbPc22/3+](n) may occur in two settings shifted by c/2 and each iodine chain in three settings shifted along [001] by one-third of the period c(I). The short-range order of iodine chains distributed over three settings results in a complicated pattern. Iodine chains of the same setting tend to form ribbons perpendicular to h [100] and running along [001].
Title:
Magnetic order-order transition in tetragonal ErB2C2
Authors:
Ohoyama, K; Indoh, K; Tobo, A; Onodera, H; Yamaguchi, Y; Soltanian, S;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 71 (7): 1746-1751; 2002
Abstract:
We have investigated magnetic properties of ErB2C2 which is an isostructural compound of the anti ferroquadrupolar ordering materials, DyB2C2 and HoB2C2, by magnetisation and neutron diffraction measurements. ErB2C2 shows magnetic transitions at T-N = 15.9K and T-l = 13.0K. The magnetic structure of the ground state is a simple Ising-type antiferromagnetic one with a propagation vector of k = (1, 0, 0). The intermediate phase between T-N and T-l under zero magnetic field is a long range magnetic ordered state with a transverse sinusoidal modulation with a propagation vector of (1 + delta, delta, 0), where delta = 0.1120(2) which is nearly the same as that in phase IV in HoB2C2.
Title:
Temperature variation of structure and magnetic properties of Ni-Mn-Ga magnetic shape memory alloys
Authors:
Heczko, O; Lanska, N; Soderberg, O; Ullakko, K; Naumov, SV;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 242 (7): 1446-1449; 2002
Abstract:
When cooling from high temperature, the Material of composition Ni48.5Mn30.3Ga21.2 Undergoes several magnetic and structural transitions, The phases are. at high temperature austenitic Cubic L2(1) phase: at 297 K 5-layered modulated tetragonal martensite: and below 210 K non-modulated tetragonal martensitic phase with c a larger than unity. Five-layered martensite exhibits giant field-induced strain of about 6% (magnetic shape memory (MSM) effect). The mechanism of the MSM effect was substantiated by simultaneous measurement of the strain and magnetization, (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Magnetic field-induced instabilities and irreversible evolution in modulated ferromagnetic phases of cobalt films
Authors:
Demand, M; Padovani, S; Hehn, M; Ounadjela, K; Bucher, JP; Sukhorukov, YP;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 247 (2): 147-152; 2002
Abstract:
Ferromagnetic films of HCP cobalt with a thickness above 50 nm possess an out-of-plane magnetization. Magnetic force microscopy (MFM) is used to investigate the modulated domains of alternatively up and down magnetization. By applying a perpendicular magnetic field, the low-energy stripe configuration undergoes a zigzag distortion. As is revealed by MFM, a further increase of the maximum applied field produces a pinching of the stripes, which break up into magnetic bubbles, We show to which extent the formation of two types of topologically different bubbles can explain the particular shape of hysteresis curves of these cobalt films. (C) 2002 Published by Elsevier Science B.V.
Title:
Crossover from antiferromagnetic to ferromagnetic ordering in TmCuSi by neutron diffraction
Authors:
Schobinger-Papamantellos, P; Ritter, C; Buschow, KHJ; Duong, NP; Bucher, JP;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 247 (2): 207-214; 2002
Abstract:
The previously reported ferromagnetic TmCuSi (P6(3)/MMC) compound (T-N = 9 K) has been reinvestigated by neutron powder diffraction and was found to order anti ferromagnetically at T-N = 6.5(1) K with a sine wave modulated structure q(1) = (q(x), 0, 0) with the Tm moments deviating from the c-axis. This phase is restricted to a narrow high-temperature range 5.1-6.5 K where the wave vector decreases linearly by only 9% (from q(x) = 0.078 to 0.071, on cooling). However, below T-C = 5.8 K by a first-order transition the wave vector jumps to the value q(2) = 0 giving rise to ferromagnetic ordering which dominates in the low-temperature range. The two phases coexist in temperature-dependent portions in the intermediate range 5.4+/-0.4K. This transition is associated with a reorientation of the Tm moments towards the c-axis below T-C. The saturation ordered moment value of 6.2(1) mu(B)/atom at 1.5K is reduced relatively to the Tm3+ free ion moment value of gmu(B)J = 7 mu(B). (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Hubert model for modulated states in systems with competing exchange interactions
Authors:
Melnichuk, PI; Bogdanov, AN; Rossler, UK; Muller, KH; Penner, RM;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 248 (1): 142-150; 2002
Abstract:
Within a continuum model for magnetic systems with competing interactions introduced by Hubert the classification of all possible modulated structures for axial easy-plane systems has been carried out, and the phase portraits for these solutions are constructed. Analytic solutions for the structure of isolated domain walls between helicoids of different chirality are presented. The equilibrium structures of the modulated phases in an applied magnetic field and the critical field for transitions from helical to fan phase are in qualitative agreement with results obtained within the corresponding discretized model and various experimental data. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Composition dependence of thermoelectric properties of AlPdRe icosahedral quasicrystals
Authors:
Kirihara, K; Kimura, K; Rossler, UK;
Source:
JOURNAL OF APPLIED PHYSICS, 92 (2): 979-986; 2002
Abstract:
We present the composition dependence of the Seebeck coefficient and the electrical conductivity of AlPdRe icosahedral alloys. As the concentration of transition metal (either Pd or Re) increases, the Seebeck coefficient rapidly increases. The strong composition dependence is related to the pseudogap structure in the electron density of states at the Fermi energy, and to the variation in bonding nature between Al and transition metal. Glass-like transport behavior in thermal conduction is also observed. The dimensionless thermoelectric figure of merit has a maximum value of approximately 0.1 in the temperature range from 600 to 700 K and reveals strong composition dependence. (C) 2002 American Institute of Physics.
Title:
A multigrid approach to the average lattices of quasicrystals
Authors:
Aragon, JL; Naumis, GG; Torres, M; Muller, KH;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 58 (2): 352-360; 2002
Abstract:
An average structure associated with a given quasilattice is a system composed of several average lattices that in reciprocal space produces strong main reflections. The average lattice of a quasicrystal is a useful concept closely related to the geometric description of the quasicrystal to crystal transformation and has been proved to be structurally significant. Here we calculate average structures for arbitrary two- and three-dimensional quasilattices using the dual generalized method. Additionally, closed analytical expressions for the coordinates of the average structure, the quasiperiodic lattice and its diffraction pattern are given.
Title:
Absolute structure-factor measurements of an Al-Pd-Mn quasicrystal
Authors:
Zhang, Y; Colella, R; Kycia, S; Goldman, AI; Penner, RM;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 58 (2): 385-390; 2002
Abstract:
A number of X-ray reflections from an icosahedral quasicrystal Al-Pd-Mn have been measured with great accuracy on an absolute basis by making use of Bragg-case diffraction. Since the specimen had high crystal quality, the dynamical theory was used for analyzing the results and to extract structure factors from measured integrated intensities. Good agreement was found between theory and experiment for strong reflections. Anomalous transmission was found to be strong in the 'good' regions of the quasicrystalline specimen and it was measured on an absolute basis, but the small residual strains present in the specimen prevented an accurate comparison between theory and experiment. A detailed discussion is presented on the parameters that mostly affect anomalous transmission in relationship to the adopted structural model.
Title:
Atomic structure of the (Al,Si)CuFe cubic approximant phase
Authors:
Puyraimond, F; Quiquandon, M; Gratias, D; Tillard, M; Belin, C; Quivy, A; Calvayrac, Y; Viglin, NA;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 58 (2): 391-403; 2002
Abstract:
The structure of the alpha-(Al, Si)CuFe approximant phase is determined by a single-crystal X-ray diffraction study and compared to the ideal structure obtained by the perpendicular shear method of the parent icosahedral phase. It is shown that the local environments (typical atomic clusters) of the two phases are similar and expand significantly farther than the size of the unit cell of the approximant. The orbit Al(2) issuing from the theoretical icosahedral model corresponding to the inner dodecahedron of the Mackay-type cluster is not found in the approximant and is replaced by a partially occupied inner icosahedron with an unusually large Debye-Waller factor.
Title:
Do quasicrystals follow Wiedemann-Franz's law?
Authors:
Macia, E; Pleimling, M;
Source:
APPLIED PHYSICS LETTERS, 81 (1): 88-90; 2002
Abstract:
In this work we present a theoretical study on the thermal and electrical conductivities of quasicrystals. By considering a realistic model for the spectral conductivity we derive closed analytical expressions for the transport coefficients which allow us to study the temperature dependence of the Lorenz ratio L( T) = kappa(e)(T)/ Tsigma( T) at different temperature regimes. We conclude that quasicrystals closely follow Wiedemann- Franz's law over a wide temperature range. (C) 2002 American Institute of Physics.
Title:
Neutron diffraction studies of the magnetic phase transitions in Ce2Fe17 compound under pressure
Authors:
Prokhnenko, O; Ritter, C; Arnold, Z; Isnard, O; Kamarad, J; Pirogov, A; Teplykh, A; Kuchin, A; Korolyov, AV;
Source:
JOURNAL OF APPLIED PHYSICS, 92 (1): 385-391; 2002
Abstract:
The influence of hydrostatic pressure (up to 5 kbar) on the magnetic structure of Ce2Fe17 was investigated using neutron diffraction in the temperature range from 2 to 300 K. The existence of a collinear ferromagnetic phase below 95 K with a magnetic moment of Fe, m(Fe)=2.0 mu(B), was confirmed at ambient pressure. Magnetic peaks present between 95 and 205 K correspond to an incommensurate antiferromagnetic structure with a wave vector changing its value from tau(1)=0.026 Angstrom(-1) at 100 K to tau(1)=0.034 Angstrom(-1) at 205 K. A helical model is used to describe the magnetic structure. Application of high pressures leads to significant changes of the magnetic structure. The ferromagnetic phase, suppressed in the studied temperature range by pressures higher than 3 kbar, gets substituted by a new incommensurate antiferromagnetic phase. This phase can be described as a superposition of the helical structure with a second antiferromagnetic coupling with propagation vector tau(2)approximate to0.078 Angstrom(-1) at 40 K under pressures above 3 kbar. The correlation with recent results of magnetization studies under pressure is analyzed and discussed. (C) 2002 American Institute of Physics.
Title:
Structure of the ternary phase Co3Al8Ga and formation of the gallium-containing decagonal phase d-Co(Al, Ga)(3)(m)
Authors:
Ellner, M; Meyer, H; Xu, W;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 340 (1-2): 118-121; 2002
Abstract:
The structure of the ternary phase Co3Al8Ga, Pearson symbol ol96, space group Immm, a=12.0081(7) Angstrom, b=7.5701(6) Angstrom, c=15.394(1) Angstrom is isotypic with Co2NiAl9. Powder diffraction data are reported for this ternary intermetallic compound. Using liquid quenching, the metastable pseudoternary decagonal phase d-Co(Al, Ga)(3)(m) was obtained in the aluminium-rich portion of the ternary system Co-Al-Ga. Gallium substitutes for aluminium atoms in the d-Co(Al, Ga)(3)(m) phase up to a mol fraction x(Ga)=0.10. In the phase of the binary system Co-Al richest in aluminium, Co2Al9, the aluminium atomic positions can be occupied by gallium up to a gallium content of x(Ga)=0.05. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Suppression of quasicrystallization by nonlinear viscous flow in Zr-Al-Ni-Cu-Pd glassy alloys
Authors:
Saida, J; Ishihara, S; Kato, H; Inoue, A; Chen, HS; Pirogov, A;
Source:
APPLIED PHYSICS LETTERS, 80 (25): 4708-4710; 2002
Abstract:
The quasicrystallization at the initial stage under viscous flow at 673 K (20 K above the glass transition temperature) was investigated in a Zr65Al7.5Ni10Cu12.5Pd5 bulk glassy alloy. The compressive deformation at strain rates of 2x10(-3) s(-1) and 1x10(-2) s(-1) was subjected to the bulk glassy alloy for 60 s followed by the preannealing for 120 s for thermal equilibration in an Ar atmosphere. The glass undergoes Newtonian and non-Newtonian flow at the strain rates of 2x10(-3) s(-1) and 1x10(-2) s(-1), respectively. The linear viscous flow brings a significant decrease in the first exothermic peak in the differential scanning calorimetry (DSC) curve corresponding to the transformation from glassy to icosahedral phase, but is identical to that in the reference sample annealed for 180 s at 673 K without deformation. However, the number of icosahedral particles in the transmission electron microscopy image as well as the decrease of the first exothermic peak in the DSC curve in the nonlinear viscous flow is much less as compared with those in the linearly deformed and reference samples. These results indicate the suppression of the transformation from the glassy to icosahedral phase by the nonlinear viscous flow. The suppression of the transformation is suggested to be originated from the retardation of the growth by the stress-induced disordered atomic configuration in the glassy state during the nonlinear viscous flow. (C) 2002 American Institute of Physics.
Title:
Synthesis route-dependent formation of quasicrystals in Zr70Pd30 and Zr70Pd20Cu10 amorphous alloys
Authors:
Sordelet, DJ; Rozhkova, E; Besser, MF; Kramer, MJ; Chen, HS;
Source:
APPLIED PHYSICS LETTERS, 80 (25): 4735-4737; 2002
Abstract:
The devitrification of mechanically milled amorphous Zr70Pd30 and Zr70Pd20Cu10 powders occurs via a single-step, first-order transformation to a stable Zr2Pd tetragonal structure. This is in sharp contrast to the devitrification of the same amorphous alloys prepared by melt spinning, in which a primary metastable quasicrystalline phase forms. Since the mechanical milling process does not involve direct liquid phase formation of an amorphous structure, it is inferred that the short-range order in the solid state derived amorphous powder is different from that in the melt spun ribbon. (C) 2002 American Institute of Physics.
Title:
Two phases of C9H12O4: why is the structure at 295 K so complicated?
Authors:
Duncan, LL; Patrick, BO; Brock, CP; Kramer, MJ;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 58 (25): 502-511; 2002
Abstract:
Molecules of 4,4'-dimethyl-2-hydroxy-6-oxocyclohexene-1-carboxylic acid, C9H12O4, crystallize at 295 K in a modulated superstructure with five half-molecules in the asymmetric unit; each molecule is located on one of the mirror planes of the space group Cmc2(1). Reflections with k not equal 5n are systematically weak; a satisfactory refinement can be obtained in a Cmcm pseudocell having b' = b/5. The important modulation involves small rotations of the molecules around axes perpendicular to the mirror plane; there is also an up/down disorder of the CMe2 fragment in four of the five molecules (two molecules with occupancy factors ca 4:1; two with occupancy factors ca 3:2). The modulation is a response to packing problems that can be traced to the differences between the thin, electron- and oxygen-rich 'head' of the molecule and the thicker, methyl-rich 'tail'. At 130 K the length of b is reduced by 2/5 and the Pmnb structure is ordered. Both structures can be described as modulated variants of the Cmcm substructure; the wavevectors are 2b'*/5 for the room-temperature structure and b'*/2 for the low-temperature structure, where b'* is the reciprocal axis of the subcell. The structure at room temperature can also be understood as a hybrid of the fully disordered pseudocell structure and the ordered structure that is found at low temperature.
Title:
Quasiperiodic long-range ferrimagnetic order in Ising model simulation in an icosahedral quasicrystal model structure
Authors:
Matsuo, S; Ishimasa, T; Nakano, H; Onuki, Y;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 246 (1-2): 223-232; 2002
Abstract:
A new type of ferrimagnetic order was found in a Monte Carlo simulation of quasiperiodic magnetic system at low temperatures, which includes Ising spins arranged on the F-type quasiperiodic lattice. The spin occupation domains (or acceptance regions) in the phason space revealed the new type of ferrimagnetism consisting of two subdomains corresponding to up- and down-spins, which definitely indicated the quasiperiodic long-range nature of this ferrimagnetic order. A structure model of the Zn-Mg-Ho icosahedral phase was adopted as a three-dimensional quasicrystal model for this simulation. Ruderman-Kittel-Kasuya-Yosida (RKKY)-like alternating exchange interaction was assumed to extend to the fourth shortest distance. The elastic magnetic diffraction patterns from spin-dependent scattering consisted of sharp spots indicating a long-range order of the magnetic structure. Each diffraction spot could be indexed by six integers of all odd or all even, and this fact indicated F-type symmetry of the ferrimagnetic order which reflects the F-type symmetry of the structure. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Microstructure and crystallization of melt-spun Ti-Ni-Zr-Y alloys
Authors:
Wang, LM; Li, CF; Ma, LQ; Inoue, A; Chen, HS;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 339 (1-2): 216-220; 2002
Abstract:
Microstructure and crystallization behavior of melt-spun Ti65Ni25Zr10-xYx (x=0, 2.5, 5, 7.5 and 10) alloys have been studied. The alloys show different microstructure with the cooling rate. Icosahedral quasicrystalline phase (1-phase) was obtained directly in alloys with x=0, 2.5, 5 and 7.5 prepared at a wheel surface velocity of 30 m/s and in x=0 alloy corresponding to a velocity of 55 m/s. Ribbons with x=2.5, 5 and 7.5 prepared at the wheel surface velocity of 55 m/s are in amorphous state. The primary precipitates for these amorphous alloys are 1-phase. It is concluded that the proper addition of Y improves the glass forming ability of the Ti-Ni-Zr system. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Cluster-glass behavior in Al70Pd20Mn10
Authors:
Nimori, S; Tsai, AP; Takikawa, H;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 241 (1): 11-16; 2002
Abstract:
We carried out precise magnetization measurements in an Al70Pd20Mn10 quasicrystalline system using a high-quality single crystal. A strange phenomena was observed at room temperature, which was a difference between zero field cooled and field cooled magnetization below 290 K. The thermoremanent magnetization also disappeared at 290K. These experimental results suggest the forming of ferrimagnetic Mn ions clusters in Al70Pd20Mn10 below 290 K. In addition. high field magnetization in the temperature range between 4.2 and 30 K up to 12 T was also measured to investigate the anisotropic molecular field between clusters. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Magnetic phase transitions in ErRhSi
Authors:
Szytula, A; Penc, B; Stusser, N; Slaski, M; Hibi, Y;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 241 (2-3): 276-282; 2002
Abstract:
Polycrystalline sample of the ErRhSi compound have been prepared and studied by powder neutron diffraction, specific heat and electrical resistivity measurements. This compound crystallizes in the orthorhombic TiNiSi-type structure, The magnetic phase transition at T-1, = 2.3 K and the Neel temperature T-N = 8.5 K have been determined by the temperature dependencies of the intensities of the magnetic peaks, specific heat and electrical resistivity. At 1.5 K a commensurate magnetic structure. described by the propagation vector k = (0 1 0) coexists with the incommensurate one with k = (0, 0,4184(4), 0). Above T, only incommensurate phase with the propagation vector k (0.0.4173(2), 0) at 4 K exist, Er magnetic moment is parallel to the a-axis for both phases below T-1 and form angle +/-19- with a-axis in the temperature range T-1 and T-c. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Magnetic properties of Ln(2)Ti(2)S(2)O(5) compounds and magnetic structure of Tb2Ti2S2O5
Authors:
Lafond, A; Leynaud, O; Andre, G; Bouree, F; Meerschaut, A; Sakakibara, T;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 338 (1-2): 185-193; 2002
Abstract:
A new series of compounds, Ln(2)Ti(2)S(2)O(5) with Ln from Pr to Er, has been recently reported. These compounds crystallize in the tetragonal I4/mmm space group, with a approximate to 3.8 Angstrom and c approximate to 22.9 Angstrom. Their 3D-structure can be schematically described as a 2D-stacking of [Ln(2)S(2)] layers alternating with [Ti2O5] ones, both layers being connected through Ln-O (x4) and Ti-S (x1) bonding. Magnetic measurements using a SQUID magnetometer indicate paramagnetic behavior over a large temperature range, obeying a Curie-Weiss law (at least between 90 and 300 K), for all the studied lanthanides. An antiferromagnetic transition at T-N < 10 K is observed for the Gd- and Tb-derivatives. The Tb2Ti2S2O5 compound was investigated by neutron diffraction studies in the 1.4-15 K temperature range. The presence of new peaks in the diffraction diagrams at low temperature confirms the phase transition from a paramagnetic state to an antiferromagnetic one (T-N approximate to 5-6 K) that has been observed by magnetic measurements. But the main result of this neutron diffraction study has to be related to the phase transition from an incommensurate antiferromagnetic order at temperatures ranging from 4.1 to 2.9 K, with a propagation vector (k) over right arrow (i) (k(x),0,0); k(x) approximate to 0.46, to a commensurate state with a change in the direction of (k) over right arrow (c) (1/2,0,1/2) when the temperature is lowered (T<2.4 K). The origin of this unusual change in direction of the propagation vector is not yet explained. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Surface preparation and characterization of the icosahedral Al-Ga-Pd-Mn quasicrystal
Authors:
Heinzig, M; Jenks, CJ; Van Hove, M; Fisher, I; Canfield, P; Thiel, PA; Matsumoto, A;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 338 (1-2): 248-252; 2002
Abstract:
Auger electron spectroscopy and low-energy electron diffraction (LEED) provide basic information about the structure and composition of the 5-fold surface of the quaternary quasicrystal, icosahedral Al67Ga4Pd21Mn8. Surface preparation techniques established previously for two of the icosahedral ternary alloys, Al-Pd-Mn and Al-Cu-Fe, appear to be similarly effective for Al-Ga-Pd-Mn. After annealing in the range 600-950 K the surface concentration of Ga is constant and low. After annealing in the range 900-950 K, a good LEED pattern is obtained. LEED indicates that Ga changes the surface structure significantly. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Towards realistic quasiperiodic structures: modelling, synthesis and structure of (Ga,Zn)(175-delta)Mg97+delta - a large 3/2-2/1-2/1 Fibonacci approximant
Authors:
Kreiner, G; Harbrecht, B;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 338 (1-2): 261-273; 2002
Abstract:
A tiling approach towards primitive hypercubic icosahedral quasicrystals of the Bergman cluster type is presented. A set of decoration rules for Bergman cluster approximants was derived from the crystal structures of the 1/1-(Al,Zn)(3)Mg-2 and the 2/1-(Al,Zn)(3+delta)Mg2-delta Fibonacci approximants. Both structures are well described as a Bergman cluster packing with two types of cluster connections. Clusters connected along threefold axes share Common hexagons and clusters along twofold axes share common edges. The cluster networks are compatible with canonical cell filings. An approximant of 3/2-2/1-2/1 type in the Ga-Mg-Zn system ((Ga,Zn)(43)Mg-26, Z=16, Cmc2(1), oC1104 a=36.8 Angstrom, b=c=22.8 Angstrom) was modelled using the next higher canonical cell and the decoration rules. Suitable single crystals of the 3/2-2/1-2/1 approximant were obtained by melting and annealing ternary alloys with target compositions with x(Mg)=0.38-0.44 and a free electron per atom ratio of e/a=2.09-2.19. The structure was successfully refined to (Ga,Zn)(175-delta)Mg97+delta (delta approximate to 3, (Ga,Zn)(67)Mg-37, x(Ga) approximate to 0.09-0.19, Z=4, Cmc2(1), a=36.840(7) Angstrom, b=22.782(5) Angstrom, c=22.931(5) Angstrom, N-ind = 23398 (9105 >2sigma(F-2); N-var = 576, R-1/wR(2) = 0.170/0.154). (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Singular spectrum of Lebesgue measure zero for one-dimensional quasicrystals
Authors:
Lenz, D; Harbrecht, B;
Source:
COMMUNICATIONS IN MATHEMATICAL PHYSICS, 227 (1): 119-130; 2002
Abstract:
The spectrum of one-dimensional discrete Schrodinger operators associated to strictly ergodic dynamical systems is shown to coincide with the set of zeros of the Lyapunov exponent if and only if the Lyapunov exponent exists uniformly. This is used to obtain the Cantor spectrum of zero Lebesgue measure for all aperiodic subshifts with uniform positive weights. This covers, in particular, all aperiodic subshifts arising from primitive substitutions including new examples such as e.g. the Rudin-Shapiro substitution.Our investigation is not based on trace maps. Instead it relies on an Oseledec type theorem due to A. Furman and a uniform ergodic theorem due to the author.
Title:
Magnetization in quasiperiodic magnetic multilayers with biquadratic exchange and uniaxial anisotropy
Authors:
Bezerra, CG; Cottam, MG; Peschel, I;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 240 (1-3): 529-531; 2002
Abstract:
A theoretical study is made of the magnetization versus applied field curves of ferromagnetic/nonmagnetic multilayers constructed according to a Fibonacci quasiperiodic sequence. The ferromagnetic films are assumed to have uniaxial anisotropy and are coupled by both bilinear and biquadratic effective exchange. The effects of quasiperiodicity in the magnetic phases are illustrated numerically for Fe/Cr systems. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Nonuniform superconducting phases in a layered ferromagnetic superconductor
Authors:
Houzet, M; Buzdin, A; Weiss, D;
Source:
EUROPHYSICS LETTERS, 58 (4): 596-602; 2002
Abstract:
We determine the phase diagram of the ferromagnetic (F)/superconducting (S) atomic superlattice with arbitrary coupling between the layers. The exchange field acting on F layers may induce different kinds of modulated superconducting phases with either in-plane modulation or a phase shift between adjacent S layers. When the exchange field is increased, the re-entrance of the superconductivity emerges and the phase where the superconducting order parameter changes its sign in successive S layers is realized.
Title:
Charge ordered state in the impurity-doped manganites
Authors:
Mori, S; Shoji, R; Yamamoto, N; Machida, A; Moritomo, Y; Katsufuji, T; Xu, HF;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 71 (5): 1280-1283; 2002
Abstract:
Impurity effect on the charge and orbital ordered (CO/OO) state in doped manganites has been studied by the transmission electron microscopy (TEM), in addition to the electric and magnetic measurements. In the Cr-doped manganites (Nd0.5Ca0.5Mn1-yCryO3), the CO/OO state characterized by the incommensurate wave vector is still realized as the microdomains with the size of 10-30 nm even at lower temperature of 20 K. On the other hand, the Sc-doped manganites (Nd0.5Ca0.5Mn1-yScyO3) clearly show an incommensurate to commensurate structural phase transition accompanying the formation of the lon-ranged CO/OO state around 60 K. From our experimental findings, it is suggested that the substituted Cr3+ and Sc3+ ions serve as the spin impurity and hole vacancy, respectively.
Title:
Magnetic structure of Ce(Ni1-xPdx)(2)Ge-2 proximate to the magnetic instability
Authors:
Fukuhara, T; Kadowaki, H; Aso, N; Takeuchi, T; Kuwai, T; Sakurai, J; Maezawa, K; Tsutsumi, K;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 71 (5): 1360-1364; 2002
Abstract:
The magnetic structure of heavy-fermion antiferromagnets Ce(Ni1-xPdx)(2)Ge-2 proximate to the magnetic instability has been studied by elastic neutron scattering using single crystals. For Ce(Ni0.65Pd0.35)(2)Ge-2, antiferromagnetic ordering with an incommensurate propagation vector q = (1/2,1/2, delta); deltasimilar to0.16 is observed below T-N = 3.4 K. The integrated intensities of magnetic Bragg peaks at 1.8 K are well fitted by assuming a sine-wave-modulated structure with the amplitude 0.55 +/- 0.04 muB and magnetic moments along [110]. For the compound very near the magnetic instability, Ce(Ni0.90Pd0.10)(2)Ge-2, the ordered moment is expected to be reduced to below 0.1 mu(beta).
Title:
Dielectric study of the phase transitions in [P(CH3)(4)](2)CuY4 (Y=Cl, Br)
Authors:
Gesi, K; Kadowaki, H;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 71 (5): 1376-1380; 2002
Abstract:
Phase transitions in [P(CH3)(4)](2)CuY4 (Y = Cl, Br) have been studied by dielectric measurements. In [P(CH3)(4)](2)CUCl4, a slight break and a discontinuous jump on the dielectric constant vs. temperature curve are seen at the normal-incommensurate and the incommensurate-commensurate phase transitions, respectively. A small peak of dielectric constant along the b-direction exists just above the incommensurate-to-commensurate transition temperature. The anisotropic dielectric anomalies of [P(CH3)(4)](2)CuBr4 at phase transitions were measured along the three crystallographic axes. The pressure-temperature phase diagram of [P(CH3)(4)]CUCl4 was determined. The initial pressure coefficients of the normal.-to-incommensurate and the incommensurate-to-coniiiiensurate transition temperatures are 0.19K/MPa and 0.27K/MPa, respectively. The incommensurate phase in [P(CH3)(4)](2)CUCl4 disappears at a triple point which exists at 335 MPa and 443 K. The stability and the pressure effects of the incommensurate phases are much different among the four [Z(CH3)(4)](2)CuY4 crystals (Z = N, P; Y = Cl, Br).
Title:
Temperature dependence of magnetic anisotropy in Ni-Mn-Ga alloys exhibiting giant field-induced strain
Authors:
Heczko, O; Straka, L; Lanska, N; Ullakko, K; Enkovaara, J; Jiang, H;
Source:
JOURNAL OF APPLIED PHYSICS, 91 (10): 8228-8230; 2002
Abstract:
Temperature dependence of structure and magnetic anisotropy of single crystalline Ni48.8Mn28.6Ga22.6 alloy exhibiting giant field-induced strain or magnetic shape memory (MSM) effect was studied in the temperature range 80-420 K. Upon cooling the alloy transforms from cubic austenite at 307 K to the martensite which exhibits five-layered (modulated) tetragonal structure (5M) with a=0.595 nm and c=0.559 nm. Reverse transformation occurs at 317 K. An additional intermartensitic transition takes place at about 95 K. The basic mechanism of the MSM effect was corroborated by direct simultaneous measurements of strain and magnetization as a function of magnetic field. The magnetic anisotropy of the martensite exhibiting the giant strain was determined from the magnetization curves measured by a vibrating sample magnetometer at different temperatures. The anisotropy of the single variant 5M martensite is uniaxial with easy axis along the tetragonal c axis. The first magnetic anisotropy constant is K-u1=2.0x10(5) J/m(3) at 283 K and increase to K-u1=2.65x10(5) J/m(3) at 130 K. Above room temperature the anisotropy steeply decreases. The second anisotropy constant is negligible and less than 4% of the first anisotropy constant. (C) 2002 American Institute of Physics.
Title:
Influence of Pr on the magnetic structure of Er
Authors:
Moze, O; Kockelmann, W; Wu, YL; Pecharsky, AO; Pecharsky, VK; Gschneidner, KA; Mankey, GJ;
Source:
JOURNAL OF APPLIED PHYSICS, 91 (10): 8531-8533; 2002
Abstract:
Time-of-flight neutron diffraction has been used to determine the temperature dependence of the magnetic structure of three binary hexagonal Er-Pr alloys, Er90Pr10, Er80Pr20, and Er60Pr40. In overall agreement with magneto-thermal measurements performed on these compounds, the addition of Pr initially increases the Curie temperature and decreases the Neel temperature, observed at 20 K and 86 K, respectively, for pure Er. The neutron diffraction data for Er90Pr10, however, also clearly show that a ferromagnetic phase, with moments parallel to the c-axis, coexists with modulated structure components, with increasing temperature up to 35 K, above which a pure sine modulated structure sets in up to the Neel temperature at approximately 65 K. A similar behavior is observed for Er80Pr20, where the sine modulated phase is observed to disappear at 48 K. In sharp contrast, only one magnetic phase, identified as ferromagnetic with moments parallel to the c-axis, is observed for Er60Pr40 from low temperatures up to the Curie point at 35 K. The propagation vectors of the sine modulated phases are found to be temperature dependent. (C) 2002 American Institute of Physics.
Title:
Sound modes in composite incommensurate crystals
Authors:
Currat, R; Kats, E; Luk'yanchuk, I; Kohler, M;
Source:
EUROPEAN PHYSICAL JOURNAL B, 26 (3): 339-347; 2002
Abstract:
We propose a simple phenomenological model describing composite crystals, constructed from two parallel sets of periodic inter-penetrating chains. In the harmonic approximation and neglecting thermal fluctuations we find the eigenmodes of the system. It is shown that at high frequencies there are two longitudinal sound modes with standard attenuation, while in the low frequency region there is one propagating sound mode and an over-damped phase mode. The crossover between these two regions is analyzed numerically and the dynamical structure factor is calculated. It is shown that the qualitative features of the experimentally observed spectra can be consistently described by our model.
Title:
Incorporation of carbon atoms in rare earth boron-rich solids and formation of superstructures
Authors:
Zhang, FX; Xu, FF; Leithe-Jasper, A; Mori, T; Tanaka, T; Sato, A; Salamakha, P; Bando, Y; Shen, J;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 337 (19): 120-127; 2002
Abstract:
The boron-rich solid of YB25 can incorporate certain amounts of carbon atoms. With increase of carbon content, two kinds of superstructures of YB25, which modulate the basic structure in the (001) plane, appeared. The framework of boron icosahedra in the superstructures remains the same as that of YB25 and the structural modulation is just caused by the variation of carbon distribution in the voids of the framework. In addition, one superstructure with a large unit cell is quenchable and transformed into another superstructure by thermal annealing at 1400degreesC for 80 h. (C) 2002 Elsevier Science BV All rights reserved.
Title:
Crystal structure of monophosphate tungsten bronze K1.33P4W8O32 at 110 K
Authors:
Dusek, M; Ludecke, J; van Smaalen, S; Goldman, RS;
Source:
JOURNAL OF MATERIALS CHEMISTRY, 12 (5): 1408-1414; 2002
Abstract:
K1.33P4W8O32 belongs to the homologous series of monophosphate tungsten bronzes with hexagonal tunnels A(x)(PO2)(4)(WO3)(2m) with 0 < x < 2 and 4 < m < 14. K1.33P4W8O32 exhibits a phase transition at T-c = 165 K, that is characterized by an anomaly in the temperature dependence of the electrical resistivity and by the occurrence of extra reflections in the X-ray scattering. Here we report the 2a x b x c superstructure at T = 120 K, as it was measured by X-ray diffraction with synchrotron radiation. The superstructure is found to be monoclinic P2(1) with lattice parameters a = 13.373( 7) Angstrom, b = 5.3282(1) Angstrom, c = 8.926(4) Angstrom, and beta =100.65degrees. The structure was refined within the superspace approach with superspace group P2(1)(alpha, 0, gamma) with alpha = 0.5 and gamma = 0. Final agreement was obtained at R = 0.032 (R = 0.025 for the main reflections and R = 0.153 for the superstructure reflections). The maximum shift out of the average position was 0.25 Angstrom for one of the oxygen atoms. An analysis of the displacements and variations of interatomic distances is used to show that the mechanism of the phase transition is to resolve the internal strain between the K atoms and the surrounding PO4 groups. The comparison with the CDW structure of (PO2)(4)(WO3)(2m) shows that the phase transition is not a charge-density wave, but rather that the anomaly in the resistivity is caused by the changes in the structure when going through the phase transition.
Title:
Pt thickness and buffer layer effects on the structure and magnetism of Co/Pt multilayers
Authors:
Huang, JCA; Chen, MM; Lee, CH; Wu, TH; Wu, JC; Fu, CM; Norman, AG;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 239 (1-3): 326-328; 2002
Abstract:
[Co(3Angstrom)/Pt(t(Pt))](30) (111) multilayers were prepared by molecular beam epitaxy, X-ray diffractions show clear satellite peaks around the Co/Pt fundamental peak. indicative of a good modulated structure for all Co/Pt multilayers. The optimal perpendicular magnetic properties were obtained for 6 Angstrom < t(Pt) < 10 Angstrom. The effect of Pt buffer (B-Pt) upon the magnetic property of [Co(3 Angstrom)/Pt(10 Angstrom)](30)/Pt(B-Pt) is also studied. X-ray diffractions reveal that the superlattice peaks of [Co(3 Angstrom)/Pt(10 Angstrom)](30)/Pt(B-Pt) increase with increasing, B-Pt. The Kerr rotations and polar coercivity H-c increase with increase in B-Pt but both saturate at about B-Pt = 200 Angstrom. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Origin of the vertical-anticorrelation arrays of InAs/InAlAs nanowires with a fixed layer-ordering orientation
Authors:
Sun, ZZ; Yoon, SF; Wu, J; Wang, ZG; Shiono, T;
Source:
JOURNAL OF APPLIED PHYSICS, 91 (9): 6021-6026; 2002
Abstract:
InAs/In0.52Al0.48As nanowire multilayer arrays were grown on (001) InP substrate by molecular-beam epitaxy. The structural property of the arrays was investigated by transmission electron microscopy. The results clearly showed the formation of InAs nanowires, evolution of InAs/InAlAs interface, and composition and thickness modulations in the InAlAs spacer layer. A fixed spatial ordering of InAs/InAlAs nanowires was revealed for all the samples. Regardless of the change in InAlAs spacer thickness of different samples, (i) the nanowires of one InAs layer are positioned above the nanowire spacing in the previous InAs layer and (ii) the layer-ordering orientation angle of nanowires is fixed. The results were explained from the viewpoint of the growth kinetics. The effect of InAlAs spacers is suggested to play an important role on the spatial ordering of the nanowire arrays. (C) 2002 American Institute of Physics.
Title:
Symmetry-induced perfect transmission of light waves in quasiperiodic dielectric multilayers
Authors:
Peng, RW; Huang, XQ; Qiu, F; Wang, M; Hu, A; Jiang, SS; Mazzer, M; Mascarenhas, A;
Source:
APPLIED PHYSICS LETTERS, 80 (17): 3063-3065; 2002
Abstract:
Resonant transmission of light has been observed in symmetric Fibonacci TiO2/SiO2 multilayers, which is characterized by many perfect transmission peaks. The perfect transmission dramatically decreases when the mirror symmetry in the multilayer structure is deliberately disrupted. Actually, the feature of perfect transmission peaks can be considered as general evidence for dielectric multilayers with symmetric internal structure. It opens a unique way to control light propagation. (C) 2002 American Institute of Physics.
Title:
Antiferromagnetic ordering in TmCu2
Authors:
Svoboda, P; Vejpravova, J; Hofmann, M; Schneider, R; Rotter, M; Doerr, M; Loewenhaupt, M; Kamiyama, S;
Source:
CZECHOSLOVAK JOURNAL OF PHYSICS, 52 (2): 267-270; 2002
Abstract:
Intermetallic compound TmCu2 crystalizes in the orthorhombic structure, orders antiferromagnetically (AF) and exhibits four different AF phases below T-N = 6.5 K. In all these phases the Tm magnetic moment is parallel to the b-axis. The ground-state AF1 (T < 3.4 K) corresponds to the squared-up AF structure with propagation vector τ(01) = (5/8, 0, 0) and magnetic unit cell 8a x b x c. Narrow phases AF2 and AF3 (3.3 K < T < 3.7 K and 3.6 K< T < 4.6 K) axe 'spin-slip'-derivatives from the AF1 structure, yielding propagation vectors τ(02) = (0.633, 0, 0.02) and τ(03) = (0.618, 0, 0), respectively. The phase AF4 (4.4 K < T < T-N) is then incommensurate transversal spinwave with the propagation τ(04) = (0,64, 0, 0). The co-existence of AF phases indicates the first-order transitions between them.
Title:
Modulated distribution of differently ordered tetrahedral chains in the brownmillerite structure
Authors:
Lambert, S; Leligny, H; Grebille, D; Pelloquin, D; Raveau, B; Doerr, M;
Source:
CHEMISTRY OF MATERIALS, 14 (4): 1818-1826; 2002
Abstract:
Two crystal structures Ca2CO2-xAlxO5 (x approximate to 0.75) of brownmillerite type, have been investigated by single-crystal X-ray diffraction methods. The X-ray and electron diffraction patterns show satellite reflections, with commensurate positions along [100]* (a = 5.509 Angstrom; b = 5.278 Angstrom; c = 14.703 Angstrom; q* = alphaa* with alpha = 5/8 and 2/3). The 4D superspace formalism was used for the refinement of these modulated structures. The average framework can be described as an alternate stacking along [001] of tetrahedral and octahedral layers formed from the metal (Co, Al) and interconnected via apical oxygen atoms. Two kinds of orientation of the tetrahedral chains, noted L (left) and R (right-hand), are evidenced, running along the [010] direction. It is shown that the L and R chains are ordered with various sequences along the modulation direction [100].
Title:
Evidence of phase transition in decagonal Al-Co-Ni at low temperatures
Authors:
Kupsch, A; Meyer, DC; Gille, P; Paufler, P; Hackbarth, T;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 336 (1-2): 154-158; 2002
Abstract:
Powder samples of Al70.7Co13.3Ni16.0 were investigated by X-ray diffraction in the temperature range 15-300 K. At T= 150 K at least three additional reflections were observed, The onset temperature and hysteresis-like behaviour was monitored more closely. The reflections cannot be indexed using integers of reflections of the known decagonal lattice. Moreover, near this temperature lattice parameters of the decagonal phase showed deviations from a smooth curve. We suggest the occurrence of an intermediate phase, which, however, seems to be a property of the powdered sample, i.e. caused by milling single crystals. We will solely describe the experimental facts as they are and make a suggestion for the transition mechanism. It is assumed that the new reflections are due to a periodic superorder of the decagonal lattice as described for a Ni-rich alloy in the literature. From the distance of those satellite reflections to main (Bragg) reflections in reciprocal space we estimate the modulation length of the quasicrystalline substructure to be 10a, i.e. similar to38 Angstrom. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Modulated crystal structure and spin/hole arrangement in the chain compound CaxCuO2 (x-0.8240)
Authors:
Isobe, M; Kimoto, K; Takayama-Muromachi, E; Jonas, KL;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 71 (3): 782-789; 2002
Abstract:
The crystal structure of CaxCuO2 (x = 0.8240) has been studied by the Rietveld refinement of X-ray diffraction data using a modulated-structure analysis technique. Hole distribution was determined by bond-valence sum calculation using the obtained Cu-O inter-atomic distances. The results revealed that every third Cu site along a chain tends to be occupied by a hole. Furthermore, it was found that the Cu-O-Cu bond-angles for hole-unoccupied Cu sites are smaller than 90degrees. This suggests that the nearest neighbor magnetic interaction J(1) is ferromagnetic and its magnitude is comparable to the next nearest neighbor anti ferromagnetic interaction J(2). Based on the obtained hole distribution and the signs of the magnetic interactions between spins, we proposed a possible spin/hole arrangement model in the chain, which includes a main sequence of... up arrowOdown arrowdown arrowOdown arrow... in most parts of the chain.
Title:
Nanostructured icosahedral phase formation in Al70Cu20Fe10 by mechanical alloying: Comprehensive study
Authors:
Barua, P; Murty, BS; Mathur, BK; Srinivas, V; Yoo, KH;
Source:
JOURNAL OF APPLIED PHYSICS, 91 (8): 5353-5359; 2002
Abstract:
A systematic study on the formation and the stability of Al70Cu20Fe10 quasicrystalline alloy has been carried out through mechanical alloying. The influence of the milling parameters, sequence of additive elements, and heat treatment on the formation of icosahedral phase has been investigated through x-ray diffraction analysis and transmission electron microscopy. A combination of milling and heat treatment of Al70Cu20Fe10 composition resulted in the formation of a single icosahedral phase (i-phase) quasicrystal with face-centered structure. We present evidence that suggests the i phase is of a nanoquasicrystalline nature. From the present investigations, we propose an i-phase formation mechanism in Al-Cu-Fe system. (C) 2002 American Institute of Physics.
Title:
Automatic indexing of area-detector data of periodic and aperiodic crystals
Authors:
Pilz, K; Estermann, M; van Smaalen, S; Hernandez, C;
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 35 (8): 253-260; 2002
Abstract:
An autoindexing procedure is described that produces the indexing of diffraction data of aperiodic crystals. The procedure has been designed for indexing the data obtained with an area detector, but it can also be applied to data obtained with a single-point detector. The essential step in the indexing process is the ability to discriminate between reflections that fit to a reciprocal lattice, the satellite reflections and possible reflections that do not belong to this indexing. To achieve this goal, the refinement of the orientation matrix and the diffractometer parameters is made an intrinsic part of the process of indexing. The proposed autoindexing procedure has been implemented in a computer program called BAYINDEX. Successful application to data sets of three different one-dimensionally modulated structures, one two-dimensionally modulated structure and a periodic crystal is presented. Very good agreement between experimental and theoretical reflection positions is found. The indexing produced by BAYINDEX can serve as the basis for integration routines.
Title:
Intersubsystem chemical bonds in the misfit layer compounds (LaS)(1.13)TaS2 and (LaS)(1.14)NbS2
Authors:
Jobst, A; van Smaalen, S; Duppel, V;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 58 (8): 179-190; 2002
Abstract:
The modulated structures of incommensurate composite crystals (La0.912S)(1.13)TaS2 at room temperature and of (La0.949S)(1.14)NbS2 at T = 115 K are refined against high-resolution X-ray data. The compounds are isostructural with superspace group F' m2m(alpha,0,0)00s. For (LaS)(1.13) TaS2, lattice parameters of the first subsystem TaS2 were obtained as a = 3.2922 (1), b = 5.7776 (2) and c = 23.013 (2) Angstrom. For the second subsystem LaS, the same b and c parameters were found, but a = 5.8090 (8) Angstrom. Refinements led to a final structure model with R = 0.036 for 4767 observed unique reflections (R = 0.023 for 2147 main reflections, R = 0.099 for 1554 first-order satellites and R = 0.112 for 1042 second-order satellites). The final model includes modulation parameters up to the second-order harmonics for the displacements of the atoms, for the occupational parameters and for the temperature parameters. A clear correlation is found between the relative positions of the subsystems, the displacement modulation, the occupational modulation and the modulation of the temperature parameters. The analysis shows that the variations in environments are resolved by correlated variations in the temperature factors. For (LaS)(1.14)NbS2, lattice parameters at T = 115 K of the NbS2 subsystem were obtained as a = 3.3065 (4), b = 5.7960 (5) and c = 22.956 (3) Angstrom. For the LaS subsystem, the same values for b and c were obtained, but a = 5.7983 (7) Angstrom. Refinements led to a final structure model with R = 0.048 for 5909 observed unique reflections (R = 0.034 for 2528 main reflections, R = 0.092 for 2171 first-order satellites and R = 0.113 for 1103 second-order satellites). The final structure model is similar to that of (LaS)(1.13)TaS2. In particular, it is found that the values of the modulation parameters are almost equal and it is concluded that the modulations are independent of the temperature and the replacement of Ta with Nb, and thus represent a general mech
Title:
Structural, magnetic and transport properties of NpIrSn
Authors:
Javorsky, P; Havela, L; Wastin, F; Griveau, JC; Rebizant, J; Lander, GH; Rousse, G; Kamiyama, S;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 335 (1-2): 77-80; 2002
Abstract:
Structural, magnetic and electrical transport properties of a new compound, NpIrSn, crystallizing in the ZrNiAl-type hexagonal structure are reported. NpIrSn orders antiferromagnetically below T-N = 40 K and undergoes a second magnetic phase transition around 22 K. The antiferromagnetic order is not affected by magnetic fields up to 9 T. Powder neutron diffraction revealed an incommensurate magnetic structure in both magnetic phases. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
New periodic and aperiodic triangular prismatic sheet carbides obtained by crystallization of Mn1-xCx amorphous films and described by the chemical twinning model
Authors:
Aouni, A; Bauer-Grosse, E; Wastin, F;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 335 (1-2): 157-164; 2002
Abstract:
Mn1-xCx amorphous alloys with x varying from 0.25 to 0.34 were prepared by RF magnetron sputtering. Their crystallization studied by in situ transmission electron microscopy leads at nearly T=650 K to carbides with feather-shaped or lath-shaped morphologies, The SAED patterns show that it is matter of a set of new triangular prismatic sheet (TPS) carbides deriving from Mn5C2 with either periodic or one-dimensional aperiodic structures. For the periodic structures, we identify three new carbides: Mn7C3, Mn9C4 and Mn2C. Aperiodic TPS structures transform with an increase of the temperature into the concentration-nearest periodic: TPS structures. All these structures are well-interpreted by the chemical twinning model. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Change of quasilattice constant during amorphous-to-quasicrystalline phase transformation in Zr65Al7.5Ni10Cu7.5Ag10 metallic glass
Authors:
Jiang, JZ; Rasmussen, AR; Jensen, CH; Lin, Y; Hansen, PL; Basu, P;
Source:
APPLIED PHYSICS LETTERS, 80 (12): 2090-2092; 2002
Abstract:
The amorphous-to-quasicrystalline phase transformation in a Zr65Al7.5Ni10Cu7.5Ag10 metallic glass has been investigated by monitoring the quasilattice constant and the composition of quasicrystalline particles in the samples annealed in vacuum at 663 K for various times. It is found that the quasilattice constant decreases with annealing time and saturates after 90 min while the zirconium and silver contents in quasicrystalline particles differ from those in the remaining amorphous matrix. The results provide evidence that the amorphous-to-quasicrystalline phase transformation in the Zr65Al7.5Ni10Cu7.5Ag10 metallic glass is a nonpolymorphous reaction. (C) 2002 American Institute of Physics.
Title:
Study by high resolution electron microscopy and electron diffraction of the La0.03Sr0.255Ba0.7Nb2-yTiyO6-y/2 ferroelectric ceramic
Authors:
Martinez, E; Fundora, A; Amorin, H; Portelles, J; Siqueiros, JM; Basu, P;
Source:
JOURNAL OF APPLIED PHYSICS, 91 (5): 3154-3159; 2002
Abstract:
The stoichiometric La0.03Sr0.255Ba0.7Nb2-yTiyO6-y/2 (LSBNT) ceramic system was obtained for three different concentrations of titanium ions (y=1%, 3%, and 5%) where the Nb5+ was substituted by Ti4+ according to the expression La0.03Sr0.255Ba0.7Nb2-yTiyO6-y/2. The incommensurate modulation in the LSBNT structure has been studied by high-resolution transmission electron microscopy (HRTEM) and electron diffraction. The location of the incommensurate superlattice spots in the tetragonal phase through the [110] zone in the electron diffraction patterns was measured to determine the incomensuration parameter delta. Structural modulation was also evident by HRTEM for the [001] zone, where a sinusoidal variation along [110] and [1 (1) over bar0] was identified in coincidence with the electron diffraction patterns. Random occupation of the crystallographic sites that promotes structural variations may be the cause for structural incommensuration. It was possible to identify directly the tetragonal tungsten bronze structure and the presence of point defects that influence the dielectric properties. (C) 2002 American Institute of Physics.
Title:
A new kind of structural state for the Al-Ni-Ru decagonal quasicrystal with 0.4 nm periodicity
Authors:
Sun, W; Hiraga, K; McDowall, A;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 71 (2): 381-384; 2002
Abstract:
An Al-Ni-Ru decagonal quasicrystal with 0.4nm periodicity, which has a good long-range basic quasiperiodic order, was observed to form in rapidly solidified Al-Ni-Ru alloys. Its structure has been studied by means of high-resolution electron microscopy and high-angle annular detector dark-field techniques, and compared with that of a superlattice Al-Ni-Ru decagonal quasicrystal formed by conventional solidification. The results reveal that the rapidly solidified Al-Ni-Ru decagonal quasicrystal with 0.4nm periodicity has a new basic structural state which is characterized by a mixture of 2nm atomic columnar clusters with and without pentagonal symmetry.
Title:
Modulated structure of the thermoelectric compound [Ca2CoO3](0.62)CoO2
Authors:
Miyazaki, Y; Onoda, M; Oku, T; Kikuchi, M; Ishii, Y; Ono, Y; Morii, Y; Kajitani, T; Akasaki, I;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 71 (2): 491-497; 2002
Abstract:
We have determined the crystal structure of the composite crystal [Ca2CoO3](0.62)CoO2, known as Ca3Co4O9, by a superspace group approach. Structural parameters were refined with a superspace group of Cm (0 1 - p 0) using powder X-ray and neutron diffraction data. The compound consists of two interpenetrating subsystems of a CoO2 sheet and a distorted triple-layered NaCl-type Ca2CoO3 block, being incommensurate parallel to the b-axis. The CoO2 sheet is composed of a CdI2-type triangular Co lattice with sharing an edge of the CoO6 octahedra. In the Ca2CoO3 subsystem, "<"-shaped buckled arrangement of the atoms is found, due to the ordered arrangement of the Ca and Co atoms parallel to the c-axis. Both the subsystems have common a-, c-axes and beta-angle with a=4.8339(3)Angstrom, c = 10. 8436(7)Angstrom and beta = 98.14(1)degrees. The b-axis lengths are refined to be b(1) = 2.8238(2)Angstrom for the [CoO2] subsystem and b(2) = 4.5582(2)Angstrom for the [Ca2CoO3] subsystem. An undulating arrangement of the O atom sites in the CoO2 sheets is revealed but the modulation of the Co atom site is less marked. Remarkable displacive modulation of the Co and O sites in the [Ca2CoO3] subsystem has also been observed, suggesting that a regular NaCl-type coordination is very severe for the Co-O bonds in the present compound.
Title:
Quasicrystals-2001
Authors:
Mukhopadhyay, NK; Rapp, RE;
Source:
CURRENT SCIENCE, 82 (3): 251-253; 2002
Abstract:
Using magnetic specific heat [C-M(T)], we investigated the character and dimensionality of the spin wave excitations within the coexistence phase of single crystal ErNi2B2C. As known, the magnetic structure of ErNi2B2C consists of a transversely polarized sinusoidally modulated state that is squared-up, presumably, below the onset point of the weak ferromagretic state T-WF approximate to 2.2 K. We observed that the thermal evolution of C-M(T) within the sinusoidally modulated state (T (WF) < T < T-N) is distinctly different from the one below T-WF: for T-WF < T < T-N, C-M(T) evolves as 0.45 T-2 J/mol K suggesting a 2d excitations with a gapless linear dispersion relation. On the other hand, for T < T-WF, C-M(T) is dominated by an exponential factor, indicative of gapped AF excitations. The gap (similar to6 K) is approximately equal to T-N and to the separation between the lowest lying Kramer doublets. Finally, based on entropy arguments and on features of the exchange striction, we comment on the influence of the malpetoclastic coupling on the low-temperature magnetic properties of this compound.
Title:
Study of the effect of natural oxidation and thermal annealing on microstructures of AlOx in the magnetic tunnel junction by high-resolution transmission electron microscopy
Authors:
Bae, JS; Shin, KH; Lee, TD; Lee, HM; Flores, J;
Source:
APPLIED PHYSICS LETTERS, 80 (7): 1168-1170; 2002
Abstract:
In a magnetic tunnel junction, the formation of an insulator is sensitive and critical to the stable performance and reproducibility of the junction. The oxidation path and the microstructural change with time of the insulator in natural oxidation have been studied by the high-resolution transmission electron microscopy. It has been observed that the oxidation path is primarily through the grain boundary at an early stage of oxidation and then through the grains at a later stage. The morphology of the oxide layer was rugged and modulated. There also occurred an isotropic volume expansion with increased oxidation. It was observed that the ferromagnetic Co layer below an insulator was partially oxidized because of the preferred grain boundary oxidation. When this multilayer was annealed, the locally oxidized Co layer was reduced and the metallic layer formed as a continuous film type, thereby improving the interface. (C) 2002 American Institute of Physics.
Title:
General periodic average structures of decagonal quasicrystals
Authors:
Cervellino, A; Steurer, W; Lee, TD;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 58 (7): 180-184; 2002
Abstract:
The concept of periodic average structure is mutuated from the theory of incommensurately modulated structures. For quasicrystals, this concept (up to now explored only in few cases) is becoming increasingly useful to understand their properties and to interpret some important structural features. The peculiar property of quasicrystals is that they admit not one but many (infinite) possible different average structures. Few of them, however, will be meaningful. Here are given a simple method (based on reciprocal space) for generating all the possible periodic average structures of decagonal quasicrystals and some new ideas about their meaning. By this method, the most significant average structures can be recognized from the diffraction pattern.
Title:
Comments on quasicrystalline phases and examples of quasicrystalline phase nomenclature in Nomenclature of magnetic, incommensurate, compositionchanged morphotropic, polytype, transient-structural and quasicrystalline phases undergoing phase transitions. II. Report of an IUCr Working Group on Phase Transition Nomenclature by J.C. Toleddano et al. (2001). Acta. Cryst. A57, 614-626
Authors:
Kuo, KH; Steurer, W;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 58 (7): 209-209; 2002
Abstract:
The concept of periodic average structure is mutuated from the theory of incommensurately modulated structures. For quasicrystals, this concept (up to now explored only in few cases) is becoming increasingly useful to understand their properties and to interpret some important structural features. The peculiar property of quasicrystals is that they admit not one but many (infinite) possible different average structures. Few of them, however, will be meaningful. Here are given a simple method (based on reciprocal space) for generating all the possible periodic average structures of decagonal quasicrystals and some new ideas about their meaning. By this method, the most significant average structures can be recognized from the diffraction pattern.
Title:
Response to K. H. Kuo's Comments on quasicrystalline phases and examples of quasicrystalline phase nomenclature in Nomenclature of magnetic, incommensurate, composition-changed morphotropic, polytype, transient-structural and quasicrystalline phases undergoing phase transitions. II. Report of an IUCr Working Group on Phase Transition Nomenclature by J.-C. Toledano et al. (2001). Acta Cryst. A57, 614-626
Authors:
Toledano, JC; Berry, RS; Brown, PJ; Glazer, AM; Metselaar, R; Pandey, D; Perez-Mato, JM; Roth, RS; Abrahams, SC; Akasaki, I;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 58 (7): 210-210; 2002
Abstract:
The concept of periodic average structure is mutuated from the theory of incommensurately modulated structures. For quasicrystals, this concept (up to now explored only in few cases) is becoming increasingly useful to understand their properties and to interpret some important structural features. The peculiar property of quasicrystals is that they admit not one but many (infinite) possible different average structures. Few of them, however, will be meaningful. Here are given a simple method (based on reciprocal space) for generating all the possible periodic average structures of decagonal quasicrystals and some new ideas about their meaning. By this method, the most significant average structures can be recognized from the diffraction pattern.
Title:
X-ray and neutron diffraction study of crystal structure and spin arrangement of the distorted-triangular-lattice antiferromagnet RbMnBr3
Authors:
Kato, T; Gunasekara, HPNJ;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 71 (1): 300-307; 2002
Abstract:
Single-crystal X-ray and neutron diffraction study of the distorted-triangular-lattice antiferromagnet RhMnBr3 was carried out in order to clarify the crystal structure below T-4 similar to 222 K (phase V) and to find the origin of spin arrangement below T-N = 8.5 K. The phase-V diffraction pattern showed some systematic and accidental extinction of possible reflections with triple-domain formation. An orthorhombic structure of a space group symmetry Pbca with a unit cell 2a(0) x root3a(0) x c(0) (Z = 8) was proposed. The triangular lattice of Mn2+ ions is distorted in a novel form, coined as a zigzag-row model. Spin arrangement of this model was deduced using the mean-field theory. Spin structures of RbMnBr3 in the incommensurately modulated LT (low-field triangular) and the commensurately modulated HT (high-field triangular,) phases are described.
Title:
A neutron diffraction study of HfFe6Ge6-type TbMn6Ge6-xGax compounds (x=0.1, 0.2 and 1.0)
Authors:
Lefevre, C; Venturini, G; Malaman, B; Lim, H;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 333 (1-2): 41-50; 2002
Abstract:
ThMn6Ge6-xGax compounds (x = 0.1, 0.2, 1.0) were studied by magnetization measurements and neutron diffraction. The three compounds order ferrimagnetically at 449, 449 and 406 K, respectively, and display various transitions at lower temperatures. TbMn6Ge5.9Ga0.1 displays a conical structure below 71 K (mu(rb) = 8.71(9) mu(B), mu(Mn) = 2.24(5) mu(B) at 2 K) and a helimagnetic structure from 71 K to room temperature, where an additional ferrimagnetic component occurs. TbMn6Ge5.8Ga0.2 is ferrimagnetic below 102 K and above 212 K, and displays a complex magnetic structure where commensurate and incommensurate components coexist in the intermediate temperature range. At 2 K, the moments are aligned along the c-axis (mu(rb) = 8.5(1) mu(B), mu(Mn) = 2.24(5) mu(B), at 2 K) and are perpendicular to the c-axis at 300 K. TbMn6Ge5Ga is ferrimagnetic over the whole ordered range and displays a moment reorientation process at 214 K. At 2 K, the moments (mu(rb) = 9.0(1) mu(B), mu(Mn) = 2.24(6) mu(B)) are aligned along the c-axis and they are close to the (001) plane at 300 K. The results are discussed and compared with the behavior of the other RMn6Ge6-xGax compounds (R=Ho, Tm, Lu). (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Intergrowth of structures in the Tl-Ba-Ca-Cu-O system
Authors:
Hopfinger, T; Shcherban, OO; Galez, P; Gladyshevkii, RE; Lomello-Tafin, M; Jorda, JL; Couach, M; Nath, KG;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 333 (1-2): 237-248; 2002
Abstract:
Three intergrowth phases between the high-71, superconducting cuprates TIBa2Ca2Cu3Ox (TI-1223) and Tl2Ba2Ca2Cu3Oy (TI-2223) have been detected and identified in a non-equilibrium sample with composition Tl1.05Ba2Ca2Cu3Ox. Complete structure models including space group, cell parameters and atom coordinates are derived for quantitative analysis. X-Ray diffraction, AC susceptibility and scanning electron microscopy experiments show that these intermediate phases have a long range order. The results are discussed in the light of the formation path for TI-1223 whose final step is the transformation from TI-2223 to TI-1223. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
NaCeP2Se6, Cu0.4Ce1.2P2Se6, Ce-4(P2Se6)(3), and the incommensurately modulated AgCeP2Se6: New selenophosphates featuring the ethane-like [P2Se6](4-) anion
Authors:
Aitken, JA; Evain, M; Iordanidis, L; Kanatzidis, MG; Lomello-Tafin, M;
Source:
INORGANIC CHEMISTRY, 41 (2): 180-191; 2002
Abstract:
NaCeP2Se6, Cu0.4Ce1.2P2Se6, and AgCeP2Se6 were prepared from nearly stoichiometric proportions of the starting materials plus extra selenium at 750-850 degreesC. Ce1.33P2Se6 (or Ce-4(P2Se6)(3)) was obtained from the same reaction that produced Cu0.4Ce1.2P2Se6. The structure of all four compounds was determined by single-crystal X-ray diffraction. NaCeP2Se6, Cu0.4Ce1.2P2Se6, and Ce1.33P2Se6 crystallize in, the monoclinic space group, P2(1)/c, with a = 12.1422(2), b = 7.6982(1), c = 11.7399(2) Angstrom, beta = 111.545(1)degrees and Z= 4 for NaCeP2Se6; a = 12.040(1), b = 7.6418(8), c = 11.700(1) Angstrom, beta = 111.269(2)degrees and Z = 4 for Cu0.4Ce1.2P2Se6; and a = 6.8057(5), b = 22.969(2), c = 11.7226(8) Angstrom, beta = 124.096(1)degrees and Z = 6 for Ce1.33P2Se6. NaCeP2Se6 has a two-dimensional character and is isostructural to the KLnP(2)Q(6) family of compounds, where Ln = La, Ce, and Pr for Q = Se and Ln = La for Q = S. The structure consists of [CeP2Se6](n)(n-) layers which are separated by Na+ cations. Each layer contains CeSeg distorted, tricapped trigonal prisms and [P2Se6](4-) ethane-like anions. Cu0.4Ce1.2P2Se6 possesses a similar structure; however, substitution of the alkali metal by copper and cerium atoms renders the structure three dimensional. Ce1.33P2Se6 is the pure lanthanide member of this structure type. In this three-dimensional structure, there are three cerium metal sites which are partially occupied. The structure of AgCeP2Se6 was solved in the superspace,group P2(1)/c(alpha0gamma) and represents an incommensurately modulated version of the KLnP(2)Q(6) structure type, with a = 9.971(5), b = 7.482(3), c = 11.757(4) Angstrom, beta = 145,630(9)degrees, q = 0.3121(18)a* + 0.4116(19)c*, and Z = 2. The structures of the compounds reported here and those of the KLnP(2)Q(6) family are highly related to the monoclinic-II, M(\\)PQ(3) structure type (where M = Pb, Sn, Ca, and Sr for Q S and M Pb and Sn for Q Se). Optical and vibrational spectroscop
Title:
Evidence of polymorphous amorphous-to-quasicrystalline phase transformation in Zr66.7Pd33.3 metallic glass
Authors:
Jiang, JZ; Saksl, K; Saida, J; Inoue, A; Franz, H; Messel, K; Lathe, C; Nath, KG;
Source:
APPLIED PHYSICS LETTERS, 80 (5): 781-783; 2002
Abstract:
The amorphous-to-quasicrystalline phase transformation and the pressure effect on the transformation in a Zr66.7Pd33.3 metallic glass have been investigated by in situ x-ray diffraction measurements using synchrotron radiation. It is found that the transformation is a polymorphous reaction and external pressure enhances the onset temperature for the formation of quasicrystals with a rate of 22 K/GPa while the temperature interval for the stability of quasicrystals remains almost unchanged in the pressure range of 0-4 GPa. The enhancement of the onset temperature for the formation of quasicrystals has been further discussed with the nucleation theory. (C) 2002 American Institute of Physics.
Title:
Two-dimensional intensity profiles of effective satellites
Authors:
Morelhao, SL; Avanci, LH; Quivy, AA; Abramof, E; Williams, ED;
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 35 (3): 69-74; 2002
Abstract:
The observation of a new X-ray scattering process with synchrotron radiation is reported. The phenomenon is analogous to three-beam diffraction in a single crystal; however, the features in the azimuthal scans are provided by superlattice-satellite reflections instead of bulk reflections. These features were named effective satellites and they are observed over the ordinary satellite reflections as a function of the azimuthal angle. Their occurrences have been monitored in completely different superlattices by mapping the incidence and azimuthal angles of the incident X-ray beam. Effects of structural parameters of the superlattices on the effective satellites as well as the information that can be extracted by measuring their positions are discussed.
Title:
A database of incommensurate phases
Authors:
Caracas, R; Avanci, LH;
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 35 (3): 120-121; 2002
Abstract:
A database of incommensurate phases is currently available at http://www.mapr.ucl.ac.be/similar tocrystal/index.html. The present database offers a fast direct retrieval system for structural, physical and bibliographical data of incommensurate phases. The database contains data about inorganic, non-composite, nonmagnetic and non-superconducting incommensurate phases only. Classification is according to the physical mechanisms responsible for the incommensurate phase transition. The main classes of incommensurate phases thus obtained are: the A(2)BX(4) dielectrics family, zone-centre lock-in transition phases, cooperative Jahn-Teller incommensurates, tetragonal tungsten bronzes, charge-density wave systems and miscellaneous incommensurate phases. The latter class, because of the lack of available data, is classified on a chemical basis in several subclasses: silicates, perovskites, Mn-bearing oxides, other oxides, group VI compounds, intermetallics and other compounds. The database contains a brief description of the main physical, chemical and structural features of each phase, as stated in the literature. This description is very material- and bibliography-dependent and it is preceded by the phase transition sequence.
Title:
Structure solution of the basic decagonal Al-Co-Ni phase by the atomic surfaces modelling method
Authors:
Cervellino, A; Haibach, T; Steurer, W; Abramof, E;
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 58 (4): 8-33; 2002
Abstract:
The atomic surfaces modelling technique has been used to solve the structure of the basic Ni-rich Al-Co-Ni decagonal phase. Formula Al70.6Co6.7Ni22.7, space group P (10) over bar, five-dimensional unit-cell parameters: d(1) = d(4) = 4.752 (3) Angstrom, d(2) = d(3) = 3.360 (2) Angstrom, d(5) = 8.1710 (2) Angstrom; alpha(12) = alpha(34) = 69.295degrees, alpha(13) = alpha(24) = 45degrees, alpha(14) = 41.410degrees, alpha(23) = alpha(i5) = 90degrees (i = 1-4), V = 291.2 (7) Angstrom(5); D-x = 3.887 Mg m(-3). Refinement based on |F|; 2767 unique reflections (|F| > 0), 749 parameters, R = 0.17, wR = 0.06. Describing the structure of quasicrystals embedded in n-dimensional superspace in principle takes advantage of n-dimensional periodicity to select the minimal set of degrees of freedom for the structure. The method of modelling of the atomic surfaces yielded the first fully detailed structure solution of this phase. Comparison with numerous former, less accurate models confirms several features already derived, but adds a new essential insight of the structure and its complexity. The atoms fill the space forming recurrent structure motifs, which we will (generically) refer to as clusters. However, no unique cluster exists, although differences are small. Each cluster shows a high degree of structural disorder. This gives rise to a large configurational entropy, as much as expected in a phase which is stable at high temperature. On the other side, the cluster spatial arrangement is perfectly quasiperiodic. These considerations, corroborated by analysis of the structural relationship with neighbouring periodic phases, strongly suggest the existence of a non-local, long-range interaction term in the total energy which may be essential to the stability.
Title:
Aubry transition in a real material: Prediction for its existence in an incommensurate gold/gold interface
Authors:
Lancon, F; Garcia-Hoz, AM;
Source:
EUROPHYSICS LETTERS, 57 (1): 74-79; 2002
Abstract:
Recent studies have shown that a special grain boundary in gold is stable and is an incommensurate interface related to the irrational number root2. Using the theoretical framework of quasicrystals, we show that this system can undergo an Aubry transition: the two grains can glide freely along the ideal interface; if we increase the interactions between the grains by applying a compression perpendicular to the interface, there is a threshold after which the grains are pinned to each other. With a numerical analysis of the energy landscape corresponding to the shift of the grains, we determine the atomistic mechanism of the grain sliding.
Title:
Comment on "The defect density waves in Zn0.98Sn0.02TiO4 single crystal with incommensurately modulated structures: Neutron diffraction study" by Y. Park
Authors:
Bagautdinov, B; Garcia-Hoz, AM;
Source:
EUROPHYSICS LETTERS, 57 (1): 148-148; 2002
Abstract:
Recent studies have shown that a special grain boundary in gold is stable and is an incommensurate interface related to the irrational number root2. Using the theoretical framework of quasicrystals, we show that this system can undergo an Aubry transition: the two grains can glide freely along the ideal interface; if we increase the interactions between the grains by applying a compression perpendicular to the interface, there is a threshold after which the grains are pinned to each other. With a numerical analysis of the energy landscape corresponding to the shift of the grains, we determine the atomistic mechanism of the grain sliding.
Title:
Neutron diffraction studies of magnetic structure of ErRu2Ge2
Authors:
Szytula, A; Penc, P; Stusser, N; Ren, ZF;
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 238 (1): 65-67; 2002
Abstract:
Neutron diffraction measurements have been performed on ErRu2Ge2 at low temperatures. The compound crystallise in the tetragonal ThCr2Si2-type crystal structure (space group 14/mmm). ErRu2Ge2 is antiferromagnetic below T-N = 4.9 K. In the temperature range 1.5-3.4 K the erbium. magnetic moments form a square-modulated structure described by the propagation vectors k(1) = (k(x), 0, 0) and k(2) = (3k(x), 0, 0), where k(x) = 0.2174(3). About 3.4K the magnetic order turns on to be of a sine-wave modulated type. In both phases, the magnetic moments are parallel to the b-axis. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Interaction of hydrogen with magnetism in Y-Gd alloys
Authors:
Vajda, P; Zogal, OJ; Andreica, D;
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 330 (1): 381-383; 2002
Abstract:
When introduced into the h.c.p. rare earths, hydrogen either precipitates, at low enough temperatures, into the beta-phase dihydride or forms the peculiar alpha*-phase composed of H-R-H pairs occupying second-neighbour tetrahedral sites along the c-axis. In order to understand the origin of these structures, we have investigated the interaction of H with the magnetic configurations present in some Y-R systems by electrical resistivity measurements. Recent experiments on YyTb1-yHx have shown a correlation between the (y-dependent) existence of the alpha*-phase and eventual modulated magnetism, via the Fermi surface topology. The present results obtained on the (Y-Gd)H-x system seem to confirm the idea regarding the analogy between magnetic and structural modulations (spin-density vs. charge-density waves). (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Optical investigation of the quasi two-dimensional monophosphate tungsten bronzes KxP4W8O32 (x=0-1.57)
Authors:
Haffner, S; Dressel, M; Groult, D; Schlenker, C; Schenck, A;
Source:
EUROPEAN PHYSICAL JOURNAL B, 24 (2): 167-175; 2001
Abstract:
The potassium doped monophosphate tungsten bronzes KxP4W8O32 are two-dimensional metals which show a metal-to-metal transition at a critical temperature which depends on the doping level. The metal-to-metal transition is accompanied by the formation of a commensurate charge density wave with wave vector (pi/b,0) which is independent of the doping level. Undoped P4W8O32, on the other hand, has two metal-tu-metal transitions which are connected to the formation of incommensurate charge density waves. We measured the infrared reflectivity of the series KxP4W8O32 (x = 0-1.57) in the spectral range from 100 to 10000 cm(-1) for room temperature and well below the critical temperature. Polarization-dependent, infrared spectra find a two-dimensional behavior in the normal and the charge density wave state and show signatures of hybridization between one- and two-dimensional conduction bands. In undoped P4W8O32 the essentials of the charge density wave state can be understood from the nesting vectors of the calculated Fermi surface and two gaps are observed in the infrared spectra. The gap sizes are a factor of about 2.5 bigger than the predictions from mean-field theory in the weak-coupling limit which suggests medium- or strong electron-phonon coupling. For potassium doped KxP4W8O32 one gap is observed in the charge density wave state. The energetics of the charge density formation may be dominated by the energy required for the lattice modulation.
Title:
Monoclinic AlPO4 tridymite at 473 and 463 K from X-ray powder data
Authors:
Graetsch, HA; Nagai, T;
Source:
ACTA CRYSTALLOGRAPHICA SECTION C-CRYSTAL STRUCTURE COMMUNICATIONS, 58 (2): I18-I20; 2002
Abstract:
Upon cooling from its hexagonal high-temperature modification, AlPO4 (aluminium phosphate) tridymite successively transforms to several displacively distorted forms, including a normal structure-incommensurate-lock-in phase transition sequence. The space-group symmetries in this series are P112(1), P112(1) (alphabeta0) and P2(1)2(1)2(1), respectively. The distortion pattern of the intermediate P112(1) phase can be described as alternate shifts of adjacent layers of tetrahedra coupled with tilting of the tetrahedra. The symmetry and direction of the shifts are different from the analogous SiO2 tridymite modification. The atomic displacement parameters of the O atoms are strongly anisotropic due to thermal motions of the rigid tetrahedra. Condensation of a lattice vibration mode results in the formation of an incommensurate structural modulation below 473 K. The 3+1 superspace-group symmetry of the modulated phase is P112(1) (alphabeta0).
Title:
Simple and composite octagonal quasicrystal tilings
Authors:
Escudero, JG; Garcia, JG; Saeki, M;
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 70 (12): 3511-3516; 2001
Abstract:
Several species of tilings with eight-fold symmetry generated by means of inflation rules are studied. They can also be obtained by superposition of other patterns. The complexity of the structures is reflected in the sets of vertex configurations. Composition of the basic inflation rules gives face to face tilings. The diffraction patterns of the simple tilings show Bragg peaks.
Title:
Lateral composition modulation in AlAs/InAs and GaAs/InAs short period superlattices structures: The role of surface segregation
Authors:
Dorin, C; Millunchick, JM; Saeki, M;
Source:
JOURNAL OF APPLIED PHYSICS, 91 (1): 237-244; 2002
Abstract:
The effect of In surface segregation on the microstructure of short period superlattices (SPSs) in two different material systems with nominally equivalent lattice misfit, AlAs/InAs and GaAs/InAs, has been investigated and compared. It was found that the quality of the SPSs and the appearance of lateral composition modulation are remarkably different in these two systems. For AlAs/InAs SPSs grown at temperatures of T=500 degreesC, uniform structures devoid of lateral composition modulation were obtained. Samples grown at T>500 degreesC exhibit lateral composition modulation. Uniform and homogeneous SPS structures were not obtained in the GaAs/InAs structures over the entire temperature range examined in this study (475 degreesC less than or equal toT less than or equal to 510 degreesC). Instead, lateral composition modulation with varying degrees of regularity was always observed. It was found that In segregation and roughening determine the microstructure. A kinetic exchange model predicts that at an optimum temperature the SPS layers are more intermixed for the AlAs/InAs SPSs. Thus, the lattice mismatch is lower and the driving force for roughening is reduced, resulting in uniform SPS structures. Growing the structure away from the optimum temperature for smooth growth may induce roughening-driven composition modulation. The GaAs/InAs structures are less intermixed over the temperatures studied, which results in higher mismatch between the individual layers and a higher driving force for roughening and lateral composition modulation. (C) 2002 American Institute of Physics.
Title:
Glass based on a single proto-tile and inflation species without discrete diffractogram
Authors:
Mandal, RK; Neto, AHC;
Source:
CURRENT SCIENCE, 81 (11): 1466-1470; 2001
Abstract:
The discovery of quasicrystals in the 80s has led to a qualitative change in our understanding about atomic arrangements, including definition of solids having discrete diffractograms. Owing to this, the emphasis has now been shifted to reciprocal space from direct space that was in vogue prior to the seminal finding of quasi-periodic atomic arrangements having noncrystallographic point group symmetry. The purpose of this communication is to cite two specific examples of two-dimensional tiling from literature that do not possess discrete diffractograms, but have subtle distinctions in direct space. It will be shown that one of the above constructs offers the first ever example of an isotropic glass based on a single proto-tile. The second example, on the other hand, displays characteristics which are akin to those of glasses in reciprocal space, but possesses finite rank in direct space. The consequence of these will be discussed in relation to Pisot-Vijayaraghavan (PV) number. It will be concluded that foundation of Copernican crystallography incorporating these is still missing and needs further substantiation.
Title:
Charge ordering in a 2D manganite, Pr0.25Ca1.75MnO4
Authors:
Autret, C; Retoux, R; Hervieu, M; Raveau, B; Mosunov, AV;
Source:
CHEMISTRY OF MATERIALS, 13 (12): 4745-4752; 2001
Abstract:
The structural study of the manganite Pr0.25Ca1.75MnO4, n = 1 member of the Ruddlesden-Popper (RP) family, has been carried out using high-resolution electron microscopy and neutron powder diffraction. At room temperature, the K2NiF4-type structure is characterized by its ability to microtwine and form perovskite-like "pancake" defects, coherent with the matrix. The most important point concerns the appearance at low temperature of an incommensurate structure with a modulation vector (q) over right arrow approximate to 0.28 (c) over right arrow*, never observed to date in these 2D manganites. The reconstruction of the reciprocal space, using electron diffraction technique, evidences Cmca(00 gamma )s00 as the superspace group. The transition temperature, T-CO = 275 K, explains the anomalies of the rho (T) and M(T) curves, characterized by an increase of resistivity and appearance of antiferromagnetic fluctuations below this temperature.
Title:
A simple isohedral tiling of three-dimensional space by infinite tiles and with symmetry Ia (3)over-bard
Authors:
Friedrichs, OD; Plevert, J; O'Keeffe, M; Raveau, B;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 58 (12): 77-78; 2002
Abstract:
A tiling of space by tiles that have all hexagonal faces and are infinite in one direction is described. The tiling is simple (four tiles meet at each vertex, three at each edge and two at each face) and carries a 4-connected net whose vertices are the lattice complex S* with symmetry Ia (3) over bard . The tiling is closely related to the densest cubic cylinder packing, Gamma. It is shown that the other invariant cubic lattice complexes unique to Ia (3) over bard (Y** and V*) are also related to the same cylinder packing.
Title:
Nomenclature of magnetic, incommensurate, composition-changed morphotropic, polytype, transient-structural and quasicrystalline phases undergoing phase transitions. II. Report of an IUCr Working Group on Phase Transition Nomenclature (vol A57, pg 614, 2001)
Authors:
Toledano, JC; Berry, RS; Brown, PJ; Glazer, AM; Metselaar, R; Pandey, D; Perez-Mato, JM; Roth, RS; Abrahams, SC; Arakawa, Y;
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 58 (12): 79-79; 2002
Abstract:
A tiling of space by tiles that have all hexagonal faces and are infinite in one direction is described. The tiling is simple (four tiles meet at each vertex, three at each edge and two at each face) and carries a 4-connected net whose vertices are the lattice complex S* with symmetry Ia (3) over bard . The tiling is closely related to the densest cubic cylinder packing, Gamma. It is shown that the other invariant cubic lattice complexes unique to Ia (3) over bard (Y** and V*) are also related to the same cylinder packing.
Title:
Dynamical molecular disorder and diffuse scattering in an alkane/urea incommensurate inclusion compound
Authors:
Lefort, R; Toudic, B; Etrillard, J; Guillaume, F; Bourges, P; Currat, R; Breczewski, T; Karczewski, G;
Source:
EUROPEAN PHYSICAL JOURNAL B, 24 (1): 51-57; 2001
Abstract:
The diffraction pattern of n-alkane/urea inclusion compounds is known to contain a broad diffuse scattering related to the molecular form factor of the alkane species, indicating individual rotational and/or translational disorder of these molecules. Inelastic coherent neutron scattering reveals for the first time the entirely dynamical character of the alkane molecular disorder around room temperature. This observation fully agrees with a recent model of the coherent scattering cross section of totally uncorrelated motions. In the ordered phase this diffuse scattering remains, but elastic, and very low energy molecular vibrational modes are evidenced. These observations are discussed in relation with previous incoherent neutron scattering results.
Title:
Cl-35 nuclear magnetic resonance study of critical fluctuations in bis(4-chlorophenyl)sulphone [(ClC6H4)(2)SO2]
Authors:
Taye, A; Michel, D; Petersson, J; Park, MS;
Source:
PHYSICAL REVIEW B, 66 (17); 2002
Abstract:
The temperature dependence of the resonance frequency of the Cl-35 NMR central transitions lines -1/2<---->+1/2 has been measured using a high-quality organic single crystal of bis(4-chlorophenyl)sulphone. The recorded spectra show an increasing characteristic broadening of the NMR line indicating the phase transition in a structurally incommensurate phase at the temperature T-i=149.7 K. Moreover, the dynamics of the incommensurate modulation is investigated in the normal high-temperature phase close to the temperature T-i by means of nuclear spin-lattice relaxation measurements. The temperature dependence of the critical contribution to the spin-lattice relaxation rate above T-i can be described by the critical exponent zetaapproximate to0.67 which is fully consistent with the predictions of the universality class of the three-dimensional XY model. The results from a conventional treatment of the critical contribution are compared with the predictions of a comprehensive field-theoretical model.
Title:
X-ray scattering study of the incommensurate phase in Mg-doped CuGeO3
Authors:
Christianson, RJ; Wang, YJ; LaMarra, SC; Birgeneau, RJ; Kiryukhin, V; Masuda, T; Tsukada, I; Uchinokura, K; Keimer, B;
Source:
PHYSICAL REVIEW B, 66 (17); 2002
Abstract:
We present results of a systematic x-ray scattering study of the effects of Mg doping on the high-field incommensurate phase of CuGeO3. Lorentzian-squared line shapes, the changing of the first-order transition to second order, and the destruction of long-range order with infinitesimal doping are observed, consistent with random-field effects in a three-dimensional XY system. Values for the soliton width in pure and lightly doped CuGeO3 are deduced. We find that even a very small doping has a drastic effect on the shape of the lattice modulation.
Title:
Universal features in the electrical conductivity of icosahedral Al-transition-metal quasicrystals
Authors:
Macia, E; Wang, YJ;
Source:
PHYSICAL REVIEW B, 66 (17); 2002
Abstract:
In this work we report the existence of certain universal features in the temperature dependence of the electrical conductivity of Al-transition-metal icosahedral quasicrystals, extending the results previously reported on the inverse Matthiessen rule [D. Mayou, C. Berger, F. Cyrot-Lackmann, T. Klein, and P. Lanco, Phys. Rev. Lett. 70, 3915 (1993)]. We propose a tentative classification scheme providing a unified description of the electrical conductivity curves over a broad temperature range. We introduce a phenomenological model describing the electrical conductivity of icosahedral quasicrystals, deriving closed analytical expressions. We compare our analytical results with suitable experimental data and illustrate the use of the introduced phenomenological coefficient in order to extract information about the electronic structure of the samples from a fitting analysis of the experimental conductivity curves.
Title:
Spin-orbit induced noncubic charge distribution in cubic ferromagnets. I. Electric field gradient measurements on 5d impurities in Fe and Ni
Authors:
Seewald, G; Hagn, E; Zech, E; Kleyna, R; Voss, M; Burchard, A; Tsukada, I;
Source:
PHYSICAL REVIEW B, 66 (17); 2002
Abstract:
The spin-orbit induced electric field gradient at the nuclear site of Os-183 and Re-183 impurities in Fe and of Pt-191 and Ir-186 impurities in Ni was determined for [100], [110], and [111] orientations of the magnetization. The measurements were performed on single-crystal samples using nuclear magnetic resonance on oriented nuclei and modulated adiabatic fast passage on oriented nuclei. In the Ni experiments the electric field gradient was also determined for other orientations of the magnetization in the (110) plane. These data, together with previous results on the 5d impurities, provide the first fairly complete data set on the spin-orbit induced electric field gradient in cubic Fe, Co, and Ni. Our results establish in particular that the effect depends in general considerably on the direction of the magnetization. We summarize the present knowledge of these electric field gradients, their magnitude, their systematics, and the form and magnitude of their dependence on the direction of the magnetization. The properties of the effect are explained within the tight-binding model in terms of the spin-orbit induced deformation of the electron distribution. We also present and discuss data on the dependence of the hyperfine field on the direction of the magnetization, which was found to be smaller than 10(-3), and on the inhomogeneous broadening of the electric field gradient.
Title:
Surface structures of approximant phases in the Al-Pd-Mn system
Authors:
Fournee, V; Ross, AR; Lograsso, TA; Anderegg, JW; Dong, C; Kramer, M; Fisher, IR; Canfield, PC; Thiel, PA;
Source:
PHYSICAL REVIEW B, 66 (16); 2002
Abstract:
We present a study of the surface of the xi'-Al-Pd-Mn approximant phase based upon scanning tunneling microscopy and low-energy electron diffraction. Several structures are observed on two different samples grown either by the Bridgman technique or by a self-flux method, and which contain various degrees of disorder. We also describe some other complex crystalline phases that are sometimes observed on the fivefold surface of Al-Pd-Mn quasicrystalline samples after the sputter-annealing cleaning process under ultrahigh vacuum conditions. This includes the T approximant phase resulting from surface decomposition after a high-temperature annealing.
Title:
Electronic transport of the icosahedral Zn-Mg-Sc quasicrystal and its cubic approximant Zn17Sc3
Authors:
Hasegawa, J; Tamura, R; Takeuchi, S; Anderegg, JW;
Source:
PHYSICAL REVIEW B, 66 (13); 2002
Abstract:
The electrical resistivity and specific-heat measurements have been performed for the recently discovered P-type icosahedral Zn-Mg-Sc of high structural perfection and its crystalline approximant Zn17Sc3. The temperature coefficient of the resistivity is found to be negative with rho(300K)=330 muOmega cm for the quasicrystal, while it is positive with rho(300K)=250 muOmega cm for the crystalline approximant. The electronic specific-heat coefficient gamma is found to be small and nearly the same for both alloys; 0.55 and 0.65 mJ/(mole K-2) for the quasicrystal and the crystalline approximant, respectively. Such small gamma values are consistent with the recent electronic structure calculation [Ishii and Fujiwara, J. Alloys. Compd. 342, 343 (2002)], and can be taken as an indication of the existence of a pseudogap in the density of states at the Fermi level for the P-type i phase.
Title:
Phason dispersion in deuterated thiourea by inelastic neutron scattering
Authors:
Hlinka, J; Petzelt, J; Brezina, B; Currat, R; Dong, C;
Source:
PHYSICAL REVIEW B, 66 (13); 2002
Abstract:
The phason origin of the quasielastic diffuse scattering in the incommensurate phase of thiourea is demonstrated by inelastic neutron scattering on a deuterated crystal. The analysis of its frequency spectrum allows one to draw the dispersion of the phason relaxational frequency along the modulation direction. Results indicate that the lowest-frequency mode seen in submillimeter infrared spectra is an overdamped inhomogeneous phason mode corresponding to the antiphase motion of the nearest-neighbor nodes of the modulation profile.
Title:
Magnetic structure of antiferromagnetic NdRhIn5
Authors:
Chang, S; Pagliuso, PG; Bao, W; Gardner, JS; Swainson, IP; Sarrao, JL; Nakotte, H; Canfield, PC;
Source:
PHYSICAL REVIEW B, 66 (13); 2002
Abstract:
The magnetic structure of antiferromagnetic NdRhIn5 has been determined using neutron diffraction. It has a commensurate antiferromagnetic structure with a magnetic wave vector (1/2 0 1/2) below T-N=11 K. The staggered Nd moment at 1.6 K is 2.5(1)mu(B) aligned along the c axis. This magnetic structure is closely related to the low-temperature magnetic structure of the cubic parent compound NdIn3.
Title:
Superconductivity and microstructure of YSr2Cu3O6.875
Authors:
Lebedev, OI; Van Tendeloo, G; Licci, F; Gilioli, E; Gauzzi, A; Prodi, A; Marezio, M; Canfield, PC;
Source:
PHYSICAL REVIEW B, 66 (13); 2002
Abstract:
The crystal structure of YSr2Cu3O6+x synthesized under high pressure has been studied in detail using transmission electron microscopy and powder neutron diffraction. It has been shown that YSr2Cu3O6+x and YBa2Cu3O6+x are not isostructural after all. The much lower T-c of YSr2Cu3O6+x (YSCO) with respect to that of YBa2Cu3O6+x has to be ascribed to the different structural arrangement of the reservoir blocks. The different oxygen ordering and the consequent displacement of the Sr and Cu1 cations in YSCO yield an orthorhombic modulated structure with a propagation vector of 1/4[012]*. Perfectly ordered YSCO would have an oxygen stoichiometry equal to 6.875. Powder neutron-diffraction data yielded O-7.20 and O-6.92 for the as-prepared and annealed phases, respectively.
Title:
Features of the incommensurate phase in Pb(Zr1-xTix)O-3
Authors:
Watanabe, S; Koyama, Y; Licci, F;
Source:
PHYSICAL REVIEW B, 66 (13); 2002
Abstract:
The features of the incommensurate phase in Pb(Zr1-xTix)O-3, which has a simple perovskite structure, have been investigated in the whole incommensurate region of the phase diagram by transmission electron microscopy. The incommensurate phase basically exists in the Ti-content range of 0less than or equal toxless than or equal to0.10, though the coherence length of the incommensurate modulation in samples with x=0.10 is very short. In view of its modulated structure, the normal phase of the commensurate phase is not the high-temperature paraelectric phase and its crystal structure involves both the M-5' antiferroelectric and ferroelectric displacements. The phase transition from the normal phase to the incommensurate phase then takes place by the introduction of the M-3 rotational displacement of the oxygen octahedra. That is, the incommensurate modulation can be identified as the modulation of the rotational angle of the oxygen octahedron, which results in an alternating array of two M-3 microdomains, as was proposed in our previous paper [S. Watanabe and Y. Koyama, Phys. Rev. B 63, 134103 (2001)]. The antiphase boundaries of the M-5' displacement present in the normal phase may also play the role of a discommensuration with a phase slip of pi in the incommensurate phase. In addition to these features as a modulated structure, the slight increase in the periodicity of the incommensurate modulation and the growth of the one-variant region on heating were observed in the incommensurate phase with a long coherence length of about 1 mum. Of these two phenomena, the former increase can be explained as being due to the increase in the size of the M-3 microdomain, which would be produced by the decrease in the rotational angle via the spontaneous strain coupled to the angle. Based on this, the size of every incommensurate-variant region should be enlarged as a total. However, only the one-variant region was observed to grow on heating. This suggests that the growth of
Title:
Magnetism of layered cobalt oxides investigated by muon spin rotation and relaxation
Authors:
Sugiyama, J; Itahara, H; Tani, T; Brewer, JH; Ansaldo, EJ; Prodi, A;
Source:
PHYSICAL REVIEW B, 66 (13); 2002
Abstract:
Muon spin rotation-relaxation (muSR) spectroscopy has been used to investigate the magnetic properties of polycrystalline Ca3-xMxCo4O9 (xless than or equal to0.5,M=Sr,Y, and Bi) and Na0.7CoO2 samples in the temperature range between 2.5 and 300 K. It was found that Ca3Co4O9 exhibits a magnetic transition at around T-c=100 K; at lower temperatures, two types of relaxation were observed using a weak transverse field muSR technique with H=104 Oe: one with a fast relaxation rate lambda(F)similar to10 mus(-1) and the other with a slow lambda(S)similar to0.1 mus(-1). Zero-field muSR measurements suggest the existence of an incommensurate spin-density-wave (SDW) state below T-c (i.e., T-c=T-SDW), although a ferrimagnetic M-H loop was observed by a dc susceptibility measurement below 19 K. The substitution of Y or Bi for Ca increased T-SDW, while the substitution of Sr for Ca did not affect T-SDW. This indicates that the SDW transition depends strongly on the average valence of the Co ions. The related material Na0.7CoO2 showed no magnetic transitions below 30 K. Considering the difference between the crystal structures of Ca3Co4O9 and Na0.7CoO2, we suggest that Co ions in the rocksalt-type layers of Ca3Co4O9 are likely to play a significant role in inducing the SDW transition around 100 K.
Title:
Synchrotron radiation study of neptunium phosphide
Authors:
Longfield, MJ; Paixao, JA; Bernhoeft, N; Lander, GH; Wastin, F; Rebizant, J; Marezio, M;
Source:
PHYSICAL REVIEW B, 66 (13); 2002
Abstract:
NpP orders at T(N)similar to120 K into an incommensurate longitudinal antiferromagnetic structure and becomes commensurate with k=<1/3 0 0> at T-com=70 K with a first-order phase transition. We have examined the magnetic phase diagram with resonant x-ray magnetic scattering (RXMS) on a single crystal of NpP with the photon energy tuned to the Np M-4 edge at 3.846 keV. A number of phases are present just above T-com but in the lower 3+, 3- phase a single peak is observed, together with a tetragonal distortion. Our study is in agreement with earlier neutron work, but the increased wave vector resolution with RXMS gives more details. A satellite at 2k was observed below T-com in the unrotated sigma-->sigma polarization channel with a strong dependence on the incident photon energy. A model for this is proposed by considering small differences in the charge distribution around the two independent Np sites in the commensurate 3+, 3- phase, and is consistent with the observation by Mossbauer spectroscopy of two different electric quadrupole moments in this temperature range. However, to determine the origin of this signal its intensity as a function of the azimuthal angle must be determined.
Title:
Change in charge and orbital alignment upon antiferromagnetic transition in the A-site-ordered perovskite manganese oxide RBaMn2O6 (R=Tb and Sm)
Authors:
Arima, T; Akahoshi, D; Oikawa, K; Kamiyama, T; Uchida, M; Matsui, Y; Tokura, Y; Stuchbery, AE;
Source:
PHYSICAL REVIEW B, 66 (14); 2002
Abstract:
A neutron-diffraction study on an A-site-ordered perovskite manganite RBaMn2O6 (R=Tb) has revealed that the magnetic structure is characterized by two modulation vectors, (1/2 0 1/4) and (1/4 1/4 1/4), in the primitive cubic setting. The appearance of the magnetic order is accompanied by change in stacking of charge-ordered/orbital-ordered MnO2 sheets along the c axis, which has also been confirmed by electron-diffraction and x-ray-diffraction studies on the R=Tb and Sm compounds. The charge ordering in the antiferromagnetic phase is an unprecedented one, i.e., NaCl type, which is stabilized by the ordering of R and Ba in the A site.
Title:
Minimal model of the phonon-phason dynamics in icosahedral quasicrystals and its application to the problem of internal friction in the i-AlPdMn alloy
Authors:
Rochal, SB; Lorman, VL; Oikawa, K;
Source:
PHYSICAL REVIEW B, 66 (14); 2002
Abstract:
Different existing elastodynamical models of icosahedral quasicrystals are analyzed. The simplest minimal model of the phonon-phason dynamics is formulated. Physical restrictions and possible applications of the proposed model are considered. Several generalizations of the minimal model are discussed. It is shown that the phonon-phason coupling induces a resonant absorption peak of low-frequency sound waves in the temperature region corresponding to a thermal activation of phason excitations. The maximum value of the logarithmic decrement of the sound wave damping depends on the propagation direction and the wave polarization. The anisotropy is proportional to the square of the phonon-phason coupling constant K-3. Our estimation shows that the effect can be resolved experimentally if the relative value of K-3 is not negligible with respect to four other elastic constants of the icosahedral quasicrystal. Namely, the difference should not exceed two orders of magnitude.
Title:
Vacancies in quasicrystals: Effects of electron irradiation
Authors:
Sato, K; Baier, F; Sprengel, W; Schaefer, HE; Saito, R;
Source:
PHYSICAL REVIEW B, 66 (9); 2002
Abstract:
Effects of electron irradiation in icosahedral Mg26Zn64Ho10 and Al70.2Pd21.3Mn8.5 quasicrystals were investigated by simultaneous measurements of the positron lifetime and the two-detector coincident Doppler broadening spectra at ambient temperature. Irradiation-induced vacancies could be detected in the Mg26Zn64Ho10 quasicrystal by their agglomeration due to annealing effects at room temperature by positron lifetime measurements and in the Al70.2Pd21.3Mn8.5 quasicrystal with the more sensitive coincident Doppler broadening measurements of the positron-electron annihilation photon line, in addition to the structural vacancies in both systems.
Title:
Monitoring an insulator-metal transition in icosahedral AlPdRe by neutron irradiation
Authors:
Karkin, AE; Goshchitskii, BN; Voronin, VI; Poon, SJ; Srinivas, V; Rapp, O; Unlu, MS;
Source:
PHYSICAL REVIEW B, 66 (9); 2002
Abstract:
The intrinsic disorder effect on the electrical resistivity and magnetoresistance (MR) of icosahedral AlPdRe is studied by use of high-energy neutron irradiation. The icosahedral phase is preserved under irradiation with a decrease of x-ray peak intensity and volume of the coherent icosahedral phase. An insulator-metal transition, as observed in the MR, can be driven by the irradiation and is monitored by the resistance ratio R[=rho(4.2 K)/rho(295 K)]. The relation of MR vs R was found to be similar for samples of a widely different history.
Title:
Incommensurate and superconducting phases in an exactly solvable model
Authors:
Karnaukhov, IN; Goshchitskii, BN;
Source:
PHYSICAL REVIEW B, 66 (9); 2002
Abstract:
An integrable lattice model of strongly interacted electrons with nearest-neighbor and next-nearest-neighbor hoppings is proposed and investigated. The exact ground-state phase diagram is calculated as a function of an on-site interaction, a value of the hopping integral between next-nearest-neighbor lattice sites and a band filling (the nearest-neighbor hopping integral is chosen equal to unity). The model describes incommensurate and superconducting phases which are realized simultaneously in a definite region of interaction parameters and a band filling. The long-distance asymptotics of the density-density and one-particle correlation functions are calculated in the incommensurate phase.
Title:
Penrose structures: Gap labeling and geometry
Authors:
de Prunele, E; Malinowski, N;
Source:
PHYSICAL REVIEW B, 66 (9); 2002
Abstract:
The electronic eigenvalues and eigenstates of finite parts of Penrose structures are studied on the basis of a recently proposed three-dimensional solvable model [J. Phys. A 30, 7831 (1997)]. This model allows to take explicitely into account the geometry in three-dimensional space and involves no assumptions such as only nearest neighboring atoms coupling. For finite parts of a Penrose tiling, it is shown that the positions of some of the gaps in the integrated density of states are directly related to the geometry of the systems. As a result, the explicit expressions for ten gaps relative to infinite tilings are obtained from the known frequencies of vertex stars of Penrose tilings.
Title:
X-ray diffuse scattering in the icosahedral quasicrystal Al-Pd-Mn
Authors:
Zhang, Y; Ehrlich, SN; Colella, R; Kopecky, M; Widom, M; Veal, BW;
Source:
PHYSICAL REVIEW B, 66 (10); 2002
Abstract:
Several isointensity contour plots of diffuse scattering around Bragg reflections have been obtained at 300 and 20 K on planar sections of reciprocal space perpendicular to twofold axes. The geometry of the experiments was such that circular contours were expected on the basis of elastic isotropy, demonstrated by the speed of sound being uniform in all directions. Instead, the profiles were markedly elongated along a twofold axis, a direct indication of scattering due to phason fluctuations. The 1/q(2) dependence of diffuse scattering was verified in the neighborhood of the (0 4 6 0 (4) over bar6) Bragg reflection, but not near the (5 3 3 3 1 (1) over bar), a possible indication of lack of equilibrium in the phason fluctuations.
Title:
Atomic jumps in quasiperiodic Al72.6Ni10.5Co16.9 and related crystalline material
Authors:
Dolinsek, J; Apih, T; Jeglic, P; Feuerbacher, M; Calvo-Dahlborg, M; Dahlborg, U; Dubois, JM; Mook, HA;
Source:
PHYSICAL REVIEW B, 65 (21); 2002
Abstract:
Al-27 NMR measurements of the transverse magnetization decay in a decagonal quasicrystal Al72.6Ni10.5Co16.9 detected at temperatures between 300 and 4 K slow, low-activation-energy, diffusive atomic jumps that exhibit properties compatible with the elementary excitations of the quasiperiodic lattices in the form of phason jumps. However, identical atomic motion was observed also in "vacancy-ordered" bcc crystalline Al50Cu35Ni15, indicating that this motion is not quasicrystals specific, but a feature of close-packed atomic structures-either periodic or quasiperiodic-that contain structural vacancies.
Title:
Anomalous NMR response of quasicrystalline icosahedral Al72.4Pd20.5Mn7.1 at low temperatures
Authors:
Gavilano, JL; Rau, D; Mushkolaj, S; Ott, HR; Dolinsek, J; Urban, K; Dubois, JM;
Source:
PHYSICAL REVIEW B, 65 (21); 2002
Abstract:
We report the observation of an anomalous Al-27-NMR response of a single grain Al72.4Pd20.5Mn7.1 icosahedral quasicrystal at low temperatures. In an external magnetic field of 6 T and upon decreasing temperature, we observe a sharp 100% increase of the resonance linewidth at 2.5 K. No further changes of the linewidth are observed down to 0.05 K. The linewidth enhancement is accompanied by a small but distinct increase of the spin-lattice relaxation rate T-1(-1). These anomalies are absent in external fields of 2.5 T and below. Our observations indicate unusual variations in the stability of isolated magnetic moments in a quasiperiodic metallic environment.
Title:
Positron lifetimes in a binary quasicrystal Cd-Yb and its crystalline approximant
Authors:
Sato, K; Uchiyama, H; Arinuma, K; Kanazawa, I; Tamura, R; Shibuya, T; Takeuchi, S; Mook, HA;
Source:
PHYSICAL REVIEW B, 66 (5); 2002
Abstract:
The positron lifetime measurements for a recently discovered binary icosahedral quasicrystal (Cd84.6Yb15.4) and its cubic approximant (Cd6Yb) have shown that the lifetime spectra in both alloys are composed of a single component with the lifetime of 230+/-3 ps for the quasicrystal and 234+/-3 ps for the cubic approximant; these values being close to the reported lifetime (250 ps) of positrons trapped in lattice vacancies in crystalline Cd. Based on the atomic structure of the cubic approximant, the positrons are most likely to be annihilated inside the dodecahedral Cd clusters in which half of the eight cubic Cd sites are unoccupied. Essentially the same lifetimes in the quasicrystal and the cubic approximant strongly suggest that the positrons are trapped in the same type of structural vacancies common to both alloys, implying that the quasicrystal is also composed of the same cluster units as the cubic approximant.
Title:
Exact one-component order parameter distributions for the thermodynamic potential of Landau-Ginzburg type with higher gradient and power nonlinearities
Authors:
Sereda, YV; Liu, ZH;
Source:
PHYSICAL REVIEW B, 66 (5); 2002
Abstract:
A number of exact one-component order parameter distributions for the Michelson thermodynamic potential is obtained. The exact partial distribution with energy, which is lower at some temperature interval than for the best of the known order parameter models in the form of an elliptic Jacobi sine, is obtained for the thermodynamic potential of the Ginzburg-Landau type. By varying its coefficients, the model phi(x)=a sn(bx,k).dn(bx,k) is obtained which is able to reflect the properties of an incommensurate phase in systems with a one-component order parameter in a better way, particularly in the proper uniaxial Sn2P2Se6 ferroelectric.
Title:
Magnetoresistance of Al70Pd22.5Re7.5 quasicrystals in the variable-range hopping regime
Authors:
Su, TI; Wang, CR; Lin, ST; Rosenbaum, R; Wu, GH;
Source:
PHYSICAL REVIEW B, 66 (5); 2002
Abstract:
The temperature dependence of the magnetoresistance (MR) of insulating Al70Pd22.5Re7.5 quasicrystals taken at liquid-helium temperatures can be explained by the theories of MR-the forward interference and the wave-function shrinkage-in the variable-range hopping (VRH) regime. By analyzing the MR data with the theories mentioned above, a crossover from Mott VRH conduction to Efros-Shklovskii VRH conduction at liquid helium temperatures was identified in a highly resistive Al70Pd22.5Re7.5 sample. The rapid decrease in the negative MR of highly resistive samples at low temperatures might be attributed to the conduction via the states in the Coulomb gap.
Title:
Atomic vacancies in quasicrystals: Positron annihilation spectroscopy and time-differential dilatometry
Authors:
Baier, F; Schaefer, HE; Boebinger, GS;
Source:
PHYSICAL REVIEW B, 66 (6); 2002
Abstract:
For specific studies of atomic vacancies in quasicrystals the sensitive techniques of positron annihilation spectroscopy and time-differential dilatometry are employed. In the quasicrystals and approximants studied here, structural vacancies can be observed at ambient temperatures with atomic concentrations higher than 10(-4). With in situ measurements of the positron lifetime and of time-differential dilatometry after fast temperature changes at high temperatures on i-Al70.2Pd21.3Mn8.5 the formation and migration of thermal vacancies can be observed. We additionally demonstrate that the chemical environment of structural vacancies in i-Al70.2Pd21.3Mn8.5 at ambient temperatures is dominated by Al atoms. This is shown by the characteristic core electron momentum distribution as monitored by coincident Doppler broadening studies of the positron-electron annihilation photon line.
Title:
Structure factor of a dimerized Fibonacci lattice
Authors:
Moitra, RK; Chakrabarti, A; Karmakar, SN; Ledbetter, H;
Source:
PHYSICAL REVIEW B, 66 (6); 2002
Abstract:
The calculation of the static and dynamic structure factors of a dimerized Fibonacci chain are presented. This lattice has four kinds of bonds with an underlying quasiperiodicity, but does not preserve the scale invariance like the undistorted Fibonacci chain. This lattice is of interest from the point of view of possible Peierls' distortion in the presence of electron-phonon interactions. To calculate the static structure factor we use the "cut and projection" method, while a proposed numerical renormalization-group algorithm has been utilized to find the dynamic one. Our proposed algorithm is, in principle, exact, and can be implemented to any arbitrary degree of accuracy.
Title:
Atomic structures and magnetic behavior of Mn clusters
Authors:
Briere, TM; Sluiter, MHF; Kumar, V; Kawazoe, Y; Galli, F;
Source:
PHYSICAL REVIEW B, 66 (6); 2002
Abstract:
The structures and magnetic properties of Mn clusters containing 13, 15, 19, and 23 atoms have been predicted from ab initio electronic structure calculations. The lowest energy structures of the 13-, 19-, and 23-atom clusters are icosahedral and have ordered spin configurations in which blocks of ferromagnetically coupled spins are antiferromagnetically coupled with each other. The 15-atom cluster is body-centered cubic with antiferromagnetic coupling. The net moments are small and lie in the range of 0.2-1.2mu(B)/atom; however, the average local atomic moments have high values close to 4mu(B). These results are discussed in light of recent Stern-Gerlach experiments.
Title:
Sliding charge density wave in the monophosphate tungsten bronze (PO2)(4)(WO3)(2m) with alternate stacking of m=4 and m=6 WO3 layers
Authors:
Foury-Leylekian, P; Sandre, E; Ravy, S; Pouget, JP; Elkaim, E; Roussel, P; Groult, D; Labbe, P; Kakizaki, A;
Source:
PHYSICAL REVIEW B, 66 (7); 2002
Abstract:
The monophosphate tungsten bronzes (PO2)(4)(WO3)(2m) form family of two-dimensional metals which exhibit charge density wave (CDW) instabilities. These materials are generally built by the regular stacking of (a,b) layers in which chains made of segments of m WO6 octahedra directed along the a and a+/-b directions are delimited. Their electronic structure thus originates from quasi-one-dimensional (1D) bands located on these chains. As a consequence their Fermi surface (FS) exhibits large flat portions whose nesting gives rise to successive CDW instabilities. Here we present a structural study of the CDW instability of the (PO2)(4)(WO3)(10) member formed by the alternate stacking of layers built with segments of m=4 and m=6 WO6 octahedra. Its ab initio electronic structure calculation shows that the FS of this member exhibits large flat portions which can be extremely well nested. Its best nesting wave vector accounts for the modulation wave vector stabilized by the CDW transition which occurs at 156 K. Because of the regular stacking of layers of different m values the FS is slightly split. The unusual thermal dependence of the x-ray satellite intensity provides evidence that the two types of layers become modulated at different temperature. This also leads to a slight thermal sliding of the CDW-nesting modulation wave vector, which can be accounted for within the framework of a Landau-Ginzburg theory. In addition, the observation of a global hysteresis in the thermal cycling of the satellite intensity, as well as the degradation of the interlayer order upon cooling, suggest the formation of a disordered lattice of dilute solitons. Such solitons allow to accomodate the charge transferred between the two types of layer. Finally the relevance of local charge transfers, at intergrowth defects, for example, to create pinned discommensurations that break the CDW coherence is emphasized in this whole family of bronzes.
Title:
Fermi surface nesting and magnetic structure of ErGa3
Authors:
Biasini, M; Ferro, G; Kontrym-Sznajd, G; Czopnik, A; Elkaim, E;
Source:
PHYSICAL REVIEW B, 66 (7); 2002
Abstract:
A three-dimensional mapping of the Fermi surface (FS) of the rare-earth compound ErGa3 was determined via measurements of the angular correlation of the electron-positron annihilation radiation. The topology of the electronlike FS does show nesting properties which are consistent with the modulated antiferromagnetic structure of the system. We determine the density of states at the Fermi energy N(E-F) and the electronic contribution to the gamma constant to be N(E-F)=16 states/ Ryd /cell and gamma=2.7 (mJ/mol K-2), respectively.
Title:
Universal mechanism of discontinuity of commensurate-incommensurate transitions in three-dimensional solids: Strain dependence of soliton self-energy
Authors:
Levanyuk, AP; Minyukov, SA; Cano, A; Agren, H;
Source:
PHYSICAL REVIEW B, 66 (1); 2002
Abstract:
We show that there exists a universal mechanism of long-range soliton attraction in three-dimensional solids and, therefore, of discontinuity of any commensurate-incommensurate (C-IC) phase transition. This mechanism is due to the strain dependence of the soliton self-energy and specific features of the solid-state elasticity. The role of this mechanism is studied in detail for a class of C-IC transitions where the IC modulation is one dimensional, the anisotropy in the order parameter space is small, and the symmetry of the systems allows the existence of the Lifshitz invariant. Two other mechanisms of soliton attraction are operative here but the universal mechanism considered in this paper is found to be the most important one in some cases. Comparison with the most extensively studied C-IC transition in K2SeO4 shows that the experimentally observed thermal anomalies can be understood as a result of the smearing of the theoretically predicted discontinuous transition.
Title:
Magnetic and charge structures in itinerant-electron magnets: Coexistence of multiple spin-density and charge-density waves
Authors:
Ohkawa, FJ; Minyukov, SA;
Source:
PHYSICAL REVIEW B, 66 (1); 2002
Abstract:
A theory of Kondo lattices is applied to studying possible magnetic and charge structures of itinerant-electron antiferromagnets. Even helical spin structures can be stabilized when the nesting of the Fermi surface is not sharp and the superexchange interaction, which arises from the virtual exchange of pair excitations across the Mott-Hubbard gap, is mainly responsible for magnetic instability. Sinusoidal spin structures or spin-density waves (SDW's) are only stabilized when the nesting of the Fermi surface is sharp enough or when an exchange interaction arising from that of pair excitations of quasiparticles is mainly responsible for magnetic instability. In particular, multiple SDW's are stabilized when their incommensurate ordering wave numbers +/-Q are multiple; magnetizations of different +/-Q components are orthogonal to each other in double and triple SDW's when magnetic anisotropy is weak enough. Unless +/-2Q are commensurate, charge-density waves (CDW's) with +/-2Q coexist with SDW's with +/-Q. Because the quenching of magnetic moments by the Kondo effect or local quantum spin fluctuations depends on local numbers of electrons, the phase of CDW's or electron densities is such that magnetic moments are large where the quenching is weak. It is proposed that the so-called stripe order must be the coexisting state of double incommensurate SDW's and CDW's in tetragonal cuprate-oxide high temperature superconductors, in particular, those with the square CuO2 lattices.
Title:
Crystal structure of the Mg1-xAlxB2 superconductors near x approximate to 0.5
Authors:
Margadonna, S; Prassides, K; Arvanitidis, I; Pissas, M; Papavassiliou, G; Fitch, AN; Sera, M;
Source:
PHYSICAL REVIEW B, 66 (1); 2002
Abstract:
Precise structural information on the Mg1-xAlxB2 superconductors in the vicinity of xapproximate to0.5 is derived from high-resolution synchrotron x-ray powder diffraction measurements. We find that a hexagonal superstructure, accompanied by doubling of the c axis, ordering of Mg and Al in alternating layers, and a shift of the B layers towards Al by similar to0.12 Angstrom, is formed. The unusually large width of the (00 1/2) superlattice peak implies the presence of microstrain broadening, arising from anisotropic stacking of Al and Mg layers and/or structural modulations within the ab plane. The ordered phase survives only over a limited range of compositions away from the optimum x=0.5 doping level.
Title:
Landau orbital description of the vortex state in a two-dimensional extremely type-II superconductor
Authors:
Zhuravlev, V; Maniv, T; Welp, U;
Source:
PHYSICAL REVIEW B, 66 (1); 2002
Abstract:
We extend the application of the recently developed Landau orbital approach to the fluctuating vortex lattice in two-dimensional (2D) extremely type-II superconductors at high magnetic fields to the region above the melting point. We find that the abrupt incomplete melting of the quasicrystalline vortex phase at T=T-m<
Title:
Interaction between the Fermi-edge singularity and optical phonons in AlxGa1-xAs/InyGa1-yAs/GaAs heterostructures
Authors:
Mazur, YI; Tarasov, GG; Zhuchenko, ZY; Kissel, H; Muller, U; Kunets, VP; Masselink, WT; Dhesi, SS;
Source:
PHYSICAL REVIEW B, 66 (3); 2002
Abstract:
Many-electron effects in pseudomorphically strained modulation-doped AlxGa1-xAs/InyGa1-yAs/GaAs (x=0.20, y=0.19) heterostructures are investigated using photoluminescence as a function of magnetic field B, temperature T, and excitation density I. The interaction of the many-body exciton (Fermi-edge singularity) with the longitudinal-optical-phonon is observed. Both the Fermi-edge singularity and the enhancement of the exciton-longitudinal optical phonon interaction can be controlled by varying the magnetic field; the strengths of these two many-body effects change with filling factor. They are synchronous both with each other and with the resonance of the upper Landau level with the Fermi level. The strength of this phonon replica when the Fermi level is resonant with a Landau level is attributed to the magnetic-field-dependent screening properties of the two-dimensional electron gas in the quantum well.
Title:
Morphological evolution of the fivefold surface of i-AlPdMn quasicrystals
Authors:
Cappello, G; Chevrier, J; Schmithusen, F; Stierle, A; Formoso, V; Comin, F; de Boissieu, M; Boudard, M; Lograsso, T; Jenks, C; Delaney, D; Kohgi, M;
Source:
PHYSICAL REVIEW B, 65 (24); 2002
Abstract:
Morphology of the fivefold symmetric quasicrystal surface of AlPdMn was investigated by x-ray reflectivity and by x-ray diffraction. X-ray experiments revealed two different morphologies depending on the surface preparation. Sputtering and annealing up to 900 K, under UHV conditions, produced a rough and facetted quasicrystal surface. These features were confirmed by atomic force microscopy and scanning tunnel microscopy measurements. We also observed that an annealing above 900 K induces a rapid and irreversible transition toward a flat surface.
Title:
Quantum dynamics in two- and three-dimensional quasiperiodic tilings
Authors:
Triozon, F; Vidal, J; Mosseri, R; Mayou, D; Frauenheim, T;
Source:
PHYSICAL REVIEW B, 65 (22); 2002
Abstract:
We investigate the properties of electronic states in two- and three-dimensional quasiperiodic structures: the generalized Rauzy tilings. Exact diagonalizations, limited to clusters with a few thousands sites, suggest that eigenstates are critical and more extended at the band edges than at the band center. These trends are clearly confirmed when we compute the spreading of energy-filtered wave packets, using an algorithm that allows us to treat systems of about 10(6) sites. The present approach to quantum dynamics, which gives also access to the low-frequency conductivity, opens interesting perspectives in the analyzis of two- and three-dimensional models.
Title:
Continuous transition between decagonal quasicrystal and approximant by formation and ordering of out-of-phase domains
Authors:
Doblinger, M; Wittmann, R; Gerthsen, D; Grushko, B; Scharmann, A;
Source:
PHYSICAL REVIEW B, 65 (22); 2002
Abstract:
The transformation between a quasicrystal and an orthorhombic approximant is studied at the nominal composition Al72.7Ni8.3Co19 by electron diffraction and high-resolution transmission electron microscopy. A series of transition states indicating a continuous transformation is monitored. First, the material transforms to a single-oriented one-dimensional quasicrystal. In the course of this process out-of-phase domains are formed. The approximant results from ordering of these domains to a periodic structure.
Title:
Comparative study of the binary icosahedral quasicrystal Cd5.7Yb and its crystalline approximant Cd6Yb by low-temperature ultrahigh-resolution photoemission spectroscopy
Authors:
Tamura, R; Murao, Y; Takeuchi, S; Kiss, T; Yokoya, T; Shin, S; Bouree, F;
Source:
PHYSICAL REVIEW B, 65 (22); 2002
Abstract:
Low-temperature ultrahigh-resolution photoemission (PE) spectroscopy of the recently discovered binary icosahedral (i) Cd5.7Yb and its 1/1-cubic approximant Cd6Yb has commonly revealed a sharp Fermi edge with a marked spectral intensity decrease towards the Fermi level (E-F), indicating the presence of a dip near E-F which is consistent with the recent result of electronic structure calculations [Y. Ishii and T. Fujiwara, Phys. Rev. Lett. 87, 206408 (2001)], and the dip at E-F is found to be much deeper in i-Cd5.7Yb than in 1/1-Cd6Yb. Moreover, surface core-level shifts (SCS's) are clearly observed in the quasicrystal and the approximant, and the SCS's are found to be substantially different between these two compounds of different long-range orders.
Title:
First-principles study of Pb2MgTeO6: High-T cubic phase and average low-T rhombohedral phase
Authors:
Caracas, R; Gonze, X; Guo, JH;
Source:
PHYSICAL REVIEW B, 65 (18); 2002
Abstract:
The Pb2MgTeO6 double perovskite is cubic at high temperature and becomes incommensurately modulated with a rhombohedral R (3) over bar average structure at lower temperatures. Both the cubic and rhombohedral average structures are investigated using the local-density approximation within the density-functional theory: We determine the electronic, structural, dielectric, and zone-center dynamical properties. The computed structural parameters are in reasonable agreement with the experiment, with differences up to 2% for the lattice constants. There are two unstable zone-center vibration modes in the cubic phase. The first unstable mode T-1g, 91.19i cm(-1), has an antiferrodistortive character, while the second, T-1u, 13.92i cm(-1), has a ferrodistortive character. There is no unstable zone-center mode in the rhombohedral phase. We establish the correspondence between the zone-center modes in the two phases.
Title:
Mechanism of the incommensurate phase in hexamethylene-tetramine suberate: A molecular-dynamics study
Authors:
Pan, YS; Chapuis, G; Brown, D; Nordgren, J;
Source:
PHYSICAL REVIEW B, 65 (18); 2002
Abstract:
Hexamethylene-tetramine suberate (C6H12N4)[HOOC-(CH2)(6)-COOH] is an incommensurate structure which has been solved from single-crystal x-ray-diffraction data. A molecular-dynamics simulation of this system was carried out from 15 to 580 K. A second-generation consistent force field (CFF), was used to describe the interactions between atoms. In order to account for deficiencies in the force field, a compensating pressure tensor field was applied during the simulation. The experimental structure at 298 K was taken as the starting structure, and the phase transitions were investigated over an extended temperature range. A high-symmetry commensurate structure exists at temperatures between 410 and 290 K. For temperatures lower than 290 K, a periodicity appears in the structure. The system reaches a low-symmetry lock-in phase at about 150 K. An incommensurate structure appears between the high- and low-symmetry phases between 290 and 150 K. The periodicity associated with the incommensurate modulation is due to the appearance of additional long-range ordering of the carbon chains. The present molecular-dynamics simulation reproduces well the experimental x-ray-diffraction results, and provides insight into the origin of the incommensurate behavior.
Title:
Icosahedral quasicrystal Al71Pd21Mn08 and its xi ' approximant: Linear expansivity, specific heat, magnetic susceptibility, electrical resistivity, and elastic constants
Authors:
Swenson, CA; Fisher, IR; Anderson, NE; Canfield, PC; Migliori, A; Shin, S;
Source:
PHYSICAL REVIEW B, 65 (18); 2002
Abstract:
Linear thermal expansivity (alpha, 1-300 K), heat capacity (C-p, 1-108 K), magnetic susceptibility (chi, 1-300 K), and electrical resistivity (rho, 1-300 K) measurements are reported for a single-grain i-Al71Pd21Mn08 quasicrystal and its Al72Pd25Mn03 approximant, and 300 K elastic constants for the quasicrystal. The approximant alpha (alpha(Ap)) and C-p (C-pAp) data show "metallic" behavior, while the previously reported onset of a transition to a spin-glass state (T-f<1.8 K) dominates alpha(Q) and C-pQ below 11 K. C-pAp and C-pQ superimpose above 16 K when plotted vs T/Theta(0) using the experimental Theta(0Ap)=455(3) K and an adjusted Theta(0ApQ)=480(4) K. The 300 K elastic constants extrapolated to T=0 give Theta(0Q)(el)=505(1) K, suggesting that the normalization is valid only above 16 K. The lattice contribution to C-pAp (and, indirectly, C-pQ) shows strong (unique) deviations from Debye-like behavior (+3% at 0.84 K for the C-pAp data fit). The various Gruneisen parameters (Gamma) that are calculated from these data all are positive and normal in magnitude except for a large limiting approximant lattice value, Gamma(0Ap)(lat)=11.3, which may be related to the large dispersion effects in C-p. For the approximant, the combination of anisotropic and large resistivities, a small diamagnetic susceptibility, and a "large" linear (electronic) contribution to C-pAp (gamma(Ap)=0.794 mJ/mol K-2) suggests the existence of a pseudogap in the electronic density of states. The unusually large, highly volume dependent, dispersion at low temperatures for the quasicrystal and its approximant are not consistent with inelastic neutron scattering and other data, and raise questions about the role of phonons in quasicrystals. The present 300 K resistivities can be used with a published correlation to estimate gamma(Q)approximate to0.25 mJ/mol K-2.
Title:
Total-energy-based prediction of a quasicrystal structure
Authors:
Mihalkovic, M; Al-Lehyani, I; Cockayne, E; Henley, CL; Moghadam, N; Moriarty, JA; Wang, Y; Widom, M; Ohl, M;
Source:
PHYSICAL REVIEW B, 65 (10); 2002
Abstract:
Quasicrystals are metal alloys whose noncrystallographic symmetries challenge traditional methods of structure determination. We employ quantum-based total-energy calculations to predict the structure of a decagonal quasicrystal from first-principles considerations. Our Monte Carlo simulations take as input the knowledge that a decagonal phase occurs in Al-Ni-Co near a given composition and use a limited amount of experimental structural data. The resulting structure obeys a nearly deterministic decoration of tiles on a hierarchy of length scales related by powers of tau, the golden mean.
Title:
Magnetic structures of RbCuCl3 in a transverse field
Authors:
Jacobs, AE; Nikuni, T; Fukuyama, H;
Source:
PHYSICAL REVIEW B, 65 (17); 2002
Abstract:
A recent high-field magnetization experiment found a phase transition of unknown character in the layered, frustrated antiferromagnet RbCuCl3, in a transverse field (in the layers). Motivated by these results, we have examined the magnetic structures predicted by a model of RbCuCl3, using the classical approximation. At small fields, we obtain the structure already known to be optimal, an incommensurate (IC) spiral with wave vector q in the layers. At higher fields, we find a staircase of long-period commensurate (C) phases (separated initially by the low-field IC phase), then two narrow IC phases, then a fourth IC phase (also with intermediate C phases), and finally the ferromagnetically aligned phase at the saturation field H-S. The three-sublattice C states familiar from the theory of the triangular antiferromagnet are never optimal. The C phases and the two intermediate IC phases were previously unknown in this context. The magnetization is discontinuous at a field approximate to0.4H(S), in qualitative agreement with experiment, though we find much fine structure not reported.
Title:
Linear increase of the conductivity with the concentration of local defects in AlPdMn quasicrystals
Authors:
Prejean, JJ; Berger, C; Sulpice, A; Calvayrac, Y; Thiel, PA;
Source:
PHYSICAL REVIEW B, 65 (14); 2002
Abstract:
We find a linear relation between the conductivity sigma and the Mn spin concentration x in pure AlPdMn single grains of high structural quality. We associate the vanishing concentration of Mn spins (down to 4x10(-5) moments) to local defects in the Mn atoms local environments. Both sigma and x are set by the nominal composition and can be reversibly tuned by careful heat treatments. We deduce that low sigma characteristics of perfect AlPdMn quasicrystals can only be observed for concentrations of magnetic Mn lower than x<5x10(-4), i.e., for defects more than about 30 Angstrom apart. In addition, we show that a Kondo-like effect explains the low-temperature sigma upturn, also linear with x.
Title:
Organic superconductor with an incommensurate anion structure: (MDT-TSF)(AuI2)(0.44)
Authors:
Kawamoto, T; Mori, T; Takimiya, K; Kataoka, Y; Aso, Y; Otsubo, T; Zayats, AV;
Source:
PHYSICAL REVIEW B, 65 (14); 2002
Abstract:
The degree of charge transfer and the upper critical field of the organic superconductor (MDT-TSF)(AuI2)(x) have been investigated (MDT-TSF: methylenedithio-tetraselenafulvalene). The x-ray oscillation photograph indicates that the anion lattice is incommensurate with the donor lattice, and the chemical composition is (MDT-TSF)(AuI2)(0.44). The charge-transfer degree of this salt is 0.44. The electrical resistivity and the Seebeck coefficient indicate that this salt is a good Fermi liquid above the superconducting transition temperature. The upper critical fields show anisotropic three-dimensional character in spite of the complicated incommensurate structure, and are within the Clogston-Chandrasekhar paramagnetic limit in all directions.
Title:
Optical conductivity of Al-Cr-Fe approximant compounds
Authors:
Demange, V; Milandri, A; de Weerd, MC; Machizaud, F; Jeandel, G; Dubois, JM; Zayats, AV;
Source:
PHYSICAL REVIEW B, 65 (14); 2002
Abstract:
We have studied the optical conductivity of several intermetallic compounds of the Al-Cr-Fe system in a broad range of frequencies. Depending on composition, the crystallographic structure of these compounds evolves from that of a close approximant of the decagonal phase to a gamma-brass structure, a superstructure of the beta-cubic phases. For comparison, pure icosahedral samples were studied as well in the same experimental conditions. Characteristically, as for this kind of aperiodic crystal, no Drude peak was observed at low frequencies in the Al-Cr-Fe approximant samples. By contrast, such a peak was recovered in the gamma-brass sample, which furthermore showed evidence of anisotropic conductivity. Using our crystallographic data, the conductivity measurements and the corresponding optical indices were interpreted on the basis of tunneling transitions. We found good agreement between these results and a theoretical approach developed for aperiodic intermetallics assuming an anomalous diffusion of the electron wavepacket.
Title:
Antiferromagnetism in the Kondo lattice compound Ce2Pd3Si5
Authors:
Huo, DX; Sakurai, J; Kuwai, T; Mizushima, T; Isikawa, Y; Fernandez-Diaz, MT;
Source:
PHYSICAL REVIEW B, 65 (14); 2002
Abstract:
The antiferromagnetic ordering state of the Kondo lattice compound Ce2Pd3Si5 is ascertained by measuring the magnetic susceptibility chi, electrical resistivity rho, thermoelectric power S, and specific heat C. The system undergoes an antiferromagnetic transition through two steps at T-N1=8.0 K and T-N2=7.4 K. The ordering occurred at T-N1 might be incommensurate with the lattice, and followed by a change of magnetic structure from incommensurate to commensurate with the lattice at T-N2. The magnetic entropy reaches 0.8R ln 2 at 8.0 K. Thermoelectric power shows two positive peaks, one around 150 K and the other at 1.3 K, and a negative peak at 12 K. The crystal electric-field splitting levels are estimated to be Delta(1)=90+/-10 K and Delta(2)=470+/-50 K above the ground state, respectively.
Title:
Random anisotropy causes wide distributions of relaxation rates in Tb-Mg-Zn quasicrystals and amorphous DyAg
Authors:
Noakes, DR; Kalvius, GM; Hartmann, O; Mizushima, T;
Source:
PHYSICAL REVIEW B, 65 (13); 2002
Abstract:
"Power-exponential" zero-field (ZF) muon spin relaxation (muSR), where the power varies with temperature, as observed in icosahedral Tb8Mg42Zn50 and in amorphous (am-)DyAg, is shown to be consistent with a wide distribution of relaxation rates by construction of a closed-form relaxation function representing such a distribution that fits the muSR data. This relaxation function is obtained by Laplace transform of a "double-square" distribution of relaxation rates, an example of a distribution that is asymmetric about its mean so that its width can be larger than that mean, a property that is necessary to fit the more extremely nonexponential cases. Combination with the results of Dy-161 Mossbauer effect measurements in DyAg indicates that this behavior is due to random axial crystalline electric-field (CEF) anisotropy. In addition to creating the random distribution of moment pointing directions in the asperomagnetic ordered state of am-DyAg, this creates a wide distribution of splittings between the J(z)=J ground doublet and the first excited state, thus causing a wide distribution of rare-earth paramagnetic fluctuation rates, leading to the wide distribution of muon spin relaxation rates deduced above. The contrast of simple-exponential ZF-muSR in i-Gd8Mg42Zn50 with double-square-distribution relaxation in the Tb quasicrystal clearly indicates that a CEF mechanism, probably the same one, is causing the nonexponential relaxation in the Tb quasicrystal, as well.
Title:
Splitting rules for the electronic spectra of two-dimensional Fibonacci-class quasicrystals with one kind of atom and two bond lengths
Authors:
Yang, XB; Xing, D; Hartmann, O;
Source:
PHYSICAL REVIEW B, 65 (13); 2002
Abstract:
On the basis of the substitution rules for a one-dimensional Fibonacci-class chain, we construct two-dimensional Fibonacci-class quasicrystals with one kind of atom and two bond lengths. In the framework of the single-electron tight-binding nearest-interaction transfer model, we study the splitting rules of the electronic energy spectra for two-dimensional Fibonacci-class quasicrystals by means of a decomposition-decimation method based on a renormalization-group technique, and we also calculate the electronic energy spectra numerically. It is found that there exist only three kinds of clusters-nxn, nx(n+1), and (n+1)x(n+1)-for all classes of two-dimensional quasilattices, and that the electronic energy bands split as Ym-n-l. The general formula of the number for energy levels is obtained. We discover that there is a kind of so-called Fibonacci-class-number set for the parameters used to describe the energy-level number, and we obtain the set formulas. The experienced formula are sought out. The analytical results are confirmed by numerical simulations.
Title:
Electronic transport properties of high-resistivity icosahedral AlPdRe below 1 K
Authors:
Srinivas, V; Rodmar, M; Konig, R; Poon, SJ; Rapp, O; Cheong, SW;
Source:
PHYSICAL REVIEW B, 65 (9); 2002
Abstract:
The temperature dependence of the conductivity, sigma(T), and the magnetoresistance up to B = 6 T have been studied in the temperature range 0.01 Kless than or equal toTless than or equal to1 K for two differently prepared i-AlPdRe samples on the insulating side of the metal-insulator transition. sigma(T) for both samples was observed to saturate in zero magnetic field below about 20 mK. With increasing magnetic field the temperature dependence of the conductivity increased, and at 6 T, or(T,B = 6 T) was found to decrease linearly with decreasing temperature down to the lowest measurement temperature of 10 mK. The estimated value of the conductivity at T=0 K, sigma(0 K), was found to decrease strongly with increasing resistance ratio R [ = rho(4 K)/rho(295 K)] over a wide range of R values and for differently prepared samples, suggesting that a finite sigma(0,R) is a characteristic property of the icosahedral phase of high-resistivity i-AlPdRe. The magnetoresistance is positive below 1 K. The relation Deltarho(B)/rhosimilar toB(2) is followed at larger fields by a B-2/3 dependence. With decreasing temperature these characteristic field regions are successively depressed towards smaller magnetic fields and eventually become unobservable. A scaling of the magnetoresistance is found for data in the region Tless than or equal to1 K, Bless than or equal to6 T of the form [Deltarho(B)/rho]/T-alpha=f(B/T) for each sample, with alpha about 0.3 for both samples.
Title:
Scanning tunneling microscopy of an Al-Ni-Co decagonal quasicrystal
Authors:
Kishida, M; Kamimura, Y; Tamura, R; Edagawa, K; Takeuchi, S; Sato, T; Yokoyama, Y; Guo, JQ; Tsai, AP; Pavel'ev, DG;
Source:
PHYSICAL REVIEW B, 65 (9); 2002
Abstract:
The structure of an Al-Ni-Co decagonal (d-) quasicrystal has been investigated by scanning tunneling microscopy (STM). STM images with atomic-scale resolution have been obtained successfully for the surfaces of both tenfold and twofold planes. On the tenfold surface, large terraces and monoatomic-layer steps are formed. The symmetry of each layer is not decagonal but pentagonal and the two adjacent layers are related by the inversion symmetry. The step lines are rough, which can be attributed to the existence of many symmetrically equivalent low-energy steps. The atom adsorptions are often observed at locally symmetric sites. An analysis based on the high-dimensional description of the quasicrystalline structure has shown that the structure has nearly perfect quasiperiodic order for the decagonal quasicrystal. On the twofold surface, interlayer phason defects are observed, but the density of them is quite low. This fact indicates that the d-quasicrystal of the present sample is not in the random tiling state in which the configurational entropy related to the phason disorder stabilizes the quasicrystal.
Title:
Effective interactions in the stripe state of the two-dimensional Hubbard model
Authors:
Varlamov, S; Seibold, G; Cohen, E;
Source:
PHYSICAL REVIEW B, 65 (7); 2002
Abstract:
We investigate the structure of the pairing potential in the stripe phase of the two-dimensional Hubbard model. Based on the random-phase approximation we discuss in detail the interactions in the charge and spin channel and compare our calculations with related considerations in commensurate antiferromagnets. Our main finding is that due to the incommensurate charge-density wave formation the exchange of collective modes in the charge channel is significantly enhanced with respect to the spin-bag approach whereas due to the inhomogeneous charge distribution the coupling to transverse spin fluctuations tends to be suppressed.
Title:
Transversely modulated crystal structure of charge-orbital ordered manganites Nd1-xSr1+xMnO4 (x=2/3, 3/4)
Authors:
Nagai, T; Kimura, T; Yamazaki, A; Asaka, T; Kimoto, K; Tokura, Y; Matsui, Y; Wojtowicz, T;
Source:
PHYSICAL REVIEW B, 65 (6); 2002
Abstract:
The crystallographic superstructures of the charge-orbital ordered phases were investigated for layered manganites, Nd1-xSr1+xMnO4 (x=2/3, 3/4), by high-resolution electron microscopy (HREM) at low temperature. Transverse and sinusoidal structural distortion giving rise to the superstructure were successfully observed in HREM images at 80 K. We also performed the simulations of electron diffraction patterns and HREM images, which support the transverse modulations. The observation implies that a new kind of "Wigner-crystal" model-accompanied with a charge-density wave (CDW) of e(g) electrons-best explains the charge-orbital ordered state in the manganites.
Title:
Commensuration of the antiferroelectric incommensurate phase in Pb(CO1/2W1/2)O-3
Authors:
Watanabe, S; Koyama, Y; Yamazaki, A;
Source:
PHYSICAL REVIEW B, 65 (6); 2002
Abstract:
The antiferroelectric incommensurate phase in Pb(Co1/2W1/2)O-3 is incommensurate in both wavelength and direction of the wave vector characterizing the modulation. In this study, the crystallographic features of the incommensurate and commensurate phases in Pb(Co1/2W1/2)O-3 have been investigated by transmission electron microscopy to elucidate the details of commensuration to the commensurate phase. The wave vector of the modulation in the incommensurate phase was found to be k(I)=[1 - delta(I) 1 - delta(I) Delta(I)] with delta(I)approximate to0 and Delta(I)approximate to0, while the wave vector in the commensurate phase is given by k(c)=[1/2 1/2 0]. The important features of the incommensurate and commensurate phases are that the modulation modes with k(1) and k(c1) are transverse atomic displacements of the Pb ions associated with the Sigma(3) irreducible representation of the C-2v point group, and that another modulation with k(c2) = [110] takes place in the commensurate phase. The k(c2) modulation is associated with the X-10 representation corresponding to the antiparallel displacement of the Pb ions. The appearance of the k(c2) modulation is accompanied by that of a pseudoperiodic array of antiphase boundaries with a phase shift of pi, and thus the commensurate phase is a nearly commensurate phase. That is, commensuration of both wavelength and direction of the incommensurate modulation takes place via the introduction of the X-10 displacement with the antiphase boundaries. If the antiphase boundary is regarded as a discommensuration, the commensuration process of the antiferroelectric incommensurate phase to the commensurate phase is therefore characterized by the appearance of a discommensuration, not by its annihilation.
Title:
Electron spin resonance in an icosahedral Al63Cu25Fe12 quasicrystal
Authors:
Dolinsek, J; Arcon, D; Zorko, A; Klanjsek, M; Saylor, C; Brunel, LC; Brunet, P; Dubois, JM; Karczewski, G;
Source:
PHYSICAL REVIEW B, 65 (6); 2002
Abstract:
An electron spin resonance (ESR) study of an icosahedral Al63Cu25Fe12 quasicrystal is presented. The ESR signal originates from two kinds of electronic spins-the itinerant conduction electrons and the localized d moments of magnetic Fe atoms, The ESR spectra are very broad, extending over up to 5 T in the magnetic-field-sweep experiment. The ESR signal could be detected by a high-field transmission ESR spectrometer operating at a frequency 109.270 GHz, whereas the too-small field sweep of 0-1 T prevented the ESR signal of the Al63Cu25Fe12 quasicrystal to be fully observed by the conventional X-band reflection spectrometer. The ESR spectra are compared to the NMR spectra of the same sample. Both spectra are extremely broad and the origin of this large broadening is found to be similar in both cases, It results from the distribution of local electric fields that are present in quasicrystals due to the lack of translation periodicity of the quasiperiodic lattice and from the s-d exchance interaction between the conduction electrons and the localized Fe d moments. An anomalous temperature dependence of the ESR linewidth that broadens on cooling above 20 K, but narrows from 20 to 5 K by a factor 3.7, was detected. General aspects of the ESR spectroscopy in quasicrystals are also discussed.
Title:
Static magnetic correlations near the insulating-superconducting phase boundary in La2-xSrxCuO4
Authors:
Fujita, M; Yamada, K; Hiraka, H; Gehring, PM; Lee, SH; Wakimoto, S; Shirane, G; Dubois, JM;
Source:
PHYSICAL REVIEW B, 65 (6); 2002
Abstract:
An elastic neutron-scattering study has been performed on several single crystals of La2-xSrxCuO4 for x near a lower critical concentration x(c) for superconductivity. In the insulating spin-glass phase (x=0.04 and 0.053), the previously reported one-dimensional spin modulation along the orthorhombic b axis is confirmed. Just inside the superconducting phase (x=0.06), however, two pairs of incommensurate magnetic peaks are additionally observed corresponding to the spin modulation parallel to the tetragonal axes. These two types of spin modulations with similar incommensurabilities coexist near the boundary. The peak width kappa along the spin-modulation direction exhibits an anomalous maximum in the superconducting phase near x(c), where the incommensurability delta increases monotonically upon doping across the phase boundary. These results are discussed in connection with the doping-induced superconducting phase transition.
Title:
Electronic properties of quasiperiodic heterostructures
Authors:
Zarate, JE; Velasco, VR; Garzon, IL;
Source:
PHYSICAL REVIEW B, 65 (4); 2002
Abstract:
We study the electronic states of different GaAs-AlAs Fibonacci, Thue-Morse and Rudin-Shapiro quasiperiodic heterostructures grown along the [001] direction. We employ an empirical tight-binding Hamiltonian including spin-orbit coupling together with the surface Green-function matching method. We present results for different generations of the quasiperiodic heterostructures, formed by different building blocks. We compare these results with those of the constituent quantum wells and with those of heterostructures containing the same total number of GaAs and AlAs slabs after periodic repetition of the building blocks. The states in the energy regions near the conduction- and valence-band edges of GaAs do not exhibit any spectrum fragmentation. They show a strong localization of the local density of states in the GaAs layers, and they can be traced to the states of the isolated quantum wells.
Title:
Magnetic phase diagram Of CsCuCl3 for in-plane magnetic fields up to 14 T
Authors:
Bugel, R; Faisst, A; von Lohneysen, H; Wosnitza, J; Schotte, U; Wakimoto, S;
Source:
PHYSICAL REVIEW B, 65 (5); 2002
Abstract:
High-resolution specific-heat and magnetocaloric-effect measurements have been utilized to complement the magnetic phase diagram of the hexagonal antiferromagnet CsCuCl3 in fields up to 14 T aligned perpendicular to the c axis. The recently found additional incommensurate phase induced by thermal fluctuations could be resolved completely. It appears at about 4 T in a narrow temperature range, with a maximum width of only similar to70 mK and narrows towards higher fields extending up to similar to11 T. Within the low-temperature incommensurate phase, the magnetocaloric-effect data confirm another phase transition that may be explained by quantum fluctuations.
Title:
Resonant x-ray scattering study of magnetic ordering due to Fermi-surface nesting in SmNi2Ge2
Authors:
Islam, Z; Lang, JC; Vasiliu-Doloc, L; Srajer, G; Canfield, PC; Wakimoto, S;
Source:
PHYSICAL REVIEW B, 65 (5); 2002
Abstract:
We report the results of x-ray resonant scattering studies of samarium nickel germanide (SmNi2Ge2) compound. We confirm that the magnetic structures of this material are in accordance with Fermi-surface nesting as was hypothesized earlier, SmNi2Ge2 orders in an incommensurate anti ferromagnetic (AF) structure characterized by a single propagation vector q = (0,0,q(z)). The value of q(z) is temperature dependent and approaches similar to0.775 r.l.u. near T-N = 17.7 K. Below T-t = 11.8 K, the AF structure is characterized by q(z) = 0.79 +/- 0.002, indicating a long-period-ordered phase. Ordered moments are confined to the basal plane in both the phases, as evidenced by the Q dependence of the magnetic-peak intensities. The temperature dependence of the magnetic structures is consistent with the "superzone" gap theory. In addition, a strong quadrupolar resonance below the Sm L-III edge was observed and compared to recent theoretical work.
Title:
Effects of the biquadratic exchange coupling on the localization and scaling laws of spin waves in Fibonacci superlattices
Authors:
Bezerra, CG; Cottam, MG; Vasiliu-Doloc, L;
Source:
PHYSICAL REVIEW B, 65 (5); 2002
Abstract:
In this paper we study the spin wave spectra of quasiperiodic magnetic superlattices following a Fibonacci sequence. We consider superlattices that are composed of two simple cubic ferromagnetic materials which interact by bilinear and biquadratic exchange couplings at the interfaces. A transfer matrix treatment is employed with the calculations carried out for the exchange dominated regime within the framework of the Heisenberg model and taking into account the random phase approximation (RPA). The numerical results obtained show the effects of the biquadratic exchange coupling on the localization and scaling laws of the spin wave bulk bands.
Title:
Local order in liquids forming quasicrystals and approximant phases
Authors:
Simonet, V; Hippert, F; Audier, M; Bellissent, R; Mochizuki, H;
Source:
PHYSICAL REVIEW B, 65 (2); 2002
Abstract:
Neutron-scattering experiments were performed on liquid Al-88.5(MnxCr1-x)(11.5) alloys (0less than or equal toxless than or equal to1), giving rise to equilibria with mu phase compounds whose structure is closely related to those of quasicrystalline phases. Assuming a Mn/Cr isomorphic substitution like the one existing in the A phase, partial pair structure factors and corresponding correlation functions were determined in these liquids. The results show a strong (Mn-Cr)-Al chemical order where the average first coordination shell around transition-metal atoms appears to be in agreement with an icosahedral local order. Simulations based on liquid models containing icosahedral clusters like those existing in many Al-Mn-Cr intermetallic structures are found to reproduce the liquid total structure factors measured at large momentum transfer where the influence of local order is preponderant. Information on icosahedral local order is also obtained when such a simulation method is applied to other liquid alloys, Al92.3Mn7.7, Al81Pd19, and Al72.1Pd20.7Mn7.2, giving rise to approximant or quasicrystalline phases, but in which partial functions are not determined.
Title:
Electronic transport in quasiperiodic decagonal aluminum
Authors:
Krajci, M; Hafner, J; Mihalkovic, M; Bellissent, R;
Source:
PHYSICAL REVIEW B, 65 (2); 2002
Abstract:
We present ab initio calculations of the electronic transport properties of a hypothetical monoatomic quasiperiodic system, decagonal aluminum (d-Al). Our aim is to study the influence of quasiperiodicity on the transport properties at the example of a system which is sufficiently realistic to represent real Al-based quasicrystals, but does not involve the additional complexity of a strong s,p-d hybridization which determines the properties of many crystalline and quasicrystalline Al-transition-metal alloys. The structure of d-Al is based on the densest known quasicrystalline sphere packing, the local atomic arrangement is closely related to crystalline face-centred-cubic Al. The investigation of the transport properties of a series of six periodic approximants with increasing Linear dimensions is based on a self-consistent calculation of the electronic eigenstates and the Kabo-Greenwood formula. A detailed scaling analysis demonstrates small deviations of the eigenstates from extended behavior and shows that the transport properties belong to the sub-ballistic regime, which a scaling exponent of the electronic diffusivity of betasimilar to0.6 that is somewhat larger than the quantum-diffusion limit (beta = 0.5), but distinctly smaller than for ballistic transport (beta = 1). In this sub-ballistic or overdiffusive regime them conductivity diverges in the thermodynamic limit, leading to metallic behavior.
Title:
Comment on "Low-temperature lattice excitation of icosahedral Al-Mn-Pd quasicrystals"
Authors:
Wang, JB; Qin, YL; Maradudin, AA;
Source:
PHYSICAL REVIEW B, 65 (2); 2002
Abstract:
By generalizing the wave propagation theory in crystalline solids to icosahedral quasicrystals (IQC's), Li and Liu [Phys. Rev. B 63, 064203 (2001)] introduced the contribution of phasons to the lattice vibration of quasicrystals to interpret the distinctly large heat capacities of Al-MD-Pd IQC at low temperature [Phys. Rev. B 57, 10 504 (1998)]. However, we find that Li and Liu adopted several different coordinate systems for IQC's in their paper without any appropriate coordinate transformation. When the correct coordinate transformation is exploited, the calculated results disagree totally with the experimental ones.
Title:
Reply to "Comment on 'Low-temperature lattice excitation of icosahedral Al-Mn-Pd quasicrystals' "
Authors:
Li, CL; Liu, YY; Maradudin, AA;
Source:
PHYSICAL REVIEW B, 65 (2); 2002
Abstract:
In response to the comment by Wang and Qin, we have rewritten our equation (22) following the coordinate system of Dina, et al. [J. Wuhan Univ. (Nature Science Edition) 3, 23 (1992)]. According to the thermodynamic stability condition and the experiment of Capitan et al., we have chosen the new parameters of the phason elastic constants. Based on this, we have recalculated the coefficients of the expressions on the vibrational denty of states and the specific heat of the icosahedral Al-Nin-Pd quasicrystal. Our results are still in agreement with the experimental data measured by Walti et al. [Phys. Rev. B 57, 10 504 (1998)]. It demonstrates that our method is useful for dealing with the low-temperature vibrational excitation of icosahedral quasicrystals.
Title:
Critical statics and dynamics of the one-dimensionally incommensurately modulated crystal Rb2ZnBr4 studied by NMR
Authors:
Decker, F; Petersson, J; Irsch, M; Michel, D; Ogale, SB;
Source:
PHYSICAL REVIEW B, 65 (1); 2002
Abstract:
The critical statics and dynamics of the prototype incommensurate crystal Rb2ZnBr4 is investigated by nuclear-magnetization relaxation measurements in quadrupolar-perturbed nuclear magnetic resonance of Rb-87. Within the frame of the so-called conventional model and for an order-disorder phase-transition mechanism a general relationship is established between the anomalous behavior of the nuclear spin-lattice relaxation rate and the critical behavior of the crystal under investigation, which is assumed to be generally a nonclassical one. Based on this approach the experimental data can be consistently interpreted. The critical exponents derived fit nicely to the universality class of the three-dimensional XY model. The characteristic frequency of die critical dynamics of the order parameter (OP) slows down below the Larmor frequency used in the Rb-87 nuclear-magnetic-resonance relaxation-time measurements. In this particular case one can derive the characteristic frequency of the critical dynamics of the OP above T-t and of the phason below T-t from the Larmor frequency dependence of T-t. The amplitudon mode behaves like a usual soft mode whereas the phason mode stays soft in the entire incommensurately modulated phase. The latter can be described by a very small frequency gap below about 0.4 MHz. The critical behavior is discussed in a general context.
Title:
Tunneling states in Al-Li-Cu quasicrystals
Authors:
Bert, F; Bellessa, G; Giamarchi, T;
Source:
PHYSICAL REVIEW B, 65 (1); 2002
Abstract:
We report on measurements of the velocity of sound at low temperature in three samples of the alloy Al-Li-Cu: a single crystal of the cubic approximant phase R and two samples of the imperfect icosahedral phase T2, one of them after annealing to improve its structural quality. All samples exhibit glasslike properties. We analyze our results within the tunneling state model and show that the tunneling strength increases with the degree of the quasicrystalline order in the sample.
Title:
Characterization of modulation structure in La2CuO4.12 by electron diffraction
Authors:
Gao, M; Liu, GD; Che, GC; Zhao, ZX; Peng, LM; Laabs, FD;
Source:
PHYSICAL REVIEW B, 64 (22); 2001
Abstract:
The technique of electron diffraction has been used for characterizing the modulation structure in a heavily oxygenated La2CuO4.12 sample. Ordering with modulation directions in bc and ab plane was observed, and the strong dependence of the bc plane ordering on temperature and doping level was established. It was found that low temperature and high doping level enhance the ordering and favor a longer modulation period than otherwise. In some regions, a kind of modulation along c axis has also been found and concluded to be an indication of the staging behavior of the interstitial oxygen ions.
Title:
Crystalline ground states of an entropically stabilized quasicrystal model
Authors:
Lee, HK; Swendsen, RH; Widom, M; Zhao, ZX;
Source:
PHYSICAL REVIEW B, 64 (22); 2001
Abstract:
A binary Lennard-Jones alloy exhibits an entropically stabilized quasicrystal state in two dimensions at elevated temperatures. We consider the ground states of this model by calculating the convex hull of cohesive energy as a function of alloy composition. Only crystalline structures with rational values of the composition appear on vertices of the convex hull. In particular, at the irrational composition of the ideal quasicrystal structure, the ground state is a coexisting mixture of two nearby quasicrystal approximants.
Title:
Unusual spin-glass phase in icosahedral Tb-Mg-Zn quasicrystals
Authors:
Dolinsek, J; Jaglicic, Z; Chernikov, MA; Fisher, IR; Canfield, PC; Laabs, FD;
Source:
PHYSICAL REVIEW B, 64 (22); 2001
Abstract:
The nature of the spin state below the spin freezing temperature was studied in an icosahedral Th-Mg-Zn quasicrystal by thermoremanent dc magnetization time decay as a function of aging time and magnetic field. The system does not exhibit a highly degenerate free-energy landscape obeying an ultrametric organization of metastable states, which makes it essentially different from canonical spin glasses. The Th-Mg-Zn system can be considered as a special class of spin glass, which possesses some local order, but still preserves the notion of spin freezing.
Title:
Doping and temperature dependence of incommensurate antiferromagnetism in underdoped lanthanum cuprates
Authors:
Yuan, F; Feng, SP; Su, ZB; Yu, L; Canfield, PC;
Source:
PHYSICAL REVIEW B, 64 (22); 2001
Abstract:
The doping, temperature, and energy dependence of the dynamical spin structure factors of the underdoped lanthanum cuprates in the normal state are studied within the t-J model using the fermion-spin transformation technique. Incommensurate peaks are found at [(1 +/- delta) pi, pi], [pi, (1 +/- delta) pi] at relatively low temperatures, with delta linearly increasing with doping at the beginning and then saturating at higher dopings, These peaks broaden and weaken in amplitude with temperature and energy, in good agreement with experiments. The theory also predicts a rotation of these peaks by pi /4 at even higher temperatures, being shifted to [(1 +/- delta/ root2)pi, (1 +/- delta/ root2)delta].
Title:
Debye-Waller factors in a quasicrystal (vol B 63, art. no. 014202, 2000)
Authors:
Colella, R; Zhang, Y; Sutter, JP; Ehrlich, SN; Kycia, SW; Laabs, FD;
Source:
PHYSICAL REVIEW B, 64 (22); 2001
Abstract:
We examine the electronic state of the electron stripe which can be realized to stabilize local polarization mainly caused by the ion displacement in the c axis direction. In an undoped state, the electrons in the ground state are well localized to form a 2D electron-hole lattice with an antiferromagnetic (AF) order in the stripe direction. From the stability of the elementary excitation of the electron stripe, the lattice constant in the stripe direction, D-a, is restricted as 6 Angstrom less than or similar to D-a less than or similar to 8 Angstrom. Upon doping carriers, when the AF state is partially violated due to the transfer (hopping) of the localized charges, the lower bound to D-a tends to be reduced to around 4 A. Given the superconductivity (SC) mediated through the interaction with the elementary excitation of the electron stripe, the optimal transition temperature T-c can be written as T(c)approximate toc/D-a(5/2), where c is some structure-dependent constant. If the electron stripe exists in layered cuprates, where c is around 100 K.(4 Angstrom)(5/2), it is found that SC with T-c of order 100 K can be realized.
Title:
Powder neutron diffraction and TEM investigations of Bi(0.775)Ln(0.225)O(15) oxide conductors (Ln=La, Pr, Nd, Sm,Tb, Dy) with rhombohedral Bi-Sr-O type: Structural relationships with monoclinic epsilon-Bi4.86La1.14O9 form
Authors:
Obbade, S; Huve, M; Suard, E; Drache, M; Conflant, P;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 168 (1): 91-99; 2002
Abstract:
Structural investigations of Bi(0.775)Ln(0.225)O(1.5) phases with rhombohedral Bi-Sr-O type, have been carried out using complementary techniques. Average crystal structures were refined from neutron diffraction powder data using the Rietveld method for Ln = La, Pr, Nd and Th. The comparison with the monoclinic Bi4.86La1.14O9 structure previously determined using the same technique has been done. For both types of structure, a piling of slabs constituted of a (Bi-(1), Ln) oxide layer, inserted between two Bi-(2) oxide layers, is observed. In the rhombobedral phases there are moreover oxide ions in the inter-slab spaces responsible for the well-known conductivity of these phases, while in the monoclinic Bi4.86La1.14O9 structure, the absence of oxygen in the inter-slab spaces, is compensated with the presence of the B-(2) lone pair electrons localized at a significant distance (congruent to1.20 Angstrom), which participate in the cohesion of the crystal structure. TEM study of Bi(0.775)Ln(0.225)O(1.5) samples, has confirmed the existence of superstructures for these phases and has allowed to propose two types (respectively for La and for Nd, Sm, Tb or Dy) of q(1)* and q(2)* modulation wave vectors. (C) 2002 Elsevier Science (USA).
Title:
Relationship between the structure modulation and cation non-stoichiometry in the "Bi-232" ferrate
Authors:
Sedykh, V; Smirnova, IS; Bagautdinov, B; Hagiya, K; Suvorov, EV; Dubovitskii, AV; Shekhtman, VS;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 377 (4): 553-560; 2002
Abstract:
The behavior of the modulated structure in the single crystals of Bi-232 ferrates, which are isostructural with superconducting Bi-2212 cuprates, depending on the variation of the Bi and Sr content has been investigated by X-ray diffraction methods, electron microscopy and Mossbauer spectroscopy. It has been shown that in the synthesis a molar ratio Bi:Sr differs always from 2:2, there are the excess of Bi and deficiency of Sr. The optimal composition (Bi-2(Bi0.4Sr1.4)SrFe2Ox) exists at which, as a rule, the 232Fe compound with a higher symmetry is synthesized, in this case the distortions of environment of atoms are minimal and the modulation is commensurate, q* = 0.2b* + c*. When the Bi concentration is deviated from the optimal composition, the structure becomes monoclinic, the lattice parameters b, c, and V increase, the lattice parameter a increases as the Bi content increases. The increase in the Bi concentration relative to the optimal composition leads to the increase in the modulation wave vector q* = 0.215b* + c*, the modulation becomes incommensurate. The deviation of the Bi concentration from the optimal composition results in the increase in the value of quadrupole splitting (QS) of the main doublet of the Mossbauer spectrum (from 1.02 mm/s for the optimal composition with a higher symmetry to similar to1.08 mm/s when the composition is deviated from it), i.e. the increase in the distortion of environment of Fe atoms occurs. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Effect of Bi doping on the modulated composite structure of (Sr2Cu2O3)(0.70)CuO2, "Sr14Cu24O41"
Authors:
Gotoh, Y; Yamaguchi, I; Akimoto, J; Takahashi, Y; Akimitsu, J; Dubovitskii, AV;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 378 (4): 131-136; 2002
Abstract:
The effect of Bi doping on the modulated composite structure of (Sr2Cu2O3)(0.70)CuO2 has been extensively investigated on the basis of (3 + 1)-dimensional superspace group approach. By applying the bond-valence-sum method for the modulated composite structure, it has become apparent that the valence state of the Cu atom in any sites of the Cu2O3 ladder in (Sr2-xBixCu2O3)(0.70)CuO2 is maintained divalent. The interatomic distance between the Cu atom in the two-legged Cu2O3 ladder and the 0 atom in the CuO2 chain becomes larger with Bi doping, in spite of the slight shrinkage of lattice dimension along the stacking direction. The hole transfer from the CuO2 chain to the Cu2O3 ladder in (Sr2Cu2O3)(0.70)CuO2 is depressed by the effect of Bi doping on the atomic modulations. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Crystallographic features of La1-xSrxMO3 with M = Cr and Fe in the vicinity of the R(3)over-bar-c/Pbnm phase boundary
Authors:
Arao, M; Shindo, H; Asada, T; Koyama, Y; Akimitsu, J;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 378 (4): 137-141; 2002
Abstract:
Crystallographic features of La1-xSrxMO3 with M = Cr and Fe in the vicinity of the R3c/Pbnm phase boundary have been examined mainly at room temperature by transmission electron microscopy. When the Sr content x increases from x = 0, the change in crystal structure from Pbnm to R (3) over barc was confirmed to occur at room temperature in La1-xSrxCrO3 around x = 0.2. In La1-xSrxFeO3, On the other hand, the incommensurate phase was found to exist between the Pbnm and the R (3) over barc phases. The analysis of the electron diffraction patterns obtained in the work indicated that the normal structure of the incommensurate structure and the direction of the modulation could, respectively, be identified as the Pbnm structure and one of the <323> directions. It was also suggested that the rotational displacement Of the oxygen octahedra involved in the Pbnm structure should be modulated in the incommensurate structure. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
In-plane anisotropy on the transport properties in the modulated Bi2O2-based conductors Bi-2212 and Bi-Sr-Co-O
Authors:
Fujii, T; Terasaki, I; Watanabe, T; Matsuda, A; Akimitsu, J;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 378 (4): 182-186; 2002
Abstract:
We investigated the in-plane anisotropy on the resistivity and thermopower of the Bi2Sr2CaCu2O8+delta (Bi-2212) and Bi-Sr-Co-O (BiCo) single crystals. In Bi-2212, the b-axis resistivity is higher than the a-axis resistivity, and is expressed as a sum of the a-axis resistivity and an additional residual resistivity. A downward deviation due to pseudogap is observed below a characteristic temperature T* which is isotropic in the form of conductivity. These results suggest that the modulation structure along the b-axis works as an anisotropic scattering center, but does not affect the pseudogap formation. On the other hand, the anisotropy of the resistivity and the thermopower in Pb-doped BiCo is substantial, probably owing to the misfit structure between the hexagonal CoO2 layer and the rock-salt Bi2O2 layer. However, the anisotropy in the resistivity in Pb-free BiCo is very small, suggesting that the inplane anisotropy is averaged by the modulation structure, whose direction is tilted by 45degrees from the a- and b-axis. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Stripes in the three-band Hubbard model of high-T-c cuprates
Authors:
Yanagisawa, T; Koike, S; Miyazaki, M; Koikegami, S; Yamaji, K; Dubovitskii, AV;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 378 (4): 292-297; 2002
Abstract:
We study the incommensurate ground state of the two-dimensional three-band Hubbard model for the oxide high-T-c superconductors by using a variational Monte Carlo method. We examine the effect of holes doped into the antiferromagnetic background in the underdoped region. It is shown that the modulated spin structures are stabilized and there is a region where the incommensurability is proportional to the doping ratio. Our results give a consistent description of stripes observed by the neutron-scattering experiments. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Anomalous states of the crystal structure of (Rb-0.1(NH4)(0.9))(2)SO4 solid solutions in the temperature range 4.2-300 k
Authors:
Shmyt'ko, IM; Afonikova, NS; Torgashev, VI; Tanabe, K;
Source:
PHYSICS OF THE SOLID STATE, 44 (11): 2165-2170; 2002
Abstract:
Crystals of (Rb-0.1(NH4)(0.9))(2)SO4 solid solutions are studied using x-ray diffractometry. It is revealed that the temperature dependence of the lattice parameter a exhibits an anomalous behavior, namely, the "invar effect" at temperatures above the ferroelectric phase transition point T-c and an anomalous increase in the temperature range from T-c to the liquid-helium temperature. An anomalous increase in the lattice parameter a and an increase in the intensity of Bragg reflections with a decrease in the temperature are interpreted within the model of the coexistence of two sublattices hypothetically responsible for the ferroelectric phase transition. A series of superstructure reflections observed along the basis axes corresponds to a sublattice formed in the matrix of the host structure. Analysis of the ratio between the lattice parameters of these structures allows the inference that, in the temperature range 4.2-300 K, the structure of the crystal under investigation can be considered an incommensurate single-crystal composite. (C) 2002 MAIK "Nauka/Interperiodica".
Title:
Structural realization of the polytope approach for the geometrical description of the transition of a quasicrystal into a crystalline phase
Authors:
Kraposhin, VS; Talis, AL; Dubois, JM; Gupta, A;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (39): 8987-8996; 2002
Abstract:
A geometrical model is proposed for the recently observed transformation under the action of highly localized stresses during the surface scratch test of the icosahedral phase into a body-centred cubic (BCC) phase, the disordered version of the B2 phase with the CsCl structure, which occupies a large portion of the Al-Cu-Fe phase diagram around the Al-50(Cu, Fe)(50) concentration. The model is founded on a polytope concept and the concept of the eight-dimensional root lattice E-8. In accordance with these concepts many crystalline or quasicrystalline structures can be derived from the polytope (the four-dimensional polyhedron) by fulfilling operations of lowering its local curvature with subsequent mapping of decurved polytope fragments onto Euclidian three-dimensional space. The properties of the Es lattices crive foundation to the possibility of mapping a quasicrystalline structure on a crystalline structure. The structural transformation is effected through intermediate atomic configurations coinciding with both structures, which are determined by a four-dimensional icosahedron the (3, 3, 51 polytope). For the transformation of the icosahedron of the icosahedral phase into a rhombic dodecahedron of the cubic B2 phase, the cubic A15 structure plays the role of an intermediate configuration since it can be represented as a three-dimensional packing of linearly interlaced chains of Frank-Kasper polyhedra with coordination numbers Z = 12 (icosahedron) and Z = 14. The transition between the rhombic dodecahedron of a B2 structure and the Frank-Kasper polyhedron with Z = 14 requires insertion of disclination quadruplets into some facets of the rhombic dodecahedron. The proposed geometrical model can be applied also to the polymorphic BCC-FCC transformation since the Miller indices of the Frank-Kasper polyhedron with Z = 14 coincide with the observed indices of habit planes of iron martensites.
Title:
Nuclear quadrupole resonance spectrum and transition from the incommensurate phase to the commensurate phase of a crystal
Authors:
Popov, MA; Tikhonov, D;
Source:
PHYSICS OF THE SOLID STATE, 44 (10): 1944-1948; 2002
Abstract:
The relationships describing the nuclear quadrupole resonance spectrum in the vicinity of the transition from the incommensurate phase to the commensurate phase of a crystal are derived in the adiabatic approximation. It is demonstrated that the intensity of the nuclear quadrupole resonance peaks depends on the mutual orientation of the order parameter and the electric field gradient. (C) 2002 MAIK "Nauka/Interperiodica".
Title:
Crystal structure of diserinesulfate monohydrate
Authors:
Smolin, YI; Lapshin, AE; Drozdova, IA; Westerholt, K;
Source:
PHYSICS OF THE SOLID STATE, 44 (10): 1972-1975; 2002
Abstract:
The crystal structure of DL-Serine H2SO4 . H2O is determined by single-crystal x-ray diffraction. The intensities of x-ray reflections are measured at three temperatures, namely, 295, 343, and 233 K. The crystal structure of the studied compound is refined using all three sets of intensities. It is demonstrated that, at a temperature of 233 K, the structure transforms into an incommensurately modulated state. This transformation is assumed to be responsible for the disappearance of the piezoresponse at this temperature. (C) 2002 MAIK "Nauka/Interperiodica".
Title:
Quasicrystalline epitaxial single element monolayers on icosahedral Al-Pd-Mn and decagonal Al-Ni-Co quasicrystal surfaces
Authors:
Franke, KJ; Sharma, HR; Theis, W; Gille, P; Ebert, P; Rieder, KH; Narayanasamy, A;
Source:
PHYSICAL REVIEW LETTERS, 89 (15): 1972-1975; 2002
Abstract:
Single element quasicrystalline monolayers were prepared by deposition of antimony and bismuth on the fivefold surface of icosahedral Al71.5Pd21Mn8.5 and the tenfold surface of decagonal Al71.8Ni14.8Co13.4. Elastic helium atom scattering and low energy electron diffraction of the monolayers show Bragg peaks at the bulk derived positions of the clean surfaces, revealing highly ordered quasicrystalline epitaxial films. Their adatom densities of (0.9+/-0.2)x10(15) cm(-2) and (0.8+/-0.2)x10(15) cm(-2) on Al-Pd-Mn and Al-Ni-Co, respectively, correspond to roughly one adatom per Al atom of the quasicrystalline substrate surfaces.
Title:
Electrical transport and optical properties of the incommensurate intergrowth compounds (SbS)(1.15)(TiS2)(n) with n=1 and 2
Authors:
Ren, Y; Ruscher, CH; Haas, C; Wiegers, GA; Gerbaldo, R;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (34): 8011-8023; 2002
Abstract:
The in-plane electrical transport and optical properties of the incommensurate intergrowth compounds (SbS)(1.15)(TiS2)(n) with n = 1, 2 have been investigated by means of measurements of the electrical resistivity, Hall coefficient and thermopower in the temperature range from 4.2 to 350 K, and by optical spectroscopy in the frequency range 1000-20000 cm(-1) at room temperature. Both the Hall effect and the thermopower indicate transport by electrons. The Hall coefficients show electron donation of about 0.57 and 0.34 of an electron per Ti atom for (SbS)(1.15)(TiS2)(n) with n = 1 and 2, respectively. The in-plane resistivity rho(ab)(T) exhibits a non-linear dependence on temperature, which can be described with the formula rho(ab)(T) = rho(0) + A(ee) (T/TF)(2) ln(T-F/T) as for a two-dimensional Fermi liquid. Fits according to the Drude model to the room temperature optical reflectivity show that the relaxation rate has a quadratic variation with frequency 1/tau(omega) similar to omega(2), also indicating Fermi-liquid behaviour with interelectronic collisions of quasiparticles, Only a small anisotropy in the ab-plane is observed in the optical spectra for the electrical field polarized parallel and perpendicular to the incommensurate direction.
Title:
Metallic mean-field stripes, incommensurability, and chemical potential in cuprates
Authors:
Lorenzana, J; Seibold, G; Haas, C;
Source:
PHYSICAL REVIEW LETTERS, 89 (13): 8011-8023; 2002
Abstract:
We perform a systematic slave-boson mean-field analysis of the three-band model for cuprates with first-principle parameters. Contrary to widespread belief based on earlier mean-field computations low doping stripes have a linear density close to 1/2 added hole per lattice constant. We find a dimensional crossover from 1D to 2D at doping similar to0.1 followed by a breaking of particle-hole symmetry around doping 1/8 as doping increases. Our results explain in a simple way the behavior of the chemical potential, the magnetic incommensurability, and transport experiments as a function of doping. Bond centered and site-centered stripes become degenerate for small overdoping.
Title:
The crystal structure of Sr2TiSi2O8
Authors:
Hoche, T; Neumann, W; Esmaeilzadeh, S; Uecker, R; Lentzen, M; Russel, C; Hellstrom, EE;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 166 (1): 15-23; 2002
Abstract:
Sr2TiSi2O8 single crystals were grown by Czochralski pulling and from a high-temperature solution. X-ray diffractometry revealed the modulated crystal structure of Sr2TiSi2O8 to belong to the 5D superspace group P4bm (- alpha, alpha, 1/2; alpha, alpha, 1/2) with alpha = 0.3. Atomic positions, anisotropic displacement factors and positional modulation parameters for Sr2TiSi2O8 are determined and discussed. The positional modulation is further investigated by electron diffraction and high-resolution transmission electron microscopy. In the latter experiments, the 2D modulation appears to be superimposed by some 1D modulation waves. This effect is discussed in terms of growth conditions. (C) 2002 Elsevier Science (USA).
Title:
Low-temperature magnetic properties of LuBaCuFeO5+delta and TmBaCuFeO5+delta
Authors:
Mombru, AW; Goeta, AE; Pardo, H; Lisboa, PN; Suescun, L; Mariezcurrena, RA; Ventura, ON; Behak, R; Andersen, KH; Araujo-Moreira, FM; Kim, MD;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 166 (1): 251-258; 2002
Abstract:
The crystal and magnetic structures of the perovskites LuBaCuFeO5+delta and TmBaCuFeO5+delta have been studied in the temperature range 2-170K by neutron powder diffraction. The best fit using the Rietveld method is obtained for the acentric tetragonal space group P4mm, with lattice constants a = 3.774(1)Angstrom, c = 7.474(2)Angstrom and a = 3.7812(2)Angstrom, c = 7.4854(4)Angstrom, for LuBaCuFeO5+delta and TmBaCuFeO5+delta, respectively (T = 2 K). The lattice parameters of the unit cell of the magnetic structure for these samples are a(M) = 2a and c(M) = 2c, with a magnetic propagation vector k = (1/2, 1/2, 1/2). A commensurate magnetic superstructure is detected by the presence of satellites surrounding the (1/2, 1/2, 1/2) magnetic peak at d similar to 5. 1 Angstrom, determined by c(Mcomm) = 8c. This superstructure could evolve at T > 170 K to a distribution of commensurate and even incommensurate superstructures. A transition to a simple antiferromagnetic structure occurs at T-2 = 303(3) K for LuBaCuFeO5+delta. Evidence of a strong spin freezing effect at T-1 = 14.0(5) K is provided through DC-susceptibility measurements. (C) 2002 Elsevier Science (USA).
Title:
Electronic structure in quasicrystalline compounds and related crystals
Authors:
Belin-Ferre, E; Svensson, G;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (31): R789-R817; 2002
Abstract:
This article reviews and discusses the most relevant results achieved over recent years from the study of the electronic structure of quasicrystals (QCs) and related alloys using basically densities-of-states calculations and the x-ray emission, x-ray absorption, and photoemission spectroscopic techniques, in agreement with information obtained by other experimental means. It focuses on Al-based systems, the most widely analysed so far, and also reports data for Zr-Ni-Ti as well as Mg-based compounds. The present knowledge of QCs and approximants as compared to conventional crystals of the same phase diagrams may be summarized as follows: (i) the occurrence of a pseudogap at the Fermi level that is also present at the very surface is well established for icosahedral QCs whose formation derives from both Hume-Rothery and Al-transition metal hybridization effects; (ii) the pseudogap does not exist in the total densities of states of decagonal QCs but always exists in the Al sub-bands; (iii) states in QCs and close approximants are of more localized-like character in the vicinity of the pseudogap at the Fermi level than in conventional intermetallics, and at greater distances, above as well as below the Fermi level, they are extended-like in character, signalling a clear tendency to weak electron localization especially effective on either side of the pseudogap. As a result, there is a progressive loss of the metallic character, that can be tuned intentionally, when going from usual crystals to approximants and QCs.
Title:
Interface-induced states with an incommensurate spin-density wave in Fe/Cr-type multilayers
Authors:
Men'shov, VN; Tugushev, VV; Bovin, JO;
Source:
PHYSICS OF THE SOLID STATE, 44 (9): 1727-1735; 2002
Abstract:
A model is proposed for magnetic ordering in Fe/Cr-type multilayers substantially above the Neel temperature of bulk chromium. Redistribution of the charge (and, hence, spin) density near the Fe/Cr interfaces gives rise to the formation of an essentially inhomogeneous spin-density-wave (SDW) state in the chromium spacer. The spatial structure of the antiferromagnetic order parameter in thick spacers is described. The SDW contribution to the effective exchange coupling between the moments in adjacent iron layers is calculated. The data obtained are used in the interpretation of experimental data on the tunneling spectroscopy of trilayers and neutron diffraction from Fe/Cr superlattices. (C) 2002 MAIK "Nauka/Interperiodica".
Title:
Cu-based icosahedral quasicrystal formed in Cu-Ga-Mg-Sc alloys
Authors:
Kaneko, Y; Maezawa, R; Kaneko, H; Ishimasa, T; Wahl, A;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 82 (9): 483-493; 2002
Abstract:
The first-reported Cu-based icosahedral quasicrystal has been found as an almost single phase in Cu48Ga34Mg3Sc15 alloy annealed at 1043 K for 61 h. On the basis of our experiments, this icosahedral quasicrystal is expected to be one of the equilibrium phases in this alloy system. Powder X-ray diffraction and electron diffraction experiments revealed that the quasicrystal exhibits a high degree of structural perfection and has a primitive type quasilattice with a six-dimensional lattice parameter a(6D) = 0.6938 nm. The existence of a Cu3.7Ga2.3Sc-type structure, which is a bee structure with diffraction symmetry m(3) over bar, suggests that the Cu-Ga-Mg-Sc quasicrystal is to be classified into a new structural type to which Cd-based icosahedral quasicrystals and the Zn-Mg-Sc quasicrystal belong. This new type has a characteristic local atomic configuration different from both Mackay-type and Bergman-type quasicrystals.
Title:
Persistent currents in k-component Fibonacci mesoscopic rings threaded by a magnetic flux
Authors:
Liu, YM; Peng, RW; Jin, GJ; Huang, XQ; Wang, M; Hu, A; Jiang, SS; Behak, R;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (30): 7253-7263; 2002
Abstract:
On the basis of the tight-binding model, we have studied the. energy spectra and persistent currents (PCs) in one-dimensional k-component Fibonacci (KCF) mesoscopic rings threaded by,a magnetic flux. The KCF structures, which contain k basic units, can be periodic (if k = 1), quasiperiodic (if 1 < k < 6), and intermediate cases between quasiperiodicity and disorder. (if k greater than or equal to 6). It. is shown that the flux-dependent eigenenergies form 'band' structure in the KCF rings. The subbatids possess the hierarchical characteristic with. self-similarity if 1 < k < 6, while if k greater than or equal to 6, there, is no obvious self-similarity in the subbands. In fact, the energy spectra ultimately determine the behaviour of the PCs in the mesoscopic KCF rings. On one hand, the PC depends on the. total energy bandwidth: the narrower the bandwidth, the smaller the PC. On the other hand, the parity effect of electrons is dissimilar in different KCF rings. As k increases, there is less likelihood of observing a dramatic change in currents of several orders of magnitude when one electron is added to or removed from the KCF rings. If k is large. enough, the current behaviour may approach some features of disordered systems.
Title:
Planar defects and incommensurate phases in highly ordered perovskite solid solutions
Authors:
Kornev, IA; Bellaiche, L; Kawasaki, Y;
Source:
PHYSICAL REVIEW LETTERS, 89 (11): 7487-7491; 2002
Abstract:
A first-principles-derived approach is used to study the effects of planar defects on structural properties of a rocksalt-ordered Pb(Sc0.5Nb0.5)O-3 alloy. These defects lead to unusual features, in-cluding a less symmetrical ground state with respect to the perfectly ordered material. We also propose that a simple and original mechanism, involving these defects, may be responsible for the existence and anomalous characteristics of the incommensurate phases observed in insulating perovskites.
Title:
Mechanical milling assisted by electrical discharge
Authors:
Calka, A; Wexler, D; Scalettar, RT;
Source:
NATURE, 419 (6903): 147-151; 2002
Abstract:
Mechanical milling is an effective technique for the preparation of fine metallic and ceramic powders and can also be used to drive a wide range of chemical reactions. Milling devices include planetary machines, attritors and vibrational mills; products include amorphous, nanocrystalline and quasicrystalline materials, supersaturated solid solutions, reduced minerals, high-surface-area catalysts and reactive chemicals(1-3). During milling, solid-solid, solid-liquid and solid-gas reactions are initiated through repeated deformation and fracture of powder particles. A separate materials synthesis and processing technique involves reacting a material in a gas atmosphere under an electrical discharge(4-7). Here we show that the application of low-current, high-voltage electrical impulses during milling can result in both faster reactions and new synthesis and processing routes. We demonstrate the effects of glow (cold) and spark (hot) discharge milling on particle fracture for brittle, low-conductivity materials and ductile metals. Glow discharge milling was found to promote solid-gas reactions whereas spark discharge milling promotes fast fracturing, recrystallization, mineral reduction and solid-solid reactions.
Title:
A new well-ordered simple icosahedral quasicrystalline phase in the Zn-Mg-Er system
Authors:
Sterzel, R; Gross, C; Kounis, A; Miehe, G; Fuess, H; Reutzel, S; Holland-Moritz, D; Assmus, W; DePinho, RA;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 82 (8): 443-450; 2002
Abstract:
A well-ordered simple icosahedral quasicrystalline phase has been found in the Zn-Mg-Er system. The structure of a splat-cooled and annealed sample was investigated by electron and X-ray powder diffraction. A quasilattice constant of 0.513 nm was determined by the Elser method.
Title:
Origin of the maximum in the temperature-dependent electrical resistivity of quasicrystals
Authors:
Dolinsek, J; Klanjsek, M; Jaglicic, Z; Bilusic, A; Smontara, A; Reutzel, S;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (28): 6975-6988; 2002
Abstract:
We discuss the origin of the maximum in the electrical resistivity rho(T) of quasicrystals (QCs) and show that it can be consistently explained as a magnetic effect due to the presence of localized magnetic scattering centres within the quasiperiodic lattice. On the experimental side we present a comparative electrical resistivity-magnetic susceptibility study of icosahedral AlPdMn and CdCa QCs and show correlation between the temperature of the rho(T) maximum and the electronic paramagnetic magnetization of localized magnetic centres. We propose a theoretical explanation in terms of the Korringa-Gerritsen (KG) model, originally developed for noble metals with diluted transition metal impurities. Unlike the other existing models of electrical conduction in QCs, the KG model describes the rho(T) maximum as a magnetic effect and predicts its shift to higher temperatures for an increased concentration of magnetic moments.
Title:
Composite crystal Sr8/7TiSy with y=2.84-2.97
Authors:
Saeki, M; Ohta, M; Kurashima, K; Onoda, M; Smontara, A;
Source:
MATERIALS RESEARCH BULLETIN, 37 (8): 1519-1529; 2002
Abstract:
Sr8/7TiSy (y = 2.84-2.97) has been prepared by controlling the partial pressure of sulfur. The XRD and the ED patterns could not be indexed because of incommensurate structures; they were, therefore, indexed by four-dimensional formalism with simple lattice parameters of A, C-Ti and C-Sr, in a hexagonal setting. However, a commensurate structure was obtained at y = 2.84 in Sr8/7TiSy, the XRD and ED patterns of which were indexed by three- and four-dimensional formalisms. The sulfides, including incommensurate and commensurate structures, could be regarded as a single phase with a homogeneity range of sulfur of y = 2.84-2.97, when the four-dimensional formalism was used. On the other hand, from the viewpoint of three-dimensional formalism, the structure contains two penetrating hexagonal subcells. The lattice parameter "a" in hexagonal setting is common to both subcells, while c is given by c = pC(Ti) = qC(Sr), where p and q are integers, and C-Ti and C-Sr are the periodicities in c-direction of the two subcells, respectively. Hence, there is an infinite number of the structures in the composition range of y = 2.84-2.97 in Sr8/7TiSy. (C) 2002 Published by Elsevier Science Ltd.
Title:
Atomic structure determination, electronic structure calculations and interpretation of electron transport properties of various 1/1-1/1-1/1 approximants
Authors:
Mizutani, U; Takeuchi, T; Sato, H; Onoda, M;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (27): R767-R788; 2002
Abstract:
The atomic structure of various 1/1-1/1-1/1 approximants has been extensively studied in the last decade to bridge the gap to that of the corresponding quasicrystal. Reliable information about electronic states in their valence bands has also been accumulated by using the atomic structure determined theoretically and experimentally. In this article, we have classified 1/1-1/1-1/1 approximants into three groups in terms of the structure type (P or F) and space group (Im (3) over bar or Pm (3) over bar) and discussed characteristic features of both atomic and electronic structures of 1/1-1/1-1/1 approximants in each group. The electrical resistivity behaviour is then discussed on the basis of the atomic and electronic structures thus determined.
Title:
Mossbauer and transport studies of amorphous and icosahedral Zr-Ni-Cu-Ag-Al alloys
Authors:
Stadnik, ZM; Rapp, O; Srinivas, V; Saida, J; Inoue, A; Reutzel, S;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (27): 6883-6896; 2002
Abstract:
The alloy Zr65Al7.5Ni10Cu7.3Fe0.2Ag10 in the amorphous and icosahedral states, and the bulk amorphous alloy Zr65Al7.5Ni10Cu7.5Ag10, have been studied with Fe-57 Mossbauer spectroscopy, electrical resistance and magnetoresistance techniques. The average quadrupole splitting in both alloys decreases with temperature as T-3/2. The average quadrupole splitting in the icosahedral alloy is the largest ever reported for a metallic system. The lattice vibrations of the Fe atoms in the amorphous and:icosahedral alloys are well described by a simple Debye model, with the characteristic Mossbauer temperatures of 379(29) and 439(28) K, respectively. Amorphous alloys Zr65Al7.5Ni10Cu7.5Ag10 and Zr65Al7.5Ni10Cu7.3Fe0.2Ag10 have been found to be superconducting with the transition temperature, T, of about 1.7 K. The magnitude of T, and the critical field slope at T, are in agreement with previous work on Zr-based amorphous superconductors, while the low-temperature normal state resistivity is-larger than typical results for binary and ternary Zr-based alloys. The resistivity of icosahedral Zr65Al7.5Ni10Cu7.3Fe0.2Ag10 is larger-than that for the amorphous ribbon of the same composition, as inferred both from direct measurements on the ribbons and from the observed magnetoresistance. However the icosahedral sample is non-superconducting in the measurement range down to 1.5 K. The results for the resistivity and the superconducting T-c both suggest a stronger electronic disorder in the icosahedral phase than in the amorphous phase.
Title:
Spin and charge order around vortices and impurities in high-T-c superconductors
Authors:
Zhu, JX; Martin, I; Bishop, AR; Mattausch, H;
Source:
PHYSICAL REVIEW LETTERS, 89 (6): 1607-1614; 2002
Abstract:
A comparative study is made for the spin and charge structure around superconducting vortices and unitary impurities, by solving self-consistently an effective Hamiltonian including interactions for both antiferromagnetic spin-density wave (SDW) and d-wave superconducting orderings. Around vortices, we show the induction of an SDW two-dimensionally modulated with a period of eight lattice constants (8a(0)) and an associated charge-density wave (CDW) with a period of 4a(0), which explains very well recent experimental observations. In the case of unitary impurities, an SDW modulation with identical periodicity, but without an associated CDW, is also predicted.
Title:
Evolution of the local structure with hydrogenation in Ti-Zr-Ni quasicrystals and approximants
Authors:
Sadoc, A; Majzoub, EH; Huett, VT; Kelton, KF; Collinson, I;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (25): 6413-6426; 2002
Abstract:
The effect of hydrogenation on the local structure of Ti-Zr-Ni alloys has been studied by means of extended x-ray absorption fine structure. The alloys were either icosahedral quasicrystals or crystalline approximants. They were loaded to different hydrogen-to-metal ratios 1.2 less than or equal to H/M less than or equal to 1.7. The desorption process was also investigated by studying the local order in an alloy charged to H/M = 1.2 then desorbed to H/M = 0.84. The local structure was identical in the crystalline and quasicrystalline alloys with the same H/M ratio (0 or 1.2) and that of the desorbed sample was intermediate between that of the nonhydrogenated samples and that of the samples charged to 1.2. Therefore, it is possible to follow the evolution of the local structure with hydrogenation from H/M = 0 to 1.7. A general increase-of all the mean first distances was found except for the Zr-Ni (Ni-Zr) one. There is a remarkable inversion of the atomic subshells of titanium and nickel in the first environment of zirconium atoms around H/M = 1. For the 1.56 hydrogenated sample, the effect of adding a small amount of lead, which stabilizes the icosahedral phase, was studied and it was demonstrated that lead atoms substitute for the nickel atoms and are, therefore, incorporated into the quasilattice.
Title:
HRTEM observations of structural and chemical modulations in cosalite and its relationship to the lillianite homologues
Authors:
Pring, A; Etschmann, B; Baughman, RH;
Source:
MINERALOGICAL MAGAZINE, 66 (3): 451-458; 2002
Abstract:
The results of a HRTFM and electron diffraction investigation of a Cu- and Ag-rich cosalite, Cu1.2Ag0.9Pb6.7Bi8.2S20. from Ivigtut. Greenland, are presented. Electron diffraction patterns down [001] show pairs of satellite reflections at G(p)+/-similar to1/8[140]* and G(p)+/-similar to1/8[(1) over bar 40]* in addition to the strong Bragg reflections of the Underlying average structure. The superlattice corresponds to a compositional and displacive modulation G+/-q(prim) where q(prim) is the primary modulation vector 1 18[140]*, The superlattice is attributed to Coupled Ag/Pb/Bi and Cu/square ordering and associated structural relaxation. The HRTEM images show a complex moire texture due to the structural modulations. Cosalite from Ivigtut, Greenland, also forms coherent intergrowths with members of the lillianite-gustavite series (Pb3Bi2S6-PbAgBi3S6). A model for the intergrowth between the structures is presented based on sharing both S and Pb atoms in the PbS-like slabs in both structures along [010](cosalite).
Title:
Magnetic field induced charge and spin instabilities in cuprate superconductors
Authors:
Franz, M; Sheehy, DE; Tesanovic, Z; Huang, GL;
Source:
PHYSICAL REVIEW LETTERS, 88 (25): 5979-6004; 2002
Abstract:
A d-wave superconductor, subject to strong phase fluctuations, is known to suffer an antiferromagnetic instability closely related to the chiral symmetry breaking in (2 + 1)-dimensional quantum electrodynamics (QED(3)). Based on this idea we formulate a "QED(3) in a box" theory of local instabilities of a d-wave superconductor in the vicinity of a single pinned vortex undergoing quantum fluctuations. As a generic outcome we find an incommensurate 2D spin density wave forming in the neighborhood of a vortex with a concomitant "checkerboard" pattern in the local electronic density of states, in agreement with recent neutron scattering and tunneling spectroscopy measurements.
Title:
Transformation of the decagonal quasicrystalline phase to a B2 crystalline phase in the Al-Cu-Co system by high-energy ball milling
Authors:
Mukhopadhyay, NK; Murthy, GVS; Murty, BS; Weatherly, GC; Nakano, T;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 82 (7): 383-392; 2002
Abstract:
Samples of a decagonal quasicrystalline phase, located in the Al-Cu-Co system and synthesized by a slow cooling technique, have been mechanically milled in a high-energy planetary ball mill for 10, 20 and 30 h. The milled powders, as well as powders that had been annealed (after milling) for times ranging from 30 to 150 min at 600degreesC, were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. A phase transformation from the decagonal phase to a B2 crystalline phase during high-energy ball milling is reported here for the first time. Powders milled for more than 10 h contained predominantly the B2-type crystalline phase with a lattice parameter of 0.29 nm. This crystalline phase was found to be quite stable after milling for 30 h and also on subsequent annealing at 600degrees C. These experimental results lend support to an earlier suggestion that the decagonal phase in Al-Cu-Co is actually less stable than the B2 phase at low temperatures.
Title:
Coexistence of charge density wave and antiferromagnetism in Er5Ir4Si10
Authors:
Galli, F; Feyerherm, R; Hendrikx, RWA; Dudzik, E; Nieuwenhuys, GJ; Ramakrishnan, S; Brown, SD; van Smaalen, S; Mydosh, JA; Dong, C;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (20): 5067-5075; 2002
Abstract:
Er5Ir4Si10 exhibits three phase transitions upon cooling below room temperature. At T-CDW = 151 K a combined commensurate and incommensurate superstructure develops, that has been attributed to the formation of charge density waves (CDWs). At T-LI = 60 K (LI = lock-in) the superstructure becomes commensurate, and at T-N = 2.8 K a state with long-range antiferromagnetic order develops. In this contribution we report the results of high-intensity, high-resolution x-ray diffraction for the temperature region encompassing all four phases. We have found that above T-CDW the critical scattering of the commensurate superlattice reflections persists up to much higher temperatures than the critical scattering of the incommensurate satellites. It is argued that this finding substantiates the hypothesis in which the mechanism of the CDW transition involves a structural transition towards a twofold superstructure. The superlattice reflections are found to be broader in the lock-in phase than above T-LI. This suggests that the lock-in transition results in relatively small domains, that are responsible for the broadening of the reflections. Finally, the anti ferromagnetic order is observed by resonant x-ray scattering. The commensurate superlattice reflections persist down to 1.87 K, and no effect of the magnetic transition on their positions or intensities is found. Thus the magnetic order and the CDW coexist below T-N in this compound.
Title:
A neutron diffraction study of the magnetic phases of CsCuCl3 for in-plane fields up to 17 T
Authors:
Stusser, N; Schotte, U; Hoser, A; Meschke, M; Meissner, M; Wosnitza, J; Brown, SD;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (20): 5161-5172; 2002
Abstract:
Neutron diffraction investigations have been performed to study the magnetization process of CsCuCl3 with the magnetic field aligned within the ab-plane. In zero field the stacked, triangular-lattice antiferromagnet (TLA) CsCuCl3 has a helical structure incommensurate in the chain direction normal to the ab-plane. The magnetic phase diagram was investigated from 2 K up to T-N in fields up to 17 T. The phase line for the expected incommensurate-commensurate (IC-C) phase transition could be determined throughout the whole phase diagram. At low temperature the IC-C transition is roughly at half the saturation field HS. The neutron diffraction patterns were found to be well described by a sinusoidally modulated spiral in fields up to H-S/3. The initial increase of the scattering intensity in rising field indicates a continuous reduction of the spin frustration on the triangular lattice. Between H-S/3 and H-S/2 a new phase occurs where the spiral vector has a plateau in its field dependence. Close to the IC-C transition a growing asymmetry of magnetic satellite-peak intensities indicates domain effects which are related to the lifting of the chiral degeneracy in the ab-plane in rising field. The phase diagram obtained has some similarities with those calculated for stacked TLAs by considering the effects of quantum and thermal fluctuations.
Title:
Electron microscopy studies of microstructures in beta-Ga2O3 single crystals
Authors:
Villora, EG; Murakami, Y; Sugawara, T; Atou, T; Kikuchi, M; Shindo, D; Fukuda, T; Konvicka, C;
Source:
MATERIALS RESEARCH BULLETIN, 37 (4): 769-774; 2002
Abstract:
Microstructures of as-grown and annealed beta-Ga2O3 single crystals were studied by electron microscopy. Energy filtered electron diffraction patterns exhibited weak diffuse scattering at 1/2 and 1/4 positions between the fundamental reflections along the q (20)((4)) over bar vector. Dark-field images observed with the 1/2 diffuse scattering showed a characteristic domain-like structure, where the size of each domain was less than 5 nm. The diffused scattering was somewhat weakened by annealing the specimen. The observations indicate a non-homo geneous structural modulation, which is considered to be related to the distribution of oxygen vacancies. (C) 2002 Elsevier Science Ltd. All rights reserved.
Title:
Phase separation in (Bi,Pb)(2.2)Sr2CaCu2O8+delta single crystals at an annealing at high oxygen pressure
Authors:
Kulakov, AB; Bdikin, IK; Zver'kov, SA; Emel'chenko, GA; Yang, G; Abell, JS; Fukuda, T;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 371 (1): 45-51; 2002
Abstract:
We report the phase transformation resultant from annealing of Bi-2212 single crystals doped by Pb (Pbo(0.3) per formula unit) under elevated oxygen pressure. General T-c vs. p(O2) dependence plotted by us in the range 7 x 10(-6) to 115 atm demonstrates a sharp bend. This knee indicates the phase transformation at annealings under p(O2) > I atm. The Xray topography data suggest that in addition to the phase of Pb-type modulation (q = 0.131b*) this transformation gives rise to another phase of Bi-type modulation (q = 0.200b* + c*). This process is reversible. We observed on individual crystals the twinning system analogous to that known for La2-xSrxCuO4 crystals. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
The crystal structure of Bi2PbMnO4(PO4)(2), a member of a new solid solution series in the Bi-Pb-Mn-P oxide system
Authors:
Cousin, O; Huve, M; Roussel, P; Perez, O; Steinfink, H; Abell, JS;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 165 (2): 324-333; 2002
Abstract:
Single crystals of a new oxyphosphate were found while exploring the Bi-Pb-Mn-P oxide phase diagram. The reaction product from a mixture of Bi2O3, PbO, MnO2, and (NH4)(2)HPO4 in the ratio 1:1:2:2 displayed several phases including a Bi-rich phase with the approximate composition (Bi3-xPbx)MnP2Oy and a Pb-rich phase with the approximate composition (BixPb4-x)MnP3Oy. A single crystal of the Bi-rich phase was selected. The title compound is tetragonal, P (4) over bar2(1)c, a = 13.275(3) Angstrom, c = 5.500(2) Angstrom, Z = 4. The structure refinement converged to R1 = 0.0442. On the basis of the X-ray diffraction refinement, the formula is Bi2PbMnP2O12. The crystal is an inverse twin. Electron diffraction revealed that the X-ray diffraction lattice parameters are from a subcell and the unit cell is 2a(sub), 2b(sub), 3c(sub). The detailed study of reciprocal space, reconstructed from observations made using single-crystal electron diffraction data, leads us to an apparent wave vector q* = 1/2a* + 1/2b* + 1/3c*, compatible with the Bravais lattice 4/mmmP (1/2 1/2 gamma). However, this choice leads to forbidden reflections, e.g. h00, h = 2n + 1, due to the presence of a 2, axis. An assumption that the crystal consists of a modulated, twinned orthorhombic structure with space group Ccc2 based on the cell root2a, root2a, c leads to a modulation vector q* = a* + gammac*. The (3 + 1)-dimensional Bravais lattice becomes mmmC(10gamma) and the super space group is Ccc2(10gamma). The refinement of the single crystal X-ray diffraction data based on Ccc2 consisting of two 90degrees twin domains led, as expected, to the identical result as the refinement in P (4) over bar2(1)c.The crystal structure was determined from the X-ray diffraction intensities based on the subcell and hence represents an averaged structure. The PO4 radical can be present in two orientations. Pb occupies only 1/2 of the crystallographic 8e positions. The Ph atoms bond through oxygen atoms from PO4 to form
Title:
Arrangement of atomic clusters in a 2/1 cubic approximant in the Al-Zn-Mg alloy system
Authors:
Hiraga, K; Sugiyama, K; Ishii, Y; Osterwalder, J;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 82 (6): 341-347; 2002
Abstract:
An arrangement of the so-called Bergman clusters of atoms in a 2/1 cubic crystalline approximant phase, which is closely related to Frank-Kasper-type icosahedral quasicrystals, in an Al-Zn-Mg alloy system is discussed in detail. The 2/1 cubic structure has eight Bergman clusters in its unit cell and the positions of the clusters can be understood as twelvefold sites in the 2/1 cubic approximant of the three-dimensional Penrose lattice. The atomic clusters are located at vertices of two types of rhombohedron, which are formed by six rhombic planes with an edge length of 3(1/2) atau(2)/(tau(2) + 1)(1/2) and a shorter diagonal of 2atau(2)/(tau(2) + 1)(1/2) (tau is the golden ratio and a is a quasilattice constant), which correspond to half a body diagonal and an edge length respectively of the 1/1 cubic approximant unit cell. The present results provide an important key for understanding the arrangements of atomic clusters in icosahedral quasicrystals.
Title:
Stable icosahedral quasicrystals in the Ag-In-Ca, Ag-In-Yb, Ag-In-Ca-Mg and Ag-In-Yb-Mg systems
Authors:
Guo, JQ; Tsai, AP; Ishii, Y;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 82 (6): 349-352; 2002
Abstract:
On the basis of the idea that a quasicrystal is a compound in which the average number of valence electrons per atom is around 2.0 and that its formation is dominated by atom size, stable icosahedral quasicrystals have been successfully synthesized in Ag-In-Ca, Ag-In-Yb, Agn In-Ca-Mg and Ag- In-Yb-Mg systems. The Ag-In-Ca and Ag-In-Yb icosahedral quasicrystals have stoichiometry around Ag42In42Ca16 and Ag42In42Yb16. The Ag-In-Ca-Mg and Ag-In-Yb-Mg quasicrystals form in the composition ranges Ag42-x/2In42-x/2Ca16Mgx (x = 0-7.5 at.%) and Ag42-x/2In42-x/2Yb16Mgx (x = 0-10 at.%). Electron diffraction studies confirmed that the icosahedral quasicrystals have a primitive lattice. The average number of valence electrons per atom in all these quasicrystals is 2.0.
Title:
Synthesis of amorphous and quasicrystal phases by mechanical alloying of Ti45Zr38Ni17 powder mixtures, and their hydrogenation
Authors:
Takasaki, A; Han, CH; Furuya, Y; Kelton, KF; Steinfink, H;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 82 (6): 353-361; 2002
Abstract:
Mechanical alloying of Ti45Zr38Ni17 powder mixture forms an amorphous phase, but subsequent annealing causes the formation of an icosahedral (i) phase. The maximum hydrogen concentration that can be loaded at 573 K at a hydrogen pressure of 3.8 MPa is the same ([H]/[M] approximate to 1.5) for the amorphous and i-phase powders. With hydrogenation, the i-phase is almost stable, forming no hydrides, whereas the amorphous phase transforms to a fcc hydride. The activation energy for hydrogen desorption for the i-phase is about 127 kJ mol(-1), which is lower than that for the amorphous phase, suggesting that the i-phase powder may have better properties for hydrogen-storage applications.
Title:
Direct observation of the modulation of the 4f-electron orbital state by strong p-f mixing in CeSb
Authors:
Iwasa, K; Hannan, A; Kohgi, M; Suzuki, T; Bertel, E;
Source:
PHYSICAL REVIEW LETTERS, 88 (20): 4199-4209; 2002
Abstract:
Low-temperature x-ray diffraction experiment has been carried out to investigate the 4f -electron state of the low carrier density system CeSb which shows complicated magnetic phase diagrams at low temperatures. The scattering pattern of the satellite peaks observed in the magnetically ordered state AFP3 is explained well by the model which takes into account both the lattice and charge modulations corresponding to the complex magnetic structure. The present result gives direct evidence for the strong modulation of the 4f -electron orbital state in CeSb due to the combined effect of the strong p-f mixing and carrier localization.
Title:
Superstructural ordering and electronic-density modulation in oxide HTSC systems
Authors:
Anshukova, NV; Golovashkin, AI; Ivanova, LI; Rusakov, AP; Martinez, JL;
Source:
PHYSICS OF THE SOLID STATE, 44 (5): 799-803; 2002
Abstract:
New experimental data obtained on the lattice and spin modulation in oxide HTSCs are explained in terms of superstructural ordering in the CuO2 planes without invoking the stripe model. The effect of doping on superstructural ordering in HTSCs is considered. The shape of the Fermi surface in oxide HTSCs and its variation with doping are also explained. (C) 2002 MAIK "Nauka/Interperiodica".
Title:
Effect of electron irradiation on the heat capacity of [NH2(CH3)(2)](2)center dot CuCl4 in the phase transition region
Authors:
Dekola, TI; Sheleg, AU; Tekhanovich, NP; Rusakov, AP;
Source:
PHYSICS OF THE SOLID STATE, 44 (5): 985-988; 2002
Abstract:
The specific heat of crystalline [NH2(CH3)(2)](2) . CuCl4 in the ferroelectric phase, both nonirradiated and irradiated by electrons, was measured calorimetrically. The temperature region of existence of the ferroelectric phase was shown to broaden under electron irradiation. The existence of an incommensurate phase above the Curie point T-c1 in the crystal was confirmed. The phase-transition sequence observed in [NH2(CH3)(2)](2) . CuCl4 is shown to be described by a phenomenological model for A(2)BX(4)-type ferroelectrics with an organic cation. (C) 2002 MAIK "Nauka/Interperiodica".
Title:
Incommensurate magnetic ordering in Sr2Ru1-xTixO4
Authors:
Braden, M; Friedt, O; Sidis, Y; Bourges, P; Minakata, M; Maeno, Y; Wasiela, A;
Source:
PHYSICAL REVIEW LETTERS, 88 (19): 985-988; 2002
Abstract:
In Sr2RuO4 the spin excitation spectrum is dominated by incommensurate fluctuations at q=(0.3 0 .3q(z)) , which arise from Fermi-surface nesting. We show that upon Ti substitution, known to suppress superconductivity, a short range magnetic order develops with a propagation vector (0.307 0.307 1). In Sr2Ru0.91Ti0.09O4 , the ordered moment points along the c direction. This finding shows that superconducting Sr2RuO4 is extremely close to an incommensurate spin density wave instability.
Title:
Response to tilted magnetic fields in Bi2Sr2CaCu2O8 with columnar defects: Evidence for transverse Meissner effect
Authors:
Phuoc, VT; Olive, E; De Sousa, R; Ruyter, A; Ammor, L; Soret, JC; Wasiela, A;
Source:
PHYSICAL REVIEW LETTERS, 88 (18): 250-253; 2002
Abstract:
The transverse Meissner effect (TME) in the highly layered superconductor Bi2Sr2CaCu2O8+y with columnar defects is investigated by transport measurements. We present evidence for the persistence of the Bose glass phase for H-perpendicular to < H-&BOTTOM;c: (i) the variable-range vortex hopping process crosses over to the half-loop regime; (ii) near H-&BOTTOM;c the energy barriers vanish linearly with H-&BOTTOM;; (iii) the transition temperature is governed by T-BG(H-&PAR;, 0) - T-BG(H-&PAR;, H-&BOTTOM;) &SIM; \H-&BOTTOM;\(1/ν&BOTTOM;) with ν(&BOTTOM;)= 1.0 +/- 0.1. Furthermore, above the transition as H-&BOTTOM; --> H-perpendicular toc(+), moving kink chains consistent with a commensurate-incommensurate transition scenario are observed. These results show the existence of the TME for H-perpendicular to < H-&BOTTOM;c.
Title:
Preparation of Al-Cu-Fe thin films by vapor deposition technique from a single source
Authors:
Kanjilal, A; Tiwari, U; Chatterjee, R; Ding, ZJ;
Source:
MATERIALS RESEARCH BULLETIN, 37 (2): 343-351; 2002
Abstract:
In this paper, we report the formation of stable icosahedral Al-Cu-Fe quasicrystalline thin films by thermal vapor deposition techniques (indirect heating and e-beam heating) from a single source. Deposition of these films by a single-source indirect heating method, in the stable icosahedral phase, is reported for the first time. A direct comparison between the two different heating methods has been made. The final compositions of the prepared films with desired properties were found to be Al62.9Cu24.6Fe12.5 (indirect heating method) and Al63.1Cu24.5Fe12.4 (e-beam method), respectively. The resistivities of the films prepared by both methods were similar to2000 muOmega cm at room temperature and similar to4000 kOmega cm at 10 K. (C) 2002 Elsevier Science Ltd. All rights reserved.
Title:
Structure of Rb-III: Novel modulated stacking structures in alkali metals
Authors:
Nelmes, RJ; McMahon, MI; Loveday, JS; Rekhi, S; Krushelnick, K;
Source:
PHYSICAL REVIEW LETTERS, 88 (15): 343-351; 2002
Abstract:
The crystal structure of Rb-III, stable between 13 and 17 GPa, has been determined from quasi-single-crystal x-ray diffraction data. It is orthorhombic, space group C222(1) , with 52 atoms in the unit cell, and has an 8-10-8-8-10-8 stacking of 8- and 10-atom layers. The recently reported 84-atom structure of Cs-III can be understood as an 8-8-10-8-8-8-8-10-8-8 stacking of the same layers. These represent a new class of modulated elemental structures.
Title:
RuGavSnw nowotny chimney ladder phases and the 14-electron rule
Authors:
Lu, GX; Lee, S; Lin, JH; You, LP; Sun, JL; Schmidtt, JT; Allott, RM;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 164 (2): 210-219; 2002
Abstract:
A series of ruthenium gallium stannides have been prepared with stoichiometry RuGavSnw, where 8+3v+4w=14 and 0 < v < 0.70. These samples have been analyzed by X-ray powder diffraction and transmission electron microscopy (TEM). The data show that these compounds are Nowotny chimney ladder phases with both commensurate and incommensurate structures. We show that there are special characteristics in chimney ladder powder diffraction patterns that allow one to determine the ratio of main group atom-sites to transition metal atom-sites to high accuracy. Our results confirm earlier work which suggest that both the stoichiometry and the structure of chimney ladder phases are dominated by electronic factors. The structures reported in this paper adhere to the 14-electron rule, i.e., there are 14 valence electrons per transition metal ion. The interplay of main group and transition metal structures leads to a pseudo c-axis, the presence of which is confirmed by the TEM data. We discuss the relation between these phases and the Fibonacci sequence. (C) 2002 Elsevier Science (USA).
Title:
Sr3NiRhO6 and Sr3CuRhO6-two new one-dimensional oxides. Magnetic behavior as a function of structure: Commensurate vs incommensurate
Authors:
Stitzer, KE; Henley, WH; Claridge, JB; zur Loye, HC; Layland, RC; Schmidtt, JT;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 164 (2): 220-229; 2002
Abstract:
Two new compounds, Sr3NiRhO6 and Sr3CuRhO6, belonging to a family of 2H-perovskite related materials, were synthesized in both a commensurate and an incommensurate form. The oxides were structurally characterized by powder X-ray Rietveld refinements and magnetic measurements. The commensurate structure of Sr3NiRhO6 is isostructural with the rhombohedral K4CdCl6 structure (space group R (3) over barc; Z = 6; a= 9.5951(1) Angstrom, c = 11.0621(2) Angstrom) while the structure of Sr3CuRhO6 forms in a monoclinic distortion of the K4CdCl6 structure (space group C 2/c; Z = 4; a = 9.2226(2) Angstrom, b = 9.6882(2) Angstrom, c = 6.6926(2) Angstrom, P = 92.440(2)degrees). The structures of Sr3NiRhO6 and Sr3CuRhO6 contain chains of alternating face-sharing NiO6/CuO6 trigonal prisms and RhO6 octahedra. The magnetic susceptibility of Sr3NiRhO6 shows an abrupt drop at 30 K, suggesting antiferromagnetic correlations between the transition metal containing chains. Sr3CuRhO6 displays ferromagnetic-type ordering below 10 K. When the samples are heated for prolonged periods of time, a transition to an incommensurate structure takes place. Depending on the specific synthesis conditions, different incommensurate structures can be obtained. The fitted lattice parameters with space group R3m (cell 1) and P31c (cell 2) are a = 9.6201(6) Angstrom, c(1) = 2.6732(2) k, c(2) = 3.9803(8) Angstrom for Sr3NiRhO6+delta and a = 9.624(2) Angstrom, c(1) = 2.6981(5) Angstrom, c(2) = 3.9539(5) Angstrom for Sr3CuRhO6+delta. The magnetic susceptibilities of the incommensurate compounds are quite different from their commensurate analogues, as all signs of long-range magnetic order disappear. (C) 2002 Elsevier Science (USA).
Title:
Toward a unified approach to the crystal chemistry of aurivillius-type compounds. - 1. The structural model
Authors:
Boullay, P; Trolliard, G; Mercurio, D; Perez-Mato, JM; Elcoro, L; Schmidtt, JT;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 164 (2): 252-260; 2002
Abstract:
A generalized structural model of Aurivillius-type compounds is presented using a 4D superspace group analysis where Aurivillius structures are considered as cation-deficient perovskites with the general formula AB(1-x)0(3). Being essentially composition independent, the model is valid for any Aurivillius-type compounds where x is the only composition-dependent parameter. The atomic domains representing the atoms in superspace are described by means of crenel functions. For any composition, the conventional space groups can be easily derived from a unique superspace group. This work is supported by a TEM investigation where the continuously variable character of the diffraction diagram indicates that the various stacking sequences can be interpreted in terms of a structural modulation over a common average structure. (C) 2002 Elsevier Science (USA).
Title:
Toward a unified approach to the crystal chemistry of aurivillius-type compounds - II. Bi7Ti4NbO21, a case study
Authors:
Boullay, P; Trolliard, G; Mercurio, D; Perez-Mato, JM;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 164 (2): 261-271; 2002
Abstract:
In part I of this paper, a generalized structural model of Aurivillius-type compounds has been presented using a 4D superspace group analysis where Aurivillius structures are considered as cation-deficient perovskites with the general formula AB(1-x)O(3). Being essentially composition independent, the model is valid for any Aurivillius-type compounds where x is the only composition-dependent parameter. For any composition, the conventional space groups can be easily derived from a unique superspace group. In this second part, a practical example of a structural refinement using the superspace approach is presented for the compound Bi7Ti4NbO21 and compared with a conventional 3D refinement. Similarities with other compositionally flexible systems are discussed. (C) Elsevier Science (USA).
Title:
Metastability and disorder effects in nonstoichiometric VS2
Authors:
Poddar, P; Rastogi, AK; Mancini, DC;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (10): 2677-2689; 2002
Abstract:
In this detailed study we have reported on single-crystal and polycrystalline phases Of V1+xS2; 0.10 < x < 0.25, prepared using excess sulfur in a sealed quartz tube and investigated their structural, transport and magnetic properties. The crystal flakes have trigonal symmetry with 2c and incommensurate >2(root3)a superlattice ordering in the a-b plane. As-grown flakes showed complex irreversible behaviour in resistivity on cycling to low temperatures, related to the metastability of the structure. The annealing of the crystal flakes and addition of 5-10% Al stabilizes the superstructure. We observe an anomalous contribution to the resistance of these crystal flakes with a maximum around 100-150 K. The contribution is more pronounced for better-ordered phases. The magnetic susceptibility and thermopower values of these compounds are large and vary smoothly on cooling around this temperature interval. The polycrystalline phase, obtained at a higher temperature, on the other hand, showed absence of superlattice distortions and gave a smooth behaviour in its resistance, but with a large T-2-contribution. The structural and electronic properties of different phases are discussed in terms of disorder among the interstitial V atoms and the effect of in-plane vacancies on the charge-density-wave instability in these and similar compounds.
Title:
Electronic structure of quasicrystals deduced from Auger and x-ray photoelectron spectroscopies
Authors:
Fournee, V; Anderegg, JW; Ross, AR; Lograsso, TA; Thiel, PA; Shuh, DK;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (10): 2691-2703; 2002
Abstract:
Specific features in the electronic structure of Al-transition metal quasicrystals are analysed by a combination of Auger and x-ray photoelectron spectroscopies. We first demonstrate that different degrees of asymmetry in the transition metals' 2p core-level lineshape observed across different types of surface structure correspond to variations in the density of states at the Fermi level, DOS(E-F). Using this effect, we explore the controversial issue of whether the quasicrystalline, decagonal AlNiCo system is electronically stabilized. We find strong evidence for the presence of a reduced DOS(EF) in this system, as expected for electronically stabilized compounds, and as observed in the quasicrystalline, icosahedral AlPdMn and AlCuFe alloys. Finally, qualitative information on the nature of the electronic states in quasiperiodic structures extracted from the core-valence-valence Auger lines are presented and discussed.
Title:
Mechanical behaviour versus structure of Al63.6Cu24.0Fe12.4
Authors:
Giacometti, E; Fikar, J; Baluc, N; Bonneville, J; Vos, WL;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 82 (4): 183-189; 2002
Abstract:
A series of polyquasicrystalline ingots with the nominal composition Al63.6Cu24.0Fe12.4 has been prepared by conventional drop casting and subsequent annealing at 1088 K for 24 h. Compression specimens prepared from the different ingots have been deformed at temperatures ranging from 750 to 1050 K. The details of the structure and microstructure of the as-cast, annealed and deformed materials have been investigated by optical, scanning and transmission electron microscopy. Whatever their initial structure (i.e. pure icosahedral, modulated or relevant to approximant phases) and their defect microstructure (dislocations and crystalline platelets), all the specimens, which have been compression tested, exhibit similar mechanical behaviours.
Title:
Formation and hydrogen adsorption properties of Ti-Hf-Ni quasicrystals and crystal approximants
Authors:
Huett, VT; Kelton, KF; Baluc, N;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 82 (4): 191-198; 2002
Abstract:
The formation of a high-order rational approximant (RA) phase in rapidly quenched Ti-Hf-Ni alloys and the hydrogen absorption properties of that phase are reported. Electron diffraction patterns show systematic shifts of the diffraction spots from their expected positions for the icosahedral phase (i-phase); the diffraction patterns are consistent with those expected for a 3/2 RA phase RA-( Ti-Hf-Ni). Based on differential scanning calorimetry studies, RA-(Ti-Hf-Ni) is metastable, transforming between 350 and 500degrees C to a quasicrystal with strong phason disorder. This crystallizes at 620degrees C to a Ti2Ni-type phase. RA-(Ti-Hf-Ni) readily absorbs hydrogen, up to 1.2 hydrogen atoms per metal atom ([H]/[M] = 1.2). Pressure-composition isotherm studies for gas-phase loading show that the pressure plateau for RA-(Ti-Hf-Ni) is similar to that observed for the i-(Ti-Zr-Ni) phase, although it occurs at a slightly higher pressure and extends over a smaller range of hydrogen concentrations. Unlike i-(Ti-Zr-Ni), no irreversible hydride phase forms with hydrogen loading at 250degrees C, suggesting that RA-(Ti-Hf-Ni) may have superior cycling properties, of interest for hydrogen storage applications.
Title:
Icosahedral-phase formation in as-cast Ti-Zr-Ni alloys
Authors:
Lee, GW; Croat, TK; Gangopadhyay, AK; Kelton, KF; Vos, WL;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 82 (4): 199-205; 2002
Abstract:
Previously, the formation of the thermodynamically stable icosahedral Ti-Zr- Ni i-(Ti-Zr-Ni) phase has been observed in rapidly quenched alloys, or by a low-temperature solid-state transformation from crystal phases that form at higher temperatures. Here we report the nucleation and growth of the icosahedral (i) phase directly from the liquid in as-cast Ti33Zr46Ni21 and Ti37Zr42Ni21 alloys. Diffraction patterns obtained by transmission electron microscopy and X-ray diffraction confirm the phase identity. Differential scanning calorimetry measurements show an endothermic transformation from the i- phase to a phase mixture of a C14 Laves phase and a solid-solution phase, demonstrating that this i- phase is also stable. The short time that the liquid remains in the Laves-phase-forming field and the higher nucleation rate for the i- phase, owing to strong similarities in the local structures of the i- phase and liquid, allow i- phase nucleation and growth directly from the liquid.
Title:
New stable icosahedral phases in Al-Pd-Ru and Al-Pd-Os systems
Authors:
Asao, T; Tamura, R; Takeuchi, S; Kelton, KF;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 82 (4): 217-223; 2002
Abstract:
We have found stable icosahedral (i) phases in alloys with nominal compositions around Al72Pd17Ru11 and Al72Pd17Os11. They display very sharp X-ray diffraction peaks, indicating high structural order as in other Al-based i-phases such as i-(Al-Pd-TM) (transition metal TM = Mn or Re) and i-(Al-Cu-TM) (TM = Fe, Ru or Os). The i phases are formed via peritectic reaction and, upon heating, they transform into a mixture of a liquid and the 1/0 cubic approximant phase. The electrical resistivity of the i phases was measured in a wide temperature range from 14 K to above their melting points and a reversible change of the resistivity across the melting point has been observed in situ for the first time.
Title:
Preparation of decagonal Zn-Mg-Y by melt spinning
Authors:
Sterzel, R; Dahlmann, E; Assmus, W; Saitoh, K; Fuess, H; Mihalkovic, M; Suck, JB; Clarke, RJ;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 82 (4): 235-239; 2002
Abstract:
It is shown, for the first time, how pure decagonal Zn-Mg-Y can be prepared by melt spinning and annealing. Study of the phase formation was performed by differential scanning calorimetry and the sample was further investigated by Xray and electron diffraction. The lattice constants of the decagonal phase are a(q) = 4.592 Angstrom and c = 5.198 Angstrom calculated from a physical space model, or a(q) = 4.485 Angstrom and c = 5.193 Angstrom from a hyperspace model.
Title:
Spin waves in quasi-periodic Fe/Cr(100) thin films
Authors:
Mauriz, PW; Albuquerque, EL; Bezerra, CG; Renzoni, F;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (8): 1785-1797; 2002
Abstract:
In this work we have calculated the ferromagnetic (FM) resonance curves of Fe/Cr(100) thin films, which follow the Fibonacci sequence. Our approach is based on the equations of motion for the small-signal magnetization deviation from the equilibrium directions. The equilibrium positions of the magnetizations are calculated from the total energy, which includes the following contributions: Zeeman, bilinear exchange, biquadratic exchange, dipolar, cubic anisotropy and surface anisotropy terms. We also consider the presence of an external magnetic field applied in the plane, of the films and parallel to the easy axes. The experimental parameters used in our calculations were recently reported and lie in three regions of interest, namely (i) near to the first antiferromagnetic (AF) peak (strong bilinear exchange coupling), (ii) near to the first FM-AF transition (moderate bilinear exchange coupling) and (iii) near to the second AF peak (weak bilinear exchange coupling comparable to the biquadratic exchange coupling). Our results show the effect of the quasi-periodic arrangement in the spin wave dispersion relation of these artificial structures.
Title:
Magnetoconductance related to change in density-of-states of decagonal quasicrystals - observation of a scaling behaviour
Authors:
Zhang, DL; Li, GH; Lu, L; Wang, ZM; He, HF; Wang, YP; Jing, XN; Li, SL; Bruynseraede, Y;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (5): 1011-1020; 2002
Abstract:
The magnetoresistance of fully oriented decagonal AlCuCo films has been carefully measured. From this, together with observations of the temperature dependence of the film resistivity and tunnelling experiments on a single quasicrystal of a similar material (AlNiCo), a scaling behaviour has been found. This behaviour strongly suggests that the drastic change of magnetoresistance occurs within an energy scale where a pseudogap appears in the materials.
Title:
Modulated magnetic ordering in the Cu-doped pseudoperovskite system CaCuxMn3-xMn4O12
Authors:
Przenioslo, R; Regulski, M; Sosnowska, I; Schneider, R; He, HF;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (5): 1061-1065; 2002
Abstract:
The crystal and magnetic structures of the CaCuxMn3-xMn4O12 compounds with x = 0.3 and 0.7 were investigated by means of x-ray and neutron powder diffraction. The crystal structure parameters of the x = 0.3 compound at 60 K have been refined within the trigonal space group R. The magnetic moments of Mn ions in the x = 0.3 sample become ordered below 40 K. The magnetic ordering is modulated with a propagation vector (0, 0, kappa). A model of the magnetic structure which is in agreement with the experimental data is proposed along with an estimation of the temperature dependence of the magnetic moment value. The magnetic ordering has a reduced correlation length of about 250 A. The x = 0.7 compound does not show any long-range magnetic ordering down to 1.5 K.
Title:
Charge and spin structure in YBa2Cu3O6.35
Authors:
Mook, HA; Dai, PC; Dogan, F; Schneider, R;
Source:
PHYSICAL REVIEW LETTERS, 88 (9): 1061-1065; 2002
Abstract:
Neutron scattering has been used to measure the charge and spin structure in the highly underdoped superconductor YBa2Cu3O6.35. Incommensurate static charge ordering is found that remains at high temperatures. The magnetic pattern is complex with a resonance and incommensurate structure observed at low temperatures. The results clarify the role of striped phases in YBa2Cu3O6+x superconductors.
Title:
Quasicrystal surfaces: structure and potential as templates
Authors:
McGrath, R; Ledieu, J; Cox, EJ; Diehl, RD; He, HF;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (4): R119-R144; 2002
Abstract:
We present a review of recent progress in determining the surface structure of quasicrystals, with emphasis on their connections to mathematical tiling models. The review focusses in particular on the five-fold surface of icosahedral Al-Pd-Mn and the ten-fold surface of decagonal AI-Ni-Co. We also assess their potential as templates for the formation of two-dimensional quasicrystalline overlayers with reference to recent investigations of atomic and molecular adsorption.
Title:
Low-temperature thermodynamic investigation of the sulphur organic salts (TMTTF)(2)PF6 and (TMTTF)(2)Br (TMTTF equivalent to tetramethyltetrathiafulvalene): I. General aspects
Authors:
Lasjaunias, JC; Brison, JP; Monceau, P; Staresinic, D; Biljakovic, K; Carcel, C; Fabre, JM; Li, SL;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (4): 837-847; 2002
Abstract:
A detailed thermodynamical investigation of the quasi-one-dimensional sulphur-based organic salts (TMTTF)(2)PF6 and (TMTTF)(2)Br is presented in the temperature range from 30 mK to 7 K. In this part (part I), we consider the general aspects of the low-temperature specific heat of these materials in relationship with their ground states and we compare them with those previously measured for selenium members of the same family. All these compounds exhibit very similar thermodynamical behaviour, despite a variety of electronic ground states: spin-Peierls for (TMTTF)(2)PF6, commensurate antiferromagnetic spin modulation for (TMTTF)(2)Br, incommensurate spin-density wave for (TMTSF)(2)PF6 (TMTSF drop tetramethyltetraselenafulvalene). We show that the low-energy excitations which are predominant below 1 K have a similar character to that observed in glassy systems, at least on short timescales of measurements. The dynamical aspects of the non-equilibrium thermodynamics will be presented separately in the following part (part H).
Title:
Identification of the atomic structure of the fivefold surface of an icosahedral Al-Pd-Mn quasicrystal: Helium diffraction and scanning tunneling Microscopy studies
Authors:
Barbier, L; Le Floc'h, D; Calvayrac, Y; Gratias, D; Biljakovic, K;
Source:
PHYSICAL REVIEW LETTERS, 88 (8): 837-847; 2002
Abstract:
High resolution He diffraction and scanning tunneling microscopy images of the fivefold surface of a single-grain i-AlPdMn quasicrystal are obtained showing an almost perfect quasicrystal order. Observed configurations can be identified within the framework of polyhedral models. The terrace terminations are found to be Al-rich planes and successions of step heights agree with distances between dense Al planes in the model. This shows the ability of recent 6D polyhedral models to describe real quasicrystalline atomic configurations.
Title:
Faceted etch pits and light figures of icosahedral Zn-Mg-Y quasicrystals
Authors:
Suchodolskis, A; Babonas, GJ; Jasutis, V; Karpus, V; Reza, A; Simkiene, I; Assmus, W; Sterzel, R; Bruynseraede, Y;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 82 (3): 157-165; 2002
Abstract:
Faceted etch pits have been observed on chemically etched single-grain icosahedral Zn Mg Y quasicrystal samples with C-2, C-3 and C-5 symmetry rotation axes perpendicular to their surfaces. The anisotropic etching was produced by 2.5-5% HCl solution in ethylene. The etch pits, analysed by scanning electron microscopy (SEM), follow the icosahedral symmetry of a rhombic triacontahedron. Light figures were observed on a screen placed in between a 10 mW He Ne laser and the reflecting quasicrystal surface. Both the SEM images and the light figures can be used to determine the twofold. threefold and fivefold symmetry axes of the quasilattice as well as for investigations of intrinsic and growth defects in the quasicrystals.
Title:
Crystal structure of pseudorhombohedral InFe1-xTixO3+x/2 (x=2/3)
Authors:
Michiue, Y; Onoda, M; Watanabe, A; Watanabe, M; Brown, F; Kimizuka, N; Assmus, W;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 163 (2): 455-458; 2002
Abstract:
The structure of pseudorhombohedral-type InFe1-xTixO3-(x/2) (x = 2/3) was refined by Rietveld profile fitting. The crystal is a commensurate member of a series in a solution range on InFeO3-In2Ti2O7 including incommensurate structures. The structure with the unit cell of a = 5.9188(1), b = 10.1112(2), and c = 6.3896(t) Angstrom, beta = 108.018(2)degrees, and a space group P2(1)/a is the alternate stacking of an edge-shared InO6 octahedral layer and an Fe/Ti-O plane along c*. Metal sites on the Fe/Ti-O plane are surrounded by four oxygen atoms on the Fe/Ti-O plane and two axial ones. Electric conductivities of the order 10(-4) S/cm were observed for the samples at 1000 K, while the oxide ion transport number is almost zero as no electromotive force was detected by an oxygen concentration cell. (C) 2002 Elsevier Science.
Title:
Microstructures of some Bi-W-Nb-O phases
Authors:
Zhou, WZ; Onoda, M;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 163 (2): 479-483; 2002
Abstract:
Microstructures of three Bi-W-Nb-O phases have been examined by using high-resolution transmission electron microscopy. Bi17W2Nb3O39, and Bi17WNb3O36 have incommensurate superstructures derived from the defect fluorite-type delta-Bi2O3 and can be regarded as intermediate phases between the type II solid solutions in the Bi-Nb-O and Bi-W-O systems. Bi8W2M2O23 has a Bi2WO6-like subunit cell with a stepped superstructure. Formation mechanisms of various superstructures are discussed. (C) 2002 Elsevier Science.
Title:
Modulated structure of the composite crystal Ca0.83CuO2
Authors:
Miyazaki, Y; Onoda, M; Edwards, PP; Shamoto, S; Kajitani, T; Kimizuka, N;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 163 (2): 540-545; 2002
Abstract:
We have determined the crystal structure of the quasi one-dimensional cuprate Ca0.83CUO2, known as Ca4CU5O10, etc., by a superspace group approach. The compound consists of two interpenetrating subsystems Of CuO2 chains and Ca atoms. Structural parameters were refined with a superspace group of F2/m(1+alpha 0 gamma)0s using powder X-ray and neutron diffraction data. Lattice parameters were refined to be a(1) = 2.8043(2) Angstrom, b = 6.3179(2) Angstrom, C-1 = 10.5744(5) Angstrom, and beta(1) = 90.10(1)degrees for the [CuO2] subsystem and a(2) = 3.3652(2) Angstrom, b = 6.3179(2) Angstrom, c(2) = 10.5893(5) Angstrom, and beta(2) = 93.04(1)degrees for the [Ca] subsystem. Remarkable displacive modulation of the O and Ca atom sites is observed parallel to the b-axis and the c-axis, respectively. On the other hand, the Cu atom sites deviate mainly in the a direction to yield a periodic fluctuation between the nearest Cu-Cu distances. The Ca atoms suitably sit in the center of the modulated 06 octahedra. (C) 2002 Elsevier Science.
Title:
Physical properties of the quasicrystal YbCd5.7 and its approximant YbCd6
Authors:
Dhar, SK; Palenzona, A; Manfrinetti, P; Pattalwar, SM; Kajitani, T;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (3): 517-522; 2002
Abstract:
We have measured the magnetization, low-temperature heat capacity and electrical resistivity of the binary quasicrystal YbCd5.7 and its crystalline approximant, cubic YbCd6. Magnetization data reveal that Yb ions are divalent in both compounds. The coefficient of the linear term in the heat capacity, gamma, is 51 and 7.5 mJ mol(-1) K-2 in YbCd6 and YbCd5.7, respectively. The heat capacity data thus reveal a significant reduction in the electronic density of states in the quasicrystalline phase. However, the Debye temperatures of the two compounds are comparable; 144 and 138 K, respectively. The electrical resistivity of YbCd6 shows typical metallic behaviour while the resistivity of YbCd5.7, larger than that of YbCd6, is characterized by a negative temperature coefficient below 300 K with a peak around 50 K.
Title:
Electron momentum distribution of decagonal Al72Ni12Co16 studied by Compton scattering
Authors:
Okada, JT; Watanabe, Y; Yokoyama, Y; Hiraoka, N; Itou, M; Sakurai, Y; Nanao, S; Wang, ZW;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (2): L43-L48; 2002
Abstract:
The electron-momentum-density distributions (Compton profiles) in decagonal Al72Ni12Co16 have been measured along the [00002] and [11000] directions with a momentum resolution of 0.14 au. The experimental valence-electron profile is decomposed into two partial profiles: an inverted parabola-like profile and a broad Gaussian-like profile. By fitting the broad partial profile with a profile made up of atomic 3d wavefunctions, it is found that a considerable portion of the 3d-electron holes of Ni and Co are filled with electrons. The directionally averaged radius of the Fermi sphere is estimated from the number of electrons under the parabolic partial profile. The radius is larger than that of the inscribed sphere of the quasi-Brillouin zone. This leads to the Hume-Rothery mechanism does not play an important role in explaining the stability of the decagonal quasicrystal. Slight anisotropies of the Compton profile are observed.
Title:
Formation of a dodecagonal phase in the nano-sized Ag-Pt multilayers upon solid-state reaction
Authors:
Li, ZC; Kong, LT; Liu, BX; Hiraoka, N;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (1): 1-5; 2002
Abstract:
A dodecagonal quasicrystalline phase was grown in nano-sized Ag-Pt multilayers upon solid-state reaction and the existence of the respective metastable state in the Ag-Pt system was also confirmed by ion-beam mixing experiments. The major driving force for intermixing between the nano-sized Ag and Pt layers, as well as for the crystal-to-quasicrystal transition, was thought to be the interfacial free energy, which elevated the initial Ag-Pt multilayers up to an energetic state corresponding to the dodecagonal phase.
Title:
Electronic structure of Al-Pd-Mn crystalline and quasicrystalline alloys
Authors:
Fournee, V; Belin-Ferre, E; Pecheur, P; Tobola, J; Dankhazi, Z; Sadoc, A; Muller, H; Wang, ZW;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (1): 87-102; 2002
Abstract:
An experimental and theoretical analysis of the electronic structure of Al-Pd alloys is presented. The experimental study, based on soft x-ray emission and absorption spectroscopies, is further extended to the case of quasicrystalline Al-Pd-Mn alloys and their approximants. The electronic structure is dominated by the sp-d hybridization. The Al-sp band is strongly modified by the interaction with the Pd-d states in the middle of the valence band. Close to the Fermi level, hybridization with the Mn-d states is found to enhance the structure induced pseudo-gap in the Al partial density of states, both in the icosahedral and the decagonal quasicrystalline phases.
Title:
A 4D structural study of a Ca-rich composite-type crystal [A(2)Cu(2)O(3)](7+delta)[CuO2](10) with disorder phenomena in CuO2 sublattice
Authors:
Leligny, H; Raveau, B; Leonyuk, LI; Maltsev, V; Garreau, Y;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 163 (1): 17-26; 2002
Abstract:
The structure of a Ca-rich composite-type crystal [A(2)CU(2)O(3)](7+delta) [CuO2] M with A = Sr-0.43 Ca0.55Bi0.03 and delta = 0.04 was determined by single-crystal X-ray diffraction using the 4D superspace group formalism. Thanks to the existence of a significant number of first-order satellite reflections, reliable results were obtained concerning the displacive modulation within each subsystem. A comparison is made with the accurate structural results obtained by Frost Jensen on similar composite crystals containing less calcium. A larger modulation amplitude is observed in our crystal. Weak interactions (Cu-O approximate to 2.72 Angstrom) are involved locally between the copper atoms of a [Cu2O3] layer and one oxygen atom of a [CuO2] layer, leading in some unit cells to a pyramidal coordination of copper. Such an interaction is not observed in the Ca-less-containing crystal of Frost-Jensen. However, the most important point of this study concerns the evidence for the first time of disorder phenomena inside the [CuO2] subsystem; this disorder was modeled with both Cu and O splitted sites. Two main configurations with realistic Cu-O bonds are privileged for the CuO4 squares inside the [CuO2] sublattice. The refinement results and the bond valence forma ism give strong evidence that the A sites are occupied at random by Sr and Ca atoms, which display two types of coordination, 7 and 8, in the crystal. (C) 2002 Elsevier Science.
Title:
HREM study of compounds in the bi-rich part of the Ba-Bi-O system
Authors:
Nikolaichik, VI; Amelinckx, S; Klinkova, LA; Barkovskii, NV; Lebedev, OI; Van Tendeloo, G; Sauvage-Simkin, M;
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 163 (1): 44-64; 2002
Abstract:
A series of perovskite-like compounds with general composition BanBin+mOy (m, n-integer) has been studied by means of electron diffraction and high-resolution electron microscopy. For a number of simple, discrete values of the cation composition ratio Ba: Bi the structures were found to be Ruddlesden-Popperlike derivatives of the perovskite structures of BaBiO3, with composition-dependent long periods. For more complicated values of the cation composition ratio the perovskite blocks are further fragmented by planar interfaces into a two-dimensional periodic island structure. This fragmentation gives rise to complicated local structures formed by a mosaic of square or (and) rectangular islands, which often produce incommensurate diffraction patterns. Such diffraction patterns are interpreted in the framework of the "fractional shift" method for interface modulated structure. Structure models and compositions can be made compatible by assuming that substitution of barium ions by bismuth ions must take place, predominantly along the island boundaries. (C) 2002 Elsevier Science.
Title:
A new modulated structure in GaN nanoparticles
Authors:
Li, H; Sun, HP; Shen, F; Zhang, Z; Noren, L;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 82 (2): 91-98; 2002
Abstract:
A new modulated structure with a superlattice having parameters a = 2.209 nm, b = 3.826 nm, c = 1.037 nm and alpha = beta = gamma = 90degrees has been found in GaN nanoparticles synthesized by a dc arc plasma method. The nanoparticles transformed further into particles with holes at their centres under electron-beam irradiation during high-resolution electron microscopy observations. At the same time, Ga atoms were extruded on to the surface of the nanoparticles and formed an amorphous layer. A series of simulations of high-resolution images and electron diffraction patterns revealed that the modulation could be attributed to aggregations of N vacancies founded during the electron bombardment. Molecular mechanics calculations show that the aggregation of N vacancies is far more energetically favourable than that of Ga vacancies. The stability of the GaN particles is discussed.
Title:
Effect of vacuum annealing on the structure and superconductivity of Bi2Sr2CaCu2O8+delta single crystals
Authors:
Liang, B; Lin, CT; Maljuk, A; Yan, Y; Troyanov, SI;
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 366 (4): 254-262; 2002
Abstract:
The effect of annealing on the structure and superconductivity of Bi2Sr2CaCU2O8-delta has been investigated on high-quality and large single crystals grown by the traveling solvent floating zone technique, Vacuum annealing was carried out on crystals sealed in quartz ampoules under different oxygen pressure ranging from 8 x 10(-1) to 5 x 10(-4) bar. The as-grown and post-annealed crystals were explored by induction-coupled plasma atomic emission spectroscopy, X-ray diffraction (XRD). transmission electron microscopy (TEM) and magnetization measurements. It was demonstrated that the oxygen homogeneity of the as-grown crystals has a direct influence on the post-annealed samples. The superconducting transition temperature. T-c was found to be affected more strongly by the annealing oxygen partial pressures. rho(O-2) than by the annealing temperature, T-c decreases considerably from 92 to 29 K with decreasing rho(O-2) from 1 down to 4 x 10(-2) bar. however. increases surprisingly to 62 K with further decreasing rho(O-2) to 5 x 10(-4) bar. The transitions remain relatively sharp for the samples annealed under rho(O-2) = 8 x 10(-1) -4 x 10(-2) bar, with no evidence of significant structural change by powder XRD measurement. XRD studies indicate that the crystals have orthorhombic symmetry. The refinement result for XRD data shows that the c-axis expands. while both a- and b-axis contract slightly with decreasing rho(O-2). The relation between T-c and the c-axis lattice parameter suggests that the change of T-c is correlated with a redistribution of holes between the Bi-O layers and the Cu-O planes. Impurity phases were found to segregate from samples annealed under rho(O-2) < 4 x 10(-2) bar. The one-dimensional incommensurate superstructure along the b-axis was observed by TEM in the crystal annealed at rho(O-2) = 1 x 10(-3) bar. The lattice strain caused by the high-vacuum annealing possibly affect the Cu-O-Cu angle and lead to an anomalous change in T-c (D 2002 Elsev
Title:
The role of the incommensurate phase in the opalescence of quartz
Authors:
Dolino, G; Bastie, P; Sundberg, M;
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 13 (50): 11485-11501; 2001
Abstract:
Forty five years ago, an intense light scattering was observed at the alpha-beta transition of quartz but the origin of this opalescence has-remained mysterious for a long time. Recently Saint-Gregoire et al and Aslanyan et al have explained the origin of the opalescence by introducing new incommensurate ('inc') phases with ferroelastic properties in the transition region. In this paper we recall the main features of the alpha-beta transition, of the inc phase and of the opalescence of quartz, which presents different properties in two regions of the alpha-inc phase boundary. We also describe the three typical structures observed in the phase boundary regions by electron microscopy. We present briefly the two previous ferroelastic models and we propose our own explanation for the origin of the opalescence. We discuss the relations of these three models with experimental results concerning thermal behaviour, microscopic structures and the origin of the refractive index variations. Most experimental results are in agreement, at least qualitatively, with our model where the two opalescence regions correspond respectively to the presence of inc rotation patches and of irregular Dauphine microtwins, both in a non-equilibrium state.
Title:
Multiple nonlinear optical interactions with arbitrary wave vector differences
Authors:
Fradkin-Kashi, K; Arie, A; Urenski, P; Rosenman, G; Troyanov, SI;
Source:
PHYSICAL REVIEW LETTERS, 88 (2): 11633-11639; 2002
Abstract:
We present a novel method for simultaneously phase matching several nonlinear optical interactions within a single crystal. Quasiperiodic modulation of the nonlinear coefficient enables one to achieve high frequency mixing efficiencies for interactions with arbitrary wave vector differences. Doubling of two different frequencies as well as direct frequency tripling is experimentally demonstrated. The temperature- and wavelength-dependent properties of these interactions are explored. We discover that periodic approximation to the quasiperiodic structure shifts the phase-matched wavelengths.
Title:
Frank's 'cubic' hexagonal phase: an intermetallic cluster compound as an example
Authors:
Ranganathan, S; Singh, A; Tsai, AP; Ren, ZF;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 82 (1): 13-19; 2002
Abstract:
Frank introduced in 1965 the novel idea of projection from a four-dimensional cube to recover the points of a hexagonal lattice with a special c/a ratio of (3/2)(1/ 2). This was called a cubic hexagonal crystal, as there was a similarity to the conventional cubic crystals in that directions were perpendicular to planes with the same Miller-Bravais indices. While a number of crystals in the NiAs- Ni2In family have been reported with this special axial ratio, the number of atoms in the unit cell is small. As the first example of an intermetallic cluster compound, we identify mu-Al4Mn, mu-Al4Cr, Zn-Mg-Sm and a host of related intermetallics featuring a special aggregate of icosahedra as Frank's 'cubic' hexagonal phase or its variant. The metric is generated by the Friauf polyhedra and the icosahedral linkages and leads to a multimetric crystal and several interesting connections with hexagonal quasicrystals, hexagonal phases and derivative orthorhombic and lower-symmetry structures.
Title:
Stable Cd-Mg-Yb and Cd-Mg-Ca icosahedral quasicrystals with wide composition ranges
Authors:
Guo, JQ; Abe, E; Tsai, AP; Ren, ZF;
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 82 (1): 27-35; 2002
Abstract:
Stable icosahedral quasicrystals with wide composition ranges have been found in the systems Cd-Mg-Yb and Cd-Mg-Ca. The icosahedral quasicrystals form in the following composition ranges: 25-85 at.% Cd, 0-60 at.% Mg and 10-20 at.% Yb for the Cd-Mg-Yb system; 33-85 at.% Cd, 0-52 at.% Mg and 10-20 at.% Ca for the Cd-Mg-Ca system. An electron diffraction study confirmed that the icosahedral quasicrystals have a primitive lattice. Its quasilattice constant is proportional to a Goldschmidt atom diameter of the quasicrystals weighted by a factor of 1.75 in the range 0.5681- 0.5799 nm for the Cd-Mg-Yb system and 0.5697-0.5778 nm for the Cd-Mg-Ca system. The closely similar atom sizes of Cd and Mg, the valence electron ratio e/a=2.0 and the large atom sizes of Yb and Ca cause the wide composition ranges of the Cd-Mg-Yb and Cd-Mg-Ca quasicrystals. The metallurgical behaviour of the quasicrystals is discussed.
Title:
Dynamics of the pinned modulation wave in incommensurate bis (4-chlorophenyl) sulfone (BCPS)
Authors:
Blinc, R; Mikac, U; Apih, T; Dolinsek, J; Seliger, J; Slak, J; Zumer, S; Guibe, L; Ailion, DC; Maeno, T;
Source:
PHYSICAL REVIEW LETTERS, 88 (1): 433-436; 2002
Abstract:
We show that both the anomalously huge resonance-frequency dependence of the Cl-35 nuclear quadrupole resonance (NQR) spin-lattice relaxation time in BCPS, reported here for the first time, and its anomalous temperature dependence can be explained by large-scale fluctuations of the pinned modulation wave instead of small-scale fluctuations (phasons and amplitudons). The results were obtained by measuring the laboratory (T-1Q) and rotating frame (T-1Q.rho) Cl-35 relaxation times. This is the first time that an effective resonance frequency dependence of the spin-lattice relaxation rate was measured in pure NQR.
Title:
Structural and superconducting properties of La2CuO4+delta oxidized by KMnO4 under hydrothermal conditions
Authors:
Tu, QY; Ma, BK; Chen, XL; Lan, YC; Xu, YX; Liang, JK; Zhao, ZX; Li, JQ; Ailion, DC;
Source:
MODERN PHYSICS LETTERS B, 15 (26): 1171-1179; 2001
Abstract:
A series of samples of La2CuO4+delta chemically oxidized in KMnO4 solution under hydrothermal conditions have been prepared. A large orthorhombic distortion and the increased unit cell volume of the oxidized sample have been observed by means of X-ray powder diffraction, compared with that of the starting material. Selected-area electron diffraction investigations reveal that two kinds of incommensurate modulation structures exist in the oxidized samples. Magnetic susceptibility measurements indicate that the oxidized samples axe multiphase with two superconducting phases, one is dominant with onset of superconducting transition temperature at 43 K or 40 K, and the other at 19 K. Up to now, a T-c of 43 K is the highest value achieved in KMnO4-treated samples. The excess oxygen content determined by iodometric titration increases with the oxidation temperature. Average grain sizes observed by scanning electron microscope have no obvious changes for the samples before and after oxidation.
Title:
Identifying and indexing icosahedral quasicrystals from powder diffraction patterns
Authors:
Lu, PJ; Deffeyes, K; Steinhardt, PJ; Yao, N; Zhilyaeva, EI;
Source:
PHYSICAL REVIEW LETTERS, 87 (27): 8-15; 2001
Abstract:
We present a scheme to identify quasicrystals based on powder diffraction data and to provide a standardized indexing. We apply our scheme to a large catalog of powder diffraction patterns, including natural minerals, to look for new quasicrystals. Based on our tests, we have found promising candidates worthy of further exploration.
Title:
Effect of partial substitution of Cu in Al65Cu35 by transition metal in mechanical alloying of Al65Cu20Tm15
Authors:
Chattopadhyay, PP; Manna, I;
Source:
MATERIALS AND MANUFACTURING PROCESSES, 17 (5): 583-594; 2002
Abstract:
Mechanical alloying (MA) of Al-Cu yields a single-phase disordered bcc solid solution in a wide composition range (35-65 at.% Al). In the present work, a systematic effort is made to investigate the effect of partial substitution of Cu with a transition metal (TM) on the identity and sequence of phase evolution in MA in a high-energy ball mill. The ternary elements (Zn, Fe, Cr, Ti, Nb, and Zr) were added maintaining an initial composition of Al65Cu20TM15. While addition of Zn yields nanocrystalline solid solution phases, ternary addition of Fe and Cr, in accordance with the earlier reported studies, leads to formation of quasicrystalline (QC) phases. On the other hand, MA of Al65Cu20TM15 with TM = Ti, Nb, and Zr for an appropriate time develops a completely amorphous product under the present set of milling conditions. Thus, the present results indicate that MA of Al65Cu20TM15 with Ti, Nb, and Zr is a potential route of synthesizing Al-rich amorphous alloys or nanocrystal dispersed amorphous matrix composite.
Title:
Effect of incommensurate charge-density wave scattering on the electronic structure of high-T-c cuprates
Authors:
Seibold, G; Varlamov, S;
Source:
JOURNAL OF SUPERCONDUCTIVITY, 15 (6): 505-506; 2002
Abstract:
We argue that the collective mode as observed in angle resolved photoemission spectroslopy (ARPES) on a large class of cuprates can be associated with dynamic incommensurate CDW fluctuations present in these materials. This scenario is substantiated by a comparison of calculated spectra with experimental ARPES data where we obtain a mode frequency that decreases toward optimal doping, thus strongly supporting the existence of a quantum critical point around this concentration. Moreover, we extract the temperature dependence of the associated bosonic spectrum from ARPES data, where it turns out that there is a continuous evolution from mode-type behavior below T-c to a marginal Fermi liquid structure well above T-c.
Title:
Analysis of the texture of heterogeneous Al-Cu-Fe coatings containing quasicrystalline phase
Authors:
Ustinov, AI; Polischuk, SS;
Source:
SCRIPTA MATERIALIA, 47 (12): 881-886; 2002
Abstract:
The structure of heterogeneous Al-Cu-Fe coatings produced by electron beam physical vapour deposition was studied. The coating compositions were varied close to the optimal composition of icosahedral phase. Axial textures of both icosahedral and beta-cubic phase were observed. The type of axial texture of quasicrystalline component correlates with the texture type of the crystalline phase. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
A TEM and RUM study of the inherent displacive flexibility of the fresnoite framework structure type
Authors:
Withers, RL; Tabira, Y; Liu, Y; Hoche, T;
Source:
PHYSICS AND CHEMISTRY OF MINERALS, 29 (9): 624-632; 2002
Abstract:
A careful electron diffraction study has been made of the incommensurately modulated room-temperature phases of the fresnoites Ba2TiGe2O8 (BTG) and Ba2TiSi2O8 (BTS) and used to determine their (3 + 1)- and (3 + 2)-dimensional superspace group symmetries. The primitive primary modulation wave vectors in both materials are found to occur close to the same position in the parent Brillouin zone, near similar to 0.3<110>(p)* + 1/2c(p)*. A rigid unit mode (RUM) analysis of the inherent displacive structural flexibility of the ideal fresnoite framework structure type is then carried out in an attempt to understand the significance of this particular modulation wave vector. Six zero-frequency RUM modes and two close to zero frequency quasi-RUM (Q-RUM) modes are found to exist for any modulation wave vector. These RUM modes are all primarily associated with rotations of the constituent TO4 (T = Si or Gel tetrahedra and TiO5 square pyramids around in-plane i.e. perpendicular to c rotation axes. A seventh RUM mode involving rotation of the constituent rigid polyhedra around c combined with shifts in the basal plane is found but only at a very specific modulation wave vector q similar to 0.30<110>(p)*, in close agreement with P the condensed RUM mode found in the electron diffraction study. It is the condensation of just such a RUM mode that appears to play a major role in the various incommensurately modulated structures observed in Ba2TiGe2O8, Ba2TiSi2O8 and Sr2TiSi2O8, respectively.
Title:
Formation of icosahedral Al-Cu-Fe quasicrystal in annealed metallic multilayers
Authors:
Grenet, T; Giroud, F; Joulaud, JL; Capitan, M;
Source:
PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 82 (16): 2909-2922; 2002
Abstract:
We study the formation of the icosahedral Al-Cu-Fe quasicrystalline phase in heat-treated elemental multilayers. Pure quasicrystalline films can be obtained in similar annealing conditions independently of the stacking sequence of the multilayers. Using synchrotron radiation diffraction, we study in real time the succession of the intermediate phases formed during ramp heat treatments of Al/ Cu/Fe/Cu/Al and At/Fe/Cu/Fe/Al sandwiches. Al-Cu binary phases are first formed in the early stages for both stacking sequences, despite the presence of Fe layers between Al and Cu in the second configuration. The role played by Fe is discussed. The transient formation of theta-Al3Fe is not observed, although it was believed to be a necessary precursor for the quasicrystal formation.
Title:
An investigation on the transformation of the icosahedral phase in the Al-Fe-Cu system during mechanical milling and subsequent annealing
Authors:
Mukhopadhyay, NK; Yadav, TP; Srivastava, ON; Capitan, M;
Source:
PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 82 (16): 2979-2993; 2002
Abstract:
Icosahedral quasicrystalline material in the Al-Fe-Cu system was mechanically milled in an attritor ball mill (Szegvari attritor) for 1, 3, 6 and 10 h in dry air, at a speed of 400 rev min(-1) and with a ball-to-powder ratio of 20 to 1. Structural transformations and the consequent phase evolutions during mechanical milling and subsequent heat treatments were studied by X-ray diffraction, differential thermal analysis (DTA) and transmission electron microscopy techniques. After milling for 1 h, the evolution of disordered B2 phase (a = 0.29 nm) was observed to coexist with the parent icosahedral phase, whereas a microstructure consisting of nanosized B2 particles distributed in an amorphous matrix was observed after further milling (3-10 h). However, no sharp peak corresponding to the phase transformation was identified in DTA, but the microstructure of the powder milled for 10 h after the DTA experiment was found to transform to a mixture of icosahedral and B2 phases, where B2 appears to be the major phase in contrast with that in as-cast material. Isothermal heat treatment of powder mechanically milled at 850degreesC for 10 and 20 h led to complete transformation to a single B2 phase with a high degree of long-range ordering. The implication of these transformations will be discussed with reference to their relative stabilities among the competing phases during milling and subsequent heat treatment.
Title:
Structural studies of (Al1-xGex)(65)Cu10+yMn25-y (0 <= x <= 0.4, 0 <= y <= 10)
Authors:
Chatterjee, R; Kanjilal, A; Dunlap, RA; Srivastava, ON;
Source:
MATERIALS LETTERS, 57 (3): 689-696; 2002
Abstract:
In this paper, we present a systematic structural study on the (Al1-xGex)(65)Cu10+yMn25-y. alloy system. The emphasis of the work is to understand the effect of Ge concentration on the occurrence, growth and morphology of the quasicrystalline phases in the system, as we move from Cu/Mn ratio of 20:15 to 10:25 in order to span the varied electronic behavior (as shown in the literature) of this quaternary system. Throughout the series, coexistence of icosahedral and decagonal phases has been observed. To the best of our knowledge, these are the first observations of their type in the alloy system (AlGe) CuMn. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Magnetoelectric effect in YMn2O5 in strong pulsed magnetic fields
Authors:
Popov, YF; Kadomtseva, AM; Krotov, SS; Vorob'ev, GP; Lukina, MM;
Source:
FERROELECTRICS, 279 (3): 147-156; 2002
Abstract:
The electric polarization of single crystal YMn2O5 was investigated in strong pulsed magnetic fields up to H = 250 kOe at low temperatures. It was shown that at T similar to 40 K magnetic and structural phase transitions occur, with the structural changes taking place improperly (magnetically induced). We have also shown the existence of the structural phase transition at T similar to 20 K with the onset of spontaneous polarization P-b . The quadratic magnetoelectric effect at temperatures T < 40 K was observed (with b-component domination), the magnetoelectric susceptibility below T = 20 K greatly increased for all field orientations. When H&PAR;a the magnetoelectric effect changed its sign which in analogue with EuMn2O5 was attributed to non-commensurate to commensurate structural change. The polarization anomalies in strong magnetic fields were observed with the former being due to complex magnetic structure changes and the process of spontaneous polarization induction by magnetic field.
Title:
Structure of heavy-metal sorbed birnessite: Part 2. Results from electron diffraction
Authors:
Drits, VA; Lanson, B; Bougerol-Chaillout, C; Gorshkov, AI; Manceau, A;
Source:
AMERICAN MINERALOGIST, 87 (11-12): 1646-1661; 2002
Abstract:
Selected-area electron diffraction (SAED) and energy-dispersive analysis were used to study the structure of synthetic heavy-metal sorbed birnessites (MeBi). Samples were prepared by equilibrating a suspension of Na-rich buserite (NaBu) at pH 4 in the presence of various heavy metal cations (Me), including Pb, Cd, Zn, and Cu.Five main types of SAED patterns were observed. Types I and II were observed only for ZnBi micro-crystals, and they both consist of two super-cell reflection networks related by a mirror plane parallel to the a-c plane. In direct space, these twinned networks correspond to hexagonal supercells with A(H) = B-H = root7b/root3, and A(H)= B-H= root7b, for ZnBi type I and 11, respectively. The supercells in the two varieties result from an ordered distribution of vacant layer octahedra capped by interlayer Zn in ZnBi layers. This distribution is described by a hexagonal cell with A(H) = root7b. In ZnBi micro-crystals of type 1, interstratified twinned right- and left-handed fragments are similar to chalcophanite (ZnMn3O7.3H(2)O; Wadsley 1955; Post and Appleman 1988), and distributions of vacant layer octahedra from adjacent layers are regularly shifted with respect to each other by 1/3 of the long diagonal of the hexagonal layer unit cell. In ZnBi micro-crystals of type 11, distributions of vacant layer octahedra are not regularly shifted from one layer to the adjacent one.SAED patterns of types III and IV occur for PbBi, ZnBi, and CdBi micro-crystals and contain super-cell reflections distributed parallel to [100]* with a periodicity that is not commensurate with that of the MeBi sub-structure (a*/2.15 and a*/5.25, respectively). The super-cell reflections result from the ordered distribution within MeBi layers of vacant layer sites capped by Me as pairs along the a axis. Within each pair, vacant sites are separated by 2a for type 111, and by 5a for type IV. In one-layer monoclinic structures, the apparent incommensurability arises from the +a/
Title:
Structure of synthetic Na-birnessite: Evidence for a triclinic one-layer unit cell
Authors:
Lanson, B; Drits, VA; Feng, Q; Manceau, A; Manceau, A;
Source:
AMERICAN MINERALOGIST, 87 (11-12): 1662-1671; 2002
Abstract:
The structure of a synthetic analogue of Na-birnessite (NaBi) was studied by powder X-ray diffraction (XRD). It is shown that NaBi has a one-layer triclinic structure with sub-cell parameters: a(p) = 2.9513(4) Angstrom, b(p) = 2.9547(4) Angstrom, c(p) = 7.334(1)Angstrom, alpha(p) = 78.72(2)degrees, beta(p) = 101.79(1)degrees, gamma(p) = 122.33(1)degrees, and space group P (1) over bar. This sub-cell is equivalent to the base-centered sub-cell with parameters: a = 5.174 Angstrom, b = 2.848 Angstrom, c = 7.334 Angstrom, alpha = 90.53degrees, beta = 103.20degrees, and gamma = 90.07degrees. A structure model has been refined using the Rietveld technique. NaBi consists of vacancy-free Mn-bearing octahedral layers whose negative charge arises mostly from the substitution of Mn 31 for Mn4+. The departure from the hexagonal symmetry of layers results from Jahn-Teller distortion of Mn3+ octahedra, which are elongated along the a axis, segregated in Mn3+-rich rows parallel to the b axis, and separated from each other along the a axis by two Mn4+-rows. Structural sites of interlayer Na cations and H2O have been determined as well as their occupancies. The sub-cells of the two NaBi modifications described by Drits et al. (1997) as types I and 11 likely contain four sites for interlayer species, two of which are occupied by Na and the other two by H2O molecules. In the two NaBi varieties, these pairs of sites are split along the c axis and related by a center of symmetry. This splitting is consistent with the modulated structure of both NaBi types, which arises from the periodic displacement of interlayer species along the b axis with a periodicity lambda = 6b (Drits et al. 1997).
Title:
Stability of glassy state in Zr-based glassy alloys correlated with nano icosahedral phase formation
Authors:
Saida, J; Kasai, M; Matsubara, E; Inoue, A; Manceau, A;
Source:
ANNALES DE CHIMIE-SCIENCE DES MATERIAUX, 27 (5): 77-89; 2002
Abstract:
Stability of glassy state in Zr-based glassy alloys correlated with nano icosahedral phase formation. We investigated the stability of the glassy state by examination of transformation behaviour and structural analysis in Zr-based binary and ternary glassy alloys. It is well known that the melt-spun Zr-Cu binary alloys have a distinct glass transition prior to crystallization in a wide composition region of 20 to 70 at% Cu, while no supercooled liquid state appears in the melt-spun Zr-Ni binary alloys. It is expected that the local structure of the disordered state in the two alloy systems is different. The icosahedral quasicrystalline phase (I-phase) is formed as a primary phase in the Zr70Cu30 binary glassy alloy by substitution of Pd for Cu. The minimum Pd concentration for I-phase formation is 0.5 at%. In contrast, the primary phase is a tetragonal Zr2Ni phase in a Zr70Ni30 amorphous alloy by substitution of Pd by less than 10 at% for the Ni element. The radial distribution function (RDF) of the Zr70Cu30 glassy alloy is different from that of the Zr70Ni30 amorphous alloy. The coordination numbers around Zr in the melt-spun Zr-70(Cu or Ni)(30) binary alloys are 12.4 and 10.7, respectively, indicating the possibility of existence of the icosahedral local atomic configuration in the Zr70Cu30 glassy alloy. It is also realized that a tetragonal Zr2Ni-like local atomic configuration is formed in the Zr70Ni30 amorphous alloy. Considering that the I-phase is also formed in the Zr(60)Ni(25)AI(15) glassy alloy by addition of 3 at% Pd, where the distinct glass transition is observed, the appearance of the supercooled liquid region is attributed to the existence of the icosahedral local atomic configurations consisting of Zr-Cu or Zr-Ni-Al. These results show that the icosahedral short- and medium-range orders exist in the supercooled liquid as well as in the glassy phase and they stabilize the glassy state in the Zr-based alloys.
Title:
Nanoscale cF96 cubic versus icosahedral phase in devitrified Hf-based metallic glasses
Authors:
Louzguine, DV; Ko, MS; Inoue, A; Inoue, A;
Source:
ANNALES DE CHIMIE-SCIENCE DES MATERIAUX, 27 (5): 91-97; 2002
Abstract:
The devitrification behaviour of the rapidly solidified quaternary hafnium-based alloys of Hf65NM17.5TM10Al7.5 composition (NM- noble metal, TM- 3d transition metal) was studied using differential scanning calorimetry. The purpose of the study was to evaluate the influence of composition on the devitrification products at the primary stage. The structure was analysed by using X-ray diffraction and transmission electron microscopy. The formation of the nanoparticles of the Hf-based quasicrystalline icosahedral or cubic cF96 Fd(3)(-)m Ti2Ni-type phase about 10 nm in size was observed at the primary devitrification stage in different metallic glasses with close compositions. The icosahedral phase consists of 137-atom Bergmann rhombic triacontahedra. The alloys in systems in which the stable Hi-based cF96 phase exists do not show the formation of the icosahedral phase from the amorphous matrix. The cF96 phase and the icosahedral phase formed by primary devitrification from the amorphous phase may inherit the local order of the icosahedral clusters in the amorphous matrix.
Title:
The crystal structure of the intergrowth compound Ba11TiNb8O33
Authors:
Teneze, N; Boullay, P; Trolliard, G; Mercurio, D; Kim, WT;
Source:
SOLID STATE SCIENCES, 4 (9): 1119-1128; 2002
Abstract:
The ternary oxide Ba11TiNb8O33 was synthesized and, based on a combined X-ray and Neutron powder diffraction refinement, its crystal structure was examined. Ba11TiNb8O33 is a B-site deficient "hexagonal" perovskite with a 33R stacking sequence of the BaO3 layers leading to the cell parameters a = 5.78634(2) Angstrom, c = 77.8011(4) Angstrom with a space group R (3) over barm. It is an intergrowth compound whose crystal structure derives from that of the simple terms which constitute it, but possess its specific structural characteristics. No rotation of the oxygen octahedral network is observed in this compound. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.
Title:
Nanoquasicrystallites formation in stable icosahedral Al-Cu-Fe quasicrystalline thin films
Authors:
Kanjilal, A; Pautov, L;
Source:
NANOTECHNOLOGY, 13 (5): 682-685; 2002
Abstract:
The formation of nanoquasicrystallites in stable icosahedral Al-Cu-Fe quasicrystalline thin films by implementing an indirect heating method from a single source is discussed in this paper. The final composition of the quasicrystalline thin films is found to be Al62.9Cu24.6Fe12.5 Using x-ray fluorescence spectroscopy. The icosahedral nanoquasicrystallites formation is studied by glancing-angle x-ray diffraction and transmission electron microscopy. The size of the nanoquasicrystallites is estimated to be 4-20 nut. The density of nanoquasicrystallites is calculated as (I +/- 2) x 10(12) cm(-2). The improvement of the icosahedral phase formation with increasing annealing temperature is also verified by measuring the change in resistivity with temperature in the range 10-300 K. The resistivity of the best film, which is obtained by annealing the as-deposited films at 700degreesC for I h, is calculated to be similar to2000 muOmega cm at room temperature and similar to4000 muOmega c m at 10 K.
Title:
Covering of discrete quasiperiodic sets: Concepts and theory
Authors:
Kramer, P; Lin, JH;
Source:
COVERINGS OF DISCRETE QUASIPERIODIC SETS: THEORY AND APPLICATIONS TO QUASICRYSTALS, 180 (11): 1-21; 2003
Abstract:
The n = 2 member in hexagonal perovskite manganate family A(n+1)Mn(n)O(3n+3)(Ca2O) was obtained in a complex composition La2Ba0.8Sr0.6Ca1.6Mn2O10, but simple hexagonal structure. It crystallizes in the hexagonal P6(3)/mmc space group [a = 5.63591(5) Angstrom, c = 16.2843(3) Angstrom, V = 447.948(9) Angstrom(3); Z = 2] and consists of double hexagonal perovskite layers (2H-type) and graphite-like [Ca2O] layer. The manganese octahedra share faces resulting in localized magnetic property. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Covering clusters in icosahedral quasicrystals
Authors:
Duneau, M; Gratias, D; Wang, YX;
Source:
COVERINGS OF DISCRETE QUASIPERIODIC SETS: THEORY AND APPLICATIONS TO QUASICRYSTALS, 180 (11): 23-61; 2003
Abstract:
The structural analysis of various approximant phases of icosahedral quasicrystals shows local environments with icosahedral symmetry: icosahedra, Mackay clusters, and Bergman clusters. For the icosahedral phases i-AlCuFe and i-AlPdMn, these clusters have been proposed as complementary building blocks centered on particular nodes. However, computations have shown that these 2-shell or 3-shell clusters do not cover all atomic positions given by 6D models. On the other hand, the recent concept of a unique covering cluster has been shown to apply to 2D Penrose tilings and Ammann-Beenker tilings. In this chapter we examine the local environments in i-AlCuFe and i-AlPdMn models about Wyckoff positions of the 6D lattice. We consider extended Bergman clusters of 6 shells that appear naturally in the Katz-Gratias model. We discuss the cell decomposition of the atomic surfaces and the variable occupation number of some of the shells. We show that a fixed extended Bergman cluster of 6 shells and 106 atoms covers about 98% of atomic positions. We also prove that a variable extended Bergman cluster of 6 shells, which contains the previous fixed cluster, covers all atomic positions of the theoretical model.
Title:
Generation of quasiperiodic order by maximal cluster covering
Authors:
Gahler, R; Gummelt, P; Ben-Abraham, SI; Loong, CK;
Source:
COVERINGS OF DISCRETE QUASIPERIODIC SETS: THEORY AND APPLICATIONS TO QUASICRYSTALS, 180 (11): 63-95; 2003
Abstract:
The structural analysis of various approximant phases of icosahedral quasicrystals shows local environments with icosahedral symmetry: icosahedra, Mackay clusters, and Bergman clusters. For the icosahedral phases i-AlCuFe and i-AlPdMn, these clusters have been proposed as complementary building blocks centered on particular nodes. However, computations have shown that these 2-shell or 3-shell clusters do not cover all atomic positions given by 6D models. On the other hand, the recent concept of a unique covering cluster has been shown to apply to 2D Penrose tilings and Ammann-Beenker tilings. In this chapter we examine the local environments in i-AlCuFe and i-AlPdMn models about Wyckoff positions of the 6D lattice. We consider extended Bergman clusters of 6 shells that appear naturally in the Katz-Gratias model. We discuss the cell decomposition of the atomic surfaces and the variable occupation number of some of the shells. We show that a fixed extended Bergman cluster of 6 shells and 106 atoms covers about 98% of atomic positions. We also prove that a variable extended Bergman cluster of 6 shells, which contains the previous fixed cluster, covers all atomic positions of the theoretical model.
Title:
Voronoi and Delone clusters in dual quasiperiodic tilings
Authors:
Kramer, P; Gummelt, P;
Source:
COVERINGS OF DISCRETE QUASIPERIODIC SETS: THEORY AND APPLICATIONS TO QUASICRYSTALS, 180 (11): 97-164; 2003
Abstract:
The structural analysis of various approximant phases of icosahedral quasicrystals shows local environments with icosahedral symmetry: icosahedra, Mackay clusters, and Bergman clusters. For the icosahedral phases i-AlCuFe and i-AlPdMn, these clusters have been proposed as complementary building blocks centered on particular nodes. However, computations have shown that these 2-shell or 3-shell clusters do not cover all atomic positions given by 6D models. On the other hand, the recent concept of a unique covering cluster has been shown to apply to 2D Penrose tilings and Ammann-Beenker tilings. In this chapter we examine the local environments in i-AlCuFe and i-AlPdMn models about Wyckoff positions of the 6D lattice. We consider extended Bergman clusters of 6 shells that appear naturally in the Katz-Gratias model. We discuss the cell decomposition of the atomic surfaces and the variable occupation number of some of the shells. We show that a fixed extended Bergman cluster of 6 shells and 106 atoms covers about 98% of atomic positions. We also prove that a variable extended Bergman cluster of 6 shells, which contains the previous fixed cluster, covers all atomic positions of the theoretical model.
Title:
Lines and planes in 2-and 3-dimensional quasicrystals
Authors:
Pleasants, PAB; Gummelt, P;
Source:
COVERINGS OF DISCRETE QUASIPERIODIC SETS: THEORY AND APPLICATIONS TO QUASICRYSTALS, 180 (11): 185-225; 2003
Abstract:
The structural analysis of various approximant phases of icosahedral quasicrystals shows local environments with icosahedral symmetry: icosahedra, Mackay clusters, and Bergman clusters. For the icosahedral phases i-AlCuFe and i-AlPdMn, these clusters have been proposed as complementary building blocks centered on particular nodes. However, computations have shown that these 2-shell or 3-shell clusters do not cover all atomic positions given by 6D models. On the other hand, the recent concept of a unique covering cluster has been shown to apply to 2D Penrose tilings and Ammann-Beenker tilings. In this chapter we examine the local environments in i-AlCuFe and i-AlPdMn models about Wyckoff positions of the 6D lattice. We consider extended Bergman clusters of 6 shells that appear naturally in the Katz-Gratias model. We discuss the cell decomposition of the atomic surfaces and the variable occupation number of some of the shells. We show that a fixed extended Bergman cluster of 6 shells and 106 atoms covers about 98% of atomic positions. We also prove that a variable extended Bergman cluster of 6 shells, which contains the previous fixed cluster, covers all atomic positions of the theoretical model.
Title:
Thermally-induced tile rearrangements in decagonal quasicrystals - Superlattice ordering and phason fluctuation
Authors:
Edagawa, K; Gummelt, P;
Source:
COVERINGS OF DISCRETE QUASIPERIODIC SETS: THEORY AND APPLICATIONS TO QUASICRYSTALS, 180 (11): 227-256; 2003
Abstract:
The structural analysis of various approximant phases of icosahedral quasicrystals shows local environments with icosahedral symmetry: icosahedra, Mackay clusters, and Bergman clusters. For the icosahedral phases i-AlCuFe and i-AlPdMn, these clusters have been proposed as complementary building blocks centered on particular nodes. However, computations have shown that these 2-shell or 3-shell clusters do not cover all atomic positions given by 6D models. On the other hand, the recent concept of a unique covering cluster has been shown to apply to 2D Penrose tilings and Ammann-Beenker tilings. In this chapter we examine the local environments in i-AlCuFe and i-AlPdMn models about Wyckoff positions of the 6D lattice. We consider extended Bergman clusters of 6 shells that appear naturally in the Katz-Gratias model. We discuss the cell decomposition of the atomic surfaces and the variable occupation number of some of the shells. We show that a fixed extended Bergman cluster of 6 shells and 106 atoms covers about 98% of atomic positions. We also prove that a variable extended Bergman cluster of 6 shells, which contains the previous fixed cluster, covers all atomic positions of the theoretical model.
Title:
Tilings and coverings of quasicrystal surfaces
Authors:
McGrath, R; Ledieu, J; Cox, EJ; Diehl, RD; Zhou, GR;
Source:
COVERINGS OF DISCRETE QUASIPERIODIC SETS: THEORY AND APPLICATIONS TO QUASICRYSTALS, 180 (11): 257-268; 2003
Abstract:
The structural analysis of various approximant phases of icosahedral quasicrystals shows local environments with icosahedral symmetry: icosahedra, Mackay clusters, and Bergman clusters. For the icosahedral phases i-AlCuFe and i-AlPdMn, these clusters have been proposed as complementary building blocks centered on particular nodes. However, computations have shown that these 2-shell or 3-shell clusters do not cover all atomic positions given by 6D models. On the other hand, the recent concept of a unique covering cluster has been shown to apply to 2D Penrose tilings and Ammann-Beenker tilings. In this chapter we examine the local environments in i-AlCuFe and i-AlPdMn models about Wyckoff positions of the 6D lattice. We consider extended Bergman clusters of 6 shells that appear naturally in the Katz-Gratias model. We discuss the cell decomposition of the atomic surfaces and the variable occupation number of some of the shells. We show that a fixed extended Bergman cluster of 6 shells and 106 atoms covers about 98% of atomic positions. We also prove that a variable extended Bergman cluster of 6 shells, which contains the previous fixed cluster, covers all atomic positions of the theoretical model.
Title:
X-ray and electrostatic levitation undercooling studies in Ti-Zr-Ni quasicrystal forming alloys
Authors:
Kelton, KF; Gangopadhyay, AK; Lee, GW; Hannet, L; Hyers, RW; Krishnan, S; Robinson, MB; Rogers, J; Rathz, TJ;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 312 (11): 305-308; 2002
Abstract:
The first undercooling measurements on electrostatic-levitated droplets of TiZrNi alloys that form the icosahedral quasicrystal phase are presented. The reduced undercooling for crystallization decreases with an increasing polytetrahedral order of the primary solidifying phase, suggesting the development of icosahedral short-range order in the undercooled liquid. X-ray diffraction measurements made at the advanced photon source on liquid droplets of these alloys, aerodynamically levitated and heated to near their liquidus temperature, however, show only weak evidence for increased icosahedral order. This suggests that significant ordering occurs below the melting temperature. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Electronic structures and cohesion mechanism of Cd-based quasicrystals
Authors:
Ishii, Y; Fujiwara, T; Lee, GW;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 312 (11): 494-497; 2002
Abstract:
Electronic structures of cubic Cd6M (M = Yb, Ca and Mg), which are approximant phases of newly discovered Cd-based quasicrystals, are studied by the tight-binding linear muffin-tin orbitals method. It is found that stabilization due to alloying is obtained when M is an element with low-lying unoccupied d states. Although a shallow dip in the density of states appears near the Fermi level and the diameter of the Fermi sphere coincides with the (222100) and (311111) reciprocal lattice vectors, the Brillouin-zone-Fermi-sphere interaction does not play a principal role in the Cd-based systems, because neither a distinct dip nor additional stabilization due to alloying is obtained for isostructural Cd-Mg. These observations lead to the conclusion that the cohesion of the Cd-based compounds is certainly due to the hybridization of the d states of Yb/Ca with a wide sp band. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Icosahedral quasicrystalline phase formation in Zr-Al-Ni-Cu glassy alloys by the addition of V, Nb and Ta
Authors:
Saida, J; Inoue, A; Lee, GW;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 312 (11): 502-507; 2002
Abstract:
The formation of an icosahedral quasicrystalline phase as a primary phase was found in Zr65Al7.5Ni10Cu12.5X5 (X = V, Nb or Ta) glassy alloys. The icosahedral phase was precipitated during the first exothermic reaction in a two-stage crystallization process after a distinct glass transition. The diameters of the icosahedral particles are as small as 10-50 nm, similar to those found in Zr-based glassy alloys made with the addition of noble metals. Based on a Johnson-Mehl-Avrami analysis, we suggest that nano-quasicrystallization proceeds by a diffusion-controlled growth mode. The icosahedral phase in the Zr65Al7.5Ni10Cu17.5-xTax (x = 0-4) glassy alloys was formed at a Ta concentration of as little as 1 at.%, the primary crystallization phases were the fcc Zr2Ni and icosahedral phases. For Ta concentrations above 3 at.%, a nearly single icosahedral phase was formed as the primary phase. The formation of a nano-scale icosahedral phase in Zr-Al-Ni-Cu glassy alloys with the addition of V, Nb or Ta, as well as noble metals, indicates that an increasing nucleation rate contributes to the precipitation of the icosahedral phase, leading to the concept that icosahedral short- or medium-range order exists in the glassy state of the Zr-Al-Ni-Cu alloy. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Nuclear resonant inelastic scattering of synchrotron radiation by icosahedral quasicrystal i-Al62Cu25.5Fe12.5 and tetragonal crystal omega-Al70Cu20Fe10
Authors:
Suzuya, K; Shibata, K; Seto, M; Kitao, S; Yoda, Y; Kashihara, Y; Tsai, AP; Rogers, J;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 312 (11): 508-512; 2002
Abstract:
The local vibrational densities of states (VDOS) G(E) of Fe in icosahedral quasicrystal i-Al62Cu25.5Fe12.5 and tetragonal crystal omega-Al70Cu20Fe10 were measured at room temperature by using the Fe-57 nuclear resonant scattering of synchrotron radiation. We found a single-band structure at about 28 meV in both the Fe-partial G(E) for i-Al62Cu25.5Fe12.5 and omega-Al70Cu20Fe10. The single-band of i-Al62Cu25.5Fe12.5 quasicrystal is broader than that of the omega-Al70Cu20Fe10 crystal. It contrasts with a strongly structured VDOS expected on theoretical grounds for the icosahedral quasicrystal. The VDOS are discussed in comparison with those obtained by inelastic cold neutron scattering. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Quasicrystalline phase formation by heating a mechanically alloyed Al65Cu23Fe12 powder mixture
Authors:
Tcherdyntsev, VV; Kaloshkin, SD; Salimon, AI; Tomilin, IA; Korsunsky, AM; Waseda, Y;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 312 (11): 522-526; 2002
Abstract:
Elemental powder mixtures of a Al(65)Cu(23)Fe(12)composition milled for two and four hours in a planetary ball mill were used to form quasicrystals. Annealing of the as-milled samples led to complex solid-state transformations. During the heat-up a sequence of solid-state reactions takes place in the as-milled powder. These reactions were studied both by differential scanning calorimetry and X-ray diffraction methods. An analysis of the phase formation shows the effect of the difference in the thermodynamic driving forces, such as the positive heats of mixing for the Cu-Fe system and the negative ones for the Al-Fe and Al-Cu systems, on the phase transformation consequence. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Structural study of quasicrystallization in Zr-NM (NM=Pd or Pt) metallic glasses
Authors:
Kitada, M; Imafuku, M; Saida, J; Inoue, A; Korsunsky, AM;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 312 (11): 594-598; 2002
Abstract:
Glassy Zr70Pd30 and Zr80Pt20 alloys were prepared by melt spinning. Icosahedral-like local atomic configurations were identified in these alloys by ordinary and anomalous X-ray scattering measurements. In the case of Zr70Pd30 alloy, the total coordination numbers (N) around Zr and Pd in the nearest neighboring region were 11.3 and 8.9, respectively, which implies the existence of an icosahedral-like local atomic structure around Zr. On the other hand, the glassy Zr80Pt20 alloy shows a pronounced pre-peak in its X-ray scattering intensity profile, indicating strong chemical short-range-ordered clusters. The N values around Zr and Pt are both 11.1, and close to 12.0. Furthermore, the atomic distances of Zr-Zr and Pt-Pt are almost the same. Thus, icosahedral-like local atomic structures with strong correlations are already formed both around Zr and Pt. The stronger chemical affinity of the Zr-Pt pair over the Zr-Pd pair seems to contribute to the stabilization of the quasicrystalline phase through the rigid icosahedral clusters. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Transformation in the initial crystallization stage of Zr-Al-Ni-Cu glassy alloys made with low oxygen concentrations
Authors:
Saida, J; Matsushita, M; Inoue, A; Inoue, A;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 312 (11): 617-621; 2002
Abstract:
We investigated the transformation behavior of glassy phase in the Zr65+xAl7.5Ni10Cu17.5-x (x = 0-9) alloys with low oxygen concentrations below 500 mass ppm. In the initial crystallization stage, metastable fcc Zr2Ni, Zr2Cu and Zr6NiAl2 phases are precipitated in the alloy where x = 0. A weak diffraction peak corresponding to an icosahedral phase is found in addition to the mixture phases of fcc Zr2Ni, Zr2Cu and Zr6NiAl2 in alloys with x = 1 and 2. The primary phase changes to the single icosahedral phase in the range of x = 3-6 and a bcc Zr phase is precipitated above x = 7. The icosahedral particles have a dendritic morphology with a grain diameter ranging from 500 to 2000 nm for the Zr70Al7.5Ni10Cu12.5 glassy alloy. A slight concentration redistribution leading to the enrichment of Zr and the rejection of Ni in the icosahedral phase is confirmed. The nucleation rate of the icosahedral phase at the crystallization temperature is calculated to be 1.5 x 10(14) m(-3) s(-1), which is 10(2) times lower than that of the fcc Zr,Ni phase. It is suggested that the formation of the icosahedral phase with such a low nucleation rate is attributed to the existence of icosahedral clusters in the glassy state, and the high grain growth rate of the icosahedral phase is due to the slight redistribution of constituent elements during quasicrystallization. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
EXAFS study of the Fe local environment in icosahedral AlCuFe and its relation to magnetism of quasicrystals
Authors:
Gomilsek, JP; Arcon, I; Kodre, A; Dolinsek, J; Korsunsky, AM;
Source:
SOLID STATE COMMUNICATIONS, 123 (12): 527-530; 2002
Abstract:
An extended X-ray absorption fine structure study of the transition metal sites in an icosahedral Al63Cu25Fe12 quasicrystal was performed. The nearest-neighbor coordination shell of the Fe atoms was found to contain Al atoms only, whereas the Cu atoms are surrounded predominantly by the Al atoms and some Cu atoms as the nearest neighbors, but no Fe atoms. The results give experimental support to the physical Picture of Fe atoms embedded in an Al-rich environment without direct contacts to other Fe's, providing a basis for the study of unusual magnetism in transition-metal-containing aluminum-based quasicrystals. (C) 2002 Elsevier Science Ltd. All rights reserved.
Title:
The longest curves of given degree and the quasicrystallic Harnack theorem in pseudoperiodic topology
Authors:
Arnold, VI; Siska, CC;
Source:
FUNCTIONAL ANALYSIS AND ITS APPLICATIONS, 36 (3): 165-171; 2002
Abstract:
Upper bounds for ergodic averages of topological characteristics of pseudoperiodic functions and manifolds are found in terms of the degrees of trigonometric polynomials defining these functions and manifolds. The bounds are based on finding the longest trigonometric and spherical curves of a fixed degree.
Title:
An analysis of elementary dislocations in icosahedral Al-Pd-Mn by large angle convergent-beam electron diffraction (LACBED)
Authors:
Caillard, D; Morniroli, JP; Vanderschaeve, G; Bresson, L; Gratias, D; Melikhova, O;
Source:
EUROPEAN PHYSICAL JOURNAL-APPLIED PHYSICS, 20 (1): 3-8; 2002
Abstract:
Large Angle Convergent Beam Electron Diffraction (LACBED) experiments on dislocations located in the mirror planes of icosahedral AlPdMn single grains show that as previously inferred from standard image contrast technique the direction of the Burgers vector is perpendicular to the mirror plane of movement, thus confirming the fact that climb should be an important process for the plasticity mechanisms in icosahedral quasicrystals.
Title:
Incommensurate modulation in the microporous silica SSZ-24
Authors:
Liu, Z; Fujita, N; Terasaki, O; Ohsuna, T; Hiraga, K; Camblor, MA; Diaz-Cabanas, MJ; Cheetham, AK; Rathz, TJ;
Source:
CHEMISTRY-A EUROPEAN JOURNAL, 8 (19): 4549-4556; 2002
Abstract:
A detailed investigation of the structure of microporous silica, SSZ-24, is presented. It is shown by X-ray powder diffraction and Si-29 MAS NMR experiments that the structure deviates from the previously proposed AlPO4-5-type structure. At room temperature, electron diffraction (ED) patterns exhibit extra diffraction spots, which can be attributed to an incommensurate structural modulation along the c axis. This in turn results in a pleat pattern in real space with two different intervals arranged aperiodically along the c axis, as observed with high-resolution electron microscopy (HREM). The modulated structure may easily turn into a disordered one through excessive electron irradiation or heat-treatment. In order to understand the origin of the modulation, soft phonon-modes of the ideal premodulated structure were analyzed by the use of the rigid-unit-mode model. The distribution of soft modes in reciprocal space might correspond roughly to diffuse streaks that could be observed in the diffraction patterns at higher temperatures. It was found that several phonon branches soften at specific wave vectors, which are incommensurate with respect to the original period and might be responsible for the modulation. We present a simple analytic treatment to deduce the wave vectors and associated displacement eigenvectors for the incommensurate soft-modes.
Title:
Atomic-scale observations of franckeite surface morphology
Authors:
Henriksen, RB; Makovicky, E; Stipp, SLS; Nissen, C; Eggleston, CM; Camblor, MA;
Source:
AMERICAN MINERALOGIST, 87 (10): 1273-1278; 2002
Abstract:
Franckeite, approximately Pb4.6Ag0.2Sn2.5Fe0.8Sb2S12.6, consists of alternating pseudohexagonal (H) and pseudotetragonal (Q) layers. Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) of freshly cleaved franckeite, from San Jose, Bolivia, revealed the atomic structure of the pseudohexagonal component. On AFM images, the expected pattern with b = 3.2 Angstrom was observed. STM revealed a root3 x root3 superstructure, with b' = 6.3 Angstrom, interpreted to be caused by tunneling effects. The pseudotetragonal layer was not identified in any images.Layer modulation, which results from the non-commensurate fit of the alternating H and Q layers, was observed with both AFM and STM. Modulation waves are sinusoidal and regular and they are always parallel. The calibrated modulation wavelengths averaged to 3.77, 4.10, 4.45, and 4.74 nm (with uncertainty less than or equal to0.10 nm) corresponding to pseudotetragonal/pseudohexagonal (Q/H) matches of 13/12, 14/13, 15/14, and 16/15, respectively. These correspond with observations made using bulk analytical methods on individual members from the franckeite-cylindrite family but scanning probe microscopy (SPM) was able to show that Q/H match varies on a local scale, with sharp domain boundaries. Domains can be on the order of 150 nm in width.
Title:
Formation and mechanical properties of Ti-Zr-Ni-Cu amorphous alloy containing icosahedral nanoscale quasicrystalline phase
Authors:
Wang, LM; Ma, LQ; Inoue, A; Fridriksson, T;
Source:
MATERIALS TRANSACTIONS, 43 (9): 2346-2349; 2002
Abstract:
Amorphous Ti60Zr15Ni15Cu10 alloy ribbons containing an icosahedral quasicrystalline phase were prepared by melt-spinning. The microstructure of this alloy strongly depends on cooling rate, which controlled by the circumferential velocity of copper roll. At a low velocity of 10 m/s, stable alpha-Ti/Zr, Ti2Ni and Ti2Cu crystalline phases are formed. At the velocities of 15 and 20 m/s, an icosahedral quasicrystal phase (I-phase) is formed directly. At the velocities of 25, 30 and 35 m/s, a mixed structure consisting of I- and amorphous phases is formed and the size of I-phase is in the range of 5-50 nm. At the high velocity of 40 m/s, a single amorphous phase is formed. The DSC traces of these melt-spun alloys obtained during continuous heating from room temperature to 1000 K at a heating rate of 0.67 K/s show distinct exothermic peaks. The amount of the first exothermic heat decreases with a decrease of cooling rate, indicating an increase of the precipitated I-phase in these melt-spun ribbons. For the single amorphous phase ribbon, the Vickers microhardness (H-v), tensile fracture strength (sigma(f)) and distinct plastic elongation (epsilon) are 460, 1480 and 1.42% respectively. For the nano-scale I-phase bearing amorphous composite ribbons, the sigma(f), Hv and epsilon depend on the volume fraction (V-f) of the I-phase. The maximum sigma(f) (1650 MPa) and epsilon (1.52%) was obtained at about V-f = 28% with particle size of 5-20 nm.
Title:
Peculiarities of second-harmonic generation in TlInS2 crystals
Authors:
Ibragimov, TD; Aslanov, II; Rao, CS;
Source:
SOLID STATE COMMUNICATIONS, 123 (8): 339-341; 2002
Abstract:
The temperature dependence of optical second-harmonic generation in TlInS2 crystals in the vicinity of phase transitions has been investigated. It is established that in an incommensurate phase the generation is observed only for propagation of the fundamental wave along the superstructure axis and its existence for certain experimental configurations confirms C-2(3) space group of the low-temperature polar phase. The dependence of the spectra on thermocycling process is explained by the formation and the annihilation of the incommensurate-like structures inside the commensurate phase. (C) 2002 Elsevier Science Ltd. All rights reserved.
Title:
Magnetic phase diagram and critical scattering of UNi2Si2
Authors:
Svoboda, P; Javorsky, P; Sechovsky, V; Menovsky, AA; Hofmann, M; Stusser, N; Sankey, OF;
Source:
PHYSICA B-CONDENSED MATTER, 322 (3-4): 248-251; 2002
Abstract:
In this paper, we present the results of a neutron-scattering study on a single crystal of UNi2Si2. This material crystallizes in the tetragonal ThCr2Si2-type structure and orders antiferromagnetically (AF) at T-N = 125 K. Below T-N, it exhibits three different AF phases in zero magnetic field. The phases are strongly anisotropic with the U moment parallel to the c-axis, forming ferromagnetic basal planes. Between T-N and 108 K, the incommensurate AFI phase with q = (0, 0, q(z)) is established (q(z) similar to 0.74). The intermediate phase AF2, between 108 and 40 K, is of the AF-I type with q = (0, 0, 1) and the ground-state phase AF3 is an uncompensated squared-up AF structure with (+ + -) stacking of the basal planes along the c-axis (q = (0, 0, 2/3)). Both the 108 and 40 K transitions are of the first order. The complex magnetic phase diagram of UNi2Si2 was studied in horizontal magnetic fields parallel to the c-axis up to 6 T. Above T-N, the critical scattering was studied in zero field. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Confirmation of the existence of modulation wave motion in incommensurate Rb2ZnCl4 by Hahn echo and 2D NMR
Authors:
Muntean, L; Mikac, U; Subramanian, RK; Ailion, DC; Reinhardt, L;
Source:
ZEITSCHRIFT FUR NATURFORSCHUNG SECTION A-A JOURNAL OF PHYSICAL SCIENCES, 57 (6-7): 353-362; 2002
Abstract:
Rb-87 Hahn echo nuclear magnetic resonance (NMR) and Cl-35 Hahn echo nuclear quadrupole resonance (NQR) measurements were performed at 293 - 302 K in the incommensurate (I) phase of Rb2ZnCl4. The existence of a Hahn echo decay that is shorter than the true T-2 and one that has an exponential dependence on the cube of the echo time indicates the presence of slow motions. The diffusion coefficient D can be obtained from the rate of decay of the Hahn echo. Similar values for D were obtained from the two different measurements, indicating that both the Rb and the Cl atoms are experiencing the same motional mechanism. This mechanism must be due to simultaneous motions of each and can not be due to individual motions of only one type of atom. Further confirmation of the presence of modulation wave motion was obtained from Rb-87 two-dimensional (2D) exchange-difference NMR measurements.
Title:
Cl-35 NQR study of phase soliton formation and residual commensurations in K2ZnCl4
Authors:
Oh, DK; Lee, CE; Jeong, SY; Ailion, DC;
Source:
ZEITSCHRIFT FUR NATURFORSCHUNG SECTION A-A JOURNAL OF PHYSICAL SCIENCES, 57 (6-7): 363-368; 2002
Abstract:
In order to investigate the dynamics of the ZnCl4 tetrahedra in K2ZnCl4, Cl-35 nuclear quadrupole resonance was employed for the spin-lattice relaxation measurements of each of the triplicated Cl sites in the lock-in phase. The temperature dependence of the spin-lattice relaxation rate (1/T-1Q) indicates that the domain peak observed in the incommensurate phase arises from the ZnCl4 tetrahedral site with a negligible reorientational motion. On the other hand, an activated reorientational motion of the other two ZnCl4 tetrahedral sites appears to lead to the phase solitons. Molecular motions in Rb2ZnCl4 and in Cs2ZnCl4, undergoing an incommensurate an not incommensurate phase transition, respectively, were also compared.
Title:
H-1, H-2 and C-13 NMR studies of cation dynamics in a layered perovskite-type incommensurate compound (n-C3H7NH3)(2)CdCl4
Authors:
Suzuki, K; Fujimori, H; Asaji, T; Ishimaru, S; Ikeda, R; Bershtein, V;
Source:
ZEITSCHRIFT FUR NATURFORSCHUNG SECTION A-A JOURNAL OF PHYSICAL SCIENCES, 57 (6-7): 451-455; 2002
Abstract:
Cation dynamics in (n-C3H7NH3)(2)CdCl4 and (n-C3H7ND3)(2)CdCl4 were investigated by H-1, H-2, and C-13 NMR measurements. An overall motion of the cation being associated with the fluctuation of the molecular axis is suggested to be activated with increasing temperature. The cationic motion is enhanced at the counter side of the -NH3+ group probably because the group is bound with the inorganic layer through the N-H...Cl hydrogen bonds.
Title:
Incommensurability and domain structure of K2SbF5
Authors:
Panich, AM; Zemnukhova, LA; Davidovich, RL; Ishimaru, S;
Source:
ZEITSCHRIFT FUR NATURFORSCHUNG SECTION A-A JOURNAL OF PHYSICAL SCIENCES, 57 (6-7): 456-460; 2002
Abstract:
Phase transitions and incommensurability in K2SbF5 have been studied by means of Sb-123 NQR spectra and spin-lattice relaxation measurements. The phase transitions occur at 117, 135 and 260 K. The line shape and temperature dependence of the spin-lattice relaxation time T, at 135 to 260 K are characteristic for an incommensurate state with a plane wave modulation regime. At 117 to 135 K a distinct fine structure of the NQR spectra has been observed. The X-ray diffraction pattern of this phase is interpreted as a coexistence of two modulation waves along the a and b axis with wave vectors (a*/6 +b*/6) and (a*/2 +b*/2), respectively. The best interpretation that fits our NQR data is a coexistence of two domains, the structures of which are modulated with different periods in such a manner that each domain exhibits only one of the aforementioned modulation waves. Redistribution of line intensities with the variation of temperature shows that one of the domains becomes energetically preferable on cooling and is transformed into the low temperature phase at 117 K. The Sb-123 NQR measurements in K2SbF5 show unusually short values of T-1, which become close to the spin-spin relaxation time T-2 with increasing temperature. - Pacs: 61.44.Fw, 64.60, 64.70, 64.70.Rh, 76.60.
Title:
Structure of Dy13Zn57 a binary quasicrystal approximant
Authors:
Gomez, CP; Lidin, S; Davidovich, RL;
Source:
SOLID STATE SCIENCES, 4 (7): 901-906; 2002
Abstract:
The title compound Dy13Zn57, crystallizes in the orthorhombic space group Pnma (No. 62) with the cell parameters a = 14,060(5), b = 14.260(5) and c = 24.700(3) Angstrom. The structure has formerly been described as Dy13Zn58 with the hexagonal type structure of Gd13Zn58. Single-crystal X-ray diffraction measurements however, show extra reflections breaking the C-centering of the corresponding orthorhombic cell with the parameters a(o) approximate to c(h), b(o) approximate to a(h) and c(o) approximate to root3 x a(h) and thereby making it primitive. The title compound is comprised of structural building units that also are encountered in the other RE13Zn58 (RE = rare earth) compounds. the related RE13Cd58, the RECd6 phases and the newly found binary quasicrystal YbCd5.7. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.
Title:
Stability of supercooled liquid and transformation Behavior in Zr-based glassy alloys
Authors:
Saida, J; Matsushita, M; Inoue, A; Audier, M;
Source:
MATERIALS TRANSACTIONS, 43 (8): 1937-1946; 2002
Abstract:
We investigated the stability of the supercooled liquid in Zr-based glassy alloys by examination of their transformation behavior. The primary phase is an fee Zr2Ni phase in a Zr65Al7.5Ni10Cu17.5 glassy alloy with high glass-forming ability (GFA). By substitution of Ag, Pd, Au or Pt for only 1 at%Cu, an icosahedral quasicrystalline phase (I-phase) precipitates with the fee Zr2Ni phase. The primary phase changes to the single I-phase at higher noble metal contents. It is further found that the I-phase precipitates by a small amount of substitution for Cu with other elements as well as the noble metals, which have a weak or positive chemical affinity with one of the constitutional elements in the Zr-Al-Ni-Cu glassy alloy. Thus, the slight deviation from the three component rules for high GFA is effective for the I-phase formation. The I-phase is also formed as a primary phase in the Zr65+yAl7.5Ni10Cu17.5-y (y = 1-7) glassy alloys. A slight change in the composition has the similar effect as the addition of element such as noble metals and so on. An icosahedron is contained as a structure unit in the fee Zr2Ni and I-phases and hence the glassy structure is correlated with the local icosahedral atomic configuration. The high-resolution transmission electron microscopy image of the Zr70Al7.5Ni10Cu12.5 glassy alloy reveals a possibility of the existence of the icosahedral ordered regions. It is therefore, concluded that the icosahedral short- or medium-range order exists in the supercooled liquid as well as in the glassy phase and it stabilizes the supercooled liquid state in the Zr-based alloys. An I-phase also precipitates as a primary phase by substituting Pd, Au or Pt for only 1 at%Cu in the Zr70Cu30 glassy alloy. From these results, the appearance of the supercooled liquid region is attributed to the existence of the icosahedral atomic configuration consisting of Zr and Cu.
Title:
Structural characterisation and mechanical properties of nanocomposite Al-based alloys
Authors:
Audebert, F; Prima, F; Galano, M; Tomut, M; Warren, PJ; Stone, IC; Cantor, B; Cheetham, AK;
Source:
MATERIALS TRANSACTIONS, 43 (8): 2017-2025; 2002
Abstract:
Nanocomposite Al-based alloys can be obtained with a combination of amorphous, crystalline and quasicrystalline phases. In order to understand the correlation between the nanostructure and the mechanical behaviour, four nanocomposite alloys with different characteristics were studied: two alloys from the Al-Fe-Cr-Ti system consisting of a spherical nanoquasicrystalline phase in an alpha-Al matrix; one alloy from the Al-Fe-V-Ti system consisting of a mixture of amorphous and alpha-Al phases; and one alloy from the Al-Mn-Cr-Cu system consisting of nanocrystalline particles embedded in an alpha-Al matrix. Melt-spun samples were prepared and the structure was characterised by means of X-ray diffraction and transmission electron microscopy. Differential scanning calorimetry was used to study the thermal stability and the transformation processes. Tensile tests, fractographic analysis and Vickers microhardness at room temperature were performed in order to evaluate the mechanical behaviour. A combination of solid solution, particle dispersion and grain refinement strengthening was responsible for the high strength of the alloys. The microstructure of the alloy Al93Fe3Cr2Ti2 (at%) remained acceptably stable up to 703 K, due to the slow coarsening rate of the icosahedral phase.
Title:
Hydrogen pressure-composition isotherms for Ti45Zr38Ni17 amorphous and quasicrystal powders produced by mechanical alloying
Authors:
Takasaki, A; Huett, VT; Kelton, KF; Inoue, A;
Source:
MATERIALS TRANSACTIONS, 43 (8): 2165-2168; 2002
Abstract:
Pressure-composition isotherms (PCTs) for amorphous and icosahedral (i) quasicrystal powders produced by mechanical alloying of Ti45Zr38Ni17 powder mixtures were measured at temperatures of 473K and 523K at low-hydrogen pressures, lower than 0.1 MPa. Sloping plateau-like features on PCTs were observed at equilibrium hydrogen pressures lower than 1kPa, below an H/M (hydrogen to metal atom ratio) approximate to 1.2 and approximate to 1 for the amorphous and i-phase powders respectively. The plateau-like region for the i-phase powder was steeper and narrower than that for the amorphous powder, implying some small differences between the local structures of the i-phase and the amorphous phase. After the PCT measurements, an increase in the nearest-neighbor atom spacing and an expansion of the quasilattice were observed for the amorphous and i-phase powders respectively. Impurities from some unsynthesized elemental material and a Ti2Ni type phase were also present. These also absorbed hydrogen, shown by an expansion of their crystal lattices. However, no crystal hydride formation was observed in any of the powders.
Title:
Studies of the R-phase transformation in a Ti-51at.%Ni alloy by transmission electron microscopy
Authors:
Stroz, D; Yamamoto, A;
Source:
SCRIPTA MATERIALIA, 47 (6): 363-369; 2002
Abstract:
The R-phase transformation in a Ti-51at.%Ni shape memory alloy was studied by transmission electron microscopy including high resolution microscopy and in situ observations on cooling. It was found that prior to this transformation there is a wide temperature range at which an incommensurate phase exists in the alloy. The incommensurability decreases with the temperature decrease reaching finally the lock-in R-phase state. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
An aperiodic tiles machine
Authors:
Caceres, J; Marquez, A; Cerny, P;
Source:
COMPUTATIONAL GEOMETRY-THEORY AND APPLICATIONS, 23 (2): 171-182; 2002
Abstract:
The results we introduce in this work lead to get an algorithm which produces aperiodic sets of tiles using Voronoi diagrams. This algorithm runs in optimal worst-case time O(n log n). Since a wide range of new examples can be obtained, it could shed some new light on non-periodic tilings. These examples are locally isomorphic and exhibit the 5-fold symmetry which appears in Penrose tilings and quasicrystals. Moreover, we outline a similar construction using Delaunay triangulations and propose some related open problems. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Meta-stable region of Al5Ti3 single-phase in time-temperature-transformation (TTT) diagram of Ti-62.5 at.% Al single crystal
Authors:
Hayashi, K; Nakano, T; Umakoshi, Y; Jones, RD;
Source:
INTERMETALLICS, 10 (8): 771-781; 2002
Abstract:
A time-temperature-transformation (TTT) diagram in an annealing temperature range between 500 and 900 degreesC within 100 h was examined focusing on the constituent long-period superstructures in Ti-62.5 at.% Al single crystals after the plate-like r-Al2Ti precipitates were removed by quenching at 1200 degreesC. The h-Al2Ti and Al5Ti3 superstructures with three and four-fold periodicities, respectively, with respect to a unit of the L1(0) structure appeared in accordance with annealing temperature and time. In the transition from h-Al2Ti to Al5Ti3, a modulated structure with 12-fold periodicity appeared and it was explained by a hypothetical structure overlapping h-Al2Ti and Al5Ti3. Although r-Al2Ti was a stable phase in Ti-62.5 at.% Al single crystals annealed at temperatures below 1200 degreesC, the Al5Ti3 single-phase single crystals without the L1(0) phase and other superstructural phases, which are never available under an equilibrium condition, were obtained in a wide time range for annealing at 700 and 750 degreesC. (C) 2002 Elsevier Science Ltd. All rights reserved.
Title:
Quasicrystalline Al-based alloys by physical laser deposition
Authors:
Copola, J; Audebert, F; Duhalde, S; Ogletree, DF;
Source:
METASTABLE AND NANOSTRUCTURED MATERIALS - NANOMAT-2001, PROCEEDINGS, 403 (5588): 27-32; 2002
Abstract:
The icosahedral quasicrystalline phase (i-phase), has a five-fold symmetry axes and shows relevant properties. Potential applications of quasicrystalline coatings typically involve their use as solar selective absorbers. Moreover, the combination of its high hardness and Young's modulus values with a low friction coefficient make these alloys attractive for tribological applications. In a previous work, the process to produce quasicrystalline coatings by laser cladding was described [1]. That thick coating resulted very hard, although the presence of microcracks on the surface limits their use as tribological. coatings.In this work, first results concerning the preparation of Al-based quasicrystalline thin films by pulsed laser deposition (PLD) are presented. The influence of deposition parameters, such as fluence, nature of the target and substrate structure on the deposited films was analysed. Different phases were obtained depending on the deposition parameters. The amorphous films were annealed under different conditions in order to obtain the icosahedral phase. Crystalline phases were favoured to form when metallic substrates were used.
Title:
Topological invariants for projection method patterns
Authors:
Forrest, A; Hunton, J; Kellendonk, J; Ogletree, DF;
Source:
MEMOIRS OF THE AMERICAN MATHEMATICAL SOCIETY, 159 (758): 1-+; 2002
Abstract:
This memoir develops, discusses and compares a range of commutative and non-commutative invariants defined for projection method tilings and point patterns. The projection method refers to patterns, particularly the quasiperiodic patterns, constructed by the projection of a strip of a high dimensional integer lattice to a smaller dimensional Euclidean space. In the first half of the memoir the acceptance domain is very general - any compact set which is the closure of its interior - while in the second half we concentrate on the so-called canonical patterns. The topological invariants used are various forms of K-theory and cohomology applied to a variety of both C*-algebras and dynamical systems derived from such a pattern.The invariants considered all aim to capture geometric properties of the original patterns, such as quasiperiodicity or self-similarity, but one of the main motivations is also to provide an accessible approach to the the K-0 group of the algebra of observables associated to a quasicrystal with atoms arranged on such a pattern.The main results provide complete descriptions of the (unordered) K-theory and cohomology of codimension 1 projection patterns, formulae for these invariants for codimension 2 and 3 canonical projection patterns, general methods for higher codimension patterns and a closed formula for the Euler characteristic of arbitrary canonical projection patterns. Computations are made for the Ammann-Kramer tiling. Also included are qualitative descriptions of these invariants for generic canonical projection patterns. Further results include an obstruction to a tiling arising as a substitution and an obstruction to a substitution pattern arising as a projection. One corollary is that, generically, projection patterns cannot be derived via substitution systems.
Title:
The structure of quasicrystals studied by atomic-scale observations of transmission electron microscopy
Authors:
Hiraga, K; Balasubramanian, S;
Source:
ADVANCES IN IMAGING AND ELECTRON PHYSICS, VOL 122, 122 (3): 1-86; 2002
Abstract:
---
Title:
'Size-effect'-like distortions in quasicrystalline structures
Authors:
Welberry, TR; Honal, M; Kellendonk, J;
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 217 (7-8): 422-426; 2002
Abstract:
We show in this paper that by applying size-effect distortions to a perfect Penrose tiling, on the basis that rhomb-edges which connect different types of vertices assume different lengths, we can obtain a diffraction pattern which shows remarkable similarity to the zero-level (h(5) = 0) section observed in decagonal Al71Co13Ni16. In particular a central clearly delineated decagon is observed, on the inside of which there is reduced intensity, and on the outside of which there is enhanced intensity. Such a transfer of intensity is characteristic of size-effect distortions in crystals but for these systems it is necessary to have disorder involving (at least) two types of atoms. In the present case the effect is observed with all vertices occupied by a single scatterer and the system remains topologically equivalent to the Penrose pattern with long range quasicrystallinity.
Title:
Low-temperature X-ray studies of a [CH3)(2)NH2](2)center dot Cul(4) crystal
Authors:
Sheleg, AU; Zub, EM; Yachkovskii, AY; Kirpichnikova, LF; Salmeron, M;
Source:
CRYSTALLOGRAPHY REPORTS, 47 (4): 577-580; 2002
Abstract:
The a, b, c lattice parameters of a [(CH3)(2)NH2](2).CuCl4 crystal have been measured by the X-ray diffraction method within the temperature range of 100-300 K. The temperature dependences of thermal expansion coefficients alpha(a) =f(T), alpha(b) =f(T), and alpha(c) =f(T) along the principal crystallographic axes and thermal expansion coefficient of the unit-cell volume alpha(V) =f(T) are determined. It is found that all the three parameters, a, b, and c, vary with temperature in a complicated way and show jumplike anomalies in the a =f(T), b = f(T), and c =f(T) curves at phase-transition temperatures T-c1 = 255 K and T-c2 = 279 K. An incommensurate phase with the modulation wave vector q(i) = (1/2 + delta)(a* + c*) is revealed in the temperature range 279-296 K. It is shown that the incommensurability parameter delta increases with an increase in temperature. (C) 2002 MAN "Nauka/Interperiodica".
Title:
Positron diffusion in icosahedarl quasicrystals
Authors:
Sato, K; Uchiyama, H; Kanazawa, I; Tamura, R; Kimura, K; Takeuchi, S; Takeuchi, T; Mizutani, U; Rathz, TJ;
Source:
APPLIED SURFACE SCIENCE, 194 (1-4): 155-159; 2002
Abstract:
We have analyzed the measured S-parameters as a function of positron incident energy for the icosahedral quasicrystal (QC) Al71.5Pd20.3Mn8.2 and Al70.7Pd21.34Re7.96 within the framework of the structural model of approximant crystal. Highly resistive icosahedral QC Al72Pd21Re7 was investigated by the slow positron beam technique. The result indicated that icosahedral QC Al72Pd21Re7 contains a dense distribution of structural vacancy-type sites like another icosahedral QCs. Considerably high structural vacancy densities (on the order. of 10(20) cm(-3)) Were determined. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Observation of multiple stop bands in photonic bandgap structures doped with organic dyes
Authors:
Nozar, P; DiDomenico, D; Dionigi, C; Losurdo, M; Muccini, M; Taliani, C; Takeuchi, T;
Source:
ADVANCED MATERIALS, 14 (15): 1023-+; 2002
Abstract:
Intensity enhancement of the optical stop band of a periodic quasicrystalline structure is achieved by infiltrating this structure with a suitable dye, as demonstrated for monodisperse polystyrene beads doped with the organic dye Oil Red EGN. A detailed discussion of the optical properties of the system is given in terms of the Bragg and Snell laws, and constraints concerning the refractive index of the dye, LATEX bead diameter, and quasicrystal lattice are extracted. Following some simple geometrical constraints the opening of the photonic bandgap can thus be tuned.
Title:
Thermoelectric properties of binary Cd-Yb quasicrystal and its approximant
Authors:
Muro, Y; Sasakawa, T; Suemitsu, T; Takabatake, T; Tamura, R; Takeuchi, S; Torres, JM;
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 41 (6A): 3787-3790; 2002
Abstract:
The thermoelectric properties of the binary quasicrystal Cd84.6Yb15.4 and its approximant Cd6Yb are reported. The thermopowers decrease linearly from 14 and 12 muV/K, respectively, with decreasing temperature from 300 K. The resistivities at 300 K are 180 and 150 muOmega.cm, respectively, and decrease rapidly on cooling below 100 K. These results indicate that Cd-Yb compounds possess a metallic nature, in contrast to the semiconductor-like behavior of conventional ternary quasicrystals. The phonon thermal conductivity kappa(ph)(T) of Cd-Yb compounds shows no maximum, but is described by a power law, K-ph infinity T-n, with n = 0.5 and 1.0, respectively, for Cd84.6Yb15.4 and Cd6Yb. The thermoelectric dimensionless figures of merit ZT are estimated to be 0.003 and 0.004 at 300 K, respectively.
Title:
Incommensurate and inhomogeneous phases in improper ferroelastic MgSiF6 center dot 6H(2)O: Mn2+ studied by EPR
Authors:
Skrylnik, PG; Ziatdinov, AM; Suemitsu, T;
Source:
FERROELECTRICS, 249 (3-4): 279-299; 2001
Abstract:
The results of EPR study of inhomogeneous and incommensurate phases in improper ferroelastic crystals MgSiF6.6H(2)O:Mn2+ are presented. On the basis of analysis of temperature and angular dependences of experimental parameters and numerical calculations the conclusion has been drawn that at T-i1=370+/-0.3 K considered crystals undergo transition to structurally incommensurate phase and the order parameter of this transition may be angle of Mg[H2O](6)(2+) octahedra rotation around crystal C-3 axis. From T-i1 to T-i2=343+/-0.3 K the incommensurate phase evolve according to classical complete scenario; origin of incommensurate structure with plane-wave modulation at T-i1, appearance of structural phase soliton lattice with temperature decrease, and, finally, abrupt decrease in soliton density at T-i2 down to values approximate to0.1. The assumption was expressed that at T-i2 the crystals investigated undergo phase transition from incommensurate phase to another inhomogencous phase, in which studied crystals consist of two types of regions characterized by homogeneous and inhomogeneous structural organization. The performed calculation of spectral density functions has shown that the structure of former regions almost does not change with temperature variation whereas that of latter ones considerably modifies when the temperature tends to the improper ferroelastic phase transition temperature T-C=296.5+/-03 K.
Title:
Three-component quasiperiodic superlattice and its Fourier spectrum
Authors:
Wei, H; Zhang, C; Zhu, YY; Zhu, SN; Ming, NB; Takeuchi, S;
Source:
FERROELECTRICS, 253 (1-4): 803-810; 2001
Abstract:
The domain-inverted ferroelectric materials, or simply the dielectric superlattice, can be patterned into different configurations. For example, there are the periodic, quasiperiodic, Thue-Morse and several other types. The periodic superlattice is widely used for the second-harmonic generation, sum-frequency generation and optical parametric oscillation, for which only one optical parametric process is involved. The two-components quasiperiodic superlattice has been proved useful to some coupled parametric processes such as the direct third-harmonic generation. In this paper a three-component quasiperiodic superlattice has been discussed theoretically. Using the projection method, the analytical expression of its Fourier spectrum has been derived. Relations with the periodic and two-components quasiperiodic superlattices has been given. The results might be useful to the design of nonlinear optical devices related to the coupled parametric processes.
Title:
X-ray photoelectron spectroscopic studies on nanoquasicrystalline powders of Al70Cu20Fe10 obtained by mechanical alloying
Authors:
Barua, P; Srinivas, V; Dhabal, S; Ghosh, TB; Guranich, PP;
Source:
JOURNAL OF MATERIALS RESEARCH, 17 (8): 1892-1895; 2002
Abstract:
Surface chemical properties of nanoguasicrystalline powders of Al-Cu-Fe synthesized by the ball-milling technique have been investigated using x-ray photoelectron spectroscopy (XPS). The samples were exposed to ambient conditions at room temperature as well as higher temperatures. Our XPS results reveal that the surfaces of nanopowders of Al70Cu20Fe10 are coated with an Al2O3 layer within which the quasicrystalline phase resides. It also appears that the thickness of this layer does not increase significantly on either heating below 873 K or prolonged exposure to ambient conditions.
Title:
Electronic conduction in quasicrystals at low temperatures
Authors:
Vekilov, YK; Isaev, EI; Binder, K;
Source:
JETP LETTERS, 75 (11): 583-584; 2002
Abstract:
At low temperatures, a perfect quasicrystal is in the "critical" state of metal-insulator transition. A power-law temperature dependence of conductivity, which was experimentally observed at T < 5 K in the icosahedral phase of Al-Pd-Re, was obtained using the critical wave functions. Mott's hopping law was also observed in the Al-Pd-Re samples and explained by the delocalization of electronic states in the momentum space. (C) 2002 MAIK "Nauka/Interperiodica".
Title:
Sign reversals of the carriers and the volume change in Al-Cu-Fe quasicrystalline alloys
Authors:
Prekul, AF; Kazantsev, VA; Kuz'min, NY; Shchegolikhina, NI; Guranich, PP;
Source:
JETP LETTERS, 75 (11): 585-587; 2002
Abstract:
New results of dilatometric experiments with rapidly quenched Al-Cu-Fe quasicrystalline alloys in the course of their thermal annealing are presented. It is established that the icosahedral (I) phases with different types of carriers exhibit different signs of volume changes with ordering. The observed effect is a direct experimental proof of the fact that structural defects in icosahedral quasicrystals are electrically active centers. (C) 2002 MAIK "Nauka/Interperiodica".
Title:
Influence of electric field in commensurate-incommensurete phase transition of Rb2ZnCl4
Authors:
Martin-Olalla, JM; Ramos, S; del Cerro, J; Vasiliev, AA;
Source:
FERROELECTRICS, 271 (1-4): 1957-1962; 2002
Abstract:
The commensurate-incommensurate phase transition in Rb2ZnCl4 single crystal is studied under three external applied field. We measured simultaneously the dielectric permittivity and the heat flux exchanged by the sample. We study the evolution of the transition enthalpy with the applied field. We also observe the formation of a polar incommensurate phase during the cooling process with external field.
Title:
The phase transitions in ferroelectric crystals of A(2)MX(4) and AMX(3) type
Authors:
Kaluza, S; Suchanska, M; Belka, R; Lesniewski, S; Shigenari, T;
Source:
FERROELECTRICS, 273 (1-4): 2521-2526; 2002
Abstract:
Investigations of characteristics the ferroelectric crystals of A(2)MX(4) and AMX(3) type with incommensurate phases are very interesting both from a scientific and practical point of view. Some aspects of behaviour phase transitions of these crystals are discussed. Special attention is paid to the temperature dependence of series of different type phase transitions. Analysis of the literature data and results of our research let us to consider potential possibilities of practical applications of these materials for optoelectronic devices. Observed temperature hysteresis of birefringence and absorption coefficient in incommensurate phases are especially important for application as optical memories.
Title:
Resistivity studies on Al-Zn-Mg system
Authors:
Joshi, SK; Mehta, L; Deshpande, AP; Trasobares, S;
Source:
INDIAN JOURNAL OF PURE & APPLIED PHYSICS, 40 (7): 482-488; 2002
Abstract:
The preparation, characterisation and resistivity studies of Al-Zn-Mg system have been reported. The samples included in the present paper are: (i) Al21Zn42Mg37, (ii) Al21Zn41Mg38, (iii) Al21Zn40Mg39, (iv) Al21Zn39Mg40 and (v) Al21Zn38Mg41, The X-ray diffraction (XRD) studies indicate the presence of the icosahedral phase in these samples. Measurements of resistivity (rho) of the samples and its variation with temperature have been carried out. The plot of (rho) versus T indicate negative slope. The mechanism of transport for the icosahedral phase of Al-Zn-Mg samples over the temperature range 25300 K is explained on the basis of mechanism of hopping through the critical states.
Title:
Ta97Te60: A crystalline approximant of a tantalum telluride quasicrystal with twelvefold rotational symmetry
Authors:
Conrad, M; Harbrecht, B; Deshpande, AP;
Source:
CHEMISTRY-A EUROPEAN JOURNAL, 8 (14): 3094-3102; 2002
Abstract:
The crystal structure of a rational approximant of an unprecedented dodecagonal quasicrystal is reported. The atomic arrangement of the tantalum-rich telluride Ta97Te60 has been determined from 30458 symmetrically independent X-ray intensities of a crystal twinned by metric merohedry: a = 2767.2(2), b = 2767.2(2), c = 2061.3(2) pm, space group P2(1)2(1)2(1), Pearson symbol oP628, 1415 variables, R(F) = 0.059. A dodecagonal-shaped, vaulted Ta151Te74 cluster with maximum symmetry 6mm can be seen as a characteristic motif of the structure. Each cluster measures about 2.5 nm across and consists of nineteen concentrically condensed hexagonal antiprismatic Ta-13 clusters which are capped with Te atoms. The Ta151Te74 clusters can cover the plane distinctly in different ways, thereby forming a series of phases which are closely related both structurally and compositionally. In Ta97Te60 the buckled clusters decorate the vertices of a square tiling at a 2 nm length scale to result in corrugated lamellae (2)(infinity)[Te30Ta41Ta15Ta41Te30] each about 1 nm thick. The lamellae are stacked along the c axis, corresponding to the direction of the b pseudo-twelve fold axis of symmetry. Symmetry arguments are proposed that the twinning of the structure may be associated with a fine-tuning of weak interlayer Te - Te interactions which are reflected in a minimization of the deviation from the mean distance [d(Te-Te)] and a doubling, of the stacking vector c.
Title:
Processing, structure and mechanical behavior of rapidly solidified aluminum alloys containing quasicrystalline particles
Authors:
Milman, YV; Lotsko, DV; Neikov, OD; Sirko, AI; Yefimov, NA; Bilous, AN; Miracle, DB; Senkov, ON; Radnoczi, G;
Source:
ALUMINUM ALLOYS 2002: THEIR PHYSICAL AND MECHANICAL PROPERTIES PTS 1-3, 396-4 (14): 723-728; 2002
Abstract:
Aluminum-based alloys containing quasicrystalline particles of 50 - 600 nm in diameter as a reinforcing phase were produced in the form of powder or ribbons by water atomization or melt spinning techniques, respectively. Rods were compacted from the powders and some ribbons, and their mechanical properties were determined. Microstructures and phases in powders, ribbons and compacted rods were investigated using TEM and X-ray diffraction. Several alloys produced had high strength (about 300 MPa) at temperatures up to 300 degreesC. The quasicrystalline particles were stable for coarsening and decomposition at temperatures up to 400 degreesC.
Title:
Novel charge density wave transition in crystals of R5Ir4Si10
Authors:
Ramakrishnan, S; Yamanaka, M;
Source:
PRAMANA-JOURNAL OF PHYSICS, 58 (5-6): 827-837; 2002
Abstract:
We review the observation of novel charge density wave (CDW) transitions in ternary R5Ir4Si10 compounds. A high quality single crystal of Lu5Ir4Si10 shows the formation of a commensurate CDW along c-axis below 80 K in the (h, 0, 1) plane that coexists with BCS type superconductivity below 3.9 K. However, in a single crystal of Er5Ir4Si10, one observes the development of a I D-incommensurate CDW at 155 K, which then locks into a purely commensurate state below 55 K. The well-localized Er-3 moments are antiferromagnetically ordered below 2.8 K which results in the coexistence of strongly coupled CDW with local moment antiferromagnetism in Er5Ir4Si10. Unlike conventional CDW systems, extremely sharp transition (width similar to 1.5 K) in all bulk properties along with huge heat capacity anomalies in these compounds makes this CDW transition an interesting one.
Title:
Magnetism and superconductivity in ErNi2B2C
Authors:
Bancroft, NJ; Paul, DM; McIntyre, G; Dewhurst, CD; Cubitt, R; Bilous, AN;
Source:
PRAMANA-JOURNAL OF PHYSICS, 58 (5-6): 907-911; 2002
Abstract:
We have performed a series of neutron diffraction experiments from the magnetic order and the vortex lattice in single crystal ErNi2B2C. The incommensurate magnetic structure develops additional even harmonics below the 'ferromagnetic' ordering temperature, T-F of 2.3 K. This feature and the existence of rods of diffuse scattering suggest the development of ferromagnetic microdomain walls. The magnetic structure is very sensitive to the application of a magnetic field with changes in modulation vector and harmonic content. Studies of the vortex lattice show the presence of a 45degrees reorientation transition and a distorted hexagonal to square transition as a function of applied field. Further distortions of the vortex lattice occur at T-N, but no changes are seen at TF.
Title:
Commensurability oscillations in NdBa2Cu3Oy single crystals
Authors:
Kupfer, H; Ravikumar, G; Wolf, T; Zhukov, AA; Wuhl, H; Bilous, AN;
Source:
PRAMANA-JOURNAL OF PHYSICS, 58 (5-6): 919-924; 2002
Abstract:
Commensurability between inter-vortex distance and crystal lattice constant is investigated by angular dependent magnetization in very pure twinned and twin-free NdBa2 Cu-3 O-y single crystals. With increasing temperature the incommensurate states split up and become finally commensurate with half the vortex distance. These new commensurate states are related to a substructure of the intrinsic pinning potential within the unit cell and discussed with respect to temperature, field, anisotropy, and twin structure.
Title:
Low-temperature studies on the two-dimensional modulations in akermanite-type crystals: Ca2MgSi2O7 and Ca2ZnSi2O7
Authors:
Bagautdinov, B; Hagiya, K; Noguchi, S; Ohmasa, M; Ikeda, N; Kusaka, K; Iishi, K; Senkov, ON;
Source:
PHYSICS AND CHEMISTRY OF MINERALS, 29 (5): 346-350; 2002
Abstract:
Two-dimensional modulation in synthetic akermanite (Ca2MgSi2O7) and hardystonite (Ca2Zn Si2O7) has been studied by the single-crystal X-ray diffraction methods in the temperature range between 18 and 297 K. It is found that change of the modulation wavelength Ca2MgSi2O7 is slight, but that in Ca2ZnSi2O7 it is noticeable and indicates a plateau-like temperature dependence. The plateau-like region may be regarded as an independent phase with a specific q [similar to0.2924(3)].
Title:
A neutron scattering and mu SR investigation of the magnetic phase transitions of CuB2O4
Authors:
Boehm, M; Roessli, B; Schefer, J; Ouladdiaf, B; Amato, A; Baines, C; Staub, U; Petrakovskii, GA; Radnoczi, G;
Source:
PHYSICA B-CONDENSED MATTER, 318 (4): 277-281; 2002
Abstract:
We have investigated the magnetic ground state in CuB2O4, copper metaborate, by means of neutron diffraction and muSR measurements. At T-N = 21 K CuB2O4 undergoes a second-order phase transition from a paramagnetic to an antiferromagnetic commensurate state followed by a second transition at T* = 10 K where the two magnetic sublattices form a soliton lattice, as reported earlier. We give a detailed analysis of the magnetic structure in the commensurate phase which is found to be different from the one published recently. New experimental results are presented which show the existence of a third transition below T approximate to 1.8 K. The magnetic structure remains incommensurate at very low temperatures, but a re-distribution of the magnetic intensities is observed in the neutron diffraction data set which suggests that the phases between the Cu2+ spins are changed. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Precipitation of icosahedral quasicrystalline and crystalline approximant phases in Zr-Cu-(Co, Rh or Ir) metallic glasses
Authors:
Li, CF; Wang, LM; Inoue, A; Vasenkov, S;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 306 (2): 175-181; 2002
Abstract:
Zr70Cu30, Zr70Cu20Co10, Zr70Cu20Rh10 and Zr70Cu20Ir10 glassy alloys were prepared by the single roller melt-spinning method and the crystallization process was studied by differential scanning calorimetry, X-ray diffraction and transmission electron microscopy, with an emphasis on the initial stage. The Zr70Cu30 metallic glass crystallizes through the direct precipitation of the stable crystalline phase from the matrix. The addition of Co, Rh and Ir to the Zr70Cu30 metallic glass induces the precipitation of metastable phases prior to the formation of the stable ones. The metastable phases are a Ti2Ni-type compound for Zr70Cu20Co10, a mixture of the Ti2Ni-type compound and an icosahedral quasicrystalline phase (I-phase) for Zr70Cu20Rh10, and the I-phase for Zr70Cu20Ir10 metallic glasses. The different effects of Co, Rh and Ir addition are explained based on their difference in atomic radius. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Quasicrystals, aperiodic order, and groupoid von Neumann algebras
Authors:
Lenz, D; Stollmann, P; Kalugin, V;
Source:
COMPTES RENDUS MATHEMATIQUE, 334 (12): 1131-1136; 2002
Abstract:
We introduce tight binding operators for quasicrystals that are parametrized by Delone sets. These operators can be regarded in a natural operator algebra framework that encodes the long range aperiodic order. This algebraic point of view allows us to study spectral theoretic properties. In particular, the integrated density of states of the tight binding operators is related to a canonical trace on the associated von Neumann algebra. (C) 2002 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.
Title:
The transition from elastic to plastic behaviour in an Al-Cu-Fe quasicrystal studied by cyclic nanoindentation
Authors:
Dub, S; Novikov, N; Milman, Y; Volkova, N;
Source:
PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 82 (10): 2161-2172; 2002
Abstract:
Comparative mechanical tests of an Al-Cu-Fe quasicrystal and a tungsten (001) single crystal have been carried out using cyclic nanoindentation by a Berkovich indenter. The first loading-unloading cycle up to 30 mN formed the initial indent. On reloading of the indenter up to 50 mN, a transition from elastic to plastic deformation of the material was observed. To reveal the region of the transition better, the reloading curve was differentiated with respect to time. It was found that, for tungsten, the transition from elastic to plastic behaviour vas smooth. The transition began at 25 mN and terminated at 34 mN only. During the transition the strain rate in the indent trebled. In the Al-Cu-Fe quasicrystal, the transition from elastic to plastic deformation was very abrupt. No evidence of plastic deformation in the indent was observed up to 32 mN. Only a further increase in the load by 0.35 mN caused the onset of plastic deformation. A pop-in was observed in the reloading curve at this point. The displacement increased by about 10 nm and the pressure in the indent dropped by 360 MPa. This was probably due to the destruction of the quasicrystalline structure and the formation of the crystalline structure, A plastic crystalline phase appeared to be pressed between the indenter and the hard quasicrystal substrate and then to be extruded from the indent. Because of this, the pressure in the quasicrystal drops during the transition from elastic to plastic deformation.
Title:
Impurity effect on the charge ordered state in manganites - in case of Sc doped manganites
Authors:
Mori, S; Shoji, R; Yamamoto, N; Katsufuji, T; Nigmatulina, E;
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 63 (6-8): 929-933; 2002
Abstract:
We investigated an influence of substituting Sc for Mn sites on the charge and orbital ordered (CO/OO) state in Nd0.5Ca0.5MnO3. In the 3% Sc-doped sample, it is found that a magnetic susceptibility curve shows an anomalous cusp around 60 K on cooling. Electron diffraction measurement revealed that an incommensurate (IQ to commensurate (C) structural phase transition takes place around 60 K on cooling and it has a large thermal hysteresis. Furthermore, real space image in the IC phase by electron microscopy shows the presence of the discommensurastions with a phase slip of pi. (C) 2002 Published by Elsevier Science Ltd.
Title:
Pressure dependence on the magnetic structures of TbNi1-xCux (x=0.3 & 0.4) using neutron techniques
Authors:
Senas, A; Fernandez, JR; Sal, JCG; Goncharenko, I; Yamaguchi, Y;
Source:
HIGH PRESSURE RESEARCH, 22 (1): 199-204; 2002
Abstract:
In the TbNi1-xCux series, the Cu substitution has two main effects: the increase of the cell volume (similar to4.3% from TbNi to TbCu), and the increasing importance of antiferromagnetic interactions. In this sense, the magnetic structures of these compounds evolve from a non-collinear ferromagnetic (FM) arrangement to an incommensurate antiferromagnetic (AFM) one for Cu concentration larger than 35%. In this paper, we present the effects of pressure on the magnetic structures of the compounds which are closer to this critical concentration: TbNi0.7Cu0.3 (FM) and TbNi0.6Cu0.4 (AFM). It appears that a global antiferromagnetic behaviour is favoured by pressure.
Title:
Quasicrystals with the infinite point group as a symmetry base of diamond-like structures
Authors:
Samoilovich, MI; Talis, AL; Mironov, MI; Goncharenko, I;
Source:
DOKLADY PHYSICS, 47 (6): 447-450; 2002
Abstract:
We study the global attractor of the non-autonomous 2D Navier-Stokes system with time-dependent external force g(x,t). We assume that g(x, t) is a translation compact function and the corresponding Grashof number is small. Then the global attractor has a simple structure: it is the closure of all the values of the unique bounded complete trajectory of the Navier-Stokes system. In particular, if g(x, t) is a quasiperiodic function with respect to t, then the attractor is a continuous image of a torus. Moreover the global attractor attracts all the solutions of the NS system with exponential rate, that is, the attractor is exponential. We also consider the 2D Navier-Stokes system with rapidly oscillating external force g(x,t,t/epsilon), which has the average as epsilon --> 0+. We assume that the function g(x,t,z) has a bounded primitive with respect to z and the averaged NS system has a small Grashof number that provides a simple structure of the averaged global attractor. Then we prove that the distance from the global attractor of the original NS system to the attractor of the averaged NS system is less than a small power of epsilon.
Title:
TEM studies of an incommensurate charge ordering modulation in La0.5Ca0.5MnO3
Authors:
Wang, YQ; Duan, XF; Wang, ZH; Shen, BG; Yamaguchi, Y;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 333 (1-2): 80-84; 2002
Abstract:
Electron energy-loss spectroscopy in the transmission electron microscope has been used to determine the valence state of manganese in La0.5Ca0.5MnO3 at room temperature and at 93 K, An incommensurate charge ordering modulation ill La0.5Ca0.5MnO3 was detected by transmission electron microscopy. A structural model. based oil the selected area electron diffraction and high-resolution electron microscopy observation, is proposed for the incommensurate modulation. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Formation and stability of quasicrystalline and hexagonal approximant phases in an Al-Mn-Be alloy
Authors:
Song, GS; Fleury, E; Kim, SH; Kim, WT; Kim, DH; Almeida, A;
Source:
JOURNAL OF MATERIALS RESEARCH, 17 (7): 1671-1677; 2002
Abstract:
Phase formation and thermal stability for an Al-Mn-Be alloy have been investigated by melt-spinning and conventional casting. Significant differences in the phase formation and the thermal stability of the microstructure were found as a result of the different cooling rates. In the melt-spun ribbons, a large volume fraction of a metastable icosahedral phase was found to coexist with an Al solid solution. In the bulk cast ingots, the primary phase formed in the two-phase microstructure was a hexagonal approximant phase of quasicrystals. This phase that solidified in the form of faceted particles embedded in the Al solid matrix proved to be thermodynamically stable during annealing at 540 degreesC for 100 h. The effect of Be addition on the formation of the stable approximant phase is discussed in terms of the Hume-Rothery mechanism.
Title:
Transport in the Al71Pd21Mn8-XReX quasicrystalline system
Authors:
Pope, AL; Tritt, TM; Gagnon, R; Strom-Olsen, J; Legault, S; Schneidmiller, R; Kolis, J; Zadrozna, G;
Source:
JOURNAL OF MATERIALS RESEARCH, 17 (7): 1814-1819; 2002
Abstract:
In an effort to understand the effects of a quartenary element introduced into a ternary quasicrystalline system, quartenary Al71Pd21Mn8-XReX quasicrystals were grown, where X had values of 0, 0.08, 0.25, 0.4, 0.8, 2, 5, and 8. X-ray data confirm that the addition of a fourth element does not alter the quasi periodicity of the sample. Because electronic transport is governed by different mechanisms in the parent systems (Al71Pd21Mn8 and Al71Pd21Re8), electrical and thermal transport measurements in the alloyed system have been performed on these samples and are presented here.
Title:
Microdomains of decagonal approximants in Al67Cr15Cu18 alloy
Authors:
Ma, XL; Shau, YH;
Source:
PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 231 (2): 601-606; 2002
Abstract:
In an alloy with nominal composition of Al67Cr15Cu18 annealed at 900 degreesC and below, microdomains of decagonal approximants have been identified by means of transmission electron microscopy. High-resolution images show that the microdomains, whose electron diffraction patterns display almost perfect tenfold rotation symmetry, are composed of three crystalline approximants intergrown with each other. The crystallographic relationships between these phases are given; and phase transformation between decagonal quasicrystal and its approximants is discussed.
Title:
Laterally-graded SiGe crystals for high resolution synchrotron optics
Authors:
Erko, A; Abrosimov, NV; Alex, V; Lo, CH;
Source:
CRYSTAL RESEARCH AND TECHNOLOGY, 37 (7): 685-704; 2002
Abstract:
A novel type of optical element for synchrotron radiation applications in the X-ray region: namely laterally-graded aperiodic crystals on the basis of Si1-xGex mixed crystal is presented. The lattice parameter of such gradient crystals containing up to some at. % Ge changes nearly linearly along the plane of diffraction. Thus the variation of the Bragg angle of divergent incident light on the crystal can be compensated, This opens up the possibility to operate a crystal monochromator in nearly crystal limited resolution in the whole energy range above 2 keV at the full vertical synchrotron source divergence without a collimating pre-mirror. Simultaneously the reflected spectral intensity can be increased considerably as compared with a conventional Si-crystal monochromator.
Title:
The structure of Nb5O12F
Authors:
Lidin, S; Rohrer, F; Larsson, AK; Lo, CH;
Source:
SOLID STATE SCIENCES, 4 (6): 767-772; 2002
Abstract:
The title compound was synthesized according to Andersson Acta Chem. Scand. 18 (1964) 2233. The structure is an incommensurately modulated variation of the UO3 structure, in a (3 + 1)-dimensional super space description isostructural to the composite phases (1 - x)Ta2O5.xWO(3) Acta Crystallogr., Sect. B 52 (1996) 223 and Acta Crystallogr., Sect. B 51 (1995) 709. The compound crystallizes in the orthorhombic system with cell parameters 3.936(3), 6.153(2), 3.656(l) Angstrom. The superspace group is X:Pmmm(00gamma): l s (l) over bar, where X refers to a non-standard superspace centering with the lattice vector (0 1/2 1/2 1/2), and gamma = 1.61 is the modulation wave vector. (C) 2002 Editions scientitiques et medicales Elsevier SAS. All rights reserved.
Title:
Magnetic properties of a single quasicrystal Al70.2Pd21.3Mn8.5
Authors:
Rempel', AA; Nazarova, SZ; Gusev, AI; Lo, CH;
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 93 (2-3): S74-S77; 2002
Abstract:
The magnetic susceptibility of an icosahedral single quasicrystal Al70.2Pd21.3Mn8.5 was studied at temperatures from 4 to 1100 K. It was shown that the quasicrystal susceptibility included a temperature-independent diamagnetic contribution and temperature-dependent paramagnetic Curie contribution and the contribution owing to the fact that the electronic system had an energy gap. From the analysis of the low-temperature susceptibility, it followed that the quasicrystal contained about 0.008% ions with a magnetic moment of 4 mu(B) at 4 K. It was assumed that ions with a noncompensated magnetic moment appeared near structural vacancies in the quasicrystal lattice. The energy gap width Delta = 0.64 eV between the valence band and the conduction band and the effective mass of charge carriers, which was equal to similar to70 times the electron mass, were determined.
Title:
The magnetic state and spin dynamics of single crystal CuB2O4
Authors:
Petrakovskii, G; Pankrats, A; Balaev, A; Vorotinov, A; Sablina, K; Popov, M; Roessli, B; Amato, A; Schefer, J; Ouladdiaf, B;
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 93 (2-3): S102-S106; 2002
Abstract:
The magnetic ground state of copper metaborate CuB2O4 is investigated by means of magnetic, resonant, neutron, thermal, and muSR measurements. The magnetic structure is incommensurate below 10 K and is in a noncollinear commensurate anti ferromagnetic state above 10 K. The theoretical calculations predict that the incommensurate-commensurate phase transition should exist with temperatures decreasing to similar to1 K.
Title:
Magnetic phase transitions in substituted spinels of Zn1-xCuxCr2Se4; 0.0 <= x <= 0.3
Authors:
Hidaka, M; Tokiwa, N; Wai, TT; Fujii, H; Ohoyama, K; Mizusima, S; Sakaurai, J; Ichikawa, F; Itoh, K; Ouladdiaf, B;
Source:
PHASE TRANSITIONS, 75 (3): 273-287; 2002
Abstract:
Magnetic and crystallographic properties have been studied by neutron powder diffraction and measurements of magnetization and magnetization hysteresis-loops for substituted spinels of Zn1-xCuxCr2Se4 with 0.0less than or equal toxless than or equal to0.3. It is found that the Zn0.85Cu0.15Cr2Se4 spinel has two magnetic phase transitions at 23.0 K (Neel temperature: T-N) and 410 K (Curie temperature; T-C) and that the Zn0.70Cu0.30Cr2Se4 spinel has magnetic transitions at 24.5 K (T-N) and 415 K (T-C) on heating. The low-temperature magnetic phase transition is from a spiral antiferromagnet to a ferromagnet, and the high-temperature magnetic phase transition is from a ferromagnet to a paramagnet, while ZnCr2Se4 shows a magnetic phase transition only from a spiral antiferromagnet to a paramagnet at about 21.0 K. From neutron powder diffraction, it is also found that the spinels of Zn1-xCuxCr2Se4 0.0 less than or equal to x less than or equal to 0.3. show satellite-like magnetic reflection having indexes (h +/- Q, k, l) with Q = 0.470 below T-N and short-range order of spins (spin glass-like) above T-N. The incommensurate antiferromagnetic phase below T-N, results from a spiral long-range order of the spins of Cr3+. The intermediate ferromagnetic phase between T and T-C is related not to the spiral spin order but to double-exchange magnetic interaction among Cr3+ and Cr4+ mediated by current carriers, positive holes, which is made by the substitution of Zn2+ ions with Cu1+ ions in Zn1-xCuxCr2Se4.
Title:
Quasicrystals and related approximant phases in Mg-Zn-Y
Authors:
Yi, S; Park, ES; Ok, JB; Kim, WT; Kim, DH; Mizusima, S;
Source:
MICRON, 33 (6): 565-570; 2002
Abstract:
As-cast microstructure of Mg-rich Mg68Zn28Y4 has been investigated by a detailed transmission electron microscopy study. The as-cast Mg68Zn28Y4 alloy consisted of three different types of phases: 10-20 mum size primary solidification phase, dendritic phase grown from the primary phase and a eutectic structure formed at the later stage of solidification. The primary solidification phase has an icosahedral structure with a large degree of phason strain. 1/1 rhombohedral approximant phase with lattice parameters a = 27.2 Angstrom and alpha = 63.43degrees is first observed in Mg-Zn-Y system. The rhombohedral structure can be obtained by introducing phason strain in the six-dimensional face centered hyper-cubic lattice. The decagonal phase nucleates with orientation relationship with the icosahedral phase. and Mg4Zn7 nucleates with orientation relationship with the decagonal phase. indicating a close structural similarity between the three phases. Gradual depletion of Y during solidification plays an important role in heterogeneous nucleation of decagonal and Mg4Zn7 phases from icosahedral and decagonal phases, respectively. (C) 2002 Elsevier Science Ltd. All rights reserved.
Title:
Stable quasicrystalline phase in Al-Cu-Fe-Cr coating materials
Authors:
Li, XZ; Marks, LD; Maciejewski, J; Fehrenbacher, L; Zabinski, J; O'Neill, J; Sakaurai, J;
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 33 (3): 675-679; 2002
Abstract:
Transmission electron microscopy (TEM) studies have been carried out on magnetron-sputtered coatings in the Al-rich region of the Al-Cu-Fe-Cr quasicrystalline phase field, focusing on the composition that exhibited the best tribological performance among a group of sputtered coatings. The size of the particles in the as-deposited coating is around 10 nm. The TEM experiments on annealed coatings (450 degreesC for 6 hours + 400 degreesC for 7 hours) revealed that the material is composed of a decagonal quasicrystalline phase with a periodicity of 1.24 urn along the unique axis and a hexagonal crystalline phase, with a = 2.48 nm and c = 1.24 nm. These results show that a thermodynamically stable quasicrystalline phase exists in the Al-Cu-Fe-Cr alloy system, in addition to previously reported microcrystalline structures and orthorhombic and monoclinic approximants. The hexagonal phase is a crystalline approximant of the decagonal phase, structurally related to hexagonal crystalline phases previously reported in Al-Mn and Al-Cr-Ni quasicrystalline alloys.
Title:
Average structure of cubic lazurite with a three-dimensional incommensurate modulation
Authors:
Rastsvetaeva, RK; Bolotina, NB; Sapozhnikov, AN; Kashaev, AA; Schoenleber, A; Chapuis, G; Sakaurai, J;
Source:
CRYSTALLOGRAPHY REPORTS, 47 (3): 404-407; 2002
Abstract:
Three-dimensional incommensurately modulated cubic lazurite from the Malo-Bystrinskoe deposit (the Baikal region) was studied by the methods of X-ray diffraction analysis. The a parameter of the cubic unit cell is 9.077(1) Angstrom. The calculations performed within the sp. gr. P23 (R = 0.056, 309 independent reflections) provided detailed information on the average structure of the mineral (the satellite reflections were ignored). (C) 2002 MAIK "Nauka/Interperiodica".
Title:
Mackay, anti-Mackay, double-Mackay, pseudo-Mackay, and related icosahedral shell clusters
Authors:
Kuo, KH; Saida, J;
Source:
STRUCTURAL CHEMISTRY, 13 (3-4): 221-230; 2002
Abstract:
Mackay introduced two important crystallographic concepts in a short paper published 40 years ago. One is the icosahedral shell structure (iss) consisting of concentric icosahedra displaying fivefold rotational symmetry. The number of atoms contained within these icosahedral shells and subshells agrees well with the magic numbers in rare gas clusters, (C-60)(N) molecules, and some metal clusters determined by mass spectroscopy or simulated on energy considerations. The cluster of 55 atoms within the second icosahedral shell occurs frequently and has been called Mackay icosahedron, or simply MI, which occurs not only in various clusters, but also in intermetallic compounds and quasicrystals. The second concept is the hierarchic icosahedral structures caused by the presence of a stacking fault in the fcc packing of the successive triangular faces in the iss. For instance, a fault occurs after the ABC layers resulting an ABCB packing. This is, in fact, a hierarchic icosahedral structure of a core icosahedron connected to 12 outer icosahedra by vertex sharing, or an icosahedron of icosahedra (double MI. Contrary to Mackay's iss, a faulted hierarchic icosahedral shell is, in fact, a twinlike face capping of the underlying triangles; it is, therefore, called an anti-Mackay cluster. The hierarchic icosahedral structure in an Al-Mn-Pd icosahedral quasicrystal has a core of body-centered cube rather than an icosahedron and, therefore, is called a pseudo-Mackay cluster. The hierarchic icosahedral structures have been studied separately in the past in the fields of clusters, nanoparticles, intermetallic compounds, and quasicrystals, but the underlying geometry should be the same. In the following a unified geometrical analysis is presented.
Title:
Covering presentation and coloring of dual canonical tilings
Authors:
Kramer, P; Ogawa, T;
Source:
STRUCTURAL CHEMISTRY, 13 (3-4): 315-319; 2002
Abstract:
In the crystallography of quasicrystals, the space for the structure description is taken as a subspace E-parallel to, embedded irrationally in an N-dimensional space equipped with a lattice Lambda. Quasiperiodic dual canonical tilings (cal T, Lambda), (cal T-*, Lambda) arise from the geometry and projection of Voronoi and Delone polytopes, respectively, associated with Lambda. In a new approach to quasicrystals, tiles are replaced by a few covering clusters. As a typical example, the tiling (cal T-*, A(4)) of fivefold symmetry is covered by two Delone clusters. This construction is called a covering presentation compatible with the tiling. We show that any given tile in the tiling can be uniquely associated with a specific overlap of Delone clusters. Each specific overlap is called a color for this tile. The range of colors and their relative frequencies are explicitly determined.
Title:
Energetics of nucleation for the icosahedral Al-Mn phase in HTSD-deposited thin films
Authors:
Manaila, R; Alexe, G; Barna, PB; Giusca, C; Devenyi, A; Chapuis, G;
Source:
STRUCTURAL CHEMISTRY, 13 (3-4): 365-371; 2002
Abstract:
The cohesive energy of the Al-Mn Mackay icosahedron (MI) was estimated for different variants of chemical order, using pair-bonding energies. This problem is related to the nucleation of i-AlMn phase in sequentially deposited thin films. The chemically ordered MI comes out as the thermodynamically most stable configuration. The role of kinetic factors during deposition is also discussed.
Title:
Experimental overview of complex intermetallic structures
Authors:
Laridjani, M; Donnadieu, P; Denoyer, F; Giusca, C;
Source:
STRUCTURAL CHEMISTRY, 13 (3-4): 385-396; 2002
Abstract:
A complete investigation of the Fourier space of complex intermetallic Mg39Al61 is reported. X-ray patterns reveal the reciprocal space of the whole system consisting in selective reflections and coherent diffuse scattering. Their temperature dependence are studied. Selective reflections are interpreted as incommensurately modulated states and a structural analysis of the coherent diffuse scattering is presented. The same type of coherent diffuse scattering curve was also observed in several quasicrystalline alloys. In all the studied cases, the disorder is interpreted by the presence of icosahedral arrangements that are reminiscent of Frank units in supercooled alloys.
Title:
Critical behavior of heat capacity of the SC(NH2)(2) ferroelectric in the region of incommensurate phase transition
Authors:
Kallaev, SN; Kamilov, IK; Aliev, AM; Abdulvagidov, SB; Batdalov, AB; Chapuis, G;
Source:
JETP LETTERS, 75 (8): 415-417; 2002
Abstract:
The anomalous (nonclassical) behavior of heat capacity in the region of the second-order phase transition "initial phase-incommensurate phase" was experimentally observed in the SC(NH2)(2) ferroelectric. Such a critical behavior of heat capacity above and below the temperature of incommensurate phase transition is shown to be qualitatively consistent with the fluctuation theory of XY-type systems. (C) 2002 MAIK "Nauka / Interperiodica".
Title:
Mn/Cr isomorphic substitution in mu Al4MnxCr1-x phase compounds (0 <= x <= 1)
Authors:
Simonet, V; Hippert, F; Audier, M; Bellissent, R; Sasa, S;
Source:
PHYSICA B, 315 (1-3): 187-200; 2002
Abstract:
Neutron scattering experiments were performed on hexagonal muAl(1)4Mn(x)Cr(1-x) (0 less than or equal to x less than or equal to 1) compounds, approximants of Al-Mn and Al-Cr quasicrystalline phases, whose structures exhibit a local icosahedral order. The Mn/Cr substitution on the 10 different Wyckoff sites in the mu-phase structure is shown to be isomorphic from an analysis of partial pair structure factors and from simulations based on crystallographic data. The nature of the local icosahedral order, common to almost all the Al-rich solid phases of the Al-Mn and Al-Cr systems, is explicited. As an example, the very close similarity between measured structure factors of muAl(4)Mn and lambdaAl(4.5)Mn phases can be interpreted from structural descriptions made in terms of icosahedral units where large arrangements of these units appear to be common to both phases. (C) 20021 Elsevier Science B.V. All rights reserved.
Title:
Formation and oxidation behavior of Al-Cu-Fe quasicrystal
Authors:
Zhou, CG; Xu, HB; Gong, SK; Kang, GM; Sasa, S;
Source:
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY, 18 (3): 251-253; 2002
Abstract:
Al62.5Cu25Fe12.5 alloy was prepared by arc melting. It was found that the formation of quasicrystalline phase is related to the condition of annealing, such as temperature and duration. Weight gain of Al-Cu-Fe quasicrystal during the oxidation at 700 and 800degreesC in dry air was measured by means of thermal balance. The oxidation kinetics showed that the quasicrystal has good oxidation resistance. Only alpha-Al2O3 was formed on Al62.5Cu25Fe12.5 quasicrystal. The surface morphologies of Al-Cu-Fe quasicrystal after isothermal oxidation for different times were observed.
Title:
Crystal-structure modulation in the anomalous low-temperature phase of PrFe4P12
Authors:
Iwasa, K; Watanabe, Y; Kuwahara, K; Kohgi, M; Sugawara, H; Matsuda, TD; Aoki, Y; Sato, H; Itoh, K;
Source:
PHYSICA B-CONDENSED MATTER, 312 (3): 834-836; 2002
Abstract:
Nature of mysterious phase transition of the filled-skutterudite PrFe4P12 has been studied by X-ray diffraction experiments. Superlattice reflections characterized by a wave vector q = (1, 0, 0) were observed below the transition temperature of 6.5 K at zero magnetic field. The observed pattern in the reciprocal space is explained by the formation of modulated structure with dominant Fe-ion displacements by about 0.02% of the lattice constant. This result is consistent with the theoretically predicted nesting of Fermi surface producing a gap formation in electronic structure. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Growth condition and X-ray analysis of single Al64Cu23Fe13 icosahedral quasicrystal by the Czochralski method
Authors:
Yokoyama, Y; Matsuo, Y; Yamamoto, K; Hiraga, K; Sauer, RT;
Source:
MATERIALS TRANSACTIONS, 43 (4): 762-765; 2002
Abstract:
Growth conditions for the preparation of a single Al64Cu23Fe13 icosahedral (I-) quasicrystal with excellent quasicrystallinity were examined using the Czochralski method. The appreciation of the quasicrystallinity of the grown single quasicrystal was performed by X-ray structural analysis. The full widths at half-maximum (FWHNI) of the Bragg reflections along 2-, 3- and 5-told symmetry directions have no Q(h) and Q(perpendicular to) dependence. Where the Q(i) and Q(perpendicular to) mean the phason momentum and real scattering vector. Furthermore. peak shifts from ideal Bragg positions were not observed. These means that the grown Al64Cu23Fe13 quasicrystal by the Czochralski method has perfect I-phase structure.
Title:
Precipitation of icosahedral quasicrystalline phase in Zr-Cu-Rh metallic glasses: dependence of particle size on Rh concentration
Authors:
Li, C; Wang, L; Inoue, A; Warren, WS;
Source:
EUROPEAN PHYSICAL JOURNAL-APPLIED PHYSICS, 18 (2): 109-113; 2002
Abstract:
The crystallization processes of Zr70Cu20Rh10 and Zr70Cu27.5Rh2.5 metallic glasses were studied. The initial precipitates are the mixture of an icosahedral quasicrystalline phase (I phase) and a face centered cubic Zr2Rh phase (fcc-Zr2Rh) for Zr70Cu20Rh10 alloy and that for the Zr70Cu27.5Rh2.5 alloy is a single I phase. Under optimum annealing conditions, the largest I phase particle size is 40 nm and 80 nm for Zr70Cu20Rh10 and Zr70Cu27.5Rh2.5, respectively. To explain these results, it is assumed that icosahedral atomic cluster exists in the metallic glasses, which serves as the seeds for the precipitation of metastable I and FCC-Zr2Rh phases. Further, it is suggested that the number density of icosahedral atomic cluster and the ease of fcc-Zr2Rh phase formation depend on the Rh concentration, which explain the above-mentioned dependence of the I phase particle size on Rh concentration.
Title:
The electrical conductivity of single-grain Al-Pd-Re quasicrystals
Authors:
Fisher, IR; Xie, XP; Tudosa, I; Gao, CW; Song, C; Canfield, PC; Kracher, A; Dennis, K; Abanoz, D; Kramer, MJ;
Source:
PHILOSOPHICAL MAGAZINE B-PHYSICS OF CONDENSED MATTER STATISTICAL MECHANICS ELECTRONIC OPTICAL AND MAGNETIC PROPERTIES, 82 (9): 1089-1098; 2002
Abstract:
Systematic electrical transport data are presented for single quasicrystals in the Al-Pd-Re family across the accessible width of formation. The temperature dependence of the electrical conductivity can be accounted for in terms of weak localization and electron-electron interactions for all compositions studied, in contrast with previous studies of cast and annealed polygrain material. These results indicate that the conductivity mechanism in the Al-Pd-Re system is not dramatically different from that of other quasicrystal families.
Title:
Deformation behavior of Mg-Zn-Y alloys reinforced by icosahedral quasicrystalline particles
Authors:
Bae, DH; Kim, SH; Kim, DH; Kim, WT; Andreoli, MAG;
Source:
ACTA MATERIALIA, 50 (9): 2343-2356; 2002
Abstract:
New Mg-rich Mg-Zn-Y alloys, reinforced by quasicrystalline particles, have been developed by thermomechanical processes. The deformation behavior of these alloys at room and elevated temperatures has been investigated. Yield strength of these alloys, which increases with an increase in the volume fraction of quasicrystalline particles, is relatively high due to their strengthening effect. The variation of the flow stress in the alloys is characterized by linking the microstructural evolution during deformation at high temperatures. The flow softening is related to dynamic recrystallization developed under the dislocation climb controlled creep; the flow hardening is related to grain growth that occurs under the grain boundary diffusion controlled creep. Quasicrystalline particles in the Mg-Zn-Y alloys resist coarsening due to their low interfacial energy, thereby forming of stable quasicrystalline particle/matrix interface and also prohibit against microstructural evolution of the alpha-Mg matrix during deformation at temperatures up to near the eutectic temperature. Stability of both quasicrystalline particles and matrix microstructure in the Mg-Zn-Y alloys provides large elongation to failure with no void formation at the quasicrystalline particle/matrix interface. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
Indications of incommensurate spin fluctuations in doped triangular antiferromagnets
Authors:
Liang, Y; Feng, SP; Kim, DH;
Source:
PHYSICS LETTERS A, 296 (6): 301-306; 2002
Abstract:
The incommensurate spin fluctuation of the doped triangular antiferromagnet is studied within the t-J model. It is shown that the commensurate peak near the half-filling is split into six incommensurate peaks in the underdoped and optimally doped regimes. The incommensurability increases with the hole concentration at lower dopings, and saturates at higher dopings. Although the incommensurability is almost energy independent. the weight of these incommensurate peaks decreases with energy and temperature. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
A HREM and analytical STEM study of precipitates in an AZ91 magnesium
Authors:
Bursik, J; Svoboda, M; Kim, DH;
Source:
MIKROCHIMICA ACTA, 139 (1-4): 39-42; 2002
Abstract:
The paper focuses on the microstructural characterisation of secondary phases in an AZ91 magnesium alloy. The orientation relationship and atomic structure of semi-coherent Mg/Mg17Al12 interfaces are studied by means of selected area diffraction, EDS and high resolution TEM. Besides the common Mg17Al12 semi-coherent platelets of high density and coarser incoherent Mg17Al12 particles, other, less frequent precipitates were found, rich in Al and Mn. The quasi crystalline nature of these precipitates was detected by means of electron diffraction.
Title:
A low-temperature order-disorder transition in a cubic Cd6Yb crystalline approximant
Authors:
Tamura, R; Murao, Y; Takeuchi, S; Ichihara, M; Isobe, M; Ueda, Y; Kracher, A;
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 41 (5A): L524-L526; 2002
Abstract:
Electrical resistivity. specific heat and electron diffraction experiments at low temperatures, unambiguously reveal that the cubic Cd6Yb crystal. which is a 1/1 cubic approximant to the recently discovered icosahedral Cd-5 Yb-7, undergoes a reversible order-disorder transition at about I 10 K. The transition is most probably due to the orientational ordering of tetrahedral 4Cd clusters sitting at the center of dodecahedral cages: above 110 K the central 4Cd cluster is disordered over two orientations forming a bcc structure (Im (3) over bar), whereas below 110 K it is ordered in mixed B2(Pn (3) over bar) and B32(Fd (3) over barm) structures.
Title:
Diffraction from long-period out-of-phase superstructures
Authors:
Shao, G; Murao, Y;
Source:
INTERMETALLICS, 10 (5): 493-496; 2002
Abstract:
Structural models of long-period out-of-phase superstructures are discussed on the basis of diffraction physics. The paper analyses the structural factors of one-dimensional out-of-phase superstructures of both constant periods and incommensurate arrangements. showing excellent agreement with experimentally observed diffraction patterns. (C) 2002 Elsevier Science Ltd. All rights reserved.
Title:
Icosahedral quasicrystalline and hexagonal approximant phases in the Al-Mn-Be alloy system
Authors:
Kim, SH; Song, GS; Fleury, E; Chattopadhyay, K; Kim, WT; Kim, DH; Kracher, A;
Source:
PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 82 (8): 1495-1508; 2002
Abstract:
We report the formation of a primitive icosahedral quasicrystal with increased stability in Al Mn-Be alloys close to the compound Al15Mn13Be2, by melt spinning and injection casting. The crystal structure of this compound was unknown. We show that in as-cast as well as heat treated condition the intermetallic phase H1 has a hexagonal structure with lattice parameters a = 1.2295 run and c = 2.4634 nm. The space group is P6(3)/mmc In the injection-cast samples, the quasicrystal coexists with another closely related hexagonal phase H2 with a = 1.2295 nm and c = 1.2317 nm with a possible space group of P6/mmm. This phase exhibits specific orientation relationships with the icosahedral quasicrystal given by [0001](hex)//2f(QC) and [01 (1) over bar0](hex)//5f(QC) where 2f(QC) and 5f(QC) represent twofold and fivefold axes respectively. Electron diffraction patterns from both phases exhibit a close resemblance to the quasicrystalline phase. It is shown that the H1 phase is closely related to mu-Al4Mn with the same e parameter while the a parameter is reduced by tau. Following Kreiner and Franzen, it is postulated that both structures (H1 and H2) can be understood by a simple hexagonal packing of I13 clusters.
Title:
Two-subgrain single quasicrystals Al-Cu-Co alloy growth and characterisation
Authors:
Bogdanowicz, W; Raith, JG;
Source:
JOURNAL OF CRYSTAL GROWTH, 240 (1-2): 255-266; 2002
Abstract:
Two-subgrain single quasicrystals with subgrain boundaries parallel to the direction of solidification were obtained by the modification of Bridgman method. with asymmetric heat abstraction. One of the subgrains of single quasicrystals was formed through the peritectic reaction of the Al(Cu,Co) phase. The other subgrain solidified directly from the melted phase. Two different types of band structures of single quasicrystals were determined by X-ray topography and metallography methods. The orientation of these structures in relation to the ten-fold symmetry axis of single quasicrystal and the solidification front was investigated. The formation mechanism of both kinds of structure were suggested. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Decagonal quasicrystal patterns with eight prototiles
Authors:
Escudero, JG; Garcia, JG; Hutchings, M;
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B, 16 (8): 1205-1215; 2002
Abstract:
Substitutional decagonal patterns with the golden number squared as inflation factor are studied. Two types of patterns are derived starting from the basic geometric construction. The inflation rules can be composed in an arbitrary order giving new types of patterns. A high number of vertex configurations appear in the structures. The patterns can also be obtained by superposition of two subpatterns.
Title:
Infinite point group quasicrystals: Symmetry basis for noncrystalline diamond-like materials
Authors:
Samoilovich, MI; Talis, AL; Mironov, MI; Chattopadhyay, K;
Source:
INORGANIC MATERIALS, 38 (4): 357-362; 2002
Abstract:
The construction of a diamond-like tetracoordinated quasicrystal (possible only in the infinite point group R) is considered in the framework of algebraic geometry. The physical and materials research applications of this approach are discussed.
Title:
Monte Carlo study of the quasicrystal-to-crystal transformation using an approach based on the Gummelt covering
Authors:
Honal, M; Welberry, TR; Deroche, C;
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 217 (3): 109-118; 2002
Abstract:
A tiling representation and associated possible tiling flips are developed for the "unit-cluster" description of decagonal quasicrystals with reference to the example of decagonal Al70Co15Ni15. A perfect PI tiling is a suitable model of the ideal quasiperiodic structure and a 180degrees flip of a pentagon tile can be used as an analogue of the hexagon flips in Penrose rhomb tilings. Monte Carlo simulations and calculated diffraction patterns are used to study the effect of those tiling flips on the cluster scale for some example cases. Some of these have a special importance for the quasicrystal-to-crystal transformation. Starting with the perfect PI tiling the system is allowed to evolve using phason fluctuations whose probabilities depend on the resulting local tile configurations. The degree of order/disorder introduced and its effects on the diffraction pattern are investigated.
Title:
Characterization of the icosahedral phase in as-cast quasicrystalline Al65CU20Fe15 alloy
Authors:
Cheung, YL; Chan, KC; Zhu, YH; Hollingsworth, MA;
Source:
MATERIALS CHARACTERIZATION, 47 (3-4): 299-305; 2001
Abstract:
Morphology features and microstructures of a quasicrystalline Al65Cu20Fe15 alloy were studied using X-ray diffraction, scanning electron microscopy (SEM), electron probe microanalysis, electron backscattered diffraction (EBSD), and transmission electron microscopy (TEM) techniques. A typical layer dendritic microstructure of the as-cast quasicrystalline alloy consisted of four phases: an Al71Cu5Fe24 phase as a core of the dendritic structure, which was surrounded by a quasicrystalline Al60Cu26Fe14 phase and a crystalline Al50Cu45Fe5 phase being in the interdendritic regions, and a Cu-rich Al44Cu54Fe2, phase. The quasicrystalline phase was characterized of three symmetries: five-, three-, and twofold. The Kikuchi diffraction patterns obtained from both SEM and TEM are very similar. It is shown that without the need to prepare thin film specimen, EBSD is an alternative method to characterize quasicrystals. (C) 2001 Published by Elsevier Science Inc.
Title:
Mechanical Spectroscopy of icosahedral Al-Cu-Fe quasicrystals metal-based composites
Authors:
Fikar, J; Schaller, R; Guilbaud, N; Baluc, N; Harris, A;
Source:
DEFECTS AND DIFFUSION IN METALS: AN ANNUAL RETROSPECTIVE IV, 203-2 (3-4): 289-292; 2002
Abstract:
Since the bulk AlCuFe quasicrystals are extremely brittle and therefore not suitable for mechanical spectroscopy, two different types of AlCuFe quasicrystals metal-based composites have been studied. One is AlMg3% based metal matrix composite reinforced with quasicrystalline particles and the second is a quasicrystalline coating deposited on a steel substrate using thermal spraying. The internal friction of these composites was measured in a forced torsion pendulum and in a free-free bar apparatus. The obtained results are discussed.
Title:
Penrose mosaic as a quasistochastic tree-graph lattice
Authors:
Yudin, VV; Pisarenko, TA; Lyubchenko, EA; Chudnova, OA; Karygina, YA; Marrows, CH;
Source:
CRYSTALLOGRAPHY REPORTS, 47 (2): 189-195; 2002
Abstract:
The Penrose mosaic as the minimum representative of quasicrystals is discussed in terms of generalized planar lattice models. The role of these models is played by Cayley's tree graphs which, in the general case, are characterized by quasi-random branching. A three-level golden alphabet is defined, and a Penrose mosaic is synthesized with the aid of its highest level. The algebras of the suggested grammar are formulated in an explicit form. It is shown that the statistics of a Penrose mosaic at the level of golden rhombuses belongs to the class of Zipf-Mandelbrot distributions. The algorithm for mapping a Penrose mosaic into Cayley's tree graphs based on the [2q x 2p] alphabet is also formulated. The problem of the entropy percolation for quasistochastic Cayley's trees of Penrose mosaics is solved. The entropy percolation of these trees is characterized by an obvious minimum periodicity and, on average, by the invariance principle of the golden entropy. (C) 2002 MAIK "Nauka/Interperiodica".
Title:
Perturbation theory of 2D decagonal quasicrystals
Authors:
Peng, YZ; Fan, TY; Nordmark, AB;
Source:
PHYSICA B-CONDENSED MATTER, 311 (3-4): 326-330; 2002
Abstract:
A perturbation method for solving elastic 3D problems for 2D decagonal quasicrystals with point groups 10 mm, 1022. 10m2 and 10/mmm is proposed. We obtain a uniformly valid asymptotic solution of the elastic field by regarding phason field as a perturbation to phonon field and introducing a perturbation parameter epsilon = R/c(11), where c(11) and R are elastic constants of phonon field and phonon-phason coupling, respectively. A general solution for the equations of order zero is given in terms of five "harmonic" functions. As a simple application of the above theory. considering an infinite 2D decagonal quasicrystal of point group 10 mm weakened by a circular crack, A e obtain the uniformly valid asymptotic solutions up to O(epsilon(2)) for the mode I loading. (C) 2002 Published by Elsevier Science B.V.
Title:
Axisymmetric contact problem of cubic quasicrystalline materials
Authors:
Zhou, WM; Fan, TY; Yin, SY; Izumi, K;
Source:
ACTA MECHANICA SOLIDA SINICA, 15 (1): 68-74; 2002
Abstract:
The axisymmetric elasticity theory of cubic quasicrystal was developed in Ref. [1]. The axisymmetric elasticity problem of cubic quasicrystal is reduced to a single higher-order partial differential equation by introducing a displacement function, based on which, the exact analytic solutions for the elastic field of an axisymmetric contact problem of cubic quasicrystalline materials are obtained for universal contact stress or contact displacement. The result shows that if the contact stress has order - 1/2 singularity on the edge of the contact domain, die contact displacement is a constant in the contact domain. Conversely, if the contact displacement is a constant, the contact stress must have order - 1/2 singularity on the edge of die contact domain.
Title:
Quasicrystal formation, phase selection and crystallization kinetics in Zr-Cu-Ni-Al based metallic glasses
Authors:
Koster, U; Zander, D; Janlewing, R; Starozhilova, TK;
Source:
METASTABLE, MECHANICALLY ALLOYED AND NANOCRYSTALLINE MATERIALS, 386-3 (2): 89-98; 2002
Abstract:
Quaternary Zr-Cu-Ni-Al is one of the best glass forming alloys known. In a narrow concentration range icosahedral quasicrystals are formed upon annealing; in Zr69.5Cu12Ni11Al7.5 the metastable primitive icosahedral phase is probably oxygen stabilized. At slightly higher oxygen contents (about 1 at.%) the formation of a metastable fcc "big-cube" phase (NiTi2-type) is competing with very high nucleation rates.The aim of this paper is to investigate in detail the formation of quasicrystals as well as microstructures consisting of the "big-cube" phase in order to design in particular nanocrystalline structures by controlled crystallization. Nucleation rates were measured by means of crystallization statistics. By modeling the obtained nucleation rates in the framework of diffusion controlled classical nucleation interfacial energies as well as melting temperatures for the metastable phases could be derived. Atomic mobility was estimated from growth data. Using these data TTT-diagrams can be drawn and microstructures (for example nanocrystalline) predicted.The phase selection during the formation of the metastable structures was observed to depend strongly not only on the exchange of the Zr by Hf or Ti, but also on the late transition elements chosen, hydrogen or oxygen contamination as well as on alloying with small amounts of other elements for example Si, Sn, Y or Mo. Regarding the influence of the late transition metals there is some evidence that the quasicrystals are a hybrid of two structural elements, i.e. the tetragonal Zr2Ni (Al2Cu) and the tetragonal Zr2Cu (MoSi2) structure. The mentioned alloying elements as well as oxygen and hydrogen are assumed to influence the arrangement of the structural elements towards one or the other structure.
Title:
Formation of quasicrystals and crystallization sequence in the Zr46.8Ti8.2CU7.5Ni10Be27.5 bulk glass
Authors:
Macht, MP; Mechler, S; Muller, M; Wanderka, N; Riznichenko, GY;
Source:
METASTABLE, MECHANICALLY ALLOYED AND NANOCRYSTALLINE MATERIALS, 386-3 (2): 99-104; 2002
Abstract:
The crystallization sequence and the structure of the crystalline phases which form during annealing of the Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass were investigated by X-ray powder diffraction, transmission electron microscopy and scanning electron microscopy in combination with differential scanning calorimetric analysis. During isothermal annealing at temperatures below and above the calorimetric crystallization temperature nanosized quasicrystals form as a first step of the crystallization. In the course of further isothermal annealing by and by at least four intermetallic phases (Be2Zr, Zr2Cu, and two not yet fully identified ones) crystallize. Simultaneously the quasicrystals vanish. The complicated crystallization sequence is linked to a strong diffusion controlled decomposition of the alloy. The small mobility of the alloy components may be one reason for the good stability of the glass.
Title:
Decagonal quasicrystal formed directly from the undercooled Al72Ni16Co12 alloy melt
Authors:
Liu, XB; Yang, GC; Fan, JF; Wang, JC; Song, GS; Rubin, AB;
Source:
JOURNAL OF MATERIALS SCIENCE LETTERS, 21 (5): 367-369; 2002
Abstract:
The crystallization sequence and the structure of the crystalline phases which form during annealing of the Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass were investigated by X-ray powder diffraction, transmission electron microscopy and scanning electron microscopy in combination with differential scanning calorimetric analysis. During isothermal annealing at temperatures below and above the calorimetric crystallization temperature nanosized quasicrystals form as a first step of the crystallization. In the course of further isothermal annealing by and by at least four intermetallic phases (Be2Zr, Zr2Cu, and two not yet fully identified ones) crystallize. Simultaneously the quasicrystals vanish. The complicated crystallization sequence is linked to a strong diffusion controlled decomposition of the alloy. The small mobility of the alloy components may be one reason for the good stability of the glass.
Title:
Microstructure investigation of rapidly solidified Al-V-Fe alloys
Authors:
He, G; Shek, CH; Lai, JKL; Bian, Z; Hui, XD; Chen, GL; Macintyre, DS;
Source:
JOURNAL OF MATERIALS RESEARCH, 17 (4): 814-820; 2002
Abstract:
The microstructures and their thermal behaviors of quenched Al94V4Fe2, Al90V8Fe2, Al86V8Fe6, and Al85V9Fe2Ni4 alloys were investigated by x-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. The as-quenched microstructures, of the four alloys consist of quasicrystal particles and a fcc-alpha-Al matrix. The as-quenched Al86V8Fe6 and Al85V9Fe2Ni4 alloys also contain a small volume fraction of amorphous phase. All phases observed have fine morphologies with grain sizes of less than 100 nm. With the increase in V from 4 to 8 at.% at 2 at.% Fe. the average grain size decreases from 100 to 70 nm and the melting temperature of alpha-Al solid solution increases from 640 to 653 degreesC. The alloy with 8 at.% V has a finer and more stable microstructure than that of the alloy with 4 at.% V. The Fe addition has minor effect on grain size but improves the glass-forming ability. The Ni addition significantly improves the glass-forming ability and refines the microstructure. The metastable amorphous and quasicrystalline phases transform into a stable crystalline phase during continuous heating and cooling. The stable phases in these Al-V-Fe alloys include alpha-Al(V, Fe), Al10V, and Al80V12.5Fe7.5.
Title:
Inductively coupled plasma mass spectrometric study of laser sputtering from the surface of an Al-Cu-Fe alloy and quasicrystal
Authors:
Mele, A; Liu, HC; Russo, RE; Mao, XL; Giardini, A; Satta, M; Macintyre, DS;
Source:
APPLIED SURFACE SCIENCE, 186 (1-4): 322-328; 2002
Abstract:
The fractionation behavior induced by laser desorption and ablation of the Al70Cu20Fe10 intermetallic alloy and of the Al65Cu23Fe12 quasicrystal has been examined in terms of the structural properties of the two compounds. Elemental fractionation during laser desorption and ablation sampling was investigated by using inductively coupled plasma mass spectrometry. The experiments were carried out in two different power density regimes by using a Nd-YAG laser with 266 nm C) the effect of the laser power wavelength and single 6 ns laser pulses. In the high power density regime (>0.04-0.07 GW/cm(2) density on ablation behavior was similar for the two materials. In the low power density regime (<0.04-0.07 GW/cm(2)) large differences have been found between the alloy and the quasicrystal, The results are interpreted on the basis of a thermodynamic vaporization process for the intermetallic alloy. An electronic model of localized excitation is suggested for the physical process of surface material removal from a quasicrystal. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Electrical and thermal studies in the commensurate incommensurate phase region of (NH4)(2)ZnCl4 single crystal
Authors:
Amin, M; El-Korashy, A; Ibrahim, SS; Dabour, M; Arafa, S; Satta, M;
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 63 (5): 869-874; 2002
Abstract:
DC electrical conductivity for a virgin and poled annealed (NH4)(2)ZnCl4 b-axis single crystal shows a defect controlled property. A Schottky mechanism is a probable mechanism of conduction in regions of strong structural transitions. The rise of conductivity in the incommensurate and paraelectric phases is linked to an increase in discommensurations density. The activation energies (DeltaE) in the three phases region were calculated. DTA measurements shows that the crystal is stable up to 200 degreesC and the phase transition temperatures were observed at 42, 94.8 and 137 degreesC. The effective activation energy (E-e) was obtained using Kissinger and Mahadevan equations. It was found to be equal to 0.49 eV. This correlates with the value obtained through DC conductivity. (C) 2002 Published by Elsevier Science Ltd.
Title:
At-Cu-Fe quasicrystal/ultra-high molecular weight polyethylene composites as biomaterials for acetabular cup prosthetics
Authors:
Anderson, BC; Bloom, PD; Baikerikar, KG; Sheares, VV; Mallapragada, SK; Satta, M;
Source:
BIOMATERIALS, 23 (8): 1761-1768; 2002
Abstract:
Polymer composites of Al-Cu Fe quasicrystals and ultra-high molecular weight polyethylene (UHMWPE) were investigated for use in acetabular cup prosthetics. The wear properties of the Al Cu-Fe/UHMWPE samples and a 440 steel ball counterface were measured. The mechanical strength of the Al Cu Fe/UHMWPE composites was compared to UHMWPE and alumina/UHMWPE. The biocompatibility of the composite material was tested using a direct contact cytotoxicity assay. At-Cu-Fe/UHMWPE demonstrated lower volume loss after wear and higher mechanical strength than UHMWPE. This composite material also showed no increase in counterface wear or cytotoxicity relative to UHMWPE. These combined results demonstrate that Al Cu Fe/UHMWPE composites are promising candidate materials for acetabular cup prosthetics. (C) 2002 Elsevier Science Ltd. All rights reserved.
Title:
Single-crystal growth of the Al-Cu-Ru icosahedral quasicrystal from the ternary melt
Authors:
Guo, JQ; Hasegawa, H; Tsai, AP; Takeuchi, S; McKeon, DGC;
Source:
JOURNAL OF CRYSTAL GROWTH, 236 (1-3): 477-481; 2002
Abstract:
An Al-Cu-Ru partial phase diagram involving the icosahedral quasicrystal has been constructed along an Al-62-CU38-xRux = (x = 2.5-25 at%) isopleth. The icosahedral quasicrystal forms at 1020degreesC via a peritectic reaction between a liquid and Al68Cu12Ru20 phase and coexists with a liquid phase at temperature below the peritectic reaction. The icosahedral quasicrystal solidifies as a primary phase in the temperature range of 800-1020degreesC from the alloys in the composition range of 60-67.5 at% Al, 29.5-37.5 at% Cu, and 2.5-4 at% Ru. On the basis of the phase diagram, single grains of the Al-Cu-Ru icosahedral quasicrystal with a maximum size of 5 mm were successfully grown from Al-CuRu melts. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Role of the antiphase-boundary energy in periodic-to-quasiperiodic superlattice transitions: a Monte Carlo simulation of ordering in Al-rich gamma-TiAl
Authors:
Kulkarni, UD; Bachir, M;
Source:
PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 82 (5): 1017-1032; 2002
Abstract:
Results of the strip projection method have established that formation of antiphase boundaries (APBs) is the initial stage of a periodic-to-quasiperiodic transformation in superlattices. The Al5Ti3-to-quasiperiodic superlattice transformation, observed in Al-rich gamma-TiAl intermetallics, is a classic example of such a transition. Energy of the relevant APBs would, therefore, be expected to play an important role in the occurrence of this transition. In the two-dimensional Monte Carlo simulations carried out in this work, change in the APB energy, accomplished by suitably altering the pair interaction energies, was found to explain the diffraction effects observed in the alloys with various compositions depicting this transition. The results of the simulation bring out salient features of the atomic arrangements in imperfectly ordered quasiperiodic and near-quasiperiodic structures encountered in this transition.
Title:
Icosahedral phase formation domain in Al-Cu-Fe system by mechanical alloying
Authors:
Barua, P; Murty, BS; Mathur, BK; Srinivas, V; McKeon, DGC;
Source:
JOURNAL OF MATERIALS RESEARCH, 17 (3): 653-659; 2002
Abstract:
A systematic composition dependence study on icosahedral phase (i-phase) formation in the Al-Cu-Fe system has been carried out. Structural evolution during mechanical alloying and on subsequent heat treatment has been investigated by x-ray diffraction and transmission electron microscopy. The i-phase is observed to evolve from the reaction between the Al2Cu and P phases. The influence of the Cu to Fe ratio (RC,,Fe), Al to transition metal ratio (R-AITM), and the electron to atom ratio (e/a) on the volume fraction of the i-phase has been studied. The analysis of the present results and those published earlier indicates that quasicrystal-forming ability correlates better with the R-AITM and e/a ratios. The volume fraction of the i-phase is maximum when the R-AITM similar to 2.3 and e/a ratio similar to 2.0. Formation of the i-phase in Al65Cu25Fe10 by mechanical alloying is reported for the first time.
Title:
Formation of Zr70Ni23Ti7 glassy alloy and phase transformation upon annealing
Authors:
Wang, LM; Li, CF; Ma, LQ; Inoue, A; McKeon, DGC;
Source:
JOURNAL OF MATERIALS RESEARCH, 17 (3): 693-696; 2002
Abstract:
Zr70Ni23Ti7 alloy contains a single amorphous phase when it is melt-spun at a wheel surface velocity over 20 m/s. The crystallization of these amorphous ribbons takes place through two exothermic reactions and shows a significant supercooled liquid region of about 30 K, indicating that the Zr70Ni23Ti7 alloy has a good glass-forming ability. The crystallization products of the first exothermic reaction for the ribbon prepared at a wheel surface velocity of 40 m/s are mainly an icosahedral quasicrystalline phase (I-phase) and some Zr2Ni phases. Further heating to a higher temperature will lead to the transformation of the metastable I-phase to Zr2Ni. Some icosahedral atomic clusters with a structure similar to those in face-centered-cubic Zr2Ni may exist in the alloy after rapid quenching, and most of them may act as nuclei of I-phase. The formation of I-phase in this alloy without any noble metals may be due to the proper atomic ratios in the system.
Title:
Cd(OH)(2)-NiAs related phases in the Co-Se system
Authors:
Noren, L; Withers, RL; Garcia-Garcia, FJ; Larsson, AK; McKeon, DGC;
Source:
SOLID STATE SCIENCES, 4 (1): 27-36; 2002
Abstract:
The reported high temperature, wide range non-stoichiometric Co2-xSe2, 0 less than or equal to x less than or equal to 0.50, solid solution field has been carefully reinvestigated using electron and X-ray powder diffraction. Close investigation shows that the 'solid solution' should be separated into four distinct phase regions (i)-(iv), even though the underlying average structure unit cell appears to distort smoothly and continuously as a function of composition. For values of x between 0 and 0.06 (structure type (i)), the structure is of 'defect' NiAs-type as only NiAs type parent reflections are observed. For 0.06 < x < 0.25 (structure type (ii)), sharp incommensurate satellite reflections are observed in addition to Cd(OH)(2)-type parent reflections leading to a previously unreported (3 + 2)-dimensional incommensurately modulated superstructure phase. For 0.25 < x < 0.40 (structure type (iii)), a commensurate superstructure phase is observed which appears to be of Cr7Se8 type, space group C2/m (a = 12.4236(8) Angstrom, b = 7.1794(13) Angstrom, c = 8.1835(6) Angstrom, beta = 139.926(7)degrees for x = 0.30). Finally, for 0.40 < x < 0.50 (structure type (iv)), a further commensurate superstructure phase is observed which appears to be of Cr3S4 type, space group C2/m (a = 11.9439(2) Angstrom, b = 3.5753(4) Angstrom, c = 6.1429(7) Angstrom, beta = 119.384(8) for x = 0.50). (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.
Title:
La1.18Rh3In2 - an incommensurate composite structure
Authors:
Esmaeilzadeh, S; Zaremba, VI; Kalychak, YM; Hoffmann, RD; Pottgen, R; Sherry, TN;
Source:
SOLID STATE SCIENCES, 4 (1): 93-102; 2002
Abstract:
New indide La1.18Rh3In2 was prepared by reaction of the elements in an arc-melting furnace and subsequent annealing at 870 K for four cheeks. La1.18Rh3In2 was investigated h X-ray diffraction on both powders and single crystals. Its structure was found to be of an incommensurate composite type with two intergrown sub-lattices determined and refined by using single crystal X-ray data and superspace group formalism. An incommensurate intergrowth structure model including twinning, with the superspace groups pairs R:P3m1:11 and P:R3m:11, was found to he the hest model for the refinement and description of this structure, The structure refinement resulted in freighted R-values of 0.046 total the total structure factors including both basic and satellite reflections, 0.043 for the main reflections belonging to the two basic substructures and 0.054 for the first order satellites. The rhodium atoms form 3.6.3.6 Kagome nets kith Rh-Rh distances ranging from 2.74 to 2.92 Angstrom. The nets are stacked one upon each other and the resulting trigonal prismatic voids are filled with indium atoms at Rh-In distances of 2.64 to 2.77 Angstrom. The rigid three-dimensional [Rh3In2] network has large flexagonal channels which are filled with lanthanum atoms giving the composition La1.18Rh3In2. The lanthanum sub-lattice is ordered in the hexagonal tunnels with a rhombohedral symmetry. The c-axis of the [Rh3In2] lattice is 4.3725(0) Angstrom while it is 3.695(3) Angstrom for the lanthanum lattice. This mismatch clearly shoals the incommensurability of the structure. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.
Title:
Analytical expression for the Fourier spectrum of a quasiperiodic Fibonacci superlattice with k components (k <= 3)
Authors:
Wei, H; Zhang, C; Zhu, YY; Zhu, SN; Ming, NB; Ozaki, H;
Source:
PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 229 (3): 1275-1282; 2002
Abstract:
The two-component quasiperiodic optical superlattice has been proved useful to some coupled parametric processes such as the direct third-harmonic generation. In this paper a three-component quasiperiodic superlattice has been studied theoretically. Using the projection method, the analytical expression of its Fourier spectrum has been deduced. The results might be conducive to the design of nonlinear optical devices related to the coupled parametric processes, such as the fifth-harmonic generation.
Title:
Quasicrystals
Authors:
Cahn, JW; Zhang, C;
Source:
JOURNAL OF RESEARCH OF THE NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, 106 (6): 975-982; 2001
Abstract:
The discretely diffracting aperiodic crystals termed quasicrystals, discovered at NBS in the early 1980s, have led to much interdisciplinary activity involving mainly materials science, physics, mathematics, and crystallography. It led to a new understanding of how atoms can arrange themselves, the role of periodicity in nature, and has created a new branch of crystallography.
Title:
Crystal structure of natrite, gamma-Na2CO3
Authors:
Zubkova, NV; Pushcharovsky, DY; Ivaldi, G; Ferraris, G; Pekov, IV; Chukanov, NV; Lambert, D;
Source:
NEUES JAHRBUCH FUR MINERALOGIE-MONATSHEFTE, 8 (2): 85-96; 2002
Abstract:
A new occurrence of natrite, gamma-Na-2(CO3), was discovered as monomineral lenses (more than 20 cm in size) in pegmatites of Mt. Koashva, Khibiny alkaline massif, Kola peninsula, Russia. Electron microprobe, XRD, IR and optical data for natrite of this new occurrence are given. A single-crystal fragment isolated from polysynthetic twinned material was used for collecting X-ray single-crystal data: lambda(MoKalpha) = 0.71073 Angstrom, C2/m, a = 8.905 (4), b = 5.237(3), c = 6.045 (2) Angstrom, beta = 101.32(3)degrees, 1290 reflections. Satellite reflections on oscillation photographs indicate the presence of modulation in the structure of natrite. The average structure converged to R = 0.106; models with (i) all atomic positions split and (H) anharmonic thermal displacement parameters applied to unsplit atoms converged to R = 0.036 and 0.029 respectively. The structure of natrite contains [001] columns formed by face sharing Na octahedra and further 7-fold coordinated Na polyhedra; the columns are connected by CO3 groups.
Title:
Solidification paths for an icosahedral quasicrystalline phase in cast Al62Cu25.5Fe12.5 and Al55Cu25.5Fe12.5Be7 alloys
Authors:
Song, GS; Lee, MH; Kim, WT; Kim, DH; Pekov, IV;
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 297 (2-3): 254-262; 2002
Abstract:
The solidification behavior of the icosahedral (i) phase in (Al6(2-x)Be(x)) Cu25.5Fe12.5 (x = 0, 7) alloys has been irivestigated using a conventional casting technique. It was observed that the addition of beryllium (Be) modified the i-phase formation mechanism from peritectic reaction to primary solidification compared to as-cast Al62Cu25.5Fe12.5 alloy. The establishment of the new solidification path is attributed to the narrowing of the freezing range resulting from the beryllium addition. However, the resolidification at a slow cooling rate could result in the formation of the i-phase by peritectic reaction. The conversion of the initial solidification path to the peritectic solidification was attributed to a cooling rate effect resulting from the elaboration process. A new decomposition process of the bulk single i-phase in the Be-containing alloy is also proposed in the present paper. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
A brief survey of quasicrystallography
Authors:
Gratias, D; Illner, R;
Source:
FERROELECTRICS, 250 (1-4): 1-6; 2001
Abstract:
We describe some main basic crystallographic tools used for characterizing the atomic structures of idealized quasicrystals.
Title:
The crystallography of aperiodic inclusion compounds
Authors:
Boysen, H; Illner, R;
Source:
FERROELECTRICS, 250 (1-4): 7-12; 2001
Abstract:
The general diffraction phenomena characteristic of 1-dim inclusion compounds are outlined. These are Bragg reflections from the 3-dim host framework and diffuse layers from the 1-dim guest chains located in the tunnels of the host. Mutual interactions between guest chains in different tunnels and between host and guest cause additional satellite reflections and satellite layers. Examples with increasing complexity of the guest are presented: single ions (K+ in K-hollandite), small (I3- in E2PI1.6) and larger molecules (n-alkanes in urea).
Title:
Composite structures beyond a perturbative modulated picture
Authors:
Perez-Mato, JM; Zakhour-Nakhl, M; Darriet, J; Elcoro, L; Pekov, IV;
Source:
FERROELECTRICS, 250 (1-4): 13-18; 2001
Abstract:
Commensurate and incommensurate structures, which can be described as composites but do not fit into the usual picture of a composite are briefly reviewed. The modulation is an essential part of these systems and cannot be considered as a perturbation. In many cases, the superspace phason sliding mode does not have a physical meaning.
Title:
Modulated structure analysis of composite crystal (Sr2Cu2O3)(0.70)CuO2, "Sr14Cu24O41" with two-legged ladder and one-dimensional chain
Authors:
Gotoh, Y; Yamaguchi, I; Takahashi, Y; Akimoto, J; Mizuta, S; Onoda, M; Fujino, H; Nagata, T; Akimitsu, J; Kramer, MJ;
Source:
FERROELECTRICS, 250 (1-4): 19-22; 2001
Abstract:
The modulated composite structure of (Sr2Cu2O3)(0.70)CuO2, "Sr14Cu24O41" with two-legged Cu2O3 ladder and one-dimensional CuO2 chain has been investigated by (3+1)-dimensional superspace group approach. By considering the x-ray reflections, centrosymmetric superspace groups were confirmed for both the CuO2 part and the Sr(2)Cu(2)O(3)one. In (Sr2Cu2O3)(0.70)CuO2, displacive modulation of O atom in the CuO2 is considerably large.
Title:
Structure refinement of the composite crystal Sc2B1.1C3.2 in a five-dimensional formalism
Authors:
Onoda, M; Shi, Y; Leithe-Jasper, A; Tanaka, T; Mizuta, S;
Source:
FERROELECTRICS, 250 (1-4): 23-26; 2001
Abstract:
The crystal structure of a new layered compound Sc2B1.1C3.2 has been refined based on a five-dimensional formalism using single crystal X-ray diffraction data. R-F was 0.043 for 1398 reflections with I>4sigma(I) using 41 structural parameters on a commensurate composite crystal model. The generator set of symmetry operations of the trigonal superspace group employed are x,y,z,u,v; - y,x-y,z,-v,u-v; y,x,-z,v,u; -x,-y,-z,-u,-v. The unit cell and other crystal data are a=b=3.387(1), c=6.703(2)Angstrom, sigma(1)=(9/7 0 0), sigma(2)=(0 9/7 0), Z=1, D-x=3.501 Mg/mm(3).
Title:
Structures in superspace of intergrowth polytypoids LaTi1-xO3 and (Ba1-4xLa4x) Ti1-xO3 with x=1/5
Authors:
Petricek, V; Elcoro, L; Perez-Mato, JM; Darriet, J; Teneze, N; Mercurio, D; Fujino, H;
Source:
FERROELECTRICS, 250 (1-4): 31-34; 2001
Abstract:
New Rietveld refinements of powder diffraction data of the cation deficient perovskite-related compounds mentioned in the title were performed in 4D using a recently proposed superspace model with discrete atomic occupation domains. The results confirm the validity and efficiency of the superspace description of these layered systems. The resulting 3D structure for La5Ti4O15 corrects a previously reported model.
Title:
Phase analysis, local crystal chemistry and the crystallography of incommensurate crystal phases
Authors:
Withers, RL; Schmid, S; Noren, L; Tabira, Y; Thompson, JG; Mercurio, D;
Source:
FERROELECTRICS, 250 (1-4): 47-52; 2001
Abstract:
The notion of multiple (partial) occupancy is shown to be an inadequate descriptive tool for continuously variable, composition dependent solid solutions. Instead of random substitution on partially occupied sites, such solid solution phases are usually found to be modulated either in a long range ordered modulated structure form (composite or conventional) or in a locally ordered form leading to a highly structured diffuse distribution.
Title:
The use of crenel functions in the description of the hexagonal perovskite-like A(1+x)BX(3) oxides and sulfides
Authors:
Evain, M; Gourdon, O; Petricek, V; Tabira, Y;
Source:
FERROELECTRICS, 250 (1-4): 53-58; 2001
Abstract:
The use of crenel functions is demonstrated to be a key factor for the resolution of the hexagonal perovskite-like A(1+x)BX(3) oxide and sulfide aperiodic structures. The models developed using those crenel functions revealed interesting unforeseen features for Ni-II and Co-II in the oxides, that is their instability in the center of the trigonal prism, and showed the particularity of the sulfur structures, bringing to light new [MS6] units and original [MS3] chain sequences.
Title:
Two-dimensional incommensurate structures of (Sr0.13Ca0.87)(2)CoS(i)2O(7) and Ca2CoSi2O7: Effects of substitution of interlayer cations
Authors:
Bagautdinov, B; Hagiya, K; Kusaka, K; Ohmasa, M; Iishi, K; Mercurio, D;
Source:
FERROELECTRICS, 250 (1-4): 59-62; 2001
Abstract:
The modulated structures of (Sr0.13Ca0.87)(2)CoSi2O7 at 293K and Ca2CoSi2O7 at 293, 393, 468K are compared to find the peculiarity of the partial substitution of Ca by larger alkaline-earth atoms such as Sr. The similarities in structural effects of this substitution and heating are found.
Title:
3-dimensional modulations in bismuth oxide based compounds with average fluorite type structures
Authors:
Esmaeilzadeh, S; Hagiya, K;
Source:
FERROELECTRICS, 250 (1-4): 63-66; 2001
Abstract:
Two new cubic fluorite type related high temperature phases have been found with the compositions Bi0.84Mo0.16O1.74 and Bi1-xCrxO1.5+1.5x 0.05 < x < 0.15. A 3-dimensional (3D) incommensurate modulation was observed by analysing electron diffraction (ED) as well as X-ray diffraction (XRD) data, indicating the superspace group symmetry Fm (3) over barm : Fm (3) over barm The structures of these new phases have been compared with the 3D modulated structure of Bi(1-x)Nb(x)O(1.5+x)0.06 < x < 0.23 with the superspace group symmetry P : Fm (3) over barm : Fd (3) over barm.
Title:
HRTEM imaging of {110} twin domains in incommensurately modulated Ba2TiGe2O8
Authors:
Hoche, T; Neumann, W; Kusaka, K;
Source:
FERROELECTRICS, 250 (1-4): 67-70; 2001
Abstract:
A (110) twin domain in Ba2TiGe2O8 was imaged using high-resolution transmission electron microscopy, HRTEM. The interface would not be visible due to the very weak orthorhombic deformation of the unit cell (0.15 %) alone. But since a modulated structure along the b*-direction is developed, the boundary can be localised. An experimental method for the detailed characterisation of the atomistic domain-boundary structure is proposed.
Title:
Disordered state in IC(incommensurate)- and N(normal)-phases of Ca2CoSi2O7 deduced from variation of thermal displacement factors
Authors:
Kusaka, K; Hagiya, K; Haga, N; Ohmasa, M; Iishi, K; Mercurio, D;
Source:
FERROELECTRICS, 250 (1-4): 71-74; 2001
Abstract:
The structure of Ca2CoSi2O7, has been determined at several temperatures in the range between 297 and 773K. Analyses of the anisotropic displacement parameters clarifies the disorder of the modulation waves that develop in the structure at higher temperatures. The evolution of the disorder in the structures was ascertained by observation of circular diffuse streaks in the vicinity of the transition temperature (TIC-N) between the IC- and N-phase.
Title:
Variation of ordered arrangement of atoms in incommensurate Ca2CoSi2O7 accompanied by change of modulation wavelength
Authors:
Kusaka, K; Hagiya, K; Ohmasa, M; Iishi, K; Toudic, B;
Source:
FERROELECTRICS, 250 (1-4): 79-82; 2001
Abstract:
A program to visualize an incommensurate structure in the three-dimensional space has been developed and applied to study the changes of long range order in the incommensurate structure Of Ca2CoSi2O7 with respect to the variation of the components q of the modulation wave vectors. The results indicate that the incommensurate structure is characterized by variations of the octagonal distribution of bundles along c that are formed by four arrays of six-coordinated Ca-O polyhedra surrounding a central array of CoO4 tetrahedra.
Title:
The superspace description of the incommensurately modulated structure of quininium (R)-mandelate
Authors:
Schonleber, A; Chapuis, G; Ohmasa, M;
Source:
FERROELECTRICS, 250 (1-4): 91-94; 2001
Abstract:
Quininium (R)-mandelate is an organic compound presenting a one-dimensional modulation with strong satellite reflections up to high order. The structure was first solved in two commensurate approximations. This allowed the refinement of this incommensurate structure in the superspace group formalism, using displacive modulation functions.
Title:
EPR investigation of phase transitions and incommensurate phases in improper ferroelastic MgGeF6 center dot 6H(2)O : Mn2+
Authors:
Ziatdinov, AM; Skrylnik, PG; Ohmasa, M;
Source:
FERROELECTRICS, 250 (1-4): 95-98; 2001
Abstract:
The results of EPR investigation of improper ferroelastic crystals MgGeF6.6H(2)O:Mn2+ allow to conclude that at T-i1=403 K these crystals undergo transition to structurally incommensurate phase. The order parameter of this transition is probably the angle of Mg[H2O](6)(2+) octahedra rotation around crystal C-3 axis, which determines the presence of only even terms in expanding the EPR spectra fine structure parameter on the powers of order parameter. Below 360K the appearance of structural phase soliton lattice and effect of variation of the spin-lattice relaxation rate over the spectrum have been taken into account.
Title:
Molecular dynamics simulation of incommensurate structure
Authors:
Pan, YS; Brown, D; Chapuis, G; Iishi, K;
Source:
FERROELECTRICS, 250 (1-4): 107-110; 2001
Abstract:
Molecular dynamics was used to simulate the incommensurate crystal N-4(CH2)(6).(CH2)(6)(COOH)(2). At normal pressure, no clear incommensurate structure is obtained between 120K and 295K. Small discrepancies between MD results and experimental lattice constants and angle are observed. Pressure tensor correction is needed to reduce the difference between experiment and simulation. After correction, the simulation results show that the crystal structure is incommensurate at 120K and 160K and commensurate at 220K or higher.
Title:
Can aperiodicity cause superlubricity?
Authors:
Consoli, L; Fasolino, A; Knops, HJF; Janssen, T; Toudic, B;
Source:
FERROELECTRICS, 250 (1-4): 111-114; 2001
Abstract:
The ground state of incommensurate structures is determined by the modulation due to the substrate potential. This causes an interplay between the motion of the center of mass and frequencies related to the modulation wavevector q. We build for the one-dimensional Frenkel-Kontorova model an analytical framework which enables us to interpret the initial behavior of the system for a broad range of initial velocities in terms of these relevant phonon modes, and to investigate the occurrence of superlubricity.
Title:
Hybridization of low frequency phonon branches and incommensurate instability in Sn2P2Se6
Authors:
Hlinka, J; Smirnov, MS; Janssen, T; Janssen, T;
Source:
FERROELECTRICS, 250 (1-4): 123-126; 2001
Abstract:
Dispersion curves of the low frequency phonon modes related to the order parameter of the structural phase transition to the incommensurate phase in Sn2P2Se6 crystal are analyzed in the framework of a simple semi-empirical model. It is shown that the phase transition instability appears out of the Brillouin zone center due to the hybridization (eigenvector mixing) of these branches.
Title:
Peculiarity of incommensurate phase connected with electronic system dynamics
Authors:
Mamin, RF; Smirnov, MS;
Source:
FERROELECTRICS, 250 (1-4): 127-130; 2001
Abstract:
A new approach is proposed for describing memory effect and global hysteresis in incommensurate phase. This approach is to take account into the dynamics of the nonuniform electron density in trapping levels in the semiconductor. A correlation between the abnormal physical properties of crystals and characteristics of semiconducting subsystem is established.
Title:
Diffraction analysis of sinusoidal modulated structures in average unit cell approach
Authors:
Urban, G; Wolny, J; Janssen, T;
Source:
FERROELECTRICS, 250 (1-4): 131-134; 2001
Abstract:
A reference lattice has been constructed for some one-dimensional sinusoidal modulated structures with commensurate and incommensurate values of modulation vector. Fourier transform of the probability distribution for closed distances of atomic positions with respect to the so-called reference lattice allows to calculate the envelope function connecting peak maxima of the main reflection and their satellites.
Title:
A lattice model for Sn2P2(S1-xSex)(6)
Authors:
Van Raaij, GHF; Janssen, T; Janssen, T;
Source:
FERROELECTRICS, 250 (1-4): 135-138; 2001
Abstract:
A lattice model for a crystal with an incommensurate phase intermediate between the ferroelectric and paraelectric phases is applied to Sn2P2(S1-xSex)(6). The phase diagram for 0 less than or equal to x less than or equal to 1 and the temperature dependence of the modulation wave vector for Sn2P2Se6 are calculated, and compared with experiments.
Title:
Algebraic numbers and Ammann bars in cut-and-project schemes
Authors:
Pleasants, P; Janssen, T;
Source:
FERROELECTRICS, 250 (1-4): 151-156; 2001
Abstract:
Ammann bars have been observed in many quasicrystals and have a number of uses. However, they are a non-generic feature of cut-and-project sets with random placings of the physical and internal spaces relative to the lattice. I shall describe an intimate connexion between Ammann bars and the method of constructing a cut-and-project set from a module over an algebraic number field K: namely that Ammann bars are derived from K-subspaces of K-n but not from Q-subspaces of K-n.
Title:
Wulff-shape, minimal energy and maximal density
Authors:
Wills, JM; Janssen, T;
Source:
FERROELECTRICS, 250 (1-4): 157-161; 2001
Abstract:
The Gibbs-Curie minimum energy principle leads to the Wulff-shape of dense atomic packing with respect to the underlying structure, periodic or aperiodic. We show that an appropriate maximum density also leads to Wulff shapes of crystals or quasicrystals. This underlines the close relation of minimal energy and maximal density. A final example shows the striking coincidance between experiment and mathematical model.
Title:
An alternative description of random tilings
Authors:
Richard, C; Janssen, T;
Source:
FERROELECTRICS, 250 (1-4): 169-174; 2001
Abstract:
We present an alternative framework for the description of random tiling ensembles. Including the conventional description, it is also applicable to tiling ensembles without a height representation. We discuss a quasicrystallographic example in order to demonstrate the consistency of the two description schemes. Following our approach, we prove a generalization of the first random tiling hypothesis. We present an exactly solvable crystallographic random tiling violating the analogue of the second random tiling hypothesis.
Title:
s-convexity and cut-and-project sets
Authors:
Svobodova, M; Janssen, T;
Source:
FERROELECTRICS, 250 (1-4): 175-177; 2001
Abstract:
Cut-and-project sets with convex acceptance window based on irrationalities tau = 1/2(1 + root5), beta = 1 + root2, mu = 2 + root3 are models for experimentally observed quasicrystals - materials with diffraction patterns consisting of sharp Bragg peaks in crystalographically disallowed patterns. We show that for each of these three irrationalities there exists a unique bilinear operation of the type sx +(1 - s)y (where s is a parameter) such that one-dimensional cut-and-project sets are precisely Delone sets closed under this operation.
Title:
Paramagnetic NMR relaxation in icosahedral quasicrystals
Authors:
Dolinsek, J; Klanjsek, M; Apih, T; Janssen, T;
Source:
FERROELECTRICS, 250 (1-4): 195-200; 2001
Abstract:
The nuclear spin-lattice relaxation in icosahedral quasicrystals containing magnetic transition-metal atoms is governed by two mechanisms of competing strength: the relaxation via conduction electrons and the relaxation via paramagnetic centers in combination with spin diffusion. The Al-27 NMR relaxation experiments on icosahedral AlPdMn and AlCuFe have shown that the paramagnetic relaxation dominates at temperatures below 100.
Title:
BCC derivative structures and their relation to rational approximants to quasicrystals
Authors:
Ranganathan, S; Subramaniam, A; Tsai, AP; Dong, C; Toudic, B;
Source:
FERROELECTRICS, 250 (1-4): 201-206; 2001
Abstract:
Vacancy ordered phases have been earlier shown to be rational approximants to one-dimensional quasicrystals. The orientation relation between gamma brass and quasicrystals has also been pointed out in earlier work. Hexagonal phases in AI-Cr, Al-Mn and Mg base alloys have been shown to have a c/ a ratio close to 1.225 (=Frank's ratio) and thus display pseudocubic symmetry. In this paper the interrelationships among these three classes of structures will be emphasised as derivatives of the BCC lattice.
Title:
ALCHEMI study of an Al72Ni20Co8 decagonal quasicrystal
Authors:
Saitoh, K; Tanaka, M; Tsai, AP; Rossouw, CJ; Toudic, B;
Source:
FERROELECTRICS, 250 (1-4): 207-212; 2001
Abstract:
Electron channeling patterns, which record the intensity variation of characteristic X-ray emission as a function of the incident direction of an electron beam, have been taken from an Al72Ni20Co8 decagonal quasicrystal for the first time, The channeling patterns show that Al atoms and transition metals occupy respectively different lattice sites, but that both of Ni and Co atoms occupy in disorder the same lattice sites. This supports that the alloy is an electron compound, where the composition of Ni and Cc adjusts the value of the electron atom ratio of the alloy.
Title:
Silicon and carbon structures with icosahedral order, phason jumps, and disorder
Authors:
Dmitrienko, VE; Kleman, M; Mauri, F; Rossouw, CJ;
Source:
FERROELECTRICS, 250 (1-4): 213-218; 2001
Abstract:
After an introductory survey, a recent development in the theory of quasicrystal-related four-coordinated structures is presented. Two crystalline approximants, 1/0 (known as the BC8 phase) and 1/1, are studied in detail. A novel method for construction of four-coordinated structures from the Frank-Kasper dense-packed systems is suggested and several new structures are constructed. The energies of those structures and topological phason disorder are studied ab initio.
Title:
Growth models for aperiodic tilings
Authors:
Joseph, D; Kleman, M;
Source:
FERROELECTRICS, 250 (1-4): 219-+; 2001
Abstract:
In this contribution we present a survey of the approaches to explain the growth of aperiodic structures on the basis of tiling models and coverings. Thereby, we will touch the growth of ideal and random aperiodic structures, review the basic problems and discuss the known results. We will compare these models with growth models for periodic crystals to give an impression of the state of the art, of what we know and what is missing. At the end, we close with an outlook on what should be done in future.
Title:
Fibonacci sequence in the structure of the icosahedral quasicrystal
Authors:
Bolliger, B; Erbudak, M; Hensch, A; Rossouw, CJ;
Source:
FERROELECTRICS, 250 (1-4): 225-+; 2001
Abstract:
The surface of the icosahedral Al70Pd20Mn10 quasicrystal possesses a bulk-terminated structure. Sputtering the pentagonal surface followed by a brief annealing favors the formation of terraces with step heights arranged according the Fibonacci sequence.
Title:
The vibrational density of states revisited in the archetypical icosahedral quasicrystal Al62Cu25.5Fe12.5
Authors:
Brand, RA; Dianoux, AJ; Calvayrac, Y; Rossouw, CJ;
Source:
FERROELECTRICS, 250 (1-4): 229-232; 2001
Abstract:
We have studied the phonon dynamics of icosahedral i-Al62Cu25.5Fe12.5 using inelastic neutron scattering (INS) in isotope-doped samples, and have combined this with previous inelastic nuclear-resonant absorption (INA) of synchrotron radiation measurements. We are able to show that the maximum in the vibrational density of states (VDOS) at 14 meV is heavily weighted by copper. The INA results have shown that the upper peak at 27 meV is dominated by iron. We are able to explain previous lattice specific heat results from the low-energy region of the neutron-weighted VDOS, including the non-integer power behaviour.
Title:
Modelling and solving decagonal quasicrystals
Authors:
Cervellino, A; Haibach, T; Steurer, W; Rossouw, CJ;
Source:
FERROELECTRICS, 250 (1-4): 237-+; 2001
Abstract:
The n-dimensional atomic surfaces modelling technique has been applied to solve the basic decagonal phase of Al71Ni22Co7. This means describing the quasicrystal structure by means of a probability density in perpendicular space. The atomic surfaces are the supports of this probability function. n-dimensional atomic surfaces models were bora as ideal structures. We extend the technique to deal with the several different disorder phenomena characterizing real structures.
Title:
A transition state between quasicrystal and approximant in the system Al-Ni-Co
Authors:
Doblinger, M; Wittmann, R; Gerthsen, D; Grushko, B; Toudic, B;
Source:
FERROELECTRICS, 250 (1-4): 241-244; 2001
Abstract:
Correlated domains without strict periodicity but with only a periodic substructure (a, b = 5.18 nm, c = 0.82 nm, gamma = 108degrees) were observed in the system Al-Ni-Co by high-resolution transmission microscopy and electron diffraction. A periodic substructure is sufficient to produce a diffraction pattern corresponding to a nanodomain structure of a twinned approximant.
Title:
Structure solution of a high-order decagonal approximant Al71Co14.5Ni14.5 by maximum entropy Patterson deconvolution
Authors:
Estermann, MA; Lemster, K; Steurer, W; Gruskho, B; Doblinger, M; Mercurio, D;
Source:
FERROELECTRICS, 250 (1-4): 245-248; 2001
Abstract:
Single-crystals with the nominal composition Al71Co14.5Ni14.5 were studied with X-ray diffraction and electron microscopy methods. The "brute-force" deconvolution of the autocorrelation function allowed to unravel the approximant structure in a semi-quantitative way despite the complex underlying nanodomain intergrowth of two approximant domains.
Title:
Low-temperature thermoelectric power and thermal conductivity of two icosahedral Al-Pd-Re quasicrystals
Authors:
Gianno, K; Sologubenko, AV; Liechtenstein, L; Chernikov, MA; Ott, HR; Mercurio, D;
Source:
FERROELECTRICS, 250 (1-4): 249-252; 2001
Abstract:
We report on a study comparing the thermoelectric power S and the thermal conductivity K of two icosahedral quasicrystals with nominal compositions Al70Pd21.4Re8.6 and Al70Pd20Re10 between 0.4 and 300 K. A remarkable sensitivity of the thermoelectric properties on the chemical composition seems to be compatible with the existence of narrow features in the electronic density of states. Our description of the thermal conductivity data reveals the dominating sources of phonon scattering at temperatures below 40 K. We also discuss the evidence for the localization of the vibrational modes at higher temperatures.
Title:
Growth of the Al-Pd-Re and Al-Cu-Fe single quasicrystals
Authors:
Guo, JQ; Sato, TJ; Abe, E; Takakura, H; Tsai, AP; Mercurio, D;
Source:
FERROELECTRICS, 250 (1-4): 253-256; 2001
Abstract:
Partial phase diagrams involving Al-Pd-Re and Al-Cu-Fe icosahedral quasicrystals were constructed to grow their single quasicrystals. On the basis of the phase diagrams, Al-Pd-Re and Al-Cu-Fe single icosahedral quasicrystals were grown by a slow cooling method. Electrical resistivity of the Al-Pd-Re single quasicrystals, rho, was measured to be 2000similar to4000 muOmegacm at 300K and 3000similar to6000 muOmegacm at 2K, revealing negative temperature dependence with a value of rho(4.2K)/rho(300K) smaller than 2.
Title:
Variable Fe-valence as an effect of angular correlations?
Authors:
Lang, M; Schwalbe, G; Madel, C; Haberkern, R; Haussler, P; Mercurio, D;
Source:
FERROELECTRICS, 250 (1-4): 257-260; 2001
Abstract:
Long-range order starts to form as a spherical periodic electron - static-structure resonance. The selforganized adjustments of the static structure to the electronic constraints, and, vice versa, the electronic system via variations of the mass-density or the effective valency to the static structure, all optimize the resonance. The latter effect plays an important role in amorphous and quasicrystalline alloys containing late transition elements and aluminium.
Title:
Fivefold Metallo-Organic Aperiodic Crystal Structure and its specific role in Vegetable Fibers
Authors:
Tri, NV; Vung, PT; Hung, LH; Thang, NV; Hennion, B;
Source:
FERROELECTRICS, 250 (1-4): 265-+; 2001
Abstract:
The particular molecular-electronic structure and properties of different genera of vegetable fibers (such as cotton, jute, sisal, pineapple) have been studied with ESR in combination with many other methods. A complicated Fivefold Metallo-Organic Aperiodic Crystal Structure of the Vegetable Fiber has been discovered. This structure plays a decisive role in the formation of an "elementary fiber" as well as of a "macroscopic practical fiber" and in the specific features of the fibers.
Title:
High-pressure X-ray diffraction experiments on icosahedral Ti-Zr-Ni - Evidence for a low shear modulus and a high Poisson's ratio
Authors:
Ponkratz, U; Nicula, R; Jianu, A; Burkel, E; Hennion, B;
Source:
FERROELECTRICS, 250 (1-4): 269-272; 2001
Abstract:
In situ high-pressure X-ray diffraction experiments have been performed on quasicrystalline Ti-Zr-Ni in energy dispersive mode using synchrotron radiation. Pressures up to 30 GPa were generated using a diamond anvil cell. When plotting the hypercubic lattice parameter versus pressure an additional expansive strain could be observed which is caused by non-hydrostatic stress. Using the model of Singh and Kennedy the shear modulus of Ti-Zr-Ni could be stimated to be mu approximate to 7 GPa, Poisson's ratio was calculated to v = 0.48 +/- 0.015.
Title:
Atomic structure of the cubic 1/1 approximant alpha-(Al,Si)CuFe
Authors:
Puyraimond, F; Tillard, M; Belin, C; Quiquandon, M; Gratias, D; Quivy, A; Calvayrac, Y; Nagata, T;
Source:
FERROELECTRICS, 250 (1-4): 281-284; 2001
Abstract:
A X-ray diffraction structural analysis has been performed on single crystals of the alpha-(Al,Si)CuFe cubic 1/1 approximant of the parent icosahedral phase i-AlCuFe. It shows that the atomic clusters in the cubic phase are similar to those of the icosahedral phase but connect differently in agreement with the model of approximant obtained by the perpendicular shear method of the parent quasicrystal.
Title:
Formation of nano Icosahedral quasicrystalline phase in Zr-Ni-M (M=Pd, Au, Pt) ternary glassy alloys
Authors:
Saida, J; Matsushita, M; Li, CF; Inoue, A; Gratias, D;
Source:
FERROELECTRICS, 250 (1-4): 285-288; 2001
Abstract:
A nano icosahedral quasicrystalline phase was confirmed as a primary precipitation phase in the melt-spun Zr70Ni10M20 (M=Pd, Au and Pt) ternary glassy alloys. It is clarified that the precipitation of the icosahedral phase takes place by a diffusion-controlled growth mode with increasing nucleation rate. The formation of the nano scale icosahedral phase also indicates the existence of short-range order correlated with an icosahedral structure in the glassy state.
Title:
Periodic X-ray Standing Waves in quasiperiodic systems
Authors:
Schmithusen, F; Cappello, G; Chevrier, J; Inoue, A;
Source:
FERROELECTRICS, 250 (1-4): 289-+; 2001
Abstract:
X-ray Standing Waves (XSW) in Bragg position are the direct space modulation of the electromagnetic (e.m.) field in a diffracting sample. Specifically in the two beam approximation, a modulation of the e.m. field intensity with a periodicity of 2pi/Q(parallel to) has to be considered in a quasiperiodic structure. As it is fully described within the Dynamical Theory of X-ray Diffraction (DTXD), the XSW can be smoothly displaced with respect to atomic positions in a perfect crystal. This results in a strong modulation of the absorption processes as the crystal position crosses the Bragg condition. In the special case of quasicrystals (QC) the application of this technique, probing the long range order, opens several basic questions. Using a Fibonacci sequence of diffracting planes, we show that the XSW signal highly depends on the q(perp) component of the Bragg peak. Within this model, we then test the XSW response as phason defects are introduced in the structure. A rapid decrease of the XSW signature is observed when high q(perp) peaks are considered.
Title:
Ab initio structure solutions of quasicrystals by a density modification method
Authors:
Shiono, M; Takakura, H; Yamamoto, A; Inoue, A;
Source:
FERROELECTRICS, 250 (1-4): 293-296; 2001
Abstract:
A unique and powerful density modification method for solving multi-dimensional crystal structures has been developed. The method is an extension of the Low Density Elimination (LDE) method(1,2,3). The LDE method was made applicable to multi-dimensional crystal structures and applied to several quasicrystals including an unknown structure, Tests on the X-ray single crystal data of icosahedral AlPdMn4 and synthetic data of decagonal AlNiCo quasicrystals suggests that the multi-dimensional LDE method can easily solve quasicrystal structures starting from completely random phases. The procedure has also been applied to an unknown structure of icosahedral ZnMgHo quasicrystal. Multi-solution strategy was employed and 28 resultant maps clearly showed the positions and shapes of occupation domains. We were convinced by analyzing the map that the 28 results were the solutions.
Title:
Structure of icosahedral Zn-Mg-Ho quasicrystals determined by a density modification method
Authors:
Takakura, H; Shiono, M; Sato, TJ; Yamamoto, A; Tsai, AP; Quivy, A;
Source:
FERROELECTRICS, 250 (1-4): 301-304; 2001
Abstract:
The structure of icosahedral Zn60Mg31Ho9 quasicrystal has been determined, by means of ab initio structure determination, by applying a novel density modification method (low density elimination method) within a framework of 6D description. The suggested Ho sites in the 3D structure obtained as a section of resulting 6D electron density are consistent with the results of magnetic diffuse scattering.
Title:
Electrical conductivity and localization in quasiperiodic lattices
Authors:
Wang, C; Oviedo-Roa, R; Perez, LA; Sanchez, V; Tsai, AP;
Source:
FERROELECTRICS, 250 (1-4): 305-308; 2001
Abstract:
The electrical conductivity of Fibonacci lattices at zero temperature is studied by means of Kubo and Landauer formalisms, in which a tight-binding Hamiltonian of the system is considered. The localization of the eigenstates is quantified by using the participation ratio and the Lyapunov exponent. The results show a close behavior between the dc conductivity and the Lyapunov exponent. In addition, the effects of the boundary conditions on the ac conductivity are also analyzed in detail.
Title:
Data collection of quasicrystals by IP Weissenberg camera
Authors:
Yamamoto, A; Takakura, H; Tsai, AP; Sanchez, V;
Source:
FERROELECTRICS, 250 (1-4): 309-312; 2001
Abstract:
For a data collection by an imaging plate (IP) Weissenberg camera, a set of softwares has been developed, which enables us to index diffraction patterns of quasicrystals and any other quasi-periodic crystals and to obtain their integrated intensities. The indexing uses two Weissenberg photographs taken with different coupling constants. In IP Weissenberg cameras, a higher-order correction of the Lorenz factor is necessary for some reflections and a correction of the fading phenomenon of IP is important.
Title:
Dodecagonal tilings almost covered by a single cluster
Authors:
Ben-Abraham, SI; Gummelt, P; Luck, R; Gahler, F; Tsai, AP;
Source:
FERROELECTRICS, 250 (1-4): 313-316; 2001
Abstract:
A single covering cluster cannot produce a rigorously quasiperiodic dodecagonal structure but may almost do so and thus be relevant to real quasicrystals. Such 'almost covering' patches are shown for the ship, shield, square-triangle and Socolar tiling. The 'almost covering' of the Socolar tiling has a fractal feature.
Title:
A group-theoretic approach of quasicrystals
Authors:
Cotfas, N; Gummelt, P;
Source:
FERROELECTRICS, 250 (1-4): 317-320; 2001
Abstract:
A quasicrystal can be regarded as a packing of G-invariant atomic clusters, where the finite group G is the symmetry group of its diffraction pattern. We prove that a large variety of packings of G-invariant clusters can be obtained in an elegant way for any finite group G by using the strip projection method and some results from group theory.
Title:
Growth of different facets in icosahedral quasicrystals: Monte Carlo studies
Authors:
Dmitrienko, VE; Astaf'ev, SB; Kleman, M; Gahler, F;
Source:
FERROELECTRICS, 250 (1-4): 321-325; 2001
Abstract:
The three-dimensional Monte-Carlo growth model, developed earlier for icosahedral quasicrystals (V.E. Dmitrienko, et al., Phys. Rev., B59, 286, 1999), are used for the comparative study of quasicrystal facets with different symmetry (two-, three-, and fivefold). For all the facets the growth rates, the roughness, and the phason defects are analyzed. The relative growth rates of the facets depend on supercooling that could result in different growth shapes.
Title:
Deterministic and nondeterministic quasicrystal patterns with even symmetries
Authors:
Escudero, JG; Astaf'ev, SB;
Source:
FERROELECTRICS, 250 (1-4): 327-330; 2001
Abstract:
Quasicrystal patterns with symmetries found in diffraction experiments are studied. Nondeterministic models of quasicrystal structures can be obtained by composition of the inflation rules that generate the deterministic patterns.
Title:
Connection of one-dimensional aperiodic lattices to Fibonacci-chains
Authors:
Farkas-Jahnke, M; Astaf'ev, SB;
Source:
FERROELECTRICS, 250 (1-4): 331-334; 2001
Abstract:
One-dimensional aperiodic lattices of a row of materials are closely related to certain physical properties of the material. For characterizing the stacking of an aperiodic lattice built up of translationally equivalent layers it is required to find the relationship between characteristic data, derived directly from the intensity distribution on X-ray oscillation pattern of the disordered crystal region in question, and a corresponding quasiperiodic Fibonacci-chain, describing a longer part of the lattice.
Title:
Dodecagonal tilings as maximal cluster coverings
Authors:
Gahler, F; Luck, R; Ben-Abraham, SI; Gummelt, P; Tsai, AP;
Source:
FERROELECTRICS, 250 (1-4): 335-338; 2001
Abstract:
It is shown that the Socolar tiling, which is quasiperiodic and 12-fold symmetric, can be characterized as the unique tiling which is maximally covered by a suitably pair of clusters, Analogous results can be obtained also for other dodecagonal tilings, among them the shield tiling.
Title:
Influence of chemical disorder, magnetic field and phason flips on the localization of electronic states in a regular icosahedral quasicrystal
Authors:
Vekilov, YK; Isaev, EI; Arslanov, SF; Gummelt, P;
Source:
FERROELECTRICS, 250 (1-4): 339-342; 2001
Abstract:
The influence of substitutional chemical disorder, magnetic field and phasons, on the electronic spectrum and wave functions of icosahedral quasicrystals is investigated by means of tight-binding approximation and level statistic method. The results show that the localization of electronic states in an ideal quasicrystal exists due to their coherent interference at the Fermi level which is caused by the symmetry and aperiodic long-range order.
Title:
Variable range hopping conductivity in quasicrystals
Authors:
Vekilov, YK; Isaev, EI; Arslanov, SF;
Source:
FERROELECTRICS, 250 (1-4): 343-345; 2001
Abstract:
The Fermi surface of a perfect icosahedral quasicrystal at zero temperature consists of infinite number of electron-hole pockets, and therefore electronic states are localized. It is shown that in this state the Mott law for the variable range hopping conductivity is fulfilled at very low temperatures.
Title:
Superstructures, modulations and approximants in quasiperiodic tilings
Authors:
Luck, R; Scheffer, M; Arslanov, SF;
Source:
FERROELECTRICS, 250 (1-4): 351-355; 2001
Abstract:
Concerning different variants of quasicrystalline phases we present quasiperiodic tilings which combine properties of superstructures with those of modulated structures or nanostructured domains of approximants.
Title:
Healing of slip planes and interfaces in quasiperiodic patterns
Authors:
Warrington, DH; Luck, R; Arslanov, SF;
Source:
FERROELECTRICS, 250 (1-4): 357-360; 2001
Abstract:
The recovery of slip planes in quasicrystals is investigated on the basis of the formation of perfect tiles due to a flipping procedure. The procedure is focused on tilings with single translation classes. The minimum number of new vertices or the number of necessary flips to reform the tiles is taken as a measure of disorder of the slip process. Different ranges of the density of new vertices depending on the slip vector could be derived. Short displacements lead to the formation of a domain of ID quasicrystal.
Title:
A new method for the determination of the Fourier image of quasicrystalline objects
Authors:
Mochtchenko, IN; Klimova, EN; Arslanov, SF;
Source:
FERROELECTRICS, 250 (1-4): 361-364; 2001
Abstract:
The iteration method of the computation of diffraction spectrums is presented. It allows to determine the Fourier coefficients of the incommensurate structures for continuous region of reciprocal space. Besides the concrete calculations we perform the general investigation of the spectrum form. It was shown the discrete spectrums inherent to the structures described by continuous atom surface forming a manifold. We also obtain that the phason deformations of such structures are connected only with continuous atom shifts.
Title:
Shock waves in quasicrystals
Authors:
Roth, J; Klimova, EN;
Source:
FERROELECTRICS, 250 (1-4): 365-368; 2001
Abstract:
Shock waves in quasicrystals of the AlCuLi type and in approximant crystals of the C15 Laves phase have been studied by MID simulations. Three regimes are found: at low shock wave intensity the system reacts elastically, at high intensities it is turned amorphous. In the intermediate region we find a continuous transition with growing defective domains. The intensities where the behavior changes are different for the quasicrystal and the crystal, but the behavior itself is similar.
Title:
The Quasicrystal Online Database
Authors:
Scholpp, T; Steurer, W; Arslanov, SF;
Source:
FERROELECTRICS, 250 (1-4): 373-376; 2001
Abstract:
A database dedicated to quasicrystal research is made publicly available to the quasicrystal research community. The database is freely accessible via the World Wide Web at "http://www.quasicrystal.ethz.ch/QDB" and includes experimental diffraction data, high-resolution electron micrographs, phase diagrams, software, structural and theoretical models, and literature references.
Title:
Aperiodic crystal structure and conductivity of dental enamels and special porcelain enamel
Authors:
Tri, NV; Steurer, W;
Source:
FERROELECTRICS, 250 (1-4): 385-388; 2001
Abstract:
From the experimental results a peculiar conduction effect of dental enamels as well as of a special porcelain enamel and a very outstanding ESR angular dependence effect of these non-crystalline enamel films were revealed. The careful studies suggest that these effects are in close connection with the fivefold symmetry combination clusters distributed in the enamel film, whose planes are parallel to the enamel surface.
Title:
Icosahedral quasiperiodic packing of fibres for composite materials
Authors:
Audier, M; Duneau, M; Blandin, JJ; Dendievel, R; Fivel, M; Quivy, A;
Source:
FERROELECTRICS, 250 (1-4): 389-392; 2001
Abstract:
First results on theoretical and experimental studies of mechanical properties of icosahedral quasiperiodic packings of fibres are reported.
Title:
Delone covering of canonical tilings tau*(D-6)
Authors:
Papadopolos, Z; Kasner, G; Blandin, JJ;
Source:
FERROELECTRICS, 250 (1-4): 409-412; 2001
Abstract:
We consider canonical quasiperiodic tiling projected from a lattice T-*(D6) whose window in perpendicular space is projected Voronoi cell, V-perpendicular to, and whose tiles in parallel space are projected boundaries of Delone cells, X-parallel to* six golden tetrahedra. The tiles are coded by corresponding dual Voronoi boundaries projected to IEperpendicular to, denoted by X-perpendicular to. We try to obtain the Delone covering of the tiling by projecting to the parallel space some of the Delone cells (D-h, h = a, c, b) of the D-6 lattice. We determine the coding in orthogonal space for these Delone clusters and their fillings by the tiles. The covering of the tiling by the corresponding Delone clusters is considered.
Title:
An improved algorithm for the application of the Maximum Entropy Method on superspace periodic sections
Authors:
Perez-Etxebarria, A; Madariaga, G; Elcoro, L; Dendievel, R;
Source:
FERROELECTRICS, 250 (1-4): 413-416; 2001
Abstract:
An algorithm to recover the internal space of a quasicrystalline structure is proposed. This new algorithm applies the Maximun Entropy Method on superspace periodic sections guaranteeing that the obtained solution is formally unique. A priori information is introduced in data space.
Title:
The pseudocubic approximant Mg51Zn20 interpreted as a modulated crystal
Authors:
Uchida, M; Matsui, Y; Mosekilde, E;
Source:
PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 82 (4): 831-839; 2002
Abstract:
The structure of the pseudocubic Mg51Zn20 phase, which is related to icosahedral quasicrystals, was interpreted as a modulated crystal. It basically comprises distorted close-packed layers with ordered atomic vacancies. The basic reciprocal-lattice vectors point to the vertices of a distorted icosahedron. A relationship in reciprocal space between the Mg51Zn20 phase and the icosahedral Zn-Mg-Dy quasicrystal was also investigated.
Title:
Yb-based Kondo lattices: Insight from Yb-170 Mossbauer, positive Muon and gamma-gamma perturbed angular correlations spectroscopies
Authors:
Bonville, P; Rand, RH;
Source:
HYPERFINE INTERACTIONS, 134 (1-4): 5-12; 2001
Abstract:
The usefulness of local hyperfine techniques in the investigation of the physical properties of Kondo lattices is illustrated through three examples. First, we show how Mossbauer spectroscopy on Yb-170 down to very low temperature (0.025 K) provides evidence for the existence of an incommensurate modulated magnetic structure close to T = 0 in YbPtAl; a modulated structure at T = 0 is in principle forbidden for Kramers ions. but it is made possible in YbPtAl due to the presence of the Kondo coupling, Second, we present a muSR study of the Kondo insulator YbB12, and we evidence the persistence of fluctuations of very small correlated Yb moments close to T = 0. Third, we report on a study by Perturbed Angular Correlation spectroscopy on the isotope Yb-172 of the Kondo lattice Yb2Co3Ga9, which is characterised by a high Kondo temperature (T-0 similar or equal to 260 K). Our aim was to compare, on a large temperature range, the thermal variations of the 4f quadrupole moment and of the magnetic susceptibility, to check whether the scaling property predicted by theory could be observed.
Title:
Thermal expansion of decagonal Al70.7Co13.3Ni16.0 in the temperature range 15-300 K
Authors:
Kupsch, A; Meyer, DC; Gille, P; Paufler, P; Fivel, M;
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 216 (12): 607-610; 2001
Abstract:
The temperature dependence of lattice parameters a in the quasiperiodic plane and c in the periodic direction of decagonal Al70.7Co13.3Ni16.0 was probed using X-ray powder diffraction in the temperature range 15-300 K. Both parameters were fitted by means of positions of 22 Bragg reflections for each temperature. Temperature dependences were modelled best by second order polynomials leading to linear thermal expansion coefficients alpha(T) 8.1(33).10(-7) K-1 + 3.9(2).10(-8) K-2 T in the quasiperiodic plane and gamma(T) = 1.7(6).10(-6) K-1+3.8(3).10(-8) K-2 T in the periodic direction, respectively. Thus we found the anisotropy ratio gamma(T)/alpha(T) to decrease with increasing temperature from 1.60 (at 15 K) to 1.05 (at 300K) Besides pecularities around 150 K indicating an intermediate phase formed by superordering, we observed deviations from the general smooth course between 15 K and 50 K for both lattice parameters.
Title:
Icosahedral and amorphous phases in melt-spun Ti-Zr-Ni-Cu alloys
Authors:
Wang, LM; Inoue, A; Turner, CV;
Source:
MATERIALS TRANSACTIONS, 42 (12): 2637-2640; 2001
Abstract:
Structure of melt-spun Ti60Zr15Ni25-xCux (x = 0, 5, 10, 15, 20 and 25) alloys and crystallization behavior of the amorphous alloys have been studied. The alloys have different structures depending on cooling rate. An icosahedral quasicrystal phase (I-phase) is formed directly upon cooling at a wheel velocity of 20 m/s for x = 0-15, and at wheel velocities of 40 and 60 m/s for x = 0. The high cooling rate at 60 m/s for x = 5-25 causes the formation of a single amorphous phase. DSC traces of the amorphous alloys obtained during continuous heating to 1000 K showed distinct exothermic peaks. The first exothermic reaction at low temperatures for x = 5, 10 and 15 is due to the precipitation of I-phase, and the following reactions at higher temperatures result from the formation of alpha-Ti and Ti2Ni or Ti2CU phases. The simultaneous addition of Cu and Ni to Ti-Zr base alloys can enhance the forming ability of I-phase as well as amorphous phase.
Title:
Sliding friction and wear behavior of Al-Ni-Co-Si quasicrystalline coatings deposited by the high-velocity oxy-fuel spraying technique
Authors:
Fleury, E; Kim, YC; Kim, JS; Ahn, HS; Lee, SM; Kim, WT; Kim, DH; Nagata, T;
Source:
JOURNAL OF MATERIALS RESEARCH, 17 (2): 492-501; 2002
Abstract:
The sliding friction and wear performance of Al-Ni-Co-Si quasicrystalline coatings deposited by the high-velocity oxy-fuel technique were investigated under dry sliding conditions. This study indicated that changes in the imposed sliding test conditions modified the friction and wear behavior of quasicrystalline coatings. Qualitative analysis of the contact interface and wear debris were performed with the aim of understanding the role of the third body on the friction and wear processes. The dependence of the coefficient of friction on the sliding velocity and counterpart material was explained by the stick-slip behavior. It was also shown that test conditions favorable for the formation of thick intermediate layers and the densification of the coating subsurface led to low wear rates. Large cylindrical particles, formed by agglomeration of small wear debris. were suggested as a beneficial factor for the reduction of the coefficient of friction.
Title:
Icosahedral phase in rapidly solidified Al-Fe-Ce alloy
Authors:
Zhang, CJ; Wu, YS; Cai, XL; Fang, Z; Zheng, SQ; Zhou, GR; Wu, S; Nagata, T;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 323 (1-2): 226-231; 2002
Abstract:
To study the mechanisms for the high strength of Al-TM-Re alloys. we synthesized metallic glasses Al90Cu5Ce5 and Al90Fe5Ce5 by melt spinning. Icosahedral particles surrounded by f.c.c.-Al were found to appear as a primary precipitation phase in the amorphous Al90Fe5Ce5 alloy. The mechanical properties of the amorphous Al90Fe5Ce5 alloy can be enhanced by using a mixed structure of icosahedral nanoparticles, Al nanoparticles and amorphous matrix, Microstructure analysis suggests that icosahedral structural units are homogeneously distributed in the matrix of the amorphous Al90Fe5Ce5 alloy. These structural units can be identified by the characteristic isothermal calorimetric signals associated with their transformation to fine quasicrystalline grains. The unusual glass formability of the Al-Fe-Ce alloy is discussed in this report. A distinct pre-peak is observed in the X-ray diffraction patterns of the amorphous Al90Cu5Ce5 and the Al90Fe5Ce5 alloys. The relaxation and glass transition phenomena are clearly observed for the Al90Cu5Ce5 alloy. Based on the structure difference between Al90Fe5Ce5 and Al90CU5Ce5, the origin of the pre-peak can be attributed to the inter-metallic compounds pre-existent in the amorphous matrix. (C) 2002 Elsevier Science B.V. All rights reserved.
Title:
Electrical investigations in the normal and incommensurate phases of [N(CH3)(4)](2)ZnCl4 single crystals
Authors:
El-Fadl, AA; El-Korashy, A; El-Zahed, H; Fang, Z;
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 63 (3): 375-381; 2002
Abstract:
The dielectric permittivity (epsilon) of TMA-ZC single crystals was measured along the mean crystallographic axes a, b and c, in a temperature range from 273 to 340 K. The epsilon-T relationship exhibited peak values at T-i = 296 K and T-c1 = 279 K for the three axes. These peaks are attributed to the contribution of discommensurations. The d.c. and a.c. electrical conductivity showed anomalous variation at the same transition temperatures, with a remarkable change in the value of the activation energy around the transition temperatures. The j-E characteristic indicates different types of electrical conduction. The mechanism of the phase transition and the electrical process were discussed on the basis of Shottky and Frenkel conduction mechanisms. (C) 2002 Elsevier Science Ltd. All rights reserved.
Title:
Electronic transport in quasicrystals
Authors:
Vekilov, YK; Isaev, EI; Livanov, DV; Fang, Z;
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 94 (1): 172-177; 2002
Abstract:
Mobility of electrons in quasicrystals is considered in the framework of the fractional Fermi surface (FS) model, i.e., a multiconnected FS with many electron-hole pockets. The Mott law for the variable range hopping conductivity is obtained when intervalley scattering processes with small momentum transfer are taken into account. The transition to the power-law temperature dependence is discussed. (C) 2002 MAIK "Nauka/Interperiodica".
Title:
Microstructures and structural phase transition in (Mg,Fe)SiO3 majorite
Authors:
Tomioka, N; Fujino, K; Ito, E; Katsura, T; Sharp, T; Kato, T; Wu, S;
Source:
EUROPEAN JOURNAL OF MINERALOGY, 14 (1): 7-14; 2002
Abstract:
(Mg1-xFex)SiO3 majorites with the compositions of X=0.0-0.20 were synthesized at 20 GPa and 1950-2200 degreesC in a uniaxial split-sphere apparatus, and the recovered samples were examined by analytical transmission electron microscopy. Although the diffraction patterns of synthetic majorites in all the recovered specimens show a tetragonal (I4(1)/a) symmetry, specimens quenched from temperatures above similar to1950 degreesC show frequent pseudomerohedral twins and modulated "tweed" structures, while specimens quenched from temperatures below similar to1950 degreesC show few or no twins. Right-angled pseudomerohedral twin domains occur without dislocations to relax strain at the domain corners. These observations suggest that twin and tweed structures in tetragonal majorite form by the cubic-tetragonal phase transition during quenching and that cubic majorite is stable at temperatures above similar to1950 degreesC at 20 GPa. Natural majorites in shocked chondrites appear to be cubic. The difference between natural cubic majorites in shocked meteorites and synthetic tetragonal majorites is attributed to the faster cooling rate in natural samples.
Title:
Stacking sequences and symmetry properties of trigonal vacancy-ordered phases (tau phases)
Authors:
Lord, EA; Ranganathan, S; Subramaniam, A; Koenraad, P;
Source:
PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 82 (2): 255-268; 2002
Abstract:
The vacancy-ordered phases known as tau phases are described and the literature dealing with the observed stacking sequences is reviewed. It is shown that the stacking sequences along the threefold axis can be derived from a projection method involving projection on to an axis of type [rr (q) over bar]. The structure has alternating filled and empty lamellae parallel to planes of type (rr (q) over bar). The particular cases in which r and q are consecutive numbers of the Fibonacci sequence can be regarded as rational approximants to a one-dimensional quasiperiodic structure. Some mathematical properties of the sequences, and their relationship with the three-dimensional structures, are presented.
Title:
Commensurately modulated states in the Mg-Al system
Authors:
Donnadieu, P; Denoyer, F; Lauriat, JP; Ochin, P; Neuefeind, J;
Source:
PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 82 (2): 297-316; 2002
Abstract:
We report an electron and X-ray diffraction study of commensurately modulated states corresponding to the high-temperature equilibrium states in the Mg-Al system. The aluminium contents (49-54 at.%) and temperatures (425-445degreesC) of interest here are located within the large gamma-phase domain of the Mg-Al phase diagram. The present work is focused on the indexation of these three-dimensionally modulated states which are required to be reliable to combine electron and X-ray diffraction information. We finally obtain an indexation in terms of a P-type cubic lattice for the mean lattice and an F-type cubic lattice for the modulation. In this indexation scheme, the stable crystalline phases gamma-Mg17Al1/2 and beta-Mg2Al3 appear as lock-in states characterized by the rational values 1/3 and 3/8 respectively.
Title:
Plastic deformation of icosahedral Al-Pd-Mn single quasicrystals to large strains - I. Experiments
Authors:
Kabutoya, E; Edagawa, K; Tamura, R; Takeuchi, S; Guo, JQ; Tsai, AP; Wu, S;
Source:
PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 82 (2): 369-377; 2002
Abstract:
Icosahedral Al-Pd-Mn single quasicrystals, grown by the Czochralski method, were deformed in compression along a twofold direction to large strains. The true stress versus true strain curves showed three stages: the initial work-hardening stage, a large work-softening stage followed by a weak work-hardening stage. The minimum flow stress was about half the maximum flow stress. The stress relaxation experiments showed temperature-dependent activation volume versus applied stress relations. Assuming that the now stress is composed of the effective stress, the temperature-dependent dragging stress and the internal stress, the effective stress dependence of the activation enthalpy was analysed for both the maximum-flow-stress state and the minimum-flow-stress state. The activation enthalpy of the latter state was found to be about 20% smaller than the former state, and the work softening is due to a decrease in the activation enthalpy with increasing plastic strain.
Title:
Plastic deformation of icosahedral Al-Pd-Mn single quasicrystals to large strains - II. Deformation mechanism
Authors:
Takeuchi, S; Tamura, R; Kabutoya, E; Edagawa, K; Guo, JQ;
Source:
PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 82 (2): 379-385; 2002
Abstract:
In part I, we have shown experimentally that the large amount of work softening is due to decreasing activation enthalpy for plastic deformation with increasing plastic strain. Based on the Peierls mechanism of the dislocation glide, the plastic deformation process in a quasiperiodic lattice is modelled. In the model, we assume high and low activation enthalpies, corresponding to large and small Peierls potentials, of the kink pair formation in the quasiperiodic Peierls potential. In an unstrained high-quality quasicrystal, the dislocation glide is essentially controlled by the high activation enthalpy whereas, in a highly strained state where a high density of phason defects is introduced, the dislocation glide is controlled by the low activation enthalpy; parts with a large Peierls potential can be overcome by the side motion of kinks produced at parts with a small Peierls potential.
Title:
The structure of the decagonal approximant Al3Mn interpreted as a modulated crystal
Authors:
Uchida, M; Matsui, Y; Kabutoya, E;
Source:
PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 82 (2): 387-391; 2002
Abstract:
The structure of the decagonal approximant Al3Mn phase, which has been described in terms of the aggregation of clusters until now, is interpreted as a modulated crystal structure. It contains everywhere the same stacking motif as observed in icosahedral approximants such as the mu- and lambda-Al4Mn phases as reported by Uchida and Matsui (2000, Acta crystallogr., B, 56, 654) and is suggested to be a crystal subjected to a shear transformation on the unit-cell scale.
Title:
Deformation mechanism of quasicrystals
Authors:
Takeuchi, S; Edagawa, K; Tamura, R; Edagawa, K;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 319 (7): 93-96; 2001
Abstract:
Characteristics of the high-temperature compressive deformation behavior of icosahedral and decagonal quasicrystals are reviewed. In icosahedral quasicrystals, the true stress versus true strain relation shows a pronounced yield drop. followed by gradual softening towards a minimum at a large true strain of about 0.5 and then changes to hardening at higher strain; the yield and flow stresses are quite sensitive to temperature and strain rate. In decagonal quasicrystals, the yield stress depends weekly on orientation in spite of its anisotropic structure. In both types of quasicrystals. the yield stress is higher in higher quality samples. The deformation mechanism of the quasicrystals is discussed in terms of dislocations glide in the quasicrystalline lattice governed by the Peierls mechanism. The Peierls mechanism in quasicrystals differs from that in crystals in that the dislocation glide is accompanied by a phason atrain relaxation and the Peierls potential is not periodic but quasiperiodic. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Dislocation mobility versus dislocation substructure controlled deformation of icosahedral Al-Pd-Mn single quasicrystals
Authors:
Messerschmidt, U; Petukhov, BV; Bartsch, M; Dietzsch, C; Geyer, B; Haussler, D; Ledig, L; Feuerbacher, M; Schall, P; Urban, K;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 319 (7): 107-110; 2001
Abstract:
This paper compares new high-voltage electron microgaphs of the dislocation structure of icosahedral Al-Pd-Mn specimens deformed at a high temperature ( congruent to 800degreesC) with those deformed at a low temperature (610degreesC). At all temperatures, the dislocations consist of almost straight segments on different planes. However. planar faults trailed by the dislocations have been observed at low temperatures only. The temperature dependence of the steady-state flow stress is modelled based on an evolution law of the dislocation density proposed before including recovery, and by considering the contribution of long-range dislocation interactions to the flow stress. Owing to the thermally activated recovery of the microstructure, the activation energy of deformation measured experimentally turns out to be higher than the energy of the dislocation mobility, explaining the unreasonably high experimental values. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Plastic behaviour of icosahedral Al-Cu-Fe quasicrystals: Experiment and modelling
Authors:
Giacometti, E; Guyot, P; Baluc, N; Bonneville, J; Geyer, B;
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 319 (7): 429-433; 2001
Abstract:
Constant strain-rate and creep tests have been performed on poly-quasicrystalline specimens of the icosahedral Al-Cu-Fe system. Three temperatures (870, 960 and 1000 K) have been investigated by creep for samples predeformed at constant strain-rate before and beyond the upper yield stress, over the stress range 30-320 MPa. The influence of the creep stress level and plastic strain amount on the stress-strain curve has also been studied when the samples are deformed again at constant strain rate. Depending on temperature, stress and initial predeformation states, single or two-stage creep curves have been observed. When performed before the upper yield stress, in the high work-hardening portion of the stress-strain curve, only a primary stage of continuous decreasing creep rate is observed. At higher stresses, close to the upper yield stress, the primary stage is followed by a second stage of work-softening leading to an increasing strain-rate. The shape of the constant strain-rate and creep curves, as well as the transients observed when creep is switched-back to constant strain-rate conditions, are in fair agreement with the predictions of the dislocation model recently proposed by Guyot and Canova on the basis of an irreversible strain dependent friction stress [P. Guyol, G. Canova, Phil. Mag. A 79 (1999) 28151]. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Charge-density waves and superlattices in the metallic layered transition metal dichalcogenides (Reprinted from Advances in Physics, vol 32, pg 882, 1974)
Authors:
Wilson, JA; Di Salvo, FJ; Mahajan, S; Bonneville, J;
Source:
ADVANCES IN PHYSICS, 50 (8): 1171-1248; 2001
Abstract:
The d(1) layer metals TaS2, TaSe2, NbSe2, in all their various polytypic modifications, acquire, below some appropriate temperature, phase conditions that their electromagnetic properties have previously revealed as 'anomalous'. Our present electron-microscopic studies indicate that this anomalous behaviour usually included the adoption, at some stage, of a superlattice. The size of superlattice adopted often is forecast in the pattern of satellite spotting and strong diffuse scattering found above the transition.Our conclusions are that charge-density waves and their concomitant periodic structural distortions occur in all these 4d(1)/5d(1) dichalcogenides. We have related the observed periodicities of these CDW states to the theoretical form of the parent Fermi surfaces. Particularly for the 1T octahedrally coordinated polytypes the Fermi surface is very simple and markedly two-dimensional in character, with large near-parallel walls. Such a situation is known theoretically to favour the formation of charge and spin-density waves. When they first appear, the CDWs in the 1T (and 4Hb) polytypes are incommensurate with the lattice. This condition produes a fair amount of gapping in the density of states at the Fermi level. For the simplest case of 1T-TaSe2, the room temperature superlattice is realized when this existing CDW rotates into an orientation for which it then become commensurate. At this first-order transition the Fermi surface energy gapping increases beyond that generated by the incommensurate CDW, as is clearly evident in the electromagnetic properties.For the trigonal prismatically coordinated polytypes, CDW formation is withheld to low temperatures, probably because of the more complex band structures. This CDW state (in the cases measured) would seem at once commensurate, even though the transition is, from a wide variety of experiments, apparently second order.A wide range of doped and intercalated materials have been used to substantiate the pre
Title:
Microscopic dielectric and gyration tensors of incommensurately modulated insulators
Authors:
Kushnir, OS; Lokot, LO; Mahajan, S;
Source:
PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 228 (3): 919-935; 2001
Abstract:
Crystal optical properties of insulating materials possessing incommensurately modulated phases are studied in the framework of a microscopic model. Quantum-mechanical expressions for the microscopic dielectric permittivity tensor are derived. It is shown that the contributions from the long-wavelength reciprocal lattice vectors with the lowest microscopic indices should be taken into account in the optical response of the incommensurate crystals. This justifies, from the standpoint of microscopic theory, a mesoscopic approach to the problem of light propagation in incommensurate crystals adopted in a number of earlier studies. The mesoscopic tensors associated with the first-order spatial dispersion are obtained and analyzed in detail. The optical gyration is revealed to be described by the dielectric tensor components linear in both the light wave vector and the mesoscopic incommensurate modulation wave vector. The latter contributions correspond to the gyration mechanism related to the mesoscopic inhomogeneity of the optical medium under study.
Title:
Li10Mg6Zn31Al3: A new intermetallic phase containing building blocks for decagonal quasicrystals
Authors:
Lee, CS; Miller, GJ; Odin, C;
Source:
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 40 (24): 4740-+; 2001
Abstract:
The stability of a poorly conducting fluid in a constant electric field of a horizontal capacitor is investigated under a variable temperature gradient. It is assumed that free charge in the fluid is generated only due to the nonhomogeneous conductivity of the fluid. The Floquet theory is used to determine the convection thresholds. The instability boundaries and the characteristics of critical perturbations are determined. In addition to the synchronous and subharmonic responses to an external action, the instability can be attributed to quasiperiodic perturbations. The low-frequency limit of modulation is considered by an asymptotic method. The critical electric Rayleigh number is represented as a function of inverse frequency and heating level. (C) 2001 MAIK "Nauka / Interperiodica".
Title:
The quasicrystal-to-crystal transformation. II. Landau theory
Authors:
Beraha, L; Steurer, W; Perez-Mato, JM; Aubry, R;
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 216 (11): 573-585; 2001
Abstract:
A phenomenological description of the quasicrystal-to-crystal transformation is presented in terms of Landau theory. The basic idea is to describe the structures of quasicrystals as incommensurately modulated structures and to use the tools developed for phase transitions of this kind. The usefulness of this description is demonstrated on quasiperiodic model structures: the one-dimensional (1D) Fibonacci sequence and the 2D Penrose tiling. The transformation to periodic structures is discussed generally for rational approximants.
Title:
Structural characteristics of Al-Co-Ni decagonal quasicrystals and crystalline approximants
Authors:
Hiraga, K; Ohsuna, T; Sun, W; Sugiyama, K; Mattauch, S;
Source:
MATERIALS TRANSACTIONS, 42 (11): 2354-2367; 2001
Abstract:
The structural characteristics of several modulations of AI-Co-Ni decagonal quasicrystals and crystalline approximants, all of which are found in and around an Al-Co-Ni decagonal phase with a wide compositional range, are discussed systematically. The structures of a Ni-rich basic structure and the other modulations are characterized as quasiperiodic arrangements Of Columnar clusters of atoms with decagonal sections of 3.2 and 2.0 nm in diameter. respectively. Various types of electron diffraction patterns including so-called superlattice reflections are interpreted by tiling features of the atomic clusters as well as ordered arrangements of the atomic clusters with pentagonal symmetry in the tilings. From the structure of a crystalline approximant (W-(AlCoNi) phase). precise models of the atomic clusters are proposed. and also the origin of diffuse reflections often observed in the Al-Co-Ni decagonal quasicrystals may be interpreted.
Title:
Anisotropic diffusion behaviour of Co-60 in decagonal Al-Ni-Co single quasicrystals
Authors:
Zumkley, T; Nakajima, H; Guo, JQ; Tsai, AP; Lancin, M;
Source:
PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 82 (1): 205-213; 2002
Abstract:
The orientation dependence of Co-60 self-diffusion has been investigated in stable decagonal single quasicrystals of Al72.2Ni11.8Co16.0 by means of the radiotracer method. Over a wide range from 803 to 1210 K the temperature dependence of the Co diffusivities along the periodic (tenfold- axis) and the aperiodic (twofold- axis) directions can be described each by a single set of Arrhenius parameters. The temperature dependence of the diffusion coefficients yields the Arrhenius parameters D-0(per) = 1.54 x 10(-1) m(2) s(-1), Q(per) = 277.4 kJ mol(-1), D-0(aper) = 3.96 x 10(-1) m(2) s(-1) and Q(aper) = 289.0 kJ mol(-1), respectively. The mobility of Co is slightly faster along the periodic direction. This anisotropic effect is discussed in the content of results of analogous diffusion investigation in icosahedral quasicrystals from our laboratory and with literature data on quasicrystals. It is concluded that Co diffusion in decagonal Al-Ni-Co quasicrystals in the periodic as well as in the aperiodic direction in the entire temperature range very probably occurs via a vacancy mechanism.
Title:
Fractal images of quasicrystals as an example of Penrose lattice
Authors:
Yudin, VV; Karygina, YA; Boynton, WV;
Source:
CRYSTALLOGRAPHY REPORTS, 46 (6): 922-926; 2001
Abstract:
The Penrose lattice, an example of quasicrystals, is considered as a fractal set. The generation of these sets in the graph tree form is considered. The problem of percolation of informodynamic characteristics and fractal dimensions defined in terms of the information entropy is solved for the constructed graphs, (C) 2001 MAIK "Nauka/Interperiodica".
Title:
Nature of large-scale oscillations in oxygen concentration along the growth axis in czochralski-grown silicon crystals
Authors:
Litvinov, VV; Petukh, AN; Pokotilo, YM; Tsai, AP;
Source:
CRYSTALLOGRAPHY REPORTS, 46 (6): 1046-1048; 2001
Abstract:
Oxygen distribution in a Si crystal (100 mm in diameter) has been studied by the absorption method in the range of the absorption band of interstitial oxygen, lambda = 5.81 mum. Large-scale fluctuations (similar to1 cm) of the oxygen concentration (NO) along the growth axis were determined. Depending on the melt height, the regions of the chaotic and quasiperiodic changes were established, as well as the region of the constant No value, and their relation to turbulent, quasiperiodic, and stationary modes of melt convection in crystallization. The values of the critical Rayleigh number for the melt transition from stationary to quasiperiodic (3 x 10(3)) and from quasiperiodic to turbulent (1.7 x 10(4)) convection modes are determined for growth of silicon crystals by the Czochralski method. The dominating modes of N-0 concentration oscillations at two incommensurable frequencies, f(1) = 1.3 x 10(-3) and f(2) = 6 x 10(-4) Hz, are assumed to be related to the oscillatory transfer of oxygen from the walls of the quartz crucible to the crystallization front and restructurization of the convective flow pattern of the melt in the course of crystal growth. (C) 2001 MAIK "Nauka/Interperiodica".

Update: 21-Jan-2002

Title:
The quasicrystal-to-crystal transformation. II. Landau theory
Authors:
Beraha L. Steurer W. Perez-Mato JM.
Source:
Zeitschrift fur Kristallographie. 216(11):573-585, 2001.
Abstract:
A phenomenological description of the quasicrystal-to-crystal transformation is presented in terms of Landau theory. The basic idea is to describe the structures of quasicrystals as incommensurately modulated structures and to use the tools developed for phase transitions of this kind. The usefulness of this description is demonstrated on quasiperiodic model structures: the one-dimensional (1D) Fibonacci sequence and the 2D Penrose tiling. The transformation to periodic structures is discussed generally for rational approximants.
Title:
Structural aspects of the fivefold quasicrystalline Al-Cu-Fe surface from STM and dynamical LEED studies
Authors:
Cai T. Shi F. Shen Z. Gierer M. Goldman AI. Kramer MJ. Jenks CJ. Lograsso TA. Delaney DW. Thiel PA. Van Hove MA.
Source:
Surface Science. 495(1-2):19-34, 2001 Dec 10.
Abstract:
We investigate the atomic structure of the fivefold surface of an icosahedral Al-Cu-Fe alloy, using scanning tunneling microscopy (STM) imaging and a special dynamical low energy-electron diffraction (LEED) method. STM indicates that the step heights adopt (primarily) two values in the ratio of tau, but the spatial distribution of these two values does not follow a Fibonacci sequence, thus breaking the ideal bulk-like quasicrystalline layer stacking order perpendicular to the surface. The appearance of screw dislocations in the STM images is another indication of imperfect quasicrystallinity. On the other hand, the LEED analysis, which was successfully applied to Al-Pd-Mn in a previous study, is equally successful for Al-Cu Fe. Similar structural features are found for both materials, in particular for interlayer relaxations and surface terminations. Although there is no structural periodicity, there are clear atomic planes in the bulk of the quasicrystal, some of which can be grouped in recurring patterns. The surface tends to form between these grouped layers in both alloys. For Al-Cu-Fe, the step heights measured by STM are consistent with the thicknesses of the grouped layers favored in LEED, These results suggest that the fivefold Al-Cu-Fe surface exhibits a quasicrystalline layering structure, but with stacking defects. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Fermi surface of 2H-NbSe2 and its implications on the charge-density-wave mechanism - art. no. 235119
Authors:
Rossnagel K. Seifarth O. Kipp L. Skibowski M. Voss D. Kruger P. Mazur A. Pollmann J.
Source:
Physical Review B. 6423(23):5119-+, 2001 Dec 15.
Abstract:
We report a detailed experimental and theoretical investigation of the Fermi-surface topology of the layered transition-metal dichalcogenide 2H-NbSe2, which undergoes a second-order phase transition into an incommensurate two-dimensional charge-density-wave phase at 33.5 K. High-resolution angle-resolved photoemission with synchrotron radiation yields two Nb 4d-related Fermi-surface cylinders and a Se 4p(z)-derived pocket around the center of the Brillouin zone. in good agreement with the result; of fully relativistic ab initio calculations within the local-density approximation of density-functional theory. The measurements were carried out at 50 K to identify characteristic features in the electronic structure of the normal phase that can give important clues as to the origins of the phase transition, and to achieve high resolution, at the same time. The implications of our results on the charge-density-wave mechanism in 2H-NbSe2 are discussed. Our results together with previous data from the literature seem to rule out the saddle-point mechanism, but they reveal at the same time that the driving mechanism for the transition into the charge-density-wave state is trot a simple Fermi-surface nesting, as recently suggested by Straub et al.
Title:
Simple and composite octagonal quasicrystal tilings
Authors:
Escudero JG. Garcia JG.
Source:
Journal of the Physical Society of Japan. 70(12):3511-3516, 2001 Dec.
Abstract:
Several species of tilings with eight-fold symmetry generated by means of inflation rules are studied. They can also be obtained by superposition of other patterns. The complexity of the structures is reflected in the sets of vertex configurations. Composition of the basic inflation rules gives face to face tilings. The diffraction patterns of the simple tilings show Bragg peaks.
Title:
Structural phase evolution in the equilibrium immiscible Co-Cu system studied by solid-state reaction/ion beam mixing of nano-sized multilayers
Authors:
Li ZF. Liu BX.
Source:
Journal of the Physical Society of Japan. 70(12):3596-3605, 2001 Dec.
Abstract:
Unique structural phase evolution was observed in the nano-sized Co Cu multilayers upon solid-state reaction/ion beam mixing and resulted in the formation of several metastable phases in the equilibrium immiseible Co-Cu system. Despite of a positive heat of formation of the Co-Cu system a superlattice was obtained in the nano-sized Co-33-Cu-66 multilayered films upon 600 K thermal annealing, and it later evolved into a dodecagonal phase when the annealing temperature was risen up to 800 K. Comparatively, by ion beam mixing, other metastable phases were obtained e.g., an amorphous phase and a dodecagonal phase were obtained in the Co15Cu85 films. The same dodecagonal phase was also formed in the Co50Cu50 films and the ion mixed dodecagons tended to assemble themselves into a fourfold rotational symmetry at relatively high irradiation dose. In the present paper, thermodynamic modeling and the formation mechanism of the metastable phases were also discussed based on Miedima's model and consideration of the physical process driven far-from-equilibrium by ion beam mixing.
Title:
Structural modulation in Sr1.4Ta0.6O2.9: non-harmonicity on ADPs during Rietveld refinement
Authors:
Deniard P. Caldes MT. Zou XD. Diot N. Marchand R. Brec R.
Source:
International Journal of Inorganic Materials. 3(8):1121-1123, 2001 Dec.
Abstract:
The perovskite-like material Sr1.4Ta0.6O2.9 presents structural modulations due to oxygen vacancies. A non-harmonic treatment of atomic displacement parameters was used to obtain information on atom mean localization in addition to correlative displacement of cations located near oxygen vacancies. (C) 2001 Elsevier Science Ltd. All rights reserved. [References: 6]
Title:
Glass based on a single proto-tile and inflation species without discrete diffractogram
Authors:
Mandal RK.
Source:
Current Science. 81(11):1466-1470, 2001 Dec 10.
Abstract:
The discovery of quasicrystals in the 80s has led to a qualitative change in our understanding about atomic arrangements, including definition of solids having discrete diffractograms. Owing to this, the emphasis has now been shifted to reciprocal space from direct space that was in vogue prior to the seminal finding of quasi-periodic atomic arrangements having noncrystallographic point group symmetry. The purpose of this communication is to cite two specific examples of two-dimensional tiling from literature that do not possess discrete diffractograms, but have subtle distinctions in direct space. It will be shown that one of the above constructs offers the first ever example of an isotropic glass based on a single proto-tile. The second example, on the other hand, displays characteristics which are akin to those of glasses in reciprocal space, but possesses finite rank in direct space. The consequence of these will be discussed in relation to Pisot-Vijayaraghavan (PV) number. It will be concluded that foundation of Copernican crystallography incorporating these is still missing and needs further substantiation.
Title:
Charge ordering in a 2D manganite, Pr0.25Ca1.75MnO4
Authors:
Autret C. Retoux R. Hervieu M. Raveau B.
Source:
Chemistry of Materials. 13(12):4745-4752, 2001 Dec.
Abstract:
The structural study of the manganite Pr0.25Ca1.75MnO4, n = 1 member of the Ruddlesden-Popper (RP) family, has been carried out using high-resolution electron microscopy and neutron powder diffraction. At room temperature, the K2NiF4-type structure is characterized by its ability to microtwine and form perovskite-like "pancake" defects, coherent with the matrix. The most important point concerns the appearance at low temperature of an incommensurate structure with a modulation vector (q) over right arrow approximate to 0.28 (c) over right arrow*, never observed to date in these 2D manganites. The reconstruction of the reciprocal space, using electron diffraction technique, evidences Cmca(00 gamma )s00 as the superspace group. The transition temperature, T-CO = 275 K, explains the anomalies of the rho (T) and M(T) curves, characterized by an increase of resistivity and appearance of antiferromagnetic fluctuations below this temperature.
Title:
A simple isohedral tiling of three-dimensional space by infinite tiles and with symmetry Ia (3)over-bard
Authors:
Friedrichs OD. Plevert J. O'Keeffe M.
Source:
Acta Crystallographica - Section a - Foundations of Crystallography. 58(Part 1):77-78, 2002 Jan.
Abstract:
A tiling of space by tiles that have all hexagonal faces and are infinite in one direction is described. The tiling is simple (four tiles meet at each vertex, three at each edge and two at each face) and carries a 4-connected net whose vertices are the lattice complex S* with symmetry Ia (3) over bard . The tiling is closely related to the densest cubic cylinder packing, Gamma. It is shown that the other invariant cubic lattice complexes unique to Ia (3) over bard (Y** and V*) are also related to the same cylinder packing.
Title:
Nomenclature of magnetic, incommensurate, composition-changed morphotropic, polytype, transient-structural and quasicrystalline phases undergoing phase transitions. II. Report of an IUCr Working Group on Phase Transition Nomenclature (vol A57, pg 614, 2001)
Authors:
Toledano JC. Berry RS. Brown PJ. Glazer AM. Metselaar R. Pandey D. Perez-Mato JM. Roth RS. Abrahams SC.
Source:
Acta Crystallographica - Section a - Foundations of Crystallography. 58(Part 1):79, 2002 Jan.
Title:
Characterization of modulation structure in La2CuO4.12 by electron diffraction - art. no. 224113
Authors:
Gao M. Liu GD. Che GC. Zhao ZX. Peng LM.
Source:
Physical Review B. 6422(22):4113-+, 2001 Dec 1.
Abstract:
The technique of electron diffraction has been used for characterizing the modulation structure in a heavily oxygenated La2CuO4.12 sample. Ordering with modulation directions in bc and ab plane was observed, and the strong dependence of the bc plane ordering on temperature and doping level was established. It was found that low temperature and high doping level enhance the ordering and favor a longer modulation period than otherwise. In some regions, a kind of modulation along c axis has also been found and concluded to be an indication of the staging behavior of the interstitial oxygen ions.
Title:
Crystalline ground states of an entropically stabilized quasicrystal model - art. no. 224201
Authors:
Lee HK. Swendsen RH. Widom M.
Source:
Physical Review B. 6422(22):4201-+, 2001 Dec 1.
Abstract:
A binary Lennard-Jones alloy exhibits an entropically stabilized quasicrystal state in two dimensions at elevated temperatures. We consider the ground states of this model by calculating the convex hull of cohesive energy as a function of alloy composition. Only crystalline structures with rational values of the composition appear on vertices of the convex hull. In particular, at the irrational composition of the ideal quasicrystal structure, the ground state is a coexisting mixture of two nearby quasicrystal approximants.
Title:
Unusual spin-glass phase in icosahedral Tb-Mg-Zn quasicrystals - art. no. 224209
Authors:
Dolinsek J. Jaglicic Z. Chernikov MA. Fisher IR. Canfield PC.
Source:
Physical Review B. 6422(22):4209-+, 2001 Dec 1.
Abstract:
The nature of the spin state below the spin freezing temperature was studied in an icosahedral Th-Mg-Zn quasicrystal by thermoremanent dc magnetization time decay as a function of aging time and magnetic field. The system does not exhibit a highly degenerate free-energy landscape obeying an ultrametric organization of metastable states, which makes it essentially different from canonical spin glasses. The Th-Mg-Zn system can be considered as a special class of spin glass, which possesses some local order, but still preserves the notion of spin freezing.
Title:
Quantum mechanical relaxation of open quasiperiodic systems - art. no. 224210
Authors:
Ossipov A. Weiss M. Kottos T. Geisel T.
Source:
Physical Review B. 6422(22):4210-+, 2001 Dec 1.
Abstract:
We study the time evolution of the survival probability P(t) in open one-dimensional quasiperiodic tight-binding samples of size L, at critical conditions. We find that it decays algebraically as P(t) similar to t(-alpha) up to times t*similar toL(gamma), where alpha =1-D-0(E), gamma =1/D-0(E) and D-0(E) is the fractal dimension of the spectrum of the closed system. These results were obtained for the Harper model at the metal-insulator transition and for Fibonacci lattices, and are supported by a perturbative argument. These relaxation phenomena should be observable in propagation experiments with electrons or classical waves in quasiperiodic superlattices or dielectric multilayers.
Title:
Doping and temperature dependence of incommensurate antiferromagnetism in underdoped lanthanum cuprates - art. no. 224505
Authors:
Yuan F. Feng SP. Su ZB. Yu L.
Source:
Physical Review B. 6422(22):4505-+, 2001 Dec 1.
Abstract:
The doping, temperature, and energy dependence of the dynamical spin structure factors of the underdoped lanthanum cuprates in the normal state are studied within the t-J model using the fermion-spin transformation technique. Incommensurate peaks are found at [(1 +/- delta) pi, pi], [pi, (1 +/- delta) pi] at relatively low temperatures, with delta linearly increasing with doping at the beginning and then saturating at higher dopings, These peaks broaden and weaken in amplitude with temperature and energy, in good agreement with experiments. The theory also predicts a rotation of these peaks by pi /4 at even higher temperatures, being shifted to [(1 +/- delta/ root2)pi, (1 +/- delta/ root2)delta].
Title:
Debye-Waller factors in a quasicrystal (vol B 63, art. no. 014202, 2000) - art. no. 229901
Authors:
Colella R. Zhang Y. Sutter JP. Ehrlich SN. Kycia SW.
Source:
Physical Review B. 6422(22):9901, 2001 Dec 1.
Title:
Anisotropic diffusion behaviour of Co-60 in decagonal Al-Ni-Co single quasicrystals
Authors:
Zumkley T. Nakajima H. Guo JQ. Tsai AP.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 82(1):205-213, 2002 Jan.
Abstract:
The orientation dependence of Co-60 self-diffusion has been investigated in stable decagonal single quasicrystals of Al72.2Ni11.8Co16.0 by means of the radiotracer method. Over a wide range from 803 to 1210 K the temperature dependence of the Co diffusivities along the periodic (tenfold- axis) and the aperiodic (twofold- axis) directions can be described each by a single set of Arrhenius parameters. The temperature dependence of the diffusion coefficients yields the Arrhenius parameters D-0(per) = 1.54 x 10(-1) m(2) s(-1), Q(per) = 277.4 kJ mol(-1), D-0(aper) = 3.96 x 10(-1) m(2) s(-1) and Q(aper) = 289.0 kJ mol(-1), respectively. The mobility of Co is slightly faster along the periodic direction. This anisotropic effect is discussed in the content of results of analogous diffusion investigation in icosahedral quasicrystals from our laboratory and with literature data on quasicrystals. It is concluded that Co diffusion in decagonal Al-Ni-Co quasicrystals in the periodic as well as in the aperiodic direction in the entire temperature range very probably occurs via a vacancy mechanism.
Title:
Diffraction and transmission of light in low-refractive index Penrose-tiled photonic quasicrystals
Authors:
Kaliteevski MA. Brand S. Abram RA. Krauss TF. Millar P. De la Rue RM.
Source:
Journal of Physics-Condensed Matter. 13(46):10459-10470, 2001 Nov 19.
Abstract:
We report the measurements of the diffraction pattern of a two-dimensional Penrose-tiled photonic quasicrystal, obtained by etching air cylinders in a silica substrate, and the modelling of the light propagation and dispersion relations of photons inside such a structure. The calculated transmission spectra exhibit dips whose positions are insensitive to the direction of propagation and whose depth increases with increasing structure length. An approach is developed for the calculation of the dispersion relations which is based on a set of reciprocal vectors defined by the diffraction pattern. The dispersion curves exhibit gap-like features at frequencies corresponding to the dips in the transmission spectra.
Title:
Dynamical molecular disorder and diffuse scattering in an alkane/urea incommensurate inclusion compound
Authors:
Lefort R. Toudic B. Etrillard J. Guillaume F. Bourges P. Currat R. Breczewski T.
Source:
European Physical Journal B. 24(1):51-57, 2001 Nov.
Abstract:
The diffraction pattern of n-alkane/urea inclusion compounds is known to contain a broad diffuse scattering related to the molecular form factor of the alkane species, indicating individual rotational and/or translational disorder of these molecules. Inelastic coherent neutron scattering reveals for the first time the entirely dynamical character of the alkane molecular disorder around room temperature. This observation fully agrees with a recent model of the coherent scattering cross section of totally uncorrelated motions. In the ordered phase this diffuse scattering remains, but elastic, and very low energy molecular vibrational modes are evidenced. These observations are discussed in relation with previous incoherent neutron scattering results.
Title:
A crystallographic model for describing of exact location of atoms in quasicrystals
Authors:
Goulliaev VC.
Source:
Doklady Physics. 46(11):780-783, 2001 Nov.
Title:
Fractal images of quasicrystals as an example of Penrose lattice
Authors:
Yudin VV. Karygina YA.
Source:
Crystallography Reports. 46(6):922-926, 2001 Nov-Dec.
Abstract:
The Penrose lattice, an example of quasicrystals, is considered as a fractal set. The generation of these sets in the graph tree form is considered. The problem of percolation of informodynamic characteristics and fractal dimensions defined in terms of the information entropy is solved for the constructed graphs, (C) 2001 MAIK "Nauka/Interperiodica". [References: 5]
Title:
Nature of large-scale oscillations in oxygen concentration along the growth axis in czochralski-grown silicon crystals
Authors:
Litvinov VV. Petukh AN. Pokotilo YM.
Source:
Crystallography Reports. 46(6):1046-1048, 2001 Nov-Dec.
Abstract:
Oxygen distribution in a Si crystal (100 mm in diameter) has been studied by the absorption method in the range of the absorption band of interstitial oxygen, lambda = 5.81 mum. Large-scale fluctuations (similar to1 cm) of the oxygen concentration (NO) along the growth axis were determined. Depending on the melt height, the regions of the chaotic and quasiperiodic changes were established, as well as the region of the constant No value, and their relation to turbulent, quasiperiodic, and stationary modes of melt convection in crystallization. The values of the critical Rayleigh number for the melt transition from stationary to quasiperiodic (3 x 10(3)) and from quasiperiodic to turbulent (1.7 x 10(4)) convection modes are determined for growth of silicon crystals by the Czochralski method. The dominating modes of N-0 concentration oscillations at two incommensurable frequencies, f(1) = 1.3 x 10(-3) and f(2) = 6 x 10(-4) Hz, are assumed to be related to the oscillatory transfer of oxygen from the walls of the quartz crucible to the crystallization front and restructurization of the convective flow pattern of the melt in the course of crystal growth. (C) 2001 MAIK "Nauka/Interperiodica".
Title:
Sign of covalency in AlPdRe icosahedral quasicrystals obtained from atomic density and quasilattice constant - art. no. 212201
Authors:
Kirihara K. Kimura K.
Source:
Physical Review B. 6421(21):2201-+, 2001 Dec 1.
Abstract:
Atomic density and quasilattice constant of AlPdRe icosahedral quasicrystals decreases and slightly increases. respectively, with increasing concentration of transition metals, which have smaller atomic radii. Average atomic packing could not be described simply by rigid sphere packing, that is, the covalent nature of icosahedral clusters may form in metallic bonds.
Title:
Absence of fine structure in the photoemission spectrum of the icosahedral Al-Pd-Mn quasicrystal - art. no. 214202
Authors:
Stadnik ZM. Purdie D. Baer Y. Lograsso TA.
Source:
Physical Review B. 6421(21):4202-+, 2001 Dec 1.
Abstract:
The results of the low-temperature ultrahigh-energy-resolution photoemission studies of a single-grain icosahedral alloy Al70Pd21.5Mn8.5 have been presented. The existence of the theoretically predicted pseudogap in the density of states at the Fermi energy has been confirmed. No evidence of the theoretically predicted spikiness of the density of states could be observed. It has been suggested that the failure to detect the predicted spikiness of the density of states in icosahedral quasicrystals is consistent with the results of Zijlstra and Janssen [Europhys. Lett. 52, 578 (2000)] who showed that the spikiness occurs only in lower-order periodic approximants to icosahedral quasicrystals, but does not survive in the quasiperiodic limit.
Title:
Phase separation in InGaN epitaxial layers
Authors:
Westmeyer AN. Mahajan S.
Source:
Physica Status Solidi B-Basic Research. 228(1):161-164, 2001 Nov.
Abstract:
Epitaxial layers of InGaN were deposited by metalorganic chemical vapor deposition on a GaN laver/sapphire substrate in order to ascertain compositional variation in the GaN-InN system. Samples were examined with In contents from x = 0.09 to 0.31. Plan-view images obtained by transmission electron microscopy reveal a domain structure within which the composition is modulated. Satellites appear around the fundamental reflections in the diffraction pattern. Tbe spacing between the satellite and the reflection can be related to the wavelength of the modulations. Equations are derived for modulations in the [10 (1) over bar0] and [11 (2) over bar0] directions. Modulations were measured in the [10 (1) over bar0] direction and found to be about Z = 3.2 nm for all samples. Strain energy considerations explain the observation of modulations along different directions.
Title:
Crystal structure of a modulated composite structure with two subsystems: Ba1.1064CoO3
Authors:
El Abed A. Elqebbaj SE. Zakhour M. Champeaux M. Perez-Mato JM. Darriet J.
Source:
Journal of Solid State Chemistry. 161(2):300-306, 2001 Nov 1.
Abstract:
The structure of Ba1.1064CoO3 has been solved in the (3 + 1)-dimensional formalism. The structure is described as a modulated chain composite with two subsystems, [Coos] and [Ba], respectively. The superspace group is R-3m (00 gamma )0s with a = 9.8842(20) Angstrom, c = 2.4785(12) Angstrom, and q = 0.5532(4) c* (Z = 3). A saw-tooth function was used to model both the occupational and displacive modulations. Each atomic saw-tooth function is defined by its center (x) over cap (4), along the fourth dimension, its width (A), and the maximum amplitude of the displacive modulation (delta). The paper describes how, as a first approximation, the columns (CoO3) can be mainly described by a single free parameter, based on the height difference of the trigonal prisms and octahedra that constitute the transition metal chains. As a result, this superspace formalism requires only a small number of variables to be refined, compared to the conventional superstructure description. (C) 2001 Academic Press.
Title:
Influence of the metal-metal sigma bonding on the structures and physical properties of the hexagonal perovskite-type sulfides Sr9/8TiS3,Sr8/7TiS3, and Sr-8/7[Ti6/7Fe1/7]S-3
Authors:
Gourdon O. Jeanneau E. Evain M. Jobic S. Brec R.
Source:
Journal of Solid State Chemistry. 162(1):103-112, 2001 Nov 15.
Abstract:
The structural and electronic consequences of the metal-metal sigma bonding in the hexagonal perovskite sulfides were examined by calculating the electronic band structures of Sr9/8TiS3 and Sr8/7TiS3, by synthesizing Sr-8/7[Ti6/7Fe1/7]S-3 and characterizing its crystal structure, and by measuring the magnetic susceptibilities of Sr9/8TiS3, Sr8/7TiS3 an Sr-8/7[Ti6/7Fe1/7]S-3. The (TiS3)(infinity) chains of Sr9/8TiS3 and Sr8/7TiS3 contain oligomer units (Oh)(n) (n = 4, 5) made up of face-sharing TiS6 octahedra (Oh)(n) Given the (TiS3)(infinity) chains aligned along the z direction, the only occupied d-block levels of each (TiS3)(infinity) chain are the most sigma bonding level of each (Oh), oligomer, which is constructed from its n z(2) orbitals. This "n-orbital two-electron" metal-metal sigma bonding controls the d-orbital density distribution and the Ti-Ti distances of the (Oh)(n) oligomers and is ultimately responsible for the semiconducting property of Sr9/8TiS3, Sr8/7TiS3, and Sr-8/7[T6/7Fe1/7]S-3. The Sr-8/7[Ti-6/7 Fe-1/7]S-3 structure is described by the trigonal symmetry, Kim (00y)0s superspace group with the following parameters: a(s) = 11.4935(11) Angstrom, c(s) = 2.9986(7) Angstrom, q = 0.57161(15) c*, and V-s = 343.05(15) Angstrom (3). (C) 2001 Academic Press.
Title:
The real (incommensurate interface modulated) structure of Ni6 +/- xSe5
Authors:
Noren L. Van Tendeloo G. Withers RL.
Source:
Journal of Solid State Chemistry. 162(1):122-127, 2001 Nov 15.
Abstract:
The high-temperature Ni6 +/-xSe5 phase has been carefully reinvestigated via electron diffraction and TEM imaging. Electron diffraction reveals an (in general) incommensurately modulated, continuously variable (within narrow limits) reciprocal lattice, indirectly confirming the notion of a continuously variable (within narrow limits) Ni6 +/-xSe5 solid solution phase. The superspace group symmetry of the incommensurate interface modulated structure is determined and used to predict the allowed conventional three-dimensional space group symmetries when the primary modulation wavevector locks in to 1/2a*. The mechanism for accommodating nonstoichiometry is suggested to be the introduction into a 2 x 1 x 1 superstructure of variably spaced, nonconservative (100) APB's characterized by the displacement vector R = [1/4, 1/2, 0]. (C) 2001 Academic Press.
Title:
Investigation of the stability of glassy state in the Zr- and Hf-based glassy alloys correlated with their transformation behavior
Authors:
Saida J. Li CF. Matsushita M. Inoue A.
Source:
Journal of Materials Research. 16(12):3389-3401, 2001 Dec.
Abstract:
The transformation behavior from glassy state was investigated in Zr- and Hf-based glassy alloys. The primary phases are metastable face-centered-cubic (fcc) Zr2Ni and fee Hf2Ni phases in the Zr65Al7.5Ni10Cu17.5 and Hf65Al7.5Ni10Cu17.5 glassy alloys, respectively. By substitution of 5 at.% Pd for Cu, the primary phase changes to an icosahedral quasicrystalline phase in both alloys. It is found that the addition of elements, which have a positive or weak chemical affinity with one of the constitutional elements in the Zr-Al-Ni-Cu and Hf-Al-Ni-Cu glassy alloys, is effective for the precipitation of the icosahedral phase. It is suggested that Pd plays a dominant role in an increase in the number of nucleation sites. Since an icosahedron is contained as a structure unit in the icosahedral, fee Zr2Ni and fee Hf2Ni phases, it is implied that these phases are correlated with the local icosahedral order. The high-resolution transmission electron microscopy images of the as-spun Zr65Al7.5Ni10Cu7.5Pd10 and Hf65Al7.5Ni10Cu12.5Pd5 alloys reveal a possibility of the existence of the icosahedral ordered regions. It is therefore, concluded that the icosahedral short- or medium-range order exists and it stabilizes the glassy state in the Zr- and Hf-based multicomponent alloys.

Update: 7-Jan-2002

Title:
Sign of covalency in AlPdRe icosahedral quasicrystals obtained from atomic density and quasilattice constant - art. no. 212201
Authors:
Kirihara K. Kimura K.
Source:
Physical Review B. 6421(21):2201-+, 2001 Dec 1.
Abstract:
Atomic density and quasilattice constant of AlPdRe icosahedral quasicrystals decreases and slightly increases. respectively, with increasing concentration of transition metals, which have smaller atomic radii. Average atomic packing could not be described simply by rigid sphere packing, that is, the covalent nature of icosahedral clusters may form in metallic bonds.
Title:
Absence of fine structure in the photoemission spectrum of the icosahedral Al-Pd-Mn quasicrystal - art. no. 214202
Authors:
Stadnik ZM. Purdie D. Baer Y. Lograsso TA.
Source:
Physical Review B. 6421(21):4202-+, 2001 Dec 1.
Abstract:
The results of the low-temperature ultrahigh-energy-resolution photoemission studies of a single-grain icosahedral alloy Al70Pd21.5Mn8.5 have been presented. The existence of the theoretically predicted pseudogap in the density of states at the Fermi energy has been confirmed. No evidence of the theoretically predicted spikiness of the density of states could be observed. It has been suggested that the failure to detect the predicted spikiness of the density of states in icosahedral quasicrystals is consistent with the results of Zijlstra and Janssen [Europhys. Lett. 52, 578 (2000)] who showed that the spikiness occurs only in lower-order periodic approximants to icosahedral quasicrystals, but does not survive in the quasiperiodic limit.
Title:
Phase separation in InGaN epitaxial layers
Authors:
Westmeyer AN. Mahajan S.
Source:
Physica Status Solidi B-Basic Research. 228(1):161-164, 2001 Nov.
Abstract:
Epitaxial layers of InGaN were deposited by metalorganic chemical vapor deposition on a GaN laver/sapphire substrate in order to ascertain compositional variation in the GaN-InN system. Samples were examined with In contents from x = 0.09 to 0.31. Plan-view images obtained by transmission electron microscopy reveal a domain structure within which the composition is modulated. Satellites appear around the fundamental reflections in the diffraction pattern. Tbe spacing between the satellite and the reflection can be related to the wavelength of the modulations. Equations are derived for modulations in the [10 (1) over bar0] and [11 (2) over bar0] directions. Modulations were measured in the [10 (1) over bar0] direction and found to be about Z = 3.2 nm for all samples. Strain energy considerations explain the observation of modulations along different directions.
Title:
Crystal structure of a modulated composite structure with two subsystems: Ba1.1064CoO3
Authors:
El Abed A. Elqebbaj SE. Zakhour M. Champeaux M. Perez-Mato JM. Darriet J.
Source:
Journal of Solid State Chemistry. 161(2):300-306, 2001 Nov 1.
Abstract:
The structure of Ba1.1064CoO3 has been solved in the (3 + 1)-dimensional formalism. The structure is described as a modulated chain composite with two subsystems, [Coos] and [Ba], respectively. The superspace group is R-3m (00 gamma )0s with a = 9.8842(20) Angstrom, c = 2.4785(12) Angstrom, and q = 0.5532(4) c* (Z = 3). A saw-tooth function was used to model both the occupational and displacive modulations. Each atomic saw-tooth function is defined by its center (x) over cap (4), along the fourth dimension, its width (A), and the maximum amplitude of the displacive modulation (delta). The paper describes how, as a first approximation, the columns (CoO3) can be mainly described by a single free parameter, based on the height difference of the trigonal prisms and octahedra that constitute the transition metal chains. As a result, this superspace formalism requires only a small number of variables to be refined, compared to the conventional superstructure description. (C) 2001 Academic Press.
Title:
The real (incommensurate interface modulated) structure of Ni6 +/- xSe5
Authors:
Noren L. Van Tendeloo G. Withers RL.
Source:
Journal of Solid State Chemistry. 162(1):122-127, 2001 Nov 15.
Abstract:
The high-temperature Ni6 +/-xSe5 phase has been carefully reinvestigated via electron diffraction and TEM imaging. Electron diffraction reveals an (in general) incommensurately modulated, continuously variable (within narrow limits) reciprocal lattice, indirectly confirming the notion of a continuously variable (within narrow limits) Ni6 +/-xSe5 solid solution phase. The superspace group symmetry of the incommensurate interface modulated structure is determined and used to predict the allowed conventional three-dimensional space group symmetries when the primary modulation wavevector locks in to 1/2a*. The mechanism for accommodating nonstoichiometry is suggested to be the introduction into a 2 x 1 x 1 superstructure of variably spaced, nonconservative (100) APB's characterized by the displacement vector R = [1/4, 1/2, 0]. (C) 2001 Academic Press.
Title:
Investigation of the stability of glassy state in the Zr- and Hf-based glassy alloys correlated with their transformation behavior
Authors:
Saida J. Li CF. Matsushita M. Inoue A.
Source:
Journal of Materials Research. 16(12):3389-3401, 2001 Dec.
Abstract:
The transformation behavior from glassy state was investigated in Zr- and Hf-based glassy alloys. The primary phases are metastable face-centered-cubic (fcc) Zr2Ni and fee Hf2Ni phases in the Zr65Al7.5Ni10Cu17.5 and Hf65Al7.5Ni10Cu17.5 glassy alloys, respectively. By substitution of 5 at.% Pd for Cu, the primary phase changes to an icosahedral quasicrystalline phase in both alloys. It is found that the addition of elements, which have a positive or weak chemical affinity with one of the constitutional elements in the Zr-Al-Ni-Cu and Hf-Al-Ni-Cu glassy alloys, is effective for the precipitation of the icosahedral phase. It is suggested that Pd plays a dominant role in an increase in the number of nucleation sites. Since an icosahedron is contained as a structure unit in the icosahedral, fee Zr2Ni and fee Hf2Ni phases, it is implied that these phases are correlated with the local icosahedral order. The high-resolution transmission electron microscopy images of the as-spun Zr65Al7.5Ni10Cu7.5Pd10 and Hf65Al7.5Ni10Cu12.5Pd5 alloys reveal a possibility of the existence of the icosahedral ordered regions. It is therefore, concluded that the icosahedral short- or medium-range order exists and it stabilizes the glassy state in the Zr- and Hf-based multicomponent alloys.
Title:
Melting and freezing of gold nanoclusters
Authors:
Chushak YG. Bartell LS.
Source:
Journal of Physical Chemistry B. 105(47):11605-11614, 2001 Nov 29.
Abstract:
Molecular dynamics simulations were performed on series of gold nanoclusters comprised of 459, 1157, and 3943 atoms, to study their structures and properties during heating and cooling. The increased depression of melting point as particle size decreases has been interpreted in terms of Pawlow's triple point theory, the liquid shell model, and extensions of the two. The solid-liquid interfacial free energy sigma (sl) of similar to0.15 J/m(2) inferred from the liquid shell model was close to the values predicted by several empirical relations. When molten particles in a given series were frozen, several different final structures were obtained even though conditions had been identical. Most of the frozen clusters attained an icosahedral structure, a structure found to be stable to mild annealing. Other structures observed were imperfect truncated decahedra, twinned truncated octahedra, and hexagonal close packed structures. The rate of crystal nucleation in liquid clusters was analyzed in terms of classical nucleation theory and the diffuse interface theory. The interfacial free energy of 0.084 J/m(2) inferred from the kinetics of freezing was appreciably lower than that inferred from the melting points. Since existing theories of the melting of small particles and the nucleation of crystals in them are far from rigorous, a close agreement between the quasi-thermodynamic and kinetically based free energies cannot be taken for granted. Sources of error in the models of melting are discussed.
Title:
Magnetic structures and magnetic phase transitions in RAuIn (R = Tb, Ho) compounds
Authors:
Bazela W. Gondek L. Penc B. Szytula A. Stusser N. Zygmunt A.
Source:
Acta Physica Polonica B. 32(10 Special Issue SI):3387-3392, 2001 Oct.
Abstract:
TbAuIn and HoAuIn compounds crystallize in the hexagonal ZrNiAl-type structure and order magnetically below 35 K for R = Tb and 4.8 K for R = Ho. In the case of TbAuIn a noncollinear antiferromagnetic structure described by the propagation vector k = (0, 0, 1/2) is stable in the temperature range from 1.5 K up to T-N. The magnetic structure of HoAuIn determined at 1.5 K is noncollinear antiferromagnetic one. This low temperature magnetic structure could be described by two propagation vectors k(1) = (0, 1/2, 1/2) and k(2) = (0, 0, 1/2) - At T = 2.5 K an additional phase transition to a modulated structure is observed. [References: 2]
Title:
Structure analysis of two-dimensional quasicrystals
Authors:
Soltmann C. Beeli C.
Source:
Philosophical Magazine Letters. 81(12):877-884, 2001 Dec.
Abstract:
Aperiodic materials, such as two-dimensional quasicrystalline structures, show characteristic elements in transmission electron microscopy images that are closely related to structure elements in the corresponding material. Although the arrangement of these structure elements fundamentally influences the properties of the two-dimensional quasicrystalline structures, it cannot be determined in a satisfactory way by conventional diffraction-based methods. We have developed an automated procedure for analysing images obtained by high-resolution transmission electron microscopy. The method, which is based on image processing, determines the two-dimensional arrangement of the characteristic features and enables subsequent statistical data analysis. It is illustrated with new tiling analyses of highly perfect decagonal Al-Co-Ni quasicrystals. [References: 8]
Title:
Extended X-ray absorption fine-structure study of the hydrogen location in a Ti-Zr-Ni icosahedral quasicrystal and a 1/1 bcc crystal approximant
Authors:
Sadoc A. Kim JY. Kelton KF.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 81(12):2911-2924, 2001 Dec.
Abstract:
Extended X-ray absorption fine-structure measurements have been performed on Ti-Zr-Ni alloys using the Dispositif de Collision dans l'Igloo synchrotron radiation facility. Both a multigrained icosahedral quasicrystal and a 1/1 bcc polycrystalline approximant were studied. Alloys hydrogenated to a hydrogen-to-metal ratio of 1.7 for the icosahedral phase and 1.4 for the crystalline phase were also studied. The local atomic structures, which are different around the different types of atom, titanium, zirconium and nickel, are very similar in the non-hydrogenated alloys, crystal or quasicrystal. Drastic changes are observed in the local order in both hydrogenated alloys with modifications of distances and an increase in the disorder. Moreover, these modifications are slightly different in the 1/1 and icosahedral alloys after hydrogenation.
Title:
Spin-phonon coupled modes in the incommensurate phase of CuGeO3
Authors:
Takehana K. Takamasu T. Hase I. Kido G. Uchinokura K.
Source:
Journal of the Physical Society of Japan. 70(11):3391-3397, 2001 Nov.
Abstract:
The folded phonon mode at 98 cm(-1) on CuGeO3, which was found in our previous study, was determined to be strongly coupled to the spin system. The splitting of the folded phonon mode was formulated to be caused by the interaction between the spin-phonon coupled modes at k = +/- (q(SP) - Deltaq) through the modulation of the spin polarization vith periodicity of 2 Deltaq in the incommensurate (IC) phase. This mode can successfully explain the behavior of the 98 cm(-1) folded phonon mode in the IC phase. Ve have also formulated the reason why the intensity of the folded modes in general decreases in the IC phase.
Title:
Site and barrier energy distributions that govern the rate of hydrogen motion in quasicrystalline Ti45Zr38Ni17Hx
Authors:
McDowell AF. Adolphi NL. Sholl CA.
Source:
Journal of Physics-Condensed Matter. 13(43):9799-9812, 2001 Oct 29.
Abstract:
The first application of a recent theory linking nuclear magnetic resonance spin-lattice relaxation rates to interstitial atom motion in disordered systems is presented. Laboratory and rotating frame relaxation rate data taken as a function of temperature for H-1 moving in quasicrystalline Ti45Zr38Ni17H163 are fitted with the new theory, yielding a hydrogen site energy distribution of Gaussian shape and width 47 +/-5 meV. The energy barriers for hydrogen motion show a Gaussian distribution of width 50 +/-5 meV, and the difference between the means of the distributions is 0.42 +/-0.01 eV. This is the first time relaxation rates have been analysed to provide information on both hydrogen site energy and barrier energy distributions simultaneously. The data are also fitted using an approach popular for disordered systems: the integration of the Bloembergen, Purcell, and Pound relaxation theory over a distribution of activation energies. The relative merits of this traditional approach and the recent theory in fitting the relaxation data, and also in fitting measurements of the static and magic angle spinning linewidths, are discussed. Although the traditional approach can fit all the data self-consistently, the theory's unsupported assumptions are undermined by the new approach.
Title:
Structure of the charge-density wave in (TaSe4)(2)I
Authors:
van Smaalen S. Lam EJ. Ludecke J.
Source:
Journal of Physics-Condensed Matter. 13(44):9923-9936, 2001 Nov 5.
Abstract:
(TaSe4)(2)I is a quasi-one-dimensional (ID) electrical conductor. It exhibits a phase transition at T-CDW = 263 K towards a charge-density-wave (CDW) state at low temperatures. We report a fall structure refinement of the incommensurately modulated structure in the CDW state at T = 110 K against synchrotron radiation, single-crystal x-ray diffraction data. At room temperature the crystal structure has tetragonal symmetry with space. group I422. In the CDW state each main reflection in the x-ray scattering is surrounded by eight incommensurate satellites at ( +/-0.064, +/-0.064, +/-0.151). The CDW state is found to comprise four domains, and it is characterized by one modulation wavevector. With respect to a root2 x root2 x 1 supercell it has the symmetry of the superspace group F2(0,beta, gamma) with beta = 0.128 and gamma = 0.151. The first part of the modulation is found to be a transverse acoustic wave, involving amplitudes of similar magnitudes of about 0.13 Angstrom on all atoms. The second part of the modulation involves displacements of the Ta atoms of about 0.03 Angstrom, that are parallel to the 1D chains. These are interpreted as reflecting the CDW. A Landau free-energy model is developed, that shows that symmetry arguments allow the phase transition to be second order.
Title:
Epitaxial film growth of Au-Al alloy on a quasiperiodic surface of icosahedral Al72Pd19.5Mn8.5
Authors:
Shimoda M. Guo JQ. Sato TJ. Tsai AP.
Source:
Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes & Review Papers. 40(10):6073-6076, 2001 Oct.
Abstract:
We have found that an epitaxial film of Au-Al alloy can be formed on a quasiperiodic surface of icosahedral Al72Pd19.5Mn8.5. Depositions of An onto the quasiperiodic surface, which is perpendicular to one of the fivefold axes of Al72Pd19.5Mn8.5, were attempted in order to create a quasicrystal of a single element as an epitaxial film. Although the desired film was not obtained on the clean surface, an ordered layer of Au-Al alloy with icosahedral symmetry was formed in the presence of predeposited In, which worked as a surfactant. X-ray photoelectron diffraction (XPD) images for Au 4f and Al 2s emissions from the ordered layer indicate clear fivefold symmetric patterns which are coherent with the symmetry of the substrate. In addition, symmetric elements specific to the icosahedral symmetry are clearly recognized in these patterns, indicating that both Au and Al atoms are located in an icosahedral environment with long-range bond-orientational order.
Title:
Precipitation of nanoscale icosahedral quasicrystalline phase in Hf-Cu-(Rh, Ir) amorphous alloys
Authors:
Li C. Wang L. Inoue A.
Source:
European Physical Journal-Applied Physics. 16(3):183-186, 2001 Dec.
Abstract:
Hf70Cu25Rh5 and Hf70Cu25Ir5 amorphous alloys were prepared by a single roller melt-spinning method and the crystallization processes were studied by X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. For both of the two alloys, the crystallization proceeds through the reactions of Am -->I-phase --> Hf2Cu+alpha -Hf, where Am and I-phase represent the amorphous and icosahedral quasicrystalline phases, respectively. Under optimum annealing conditions, the particle size of the I-phase is 10-25 and 10-20 nm for Rh- and Ir-containing alloys, respectively. Considering the fact that the crystallization process of Hf70Cu30 amorphous alloy does not accompany the precipitation of an I-phase, the present result demonstrates that the addition of Rh or Ir is significant. It is suggested that icosahedronlike atomic clusters exist in the amorphous state of Hf70Cu25Rh5 and Hf70Cu25Ir5 alloys, which serve as the seeds for the precipitation of the I-phase in the initial crystallization process.
Title:
Elastic theory of icosahedral quasicrystals - application to straight dislocations
Authors:
Ricker M. Bachteler J. Trebin HR.
Source:
European Physical Journal B. 23(3):351-363, 2001 Oct.
Abstract:
In quasicrystals, there are not only conventional, but also phason displacement fields and associated Burgers vectors. We have calculated approximate solutions for the elastic fields induced by two-, three- and fivefold straight screw- and edge-dislocations in infinite icosahedral quasicrystals by means of a generalized perturbation method. Starting from the solution for elastic isotropy in phonon and phason spaces, corrections of higher order reflect the two-, three- and fivefold symmetry of the elastic fields surrounding screw dislocations. The fields of special edge dislocations display characteristic symmetries also, which can be seen from the contributions of all orders.
Title:
Studies on the properties of electronic energy spectra for two-dimensional Fibonacci-class quasicrystals with one kind of atoms [Chinese]
Authors:
Yang XB. Xing D. Liu YY.
Source:
Acta Physica Sinica. 50(10):2032-2037, 2001 Oct.
Abstract:
In the framework of the single-electron tight-binding nearest interaction on-site model, we have studied the splitting rules of electronic energy spectra for two-dimensional Fibonacci-class quasicrystals FC(n) with one kind of atoms by means of the decomposition-decimation method based on the renormalization-group technique and have also calculated the electronic energy spectra numberically. It was found that there are only three kinds of clusters, n x n, n x (n+1) and (n+1) x (n+1) for all of the two-dimensional quasilattices FC(n) and the electronic. energy bands split as Ym-n-l. The general formula of the energy level numbers was obtained. We discovered that there was a kind of so-called Fibonacci-class-number sets for the parameters used to describe the energy level number and got the first 11 determined integers of the sets. The experienced formula have been sought out. The analytic results are confirmed by numerical simulations.
Title:
Five-dimensional structure refinement of natural melilite, (Ca1.89Sr0.01Na0.08K0.02)(Mg0.92Al0.08)-(Si1.98Al0.02)O-7
Authors:
Bindi L. Bonazzi P. Dusek M. Petricek V. Chapuis G.
Source:
Acta Crystallographica - Section B, Structural Science. 57(Part 6):739-746, 2001 Dec.
Abstract:
The structure of a crystal of natural melilite from San Venanzo, Umbria (Italy) of the general formula X(2)T1(T2)(2)O-7, where X = Ca0.945Sr0.005Na0.04K0.01, T1 = Mg0.92Al0.08 and T2 = Si0.99Al0.01, has been solved and refined as an incommensurate structure in five-dimensional superspace. The structure is tetragonal, superspace group P (4) over bar2(1)m:p4mg, cell parameters a = 7.860 (1), c =5.024 (1) Angstrom, modulation vectors q(1) = 0.2815 (3)(a* +b*), q(2) = 0.2815 (3)(-a* +b*). The data collection was performed on a KumaCCD diffractometer. The structure was refined from 7606 reflections to final R = 0.0481. A special modification of the refinement program Jana2000 was necessary to take into account overlapping of satellite reflections m x n = +/- 1, which could not be properly separated in the integration procedure. The final model includes modulations of the atomic positions as well as modulations of the thermal parameters. The latter are induced by strong differences in the neighbourhood of the actual modulated positions. The occupational modulation was neither significant for X nor for T1 sites and the sites were supposed to be occupied only by Ca and Mg, respectively. As a consequence of the Ca and O positional modulations six-, seven- and eightfold Ca coordination occur throughout the structure and the thermal ellipsoid changes its shape correspondingly. The positional modulation of the atoms causes variations in the interatomic distances which, however, do not affect bond-valence sums considerably, but induce flattening and rotation in T1 and T2 tetrahedra, respectively.
Title:
Hybridization mechanism for cohesion of Cd-based quasicrystals - art. no. 206408
Authors:
Ishii Y. Fujiwara T.
Source:
Physical Review Letters. 8720(20):6408-+, 2001 Nov 12.
Abstract:
The cohesion mechanism of cubic approximant crystals in newly discovered binary quasicrystals, Cd6M (M = Yb or Ca), is studied theoretically. It is found that stabilization due to alloying is obtained if M is an element with low-lying unoccupied d states. This leads to the conclusion that the cohesion of Cd-based compounds is due to hybridization of the d states of Yb and Ca with a wide sp band. The Hume-Rothery mechanism does not play a principal role in the stability because neither a distinct pseudogap nor stabilization due to alloying is obtained for isostructural Cd-Mg. In addition to the electronic origin, matching of the atomic size is very crucial for quasicrystal formation in Cd-based compounds.
Title:
Structures of [(CH3)(4)P](2)CoCl4, [(CH3)(4)Sb](2)CuCl4 and [(CH3)(4)Sb](2)ZnBr4 and a correlation of pseudo-antifluorite [(CH3)(4)Pn](2)MX4 salts
Authors:
Pressprich MR. Bond MR. Willett RD.
Source:
Journal of Physics & Chemistry of Solids. 63(1):79-88, 2002 Jan.
Abstract:
The room temperature structure of three members of the A(2)MX(4) cubic antifluorite family are reported. [(CH3)(4)P](2)COCl4 is orthorhombic, Pnma, a = 18.385(2), b = 25.134(3), c = 12.758(3) Angstrom, V = 5895(2) Angstrom (3) with Z = 12. [(CH3)(4)Sb](2)CuCl4 is cubic, F (4) over bar 3c, a = 25.020(3) Angstrom with V = 15,663(3) Angstrom (3). [(CH3)(4)Sb](2)ZnBr4 is also cubic, F (4) over bar 3c, a = 25.977(3) Angstrom, V = 17,529(4) Angstrom (3) with Z = 32. The structures are composed of discrete (CH3)(4)P+ or (CH3)(4)Sb+ cations and tetrahedral CoCl42-, CuCl42- or ZnBr42- anions. All three are commensurately modulated and the superspace group is subsequently assigned to (TMSb)(2)CuCl4 and (TMSb)(2)ZnBr4. The structures are correlated by an ascent of symmetry diagram with a fictional, pseudo-antifluorite Fr (3) over barm aristotype having approximate to 12.7 Angstrom axes. The previously reported room temperature structures of [(CH3)(4)As](2)ZnCl4 and [(CH3)(4)As](2)CoCl4, as well as the structures of their estimated, higher temperature phases, are similarly correlated. (C) 2001 Elsevier Science Ltd. All rights reserved.
Title:
NADA - a computer program for the simultaneous refinement of orientation matrix and modulation vector(s)
Authors:
Schonleber A. Meyer M. Chapuis G.
Source:
Journal of Applied Crystallography. 34(Part 6):777-779, 2001 Dec.
Abstract:
NADA is a computer program for the simultaneous refinement of the components of the orientation matrix and the components of up to three modulation vectors by the method of least squares. Using the spatial peak positions and the orientation matrix of the main reflections from a single-crystal diffraction experiment and rough estimates of the modulation vector(s) components, NADA re-indexes the peaks (main and satellite reflections) with integers in higher dimensions (hklm(1), hklm(1)m(2) or hklm(1)m(2)m(3), respectively) and refines the orientation matrix and modulation vector(s) components from the observed peak positions. Standard uncertainties on all refined parameters are calculated analytically. [References: 7]
Title:
The dielectric properties and phase transition of (1-x)Pb(Yb1/2Ta1/2)O-3-xPb(Yb1/2Nb1/2)O-3
Authors:
Kim HJ. Lee JH. Choo WK.
Source:
Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes & Review Papers. 40(9B):5668-5670, 2001 Sep.
Abstract:
The dielectric properties and phase transition behaviors of (1-x)Pb(Yb1/2Ta1/2)O-3-xPb(Yb1/2Nb1/2)O-3 (PYT1-xPYNx) solid solution have been investigated. The primary transition that occurs at 310 degreesC of PYT is not affected by substitution of Ta5+ by Nb5+. The secondary phase transition of PYT which happens to be relaxor-like in character is critically affected by Nb5+ substitution. Although the profiles of X-ray diffraction of the. solid solution are not noticeably changed by Nb5+ substitution, its selected area electron diffraction reveals that the superlattice diffraction spots become incommensurate due to Nb-5+ substitution. This incommensuration. coincides with disappearance of the secondary phase transition on Nb5+ substitution.
Title:
Structure of Ca13Cd76: A novel approximant to the MCd5.7 quasicrystals (M = Ca, Yb)
Authors:
Gomez CP. Lidin S.
Source:
Angewandte Chemie-International Edition. 40(21):4037-+, 2001.
Title:
The observation of oscillatory behaviour in swift heavy ion irradiated quasicrystals
Authors:
Chatterjee R. Kanjilal A. Dunlop A. Tiwari U. Ramillon JM.
Source:
Solid State Communications. 120(7-8):289-293, 2001.
Abstract:
The effect of 835 MeV Kr irradiation at 90 K on a stable icosahedral quasicrystal (Al65Cu25Fe5V5) is discussed here. A Kr-bearn of this energy was chosen in order to keep the stopping power similar to 1300 eV/Angstrom in accordance with our previous work [Nucl. Instrum. Meth. B, 156 (1999) 201], while increasing the travelled path in which strong electronic excitations occur (much greater than sample thickness). The ratio rho(phi)/rho (0) {resistivity at fluence phi /resistivity at zero fluence} of quasicrystal goes through oscillatory changes, up to similar to 1 X 10(12) ions/cm(2) where this ratio drops considerably. The ex situ XRD on the irradiated samples however shows the evidence of degradation of the structure after a critical fluence of 1 X 10(11) ions/cm(2). From the ex situ XRD measurements, this degradation does not seem to increase with further fluence up to phi = 1 X 10(13) ions/cm(2). (C) 2001 Elsevier Science Ltd. All rights reserved.
Title:
"Latent" paramagnetism and incommensurate structures in three-sublattice magnets
Authors:
Zavorotnev YD. Medvedeva LI.
Source:
Physics of the Solid State. 43(11):2126-2129, 2001.
Abstract:
The formation of superstructures due to the interaction of one-component and two-component order parameters in three-sublattice magnets is considered. It is shown that, in the general case, the propagation vector is located in the XOY plane and the irreducible vectors can rotate either within one plane or in two mutually perpendicular planes. Under the conditions of "latent" paramagnetism, no superstructure is formed. (C) 2001 MAIK "Nauka/ Interperiodica".
Title:
Precipitation of nanoscale icosahedral quasicrystalline phase in Hf-Cu amorphous alloy promoted by the addition of Ni
Authors:
Li CF. Wang LM. Inoue A.
Source:
Materials Letters. 51(3):203-207, 2001 Nov.
Abstract:
Hf70Cu30 and Hf70Cu20Ni10 amorphous alloys were prepared by a single roller melt-spinning method and the crystallization processes were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). For the Hf70Cu30 alloy, the stable Hf,Cu crystalline phase precipitates directly from the amorphous matrix. For the Hf70Cu20Ni10 alloy, the crystallization proceeds through the reactions of Am --> I-phase --> Hf-2(Cu, Ni), where Am- and I-phase represent the amorphous and icosahedral quasicrystalline phases. respectively, The present result demonstrates that the addition of Ni to the Hf-Cu alloy is effective in promoting the precipitation of the I-phase. To explain the above experimental results. the existence of icosahedron-like atomic clusters in the amorphous state of Hf70Cu20Ni10 alloy is suggested. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Neutron diffraction studies of the magnetic structures of HoAuGe and ErAuGe
Authors:
Baran S. Hofmann M. Lampert G. Stusser N. Szytula A. Tobbens D. Smeibidl P. Kausche S.
Source:
Journal of Magnetism & Magnetic Materials. 236(3):293-301, 2001 Nov.
Abstract:
The magnetic structures of HoAuGe and ErAuGe, both crystallizing in the hexagonal LiGeGa-type structure, have been investigated by high resolution neutron diffractometry in the temperature range between 1.5 and 7.7 K. For ErAuGe, additional low temperature diffraction experiments have been performed between 40 mK and 1.4 K. Both compounds order antiferromagnetically at low temperatures. The magnetic structure of HoAuGe at 1.5 K is described by a propagation vector k = [1/2, 0, 0]. The low temperature diffraction pattern of ErAuGe is similar to that obtained for HoAuGe. however, some magnetic reflections of ErAuGe show a significant broadening. This broadening is due to a magnetic domain size effect. Transversal sine wave incommensurate magnetic structures appear close to the Neel temperatures. These structures can be described by a propagation vector k = [0,4461(5), 0, 0] at 4.5 K for HoAuGe and k = [0.4185(40),0, 0 ] at 3.0 K for ErAuGe. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Incommensurate magnetic structure in copper metaborate
Authors:
Petrakovskii GA. Popov MA. Roessli B. Ouladdiaf B.
Source:
Journal of Experimental & Theoretical Physics. 93(4):809-814, 2001.
Abstract:
Based on the experimental data on copper metaborate single crystals obtained in X-ray and neutron diffraction studies and heat capacity, magnetic susceptibility, and muon spin relaxation measurements, a phenomenological theory of the incommensurate magnetic structure of this crystal was developed. Considering the space group of the crystal, I (4) over bar 2d, Lifshits invariants were included into its thermodynamic potential. An analysis showed that magnetic structure formation at 10-20 K was dominated by the subsystem of copper spins in 4b unit cell sites. Below 10 K, the role played by the magnetic subsystem of copper spins in 8d unit cell sites in the formation of the magnetic structure of copper metaborate substantially increased. This caused a sharp increase in the wave vector of the incommensurate structure as temperature lowered. Numerical simulation of the temperature dependence of the wave vector of the helix and the heat capacity of the crystal gave a satisfactory description of the experimental data. This simulation was used to estimate the parameters of the phenomenological thermodynamic potential of the magnetic system of copper metaborate. (C) 2001 MAIK "Nauka/Interperiodica".
Title:
The stability of icosahedral cluster and the range of interaction potential
Authors:
Ding F. Wang JL. Shen WF. Wang BL. Li H. Wang GH.
Source:
Communications in Theoretical Physics. 36(4):459-462, 2001 Oct 15.
Abstract:
The relation between the stability of icosahedral clusters and the range of interaction potential is discussed. We found that the stability of icosahedral clusters may decrease with decreasing range of interaction potential. A simple, formula. about the critical number of icosahedral clusters and the range of interaction potential (M-c(1/3) = A(1) + A(2)r(eff)(2)) was proposed. The calculation of the stability of icosahedral fullerence molecular clusters shows that our idea is right.
Title:
Change in electrical resistivity due to icosahedral phase precipitation in Zr70Pd20Ni10 and Zr65Al7.5Cu7.5Ni10Ag10 glasses (vol 79, pg 758, 2001)
Authors:
Haruyama O. Miyazawa T. Saida J. Inoue A.
Source:
Applied Physics Letters. 79(19):3197, 2001 Nov 5.
Title:
Mechanochemical synthesis of an icosahedral phase of composition Ti45Zr38Ni17 and its interaction with hydrogen
Authors:
Konstanchuk IG. Ivanov EY. Boldyrev VV. Bokhonov BB.
Source:
Russian Journal of Physical Chemistry. 75(10):1723-1727, 2001 Oct.
Abstract:
An icosahedral phase of composition Ti45Zr38Ni17 was synthesized, and its interaction with hydrogen was studied. It was shown that, unlike icosahedral phases of the same composition formed by the fast hardening of a melt or by the annealing of alloys, the hydrogenation of the mechanochemically synthesized icosahedral phase at 230 degreesC has no induction period and begins at a maximum rate even at hydrogen pressures lower than 1 atm. Analysis of an experimental hydrogen pressure-icosahedral phase composition isotherm and XRD data suggests that the hydrogen absorption by the icosahedral phase is similar to that for hydrides. This phenomenon was explained based on the assumption that, in the structure of the hydrogenated icosahedral phase, there are two types of hydrogen: chemically bonded hydrogen occupying distorted tetrahedral positions in Bergman structure-forming icosahedral clusters and hydrogen located between these clusters in the form of a solid solution.
Title:
Second-order terms in the phonon-phason dynamic matrix of an icosahedral quasicrystal
Authors:
Rochal SB.
Source:
Physics of the Solid State. 43(10):1962-1967, 2001 Oct.
Abstract:
They fourth-order terms (in the wave vector components) of the phonon-phason dynamic matrix are obtained for an icosahedral quasicrystal. In this order, the dynamic matrix has nine independent coefficients: three phonon-phonon, three phason-phonon, and three phason-phason coefficients. The number of independent coefficients in the phonon block of the constructed dynamic matrix is greater by unity than that for an isotropic medium. The corresponding features of acoustic phonon dispersion in the i-AlPdMn alloy are considered. It is shown that when the fourth-order terms are taken into account, the intensity of diffuse scattering in the vicinity of Bragg reflections decreases in accordance with the law alpha/(q(2) + betaq(4)), where q is the distance to a reflection in the reciprocal space and coefficients alpha and beta depend on the direction of vector q. (C) 2001 MAIK "Nauka/Interperiodica".
Title:
Metastable transformation states of decagonal Al-Co-Ni due to inhibited decomposition - art. no. 134208
Authors:
Doblinger M. Wittmann R. Grushko B.
Source:
Physical Review B. 6413(13):4208-+, 2001 Oct 1.
Abstract:
The transformation behavior of high-Co decagonal AI-Co-Ni is studied. Starting from stability considerations based on a number of annealing treatments we check theoretical predictions of the stabilization mechanism and transformation mechanism by phason strain analysis and tiling analysis. The quasicrystal transforms in the first stages into nanodomain structures and finally decomposes into a quasicrystal and a normal crystalline phase. Before decomposition, the material is locked in a disordered state exceeding the periodic order allowed for a one-dimensional quasicrystal. This is interpreted as the maximum periodic order achievable without diffusion. From considering different reasons for phason strain we conclude that disorder in tilings related to phase transformations can wrongly be associated with that suggested by the random tiling hypothesis.
Title:
Spherical neutron polarimetry of the magnetic structure in UNi2Al3 - art. no. 134413
Authors:
Hiess A. Brown PJ. Lelievre-Berna E. Roessli B. Bernhoeft N. Lander GH. Aso N. Sato NK.
Source:
Physical Review B. 6413(13):4413-+, 2001 Oct 1.
Abstract:
Spherical neutron polarimetry in the antiferromagnetic state of monocrystalline UNi2Al3 has established that the magnetic structure in zero field is an amplitude modulated magnetization density wave with moment axis along the a* direction of the basal plane in the hexagonal structure. There is no observable change in the orientation of the magnetic moments when the material becomes superconducting below 1 K.
Title:
Quasiperiodic spin chains in a magnetic field - art. no. 134419
Authors:
Arlego M. Cabra DC. Grynberg MD.
Source:
Physical Review B. 6413(13):4419-+, 2001 Oct 1.
Abstract:
We study the interplay between a (quasi) periodic coupling array and an external magnetic field in a spin-1/2 XXZ chain. A new class of magnetization plateau is obtained by means of Abelian bosonization methods which gives rise to a sufficient quantization condition. The investigation of magnetic phase diagrams via exact diagonalization of finite clusters finds a complete agreement with the continuum treatment in a variety of situations.
Title:
Specific heat of field-dependent magnetic orderings in HoNi2B2C
Authors:
Choi JH. Doh H. Choi EM. Kim HJ. Lee SI. Yamamoto T. Kawae T. Takeda K.
Source:
Journal of the Physical Society of Japan. 70(10):3037-3041, 2001 Oct.
Abstract:
We have investigated the, low-temperature specific heat of HoNi2B2C down to T = 1 K in various magnetic fields from 0 T to 5 T. At zero field, the specific heat exhibits a large peak at T-N = 5.1 K, which is due to commensurate antiferromagnetic ordering, and other Smaller peak at T-1 = 5.5 K, which is related to incommensurate ordering. As the field is increased up to 0.5 T, the first peak broadens and moves to a lower temperature, while the other peak at T-1 moves to a higher temperature, which indicates that the phase between T-N and T-1 is more favored in magnetic fields. Among possible candidates for the phase, the a-axis modulation phase, which is an extension of a low temperature metamagnetic state, is the most probable. In the high-field region above 1 T, the two-peak feature is replaced by a broad-hill one that fades away with increasing fields, which is the typical smearing feature of the magnetic order at high fields.
Title:
On the lattice instability in incommensurate phase transition of K2SeO4
Authors:
Ishibashi Y. Iwata M. Janssen T.
Source:
Journal of the Physical Society of Japan. 70(10):3178-3179, 2001 Oct.
Title:
High-nuclearity palladium carbonyl trimethylphosphine clusters containing unprecedented face-condensed icosahedral-based transition-metal core geometries: proposed growth patterns from a centered Pd-13 icosahedron [Review]
Authors:
Tran NT. Kawano M. Dahl LF.
Source:
Journal of the Chemical Society-Dalton Transactions. (19):2731-2748, 2001 Oct 7.
Abstract:
The preparation, isolation, and structural/bonding characterization of four high-nuclearity neutral homopalladium clusters, Pd-16(CO)(13)(PMe3)(9) 1, Pd-35(CO)(23)(PMe3)(15) 2, Pd-39(CO)(23)(pMe(3))(16) 3 and Pd-59(CO)(32)(PMe3)(21), 4, and a minor bimetallic product, Pd29Ni3(CO)(22)(PMe3)(13) 5, are given. The four homopalladium clusters were characterized by CCD X-ray crystallographic determinations, elemental analyses, IR, multinuclear NMR, and cyclic voltammetry; because 5 was obtained in very low yields, both its molecular geometry and composition were established from the X-ray crystallographic analysis. These five clusters, obtained from reactions of a cep Pd-Ni carbonyl cluster precursor and PMe3 (with or without acetic acid), exhibit five different types (four unprecedented) of centered icosahedral-based transition-metal frameworks: (1) the Pd-16 core in 1 possesses a centered Pd-13 icosahedron. (2) The Pd-35 and Pd-39 core's in 2 and 3 each have a face-fused centered Pd-23 biicosahedron with linear (pseudo-D-3h) and bent (pseudo-C-2v) geometries, respectively; the pseudo-D-3h central Pd-29 polyhedron of the Pd-35 core in 2 approximately conforms to five interpenetrating centered icosahedra. (3) The crystallographic-D-3 (32) Pd-59 core in 4 has two centered Pd-13 icosahedra that are indirectly connected via trans double face-sharing with an inner face-fused Pd-9 bioctahedron; the entire nanosized face-condensed Pd-59 core has 11 interior Pd(i) atoms. (4) The Pd29Ni3 core in 5 contains a pseudo-T-d central Pd, polyhedron comprised of four interpenetrating centered icosahedra. The existence of these highly condensed icosahedral-based metal carbonyl clusters, found only for Pd but not for the other eight Group 8-10 transition metals, may be ascribed to Pd metal having the weakest metal-metal bonding (i.e., smallest cohesive energy). Electronic closed-shell stabilization of each of these clusters is indicated by electron-counting condensation rules giving calculated values in exact agreement with observed electron counts for the metal cores in 1, 2, 4, and 5 (i.e., irregular condensations prevent a reliable electron count in 3). Proposed growth sequences provide logical pathways in the formation of the central palladium fragments in 2, 3, 4 and 5 from the centered Pd-13 icosahedral fragment in 1. [References: 128]
Title:
High-pressure neutron diffraction studies of the magnetic structures of cubic Pd3Mn and Pd3MnD0.7
Authors:
Tellgren R. Andersson Y. Goncharenko I. Andre G. Bouree F. Mirebeau I.
Source:
Journal of Solid State Chemistry. 161(1):93-96, 2001 Oct.
Abstract:
High-pressure anvil technique and neutron powder diffraction have been used to study the magnetic structures of cubic Pd3Mn and Pd3MnD0.7 at pressure of 4.6 GPa and 4.2 GPa, respectively. The incommensurate helix structure of Pd,Mn is retained tinder pressure. The ferrimagnetic structure of Pd3MnD0.7 obtained at ambient pressure changes to a pure ferromagnetic one with the moments in the [100] direction. (C) 2001 Academic Press. [References: 9]
Title:
An empirical study of the Mn partial density of states in icosahedral Al70Pd20Mn10
Authors:
Erbudak M. Hensch A. Keller J. Rossner B. Kortan AR.
Source:
Journal of Electron Spectroscopy & Related Phenomena. 120(1-3):47-53, 2001 Oct.
Abstract:
Using the line-shape analysis of the Mn 2p(3/2)3d3d Auger transitions and by observing the Mn 3p --> 3d transitions in electron energy-loss spectroscopy, we have studied the local density of electronic states of the crystalline cubic and the quasicrystalline icosahedral phases of Al70Pd20Mn10. We find that, in the cubic phase the Mn 3d states coincide with the Fermi level EF, but in the quasicrystalline state the Mn 3d band is fully occupied and shifted to lower binding energies causing a significant reduction in the density of states at E-F. (C) 2001 Elsevier Science BY. All rights reserved.
Title:
A new phasing method based on the principle of minimum charge
Authors:
Kalugin P.
Source:
Acta Crystallographica - Section a - Foundations of Crystallography. 57(Part 6):690-699, 2001 Nov.
Abstract:
A new method for phase determination in X-ray crystallography is proposed. The method is based on the so-called 'minimum-charge' principle, recently suggested by Elser [Acta Cryst. (1999), A55, 489-499]. The electron-density function rho is sought in the form rho (x) = \ psi (x)\ (2), where psi is an n-component real function. The norm integral \ psi (x)\ (2) dx is minimized under the constraint imposed by the measured data on the amplitudes of Fourier harmonics of rho. Compared with the straightforward implementation of the 'minimum-charge' scheme, the method attenuates the Gibbs phenomenon and is also capable of extrapolation of the diffraction data beyond the set of measured amplitudes. The method is applicable to quasicrystals under the condition that the number of components n of the function psi is bigger than the dimensionality of the 'atomic surface'. It has been successfully tested on synthetic data for a Fibonacci chain and octagonal tiling. In the latter case, the reconstructed density map shows the shape of the atomic surface, despite relatively low resolution data.
Title:
Tiling of the fivefold surface of Al70Pd21Mn9
Authors:
Ledieu J. McGrath R. Diehl RD. Lograsso TA. Delaney DW. Papadopolos Z. Kasner G.
Source:
Surface Science. 492(3):L729-L734, 2001 Oct 20.
Abstract:
The nature of the fivefold surface of Al70Pd21Mn9 has been investigated using scanning tunnelling microscopy. From high resolution images of the terraces, a tiling of the surface has been constructed using pentagonal prototiles. This tiling matches the bulk model of Boudard et al. [J. Phys.: Cond. Matter 4 (1992) 10149], which allows us to elucidate the atomic nature of the surface. Furthermore, it is consistent with a Penrose tiling F*(((P1)r)) obtained from the geometric model based on the three-dimensional tiling F*((2F)). The results provide direct confirmation that the fivefold surface of i-Al-Pd-Mn is a termination of the bulk structure. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Oxidation of Al-Pd-Mn quasicrystal surfaces
Authors:
Popovic D. Naumovic D. Bovet M. Koitzsch C. Schlapbach L. Aebi P.
Source:
Surface Science. 492(3):294-304, 2001 Oct 20.
Abstract:
The oxidation of both,, quasicrystalline and crystalline surfaces of an icosahedral Al-Pd-Mn quasicrystal cut perpendicular to its five-fold axis and of Al(1 1 1) has been studied by means of X-ray photoelectron spectroscopy, ultraviolet photoemission spectroscopy, low-energy electron diffraction and X-ray photoelectron diffraction. The oxidation of the elements of the alloy is quantified and compared for the different phases and Al(1 1 1). The quasicrystalline surface is found to react less with oxygen than the crystalline surface and more rapidly compared to Al(I 11). The observed behaviour is discussed in terms of the termination of the corresponding surfaces. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Stripes and spin incommensurabilities are favored by lattice anisotropies - art. no. 167005
Authors:
Becca F. Capriotti L. Sorella S.
Source:
Physical Review Letters. 8716(16):7005-+, 2001 Oct 15.
Abstract:
Structural distortions in cuprate materials give a natural origin for anisotropies in electron properties. We study a modified one-band t-J model in which we allow for different hoppings and antiferromagnetic couplings in the two spatial directions (t(x) not equal t(y) and J(x) not equal J(y)). Incommensurate peaks in the spin structure factor show up only in the presence of a lattice anisotropy, whereas charge correlations, indicating enhanced fluctuations at incommensurate wave vectors, are present but almost unaffected with respect to the isotropic case.
Title:
Excitations of the field-induced quantum soliton lattice in CuGeO3 - art. no. 177203
Authors:
Enderle M. Ronnow HM. McMorrow DF. Regnault LP. Dhalenne G. Revcholevschi A. Vorderwisch P. Schneider H. Smeibidl P. Meissner M.
Source:
Physical Review Letters. 8717(17):7203-+, 2001 Oct 22.
Abstract:
The incommensurate magnetic soliton lattice in the high-field phase of a spin-Peierls system results from quantum fluctuations. We have used neutron scattering techniques to study CuGeO3, allowing us to obtain the first complete characterization of the excitations of the soliton lattice. Three distinct excitation branches are observed, all of which are gapped. The two highest energy modes have minimum gaps at the commensurate wave vector and correspond to the creation or annihilation of soliton pairs. The third mode is incommensurate and is discussed in relation to theoretical predictions.
Title:
Classical generalization of the Drude formula for the optical conductivity - art. no. 155106
Authors:
Smith NV.
Source:
Physical Review B. 6415(15):5106-+, 2001 Oct 15.
Abstract:
A simple classical generalization of the Drude formula is derived based on the impulse response approach and Poisson statistics. The new feature is a parameter c, which is a measure of persistence of velocity. With negative values of c, it is possible to mimic the infrared properties of poor metals that display a minimum in the optical conductivity at zero frequency. The electron current in these cases reverses direction before decaying to zero. Specific examples considered are Hg and its amalgams, liquid Te, and the quasicrystal Al63.5Cu24.5Fe12. Discussion is offered on the connection with interband transitions, on the distinction between the electron lifetime and the transport relaxation time, and on other generalizations of the Drude formula.
Title:
Icosahedral quasicrystal in annealed Zn-Mg-Sc alloys
Authors:
Kaneko Y. Arichika Y. Ishimasa T.
Source:
Philosophical Magazine Letters. 81(11):777-787, 2001 Nov.
Abstract:
A new icosahedral quasicrystal has been found in Zn85MgSc15 (x = 3, 4, 5) alloys annealed at 922 K for 5-100 h. Electron diffraction and powder X-ray diffraction experiments indicate that this quasicrystal has a primitive icosahedral quasilattice (P type) and a six-dimensional lattice parameter alpha (6D) = 0.7115 nm. The stoichiometric composition of the icosahedral quasicrystal was estimated to be close to Zn80Mg5Sc15, since the icosahedral quasicrystal coexists in the x = 5 samples with small amounts of a MgZn2-type Laves phase and a Zn17Sc3-type cubic phase with lattice parameter alpha = 1.3854 nm. The latter is interpreted to be a 1/1-type approximant crystal of the icosahedral quasicrystal. The atomic cluster included in the Zn17Sc3-type cubic phase indicates a structural similarity between the Zn-Mg-Sc quasicrystal and the Cd-Yb (and Cd-Ca) icosahedral quasicrystals recently reported.
Title:
X-ray diffraction study of a phason strain in an Al-Cu-Fe icosahedral quasicrystal
Authors:
Jono M. Matsuo Y. Yamamoto K. Ishii Y.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 81(11):2577-2590, 2001 Nov.
Abstract:
Detailed examinations of the peak profiles and the positions of the Bragg peaks are carried out with the X-ray diffractometer for single-grain samples of the Al-Cu-Fe icosahedral quasicrystal. Notable peak shifts from the ideal positions with linear Q(perpendicular to) dependence are observed along the fivefold directions. This means that the sample contains linear phason strain. The amplitude of the linear phason strain is estimated as -0.0543, which is close to a theoretical value for the phason-strain-inducing transformation from the icosahedral phase to the pentagonal phase (P2 phase), -1/tau (6). The two-dimensional intensity distributions around the Bragg peaks on the twofold, threefold and fivefold axes are interpreted as consequences of the phason-strain-inducing pentagonal deformation.
Title:
Quasicrystals: tiling versus clustering
Authors:
Lord EA. Ranganathan S. Kulkarni UD.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 81(11):2645-2651, 2001 Nov.
Abstract:
A quasiperiodic covering of a plane by regular decagons is described, and an analogous structure in three dimensions is deduced. This consists of a pattern of interpenetrating congruent triacontahedral clusters, related to the tau (3) inflation rule for quasiperiodic Ammann tiling patterns. The overlap regions are triacontrahedron faces, oblate hexahedra, rhombic dodecahedra and rhombic icosahedra. The structure leads to a plausible model for T2 icosahedral quasicrystalline phases.
Title:
Modification of icosahedral quasicrystal Al65Cu20Fe15 by 170-MeV Ni-58(+12) beam
Authors:
Kanjilal A. Singh R. Chatterjee R.
Source:
Materials Research Bulletin. 36(13-14):2323-2331, 2001 Nov 1.
Abstract:
Thin ribbons of stable icosahedral quasicrystal Al65Cu20Fe15 were irradiated with swift heavy ion (SHI) beam of 170 million electron volt (MeV) Ni-58(+12) in high and clean vacuum environment at a temperature of 80 K to study the modification of its properties. Dynamic variation of resistance was studied on-line during and after irradiation for the first time, to understand the effect of SHI. The resistance decreased sharply at the time of incidence of ion beam due to creation of a large number of charge carriers by intense ionization by SI-H and did oscillate around a mean value during irradiation due to defect creation and annihilation. The resistance increased rapidly just after the beam was stopped from its mean value during irradiation. The quasicrystalline peaks of the XRD data on these samples irradiated by SHI, were prominent till the ion beam fluence of 5 X 10(12) particles/cm(2), but the peak height consistently decreased with increasing fluence after a fluence of 1012 articles/cm(2). (C) 2001 Elsevier Science Ltd. All rights reserved.
Title:
Comment on 'Atomic motions in the crystalline Al50Cu35Ni15 alloy'
Authors:
Coddens G.
Source:
Journal of Physics-Condensed Matter. 13(39):8869-8872, 2001 Oct 1.
Abstract:
It was recently stated that fast atomic jumps observed in quasicrystals are a common feature in metallic alloys. We explain why this is not correct.
Title:
Anomalous transport behavior of a binary Cd-Yb icosahedral quasicrystal
Authors:
Tamura R. Murao Y. Takeuchi S. Tokiwa K. Watanabe T. Sato TJ. Tsai AP.
Source:
Japanese Journal of Applied Physics Part 2-Letters. 40(9AB):L912-L914, 2001 Sep 15.
Abstract:
Electronic properties of the recently discovered binary Cd-Yb icosahedral(i) phase have been found to be strikingly different from those of ternary i-phases studied so far: The resistivity decreases rapidly (by 10-80% depending on the composition) with decreasing temperature down to about 10 K and levels off below 10 K. A giant magnetoresistance reaching as high as 200% at 9 T is observed at low temperatures. The electronic specific heat coefficient gamma is very large, i.e., 2.87 mJ/(mole(.)K(2)), and the Debye temperature Theta (D) is as low as 140 K, which are in striking contrast with the trend observed in ternary i-phases. These anomalous features indicate that a different transport mechanism other than those proposed for ternary i-phases has to be considered for the present binary i-phase.
Title:
Supramolecular self-assembly and selective step decoration on the Au(111) surface
Authors:
Vladimirova M. Stengel M. De Vita A. Baldereschi A. Bohringer M. Morgenstern K. Berndt R. Schneider WD.
Source:
Europhysics Letters. 56(2):254-260, 2001 Oct.
Abstract:
Scanning tunneling microscopy of low coverages of 1-nitronaphtalene ( NN) on reconstructed Au( 111) reveals that the face-centered-cubic ( fcc) reconstruction domains of steps are densely and selectively decorated. Molecular dynamics simulations identify this phenomenon as the self-assembly of hydrogen-like bonded supramolecular chains driven by the step electrostatic potential. First principles calculations predict weak adsorption at domain boundaries, and stable adsorption at the step edge of the fcc domains, explaining the selective decoration.

Update: 5-Nov-2001

Title:
X-ray studies of phase transitions of (Ca,Sr)-(a)over-circle-kermanite solid solutions
Authors:
Kusz J. Bohm H.
Source:
Zeitschrift fur Kristallographie. 216(9):509-512, 2001.
Abstract:
The phase transitions of the solid solutions (Ca1-xSrx)(2)MgSi2O7 (0 less than or equal to x less than or equal to 0.32) of modulated melilites are studied by X-ray diffraction. The variation of the intensity and the FWHM of satellite reflections reveal different transition temperatures. Two ranges of different ordering are found in the range of incommensurate modulation. The mechanism of the phase transition into the incommensurately modulated structure is discussed by including the diffuse scattering above the transition.
Title:
Less singular quasicrystals: The case of low codimensions - art. no. 140201
Authors:
Jagannathan A.
Source:
Physical Review B. 6414(14):0201-+, 2001 Oct 1.
Abstract:
We consider a set of tilings proposed recently as d-dimensional generalizations of the Fibonacci chain, by Vidal and Mosseri. These tilings have a particularly simple theoretical description, making them appealing candidates for analytical solutions for electronic properties. Given their self-similar geometry, one could expect that the tight-binding spectra of these tilings might possess the characteristically singular features of well-known quasiperiodic systems such as the Penrose or the octagonal tilings. We show here, by a numerical study of statistical properties of the tight-binding spectra that these tilings fall rather in an intermediate category between the crystal and the quasicrystal, i.e., in a class of almost integrable models. This is certainly a consequence of the low codimension of the tilings.
Title:
Theory of the martensitic transformation in cobalt - art. no. 144104
Authors:
Toledano P. Krexner G. Prem M. Weber HP. Dmitriev VP.
Source:
Physical Review B. 6414(14):4104-+, 2001 Oct 1.
Abstract:
A phenomenological theory of the martensitic fcc-hcp transformation is proposed and applied to the illustrative example of cobalt. The fcc and hcp structures are shown to result from different ordering mechanisms from a disordered polytypic structure and to be intrinsically faulted. The three, fcc, hcp, and disordered polytype, structures are inserted in the framework of the segregation process which leads to the formation of close-packed structures from the melt. The essential features reported for the fcc-hep transformation in cobalt are explained within the preceding model, namely, the asymmetry of the interphase region, the phonon spectrum, the delta -shape of its specific heat anomaly, and the existence of an intermediate modulated structure. The property of the transformation enthalpy to be different on heating and cooling is related to the different degree of order of the hcp and fcc structures. The partial dislocation mechanism currently assumed for the transformation is deduced from the secondary shear strains involved at the transformation.
Title:
Second-order terms of the phonon-phason dynamic matrix of an icosahedral quasicrystal: Diffuse intensity and the profile shape around the Bragg peaks - art. no. 144204
Authors:
Rochal SB.
Source:
Physical Review B. 6414(14):4204-+, 2001 Oct 1.
Abstract:
Second-order terms of phonon-phason dynamical matrix of an icosahedral quasicrystal are expressed as polynomial functions of fourth degree with respect to the wave vector components. In terms of this degree there are three independent elastic constants in the phonon block of the dynamical matrix, which is one more than for the case of an isotropic medium. Corresponding peculiarities of acoustic phonons are discussed. Three independent second order elastic constants belong to the phason block and three correspond to the phonon-phason coupling term. Revised theory of the diffuse scattering in the vicinity of Bragg peaks taking into account diffusive nature of phason modes is proposed. Both cases of thermal and quenched phason fluctuations are considered. With taking into account of the second order terms the intensity of the diffuse scattering in the vicinity of Bragg peaks decays likely alpha/(q(2) + betaq(4)), where q is the distance from peaks and coefficients alpha and beta depend on the direction of the q vector.
Title:
Nanoscale phase separation and local icosahedral order in amorphous alloys of immiscible elements - art. no. 144206
Authors:
He JH. Ma E.
Source:
Physical Review B. 6414(14):4206-+, 2001 Oct 1.
Abstract:
We demonstrate that local icosahedral ordering, as well as spinodal compositional modulations with nanometer scale wavelengths, are characteristic of amorphous structures formed in an immiscible system with large positive heat of mixing. This unique nature of the atomic-level structures allows the amorphous alloy to lower its enthalpy such that the heat of crystallization is of a magnitude comparable to that typically seen for amorphous phases in easy glass-forming systems. The development of such chemical decomposition and topological order in the short to medium range has been monitored in the Ag-Ni model system using molecular dynamics (MD) simulations. The MD findings of the structural features and enthalpies, as well as their correlation, are consistent with the experimental characterization results of vapor-deposited Ag-Ni amorphous phases.
Title:
Electronic properties of ternary quasicrystals in one dimension - art. no. 144207
Authors:
Fujita N. Niizeki K.
Source:
Physical Review B. 6414(14):4207-+, 2001 Oct 1.
Abstract:
The one-electron properties of a certain class of one-dimensional ternary quasicrystals (QC's) are investigated. In particular, we show in detail the presence of a special kind of critical states called marginal critical states in these QC's. By the use of a real-space renormalization-group method, it is shown that the scaling properties of marginal critical states are characterized by stretched exponentials. These states are virtually localized, so that their presence may make a QC less conductive.
Title:
Initial crystallization processes of Zr-Cu-Rh metallic glasses
Authors:
Li CF. Wang LM. Inoue A.
Source:
Journal of Physics-Condensed Matter. 13(35):L803-L809, 2001 Sep 3.
Abstract:
Zr70Cu30 and Zr70Cu20Rh10 glassy alloys were prepared by a single-roller melt-spinning method and their crystallization processes were studied by differential scanning calorimetry, x-ray diffraction and transmission electron microscopy. For the Zr70Cu30 alloy, the glassy state crystallizes through a single exothermic reaction due to the precipitation of the stable Zr2Cu crystalline phase. For the Zr70Cu20Rh10 alloy, metastable icosahedral quasicrystalline and FCC-Zr2Rh phases precipitate from the glassy matrix in the initial crystallization process, followed by the phase transformation to Zr2Cu and ZrRh crystalline phases upon further annealing. These results illustrate that the partial substitution of Cu by Rh in the Zr70Cu30 glassy alloy is effective in promoting the precipitation of the metastable icosahedral quasicrystalline phase. To explain these experimental results, the existence of icosahedron-like atomic clusters in the Zr70Cu2Rh10 glassy alloy is suggested. [References: 19]
Title:
Magnetic structure of HoPd2Si2 redefined on the basis of new neutron diffraction data
Authors:
Szytula A. Jaworska-Golab T. Baran S. Penc B. Leciejewicz J. Hofmann M. Zygmunt A.
Source:
Journal of Physics-Condensed Matter. 13(35):8007-8014, 2001 Sep 3.
Abstract:
A new sample of HoPd2Si2 (ThCr2Si2-type structure, space group I4/mmm) has been prepared and investigated. Magnetic susceptibility and magnetization data indicate antiferromagnetic behaviour below T-N = 5.8 K. On the basis of powder neutron diffraction data the magnetic structure of the compound has been redefined and found to be more complex than reported earlier. In the temperature region from 20 K to 5 K a short-range magnetic order develops. Between 1.5 K and 5 K a long-range magnetic ordering, that could be described in an enlarged magnetic unit cell (a(m) = 7a, b(m) = a and c(m) = 6c), is observed. A complex magnetic structure of sine-wave modulated type with two propagation vectors and Ho magnetic moments parallel to the b-axis is proposed. Moreover, a new attempt to understand the transition from long- to short-range magnetic ordering observed in some rare earth compounds with Pd is made.
Title:
High-pressure synchrotron radiation diffraction studies of icosahedral Ti-Zr-Ni and hydrogenated Ti-Zr-Ni quasicrystals
Authors:
Sadoc A. Itie JP. Polian A. Kim JY. Kelton KF.
Source:
Journal of Physics-Condensed Matter. 13(37):8527-8536, 2001 Sep 17.
Abstract:
We present results from in situ x-ray diffraction studies of hydrogenated icosahedral Ti-Zr-Ni quasicrystals carried out under high pressure. The icosahedral Ti53Zr27Ni20 phase and hydrogenated icosahedral Ti45Zr38Ni17 samples that contain 0.32 and 1.45 hydrogen atoms for each metal atom were studied. The icosahedral quasicrystal structure is retained up to the highest pressures investigated. The six-dimensional lattice parameter was obtained as a function of pressure for the different samples. The zero-pressure bulk modulus and its pressure derivative were determined by fitting a Murnaghan-type equation of state to the relative volume change V/V-0. The zero-pressure bulk modulus is respectively obtained as B-0 = 130 +/- 10, 105 +/- 10, and 110 +/- 20 GPa for H/M equal to 0, 0.32, and 1.45 using a constant value for the first derivative B-0': 5.5 +/- 1. It seems, therefore, that the icosahedral Ti-Zr-Ni phase may be more compressible after hydrogenation, but there is no clear difference for different H/M contents. These results are tentatively related to the local structure of these materials.
Title:
Nanoicosahedral quasicrystalline phase in Zr-Pd and Zr-Pt binary alloys
Authors:
Saida J. Matsushita M. Inoue A.
Source:
Journal of Applied Physics. 90(9):4717-4724, 2001 Nov 1.
Abstract:
It is found that a nanoicosahedral phase in the diameter less than 20 nm is formed as a primary crystalline phase in the melt-spun Zr70Pd30 and Zr80Pt20 binary amorphous alloys. The nanoicosahedral phase is also formed in the as-quenched state in the Zr80Pt20 binary alloy by controlling the quenching rate. The slight redistribution of approximately 3 at % is observed during the quasicrystallization in the Zr70Pd30 alloy. In contrast, no significant compositional change between the nanoicosahedral and residual amorphous phases is observed in the Zr80Pt20 alloy. It is suggested that the precipitation of nanoicosahedral phase in the Zr70Pd30 alloy takes place by a diffusion-controlled growth mode accompanying an increase in nucleation rate. The activation energy for grain growth is calculated to be 270 kJ mol(-1), which implies the growth of icosahedral phase without a long-range atomic redistribution. The icosahedral medium-range order in the diameter range less than similar to2 nm is observed in the high-resolution electron micrographs of the melt-spun Zr70Pd30 and Zr80Pt20 amorphous alloys. It is realized that the icosahedral quasicrystalline phase can grow easily with assimilating the icosahedral medium-range order due to a slight redistribution of constitutional elements during quasicrystallization. The formation of the nanoicosahedral phase in the Zr70Pd30 and Zr80Pt20 binary alloys appears to be attributed to the existence of the icosahedral medium-range order in the amorphous and/or liquid states. (C) 2001 American Institute of Physics.
Title:
Some properties of the transverse elastic waves in quasiperiodic structures
Authors:
Tutor J. Velasco VR.
Source:
International Journal of Modern Physics B. 15(21):2925-2934, 2001 Aug 20.
Abstract:
We have studied the integrated density of states and fractal dimension of the transverse elastic waves spectrum in quasiperiodic systems following the Fibonacci, Thue-Morse and Rudin-Shapiro sequences. Due to the finiteness of the quasiperiodic. generations, in spite of the high number of materials included, we have studied the possible influence of the boundary conditions, infinite periodic or finite systems, together with that of the different ways to generate the constituent blocks of the quasiperiodic systems, on the transverse elastic waves spectra. No relevant differences have been found for the different boundary conditions, but the different ways of generating the building blocks produce appreciable consequences in the properties of the transverse elastic waves spectra of the quasiperiodic systems studied here.
Title:
Photonic band gaps and localization in two-dimensional metallic quasicrystals
Authors:
Bayindir M. Cubukcu E. Bulu I. Ozbay E.
Source:
Europhysics Letters. 56(1):41-46, 2001 Oct.
Abstract:
We report on experimental observation of photonic stop bands in two-dimensional metallic Penrose lattice. We investigated the defect characteristics, and observed strongly localized cavity modes below the plasma frequency. The absence of the translational symmetry allowed to change the defect frequencies and localization properties of the defect modes. Propagation of photons along highly localized coupled-cavity modes was experimentally demonstrated in quasiperiodic metallic structures.
Title:
Structural stability of binary CdCa quasicrystal under high pressure
Authors:
Jiang JZ. Gerward L. Olsen JS.
Source:
Applied Physics Letters. 79(16):2538-2539, 2001 Oct 15.
Abstract:
The structural stability of a binary CdCa quasicrystal with a primitive icosahedral structure has been investigated by in situ high-pressure x-ray powder diffraction at an ambient temperature using synchrotron radiation. It is demonstrated that the icosahedral quasicrystalline structure of the sample is intrinsically stable up to 47 GPa. The bulk modulus at zero pressure and its pressure derivative of the icosahedral CdCa quasicrystal is 68.1 +/-2.0 GPa and 4.3 +/-0.2, respectively. The compression behavior of different Bragg peaks is isotropic, indicating no pressure-induced anisotropic elasticity in the stable binary icosahedral CdCa quasicrystals. (C) 2001 American Institute of Physics. [References: 9]
Title:
Periodic composition modulations in InGaN epitaxial layers
Authors:
Westmeyer AN. Mahajan S.
Source:
Applied Physics Letters. 79(17):2710-2712, 2001 Oct 22.
Abstract:
InGaN epitaxial layers grown by metalorganic chemical vapor deposition were investigated in order to understand the occurrence of composition modulations in the GaN-InN system. The In contents of the samples were determined to be x=0.21 and 0.31. Transmission electron microscopy was performed on [0001], [10 (1) over bar0], and [11 (2) over bar0] zone-axis specimens. Plan-view images display a domain structure, representing regions in which the directions of the modulations differ. Intersections between domains occur in < 10 (1) over bar0 >, and < 11 (2) over bar0 >, and other directions. Satellite spots appear in selected-area diffraction patterns. These observations can be explained by diffraction effects resulting from periodic composition modulations. An equation was derived relating the spacing between the satellites and the reflections to the wavelength of the modulations in the wurtzite structure. The sample with x=0.21 had a wavelength of lambda =3.1 +/-1.3 nm and the one with x=0.31 had lambda =3.2 +/-1.3 nm. Since Young's modulus is isotropic in the (0001) plane, no particular direction is favored for the modulations based on strain energy considerations. This result is consistent with the observation of the variously oriented domains and satellites. (C) 2001 American Institute of Physics.
Title:
Nanoquasicrystalline phase formation in binary Zr-Pd and Zr-Pt alloys
Authors:
Murty BS. Ping DH. Ohnuma M. Hono K.
Source:
Acta Materialia. 49(17):3453-3462, 2001 Oct 9.
Abstract:
This paper reports nanoquasicrystalline phase formation in Zr100-xPdx (x = 30 and 35) and Zr80Pt20 binary alloys and the kinetics of the nanoquasicrystallization process. While the icosahedral phase (i-phase) forms as a metastable phase in the transient stage during the crystallization of Zr-Pd amorphous alloy, it forms directly from the liquid during melt-spinning of Zr-Pt alloy, The isothermal kinetics studies show that i-phase forms from the Zr70Pd30 amorphous alloy by the primary crystallization process with the Avrami exponent in the range of 1.5-2.5. Three-dimensional atom probe analysis results suggest that the i-phase is slightly enriched with Zr with respect to the matrix and its composition is close to Zr75Pd25. The tendency of quasicrystallization of Zr-based alloys appears to have correlation with the enthalpy of mixing of the system. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
A transmission electron microscope study of exsolution and coarsening in iron-bearing clinopyroxene from synthetic analogues of chondrules
Authors:
Weinbruch S. Muller WF. Hewins RH.
Source:
Meteoritics. 36(9):1237-1248, 2001 Sep.
Abstract:
The microstructure of Fe-rich clinopyroxene from synthetic analogues of chondrules was studied by transmission electron microscopy. The samples were cooled at various rates from 1455 degreesC to the quench temperature of 1000 degreesC. Slow cooling at rates below approximately 50-60 degreesC/h leads to the development of coherent pigeonite/augite exsolution lamallae on (001). A final wavelength of 19.6 +/- 1.1 nm was obtained at a cooling rate of 10 degreesC/h, and 17.4 +/- 2.4 nm at a cooling rate of 50 degreesC/h. Faster cooling at rates between approximately 50 and 450 degreesC/h yields only modulated structures with a wavelength on the order of 17-19 nm for the (001) orientation. Coherent exsolution lamellae on (001) in clinopyroxene occur in chondrules of H, L, LL, and CV chondrites, indicating that slow cooling of chondrules at subsolidus temperatures is a widespread phenomenon. The variation of the lamellar wavelength observed in natural chondrules corresponds to a variation of the subsolidus cooling rates between similar to0.1 and 50 degreesC/h. The low cooling rates at subsolidus temperatures deduced from the microstructure of Fe-rich clinopyroxene point to nonlinear cooling, with cooling rates decreasing with decreasing temperature. [References: 51]
Title:
Electronic transport in Cd-Yb and Y-Mg-Zn quasicrystals
Authors:
Pope AL. Tritt TM. Gagnon R. Strom-Olsen J.
Source:
Applied Physics Letters. 79(15):2345-2347, 2001 Oct 8.
Abstract:
Electronic transport properties of the stable binary Cd5.7Yb quasicrystal and a quasicrystal in the Y-Mg-Zn family is presented. Electrical conductivity in these systems is an order of magnitude higher than other quasicrystals, resulting in larger thermal conductivity values due to enhanced electronic contributions (lambda (E)=L(0)sigmaT). Room temperature Hall measurements provide a charge carrier density of 2.3x10(21) and 3.1x10(20) cm(-3) in Cd5.7Yb and Y-Mg-Zn, respectively, indicating these materials have a higher carrier concentration and are better conductors than other quasicrystalline counterparts. Thermoelectric power in both Cd5.7Yb and Y-Mg-Zn have relatively small magnitudes (16 and 8 muV/K, respectively). Despite many similarities between these two systems, low temperature specific heat reveals a low Debye temperature in Cd5.7Yb(140 K) while the Debye temperature of Y-Mg-Zn and other quasicrystals is at least twice as large. Consequences of the electrical transport in these systems will be discussed. (C) 2001 American Institute of Physics.
Title:
Alternative model for the structural modulation in NbSe3 and m-TaS3 - art. no. 115423
Authors:
Prodan A. Jug N. van Midden HJP. Bohm H. Boswell FW. Bennett JC.
Source:
Physical Review B. 6411(11):5423-+, 2001 Sep 15.
Abstract:
A model is proposed for the sliding charge density wave mechanism in the isostructural quasi-one-dimensional compounds NbSe3 and m-TaS3. It is based on an assumption that below either of the two onset temperatures T-1 and T-2 both modulation modes are present and form small statistically distributed domains along particular trigonal prismatic columns, i.e., along type III below T-1 and in addition along type I below T-2. Presuming the domains are of comparable sizes to the coherence lengths in the diffraction experiments, their disordered distribution results in a selective contribution to the reciprocal space in both temperature regions, which is in good accord with the diffraction experiments. The model might form the basis for a better explanation of the twinkling domains and low temperature tunneling microscopic images, which were not fully understood on basis of the old model with a selective occupation of the two column types by the two modulation modes.
Title:
Double-q magnetic structure and spin-block metamagnetism of ErRU2Si2 as studied by neutron diffraction
Authors:
Sato M. Takeuchi T. Watanabe K. Kawarazaki S.
Source:
Journal of the Physical Society of Japan. 70(9):2717-2723, 2001 Sep.
Abstract:
Neutron diffraction experiments with use of horizontal magnetic field have been carried out to study the magnetic structure of the ground state and the origin of the metamagnetism of the compound ErRu2Si2. Combination of the results of the previous magnetization measurements and of the present intensity measurements of several satellite reflections from a single-crystalline sample in mill field leads to a conclusion that the ground-state magnetic structure consists of a double-q superimposed structure of long-period transverse modulations. The metamagnetism together with the response of the satellite reflections to magnetic field have been satisfactorily explained on the basis of this double-q structure under assumptions of strong Ising anisotropy and persisting molecular field. [References: 9]
Title:
Three forms of the misfit layered cobaltite [Ca2CoO3] [CoO2](1.62) - A 4D structural investigation
Authors:
Lambert S. Leligny H. Grebille D.
Source:
Journal of Solid State Chemistry. 160(2):322-331, 2001 Sep.
Abstract:
Three misfit layer compounds with the same chemical formula Ca3CO4-xO9+delta were isolated in the Ca-Co-O system. They exhibit either a monoclinic or an orthorhombic symmetry. These crystals are constituted of two interpenetrating C sublattices showing incommensurate periods along the b axis. The structure of the three crystals can be described as an alternate stacking along [001] of distorted rock-salt-type slabs [Ca2CoO3] and of [CoO2] layers displaying a distorted CdI2-type structure. Relating to the symmetry and the different observed c periods, different sequences are found for the [CoO2] layers running along [001] within the three crystals. Two of them were determined by single X-ray diffraction using the 4D superspace formalism. A significant displacive modulation is implied, acting mainly on Ca and O atoms involved in the intersystem bonding scheme. This modulation leads to a noticeable distortion of the CoO6 octahedra of the [CoO2] layers. Strong interactions, via Ca-O bonds, are evidenced between the two sublattices. A systematic positional disorder is observed inside the [CoO] layer. (C) 2001 Academic Press.
Title:
Observation of a large magnetic anisotropy in the new 2H-Perovskite related oxide Ba8CoRh6O21: Magnetic measurements on aligned single crystals
Authors:
zurLoye HC. Stitzer KE. Smith MD.
Source:
Inorganic Chemistry. 40(20):5152-5156, 2001 Sep 24.
Abstract:
Single crystals of Ba8CoRh6O21, grown out of a potassium carbonate flux, were characterized by single-crystal X-ray diffraction and magnetic measurements. X-ray data were collected in a superspace group approach and solved using the JANA2000 software package. Ba8CoRh6O21 represents the first example of a structurally characterized m = 5, n = 3 member of the A(3n+3m)A ' nB3m+nO9m+6n family of 2H hexagonal perovskite related oxides and contains chains consisting of six consecutive RhO6 octahedra followed by one distorted CoO6 trigonal prism. Magnetic measurements were carried out on large aligned single crystals, and a very large magnetic anisotropy in the magnetic susceptibility, persisting up to room temperature, was observed.
Title:
Strain modulation around inclusions in an annealed natural cordierite
Authors:
Capitani GC. Doukhan JC. Malcherek T. Carpenter M.
Source:
European Journal of Mineralogy. 13(5):921-928, 2001 Sep-Oct.
Abstract:
A natural ferromagnesian cordierite which had been annealed at 1355 degreesC has been found, by TEM, to contain submicroscopic cross hatched modulated microstructures (tweed) localised near Al2O3 inclusions, while most of the sample, apart from some melting features, remained homogeneous and orthorhombic in symmetry. SAED patterns from regions with the tweed textures exhibited splitting parallel to [3 (1) over bar0]* and [110] * of the orthorhombic cell. Such features in cordierite have been interpreted in previous investigations as intermediate metastable states formed during the high-to-low transition associated with Ai,Si ordering. Such metastable states appear to be favoured in K-bearing cordierites because the substitution Si4+ + square (channel) K+ + Al3+, which increases the number of the Al-O-Al bonds, hinders the development of long range Al,Si ordering and the high-to-low transition. In the present cordierite studied here, the mechanism of modulated structure formation is most probably similar but the chemical exchange involved is different and of the type R2+ + Si4+ --> 2Al(3+) (where R2+ is an octahedral cation). This entails the presence of some Al in octahedral coordination. It is suggested that octahedral Al would stabilise the hexagonal form of cordierite.
Title:
Ab initio study of incommensurately modulated crystals
Authors:
Caracas R. Gonze X.
Source:
Computational Materials Science. 22(1-2):112-117, 2001 Nov.
Abstract:
We present an ab initio study of the average structure of some incommensurately (IC) modulated materials: K2SeO4, Mo2S3, AuTe2 (calaverite) and Pb2MgTeO6 (elpasolite structure). All the calculations are done using the local density approximation (LDA) and/or the general gradient approximation (GGA) of the density functional theory (DFT). The electronic band structures. the corresponding density of states and the valence electron density distributions are determined for all the materials. Three-dimensional representations of the valence electron density distributions help to identify the important structural groups present in the structures and the chemical bonds between the atoms. Partial valence electron density maps are generated in order to link the electronic bands to different atomic orbitals or to linear combinations of atomic orbitals. K2SeO4 and Pb2MgTeO6 are insulators. For both materials the electron band structure is made of weakly dispersive electronic bands, Mo2S3 and AuTe2 present a metallic character. Consequently for these two materials the Fermi surface has been also analyzed in order to find the instabilities and possible nesting of the Fermi surface. Results of the ab initio determination of the average structure are also reported. The accuracy of these results, compared to the experimental data. is very material-dependent, the final results varying within 1% and 10% of the experimental data. For AuTe2 the LDA gave 6-8% differences, while the GGA improved considerably the quality of the results, reducing the differences of up to 3-4%. For Mo2S3, LDA is within 2% of the experiment, while for the other materials the agreement lies between the one for AuTe2 and the one for Mo2S3. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Phosphate tungsten bronze series: crystallographic and structural properties of low-dimensional conductors [Review]
Authors:
Roussel P. Perez O. Labbe P.
Source:
Acta Crystallographica - Section B, Structural Science. 57(Part 5):603-632, 2001 Oct.
Abstract:
Phosphate tungsten bronzes have been shown to be conductors of low dimensionality. A review of the crystallographic and structural properties of this huge series of compounds is given here, corresponding to the present knowledge of the different X-ray studies and electron microscopy investigations. Three main families are described, monophosphate tungsten bronzes, A(x)(PO2)(4) (WO3)(2m), either with pentagonal tunnels (MPTBp) or with hexagonal tunnels (MPTBh), and diphosphate tungsten bronzes, A(x)(P2O4)(2) (WO3)(2m), mainly with hexagonal tunnels (DPTBh). The general aspect of these crystal structures may be described as a building of polyhedra sharing oxygen corners made of regular stacking of WO3-type slabs with a thickness function of m, joined by slices of tetrahedral PO4 phosphate or P2O7 diphosphate groups. The relations of the different slabs with respect to the basic perovskite structure are mentioned. The structural description is focused on the tilt phenomenon of the WO6 octahedra inside a slab of WO3-type. In this respect, a comparison with the different phases of the WO3 crystal structures is established. The various modes of tilting and the different possible connections between two adjacent WO3-type slabs involve a great variety of structures with different symmetries, as well as the existence of numerous twins in MPTBp's. Several phase transitions, with the appearance of diffuse scattering and modulation phenomena, were analysed by X-ray scattering measurements and through the temperature dependence of various physical properties for the MPTBp's. The role of the W displacements within the WO3-type slabs, in two modulated structures (m = 4 and m = 10), already solved, is discussed. Finally, the complexity of the structural aspects of DPTBh's is explained on the basis of the average structures which are the only ones solved. [References: 113]
Title:
Ab initio determination of the valence electron distribution in the average structure of the incommensurately modulated calaverite AuTe2
Authors:
Caracas R. Gonze X.
Source:
Acta Crystallographica - Section B, Structural Science. 57(Part 5):633-637, 2001 Oct.
Abstract:
The valence-electron density distribution of the average structure of incommensurately modulated calaverite, AuTe2, has been computed using density-functional theory. High-density regions, centered around the Au and Te atoms, are not spheric, but present charge concentrations along the Au-Te and Te-Te bonds. The electronic band structure and its corresponding density of states reveal the presence of three electronic band groups, constituted mainly by Te 5s, Au 5d and hybrids of Te 6p + Au 6s + Au 5d orbitals. The electrons belonging to the last block are responsible for the chemical bonds.
Title:
A pentagonal cluster in certain approximants to decagonal quasicrystals
Authors:
Bostrom M. Hovmoller S.
Source:
Acta Crystallographica - Section B, Structural Science. 57(Part 5):646-651, 2001 Oct.
Abstract:
A certain pentagonal cluster occurring in several approximants to the decagonal quasicrystal is discussed. The term 'cluster' is used here to denote a structure motif which is a certain assemblage of coordination polyhedra. The cluster resembles a wheel with an 'axis' and a 'tyre'. It is built up of seven intergrown icosahedra. The 'wheel cluster' builds up structures of infinite strands or nets perpendicular to the pentagonal wheel cluster axis. The wheel cluster is the main constituent of the decagonal approximant structure types Al3Mn, Al60Mn11Ni4 and Ga137Mn123.
Title:
Perchlorophenalenyl radical, C13Cl9: a modulated structure with nine threefold-symmetric molecules in the asymmetric unit
Authors:
Koutentis PA. Haddon RC. Oakley RT. Cordes AW. Brock CP.
Source:
Acta Crystallographica - Section B, Structural Science. 57(Part 5):680-691, 2001 Oct.
Abstract:
The odd-alternant perchlorophenalenyl radical, C13Cl9, forms molecular stacks centered on crystallographic threefold rotation axes, but the spacing within the stacks (3.78 Angstrom) is too large to allow good overlap of the orbitals in which the spin density is localized. The radical is ruffled because of the intramolecular repulsions between alpha Cl atoms (the Cl . . . Cl peri interactions); the average displacement of an alpha Cl atom from the molecular plane is similar to0.7 Angstrom. The deviations from molecular planarity do not, however, determine the spacing within the stacks, which is determined instead by interactions between stacks. The modulations found in the P3c1 super-structure are a response to the short interstack contacts that would occur in the average pseudocell structure (R (3) over barm, c' = c/6). The primary modulation is a pattern of enantiomeric alternation; a secondary modulation involves small rotations of the molecules around their threefold axes. The number (9) of independent molecules in the true cell is exceptionally large because of the conflict between the preference within the molecular stacks for threefold rotational symmetry and the preference in directions perpendicular to the stack axes for twofold alternation of enantiomers. The structural complexity reduces the precision of the distances and angles determined, but the average values found are in excellent agreement with those calculated by density functional theory.
Title:
On the generation of point groups in spaces of various dimensions
Authors:
Pokorny A. Herzig P. Altmann SL.
Source:
Spectrochimica Acta Part A-Molecular Spectroscopy. 57(10):1931-1939, 2001 Sep 1.
Abstract:
In this paper the use of Clifford algebra in the parametrization of point groups in spaces of various dimensions is shown. Higher-dimensional spaces are of great interest especially when modulated crystals or quasicrystals are studied. While the quaternion units, which are useful to parametrize rotations in 3 dimensions, can be identified with rotations, the basic Clifford units may be regarded as mirrors from which all proper and improper symmetry operations can be generated. The practical implementation of this method of parametrization is demonstrated for the group of the hypercube in the 4-dimensional space, and generalisations to spaces of dimensions higher than 4 are suggested. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Scaling properties of the electronic structure of quasiperiodic GaAs/AlxGa1-xAs superwires and superdots
Authors:
Ribeiro J. de Carvalho RRL. Farias GA. Freire VN. Albuquerque EL.
Source:
Physica B. 305(1):38-47, 2001 Oct.
Abstract:
We investigate the scaling properties of GaAs/AlxGa1-xAs quasiperiodic superwires (superdots) structures building up following the Fibonacci, Thue-Morse and double-period sequences of concentric cylindrical (spherical) shells. We perform a quantitative analysis on the electronic structure of their allowed bands in order to find how the scaling properties are related with the number of generations of the sequences. We show that the total allowed bandwidth (the Lebesgue measure of the energy spectrum) Delta scales as the power law Delta similar to (F-n)(-delta) for the Fibonacci sequence, where F-n is the Fibonacci number and delta is the diffusion constant of the spectra. For both the Thue-Morse and double-period sequences, the power law is given by Delta similar to (2(n))(-delta), with n being the number of the generation of the sequence. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Characterization of quasicrystalline primary intermetallic particles in Mg-8wt% Zn-4 wt% Al casting alloy
Authors:
Bourgeois L. Mendis CL. Muddle BC. Nie JF.
Source:
Philosophical Magazine Letters. 81(10):709-718, 2001 Oct.
Abstract:
The quasicrystal structure of primary intermetallic particles found in the as-cast microstructure of a permanent mould-cast Mg-8 wt% Zn-4 wt% Al alloy has been characterized using transmission electron microscopy. Most primary intermetallic particles have an average composition of Mg9+/-2Zn4+/-1Al3+/-1 and a primitive icosahedral structure, with a quasilattice parameter of 0.515 nm and a point group of m (3) over bar(5) over bar. The metastable quasicrystalline phase persists for extended periods at elevated temperatures; while the volume fraction decreases with thermal exposure at 325 degreesC, the decrease is small up to 120 h and a fraction persists after 720 h. There is no evidence of transformation of or within the quasicrystalline phase during this period. Instead, the metastable quasicrystalline phase is gradually replaced by the equilibrium Phi phase (Mg-21(Al, Zn)(17); space group, Pbcm). The relationship between the quasicrystalline phase, its cubic approximant T phase (Mg-32(Al, Zn)(49); space group, Im (3) over bar) and the Phi phase is discussed.
Title:
Transient ordering states in decagonal Al-Co-Ni and Al-Cu-Co-Si phases
Authors:
Weidner E. Frey F. Hradil K.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 81(10):2375-2389, 2001 Oct.
Abstract:
X-ray diffraction patterns of decagonal Al70Co15Ni15, Al72Ni12Co16 and Al62Cu20Co15Si3 show, apart from 'sharp' reflections, prominent diffuse maxima and diffuse streaks. From an analysis of high-resolution synchrotron data, arguments are given in favour of a more uniform interpretation of all these phenomena in terms of linear phason strain and phason fluctuations. Thus structural modifications, including one-dimensional quasicrystalline domains and periodic domains (approximants) can be conveniently described as transient ordering states, depending on temperature and composition.
Title:
An analysis of microhardness of single-quasicrystals in the Al-Cu-Co-Si system
Authors:
Mukhopadhyay NK. Weatherly GC. Embury JD.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 315(1-2):202-210, 2001 Sep 30.
Abstract:
Microhardness tests were conducted on single grain quasicrystals of the decagonal phase in a Al-Cu-Co-Si system by varying the load from 15 to 500 g on the ten-fold plane and two-fold planes. Ultrasonic tests were also performed on ten-fold plane and its perpendicular planes. No significant difference was found in the microhardness and elastic properties measured on these two planes. The microhardness was found to be load dependent, varying from 9.01 to 7.86 GPa. The variation of hardness i.e. the indentation size effect (ISE) was attributed to both elastic recovery (important at small loads) and to cracking. The cracks arising during indentation up to a 200 g load were observed to be the Palmqvist type. Lateral cracks other than Palmqvist were also observed at 300 and 500 g loads. At 15 and 25 g loads, cracks were not observed, indicating a limited amount of plasticity. At a 100 g load the four corners of the indentation yielded well-developed and symmetrical radial cracks without any lateral cracks. The fracture toughness (K-IC) was calculated from the fracture mechanics relation developed for Palmqvist type of cracking. The measured value was 1.40 +/- 0.1 MPa rootm, comparable to other data reported in the literature for quasicrystals. A simple model of cracking at indentations equating the release of stored elastic energy to the work of fracture, was used to explain the critical indentation size observed for crack nucleation. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Precipitation of icosahedral quasi crystalline phase in metallic Zr65Al7.5Ni5Cu17.5Re5 glass
Authors:
Li CF. Inoue A.
Source:
Materials Letters. 50(5-6):318-321, 2001 Sep.
Abstract:
Recently, the precipitation of an icosahedral quasicrystal line phase (I-phase) in metallic Zr65Al7.5Ni10Cu12.5M5 (M = Pd, Pt, Au and Ag) classes, which were obtained by adding noble metals to the well-known metallic Zr65Al7.5Ni10Cu17.5 glass, was reported. In the present work, the crystallization process of a metallic Zr65Al7.5Ni5Cu17.5Re5 glass, which was obtained by adding non-noble metal Re to Zr65Al7.5Ni10Cu17.5, was studied. Two exothermic peaks were observed in the differential scanning calorimetry curve of the metallic glass, of which the low temperature one corresponds to the precipitation of an I-phase. The present result demonstrates that the addition of Re is effective in promoting the precipitation of I-phase, in addition to the previously reported noble metals (Pd, Pt, An and Ag). The atomic radii of these elements are limited to the range of 0.137 to 0.144 nm, implying that atomic size is a significant factor. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Formation of nanoscale icosahedral quasicrystals and glass-forming ability in Zr-Nb-Ni-Cu-Al metallic glasses
Authors:
Fan C. Inoue A.
Source:
Scripta Materialia. 45(1):115-120, 2001 Jul 13.
Title:
Structure of the two-dimensional incommensurate charge-density wave in (PO2)(4)(WO3)(8) at 20 K - art. no. 104105
Authors:
Ludecke J. Jobst A. Geupel S. van Smaalen S.
Source:
Physical Review B. 6410(10):4105-+, 2001 Sep 1.
Abstract:
The incommensurate charge-density waves (CDW's) in the m=4 phosphate bronze (PO2)(4)(WO3)(2m) have been studied by synchrotron-radiation x-ray scattering. The CDW is found to correspond to a 2-q state for all temperatures below the first phase transition at T-c1 = 80 K. The second phase transition at T-c2 = 52 K is found to involve the development of mixed second-order satellites within the primary CDW. The incommensurately modulated structure has been determined at T=20 K. The structure remains orthorhombic down to T = 20 K. At 20 K the lattice parameters are a = 5.294(1) Angstrom, b = 6.591(2) Angstrom, and c = 17.415(16) Angstrom. The two-dimensional CDW is characterized by the modulation wave vectors (q) over right arrow (1) =[0.330(2),0.292(2),0.000(2)] and (q) over right arrow (2)=(-0.330,0.292,0). The (3+2)D superspace group was found as P2(1)2(1)2(1)(alpha,beta ,0)(-alpha,beta ,0). The, primary CDW comprises the satellite reflections (hklm(1)m(2)) with (m(1)m(2)) equal to (+/-1,0) and (0,+/-1). Below T-c2 additional satellite reflections develop, that correspond to (m(1)m(2)) = +/-(1, - 1). Accordingly, harmonic modulation amplitudes (1,0), (0, 1), and (1,- 1) were incorporated into the structure model. Refinement against 4970 observed reflection intensities resulted in a fit with R = 0.039, The periodic lattice distortion shows that the CDW is located at the centers of the WO3 slabs. The CDW is interpreted in terms of the formation of clusters of six tungsten atoms, that are linked together to form larger clusters of 12 to 18 atoms.
Title:
Irreversible dynamics in incommensurate biphenyl studied by thermocycling of spectral holes - art. no. 104203
Authors:
Zazubovich V. Suisalu A. Kikas J.
Source:
Physical Review B. 6410(10):4203-+, 2001 Sep 1.
Abstract:
Both photochemical and nonphotochemical spectral hole burning mechanisms were observed in the incommensurate phase III (ICIII) of chlorin-doped biphenyl. Distributions of corresponding energetic barriers for the back reaction were acquired from temperature cycling experiments. The non-photochemical mechanism is characterized by finite (unlike to glasses) but low (compared to the photochemical mechanism) threshold of 6-7 K and is interpreted as a photoinduced depinning-repinning of the incommensurate modulation wave. Holewidth dependence on cycling temperature up to 28 K was measured, crossing at 17 K the phase transition between two incommensurate phases in pure biphenyl. The measured irreversible hole broadening exhibits a fast (close to cubic) increase up to 17 K and then changes abruptly to a linear in the higher-temperature incommensurate phase II, which extrapolates back to zero at T -->0 K. The results support the view that ICIII is a metastable state.
Title:
Magnetic behavior of the rare-earth compounds RNiBC by neutron scattering - art. no. 104410
Authors:
Bourdarot F. Lynn JW. Baggio-Saitovitch E. Huang Q. Sanchez DR. Skanthakumar S.
Source:
Physical Review B. 6410(10):4410-+, 2001 Sep 1.
Abstract:
Neutron diffraction and small angle neutron scattering measurements have been carried out on RNiBC (R=Er, Th, Dy) to investigate the crystallography, magnetic correlations, and long range magnetic ordering. Crystallographic refinements show a strong boron-carbon and nickel-carbon bonding similar to RNiZB2C, but the rare-earth-carbon plane exhibits a buckling which does not exist in the RNi2B2C series. The magnetism in the RNiBC series is quite simple, with a magnetic moment direction going from the a-b plane to the c axis as the atomic number of the rare-earth increases. Er becomes ferromagnetic at T-C= 4.6 K, with a saturated moment of 7.2 mu (B) along the c axis. Th orders ferromagnetically at T-C= 15 K. Below 12.5 K an incommensurate modulation develops with a modulation wave vector of (0 0 1/8), as well as an antiferromagnetic component with k= (0 0 1/2). The moments, which vary in both magnitude and direction, are in the a-b plane with an average value of 7.79 mu (B). DyNiBC exhibits the same behavior, with a T-C and T-N of 17.5 and 13.5 K, respectively.
Title:
Comment on "Incommensurate composite structure of the superconductor Bi2Sr2CaCu2O8+delta" - art. no. 106501
Authors:
Grebille D. Leligny H. Perez O.
Source:
Physical Review B. 6410(10):6501-+, 2001 Sep 1.
Abstract:
J. Etrillard, P. Bourges, and C.T. Lin [Phys. Rev. B 62, 150 (2000)] compared the structural description of the aperiodic structure of the so-called high-T-c superconductor Bi-2212 in the incommensurate modulated structure model and in the composite, model. According to neutron diffraction data, they disqualified the first one. Another calculation proves that this conclusion is not justified. The structural equivalence between both descriptions is demonstrated, using previous structural results, and using the 4D formalism for aperiodic crystals. [References: 16]
Title:
Plastic deformation properties of the orthorhombic xi '-(Al-Pd-Mn) quasicrystal approximant
Authors:
Feuerbacher M. Klein H. Urban K.
Source:
Philosophical Magazine Letters. 81(9):639-647, 2001 Sep.
Abstract:
The macroscopic plastic deformation behaviour of orthorhombic xi'-(Al-Pd-Mn), an approximant of the icosahedral phase in the,Al-Pd-Mn alloy system, has been investigated in the high-temperature regime between 650 and 775 degreesC. Uniaxial deformation tests at a constant strain rate of 10(-5) s(-1) were performed on single-crystal samples. Stress relaxation tests, strain-rate changes and temperature changes were carried out in order to determine the thermodynamic activation parameters of the deformation process.
Title:
A new stacking motif in the decagonal approximant Mn3Ga5
Authors:
Uchida M. Matsui Y.
Source:
Philosophical Magazine Letters. 81(9):667-671, 2001 Sep.
Abstract:
The structure of the decagonal approximant Mn3Ga5 phase, which has previously been described in terms of an aggregation of clusters, is interpreted as a modulated structure. It basically consists of modulated layers, in which an ordering of atomic vacancies takes place in the distorted close-packed layers. A stacking motif in this phase is different from the motif that we have found in many icosahedral approximants such as the mu -Al4Mn phase. [References: 8]
Title:
Growth of Sr6Rh5O15 single crystals from high-temperature solutions: Structure determination using the traditional 3-D and the 4-D superspace group methods and magnetic measurements on oriented single crystals
Authors:
Stitzer KE. El Abed A. Darriet J. zur Loye HC.
Source:
Journal of the American Chemical Society. 123(36):8790-8796, 2001 Sep 12.
Abstract:
Single crystals of Sr6Rh5O15 were grown from a molten potassium carbonate flux. The structure was solved by both the traditional 3-D crystallographic approach and the 4-D superspace group approach using JANA2000. Both methods produced an equivalent structure determination, thereby confirming the 4-D superspace group approach as an effective structure solution method for 3-D commensurate composite structures. Sr6Rh5O15 corresponds to the n = 1, m = I member of the A(3n+3m)A ' nB3m+nO9m+6n family of 2H hexagonal perovskite-related oxides. This compound is characterized by pseudo-one-dimensional polyhedral chains of four face-sharing RhO6 octahedra followed by one RhO6 trigonal prism. These chains in turn are separated by [Sr](infinity) chains. Magnetic measurements were carried out on oriented single crystals, and a very large magnetic anisotropy in the magnetic susceptibility was observed.
Title:
Formation of nano-scale icosahedral quasicrystalline phase in amorphous Zr60Ni25Ti15 alloy
Authors:
Ma L. Wang L. Inoue A.
Source:
Journal of Materials Science Letters. 20(17):1615-1617, 2001.
Title:
Small angle neutron scattering with single grain quasicrystals
Authors:
Janot C. de Boissieu M. Agliozzo S. Loreto L. Farinato R. Sato TJ. Tsai AP. Grillo I.
Source:
Physica B. 300(1-4):52-60, 2001 Jul.
Abstract:
Icosahedral Al-Pd-Mn and decagonal Al-Ni-Co quasicrystals were investigated using small angle neutron scattering. Both isotropic and anisotropic scattering were observed. It is consistent with the existence of free volume due to dodecahedral and quasi-spherical voids in the icosahedral quasicrystal. In the decagonal specimens prismatic holes and chemical inhomogeneities seem to be responsible for scattering observed at small angles. (C) 2001 Elsevier Science BY. All rights reserved.
Title:
Quasicrystals
Authors:
Dubois JM.
Source:
Journal of Physics-Condensed Matter. 13(34):7753-7762, 2001 Aug 27.
Abstract:
This article aims at a simple introduction to the structure, properties and usefulness of quasicrystals. Since space is limited, the reader will essentially find a selection of references that may be used to obtain better insight into this rather new part of materials science.
Title:
Formation rule for Al-based ternary quasi-crystals: Example of Al-Ni-Fe decagonal phase
Authors:
Qiang JB. Wang DH. Bao CM. Wang YM. Xu WP. Song ML. Dong C.
Source:
Journal of Materials Research. 16(9):2653-2660, 2001 Sep.
Abstract:
After examining ternary Al-based quasi-crystalline phase diagrams, we pointed out that the presence of e/a-constant and e/a-variant lines is a common phenomenon. Ternary quasi-crystal compositions are located at the crossing point of these lines in ternary phase diagrams. Such an empirical rule can be used to predict the ternary quasi-crystal compositions from binary ones. We applied this rule to the Al-Fe-Ni system and clarified the decagonal phase composition zone. There are two decagonal phases, D-Al72.5Fe14.5Ni13 and D'-Al705Fe12Ni17.5, that correspond respectively to Al-Fe-based and Al-Ni-based decagonal phases in the same ternary system.
Title:
Effect of Mo addition on the formation of metastable fcc Zr2Ni and icosahedral phases in Zr-Al-Ni-Cu glassy alloy
Authors:
Saida J. Inoue A.
Source:
Japanese Journal of Applied Physics Part 2-Letters. 40(7B):L769-L772, 2001 Jul 15.
Abstract:
We investigated the transformation behavior at the initial crystallization stage in the Zr-Al-Ni-Cu-Mo glassy alloy. In the Zr65Al7.5Ni10Cu12.5Mo5 alloy, the crystallization reaction changes to two reactions and the first reaction corresponds to the nanoscale fee Zr2Ni phase formation. The two-stage crystallization reaction is also observed in the Zr65Al7.5Ni5Cu17.5Mo5 alloy, where the primary phase is the nanoscale icosahedral quasicrystalline phase. The difference in the primary phase between the two alloys is attributed to the difference in the chemical affinities of Mo with Cu and Ni. The formation of nanoscale icosahedral and fcc Zr2Ni phases leads to the hypothesis that the icosahedral short-range order exists in the glassy state of the Zr-Al-Ni-Cu alloy as a unit structure in both phases.
Title:
The Gummelt decagon as a 'quasi unit cell'
Authors:
Lord EA. Ranganathan S.
Source:
Acta Crystallographica - Section a - Foundations of Crystallography. 57(Part 5):531-539, 2001 Sep.
Abstract:
Steinhardt, Jeong, Saitoh, Tanaka, Abe & Tsai [Nature (London) (1998), 396, 55-57] have demonstrated that the structure of decagonal Al-Ni-Co can be built from overlapping clusters of a single type. The structure arises from a decoration of the decagons of a Gummelt covering. The unit (essentially a decagonal prism) was called by Steinhardt et al. a 'quasi unit cell'. In this work, a classification scheme is proposed for 'G patterns'-quasiperiodic patterns obtained by decorating a decagonal quasi unit cell. The classification makes use of the fact that G patterns can also be derived from decoration of a tiling. The tiles are analogues, for decagonal quasiperiodic patterns, of the 'asymmetric units' of a periodic pattern; they provide a simple mode of description and classification of the 'Gummelt-type structures'. Four existing models for decagonal phases are considered from this viewpoint.
Title:
Electron crystallographic image-processing investigation and superstructure determination for (Pb0.5Sr0.3Cu0.2)Sr-2(Ca0.6Sr0.4)Cu2Oy
Authors:
Liu J. Li FH. Wan ZH. Fan HF. Wu XJ. Tamura T. Tanabe K.
Source:
Acta Crystallographica - Section a - Foundations of Crystallography. 57(Part 5):540-547, 2001 Sep.
Abstract:
An electron crystallographic image-processing technique based on the combination of high-resolution electron microscopy and electron diffraction has been developed to investigate the commensurate structural modulation in the high-T-c superconductor (Pb0.5Sr0.3Cu0.2)Sr-2(Ca0.6Sr0.4)Cu2Oy. After symmetry averaging, a structure image was obtained by image deconvolution at the resolution limited by that of the electron microscope. Then phase extension was employed to enhance the image resolution up to about 1.25 Angstrom by means of the electron diffraction data corrected with an empirical method. In the final projected potential map, the occupational and/or positional modulation is clearly observed for all atoms, including oxygen. The key points of determining superstructures by the technique are studied and discussed.
Title:
Theoretical investigation of metastable Al2SiO5 polymorphs
Authors:
Oganov AR. Price GD. Brodholt JP.
Source:
Acta Crystallographica - Section a - Foundations of Crystallography. 57(Part 5):548-557, 2001 Sep.
Abstract:
Using theoretical simulations based on density functional theory within the generalized gradient approximation, a series of metastable phase transitions occurring in low-pressure Al2SiO5 polymorphs (andalusite and sillimanite) are predicted; similar results were obtained using semiclassical interatomic potentials within the ionic shell model. Soft lattice modes as well as related structural changes are analysed. For sillimanite, an isosymmetric phase transition at ca 35 GPa is predicted; an incommensurately modulated form of sillimanite can also be obtained at low temperatures and high pressures. The high-pressure isosymmetric phase contains five-coordinate Si and Al atoms. The origin of the fivefold coordination is discussed in detail. Andalusite was found to transform directly into an amorphous phase at ca 50 GPa. This study provides an insight into the nature of metastable modifications of crystal structures and the ways in which they are formed. Present results indicate the existence of a critical bonding distance, above which interatomic interactions cannot be considered as bonding. The critical distance for the Si-O bond is 2.25 Angstrom.
Title:
The structure of a decagonal Al72Ni20Co8 quasicrystal
Authors:
Takakura H. Yamamoto A. Tsai AP.
Source:
Acta Crystallographica - Section a - Foundations of Crystallography. 57(Part 5):576-585, 2001 Sep.
Abstract:
The structure of a decagonal Al72Ni20Co8 quasicrystal with space group P10(5)/mmc has been determined on the basis of a single-crystal X-ray data set using the five-dimensional description. The best-rt model structure based on a cluster model having lower symmetry than the decagonal symmetry with 103 parameters gives wR=0.045 and R=0.063 for 449 reflections. The structure is well described by the hexagon, boat and star tiling with an edge length of 6.36 Angstrom and is very consistent with recent high-resolution electron-microscopy images. The refined structure is compared with previously discussed model structures including cluster-based models having 20 Angstrom tenfold symmetric clusters.
Title:
Nomenclature of magnetic, incommensurate, composition-changed morphotropic, polytype, transient-structural and quasicrystalline phases undergoing phase transitions. II. Report of an IUCr Working Group on Phase Transition Nomenclature
Authors:
Toledano JC. Berry RS. Brown PJ. Glazer AM. Metselaar R. Pandey D. Perez-Mato JM. Roth RS. Abrahams SC.
Source:
Acta Crystallographica - Section a - Foundations of Crystallography. 57(Part 5):614-626, 2001 Sep.
Abstract:
A general nomenclature applicable to the phases that form in any sequence of transitions in the solid state has been recommended by an IUCr Working Group [Acta Cryst. (1998). A54, 1028-1033]. The six-field notation of the first Report, hereafter I, was applied to the case of structural phase transitions, i.e. to transformations resulting from temperature and/or pressure changes between two crystalline (strictly periodic) phases involving modifications to the atomic arrangement. Extensive examples that illustrate the recommendations were provided. This second Report considers, within the framework of a similar six-field notation, the more complex nomenclature of transitions involving magnetic phases, incommensurate phases and transitions that occur as a function of composition change. Extension of the nomenclature to the case of phases with less clearly established relevance to standard schemes of transition in equilibrium systems, namely polytype phases, radiation-induced and other transient phases, quasicrystalline phases and their transitions is recommended more tentatively. A uniform notation for the translational periodicity, propagation vector or wavevector for magnetic and/or incommensurate substances is specified. The notation adopted for incommensurate phases, relying partly on the existence of an average structure, is also consistent with that for commensurate phases in a sequence. The sixth field of the nomenclature is used to emphasize the special features of polytypes and transient phases. As in I, illustrative examples are provided for each category of phase sequence. [References: 53]
Title:
Local electronic density of states at the surface of the bulk quasicrystal Al70Pd20Mn10
Authors:
Hensch A. Rossner B. Bolliger B. Erbudak M.
Source:
Surface Science. 489(1-3):169-173, 2001 Aug 20.
Abstract:
At the surface of the bulk Al70Pd20Mn10 quasicrystal, different surface phases can be induced upon changing the chemical composition. Using combined Auger electron and X-ray photoelectron spectroscopy, information was obtained on the local density of states of the alloy components. In the quasicrystalline state the Mn 3d band moves away from the Fermi level thus lowering the density of states and opening the pseudogap. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Interaction of superconductivity and magnetism in borocarbide superconductors [Review]
Authors:
Muller KH. Narozhnyi VN.
Source:
Reports on Progress in Physics. 64(8):943-1008, 2001 Aug.
Abstract:
The interaction of rare-earth magnetism and superconductivity has been a topic of interest for many years. In classical magnetic superconductors (Chevrel phases, ternary rhodium borides, etc) as well as in the high-T-c cuprates the superconducting state usually coexists with antiferromagnetic order on the rare-earth sublattice. In these compounds the magnetic ordering temperature T-N is much below the superconducting transition temperature T-c. The discovery of superconducting borocarbides RT2B2C with R = Sc, Y, La, Th, Dy, Ho, Er, Tm or Lu and T = Ni, Ru, Pd or Pt (where not all of these combinations of R and T result in superconductivity) has reanimated the research on the coexistence of superconductivity and magnetic order. Most of these borocarbides crystallize in the tetragonal LuNi2B2C type structure which is an interstitial modification of the ThCr2Si2 type. Contrary to the behaviour of Cu in the cuprates Ni does not carry a magnetic moment in the borocarbides. Various types of antiferromagnetic structures on the rare-earth sublattice have been found to coexist with superconductivity in RNi2B2C for R = Tm, Er, Ho and Dy. Particularly of interest is the case of HoNi2B2C for which three different types of antiferromagnetic structures have been observed: (i) a commensurate one with Ho moments aligned ferromagnetically within layers perpendicular to the tetragonal c axis where consecutive layers are aligned in opposite directions, (ii) an incommensurate spiral along the c axis and (iii) an incommensurate a-axis-modulated structure with a modulation vector tau approximate to (0.55, 0, 0). This wave vector emerges in various RNi2B2C compounds with magnetic as well as nonmagnetic R elements and is connected with Fermi surface nesting. Both incommensurate magnetization structures have been shown to be related to the near-reentrant behaviour observed in HoNi2B2C whereas the commensurate structure coexists well with the superconducting state in this compound. The variation of T-N and T-c with the de Gennes factor can roughly be drawn on straight lines from Lu to Gd and from Lu to Tb, respectively, with the exception of Yb. Consequently, T-c > T-N holds for Tm, Er, Ho and T-c < T-N for Dy. However, the study of various pseudoquaternary (R, R')Ni2B2C compounds has shown that this so-called de Gennes scaling is not universal for the borocarbides and it breaks down in some cases, which is attributed to effects of details of the electron structure, crystalline electric fields, the difference in the R and R' ionic radii or to the effect of nonmagnetic impurities in an antiferromagnetic superconductor. In an external magnetic field some of the RNi2B2C compounds show metamagnetic transitions combined with a large negative magnetoresistance. A small net magnetization found at low temperatures and zero magnetic field in ThNi2B2C has been interpreted as weak ferromagnetism of Dzyaloshinsky-Moriya type. A similar phenomenon observed for superconducting ErNi2B2C is still under discussion. [References: 347]
Title:
Nature of e(g) electron order in La1-xSr1+xMnO4 - art. no. 095502
Authors:
Larochelle S. Mehta A. Kaneko N. Mang PK. Panchula AF. Zhou L. Arthur J. Greven M.
Source:
Physical Review Letters. 8709(9):5502-+, 2001 Aug 27.
Abstract:
X-ray scattering measurements of the low-temperature structure of La1-xSr1+xMnO4 (0.33 less than or equal to x less than or equal to 0.67) indicate the existence of three distinct regions: a disordered phase (x < 0.4), a charge-ordered phase (x <greater than or equal to> 0.5), and a mixed phase (0.4 less than or equal to x < 0.5). For x > 0.5, the modulation vector associated with the charge order is incommensurate with the lattice and depends linearly on the concentration of e(g) electrons. The primary superlattice reflections are strongly suppressed along the modulation direction and the higher harmonics are weak, implying the existence of a largely transverse and nearly sinusoidal structural distortion, consistent with a charge-density wave of the e(g) electrons.
Title:
Theoretical prospective of quasicrystals as thermoelectric materials - art. no. 094206 [Review]
Authors:
Macia E.
Source:
Physical Review B. 6409(9):4206-+, 2001 Sep 1.
Abstract:
In this work we present a theoretical study on the possible use of quasicrystals as potential thermoelectric materials. By considering a suitable model for the spectral conductivity we show that high values of the thermoelectric figure of merit, beyond the practical upper limit ZT=1, may be expected for certain quasicrystalline alloys. We also study their performance at different working temperature ranges, favoring low temperature thermoelectric applications for these materials. By comparing our analytical results with available experimental data on the transport coefficients of different quasicrystalline families. we suggest the icosahedral Cd-Yb and the dodecagonal Ta-Te binary phases as two promising candidates for further research. [References: 104]
Title:
Identification of the Brillouin zone planes in the Hume-Rothery matching rule and their role in the formation of the pseudogap from ab initio band calculations for the Al-Mg-Zn 1/1-1/1-1/1 approximant - art. no. 094207
Authors:
Sato H. Takeuchi T. Mizutani U.
Source:
Physical Review B. 6409(9):4207-+, 2001 Sep 1.
Abstract:
The Hume-Rothery matching rule has been widely used for many years as a practically useful guide to search for new quasicrystals and their approximants. In this work, we have performed the linear muffin-tin orbital atomic-sphere approximation band calculations for the nearly-free-electron-like Al30Mg40Zn30 1/1-1/1-1/1 approximant. It is shown that highly degenerate free-electron states in the vicinity of the center of (543), (710), and (550) planes, whose reciprocal lattice vectors well coincide with the Fermi diameter 2k(F) in the extended zone scheme, are all reduced to the regions centered at the point N corresponding to the center of the (110) zone planes in the reduced-zone scheme and that the lifting of these degenerate states leads to the sizable pseudogap at the Fermi level, thereby lowering the electronic energy in this system. This is, to our knowledge the first attempt to identify the Brillouin zone planes in the empirical Hume-Rothery rule and to extract their role in the formation of the pseudogap from ab initio band calculations. [References: 17]
Title:
Formation of quasicrystals and amorphous-to-quasicrystalline phase transformation kinetics in Zr65Al7.5Ni10Cu7.5Ag10 metallic glass under pressure - art. no. 094208
Authors:
Jiang JZ. Zhuang YX. Rasmussen H. Saida J. Inoue A.
Source:
Physical Review B. 6409(9):4208-+, 2001 Sep 1.
Abstract:
The effect of pressure on the formation of quasicrystals and the amorphous-to-quasicrystalline phase transformation kinetics in the supercooled liquid region for a Zr65Al7.5Ni10Cu7.5Ag10 metallic glass have been investigated by in situ high-pressure and high-temperature nonisothermal and isothermal x-ray powder diffraction measurements using synchrotron radiation, respectively. It is found that with increasing pressure, the onset temperature for the formation of quasicrystals increases with a slope of 9.4 K/GPa while the temperature interval of the stability and the average grain size of quasicrystals decrease, Atomic mobility is important for the formation of quasicrystals from the metallic glass whereas the relationship of the crystallization temperature vs pressure for the transition from the quasicrystalline state to intermetallic compounds may mainly depend on the thermodynamic potential energy barrier. To study the amorphous-to-quasicrystalline phase transformation kinetics in the metallic glass, relative volume fractions of the transferred quasicrystalline phase as a function of annealing time, obtained at 663, 673, 683, and 693 K, have been analyzed in details using 14 nucleation and growth models together with the Johnson-Mehl-Avrami model. The Avrami exponent was found to be near I at all four temperatures, also indicating that atomic diffusion might involve in the amorphous-to-quasicrystalline phase transformation for the Zr65Cu7.5Al7.5Ni10Ag10 metallic glass. It is found that the time-dependent transient nucleation is essential for the transformation and different nucleation and growth models have been critically assessed. [References: 53]
Title:
Precipitation of nano-scale icosahedral quasicrystalline phase in amorphous Hf70Ni10Pd20 alloy
Authors:
Li CF. Inoue A.
Source:
Journal of Non-Crystalline Solids. 289(1-3):163-167, 2001 Aug.
Abstract:
An amorphous Hf70Ni10Pd20 ternary alloy was prepared and its crystallization process was studied. The crystallization proceeds through two exothermic reactions, of which the low temperature one corresponds to the precipitation of an icosahedral quasicrystalline phase. Further annealing at higher temperature leads to its decomposition to stable crystalline phases, indicating the metastable character of the initial icosahedral quasicrystalline phase. In comparison with the crystallization process of other Hf-based amorphous alloys, factors affecting the precipitation of the icosahedral quasicrystalline phase in Hf-based amorphous alloy were discussed. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 7]
Title:
Neutron scattering study of the static and dynamic magnetic properties of UNi2Al3
Authors:
Hiess A. Brown PJ. Aso N. Roessli B. Bernhoeft N. Sato NK. Lander GH.
Source:
Journal of Magnetism & Magnetic Materials. 226(Part 1 Special Issue SI):54-56, 2001 May.
Abstract:
The static and dynamic magnetic properties of the heavy fermion superconductor UNi2Al3 have been studied using spherical neutron polarimetry (SNP) and three-axis spectroscopy (TAS), respectively. The SNP measurements give strong evidence that. in the incommensurate antiferromagnetic state and without applied external field. the magnetic moments lie in the basal plane with a dominant component along the a*-direction. The form of the structure is a longitudinally modulated spin-density wave. The TAS experiments reveal quasi-elastic magnetic scattering in the vicinity of the ordering wave vector. These results are compared to those determined for the isostructural compound UPd2Al3. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Field dependence of the incommensurate magnetic order in UNiGe
Authors:
Nakotte H. Chang S. Tun Z. Prokes K. Svoboda P. Sechovsky V. Bruck E.
Source:
Journal of Magnetism & Magnetic Materials. 226(Part 1 Special Issue SI):70-71, 2001 May.
Abstract:
Between 42 and 50 K, UNiGe exhibits an incommensurate phase (TIP) with q = (0, delta,delta) with a delta that is slightly larger than 1/3 in zero field. We have studied the field dependence of this magnetic structure by means of neutron diffraction on single-crystalline UNiGe. It has been found that delta increases almost linearly with decreasing temperature at fixed fields, while it is only weakly field dependent at fixed temperatures. The results favor the interpretation of the IP in terms of moment modulation instead of the previously proposed spin-slip phase. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 2]
Title:
Statics and dynamics of the magnetic soliton lattice in the high-field phase of CuGeO3
Authors:
Enderle M. Ronnow HM. McMorrow DF. Regnault LP. Vorderwisch P. Meissner M. Smeibidl P. Dhalenne G. Revcolevschi A.
Source:
Journal of Magnetism & Magnetic Materials. 226(Part 1 Special Issue SI):465-467, 2001 May.
Abstract:
Driven by antiferromagnetic quantum fluctuations on a deformable lattice, spin-Peierls systems dimerize magnetically and structurally at low temperatures. In this dimer phase all excitations with non-zero magnetization have a finite energy. The energy gain by a finite induced magnetization overcomes the energy gap at a critical magnetic field strength H-c. Above H-c, an incommensurately modulated magnetic and distortive domain wall pattern is formed. The magnetic modulation pattern and the low-energy excitation spectrum in this high-field phase of the inorganic spin-Peierls compound CuGeO3 are fully determined by elastic and inelastic neutron scattering and discussed together with theoretical predictions as well as other experimental results. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Magnetic phase diagram of UNi2Si2 under magnetic field and high-pressure
Authors:
Honda F. Oomi G. Svoboda P. Syshchenko A. Sechovsky V. Khmelevski S. Divis M. Andreev AV. Takeshita N. Mori N. Menovsky AA.
Source:
Journal of Magnetism & Magnetic Materials. 226(Part 1 Special Issue SI):585-587, 2001 May.
Abstract:
Measurements of electrical resistance under high pressure and neutron diffraction in high-magnetic field of single crystalline UNi2Si2 have been performed. We have found the analogy between the p-T and B-T magnetic phase diagrams. It is also found that the propagation vector qz of incommensurate antiferromagnetic phase decreases with increasing magnetic field. A new pronounced pressure-induced incommensurate-commensurate magnetic phase transition has been detected. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 8]
Title:
Origin of magnetism in Al-Mn and Al-Pd-Mn quasicrystals, related crystals and liquids
Authors:
de Laissardiere GT. Mayou D. Simonet V. Hippert F. Audier M. Bellissent R.
Source:
Journal of Magnetism & Magnetic Materials. 226(Part 1 Special Issue SI):1029-1031, 2001 May.
Abstract:
Whereas most of crystalline Al(Si)-Mn and Al(Si)-Pd-Mn phases are non-magnetic, measurements show the existence of localized magnetic moments on a small fraction of the Mn atoms in quasicrystals and in a few crystalline approximants. We develop a new model that shows that an indirect Mn-Mn interaction via. the conduction band is determinant for the existence or not of a magnetic moment, even when Mn-Mn distance is 5 Angstrom or more, These models allow us to understand experimental measurements. (C) 2001 Elsevier Science B.V, All rights reserved.
Title:
Neutron diffraction study of the CeFeSi-type RTiGe compounds (R=Pr, Nd, Tb-Er)
Authors:
Verniere A. Klosek V. Welter R. Venturini G. Isnard O. Malaman B.
Source:
Journal of Magnetism & Magnetic Materials. 234(2):261-273, 2001 Sep.
Abstract:
Neutron diffraction experiments were carried out on polycrystalline RTiGe (R = Pr, Nd, Tb-Er) samples. These compounds crystallise with the tetragonal CeFeSi-type structure (space group P4/nmm). This structure is closely related to the ThCr2Si2-type and can be described as "BaAl4 blocks" connected via R-R. contacts ("W blocks"). All the compounds are antiferromagnetic. PrTiGe and NdTiGe are characterised by an easy-plane sine-modulated structure characterised by a wave vector k = 0, 0, q(z) = 0.242 and 0.334 below 62 and 128 K, respectively. Below 80 K, NdTiGe exhibits a commensurate arrangement, which consists on ferromagnetic (0 0 1) Nd layers coupled anti ferromagnetically along the c direction with the sequence + + - - This commensurate magnetic ordering also occurs in TbTiGe, DyTiGe, HoTiGe and ErTiGe below 312, 185, 124 and 36K, respectively. In the first three compounds (R=Tb-Ho), the magnetic moment is aligned along the c-axis whereas it is localised in the basal plane in ErTiGe. In all the RTiGe compounds, the magnitude of the ordered moments at 2 K amounts nearly to the free ion magnetic moment (gJ) values for the respective R3+ ions. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Formation of an icosahedral quasicrystal in the Mg-Al-Pt system
Authors:
Koshikawa N. Yoda S. Edagawa K. Takeuchi S.
Source:
Japanese Journal of Applied Physics Part 2-Letters. 40(6B):L628-L630, 2001 Jun 15.
Abstract:
A Frank-Kasper-type (FK-type) icosahedral phase (i-phase) has been found to form in the Mg-Al-Pt system of Mg45Al42Pt13 composition, The i-phase is formed by heating an amorphous phase produced by a melt-spinning technique up to 673 K. We have also investigated the formation of the FK-type i-phase in the ternary Mg-Al-X (X = Co, Ni, R-h and Au) systems and rind no trace of the FK-type i-phase. The formation criteria for the FK-type i-phase have been discussed in terms of the electron number in the outer shell, the atomic size and the electronegativity of the third element in Mg-Al-X.
Title:
Phase equilibria of the SrO-Yb2O3-CuOx system in air
Authors:
Dillingham J. Wong-Ng W. Levin I.
Source:
International Journal of Inorganic Materials. 3(6):569-573, 2001 Sep.
Abstract:
The phase diagram for the SrO-Yb2O3-CuOx system was, investigated in air. The solid solution (Sr14-xYbx)Cu24Oz (0<x<less than or equal to>1) (the '14-24' phase) was the only ternary phase formed. This phase exhibits a smaller range of solid solution compared with similar phases containing larger lanthanide ions. Transmission electron microscopy (TEM) studies of (Sr,,Yb)Cu,,O, indicated that the phase was incommensurate, with the modulation wave vector q=(1/2-z)c*, z approximate to0.066. The Sr-analogs of the Ba2YbCu3O6+x high T-c superconductor and the associated BaYb2CuO5 'green phase' were not observed in the system. The ionic size of lanthanides 'R' in the SrO-R2O3-CuOx systems affects the number of compounds formed and their crystal chemistry. The phase diagrams exhibit a smaller number of solid-solution phases with decreasing size of R-cations, reflecting the lanthanide contraction. (C) 2001 Published by Elsevier Science Ltd.
Title:
"Devil's staircase"-type phase transition in NaV2O5 under high pressure - art. no. 086402
Authors:
Ohwada K. Fujii Y. Takesue N. Isobe M. Ueda Y. Nakao H. Wakabayashi Y. Murakami Y. Ito K. Amemiya Y. Fujihisa H. Aoki K. Shobu T. Noda Y. Ikeda N.
Source:
Physical Review Letters. 8708(8):6402-+, 2001 Aug 20.
Abstract:
The "devil's staircase"-type phase transition in the quarter-filled spin-ladder compound NaV2O5 has been discovered at low temperature and high pressure by synchrotron radiation x-ray diffraction. A large number of transitions are found to successively take place among higher-order commensurate phases with 2a x 2b x zc type superstructures. The observed temperature and pressure dependence of modulation wave number q(c). defined by 1/z. is well reproduced by the axial next nearest neighbor Ising model. The q(c) is suggested to reflect atomic displacements presumably coupled with charge ordering in this system.
Title:
Plane elasticity problem of two-dimensional octagonal quasicrystals and crack problem
Authors:
Zhou WM. Fan TY.
Source:
Chinese Physics. 10(8):743-747, 2001 Aug.
Abstract:
The plane elasticity theory of two-dimensional octagonal quasicrystals is developed in this paper. The plane elasticity problem of quasicrystals is reduced to a single higher-order partial differential equation by introducing a displacement function. As an example, the exact analytic solution of a Mode I Griffith crack in the material is obtained by using the Fourier transform and dual integral equations theory, then the displacement and stress fields, stress intensity factor and strain energy release rate can be calculated. The physical significance of the results relative to the phason and the difference between the mechanical behaviours of the crack problem in crystals and quasicrystals are figured out. These provide important information for studying the deformation and fracture of the new solid phase.
Title:
Transition from the incommensurately modulated structure to the lock-in phase in Co-akermanite
Authors:
Schaper AK. Schosnig M. Kutoglu A. Treutmann W. Rager H.
Source:
Acta Crystallographica - Section B, Structural Science. 57(Part 4):443-448, 2001 Aug.
Abstract:
The adaptation of the incommensurate structure modulation in Ca2COSi2O7 (dicalcium cobalt disilicate) single crystals to decreasing temperature has been examined using in situ high-resolution transmission electron microscopy and electron diffraction. The transition from the incommensurate to the commensurate lock-in phase of Co-(a) over circle ermanite exhibits a pronounced hysteresis of a highly strained metastable state with a characteristic microdomain morphology. A network of domain walls surrounding single orientation domains develops out of the room-temperature tartan pattern, the domains increase in size and their alignment changes from crystallographic to random. At 100 K the phase transition becomes almost complete. In parallel, the evolution of the modulation structure can be described by a change from a loose arrangement of octagonal tilings into a close-packed configuration of overlapping octagons in the commensurate low-temperature lock-in phase. Thereby, the octagon represents the ordered distribution of low-coordinated Ca clusters within a nanodomain extending over 4 x 4 subunits, on average [Riester et al. (2000). Z. Kristallogr. 215, 102-109]. The modulation wavevector was found to change from q(1,2) = 0.295 (a* +/- b*) at 300 K to q(1,2) = 0.320 (a* + b*) at 100 K.
Title:
Structure refinement of the layered composite crystal SC2B1.1C3.2 in a five-dimensional formalism
Authors:
Onoda M. Shi Y. Leithe-Jasper A. Tanaka T.
Source:
Acta Crystallographica - Section B, Structural Science. 57(Part 4):449-457, 2001 Aug.
Abstract:
The crystal structure of a layered compound Sc2B1.1C3.2, scandium boride carbide (M-r = 140.43), has been re-refined as a commensurate composite crystal using 1795 single-crystal Xray diffraction intensities with I > 2 sigma (I) collected by Shi, Leithe-Jasper, Bourgeois, Bando & Tanaka [(1999), J. Solid State Chem. 148, 442-449]. The crystal is composed of two layered subsystem structures, i.e. Sc-C-Sc sandwiches and graphite-like layers of the composition B1/3C2/3. The structure refinement was performed in a five-dimensional formalism based on the trigonal superspace group P(3) over bar ml (p00)(0p0)0m0. The unit cell and other crystal data are a = b = 3.387 (1), c = 6.703 (2) Angstrom. V = 66.59 (1) (3), sigma (1) = (9/7 0 0), sigma (2) = (0 9/7 0), Z = 1, D-x = 3.501 Mg m(-3). Two different three-dimensional sections through the superspace were analyzed, corresponding to two different superstructure models, one with P(3) over bar ml and the other with P3ml. A random distribution of B and C was assumed in the graphite-like laver and 41 structural parameters were introduced. R-F/wR(F) were 0.0533/0.0482 and 0.0524/0.0476, respectively, for the first and second models. Although the difference between these R-F or wR(F) values was too fine to exclude one of the models definitely, the advantages of using a superspace group were obvious. It not only brought about better convergence of refinement cycles by virtue of fewer parameters, but also gave an insight into the problem of symmetry of the superstructure.
Title:
Modulated structure of the pseudohexagonal InFe1-x-4 delta,Tix+3 delta O3+x/2 (x=0.61) composite crystal
Authors:
Michiue Y. Onoda M. Watanabe M. Brown F. Kimizuka N.
Source:
Acta Crystallographica - Section B, Structural Science. 57(Part 4):458-465, 2001 Aug.
Abstract:
The structure of pseudohexagonal-type InFe1-x-4 deltaTix+3 deltaO3+x/2 (x = 0.61, delta = 0.04), indium iron titanium oxide, was refined on the basis of a four-dimensional superspace group. The crystal has a compositely modulated structure consisting of two orthorhombic subsystems mutually incommensurate in b. The first subsystem InFe1-x-4 deltaTix+3 deltaO2 has a delafossite structure with lattice parameters a = 5.835 (3), b(1) = 3.349 (1) and c 12.082 (7) Angstrom. The second subsystem with b(2) = 2.568 (6) Angstrom consists of O atoms. The superspace group of the overall structure is Ccmm(1, 1.305, 0)s00, which can be converted to Amam(0, 0, 0.305)0s0 (No. 63.8). Refinement on 1105 unique reflections converged to R = 0.0303 and wR = 0.0325 with 63 structural parameters. The structure of the first subsystem is the alternate stacking of an edge-shared InO6 octahedral layer and an Fe/Ti triangle-lattice plane along c. A sheet of O atoms in the second subsystem is also extending on the Fe/Ti plane, where displacive modulation of atoms is prominent.
Title:
Hexagonal Frank-Kasper phases interpreted as modulated crystals
Authors:
Uchida M. Matsui Y.
Source:
Acta Crystallographica - Section B, Structural Science. 57(Part 4):466-470, 2001 Aug.
Abstract:
The structures of the hexagonal Frank-Kasper phases F and K, which have been described in terms of the aggregation of clusters. are interpreted as modulated crystal structures. They are basically composed of two close-packed layers with ordered atomic vacancies rotated by 90 degrees to each other about their normal.
Title:
Intergrowth polytypoids as modulated structures: a superspace description of the Sr-n(Nb,Ti)(n)O3n+2 compound series
Authors:
Elcoro L. Perez-Mato JM. Withers RL.
Source:
Acta Crystallographica - Section B, Structural Science. 57(Part 4):471-484, 2001 Aug.
Abstract:
A new, unified superspace approach to the structural characterization of the perovskite-related Sr-n(Nb,Ti)(n)O3n+2 compound series, strontium niobium/titanium oxide. is presented. To a first approximation, the structure of any member of this compound series can be described in terms of the stacking of (110)-bounded perovskite stabs, the number of atomic layers in a single perovskite slab varying systematically with composition. The various composition-dependent layer-stacking sequences can be interpreted in terms of the structural modulation of a common underlying average structure. The average interlayer separation distance is directly related to the average structure periodicity along the layer stacking direction, while an inherent modulation thereof is produced by the presence of different types of layers (particularly vacant layers) along this stacking direction. The fundamental atomic modulation is therefore occupational and can be described by means of crenel (step-like) functions which define occupational atomic domains in the superspace, similarly to what occurs for quasicrystals. While in a standard crystallographic approach, one must describe each structure (in particular the space group and cell parameters) separately for each composition, the proposed superspace model is essentially common to the whole compound series. The superspace symmetry group is unique, while the primary modulation wavevector and the width of some occupation domains vary linearly with composition. For each rational composition, the corresponding conventional three-dimensional space group can be derived from the common superspace group. The resultant possible three-dimensional space groups are in agreement with all the symmetries reported for members of the series. The symmetry-breaking phase transitions with temperature observed in many compounds can be explained in terms of a change in superspace group, again in common for the whole compound series. Inclusion of the incommensurate phases, present in many compounds of the series. lifts the analysis into a five-dimensional superspace. The various four-dimensional superspace groups reported for this incommensurate phase at different compositions are shown to be predictable from a proposed five-dimensional superspace group apparently common to the whole compound series. A comparison with the scarce number of refined structures in this system and the homologous (Nb,Ca)(6)Ti6O20 compound demonstrates the suitability of the proposed formalism.

Update: 9-Sep-2001

Title:
Surface plasmon-polaritons' contribution to the specific heat of quasiperiodic GaAS/SiO2 structures
Authors:
Mauriz PW. Vasconcelos MS. Albuquerque EL.
Source:
Surface Science. 482(Part 1):537-539, 2001 Jun 20.
Abstract:
It is quite interesting that the energy spectra of a variety of collective modes on quasiperiodic structures, exhibit a complex fractal profile due to the underlying long range order induced by the specific deterministic sequences used to build them up. In order to have a deep insight on the relevant thermodynamic implications of the above mentioned long range order, we have performed analytical and numerical calculations of the surface plasmon-polariton's contribution to the specific heat associated with successive hierarchical sequences of quasiperiodic Fibonacci structures. They can be traced back to the surface plasmon-polariton's self-similar energy spectra. We consider the building blocks, used to set up these structures, as the semiconductor GaAs and the insulator SiO2. At the interfaces there is a two-dimensional electron gas, modeled due to the presence of a surface density of current. We have also calculated the specific heat at the two temperature limit cases. namely when T goes to zero and infinity. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Surfactant-mediated growth of AuAl2 film on a decagonal Al72Ni12Co16 quasicrystal
Authors:
Shimoda M. Guo JQ. Sato TJ. Tsai AP.
Source:
Surface Science. 482(Part 2):784-788, 2001 Jun 20.
Abstract:
In an effort to produce an epitaxial quasicrystalline film of simple substances, Au was deposited on the quasiperiodic surface of a decagonal Al72Ni12Co16 quasicrystal. In the case of a submonolayer deposition, the Au layer is crystallized with annealing and transformed into a multiply twinned AuAl2 crystalline layer with (110)-oriented surface. This was not the case for multilayer Au. However, predeposition of In on the quasiperiodic surface affected the behavior of the Au overlayer significantly. It was found that In acted as a surfactant and promoted the epitaxial crystallization of the Au overlayer, giving rise to the formation of multiply twinned AuAl2 crystals with annealing. (C) 2001 Elsevier Science B.V. All right reserved.
Title:
Elastic waves in quasiperiodic structures
Authors:
Velasco VR. Zarate JE.
Source:
Progress in Surface Science. 67(1-8):383-402, 2001 May-Aug.
Abstract:
We study the transverse and sagittal elastic waves in different quasiperiodic structures by means of the full transfer-matrix technique and surface Green-function matching method. The quasiperiodic structures follow Fibonacci, Thue-Morse and Rudin-Shapiro sequences, respectively. We consider finite structures having stress-free bounding surfaces and different generation orders, including up to more than 1000 interfaces. We obtain the dispersion relations for elastic waves and spatial localization of the different modes. The fragmentation of the spectrum for different sequences is evident for intermediate generation orders, in the case of transverse elastic waves, whereas, for sagittal elastic waves, higher generation orders are needed to show clearly the spectrum fragmentation. The results of Fibonacci and Thue-Morse sequences exhibit similarities not present in the results of Rudin-Shapiro sequences. (C) 2001 Elsevier Science Ltd. All rights reserved.
Title:
Moser's C-line, the apparent multiplicity m ' and modules in descriptions of L-Ta2O5 and related structures
Authors:
Marinder BO.
Source:
Journal of Solid State Chemistry. 160(1):62-68, 2001 Aug.
Abstract:
Several L-Ta2O5 related phases, often classified as type I and type II structures, are described as composed of elements of alpha- and beta -U3O8 type. Published powder patterns are reindexed in a four-index notation using a modulation vector q = qb*. From the so-called C-line a relation between the apparent multiplicity m' and q is obtained: m' = 1/\2-3q\. A modified (AB) module based on the alpha -U3O8 structure, is given and used in modeling the structures. It is shown that the proportion of metal atom sites with octahedral surrounding, f(oct), is linearly related to q. (C) 2001 Academic Press.
Title:
Spin-density waves in Fe/Cr trilayers and multilayers [Review]
Authors:
Fishman RS.
Source:
Journal of Physics-Condensed Matter. 13(13):R235-R269, 2001 Apr 2.
Abstract:
This paper reviews the behaviour of spin-density waves (SDWs) in Fe/Cr trilayers and multilayers. After providing an overview of SDWs in bulk Cr, we discuss the predicted effects of SDWs on the exchange coupling of an Fe/Cr trilayer with perfect interfaces, which is nearly realized experimentally by a Cr wedge grown atop an Fe whisker and covered with a thin Fe film. While the observed phase slips in the exchange coupling are produced by transitions between collinear SDW phases with different numbers of nodes, the growth in the distance between phase slips with increasing temperature is attributed to a transition between incommensurate and commensurate SDWs. The theoretical consequences of Fe-Cr interdiffusion and interfacial steps at imperfect interfaces are then described. Whereas Fe-Cr interdiffusion causes the observed sign change in the exchange coupling, the effects of interfacial steps depend on which of the interfacial, magnetostatic, or bulk energies are dominant. For rough interfaces, the non-collinear coupling between the Fe moments can be explained by two competing models, one of which requires the formation of a non-collinear, helical SDW that is unstable in bulk Cr. Although both collinear and non-collinear SDWs have been directly observed in Fe/Cr multilayers with neutron scattering, the role of SDWs in the exchange coupling remains uncertain. This review focuses on the following open questions. Can a SDW be detected from the exchange coupling alone? What are the requirements for a non-collinear SDW in an Fe/Cr trilayer or multilayer? Can the proximity to a SDW instability be observed? Finally, what is the origin of the discrepancy between the observed exchange coupling and the much larger coupling predicted by phenomenological, tight-binding, and first-principles calculations?. [References: 158]
Title:
Magnetoresistance of an insulating quasicrystalline AlPdRe film in large magnetic fields
Authors:
Rosenbaum R. Milner A. Haberkern R. Haussler P. Palm E. Murphy T. Hannahs S. Brandt B.
Source:
Journal of Physics-Condensed Matter. 13(13):3169-3185, 2001 Apr 2.
Abstract:
A metal-insulator transition in a quasicrystalline icosahedral AlPdRe film series was recently observed. The resistance of one of the films follows an activated Mott variable-range hopping law, thus indicating insulating behaviour. The magnetoresistance (MR) ratios r = R(B, T)/R(0, T) of this insulating film exhibited large positive values at low temperatures of 93 mK and magnetic fields up to 17 T. The data are fitted using the wave function shrinkage model for insulating films, and the fits to the data above 1 K are acceptable. The low temperature MR data exhibit anomalous behaviour at high fields above 12 T, characterized by a saturation of the ratio data and followed by a turnover to smaller values. A possible explanation for the saturation of the R(B, T)/R(0, T) ratio is proposed involving a field dependence of the localization length and of the density of states, which both appear in the wave function shrinkage theory. In contrast, the weak localization theory and electron-electron interaction theory, used to describe electronic transport in metallic films, failed badly to describe the transport data of this insulating film. [References: 57]
Title:
In situ real-time analysis of the formation of a quasicrystalline phase in Al-Co multilayers by solid-state reaction
Authors:
Bergman C. Joulaud JL. Capitan M. Clugnet G. Gas P.
Source:
Journal of Non-Crystalline Solids. 287(1-3):193-196, 2001 Jul.
Abstract:
An in situ analysis of the reactions involved in the formation of decagonal Al-Co films was performed using the synchrotron radiation at ESRF taking advantage of the high-flux source and the fast detection system. The samples are Al/Co multilayers deposited by successive electron-beam evaporations of elements. The total thickness is 300 nm with a period of 60 nm and a global atomic composition of 13Al/4Co. From the initial stage of elements, the formation of the decagonal phase proceeds in three steps; the last one is the growth of the decagonal phase through a peritectoid reaction between Al9CO2 and Co. X-ray patterns were obtained following scanning and isothermal heating modes. The results obtained in the scanning mode are in very good agreement with those obtained recently by differential scanning calorimetry, ramped resistance measurements and post mortem X-ray diffraction (XRD). From isothermal anneals carried out at given temperature we characterize the kinetics of each reaction step including the growth of the quasicrystalline phase. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Dynamics in the icosahedral quasicrystal i-Al62Cu25.5Fe12.5: phonons and phasons
Authors:
Brand RA. Voss J. Calvayrac Y.
Source:
Journal of Non-Crystalline Solids. 287(1-3):210-215, 2001 Jul.
Abstract:
This work concerns both the atomic-partial phonon (vibrational) density of states (VDOS), as well as phason-hopping at high temperatures. Quasielastic Mossbauer spectroscopy (QMS) was used to probe the iron phason dynamics. Inelastic nuclear-resonant absorption (INA) of synchrotron radiation and inelastic neutron scattering (INS) were used to study the iron-partial as well as the neutron-weighted vibrational DOS, g(E). The lattice specific heat, C-latt(T), calculated from the neutron-weighted g(E) agrees with the experimental one in the low temperature range where an anomalous power law had previously been found. These results are discussed in terms of possible non-acoustic modes at low energy. We find from QMS studies that iron atoms jump two orders of magnitude slower than copper. The EFG shows a change in slope at ca. 825 K related to a transition from simple to more complicated phason jumps. These different properties are related to the specific local environments of Al, Cu and Fe in i-AlCuFe. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Fracture mode for self-fragmentation of carbon contaminated icosahedral Al-Cu-Fe quasicrystalline phase
Authors:
Song GS. Kim SH. Kim WT. Kim DH.
Source:
Journal of Materials Science Letters. 20(14):1281-1284, 2001.
Title:
Frustration in rare earth intermetallic compounds
Authors:
Gignoux D. Schmitt D.
Source:
Journal of Alloys & Compounds. 326(1-2):143-150, 2001 Aug 9.
Abstract:
The intermetallic compounds of rare earths with non-magnetic metals exhibit a large variety of magnetic behaviours arising from the competition of Iona-range exchange interactions between 4f ions in the presence of magnetocrystalline anisotropy. This competition results in frustrated magnetic states such as collinear incommensurate, helimagnetic, fan, long-period commensurate or antiphase structures. The anisotropy plays a crucial role in the existence and temperature dependence of these structures, according to the uniaxial (Ising-like) or planar (XY) character of the compounds, as well as to the Kramers or non-Kramers type of the rare earth. In some peculiar situations, mixed magnetic structures may even occur at low temperature, where two kinds of equivalent magnetic sites coexist, with a high- and a low-moment state, respectively. The addition of antiferroquadrupolar coupling may also favour multiaxial, multi-Q antiferromagnetic structures, in particular in cubic systems. In all these cases, applying a magnetic field results in magnetization processes showing a metamagnetic behaviour, with the presence of one or several well-defined plateaus separated by more or less sharp transitions. A thorough microscopic analysis of all these phenomena can be carried out by using an appropriate model, such as the self-consistent periodic field model. A few examples will illustrate the various effects of frustration in these intermetallic magnetic systems. (C) 2001 Elsevier Science BY All rights reserved.
Title:
Commensurate and incommensurate magnetic structures in rare-earth hydrides
Authors:
Vajda P. Andre G.
Source:
Journal of Alloys & Compounds. 326(1-2):151-156, 2001 Aug 9.
Abstract:
The rare-earth-hydrogen systems possess phase diagrams with rather extended solid solution (alpha -RHx) and dihydride (beta -RH2+x) regions, leading eventually - for high enough concentrations and low enough temperatures - to ordering interactions between the x-hydrogens. In the case of magnetic Rs, this gives rise to a multitude of fascinating phenomena caused by the competition between magnetic anisotropy and RKKY interactions, on the one hand, and the H-sublattice (via the crystal field), on the other. Thus, in the beta -RH2+x-phase, the excess x-hydrogens occupying the octahedral sites of the CaF2-type dihydride lattice often order in a tetragonal sublattice, of DO22 symmetry corresponding to a RH2.25 stoichiometry. This strongly modifies the various coexisting and/or overlapping commensurate and incommensurate magnetic structures present, sometimes leading to their complete disappearance or to the appearance of magnetic short-range order. Recent neutron-scattering results obtained on the systems RH(D)(2+x), with R = Tb, Dy, Ho, are given as an illustration. (C) 2001 Elsevier Science BY All rights reserved.
Title:
Internal self-ordering in In(Sb,As), (In,Ga)Sb, and (Cd,Zn,Mn)Se nano-agglomerates/quantum dots
Authors:
Mock P. Topuria T. Browning ND. Booker GR. Mason NJ. Nicholas RJ. Dobrowolska M. Lee S. Furdyna JK.
Source:
Applied Physics Letters. 79(7):946-948, 2001 Aug 13.
Abstract:
Nano-agglomerates of In(Sb,As) in InAs, (In,Ga)Sb in GaSb, and (Cd,Zn,Mn)Se in (Zn,Mn)Se are classified by transmission electron microscopy. In scanning transmission electron microscopy, atomic resolution Z-contrast images reveal different modes of internal compositional modulation on the atomic length scale, resulting for all three material systems in nano-agglomerates of an appropriate size that may constitute a new type of quantum dot. For other nano-agglomerates of In(Sb,As) in InAs and (In,Ga)Sb in GaSb, we observed a second type of nanoscale ordering that results in nano-agglomerates with an internal compositional modulation on a length scale of a few nm. Both types of compositional modulation are discussed as having arisen from a rather long-term structural response to a combination of internal and external strains. (C) 2001 American Institute of Physics.
Title:
Effects of Nb addition on icosahedral quasicrystalline phase formation and glass-forming ability of Zr-Ni-Cu-Al metallic glasses
Authors:
Fan C. Li CF. Inoue A. Haas V.
Source:
Applied Physics Letters. 79(7):1024-1026, 2001 Aug 13.
Abstract:
This work shows that the crystallization process of Zr-Ni-Cu-Al metallic glass is greatly influenced by adding Nb as an alloying element. Based on the results of the differential scanning calorimetry experiments for metallic glasses Zr69-xNbxNi10Cu12Al9 (x=0-15 at. %), the crystallization process takes place through two individual stages. For Zr69Ni10Cu12Al9 (x=0), metastable hexagonal omega -Zr and a small fraction of tetragonal Zr2Cu are precipitated upon completion of the first exothermic reaction. Contrary to this alloy, the precipitation of a nanoquasicrystalline phase is detected when 5-10 at. % Nb is added. Furthermore, the crystallization temperature T-x, supercooled liquid region DeltaT(x) and reduced temperature T-g/T-L (T-g is the glass transition temperature, T-L the liquidus temperature) increase with increasing Nb content. These results indicate that adding Nb content to Zr-Ni-Cu-Al metallic glasses not only induces quasicrystalline phase formation, but also enhances glass-forming ability. (C) 2001 American Institute of Physics.
Title:
The lock-in phase in the urotropine-sebacic acid system
Authors:
Gardon M. Schonleber A. Chapuis G. Hostettler M. Bonin M.
Source:
Acta Crystallographica - Section C - Crystal Structure Communications. 57(Part 8):936-938, 2001 Aug.
Abstract:
The 1,10-decanedioic acid-1,3,5,7-tetraazatricyclo[3.3.1.1(3,7)]decane (1/1) system, C10H18O4.C6H12N4, was studied at 215 (2) K. Its analysis provides important information with regard to the long-standing acid-carboxylate controversy in the urotropine-alkanedioic acid system. In the present structure, all the chain end-groups display a clear acid character. The asymmetric unit of this commensurate modulated phase contains two molecules of diacid as well as two molecules of urotropine. Furthermore, the chain packing suggests a possible order parameter for the lock-in transition. [References: 9]
Title:
Modular design of icosahedral metal clusters [Review]
Authors:
Bulienkov NA. Tytik DL.
Source:
Russian Chemical Bulletin. 50(1):1-19, 2001 Jan.
Abstract:
The concept of crystalline "module," that is, an unambiguously isolated, repeated quasimolecular element, is introduced. This concept is more general than the concept of crystal lattice. The generalized modular approach allows extension of the methods and principles of crystallography to quasi-crystals, clusters, amorphous solids, and periodic biological structures. Principles of construction of aperiodic, nonequilibrium regular modular structures are formulated. Limitations on the size of icosahedral clusters are due to the presence of spherical shells with non-Euclidean tetrahedral tiling in their structure. A parametric relationship between the structures of icosahedral fullerenes and metal clusters of the Chini series was found.
Title:
Pressure dependent incommensuration in Rb-IV - art. no. 055501
Authors:
McMahon MI. Rekhi S. Nelmes RJ.
Source:
Physical Review Letters. 8705(5):5501-+, 2001 Jul 30.
Abstract:
Rb-IV is found to have an incommensurate composite structure, comprising a tetragonal host framework and a simple body-centered tetragonal guest. This does not have the unexpectedly short Rb-Rb distances of the previously reported structure [U. Schwarz et al., Phys. Rev. Lett. 83, 4085 (1999)]. The ratio of the c-axis lattice parameters is strongly pressure dependent and approaches the commensurate value of 5/3 at the transition to phase V. A reversible broadening of the guest structure is observed below 16.5(2) GPa.
Title:
Structure of a cubic phase related to Cd-Mg-rare-earth quasicrystals
Authors:
Abe E. Guo JQ. Tsai AP.
Source:
Philosophical Magazine Letters. 81(8):563-568, 2001 Aug.
Abstract:
The structure of a Cd68Mg12Dy20 crystalline phase denoted as the phi -phase, which has a composition close to that of the Cd(66)Mg(21)Dv(13) icosahedral quasicrystalline phase. has been investigated by electron diffraction and scanning transmission electron microscopy (STEM). The phase has a fcc lattice with a = 21.6 Angstrom. High-angle annular dark-field STEM with Z contrast confirms that the phase has the Cd45Sm11-type structure. The atomic cluster in the structure is shown to be characterized by a Friauf polyhedron with tetrahedral symmetry.
Title:
The structure and mechanical properties of bulk Zr50Ti16.5Cu15Ni18.5 metallic glasses
Authors:
Abrosimova G. Aronin A. Matveev D. Zverkova I. Molokanov V. Pan S. Slipenyuk A.
Source:
Journal of Materials Science. 36(16):3933-3939, 2001 Aug.
Abstract:
The structure and mechanical properties of bulk Zr50Ti16.5Cu15Ni18.5 metallic glasses were studied by X-ray diffraction, scanning and transmission electron microscopy and by measurements of mechanical properties. The transition from heterogeneous to homogeneous deformation was found to occur at 575 K. The crystallization was found to begin in the testing part of the sample earlier than in the part placed in a holder during the mechanical testing. The crystallization leads to the formation of the quasicrystalline phase with a(0) = 2.54 Angstrom, hexagonal phase ZrTi(Ni,Cu) and hexagonal phase (Zr6CoAl2 type). The difference of the structure in different parts of the sample has been observed and analyzed. The deformation does not effect on the crystallization processes occurring during the tensile testing at this temperature and the crystallization proceeds owing to the self-heating of the samples during the phase transition. The correlation between mechanical properties, structure and fracture surfaces is discussed. (C) 2001 Kluwer Academic Publishers. [References: 9]
Title:
Composition modulation away from the polar direction in Pb(Sc,Nb)O-3 alloys - art. no. 060102
Authors:
George AM. Bellaiche L.
Source:
Physical Review B. 6406(6):0102-+, 2001 Aug 1.
Abstract:
A first-principles-derived approach is used to study properties of Pb(Sc,Nb)O-3 alloys that are compositionally modulated along the [001] pseudocubic direction. The direction of the local electrical polarizations is found to be spatially-dependent, and can be adjusted with the modulation parameters. Furthermore, modulated structures with large composition gradients adopt a monoclinic phase-in which the total electrical polarization lies between the [111] and [110] directions-for their ferroelectric ground state, and exhibit large electromechanical responses.
Title:
Spin waves and large electron-phonon coupling near the metal-insulator transition in hole-doped high-T-c oxides - art. no. 060507
Authors:
Jarlborg T.
Source:
Physical Review B. 6406(6):0507-+, 2001 Aug 1.
Abstract:
The effects of spin and lattice modulations on the band structure of high-T-c oxides are described, with HgBa2CuO4 as an example. A simple model for band gaps induced by potential perturbations with long-range Fourier components is applied to the barrel band. The opening of gaps is confirmed in self-consistent band calculations for modulations in elongated supercells, where spin waves and phonon coupling compete for equal q vectors. It is argued that the wavelengths of spin-wave modulations, and of the phonon modes with large coupling, depend on the doping. This mechanism supports the idea that pseudogaps are caused by stripelike spin modulations in underdoped systems, while superconductivity is attributed to enhanced electron-phonon coupling for long-wavelength phonons.
Title:
Charge/orbital ordering structure and microstructure of Pr1-xCaxMnO3 (x <= 0.5) studied by low-temperature TEM
Authors:
Asaka T. Tsutsumi S. Yamada S. Arima T. Tsuruta C. Kimoto K. Matsui Y.
Source:
Physica C. 357(Part 1):313-317, 2001 Aug.
Abstract:
The crystal structure of perovskite-type manganese oxides, Pr1-xCaMnO3 (x less than or equal to 0.5) in the charge/orbital ordering state has been investigated by means of low-temperature transmission electron microscopy (TEM). The superlattice reflection spots with wave vector a*[0,1/2,0] appear for 0.3 less than or equal to x less than or equal to 0.5 compounds below near the charge-ordering transition temperature (similar to 230 K). With further decreasing of temperature, the new structural modulation is generated additionally with the superstructure for 0.36 less than or equal to x less than or equal to 0.4 compounds. The superlattice reflections appear as sharpen spots with wave vector a*[1/4,1/4,1/2] below similar to 100 K. Such modulation structure can be interpreted in terms of ordering of d(3z2-r2)-type of e(g) electrons, which are caused by a deviation of x from 1/2, along c-axis. The relations between chemical composition and microstructures in charge-ordering phase were discussed. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Study of superconducting and non-superconducting (Cu,Cr)-1212 compounds by high-resolution TEM and electron energy loss spectroscopy
Authors:
Anan Y. Asaka T. Kurami H. Hatano J. Tsutsumi S. Kimoto K. Matsui Y.
Source:
Physica C. 357(Part 1):371-375, 2001 Aug.
Abstract:
Structure of YSr2-xBaxCu2.8Cr0.2Oy (x = 0-1.5) superconductors are examined by electron diffraction, HRTEM and electron energy loss spectroscopy (EELS). YSr2Cu2.8Cr0.2Oy (x = 0) shows incommensurate superstructure with 3.67a(0) due to lattice strain and mixed intergrowth of -(Cr-Cu-Cu-Cu-Cr)- and -(Cr-Cu-Cu-Cr)- sequences. In the h0l electron diffraction pattern the wavevector [similar to 0.27, 0, 1/2] due to the incommensurate superstructure disappear in the crystal with high Ba contain (x greater than or equal to 1.0). This suggests that structural distortion decreases with Ba substitution. At the same time, Cr-L3, L2 edge of EELS spectra shifts toward low-energy side with increase of Ba content. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 13]
Title:
Superspace group description of modulated composite crystal (Sr2Cu2O3)(0.70)CuO2, "Sr14Cu24O41" with two-legged ladder and 1D chain
Authors:
Gotoh Y. Yamaguchi I. Takahashi Y. Akimoto J. Mizuta S. Nagata T. Akimitsu J.
Source:
Physica C. 357(Part 1):384-387, 2001 Aug.
Abstract:
The modulated structure of single composite crystal, (Sr2Cu2O3)(0.70)CuO2, "Sr14Cu24O41" with two-legged Cu2O3 ladder and one dimensional CuO2 chain has been investigated by means of the X-ray diffraction method and (3+1)-dimensional superspace group approach. The model of the modulated composite structure of (Sr2Cu2O3)(0.70)CuO2 with centrosymmetric superspace group has been compared with the model with acentric superspace group. By considering all of the Sr-O lengths and the magnitude of their modulation amplitudes, it has been deduced that the atomic modulation waves with centrosymmetric symmetry are more significant for the modulated structure of (Sr2Cu2O3)(0.70)CuO2 than the waves with acentric symmetry. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 7]
Title:
Low temperature TEM study of electronic phase separation in Cr-doped Nd0.5Ca0.5MnO3
Authors:
Xu J. Matsui Y. Kimura T. Tokura Y.
Source:
Physica C. 357(Part 1):401-405, 2001 Aug.
Abstract:
The electronic phase separation in Cr-doped Nd0.5Ca0.5MnO3 single crystals is investigated by means of transmission electron microscopy at low temperatures. Both dark field and high resolution lattice images reveal the coexistence of charge ordered (CO) regions and charge disordered ferromagnetic (FM) regions below the CO temperature similar to 230 K. Long range ordered commensurate CO domains (can be larger than 100 nm) which are characterized by double periodicity with 2a spacing, only exist below the commensurate-to-incommensurate CO transition temperature similar to 130 K for 2% Cr doped sample. Short range ordered incommensurate CO nanodomains are observed to exist at higher temperature for 2% Cr doped sample and at all temperatures for 4% and 6% Cr doped samples. Antiphase boundaries which are revealed from high resolution lattice images are believed to play an important role in the evolution from commensurate-to-incommensurate CO transition, and in the nucleation of FM nanodomains. This study is a direct structure evidence for electronic phase separation in manganites. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 2]
Title:
Structural relationship between the mu phase and the lambda phase in the Al-Mn system
Authors:
Uchida M. Matsui Y.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 81(9):2121-2126, 2001 Sep.
Abstract:
A structural relationship between the mu -Al4Mn phase and the lambda -Al4Mn phase, which are approximants of icosahedral and decagonal quasicrystals respectively, was studied from the viewpoint of the modulated structure. The difference between these phases is basically understood by the difference in the ordered arrangements of atomic vacancies in the close-packed layers (or the modulation wave-vectors). The modulation is considered to be due to the rearrangement of atomic vacancies as a response to the occurrence of charge-density waves. [References: 9]
Title:
Tetrahedral structures with icosahedral order and their relation to quasicrystals
Authors:
Dmitrienko VE. Kleman M.
Source:
Crystallography Reports. 46(4):527-533, 2001 Jul-Aug.
Abstract:
The possible existence of quasicrystals in tetrahedral phases is considered. It is shown that one of the well-known crystalline silicon phases (the BC8 phase or silicon III) is characterized by the icosahedral local order with three-quarters of the interatomic bonds being directed along the fivefold axes of an icosahedron. This crystal is considered as an approximant of an icosahedral quasicrystal. Higher order approximants and other tetrahedral structures related to quasicrystals are also constructed. It is shown that in these structures, the formation of the intrinsic phason disorder with the preservation of the energetically favorable coordination number four is possible. The ab initio quantum-mechanical calculations for carbon and silicon show that, although all the considered phases are metastable, their energies only slightly differ from the energies of the corresponding stable phases. (C) 2001 MAIK "Nauka/Interperiodica".
Title:
Determination of Auger sensitivity factors for Al-rich quasicrystals
Authors:
Jenks CJ. Bloomer TE. Kramer MJ. Lograsso TA. Delaney DW. Ross AR. Sordelet DJ. Besser MF. Thiel PA.
Source:
Applied Surface Science. 180(1-2):57-64, 2001 Aug 1.
Abstract:
We discuss and compare approaches to using Auger data for semi-quantitative determination of surface compositions of Al-based quasicrystals. We have examined two quasicrystalline phases: icosahedral Al-Cu-Fe and Al-Pd-Mn. We find that sensitivity factors obtained from pure elemental standards lead to underestimation of concentrations by as much as a factor of 2.5 for the minor constituents, Fe and Mn, and to overestimation by as much as a factor of 1.2 for the major constituent, Al. Surprisingly, calibration with a crystalline phase close in composition to the quasicrystal does not necessarily lead to more accurate results. Auger analyses of fractured surfaces, which are then compared to bulk analyses, is the best option for sensitivity factor calibration. Even without absolute calibration of sensitivity factors, however, surface analysis is extremely useful for detection of secondary phases, and is superior to common bulk analysis methods. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
High-pressure x-ray diffraction of icosahedral Zr-Al-Ni-Cu-Ag quasicrystals
Authors:
Jiang JZ. Saksl K. Rasmussen H. Watanuki T. Ishimatsu N. Shimomara O.
Source:
Applied Physics Letters. 79(8):1112-1114, 2001 Aug 20.
Abstract:
The effect of pressure on the structural stability of icosahedral Zr-Al-Ni-Cu-Ag quasicrystals forming from a Zr65Al7.5Ni10Cu7.5Ag10 metallic glass with a supercooled liquid region of 44 K has been investigated by in situ high-pressure angle-dispersive x-ray powder diffraction at ambient temperature using synchrotron radiation. The icosahedral quasicrystal structure is retained up to the highest hydrostatic pressure used (approximately 28 GPa) and is reversible after decompression. The bulk modulus at zero pressure and its pressure derivative of the icosahedral Zr-Al-Ni-Cu-Ag quasicrystal are 99.10+/-1.26 GPa and 4.25+/-0.16, respectively. The compression behavior of different Bragg peaks is isotropic and the full width at half maximum of each peak remains almost unchanged during compression, indicating no anisotropic elasticity and no defects in the icosahedral Zr-Al-Ni-Cu-Ag quasicrystals induced by pressure. (C) 2001 American Institute of Physics. [References: 41]
Title:
Intermartensitic transformation and magnetic-field-induced strain in Ni52Mn24.5Ga23.5 single crystals
Authors:
Wang WH. Wu GH. Chen JL. Gao SX. Zhan WS. Wen GH. Zhang XX.
Source:
Applied Physics Letters. 79(8):1148-1150, 2001 Aug 20.
Abstract:
We have found a complete thermoelastic intermartensitic transformation between modulated and unmodulated martensite in single-crystal Ni52Mn24.5Ga23.5. This intermartensitic transformation provides a much larger strain than that of the martensitic transformation. A giant switching-like strain of +/-5.0% can be achieved by a small magnetic field of 0.2 T upon the intermartensitic transformation. In the modulated martensite, a large recoverable magnetic-field-induced strain of up to 1.2% has been obtained. (C) 2001 American Institute of Physics.
Title:
Incommensurate cooperative tilting modes of MnF6 octahedra related to the structural phase transitions in BaMnF4
Authors:
Hidaka M. Yoshimura M. Nishimori H. Fujii H. Choi JY. Park YJ. Park JH. Lee KB.
Source:
Phase Transitions. 73(4 Part A):503-522, 2001.
Abstract:
The structural phase transitions of the layer compound BaMnF4 were studied by high-resolution X-ray diffraction using synchrotron radiation. The intensities and profiles of two kinds of superlattice reflections having incommensurate reduced wave vectors q(1) = (similar to +/- 1/5,0,0)p and q(2) = (similar to +/-2/5,1/2,1/2)(p), respectively, were measured as a function of temperature from 25K to 280K. These temperature dependencies show that incommensurate structural phase transitions of second order occur at 234K and 244 K. These structural phase transitions are interpreted as successive condensations of a folding-screen-like incommensurate plane-distortion mode and a commensurate anti-ferro-distortive tilting mode of the MnF6 octahedra around the primitive a(o)- and b(o)-axes, when cooled down. It is also found that there is another structural phase transition at about 45K related to a precursor structural distortion for the antiferromagnetic transition occurring at about 26 K.
Title:
Second harmonic generation in layered TlInS2 in the vicinity of the low-temperature phase transitions
Authors:
Allakhverdiev K. Salaev E. Salaeva Z. Onari S. Kulibekov A. Mamedov T.
Source:
Phase Transitions. 73(4 Part A):579-588, 2001.
Abstract:
Second-harmonic generation in the ternary layered semiconductor T1InS(2) excited with the wavelength lambda = 1.06 mum of YAG:Nd3+ laser is investigated in the temperature range corresponding to the low-temperature phase transitions. It is shown that the intensity of the second-harmonic signal corresponding to the non-linear coefficients d(eff), d(21), d(22) reveals peculiarities close to the commensurate-incommensurate phase transitions. The temperature hysteresis of the second-harmonic signal in the low-temperature region (below and close to T-i2=206K) is explained assuming that an incomplete lock-in transition in T1InS2 takes place at T-c1 = 204 K within the temperature range between a ferroelectric (T-c2 = 201 K) and an incommensurate (T-i2 = 206 K) phases. II is shown that the monoclinic point group symmetry Ca is preserved also at temperatures lower than the phase transition temperature T-c4 = 79K to a weak ferroelectric state.
Title:
Commensurate-incommensurate transition perpendicular to chains in quasi-one-dimensional quarter-filled SDW state
Authors:
Itakura T. Suzumura Y.
Source:
Journal of the Physical Society of Japan. 70(7):2025-2032, 2001 Jul.
Abstract:
The commensurate- incommensurate transition, which occurs perpendicular to chains in quasi-one-dimensional quarter-filled spin density wave (SDW) state, has been examined within the classical treatment. By applying the renormalization group method, we derive phase diagram of commensurate and incommensurate states on the plane of temperature and the transverse misfit corresponding to the difference of phases between chains. The response functions for 2k(F) SDW and 4k(F) CDW (k(F) being the Fermi wave vector) are calculated to examine the role of the misfit and the sign of commensurability energy. The relevance to the SDW state in (TMTSF)(2)X salts is discussed.
Title:
A new crystalline phase related to an Al-Ni-Co decagonal phase
Authors:
Hiraga K. Ohsuna T. Nishimura S.
Source:
Journal of Alloys & Compounds. 325(1-2):145-150, 2001 Jul 26.
Abstract:
A new crystalline phase (called 'W-(AlNiCo) phase'), which is closely related to Al-Ni-Co decagonal quasicrystals with 0.4 nm and 0.8 nm periodicity, has been found in an Al72.5Ni7.5Co20 alloy annealed at 950 degreesC. The W-(AlNiCo) phase has a monoclinic structure with lattice parameters a=3.99 nm, b=0.82 nm, c=2.36 nm and beta =90 degrees, and the space group of Cm (No. 8). Structural characteristics of the W-(AlNiCo) phase and the resemblance to those of an Al-Ni-Co pentagonal quasicrystal are discussed from atom-scale observations using high-angle annular detector dark-held scanning transmission electron microscopy and high-resolution electron transmission microscopy. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Effect of Zn addition on the crystallization process in Zr65Al7.5Ni10Cu17.5 metallic glass
Authors:
Li CF. Inoue A.
Source:
Journal of Alloys & Compounds. 325(1-2):230-235, 2001 Jul 26.
Abstract:
Zr65Al7.5Ni10Cu12.5Zn5 and Zr65Al7.5Ni5Cu17.5Zn5 metallic glasses, which were obtained by adding Zn to the well-known glass-former Zr65Al7.5Ni10Cu17.5, were prepared by a melt-spinning method and the crystallization process was studied by differential scanning calorimetry (DSC), X-ray diffraction and transmission electron microscopy. Two exothermic peaks were observed in the DSC curves. The low temperature one corresponds to the simultaneous precipitation of an icosahedral quasicrystalline phase (I-phase) and the face centered cubic Zr2Ni (FCC-Zr2Ni) phase in the Zr65Al7.5Ni10Cu12.5Zn5 alloy. The initial precipitate for the Zr65Al7.5Ni5Cu17.5Zn5 alloy is a single I-phase. Since an I-phase does not occur in the crystallization process of Zr65Al7.5Ni10Cu17.5 metallic glass, the present results demonstrate that the addition of Zn is effective in promoting the precipitation of an I-phase, in addition to the previously reported noble metals. Further annealing leads to the precipitation of other stable crystalline phases, indicating the metastable character of the I-phase and the FCC-Zr2Ni phase. The reason for the change in the crystallization process caused by the addition of Zn was discussed on the basis of the chemical affinity and atomic radius of the constituent elements. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Formation of a single icosahedral quasicrystalline phase in Hf60Ni15Cu10Ti15 metallic glass
Authors:
Wang LM. Li CF. Inoue A.
Source:
Journal of Alloys & Compounds. 325(1-2):L7-L10, 2001 Jul 26.
Abstract:
A Hf60Ni15Cu10Ti15 metallic glass was prepared by a single roller melt-spinning method and the crystallization process was studied by differential scanning calorimetry (DSC), X-ray diffraction and transmission electron microscopy. Two exothermic peaks were observed in the DSC curve of the as-quenched ribbon, of which the low temperature one corresponds to the precipitation of a single icosahedral quasicrystalline phase (I-phase). The particle size of the I-phase is in the range of 20-40 nm. Further annealing at higher temperatures leads to the phase transformation from the I-phase to stable crystalline phases, indicating that the initial I-phase is in a metastable state. The reason for the precipitation of the I-phase from the glassy matrix was discussed based on the chemical affinity between the constituent elements. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Positron-annihilation studies of rhombic triacontahedral-type icosahedral quasicrystals and their 1/1 and 2/1 approximants in the Al-Mg-Zn alloy system - art. no. 024202
Authors:
Sato K. Uchiyama H. Takahashi Y. Kanazawa I. Suzuki R. Ohdaira T. Takeuchi T. Mizuno T. Mizutani U.
Source:
Physical Review B. 6402(2):4202-+, 2001 Jul 1.
Abstract:
Rhombic triacontahedral-type icosahedral quasicrystal and its 1/1 and 2/1 approximants in Al-Mg-Zn alloy system were systematically studied by means of positron-annihilation lifetime measurements and positron-annihilation lifetime and Doppler-broadening measurements using the slow-positron-beam technique. We could successfully derive the structural vacancy density in this alloy system. The structural vacancy densities were similar to4.56 x 10(-3) for the 1/1 approximants, 4.82x10(-3) for the 1/2 approximant, and 5.05 x 10(-3) for the icosahedral quasicrystal. In addition, the positron motions were investigated. The average positron-diffusion length, average positron-diffusion length in matrix, positron-diffusion coefficient, and positron mobility in this alloy system including the icosahedral quasicrystal were estimated. The positron-diffusion coefficients for the 1/1 approximants were almost identical (similar to1.79 cm(2) s(-1)) to each other, but decrease down to 1.61 x 10(-1) cm(2) s(-1) for the 2/1 approximant and 1.44 x 10(-1) cm(2) s(-1) for the icosahedral quasicrystal. This first experimental estimation was performed by coupling the positron-annihilation lifetime measurements to the positron-annihilation Doppler-broadening measurements using the slow-positron beam excellently. The results indicated that the thermarized positrons in matrix tend to localize as the order of the approximant increases.
Title:
Mn magnetism in icosahedral quasicrystalline Al72.4Pd20.5Mn7.1 - art. no. 024203
Authors:
Dolinsek J. Klanjsek M. Apih T. Gavilano JL. Gianno K. Ott HR. Dubois JM. Urban K.
Source:
Physical Review B. 6402(2):4203-+, 2001 Jul 1.
Abstract:
The unusual magnetism of manganese atoms in an icosahedral Al72.4Pd20.5Mn7.1 single-grain quasicrystal was studied by Al-27 nuclear magnetic resonance (NMR), magnetic susceptibility, and electrical resistivity measurements. Between room temperature and 50 K both the Al-27 NMR linewidth and the frequency shift exhibit a Curie-Weiss-type, 1/(T-theta) temperature dependence. At lower temperatures a significant narrowing of the linewidth, concomitant with a reduction of the frequency shift is observed. These features can be explained by a gradual reduction of the local exchange magnetic field at the position of the Al-27 nuclei that is transferred from the manganese d moments via the conduction electrons. Two possible origins of this phenomenon are discussed: (i) the Kondo-like screening of manganese moments by the conduction electrons and (ii) the ''resistivity'' -damping of the RKKY interaction due to increasing electron localization at low temperatures.
Title:
Formation of a dodecagonal phase in an equilibrium immiscible Co-Cu system induced by ion irradiation and associated evolution
Authors:
Li ZF. Liu BX.
Source:
Journal of Physics-Condensed Matter. 13(25):L583-L587, 2001 Jun 25.
Abstract:
Abnormal structural changes were observed in the equilibrium immiscible Co50Cu50 multilayers induced by 200 keV xenon-ion irradiation at 77 K. First, a dodecagonal quasicrystal phase was formed at an irradiation dose of 1 x 10(15) Xe+ cm(-2). Secondly, series of selected diffraction patterns taken later showed that the dodecagonal phase formed evolved to feature a high degree of ordering with increasing ion dose. Moreover, molecular dynamics simulations verified the possibility of formation of a metastable phase in the Co-Cu system. A mechanism possibly responsible for the observed structural changes upon ion irradiation is also discussed.
Title:
Transmission electron microscopy study of Y1-x square xCr2S4, x similar to 1/3 phase
Authors:
Gomez-Herrero A. Landa-Canovas AR. Johnson AWS. Otero-Diaz LC.
Source:
Journal of Alloys & Compounds. 323:86-90, 2001 Jul 12.
Abstract:
A preliminary transmission electron microscopy study of the YCr3S6 phase has been performed. The compound crystallises with an orthorhombic average structure, space group Pmnb, a = 3.385 (2) Angstrom, b = 10.847 (3) Angstrom, c = 12.701 (3) Angstrom. The average crystal structure can be related to the CaFe2O4-type. In addition, the electron diffraction patterns show a three-fold superstructure along the a axis due to an ordered occupancy of the trigonal prismatic environment position by the yttrium atoms. In some cases it has been found that the modulation is slightly incommensurate. The presence of disorder giving rise to layers of diffuse intensity perpendicular to a* is related to the electron beam interaction as well as changes in the phase of the structure modulation. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Synthesis and structure of bis(triethanolamine)europium(II) diperchlorate
Authors:
Starynowicz P.
Source:
Journal of Alloys & Compounds. 323:159-163, 2001 Jul 12.
Abstract:
The crystal structure of the title compound was determined at 293 and 100 K. The structure contains bis(triethanolamine)europium(II) cations, and perchlorate anions. The metal ion coordination environment is composed of two N and six O atoms. At room temperature, all triethanolamine molecules are partially disordered. On going to 100 K, the disorder partially disappears, giving rise to a commensurate modulation of the structure. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Study of the incommensurate-commensurate magnetic transition in HoMnO3 perovskite
Authors:
Munoz A. Alonso JA. Casais MT. Martinez-Lope MJ. Martinez JL. Fernandez MT.
Source:
Journal of Alloys & Compounds. 323:486-489, 2001 Jul 12.
Abstract:
The low-temperature magnetic structures of the orthorhombic perovskite HoMnO3 have been studied on a polycrystalline sample from neutron diffraction, specific heat and susceptibility data. With cooling, HoMnO3 exhibits three singularities at T-N = 41 K, T approximate to 26 K and T approximate to 6.5 K, which suggests a rich magnetic phase diagram. At T-N, the Mn3+ magnetic moments become ordered in an incommensurate antiferromagnetic (AFM) arrangement, defined by a (C-x,0,0) mode, adopting a modulated sinusoidal magnetic structure which becomes commensurate with the unit cell below 29 K. Finally, below 22 K, an ordered magnetic moment appears on Ho3+ cations in an antiferromagnetic arrangement defined by a (A(x),0,C-z) mode; this moment significantly increases below 6.5 K, reaching a value of 7.27(11) mu (B) at 1.8 K. The different magnetic structures are interpreted on the basis of competing superexchange interactions of opposite signs. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Acoustic phonons in the aperiodic layered crystal of Bi2Sr2CaCu2O8+delta
Authors:
Etrillard J. Bourges P. He HF. Keimer B. Liang B. Lin CT.
Source:
Europhysics Letters. 55(2):201-207, 2001 Jul.
Abstract:
We present neutron scattering investigations of the structural dynamical properties of the aperiodic layered compound, Bi2Sr2CaCu2O8+delta. Acoustic phonons behave identically around the assumed average structure Bragg reflection and around the first satellite. This observation prove that the collective dynamics related to the incommensurate structure are quite different from what is expected in a modulated incommensurate model. Our data indicate two acoustic-like longitudinal branches along the incommensurate direction. Such behavior is compatible with a composite incommensurate structure where these two Bragg peaks correspond to the main reflections of each subsystem.
Title:
Exceptional algebraic properties of the three quadratic irrationalities observed in quasicrystals
Authors:
Masakova Z. Patera J. Pelantova E.
Source:
Canadian Journal of Physics. 79(2-3):687-696, 2001 Oct.
Abstract:
There are only three irrationalities directly related to experimentally observed quasicrystals, namely, those which appear in extensions of rational numbers by root5, root2, root3. In this article, we demonstrate that the algebraically defined aperiodic point sets with precisely these three irrational numbers play an exceptional role. The exceptional role stems from the possibility of equivalent characterization of these point sets using one binary operation. [References: 8]
Title:
Local structure of amorphous Zr70Pd30 alloy studied by electron diffraction
Authors:
Takagi T. Ohkubo T. Hirotsu Y. Murty BS. Hono K. Shindo D.
Source:
Applied Physics Letters. 79(4):485-487, 2001 Jul 23.
Abstract:
The structures of melt-spun, and subsequently annealed, Zr70Pd30 alloys, which form a nanosized icosahedral quasicrystalline phase during the primary crystallization of the amorphous phase, have been investigated by means of electron-diffraction pair-distribution-function (PDF) analysis. The PDF analysis for this alloy was performed by precise measurements of elastic halo-electron-diffraction intensities. Possible structure models for as-quenched and annealed amorphous structures were constructed with the help of reverse Monte Carlo simulations. In order to obtain the local atomic structures, the Voronoi-polyhedra analysis was performed. A considerable number of icosahedral clusters with Zr atoms in the center are present in the simulated structure of the as-quenched state, and the number of the clusters increases by annealing. (C) 2001 American Institute of Physics.
Title:
T=0 phase diagram of the double-exchange model - art. no. 012416
Authors:
Chattopadhyay A. Millis AJ. Das Sarma S.
Source:
Physical Review B. 6401(1):2416-+, 2001 Jul 1.
Abstract:
We present the T=0 phase diagram of the double-exchange model (ferromagnetic Kondo lattice model) for all values of the carrier concentration n and Hund's couplng J, within dynamical mean field theory. We find that depending on the values of n and J, the ground state is either a ferromagnet, a commensurate antiferromagnet or some other incommensurate phase with intermediate wave vectors. The antiferromagnetic phase is separated by first order phase boundaries and wide regimes of phase separation. The transition from the ferromagnetic phase to an incommensurate phase is second order.
Title:
Interface-mediated structural evolution of immiscible Co-Cu multilayers upon solid-state reaction - art. no. 014102
Authors:
Li ZF. Zhang Q. Yu DP. Lin C. Liu BX.
Source:
Physical Review B. 6401(1):4102-+, 2001 Jul 1.
Abstract:
Anomalous structural evolution was observed in the Co-Cu multilayers upon solid-state reaction, i.e., the polycrystalline Co and Cu first transformed into a fee-structured Co-Cu superlattice, which later decomposed into a dodecagonal quasicrystalline phase. The interfacial free energy is thought to be the major driving force for intermixing and alloying between the nanosized Co and Cu layers in solid-state reactions. A detailed thermodynamic calculation is carried out to gain a better understanding of the observed alloying behavior. The possibility of improving the thermal stability of the Co-Cu multilayers for magnetic device application is also discussed.
Title:
Antiphase domains in plastically deformed Zn-Mg-Dy single quasicrystals - art. no. 014202
Authors:
Heggen M. Feuerbacher M. Schall P. Urban K. Wang R.
Source:
Physical Review B. 6401(1):4202-+, 2001 Jul 1.
Abstract:
The results of microstructural investigations of plastically deformed and undeformed Zn-Mg-Dy single quasicrystals by means of transmission electron microscopy are presented. Planar defects were observed in hear-treated quenched samples and in deformed samples, which could be identified as antiphase boundaries of the face-centered icosahedral structure. A strong increase of the density of antiphase boundaries during plastic deformation was observed, which could be attributed to the movement of partial dislocations. The plane normals of the antiphase boundaries were determined for differently treated samples. In heat-treated and quenched samples 90% of the plane normals were found to be parallel to fivefold directions. In deformed samples, planes perpendicular to pseudo-twofold (1/1 2/1 1/2) directions are most frequently observed. These planes are inclined by an angle of 46 degrees with respect to the [0/0 0/0 0/2] compression direction and therefore possess a high Schmid factor.
Title:
A constitutive model for quasicrystal plasticity
Authors:
Feuerbacher M. Schall P. Estrin Y. Brechet Y.
Source:
Philosophical Magazine Letters. 81(7):473-482, 2001 Jul.
Abstract:
A constitutive model for quasicrystal plastic deformation is presented. The constitutive description incorporates an order parameter that accounts for deformation-induced disordering and thermally activated reordering. An evolution equation for the order parameter constitutes part of the model. Model predictions, such as the calculated dislocation density evolution and the attendant stress-strain behaviour, are compared with experimental data. A good accord between the calculations and the experiment gives us the confidence that the model captures the salient features of quasicrystal plasticity.
Title:
Formation of a single quasicrystalline phase in an Al55Cu25.5Fe12.5Be7 alloy
Authors:
Lee SM. Kim BH. Kim SH. Kim WT. Kim DH.
Source:
Philosophical Magazine Letters. 81(7):483-493, 2001 Jul.
Abstract:
An alloy with a single quasicrystalline icosahedral phase (I phase) can be produced by partial replacement of Al with Be (7 at.%) in an Al62Cu25.5Fe12.5 alloy. The I phase nucleates first and then grows in a dendritic manner and the remaining liquid solidifies into the metastable tau phase at a later stage of solidification during conventional casting with a Cu mould. With a lower cooling rate (crucible cooling), the liquid melt solidifies into an almost single I phase without heat treatment. The present study shows that the addition of Be stabilizes the I phase and expands the I-phase region. The Al55Cu25.5Fe12.5Be7 I phase exhibits a highly ordered F-type structure like the Al-Cu-Fe I phase, and the intensities of the superlattice peaks in the electron or X-ray diffraction patterns do not vary on the addition of Be.
Title:
The anomalous behavior of Al-Cu-Fe quasicrystal during nanoindentation
Authors:
Dub SN. Milman YV. Lotsko DV. Belous AN.
Source:
Journal of Materials Science Letters. 20(11):1043-1045, 2001 Jun.
Title:
Microstructural features associated with spray atomization and deposition of Al-Mn-Cr-Si alloy
Authors:
Srivastava AK. Ojha SN. Ranganathan S.
Source:
Journal of Materials Science. 36(14):3335-3341, 2001 Jul.
Abstract:
An inert gas atomization process was employed in production of rapidly solidified powders as well as disc-shape preform by spray deposition of an Al(7)5Mn(1)0Cr(5)Si(1)0 alloy. Microstructural features of atomized powders and spray deposited preforms were evaluated by scanning and transmission electron microscopy and X-ray diffractometry techniques. Solidification structure of powders revealed cellular and dendritic morphology, depending on their size. The interdendritic regions consisted of second phase particles. In contrast the spray formed alloy exhibited microstructural homogeneity with distribution of ultra-fine second phase particles of intermetallic compound. The structure of second phase intermetallics was identified as a cubic alpha -Al(Mn,Cr)Si, in both the atomized powders and the spray-deposits. The formation of cubic phase is discussed as rational approximant structure of an icosahedral quasicrystal. (C) 2001 Kluwer Academic Publishers.
Title:
Coherent X-ray diffraction and phason fluctuations in quasicrystals
Authors:
Letoublon A. Yakhou F. Livet F. Bley F. de Boissieu M. Mancini L. Caudron R. Vettier C. Gastaldi J.
Source:
Europhysics Letters. 54(6):753-759, 2001 Jun.
Abstract:
Frozen-in phason fluctuations in single grains of icosahedral Al-Pd-Mn quasicrystals have been studied by high-resolution coherent X-ray scattering. Bragg peak widths scale as expected for a distribution of uniform phason strains. Strong relaxation of the uniform phason strain is observed after sample annealing. Large intensity fluctuations or speckle patterns are observed in the Bragg peaks due to the uniform phason strain distribution in the sample. Speckle patterns are also observed in the diffuse scattering located close to the Bragg reflections and are related to long-wavelength phason fluctuations taking place in the sample.
Title:
Incommensurate modulated magnetic structure in orthorhombic EuPdSb
Authors:
Bonville P. Hodges JA. Shirakawa M. Kasaya M. Schmitt D.
Source:
European Physical Journal B. 21(3):349-355, 2001 Jun.
Abstract:
Orthorhombic EuPdSb is known to undergo two magnetic transitions, at 12 K and at T-N similar or equal to 18 K, and in phase III (T < 12K), single crystal magnetisation data have shown that the spin structure is collinear antiferromagnetic, with magnetic moments along the crystal a axis. From a Eu-151 Mossbauer absorption study, we show that, at any temperature within phase III, all the moments have equal sizes: and that in phase II (12K < T < 18 K) the magnetic structure is modulated and incommensurate with the lattice spacings. The modulation is close to a pure sine-wave just below T-N = 18K, and it squares up as temperature is lowered. We measured the thermal variations of the first and third harmonics of the moment modulation, and we could determine the first and third harmonics of the exchange coupling. We furthermore show that the antiferromagnetic-incommensurate transition at 12 K is strongly first order, with a hysteresis of 0.05 K, and that the incommensurate-paramagnetic transition at 18 K is weakly first order. Finally, we present an explanation of the spin-flop transition observed in the single crystal magnetisation data in phase III when H parallel to a in terms of an anisotropic molecular field tenser.
Title:
Crystallography of modulated structures in superspace
Authors:
Chapuis G. Schonleber A.
Source:
Chimia. 55(6):523-527, 2001.
Abstract:
Since the discovery of X-ray diffraction, it was believed that the discrete distribution of diffracted intensities was a direct consequence of the periodic arrangement of atoms in the three dimensions of space. However, in the last thirty years many examples of new types of crystals have been found which do not fulfil this criterion but nevertheless give perfectly discrete diffraction patterns. The new category of crystals which exhibits this property is called aperiodic. It includes incommensurate crystals, quasicrystals and composite crystals. These structures are best described in superspace, an extension of the three-dimensional space up to six dimensions. Aperiodic structures can be interpreted as three-dimensional cuts of higher dimensional periodic objects. The description of an incommensurate structure in 3+1 dimensions along with the concept of symmetry in superspace is presented as an example.
Title:
Ordering principles in decagonal Al-Co-Ni quasicrystals
Authors:
Steurer W. Cervellino A. Lemster K. Ortelli S. Estermann MA.
Source:
Chimia. 55(6):528-533, 2001.
Abstract:
The discovery of quasicrystals has extended the traditional concept that crystalline matter is a periodic arrangement of identical units such as atoms or molecules. The typical quasicrystal is an intermetallic compound in which the building blocks are arranged in a non-periodic but highly ordered way. Of particular interest is the study of these ordering principles as a function of chemical composition and temperature in decagonal quasicrystals where periodic and aperiodic ordering even coexists in the same crystal structure. Structural information from diffraction experiments is the key for revealing these ordering principles and the prerequisite for a comprehensive study of the structure-property relationships. We present here the first all-inclusive in-situ high-temperature X-ray diffraction study of decagonal Al70Co12Ni18, a stable quasicrystal with a wealth of diffraction phenomena. [References: 19]
Title:
Direct observation of icosahedral cluster in Zr70Pd30 binary glassy alloy
Authors:
Saida J. Matsushita M. Inoue A.
Source:
Applied Physics Letters. 79(3):412-414, 2001 Jul 16.
Abstract:
The medium-range order in the Zr70Pd30 binary glassy alloy, where the nanoicosahedral phase precipitates as a primary phase, was examined using the high-resolution electron microscopic technique. The ordered region in the diameter of similar to2 nm was observed in the as-quenched glassy state. This region grows slightly to the diameter of 3-4 nm by annealing for 120 s at 690 K, where the amorphous structure remains. The nanobeam electron diffraction pattern taken from the medium-range order shows the fivefold symmetry, indicating that this region has the icosahedral structure. This result is recognized as a direct evidence for the existence of the icosahedral cluster in the alloy. For further annealing for 600 s at 690 K, the icosahedral quasicrystalline phase in the diameter of 5-8 nm precipitates by assimilating the icosahedral cluster. The formation of the nanoicosahedral phase originates from the existence of the quenched-in icosahedral clusters in the glassy state followed by their easy growth to the icosahedral particle without significant rearrangement of the constitutional elements. (C) 2001 American Institute of Physics.
Title:
X-ray powder diffraction study on the modulated high temperature forms of SiO2 tridymite between 110 and 220 degrees C
Authors:
Graetsch H.
Source:
Physics & Chemistry of Minerals. 28(5):313-321, 2001 Jun.
Abstract:
The crystal structure of intermediate incommensurate tridymite was refined at 150 degreesC from powder data. Upon cooling from above 220 degreesC, the basic structure with space group symmetry C222(1) is gradually distorted from orthorhombic to monoclinic symmetry. With decreasing temperature, the monoclinic angle gamma smoothly opens up to 90.3 degrees, while a displacive modulation with temperature-dependent wavelength develops. The 3 + 1 dimensional superspace group of the incommensurate phase is C112(1)(alpha beta0). The modulation mainly consists of two sinusoidal transverse displacement waves for the silicon atoms coupled to rotations of the rigid SiO4/2 tetrahedra. The wave vector is r=0.1192(1)a* - 0.0043(1)b* at 150 degreesC. Below 150 OC tridymite discontinuously transforms to another orthorhombic phase and the modulation partially locks in at the wave vector r(1) = 1/3a*. Simultaneously, an additional incommensurate modulation with r(2) = 0.0395(1)b* - 0.3882(1)c* is formed. The two-dimensional modulation does not vary significantly with the temperature.
Title:
Anisotropic magnetic phase diagram of PrB6 dominated by the O-xy antiferro-quadrupolar interaction
Authors:
Kobayashi S. Sera M. Hiroi M. Nishizaki T. Kobayashi N. Kunii S.
Source:
Journal of the Physical Society of Japan. 70(6):1721-1730, 2001 Jun.
Abstract:
We have studied the specific heat, magnetoresistance and magnetization of PrB6 which shows two successive phase ransitions at T-IC from the commensurate (C) to incommensurate (IC) magnetic phase and at TN from the IC to paramagnetic phase and obtained the magnetic phase diagram. The suppression of TN by the magnetic field shows the following anisotropy. Below similar to 12T, T-N(< 111 >) < T-N(< 110 >) < T-N(< 001 >) and above similar to 12T, T-N(< 110 >) < T-N(< 111 >) < T-N(< 001 >). T-IC is suppressed by the magnetic field for H // < 001 > and < 110 > but T-IC(< 111 >) is enhanced largely with increasing magnetic field up to similar to 10T. It was found that the IC phase is divided into two phases below and above similar to 7T for the magnetic field around the H // < 111 > direction. The anisotropy of T-N is explained by the different magnitude of tile parallel alld perpendicular magnetic susceptibility whose weights depend on the magnetic field direction. The anisotropic field dependence of T-IC at low magnetic field is explained by the different magnitude of the in-plane (H // < 110 >) and out-of-plane (H // z) perpendicular magnetic susceptibility in the C phase which originates from tile coexistence with the O-xy, quadrupole order. The small ordered moment and twofold easy axis in the C phase are explained by tile coexistence alld competition between the O-xy quadrupolar and antiferromagnetic exchange interactions in the Gamma (5) triplet ground state.
Title:
Symmetry analysis of static soliton structures and elementary excitations in incommensurately modulated crystals
Authors:
Kirschner I. Meszaros C.
Source:
Journal of Physics-Condensed Matter. 13(23):5399-5411, 2001 Jun 11.
Abstract:
The most important symmetry properties of the incommensurately modulated crystal structures are investigated by use of exact symmetry theory of quasi-one-dimensional systems in the framework of group theory, it is shown that typical characteristic formulae developed for the description of scattering cross sections of one-dimensionally modulated crystals can be directly derived by the line-group technique. A symmetry analysis of static soliton structures is performed, representing a new method for the investigation of elementary excitations of crystals modulated incommensurately. It leads to the description of symmetry breaking, to the selection rules and hints at the similarity of symmetry behaviour of static and dynamic solitons. The actual formulae for Debye-Waller factors in the case of incommensurately modulated crystals are calculated and tabulated by using generating elements of the line groups concerned.
Title:
Microstructural characterization of rapidly solidified Al-Fe-Si, Al-V-SI, and Al-Fe-V-Si alloys
Authors:
Srivastava AK. Ranganathan S.
Source:
Journal of Materials Research. 16(7):2103-2117, 2001 Jul.
Abstract:
The present study of rapidly solidified melt-spun Al80Fe14Si6 Al80V14Si6, and Al80Fe10V4Si6 alloys by electron microscopy techniques, x-ray diffractometry, and differential scanning calorimetry leads to a number of microstructural results. Coexistence of a micro-quasicrystalline state of an icosahedral phase with monoclinic theta -Al13Fe4 and hexagonal beta -Al6V in Al-Fe-Si and Al-V-Si alloys, respectively, is reported. Also, the growth morphology of the icosahedral phase surrounded by a crystalline ring was investigated in an Al-Fe-V-Si alloy. The crystalline ring has the particles of the cubic alpha -Al-12(Fe,V)(3)Si silicide phase. Evidence of irrational twinning of cubic crystals, giving rise to a symmetry not deviating much from icosahedral symmetry was found in this alloy. In all the three alloys crystalline intermetallics were elucidated in the context of rational approximants of an icosahedral quasicrystal. It was noticed that while the icosahedral phase in Al-Fe-Si and AI-V-Si alloys transforms to crystalline intermetallics at about the same temperature (approximately 610 K), the transformation of icosahedral phase in Al-Fe-V-Si alloy occurred at a relatively lower temperature (540 K). The origin of different metastable microstructures and their stability at elevated temperatures, in these alloys, are compared and discussed. [References: 68]
Title:
Phase transitions in ferromagnetic Ni2+xMn1-xGa alloys with regard for the modulation order parameter
Authors:
Buchel'nikov VD. Zayak AT. Vasil'ev AN. Dalidovich DL. Shavrov VG. Takagi T. Khovailo VV.
Source:
Journal of Experimental & Theoretical Physics. 92(6):1010-1018, 2001.
Abstract:
The phase diagram of ferromagnetic alloys Ni2+xMn1- xGa is reconstructed on the basis of temperature dependences of the resistance. It is seen from this diagram that for small x, structural transitions from the cubic to the tetragonal phase are preceded by structural transformations in the cubic phase. In the framework of the phenomenological Landau theory of phase transitions, phase diagrams of the structural and magnetic phase transitions in these alloys are analyzed with regard for the modulation order parameter. It is shown that premartensitic and postmartensitic phase transitions related to the appearance of the modulated structure can occur along with martensitic transformations. The strain and modulation order parameters substantially affect the magnetic phase transitions via the interaction with the magnetic order parameter. (C) 2001 MAIK "Nauka/ Interperiodica".
Title:
Effect of Fe substitution on the stabilization of the icosahedral phase in Al-Cu-V alloys
Authors:
Misra DK. Tiwari RS. Srivastava ON.
Source:
Crystal Research & Technology. 36(4-5):419-427, 2001.
Abstract:
The effect of Fe substitution on the formation and stabilization of icosahedral phase in AI-Cu-V alloys has been investigated by employing transmission electron microscope and X-ray diffraction. In the as quenched Al75-xCu15-xFe5V5 alloys with x=0, 5 and 10 it has: been found that grain size of icosahedral phase increases from 156nm to 0.53 mum with increasing x. All the three alloys exhibit the formation of alpha -Al and 0-Al2Cu phases along with the i-phase. The nanoquasicrystalline and alpha -Al phases: in Al75Cu15Fe5V5 alloy transform to Al7Cu2Fe phase by annealing at 550 degreesC for 4 hrs by peritectic type of reaction. A curious type of pseudo-twelve fold electron diffraction pattern devoid of any diffuse scattering has been observed in some local regions of AI,,Cu,,Fe,V, alloy. The angles and details of twelve sectors are varying alternatively. A plausible explanation in terms of microtwin domains of 0-Al2Cu structure in [(1) over bar 10] orientation has been given to explain the characteristic features of the pseudo-twelve fold pattern. [References: 19]
Title:
Kinetic evidence for the structural similarity between a supercooled liquid and an icosahedral phase in Zr65Al7.5Ni10Cu12.5Ag5 bulk metallic glass
Authors:
Chen MW. Dutta I. Zhang T. Inoue A. Sakurai T.
Source:
Applied Physics Letters. 79(1):42-44, 2001 Jul 2.
Abstract:
By differential scanning calorimetric measurement, the kinetics of the phase transformation present in Zr65Al7.5Ni10Cu12.5Ag5 bulk metallic glass during continuous heating was investigated. It was found that the effective activation energy from a supercooled liquid to an icosahedral quasicrystalline phase is much lower than that from the supercooled liquid to eutectic crystalline phases. In addition, the activation energy from the icosahedral phase to the crystalline phases is almost the same as that from the supercooled liquid to the crystalline phases. Both of them support that the local atomic structure is similar for the supercooled liquid and the icosahedral phase in the bulk metallic glass. (C) 2001 American Institute of Physics.
Title:
Nanostructural study of the charge ordering vs. x and T in the Cr doped Pr0.5Ca0.5Mn1-xCrxO3 manganites
Authors:
Hervieu M. Martin C. Barnabe A. Maignan A. Mahendiran R. Hardy V.
Source:
Solid State Sciences. 3(4):391-406, 2001 May.
Abstract:
This paper presents the nanostructural characterisation of the Cr doping effect in Pr0.5Ca0.5Mn1-xCrxO3, x ranging from 0 to 0.1, by using electron microscopy techniques. This study carried out at room and low temperatures showed that the Pnma-type distortion of the perovskite cell is retained for 0 less than or equal to x less than or equal to 0.1 and that the different species (Mn, Cr) can be considered as randomly distributed. Increasing the Cr content does not induce specific extended defects. At 92 K, due to charge ordering effect, an incommensurate modulated superstructure is observed, characterised by a q value decreasing with x. For x = 0.05, considered as the "limit" composition of the charge ordered phase, three classes of crystallites have been observed. The impurity effect in the low temperature form is analysed and the charge ordering has been characterised, in the x = 0.02 Field Cooled and Zero Field Cooled crystallites. These observations are discussed in relations with the magnetotransport and magnetic studies. They support that I-M transition in absence of external magnetic field in Pr0.5Ca0.5Mn1-xCrxO3 is brought by percolation of ferromagnetic clusters in the charge ordered antiferromagnetic background. The charge ordered antiferromagnetic background diminishes and the size of FM clusters increases with increasing x. (C) 2001 Editions scientifiques et medicales Elsevier SAS. All rights reserved.
Title:
Theory of diffuse scattering of quasicrystals due to fluctuations of thermalised phonons and phasons
Authors:
Wang RH. Hu CZ. Lei JL.
Source:
Physica Status Solidi B-Basic Research. 225(1):21-34, 2001 May.
Abstract:
General theory of diffuse scattering of quasicrystals at high temperature due to thermally equilibrated phonon and phason fluctuations has been developed using three different methods. These methods give same results and these results are modifications of those put forward by Jaric and Nelson [Phys. Rev. B 37, 4458 (1988)]. The formulas derived here are not limited to simple quasilattice and may be used for any decorated quasicrystals. At low temperature T, phonon fluctuation is equilibrated under frozen phason-type displacement field. By supposing that this frozen phason-type field was equilibrated at some high temperature T-q (quenched phasons), formulas of diffuse scattering at T are derived. These formulas evolve automatically into those of thermally equilibrated phasons when T is equal to T-q.
Title:
Fibonacci, Koch, and Penrose structures: Spectrum of finite subsystems in three-dimensional space
Authors:
de Prunele E. Bouju X.
Source:
Physica Status Solidi B-Basic Research. 225(1):95-114, 2001 May.
Abstract:
The electronic eigenvalues and eigenstates of finite Fibonacci, Koch, and Penrose structures are studied on the basis of a recently proposed three-dimensional solvable model [J. Phys. A 30, 7831 (1997)]. This model allows to take into account explicitly the geometry of the aperiodic structures in three-dimensional space and involves no assumption such as the coupling of nearest-neighbouring atoms only.
Title:
Diffusive motions in crystalline AlCuNi by neutron quasielastic scattering
Authors:
Howells WS. Dahlborg U. Calvo-Dahlborg M. Dubois JM.
Source:
Physica B. 301(1-2):78-82, 2001 Jul.
Abstract:
Quasi-elastic neutron scattering experiments have been performed on the Al50Cu35Ni15 alloy on the IRIS spectrometer at ISIS and on the MIBEMOL spectrometer at LLB, Saclay. The aim was to investigate if atomic hopping motions are restricted to occur in systems with quasicrystalline local order. It is found that frequent jumps of Cu and Ni atoms between different interstitial lattice positions on the time scale 1-100 ps are taking place in this alloy at high temperature, This is the same time scale that has been found earlier in quasicrystals and it suggests that this kind of motion is likely to take place in any metallic alloy at high temperature and that it is not a special property of quasicrystals. (C) 2001 Elsevier Science B,V. All rights reserved. [References: 4]
Title:
Modeling the electronic transport properties of Al-Cu-Fe phases
Authors:
Landauro CV. Solbrig H.
Source:
Physica B. 301(3-4):267-275, 2001 Aug.
Abstract:
The temperature dependence of transport coefficients is theoretically examined for Al-Cu-Fe phases. We investigate the electronic conductivity, the thermoelectric power, the Hall coefficient, the thermalconductivity, and the Lorenz number. The spectral dependence of the resistivity is modeled by means of a wide and a narrow Lorentzian in accordance with results of ab initio calculations (LMTO-ASA, Kubo-Greenwood formula). This model extracts those properties from the ab initio results which are indispensables to consistently explain the transport coefficients mentioned above. Sub-diffusive transport is found in our ab initio results. The validities of both the Matthiessen rule and the Wiedemann-Franz law are analyzed. We generalize to the bulk quasicrystal where the narrow Lorentzian is found to become more pronounced than in the (1/1) approximant. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
NiAs/Ni2In-type phase Ni1+xSn (0.35x0.45) with incommensurate occupational ordering of Ni
Authors:
Leineweber A. Ellner M. Mittemeijer EJ.
Source:
Journal of Solid State Chemistry. 159(1):191-197, 2001 Jun.
Abstract:
The previously reported, ordered low-temperature NiAs/Ni2In-type phase Ni1+xSn comprises in the concentration range 0.35 < x < 0.53 in fact two separate, ordered phases. Both phases are based on a NiAs-type arrangement, "NiSn," with the additional Ni atoms distributed over the trigonal-bipyramidal interstitial sites in an ordered way, Around the ideal composition Ni3Sn2 (0.45 < x < 0.53), the earlier reported commensurate structure occurs, termed the "LT phase," in which the long-range ordering leads to Pbnm symmetry with unit cell parameters a(LT) approximate to 2a(HT), b(LT) approximate to 3(1/2)a(HT), c(LT) approximate to c(HT), where the subscript I-IT refers to the corresponding, disordered hexagonal high-temperature phase. For lower Ni contents (0.35 < x < 0.45) an incommensurate phase, that is termed "LT' phase," occurs with a crystal structure closely related to the LT phase. According to X-ray powder diffraction and selected area electron diffraction analyses, the average unit cell exhibits orthorhombic Cmcm symmetry, has unit cell parameters a(orth) approximate to a(HT), b(orth) approximate to 3(1/2)b(HT), c(orth) approximate to c(HT), and a modulation vector (q) over right arrow = alpha(a) over right arrow*(orth) with alpha approximate to 0.493 for x = 0.44 and alpha approximate to 0.428 for x = 0.35, The LT phase may be regarded as a "lock-in" phase of the LT' phase with alpha = 1/2 A model for the long-range occupational ordering of Ni on the trigonal-bipyramidal interstitial sites has been suggested. (C) 2001 Academic Press.
Title:
Refinement of modulated structures against X-ray powder diffraction data with JANA2000
Authors:
Dusek M. Petricek V. Wunschel M. Dinnebier RE. van Smaalen S.
Source:
Journal of Applied Crystallography. 34(Part 3):398-404, 2001 Jun.
Abstract:
JANA is a computer program for the refinement and analysis of periodic and aperiodic (incommensurately modulated structures and composite crystals) crystal structures. Here a new module is introduced that allows Rietveld refinements against powder diffraction data. It is shown that JANA2000 provides a state-of-the-art description of the peak profiles. A re-analysis of the low-temperature structure of (CO)(x)C-60 showed that the application of icosahedral symmetry restrictions to the C-60 molecule leads to a better description of the electron density and to a corrected position of the CO molecule as compared with a rigid-body refinement. The incommensurately modulated structure of NbTe4 has been successfully refined against X-ray powder diffraction data. The structural parameters are equal to, but less accurate, than the parameters obtained from a single-crystal study.
Title:
Magnetic structures of the TbCuSb2 compound
Authors:
Kolenda M. Oles A. Szytula A.
Source:
Journal of Alloys & Compounds. 322(1-2):55-58, 2001 Jun 28.
Abstract:
Results of neutron diffraction measurements carried out for the TbCuSb2 compound are reported. This compound crystallizes in the tetragonal ZrCuSi2-type crystal structure and is an antiferromagnet below 9 K. The magnetic order at T=1.4 K is collinear, described by the propagation vector k=(1/2, 0, 0). With an increasing temperature, near T-t=5 K the magnetic structure changes to a collinear one with k=(0, 1/4, 1/2). Near the temperature of the phase transition, T(t)approximate to5 K the new phase which is probably sine wave modulated described by the propagation vector k=(0.423(1), 0, 0). (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Crack and indentation problems for one-dimensional hexagonal quasicrystals
Authors:
Peng YZ. Fan TY.
Source:
European Physical Journal B. 21(1):39-44, 2001 May.
Abstract:
In this paper we develop a general method to solve elastic three-dimensional problems for one-dimensional hexagonal quasicrystals with point groups 6mm, 62(h)2(h), (6) over bar m2(h) and 6/mmm, including crack and indentation problems. Exact solutions are obtained by using Fourier series and Hankel transform methods. These results automatically reduce to those in the classical elasticity theory when the phason field is absent.
Title:
Dynamical properties of three component Fibonacci quasicrystal
Authors:
Ghosh A.
Source:
European Physical Journal B. 21(1):45-51, 2001 May.
Abstract:
We present a real space renormalization group (RSRG) method to study the lattice dynamics of a three component Fibonacci (3CF) quasicrystal. Phonon dispersion relations corresponding to different models of this lattice are obtained. Some features of the phonon dispersion curves are compared with experiments on real quasicrystal. It is observed that the positions of the strongest Bragg peaks calculated analytically are in perfect agreement with our RSRG calculations.
Title:
Introduction to a general crystallography
Authors:
Janner A.
Source:
Acta Crystallographica - Section a - Foundations of Crystallography. 57(Part 4):378-388, 2001 Jul.
Abstract:
The definition of an extended crystallographic group is given, based on an n-dimensional Euclidean space, carrier of a faithful integral representation of a permutation group of atomic positions. The Euclidean crystallography of normal crystals and the higher-dimensional one applied to incommensurately modulated crystals, intergrowth crystals and quasicrystals are special cases of a general crystallography. The same is true for the multimetrical crystallographic characterization of ice and of snow crystals. This approach can also be applied to single molecules, leading to what may be denoted as molecular crystallography. It possibly allows non-trivial structural relations between atomic positions belonging to the asymmetric unit of the molecular point group to be obtained. Two simple molecules, polycyclic aromatic hydrocarbons, are treated as illustrative examples.
Title:
The joint probability distributions of structure-factor doublets in displacive incommensurately modulated structures and their applicability to direct methods
Authors:
Peschar R. Israel R. Beurskens PT.
Source:
Acta Crystallographica - Section a - Foundations of Crystallography. 57(Part 4):461-472, 2001 Jul.
Abstract:
In 1993, alternative normalized structure factors for incommensurately modulated structures were defined [Lam, Beurskens & van Smaalen (1993). Acta Cryst. A49, 709-721]. The probability distribution associated with the structure invariants E(-H)E(H')E(H - H') has approximately the same functional form as the Cochran distribution. It was shown, however, that triplet-phase relations are relatively less reliable when satellites are involved [de Gelder, Israel, Lam, Beurskens, van Smaalen, Fu & Fan (1996). Acta Cryst. A52, 947-954]. In the present paper, an alternative approach is presented: instead of studying the distribution of a three-phase invariant, the probability distribution of the phase sum of two first-order satellite reflections (h,k,l,1 and h', k',l', - 1) has been derived under the assumption that the phase of the associated main reflection (h + '0,k + k',l + l',0) can be calculated from the known main (or averaged) structure. Intensive tests with randomly generated artificial structures and one real structure show a significant improvement of direct-methods phase-sum statistics. Functional similarities with conventional direct methods, employing normalized structure factors and the Cochran distribution, are discussed.
Title:
Metastable phases, quasicrystals and solid solutions in Zr-based bulk glass-forming alloys
Authors:
Yavari AR. Inoue A. Zhang T. Botta WJ. Kvick A.
Source:
Scripta Materialia. 44(8-9):1239-1244, 2001 May 18.
Title:
Nano icosahedral phase formation by crystallization of Zr-based ternary glassy alloys
Authors:
Saida J. Matsushita M. Inoue A.
Source:
Scripta Materialia. 44(8-9):1245-1249, 2001 May 18.
Title:
Precipitation of nano-scale icosahedral quasicrystalline phase in Hf-Al-Ni-Cu metallic glass promoted by addition of Ti
Authors:
Li CF. Saida J. Inoue A.
Source:
Scripta Materialia. 44(8-9):1257-1260, 2001 May 18.
Title:
Preparation and mechanical properties of nanoquasicrystalline base bulk alloys
Authors:
Inoue A. Zhang T. Ishihara S. Saida J. Matsushita M.
Source:
Scripta Materialia. 44(8-9):1615-1619, 2001 May 18.
Title:
Development of nano-sized (icosahedral phase plus (Ti,Zr) solid solution) two phase microstructures by mechanical alloying
Authors:
Yi S. Kim KB. Kim WT. Kim DH.
Source:
Scripta Materialia. 44(8-9):1757-1760, 2001 May 18.
Title:
Melting behaviour of bismuth nanoparticles embedded in Al-Cu-Fe quasicrystalline matrix
Authors:
Singh A. Tsai AP.
Source:
Scripta Materialia. 44(8-9):2005-2008, 2001 May 18.
Title:
Environmental structural studies in amorphous and quasicrystalline Zr70Al6Ni10Pt14 alloys
Authors:
Matsubara E. Sakurai M. Nakamura T. Imafuku M. Sato S. Saida J. Inoue A.
Source:
Scripta Materialia. 44(8-9):2297-2301, 2001 May 18.
Title:
Effects of nonsinusoidal character of atomic modulation on NQR spin-lattice relaxation time of incommensurate phases - art. no. 224411
Authors:
Perez SC. Schurrer C. Wolfenson A.
Source:
Physical Review B. 6322(22):4411-+, 2001 Jun 1.
Abstract:
The present work is an extention of the theoretical calculation developed by Blinc to explain the temperature and frequency dependence of the spin-lattice relaxation time in incommensurate phases. We have evaluated the influence of the nonsinusoidal character of the atomic modulation, in the linear approximation, over the NQR spectra and over the spin-lattice relaxation due to direct and Raman processes. It is shown that the peak with lower intensity in the NQR spectra always has a larger T-1 and viceversa. The results have been applied to bis(4-chlorophenyl)sulfone T-1 and line-shape data. The temperature and frequency dependence of T-1 are well reproduced if Raman processes are considered.
Title:
The structure modulation in the Bi2Sr4Fe2O10 compound
Authors:
Sedykh V. Smirnova IS. Bagautdinov B. Hagiya K. Ohmasa M. Suvorov EV. Dubovitskii AV. Shekhtman VS.
Source:
Physica C. 355(1-2):87-96, 2001 Jun 1.
Abstract:
The influence of the extra Sr layer introduced into Bi2Sr3Fe2O9 (the obtained Bi2Sr4Fe2O10 compound) on the structure modulation has been investigated by X-ray diffraction analysis, electron microscopy and Mossbauer spectroscopy. It has been found that the obtained single crystals are characterized by the averaged orthorhombic cell with the lattice parameters a = 5.4227(7) Angstrom, b = 5.4248(8) Angstrom and c = 18.600(3) Angstrom and two-component modulations of the structure with the vector (0,1 1/4.97, 1/2). The real structure of the compound consists of domains tilted relative to each other by 90 degrees around the c-axis. (C) 2001 Elsevier Science B,V. All rights reserved.
Title:
Ordered structures in decagonal quasicrystals with simple and body-centered hypercubic lattices
Authors:
Hiraga K. Ohsuna T. Sun W.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 312(1-2):1-8, 2001 Aug 15.
Abstract:
Ordered structures in decagonal quasicrystals are discussed by the projection of five-dimensional periodic lattices on two-dimensional space. Superlattices in rhombic and pentagonal Penrose lattices can be derived from simple and body-centered hypercubic lattices, respectively. The superlattices are compared with ordered structures observed in AI-Ni-Co and Al-Ni-Ru decagonal quasicrystals in which two types of atom clusters with different orientations of pentagonal symmetry are placed at lattice points in pentagonal or rhombic quasiperiodic lattices with definite ordered manners. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Nanoquasicrystallization of Zr-based metallic glasses
Authors:
Murty BS. Hono K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 312(1-2):253-261, 2001 Aug 15.
Abstract:
Nanoquasicrystallization occurs in a number of Zr based metallic glasses. This paper reviews the influence of various elements on the icosahedral phase formation in Zr-based metallic glasses in order to understand the necessary conditions for nanoquasicrystallization. Icosahedral phase is stabilized in Zr65-xCu27.5Al7.5Ox alloys beyond a critical oxygen level, suggesting that oxygen is a factor to stabilize icosahedral phase formation in Zr-Cu(-Ni)-Al based metallic glasses. On the other hand, Zr-based alloys containing Pd do not require oxygen for icosahedral phase formation. In the presence of Pd, even binary Zr100-xPdx (x = 30 and 35) alloys show nanoquasicrystallizaiton in the course of amorphous to crystal transformation. Based on our recent results together with other published investigations, the necessary conditions for quasicrystallization are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
High-temperature specific heat of quasicrystals and a crystal approximant
Authors:
Edagawa K. Kajiyama K. Tamura R. Takeuchi S.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 312(1-2):293-298, 2001 Aug 15.
Abstract:
Specific heat measurements have been performed by DSC in the temperature range from 430 to 10SO K for an icosahedral quasicrystal of Al-Pd-Mn, a decagonal quasicrystal of AI-Cu-Co and a crystal approximant of Al-Pd-Fe. The measured specific heat per atom at constant pressure c(p)(T) has been converted to that at constant Volume c(v)(T) by use of the data of bulk modulus previously reported and the data of the thermal expansion coefficient which we measured by dilatometry. c(v)(T) of all three samples stay at around 3k(B) up to about 700 K, as expected from Dulong-Petit's law. For the two quasicrystals, however, c(v)(T) increases dramatically and reaches 4.7k(B) at 1080 K. In contrast, the deviation in c(v)(T) of the crystal approximant is small; it is about 3.6k(B) at 1080 K. The origin of the large deviations in c(v)(T) of the quasicyrstals from Dulong-Petit's value is discussed in light of thermal excitation of phasons. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 35]
Title:
Electron rich manganites Pr(0.4)A(0.6)MnO(3): influence of A cations upon structure, magnetism and conductivity
Authors:
Barnabe A. Hervieu M. Martin C. Maignan A. Raveau B.
Source:
Journal of Physics & Chemistry of Solids. 62(8):1365-1374, 2001 Jul.
Abstract:
The role of the A-site average cationic size ([r(A)] upon the structure, the magnetic and resistive properties of Pr0.4Ca0.6MnO3 has been studied by substituting strontium and barium for calcium. At room temperature, the electron microscopy study and refinements of the X-ray diffraction data demonstrate a progressive transformation from an orthorhombic Pnma structure to a cubic Pm3m one, through a tetragonal I4/mcm cell as [r(A)] increases. At low temperature (92K), the electron diffraction study reveals a more complex situation depending on (TA) Three types of charge-ordered (CO) phases with modulated structures are observed for the smaller ([r(A)] values. For the largest ([r(A)] values, two phases (without CO) are observed: a monoclinic distorted structure (involving an orthorhombic Fmmm supercell) and a cubic Pm3m structure. Accordingly, the resistivity p (T) and magnetization M (T) curves exhibit the characteristic signature of CO below T-CO, i.e. rho increases and M decreases. In contrast, the CO is suppressed by increasing ([r(A)] but P shows a slight decrease, which is reminiscent of the A-type antiferromagnetism. This suggests a change of orbital filling, from d(z)(2) to d(x)(2) - (2)(y) for the e(g) electron, as (rA) is increased. (C) 2001 Elsevier Science Ltd. All rights reserved.
Title:
Precipitation of nanoscale icosahedral quasicrystalline phase in amorphous Hf70Cu20Pt10 alloy
Authors:
Li C. Wang L. Inoue A.
Source:
Journal of Materials Science Letters. 20(9):781-783, 2001.
Title:
Phase transformation reactions in rapidly solidified Al-6.5Fe-1.5V alloys
Authors:
Tongsri R. Minay EJ. Thackray RP. Dashwood RJ. Mcshane HB.
Source:
Journal of Materials Science. 36(13):3197-3206, 2001 Jul.
Abstract:
Phase transformation reactions, occurring during heating of as-atomised Al-6.5Fe-1.5V powders, extrusion of the powders, and heating of the as-extruded alloys produced from the powders, have been studied by DSC, XRD and TEM. The DSC studies of the as-atomised powders revealed several phase transformation reactions. The solid solution in zone A decomposed to form metastable phases at 360 degreesC. These metastable phases further transformed to form equilibrium phases at 500 degreesC. The microquasi-crystalline icosahedral (MI) phase particles present in zone A and zone B transformed to equilibrium phases at 500 degreesC. The globular clusters of microquasi-crystalline icosahedral (GCMI) phase particles in zone C transformed polymorphously to icosahedral (I) phase particles at 450 degreesC. These reactions were believed to occur during extrusion of the powders. During heating of the as-extruded alloys produced from coarse powder particles, I phase transformed polymorphously to hexagonal phase at 550 degreesC. The hexagonal phase decomposed to monoclinic Al(4)5(V, Fe)(7) and Al(1)3Fe(4) phases upon heating for longer times. (C) 2001 Kluwer Academic Publishers.
Title:
Initial crystallization processes of Hf-Cu-M (M=Pd, Pt or Ag) amorphous alloys
Authors:
Li C. Ranganathan S. Inoue A.
Source:
Acta Materialia. 49(11):1903-1908, 2001 Jun 22.
Abstract:
Hf70Cu30, Hf70Cu20Pd10, Hf70Cu20Pt10, Hf70Cu20Ag10, Hf73Pd27 and Hf73Pt27 amorphous alloys were prepared by a single roller melt-spinning method and the crystallization process was studied by differential scanning calorimetry (DSC), X-ray diffraction and transmission electron microscopy. A single exothermic peak was observed in the DSC curves of Hf70Cu30, Hf70Cu20Ag10 and Hf73Pt27 amorphous alloys, which corresponds to the precipitation of stable crystalline phases. Multiple exothermic peaks were observed in the DSC curves of Hf70Cu20Pd10, Hf70Cu20Pt10 and Kf(73)Pd(27) alloys, of which the low-temperature one corresponds to the precipitation of nanoscale icosahedral quasicrystalline phase (I-phase). The I-phase is in a metastable state since further annealing leads its transformation to other stable crystals. The relation among the atomic configurations of the amorphous alloy, I-phase and stable crystalline phases is discussed. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
Commensurate-incommensurate transition in the melting process of orbital ordering in Pr0.5Ca0.5MnO3: A neutron diffraction study - art. no. 212407
Authors:
Kajimoto R. Yoshizawa H. Tomioka Y. Tokura Y.
Source:
Physical Review B. 6321(21):2407-+, 2001 Jun 1.
Abstract:
The melting process of the orbital order in Pr0.5Ca0.5MnO3 single crystal has been studied in detail as a function of temperature by neutron diffraction. It is demonstrated that a commensurate-incommensurate (C-IC) transition of the orbital ordering takes place in a bulk sample, being consistent with the electron diffraction studies. The lattice structure and the transport properties go through drastic changes in the IC orbital ordering phase below the charge/orbital ordering temperature T-CO/OO, indicating that the anomalies are intimately related to the partial disordering of the orbital order, unlike the consensus that it is related to the charge disordering process. For the same T range, partial disorder of the orbital ordering turns on the ferromagnetic spin fluctuations which were observed in a previous neutron scattering study.
Title:
Atomic dynamics in Al-rich Al-Co alloys near the composition of the decagonal quasicrystal - art. no. 214301
Authors:
Mihalkcovic M. Elhor H. Suck JB.
Source:
Physical Review B. 6321(21):4301-+, 2001 Jun 1.
Abstract:
We used realistic Al-Co pair potentials [R. Phillips, J. Zou, A. E. Carlsson, and M. Widom, Phys. Rev. B 49, 9322 (1994); J. A. Moriarity and M. Widom, ibid. 56, 7905 (1997)] to study the atomic dynamics of Al1-xTMx crystalline structures with the fractional content x of the transition metal (TM) atom x less than or similar to 0.3. Our list comprises rather simple structures of Al3Ni and Al5Co2 alloys, complex structures related to the decagonal quasicrystal (Al9Co2Ni, O-Al13Co4), and a model of the crystalline approximant of the decagonal quasicrystal d-AlNiCo. Within the harmonic approximation, we assess the impact of the structural complexity on the phonon density of states, sound velocity, Debye-Waller factor, and the character of the phonon states at low energies. In complex structures related to the decagonal quasicrystal, a significant fraction of low-energy vibrations have nonacoustic, strongly localized character. In a molecular-dynamics annealing of the decagonal approximant model performed at elevated temperature, a fraction of aluminum atoms display signs of diffusive motion, while the equilibrium positions of the cobalt atoms do not change.
Title:
Simple and double modulations in Bi2-xPbxSr2CaCu2O8+delta - art. no. 214511
Authors:
Jakubowicz N. Grebille D. Hervieu M. Leligny H.
Source:
Physical Review B. 6321(21):4511-+, 2001 Jun 1.
Abstract:
Two single crystals of the Pb-doped high-T-c superconductor Bi2-xPbxSr2CaCu2O8 + delta phase have been isolated with x=0.4 and 0.2. In the first case, the structure is monoincommensurately modulated with the so-called Pb-type modulation (q(II)=0.11b*). In the second case, the structure is characterized by a double modulation (9(I)=0.2b*+c*; q(II)=0.15b*). The two modulated structures have been refined from single crystal x-ray diffraction data using the four- and five-dimensional superspace groups' formalism, respectively. Considering these substituted phases and the well-known lead-free phase, the same symmetry is observed for their average structures, while their structural modulations exhibit significant discrepancies. Different disordered regions are characterized in relation to the modulation period. The results are confirmed by high-resolution electron-microscopy observations. The relative structures are compared with each other and the structure of the lead-free phase. particularly about the stacking scheme of the structural layers.
Title:
Magnetic structure and magnetic phase transitions in TbPtGe2
Authors:
Penc B. Hofmann M. Szytula A. Zygmunt A.
Source:
Journal of Physics-Condensed Matter. 13(20):4471-4483, 2001 May 21.
Abstract:
Magnetic and neutron diffraction measurements have been performed on TbPtGe2 at low temperatures. The compound crystallizes in the orthorhombic YIrGe2-type structure (space group Immm); crystal structure parameters have been refined on the basis of the neutron diffraction pattern collected at T = 30.7 K (paramagnetic region). TbPtGe2 is antiferromagnetic below T-N = 24.2 K. Below this temperature only one of the two Tb sublattices is ordered; the Tb magnetic moments localized at the 4(i) sites order with the simple propagation vector k = 0. Below T-t1 = 11.4 K the magnetic moments at the other Tb sites, 4(h), show an ordering with the propagation vector k(1) = [0.2677(8), 0.1312(24), 0.6989(27)]. At T-t2 = 7 K a further phase transition to a new modulated phase described by the propagation vector k(2) = [0,2584(5), 0, 0.5895(6)] is observed.
Title:
Quasicrystalline phase formation in Al62Cu22.5Fe12.5 and Al55Cu22.5Fe12.5Be7 alloys
Authors:
Lee SM. Kim BH. Kim DH. Kim WT.
Source:
Journal of Materials Research. 16(6):1535-1540, 2001 Jun.
Abstract:
Formation of the icosahedral quasicrystalline phase in conventionally cast Al62Cu25.5Fe12.5 and Al55Cu25.5Fe12.5Be7 alloys were investigated. The icosahedral phase (I-phase) forming ability was greatly improved by partial replacement of Al by 7 at.% Be. The as-cast Al55Cu25.5Fe12.5Be7 alloy consisted of dendritic primary I-phase and interdendritic tau -phase, whereas that of an as-cast Al62Cu25.5Fe12.5 alloy consisted of various phases such as the beta-, I-, and tau -phases, together with a small amount of the lambda- and eta -phases. The kinetic barrier for transformation into single I-phase by heat treatment was greatly reduced in an Al55Cu25.5Fe12.5Be7 alloy. The I-phase in an Al55Cu25.5Fe12.5Be7 alloy has the same face centered icosahedral structure as that in an Al62Cu25.5Fe12.5 alloy and is of high quality without phason strain.
Title:
Magnetic ordering of PrCoAl4 a neutron diffraction study
Authors:
Schobinger-Papamantellos P. Andre G. Rodriguez-Carvajal J. Moze O. Kockelmann W. Tung LD. Buschow KHJ.
Source:
Journal of Magnetism & Magnetic Materials. 231(2-3):162-171, 2001 Jun.
Abstract:
The magnetic ordering of the orthorhombic (Pmma space group) PrCoAl4 compound has been studied by neutron diffraction. Only the Pr moments order. Below TN = 17 K they adopt a longitudinal amplitude modulated structure. The magnetic moments are confined to the c direction with the wave vector q = (0, 0, q,) with an almost temperature independent length. At 1.5 K the amplitude of the wave is 2.24(4) mu (B)/Pr atom and the wave vector q(z) = 0.437(2) can be approximated within error limits by a rational fraction (11)/(25) which alternatively gives the possibility to consider the structure as a commensurate phase. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Lattice contraction and cation ordering of ZrTiO4 in the normal-to-incommensurate phase transition
Authors:
Kim YK. Jang HM.
Source:
Journal of Applied Physics. 89(11 Part 1):6349-6355, 2001 Jun 1.
Abstract:
It is known that microwave dielectric ZrTiO4 undergoes a normal-to-incommensurate phase transition (NICPT) near 1125 degreesC. The role of the cation ordering and its relation to the anomalous lattice contraction observed in the NICPT were studied by x-ray diffraction and Raman scattering of ZrTiO4 specimens prepared employing various cooling rates between 1250 and 1000 degreesC. It was shown that the lattice parameter b underwent a substantial change even if the long-range cation ordering was absent. Analysis of the Raman spectra indicated that the compositional fluctuation-induced line broadening was mainly responsible for the extrapolated linewidth at 0 K, suggesting that the observed lattice contraction was initiated by the local short-range cation ordering. Based on thermodynamic arguments, the anomalous lattice contraction of ZrTiO4 was attributed to a direct consequence of the gradient coupling between the two order parameters that describe a compositional modulation and a displacive modulation in the NICPT. (C) 2001 American Institute of Physics.
Title:
Interactions in quasicrystals
Authors:
Vidal J. Mouhanna D. Giamarchi T.
Source:
International Journal of Modern Physics B. 15(10-11):1329-1337, 2001 May 10.
Abstract:
Although the effects of interactions in solid state systems still remains a widely open subject, some limiting cases such as the three dimensional Fermi liquid or the one-dimensional Luttinger liquid are by now well understood when one is dealing with interacting electrons in periodic crystalline structures. This problem is much more fascinating when periodicity is lacking as it is the case in quasicrystalline structures. Here, we discuss the influence of the interactions in quasicrystals and show, on a controlled one-dimensional model, that they lead to anomalous transport properties, intermediate between those of an interacting electron gas in a periodic and in a disordered potential.
Title:
Coupling between lattice distortions and magnetism in La0.9Sr0.1MnO3 thin films
Authors:
Vigliante A. Gebhardt U. Ruhm A. Wochner P. Razavi FS. Habermeier HU.
Source:
Europhysics Letters. 54(5):619-625, 2001 Jun.
Abstract:
X-ray scattering experiments have demonstrated that for thin lms (100 Angstrom to 500 Angstrom) of La0.9Sr0.1MnO3 epitaxially grown on SrTiO3 (100) substrates, the accommodation of the lattice mismatch between lm and substrate gives rise to a modulated structure. The non-bulk like structural properties of these thin lms are the origin of anomalies in the electronic and magnetic behavior. Studies of the lattice as a function of temperature clearly reveal a magnetostrictive effect close to the Curie temperature. For thicker lms the strain relief mechanism is replaced by formation of coherent microtwins and some of the bulk properties are recovered, but some differences are still observed.
Title:
Commensurate structure of Ca2CoSi2O7, a new twinned orthorhombic structure
Authors:
Hagiya K. Kusaka K. Ohmasa M. Iishi K.
Source:
Acta Crystallographica - Section B, Structural Science. 57(Part 3):271-277, 2001 Jun.
Abstract:
The crystal structure of the commensurate phase of Ca2CoSi2O7, dicalcium cobalt disilicate, has been derived from the modulated structure described in (3 + 2)-dimensional space. The structure is orthorhombic P2(1)2(1)2; a = 23.510 (4), b = 23.510 (4), c = 5.025 (1) Angstrom (at 170 K), Z = 18. Since the crystal is twinned and the apparent diffraction symmetry is 4/mmm, the parameters were refined by a newly developed leasts-quares program for the refinement of twinned crystals. The structure is essentially similar to the known structure of the melilite group, but with regular arrangement of the bundles along [001] formed with four arrays of the sixfold coordinated Ca polyhedra and an array of CoO4 tetrahedra. The distribution of the bundles found in the present structure is different from that reported by Riester et al. [(2000), Z. Kristallogr. 215, 102-109].
Title:
Superspace description of the structure of the composite crystal urea/n-octane at room temperature
Authors:
Peral I. Madariaga G. Petricek V. Breczewski T.
Source:
Acta Crystallographica - Section B, Structural Science. 57(Part 3):378-385, 2001 Jun.
Abstract:
A structural model for the composite crystal urea/n-octane is proposed. Despite the lack of information from the largely disordered guest substructure, the final model is consistent with the collected diffraction pattern. The use of the superspace approach stresses the composite character of the inclusion compounds and makes easier a unified view of the whole urea/n-alkane family. In particular, a comparison between the octane and heptadecane derivatives shows a common pattern for the origin of the modulation of the guest chains based on the distribution of the NH2 groups within each tunnel wall.
Title:
Average structure of the composite crystal urea/octanedioic acid at room temperature within the superspace formalism
Authors:
Peral I. Madariaga G. Petricek V. Breczewski T.
Source:
Acta Crystallographica - Section B, Structural Science. 57(Part 3):386-393, 2001 Jun.
Abstract:
The average structure of the composite urea/octanedioic acid has been refined using the superspace formalism [superspace group H'3(1)21(00 gamma )00 (1) over bar]. Modulation effects seem to be almost negligible. The guest substructure appears to be largely disordered and has been modelled using rigid units occupying 12 equiprobable different orientations inside the urea tunnels. Guest molecules are slightly tilted with respect to the tunnel axis favouring a stronger guest-guest intratunnel interaction.
Title:
Dislocations in quasicrystals
Authors:
Edagawa K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 309(Special Issue SI):528-538, 2001 Jul 15.
Abstract:
Quasicrystals have additional elastic degrees of freedom not found in conventional crystals, which are termed phason degrees of freedom. Dislocations in quasicrystals are special in that they are inevitably accompanied by the phason strain in addition to the conventional elastic strain. Characteristic features of such quasicrystalline dislocations and plastic properties of quasicrystals are reviewed. Deformation mechanisms in quasicrystals by dislocation motion are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Plastic deformation of decagonal Al-Ni-Co single quasicrystals
Authors:
Schall P. Feuerbacher M. Urban K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 309(Special Issue SI):548-551, 2001 Jul 15.
Abstract:
Decagonal phases are quasicrystals which exhibit quasiperiodic order in two spatial directions and translational order along the third spatial direction. We present results of a series of uniaxial compression experiments on decagonal Al-Ni-Co single quasicrystals in two modifications, the type I superstructure and the basic cobalt-rich state. We have chosen different orientations of the deformation samples, parallel, inclined by 45 degrees and perpendicular to the periodic axis. The samples were deformed at a strain rate of 10(-5) s(-1) at temperatures between 710 and 860 degreesC corresponding to 70 and 81% of the melting temperature, respectively. Stress relaxation tests were carried out to determine the activation volume and the stress exponent. The two modifications show anisotropies in the plastic behaviour which differ distinctly. The macroscopic deformation tests are accompanied by a study of the microstructure of deformed material by means of transmission electron microscopy. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 8]
Title:
Dislocation and shear strength of model quasiperiodic lattice
Authors:
Tamura R. Takeuchi S. Edagawa K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 309(Special Issue SI):552-556, 2001 Jul 15.
Abstract:
To understand the intrinsic resistance for the dislocation glide in quasicrystals, the glide deformation process in a simple Fibonacci quasiperiodic lattice, consisting of L and S lattice spacings, has been simulated. The Gamma -surfnce of the model fluctuates quasiperiodically and the minima corresponding to the Fibonacci-numbers decrease inversely proportional to the displacement. The Burgers vectors of dislocations, which correspond to neighboring distances of the Gamma -surface minima, are almost equal to the lattice spacings. The stress necessary for dislocation glide consists of two components: the phason-defect formation stress and the Peierls stress. Glide of a group of dislocations of a Fibonacci number, associated with one another bounding phason faults, reduces drastically the former stress component and the remaining glide resistance mainly due to the Peierls potential is about 0.015G (G: the shear modulus). (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
The variation of quasicrystal defect contrast: how and why
Authors:
Klein H. Agliozzo S. Mancini L. Gastaldi J. Hartwig J. Baruchel J.
Source:
Journal of Physics D-Applied Physics. 34(10A Special Issue SI):A98-A102, 2001 May 21.
Abstract:
We carried out a systematic study of typical defect contrasts in various single grains of icosahedral Al-Pd-Mn quasicrystals. White-beam topographs with different sample-to-detector distances and multiple-crystal topographs with different sample-to-detector distances, different working points on the rocking curve and different harmonic reflections have been recorded. Despite the extreme geometrical resolution at the ID19 topography beamline of the ESRF, white-beam topography showed reasonable (not blurred) contrast only for very short sample-to-detector distances (<4 cm). Depending on the defect type, in synchrotron multiple-crystal topography the defect contrast changes considerably as a function of the position of the working point on the rocking curve. Under the special conditions chosen, the dependence of contrast shape and size on the harmonic reflection used was rather weak. [References: 1]
Title:
Anomalous transmission of x-rays in quasicrystals
Authors:
Hartwig J. Agliozzo S. Baruchel J. Colella R. de Boissieu M. Gastaldi J. Klein H. Mancini L. Wang J.
Source:
Journal of Physics D-Applied Physics. 34(10A Special Issue SI):A103-A108, 2001 May 21.
Abstract:
The perfection of one of the quasicrystal grains with the highest degrees of perfection was checked by means of x-ray diffractometry and x-ray topography. Full widths at half maximum of de-convoluted reflectivity curves were close to the theoretical values and a partial Borrmann effect was clearly visible in the measured reflection and transmission curves, whereas the topographs still showed rather strong intricate contrast, which means that strong deformations (defects) still exist in the grain. Consequently, dynamical effects like anomalous transmission were confirmed to exist in selected quasicrystalline grains, but even then the structural quality is still far from being 'highly perfect'.
Title:
Low-frequency dielectric spectroscopy of commensurate density waves
Authors:
Tomic S. Pinteric M. Vuletic T. von Schutz JU. Schweitzer D.
Source:
Synthetic Metals. 120(1-3 Special Issue SI):695-698, 2001 Mar 15.
Abstract:
We overview complex conductivity measurements (20Hz - 1MHz) in low-dimensional organic systems kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl, and deuterated Cu-DCNQI and its alloys, with commensurate density wave ground states. We discuss the obtained results in comparison with those for the incommensurate density waves, like in (TMTSF)(2)PF6, in which the phason relaxation in a disordered background dominates. We show that in the commensurate systems with a random domain structure charged domain walls provide a more appropriate description of the observed dielectric relaxation.
Title:
Friedel oscillations and charge-density waves pinning in quasi-one-dimensional conductors
Authors:
Ravy S. Rouziere S. Pouget JP. Brazovskii S.
Source:
Synthetic Metals. 120(1-3 Special Issue SI):1075-1076, 2001 Mar 15.
Abstract:
We present an x-ray diffraction study of 2.8 at. % V-doped blue bronzes. At low temperature, we have observed both an intensity asymmetry of the +/- 2k(F) satellite reflections relative to the pure compound, and a profile asymmetry of each satellite reflections. The profile asymmetry is due to Friedel oscillation around the V substituant and the intensity asymmetry is related to the charge density wave (CDW) pinning. These two affects give access to the local properties of CDW in disordered systems, including the pinning and even the phase shift of Friedel oscillations.
Title:
Exploiting quasiperiodic order in the design of optical devices - art. no. 205421
Authors:
Macia E.
Source:
Physical Review B. 6320(20):5421-+, 2001 May 15.
Abstract:
In this work we present a prospective study on the potential capabilities of optical devices based on Fibonacci dielectric multilayers. We perform a detailed analytical comparison of the linear optical response of periodic versus quasiperiodic multilayers. Based on this study we will suggest the use of hybrid-order devices, composed of both periodic and quasiperiodic subunits to design microcavities of practical interest, and we provide some illustrative examples. From our study we conclude that the inclusion of quasiperiodically ordered subunits substantially widens the possibilities of engineering modular optical structures.
Title:
Structure of a Zn-Mg-Er cubic phase and its relation to icosahedral phases
Authors:
Kounis A. Miehe G. Saitoh K. Fuess H. Sterzel R. Assmus W.
Source:
Philosophical Magazine Letters. 81(6):395-403, 2001 Jun.
Abstract:
The crystal structure of a cubic phase in the system Zn-Mg-Er has been solved by a combination of high-resolution electron microscopy and X-ray powder diffraction. This phase is considered to be related to that of the quasicrystalline phase. The structure consists of 448 atoms in the unit cell with lattice constant of a(0) = 20.20 Angstrom and the space group is F<(4)over bar >3m. Important structural elements in the cubic structure are interpenetrating icosahedral units around Zn and Mg atoms and Frank-Kasper polyhedra around the Mg atoms. No giant icosahedral atomic cluster, such as the 136-atom Bergman cluster, was found in the stucture.
Title:
Crystal and quasicrystal structures in Cd-Yb and Cd-Ca binary alloys
Authors:
Takakura H. Guo JQ. Tsai AP.
Source:
Philosophical Magazine Letters. 81(6):411-418, 2001 Jun.
Abstract:
We show that the structures of cubic Cd6Yb and Cd6Ca crystals are closely related to those of recently found stable icosahedral Cd-Yb and Cd-Ca alloys. These structures are described as a periodic packing of rhombohedra having different atomic decoration in terms of three-dimensional Penrose tiling. A new type of icosahedral cluster composed of 66 atoms is found. The innermost shell of the cluster consisting of four Cd atoms breaks its entire icosahedral symmetry.
Title:
Structural characteristics of a high-quality Al-Ni-Ru decagonal quasicrystal with 1.6 nm periodicity, studied by atomic-scale electron microscopy observations
Authors:
Sun W. Ohsuna T. Hiraga K.
Source:
Philosophical Magazine Letters. 81(6):425-431, 2001 Jun.
Abstract:
We report the structural characteristics of a high-quality stable decagonal quasicrystal (D phase) with 1.6 nm periodicity, formed in Al75Ni15Ru10 alloy annealed at 890 degreesC for 24 h. The tiling structure and the arrangement of transition-metal atoms (Ru and Ni) in this Al-Ni-Ru D phase have been clearly revealed by high-resolution electron microscopy (HREM) and by high-angle annular detector dark-held (HAADF) scanning transmission electron microscopy (STM) respectively. On the basis of the HREM and HAADF STM observations, the relationship between the arrangement of local structural units and the formation of the long-range quasiperiodic tiling structure is discussed.
Title:
Wavevector-dependent susceptibility in quasiperiodic Ising models
Authors:
Au-Yang H. Jin BQ. Perk JHH.
Source:
Journal of Statistical Physics. 102(3-4):501-543, 2001 Feb.
Abstract:
Using the various functional relations for correlation functions in planar Ising models, new results are obtained for the correlation functions and the q-dependent susceptibility fbr Ising models on a quadratic lattice with quasiperiodic coupling constants. The effects are dearest if the interactions are both attractive and repulsive according to a quasiperiodic pattern. In particular, an tract scaling limit result for the two-point correlation function of the Z-invariant inhomogeneous Ising model is presented and the q-dependent susceptibility is calculated for some cases where the coupling constants vary according to Fibonacci rules. It is found that the ferromagnetic case differs drastically From the case with both ferro- and antiferromagnetic bonds. In the mixed case, the peaks of the q-dependent susceptibility are everywhere dense for temperature T both above or below the critical temperature T,, but due to overlap only a finite number of peaks is visible. This number of visible peaks decreases as T moves away from T,. In the ferromagnetic case, there is typically only one single peak at q = 0, in spite of the aperiodicity present in the lattice. These results provide evidence that in real systems, even if the atoms arrange themselves aperiodically, there will be no dramatic difference in the diffraction pattern, unless the pair correlation function has clear aperiodic oscillations. The number of oscillations per correlation length determines the number of visible peaks. [References: 62]
Title:
Perturbative method for solving elastic problems of one-dimensional hexagonal quasicrystals
Authors:
Peng YZ. Fan TY. Jiang FR. Zhang WG. Sun YF.
Source:
Journal of Physics-Condensed Matter. 13(18):4123-4128, 2001 May 7.
Abstract:
A new perturbation technique for solving elastic three-dimensional problems of quasicrystals is supplied. The key idea of this technique is to simplify the equations by introducing a parameter which does not exist in the original equations, and then look for the perturbation solution for the problems of interest. To illustrate the utility of our method and for comparison, we consider the crack problem for one-dimensional hexagonal quasicrystals with point groups 6mm, 62(h)2(h), 6(m)2(h) and 6/m(h)mm, whose exact solution has been obtained by the first two authors of this paper. Only up to the order zero approximation, we get the exact expression for the stress intensity factor, which is the most important physical quantity in fracture theory. Moreover, the same procedure can be used to deal with the elastic problems for two- and three-dimensional quasicrystals. A simple review of the method is finally given.
Title:
A dodecagonal phase formed in an immiscible Co-Ag system by ion mixing of multilayers
Authors:
Li ZC. Li ZF. Liu BX.
Source:
Journal of Physics-Condensed Matter. 13(19):L367-L370, 2001 May 14.
Abstract:
In an immiscible Co-Ag system, a new Co-Ag dodecagonal phase is formed in the Co50Ag50 multilayers upon room temperature 200 keV xenon-ion irradiation to a dose of 5 x 10(14) Xe+ cm(-2). The mechanism of formation of the quasicrystalline phase is also discussed in terms of the far-from-equilibrium process of ion mixing, as well as the role of the interfacial free energy, stresses caused by size mismatch and the radiation-enhanced diffusion.
Title:
Crystallochemical aspects of solid state reactions in mechanically alloyed Al-Cu-Fe quasicrystalline powders
Authors:
Salimon AI. Korsunsky AM. Shelekhov EV. Sviridova TA. Kaloshkin D. Tcherdyntsev VS. Baldokhin YV.
Source:
Acta Materialia. 49(10):1821-1833, 2001 Jun 13.
Abstract:
A number of elemental mixtures having initial compositions close to Al65Cu23Fe12 were mechanically alloyed at different energy intensities using a planetary mill. Laboratory X-ray diffraction analysis, differential scanning calorimetry and Mossbauer spectroscopy were used for characterization of the phase and structural state of mechanically alloyed powders after different periods of milling and annealing. Several exothermic effects were found, and these were ascribed to specific solid-state reactions. Quantitative phase analysis was applied in order to identify the mechanism of solid-state reactions laking place in the vicinity of the quasicrystalline phase domain in the Al-Cu-Fe system as a result of mechanical and thermal excitation and homogenization, Metastable intermetallics were identified which possess certain structural and topological elements identical to those found in quasicrystals. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
High temperature crystal structure of a 3 : 2 mullite from neutron diffraction data
Authors:
Brunauer G. Boysen H. Frey F. Hansen T. Kriven W.
Source:
Zeitschrift fur Kristallographie. 216(5):284-290, 2001.
Abstract:
High temperature neutron investigations up to 1950 K of 3:2-sintered mullite show a smooth reversible behaviour which can be described by a rotation of more or less rigid TO4 (T = Al(2),Si)-tetrahedra and accompanying distortions of the Al(l)O-6-octahedra. Large atomic displacement parameters along the c-direction, including static parts, match to respective structural modulations in the mullite structure. A comparison of a pristine and a preheated sample reveals an irreversible depopulation of the Al(2) atomic site in favour of the Al(*) site.
Title:
Figure of merit of quasicrystals: the case of Al-Cu-Fe
Authors:
Bilusic A. Pavuna D. Smontara A.
Source:
Vacuum. 61(2-4):345-348, 2001 May 14.
Abstract:
Quasicrystals exhibit low thermal and moderate electrical conductivity, accompanied by a relatively high absolute magnitude of thermopower, which makes them suitable candidates for use as thermoelectric devices. Theoretical explanations of electrical and thermal conductivity and thermopower of two representative members of the Al-Cu-Fe icosahedral quasicrystal family (i-Al62Cu25.5Fe12.5 and i-Al63Cu25Fe12) are given. Their figures of merit are relatively low compared with the best-known thermoelectric materials. (C) 2001 Elsevier Science Ltd. All rights reserved.
Title:
Specific heat properties of polariton modes in quasicrystals - art. no. 184203
Authors:
Mauriz PW. Albuquerque EL. Vasconcelos MS.
Source:
Physical Review B. 6318(18):4203-+, 2001 May 1.
Abstract:
We investigate the thermodynamical properties of plasmon polaritons that propagate in multiple semiconductor layers arranged in a quasiperiodical fashion. This quasiperiodicity can be of the so-called deterministic (or controlled) disorder type, i.e., they are neither random nor periodic. Also, they are characterized by the nature of their Fourier spectrum, which can be dense pure point (Fibonacci sequence) or singular continuous (Thue-Morse sequence). The sequences are described in terms of a series of,generations that obey peculiar recursion relations. We present both analytical and numerical studies on the temperature dependence of the polariton's specific heat associated with the generation number n = 1,2,3,... for their multiscale fractal energy spectra. We show that when T-->0, the specific heat displays oscillations and when T-->infinity, the specific heat goes to zero with T-2 (because the energy spectrum considered is bounded).
Title:
ET0L systems for composite dodecagonal quasicrystal patterns
Authors:
Escudero JG.
Source:
International Journal of Modern Physics B. 15(8):1165-1175, 2001 Mar 30.
Abstract:
Two types of deterministic substitution tilings with 12-fold symmetry and a Pisot number as inflation factor are generated and described in terms of bracketed L-systems. Composition of the inflation rules allows to construct other types of dodecagonal patterns which can be described with the help of ET0L-systems and may be used in order to derive nondeterministic models of quasicrystal structures.
Title:
A computer program written in Mathematica for calculating H-2 quasicrystals and their diffraction patterns
Authors:
Grodzicky R.
Source:
Computer Physics Communications. 136(3):236-249, 2001 May 15.
Abstract:
A computer program for generating and drawing finite H-2 quasicrystal fragments and their diffraction patterns is presented. The program also draws the quasicrystal points after their having been mapped onto the "window" space. The window and/or fragment do not necessarily have to he simply connected. The concept of a "threshold intensity for detection" has been incorporated into the program. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 3]
Title:
Scanning tunneling microscope images of locally modulated structures in layered materials, MoS2(0001) and MoSe2(0001), induced by impurity atoms
Authors:
Murata H. Kataoka K. Koma A.
Source:
Surface Science. 478(3):131-144, 2001 May 10.
Abstract:
The effect of impurity atoms on the surface electronic structure of semiconducting transition metal dichalcogenides, MoS2 and MoSe2, has been investigated by a scanning tunneling microscope (STM) and by its spectroscopic mode, scanning tunneling spectroscopy. The following impurity atoms have been studied: (I)alkali metal atoms deposited by using alkali dispensers, (2) impurity atoms unintentionally doped during the synthesizing process, and (3) a donor dopant of Re. STM images show locally modulated structures with bright area surrounded by dark area in nm scale at negative sample bias, and their global features depend on the bias polarity. The center region of the structure observed at negative sample bias is flat or caved in regardless of a kind of the impurity atom. It is concluded that the locally modulated STM image arises from the interaction between the electron donated by the impurity and electrons in the d-orbitals of neighboring Mo atoms. This interaction extends by about one Mo-Mo distance, which gives the image of 0.7 nm in diameter. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Plastic deformation behaviour of decagonal Al70Ni15Co15 single quasicrystals
Authors:
Schall P. Feuerbacher M. Urban K.
Source:
Philosophical Magazine Letters. 81(5):339-349, 2001 May.
Abstract:
High-temperature deformation experiments have been performed on decagonal Al70Ni15Co15 single quasicrystals at a constant strain rate of 10(-5) s(-1) in the temperature range between 700 and 860 degreesC. The samples were deformed in compression with the compression axis in different orientations, parallel to, inclined by 45 degrees and perpendicular to the tenfold symmetry axis. Stress relaxation tests and temperature changes were carried out to determine thermodynamic activation parameters. The how stress and the activation enthalpy were found to depend on the sample orientation whereas dependences of the activation volume and the stress exponent on the orientation were not observed. Additionally, deformation tests were performed on samples of the basic Co-rich modification of the decagonal phase at the temperature of 860 degreesC in the same three orientations. The deformation behaviours of the two different modifications of the decagonal phase are discussed.
Title:
Fermi surfaces and electronic transport properties of quasicrystalline approximants
Authors:
Krajci M. Hafner J.
Source:
Journal of Physics-Condensed Matter. 13(17):3817-3830, 2001 Apr 30.
Abstract:
We present ab initio calculations of the Fermi surfaces and of the electronic transport properties of the 1/1 and 2/1 approximants to icosahedral AlPdRe and AlPdMn quasicrystals. Our investigations are based on realistic structural models produced by a cut-and-projection method, a self-consistent tight-binding linearized muffin-tin orbital (TB-LMTO) Hamiltonian and Bloch-Boltzmann as well as Kubo-Greenwood theories for the electronic transport properties. Our results are analysed in the light of the current discussions of the character of electronic eigenstates in quasicrystals in general and of the very exotic transport properties of icosahedral AlPdRe in particular.
Title:
Finite graphs associated with a cut-and-project set
Authors:
Cotfas N.
Source:
Czechoslovak Journal of Physics. 51(4):301-304, 2001 Apr.
Abstract:
A chain of finite graphs G(m), can be associated with a cut-and-project set in a natural way [J. Phys. A: Math. Gen. 33 (2000) 2917]. The chain of Schrodinger type operators H-m we define in this short note, may be useful in the description of the physical properties of quasicrystals. [References: 6]
Title:
An affine extension of non-crystallographic Coxeter groups with applications in the theory of quasicrystals and integrable systems
Authors:
Twarock R.
Source:
Czechoslovak Journal of Physics. 51(4):400-408, 2001 Apr.
Abstract:
Similarly as in the theory of Kac-Moody algebras, affine extensions of the non-crystallographic Coxeter groups H-k, (k = 2, ..., 4) can be derived via an appropriate extension of :he Cartan matrix. These groups lead to novel applications in the theory of quasicrystals and integrable models. In the former case, a new model for quasicrystals with five-fold symmetries could be established; in the latter case, subgroups have been used to obtain a Calogero model related to a non-integrally laced group.
Title:
Average unit cell approach to diffraction analysis of some aperiodic structures - decorated Fibonacci chain
Authors:
Wolny J.
Source:
Czechoslovak Journal of Physics. 51(4):409-419, 2001 Apr.
Abstract:
The average unit cell approach has been successfully used to construct the probability distributions of atomic distances from the reference lattice points and to calculate the diffraction patterns for decorated Fibonacci chains with non-Fibonacci type of decoration. General method able to distinguish between various quasilattice decorations has been elaborated and tested for decorated Fibonacci chains.

Update: 1-Jun-2001

Title:
Precipitations of icosahedral quasicrystalline and crystalline approximant phases in Zr-Al-Ni-Cu-Ir metallic glasses - art. no. 172201
Authors:
Li CF. Inoue A.
Source:
Physical Review B. 6317(17):2201-+, 2001 May 1.
Abstract:
Metallic Zr65Al7.5Ni5Cu17.5Ir5 and Zr65Al7.5Ni10Cu12.5Ir5 glasses have been prepared and their crystallization process has been studied with emphasis on the initial stage. The initial precipitation phase is an icosahedral quasicrystalline phase (1 phase) for the former alloy and a face-centered cubic Zr2Ni (fcc-Zr2Ni) phase for the latter one. Structural analysis revealed that the crystal structure of fcc-Zr2Ni contains icosahedral atomic clusters, implying that fcc-Zr2Ni can be regarded as the crystalline approximant for the Zr-based I phase. The preferential precipitation of quasicrystalline/approximant phases in the initial crystallization stage implies the existence of an icosahedral atomic cluster in the glassy states. The compositions of the two alloys were obtained by adding Ir to the Zr65Al7.5Ni10Cu17.5 alloy, which is well known for the formation of a bulk amorphous alloy. The probable existence of icosahedral atomic clusters provided an explanation for the stability of the metallic Zr65Al7.5Ni10Cu17.5 glass.
Title:
Precipitation of icosahedral phase from amorphous Zr65Cu17.5-xAl7.5Ni10Agx (x=0, 5) alloys
Authors:
Lee JK. Choi G. Kim WT. Kim DH.
Source:
Journal of Materials Research. 16(5):1311-1317, 2001 May.
Abstract:
Crystallization behavior of amorphous Zr65Cu17.5-xAl7.5Ni10Agx (x = 0, 5) alloys prepared by melt spinning and injection casting techniques has been studied using differential scanning calorimetry, x-ray diffractometry, and transmission electron microscopy. Ag addition changes crystallization sequence of the amorphous phase. The amorphous Zr65Cu17.5Al7.5Ni10 alloy crystallizes via simultaneous precipitation of icosahedral phase and NiZr2 phase in the first crystallization step whereas that in Zr65Cu12.5Al7.5Ni10Ag5 alloy crystallizes via precipitation of only icosahedral the phase. Partial replacement of Cu by Ag in Zr65Cu17.5Al7.5Ni10 alloy stabilized the icosahedral phase relative to competing intermetallic phases resulting in suppression of the precipitation of the NiZr2 phase, enhancement of the precipitation of icosahedral phase, and reduction of undercooled liquid range. Crystallization behavior of the amorphous Zr65Cu12.5Al7.5Ni10Ag5 alloy is not affected by cooling rate during solidification. Johnson-Mehl-Avrami analysis of isothermal transformation data suggests that the formation of the quasicrystalline phase is not entirely polymorphic in nature and may involve partitioning of the solute at later state.
Title:
High resolution photoemission spectroscopy study near the Fermi edge for different surfaces prepared on the icosahedral AlPdMn phase
Authors:
Schaub T. Delahaye J. Berger C. Guyot H. Belkhou R. Taleb-Ibrahimi A. Calvayrac Y.
Source:
European Physical Journal B. 20(2):183-188, 2001 Mar.
Abstract:
High resolution photoemission measurements performed at low temperatures on a single-grained sample of tile AIPdMn icosahedral phase show that the density of states N(E) strongly depends on tile nature of tile surface. For an ordered quasicrystalline surface, prepared by Ar etching and ultra high vacuum annealing;, a dip feature is observed in N(E) near the Fermi level, which energy dependence can Le analyzed with a simple square-root power law. By contrast, N(E) varies only little with energy both for a disordered surface and a crystalline surface of the same sample. A sharp Fermi edge is then clearly observed. This shows that the metallic character oi the surface of a quasicrystal is strongly reduced when the surface presents a quasicrystalline ordering.
Title:
Hardystonite from Franklin furnace: A natural modulated melilite
Authors:
Bindi L. Czank M. Rothlisberger F. Bonazzi P.
Source:
American Mineralogist. 86(5-6):747-751, 2001 May-Jun.
Abstract:
Natural hardystonite, (Ca3.85Na0.14Pb0.01)(Zn0.85Al0.07Mg0.03Mn0.043+Fe0.023+)Si2.00O7.00, from the type locality was reinvestigated with single crystal X-ray diffraction, microprobe analysis, and electron diffraction. The average structure, space group P (4) over bar2(1)m, a = 7.800(1) Angstrom. c = 5.000(1) Angstrom, was refined to R = 1.91% using 331 independent reflections. Hardystonite exhibits an incommensurate modulated structure. As in synthetic melilite-type compounds, modulation is two-dimensional, with tartan-like appearance: modulation vectors are q(1) = alpha (a(1)* + a(2)*) and q(2) = alpha(-a(1)* + a(2)*). A modulation wavelength lambda = 19.0(4) Angstrom was estimated by centering satellite reflections using a single-crystal diffractometer. TEM-EDX investigations proved the chemical composition of the sample to be slightly inhomogeneous, with stronger and sharper satellites in the regions where the composition approaches the Ca2ZnSi2O7 end-member. Geometrical parameters as well as anisotropic displacement ellipsoids of hardystonite are consistent with those of the other melilite-type compounds having a modulated character. [References: 37]
Title:
Features of the optical response of dielectric crystals with incommensurate phases
Authors:
Kushnir OS. Lokot LO.
Source:
Physics of the Solid State. 43(5):818-822, 2001.
Abstract:
The constitutive relation describing the optical response of dielectric crystals in incommensurately modulated phases is derived for the plane-wave range of modulation. The symmetry properties of modulation corrections to the permittivity tensor of such crystals are analyzed with allowance for spatial dispersion. These properties are dictated by the Onsager principle for a nonabsorbing medium and by the mesoscopic periodicity of the medium. It is shown that the basic results are consistent with the general conventional approach in crystal optics of spatially inhomogeneous media. (C) 2001 MAIK "Nauka/ Interperiodica".
Title:
Surface properties of the B2-based approximants in relation to quasicrystals
Authors:
Dong C. Zhang LM. Belin-Ferre E. Brunet P. Dubois JM.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 304(Special Issue SI):172-177, 2001 May 31.
Abstract:
Quasicrystals and their approximants are Hume-Rothely compounds having similar valence electron concentrations. According to this new understanding of approximants, some B2 superstructures can be regarded as a special group of approximants. The present paper examines surface characteristics of this group of approximants synthesized by hoc pressing. Friction coefficient, surface energy and hardness are analyzed and influences from factors such as valence electron concentration and Al-3p partial density of states at the Fermi energy are discussed. Specifically, we show that samples containing the B2 structure and its superstructures exhibit a friction coefficient which decreases with increasing e/a and reaches minimum at 1.86, the value of the quasicrystal. Therefore. the B2-based approximants and quasicrystals belong to one group of phases whose surface properties are mainly determined by electronic structure characteristics rather than crystal structures. (C) 2001 Elsevier Science S.A. All rights reserved.
Title:
Solidification behaviour of Sn droplets embedded in an icosahedral Al-Cu-Fe matrix
Authors:
Park JC. Kim WT. Kim DH. Kim JR.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 304(Special Issue SI):225-230, 2001 May 31.
Abstract:
The solidification behaviour of Sn droplets embedded in an icosaheral quasicrystalline Al-Cu-Fe matrix has been studied by a combination of differential scanning calorimetry (DSC), X-ray diffractometry and transmission electron microscopy. The as-melt spun-ribbon consists of mainly dendritic quasicrystalline phase with Sn particles distributed at the interdendritic region with some minor crystalline phase at the interdendritic region. A single phase icosahedral quasicrystalline matrix was obtained by the heat treatment for 15 min at 750 degreesC. Faceted Sn particles distributed through the quasicrystalline matrix with an orientation relationship. (121)(Sn) is perpendicular to the fivefold axis of quasicrystal. Sn solidification exotherm consisted of two broad peaks: a small exotherm with onset temperature of about 204 degreesC, and the second bred exotherm with 137 degreesC, which is about 28 and 95 degreesC below the Sn melting temperature, respectively. With increasing cooling rate in DSC, peak temperatures decreased and both the peak height and peak width increased. Contact angles calculated from the cooling rate dependences of peak temperature and peak height were about 26 and 52 degrees for the high temperature and low temperature exotherms, respectively. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Influence of palladium on hydrogenation and crystallization of Zr-Cu-Ni-Al glasses
Authors:
Zander D. Koster U.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 304(Special Issue SI):292-295, 2001 May 31.
Abstract:
Hydrogenation of glassy Zr-Cu-(Ni. Pd)-Al alloys was performed electrochemically in a 2:1 glycerin-phosphoric acid electrolyte. In comparison to Zr-Cu-Ni-Al quasicrystals the absorption kinetics in amorphous Zr-Cu-Ni-Al were found to be slower, but the storage capacity is similar. Desorption is probably hindered by the formation of thin ZrO2 layers. Partial replacement of Ni by Pd in an amorphous Zr68.5Cu13Ni11Al7.5 alloy was found to accelerate absorption kinetics. The observed increase in lenght during hydrogenation indicates an Interesting new result: instead of a continuous increase of the specific volume per hydrogen atom, a decrease from rather high value at very low hydrogen content is observed. This means that not only the site for the hydrogen atom is expanded but also the neighboring still empty ones. Thermal stability was studied by X-ray diffraction and TEM. Amorphous Zr68.5Cu13Ni10Pd1Al7.5 and Zr68.5Cu13Ni5.5Pd5.5Al7.5 was found to transform into a nanocrystalline microstructure of an icosahedral quasicrystalline phase. Zr68.5Cu13Pd11Al7.5 transform mainly into tetragonal Zr-2(Cu, Pd) and an unidentified phase. Above a hydrogen content of H/M = 0.05, the formation of quasicrystals is replaced by a tetragonal phase with lattice parameters close to those of Zr2Ni. At high hydrogen contents (about H/M = 1.0) phase separation is assumed to take place followed by the formation of nanocrystalline ZrH2. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
APFIM and TEM study of the oxygen behavior during crystallization of Zr65Cu27.5Al7.5 metallic glass
Authors:
Murty BS. Ping DH. Hono K. Inoue A.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 304(Special Issue SI):706-709, 2001 May 31.
Abstract:
The influence of oxygen on the crystallization behavior of Zr65-xCu27.5Al7.5Ox (x = 0.14, 0.43 and 0.82%) metallic glasses has been studied, The supercooled liquid regime (DeltaT(x)) decreases with increase in oxygen. At low oxygen level (0.14%), the alloy crystallizes in a single stage by the formation of Zr-2(Cu, Al). At higher oxygen content, the,amorphous phase crystallizes in two stages bg the precipitation of a quasicrystalline phase first and subsequently the stable Zr-2(Cu, Al). The present paper is the first evidence of icosahedral phase formation in ternary Zr-Cu-Al system. The temperature and time window for the formation of quasicrystalline phase is quite narrow. Three-dimensional atom probe studies have shown that the quasicrystalline phase has a composition of Zr65Cu27.5Al7.5 suggesting that it is rich in Zr and O anti is depleted in Cu. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Vibrational dynamics of some amorphous and quasicrystalline alloys
Authors:
Gupta A. Shah P. Lalla NP. Dasannacharya BA. Harami T. Yoda Y. Seto M. Yabashi M. Kikuta S.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 304(Special Issue SI):731-734, 2001 May 31.
Abstract:
Inelastic nuclear resonance scattering has been used to get partial vibrational density of states (PVDOS) of iron in two classes of systems: (i) quasicrystalline Al63.5Cu24Fe12.5, its rhombohedral approximant and Al70Cu20Fe10 crystalline (tetragonal) phase and (ii) amorphous Fe80B20 and its crystalline counterpart. PVDOS in quasicrystalline phase consists of a rather broad maximum at 28 meV with a small hump at 21 meV, and is somewhat similar to that in crystalline Al70Cu20Fe10. Results suggest some similarity in the iron environment in quasicrystalline, approximant and crystalline phases. Amorphous Fe80B20 exhibits an er;cess density of states as compared to the crystalline phase in the energy range 4-21 meV, which may be attributed to the boson peak. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Magnetic and Mossbauer studies of quasicrystalline Al70-xPd15T15Mx (T = Mn, Fe; M = Si, Ge; 0 <= x <= 8)
Authors:
Bahadur D. Srivastava CM. Foldeaki M. Giguere A. Dunlap RA.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 304(Special Issue SI):830-832, 2001 May 31.
Abstract:
Our magnetisation and Mossbauer effect investigations of magnetic icosahedral quasicrystals (Al,Ge)(70)Pd15Mn15 and (Al,Si)(70)Pd15Fe15 have shown that the magnetic atoms Mn and Fe occupy two types of sites, one of which is magnetic and one which is non-magnetic. In certain cases the magnetic atoms couple ferromagnetically. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 9]
Title:
Nucleation in crystallization of Zr-Cu-Ni-Al metallic glasses
Authors:
Janlewing R. Koster U.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 304(Special Issue SI):833-838, 2001 May 31.
Abstract:
Zr-Cu-Ni-Al alloys belong to the best glass forming systems known. Zr68.5Cu13Ni11Al7.5 metallic glasses [1] are known to transform by primary crystallization into a quasicrystalline structure. Since small Hf-addition were found to stabilize the formation of quasicrystals, i.e, to reduce the influence of oxygen on the crystallization, a glass with 5 at.% Hf as a replacement of Zr was chosen to compare with the transformation kinetic of Zr69.5Cu12Ni11Al7.5. From crystallization statistics nucleation was found to be homogeneous in the temperature regime between 653 and 713 K with transient rates. In order to understand the observed crystallization process in more detail a new virtual space algorithm is presented. It is capable of calculating the real projected distribution of crystallite sizes in a thin TEM transparent layer including hard impingement up to a crystalline volume fraction of 100%. Another improvement as compared to the standard Kolmogorov-Johnson-Mehl-Avrami (KJMA) procedure [J. Chem. Phys. 7 (1939) 1103; J. Chem. Phys. 8 (1940) 212; J. Chem. Phys. 9 (19-41) 177] is the parallel fit of several experimental distributions with large ensembles of crystallites for one temperature and different annealing times. A least sum of error squares optimization method is implemented, yielding the. set of relevant parameters, i,e. the stationary nucleation rate, the incubation time and the effective diffusion coefficient for the primary crystallization, By fitting the nucleation rates with a diffusion controlled classical model, the interface energies and the metastable melting temperature of both alloys are estimated. Based on these data is the evaluation of a TTT diagram for the crystallization of the icosahedral phase in Zr64.5Cu12Ni11Al7.5Hf5 and Zr69.5Cu12Ni11Al7.5. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Stabilization of icosahedral phase in Si substituted version of Al65Cu20Cr15 alloy
Authors:
Khare V. Tiwari RS. Srivastava ON.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 304(Special Issue SI):839-843, 2001 May 31.
Abstract:
In order to find out the effect of Si on quasicrystalline (QC) and related phases, Si has been substituted in place of Al in Al-Cu-Cr system. In the present investigation, various alloys corresponding to Al65-xCu20Cr15Six (x = 1, 3, 5, 7 and 10) composition have been synthesized and characterized. The investigations reveal that at 1 at.% Of Si both QC and crystalline (b.c.c., a = 8.90 Angstrom) phases are present but after annealing, the alloy becomes QC. The alloys having 3 at.% of Si has been found to show the formation of icosahedral phase which exhibits high degree of disorder. At 7 at.% Si, the dissociation of the icosahedral phase commences. The dissociated phases have been found to be icosahedral and disordered diamond cubic phase (a = 7.87 Angstrom). At the highest silicon concentration (10 at.%) another crystalline phase: primitive cubic phase (a approximate to 10.90 Angstrom) results along with the icosahedral phase. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 8]
Title:
Microstructure and chemistry of Al-V-Fe-Si nancquasicrystalline alloys
Authors:
Humphreys ES. Warren PJ. Titchmarsh JM. Cerezo A.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 304(Special Issue SI):844-848, 2001 May 31.
Abstract:
Rapidly solidified Al94V4Fe2 allows have been produced by the single roller melt spinning technique. The microstructures were analysed using TEM and the fine-scale chemistry was studied using EDX. The tensile and hardness properties were investigated and the effect of heating on the microstructures was analysed using a combination of DSC and in situ TEM heat treatments. The microstructures of all of the ribbons were found to consist of solute-rich nanoscale quasicrystalline anti crystalline particles in an aluminium-rich fee matrix. It was found that the higher the quench rate, the finer the microstructures. The addition of silicon to the master alloys had the effect of further reducing the scale of the microstructure. From tensile testing of the ribbons, it was found that although some of the UTS values were high, up to 960 MPa, the scatter of data was large. The scatter in the hardness test data was lower indicating that the material could potentially be developed far use in compressive applications. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 6]
Title:
Formation of nano-sized Ti68Fe26Si6 icosahedral quasicrystalline phase by rapid quenching and mechanical alloying
Authors:
Lee JH. Kim KB. Lee JS. Kim DH. Kim WT.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 304(Special Issue SI):849-854, 2001 May 31.
Abstract:
Investigation using rapid quenching (RQ) and mechanical alloying (MA) were conducted to produce Ti68Fe26Si6 icosahedral quasicrystals. Subsequent heat treatment was performed on both rapidly quenched ribbons and mechanically alloyed powders in a vacuum furnace under various heat treatment conditions of temperature ranging from 440 to 900 degreesC with a constant heating rate of 10 degreesC/min and holding time up to 30 h. The amorphous phase of Ti68Fe26Si6 ribbon was successively achieved by RQ for the first time from the present investigation. During the heat treatment, the icosahedral quasicrystalline phase was transformed from the melt-spun amorphous ribbon at the glass transition temperature of 430 degreesC and remained up to approximately 520 degreesC. The quasicrystalline phase, however was somewhat difficult to be obtained from heat treatment of the Ti68Fe26Si6 powder milled for 5 h under the present experimental conditions. (C) 2001 Elsevier Science B.V, All rights reserved.
Title:
Formation of quasicrystalline and vacancy ordered phases in vapour deposited thin films of Al-Cu-Co alloys
Authors:
Mukhopadhyay NK. Weatherly GC.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 304(Special Issue SI):855-859, 2001 May 31.
Abstract:
Thin films of Al-Cu-Co alloys were grown by thermal vapour deposition technique by varying the composition of the target material. The films were characterized by scanning and transmission electron microscopes together with EDX and,X-ray diffraction techniques. It was observed that quasicrystalline decagonal phase does not form in thin film when the composition of the target material is close to that of quasicrystalline phase, i.e., Al65Cu15Co20 The deposited film of lower thickness (< 200 nm was always found to contain amorphous phase which transforms mainly to crystalline phases. By several trials of changing the composition of the target material it was found that target alloy composition close to Al50Cu20Co30, yielded maximum amount of Al65Cu15Co20 quasicrystalline phase, coexisting with ternary tau (3) phase in the film of thickness 1000-2000 nm. The composition variation between the target alloy and the deposited film was explained based on differential deposition rate due to the significant differences in partial vapour pressure among the constituent elements. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
On the formation of nano-sized quasicrystals in Ti53Zr27Ni20 alloy
Authors:
Shaz MA. Mandal RK. Srivastava ON.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 304(Special Issue SI):860-862, 2001 May 31.
Abstract:
We report here the formation of a nano-quasicrystalline (qc) phase in the melt spun ribbons of Ti53Zr27Ni20 alloy based on the results of transmission electron microscopy (TEM) Such a phase was formed by employing melt spinning of the alloy, at a wheel speed of 40 m/s. The nano-qc phase (30-40 nm) was detected through diffraction monitored by 30 nm electron probe using TEM. Together with this crystalline phases were found to coexist. These crystalline phases were found to be belonging to cubic crystal system (a = 3.30 Angstrom) and a hexagonal phase (a = 5.21 Angstrom, c = 8.53 Angstrom). (C) 2001 Elsevier Science B.V. All rights reserved. [References: 5]
Title:
Mechanical alloying of Al-Cu-Fe elemental powders
Authors:
Barua P. Murty BS. Srinivas V.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 304(Special Issue SI):863-866, 2001 May 31.
Abstract:
The formation of quasicrystalline powders by mechanical alloying of crystalline elemental powders has been investigated for Al70-x(Cu,Fe)(30+x) (x = 0, 5, 7) alloy systems. The alloying process during milling and additional annealing at elevated temperature has been characterized by X-ray diffraction and transmission electron microscopy. It is observed that as x increases, tendency of i-phase formation decreases in these mechanically alloyed powder compositions. The cubic solid solution identified as beta -phase is observed to be present as one of the major phases in all the above alloy compositions. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Decagonal quasicrystals in the Zn-Mg-R alloys (R = rare-earth and Y)
Authors:
Sato TJ. Abe E. Tsai AP.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 304(Special Issue SI):867-870, 2001 May 31.
Abstract:
We report formation of decagonal quasicrystals in the Zn-Mg-R (R = rare-earth and Y) alloys. Exemplified by the R = Dy alloy, the composition of the decagonal phase was determined as Zn58Mg10Dy2. The decagonal phase is thermodynamically stable, and probably forms through a peritectic reaction between the crystalline Zn66Mg32Dy2 and Zn-Mg liquidus phases. The existence of the decagonal phase was confirmed for R = Y, Ho, Er, Tm and Hu in addition to the Dy alloy. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 9]
Title:
Solidification sequence of the icosahedral quasicrystal forming Al-Cu-Fe alloys
Authors:
Lee SM. Jeon HJ. Kim BH. Kim WT. Kim DH.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 304(Special Issue SI):871-878, 2001 May 31.
Abstract:
The solidification sequence of the icosahedral quasicrystal forming Al-Cu-Fe alloys was investigated as functions of cooling rate during solidification, compositional variation, and additional Si amount., Annealing treatment was also carried out to obtain the single icosahedral quasicrystalline phase. Two different formation mechanisms of the icosahedral quasicrystalline phase can be suggested as a function of cooling rate. For a moderate cooling rate regime, the icosahedral phase is formed by a peritectic reaction? which is consistent with the previous reports. For a high cooling rate regime, where large undercooling of the liquid is obtainable, the i-phase (icosahedral phase) is formed directly from the undercooled melt, without the formation of the primary lambda or beta phases. The tau phase was formed at the inter-dendritic region of the i-phase grains from the remaining liquid at the final stage of solidification. AS the Si element was added up to 5 at.%, the relative volume fraction of the i-phase gradually decreased in both as-cast and heat treated Al-Cu-Fe alloys. For an as-cast Al50Cu20Fe15Si15 alloy, however, the major phase was identified as an i-phase related 1/1 simple cubic approximant. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Soft X-ray spectroscopy study of the electronic structure of hydrogenated Ti-Ni-Zr quasicrystal
Authors:
Belin-Ferre E. Dankhazi Z. Fournee V. Sadoc A. Kim JY. Kelton KF.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 304(Special Issue SI):884-887, 2001 May 31.
Abstract:
Investigation of the electronic structure of a material is useful to understand its properties. For such a purpose, it is interesting to use spectroscopic techniques that allow for direct insight into the electronic distributions of a solid. X-ray emission and photoabsorption spectroscopies are especially attractive as they probe separately occupied and unoccupied states of selected angular momentum around each component of,ui alloy or a compound. In the present work we used these techniques to analyze the nature of the interaction between H and Zr, Ni and Ti. We studied occupied and unoccupied p and s. d states in hydrogenated icosahedral Zr-Ni-Ti as compared to the non-hydrogenated quasicrystal and the pure elements. We present here first results. The spectral curves for Zr 4d occupied states show additional states, induced by the hybridization with H. The same is observed for Ni 3d states although the spectroscopic signature of the H-metal interaction is of lower intensity than for Zr. In the unoccupied states, changes of the shapes of the various spectral curves for Zr us well as Ni and Ti display significant modifications which we attribute to changes in hybridizations owing to the interaction with H. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Rational approximant structures to decagonal quasicrystals
Authors:
Ranganathan S. Subramaniam A. Ramakrishnan K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 304(Special Issue SI):888-891, 2001 May 31.
Abstract:
We have shown earlier that the decagonal quasicrystalline phase can be derived by the twinning of the icosahedral cluster about the five-fold axis by 36 degrees. It is shown here that in a similar fashion, the rational approximant structures (RAS) to the decagonal quasicrystal can be constructed by the twinning of RAS to the icosahedral quasicrystalline phase. The twinning of the Mackay (cubic) type RAS leads to the Taylor (q1/p1, q1/p1) phases, while the twinning of the orthorhombic Little phase leads to the Robinson (q1/p1, q2/p2) approximants to the decagonal quasicrystal. With increasing order of q1/p1 or q2/p2, wt approach the digonal quasicrystal with one-dimensional quasiperiodicity. (C) 2001 Published by Elsevier Science B.V.
Title:
On the crystal structure of Ln(2)O(2)CO(3) II (Ln = La and Nd)
Authors:
Olafsen A. Larsson AK. Fjellvag H. Hauback BC.
Source:
Journal of Solid State Chemistry. 158(1):14-24, 2001 Apr.
Abstract:
The crystal structures of La2O2CO3 II and Nd2O2CO3 IT have been shown by means of high-resolution powder neutron (PND) and synchrotron X-rag diffraction (SXRD) combined with selected area electron diffraction (SAED) studies to be far more complex than earlier anticipated, owing to ordering of carbonate groups between (Ln(2)O(2)(2+))(n) layers. In contrast to earlier descriptions, the carbonate groups appear to be rather regular, Relative to an average model, the SAED patterns show additional scattering in the form of closely distributed, but essentially discrete, spots along <1/3, 1/3, l >*. Most of the observed scattering, H, can be described as H = G +/- mq(1) + nq(2), where G is the Bragg reflections of the underlying average P6(3)/mmc lattice, q(1) = [1/3, 1/3, +/-1/2]*, q(2) = [1/3, 1/3, +/-2/3]*, and m and n are integers. The additional scattering reflects ordering of the carbonate groups into trigonal layers between the (Ln(2)O(2)(2+))(n) layers, but it remains open whether q(1) and q(2) represent two separate structures with different stacking sequences of such lavers or whether they correspond to an even more complex stacking sequence. In any case, some disorder and rotational domain twinning are present. Two structure models, one for each modulation wave vector, n;ere constructed. Rietveld-type refinements of PND data of La2O2CO3 II were performed, approximating the complex, and at least partly disordered. stacking sequence as a two-phase mixture of the two modulated phases, Satisfactory convergence was achieved with R-p = 6,4%, R-wp = 8.3%, and chi (2) = 3.32, The isothermal espansivities, alpha (p), for La2O2CO3 II and Nd2O2CO3 II between 298 and 893 K were determined as 2.92x10(-5) and 2.70x10(-5) K-1, respectively. (C) 2001 Academic Press.
Title:
Some elementary questions in the theory of quasiperiodic heterostructures
Authors:
Perez-Alvarez R. Garcia-Moliner F. Velasco VR.
Source:
Journal of Physics-Condensed Matter. 13(15):3689-3698, 2001 Apr 16.
Abstract:
The characterization of the spectrum of eigenstates of quasiperiodic heterostructures is discussed by focusing on three questions. Arguments are advanced to justify the often indiscriminate use of different approximants in the calculation of;he eigenvalue spectra. It is stressed that the calculation of the fractal dimension may be rather inaccurate if the high eigenvalue range is not included, even if physically the interest is limited to the low range. The question of self-similarity is critically examined and found to have a very limited range of validity in practice. The unique properties of the Rudin-Shapiro sequence are also stressed.
Title:
Synthesis and mechanical properties of cast quasicrystal-reinforced Al-alloys
Authors:
Schurack F. Eckert J. Schultz L.
Source:
Acta Materialia. 49(8):1351-1361, 2001 May 8.
Abstract:
We report on the preparation and mechanical properties of Al-based-composites with quasicrystalline particles as reinforcement. Al-Mn-Ce/Fe and Al-Mn-Pd bulk samples were synthesized by die casting into a copper mould at moderate cooling rate. Thin ribbons were prepared by melt-spinning as a reference state for the phase formation under most rapid quenching conditions. Microstructural analysis was done using X-ray diffraction, scanning and transmission electron microscopy as well as calorimetric methods. Significant differences in the phase formation, the composite microstructure and the thermal stability of the microstructure were found for different alloy compositions. The deformation behaviour was characterized by constant-rate compression tests at room temperature for a number of alloy variations yielding excellent properties compared to conventionally produced Al-alloys. The mechanical properties vary within a wide range of strength and ductility as a function of the quasicrystal volume fraction and their morphology. Also first tests at elevated temperatures were carried out, revealing a promising high temperature stability of the composite. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
Incommensurately modulated Nowotny Chimney-ladder phases Cr1-xMoxGe similar to 1.75 with x=0.65 and 0.84
Authors:
Rohrer FE. Lind H. Eriksson L. Larsson AK. Lidin S.
Source:
Zeitschrift fur Kristallographie. 216(4):190-198, 2001.
Abstract:
The crystal structures: of two new ternary, incommensurately modulated phases in the Cr/Mo/Ge system, Cr1-xMoxGesimilar to1.75 with x = 0.65 and 0.84, have been refined using the same composite approach as for the earlier reported compounds. (Mo/Rh)(11)Ge-18 and (Mo/Rh)(13)Ge-22, from the Mo/Rh/Ge system. The composite model consists of a rather stable diamond-like transition metal substructure and a helical main roup element arrangement. The same super space group pair, W: P4/nnc: q (1) over bar q1 P: I41/amd: 1 (1) over bar ss, the same positions and modulation waves were used. The refinements of the new phases in the Cr/Mo/Ge system converged rapidly to R-values below 5% with GOF of 2.53 and 3.71, respectively. Each structure is built by two sub lattices with the parameters - alpha, c(x) and the modulation vector q(x) - for Ge and alpha, c(T) and q(T) for the transition metals, The refined data for x = 0.65 are found to he alpha = 5.935(2), c(x) = 2.770(1), c(T) = 4.839(1), q(X) = 0.428 [001]*, q(T) = 0.253 [001]* and for x = 0.84, alpha = 5.963(1), c(x),= 2.786(1), c(T) = 4.875(1), q(X) = 0.430 [001]*, q(T) = 0.264 [001]*, It is clearly shown the composite approach is applicable to different chimney-ladder compounds, even though they have quite different compositions and hence q-vectors.
Title:
Magnetic structures and magnetic phase transitions in TbMn0.33Ge2
Authors:
Gil A. Hofmann M. Penc B. Szytula A.
Source:
Journal of Alloys & Compounds. 320(1):29-32, 2001 May 10.
Abstract:
A study of the magnetic structure of TbMn0.33Ge2 has been made using a neutron diffractometer of better resolution and new results have been obtained. The paramagnetic neutron diffraction data confirmed the CeNiSi2-type of crystal structure reported earlier for this compound. The magnetic moments are located on terbium. At 1.5 K the Tb magnetic moments have two components: a collinear and sine wave modulated one so the magnetic order at this temperature has a complex character. With increasing temperature, the change of the magnetic structure to the sine wave modulated one is observed near the Neel temperature T-N = 28 K. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 9]
Title:
High pressure magnetic phase diagram of an antiferromagnetic Cr+0.50 at.% Re alloy single crystal
Authors:
Lodya JAL. Alberts HL. Smit P.
Source:
Journal of Alloys & Compounds. 320(1):40-45, 2001 May 10.
Abstract:
The pressure-temperature magnetic phase diagram of a Cr + 0.50 at.% Re alloy single crystal has been obtained from high pressure ultrasonic wave velocity measurements. A triple point exists on the magnetic phase, diagram where the incommensurate (I) and commensurate (C) pin-density-wave (SDW) phases coexist with the paramaguetic (P) phase. The ISDW-CSDW phase transition is a first-order transition while the CSDW-P and ISDW-P Neel transitions ale continuous. Both the ISBW-CSDW/CSDW-ISDW and CSDW-P phase lines are nonlinear with exceptionally large pressure derivatives near the triple point pressure. Thermal expansion measurements on the crystal together with the high pressure measurements give a latent heat nf 13.7 J mol(-1) associated with the first-order ISDW-CSDW phase transition. Thr temperature dependence of the magnetovolume, Delta omega, has been observed to fit the equation \ Delta omega \ = A(0) + A(1)T(2) + A(2)T(4) fairly well in the CSDW phase. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Metastability in the commensurate phase of K2ZnCl4
Authors:
Ahn HY. Jeong SY.
Source:
Europhysics Letters. 54(3):361-365, 2001 May.
Abstract:
A new dielectric anomaly is found at the temperature T-x (260-290 K) in the commensurate (C) phase of K2ZnCl4, which separates the commensurate phase into two states. The C phase above T-x is a metastable state, in which the relaxation of the polarization is expressed by the stretched exponential form, and the C phase below T-x is a stable state in which the dielectric constant and polarization are independent of time. It is speculated that the dielectric anomaly found at the temperature T-x is a stabilization process of discommensurations. This anomaly could be observed only in a measurement performed using a liquid-nitrogen cooler (LNC) without mechanical vibration of the measurement system. [References: 13]
Title:
Charge-ordering modulation observed in the (La0.5Mn0.5)MnO3 phase of the multiphased manganite La0.9Sn0.1MnO3 at room temperature
Authors:
Wang YQ. Duan XF. Wang ZH. Sun JR. Shen BG.
Source:
Applied Physics Letters. 78(17):2479-2481, 2001 Apr 23.
Abstract:
At room temperature, the lattice image of a modulated structure associated with charge ordering has been observed in the (La0.5Mn0.5)MnO3 phase of La0.9Sn0.1MnO3, which is composed of two-type phases: ABO(3) and A(2)B(2)O(7). Results of electron energy loss spectroscopy and energy dispersive x-ray spectroscopy show that the need of the chemical balance and small A-site radius for the (La0.5Mn0.5)MnO3 phase are the main reasons for the appearance of charge ordering stripes. (C) 2001 American Institute of Physics.
Title:
Notes on the normalizer of a finite subgroup of GL(n, d, Z) in GL(n, d, Z)
Authors:
Zeiner P. Janssen T.
Source:
Acta Crystallographica - Section a - Foundations of Crystallography. 57(Part 3):256-263, 2001 May.
Abstract:
A finite algorithm for calculating a finite set of generators for the normalizer of a finite subgroup G of GL. (n, d, Z) in GL(n, d, Z) is presented. It is based on an algorithm for the normalizer of a finite subgroup G in GL (n, Z), which has been developed recently by Opgenorth. The normalizer of G in GL (n, d, Z) plays a role for superspace groups analogous to the role that the normalizer of G in GL (n, Z) plays for n-dimensional space groups. It is important for calculating superspace groups with the Zassenhaus algorithm and is needed for testing equivalence of superspace groups.
Title:
Quasiperiodicity in decagonal phases forced by inclined net planes?
Authors:
Steurer W. Cervellino A.
Source:
Acta Crystallographica - Section a - Foundations of Crystallography. 57(Part 3):333-340, 2001 May.
Abstract:
It is generally assumed that decagonal quasicrystals show periodically arranged atomic layers only on net planes perpendicular to the tenfold axis and quasiperiodically arranged ones parallel to it. However, there also do exist only slightly puckered atomic layers that are periodically arranged and inclined to the tenfold axis. They coincide with the net planes of the periodic average structures of the decagonal phase and are related to the strongest Bragg reflections. Since they link quasiperiodic and periodic directions, inclined net planes may play a crucial role for growth and stabilization of decagonal quasicrystals. In fact, it is shown how ideal quasiperiodic long-range order and inflation symmetry allow for the existence of inclined net planes with small corrugation and reinforce the relation with the periodic average structures.
Title:
Determination of structures of Ca2COSi2O7, Ca2MgSi2O7, and Ca-2(Mg0.55Fe0.45)Si2O7 in incommensurate and normal phases and observation of diffuse streaks at high temperature
Authors:
Kusaka K. Hagiya K. Ohmasa M. Okano Y. Mukai M. Iishi K. Haga N.
Source:
Physics & Chemistry of Minerals. 28(3):150-166, 2001 Apr.
Abstract:
The structures of Ca2CoSi2O7, Ca2MgSi2O7, and Ca-2(Mg0.55Fe0.45)Si2O7 have been determined in the temperature range between 297 and 773 K with arbitrary intervals. The structures of the incommensurate phase of the three compounds are characterized by the presence of the six-, seven-, and eight-coordinated Ca-O polyhedra and of the bundles along the c-axes consisting of four arrays of the six-coordinated Ca-O polyhedra and an array of (TO4)-O-1 (T-1: Co, Mg, or Mg-Fe) tetrahedra in the structures. The number of bundles in each material decreases at elevated temperatures. The incommensurate phase undergoes a phase transition into the normal phase at 493 K in Ca2CoSi2O7, at 360 K in Ca2MgSi2O7, and at 510 K in Ca-2(ME0.55Fe0.45)Si2O7. The features of the structures of the normal phase are almost the same as those found in the basic structures (the averaged structures of the incommensurate structures), and this fact implies that the characteristics of the structures, such as the six-coordinated Ca-O polyhedra or fragments of the bundles, should be partially preserved at higher temperatures both in the incommensurate structures and also in the structures of the normal phase. Analyses of anisotropic displacement parameters clarified that disorder of the modulation waves is developed in the structures at higher temperatures. The evolution of a disorder in the structures was ascertained by observation of the circular diffuse streaks in the vicinity of the transition temperature between the incommensurate and normal phases.
Title:
Synthesis, crystal structure and TEM study of the new hollandite-type Ba similar to 8/7Mo8O16
Authors:
Barrier N. Gougeon P. Retoux R.
Source:
Journal of Alloys & Compounds. 317:120-126, 2001 Apr 12.
Abstract:
Investigation of the Cs-Ba-Mo-O system by fused salt electrolysis at 960 degreesC has led to the new related-hollandite compound Ba?????. Single-crystals of Bax8/7Mo8O16 were examined by election diffraction and high-resolution electron microscopy. Bax8/7Mo8O16 was found to present a tetragonal I basic unit-cell (a=10.21 Angstrom, c=2.89 Angstrom) with a one-dimensional modulation of wavevector q close to 4/7 along c* at room temperature. Refinement of the crystal structure was made on X-ray single crystal data in the seven-fold supercell in the three-dimensional space group I4(a=10.214(2) Angstrom, c=20.255(5) Angstrom, R-w(F-2)=0.0844 for all 7767 independent triangles and planar rhomboidal MO4 clusters that coexist in equal proportions. The Mo-Mo distances vary from 2.5341(8) to 2.696(2) Angstrom (3) and from 2.5341(8) to 2.894(4) Angstrom in the Mo-3 and Mo-4 clusters, respectively. The shortest intercluster distance is 3.047(4) Angstrom. The Mo-O distances range between 1.81(1) to 2.418(8) Angstrom as usually observed in reduced molybdenum oxides. The Ba2+ cations occupy the large square channels in square prismatic environment of oxygen atoms with the distribution sequence ... Ba-square -Ba-Ba-square Ba-square .... (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
R9Mg34Zn57 icosahedral quasicrystals: The tuning of a model spin glass
Authors:
Canfield PC. Fisher IR.
Source:
Journal of Alloys & Compounds. 317:443-447, 2001 Apr 12.
Abstract:
The growth of large single grains of face-centered icosahedral R9Mg34Zn57 (R=Y Gd-Er) quasicrystals (referred to as RMgZn from here on) has allowed the detailed study of the intrinsic properties of single phase samples that contain a quasiperiodic rare earth sublattice. By comparison of GdMgZn (Heisenberg moment) to TbMgZn or DyMgZn (non-Heisenberg moments) a clearly reduced freezing temperature (T-f) for GdMgZn can be observed. In order to explore this further pseudo-ternary series such as (Y1-xGdx)MgZn, (Tb1-xGdx)MgZn, (Dy1-xGdx)MgZn, and (Dy1-xTbx)MgZn were grown. Whereas T-f changes monotonically with x for the Gd/Y and Tb/Dy series, there is a rapid rise in T-f for the addition of small amounts of tile non-Heisenberg moments Tb or Dy into GdMgZn. For approximately 30% non-Heisenberg substitution on the Gd site T-f passes through a local maximum and is reduced in a roughly linear manner for further increases in the concentration of non-Heisenberg moments. Analysis of these data lead to the conclusion that there is a threshold concentration of non-Heisenberg moments needed to force the whole system to act in a non-Heisenberg manner. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 11]
Title:
Ternary nitrides prepared in the Li3N-Mg3N2 system at 900-1000 K
Authors:
Yamane H. Okabe TH. Ishiyama O. Waseda Y. Shimada M.
Source:
Journal of Alloys & Compounds. 319(1-2):124-130, 2001 Apr 26.
Abstract:
Three phases, (LixMg1-x)(3)N2-x (0<x<0.20), LiMgN and (LigMg1-x)(2)N(2-x)2/3(0.5<x<0.6), were prepared in Li3N - Mg3N2 system at 900 and 1000 K, and their crystal structures were investigated by applying the Rietveld method to the X-ray powder diffraction patterns. (Li-x Mg1-x)(3)N2-x crystallizes in a cubic superlattice (a=9.9767(5) Angstrom at x=0.17). Mg atoms in the Mg3N2 structure (space group Ia3) were found to be partially replaced by Li atoms and the resultant structure was distorted with a lower symmetry space group 1213. The crystal structure of LiMgN (orthorhombic, a=7.1586(2), b=3.5069(8), c=5.01424(13) Angstrom, space group Pnma) was determined sb initio from the X-ray powder diffraction data. It revealed a cation-ordered antifluorite-type structure. (LixMg1-x)(2)N(2-x)2/3 was prepared by rapid cooling from 1000 K to room temperature. It was also found to be stable at 900 and 1000 K and decomposed into LiMgN and Li3N on slow cooling in the furnace. Broad tails of the X-ray diffraction peaks suggest a modulated structure. A cation-disordered simple antifluorite type (space group Fm (3) over barm, a=4.99559(11) Angstrom at x=0.57) was proposed as the fundamental structure of (LixMg1-x)(2)N(-x)(2/32). (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Phason-strain influence on low-temperature specific heat of the decagonal Al-Ni-Co quasicrystal
Authors:
Li CL. Liu YY.
Source:
Chinese Physics Letters. 18(4):570-573, 2001 Apr.
Abstract:
According to the quasicrystal continuum model and linear elasticity theory, based on the equivalence assumption of phonons and phasons in quasicrystals, we have deduced five phase velocities of elastic wave propagating in the decagonal quasicrystals. By inserting these velocities into the specific heat expression, rye have succeeded in explaining the experiment of specific heat performed on the single-grained decagonal AI-Ni-Co quasicrystals at low temperature. Our results show that the contribution of the phason strain to the specific heat cannot be neglected at low temperature. Moreover, the phason-strain may be a main reason for the decagonal quasicrystals possessing anisotropic thermal conductivity.
Title:
Inhomogeneous superconducting state in quasi-one-dimensional systems - art. no. 140511
Authors:
Yang K.
Source:
Physical Review B. 6314(14):0511-+, 2001 Apr 1.
Abstract:
We report on results of theoretical study of nonuniform superconducting states in quasi-one-dimensional systems, with attractive interactions and Zeeman splitting between electron spins. Using bosonization to treat intrachain electron-electron interactions, and a combination of renormalization group and mean-field approximation to tackle interchain couplings, we obtain the phase diagram of the system, and show that the transition between the uniform and nonuniform superconducting phases is a continuous transition of the commensurate-incommensurate type.
Title:
Structure and charge-ordering transition in Bi-based bilayered Bi0.44Ca2.56Mn2O7 manganite - art. no. 144108
Authors:
Qin YL. Garcia-Munoz JL. Zandbergen HW. Alonso JA.
Source:
Physical Review B. 6314(14):4108-+, 2001 Apr 1.
Abstract:
The normal and charge-ordered phases in Bi2-2xCa1+2xMn2O7 With a hole-doping level of x = 0.78 have been investigated by transmission electron microscopy. Bio(0.44)Ca(2.56)Mn(2)O(7), the first identified member of the 327-type Bi-Ca-Mn-O family, was obtained under high oxygen pressure, and presents an orthorhombic structure with Amam symmetry at room temperature. A structural modulation is observed in this unusual layered manganite below 210 K, characterized by the one-dimensional wave vector q = 0.22b* and a single transverse component. At low temperature the superspace group of the charge ordered state is P-s-11(Amam).
Title:
Magnetic properties of the S=1/2 quasi-one-dimensional antiferromagnet CaCu2O3 - art. no. 144418
Authors:
Kiryukhin V. Kim YJ. Thomas KJ. Chou FC. Erwin RW. Huang Q. Kastner MA. Birgeneau RJ.
Source:
Physical Review B. 6314(14):4418-+, 2001 Apr 1.
Abstract:
We report single-crystal growth and magnetic susceptibility and neutron diffraction studies of the S = 1/2 quasi-one-dimensional antiferromagnet CaCu2O3. The structure of this material is similar to that of the prototype two-leg spin-ladder compound SrCu2O3. However, the Cu-O-Cu bond angle in the ladder rungs in CaCu2O3 is equal to 123 degrees, and therefore the magnetic interaction along the rung is expected to be much weaker in this material. At high temperatures, the magnetic susceptibility of CaCu2O3 can be decomposed into a contribution from one-dimensional antiferromagnetic chains or finite-size chain segments together with a weak Curie contribution. The intrachain magnetic exchange constant J(parallel to), determined from the magnetic susceptibility measurements, is 2000+/-300 K. CaCu2O3 undergoes a Neel transition at T-N = 25 K with ordering wave vector of [0.429(5), 1/2, 1/2]. The magnetic structure is incommensurate in the direction of the frustrated interchain interaction. Weak commensurate magnetic Bragg peaks with the reduced wave vector (1/2, 1/2, 1/2) are also observed below T-N. Application of a magnetic field induces a metamagnetic transition at which the incommensurability of the magnetic structure is substantially reduced. Above the transition field, the material possesses only short-range magnetic order, and no well defined temperature-driven transition is observed.
Title:
Phason elastic constants of the icosahedral Al-Pd-Mn phase derived from diffuse scattering measurements
Authors:
Letoublon A. de Boissieu M. Boudard M. Mancini L. Gastaldi J. Hennion B. Caudron R. Bellissent R.
Source:
Philosophical Magazine Letters. 81(4):273-283, 2001 Apr.
Abstract:
The diffuse scattering in the diffraction pattern of the icosahedral Al-Pd-Mn quasicrystalline phase has been measured on an absolute scale by X-ray and neutron scattering on single-grain samples. Most of the diffuse scattering can be interpreted in the framework of the elasticity theory of icosahedral quasicrystals considering only phason fluctuations. At room temperature the absolute values of the K-1/k(B)T and K-2/k(B)T phason elastic constants are of the order of 0.06 and 0.031 atom(-1). The amount of diffuse scattering intensity is insensitive to the sample annealing treatment.
Title:
Does density-functional theory predict a spin-density-wave ground state for Cr?
Authors:
Hafner R. Spisak D. Lorenz R. Hafner J.
Source:
Journal of Physics-Condensed Matter. 13(11):L239-L247, 2001 Mar 19.
Abstract:
We present ab initio spin-density-functional investigations of static long-period spin-density waves (SDWs) in Cr. Calculations performed in the generalized-gradient approximation (GGA) and using both projector-augmented-wave and muffin-tin orbital techniques show that the overestimation of the strength of the antiferromagnetism suppresses the formation of an SDW. In the local density approximation we find that a static SDW is also higher in energy than a commensurate antiferromagnetic structure, but with an energy difference that tends towards zero as the lattice constant shrinks to its low-temperature limit. A possible scenario for the origin of the observed SDW state is developed.
Title:
Evidence for interpenetrating magnetic structures across an IC-C phase transition in Mn0.88Fe0.12WO4
Authors:
Stusser N. Ding Y. Hofmann M. Reehuis M. Ouladdiaf B. Ehlers G. Gunther D. Meissner M. Steiner M.
Source:
Journal of Physics-Condensed Matter. 13(12):2753-2766, 2001 Mar 26.
Abstract:
Neuron diffraction, specific heat and magnetization measurements were applied to study the magnetic structures in Mn0.88Fe0.12WO4 using single crystal and powder samples. A commensurate antiferromagnetic structure with a propagation vector k = (1/4, 1/2, 1/2) below 13.5 K and an incommensurate structure with k = (0.23, 0.5, 0.508) between 13.5 K and 15.5 K were found to be th e dominating ordered states. The temperature behaviour of the propagation vector above the IC-C phase transition shows a logarithmic behaviour. An ;FeWO4-type ordering of spins with k approximate to (1/2, 0, 0) is observed below 19 K and coexists between 15.5 K and 13.5 K with the MnWO4-type structure. Our experimental results indicate a cluster-like FeWO4-type magnetic ordering on a diluted 3D lattice, which interpenetrates the dominating MnWO4-type spin ordering. Below 13 K, with the majority of spins ordered in the commensurate MnWO4-type structure, reflections which can be indexed to a unit cell doubled along the crystallographic a-axis appear again; however, these intensities cannot purely be related to Bragg diffraction by ordered local magnetic moments at the (Mn, Fe) positions.
Title:
It takes two to tango: New quasicrystals and novel superconductors
Authors:
Ranganathan S.
Source:
Current Science. 80(6):729-732, 2001 Mar 25.
Title:
Composition-dependent electrical resistivity in an Al-Re-Si 1/1-cubic approximant phase: An indication of electron confinement in clusters
Authors:
Tamura R. Asao T. Takeuchi S.
Source:
Physical Review Letters. 86(14):3104-3107, 2001 Apr 2.
Abstract:
We report the synthesis of alpha -AlReSi and show that it is a 1/1-cubic approximant phase of the icosahedral quasicrystal with a = 12.9 Angstrom. The trend of the resistivity of the new approximant phase shows a nonmetallic character, similar to those seen in the stable icosahedral phases. The resistivity depends sensitively on the Re concentration and the nonmetallic transport is observed only at the Re concentration close to 17.4 at. %, where the transition metal sites in the icosahedral cluster are exclusively occupied by Re atoms. In view of a recent ab initio calculation, the present result suggests strongly the formation of the virtual bound states, or confinement of electrons, in the icosahedral clusters of transition metal atoms.
Title:
Elasticity of a one-dimensional tiling model and its implication to the phason elasticity of quasicrystals - art. no. 132205
Authors:
Jeong HC.
Source:
Physical Review B. 6313(13):2205-+, 2001 Apr 1.
Abstract:
A one-dimensional tiling model with matching rule energy (antiferromagnetic Ising Hamiltonian) is studied. We present an analytic study of a transition from the unlocked phase, where free energy is proportional to the square gradient of the perp-space field [f similar to(partial derivativew)(2)], to the locked phase (f similar to\partial derivativew\) in perp-space elasticity. The phase diagram and the temperature dependence of the elastic constant in the unlocked phase show similarity with the two-dimensional Penrose tiling. The results imply that the unlocking transition of a two-dimensional Penrose tiling model is related to the disordering transition in a one-dimensional Ising model.
Title:
Roles of ferroelectricity, antiferroelectricity, and rotational displacement in the ferroelectric incommensurate phase of Pb(Zr1-xTix)O-3 - art. no. 134103
Authors:
Watanabe S. Koyama Y.
Source:
Physical Review B. 6313(13):4103-+, 2001 Apr 1.
Abstract:
Crystallographic features of the ferroelectric incommensurate phase in Pb(Zr1-xTix)O-3 have been investigated by transmission electron microscopy, mainly using x = 0.05 samples obtained by cooling from a high-temperature paraelectric phase under an electric field of 500 V/cm. The present experimental data clearly indicate that the incommensurate and ferroelectric domains coexist independently, and that the incommensurate structure is characterized by not only a periodic-microdomain structure consisting of two M-3 variants, but also a periodic array of antiphase boundaries for the M-5' antiferroelectric displacement. These observations suggest that the normal structure of the incommensurate structure should be ferroelectric and that the rotational angle of the M-3 rotational displacement can be identified as a modulation mode. In addition, the antiphase boundary of the M-5' antiferroelectric displacement may play the role of discommensuration with a phase slip of pi.
Title:
Nuclear spin relaxation in quasicrystals via hierarchically variable-range electron hopping - art. no. 134203
Authors:
Dolinsek J. Klanjsek M.
Source:
Physical Review B. 6313(13):4203-+, 2001 Apr 1.
Abstract:
A model of NMR spin-lattice relaxation in quasicrystals is presented, which takes into account two important quasicrystals-specific features: (i) the critical nature of the electronic states and (ii) the phonon-assisted hopping nature of electronic conduction within the self-similar quasiperiodic structure of hierarchical clusters. The model is derived for highly resistive quasicrystals that undergo a metal-to-insulator transition in the T --> 0 limit. The applicability of the model was tested by Al-27 NMR spin-lattice relaxation experiment on several samples including structurally perfect icosahedral Al70.5Pd21Re8.5 and Al62Cu25.5Fe12.5 and less perfect icosahedral Al63Cu23Fe12 quasicrystals, as well as on the metallic Al32.2Cu56.6Fe11.2. The results show that the model applies well to the structurally perfect samples with high-electrical resistivity, whereas it does not apply to the less perfect samples with an increased metallic character. However, the NMR relaxation data show a precursor of the electron hopping conduction also in less perfect samples, suggesting that this phenomenon may not be restricted to high-quality quasicrystals only.
Title:
Spin fluctuations in the underdoped High-T-c cuprate La1.93Sr0.07CuO4
Authors:
Hiraka H. Endoh Y. Fujita M. Lee YS. Kulda J. Ivanov A. Birgeneau RJ.
Source:
Journal of the Physical Society of Japan. 70(3):853-858, 2001 Mar.
Abstract:
We performed magnetic inelastic neutron-scattering experiments on La1.93Sr0.07CuO4 over a wide range of omega and T; 2 less than or equal to omega less than or equal to 44meV and 1.5 less than or equal to T < 300 K. The dynamic susceptibility <chi>" (q, omega) of this underdoped high-T-c superconductor (T-c = 17K) is characterized by broad, incommensurate peaks. Here, the incommensurate wavevector delta (omega) is approximately 0.07 reciprocal lattice units at low T and omega. The superconducting phase does not possess an observable gap in the spin excitation spectrum down to at least 2 meV. Scaling behavior is demonstrated for the Q-integrated energy spectrum chi "(omega)(T) with respect to (omega /k(B)T). This scaling establishes a connnection between the magnetic excitations of the compositions on either side of the insulator-superconductor boundary in the La2-xSrxCuO4 phase diagram. We note a possible cross-over from an incommensurate to a commensurate response for omega > 20 meV or T > 300 K.
Title:
On some discrepancies in the literature about the formation of icosahedral quasi-crystal in Al-Cu-Fe alloys
Authors:
Gui JN. Wang JB. Wang RH. Wang DH. Liu J. Chen FY.
Source:
Journal of Materials Research. 16(4):1037-1046, 2001 Apr.
Abstract:
To clarify some discrepancies in the literature about the formation of icosahedral quasi-crystal (IQC) in Al-Cu-Fe alloys, microstructures, and constituent phases of Al62.5Cu25Fe12.5 and Al65Cu20Fe15 alloys were studied, Each dendritic arm of the primarily solidified lambda -Al13Fe4 phase is a single crystal that possesses no definite orientation relationship with the IQC, formed by peritectic reaction (L + lambda + beta --> IQC) or a solid-state reaction (Cu-rich phases + lambda + beta --> IQC), This fact disproves an assumption that h-phase is an approximant of the IQC, Two types of cubic phase, beta -phase with CsCl structure containing more Fe and tau (3) phase, which is a superstructure and contains less Fe, were observed depending on the composition and thermal history of the samples.
Title:
Precipitation of icosahedral quasicrystalline phase in Hf69.5Al7.5Ni11Cu12 metallic glass
Authors:
Li CH. Inoue A.
Source:
Journal of Materials Research. 16(4):1190-1194, 2001 Apr.
Abstract:
A Hf69.5Al7.5Ni11Cu12 metallic glass was prepared by a single roller melt-spinning method, and the crystallization process was studied by x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The metallic glass crystallizes through three exothermic reactions. The low-temperature exothermic reaction corresponded to the precipitation of an icosahedral quasicrystalline phase. Further annealing at higher temperature led to the decomposition of the icosahedral quasicrystalline phase to other stable crystalline phases, indicating that the precipitated icosahedral quasicrystalline phase was in a metastable state. The crystallization process of the present alloy was compared with that of other Hf-Al-Ni-Cu alloys, and the reason for the precipitation of the icosahedral quasicrystalline phase was discussed.
Title:
The spectroscopic properties of 1D Peierls systems
Authors:
Grioni M. Perfetti L. Rojas C. Berger H. Margaritondo G. Voit J. Hoechst H.
Source:
Journal of Electron Spectroscopy & Related Phenomena. 114:653-657, 2001 Mar.
Abstract:
We have studied by high resolution ARPES the spectroscopic properties of the prototype charge density wave system (TaSe4)(2)I and of the closely related insulating compound (NbSe4)(3)I. We observe features dispersing with the lattice periodicity, including commensurate (in (NbSe4)(3)I) and incommensurate (in (TaSe4)(2)I) superlattice shadow bands. The spectral lineshape is anomalous in the normal metallic state, and the intensity is strongly suppressed near the Fermi surface. In the insulating CDW state the linear extrapolation of the leading edge rather than the peak position identifies the gap energy scale. (C) 2001 Elsevier Science B.V; All rights reserved.
Title:
Transmission electron microscopy studies of the effect of A-site cation size mismatch and disorder on charge ordering behavior in (La1-xYx)(0.5)(Ca1-ySry)(0.5)MnO3
Authors:
Wang YQ. Duan XF. Wang ZH. Shen BG.
Source:
Applied Physics Letters. 78(15):2157-2159, 2001 Apr 9.
Abstract:
The effects of A-site cation mismatch and disorder on the charge ordering (CO) behavior in the manganites (La1-xYx)(0.5)(Ca1-ySry)(0.5)MnO3 have been studied by transmission electron microscopy. The presence of the size mismatch and disorder suppresses the CO transition. Incommensurate CO modulations are observed in three samples with 0 less than or equal to sigma (2)less than or equal to0.003. Structural models, based on the selected area electron diffraction and high-resolution electron microscopy observation, are suggested for such kinds of incommensurate modulations. (C) 2001 American Institute of Physics.
Title:
Measurement of the density of states of a Al6Ru quasicrystalline alloy by ultrafast thermomodulation
Authors:
Ferreira TAE. Acioli LH. Machado FLA.
Source:
Solid State Communications. 118(1):37-41, 2001.
Abstract:
In this paper, we present results of time-resolved optical measurements of electron dynamics in the metastable quasicrystal Al6Ru. A hot electron distribution is photo-excited by femtosecond laser pulses and the relaxation rates of the hot electron distribution cooling are measured. These rates are observed to change drastically close to the Fermi level and our results are compatible with the presence of a strong depression in the density of states (DOS) over an energy range of approximately 45 meV. These features have been predicted from numerical calculations of the density of states in many quasicrystalline materials and ours are the first experimental results in the optical domain to confirm these predictions. (C) 2001 Elsevier Science Ltd. All rights reserved.
Title:
Initial stages of Fe-C martensite decomposition
Authors:
Han K. van Genderen MJ. Bottger A. Zandbergen HW. Mittemeijer EJ.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 81(3):741-757, 2001 Mar.
Abstract:
The decomposition of Fe-C martensite (alpha') was studied using conventional transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffractometry and differential scanning calorimetry. The ageing and tempering of a at temperatures between room temperature and 423 K result in changes in the atomic structure of a' and subsequently precipitation of iron carbide. In an early stage of decomposition, carbon enrichments develop in the iron matrix. At temperatures below about 363 K, this development of carbon-enriched and carbon-depleted zones leads gradually to the formation of a modulated structure, as revealed by the observation of specific diffraction phenomena. The carbon enrichments possess variable carbon content. Their misfit with the matrix is, at least initially, accommodated elastically. At temperatures above about 363 K, the transition carbide precipitates. It could be shown that the transition carbide has the eta -carbide crystal structure and the orientation relationship with the matrix was determined.
Title:
Evidence of a stable binary CdCa quasicrystalline phase
Authors:
Jiang JZ. Jensen CH. Rasmussen AR. Gerward L.
Source:
Applied Physics Letters. 78(13):1856-1857, 2001 Mar 26.
Abstract:
Quasicrystals with a primitive icosahedral structure and a quasilattice constant of 5.1215 Angstrom have been synthesized in a binary Cd-Ca system. The thermal stability of the quasicrystal has been investigated by in situ high-temperature x-ray powder diffraction using synchrotron radiation. It is demonstrated that the binary CdCa quasicrystal is thermodynamic stable up to its melting temperature. The linear thermal expansion coefficient of the quasicrystal is 2.765x10(-5) K-1. (C) 2001 American Institute of Physics.

Update: 16-Apr-2001

Title:
A new three-dimensional incommensurately modulated cubic phase (in ZrP2B7) and its symmetry characterization via temperature-dependent electron diffraction
Authors:
Withers RL. Tabira Y. Evans JSO. King IJ. Sleight AW.
Source:
Journal of Solid State Chemistry. 157(1):186-192, 2001 Feb 15.
Abstract:
A detailed electron diffraction study has been made of the ZrP2O7 member of the AM(2)O(7) family of framework structures and of its temperature-dependent structural phase transformations. The room-temperature phase corresponds to a primitive 3 x 3 x 3 superstructure phase of probable space group symmetry Pa3. An observed glide extinction condition when viewed down < 001 > ages could, however, also be compatible with resultant Pbca space group symmetry. The high-temperature phase corresponds to the normal unmodulated parent structure. An intervening intermediate phase that exists over a relatively narrow temperature window (similar to 5-10 degreesC) around 294 degreesC is shown to be a three-dimensional incommensurately modulated cubic phase characterized by incommensurate primary modulation wave vectors in the close vicinity of 0.31 < 100 >* and probable superspace group symmetry P: Pa (3) over bar: Ia (3) over bar. (C) 2001 Academic Press.
Title:
Triangular lattices of charge- and spin-density waves in chemisorbed metal monolayers on the surface of diamond structure semiconductors
Authors:
Avignon M. Men'shov VN. Tugushev VV.
Source:
Physics of the Solid State. 43(3):563-568, 2001.
Abstract:
The electronic spectrum of a planar triangular lattice is analyzed, and the possible occurrence of charge (CDWs) and spin density waves (SDWs) in the lattice is discussed. Commensurate CDW and SDW structures of two types are considered in the weak and strong electron-electron interaction approximations. The CDW and SDW models are applied to the specific case of chemisorbed metal monolayers on the (111) surface of diamond structure semiconductors with a coverage close to 1/3. (C) 2001 MAIK "Nauka/Interperiodica".
Title:
High-resolution resonant magnetic x-ray scattering on TbNi2B2C: Determination of the modulation wave vector in the orthorhombic phase - art. no. 104507
Authors:
Song C. Wermeille D. Goldman AI. Canfield PC. Rhee JY. Harmon BN.
Source:
Physical Review B. 6310(10):4507-+, 2001 Mar 1.
Abstract:
Resonant magnetic x-ray scattering measurements have been performed on a single crystal of TbNi2B2C to uniquely determine the modulation wave vector in the low-temperature orthorhombic phase. Below the transition temperature of 14.4(+/-0.1) K, two magnetic satellite peaks develop, centered on (h0)(orth) charge reflections. Our study shows that the longitudinal modulation of the magnetic moment is along, the longer basal plane axes of the orthorhombic phase. Power law fits to the temperature dependence of the structural distortion, a/b-1, and the magnetic scattering intensity result in the same exponent, beta, and transition temperature evidencing explicitly that the structural phase transition is magneto-elastic in origin.
Title:
Structural study of a superlattice Al-Ni-Ru decagonal quasicrystal using high-resolution electron microscopy and a high-angle annular dark-field technique
Authors:
Sun W. Hiraga K.
Source:
Philosophical Magazine Letters. 81(3):187-195, 2001 Mar.
Abstract:
A high-quality superlattice Al-Ni-Ru decagonal quasicrystal with 0.4 nm periodicity, formed in the conventionally solidified Al70Ni20Ru10 alloy, has been studied by high-resolution electron microscopy and a high-angle annular dark-field (Z-contrast) technique. It has been clearly revealed that its structure is characterized as an a periodically ordered arrangement of decagon-shaped atomic columnar clusters which have a diameter of 2 nm and show pentagonal symmetry. On the basis of high-resolution electron microscopy structure images, and the atom-resolution Z-contrast observations which highlight the transition-metal sites, the arrangement of atoms in the superlattice decagonal quasicrystal are proposed.
Title:
Disorder versus structure analysis in intergrowth urea inclusion compounds
Authors:
Rabiller P. Etrillard J. Toupet L. Kiat JM. Launois P. Petricek V. Breczewski T.
Source:
Journal of Physics-Condensed Matter. 13(8):1653-1668, 2001 Feb 26.
Abstract:
Alkane/urea inclusion compounds constitute a class of incommensurate composite materials, characterized by a pronounced one dimensional character and strong disorder of the alkane molecules. Intrinsic features of the alkane molecular form factor can be used to obtain a quantitative interpretation of the alkane subsystem translational degree of freedom whereas they lead to the restriction of observable Bragg reflections. A rigid body approach is also presented, which gives a simple description of the alkane sublattice modulation in the frame of (3 + 1) dimensional structure refinement.
Title:
Generalized matching rules for aperiodic tilings
Authors:
Bellingeri P. Ossi PM.
Source:
Journal of Alloys & Compounds. 316(1-2):39-45, 2001 Mar 2.
Abstract:
In this work we briefly discuss the substitution process, the most common tool to study aperiodicity, and some results which derive from this concept. Using k-coronas, we prove then some theorems about the link between aperiodicity and periodicity. Finally we propose a new approach to the 'aperiodicity problem'. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Magnetic properties and magnetic structures of RIrSi (R=Tb-Er) series of compounds
Authors:
Szytula A. Hofmann M. Leciejewicz J. Penc B. Zygmunt A.
Source:
Journal of Alloys & Compounds. 316(1-2):58-63, 2001 Mar 2.
Abstract:
Magnetic properties and magnetic structures of RIrSi (T=Tb, Dy, Ho, Er) series of ternary intermetallic were determined by X-ray and neutron diffraction and by magnetometric methods. Ail these compounds exhibit the orthorhombic TiNiSi-type crystal structure and are antiferromagnetic at low temperatures. Below the Neel point (T-N=32 K) TbIrSi shows a sine modulated magnetic order described by the wave vector k=[0.2938(2), 0] with the Tb magnetic moments equal 8.96(16) mu (B) and parallel to the c-axis at 1.5 K. The collinear antiferromagnetic structure with the wave vector k=[1/2, 0, 1/2] and the magnetic moment of 9.9(1) mu (B) parallel to the b-axis is observed in HoIrSi at 1.5 K. In the vicinity of the Neel temperature (T-N=4.6 K) this structure coexists with the sine modulated order described by the wave Vector k=[0.215(2), 0, 0.458(2)]. DyIrSi is antiferromagnetic below the Neel temperature (T-N=7 K). Below the Neel temperature (T-N =3.8 K), ErIrSi has a sine modulated magnetic structure described by the wave vector k=[0, 0.184(1), 0.297(3)] and the magnetic moment of 6.5(2) mu (B) is aligned in the (100) plane at 1.5 K. (C) 2001 Elsevier Science B.V. All lights reserved.
Title:
Commensurate-incommensurate transition in two-coupled chains of nearly half-filled electrons
Authors:
Tsuchiizu M. Donohue P. Suzumura Y. Giamarchi T.
Source:
European Physical Journal B. 19(2):185-193, 2001 Jan.
Abstract:
We investigate the physical properties of two coupled chains of electrons, with a nearly half-filled band, as a function of the interchain hopping t(perpendicular to) and the doping. Mie show that upon doping, the system undergoes a metal-insulator transition well described by a commensurate-incommensurate transition. By using bosonization and renormalization we determine the full phase diagram of the system, and the physical quantities such as the charge gap. In the commensurate phase two different regions, for which the interchain hopping is relevant and irrelevant exist, leading to a confinement-deconfinement crossover in this phase. A minimum of the charge gap is observed for values of ti close to this crossover. At large t(perpendicular to) the region of the commensurate phase is enhanced, compared to a single chain. At the metal-insulator transition the Luttinger parameter takes the universal value K-rho* = 1, in agreement with previous results on special limits of this model.
Title:
Local structure of Co and Ni in decagonal AlNiCo investigated by polarized EXAFS
Authors:
Zaharko O. Meneghini C. Cervellino A. Fischer E.
Source:
European Physical Journal B. 19(2):207-213, 2001 Jan.
Abstract:
The local structure of cobalt and nickel in single crystals of decagonal quasicrystals with composition Al71.5Ni15.5CO13 and Al75Ni14.5CO10.5 have been studied by polarized EXAFS. Significant differences between the Ni and Co local environments have been detected. The effective absence of the 4 Angstrom periodicity along the decagonal axis in these QCs is confirmed and indications about its reasons are presented.
Title:
Surface oxidation of Al-Cr-Fe alloys characterized by X-ray photoelectron spectroscopy
Authors:
Demange V. Anderegg JW. Ghanbaja J. Machizaud F. Sordelet DJ. Besser M. Thiel PA. Dubois JM.
Source:
Applied Surface Science. 173(3-4):327-338, 2001 Mar 29.
Abstract:
We present X-ray photoelectron spectroscopy (XPS) measurements of several Al-Cr-Fe samples which are mixtures of approximants of the decagonal phase. Some samples also contain a hexagonal gamma -brass phase. Our purpose is to evaluate the effect of chemical composition, particularly Cr content, on the response of the surface to oxidation. Under mild conditions only aluminium oxidizes, but under extreme conditions (water immersion at room temperature, or oxygen exposure at high temperatures), chromium oxidizes as well. XPS data also provide a measure of the oxide thickness. Cr has no discernible effect on oxide thickness when the oxidizing environment is the gas phase, but provides significant protection against water immersion, where high concentrations of Cr reduce the thickness by as much as 40%. These results for the Al-Cr-Fe samples are compared with results for approximants and quasicrystals in other systems. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Crystal and magnetic structure of orthorhombic HoMnO3 - art. no. 094411
Authors:
Brinks HW. Rodriguez-Carvajal J. Fjellvag H. Kjekshus A. Hauback BC.
Source:
Physical Review B. 6309(9):4411-+, 2001 Mar 1.
Abstract:
o-HoMnO3 crystallizes in the GdFeO3-type structure (Pbnm) with no crystal structure anomalies below 295 K and with the Mn-O-Mn angle as low as 144.1 degrees. The Mn3+ and Ho3+ magnetic moments are ordered below T-N = 38 K and T-Ho = 11 K, respectively. The ordering is incommensurate with a propagation vector k = k(y)b*, where k(y) is between 0.395 and 0.431 depending on temperature. Symmetry analyses have been carried out for both magnetic sites. The ordering was determined to be A(y) for the Mn3+ moments, modulated in a longitudinal sinusoidal wave along the propagation vector. The Ho3+ moments order with the same propagation vector as Mn3+, but the site is split in two orbits of two ions, each ordered in an a(x)f(y) pattern with a phase factor between them. At the lowest temperatures an antiferromagnetic (commensurate) magnetic phase appears in competition with the main (incommensurate) magnetic phase. The arrangement of the moments is discussed in terms of the magnetic exchange interactions and compared with the closely related magnetic structures of LaMnO3, TbMnO3, and o-YMnO3. k(y) is found to increase with decreasing size of the rare-earth component. [References: 27]
Title:
Influence of the dipolar interaction on phase diagram, magnons, and magnetization in quasi-one-dimensional antiferromagnets on a hexagonal lattice - art. no. 094425
Authors:
Hummel M. Schwabl F. Pich C.
Source:
Physical Review B. 6309(9):4425-+, 2001 Mar 1.
Abstract:
The role of the dipole-dipole interaction in quasi-one-dimensional antiferromagnets is investigated within a Heisenberg model with nearest-neighbor exchange. We deal with systems in which the magnetic ions are located on a hexagonal lattice, i.e., frustration is present when three-dimensional order sets in. We perform a ground-state calculation for different ratios of dipolar energy to interchain-exchange energy and find several commensurate and incommensurate phases. This is a consequence of the competing character of these two interactions. For the commensurate phases the influence of fluctuations is studied by means of linear spin-wave theory. It turns out that all commensurate phases are stable against fluctuations. The theoretical spin-wave spectra are compared with experiments on CsMnBr3 and RbMnBr3. The results suggest that the most important source of anisotropy in these Mn compounds is the dipole-dipole interaction. Furthermore the magnetic phase-diagram for small dipolar energies is investigated. A spin-wave calculation allows one to calculate the influence of the fluctuations on physical properties like ground-state energy and magnetization. These results compare favorably with measurements on CsMnBr3.
Title:
Specific study on 1T-TaSe2 in the context of Commensurate Charge Density Wave
Authors:
Balaguru RJB. Lawrence N. Raj SAC.
Source:
Physica Status Solidi B-Basic Research. 223(3):779-784, 2001 Feb.
Abstract:
The Charge Density Wave (CDW) in the layered compound 1T-TaSe2 at low temperatures has a commensurate phase which causes superlattice points to appear in the Brillouin zone of the undistorted phase. The phonon frequency distribution of this system for both the normal and the Commensurate Charge Density Wave (CCDW) phases have been worked out theoretically using the Born-von Karmann formalism. With these results the thermal properties such as specific heat capacity, Debye-Waller factor and thermal conductivity have been worked out and are compared with the available experimental results.
Title:
Characterization of cut-and-project sets using a binary operation
Authors:
Masakova Z. Pelantova E. Svobodova M.
Source:
Letters in Mathematical Physics. 54(1):1-10, 2000 Oct.
Abstract:
Cut-and-project sets with convex acceptance windows, based on irrationalities tau =1/2(1+root5), beta =1+root2, mu =2+root3 are models for experimentally observed quasicrystals - materials with diffraction patterns consisting of sharp Bragg peaks in crystallographically disallowed patterns. We show that for each of these three irrationalities there exists a unique binary operation of the type x proves (s)y:=sx+(1-s)y, such that one-dimensional cut-and-project sets are precisely Delone sets closed under this operation. [References: 9]
Title:
Nuclear quadrupole resonance study of phase transitions and incommensurability in K2SbF5
Authors:
Panich AM. Zemnukhova LA. Davidovich RL.
Source:
Journal of Physics-Condensed Matter. 13(7):1609-1616, 2001 Feb 19.
Abstract:
Phase transitions and incommensurability in K2SbF5 has been studied by means of Sb-123 NQR spectra and spin-lattice relaxation measurements. The phase transitions have been obtained at 117, 135 and 260 K. Line shape and temperature dependence of the spin-lattice relaxation time T-1 in the temperature range from 135 to 260 K are characteristic for the incommensurate state with the plane wave modulation regime. At 117 to 135 K, a distinct fine structure of NQR spectra has been observed. Redistribution of line intensities with the variation of temperature allows us to suggest that this phase exhibits domain structure, and that one of the domains becomes energetically beneficial on cooling and transforms into the low temperature phase at 117 K. The Sb-123 NQR measurements in K2SbF5 show unusually short values of T-1, which become close to the spin-spin relaxation time T-2 With increasing temperature.
Title:
Formation of a magnetic soliton lattice in copper metaborate
Authors:
Roessli B. Schefer J. Petrakovskii GA. Ouladdiaf B. Boehm M. Staub U. Vorotinov A. Bezmaternikh L.
Source:
Physical Review Letters. 86(9):1885-1888, 2001 Feb 26.
Abstract:
The magnetic ground state of CuB2O4 is incommensurate at T = 1.8 K and undergoes a continuous phase transition to a noncollinear commensurate antiferromagnetic state at T* similar to 10 K. Close to T* higher-order magnetic satellites are observed. Coexistence of long- and short-range magnetic order is observed in both magnetic phases. This suggests that the association of the Dzyaloshinskii-Moriya interaction and anisotropy leads to the formation of a magnetic soliton lattice.
Title:
Absolute photonic band gaps in 12-fold symmetric photonic quasicrystals - art. no. 081105
Authors:
Zhang XD. Zhang ZQ. Chan CT.
Source:
Physical Review B. 6308(8):1105-+, 2001 Feb 15.
Abstract:
A recent publication [Nature (London) 404, 740 (2000)] claimed that absolute photonic gaps carl be realized in 12-fold quasicrystalline arrangement of small airholes in a matrix of silicon nitride or glass. The result is rather surprising since silicon nitride (n = 2.02) and in particular, glass (n = 1.45) have rather low refractive index. In this work, we have studied the transmission properties of the same systems by using the multiple-scattering method. We found that the 12-fold triangle-square tiling is indeed very good for the realization of photonic gaps and we found absolute gaps in systems with airholes in dielectric, dielectric cylinders in air, and metal cylinders in air. However, for the case of air-holes in a dielectric background, absolute gaps appear only when the dielectric contrast is sufficiently high, and both silicon nitride and glass have refractive indices below the threshold.
Title:
Scaling exponents in the incommensurate phase of the sine-Gordon and U(1) Thirring models - art. no. 085109
Authors:
Papa E. Tsvelik AM.
Source:
Physical Review B. 6308(8):5109-+, 2001 Feb 15.
Abstract:
In this paper we study the critical exponents of the quantum sine-Gordon model and U(1) Thirring models in the incommensurate phase. This phase appears when the chemical potential h exceeds a critical value and is characterized by a finite density of solitons. The low-energy sector of this phase is critical and is described by the Gaussian model (Tomonaga-Luttinger liquid) with the compactification radius dependent on the soliton density and the sine-Gordon model coupling constant beta. For a fixed value of beta, we find that the Luttinger parameter K is equal to 1/2 at the commensurate-incommensurate transition point and approaches the asymptotic value beta (2)/8 pi away from it. We describe a possible phase diagram of the model consisting of an array of weakly coupled chains. The possible phases are Fermi liquid, spin density wave, spin-Peierls, and Wigner crystal.
Title:
Simulation of modulated structures in quartz
Authors:
Dmitriev SV. Yajima M. Makita Y. Semagin DA. Abe K. Shigenari T.
Source:
Journal of the Physical Society of Japan. 70(2):428-436, 2001 Feb.
Abstract:
We report the results of molecular-dynamics calculation of equilibrium modulated phases of quartz in the vicinity of pressure induced alpha - beta transition. A numerical method suitable for simulation of modulated phases in the vicinity of transition point was developed. The phase diagram with respect to the unit cell deformations was obtained from the pairwise interatomic potentials by [Tsuneyuki et al.: Phys. Rev. Lett. 61 (1988) 869]. The results show that the modulated structures with various wavevectors appear between alpha- and beta -phases suggesting that the softening may occur at any point on the Sigma line in the Brillouin zone and that a structure with large wavevector seems to be more probable than one with a small wavevector.
Title:
Computer modeling and description of nonstoichiometric apatites Cd5-eta/2(VO4)(3)I1-eta and Cd5-eta/2(PO4)(3)Br1-eta as modified chimney-ladder structures with ladder-ladder and chimney-ladder coupling
Authors:
Christy AG. Alberius-Henning P. Lidin SA.
Source:
Journal of Solid State Chemistry. 156(1):88-100, 2001 Jan.
Abstract:
Diffraction patterns from apatite-structure compounds Cd5-eta /2(TO4)(3)X1-eta with T= P, V and X = Br, I show sheets of diffuse scattering normal to c* at incommensurate l = q (q = 1.63 for Cd-V-I apatite and q = 1.78 for Cd-P-Br apatite), because the c repeat of the average unit cell is shorter than two X diameters. The equilibrium X,,X spacing along c defines the incommensurate periodicity clq and stoichiometry (1-eta) = q/2, The layers show a honeycomb texture for the Cd-V-I apatite, which is condensed into discrete spots for the Cd-P-Br compound. In both phases, X..X repulsions along < 100 > force neighboring rods of X atoms out of phase. In the Cd-P-Br phase, additional < 210 > attractions drive incipient formation of a rhombohedral superstructure. Average structure site occupancies and the observation of second-order diffuse layers at both l = 2q and l = q+2 imply the existence of strong Cd..X in addition to X..X interactions. A three-dimensional computer model was used to produce finite-temperature structure simulations as a function of X..X interactions along < 001 >, < 100 >, and < 210 >, and X..Cd interactions, from which diffraction patterns were calculated, The experimental patterns were fit and approximate values for the interaction energies obtained (hundreds to thousands of joules per mole). It was apparent that lock-in to commensurability caused by the X..Cd term and the formation of nonprimitive incommensurate modulated structures driven by X..X interactions were mutually antagonistic, and the actual structures are compromises between the two. (C) 2001 Academic Press.
Title:
Bi1-xCrxO1.5+1.5x, 0.05 <= x <= 0.15: A new high-temperature solid solution with a three-dimensional incommensurate modulation
Authors:
Esmaeilzadeh S. Lundgren S. Halenius U. Grins J.
Source:
Journal of Solid State Chemistry. 156(1):168-180, 2001 Jan.
Abstract:
A new metastable solid solution Bi1-xCrxO1.5+1.5x with 0.05 less than or equal to x less than or equal to 0.15 was synthesized by quenching Bi-Cr-O melts and structurally investigated using electron microscopy and X-ray diffraction, The oxidation state of Cr was determined to be + VI by thermogravimetry, optical spectroscopy, and magnetic measurements. Infrared spectra indicate for x = 0.05 isolated CrO42- tetrahedra and also smaller fractions of Cr2O72- units. The phase exhibits an average structure of the Fm3m fluorite type and a 3D incommensurate modulation, with wave vectors q(1) = [alpha, 0, 0]*, q(2) = [0, alpha, 0]*, q(3) = [0, 0, alpha]*, a = 5.6025(3)Angstrom, and a = 0.2866(2) for x = 0.15, and with the 3 + 3D superspace group symmetry P:Fm3m:Fm3m. Atomic modulation functions and periodic nodal surfaces were deduced for observed satellite reflections and a commensurate structure model derived for x = 0.05. The modulated structure was compared with that of Bi0.78Nb0.22O1.72, with symmetry P:Fm3m:Fd3m. (C) 2001 Academic Press.
Title:
Atomic short-range order in an Al72Ni20Co8 decagonal quasicrystal by anomalous-X-ray scattering
Authors:
Abe H. Matsuo Y. Saitoh H. Kusawake T. Ohshima K. Nakao H.
Source:
Japanese Journal of Applied Physics Part 2-Letters. 39(11A):L1111-L1114, 2000 Nov 1.
Abstract:
By anamalous-X-ray scattering, the diffuse scattering around Bragg reflections was observed in a single decagonal quasicrystal of Al72Ni20Co8 which has no phason strain. The diffuse scattering is distributed around the center of the superstructure points. Intensity modulations of the diffuse scattering occur at each incident wavelength. The contrast of diffuse scattering shows the presence of atomic short-range order (SRO) in three kinds of pair correlation functions: between Al and Ni, between Ni and Co and between Co and Al. The correlation length of the diffuse scattering is estimated to be 22.5 Angstrom.
Title:
Positron-annihilation studies of Frank-Kasper-type quasicrystals of the Mg-Zn-Ga-Al and the Mg-Zn-rare-earth system
Authors:
Hamada E. Sato K. Takahashi Y. Uchiyama H. Kanazawa I. Oshima N. Suzuki T. Nakata M. Yoshida T. Takeuchi S.
Source:
Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes & Review Papers. 40(1):259-262, 2001 Jan.
Abstract:
We have performed positron-annihilation experiments thr a Frank-Kasper (F-K)-type icosahedral quasicrystal, 2/1 and 1/1 approximant crystals of Mg-Zn-Ga-Al, and the stable F-K-type icosahedral quasicrystals of Mg-Zn-RE (RE=rare-earth metal, Y, Ho and Gd) alloys. It is shown that a high density of vacant centers in triacontahedral clusters exists in both icosahedral and approximant phases of Mg-Zn-Ga-Al. Furthermore, in the present study, we report a very interesting finding that stable non-Al-based quasicrystals such as the icosahedral quasicrystal Mg-Zn-RE system also contain a high density of structural vacancies, similar to the stable Al-based quasicrystals. In particular, it is estimated experimentally that the structural vacancy densities for icosahedral quasicrystal Mg34Zn58Y8 and Mg40Zn52Ho8 are 3 x 10(20) and 4 x 10(20) cm(-3), respectively. These results provide important information on the structural modeling of the stable icosahedral quasicrystal Mg-Zn-RE, which is 3 recent research topic of the icosahedral quasicrystals.
Title:
The thermal expansion coefficient of mechanically alloyed Al-Cu-Fe quasicrystalline powders
Authors:
Korsunsky AM. Salimon AI. Pape I. Polyakov AM. Fitch AN.
Source:
Scripta Materialia. 44(2):217-222, 2001 Feb 2.
Title:
Easter is a quasicrystal
Authors:
Stewart I.
Source:
Scientific American. 284(3):80-+, 2001 Mar.
Title:
Chemical ordering in Al72Ni20Co8 decagonal quasicrystals
Authors:
Yan YF. Pennycook SJ.
Source:
Physical Review Letters. 86(8):1542-1545, 2001 Feb 19.
Abstract:
First-principles total energy calculations of the 2-nm clusters seen in high-perfection Al72Ni20Co8 decagonal quasicrystals demonstrate that chemical ordering between Al and transition metals in the central ring is energetically highly favorable. The chemical ordering introduces extensive structure relaxation and results in broken decagonal symmetry. Such broken symmetry is sufficient to enforce the perfect quasiperiodic tiling.
Title:
An ordered arrangement of columnar clusters of atoms in a rhombic quasiperiodic lattice in an Al-Ni-Co decagonal phase
Authors:
Hiraga K. Ohsuna T. Nishimura S. Kawasaki M.
Source:
Philosophical Magazine Letters. 81(2):109-115, 2001 Feb.
Abstract:
We have found that the structure of an Al-Ni-Co decagonal quasicrystal, which shows a diffraction pattern with many superlattice reflections (called a 'type I superlattice'), can be described as an ordered arrangement of two kinds of atomic columnar cluster with different orientations of their pentagonal symmetry. The fundamental lattice, which is constructed by connecting the clusters, is a rhombic quasiperiodic lattice with a bond length of about 2 nm. The two kinds of cluster are placed at the lattice points in a definite,manner such that the two connected clusters have different orientations.
Title:
A large columnar cluster of atoms in an Al-Cu-Rh decagonal quasicrystal studied by atomic-scale electron microscopy observations
Authors:
Hiraga K. Ohsuna T. Park KT.
Source:
Philosophical Magazine Letters. 81(2):117-122, 2001 Feb.
Abstract:
We have found a columnar atomic cluster with a decagonal section of about 3.2 nm in diameter as a structural unit of an Al-Cu-Rh decagonal quasicrystal with 0.4 nm periodicity, using atomic-scale observations of high-resolution transmission electron microscopy (HRTEM) and high-angle annular detector dark-field (HAADF) scanning transmission electron microscopy (STEM). The decagonal cluster is tau times (tau is the golden ratio) the largest cluster (2.0 nm in diameter) previously found in Al-Ni-Co and Al-Pd-Mn decagonal quasicrystals. A structural model of the cluster is proposed from HRTEM and HAADF STEM images.
Title:
The structure of an Al-Ni-Co pentagonal quasicrystal studied by high-angle annular detector dark-field electron microscopy
Authors:
Hiraga K. Ohsuna T. Nishimura S.
Source:
Philosophical Magazine Letters. 81(2):123-127, 2001 Feb.
Abstract:
An Al-Ni-Co pentagonal quasicrystal, showing electron diffraction patterns with pentagonal symmetry and including so-called superlattice reflections, has been examined by the high-angle annular detector dark-field technique with scanning transmission electron microscopy. Columnar clusters with pentagonal arrangement of transition-metal atoms around their centres are arrayed in a rhombic tiling with a bond length of 2 nm, all the clusters having the same orientation of pentagonal symmetry.
Title:
On the transformations of the psi-AlCuFe icosahedral phase
Authors:
Rosas G. Perez R.
Source:
Materials Letters. 47(4-5):225-230, 2001 Feb.
Abstract:
In the present investigation. different alloy compositions close to the ternary composition values, where the icosahedral phase in AlFeCu is obtained have been studied. The specimens were obtained using a rapid solidification technique with subsequent thermal treatments of 600 degreesC, 700 degreesC, 800 degreesC and 900 degreesC. The obtained specimens were characterized with X-ray diffraction patterns (XRD) and transmission electron microscopy (TEM). The experimental results show different transformations of the icosahedral phase to crystalline phases between 800 degreesC and 700 degreesC. The cubic beta -phase is a solid solution which regulates the formation and decomposition of the psi -Al6Cu2Fe phase to different crystalline phases such as, the tetragonal (Al7Cu2Fe) and monoclinic (Al13Fe4) phases. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 9]
Title:
Magnetic structures of RTSb2 (R=Pr,Nd; T=Cu,Pd) compounds
Authors:
Kolenda M. Hofmann M. Leciejewicz J. Penc B. Szytula A. Zygmunt A.
Source:
Journal of Alloys & Compounds. 315(1-2):22-27, 2001 Feb 9.
Abstract:
RTSb2 (R=Pr,Nd: T=Cu.Pd) compounds crystallize in the tetragonal ZrCuSi2-type of crystal structure and are antiferromagnets with Neel temperatures of 7.6 K for PrPdSb2. 3.78 K for NdCuSb2 and 7.0 K for NdPdSb2. Neutron diffraction data indicate that at 1.5 K all these compounds show sine-wave modulated magnetic ordering with different values of the wave vector: k=(0,0,0.743(2)) for PrPdSb2, (0.0.3336(13).0) for NdCuSb2 and (0.0.0.2274(15)) for NdPdSb2. (C) 2001 Elsevier Science B.V. All rights received.
Title:
Complex magnetism and magnetic structures of the metastable HoMnO3 perovskite
Authors:
Munoz A. Casais MT. Alonso JA. Martinez-Lope MJ. Martinez JL. Fernandez-Diaz MT.
Source:
Inorganic Chemistry. 40(5):1020-1028, 2001 Feb 26.
Abstract:
The magnetic properties and the low-temperature magnetic structures of the orthorhombic perovskite HoMnO3 (space group Pnma) have been studied on polycrystalline samples by magnetization, specific heat, and neutron diffraction measurements. By cooling, HoMnO3 exhibits three singularities at T-N = 41 K, T approximate to 26 K, and T approximate to 6.5 K, suggesting a rich magnetic phase diagram. The neutron diffraction data show that below T-N = 41 K, the Mn3+ magnetic moments become ordered in an antiferromagnetic arrangement, adopting a modulated sinusoidal magnetic structure characterized by the wave vector k = (k(x),0,0) (k(x) = 0.40 at 41 K) and defined by the magnetic mode (C-x,0,0). When the temperature is decreased, the propagation vector varies and at I approximate to 29 K a transition to a commensurate magnetic structure defined by k = (1/2,0,0) takes place. Below T approximate to 22 K, a small ordered magnetic moment appears on the Ho3+ cations, strongly increasing below 9 K and reaching 7.3(1) mu (B) at T = 1.8 K. The magnetic structure of the Ho3+ moments is defined by a (A(x),0,C-z) mode. The (H,T) phase diagram has been mapped out and the different magnetic structures interpreted on the basis of competing superexchange interactions.
Title:
Mode-locking of incommensurate phase by quantum zero-point energy in the Frenkel-Kontorova model
Authors:
Hu B. Li B. Zhao H.
Source:
Europhysics Letters. 53(3):342-347, 2001 Feb 1.
Abstract:
In this paper, it is shown that a configuration-modulated system described by the Frenkel-Kontorova model can be locked at an incommensurate phase when the quantum zero-point energy is taken into account. It is also found that the specific heat for an incommensurate phase shows a different parameter dependence in the sliding phase and pinning phase. These findings provide a possible way for experimentalists to verify the phase transition by breaking of analyticity.
Title:
Quasiperiodic hubbard chains
Authors:
Hida K.
Source:
Physical Review Letters. 86(7):1331-1334, 2001 Feb 12.
Abstract:
Low-energy properties of half-filled Fibonacci Hubbard models are studied by weak-coupling renormalization group and density matrix renormalization group methods. In the case of diagonal modulation, weak Coulomb repulsion is irrelevant and the system behoves as a free Fibonacci chain, while for strong Coulomb repulsion the charge sector becomes a Mott insulator and the spin sector behaves as a uniform Heisenberg antiferromagnetic chain. The off-diagonal modulation always drives the charge sector to a Mott insulator and the spin sector to a Fibonacci antiferromagnetic Heisenberg chain.
Title:
Low-temperature lattice excitation of icosahedral Al-Mn-Pd quasicrystals - art. no. 064203
Authors:
Li CL. Liu YY.
Source:
Physical Review B. 6305(6):4203-+, 2001 Feb 1.
Abstract:
We suggest a theoretical method for dealing with the contribution of phasons to the lattice vibration of quasicrystals. Based on this, we derive the density of vibrational states (DOVS) and specific-heat expressions of the icosahedral Al-Mn-Pd quasicrystal, and obtain corresponding numerical solutions which are in agreement with the experimental data measured by Walti ct nl. [Phys. Rev. B 57, 10 504 (1998)]. This consistency shows that the: contribution of the phasons to either the DOVS or specific heat cannot be neglected at low temperature. Our theory would be also helpful to study further the thermal conductivity of the icosahedral quasicrystal.
Title:
Icosahedral quasicrystalline phase formation in Zr-Al-Ni-Cu glassy alloys by addition of Nb, Ta and V elements
Authors:
Saida J. Inoue A.
Source:
Journal of Physics-Condensed Matter. 13(4):L73-L78, 2001 Jan 29.
Abstract:
It is found that an icosahedral quasicrystalline phase is formed in the Zr-Al-Ni-Cu glassy alloy by addition of Nb, Ta or V elements. The icosahedral phase was confirmed as a primary precipitation phase in the melt-spun Zr65Al7.5Ni10Cu12.5X5 (X=Nb Ta or V) glassy alloys with a two-stage crystallization process after the distinct glass transition. The onset temperature of the transformation from glass to icosahedral phase is 705 K fur Nb, 710 K for Ta and 702 K for V at the heating rate of 0.67 Ks(-1). The size of the icosahedral particles is in the range of 10 to 50 nm. The second crystallization reaction results in the formation of Zr2Cu + Zr2Ni + Zr3Al2 phases through a sharp exothermic reaction. The formation of a nano scale icosahedral phase in the Zr-Al-Ni-Cu glassy alloy by addition of Nb, Ta or V, as well as noble metals, indicates that the increase of the nucleation rate contributes to the precipitation of the icosahedral phase, leading to the concept that the icosahedral short-range order exists in the glassy state in the Zr-Al-Ni-Cu alloy.
Title:
Magnetic properties of the icosahedral Cd-Mg-rare-earth quasicrystals
Authors:
Sato TJ. Guo JQ. Tsai AP.
Source:
Journal of Physics-Condensed Matter. 13(4):L105-L111, 2001 Jan 29.
Abstract:
We report de and ac magnetization of the newly discovered Cd-Mg-RE quasicrysrals (RE = Gd, Tb, Dy, Ho, Er, Tm and Yb). For all the RE atoms except Yb, the temperature dependence of the de magnetization obeys the Curie-Weiss law at higher temperatures, T > 50 K. Estimated effective moments indicate that these atoms are in the trivalent states. In contrast, the Cd-Mg-Yb quasicrystal shows very small magnetization, suggesting that Yb is in the non-magnetic divalent state. At lower temperatures, spin-glass-like freezing was observed for the RE atoms except Tm and Yb. In particular, the freezing proceeds in two successive steps for RE Cd, Tb, Dy and Ho, being quite different from canonical spin-glasses.
Title:
In situ high-pressure x-ray diffraction study of icosahedral Al-Cu-TM (TM = V, Cr, M) alloys
Authors:
Ponkratz U. Nicula R. Jianu A. Burkel E.
Source:
Journal of Physics-Condensed Matter. 13(4):549-555, 2001 Jan 29.
Abstract:
Icosahedral AI-Cu-TM (TM: transition metals = V, Cr, Mn) alloys were obtained by single-roller melt-spinning in a protective inert-gas atmosphere. The high-pressure properties up to 20 GPa were investigated by in situ energy-dispersive x-ray diffraction at a synchrotron source using a gas-membrane diamond-anvil cell. No phase transitions could be observed. The bulk modulus of the Al-Cu-TM quasicrystalline phases was found to increase with the Hume-Rothery factor. Moreover, the bulk modulus of the quasicrystalline phase is imposed by the bulk modulus of the transition metal element. The derived values for the first pressure derivative B'(0) indicate strong anharmonic contributions in the lattice potentials.
Title:
Improper and proper ferroelectric phase transitions in TlInS2 layered crystal with incommensurate structure
Authors:
Mikailov FA. Basaran E. Senturk E.
Source:
Journal of Physics-Condensed Matter. 13(4):727-733, 2001 Jan 29.
Abstract:
The dielectric constant of TlInS2 crystal was measured in the temperature range including incommensurate (IC1 and IC2) and commensurate (C1 and C2) phase transitions under external bias electric field. It has been revealed that maxima in the temperature dependence of dielectric constant of TlInS2 at the C1 and C2 phase transition points shift to higher temperatures. The anomaly at IC2 transition point shifts to lower temperatures on applying the external electric fields. A new complete theoretical model including the presence of two order parameters and two polar sublattices in TlInS2 has been suggested.
Title:
Magnitude of spin and charge density wave amplitudes in underdoped cuprates
Authors:
Eremin M. Varlamov S. Eremin I.
Source:
Applied Magnetic Resonance. 19(3-4):355-362, 2000.
Abstract:
Self-consistent calculation of spin (charge) density wave (S(C)DW) order parameters have been performed for bilayered cuprates on the basis of a singlet-correlated band model. Evolution of the Fermi surface in the strongly underdoped regime is described by a two-band approach. The smooth development of the pseudogap formation temperature from underdoped to overdoped states is explained and the Fourier amplitudes [s(q)] (spin) and [e(q)] (charge) modulations are calculated. We have found a maximum of the incommensurability for doping 0.09 divided by0.11 holes per copper site.
Title:
Magnetic resonance investigations of phase transitions and modulation wave motions in incommensurate solids
Authors:
Muntean L. Subramanian RK. Ailion DC.
Source:
Applied Magnetic Resonance. 19(3-4):403-411, 2000.
Abstract:
We measured Rb-87 nuclear magnetic resonance (NMR) and Cl-35 nuclear quadrupole resonance (NQR) Hahn spin-echo magnetization decays in the incommensurate (I) phase of Rb2ZnCl4 and, in each case. obtained a Hahn echo decay that Mas shorter than the Carr-Purcell-Meiboom-Gill decay and one which decayed with a lime constant proportional to the: cube of the echo lime. From these measurements we obtained from both the Rb-87 NMR and Cl-35 NQR measurements values for the diffusion coefficients that are comparable in magnitude. a fact that strongly supports the existence of slow modulation wave diffusionlike motions in the I phase, since such motions should affect both Rb and CI ions similarly. In addition, we used Rb-87 two-dimensional exchange-difference NMR to study atomic motions in the incommensurate (1) and paraelectric (P) phases to elucidate the nature of the I-P transition. We measured as a function of the mixing time the frequency shifts of the cross peaks from the main diagonal and observed a gradual increase towards an asymptotic value in the I phase but a sudden jump to the final value in the P phase. We interpreted the motions observed in the P phase as normal modes arising from simultaneous reorientations of ZnCl4 tetrahedra and corresponding Rb ions displacements between two sites. These normal modes freeze out in the 1 phase and change to the diffusionlike motion of the modulation wave. We also performed Cl-15 NQR lineshape and T-1 measurements in K2ZnCl4 and obtained conclusive evidence for the presence of a narrow Iq (singly modulated) I phase between 146 and 149 K.
Title:
C-60 adsorption on the quasicrystalline surface of Al70Pd21Mn9
Authors:
Ledieu J. Muryn CA. Thornton G. Diehl RD. Lograsso TA. Delaney DW. McGrath R.
Source:
Surface Science. 472(1-2):89-96, 2001 Jan 20.
Abstract:
Room temperature adsorption of C-60 on the flat quasicrystalline surface of Al70Pd21Mn9 has been investigated using scanning tunnelling microscopy. A dispersed overlayer is formed at low coverage, with avoidance of step-edges. There is no evidence of island formation or clustering. As the coverage is increased, a higher density layer is formed with no evidence of the formation of hexagonal ordered adsorbate structures seen on other substrates. This is followed by the onset of second layer formation. A range of bonding sites for C60 molecules is implied from measurements of apparent molecular heights and from thermal effects. Detailed analysis of the surface at a low coverage (similar to0.065 ML) provides evidence of adsorbate local order, with Fibonacci (iota -scaling) relationships between the C-60 molecules. Where this occurs, the preferred adsorption site is tentatively identified as the pentagonal hollow. These local correlations however are not found to extend over larger regions of the surface. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
X-ray diffraction study of a sequence of phase transitions in Cs2HgCl4 crystals
Authors:
Bagautdinov BS. Brown ID. Yuzyuk YI. Dmitriev VP.
Source:
Physics of the Solid State. 43(2):350-354, 2001.
Abstract:
The temperature behavior of lattice parameters and diffraction patterns of the reciprocal lattice in Cs2HgCl4 crystals is studied by x-ray diffraction in the temperature range from 4.2 to 300 K. A sequence of phase transitions is observed and attributed to the evolution of incommensurate and commensurate modulations along the crystallographic a and c axes of a unit cell in the initial Pnma structure. (C) 2001 MAIK "Nauka/Interperiodica".
Title:
Observation of the interplay of microstructure and thermopower in the Al71Pd21Mn8-xRex quasicrystalline - art. no. 052202
Authors:
Pope AL. Schneidmiller R. Kolis JW. Tritt TM. Gagnon R. Strom-Olsen J. Legault S.
Source:
Physical Review B. 6305(5):2202-+, 2001 Feb 1.
Abstract:
In an effort to garner further insight into the behavior of thermopower in quasicrystalline materials, a series of quartenary Al71Pd21Mn8-xRex polygrain quasicrystals was synthesized. X-ray data confirm that the addition of a fourth element does not alter the quasiperiodicity. It is found that there is an intricate interplay of the microstructure and the magnitude and temperature dependence of the thermopower in this series of materials. Results are presented relating the temperature dependence of the thermopower to the presence and nature of secondary phases within the microstructure.
Title:
Epitactic textures of fcc Al on icosahedral Al-Pd-Mn quasicrystal - art. no. 052203
Authors:
Bolliger B. Dmitrienko VE. Erbudak M. Luscher R. Nissen HU. Kortan AR.
Source:
Physical Review B. 6305(5):2203-NIL_17, 2001 Feb 1.
Abstract:
An aluminum film is deposited on the fivefold-symmetric surface of icosahedral Al-Pd-Mn quasicrystal. Its orientation with respect to the bulk structure is studied using low-energy electron diffraction. It is found that Al nanocrystals grow in the face-centered cubic structure in five different sets of domains composing the film, and that their [111] axes are aligned parallel to one of five threefold-symmetry axes of the substrate quasicrystal at 37.37 degrees away from the surface normal.
Title:
Magnetic structures of MFe4+delta Al8-delta (M = Lu,Y) - art. no. 054410
Authors:
Paixao JA. Silva MR. Waerenborgh JC. Goncalves AP. Lander GH. Brown PJ. Godinho M. Burlet P.
Source:
Physical Review B. 6305(5):4410-+, 2001 Feb 1.
Abstract:
The magnetic structure of nonstoichiometric LuFe4+deltaAl8-delta and YFe4+deltaAl8-delta compounds with a small Fe excess (delta similar to0.40) was investigated by Mossbauer spectroscopy, magnetization measurements, and both polarized and unpolarized neutron-scattering experiments on single crystals. The small excess of Fe atoms substitute Al at the 8j positions and have a pronounced effect on the magnetic properties. The Neel temperature decreases from similar to 190 to 100 K and the magnetic ordering changes from the cycloid modulation found in the stoichiometric compounds to an amplitude modulated wave with a much shorter period.
Title:
Quasiperiodic fluctuation effect on a first-order phase transition: A Monte Carte investigation - art. no. 054425
Authors:
Ledue D. Landau DP.
Source:
Physical Review B. 6305(5):4425-+, 2001 Feb 1.
Abstract:
The influence of quasiperiodicity on a first-order phase transition is investigated by means of Monte Carlo simulations within the canonical ensemble. The eight-state Potts model on the octagonal tiling with two ferromagnetic interactions, J along the edges of the unit cells and J' = 10J which can only connect the spins into very small clusters of maximal size equal to 8, has been considered. Our results indicate that the transition remains first order. However, relative to the pure eight-state Potts model on the square lattice, the latent heat is smaller by about a factor 2.6. The infinite tiling transition temperature has been estimated as kT(c)/J = 1.936 +/- 0.003.
Title:
Phase separation and destabilization of the charge-ordered state in Cr-doped manganites
Authors:
Shoji R. Mori S. Yamamoto N. Machida A. Moritomo Y. Katsufuji T.
Source:
Journal of the Physical Society of Japan. 70(1):267-271, 2001 Jan.
Abstract:
Destabilization of the charge-ordered (CO) state in half-doped manganites by chromium (Cr) doping in the: manganese (Mn) sites was investigated. The Cr doping: in the half-doped manganites makes the CO state short-ranged and induces new ferromagnetic metallic (FMM) phase at low temperature. Real space images taken in the CO state by electron microscope clearly show coexistence of the short-ranged CO and FMM states, which is characterized as a microscopic scale phase separation. Furthermore, the CO state in the Cr-doped manganites has a superlattice structure with the incommensurate wave vector q = (1/2 - epsilon )a(o)(*); where epsilon depends on the Cr concentration. These results suggest that the Cr doping suppresses the incommensurate to commensurate structural transition found in the half-doped manganites and produces new FMM phase.
Title:
Comparison of Al-Cu-Fe quasicrystalline particle reinforced Al composites fabricated by conventional casting and extrusion
Authors:
Fleury E. Lee SM. Choi G. Kim WT. Kim DH.
Source:
Journal of Materials Science. 36(4):963-970, 2001 Feb.
Abstract:
Aluminum matrix composites reinforced by Al62Cu26Fe12 gas atomized powders were produced by conventional metallurgical processes, such as gravity casting with stirring and hot extrusion. This investigation was mainly focused on the dependency of the yield stress at room temperature as a function of the volume fraction of reinforcement, but other variables such as the matrix, coating layer around the particles, and processing were also investigated. For as-extruded composites, the addition of the Al-Cu-Fe particles improved the yield stress, although not dramatically owing to the large particle size. In contrast, it was found that the yield stress was considerably enhanced for the as-cast composites up to 10%(AlCuFe)p, while an asymptotic value was observed afterward. The dominant parameter appeared to be the strength of the matrix, which was found to be proportional to the volume fraction of the reinforcement. These results are discussed in relation with the possible strengthening mechanisms in order to estimate the role of the icosahedral and related crystalline phases on the increase of yield stress. (C) 2001 Kluwer Academic Publishers.
Title:
Magnetic phase diagram of ErCuSi studied by neutron diffraction and magnetic measurements
Authors:
Schobinger-Papamantellos P. Buschow KHJ. Duong NP. Ritter C.
Source:
Journal of Magnetism & Magnetic Materials. 223(3):203-214, 2001 Feb.
Abstract:
The magnetic phase diagram of the hexagonal ErCuSi (P6(3)/mmc) compound has been studied by neutron powder diffraction and magnetic measurement. Magnetic ordering occurs below T-N = 6.8 K and is associated with the wave vector, q = (1/12, 0, 0), with a temperature-independent length. The magnetic structure can be described by a transverse sine-wave-modulated arrangement of the Er moments oriented \\c with a maximum moment amplitude of 9.1(1) mu (B)/Er atom or alternatively by an antiphase domain structure having three amplitudes. At lower temperatures, T = 3.5 K, the appearance of the weak 3q harmonic indicates the onset of a squaring up transition to an antiphase domain structure with equal amplitudes. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Precipitation of nanoscale icosahedral quasicrystalline phase in amorphous Hf70Cu20Pd10 alloy
Authors:
Li CF. Inoue A.
Source:
Japanese Journal of Applied Physics Part 2-Letters. 39(12B):L1317-L1319, 2000 Dec 15.
Abstract:
An amorphous Hf70Cu20Pd10 ternary alloy was prepared and its crystallization process was studied. The crystallization proceeds through two exothermic reactions. Anncaling of the specimen at a temperature lower than the onset point of the low-temperature exothermic reaction resulted in the precipitation of an icosahedral quasicrystalline phase. Further annealing at the same temperature caused the phase transformation to Hf2Cu crystalline phase, indicating the metastable character of the icosahedral quasicrystalline phase. In comparison with the crystallization process of other Hf-based amorphous alloys, the effect of Pd addition on the precipitation of the icosahedral quasicrystalline phase was discussed from the point of view of atomic radius. [References: 9]
Title:
Crystal chemistry of strontian soda melilite from nephelinite lava of Mt. Etinde, Cameroon
Authors:
Bindi L. Bonazzi P. Fitton JG.
Source:
European Journal of Mineralogy. 13(1):121-125, 2001 Jan-Feb.
Abstract:
The crystal structure and chemical composition of two crystals (labelled ET1 and ET2) of strontian soda melilite from Mt. Etinde, Cameroon , are investigated. Quantitative analysis leads to the following formulae: (Ca0.84Sr0.45Na0.71)(Mg0.19Fe0.062+Mn0.03Zn0.02Al0.46Fe0.233+Ti0.01)(Si1 .9 9Al0.01)O-7.00 and (Ca0.83Sr0.45Ni0.72) (Mg0.20Fe0.062+Mn0.03Zn0.01Al0.45Fe0.243+Ti0.02)(Si1.99Al0.01)O-7.00 for ET1 and ET2 respectively. Lattice parameters are: a = 7.754(1), c = 5.101(1) A for ET1 and a = 7.764(1), c = 5.095(1) Angstrom for ET2. The structure is refined up to R-all = 2.64 and 2.78%, respectively, using 430 independent reflections. Substitution of Sr for Ca causes sufficient modification of the tetrahedral laver to destabilize the incommensurate modulated structure.
Title:
Preliminary characterization of loop-shaped defect in the AlPdMn icosahedral quasicrystal by conventional x-ray topography
Authors:
Wang JB. Gastaldi J. Wang RH.
Source:
Chinese Physics Letters. 18(1):88-90, 2001.
Abstract:
Loop-shaped contrasts were observed in the as-grown Al70.3Pd20.6Mn9.1 icosahedral quasicrystal (IQC) by means of x-ray diffraction topography (Lang's method). One possible direction of the apparent Burger vectors of loop-shaped defects (LSDs) was determined to be B = [110101] by the invisibility criterion, whose physical component is parallel to the two-fold axis 1/ tau [1/0, 1/1, 0/1] of the IQC. Apart from the relaxation of strain fields around the faceted dodecahedral holes and lamellar precipitates, LSDs may well originate from the growth of the quasicrystal, which shows that these defects could be a kind of intrinsic defect in the quasicrystals.
Title:
Binary quasicrystals discovered that are stable and icosahedral
Authors:
Day C.
Source:
Physics Today. 54(2):17-18, 2001 Feb.
Title:
Debye-Waller factors in a quasicrystal - art. no. 014202
Authors:
Colella R. Zhang Y. Sutter JP. Ehrlich SN. Kycia SW.
Source:
Physical Review B. 6301(1):4202-+, 2001 Jan 1.
Abstract:
The mean-square vibrational amplitude [U-2] for five reflections located on a twofold axis of an icosahedral quasicrystal Al71.0Pd20.5Mn8.5 have been determined between room temperature (RT) and below 20 K by x-ray diffraction. Their Q vectors (Q=2 sin theta/lambda) range from 1.278 Angstrom (-1) to 2.556 Angstrom (-1). For four reflections, the logarithm of the integrated intensity is linear, proportional to temperature, near and below RT, and tends to saturate to a constant value at low temperature (LT), an effect of the zero-point energy. All plots for these four reflections ar indeed linear at RT and below,and saturate at LT to values that are different from those predicted by Debye theory. This behavior is reminiscent of that of layered crystals such as graphite or TaS2, in which the anomaly could be explained by considering the effect of reduced dimensionality and anisotropy, none of which can be applied to icosahedral quasicrystals. The effect may be due to a change of Debye temperature below 100 K. The fifth reflection (Q=2.252 Angstrom-(1)) displays a temperature dependence that does not lead to a single mean-square vibrational amplitude. The Debye temperature obtained from the first four plots is in the neighborhood of 312 K.
Title:
(Icosahedral phase + alpha-Mg) two phase microstructures in the Mg-Zn-Y ternary system
Authors:
Yi S. Park ES. Ok JB. Kim WT. Kim DH.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 300(1-2):312-315, 2001 Feb 28.
Abstract:
Structural applications of monolithic icosahedral phase (I-phase) materials have been limited by the brittleness of I-phases. Composite material design, including a ductile phase, can be a solution for the structural applications of the I-phase materials. Two phase microstructures, including thermodynamically stable I-phase, are studied in the Mg-rich corner of the alloy system Mg-Zn-Y. An (I-phase + alpha -Mg) eutectic microstructure is reported for the first time in the as-cast samples. By controlling thermal processing procedures, a very different (I-phase + alpha -Mg) microstructure from the eutectic microstructure can be developed, expanding the microstructural options available for the structural composite materials, comprising the I-phase and alpha -Mg solid solution. (C) 2001 Elsevier Science B.V. All rights reserved.

Update: 22-Feb-2001

Title:
Atomic clusters in icosahedral F-type quasicrystals - art. no. 024202
Authors:
Gratias D. Puyraimond F. Quiquandon M. Katz A.
Source:
Physical Review B. 6302(2):4202-+, 2001 Jan 1.
Abstract:
We present a detailed study of the geometry of the atomic clusters encountered in icosahedral F-type quasicrystals using the cell decomposition of the prototypic atomic surfaces introduced several years ago for modeling i-AlCuFe. This includes an exhaustive and quantitative characterization of the geometrical features of the two major (Bergman- and Mackay-type) atomic clusters usually considered as the building blocks of these structures together with a study of the extended Bergman cluster proposed by M. Duneau (Clusters in Quasicrystals, to be published in the Proceedings of the 7th International Conference on Quasicrystals, Stuttgart, Sept. 1999) as a template of self-overlapping atomic clusters describing ail atoms of the structure and show that this large cluster splits into a total of ten different configurations.
Title:
On the relationships between isothermal phase diagrams and quasicrystalline phase transformations in AlCuFe alloys
Authors:
Rosas G. Perez R.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 298(1-2):79-83, 2001 Jan 31.
Abstract:
In order to determine the crystalline phases which coexist with the icosahedral quasicrystalline phase at high temperatures, an isothermic section of the AlCuFe equilibrium phase diagram at 850 degreesC was studied. This section is near to composition and temperature values where the icosahedral phase was formed from the cubic phase. The quasicrystalline phase is not found in a region of a single phase. However, it has binary stability fields with the cubic beta -Al-5(Cu,Fe)(5) phase and ternary stability fields with the beta + lambda -Al13Fe4. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 10]
Title:
On the temperature dependence of the hardness of quasicrystals
Authors:
Wolf B. Bambauer KO. Paufler P.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 298(1-2):284-295, 2001 Jan 31.
Abstract:
Results of mechanical micro- and nanotesting of single-quasicrystalline phases in the Al-Co-Ni-, Al-Pd-Mn- and RE-Mg-Zn-systems (RE = Y. Ho or Dy) are reported. Particular emphasis was devoted to the icosahedral phase in the Y-Mg-Zn-system, since - owing to its low melting point - high homologous temperatures T-h, can be attained almost without heating. At room temperature indentation of quasicrystals with icosahedral structure results in extended formation of type-III cracks, i.e. shear cracks with different height levels of the crack banks. This indentation-induced surface fragmentation is considerably less pronounced with decagonal phases, indicating that the quasicrystalline structure has a strong influence on brittleness. In contrast to the fracture behaviour the Meyer hardness value H-M does not seem to follow a sequence H-M (three-dimensional quasicrystal)much greater thanH(M) (two-dimensional quasicrystal)much greater thanH(M) (crystalline matter) but is mainly determined by the sequence of the solid --> liquid transformation (or decomposition) temperature T-m, i.e. H-M(Al73Ni14Co13) > H-M(Al70Pd21Mn9) > H-M(Y10Mg30Zn60). The hardness seems to be primarily governed by the complexity of the structure and by type and strength of bonding. At room temperature, all quasicrystals exhibit a strong indentation size effect with the hardness increasing with decreasing load. This effect becomes inverted at higher temperatures. The hardness variation with temperature depends on load: negligible variation for very small loads (nanotesting), very strong variation for moderate loads, and less drastic variation for higher loads. This observation is interpreted in the frame of two models: indentation-induced fragmentation, and dislocation involved deformation. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Synthesis, structure and magnetic properties of a new hollandite: Sr0.75Rh4O8
Authors:
Plaisier JR. van Vliet AAC. IJdo DJW.
Source:
Journal of Alloys & Compounds. 314(1-2):56-61, 2001 Jan 16.
Abstract:
The synthesis, structure and magnetic properties of a new synthetic hollandite, SrxRh4O8 (x approximate to 0.75) are discussed. The compound crystallizes in the monoclinic space group I2/m, a = 10.4399(5) A, b = 3.0616(1) Angstrom, c = 9.2135(5) Angstrom, beta = 95.261(3)degrees, Z = 2. Electron diffraction patterns show satellites, indicative of an incommensurate distribution of the strontium cations in the channels. The modulation vector was found to be (-0.5, similar to0.25, 0.5). The compound shows Pauli-paramagnetic behavior between 5 and 300 K. (C) 2001 Elsevier Science BSI. All rights reserved.
Title:
Preparation and crystal structure of the novel decagonal approximant Mn123Ga137
Authors:
Bostrom M. Hovmoller S.
Source:
Journal of Alloys & Compounds. 314(1-2):154-159, 2001 Jan 16.
Abstract:
A new approximant to a decagonal quasicrystal has been found in the Ga-Mn binary system. Single crystals of Mn123Ga137 were synthesised from pieces of manganese in a self flux of gallium. Still at the reaction temperature, the liquid flux and the solid Mn123Ga137 crystals weir separated from each other by centrifugal action filtering. The crystal structure of Mn123Ga137 was determined from single crystal X-ray diffraction data. Mn123Ga137 crystallises in the monoclinic space group C2/c, a = 20.239(3) Angstrom, b = 14.790(2) Angstrom, 14.908(2) Angstrom, beta = 120.93(2)degrees, R-w = 4.0%. The structure consist mainly of a fundamental type of wheel shaped pentagonal clusters with 5/mm point group pseudo symmetry. The cluster consists of seven intergrown icosahedra. Each cluster is fused to three other in the plane perpendicular to the pseudo five-fold axis. In that way they make up infinite honeycomb nets parallel to the a-b plane. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Commensurate versus incommensurate spin-ordering in the triangular Hubbard model
Authors:
Caprara S. Capone M. Capriotti L. Becca F.
Source:
International Journal of Modern Physics B. 14(29-31):3386-3391, 2000 Dec 20.
Abstract:
The presence of incommensurate spin structures in the half-filled triangular Hubbard model, where frustration leads to a competition among different magnetic phases, is investigated using both the slave-boson technique, and exact diagonalization of finite clusters. We also investigate the metal-insulator transition which, due to the lack of perfect nesting, takes place at a finite value of U. Within the slave-boson approach. as the interaction grows the paramagnetic metal turns into a metallic phase with incommensurate spiral ordering. Increasing further the interaction, a linear spin-density-wave is stabilized, and finally for strong coupling the latter phase undergoes a first-order transition towards an antiferromagnetic insulator. No trace of the intermediate phases is instead found in the exact diagonalization results.
Title:
Fermi surface and photoemission lineshape of incommensurate CDW systems
Authors:
Seibold G. Castellani C. Di Castro C. Grilli M.
Source:
International Journal of Modern Physics B. 14(29-31):3679-3684, 2000 Dec 20.
Abstract:
We study the single-particle spectra of a model which shows an incommensurate charge-density wave (CDW) instability arising from the competition between phase separation and long-range Coulomb interactions. Starting from an open Fermi surface we find that the resulting CDW is oriented along the (1,0)- and (or) (0,1)-direction which (besides a purely one-dimensional structure) allows for a two-dimensional "eggbox type" charge modulation. This leads to a substantial enhancement of the van Hove singularities and the spectral weight of Fermi surface states near the M-points tends to be suppressed. Remarkably, a leading edge gap arises near these points, which, in the eggbox case, leaves finite arcs of the Fermi surface gapless. Extending this approach to the inclusion of dynamic incommensurate CDW fluctuations in the superconducting state we calculate the photoemission lineshape which agrees well with experimental data of underdoped Bi2212 compounds.
Title:
Structure and properties of an intragranular weak link in Bi2Sr2CaCu2O8+x single crystals
Authors:
Tsu IF. Wang JL. Babcock SE. Polyanskii AA. Larbalestier DC. Sickafus KE.
Source:
Physica C. 349(1-2):8-18, 2001 Jan 1.
Abstract:
Coupled magneto-optic imaging, four-point probe electrical characterization and transmission electron microscopy (TEM) of Bi2ST2CaCu2O8+x (2212) single crystals grown by directional solidification has revealed the presence of extensive, lamellar defects that lie parallel to the (010) planes of the structure. These defects block the supercurrent over areas that can reach hundreds of micrometers squared. Diffraction-contrast and high-resolution TEM revealed sheet-shaped defects that lie parallel to the (010) plane and in which the wavelength of the incommensurate modulation is perturbed. These lamellae are a few nanometers wide and, extends to tens to hundreds of micrometers on the (010) plane. The approximate doubling of the wavelength of the incommensurate modulation within these lamellae indicates severe oxygen deficiency. High-spatial-resolution X-ray spectroscopy indicates that the defects are also Ca deficient. These macroscopic defects which are common in directionally-solidified 2212 single crystals, must be recognized in the interpretation of single and synthetic bicrystal data, and may play a role in determining the percolative current path in bulk-scale 2212 materials. (C) 2001 Elsevier Science B.V. All rights reserved.
Title:
Preparation and structural properties of 7,8-dioxa[6]helicenes and 7a,14c-dihydro-7,8-dioxa[6]helicenes
Authors:
Eskildsen J. Krebs FC. Faldt A. Sommer-Larsen P. Bechgaard K.
Source:
Journal of Organic Chemistry. 66(1):200-205, 2001 Jan 12.
Abstract:
The potentially chiral 7,8-dioxa[6]helicenes 1-1c have been prepared by oxidation of their precursors the 7a,14c-dihydro-7,8-dioxa[6]helicenes 3. The crystal structure determination of 3b cis-7a,14c-dihydro-3,12-dibromo-7,8-dioxa[6]helicenes unambiguously confirms the cis configuration of the 7a,14c hydrogens in compounds 3 as previously implied from NMR measurements and also shows that; 3b crystallizes in a chiral conformation in the solid state. Selective deuteration of the sterically crowded 1,14 positions of 7,8-dioxal[6]helicene 1 influenced the crystal structure. The deuterium labeled compound D-2-1 exhibits a disordered structure, whereas 1 had been found to crystallize in a complex structure which can be described as an analogous partly ordered modulated superstructure. When dehydrogenation of compound 3 to obtain compound 1 was attempted, harsh synthetic conditions gave the unexpected halogenated compounds 5-chloro-7,8-dioxa[6]helicene 1c and cis-7a,14c-dibromo-7,8-dioxa[6]helicene 3c. Compounds 1d and 3b were identified by solving their crystal structure.
Title:
Experimental and theoretical studies of elemental site preferences in quasicrystalline approximants (R-phases) within the Li-Mg-Zn-Al system
Authors:
Lee CS. Miller GJ.
Source:
Inorganic Chemistry. 40(2):338-345, 2001 Jan 15.
Abstract:
A series of ternary and quaternary R-phase compounds in the Li-Mg-Zn-Al system are synthesized from pure elements in sealed Ta tubes with starting compositions based on the suggestions from electronic structure calculations using relative Mulliken populations to quantify the site preferences for the various elements. Single-crystal structural analyses reveal new R-phase compounds with various Li/Mg and Zn/Al ratios. The space group of all compounds is Im (3) over bar (No. 204). Five quaternary phases [Li1.00(1)Mg0.63(2)Zn1.23(1)Al2.14(1) (1), a = 14.073(3) Angstrom; Li1.00(1)Mg0.63(1)Zn1.42(1)Al1.96(1) (2), a = 14.088(3) Angstrom; Li1.01(1)Mg0.62(1)Zn1.31(1)Al2.14(1) (3), a = 14.096(5) Angstrom; Li1.03(1)Mg0.60(1)Zn1.78(3)Al1.59(3) (4), a = 13.993(5) Angstrom; Li0.78(2)Mg0.85(2)Zn2.47(1)Al0.94(1) (5), a = 13.933(2) Angstrom] and four ternary compounds [Li1.63Zn0.81(1)Al2.56(1) (6), a = 14.135(3) Angstrom; Li1.63Zn1.42(1)Al1.95(1) (7), a = 13.966(5) Angstrom; Li1.63Zn1.59(1)Al1.78(1) (8), a = 13.947(2) Angstrom; and Li1.63Zn1.77(1)Al1.60(1) (9), a = 13.933(4) Angstrom] are identified. The crystal structure exhibits an Al/Zn (M sites) network constructed from M-12 icosahedra and M-60 buckyball-type clusters. Li/Mg atoms (A sites) fill cavities within the Al/Zn network to give pentagonal dodecahedra (A(20)). The site-potential studies (relative Mulliken populations) indicate two groups of atomic sites (positively and negatively polarized), which are consistent with the single-crystal studies. Further differentiation of site potentials among the various electropositive sites leads to segregation of Li and Mg, which is also verified experimentally. The analysis of relative Mulliken populations in an intermetallic framework provides a useful method for elucidating elemental site preferences when diffraction techniques cannot unequivocally solve the site preference problem.
Title:
The commensurate and incommensurate TGBC* liquid crystal phases
Authors:
Galerne Y.
Source:
European Physical Journal A. 3(4):355-368, 2000 Dec.
Abstract:
We propose complements to the Renn model of the liquid crystal TGBC* phase. We argue that the rotation angle per helislab is spontaneously in the radian range, not too small to limit the energy cost of the twist grain boundaries between the helislabs, not too large to preserve the double twisting efficiency. Taking the elastic interactions between the helislabs into account, we show that the structure may undergo two different lock-ins, provided that the uncontrolled interactions at the sample surfaces are small enough. First, for appropriate values of the elastic constants, an angular lock-in may fix the rotation angle per helislab at values exactly commensurate to pi. Three characteristic lengths of the TGBC* phase, the TGB period and the thicknesses of both the smectic blocks and of the helislabs are then commensurate to one another, with moreover, integer ratios at the most efficient commensurabilities. The TGBC* phase could thus exist in several versions, incommensurate and commensurate, according to the steps of a restricted Devil's staircase. A second elastic lock-in should then arise in the commensurate TGBC* phases, to set the arrays of disclination lines between the helislabs in simple rectangular lattices, arranged in a helical manner. Being placed right behind one another, the disclination lines then coincide when observed along the TGB axis. This could explain the typical textures with square or hexagonal grids, observed in oriented samples. The commensurability of the TGBC* phases could be analyzed with X-ray scattering experiments in the same manner as already reported for the TGBC phase.
Title:
Intergrowth polytypoids as modulated structures: the example of the cation deficient oxides LaTi1-xO3
Authors:
Elcoro L. Perez-Mato JM. Withers R.
Source:
Zeitschrift fur Kristallographie. 215(12):727-739, 2000.
Abstract:
A new, essentially composition-independent structural model is proposed for the perovskite-related compound series LanTin-deltaO3n, with delta less than or equal to n/4, based on superspace formalism, Tn the standard 3-dimensional crystallographic approach, one must specify space group and cell parameters separately fur each composition. In the superspace approach, the superspace group is invariant while the cell parameters and primary modulation wavevector vary slowly and continuously with composition. To a first approximation, the structure at any particular composition carl be described in terms of mixed cubic and hexagonal stacking of close-packed LaO3 (and Ti) layers along the z-axis. The actual layer stacking sequence varies abruptly with composition, and the titanium vacancies occur as entire layers between neighbouring hexagonal close-packed LaO3 layers. The continuously variable, composition-dependent character of reciprocal space indicates that the various layer stacking sequences must be intimately correlated and shows that all the compounds can be interpreted in terms of a structural modulation over a common average structure. It is shown that a very simple model in superspace is sufficient to describe the layer stacking sequences for any particular composition. The atomic surfaces representing the atoms in superspace are shown to be well described by means of crenel functions. The cation displacive modulations are approximately described by sawtooth functions. The only variable parameters are the composition-dependent (but smoothly varying) primary modulation wave-vector and associated Ti occupation domain width. Conventional space groups can be easily determined from the superspace group and the composition. From a practical point of view, this means that we have a very good single starting point to refine the actual atomic positions for any composition, including incommensurate or long period structures. Even more importantly, the superspace approach has the flexibility to represent in a simple manner the symmetry-allowed deviations from the ideal model. A comparison with the scarce number of refined structures in this system and in the homologous (Ba,La)(n)Tin-1O3n system, demonstrates the suitability of the formalism for the analysis of these compound series and for the analysis of compositionally flexible systems in general.
Title:
The inherent displacive flexibility of the hexacelsian tetrahedral framework and its relationship to polymorphism in Ba-hexacelsian
Authors:
Withers RL. Tabira Y. Valgoma JA. Aroyo M. Dove MT.
Source:
Physics & Chemistry of Minerals. 27(10):747-756, 2000 Dec.
Abstract:
The results of a rigid unit mode (RUM) analysis of the inherent displacive structural flexibility of the tetrahedral framework of the ideal hexacelsian structure type are presented. One of the three types of RUM found to exist is characterized by modulation wave vectors perpendicular to [110] and atomic displacement patterns involving tetrahedral rotation around the parent c axis while a second type of RUM is found to be soft at any modulation wave vector and to involve tetrahedral rotation about in-plane rotation axes. It is shown how a combination of these two types of RUM motion associated with the same q=1/2[(1) over bar 101]* modulation wave vector enables the outstanding crystal chemical problems and apparently mutually contradictory results as regards polymorphism in Ba-hexacelsian to be resolved.
Title:
Ab initio structure determination of icosahedral Zn-Mg-Ho quasicrystals by density modification method
Authors:
Takakura H. Shiono M. Sato TJ. Yamamoto A. Tsai AP.
Source:
Physical Review Letters. 86(2):236-239, 2001 Jan 8.
Abstract:
A novel density modification method is applied for the first time to phase reconstruction of x-ray single crystal data of quasicrystals. The structure of icosahedral Zn-Mg-Ho quasicrystals has been determined by means of this ab initio structure determination within a framework of a 6D description. The location, size, and shape of the occupation domains are deduced. The suggested Ho sites in the 3D structure are consistent with the results of magnetic diffuse scattering [T.J. Sate er al., Phys. Rev. Lett. 81, 2364 (1998)].
Title:
Friedel oscillations and charge-density wave pinning in quasi-one-dimensional conductors: An x-ray diffraction study
Authors:
Rouziere S. Ravy S. Pouget JP. Brazovskii S.
Source:
Physical Review B. 62(24):R16231-R16234, 2000 Dec 15.
Abstract:
We present an x-ray diffraction study of the vanadium-doped blue bronze K-0.3(Mo0.972V0.028)O-3 At low temperature, we have observed both an intensity asymmetry of the +/- 2k(F) satellite reflections relative to the pure compound, and a profile asymmetry of each satellite reflections. We show that the profile asymmetry is due to Friedel oscillation around the V substituant and that the intensity asymmetry is related to the charge-density-wave (CDW) pinning. These two effects, intensity, and profile asymmetries, give access to the local properties of CDW in disordered systems, including the pinning and even the phase shift of Friedel oscillations.
Title:
A new stable icosahedral quasicrystal in the Cd-Mg-Dy system
Authors:
Guo JQ. Abe E. Tsai AP.
Source:
Philosophical Magazine Letters. 81(1):17-21, 2001 Jan.
Abstract:
A new stable icosahedral quasicrystal has been found in annealed Cd-Mg-Dy alloys. The composition of the icosahedral phase was determined to be approximately Cd66Mg21Dy13. Powder X-ray and electron diffraction patterns revealed that the phase has a primitive icosahedral lattice with a quasilattice parameter a(R) = 0.5634 nm. The electron diffraction study confirmed that the phase has a well ordered primitive icosahedral structure. [References: 7]
Title:
Formation of the icosahedral quasicrystalline phase in Zr70Pd30 binary glassy alloy
Authors:
Saida J. Matsushita M. Li C. Inoue A.
Source:
Philosophical Magazine Letters. 81(1):39-44, 2001 Jan.
Abstract:
It is found that a single icosahedral quasicrystalline phase is formed as a primary precipitation phase in the melt-spun Zr70Pd30 binary glassy alloy with a two-stage crystallization process. The onset temperature of the transformation from the amorphous to the icosahedral phase is 701 K at the heating rate of 0.67 K s(1). The size of the icosahedral particles lies in the diameter range below 10 nm and the particles are distributed homogeneously. The second-stage crystallization reaction results in the formation of a Zr2Pd phase through a single exothermic reaction. The formation of the nanoscale icosahedral phase indicates the possibility that icosahedral short-range order exists in the Zr-Pd binary glassy state. Comparison with the thermal stability of an icosahedral phase in the Zr-Ni-Pd system shows that the icosahedral phase is stabilized by the addition of Ni. The stabilization is due to the restraint of the long-range rearrangement of the constitutional elements resulting from the strong chemical affinity between Zr and Ni.
Title:
ICQ7, proceedings of the 7th International Conference on Quasicrystals, 20-24 September, 1999, Stuttgart, Germany - Preface
Authors:
Gahler F. Kramer P. Trebin HR. Urban K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):1-3, 2000 Dec 15.
Title:
New prospects from potential applications of quasicrystalline materials
Authors:
Dubois JM.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):4-9, 2000 Dec 15.
Abstract:
Since 1984, several quasicrystalline materials were selected for possible technological applications as coatings and composites. A few examples of products derived from such materials are now on the market. The aim of this review is along several key points raised by the technological prospects of quasicrystals, namely composition tailoring and industrial processing of thick coatings, surface preparation and properties, and new potential applications. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Growth of large single-grain quasicrystals from high-temperature metallic solutions
Authors:
Fisher IR. Kramer MJ. Islam Z. Wiener TA. Kracher A. Ross AR. Lograsso TA. Goldman AI. Canfield PC.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):10-16, 2000 Dec 15.
Abstract:
Flux-growth techniques have been successfully applied to the preparation of several families of quasicrystals and related approximant phases. Large (up to 1 cm(3)) single-grain samples have been obtained for icosahedral R-Mg-Zn (R=Y, Gd, Tb, Dy, Ho and Er), decagonal Al-Ni-Co, icosahedral Al-Pd-Mn, icosahedral Al-Ga-Pd-Mn, and the xi' Al-Pd-Mn approximant phase. The samples are obtained by slowly cooling ternary (or quaternary) melts of a composition that intersects the primary solidification surface of the desired phase in the equilibrium ternary alloy phase diagram (i.e. this is a self-flux technique). The technique clearly reveals the growth habit, and results in remarkably strain-free quasicrystals. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Phase transitions in quasicrystals - the example of decagonal Al-Co-Ni
Authors:
Haibach T. Estermann MA. Cervellino A. Steurer W.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):17-22, 2000 Dec 15.
Abstract:
The numerous phase transformations of quasicrystals observed can be separated into two distinct classes, the transitions from quasicrystals-to-quasicrystals and from quasicrystals-to-crystals of periodic approximants. The formation of modulated quasicrystals driven by chemical ordering represents a member of the first class. The transformation of a quasicrystal to orientationally twinned domain structures of approximants belongs to the latter class. The characteristics of some class-one transformations with special emphasis on their experimental evidence are discussed on the example of phase transformations in the ternary alloy system Al-Co-Ni. State-of-the-art techniques for acquiring in situ X-ray diffraction data at high temperature of quasicrystalline material undergoing a phase transition are presented. Methods suitable for accurate and reproducible determination of structural changes of specimens in thermodynamic equilibrium are shown. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
High-resolution electron microscopy of quasicrystals
Authors:
Beeli C.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):23-28, 2000 Dec 15.
Abstract:
Our present knowledge on the structure of icosahedral and decagonal quasicrystals has strongly profited from the combined information inferred from electron diffraction patterns and high-resolution transmission electron microscopy (HRTEM) images. Many structural properties of quasicrystals can be recognized and quantified by the analysis of electron diffraction patterns alone. Nevertheless, a much more complete understandings of the real structure of quasicrystals can be achieved by the additional analysis of the HRTEM images. Compared to only diffraction-based techniques, transmission electron microscopy offers several advantages. Especially for decagonal quasicrystals, the HRTEM has been very successful in analyzing the atomic as well as the long-range structure. This is linked with the fact that decagonal quasicrystals are periodic along one direction and the atoms thus form periodic atom columns as in crystalline materials. Accordingly, the imaging theory established for crystals can also be applied to the HRTEM images of decagonal quasicrystals taken with the electron beam parallel to the 10-fold axis. The HRTEM images of decagonal Al-Mn-Pd and Al-Co-Ni quasicrystals have been used to distinguish between disorder and order: such as, the difference between a random tiling acid perfect quasiperiodicity. The structural analysis of icosahedral quasicrystals by HRTEM is briefly, but critically, analyzed and applications for icosahedral Al-Mn-Pd quasicrystals are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Structure and phase transformation of the Zn-Mg-rare-earth quasicrystals
Authors:
Abe E. Sato TJ. Tsai AP.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):29-32, 2000 Dec 15.
Abstract:
We report transformations between the quasicrystalline and crystalline phases in the Zn-Mg-rare-earth (RE) alloys. Both the icosahedral and decagonal quasicrystals are shown to be formed through the crystalline compounds being not composed of giant highly symmetric atomic clusters. This suggests that the formation of Zn-Mg-RE quasicrystals can be reduced to the behavior of smaller atomic clusters which should be favorable energetically in terms of given elements and stoichiometry. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Formation conditions of two quasiperiodic modifications of Al-Pd-Mn icosahedral phase studied by annealing method
Authors:
Hirai I. Ishimasa T. Letoublon A. Boudard M. de Boissieu M.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):33-36, 2000 Dec 15.
Abstract:
Formation conditions of F-phase, F2-phase and F2(M)-phase were systematically studied at alloy composition of Al71Pd21Mn8 by annealing and succeeding quenching method. The results indicated that the transformation from the F-phase to the F2(M)-phase occurs in two steps between 734 and 743 degreesC; in the first step the F-phase is transformed to the F2-phase, in the second step the F2-phase is transformed to the F2(M)-phase. It was reconfirmed that the F-phase is a high-temperature phase stable above approximately 748 degreesC, and the F2(M)-phase is a low-temperature phase stable below approximately 743 degreesC. The present experiment also indicated that the F2-phase is a transient stare between the F-phase and the F2(M)-phase. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 9]
Title:
Hexagonal approximants of a dodecagonal tantalum telluride - the crystal structure of Ta21Te13
Authors:
Conrad M. Krumeich F. Reich C. Harbrecht B.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):37-40, 2000 Dec 15.
Abstract:
The structure of a hexagonal approximant of the dodecagonal tantalum telluride dd-Ta1.6Te was studied by means of high resolution transmission electron microscopy and electron diffraction. A hierarchical building principle underlying the structures of two other approximants, Ta97Te60 and Ta181Te112, was applied in order to deduce the crystal structure of the approximant with highest tellurium content, Ta21Te13. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 7]
Title:
Phason-strain field and grain growth: a scanning focused ion beam and transmission electron microscopy study in Al-Li-Cu icosahedral phase
Authors:
Wang K. Donnadieu P. Garoche P.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):41-44, 2000 Dec 15.
Abstract:
We succeeded to favour grain growth in single-phased Al-Li-Cu quasicrystal samples by annealing treatment under confined atmosphere. Using scanning focused ion beam (FIB) microscopy we can image the monograins with a good spatial and angular resolution. FIB observations carried out on Al-Li-Cu quasicrystal samples show that grain size, which is below 0.1 mm in the starring samples, reaches 0.5 mm after 10 days annealing. It reveals regular grain boundaries both before and after annealing. According to electron diffraction performed on these samples, the grain growth is accompanied by a reduction of the deviations to icosahedral symmetry, i.e., a phason-strain field reduction. Since, for symmetry reasons, the phason-strain field in Al-Li-Cu quasicrystal is not coupled to the phonon strain field, its reduction cannot be a consequence of phonon strain elimination. Our observations suggest that phason-strain field elimination occurs during grain growth. We propose an interpretation for such effect based on the grain boundary displacement. In this frame it is shown that grain boundary displacement is associated with phason-strain relaxation. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 4]
Title:
Composition and precipitation behavior of icosahedral Al-Pd-Mn quasicrystals
Authors:
Grushko B.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):45-48, 2000 Dec 15.
Abstract:
Icosahedral Al-Pd-Mn phase was found to be stable in a compositional range [B. Grushko, et al., J. Alloys Comp. 290 (1999) 164]. Its stability range also depends on temperature. This is favorable for the formation of precipitates in the icosahedral phase by cooling. We demonstrate the precipitation in the "standard" single icosahedral quasicrystals produced by the Czochralski technique. Annealing of the quasicrystals at 800-840 degreesC resulted in the dissolution of the precipitates and they reappeared after annealing at 700-500 degreesC. The relation of this effect to the diffuse scattering in the icosahedral phase is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Effect of annealing on the structural perfection of Al-Pd-Mn icosahedral quasicrystal grains
Authors:
Mancini L. Letoublon A. Agliozzo S. Wang J. Gastaldi J. de Boissieu M. Hartwig J. Klein H.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):57-60, 2000 Dec 15.
Abstract:
The effect of annealing (up to 750 degreesC) on the structural perfection of stable quasicrystals has been studied, for the first time, in large grains of the icosahedral Al-Pd-Mn phase. This study was performed by combined synchrotron X-ray diffractometry and imaging techniques. It has revealed that the quasicrystalline quality improves as long as no precipitates are formed. The improvement was mainly ascribed to the relaxation of the strain field around voids, which are often observed in quasicrystals after growth. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Production of quasicrystals and crystalline approximants in the Al-Pd-(Fe,Ru,Os) systems
Authors:
Shibuya T. Asao T. Tamura M. Tamura R. Takeuchi S.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):61-64, 2000 Dec 15.
Abstract:
We report the formation regions of single icosahedral phases (i-phase) and crystalline approximants in the Al-Pd-(Fe,Ru,Os) ternary systems. In the Al-Pd-Fe system, a single F-type i-phase is produced in a narrow composition region around Al71Pd18Fe11 in melt-spun ribbon samples, but it transforms to a (1/0)-cubic approximant on annealing at 600 degreesC. In the Al-Pd-(Ru,Os) system, a structurally ordered i-phase is obtained on heating the melt-spun samples at a high temperature of 1000 degreesC for Ih in a composition region along e/a = 1.8, but after prolonged annealing at the same temperature the i-phase transforms to a (1/0)-cubic approximant. A bulk single i-phase is also produced by annealing of the as-cast. Al73Pd15Ru12 alloy at 1000 degreesC. (C) 2000 Elsevier science B.V. All rights reserved.
Title:
On icosahedral phase formation in mechanically alloyed Al70Cu20Fe10
Authors:
Srinivas V. Barua P. Murty BS.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):65-67, 2000 Dec 15.
Abstract:
The formation of icosahedral phase by mechanical alloying of crystalline elemental powders has been investigated. The effect of milling energy on icosahedral phase formation in Al70Cu20Fe10 has been studied using X-ray diffraction and energy dispersive X-ray (EDX) microanalysis. In order to study the alloying process during milling, different starting compositions of Al, Cu and Fe elemental blends have been used. The present study indicates that even though the intermediate phases formed during milling are the same, the icosahedral phase formation is sensitive to the way in which the nominal composition is reached. (C) 2000 Elsevier Science S.V. All rights reserved.
Title:
Production of single Al64Cu23Fe13 icosahedral quasicrystal with the Czochralski method
Authors:
Yokoyama Y. Fukaura K. Sunada H. Note R. Hiraga K. Inoue A.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):68-73, 2000 Dec 15.
Abstract:
We have investigated formation mechanisms of the icosahedral (i-) phase in a Cu-enriched region of the Al-Cu-Fe system. The formation of i-phase in the Al-Cu-Fe alloy system is characterized by the peritectic reaction: lambda (2)+-->I (lambda (2) is an Al3Fe compound with over 5 at.% Cu), which has been observed even in the Cu-enriched region. Therefore, we have tried to avoid the lambda (2)-crystallization by preliminary metallurgical treatments for molten alloy. As a result, we have succeeded in growing a single Al61Cu23Fe13 i-quasicrystal with the Czochralski method. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Comparative study of microstructural and tribological properties of sintered, bulk icosahedral samples
Authors:
Brunet P. Zhang LM. Sordelet DJ. Besser M. Dubois JM.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):74-78, 2000 Dec 15.
Abstract:
We have investigated a number of quasicrystalline and related samples prepared by sintering under either hot isostatic pressure (HIP) or low uniaxial pressure (LUP). Attention was focused to the influence of the preparation process parameters onto the resulting crystallographic structure and morphology of the phases. Altogether, we found some differences between the two kinds of samples as far as hardness and friction coefficient were concerned. For instance, HIPed specimens containing boron exhibited small rod-shaped precipitates whereas LUPed samples did not. The LUPed specimens revealed better wear resistance and lower friction towards steel and tungsten carbide riders than the HIPed materials. The present study clearly points out that pressure-temperature-composition phase diagrams and preparation processes of quasicrystals, as well as for most other materials, have a significant influence on the final properties which may be eventually used in view of technological applications. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 6]
Title:
Laser ablation synthesis of Al-based icosahedral powders
Authors:
Nicula R. Jianu A. Grigoriu C. Barfels T. Burkel E.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):86-89, 2000 Dec 15.
Abstract:
The laser ablation (LA) synthesis of ultra-fine-grained powders with dominant icosahedral structure has been attempted using Al-Cu-Fe and Al-Pd-Mn targets. The structure of the Al-Cu-Fe LA powders was examined using synchrotron radiation diffraction experiments which revealed the presence of the icosahedral Al-Cu-Fe phase. The Al-Pd-Mn powders were studied using scanning electron microscopy (SEM) and energy dispersive synchrotron radiation diffraction. For Al-Pd-Mn, the icosahedral phase is also a constituent phase of the LA alloy powders. Our results indicate that LA may be successfully used for obtaining quasicrystalline-based ultra-fine grained powders and/or surface coatings, while also providing a basis for the powder metallurgy processing of these materials. (C) 2000 Elsevier Science B.V, All rights reserved.
Title:
Icosahedral phase formation in Ag-substituted Ti-Zr-Ni rapidly-quenched alloys
Authors:
Nicula R. Ponkratz U. Jianu A. Schick C. Burkel E.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):90-92, 2000 Dec 15.
Abstract:
The formation of icosahedral phases in Ag-substituted Ti-Zr-Ni alloys was investigated by in situ annealing diffraction experiments using synchrotron radiation. The as-quenched (Ti1-xAgx)-Zr-Ni alloys (x=2, 5, 7 and 10 at.%) are amorphous and/or in a mixed nanostructured state. Upon heating, the Ti-Zr-Ni-Ag alloys transform to either a crystalline or a quasicrystalline state, depending on the Ag content. Differential scanning calorimetry (DSC) studies were performed to identify the nature and sequence of the phase transitions. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 7]
Title:
Effect of Si addition on the formability of the icosahedral quasicrystalline phase in an Al65Cu20Fe15 alloy
Authors:
Lee SM. Kim BH. Kim SH. Fleury E. Kim WT. Kim DH.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):93-98, 2000 Dec 15.
Abstract:
The effect of Si addition on the icosahedral forming Al65Cu20Fe15 alloy was investigated. Conventional casting and melt spinning were employed with the addition of Si element. As Si was added up to 5 at.% replacing the Al atoms, the volume fraction of the i-phase gradually decreased. However, with increasing Si content further up to 15 at.%, an 1/1 cubic approximant phase formed instead of the i-phase. After heat treatment at 750 degreesC for 3 h, the volume fraction of the beta -phase increased in an Al64Cu20Fe15Si1 alloy, while the volume fraction of the 1/1 approximant phase increased in an Al50Cu20Fe15Si15 alloy. The Al50Cu20Fe15Si15 alloy showed a relatively high hardness and fracture toughness compared to the other Si containing Al-Cu-Fe alloys. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Metal matrix composites reinforced by gas-atomised Al-Cu-Fe powders
Authors:
Lee SM. Jung JH. Fleury E. Kim WT. Kim DH.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):99-103, 2000 Dec 15.
Abstract:
An Al62Cu26Fe12 alloy was gas-atomised to prepare powders containing icosahedral quasicrystalline phase. For synthesizing composites, pure Al was selected as matrix material, and the Al62Cu26Fe12 powders were added to the molten aluminum during the casting. A Ni coating with a thickness of approximately 5 mum deposited onto the Al62Cu26Fe12 particles proved to be effective in preserving the original powder structure during casting. The composites showed a relatively good bonding between the Al62Cu26Fe12 particles and matrix, despite the partial dissolution of the small satellite particles. Mechanical properties evaluated through compression and indentation tests of the composites indicated a significant increase of the yield stress especially in the range up to 10% volume fraction of reinforcing particles. Strengthening mechanisms were reviewed to estimate the role of the icosahedral and coexisting crystalline phases on the increase of the yield stress. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 9]
Title:
Ternary phase diagram studies in Ti-Zr-Ni alloys
Authors:
Davis JP. Majzoub EN. Simmons JM. Kelton KF.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):104-107, 2000 Dec 15.
Abstract:
Equilibrium phase formation is reported for ternary Ti-Zr-Ni alloys near the i-phase-forming composition, for temperature slices between 500 and 700 degreesC. Selected microstructural results in as-cast and annealed samples are discussed. Dominant equilibrium phases identified are the C-14-like Laves phase, a Ti2Ni-like phase, alpha (Ti/Zr), the b.c.c. 1/1 W-phase and the i-phase. The i-phase forms over a small compositional range from a high-temperature equilibrium phase mixture of the Laves and alpha (Ti/Zr) solid solution phases. Lower annealing treatments have not been found to transform the i-phase, suggesting that in this alloy, the quasicrystal phase might be the ground state phase. Additions of small amounts of Pb and Pd, 1-2 at.%, are demonstrated to substantially effect the equilibrium phase formation for the i-phase and the W-phase. The addition of 1 at.% of Pb significantly orders the i-phase structure. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 6]
Title:
Cluster structure and hydrogen in Ti-Zr-Ni quasicrystals and approximants
Authors:
Majzoub EH. Kim JY. Hennig RG. Kelton KF. Gibbons PC. Yelon WB.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):108-111, 2000 Dec 15.
Abstract:
Elastic neutron diffraction data from icosahedral Ti45Zr38Ni17 are presented and analyzed using information from the 1/1 approximant Ti50Zr35Ni15. These data indicate that similar clusters exist in the approximant and the i-phase. This is shown to be consistent with simulated diffraction from an icosahedral glass model of the quasicrystal, placing a Bergman cluster on the glass sites. An electrochemical method was used to hydrogenate Ti-based quasicrystals and their crystal approximants. This technique gives a consistently high hydrogen to metal atom ratio of 1.9, without crystal hydride formation in the quasicrystal. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Influence of hydrogen on formation and stability of Zr-based quasicrystals
Authors:
Zander D. Koster U. Eliaz N. Eliezer D.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):112-115, 2000 Dec 15.
Abstract:
Hydrogenation of quasicrystalline Zr69.5Cu12Ni11Al7.5 was performed electrochemically in a 2:1 glycerine-phosphoric acid electrolyte. Hydrogen absorption/desorption as well as the influence of hydrogen on the formation and stability was studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM?) and thermal desorption spectroscopy (TDS). In comparison to amorphous Zr-Cu-Ni-Al the absorption kinetics in quasicrystalline Zr-Cu-Ni-Al were found to be faster. Desorption is hindered in both materials probably due to the formation of thin ZrO2 layers. Only partial desorption of hydrogen was observed by means of TDS to occur prior to the decomposition of the quasicrystalline phase. The observed increase in length during hydrogen charging indicates an interesting new result. Instead of the continuous increase of the specific volume per hydrogen atom at very low hydrogen concentration typical for the filling up of larger trapping sites, a decrease from a rather high value is observed. This means that not only the site for the hydrogen atom is expanded, but also the neighboring still empty ones. Above a hydrogen content of H/M=0.05 the formation of Zr-Cu-Ni-Al quasicrystals is replaced by tetragonal Zr2Cu, tetragonal Zr2Ni and hexagonal Zr6NiAl2. At high hydrogen contents (about H/M=1.0) phase separation is assumed to take place followed by the formation of nanocrystalline ZrH2. Icosahedral Zr69.5Cu12Ni11Al7.5 was found to decompose through a discontinuous transformation by complex precipitation reactions; it transforms mainly into tetragonal Zr2Cu, tetragonal Zr2Ni and hexagonal Zr6NiAl2. Hydrogenation of quasicrystals at low concentrations does not change the phases formed during decomposition. At hydrogen contents higher than H/M=1.1 decomposition of quasicrystals starts with the precipitation of tetragonal ZrH2-x. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 9]
Title:
Structure of liquid Al-Mn-Cr alloys in equilibrium with the mu Al-4(MnyCr1-y) approximant phase
Authors:
Simonet V. Hippert F. Audier M. Bellissent R.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):116-119, 2000 Dec 15.
Abstract:
The structure of Liquid Al-88.5(MnxCr1-x)(11.5) alloys (0 less than or equal tox less than or equal to1) in equilibrium with the hexagonal mu Al-4(MnyCr1-y) approximant phase (0 less than or equal toy less than or equal to1) was investigated by neutron scattering. The nature of the Mn/Cr substitution in these liquids was assumed to be isomorphic on the basis of preliminary results, showing that a complete Mn/Cr isomorphic substitution does occur in their primary solidified mu -phase. From the analysis of the partial pair distribution functions, as well as from the comparison between experimental and simulated structure factors at large Q values, we found that liquids exhibit a strong local icosahedral order similar to the one observed in Al-Mn and Al-Cr approximant phases, i.e. icosahedral clusters formed by one transition metal surrounded by 12 atoms, mainly Al. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Modulated states in Mg-Al alloys and classical Frank-Kasper phases: a high resolution X-ray diffraction study
Authors:
Donnadieu P. Denoyer F. Lauriat JP. Ochin P.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):120-123, 2000 Dec 15.
Abstract:
The Mg-Al system shows for composition in the 50-60 at.% Al range several states, either periodic or quasiperiodic, related to tetrahedral and icosahedral motif structures. The Mg-Al (61 at.%) rapidly solidified alloy shows a cubic quasiperiodic state with inflation symmetry characterized by the algebric number 2 - root3. The main question is to know if this state is an example of a new kind of quasicrystal or if this inflation property is only due to a continuous variation of the wavenumber. We report high resolution X-ray diffraction studies of this Mg-Al (61 at.%) metastable state and the related stable Frank-Kasper phase (beta -phase). These experiments clearly show fluctuations of the wavenumber. The quasiperiodic Mg-Al (61 at.%) state appears thus to have typical features of incommensurately modulated phases, but with a persisting connection with Frank-Kasper phases. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 6]
Title:
Preparation of Zn-Mg-rare earth quasicrystals and related crystalline phases
Authors:
Sterzel R. Dahlmann E. Langsdorf A. Assmus W.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):124-126, 2000 Dec 15.
Abstract:
We present our results in growing large single quasicrystals of the icosahedral phase in the Zn-Mg-Ho system with the top-seeded solution growth method. We also show new results of investigations on the Zn-Mg-Y phase diagram focussing on the sector with low Y content, to obtain some information about the solidification behavior of the decagonal phase. In addition, the R-phase, a novel cubic approximant for the icosahedral phase in the Zn-Mg-Er system, is presented. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Phason strain and structural perfection in the Zn-Mg-rare-earth icosahedral phases
Authors:
Letoublon A. Fisher IR. Sato TJ. de Boissieu M. Boudard M. Agliozzo S. Mancini L. Gastaldi J. Canfield PC. Goldman AI. Tsai AP.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):127-130, 2000 Dec 15.
Abstract:
The structural perfection of eight samples of icosahedral Zn-Mg-R (R=Y, Ho and Tb) single grains has been studied by high resolution X-ray diffraction, Four samples present a systematic peak shift proportional to Q(per) characteristic of a linear phason strain. Two other samples present a peak splitting proportional to Q(per). Only two samples had their Bragg peak position corresponding to the ideal one, with a width increasing linearly with Q(per). The perfection of one of these last two samples was investigated by synchrotron monochromatic X-ray topography. It was found to be a microstructure similar to the one exhibited by conventional crystals grown by the same technique (flux-growth). (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
On the analysis of diffuse intensity and striation contrast in electron microscopy images of Al-Cu-Co-Si decagonal phases
Authors:
Mukhopadhyay NK. Weatherly GC. Sastry GVS.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):135-138, 2000 Dec 15.
Abstract:
Electron microscopy and diffraction experiments were carried out to analyze diffraction features and correlate with the striation contrast observed in the images of Al-Cu-Co-Si decagonal phase. There are two important diffraction features identified which include the diffuse streak and the extra satellite spots. The extra satellite spots can indicate some sort of superlattice chemical ordering among the clusters while the diffuse streaks indicate presence of some kind of phason disorder leading to the observation of striation contrast in the imaging modes. (C) 2000 Elsevier Science B.V. Ali rights reserved.
Title:
A study of the Al-Pd-Co alloy system
Authors:
Yurechko M. Grushko B.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):139-142, 2000 Dec 15.
Abstract:
Partial isothermal sections of the Al-Pd-Co phase diagram at 1050 and 790 degreesC are presented. In contrast to Al-Ni-Co no stable quasicrystals were found under the investigated conditions. Instead, at the compositions corresponding to the high-Co limit of the Al-Ni-Co decagonal phase a periodic phase closely related to the decagonal phase is formed. Orthorhombic "Al3Pd", whose structure is known to resemble quasicrystals, extends up to 17 at.% Co and exhibits structural variations with composition. At the Al concentrations slightly lower than Al3Pd(CD) several new ternary periodic phases were found. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Czochralski growth and characterization of large decagonal Al-Co-Ni quasicrystals
Authors:
Graber M. Barz RU. Dreier P. Gille P.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):143-146, 2000 Dec 15.
Abstract:
In the ternary Al-Co Ni system, decagonal quasicrystals occur that are thermodynamically stable and can be grown using rather conventional crystal growth techniques at near-equilibrium conditions. Derailed studies of the Al-rich part of the ternary phase diagram including the primary crystallization field of the decagonal phase are known from the literature. Using these data quasicrystal growth by the Czochralski method from off-stoichiometric (Al-rich) melts has proved to be successful. In a series of growth experiments with varying Co:Ni ratio along the 1050 and 1100 degreesC isotherms, single-grain quasicrystals up to 1 cm(3) in size have been grown. Use was made of very low growth rates (0.2-0.5 mm/h) as to meet the needs of the constitutional supercooling criterion as well as those arising from the anisotropic growth kinetics of the decagonal phase. The segregation behaviour was studied by electron probe microanalysis (EPMA) measurements concerning the change in the Al concentration during growth and the shift in the Co:Ni ratio which marks the main extension of the decagonal stability region. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 9]
Title:
Formation and structures of decagonal quasi-crystals in the Al-Ni-Ru system
Authors:
Sun W. Hiraga K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):147-151, 2000 Dec 15.
Abstract:
Two new decagonal quasi-crystals (D-phases), which have periods of 0.4 and 1.6 nm, respectively, have been found to form with different compositions in conventionally solidified Al-Ni-Ru alloys. The diffraction patterns of these two D-phases display a large number of sharp diffraction spots located at exact tenfold symmetry positions and almost no diffuse streaks, indicating that they are highly ordered quasi-crystals. The D-phase with 0.4-nm periodicity exhibits a pronounced SI-type superlattice order. The D-phase with 1.6-nm periodicity can be formed as a major phase by annealing at around 900 degreesC. By means of high-resolution electron microscopy, the structural characteristics of the D-phase with 1.6-nm periodicity have been revealed. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Periodic and aperiodic arrangements of dodecagonal (Ta, V)(151)Te-74 clusters studied by transmission electron microscopy - The method's merits and limitations
Authors:
Krumeich F. Reich C. Conrad M. Harbrecht B.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):152-155, 2000 Dec 15.
Abstract:
A series of metal-rich tellurides in the ternary system Ta/V/Te crystallizes in closely related structures representing different arrangements of a basic disc-like (Ta, V)(151)Te-74 cluster. The centres of these clusters define various periodic or aperiodic square-triangle tilings on a length scale of about 2 nm. The structure of the approximant Ta83V14Te60 with its underlying square tiling has been studied under various imaging conditions by high-resolution transmission electron microscopy and complementary image simulations. At a large defocus epsilon approximate to -180 nm, a (Ta, V)(151)Te-74 cluster is represented by a bright dot surrounded by 12 others forming a dodecagon. The application of this selective imaging technique allows us to determine the tilings, i.e., the cluster arrangements, of new approximants and of quasicrystalline phases almost unambiguously. More complex contrast features as observed in some regions of the sample and the streaks turning up in reciprocal space are interpreted as stacking faults along the pseudo-12-fold axis. (C) 2000 Elsevier Science B.V. All nights resented.
Title:
Development of novel polymer/quasicrystal composite materials
Authors:
Bloom PD. Baikerikar KG. Otaigbe JU. Sheares VV.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):156-159, 2000 Dec 15.
Abstract:
We report on a new class of materials, polymer/quasicrystal composites with useful properties for beneficial exploitation in applications, such as dry bearings and composite gears. Our preliminary results indicate that our new composites are a means of enhancing the properties of certain organic polymers while providing a new means of processing quasicrystals. Al-Cu-Fe quasicrystalline materials significantly improved wear resistance to volume loss in polymer-based composites. Furthermore, mechanical testing results showed a two-fold increase in the storage modulus of the reinforced composites compared with the polymer samples. The fabrication in addition to the thermal, mechanical, and wear properties of these unique materials will be described. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
The nature of lead-quasicrystal interfaces and its effect on the melting behaviour of lead nanoparticles embedded in quasicrystalline matrices
Authors:
Singh A. Tsai AP.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):160-163, 2000 Dec 15.
Abstract:
Nanoparticles of lead were embedded in Al-Cu-Fe icosahedral matrix by rapid solidification. The embedded particles showed definite orientation relationship with the matrix and the interface, facetted on the major symmetry planes of the matrix, showed coherency. Annealing treatments at 600 and 800 degreesC showed that this particle-matrix interface is unstable. The coherency at this interface is supported by the phason strains formed on rapid quenching. This coherency breaks down on annealing in the stability region of the icosahedral phase, leading to a lowering in the melting temperature of the lead particles. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Quasicrystalline Al-alloys with high strength and good ductility
Authors:
Schurack F. Eckert J. Schultz L.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):164-167, 2000 Dec 15.
Abstract:
The formation of quasicrystalline phase in Al-Mn and Al-Mn-Ce/Fe alloys by solid state reaction via mechanical alloying of elemental powder mixtures and ball milling of prealloys was investigated. The samples were analysed by X-ray diffraction, transmission-and scanning-electron microscopy and differential-scanning calorimetry. The formation of a stable fci-phase in the Al-Mn-Pd system by mechanical alloying is described. A dual-phase microstructure of Al-matrix and quasicrystalline phase was created by an initial excess of aluminium or subsequent blending of quasicrystalline powder with purr aluminium. Bulk samples,were processed by squeeze casting revealing excellent mechanical properties. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 6]
Title:
Formation, microstructure and mechanical properties of Al-Fe base quasicrystalline alloys
Authors:
Kimura HM. Sasamori K. Inoue A.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):168-172, 2000 Dec 15.
Abstract:
An icosahedral (I) phase in coexistence with Al-phase was formed in the size fraction range up to 125 mum of atomized Al93Fe3Cr2Ti2 powder. The decomposition temperature of the I-phase is about 790 K. As per energy dispersive X-ray spectroscopy analysis, the constituent composition of the I-phase is Al84.2Fe7.0Cr6.3Ti2.5. It is found that the Al84.2Fe7.0Cr6.3Ti2.5 alloy forms a mostly single I-phase in the melt-spun state. Bulk I-alloys in a rod form were produced by extrusion of the atomized powders at 673 K and an extrusion ratio of 10. The extruded Al93Fe3Cr2Ti2 alloys have good mechanical properties, i.e., sigma (0.2) of 550 MPa, sigma (UTS) of 660 MPa and epsilon (p) Of 4.5% at room temperature and sigma (0.2) of 330 MPa, sigma (UTS) of 350 MPa and epsilon (p) Of 1.5% at 573 K. The I-based Al93Fe3Cr2Ti2 alloy is expected to be useful as a new type of high-elevated temperature strength material. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Effect of composition on the streaking and diffuse intensity in decagonal phase in Al70-XCo15CuX+YNi15-Y system
Authors:
Pramanick AK. Mandal RK. Sastry GVS.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):173-177, 2000 Dec 15.
Abstract:
We report here the transmission electron microscopic examination of alloys of three compositions in the system Al70-XCo15CuX+YNi15-Y. They have been chosen on the basis of: (a) Ela ratio lying between Al65Co15Cu20 (ACC) and Al70Co15Ni15 (ACN) and (b) a possible observation of change in order from ACN to ACC, the end members. The selected area diffraction studies of the melt-spun ribbons of the above compositions have revealed the presence of streaking around some spots and also diffuse rows. These have led to the transformation of a basic P10(5)/mmc structure to that of P10/mmm having a periodicity of similar to8 Angstrom. Such a transformation has been explained based on the SD model earlier proposed by us. The chemical ordering in the layers is shown to accomplish the transformation. However, streaking arises owing to the presence of planar faults with a fault vector having periodic and quasiperiodic components. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Disorder diffuse scattering of decagonal quasicrystals
Authors:
Frey F.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):178-185, 2000 Dec 15.
Abstract:
Diffuse scattering in decagonal phases is due to deviations from strict aperiodic and periodic order in the quasiperiodic plane and along the unique direction, respectively. Results from X-ray (synchrotron) and neutron diffraction experiments, mainly carried out with decagonal Al-Ni-Co, are presented. Most prominent are diffuse maxima, diffuse streaks, phason affected reflection profiles, and diffuse layers perpendicular to the unique axis. Disorder models in decagonal qc-structures, in particular lamellar domain-like ordering in super-space are outlined. The terms structure and phase in context with disordered structures are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
The impact of aperiodic order on mathematics
Authors:
Lagarias JC.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):186-191, 2000 Dec 15.
Abstract:
Mathematics has been strongly influenced by problems arising from physics. The existence of quasicrystals as strongly ordered structures which cannot be periodic has raised various mathematical questions that have stimulated developments in the areas of discrete geometry, harmonic analysis, group theory and ergodic theory. It seems that extra "internal dimensions" are useful in describing certain features of quasicrystal structure and their diffraction spectra. In particular N-dimensional crystalline symmetries can appear in the diffraction spectra of model sets. This paper describes recent work in discrete geometry suggested by the modeling of atomic positions in quasicrystals by Delone sets with restrictions on interpoint distances. It suggests one mechanism for the appearance and usefulness of "internal dimensions" in describing ordered aperiodic structures. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Covering clusters in the Katz-Gratias model of icosahedral quasicrystals
Authors:
Duneau M.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):192-198, 2000 Dec 15.
Abstract:
A variety of clusters with icosahedral symmetry can be identified in periodic approximant phases of quasicrystals: icosahedra, Mackay clusters (MC) and Bergman clusters (BC). For i-Al-Cu-Fe and i-Al-Pd-Mn, MCs and BCs have been proposed as complementary building blocks centred on a primary structure. However, theoretical studies showed that these 2-shell or 3-shell clusters could not cover all atomic positions given by hyperspace models. On the other hand, the recent concept of a unique covering cluster was shown to apply to 2D Penrose tilings and octagonal tilings. In this paper, we consider extended MCs of 5-shells and extended BCs of 6-shells that appear naturally in the Katz-Gratias model. We discuss the variable occupation number of some of the shells. We show that a fixed extended BC of B-shells and 105 atoms covers about 98% of atomic positions, while extended MCs of 101 atoms only fill 93% of sites. We also prove that a variable extended BC of 6-shells covers all atomic positions of the Katz-Gratias model. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Cluster coverings as an ordering principle for quasicrystals
Authors:
Gahler F.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):199-204, 2000 Dec 15.
Abstract:
Cluster density maximization and (maximal) cluster covering have emerged as ordering principles for quasicrystalline structures. The concepts behind these ordering principles are reviewed and illustrated with several examples. For two examples, Gummelt's aperiodic decagon model and a cluster model for octagonal Mn-Si-Al quasicrystals, these ordering principles can enforce perfectly ordered, quasiperiodic structures. For a further example, the Tubingen triangle tiling (TTT), the cluster covering principle fails to enforce quasiperiodicity, which sheds some light on the limitations of this approach. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Penrose tilings, cluster models and the quasi-unit cell picture
Authors:
Steinhardt PJ.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):205-210, 2000 Dec 15.
Abstract:
The quasi-unit cell picture proposes that quasicrystals can be decomposed into a single, repeating cluster of atoms with overlap (atom-sharing) rules between neighbors that force a perfect quasiperiodic structure. In this paper, we introduce the basic features of the model and how it differs from the earlier Penrose tiling and cluster models. We also report on recent advancements in applying the model to determine the structure of the decagonal phase, Al72Ni20Co8, including new evidence supporting the quasi-unit cell picture based on clusters with broken 10-fold symmetry in favor of models based on unbroken symmetry. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Z-contrast imaging of decagonal quasicrystals: an atomistic model of growth
Authors:
Yan YF. Pennycook SJ.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):211-216, 2000 Dec 15.
Abstract:
The structure of Al-Ni-Co decagonal quasicrystals is studied by atomic-resolution Z-contrast imaging technique. We propose that the presence of "rotational ordering" is the key reason leading to the formation of the 2 nm clusters and the overlaps necessary in the coverage model. Every detail of the Z-contrast images of the 2 nm clusters can be reproduced by a superposition of rotational variants of the 2 nm clusters seen in the ordered tau (2)-inflated Al13Co4 approximant phase. introducing this rotational ordering, it is clear how one cluster can nucleate neighboring clusters. Continuing this process automatically generates all the intercluster separations necessary for quasiperiodic tiling. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 22]
Title:
Phase transition and diffuse scattering studies in the Al-Cu-Fe ternary system
Authors:
Boudard M. Letoublon A. de Boissieu M. Ishimasa T. Mori M. Elkaim E. Lauriat JP.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):217-220, 2000 Dec 15.
Abstract:
The reversible phase transformation between the crystalline multidomain structure of the rhombohedral phase to the perfect icosahedral quasicrystalline state at high temperature has been studied by in situ X-ray diffraction on a four-circle diffractometer using synchrotron radiation. The transient state known as the 5-fold modulated state has been observed and its evolution with temperature is characterised. Diffuse scattering located close to the Bragg reflections is observed in the studied temperature range. Its evolution with temperature shows a reversible transformation with an important change of shape in agreement with the proximity of a S-fold phason instability. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Dense sphere packings and the Wulff-shape of crystals and quasicrystals
Authors:
Schnell U.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):221-223, 2000 Dec 15.
Abstract:
The classical models for the shape of crystals and quasicrystals are based on various minimum energy principles and lead to dense atomic packings. We give a pure geometric model which is based on a volume density only. The optimal shapes obtained by this method coincide in many cases with the real shapes of crystals and quasicrystals. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Generation of quasicrystals via a single cluster
Authors:
Cockayne E.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):224-227, 2000 Dec 15.
Abstract:
We present a columnar cluster with 46 atoms per repeat distance which forces a quasicrystal when space is filled by interpenetrating copies of itself. The atomic positions in the resultant quasicrystal are remarkably similar to those in models for real decagonal quasicrystals. The axes of the pentagonal antiprism subclusters of this model reveal an even simpler tile decoration, with only three atoms, that forces a quasicrystal under certain constraints. Published by Elsevier Science B.V.
Title:
Six-dimensional model of an i-Al-Pd-Mn quasicrystal compatible with its 2/1 approximant
Authors:
Yamamoto A. Hiraga K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):228-231, 2000 Dec 15.
Abstract:
A six-dimensional (6D) model of the icosahedral Al-Pd-Mn quasicrystal is given, which is obtained from our old model with slight modification and leads to the 2/1 approximant structure by the introduction of an appropriate phason strain. In the old model, two clusters are situated at even- and odd-parity vertices of the 3D Penrose pattern with an edge length of about 20 Angstrom. One of them is quite similar to that of the 2/1 approximant but the third and ninth shells of the cluster in the approximant cannot be derived. After adding small occupation domains in the 6D model, we could reproduce all atom sites in the approximant structure by the introduction of appropriate cubic phason strain. (C) 2000 Elsevier Science B.V. Ail rights reserved. [References: 2]
Title:
Weak Bragg scattering in icosahedral Mg-Y-Zn
Authors:
Estermann MA. Haibach T. Steurer W. Langsdorf A. Wahl M.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):237-241, 2000 Dec 15.
Abstract:
The mathematical framework of higher-dimensional crystallography intrinsically assumes the ideally perfect crystal as the underlying basis for solving, modelling and refining crystal structures with a quasiperiodic ordering scheme. Such an ideally perfect crystal will result in a Fourier spectrum with sharp Bragg peaks and no diffuse scattering. However, most quasicrystalline materials do exhibit diffuse scattering phenomena, and therefore contain a certain amount of disorder. Only recently, single-crystals from the system Mg-Y-Zn emerged as possible candidates for ideally perfect crystals. We employed X-ray diffraction techniques on a particular sample of Mg-Y-Zn. Techniques, based on area detector systems, which are usually used to study weak diffuse scattering phenomena, are employed. There is no indication of disorder diffuse scattering which normally obscures the weak Bragg scattering. The experimental conditions are discussed under which a full data collection may he performed with area detectors. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
A family of hexagonal approximants of decagonal quasicrystals
Authors:
Mo ZM. Kuo KH.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):242-245, 2000 Dec 15.
Abstract:
By means of high resolution electron microscopy, the hexagonal phases with about the same c = 12.4-12.6 Angstrom but different a parameters (kappa :17.674 Angstrom; lambda :28.382 Angstrom; upsilon :40.687 Angstrom) in Al-rich Al-TM (TM: transitional metal) alloys were found to consist of similar icosahedral cluster of about 30 Angstrom in size. Using the known atomic sites of kappa and lambda in this cluster, the crystal structure of upsilon was solved by direct methods of X-ray diffraction analysis. Various icosahedral connections in this: cluster were analyzed. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Icosahedral order and disorder in tetrahedral semiconductors - Three-dimensional and six-dimensional views
Authors:
Dmitrienko VE. Kleman M.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):246-249, 2000 Dec 15.
Abstract:
Different approaches to tetrahedrally coordinated quasicrystals are discussed. It is shown that the BC8 phase, which is observed in silicon and germanium, has a hidden icosahedral symmetry of tetrahedral interatomic bonds. In this cubic crystal with the Ia (3) over bar space group, 75% of all bonds are directed almost exactly along fivefold icosahedral axes. This structure (16 atoms per unit cell) is the 1/0 approximant of a hypothetical icosahedral quasicrystal with a body-centered six-dimensional lattice. The 1/1 approximant is also constructed (64 atoms per unit cell with Ia (3) over bar space symmetry). A specific type of topological disorder, related with partial phason flips, is shown to be possible in both the approximants. The structure of the approximants and the atomic flips are analyzed both in physical and in perpendicular space and their energies are studied ab initio within the density functional theory. The considered phason disorder provides a new insight into crystalline-to-amorphous transformations. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
A cluster approach to random Penrose tilings
Authors:
Gummelt P. Bandt C.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):250-253, 2000 Dec 15.
Abstract:
An experimentally relevant subclass of the full random Penrose pentagon tiling ensemble is generated using a single cluster. Local matching rules based on cluster overlaps are equivalent to relatively weak axioms on minimal cluster distances. Energy and entropy arguments and recent results on constituent atomic clusters in decagonal quasicrystals are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
The growth of entropically stabilized quasicrystals
Authors:
Joseph D. Elser V.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):254-257, 2000 Dec 15.
Abstract:
We introduce a growth model for entropically stabilized quasicrystals. The dominating feature of this model is a fluctuating growth front which enables growth near equilibrium with small phason components. We summarize the results obtained for 2D and give a first presentation of 3D calculations. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Icosahedral quasiperiodic packing of fibres
Authors:
Duneau M. Audier M.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):258-262, 2000 Dec 15.
Abstract:
Methods for constructing icosahedral packing of fibres are reported. Closest packing constructions were realised using straight fibres of circular cross-section and threaded parallel to five- or three-fold icosahedral axes, or both. Their symmetry point group and related 2D tiling as obtained by cut and projection from periodic hyperspace, are presented in the case of the closest packings of fibres only parallel to the six five-fold axes. As a result of the analysis of the related 2D tiling, constructions can also be made using simple 2D building rules. Future experiments on elasticity properties of composite materials with a quasiperiodic fibrous reinforcement are discussed. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 9]
Title:
Durer-Kepler-Penrose, the development of pentagon tilings
Authors:
Luck R.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):263-267, 2000 Dec 15.
Abstract:
As Kepler's Aa tiling is sometimes regarded as the pentagon tiling described by Penrose, the two tilings are compared considering their acceptance domains. The acceptance domain of the Penrose tiling is a decagon, whereas the acceptance domain of Kepler's Aa tiling looks like a 10-fold toothed wheel: it exhibits a hole in the centre and it has therefore unusual inflation properties. A related tiling proposed by Durer a century earlier than Kepler's starts with an inflated pentagon and Durer described the possibility of glueing tiles with random distribution. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Geometry of quasicrystal-to-crystal transformations
Authors:
Steurer W.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):268-271, 2000 Dec 15.
Abstract:
The geometrical relationships between quasiperiodic structures and the cubic beta -phase (CsCl-type) formed in a continuous phase transformation is discussed on the examples of decagonal Al-Co-Me (Me=Cu, Ni) and icosahedral Al-Mn-Pd. For these purposes, first the alternative higher-dimensional embedding of decagonal Al-Co-Ni as incommensurately modulated structure is introduced. By projection onto the physical space, a periodic average structure of the decagonal quasicrystal can be obtained. It is demonstrated that the lattice of the periodic average structure of the quasiperiodic phases matches very well the lattice of the cubic beta -phase. In this way, the experimentally observed orientational order and registry of the cubic beta -phase with regard to the quasiperiodic structure can be nicely explained. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
The quasicrystal-to-crystal transformation by Landau theory
Authors:
Beraha L. Steurer W.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):272-275, 2000 Dec 15.
Abstract:
A phenomenological description of the quasicrystal-to-crystal transformation is presented in terms of Landau theory. The basic idea is to describe the structures of quasicrystals as incommensurately modulated structures and to use the tools developed for phase transitions of this kind. The usefulness of this description is demonstrated on the one-dimensional Fibonacci sequence. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 8]
Title:
Modeling atomic surfaces for the Al-Ni-Co basic decagonal phase
Authors:
Cervellino A. Haibach T. Steurer W.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):276-278, 2000 Dec 15.
Abstract:
The atomic surfaces (ASs), supports of a probability density in perpendicular space, are a powerful instrument for describing quasicrystal structure. The attainable resolution of diffraction data does not allow a direct ASs determination hence they need to be modeled and refined. A simple set of geometric rules can be found for modeling ASs. The ASs shapes are constrained by interatomic distances, density and symmetry of the physical 3D structure. Basic decagonal Al71Ni22Co7 is simultaneously the simplest (with only two 2D independent ASs) and the toughest proof for the technique, as the mentioned physical constraints are extremely difficult to be satisfied. It is hence necessary to allow for a probability smaller than one (i.e. partial atomic site occupancy) in part of the ASs. This adds further parameters to the model. Further, some physical constraints may be weakened, evidencing structural features such as pseudo symmetry elements, puckering of the periodic layers, chemical and geometric disorder. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
From the disordered via the quasicrystalline to the crystalline state
Authors:
Haussler P. Nowak H. Haberkern R.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):283-286, 2000 Dec 15.
Abstract:
We report on structural similarities at short- and medium-range distances of the amorphous and the quasicrystalline state and their consequences on structural stability and electronic transport. In the former the nearest neighbour atoms are onion-shell-like radially ordered around any ad-atom. The spacing between the concentrical shells is up to relatively large distances unique and matches the Friedel wavelength. Their occupation by the ions is random. We interpret this in terms of a resonance, based on spherical waves, between the conduction electrons and the static structure. The spherical arrangement of the atoms plays the role of mirror-spheres for spherical electron waves at short and medium-range distances, quite similar to mirror-planes for the plane electron waves in a crystal. The conducting quasiparticles become localised as there is better spherical correlation and hence the resonance condition is fulfilled. The quasicrystals are between the disordered and the crystalline case. Radial order becomes more strict but lasts for shorter distances (cluster-like), and in addition exists only at particular sites. On the other hand, long-range orientational order, e.g. order at the spheres acid between the spheres has emerged, causing planar resonances between planar electron waves and mirror-planes. Long-range periodicity is still missing. The path from the disordered via the quasicrystalline to the crystalline state seems to be triggered by the improvement of resonances between electrons and the forming static structure. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Phase transformations in decagonal Al-Cu-Co-Si alloy
Authors:
Denoyer F. Reich R. Lauriat JP.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):287-290, 2000 Dec 15.
Abstract:
A high quality single grain of Al63Cu17.5Co17.5Si2 was studied by high resolution X-ray diffraction (synchrotron radiation) as a function of annealing temperature, until its transformation into the decagonal quasicrystal. An assembly of phason-strain quasicrystalline domains with orientations which differ by 2 pin/10 (n=0,...,4) around the tenfold axis, allow us to accurately explain the peak splitting of the quasicrystal diffraction peaks, if we consider the domains periodic along the twofold 'P' direction (direction of the phason-strain) and quasiperiodic along their corresponding orthogonal twofold 'D' axis. This 1D quasicrystal is transformed into the 2D decagonal quasicrystal at 830 degreesC. Intensity anomalies were observed at about 770 degreesC and interpreted as resulting of a phason ordering transformation. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Is d-Al-Cu-Co a random tiling?
Authors:
Zeger G. Plachke D. Carstanjen HD. Trebin HR.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):291-294, 2000 Dec 15.
Abstract:
Channeling Monte Carlo simulations, in combination both with Rutherford backscattering (RBS) and pal-ride-induced X-ray emission (PIXE), have been performed on model quasicrystals of decagonal Al-Cu-Co with different amount of phason disorder. Comparing our simulation results to experimental data we obtain the best agreement For those models with a large amount of phason disorder. This leads us to the conclusion that the sample of d-Al-Cu-Co used in the measurements is a random tiling. Besides the aspect of phason disorder we also examined the Cu and Co distribution given by the Burkov models (S.E. Burkov, Phys. Rev. B 47 (1993) 12325). We show that the chemical distribution is in contrast to the experimental PIXE yield profiles. By exchanging some of the Cu and Co positions it is possible to eliminate the discrepancy. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Ab initio energetics of transition metal ordering in decagonal Al-Co-Cu
Authors:
Widom M. Al-Lehyani I. Wang Y. Cockayne E.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):295-298, 2000 Dec 15.
Abstract:
We perform ab initio total energy calculations fur approximants to a model of decagonal Al-Co-Cu. These calculations support previously proposed chemical ordering of Co and Cu atoms along tile edges. Preferred arrow orientations are identified and shown to obey a subset of the single-arrow Penrose matching rules. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 9]
Title:
Anomalous-X-ray scattering associated with short-range order in an Al70Ni15Co15 decagonal quasicrystal
Authors:
Abe H. Tamura N. Le Bolloc'h D. Moss SC. Matsuo Y. Ishii Y. Bai JM.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):299-302, 2000 Dec 15.
Abstract:
The diffuse scattering around Bragg reflections was observed in a single decagonal quasicrystal of Al70Ni15Co15 using anomalous-X-ray scattering. The intensities of diffuse scattering vary with the three incident X-ray wavelengths, near the Co K-edge and the Ni K-edge and between them. The contrast of diffuse scattering shows the existence of atomic short-range order (SRO) between Ni and Co. The distributions of diffuse scattering are anisotropically modulated and the diffuse shapes vary from one reciprocal lattice point to another. in quasicrystals, anisotropic diffuse shapes derive from phason strain. It is concluded that both SRO and phason strains exist in Al70Ni15Co15. in addition, as the first neighbor of Ni, Ni is preferred to Co statistically, since SRO intensities appear about zone-centers, i.e. there is local clustering of these species. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Neutron and X-ray investigation of disordered quasicrystals
Authors:
Hradil K. Scholpp T. Frey F. Haibach T. Estermann MA. Capitan M.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):303-307, 2000 Dec 15.
Abstract:
Disorder in decagonal quasicrystals is studied by "contrasting methods", i.e. by joint analysis of X-ray and neutron data and by use of the anomalous dispersion method, to learn about the relative influence of the transition metals. First experimental results with decagonal Al-Ni-Co samples of different origin are discussed qualitatively. A comparative study of Patterson maps from neutron and X-ray Bragg data of d-Al72.5Ni16.5Co11 gives direct evidence for particular sites occupied by Co. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 7]
Title:
High resolution X-ray and neutron diffraction of super- and disorder in decagonal Al-Co-Ni
Authors:
Weidner E. Hradil K. Frey F. de Boissieu M. Letoublon A. Morgenroth W. Krane HG. Capitan M. Tsai AP.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):308-314, 2000 Dec 15.
Abstract:
Synchrotron measurements at DESY and ESRF of decagonal quasicrystals with the nominal composition Al70Co15Ni15 and Al72Co16Ni12, show that Bragg reflections with high IH,il values are surrounded by up to four weak subsidiary peaks. The positions of these additional peaks depend solely on the position of the Bragg reflection in the reciprocal perpendicular subspace and can be explained by a linear phason strain model. This model sheds new light on the current superorder models [K. Hradil et al. Phil. Mag. A 79 (1999) 1963] and is a further step towards an understanding of the real structures of decagonal quasicrystals. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 8]
Title:
Quasicrystal element correlations from X-ray standing waves
Authors:
Jach T.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):315-318, 2000 Dec 15.
Abstract:
X-ray standing waves associated with dynamical diffraction in perfect crystals are also present during diffraction in high-quality quasicrystals. The fluorescence observed from quasicrystals while scanning the rocking curve of a particular Bragg reflection shows an identical form to that observed from periodic planes in a perfect crystal. In this case, however, the coherent fraction is the value of a correlation function: the Fourier component of a given elemental distribution at the wavevector associated with the Bragg peak. We show, using a model fur Al-Pd-Mn, how the observed value for the coherent position at a given reflection is a sensitive indicator of the centrosymmetry of the distribution, and the observed value for the coherent fraction is a test of the elemental distribution predicted from the model. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Finite-resolution correction to the diffraction intensity in icosahedral quasicrystals
Authors:
Fradkin MA.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):319-322, 2000 Dec 15.
Abstract:
The correction to the intensity of Bragg scattering by an ideal quasicrystal due to finite experimental resolution is calculated. Intrinsic background intensity is shown to appear due to close filling of the 'parallel' reciprocal space by the diffraction spots. This intensity is found as a function of the 'perpendicular' wavevector of the strongest peak falling into a particular resolution window and is estimated in a continuous approximation for the one- and three-dimensional quasicrystals. Recent data on the diffraction from a single-grain perfect Al-Pd-Mn quasicrystal are analyzed in a proposed model, (C) 2000 Elsevier Science B.V. Ali rights reserved. [References: 4]
Title:
Investigation of icosahedral phases in the Zn-Mg-(Y, Er) system by high resolution transmission electron microscopy
Authors:
Kounis A. Miehe G. Fuess H.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):323-326, 2000 Dec 15.
Abstract:
Icosahedral phases in Zn-Mg-RE(RE=Er, Y) alloys have been studied by high resolution transmission electron microscopy (HRTEM) and electron diffraction fur different RE contents. From the electron diffraction patterns along the twofold axis, for Zn60Mg30+xY10-x a face centered icosahedral structure was found with x=0 whereas crystals with x in the range of 4 display a simple icosahedral structure. In the system with RE=Er a cubic approximant of the icosahedral quasicrystalline phase, the so-called 'R-phase', was found. The R-phase crystallizes in the space group F (4) over bar 3m with a(0)=2.02 nm. The close relation between the R-phase and the icosahedral quasicrystal is shown by HRTEM imaging. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 9]
Title:
Structure refinement of (Al, Zn)(49)Mg-32-type phases by single-crystal X-ray diffraction
Authors:
Sun W. Lincoln FJ. Sugiyama K. Hiraga K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):327-330, 2000 Dec 15.
Abstract:
Detailed structures of (Al, Zn)(49)Mg-32-type crystalline phases, which are closely related to the Mg-Al-Zn icosahedral quasicrystal in Mg40Al60-xZnx (x=14-51) alloys, were examined by single-crystal X-ray diffraction analysis. The structures have been determined with final R factors less than 0.04, and show good correspondence between chemical compositions obtained from structural refinements and those determined by electron probe microanalysis. The refined structures are somewhat different from that proposed by Bergman et al. [G. Bergman, J.L.T. Waugh, L. Pauling, Acta Crystallogr. 10 (1957) 254] in that they have no central atom in the Bergman-type atom cluster. The atom site occupancy is also discussed as a function of Zn content. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 9]
Title:
Fe-57 Mossbauer study of icosahedral Al55Si7Cu25.5Fe12.5 and its 1/1 approximant
Authors:
Stadnik ZM. Takeuchi T. Mizutani U.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):331-334, 2000 Dec 15.
Abstract:
The icosahedral Al55Si7Cu25.5Fe12.5 alloy and its 1/1 approximant of the same composition have been studied with Fe-57 Mossbauer spectroscopy (MS) in the temperature range 4.3-473.2 K. The average quadrupole splitting decreases with temperature as T-3/2 for both alloys and its value is significantly larger for the icosahedral alloy. The vibrations of the Fe atoms in both alloys are well described by a simple Debye model, with characteristic Mossbauer temperatures of 454(22) and 491(25) K for the icosahedral and approximant alloys. The local properties measured by zero-field Fe-57 Mossbauer spectroscopy are insensitive to the different nature of the long-range order, quasicrystalline vs. crystalline, in the investigated alloys. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Comparison of local order in icosahedral Al-Pd-Mn quasicrystal and in approximant phase by thermal neutron scattering
Authors:
Shramchenko N. Klein H. Caudron R. Bellissent R.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):335-339, 2000 Dec 15.
Abstract:
In a previous paper [R. Caudron, A. Finel, Y. Calvayrac, M. Fradkin, R. Bellissent, in: S. Takeuchi, T. Fujiwara (Eds.), Proceedings of the Sixth International Conference on Quasicrystals, Tokyo, May 26-30, 1997, World Scientific, Singapore, 1998, pp. 375-378], we presented the results uf neutron diffuse scattering in an icosahedral Al-Pd-Mn single grain. The background intensity, measured away from any intense Bragg peak was in good agreement with a calculation based on the chemical disorder of the xi' approximant of the icosahedral phase whose structure has been resolved by Boudard ct al. [M. Boudard, H. Klein, M. de Boissieu, M. Audier, H. Vincent, Philos. Mag. A 74 (1996) 939-956], by using X-ray diffraction. In order to cheek the generality of this diffuse background and to legitimate this interpretation of local order in quasicrystalline Al-Pd-Mn, we have now measured the diffuse scattering of the xi' phase itself and other icosahedral samples. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Local atomic structure of icosahedral quasicrystals and 1/1 approximant in the Ti-Ni-Zr alloy system
Authors:
Sadoc A. Kim JY. Kelton KF.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):348-350, 2000 Dec 15.
Abstract:
Extended X-ray absorption fine-structure (EXAFS) experiments were performed above the Ti, Ni and Zr K absorption edges in the icosahedral Ti45Zr38Ni17 phase and in its 1/1 approximant, the Ti50Zr35Ni15 phase. The EXAFS spectra show a strong similarity for both samples, indicating that the local structures around the Ti, Ni and Zr atoms are similar in the icosahedral and 1/1 phases. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 6]
Title:
An ab initio based structure model of i(Al-Pd-Mn)
Authors:
Quandt A. Elser V. Kresse G. Hafner J.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):351-354, 2000 Dec 15.
Abstract:
We illustrate how ab initio numerical simulation methods can be used to cheek and improve structure models for i(Al-Pd-Mn). By focusing our study on the optimization of a small approximant, we obtain a number of general structural and compositional rules simple enough to be applicable to the quasicrystalline structure itself. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Atomic decoration of Katz-Gratias-de Boissieu-Elser model applied to the surface structure of i-Al-Pd-Mn
Authors:
Kasner G. Papadopolos Z. Kramer P.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):355-360, 2000 Dec 15.
Abstract:
The Karz-Gratias-de Boissieu-Elser (KGdeBE) model for icosahedral quasicrystals is studied in order to provide an atomic bulk model for i-Al-Pd-Mn and i-Al-Cu-Fe. We interpret the KGdeBE model as the tiling T*((2F)) decorated by Bergman and Mackay polytopes. Using information stemming from the inflation properties of the tiling T*((2F)) (arrows on the edges of the tiles), we propose rules to make a unique choice between split positions and derive the corresponding vertex-windows. The resulting bulk model is used to provide atomic models of the five-, three-, and twofold surfaces of i-Al-Pd-Mn, as well as the terrace structure found in these materials. In order to stimulate new LEED calculations for these surfaces, we make the data sets (ranging up to some 10(6) atoms) public. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Structural modelling of the Ti-Zr-Ni quasicrystal
Authors:
Hennig RG. Majzoub EH. Carlsson AE. Kelton KF. Henley CL. Yelon WB. Misture S.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):361-365, 2000 Dec 15.
Abstract:
The atomic structure of the icosahedral Ti-Zr-Ni quasicrystal is studied using a canonical cell tiling approach. An investigation of the previously proposed structure for W-Ti-Zr-Ni, the 1/1 crystal approximant to the Ti-Zr-Ni icosahedral quasicrystal, has revealed improbable occupation of sites in the region between the Bergman clusters and at the cluster centre. The 1/1 structure is refined for a better-ordered sample of the approximant, using X-ray and neutron diffraction measurements and ab initio relaxation studies. Based on this refined structure, an atomic decoration model for large canonical cell tilings is developed. Calculated diffraction patterns from the generated structures are in reasonable agreement with those measured for the icosahedral quasicrystal. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Structural characteristics of vacancy-ordered tau-phases
Authors:
Mandal RK. Lele S.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):366-368, 2000 Dec 15.
Abstract:
The vacancy-ordered tau -phases (VOPs) in Al-transition-metal (TM) alloys can be classified into three distinct categories in the commensurate limit. These are: (a) tau (3) and its tau (3) inflated phases possessing inversion centres on Al and V layers, (b) tau (5) and its tau (3) related phases displaying centres on Al andTM layers and (c) tau (8) and those generated after tau (3) inflation having centres on TM and V layers. The six-dimensional model proposed by us earlier generates all of them in three-dimensional physical space with the above structural characteristics. The consequence of taking a physical space cut from a six-dimensional anti-phase domain leads to an anti-phase domain for tau (3) and tau (infinity), but it will be shown that such a cut leads to the generation of translational twins for other phases. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 8]
Title:
Investigations of the short-range order in melts of quasicrystal-forming Al-Cu-Co alloys by EXAFS
Authors:
Holland-Moritz D. Jacobs G. Egry I.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):369-372, 2000 Dec 15.
Abstract:
It was predicted by Frank that an icosahedral short-range order prevails in undercooled metallic melts. This suggestion bases upon the fact that the icosahedron has the lowest energy per atom of all clusters, if the atomic interactions are described by Lennard-Jones potentials. The proposed icosahedral short-range order might even be more pronounced for melts forming quasicrystalline phases, which themselves are built from polytetrahedral structural units. In this work, the short-range order of quasicrystal-forming Al-Cu-Co melts is studied by extended X-ray absorption, fine structure investigations at K-absorption edge of Co. The analysis of the spectra indicates that the absorbing Co-atom is mainly surrounded by aluminium atoms. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Diffraction of the dart-rhombus random tiling
Authors:
Hoffe M.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):373-376, 2000 Dec 15.
Abstract:
The diffraction spectrum of the dart-rhombus random tiling of the plane is derived in rigorous terms. Using the theory of dimer models, it is shown that it consists of Bragg peaks and an absolutely continuous diffuse background, but no singular continuous component. The Bragg part is given explicitly. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Anisotropic phasonic diffuse scattering from decagonal quasicrystals
Authors:
Ishii Y.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):377-380, 2000 Dec 15.
Abstract:
In spite of its isotropic elastic (phonon) properties, anisotropic diffuse scattering is observed in icosahedral quasicrystals and interpreted as a consequence of softening of a particular mode of phasons near hydrodynamic instability. In a decagonal case, the phason elastic energy is isotropic and no anisotropic phason disorder is expected. We show that, nevertheless, the anisotropic diffused scattering from the decagonal quasicrystals is expected through the phason-phonon coupling. We calculate a line shape of the diffuse scattering based on the elasticity theory for 10/mmm and (10) over barm(2) symmetries. Physical meanings of such diffuse scattering are discussed in contrast to Huang scattering. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Average unit-cell approach to diffraction on in Thue-Morse sequence and decorated quasicrystals
Authors:
Wolny J. Wnek A. Verger-Gaugry JL. Pytlik L.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):381-384, 2000 Dec 15.
Abstract:
The average unit cell approach has been successfully used to construct the probability distributions of atomic displacements from the reference lattice points and to calculate the diffraction patterns for two aperiodic structures - the Thue-Morse sequence and decorated Fibonacci chains. For the singular continuous diffraction pattern of the Thue-Morse sequence fractal exponents and multiplication factors have been found for scaling with the number of atoms. General method able to distinguish between various quasilattice decorations has been elaborated and tested for decorated Fibonacci chains. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
On inflation rules for Mosseri-Sadoc tilings
Authors:
Papadopolos Z. Ogievetsky O.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):385-388, 2000 Dec 15.
Abstract:
We give the inflation rules for the decorated Mosseri-Sadoc tiles in the projection class of tilings T-(MS). Dehn invariants related to the stone inflation of the Mosseri-Sadoc tiles provide eigenvectors of the inflation matrix with eigenvalues equal to tau=(1+root5)/2 and (-tau (-1)). (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Stochastic L-systems and quasicrystal patterns
Authors:
Escudero JG.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):389-392, 2000 Dec 15.
Abstract:
Bracketed stochastic Lindenmayer systems (L-systems) are used for the description of certain species of non-deterministic quasicrystal patterns. Several classes of substitution tilings with eight-fold symmetry are introduced. They form the basis for non-deterministic octagonal structures which can be described with stochastic DT0L-systems. Heptagonal structures can also be described with stochastic DT0L-systems, whereas the appropriate scheme for structures with nine-fold symmetry is a stochastic ET0L-system. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Three-dimensional quasicrystalline structures with non-icosahedral global symmetry
Authors:
Borodin VA.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):393-396, 2000 Dec 15.
Abstract:
The paper discusses a possible atomic structure of a three-dimensional (3D) quasicrystal with the global symmetry that differs from the icosahedral one. The construction of such atomic cluster is performed by expansion of a small initial 'seed' using the 1/3 deflation. Here we use a non-icosahedral seed, namely, the Frank-Kasper polyhedron with the coordination number 14. As a result, a 525-atomic cluster is obtained that demonstrates the X-ray diffraction pattern typical rather for quasi-2D quasicrystals. With all atomic positions in the cluster being specified, it is possible to estimate the influence of geometrical restrictions on the possibility of formation of large atomic clusters with such specific symmetry. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 13]
Title:
Boerdijk-Coxeter helix and biological helices as quasicrystals
Authors:
Sadoc JF. Rivier N.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):397-400, 2000 Dec 15.
Abstract:
Helices and dense packing of spherical objects are two closely related problems. The Boerdijk-Coxeter helix (B-C), a linear stacking of regular tetrahedra, is a very efficient solution to some close-packing problems, including protein folding. The structure of biological helices (alpha -helix, collagen) is determined chiefly by steric repulsion. Thus, maximum density leads directly to structures related to the B-C helix. We show that the B-C helix is a quasicrystalline structure with 1+root3 edges per turn, which can be disclinated and inflated. The collagen molecule consists of three intertwined helicoidal chains on the fibres of an inflated Hopf fibration. The central core is a B-C helical packing of the hydrogen atoms side-groups of the amino acid Gly. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
The cover story: Fibonacci, Penrose, Kepler
Authors:
Kramer P.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):401-404, 2000 Dec 15.
Abstract:
Coverings and fundamental domains for quasicrystals are analyzed and predicted from Delone-and Voronoi-clusters in dual canonical tilings of five-fold and icosahedral symmetry, projected from lattices Lambda = A(4), D-6, P. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 11]
Title:
Clusters in quasicrystals: tiling versus covering and porosity
Authors:
Janot C. Loreto L. Farinato R.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):405-408, 2000 Dec 15.
Abstract:
Diffraction data and quasicrystallography provide average perfect quasiperiodic structures for quasicrystals. These patterns are prototypes of atomic clusters which may be used to model quasicrystal structures. Three alternative schemes are presented in this paper: (1) a perfect quasiperiodic arrangement that exhibits a hierarchical distribution of holes; (2) a dense random covering (DRC) structure; and (3) a long range ordered structures with successive layers of interpenetrating clusters. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Two-dimensional random tilings of large codimension: new progress
Authors:
Destainville N. Widom M. Mosseri R. Bailly F.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):409-412, 2000 Dec 15.
Abstract:
Two-dimensional random tilings of rhombi can be seen as projections of two-dimensional membranes embedded in hypercubic lattices of higher dimensional spaces. Here, we consider tilings projected from a D-dimensional space. We study the limiting case, when the quantity D, and therefore the number of different species of tiles, become large. We had previously demonstrated [M. Widom, N. Destainville, R. Mosseri, F. Bailly, in: Proceedings of the Sixth International Conference on Quasicrystals, World Scientific, Singapore, 1997.] that, in this limit, the thermodynamic properties of the tiling become independent of the boundary conditions. The exact value of the limiting entropy and finite D corrections remain open questions. Here, we develop a mean-field theory, which uses an iterative description of the tilings based on an analogy with avoiding oriented walks on a random tiling. We compare the quantities so-obtained with numerical calculations. We also discuss the role of spatial correlations. (C) 2000 Elsevier Science B.V. All lights reserved.
Title:
Growth, melting, and clustering of icosahedral quasicrystals: Monte Carlo simulations
Authors:
Dmitrienko VE. Astaf'ev SB. Kleman M.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):413-417, 2000 Dec 15.
Abstract:
Details of the three-dimensional Monte Carlo simulations for atomic growth (up to 10(6) atoms) and melting of icosahedral quasicrystals are presented. The local atomic order is supposed to be similar to that found in crystalline approximants of quasicrystals whereas the quasiperiodic long-range structure arises during the growth process according to statistical and energetical criteria. The complementary picture in the perpendicular space is found to be very informative for better understanding of quasicrystal formation. It is shown that melting of quasicrystals is accompanied by formation of large atomic clusters on the surface (the clustering is less pronounced for growth). (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
The 'random' square-triangle tiling: simulation of growth
Authors:
Rubinstein B. Ben-Abraham SI.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):418-420, 2000 Dec 15.
Abstract:
Some alloy systems, such as Ni-Cr, V-Ni-Si and Ta-Te, have quasicrystalline phases with 12-fold symmetry. These structures may be described in terms of dodecagonal tilings by equilateral triangles and squares. The formation of quasicrystals still poses a problem, since local information is insufficient for the construction of a perfect quasiperiodic structure. The growth of real quasicrystals may be due to several mechanisms. We have simulated the growth of a quasicrystal from a melt, consisting of squares and equilateral triangles of equal edge length. We are interested in the abundancies of the vertex configurations formed, both regular and defective. Unrestricted random growth tends to result in segregation of triangles from squares. Favoring triangles to attract squares and vice versa brings about nearly perfect patterns with nearly perfect vertex abundancies, as well as realistic defect concentrations. We have also calculated the exact vertex frequencies of the ideal square-triangle tiling by relying on inflation symmetry. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Ground states of quasilattice-gas models
Authors:
Gazeau JP. Krejcar R. Miekisz J.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):421-424, 2000 Dec 15.
Abstract:
We introduce quasilattice-gas models in which every vertex of certain two-dimensional grids can be occupied by one of two different types of particles interacting through Lennard-Jones potentials. Such grids are quasiperiodic analogs of regular lattices present in periodic systems. To find ground-state configurations of our models, we performed Monte Carlo simulations and obtained structures with local five-fold symmetries and five-fold diffraction patterns. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
From quasiperiodic tilings with tau-inflation to tau-wavelets
Authors:
Gazeau JP. Kramer P.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):425-428, 2000 Dec 15.
Abstract:
We construct wavelets on quasiperiodic tilings I with stone-inflation symmetry. All tiles of I when scaled by the factor tau can be packed face-to-face from the original ones. For the planar Tubingen triangle and the Penrose-Robinson tiling, we give the geometric generators of the deflation as affine Euclidean pairs (t, g) of(translations, reflection/rotations) with t from the fivefold module and g from the Coxeter group I-2(5). Deflation generates levels of subdivisions of the tilings. On these subdivisions, we give the Haar wavelet construction. On each level of deflation, we transform from the set of characteristic functions to explicit orthogonal wavelet bases. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 8]
Title:
On the relationship between cubic crystalline coincidence site lattices and quasiperiodic superlattices
Authors:
Ranganathan S. Ramakrishnan K. Kulkarni UD. Mukhopadhyay NK.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):429-433, 2000 Dec 15.
Abstract:
Quasiperiodic superlattice (QPSL) can be understood as a structure consisting of quasiperiodic arrangements of tiles of rational dimension and can be viewed as a quasiperiodic atomic decoration of a disordered lattice. Varieties of QPSLs have been generated by varying the orientation of the projection plane in the projection formalism. The coincidence site lattice (CSL) has been found to be related to the interfaces of these QPSLs. The structural relationship between the CSLs and the QPSLs related to the octagonal quasilattice has been pointed out fur the first time. The physical significance of CSLs have been discussed in the context of the projection formalism. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Special Lie algebras for quasicrystals
Authors:
Twarock R.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):434-437, 2000 Dec 15.
Abstract:
A new type of infinite-dimensional Lie algebra, called aperiodic Virasoro algebra is presented which is by construction compatible with the structure of cut-and-project quasicrystals. The properties of the algebra depend on the acceptance window and thus on the structure of the cut-and-project quasicrystal, and its generators are in a one-to-one correspondence with the points of the latter. By construction, there is a formal resemblance between the aperiodic Virasoro algebra and the usual Virasoro algebra, but due to the influence of the acceptance window, the corresponding properties differ crucially and thus the aperiodic Virasoro algebra is indeed a new algebraic structure. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 8]
Title:
Cohomology groups for projection tilings of codimension 2
Authors:
Gahler F. Kellendonk J.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):438-440, 2000 Dec 15.
Abstract:
The gap-labelling group, which provides the set of possible values of the integrated density of states on Saps in the spectrum of a Hamiltonian describing particles in a tiling, is frequently related to the cohomology of the tiling. We present explicit results for the cohomology of many well-known tilings obtained from the cut and projection method with codimension 2, including the (generalized) Penrose tilings, the Tubingen triangle tiling, the Ammann-Beenker tiling, and the Secular tiling. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Averaged shelling for quasicrystals
Authors:
Baake M. Grimm U. Joseph D. Repetowicz P.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):441-445, 2000 Dec 15.
Abstract:
The shelling of crystals is concerned with counting the number of atoms on spherical shells of a given radius and a fixed centre, Its straight-forward generalization to quasicrystals, the so-called central shelling, leads to non-universal answers. As one way to cope with this situation, we consider shelling averages over all quasicrystal points. We express the averaged shelling numbers in terms of the autocorrelation coefficients and give explicit results for the usual suspects, both perfect and random. (C) 2000 Michael Baake. Published by Elsevier Science B.V. All rights reserved.
Title:
Mathematical quasicrystals with toric internal spaces, diffraction and rarefaction
Authors:
Verger-Gaugry JL. Wolny J.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):446-449, 2000 Dec 15.
Abstract:
Aperiodic crystals viewed as Delone sets of points on the real line, having an average lattice, are studied as congruence model h-sets (physical space is Euclidean and the equivalent of the internal space is toric) in the context of cut-and-congruence lambda -schemes, a new concept. When windows are finite point sets, the fractal rates of occupancy, at infinity, of the affine lattices associated with such Delone sets are shown to be simply related to the scaling exponents of the Fourier transform of the autocorrelation measure, completing results of Hof. These fractal rates of occupancy an named rarefaction laws. The case of the Thue-Morse quasicrystal, as a Meyer set, is explicitly developed. We present the arithmetics of 3-rarefaction phenomenon, the fractality of the Fourier transform of the autocorrelation measure. This new approach provides explicit formulae for singular continuous peaks and allows to discuss their possible extinction. In particular, this gives a possible sieve among Delone sets to be crystals in the new definition of a crystal by the IUCr in 1992. Ponctual scaling laws and the Bombieri-Taylor argument are considered. (C) 2000 Elsevier Science B.V. All rights resented.
Title:
Anomalous transport: results, conjectures and applications to quasicrystals
Authors:
Bellissard J.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):450-457, 2000 Dec 15.
Abstract:
We review the main rigorous results accumulated during the last 5 years concerning the theory of transport in aperiodic media. Motivated by the transport properties of quasicrystals, we introduce the mathematical background needed to describe transport in aperiodic media. We then give the definitions and the properties of spectral and diffusion exponents with an emphasis on 'anomalous transport'. The last section is devoted to discussing the relevance of this theory for quasicrystals. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Electronic transport properties of quasicrystals: the unique case of the magnetoresistance
Authors:
Rapp O.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):458-463, 2000 Dec 15.
Abstract:
The magnetoresistance (MR) is but one of several anomalies in electronic transport properties of quasicrystals. However, it is an exceptional one since only in this case a large part of the results can be quantitatively described within an existing theoretical framework. Evidence is discussed that quantum interference effects (QIE) describe observations in alloys with resistivity rho (4 K) less than or equal to 0.1 Omega cm. This is useful fur understanding electronic transport in quasicrystals. Examples of information derived from QIE are given. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Electron transport mechanism in the pseudogap system: quasicrystals, approximants and amorphous alloys
Authors:
Mizutani U.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):464-469, 2000 Dec 15.
Abstract:
We have analyzed the electron transport mechanism in quasicrystals and their approximants in diverse classes as being typical of the pseudogap systems by employing the Mott conductivity formula. The transport mechanism is divided into two regimes dominated by the mean foe path effect and the g(2)-dependent electronic structure effect, the latter of which is specific to the pseudogap system. The critical resistivity rho (0) is defined as the resistivity across which the former is taken over by the latter. It is shown that the rho -T dependence of quasicrystals and their approximants can be well interpreted in terms of the critical resistivity line drawn in the resistivity versus the g-parameter diagram. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Photoemission studies of quasicrystals
Authors:
Stadnik ZM.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):470-474, 2000 Dec 15.
Abstract:
The results of the photoemission spectroscopy studies of the electronic structure of quasicrystals are reviewed. The presence and location of the features in the measured valence bands are in accordance with those in the calculated density of states. The existence of the theoretically predicted pseudogap at the Fermi level is confirmed. No evidence of the theoretically predicted spikiness of the density of states could be observed in the photoemission experiments of the highest energy resolution presently achievable. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Electronic transport properties of quasicrystalline thin films
Authors:
Haberkern R. Khedhri K. Madel C. Haussler P.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):475-480, 2000 Dec 15.
Abstract:
We focus on the question if electronic transport properties of quasicrystals can be understood by a Hume-Rothery like interaction between the atomic structure and the electronic system. Therefore, we report about composition and temperature dependent investigations of the electrical conductivity, the thermopower and the Hall effect of quasicrystalline films, mainly for i-Al-Pd-Re and i-Al-Cu-Fe and compare it to the amorphous counterparts which are known to be electronically stabilized and are much simpler to understand due to their isotropy. Thin films provide the possibility to measure the thermopower and the Hall effect at elevated temperatures up to 1000 K. Both indicate a strongly increasing charge-carrier density as a function of temperature. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Magnetic correlations in the Zn-Mg-rare-earth icosahedral quasicrystals
Authors:
Sato TJ. Takakura H. Tsai AP. Ohoyama K. Shibata K. Andersen KH.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):481-487, 2000 Dec 15.
Abstract:
The previously reported magnetic long-range order has been revisited in the Zn-Mg-rare-earth systems by means of neutron diffraction, magnetic susceptibility and microstructural analysis. It was found that the long-range order is absent in icosahedral quasicrystals, where only short-range spin correlations develop even at the lowest temperatures. The long-range order was attributed to the (ZnxMg1-x)(5)-rare-earth crystalline phase, which was shown to be a contaminating phase in the previously used samples. The short-range spin correlations have been investigated in detail by single quasicrystal neutron scattering. A close relation has been suggested between the short-range correlations and the quasiperiodic structure. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Magnetic neutron scattering from quasicrystalline Zn-Mg-Ho and Zn-Mg-Y at low temperatures
Authors:
Scheffer M. Rouijaa M. Suck JB. Sterzel R. Lechner RE.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):488-491, 2000 Dec 15.
Abstract:
In contrast to the magnetic transition metal ions in other quasiperiodic alloys, the RE (RE=rare earth) ions in icosahedral Zn-Mg-RE show localised magnetic moments due to localised 4f electrons. Long range as well as short range order of these moments are still under discussion. To investigate the magnetic properties of these fci-structures of Frank-Kasper type, we performed inelastic neutron scattering experiments at temperatures between 1.6 and 25.0 K and measured the DC magnetic susceptibility. The results show mainly paramagnetic scattering of the samples. Comparison with the data of Zn-Mg-Y ensures, that the observed scattering is not of phononic or phasonic nature. The lineshape of the quasielastic peak can be modeled by a shifted Lorentzian. The observed shift is small (approximately 0.6 meV) and shows no dispersion. The linewidth is constant in Q and increases with temperature. A possible interpretation of this behaviour is the existence of a crystal field splitting. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Electronic stabilization of amorphous and quasicrystalline metals: importance of quantum correlations
Authors:
Kroha H.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):500-503, 2000 Dec 15.
Abstract:
Numerous experimental indications suggest that the Hume-Rothery mechanism plays an important role in stabilizing quasicrystalline and amorphous phases. However, the exponential damping of the conventional Friedel oscillations at the relevant, elevated temperatures T poses a severe challenge to the HR stabilization. In order to resolve this problem it is shown using a Feynman diagram technique that quantum correlations in the electron sea, arising from the interplay of Coulomb interaction and impurity scattering, can strongly enhance the Friedel oscillations in these systems even at elevated temperature. The resulting corrections to the Friedel potential are in agreement with available experimental results on amorphous HR alloys. It is proposed to include the enhancement of the Friedel amplitude derived in the present work into pseudopotentials through the local field factor. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Low temperature calorimetric investigation of an insulating icosahedral Al-Pd-Re quasicrystal
Authors:
Prejean JJ. Lasjaunias JC. Berger C. Sulpice A.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):504-507, 2000 Dec 15.
Abstract:
We report on a very low temperature heat capacity investigation of an icosahedral Al-Pd-Re sample which, from resistivity measurements, is believed to lie on the insulating side of a metal-insulator (M-I) transition. Our main results are: (i) The electronic contribution, which possibly obeys a gammaT variation above 1 K, follows a power T-a law (a approximate to0.1) below 1 K, in agreement with early results obtained for systems crossing the M-I transition. Here T denotes the absolute temperature. (ii) The large nuclear hyperfine contribution of quadrupolar origin, dominant below 300 mK, can only be due to the Re nuclei. We reach this conclusion from a comparative study of icosahedral Al-Cu-Fe and Al-Pd-Mn quasicrystals. In addition, from the study of the thermal relaxation of the sample after a heat pulse, we are able to estimate the relaxation times T-1 of the different kinds of nuclei, for those which relax during our experimental time span. (iii) We finally propose a microscopic origin of the quadrupolar-electric field-gradient on the nuclei in terms of local electronic density and atomic structure. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Magnetic quasicrystals: what can we expect to see in their neutron diffraction data?
Authors:
Lifshitz R.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):508-511, 2000 Dec 15.
Abstract:
The theory of magnetic symmetry in quasicrystals is used to characterize the nature of magnetic peaks expected in elastic neutron diffraction experiments. It has been established that then is no symmetry-based argument which forbids the existence of quasiperiodic long-range magnetic order. Suggestions are offered as to where one should look for the simplest kinds of antiferromagnetic quasicrystals. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
High resolution experiment on the electronic density of states in icosahedral-Al-Pd-Mn
Authors:
Schaub T. Delahaye J. Berger C. Grenet T. Guyot H. Belkhou R. Taleb-Ibrahimi A. Prejean JJ. Calvayrac Y.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):512-515, 2000 Dec 15.
Abstract:
We present experiments of photoemission and tunneling spectroscopy which indicate the presence of a dip in the density of states around the level E-F in the icosahedral-Al-Pd-Mn (i-Al-Pd-Mn) phase. From high resolution photoemission experiments on a single grain of i-Al-Pd-Mn, we have got clear evidence that the surface state (quasicrystalline or disordered) strongly affects the measured density of states. For a quasicrystalline surface we observe a pseudo-gap feature at E-F. The remaining density of states at E-F is compatible with the gamma term of specific heat. The band edge shows a square root dependence in the vicinity of E-F. This is similar to the single square root anomaly found by tunneling spectroscopy around E-F in the range +/-300 meV. The photoemission data show a filling of this feature for the disordered surface where a Fermi edge clearly develops. (C) 2000 Elsevier Science B.V. Ail rights reserved. [References: 23]
Title:
Investigation of Al and Mg occupied densities of states of Al-Mg-Zn alloys
Authors:
Belin-Ferre E. Fournee V. Mizutani U. Takeuchi T. Muller H.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):516-518, 2000 Dec 15.
Abstract:
In this paper we report first results on the investigation of the electronic distributions in a series of Al-Mg-Zn alloys by means of X-ray emission spectroscopy. This technique was selected as it allows to probe separately partial densities of states around each constituent in a compound. Differences are observed in the shapes and energy extent of the partial spectral curves from quasicristalline to 1/1- and 2/1-approximants in this system. This indicates modifications in the electronic interactions according to the atomic structure of the specimen. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 2]
Title:
Modulated photocurrent measurements on an Al-Pd-Re icosahedral quasicrystal
Authors:
Sakairi Y. Takeda M. Tamura R. Edagawa K. Kimura K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):519-521, 2000 Dec 15.
Abstract:
Modulated photocurrent measurements, originally developed for analyzing the electronic starts of semiconductors have been performed on an Al-Pd-Re quasicrystal having high electrical resistivity using two kinds of lasers with different excitation energies, No noticeable difference has been found in the phase shift between the two excitation energies. The data of the amplitude and phase shift of modulated photocurrent can be explained well by a simple model in which only the two processes, carrier generation and recombination, are involved. The recombination time is by about six orders larger than those reported for conventional semiconductors. The results obtained are discussed in terms of electron density of states and energy dependence of carrier mobility. (C) 2000 Published by Elsevier Science B.V.
Title:
Magic number of electron concentration in the icosahedral cluster of AlxMg40X60-x (X=Zn, Cu, AE, and Pd) 1/1-cubic approximants
Authors:
Takeuchi T. Mizuno T. Banno E. Mizutani U.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):522-526, 2000 Dec 15.
Abstract:
A X-ray Rietveld analysis is carried out for the AlxMg40X60-x (X=Zn, Cu, Ag, and Pd) 1/1-cubic approximants. The electronic structure of the icosahedral cluster was calculated by means of the DVX alpha method with the refined atomic positions. The results obtained from the Rietveld refinement revealed that, regardless of the alloy systems, the number of the valence electrons per atom in the 12 atoms icosahedron, e.a(ico), always shows a unique dependence on the total number of the valence electron in the lattice, e/a(lat). This suggests that the cluster is stabilized at a certain number of the valence electrons. The number of the valence electrons per atom in this cluster e/a(ico) is found to be 2.14-2.18, which is lower than that of the overall e/a(lat)=2.2-2.35. Notably, at this particular number e/a=2.15, the Frank-Kasper-type icosahedral quasicrystal is the most stabilized and a thermodynamically stable quasicrystal is formed in the Al-Mg-Pd and Al-Mg-Zn alloy systems. We found from the DVX alpha calculation that an energy gap is formed at the Fermi level at this critical e/c(ico) value. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Thermal activation of carriers and characteristic features of the electronic structure of quasicrystalline systems
Authors:
Prekul AF. Kuzmin NY. Shchegolikhina NJ.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):527-530, 2000 Dec 15.
Abstract:
The electric conductivity and magnetic susceptibility of the quasicrystalline alloy Al62Cu25.5Fe12.5 are studied in the temperature range from 3.9 to 1200 K. The results are analysed under the assumption that the thermal activation of carriers is the main temperature effect. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 6]
Title:
Relationship of phason strain and electronic properties in icosahedral Al-Pd-(Re,Mn) and Al-Cu-Os
Authors:
Beeli C. Soltmann C. Poon SJ.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):531-534, 2000 Dec 15.
Abstract:
Single-phase icosahedral Al70.5Pd21 (Re,Mn)(8.5) and Al65Cu20Os15 samples have been studied in order to find a relationship between electronic localization and structural properties of icosahedral quasicrystals. Annealed at high temperatures (HT), e.g. 940 degreesC, the Al-Pd-Re samples exhibit a behavior which can be described as nearly localized, while annealed at low temperatures (LT), e.g. 600-640 degreesC, localization has been observed. Similar observations have been made for icosahedral Al-Cu-Os. Accordingly, Al-Pd-Re and Al-Cu-Os can be considered as model systems for this type of investigation. Performing transmission electron microscopy measurements, we have observed and quantified the phason strain in these samples: For the two model systems the MT-states are closer to a perfect icosahedral state containing some random phason strain, in the LT-states we observed a strongly phason-perturbed i-phase. Additionally, the influence of chemical disorder was studied by the addition of Mn into icosahedral Al-Pd-Re. (C) 2000 Elsevier Science B.V. Al rights reserved.
Title:
Hume-Rothery effects in amorphous and quasicrystalline Al-Cu-Fe
Authors:
Madel C. Schwalbe G. Haberkern R. Haussler P.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):535-538, 2000 Dec 15.
Abstract:
A detailed comparison of the amorphous and the quasicrystalline state of Al-Cu-Fe is presented. The samples were prepared amorphously at low temperature. After several annealing steps within the amorphous phase they were transformed into the quasicrystalline state at T=700 K. The atomic structure as well as electronic transport properties for both phases have been investigated. Electron diffraction measurements of amorphous Al-Cu-Fe show the atomic structure as electron induced. The dominant structural peak shifts nearly parallel to 2k(F):, the diameter of the Fermi-sphere, as a function of composition. At the corresponding composition its position is exactly coinciding with one of the two most dominant peaks of the icosahedral phase, indicating that this phase is Hume-Rothery stabilized as well. The electrical conductivity as well as the Hall coefficient indicate strong similarities between both phases. In the amorphous phase magnetic effects are observed. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Mossbauer spectroscopy study of Ti-Zr-Ni-Fe icosahedral and approximant phases
Authors:
Nicula R. Kuncser V. Jianu A. Filoti G. Burkel E.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):539-541, 2000 Dec 15.
Abstract:
Quaternary Ti53Zr21Ni13Fe13 alloys were prepared by melt-spinning using peripheral wheel speeds omega =19.5, 24.2 and 30m/s. The icosahedral (i-) phase formation was studied using high resolution synchrotron radiation powder diffraction. An amorphous phase component is present irrespective of the rapid solidification conditions, its volume fraction decreasing towards lower quenching speed values. The amorphous phase coexists with a b.c.c. rational approximant phase (W-phase). For omega below 20 m/s the formation of an i-phase was also noticed. Transmission Fe-57 Mossbauer spectroscopy measurements indicate that the number of asymmetrical Fe positions decreases with decreasing w in agreement with the improved structural perfection of the W-phase and with the formation of an additional i-phase. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Development of 3D Visualization system for the study of physical properties of quasicrystals
Authors:
Nakano H. Sato Y. Matsuo S. Ishimasa T.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):542-547, 2000 Dec 15.
Abstract:
We have developed a 3D visualization system helpful for the study of physical properties of quasicrystals which have complex structures and characteristic rotation symmetries. Our system consists of two software packages; one for real space and another reciprocal space. Both packages are distributed as open-source software and are equipped with some commands useful for icosahedral symmetry in order to treat not only crystals but also quasicrystals. The package for real space can visualize arrangement of atoms and Patterson maps of Ising model simulations for structural and magnetic studies. It has flexibility to control various geometric parameters and can set the view direction by Cahn's indices. This package is developed using Java 3D which runs the same code under many operating systems. The package for reciprocal space can visualize the first Brillouin zone and larger zones and can calculate the intersection with a Fermi sphere for the study of electronic properties like stabilization mechanisms of quasicrystals. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Short-range order and the electronic structure of decagonal Al-Ni-Co
Authors:
Krajci M. Hafner J. Mihalkovic M.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):548-552, 2000 Dec 15.
Abstract:
Detailed investigations of the atomic and electronic structures of decagonal Al-Ni-Co alloys have been performed. The topology of the structural model has been refined on the basis of the existing X-ray diffraction data. The chemical order on the decagonal lattice has been optimized via the comparison of the calculated electronic spectra with photoemission and soft-X-ray data and using total-energy calculations. The electronic structure calculations for large periodic approximants with up to 1276 atoms/cell have been performed self-consistently using a real-space tight-binding linear-muffin-tin orbital technique. The best agreement with the experimental spectra is achieved for a model with the innermost ring of the pentagonal columnar clusters occupied by Ni-atoms only. This configuration also has the lowest total energy. As in decagonal Al-Cu-Co we find a high density of states at the Fermi level, but the chemical orderings is very different: whereas in d-Al-Cu-Co direct Cu-Cu neighbours are suppressed and there is a slight preference for Go-Co homocoordination, in d-Al-Ni-Co a strong Ni-Ni interaction stabilizes the innermost Ni-ring, direct Go-Co neighbours are suppressed and there is a strong Co-Al interaction. (C) 2000 Published by Elsevier Science B.V.
Title:
Electronic spectrum of the two-dimensional Fibonacci lattice
Authors:
Vekilov YK. Isaev EI. Gordeev IA.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):553-555, 2000 Dec 15.
Abstract:
The electron spectrum and wave functions of the two-dimensional Fibonacci lattice with "central" and "vertex" decorations are considered. The energy spectrum contains a singular parr hut does not contain a hierarchical gap structure. The measure of permittable states of the spectrum (the Lebesgue measure) is not equal to zero and in the case of central decoration is close to unity. Most of the wave functions are critical. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 3]
Title:
Electronic spectrum and localization of electronic states in three-dimensional quasicrystals
Authors:
Vekilov YK. Isaev EI. Arslanov SF. Slobodyanyuk PV.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):556-559, 2000 Dec 15.
Abstract:
The influence of phasons, magnetic field, and substitutional atomic disorder on the electronic spectrum and wave functions of icosahedral quasicrystals is investigated in a tight-binding approximation and level statistic (LS) method. The localization of the wave functions has been studied and their "critical" behavior has been detected. Phasons smooth the electronic spectrum and produce a greater delocalization of the critical wave functions. A magnetic field shifts the boundaries of the spectrum, smoothes the spectrum, lifts the degeneracy and also delocalizes the wave functions. The small degree of chemical substitutional disorder delocalizes the wave functions, but at greater degree the disorder leads to the Anderson type localization. The results show that the localization of electronic states in an ideal quasicrystal exists due to their coherent interference at the Fermi level which is caused by the specific symmetry and aperiodic long-range order. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Localization properties of electronic wave functions of the Hubbard model on the Fibonacci lattice
Authors:
Fujita N. Niizeki K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):560-563, 2000 Dec 15.
Abstract:
We employ the Hubbard model on the Fibonacci lattice to study the effect of the repulsive Coulomb interaction on the electronic properties of quasicrystals. Localization properties of the electronic wave functions are analyzed numerically within the Hartree-Fock approximation. For the case when the Fermi energy locates in a gap, all the wave functions remain critical as indicated by a previous report. For the case when the Fermi energy lies on an accumulation point of the energy spectrum, the critical wave function is expected to be unstable because the self-consistent one-electron potential strongly breaks Conway's theorem on account of the long-range nature of the Friedel oscillation. Still, it is found that the critical nature remains stable provided the interaction is sufficiently weak. Instead, when the strength of the interaction is increased, the system becomes magnetically unstable much more easily than in the former case. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 7]
Title:
Universal level-spacing statistics in quasiperiodic tight-binding models
Authors:
Grimm U. Romer RA. Schreiber M. Zhong JX.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):564-567, 2000 Dec 15.
Abstract:
We studied statistical properties of the energy spectra of two-dimensional quasiperiodic tight-binding models. The multifractal nature of the eigenstates of these models is corroborated by the scaling of the participation numbers with the system size. Hence one might have expected 'critical' or 'intermediate' statistics for the level-spacing distributions as observed at the metal-insulator transition in the three-dimensional Anderson model of disorder. However, our numerical results are in perfect agreement with the universal level-spacing distributions of the Gaussian orthogonal random matrix ensemble, including the distribution of spacings between second, third, and fourth neighbour energy levels. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Electronical properties of quasicrystalline model systems: influence of phason flips
Authors:
Schwabe H. Kasner G. Bottger H.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):568-571, 2000 Dec 15.
Abstract:
The influence of single phason Rips on the electronic properties of quasicrystalline model systems is investigated instead of using random tiling models. in a tight binding model of the Penrose lattice there are seven different types of possible phason flips according to the involved vertexstars. Tolerating a random number of flips of only one type simultaneously and avoiding multiple flips the spectrum, the eigenstates and the dc-conductance of this model system as a function of the flip type are calculated. Every Rip in the lattice leads to a defect state localized at the flipped atom sites with an eigenenergy outside the spectrum of the unflipped lattice. All types of flips result in smoothing out the density of states and the very strong fluctuations of the conductance in most of the energy regions. But the strength of this effect at a given energy depends strongly on the type of the flips in the lattice. A certain quasicrystalline pattern showing resonance at this energy can be more or less influenced by the Rips resulting in a strong or weak effect to the conductance. So, the investigation of the conductance under the influence of special Rips offers the possibility to study the relevance of several local configurations to the electronic properties at a given energy. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Generalized Rauzy tilings: construction and electronic properties
Authors:
Vidal J. Mosseri R.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):572-575, 2000 Dec 15.
Abstract:
We study a new class of quasiperiodic codimension one tilings based on a natural generalization of the Fibonacci chain. These so-called generalized Rauzy tilings allow for simple and explicit expressions of the site coordinates, and their associated tight-binding Hamiltonians are quickly written as band (Toeplitz-like) matrices. First results are given for their electronic properties which display similar behaviors as higher codimension tilings. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Observation of 2D quantum interference effects in quasicrystalline i-Al-Cu-Fe thin films
Authors:
Grenet T. Giroud F.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):576-579, 2000 Dec 15.
Abstract:
We have fabricated quasicrystalline Al-Cu-Fe thin films down to a thickness of 125 Angstrom. We observed a change of regime in the temperature dependence of the conductivity sigma, as well as an anisotropy of its magnetic field dependence when the film thickness is decreased. These are clear signatures of a dimensional crossover of QIE contributions to sigma. These observations give a strong qualitative confirmation of the relevance of disorder induced QIE effects in quasicrystals, and allow a precise determination of the electronic and microscopic parameters. [References: 9]
Title:
Is there a metal-insulator transition in the quasicrystalline phase i-Al-Pd-Re?
Authors:
Delahaye J. Brison JP. Berger C. Fourcaudot G.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):580-583, 2000 Dec 15.
Abstract:
We discuss measurements of the electrical conductivity a performed at very low temperature on highly resistive ribbons of the i-Al-Pd-Re phase. Between 1 K and 20 mK, we observe a drop in a, and the curvature gets stronger and stronger as T tends to zero. Below 20 mK, the samples show signs of insufficient thermalisation. This a drop can be well described by Mott's law sigma (T) = sigma (0) exp[-(T-0/T)(1/4)] but the extracted parameter T-0 is quite different from other studies on i-Al-Pd-Re. We show that T-0 strongly depends on the temperature range of the analysis. Here, the insulating character of the samples is determined using the divergence of the logarithmic derivative of sigma, i.e. d ln sigma (T)/d ln(T), at low temperature. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Variable-range hopping conductivity in quasicrystals
Authors:
Rivier N. Durand M.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):584-587, 2000 Dec 15.
Abstract:
The electronic density of states (DOS) of 1D quasicrystals looks like that of a highly doped, p-type semiconductor: the Fermi level lies in the "impurity band", which consists of localized states. At low temperatures, the conductivity of an electronic structure of this type is by variable-range hopping, as observed recently in i-Al-Pd-Re. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Dependence of electrical resistivity and magnetoresistance on long-range (F-type) ordering in Zn-Mg-Ho icosahedral quasicrystals
Authors:
Kashimoto S. Nakano H. Arichika Y. Ishimasa T. Matsuo S.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):588-591, 2000 Dec 15.
Abstract:
Electrical resistivity and magnetoresistance were measured in Zn60Mg30Ho10 icosahedral quasicrystals annealed at various temperatures that have different degrees of long-range F-type ordering. In the temperature dependence of the electrical resistivity, the sample annealed at 832 K (higher annealing temperature) exhibits a broad maximum at 125 K, which can be interpreted on the basis of the weak localization theory under strong spin-orbit effect. On the other hand, the samples annealed at lower temperatures have negative temperature coefficients of the resistivity in the whole temperature region between 2 K and room temperature. In the case of magnetoresistance, a gradient of magnetoresistance above 40 kOe changes from negative to positive at low temperatures as annealing temperature is raised. Our present results indicate that the long-range F-type ordering systematically affects the behavior of electrical resistivity and magnetoresistance in the Zn60Mg30Ho10 icosahedral quasicrystal. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Modeling the electrical conductivity of Al-Cu-Ru icosahedral quasicrystals
Authors:
Macia E.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):592-595, 2000 Dec 15.
Abstract:
On the basis of suitable experimental observations, we propose a model for the electronic structure of i-Al-Cu-Ru which allows us to obtain a closed expression for the electrical conductivity accurately describing the most characteristic features observed in the sigma (T) curves of high quality quasicrystals. By comparing the theoretical predictions with a series of experimental data, we unveil a relationship between the density of states (DOS) structure, the sample stoichiometry, and the electrical conductivity at different temperature ranges. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Electronic transport in Al-Mn systems with icosahedral clusters
Authors:
Solbrig H. Landauro CV. Loser A.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):596-599, 2000 Dec 15.
Abstract:
The electronic transport in alpha -Al-Mn(Si) is examined in view of the co-operation of Mackay icosahedra Al42Mn12. We calculate resistivities and resistances by means of the Kubo formula and the Buttiker formula, respectively. We find the following: (i) Large resistances result from the electronic coherence in the Mn subsystem just beyond the length scale of the unit cell. Most important in this respect is the orientation order of the Mackay icosahedra. After randomizing the cluster orientation the system behaves like amorphous metals. (ii) Direct links between icosahedra via Al-glue atoms can considerably change the transport behavior (shifts of narrow spectral features). (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Temperature dependence of the electronic transport in Al-Cu-Fe phases
Authors:
Landauro CV. Solbrig H.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):600-603, 2000 Dec 15.
Abstract:
The temperature dependences of the electronic conductivity and the thermoelectric power are theoretically examined for the i-Al-Cu-Fe (1/1) approximant in comparison with both crystalline omega -Al7Cu2Fe and amorphous Al84Fe16. Our study is based on ab initio results for the spectral curves which are obtained by means of the linear muffin-tin orbitals (LMTO) method and the Kubo-Greenwood formula. Thermopowers are calculated after the Mott formula. We show that a realistic variety of thermopower curves versus temperature results from small shifts of the Fermi energy in a narrow resistivity peak. A simple model of the energy-dependent resistivity is suggested which supports the interpretation of the thermopower curves. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Electrical resistivities of Al-Pd-Os and Al-Pd-Os-Re icosahedral quasicrystals
Authors:
Asao T. Endo J. Tamura R. Takeuchi S. Shibuya T.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):604-606, 2000 Dec 15.
Abstract:
Electrical resistivities of structurally ordered Al-Pd-Os icosahedral quasicrystalline phase (I-phase) of various compositions were investigated. High resistivity of rho (290) (K) = 8000 mu Omega cm and a large resistivity ratio of rho (12 K)/rho (290 K) = 2.0 has been obtained at a nominal composition Al70Pd19Os11. In addition, the effect of rhenium substitutions on the resistivity of Al-Pd-Os I-phase was studied in view of a strong scattering effect by rhenium atoms. A drastic increase in the resistivity and its temperature dependence has been observed ranging up to rho (300 K) = 12 000 mu Omega cm and rho (12 K)/rho (290 K) = 5.0, indicating the peculiar role of rhenium atoms on the electronic transport of I-phases. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Quasicrystals as potential candidates for thermoelectric materials
Authors:
Cyrot-Lackmann F.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):611-612, 2000 Dec 15.
Abstract:
Quasicrystals have unusual thermal and electronic properties, such as low thermal conductivity, electronic conductivity increasing with temperature and defects and a thermoelectric power which can be large and positive in some cases. Ail these properties can be understood in a scheme where their peculiar atomic structure induces a complex Fermi surface. Applications of quasicrystals as new thermoelectric materials are discussed in terms of their figure of merit. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Magnetoconductivity of icosahedral and amorphous Al-Pd-Re films - a comparison
Authors:
Haberkern R. Rosenbaum R. Bekar H. Pilosof M. Milner A. Gerber A. Haussler P.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):613-616, 2000 Dec 15.
Abstract:
The magnetoconductivity of quasicrystals is often discussed in the frame of quantum corrections, namely weak (anti-) localisation and electron-electron interaction. A premise for both effects is a strong elastic scattering of conduction electrons. Amorphous and icosahedral phases are discussed as Hume-Rothery alloys with an electronically induced structural peak at the diameter of the Fermi sphere. Therefore, both should exhibit quantum corrections. The preparation of quasicrystalline films via the amorphous route offers the possibility to compare the magnetoconductivity on samples of identical composition but different structure. We report on magnetoconductivity measurements at temperatures between 0.2 and 22 K and for magnetic fields up to 16 T. With the exception of the electronic diffusion constant, amorphous as well as icosahedral Al-Pd-Re films can be described by nearly the same set of parameters if the samples are well on the metallic side of the metal-insulator transition. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
X-ray magnetic circular dichroism in quasicrystals
Authors:
Watanabe Y. Tamura J. Shoji H. Nanao S. Nakamura T. Yokoyama Y.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):617-620, 2000 Dec 15.
Abstract:
The spectra of X-ray magnetic circular dichroism (XMCD) and extended X-ray absorption fine structure (EXAFS) were measured in the ferromagnetic quasicrystals (a stable decagonal phase of Al40Mn25Fe15Ge20, a unstrained icosahedral phase of Al50Pd15Mn20B15, a strained icosahedral phase of Al42.5Pd7.5Mn30B20) and the orthorhombic approximant crystalline phase of Al30Mn40B30. In Al40Mn25Fe15Ge20, the intensity of XMCD at Mn K-edge and Fe K-edge were -7x10(-5) and -5x10(-5), respectively, which are normalized by the edge jump of the normal absorption spectra. The values suggest that Mn and Fe in this alloy contribute to the magnetism to the same degree. From the result of EXAFS, the nearest neighbors of Mn atoms and Fe atoms were analyzed to be at the same distance. The environment around Mn and Fe were found not so similar except for the nearest neighbor distance. In Al50Pd15Mn20B15, Al42.5Pd7.5Mn30B20 and Al30Mn40B30 alloys, the intensity of XMCD around the Mn K-edge were about -3x10(-4). The magnetic moments of Mn atoms in these alloys are roughly estimated to be 0.8 mu (B). The difference of a magnetic structure was detected between the quasicrystals and the approximant. The result of EXAFS analysis indicates that the distances from Mn to its first nearest neighbor and its second nearest neighbor are almost equal. The existence of phason strain field have no appreciable influence on the moment of Mn. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Conditions on the occurrence of magnetic moments in quasicrystals and related phases
Authors:
de Laissardiere GT. Mayou D.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):621-624, 2000 Dec 15.
Abstract:
We analyze the criterion for the appearance of magnetic moments in quasicrystals approximants and liquids Al-Mn. In a Hartree-Fock scheme, it is shown that the Stoner criterion (Un(d)(E-F)greater than or equal to1) does not apply to these systems due to the presence of the pseudogap in the density of states. We give a generalized criterion that can take into account the particular density of state. The main result is that the appearance of a magnetic moment on a Mn atom depends strongly on its position in the crystalline structure. Indeed, some particular positions of the Mn atoms lead to magnetic moments whereas other positions are more stable when the Mn is non-magnetic. This criterion is used to analyze the electronic structure of two approximants (1/1-Al-Pd-Mn-Si and T-AI-Pd-Mn) calculated by the self-consistent linear muffin tin orbitals (LMTO)-ASA method. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 18]
Title:
Magnetism of approximants in the Al-Mn and Al-Pd-Mn systems
Authors:
Simonet V. Hippert F. Audier M. Calvayrac Y.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):625-628, 2000 Dec 15.
Abstract:
Magnetic properties of approximants in the Al-Mn and Al-Pd-Mn systems have been investigated. Whereas most phases are non-magnetic, localized moments are found on a fraction of the Mn atoms in the hexagonal mu -Al4Mn, orthorhombic T-Al73.1Pd5.2Mn21.7 and cubic 1/1-Al68Pd11Mn14Si7 phases. In all these phases we could identify the crystallographic sites occupied by magnetic Mn. Localized moments are associated with a few particular sites. The moment formation is influenced by the sp-d hybridization. These results contribute to clarify the origin of magnetism in quasicrystalline phases. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 23]
Title:
Influence of vacancies on the magnetic properties of icosahedral Al7.10Pd20.0Mn9.0
Authors:
Scheffer M. Suck JB.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):629-632, 2000 Dec 15.
Abstract:
Quenched samples of the icosahedral alloy of the ternary system Al-Pd-Mn contain a high amount of vacancies depending on the annealing temperature and the quench rate. As shown before [M. Scheffer, R. Luck, Proceedings Aperiodic '97, 1998, pp. 469-472], these vacancies result in a change from a diamagnetic to a paramagnetic state at room temperature. We investigated the behaviour of the magnetic moments at low temperatures of a quenched and an annealed sample. At this temperatures a strong decrease of the total magnetic moment after the annealing was observed. The number and the magnitude of the magnetic moments were determined by measurements of the field and temperature: dependence of the total magnetic moment. Evaluation of the data yields only a small number of magnetic moments. We relate the observed moments to a high amount of vacancies and to a disorder of Al and Mn, respectively. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Antiferromagnetic orders in Ising model simulations in an icosahedral Zn-Mg-Ho structure
Authors:
Matsuo S. Ishimasa T. Nakano H.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):633-637, 2000 Dec 15.
Abstract:
Antiferromagnetic orders were investigated in an icosahedral Zn-Mg-Ho model structure in simulated annealing of 12524 and 67896 Ising spins interacting via a Ruderman-Kittel-Kasuya-Yosida (RKKY)-like alternating exchange. Magnetic orders were analyzed by means of diffraction patterns arising from spin-dependent elastic scattering amplitudes. The diffraction patterns from the magnetic structure consisted of spots at low temperatures in the case of an antiferromagnetic interaction for the shortest distance (3.37 Angstrom) and a ferromagnetic interaction for the second shortest one (5.46 Angstrom). A reversed sign interaction, ferromagnetic for the shortest distance and antiferromagnetic for the second shortest one, resulted in broad intensity minima. The characteristics were clearer in the larger system consisting of 67896 spins. The broad feature in the patterns for the reversed sign interactions was concluded to result from the frustrated second shortest interactions on the basis of an energetic view of the neighboring magnetic connections. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Planar quasiperiodic Ising models
Authors:
Repetowicz P. Grimm U. Schreiber M.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):638-641, 2000 Dec 15.
Abstract:
We investigate zero-field Ising models on periodic approximants of planar quasiperiodic tilings by means of partition function zeros and high-temperature expansions. These are obtained by employing a determinant expression for the partition function. The partition function zeros in the complex temperature plane yield precise estimates of the critical temperature of the quasiperiodic model. Concerning the critical behaviour, our results are compatible with Onsager universality, in agreement with the Harris-Luck criterion based on scaling arguments. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Renormalization of two-dimensional Ising systems with irrelevant, marginal and relevant aperiodic (dis)order
Authors:
Hermisson J.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):642-645, 2000 Dec 15.
Abstract:
We introduce a class of 2d Ising models with aperiodic modulations of the coupling constants following a 2d substitution rule. The relevance of the aperiodicity to the phase transition is examined through an approximative real space renormalization group approach known as the cumulant approximation. We find that the relevance of the aperiodic disorder is determined by the fluctuations of the mean coupling as predicted by the Harris-Luck criterion. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
High temperature specific heat of Al-Pd-Mn and Al-Cu-Co quasicrystals
Authors:
Edagawa K. Kajiyama K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):646-649, 2000 Dec 15.
Abstract:
For the purpose of investigating the behavior of thermally excited phasons, specific heat has been measured by differencial scanning calorimetry (DSC) for icosahedral Al-Pd-Mn (i-Al-Pd-Mn) in the temperature range from 550 to 1080 K and for decagonal Al-Cu-Co (d-Al-Cu-Co) in the range from 890 to 1070 K. The measured specific heat per atom at constant pressure c(p) has been converted to that at constant volume c(v) by use of the data of bulk modulus previously reported and the data of thermal expansion coefficient which we measured by X-ray diffractometry. c(v) of i-Al-Pd-Mn is about three k(B) up to about 700 K, as expected from the Dulong-Petit's law. However, it starts deviating upward from three k(B) at about 700 K, increases dramatically and reaches five k(B) at 1080 K. The Similar behavior has been observed also for d-Al-Cu-Co. The origin of such a dramatic increase in c(v) is discussed in light of possible thermal excitation of phasons. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Atomic defects in quasicrystals: an approach with positron annihilation spectroscopy and time-differential dilatometry
Authors:
Baier F. Muller MA. Grushko B. Schaefer HE.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):650-653, 2000 Dec 15.
Abstract:
Atomic defects have been studied in Al-Pd-Mn and Zn-Mg-Ho icosahedral quasicrystals by means of positron annihilation spectroscopy and time-differential dilatometry. In addition, the first in situ positron lifetime measurements on Al-Pd-Mn quasicrystals at high temperatures are performed. In the time-differential dilatometry studies, after fast cooling at high temperatures an anomalous time-dependent isothermal expansion of the specimen was observed. If this length change is attributed to atomic defects the defect formation and the migration can be studied. Positron lifetimes could be derived for icosahedral Al70.2Pd21.3Mn8.5 and icosahedral Zn61Mg28Ho11 with 214 and 212 ps, respectively. These lifetimes are ascribed to structural vacancies in these quasicrystalline systems, which are supported, by electron irradiation and long-term annealing experiments. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Low-energy phonon excitations in the decagonal quasicrystal Al70Co15Ni15 and in crystalline Al13Co4 phases
Authors:
Mihalkovic M. Elhor H. Suck JB.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):654-657, 2000 Dec 15.
Abstract:
We compare the experimentally measured generalized vibrational density of states (DOS) in Al70Co15Ni15 and the related crystalline Al13Co4, with the phonon spectra resulting from the numerical simulation based on realistic binary Al-Co pair potentials [R. Phillips, J. Zou, A.E. Carlsson, M. Widom, Phys. Rev. B 49 (1994) 9322], the Al13Co4 structure model after Grin et al. [J. Grin, U. Burkhardt, M. Ellner, K. Peters, J. Alloys Compounds 206 (1994) 243], and an Al70Co15Ni15 atomic structure model with 20 Angstrom clusters decorating vertices of a Penrose tiling. The experimentally measured low-omega part of the VDOS is appreciably higher than the Debye VDOS with the mean sound velocity measured by Bianchi et al. [M.A. Chernikov, H.R. Ott, A. Bianchi, A. Migliori, T.W. Darling, Phys. Rev. Lett. 80 (1998) 321]. The VDOS calculated in the harmonic approximation using pair potentials has acoustics modes with the corresponding mean sound velocity close to the experimental value, but shows an even bigger excess DOS at low omega than the experimental neutron generalized VDOS, due to the non-acoustic character of a significant fraction of modes at low omega. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Temperature dependence of the phonon density of states in decagonal Al-Ni-Co
Authors:
Elhor H. Mihalkovic M. Suck JB.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):658-661, 2000 Dec 15.
Abstract:
We have analyzed the experimentally measured temperature dependence of the phonon density of states (DOS) in d-Al-Ni-Co [1] in the range 300-1100 K, assuming that the relationship between the DOS at different temperatures can be expressed in terms of frequency shifts of the phonon modes. The omega -dependent frequency shifts were determined using a Monte Carlo method. They exhibit a pronounced structure, with two prominent features: a broad maximum near 30 meV and a local minimum around 11 meV. For omega > 11 meV, the frequency shifts change with the temperature such that the Gruneisen parameter, relating frequency shifts to the volume expansion, remains approximately constant, gamma similar to3.5. For the modes with gamma <11 meV, the frequency shifts increase faster and <gamma> is temperature dependent, varying from gamma similar to1.2 at 470 K to gamma similar to4.6 at T=1100 K. Finally, we estimate that the frequency shifts relating the phonon DOS at 300 K and at 1100 K contribute similar to0.42k(B) per atom extra vibrational entropy at the higher temperature. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 6]
Title:
The phonon density of states in the archetypical icosahedral quasicrystal Al62Cu25.5Fe12.5
Authors:
Brand RA. Coddens G. Chumakov AI. Dianoux AJ. Calvayrac Y.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):662-665, 2000 Dec 15.
Abstract:
We study the vibrational density of states (VDOS) in the i-AlCuFe quasicrystal measured by different methods: (i) Fe-57 inelastic nuclear-resonant absorption (INA) of X-rays (ii) and time-of-flight inelastic neutron scattering (INS). The samples studied were i-Al62Cu25.5Fe12.5 with different isotopic substitutions. INA measures the Fe-partial VDOS while INS the neutron-weighted 'generalised' GVDOS. We find the unexpected result that the iron-partial VDOS has a single sharp maximum. The neutron-weighted GVDOS for different isotopes (natural Cu and Cu-65; natural Fe and Fe-57 shows that the copper-partial VDOS is strongly peaked as well but at significantly lower energy. These results are discussed in light of the icosahedral quasicrystal model of Katz and Gratias. as well as specific heat results which indicate a discrepancy between the speed of sound, the specific heat and the low energy limit of the VDOS. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 17]
Title:
Phason-dynamics studied by quasielastic mossbauer scattering in i-Al-Cu-Fe quasicrystals
Authors:
Brand RA. Voss J. Calvayrac Y.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):666-669, 2000 Dec 15.
Abstract:
Quasicrystals can show a new type of localised defect termed a 'phason'. At high temperature, these defects become mobile and lead to short-ranged atomic motion without involving vacancies. Cu in i-Al-Cu-Fe is involved in such phason jump process at high temperatures T on a time scale tau of h/250 mu eV. Surprisingly, tau (Cu) was found independent of the temperature, indicating a type of 'assisted' jump process. In order to investigate the iron dynamics in this system, we have studied i-Al62Cu25.5 Fe-57(12.5) using quasielastic Mossbauer spectroscopy for T less than or equal to 1100 K. We find a temperature-dependent iron phason jump process with tau (Fe) typically two orders of magnitude slower than copper. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Diffusive motions in a crystalline Al50Cu35Ni15 alloy
Authors:
Dahlborg U. Howells WS. Calvo-Dahlborg M. Dubois JM.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):670-674, 2000 Dec 15.
Abstract:
In this report, quasielastic neutron scattering experiments on the Al50Cu35Ni15 alloy are briefly described. It is found that frequent jumps of Cu and Ni atoms between different interstitial lattice positions are taking place in this alloy at high temperature indicating that hopping motions are not restricted to occur in systems with quasicrystalline local order. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 9]
Title:
Molecular dynamic studies of atomic jumps in d-Al-Cu-Co
Authors:
Bunz D. Zeger G. Roth J. Hohl M. Trebin HR.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):675-679, 2000 Dec 15.
Abstract:
The structure of quasicrystals permits phason flips: atoms may jump to equivalent alternate positions. The jumps represent the discrete representation of the phason strain in the continuum description. We have studied jumps in one of the Burkov models for decagonal Al-Cu-Co quasicrystals in molecular dynamics (MD) simulations by direct detection acid with the help of correlation functions. In the decagonal structures, we find correlated jumps of two atoms within a layer. These are equivalent to flips predicted in a tiling description for the model. We will also give an overview of correlated atomic motions in different quasiperiodic layers. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 18]
Title:
A phason strain in an Al-Cu-Fe icosahedral quasicrystal
Authors:
Jono M. Matsuo Y. Ishii Y.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):680-684, 2000 Dec 15.
Abstract:
The peak profiles and peak positions for an icosahedral Al-Cu-Fe single quasicrystal were measured using a high-resolution four-circle X-ray diffractometer. Notable peak shifts from the ideal Bragg positions with Q(perpendicular to) dependence were observed only for the reflections on the five-fold axis. This means that the specimen has the linear phason strain along the five fold direction. The amplitude of this linear phason strain is estimated as -0.0543 by using matrix elements for I-h to D-5d deformation. This value corresponds to the phase transformation from the icosahedral phase to the pentagonal phase. Furthermore, two-dimensional intensity distributions around the Bragg reflections on the two-, three- and five-fold axes are well interpreted with this deformation scheme. (C) 2000 Elsevier Science S.A. All rights reserved. [References: 8]
Title:
Quasiperiodic tilings and self-organized criticality
Authors:
Joseph D.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):685-688, 2000 Dec 15.
Abstract:
Self-organized critical models are used to describe the 1/f-spectra of rather different physical situations like snow avalanches, noise of electric currents or luminosities of stars. The prototype of these models is the sandpile model of Bak et al. [Phys. Rev. Lett. 59 (1987) 381]. We implement this model on the eight-fold Ammann-Beenker tiling where the model can become either isotropic or anisotropic and investigate its properties. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Diffusion in icosahedral Al-Pd-Mn quasicrystals: temperature and pressure dependence
Authors:
Galler R. Mehrer H.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):693-696, 2000 Dec 15.
Abstract:
The temperature and pressure dependence of diffusion in monocrystalline icosahedral Al-Pd-Mn quasicrystals (i-Al-Pd-Mn) was investigated by radiotracer techniques using serial sectioning for depth profiling. Recent results on the temperature dependence of Zn-65, In-114m and Pd-103 diffusion are presented together with previous ones on Mn-54 and Fe-59 diffusion from our laboratory. The temperature dependence of diffusion is discussed in connection with results on i-Al-Pd-Mn from other groups and compared with the diffusion of foreign elements in Al. This comparison suggests a vacancy mechanism for diffusion in i-Al-Pd-Mn at least at higher temperatures. Magnitude and sign of the activation volumes also support a vacancy mechanism. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Diffusion of Co-57 in decagonal Al-Ni-Co-quasicrystals
Authors:
Khoukaz C. Galler R. Mehrer H. Canfield PC. Fisher IR. Feuerbacher M.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):697-701, 2000 Dec 15.
Abstract:
Self-diffusion of Co-57 in decagonal Al-Ni-Co single quasicrystals was studied for both principal directions as a function of the temperature by means of the radiotracer method. In combination with serial sectioning, diffusivities were measured over a large temperature range from 732 to 1273 K. Below about 1120 K diffusion is described by an Arrhenius behaviour along both the periodic and the quasiperiodic directions. The magnitude of the activation enthalpies and pre-exponential factors support a vacancy-type diffusion mechanism. A small anisotropy of diffusion which is temperature-dependent but never exceeds 30% was detected. Above 1120 K, a kink in the Arrhenius curve is observed. We attribute this behaviour to a phase transition from the decagonal basic Go-rich phase to an ordered modification. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Diffusion in quasicrystalline Al-Ni-Co and Al-Pd-Mn
Authors:
Zumkley T. Guo JQ. Tsai AP. Nakajima H.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):702-705, 2000 Dec 15.
Abstract:
Diffusion coefficients of Co-60 in single decagonal (d-)Al72.2Ni11.8Co16.0 quasicrystals and of Ni-63 in single icosahedral (i-)Al70Pd21Mn9 were measured by the radioactive tracer method. The volume diffusion coefficients can be described by an Arrhenius equation. Anisotropic diffusion behaviour was observed in the d-Al-Ni-Co quasicrystals, in which the mobility of Co is slightly faster along the periodic direction. The activation enthalpies for Co diffusion in d-Al-Ni-Co are Q=277.4 kJ mol(-1) (periodic direction), Q=289.0 kJ mol(-1) (aperiodic direction) and for Ni diffusion in i-Al-Pd-Mn Q=209.0 kJ mol(-1). The results are discussed together with data of similar diffusion investigations in icosahedral quasicrystals, and a diffusion mechanism via vacancies is suggested. In addition, we have determined surface self-diffusion coefficients of Co-60 in the d-Al-Ni-Co quasicrystalline alloy and have obtained different activation energies of surface diffusion for the periodic (Q=147 kJ mol(-1)) and the quasiperiodic direction (Q=137 kJ mol(-1)). (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Low-temperature thermal conductivity of icosahedral Al63Cu25Fe12 and Al62Cu25.5Fe12.5 quasicrystals
Authors:
Smontara A. Lasjaunias JC. Paulsen C. Bilusic A. Calvayrac Y.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):706-710, 2000 Dec 15.
Abstract:
We present measurements of thermal and electrical conductivity of icosahedral Al63Cu25Fe12 and Al62Cu25.5Fe12.5 quasicrystals in the temperature range 0.1-6 K. Electrical conductivity Delta sigma (T)=sigma (T)-sigma (4.2 K) of Al63Cu25Fe12 contrary to aa(T) of Al62Cu25.5Fe12.5 shows a linear increase with rootT up to 2 K, as predicted by electron-electron interaction theories, followed by a strong change of regime at around 2 K. Low-temperature phonon thermal conductivity, kappa (ph)(T), Of Al63Cu25Fe12 shows a deviation from the expected T-3 law: in the T-range 0.1-0.8 K, kappa (ph)(T)similar toT(2.7). An anomaly in phonon thermal conductivity appears near 1 K, which superposes to the monotonous increase of kappa (ph)(T) With T obeyed up to higher T. We suppose that the origin of this anomaly in phonon thermal conductivity is related to the strong change of the regime in the variation of the Delta sigma (T), which appears in the same temperature range. For Al62Cu25.5Fe12.5, kappa (ph)(T) varies almost linearly between 0.28 and 1.2 K, and exhibits a crossover towards a very rapid variation below 150 mK, much more rapid than T-3. There is no evidence for phase transitions from specific heat measurements in the temperature range of the crossover of kappa (T). (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Thermal and thermoelectric properties of icosahedral Al62Cu25.5Fe12.5 quasicrystal
Authors:
Bilusic A. Smontara A. Lasjaunias JC. Ivkov J. Calvayrac Y.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):711-714, 2000 Dec 15.
Abstract:
Experimental results on thermal and thermoelectric properties of icosahedral i-Al62Cu25.5Fe12.5 quasicrystal in temperature range 4.2-340 K are examined, and comparison with icosahedral i-Al63Cu25Fe12 quasicrystal is made. The results of thermoelectric properties tan be consistently explained by a two-band model. Although the picture that overlaps with the valence and the conduction bands at Fermi level is responsible for the coexistence of both types of carriers enables us to describe quasicrystals as semi-metals, the situation in which temperature: variation of the electrical conductivity is determined by that of carrier density is essentially the same as in the case of normal semiconductor. The phonon thermal conductivity increases monotonically with temperature showing a shallow maximum at about 25 K, followed by a minimum around 70 K, and a subsequent increase. The shallow maximum in phonon thermal conductivity could be interpreted as a crossover from the regime of a dominant scattering on tunneling states of an unspecified nature to the regime where quasiperiodic Umklapp processes are important. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Electrical resistivity, thermopower, and thermal conductivity of single grained (Y, Tb, Ho, Er)-Mg-Zn icosahedral quasicrystals
Authors:
Gianno K. Sologubenko AV. Chernikov MA. Ott HR. Fisher IR. Canfield PC.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):715-718, 2000 Dec 15.
Abstract:
We report on measurements of the temperature dependence of the electrical resistivity rho, the thermopower S, and the thermal conductivity lambda of single grained RE-Mg-Zn (RE=Y, Tb, Ho, Er) icosahedral quasicrystals between 5 acid 300 K. The resistivity of all four samples is very weakly temperature dependent with a negative slope d rho /dT. The S/T versus temperature curves exhibit a maximum at temperatures between 12 and 15 K. This feature is observed for all here investigated quasicrystalline materials. The appearance of a maximum in the thermal conductivity of (Y, Ho, Er)-Mg-Zn, and a plateau in that of Tb-Mg-Zn is ascribed to a power-law temperature dependence of the mean free path of delocalized quasilattice excitations at intermediate temperatures. A progressive suppression of the maximum in the thermal conductivity data as the de Gennes factor increases indicates for a coupling of the spin system to the lattice. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 16]
Title:
Thermal conductivity and critical modes in one-dimensional Fibonacci quasicrystals
Authors:
Macia E.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):719-722, 2000 Dec 15.
Abstract:
We consider a general Fibonacci harmonic lattice in which both the masses and the elastic constants are aperiodically arranged. Making use of a suitable decimation scheme, inspired in real-space renormalization group concepts, we obtain closed analytical expressions for the global transfer matrix and transmission coefficient for several resonant critical normal modes. The fractal structure of the frequency spectrum has a significant influence in the cumulative contribution of the different normal modes to the thermal transport. A sudden enhancement of the thermal coefficient around a set of special frequencies indicates the importance of resonance effects in the thermal conductivity of Fibonacci quasicrystals. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Heat capacities of icosahedral and hexagonal phases of Zn-Mg-Y system
Authors:
Inaba A. Takakura H. Tsai AP. Fisher IR. Canfield PC.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):723-726, 2000 Dec 15.
Abstract:
Heat capacity measurements have been performed in the temperature range 4-300 K for an icosahedral phase of Zn-Mg-Y alloy (Zn55Mg35Y10) and the related crystalline phases, a hexagonal phase (Zn65.2Mg27.9Y6.9) and the Laves phase of MgZn2, to study the feature of lattice vibrations in quasicrystals. A single quasicrystal of Zn56.8Mg34.6Y8.7 was also investigated for comparison. The vibrational density of states is delineated in terms of the temperature dependence of the apparent Debye temperature (Theta (D)) on a reduced basis using the limiting value at high temperature (Theta (infinity)). A deeper minimum (Theta (D)/Theta (infinity)similar to0.82) is observed at substantially lower temperatures (T/Theta (infinity)similar to0.055) in the quasicrystals than in the crystals, which suggests significant enhancement of the density of states at the corresponding energies. The fact is compatible to that obtained previously for Al-Cu-Ru, Al-Pd-Re and Al-Pd-Mn systems. The presence of some defects or inhomogeneity in quasicrystals might be responsible for the anharmonic lattice vibrations. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
High-strength aluminum- and zirconium-based alloys containing nanoquasicrystalline particles
Authors:
Inoue A. Kimura HM. Zhang T.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):727-735, 2000 Dec 15.
Abstract:
By the dispersion of nanoscale quasicrystalline (Q) particles in f.c.c.-Al or Zr-based glassy phase, new Al- and Zr-based alloys with good mechanical properties were developed in a high Al content range of 93-95 at.% of Al-Cr(or Mn)-Co-Ce, Al-Mn-Co-Cu and Al-Cr-Fe-Ti systems and in Zr65Al7.5Ni10Cu17.5-xMx (M = Ag or Pd; x = 5 and 10 at.%) systems. The structure consists of Q-particles with a size of 30-50 nm surrounded by Al with a thickness of 5-10 nm for the Al-based alloys and Q-particles with a size of about 30 nm surrounded by glassy phase with a thickness of less than 1 nm for the Zr-based alloys. The Q-phase has high volume fractions (V-f) of 60-70% for the former alloys and 80-90% fur the latter alloys. The former structure is formed by the solidification mode in which the Q-phase precipitates as a primary phase, followed by precipitation of Al from the remaining liquid. The latter structure results from homogeneous nucleation and slow growth from the glassy phase. The high V-f of the Q-particles is presumably due to the existence of randomly oriented icosahedral clusters in the supercooled liquid of the Al- and Zr-based alloys. The features of mechanical properties are classified into four types, i.e., high-strength type of 800 MPa in Al-(Mn, Cr)-Ce-Co systems, high elongation type of 30% in Al-Mn-Co-Cu system, high-elevated temperature strength type of 350 MPa at 573 K in Al-Fe-Cr-Ti system, and high-strength type of 1900 MPa in the Zr-based system. These mechanical properties are promising for the future extension of the new Al- and Zr based alloys to practical materials. (C) 2000 Published by Elsevier Science B.V.
Title:
A comparative study of the plastic behaviour of icosahedral and xi '-Al-Pd-Mn
Authors:
Feuerbacher M. Klein H. Bartsch M. Messerschmidt U. Urban K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):736-741, 2000 Dec 15.
Abstract:
In the Al-Pd-Mn system, large single crystals of high structural quality can be grown of the icosahedral and the xi'-phase. The latter is an approximant of the icosahedral phase. Though the structure of xi'-Al-Pd-Mn is periodic, it possesses a local order which is very close to that of the icosahedral phase. In this paper, we present a comparative study of the plastic behaviour of single crystals of the icosahedral and the xi'-phase. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Dislocation mechanism of high-temperature plastic deformation of Al-Cu-Fe and Al-Pd-Mn icosahedral quasicrystals
Authors:
Wang RH. Yang WG. Gui JN. Urban K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):742-747, 2000 Dec 15.
Abstract:
Microstructures in hot-impacted Al62.5Cu25Fe12.5 and Al70.4Pd21.2Mn8.4 icosahedral quasicrystals (IQCs) were studied by transmission electron microscopy (TEM). Densely distributed dislocations and stacking fault (SF) type contrast were observed for the first time in Al-Cu-Fe IQC. This result confirms that dislocation motion is an important deformation mechanism for Al-Cu-Fe IQC. Moving dislocations in quasicrystalline materials leave phason-type SFs behind. In situ TEM observation shows these phasonic SFs disappear due to intense diffusion at high temperatures. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Plasticity of Al-Ni-Co decagonal single quasicrystals
Authors:
Edagawa K. Ohta S. Takeuchi S. Kabutoya E. Guo JQ. Tsai AP.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):748-752, 2000 Dec 15.
Abstract:
Compression experiments have been performed for Al-Ni-Co decagonal single quasicrystals grown by a floating zone method with different orientations of the compression axes: the tenfold direction (c(parallel to)) a twofold direction perpendicular to it (c(perpendicular to)) and a direction inclined from the tenfold direction by about 45 degrees (c(45 degrees)). The yield stresses obtained range from 700 to 1050 MPa at 973 K, which are much larger than those previously reported. The anisotropy in the yield stress is less than a factor of two. For the c(45 degrees) compressed samples, a slip deformation has been observed on a twofold prismatic slip plane and in the tenfold slip direction. Long straight screw dislocations have been observed by transmission electron microscopy (TEM in the c(45 degrees) compressed samples, indicating the existence of deep Peierls-potential valleys for the dislocation glide. The c(parallel to) and c(perpendicular to) compressed samples have shown slip deformations along more than two types of pyramidal slip planes. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Shock waves in quasicrystals
Authors:
Roth J.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):753-756, 2000 Dec 15.
Abstract:
Shock waves represent a heavy load on materials. In solids, they create a variety of defects like shear bands or crystal domains. Waves of large amplitude may destroy the structural order completely. We study shock waves in an Al-Cu-Li-type model quasicrystal, in a closely related crystal structure, the C15 (MgCu2) Laves phase, and in an amorphous solid. If we take the slightly different composition and binding energy into account, we find that the sound velocity in all the structures is about the same. If the shock waves are weak, only point defects occur. With increasing intensity, we observe broad defect bands in the crystal and the quasicrystals, if the cross section of the sample is large enough. Otherwise the structure looks like an amorphous state. At large shock wave intensities, the shock front velocity approaches the universal material-independent behavior. The structure is destroyed completely in this regime. The crystal occurs to be slightly more stable than the quasicrystal which means that defects and destruction of the sample are found at higher shock wave intensities. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 9]
Title:
Microprocesses of the plastic deformation of icosahedral Al-Pd-Mn single quasicrystals
Authors:
Messerschmidt U. Haussler D. Bartsch M. Geyer B. Feuerbacher M. Urban K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):757-760, 2000 Dec 15.
Abstract:
Recent experimental observations on the plastic deformation of icosahedral Al-Pd-Mn single quasicrystals are described originating from conventional transmission electron microscopy in a high-voltage electron microscope (HVEM), from in situ straining experiments in an HVEM and from the determination of activation parameters from macroscopic compression tests at low temperatures. The moving dislocations are created by multiplication events initiated by cross slip. They trail planar faults of different electron microscopy contrast. Since recovery occurs at high temperatures, the dislocation mobility should be discussed on the basis of low-temperature data. While it was previously interpreted in terms of an extended cluster friction model, the present paper shows that it can equivalently be explained by the Peierls mechanism on the cluster scale. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Plastic properties of icosahedral Al-Pd-Mn single quasicrystals
Authors:
Bartsch M. Geyer B. Haussler D. Feuerbacher M. Urban K. Messerschmidt U.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):761-764, 2000 Dec 15.
Abstract:
Plastic deformation propel-ties of icosahedral Al-Pd-Mn single quasicrystals have been measured over a wide range of temperature in constant strain rate experiments including stress relaxation tests. The properties are different in the low and high-temperature ranges. At low temperatures, the deformation is controlled by the lattice friction of the gliding dislocations and a very effective work-hardening mechanism. At high temperatures, the deformation properties are discussed in terms of recovery-controled plastic deformation. (C) 2000 Elsevier Science B.V. Ail rights reserved.
Title:
Dislocation arrangement and density in deformed Al-Pd-Mn single-quasicrystals
Authors:
Schall P. Feuerbacher M. Bartsch M. Messerschmidt U. Urban K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):765-768, 2000 Dec 15.
Abstract:
We present results of microstructural investigations on plastically deformed Al-Pd-Mn single-quasicrystals. Deformations were carried out in uniaxial geometry at different temperatures and to different values of plastic strain and in bending geometry. In the uniaxial geometry, various glide systems are activated. The dependence of the total dislocation density on temperature and on plastic strain is studied. Additional heat treatments on deformed samples show that recovery processes occurring at the high deformation temperatures significantly influence the deformation process. The experimental data are interpreted using a kinetic equation describing the evolution of the dislocation density during deformation. In the bending geometry a defined arrangement of geometrically necessary dislocations of edge type is observed. We find straight dislocation lines with line directions in the plane spanned by the direction of the applied force and the bending axis. The Burgers vectors have twofold direction corresponding to glide planes with the highest shear stress. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 9]
Title:
Dislocations in Al-Pd-Mn approximants: a high resolution electron microscopy study
Authors:
Klein H. Feuerbacher M. Urban K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):769-772, 2000 Dec 15.
Abstract:
In plastically deformed crystals of the xi'-Al-Pd-Mn phase dislocations with different Burgers vectors were observed in a high-resolution electron microscopy (HREM) study. The Burgers vector magnitudes are equal to the physical space components of the Burgers vectors found in the icosahedral phase. In particular, they also show a scaling behavior in the approximant involving the golden mean tau. Through the orientation relationships between the icosahedral phase and the approximant we have found that the Burgers vector directions are equivalent in both phases. This is surprising as some of the Burgers vector directions do not correspond to any crystallographic orientation in the approximant crystal, indicating that local (icosahedral) order is more important to dislocations than long range (crystalline) order. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 7]
Title:
The strain-softening phenomenon of icosahedral Al-Pd-Mn single quasicrystals
Authors:
Brunner D. Plachke D. Carstanjen HD.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):773-776, 2000 Dec 15.
Abstract:
For studying the strain-softening phenomenon of icosahedral Al-Pd-Mn single quasicrystals, compression tests with constant plastic strain rate were performed in the strain regime following the upper yield stress and combined with stress-relaxation experiments and temperature changes along the stress-strain curves at selected strains, it is found that both the strain-rate sensitivity and the temperature sensitivity of the flow stress decrease in the above strain regime with increasing strain. These results favour a model which assumes strain softening being caused by a change of the configuration of large cluster-like obstacles (e.g., the icosahedral clusters present in i-Al-Pd-Mn quasicrystals) by the moving dislocations thus reducing the stress needed to maintain the deformation. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Creep behaviour of icosahedral Al-Cu-Fe
Authors:
Giacometti E. Baluc N. Bonneville J.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):777-780, 2000 Dec 15.
Abstract:
Transient creep experiments have been performed on poly-quasicrystalline specimens of the icosahedral Al-Cu-Fe phase. Three temperatures (870, 960 and 1000 K) have been selected in the ductile regime for creep stresses that range between 30 and 320 MPa. In these experiments, the specimens are first loaded in constant strain-rare conditions, then the testing machine is switched to load control and the specimens are allowed to deform under creep conditions. One- or two-stage creep curves have been obtained depending on temperature, stress and on the deformation level of the stress-strain curve at which the creep tests were performed. When creep conditions are applied before the upper yield stress, at low stress, only a stage of continuous decrease in creep rate is observed, while at higher stress this primary stage is followed by a stage of accelerated creep rate. These two-stage creep curves are predicted within the framework of the strain dependent friction stress model. For creep tests beyond the upper yield stress, only the stage of accelerated creep rate is observed. No distinct steady-state stage has been observed for all investigated creep conditions. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Plasticity of icosahedral Zn-Mg-Dy single quasicrystals
Authors:
Heggen M. Feuerbacher M. Schall P. Klein H. Fisher IR. Canfield PC. Urban K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):781-785, 2000 Dec 15.
Abstract:
We present the results of first deformation experiments on Zn-Mg-Dy icosahedral single quasicrystals. The samples were produced by the flux growth technique. The plastic deformation experiments were performed at temperatures between 490 and 530 degreesC at strain rates of 10(-5) and 10(-6) s(-1). The thermodynamic activation parameters of the deformation process were determined. The stress-strain curves show strong yielding followed by a steady state regime with a constant flow stress level up to strains of about 8%. Microstructural investigations by transmission electron microscopy on deformed samples indicate a deformation mechanism mediated by dislocations. We found a high density of planar defects which were interpreted as slip planes of moving dislocations. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Plastic deformation and hardness in Mg-Zn-(Y,Ho) icosahedral quasicrystals
Authors:
Yoshida T. Itoh K. Tamura R. Takeuchi S.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):786-789, 2000 Dec 15.
Abstract:
High-quality icosahedral poly-quasicrystalline samples have been produced for Mg30Zn60Y10 and Mg30Zn60H10 to alloys by melting and annealing the constituent elements in a sealed tantalum ampoule. Compression tests with a constant crosshead speed and stress-relaxation tests at about 10% compressive strain have been performed at high temperatures. The Vickers hardness has also been measured at high temperatures for undeformed and compressed samples. The thermal activation analysis of plastic deformation has been successfully performed by estimating the dragging stresses at various temperatures from the stress dependence of the activation volume; the total activation enthalpy is about 2.5 eV in both alloys. The higher the plastic strain, the lower is the Vickers hardness at high temperature. This work softening phenomenon is interpreted to be caused by the effects of the deformation-induced phason strain on the dislocation motion. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
A tiling approach to the recovery of a slip plane and the interfaces between domains in ice-related quasicrystals
Authors:
Warrington DH. Luck R.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):790-794, 2000 Dec 15.
Abstract:
A physical displacement across a slip plane or a domain boundary may be resolved into a sequence of phason flips which restore the nearest neighbour configurations and the tile forms of the original quasicrystal. The number or density of required new vertices is correlated with the square of the implied internal space component of the physical shift. Examples are shown which are relevant to domain boundary widths and the ease of progress of physical slip in the relevant quasicrystal. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Dislocation kinetics in quasicrystals under small applied stress
Authors:
Fradkin MA.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):795-798, 2000 Dec 15.
Abstract:
The sliding of dislocations in quasicrystals under small applied stress is considered within phenomenological model. Implications of the quasi-periodic Peierls potential for the dislocation pinning is analyzed and associated activation mechanism is shown to be relevant for the plastic deformation of quasicrystals. The dependence of the dislocation velocity and strain rate on the applied stress is estimated. Kinetics of the dislocation movement in the quasi-periodic pinning potential is analyzed in exactly solvable one-dimensional model. The spectrum of the dislocation jump lengths is found to be a universal function of applied stress. The critical values of resolved stress leading to the drastic changes in the dislocation velocity are shown to form periodical sequence in a logarithm scale. Recent experiments on the mechanical properties of quasicrystals are discussed within proposed model. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Numerical simulation of dislocation motion in an icosahedral quasicrystal
Authors:
Schaaf GD. Mikulla R. Roth J. Trebin HR.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):799-803, 2000 Dec 15.
Abstract:
In a large number of experiments it has been proven that plastic deformation of quasicrystals can occur by a dislocation mechanism. By the use of molecular dynamics simulations, we have investigated the application of shear stress to a three-dimensional model quasicrystal in which we had built an edge dislocation of the Peierls-Nabarro type. To determine suitable Burgers vectors we have calculated the gamma surface, i.e. the misfit energy obtained by a rigid shift of two sample halves along a glide plane. The sample was an approximant of the Ammann-Kramer-Penrose tiling decorated according to Henley and Elser (Phil. Mag. B 53 (1986) 59). It consisted of 1 504 080 atoms interacting via Lennard-Jones potentials. We performed simulations in the microcanonical ensemble at zero temperature. To detect the dislocation line we have used several visualization methods. We have plotted only particles with a potential energy above a threshold leading to pictures of both the atoms in the dislocation core and in the stacking fault in the wake of the dislocation. To distinguish among them we have used image processing algorithms. The displacement field of the configuration has also been computed. We have observed climb and glide motion of the dislocation. The climb motion is caused mainly by boundary effects due to the sample geometry. The glide motion shows kinks due to structural elements that act as pinning centers, The width of the kinks is about 20 quasilattice constants. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Icosahedral Ti-Zr-Ni and hydrogenated Ti-Zr-Ni quasicrystals under high pressure
Authors:
Sadoc A. Itie JP. Polian A. Kim JY. Kelton KF.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):804-805, 2000 Dec 15.
Abstract:
We present results from the first X-ray diffraction studies under high pressure in icosahedral Ti-Ni-Zr quasicrystals (QCs). The icosahedral Ti53Zr27Ni20 phase and an icosahedral Ti45Zr38Ni17 phase that also contains 0.32 hydrogen atoms for each metal atom were investigated. The icosahedral QC structure is retained up to the highest pressures used. The six-dimensional (6D) lattice parameters were obtained as a function of pressure. The zero-pressure bulk modulus and its pressure derivative were determined for the different samples by fitting the 6D parameter change to a Murnaghan-type equation of state. It is worthwhile mentioning that the hydrogenated sample appears more compressible than the one without hydrogen. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 10]
Title:
Mechanical spectroscopy of i-Al-Pd-Mn and d-Al-Ni-Co
Authors:
Damson B. Weller M. Feuerbacher M. Grushko B. Urban K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):806-809, 2000 Dec 15.
Abstract:
Mechanical spectroscopy was applied for the study of defect properties in i-Al-Pd-Mn and d-Al-Ni-Co by applying measuring frequencies between 10(-2) and 10(4) Hz in the temperature ranging from 200 to 1220 K. i-Al-Pd-Mn single quasicrystals exhibit two mechanical loss peaks at 370 (peak A) and 870 K (peak B) for f=3 Hz. Peak A with an activation enthalpy of H=0.98 eV and an attempt frequency t(infinity)(-1) = 2 x 10(15) s(-1) is attributed to atomic jumps enabled by phason flips or vacancies. Peak B (N=4 eV, tau (-1)(infinity) = 3 x 10(24) s(-1)) shows nonlinear Arrhenius behaviour for higher frequencies (f>1 kHz) and is attributed to a relaxation process in which dislocation movement is controlled by creation and movement of phason defects. First measurements on Al-Ni-Co alloys (decagonal or with fivefold symmetry) show a loss maximum at 870 (f=2 kHz) indicating reorientation of atomic defects. A high temperature background (H=2.3 eV) is assigned to diffusion controlled deformation. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Influence of valence electron concentration over friction coefficient of B2-based approximants
Authors:
Zhang LM. Dong C. Brunet P. Dubois JM.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):810-812, 2000 Dec 15.
Abstract:
According to the valence electron concentration e/a criterion for approximants, some B2 superstructures may be regarded as a special group of approximants. The present paper reports on an investigation of the friction behavior of this group of phases. The results are compared with data specific to quasicrystals. We show that samples containing the B2 structure and its superstructures exhibit friction coefficients that decrease with increasing ela and reach minimum at e/a=1.86, i.e. where the quasicrystal is stable. Therefore, the B2-based approximants and quasicrystals belong to a group of phases whose surface properties are mainly determined by electronic structure rather than crystal structure. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Interfaces in quasicrystals: problems and prospects
Authors:
Mandal RK. Lele S.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):813-817, 2000 Dec 15.
Abstract:
We propose to discuss the importance of unified 6D description for understanding the geometrical aspects of interfaces in quasicrystalline and its related phases. These will in particular be presented in relation to the icosahedrally related phases. However, the viewpoints adopted will be sufficiently general to help discuss interfaces in any quasiperiodic systems. The consequence of 6D homophase/heterophase interfaces on 3D physical space will be considered by taking examples. These include RAs/IQC, IQC/DQC interfaces apart from the hypertwin and antiphase domain boundaries. It will be shown that such a description does not promise to solve the problems of energetics of interfaces in these systems. It will be concluded that 3D and hypercrystal structural description need to supplement each other for unravelling the underlying mechanism of growth of a particular interface during processing of these materials. The importance of HREM studies in understanding the interface structures in aperiodic systems will be clearly brought out. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
About the Al 3p density of states in Al-Cu-Fe compounds and its relation to the compound stability and apparent surface energy of quasicrystals
Authors:
Belin-Ferre E. Dubois JM. Fournee V. Brunet P. Sordelet DJ. Zhang LM.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):818-821, 2000 Dec 15.
Abstract:
We report the characteristic parameters of the Al 3p densities of stares gained from a thorough study of many Al-Cu(-Fe) intermetallics including quasicrystalline and approximant phases using X-ray emission spectroscopy. These parameters are the density of states at the Fermi energy E-F, the average binding energy due to Al 3p states and the second moment of their distribution. Hence, we demonstrate that the contribution to the compound stability arising from localization of Al 3p states via the Hume-Rothery mechanism is maximum for the icosahedral state. We also show that Al-transition metal sp-d hybridization is enhanced in the presence of icosahedral order. Finally, we confirm the already pointed out relationship between depth of the pseudo-gap at E-F and apparent surface energy of the samples. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Characterization of surface morphologies at the Al-Pd-Mn fivefold surface
Authors:
Cappello G. Schmithusen F. Chevrier J. Comin F. Stierle A. Formoso V. de Boissieu M. Boudard M. Lograsso TA. Jenks C. Delaney D.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):822-825, 2000 Dec 15.
Abstract:
Fivefold surfaces of Al-Pd-Mn quasicrystal have been prepared under ultra-high vacuum (UHV) by sputtering and annealing above 700 K and characterized by electron diffraction, Auger spectroscopy and X-ray photoemission spectroscopy (LEED, AES, XPS). X-ray reflectivity at grazing incidence reveals that an in situ temperature annealing at 900 K is necessary to irreversibly produce the signature of a Bat and bulk terminated surface. Air-AFM investigations of surfaces prepared below or in the vicinity of this transformation temperature show a large scale structure in the micrometer range with high steps and parallel terraces. Terrace morphology is dominated by clusters with a typical size of about 10 nm. Nanometer steps can coexist with this cluster structure. With UHV-STM, terrace roughness based on cluster assembly is found to extend down to the nanometer scale. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Scanning tunneling microscopy of defects in quasiperiodically ordered surfaces
Authors:
Ebert PH. Chao KJ. Niu Q. Shih CK. Plummer EW. Urban K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):826-829, 2000 Dec 15.
Abstract:
We demonstrate that the limited coherence length of a one-dimensional quasiperiodically ordered superstructure of a thin Ag film on GaAs(110) surfaces is due to structural defects. We identify dislocations, phason defects, and domain walls. The domain walls end at dislocations, whose stress field is found to induce a wide distribution of oriented phason defects. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 18]
Title:
Oxidation of Al-Cu-Fe and Al-Pd-Mn quasicrystals
Authors:
Wehner BI. Koster U. Rudiger A. Pieper C. Sordelet DJ.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):830-833, 2000 Dec 15.
Abstract:
Oxidation of Al-Cu-Fe and Al-Pd-Mn quasicrystals as compared to related crystalline phases was studied in air at high temperatures, Parabolic rate constants at 840 degreesC were about 6 x 10(-12) g(2) cm(-4) s(-1) for icosahedral Al-Cu-Fe, but only 3 x 10(-13) g(2) cm(-4) s(-1) for cubic AlFe. The oxide layer formed on the icosahedral alloy was inhomogeneous with respect to the oxide growth morphology. Oxide compositions were studied by Auger electron spectroscopy (AES) and X-ray induced photo electron spectroscopy (XPS). The theta -Al2O3 layer on Al-Cu-Fe did not contain any quantities of Cu or Fe that were significant according to the analyses by AES and XPS. In an advanced oxidation stage the theta -Al2O3 layer was penetrated by alpha -Al2O3 nodules, which contained about 5% CU. Oxidation of Al-Pd-Mn quasicrystals was found to be strongly influenced by evaporation of Mn. Whereas the formation of delta -Al2O3 was observed at 800 degreesC on Al-Pd-Mn quasicrystals followed by growth of needle-like theta -Al2O3, oxidation of hot isostatically pressed (HIPed) specimens at 850 degreesC led to the formation of a theta -Al2O3 layer containing also extremely thin areas. The metallic AI(LMM) Auger peak observed in these areas was four times the oxidic AI(LMM) peak. Neither in the thick nor the thin oxide areas were Pd or Mn observed. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Characterization of a commercially produced Al-Cu-Fe-Cr quasicrystalline coating
Authors:
Sordelet DJ. Widener SD. Tang Y. Besser MF.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):834-837, 2000 Dec 15.
Abstract:
A commercially produced Al-Cu-Fe-Cr thermal spray cookware coating was characterized. Gas-atomized powders with a nominal composition of Al71Cu10Fe8.5Cr10.5 were apparently used to form the coatings. The coating is very uniform and contains a quasicrystalline icosahedral phase along with a second phase that is either a quasicrystalline decagonal phase or its nearly identical crystalline approximant. The phases show evidence of structural imperfection and appear to be in a highly transitional state, which is likely caused by the rapid cooling during thermal spraying. A large fraction of unmelted particles and microcracks were observed throughout the coating. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 6]
Title:
Real time study of the quasicrystal formation in annealed Al-Cu-Fe metallic multilayers
Authors:
Grenet T. Giroud F. Loubet C. Joulaud JL. Capitan M.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):838-841, 2000 Dec 15.
Abstract:
We present a study of the formation of the icosahedral Al-Cu-Fe quasicrystalline phase, when (Al, Cu, Fe) multilayers an heat treated. We first show that pure quasicrystalline films can be obtained in similar conditions, whatever the stacking sequence of the multilayers, even for quite thick elemental layers (hundreds or thousands of angstroms). Using synchrotron radiation diffraction, we, furthermore, study in real time the succession of intermediate phases forming during ramp heat treatments of the sandwiches. This study shows that in contrary to previous suggestions, the purl quasicrystalline phase can be prepared even when (Al, Cu) (and not (Al, Fe)) binary alloys form first. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Preparation of quasicrystalline thin films and fine particles by gas evaporation
Authors:
Takeda M. Sakai S. Kawasaki A. Hattori Y. Katoh M.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):842-845, 2000 Dec 15.
Abstract:
Quasicrystalline fine particles were prepared by gas evaporation using a tungsten heater as well as a pulsed laser. Particles obtained were spherical, and their average size increased with increasing gas pressure. When particles were produced by pulsed laser, their size was more uniform than those produced by use of a tungsten heater because fast expansion of vapor from a source leads to negligible convection. Utilization of the fine particles was also demonstrated. For example, fine particles were accelerated by gas flow and sprayed on a substrate. A film with metallic luster was formed at room temperature. This suggests that a dense film is obtained by the method. This technique will enable us to prepare quasicrystalline films with fine grain size at low temperature. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Scratch-induced surface microstructures on the deformed surface of Al-Cu-Fe icosahedral quasicrystals
Authors:
Wu JS. Brien V. Brunet P. Dong C. Dubois JM.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):846-849, 2000 Dec 15.
Abstract:
Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations of sintered Al-Cu-Fe icosahedral quasicrystal (IQC) have been carried out to understand the origin of some ductility previously noticed within tracks produced by standard tribological scratch tests. Transformation of the icosahedral phase to a modulated structure is shown and a transformation of the IQC to a bce phase has been found beneath the tracks. Twins and dislocations have also been observed. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 8]
Title:
Presence of oxygen in the structure of quasicrystalline phases in in-situ heated thin films of the Al-Co-Cr-Fe-O and Al-Mn-Si-O systems
Authors:
Reyes-Gasga J. Pita-Larranaga A. Mondragon-Galicia G. Valles-Gonzalez MP. Sanchez-Pascual A.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):850-853, 2000 Dec 15.
Abstract:
Quasicrystalline and crystalline phase transitions from amorphous thin films of the Al-Co-Cr-Fe-O and Al-Mn-Si-O systems have been studied in the case of in-situ heating treatment in the transmission electron microscope. Heating the films up to 800 degreesC, grains with quasicrystalline decagonal phase as structure were developed in both systems. The structural and chemical analysis indicates that, in both cases, the decagonal phase is an oxygen-containing quasicrystalline phase. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
TEM investigations on the growth of the icosahedric phase in AlMn films produced by simultaneous deposition of the components
Authors:
Kreutzer P. Anton R.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):854-858, 2000 Dec 15.
Abstract:
Thin AlMn films were grown by simultaneous deposition of the components on carbon substrates (a-C, HOPG). The films were characterized by transmission electron microscopy, electron diffraction and EDX. Depending on composition, deposition rate, and substrate temperature, different phases were found, which partly coexist. At substrate temperatures between 300 and 500 degreesC, and at a total deposition rate of as low as 0.01 nm/s, the pure icosahedric phase developed for Mn concentrations near 14 at.%, while higher rates caused segregation of Al6Mn crystallites at 400 degreesC. At lower Mn contents, Al was segregated, at higher deposition rates even for Mn contents up to 19 at.%. At Mn contents between 19 and 54 at.%, precipitates of Al8Mn5 were found. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Surface structural phase transitions on icosahedral Al-Pd-Mn
Authors:
Bolliger B. Erbudak M. Hensch A. Vvedensky DD.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):859-862, 2000 Dec 15.
Abstract:
The sputtering of alloy surfaces with Ar+ ions may change their chemical composition by preferentially removing particular atomic species. For the icosahedral quasicrystal Al-Pd-Mn this produces reversible surface phase transitions either to a cubic structure or to a decagonal quasicrystal, depending on the temperature. In both the cases, the original icosahedral structure is restored upon annealing. We discuss the orientation of these phases relative to the underlying icosahedral bulk and the processes responsible for the restoration of the icosahedral structure. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Bulk and surface evidence for the long-range spatial modulation of X-ray absorption in the Al-Pd-Mn quasicrystal at Bragg incidence
Authors:
Cappello G. Dechelette A. Schmithusen F. Decossas S. Chevrier J. Comin F. Formoso V. de Boissieu M. Jack T. Colella R. Lograsso TA. Jenks C.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):863-866, 2000 Dec 15.
Abstract:
An X-ray standing waves experiment was performed at the ID32 beam line of the ESRF on an Al-Pd-Mn quasicrystal with the X-ray beam at normal incidence. The X-ray photoemission core levels for each element were recorded to probe the surface. The drain current, i.e. the electron current from ground needed to neutralize the irradiated sample and to compensate the photoemitted electrons was also recorded as a bulk probe that integrates over all atoms of the sample. Within the two-beam approximation applied to quasicrystals, a simple analysis of this effect is proposed. This provides a direct-space illustration of the diffraction process in a quasiperiodic structure. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Electron energy loss spectroscopy investigation of volume and surface plasmons at the Al-Pd-Mn fivefold surface
Authors:
Schmithusen F. de Boissieu M. Boudard M. Chevrier J. Comin F.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):867-870, 2000 Dec 15.
Abstract:
We have measured the electron energy losses on different Al-Pd-Mn quasicrystal surface states established by low energy electron diffraction, X-ray photoelectron spectroscopy and Auger electron spectroscopy. On the well characterized and ordered Al-Pd-Mn quasicrystalline surfaces, the energy loss signal with an energy of incident electrons at 2 keV shows a strong peak at 16 eV and a satellite at about 33 eV, As the electron primary energy is decreased to 260 eV, an energy loss at 10.5 eV is clearly observed. A short ion bombardment (1 muA at 500 eV during 1 min) erases this loss at 10.5 eV which can be recovered by annealing at 800 K. All these observations are simply attributed to the existence of a bulk plasmon at about 16 eV and a surface plasmon at 10.5 eV. The ratio between these two energies is 1.52. This is quite close to the expected root2 from the classical plasmon model. On the crystalline partially annealed surface, a bulk plasmon is observed at about 16.5 eV. Oxygen-contaminated surface presents a bulk plasmon shifted towards higher energy of about 20 eV. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Decomposition of the five-fold surface of Al70Pd21Mn9 at elevated temperature
Authors:
Ledieu J. Muryn CA. Thornton G. Cappello G. Chevrier J. Diehle RD. Lograsso TA. Delaney D. McGrath R.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):871-873, 2000 Dec 15.
Abstract:
Several surface phases have previously been identified on the five-fold surface of the Al70Pd21Mn9 quasicrystal. Two of these, the clustered and terraced phases, have been discovered by scanning tunnelling microscopy (STM) studies. In this paper, we report STM images showing the existence of a new phase on this surface. This new topography was obtained by annealing the sample close to its melting point for several minutes. A model is presented which exhibits the main features of the structure. The unit-cell dimensions match those of the Al3Mn orthorhombic phase. Mechanical polishing followed by sputtering and annealing restored a pentagonal quasicrystalline surface indicating that the decomposition is a near-surface phenomenon. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Influence of grown-in voids on the structure of cleaved icosahedral Al-Pd-Mn quasicrystal surfaces
Authors:
Kluge F. Ebert P. Grushko B. Urban K.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):874-877, 2000 Dec 15.
Abstract:
We investigated the changes in structure induced by heat treatment of cleaved fivefold icosahedral Al-Pd-Mn quasicrystal surfaces close to, and far away from, grown-in voids. Areas far away from grown-in voids exhibit a roughening connected above 620 K with a decrease of the Al concentration, and above 820 K a recovery of the surface composition. No change of the surface structure can be detected close to grown-in voids in the same temperature range. The results indicate that the surface structure is influenced by the presence of vacancies in the quasicrystals and that vacancies enhance the surface roughening during heat treatment. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Scanning probe microscopy studies of the surface of decagonal quasicrystals in ambient conditions
Authors:
Drobek T. Heckl WM.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):878-881, 2000 Dec 15.
Abstract:
The surface preparation of decagonal Al-Ni-Fe and Al-Ni-Co quasicrystals using chemical polishing and mechanical fracture was investigated with regard to the requirements of scanning probe microscopy. Scanning tunnelling microscopy and atomic force microscopy studies of the morphology of fracture surfaces were carried out in ambient conditions, showing a typical dimension of 60 nm for surface corrugations. Oxidic corrosion of the quasicrystal surfaces was observed. On the oxide layer, the friction between the surface and the tip is reduced. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Atomic and electronic structure of five-fold i-Al-Pd-Mn surfaces
Authors:
Naumovic D. Aebi P. Schlapbach L. Beeli C.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):882-885, 2000 Dec 15.
Abstract:
Differently prepared surfaces of quasicrystalline icosahedral Al-Pd-Mn cut perpendicularly to a five-fold symmetry axis are analysed using angle-resolved photoemission in the X-ray and in the ultraviolet range of photon energies, in order to study the geometrical and electronic structure, respectively. Depending on the preparation, we find both, surfaces with crystalline structure, metallic character and surfaces with quasicrystalline structural fingerprints and a suppressed density of states at the Fermi level compatible with a pseudogap. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Localization of electrons and influence of surface states on the density of states in a tight-binding model on the Penrose tiling
Authors:
Zijlstra ES. Janssen T.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):886-889, 2000 Dec 15.
Abstract:
The distribution of participation numbers of electronic states in the vertex model of the Penrose tiling (PT) is calculated for a series of approximants and eight fixed values of the energy by means of contour integrations in the first Brillouin zone. Localization of electrons is seen to depend on energy. The local density of states at the surface of a small approximant of the PT is compared to the density of states (DOS) of the same approximant with periodic boundary conditions. The large difference between the two curves indicates that surface states might be responsible for the fact that experimentally surface sensitive techniques do not resolve spikes in the DOS of quasicrystals. The DOS of the (8,5) approximant of the three-dimensional PT is shown to be less spiky than expected. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 17]
Title:
Corrosion behavior of Al-Cu-Fe quasicrystals
Authors:
Rudiger A. Koster U.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 294(Special Issue SI):890-893, 2000 Dec 15.
Abstract:
For any application of quasicrystals or quasicrystalline coatings, e.g. for extruders, turbine blades or frying pans, corrosion resistance is of utmost importance. Therefore, corrosion of the quasicrystalline as well as related crystalline phases in the system Al-Cu-Fe was studied in particular at intermediate pH values in order to clarify the influence of the quasicrystalline structure. Salt spray tests were performed at 35 degreesC with several single phase materials in the Al-Cu-Fe system. Highest corrosion resistance was observed in crystalline aluminides AlFe as well as Al5Fe2 where a protective oxide film had developed. The quasicrystalline alloy as well as crystalline Al7Cu2Fe exhibit severe corrosion accompanied with the formation of Cu, Cu2O and Al(OH)(3). Anodic polarization of Al63Cu25Fe12 icosahedral quasicrystals reveal after a potentiodynamic scan in 0.1N NaOH the formation of an oxide layer consisting of FeO and Cu2O; there is only very little evidence for a phase transformation of the quasicrystal due to Al loss by selective corrosion. During further polarization in the passive region the oxide layer was observed to transform into probably higher oxidized states. The overall thickness of the oxide layer depends on the scan time, however, not on further polarization time at a distinct potential. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 5]
Title:
Effects of air plasma spraying parameters on the Al-Cu-Fe quasicrystalline coating layer
Authors:
Fleury E. Lee SM. Kim WT. Kim DH.
Source:
Journal of Non-Crystalline Solids. 278(1-3):194-204, 2000 Dec.
Abstract:
The focus of this study has been the effect of air plasma spray processing parameters on the characteristics of the Al-Cu-Fe quasicrystalline coatings. Key variables controlling the particle temperature and velocity and substrate temperature, such as the are current, spraying distance, powder flow rate, and preheating of the substrate surface, were of primary interest. Significant effects of the process parameters on the microstructure and subsequent mechanical properties of the coatings were observed. Process conditions favorable for the formation of coating layers with larger amount of quasicrystalline phase led to the higher values of the microhardness, although it resulted in a relatively large porosity level. The bonding strength was found to be slightly dependent on the spraying distance, powder feeding rate, and preheating of the substrate. However, the predominant variable appeared to be the coating thickness, where a significant reduction of the bonding strength was reported as the coating thickness was increased up to 100 mum. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Formation of icosahedral quasicrystal by crystallization of Zr-70(Ni, Cu, Pd)(30) amorphous alloys
Authors:
Zhang T. Inoue A. Matsushita M. Saida J.
Source:
Journal of Materials Research. 16(1):20-23, 2001 Jan.
Abstract:
An icosahedral phase was found to be formed as a primary precipitation phase in the crystallization process of binary Zr70Pd30, ternary Zr70Ni30-xPdx and Zr70Cu30-xPdx (x = 10 and 20 at.%) and quaternary Zr70Ni10Cu10Pd10 amorphous alloys. The maximum volume fraction of the icosahedral phase was nearly 100% for the 20% Pd alloys and the grain size tended to decrease in the range from 40 to 70 nm with increasing Pd content. No icosahedral phase was formed in the Zr-Ni-Cu alloys without Pd, and hence, the addition of Pd was concluded to be essential for the formation of the icosahedral phase in the Zr-based amorphous alloys. It also was noticed that the icosahedral phase was formed even in the binary Zr70Pd30 amorphous alloy. The icosahedral phase was in a metastable state and changes to equilibrium crystalline phases by annealing in the higher temperature range. The finding of the formation of the icosahedral phase in the binary alloy system allowed us to predict the future appearance of a number of icosahedral base alloys in other alloy systems. [References: 20]
Title:
Commensurate ferrimagnetic and incommensurate antiferromagnetic order in the ThCr2Si2-type phosphide PrFe2P2
Authors:
Reehuis M. Kotzyba G. Jeitschko W. Hofmann M.
Source:
Journal of Magnetism & Magnetic Materials. 221(3):307-316, 2000 Nov.
Abstract:
The nuclear and the magnetic structures of PrFe2P2 have been investigated by neutron powder diffraction. Complementary studies of the magnetic order were carried out on single crystals of PrFe2P2 using a SQUID magnetometer. The nuclear structure of this phosphide was confirmed to be isotypic with ThCr2Si2 (space group I4/mmm, Z = 2). No magnetic order could be found for the iron atoms down to 1.6K. The order of the praseodymium moments is antiferromagnetic with a most likely incommensurate sine-wave modulated magnetic structure from the Neel temperature T-N = 28(1)K down to 16 K. The propagation vector is k = (0, 0, 0.799(3)) and the moment direction is parallel to the tetragonal c-axis. Below 16 K the magnetic structure changes to a corresponding square-wave modulated structure. The presence of a net ferromagnetic component mu (exp) = 0 600(6) mu (B) along the c-axis indicates a commensurate ferrimagnetic structure with k = (0, 0, 4/5) and a magnetic unit cell of a x b x 5c, where the Pr moments have the spin sequence + - + + - + - + + -, + - ... along the tetragonal axis. The magnetic moment mu (exp) = 3.00(3)mu (B), is close to the theoretical moment of the free Pr3+ ion mu (eff) = 3.20 mu (B). From the SQUID data a second-order crystal field parameter of B-2(0) = - 5.8( +/- 0.2)K was deduced. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 39]
Title:
Au-197 and Fe-57 Mossbauer study of Au-substituted Al-Cu-Fe quasi-crystalline alloys
Authors:
Kyek A. Wagner FE. Palade P. Jianu A. Macovei D. Popescu R. Manaila R. Filoti G.
Source:
Journal of Alloys & Compounds. 313:13-20, 2000 Dec 15.
Abstract:
The substitution of up to 7 at. % of gold into icosahedral Al62Cu25.5Fe32.5, quasicrystals has been investigated by Au-197 and Fe-57 Mossbauer spectroscopy. Gold was found to replace copper on BC1 sites and to hybridise strongly with its Al neighbours. In addition, particularly at the higher Sold concentrations, the precipitation of small amounts of AuAl2 and beta -FeAl was observed. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Pulsed laser ablation of Al-Cu-Fe quasicrystals
Authors:
Teghil R. D'Alessio L. Simone MA. Zaccagnino M. Ferro D. Sordelet DJ.
Source:
Applied Surface Science. 168(1-4):267-269, 2000 Dec 15.
Abstract:
Quasicrystalline Al-65-Cu-23-Fe-12 targets have been ablated by a doubled Nd:YAG laser and deposited on silicon substrates. The results show evidence of distinct ablation mechanisms, which lead to different gas phase composition, as a function of the laser fluence. Films containing the quasicrystalline phase can be deposited only at fluences higher than about 6.5 J/cm(2) while at lower fluences the aluminium content exceeds the stoichiometric value. The films obtained by laser ablation of quasicrystalline Al-65-Cu-23-Fe-12 were compared with those obtained from the metallic alloy Al-70-Cu-20-Fe-10. The differences between the two systems could be explained on the basis of the low thermal conductivity of the quasicrystalline phase. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 7]
Title:
Overview of the thermoelectric properties of quasicrystalline materials and their potential for thermoelectric applications Book Editors Tritt TM
Authors:
Tritt TM. Pope AL.
Source:
RECENT TRENDS IN THERMOELECTRIC MATERIALS RESEARCH II. 70 PG. 77-115. 2001 [Figures] [Plates].
Title:
Effect of uniaxial pressures on the phase transitions in (NH4)BeF4 crystals
Authors:
Stadnik VI.
Source:
Crystallography Reports. 45(6):968-970, 2000 Nov-Dec.
Abstract:
The effect of uniaxial mechanical pressure along the principal crystallophysical directions on the phase transitions paraelectric-incommensurate-commensurate ferroelectric phases in (NH4)(2)BeF4 crystals is studied by the optical method. It is established that the G(x) and G(y) pressures applied along the x- and y-axes shift the phase transitions towards lower temperatures, whereas the G(z) pressure applied along the z-axis, towards higher temperatures. The possible existence of a triple point on the phase diagram is indicated. (C) 2000 MAIK "Nauka/Interperiodica". [References: 9]
Title:
Stable icosahedral quasicrystals in binary Cd-Ca and Cd-Yb systems
Authors:
Guo JQ. Abe E. Tsai AP.
Source:
Physical Review B. 62(22):R14605-R14608, 2000 Dec 1.
Abstract:
Stable icosahedral quasicrystals have been found in binary Cd-Ca and Cd-Yb systems in an as-solidified state as well as an annealed state. The icosahedral quasicrystals are identified to form at the composition of Cd85Ca15 and Cd84Yb16 An electron diffraction study confirmed that the icosahedral quasicrystals have a primitive lattice. Quasilattice parameters are 0.5731 nm for Cd85Ca15 and 0.5681 nm for Cd84Yb16.
Title:
Evolution of magnetic structures in NpAs1-xSex solid solutions
Authors:
Bombardi A. Bourdarot F. Burlet P. Sanchez JP. Vulliet P. Colineau E. Rebizant J. Wastin F. Lander GH. Vogt O. Mattenberger K.
Source:
Physical Review B. 62(22):14920-14927, 2000 Dec 1.
Abstract:
We report Mossbauer spectroscopy, magnetization, and neutron-diffraction measurements on four samples (x=0.05, 0.10, 0.15, and 0.20) in the mixed system NpAs1-xSex. The evolution of magnetic phase diagram vs the temperature T and the Se concentration x has been determined. Up to x=0.15, three distinct phase transitions an present. The first antiferromagnetic (AF) at T-m(x) is from paramagnetism to an incommensurate phase, the second, at Tc(x), is to a ferromagnetic (FM) phase, the third at T-m(x) is from pure FM to a mixed phase where AF and FM ordering coexist along perpendicular directions. The temperatures of the transitions are functions of Se concentration x. The incommensurate structure is described by a longitudinal amplitude modulated sinusoidal wave with a wave vector (k) over right arrow in the range (0 0 0.14-0.24) that is shifted toward the center of the Brillouin zone with increasing x. A squaring up of this wave, if present, is too small to be detected. At T-C(x) all Np sites become equivalent and the moment directions become [1 1 1]. Surprisingly, at T-m(x) AF interactions again become important and cause the moments to rotate and to align along [221] directions. Measurements in an external magnetic field up to 4.8 T have allowed us to determine the 1 (k) over right arrow nature of the AF component for T<T-m and to establish the moment directions. Increasing Se content reduces the incommensurate phase to a small range of ir and reduces the AF interactions. At x = 0.20 pure FM behavior, as shown by the magnetization measurements, is recovered. The saturated Np moments at low T decrease slightly with increasing x.
Title:
Commensurate and incommensurate spin fluctuations in YBa2Cu3O6+y
Authors:
Vos KK. Wu WC.
Source:
Physica C. 340(4):285-291, 2000 Dec 15.
Abstract:
We present an interpretation of the recent neutron data on the commensurate and incommensurate spin fluctuations found in YBa2Cu3O6+y based on a special configuration of the electronic dispersion and intervention from the d(x2-y2)-wave superconducting phase. The observed switch-over between the commensurate and incommensurate fluctuation spectra at the change of frequency or temperature is naturally accounted within this scenario. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Two-dimensional Penrose-tiled photonic quasicrystals: from diffraction pattern to band structure
Authors:
Kaliteevski MA. Brand S. Abram RA. Krauss TF. DeLa Rue R. Millar P.
Source:
Nanotechnology. 11(4):274-280, 2000 Dec.
Abstract:
We report measurements of the diffraction pattern of a two-dimensional photonic quasicrystal structure and use the set of plane waves defined by the diffraction pattern as the basis of a theoretical approach to calculate the photonic band structure of the system. An important feature of the model is that it retains the essence of the rotational and inflational properties of the quasicrystal at all levels of approximation: properties lost in approximate models which artificially introduce elements of periodicity. The calculated density of modes of the quasicrystals is found to display a weakly depleted region analogous to the bandgap that occurs in a periodic system. The calculated transmission spectra for different polarizations and directions of propagation show features that correlate with the behaviour of the density of modes.
Title:
Electronic structure of Al-Cu-Fe quasicrystals
Authors:
Mitrokhin YS. Belash VP. Klimova IN.
Source:
Journal of Structural Chemistry. 41(3):427-432, 2000 May-Jun.
Abstract:
The electronic structure of the Al-Cu-Fe quasicrystal is calculated by the TB-LMTO-ASA method in reciprocal space. The atomic structure of the quasicrystal is modeled by three approximants with 8, 16, and 40 atoms per unit cell. The following characteristics are calculated: partial densities of states for all components of the alloy, total density of states, and charge redistribution between the alloy components. The calculated densities of states are compared with the experimental data obtained by X-ray photoelectron spectroscopy. Good agreement between the experimental spectrum and the theoretical density of states curve is observed for the approximant with 40 atoms per unit cell. In other cases, the agreement is much worse. The calculated data are used to interpret the fundamental features of the experimental spectrum. The results of calculations show that the charge is transferred from transition metal to aluminum atoms, giving rise to d states of aluminum in the occupied part of the band.
Title:
A superspace approach to the composition flexible composite Ba1+x(CuxIr1-x)O-3 (x=0.2708)
Authors:
Zakhour-Nakhl M. Darriet J. Claridge JB. zur Loye HC. Perez-Mato JM.
Source:
International Journal of Inorganic Materials. 2(6):503-512, 2000 Dec.
Abstract:
The structure of Ba1+xCuxIr1-xO3, x = 0.2708 has been solved using the superspace formalism. The superspace group is R (3) over barm(00 gamma )0s with a=10.1490(8) Angstrom, c=2.7164(3) Angstrom and q=0.6354(2)c(1)* (Z=3). The structure can be described as a modulated columnar composite containing two subsystems [(Cu, Ir)O-3] and [Ba]. A sawtooth function was used to model the z-component of the atomic modulation functions. Each atomic sawtooth function is defined by its center (x) over cap (4) along the fourth dimension, its width (Delta) and the maximum amplitude of the displacive modulation (delta). The paper describes how, as a first approximation, the columns (CuxIr1-x)O-3 can be simply described by a single free parameter, based on the height difference of the prisms and octahedra that make up the transition metal chains. As a result, this superspace approach requires only a very small number of variables to be refined, compared to the conventional superstructure description. In addition, this paper presents a structural comparison of this structure with other members of this family and outlines how the structure determination is completely general and can be applied to other modulated composite structures of this family. The structural analysis presented in this paper is another demonstration of the efficiency of the 4-dimensional superspace formalism for describing the structures of so-called 'composition flexible' systems. (C) 2000 Elsevier Science Ltd. All rights reserved.
Title:
High-temperature in situ neutron powder diffraction study of monoclinic Tl2Ba2CuO6+delta
Authors:
Pederzolli DR. Attfield JP.
Source:
International Journal of Inorganic Materials. 2(6):533-541, 2000 Dec.
Abstract:
The monoclinic form of the Tl2Ba2CuO6+delta superconductor (F112/m symmetry) has been studied using high-resolution high-temperature in situ time-of-flight neutron powder diffraction. The amount of excess oxygen controls both the crystal structure and electronic properties: the as-prepared material (a=5.4412 Angstrom, b=5.5026 Angstrom, c=23.1523 Angstrom, gamma =90.127 degrees, delta =0.15) is non-superconducting, whereas the 700 K vacuum-annealed sample (a=5.4874 Angstrom, b=5.5288 Angstrom, c=23.3076 Angstrom, gamma =90.034 degrees, delta =0.11) is superconducting below T-c = 73 K. Thermal variations of atomic c axial displacements and bond valence sums demonstrate an electronic charge transfer from the TlO layers to the CuO2 planes. The peak widths of the Bragg reflections indicate microscopic strains in the c-axial direction, due to disordering of interstitial oxygen in the Tl2O2+delta bilayer, and in the ab-plane, due to the monoclinic and orthorhombic distortions, or static displacements of the Tl and O atoms in the TlO layers. Superstructural diffraction peaks due to an incommensurate structural modulation decrease in intensity with oxygen loss over the monoclinic-to-orthorhombic progression. (C) 2000 Elsevier Science Ltd. All rights reserved.
Title:
Superlattice structures between YBa2Cu3O7-delta and (Pb,Cu)Sr-2(Ca,Y)Cu2O7-delta high-T-c cuprates
Authors:
Hu SF. Liu RS. Jefferson DA.
Source:
International Journal of Inorganic Materials. 2(6):645-649, 2000 Dec.
Abstract:
A solid solution range exists between the systems YBa2Cu3O7-delta and (Pb,Cu)Sr-2(Ca,Y)Cu2O7-delta has been successfully synthesized. The microstructures across the solid solution are complicated by the presence of an incommensurate or commensurate modulation. However, the studies indicate unambiguously that the structural modulation is neither a necessary nor sufficient condition for superconductivity among the composition across the solid solution. The modulation may be controlling the cation/oxygen positions in the charge reservoir layers, originating from the different oxygen positions in the perovskite-type (123-type) YBa2Cu3O7-delta and the rock salt-type (1212-type) (Pb,Cu)Sr-2(Ca,Y)Cu2O7-delta. The discovery of the superlattice structures between YBa2Cu3O7-delta and (Pb,Cu)Sr-2(Ca,Y)Cu2O7-delta adds yet a further chemical dimension to these systems, and may extend the possible avenues of research not only for superconductivity but also for structural chemistry. (C) 2000 Elsevier Science Ltd. All rights reserved. [References: 9]
Title:
Special defects in quasicrystals
Authors:
Janot C. Loreto L. Farinato R.
Source:
Physica Status Solidi B-Basic Research. 222(1):121-132, 2000 Nov.
Abstract:
Beyond usual lattice defects such as vacancies or dislocations, various levels of disorder can be observed in quasicrystals due to phason defects. These defects may be the key factor for structure stability. They are also involved in phase transformations and influence the physical properties.
Title:
Incommensurate modulation of spin magnetic susceptibility in single band Hubbard model
Authors:
Citro R. Di Matteo S. Marinaro M.
Source:
Physica C. 341(Part 1):247-248, 2000 Nov.
Abstract:
By means of a cumulant expansion method, we investigate the incommensurate phase in the low doping region of the two dimensional single-band Hubbard model. We calculate the spin magnetic susceptibility as a function of doping and analyze the effect of a Van Hove singularity on a commensurate-incommensurate transition. A comparison with the experimental results of LSCO is discussed. [References: 6]
Title:
Low-temperature structure and hole localization in a one-dimensional chain-ladder composite material Sr0.4Ca13.6Cu24+yO41+z
Authors:
Isobe M. Onoda M. Ohta T. Izumi F. Hewat AW. Takayama-Muromachi E.
Source:
Physica C. 341(Part 1):465-466, 2000 Nov.
Abstract:
The low-temperature crystal structure of a composite crystal Sr0.4Ca13.6Cu24+yO41+z was determined by Rietveld analysis of neutron diffraction data using a superspace group approach. Distributions of localized holes was estimated by the bond-valence sum (BVS) calculation based on Cu-O interatomic distances. The maximum of the BVS wave of ladder-Cu (Cu1) sites was shown to fall with decreasing temperature. It indicates that holes are moved from the ladder to the chain at low temperature. [References: 8]
Title:
Role of structural modulation in the composite crystal (Sr2Cu2O3)(0.70)CuO2, "Sr14Cu24O41" with two-legged spin ladder
Authors:
Gotoh Y. Takahashi Y. Akimoto J. Mizuta S. Onoda M. Fujino H. Nagata T. Akimitsu J.
Source:
Physica C. 341(Part 1):469-470, 2000 Nov.
Abstract:
Modulated structure analysis of the mutually incommensurate composite crystal (Sr2Cu2O3)(0.70)CuO2 with two-legged spin ladder has been performed on the basis of (3+1)-dimensional superspace group approach. It has been found that the symmetry of (Sr2Cu2O3)(0.70)CuO2 Should be described by a centrosymmetric superspace group. In the modulated composite structure of (Sr2Cu2O3)(0.70)CuO2, displacive modulation of O atoms in the CuO2 chain is fairly large and plays an important role. Structural interaction between the CuO2 chain and the Cu2O3 ladder has been extensively investigated. [References: 4]
Title:
The incommensurate modulated structure of Sr14-xCaxCu24O41 as a function of temperature and composition
Authors:
Bougerol-Chaillout C. Bordet P. Berar JF. Darie C. Pachot S.
Source:
Physica C. 341(Part 1):479-480, 2000 Nov.
Abstract:
From synchrotron x-ray powder data collected on the BM16 beam line at ESRF, we have determined the incommensurate modulated structure of Sr14-xCaxCu24O41 (x=6, 13.6) from 10K to 300K, using the XND software. No major structural change occurs as a function of temperature. The comparison of the atomic positions and Cu-O interatomic distances between the two compounds indicates a charge transfer from the chain to the ladder sublattice as the Ca content increases. Furthermore, whereas the charges appear localized in both sublattices for the x=6 compound, those on the ladder sublattice of the x=13.6 metallic compound are delocalized. This behavior has been correlated with the degree of disorder induced by the substitution in the adjacent Sr/Ca layer. [References: 5]
Title:
34K superconductivity of Bi2201 system
Authors:
Zhang YH. Zhang JW. Tan S. Xu GJ.
Source:
Physica C. 341(Part 1):643-644, 2000 Nov.
Abstract:
In this paper it is analyzed that Bi2201 phase possesses strong incommensurate modulation structure while T12201 phase does not show any modulation characteristic, which is the origin of great difference between superconducting transition temperature of T12201 (T-c=90K) and Bi2201 (T-c=10K). Pb doping was performed to weaken the modulation structure of Bi2201 system, and then by adjusting the oxygen concentration to optimal level, the Tc of Bi2201 phase was improved to T-c(0) =34K (T-c(onset) =41K). [References: 6]
Title:
Commensurate and incommensurate structure of the neutron cross section in LaSrCuO and YBaCuO
Authors:
Kao YJ. Si QM. Levin K.
Source:
Physica C. 341(Part 4):2165-2166, 2000 Nov.
Abstract:
We study the evolution of the d-wave neutron cross-section with variable frequency omega and fixed T (below and above T-c) in two different cuprate families. The evolution from incommensurate to commensurate to incommensurate peaks is rather generic within an RPA-like scheme. This behavior seems tea be in reasonable accord with experiments, and may help distinguish between this and the "stripe" scenario.
Title:
The defect density waves in Zr0.98Sn0.02TiO4 single crystal with incommensurately modulated structures: Neutron diffraction study
Authors:
Park Y.
Source:
Europhysics Letters. 52(5):557-563, 2000 Dec.
Abstract:
We demonstrate the formation of defect-density waves in incommensurately modulated phases of Zr0.98Sn0.02TiO4 single crystal using neutron diffraction. A new state of the modulation structure can be explained in terms of a superposition of several modulation waves along a single crystallographic direction.
Title:
Non-spiky density of states of an icosahedral quasicrystal
Authors:
Zijlstra ES. Janssen T.
Source:
Europhysics Letters. 52(5):578-583, 2000 Dec.
Abstract:
The density of states of the ideal three-dimensional Penrose tiling, a quasicrystalline model, is calculated with a resolution of 10 meV. It is not spiky. This falsifies theoretical predictions so far, that spikes of width 10 20 meV are generic for the density of states of qua sicrystals, and it confirms recent experimental findings. The qualitative difference between our results and previous calculations is partly explained by the small number of k points that has usually been included in the evaluation of the density of states of periodic approximants of quasicrystals. It is also shown that both the density of states of a small approximant of the three-dimensional Penrose tiling and the density of states of the ideal two-dimensional Penrose tiling do have spiky features, which also partly explains earlier predictions.

Update: 6-Jan-2001

Title:
ac conductivity of the transparent states in Fibonacci chains
Authors:
Oviedo-Roa R. Perez LA. Wang CM.
Source:
Physical Review B. 62(21):13805-13808, 2000 Dec 1.
Abstract:
The electrical transport in quasiperiodic systems at zero temperature is studied by means of the Kubo-Greenwood formula within a tight-binding model. Their de conductivity is compared,with that obtained from the Landauer formula. Special attention is paid to the transparent states, whose transmittance is unity. The ac conductivity of these states shows a rapid diminution as a function of the frequency, in comparison with that of periodic systems. Minima in these conduction spectra are observed, which are located at (N-1)h omega =4n pi /t/ for the periodic case. Finally, the localization of the eigenstates is analyzed by looking at the Lyapunov exponent and the participation ratio. The latter is shown to be an inappropriate quantity to characterize the critically localized states.
Title:
Influence of phason flips, magnetic field, and chemical disorder on the localization of electronic states in an icosahedral quasicrystal
Authors:
Vekilov YK. Isaev EI. Arslanov SF.
Source:
Physical Review B. 62(21):14040-14048, 2000 Dec 1.
Abstract:
The influence of phasons, magnetic held, and substitutional chemical disorder on the electronic spectrum and wave functions of icosahedral quasicrystals is investigated by means of tight-binding approximation and level statistic method. The localization of the wave functions has been studied and we show that they are "critical." Phasons smear the electronic spectrum and reduce localization of the critical wave functions. A magnetic held shifts the boundaries of the spectrum, smears it, and lifts its degeneracy. At small magnetic fields (< 10 T) the wave functions also become less localized. The small degree of chemical substitutional disorder delocalizes the wave functions, but at greater degree the disorder leads to the Anderson type localization. The results show that the localization of electronic states in an ideal quasicrystal exists due to their coherent interference at the Fermi level which is caused by the specific symmetry and aperiodic long-range order.
Title:
Electronic structure of quasicrystalline surfaces: Effects of surface preparation and bulk structure
Authors:
Fournee V. Pinhero PJ. Anderegg JW. Lograsso TA. Ross AR. Canfield PC. Fisher IR. Thiel PA.
Source:
Physical Review B. 62(21):14049-14060, 2000 Dec 1.
Abstract:
We elucidate the nature of the surface electronic properties of quasicrystalline Al-Pd-Mn. We do this by using photoelectron and Auger electron spectroscopies, and by making a variety of comparisons-across types of bulk samples, and across methods of surface preparation. The main conclusions are these: (i) The narrow Mn 2P(3/2) core-level line observed in the icosahedral phase is a fingerprint of a suppression in the density of states (a pseudogap) at the Fermi level and is Pot unique to the quasicrystalline phase. It is also independent of the symmetry of the quasicrystalline surface. The Auger line shape is also affected and may be used as a fingerprint of a pseudogap. (ii) A similarly narrow Fe 2P3/2 core-level line characterizes the icosahedral Al-Cu-Fe quasicrystal, consistent with the expectation that the electronic structure is of general importance in the stabilization of icosahedral phases. (iii) In icosahedral AI-Pd-Mn, the pseudogap of the bulk is not retained up to the surface immediately after fracture, but can be restored by annealing, or by sputter annealing to sufficiently high temperatures. Assuming that the pseudogap reflects an electronic stabilization of the atomic structure, these results suggest that the heat-treated surfaces are more stable than the surface obtained by fracturing at room temperature.
Title:
Conduction-electron mediated H-1 nuclear spin-lattice relaxation in Ti45Zr38Ni17Hx icosahedral quasicrystals
Authors:
Stojanovich NA. Pfitsch DW. McDowell AF. Adolphi NL. Majzoub EH. Kim JY. Kelton KF.
Source:
Philosophical Magazine Letters. 80(12):763-776, 2000 Dec.
Abstract:
Nuclear magnetic resonance spin-lattice relaxation rates for H-1 in quasicrystalline Ti45Zr38Ni17Hx are presented as a function of temperature and hydrogen concentration x. The temperature dependence demonstrates that the relaxation is via interaction with conduction electrons. The relaxation rate is extremely sensitive to hydrogen content, with the rate changing by a factor of as munch as two for samples that differ in x by at most 2%. We interpret the changes in the conduction-electron-mediated spin-lattice relaxation as due to fine structure ('spikiness') in the electronic density rho (E) of states and estimate that rho (E) changes by 40% over an energy range of 75 meV.
Title:
Al-Fe-based bulk quasicrystalline alloys with high elevated temperature strength
Authors:
Kimura HM. Sasamori K. Inoue A.
Source:
Journal of Materials Research. 15(12):2737-2744, 2000 Dec.
Abstract:
An icosahedral (I) phase in coexistence with Al phase was found to precipitate in atomized Al93Fe3Cr2Ti2 and Al93Fe3Cr2V2 powders. The mixed structure was formed in the size fraction range up to 125 mum for the AI-Fe-Cr-V alloy, while the increase of the particle size to 125 IJ-m for the Al-Fe-Cr-Ti powder led to the precipitation of Al23Ti9. The replacement of Cr by Mn for the Al93Fe3Cr2Ti2 powder caused a mixed structure of Al + I + Al23Ti9 + Al6Mn even for the -26 mum powder. The formation tendency of the I-phase increased in the order of AI-Fe-Cr-V > Al-Fe-Cr-Ti > Al-Fe-Mn-Ti system. The decomposition temperature of the I-phase was about 790 K. The I particles were analyzed to have approximate compositions of Al84.2Fe7.0Cr6.3Ti2.5 and Al82.9Fe9.0Mn6.4Ti1.7, and the use of the analytical compositions enabled the formation of a mostly single I phase with an average grain size of 90 to 130 nm in the melt-spun state. Bulk I alloys in a cylindrical rod form were produced by extrusion of the atomized powders at 673 K and an extrusion ratio of 10. The extruded Al93Fe3Cr2Ti2 alloys exhibited good mechanical properties; i.e., sigma (0.2) of 550 MPa, sigma (UTS) of 660 MPa, and epsilon (p) of 4.5% at room temperature, and sigma (0.2) of 330 MPa, sigma (UTS) of 350 MPa, and epsilon (p) of 1.5% at 573 K. The high sigma (UTS) exceeding 350 MPa at 573 K was superior to the final target of the United States Air Force and hence the I-based Al93Fe3Cr2Fe2 alloy is expected to be extended as a new type of high elevated temperature strength material.
Title:
Formation of quasicrystals in Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass
Authors:
Wanderka N. Macht MP. Seidel M. Mechler S. Stahl K. Jiang JZ.
Source:
Applied Physics Letters. 77(24):3935-3937, 2000 Dec 11.
Abstract:
The formation of the quasicrystalline phase is observed as a first step of crystallization during isothermal annealing of the Zr46.7Ti8.3Cu7.5Ni10Be27.5 bulk glass. The structure of the quasicrystals and the sequence of phase formation have been investigated by x-ray powder diffraction and transmission electron microscopy. The structure of the quasicrystals is determined to be primitive icosahedral with a quasilattice constant of 4.779 Angstrom. The quasicrystals decompose into several intermetallic compounds after prolonged annealing at lower temperatures or in a short time period (less than 5 min) at high temperatures above 683 K. (C) 2000 American Institute of Physics. [S0003-6951(00)00949-9].
Title:
Modulated structure of La2Co1.7 from neutron and X-ray diffraction data
Authors:
Dusek M. Chapuis G. Schobinger-Papamantellos P. Wilkinson C. Petricek V. Tung LD. Buschow KHJ.
Source:
Acta Crystallographica - Section B, Structural Science. 56(Part 6):959-971, 2000 Dec.
Abstract:
An La2Co1.7 crystal was investigated by single-crystal neutron and X-ray diffraction. The neutron measurement was performed with a Laue white-beam technique at 15 K and room temperature, using a large position-sensitive detector. The X-ray measurements were obtained at room temperature from a CCD detector. The average structure of La2Co1.7 is hexagonal with cell parameters a = 4.885 (1), c = 4.273 (2) Angstrom and space group P6(3)/mmc. The satellites are located at the vertices of small hexagons perpendicular to the c axis. The modulated crystal was indexed assuming a sixfold twinned 3 + 1 dimensional structure with q = (alpha, 0, gamma). The structure was solved in the pseudoorthorhombic cell, with a = 8.461 (1), b = 4.885 (1), c = 4.273 (2) Angstrom, in the superspace group C2/m(alpha, 0, gamma). Owing to space requirements, the Co atoms cannot rt precisely into the octahedral sites of the La h.c.p. (hexagonal close packing). Instead, the Co atoms adopt a different periodicity, which is not commensurate with the periodicity of the La atoms. Two structure models have been refined in order to describe this behaviour, one using the sawtooth function for the positional modulation of cobalt and the other describing the structure as a composite system. The chemical composition calculated from the composite model is La2Co1.8(1) with the estimated standard deviation arising from the variation of q for different samples. In both models lanthanum is incommensurately modulated, while the position of cobalt seems not to be affected by any relative periodic displacement.
Title:
On the question of commensurability - The Nowotny chimney-ladder structures revisited
Authors:
Rohrer FE. Lind H. Eriksson L. Larsson AK. Lidin S.
Source:
Zeitschrift fur Kristallographie. 215(11):650-660, 2000.
Abstract:
A composite approach was used for the structure solution and refinement of two new Nowotny chimney-ladder phases, (Mo/Rh)(11)Ge-18 and (Mo/Rh)(13)Ge-22, found during investigations in the Mo/Rh/Ge system. The descriptions of the phases with conventional models (in I (4) over bar 2d (No. 122) with a = 5.885(2) Angstrom, c = 52.62(2) Angstrom for (Mo/Rh)(11)Ge-18 and a = 5.922(1) Angstrom, c = 62.88(4) Angstrom for (Mo/Rh)(13)Ge-22) led to high numbers of unobserved reflections, high parameter/reflection ratios and an unstable refinement in the case of (Mo/Rh)(13)Ge-22. Microscopy studies showed that the phases were in fact incommensurately modulated. Therefore, a composite model consisting of a rather stable diamond-like transition-metal substructure and a helical main-group-metal arrangement was developed. For the refinement of both phases, (Mo/Rh)(11)Ge-18 as well as (Mo/Rh)(13)Ge-22, the same model - same space group pair (W : P4/nnc : q (1) over bar q1 P : I4(1)/amd : 1 (1) over bar ss), same atom positions and modulation waves - was used. The refinements converged rapidly, showing that the presented structure model is very general, and may well be applicable to any Nowotny chimney-ladder phase.
Title:
An electron diffraction study of Cu ordering in CU2.33-xV4O11
Authors:
Withers RL. Rozier P.
Source:
Zeitschrift fur Kristallographie. 215(11):688-692, 2000.
Abstract:
A temperature-dependent electron diffraction study has been made of Cu ion ordering in the vanadium oxide bronze Cu2.33-xV4O11 Evidence is thereby found (at low temperature) for two distinct incommensurate modulations associated with the three-dimensional ordering of Cu ions in each of two distinct channel types which run along b between the V4O11 layers of the average structure. The primary modulation wave-vector associated with the first modulation q(1) = 1/2c*+ similar to0.12b* is associated with Cu ion ordering and associated structural relaxation in the first type of tunnel while the second type of modulation (characterized by the primary modulation wave-vector q(2) = +/- 1/2a*+ similar to0.16b*) is presumed to be associated with Cu ion ordering in the remaining, or tetrahedral, tunnel type. This second modulation only appears to con dense out at low temperature. [References: 7]
Title:
Thermodynamic and kinetic properties of an icosahedral quasicrystalline phase in the Al-Pd-Tc system
Authors:
Mikheeva MN. Panova GK. Teplov AA. Khlopkin MN. Chernoplekov NA. Shikov AA.
Source:
Physics of the Solid State. 42(12):2177-2183, 2000.
Abstract:
The properties of a quasicrystalline phase in the Al-Pd-Tc system are studied for the first time. X-ray investigations demonstrate that the quasicrystalline phase in the Al70Pd21Tc9 alloy has a face-centered icosahedral quasi-lattice with parameter a = 6.514 Angstrom. Annealing experiments have revealed that this icosahedral phase is thermodynamically stable. The heat capacity of an Al70Pd21Tc9 sample is measured in the temperature range 3-30 K. The electrical resistivity and magnetic susceptibility are determined in the temperature range 2-300 K. The electrical resistivity is found to be high (600 mu Omega cm at room temperature), which is typical of quasicrystals. The temperature coefficient of electrical resistivity is small and positive at temperatures above 50 K and negative at temperatures below 50 K. The magnetic susceptibility has a weakly paramagnetic character. The coefficient of linear contribution to heat capacity (gamma = 0.24 mJ/(g-atom K-2)) and the Debye characteristic temperature (Theta = 410 K) are determined. The origin of the specific features in the vibrational spectrum of the quasicrystals is discussed. (C) 2000 MAIK "Nauka/Interperiodica".
Title:
Direct 3D imaging of Al70.4Pd21Mn8.6 quasicrystal local atomic structure by x-ray holography
Authors:
Marchesini S. Schmithusen F. Tegze M. Faigel G. Calvayrac Y. Belakhovsky M. Chevrier J. Simionovici AS.
Source:
Physical Review Letters. 85(22):4723-4726, 2000 Nov 27.
Abstract:
Inverse x-ray fluorescence holography was used to explore the local atomic order of a nearly perfect quasicrystal with composition Al70.4Pd21Mn8.6. We have demonstrated the possibility of direct 3D imaging of the atomic decoration in a quasicrystal. We have obtained the average 3D environment of selected coordination shells around the Mn atoms. These results open the way to obtaining further and more complete :information about the various coordination shells in complex materials by measuring multiple energy x-ray holograms at different sites.
Title:
New classes of quasicrystals and marginal critical states
Authors:
Fujita N. Niizeki K.
Source:
Physical Review Letters. 85(23):4924-4927, 2000 Dec 4.
Abstract:
One-dimensional quasilattices, namely, the geometrical objects that represent quasicrystals, are classified into mutual local-derivability (MLD) classes. Besides the familiar class, there exist an infinite number of new MLD classes, and different MLD classes are distinguished by the inflation rules of their representatives. It has been found that electronic properties of a new MLD class are characterized by the presence of marginal critical states, which are considered to be nearly localized states.
Title:
Crystal structures of {P(CH3)(4)}(2)CuCl4 in phases I, II and III
Authors:
Nishijima Y. Mashiyama H.
Source:
Journal of the Physical Society of Japan. 69(11):3581-3588, 2000 Nov.
Abstract:
The crystal structures of {P(CH3)(4)}(2)CuCl4 in phase I, II and III are determined by single crystal X-ray diffractometry. The phase I is isomorphous to the normal phase of {N(CH3)(4)}(2)ZnCl4- type crystal, though the CuCl4 tetrahedron is fairly distorted from the regular tetrahedral shape. The incommensurate phase II is refined by the use of the 4-dimensional superspace group. The second harmonics of the modulation is comparably strong as the primary modulation at 360 K. The incommensurate structure is compared with the room temperature phase III; where the cell dimension along the c axis is tripled. The structural transition sequence is discussed in connection to the size of tetrahedral monovalent cation.
Title:
Fermi surface and electronic structure of incommensurate charge-density wave systems
Authors:
Seibold G. Castellani C. Di Castro C. Grilli M.
Source:
Journal of Superconductivity. 13(6):911-912, 2000 Dec.
Abstract:
We study the single-particle spectra of a model that shows an incommensurate charge-density wave (CDW) instability arising from the competition between phase separation and long-range Coulomb interactions. Starting from an open Fermi surface, we find that the resulting CDW is oriented along the (1, 0) and (or) (0, 1) direction, which allows for a purely one-dimensional (1D) or a two-dimensional (2D) eggbox type charge modulation. In both cases, the van Hove singularities are substantially enhanced, and the spectral weight of Fermi surface states near the M points tends to be suppressed. Remarkably, a leading edge gap arises near these point, which, in the eggbox case, leaves finite arcs of the Fermi surface gapless. [References: 8]
Title:
Quantification of the interlayer charge transfer, via bond valence calculation, in 2D misfit compounds: The case of (Pb(Mn, Nb)(0.5)S-1.5)(1.15)NbS2
Authors:
Deudon C. Lafond A. Leynaud O. Moelo Y. Meerschaut A.
Source:
Journal of Solid State Chemistry. 155(1):1-8, 2000 Nov 15.
Abstract:
The new layered misfit sulfide of the 1.5Q/1H homologue type, (Pb(Mn, Nb)(0.5)S-1.5)(1.15)NbS2, has been synthesized. Electron probe microanalysis gives the chemical formula (Pb1.02Mn0.33Nb0.16S1.50)(1.15)NbS2, indicating Nb incorporation in the rock-salt-type part (Q layer). Its crystal structure has been solved through a superspace approach: orthorhombic symmetry, superspace group Cm2m(alpha 00), cell parameters a = 3.326(1), b = 5.788(1), c = 14.326(3) Angstrom, q vector (0.5744(2),0,0); R = 2.27% for 688 reflections and 36 variables. Nb-for-Mn substitution in the central part of the Q layer is clearly proved. Bond valence calculation on this compound, compared to some other misfit compounds, makes it possible to evaluate the charge transfer that governs the stability of such composite materials. This calculation, which takes into account the modulation of Pb-S-H bondings at the Q/H interface through the superspace approach, shows that the transfer depends on the nature of cations in the Q layer. This leads to a formal oxidation state for Nb, within the H layer, varying between similar to3 and 3.6. (C) 2000 Academic Press.
Title:
High-temperature incommensurate-to-commensurate phase transition in the Bi2MoO6 catalyst
Authors:
Buttrey DJ. Vogt T. White BD.
Source:
Journal of Solid State Chemistry. 155(1):206-215, 2000 Nov 15.
Abstract:
The temperature-dependent behavior of the low- and intermediate-temperature phases of gamma -Bi2MoO6 were investigated, As revealed by high-resolution neutron and synchrotron powder diffraction as well as electron diffraction, the low-temperature Aurivillius phase shows a previously undetected incommensurate modulation: along the pseudo-tetragonal a (q(a) = 0.5626(2)) and c (q(c) = 0.2844(2)) axes, A reversible incommensurate-to-commensurate phase transition to the intermediate-temperature phase occurs near 840 K, before irreversibly transforming near 880 K into the fluorite-related high-temperature polymorph described in detail by two of us in an earlier study (Buttrey et al,, J, Solid State Chem. 111, 118-127 (1994)), (C) 2000 Academic Press.
Title:
Elastic theory of 1D-quasiperiodic stacking of 2D crystals
Authors:
Peng YZ. Fan TY.
Source:
Journal of Physics-Condensed Matter. 12(45):9381-9387, 2000 Nov 13.
Abstract:
A general solution of the elastic fields in 1D hexagonal quasicrystals with point groups 6mm, 62(h)2(h), (6) over bar m2(h) and 6/m(h)mm is given in terms of four 'harmonic' functions F-i (i = 1, 2, 3, 4). Then we consider the problem of a circular crack embedded in an infinite ID hexagonal quasicrystal of point group 6mm. The results obtained in this paper automatically reduce to those in the classical elasticity theory when the phason held is absent.
Title:
The cation-vacancy ordering transition in dehydrated Na-6 sodalite
Authors:
Campbell BJ. Delgado JM. Cheetham AK. Iversen BB. Blake NP. Shannon SR. Latturner S. Stucky GD.
Source:
Journal of Chemical Physics. 113(22):10226-10239, 2000 Dec 8.
Abstract:
Variable-temperature synchrotron x-ray powder diffraction data from dehydrated Na-6[Al6Si6O24] reveal a structural phase transition that involves both the commensurate ordering of the extra-framework Na cations and a one-dimensional incommensurate modulation of the framework. Peak splittings and superlattice reflections implicate an orthorhombically-distorted volume-doubled supercell at room temperature (a=12.9432 Angstrom, b=12.8403 Angstrom, and c=9.1372 Angstrom) similar to(root(2) over bara x root(2) over bar axa). These data also included additional superlattice peaks associated with an incommensurate long-period modulation with tau=(3/2 1/2 1)/8.9. All unique orderings of the 12 Na cations among the 16 available sites of the commensurate supercell are enumerated. A unique solution is identified that minimizes the structural energy and accounts for the observed superlattice peaks. Rietveld analysis reveals a significant Pauling "partial-collapse" tilt angle in the cation-ordered phase, that appears to decrease with increasing temperature. (C) 2000 American Institute of Physics. [S0021-9606(00)00844-8].
Title:
Alloys - A stable binary quasicrystal
Authors:
Tsai AP. Guo JQ. Abe E. Takakura H. Sato TJ.
Source:
Nature. 408(6812):537-538, 2000 Nov 30.
Title:
Chemical, structural and electrical characterizations in the BIZNVOX family
Authors:
Vernochet C. Vannier RN. Huve M. Pirovano C. Nowogrocki G. Mairesse G. Van Tendeloo G.
Source:
Journal of Materials Chemistry. 10(12):2811-2817, 2000.
Abstract:
The BIZNVOX solid solution domain, stable at room temperature, has been determined. alpha-, beta- and gamma -type compounds can be stabilized depending on the x and y values of the general Bi-2(V1 - x - yZnxBiy)O-z formula. The alpha- and beta -type phases exhibit incommensurate modulations studied by X-ray powder diffraction. The lock-in of their wave vectors on the three-fold and two-fold superstructures of the undoped alpha- and beta -Bi4V2O11, respectively, is clearly evidenced. SAEDand HREM observations reveal very complex disorder correlated with the attractive oxide ion conductivity of these materials.
Title:
Growth of entropy stabilized quasicrystals
Authors:
Kalugin P.
Source:
European Physical Journal B. 18(1):77-84, 2000 Nov.
Abstract:
A simplified version of the model by Elser and Joseph for the process of growth of an entropicaily stabilized, two-dimensional quasicrystal with no dynamics in the bulk, is proposed. The phason fluctuations are modeled by a scalar field on a periodic lattice. The choice of the master equation for the growth is restricted by the requirement that its detailed balance solution describes the equilibrium fluctuations of the field with a quadratic Hamiltonian. The model is parametrized by the chemical potential bias delta mu and the microscopic surface tension coefficient sigma. The phase diagram of the system on the plane (sigma, delta mu) shows several distinct regimes of growth, separated by relatively narrow transition zones. Within the regions corresponding to these regimes, the phason fluctuations do not depend on delta mu and sigma. Analytic expressions for the spectra of phason fluctuations are obtained and confirmed by numerical simulation.
Title:
Proceedings of the Workshop on Quasicrystal Structure Analysis - a satellite meeting to ICQ7 - Stuttgart, Germany, September 24(th)-25(th), 1999 - Preface
Authors:
Beeli C. Steurer W.
Source:
Zeitschrift fur Kristallographie. 215(10):II, 2000.
Title:
Structure determinations for random-tiling quasicrystals
Authors:
Henley CL. Elser V. Mihalkovic M.
Source:
Zeitschrift fur Kristallographie. 215(10):553-568, 2000.
Abstract:
How, in principle, could one solve the atomic structure of a quasicrystal, modeled as a random tiling decorated by atoms, and what techniques are available to do it? One path is to solve the phase problem first, obtaining the density in a higher dimensional space which yields the averaged scattering density in 3-dimensional space by the usual construction of an incommensurate cut. A novel direct method for this is summarized and applied to an i(ALPdMn) data set. This averaged density falls short of a hue structure determination (which would reveal the typical unaveraged atomic patterns.) We discuss the problematic validity of inferring an ideal structure by simply factoring out a "perp-space" Debye-Waller factor, and we test this using simulations of rhombohedral tilings. A second, "unified" path is to relate the measured and modeled intensities directly, by adjusting parameters in a simulation to optimize the fit. This approach is well suited for unifying structural information from diffraction and from minimizing total energies derived ultimately from ab-initio calculations. Finally, we discuss the special pitfalls of fitting random-tiling decagonal phases.
Title:
X-ray structure determination of quasicrystals - Limits and potentiality
Authors:
Haibach T. Cervellino A. Estermann MA. Steurer W.
Source:
Zeitschrift fur Kristallographie. 215(10):569-583, 2000.
Abstract:
State-of-the-art X-ray diffraction techniques allow quasicrystals to be characterised quantitatively. Based on two-dimensional scans of Bragg reflections with high spatial resolution twinned approximants or nanodomain structures can be reliably distinguished from quasiperiodic average structures. Linear phason strain as well as mosaicity can directly be detected in situ under non-ambient conditions. Accurate cell parameters can be obtained. The experimental limitations are discussed. Methods to determine the space group and the optimum n-dimensional unit cell are shown. The phases of the reduced structure amplitudes can be obtained by several techniques. Highly resolved electron density distributions are derived from a combination of Patterson deconvolution techniques with maximum entropy methods. Special emphasis is put on the achievable resolution of experimentally determined electron density distributions. Based on a subtle n-dimensional atomic surface modelling the structure can be described in an accurate way according to the standards in conventional crystallography. All relevant structural parameters are determined quantitatively by an n-dimensional structure refinement. Different structure models are distinguished by their likelihood. The reliability of a quantitative structure determination is examined.
Title:
Towards the real structure of quasicrystals and approximants by analysing diffuse scattering and deconvolving the Patterson
Authors:
Estermann MA. Lemster K. Haibach T. Steurer W.
Source:
Zeitschrift fur Kristallographie. 215(10):584-596, 2000.
Abstract:
Methods based on X-ray area detectors are presented for acquiring and analysing single-crystal X-ray diffraction data from quasicrystals and approximants. These methods are complementary to high-resolution diffractometry and fully exploit the possibilities of modern two-dimensional X-ray detector systems (imaging plates and charge coupled devices) such as the on-line read-out capability and the possibility to collect large volumes of reciprocal space in a quantitative and rapid way. Ln contrast to a classical point detector, area detectors allow the measurement of a very large number of Bragg reflections in a reasonable time scale, as is shown with a large unit-cell periodic approximant in the Al-Co-Ni alloy system. For large approximants exhibiting strong pseudosymmetry, direct methods for structure solution usually fail. Recently implemented Patterson deconvolution techniques are shown to succeed. The extension of techniques for area detectors - beyond the standard application of collecting integrated Bragg intensities - to the quantitative acquisition of continuous and diffuse scattering data is presented with particular emphasis on quasicrystals. One of the key techniques is the quantitative reconstruction of undistorted layers and volumes in reciprocal space. This is crucial for developing and comparing possible models for structural disorder in quasicrystals. Examples for decagonal Al-Co-Ni and icosahedraI Al-Mn-Pd are given in respect to possibilities and limitations of X-ray area detectors.
Title:
Structure determination of quasicrystals and neutron scattering
Authors:
de Boissieu M.
Source:
Zeitschrift fur Kristallographie. 215(10):597-605, 2000.
Abstract:
We review the use of neutron scattering in the structure determination of quasicrystals. The contrast between X-ray and neutron cross-section gives a useful complementary information. When feasible, contrast variation techniques allow to disentangle the different atomic contribution. Diffuse scattering studies are also simplified, thanks to the possibility of an energy analysis. We discuss results obtained in the case of the i-AlPdMn phase.
Title:
Quasicrystal structures studied by high-resolution transmission electron microscopy
Authors:
Beeli C.
Source:
Zeitschrift fur Kristallographie. 215(10):606-617, 2000.
Abstract:
Structural investigations, using a transmission electron microscope (TEM), have been highly beneficial for the analysis of icosahedral and decagonal quasicrystals. Many structural properties of quasicrystals can be recognized and quantified by electron diffraction patterns alone. Nevertheless, a much more complete understanding of the real structure of quasicrystals can be achieved by the analysis of high-resolution transmission electron microscopy (HRTEM) images. Compared to diffraction- based techniques, HRTEM offers several advantages, however, special points which must be considered in the interpretation of HRTEM images will be discussed. For the case of 2-dimensional quasicrystals, e.g. the decagonal phases, HRTEM images can directly reveal the (projected) atomic structure as well as the long-range translational order. This is possible because 2-dimensional quasicrystals are periodic along one direction and the atoms thus form periodic atom columns as in crystalline materials. Therefore, the imaging theory established for crystals can similarly be applied to electron micrographs of 2-dimensional quasicrystals taken with the electron beam parallel to the unique periodic axis. It is evident, that possible limitations due to projection effects along the electron beam direction have to be considered in the interpretation of the images. HRTEM images of decagonal quasicrystals have frequently been employed to differentiate between disorder and order, i.e., to infer the difference between a random and perfect quasiperiodic tiling, respectively.
Title:
Structural studies on decagonal quasicrystals using the HAADF-STEM and CBED methods
Authors:
Saitoh K. Tsuda K. Tanaka M. Tsai AP.
Source:
Zeitschrift fur Kristallographie. 215(10):618-626, 2000.
Abstract:
The applications of the high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) and convergent-beam electron diffraction (CBED) methods to decagonal quasicrystals and its approximant are presented by giving some examples. The HAADF method can show the atomic arrangement mainly composed of transition metal (TM) atoms in Al-TM systems. The CBED method can determine the super point and space-groups of quasicrystals, and furthermore can be used to refine the structural parameters.
Title:
Anisotropic nonlinear elastic properties of an icosahedral quasicrystal
Authors:
Duquesne JY. Perrin B.
Source:
Physical Review Letters. 85(20):4301-4304, 2000 Nov 13.
Abstract:
We show that the nonlinear behavior of transverse acoustic waves can reveal the anisotropic structure of an icosahedral quasicrystal, at the macroscopic level. We report experiments performed in i-Al-Pd-Mn. We observe that a primary transverse acoustic wave can generate a second harmonic transverse acoustic wave. We also observe a specific relation between the polarization directions of those waves. These observations are manifestations on a macroscopic scale of the long-range order in
Title:
Ground states of a generalized Frenkel-Kontorova model
Authors:
Xu AG. Wang GR. Chen SG. Yang ZR.
Source:
Communications in Theoretical Physics. 34(3):419-432, 2000 Oct 30.
Abstract:
We studied the modulated structures and commensurate-incommensurate transitions in a generalized Frenkel-Kontorova (FK) model where the chain is composed of three kinds of atoms. For the classical ground states, the phase diagram and the phonon spectrum show the multi-atomic effects. For the quantum ground states, the multi-atomic effects are reflected by the distribution of atoms in external potential, the phase diagram, the correspondences between the ground states and the orbits of the area-preserving maps, as well as the phonon spectrum and coherence length. For the most incommensurate structure, the critical point K-c at which the transition by breaking of analyticity occurs does not vary monotonically with A. For the case of mu (A) = mu (B) = 1 and mu (C) = 2, with the increasing of (h) over bar, the critical point K-c first decreases, then increases. The minimum value of K-c occurs at nearly (h) over bar = 0.035. When K < K-c, the phonon gap <Omega>(G) = 0 and the Lyapunov exponent gamma = 0, the system is in the sliding state. When K > K-c, the phonon gap and the Lyapunov exponent show great difference from those of the standard FK model.
Title:
Alloys - A stable binary quasicrystal
Authors:
Tsai AP. Guo JQ. Abe E. Takakura H. Sato TJ.
Source:
Nature. 408(6812):537-538, 2000 Nov 30.
Title:
Chemical, structural and electrical characterizations in the BIZNVOX family
Authors:
Vernochet C. Vannier RN. Huve M. Pirovano C. Nowogrocki G. Mairesse G. Van Tendeloo G.
Source:
Journal of Materials Chemistry. 10(12):2811-2817, 2000.
Abstract:
The BIZNVOX solid solution domain, stable at room temperature, has been determined. alpha-, beta- and gamma -type compounds can be stabilized depending on the x and y values of the general Bi-2(V1 - x - yZnxBiy)O-z formula. The alpha- and beta -type phases exhibit incommensurate modulations studied by X-ray powder diffraction. The lock-in of their wave vectors on the three-fold and two-fold superstructures of the undoped alpha- and beta -Bi4V2O11, respectively, is clearly evidenced. SAEDand HREM observations reveal very complex disorder correlated with the attractive oxide ion conductivity of these materials.
Title:
Growth of entropy stabilized quasicrystals
Authors:
Kalugin P.
Source:
European Physical Journal B. 18(1):77-84, 2000 Nov.
Abstract:
A simplified version of the model by Elser and Joseph for the process of growth of an entropicaily stabilized, two-dimensional quasicrystal with no dynamics in the bulk, is proposed. The phason fluctuations are modeled by a scalar field on a periodic lattice. The choice of the master equation for the growth is restricted by the requirement that its detailed balance solution describes the equilibrium fluctuations of the field with a quadratic Hamiltonian. The model is parametrized by the chemical potential bias delta mu and the microscopic surface tension coefficient sigma. The phase diagram of the system on the plane (sigma, delta mu) shows several distinct regimes of growth, separated by relatively narrow transition zones. Within the regions corresponding to these regimes, the phason fluctuations do not depend on delta mu and sigma. Analytic expressions for the spectra of phason fluctuations are obtained and confirmed by numerical simulation.

Update: 1-Dec-2000

Title:
The theory of spatiotemporal pattern in nonequilibrium systems [Review]
Authors:
Olemskoi AI. Klepikov VF.
Source:
Physics Reports-Review Section of Physics Letters. 338(6):571-677, 2000 Nov.
Abstract:
Stationary states and evolution of the spatially periodic and self-similar structures arising in the course of phase transformations are considered. Stationary inhomogeneous structures are studied in the framework of the thermodynamic approach, investigation of the dynamics of their formation is based on the field representation which makes it possible to describe behavior of the most probable values of stochastic variables. In the framework of unified conceptions, peculiarities of the behavior of thermodynamic, self-organizing and stochastic systems with multiplicative noise are studied. The concepts of the fractional integral and derivative are introduced which allow one to write the equation of evolution of an arbitrary system in a general form. Investigation of stationary inhomogeneous distributions is carried out by using the two- and one-component representations of the order parameter. A qualitative analysis based on the method of phase plane shows that under the transition from the disordered phase into the ordered one the harmonic distribution with a short period transforms into the step-like distribution with a long period. In the framework of the eta (4)-model the stationary distribution of the order parameter reduces to the elliptic cosine and passing to the more complicated eta (6)-model results in the fact that the (approximate) solutions will be the elliptic sine, cosine and delta of amplitude. The first of them describes the order parameter distribution, the second describes the antiphase boundaries and the form of the last one is defined by the two first ones. Creation of incommensurate long-period structures in ordered alloys is connected with the attraction of antiphase boundaries via the optical waves of atomic displacements. On the basis of the synergetic approach it is shown that, with increasing the concentration of the antiphase boundaries the optical-phonon exchange leads to stabilization of the long-period structure. The value of the force of the coherent bond between the boundaries is found. It is shown that creation of the long period is realized by the mechanism of phase transition of the first order. When describing the kinetics of transition into the stationary state, the simplest picture is first studied, in the framework of which the phase transition is represented by a single-order parameter. It is shown that under the parallel regime of phase transition the Debye character of relaxation is transformed into slowly decreasing dependencies of the type of the stretched Kohlrausch exponent, power, logarithmic and double logarithmic ones. The synergetic picture of phase transformations of the first and second orders is investigated, which is represented by the order parameter, conjugate field and control parameter. Analytical and numerical investigations of phase portraits have been carried out in different kinetic regimes. It is shown that owing to the critical increase of the times of relaxation of the order parameter and conjugate field the oscillatory behavior is realized if the initial relaxation time of the control parameter is much larger than its value for other degrees of freedom. In the opposite case, all the phase trajectories quickly converge to the universal zone. For a stochastic system with additive noise a self-consistent evolution of the order parameter and the amplitude of conjugate field fluctuations is considered. Investigation of the corresponding phase portraits shows that, depending on the ratio of the inhomogeneity scales, stable and unstable stationary states are possible. When passing to the multiplicative noise with an amplitude depending on the order parameter, the phase plane is divided into isolated domains of large, intermediate and small values of the order parameter. In the first one, in the course of time the trajectories converge to infinite values and the probability of their realization is vanishing. In the intermediate domain, the configurational point tends to the attractive node which corresponds to the stationary ordered state. Finally, in the region of small values of the order parameter, an absorbing state can arise where the system behaves in a deterministic way. The investigation of quasiperiodic distribution of the type which is observed in quasicrystals is based on the fact that it is generated by the same class of mapping, as incommensurate structures: the long-period structures correspond to points of the monofractal set which is contained in the,given multifractal to the maximum extent; the quasicrystal sequence is the most rarely realized. A regular method for constructing this sequence is described and the distribution of wave vectors for which the radiation penetrating the quasicrystal yields the diffraction maxima is found. The mode-locking phenomenon is considered, whose spectra of frequencies and wave vectors represent "the devil's staircase". In the framework of fractal ideology, the processes are considered which evolve in space-time in a non-local way. It is shown that in the presence of the non-perfect memory the generalized force leads to a flux which is expressed in the form of a fractional integral. Accordingly, increase of the share of dissipative channels leads to the transformation of the wave-type equation into the heat conduction equation. With decrease of the number of channels with the conserved order parameter, a smooth decrease of the order of the spatial derivative occurs. The method developed allows one to obtain not only a linear fractional-order equation of motion, but also to generalize it for the non-linear case. The latter case contains, in particular, such expressions, as the non-linear Schrodinger equation, the Korteweg-de Vries and sine Gordon equations. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Solving the crystallographic phase problem in i(AlPdMn)
Authors:
Brown KS. Avanesov AA. Elser V.
Source:
Physical Review Letters. 85(19):4084-4087, 2000 Nov 6.
Abstract:
We apply a new technique for ab initio phase determination [Acta Crystallogr. Sect. A 55, 48 (1999)] to solve for the average structure of the icosahedral (i) phase of AlPdMn. After an introduction to the crystallographic phase problem and a description of the method, we present a brief report of our findings for the structure of i(AlPdMn). Despite the use of data from extremely high quality samples, we find strong evidence of disorder in the structure, lending support to the random tiling model of quasicrystal stabilization.
Title:
Epitaxial crystalline film with psuedo-tenfold symmetry formed by Au-deposition on a decagonal Al72Ni12Co16 quasicrystal
Authors:
Shimoda M. Sato TJ. Tsai AP. Guo JQ.
Source:
Physical Review B. 62(17):11288-11291, 2000 Nov 1.
Abstract:
We have succeeded in growing an epitaxial film on a quasicrystal. Au-depositions on a quasiperiodic surface of a decagonal Al-Ni-Co quasicrystal gave rise to an epitaxial film with a tenfold symmetry, i.e., a layer of multiply twinned AuAl2 crystals with (110)-oriented surfaces and azimuthal orientations corresponding to the tenfold symmetry of the substrate.
Title:
Nature of the incommensurate-paraelectric transition: A two-dimensional exchange-difference NMR study
Authors:
Muntean L. Ailion DC.
Source:
Physical Review B. 62(17):11351-11354, 2000 Nov 1.
Abstract:
Rb-87 two-dimensional exchange-difference NMR was used to study collective motions in the incommensurate (I) and paraelectric (P) phases of Rb2ZnCl4, which elucidate the nature of the I-P transition. We measured the cross-peak frequency displacement vs mixing time and observed a gradual increase towards an asymptotic value in the I phase but a sudden jump to the final value in the P phase. The P phase results are identified as normal modes arising from simultaneous displacement of the Rb ions and rotations of the ZnCl4 between two sites, and these modes freeze out in the I phase to become the modulation wave.
Title:
Polarization-flip phase transitions under an electric field in displacive systems with competing periodicities
Authors:
Perez-Mato JM. Aramburu I. Quilichini M. Ivantchev S. Hernandez O.
Source:
Physical Review B. 62(17):11418-11422, 2000 Nov 1.
Abstract:
As an alternative to the usual Landau-Ginzburg-type continuous field approximation, a free energy featuring two anticrossed phonon branches and defined in a discrete lattice is proposed for dealing with modulated phases with inherent discrete lattice effects. Using this approach, it is shown that, at some threshold electric (or conjugate) field, phases may appear in the phase diagram of solids having several modulated phases of different periods. These phases are the result of the sign-reversal of a particular polar local mode in a spinlike modulation of the order parameter, and have indeed been recently observed in the modulated ferroelectric betaine calcium chloride dihydrate (BCCD). This type of field-driven polarization-flip transition had not been anticipated by previous theoretical approaches, including microscopic ones such as the ANNNI model. The model proposed also explains the quite peculiar topological features of the phase diagram under the electric field observed in BCCD.
Title:
Glasslike lattice vibrations in the quasicrystal Al72.1Pd20.7Mn7.2
Authors:
Thompson E. Vu PD. Pohl RO.
Source:
Physical Review B. 62(17):11437-11443, 2000 Nov 1.
Abstract:
The internal friction, speed of transverse sound, and thermal conductivity have been measured of a single grain of icosahedral Al72.1Pd20.7Mn7.2 (composition in the melt) that was grown by the Czochralski technique at Forschungszentrum Julich. The three sets of data could be consistently described with the tunneling model using the tunneling strength C-t = (0.51 +/- 0.1) x 10(-4). This value of C-t, which is close to the one obtained by speed of sound measurements by Vernier et al. on a sample of i-AlPdMn grown by the Bridgman technique, and from thermal conductivity of a sample grown by the Czochralski technique by Legault et al., and of a Bridgman sample measured by Chernikov et al., is close to the range observed for most amorphous solids, 10(-4)-10(-3). It is concluded that the lattice vibrations of this icosahedral quasicrystal, grown from the melt in thermal equilibrium, are indistinguishable from those of amorphous solids, and of many chemically disordered crystals.
Title:
NMR second-moment study of hydrogen sites in icosahedral Ti45Zr38Ni17 quasicrystals
Authors:
Faust KR. Pfitsch DW. Stojanovich NA. McDowell AF. Adolphi NL. Majzoub EH. Kim JY. Gibbons PC. Kelton KF.
Source:
Physical Review B. 62(17):11444-11449, 2000 Nov 1.
Abstract:
Quasicrystalline Ti45Zr38Ni17Hx samples were prepared with hydrogen-to-metal ratios (H/M) ranging from 0.25 to 1.85. The higher-concentration samples lost hydrogen, falling to H/M approximate to 1.6 over the course of days to weeks. The calibration of x-ray peak shifts as a measure of H/M, previously based on an extrapolation for H/M > 1.6, has been confirmed. Nuclear magnetic resonance measurements of the second moments (M-2) of the dipole-broadened H-1 line show the dependence on H/M expected for uniform filling of the quasicrystal with hydrogen. M-2 data were also consistent with canonical cell-tiling models of the host structure when hydrogen was sited preferentially near Ti or Zr neighbors. The quasicrystalline structure allows the chemical preference in hydrogen siting to be compatible with spatially uniform filling of the quasicrystal.
Title:
Low-temperature crystal and magnetic structures of the chain-ladder composite material Sr0.4Ca13.6CU24+yO41+z: Hole redistribution and antiferromagnetic order
Authors:
Isobe M. Onoda M. Ohta T. Izumi F. Kimoto K. Takayama-Muromachi E. Hewat AW. Ohoyama K.
Source:
Physical Review B. 62(17):11667-11676, 2000 Nov 1.
Abstract:
The low-temperature crystal structure of a one-dimensional chain-ladder composite material Sr0.4Ca13.6Cu24+yO41+z was determined by the Rietveld analysis of neutron diffraction data using a superspace group approach. The hole distribution between the chain and ladder planes was estimated by the bond-valence sum (BVS) calculation based on Cu-O interatomic distances. The minimum of the distance between ladder-copper and chain-oxygen atoms [Cu(1)-O(3)] was revealed to expand with lowering temperature. The BVS calculation indicated that such a structural change corresponds to a redistribution of holes from the ladder to the chain and that almost all of the holes are localized in the chain below or near the Neel temperature. By assuming reasonable magnetic interactions between hole-unoccupied Cu sites on the chain plane, we propose a possible magnetic structure model taking into account the distribution of holes and observed magnetic neutron Bragg reflections. The results suggest the presence of spin dimers, spin trimers, and ''lone'' spins in the chain, of which the latter two have effective magnetic moments. These moments may be an origin of staggered antiferromagnetic spin modulation onto the spin-liquid state.
Title:
Lifshitz point in the three-dimensional magnetic phase diagram of CoNb2O6
Authors:
Weitzel H. Ehrenberg H. Heid C. Fuess H. Burlet P.
Source:
Physical Review B. 62(18):12146-12155, 2000 Nov 1.
Abstract:
Neutron-diffraction and magnetization experiments have been performed on a single crystal of CoNb2O6 with an external magnetic field applied along different directions within the ac plane. Intermediate magnetic phases with long periodicities along the b axis are observed. Exchange and crystal-field parameters in a proposed model are determined by fitting the magnetization curves, and the comparison between calculated and observed magnetic phase diagrams provides a severe test of the applied model. The behavior of the propagation vector (0,k(y),0) at a transition point from an incommensurate phase to a commensurate one in zero field and near a Lifshitz paint with a magnetic field applied is discussed in the Light of theoretical considerations on multicritical phenomena.
Title:
Charge and spin ordering process in the mixed-valence system LuFe2O4: Charge ordering
Authors:
Yamada Y. Kitsuda K. Nohdo S. Ikeda N.
Source:
Physical Review B. 62(18):12167-12174, 2000 Nov 1.
Abstract:
The charge ordering process in a mixed valence system LuFe2O4 is investigated both experimentally and theoretically. The experimental results using various types of diffraction techniques reveal the following unique features. (i) The system undergoes sequential transitions: disorder-->2D-CDW-->3D-CDW. (ii) The structure stabilized in the lowest temperature is characterized by an incommensurate charge-density-wave (CDW) state. (iii) In the intermediate temperature range, there appear strong diffuse streaks running along the rhombohedral unique axis which show subtle zig-zag modulation. These experimental results are analyzed based on the assumption that the ordering charges are essentially localized on Fe sites. The energy between the electron pairs up to the nearest-neighbor hexagonal double layers are taken into account to discuss the stable charge configuration and the properties of charge fluctuations. It has been shown that the experimentally observed unique features of the charge ordering process are satisfactorily explained only when the intercharge interaction between the neighboring layers is taken to be attractive.
Title:
Effects of Ag and Pd on the nucleation and growth of the nano-icosahedral phase in Zr65Al7.5Ni10Cu7.5M10 (M = Ag or Pd) metallic glasses
Authors:
Saida J. Matsushita M. Li C. Inoue A.
Source:
Philosophical Magazine Letters. 80(11):737-743, 2000 Nov.
Abstract:
The nucleation and growth of a nano-icosahedral phase from a supercooled liquid region of Zr65Al7.5Ni10Cu7.5M10 (M = Ag Or Pd) glasses have been examined by differential scanning calorimetry and transmission electron microscopy. The growth rate of the icosahedral phase is nearly constant at the initial stage and much slower than that of the Zr2Ni phase in the Zr65Al7.5Ni10Cu17.5 metallic glass. The homogeneous nucleation rate has a maximum value of 4.4 x 10(20) m(-3) s(-1) at 695 K in the Zr65Al7.5Ni10Cu7.5Ag10 glass, which is approximately 10(2) times higher than that for the formation of quasicrystalline phase in the Zr69.5Al7.5Ni11Cu12 glass and 10(4) times higher than that of the Zr2Ni phase in the Zr65Al7.5Ni10Cu17.5 glass. With increasing Pd content, the nucleation rate of the primary phase increases significantly and the growth rate decreases at the crystallization temperature. Thus, the addition of Ag and Pd is effective for an increase in the number of nucleation sites and the suppression of grain growth, which is the main reason for the formation of icosahedral nanoparticles. The significant increase in the nucleation rate is due to an increase in the number of nucleation sites resulting from the short-range ordering consisting of Zr-(Ag or Pd) strong pairs. It is implied that the strong pair Zr-(Ag or Pd) also contributes to the restraint of the long-range rearrangements of the constitutional elements. The formation of the nanoicosahedral phase suggests that icosahedral short-range order exists in the glassy state in the present alloys.
Title:
Boron quasicrystals and boron nanotubes: Ab initio study of various B-96 isomers
Authors:
Boustani I. Quandt A. Rubio A.
Source:
Journal of Solid State Chemistry. 154(1):269-274, 2000 Oct.
Abstract:
The rhombohedral unit cells of alpha -boron crystals and of hypothetical alpha -boron quasicrystals were investigated by applying ab initio quantum-chemical methods. The atomic decorations of such unit cells are generally based on a suitable arrangement of eight boron icosahedra, and thus the mechanism of their cohesion was simulated by relaxing a B-96 supercluster composed of icosahedral boron clusters located at the vertices of the rhombohedral unit cells. Also, several alternative structures of B-96 clusters were proposed and compared to the rhombohedral phases. To this end, total energies of those structures were computed on the basis of all-electron calculations at the Hartree-Fock self-consistent field level of theory using the standard STO3G basis set. Due to the large number of degrees of freedom, the geometries of all isomers were optimized under reasonable symmetry constraints, but using analytical gradient methods. The resulting total energies show that segments of nanotubes and quasiplanar sheets turn out to be more stable than the unit cells of alpha -boron (quasi) crystals, indicating new kinds of materials. (C) 2000 Academic Press.
Title:
Correlation functions and the dynamical structure factor of quasicrystals
Authors:
Hohl M. Roth J. Trebin HR.
Source:
European Physical Journal B. 17(4):595-601, 2000 Oct.
Abstract:
The icosahedral or decagonal symmetry of quasicrystals is well described by a periodic structure in higher dimensions. One consequence is the existence of dynamic phason modes in addition to the phonon modes. In an atomistic model phasons show up as correlated atomic jumps. We detect the phasons by the calculation of correlation functions and the dynamical structure factor ire molecular dynamics simulations similar to the procedure used for phonons. In the simulations it is also possible to observe atomic jump processes directly. The models studied here represent icosahedral AlCuLi and decagonal AlCuCo quasicrystals. Ring processes are observed in the icosahedral case, and flips in the decagonal model.
Title:
As-cast quasicrystalline phase in a Zr-based multicomponent bulk alloy
Authors:
Kuhn U. Eckert J. Mattern N. Schultz L.
Source:
Applied Physics Letters. 77(20):3176-3178, 2000 Nov 13.
Abstract:
An icosahedral quasicrystalline phase is obtained directly from the melt by copper mold casting of a Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 alloy. On the other hand, rapid quenching of the alloy leads to an amorphous phase. Upon annealing, the amorphous structure precipitates quasicrystals in the first stage of crystallization. The microstructure of the quasicrystalline state is quite different for the two preparation routes, which is correlated with the asymmetry of the nucleation and growth rate upon cooling or heating. The quasicrystals formed upon slow cooling from the melt have a size of about 1 mum. In contrast, the quasicrystals formed by annealing do not exceed a size of 5-10 nm. (C) 2000 American Institute of Physics. [S0003-6951(00)03246-0].
Title:
Incommensurate suprastructures: New problems of inorganic solid-state chemistry [Review] [Russian]
Authors:
Pervov BS. Makhonina EV.
Source:
Uspekhi Khimii. 69(6):528-537, 2000.
Abstract:
Data for a new type of inorganic incommensurate intergrowth suprastructures - misfit layer compounds - are generalised and described. Their physical properties are discussed. The possible mechanisms of the effect of electronic structure and of incommensurability parameters on the structural elements of suprastructures and their recognition in molecular ensembes. General criteria for self-organisation of incommensurate suprastructures are proposed. The conditions for fragmenting of one of the sublattices (formation of nanocomposites) are considered.
Title:
Transformation kinetics of nanoicosahedral phase from a supercooled liquid region in Zr70Pd30 binary glassy alloy
Authors:
Saida J. Matsushita M. Inoue A.
Source:
Journal of Applied Physics. 88(10):6081-6083, 2000 Nov 15.
Abstract:
The formation of a nanoicosahedral phase in the diameter range below 20 nm from the melt-spun Zr70Pd70 binary glassy alloy was confirmed, and the kinetics of the precipitation upon isothermal annealing in the supercooled liquid region was examined by differential scanning calorimetry. Based on the kinetic analysis, it is clarified that the precipitation in the supercooled liquid region takes place by a diffusion-controlled growth with increasing nucleation rate. The Arrhenius plot between effective time lag, tau, of nucleation and isothermal annealing temperature yields a single linear relation, in which the activation energy for nucleation is evaluated to be 267 kJ mol(-1). The activation energy in the present alloy is much lower than that of the Zr65Al7.5Ni10Cu7.5Pd10 alloy, which is due to the difference in the magnitude as well as the number of atoms for the rearrangements in the nucleation stage. It is concluded that the formation of a nanoscale icosahedral quasicrystalline phase is attributed to the transformation mode of an increase of nucleation rate, which is different from that of Zr65Al7.5Ni10Cu7.5Ag10 quasicrystal arising from an interfacial controlled growth with a steady-state nucleation rate. The formation of a nanoicosahedral phase in the Zr70Pd30 binary glassy alloy implies the existence of the icosahedral short-range order in the glassy state. (C) 2000 American Institute of Physics. [S0021-8979(00)00624-1].
Title:
May quasicrystals be good thermoelectric materials?
Authors:
Macia E.
Source:
Applied Physics Letters. 77(19):3045-3047, 2000 Nov 6.
Abstract:
We present a theoretical analysis of quasicrystals (QCs) as potential thermoelectric materials. We consider a self-similar density of states model and extend the framework introduced in [G. D. Mahan and J. O. Sofo, Proc. Natl. Acad. Sci. U.S.A. 93, 7436 (1996)] to systems exhibiting correlated features in their electronic structure. We show that relatively high values of the thermoelectric figure of merit, ranging from 0.01 up to 1.6 at room temperature, may be expected for these systems. We compare our results with available experimental data on transport properties of QCs and suggest some potential candidates for thermoelectric applications. (C) 2000 American Institute of Physics. [S0003-6951(00)03545-2]. [References: 51]
Title:
Low-temperature conduction mechanism near the metal-insulator transition of Al70Pd22.5Re7.5 quasicrystals
Authors:
Wang CR. Su TI. Lin ST.
Source:
Journal of the Physical Society of Japan. 69(10):3356-3359, 2000 Oct.
Abstract:
We have found that near the metal-insulator transition of Al70Pd22.5Re7.5 quasicrystal, the conductivity sigma>(*) over bar * (T) obeys sigma>(*) over bar * (T) = sigma>(*) over bar * (0) + mT(1/3) between 1.5K and similar to 10K on both sides of the metal-insulator transition, as found in disorder systems. This indicates that the conductivity near the metal-insulator transition of the Al-Pd-Re quasicrystals is mainly controlled by electron-electron interactions. The quantum interference theory is found to be able to interpret the conductivity of the samples in the scaling region up to 30 K. The inelastic scattering which causes the phase breaking at low temperature is chiefly due to the electron-electron scattering with the relaxation time tau (ie) similar to 10(-11)T(-alpha) sec (alpha similar to 1.0).
Title:
Covalent bonds in AlMnSi icosahedral quasicrystalline approximant
Authors:
Kirihara K. Nakata T. Takata M. Kubota Y. Nishibori E. Kimura K. Sakata M.
Source:
Physical Review Letters. 85(16):3468-3471, 2000 Oct 16.
Abstract:
Electron density distributions were obtained using the maximum entropy method with synchrotron radiation powder data. In the metallic Al12Re, metallic bonding was observed for the icosahedral Al-12 cluster with central Re atom. In the nonmetallic alpha-AlMnSi 1/1 approximant, covalent bonds were found in the electron density distribution of the Mackay icosahedral cluster without central atom. Rather than the Hume-Rothery mechanism, the covalency of Al (Si) icosahedron and that between Al (Si) and Mn atoms is considered to be the origin of the pseudogap and nonmetallic behavior of alpha-AlMnSi.
Title:
On the structure of the microscopic dielectric tensor in incommensurate crystals
Authors:
Kushnir OS. Lokot LO.
Source:
Phase Transitions. 72(3 Part A):157-164, 2000.
Abstract:
A microscopic model for calculating the optical response of incommensurately modulated phases in insulating crystals is presented. The dominant contribution to the dielectric permittivity tensor is shown to originate from the lowest-index reciprocal lattice vectors, thus proving the validity of the mesoscopic approach developed in several earlier studies. The expression for the mesoscopic Fourier component of the dielectric tensor is obtained. These results may be useful in relation to the controversial problem of the optical activity observed in the incommensurate phases of some A(2)BX(4) family crystals.
Title:
Quasicrystal-filled polymers outperforms other polymer composite in wear-resistance properties
Source:
MRS Bulletin. 25(10):8-9, 2000 Oct.
Title:
Quasicrystals of AlNiCo exhibit band structure
Source:
MRS Bulletin. 25(10):9, 2000 Oct.
Title:
Critical exponents of the transport properties at the B2 double left right arrow IC double left right arrow C(R) transitions in Ti-Ni-Me shape memory alloys
Authors:
Kolomytsev V. Nevdacha V. Bataillard L. Gotthardt R.
Source:
International Journal of Modern Physics B. 14(17):1729-1742, 2000 Jul 10.
Abstract:
Critical behaviour of the physical properties at the B2 double left right arrow IC double left right arrow C(R) phase transitions in TiNi-based shape memory alloys has been analyzed in the frame of the charge density wave (CDW) model. Variation of total resistance at the Peierls-type B2 double left right arrow IC double left right arrow C(R) transition in TiNiMe (Me=Cr, Fe, Al, Ge) alloys has been found to be a sum of the beta-phase normal contribution, fluctuating CDW resistance rho(f)(T) in the incommensurate state and resistance change due to the energy gap formation rho(c)(T) in the commensurate state. The fitting parameters such as the energy gap at saturation Delta(0) and the number of electrons involved in the process of the CDW's formation psi(0) have been determined as a function of the alloy chemical composition and thermal treatment at moderate temperature. The critical resistive fluctuations in the incommensurate phase follow a power law d(rho f)/dt* similar to t(*m) with critical exponent m = -1. In the frame of the CDW model this means that the process of electron scattering from periodic distortion is strongly limited to a definite plane of the crystal and system is two-dimensional, The change of rho(c) with temperature is controlled by the activation energy law corresponding to electron single excitations through the gap Delta(T), with a varying psi(T) effective number of the electrons involved in the process. The total enthalpy measured during cooling is compared with the heat calculated for the energy gap opening at the Fermi level during the IC double right arrow C(R) transition in the frame of the Shottky anomaly approximation. Both values are of the same order. When hydrostatic pressure is applied to the material, a small drop in the conductivity is observed around P similar to 2 GPa and interpreted as CDW pinning by commensurability locking at a temperature higher than the transition temperature at normal pressure.
Title:
Modulated crystal structure and electronic properties of semiconductor Cu47Si91P144
Authors:
Mozharivskyj Y. Lang O. Franzen HF.
Source:
Zeitschrift fur Anorganische und Allgemeine Chemie. 626(10):2153-2160, 2000 Oct.
Abstract:
Crystals of the copper silicon phosphide were synthesized by the iodine gas transport technique. The x-ray single crystal methods revealed a big superstructure with the lattice parameters a = b = 44.510 and c = 20.772 Angstrom and a basic tetragonal substructure with a = 3.7092 and c = 5.1930 Angstrom. Analysis of the intensities showed that the superstructure has a 1/2, 1/2,1/2 tetragonal substructure with a = 22.255 and c = 10.386 Angstrom. This 1/2, 1/2, 1/2 substructure (Cu47Si91P144) and the basic tetragonal structure (Cu0.71Si1.29P2) were solved by the direct methods and refined in the I (4) over bar m2 space group. The phosphide is a semiconductor with a small energy gap of 0.0269(1) eV. The electrical properties are considered in terms of Anderson localization. The density of states was calculated using the extended Huckel tight binding method.
Title:
Disclinations in quasiperiodic tilt grain boundaries
Authors:
Mikaelyan KN. Ovid'ko IA. Romanov AE.
Source:
Physics of Metals & Metallography (English Translation of Fizika Metallov i Metallovedenie). 90(3):224-230, 2000 Sep.
Abstract:
A disclination-structural model of quasiperiodic tilt grain boundaries of finite length in polycrystalline and nanocrystalline materials is suggested, The model is exemplified by calculations of stress fields and energy characteristics of some quasiperiodic tilt grain boundaries of finite length. The results of calculations of energy characteristics are compared with analogous results obtained within the dislocation-structural model and with experimental data. The disclination description is shown to be more efficient, in particular, when considering tilt boundaries in nanocrystalline materials.
Title:
Magnetism in Al(Si)-Mn quasicrystals and related phases
Authors:
de Laissardiere GT. Mayou D.
Source:
Physical Review Letters. 85(15):3273-3276, 2000 Oct 9.
Abstract:
An extreme sensitivity of the magnetic properties to the atomic structure has been observed in Al(Si)-Mn and Al-Pd-Mn quasicrystals, approximants, and liquids with similar Mn concentrations (of the order of 8%-20%). Here, we show that the effect of the local environment of the Mn atoms is not sufficient to explain this complex behavior. A new model is presented, which, taking into account Mn-Mn interactions mediated by the conduction electrons over large distances (5 Angstrom and more), allows one to understand why only a small fraction of the Mn atoms carry a localized magnetic moment in quasicrystals and why a large proportion is magnetic in liquids.
Title:
Zr0.98Sn0.02TiO4 single crystal in a low electric field: Birefringence, dielectric, and synchrotron x-ray studies
Authors:
Park Y.
Source:
Physical Review B. 62(13):8794-8801, 2000 Oct 1.
Abstract:
The temperature dependence of linear birefringence and complex dielectric constants of Zr0.98Sn0.02TiO4 single crystal under low de electric fields (E less than or equal to 1.5 kV/cm) have been investigated in combination with synchrotron x-ray diffraction. Two anomalies for ZrTiO4 were found to be related with the transitions to intermediate commensurate (C) phases with commensurate (or incommensurate) deviation factor delta = 1/70 and delta = 1/50 at 855 and 875 degrees C, respectively, while those of Zr0.98Sn0.02TiO4 completely vanished. This manifests that Sn impurity prevents the incommensurate (IC) phase from passing over to the intermediate C phase. A de electric (E) field made the dielectric anomaly related with IC-C phase transitions T-c split into two peaks. One in zero field has a maximum at T-c2 = 845 degrees C and its E field dependence is found to be dT(c2)/dE = 1.5 degrees C cm/kV. The other T-c1 remains nearly invariant with respect to E fields. i.e., at 845 degrees C under zero E field. It was evinced by the synchrotron x-ray diffraction not only that the E field induced phase in T-c1 < T = T-c2 consists of the C phase with delta = 0 and the IC phase with delta = 1/68, but also that the increase in E field stabilizes the C phase. The frequency (f) dependent dielectric relaxation at E = 1.0 kV/cm with 10(-5) less than or equal to f less than or equal to 10(11) Hz demonstrates three distinct dielectric modes in T-c1 < Te < T-c2. The dielectric data, just below T-c1, between T-c1 and T-c2, and just above T-c2, can be analyzed to show that the low-frequency mode is due to the pinned discommensurations, while the high-frequency one to the C phase.
Title:
High-pressure stability of Ti-Zr-Ni quasicrystals
Authors:
Nicula R. Jianu A. Ponkratz U. Burkel E.
Source:
Physical Review B. 62(13):8844-8848, 2000 Oct 1.
Abstract:
The room-temperature compressibility and stability of single-phase icosahedral Ti-Zr-Ni alloys were investigated for pressures up to 30 GPa, using synchrotron radiation energy dispersive diffraction. The icosahedral Ti-Zr-Ni single phase is stable over this pressure range, no phase transition being noticed. The pressure-volume data were least-squares fitted to a Birch-Murnaghan equation of state to obtain the zero-pressure bulk modulus B-0 = (173+/-5) GPa and its pressure derivative B-0' = 2.3+/-0.5.
Title:
Vibrational density of states in the archetypical icosahedral quasicrystal i-Al62Cu25.5Fe12.5: Neutron time-of-flight results
Authors:
Brand RA. Dianoux AJ. Calvayrac Y.
Source:
Physical Review B. 62(13):8849-8861, 2000 Oct 1.
Abstract:
We study the neutron-weighted vibrational density of states g(E) in the i-AlCuFe quasicrystal measured by time-of-flight inelastic neutron scattering (INS). The samples studied were i-Al62Cu25.5Fe12.5 with different isotopic substitutions. These results are compared to our previous Fe-57 inelastic nuclear-resonant absorption (INA) results for the iron-partial g(E) [R. A. Brand et at, Phys. Rev. B 59, R14 145 (1999)]. The neutron-weighted g(E) measured on samples with different isotopes (natural Cu and Cu-65; natural Fe and Fe-57) shows that the aluminum and copper-partial g(E) is strongly peaked at a significantly lower energy than that for iron. We show in addition that the low-energy square term in g(E) is the same for both INS and INA but a significant quartic term exists in the neutron-weighted g(E). The neutron-weighted and iron-partial g(E) are used to calculate lattice-dynamical properties such as the lattice specific heat C-latt(T). The C-latt(T) as calculated from the neutron-weighted g(E) agrees with the experimental C-latt in the low T range where an anomalous power law had previously been found [J. C. Lasjaunias et al., J. phys. I 7, 959 (1997)]. These results are discussed in terms of possible non-acoustic modes at low energy.
Title:
Searching for sharp features in the pseudogap of icosahedral quasicrystals by NMR
Authors:
Dolinsek J. Klanjsek M. Apih T. Smontara A. Lasjaunias JC. Dubois JM. Poon SJ.
Source:
Physical Review B. 62(13):8862-8870, 2000 Oct 1.
Abstract:
In a search for sharp features in the electronic density of states (DOS) of quasicrystals, a systematic comparative study of the DOS in the vicinity of Fermi energy E-F was performed in icosahedral Al72.4Pd20.5Mn7.1, Al62Cu25.5Fe12.5, and Al70.5Pd21Re8.5 by the Al-27 NMR spin-lattice relaxation. The investigated samples differ markedly in their electrical conductivity (and thus the DOS at E-F) and the content of paramagnetic centers. The paramagnetism of Mn and Fe d-electron moments in AlPdMn and AlCuFe introduces a strong relaxation mechanism of spin diffusion to paramagnetic centers that competes with the relaxation via conduction electrons and becomes dominant at low temperatures, typically below 100 K. The Al72.4Pd20.5Mn7.1 and Al62Cu25.5Fe12.5 show a paraboliclike variation of the pseudogap in the DOS in the vicinity of E-F, bur no sharp features were detected. In the AlPdRe8.5 the paramagnetic relaxation is absent except at temperatures below 7 K and a single sharp feature of the full width at half height 14 meV, displaced by 11 meV from E-F. was detected. The sharp feature is very deep, reducing the DOS at the minimum to a few percent of its value in the metallic aluminum. The effect of the sharp feature in the DOS on the NMR spin lattice relaxation rate T-1(-1) shown theoretically to introduce a minimum in the (T1T)(-1) product at a temperature that is crucially related to the displacement of the sharp feature from E-F.
Title:
On the one-dimensional 8A periodic superstructure in decagonal phases
Authors:
Frey F. Weidner E. Hradil K. De Boissieu M. Currat R. Shibata K. Tsai AP. Sato TJ.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 80(10):2375-2391, 2000 Oct.
Abstract:
Diffuse layers which are observed in different decagonal quasicrystals perpendicular to the unique 'periodic' axis are explained by one-dimensional (1D) columns of icosahedral Al clusters along this axis. From results of X-ray and purely elastic neutron diffraction experiments we give a qualitative explanation by basically off-layer atomic displacements which are grossly uncorrelated in different columnar clusters. A reversible temperature behaviour of the 1D superstructure which vanishes at high temperatures can be understood in the framework of this interpretation. Diffuse intensity modulations within the diffuse layers are discussed in terms of atomic displacements and chemical ordering within the icosahedral clusters which are the basic structural units of the columns. Computer simulations of different columnar models are carried out, their Fourier transforms are compared with the observed patterns.
Title:
Symmetry peculiarities of dielectric tensor in incommensurately modulated crystal phases
Authors:
Kushnir OS. Lokot LO. Polovinko II.
Source:
Journal of Physics-Condensed Matter. 12(38):8321-8330, 2000 Sep 25.
Abstract:
The dielectric permittivity tensor for incommensurately modulated phases in insulating crystals is considered. The main attention is paid to the spatial dispersion giving rise to optical gyration effects and the influence of the modulation phase on those effects. General properties of the dielectric tensor are analysed in relation to the lattice and incommensurate superlattice periodicity requirements, the Onsager principle and the condition of absence of the radiation losses in the optical medium. The structure of the microscopic components of the tensor and a macroscopic averaging procedure for the plane-wave modulation region are discussed. The possibility of existence of an and-Hermitian part in the dielectric tensor of lossless incommensurate crystals originating from the modulation-induced spatial dispersion is revealed. The performed analysis shows a necessity for introduction into the constitutive equation of the term including spatial derivatives of the optical activity tensor.
Title:
Studies of mechanical properties of quasicrystalline Al-Cu-Fe phase by the indentation technique
Authors:
Trefilov VI. Mil'man YV. Lotsko DV. Belous AN. Chugunova SI. Timofeeva II. Bykov AI.
Source:
Doklady Physics. 45(8):363-366, 2000 Aug.
Title:
Transmission electron microscopy and differential thermal studies of lazurite polymorphs
Authors:
Hassan I.
Source:
American Mineralogist. 85(10):1383-1389, 2000 Oct.
Abstract:
Transmission electron microscopy (TEM) and thermal (DTA-TG) analyses of lazurite, (Na,Ca)(8) [Al6Si6O24] (SO4,S)(2), indicate three forms: cubic, modulated, and orthorhombic. Cubic lazurite contains mainly [Na3Ca . SO4](3+) clusters that are disordered together with the O1 and O2 oxygen atoms, and no satellite reflections occur. In the modulated lazurite structure, [Na3Ca . SO4](3+) and [Na3Ca . S](3+) clusters are ordered and possibly cause ordering of the framework oxygen atoms on the O1 and O2 positions and produce satellite reflections. Different ordering of these clusters gives an orthorhombic supercell with parameters of 2d(110) x 6d1 (1) over bar 0 x c with respect to the cubic subcell. The DTA-TG study indicates that the orthorhombic to the modulated phase transition occurs at a peak temperature of 489 degrees C. A single-crystal fragment of lazurite may contain all three phases, as was observed by TEM in this study. Such intergrowths indicate a continuous framework with different regions of the crystal containing different ordering and chemistries. Two new lazurite superstructures were observed with dimensions of 6d(110) x 3d(001), and 3d(112) x 3d (1) over bar 11 with respect to the cubic subcell.
Title:
Origin and structural character of hauyne(ss) in spinel dunite xenoliths from La Palma, Canary Islands
Authors:
Wulff-Pedersen E. Neumann ER. Burke EAJ. Vannucci R. Bottazzi P. Ottolini L. Gjonnes J. Hansen V.
Source:
American Mineralogist. 85(10):1397-1405, 2000 Oct.
Abstract:
Two spinel dunite xenoliths (Fo(89.8-91.2) in olivine) from La Palma contain minor amounts (<1%) of a pale-blue sodalite-group mineral with hauyne/lazurite chemistry. Selected-area electron diffraction (SAED) patterns of this phase indicate a cubic unit cell with dimensions 9.12 +/- 0.02 Angstrom, and space group P (4) over bar 3n. Superstructure spots along three <110> directions are common, implying commensurate or incommensurate modulations along <110> directions. Raman spectra show peaks typical of both lazurite and hauyne. It is concluded that the mineral has a structure intermediate between those of pure lazurite and pure hauyne, and it is here referred to as hauyne(ss). The hauyne(ss) occurs together with strongly nepheline-normative glass in thin veinlets (<0.1 mm), in interstitial glass pockets, and as inclusions in olivine porphyroclasts. To our knowledge lazurite or hauyne has not previously been described in mantle rocks. The hauyne(ss) is strongly depleted in REE and most other highly lithophile elements relative to the coexisting glass, whereas D-mineral/glass for Sr is approximate to 1.0, and D-Eu higher than the other REE. The hauyne(ss) crystallized from a melt now present as phonolitic glass, probably in response to rapidly decreasing pressure during transport of the xenoliths to the surface. The coexistence of hauyne(ss) and FeS-rich sulfide globules in some samples suggests slightly more oxidizing conditions than for samples in which the glass contains sulfide globules alone.

Update: 2-Nov-2000

Title:
In situ electron diffraction study of synthetic (Ca1-xSrx)(2)MgSi2O7 akermanites
Authors:
Schosnig M. Schaper AK. Kutoglu A. Treutmann W. Rager H.
Source:
Zeitschrift fur Kristallographie. 215(9):495-498, 2000.
Abstract:
This paper deals with transmission electron microscope experiments of Ca, Sr-akermanite solid solutions at temperatures between 100 K and 375 K. The aim of the investigations was to study the compositional and temperature dependence of phase transitions from the normal to the incommensurately modulated structure of (Ca1-xSrx)(2)MgSi2O7 Single crystals observed by electron diffraction. With increasing Sr-content the normal to incommensurate phase transition temperature decreases linearly from ca. 350 K (x = 0.04) to 295 K (x = 0.22). Depending on temperature and composition, the incommensurate phase is structurally not uniform, its stability field can be divided into two regions. The transition between the two regions can be recognized by the additional appearance of higher order satellite reflections in the diffraction pattern. Additionally, the transition is characterized by an abrupt change of the modulation wavelength. Within the high-temperature, low ordered region, the modulation wavelength varies between 18.1 Angstrom and 20.5 Angstrom, whereas no changes of the wavelength have been found in the low-temperature, higher ordering region. With increasing Sr-content the high-temperature, low ordered phase covers a steadily increasing temperature range.
Title:
Triple-axis neutron-scattering study of phason dynamics in Al-Mn-Pd quasicrystals [Review]
Authors:
Coddens G. Lyonnard S. Hennion B. Calvayrac Y.
Source:
Physical Review B. 62(10):6268-6295, 2000 Sep 1.
Abstract:
We present an extensive triple-axis neutron-scattering study of phason hopping in a single-domain sample of a perfect icosahedral Al70.4Mn8.6Pd21.0 quasicrystal. The quasielastic intensities exhibit important anisotropies. They are compared with models at various levels of sophistication. This comparison strongly suggests the occurrence of simultaneous correlated jumps. The important correlations are directed along the threefold axes. [References: 154]
Title:
Neutron scattering phase study of the normal-incommensurate transition in Rb2ZnBr4
Authors:
Shigematsu H. Mashiyama H. Takesada M. Ohshima K. Oohara Y. Matsui T.
Source:
Journal of the Physical Society of Japan. 69(9):2905-2909, 2000 Sep.
Abstract:
The soft phonon modes, which are related to the normal-incommensurate phase transition of Rb2ZnBr4, have been measured by inelastic neutron scattering. The existence of both phase and amplitude modes has been confirmed, and the phonon dispersion curves have been determined in the low-temperature commensurate phase. On the other hand, the phonon dispersion curve of the transverse acoustic phonon along the (0 0 xi) direction does not vary appreciably in the normal phase. The soft mode is fully overdamped above the normal-incommensurate phase transition. Diffuse scattering develops around h0l +/- 5/17 as temperature approaches T-i = 347 K from above.
Title:
High-pressure x-ray diffraction experiments on icosahedral Ti-Zr-Ni-unusual effects due to a low shear modulus and a high Poisson's ratio
Authors:
Ponkratz U. Nicula R. Jianu A. Burkel E.
Source:
Journal of Physics-Condensed Matter. 12(37):8071-8080, 2000 Sep 18.
Abstract:
In situ high-pressure x-ray diffraction experiments have been performed on quasicrystalline Ti-Zr-Ni in energy-dispersive mode using synchrotron radiation. Pressures up to 30 GPa were generated using a diamond anvil cell. The bulk modulus of Ti-Zr-Ni was determined to be B-0 = 166 GPa +/- 13 GPa. Some of the experiments were performed under slightly nonhydrostatic conditions. In these runs, deviations from a standard equation of state could be observed and these are due to additional strains. According to the model of Singh and Kennedy for elastically isotropic solids, these strains are proportional to the non-hydrostatic stress component and indirectly proportional to the shear modulus of the sample. From our measurements, the shear modulus of icosahedral Ti-Zr-Ni was estimated to be mu approximate to 7 GPa with a relative error of about 50%. This value is low compared to the shear moduli of icosahedral Al-Cu-Fe, Al-Pd-Mn (for both, mu approximate to 65 GPa) and Al-Li-Cu (mu = 38 GPa). The Poisson's ratio of Ti-Zr-Ni was determined to be nu = 0.48 +/- 0.015. This value is close to the maximum value which is allowed by the laws of thermodynamics, namely nu = 0.5. The Poisson's ratios of common metals (nu approximate to 1/3) and other icosahedral alloys like Al-Cu-Fe (nu = 0.19), Al-Pd-Mn (nu = 0.28) and Al-Li-Cu (nu = 0.25) are much lower.
Title:
X-ray study of structural modulations in Cs2HgCl4
Authors:
Bagautdinov B. Brown ID.
Source:
Journal of Physics-Condensed Matter. 12(37):8111-8125, 2000 Sep 18.
Abstract:
High resolution x-ray diffraction at temperatures from 7 to 300 K shows that at room temperature caesium tetrachloromercurate Cs2HgCl4 has the beta-K2SO4 structure but On cooling exhibits a sequence of incommensurate and commensurate modulations along a* and c* axes. Two modulation phases, one of which is incommensurate, are found between 184 and 221 K with wavevectors along a* and, below 184 K, six further modulation phases, one of which is incommensurate, are found with wavevectors along c*.
Title:
Al 3p occupied states in Al-Cu-Fe intermetallics and enhanced stability of the icosahedral quasicrystal
Authors:
Belin-Ferre E. Fournee V. Dubois JM.
Source:
Journal of Physics-Condensed Matter. 12(37):8159-8177, 2000 Sep 18.
Abstract:
This paper concentrates on a comparison of Al 3p occupied densities of stares in crystalline and quasicrystalline Al-Cu-Fe intermetallics. This comparison is made quantitative by computing the two first moments of this partial distribution, which correspond to the partial contribution of Al atoms to the cohesive energy of the material and to the orbital overlap modulated by the coordination number, respectively. From these data, we conclude that the icosahedral quasicrystal and its approximants represent a region of specifically enhanced stability in the Al-Cu-Fe phase diagram. We assign this effect to the specific role played by Al 3p states in the Hume-Rothery mechanism. We confirm the occurrence of a stronger hybridization between Al 3p and Fe 3d states in the icosahedral structure whereas we point out a weaker interaction with Cu 3d states in the icosahedral compounds as compared to stable approximants.
Title:
Fractal behaviour of diffraction pattern of Thue-Morse sequence
Authors:
Wolny J. Wnek A. Verger-Gaugry JL.
Source:
Journal of Computational Physics. 163(2):313-327, 2000 Sep 20.
Abstract:
The Thue-Morse sequence is an example of an aperiodic structure with a singular continuous contribution to the diffraction pattern. Many satellites observed near the main diffraction peaks have been indexed and their intensities have been numerically calculated. Details of such a calculation are presented for satellite peaks indexed by 1/3. An average-unit-cell approach was successfully used to describe probabilities of atomic displacements from the points of the reference lattice. For a certain parameterisation of such probabilities, the results of fairly simple integer calculations could be easily generalised, For some defined sets of points, the analytical expressions for diffraction intensities were found and tested numerically on a wide range of scattering vectors and for up to 2(32) atoms. (C) 2000 Academic Press.
Title:
Perturbation method solving elastic problems of icosahedral quasicrystals containing a circular crack
Authors:
Peng YZ. Fan TY.
Source:
Chinese Physics. 9(10):764-766, 2000 Oct.
Abstract:
Perturbation method for solving elastic three-dimensional (3D) problems for 3D icosahedral quasicrystals is proposed. Considering an infinite 3D icosahedral quasicrystal weakened by a circular crack, we obtain the uniformly valid asymptotic solutions up to O(R-2) for the mode I loading, where R is the elastic constant of phonon-phason coupling. [References: 13]
Title:
Influence of oxygen on the crystallization behavior of Zr65Cu27.5Al7.5 and Zr66.7Cu33.3 metallic glasses
Authors:
Murty BS. Ping DH. Hono K. Inoue A.
Source:
Acta Materialia. 48(15):3985-3996, 2000 Sep 25.
Abstract:
The influence of oxygen on the crystallization behavior of Zr-65 - xCu27.5Al7.5Ox (x = 0.14, 0.43 and 0.82) and Zr-66.7 (-) xCu33.3Ox (x = 0.14 and 0.82) metallic glasses has been studied. The supercooled liquid regime (Delta T-x) decreases with increase in oxygen content for the Zr-Cu-Al alloy, while it increases for the Zr-Cu metallic glass. In the case of the Zr-Cu metallic glass, the crystallization product (Zr,Cu) is not influenced by the oxygen content, while in Zr-Cu-Al alloys the oxygen level has a strong influence on the crystallization sequence. At low oxygen level (x = 0.14), the ternary glass crystallizes polymorphously to Zr-2(Cu,Al). At higher oxygen content, the ternary amorphous alloy crystallizes in two stages by primary crystallization into an icosahedral phase and subsequently to the stable Zr-2(Cu,Al) phase. Three-dimensional atom probe results have shown that the composition of the icosahedral and amorphous phases is close to Zr75Cu15Al5O5 and Zr62Cu24Al14, respectively. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
Decagonal quasicrystal growth in chill cast Al72Ni12Co16 alloy
Authors:
Liu YC. Yang GC. Zhou YH.
Source:
Materials Research Bulletin. 35(6):857-863, 2000 Apr 1.
Abstract:
The single-phase decagonal quasicrystal alloy Al72Ni12Co16 was melted by containerless processing and chilled on a copper substrate in an electromagnetic facility. X-ray, TEM, and SEM techniques were used to investigate the microstructure and identify the phase composition. The approximately directionally solidified decagonal quasicrystal in the chill cast sample showed facet morphology and grew in a lateral growth mode along the twofold axis normal to the plane (00002). The experimental results fit well with the prediction of Toner's theoretical atomistic growth model. (C) 2000 Elsevier Science Ltd. All rights reserved.
Title:
Investigation of the fivefold icosahedral AlPdMn surface by photoemission and Auger electron spectroscopy
Authors:
Dubot P. Cenedese P. Lorang G.
Source:
Surface & Interface Analysis. 30(1):346-349, 2000 Aug.
Abstract:
Surface composition and electronic structure of AlPdMn quasicrystalline alloy have been studied for temperature ranging from 300 K to 873 K, The quasicrystalline nature of the in-situ prepared surface was identified by the unusual behaviour of the core level photoemission peaks of Mn as already demonstrated by Thiel et al, Quantitative estimation of surface concentration by measuring the peak on background ratio in Auger electron spectroscopy (AES) do not allow to concluded to surface segregation of one element whatever the substrate temperature. Anger transitions implying valence band electrons in the Auger relaxation reveal interesting shapes and energies modifications that can be correlated with the typical electronic structure of this alloy, The appearance of strong satellite structure in the Auger and photoemission spectrum can be attributed to bulk plasmon of the quasicrystalline phase, Copyright (C) 2000 John Wiley & Sons, Ltd.
Title:
Systems with icosahedral clusters: Direct links between atoms in cluster-recursion methods and DOS spectral fine structure
Authors:
Solbrig H. Landauro CV.
Source:
Physica B. 292(1-2):47-53, 2000 Oct.
Abstract:
The origin of narrow pseudogaps close to the Fermi energy is examined in two model systems: alpha-AlMn(Si) and i-AlCuFe (1/1). We show that long-range electronic interferences in the Mn/Fe sub-systems give rise to such narrow spectral features which are highly important for the electronic transport. Besides the ASA-LMTO and the TB-LMTO recursion method we employ a cluster-recursion method within the muffin-tin scattered wave concept which reveals interference results on arbitrary length scales. We conclude that certain properties of quasicrystals are due to the physics in chemically defined sub-systems. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Magnetic structures of RAgSb2 compounds
Authors:
Andre G. Bouree F. Kolenda M. Lesniewska B. Oles A. Szytula A.
Source:
Physica B. 292(1-2):176-189, 2000 Oct.
Abstract:
Results of neutron diffraction measurements carried out for RAgSb2 (R = Ce, Pr, Nd, Tb, Dy, Ho, Er, Tm) compounds are reported. All compounds crystallize in the tetragonal ZrCuSi2-type crystal structure and, except CeAgSb2, they are collinear antiferromagnets with the Neel temperatures between 11.1 K for R = Tb and 2.0 K for R = Tm. Below T-c = 9.5 K CeAgSb2 is a ferromagnet with the Ce magnetic moment equal to 0.33 mu(B) and parallel to the c-axis. PrAgSb2 has an antiferromagnetic structure of AF II type with the magnetic unit cell (a, a, 2c). In the case of NdAgSb2 a sine-wave-modulated magnetic ordering, described by the wave vector It = (0.5435, 0, 0), is observed. The compounds with R = Tb, Dy and Er order antiferromagnetically with the magnetic unit cell (2a, a, c). At T = 1.4 K the magnetic structure of HoAgSb2 is similar to the one observed for TbAgSb2 and DyAgSb2 while at T = 2.7 K the peaks of magnetic origin correspond to a new incommensurate magnetic phase with the propagation vector k = (k(x), 0, k(z)). Up to the Neel temperature equal to 5.5 K a commensurate antiferromagnetic structure and an incommensurate sine-wave-modulated one coexist. Two magnetic phases are also observed in TmAgSb2 at T = 1.4 K. An increase in the temperature causes that the commensurate phase with the magnetic unit cell (2a, cc, c) disappears. The magnetic moment is parallel to the b-axis in the case of R = Tb, to the [1 1 0] direction for R = Dy and parallel to the c-axis in the case of R = Er and Tm ones which correlates well with the respective signs of CEF B-2(0)-parameter. In HoAgSb2 the magnetic moment lies in the b-c plane and forms the angle phi(b) = 13.5 degrees with the b-axis at 1.4 K. With increasing temperature the angle cp, increases up to 32 degrees about the Ni el temperature. The obtained data are analysed in terms of the exchange interaction theory and crystal electric field. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Electronic structure study of the dependence of the pseudogap on the icosahedral cluster size and the glue atoms
Authors:
Modak P. Rao RS. Godwal BK. Chidambaram R.
Source:
Philosophical Magazine B-Physics of Condensed Matter Structural Electronic Optical & Magnetic Properties. 80(9):1681-1692, 2000 Sep.
Abstract:
Electronic structures of crystalline Al12Mn, Al42Mn13 and Al54Mn13 are calculated by the tight-binding linear muffin-tin orbital method with the atomic sphere approximation in the local density functional framework. The density of states for Al12Mn shows a pseudogap at the Fermi level, whereas it is very much reduced and away from Fermi level in the case of the Al42Mn13 crystal. The evolution of a pseudogap near the Fermi level is observed in Al54Mn13 With the addition of glue atoms. Our results show that the pseudogap does not depend upon the icosahedral cluster size, for the AI-Mn system; however, it is sensitive to the presence of the glue atoms.
Title:
In situ high pressure X-ray diffraction and EXAFS spectroscopy of icosahedral Al-Cu-Ru quasicrystals
Authors:
Sadoc A. Itie JP. Polian A.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 80(9):2057-2071, 2000 Sep.
Abstract:
In situ X-ray diffraction and EXAFS experiments have been carried earned out for an icosahedral quasicrystalline Al-Cu Ru alloy under high pressure in quasihydrostatic conditions. The EXAFS measurements, performed above the Cu K absorption edge, have given the evolution of the local order around Cu atoms, which has been compared to that of the long range order yielded by diffraction. Diffraction measurements of the bulk modulus B-0 and its pressure derivative B-0' compare well with the 'local' values obtained around Cu atoms from the evolution of the mean first neighbour distance with pressure. While the six-dimensional lattice parameter and the first neighbour distance decrease monotonically with increasing pressure, showing the stability of the icosahedral phase, the widths of the Brags peaks show a systematic step broadening at about 10 GPa before following a plateau behaviour at higher pressures. At the same time, the sigma disorder parameter, associated with the first neighbour distance around Cu atoms, decreases with increasing pressure up to about 10 GPa, then remains almost constant. Both types of evolution could be the fingerprint of an order-disorder transformation, possibly induced by some phason disorder arising during the compression.
Title:
Surface oxidation of the Al62CU25.5Fe12.5 icosahedral quasicrystal
Authors:
Gil-Gavatz M. Rouxel D. Pigeat P. Weber B. Dubois JM.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 80(9):2083-2097, 2000 Sep.
Abstract:
The surface oxidation of the Al62Cu25.5Fe12.5 icosahedral quasicrystal was studied by Auger electron microscopy. Before oxidation, a chemisorption step occurs, the duration of which varies with temperature and oxygen pressure. At low temperature, between room temperature and 673 K, a very thin and passivating layer is found at the surface, where aluminium is only partially oxidized and the ratio between metal constituents remains equal to that of the nominal composition in the bulk. Above 673 K, except at very low oxygen pressure, a segregation of aluminium takes place at the surface and leads to the: growth of a nearly purr alumina layer in which the aluminium is completely oxidized. Under 2 x 10(-8) Torr of oxygen, no segregation of aluminium occurs and almost no oxide is formed at the surface after 24 h of exposure (1700 L).
Title:
Structural properties and interlayer interaction in (MX)(x)TX2-type ternary chalcogenides with layered composite crystal structure
Authors:
Gotoh Y. Akimoto J. Onoda M.
Source:
Molecular Crystals & Liquid Crystals. 341:885-890, 2000.
Abstract:
Structural properties and interlayer interaction in mutually incommensurate (MX)(2)TX2-type ternary chalcogenides with layered composite crystal structure have been investigated on the basis of structure analysis including superspace group symmetry. It has been confirmed that charge transfer between substructures occur in (LaS)(x)TiS2 from the results of Ti K XANES spectra. The lattice stability and interlayer interaction in the (MX)(x)TX2 have been discussed with the use of bond-valence sum (BVS) method by considering modulated structure analysis.
Title:
Frustrated magnetic behaviour of TbRh1.2Ru0.8Si2
Authors:
Bazela W. Leciejewicz J. Hofmann M. Penc B. Szytula A.
Source:
Journal of Alloys & Compounds. 308:56-59, 2000 Aug 10.
Abstract:
TbRh1.2Ru0.8Si2 shows two magnetic ordering schemes coexisting at 1.5 K: a sine wave modulated antiferromagnetic structure described by the wave vector k= (0.445(1),0.015(1),0) and a collinear antiferromagnetic structure characterized by the wave vector k = (1/2,1/2,1/2). The first phase is observed below the Neel point at 10 K, and the second coexists with the first below 5 K. In both structures the magnetic moments are localized on Tb3+ ions and are aligned along the tetragonal axis. The magnetic structure of TbRhRuSi2 has been confirmed to be a sine wave modulated antiferromagnetic structure described by the wave vector k = (0.413(4),0,0) with magnetic moments parallel to the tetragonal axis. This structure is stable in the temperature range from 1.5 K to the Neel point at 15.5 K. (C) 2000 Elsevier Science S.A. All rights reserved. [References: 9]
Title:
Magnetic properties of a monocrystalline quasicrystal in the Al-Pd-Mn system
Authors:
Rempel' AA. Nazarova SZ. Gusev AI.
Source:
JETP Letters. 72(3):144-147, 2000.
Abstract:
Magnetic susceptibility of a monocrystalline icosahedral Al70.2Pd21.3Mn8.5 quasicrystal was measured over the temperature range from 4 to 1100 K. The susceptibility was found to include the temperature-independent diamagnetic contribution, the temperature-dependent Curie's contribution, and the contribution from the Pauli paramagnetism of an electron system with energy gap. An analysis of the low-temperature susceptibility revealed the presence of about 0.008% of ions with magnetic moment 4 mu(B) in the quasicrystal at 4 K. It is assumed that the ions with uncompensated magnetic moments appear near the structural vacancies in the quasicrystal lattice. The energy gap between the valence and conduction bands is estimated at Delta = 0.64 eV, and the effective mass of charge carriers is equal to approximately 70 electron masses. (C) 2000 MAIK "Nauka/Interperiodica".
Title:
Growth of decagonal quasicrystal phase in laser resolidified Al72Ni12Co16
Authors:
Liu YC. Yang GC. Liu XB. Zhou YH.
Source:
Chinese Science Bulletin. 45(14):1315-1319, 2000 Jul.
Abstract:
An ultra-high temperature gradient directional solidification process produced by a widened laser beam was adopted to achieve the directionally solidified microstructure of the stable decagonal quasicrystal phase in Al72Ni12Co16 alloy. X-ray, SEM, TEM and optical microscopy techniques were used to investigate the microstructures and identify the phase. The directionally solidified decagonal quasicrystal showed the facet morphology and grew in lateral growth mode. The unusual periodic and quasiperiodic atomic structures of the decagonal quasicrystal and the epitaxial growth in the melt pool were considered to be the key factors influencing the growth morphology. The experimental results were consistent with the Toner's theoretical atomistic growth model. [References: 8]
Title:
Relation between short-range order and crystallization behavior in Zr-based amorphous alloys
Authors:
Xing LQ. Hufnagel TC. Eckert J. Loser W. Schultz L.
Source:
Applied Physics Letters. 77(13):1970-1972, 2000 Sep 25.
Abstract:
We have examined the effect of Ti and cooling rate on the crystallization of Zr62-xTixCu20Ni8Al10(0 less than or equal to x less than or equal to 10) amorphous alloys. Ti stabilizes an icosahedral phase in Zr62-xTixCu20Ni8Al10(0 less than or equal to x less than or equal to 10) alloys. Without Ti (x=0), crystallization produces cubic and tetragonal intermetallic phases, and the crystallization temperature shows no dependence on the cooling rate at which the amorphous alloy was produced. The alloys containing Ti (3 less than or equal to x less than or equal to 10) precipitate an icosahedral quasicrystalline phase upon annealing, and show a significant reduction of crystallization temperatures with decreasing cooling rates of casting. We propose that the undercooled melts and amorphous alloys have icosahedral short-range order. The degree of short-range order or medium-range order in the amorphous alloys increases with decreasing cooling rate. Crystallization is easier when the precipitating phase resembles the short-range order of the amorphous solid. Therefore, the crystallization temperature is reduced when the precipitates are icosahedral. The dissimilarity between the structures of the precipitates and the short-range order in amorphous Zr62Cu20Ni8Al10 may be one of the reasons for its very wide supercooled liquid region. (C) 2000 American Institute of Physics. [S0003-6951(00)04739-2]. [References: 23]

Update: 2-Oct-2000

Title:
Formation of quasicrystal in Zr70Ni10Mn20 alloy during rapid solidification
Authors:
Li C. Saida J. Inoue A.
Source:
Scripta Materialia. 42(11):1077-1081, 2000 May 31.
Title:
Icosahedral phase formation by the primary crystallization of a Zr-Cu-Pd metallic glass
Authors:
Murty BS. Ping DH. Hono K. Inoue A.
Source:
Scripta Materialia. 43(2):103-107, 2000 Jul 3.
Title:
Single-crystal deuterium NMR study of the symmetry breaking in an incommensurate organic inclusion compound
Authors:
Le Lann H. Odin C. Toudic B. Ameline JC. Gallier J. Guillaume F. Breczewski T.
Source:
Physical Review B. 62(9):5442-5451, 2000 Sep 1.
Abstract:
A single-crystal deuterium NMR study of the phase transition of the incommensurate organic inclusion compound of n-nonadecane in urea is presented. In agreement with diffraction measurements, we found that the urea host sublattice is not significantly modulated in the high-symmetry phase. Whereas at room temperature the NMR profiles reflect the fast reorientational disorder of the guest molecules, we report a temperature-dependent inhomogeneous broadening of the resonance lines on approaching T-c from above. This effect is assigned to a pretransitional clustering of the guest molecules and a heuristic model is developed to describe it, At very low temperature below T-c. NMR measurements give direst information on the mode of ordering of the alkane sublattice inside the urea frame. Remaining static disorder could be attributed to the incommensurate feature of the composite crystal. [References: 36]
Title:
Structural state of beta-solid solution in quenched quasicrystal-forming alloys of Al61Cu26Fe13
Authors:
Shalaeva EV. Prekul AF.
Source:
Physica Status Solidi A-Applied Research. 180(2):411-425, 2000 Aug 16.
Abstract:
Electron microscopic investigations of the structural state have been carried out for the beta(CsCl-type)-phase in the quenched quasicrystal-forming two-phase (iota + beta) alloy Al61Cu26Fe13. We conclude that in the vicinity of compositions at which the icosahedral phase (iota) is formed, at deviations from the composition Al-3(Cu,Fe)(2) towards Al(Cu,Fe), the beta(CsCl-type)-solid solution has a heterogeneous structure (a state similar to the diffuse incommensurable omega-phase in b.c.c.-solid solutions). This structure includes the beta-matrix with fine regions of correlated omega-like displacements which in a certain way are interrelated with the tau(3)-short-range order of substitution. It is concluded that the beta(CsCl-type)-phase of Al61-xCu26+yFe13-z reveals structural signs typical for electron-stabilized solid solutions, and because of this, the beta-phase demonstrates a "dielectric" behavior of its electronic properties. An assumption has been made that the regions with omega-displacements are involved in the structural transformation beta-phase --> iota-phase. [References: 32]
Title:
Precipitation of an icosahedral quasicrystalline phase in Hf59Ni8CU20Al10Ti3 metallic glass
Authors:
Li CF. Saida J. Matsushita M. Inoue A.
Source:
Philosophical Magazine Letters. 80(9):621-626, 2000 Sep.
Abstract:
The crystallization process of a Hf59Ni8Cu20Al10Ti3 metallic glass was studied using differential scanning calorimetry (DSC), X-ray diffraction and transmission electron microscopy. Two exothermic peaks are observed in the DSC curve of the as-quenched sample. It was revealed that the two reactions correspond to the phase transformations amorphous --> icosahedral phase + fee phase and icosahedral phase + fcc phase --> Hf2Cu + Al16Hf6Ni7 + Hf3Al2, where a = 0.254nm for the icosahedral phase and a = 0.53nm for the fee phase. Nanobeam electron diffraction patterns corresponding to the fivefold, threefold and twofold symmetries of a quasicrystal were obtained, revealing that the quasicrystal is an icosahedral phase. It is suggested that the present report on a Hf-based icosahedral phase is helpful for understanding the structural relationship between amorphous and icosahedral phases. [References: 11]
Title:
An ordered arrangement of atom columnar clusters in a pentagonal quasiperiodic lattice of an Al-Ni-Co decagonal quasicrystal
Authors:
Hiraga K. Ohsuna T. Nishimura S.
Source:
Philosophical Magazine Letters. 80(9):653-659, 2000 Sep.
Abstract:
The structure of an AI-Ni-Co decagonal quasicrystal (called the S1-type superstructure), which shows diffraction patterns with superlattice reflections, has been studied by atomic-scale observations of electron microscopy. The structure of the decagonal quasicrystal can be characterized as an ordered arrangement of two kinds of atom columnar cluster with different directions of pentagonal symmetry. A fundamental lattice, which is constructed by connecting all the atom dusters, shows st pentagonal quasiperiodic lattice with a bond length of about 2 nm. The pentagonal lattice is divided into two superlattices, which are constructed by connecting atom clusters with the same directions of pentagonal symmetry, with a bond length of 2 tau nm (tau is the golden ratio). [References: 8]
Title:
Preparation and crystal structure of the pseudo-decagonal approximant Mn3Ga5
Authors:
Bostrom M. Hovmoller S.
Source:
Journal of Solid State Chemistry. 153(2):398-403, 2000 Sep.
Abstract:
The crystal structure of tetragonal Mn3Ga5 has been determined from single-crystal X-ray diffraction data. The space group is P4(2)/nmc with a = 12.659(2) Angstrom and b = 24.616(6) Angstrom. R-w = 1.50%. The structure is mainly made up of 38 atoms clusters isotypic to those found in gamma-brass, Cu5Zn8. (C) 2000 Academic Press. [References: 12]
Title:
Quasicrystalline coatings: Thermal evolution of structure and properties
Authors:
Lang CI. Sordelet DJ. Besser MF. Shechtman D. Biancaniello FS. Gonzalez EJ.
Source:
Journal of Materials Research. 15(9):1894-1904, 2000 Sep.
Abstract:
Quasicrystals (QCs) are known to exhibit unique properties as a result of their unique quasiperiodic structure. Real quasicrystalline (QC) materials, however, may exhibit complex phase structures, and as a consequence, their properties may differ from expectations. In the present work, QC coatings of the Al-Cu-Fe, Al-Cu-Fe-Cr, and Al-Pd-Mn systems were prepared by a plasma spray process, followed by heat treatments in the range 500-800 degrees C. The phase structure and evolution of the coatings were evaluated, and thermal diffusivity, hardness, and friction coefficient were measured. The presence of quasicrystalline and crystalline phases and their influence on these properties is systematically considered for the first time. Broadly, the coatings exhibit the properties expected of QC materials, low thermal diffusivity, high hardness, and low coefficients of friction, but it is also shown that these properties can be sensitive to the phase structure of the coatings. This suggests that phase structure may be manipulated by heat treatment to optimize the properties of QC coatings. [References: 41]
Title:
Cation ordering in complex oxides [Review]
Authors:
Davies PK.
Source:
Current Opinion in Solid State & Materials Science. 4(5):467-471, 1999 Oct.
Abstract:
Several recent papers have addressed the fundamental aspects of the stability and kinetics of ordering in complex oxides, and investigated systems where the properties are mediated by the degree of order. Cation ordering reactions have been shown to induce large alterations in the dielectric, ferroelectric, magnetic, and electronic response of many complex oxides. The majority of the cited publications focus on ion ordering in perovskite-related structures; however, additional examples include the ordering of structural slabs and formation of modulated intergrowth structures. (C) 2000 Elsevier Science Ltd. All rights reserved. [References: 41]
Title:
Metastable phase formation during the decomposition of Fe-20 at.% Mo
Authors:
Isheim D.
Source:
Acta Materialia. 48(11):2873-2883, 2000 Jun 30.
Abstract:
The early stages of the isothermal decomposition of an Fe-20 at.% Mo alloy at 500 degrees C have been studied by means of atom-probe (AP) and field-ion microscopy (FIM), as well as high-resolution (HREM) and conventional (CTEM) transmission electron microscopy. CTEM reveals a characteristic modulated structure oriented along the (100)-type directions of the b.c.c. matrix. Electron diffraction patterns show satellite-like intensities close to the fundamental reflections in (100)-type directions, indicating an approximate 6 nm characteristic length scale of the decomposition microstructure. FIM and HREM reveal precipitates about 2 nm in size with a b.c.c. structure formed coherently within the matrix. AP analyses show these precipitates to consist of almost pure Mo. The size misfit between the Mo-rich precipitates and the Fe-rich matrix causes large coherency strains, resulting in precipitate alignment along (100)-type directions. The Mo-rich b.c.c. solid solution precipitates in a metastable equilibrium with the Fe-rich b.c.c. matrix, whereas the formation of the equilibrium intermetallic phases is kinetically suppressed. A coherent metastable miscibility gap between the Fe-rich and the Mo-rich b.c.c. solid solution is assessed by incorporating a continuum elasticity strain-energy term into the Gibbs free energy. (C) 2000 Acta Metallurgica me. Published by Elsevier Science Ltd. All rights reserved. [References: 41]

Update: 27-Sep-2000

Title:
Cleavage dislocations and cracks in quasicrystals
Authors:
Khannanov SK.
Source:
Physics of Metals & Metallography (English Translation of Fizika Metallov i Metallovedenie). 90(1):1-9, 2000 Jul.
Abstract:
A continuum theory of cracks in quasicrystals is developed, in which the cracks are described by distributions of cleavage dislocations. The distribution functions of cleavage dislocations obey a set of integral equations whose kernels are determined by special solutions to the elastic problem for a quasicrystal. Therefore, the problems of the theory of elasticity of quasicrystals are also considered in much detail. As an application, an analytic solution for a straight crack is obtained for an important case of uniform external stresses.
Title:
High resolution transmission electron microscopy observation of thermally fluctuating phasons in decagonal Al-Cu-Co
Authors:
Edagawa K. Suzuki K. Takeuchi S.
Source:
Physical Review Letters. 85(8):1674-1677, 2000 Aug 21.
Abstract:
In situ high-temperature, high resolution transmission electron microscopy (HRTEM) was performed on an Al-Cu-Co decagonal quasicrystal, to investigate thermal fluctuation of phasons. A tiling pattern constructed from the HRTEM image was analyzed in the framework of the strip-projection method. Transitions between two local tile arrangements were observed at high temperature for the first time, and were shown to correspond to a thermal phason fluctuation.
Title:
ALCHEMI study of an Al72Ni20Co8 decagonal quasicrystal
Authors:
Saitoh K. Tanaka M. Tsai AP. Rossouw CJ.
Source:
Journal of the Physical Society of Japan. 69(8):2379-2382, 2000 Aug.
Abstract:
Two-dimensional channelling patterns, derived from variations in characteristic X-ray emission rates as a function of incident electron beam orientation, have been recorded from an Al72Ni20Co8 decagonal quasicrystal for the first time. These channelling patterns indicate that the Al and transition metal atoms occupy different sets of sublattice sites, and that (to a good approximation) both Ni and Co atoms randomly occupy a similar set of sublattice sites, i.e. they are mutually disordered. This is shown to support the view that the structure of this alloy is determined primarily by the number of electrons per atom; e/a.
Title:
Quasiperiodic superstructure with an ordered arrangement of atom columnar clusters in an Al-Ni-Ru decagonal quasicrystal with 0.4 nm periodicity
Authors:
Sun W. Ohsuna T. Hiraga K.
Source:
Journal of the Physical Society of Japan. 69(8):2383-2386, 2000 Aug.
Abstract:
We have found a highly perfect quasiperiodic superstructure of a decagonal quasicrystal (D-phase), which is formed bi the ordered arrangement of atom columnar clusters. The D-phase with 0.4 nm periodicity, which has been found in a conventionally solidified Al70Ni20Ru10 alloy, shows many superlattice reflections in its tenfold electron diffraction pattern. High-resolution electron microscopy of the D-phase reveals that the ordered arrangement of two types of atom columnar clusters with different directions of pentagonal symmetry allows the fundamental lattice of a pentagonal tiling to be subdivided into two sublattices of rhombic tilings with edge length enlarged tau times (tau is the golden ratio).
Title:
Neutron study of magnetic phase transitions in TbCo2Si2 and DyCo2Si2
Authors:
Szytula A. Balanda M. Penc B. Hofmann M.
Source:
Journal of Physics-Condensed Matter. 12(33):7455-7462, 2000 Aug 21.
Abstract:
Neutron diffraction and magnetic measurements reveal a phase transition in TbCo2Si2 and DyCo2Si2 from a collinear antiferromagnetic AFI type order with the k-vector [001] to an incommensurate sine-modulated magnetic structure described by the wavevector k = (0, 0, 1-k(z)). The transition above occurs directly below the Neel temperature and k, is equal to 0.042(1) for TbCo2Si2 and 0.049(1) for DyCo2Si2 In both phases magnetic moments localized on rare earth ions are parallel to the c-axis.
Title:
Charge ordering in Pr0.5Ca0.5MnO3 thin films: A new form initiated by strain effects of LaAlO3 substrate
Authors:
Haghiri-Gosnet AM. Hervieu M. Simon C. Mercey B. Raveau B.
Source:
Journal of Applied Physics. 88(6):3545-3551, 2000 Sep 15.
Abstract:
The growth of [101] epitaxial films of Pr0.5Ca0.5MnO3 on LaAlO3 substrates has been achieved. The structure, nanostructure, and magnetotransport properties are reported and compared to those of the bulk material. The electron diffraction study evidences, at RT, a monoclinic cell with a approximate to c approximate to 5.4 Angstrom, b approximate to 7.6 Angstrom, and beta approximate to 91 degrees. The monoclinic distortion is assumed to be due to strain effects. At 92 K, a system of extra reflections is observed which implies an incommensurate modulated structure. The component q of the modulation vector along a* ranges between 0.35 and 0.40. The lattice images show that the modulation is established throughout the whole film. The q value observed in the film is significantly lower than the one of the bulk material. This effect is correlated to strain effects of the substrate, limiting the cell distortion induced by charge ordering. An unusual insulating-ferromagnetic phase is observed with a critical temperature of 240 K, close to the T-CO. (C) 2000 American Institute of Physics. [S0021- 8979(00)08415-2].
Title:
The modulated crystal structure of the molecular adduct of 2,4,6-trinitrobenzoic acid with 2,6-diaminopyridine
Authors:
Smith G. Bott RC. Rae AD. Willis AC.
Source:
Australian Journal of Chemistry. 53(6):531-534, 2000.
Abstract:
The 1 : 1 adduct of 2,4,6-trinitrobenzoic acid (tnba) with 2,6-diaminopyridine (2,6-dap), [(2,6-dap)(+)(tnba)(-)], has been prepared and the low-temperature crystal structure has been determined by X-ray crystallography. A modulated structure has been identified and refined by using a stacking fault model that requires reflection data to be put on three scales depending on an index condition. Crystals are triclinic, space group P (1) over bar, with Z 8 in a cell of dimensions a 13.538(3), b 14.516(4), c 16.480(4) Angstrom; alpha 97.17(2), beta 105.69(2), gamma 106.09(2)degrees. The structure involves proton transfer from the tnba molecule to the 2,6-dap molecule, with the resulting pyridinium proton and an amine proton interacting with the carboxyl oxygens of the tnba molecule in a primary cyclic hydrogen-bonding association. Additional peripheral hydrogen bonding completes a two-dimensional sheet structure. [References: 13]
Title:
First-principles interatomic potentials for transition-metal aluminides. III. Extension to ternary phase diagrams
Authors:
Widom M. Al-Lehyani I. Moriarty JA.
Source:
Physical Review B. 62(6):3648-3657, 2000 Aug 1.
Abstract:
Modeling structural and mechanical properties of intermetallic compounds and alloys requires detailed knowledge of their interatomic interactions. The first two papers of this series [Phys. Rev. B 56, 7905 (1997); 58, 8967 (1998)] derived first-principles interatomic potentials for transition-metal (TM) aluminides using generalized pseudopotential theory (GPT). Those papers focused on binary alloys of aluminum with first-row transition metals and assessed the ability of GPT potentials to reproduce and elucidate the alloy phase diagrams of Al-Co and Al-Ni. This paper addresses the phase diagrams of the binary alloy Al-Cu and the ternary systems Al-Co-Cu and Al-Co-Ni, using GPT pair potentials calculated in the limit of vanishing transition-metal concentration. Despite this highly simplifying approximation, we find rough agreement with the known low-temperature phase diagrams, up to 50% total TM concentration provided the Co fraction is below 25%. Full composition-dependent potentials and many-body interactions would be required to correct deficiencies at higher Co concentration. Outside this troublesome region, the experimentally determined stable and metastable phases all lie on or near the convex hull of a scatter plot of energy versus composition. We verify, qualitatively, reported solubility ranges extending binary alloys into the ternary diagram in both Al-Co-Cu and Al-Co-Ni. Finally, we reproduce previously conjectured transition-metal positions in the decagonal quasicrystal phase.
Title:
A quasicrystallic domain wall in nonlinear dissipative patterns
Authors:
Malomed BA. Rotstein HG.
Source:
Physica Scripta. 62(2-3):164-168, 2000 Aug-Sep.
Abstract:
We propose an indirect approach to the generation of a two-dimensional quasiperiodic (QP) pattern in convection and similar nonlinear dissipative systems where a direct generation of stable uniform QP planforms is not possible. An eightfold QP pattern can be created as a broad transient layer between two domains filled by square cells (SC) oriented under an angle of 45 degrees relative to each other. A simplest particular type of transient layer is considered in detail. The structure of the pattern is described in terms of a system of coupled real Ginzburg-Landau (GL) equations, which are solved by means of combined numerical and analytical methods. It is found that the transient "quasicrystallic" pattern exists exactly in a parametric region in which the uniform SC pattern is stable. In fact, the transient layer consists of two different sublayers, with a narrow additional one between them. The width of one sublayer (which locally looks like the eightfold QP pattern) is large, while the other sublayer (that seems like a pattern having a quasiperiodicity only in one spatial direction) has a width similar to 1. Similarly, a broad stripe of a twelvefold QP pattern can be generated as a transient region between two domains of hexagonal cells oriented at an angle of 30 degrees.
Title:
Aperiodic self-replicating inorganic structures
Authors:
Bursill LA.
Source:
Modern Physics Letters B. 14(10):337-344, 2000 Apr 30.
Abstract:
A prototype model is introduced for self-replicating octahedral shell structures. The structure is inherently aperiodic and unable to grow like a normal crystal. Conditions under which this growth mechanism may become favored energetically are discussed. High-resolution electron microscope images of the clay mineral allophane, an analog of the spheroidal fullerenes, are described. Kinetic equations are derived assuming an autocatalytic self-replicating growth mechanism for this model. More general mathematical treatments of self-replicating systems are also reviewed and discussed.
Title:
High-strength aluminum alloys containing nanoquasicrystalline particles
Authors:
Inoue A. Kimura H.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 286(1):1-10, 2000 Jun 30.
Abstract:
By the use of homogeneous dispersion of nanoscale quasicrystalline particles in fee-Al phase, new Al-based alloys with useful mechanical properties were developed. The structure consists of nanoscale icosahedral particles with a size of 30-50 nm surrounded by fee-Al with a thickness of about 5-10 nm and no high-angle grain boundary is observed in the Al phase. The icosahedral phase has a high volume fraction of 60-70%. The unique structure is formed by the unique solidification mode in which the icosahedral phase precipitates as a primary phase followed by solidification of Al phase from the remaining liquid. The features of mechanical properties for the nanoquasicrystalline alloys are classified into three types, i.e. high tensile strength type of 800 MPa in Al-Cr-Ce-Co and Al-Mn-Ce-Co systems high elongation type of 30% in Al-Mn-Cu-Co system and high elevated temperature strength type of 500 MPa at 473 K and 350 MPa at 573 K in Al-Fe-Cr-Ti system. These mechanical properties are superior to those for the conventional Al-based crystalline alloys and the extension of the new Al-based alloys to practical. application has also been described. Published by Elsevier Science S.A.
Title:
Stable icosahedral quasicrystals in the Cd-Mg-RE (RE = rare earth element) systems
Authors:
Guo J. Abe E. Tsai AP.
Source:
Japanese Journal of Applied Physics Part 2-Letters. 39(8A):L770-L771, 2000 Aug 1.
Abstract:
A stable icosahedral phase has been found in a series of Cd65Mg20RE15 (RE = Y, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) alloys. These icosahedral alloys have quasilattice parameters from 0.5571 to 0.5799 nm. Electron diffraction study confirmed that the icosahedral quasicrystals have a primitive icosahedral structure. [References: 9]
Title:
Melting and solidification behaviour of lead nanoparticles embedded in amorphous and quasicrystalline matrices of Al-Cu-V
Authors:
Singh A. Tsai AP.
Source:
Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes & Review Papers. 39(7A):4082-4087, 2000 Jul.
Abstract:
Melting and solidification behaviour of lead particles of size about 30 nm has been studied in amorphous and quasicrystalline matrices of an Al75Cu15V10 alloy. The lead particles had semi-shperical morphology, and often showed twinning. The particles showed a depression in the melting temperature by about 17 degrees C in the amorphous matrix and about 6 degrees C in the quasicrystalline matrix, as compared to the bull; melting temperature. On solidification an undercooling of greater than 60 degrees C is obtained. The lowering of the melting temperature and a high undercooling on solidification is qualitatively explained to be due to the interfacial energies of the liquid or solid lead with the matrix.
Title:
Persistence of a non-antiphase modulated magnetic structure to T -> 0 in the heavy electron compound YbPtAl
Authors:
Bonville P. Malaman B. Ressouche E. Sanchez JP. Abd-Elmeguid M. Geibel C. Trovarelli O.
Source:
Europhysics Letters. 51(4):427-433, 2000 Aug.
Abstract:
Measurements by Yb-170 Mossbauer spectroscopy down to 0.025 K and by neutron diffraction down to 1.7 K have been performed in the heavy electron compound YbPtAl (T-N similar or equal to 5.8 EC). At 0.025 K, the Mossbauer spectrum evidences a non-square modulation of the magnetic moment, incommensurate with the lattice spacings. This is the first clear example of a Kramers local moment Yb-based system where the Kondo singlet ground state allows a modulated magnetic structure to persist to T --> OK. The 3rd- and 5th-order harmonics of the modulation could be measured, and their thermal variation was followed from 0.025 K to 5 K. An abrupt decrease of both harmonics at 3 K is concomitant with a peak in the specific heat, suggesting a first-order phase transition where the modulation transforms into a pure sine wave.
Title:
On the fractal nature of Penrose tiling
Authors:
Ramachandrarao P. Sinha A. Sanyal D.
Source:
Current Science. 79(3):364-366, 2000 Aug 10.
Abstract:
An earliest preoccupation of man has been to find ways of partitioning infinite space into regions having a finite number of distinct shapes and yielding beautiful patterns called tiling. Archaeological edifices, everyday objects of use like baskets, carpets, textiles, etc. and many biological systems such as beehives, onion peels and spider webs also exhibit a variety of tiling. Escher's classical paintings have not only given a new dimension to the artistic value of tiling but also aroused the curiosity of mathematicians. The generation of aperiodic tiling with five-fold rotational symmetry by Penrose in 1974 and the more recent production of decorated pentagonal tiles by Rosemary Grazebrook have heightened the interest in the subject among artists, engineers, biologists, crystallographers and mathematicians(1-5). In spite of its long history, the subject of tiling is still evolving. In this communication, we propose a novel algorithm for the growth of a Penrose tiling and relate it to the equally fascinating: subject of fractal geometry pioneered by Mandelbrot(6). The algorithm resembles those for generation of fractal objects such as Koch's recursion curve, Peano curve, etc. and enables consideration of the tiling as cluster growth as well. Thus it clearly demonstrates the dual nature of a Penrose tiling as a natural and a nonrandom fractal.
Title:
Formation of icosahedral phase from amorphous Zr65Al7.5Cu12.5Ni10Ag5 alloys
Authors:
Lee JK. Choi G. Kim DH. Kim WT.
Source:
Applied Physics Letters. 77(7):978-980, 2000 Aug 14.
Abstract:
The kinetic behavior of quasicrystalline phase formation in amorphous Zr65Al7.5Cu12.5Ni10Ag5 alloys has been studied by using differential scanning calorimetry (DSC), x-ray diffractometry, and transmission electron microscopy. DSC trace obtained during continuous heating from 473 to 873 K shows two distinct exotherms with peak temperatures of 727 and 776 K. The first and second exothermic reactions, respectively, correspond to the formation of quasicrystalline phase from the amorphous matrix and the formation of tetragonal CuZr2 and hexagonal Zr6NiAl2 phases from the previously formed quasicrystalline phase. Partial replacement of Cu by Ag enhanced the formation of quasicrystalline phase from the amorphous structure. Johnson-Mehl-Avrami analysis of isothermal transformation data suggests that the formation of quasicrystalline phase is not entirely polymorphic in nature and may involve partitioning of solute at a later stage. (C) 2000 American Institute of Physics. [S0003-6951(00)04833-6].
Title:
Incommensurate structures studied by a modified density-matrix renormalization-group method
Authors:
Gendiar A. Surda A.
Source:
Physical Review B. 62(6):3960-3967, 2000 Aug 1.
Abstract:
A modified density-matrix renormalization-group (DMRG) method is introduced and applied to classical two-dimensional models: the anisotropic triangular nearest-neighbor Ising model and the anisotropic triangular next-nearest-neighbor using model. Phase diagrams of both models have complex structures and exhibit incommensurate phases. It was found that the incommensurate phase completely separates the disordered phase from one of the commensurate phases, i.e., the nonexistence of the Lifshitz paint is conjectured in phase diagrams of both models with the DMRG method. It is shown that the DMRG method is also an effective-field approximation, but in spite of that it yields the correct value of the domain wall density critical exponent.

Update: 5-Sep-2000

Title:
Structural aspects of the threefold surface of icosahedral Al-Pd-Mn
Authors:
Rouxel D. Cai TH. Jenks CJ. Lograsso TA. Ross A. Thiel PA.
Source:
Surface Science. 461(1-3):L521-L527, 2000 Aug 1.
Abstract:
We report the first STM study of a threefold surface of an icosahedral quasicrystal. We find that a rough, cluster-dominated structure evolves into a terrace-step morphology, with increasing temperature. The terraces display a fine structure whose long-range order is consistent with threefold symmetry. The fine structure includes small, deep holes. The steps can be very straight, serving to bound equilateral triangles (or portions thereof). These straight steps can cut directly across meandering step edges, superimposing a triangular 'shadow' upon the other terrace-step landscape. The data suggest that the triangles grow outward from a special type of central point. The triangles may represent the initial stages of facetting. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Generalized Drude formula for the optical conductivity of quasicrystals
Authors:
Mayou D.
Source:
Physical Review Letters. 85(6):1290-1293, 2000 Aug 7.
Abstract:
We derive a generalized Drude formula for the optical conductivity of quasicrystals, assuming a diffusion law in a perfect quasicrystal L(t) proportional to t(beta), where L(t) measures the spreading of a wave packet in a time t. We show that these-called Drude peak in the optical conductivity, characteristic of metals, is strongly modified. If beta < 1/2 the Drude peak is even replaced by a dip and the de conductivity increases when disorder increases. An interpretation of the experimental results on icosahedral and decagonal phases is proposed.
Title:
Phase transitions in the adsorption system Li/Mo(112)
Authors:
Fedorus A. Kolthoff D. Koval V. Lyuksyutov I. Naumovets AG. Pfnur H.
Source:
Physical Review B. 62(4):2852-2861, 2000 Jul 15.
Abstract:
Experimental studies of the phase transitions in the adsorption system Li/Mo(112) are presented. This system is a model system for highly anisotropic interactions. From measurements of the half-widths of the low-energy electron diffraction spot profiles a phase diagram is derived for the whole submonolayer region of coverage in the temperature range 100-500 K. The commensurate low-coverage phases below theta=0.6 form chains normal to the troughs of the substrate. The commensurate p(4X1) phase, which is completed at a coverage, theta, of 0.25 monolayers (ML), seems to he truly long range ordered, whereas the p(2x1) phase at theta=0.5 still contains domain boundaries even at the lowest temperature of 100 K. Both undergo temperature driven order-disorder phase transitions. In contrast, the incommensurate phases existing in the coverage range theta=0.66-0.90 form chains along the troughs, which are only weakly coupled normal to the troughs of the substrate. These phases exhibit two coverage-driven phase transitions from rectangular to oblique units cells and back at critical coverages of 0.66 and 0.85, respectively, and represent floating solids. As a function of temperature, they undergo a two-dimensional melting transition. Close to the critical coverages, the melting temperatures show a sharp drop below the temperature range accessible in our experiments. Both functional dependences of the angular deviation from 90 degrees and of the melting temperature on coverage are in good agreement with a phenomenological theoretical model, assuming an instability of the shear modulus of the adsorbate unit cell at the critical coverages.
Title:
Electron diffraction study of octagonal-cubic phase transitions in Mn-Si-Al
Authors:
Xu L. Wang N. Lee ST. Fung KK.
Source:
Physical Review B. 62(5):3078-3082, 2000 Aug 1.
Abstract:
We report the observation of two kinds of octagonal-cubic transition to either the beta-Mn-type structure or the Mn3Si crystal following annealing Mn-Si-Al octagonal quasicrystal at different heating speeds. A theoretical analysis has been given and the simulated diffraction patterns match the experimental results well. It is confirmed that there exist two kinds of phason strain fields, which transform the octagonal phase into the two cubic crystalline phases, respectively. It is conjectured that the octagonal-cubic transitions feature the formation of local periodic structures.
Title:
Evidence for existence of two different phases in Bi1.8Pb0.2Sr2Ca2Cu3Ox
Authors:
Zhang H. Cheng LL. Zhao Y. Du X.
Source:
Physica C. 337(1-4):245-248, 2000 Jul.
Abstract:
The elaborated and well characterized samples of Bi1.8Pb0.2Sr2Ca2Cu3Ox (2223 phase), as prepared, quenched from a partially melting state, and after melting, were studied carefully by X-ray diffraction (XRD), thermal analysis, electron diffraction (ED), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX) microanalysis. Some evidence for the existence of two different phases in the :2223 phase has been obtained, in which one has incommensurate modulation and the other has none. Our experiment preliminarily gives the conditions for the existence of the two different phases. The phase within commensurate modulation decomposes before melting, and the phase without it can exist in partially melting state. Based on the above fact, we tried to grow the single crystal of the 2223 phase from a partially melting state and got a small one. Unfortunately, the crystal is very unstable. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 9]
Title:
A possible cause of the peak effect in Y-Ba-Cu-O melt-grown bulks: modulation in oxygen distribution
Authors:
Suematsu H. Okamura H. Lee S. Nagaya S. Yamauchi H.
Source:
Physica C. 338(1-2):96-102, 2000 Aug 1.
Abstract:
A novel transmission electron microscopic technique, termed as large-area high-resolution transmission electron microscopy (LA-HRTEM), has been developed for nanoscopic observations of the lattice defects in an area as wide as 20 X 20 mu m(2). Utilizing LA-HRTEM, a number of twin boundaries in the YBa2Cu3O7-d (Y-123) matrix are observed so that statistical analyses may be made on the inter-twin-boundary distance (d(tw)). After the annealing of a sample exhibiting no peaks in the critical current density (J(c)) vs. applied magnetic field (H) curve, the peak effect re-appeared as the value of d(tw) decreased. This fact implies that d(tw) is undoubtedly correlated with the degree of peak effect. Some HRTEM images have revealed that the oxygen-depleted regions in the vicinity of twin boundaries are wider for samples exhibiting a pronounced peak effect than for those with less pronounced peak effect. The oxygen-depleted regions, whose width is related to the value of d(tw), may be thought to have lower critical temperatures (T-c) than the rest. Then, the variation in T-c due to the oxygen-depleted region in the vicinity of somewhat regularly arranged twin boundaries is likely to work towards some sort of flux pinning to cause the peak effect. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
The magnetic properties of the ternary intermetallic RPtGa (R = Gd-Er) compounds
Authors:
Penc B. Hofmann M. Slaski M. Szytula A. Zygmunt A.
Source:
Physica B. 291(1-2):19-28, 2000 Aug.
Abstract:
Neutron diffraction and magnetometric data for the RPtGa compounds (R = Gd-Er) are presented. These compounds crystallize in the orthorhombic TiNiSi-type structure. The crystallographic space group is Pnma. The temperature dependence of the magnetic susceptibility indicates that these compounds are antiferromagnets with the Neel temperature between 23 K for GdPtGa and 3.2 K for ErPtGa. The structural parameters and the magnetic structures of RPtGa (R = Tb-Er) compounds have been determined on the basis of neutron diffraction data. At 1.5 K, TbPtGa and 21 and DyPtGa exhibit a collinear magnetic structure described by the wave vector k = (0, 1.2, 0). The magnetic moments are located on the rare-earth ions. Increase of temperature above T-1 = 18 K for TbPtGa and above 7 K for DyPtGa, leads to a change of this structure into a sine-modulated one. The collinear magnetic order in HoPtGa described by the wave vector k = (1/2, 1/2, 0) at 1.5 K changes into a sine-modulated structure at T-t = 2.4 K. In ErPtGa a sine-modulated structure exists between 1.5 K and the Ni el temperature of 3.2 K. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Decagonal quasicrystal with ordered body-centred (CsCl-type) hypercubic lattice
Authors:
Ohsuna T. Sun W. Hiraga K.
Source:
Philosophical Magazine Letters. 80(8):577-583, 2000 Aug.
Abstract:
An ordered structure, which was found in a decagonal quasicrystal with 0.4 nm periodicity in a conventionally solidified Al70Ni20Ru10 alloy, has been examined theoretically by the projection of an ordered body-centred (CsCl-type) hypercubic lattice. The ordered structure can be characterized as an ordered arrangement of two kinds of atom columnar cluster with different directions of pentagonal symmetry. Two lattices, which are constructed by connecting the atom clusters in the same directions, can be interpreted as ordered sublattices formed by each of vertex and body-centred positions of the CsCl-type hypercubic lattice. Diffraction patterns calculated from the ordered and disordered body-centred hypercubic lattices replicate well the electron diffraction patterns observed from the Al-Ni-Ru and other decagonal quasicrystals. [References: 13]
Title:
Structural study of electrochemically obtained Li2+xTi3O7
Authors:
de Dompablo MEAY. Varez A. Garcia-Alvarado F.
Source:
Journal of Solid State Chemistry. 153(1):132-139, 2000 Aug.
Abstract:
Li2Ti3O7, a ramsdellite-type compound, is able to reversibly insert approximately 2.3 lithium ions per formula down to 1 V versus lithium. Both electron and X-ray diffraction techniques show that the electrochemically inserted compounds Li2+xTi3O7, with x < 2, maintain the ramsdellite structure, although some important microstructural differences are observed. For example the compound with x = 0.55 exhibits an incommensurate modulation (q approximate to 1/3 c*), On the other hand, for Li2+xTi3O7 with x > 2, a commensurable a x 2b x c cell can be proposed. A close structural relationship between the intercalated compounds and host compound, together with the small changes in the basic ramsdellite cell parameters during the intercalation process, is likely at the origin of the good cycling behavior of a lithium cell using Li2Ti3O7 as the positive electrode. (C) 2000 Academic Press.
Title:
Independent (q)over-right-arrow and 2(q)over-right-arrow distortions in the incommensurately modulated low-temperature structure of NiTa2Se7
Authors:
Ludecke J. Schneider M. van Smaalen S.
Source:
Journal of Solid State Chemistry. 153(1):152-157, 2000 Aug.
Abstract:
The modulated low-temperature structure of NiTa1.98Nb0.02Se7 has been determined by X-ray diffraction using synchrotron radiation. The superspace group of the modulated structure at 15 K is C2/m (0, q(b), 0)s0 with q(b) = 0.483(2). The lattice parameters were determined to a = 13.807(6) Angstrom, b = 3.483(1) Angstrom, c = 18.564(11) Angstrom, and beta = 108.95(4)degrees with Z = 4, Satellite reflections up to second order were measured. Refinement with first- and second-order harmonic components of the modulation functions converged to R = 0.059. The first-order harmonic was found predominantly on the double chain of Ni and Se2 atoms. Shifts were found parallel to the (a) over right arrow and (c) over right arrow axes, in good agreement with earlier investigations, The major part of the second harmonic was found on the Ta2 atoms, with amplitudes of secondary importance on the surrounding Se atoms. Shifts of the Ta2 atoms were found parallel to (b) over right arrow, thus forming a longitudinal wave. It is argued that the modulations according to the first-order and the second-order harmonics should be considered as independent CDW'S. (C) 2000 Academic Press.
Title:
A hexagonal perovskite intergrowth compound: La2Ca2MnO7
Authors:
Wang YX. Lin JH. Du Y. Qin RW. Han B. Loong CK.
Source:
Angewandte Chemie-International Edition. 39(15):2730-2732, 2000.
Title:
Towards a unified description of the AMOB(2)O(5) (A = K, Rb, Cs, Tl; M = Nb, Ta) family of compounds
Authors:
Schmid S. Withers RL. Corker D. Baules P.
Source:
Acta Crystallographica - Section B, Structural Science. 56(Part 4):558-564, 2000 Aug.
Abstract:
Single-crystal X-ray diffraction data (Mo K alpha radiation) are used to re-refine the structure of RbNbOB2O5, rubidium niobium oxo pyroborate. The structure is refined as an incommensurate modulated structure with superspace group symmetry Pmn2(1)(0,0.4,0)s and lattice parameters a = 7.406 (2), b = 3.939 (2) and c = 9.475 (2) Angstrom. Refinement on 3242 unique reflections converged to R = 0.031, while a previous conventional superstructure refinement led to R = 0.090. This lowering of the R factor goes hand-in-hand with a substantial reduction in the number of refined parameters. The refinement strongly suggests that the structure is effectively incommensurately modulated, despite an apparently rational magnitude of the primary modulation wavevector and overlap of satellite reflections.
Title:
Neutron Rietveld refinement of the incommensurate phase of the ordered perovskite Pb2CoWO6
Authors:
Baldinozzi G. Calvarin G. Sciau P. Grebille D. Suard E.
Source:
Acta Crystallographica - Section B, Structural Science. 56(Part 4):570-576, 2000 Aug.
Abstract:
The incommensurate structure of lead cobalt tungstate has been refined by the Rietveld method on neutron data collected at 250 K. The space group is planar monoclinic I2/m(alpha 0 gamma)0s [a = 7.9602 (4), b = 5.6779 (3), c = 5.6967 (3) Angstrom, beta = 90.047 (5)degrees, q(inc) = 0.9000 (9)a* + 0.1735 (6)c*]. The use of powder diffraction techniques to investigate ferroelastic modulated phases is discussed and compared with a previous polydomain single-crystal structural analysis. The modulated displacements of light atoms have been determined, allowing an accurate description of the modulation of both the cations and the O-atom framework. The refinement suggests a displacive model for the phase transition, involving significant atomic shifts for Pb atoms and a quite complex mixing of tilt and deformation of the oxygen octahedra. The average character of this modulated structure is antiferroelectric.
Title:
A new stacking motif: complex alloy structures interpreted as modulated structures
Authors:
Uchida M. Matsui Y.
Source:
Acta Crystallographica - Section B, Structural Science. 56(Part 4):654-658, 2000 Aug.
Abstract:
The structures of lambda-Al4Mn, manganese aluminide, kappa-Al177Cr49Ni, chromium nickel aluminide, and epsilon-Al4Cr, chromium aluminide, which have been described in terms of the aggregation of clusters until now, are interpreted as modulated structures. They are basically composed of close-packed layers with ordered atomic vacancies. The observed stacking motif of the atoms can be found in many phases related to icosahedral and decagonal quasicrystals. This analysis will be helpful in the study of not only many complex alloys, but also quasicrystals.
Title:
Quasicrystals - Electrons in a strange sea
Authors:
Thiel PA. Dubois JM.
Source:
Nature. 406(6796):570-573, 2000 Aug 10.
Title:
Quasicrystalline valence bands in decagonal AlNiCo
Authors:
Rotenberg E. Theis W. Horn K. Gille P.
Source:
Nature. 406(6796):602-605, 2000 Aug 10.
Abstract:
Quasicrystals are metallic alloys that possess perfect long-range structural order, in spite of the fact that their rotational symmetries are incompatible with long-range periodicity. The exotic structural properties of this class of materials(1) are accompanied by physical properties that are unexpected for metallic alloys. Considerable progress in resolving the geometric structures of quasicrystals has been made using X-ray and neutron diffraction, and concepts such as the quasi-unit-cell model(2) have provided theoretical insights. But the basic properties of the valence electronic states-whether they are extended as in periodic crystals or localized as in amorphous materials-are still largely unresolved(3). Here we investigate the electronic bandstructure of quasicrystals through angle-resolved photoemission experiments on decagonal Al71.8Ni14.8Co13.4. We rnd that the s-p and d states exhibit band-like behaviour with the symmetry of the quasiperiodic lattice, and that the Fermi level is crossed by dispersing d-bands. The observation of free-electron-like bands, distributed in momentum space according to the surface diffraction pattern, suggests that the electronic states are not dominated by localization.
Title:
Incommensurate magnetic structure of the heavy fermion antiferromagnet Ce7Ni3
Authors:
Kadowaki H. Motoya K. Kawasaki T. Osakabe T. Okumura H. Kakurai K. Umeo K. Takabatake T.
Source:
Journal of the Physical Society of Japan. 69(7):2269-2279, 2000 Jul.
Abstract:
Magnetic structures of the heavy fermion antiferromagnet Ce7Ni3 have been studied by neutron diffraction using a single crystal. It undergoes the two successive phase transitions at T-N1 = 1.8K and T-N2 = 0.7K in zero field. At T-N1 Ordering of a single-k type magnetic structure with an incommensurate modulation vector k(IC) similar or equal to 0.22c* takes place. This structure is approximately a sinusoidally modulated structure of c-axis moments, which belongs to the Gamma(2) and Gamma(3) irreducible representations of the space group P6(3)mc. Root mean squares of the moments at T = 1.4K are 0.46 +/- 0.07, 0.70 +/- 0.03 and 0.10 +/- 0.05 mu(B) for the Ce1, Ce2 and Ce3 sites, respectively. Below T-N2 the incommensurate modulation vector becomes temperature independent, and a commensurate structure with k(C) = 1/4c* appears in addition to the incommensurate structure. The metamagnetic transition under the magnetic field of H-\\c = 0.16T at T = 1.5 K is a first order transition to a ferromagnetic state.
Title:
Production of single quasicrystals and their electrical resistivity in the Al-Pd-Re system
Authors:
Guo JQ. Sato TJ. Abe E. Takakura H. Tsai AP.
Source:
Philosophical Magazine Letters. 80(7):495-502, 2000 Jul.
Abstract:
Single Al-Pd-Re icosahedral quasicrystals with a maximum diameter of 5 mm have been grown by a slow cooling method on the basis of a partial phase diagram determined in the present study. Laue X-ray and electron diffraction verified the highly ordered structure of the single icosahedral quasicrystals. The electrical resistivity p of the single quasicrystals was measured to be 2000-4000 mu Omega cm at 300K and 3000-6000 mu Omega cm at 2K, revealing a negative temperature dependence with a rho(4.2K)/rho(300K) value smaller than 2.
Title:
Stability and compression behaviour of icosahedral Zn-Mg-Y quasicrystal under high pressures up to 70 GPa
Authors:
Hasegawa M. Tsai AP. Yagi T.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 80(8):1769-1778, 2000 Aug.
Abstract:
The stability of atl icosahedral Zn55Mg35Y10 quasicrystal has been investigated under uniaxial high pressures up to 70 GPa by means of an in-situ angle-dispersive X-ray powder diffraction method using synchrotron radiation and diamond anvil cell. The icosahedral structure of the Zn55Mg35Y10 quasicrystal is found to be essentially stable under high pressures up to 70 GPa. It is found that no anisotropy of the pressure dependence of d/d(0) can be distinguished for each index, indicating isotropic compression of the quasicrystal. The zero-pressure bulk modulus and its pressure derivative are calculated to be 73 +/- 1 GPa and B-0' = 3.6 +/- 0.1 respectively. This indicates that the icosahedral Zn55Mg35Y10 quasicrystal as well as the icosahedral Al60Li30Cu10 quasicrystal, both of which are of Zn-Mg-Al type, is more compressible than icosahedral Al-transition metal type quasicrystals reported so far. The sample recovered from 70 GPa is essentially of quasicrystal structure and estimated to have about 0.73% residual strain.
Title:
Electron microscopy analysis of decagonal quasicrystals in the Al-Cu-Co-Si system
Authors:
Mukhopadhyay NK. Sastry GVS. Weatherly GC.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 80(8):1795-1809, 2000 Aug.
Abstract:
Large needle-shapoed Grains of a decagonal quasicrystal in the Al-Cu-Co-Si quaternary system were prepared by slow cooling From the melt. Scanning electron microscopy, X-ray diffraction and convergent-beam electron diffraction patterns confirmed that the needles have a decagonal quasicrystal structure. Thin slices normal to the tenfold directions were prepared for transmission electron microscopy. Diffuse streaks along symmetric directions around the fundamental spots and in between weaker diffraction spots as well as satellite spots were observed in the tenfold diffraction patterns. Bright-field and dark-field images showed discontinuous lines or striations lying perpendicular to the direction of diffuse streaking. Dark contrast at the point of discontinuity of the fringes are observed along a particular direction. High-resolution electron microscopy images also indicated features corresponding to the striation contrast. The striation contrast is shown to be associated with a phason disorder boundary in the partially ordered decagonal phase. Satellite spots are attributed as a characteristic feature of the partially ordered decagonal superlattice structure, which is an intermediate state between a fully disordered and fully ordered structure of the decagonal phase. The atomic rearrangement or phason displacements in certain symmetric directions (along the pentagrids or Ammann lines in the structure) give rise to the striation contrast observed in the images. The evolution of domains consisting of periodic and quasiperiodic parallel boundaries in localized regions can be interpreted as one of the signatures of an intermediate structural state prior to the formation of a fully ordered decagonal lattice.
Title:
X-ray diffraction from perfect silicon crystals distorted by surface acoustic waves
Authors:
Tucoulou R. Pascal R. Brunel M. Mathon O. Roshchupkin DV. Schelokov IA. Cattan E. Remiens D.
Source:
Journal of Applied Crystallography. 33(Part 4):1019-1022, 2000 Aug 1.
Abstract:
High-resolution X-ray diffraction measurements were carried out on ZnO/Si devices under surface acoustic wave excitation and revealed some very clear satellite diffraction peaks that are obtained from the sinusoidal modulation of the near-surface region. This experiment shows that the propagation of a Rayleigh surface acoustic wave in a perfect crystal acts as a dynamical diffraction grating. The variation of the acoustic velocity has been followed across the crystal surface from the acoustic source region (beneath the ZnO film) to the far field region (not covered by the ZnO film).
Title:
Fe-57 NMR study of a spatially modulated magnetic structure in BiFeO3
Authors:
Zalesskii AV. Zvezdin AK. Frolov AA. Bush AA.
Source:
JETP Letters. 71(11):465-468, 2000.
Abstract:
The Fe-57 spin echo spectra were studied in local magnetic fields of a BiFeO3 ferroelectric antiferromagnet over the temperature range 77-304 K. The line shape analysis confirmed the presence of a spatially modulated, incommensurate cycloidal spin structure in BiFeO3 and allowed the actual spin distribution to be reproduced throughout the cycloid length. The distribution was found to be essentially anharmonic. The modulated structure is stable over the whole temperature range studied. The cycloid wave becomes more harmonic with temperature elevation. (C) 2000 MAIK "Nauka / Interperiodica".
Title:
Brillouin scattering study of structural phase transition in thiourea
Authors:
Takagi Y.
Source:
Ferroelectrics. 239(1-4):1027-1034, 2000.
Abstract:
Thiourea SC(NH2)(2) is a typical crystal which has many incommensurate phases. Phase transitions of thiourea have been studied by many workers. Thier temperature dependences of Brillouin scattering spectra have been studied in detail. Following results were obtained; (1) frequency shifts Delta nu of TA-mode(C-66) showed a small bend at Ti and a small jump at T-c, (2) Delta nu of LA-mode (C-11) had a small jump at T-i and bends at T-8 (modulation wave number delta=1/8) and T-c Integrated intensities of each spectra exhibited various anomalies.

Update: 19-Aug-2000

Title:
Production of single quasicrystals and their electrical resistivity in the Al-Pd-Re system
Authors:
Guo JQ. Sato TJ. Abe E. Takakura H. Tsai AP.
Source:
Philosophical Magazine Letters. 80(7):495-502, 2000 Jul.
Abstract:
Single Al-Pd-Re icosahedral quasicrystals with a maximum diameter of 5 mm have been grown by a slow cooling method on the basis of a partial phase diagram determined in the present study. Laue X-ray and electron diffraction verified the highly ordered structure of the single icosahedral quasicrystals. The electrical resistivity p of the single quasicrystals was measured to be 2000-4000 mu Omega cm at 300K and 3000-6000 mu Omega cm at 2K, revealing a negative temperature dependence with a rho(4.2K)/rho(300K) value smaller than 2.
Title:
Stability and compression behaviour of icosahedral Zn-Mg-Y quasicrystal under high pressures up to 70 GPa
Authors:
Hasegawa M. Tsai AP. Yagi T.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 80(8):1769-1778, 2000 Aug.
Abstract:
The stability of atl icosahedral Zn55Mg35Y10 quasicrystal has been investigated under uniaxial high pressures up to 70 GPa by means of an in-situ angle-dispersive X-ray powder diffraction method using synchrotron radiation and diamond anvil cell. The icosahedral structure of the Zn55Mg35Y10 quasicrystal is found to be essentially stable under high pressures up to 70 GPa. It is found that no anisotropy of the pressure dependence of d/d(0) can be distinguished for each index, indicating isotropic compression of the quasicrystal. The zero-pressure bulk modulus and its pressure derivative are calculated to be 73 +/- 1 GPa and B-0' = 3.6 +/- 0.1 respectively. This indicates that the icosahedral Zn55Mg35Y10 quasicrystal as well as the icosahedral Al60Li30Cu10 quasicrystal, both of which are of Zn-Mg-Al type, is more compressible than icosahedral Al-transition metal type quasicrystals reported so far. The sample recovered from 70 GPa is essentially of quasicrystal structure and estimated to have about 0.73% residual strain.
Title:
Electron microscopy analysis of decagonal quasicrystals in the Al-Cu-Co-Si system
Authors:
Mukhopadhyay NK. Sastry GVS. Weatherly GC.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 80(8):1795-1809, 2000 Aug.
Abstract:
Large needle-shapoed Grains of a decagonal quasicrystal in the Al-Cu-Co-Si quaternary system were prepared by slow cooling From the melt. Scanning electron microscopy, X-ray diffraction and convergent-beam electron diffraction patterns confirmed that the needles have a decagonal quasicrystal structure. Thin slices normal to the tenfold directions were prepared for transmission electron microscopy. Diffuse streaks along symmetric directions around the fundamental spots and in between weaker diffraction spots as well as satellite spots were observed in the tenfold diffraction patterns. Bright-field and dark-field images showed discontinuous lines or striations lying perpendicular to the direction of diffuse streaking. Dark contrast at the point of discontinuity of the fringes are observed along a particular direction. High-resolution electron microscopy images also indicated features corresponding to the striation contrast. The striation contrast is shown to be associated with a phason disorder boundary in the partially ordered decagonal phase. Satellite spots are attributed as a characteristic feature of the partially ordered decagonal superlattice structure, which is an intermediate state between a fully disordered and fully ordered structure of the decagonal phase. The atomic rearrangement or phason displacements in certain symmetric directions (along the pentagrids or Ammann lines in the structure) give rise to the striation contrast observed in the images. The evolution of domains consisting of periodic and quasiperiodic parallel boundaries in localized regions can be interpreted as one of the signatures of an intermediate structural state prior to the formation of a fully ordered decagonal lattice.
Title:
X-ray diffraction from perfect silicon crystals distorted by surface acoustic waves
Authors:
Tucoulou R. Pascal R. Brunel M. Mathon O. Roshchupkin DV. Schelokov IA. Cattan E. Remiens D.
Source:
Journal of Applied Crystallography. 33(Part 4):1019-1022, 2000 Aug 1.
Abstract:
High-resolution X-ray diffraction measurements were carried out on ZnO/Si devices under surface acoustic wave excitation and revealed some very clear satellite diffraction peaks that are obtained from the sinusoidal modulation of the near-surface region. This experiment shows that the propagation of a Rayleigh surface acoustic wave in a perfect crystal acts as a dynamical diffraction grating. The variation of the acoustic velocity has been followed across the crystal surface from the acoustic source region (beneath the ZnO film) to the far field region (not covered by the ZnO film).
Title:
Fe-57 NMR study of a spatially modulated magnetic structure in BiFeO3
Authors:
Zalesskii AV. Zvezdin AK. Frolov AA. Bush AA.
Source:
JETP Letters. 71(11):465-468, 2000.
Abstract:
The Fe-57 spin echo spectra were studied in local magnetic fields of a BiFeO3 ferroelectric antiferromagnet over the temperature range 77-304 K. The line shape analysis confirmed the presence of a spatially modulated, incommensurate cycloidal spin structure in BiFeO3 and allowed the actual spin distribution to be reproduced throughout the cycloid length. The distribution was found to be essentially anharmonic. The modulated structure is stable over the whole temperature range studied. The cycloid wave becomes more harmonic with temperature elevation. (C) 2000 MAIK "Nauka / Interperiodica".
Title:
Brillouin scattering study of structural phase transition in thiourea
Authors:
Takagi Y.
Source:
Ferroelectrics. 239(1-4):1027-1034, 2000.
Abstract:
Thiourea SC(NH2)(2) is a typical crystal which has many incommensurate phases. Phase transitions of thiourea have been studied by many workers. Thier temperature dependences of Brillouin scattering spectra have been studied in detail. Following results were obtained; (1) frequency shifts Delta nu of TA-mode(C-66) showed a small bend at Ti and a small jump at T-c, (2) Delta nu of LA-mode (C-11) had a small jump at T-i and bends at T-8 (modulation wave number delta=1/8) and T-c Integrated intensities of each spectra exhibited various anomalies.

Update: 14-Aug-2000

Title:
The incommensurately modulated structure of NiBi
Authors:
Lidin S. Petricek V. Stenberg L. Furuseth S. Fjellvag H. Larsson AK.
Source:
Solid State Sciences. 2(3):353-363, 2000 May.
Title:
Structural studies of charge disproportionation and magnetic order in CaFeO3
Authors:
Woodward PM. Cox DE. Moshopoulou E. Sleight AW. Morimoto S.
Source:
Physical Review B. 62(2):844-855, 2000 Jul 1.
Abstract:
The crystal and magnetic structures of CaFeO3 have been determined at 300 and 15 K using synchrotron x-ray and neutron powder-diffraction techniques. At 300 K, CaFeO3 adopts: the GdFeO3 struture, space group P-bnm with unit-cell dimensions a = 5.326 30(4), b = 5.352 70(4), and c = 7.539 86(6) Angstrom. This structure is distorted from the ideal perovskite structure by tilting of the FeO6 octahedra about [110] and [001]. The average Fe-O distance is 1.922(2) Angstrom, and the Fe-O-Fe angles are 158.4(2)degrees and 158.1(1)degrees. At 15 K the crystal structure belongs to space group P2(1)/n with a = 5.311 82(3), b = 5.347 75(4), c = 7.520 58(5) Angstrom and beta = 90.065(1)degrees, and contains two distinct Fe sites. The average Fe-O bond length is 1.872(6) Angstrom about the one iron site, and 1.974(6) Angstrom about the second site. with bond valence sums of 4.58 and 3.48, respectively. This provides quantitative evidence for charge disproportionation. 2Fe(4+) --> Fe3+ + Fe5+, at low temperature. The temperature evolution of the lattice parameters indicates a second- (or higher-) order phase transition from the orthorhombic charge-delocalized state to the monoclinic charge-disproportionated state, beginning just below room temperature. The magnetic structure at 15 K is incommensurate, having a modulation vector [delta,0,delta] with delta similar to 0.322, corresponding to one of the < 111 > directions in the pseudocubic cell. A reasonable fit to the magnetic intensities is obtained with the recently proposed screw spiral structure [S. Kawasaki et al., J. Phys. Sec. Jpn. 67, 1529 (1998)], with Fe moments of 3.5 and 2.5 mu(B), respectively. However, a comparable lit is given by a sinusoidal amplitude-modulated model in which the Fe moments are directed along [010], which leaves open the possibility that the true magnetic structure may be intermediate between the spiral and sinusoidal models (a fan structure).
Title:
Anisotropy of acoustic-phonon properties of an icosahedral quasicrystal at high temperature due to phonon-phason coupling
Authors:
Rochal SB. Lorman VL.
Source:
Physical Review B. 62(2):874-879, 2000 Jul 1.
Abstract:
The equations of motions for the medium with an icosahedral qusicrystalline symmetry are generalized. It is shown that phonon-phason coupling in an icosahedral quasicrystal leads to the dependence of the acoustic phonons; velocity and the attenuation coefficient on the propagation direction in a temperature region close to the fusion point. The analytical expressions for the dispersion of waves propagating along the symmetry axes are obtained. The anisotropy of acoustic properties of decagonal and dodecagonal quasicrystals due to phonon-phason interaction is shown to be impossible. The obtained results may be used for experimental acoustic determination of the elastic constants of icosahedral quasicrystals.
Title:
High-resolution powder neutron diffraction study of helimagnetic order in CrP1-xVxO4 solid solutions
Authors:
Wright JP. Attfield JP. David WIF. Forsyth JB.
Source:
Physical Review B. 62(2):992-997, 2000 Jul 1.
Abstract:
High-resolution powder neutron diffraction measurements on CrP1-xVxO4 samples with x = 0, 0.02, 0.04, 0.06 and 0.08 have yielded precise parameters for their low temperature helimagnetic structures which have a magnetic propagation vector (k(x),0,0). The refined values of k(x) increase from k(x) = 0.331 for x = 0 to k(x) = 0.337 for x = 0.08 and no tendency of the incommensurate spiral to "lock-in" to the commensurate periodicity k(x) = 1/3 is observed. The ordered Cr3+ magnetic moment decreases from 2.32(3)mu(B) to 1.72(6)mu(B) for x = 0 to x = 0.08. Field and zero-field cooled magnetic susceptibility measurements evidence increasing static magnetic disorder with x, in agreement with the neutron-diffraction results.
Title:
Raman study of Bi2-xPbxSr2Can-1CunO4+2n+delta (n=2,3) superconductors
Authors:
Williams GVM. Pooke DM. Pringle DJ. Trodahl HJ. Tallon JL. Quilty J. Malde N. Macmanus-Driscoll JL. Crossley A. Cohen LF.
Source:
Physical Review B. 62(2):1379-1386, 2000 Jul 1.
Abstract:
We report a Raman study of the n=2 and n=3 Bi2-xPbxSr2Can-1CunO4+2n+delta high-temperature super conducting cuprates. We find that the frequency of the O(2)(Sr) A(1g) mode systematically decreases with additional oxygen in the weakly coupled BiO layers. We speculate that this could be due to an expansion of the Cu-O-Bi bond length caused by an oxygen-induced compression of the weakly coupled BiO layers. It is shown that approximately one half of the decrease in the frequency of the O(2)(Sr) A(1g) mode in Bi2Sr2Ca1-zYzCu2O8+delta reported by Kahihana et al. can be attributed to the effect of additional oxygen and hence charge transfer effects are negligible for this Raman mode. The effect of Pb on the frequency of the O(2)(Sr) A(18) mode, while being systematic, can not be explained. We attribute the small increase in hole concentration with increasing Pb concentration to a partial charge compensation by a reduction in oxygen content. We provide evidence that the 655 cm(-1) peak can be attributed to epical oxygen sites at the boundaries of the supercell induced by the incommensurate modulation in the BiO layers.
Title:
Electron microscopy study of scratch-induced surface microstructures in an Al-Cu-Fe icosahedral quasicrystal
Authors:
Wu JS. Brien V. Brunet P. Dong C. Dubois JM.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 80(7):1645-1655, 2000 Jul.
Abstract:
Microstructure modifications induced by sliding a WC-Co indenter in scratch tests on the surface of a single-phase Al-Cu-Fe icosahedral quasicrystal (IQC) was studied by scanning electron microscopy and transmission electron microscopy. The scratch track was shown to consist of many smaller tracks. Dislocations were discovered to emerge from the edges of the smaller scratch tracks. Along a small track where the shear stress is concentrated, a phase transition from an IQC re, a bcc phase with lattice parameter a = 0.29 nm was found to occur. a modulated quasicrystal state as well as a deformation twin of IQC were determined in the region beneath the scratch.
Title:
Numerical simulation of dislocation motion in three-dimensional icosahedral quasicrystals
Authors:
Schaaf GD. Roth J. Trebin HR.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 80(7):1657-1668, 2000 Jul.
Abstract:
In a large number of experiments it has been shown that plastic deformation of quasicrystals can occur by a dislocation mechanism. By molecular dynamics simulations close to zero temperature we have investigated the application of shear stress to a three-dimensional model quasicrystal consisting of Lennard-Jones particles and containing an edge dislocation of the Peierls-Nabarro type. Various visualization methods have been used to trace the dislocation line. To determine suitable Burgers vectors we have calculated the gamma surface, that is the misfit energy obtained by a rigid shift of two probe halves along a glide plane. Glide motion of the dislocation on different glide planes was observed. In its wake a plane of phasonic defects was detected.
Title:
X-ray scattering studies of 2H-NbSe2, a superconductor and charge density wave material, under high external magnetic fields
Authors:
Du CH. Lin WJ. Su Y. Tanner BK. Hatton PD. Casa D. Keimer B. Hill JP. Oglesby CS. Hohl H.
Source:
Journal of Physics-Condensed Matter. 12(25):5361-5370, 2000 Jun 26.
Abstract:
Using x-ray scattering we have measured the response of the incommensurate charge-density wave (CDW) modulation in the quasi-low-dimensional material 2H-NbSe2 to applied magnetic fields at low temperatures. The application of a magnetic field, either perpendicular or parallel to the layers of a single crystal of 2H-NbSe2, caused no significant change to either the correlation length or the intensity of the CDW satellites for magnetic fields up to 10 T. These results suggest that the enhancement of the resistance observed in low-dimensional CDW materials exposed to the applied magnetic field does not result from an appreciable conversion of carriers from the normal state to the CDW state. In addition 2H-NbSe2 is a superconductor at low temperatures (T-c = 7.2 K), whilst still within the incommensurate CDW state. This material therefore affords an opportunity to study any interaction between the CDW and superconducting condensates. High magnetic fields can suppress the superconducting stale yet no change in the incommensurate CDW satellite correlation length or intensity was observed at high applied magnetic fields. These results conflict with spectroscopic measurements, which suggest a coupling between the superconducting gap excitations and the CDW.
Title:
Structural changes with lead substitution in Bi2-xPbxSr2CoO6
Authors:
Jakubowicz N. Grebille D. Hervieu M. Leligny H. Raveau B.
Source:
Journal of Physics-Condensed Matter. 12(25):5371-5389, 2000 Jun 26.
Abstract:
Structures refined for two members of the group of Bi2-xPbxSr2CoO6-type compounds are proposed. For x = 0.16, the structure is incommensurately modulated (a = 5.453(2) Angstrom, b = 5.426(2) Angstrom, c = 23.43(1) Angstrom. (q) over right arrow(star) = 0.245(2)(b) over right arrow(star) + (c) over right arrow(star), F2mm(0 beta 1)00s). For x = 0.8, the modulation becomes very weak and has been neglected in the structural refinement (a = 5.3117(7) Angstrom, b = 5.4232(6) Angstrom, c = 23.590(2) Angstrom, Pnan). A new interpretation of me undoped modulated Bi2Sr2CoO6 phase is given. A new type of configuration for the [BiO] layers is confirmed and original modulation features are elucidated in comparison with the related super-conducting cuprate phases. [References: 9]
Title:
Hidden dimers and their effect on the optical and electronic transmission in Thue-Morse aperiodic structures
Authors:
Chattopadhyay S. Chakrabarti A.
Source:
Journal of Physics-Condensed Matter. 12(26):5681-5689, 2000 Jul 3.
Abstract:
We show that a Thue-Morse aperiodic structure presents a unique kind of positional correlation between its constituents, leading to an unattenuated transmission of light as well as electrons through it. The reason for this is a resonant tunnelling, whose origin can be traced back to the presence of certain 'dimers' which are not explicitly displayed in the structure. It is interesting to observe that under suitable conditions, two apparently uncorrelated constituents in a Thue-Morse sequence combine together to form a dimer and the entire system can be thought of as being composed of nested dimers only. This aspect has been analysed in terms of light propagation through a Thue-Morse multilayered system and its electronic counterpart.
Title:
La24Li18.67Ti5.33O56: a novel columnar intergrowth structure of perovskite and distorted, cation-excess zinc blende
Authors:
Kirk CA. Lachowski EE. West AR.
Source:
Chemical Communications. (15):1437-1438, 2000.
Abstract:
The structure of the new phase, La24Li18.67Ti5.33O56, tetragonal, space group P4/mbm, a = 13.2443(13), c = 14.9258(20) Angstrom, consists of alternating columns, rotated by 45 degrees relative to each other, of perovskite-like structure, with Ti and Li in alternate octahedral sites, and twinned, distorted, zinc blende-like structure. [References: 2]
Title:
Precipitation of icosahedral quasicrystalline phase in Hf65Al7.5Ni10Cu12.5Pd5 metallic glass
Authors:
Li CF. Saida J. Matsushita M. Inoue A.
Source:
Applied Physics Letters. 77(4):528-530, 2000 Jul 24.
Abstract:
An icosahedral quasicrystalline phase was found in a Hf65Al7.5Ni10Cu12.5Pd5 metallic glass annealed in the supercooled liquid region. Upon annealing at high temperature, the quasicrystalline phase was found to decompose to regular crystalline phases, indicating that it is a metastable phase. The present alloy was compared with the previously reported Zr- and Ti-based alloys with the formation of icosahedral quasicrystalline phases. Hf, Zr, and Ti belong to the same 4A column in the element periodical table. Based on the above comparison, conditions in terms of atomic radius and alloy composition which favor the formation of icosahedral quasicrystalline phase in 4A element based alloys, were suggested. (C) 2000 American Institute of Physics. [S0003-6951(00)04530-7].
Title:
Charge-density-wave transitions in the local-moment magnet Er5Ir4Si10
Authors:
Galli F. Ramakrishnan S. Taniguchi T. Nieuwenhuys GJ. Mydosh JA. Geupel S. Ludecke J. van Smaalen S.
Source:
Physical Review Letters. 85(1):158-161, 2000 Jul 3.
Abstract:
We report the observation of a new type of charge-density wave (CDW) in the large magnetic-moment rare-earth intermetallic compound, Er5Ir4Si10, which then orders magnetically at low temperatures. Single crystal x-ray diffraction shows the development of a ID incommensurate CDW at 155 K, which then locks into a purely commensurate state below 55 K. The well-localized Er3+ moments are antiferromagnetically ordered below 2.8 K. We observe very sharp anomalies in the specific heat at 145 and 2.8 K, signifying the bull; nature of these transitions. Our data suggest the coexistence of strongly coupled CDW with local-moment antiferromagnetism in Er5Ir4Si10.
Title:
Incommensurate composite structure of the superconductor Bi2Sr2CaCu2O8+delta
Authors:
Etrillard J. Bourges P. Lin CT.
Source:
Physical Review B. 62(1):150-153, 2000 Jul 1.
Abstract:
We have performed elastic neutron scattering experiments, using a high-quality single crystal of the high-T-c superconductor Bi2Sr2CaCu2O8+delta a By a systematic comparison of intensities between superlattice reflections, we show that the one-dimensional incommensurate modulated model, usually used to interpret the structural characteristics, exhibits important failures. In contrast, in accordance with theoretical predictions [M. B. Walker and W. Que, Phys. Rev. B 45, 8085 (1992)], a composite structure made of two interpenetrating subsystems can alternatively describe the incommensurate structure and account for the hierarchy of the observed intensities.
Title:
P4W20O68: A complex charge-density-wave modulated structure with an antiferroelectric-like lattice distortion
Authors:
Roussel P. Labbe P. Leligny H. Groult D. Foury-Leylekian P. Pouget JP.
Source:
Physical Review B. 62(1):176-188, 2000 Jul 1.
Abstract:
The charge-density-wave (CDW) structure of the monophosphate tungsten bronze P4W20O68, the m = 10 member of the (PO2)(4)(WO3)(2m) series has been solved at room temperature from single-crystal x-ray-diffraction data. In agreement with previous x-ray diffuse scattering experiments, intense first-order satellite reflections at +/- 3/7a* reduced wave vectors as well as second-order satellite reflections at +/- 1/7a* were observed. The CDW structure was refined in a four-dimensional (4D) formalism and found to have the superspace group P2(1) (alpha 00) 0. The modulation, of the displacive type, involves mainly the tungsten atoms inside the different WO6 octahedra of the WO3-type slab. The W displacements, which are mostly oriented in the direction of the segment of 10 WO6 octahedra building the slab, tends to be oriented in opposite directions between neighboring segments. It is suggested that for the large in members these features represent a good compromise between the CDW instability of the metallic bronzes, related to their quasi-1D electronic structure, and the incipient antiferroelectric lattice distortion of the insulating oxide WO3, which corresponds to the limit m-->infinity of this series. These structural features play a crucial role in setting the coupling between the differently oriented 1D portions of the Fermi surface required for the hidden nesting mechanism at the basis of the stabilization of a CDW ground state in the ReO3-type metallic W and Mo bronzes and oxides.
Title:
Atomic and electronic structure of decagonal Al-Ni-Co alloys and approximant phases
Authors:
Krajci M. Hafner J. Mihalkovic M.
Source:
Physical Review B. 62(1):243-255, 2000 Jul 1.
Abstract:
Detailed investigations of the atomic and electronic structures of decagonal AlNiCo alloys have been performed. Several different models for the decagonal structure have been investigated: A model based on a rhombic-hexagon tiling proposed by Henley and models based on a cluster decoration of the Penrose tiling with large rhombus edge. The topology of the structural models has been refined on the basis of the existing x-ray-diffraction data which, however, do;not allow us to specify the chemical decoration uniquely. The chemical order on the decagonal lattice has been optimized via the comparison of the calculated electronic spectra with photoemission and soft-x-ray data and using total-energy calculations. The electronic structure calculations for large periodic approximants with up to 1276 atoms/cell have been performed self-consistently using a real-space tight-binding linear muffin-tin orbital technique. The best a,agreement with the experimental spectra is achieved for a large-rhombus-tiling model with the innermost ring of the pentagonal columnar clusters occupied by Ni atoms only. This configuration also has the lowest total energy. As in decagonal AlCuCo we find a high density of states at the Fermi level, but the chemical ordering is very different: whereas in d-AlCuCo direct Cu-Cu neighbors are suppressed and there is a slight preference for Co-Co homocoordination, in d-AlNiCo a strong Ni-Ni interaction stabilizes the innermost Ni ring, direct Co-Co neighbors are suppressed and there is a strong Co-Al interaction.
Title:
Low-temperature transport, thermal, and optical properties of single-grain quasicrystals of icosahedral phases in the Y-Mg-Zn and Tb-Mg-Zn alloy systems
Authors:
Chernikov MA. Paschen S. Felder E. Vorburger P. Ruzicka B. Degiorgi L. Ott HR. Fisher IR. Canfield PC.
Source:
Physical Review B. 62(1):262-272, 2000 Jul 1.
Abstract:
We present a comprehensive series of results of electrical transport (electrical conductivity, magnetoconductivity, Hall effect), thermal (specific heat), and optical (reflectivity) measurements in varying temperature ranges between 1.5 and 300 K on high-quality single-grain quasicrystals of icosahedral Y-Mg-Zn. This data set is augmented by the specific-heat and optical-reflectivity data obtained from a single-grain quasicrystal of icosahedral Tb-Mg-Zn. For Y-Mg-Zn, both the electrical conductivity sigma(T) and magnetoconductivity delta sigma(H) may be described by calculations considering quantum interference effects. A detailed comparison of the weak-localization contributions to sigma(T) and delta sigma(H) with our experimental data provides estimates of the inelastic and spin-orbit relaxation rates. The inelastic relaxation rate is found to be proportional to T-3. The dominant contributions to the optical conductivity sigma(1)(omega) spectrum, obtained from the reflectivity R(omega) data in the frequency range between 16 and 9.7 X 10(4) cm(-1), are a strong Drude feature at low frequencies and a prominent absorption signal centered at approximately 6 X 10(3) cm(-1). A comparison of the spectral weight of the Drude contribution to sigma(1)(omega) with the magnitude of the linear-in-ir term gamma T of the low-temperature specific heat C-p(T) yields the itinerant charge-carrier density n(i) = 7.62 X 10(21) cm(-3) or 0.13 charge carriers per atom. The low ni value is corroborated by the results of the Hall effect measurements. For Tb-Mg-Zn, the optical conductivity sigma(1)(omega) spectrum reveals features similar to those of Y-Mg-Zn. The low-temperature specific heat C-P(T) of Tb-Mg-Zn is strongly influenced by a spin-glass-type freezing of Tb moments and by crystal-electric-field effects.
Title:
Low-temperature thermal conductivity of a single-grain Y-Mg-Zn icosahedral quasicrystal
Authors:
Gianno K. Sologubenko AV. Chernikov MA. Ott HR. Fisher IR. Canfield PC.
Source:
Physical Review B. 62(1):292-300, 2000 Jul 1.
Abstract:
We report measurements of the thermal conductivity kappa(T) of a single-grain icosahedral Y8.6Me34.6Zn56.8 in the temperature range between 0.1 and 300 K. The quasilattice thermal conductivity kappa(ph) increases monotonically with T by three orders of magnitude between 0.1 and 23 K. Above 23 K, kappa(ph)(T) decreases substantially with increasing temperature, typical for high-quality single grain quasicrystals. The decrease ends in a minimum at approximately 140 K. The interpretation of our data is based on a Debye-type relaxation time approximation. At very low temperatures, the corresponding fit reveals that the phonon mean free path is of the order of the smallest sample dimension, while at high temperatures, a power-law decrease of the phonon scattering time with increasing temperature evidences the effect of structural scattering on the mean free path of itinerant quasilattice excitations. The behavior of kappa(ph)(T) at intermediate temperatures may best be fit by assuming the existence of stacking-fault-like phonon scatterers. No clear evidence for a scattering of phonons by tunneling states has been observed. If compared to previously reported measurements of the thermal conductivity of quasicrystals, these data indicate the very high structural perfection of this quasiperiodic material.
Title:
Magnetic dynamics and discommensuration in charge-ordered Pr1-xCaxMnO3 (x=1/3 and 1/2)
Authors:
Llobet A. Garcia-Munoz JL. Frontera C. Respaud M. Rakoto H. Lord JS.
Source:
Physica B. 289:73-76, 2000 Aug.
Abstract:
Muon relaxation techniques are used in a comparative study of charge-ordered Mn perovskites with commensurate (Pr1/2Ca1/2MnO3) and incommensurate (Pr2/3Ca1/3MnO3) charge concentration. A strong modification of the spin dynamics is observed in Pr2/3Ca1/3MnO3 for which the ferromagnetic correlations are the dominant relaxation mechanism. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Spin-slip structure induced by the crystalline electric field in the incommensurate magnetic ordering of CePtSn
Authors:
Noakes DR. Kalvius GM.
Source:
Physica B. 289:248-251, 2000 Aug.
Abstract:
While neutron scattering shows incommensurate magnetic Bragg peaks in CePtSn and CePdSn, zero-field muon-spin relaxation (ZF-mu SR) displays coherent oscillations indicating local commensurate ordering. To reconcile these, we had suggested spin-slip structure similar to that in holmium metal. Kadowaki has demonstrated some examples of this that are consistent with the neutron data. Numerical modeling shows that, given a simple incommensurate ordering mechanism, represented by a spiraling effective field at the cerium sites, the known Ce crystalline electric field (CEF) in CePtSn will generate that kind of spin-slip structure. Further numerical modeling shows that such CEF spin-slip structures generate field distributions at the muon sites with sharp peaks generally consistent with the coherent oscillations observed in mu SR. CePdSn is likely to behave in a similar manner. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
On the modulated structure of La2Co1.7: a neutron Laue diffraction study
Authors:
Wilkinson C. Schobinger-Papamantellos P. Myles D. Tung LD. Buschow KHJ.
Source:
Journal of Magnetism & Magnetic Materials. 217(1-3):55-64, 2000 Jul.
Abstract:
A preliminary analysis is presented of neutron Laue diffraction data from a single crystal of La2Co1.7 at temperatures between 295 and 15 K, recorded on neutron-sensitive image plates using a thermal neutron beam. The data can be interpreted in terms of a charge (nuclear) density wave with a propagation vector q(n) = (q(x), 0, q(z)) with q(x) = 0.113(1)a* and q(z) = 0.203(2)c*. It has also been confirmed by using a band-pass filter with a cold neutron beam that antiferromagnetic Bragg reflections which have a magnetic propagation vector q(m) =(1/3, 1/3, 0) exist below 144(1)K and correspond to a cobalt atom moment of 0.80(15) mu(B). Magnetic satellite reflections with wave vectors corresponding to q(n) +/- q(m) have also been observed on the Lane diagrams below this temperature. The values of the propagation vector and magnetic moment have been confirmed from neutron powder diffraction diagrams taken at 150 and 1.5 K. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Quasimagnetic clusters in icosahedral Al-Pd-Mn system
Authors:
Nimori S. Tsai AP.
Source:
Applied Physics Letters. 77(2):280-282, 2000 Jul 10.
Abstract:
We have studied the magnetization of the Al-Pd-Mn system using high-quality single crystals. Below room temperature, field-cooled magnetization exceeds zero-field-cooled magnetization. In addition, thermoremanent magnetization has disappeared at the same temperature. The results suggest the formation of quasimagnetic clusters in the Al-Pd-Mn system, although the relaxation of the thermoremanent magnetization was not observed. We discuss this anomalous magnetic phase in the Al-Pd-Mn system and refer to the origin of the behaviors. (C) 2000 American Institute of Physics. [S0003-6951(00)03828-6].
Title:
Surface structure and structural transition of decagonal Al-Ni-Co quasicrystal
Authors:
Shimoda M. Guo JQ. Sato TJ. Tsai AP.
Source:
Surface Science. 454:11-15, 2000 May 20.
Abstract:
X-ray photoelectron diffraction (XPD) and reflection high-energy electron diffraction (RHEED) measurements have been performed to investigate the surface structure of the decagonal Al72Ni12Co16 quasicrystal, which is known as a two dimensional quasicrystal. RHEED patterns for the surface parallel to the quasiperiodic planes are almost identical to the selected area electron diffraction (SAD) patterns taken along the twofold axes of the bulk sample. The XPD images show clear tenfold-symmetric patterns consistent with the long range orientational order of the decagonal quasicrystal. These facts suggest that the surface has the same quasiperiodic structure as in the bulk. The surface phase transition induced by Ar+ ion bombardment is also investigated. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Electronic characterization of quasicrystalline surface transformations
Authors:
Hensch A. Bolliger B. Erbudak M. Willis RF.
Source:
Surface Science. 454:453-457, 2000 May 20.
Abstract:
When ion bombarded at room temperature, the surface of the icosahedral quasicrystal Al70Pd20Mn10 converts to a cubic structure. Bombarded at elevated temperatures, the surface remains quasicrystalline but converts to a tenfold-symmetric structure, In this paper, we search for a change in the electronic properties as the structure is modified and argue a case against the Hume-Rothery rule for these alloys. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Excitons at a single localized center induced by a natural composition modulation in bulk Ga0.5In0.5P
Authors:
Sugisaki M. Ren HW. Nishi K. Sugou S. Masumoto Y.
Source:
Physical Review B. 61(23):16040-16044, 2000 Jun 15.
Abstract:
Optical properties of Ga0.5In0.5P grown by gas-source molecular beam epitaxy are reported. A strong optical anisotropy due to the spontaneous lateral composition modulation of Ga and In was observed in macro- and micro-photoluminescence (PL) spectra. The micro-PL study revealed that the PL band is composed of sharp lines that arise from the radiative decay of excitons trapped at local potential minima caused by the composition modulation. Anisotropy in PL rise and decay times was also observed. The detection energy dependence of the PL decay time is well explained by considering the relaxation process of excitons from shallow traps to deep traps.
Title:
Uniform spectral properties of one-dimensional quasicrystals, III. alpha-continuity
Authors:
Damanik D. Killip R. Lenz D.
Source:
Communications in Mathematical Physics. 212(1):191-204, 2000 Jun.
Abstract:
We study the spectral properties of one-dimensional whole-line Schrodinger operators, especially those with Sturmian potentials. Building upon the Jitomirskaya-Last extension of the Gilbert-Pearson theory of subordinacy, we demonstrate how to establish alpha- continuity of a whole-line operator from power-law bounds on the solutions on a half-line. However, we require that these bounds hold uniformly in the boundary condition. We are able to prove these bounds for Sturmian potentials with rotation numbers of bounded density and arbitrary coupling constant. From this we establish purely alpha-continuous spectrum uniformly for all phases. Our analysis also permits us to prove that the point spectrum is empty for all Sturmian potentials.
Title:
Nanoscale icosahedral quasicrystalline phase formation in a rapidly solidified Zr80Pt20 binary alloy
Authors:
Saida J. Matsushita M. Inoue A.
Source:
Applied Physics Letters. 77(1):73-75, 2000 Jul 3.
Abstract:
It is found that an icosahedral quasicrystalline phase is directly formed in a Zr80Pt20 binary alloy during rapid solidification from the melt. The size of the icosahedral particles lies in the diameter range below 10 nm, and the particles are distributed homogeneously. The formation of the nanoscale icosahedral phase indicates that the icosahedral short-range order exists in the melted state of Zr-Pt binary alloy. The strong chemical affinity between Zr and Pt contributes to the restraint of the long-range rearrangement of constitutional elements to form a stable crystalline phase, which is the important factor of the stabilization of an icosahedral phase. (C) 2000 American Institute of Physics. [S0003-6951(00)05027-0].
Title:
Crystal growth and structural investigations of the oxygen ion conductor BaBi3O5.5
Authors:
Esmaeilzadeh S. Berastegui P. Grins J. Rundlof H.
Source:
Journal of Solid State Chemistry. 152(2):435-440, 2000 Jul.
Abstract:
Large single crystals of the oxygen ion conductor BaBi3O5.5 have been obtained, and its structure was investigated by single-crystal X-ray diffraction (XRD) and neutron diffraction (ND), electron diffraction, and high-resolution electron microscopy (HREM), The basic three-dimensional structure was refined, using single crystal ND data, in space group Im (3) over bar m to a weighted R value of 5.3% for 17 unique reflections, with Ba and Bi atoms statistically distributed on the 2(a) sites (0, 0, 0) and the O atoms on the 6(b) sites (1/2, 0, 0) with a refined occupancy of 36(1)%, The refined thermal-displacement parameters for the O atoms are highly anisotropic, with U-11 = U-22 = 0.27(1) and U-33 = 0.082(7) Angstrom(2). In addition, the structure is incommensurately modulated with the systematic absence conditions F < hklmnp > = 0 unless h + k + l = 2j and m + n + p = 2j, implying the six-dimensional superspace group P:Im (3) over bar m:Im (3) over bar m, with 4.3798(2) Angstrom and modulation vectors q(1) = [alpha, 0, 0]*, q(2) = [ 0, alpha, 0]*, and q(3) = [0, 0, alpha]* with alpha = 0.3835(1), The diffraction data and the HREM images indicate that the modulation is predominantly occuptional. The satellite reflections have comparable intensities in powder XRD and ND patterns, indicating furthermore that the modulation originates from ordering of both O atoms/vacancies and metal atoms. (C) 2000 Academic Press. [References: 9]
Title:
A new high-temperature cubic fluorite-type phase Mo0.16Bi0.84O1.74 with a rare three-dimensional incommensurate modulation
Authors:
Valldor M. Esmaeilzadeh S. Pay-Gomez C. Grins J.
Source:
Journal of Solid State Chemistry. 152(2):573-576, 2000 Jul.
Abstract:
A new high-temperature phase Mo0.16Bi0.84O0.17 was obtained by quenching from 800 degrees C, Its average structure is of the cubic Fm (3) over bar m flourite type with a = 5.6478(1) Angstrom and was refined from single-crystal Mo K alpha X-ray diffraction (XRD) data to a weighted R-value of 3.7% for 16 unique reflections and isotropic thermal displacement parameters refined for the metal atoms, U-iso = 0.0564(4) Angstrom(2), and the O atoms, U-iso = 0.186(6) Angstrom(2). The structure exhibits in addition a novel 3-D incommensurate modulation that was studied by electron diffraction and both powder and single crystal XRD, Extinction conditions indicate the symmetry P:Fm (3) over bar m:Fm (3) over bar m, which has previously only been reported once. The three q-vectors are along the unit cell axes and have lengths of 0.29256(6) unit cells in reciprocal space. The modulated structure is compared with the previously reported and similarly modulated structure of the solid solution NbxBi1-xO1.5+x, with 0.12 less than or equal to x less than or equal to 0.46 and symmetry P:Fm (3) over bar m: Fd (3) over bar m. (C) 2000 Academic Press. [References: 8]
Title:
Monte-Carlo simulation of the phase diagrams in Ising model of [Sn(Pb)](2)P-2[S(Se)](6) crystals
Authors:
Drobnich A. Vysochanskii Y.
Source:
Ferroelectrics. 233(1-2):145-158, 1999.
Abstract:
In Sn2P2S6 crystals Ferroelectric second order phase transition (PT) occurs. In this case the number of formula units in elementary cell stays unchanged. In Sn2P2Se6 crystals the intermediate incommensurate phase exists. A dipole Ising model of Sn2P2[S(Se)](6) ferroelectrics has been developed. To consider the dipole long-range interaction around the dipole an area of simple form is singled out. Within this area the interaction between the dipoles is calculated precisely. The interaction with the other dipoles is considered by introduction of a local field. For better accordance with the real experiment an amendment on the short-range interaction with two nearest neighbours has been introduced. As a result of calculations made by Monte-Carlo method it has been found that when a certain short-range interaction coefficient in Sn2P2S6 is selected the intermediate modulated phase disappears. In this case the temperatures of PTs are as follows: for Sn2P2S6 model T-o* similar to 10.3; for Sn2P2Se6 model T-c* similar to 8.7, T-i* similar to 9.7 (in the effective temperatures). These data are in satisfactory agreement with the results of the real experiment. The concentration dependences of temperatures of PTs in Sn2P2(SxSe1-x)(6) crystals are simulated and the Lifshitz point was observed. In mixed (PbySn1-y)(2)P2S6 and (PbySn1-y)(2) P2Se6 crystals increase of ph concentration causes reduction of temperatures of PTs to 0 K. In this case the character of PTs stays unchanged. By the method of diluted Ising lattice the concentration dependences of temperatures of PTs in this crystals are simulated.
Title:
Neutron scattering studies of incommensurate systems
Authors:
Currat R.
Source:
Ferroelectrics. 236(1-4):11-22, 2000.
Abstract:
Since the early experimental work on the characteristic excitations of displacively modulated systems, progress has been achieved on several fronts. A model which extends the usual phenomenological description of the phason-amplitudon decoupling below Ti, has been used successfully to describe the low-frequency excitations in modulated betaine calcium chloride dihydrate (BCCD). In another modulated molecular compound, bis-(4-chlorophenyl)-sulfone (BCPS), the close connection between the soft mode saturation frequency, as T-->T-i(+), and the phason gap (T < T-i) has recently been established by means of high resolution inelastic neutron scattering. Finally, experimental results on the excitation spectrum of composite systems, such as the alkane-urea intergrowth compounds, are reviewed.
Title:
Dynamics of aperiodic crystals
Authors:
Janssen T.
Source:
Ferroelectrics. 236(1-4):157-168, 2000.
Abstract:
Due to a lack of translational symmetry, aperiodic crystals do not have a Brillouin zone, and their vibrational elementary excitations can be different in character from those in lattice periodic crystals. The relation between structure and vibrations is discussed for incommensurate crystal phases and for incommensurate composites. In particular attention is paid to the phason or sliding mode, which is an excitation not present in periodic crystals.
Title:
Elastically hinged molecule model for computer simulation of incommensurate phase in crystals
Authors:
Dmitriev SV. Abe K. Shigenari T.
Source:
Ferroelectrics. 237(1-4):321-328, 2000.
Abstract:
The results of analytical and numerical studies of a microscopic model of crystal with modulated structures are reviewed. Thr relation between our model and previous models is established. Some new phenomena related to the hysteresis of the lock-in transition are discussed.
Title:
Dielectric study of purified Rb2ZnCl4 in weak AC-fields
Authors:
Mueller V. Shchur Y. Fuchs E. Beige H.
Source:
Ferroelectrics. 240(1-4):1325-1332, 2000.
Abstract:
The strongly enhanced domain wall response in the ferroelectric phase of purified Rb2ZnCl4 is studied at low ac-field level E((ac))less than or equal to 0.3V/cm. In the incommensurate-commensurate transition range, the thermal hysteresis of the imaginary part epsilon"(T) of permittivity is much bigger than those of epsilon'(T). At low frequencies, an anomaly of epsilon"(T) is observed at T approximate to 170K.
Title:
Structural modulation of the commensurate phases of betaine calcium chloride dihydrate (BCCD) within a model with nearest neighbour anharmonic couplings
Authors:
Etxebarria I. Ezpeleta JM.
Source:
Ferroelectrics. 240(1-4):1375-1382, 2000.
Abstract:
The structural modulation of the four-fold phase of BCCD has been studied by neutron and X-ray difraction, and the discrepancies between the results given by both techniques are quite remarkable. Although neutron measurements show that the modulation is clearly anharmonic and the effect of third order satellites is essential to describe the structural modulation, the intensity of these satellites is very low in the case of X-rays. In the present work the theoretical structural modulation is analyzed within the framework of a symmetry based semi-microscopic model in the mean-field approximation. The model takes into account the three degrees of freedom associated with the lowest energy phonon branches as well as the anharmonic interactions between nearest neighbours to reproduce the essential experimental features of the phase diagram. Although the model is not able to predict the structural modulation at the atomic level, the well defined symmetry of the variables allows a comparison of the theoretical and experimental modulations. [References: 15]
Title:
Wanted: Amplitudon mode in Raman spectra of BCCD
Authors:
Gregora I. Hlinka J. Vorlicek V.
Source:
Ferroelectrics. 240(1-4):1383-1390, 2000.
Abstract:
Polarised Raman scattering by the low-frequency totally symmetric modes in modulated phases of deuterated Betaine Calcium Chloride Dihydrate was measured in order to identify the amplitudon mode. The spectra are similar to those of non-deuterated compound. Detailed analysis based on fitting the coupled-mode lineshape to the experimental data allows to suggest the temperature dependence of the bare amplitudon mode, as well as to ascribe the previously observed sharp intensity minimum to the coupling of the amplitudon with the activated transverse acoustic mode.
Title:
The elastic properties of ferroelastic [N(CH3)(4)](2)CuCl4 single crystals near C-IC phase transition
Authors:
Park JS. Ahn HY. Park SE. Cho YC. Jeong SY.
Source:
Ferroelectrics. 240(1-4):1391-1398, 2000.
Abstract:
The behavior of the ferroelastic DCs in [N(CH3)(4)](2)CuCl4 was investigated by the measurement of the strain-stress hysteresis loop and of the bias stress field dependence of DC interaction potential. The ferroelastic double hysteresis loop observed in [N(CH3)(4)](2)CuCl4 suggested the existence of the regularly spaced ferroelastic DCs in the incommensurate phase. The oscillating behavior of the second derivative of the DC interaction energy U(x) was investigated to discuss the energy minimized positions of the ferroelastic DCs. [References: 8]
Title:
On the symmetry properties of dielectric tensor in incommensurately modulated insulators
Authors:
Kushnir OS. Lokot LO. Kityk AV. Schranz W.
Source:
Ferroelectrics. 240(1-4):1399-1404, 2000.
Abstract:
General symmetry properties of the dielectric permittivity tensor which determines nonlocal optical response of crystals with incommensurately modulated phases are analyzed. The relations resulted from the Onsager's principle and the condition of transparency of the optical medium are derived. Specific features of a macroscopic averaging procedure for the dielectric permittivity of incommensurate crystals are in brief discussed. It is revealed a possibility for existing small non-Hermitian part in the dielectric tensor related to inhomogeneity of the medium on a mesoscopic scale and originated from the modulation-induced spatial dispersion.
Title:
A new interpretation of incommensurate phase of quartz
Authors:
Shigenari T. Dmitriev SV. Abe K. Makita Y. Yajima M. Aslanyan TA.
Source:
Ferroelectrics. 240(1-4):1413-1420, 2000.
Abstract:
Optical and lattice dynamical studies were performed on the incommensurate(IC) phase in quartz. There are two different regions (fog- and m- zone) near the boundary between alpha and IC phase. The birefringence in the fog-zone was found to be much larger than that expected from the currently accepted model. The lattice dynamical calculation using the Tsuneyuki potential (Phys. Rev. Lett., 61, 869(1988)), revealed that a stable modulated structure with a short period exists between alpha and beta phases. Both results qualitatively agree with the new model recently proposed by Aslanyan et al. (J. Phys. Condens. Matter, 10, 4575(1998)) which assumes that the softening would occur near b/3 rather than close to Gamma point.
Title:
Quasi-elastic light scattering and the solitonic phase in betaine calcium chloride dihydrate (BCCD)
Authors:
Schmitt-Lewen M. Schaack G.
Source:
Ferroelectrics. 240(1-4):1421-1428, 2000.
Abstract:
The temperature (40K less than or equal to T less than or equal to 200K) and polarization dependence (z(yy)x, z(xz)x) of the integrated intensities of quasi-elastically scattered light (lambda = 514.5 nm) in a wavenumber interval of (0 +/- 3) cm(-1) around the Rayleigh line at the different phase transitions in single crystals of BCCD have been observed. Large anomalies (central peaks) are observed at the transitions into the ferroelectric, the various commensurate (c, c'), and the incommensurate phases. The widths of the anomalies on the temperature scale differ considerably, they are large in the region of quasi-harmonic modulation but narrow in the region of square-wave modulation (solitonic phase), where unusual shapes on the Taxis are displayed. The scattering phenomena at low temperatures are hypothetically interpreted by the formation or rearrangement of domain walls (solitons). The c-c' transitions are of the order-disorder type.
Title:
Simultaneous measurement of thermal and dielectric properties on incommensurate Rb2CoCl4 crystal
Authors:
Martin-Olalla JM. Gallardo MC. Del Cerro J. Ramos S.
Source:
Ferroelectrics. 240(1-4):1443-1448, 2000.
Abstract:
The commensurate-incommensurate phase transition of a Rb2CoCl4 crystal has been studied. The study covers the simultaneous measurement of thermal and dielectric properties. We obtain that transition enthalpy is 5.0Jmol(-1). This result is similar to that obtained on Rb2ZnCl4 and the relative position of dielectric permittivity anomaly and heat flux anomaly is also found to be consistent with previous experiments on Rb2ZnCl,. [References: 12]
Title:
The quasicrystal-to-crystal transformation. I. Geometrical principles
Authors:
Steurer W.
Source:
Zeitschrift fur Kristallographie. 215(6):323-334, 2000.
Abstract:
A geometrical model of the quasicrystal-to-crystal transformation is discussed on atomic scale. The central idea is to describe a quasiperiodic structure as a special type of incommensurately modulated structure. As a consequence thereof, the periodic average structure of a quasicrystal is also the average structure of all its rational and irrational approximants. Then, quasicrystals can formally be transformed to approximants by atomic displacements smaller than any interatomic distance. This transformation, however, leads to chemically partially disordered resultants, and in the case of two- and three-dimensional quasiperiodic structures also to a certain amount of positional disorder. Fully ordered approximant structures can only be obtained by atomic diffusion. One of the advantages of the present approach is that tools can be used that were developed for the description of phase transitions of incommensurately modulated phases. Examples for one- and three-dimensional quasiperiodic structures are discussed in detail.
Title:
Neutron diffraction study of metamagnetic phases in ErNi2B2C
Authors:
Campbell AJ. Paul DM. McIntyre GJ.
Source:
Solid State Communications. 115(4):213-216, 2000.
Abstract:
Neutron diffraction has been used to determine the magnetic order in the metamagnetic phases of ErNi2B2C, with the magnetic field applied parallel to the [0 1 0] and [1 1 0] crystallographic axes. Below 6 K, ErNi2B2C has an incommensurate antiferromagnetic structure with a modulation along the a-axis of wavevector delta = (0.55, 0, 0). For both orientations three first-order metamagnetic transitions are observed below 6 K as the applied field is increased. The first two transitions are to incommensurate antiferromagnetic states with different values of the a-axis modulation, and the third transition is to a saturated paramagnetic state in which the spins are aligned ferromagnetically by the applied field. With the field applied parallel to the [0 1 0] direction, which is the magnetically easy axis, the upper incommensurate state has an additional ferromagnetic component which is not observed with the field applied parallel to the [1 1 0] direction. (C) 2000 Elsevier Science Ltd. All rights reserved.
Title:
Growth morphology of decagonal quasicrystal in laser resolidified Al72Ni12Co16
Authors:
Liu YC. Yang GC. Xu DS. Xu QY. Zhou YH.
Source:
Journal of Materials Science Letters. 19(12):1095-1097, 2000 Jun.
Title:
X-ray diffraction by polydomain crystals modulated by transverse waves of atomic displacements. 1. Single-wave modulation in crystals
Authors:
Ustinov AI. Olikhovskaya LA. Shmyt'ko IM.
Source:
Crystallography Reports. 45(3):365-373, 2000 May-Jun.
Abstract:
The intensity distributions of diffuse X-ray scattering caused by domains characterized by the transverse wave of atomic displacements polarized in the (010) plane and propagating along the [001] direction are calculated by numerical methods analyzed in the kinematical approximation. The regular changes in:the intensity and half-width of the satellite peaks are revealed as functions of the wave amplitude and the average domain size. The characteristic features of diffraction are considered in the case where the defect-density wave in the crystal affects the parameters of the displacement wave. (C) 2000 MAIK "Nauka/Interperiodica".
Title:
X-ray diffraction in polydomain crystals modulated by transverse waves of atomic displacements. 2. Two-wave modulation of crystals
Authors:
Ustinov AI. Olikhovskaya LA. Shmyt'ko IM.
Source:
Crystallography Reports. 45(3):374-379, 2000 May-Jun.
Abstract:
X-ray diffraction in an orthorhombic crystal modulated by two transverse-displacement waves propagating along one of the crystallographic directions has been numerically studied within the framework of the kinematic approximation. Crystal models are considered that allow the superposition of the displacement waves or the coexistence of domains modulated by the displacement waves with different parameters. It is shown that the formation of peaks additional to the satellite ones is possible not only due to the superposition of the displacement waves, but also due to a certain correlation of the displacement waves in each domain. (C) 2000 MAIK "Nauka/Interperiodica". [References: 3]
Title:
Study of phase transitions and the incommensurate phase in ACBX(4) crystals by the Monte Carlo method
Authors:
Zinenko VI. Zamkova NG.
Source:
Crystallography Reports. 45(3):469-472, 2000 May-Jun.
Abstract:
The statistical model of successive phase transitions in the family of crystals described by the general formula ACBX(4) has been studied. It is assumed that tetrahedral BX4 groups in the disordered tetragonal phase can be located in four equally probable equilibrium positions. Five representatives with different sequences of phase transitions in this family of crystals are considered. The effective equilibrium constants of interactions between tetrahedral groups are calculated within the framework of the electrostatic model. The corresponding phase diagrams and the thermodynamic characteristics of the phase transitions are studied by the Monte Carlo method. The experimental data provided the establishment of the sequence of phase transitions in Rb2ZnCl4 and K2SeO4 crystals with the formation of an intermediate incommensurate phase. The character of the structure modulation in this phase is established. The calculated thermodynamic characteristics of the phase transitions agree quite well with the experimental data for all the crystals under consideration. (C) 2000 MAIK "Nauka/Interperiodica".
Title:
Order parameter in the quasicrystal-crystal transformation
Authors:
Roshal SB. Lebedyuk IV.
Source:
Crystallography Reports. 45(3):473-478, 2000 May-Jun.
Abstract:
Some aspects of the relationship between quasicrystal and crystal structures not considered earlier. are discussed. It is shown that the atomic positions in a quasicrystal lattice are intermediate between the positions of periodic incommensurate crystal lattice. For the octagonal symmetry, two such generating lattices can be square and equal to one another. Then any quasicrystal position lies exactly between two crystal positions in different lattices. The classical (phason) mechanism of the quasicrystal-crystal phase transition is-interpreted as a relative homogeneous deformation of generating crystal lattices leading to the commensurability of these lattices. The order parameter of such a transition is defined. (C) 2000 MAIK "Nauka/Interperiodica". [References: 13]

Update: 11-July-2000

Title:
Formation of icosahedral quasicrystalline phase in Zr70Ni10M20(M=Pd, Au, Pt) ternary metallic glasses
Authors:
Saida J. Matsushita M. Li C. Inoue A.
Source:
Applied Physics Letters. 76(24):3558-3560, 2000 Jun 12.
Abstract:
An icosahedral quasicrystalline phase was confirmed as a primary precipitation phase in melt-spun Zr70Ni10M20 (M=Pd, Au and Pt) ternary metallic glasses with two-stage crystallization process. The onset temperature of the transformation from amorphous to icosahedral phase are 687 K for Pd, 754 K for Au and 783 K for Pt at a heating rate of 0.67 K s(-1). The size of the icosahedral particles is in the range of 5-20 nm. The second crystallization reaction results in the formation of Zr2Ni+Zr2Pd and Zr2Ni+ZrPt phases in the Zr-Ni-Pd and Zr-Ni-Pt alloys, respectively, and Zr3Au phase in the Zr-Ni-Au alloy through a single exothermic reaction. The formation of nanoscale icosahedral phase indicates the possibility that icosahedral short-range order exists in the glassy state. (C) 2000 American Institute of Physics. [S0003-6951(00)00524-6].
Title:
Modulated structure of Ag2SnO3 studied by high-resolution electron microscopy
Authors:
Oku T. Carlsson A. Bovin JO. Svensson C. Wallenberg LR. Linke C. Jansen M.
Source:
Acta Crystallographica - Section B, Structural Science. 56(Part 3):363-368, 2000 Jun.
Abstract:
The modulated structure of Ag2SnO3, disilver tin trioxide, was investigated by high-resolution electron microscopy and electron diffraction along four different directions. Electron diffraction showed an incommensurate one-dimensional modulated structure with a modulation wavevector of 1/6.4a*. High-resolution images showed a large number of superstructure domains with the size range 10-100 nm and orientations related by hexagonal rotation. The modulation was determined to be displacements along the c axis of the Ag atoms both in octahedral and linear coordination. An approximate structure model with a commensurate sixfold superstructure, with an orthorhombic cell (P2(1)2(1)2(1), a = 2.922, b = 1.267, c = 0.562 nm), is proposed. Calculated images and electron diffraction patterns, based on this model, agree well with experimental observations. [References: 9]
Title:
Structure of nu-Al80.61Cr10.71Fe8.68, a giant hexagonal approximant of a quasicrystal determined by a combination of electron microscopy and X-ray diffraction
Authors:
Mo ZM. Zhou HY. Kuo KH.
Source:
Acta Crystallographica - Section B, Structural Science. 56(Part 3):392-401, 2000 Jun.
Abstract:
nu-Al80.61Cr10.71Fe8.68, P6(3)/m (No. 176), a = 40.68 (7), c = 12.546 (1) Angstrom, V = 17 983 (8) Angstrom(3), atoms/cell = 1184.56, D-x = 3.518 g cm(-3), lambda(Mo K alpha) = 0.71069 Angstrom, mu = 5.032 mm(-1), F(000) = 18 433, T = 293 K, final R = 0.075 for 3854 reflections with F-o > 4 sigma(F-o). The [001] high-resolution electron-microscopic image of the nu-AlCrFe phase clearly shows similar local characteristics to those given by the complex icosahedral cluster found in somewhat smaller hexagonal approximant structures, such as kappa-Al76Cr18Ni6 [a = 17.674 (3), c = 12.516 (3) Angstrom; Sato et al. (1997). Acta Cryst. C53, 1531-1533; Marsh (1998). Acta Cryst. B54, 925-926] and lambda-Al4.32Mn [a = 28.382 (9), c = 12.389 (2) Angstrom; Kreiner & Franzen (1997). J. Alloys Compd. 261, 83-104]. Using the known atomic distribution of this icosahedral cluster in the kappa and lambda phases as the starting point, the structure of the nu phase, a hexagonal intermetallic compound with probably the largest a parameter, was solved by X-ray single-crystal diffraction using direct methods. As in kappa and lambda phases, almost all TM (transition metal) atoms in the complex icosahedral cluster are icosahedrally coordinated. However, contrary to the lambda structure in which about 98% of the TM atoms have icosahedral coordination, the TM atoms in the nu structure also form capped pentagonal prisms in the region between these complex icosahedral clusters, yielding an average icosahedral coordination of about 70% for TM atoms. After rapid solidification, the nu phase occurs together with a decagonal quasicrystal with a periodicity of about 12.5 Angstrom along its tenfold axis and thus also consists of six layers, two flat ones each sandwiched between two puckered layers in mirror reflection, stacked along the c axis.
Title:
A new structure type in the hexagonal perovskite family; structure determination of the modulated misfit compound Sr9/8TiS3
Authors:
Gourdon O. Petricek V. Evain M.
Source:
Acta Crystallographica - Section B, Structural Science. 56(Part 3):409-418, 2000 Jun.
Abstract:
Sr9/8TiS3, strontium titanium sulfide, a new phase in the hexagonal perovskite-like SrxTiS3 system, has been prepared and its structure solved from single-crystal X-ray data within the (3 + 1)-dimensional [(3 + 1)D] formalism. Sr9/8TiS3 crystallizes with trigonal symmetry [R (3) over bar m(00 gamma)0s superspace group], with the following lattice parameters: a(s) = 11.482 (3), c(s) = 2.9843 (8) Angstrom, q = 0.56247 (7)c* and V-s = 340.7 (3) Angstrom(3). The structure was considered as commensurate [R (3) over bar c three-dimensional (3D) space group], but refined within the (3 + 1)D formalism to a residual factor R = 2.79% for 64 parameters and 1084 independent reflections. Original crenel functions were used for the sulfur and strontium description. The structure is different from that of the hexagonal perovskite-like oxide counterparts. The main difference is related to the presence of a new type of polyhedron in the [MS3] transition metal chains, intermediate between the octahedra classically found in such chains and the trigonal prismatic sites encountered in the oxides.
Title:
Structural model for the Al72Ni20Co8 decagonal quasicrystals
Authors:
Yan YF. Pennycook SJ.
Source:
Physical Review B. 61(21):14291-14294, 2000 Jun 1.
Abstract:
We propose a structure model for the Al72Ni,Co-20(8) decagonal quasicrystals based on its tau(2)-inflated Al13Co4 approximant phase: Applying a 10(5) screw operation on a monolayer obtained from the approximant reproduces almost all features of 2-nm clusters seen in atomic-resolution Z-contrast images of Al72Ni20Co8 decagonal quasicrystals. The exception is the central ring, where the symmetry is broken due to chemical ordering of Al and transition metals. By restricting possible overlaps, this enforces the perfect quasiperiodic tiling.
Title:
Growth kinetics of quasicrystalline and polytetrahedral phases of Al-Pd-Mn, Al-Co, and Al-Fe from the undercooled melt
Authors:
Schroers J. Holland-Moritz D. Herlach DM. Urban K.
Source:
Physical Review B. 61(21):14500-14506, 2000 Jun 1.
Abstract:
Melts of the alloys Al-Pd-Mn, AI-Co, and Al-Fe are containerlessly undercooled and solidified using the technique of electromagnetic levitation. The (quasi)crystal growth velocity is measured as a function of undercooling for the various phases by a high-speed infrared photosensing device. Additionally, a video image technique is applied to measure growth velocities especially at low undercoolings where sluggish growth prevails. Scanning and transmission electron microscopy as well as x-ray diffraction is utilized to identify the phases primarily solidified from distinct levels of undercooling. The experimental results are analyzed within current theories of dendritic growth. The investigations give insight into topological and chemical short-range order effects in the growth kinetics of phases with polytetrahedral ordering in the solid state.
Title:
Electronic transport in quasicrystal-like systems
Authors:
Kanazawa I.
Source:
Physica B. 284(Part 2):1161-1162, 2000 Jul.
Abstract:
We have discussed the transport property of the quasicrystal-like system, and indicated the importance of the 2k(F) phase shift scattering by the correlated clusters with the distance similar to 2 pi/2k(F). (C) 2000 Elsevier Science B.V. All rights reserved. [References: 2]
Title:
NMR studies of an icosahedral Al72.4Pd20.5Mn7.1 quasicrystal
Authors:
Gavilano JL. Mushkolaj S. Ott HR. Apih T. Dolinsek J. Dubois JM. Urban K.
Source:
Physica B. 284(Part 2):1167-1168, 2000 Jul.
Abstract:
We report the results of Al-27 nuclear magnetic resonance studies of a single-grain icosahedral Al72.4Pd20.5Mn7.1 quasicrystal at low temperatures. The Al-NMR line width displays a broad maximum near 20 K, and a sharp anomalous increase with decreasing temperatures near 2 K. The temperature dependence of the spin-lattice relaxation rate is approximately linear above 2 K, with (T1T)(-1) approximate to 0.02 (Ks)(-1). Below 2 K there is a qualitative change in the relaxation behavior, such that (T1T)(-1) increases substantially with decreasing temperatures. Our results are interpreted as evidence for an anomalous dynamics of the magnetic moments associated with the Mn ions. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 5]
Title:
Low-temperature phase transition in EuMn2O5 induced by a strong magnetic field
Authors:
Popov YF. Kadomtseva AM. Vorob'ev GP. Sanina VA. Zvezdin AK. Tehranchi MM.
Source:
Physica B. 284(Part 2):1402-1403, 2000 Jul.
Abstract:
The magnetostriction, magnetoelectric effect and phase transitions induced by a strong magnetic field in EuMn2O5 single crystal have been investigated. It is known that EuMn2O5 compounds show structural and magnetic phase transitions and incommensurate magnetic structure around 40 K. New phase transitions from a modulated spin structure to a homogeneous structure in EuMn2O5 at 26 K accompanied by a significant change of electrical polarization induced by a high magnetic field have been studied. (C) 2000 Published by Elsevier Science B.V. All lights reserved. [References: 4]
Title:
Quasicrystals and nano-quasicrystals in annealed ZrAlNiCuAg metallic glasses
Authors:
Chen MW. Inoue A. Zhang T. Sakai A. Sakurai T.
Source:
Intermetallics. 8(5-6):493-498, 2000 May-Jun.
Abstract:
Quasicrystals and nano-quasicrystals are observed in annealed Zr65Al7.5Ni10Cu12.5Ag5 and Zr65Al7.5Ni10Cu7.5Ag10 metallic glasses. Through systematic transmission electron microscopy (TEM) analyses, selected area electron diffraction (SAED) and nanobeam electron diffraction (NBED) patterns corresponding to five-, three- and twofold rotational symmetry are obtained, demonstrating that the precipitated phases in the first stage devitrification of the alloys are icosahedral quasicrystalline phases. The discovery of the quasicrystals directly reflects the intrinsic relationship between the Zr-based bulk metallic glasses and the icosahedral structure. (C) 2000 Elsevier Science Ltd. All rights reserved.
Title:
Pattern formation and quasicrystal struture in azobenzene polymer film [Chinese]
Authors:
Xu ZD. Cai ZG. Zhang LZ. Liu YF. Yang J. She WL. Zhou JY.
Source:
Acta Physica Sinica. 49(6):1091-1093, 2000 Jun.
Abstract:
Pattern formation and transverse effect are reported for azobenzene polymer film. We show, through scanning electron microscopy and polarizing optical microscopy investigation of azobenzene polymer film after being irradiated by degenerate four-wave mixing,that many peak-like islands of azobenzene polymer molecules array in some patterns. Experimental evidence that it is possible to control the photoinduced micro-patterns of the nonlinear organic film via adequately polarized write beams and appropriate power of the write beams,thus making easy growth of nanostructures crystals in azobenzene polymer film.
Title:
Structural and electric properties of beta '-CuxV2O5
Authors:
Yamada H. Ueda Y.
Source:
Journal of the Physical Society of Japan. 69(5):1437-1442, 2000 May.
Abstract:
Single crystals of beta'-CuxV2O5 have been successfully grown by a self Aux method, and their structural, magnetic, and electric properties have been systematically investigated as a function of T and x. The properties of beta'-CuxV2O5 are strikingly different from those of isostructural beta-A(x)V(2)O(5) (A = Na, Ag, etc.). With increasing x. the electrical conductivity of beta'-CuxV2O5 along the b-axis increases monotonously and the metal-insulator transition occurs around x = 0.60. The conductivity is highly anisotropic. For x < 0.43, the system undergoes a structural phase transition at ca. 200 K to an incommensurate (IC) phase. For x approximate to 0.4, the IC phase undergoes another phase transition to a commensurate one. A significant decrease in the conductivity has been found at the latter transition. The explanations of the metal-insulator transition and the structural phase transitions have been given in terms of randomness and Cu-ion ordering, respectively.
Title:
Where are the elements in complex aluminides? An experimental and theoretical investigation of the quasicrystalline approximants, Mg2-y(ZnxAl1-x)(3+y)
Authors:
Lee CS. Miller GJ.
Source:
Journal of the American Chemical Society. 122(20):4937-4947, 2000 May 24.
Abstract:
The first detailed investigation of the crystalline R-phases in the Mg-Zn-Al ternary system is reported, which will assist with the interpretation and understanding of similar quasicrystalline phases in this phase diagram. Although ''Mg-32(Zn,Al)(49)'' was originally reported by Bergman and Pauling in 1956, some details regarding its structure and the atomic arrangement remain to be solved. Single-phase product can be obtained from reaction compositions "Mg-1.63(ZnxAl1-x)(3.37)'', 0.35 less than or equal to x less than or equal to 0.65. A combination of single-crystal X-ray diffraction, powder neutron diffraction, energy dispersive spectroscopy, densities, and theoretical modeling is needed to elucidate a complete structural model for these phases. Single-crystal X-ray diffaction gave the R-phase structure (space group Im (3) over bar, Z = 32) for three difference samples: Mg1.76(1)Zn1.46(6)Al1.65(3) (a = 14.364(3) Angstrom), Mg1.75(1)Zn1.80(2)Al1.31(1) (a = 14.212(1) Angstrom), and Mg1.73(1)Zn2.46(6)Al0.69(3) (a = 14.131(1) Angstrom). Neutron powder diffraction on three similar bulk samples gave Mg1.76(1)Zn1.34(5)Al1.76(5) (a = 14.2697(1) Angstrom), Mg1.75(1)Zn1.76(5)Al1.34(6) (a = 14.1804(1) Angstrom), and Mg1.73(1)Zn2.06(3)Al1.09(3) (a = 14.11247(6) Angstrom). For all phases in this Mg-Zn-Al system, one crystallographic site (M4) has ca. 33% vacancies and shows a mixture of Mg and Zn atoms. Mg atoms occur next to vacancies on these sites. Theoretical calculations are used to explain the observed phase width involving Zn and Al, the trend in observed site occupancies, and the occurrence of vacancies in this structure. A range of nonbonding states near the Fermi level accounts for the phase width and allows a range in valence electron concentration between 2.07 and 2.48 for the existence of this structure. Valence electron concentrations in Mg-Zn-Al, however, necessitate the occupation of some metal-metal antibonding orbitals, which creates a driving force for vacancies. Since Mg can replace atoms in the (Zn,AI) framework, the R-phases are true intermediates between Zintl phases on one hand and Hume-Rothery intermetallic phases on the other.
Title:
Superstructure in a triclinic phase of tricalcium silicate
Authors:
Urabe K. Shirakami T. Iwashima M.
Source:
Journal of the American Ceramic Society. 83(5):1253-1258, 2000 May.
Abstract:
A triclinic phase of tricalcium silicate (TI) was investigated using transmission electron microscopy (TEM), Electron diffraction patterns were analyzed by introducing a subcell with the cell parameters of a = 7.081 Angstrom, b = 7.043 Angstrom, c = 25.230 Angstrom, alpha = 89.97 degrees, beta = 90.37 degrees, and gamma = 119.44 degrees, It was proven that the coordinates of all the reflections can be expressed to be ha* + kh* + lc* +/- m/6(a* + 2b* + 2c*), where m = 0, 1, 2, and 3, The result indicates that the structure modulation in TI is a one-dimensional type with a structural modulation normal to (122), The modulated structure could be observed in a high-resolution TEM image as wavy contrast streaking parallel to the plane with an interval of six times the (122) spacing.
Title:
Atomic motions in the crystalline Al50Cu35Ni15 alloy
Authors:
Dahlborg U. Howells WS. Calvo-Dahlborg M. Dubois JM.
Source:
Journal of Physics-Condensed Matter. 12(17):4021-4041, 2000 May 1.
Abstract:
This paper describes quasi-elastic neutron scattering experiments on the Al50Cu35Ni15 alloy Dcl-formed on the IRIS spectrometer at ISIS, Rutherford Appleton Laboratory, and on the MIBEMOL spectrometer at Laboratoire Leon Brillouin, Saclay. The aim was to investigate if atomic hopping motions are restricted only to occur in systems with quasicrystalline local order. It is found that frequent jumps of Cu and Ni atoms between different interstitial lattice positions on the time scale 1 to 100 ps are taking place in this alloy at high temperature. This is the same time scale that has been found earlier in quasicrystals and it suggests that this kind of motion is likely to take place in any metallic alloy at high temperature and that it is not a special property of quasicrystals.
Title:
Formation of icosahedral quasicrystalline phase in Zr70TM10Pd20 (TM = Fe, Co, or Cu) ternary glassy alloys
Authors:
Matsushita M. Saida J. Li C. Inoue A.
Source:
Journal of Materials Research. 15(6):1280-1283, 2000 Jun.
Abstract:
A nanoscale icosahedral quasicrystalline phase was confirmed as a primary precipitation phase in the melt-spun Zr70TM10Pd20 (TM = Fe, Co, or Cu) ternary glassy alloys with a two-stage crystallization process. The onset temperature of the transformation from amorphous to icosahedral phase is 713 K for Fe-, 696 K for Co-, and 680 K for Cu-containing alloys at the heating rate of 0.67 Ks(-1). The size of the icosahedral particles is in the range of 20 to 50 nm for the Zr70Cu10Pd20 glassy alloy annealed for 120 s at 720 K. The icosahedral phase has a very fine particle size in a diameter range below 10 nm for the Zr70Fe10Pd20 and Zr70Co10Pd20 alloys. The crystallization reaction after the first exothermic peak results in the transition from the icosahedral to crystalline phases through a sharp exothermic reaction. Thus, the formation of the nanoscale icosahedral phase indicates the possibility that an icosahedral short-range order exists in the present glassy alloys.
Title:
Magnetic properties of icosahedral R-Mg-Zn quasicrystals (R=Y, Tb, Dy, Ho and Er)
Authors:
Fisher IR. Islam Z. Zarestky J. Stassis C. Kramer MJ. Goldman AI. Canfield PC.
Source:
Journal of Alloys & Compounds. 303:223-227, 2000 May 24.
Abstract:
Large (up to 0.5 cm(3)) single grains of icosahedral R-Mg-Zn quasicrystals (R=Y, Tb, Dy, Ho and Er) have been grown via a self-flux technique. The samples have a composition of approximately R9Mg34Zn57, and are extremely well-ordered, with little or no evidence of phason strain. These samples have allowed a detailed investigation of the magnetic behaviour of local 4f moments in a quasiperiodic environment. Neutron scattering experiments using powdered single-grains show no evidence for long range magnetic order in the R-Mg-Zn quasicrystals. However, magnetization and magnetic susceptibility measurements indicate a spin-glass state, with freezing temperatures T-f = 5.8, 3.6, 2.0 and 1.3 K for R = Tb, Dy, Ho and Er respectively. Deviations from a Curie-Weiss temperature dependence of the susceptibility are small, and only occur for temperatures up to 5 K above T-f, indicating the absence of any significant cluster glass behaviour. In addition, the rare earth dilution series (Y1-xGdx)-Mg-Zn have lower freezing temperatures than (Y1-xTbx)-Mg-Zn, despite the larger de Gennes factor of Gd3+ over Tb3+, indicating that crystal electric fields play a significant role in the freezing phenomenon. This difference between Heisenberg and non-Heisenberg moments is further explored via several (Gd1-xRx)-Mg-Zn pseudo-ternary quasicrystal series. (C) 2000 Elsevier Science S.A. All rights reserved.
Title:
Magnetic properties of RPdGa (R=Gd-Er) compounds
Authors:
Penc B. Hofmann M. Leciejewicz J. Szytula A. Zygmunt A.
Source:
Journal of Alloys & Compounds. 305(1-2):24-31, 2000 Jun 6.
Abstract:
Lanthanide palladium gallides RPdGa (R=Gd-Er) show the orthorhombic, TiNiSi-type crystal structure. Magnetometric and neutron diffraction studies reveal that three of the title compounds are antiferromagnetic at low temperatures. TbPdGa exhibits, at 1.5 K, a complicated magnetic structure, which at 26 K transformed into a sine-wave modulated ordering described by the wave vector k=(0,0.3982(2),0). The Neel point of TbPdGa is at 34 K. A collinear antiferromagnetic order characterized by the wave vector k=(1/2,1/2,0) observed at 1.5 K in HoPdGa transforms near the Neel point at 6.8 K into a sine-wave modulated one with the wave-vector k=(0.628(1),0.475(1),0). ErPdGa has also a collinear antiferromagnetic structure at 1.5 K but with the wave vector k=(0,1/3,0). Near the Neel point at 5 K it transforms into a sine-wave modulated structure described by the wave-vector k=(0,0.3803(4),0). The magnetization curve of DyPdGa shows that this compound is ferromagnetic up to the Curie point at 20 K while the magnetic data for GdPdGa indicate antiferromagnetic ordering below 5.1 K. (C) 2000 Elsevier Science S.A. All rights reserved.
Title:
Neutron diffraction study of incommensurate magnetic order in TbOs2Si2 and HoOs2Si2
Authors:
Kolenda M. Hofman M. Leciejewicz J. Penc B. Szytula A.
Source:
Journal of Alloys & Compounds. 305(1-2):153-156, 2000 Jun 6.
Abstract:
Neutron diffraction data collected at low temperatures for TbOs2Si2 and HoOs2Si2 indicate that in the former compound magnetic moments localized on Tb3+ ions form an incommensurate, sine wave modulated structure with the wave vector k=(0.3138(5), 0, 0) and moments aligned along the tetragonal axis. This structure is stable between 1.5 K and the Neel point at 45 K. In HoOs2Si2, an incommensurate magnetic order described by two wave vectors k(1)=(0.3, 0, 0) and k(2)=(0.22, 0, 0) is observed between 1.5 and 8.6 K - the transition temperature to a new also sine wave modulated magnetic phase with the wave vector k=(0.3, 0, 0), stable up to the Neel point at 15.8 K. (C) 2000 Elsevier Science S.A. All rights reserved.
Title:
Hydrogen evolution from Zr-based amorphous and quasicrystalline alloys
Authors:
Eliaz N. Eliezer D. Abramov E. Zander D. Koster U.
Source:
Journal of Alloys & Compounds. 305(1-2):272-281, 2000 Jun 6.
Abstract:
The combination of local tetrahedral order and favorable chemical composition makes amorphous and quasicrystalline Zr-Cu-Ni-Al alloys good candidates for hydrogen storage applications. Hydrogen evolution from these alloys has been studied by means of thermal desorption spectroscopy (TDS). The characteristics of hydrogen desorption from an initially quasicrystalline phase are analyzed in detail for the first time. Spectra analysis is supported by data from variety of other experimental techniques, such as differential scanning calorimetry (DSC), Auger electron spectroscopy (AES), elastic recoil detection analysis (ERDA) and transmission electron microscopy (TEM). Hydrogen desorption from both alloys is found to be a very complex process, being affected by phase transformations that take place during annealing, by hydride formation, and by the formation of a thin zirconium oxide on the surface. (C) 2000 Elsevier Science S.A. All rights reserved.

Update: 19-June-2000

Title:
The spin excitation spectrum in superconducting YBa2Cu3O6.85
Authors:
Bourges P. Sidis Y. Fong HF. Regnault LP. Bossy J. Ivanov A. Keimer B.
Source:
Science. 288(5469):1234-1237, 2000 May 19.
Abstract:
A comprehensive inelastic neutron scattering study of magnetic excitations in the near optimally doped high-temperature superconductor YBa2Cu3O6.85 is presented. The spin correlations in the normal state are commensurate with the crystal Lattice, and the intensity is peaked around the wave vector characterizing the antiferromagnetic state of the insulating precursor, YBa2Cu3O6. Profound modifications of the spin excitation spectrum appear abruptly below the superconducting transition temperature T-c, where a commensurate resonant mode and a set of weaker incommensurate peaks develop. The data are consistent with models that are based on an underlying two-dimensional Fermi surface, predicting a continuous, downward dispersion relation connecting the resonant mode and the incommensurate excitations. The magnetic incommensurability in the YBa2Cu3O6+x system is thus not simply related to that of another high-temperature superconductor, La2-xSrxCuO4, where incommensurate peaks persist well above T-c. The temperature-dependent incommensurability is difficult to reconcile with interpretations based on charge stripe formation in YBa2Cu3O6+x near optimum doping.
Title:
Quasi-unit-cell model for an Al-Ni-Co ideal quasicrystal based on clusters with broken tenfold symmetry
Authors:
Abe E. Saitoh K. Takakura H. Tsai AP. Steinhardt PJ. Jeong HC.
Source:
Physical Review Letters. 84(20):4609-4612, 2000 May 15.
Abstract:
We present new evidence supporting the quasi-unit-cell description of the Al72Ni20Co8 decagonal quasicrystal which shows that the solid is composed of repeating, overlapping decagonal cluster columns with broken tenfold symmetry. We propose an atomic model which gives a significantly improved fit to electron microscopy experiments compared to a previous proposal by us and to alternative proposals with tenfold symmetric clusters.
Title:
Frequency evolution of neutron peaks below T-c: Commensurate and incommensurate structure in La0.85Sr0.15CuO4 and YBa2Cu3O6.6
Authors:
Kao YJ. Si QM. Levin K.
Source:
Physical Review B. 61(18):11898-11901, 2000 May 1.
Abstract:
We study the evolution of the neutron cross section with variable frequency omega and fixed T below T-c in two different cuprate families. Our calculations, which predominantly probe the role of d-wave pairing, lend to generic features, independent of Fermi-surface shapes. Among our findings, reasonably consistent with experiment, are (i) for omega near the gap energy Delta, both optimal LaO0.85Sr0.15CuO4 and slightly underdoped YBa2Cu3O6.6 exhibit (comparably) incommensurate peaks, (ii) peak sharpening below T-c is Seen in LaSrCuO, and (iii) quite generically, a frequency evolution from incommensurate to commensurate and then back to incommensurate structure is found with increasing omega. Due to their narrow omega regime of stability, commensurate peaks in LaSrCuO should be extremely difficult to observe.
Title:
The Zn-Mg-Y phase diagram involving quasicrystals
Authors:
Tsai AP. Murakami Y. Niikura A.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 80(5):1043-1054, 2000 May.
Abstract:
Isothermal sections of the Zn-Mg-Y equilibrium phase diagram at 700 K, 773 K and 873 K have been determined in the region of 30-70 at.% Zn, 20-60 at.% Mg and 0-20 at.% Y using scanning electron microscopy (SEM), wavelength dispersive X-ray, X-ray diffraction and transmission electron microscopy techniques. The icosahedral phase has equilibrium phase fields with three distinct phases (L, Z, N) at 873 It, four distinct phases (L, W, Z, H) at 773 K and five distinct phases (L, W, Z, H, alpha) at 700 K. The equilibrium range of composition for the i-phase at these temperatures was determined.
Title:
Solute diffusion of Ni in icosahedral Al-Pd-Mn quasicrystals
Authors:
Zumkley T. Nakajima H.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 80(5):1065-1074, 2000 May.
Abstract:
This paper presents the results of an experimental study of Ni solute diffusion in the single-grain icosahedral quasicrystalline compound Al70Pd21Mn9. Ni solute diffusion coefficients were measured over a temperature range from 699 to 1074 K. The radiotracer technique in combination with serial sectioning of the diffusion samples was used to determine concentration depth profiles. No deviation from Arrhenius behaviour was detected in the temperature range covered by the present experiments. The results are compared with the available diffusion data on quasicrystals and on diffusion in Al and various diffusion mechanisms proposed for quasicrystals are discussed. The most striking fact is that the diffusion of Ni and the diffusion of other transition-metal elements are found to be much slower than diffusion of non-transition-metal elements such as Ge and Zn in i-(Al-Pd-Mn) quasicrystalline alloys. Moreover, the activation enthalpies of diffusion of the transition-metal elements turned out to be considerably higher than those measured for the non-transition-metal elements. The present study shows that the diffusion of Ni atoms is Likely to proceed by a vacancy mechanism via Al and Pd sites.
Title:
Plastic deformation of icosahedral Al-Pd-Mn single quasicrystals - I. Experimental results
Authors:
Geyer B. Bartsch M. Feuerbacher M. Urban K. Messerschmidt U.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 80(5):1151-1163, 2000 May.
Abstract:
In order to compare plastic deformation along different loading axes, icosahedral Al-Pd-Mn single quasicrystals were deformed in uniaxial compression along twofold and fivefold axes, between the lowest temperatures where deformation at strain rates of 10(-5) and 10(-4) s(-1) was possible and 820 degrees C. For the first time, experiments were performed below 680 degrees C. The strain rate and temperature sensitivity of the flow stress were studied by stress relaxation and temperature change tests. In a range of strain of steady state deformation following a yield drop, the flow stress and its strain rate sensitivity increase strongly with decreasing temperature. The temperature sensitivity shows a maximum at about 700 degrees C. The data hardly depend on the specimen orientation. Repeated relaxation tests indicate changes in the microstructure during the relaxations. Transient phenomena also occurred when the relaxation tests had not been started from steady state deformation, e.g. before the upper yield point, after long relaxations or after unloading. The results will be discussed in Part II of this paper.
Title:
Plastic deformation of icosahedral Al-Pd-Mn single quasicrystals - II. Interpretation of the experimental results
Authors:
Messerschmidt U. Bartsch M. Geyer B. Feuerbacher M. Urban K.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 80(5):1165-1181, 2000 May.
Abstract:
Experimental data on the plastic deformation of icosahedral Al-Pd-Mn single quasicrystals are discussed in terms of dislocation models. The occurrence of a yield drop followed by a range of steady state deformation is explained by the effects of dislocation multiplication and recovery on both the mobile dislocation density and the internal stress. The influence of transient phenomena during the measuring procedures of the activation parameters is estimated. The activation volume of deformation is a unique function of the stress. The activation enthalpy and the Gibbs free energy, calculated by Schoeck's formula, assume approximately constant values above 700 degrees C but decrease strongly below this temperature. In the temperature range where steady state deformation is possible, probably the flow stress is controlled by both the friction mechanism of moving dislocations and the recovery processes taking place during deformation.
Title:
Synthesis of quasicrystalline phase by mechanical alloying of Al70Cu20Fe10
Authors:
Barua P. Srinivas V. Murty BS.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 80(5):1207-1217, 2000 May.
Abstract:
An icosahedral phase (i-phase) has been synthesized by mechanical alloying of an elemental blend of Al70Cu20Fe10. Mechanical alloying of Al and Fe in the stoichiometric ratio of 3:1 and continued milling after the addition of Al and Cu to yield the nominal composition of Al70Cu20Fe10 does not result in the i-phase formation which requires subsequent annealing at 600 degrees C for 4 h for its formation. h single i-phase cannot be obtained even after annealing. In all cases, an Al(Cu, Fe) solid solution (beta phase) has been found along with the i-phase. The i-phase appears to form by a peritectoid type of reaction between the beta phase and Al2Cu. The electrical resistivity of the nanocrystalline i-phase obtained in the present study was round to be about 2-3 orders higher than that found in thin films and it shows semiconducting behaviour.
Title:
Crystal structure of Ca4.78Cu6O11.60
Authors:
Galez P. Lomello-Tafin M. Hopfinger T. Opagiste C. Bertrand C.
Source:
Journal of Solid State Chemistry. 151(2):170-180, 2000 May.
Abstract:
The crystal structure of Ca4.78Cu6O11.60 (crystal system, monoclinic; space group P2/c, Z=4, rho=4.48(2) g/cm(3), a=10.9456(4) Angstrom, b=6.3192(2) Angstrom, c=16.8408(5) Angstrom, and beta=104.952(2)degrees) has been solved and refined using X-ray and neutron powder diffraction combined with Rietveld analysis. It is closely related to the NaCuO2-type structure. The phase stoichiometry and the displacements of atoms with respect to their positions in the previously reported substructure (crystal system, orthorhombic; space group, Fmmm, a=2.807(1) Angstrom, b=6.351(2) Angstrom, and c=10.597(3) Angstrom) are explained by the minimization of Ca-Ca repulsion and by a relaxation toward a more regular octahedral environment for Ca atoms, The substitution of Tl atoms for Ca atoms results in an increased thermal stability and in incommensurate structures with modulation vectors depending strongly on the Tl content. (C) 2000 Academic Press.
Title:
Incommensurate Cu/Co ordering in the TlCo2-xCuxSe2 (x similar to 1) system
Authors:
Noren L. Withers RL. Berger R.
Source:
Journal of Solid State Chemistry. 151(2):260-266, 2000 May.
Abstract:
Cu/Co ordering in TlCo2-xCuxSe2, (x similar to 1) has been investigated using electron and X-ray powder diffraction, The average structure of the x = 1 compound call be indexed on an F-centered orthorhombic cell, a = 5.5518(6) Angstrom, b = 5.4755(5) Angstrom, and c = 13.7387(17) Angstrom. Additional weak satellite reflections characterized by the primary modulation wave vector q(i) similar to 0.184a* and indicative of an incommensurate modulated structure are revealed by electron diffraction, Characteristic extinction conditions in conjunction with mmm Laue symmetry and known crystal chemical constraints imply a (3 + 1)-dimensional superspace group symmetry of Fmmm (alpha 01)00s, The incommensurate modulation is attributed to occupational ordering of the two transition metal atoms and associated structural relaxation. The real space interpretation of the Cu/Co ordering pattern is that copper and cobalt atoms form separate layers in the structure at z = 1/4 and 3/4, respectively. These layers are periodically interchanged as one moves along the x direction. Two periods of this square-wave-like modulation is close to 11a in length but is non-rational compared with the average structure. (C) 2000 Academic Press.
Title:
Jumps in icosahedral quasicrystals
Authors:
Roth J.
Source:
European Physical Journal B. 15(1):7-13, 2000 May.
Abstract:
Atomic jumps in icosahedral (AlCu)Li quasicrystals and related structures have been studied by molecular dynamics simulations. In quasicrystalline structures jumps exists with jump vectors much shorter than an average nearest neighbor distance. This is a consequence of the phasonic degree of freedom. The jumps therefore are called flips and the sites connected by the jump vector are denoted alternative positions. We find that the atoms in the quasicrystal structures studied here do not Aip to alternative positions as proposed and observed in decagonal or dodecagonal quasicrystals but jump to sites which are at least an ordinary interatomic distance apart. Furthermore we observe two diffusion regimes: below about 55% of the melting temperature only small (AlCu) atoms carry out ring processes whereas at higher temperatures both kinds of atoms contribute to long-range diffusion.
Title:
Nano-icosahedral quasicrystalline phase formation from a supercooled liquid state in Zr-Fe-Ni ternary metallic glass
Authors:
Saida J. Li CF. Matsushita M. Inoue A.
Source:
Applied Physics Letters. 76(21):3037-3039, 2000 May 22.
Abstract:
It was found that an icosahedral quasicrystalline phase was formed as a primary precipitation phase from the supercooled liquid region of the melt-spun Zr70Fe20Ni10 ternary metallic glass. The precipitation of an icosahedral phase takes place at 673 K at the heating rate of 0.67 K s(-1). The precipitated icosahedral particle has a nearly spherical morphology and a fine grain size in the diameter range of 5-10 nm. The second crystallization reaction proceeds through a broad exothermic peak and results in the formation of Zr2Ni and Zr2Fe phases. The formation of nanoscale icosahedral phase by the addition of Fe as well as noble metals such as Pd, Au, and Pt indicates the possibility of existence of an icosahedral short-range order in the various Zr-based metallic glasses. (C) 2000 American Institute of Physics. [S0003-6951(00)02921-1].
Title:
Incommensurate c-domain superstructures in calcian dolomite from the Latemar buildup, Dolomites, Northern Italy
Authors:
Schubel KA. Elbert DC. Veblen DR.
Source:
American Mineralogist. 85(5-6):858-862, 2000 May-Jun.
Abstract:
Early exposure cap microdolomites (<50 degrees C) and low-temperature hydrothermal (<177 degrees C) calcian dolomite crystals from the Latemar buildup, Dolomites, northern Italy, are microstructurally heterogeneous. Selected-area electron-diffraction patterns contain incommensurate superstructure reflections from domains that are approximately 2.5 nm wide. These domains are quasiperiodic with wavelengths of 5 to 20 nm. The scale of these modulations varies with composition of the bulk crystal. Previously described c-domain superstructures in dolomite are reported as commensurate with the host structure; c-diffraction spots are situated exactly halfway between the principal (a and b) reflections. Re-examination of published diffraction patterns reveals that some are actually incommensurate. Individual c-domains are monoclinic and have been interpreted to be more calcium-rich than the host dolomite. Newly recognized c-domains resemble previously described c-domains but are distinct because they are incommensurate with the dolomite host and produce diffraction spots with irrational indices. In samples from the Latemar buildup, the c-axes of the host and modulations are parallel, but the [110] directions are not parallel. Further, the length of c*(dolmite) approximate to c*(superstructure),but the lattice spacing of d(110)(superstructure) is more than twice d(110)(dolmite). The superstructure phase is metrically monoclinic and is interpreted to incorporate more calcium than dolomite. Domains are, however, too small to analyze directly. Excess calcium may account for the more than doubling of the domains' a-dimension relative to that of dolomite. Inclination of the domain lattice relative to the host lattice may vary as a function of calcium content.
Title:
Magnetic ordering RAgSB2 compounds
Authors:
Andre G. Bouree F. Kolenda M. Lesniewska B. Oles A. Szytula A.
Source:
Acta Physica Polonica A. 97(5):771-774, 2000 May.
Abstract:
The magnetic structures of the polycrystalline samples of RAgSb2 (R = Ce, Pr, Nd, Tb-Tm) are determined. All compounds crystallize in the tetragonal ZrCuSi2-type of crystal structure and except CeAgSb2 they are antiferromagnets with a Neel temperature of 11 K for R = Tb and 2 K for Tm. CeAgSb2 below T-C = 9.5 K is ferromagnet with the magnetic moment equal to 0.33 mu(B) and parallel to c-axis. In NdAgSb2 the sine modulated magnetic ordering described by the wave vector k = (0.5435,0,0) is observed. Below T-N a collinear antiferromagnetic structure with the magnetic (a, a, 2c) for R = Pr and (2a, a, c) for R = Tb, Dy, Ho, and Er is observed. For He-compound with an increase in temperature the coexistence of two structures is observed: commensurate collinear and incommensurate sine modulated. In TmAgSb2 the coexistence of the two phases is observed at T = 1.4 K. With an increase in temperature only the incommensurate phase stays.
Title:
Quasicrystalline decagonal phase of Si clusters evaporated in helium and annealed
Authors:
Kamalakaran R. Singh AK. Srivastava ON.
Source:
Physical Review B. 61(19):12686-12688, 2000 May 15.
Abstract:
The quasicrystalline phase of Si has been stabilized through annealing (300 to 400 degrees C) of silicon cluster films prepared by evaporation of silicon under helium ambient (similar to 200 torr). The quasicrystalline (qc) decagonal phase with a(R) = 4.56 Angstrom and the regular periodicity of 13.44 Angstrom was identified through electron microscopic exploration involving selected area diffraction patterns. A possible mode of stabilization of the qc phase has been outlined.
Title:
Icosahedral quasicrystals applied as a harmonic-free crystal analyser
Authors:
Capitan MJ. Alvarez J.
Source:
Journal of Applied Crystallography. 33(2 Part 3):888-892, 2000 Jun 1.
Abstract:
The use of quasicrystals as crystal analysers has been studied in monochromatic X-ray synchrotron radiation applications. The quasiperiodicity of their structures gives a theoretical third-harmonic rejection factor of up to 5 x 10(-4) when the icosahedral (20,32) Bragg peak is used. This ratio is compared with the intrinsic value for silicon perfect crystals in Bragg configuration, namely 2 x 10(-2). This rejection factor may be increased for some well defined configurations, as reported elsewhere for the case of periodic crystals.
Title:
Structural characterization of Y2Pd14B5
Authors:
Hough DW. Jaenicke-Roessler U. Zahn G. Belger A. Guembel A. Oertel CG. Skrotzki W.
Source:
Crystal Research & Technology. 35(4):409-417, 2000.
Abstract:
Y2Pd14B5 is the major phase in as-cast and annealed multiphase alloys with nominal compositions near YPd5B3C0.3. Its crystal structure determined the first time here by single crystal X-ray diffraction is body-centered tetragonal (space group I 4(1)/amd). Transmission electron microscopy (TEM) reveals that in as-cast specimens the tetragonal phase has a modulated structure and is oriented intergrown with a face-centered cubic phase of similar composition, namely YPd7B2. According to Rietveld analyses of the multiphase system the structure of this phase can be well-described by space group Fm (3) over bar m. Annealing the sample for 150 hrs at 973 K results in a coarsening and enrichment of the tetragonal phase as well as a disappearance of the modulations allowing a detailed structure analysis by single crystal diffractometry.
Title:
Discrete Fourier transform in arbitrary dimensions by a generalized Beevers-Lipson algorithm
Authors:
Schneider M. van Smaalen S.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A. 56(Part 3):248-251, 2000 May.
Abstract:
The Beevers-Lipson procedure was developed as an economical evaluation of Fourier maps in two- and three-dimensional space. Straightforward generalization of this procedure towards a transformation in n-dimensional space would lead to n nested loops over the n coordinates, respectively, and different computer code is required for each dimension. An algorithm is proposed based on the generalization of the Beevers-Lipson procedure towards transforms in n-dimensional space that contains the dimension as a variable and that results in a single piece of computer code for arbitrary dimensions. The computational complexity is found to scale as N log(N), where N is the number of pixels in the map, and it is independent of the dimension of the transform. This procedure will rnd applications in the evaluation of Fourier maps of quasicrystals and other aperiodic crystals, and in the maximum-entropy method for aperiodic crystals. [References: 9]

Update: 2-June-2000

Title:
Simulation of pressure induced phase transition and modulated structures of quartz
Authors:
Dmitriev SV. Yajima M. Makita Y. Abe K. Shigenari T.
Source:
Progress of Theoretical Physics Supplement. (138):243-244, 2000.
Abstract:
In the vicinity of alpha <-> beta transition in quartz there exists an incommensurate phase. We perform numerical calculations to obtain the phase diagram of quartz and estimate the period of modulation. The results show that modulation phase with a short period is preferable in contrast to the currently accepted interpretation of incommensurate phase in quartz. [References: 4]
Title:
Distribution of inequivalent lattice sites in icosahedral quasicrystal Al72.4Pd20.5Mn7.1 studied by NMR
Authors:
Apih T. Klanjsek M. Rau D. Dolinsek J.
Source:
Physical Review B. 61(17):11213-11216, 2000 May 1.
Abstract:
A local spectroscopic study of the distribution of inequivalent lattice sites in icosahedral Al72.4Pd20.5Mn7.1 single-grain quasicrystal by the Al-27 quadrupole-perturbed NMR is presented. The strongly inhomogeneously broadened Al-27 spectra show orientation dependence in the magnetic field that originates from a spatially anisotropic distribution of the electric-field gradient tensor orientations at inequivalent lattice sites. The results give spectroscopic evidence that some local atomic arrangements in the quasiperiodic structure are preferred within the manifold of the infinitely many inequivalent lattice sites. [References: 9]
Title:
Conduction mechanisms in some icosahedral and amorphous phases
Authors:
Zavaliche F. Manaila R. Haberkern R. Haussler P. Poon SJ. Belu-Marian A. Devenyi A.
Source:
Physica Status Solidi B-Basic Research. 218(2):485-494, 2000 Apr.
Abstract:
Quasicrystalline icosahedral and amorphous phases prepared as thin films or bulk samples in the systems Al-Pd-Re, Al-Cu-Fe and Ti-Zr-Ni, have been investigated with respect to their temperature dependence of conductance and thermopower, in the range between 10 and 300 K. Various conduction mechanisms yield different exponent values in the power-law temperature dependence of conductance, Tt. A semi-metal behaviour (zeta congruent to 1.5) is found in the amorphous phase and in the disordered icosahedral Al-Pd-Rt: film and Ti-Zr-Ni ribbons, as well as in icosahedral Al-Cu-Fe films. Lower zeta values found in the quasi-perfect icosahedral Al-Pd-Re bulk sample and in two of the icosahedral Al-Cu-Fe films suggest that electron localization in a hierarchy of clusters is the main conduction mechanism in these samples. The thermopower data support the existence of a pseudo-gap at the Fermi level and suggest a similar short-range order in both amorphous and icosahedral phases. The special sensitivity of the thermopower to the DOS details at E-F is responsible for the strong variation of its magnitude with the degree of icosahedral order.
Title:
A new example of a composite composition flexible phase structure of Ba(1+x)A(x)(')B(1-x)O(3) (x=0.2124, A '=Ni, B=0.51Ni+0.49Pt)
Authors:
Zakhour-Nakhl M. Weill F. Darriet J. Perez-Mato JM.
Source:
International Journal of Inorganic Materials. 2(1):71-79, 2000 Feb.
Abstract:
The structure or Ba(1-x)A(x)'B1-xO3 (x=0.2124, A'=Ni, B=0.51Ni+0.49Pt) has been solved in the superspace formalism with occupational Crenel Functions and sawtooth displacive modulations along the trigonal axis. The structure is described as an incommensurate modulated columnar composite with two subsystems, [(Ni,Pt)O-3] and [Ba], respectively. The superspace group is R (3) over bar m(00 gamma)0s with a = 9.9357(1) Angstrom, c =2.5871(1) Angstrom and q = 0.6062c* (Z=3). The structural modulation has two variable parameters: the modulation wave vector or misfit parameter, which is fixed by the composition, and the mismatch between the sizes of the octahedral and prismatic oxygen polyhedra formed in the structure. The model, although developed within the superspace formalism, is closely related to the previously reported polytype layer picture in direct space. This structure is an example of so-called composition flexible systems. The present structural analysis constitutes a merely demonstrates the efficiency of the four-dimensional superspace formalism for describing such phases. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.
Title:
Modeling the electrical conductivity of icosahedral quasicrystals
Authors:
Macia E.
Source:
Physical Review B. 61(13):8771-8777, 2000 Apr 1.
Abstract:
A model for the electronic structure of icosahedral quasicrystals is proposed on the basis of a number of pertinent experimental results. From this model we obtain a closed analytical expression for the electrical conductivity accurately describing the most remarkable features observed in the sigma(T) curves of high quality quasicrystals. As a convenient working example we compare the theoretical description provided by our treatment with a series of suitable experimental data for the i-AlCuRu, unveiling a relationship among the density-of-states structure, the sample stoichiometry, and the electrical conductivity of different samples at different temperature ranges.
Title:
Modulated magnetic structure and spin waves in hexagonal CsCuCl3-type antiferromagnets
Authors:
Sukstanskii AL. Stefanovskii EP. Reshetnyak SA. Varyukhin VN.
Source:
Physical Review B. 61(13):8843-8850, 2000 Apr 1.
Abstract:
A theory is developed for triangular helicoidal antiferromagnetic structures due to the relativistic-exchange inhomogeneous Dzyaloshinskii-Moriya interaction in hexagonal crystals. The magnetic structure observed in the CsCuCl3 system is explained, and the spin-wave spectrum and relaxation of spin waves are analyzed. The theoretical results are in agreement with experimental antiferromagnetic-resonance data.
Title:
Evidence for nonclassical critical behavior of a one-dimensional incommensurately modulated crystal: A Cl-35 NQR study of bis(4-chlorophenyl)sulfone
Authors:
Decker F. Petersson J.
Source:
Physical Review B. 61(13):8993-9000, 2000 Apr 1.
Abstract:
The temperature dependence of Cl-35 nuclear quadrupole resonance (NQR) spectra and the respective spin-lattice relaxation times have been measured between room temperature and 120 K on high quality single crystals of bis(4-chlorophenyl)sulfone [(C6H4Cl)(2)SO2]. Spectra with the typical incommensurate edge singularities were found at temperatures below the transition temperature Ti into the incommensurate (IC) phase. This holds in particular for temperatures very close to T-i. The exponent describing the temperature dependence of the distance between the edge singularities of the incommensurate spectrum is near T-i about 0.35 +/- 0.03 which is identified with the critical exponent beta of the order parameter. Above T-i a considerable critical contribution to the spin-lattice relaxation rate 1/T-1 is detected which can be described by some critical exponent zeta of about 0.69+/-0.02. The data are interpreted in terms of the three-dimensional (3D) XY model. In the IC phase T-1 stays low indicating a considerable influence of the phason excitations on every part of the IC spectrum. Contrary to the behavior of other systems the minimum of T-1 does not occur at T-i. Rather, it is shifted some degrees from T-i to lower temperatures. 2D Cl-35 NQR exchange spectra show no indication for large scale fluctuations of the modulation wave above about 500 Hz.
Title:
Modulated structures in non-stoichiometric YBa2Cu3O7-delta compounds
Authors:
Sudareva SV. Kuznetsova EI. Krinitsina TP. Bobylev IB. Romanov EP.
Source:
Physica C. 331(3-4):263-273, 2000 May 1.
Abstract:
In accordance with the spinodal decomposition theory for YBa2Cu3O7-delta (delta greater than or equal to 0.2) non-stoichiometric compound, the structure of two structurally unstable compounds, YBa2Cu3O6.8 and YBa2Cu3O6.6, annealed at 200 degrees C and 300 degrees C,has been studied by methods of electron microscopy and optical metallography in the polarized light. In the YBa2Cu3O6.8 single crystal annealed at 200 degrees C, 100 h, fine precipitates of oxygen-rich orthorhombic phase are observed in oxygen depleted matrix. The tweed quasi-periodical contrast is formed by atomic displacement waves of [110], [<1(1)over bar>0] type arising in the depleted matrix. In the YBa2Cu3O6.8 specimen, annealed at 300 degrees C, oxygen separation gives rise to high elastic stresses around precipitates of oxygen-rich phase, which results in distortions of matrix structure. In the YBa2Cu3O6.6 specimen annealed at 200 degrees C and 300 degrees C, in addition to that, the following features have been found: classic modulated structure (oxygen separation) with distinct periodicity of fine stripes and corresponding satellites in electron diffraction patterns (EDPs); coarse lamellar structure associated, in our opinion, with a discontinuous reaction; and the phases with oxygen vacancy ordering in a form of fine and coarse lamellas. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Incommensurate modulated magnetic structure in the heavy electron compound YbPtAl
Authors:
Bonville P. Abd-Elmeguid M. Malaman B. Ressouche E. Sanchez JP. Geibel C. Trovarelli O.
Source:
Physica B. 281:144-146, 2000 Jun.
Abstract:
Yb-170 Mossbauer spectroscopy measurements down to 0.025 K and neutron diffraction measurements down to 1.7 K have been performed in the heavy electron compound YbPtAl(T-N similar or equal to 5.8 K). Below T-N the neutron data show that the magnetic structure is incommensurate, with a wave-vector k = (0.30. 0. 0). At 0.035 K, the Mossbauer data reveal that the magnetic structure is modulated and that it is not an antiphase structure. YbPtAl is a clear example of a Kramers local moment system where the Kondo singlet ground state allows a modulated magnetic structure to persist down to 0 K. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Neutron diffraction study of a Nd3Pd20Ge6 sample with three successive magnetic phase transitions
Authors:
Donni A. Fischer P. Keller L. Herrmannsdorfer T. Fauth F. Komatsubara T.
Source:
Physica B. 281:155-157, 2000 Jun.
Abstract:
Low-temperature powder neutron diffraction experiments down to 100 mK were performed on an inhomogeneous Nd3Pd20Ge6 sample. The onset of magnetic order of the Nd moments on 8c site is found to split into two phase transitions with a dominant commensurate antiferromagnetic component (k(1) = [1, 1, 1] below T-N1 = 1.75 K) and an additional weak incommensurate perturbation (k(1i) = [tau, tau, tau], tau=0.79, below T-N1i = 1.40 K) The Nd moments on 4a site remain disordered down to T-N2 = 0.58 K and align perpendicular to the propagation vector k(2) = [0, 0, 1]. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 4]
Title:
Magnetic properties of heavy-fermion Ce(Ru1-xPdx)(2)Si-2
Authors:
Murayama S. Sekine C. Yotsuya S. Nakano T. Ohmori Y. Hoshi K. Tsuchiya Y. Osakabe T.
Source:
Physica B. 281:343-345, 2000 Jun.
Abstract:
Magnetic structure of single-crystalline Ce(Ru1-xPdx)(2)Si-2, x = 0.025 has been measured by neutron diffraction. The magnetic moment is oriented and modulated along the c-axis with incommensurate wave vector tau = (0,0,0.368). At 1.4 K the moment was estimated to be about 0.15 mu(B). Temperature dependence of the specific heat on polycrystalline Ce(Ru1-xPdx)(2)Si-2, x = 0.05 has also been measured in various magnetic fields, suggesting partial gapping of the Fermi surface due to a Fermi-surface nesting. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Crystal-lattice modulations associated with unusual magnetic structures in the low-carrier system CeSb
Authors:
Iwasa K. Arakaki Y. Kohgi M. Suzuki T.
Source:
Physica B. 281:437-439, 2000 Jun.
Abstract:
X-ray diffraction studies have been performed in order to investigate the p-f mixing effect producing the unusual magnetic properties in the low-carrier system CeSb. Several X-ray satellite-peak patterns were observed below T-N = 17 K. The wave numbers and the intensities of the satellite peaks are in accordance with the model of periodic arrangement of short and long distances due to two kinds of magnetic layers in the structures reported by Rossat-Mignod et al. (J. Magn. Magn. Mater. 52 (1985) 111). The shorter distance is due to the strong p-f mixing effect, which is spatially restricted within the ferromagnetic layers of Gamma(8)-like Ce ions, and the longer one due to the layers of normal Gamma(7) Ce ions. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 6]
Title:
X-ray diffraction study of the 5-fold plane surface of a Al70.4Pd21.4Mn8.2 single-grain
Authors:
Capitan MJ. Calvayrac Y. Gratias D. Alvarez J.
Source:
Physica B. 283(1-3):79-83, 2000 Jun.
Abstract:
The structure of a 5-fold symmetry quasicrystal surface of a thermodynamically stable icosahedral Al70.4Pd21.4Mn8.2 single-grain has been studied by means of the surface X-ray diffraction technique. The model used reproduces rather well both the Bragg peaks and the surface signal. The parameters obtained from the fit of the measured structure factor show a contraction of the outermost atomic layer. The surface also tends to be richer in Al and Pd atoms forming a very dense outer-layer. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Thermal expansion of TlInX2 (X = S, Se, Te)
Authors:
Kurbanov MM. Bairamov DD. Sardarova NS.
Source:
Inorganic Materials. 36(2):132-133, 2000 Feb.
Abstract:
The thermal expansion coefficients of TlInS2, TlInSe2, and TlInTe2 were measured in the range 77-350 K. The data for both single-crystal and polycrystalline TIInS2 were found to exhibit features attributable to ferroelectric and commensurate-incommensurate phase transitions. The measured thermal expansion coefficients of TlInS2, TlInSe2, and TlInTe2 were used to calculate the Debye temperatures and root-mean-square dynamic atomic displacements. In going from TlInS2 to TlInSe2 and to TlInTe2, the Debye temperature increases and the root-mean-square atomic displacement decreases, which can be attributed to the increase in bond ionicity. [References: 7]
Title:
Monte-Carlo computer simulation of the phase transitions in Sn(Pb)(2)P2S(Se)(6) crystals
Authors:
Drobnich A. Vysochanskii Y.
Source:
Ferroelectrics. 226(1-4):37-49, 1999.
Abstract:
In Sn2P2S6 crystals ferroelectric second order phase transition (PT) occurs. In this case the number of formula units in elementary cell stays unchanged. In Sn2P2Se6 crystals the intermediate incommensurate phase exists. A dipole Ising model of Sn2P2S(Se)(6) ferroelectrics has been developed. To consider the dipole long-range interaction around the dipole an area of simple form is singled out. Within this area the interaction between the dipoles is calculated precisely. The interaction with the other dipoles is considered by introduction of a local field. For better accordance with the real experiment an amendment on the short-range interaction with two nearest neighbours has been introduced. As a result of calculations made by Monte-Carlo method it has been found that when a certain short-range interction coefficient in Sn2P2S6 is selected the intermediate modulated phase disappears. In this case the temperatures of PT are as follows: for Sn2P2S6 model T(o)similar to 10.3; for Sn2P2Se6 model T(c)similar to 8.7, T-i similar to 9.7 (in the effective temperatures). These data are in satisfactory agreement with the results of the experiment. In mixed (PbySn1-y)(2)P2S6 and (PbySn1-y)(2)P2Se6 crystals increase of (Pb) concentration causes reduction of temperatures of FT to 0 K. In this case the character of PT stays unchanged. By the method of diluted Ising lattice the concentration dependences of temperatures of PT in this crystals are simulated.
Title:
Incommensurate phase in Mn2+ doped (NH4)(2)ZnCl4 studied by ESR
Authors:
Lang WG. Farach HA. Creswick RJ. Poole CP.
Source:
Ferroelectrics. 226(1-4):125-132, 1999.
Abstract:
Ferroelectric (NH4)(2)ZnCl4 crystals doped with Mn2+ were studied by electron spin resonance (ESR) in the temperatures range from 80 degrees C to 160 degrees C. The crystal was found to undergo an incommensurate phase transition at 135"C and an incommensurate-commensurate transition at 92 degrees C. The temperature dependence of the ESR line shape while passing through these changes are in good agreement with the predictions of the phase-solition theory. The parameters h(1) and h(2) determining the variation of the resonant magnetic field show a power-law behavior as a function of temperature. The critical exponent beta of this crystal was determined two independent ways to be 0.35+/-0.02. The solition density remains fairly constant throughout the incommensurate phase and drops abruptly to zero at the incommensurate-commensurate transition, a behavior that is quite different from those of other incommensurate systems.
Title:
Distinct roles of the triplicated ZnCl4 tetrahedra in phase soliton formation and residual commensurations in K2ZnCl4
Authors:
Oh DK. Kwon YM. Lee CE. Jeong SY.
Source:
Europhysics Letters. 50(2):196-201, 2000 Apr.
Abstract:
The dynamics of the ZnCl4 tetrahedra, in the ferroelectric lock-in phase of K2ZnCl4 was studied by means of pulsed Cl-35 NQR (nuclear quadrupole resonance) techniques. From the temperature dependence of the spin-lattice relaxation rate (1/T-1Q) for each of the triplicated Cl(1) sites in the lock-in phase, it is suggested that the domain peak in the incommensurate phase arises from the ZnCl4 tetrahedral site with a negligible reorientational motion, whereas the other two sites with an activated reorientational motion lead to the phase solitons.
Title:
Two-dimensional dodecagonal and decagonal quasiperiodic photonic crystals in the microwave region
Authors:
Jin CJ. Cheng BY. Man BY. Li ZL. Zhang DZ.
Source:
Physical Review B. 61(16):10762-10767, 2000 Apr 15.
Abstract:
We experimentally and numerically demonstrate dodecagonal and decagonal quasiperiodic photonic crystals in the microwave region. The results show that only a small number of rows are needed to create a frequency gap in the transmission spectrum, and that the gap position is insensitive to the incident angle. In particular, there is no defect state at the first gap of a dodecagonal quasiperiodic photonic crystal when there is a cavity in the center region, even though the cavity volume is much larger than the square of the wavelength. The decagonal quasiperiodic crystal can offer great possibilities for creating defect states. These quasiperiodic photonic crystals may find some important applications in photoelectric devices.
Title:
Determination of the Burgers vector of dislocations in icosahedral quasicrystals by a high-resolution lattice-fringe technique
Authors:
Yang WG. Wang RH. Feuerbacher M. Schall P. Urban K.
Source:
Philosophical Magazine Letters. 80(5):281-288, 2000 May.
Abstract:
A technique for the determination of the full six-dimensional Burgers vector characterizing a dislocation in an icosahedral quasicrystal is presented. It is based on the lattice-fringe analysis of two high-resolution transmission electron microscopy images taken at two different sample orientations. As an example we present the analysis of a dislocation in a bent icosahedral Al-Pd-Mn quasicrystal. We obtained a Burgers vector B = A(0)[-2,0,3,-2,3,0] where A(0) = 0.645 nm is the six-dimensional hyperlattice constant. This result is consistent with previous results obtained by diffraction contrast analysis and convergent-beam electron diffraction techniques.
Title:
Morphological study of micropits formed by anodic etching of an Al-Pd-Mn icosahedral quasicrystal
Authors:
Saito K. Sasaki T. Sugawara S. Guo JQ. Tsai AP.
Source:
Philosophical Magazine Letters. 80(5):307-315, 2000 May.
Abstract:
Faceted micropits obtained by electrochemical etching of a single quasicrystal of an Al-Pd-Mn icosahedral phase have been examined by optical and electron microscopy. Anodic etching of the flat surface of a fivefold plane in a solution composed of CH3OH and HNO3 (3:1 in volume ratio) reveals a variety of icosahedrally faceted micropits which originated from pre-existing microvoids and etch pits of pentagonal pyramid shape due to the other origins, probably structural defects inside the specimen. As the dissolution progresses, the micropits make successive changes in their shapes, ending in pentagonal pyramids before they vanish.
Title:
Complete and absolute photonic bandgaps in highly symmetric photonic quasicrystals embedded in low refractive index materials
Authors:
Zoorob ME. Charlton MDB. Parker GJ. Baumberg JJ. Netti MC.
Source:
Materials Science & Engineering B-Solid State Materials for Advanced Technology. 74(1-3):168-174, 2000 May 1.
Abstract:
It is firmly established that periodic lattice structures can support photonic bandgaps (PBG). However, complete and absolute photonic bandgaps (CAPBG) have only been achieved in high dielectric constant mediums such as GaAs (epsilon = 13.6). An artificial quasiperiodic photonic crystal based on the random square-triangle tiling system was designed and fabricated. The photonic quasicrystal possesses 12-fold symmetry and was analysed using a finite difference time domain (FDTD) approach. High orders of symmetry in photonic quasicryistals have been shown to provide isotropic bandgaps across all the directions of propagation of light. As an outcome of these properties, this new class of photonic quasicrystal has been shown, for the first time, to possess a secondary non-directional CAPBC for a relatively low index material, silicon nitride (epsilon = 4.08). These materials are compatible with integrated optical technologies. This allows the fabrication of efficient integrated optical PEG devices such as WDM filters and multiplexers to become a real possibility. (C) 2000 Elsevier Science S.A. All rights reserved.
Title:
Symmetrical staircase in the profile of lattice-modulation period versus Pr-concentration and domain configurations in Bi2Sr2(Ca1-xPrx)Cu2O8+delta
Authors:
Onozuka T. Niizeki K.
Source:
Journal of the Physical Society of Japan. 69(4):1093-1099, 2000 Apr.
Abstract:
Variation of the lattice-modulation period p(a) of the 'incommensurate' phase Bi2Sr2 (Ca1-xPrx)Cu2O8+delta (0 less than or equal to x less than or equal to 0.72) with Pr-concentration x was examined by electron diffraction, and the domain configuration by high-resolution transmission electron microscopy (HRTEM). The plot of p(a) versus x exhibits roughly a linear decrease but it has a staircase structure. The period of each stair, p(a), agrees with a value expected for a commensurate structure. We observed nine stairs which are symmetrically arranged; the central stair corresponds to the primary structure with a simple modulation, and a stair on the left (or right) is associated with an advanced (or delayed) discommensuration. On the other hand, the number of domain configurations i.e. commensurate structures observed by HRTEM is seventeen. The observed staircase structure covers a full range of commensurate structures predicted theoretically. The pattern observed in the plot of p(a) versus x is consistent with the simulation based on the Frenkel-Kontrova model and an inhomogeneity hypothesis.
Title:
Metastable phases induced by ion irradiation in the equilibrium immiscible Fe-Cu system
Authors:
Yang GW. Lai WS. Lin C. Liu BX.
Source:
Journal of Applied Physics. 87(10):7232-7241, 2000 May 15.
Abstract:
Anomalous structural evolution was induced by room-temperature 200 keV xenon ion irradiation and it results in the formation of various new metastable phases in the equilibrium immiscible Fe-Cu system. First, nanosized quasicrystals were formed in an amorphous matrix through a two-step transition of crystal to amorphous to quasicrystal in Fe70Cu30 multilayered films. The real compositions of the amorphous matrix and quasicrystals were determined to be close to Fe70Cu30 and Fe50Cu50, respectively. Moreover, the same icosahedral phase was also obtained in another similarly designed Fe50Cu50 multilayered sample upon 850 degrees C thermal annealing, confirming the existence of such a metastable state. Second, amorphous alloys were formed in a composition range of 30-50 at. % of Cu. Third, a Cu-based face-centered-cubic (fcc) solid solution was formed at an alloy composition of about Fe30Cu70 and, interestingly, another fcc structured metastable crystalline phase was obtained at a composition very close to that of Fe50Cu50. A Gibbs free energy diagram of the Fe-Cu system was calculated, with special consideration of excess interfacial free energy stored in the multilayered films, within the framework of Miedema's model and it gives a reasonable thermodynamic explanation to the metastable phase formation observed. The amorphous-to-quasicrystal transition is also discussed in terms of the similarity in the atomic configuration between the icosahedral and amorphous short-range orders. Furthermore, molecular dynamics study showed that Fe and Cu could be mixed on an atomic scale in the metastable phases observed. (C) 2000 American Institute of Physics. [S0021-8979(00)01610-8].
Title:
Microdomain structure in the disordered Zn-Mg-Ho icosahedral phase
Authors:
Ishimasa T. Shimizu T.
Source:
Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes & Review Papers. 39(3A):1235-1240, 2000 Mar.
Abstract:
Diffuse scattering related to F-type superlattice ordering was observed in the disordered icosahedral phase formed in Zn60Mg35Ho5 alloy annealed at 562 degrees C. Real space analysis of the diffuse scattering was carried out using high-resolution electron microscopy and a Fourier filtering method. Processed images revealed the presence of microdomains related to weak F-type ordering. The domain diameters range between 30 and 170 Angstrom. Each domain is separated by a boundary region, and is related to nearby domains by an antiphase relationship. These results indicate that the origin of the diffuse scattering is the presence of these domains rather than statistical homogeneous short-range ordering.
Title:
Search for possible structures of cubic approximants of icosahedral quasicrystals
Authors:
Gorokhovskii AA.
Source:
Crystallography Reports. 45(2):172-181, 2000 Mar-Apr.
Abstract:
Admissible structures of the approximants are obtained within the model of the dodecahedral local order (DLO) with due regard for the constraints imposed by the space symmetry. It is shown that the number of cubic approximants of icosahedral quasicrystals having a certain order and dodecahedral local order is finite and that the number of positions that can be occupied by the atoms from the unit cells of an approximant of each order is also finite. The corresponding estimates from above are made. In particular, it is shown that there exists only one structure for the 1/-1 approximant. It is also shown that it is possible to determine all the structures for any approximant of any order. The corresponding algorithm of the exhaustive search for these structures is suggested. The implementation of this algorithm provided the determination of all the structures of the 0/1 approximants and also some possible structures of the 0/1 and 1/1 approximants. The tables of possible approximant structures can be useful in the studies of new phases having approximant structures. (C) 2000 MAIK "Nauka/Interperiodica".
Title:
Hydrodynamics of layered and cubic quasicrystals
Authors:
Belyaev OA. Koptsik VA.
Source:
Crystallography Reports. 45(2):182-186, 2000 Mar-Apr.
Abstract:
The dissipative processes associated with sound absorption in layered and cubic quasicrystals have been studied within the framework of the hydrodynamic approach. The decagonal, octagonal, and dodecagonal quasicrystals are considered as layered quasicrystals. Proceeding from the general theory, the complex law of dispersion is calculated for various directions of the propagation and polarization of sonic waves in layered and cubic quasicrystals. The effect of the phason modes on the process of sound absorption and the role of symmetry constraints are analyzed. The validity of the macroscopic consideration is discussed in terms of the theory of the generalized color symmetry. (C) 2000 MAIK "Nauka/Interperiodica".
Title:
Hyperphasons and the effect of incommensurate modulation on elastic properties of quasicrystals
Authors:
Belyaev OA.
Source:
Crystallography Reports. 45(2):187-194, 2000 Mar-Apr.
Abstract:
Possible descriptions of phasons in incommensurate crystal phases and quasicrystals have been reviewed in terms of the theory of elasticity and superspace symmetry. The superspace symmetry of incommensurately modulated quasicrystals and its relation to the concept of the generalized symmetry are discussed. A new concept of hyperphasons, excited states of a solid characteristic of incommensurately modulated quasicrystals, is introduced using the formalism of the Landau density waves. Hyperphasons are characterized in terms of the generalized unit cells. The expression for the contribution of a hyperphason to the elastic free energy is derived, and the experimental examples of quasicrystals are considered. (C) 2000 MAIK "Nauka/Interperiodica".
Title:
X-ray structure analysis of Bi2212 using synchrotron source and high dynamic range imaging plate detector
Authors:
Lee TJ. Huang CF. Teo CC. Khor TS. Ku HC. Yeh KW. Huang Y. Hung HH. Sakabe K. Sakabe N.
Source:
Chinese Journal of Physics. 38(2 Part 2):243-261, 2000 Apr.
Abstract:
The traveling solvent floating zone method was applied in growing the single crystals of Bi2Sr2PrCu2O8+delta Diffraction patterns of 0kl, 1kl, 2kl, 3kl, 4kl were obtained with the Weissenberg camera equipped with Fuji 400 imaging plate in Photon Factory, KEK. The wavelength of the photon is tuned to 1 Angstrom. With this energy, modulation peaks of "order 3" can be recorded clearly. From the extinction conditions in the diffraction pattern indicate the main structure of the crystal can be attributed to orthorhombic Amaa. Using oscillation photograph and zero level Weissenberg photograph, cell lengths of the crystal were calculated to be a = 5.489(2), b = 5.526(5), c = 30.420(7) Angstrom. The crystal possesses an incommensurate modulation along b direction, with modulation wave vector q = 0.243b* + c* and can be expressed as super space group: N-(1) over bar 11(Amaa).
Title:
A five-dimensional structural investigation of the misfit layer compound [Bi0.87SrO2](2)[CoO2](1.82)
Authors:
Leligny H. Grebille D. Perez O. Masset AC. Hervieu M. Raveau B.
Source:
Acta Crystallographica - Section B, Structural Science. 56(Part 2):173-182, 2000 Apr.
Abstract:
The structure of the misfit layer compound [Bi0.87SrO2](2)[CoO2](1.82), bismuth strontium cobaltite, was determined by single-crystal X-ray diffraction using the five-dimensional superspace-group formalism. This composite crystal, of monoclinic symmetry, is composed of two subsystems exhibiting incommensurate periodicities along b, the binary axis direction. The first composite part [Bi0.87SrO2] displays an intrinsic modulation of planar monoclinic type characterized by the wavevector q* = 0.293a* + 0.915c*. The second composite part [CoO2] shows two different centered lattice variants. The structure of the misfit layer crystal can be described as an alternation along c of distorted rock-salt-type slabs, formed from [BiO] and [SrO] layers (first subsystem), and of [CoO2] layers (second subsystem) displaying a distorted CdI2-type structure. Two main structural results are obtained. First, as a consequence of the intrinsic modulation, disordered zones, characterized by Bi vacancies, are regularly distributed in the [BiO] layers. Second, strong chemical bonds are implied between the strontium atoms of the first subsystem and the oxygen atoms of the second one.

Update: 12-May-2000

Title:
Comment on "Quasicrystal-crystal transformation in Zn-Mg-rare-earth alloys"
Authors:
Luo ZP. Tang YL. Miller DJ.
Source:
Physical Review Letters. 84(16):3730, 2000 Apr 17.
Title:
Comment on "Quasicrystal-crystal transformation in Zn-Mg-rare-earth alloys" - Abe and Tsai reply
Authors:
Abe E. Tsai AP.
Source:
Physical Review Letters. 84(16):3731, 2000 Apr 17.
Title:
Symmetry analysis of the magnetic ordering in RFe4Al8 (R = La, Ce, Y, Lu and Tb) compounds (II)
Authors:
Sikora W. Schobinger-Papamantellos P. Buschow KHJ.
Source:
Journal of Magnetism & Magnetic Materials. 213(1-2):143-156, 2000 Apr.
Abstract:
Representation analysis of the neutron diffraction data of RFe4Al8 (R = La, Ce, Y, Lu and Tb) tetragonal compounds (I4/mmm) for the wave vectors q(2) = (0 0 q(z)), and q(3) = (q(x), q(x), 0) leads to a large variety of modulated structures and enables a systematic classification of the used models in the calculation of powder neutron diffraction patterns. All observed magnetic structures are obtained by combining two representations which corresponds to a further symmetry reduction. In the data analysis additional parameter constraints are inserted by applying some simple physical arguments. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 8]
Title:
Study on one-dimensional CI phase transition with triple-well interactions
Authors:
Xu HB. Xu AG. Wang GR. Chen SG.
Source:
Chinese Physics. 9(1):42-48, 2000 Jan.
Abstract:
To study modulated structures and commensurate-incommensurate (CI) transitions, we generalize the Frenkel-Kontorova model to the Frenkel-Kontorova-Devonshire model where the interparticle interactions are the triple-well potential. By use of the so called effective potential method, numerical solutions of the eigenvalue problem are used to work out the exact phase diagrams of W, a triple-well potential. According to the winding number omega and the rotation number Omega, we analyze the periodicity of the phase diagram and find some complex but regular phase structures. These new structures result from the triple-well interatomic interactions. A series of new transition behaviors enrich the traditional understanding on the periodicity of CI transitions.
Title:
Axisymmetric elasticity problem of cubic quasicrystal
Authors:
Zhou WM. Fan TY.
Source:
Chinese Physics. 9(4):294-303, 2000 Apr.
Abstract:
A method for analyzing the elasticity problem of cubic quasicrystal is developed. The axisymmetric elasticity problem of cubic quasicrystal is reduced to a single higher-order partial differential equation by introducing a displacement function. As an example, the solutions of elastic field of cubic quasicrystal with a penny-shaped crack are obtained, and the stress intensity factor and strain energy release rate are determined.

Update: 10-May-2000

Title:
Rigid Unit Modes in disordered nepheline: a study of a displacive incommensurate phase transition
Authors:
Hayward SA. Pryde AKA. de Dombal RF. Carpenter MA. Dove MT.
Source:
Physics & Chemistry of Minerals. 27(4):285-290, 2000 Mar.
Abstract:
Calculations of the Rigid Unit Modes (RUMs) allowed in the nepheline structure are used to explain the diffuse scattering previously seen in electron diffraction experiments. The RUM calculations also show that the modulation wavelength for incommensurate nephelines is essentially determined by the framework topology. X-ray diffraction is used to measure the intensity of the diffuse scattering asa function of temperature. The diffuse intensity increases sharply at 308 K. This effect is interpreted as being due to the softening of a phonon mode, indicating a phase transition. Measurements of this phase transition below the transition temperature are made using hard mode infrared spectroscopy. [References: 25]
Title:
Ab initio based modeling of i-AlPdMn
Authors:
Quandt A. Elser V.
Source:
Physical Review B. 61(14):9336-9344, 2000 Apr 1.
Abstract:
We discuss a structure model for icosahedral AlPdMn that is based on ab initio simulation studies. The main structural features of this model have gradually been refined after studying a series of crystalline reference structures and after optimizing a suitable crystalline approximant for i-AlPdMn. We also report on the energetics of possible internal degrees of freedom for the structure model, essentially by performing a line scan of the binding energy as selected atoms are moved within the model approximant. The structure and the decoration of the optimized approximant lead to a see of empirical rules, which apply to the case of the real quasiperiodic structure as well.
Title:
Resistive and calorimetric investigations of an insulating quasicrystal i-AlPdRe
Authors:
Prejean JJ. Lasjaunias JC. Berger C. Sulpice A.
Source:
Physical Review B. 61(14):9356-9364, 2000 Apr 1.
Abstract:
We report on resistivity, magnetic susceptibility, and very low-T specific heat (C-p) of a i-AlPdRe quasicrytalline sample which, from resistivity measurements, is believed to lie on the insulating side of a metalinsulator (MI) transition. We find an electronic contribution to C-p. which possibly obeys a gamma T variation above 1 K but follows a power Ta law (a similar to 0.1-0.3) below 1 K, in agreement with early results obtained for systems crossing the MI transition. We point out the dependence of the lattice term on the method of sample preparation. Finally, from a comparative study of i-AlCuFe and i-ALPdMn systems, we show that the large nuclear hyperfine specific heat in AlPdRe, dominant below 300 mK, is of quadrupolar origin, due only to the Re nuclei.
Title:
SANS study of magnetic phase transitions in CaMn7O12
Authors:
Przenioslo R. Sosnowska I. Strunz P. Hohlwein D. Hauss T. Troyanchuk IO.
Source:
Physica B. 276:547-548, 2000 Mar.
Abstract:
The mixed valence manganite CaMn7O12 system has a modulated magnetic ordering below 90 K which gives magnetic satellite reflections at Q < 0.2 Angstrom(-1). The results of small-angle neutron scattering (SANS) measurements on polycrystalline CaMn7O12 with and without external magnetic fields are discussed. It was found that near 50 K there is a second magnetic phase transition connected with a splitting of the satellite reflection. The Q(MAX) positions, intensities and half-widths of the reflections depend on temperature. The influence of the external magnetic held on the magnetic ordering is also discussed. (C) 2000 Elsevier Science B.V, All rights reserved. [References: 4]
Title:
Neutron diffraction studies of the magnetic structures of TbRu2Si2
Authors:
Kawano S. Lebech B. Shigeoka T. Iwata N.
Source:
Physica B. 276:572-573, 2000 Mar.
Abstract:
We have confirmed by neutron diffraction that the high-temperature phase of TbRu2Si2, exhibits a magnetic one-dimensional modulation with Q = (3/13 0 0), while for the intermediate phase the modulation becomes two-dimensional with many satellites. At low-temperature the magnetic structure changes to another two-dimensional one. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 4]
Title:
Antiferromagnetic order in TbFe2Al10 and DyFe2Al10
Authors:
Reehuis M. Fehrmann B. Wolff MW. Jeitschko W. Hofmann M.
Source:
Physica B. 276:594-595, 2000 Mar.
Abstract:
The magnetic properties of the orthorhombic aluminides TbFe2Al10, DyFe2Al10 and HoFe2Al10 have been investigated by neutron powder diffraction. Below the Neel temperatures T-N = 16.5(5) and T-N = 7.5(5)K the terbium and dysprosium moments show incommensurate magnetic order with the wave vectors k = (0, 0.7977, 0) and k = (0, 0.7836, 0), respectively. TbFe2Al10 shows a square wave modulated magnetic ordering of the terbium sublattice with a moment direction parallel to the a-axis. In DyFe2Al10 the dysprosium moments rotate within the nc-plane forming a helical. magnetic structure. For HoFe2Al10 no magnetic order could be observed down to 1.5 K. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 4]
Title:
Neutron diffraction at the magnetic structure of Mn0.88Fe0.12WO4
Authors:
Ding Y. Stusser N. Reehuis M. Hofmann M. Ehlers G. Gunther D. Meissner M. Welzel S. Wilhelm M. Steiner M. Kubanek F.
Source:
Physica B. 276:596-597, 2000 Mar.
Abstract:
Neutron diffraction of a single crystal and of powder samples of composition Mn0.88Fe0.12WO4 were performed to study the magnetic structure. A commensurate antiferromagnetic (AF) structure with the wavevector k = (0.25 0.5 0.5) between 1.5 and 13.5 K and an incommensurate AF structure with k = (0.23 0.5 0.508) mere determined. A magnetic phase similar to that of FeWO4 is observed between 19 and 13.3 K. Below 13.3 K magnetic diffraction intensities indexed to the magnetic unit. cell of FeWO4 are still present, however, cannot be related to the FeWO4-type structure alone. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 3]
Title:
Magnetic structure of DyCu2 in the virgin and in the converted state
Authors:
Reif T. Doerr M. Loewenhaupt M. Rotter M. Svoboda P. Welzel S.
Source:
Physica B. 276:600-601, 2000 Mar.
Abstract:
The orthorhombic intermetallic compound DyCu2 shows below T-N = 27 K a complex magnetic-phase diagram due to RKKY interaction in combination with a strong crystal field anisotropy. In the easy a-direction the low-field antiferromagnetic structures AF1 (commensurate) and AF2 (incommensurate sinusoidal modulated) were determined with wave vectors tau = (2/3 10) and tau* = (0.6510), respectively. In an external magnetic field parallel to a with 1.6 T < mu(0)H < 2.0 T a phase F1 exists with the same tau = (2/3 10) as AF1 but with the higher harmonic 2 tau instead of 3 tau in AF1 which corresponds to a ferromagnetic modulation. In strong magnetic fields parallel to the c-direction DyCu2 undergoes a conversion of the easy axis from a- into c-direction. This conversion remains stable after switching off the field., After the conversion the magnetic structures in fields parallel to c are similar to those measured in the virgin state in fields parallel to a. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 5]
Title:
Complex magnetic structures in TbPt1-xCux compounds
Authors:
Senas A. Fernandez JR. Sal JCG. Soldevilla JG. Carvajal JR.
Source:
Physica B. 276:612-613, 2000 Mar.
Abstract:
We present neutron diffraction measurements in TbPt1-xCux for x = 0, 0.2, 0.4, 0.6 and 0.8 samples. TbPt shows a ferromagnetic non-collinear-CxFs structure. The Cu substitution modifies the conduction band inducing amplitude modulated (AM) structures. For x = 0.2 and 0.4, these AM phases coexist with the ferromagnetic ones while for x = 0.6 and 0.8 only AM structures are observed. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 6]
Title:
Magnetic ordering of TbTSb2 (T = Cu, Pd, Ag) compounds
Authors:
Szytula A. Kolenda M. Andre G. Bouree F. Oles A.
Source:
Physica B. 276:618-619, 2000 Mar.
Abstract:
RTSb2 (T = Cu, Pd, Ag) compounds crystallize in the tetragonal ZrCuSi2-type of crystal structure and are antiferromagnets with a Neel temperatures 9 K far T = Cu, 11 K for T = Pd and Ag. In TbCuSb2 the magnetic ordering is collinear described by the propagation Vector k = (1/2, 0, 0). With an increasing temperature the change of the magnetic structure to a sine modulated one is observed. The magnetic structure of the TbPdSb2 is described by the propagation vector k = (0.577, 0, 1/2). The TbAgSb2 shows a collinear magnetic ordering described by the propagation vector k = (1/2, 0, 0). (C) 2000 Elsevier Science B.V. All rights reserved. [References: 4]
Title:
Magnetic structures of TbTX compounds
Authors:
Penc B. Baran S. Hofmann M. Leciejewicz J. Szytula A.
Source:
Physica B. 276:620-621, 2000 Mar.
Abstract:
TbTX (T = Ir, Pt and X = Si, Ge, Ga) compounds crystallize in the orthorhombic TiNTiSi-type of crystal structure and art: antiferromagnets with a Neel temperature of 32 Ii for TbIrSi, 24 K for TbIrGe and 15 K for TbPtGe and the sine-modulated magnetic ordering with the propagation vector k = (0, k(y), 0) is observed. The y-component of the propagation vector is 0.4093 for T = Tr and 0.7155 for T = Pt and 0.2938 for TbIrSi. The Tb magnetic moment is parallel to the a-axis in TbIrSi, c-axis in TbIrGe and b-axis for TbPtGe. In TbPtSi a complex magnetic ordering is observed, while in TbPtGa at T = 1.5 Ii the magnetic order of ran-earth moments is collinear and described by the propagation vector k = (0, 1/2, 0). With increasing temperature above T-t = 18 K, a change into a sine-modulated structure was observed. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 4]
Title:
Neutron diffraction study of RPtGe2 (R = Dy, Ho) compounds
Authors:
Kotsanidis PA. Schafer W.
Source:
Physica B. 276:648-649, 2000 Mar.
Abstract:
Magnetic structures of ternary RPtGe2 R = Dy,Ho compounds are determined by neutron diffraction on polycrystalline samples. The compounds crystallize in space group Immm. In DyPtGe2 the magnetic structure at 4 K is sine modulated and is characterized by the wave vector k(1) = [0.268, 0, 0]. It is transformed at 8 K into a structure also sine modulated with the wave vector k(2) = [0.495, 0, 0] and changes from a longitudinal to a nearly transverse type. The ordered Dy moments are 9.9 mu(B), and 8.5 mu(B) at 4 and 8 K, respectively. In HoPtGe2 the magnetic structure at 4.2 R is a canted antiferromagnetic. The ordered moments at Ho sites 4i and 4h are 8.1 mu(B) and 4.0 mu(B), at 4.2 K and are aligned within the ab- and bc- plane, respectively. (C) 2000 Elsevier Science B.V. AII rights reserved. [References: 6]
Title:
Magnetic structures of RAuGe (R = Pr, Nd, Tb, Ho, Er) compounds
Authors:
Baran S. Hofmann M. Penc B. Slaski M. Szytula A. Zygmunt A.
Source:
Physica B. 276:656-657, 2000 Mar.
Abstract:
RAuGe compounds crystallize in hexagonal LiGeGa-type structure at room temperature. Magnetic susceptibility measurements reveal that the investigated compounds order antiferromagnetically at low temperatures except PrAuGe which is a paramagnet down to 4.2 K. In case of other compounds, neutron diffraction data showed variety of magnetic structures from commensurate ones (propagation vector k = [1/2, 0, 0]) to incommensurate ones (propagation vector k = [k(x),0,0], where 0.3 < k(x) < 0.5) - see main text for details. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 6]
Title:
Magnetism in PrPdAl: A neutron diffraction study
Authors:
Keller L. Donni A. Kitazawa H.
Source:
Physica B. 276:672-673, 2000 Mar.
Abstract:
Magnetic ordering phenomena in the ternary intermetallic compound PrPdAl were investigated by means of neutron diffraction experiments. At temperatures below T-N.1 = 4.2 Ii the magnetic ordering is characterized by a frustrated but commensurate antiferromagnetic arrangement of the Pr3+ magnetic moments in the a-b plane with an incommensurate modulation along c. Careful measurements of the magnetic structure with cold neutrons revealed a significant splitting of the magnetic Bragg peaks into three components. Therefore, a complete description of the magnetic phase of PrPdAl below T-N.1 does not consist of a single k = (1/2, 0, tau), but of the magnetic propagation vectors k(0), k_ and k(+) with tau(0) = 0.401, tau_ = 0.377 and tau(+) = 0.418, respectively. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 2]
Title:
Neutron scattering study of the incommensurate high-field phase of CuGeO3
Authors:
Ronnow HM. Enderle M. McMorrow DF. Regnault LP. Dhalenne G. Revcolevschi A. Hoser A. Vorderwisch P. Schneider H.
Source:
Physica B. 276:678-679, 2000 Mar.
Abstract:
CuGeO3 is a good realization of a spin-Peierls system. Using neutron scattering, we have investigated the transition from the dimerized spin-Peierls phase to an incommensurately modulated high-field phase. The incommensurate period has been measured for fields up to 14.5 T and is found to be in excellent accord with the theoretical predictions. The intensities of the satellite reflections provide evidence for the existence of a magnetic contribution with the same modulation period as the structural. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 8]
Title:
Magnetic structures of R2BaCoO5 (R = rare earth)
Authors:
Hernandez-Velasco J. Saez-Puche R. Hoser A. Rodriguez-Carvajal J.
Source:
Physica B. 276:726-727, 2000 Mar.
Abstract:
R2BaCoO5 oxides (R = rare earth) have been studied by means of neutron powder diffraction. They present two structural types which belong to the orthorhombic space groups Immm and Pnma. Antiferromagnetic ordering of the R3+ and Co2+ sublattices takes place below T-N < 100 K. Different noncollinear spin arrangements and complex phase transitions from incommensurate to commensurate magnetic structures have been characterized. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 6]
Title:
Neutron diffraction studies of R2Co3Si5 (R = Tb,Dy) and Tb2Ir3Si5 compounds
Authors:
Gil A. Kolenda M. Baran S. Penc B. Hofmann M. Szytula A.
Source:
Physica B. 276:742-743, 2000 Mar.
Abstract:
The R2Co3Si5 (R = Tb,Dy) compounds crystallize in a monoclinic Lu2Co3Si5-type of crystal structure while Tb2Ir3Si5 in an orthorhombic U2Co3Si5-type. The Tb2Co3Si5 has a sine modulated structure described by the propagation vector k = (0,0.0817(6),0) in the temperature range 1.6 K-T-N = 22.6 K while the Dy2Co3Si5 shows a collinear antiferromagnetic structure between 1.6 K and T-N = 21.9 K. For R = Tb the magnetic moment is parallel to the c-axis while for R = Dy it forms an angle 25.8 degrees with the c-axis. The Tb2Ir3Si5 has in the temperature range 1.5 K-T-N = 11 K, a sine modulated magnetic ordering with the propagation vector k = (0,0,0.1328(2)). The Tb magnetic moment is parallel to the b-axis. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 6]
Title:
In situ crystallization of Zirconium-based bulk metallic glasses
Authors:
Soubeyroux JL. Pelletier JM. de la Bathie RP.
Source:
Physica B. 276:905-906, 2000 Mar.
Abstract:
Zr-based bulk metallic glasses were investigated by DSC and in-situ neutron diffraction. DSC and neutron studies were performed at different heating rates and the evolution of the characteristic temperatures, glass transition were determined as a function of dT/dt. The first phase appearing at crystallisation can be correlated to a quasicrystalline phase. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 6]
Title:
Breakdown of metallic conductivity in quasicrystals
Authors:
Berger C. Delahaye J. Grenet T. Schaub T. Fourcaudot G. Brison JP. Prejean JJ.
Source:
Physica B. 280(1-4):262-263, 2000 May.
Abstract:
In the icosahedral phases i-AlCuFe, i-AlPdMn and i-AlPdRe, the electrical conductivity is in the same range as for doped semiconductors. Strong similarities are observed between the direct and tunneling conductivity for the i-AlPdRe phase and for disordered systems on both sides of the metal-insulator (MI) transition. (C) 2000 Published by Elsevier Science B.V. All rights reserved. [References: 7]
Title:
Kikuchi bands in quasicrystals and their approximants
Authors:
Gibbons PC. Kelton KF. Ranganathan S. Daulton TL.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 80(4):843-852, 2000 Apr.
Abstract:
Kikuchi bands observed in transmission electron microscopy of crystalline approximants to quasicrystals differ from those observed from the quasicrystals only in small details. They reveal the relationship between the two phases and in the past have provided some information about the small distortions of atomic clusters that occur on going from one phase to the other.
Title:
Complete photonic bandgaps in 12-fold symmetric quasicrystals
Authors:
Zoorob ME. Charlton MDB. Parker GJ. Baumberg JJ. Netti MC.
Source:
Nature. 404(6779):740-743, 2000 Apr 13.
Abstract:
Photonic crystals are attracting current interest for a variety of reasons, such as their ability to inhibit the spontaneous emission of light(1,2). This and related properties arise from the formation of photonic bandgaps, whereby multiple scattering of photons by lattices of periodically varying refractive indices acts to prevent the propagation of electromagnetic waves having certain wavelengths. One route to forming photonic crystals is to etch two-dimensional periodic lattices of vertical air holes into dielectric slab waveguides(3-7). Such structures can show complete photonic bandgaps(8-10), but only for large-diameter air holes in materials of high refractive index (such as gallium arsenide, n = 3.69), which unfortunately leads to significantly reduced optical transmission when combined with optical fibres of low refractive index. It has been suggested that quasicrystalline (rather than periodic) lattices can also possess photonic bandgaps(11-14). Here we demonstrate this concept experimentally and show that it enables complete photonic bandgaps-non-directional and for any polarization-to be realized with small air holes in silicon nitride (n = 2.02), and even glass (n = 1.45). These properties make photonic quasicrystals promising for application in a range of optical devices(14-18).
Title:
Stability and phase transformation of icosahedral phase in a 41.5Zr41.5Ti17Ni alloy
Authors:
Yi S. Kim DH.
Source:
Journal of Materials Research. 15(4):892-897, 2000 Apr.
Abstract:
Phase stability and transformations of the icosahedral phase (I-phase) in a 41.5Zr41.5Ti17Ni alloy were investigated using melt-spun ribbons and are-melted bulk samples. A perfect I-phase can be formed directly from liquid through the melt-spinning technique. The I-phase formed in the ribbon is thermodynamically stable and transforms to W-phase, a 1/1 rational approximant above 565 degrees C. Formation of the perfect I-phase during annealing treatment of the are-melted sample is very sluggish. Various types of approximants exist as intermediate states for the transformation of crystalline phases to a perfect I-phase. [References: 16]
Title:
A unique distortion in K1/3Ba2/3AgTe2: X-ray diffraction determination and electronic band structure analysis of its incommensurately modulated structure
Authors:
Gourdon O. Hanko J. Boucher F. Petricek V. Whangbo MH. Kanatzidis MG. Evain M.
Source:
Inorganic Chemistry. 39(7):1398-1409, 2000 Apr 3.
Abstract:
The incommensurately modulated structure of a square Te-net, namely that of K1/3Ba2/3AgTe2, is determined from single-crystal X-ray diffraction data within a (3+1)D higher dimension formalism, The phase is shown-to crystallize in the monoclinic symmetry, P2(1)(alpha 0 gamma) superspace group with the following lattice parameters; a = 4.6441(10) Angstrom, b = 4.6292(22) Angstrom, c = 23.765(9) Angstrom and beta = 101.28(2)degrees with q = 0.3248(6)a* - 0.071(8)c*, that is, in a symmetry different from that reported for the average structure (tetragonal) or that assumed from electron diffraction measurements (orthorhombic). After the Introduction of a crenel function for the Te displacive description, the refinement converged to a residual factor R = 0.033 for 2583 observed reflections and 115 parameters (R = 0.024 and 0.101 for 1925 main reflections and 658 first-order satellites, respectively). The [Ag-2-Te-2] and the Ba/K layers are found to be only weakly modulated. The modulation of the square Te-net is, however, both substantial and unique. Namely, it results in two different units: a "V"-shaped Te-3 trimer and a "W"-shaped Te-5 pentamer. To examine both unit types, which are segregated in domains that aperiodically alternate within the Te layers, first principles electronic band structure calculations were carried out for three model commensurate structures using the tight-binding linear-muffin-tin-orbital method (LMTO). The calculations show that the distorted structures of V-pattern (model 2) and W-pattern (model 3) are more stable than the average structure (model 1) and that the V-pattern distortion provides a slightly larger stabilization than does the W-pattern distortion, The Fermi surface calculated for the average structure shows nesting vectors that are consistent with the occurrence of the V- and W-pattem distortions in the Te layers. However, these vectors do not predict the observed modulation vector of the incommensurately distorted structure, because the stabilization energy associated with the distortion is not mainly dominated by the energy lowering of the occupied band levels near the Fermi level.

Update: 1-May-2000

Title:
Plastic deformation of icosahedral Zn-Mg-Dy single quasicrystals
Authors:
Heggen M. Feuerbacher M. Schall P. Klein H. Fisher IR. Canfield PC. Urban K.
Source:
Philosophical Magazine Letters. 80(3):129-136, 2000 Mar.
Abstract:
Plastic deformation experiments have been performed on Zn-Mg-Dy icosahedral single quasicrystals at temperatures between 490 and 530 degrees C and at strain rates of 10(-5) and 10(-6) s(-1). The stress-strain curves show strong yielding followed by a steady-state regime with a constant flow stress level up to strains of about 8%. Thermodynamic activation parameters of the deformation process were determined and are discussed in comparison with those found for icosahedral Al-Pd-Mn. Microstructural investigations by transmission electron microscopy on deformed samples were performed and indicate a deformation mechanism mediated by dislocations.
Title:
A new highly ordered Al-Ni-Ru decagonal quasicrystal with 1.6 nm periodicity
Authors:
Sun W. Hiraga K.
Source:
Philosophical Magazine Letters. 80(3):157-164, 2000 Mar.
Abstract:
A new decagonal quasicrystal (the D phase) with a period of about 1.6 nm was found to Form in conventionally solidified and heat-treated Al75Ni15Ru10 alloys. The electron diffraction patterns of the Al-Ni-Ru D phase exhibit a large number of quite sharp diffraction spots located at precise decagonal symmetry positions, indicating a highly ordered decagonal quasicrystal with a long-range quasiperiodic correlation. The D phase is formed with a composition close to Al74Ni15Ru11, as determined by energy-dispersive X-ray analysis. By means of high-resolution electron microscopy, the structural features of the Al-Ni-Ru D phase, which are obviously different from that of the AI-Pd D phase (a typical decagonal quasicrystal with 1.6 nm periodicity reported previously), have been revealed.
Title:
Studies on Cs-133 NMR spectra and spin-lattice relaxation times in incommensurate Cs2HgCl4
Authors:
Suzuki K. Ishimaru S. Ikeda R.
Source:
Journal of the Physical Society of Japan. 69(3):729-733, 2000 Mar.
Abstract:
Cs-133 NMR spectra and the spin-lattice relaxation times, T-1, in Cs2HgCl4 crystals were measured in the ranges of 160-361 K and 160-371 K, respectively. The central lines of the spectra show small splittings characteristic of the incommensurate (IC) phase. The splitting increases with decreasing temperature. The critical exponent zeta of T-1 at the phase transition from normal (N) to IC phase was determined to be 0.615 +/- 0.025 in the high-temperature side of the transition, which is in good agreement with the three-dimensional XY model predicting the one-dimensional modulation wave in the IC phase. The frequency dependence of T-1 in the IC phase can be explained by the fluctuations of phason with a small gap, 0-5 MHz, and amplitudon.
Title:
1-D and 2-D NMR of broad-line solids: an application to quasicrystals
Authors:
Dolinsek J. Apih T. Klanjsek M. Plyushch O.
Source:
Applied Magnetic Resonance. 18(1):3-12, 2000.
Abstract:
Nuclear magnetic resonance (NMR) techniques for measuring one-dimensional absorption spectra and too-dimensional exchange spectra of solids with extremely inhomogeneously broadened lines are discussed. Among various "broad-line" solids, quasicrystals represent alloys of metallic elements, the structures of which include "forbidden" symmetry elements. NMR absorption lines of quasicrystals exhibit a strong electric-quadrupole-induced inhomogeneous broadening that originates from the lack of translational periodicity of the otherwise perfectly long-range-ordered quasiperiodic lattice. Recording an NMR spectrum of a quasicrystalline sample requires a magnetic field-sweep technique. The two-dimensional exchange experiment on quasicrystals can be performed on selectively excited portions of the NMR spectrum only. Due to the off-resonance effects in a selective excitation. the use of a simple three-pulse stimulated-echo exchange sequence is preferred. The Al-27 spectra of the Al-Pd-Mn and Al-Pd-Re families show interesting features like temperature-dependent frequency shifts and exchange effects due to atomic motion.
Title:
Stability of the F2-(Al-Pd-Mn) phase
Authors:
Letoublon A. Ishimasa T. de Boissieu M. Boudard M. Hennion B. Mori M.
Source:
Philosophical Magazine Letters. 80(4):205-213, 2000 Apr.
Abstract:
The stability of the F2-(Al-Pd-Mn) phase has been studied by in-situ neutron diffraction on a single quasicrystal with composition Al69.8Pd21.4Mn8.8 We find that the F2 phase is not stable and corresponds to a transient state in the process of the transformation of the icosahedral phase to the F2(M) phase. The icosahedral-to-F2(M) phase transition occurs at around 715 degrees C. In the F2 phase a large amount of diffuse scattering is located close to the icosahedral Bragg reflection in place of the S-1 superstructure reflections characteristic of the F2(M) phase.
Title:
Formation of icosahedral quasicrystals in an annealed Zr65Al7.5Ni10Cu12.5Ag5 metallic glass
Authors:
Chen MW. Inoue A. Zhang T. Sakai A. Sakurai T.
Source:
Philosophical Magazine Letters. 80(4):263-269, 2000 Apr.
Abstract:
The formation and thermal stability of an icosahedral quasicrystalline phase in an annealed Zr65Al7.5Ni10Cu12.5Ag5 metallic glass have been investigated by Xray diffraction and transmission electron microscopy analyses. It was found that the quasicrystalline phase can precipitate from the glassy state and the supercooled liquid of the alloy over a wide range of annealing temperatures. After optimizing the heat-treatment conditions, the volume fraction of the quasicrystalline phase in the alloy can reach as high as about 80%. Investigation of the thermal stability of the quasicrystalline phase demonstrates that it is very stable when the annealing temperature is below the glass transformation temperature T-g of the alloy.
Title:
Long-period incommensurate superstructures in Cu-Au alloys: Relation with short-period ordering
Authors:
Velikokhatnyi OI. Eremeev SV. Naumov II. Potekaev AI.
Source:
Journal of Experimental & Theoretical Physics. 90(3):479-487, 2000.
Abstract:
The nature of the stability of incommensurate long-period structures in alloys of the system Cu-Au is investigated on the basis of first-principles calculations of the electronic structure. It is shown that many structural properties of such formations can be explained only if the latter are treated as superstructures with respect to ordinary superstructures (L1(2) or L1(0)): the electron spectrum of the superstructure and not that of the initial disordered alloy must serve as the initial spectrum. The observed dependence of the long period N on the degree eta of the "short" long-range order is explained. The reasons why two-dimensional long-period superstructures from in the alloy Au3Cu are found. Arguments supporting the fact that among quasicrystalline substances long-period superstructures fall between incommensurate systems and quasicrystals are presented. (C) 2000 MAIK "Nauka/Interperiodica".
Title:
ICQ7 discussed behaviour of quasicrystalline intermetallics
Authors:
Mandal RK.
Source:
Current Science. 78(6):663-664, 2000 Mar 25.

Update: 17-Apr-2000

Title:
Thermal conductivity of one-dimensional Fibonacci quasicrystals
Authors:
Macia E.
Source:
Physical Review B. 61(10):6645-6653, 2000 Mar 1.
Abstract:
We consider a general Fibonacci quasicrystal (FQC) in which both the masses and the elastic constants are aperiodically arranged. Making use of a suitable decimation scheme, inspired by real-space renormalization-group concepts, we obtain closed analytical expressions for the global transfer matrix and transmission coefficient for several resonant critical normal modes. The fractal structure of the frequency spectrum significantly influences both the cumulative contribution of the different normal modes to the thermal transport and the dependence of the thermal conductivity with the temperature over a wide temperature range. The role of resonant effects in the heat transport through the FQC is numerically and analytically discussed.
Title:
Ultrasonic measurements on fci Zn-Mg-Y single crystals
Authors:
Sterzel R. Hinkel C. Haas A. Langsdorf A. Bruls G. Assmus W.
Source:
Europhysics Letters. 49(6):742-747, 2000 Mar.
Abstract:
Ultrasonic measurements were performed on a fci Zn-Mg-Y quasicrystal and on the related parent compound Zn2Mg. Absolute values of both the longitudinal and the transverse sound velocities as well as their temperature dependence were determined, The temperature dependence of the quasicrystal sound velocity in the millikelvin temperature range is very similar to the logarithmic behaviour observed for amorphous materials.
Title:
Effect of sputtering gas on the surface composition of an Al-Pd-Mn quasicrystal
Authors:
Jenks CJ. Burnett JW. Delaney DW. Lograsso TA. Thiel PA.
Source:
Applied Surface Science. 157(1-2):23-28, 2000 Mar.
Abstract:
We demonstrate the effects of different inert sputtering gases on the surface composition of icosahedral (i-) Al-Pd-Mn. The sputtering gases used include He, Ne, Ar, Xe, and Kr. We demonstrate that the steady-state composition is independent of the inert gas chosen. This steady-state composition falls outside of the quasicrystalline region of the Al-Pd-Mn phase diagram. However, the fluence (ions/cm(2)) to achieve steady-state depends on the inert gas. Helium requires a much higher fluence than the other gases. Because of this, He can be used to clean the surface, if the time (fluence) for sputtering is kept to a minimum, without causing the large compositional shift induced with a relatively small fluence by the most common sputtering gas, Ar. (C) 2000 Elsevier Science B.V. All rights reserved.

Update: 10-Apr-2000

Title:
Structural study of the commensurate-incommensurate low-temperature phase transition of Pb on Si (111)
Authors:
Kumpf C. Bunk O. Zeysing JH. Nielsen MM. Nielsen M. Johnson RL. Feidenhans'l R.
Source:
Surface Science. 448(2-3):L213-L219, 2000 Mar 10.
Abstract:
A close-packed lead adsorbate layer on Si(111) forms an incommensurate hexagonal phase which exhibits a reversible phase transition to a commensurate Si(111)-((3)(2)(-1)(1))-Pb structure upon cooling below 230 K. Surface X-ray diffraction measurements with synchrotron radiation reveal that the structure consists of a minimally distorted hexagonal lead overlayer with a coverage of nominally 1.2 ML on top of an essentially undisturbed silicon substrate. The interatomic distances indicate that all dangling bonds of the substrate are saturated. The stability of the commensurate phase can be explained by the presence of bonds with covalent character between the adsorbate atoms in on-top sites and the substrate atoms and within the otherwise metallic overlayer, (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Evidence of latent heat in the Rb2ZnCl4 commensurate-incommensurate phase transition
Authors:
Martin-Olalla JM. del Cerro J. Ramos S.
Source:
Journal of Physics-Condensed Matter. 12(8):1715-1722, 2000 Feb 28.
Abstract:
The commensurate-incommensurate phase transition of a Rb2ZnCl4 crystal was studied using a conduction calorimeter. By identifying the contribution of the specific heat to the transition enthalpy it was possible to show, for the first time for a compound of this type, transition latent heat. This was estimated to be Q = 2.3 J mol(-1). The result was compared with theoretical predictions for a domain wall model having repulsive-attractive interaction; satisfactory results were obtained for the first time. The same analysis was applied to the normal-incommensurate phase transition and no latent heat was observed, as expected.
Title:
High pressure Brillouin scattering and energy dispersive X-ray diffraction study of (NH4)(2)ZnCl4
Authors:
Burris JL. Tereshchenko L. Kabos P. Hochheimer HD. Luspin Y. Evenson CR. Dorhout PK.
Source:
Journal of Physics & Chemistry of Solids. 61(5):719-726, 2000 May.
Abstract:
We have performed a high pressure Brillouin scattering and energy dispersive X-ray diffraction study on (NH4)(2)ZnCl4 in the temperature range from room temperature to 150 degrees C. At ambient pressure three phase transitions occur in this temperature range. Of special interest are the phase transitions at 91 degrees C and 133 degrees C because an incommensurate phase has been detected in this temperature range. We compare the results of our high pressure Brillouin scattering study with the ones obtained from other studies of the elastic constants. Our results for the anomaly in C-33 observed at the commensurate-incommensurate transition at 133 degrees C at ambient pressure contradict the results of the other Brillouin scattering studies but agree well with the results of an ultrasonic study. This result seems to indicate that critical fluctuations of the order parameter at the phase transition are reduced by pressure. Values of the calculated adiabatic bulk modulus, B-S, and the experimentally determined isothermal bulk modulus, B-T, for various materials of the A(2)BX(4) family, are compiled and discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.
Title:
Quasicrystalline gold interface with a hypo-friction property
Authors:
Lancon F. Penisson JM. Dahmen U.
Source:
Europhysics Letters. 49(5):603-609, 2000 Mar.
Abstract:
We have studied a non-symmetric and non-periodic grain boundary in gold. An atomic model is presented and the atomic positions are found to be in agreement with the electron microscopy images. Using the diffraction pattern, we show that the structure is quasicrystalline and related to the irrational number root 2. A complete hyperspace periodic description of the interface is given. We use this theoretical view to predict that in the case of an infinite interface of this type, two crystals should glide freely along the incommensurate x-direction whereas they should be blocked along the commensurate z-direction and be adhesive along the third y-direction perpendicular to the boundary. A numerical test confirms this property.
Title:
Low-frequency dynamics in molecular incommensurate composite: Specific heat of nonadecane/urea inclusion compound
Authors:
Etrillard J. Lasjaunias JC. Toudic B. Guillaume F. Breczewski T.
Source:
Europhysics Letters. 49(5):610-616, 2000 Mar.
Abstract:
We report the first very low-temperature specific-heat data of the incommensurate n-nonadecane/urea inclusion compound. In addition to the contribution due to normal acoustic phonons, the results show a linear temperature? dependence of the specific heat below 1.5 K, assigned to the dynamical disorder of the guest molecules. The excess heat capacity around 4.5 K reveals the low-frequency contribution of nondispersive modes. In contrast to the case of modulated incommensurate compounds, no pinned sliding?; mode, phasan-like mode, could be detected.
Title:
Incommensurately modulated phase of Rb2CoBr4 at 295 and 200 K
Authors:
Friese K. Madariaga G. Breczewski T.
Source:
Acta Crystallographica - Section B, Structural Science. 56(Part 1):17-21, 2000 Feb.
Abstract:
The crystal structure of Rb2CoBr4 at 295 and 200 K has been determined. At these temperatures Rb2CoBr4 exhibits an incommensurately modulated structure with wavevector q = (1/3 + delta)a*. At room temperature only the average structure was refined. Lattice parameters are a = 9.732 (3), b = 13.328 (4), c = 7.654 (3) Angstrom, space group Pnam. The R(F) value was 0.0414 for 286 observed reflections (0.0778 for all 477 reflections). At 200 K the lattice parameters are a 9.691 (4), b = 13.278(5), c = 7.630 (6) A, superspace group P:Pnam:(1) over bar ss. Main reflections and satellite reflections of first order were measured. The refinement converged at R(F) = 0.052 for 309 observed reflections (255 main reflections and 54 satellites) and 0.2971 for all reflections (1849; 695 main reflections and 1154 satellites). Amplitudes and phases of the modulation function as well as bond distances show close relationships to those observed in the incommensurately modulated phase of Rb2ZnBr4.

Update: 1-Apr-2000

Title:
Ag-109 NMR investigation of atomic motion in the incommensurate and paraelectric phases of proustite (Ag3AsS3)
Authors:
Subramanian RK. Muntean L. Norcross JA. Ailion DC.
Source:
Physical Review B. 61(2):996-1002, 2000 Jan 1.
Abstract:
Ag-109 NMR line shape, T-1, Hahn spin echo, and Carr-Purcell-Meiboom-Gill (CPMG) spin-echo measurements were performed in proustite (Ag3AsS3) between 420 and 47 K in order to understand the role of atomic motions in phase transitions in a system containing an incommensurate phase. These measurements indicate a definite change in the motional characteristics of Ag ions near 240 K. Above 240 K, an Ag+ ion executes fast jump motions between its six inequivalent chemically shifted sites. However, below 240 K, these motions are too slow to affect the line shapes. The NMR line shape results are consistent with the existence of a 3q incommensurate phase between 60 and 50 K. Between 180 and 55 K, Hahn and CPMG spin-echo decay measurements suggest that slow motions exist. These motions are attributed (1) in the paraelectric phase (above 60 K) to slow jumping of an Ag+ ion between its inequivalent sites with a jump time of the order of the Hahn spin-echo time and (2) in the incommensurate phase (50-60 K) to ultraslow motion of the incommensurate modulation wave. This paper constitutes a report of the effect on the Hahn spin-echo decay due to atoms jumping between sites characterized by different chemical shifts.
Title:
Unique 1-q and 3-q incommensurate phases in proustite: As-75 NQR line-shape and spin-lattice relaxation study
Authors:
Apih T. Mikac U. Dolinsek J. Seliger J. Blinc R.
Source:
Physical Review B. 61(2):1003-1013, 2000 Jan 1.
Abstract:
As-75 NQR spectra and spin-lattice relaxation time T-1 have been measured between room temperature and 4.2 K in a proustite (Ag3AsS3) single crystal. In agreement with x-ray scattering data we find that the phase between T-l = 60 K and T-L = 49 K is triple-q (3-q) incommensurably modulated. Our results show unambiguously that we deal here with three independent noncoplanar incommensurate modulation wave vectors. Such a phase seems to be unique in a sense that other phases with three incommensurate modulation waves known so far (e.g., in charge-density-wave systems) are either a superposition of differently oriented 1-q modulated domains, or the three modulation waves are confined to a plane and are thus not independent. In addition the 75As NQR line shape suggests that the phase just below T-l is a single-q (1-q) modulated stripe phase. This is confirmed by the variation of TI over the NQR line in the 1-q and 3-q phases. On further cooling further into the incommensurate phase the volume fraction of the 3-q phase gradually increases and the crystal becomes fully 3-q modulated about 2 K below T-1. The nonclassical critical exponents for the amplitude of the order parameter were determined to be beta(1) = 0.3 +/- 0.02 in the 1-q stripe phase and beta(3) = 0.4 +/- 0.02 in the 3-q phase. On approaching the lock-in transition temperature in the low-temperature part of the 3-q incommensurate phase the phases of the modulation waves become nonlinear functions of the corresponding spatial coordinates, resulting in sharp peaks superimposed on the broad bell-shape frequency distribution. A comparison between experimental and theoretical line shapes allowed for a quantitative determination of the temperature dependence of the soliton density.
Title:
Magnetism and charge ordering in Pr0.5CaxSr0.5-xMnO3 (x=0.09 and 0.5)
Authors:
Jirak Z. Damay F. Hervieu M. Martin C. Raveau B. Andre G. Bouree F.
Source:
Physical Review B. 61(2):1181-1188, 2000 Jan 1.
Abstract:
The structural and magnetic transitions in two Mn3+/Mn4+(1:1) systems have been investigated using neutron diffraction and election microscopy. In Pr0.5Ca0.5MnO3, the charge and orbital order develops in the paramagnetic phase of Pnma symmetry below T-co = 250 K through a sequence of incommensurate configurations, The ordering process is accomplished at T-N = 170 K where the charge-exchange-(CE) type antifer- romagnetism sets in. Despite the superstructure, the tilt pattern of Pnma type is preserved down to the lowest temperatures. The second compound, Pr0.5Ca0.09Sr0.41MnO3, is ferromagnetic below T-C = 240 K. The charge ordering occurs at T-N = 180 K and is accompanied by the onset of the CE antiferromagnetism. The transition is associated with a change of the tilt pattern from I4/mcm to Imma type. The low-temperature phase is commensurate both in the structural and magnetic sense. It is argued that the main energy gain of the charge ordering in Mn3+/Mn4+ (1:1) perovskites results from electron-exchange interactions favored by the e(g) orbital polarization. The onset of the incommensurate configurations can be understood supposing the existence of a soft lattice mode in which the electron transfer (charge-density wave) is correlated with dynamics of e(g) orbitals.
Title:
X-ray-scattering study of copper magnetism in nonsuperconducting PrBa2Cu3O6.92
Authors:
Hill JP. McMorrow DF. Boothroyd AT. Stunault A. Vettier C. Berman LE. von Zimmermann M. Wolf T.
Source:
Physical Review B. 61(2):1251-1255, 2000 Jan 1.
Abstract:
X-ray magnetic scattering from ordered Cu spins has been observed in a high-T-c compound. The measurements were made on the anomalous cuprate PrBa2Cu3O6.92 with x-ray photon energies tuned in the vicinity of the Cu K edge. The high wave-vector resolution enabled us to observe an incommensurate double-Q Cu spin structure below T-Pr = 19 K that forms as a result of coupling between the magnetically ordered Cu and Pr sublattices. Above T-Pr, the Cu ordering is commensurate, ruling out static spin-charge stripe order as an explanation for the absence of superconductivity in this material.
Title:
Microstructure and physical properties of Bi1.9+xSr1.7-xLa0.4CuO6 system
Authors:
Xu GJ. Mao ZQ. Yan HJ. Liu DP. He J. Zhang YH.
Source:
Journal of Superconductivity. 13(1):69-72, 2000 Feb.
Abstract:
The crystal microstructure, superconductivity. and normal stale transport properties of Bi1.9+xSr1.7-xLa0.4CuO6+delta(0 less than or equal to x less than or equal to 0.4) system were investigated by means of electron diffraction (ED), resistivity, and TEP, Analyses of the experimental results indicate that with the increase of Bi content, the incommensurate modulation wavelength decreases and the distortion of CuO6 octahedron enhances. Increasing Bi content decreases the carrier concentration rapidly, and induces an MI transition. The destruction of superconductivity mainly derives from two aspects: the enhancement of structural distortion due to the introduction of more Bi and the variation of the carrier concentration of the system.
Title:
A modal of twin domains in YBa2(Cu1-xCox)(3)O-y
Authors:
Chen WM. Yao XX. Guo YC. Liu HK. Dou SX.
Source:
Journal of Superconductivity. 13(1):129-136, 2000 Feb.
Abstract:
The existence of twin domains in YBa2(Cu1-xCox)(3)O-y samples was confirmed by many experiments. However, the physical picture of the twin domains has not been reported up to now. By analyzing oxygen content, Cu and Co valences, and Co coordination in those samples: we propose a domain model, which consists of two pairs of parallel zigzag Co-O chains surrounding orthorhombic cells, one along (110) direction and the other along (1(1) over bar 0) direction. The zigzag Co-O chains are the twin walls, with neighboring walls perpendicular and the opposite ones parallel. The distance between parallel walls (i.e., zigzag Co-O chains) depends upon Co concentration of sample. The twin domain model predicts the geometry, size, and absence of systematic symmetry of the domains. The model also predicts the modulation periodicity of electron diffraction patterns, which depends on Co concentration. All the predictions by the model agree well with the experimental results reported in literatures. Furthermore, the model indicates the possible existence of two domains, which have incommensurable modulation periodicity.

Update: 27-Mar-2000

Title:
NQR study of dynamics in incommensurate phases
Authors:
Sastry VSS. Venu K. Maheswari SU. Subramanian RK.
Source:
Zeitschrift fur Naturforschung Section A-A Journal of Physical Sciences. 55(1-2):281-290, 2000 Jan-Feb.
Abstract:
Dynamic processes in solids exhibiting structurally incommensurate phases are briefly reviewed, and the application of NMR and NQR is discussed. The unique utility of these methods, - arising due to, on one hand, the microscopic resonant nature of the probe used and, on the other, the presence of periodic, though incommensurable, structure -, is brought out by presenting recent results in a prototype system (Rb2ZnCl4) in the presence of randomly quenched disorder. In particular, the interesting new methodology of measuring, by analysing NQR spin echo modulation, ultra-slow diffusion like collective motions of ensembles of atoms in the presence of pinning effects due to disorder is illustrated with new results.
Title:
Thiourea and thiourea inclusion compounds. A N-14 NQR investigation
Authors:
Guibe L. Peneau A. Gourdji M. Panich A.
Source:
Zeitschrift fur Naturforschung Section A-A Journal of Physical Sciences. 55(1-2):331-334, 2000 Jan-Feb.
Abstract:
A reinvestigation of the nitrogen-14 NQR in thiourea has permitted to record, apparently for the first time, the resonances above 169 K. The first order and second order of the transitions at 169 K and 202 K, respectively, appear clearly from the temperature dependence of the resonance frequencies; the modulated structure, incommensurate or commensurate, is also seen on the N-14 NQR spectrum. This study is the first step of a new investigation of thiourea and its inclusion compounds. [References: 7]
Title:
Specific heat and nuclear quadrupole resonance study of thiourea-hexachloroethane inclusion compound
Authors:
Chekhova GN. Goren SD. Krieger JH. Linsky D. Lusternik V. Panich AM. Semenov AR. Voronel A.
Source:
Zeitschrift fur Naturforschung Section A-A Journal of Physical Sciences. 55(1-2):335-338, 2000 Jan-Feb.
Abstract:
Specific heat and Cl-35 nuclear quadrupole resonance (NQR) measurements of the channel thiourea-hexachloroethane inclusion compound are presented. Experimental NQR data confirm the results of atom-atom potential calculations that the guest sublattice comprises two types of nearly commensurate finite molecular chains, having different structure and separated by domain walls. Specific heat measurements show phase transition near 96 K. [References: 7]
Title:
Theoretical aspects of thermal diffuse scattering from quasicrystals
Authors:
Wang RH. Hu CZ. Lei JL. Ding DH.
Source:
Physical Review B. 61(9):5843-5845, 2000 Mar 1.
Abstract:
General formulas for thermal diffuse scattering from quasicrystals are modified so that they are appropriate for decorated quasicrystals as well as Simple quasicrystals. The modified formulas appropriate for the case of quenched phasons can be automatically evolved into those appropriate for the case of thermal phasons.
Title:
Neutron-diffraction study of the metamagnetic phases in HoNi2B2C
Authors:
Campbell AJ. Paul DM. McIntyre GJ.
Source:
Physical Review B. 61(9):5872-5875, 2000 Mar 1.
Abstract:
Neutron diffraction has been used to determine the magnetic phase diagram of HoNi2B2C, in the plane of temperature and magnetic field up to 4.6 T, for two different crystallographic orientations relative to the applied magnetic field. For both orientations two first-order metamagnetic transitions are observed below 5.5 K as the applied field is increased. In both cases the first transition is to a state in which the magnetic structure is modulated along the c axis with wave vector delta=[0,0,0.667]. With the field applied parallel to the [110] direction the second transition is to a saturated paramagnetic state in which the spins are aligned ferromagnetically by the applied magnetic field. With the field parallel to the [0 (1) over bar 0] direction, the second transition is into a state in which the magnetic structure is modulated along the b axis with wave vector delta= [0,0.610,0], in disagreement with a simplified theoretical model.
Title:
Anomalous electronic conductance in quasicrystals
Authors:
Roche S. Moulopoulos K.
Source:
Physical Review B. 61(9):6048-6056, 2000 Mar 1.
Abstract:
Subtle quantum interference effects in one-dimensional quasicrystals are reported. Quite opposite to their metallic counterparts, quasiperiodic systems are shown to exhibit interesting variations of their conducting properties upon disruption of their long-range order. A sudden phason change in the structure leads to a series of transitions that proceed from extremely simple and regular to highly complex self-similar resistive patterns.
Title:
More exact results on a binary alloy with next nearest neighbor competing interactions
Authors:
Paraskevaidis CE. Haroni AA.
Source:
Physica Status Solidi B-Basic Research. 217(2):963-973, 2000 Feb.
Abstract:
We study an Ising-type binary alloy with competing interactions between first and second neighbors on a Bethe lattice, Successive layers of the Bethe lattice are occupied in an alternating fashion by magnetic moments of type (A) and (B). We impose a restriction on the system by allowing only interlayer interactions between second neighbors. We approach the problem by setting up an iteration process for the partial partition functions. This correlates the partition function for a Bethe lattice with N layers to the partial partition functions of:the Bethe lattice with N - 1 layers. The presence of competing interactions between first and second neighbors imposes frustration on these systems, which, in turn, enriches the resulting phase diagrams. We study the behavior of the system for varying degrees of competition:between first and second neighbors. Besides the ferromagnetic (F) and paramagnetic (PM) phases, a-modulated ferromagnetic phase (F') with periodicity two and an antiferromagnetic phase with periodicity four (AF-2) are present, The modulated phase (M) is present only for cases of very strong competition between first and second neighbor interactions. As the competition is reduced, the modulated phase (M) disappears, For weak competition, two new phases with periodicity four appear:Tn the first one, labeled (+++-), magnetic moments of one species align ferromagnetically, while those of the other species align antiferromagnetically. in the second phase, (++++), both species align in a ferromagnetic fashion.
Title:
Magnetic phase diagram of PrCo2Si2 with long period commensurate structure
Authors:
Kawae T. Mito M. Hitaka M. Ichikawa F. Shigeoka T. Iwata N. Takeda K.
Source:
Journal of the Physical Society of Japan. 69(2):586-591, 2000 Feb.
Abstract:
The electrical resistivity of PrCo2Si2 with a long-period commensurate spin structure has been measured in a magnetic field up to 9 Tesla, together with the heat capacity up to 5 Tesla. The resistivity changes drastically with step-like jumps at the successive transition points accompanying the change of the antiferromagnetic propagation vectors. From the resistivity measurements, four distinct phases are confirmed below the antiferromagnetic transition temperature. A temperature-magnetic field phase diagram of PrCo2Si2 is presented.
Title:
Structure determination of two new incommensurate compounds, Ba1+x[(CuxRh1-x)O-3] with x=0.1605 and x=0.1695, using a general method based on the superspace group approach
Authors:
Zakhour-Nakhl M. Claridge JB. Darriet J. Weill F. zur Loye HC. Perez-Mato JM.
Source:
Journal of the American Chemical Society. 122(8):1618-1623, 2000 Mar 1.
Abstract:
The single-crystal structures of two incommensurate compounds, Ba1+x [(CuxRh1-x)O-3] With x = 0.1605 and x = 0.1695, were solved by a general method using the superspace group approach. saw-tooth function was used to model both the occupational and displacive modulations. This approach requires very few refineable parameters and leads to low residuals, R = 0.0370 and R = 0.0330 for x = 0.1605 and x 0.1695, respectively. The idealized structures of these two compounds consist of [(CulambdaRh1-x)O-3](infinity) chains containing groups of five face-shared (RhO6) octahedra separated by (CuO6) trigonal prisms. These chains in turn are separated from each other by [Ba](infinity) chains. The idealized composition of both phases is Ba7CuRh5O18. Their modulated structures. described in the text, deviate from the ideal composition and structure. The approach used for the structure determinations of these compounds is completely general and can be applied to other modulated composite structures of this series.
Title:
Incommensurately modulated cadmium apatites
Authors:
Henning PA. Moustiakimov M. Lidin S.
Source:
Journal of Solid State Chemistry. 150(1):154-158, 2000 Feb 15.
Abstract:
Two cadmium apatites, Cd-5(PO4)(3)Br and Cd-5(VO4)(3)I, earlier reported to be halogenide deficient, mere prime suspects of being modulated, In this study, incommensurate ordering was found in satellites occurring in planes perpendicular to c*, The structure of Cd,(PO,),Br was refined from single-crystal X-ray diffraction data in the four-dimensional super space group R:P (3) over bar:(00 gamma): a = 16.932(2) Angstrom,= 6.451(1) Angstrom, Z = 6, R = 0.043. The modulation of the structure is due to a misfit between the large halogenide ions and the surrounding rigid Ca-PO4 substructure. From the refined model of the Cd,(PO,),Br structure a "chain-packing" model was confirmed with a Br-Br distance of 3.466 Angstrom. (C) 2000 Academic Press.
Title:
Gorsky-Bragg-Williams theory of phase transitions in the approximants of icosahedral quasicrystals
Authors:
Chizhikov VA.
Source:
Crystallography Reports. 45(1):122-127, 2000 Jan-Feb.
Abstract:
The Gorsky-Bragg-Williams (GBW) theory has been modified to describe phase transitions caused by the ordering of two kinds of atoms in the even and the odd sublattices of the structures of icosahedral quasicrystals with the dodecahedral local order (DLO) and their approximants. The modified method is exemplified by numerical calculations of such phase transitions in the structures of several simplest approximants. (C) 2000 MAIK "Nauka/Interperiodica".
Title:
Diffraction analysis of decorated Fibonacci chains in the average unit-cell approach
Authors:
Wolny J. Pytlik L.
Source:
Acta Crystallographica - Section a - Foundations of Crystallography. 56(Part 1):11-14, 2000 Jan.
Abstract:
A novel approach to diffraction analysis of decorated quasicrystals is discussed. An average unit cell has been constructed for a decorated Fibonacci chain and used for analysis of its diffraction pattern. After some transformation of the scattering vectors, all the diffraction peaks are described by a single envelope function which is characteristic of a given decoration. It has been shown that by knowing several diffraction intensities, in a limited range of the scattering vector, it is possible to reconstruct the envelope function successfully and distinguish between different decorated structures.
Title:
Icosahedral quasiperiodic packing of fibres parallel to fivefold and threefold axes
Authors:
Audier M. Duneau M.
Source:
Acta Crystallographica - Section a - Foundations of Crystallography. 56(Part 1):49-61, 2000 Jan.
Abstract:
Building rules are examined for an icosahedral quasiperiodic packing of fibres with axes parallel to the ten threefold axes, first employing an experimental construction and afterwards a mathematical demonstration using the cut-and-project method applied in hyperspace. As a result of this latter approach, very simple two-dimensional (2D) building rules are proposed. Similar simple 2D rules have also been proposed for the case of an-icosahedral quasiperiodic packing with fibre axes parallel to the six fivefold axes [Duneau & Audier (1999). Acta Cryst. A55, 746-754]. Finally, the construction of another icosahedral quasiperiodic packing resulting from a combination of two groups of fibres respectively parallel to six fivefold and ten threefold axes is reported. A brief discussion is given on different particular mechanical behaviours which might a priori be expected from the various enantiomorphic properties of these packings. [References: 6]

Update: 22-Mar-2000

Title:
Modulation parameters in incommensurate modulated structures with inflation symmetry
Authors:
Elcoro L. Etxebarria I. Perez-Mato JM.
Source:
Journal of Physics-Condensed Matter. 12(6):841-848, 2000 Feb 14.
Abstract:
Inflation symmetry is one of the peculiar features of the diffraction pattern of a quasicrystal. However, ii is not an exclusive property of quasicrystalline structures and it may be present in incommensurately modulated structures, as shown recently in the AI-Mg system (Donnadieu P st al 1996 J. Physique I 6 1153-64). The conditions that a single modulation parameter of an incommensurate structure must fulfil in order to have inflation symmetry are determined. Although the number of possible distinct inflation-symmetric quasilattices is infinite, from physical/experimental arguments it can be concluded that, in practice, only a few of them can be experimentally observed, the reported phase of the Al-Mg system being one of these particular cases. A quantitative criterion to classify the modulation parameters that give rise to quasilattices with observable inflation symmetry is proposed. The generalization of the analysis of incommensurate structures with more than one single modulation parameter is also discussed. Finally, the inflation parameters of diffraction patterns with rotational point groups of finite order, C-N, are compared with the parameters of the one-dimensional case.
Title:
Magnetization, electrical resistivity and neutron diffraction studies of the U-2(Ni1-xPtx)(2)In system
Authors:
Tran VH. Hoser A. Hofmann M.
Source:
Journal of Physics-Condensed Matter. 12(6):1029-1040, 2000 Feb 14.
Abstract:
X-ray powder diffraction, magnetization, electrical resistivity;and neutron diffraction experiments were performed on the dense Kondo system U-2(Ni1-xPtx)(2)In. Up to x less than or equal to 0.5 the alloys crystallize in a tetragonal structure with space group P4/mbm while for x greater than or equal to 0.6 they crystallize in space group P4(2)/mnm. The observed structural change coincides with the magnetic-nonmagnetic crossover in the system. In the concentration range 0 less than or equal to x less than or equal to 0.5, an antiferromagnetic ordering occurs, characterized by a noncollinear arrangement of the magnetic uranium moments in the tetragonal basal plane. In addition, for x = 0 and 0.2 a commensurate magnetic ordering is formed with a propagation vector k = (0, 0, 0.5) while for x = 0.5 an incommensurate one with k = (0, 0, 0.5 +/- tau), tau = 0.06 is found. fn the concentration range 0.6 less than or equal to x less than or equal to 1.0 no magnetic ordering down to 1.7 K is observed. The bulk and neutron scattering data exhibit features attributed to the interplay of the Kondo effect and magnetic exchange interactions. For interpretation of the magnetic behaviour of the U-2(Ni1-xPtx)(2)In alloys, a strong modification of the density of states at the Fermi surface has been invoked.
Title:
Sequential formation of quasicrystalline and amorphous phases in the Fe-Nb and Fe-Ta multilayers upon ion irradiation
Authors:
Lin C. Yang GW. Liu BX.
Source:
Journal of Applied Physics. 87(6):2821-2824, 2000 Mar 15.
Abstract:
An unusual phase formation sequence of first quasicrystalline and then amorphous phases was observed in the Fe-Nb and Fe-Ta multilayers upon room temperature 200 keV xenon ion irradiation. The sequential structural evolution was attributed to the gradually destroying of order in the original crystalline lattices with increasing ion dose. (C) 2000 American Institute of Physics. [S0021-8979(00)04706-X].
Title:
Magnetic ordering in RPtX (R=Gd,Tb,Dy; X=Si,Ge) compounds
Authors:
Penc B. Baran S. Hofmann M. Leciejewicz J. Slaski M. Szytula A.
Source:
Journal of Alloys & Compounds. 299(1-2):79-87, 2000 Mar 14.
Abstract:
GdPtX, TbPtX and DyPtX (X=Si, Ge) crystallize in the orthorhombic TiNiSi-type crystal structure. Magnetometric measurements show that all compounds (except GdPtSi) are antiferromagnetic at low temperatures. GdPtSi is probably ferromagnet below 16 K. The Neel temperature of GdPtGe is at 12.5 K. Neutron diffraction data indicate the presence of a complicated magnetic order in TbPtSi below the Neel point at 12.5 K, The magnetic structure of TbPtGe is of amplitude-modulated type along the b-axis with the wave vector k = [0, 0.2840(3), 0]. The Neel point of TbPtGe is at 15 K. A collinear antiferromagnetic ordering with the wave vector k = [1/2, 0, 1/2] is operating in DyPtSi and DyPtGe below the Neel points of 8.2 and 8 K, respectively. (C) 2000 Elsevier Science S.A. All rights reserved.
Title:
Synthesis, characterization, and magnetic properties of a commensurate and incommensurate phase of Sr3ZnRhO6: zinc in trigonal prismatic coordination
Authors:
Layland RC. zur Loye HC.
Source:
Journal of Alloys & Compounds. 299(1-2):118-125, 2000 Mar 14.
Abstract:
The new compound Sr3ZnRhO6 has been synthesized as both a commensurate and an incommensurate phase, The commensurate compound was structurally characterized by Rietveld refinement of powder X-ray diffraction data in the space group R (3) over bar c (no. 167), Z = 6. The lattice parameters for this compound were found to be a = 9.6193(1) Angstrom and c = 11.1061(1) Angstrom. It belongs to a family of pseudo one-dimensional materials and is isostructural with the K4CdCl6 structure. The commensurate structure contains zinc in a highly unusual trigonal prismatic coordination environment. The structure consists of infinite one-dimensional chains of alternating face-shared RhO6 octahedra and ZnO6 trigonal prisms. The strontium cations an located between the chains and are coordinated in a distorted square antiprismatic environment. Magnetic measurements were made for both compounds. The data for the commensurate structure shows that the susceptibility of Sr3ZnRhO6 increases rapidly below 20 K without the usual signs of long range ferromagnetic ordering. The magnetic susceptibility of the incommensurate phase of Sr3ZnRhO6, however, is quits different from the commensurate analog and does not exhibit the rapid increase in magnetization at low temperature and appears much more Curie-like. (C) 2000 Elsevier Science S.A. All rights reserved.
Title:
Crystal structure of a new 1/1-rational approximant for the Al-Cu-Ru icosahedral phase
Authors:
Sugiyama K. Kato T. Ogawa T. Hiraga K. Saito K.
Source:
Journal of Alloys & Compounds. 299(1-2):169-174, 2000 Mar 14.
Abstract:
The structure of a cubic Al57.3Cu31.4Ru11.3 phase, which is referred to as an 1/1-rational approximant of an Al-Cu-Ru icosahedral phase, was determined by means of a single crystal X-ray structural analysis: space group Pm3 (No. 200), a=12.3773(8) Angstrom, V=1896.2(2) Angstrom(3), MoK alpha (lambda=0.71073 Angstrom); atoms/cell=122.6, F(000)=2645, D-calc=5.04 Mg/m(3), R=0.0495 for the observed 1140 reflections with F-obs>4.0 sigma(F-obs). Cu- and Ru-rich icosidodecahedral atom clusters are recognized at the In and Lb sites of the unit cell, respectively. The atom clusters possess Ru centers and the surrounding first shells of about 2.5 Angstrom in diameter show heavily disordered features with partial breakdown of the local icosahedral symmetry. These chemically and topologically decorated Mackay-like atom clusters should be classified as the fundamental structural units for the F-type Al-Cu-Ru icosahedral phase. (C) 2000 Elsevier Science S.A. All rights reserved. [References: 28]
Title:
Plasmons in icosahedral quasicrystals: An EELS investigation
Authors:
Grenet T. Cheynet MC.
Source:
European Physical Journal B. 13(4):701-705, 2000 Feb.
Abstract:
We present the results of an electron energy loss spectroscopy (EELS) investigation of the icosahedral quasicrystals i-Al-Cu-Fe, i-Al-Pd-Mn and i-Al-Pd-Re. The spectra of the thr ee systems studied are very similar. Their main contribution comes from a broad plasmon like peak, which can be interpreted as an "s-p" electron plasmon damped by "d" electron interband transitions. We show that it is similar to those found in other simple crystalline aluminum-transition metal alloys, so that no specificity related to the quasicrystalline order of the alloys dominates.
Title:
Statics and dynamics of the modulation in incommensurate Rb2ZnBr4 as detected by NMR
Authors:
Decker F. Petersson J. Michel D.
Source:
Applied Magnetic Resonance. 17(2-3):399-411, 1999.
Abstract:
The dynamics of the incommensurate modulation of Rb2ZnBr4 is investigated near the transition to the normal high-temperature phase using first-order quadrupole effects in nuclear magnetic resonance (NMR). Rb-87 NMR spectra and two-dimensional Rb-87 NMR exchange spectra are reported. All results can be described consistently in terms of a static modulation in the incommensurate phase without any indication for "floating" or large-scale fluctuations of the modulation wave. The spectra taken about 135 K below T-i in the lower incommensurate phase well above the soliton regime show no indication for the existence of a higher-order commensurate modulation in Rb2ZnBr4.

Update: 14-Mar-2000

Title:
The commensurately modulated structure of the lock-in phase of synthetic Co-akermanite, Ca2CoSi2O7
Authors:
Riester M. Bohm H. Petricek V.
Source:
Zeitschrift fur Kristallographie. 215(2):102-109, 2000.
Abstract:
This paper deals with the structure determination of the lock-in phase of synthetic modulated Co-akermanite, Ca2CoSi2O7 The structure determination of the (3 x 3 x 1) superstructure is based on X-ray data of a twinned single crystal taken at 130 K. The deformation modes in the commensurate lock-in phase are derived and compared with the deformations found by other authors in the incommensurate phase. A model for the driving force of the modulation in melilites in general is proposed: In order to release internal stress domains with clusters of 6-and 7-fold coordinated calcium are formed which are arranged in octagons. [References: 9]
Title:
Modulated phases, magnetic phase diagrams, and the Lifshitz point in MnP from the mean field theory
Authors:
Zieba A. Slota M. Kucharczyk C.
Source:
Physical Review B. 61(5):3435-3449, 2000 Feb 1.
Abstract:
The axial next-nearest-neighbor Heisenberg (ANNNH) model with orthorhombic magnetocrystalline anisotropy was applied to describe magnetic phases and phase transitions occurring in manganese phosphide in magnetic field H applied along the lattice vectors a, b, and c. The ground state of the Hamiltonian was obtained using analytical methods of Nagamiya's theory, augmented by numerical minimization of the energy with respect to the wave vector q of the modulated magnetic structures (heli, fan, cone). The latter procedure leads to the dependence q(H) for all modulated phases, and explains both the shapes of the magnetization curves for these phases (convex for the fan and concave for the cone phase) and the weakly first-order nature of the cone-fan phase transition. The magnetic phase diagrams for the three principal directions of the applied field, H parallel to c, H parallel to b, and H parallel to a, are calculated under the assumption that the ratio of competing nearest-neighbor and next-nearest-neighbor interactions depends on the temperature. The characteristics of special points in the phase diagrams (Lifshitz points, triple point, critical end point, and terminations of critical lines) remain in a semiquantitative accordance with experiment. For the Lifshitz point the deviation from asymptotic scaling laws was analyzed by calculating the effective (fit-range-dependent) values for the crossover exponent phi, the wave vector exponent beta(k), and magnetization discontinuity exponent beta(m).(.) The results provide an explanation of their experimental values.
Title:
Direct observation of a one-dimensional static spin modulation in insulating La1.95Sr0.05CuO4
Authors:
Wakimoto S. Birgeneau RJ. Kastner MA. Lee YS. Erwin R. Gehring PM. Lee SH. Fujita M. Yamada K. Endoh Y. Hirota K. Shirane G.
Source:
Physical Review B. 61(5):3699-3706, 2000 Feb 1.
Abstract:
We report the results of an extensive elastic neutron-scattering study of the incommensurate (IC) static spin correlations in La1.95Sr0.05CuO4, which is an insulating spin glass at low temperatures. Recent work by Wakimoto et nl, has revealed the presence of new two-dimensional satellite peaks in La1.95Sr0.05CuO4 at positions rotated by similar to 45 degrees in reciprocal space from those found in superconducting samples. The present neutron-scattering experiments on the same x = 0.05 crystal employ a narrower instrumental Q resolution and thereby have revealed that the crystal has only two, rather than four, orthorhombic twins at low temperatures with relative populations of 2:1. This has made possible the precise characterization of the IC elastic peaks around (1,0,0) and (0,1,0) (orthorhombic notation) in each domain separately. We find that, in a single twin, only two satellites are observed at (1,+/- 0.064,L)(ortho) and (0,1 +/- 0.064,L)(ortho), that is, the modulation vector is only along the orthorhombic b* axis. This demonstrates unambiguously that La1.95Sr0.05CuO4 has a one-dimensional rather than two-dimensional static diagonal spin modulation at low temperatures, consistent with certain stripe models. From the L dependence we conclude that the spin correlations are predominantly two dimensional. We have also reexamined the x = 0.04 crystal that previously was reported to show a single commensurate peak. By mounting the sample in the (H,K,0) zone, we have discovered that the x = 0.04 sample in fact has the same IC structure as the x = 0.05 sample. The incommensurability parameter delta for x = 0.04 and 0.05, where delta is the distance from (1/2,1/2) in tetragonal reciprocal lattice units, follows the linear relation delta similar or equal to x. These results demonstrate that the insulator to superconductor transition in the underdoped regime (0.05 less than or equal to x less than or equal to 0.06) in La2-xSrxCuO4 is coincident with a transition from diagonal to collinear static stripes at low temperatures thereby evincing the intimate coupling between the one-dimensional spin density modulation and the superconductivity.
Title:
Effect of nonstoichiometry on the transition from ferromagnetism to antiferromagnetism in the ternary indides Ce1.95Pd2+2xIn1-x and Ce2+xPd1.85In1-x
Authors:
Giovannini M. Michor H. Bauer E. Hilscher G. Rogl P. Bonelli T. Fauth F. Fischer P. Herrmannsdorfer T. Keller L. Sikora W. Saccone A. Ferro R.
Source:
Physical Review B. 61(6):4044-4053, 2000 Feb 1.
Abstract:
Single phase polycrystalline samples of the ternary indides Ce1.95Pd2+2xIn1-x (0.05 less than or equal to x less than or equal to 0.23) and Ce2+xPd1.85In1-x (0.06 less than or equal to x less than or equal to 0.37) were synthesized and characterized by microprobe analysis and x-ray diffraction. The effect of the chemical composition on the magnetic properties was investigated by means of magnetization and specific-heat measurements as well as by neutron diffraction. The ternary indides crystallize in the parent Mo2FeB2 structure (space group P4/mbm) and form two branches of solid solutions due to different substitutional mechanisms. In the Pd-rich branch indium vacancies at the 2a site are compensated by an excess of palladium located at an additional 4e site. In the Ce-rich branch the excess of cerium replaces indium atoms at the 2a site. The magnetic properties are strongly influenced by the chemical composition. Excess of palladium favors antiferromagnetism of a sinusoidal modulated type with the propagation vector k approximate to [0.22,0,0] whereas excess of cerium induces ferromagnetism. The magnetic moments in both cases are oriented parallel to the c axis.
Title:
Ductile quasicrystalline alloys
Authors:
Inoue A. Zhang T. Chen MW. Sakurai T. Saida J. Matsushita M.
Source:
Applied Physics Letters. 76(8):967-969, 2000 Feb 21.
Abstract:
An icosahedral (I) quasicrystalline phase with a grain size below 40 nm was formed as a metastable phase in crystallization of the bulk glassy Zr65Al7.5Cu17.5-xNi10Mx (M=Ag, Pd, Au, or Pt; x=5 and 10 at %) alloys. The volume fraction (V-f) of the I phase is about 85% for the 5% M alloy and nearly 100% for the 10% M alloy. The I phase changes to Zr2Cu+Zr2Ni+Zr2Al3 in a fully annealed state. Compressive fracture strength (sigma(c,f)) and fracture elongation (epsilon(c,f)) of the 10% Pd cylinder with a diameter of 2 mm are respectively 1640 MPa and 2.2% for the glassy phase and increase to 1830 MPa and 3.1% for the I phase. The increase in sigma(c,f) is due to the suppression effect of the I particles against the shear deformation of the intergranular glassy phase, and the increase in epsilon(c,f) results from the localization effect of deformation into the glassy layer. The precipitation of the I phase implies that the glassy alloys include randomly oriented I configurations. The present work shows promise for the new class of high-strength nanoquasicrystalline materials. (C) 2000 American Institute of Physics. [S0003-6951(00)00408-3].

Update: 5-Mar-2000

Title:
Symmetry groups, physical property tensors, elasticity and dislocations in quasicrystals [Review]
Authors:
Hu CZ. Wang RH. Ding DH.
Source:
Reports on Progress in Physics. 63(1):1-39, 2000 Jan.
Abstract:
The first quasicrystal (QC) structure was observed in 1984. QCs possess long-range orientational and translational order while lacking the periodicity of crystals. An overview is given on some physical properties of QCs. It begins with group theory and symmetry, Then the thermodynamics of equilibrium properties and physical property tensors are discussed. Finally, the generalized elasticity theory of QCs and the elasticity theory of dislocations in QCs are presented. [References: 196]
Title:
Tunneling states in a single-grain Al-Cu-Fe quasicrystal
Authors:
Bert F. Bellessa G. Quivy A. Calvayrac Y.
Source:
Physical Review B. 61(1):32-35, 2000 Jan 1.
Abstract:
Velocity and attenuation of acoustic waves (190 Mhz) have been measured in a phason-free single grain of i-AlCuFe between 40 mK and 30 K. The results reveal the existence of tunneling states (TS's). The coupling parameter P gamma(2) (where P is the TS density of states and gamma is the phonon-TS coupling) is close to the one in metallic glasses. The crossover temperature from the T-3 law to the plateau regime in the attenuation is well defined. Hence, within the TS model, both P and gamma can be calculated. The TS's seem to be intrinsic to the quasicrystal structure.
Title:
Ultrasonic study of hydrogen motion in a Ti-Zr-Ni icosahedral quasicrystal and a 1/1 bcc crystal approximant
Authors:
Foster K. Leisure RG. Shaklee JB. Kim JY. Kelton KF.
Source:
Physical Review B. 61(1):241-245, 2000 Jan 1.
Abstract:
Ultrasonic attenuation measurements have been performed on the Ti-Zr-Ni alloy system over the temperature range 35-335 K. Both a multigrained icosahedral quasicrystal and a 1/1 bce polycrystalline approximant were studied. The alloys were hydrogenated to a hydrogen to metal ratio of 0.79 for the icosahedral phase and 0.20 for the crystalline phase. Temperature-dependent attenuation peaks were observed in the alloys loaded with hydrogen while the hydrogen-free materials showed no unusual features. For measurement frequencies near 1 MHz the attenuation maxima occurred near a temperature of 250 K for the crystalline phase and 220 K for the icosahedral phase. The results imply that the hydrogen motion is about one order of magnitude faster in the icosahedral phase than in the approximant phase. Whether this result is due to an intrinsic difference between the two Ti-Zr-Ni phases or to a dependence on hydrogen concentration cannot be determined from the present measurements.
Title:
Antiferromagnetic spin correlations in the Zn-Mg-Ho icosahedral quasicrystal
Authors:
Sato TJ. Takakura H. Tsai AP. Shibata K. Ohoyama K. Andersen KH.
Source:
Physical Review B. 61(1):476-486, 2000 Jan 1.
Abstract:
Magnetic diffuse scattering in the Zn-Mg-Ho icosahedral quasicrystal has been studied by neutron scattering over a wide Q range using a single-quasicrystalline sample. It was found that the diffuse scattering obeys the icosahedral symmetry, and appears as satellite peaks of the intense nuclear Bragg reflections. The diffuse-scattering patterns were successfully accounted for by assuming short-range spin correlations in a six-dimensional hypercubic crystal with a magnetic modulation vector q=(3/4,0,0,1/2,3/4,1/2)(a*). A possible origin for the six-dimensional spin correlations is discussed.
Title:
A structural study of the layered perovskite-derived Sr-n(Ti, Nb)(n)O3n+2 compounds by transmission electron microscopy
Authors:
Levin I. Bendersky LA. Vanderah TA.
Source:
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical Properties. 80(2):411-445, 2000 Feb.
Abstract:
A series of Sr-n(Nb, Ti)nO(3n+2) structures with n = 4, 4.5, 5, 6 and 7 were studied by transmission electron microscopy. These structures are composed of infinite two-dimensional slabs of the distorted perovskite structure that are n (Ti,Nb)O-6 octahedra thick and extend parallel to the {110}(perovskite) plane. The slabs are displaced with respect to each other by the translation vector 1/2[011](perovskite). All members of the Sr-n(Nb,Ti)nO(3n+2) series have an orthorhombic basic lattice with a approximate to a(perovskite) and c approximate to 2(1/2)a(perovskite), while the long b axis increases systematically with increasing n value. The compounds with n = 4, 5, 6 and 7 were observed to undergo a commensurate --> incommensurate phase transition on cooling in the temperature range 150-250 degrees C. The wave-vector of the incommensurate modulation is parallel to [100] direction of the basic orthorhombic lattice and is close but not exactly equal to 1/2 a*. The n = 5 incommensurate phase further transformed at 180 degrees C to a monoclinic structure with the space group P112(1)/b (No. 14). For the n = 4, 6 and 7 compounds, no lock-in transition was observed down to -170 degrees C. For the compound with n = 4.5, the transition from orthorhombic to monoclinic structure P112(1)/b occurred on cooling at 390 degrees C. All transitions observed in the Sr-n(Nb,Ti)(n)O3n+2 compounds were attributed to tilting of the (Ti, Nb)O-6 octahedra.
Title:
An electron diffraction and XRD study of the alpha(1)' and alpha(1)'' fluorite-related phases in the (1-x)1/2Bi(2)O(3)center dot xCaO, 0.20 < x < 0.29, system
Authors:
Withers RL. Larsson AK. Schmid S.
Source:
Journal of Solid State Chemistry. 149(2):218-225, 2000 Feb 1.
Abstract:
Two fluorite-related modulated phases (alpha(1)' and alpha(1)") occurring in the (1-x)1/2Bi(2)O(3). xCaO, 0.20 < x < 0.29, system have been carefully investigated via electron diffraction and XRD. The satellite reflections accompanying the strong fluorite-type substructure Bragg reflections were always found to be of G(F)+/- similar to 1/8[224](F)* (F for fluorite)-type and to be consistent with a lowering of the cubic m3m point group symmetry of fluorite to rhombohedral (3) over bar m point group symmetry in both cases. The type of rhombohedral symmetry, however, was found to be quite distinct. The a; phase is shown to be a two-dimensional incommensurately modulated phase of R (3) over bar m (epsilon 00) 11 superspace symmetry while the alpha(1)" phase is shown to be a rhombohedral, commensurately modulated, superstructure phase. Ca/Bi metal ion ordering on the essentially ccp cation array is shown to be largely responsible for the observed satellite reflections and an expression for this ordering is derived using a modulation wave approach to structural characterization. (C) 2000 Academic Press.
Title:
Order-disorder phenomena in the perovskite-related oxyborocarbonates SrMn1-y(B,C)(y)O3-delta
Authors:
Hervieu M. Michel C. Pelloquin D. Maignan A. Raveau B.
Source:
Journal of Solid State Chemistry. 149(2):226-235, 2000 Feb 1.
Abstract:
The electron diffraction and high-resolution electron microscopy investigation of the oxyborocarbonate SrMn1-y(C, B)(y)O3-delta shows that the carbonate and berate groups substitute for the MnO6 octahedra in the perovskite matrix, according to a mechanism based on the intergrowth and microtwinning of two basic mother structures, Sr5Mn4CO3O10 (S5M4C) and Sr4Mn3BO3O7 (S4M3B) The two structures, S5M4C and S4M3B, coexist in the same matrix in the form of intergrowths, whose coherent boundaries are parallel to the {210}(P) planes of the perovskite structure. It results in the formation of {210}(P) antiphase boundaries and diamond-shaped domains are formed by combining twinning and intergrowth phenomena. These structural phenomena are compared to the microdomain and concentration wave models observed in alloys. These oxides are antiferromagnetic with T-N = 250 K, but weak ferromagnetic couplings are detected below 100 K. (C) 2000 Academic Press.
Title:
The CDW structure of the m=4 phosphate bronze (PO2)(4)(WO3)(2m)
Authors:
Ludecke J. Jobst A. van Smaalen S.
Source:
Europhysics Letters. 49(3):357-361, 2000 Feb.
Abstract:
Low-temperature X-ray diffraction with synchrotron radiation was used to study the CDW structure of the phosphate bronze (PO2)(4)(WO3)(2m) with m = 4. The CDW state at T = 20 K can be described as a 2-dimensional, incommensurately modulated structure with Rave vectors q(1) = (0.330(5), 0.292(5), 0) and q(2) = (-0.330, 0.292, 0). The second type of modulation is found to comprise the mixed second-order satellites q(1) - q(2) at (0.340(5), 0, 0). Atomic displacements are mainly found on the wolfram atoms, whereby a tendency is observed for the CDW to concentrate in the middle of the WO3 layers. The consequences are derived for the interpretation of the CDW modulations in this homologous series of compounds.
Title:
Shell structure of dodecagonal quasicrystals associated with root system F-4 and cyclotomic field Q(zeta(12))
Authors:
Morita J. Sakamoto K.
Source:
Communications in Algebra. 28(1):255-263, 2000.
Abstract:
Using a Coxeter transformation of type F-4, Pie will construct quasicrystals of dimension 2 with twelvefold symmetry. Then, such quasicrystals will be realized as subsets of a certain cyclotomic field. And we will study a typical shell structure algebraically. In particular, we can give its mathematical meaning in terms of elementary number theory.

Update: 3-Mar-2000

Title:
Investigation of strain softening of icosahedral AlPdMn single quasicrystals
Authors:
Brunner D. Plachke D. Carstanjen HD.
Source:
Physica Status Solidi A-Applied Research. 177(1):203-217, 2000 Jan.
Abstract:
Icosahedral AlPdMn single quasicrystals were deformed in compression with constant plastic strain rate in order to study the strain-softening phenomenon which is observed in the strain regime following the upper yield stress and which characterizes the shape of the stress-strain curves of quasicrystals. Stress-relaxation experiments and temperature changes were performed along the stress-strain curves at selected strains. It is found that both the strain-rate sensitivity and the temperature sensitivity of the stress decrease in the above strain regime with increasing strain. Within the regime of constant stress following the strain softening regime at large strains both sensitivities remain constant. These results favour a model which assumes strain softening being caused by a change of the configuration of large cluster-like obstacles (e.g. the icosahedral clusters present in i-AlPdMn quasicrystals) by the moving dislocations thus reducing the stress needed to maintain the deformation.
Title:
Grain growth behaviour of quasicrystals from the supercooled liquid region of Zr(65)Cu(7.5)Al(7.)5Ni(10)Ag(10) metallic glass
Authors:
Matsushita M. Saida J. Zhang T. Inoue A. Chen MW. Sakurai T.
Source:
Philosophical Magazine Letters. 80(2):79-84, 2000 Feb.
Abstract:
The transformation and grain growth behaviour of an icosahedral phase from the supercooled liquid region of rapidly quenched Zr65Cu7.5Al7.5Ni10Ag10 metallic glass have been examined by transmission electron microscopy. The precipitation of the icosahedral phase proceeds according to a polymorphic reaction without any concentration change. The grain size increases linearly with an increase in annealing time and the growth rate strongly depends on the temperature. An Arrhenius plot of the logarithm of growth rate versus the reciprocal of annealing temperature yields a linear relationship, from which an activation energy for grain growth of 409 kJ mol(-1) is obtained. This activation energy is much higher than those in the AI-Cu-V and Al-Mn-Si systems. This activation energy is attributed to the strong bonding among constitutional elements and the necessity of the rearrangement of atoms on a long length scale for grain growth. The kinetic data suggest that the icosahedral phase is stabilized by the difficulty of rearrangement of atoms.
Title:
A stable one-dimensional quasicrystal related to decagonal Al-Co-Ni
Authors:
Ritsch S. Radulescu O. Beeli C. Warrington DH. Luck R. Hiraga K.
Source:
Philosophical Magazine Letters. 80(2):107-118, 2000 Feb.
Abstract:
A stable one-dimensional quasicrystal has been found for Al-Co-Ni which is related closely to the decagonal phase in this system. It exists as a high-temperature state above 900 degrees C in a range of compositions between approximately 71 and 71.5at.% Al between 18at.% and 22at.% Co. The modulation length along the periodic direction in its pseudo tenfold diffraction patterns is approximately 61 Angstrom. We show that the 20 Angstrom edge length defective rhomb tiling superimposed on to a corresponding high-resolution image, defined by centres of atomic clusters, can be considered as a subset of a phason-strained, 2.5 Angstrom edge length Penrose tiling that has the observed period. An ideal 20 Angstrom edge length tiling based on special configurations of this Penrose tiling can be chosen as a prototype for the observed experimental tiling.
Title:
A possible origin of anomalous properties of proper uniaxial ferroelectrics near the lock-in transition
Authors:
Berezovsky SV. Klepikov VF.
Source:
Journal of Physics-Condensed Matter. 12(3):311-322, 2000 Jan 24.
Abstract:
A mechanism which may be responsible for the anomalies in the behaviour of type II ferroelectrics near the lock-in transition is considered. The state of the system is suggested to be quasistationary. The defects of the incommensurate modulation wave are found to play an important role and give additional contributions to the thermodynamic characteristics of the system.
Title:
Neutron diffraction study of the U(Pd1-xFex)(2)Ge-2 magnetic structure
Authors:
Balagurov AM. Raspopina EV. Sikolenko VV. Lyubutin IS. Stepin AS. Gribanov AV. Andre G. Bouree F. Duh HM.
Source:
Journal of Magnetism & Magnetic Materials. 210(1-3):225-232, 2000 Feb.
Abstract:
The neutron diffraction and magnetic susceptibility studies have shown that the magnetic structure of UPd2Ge2 changes dramatically even under very low iron doping. Though the general magnetic structure of pure UPd2Ge2 and of 1%Fe-doped samples is the same, the temperature intervals of existence of different magnetic phases are different. The values of transition temperatures, where (i) the 'square' modulated longitudinal spin-density wave (LSDW) structure with the propagation vector k = (0; 0; k(z) = 3/4) starts to transform into the sinusoidal modulated LSDW structure and (ii) the commensurate phase transforms into incommensurate one, shift under the 1%Fe doping to the higher temperatures (from 50 to 65 K and from 80 to 90 K, respectively). In the pure and 1%Fe-doped UPd2Ge2, the magnetic transition from the commensurate to incommensurate phase is accompanied by the drastic decrease of the propagation vector k(z). In the 2%Fe-doped sample, besides the Neel point of T-N = 135 K, we have found two additional characteristic temperatures of 65 and 93 K. Below 65 K, the material has a simple antiferromagnetic (AF) structure with the propagation vector k = (0; 0; 1) and, at 65 K < T < T-N, the magnetic structure is LSDW with sinusoidal modulation. Over almost the total region 65 K < T < T-N, the LSDW magnetic structure is incommensurate. Only at about 93 K, the propagation vector passes the commensurate value of 3/4, whereas k(z) > 3/4 at 65 < T < 93 K and k(z) > 3/4 at 93 K < T < T-N. We have found that the magnetic susceptibility and the uranium magnetic moment are sensitive to the k(z) > 3/4 --> k(z) < 3/4 transition. With increasing iron concentration to x greater than or equal to 0.15, the simple AF structure with k = (0; 0; 1) develops over all temperature region up to the Neel point. Below T-N, the uranium magnetic moments are always parallel to the tetragonal c-axis. (C) 2000 Elsevier Science B.V. All rights reserved.
Title:
Dislocations in quasicrystals [Russian]
Authors:
Khannanov SK.
Source:
Fizika Metallov i Metallovedenie. 88(2):64-71, 1999 Aug.

Update: 21-Feb-2000

Title:
Behavior of the layered crystals TlInS2 and TlGaSe2 near phase transitions in a static electric field
Authors:
Allakhverdiev KR. Akhmed-zade ND. Mamedov TG. Mamedov TS. Seidov MGY.
Source:
Low Temperature Physics. 26(1):56-61, 2000 Jan.
Abstract:
The effect of an orienting electric field on the anomalies of the temperature dependence of the dielectric constant epsilon of the crystals TlInS2 and TlGaSe2 and of the pyroelectric current i in TlInS2 near phase transitions is investigated. It is found that the epsilon(T) profile of both crystals undergoes the same transformation at the point of the phase transition to the incommensurate phase under the influence of a static electric field applied in the plane of the layer. It is established that the maximum of epsilon(T) in TlGaSe2 and of i(T) in TlInS2 at the point of the phase transition to the commensurate polar phase is shifted in a certain range of orienting electric fields and that the sign of the temperature shift depends on the value of the external electric field. An interpretation is offered for the experimental results. (C) 2000 American Institute of Physics.
Title:
A comparison of indentations of different size and geometry in single-quasicrystalline AIPdMn
Authors:
Wolf B. Swain M. Kempf M. Paufler P.
Source:
Journal of Materials Science. 35(3):723-734, 2000 Feb.
Abstract:
The study compares impressions into one and the same single-quasicrystalline Al70Pd20Mn10 sample (surface of fivefold symmetry) that were performed by spherical and pointed indenters (Vickers- and corner-of-a-cube-geometry) and investigated using Atomic Force Microscopy (AFM). The Meyer hardness number was found to vary with indentation size in a manner similar to materials that work harden, though this behavior must have a different physical origin: for spherical indentations the hardness number slightly increases with increasing load (Meyer hardness evolution), whereas for pyramid-shaped indenters a considerable hardness increase in case of decreasing load can be stated. Spherical indentations show little piling-up only in contrast to pointed indentations where huge elevations surrounding the indent developed. Different degrees of lateral cracking can account for this observation. In case of Vickers indentations the material breaks into segments which display mutual shearing. Distinct differences can also be noticed with respect to the volume balance between the apparent piled-up volume around the impression and the volume of the displaced material. This balance proves positive for pyramidal and negative for spherical impressions. (C) 2000 Kluwer Academic Publishers.
Title:
Disorder driven lock-in transitions of 3D CDWs and related structures
Authors:
Nattermann T. Emig T. Bogner S.
Source:
Journal de Physique IV. 9(P10):11-15, 1999 Dec.
Abstract:
Thermal fluctuations are known to play an important role in low-dimensional systems which may undergo incommensurate-commensurate or (ibr an accidentally commensurate wavevector) lock-in transitions. In particular, an intermediate floating phase with algebraically decaying correlations exists only in D = 2 dimensions, whereas in higher dimensions most features of the phase diagram are mean-field like. Here we will show, that the introduction of frozen-in disorder leads to strong fluctuation effects even in D < 4 dimensions. For commensurate wavevectors the lattice pinning potential dominates always over weak impurity pinning if p < p(c) = 6/pi (D = 3), where p denotes the degeneracy of the commensurate phase. For larger p a disorder driven continuous transition between a long-range ordered locked-in phase and quasi-long-range ordered phase, dominated by impurity pinning, occurs. Critical exponents of this transition, which is characterized by a zero temperature fixed point, are calculated within an expansion in 4 - D. The generalization to incommensurate wavevectors will be discussed. If the modulation in the quasi-long-range ordered phase has hexagonal symmetry, as e.g. for flux-line lattices, the algebraic decay is nonuniversal and depends on the Poisson ratio of the elastic constants. Weakly driven transport is dominated by thermally activated creep in both phases, but with different creep exponents.
Title:
Superspace approach to the superstructures of CDW compounds and low-dimensional magnets
Authors:
van Smaalen S. Ludecke J.
Source:
Journal de Physique IV. 9(P10):371-373, 1999 Dec.
Abstract:
Studies of the incommensurate or commensurate superstructures of low-dimensional crystals provide detailed information on the location of the Charge-density wave or the magnetic order. Accordingly the combined charge- and magnetic order is analysed in NaV2O5, and the 2-dimensional CDW is characterized in the phosphate bronze (PO2)(4)(WO3)(8). It is shown that the superspace approach to the structure is essential for a successful analysis of the simple, 4-fold superstructure of NaV2O5.

Update: 15-Feb-2000

Title:
Single crystal refinement of the incommensurately modulated Mn0.55Ta0.45O1.7, an oxygen deficient fluorite type compound
Authors:
Esmaeilzadeh S. Lidin S. Nygren M. Grins J.
Source:
Zeitschrift fur Anorganische und Allgemeine Chemie. 626(1):148-159, 2000 Jan.
Abstract:
A structural investigation of the incommensurately ordered compound Mn0.55Ta0.45O1.7 has been carried out, using single-crystal X-ray diffraction data. The basic structure is related to the fluorite type with a monoclinic distortion. Electron diffraction (ED) patterns for various crystal orientations were used for determination of unit cell, incommensurate modulation vector and superspace group. The unit cell parameters and the length and direction of the incommensurate vector were refined using X-ray powder diffraction (XRPD) data. P2/m was chosen as the three-dimensional space group for a subcell with parameters a = 3.5005(2) Angstrom (root 2/2 . a(f)), b = 3.5730(2) (root 2/2 . a(f)), c = 5.0015(2) Angstrom (a(f)) and beta = 91.677(7)degrees. From the systematic absences hklm: k + m not equal 2n, the four-dimensional superspace group was determined to be B : P2/m(alpha 0 gamma) with determined modulation vector components alpha = -0.1833(1) and gamma = 0.3582(2). A total of 511 unique reflections (79 basic fluorite type, 268 first-order and 164 second-order satellites) were used in the structure refinement, which resulted in weighted R-values of 5.6% for the fluorite type sublattice reflections, 5.5% for the first-order satellites and 7.4% for the second order satellites. The Mn and Ta atoms were found to be both positionally and occupationally modulated and the oxygen atoms to be highly disordered. The structure is the first fluorite-related modulated structure of an oxide that has been determined from single-crystal data. The structural relation to the previously characterised disordered cubic phase Mn0.6Ta0.4O1.65 and the diffuse scattering exhibited by it are discussed in the article.
Title:
Alloys - Atomic structure of the quasicrystal Al72Ni20Co8
Authors:
Yan YF. Pennycook SJ.
Source:
Nature. 403(6767):266-267, 2000 Jan 20.
Title:
Alloys - Atomic structure of the quasicrystal Al72Ni20Co8 - Reply
Authors:
Steinhardt PJ. Jeong HC. Saitoh K. Tanaka M. Abe E. Tsai AP.
Source:
Nature. 403(6767):267, 2000 Jan 20.
Title:
In situ study of structural transformations of Mg44Al15Zn41 quasicrystals under heating
Authors:
Bokhonov BB. Ivanov EY. Tolochko BP. Sharaphutdinov MP.
Source:
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 278(1-2):236-241, 2000 Feb 15.
Abstract:
Structural transformations under annealing of quasicrystalline Mg44Al15Zn41 below 613 K showed that the quasicrystalline constant a(R) was increased by about 0.0019 nm. The phase transformation at 613 K from the quasicrystalline structure to the 2/1 cubic approximant is reversible and has a topotactic character. The 2/1 approximant phase formed during this transformation is metastable and decomposes irreversibly above 693 K. (C) 2000 Elsevier Science S.A. All rights reserved. [References: 8]
Title:
The Mossbauer and magnetic resonances investigations of structural phase transitions in K2ZnCl4 crystals
Authors:
Constantinescu S. Grecu MN.
Source:
European Physical Journal B. 13(2):227-233, 2000 Jan.
Abstract:
The experimental data carried out by Mossbauer and magnetic resonances investigations of the structural phase transitions in K2ZnCl4 crystals are discussed by a simple electrostatic model, calculating, the lattice contributions to the local electric potential V(r), electric field intensity E(r) a,nd electric field gradient tensor, V-alpha beta(r) and taking into account both the fractional electric point charges and rigid lattice approximations. The validity of the model is proved by a good fit of the computing results and experimental data of quadrupole splitting parameters at K Bites obtained by K-39-NMR methods in high temperature incommensurate phase (similar to Pnam symmetry). The experimental results obtained by Mossbauer and EPR methods in commensurate phase (Pna2(1) symmetry) of iron and copper doped K2ZnCl4 crystals are explained by relaxing the rigid lattice approximation. The insertion of probe ions appear to be done on not-exactly-Zn2+ site.
Title:
Grain growth and phason-strain field in quasicrystalline Al-Li-Cu
Authors:
Wang K. Donnadieu P. Garoche P.
Source:
European Physical Journal B. 13(2):279-287, 2000 Jan.
Abstract:
We report on grain growth and related structure change in single phased Al-Li-Cu quasicrystals. The icosahedral phase grains have been investigated using scanning ion microscopy and transmission electron microscopy. Regular boundaries between large grains have been observed both before and after high temperature annealing. The electron diffraction study shows that the grain growth is accompanied by a reduction of the phason-strains. The orientation relation between grains sets the 2-fold icosahedral axes parallel, and the coincidence of the planes depends on the phason strain-field. The effect of phason-strain field on these boundaries is discussed. It is proposed that the phason strain elimination can play a role in the grain growth.
Title:
Tilings, coverings, clusters and quasicrystals
Authors:
Lord EA. Ranganathan S. Kulkarni UD.
Source:
Current Science. 78(1):64-72, 2000 Jan 10.
Abstract:
A quasiperiodic covering of the plane by regular decagons and an analogous structure in three dimensions are described. The 3D pattern consists of interpenetrating triacontahedral clusters, related to the tau(3) inflation rule for the 3D Penrose tiling patterns. The overlap regions are triacontahedron faces, rhombic dodecahedra and rhombic icosahedra, The structure leads to a plausible model for the T2 icosahedral quasicrystalline phases.
Title:
Assemblage of a quasicrystal from hierarchic atomic clusters: Decagonal symmetry
Authors:
Kraposhin VS.
Source:
Crystallography Reports. 44(6):927-937, 1999 Nov-Dec.
Abstract:
Decagonal quasicrystals can be modeled by icosahedral clusters assembled in accordance with the principle of hierarchic levels, so that each cluster of each hierarchic level consists of the clusters of the previous one. Both decagonal and icosahedral quasicrystals are assembled from the same hierarchic icosahedral clusters but packed in different ways. In a decagonal quasicrystal, hierarchic clusters 10 nm in diameter form parallel rods. Distortion of clusters provides the formation of close packing of parallel rods without any voids and can be considered as an orthorhombic lattice with a period of several dozens of nanometers. The geometric characteristics of this model are quantitatively consistent with the diffraction and electron-microscopy data known for the decagonal aluminum-based alloys. The composition of this model with the sites occupied by atoms of different kinds agrees with the experimentally observed composition of the stable decagonal phase of the composition Al65Cu20Co15.
Title:
Phase transitions in cubic approximants of icosahedral quasicrystals occurring without changes of the translation symmetry
Authors:
Chizhikov VA.
Source:
Crystallography Reports. 44(6):1024-1029, 1999 Nov-Dec.
Abstract:
Possible phase transitions in cubic approximants of icosahedral quasicrystals occurring without changes of the number of atoms in their unit cells have been studied within the framework of the phenomenological Landau theory of phase transitions. The results obtained are illustrated by the 0/1 approximant. The: correlations between the transitions occurring in quasicrystals and their approximants have been established.

Update: 7-Feb-2000

Title:
Elastic moduli of a Ti-Zr-Ni icosahedral quasicrystal and a 1/1 bcc crystal approximant
Authors:
Foster K. Leisure RG. Shaklee JB. Kim JY. Kelton KF.
Source:
Physical Review B-Condensed Matter. 59(17):11132-11135, 1999 May 1.
Abstract:
Resonant ultrasound spectroscopy has been used for the measurement of the elastic moduli of a Ti-based quasicrystal, one of the major classes of quasicrystals. Both the bulk and shear elastic moduli of a Ti-Zr-Ni multigrained icosahedral quasicrystal and a polycrystalline 1/1 approximant were measured over the temperature range of 15-300 K. The elastic moduli of these two materials are very nearly the same, a result in agreement with the belief that the structures of these two materials are closely related. The temperature dependence of the moduli resembles that of ordinary metals. The results have been used to predict the acoustic contribution to the low-temperature specific heat. This contribution is much larger in these Ti-based materials than for the Al-based quasicrystals reported by others. Besides their general interest, the elastic moduli are useful for constructing atomic potentials in these unusual materials. [S0163-1829(99)09517-X].
Title:
Commensurability oscillations and smectic vortex phase transition in YBa2Cu3Oy single crystals
Authors:
Zhukov AA. Kupfer H. Perkins GK. Caplin AD. Wolf T. Kugel KI. Rakhmanov AL. Mikheev MG. Voronkova VI. Klaser M. Wuhl H.
Source:
Physical Review B-Condensed Matter. 59(17):11213-11216, 1999 May 1.
Abstract:
We have studied the oscillations of the magnetization induced by commensurability between intervortex and CuO plane distances in YBa2Cu3Oy (y = 6.97 +/- 0.02) single crystals using high angular resolution magnetometry. A sharp peak in the temperature dependence of the amplitude of oscillations was found at T-f similar to 60 K. It is followed by other changes in the behavior of the amplitude and irreversible magnetization. We suggest that T-f reflects the vortex freezing transition from smectic to solid phase; the angular phase diagram is constructed. [S0163-1829(99)08517-3].
Title:
Critical dynamics at incommensurate phase transitions and NMR relaxation experiments
Authors:
Kaufmann BA. Schwabl F. Tauber UC.
Source:
Physical Review B-Condensed Matter. 59(17):11226-11243, 1999 May 1.
Abstract:
We study the critical dynamics of crystals which undergo a second-order phase transition from a high-temperature normal phase to a structurally incommensurate (IC) modulated phase. We give a comprehensive description of the critical dynamics of such systems, e.g., valid for crystals of the A(2)BX(4) family. Using an extended renormalization scheme, we present a framework in which we analyze the phases above and below the critical temperature T-I. Above T-I, the crossover from the critical behavior to the mean-field regime is studied. Specifically, the resulting width of the critical region is investigated. In the IC modulated phase, we consider explicitly the coupling of the order parameter modes to one-loop order. Here the Goldstone anomalies and their effect on measurable quantities are investigated. We show their relation with the postulated phason gap. While the theory can be applied to a variety of experiments, we concentrate on quadrupole-perturbed nuclear magnetic resonance (NMR) experiments. We find excellent agreement with these dynamical measurements and provide answers for some questions that arose from recent results. [S0163-1829(99)03417-7].
Title:
Infrared study of the low-temperature phase transitions in incommensurate Cs2HgBr4
Authors:
Jorio A. Echegut P. Speziali NL. Pimenta MA.
Source:
Physical Review B-Condensed Matter. 59(17):11251-11256, 1999 May 1.
Abstract:
In this work we present a complete infrared reflectivity study of the five low-temperature phases of Cs2HgBr4, including the incommensurate structure. Contrarily to the predictions by group theory, no extra modes are observed at the incommensurate (T-I) and lock-in (T-c) phase transitions, showing that the structural changes associated with the modulation does not distort significantly the HgBr4 tetrahedra. The absence of predicted modes and the presence of a low-frequency relaxation mechanism are discussed in terms of the orientational disorder of the HgBr4 tetrahedra about the pseudohexagonal axis. An important increase of the infrared dielectric constant epsilon(y), observed in the incommensurate phase, is ascribed to the existence of a layered structure of polar domain walls below T-I. [S0163-1829(99)00917-0].
Title:
Magnetic incommensurability in a doped Mott insulator
Authors:
Weng ZY. Sheng DN. Ting CS.
Source:
Physical Review B-Condensed Matter. 59(17):11367-11376, 1999 May 1.
Abstract:
In this paper we explore the incommensurate spatial modulation of spin-spin correlations as the intrinsic property of the doped Mott insulator, described by the t-J model. We show that such an incommensurability is a direct manifestation of the phase-string effect introduced by doped holes in both one- and two-dimensional cases. The magnetic incommensurate peaks of dynamic spin susceptibility in momentum space are in agree ment with the neutron-scattering measurement of cuprate superconductors in both position and doping dependence. In particular, this incommensurate structure can naturally reconcile the neutron-scattering and NMR experiments of cuprates. [S0163-1829(99)03017-9].
Title:
Jahn-Teller-like phase transition of TmPd3S4 around 200 K
Authors:
Kitagawa J. Matsuoka E. Takeda N. Ishikawa M.
Source:
Physical Review B-Condensed Matter. 60(22):R15028-R15030, 1999 Dec 1.
Abstract:
We report a Jahn-Teller-like phase transition in a synthesized metallic compound, TmPd3S4, of the cubic NaPt3O4 structure type. The transition causes a very large thermal hysteresis in the electrical resistivity between 120 and 230 K and a modulated structure with a modulation vector of about 1/8a* (a*: reciprocal-lattice unit vector) at lower temperatures which was revealed by a low-temperature x-ray powder diffraction. Analyses on the low-temperature specific heat and the magnetic susceptibility suggest that the compound becomes an exchange-induced moment antiferromagnet (T-N=1.1 K) by the nonmagnetic singlet ground state of Tm3+ ions. [S0163-1829(99)51146-6].
Title:
Quasicrystalline nature of quasicrystal surfaces: A photoemission study
Authors:
Naumovic D. Aebi P. Schlapbach L. Beeli C. Lograsso TA. Delaney DW.
Source:
Physical Review B-Condensed Matter. 60(24):R16330-R16333, 1999 Dec 15.
Abstract:
Differently prepared surfaces of quasicrystalline i-Al-Pd-Mn are analyzed using angle-resolved photoemission in the x-ray and ultraviolet range of photon energies. Depending on the preparation, we find both surfaces with crystalline structure and metallic character, and surfaces with quasicrystalline structural fingerprints and a suppressed density of states at the Fermi level, compatible with a pseudogap. [S0163-1829(99)51048-5].
Title:
Bending experiments on the xi '-(Al-Pd-Mn) quasicrystal approximant
Authors:
Klein H. Feuerbacher M. Schall P. Urban K.
Source:
Philosophical Magazine Letters. 80(1):11-18, 2000 Jan.
Abstract:
Single crystals of the quasicrystal approximant phase xi'-(Al-Pd-Mn) were deformed at a high temperature in three-point bending geometry. Two different mechanisms of plastic deformation were observed in this phaser one based on the motion of phason lines and the other based on dislocations. Line directions and Burgers vector directions of the dislocations were determined. The relative importances of the two mechanisms are discussed as a function of the sample orientation with respect to the bending geometry.
Title:
Thermal expansion of icosahedral Al-Pd-Mn and decagonal Al-Cu-Co quasicrystals
Authors:
Kajiyama K. Edagawa K. Suzuki T. Takeuchi S.
Source:
Philosophical Magazine Letters. 80(1):49-56, 2000 Jan.
Abstract:
Thermal expansion measurements have been performed by X-ray diffractometry on icosahedral Al-Pd-Mn (i-(Al-Pd-Mn)) in the temperature range between 10 and 700 K and on decagonal Al-Cu-Co (d-(Al-Cu-Co)) in the range between 100 and 750 K. The linear thermal expansion coefficient alpha(T) of i-(Al-Pd-Mn) is about half of that for the pure aluminium phase at room temperature and does not show a negative thermal expansion at low temperatures. The degree of anisotropy in the thermal expansion of d-(Al-Cu-Co) is small; the ratio of the average a between the tenfold periodic direction and a quasiperiodic direction perpendicular to it is 0.93 +/- 0.05. The Gruneisen parameter gamma(T) has been evaluated from the measured alpha(T). gamma for d-(Al-Cu-Co) is almost isotropic, similar to alpha. The gamma values for the two phases lie in the range between 1.5 and 1.8, which are comparable with those for conventional metallic crystals. They are almost constant over the temperature range studied.
Title:
Icosahedral nanophases in the Al-Mn-Ce system
Authors:
Manaila R. Popescu R. Jianu A. Constantin M. Devenyi A.
Source:
Journal of Materials Research. 15(1):56-62, 2000 Jan.
Abstract:
Nano-icosahedral phases were prepared by melt-spinning in the AlMnCe system (Al greater than or equal to 89 at.%). Ce-induced structure alterations are reported by x-ray diffraction for the icosahedral (i) AlMnCe phase. They comprise apparition of superstructure diffraction lines, due to chemical ordering in the 6-dimensional icosahedral lattice, which gradually changes from a simple to a face-centered (FCI) type. Also, strong anomalies of diffracted intensities, with reference to model FCI phases, support Ce preferential location on a special set of sites. Microstructure investigations show a nanodispersion of i-AlMnCe in an Al-rich matrix, suggesting a low nucleation barrier of this metastable phase in the melt.

Update: 28-Jan-2000

Title:
Study of R-phase transformation in a Ti-50.7at%Ni alloy by in-situ transmission electron microscopy observations
Authors:
Cai W. Murakami Y. Otsuka K.
Source:
(list of journals)
Materials Science & Engineering A-Structural Materials Properties Microstructure & Processing. 275(Special Issue SI):186-189, 1999 Dec 15.
Abstract:
The R-phase transformation in a Ti-50.7at%Ni alloy was investigated by in-situ transmission electron microscopy (TEM) observations using double-tilt cooling stages, and the incommensurability of 1/3 diffuse scattering in the process of the transformation was examined by using imaging plates. It is shown that the incommensurate diffuse scattering exists in the parent phase within a wide temperature range above the Rs temperature and that the incommensurability decreases with decreasing temperature. The R-phase transformation starts at the Rs temperature where the electrical resistance starts to increase and the R-phase is commensurate even in the state just after formation. (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
Ordered Al-Pd-Ru icosahedral quasicrystal and its crystalline approximants and their electrical resistivities
Authors:
Tamura R. Asao T. Tamura M. Takeuchi S.
Source:
Journal of Physics-Condensed Matter. 11(50):10343-10351, 1999 Dec 20.
Abstract:
In the Al-Pd-Ru system, a structurally ordered icosahedral phase has been successfully produced near the composition Al73Pd15RU12 by heat treatment at 1273 K for several hours. The x-ray diffraction patterns of the Al-Pd-Ru i-phase are very sharp, indicating that the i-phase is quite stable and that samples of high structural quality are attainable by appropriate heat treatment in this system. Prolonged annealing at 1273 K, however, results in phase transformation into the 1/0 cubic approximant (a = 1.5 nm). Also, we found the formation of a 2/1 cubic approximant phase (a = 2.0 nm) near the composition Al71Pd19Ru10 when samples were annealed at 1173 K for one hour. The temperature dependence of the resistivity of the i-phase is significantly large and the resistivity ratio R (R = rho(12K)/rho(300)) reaches as high as 2.5, comparing well to that seen in the ordered Al-Cu-Ru i-phase. The resistivity and its temperature dependence for the 2/1 approximant phase are quite similar to those for the i-phase, exhibiting a large resistivity ratio R similar to 1.6, in contrast with the metallic behaviour of the 1/0 cubic approximant phase. These results indicate that the characteristic length which determines the temperature dependence of the resistivity is somewhere between 1.5 and 2.0 nm and suggest that the long-range quasiperiodicity beyond the length scale is of less significance as far as the electrical properties are concerned.
Title:
Magnetic properties of AlPdMn approximant phases
Authors:
Hippert F. Simonet V. de Laissardiere GT. Audier M. Calvayrac Y.
Source:
Journal of Physics-Condensed Matter. 11(50):10419-10435, 1999 Dec 20.
Abstract:
We investigated the magnetic properties of the following approximants of quasicrystals in the Al(Si)-Pd-Mn system: two cubic compounds, 1/1-Al68Pd11Mn14Si7 and 2/1-Al70Pd24Mn6, and three orthorhombic compounds xi'-Al71.9Pd23.5Mn4.6, T-Al-73.1 Pd5.2Mn21.7, and T-Al78.5Pd4.9Mn16.6 NO magnetic Mn atoms are present in the 2/1 and xi' phases or in the Mn-poor T phase. In contrast, a fraction of the Mn atoms carry magnetic moments in the Mn-rich T phase in which a spin-glass transition occurs at 14 K, and in the 1/1 phase in which a ferromagnetic transition occurs at 8.8 K. The crystallographic sites responsible for the magnetism were identified From spin-polarized band-structure calculations; this allows us to discuss the origin of magnetism in both approximant and quasicrystal structures.
Title:
Quasi-elastic light scattering in betaine calcium chloride dihydrate (BCCD)
Authors:
Schmitt-Lewen M. Schaack G.
Source:
Journal of Physics-Condensed Matter. 11(50):10459-10473, 1999 Dec 20.
Abstract:
We report measurements of the temperature (40 K less than or equal to T less than or equal to 200 K) and polarization (z(yy)x, z(xz)x) dependence of the integrated intensities of quasi-elastically scattered laser light (lambda = 514.5 nm) in a wavenumber interval of 0 +/-3 cm(-1) around the Rayleigh line at the different phase transitions in single crystals of BCCD. Large anomalies (central peaks) are observed at the transitions into the ferroelectric, the various commensurate (c, c'), and the incommensurate phases. The widths of the anomalies on the temperature scale are large in the regions f quasi-harmonic modulation of the structure, but narrow and distinct in the region of square-wave modulation in the solitonic phase of BCCD, where also unusual shapes on the T-axis are observed. The scattering phenomena at low temperatures are interpreted hypothetically as due to fluctuations caused by the formation or rearrangement of domain walls (solitons) in the lattice near the transitions between commensurate phases and by the variation in soliton density. The c <-> c' transitions are of the order-disorder type.
Title:
Liquid-solid equilibria in the quasicrystalline regions of the Al-Pd-Mn phase diagram
Authors:
Klein H. Durand-Charre M. Audier M.
Source:
Journal of Alloys & Compounds. 296(1-2):128-137, 2000 Jan 10.
Abstract:
Phase equilibria were investigated in the Al-Pd-Mn phase diagram in the region where quasicrystals and approximant phases form. With respect to previous thermodynamic studies, the extents of the liquidus phase fields of several approximant phases are either established or precisely determined. In particular, compositional profiles across interfaces show the ternary character of the T(AlPdMn) and xi' phases which are close to the binary Al-Mn and AI-W limits respectively. It is pointed out that the relative stability of some of the phases involves very small energy differences leading to very long transformation times and the solidification of metastable phases. (C) 2000 Elsevier Science S.A. All rights reserved.
Title:
New RNiSn4 compounds (R=rare earth): crystal structure of new LuNiSn4 type, magnetic and transport properties
Authors:
Skolozdra RV. Mudryk JS. Akselrud LG. Fruchart D. Gignoux D. Pierre J. Romaka LP. Schmitt D.
Source:
Journal of Alloys & Compounds. 296(1-2):303-311, 2000 Jan 10.
Abstract:
A series of new RNiSn4 compounds (R=Gd-Tm, Lu) has been synthesized. The crystal structure of LuNiSn4 has been determined. It is a new structure type, described as a commensurate modulated structure with space group Ammm/(ddd) and lattice parameters a=4.386 Angstrom, b=27.942 Angstrom and c=4.353 Angstrom. The other investigated compounds have the same structure. Magnetization was measured in the temperature range 1.5-300 K, and, except for the Dy compound, the resistivity was studied between 4 and 300 K. Moreover, the specific heat of the Er and Lu compounds was studied between 1.2 and 30 K. All compounds with magnetic rare earths order antiferromagnetically below their Neel temperature, which ranges from 3 K (R-Tm) to 27 It (R=Gd). Below T-N, metamagnetic transitions are observed. In the compound with Er, the specific heat reveals that, immediately below T-N=8.8 K, there is a second transition at 8.5 K. The intermediate phase is likely a modulated structure. (C) 2000 Elsevier Science S.A. All rights reserved.
Title:
Neutron diffraction and magnetic studies of the NdRh2-xRuxSi2 system
Authors:
Baran S. Hofmann M. Jaworska-Golab T. Penc B. Zygmunt A. Szytula A.
Source:
Journal of Alloys & Compounds. 297(1-2):37-42, 2000 Feb 2.
Abstract:
The magnetic (x,T) phase diagram of the solid solution NdRh2-xRuxSi2 (ThCr2Si2-type of crystal structure) has been established based on the neutron diffraction data and supplemented by magnetometric data. A collinear antiferromagnetic order AFI described by the wave vector k=(0,0,1) changes with an increase of Ru concentration to a sine modulated with the wave vector k=(0,0,k(2)). For x=1.6 ferromagnetic order is observed. In the region 1.7 less than or equal to x less than or equal to 2.0 the ferromagnetic order at low temperatures changes with increasing temperature to a sine modulated structure described by the wave vector k=(k(x),k(x),0). (C) 2000 Elsevier Science S.A. All rights reserved.
Title:
Diffuse scattering from dodecagonal quasicrystals
Authors:
Lei JL. Wang RH. Hu CZ. Ding DH.
Source:
European Physical Journal B. 13(1):21-30, 2000 Jan.
Abstract:
General formulae for thermal diffuse scattering from quasicrystals are applied to the case of dodecagonal quasicrystals from corresponding elasticity theory. Contours of constant diffuse scattering intensity are illustrated. Unlike ordinary crystals, shapes of isointensity contours are much more complicated and vary even among the collinear Bragg spots. Diffuse scattering patterns in the plane perpendicular to a given zone axis are associated with corresponding specific elastic constants. Information about elastic constants can be extracted from quantitative analysis of diffuse scattering patterns.
Title:
Spectral properties of incommensurate charge-density wave systems
Authors:
Seibold G. Becca F. Bucci F. Castellani C. Di Castro C. Grilli M.
Source:
European Physical Journal B. 13(1):87-97, 2000 Jan.
Abstract:
The concept of frustrated phase separation is applied to investigate its consequences for the electronic structure of the high T-c cuprates. The resulting incommensurate charge density wave (CDW) scattering is most effective in creating local gaps in k-space when the scattering vector connects states with equal energy. Starting from an open Fermi surface we find that the resulting CDW is oriented along the (10)- and (or) (01)-direction which allows for a purely one-dimensional or a two-dimensional "eggbox type" charge modulation. In both cases the van Hove singularities are substantially enhanced, and the spectral weight of Fermi surface states near the M-points, tends to be suppressed. Remarkably, a leading edge gap arises near these points, which, in the eggbox case, leaves finite arcs of the Fermi surface gapless. We discuss our results with repect to possible consequences for photoemission experiments.

Update: 26-Jan-00

Title:
Low-temperature conductivity of Al70Pd22.5Re7.5
quasicrystals
Authors:
Wang CR. Lin ST.
Source:
Journal of the Physical Society of Japan. 68(12):3988-3993, 1999 Dec.
Abstract:
The metal-insulator (MI) transition in Al70Pd22.5Re7.5 quasicrystals with the resistivity ratio r = rho(4.2) K/rho(300) (K) ranging from 6 to 105 is identified by investigating the low-temperature conductivity and magnetoconductivity and analyzing the temperature behavior of Tli(T) = dln sigma(T)/dlnT(T) metallic samples near the M-I transition is found to vary as sigma(0) = sigma(0)(1 - r/r(c))(nu) with nu = 1 and critical resistivity ratio r(c) = 12.8 +/- 0.5. For weakly insulating Al70Pd22.5Re7.5 quasicrystals, the conductivity sigma(T) is seen to cross over from Mott's variable-range hopping dependence to the power-law temperature dependence.
Title:
Neutron diffraction study on the low-temperature phase
transitions in Rb2ZnBr4 under hydrostatic pressure
Authors:
Shigematsu H. Matsui T. Mashiyama H. Kubota M. Nishi M. Ohshima K.
Source:
(list of journals)
Journal of the Korean Physical Society. 35(Suppl S):S1426-S1429, 1999 Dec.
Abstract:
Under hydrostatic pressure, the low-temperature phases of Rb2ZnBr4 was investigated by neutron scattering. The pressure coefficient dT/dp at phase III-to-IV was 7 K/kbar, and -45 K/kbar at phase IV-to-V. Three soft phonon modes which contribute to the phase III-to-IV transition were observed at the S point under the pressure of about 0.7 kbar. The behavior of the modes was similar to that at atmospheric pressure. The extra extinction rule observed in phase IV was not affected by hydrostatic pressure. At high pressure, two high-order pseudo-commensurate phases characterized by wave vectors q(z) similar or equal to 3/11 and 4/15 were observed in addition to the already known stable commensurate ones of q(z) = 2/7 and 1/4.
Title:
Modulated structure in
phase II of CH3NH3PbCl3
Authors:
Kawamura Y. Mashiyama H.
Source:
Journal of the Korean Physical Society. 35(Suppl S):S1437-S1440, 1999 Dec.
Abstract:
Dielectric crystal of CH3NH3PbCl3 takes a cubic perovskite structure at high temperature phase, and performs successive transitions at low temperatures. Although the high temperature structure is isomorphous to the compounds in which halogen atoms are replaced by bromine or iodine, the low temperature structure has been reported to be different from others. In order to confirm the transition sequence and to investigate the transition mechanism, X-ray diffraction from the single crystal was observed by a four-circle diffractometer. In phase II, superstructure reflections were found newly, which were missed in the previous diffraction study on powder samples. One type of superstructure reflections indicates-cell doubling, while another one incommensurate structure of phase II. The ordering of methylammonium ion is discussed.
Title:
Dielectric study of the pressure effect on the structural
phase transitions in [P(CH3)(4)](2)CuBr4
crystal
Authors:
Gesi K.
Source:
Journal of the Korean Physical Society. 35(Suppl S):S1474-S1477, 1999 Dec.
Abstract:
Effect of hydrostatic pressure on the successive phase transitions in tetramethylphosphonium tetrabromocuprate, [P(CH3)(4)](2)CuBr4, was studied by dielectric measurements. The transition temperature (406 K at 0 MPa) from the incommensurate phase (phase II) to commensurate phase (III) linearly increases with increasing pressure with a slope of 0.23 K/MPa. The incommensuate II phase seems to disappear at about 250 MPa. The transition temperature from the commensurate phase (III) to the low-temperature monoclinic phase (IV) (197 K at 0 MPa) increases linearly with the slope of 0.060 K/MPa. Any evidence for the existence of pressure-induced phases was not observed. The results are compared with the pressure-effects on the phase transitions in corresponding tetramethylammonium compound of [N(CH3)(4)](2)CuBr4 and discussed.
Title:
Peak effect caused by compositional modulation in
superconducting (Hg,Pb)(Ba,Sr)-1223 single crystal
Authors:
Akao T. Lee SR. Suematsu H. Kurashima K. Bando Y. Yamauchi H.
Source:
Journal of Low Temperature Physics. 117(3-4):933-937, 1999 Nov.
Abstract:
We have discovered fish-tail phenomenon / peak effect in a (HgPb)(Ba,Sr)(2)Ca2Cu3O8+delta [(Hg,Pb)(Ba,Sr)-1223] single crystal. Microscopic analyses and observations were performed to elucidate the origin of peak effect in terms of the micro-structure of the (Hg,Pb)(Ba,Sr)-1223 single crystal. In a [001] ED pattern of the crystal, streaks were observed along <110> at each spot. Distortions were seen along <110> in HRTE-micrograph of the (001) plane, and a compositional modulation was clearly detected with respect to the Hg/Pb ratio along [110] with an average periodicity of similar to 18 nm. Such a spinodal-wave-like inhomogeneity in the local composition may yield mesoscopically distributed weak pinning centers which is most likely responsible for the appearance of peak effect.
Title:
Direct evidence for oxygen stabilization of icosahedral
phase during crystallization of
Zr65Cu27.5Al7.5 metallic glass
Authors:
Murty BS. Ping DH. Hono K. Inoue A.
Source:
Applied Physics Letters. 76(1):55-57, 2000 Jan 3.
Abstract:
The present letter reports the formation of the icosahedral phase during crystallization of amorphous Zr65-xCu27.5Al7.5Ox (x = 0.43% and 0.82%) alloys. Three-dimensional atom probe studies have revealed that the quasicrystalline phase is enriched in oxygen. This, together with the fact that no icosahedral phase forms at low oxygen level (0.14%), clearly establishes that the quasicrystalline phase in Zr-based metallic glasses is stabilized by oxygen. (C) 2000 American Institute of Physics. .
Title:
Structure determination by electron diffraction and HREM of
the incommensurate modulated
phase BaxCuO2 (0.67 <= x <= 0.70)
Authors:
Migliori A. Gemmi M. Calestani G. Belletti D. Matacotta FC. Dionigi C. Nozar P.
Source:
Physica C. 328(1-2):89-103, 1999 Dec 1.
Abstract:
We report the structure determination, by electron diffraction and high resolution electron microscopy, of two phases, Ba0.70CuO2 and Ba0.67CuO2, that characterise the BaxCuO2 (0.67 less than or equal to x less than or equal to 0.70) system where 13 K superconductivity has been recently found. Both phases show modulated structures that can be described in terms of composite crystals, resulting from the interpenetration of mutually incommensurate sublattices consisting of Barium atoms and infinite chains of edge sharing CuO4 planar units. The average Ba0.70CuO2 structure was solved by application of direct methods to electron diffraction data. Starting from this results and on the basis of diffraction patterns and high resolution images, the related Ba0.67CuO2 structure has been described in terms of interpenetration of three mutually incommensurate sublattices associated with twinning, Owing to the extreme complexity of this structure, only a qualitative model has been developed, which is, however, able to describe all the peculiar features of this unusual and interesting structure. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Uniform spectral properties of one-dimensional
quasicrystals, I. Absence of eigenvalues
Authors:
Damanik D. Lenz D.
Source:
Communications in Mathematical Physics. 207(3):687-696, 1999 Nov.
Abstract:
We consider discrete one-dimensional Schrodinger operators with Sturmian potentials. For a full-measure set of rotation numbers including the Fibonacci case, we prove absence of eigenvalues for all elements in the hull.
Title:
Determination of the modulated structure of
Sr14/11CoO3 through a (3+1)-dimensional space description and using
non-harmonic ADPs
Authors:
Gourdon O. Petricek V. Dusek M. Bezdicka P. Durovic S. Gyepesova D. Evain M.
Source:
Acta Crystallographica - Section B, Structural Science.
55(Part 6):841-848, 1999 Dec 1.
Abstract:
Sr14/11CoO3 (i.e. Sr14Co11O33, tetradecastrontium undecacobalt tritriacontaoxide), a new phase in the hexagonal perovskite SrxCoO3 system, has been prepared and its structure solved from single-crystal X-ray data within the (3 + 1)-dimensional formalism. Sr14/11CoO3 crystallizes in the trigonal symmetry, R (3) over bar m(00 gamma)0s superspace group with the following lattice parameters: a(s) = 9.508(2), c(s) = 2.5343(7) Angstrom, q = 0.63646(11)c* and V-s = 198.40(13) Angstrom(3). With the commensurate versus incommensurate test not being conclusive, the structure was considered as commensurate (P32 three-dimensional space group), but refined within the (3 + 1)-dimensional formalism to a residual factor R = 0.0351 for 47 parameters and 1169 independent reflections. Crenel functions were used for the oxygen and cobalt description and a Gram-Charlier expansion up to the third order of the atomic displacement parameter was employed for one Co atom. The structure is similar to that of Sr6/5CoO3, but With a different sequence of the octahedra and trigonal prism polyhedra along the [CoO3] chains. An interesting feature evidenced by the non-harmonic expansion is the displacement of the prismatic Co atoms from the site center, towards the prism rectangular faces.
Title:
Modulated structures of Cs2HgCl4: the 5a
superstructure at 185 K and the 3c
superstructure at 176 K
Authors:
Bagautdinov B. Pilz K. Ludecke J. van Smaalen S.
Source:
Acta Crystallographica - Section B, Structural Science.
55(Part 6):886-895, 1999 Dec 1.
Abstract:
Crystalline dicaesium mercury tetrachloride (Cs2HgCl4) is isomorphous with beta-K2SO4 (space group Pnma, Z = 4) in its normal phase at room temperature. On cooling a sequence of incommensurate and commensurate superstructures occurs, below T = 221 K with modulations parallel to a*, and below 184 K with modulations along c*. The commensurately modulated structures at T = 185 K with q = 1/5a* and at T= 176 K with q = 1/3c* were determined using X-ray scattering with synchrotron radiation. The structure at T = 185 K has superspace group Pnma(alpha, 0, 0)0ss with alpha = 0.2. Lattice parameters were determined as a = 5 x 9.7729 (1), b = 7.5276 (4) and c = 13.3727 (7) Angstrom. Structure refinements converged to R = 0.050 (R = 0.042 for 939 main reflections and R = 0.220 for 307 satellites) for the section t = 0.05 of superspace. The fivefold supercell has space group Pn2(1)a. The structure at T = 176 K has superspace group Pnma(0, 0, gamma)0s0 with gamma = 1/3. Lattice parameters were determined as a = 9.789 (3), b = 7.541 (3) and c = 3 x 13.418 (4) Angstrom. Structure refinements converged to R = 0.067 (R = 0.048 for 2130 main reflections, and R = 0.135 for 2382 satellite reflections) for the section t = 0. The threefold supercell has space group P112(1)/a. It is shown that the structures of both low-temperature phases can be characterized as different superstructures of the periodic room-temperature structure. The superstructure of the 5a-modulated phase is analysed in terms of displacements of the Cs atoms, and rotations and distortions of HgCl4 tetrahedral groups In the 3c-modulated phase the distortions of the tetrahedra are relaxed, but they are replaced by translations of the tetrahedral groups in addition to rotations.
Title:
Electron-phonon and spin-phonon coupling in NaV2O5: Charge fluctuations
effects
Authors:
Sherman EY. Fischer M. Lemmens P. van Loosdrecht PHM. Guntherodt G.
Source:
Europhysics Letters. 48(6):648-654, 1999 Dec.
Abstract:
We show that the asymmetric crystal environment, of the V site in the ladder compound NaV2O5 leads to a strong coupling of vanadium 3d electrons to phonons. This coupling causes fluctuations of the charge on the V ions, and favors a transition to a charge-ordered state at low temperatures. In the low temperature pha se the charge fluctuations modulate the spin-spin superexchange interaction, resulting in a strong spin-phonon coupling.
Title:
The Curie-Weiss behavior of heat capacity and dielectric constant in the
incommensurate phase of K2ZnCl4
Authors:
Ahn HY. Jeong SY. Jeong YH. Cho YC. Hwang YH.
Source:
Europhysics Letters. 48(6):667-671, 1999 Dec.
Abstract:
The Curie-Weiss behavior of heat capacity and dielectric constant was observed in the incommensurate phase of K2ZnCl4, as temperature is lowered toward the incommensurate-commensurate phase transition. The exponents obtained from the dielectric and heat capacity measurements were gamma = 1.01 + 0.05 and alpha = 0.99 + 0.05, respectively. The present results support the view on the evolution of the incommensurate phase that the incommensurate phase consists of regularly placed discommensurations, and the distance between discommensurations increases and eventually a transition to the commensurate phase occurs as temperature is lowered.
Title:
Planar and cluster structure of icosahedral
quasicrystals
Authors:
Bolliger B. Erbudak M. Vvedensky DD. Kortan AR.
Source:
(list of journals)
Czechoslovak Journal of Physics. 49(11):1531-1536, 1999 Nov.
Abstract:
Twofold-, threefold-, and fivefold-symmetry elements are observed in the near-surface region of the quasicrystal Al70Pd20Mn10 using a real-space imaging technique based on secondary-electron emission. The observed icosahedral point-group symmetry implies the presence of atomic clusters within the analyzed region of the solid. The same surface produces perfect low-energy electron diffraction patterns typical for well-defined crystallographic planes. We present a model which reconciles this dual structural nature of quasicrystals. Our model is constructed from an icosahedral seed followed by concentric symmetry-preserving "growth" to form the macroscopic solid.
Title:
Nesting properties and anisotropy of the Fermi surface of LuNi2B2C
Authors:
Dugdale SB. Alam MA. Wilkinson I. Hughes RJ. Fisher IR. Canfield PC. Jarlborg T. Santi G.
Source:
(list of journals)
Physical Review Letters. 83(23):4824-4827, 1999 Dec 6.
Abstract:
The rare-earth nickel borocarbides, with the generic formula RNi2B2C, have recently been shown to display a rich variety of phenomena. Most striking has been the competition between, and even coexistence of, antiferromagnetism and superconductivity. We have measured the Fermi surface (FS) of LuNi2B2C, and shown that it possesses nesting features capable of explaining some of the phenomena experimentally observed. In particular, it had previously been conjectured that a particular sheet of FS is responsible for the modulated magnetic structures manifest in some of the series. We report the first direct experimental observation of this sheet.
Title:
Reply to the comment by G. Coddens on 'Hierarchical porosity in real
quasicrystals'
Authors:
Mancini L. Janot C. Loreto L. Farinato R. Gastaldi J. Baruchel J.
Source:
(list of journals)
Philosophical Magazine Letters. 79(12):929-930, 1999 Dec.
Title:
Crystal structure determination of an
Al-Fe-Si-Be phase by convergent-beam electron diffraction
Authors:
Zheng JG. Vincent R. Steeds JW.
Source:
(list of journals)
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical
Properties. 79(11):2725-2733, 1999 Nov.
Abstract:
The crystal structure of Al-Fe-Si-Be intermetallic precipitates has been investigated by transmission electron microscopy and convergent-beam electron diffraction. The precipitates showed Chinese script morphology with the composition Al8Fe2SiBe. The crystal structure was bce with a = 1.234 nm, point group and Im(3) over bar (No. 204) space group. This phase is an approximant to the related icosahedral quasicrystalline phase. X-ray diffraction peaks published previously by Murali et al. (1994, Scripta metall. mater., 29, 1421) are reindexed and the role of Be atoms in crystal growth is briefly discussed.
Title:
Local atomic order in icosahedral Ti-Zr-Ni and hydrogenated Ti-Zr-Ni
quasicrystals
Authors:
Sadoc A. Kim JY. Kelton KF.
Source:
(list of journals)
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical
Properties. 79(11):2763-2772, 1999 Nov.
Abstract:
We report results from the first extended X-ray absorption fine-structure studies on icosahedral Ti53Zr27Ni20 and on icosahedral Ti45Zr38Ni17 which also contains 1.7 hydrogen atoms per metal atom. The experiments performed above the Ti K, Ni K and Zr K absorption edges have allowed the determination of the local order around titanium, nickel and zirconium atoms. Significant differences are observed between these two quasicrystalline alloys in the environments of titanium and zirconium atoms, with larger Zr-Ti and Zr-Zr separations in the hydrogenated sample, suggesting that hydrogen sits preferentially near zirconium atoms.
Title:
The plasticity of icosahedral quasicrystals
Authors:
Guyot P. Canova G.
Source:
(list of journals)
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical
Properties. 79(11):2815-2832, 1999 Nov.
Abstract:
A quantitative model of plastic deformation of icosahedral quasicrystals is established. It is based on shears occurring in planes of high atomic density via a dislocational activity. A single-slip dislocation friction stress is first derived on a microscopic basis and introduced into a viscoplastic Kocks-type constitutive law where the dislocation density is the single microstructural internal variable. Dislocations are assumed to be stored and annihilated dynamically during deformation, as in simple crystals. The specificity of quasicrystals with long-range but non-periodic atomic order is the introduction of a friction stress limiting the dislocation mobility which decreases with increasing strain, as evidenced for instance by molecular dynamic simulations. Such a constitutive plastic law leads to shear localization and strain softening. The mean-field single-slip behaviour is then introduced in a multiple-slip state, where quasilattice rotation and activation of the various slip systems are calculated. The role of the quasicrystal symmetry relating the available slip systems is examined as a function of the quasilattice orientation. The results and consequences of the model are compared with experimental data on single icosahedral Al-Mn-Pd quasicrystals deformed at high temperatures at a constant strain rate or constant stress in uniaxial compression and discussed.
Title:
Molecular dynamics simulations of crack propagation in
quasicrystals
Authors:
Trebin HR. Mikulla R. Stadler J. Schaaf G. Gumbsch P.
Source:
(list of journals)
Computer Physics Communications. 122(Special Issue SI):536-539, 1999 Sep-Oct.
Abstract:
The mechanism of plastic deformation in quasicrystals is dislocation motion, Dislocations leave in their wake a phason wall where the structure is weakened. Cracks emit dislocations and follow the phason wall. These processes are revealed by large scale molecular dynamics simulations employing the package IMD. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Disorder and compositional variation in the lillianite homologous series
Authors:
Pring A. Jercher M. Makovicky E.
Source:
(list of journals)
Mineralogical Magazine. 63(6):917-926, 1999 Dec.
Abstract:
High resolution transmission electron microscopy studies on the lillianite group minerals from the Ivigtut cryolite deposit, Ivigtut, South Greenland revealed the existence of disordered intergrowths of lillianite/gustavite-like blacks (N = 4) and heyrovskyite-like (N = 7) structural blocks. One disorder sequence is examined in detail, which gave an average homologue number N = 4.92 corresponding to a composition of Pb3.92-2x Bi2+xAgxS6.92 With x approximate to 1.2. An Axial Next-Nearest Neighour Ising model was used to follow the fluctuations in the average homologue number N across the crystal. This yielded compositional fluctuations of the order of 70-170 Angstrom over a 1800 Angstrom region of the crystal, with a 202 Angstrom lamella of ordered vikingite. Trends in the randomness of the gustavite-vikingite intergrowth were evaluated and the dominant slab sequence was found to be 4,4,4,7 and 4,4,7,7, suggesting that some longer period homologues may be stable. A number of defects were noted in which changes in slab widths were accommodated. The origin of these partially ordered/disordered lillianite homologues is discussed.
Title:
Exact renormalization analysis of a self-similar phase
diagram with upsilon points for all Ising model
Authors:
Sasaki K.
Source:
(list of journals)
Journal of the Physical Society of Japan. 68(11):3562-3574,
1999 Nov.
Abstract:
The ground-state phase diagram is analyzed for a one-dimensional Ising model with long range interaction in the presence of uniform and staggered magnetic fields; the interaction is antiferromagnetic and its strength decays exponentially with distance. The exact renormalization formulas for the interactions between interfaces are derived, which is used to calculate the phase diagram hierarchically. The phase diagram is self-similar, and it contains upsilon points and del il's staircases; this agrees with the result of Aubry, Axel and Vallet [J, Phys. C 18 (1985) 753] for an equivalent model obtained by a different method. A simple "phase rule" presenting what kind of phases appear and how they are located in the phase diagram is derived. The application of this rule to the phase diagram of betaine calcium chloride dihydrate is discussed.
Title:
Modulated structure of La1/3-xLi3xNbO3 0 <=
x <= 0.06 perovskite-related materials
Authors:
Garcia-Martin S. Alario-Franco MA.
Source:
(list of journals)
Journal of Solid State Chemistry. 148(1):93-99, 1999 Nov 15.
Abstract:
The microstructure of samples of different composition belonging to the cation-deficient La1/3-xLi3xNbO3, 0 less than or equal to x less than or equal to 0.06, solid solution has been studied by selected area electron diffraction and high resolution transmission electron microscopy. The materials show a perovskite-related structure with basic lattice parameters a similar to root 2a(p), b similar to root 2a(p), c similar to 2a(p), Besides, short-range cation ordering gives place to a larger unit cell of dimensions a similar to 3.5 root 2a(p), b similar to root 2a(p), c similar to 4a(p). The lithium-containing compunds also present a complex microdomain structure of the octahedra tilting framework. (C) 1999 Academic Press.
Title:
Large wavelength magnetic modulation in (0001)Tb films
Authors:
Dufour C. Dumesnil K. Mougin A. Mangin P. Hennion M.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(44):497-503, 1999
Nov 8.
Abstract:
A large wavelength magnetic modulation, which has never been observed up to now, has been evidenced by neutron scattering experiments in (0001) terbium single crystal films. With decreasing temperature, this magnetic arrangement appears when the helical one vanishes and before the long range ferromagnetic order sets in. The large wavelength magnetic modulation is squared and it varies between 180 and 700 Angstrom, depending on the temperature and the film thickness. We assume that it is due to the stacking of ferromagnetic blocks whose net magnetization points along a basal plane direction and rotates by a given angle between two consecutive blocks. The occurrence of this phase seems to be independent of the strains induced by epitaxy but it would be related to the lattice clamping between epitaxied layers. A temperature-magnetic field phase diagram of a terbium film is presented.
Title:
A study on the specific heat of a one-dimensional hexagonal
quasicrystal
Authors:
Fan TY.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(45):L513-L517, 1999
Nov 15.
Abstract:
Extending the Debye approach for studying the specific heat of a crystal to a quasicrystal, this study gives the formula of the specific hear of a one-dimensional hexagonal quasicrystal.
Title:
Precipitation of icosahedral phase from a supercooled liquid
region in Zr65Cu7.5Al7.5Ni10Ag10 metallic glass
Authors:
Saida J. Matsushita M. Zhang T. Inoue A. Chen MW. Sakurai T.
Source:
(list of journals)
Applied Physics Letters. 75(22):3497-3499, 1999 Nov 29.
Abstract:
The formation of an icosahedral phase from the rapidly quenched Zr65Cu7.5Al7.5Ni10Ag10 metallic glass was confirmed and the kinetics of the precipitation upon isothermal annealing in the supercooled liquid region were examined by differential scanning calorimetry. Based on the kinetic analysis, it is clarified that the precipitation in the supercooled liquid region takes place by an interfacial controlled growth with a nearly steady-state nucleation rate. The Arrhenius plot between effective time lag, tau, of nucleation and isothermal annealing temperature yields a single linear relation, in which the activation energy for nucleation is evaluated to be 366 kJ/mol. It is concluded that the transformation of amorphous to quasicrystal proceeds by a homogeneous nucleation mode, which is different from those of Pd-U-Si and Al-Cu-V quasicrystals arising from an inhomogeneous distribution of quenched-in nuclei. (C) 1999 American Institute of Physics. .
Title:
Thermal expansion of quasicrystalline Al70.3Pd21.7Mn8.0 in
the temperature range 15-300 K
Authors:
Kupsch A. Paufler P.
Source:
(list of journals)
Zeitschrift fur Kristallographie. 214(11):681-683, 1999.
Abstract:
The lattice parameter a of face-centred icosahedral Al70.3Pd21.7Mn8.0 was determined using X-ray pow der diffraction in the temperature range between 15 K and 300 K. Fitting its temperature dependence by a polynomial of second order a linear thermal expansion coefficient alpha(T)= 1.19(15).10(-6) K-1 + 4.40(21).10(-8) K-2 T has been derived. After long-period low temperature ageing the appearance of an additional reflection at /k/ = 1.716 Angstrom(-1) was observed.
Title:
Symmetry of the atomic displacement field at the
quasicrystal-to-crystal
phase transition
Authors:
Rochal SB.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(18):12687-12691, 1999
Nov 1.
Abstract:
For octagonal and dodecagonal cases it is shown that the field of the atomic displacements between quasicrystal (QC) and crystal positions is completely determined by a linear continuous inhomogeneous strain of a quasicrystalline a lattice related to the initial QC structure by a similarity transformation. The translational symmetry of superstructure arising at the QC-to-crystal phase transition coincides with that of the Q lattice. This superstructure displays itself as a system of ordered defects. .
Title:
New compounds In(3)Ti(2)AO(10), In6Ti6BO22, and their solid solutions (A :
Al, Cr, Mn, Fe, or Ga; B : Mg, Mn, Co, Ni, Cu, or Zn): Synthesis and
crystal structures
Authors:
Brown F. Kimizuka N. Michiue Y. Mohri T. Nakamura M. Orita M. Morita K.
Source:
(list of journals)
Journal of Solid State Chemistry. 147(2):438-449, 1999 Nov
1.
Abstract:
New compounds, In(3)Ti(2)AO(10) (A: Al, Cr, Mn, Fe, or Ga) and In6Ti6BO22 (B: Mg, Mn, Co, Ni, Cu, or Zn) were synthesized at and above 1000 degrees C in air through solid-state reactions among the constituent cation oxide powders. They are isostructural with the monoclinic and/or orthorhombic In3Ti2FeO10 having a pyrochlore-related crystal structure with a commensurate or incommensurate modulated structure. The high-temperature phase is orthorhombic, and the low-temperature phase is monoclinic. The lattice constants of In(3)Ti(2)AO(10) are as follows: In3Ti2AlO10 (1200 degrees C): a(Angstrom)= 5.833(2), b(Angstrom)= 3.371(2), and c(Angstrom) = 12.060(6); In3Ti2AlO10 (1100 degrees C): a(Angstrom) = 5.8368(7), b(Angstrom) = 3.3721(4), c(Angstrom) = 6.3402(8), and beta(degrees) = 107.87(1); In3Ti2CrO10 (1200 degrees C): a(Angstrom) = 5.9246(8), b(Angstrom) = 3.3562(5), c(Angstrom) = 6.3546(9), and beta(degrees) = 108.10(1); In3Ti2GaO10 (1200 degrees C): a(Angstrom) = 5.861(2), b(Angstrom) = 3.385(1), and c(Angstrom) = 12.094(4); In3Ti2GaO10 (1000 degrees C): a(Angstrom) 5.8742(9), b(Angstrom) = 3.3828(5), c(Angstrom) = 6.353(1), and beta(degrees) = 107.87(1). In3Ti2AlO10 and In3Ti2GaO10 are polymorphic. The lattice constants of In6Ti6BO22 are as follows: In6Ti6MgO22 (1200 degrees C): a(Angstrom) = 5.9236(7), b(Angstrom) = 3.3862(4), c(Angstrom) = 6.3609(7), and beta(degrees) = 108.15(1); In6Ti6MnO22 (1200 degrees C): a(Angstrom) = 5.9361(9), b(Angstrom) = 3.4031(5), c(Angstrom) = 6.3435(10), and beta(degrees) = 108.26(1); In6Ti6CoO22 (1200 degrees C): a(Angstrom) = 5.9243(5), b(Angstrom) = 3.3841(3), c(Angstrom) = 6.3495(6), and beta(degrees) = 108.18(1); In6Ti6NiO22 (1200 degrees C): a(Angstrom) = 5.9191(6), b(Angstrom) = 3.3729(3), c(Angstrom) = 6.3568(6), and beta(degrees) = 108.13(1); In6Ti6CuO22 (1000 degrees C): a(Angstrom) = 5.916(2), b(Angstrom) = 3.379(1), and c(Angstrom) = 12.029(4); In6Ti6ZnO22 (1200 degrees C): a(Angstrom) = 5.9223(6), b(Angstrom) = 3.3830(3), c(Angstrom) = 6.3576(6), and beta(degrees) = 108.16(1). In6Ti6BO22 (B: Mg, Mn, Co, Ni, or Zn) are monoclinic and In6Ti6CuO22 is orthorhombic. Solid solutions mere synthesized in between In(3)Ti(2)AO(10) (A: Al, Cr, Mn, Fe, or Ga) and In6Ti6BO22 (B: Mg, Mn, Co, Ni, Cu or Zn), and their lattice constants mere determined. Temperature in the parenthesis means synthesis temperature, and all the lattice constants,were measured at room temperature. The relationship between the unit cells of In(3)Ti(2)AO(10), In6Ti6BO22, their solid solutions, and the constituent cation elements of A and B are discussed in terms of their tendency for site preference. (C) 1999 Academic Press.
Title:
Incommensurate nuclear and magnetic
structure of the oxygen-deficient perovskites
(Ba2-3xBi3x-1)(Fe2xBi1-2x)O2+3/2x (0.43 <= x <= 0.50)
Authors:
Boullay P. Grebille D. Hervieu M. Raveau B. Suard E.
Source:
(list of journals)
Journal of Solid State Chemistry. 147(2):450-463, 1999 Nov
1.
Abstract:
The actual nuclear and magnetic structures of the oxygen perovskites [Ba2-3xBi3x-1] [Fe2xBi1-2x]O2+3x/2 (0.40 < x less than or equal to 0.50) were studied combining XRPD and NPD data. The incommensurate modulated structures of the members x=0.45 and x = 0.48 were determined in the superspace formalism. It is shown that bismuth and barium cations are not distributed at random over a single site but exhibit a particular ordering which can be described by a substitutional modulation. In such structures, the displacement of the cation from its average position is much larger for bismuth than for barium. The modulated fourfold superstructure of Bi2Ba2Fe4O11 (x = 0.50), "a(p) x a(p) x 4a(p)" is closely related to those of incommensurate phases, with a "Bi1/4Ba3/4Ba1/4" ordering of the cations. Nevertheless, a certain disordering of these cations and oxygen vacancies are evidenced in the superstructure. The antiferromagnetic (AF) ordering is the same for all the members: iron spins are antiferromagnetically coupled along [110] and along [001] forming (001) AF planes. (C) 1999 Academic Press.
Title:
On the indexing and reciprocal space of icosahedral
quasicrystal
Authors:
Singh A. Ranganathan S.
Source:
(list of journals)
Journal of Materials Research. 14(11):4182-4187, 1999 Nov.
Abstract:
Important features of the icosahedral reciprocal space have been brought out. All reciprocal vectors up to sixth generation (by addition of icosahedral vectors) have been considered. Some more relationships for indexing the icosahedral phase are derived, and it is shown that the zone law using Cahn indices is also analogous to that valid for crystals. All important vectors, i.e., up to fourth generation and sixth generation, have been identified. Poles of all these vectors have been determined and shown to be one of the zone axes formed by these vectors. The types of indices that the planes and axes will have in three-dimensional and six-dimensional coordinates is discussed.
Title:
Indexing approximants of icosahedral quasicrystals
Authors:
Quiquandon M. Katz A. Puyraimond F. Gratias D.
Source:
(list of journals)
Acta Crystallographica - Section a - Foundations of
Crystallography. 55(Part 6):975-983, 1999
Nov 1.
Abstract:
It is well known that the crystallography of approximants is directly related to that of the parent quasicrystal, once its unit-cell vectors are identified as parallel projections of certain N-dimensional lattice nodes A(i). Derived here are explicit simple relations for calculating the shear matrices epsilon and the related crystallographic properties of the corresponding approximants, including diffraction indexing and the determination of the lattice in perpendicular space. Applied to low-dimensional approximants, the derivation shows that the systematic 'accidental' extinction rules observed in the pentagonal phases are generic extinctions that are due to the geometrical properties of the projected 1D lattice and are independent of the actual model of the quasicrystal.
Title:
Comment on "Tunneling spectroscopy in AlNiCo decagonal
quasicrystals"
Authors:
Berger C. Mayou D. Grenet T. Ovadyahu Z.
Source:
(list of journals)
Physical Review Letters. 83(19):3968, 1999 Nov 8.
Title:
Comment on "Tunneling spectroscopy in AlNiCo decagonal
quasicrystals" - Li Guohong et al. reply
Authors:
Li GH. He HF. Wang YP. Lu L. Li SL. Jing XN. Zhang DL.
Source:
(list of journals)
Physical Review Letters. 83(19):3969, 1999 Nov 8.
Title:
Incommensurate modulation in
phase separating binary paraffin mixtures
Authors:
Gilbert EP.
Source:
(list of journals)
Physical Chemistry Chemical Physics. 1(22):5209-5214, 1999.
Abstract:
Small-angle neutron and X-ray scattering (SANS and SAXS) has been measured on C-28-C-36 mixtures quenched from the melt for compositions varying from 15.6:1 to 1:5. Satellite peaks are observed in the SAXS whose offset in Q (where Q is the scattering vector), relative to Bragg diffraction peaks associated with the average lamellar structure, are composition dependent. The offset is close to the position of the most intense peak observed in the SANS. A model for the phase separated structure is suggested based on correlated positional and substitutional disorder.
Title:
Magnetic structures of Tb2Co3Si5 and Dy2Co3Si5 compounds
Authors:
Kolenda M. Hofmann M. Penc B. Starowicz P. Szytula A.
Source:
(list of journals)
Journal of Alloys & Compounds. 292(1-2):45-50, 1999 Nov 15.
Abstract:
Neutron diffraction studies indicate that polycrystalline R2Co3Si5 (R = Tb and Dy) intermetallic compounds with monoclinic Lu2Co3Si5-type crystal structure have different magnetic structures. Tb2Co3Si5 has a sine wave modulated structure described by the wave vector k = (0, 0.0817(6), 0) in the temperature range 1.6 K-T-N = 22.6 K while for Dy2Co3Si5 a collinear antiferromagnetic structure is observed between 1.5 K and T-N = 21.9 K, For R = Tb the magnetic moment is parallel to the c-axis while for R = Dy it forms an angle of 25.8 degrees with the c-axis. (C) 1999 Elsevier Science S.A. All rights reserved.

Update: 26-Nov-99

Title:
Indexing approximants of icosahedral quasicrystals
Authors:
Quiquandon M. Katz A. Puyraimond F. Gratias D.
Source:
(list of journals)
Acta Cryst. (1999). A55, 975-983
Abstract:
A method is derived from indexing the diffraction patterns of approximant structures from the N-dimensional indexing of the parent quasicrystal. Examples are given for the case of the approximant of the icosahedral phases with special emphasis on the origin of the so-called `systematic accidental' extinctions observed in pentagonal phases.
Title:
Thermal expansion of quasicrystalline Al70.3Pd21.7Mn8.0 in the temperature range 15--300 K 681
Authors:
Kupsch A. Paufler P.
Source:
(list of journals)
Zeitschrift fur Kristallographie. 214(11):681-683, 1999.
Abstract:
The lattice parameter a of face-centred icosahedral Al70.3Pd21.7Mn8.0 was determined using X-ray powder diffraction in the temperature range between 15 K and 300 K. Fitting its temperature dependence by a polynomial of second order a linear thermal expansion coefficient a(T) = 1.19(15) · 10-6K-1+4.40(21) · 10-8 K-2 T has been derived. After long-period low temperature ageing the appearance of an additional reflection at |k|= 1.716 Å-1 was observed.
Title:
Crystal optical studies of lithium tetraborate
Authors:
Kushnir OS. Burak YV. Bevz OA. Polovinko II.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(42):8313-8327, 1999
Oct 25.
Abstract:
Using the HAUP-type universal polarimeter and the Senarmont technique, detailed crystal optical studies of Li2B4O7, lithium tetraborate, are carried out. It is shown that the optical indicatrix rotation and the optical activity are absent from the crystal, in accordance with symmetry considerations. Measurements of optical birefringence reveal the existence of a regular staircase-like temperature behaviour in the whole range under investigation (290-480 K), a hysteresis character of the birefringence under cycling temperature and a pronounced thermooptical memory effect. The origins of the above phenomena are analysed, in particular the possible influence of the pyroelectric effect and systematic errors of the optical equipment. A conclusion is drawn that the main features of the birefringence are well explained by an incommensurately modulated superstructure which is at present a matter of debate. The peculiarities of the optical properties of lithium tetraborate are compared with those of incommensurate crystals known from the literature.
Title:
Synchrotron X-ray study of the q-fold quasicrystalline
symmetry of the smectic C twist grain boundary phase
(TGB(c))
Authors:
Barois P. Heidelbach F. Navailles L. Nguyen HT. Nobili M. Petit M. Pindak R. Riekel C.
Source:
(list of journals)
European Physical Journal B. 11(3):455-462, 1999 Oct.
Abstract:
We report the first X-ray scattering investigation of spatial variations of the q-fold quasicrystalline symmetry (so-called commensurability) of well-aligned TGB(c) samples. A spatial resolution of 20 x 40 mu m(2) was achieved using the ESRF microfocus beamline. The liquid crystal samples, contained between glass plates which were either parallel or in a wedge geometry, were scanned in order (i) to probe the mosaicity and (ii) to continuously change the balance between surface and volume effects. In the case of parallel plate cells, commensurability was observed everywhere throughout the sample, hence ruling out possible effects of mosaicity to explain the q-fold symmetry of the diffraction patterns previously reported when probed with a spatial resolution of 1 x 1 mm(2) in rotating anode experiments. In the case of wedge cells, the evolution of X-ray patterns with thickness suggested that commensurate lockin occurs for sufficiently thick samples with a width that is statistical.
Title:
Electronic properties of quasiperiodic Fibonacci chain
including second-neighbor hopping in the tight-binding model
Authors:
Ghosh A. Karmakar SN.
Source:
(list of journals)
European Physical Journal B. 11(4):575-582, 1999 Oct.
Abstract:
We present an exact real-space renormalization group (RSRG) scheme for the electronic Green's functions of one-dimensional tight-binding systems having both nearest-neighbor and next-nearest-neighbor hopping integrals, and determine the electronic density of states for the quasiperiodic Fibonacci chain. This RSRG method also gives the Lyapunov exponents for the eigenstates. The Lyapunov exponents and the analysis of the flow pattern of hopping integrals under renormalization provide information about the nature of the eigenstates. Next we develop a 4 x 4 transfer matrix formalism for this generalized tight-binding system, which enables us to determine the wave function amplitudes. Interestingly, we observe that like the nearest-neighbor tight-binding Fibonacci chain, the present generalized tight-binding system also have critical eigenstates, Cantor-set energy spectrum and highly fragmented density of states. It indicates that these exotic physical properties are really the characteristics of the underlying quasiperiodic structure.
Title:
Wavelet analysis of a quasiperiodic tiling with fivefold
symmetry
Authors:
Antoine JP. Jacques L. Twarock R.
Source:
(list of journals)
Physics Letters A. 261(5-6):265-274, 1999 Oct 18.
Abstract:
We determine all (statistical) rotation-dilation symmetries of a planar quasiperiodic tiling with fivefold symmetry, with a two-dimensional continuous wavelet transform, using a modified Cauchy wavelet and the scale-angle measure. The tiling is constructed via an affine extension of the Coxeter group H-2 and its statistical symmetries were unknown. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Title:
Evidence of a mixed-valence state for europium in the misfit layer compound
[(EuS)(1.5)](1.15)NbS2 by means of a superspace structural
determination, Mossbauer spectroscopy, and magnetic measurements
Authors:
Cario L. Lafond A. Palvadeau P. Deudon C. Meerschaut A.
Source:
(list of journals)
Journal of Solid State Chemistry. 147(1):58-67, 1999 Oct.
Abstract:
The complete structure of the misfit layer compound [(EuS)(1.5)](1.15)NbS2 is described as a (3+1)-dimensional intergrowth compound with two modulated subsystems (v = 1, 2, for NbS2 and EuS, respectively) which have the (a(v2)*, a(v3)*) reciprocal-lattice plane in common. A superspace embedding follows from four reciprocal-lattice vectors given by a(1)* = a(11)*, a(2)* = a(12)*, a(3)* = a(23)* and a(4)* = a(21)*. The symmetry is given by the superspace group G(s)=Fm2m (alpha 00) with modulation wave vector q = a(21)* = alpha a(11)* (alpha = 0.5768(1)). The structure of this composite compound is built up of an alternated sequence of two different types of slabs (i.e., NbS2 (H-part) and EuS (e-part)), stacked along the c direction. The e-part is a three-atom-thick layer (EU2S2-Eu1S1-Eu2S2), The NbS2 subsystem has cell parameters a(11) = 3.3241(4)Angstrom, a(12) = 5.7841(5)Angstrom, and a(13) = 14.816(2)Angstrom, with space group Cm2m. The EuS subsystem has lattice parameters a(21) = 5.7628(5)Angstrom, a(22) = 5.7841(5) Angstrom, and a(23) = 29.632(4) Angstrom, with space group Fm2m. Refinements on 1721 unique reflections converged to R = 3.58% (R-w = 4.75%) on a modulated structure model with 50 parameters. The largest modulation amplitudes occur on the outer Eu2 atoms. A bond-valence calculation using results from this structure determination shows that Eu atoms on the exterior sides (Eu2) of the EuS slab are in the +11 oxidation state while inner Eu atoms (Eu1) are at the +III state. Mossbauer and magnetic measurements confirm the mixed-valence (Eu2+/Eu3+) state of this compound. A ferromagnetic long-range order appears below 7 K. (C) 1999 Academic Press.
Title:
Structure of composites A(1+x) (A ' B-x(1-x))O-3 related to
the 2H hexagonal perovskite: relation between composition and
modulation
Authors:
Perez-Mato JM. Zakhour-Nakhl M. Weill F. Darriet J.
Source:
(list of journals)
Journal of Materials Chemistry. 9(11):2795-2808, 1999.
Abstract:
An idealized structural model is proposed for materials closely related to the 2H hexagonal perovskite and with general formula A(3n+3m)A(n)'B3m+nO9m+6n {or A(1+x)(A(x)'B1-x)O-3, x=[0, 1/2]}. The structures of all these compounds, considered as commensurate or incommensurate modulated composites, can be described in a first approximation by a unique structure in the superspace formalism with occupational Crenel functions and sawtooth displacive modulations along the trigonal axis. The structural modulation has only two variable parameters: the modulation wave vector or misfit parameter, which is fixed by the compound composition, and the height difference between the octahedra and triangular prisms of O-6 present in the trigonal [A',B]O-3 columns of the structure. Just by varying these parameters, the basic structural features of any compound with arbitrary composition parameter x are reproduced, including the two limiting cases ABO(3) (2H perovskite) and A(3)A'BO6. For instance, the sequence of octahedra and prisms along the [A',B]O-3 columns can be considered a generalized Fibonacci chain and its dependence on composition follows a Farey tree rule which comes out directly from the model. A comparison with available experimental data, and in particular with some fully determined structures, demonstrates the soundness of the proposed scheme as a reference for such structures and the best starting point for their refinement. The model, although developed within the superspace formalism, is closely related to the polytype layer picture in direct space. The present structural analysis constitutes a new example of the efficiency of the 4-dimensional superspace formalism for describing in a unified form the structures of so-called 'composition flexible' systems.
Title:
Microindentation of Al-Cu-Fe icosahedral quasicrystal
Authors:
Giacometti E. Baluc N. Bonneville J. Rabier J.
Source:
(list of journals)
Scripta Materialia. 41(9):989-994, 1999 Oct 8.
Title:
Comparing different approaches to model the atomic structure
of a ternary decagonal quasicrystal
Authors:
Wittmann R.
Source:
(list of journals)
Zeitschrift fur Kristallographie. 214(9):501-505, 1999.
Abstract:
It is shown that the covering approach with a single decagonal prototile can be transformed into a hexagon, boat and star tiling. Particularly the atomic decoration recently proposed by Cockayne and Widom (Phys. Rev. Lett. 81 (1998) 598-601) as a structure model for the decagonal phase is investigated. There, conflicts with the prototile approach arise which are due to specific peculiarities of the decoration. The above model is compared with recent experimental images which give strong support to its main features, but contradict competing structure proposals. The implications for the stabilization mechanism are discussed.
Title:
High-resolution electron microscopy of a modulated
structure in InMO3(ZnO)m (M = In, Fe, Ga, and Al; m =
integer): effect of solid solution formation
Authors:
Li C. Bando Y. Nakamura M. Kimizuka N.
Source:
(list of journals)
Zeitschrift fur Kristallographie. 214(9):528-533, 1999.
Abstract:
The structure of InMO3(ZnO)(m) (M = In, Fe, Ga, and Al; m = integer) is built from InO21- (In-O) and MZnmOm+l1m (M/Zn-O) layers stacked alternately A modulated structure of these compounds results from the ordering of M ions in the M/Zn-O layers. The modulated structures of InMO3(ZnO)(13) (M = In(0.5)A0.5; A = Fe, Ga, and Al), a solid solution of InInO3(ZnO)(13) and InMO3(ZnO)(13) (M =Fe, Ga, and Al), have been studied by high-resolution electron microscopy. The main and satellite spots of the electron diffraction patterns are indexed as ha* + kb* + lc* + mq by using the four dimensional superspace group approach. Based on the crystal system of the basic structure and the modulation wave vector q, the electron diffraction patterns are classified according to three categories with typical parameters: (1) monoclinic unit cell of a = 0.57nm, b = 0.33nm, c = 4.0nm, beta = 93 degrees, and q = b*/18.1; (2) monoclinic unit cell of a = 0.57nm, b = 0.33nm, c = 4.0nm, beta = 93 degrees, and q = b*/22.5 + c*/2; (3) triclinic unit cell of a = 0.57 nm, b = 0.33 nm, c = 4.0 nm, alpha = 95 degrees, beta = 95 degrees, gamma = 30 degrees, and q = a*/12.1 + b*/18.1 + c*/32.3. Among these, the first is the same as that of their constituent compounds In2O3(ZnO)(13) and InMO3(ZnO)(13) (M = Fe, and Ga), while the second and the third are different. In high-resolution image, the modulated structure appears as zig-zag contrast within the M/Zn-O layers. The periodicity of this zig-zag contrast along the M/Zn-O layer in InMO3(ZnO)(13) (M = In(0.5)A(0.5); A = Fe, Ga, and Al) is between those of InInO3(ZnO)(13) and InMO3(ZnO)(13) (M = Fe, Ga, and Al).
Title:
Fracton superconductivity in quasicrystals - a theoretical
possibility suggested by experiment
Authors:
Moulopoulos K. Cyrot-Lackmann F.
Source:
(list of journals)
Physics Letters A. 261(1-2):119-124, 1999 Oct 4.
Abstract:
Scattering of electrons due to fractons can result in a resistivity that decreases with temperature. Such a behavior also appears in real quasicrystalline materials. If this is then attributed to effective fracton scattering, fracton-superconductivity would be theoretically possible. Ey fitting with the scattering result the experimental resistivity data for the AlPdMn quasicrystal, we estimate the corresponding T-c. This effective fracton interpretation, not unexpected for a self-similar system, is also found consistent with other experiments on thermal and acoustic properties of the AlPdMn quasicrystal. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Title:
Structural modulations and phase
transitions in beta-eucryptite: an in-situ TEM study
Authors:
Xu H. Heaney PJ. Bohm H.
Source:
(list of journals)
Physics & Chemistry of Minerals. 26(8):633-643, 1999 Sep.
Abstract:
Beta-eucryptite as grown by the flux method has been investigated by in-situ cold- and hot-stage transmission electron microscopy (TEM). Using electron diffraction and dark-field TEM imaging, we found no evidence for the merohedral twinning that accompanies structural collapse at the beta-to-alpha-quartz transition, suggesting a true hexagonal symmetry for the aluminosilicate framework of beta-eucryptite. Selected-area electron diffraction (SAED) patterns exhibited a variety of incommensurate structures along the three a axes with an average modulation period of about 6.5 a. These modulated structures arise from superperiodic stacking parallel to (100) of two structural units with different Li configurations. In-situ heating experiments show that the modulated structures undergo a reversible transition to the disordered modification at elevated temperatures. This transition arises from positional order-disorder of Li ions along the main structural channels. In addition, it appears that at constant low temperature, electron beam irradiation alone can induce a sequence of transitions similar to those that are thermally induced from the ordered modification to modulated states.
Title:
Correlated simultaneous phason jumps in an icosahedral Al-Mn-Pd
quasicrystal
Authors:
Coddens G. Lyonnard S. Hennion B. Calvayrac Y.
Source:
(list of journals)
Physical Review Letters. 83(16):3226-3229, 1999 Oct 18.
Abstract:
A triple-axis neutron-scattering experiment has been performed on a large single-grain sample of an icosahedral Al-Mn-Pd quasicrystal. The scattering plane in reciprocal space was a binary plane of the quasicrystal. The intensities of the quasielastic signals collected were compared with model calculations assuming isolated single-particle jumps along two-, three-, and fivefold axes of the quasicrystal. The agreement turned out to be unsatisfactory. We were able to explain the: experimental data only by assuming the existence of correlated simultaneous jumps of several atoms.
Title:
Quasicrystal-related phases in tetrahedral
semiconductors: Structure, disorder, and ab initio
calculations
Authors:
Dmitrienko VE. Kleman M. Mauri F.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(13):9383-9389, 1999
Oct 1.
Abstract:
We show that special structural changes (phason atomic jumps) can transform the BC8 and R8 phases, known to occur in Si and Ge, into a phase with tetrahedral coordination. These structural changes are analogous to the BC8-R8 transformation, The phase has the body-centered-tetragonal symmetry (the space group C-4h(6)-I4(1)/a) with 16 atoms per unit cell or 8 atoms per primitive cell and will be referred to as BT8. All the atoms occupy equivalent general positions x,y,z and there are three different tetrahedral bonds. It is shown that all three phases, BT8, BC8, and R8 may be considered as a result of phason-ordering transitions from a disordered phase with Ia(3)over bard symmetry. An infinite number of other structures with tetrahedral bonding (ordered and disordered) can be constructed this way. The phason jumps are typical of these phases because they are related to hypothetical icosahedra! quasicrystals. In particular, the BC8 and the recently suggested BC32 structure may be considered as 1/0 and 1/1 cubic approximants of the same quasicrystal. We present a detailed ab initio study of BT8 and BC32 phases in silicon within density-functional theory in the local-density approximation. Our results show that the energetics and diffraction patterns of the BT8 phase are very similar to those of the BC8 and R8 phases. We conclude that the available diffraction data do not exclude the existence of the BT8 phase. In contrast, the energy of the BC32 structure is significantly larger (for positive pressure), and the existence of this phase is therefore questionable. The pressure dependence of the bond lengths, angles, and the lattice parameters of the BT8 phase is investigated. Our estimation of the energy barrier for phason defect formation in the BC8 phase is about 0.12 eV per jumping atom and the energy of the defect is very small (less then 0.02 eV per jumping atom), therefore this type of defect could be present in real samples. Finally, we show that the computed elastic constants of the BC8 phase are almost isotropic as expected for the approximants of icosahedral quasicrystals.
Title:
Physical nature of critical modes in Fibonacci quasicrystals
Authors:
Macia E.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(14):10032-10036, 1999
Oct 1.
Abstract:
We report on the possibility of modulating the transport properties of critical normal modes in Fibonacci quasicrystals by using the mass ratio as a tuning parameter. The relationship between the spatial structure and the transport properties of these modes is studied analytically in terms of the transmission and Lyapunov coefficients. Power spectrum analysis of the critical modes indicates a complex modulated structure in agreement with previous experimental results, .
Title:
Commensurate-incommensurate magnetic
phase transition in TbCo2Ge2 compound
Authors:
Penc B. Hofmann M. Leciejewicz J. Szytula A.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(39):7579-7584, 1999
Oct 4.
Abstract:
Neutron diffraction measurements reveal a magnetic phase transition in TbCo2Ge2 from a collinear antiferromagnetic order with the k-vector [001] to an incommensurate sine-modulated magnetic structure described by the wave vector k = [0, 0, 1 - k(z)] k(z) = 0.055(2). The transition occurs near the Neel point at 34 K. In both phases the magnetic moments localized on Tb3+ ions are parallel to the tetragonal axis.
Title:
MIMS: a program for measuring four-dimensional Fourier maps of
incommensurate modulated
structures
Authors:
Li Y. Wan ZH. Fan HF.
Source:
(list of journals)
Journal of Applied Crystallography. 32(Part 5):1017-1020,
1999 Oct 1.
Abstract:
The program MIMS (measuring incommensurate modulated structures) has been written for the determination of structural parameters of incommensurate one-dimensionally modulated structures by an automatic search routine on four-dimensional Fourier maps. Test results show that the program works accurately and efficiently.
Title:
Production of single decagonal quasicrystal in Al-Co-Cu
system
Authors:
Guo JQ. Abe EJ. Sato TJ. Tsai AP.
Source:
(list of journals)
Japanese Journal of Applied Physics Part 2-Letters. 38(9AB):L1049-L1051,
1999 Sep 15.
Abstract:
An Al-Co-Cu vertical phase diagram along the 65 at% Al isopleth was constructed with the aim of growing a single decagonal quasicrystal. The decagonal quasicrystal was formed at 1000 degrees C via a peritectic reaction between a liquid and a cubic Al-55(Co, Cu)(45) phase. The decagonal quasicrystal crystallized as a primary phase for alloys with Co content less than 8.5 at% over a temperature range of 650 to 1000 degrees C. On the basis of the phase diagram, a single decagonal quasicrystal with a composition of Al66Co17Cu17 was grown from a starting alloy of Al65Co7.5Cu27.5 by the Bridgman method.
Title:
Space groups and atomic structure of the cubic approximants
of icosahedral quasicrystals
Authors:
Chizhikov VA.
Source:
(list of journals)
Crystallography Reports. 44(5):755-762,
1999 Sep-Oct.
Abstract:
The dodecahedral method of the direct projection onto the physical space from the space of a higher dimension is used to obtain all the possible symmetry groups of the cubic approximants of icosahedral quasicrystals. It is shown that a lattice of a quasicrystal or an approximant with the dodecahedral local order (DLO) can be divided into two sublattices such that the points of each lattice would be surrounded with the points of the other lattice. It is established that in the approximants of some symmetry groups, these sublattices are equivalent. The possible occurrence of order-disorder (OD) phase transitions, and first of all, of transitions breaking the symmetry relating two equivalent sublattices of an approximant is discussed. The results obtained are illustrated on examples of well known approximants.
Title:
Polytypism and phase transitions in TlInS2 and TlGaSe2
crystals
Authors:
Plyushch OB. Sheleg AU.
Source:
(list of journals)
Crystallography Reports. 44(5):813-817,
1999 Sep-Oct.
Abstract:
Low-temperature X-ray diffraction study of TlInS2 and TlGaSe2 crystals have been performed. The thermal expansion coefficients along the [001] direction of the crystals are determined within the temperature range 80-250 K. It is shown that the incommensurate phase with the modulation wave-vector q(i) = (1/4 +/- 6)c* in these crystals is formed in the temperature ranges 196-214 and 107-114 K, respectively. The polytype modification of TlGaSe2 with the lattice parameter c approximate to 120 Angstrom is revealed. No superstructural reflections were recorded for the long-period polytype modification.
Title:
Dislocation density evolution upon plastic deformation of Al-Pd-Mn single,
quasicrystals
Authors:
Schall P. Feuerbacher M. Bartsch M. Messerschmidt U. Urban K.
Source:
(list of journals)
Philosophical Magazine Letters. 79(10):785-796, 1999 Oct.
Abstract:
Dislocation density studies have been performed on icosahedral Al-Pd-Mn single quasicrystals after plastic deformation and after subsequent heat treatment. The deformation tests were carried out at a constant strain rate of 10(-5) s(-1) at temperatures between 695 and 820 degrees C. The heat treatments were performed at 730 degrees C, corresponding to one of the deformation temperatures. The development of the dislocation density during heat treatment and that during plastic deformation are compared. The experimental data are interpreted using a kinetic equation, which describes the evolution of the dislocation density during deformation. Numerical values for the dislocation multiplication constant and the annihilation rate for icosahedral Al-Pd-Mn are presented.
Title:
On the growth of icosahedral Al-Pd-Mn quasicrystals from the
ternary melt
Authors:
Fisher IR. Kramer MJ. Wiener TA. Islam Z. Ross AR. Lograsso TA. Kracher A. Goldman AI. Canfield PC.
Source:
(list of journals)
Philosophical Magazine B-Physics of Condensed Matter Structural Electronic
Optical & Magnetic Properties. 79(10):1673-1684, 1999 Oct.
Abstract:
Icosahedral Al71Pd21Mn8 quasicrystals have been grown from the ternary melt via a 'self-flux' technique. The nucleation is exceptionally well controlled, and individual grains can have masses of up to almost 30 g (limited only by the dimensions of the growth crucible). The quasicrystals grown by this technique are readily separated from the melt by decanting and clearly manifest a dodecahedral morphology with pentagonal facets. X-ray Ind electron-diffraction data indicate a remarkably well-ordered structure, with a correlation length of over 1000 Angstrom. The magnetic susceptibility has a temperature-independent diamagnetic component and a temperature-dependent paramagnetic term. For temperatures greater than approximately 60 K, the paramagnetic term follows a Curie-Weiss temperature dependence characterized by an average effective moment of 0.62 +/- 0.02 mu(B)/Mn and a Weiss temperature of -12.8 +/- 0.1 K. Deviations from the Curie-Weiss temperature dependence for temperatures less than approximately 60 K may be due to the formation Of local (short range) magnetic correlations. The electrical resistivity has a broad maximum at approximately 90 K and a room-temperature value of 1.57 +/- 0.05 m Omega cm. We note that the previously observed empirical trend that:a very high resistivity is associated with the highest quality Al-Pd-Mn quasicrystals does not seem to be in general true and that these high-quality (as demonstrated by X-ray and electron diffraction) 'flux-grown' samples have a relatively low room-temperature resistivity. In addition to the ternary icosahedral Al-Pd-Mn quasicrystals, a novel pseudo-quaternary icosahedral quasicrystal, Al67Ga4Pd21Mn8, is described.
Title:
Commensurately modulated 1/4 and 1/5
phases of deuterated betaine calcium chloride dihydrate: a
neutron structural study
Authors:
Hernandez O. Kiat JM. Cousson A. Paulus W. Ezpeleta JM. Zuniga FJ.
Source:
(list of journals)
Acta Crystallographica - Section C -
Crystal Structure Communications. 55(Part
9):1463-1466, 1999 Sep 15.
Abstract:
The structures of the commensurate 1/4 and 1/5 phases of the displacively modulated compound D-BCCD [deuterated betaine (trimethylammonioacetate) calcium chloride dihydrate, i.e. (CD3)(3)NCD2COOCaCl2(D2O)(2) or CaCl2. C5D11NO2. 2D(2)O] have been determined by single-crystal neutron diffraction at 100 and 68 K, respectively. The structural model of the 1/4 phase is found to be quite different from that obtained previously from X-ray diffraction data of the hydrogenated compound. This discrepancy comes from the fact that X-ray irradiation induces in this compound an unusal time-dependent decrease of the intensity of high-order satellite diffraction peaks. As a consequence and due to the commensurate nature of the phases investigated, X-ray diffraction failed to detect the large anharmonicity of the structural modulation which is clearly present in the two structures determined by neutron diffraction.
Title:
Effects of band filling on magnetic structures: The case of
RNi2Ge2
Authors:
Islam Z. Detlefs C. Song C. Goldman AI. Antropov V. Harmon BN. Bud'ko SL. Wiener T. Canfield PC. Wermeille D. Finkelstein KD.
Source:
(list of journals)
Physical Review Letters. 83(14):2817-2820, 1999 Oct 4.
Abstract:
We establish that strong Fermi surface nesting drives the Neel transition in the RNi2Ge2 compounds. Generalized susceptibility, chi(0)(q), calculations found nesting to be responsible for both incommensurate wave vector, (0 0 0.793), in GdNi2Ge2, and the commensurate structure, (0 0 1), in EuNi2Ge2, as revealed by x-ray resonant exchange scattering. A continuous transition from incommensurate to commensurate magnetic structures via band filling is predicted. The surprisingly higher T-N in EuNi2Ge2 than that in GdNi2Ge2 is also explained.
Title:
Quasicrystals in a monodisperse system
Authors:
Skibinsky A. Buldyrev SV. Scala A. Havlin S. Stanley HE.
Source:
(list of journals)
Physical Review E. 60(3):2664-2669, 1999 Sep.
Abstract:
We investigate the formation of a two-dimensional quasicrystal in a monodisperse system, using molecular dynamics simulations of hard-sphere particles interacting via a two-dimensional square-well potential. We find that more than one stable crystalline phase can form for certain values of the square-well parameters. Quenching the liquid phase at a very low temperature, we obtain an amorphous phase. By heating this amorphous phase, we obtain a quasicrystalline structure with fivefold symmetry. From estimations of the Helmholtz potentials of the stable crystalline phases and of the quasicrystal, we conclude that the observed quasicrystal phase can be the stable phase in a specific range of temperatures. .
Title:
Neutron structural study of a displacively modulated
crystal: A soliton regime in betaine calcium chloride
dihydrate
Authors:
Hernandez O. Quilichini M. Perez-Mato JM. Zuniga FJ. Dusek M. Kiat JM. Ezpeleta JM.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(10):7025-7036, 1999
Sep 1.
Abstract:
We present a structural study by single-crystal neutron diffraction of the one-dimensional displacively modulated dielectric crystal betaine calcium chloride dihydrate (BCCD). The fourfold and fivefold low-temperature commensurate structures of its Devil's-staircase-type phase diagram have been investigated at 100 and 68 K, respectively. In both structures, the atomic modulation functions, deduced from a four-dimensional refinement, are highly anharmonic. Moreover, the amplitude of the third-order harmonic is as high as similar or equal to 30% of that of the first-order harmonic and the phases of the two harmonics are roughly equal. Consequently, many atomic modulation functions display a typical two-step squared shape. On the basis of four-dimensional symmetry arguments, we interpret this modulation anharmonicity as a soliton regime with respect to the lowest-temperature nonmodulated ferroelectric structure. The two-step solution of the sine-Gordon equation can indeed describe at least qualitatively the phase of the modulation for many atoms in BCCD. After the case of thiourea, our work constitutes a complete structural characterization of a soliton regime in an incommensurate system. The physical consequences of this soliton regime in BCCD are discussed. In particular, the relevance of the use of polar Ising pseudospins as a low-temperature structural model is directly established and the theoretical predictions of the double Ising spin model concerning the dielectric anomaly at T-s are confronted with our results. .
Title:
Formation of an Al-Co decagonal quasicrystal from a
tau(2)-inflated Al13Co4 approximant
Authors:
Saitoh K. Yokosawa T. Tanaka M. Tsai AP.
Source:
(list of journals)
Journal of the Physical Society of Japan. 68(9):2886-2889,
1999 Sep.
Abstract:
A model for the formation of an Al-Co decagonal quasicrystal with space group P<(10)over bar>m2 from a tau(2)-inflated monoclinic Al13Co4 approximant is constructed on the basis of the observation of high-resolution electron microscope images. It is shown that star- and crown-shaped structural units of the Al-Co decagonal quasicrystal are formed by combining elongated hexagon tiles or the basic structural unit of tau 2-Al13Co4.
Title:
The density of states and first spectral moments of a
quasiperiodic lattice
Authors:
Naumis GG.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(37):7143-7153, 1999
Sep 20.
Abstract:
The density of states of a tight-binding Hamiltonian on a two-dimensional quasiperiodic lattice (the Penrose tiling) is studied in terms of the first spectral moments. This approach shows that there is a tendency for a depletion of the local density of states at certain sites of the lattice, and a progressive localization of states at the centre of the spectrum. The effect of different kinds of phason Rips in the first moments is also studied.
Title:
A complex modulated magnetic structure in
CeNi2Al5 persisting at very low temperatures
Authors:
Givord F. Boucherle JX. Dreyer J. Isikawa Y. Ouladdiaf B. Pujol S. Schweizer J. Tasset F.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(38):7327-7338, 1999
Sep 27.
Abstract:
The orthorhombic compound CeNi2Al5 is magnetically ordered below 2.6 K. Kondotype interactions together with strong crystal-electric-field (CEF) effects give rise to a complex magnetic structure: (i) its propagation vector is three dimensional and incommensurate, Ic = (0.500, 0.405. 0.083); (ii) the Fourier components of the moment associated with this vector are tilted away from the easy-magnetization axis b. Furthermore, the magnetic structure is double Ic, as the propagation vectors k = (k(x), k(y), k(z)) and k' = (-k(x), k(y), k(z)) associated with different magnetic domains are not independent. New experiments have been undertaken to achieve a more precise determination of the magnetic structure. Magnetic peak intensity measurements with higher resolution and polarization analysis have both led to the conclusion that the Fourier component of the magnetic moment deviates slightly from the b-direction. Considering the coupling of the two propagation vectors, the resulting moment describes very Bat ellipses with most of the moments very close to b. Neutron diffraction experiments down to 0.4 K have also been performed to investigate the evolution of the magnetic structure at low temperatures.

Update: 20-Oct-99

Title:
Stability and strain of decagonal Al-Ni-Co quasicrystal
under high pressure up to 70 GPa
Authors:
Hasegawa M. Tsai AP. Yagi T.
Source:
(list of journals)
Philosophical Magazine Letters. 79(9):691-698, 1999 Sep.
Abstract:
The stability of high-quality decagonal A1(72)Ni(20)Co(8) Single quasicrystals has been investigated under high pressure up to 67 GPa by means of an in situ angular-dispersive X-ray powder diffraction method using synchrotron radiation and a diamond anvil cell. It is found that the compression behaviour is almost isotropic. On the other hand, the strain behaviour on compression is found to be fairly anisotropic. This means that the quasiperiodic structure in the decagonal A1(72)Ni(20)Co(8) quasicrystal is much more easily distorted than is the periodic structure.
Title:
Gamma-surfaces in quasicrystals
Authors:
Mikulla R. Schaaf G. Trebin HR.
Source:
(list of journals)
Philosophical Magazine Letters. 79(9):721-727, 1999 Sep.
Abstract:
The concept of generalized stacking faults and the associated gamma-surfaces provides a useful tool for the analysis of dislocation core structures in crystalline materials. Applied to quasicrystals, suitable Burgers vectors for a given slip plane can be identified by calculating the minima of the gamma-surface. Instead of using a specific interaction model, we motivate a relation between structural properties and a subset of the minima of the gamma-surface. The results agree with calculations based on pair potentials. As a consequence the continuum of possible Burgers vectors in physical space is reduced to a quasiperiodic set, described in terms of a strip-projection method. Further conclusions for the plasticity of quasicrystals are discussed.
Title:
Electronic structure of quasicrystals
[Review]
Authors:
Hafner J.
Source:
(list of journals)
Current Opinion in Solid State & Materials Science. 4(3):289-294,
1999 Jun.
Abstract:
The state-of-the-art of the theory of electronic properties of quasicrystals is reviewed. Although the existing calculations are generally in very good agreement with experimental spectroscopic data, open questions concerning the character (extended, critical, localized) of the eigenstates in real three-dimensional quasicrystals remain. As long as this fundamental problem subsists, a deeper understanding of certain aspects of electronic transport, magnetism, etc. will remain incomplete. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.
Title:
Electronic structure, density of states and properties of
quasicrystals [Review]
Authors:
Fujiwara T.
Source:
(list of journals)
Current Opinion in Solid State & Materials Science. 4(3):295-301,
1999 Jun.
Abstract:
One of the recent important developments in solid state physics in the last 15 years is certainly the discovery of quasicrystals. Quasicrystal is the new thermodynamically stable state, in which the atomic arrangement is neither periodic nor random. Not only the structural arrangement, but also the electronic structures and properties are quite exotic. Several quasicrystals show an electric conductivity smaller than Mott's minimum metallic conductivity and the temperature coefficient of conductivity is large and negative. Lots of new information is still being collated. (C) 1999 Elsevier Science Ltd. All rights reserved.
Title:
A bismuth cobaltite with an intrinsically modulated misfit
layer structure: [Bi0.87SrO2](2)[CoO2](1.82)
Authors:
Leligny H. Grebille D. Perez O. Masset AC. Hervieu M. Michel C. Raveau B.
Source:
(list of journals)
Comptes Rendus de l Academie des Sciences Serie II Fascicule C-Chimie.
2(7-8):409-414, 1999 Jul-Aug.
Abstract:
A new misfit layer cobaltite [Bi0.87SrO2](2)[CoO2](1.82) has been synthesized. Its structure, solved from a single crystal X-ray investigation, shows CdI2 type [CoO2] layers similar to those encountered in misfit chalcogenides, but different rock salt (RS)-type [Bi0.87SrO2] layers. In contrast to the chalcogenides, these RS layers exhibit an intrinsic modulation due, as in the 2201 cobaltites, to the presence of double bismuth layers. Another fundamental difference with respect to misfit chalcogenides concerns the existence of strong Sr-O bonds between the [CoO2] layers and the [Bi0.87SrO2] layers, instead of weak bonds. (C) 1999 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.
Title:
Fluctuation-induced broadening of Mn2+ EPR lines in the
incommensurate phase of Rb2ZnCl4
crystals
Authors:
Trubitsyn MP.
Source:
(list of journals)
Physics of the Solid State. 41(9):1528-1533, 1999 Sep.
Abstract:
The EPR spectra of Mn2+ ions in Rb2ZnCl4 crystals is investigated in the vicinity of the transition from the paraelectric phase to an incommensurate modulated phase. When these crystals are cooled below the transition temperature T-i=304 K, a splitting of the resonance lines is observed in the singular spectrum. A one-harmonic model is used to discuss the contributions that fluctuations in the amplitude and phase of the incommensurate displacement wave make to the local width of the singular spectra. It is shown that anomalies in the local width of the low-temperature singular peaks observed in the vicinity of T-i are caused by amplitude fluctuations. (C) 1999 American Institute of Physics. .
Title:
X-ray diffuse scattering from icosahedral Al-Pd-Mn
quasicrystals
Authors:
Capitan MJ. Calvayrac Y. Quivy A. Joulaud JL. Lefebvre S. Gratias D.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(9):6398-6404, 1999
Sep 1.
Abstract:
The diffuse scattering of the thermodynamically stable icosahedral phase i-AlPdMn has been studied by means of x-ray-diffraction technique. The overall diffuse intensity shows two main characteristics: (1) the global diffuse scattering intensity map is well taken into account by a Huang effect in the formalism developed by Jaric and Nelson [Phys. Rev. B 37, 4458 (1988)] for icosahedral symmetry which reproduces at once both the "background" diffuse intensity and the profile shape around the Bragg peaks; (2) the intensity level of the diffuse scattering is crucially dependent on the chemical composition of the sample; it varies drastically from almost free diffuse scattering samples close to an "ideal" composition, up to an overall increase by a factor of 20 of the diffuse scattering for samples with an off-stoichiometry less than 0.5% in manganese and palladium content. The relative shapes of the diffuse scattering contours around the Bragg peaks are qualitatively fairly well reproduced using the sole phason-phason term of hydrodynamical modes in the formalism of Jaric and Nelson [Phys. Rev. B 37, 4458 (1988)], suggesting that phasons in these F-type icosahedral quasicrystals induce minor relaxations in the atomic positions surrounding the flip locations. .
Title:
Friction mechanism of dislocation motion in icosahedral Al-Pd-Mn
quasicrystals
Authors:
Messerschmidt U. Bartsch M. Feuerbacher M. Geyer B. Urban K.
Source:
(list of journals)
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical
Properties. 79(9):2123-2135, 1999 Sep.
Abstract:
Results from the literature and unpublished ones of the present authors are summarized which are relevant to the mechanisms governing the mobility of dislocations in icosahedral Al-Pd-Mn quasicrystals. These results concern macroscopic deformation tests, conventional transmission electron microscopy, in situ straining experiments in a transmission electron microscope, and computer simulation experiments. These experiments can best be interpreted by assuming that the dislocation motion is controlled by the thermally activated overcoming of Mackay-type clusters. The present paper gives an estimate of the activation volume of this process. It turns out that the activation volume of overcoming the clusters individually is one order of magnitude smaller than the experimentally observed one. The experimental observations can be interpreted in a consistent way in terms of the Labusch-Schwarz theory of solution hardening in crystals, which considers the interpenetrating clusters as 'extended' obstacles, a number of which are surmounted collectively. Some implications of this new model are discussed.
Title:
Microstructural investigation of the brittle-to-ductile transition in
Al-Pd-Mn quasicrystals
Authors:
Wollgarten M. Saka H. Inoue A.
Source:
(list of journals)
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical
Properties. 79(9):2195-2208, 1999 Sep.
Abstract:
Icosahedral Al-Pd-Mn single quasicrystals were deformed between room temperature and 400 degrees C by Vickers hardness testing. The surface morphology was investigated by profiling and scanning electron microscopy. Specimens were prepared for cross-sectional observation in transmission electron microscopes using a focused ion beam system. At room temperature, we find a polygrained microstructure which suggests a deformation via grain-boundary glide. At elevated temperatures, fragmentation as well as dislocation formation are observed.
Title:
Oxygen in Ti-(Cr, Mn)-Si icosahedral phases and approximants
Authors:
Libbert JL. Kim JY. Kelton KF.
Source:
(list of journals)
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical
Properties. 79(9):2209-2225, 1999 Sep.
Abstract:
Nearly single-phase icosahedral quasicrystals can be obtained in Ti-Cr and Ti-Mn alloys by rapid quenching, when the amounts of silicon and oxygen are carefully controlled. The role of phase stabilization by these elements, however, is unknown. Here, the essential role of both oxygen and silicon for the formation of phases with local icosahedral symmetry is demonstrated in these alloys. Rapidly quenched and as-cast samples of Ti-Cr-Si and Ti-Mn-Si alloys made without oxygen form primarily the beta solid solution phase. In contrast as-cast alloys of Ti-Cr-Si containing more than 10 at. % oxygen and Ti-Mn-Si alloys made with more than 6 at.% oxygen contain significant quantities of the 1/1 crystal approximant. Correspondingly, as-quenched alloys of these compositions form the icosahedral phase. Annealing studies of samples containing the 1/1 phase demonstrate that the oxygen has a thermodynamic rather than a kinetic role in phase stabilization. It is likely that the oxygen atoms bind with Ti atoms, forming a network of octahedra in the undercooled liquid. These octahedra then become natural building blocks for the double-shell Mackay icosahedra.
Title:
Generalized Meyer sets and Thue-Morse quasicrystals with
toric internal spaces
Authors:
Verger-Gaugry JL. Wolny J.
Source:
(list of journals)
Journal of Physics A-Mathematical & General. 32(36):6445-6460,
1999 Sep 10.
Abstract:
We show that a one-dimensional aperiodic Delaunay ser of points Lambda together with the Fourier transform of its autocorrelation measure (square modulus of its structure factor) at a wavevector k = 2 pi/lambda, can be associated with a generalized Meyer set under some assumptions: (a) that the internal space is toric, R/lambda Z, with a window, assumed finite, equal to the set of affine lattices of period lambda which have a non-empty intersection with Lambda and rarefaction laws at infinity, a selection rule based on a congruence mode with respect to lambda; (b) a scaling exponent function, having values in [0: 1], can be uniquely defined on the window: from rarefaction laws, which is related to the scaling properties of the intensity function; (c) the projection mappings are adapted to the average lattice of Lambda and are not orthogonal. The case of Bragg peaks of the Thue-Morse sequence spectrum is developed explicitly in this context.
Title:
Ordered gamma-brass structures coexisting with the decagonal
quasicrystal in a Ga46Fe23Cu23Si8 alloy
Authors:
Ge SP. Kuo KH.
Source:
(list of journals)
Journal of Materials Research. 14(7):2799-2805, 1999 Jul.
Abstract:
In a moderately rapidly solidified Ga,,Fe,,Cu,,Si, alloy, a face-centered-cubic (fcc) superstructure (a = 1.78 nm) and a hexagonal superstructure (a(hex) = 2.18 nm and c(hex) = 0.77 nm), based on the same body-centered-cubic (bcc) gamma-brass structure (a = 0.89 nm), were found-by means of micro-area electron diffraction-to coexist with the decagonal quasicrystal. The fee superstructure is probably similar to one of the F-centered-gamma-brass structure and has a parallel orientation relationship with the bcc fundamental structure. The hexagonal superstructure has its (001) parallel to the (11(1) over bar) of the bcc gamma-brass structure and its c(hex) = a(bcc)[11(1) over bar]/2, and their lattice correspondence relationship has been derived. Electron diffraction evidence is presented to show that these two superstructures are possibly crystalline approximants of the decagonal quasicrystal.
Title:
Surface oxidation of a quasicrystalline Al-Cu-Fe alloy: No
effect of surface orientation and grain boundaries on the final state
Authors:
Pinhero PJ. Anderegg JW. Sordelet DJ. Lograsso TA. Delaney DW. Thiel PA.
Source:
(list of journals)
Journal of Materials Research. 14(8):3185-3188, 1999 Aug.
Abstract:
We have used x-ray photoelectron spectroscopy and Auger electron spectroscopy to examine the characteristics of oxides on two types of quasicrystalline Al-Cu-Fe samples. One type was formed by consolidation of powders, resulting in multiple grains with random surface orientations. The other was a single grain, oriented to expose a fivefold surface. Both were oxidized to saturation in a variety of environments at room temperature. We measured the elemental constituents that oxidized, the extent of oxygen-induced Al segregation, and the depth of the oxide. Under the conditions of our experiments, there was little, if any, significant difference between the two types of samples. Hence, surface orientation and bulk microstructure played little or no role on the final state of the oxide under these conditions.
Title:
Charge ordering-disordering in the Th-doped CaMnO3
Authors:
Hervieu M. Martin C. Maignan A. Van Tendeloo G. Raveau B.
Source:
(list of journals)
European Physical Journal B. 10(3):397-408, 1999 Aug.
Abstract:
The structural transitions that appear in the manganites Ca1-xThxMnO3 versus temperature are studied in connection with their magnetic and transport properties; and compared to those of the Ca(1-x)Ln(x)MnO(3) manganites. An orthorhombic to monoclinic transition is observed for low x values (x approximate to 0.08); this structural distortion, also observed for Ln-doped oxides, is related to the magnetoresistance properties. For higher x values (0.15 less than or equal to x less than or equal to 0.30), modulated commensurate and incommensurate phases are obtained at low temperature, with a = 1/qa(p)root 2, b = 2a(p) and c = a(p)root 2, which are related to Mn3+/Mn4+ charge ordering (CO) phenomena. T-CO values,determined from electron diffraction,, are in agreement with those determined from the M(T) curves. The low temperature electron microscopy shows that the CO in those oxides is more complex than in Ln-doped manganites. In particular, the destabilisation of CO and consequently of the antiferromagnetic interactions is evidenced as the thorium content increases which may explain the appearance of a spin-glass like behavior for higher x values (x approximate to 0.25 - 0.30) not seen for Ca1-xSmxMnO3 phases (x approximate to 0.50 - 0.60).
Title:
Elastic neutron scattering and dielectric behaviour of 4% brominated betaine
calcium chloride dihydrate (BCCD)
Authors:
Vieira LG. Hernandez O. Almeida A. Quilichini M. Ribeiro JL. Chaves MR. Klopperpieper A.
Source:
(list of journals)
European Physical Journal B. 10(3):447-456, 1999 Aug.
Abstract:
We report a combined experimental study by means of elastic neutron scattering and dielectric measurements of a partially deuterated and x = 4% brominated BCCD (Betaine Calcium Chloride Dihydrate) crystal. The lowest-temperature phase is one-dimensional modulated and characterized by the coexistence of different commensurate domains (with delta = 1/4, 4/17, 2/9 and 1/5 on cooling), but with a clear predominance of the five-fold phase. A huge global thermal hysteresis of the wave-vector of the modulation, attaining values of about 9 K in the incommensurate phase and up to 15 K in the "harmless" low temperature part of the phase diagram, is observed up to T-i. The role of lattice defects on this phenomenon is discussed. Similarly to the behaviour of the pure compound, the structural modulation evolves on cooling towards a soliton regime (growth of third and fifth-order satellite peaks); probably with respect tu a non-stabilized non-modulated ferroelectric phase. The critical temperatures deduced from dielectric constant and pyroelectric current measurements are in very good agreement with those obtained from neutron scattering, The dielectric anomaly observed in epsilon(b)"(T) at T similar or equal to 85 K, and known as the "T-s-anomaly", could not be related with any special feature detected in the neutron data, and in particular no correlation between this anomaly and the appearance of the soliton regime can be established.
Title:
Quasicrystals in a partially devitrified
Zr65Al7.5Ni10Cu12.5Ag5 bulk metallic glass
Authors:
Chen MW. Zhang T. Inoue A. Sakai A. Sakurai T.
Source:
(list of journals)
Applied Physics Letters. 75(12):1697-1699, 1999 Sep 20.
Abstract:
A quasicrystalline phase was discovered in a Zr65Al7.5Ni10Cu12.5Ag5 bulk metallic glass annealed in the supercooled liquid range. Through systematical transmission electron microscopy rotation analyses, the selected area electron diffraction patterns are obtained corresponding to fivefold, threefold, and twofold rotational symmetry, demonstrating that the precipitated phase is an icosahedral quasicrystalline phase with good rotational symmetry. It is concluded that the addition of Ag in the Zr-based metallic glass promotes the formation of the quasicrystalline phase. The present experimental result implies that there is a natural relationship between the Zr-based bulk metallic glasses and icosahedral quasicrystalline. (C) 1999 American Institute of Physics. .
Title:
Band gap and wave guiding effect in a quasiperiodic photonic
crystal
Authors:
Jin CJ. Cheng BY. Man BY. Li ZL. Zhang DZ. Ban SZ. Sun B.
Source:
(list of journals)
Applied Physics Letters. 75(13):1848-1850, 1999 Sep 27.
Abstract:
A two-dimensional octagonal quasiperiodic photonic crystal composed of alumina cylinders is prepared. The transmission spectra of the quasicrystal are measured in the microwave region for the TM wave. We find that the position and width of the band gap do not depend on the incident direction, while the band structure can appear for quite a small piece of the quasicrystal. Two types of waveguide, a straight guide and a bending guide with two sharp 90 degrees corners, are fabricated by removing three rows of cylinders. The measured transmittances show that the guiding efficiency for both waveguides is high. (C) 1999 American Institute of Physics. .
Title:
Thermal and electrical transport properties of the
single-phase quasicrystalline material:
Al70.8Pd20.9Mn8.3
Authors:
Pope AL. Tritt TM. Chernikov MA. Feuerbacher M.
Source:
(list of journals)
Applied Physics Letters. 75(13):1854-1856, 1999 Sep 27.
Abstract:
The electrical and thermal transport properties of a single-phase quasicrystalline material of composition Al70.8Pd20.9Mn8.3 have been measured as a function of temperature (T) over a range of 10 K < T < 320 K. The following room-temperature values were found: electrical conductivity [640 (Omega cm)(-1)], Seebeck coefficient (85 mu V/K), and thermal conductivity (1.6 W/m K). As the temperature was decreased from room temperature, the electrical conductivity decreased undergoing a minimum at T approximate to 50 K after which it increased slightly and the Seebeck coefficient decreased monotonically. The thermal conductivity decreased with temperature and exhibited a broad plateau region between 50 K < T < 150 K. This class of materials is being investigated for potential thermoelectric applications. (C) 1999 American Institute of Physics. .
Title:
New modulation structures observed in
Bi2.13Sr1.87CuO6+delta superconductors
Authors:
Cui SF. Li CR. Mai ZH. Xiong JW. Zhao ZX. Wang YT. Hatton PD.
Source:
(list of journals)
Superconductor Science & Technology. 12(9):587-591, 1999
Sep.
Abstract:
A new two-dimensional structure modulation along c- and b-axes has been discovered in superconducting single crystals of Bi2.13Sr1.87CuO6+delta (Bi2201) by x-ray scattering. Such modulation structure does not exist in non-superconducting Bi2201 single crystals, but instead lattice distortions are observed in the a-b-plane. This phenomenon may indicate that both strain relaxation and charge modulation in the a-b-plane are important to the occurrence of superconductivity in the copper oxides.
Title:
Commensurability effect on the charge ordering of
La2-xSrxNiO4
Authors:
Katsufuji T. Tanabe T. Ishikawa T. Yamanouchi S. Tokura Y. Kakeshita T. Kajimoto R. Yoshizawa H.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(8):R5097-R5100, 1999
Aug 15.
Abstract:
Measurements of Hall coefficients, thermoelectric power, and optical conductivity spectra were done for single crystals of La2-xSrxNiO4 (x=0.27- 0.50) showing prototypical charge ordering. We found that the character of the carriers in the charge-ordered state changes from electronlike to holelike when the hole concentration p crosses 1/3, and that the correlation gap in the optical spectrum for p=1/3 is collapsed when p is away from 1/3. These results indicate that the deviation of p from 1/3 can be regarded as electron or hole doping into the commensurate charge-ordered state at p=1/3. .
Title:
Symmetries of quasicrystals
Authors:
Radin C.
Source:
(list of journals)
Journal of Statistical Physics. 95(5-6):827-833, 1999 Jun.
Abstract:
We consider tiling models of "round quasicrystals" which would have diffraction patterns which are fully rotation invariant-rings instead of Bragg peaks. They can be distinguished from glasses by self-similarity of the pattern of radii of the rings.
Title:
Classical lattice-gas models of quasicrystals
Authors:
Miekisz J.
Source:
(list of journals)
Journal of Statistical Physics. 95(5-6):835-850, 1999 Jun.
Abstract:
One of the fundamental problems of quasicrystals is to understand their occurrence in microscopic models of interacting particles. We review here recent attempts to construct stable quasicrystalline phases. In particular, we compare two recently constructed classical lattice-gas models with translation-invariant interactions and without periodic ground-state configurations. The models are based on nonperiodic tilings of the plane by square-like tiles. In the first model, all interactions can be minimized simultaneously. The second model is frustrated; its nonperiodic ground state can arise only by the minimization of the energy of competing interactions. We put forward some hypotheses concerning stabilities of nonperiodic ground states. In particular, we introduce two criteria, the so-called strict boundary conditions, and prove their equivalence to the zero-temperature stability of ground states against small perturbations of potentials of interacting particles. We discuss the relevance of these conditions for the low-temperature stability, i.e., for the existence of thermodynamically stable nonperiodic equilibrium states.
Title:
Deterministic aperiodic tile sets
Authors:
Kari J. Papasoglu P.
Source:
(list of journals)
Geometric & Functional Analysis. 9(2):353-369, 1999.
Abstract:
Wang tiles are square tiles with colored edges. We construct an aperiodic set of Wang tiles that is strongly deterministic in the sense that any two adjacent edges of a tile determine the tile uniquely. Consequently, the tiling group of this set is not hyperbolic and it acts discretely and co-compactly on a CAT(0) space.
Title:
Substitution sites of Pb and Y in Bi2Sr2Ca1Cu2O8+delta: X-ray photoelectron
diffraction as fingerprinting tool
Authors:
Pillo T. Hayoz J. Schwaller P. Berger H. Aebi P. Schlapbach L.
Source:
(list of journals)
Applied Physics Letters. 75(11):1550-1552, 1999 Sep 13.
Abstract:
The substitution site of Y and Pb in the cuprate-type high temperature superconductor Bi2Sr2Ca1Cu2O8+delta is determined in a very direct and unambiguous way by means of angle-scanned x-ray photoelectron diffraction (XPD). Using XPD as a fingerprinting tool, we conclude that Y occupies the Ca sites and Pb the Bi sites, respectively. Furthermore, low-energy electron diffraction data unequivocally show the presence of the incommensurate lattice modulation which is known for pure Bi2212, but not for sufficiently Pb doped Bi2212. We can, therefore, attribute the reappearance of the modulation directly to the Y doping. (C) 1999 American Institute of Physics. .

Update: 25-Sept-99

Title:
Commensurately modulated 1/4 and 1/5 phases of deuterated betaine calcium chloride dihydrate: a neutron structural study
Authors:
Hernandez O. Kiat J-M. Cousson A. Paulus W. Ezpeleta JM. Zúñiga FJ.
Source:
(list of journals)
Acta Cryst. C55:1463-1466, 1999
Abstract:
The structures of the commensurate 1/4 and 1/5 phases of the displacively modulated compound D-BCCD [deuterated betaine (trimethylammonioacetate) calcium chloride dihydrate, i.e. (CD3)3NCD2COOCaCl2(D2O)2 or CaCl2.C5D11NO2.2D2O] have been determined by single-crystal neutron diffraction at 100 and 68 K, respectively. The structural model of the 1/4 phase is found to be quite different from that obtained previously from X-ray diffraction data of the hydrogenated compound.
Title:
Comparing different approaches to model the atomic structure of a ternary decagonal quasicrystal.
Authors:
Wittmann R.
Source:
(list of journals)
Z.Kristallogr. 214(9):501, 1999
Abstract:
It is shown that the covering approach with a single decagonal prototile can be transformed into a hexagon, boat and star tiling. Particularly, the atomic decoration recently proposed by Cockayne and Widom (Phys. Rev. Lett. 81 (1998) 598-601) as a structure model for the decagonal phase is investigated. There, conflicts with the prototile approach arise which are due to specific peculiarities of the decoration. The above model is compared with recent experimental images which give strong support to its main features, but contradict competing structure proposals. The implications for the stabilization mechanism are discussed.
Title:
High-resolution electron microscopy of a modulated structure in InMO3(ZnO)m (M = In, Fe, Ga, and Al; m = integer): effect of solid solution formation.
Authors:
Li C. Bando Y. Nakamura M. Kimizuka N.
Source:
(list of journals)
Z.Kristallogr. 214(9):528, 1999
Abstract:
The structure of InMO3(ZnO) m (M = In, Fe, Ga, and Al; m  = integer) is built from InO21- (In—O) and MZn mOm+1 1 m (M/Zn—O) layers stacked alternately. A modulated structure of these compounds results from the ordering of M ions in the M/Zn—O layers. The modulated structures of InMO3(ZnO)13 (M  =  In0.5A0.5; A  =  Fe, Ga, and Al), a solid solution of InInO3(ZnO)13 and InMO3(ZnO)13 (M  = Fe, Ga, and Al), have been studied by high-resolution electron microscopy. The main and satellite spots of the electron diffraction patterns are indexed as ha*+ kb*+ lc*+ mq by using the four dimensional superspace group approach. Based on the crystal system of the basic structure and the modulation wave vector q, the electron diffraction patterns are classified according to three categories with typical parameters: (1) monoclinic unit cell of a = 0.57 nm, b = 0.33 nm, c = 4.0 nm, b = 93°, and q = b*/18.1; (2) monoclinic unit cell of a = 0.57 nm, b = 0.33 nm, c = 4.0 nm, b = 93°, and q = b*/22.5+c*/2; (3) triclinic unit cell of a = 0.57 nm, b = 0.33 nm, c = 4.0 nm, a = 95°, b = 95°, g = 30°, and q = a*/12.1+b*/18.1+c*/32.3. Among these, the first is the same as that of their constituent compounds In2O3(ZnO)13 and InMO3(ZnO)13 (M = Fe, and Ga), while the second and the third are different. In high-resolution image, the modulated structure appears as zig-zag contrast within the M/Zn—O layers. The periodicity of this zig-zag contrast along the M/Zn—O layer in InMO3(ZnO)13 (M = In0.5 A0.5; A = Fe, Ga, and Al) is between those of InInO3(ZnO)13 and InMO3(ZnO)13 (M = Fe, Ga, and Al).
Title:
Plastic deformation of icosahedral quasicrystals
Authors:
Urban K. Feuerbacher M. Wollgarten M.
Source:
(list of journals)
Radiation Effects & Defects in Solids. 148(1-4):65-83, 1999.
Abstract:
A survey is given on results of experimental studies of the plastic deformation of icosahedral quasicrystals. In particular this concerns the stress-strain characteristics and the determination of the thermodynamic activation parameters of the deformation process. Investigations of the microstructure of plastically deformed samples by means of transmission electron microscopy yield information on dislocation density, dislocation Burgers vectors and slip systems. In addition, fracture surfaces are investigated by scanning tunneling microscopy. The results are discussed in terms of the cluster substructure of the quasicrystal. In particular, the softening observed in quasicrystals with increasing strain is explained by a reduction of quasicrystal structural and chemical order by the continuous introduction of lattice matching-rule violations during the motion of dislocations.
Title:
Diluted Ising model with competing interactions
Authors:
Andrade RFS. Salinas SR.
Source:
(list of journals)
Physica A. 270(3-4):342-352, 1999 Aug 15.
Abstract:
We introduce aperiodic, but deterministic, dilution of bonds in the Ising model with competing ferro and antiferromagnetic interactions between first and second neighbors along the branches of a Cayley tree. The problem is formulated as a non-linear dissipative map, whose attractors correspond to solutions deep inside the tree. We use a scheme of successive periodic approximations to obtain the main modulated structures of the phase diagrams. The paramagnetic lines, as well as some other features of the phase diagrams, can be obtained from closed expressions. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Superspace-group approach to the phase
transition of Cu8GeSe6
Authors:
Onoda M. Ishii M. Pattison P. Shibata K. Yamamoto A. Chapuis G.
Source:
(list of journals)
Journal of Solid State Chemistry. 146(2):355-362, 1999 Sep.
Abstract:
The high- and low-temperature forms, i.e., phase I (stable above 328 K) and phase II (stable below 328 K), of Cu8GeSe6 have been investigated by the powder X-ray diffraction method. Cu8GeSe6 II is hexagonal with A = 12.6438(2), C = 11.7570(1) Angstrom, Z = 6, and P6(3)cm, and its structure is considered to be a superstructure of the high-temperature form, Cu8GeSe6I (hexagonal, a = 7.3164(4) congruent to A/root 3, c = 11.7679(7) Angstrom, Z = 2, and P6(3)mc). Rietveld analysis of Cu8GeSe6 I (350 K) and II (290 K) has been performed using diffraction data measured by a high-resolution ponder diffractometer and synchrotron X-ray radiation. For Cu8GeSe6 II, a four-dimensional superspace group for commensurate modulation, P6(3)mc(1/3 1/3 0), with basic cell constants a = 7.2999, c = 11.7570 Angstrom has been successfully applied (R-wp = 0.054). The superspace-group description allows uniform treatment of both forms, and the phase transition of Cu8GeSe6 is explained in terms of the presence and absence of commensurate modulation waves. (C) 1999 Academic Press.
Title:
Coloured quasiperiodic patterns with tenfold symmetry and
eleven colours
Authors:
Scheffer M. Luck R.
Source:
(list of journals)
Journal of Non-Crystalline Solids. 252(Part 2):815-819,
1999 Aug.
Abstract:
We present several local isomorphism classes of tenfold patterns with eleven colours; patterns derived by dualization and by the cut-and-projection method have been used. Four coloured local isomorphism classes are derived for each pattern. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Melting entropy of Al-based quasicrystals
Authors:
Holland-Moritz D. Iu IR. Wilde G. Schroers J. Grushko B.
Source:
(list of journals)
Journal of Non-Crystalline Solids. 252(Part 2):829-832,
1999 Aug.
Abstract:
The melting enthalpies and temperatures of quasiperiodic and periodic phases in Al-Cu-Co, Al-Ni-Co, Al-Ni-Fe and Al-Cu-Fe were measured by differential thermal analysis. From these data the melting entropies of the different phases were derived. The results are discussed in terms of the mutual stability of the quasicrystalline and crystalline phases in these alloy systems, indicating that the entropy of mixing plays an important role for the stabilization of quasicrystalline phases at ternary alloy compositions. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Growing perfect quasicrystals
Authors:
Tsai AP. Sato TJ. Guo JQ. Hirano T.
Source:
(list of journals)
Journal of Non-Crystalline Solids. 252(Part 2):833-838,
1999 Aug.
Abstract:
Single quasicrystals Al72Ni12Co16 and Al72Pd19Mn9 alloys have been grown by the floating-zone method and Zn46Mg51Ho3 alloy by the Bridgman method. In these three systems, single quasicrystals with dimensions of the order of a centimeter have been successfully grown. X-ray diffraction and neutron diffraction show that these single quasicrystals are as good as the best crystals. We therefore assert that quasicrystals are a metallic bulk matter with a degree of order equal to that of best crystals. By quenching the liquid, we observed flat solid-liquid interface perpendicular to the growth directions in Al-Ni-Co and AI-Pd-Mn alloys. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Title:
On the energy of the interface between a melt and
quasicrystalline and polytetrahedral phases
Authors:
Holland-Moritz D.
Source:
(list of journals)
Journal of Non-Crystalline Solids. 252(Part 2):839-843,
1999 Aug.
Abstract:
Experiments on the undercooling of Al-based alloys show a dependence of the maximum undercooling on the structure of the primarily nucleating phase. To model the interfacial energy of the different phases a numerical method was employed, which is based on a model originally developed to estimate the interfacial energy between a melt and cubic phases. Here, it is extended to the polytetrahedral phases Al13Fe4, Al5Fe2 and to the icosahedral quasicrystalline I-phase in Al-Pd-Mn. The numerically estimated solid-liquid interfacial energies are in agreement with experimental results as inferred from undercooling data. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Quasicrystals under pressure: a comparison between Ti-Zr-Ni
and Al-Cu-Fe icosahedral phases
Authors:
Ponkratz U. Nicula R. Jianu A. Burkel E.
Source:
(list of journals)
Journal of Non-Crystalline Solids. 252(Part 2):844-848,
1999 Aug.
Abstract:
Single-phase icosahedral phases (i-phases) of TiZrNi and AlCuFe alloys were obtained by single roller melt-spinning in protective argon atmosphere. The high-pressure (up to 25 GPa) compression properties of i-TiZrNi and i-AlCuFe were investigated by in situ energy-dispersive synchrotron radiation (SR) diffraction experiments using a gas-membrane diamond-anvil cell. In contrast to i-AlCuFe, reproducible deviations from the Birch-Murnaghan equation of state were noticed in the form of hysterezis loops during the first compression cycles of i-TiZrNi alloys. This response of quasicrystalline matter to hydrostatic pressure conditions is here reported for the first time. Plastic deformation processes and effects related to the small grain size of the rapidly-quenched TiZrNi alloys are tentatively considered as possible explanations. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Temperature dependence of quasielastic neutron scattering from icosahedral
Al71Pd19Mn10
Authors:
Uhlig H. Rouijaa M. Suck JB.
Source:
(list of journals)
Journal of Non-Crystalline Solids. 252(Part 2):855-859,
1999 Aug.
Abstract:
Results from inelastic neutron scattering experiments on quasicrystalline i-AlPdMn at different temperatures between 300 and 1096 K are presented. The quasielastic scattering observed was analyzed using a modified Gauss-Lorentzian function. Above 900 K, a peak broadening is observed, which tentatively is related to the phason degree of freedom in the sample. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
A detailed comparison between the amorphous and the
quasicrystalline state of Al-Cu-Fe
Authors:
Roth C. Schwalbe G. Knofler R. Zavaliche F. Madel O. Haberkern R. Haussler P.
Source:
(list of journals)
Journal of Non-Crystalline Solids. 252(Part 2):869-873,
1999 Aug.
Abstract:
We report on a comparison of electronic transport properties and the atomic structure between the amorphous and the quasicrystalline state. The samples are prepared at T approximate to 4 or 77 K as amorphous thin films. After measuring the amorphous state as quenched and after different annealing steps to approximately T = 700 K, the films are transformed into the quasicrystalline state and are measured again. The electronic transport of both phases as well as their atomic structure show many similarities, indicating that a relationship between electronic and atomic features exists in both phases as in Hume-Rothery systems. A discussion is presented which is based on local atomic arrangements of the atoms within 'clusters' in the amorphous as well as in the quasicrystalline state. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Title:
Pseudogap in quasicrystals probed by tunneling spectroscopy
Authors:
Schaub T. Delahaye J. Gignoux C. Berger C. Fourcaudot G. Giroud F. Grenet T. Jansen AGM.
Source:
(list of journals)
Journal of Non-Crystalline Solids. 252(Part 2):874-877,
1999 Aug.
Abstract:
We present tunneling spectroscopy measurements at 4 K on three quasicrystalline phases i-AlPdMn, i-AlCuFe and i-AlPdRe. In the spectroscopic curves, dI/dU, we observe a structure centered about zero bias voltage and with a square root voltage dependence from 300 mV down to at least 5 mV. This structure can be interpreted as the preopening of a correlation gap in the electronic density of states (DOS), which is consistent with the proximity to a metal-insulator transition in the three phases. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Magnetoresistance in the region of the possible metal-insulator transition in
icosahedral AlPdRe
Authors:
Rodmar M. Oberschmidt D. Ahlgren M. Gignoux C. Berger C. Rapp O.
Source:
(list of journals)
Journal of Non-Crystalline Solids. 252(Part 2):888-892,
1999 Aug.
Abstract:
The magnetoresistance, Delta rho(B,T)/rho(T), has been measured between 200 mK and 20 K, in magnetic fields up to 12 T for: icosahedral AlPdRe quasicrystals of nominal composition Al70.5Pd21.5Re8 Samples of varying resistivities and residual resistance ratios, R [=rho(4 K)/rho(295 K)], were studied. An analysis of Delta rho(B,T)/rho(T) in terms of quantum interference effects (QIE) was made, taking into account the possibility of QIE contributions to Delta rho(T) up to room temperature. The results show that the regime of diffusive metallic conduction in i-AlPdRe extends up to R in the range of 20, corresponding approximately to rho(4 K) up to 10(5) mu Omega cm, beyond which a description of Delta rho(B, )/rho(T) in terms of QIE breaks down. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Hydrogenation of Zr-based metallic glasses and quasicrystals
Authors:
Zander D. Leptien H. Koster U. Eliaz N. Eliezer D.
Source:
(list of journals)
Journal of Non-Crystalline Solids. 252(Part 2):893-897,
1999 Aug.
Abstract:
Zr-based metallic glasses and quasicrystals were electrochemically charged with hydrogen. Hydrogen absorption/desorption as well as the influence of hydrogen on the formation and stability of quasicrystals were studied by means of X-ray diffraction, electron microscopy, differential scanning calorimetry (DSC) and thermal desorption analysis (TDA). In Zr69.5Cu12Ni11Al7.5 absorption kinetics and storage capacity were found to be better for the quasicrystalline than for the associated amorphous phase. Dissolved hydrogen was observed to play an important role not only in the stability of the quasicrystals, but also in their formation from glassy precursor material. Even hydrogen contents as low as 5 at.% changed the formation as well as the decomposition of the icosahedral quasicrystals: the formation was shifted to higher temperatures whereas decomposition temperatures were lowered. At larger hydrogen contents, changes in both transformations were observed, yet not fully understood. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Corrosion of Al-Cu-Fe quasicrystals and related
crystalline phases
Authors:
Rudiger A. Koster U.
Source:
(list of journals)
Journal of Non-Crystalline Solids. 252(Part 2):898-902,
1999 Aug.
Abstract:
Corrosion of quasicrystalline and related crystalline phases in the Al-Cu-Fe system was investigated by anodic polarization in acid and alkaline solutions at room temperature. Corrosion products as well as surface morphology ware measured by means of X-ray diffraction, scanning and transmission electron microscopy. During polarization of icosahedral quasicrystals in a strong alkaline solution a two-layered film is formed: an inner layer with reduced Al content which consists of quasicrystals and a bcc phase and an nanocrystalline oxide layer with a needle-like morphology. At low pH (<2) dissolution of the quasicrystalline phases was observed to precede deposition of a porous Cu film. In a strong alkaline medium icosahedral quasicrystals have a smaller corrosion resistance than neighboring crystalline phases, e.g. the beta-phase (Al50Cu30Fe20); in strong acid solution other crystalline phases (for example Al2Cu) show less corrosion. The open circuit potentials have been observed to vary in a similar manner. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Low temperature crystal structure of
Ni-Mn-Ga alloys
Authors:
Wedel B. Suzuki M. Murakami Y. Wedel C. Suzuki T. Shindo D. Itagaki K.
Source:
(list of journals)
Journal of Alloys & Compounds. 290(1-2):137-143, 1999 Aug
30.
Abstract:
Transmission electron microscope (TEM) observation at room temperature of the low temperature phase of Ni2.14Mn0.86Ga shows stress-induced 5 periodicity modulation along a pseudo-[111] cubic zone axis. On cooling to 173 K, the periodicity changes to 7. In stress-free areas, a [001] zone axis with new lattice parameters for the tetragonal phase was observed. The new lattice parameters are smaller by a factor of root 2 than the expected lattice parameters. A new model for the tetragonal compound Ni2MnGa and the non-stoichiometric phases was developed with the help of TEM data, X-ray powder diffraction measurements, and a computational simulation based on the X-ray powder diffraction patterns. (C) 1999 Published by Elsevier Science S.A. All rights reserved.
Title:
Temperature-induced phase transition observed at a fivefold
icosahedral quasicrystalline AlPdMn surface
Authors:
Naumovic D. Aebi P. Beeli C. Schlapbach L.
Source:
(list of journals)
Surface Science. 435:302-306, 1999 Aug 2.
Abstract:
A switch in symmetry from fivefold to tenfold has been observed at the surface of a monograin icosahedral AlPdMn quasicrystal cut perpendicularly to a fivefold axis as a function of annealing temperature and/or annealing time at a constant temperature. A continuous change in stoichiometry was simultaneously monitored by X-ray photoelectron spectroscopy. The surface structure study was performed using full-hemispherical X-ray photoelectron diffraction and low-energy electron diffraction. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Evidence for a two-step evolution of the surface structure
during heat treatment of cleaved icosahedral Al-Pd-Mn single
quasicrystals
Authors:
Ebert P. Kluge F. Urban K.
Source:
(list of journals)
Surface Science. 435:312-316, 1999 Aug 2.
Abstract:
A two-step evolution of the surface structure of in situ cleaved Czochralski-grown icosahedral Al-Pd-Mn single quasicrystals during heat treatment is found by scanning electron and scanning tunneling microscopies. At temperatures above 420 degrees C the surface becomes rough in certain areas, while in other areas the cluster-based structure of the cleavage surface remains essentially unchanged. Above 550 to 600 degrees C the rough surface areas exhibit larger faceted holes and the cluster-based surface structure reorders. Possible explanations of the two-step evolution are discussed. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Title:
Structural study of the five-fold surface of the Al70Pd21Mn9
quasicrystal
Authors:
Ledieu J. Munz AW. Parker TM. McGrath R. Diehl RD. Delaney DW. Lograsso TA.
Source:
(list of journals)
Surface Science. 435:666-671, 1999 Aug 2.
Abstract:
We report an investigation of the five-fold surface of the Al70Pd21Mn9 quasicrystal using STM, LEED and AES. Surfaces sputtered and annealed to 875 K showed excellent five-fold symmetric LEED patterns, and STM revealed cluster-like protrusions. Surfaces sputtered and annealed to 1050 K also showed sharp LEED patterns but here STM showed flat surfaces which could be imaged with atomic resolution. AES indicated these annealed surfaces were Mn deficient. Threshold analysis of images of the flat surfaces shows that the surface call be generated by tiling with pentagons. Large protrusions on the flat surfaces were found where the pentagonal tiling breaks down. Angles between these protrusions were found to match angles present in the stereographic projection of the icosahedral group . (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Effect of Y doping on the Bi-O layers of Bi2Sr2CaCu2O8+delta single
crystals: a scanning tunnelling microscopy study
Authors:
Mitchell CEJ. Whittaker E. Flavell WR. Leonyuk L.
Source:
(list of journals)
Surface Science. 435:728-733, 1999 Aug 2.
Abstract:
Scanning tunnelling microscopy measurements were performed in ultrahigh vacuum on the cleaved (001) surfaces of Bi2Sr2CaCu2O8+delta samples in which 0, 30 and 46% of the Ca2+ was substituted by Y3+. The structural modulation of the Bi-O planes along [010] was observed on all of the samples, and the average period was measured over a number of images for each sample. The measured periods were 27.1 +/- 3 Angstrom for 0% Y, 27.7 +/- 3 Angstrom for 30% Y, and 25.7 +/- 2 Angstrom for 46% Y. Atomic-resolution images of the 46% Y-doped sample revealed significant distortions in both the modulation and the underlying lattice. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Magnetic ordering in the manganese perovskite CaMn7O12
Authors:
Przenioslo R. Sosnowska I. Hohlwein D. Hauss T. Troyanchuk IO.
Source:
(list of journals)
Solid State Communications. 111(12):687-692, 1999.
Abstract:
The results of neutron powder diffraction experiments on a mixed valence oxide system CaMn7O12 with a distorted perovskite structure are discussed. Below 86 K long-range magnetic ordering of the magnetic moments of Mn3+ and Mn4+ ions was observed. Between 50 and 86 K there are two different ordered magnetic phases: one ferrimagnetic and the second modulated. Below 50 K both these magnetic phases are modulated. A model of these magnetic structures is discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.
Title:
Twist modulated phases in chiral smectic
liquid crystals
Authors:
Stott JJ. Petschek RG.
Source:
(list of journals)
Physical Review E. 60(2 Part B):1799-1807, 1999 Aug.
Abstract:
By considering short period helical planar modulations about the layer normal, we construct a model free energy for the ferriclinic phases observed in chiral smectic liquid crystals. We then use this free energy to construct the phase diagram for our model. The resulting phases are compared with the experimentally observed smectic-C* subphases (ferroclinic, antiferroclinic, and heliclinic). A strong coupling is found between the ferroclinic q=2 pi/a and the heliclinic q=:2 pi/3a modes. This coupling was not considered in previous models. The resulting additional stability of this "locked in'' phase is discussed. .
Title:
Defect-induced room-temperature modulation in NbSe2
Authors:
Ramsak N. van Midden HJP. Prodan A. Marinkovic V. Boswell FW. Bennett JC.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(7):4513-4516, 1999
Aug 15.
Abstract:
The quasi-two-dimensional compound NbSe2 was studied by scanning tunneling microscopy. Small domains of a root 13a(0) x root 13a(0) superstructure, forming an angle of about +/-14 degrees with the average structure, were observed at the edges of some surface defects.. The superstructure is unstable and disappears gradually during scanning under the influence of the strong local field between the tip and the sample. It is attributed to a modulation analogous to those known in other d(1) transition-metal dichalcogenides MX2 with octahedrally coordinated X-M-X layers. It is assumed to be triggered by a local nonstoichiometry, which transforms the trigonal prismatic 2H stacking into the octahedral 1T one. .
Title:
Manifestation of incommensurate phase in
the dielectric properties of NH4HSeO4 crystals
Authors:
Andriyevsky B. Myshchyshyn O. Czapla Z. Dacko S.
Source:
(list of journals)
Physica Status Solidi B-Basic Research. 214(2):471-478, 1999
Aug.
Abstract:
Temperature (220 to 280 K) and frequency (0.02 to 1000 kHz) dependences of the real (epsilon') and imaginary (epsilon") parts of the complex electric permittivity for the ferroelectric b-cut of NH4HSeO4 crystal have been investigated. The analysis of the experimental results has shown that the effective elastic stiffness coefficient C-eff of the crystal decreases about three to four times in the temperature range of 256 to 262 K when compared to the paraelectric phase. Small oscillations of the temperature dependence of epsilon(T) have been revealed in the temperature range of the incommensurate phase (252 to 265 K), which have been interpreted as break off in the continuous change of the wave vector of the crystal structure caused by numerous transitions between commensurate and incommensurate subphases.
Title:
On the propagation of light in incommensurately
modulated dielectric crystals
Authors:
Kushnir OS. Lokot LO. Lutsiv-Shumski LP. Polovinko II. Shopa YI.
Source:
(list of journals)
Physica Status Solidi B-Basic Research. 214(2):487-494, 1999
Aug.
Abstract:
The applicability limits for the Jones matrix technique for macroscopically inhomogeneous anisotropic media are clarified. A simple linear relation between the dielectric tensor and the Jones matrix of the medium is derived. The technique is found to be not valid for weakly inhomogeneous incommensurately modulated crystals due to a fast spatial variation of their dielectric tensor. It is shown that the optical anisotropy of incommensurate crystals related to the optical activity effect differs significantly from that of homogeneous materials and materials with slowly-varying properties.
Title:
New experimental evidence of the structural modification in single
crystal Bi2Sr2CaCu2Oy by X-ray diffraction observation
Authors:
Zhao XR. Wu WB. Sun XF. Li XG.
Source:
(list of journals)
Physica C. 320(3-4):225-232, 1999 Jul 20.
Abstract:
The variations of the high angle 0038 peak-shape by means of X-ray I scans of the 00l fundamental reflections were investigated in detail for a highly oriented Bi2Sr2CaCu2Oy (Bi2212) crystal with sufficiently small intrinsic mosaicity and the same crystal annealed in air at 250, 300, 400, 600, and 750 degrees C for 20 h in consequence. For the first time, we observed a new additional reflection almost overlapped original 00l fundamental reflection at annealing temperature below 400 degrees C by X-ray diffraction measurement, which shows that there coexisted two sets of lattice periodicity in the c-direction of the annealed crystal. The new additional reflection appeared at 250 degrees C and disappeared at 400 degrees C. Its intensity was increased at 300 degrees C. The measurements of the AC susceptibility, c-axis parameter and full width at half maximum (FNHM) of the 0038 peaks showed that the new additional reflection was associated with the oxygen diffusion in CuO2 planes and the changes of strain field. The results provide the new experimental evidence that the structural distortion is more sensitive to the oxygen diffusion in CuO2 planes than to that in Bi-O layers. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Title:
Evidence for crystal-lattice modulation due
to spatially restricted enhancement of mixing effect in the low-carrier
system CeSb
Authors:
Iwasa K. Arakaki Y. Kohgi M. Suzuki T.
Source:
(list of journals)
Journal of the Physical Society of Japan. 68(8):2498-2501,
1999 Aug.
Abstract:
In order to investigate the unusual magnetic properties of the low-carrier system CeSb, X-ray diffraction studies at low temperatures have been performed. Below the magnetic transition temperature of T-N = 17K, several X-ray satellite peaks and their temperature variations were observed, which indicate that the modulated structures of a crystal lattice coexist with the long-period magnetic structures in CeSb. The observed wave numbers of the lattice modulations and the satellite-peak intensities are explained by the periodical arrangement of short and long distances between magnetic layers. The short interlayer distance is due to enhancement of p-mixing effect which is spatially restricted within the ferromagnetic layers of Gamma(8)-like Ce ions appearing in the lattice of Gamma(7) Ce ions. The interlayer distance due to Gamma(8)-like state is shorter la 0.1% than that between normal Gamma(7) Ce layers.
Title:
Novel pressure-induced 2k(F) CDW state in organic low-dimensional compound
theta-(BEDT-TTF)(2)CsCo(SCN)(4)
Authors:
Watanabe M. Nogami Y. Oshima K. Mori H. Tanaka S.
Source:
(list of journals)
Journal of the Physical Society of Japan. 68(8):2654-2663,
1999 Aug.
Abstract:
A band structure calculation based on the X-ray structure analysis reveals that pressure raises quasi one-dimensionality of the Fermi surface of the title compound. A 2k(F) lattice modulation is observed with a wave vector q(3)' = (2/3 0 0.29) at 10.7 kbar and room temperature. This is the first observation of pressure-induced CDW. With cooling, the wave vector of the modulation changes from q(3)' to commensurate q(3) = (2/3 0 1/3) below 240 K. On the other hand, at ambient pressure and 20 K where the resistivity begins to increase rapidly, three-dimensional short range ordering occurs for the weak diffuse spot with a wave vector q(2) = (0 0 1/2), This modulation is ascribable to an occurrence of charge ordering possibly caused by the nearest neighbor Coulomb interaction V. A schematic phase diagram for the electronic state is presented.
Title:
Effect of hydrostatic pressure on the low-temperature phase
transitions in Rb2ZnBr4
Authors:
Shigematsu H. Kubota M. Nishi M. Mashiyama H. Matsui T.
Source:
(list of journals)
Journal of the Physical Society of Japan. 68(8):2679-2683,
1999 Aug.
Abstract:
The effect of hydrostatic pressure on the low-temperature structural phase transitions in Rb2ZnBr4 has been investigated by the use of neutron scattering technique. The phase III-to-IV transition temperature, T-3 = 112 K at atmospheric pressure, increased hy applying pressure with a rate of 7 K/kbar. The phase IV-to-V transition temperature, T-4 = 76 K at atmospheric pressure, decreased by applying pressure with a rate of -45 K/kbar. At high pressure, two high order pseudo-commensurate phases characterized by wave vectors q(z) similar or equal to 3/11 and 4/15 were observed in addition to the already known commensurate ones of q(z) = 2/7 and 11/4. The space group of the commensurate phase of q(z) = 1/4 under high pressure was suggested to be P2(1)/c11 from the extinction rule.
Title:
T-D incommensurate intergrowth organic
crystals: The urea inclusion compounds [French]
Authors:
Guillaume F.
Source:
(list of journals)
Journal de Chimie Physique et de Physico-Chimie Biologique. 96(8):1295-1315,
1999 Sep.
Abstract:
The aim of this paper is to emphasise the interest of intergrowth organic crystals as prototypical materials for understanding the structural and dynamical properties of quasiperiodic systems. Urea inclusion compounds are very well adapted for multitechnique analyses and are therefore particularly suitable for fundamental studies. We summarise our recent research in this field and discuss on the interesting perspectives of these materials for inclusion chemistry and fundamental physics.
Title:
Successive phase transitions in Rb2TeO4 ceramics
Authors:
Sharma S. Choudhary RNP. Shannigrahi SR.
Source:
(list of journals)
Ferroelectrics. 227(1-4):41-50, 1999.
Abstract:
Polycrystalline samples of Rb2TeO4 have been prepared by a conventional solid-state reaction technique at a low temperature (600 degrees C). Preliminary room temperature X-ray studies suggest the formation of the single phase compound of Rb2TeO4 with cell parameters a = 10.582(1)Angstrom, b = 8.448(1)Angstrom and c = 8.499(1)Angstrom in the orthorhombic crystal system. Detailed studies of dielectric constant (epsilon) and tangent loss (tan delta) as a function of frequency (400 Hz to 10(4) Hz) and temperature (- 120 to 360 degrees C) show that the compound has two successive phase transitions at -4 degrees C (referred as T-C) and at 278 degrees C (referred as T-i) in a normal-commensurate-incommensurate phase sequence.
Title:
Efficient calculation of complex multidimensional phase
diagrams of discrete-lattice models
Authors:
Neubert B.
Source:
(list of journals)
Computer Physics Communications. 120(2-3):162-176, 1999 Aug.
Abstract:
Among the tasks encountered in the treatment of models from various scientific disciplines is the classification of particular values of adjustable parameters according to the respective types of structures predicted by the model. This problem is analogous to the determination of phase diagrams used in condensed-matter theory, We focus on discrete-lattice models for modulated materials which give rise to complex phase diagrams due to the occurrence of long-period and near-degenerate modulated structures. Algorithms are presented which can in some cases replace less efficient traditional methods for the calculation of phase diagrams. They exploit topological features of the phase diagrams and - in the case of microscopic models - symmetries in the spatial variation of the model variables, provided that prior knowledge from other methods is at hand. (C) 1999 Elsevier Science B.V. All rights reserved.

Update: 13-Sept-99

Title:
The analysis of incommensurate structures
in terms of full space group theory, and the application of the method to
melilite
Authors:
McConnell JDC.
Source:
(list of journals)
Zeitschrift fur Kristallographie. 214(8):457-464, 1999.
Abstract:
This paper deals with the application of full group theoretical methods to the elucidation of the symmetry and structure of an incommensurate phase. The analysis shows that the full symmetry sind structure of the incommensurate phase can be determined unequivocably where certain minimal symmetry data are available. The theory is compared with existing methods used in the study of incommensurate structures, and is applied to the elucidation of the incommensurate structure of melilite. The analysis demonstrates that there are two symmetrically distinct distortions of the Z tetrahedral site in melilite which, when it contains Fe, is responsible for two quite independent Mossbauer signatures.
Title:
Cluster configurations in modulated EuVxMo8 +/- yO14
crystals
Authors:
Leligny H. Grebille D. Roussel P. Labbe P. Hervieu M. Raveau B. Tortelier J. Gougeon P.
Source:
(list of journals)
Acta Crystallographica - Section B, Structural Science.
55(Part 4):467-483, 1999 Aug 1.
Abstract:
Three orthorhombic crystals of chemical formula EuxVyMo8+/-zO14 were investigated by X-ray diffraction (Mo K alpha radiation, lambda = 0.71073 Angstrom). They have nearly the same lattice parameters (a similar or equal to 11.3, b similar or equal to 10.0, c similar or equal to 9.2 A), display one-dimensional incommensurate modulations of wavevector q* = gamma c* and are characterized by the same superspace group Cmca(00 gamma)s00. The crystals differ both in their compositions (namely Eu0.976(6)V1.13(5)Mo7.10(5)O14, Eu0.986(4)V1.10(3)Mo7.30(1)O14 and EuMo7.96(1)O14) and in their gamma components [0.195 (2), 0.245 (2) and 0.286 (3), respectively]. The average structures of these crystals appear closely related to the structures of LaMo7.7O14 (not modulated) and LaMo8O14 (modulated); however, two main differences are outlined: first, the modulation direction is c in the Eu-containing crystals but b in the modulated La-containing crystal [q* = (1/3)b*], second, the Eu-containing crystals have centrosymmetric structures while the La-containing crystals have polar structures (space group C2ca). The Mo (or Mo and V) atoms are stacked to form (001) layers of metallic clusters. The density modulation of these structures implies the existence of the new types of clusters Meg, Mole, Mo6V4, Mo7V3 and Mo8V2 besides the clusters M-8 (Mo-8, Mo6V2 and Mo7V) and M-7 (Mo-7 and Mo6V) which are already known. Mo-8 units with cis and trans configurations and Mo6V2 units with a trans configuration appear as the main cluster types in these crystals. The nature of the metallic clusters changes along c, but inside one (001) layer it is likely that only one cluster type with a given configuration is present. The main structural result is the formation, in some unit cells, of strong intercluster Mo-Mo, Mo-V or V-V bonds with distances close to 2.6 Angstrom within a layer as well as between two neighbouring layers.
Title:
Systematic prediction of new inorganic ferroelectrics in point group 4
Authors:
Abrahams SC.
Source:
(list of journals)
Acta Crystallographica - Section B, Structural Science.
55(Part 4):494-506, 1999 Aug 1.
Abstract:
The latest release of the Inorganic Crystal Structure Database contains a total of 87 entries corresponding to 70 different materials in point group 4. The structures reported for 11 materials in space group P4 satisfy the criteria for ferroelectricity, as do four in P4(1), one each in P4(2) and P4(3), 12 in I4, including seven that form three families, and another three in I4(1). Three previously known ferroelectrics were also listed in I4 and one in I4(1). In addition, the listing for point group 4 contains 22 entries for nonferroelectric materials and three with misassigned space groups. Among the newly predicted ferroelectrics in point group 4, assuming the validity of the underlying structural reports, are Ce5B2C6, modulated NbTe4, Na3Nb12O31F, Ca2FeO3Cl, K4CuV5O15Cl, TlBO2, CrOF3, PbTeO3, VO(HPO3)(H2O). 3H(2)O, MgB2O(OH)(6), beta-tetragonal boron, CuBi2O4, WOBr4, Na8PtO6, SbF2Cl3, Ba1.2Ti8O16, Ni(4)Cl-2, Ca2SiO3Cl2, the mineral caratiite, NbAs, beta-NbO2 and Ag3BiO3.

Update: 06-Sept-99

Title:
Three-dimensional magnetic ordering in the quasi-one-dimensional Ising magnet
CoNb2O6 with partially released geometrical frustration
Authors:
Kobayashi S. Mitsuda S. Ishikawa M. Miyatani K. Kohn K.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(5):3331-3345, 1999
Aug 1.
Abstract:
The formation of three-dimensional magnetic ordering has been studied on a quasi-one-dimensional magnet CoNb2O6 by mean-field calculations as well as neutron scattering measurements down to T = 1.5 K under magnetic fields up to H(parallel to c)similar to 600 Oe. Measurements of a deviation of the magnetic Bragg scattering function from the delta function in the ordered state reveal a surprisingly rich variety of the magnetic formation arising from an isosceles triangular arrangement of the magnetic chain with competing interchain interactions in the a-b plane. The competing interactions result in quasidegenerate ground states with different propagation wave numbers along the b* direction in the sinusoidally amplitude-modulated incommensurate magnetic (IC) phase. Our mean-field calculations qualitatively reproduce the complicated H-parallel to c-T magnetic phase diagram and give evidence for a high degeneracy of ground states by calculating the H-parallel to c-T dependence of the free energy curve in the propagation wave number space. In addition, a partial cancellation of the exchange field at the apex site from the base sites on the isosceles triangular lattice leads to a quasi-long-range ordering along the a axis in both IC and antiferromagnetic states where the correlation length along the a axis depends On the propagation wave number along the b* direction. .
Title:
Electrical resistivity of one-dimensional quasiperiodic
eta(8)-Cu5Sn4
Authors:
Rodmar M. Ahlgren M. Lidin S. Rapp O.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(6):3908-3911, 1999
Aug 1.
Abstract:
The electrical resistivity, rho of one-dimensional quasiperiodic eta(8)-Cu5Sn4 has been studied, and compared with crystalline Cu6Sn5 of identical basic structure (Bs) and closely related atomic structure, rho was measured between 1.5 and 300 K on needle-shaped crystals with their axes along the base lattice c direction, corresponding to the quasiperiodic direction in eta(8)-Cu5Sn4. rho(4 K) was found to be nine times larger in eta(8)-Cu5Sn4 compared to Cu6Sn5, and the residual ratio R [= rho(4 K)/rho(300 K)< 1] was larger by a factor of 3. The similar structures and these large differences in transport properties indicate that the effect of quasiperiodic ordering has been observed in the resistivity of a one-dimensional metal. .
Title:
Neutron diffraction determination of hydrogen atom locations in the
alpha(TiCrSiO) 1/1 crystal approximant
Authors:
Kim JY. Kim WJ. Gibbons PC. Kelton KF. Yelon WB.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(6):3912-3919, 1999
Aug 1.
Abstract:
Titanium/zirconium-based quasicrystals and their related crystal approximants have been identified as potential new materials for hydrogen storage applications. To better understand the local chemistry and atomic ordering in these phases, preferential interstitial sites for hydrogen/deuterium were determined for alpha(TiCrSiO). This is a bcc 1/1 crystal approximant to the icosahedral quasicrystal phase that contains a two-shell, Mackay-icosahedral cluster of atoms at each bce site. It absorbs hydrogen or deuterium, without formation of other hydride phases, to a maximum hydrogen to metal atom ratio (H/M) of 0.26. For fully deuterated samples, both tetrahedral and octahedral interstitial sites are occupied with fractions of 0.14 and 0.12, respectively. Here, the hydrogen/deuterium sites are determined from a Rietveld analysis of x-ray and neutron powder diffraction data taken from samples of a(TiCrSiO) loaded with deuterium. Only the octahedral sites are occupied in the partially deuterated samples (D/M = 0.11). A decrease in the oxygen concentration below the stoichiometric value for alpha(TiCrSiO) leads to an increase in the total amount of hydrogen that can be absorbed, suggesting that these interstitial atoms are competing for the same octahedral interstitial sites. .
Title:
Effect of swift heavy ion irradiation on quasicrystalline
materials
Authors:
Chatterjee R. Kanjilal D. Dunlap RA.
Source:
(list of journals)
Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions
with Materials & Atoms. 156(1-4):201-205, 1999 Jul.
Abstract:
The effect of swift heavy ion irradiation (SHII) on quasicrystalline Al65Cu20Fe15 is reported for the first time. This particular quasicrystal is chosen for this study, so that the effect of electronic excitations on the intrinsic electronic properties of quasicrystals can be studied. It is found that irradiation at 77 K improves the quasicrystalline order and results in icosahedral grain growth. These results provide experimental support to the view that the quasicrystal structures can be described as hierarchy of overlapping connecting clusters. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
High strength Al-alloys with nano-quasicrystalline
phase as main component
Authors:
Schurack F. Eckert J. Schultz L.
Source:
(list of journals)
Nanostructured Materials. 12(1-4 Part A Special Issue
SI):107-110, 1999 Jul.
Abstract:
The formation of quasicrystals by ball milling as well as by rapid quenching in the systems AlMnCe and AlMnFe was investigated. Melt spinning resulted in a nanoscale mixed structure of up to 60 vol.% quasicrystalline particles embedded in a fee AI-matrix revealing a strong influence of the alloy composition on the solidification behaviour. Milling leads to the formation of an amorphous phase, however, there was no significant effect for Ce addition on phase formation. While the use of process-control agent or different milling atmospheres mainly affects the powder morphology, the milling intensity and, hence, the temperature during milling was found to be the most important parameter concerning phase evolution. The nature of observed metastable phase transitions was clarified by DSC measurements combined with x-ray diffraction. (C) 1999 Acta Metallurgica Inc.
Title:
Superconductivity reentrance in strong magnetic fields in Mo/Si multilayers.
Authors:
Fogel NY. Mikhailov MY. Yuzephovich OI. Bomze YV.
Source:
(list of journals)
Nanostructured Materials. 12(1-4 Part A Special Issue
SI):409-412, 1999 Jul.
Abstract:
Novel reentrance phenomenon is discovered on Mo/Si multilayers which occurs in parallel to the layers and slightly inclined magnetic fields. This effect may be explained in terms of the intrinsic pinning and vortex lattice (VL) commensurability with underlying layered structure. The locations of the zero resistance regions correspond to the stable VL configurations or to the transitions between two commensurate lattices. It is suggested that resistive method may be used as a new fool of the VL structure study in layered superconductors. (C) 1999 Acta Metallurgica Inc.
Title:
Local atomic correlations of bulk amorphous ZrTiCuNiBe alloys
Authors:
Gerold U. Wiedenmann A. Bellissent R. Macht MP. Wollenberger H.
Source:
(list of journals)
Nanostructured Materials. 12(5-8 Part B Special Issue
SI):605-608, 1999 Jul.
Abstract:
Samples of bulk amorphous Zr41Ti14Cu12.5Ni10Be22.5 and two related alloys have been heat treated in the supercooled liquid state and above the crystallization temperature. Wide angle neutron scattering experiments lead to very similar total structure factors S(Q) for both states. They show the characteristic modulations of amorphous material. The total pair correlation functions g(R) obtained by Fourier transformation of S(Q) exhibit three main groups of peaks corresponding to the coordination shells. For all samples and heat treatments the total coordination numbers for the first coordination shell are Z=12 +/- 0.7 indicating a dense packing of the atoms. By assigning pair correlations to the different maxima in g(R) partial coordination numbers of Be and Zr were estimated (C) 1999 Acta Metallurgica Inc.
Title:
Behavior of quasicrystal-reinforced Al94Cr1Mn3Cu2 under
fatigue conditions
Authors:
Haas V. Cho MI. Ishii H. Inoue A.
Source:
(list of journals)
Nanostructured Materials. 12(5-8 Part B Special Issue
SI):829-834, 1999 Jul.
Abstract:
Their excellent tensile properties make quasicrystal (QC) reinforced aluminum alloys interesting for future structural applications. However, their fatigue behavior, one of the most important design properties, seems not yet to be known. We investigated the fatigue properties by means of a rotating bending test. The fatigue strength at 10(8) cycles was 210 MPa, 30% - 50% higher than conventional Al alloys. The metallographic and fractographic investigation suggested that the fatigue damage developed via slip and subsequent formation of persistent glide bands (PSB) leading to the development of extrusions on the specimen surface. Cracks nucleated at the surface primarily near inclusions present in the material During growth the crack assumed a tortuous path due to deflection at the quasicrystals. (C)1999 Acta Metallurgica Inc.
Title:
Role of intergrowths in the properties of the naturally
layered manganites
Authors:
Berger A. Osgood RM. Jiang JS. Miller DJ. Mitchell JF. Bader SD.
Source:
(list of journals)
Materials Science & Engineering B-Solid State Materials for Advanced
Technology. 63(1-2):133-139, 1999 Aug 16.
Abstract:
The structural and magnetic properties of the two-layered Ruddlesden-Popper phase SrO(La1-xSrxMnO3)(2) with x = 0.3 and x = 0.4 are investigated. These naturally layered manganites exhibit a colossal magnetoresistance, a magnetic anisotropy which is strongly composition-dependent, almost no remanence, and a non-vanishing magnetization in a extended temperature range above the Curie temperature (T-C) The magnetization in this temperature range is not intrinsic to the crystal, but is attributed to intergrowths. These two-dimensional (2D) lattice imperfections consist of additional or missing SrO layers and have been observed in transmission electron micrographs. The magnetic properties of the intergrowths differ from the bulk crystal which results in unusual magnetic behavior. (C) 1999 Published by Elsevier Science S.A. All rights reserved.
Title:
Charge segregation and antiferromagnetism in high-T-c superconductors
Authors:
Tranquada JM. Ichikawa N. Kakurai K. Uchida S.
Source:
(list of journals)
Journal of Physics & Chemistry of Solids. 60(8-9):1019-1023,
1999 Aug-Sep.
Abstract:
Local antiferromagnetism coexists with superconductivity in the cuprates. Charge segregation provides a way to reconcile these properties. Direct evidence for modulated spin and charge densities has been found in neutron and X-ray scattering studies of Nd-doped La2-xSrxCuO4. Here we discuss the nature of the modulation, and present some new results for a Zn-doped sample. Some of the open questions concerning the connections between segregation and superconductivity are described. (C) 1999 Elsevier Science Ltd, All rights reserved.
Title:
Neutron scattering study on electron-hole doping symmetry of high-T-c
superconductivity
Authors:
Yamada K. Kurahashi K. Endoh Y. Birgeneau RJ. Shirane G.
Source:
(list of journals)
Journal of Physics & Chemistry of Solids. 60(8-9):1025-1030,
1999 Aug-Sep.
Abstract:
We review recent results of neutron scattering experiment on spin correlations for both hole-doped La2-xSr2CuO4+y and electron-doped Nd1.85Ce0.15CuO4+y superconductors, For the former, hole-doping induces an incommensurate spin density modulation along the Cu-O bonds. For the latter, we observed well-defined spin fluctuations in the superconducting phase (T-c approximate to 18 K) for the first time. In contrast to the hole-doping, the electron-doping induces no well-defined incommensurate spin modulation; the magnetic signal appears at ( pi, pi) with a q-width broader than in the as-grown antiferromagnetic phase. For both systems a static magnetic order was observed in the superconducting state. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.
Title:
Critical behavior of crystal lattice of NaV2O5
Authors:
Nakao H. Ohwada K. Takesue N. Fujii Y. Isobe M. Ueda Y.
Source:
(list of journals)
Journal of Physics & Chemistry of Solids. 60(8-9):1101-1103,
1999 Aug-Sep.
Abstract:
Critical behavior of crystal lattice was investigated by X-ray scattering for both stoichiometric NaV2O5 and Na-deficient NaxV2O5 (x = 0.99-0.96). Critical exponents were determined from superlattice reflections with a wave number vector Q = (1/2, 1/2, 1/4), specifying a lattice modulation formed below T-C = 35 K. The previously observed anomalous lattice strain below Te was found to be a secondary order parameter driven by a primary order parameter which is an atomic displacement with Q governing the low-temperature crystal structure. The temperature-concentration phase diagram was also determined and the transition temperature was found to decrease linearly with increasing deficiency x as dT(C)/dx = 4.2 (K/%). (C) 1999 Elsevier Science Ltd. All rights reserved.
Title:
Spin-slip model of the incommensurate
structure of the Kondo antiferromagnets CePdSn and CePtSn
Authors:
Kadowaki H.
Source:
(list of journals)
Journal of Physics & Chemistry of Solids. 60(8-9):1199-1201,
1999 Aug-Sep.
Abstract:
Representation analysis of the neutron diffraction data of the Kondo antiferromagnets, CePdSn and CePtSn, shows that the incommensurate magnetic structures of the single-k type are the Gamma(3) irreducible representations of the space group. To solve the contradiction between the mu SR observation supporting the commensurate structure and the incommensurability, spin-slip models derived from the Gamma(3) structure are proposed. (C) 1999 Elsevier Science Ltd. All rights reserved.
Title:
Magnetic structures of ternary rare-earth compounds, TbNiSn
and DyNiSn
Authors:
Kawano S. Andoh Y. Kurisu M.
Source:
(list of journals)
Journal of Physics & Chemistry of Solids. 60(8-9):1205-1207,
1999 Aug-Sep.
Abstract:
Single-crystal neutron diffraction studies have been performed on the rare-earth ternary compounds, TbNiSn and DyNiSn, Both crystals exhibit an incommensurate magnetic structure expressed by the propagation vector, Q = (Q(x), Q(y), 0) and its higher harmonics at low temperatures: for TbNiSn, Q = (0,600, 0.345, 0) with its third and fifth harmonics, and for DyNiSn, Q = (0.641, 0.340, 0) with its third harmonics. Both propagation vectors are a little temperature-dependent, and for TbNiSn at 6 K it becomes nearly commensurate of about (2/3, 1/3, 0), In an external magnetic field TbNiSn shows commensurate modulation with Q = (2/3, 0, D) at 4.2 K along the easy magnetization direction of the b-axis. (C) 1999 Elsevier Science Ltd. All rights reserved.
Title:
Neutron scattering study of the Zn-Mg-Ho icosahedral
quasicrystal
Authors:
Sato TJ. Takakura H. Tsai AP. Shibata K. Ohoyama K. Andersen KH.
Source:
(list of journals)
Journal of Physics & Chemistry of Solids. 60(8-9):1257-1259,
1999 Aug-Sep.
Abstract:
Magnetic diffuse scattering from the Zn-Mg-Ho icosahedral quasicrystal has been observed by single-crystal neutron-scattering for a wide (Q) over right arrow-region. The diffuse scattering appears as satellites of intense nuclear Bragg reflections. This suggests that corresponding short-range spin correlations have a modulation vector defined in the six-dimensional reciprocal-lattice space. The modulation vector is proposed as (q) over right arrow(m) = (3/4, 0, 0, 1/2, 3/4, 1/2). (C) 1999 Elsevier Science Ltd. All rights reserved.
Title:
Quasicrystals: atomic coverings and windows are dual
projects
Authors:
Kramer P.
Source:
(list of journals)
Journal of Physics A-Mathematical & General. 32(31):5781-5793,
1999 Aug 6.
Abstract:
In the window approach to quasicrystals, the atomic position space E-parallel to is embedded into a space E-n = E-parallel to + E-perpendicular to. Windows are attached to points of a lattice Lambda is an element of E-n. For standard fivefold and icosahedral tiling models, the windows are perpendicular projections of dual Voronoi and Delone cells from Lambda. Their cuts by the position space E-parallel to mark tiles and atomic positions. In the alternative covering approach, the position space is covered by overlapping copies of a quasi-unit cell which carries a fixed atomic configuration. The covering and window approach to quasicrystals are shown to be dual projects: D- and V-clusters are defined as projections to position space E-parallel to of Delone or Voronoi cells. Decagonal V-clusters in the Penrose tiling, related to the decagon covering, and two types of pentagonal D-clusters in the triangle tiling of fivefold point symmetry with their windows are analysed. They are linked, cover position space and have definite windows. For functions compatible with the tilings they form domains of definition. For icosahedral tilings the V-clusters are Kepler triacontahedra, the D-clusters are two icosahedra and one dodecahedron.
Title:
High-resolution transmission electron microscopy study of the phi '- and
delta-AlON spinel phases of the pseudo-binary section
AlN-Al2O3
Authors:
Tabary P. Servant C. Guymont M.
Source:
(list of journals)
Journal of Applied Crystallography. 32(Part 4):755-760,
1999 Aug 1.
Abstract:
A previously proposed structural model [Tabary & Servant (1999). J. Appl. Cryst. 32, 253-272] for the phi'- and delta-AlON spinel phases, which allows for the double modulation of composition and displacement of cations and anions and which describes both phases and their relationships to the gamma-AlON spinel phase, is here supported by high-resolution electron microscopy observations.
Title:
Polarization kinetics of a ferroelectric with complex
modulated structure
Authors:
Gladkii VV. Kirikov VA.
Source:
(list of journals)
JETP Letters. 70(1):42-47, 1999 Jul 10.
Abstract:
Anomalous changes of the spontaneous polarization, the coercive field, and the spectrum of the distribution of polarization relaxation times in an electric field are detected in the ferroelectric TMA-ZnCl4 at uniaxial pressures in the range where a transition arises to a nonuniform state with several coexisting waves of structural modulation. The anomalies are observed only in quasistatic and weak static fields and are due to a pressure-induced decrease of large potential barriers separating different metastable states of the structure. (C) 1999 American Institute of Physics. .
Title:
The magnetic structure of orthorhombic ErNi2B2C
Authors:
Detlefs C. Abernathy DL. Grubel G. Canfield PC.
Source:
(list of journals)
Europhysics Letters. 47(3):352-357, 1999 Aug 1.
Abstract:
In a recent X-ray scattering experiment it was demonstrated that the magnetic ordering transition of ErNi2B2C at 6.0 K is accompanied by a structural distortion, which lowers the crystal symmetry from tetragonal to orthorhombic. In previous neutron magnetic scattering experiments, this lowering of the crystal lattice symmetry was not resolved. Since the magnetic modulations along the a and b crystallographic directions are equivalent in tetragonal, but not in orthorhombic systems, the magnetic structure determinations based on neutron data remained incomplete. We have performed a high-resolution non-resonant magnetic X-ray scattering experiment on a single crystal of ErNi2B2C to determine the magnetic structure. The magnetic modulation wave vector is (0.5537, 0, 0) and lies along the long side of the orthorhombic basal plane.
Title:
Electrical properties of K2ZnCl4 crystal pure and doped with
Co2+ ions between 300 and 500 K
Authors:
Abu El-Fadl A.
Source:
(list of journals)
European Physical Journal-Applied Physics. 6(3):257-262,
1999 Jun.
Abstract:
The dielectric constant epsilon and the electrical conductivity sigma were measured of crystalline plates cut perpendicular to the a-, b-, and c-axes from K2ZnCl4 (KZC) crystals, pure and doped with Co2+ ions, in the temperature range from 300 to 500 K. A pronounced broad peaks exists at the commensurate-incommensurate phase transition temperature (T-c1). A thermal hysteresis of about 10 K is observed for the transition during heating and cooling processes. The J-E characteristics along the crystallographic axes were measured below and above T-c1. Conductivity anomalies were observed at T-c1. The results of electrical conductivity temperature measurements were analyzed and the activation energies of conduction at different temperature regions have been evaluated. The mechanism of the electrical conduction of the various phases and the anomaly at the transition point was discussed.
Title:
Surface effects on phase transitions of
modulated phases and at Lifshitz points: A
mean field theory of the ANNNI model
Authors:
Binder K. Frisch HL.
Source:
(list of journals)
European Physical Journal B. 10(1):71-90, 1999 Jul.
Abstract:
The semi-infinite axial next nearest neighbor Ising (ANNNI) model in the disordered phase is treated within the molecular field approximation, as a prototype case for surface effects in systems undergoing transitions to both ferromagnetic and modulated phases. As a first step, a discrete set of layerwise mean field equations for the local order parameter m(n) in the nth layer parallel to the free surface is derived and solved, allowing for a surface field H-1 and for interactions J(S) in the surface plane which differ from the interactions J(0) in the bulk, while only in the z-direction perpendicular to the surface competing nearest neighbor ferromagnetic exchange (J(1)) and next nearest neighbor antiferromagnetic exchange (J(2)) occurs. We show that for kappa equivalent to -J(2)/J(1) < kappa(L) = 1/4 and temperatures in between the critical point of the bulk (T-cb(kappa)) and the disorder line (Td(kappa) the decay of the profile is exponential with two competing lengths xi+, xi- with xi+ proportional to [T/T-cb(kappa)- 1](-1/2) while xi- stays finite at T-cb The amplitudes of these exponentials exp(-na/xi+/-) (a is the lattice spacing) are obtained from boundary conditions that follow from the molecular field equations. For kappa < kappa(L) but T > T-d(kappa), as well as at the Lifshitz point (kappa = kappa(L) = 1/4) and in the modulated region (kappa > kappa(L)), we obtain a modulated profile m(n+1) = A cos (naq + psi)e(-na/xi), where again the amplitude A and the phase Psi can be found from the boundary conditions. As a further step, replacing differences by differentials we derive a continuum description, where the familiar differential equation in the bulk (which contains both terms of order partial derivative(2)m/partial derivative z(2) and partial derivative(4)m/partial derivative z(4) here) is supplemented by two boundary conditions, which both contain terms up to order partial derivative(2)m/partial derivative z(2). It is shown that the solution of the continuum theory reproduces the lattice model only when both the leading correlation length (xi(+) or xi, respectively) and the second characteristic length (xi- or the wavelength of the modulation lambda = 2 pi/q, respectively) are very large. We obtain for J(s) > J(sc) (kappa) a surface transition, with a two-dimensional ferromagnetic order occurring at a transition T-cs(kappa) exceeding the transition of the bulk, and calculate the associated critical exponents within mean field theory. In particular, we show that at the Lifshitz point T-cs(kappa(L)) - T-cb(kappa(L)) proportional to (J(s) - J(sc))(1/phi L) With phi(L) = 1/4 while for kappa not equal kappa(L) the crossover exponent is phi = 1/2. We also consider the "ordinary transition" (J(s) < J(sc)(kappa)) and obtain the critical exponents and associated critical amplitudes (the latter are often singular when kappa --> kappa(L)). At the Lifshitz point, the exponents of the surface layer and surface susceptibilities take the values y(11)(L) = -1/4, gamma(1)(L) = 1/2, gamma(s)(L) = 5/4, while from scaling relations the surface "gap exponent" is found to be Delta(1)(L) = 3/4 and the surface order parameter exponents are beta(1)(L) = 1, beta(s)(L) = 1/4. Open questions and possible applications are discussed briefly.
Title:
The analysis of incommensurate structures in terms of full space group theory, and the application of the method to melilite.
Authors:
McConnell JDC.
Source:
Zeitschrift fur Kristallographie. 214(1):457-465, 1999.
(list of journals)
Abstract:
This paper deals with the application of full group theoretical methods to the elucidation of the symmetry and structure of an incommensurate phase. The analysis shows that the full symmetry and structure of the incommensurate phase can be determined unequivocably where certain minimal symmetry data are available. The theory is compared with existing methods used in the study of incommensurate structures, and is applied to the elucidation of the incommensurate structure of melilite. The analysis demonstrates that there are two symmetrically distinct distortions of the Z tetrahedral site in melilite which, when it contains Fe, is responsible for two quite independent Mossbauer signatures.
Title:
Cluster configurations in modulated EuVxMoyO14 crystals
Authors:
Leligny H. Grebille D. Roussel P. Labbe Ph. Hervieu M. Raveau B. Tortelier J. Gougeon P.
Source:
(list of journals)
Acta Cryst. (1999). B55, 467 - 483
Abstract:
The modulated structures of three crystals of EuVxMo8 yO14 with different compositions and different modulation waves are studied and compared. The action of the modulation on the distribution and the geometry of the different types of metallic clusters is also studied. Evidence is presented for new types of Mo9 and Mo10 metallic clusters, formed by capping three or four faces of the octahedral Mo6 units, and strong metallic bonds between the clusters are implied in some unit cells of the three crystals.
Title:
Report of a Subcommittee on the Nomenclature of n-Dimensional Crystallography. I. Symbols for point-group transformations, families, systems and geometric crystal classes
Authors:
Janssen T. Birman JL. Koptsik VA. Senechal M. Weigel D. Yamamoto A. Abrahams SC. Hahn T.
Source:
(list of journals)
Acta Cryst. (1999). A55, 761 - 782
Abstract:
Crystallographic symbols for use in arbitrary dimensions are considered and recommendations presented together with symbols for orthogonal transformations, geometrical crystal classes and standard settings of lattices. Standard metric tensors recommended for four-, five- and six-dimensional crystal families are given in full.
Title:
Phase transitions in the ferroelectrics (Sn1-xIn(2/3)x)(2)P2S6 at high
pressures
Authors:
Guranich PP. Lukach PM. Tovt VV. Gerzanich EI. Slivka AG. Shusta VS. Kedyulich VM.
Source:
(list of journals)
Physics of the Solid State. 41(7):1166-1168, 1999 Jul.
Abstract:
New ferroelectric solid solutions (Sn1-xIn(2/3)x)(2)P2S6 were investigated at high hydrostatic pressures. The range in which the incommensurate structure exists was determined. A dynamic shift of the incommensurate-ferroelectric phase transition temperature with increasing rate of change of temperature and the appearance of "reverse hysteresis" were observed. The characteristic features in the appearance of the latter effect in these crystals are investigated. (C) 1999 American Institute of Physics. .
Title:
A new orthorhombic approximant of the Ga-Mn and Ga-Fe-Cu-Si decagonal
quasicrystals consisting entirely of uniformly oriented
'crown' subunits
Authors:
Wu JS. Ge SP. Kuo KH.
Source:
(list of journals)
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical
Properties. 79(8):1787-1803, 1999 Aug.
Abstract:
By means of high resolution electron microscopy (HREM), the orthorhombic (2/1, 1/1) approximant (a = 2.04 nm, b = 1.25 nm and c = 1.48 nm) of the decagonal quasicrystal in Ga-Mn and Ga-Fe-Cu-Si alloys was found to consist of a B-centred rectangular tessellation of the 'crown' or 'concave octagon' subunit, a binary tile composed of one thin and three fat Penrose rhombi with an edge length of 0.66 nm. Based on the atomic decoration of these Penrose rhombi, a structural model of the crown subunit and that of the Ga-Mn (2/1, 1/1) approximant have been put forward. Simulated electron diffraction patterns and HREM images compared favourably with the experimental results. Various periodic tilings of the crown subunit, either alone or intermixed with other binary tiles (hexagon, 72 degrees pentagonal star and/or decagon) were discussed and compared with a number of approximants found experimentally by HREM.
Title:
A decagonal quasicrystal with a Griffith crack
Authors:
Li XF. Fan TY. Sun YF.
Source:
(list of journals)
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical
Properties. 79(8):1943-1952, 1999 Aug.
Abstract:
The crack theory in conventional linear elasticity fracture mechanics is extended to quasicrystal linear elasticity fracture mechanics. A decagonal quasicrystal containing a Griffith crack penetrating through the solid along the period direction is considered. By means of a general solution, the analytical expressions for the entire stress field are obtained. The asymptotic behaviour of the stress around the crack tip indicates that the stress near the crack tip exhibits the square root singularity. The singularity in the phason stress field arises from that the phonon and phason fields couple with each other. The crack strain energy and energy release rate are also given.
Title:
From heavy fermion antiferromagnetism to localized ferromagnetism:
competition of two ground states in CeRu2Ge2 on cooling
Authors:
Raymond S. Haen P. Calemczuk R. Kambe S. Fak B. Lejay P. Fukuhara T. Flouquet J.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(29):5547-5560, 1999 Jul 26.
Abstract:
Resistivity, specific heat and neutron scattering measurements performed on single crystals of CeRu2Ge2 are reported. The intrinsic behaviour of this compound is to exhibit a double transition from a paramagnetic to an antiferromagnetic and then a ferromagnetic state on lowering the temperature with T-N = 8.3 K and respectively T-C = 7.5 K. For the first time the antiferromagnetic order is characterized by neutron scattering. The propagation vector of the sinewave modulated structure is k = (0.31, 0, 0) as in the Si doped compounds. This phase is found to be easily weakened by disorder, but an antiferromagnetic moment as large as 1.5 mu(B) develops between T-N and T-C for the best crystal.
Title:
Antiferromagnetism of RPtX (R = Ho, Er; X = Si, Ge) compounds
Authors:
Penc B. Baran S. Hofmann M. Leciejewicz J. Slaski M. Szytula A. Zygmunt A.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(29):5631-5642, 1999 Jul 26.
Abstract:
X-ray and neutron diffraction as well as magnetometric measurements performed for HoPtX and ErPtX (X = Si, Ge) compounds indicate that they are crystalline and that they have the orthorhombic TiNiSi-type crystal structure. They are antiferromagnetic at low temperatures. A collinear magnetic structure with the propagation vector k = \1/2, 0, 1/2\, stable between 1.5 K and the Neel point at 3.1 K is observed in HoPtSi. HoPtGe is paramagnetic at 1.8 K. A collinear magnetic order described by the wavevector k(1) = \0, 1/2, 0\ has been found in ErPtSi and ErPtGe. As the temperature rises this structure transforms in both compounds into a sine modulated one with the wavevector k(2) = \0, k(y), 0\. The Neel points of ErPtSi and ErPtGe are 4.0 and 4.1 K respectively.
Title:
Influence of defects and conductivity on the phase transitions and the domain
structure properties in ferroelectric-semiconductors
Sn2P2S(Se)(6)
Authors:
Vysochanskii YM. Molnar AA. Khoma MM.
Source:
(list of journals)
Ferroelectrics. 223(1-4):19-26, 1999.
Abstract:
The influence of the static defects and charge carriers on the dielectric permeability temperature anomalies at the phase transitions (PT) from paraelectric phase to incommensurate (IC) phase and from IC phase to ferroelectric one has been determined for Sn2P2S(Se)(6) crystals. For these crystals with controlled content of impurities the memory effect recording in IC phase was compared with the dielectric output of the domain walls in ferroelectric phase. The experimental data are analyzed in the mean-field approximation.
Title:
Investigation of acoustoelectric phenomena in Sn2P2S6 single
crystals
Authors:
Samulionis V. Banys J. Vysochanskii Y.
Source:
(list of journals)
Ferroelectrics. 224(1-4):517-524, 1999.
Abstract:
The ultrasonic measurements of electronic attenuation have been performed in the crystals of ferroelectric semiconductor Sn2P2S6, which exhibit strong piezoelectric effect. From the dependence of electronic attenuation of ultrasound on conductivity the electromechanical coupling parameters have been calculated. The temperature dependence of acoustoelectric voltage has been measured and it was shown that it mainly follows the variation of electromechanical coupling constant. The influence of the long time crystal exposure in paraelectric phase near the phase transition temperature together with illumination of the Sn2P2S6 sample on ultrasonic velocity and attenuation has been also studied. It was shown, that relaxation of electronic subsystem significantly changes the critical ultrasonic behaviour. In this case the temperature anomalies of ultrasonic velocity and attenuation become very similar to that of ferroelectric with incommensurate phase.
Title:
Quasicrystal-crystal transformation in
Zn-Mg-rare-earth alloys
Authors:
Abe E. Tsai AP.
Source:
(list of journals)
Physical Review Letters. 83(4):753-756, 1999 Jul 26.
Abstract:
We report a reversible phase transformation between the icosahedral Zn-Mg-rare-earth(RE) quasicrystal and the hexagonal crystal being not composed of any giant icosahedral atomic cluster. This clearly shows that the large atomic cluster is not an essential atomic configuration for quasicrystal formation. A structural unit of the Zn-Mg-RE icosahedral quasicrystal is suggested to be not an icosahedral atomic cluster such as the Mackay or Bergman type which have been successfully used for the structural description of the Al-based icosahedral quasicrystalline phases.
Title:
Observation of incommensurate magnetic correlations at the
lower critical concentration for superconductivity in La2-xSrxCuO4 (x=0.05)
Authors:
Wakimoto S. Shirane G. Endoh Y. Hirota K. Ueki S. Yamada K. Birgeneau RJ. Kastner MA. Lee YS. Gehring PM. Lee SH.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(2):R769-R772, 1999 Jul 1.
Abstract:
Neutron-scattering experiments have been performed on lightly doped La2-xSrxCuO4 single crystals in both the insulating (x = 0.03,0.04,0.05) and superconducting (x = 0.06) regions. Elastic magnetic peaks are observed at low temperatures in all samples with the maximum peak linewidth occurring at the critical concentration x,= 0.05. Incommensurate peaks are observed only at x = 0.05, the positions of which are rotated by 45 degrees in reciprocal space about (pi,pi) from those observed for x greater than or equal to 0.06 in the superconducting phase.
Title:
Covering cluster description of octagonal MnSiAl
quasicrystals
Authors:
Ben-Abraham SI. Gahler F.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(2):860-864, 1999 Jul 1.
Abstract:
A likely mechanism far the formation of quasicrystals is by maximally covering space with overlapping, stable atomic clusters. This notion is here applied to the experimentally determined layered structure of octagonal MnSiAl quasicrystals, which can be described in terms of a decoration of the octagonal Ammann-Beenker tiling. This decoration is abstractly represented by a two-color version of the tiling. The covering cluster of the quasicrystal corresponds to an octagonal covering patch of the colored tiling. This covering patch appears, in two variants with complementary colors. The three-dimensional quasicrystal has a centered octagonal translation module, and its space group is 18(4)/mcm.
Title:
Linear continuous inhomogeneous strains in octagonal and decagonal
quasicrystals
Authors:
Rochal SB. Lebedyuk IV. Kozinkina YA.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(2):865-873, 1999 Jul 1.
Abstract:
Linear continuous inhomogeneous strains (LCISs) are considered in decagonal and octagonal quasicrystalline lattices. At such strains, the magnitudes of position displacements are proportional to the strain value and the flip-flops of positions are absent. All possible variants of the spontaneous lowering of a quasicrystalline symmetry due to the appearance of such strains are enumerated. A possibility of the LCIS to be induced by the linear homogeneous field of mechanical stresses is shown. Manifestations of LCISs in reciprocal space are discussed.
Title:
Evolution of the composition and structure of cleaved and
heat-treated icosahedral Al-Pd-Mn quasicrystal surfaces
Authors:
Ebert P. Kluge F. Grushko B. Urban K.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(2):874-880, 1999 Jul 1.
Abstract:
We investigated the changes in composition and structure induced by heat treatment of cleaved fivefold icosahedral Al-Pd-Mn quasicrystal surfaces by scanning electron microscopy and calibrated Auger electron spectroscopy. With increasing temperature we observed five different composition ranges of the surface coupled with distinct changes in the surface morphology. The changes in composition can be explained by successive evaporation and diffusion processes occurring with increasing temperatures. First, Mn evaporates from the uppermost surface layer, then Al evaporation starts and induces a further Mn evaporation leading to an enrichment in Pd. The enrichment is reduced by Mn diffusion from the bulk, Al diffusion from the bulk, and probably simultaneously occurring Pd desorption. Finally, a recrystallization of the surface is induced by the full diffusive mobility of all elements and preferential evaporation of Mn and to a lesser degree of Al. We also discuss the signature of the bonding configuration of Al in the Auger spectra of all investigated compositions. .
Title:
Thallium overlayers on Si(111): Structures of a "new" group
III element
Authors:
Vitali L. Leisenberger FP. Ramsey MG. Netzer FP.
Source:
(list of journals)
Journal of Vacuum Science & Technology A-Vacuum Surfaces & Films. 17(4 Part
1):1676-1682, 1999 Jul-Aug.
Abstract:
The structure and growth of Tl overlayers on Si(111)7X7 surfaces have been investigated using ultraviolet photoelectron spectroscopy, low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and scanning tunneling microscopy (STM). At low coverages Tl adsorption occurs almost exclusively on the faulted half of the (7X7) unit cell and forms small, two-dimensional clusters. With increasing Tl coverage the whole surface becomes covered while the (7X7) surface periodicity is maintained as evidenced by LEED and STM. After, deposition of the first 2 monolayers (ML) the high mobility of Tl adatoms leads to the condensation of few, but large islands. At the surface of the second monolayer of Tl an interesting network of bright contrast lines is observed, which appears to be induced by the (7X7) substrate periodicity lying two layers below and which may be caused by the surface strain mediated by the (7X7) unit cell boundaries. The surface phase diagram of Tl-Si(111) at elevated temperatures contains(a (1X1) structure at 1 ML coverage and an approximate (6X6) phase. The latter is due to an incommensurate structure of the second Tl layer on top of the (1X1) ML. (C) 1999 American Vacuum Society. .
Title:
Magnetic behaviour of R2PdSi3 compounds with R = Ce, Nd, Tb-Er
Authors:
Szytula A. Hofmann M. Penc B. Slaski M. Majumdar S. Sampathkumaran EV. Zygmunt A.
Source:
(list of journals)
Journal of Magnetism & Magnetic Materials. 202(2-3):365-375, 1999 Aug.
Abstract:
The magnetic behaviour of the ternary intermetallics, R2PdSi3 (R = Ce, Nd, Tb-Er), has been investigated by magnetisation, electrical-resistivity (rho) and neutron-diffraction measurements. The neutron-diffraction data reveal that these compounds crystallise in the AlB2-type hexagonal structure and that these alloys exhibit different magnetic structures below respective magnetic-transition temperatures. In Ce2PdSi3 the Ce moments order below 2.5 K in a sinusoidally modulated antiferromagnetic structure, without extending to the entire crystal, apparently exhibiting cluster magnetism. The Nd magnetic moments in Nd2PdSi3 exhibit ferromagnetic ordering below 17 K. In Tb2PdSi3, a complex situation is observed: in the temperature range from 1.5 to (T-N =)25 K, there is a coexistence of a ferromagnetic spiral (about 75% of the magnetic moment) and a spin-glass (about 25%). For the Dy, Ho and Er compounds, below T-N (7.5, 8 and 7 K, respectively), sinusoidaly modulated structures are observed and below T-N, there are upturns in rho, indicative of the opening up of magnetic Brillouin-zone-boundary gaps in these compounds. While for the Ce compound the magnetic moment lies in the basal plane, for other compounds it is parallel to the c-axis. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Magnetic structure of U2Pt2Sn
Authors:
Prokes K. Svoboda P. Kolomiets A. Sechovsky V. Nakotte H. de Boer FR. Winand JM. Rebizant J. Spirlet JC.
Source:
(list of journals)
Journal of Magnetism & Magnetic Materials. 202(2-3):451-457, 1999 Aug.
Abstract:
U2Pt2Sn forms in a ternary derivative version (space group P4(2)/mnm) of the tetragonal U3Si2-type of structure. Clear anomalies in the magnetic susceptibility, specific heat and electrical resistivity around 15 K and their changes in magnetic fields indicate antiferromagnetic ordering below this temperature. The antiferromagnetic ground state of U2Pt2Sn is corroborated by the metamagnetic transition observed in the magnetization around 22 T measured at 4.2 K and by magnetic reflections in the neutron-powder diffraction pattern at low temperatures. The U moments of 1.16 +/- 0.07 mu(B)/U form a complex incommensurate non-collinear magnetic structure. The moments are confined to (1 1 0)-type of planes and tilted from the c-axis by 60 degrees. Moreover they are sine-wave modulated along the tetragonal axis with a propagation vector q = (0, 0, 0.1823). (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Title:
New ordered ThSi2-type derivatives in the light rare earths germanides -
Crystal structure of Nd4Ge7
Authors:
Venturini G. Ijjaali I. Malaman B.
Source:
(list of journals)
Journal of Alloys & Compounds. 289(1-2):168-177, 1999 Jul 20.
Abstract:
The RGex compounds (R=La-Nd, Sm; 1.5 less than or equal to x less than or equal to 2.3) have been examined by powder X-ray diffraction. New ordered ThSi2 derivatives related to the Y3Ge5 structure have been characterized in these systems. An increase of the Ge concentration with the rare earth size has been evidenced in these compounds. The crystal structure of Nd4Ge7 (C222(1); a=5.958 Angstrom; b=13.857 Angstrom; c=11.919 Angstrom) has been refined from single crystal data. This structure is characterized by a stacking of Y3Ge5 and ThSi2 blocks. Some LaGex and CeGex compounds display a GdSi2 subcell and an additional monoclinic deformation. A structural hypothesis related to a new ordering scheme of the Ge vacancies is proposed. The whole ordered ThSi2 derivative RGex (R=La-Ho) are reviewed and the evolution of the non-stoichiometry as a function of the R size and the electronic concentration is discussed. (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
Structural study of an Al70Ni15Fe15 decagonal quasicrystal
using high-angle annular dark-field scanning transmission electron microscopy
Authors:
Saitoh K. Tsuda K. Tanaka M. Tsai AP.
Source:
(list of journals)
Japanese Journal of Applied Physics Part 2-Letters. 38(6AB):L671-L674, 1999
Jun 15.
Abstract:
High-angle annular dark-field (HAADF) images of a melt-quenched Al70Ni15Fe15 decagonal quasicrystal have been taken using a scanning transmission electron microscope for the first time. We have found that the alloy is composed of 2-nm-diameter atom clusters with fivefold symmetry. We have also observed an inversion domain structure. A structural model has been constructed on the basis of the HAADF images and the fivefold cluster of the monoclinic tau(2)-Al13Co4 approximant model . Antiphase shifts at domain boundaries have been observed directly for the first time. The present observation has verified the results of high-resolution electron microscopy (HREM) and the dark-field imaging technique obtained by Tsuda et al.
Title:
Structure and phase behavior of the Ir(001) surface: X-ray
scattering measurements
Authors:
Jahns V. Zehner DM. Watson GM. Gibbs D.
Source:
(list of journals)
Surface Science. 430(1-3):55-66, 1999 Jun 21.
Abstract:
We present the results of X-ray scattering studies of the structure and phase behavior of the Ir(001) surface between room temperature and T = 2000 K. Two distinct phases have been identified. For temperatures above T = 1950 K, the Ir(001) surface is rough, similar to what has been observed for Pt(001) at elevated temperatures. Below about T = 1950 K, the surface reconstructs to farm a quasi-hexagonal unit cell, which is commensurate with the substrate lying beneath it. The measured X-ray intensities, both inplane and along the specular rod, are consistent with a buckled, (5 x 1) description of the structure, including a 15% expansion of the top layer spacing and an enhanced surface Debye-Waller factor. A detailed comparison is made of the phase behavior determined here for Ir(001) to that found earlier for Pt and Au(001). (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Morphology and composition of Au films on Si(100)
Authors:
Ceelen WCAN. de Ridder M. Moest B. van der Gon AWD. Brongersma HH.
Source:
(list of journals)
Surface Science. 430(1-3):146-153, 1999 Jun 21.
Abstract:
Spot profile analysis low-energy electron diffraction, low-energy ion scattering and Auger electron spectroscopy were employed to study the morphology and composition of Au films on Si(100). After annealing, two distinct surface reconstructions were observed: a two-domain c(8 x 2) phase and a four-domain incommensurate (5 x 3.2)R5.7 degrees phase. During the transition from the c(8 x 2) to the (5 x 3.2)R5.7 degrees phase, the subsurface composition changes drastically from Au-rich to Si-rich, whereas the outermost layer composition remains almost constant (about 65 at.% Au). Detailed information concerning the domain structure for the two phases is subtracted from the profiles of the LEED spots. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
X-ray study of phase transitions in CS3Sb2I9 crystal
Authors:
Bagautdinov BS. Novikova MS. Aleksandrova IP. Blomberg MK. Chapuis G.
Source:
(list of journals)
Solid State Communications. 111(7):361-366, 1999.
Abstract:
An X-ray study of three phase transitions (PTs) at 86, 78 and 72 K has been carried out for the trigonal modification of the Cs3Sb2I9 crystal (space group P-3m1, a = 8.460 Angstrom, c = 10.398 Angstrom). The T-c1 = 86 K PT preserves the trigonal symmetry and is associated with the doubling of the c-parameter. At T-c2 = 72 K a doubling of a and b is observed. An intermediate incommensurate phase with q(1) = 1/2c*, q(2) = (1/2 - delta)a* + 1/2c* has been detected in the temperature range of 78-72 K. The lock-in PT at 72 K has a first order character. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.
Title:
Stochastic growth of solids
Authors:
Paredes R. Aragon JL. Barrio RA.
Source:
(list of journals)
Revista Mexicana de Fisica. 45(Suppl 1):21-24, 1999 Jun.
Abstract:
In this paper we present a model for solid growth based upon the concept of agglomeration of small units. This model uses the method of stochastic matrices and is applied to a bidimensional lattice of triangles and squares. The only parameters are the energy barriers to form bonds. According to the values of these energies one could obtain crystalline, amorphous and quasicrystalline phases. Some of the quasicrystalline structures are reported here for the first time.
Title:
Infinite Lifshitz point in incommensurate type-I dielectrics
Authors:
Kityk AV. Zadorozhna AV. Mokry OM. Sahraoui B.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(1):10-13, 1999 Jul 1.
Abstract:
The phenomenological analysis of the pressure-temperature (P-T) phase diagram of [N(CH3)(4)](2)CuCl4 (TMATC-Cu) crystals is presented. It is shown that serious disagreement between the experimental results and theory may be removed assuming that the coefficient of the Landau free energy expansion kappa at the gradient term (dq/dz)(dq*/dz) changes the sign in the experimental range of pressures. The phase diagram in the alpha-kappa phase plane is characterized by infinite Lifshitz: point (at kappa--> infinity) in which both lines of the phase transitions into the incommensurate phase merge together, whereas the incommensurate wave vector approaches its zero value. The triple point (P(K)approximate to 55 MPa, T(K)approximate to 304 K) observed in these crystals may be considered as an artificial point, which results from the limitation of experimental resolution. Therefore, even above P-K there still exist two very close (unresolved) lines of the incommensurate phase transitions. .
Title:
Time-of-flight neutron-scattering study of phason hopping in decagonal
Al-Co-Ni quasicrystals
Authors:
Coddens G. Steurer W.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(1):270-276, 1999 Jul 1.
Abstract:
We have measured phason hopping in isotopic powder samples of decagonal Al-Co-Ni quasicrystals, by time-of-flight quasielastic neutron scattering. The three isotopic samples were based on Ni-nat, and 99.5% enriched Ni-58 and Ni-60. Two characteristic jump times have been observed. The anomalous temperature dependence observed in the icosahedral phases i-Al-Cu-Fe and Al-Mn-Pd is confirmed. .
Title:
Local electrostatic moments and periodic boundary conditions
Authors:
Schultz PA.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(3):1551-1554, 1999 Jul 15.
Abstract:
Electronic structure calculations frequently invoke the supercell approximation and solve for electrostatic potentials within periodic boundary conditions. For systems that are electronically charged, or contain dipole (or higher) moments, this artifice introduces spurious potentials due to interactions between the system and multipole moments of its periodic images in aperiodic directions. I describe a method to handle properly the multipole moments of the electron density in electronic structure calculations using supercells. The density is divided into two pieces. A model local density is constructed to match multipole moments of the full density. The potential from this piece is obtained treating this density as isolated. With the density of this local-moment countercharge removed from the full density, the remainder density no longer contains moments with long-range potentials, and its electrostatic potential can be evaluated accurately using periodic boundary conditions.
Title:
Gallium-induced nanostructures on Si(111): From magic
clusters to incommensurate structures
Authors:
Lai MY. Wang YL.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(3):1764-1770, 1999 Jul 15.
Abstract:
Scanning tunneling microscopy is used to study the nanostructures that are induced within the root 3 x root 3R30 degrees Ga/Si(111) surface by the deposition of the submonolayer of Ga and subsequent annealing. Triangular magic clusters and incommensurate islands are found after annealing at low and high temperatures, respectively. The clusters and islands have similar atomic configurations and their surrounding root 3 x root 3 R30 degrees adatom lattices also exhibit similar characteristic vacancy patterns. A type of structural model is proposed for both the clusters and islands. The model provides some insights about the structural evolution, from the root 3 x root 3 monolayer to the incommensurate bilayer structure, that is induced by increasing local Ga coverage. .
Title:
Electrical conductivity and pyroelectricity of lithium-potassium sulphate
single crystal in the temperature range 300-950 K
Authors:
Abu El-Fadl A. Gaffar MA. Omar MH.
Source:
(list of journals)
Physica B. 269(3-4):395-402, 1999 Sep.
Abstract:
The DC electrical conductivity (sigma) along the a- and c-axes and the pyroelectric coefficient (p) along the pyroelectric c-axis of lithium-potassium sulphate (LKS) single crystal are measured in the temperature range 300-950 K. The measurements of sigma show anomalous behaviour at the transition point around 705 K. The sigma-T relationship reveals an activation energy of conduction along the c-axis of 0.85 eV above and 0.37 eV below the transition temperature, respectively. The effect of thermal recycling on the electric conduction is discussed. A maximum signal at about 720 K and a variation in the sign of p at about 704 K have been observed. The phase transition reported in the literature at 333 K was not confirmed by our measurements. The current density (J) is measured as a function of the applied electric field (E) below and above the phase transition temperature along the c- and a-axes in order to estimate the type of conduction dominated and the effect of E upon the conductivity measurements of this crystal. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Absorption spectra and optical parameters of lithium-potassium sulphate
single crystals
Authors:
Abu El-Fadl A. Gaffar MA. Omar MH.
Source:
(list of journals)
Physica B. 269(3-4):403-408, 1999 Sep.
Abstract:
The optical transmittance and reflectance near the fundamental absorption region along the c- and a-axes of lithium potassium sulphate single crystal (LKS) are measured at room temperature. From the data the absorption coefficient (alpha) and the optical band gap (E-g(opt.)) were deduced. The type of transition was determined. The steepness parameter (sigma), the temperature dependence of the energy gap and the exciton energy (E-0) were also calculated. The extinction coefficient, the refractive index and both the real and imaginary parts of the dielectric permittivity were calculated as functions of the photon energy. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Bandpass crystal filter for enhanced phase-sensitive
detection
Authors:
Ivanov EV.
Source:
(list of journals)
Measurement Science & Technology. 10(7):N77-N81, 1999 Jul.
Abstract:
This paper describes a super-narrow-band bandpass filter with a crystal resonator that can be used for efficient noise filtration in measurement systems with phase-sensitive detection and a low signal-to-noise ratio. If a crystal oscillator is used in the modulator driver, the same type of crystal can be used in the super-narrow-band filter in the sensor signal processing circuit to suppress the noise in the signal as much as possible before demodulation of the signal. However, the presence of the shunt capacitance of the crystal's electrodes makes the stop band attenuation of such a filter very poor. A technique to compensate for the shunt capacitance of the crystal using a negative capacitance circuit is discussed. The problem of matching the bandpass central frequency of the super-narrow-band filter and the oscillating frequency of the modulator driver is examined.
Title:
Electrical and structural properties of Cr ion-implanted thin Au films
Authors:
Artunc N. Elgun N. Vizir A. Brown I. Bo S. Tarhan E.
Source:
(list of journals)
Materials Chemistry & Physics. 60(2):182-187, 1999 Aug 16.
Abstract:
Cr metal ions with doses of 1 x 10(14)-1 x 10(15) ions/cm(2) have been implanted at 125 keV into thin Au films prepared by DC magnetron sputtering. Electron diffraction patterns have revealed that ail the films remain in the f.c.c. structure, indicating the formation of Au-Cr solid solution. The resistivity of the films were studied in the temperature range 100-330 K. The results show increase in the resistivity with respect to the unimplanted him as a result of the implantation. Some samples show two different types of resistivity anomalies, which are attributed to the occurrence of the antiferromagnetically incommensurate spin density wave and commensurate spin density wave structures, (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
A structural study of the quasi one-dimensional compound (Ca1-xYx)(0.82)CuO2
prepared at room pressure
Authors:
Miyazaki Y. Gameson I. Edwards PP.
Source:
(list of journals)
Journal of Solid State Chemistry. 145(2):511-516, 1999 Jul.
Abstract:
A solid solution of the quasi one-dimensional cuprate, (Ca1-xYx)(0.82)CuO2 (0 less than or equal to x less than or equal to 0.435), has been successfully synthesized in an oxygen stream at room pressure. Structural changes have been determined for the basic crystal structure by means of the Rietveld method using powder X-ray diffraction. Upon Y doping, the nearest (intrachain) Cu-Cu distance increases from 1.93 to 1.98 Angstrom, while the next-nearest (interchain) Cu-Cu distance decreases from 3.46 to 3.41 Angstrom. The incommensurate superstructure, originating from differences in the periodic arrangement of the (Ca,Y) atoms and CuO2 chains, has also been examined. The modulation period along the crystal a axis implies that the stoichiometry of the solid solution shifts toward that of the cation-deficient member (Ca1-xYx)(0.80)CuO2. This compositional discrepancy might be canceled by the large change in the modulation period along the c axis. (C) 1999 Academic Press.
Title:
Infrared activity of KAl(MoO4)(2) and NaAl(MoO4)(2)
Authors:
Maczka M. Hanuza J. Lutz ETG. van der Maas JH.
Source:
(list of journals)
Journal of Solid State Chemistry. 145(2):751-756, 1999 Jul.
Abstract:
We have investigated the infrared activity of phonons in monoclinic, pseudo-trigonal NaAl(MoO4)(2) performing polarized reflectivity in the range 1200-700 cm(-1) and IR absorption measurements of polycrystalline samples in the 1200-30 cm(-1) region. To identify all modes predicted by group theory arguments, we compare the recorded spectra with similar measurements performed on trigonal KAl(MoO4)(2). The obtained results allow us to propose the assignment of all observed bands to the respective vibrational modes. Our results suggest that the ambient temperature structure of NaAl(MoO4)(2) may be described by the space group C2/c. (C) 1999 Academic Press.
Title:
Quasicrystal Lie algebras and their generalizations
Authors:
Patera J. Twarock R.
Source:
(list of journals)
Physics Reports-Review Section of Physics Letters. 315(1-3):241-256, 1999
Jul.
Abstract:
We review and extend the results about quasicrystal Lie algebras of Patera et al. [Phys. Lett. A 246 (1998) 209], which is a new family of infinite dimensional Lie algebras over the real and complex number fields, whose generators are in a one-to-one correspondence with the points of a one-dimensional quasicrystal. Some new properties of quasicrystal Lie algebras and further details on their representation theory are pointed out and the concept of generalized quasicrystal Lie algebras is presented. The latter allows to associate to the generators of the Lie algebra quasicrystal points of one-dimensional quasicrystals with acceptance windows symmetric around 0, which was not possible in the framework of Patera et al. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Incommensurate spin dynamics of underdoped superconductor
YBa2Cu3O6.7
Authors:
Arai M. Nishijima T. Endoh Y. Egami T. Tajima S. Tomimoto K. Shiohara Y. Takahashi M. Garrett A. Bennington SM.
Source:
(list of journals)
Physical Review Letters. 83(3):608-611, 1999 Jul 19.
Abstract:
The spin dynamics of the underdoped superconductor YBa2Cu3O6.7 (T-c similar to 67 K) was revealed to have an incommensurate wave vector dependence with 'pillars" in the dispersion relation at the positions (1/2 +/- d, 1/2, 0) and (1/2, 1/2 +/- d, 0). This is the same symmetry as that found in La2-xSrxCuO4. The value of the incommensurability, d = 0.11 +/- 0.01 r.l.u similar to 1/8, is very clost: to the value expected from the hole concentration. These results have demonstrated that the spin dynamics do not depend on the details of Fermi surface but have an analogous form to that for the proposed stripe domain structure.
Title:
Transmission electron microscopy characterization of the high-T-c
superconductor HgBa2Ca3Cu4O10+delta
Authors:
Luo ZP. Hashimoto H. Ihara H. Iyo A. Tokiwa K.
Source:
(list of journals)
Philosophical Magazine Letters. 79(7):429-439, 1999 Jul.
Abstract:
The structures of HgBa2Ca3Cu4O10+delta (Hg-1234) samples have been characterized by means of high-resolution electron microscopy, electron diffraction, X-ray energy-dispersive spectroscopy (XEDS) and electron-energy-loss spectroscopy (EELS) techniques. A modulated structure with a modulation vector of q = (0.036-0.048)b* + 0.5c* was found for Hg-1234. High-resolution electron microscopy on the modulated structure revealed slight displacements of atomic layers along the c direction. The anomalous contrast induced by the modulation was observed to be distributed asymmetrically between the HgOdelta, layers, leading to the breakdown of the (001) mirror symmetry of the basic structure. XEDS compositional analyses showed a depletion of mercury for the modulated Hg-1234 compared with the unmodulated Hg-1234, while EELS analysis suggested the presence of carbon in the modulated Hg-1234 phase. In addition, a side-centred ordered (Cu,Hg)-1223 phase with low mercury content was identified as one of the major impurity phases in the Hg-1234 samples.
Title:
Stable quasicrystalline sphere packing
Authors:
Cockayne E. Mihalkovic M.
Source:
(list of journals)
Philosophical Magazine Letters. 79(7):441-448, 1999 Jul.
Abstract:
Wills (1990, J. Phys., Paris, 51, 1061) found a method relating certain decagonal disc packings to decagonal sphere packings with high packing fractions. Applying this technique to the decagonal rectangle-triangle tiling generated by inflation, we obtain a sphere packing with decagonal symmetry and a packing fraction greater than 0.6953. This is the densest known stable quasicrystalline sphere packing.
Title:
Unusual adsorption behavior of polymers in layered
structures
Authors:
Sommer JU. Blumen A.
Source:
(list of journals)
Macromolecular Symposia. 139:67-75, 1999 Apr.
Abstract:
We studied the conformations of polymer chains embedded in regular lamellar matrices such as microphase-separated block copolymer melts or lipid/water systems. In such quasi-one-dimensional systems, the host plays the role of a nearly-periodic external potential. A probe chain can get trapped with the localization length L at isolated defects, when its degree of polymerization N exceeds a cross-over value N-L. Interestingly, the radius of gyration, R-g, of the chain displays a minimum as a function of the defect density, rho, the minimum being estimated by rho(c)L similar or equal to N-L/N. Using Monte Carlo simulation, we underline the non-monotonic behavior of R-g and calculate Green's function for various defect densities. On the same vein, the mean square displacement of the monomer units at large times shows a pronounced minimum as a function of the defect density, rho.
Title:
Crystal growth of low-dimensional oxides related to the 2-H
perovskite structure in K2CO3 fluxes
Authors:
Henley WH. Claridge JB. Smallwood PL. zur Loye HC.
Source:
(list of journals)
Journal of Crystal Growth. 204(1-2):122-127, 1999 Jul.
Abstract:
Single crystals of the general formula [A](x)[(A',B)O-3] were grown from K2CO3 flux. Sr3NiPtO6,Sr3CuPtO6, (1.10)[(Cu0.38Rh0.62)O-3], [Ba](1.16)[(Ni0.23Rh0.77)O-3], [Ba](1.06)[RhO3], [Ba](1.18)[(CU0.29Rh0.71)O-3], [Ba](1.06)[(Ni0.44Ir0.56)O-3], and (1.25)[RhO3], have been synthesized and characterized by X-ray diffraction, scanning electron microscopy, and electron microprobe analysis. Crystal morphology and composition have been shown to be highly dependent on several synthetic parameters including temperature and the concentration of alkaline earths in the flux. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Polar domain walls and orientational disorder in
incommensurate Cs2HgBr4
Authors:
Jorio A. Echegut P. Speziali NL. Pimenta MA.
Source:
(list of journals)
Ferroelectrics. 221(1-4):79-84, 1999.
Abstract:
The low temperature phases of Cs2HgBr4 have been studied by Raman scattering and infrared reflectivity. The anomalous behavior of the nu(1) Raman modes and the increase of the oscillator strength of the infrared modes polarized along the y-direction are discussed in terms of the orientational disorder of the HgBr4 tetrahedra and the presence of layered structure of polar domain walls at low temperatures.
Title:
EPR study of K2ZnCl4 in incommensurate phase
Authors:
Hrabanski R. Kassiba A.
Source:
(list of journals)
Ferroelectrics. 222(1-4):479-483, 1999.
Abstract:
Temperature dependence of EPR spectra of Mn2+ is studied in paraelectric and incommensurate phases of K2ZnCl4 between 390 and 580 K. The splitting and broadening of the EPR lines are analysed on the basis of phenomenological model of the incommensurate modulation of the fine structure tensor. The temperature dependence of the splitting follows the power law (T-T-1)(2 beta) with 2 beta=0.70. The temperature variation of the soliton density is also determined.
Title:
Nonlinear ferroelectric domain wall response
Authors:
Mueller V. Beige H. Zhang QM.
Source:
(list of journals)
Ferroelectrics. 222(1-4):553-562, 1999.
Abstract:
The ac-field dependence of complex dielectric coefficients in the improper ferroelectric phase of incommensurate Rb2ZnCl4 crystals is analyzed and compared with those observed in donor doped lead zirconate titanate (PZT) piezoceramics. For all coefficients examined, a threshold field for the onset of nonlinearity exists leading to qualitatively the same non-analytic scaling behavior above threshold. Due to the similar nonlinear behavior of very different ferroelectric systems, we suggest that a universal mechanism may exist in a larger class of ferroelectrics causing nonlinearity at moderate field level. This may be related to the dynamics of randomly pinned elastic interfaces driven at field strengths slightly above threshold for collective interface motion.
Title:
Manifestation of coexistence of the long-periodic phase with the
incommensurate phase
Authors:
Sveleba S. Polovinko I. Zhmurko V. Pankivskyi Y.
Source:
(list of journals)
Ferroelectrics. 222(1-4):617-624, 1999.
Abstract:
Electric and optical properties of the commensurate ferroelectric long-periodic phase in [N(CH3)(4)](2)ZnCl4 and [N(CH3)(4)](2)CoCl4 crystals are investigated to explain mechanism of the hysteresis double loops appearance.
Title:
Evolution of the structure of Rb2ZnCl4 over the temperature
range 4.2-310 K
Authors:
Bagautdinov BS. Shekhtman VS.
Source:
(list of journals)
Physics of the Solid State. 41(6):987-993, 1999 Jun.
Abstract:
X-ray diffraction is used to study the temperature dependence of the lattice parameters and the sequence of structural realignments in crystalline Rb2ZnCl4 over temperatures of 4.2-310 K. The appearance of and changes in the system of satellite reflexes indicative of structural ordering are studied. Below 74 K, on going into the monoclinic phase (space group A11a), anomalies are observed in the behavior of the lattice parameters, and superstructural reflexes develop with wave vectors q = a*/3 + b*/2 + c*/2 corresponding to an increase by a large factor in initial parameters a, b, and c of the Pnma-phase. (C) 1999 American Institute of Physics. .
Title:
Infrared spectra of bismuth family of superconductors Bi2Sr2Can-1CunO4+2n+y
Authors:
Mohan S. Kannan R.
Source:
(list of journals)
Journal of Materials Science. 34(13):3241-3247, 1999 Jul 1.
Abstract:
FTIR spectra of bismuth family of superconductors are studied. Polycrystalline samples of bismuth superconductors are prepared choosing an off-stoichiometric composition for phase stabilisation and reproducibility. Vibrational modes are strongly affected by the holes introduced into the CuO planes. Mid IR spectra of the Bismuth system was recorded using Bruker IFS 66v and the high frequency oxygen vibrations of the system is discussed based on the factor group analysis for both symmorphic and non-symmorphic space groups 14/mmm, F-mmm and A(maa) of different structures based on the modulated superstructure. (C) 1999 Kluwer Academic Publishers.
Title:
Phonon-phason coupling in icosahedral quasicrystals
Authors:
Zhu WJ. Henley CL.
Source:
(list of journals)
Europhysics Letters. 46(6):748-754, 1999 Jun 15.
Abstract:
From relaxation simulations of decoration-based quasicrystal structure models using microscopically based interatomic pair potentials, we have calculated the (usually neglected) phonon-phason coupling constant. Its sign is opposite for the two alloys studied, i-AlMn and i-(Al,Cu)Li; a dimensionless measure of its magnitude relative to the phonon and phason elastic constants is of order 1/10, suggesting its effects are small but detectable. We also give a criterion for when phonon-phason effects are noticeable in diffuse tails of Bragg peaks.
Title:
The design of a molecularly selective capillary based on an
incommensurate intergrowth structure
Authors:
Khan AA. Bramwell ST. Harris KDM. Kariuki BM. Truter MR.
Source:
(list of journals)
Chemical Physics Letters. 307(5-6):320-326, 1999 Jul 9.
Abstract:
A general design strategy for a molecularly selective capillary is proposed, based on the properties of incommensurate intergrowth materials. The strategy is illustrated for urea inclusion compounds, in which guest molecules are contained within one-dimensional tunnels in a crystalline urea host structure. It is shown that net transport of guest molecules in one direction along the tunnel can be achieved by inserting new guest molecules at one end of the crystal (by dipping it into the liquid phase of another potential guest), with the original guest molecules expelled from the other end. Such phenomena have considerable potential as the basis of highly selective micro-scare separation techniques, based on discrimination of molecular size, shape and chirality. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Modeling the time variability of accreting compact sources
Authors:
Kazanas D. Hua XM.
Source:
(list of journals)
Astrophysical Journal. 519(2 Part 1):750-761, 1999 Jul 10.
Abstract:
We present model light curves for accreting black hole candidates (BHCs) based on a recently proposed model for their spectre-temporal properties. According to this model, the observed light curves and aperiodic variability of BHCs are due to a series of soft photon injections at random (Poisson) intervals near the compact object and their reprocessing into hard radiation in an extended but nonuniform hot plasma corona surrounding the compact object. We argue that the majority of the timing characteristics of these light curves are due to the stochastic nature of the Comptonization process in the extended corona, whose properties, most notably its radial density dependence, are imprinted in them. We compute the corresponding power spectral densities (PSD), autocorrelation functions, time skewness of the light curves, and time lags between the light curves of the sources at different photon energies and compare our results to observation. Our model light curves compare well with observations, providing good fits to their overall morphology, as manifest by the autocorrelation and skewness functions. The lags and PSDs of the model light curves are also in good agreement with those observed (the model can even accommodate the presence of quasi-periodic oscillations). Finally, while most of the variability power resides at timescales approximately a few seconds, at the same time, the model allows also for shots of a few milliseconds in duration, in accordance with observation. We suggest that refinements of this type of model along with spectral and phase lag information can be used to probe the structure of this class of high-energy sources.
Title:
Electric field properties at cationic sites in normal,
incommensurate and commensurate K2ZnCl4
crystals
Authors:
Grecu MN. Constantinescu S.
Source:
(list of journals)
Applied Magnetic Resonance. 16(3):373-382, 1999.
Abstract:
The local electric properties at K and Zn sites in the normal, incommensurate and commensurate phases of K2ZnCl4, as derived from a numerical computation of the lattice contributions to the electric potential V(r), electric field intensity E(r) and electric field gradient tensor V-alpha beta(r) are reported. The numerical data obtained at each cationic position were correlated with the experimental K-39 NMR, Cu2+ and Mn2+ EPR and Fe-57 Mossbauer results in pure and doped K2ZnCl4. A proportionality between crystal field and zero-field splitting was taken into account for Mn2+, whereas for K+, Cu2+ and Fe3+ ions the electric field gradient is directly related to the crystal field parameter. By this comparison, on computations done in the ionic fractional charge and relaxed lattice approximations, the insertion of probe-species of iron, copper and manganese ions on off-center Zn sites is proposed. The K-39 electric field gradient tensor calculations in the incommensurate phase fit well with the NMR data reported recently.
Title:
Incommensurate modulation and the crystal
structure of ganophyllite
Authors:
Noe DC. Veblen DR.
Source:
(list of journals)
American Mineralogist. 84(7-8):1088-1098, 1999 Jul-Aug.
Abstract:
Incommensurate modulation in ganophyllite crystals was investigated with selected-area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), analytical electron microscopy (AEM), and single-crystal X-ray diffraction (XRD) techniques. The XRD data were used to perform a new subcell (a = 5.550 Angstrom, b = 13.539 Angstrom, c = 25.134 Angstrom, beta = 93.928 degrees) refinement of the structure with a higher precision than previous refinements (R = 0.041). Although supercell reflections were too weak for collection with the diffractometer, the supercell was modeled by comparing experimental SAED patterns and HRTEM images to their simulated counterparts. These simulations indicate that incommensurate modulation arises from offsets in the location of inverted tetrahedra between adjacent [100] strips. The true supercell of incommensurate crystals involves a tripling of the subcell a axis and at least a twelvefold increase in the b axis; previously identified supercell reflections are actually aggregates of extremely closely spaced reflections in incommensurate crystals. Unlike commensurate crystals, the subcell c axis of incommensurate ganophyllite is not doubled. AEM data suggest that the occurrence of commensurate or incommensurate forms is not compositionally dependent.
Title:
Crystal lattice and phase transitions in Na4TiP2O9 (NTP) and
Na4.5FeP2O8(O,F) (NFP) superionic conductors as a function of high pressures
and temperatures
Authors:
Maximov B. Sirota M. Werner S. Schulz H.
Source:
(list of journals)
Acta Crystallographica - Section B, Structural Science.
55(Part 3):259-265, 1999 Jun 1.
Abstract:
The lattice dynamics of Na4TiP2O9 (tetrasodium titanium diphosphorus nonaoxide, NTP) and Na4.5FeP2O8(O,F) (nonasodium diiron tetraphosphorus difluoride octadecaoxide, NFP) crystals, which are superionic conductors with Na+-ion conductivity, were studied under high pressures. Lattice constants as a function of hydrostatic pressure were measured on a four-circle diffractometer using a high-pressure cell with diamond anvils. At 1.78 +/- 0.15 GPa NTP undergoes a reversible phase transition from the modulated monoclinic (pseudo-orthorhombic) modification which is stable under atmospheric conditions. A similar phase transition in NTP is observed at 523 K. For NFP, it may be assumed that at least three phase transitions occur when the pressure increases from atmospheric to 12 GPa, at 1.39 +/- 0.08, 4.52 +/- 0.32, and 6.02 +/- 0.02 GPa, as concluded from the change in the unit-cell parameters and in the color of the crystals: the color changes from ginger (dark orange) to pink at similar to 1.5-2.0 GPa pressure and to violet at similar to 6.0 GPa.
Title:
Mossbauer spectroscopy of interlayer boundaries in magneto-noncollinear
[Fe-57/Cr](12)/MgO (100) superlattices
Authors:
Ustinov VV. Tsurin VA. Romashev LN. Ovchinnikov VV.
Source:
(list of journals)
Technical Physics Letters. 25(6):459-461, 1999 Jun.
Abstract:
Results are presented of Mossbauer analyses of [Fe-57/Cr](12)/MgO (100) superlattices. A combined approach was used, based on model calculations and a method of reconstructing the density distribution function P(H-hf) of the hyperfine fields. This procedure allowed us to systematically subtract the subspectra from the different neighborhood configurations of the resonant Fe-57 atom. A detailed structural model was obtained for the Fe-Cr transition region from a "pure" Fe layer to a "pure" Cr layer. A deflection of the magnetic moment of the Fe atoms from the plane of the superlattice layers was identified in the interface of the Fe and Cr layers. The specific magnetic structure of the interface regions with different angular orientations of the magnetic moments of the Fe atoms relative to the plane of the layers (between 0 and 90 degrees) is attributed to the coexistence of strong antiferromagnetic interaction between Fe and Cr atoms and an incommensurate spin density wave in the Cr layers. (C) 1999 American Institute of Physics. .
Title:
A Monte Carlo study of structure and intercalation in
conducting polymers
Authors:
Mao GM. Winokur MJ.
Source:
(list of journals)
Synthetic Metals. 101(1-3):124-125, 1999 May.
Abstract:
Monte Carlo (MC) calculations have been used to model the equatorial chain packing within linear ir-conjugated polymers both before and after intercalation. These calculations employ a generalized anisotropic planar rotor (GAPR) representation of the host lattice through a model Hamiltonian, introduced previously in a mean-field theory (MFT) approach by H.-Y. Choi, A.B. Harris and E.J. Mele [Phys. Rev. B 40, 3766 (1989)], in which planar rotors (representing polymer chains) are pinned onto a rigid two-dimensional triangular lattice. Equilibrium structures and transition temperatures are in good agreement with those seen in MFT but additional MC calculations show the possible existence of commensurate phases with larger unit cells than those considered in MFT studies.
Title:
Self-assembly of functionalized fullerenes
Authors:
Hong H. Davidov D. Kallinger C. Lemmer U. Feldmann J. Harth E. Gugel A. Mullen K.
Source:
(list of journals)
Synthetic Metals. 102(1-3):1487, 1999 Jun.
Abstract:
We report on the fabrication and characterization of ultrathin self-assembled fullerene films. Using a carboxy-functionalized fullerene and poly(ethylen imine) we prepare fullerene films with the technique of layer-by-layer adsorption. Our structures exhibit a modulated electron density as evidenced by the observation of a quasi-Bragg reflection in X-ray reflectivity studies. This relatively high degree of order is attributed to the formation of hydrogen bonds.
Title:
Self-assembly of functionalized fullerenes
Authors:
Hong H. Davidov D. Kallinger C. Lemmer U. Feldmann J. Harth E. Gugel A. Mullen K.
Source:
(list of journals)
Synthetic Metals. 102(1-3):1537, 1999 Jun.
Abstract:
We report on the fabrication and characterization of ultrathin self-assembled fullerene films. Using a carboxy-functionalized fullerene and poly(ethylene imine), we prepare fullerene films by the layer-by-layer adsorption technique. Our structures exhibit a modulated electron density as evidenced by the observation of a quasi-Bragg reflection in X-ray reflectivity studies. This relatively high degree of order is attributed to the formation of hydrogen bonds.
Title:
Structure and phase transitions of perylene radical cation
salts
Authors:
Buschhaus C. Dormann E. Eichhorn K. Hummer K. Moret R. Ravy S.
Source:
(list of journals)
Synthetic Metals. 102(1-3):1757-1758, 1999 Jun.
Abstract:
The quasi-one dimensional conductors (PE)(2)X . 2/3THF (PE = perylene, X = PF6,AsF6;THF = tetrahydrofurane) and (PE)(4)(SbF6)(3) were studied by X-Ray scattering. For the PF6- and AsF6-salts the Peierls- and two further structural transitions are characterized by fixed film-fixed crystal exposures. (PE)(4)(SbF6)(3) shows modulated diffuse sheets of high intensity in reciprocal space. Perylene and anion molecules form parallel separated stacks. Due to weak correlation of neighbouring anion stacks a Peierls transition is prevented.
Title:
Incommensurate phase of the organic Spin-Peierls compound
(TMTTF)(2)PF6
Authors:
Brown SE. Clark WG. Alavi B. Chow DS. Merlic CA. Tantillo DJ.
Source:
(list of journals)
Synthetic Metals. 103(1-3):2056-2057, 1999 Jun.
Abstract:
The magnetic field/temperature phase of (TMTTF)(2)PF6 is established using C-13 NMR and cantilever magnetic force measurements. At low temperatures and above a critical field B-c approximate to 19T, spectral broadening occurs signalling the onset of the incommensurate phase of the Spin-Peierls state. There is well-defined structure in the high-field C-13 lineshapes which is not included in the standard soliton lattice description for the high-field phase.
Title:
Anomalous structural transition of the beta(BEDT-TTF)(2)PF6 surface observed
by scanning tunneling microscopy
Authors:
Ishida M. Mori T. Shigekawa H.
Source:
(list of journals)
Synthetic Metals. 103(1-3):2105-2106, 1999 Jun.
Abstract:
In a unit cell of the crystal a-c plane of the beta-(BEDT-TTF)(2)PF6 crystal surface, four BEDT-TTF molecules form two dimers. Since the alternate molecular rows consisting of the dimers are observed to be bright by scanning tunneling microscopy (STM) along the crystal alpha-axis, the surface molecular structure is considered to have a periodic modulation. From the analysis of the STM images, the modulated surface structure was found to fluctuate in an anomalous manner. The two dimers are known to have a similar conformation in the crystal, and one of the BEDT-TTF molecules in each dimer is located about 0.2 nm to the surface. Despite the difference in the distance from the surface, molecules that are farther from the surface were observed to be brighter by STM.
Title:
Low Temperature X-Ray and ESR study of one-dimensional compound (TTM-TTP)I-3
Authors:
Fujimura N. Namba A. Kambe T. Nogami Y. Oshima K. Mori T. Kawamoto T. Misaki Y. Yamabe T.
Source:
(list of journals)
Synthetic Metals. 103(1-3):2111-2112, 1999 Jun.
Abstract:
(TTM-TTP)I-3 which has been considered as the typical one-dimensional half-filled band system, has been critically restudied by structural and magnetic measurements. X-ray diffuse scattering study reveals the formation of 2k(F) CDW superstructure with the wave vector q(1) =(0, 0, 0.5) below 160 K of the metal-insulator transition temperature. Another structural modulation with q(2) = (0.5, 0, 0.5) is observed below 90-100 K. modulated structure analysis using the q(2) satellite reflections and the Bragg reflections shows the large displacement in I-3 anion. Anomalies in chi line width and g-value of ESR measurements which correspond to the structural anomaly, are also reported.
Title:
H-1 NMR in the Incommensurate SDW of (TMTSF)(2)X
Authors:
Nomura K. Hosokawa Y. Iwasaki H. Takasaki S. Yamada J. Nakatsuji S. Anzai H.
Source:
(list of journals)
Synthetic Metals. 103(1-3):2147-2148, 1999 Jun.
Abstract:
The incommensurate spin-density wave (SDW) phase was investigated in (TMTSF)(2)X with the H-1 NMR. A divergent peak is observed ed at the temperature T* well below T-SDW in the temperature dependence of H-1 spin-lattice relaxation rate. The frequency independent relaxation rate observed between T* and T-SDW is well explained by the pinned phason mode. The power law behavior around T* suggests another phase transition at T*. It is proposed that the discommensuration structure is stabilized below T*.
Title:
Electronic properties of the (LaS)(1.18)VS2 incommensurate
misfit compound.
Authors:
Cario L. Corraze B. Meerschaut A. Moelo Y. Chauvet O.
Source:
(list of journals)
Synthetic Metals. 103(1-3):2640-2643, 1999 Jun.
Abstract:
We investigate the transport and magnetic properties of 2D (LaS)(1.18)VS2 misfit compound single crystals. While the conductivity is characteristic of a hopping system with localized charge carriers, the magnetic susceptibility exhibits a clear signature of a low dimensional metal. We suggest that these paradoxal observations can be reconciled by taking into account the underlying 1D character of the t(2g)-t(2g) interactions within the VS2 plans and the strong anisotropic displacive modulation on the V site. This suggestion is supported by band structure calculations.
Title:
Structure of a quasicrystal without atomic
clusters
Authors:
Abe E. Sato TJ. Tsai AP.
Source:
(list of journals)
Physical Review Letters. 82(26):5269-5272, 1999 Jun 28.
Abstract:
We show that, using high-resolution transmission electron microscopy, the first Frank-Kasper decagonal quasicrystal discovered in Zn-Mg-rare-earth alloys has a novel atomic structure in which the atomic arrangement in the tenfold symmetry plane can simply be interpreted as the Penrose tiling decorated by individual atoms. This is in sharp contrast to the idea of linking atomic clusters which have the same point symmetry as the Fourier spectrum of quasicrystals, which has been successfully used to describe the structure of quasicrystals until now. An energetically favorable quasi-unit-cell concept is applied for the structural description.
Title:
Quasicrystalline d-AlCuCo identified as random tiling by ion
channeling combined with particle-induced X-ray emission
Authors:
Zeger G. Plachke D. Carstanjen HD. Trebin HR.
Source:
(list of journals)
Physical Review Letters. 82(26):5273-5276, 1999 Jun 28.
Abstract:
In a model quasicrystal for decagonal AlCuCo the phason disorder was gradually increased and the channeling particle-induced x-ray emission (PIXE) yields were computed for 3 MeV He ions by Monte Carlo simulations. For large phason disorder good agreement with experimental data was obtained. Thus we conclude that the sample of d-AlCuCo used in the measurements is a random tiling. One remaining discrepancy, namely, that the PIXE yields of the simulations are approximately the same for Cu and Co, is eliminated by optimization of the Cu and Co positions.
Title:
Superconducting rare earth transition metal borocarbides
Authors:
Drechsler SL. Shulga SV. Muller KH. Fuchs G. Freudenberger J. Behr G. Eschrig H. Schultz L. Golden MS. von Lips H. Fink J. Narozhnyi VN. Rosner H. Zahn P. Gladun A. Lipp D. Kreyssig A. Loewenhaupt M. Koepernik K. Winzer K. Krug K.
Source:
(list of journals)
Physica C. 318:117-126, 1999 May.
Abstract:
We present an overview of selected properties of quaternary intermetallic rare earth transition metal borocarbides and related boronitride compounds, as well as of theoretical calculations with possible relevance to the mechanism of superconductivity. The interplay of superconductivity and magnetism for compounds with pure and mixed rare earth components is considered. We suggest that the incommensurate magnetic structure modulated along the a-axis is responsible for the pair breaking in HoxR1-xNi2B2C; R = Y, Lu samples. The effect of doping (Cu. Co) at the transition metal site is considered experimentally and theoretically. The possible role of correlation effects due to the presence of the transition metal component in determining the electronic structure is discussed comparing the band structure calculation results with various electronic spectroscopies as well as de Haas-van Alphen data. Important thermodynamic properties of these systems are analyzed within multiband Eliashberg theory with special emphasis on the upper critical field H-c2(T) and the specific heat. In particular, the unusual positive curvature of H-c2(T) near T-c observed for high-quality single crystals, polycrystalline samples of YNi2B2C, LuNi2B2C as well as to a somewhat reduced extent also for the mixed system Y1-xLuxNi2B2C is explained microscopically. It is shown that in these well-defined samples the clean limit of type II superconductors is achieved. The values of H-c2(T) and of its positive curvature near T, (as determined both resistively and from magnetization as well as from specific heat measurements is an intrinsic quantity generic for such samples) decrease with growing impurity content. Both quantities thus provide a direct measure of the sample quality. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Incommensurate magnetism in non-superconducting
PrBa2Cu3O6.92
Authors:
Boothroyd AT. Hill JP. McMorrow DF. Andersen NH. Stunault A. Vettier C. Wolf T.
Source:
(list of journals)
Physica C. 318:292-298, 1999 May.
Abstract:
We report the discovery of incommensurate magnetic order in non-superconducting single crystals PrBa2Cu3O6.92. Resonant X-ray magnetic scattering at the Pr L-II and L-III edges and high resolution neutron diffraction were used to characterise the magnetic order on the different magnetic sublattices. The data reveal that the Pr sublattice orders at a temperature of 19 K in an incommensurate structure with ordering wavevector (0.5 +/- delta, 0.5, 0) or (0.5, 0.5 +/- delta, 0), delta approximate to 0.006-0.008, A spin reorientation in the Pr sublattice to a commensurate antiferromagnetic structure with ordering wavevector (0.5, 0.5, 0.5) takes place at a temperature close to 9 K. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
The non-Fermi liquid behavior and diagonal lattice stripes in cuprate
superconductors
Authors:
Bianconi A. Saini NL. Lanzara A. Avila J. Asensio MC. Tajima S. Gu GD. Koshizuka N.
Source:
(list of journals)
Physica C. 318:304-311, 1999 May.
Abstract:
We have studied momentum distribution of photoemission intensity around the Fermi surface of Bi2Sr2CaCu2O8+delta (Bi2212) high T-c superconductor by angle-resolved photoemission. The line shape of the energy distribution curves show a spectral function A(k,omega) expected for a non-Fermi liquid behaviour. The Fermi surface contour in the 'even symmetry' reveals the suppression of spectral weight due to coupling with joint incommensurate charge density wave (ICDW) at q(- 0.4 pi,0.4 pi) in the diagonal direction and the spin density wave (SDW) at G(pi,pi). Additional spectral weight is found at (0.6 pi,0.6 pi) due to scattering of electrons with SDW at optimum doping as revealed by constant energy contour in 'odd symmetry'. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Title:
Superconductivity in a magnetically ordered background
Authors:
Amici A. Thalmeier P. Fulde P.
Source:
(list of journals)
Physica C. 318:471-474, 1999 May.
Abstract:
Borocarbide compounds with the formula RN2B2C show interesting superconducting and magnetic properties and the coexistence of the two phenomena. BCS theory is extended to systems with underlying commensurate magnetic order. In the case of helical phases the technique may be extended to any e-vector and there exists a well-defined limit for incommensurate values. The way magnetic order influences superconductivity depends crucially on the details of both the magnetic structure and the electron bands, but some qualitative criteria may be given. As an example, we give a brief analysis of the compound HoNi2B2C. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
High elevated-temperature strength of Al-based
nanoquasicrystalline alloys
Authors:
Inoue A. Kimura H.
Source:
(list of journals)
Nanostructured Materials. 11(2):221-231, 1999 Mar.
Abstract:
A new icosahedral (I) quasicrystalline alloy was found around thr Al-rich composition of Al84.2Fe7.0Cr6.3Ti2.5 by melt spinning. The I-phase consists of a spherical shape with a particle size of about 250 nm and contains a high density of internal defects. The I-phase is a metastable phase and decomposes to Al + Al13Cr2 + Al23Ti9 + Al13Fe4 phases in the temperature range of 620 to 1005 K by continuous heating at a heating rate of 0.67 K/s. The use of further Al-rich Al-Fe-Cr-Ti alloys enabled the production of metastable phase powders consisting mainly of Al + I phases in a wide particle size fraction of 26 to 125 mu m by high-pressure Ar gas atomization. The bulk Al93Fe3Cr2Ti2 alloys prepared by extrusion of the 26 mu m powder at 67.3 K consist of Al, I and Al23Ti9 phases and the I-phase keeps a particle size of about 300 nm. The extruded bulk I-base alloy exhibits high elevated-temperature strength of 510 MPa at 473 K and 360 MPa at 573 K as well as high room-temperature strength of 650 MPa. The elevated-temperature strength exceeds the air-force goal level (400 MPa at 473 K and 350 MPa at 573 K) for Al-based alloys. The high elevated-temperature strength and wear resistance remain almost unchanged even after annealing at 573 K for 1000 h. The extremely good elevated temperature strength is thought to result from high elevated-temperature strength of the Al-based I-phase itself containing Fe, Cr, and Ti elements which have low diffusivities in Al phase, The success of developing the new type of high elevated temperature strength Al-based alloys containing the I-phase as a main constituent phase by the use of the stoichiometric Al-Fr-Cr-Ti icosahedral alloy is promising For the future development as a new high elevated-temperature strength material. (C) 1999 Acta Metallurgica Inc.
Title:
Crossover from frustrated XY model to ANNNI model at finite temperature
Authors:
Yamashita M. Tanaka S.
Source:
(list of journals)
Journal of the Physical Society of Japan. 68(6):1797-1800, 1999 Jun.
Abstract:
To clarify the mechanism of successive phase transitions occurring in ferroelectric and antiferroelectric smectic liquid crystals, a crossover behaviour of the XY model with competing second nearest neighbour interaction exposed to a twofold field to the using model (axial next nearest neighbour Ising model) is studied at finite temperature. The phase transition line from an ordered phase with Ising symmetry to the one preserving characteristics of the,YY model is shown to lie at the low-temperature side of a critical curve between the former and a disordered phase, which leads to the result that the freedom of the XY spin is suppressed more strongly at finite temperature than at the absolute zero temperature. A phase with a structure of period 6 is analysed in detail as a typical case of modulated phases with the freedom of XY spin.
Title:
Temperature dependence of Raman scattering spectra of KSc(WO4)(2)
Authors:
Maczka M. Kojima S. Hanuza J.
Source:
(list of journals)
Journal of the Physical Society of Japan. 68(6):1948-1953, 1999 Jun.
Abstract:
Phase transitions in KSc(WO4)(2) have been studied by means of Raman spectroscopy. Two soft modes and the splitting of doubly degenerate modes into doublets have been observed below 307 K. The observed broadening of lattice modes and anomalous behavior of the librational mode around GO cm(-1) have been explained as a result of rotational disorder of the WO42- ions. This may support the conclusion derived from the ESR studies that the crystal is incommensurate below 307 K.
Title:
Cs-133 NMR spin-lattice relaxation studies in incommensurate
CS2MBr4 (M=Cd, Hg)
Authors:
Suzuki K. Ishimaru S. Ikeda R.
Source:
(list of journals)
Journal of the Physical Society of Japan. 68(6):1963-1967, 1999 Jun.
Abstract:
The Cs-133 NMR spin-lattice relaxation times (T-1) in Cs2MBr4 (M=Cd and Hg) crystals were measured in a range of 207-369K and 197-369K, respectively. Critical exponents zeta at the normal-incommensurate phase transition were determined to be zeta = 0.62 +/- 0.02 and 0.50 +/- 0.02 far M=Cd and Hg, respectively, in good agreement with the three-dimensional XY and the mean field models in the same order. Frequency dependent T-1 values observed in the incommensurate phase of both compounds could be explained by fluctuations of amplitudons and phasons with a small gap.
Title:
The A(n+2)B(n)B ' O3n+3 family (B=B '=Co): Ordered intergrowth between
2H-BaCoO3 and Ca3Co2O6 structures
Authors:
Boulahya K. Parras M. Gonzalez-Calbet JM.
Source:
(list of journals)
Journal of Solid State Chemistry. 145(1):116-127, 1999 Jun.
Abstract:
The n integer members of the A(n+2)B(n)B'O3n+3 homologous series keeping B = B' = Co the same have been characterized by selected area electron diffraction and high resolution electron microscopy. Its commensurate modulated structure is made up of chains, separated by A atoms, running along the c direction containing a succession of one Co atom (B') in prismatic trigonal sites and n Co atoms octahedrally coordinated sharing faces. All of them can be described as ordered intergrowths of two structures of the end members of the family, 2H-BaCoO3 (n = infinity) and Ca3Co2O6 (n = 1). The modulation observed in all terms can be described as a function of the difference between the c-axis of the Co sublattice with respect to the 2H structure. Members of the series can be obtained by modifying the distance between layers keeping B = Co the same, as shown in (Sr1-xBax)(6)Co5O15 (n = 4), Sr5Co4O12 (n = 3), and (Sr0.5Ca0.5)(4)Co3O9 (n = 2). (C) 1999 Academic Press.
Title:
The structure of approximant mu-Al4Mn interpreted as a
modulated crystal
Authors:
Uchida M. Horiuchi S.
Source:
(list of journals)
Journal of Applied Crystallography. 32(Part 3):417-420, 1999
Jun 1.
Abstract:
The structure of the mu-Al4Mn phase, which is an approximant of icosahedral and decagonal quasicrystals, is interpreted as a modulated crystal structure. It basically comprises modulated layers, in which the ordering of atomic vacancies takes place in the close-packed layers. The modulation is considered to be due to the rearrangement of atomic vacancies as a response to the occurrence of charge-density waves.
Title:
Exploring reciprocal space of a quasicrystal means of an
imaging plate
Authors:
Kopecky M. Colella R.
Source:
(list of journals)
Journal of Applied Crystallography. 32(Part 3):442-451, 1999
Jun 1.
Abstract:
A monochromatic Laue technique is used to extract information about the reciprocal lattice of a quasicrystal. A synchrotron beamline, normally available for protein crystallography, was used in this study. Each photograph is a planar projection of a spherical cap, a portion of the Ewald sphere, in reciprocal space. The algorithms needed to relate the images to reciprocal space are described in detail. It is found that many weak, but readily detectable, Bragg reflections are found in unexpected positions in reciprocal space, as predicted from theory. Some very weak Bragg reflections are clearly visible on the imaging plate, but could not be detected by photon counting using a four-circle diffractometer. Some images show characteristic 'rings' or 'arcs' of diffuse scattering, as previously observed in other icosahedral quasicrystals. In view of the 'extreme perfection' of the quasicrystalline specimen used in this study, it is proposed to view these rings (or arcs) as intrinsic features of the icosahedral quasicrystalline structure.
Title:
Ion beam deposition of Ag-107(111) films on Ni(100)
Authors:
Todorov SS. Bu H. Boyd KJ. Rabalais JW. Gilmore CM. Sprague JA.
Source:
(list of journals)
Surface Science. 429(1-3):63-70, 1999 Jun 10.
Abstract:
Monolayer thick silver films were grown on an Ni(100) surface using direct ion beam deposition of Ag-107(+) ions with 20 eV kinetic energy and the substrate at 25 degrees C. Deposition was performed by means of a mass-selected, low-energy, ultra-high vacuum ion beam system with a well-defined ion energy. The films were analyzed in situ by time-of-flight scattering and recoiling spectrometry (TOF-SARS) and by low energy electron diffraction (LEED). Classical ion trajectory simulations were used to model the TOF-SARS spectra. Results of the TOF-SARS spectra and azimuthal scans are consistent with the growth of a monolayer Ag film with a fcc (111) structure on the Ni(100) surface. The deposited films exhibited a faint hexagonal c(2 x 8) LEED pattern. Molecular dynamic simulations of the deposition process are in agreement with the experimental observations. The growth of such isotopically pure metal monolayers at room temperature with controlled orientations provides the opportunity for exploring a variety of unique physical properties, (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Long-period incommensurate structures in
crystals with triangular arrangement of magnetic ions
Authors:
Zavorotnev YD. Medvedeva LI.
Source:
(list of journals)
Low Temperature Physics. 25(6):420-425, 1999 Jun.
Abstract:
The possibility of formation of a long-period structure in crystals with triangular arrangement of magnetic atoms is considered. It is shown that two cycloid and one spiral structures are formed. The influence of a magnetic field and second-order magnetic crystallographic anisotropy is studied. Superstructures can be transformed into one another by turning the plane of irreducible vectors for which "anticentrifugal" effect takes place, and an intermediate structure called a "rotating skew spiral" (R (S) over tilde (S) over tilde) is formed. It is also shown that "domains" over whose length irreducible vectors turn through an angle of pi/2 can emerge in the system. These "domains" can form structures with a jump in the phase of irreducible vectors at the boundary. (C) 1999 American Institute of Physics. .
Title:
In situ TEM heating of nanosized ZrO2
Authors:
Rankin J.
Source:
(list of journals)
Journal of the American Ceramic Society. 82(6):1560-1564, 1999 Jun.
Abstract:
In situ TEM heating experiments at temperatures between 820 degrees and 860 degrees C provide significant insights into the atomistics of neck formation during the sintering of nanoscale faceted, single-crystal particles of ZrO2, High-resolution TEM was used to observe the crystallography and the relative orientation in a variety of original particle-pairs and the relative orientation of their evolving necks. Previous studies have determined that unconstrained particles can rotate during neck growth. When there is a significant amount of misalignment, the particles are not able to align completely. In these instances, the neck that forms is epitaxial with one of the particles. Additionally, in particle-pairs with significant misalignment, the neck stops growing when it forms a crystallographic facet which is continuous with the preexisting facet of the template particle. When the two particles have close to the same orientation, the particles rotate into complete alignment and the neck that forms is consequently epitaxial with both particles. When the neck-particle system is in complete registry, the growing neck is rounded: there is an aperiodic arrangement of steps, even on the atomic resolution scale, The experimental results are discussed in terms of the random starting state of the two particles, the equilibrium crystal shape of the particle-neck system, and the operative kinetic mechanisms.
Title:
Enhanced third-order nonlinear optical response of photonic bandgap materials
Authors:
Nelson RL. Boyd RW.
Source:
(list of journals)
Journal of Modern Optics. 46(7):1061-1069, 1999 Jun 15.
Abstract:
We calculate the nonlinear phase shift acquired bq a laser beam in propagating through a one-dimensional photonic bandgap material, that is a material in which the linear refractive index is periodically modulated along the direction of propagation. We find that the: nonlinear phase shift shows resonances for laser frequencies close to the edge of tilt stop hand of the photonic bandgap structure. Enhancements of the nonlinear phase: shift compared with that of a homogeneous nonlinear optical material by a factor of approximately five are predicted under realistic laboratory conditions. m-e find that similar enhancements of the two-photon absorption rare can occur for a material with an imaginary nonlinear susceptibility. We also treat the case of a photonic bandgap material containing a 'defect,' that is a central region somewhat too thick to conform to the periodicity of the system, and find that the nonlinear phase shift can be enhanced by a factor of approximately thirty.
Title:
Magnetic ordering in HoFe6Ge6 studied by neutron diffraction
Authors:
Zaharko O. Schobinger-Papamantellos P. Rodriguez-Carvajal J. Buschow KHJ.
Source:
(list of journals)
Journal of Alloys & Compounds. 288(1-2):50-56, 1999 Jun 29.
Abstract:
The crystal structure and magnetic ordering of HoFe6Ge6 annealed at 800 degrees C are studied by neutron powder diffraction. The crystal structure consists of the host (Fe, Ge) and guest (Ho/Ho* and Ge/Ge*) subsystems. In view of the complex magnetic ordering the guest subsystem was preferably described as using two types of microdomain with a 1:3 volume ratio. In the first type of microdomain (I) the guest subsystem is fully disordered (average YCo6Ge6 structure); in the second type (II) it is fully ordered (TbFe6Sn6 superstructure, wave vector q=(1/2 1/2 0) of the orthohexagonal average structure). The limited coherence of microdomains leads to an anisotropic broadening of the satellites and can be described within a needle-like model (infinite parallel to [100] and small 1 [100]) with a mean correlation length 84(6) Angstrom. The Fe-moments order antiferromagnetically below T(N)approximate to 450 K with the wave vector q(1)=(1 0 0) in the superstructure basis for both types of microdomain. The Fe-moments point along a and are arranged into ferromagnetic (1 0 0) layers stacked (+ - + -(...)) along the a-axis. The 1.5 K Fe ordered moment value is 1.80(7)mu(B)/Fe. The He-moments order antiferromagnetically below 9 K with two wave vectors q(1)=(1 0 0) and q(2)=(1/3 0 0) in the superstructure basis. The q(1) wave vector is associated with microdomain I and gives rise to a collinear arrangement of the Ho moments along a. The q, wave vector corresponds to microdomain II and leads to a modulated arrangement of the Ho moments within the (0yz) plane. The 1.5 K ordered moment values are 6.0(8)mu(B)/Ho (I) and 2.0(4)mu(B)/Ho (II). The antiferromagnetic Ho-Ho correlations have limited spatial extent with the mean correlation length 95(30) Angstrom (I) and 70(30) Angstrom (II). (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
On the first incommensurate ordering of NH4Cu7-xS4
Authors:
Noren L. Berger R. Lidin S. Eriksson L. Huster J. Petricek V.
Source:
(list of journals)
Journal of Alloys & Compounds. 288(1-2):102-109, 1999 Jun 29.
Abstract:
The first incommensurate ordering of NH4Cu7-xS4 (x = 0.16) has been investigated using X-ray single crystal diffraction at 174 K. The modulated structure is described with monoclinic symmetry with the cell parameters alpha = 10.272 (Angstrom), b = 10.272 (Angstrom), c = 7.694 (Angstrom) and beta = 90.0 degrees. It belongs to the four-dimensional space group P:P2/n:-11 {conventional setting P:P2/b:-11 (no. 13.1)}. The incommensurate modulation to the lattice (q approximate to 0.39, 0, 0) appears to be caused by the sub-stoichiometry of copper. A DSC-study of the isostructural TiCu7-xS4 relates the thermal behaviour of the two thiocuprates to changes in the copper content. A tentative 'phase stability diagram' for such compounds is presented. (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
Effective-field approximations, including DMRG method, for classical
inhomogeneous 2D spin lattice models
Authors:
Surda A.
Source:
(list of journals)
Acta Physica Slovaca. 49(3):325-336, 1999 Jun.
Abstract:
A new approach to derivation of various effective-field approximations for lattice spin models in a unique way is presented. It is shown that it can give a number of methods, including the DMRG method, that can be used to find generally inhomogeneous solutions of 2D classical lattice problems. A method, closely related to the DMRG method but without necessity to perform spin renormalization, is derived, yielding results practically not different from the DMRG ones. The matrix-product wave function of Rommer and Ostlund can be constructed from the output of the method. The computational costs of all the derived methods are smaller than those of the DMRG. Most of the results are applicable to the 1D quantum systems, as well.
Title:
Critical scattering of UNiGa
Authors:
Svobada P. Prokes K. Sechovsky V. Khmelevska T. Hofmann M. Stusser N.
Source:
(list of journals)
Acta Physica Slovaca. 49(3):461-463, 1999 Jun.
Abstract:
The hexagonal intermetallic compound UNiGa adopts the ZrNiAl structure type, orders antiferromagnetically below 39 K and exhibits several AF phases with lowering temperature. Within narrow temperature range 34 K - 39 K there exist four magnetic phase transitions in zero magnetic field. In all these phases the magnetic structure is highly anisotropic with magnetic moment parallel to the c-axis. The phase just below TN is an incommensurate antiferromagnetic structure characterised by propagation vector q = (0, 0, q(z)), where q(z) is in the range 0.36 - 0.37. We present results of magnetic critical scattering study on a UNiGa single crystal. The intensity of critical scattering drops rapidly within a very narow temperature range above TN.
Title:
The practical applicability of TMDSC to polymeric systems
Authors:
Scherrenberg R. Mathot V. Van Hemelrijck A.
Source:
(list of journals)
Thermochimica Acta. 330(1-2):3-19, 1999 May 10.
Abstract:
The practical applicability and the relevance of a classification of processes into three different regimes is examined based on some typical TMDSC experiments. It is demonstrated that this classification, simply based on the presence and temperature susceptibility of an excess process, is very useful to identify and understand phenomena observed with TMDSC. The ability to separate the base-line heat capacity from excess phenomena is undoubtedly the most valuable feature of TMDSC. Nonetheless, one has to realize that this feature is restricted to excess processes that are not susceptible to the temperature modulation such as for instance curing and enthalpy recovery. Crystallization and melting processes, on the other hand, are susceptible to the temperature modulation and thus the complex heat capacity is in that case not uniquely determined by the base-line heat capacity. In addition, the strong temperature dependence of the kinetics in combination with the generally large heat flow, imply that the conditions applied are very critical to obtain a reliable complex heat capacity. In spite of these serious limitations it is demonstrated that TMDSC can provide additional insight in the crystallization and melting behaviour using (step-wise) quasi-isothermal measurements (i.e. beta(0)=0) (C) 1994 Published by Elsevier Science B.V. All rights reserved.
Title:
Heat capacities of Al62.5Cu25Fe12.5 quasicrystals and B2
related crystals
Authors:
Wang L. Tan ZC. Zhang JB. Meng SH. Zhang LM. Zhou QG. Dong C.
Source:
(list of journals)
Thermochimica Acta. 331(1):21-25, 1999 Jun 1.
Abstract:
The heat capacities of two Al62.5Cu25Fe12.5 samples containing icosahedral quasicrystals and B2 related crystals respectively were measured with a high-precision automatic adiabatic calorimeter over the temperature range of 75-385 K. The heat capacities of both samples increase with temperature. At the low temperature range, the heat capacity of the quasicrystalline sample is higher than that of the B2 approximate. However, the heat capacity of the B2 sample becomes higher above 254.987 K. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Short-range order in a thin film of decagonal Al-Co-Ni
quasicrystal: calculated from a structure
model and measured with EXAFS
Authors:
Braun S. Meyer DC. Paufler P. Grushko B.
Source:
(list of journals)
Journal of Alloys & Compounds. 287(1-2):12-17, 1999 Jun 1.
Abstract:
Extended X-ray Absorption Fine Structure (EXAFS) measurements performed at the Co and Ni K absorption edges of thin decagonal Al73Co16Ni11 quasicrystalline films are presented. Layers were grown by solid state reaction of a multilayer stack of elemental metals. Experimental data of short range order is compared to that calculated from a modified Li-Steurer structure model. To fit the measured EXAFS function, the neighbourhood of transition metals cobalt and nickel up to 3 Angstrom was calculated from this model. Overlap of hyperatoms in the perpendicular space has been taken into account. The algorithm for the calculation of the average neighbourhood of a given element can also be applied to other quasicrystalline structures modelled by using a cut-and-projection method from a high-dimensional space. The average neighbourhood of Ni and Co atoms was found to be equal within a radius of 3 Angstrom. Sites of transition metals should be occupied statistically by Ni and Co. (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
Magnetic properties of RIrGe (R=Gd-Er) compounds from neutron diffraction and
magnetic measurements
Authors:
Penc B. Hofmann M. Leciejewicz J. Slaski M. Szytula A.
Source:
(list of journals)
Journal of Alloys & Compounds. 287(1-2):18-24, 1999 Jun 1.
Abstract:
Polycrystalline samples of the ternary intermetallics RIrGe (R = Tb,Ho,Er) were investigated by means of magnetization, X-ray and neutron diffraction measurements. For GdIrGe and DyIrGe only magnetic and X-ray diffraction measurements were performed. They crystallize in the orthorhombic TiNiSi-type structure. Magnetic measurements show antiferromagnetic ordering with Neel temperatures of 24 K for R = Gd and Tb, 15 K for R = Dy and 6.5 K for R = Er. HoIrGe is paramagnetic down to 1.5 K. Neutron diffraction data for TbIrGe indicate sine modulated magnetic ordering with the propagation vector k = (0,0.4093(2),0) and the magnetic moment parallel to the c-axis. In HoIrGe, no magnetic ordering is observed down to 1.5 K, while in ErIrGe a sine modulated structure with the moment parallel to the a-axis is observed below T-N. Below T-t = 2.9 K the coexistence two phases collinear and sine modulated is observed. (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
Neutron diffraction study of the structures of Ba5CuIr3O12
and Ba16Cu3Ir10O39
Authors:
Blake GR. Battle PD. Sloan J. Vente JF. Darriet J. Weill F.
Source:
(list of journals)
Chemistry of Materials. 11(6):1551-1558, 1999 Jun.
Abstract:
The crystal structures of Ba5CuIr3O12 and Ba16Cu3Ir10O39 have been determined using a combination of X-ray and neutron powder diffraction data. Considering their structures to be based on hcp stacks of Ba3O9 and Ba3CuO6 layers, Ba5CuIr3O12 has a 10-layer structure, space group P3c1 with a = 10.14055(2) Angstrom and c = 21.65993(9) Angstrom. Ba16Cu3Ir10O39 has a 16-layer structure, space group P321 with a = 10.13442(2) Angstrom and c = 35.0564(2) Angstrom. Sequences of trigonal prismatic and octahedral transition metal sites run in chains parallel to z, with Ba cations located between the chains. The distribution of Ir and Cu cations in the octahedral and trigonal prismatic sites is disordered in both compounds. Cu cations are displaced from the centers of the trigonal prisms toward the rectangular faces. Both materials may also be regarded as commensurate composites of two substructures, sharing common unit cell parameters a and b but with different parameters c(1) and c(2), where the ratio c(1)/c(2) is a rational fraction. The relative merits of the oxide layer model and the composite crystal model are discussed.
Title:
Morphology and coarsening behavior in Polycarbonate/Nylon6-co-12 blends with
and without compatibilizer
Authors:
Kim YH. Kikuchi M. Akiyama S. Sho K. Izawa S.
Source:
(list of journals)
Polymer. 40(19):5273-5278, 1999 Sep.
Abstract:
The morphology and the coarsening behavior with and without compatibilizer were investigated by using scanning electron microscope. As a new compatibilizer, styrene-acrylonitrile-maleic anhydride terpolymer (S-AN-MAH) was used. For Polycarbonate (PC)/Nylon6-co-12(50/50) blend, modulated structure was observed. And coarsening behavior was similar to that of spinodal decomposition. However, for PC/Nylon6-co-12(50/50) blend with S-AN-MAH, sea-island structure was developed and the size of domain did not increase although the sample was annealed for 90 min, at above T-m. It was confirmed that S-AN-MAH retards coarsening of morphology. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.
Title:
Application of the theory of algebraic systems for creating a hierarchy of
solid structures formed under equilibrium and nonequilibrium
conditions
Authors:
Domrachev GA. Lazarev AI.
Source:
(list of journals)
Physics of the Solid State. 41(5):720-724, 1999 May.
Abstract:
A unified hierarchy is proposed for molecular and solid structures formed under equilibrium (ideal crystals) or nonequilibrium conditions (real crystals, fractally ordered crystalline, quasicrystalline, and amorphous solids, as well as composite solid materials that are aperiodic on an atomic-molecular level but are periodic on a macroscopic level). The construction of this hierarchy is based on applying the theory of algebraic systems (groups, rings, and fields) to the multiplication of an initial structure in space depending on an inflation coefficient (numbers) expressed in the general form Q = (n + m root l)/k. Examples are presented of molecular and polymer structures described by groups or rings, fractally ordered solids whose structures are described by fields, and solids with damped or self oscillations in their composition, whose structures are described by fields or periodic rings of fields with complex spatial multiplication factors. (C) 1999 American Institute of Physics. .
Title:
Microstructure related to charge and orbital ordering in
Pr0.5Ca0.5MnO3
Authors:
Mori S. Katsufuji T. Yamamoto N. Chen CH. Cheong SW.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(21):13573-13576, 1999 Jun 1.
Abstract:
We have investigated the microstructure related to the charge and orbital ordering in the manganites Pr0.5Ca0.5MnO3 by transmission electron microscopy. Electron diffraction clearly shows the presence of the incommensurate structure in the paramagnetic insulator phase of Pr0.5Ca0.5MnO3 between 180 and 260 K. Our experimental results clearly show that the incommensurate-to-commensurate (IC-to-C) charge-ordering transition was correspondent with the paramagnetic to antiferromagnetic transition around 180 K. Dark field images also revealed the motion of the discommensurations during the IC-to-C transition. A model of the IC structure which involves the presence of the partial orbital disordering and the complete charge ordering is proposed.
Title:
Thermodynamic study of
commensurate-incommensurate phase
transitions in Rb2ZnCl4
Authors:
Martin-Olalla JM. Ramos S. Levanyuk A.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(22):14265-14270, 1999 Jun 1.
Abstract:
We have performed simultaneous measurements of heat capacity and dielectric constant on a high-quality single crystal of Rb2ZnCl4 near the commensurate-incommensurate transition area. Maximum heat capacity is found to be at a higher temperature than the maximum dielectric constant, both for heating and cooling and in the area of a jump-wise change of the refractive index found earlier. When measuring heat capacity a peak-type anomaly was detected and the enthalpy of transition was measured. We compare our heat-capacity data with those for the powder samples and both sets with a phenomenological theory. We concluded that the Curie law for heat capacity predicted by the theory is observed in both cases with reasonable values for the Curie constant. We were unable to discriminate latent heat as in previous experiments with the powder sample; however, we estimated an upper limit for the latent heat by subtracting the contribution of specific heat to the enthalpy transition. The latent-heat value estimated both from the Clapeyron-Clausius formula and the phenomenological theory is qualitatively in accordance with the upper limit of this value found in our results. .
Title:
Coherency of phason dynamics in Fibonacci chains
Authors:
Naumis GG. Wang CM. Thorpe MF. Barrio RA.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(22):14302-14312, 1999 Jun 1.
Abstract:
The effects of phason disorder on the dynamical structure factor of Fibonacci chains are studied, and the existence of a coherent phason field in real quasicrystals is addressed. The neutron-scattering response is modeled for coherent and random phasons. The results show that coherent and random phasons con be distinguished for high values of the momentum transfer. However, for both sorts of phasons the response in the acoustic-mode region is quite similar, since the only important quantity is the average length between atoms. In particular, it is shown that a random phason produced in thr quasicrystal's hyperspace leads to a coherent phason field in real space.
Title:
Transition to long-range magnetic order in the highly frustrated insulating
pyrochlore antiferromagnet Gd2Ti2O7
Authors:
Raju NP. Dion M. Gingras MJP. Mason TE. Greedan JE.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(22):14489-14498, 1999 Jun 1.
Abstract:
Experimental evidence from measurements of the ac and de susceptibility, and heat-capacity data show that the pyrochlore structure oxide, Gd2Ti2O7, exhibits short-range order that starts developing at 30 K, as well as long-range magnetic order at T similar to 1 K. The Curie-Weiss temperature, theta(CW) = -9.6 K, is largely due to exchange interactions. Deviations from the Curie-Weiss law occur below -10 K while magnetic heat-capacity contributions are found at temperatures above 20 K. A sharp maximum in the heat capacity at T-c = 0.97 K signals a transition to a long-range-ordered state, with the magnetic specific accounting for only similar to 50% of the magnetic entropy. The heat capacity above the phase transition can be modeled by assuming that a distribution of random fields acts on the S-8(7/2) ground state for Gd3+. There is no frequency dependence to the ac susceptibility in either the short-range- or long-range-ordered regimes, hence suggesting the absence of any spin-glass behavior. Mean-field theoretical calculations show that no long-range-ordered ground state exists for the conditions of nearest-neighbor antiferromagnetic exchange and long-range dipolar couplings. At the mean-field level, long-range order at various commensurate or incommensurate wave vectors is found only upon inclusion of exchange interactions beyond nearest-neighbor exchange and dipolar coupling. The properties of Gd2Ti2O7 are compared with other geometrically frustrated antiferromagnets such as the Gd3Ga5O12 gadolinium gallium garnet, R2Ti2O7 pyrochlores where R = Tb, Ho, and Tm, and Heisenberg-type pyrochlore such as Y2Mo2O7, Tb2Mo2O7, and spinels such as ZnFe2O4. .
Title:
Glassy nature of stripe ordering in La1.6-xNd0.4SrxCuO4
Authors:
Tranquada JM. Ichikawa N. Uchida S.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(22):14712-14722, 1999 Jun 1.
Abstract:
We present the results of neutron-scattering studies on various aspects of crystalline and magnetic structure in single crystals of La1.6-xNd0.4SrxCuO4 with x = 0.12 and 0.15. In particular, we have reexamined the degree of stripe order in an x = 0.12 sample. Measurements of the width for an elastic magnetic peak show that it saturates at a finite value below 30 K, corresponding to a spin-spin correlation length of 200 Angstrom. A model calculation indicates that the differing widths of magnetic and (previously reported) charge-order peaks, together with the lack of commensurability, can be consistently explained by disorder in the stripe spacing. Above 30 K (i.e., above the point at which a recent muon spin-rotation study has found a loss of static magnetic order), the width of the nominally elastic signal begins to increase. Interpreting the signal as critical scattering from slowly fluctuating spins, the temperature dependence of the width is consistent with renormalized classical behavior of a two-dimensional anisotropic Heisenberg antiferromagnet. Inelastic scattering measurements show that incommensurate spin excitations survive at and above 50 K, where the elastic signal is negligible. Given that the stripe order is believed to be pinned by the low-temperature tetragonal (LIT) crystal structure, we have also investigated the transition near 70 K from the low-temperature orthorhombic (LTO) structure. We show that our x = 0.12 crystal passes through an intervening less-orthorhombic phase, before reaching the LTT at similar to 40 K, whereas the x = 0.15 crystal goes directly from LTO to LTT, with coexistence of the two phases over a range of similar to 7 K. Sharp Bragg peaks in the LTT phase of the x = 0.15 crystal indicate a domain size of greater than or similar to 1000 Angstrom, with no obvious evidence for LTO domains: hence, the coexistence of stripe order and superconductivity in this sample cannot be explained by a mixture of crystalline phases. Finally, Lye present scattering evidence for small LTT-like domains in the LTO phase of the x = 0.15 sample. A correlation between the volume fraction of such domains and deviations of in-plane resistivity from linens T dependence suggest that charge stripes interact with these domains within the LTO matrix. .
Title:
Surface X-ray diffraction of 5-I-uracil/Ag(111) and 2-S-uracil/Ag(111)
Authors:
Meyerheim HL. Gloege T.
Source:
(list of journals)
Physica Status Solidi A-Applied Research. 173(1):175-181, 1999 May 16.
Abstract:
We present surface X-ray diffraction experiments on ordered large organic monolayers. As model systems we have chosen two uracil derivatives, namely 5-I-uracil (IU) and 2-S-uracil (SU) which on Ag(111) form a uniaxially incommensurate and a commensurate superstructure, respectively. These are characterized by transformation matrices [GRAPHICS] for IU and [GRAPHICS] for SU. Although the measured reflection intensities are extremely weak (about 2 to 4 orders of magnitude weaker than those near the antiphase condition along the Ag crystal truncation rods), about 40 independent inplane reflections (hk0) could be measured in each case allowing the development of structure models. In the case of IU adsorption a surface reaction rakes place where a 5-5'-di-uracil molecule is formed after separation of the I atom from the pyrimidine rings. The formation of ordered structures needs mild thermal activation (T = 400 K). The I atoms form a separate I/Ag(111)-(root 3 x root 3) phase. In the case of SU no reaction is observed and the unit cell contains four molecules. The arrangement of the SU molecules in the surface unit cell is similar to the arrangement in bulk SU. The commensurability of the SU superstructure is explained by the strong S-Ag interaction.
Title:
Electron diffraction analysis of plastically deformed icosahedral Al-Pd-Mn
single quasicrystals
Authors:
Franz V. Feuerbacher M. Wollgarten M. Urban K.
Source:
(list of journals)
Philosophical Magazine Letters. 79(6):333-342, 1999 Jun.
Abstract:
A technique is presented to determine quantitatively the phason strain fields in quasicrystals by electron diffraction analysis in a transmission electron microscope. The deviation vectors of diffraction spots from their ideal positions are measured and related to their physical and orthogonal reciprocal coordinates. Investigations have been performed on as-grown as well as plastically deformed Al-Pd-Mn single quasicrystals. It was found that the magnitudes of the shifts of the spots depend linearly on the length of the perpendicular-space component of the reciprocal coordinates, while such a correlation was not found for the respective physical-space component. This behaviour evolves more clearly with increasing plastic strain. The measured spot shifts were fitted according to a linear vector equation relating the shifts to the perpendicular reciprocal vectors. This provides the possibility of determining the entries of the first two rows of the so-called 'phason matrix'. It was found that the values of the matrix entries vary with position in a given sample and that they increase with increasing amount of plastic deformation.
Title:
Icosahedral order and disorder in semiconductors
Authors:
Dmitrienko VE. Kleman M.
Source:
(list of journals)
Philosophical Magazine Letters. 79(6):359-367, 1999 Jun.
Abstract:
Hidden icosahedral symmetry of tetrahedral interatomic bonds is found in the BC8-Ia (3) over bar phase of silicon and germanium (75% of all bonds are directed almost exactly along fivefold icosahedral axes). It is shown that this phase may be considered as a crystalline approximant of a hypothetical icosahedral quasicrystal with a body-centred six-dimensional lattice and that all the atomic positions in BC8 crystals may be obtained as projections from that six-dimensional lattice. The diffraction pattern of the BC8 phase has hierarchical organisation typical of both approximants and quasicrystals. A specific type of topological disorder, related with phason flips, is suggested. The experimentally observed BC8-R8 phase transition can be considered as resulting from coherent phason flips of this type. Dual relationships with approximants of conventional quasicrystals are used to construct a higher order approximant without dangling bonds. A new scenario for crystalline-to-amorphous transformation is discussed.
Title:
Oxygen disorder phenomena in the modulated Bi2Sr2CoO6-type
structure
Authors:
Jakubowicz N. Grebille D. Leligny H. Evain M.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(20):3997-4008, 1999 May 24.
Abstract:
The incommensurate modulated structure of Bi1.91Sr2CoO5.93 (a = 5.4614(6) Angstrom, b = 5.4471(5) Angstrom, c = 23.415(2) Angstrom) with (p) over right arrow* = 0.240(2)(b) over right arrow* (c) over right arrow* has been refined in the superspace group F2mm(0 beta 1)00s using the four-dimensional formalism for modulated structures and single-crystal x-ray diffraction data. Two different regions with different sites for Ri and O atoms are evident along the modulation direction (called M and I regions). The oxygen disorder observed in the M region leads to different possible configurations for [BiO] layers. In particular, a double-chain configuration comparable to the one observed in related compounds is outlined. Therefore, a comparison with related compounds (BiCu or BiFe) is performed.
Title:
On the atomic and magnetic ordering of hexagonal NdCuSn
Authors:
Pacheco JV. Yvon K. Gratz E. Schobinger-Papamantellos P.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(21):4135-4141, 1999 May 31.
Abstract:
The magnetic structure of the hexagonal stannide NdCuSn has been studied by neutron powder diffraction at low temperature. Magnetic ordering occurs below similar to 10 K and is associated with two magnetic wave vectors, q(1) = (0, 3/8, 0) and a = (1/2, 0, 0) or (0, 1/2, 0). The q(1) vector is attributed to a majority fraction (>90%) of the NdCuSn phase having an ordered Cu/Sn sublattice (non-centrosymmetric NdPtSb type structure, space group P6(3)mc). It can be described as originating from a transverse sine wave modulated arrangement of spins oriented \\ c with a maximum moment value of 2.2 mu(B)/Nd atom, or alternatively by an antiphase domain structure having two amplitudes. The q(2) vector is attributed to a minority fraction (<10%) of the NdCuSn phase having a disordered Cu/Sn sublattice (centrosymmetric CaIn2 type structure, space group P6(3)/mmc). It has a simple antiferromagnetic +- moment arrangement along a or b and the moments are oriented \\ c with a refined value of about 1.2 mu B.
Title:
The magnetic phase diagram of the itinerant-electron-type helical-spin-glass
re-entrant magnet Cr0.81Mn0.19Ge
Authors:
Sato T. Morita K.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(21):4231-4249, 1999 May 31.
Abstract:
The magnetic phase diagram of an itinerant-electron-type helical-spin-glass re-entrant magnet, Cr0.81Mn0.19Ge, is determined on the basis of measurements of the alternating-current (ac) susceptibility and magnetoresistivity in transverse and longitudinal fields, which are sensitive to the magnetic response of each spin component of the modulated spin ordering. The phase boundary line is essentially the same as that of typical itinerant-electron-type helical magnets, except for the appearance of spin-glass behaviour at low temperatures. The transverse ac susceptibility provides evidence of the coexistence of modulated spin order and spin-glass behaviour in the low-temperature phase, where spin freezing appears in the transverse component of the modulated spin structure. This is consistent with the mean-held picture of the vector spin glass.
Title:
The interest of x-ray imaging for the study of defects in real
quasicrystals
Authors:
Gastaldi J. Mancini L. Reinier E. Cloetens P. Ludwig W. Janot C. Baruchel J. Hartwig J. Schlenker M.
Source:
(list of journals)
Journal of Physics D-Applied Physics. 32(10A Special Issue SI):A152-A159,
1999 May 21.
Abstract:
The understanding of defects in quasicrystals has improved through x-ray imaging at ESRF, one of the first operating third-generation synchrotron radiation sources. These sources, while enhancing the possibilities of x-ray topography, opened the way to new techniques like phase contrast radiography and tomography. The combination of these techniques makes it possible to visualize and characterize both structural defects and inhomogeneities in the bulk of real quasicrystals. Defects exhibiting a loop-shaped contrast, previously observed by x-ray topography in both AlCuFe and AlPdMn quasicrystals, were related to inhomogeneities (holes and precipitates) revealed by phase radiography and tomography. The evolution of the defects after annealing provides clues on their nature and formation. The experimental results are discussed with reference to the existing structural models for quasicrystals. Those concerning holes are in fair agreement with the predictions of a theoretical model introduced by Janot et al to describe the structure of icosahedral AlPdMn quasicrystals in terms of hierarchical self-similar packing of overlapping atomic clusters.
Title:
Giant magnetoresistance in electrodeposited Co87Fe13/Cu compositionally
modulated alloys
Authors:
Kakuno EM. da Silva RC. Mattoso N. Schreiner WH. Mosca DH. Teixeira SR.
Source:
(list of journals)
Journal of Physics D-Applied Physics. 32(11):1209-1213, 1999 Jun 7.
Abstract:
In this paper we report on the giant magnetoresistance effect and oscillatory exchange coupling in electrodeposited Co87Fe13/Cu compositionally modulated alloys. The alloys are compositionally modulated over nanometre length scales with ferromagnetic CO87Fe13 (Cu) alloy layers and non-magnetic Cu layers. Co87Fe13/Cu multilayered thin films were electrodeposited from a single sulfate plating solution containing all metallic ions of interest under computer-controlled potentiostat switching on (111)-textured Cu buffers previously evaporated on Si(lll). Electrodeposits present a polycrystalline character with coexistence of face-centred cubic (fcc) and hexagonal close-packed (hcp) structures. Magnetoresistance effects as high as 8% were observed at room temperature. The dependence of the magnetoresistance effect on Cu spacer layer thickness shows an oscillation period around 1.0 nm.
Title:
Magnetic characterisation of Tm Y and Tm Lu superlattices
Authors:
Wilkins CJT. Rainford BD. Goff JP. Ward RCC. Wells MR. McMorrow DF. McIntyre GJ.
Source:
(list of journals)
Journal of Magnetism & Magnetic Materials. 199:509-512, 1999 Jun.
Abstract:
Single-crystal Tm/Lu and Tm/Lu superlattices have been grown using molecular beam epitaxy and their chemical structures have been determined using X-ray diffraction. Magnetisation measurements have revealed a more complicated phase diagram than that of pure Tm. Application of a field along the c-direction gave rise to an extra transition, and transitions were detected for the superlattices when the field was applied along the b-axis. Tn neutron diffraction studies, c-axis, longitudinally modulated magnetic structures were found for both Tm/Y and Tm/Lu, which propagate coherently through the non-magnetic layers. In the case of Tm/Lu superlattices there is evidence for ordering of the basal plane components. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Effect of phasons and magnetic fields on the electronic spectrum of a
three-dimensional quasicrystal
Authors:
Vekilov YK. Slobodyanyuk PV. Isaev EI. Arslanov SF.
Source:
(list of journals)
JETP Letters. 69(9):701-704, 1999 May 10.
Abstract:
The effect of phasons and magnetic fields on the electronic spectrum of an icosahedral quasicrystal is investigated in the tight-binding approximation. Phasons smooth the singular spectrum and produce a greater delocalization of the critical wave functions. A magnetic field shifts the limits of the spectrum, smooths the spectrum, lifts the degeneracy, and also delocalizes the wave functions. (C) 1999 American Institute of Physics. .
Title:
Incommensurate modulations in Ba2TiSi2O8, Sr2TiSi2O8, and
Ba2TiGe2O8
Authors:
Hoche T. Russel C. Neumann W.
Source:
(list of journals)
Solid State Communications. 110(12):651-656, 1999.
Abstract:
Incommensurate modulations in Ba2TiSi2O8, Sr2TiSi2O8, and Ba2TiGe2O8 are compared based on their corresponding electron diffraction patterns. The dependence of the modulations on chemical composition provides a suitable model system for the investigation of incommensurations in framework structures using high-resolution transmission electron microscopy (HRTEM). A widening of quantitative HRTEM utilising the concept of rigid units is proposed allowing for a determination of atomistic displacements responsible for the formation of incommensurately modulated structures. (C) 1999 Elsevier Science Ltd. All rights reserved.
Title:
Spontaneously forming periodic composition-modulated InGaAsP
structures
Authors:
Bert NA. Vavilova LS. Ipatova IP. Kapitonov VA. Murashova AV. Pikhtin NA. Sitnikova AA. Tarasov IS. Shchukin VA.
Source:
(list of journals)
Semiconductors. 33(5):510-513, 1999 May.
Abstract:
InGaAsP epitaxial layers, which are obtained in the instability region on InP (001) and GaAs (001) substrates, are investigated by photoluminescence and transmission-electron-microscopy methods. The results are discussed on the basis of the theory of spinodal decomposition of solid solutions. It is established experimentally that in certain temperature and composition ranges the solid solutions InGaAsP are a system of charged, alternating (in mutually perpendicular directions [100] and [010]) domains of a solid solution with two different compositions and different lattice constants. The domain structure is very clearly defined at the surface of the epitaxial film and becomes blurred in the film near the substrate. The data obtained very likely show spinodal decomposition of the solid solutions InGaAsP in the test samples. (C) 1999 American Institute of Physics. .
Title:
Dislocation structures of submonolayer films near the
commensurate-incommensurate phase
transition: Ag on Pt(111)
Authors:
Hamilton JC. Stumpf R. Bromann K. Giovannini M. Kern K. Brune H.
Source:
(list of journals)
Physical Review Letters. 82(22):4488-4491, 1999 May 31.
Abstract:
Submonolayer films of AE on Pt(111) exhibit parallel partial dislocations separated by narrow hcp domains and much wider fcc domains, the large difference in width being atypical of strained metal overlayers on close-packed substrates. Using a two-dimensional Frenkel-Kontorova model, we calculate the relative domain widths. We examine possible effects of dislocations on equilibrium island shape and calculate the energies of stable and metastable dislocation structures versus island size. Experimental results are explained by proximity to the incommensurate-commensurate phase transition. .
Title:
Incommensuration and other structural anomalies in rhenium disilicide
Authors:
Misra A. Chu F. Mitchell TE.
Source:
(list of journals)
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical
Properties. 79(6):1411-1422, 1999 Jun.
Abstract:
The structure of solidification-processed rhenium disilicide is investigated by X-ray diffraction and transmission electron microscopy. It is usually reported to have the tetragonal C11(b) MoSi2 structure and the stoichiometry of ReSi2. In the present study it is found that rhenium disilicide exhibits an off-stoichiometric Si-deficient composition of Re4Si7. In addition, several structural instabilities are observed by electron microscopy including firstly an orthorhombic distortion of about 0.6% from the tetragonal C11(b) MoSi2 structure with spot splitting across the {110} twin plane, secondly an incommensuration along the a axis with a periodicity of 1.3 nm, thirdly another longer period modulation along the c axis, fourthly a weak monoclinic distortion (beta approximate to 90.4 degrees) in some specimens, as revealed by spot splitting in the high-order Laue zone reflections of [100] diffraction patterns, accompanied by twinning on the (001) planes, and fifthly much larger distortions in some [010] patterns plus a chevron structure in the image which may result from a displacive transformation. These structural anomalies are probably related to the stoichiometry of Re4Si7 which may result in a composite modulated structure where the Si sublattice has a larger average periodicity along the a axis than the Re sublattice, as is the case with manganese silicides.
Title:
Jump kinetics on the Fibonacci quasilattice. Exactly solvable model of the
layer growth and dislocation kinetics in quasicrystals
Authors:
Fradkin MA.
Source:
(list of journals)
JETP Letters. 69(8):570-576, 1999 Apr 25.
Abstract:
The jump kinetics on a quasiperiodic pinning potential is analyzed under small external force in a 1D Fibonacci quasilattice model. The model describes planar (layer) growth of stable quasicrystals from the melt and is also relevant to the movement of quasicrystal dislocations under small stress. An exact solution is found for the spectrum of jump length as function of the driving force. The solution describes the supercooling dependence of the spectrum of nucleus heights on the growing surface of a quasicrystal. The spectrum appears to be universal and its shape has a periodic dependence on the logarithm of the supercooling. The resulting quasicrystal growth kinetics agrees well with that found in computer simulations and in the analysis of continuous thermodynamic models. (C) 1999 American Institute of Physics. .
Title:
Two-dimensional incommensurate superlattices in
precious-metals alloys: nature of formation
Authors:
Velikokhatnyi OI. Naumov II. Eremeev SV. Potekaev AI.
Source:
(list of journals)
JETP Letters. 69(8):589-595, 1999 Apr 25.
Abstract:
The nature of two-dimensional incommensurate superlattices Ll(2)(MM) obtained in the precious-metals alloys Au3Cu and Cu3Pd is investigated on the basis of first-principles calculations of the electronic structure. It is shown that their stability can be explained by the opening of energy gaps on coinciding sections of the Fermi surface in two mutually perpendicular directions. It is important that this explanation holds only if the superlattice is treated as a superstructure with respect to ordinary superstructures (Ll(2)): the electronic spectrum of the superstructure and not the disordered alloy (as in the existing electronic theory of one-dimensional long-period structures) should serve as the starting spectrum. Arguments supporting the fact that in a number of quasicrystalline substances the Ll(2)(MM) phases fall between incommensurate systems and quasicrystals are presented. (C) 1999 American Institute of Physics. .
Title:
Study of the order-disorder transition series in AuCu by in-situ temperature
electron microscopy
Authors:
Bonneaux J. Guymont M.
Source:
(list of journals)
Intermetallics. 7(7):797-805, 1999 Jul.
Abstract:
In-situ temperature observations have been performed in transmission electron microscopy on stoichiometric AuCu alloy. This alloy, on heating, undergoes the series of transitions: AuCu I (L1(0)) --> AuCu II (incommensurate long-period) --> AuCu (disordered A1). The crystallographic and morphological aspects were examined. Complete heating/cooling cycles of transformations have been performed. The evolution of A1(quenched) samples was also studied. The in-situ transition temperatures were determined, and compared with the values already reported or obtained from long-time anneals followed by quenching. This leads to unexpected results. Hysteresis is present, strongly depending on the rate of heating/cooling. This raises some questions about the relative stability of the encountered phases, which are discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.
Title:
A heat capacity investigation of the soliton lattice in the high-field
incommensurate phase of CuGeO3
Authors:
Remenyi G. Hegman N. Lasjaunias JC. Sahling S. Dhalenne G. Revcolevschi A.
Source:
(list of journals)
Europhysics Letters. 46(5):685-691, 1999 Jun 1.
Abstract:
We report on a heat capacity investigation of the spin-Peierls compound CuGeO3 by magnetic field sweeps up to 27 T at fixed temperatures. In the dimerized phase the heat capacity exhibits a simple quadratic field dependence. In contrast, non-monotonous variations occur in the incommensurate phase, with characteristic plateaus separated by steps or smoother variations, depending on the quality of the samples. Such a plateau-type structure is attributed to the dynamics of solitons where a pinning mechanism blocks the continuous rearrangement of the soliton lattice driven by the magnetic field.
Title:
Heat capacity of high-purity bis(4-chlorophenyl)methanone below room
temperature
Authors:
Huzisawa S. Saito K. Ikemoto I.
Source:
(list of journals)
Journal of Physics & Chemistry of Solids. 60(6):723-727, 1999 Jun.
Abstract:
Heat capacity of a zone-refined sample of bis(4-chlorophenyl)methanone was measured by adiabatic calorimetry. Anomalies caused by the successive first-order incommensurate phase transitions were observed as rather sharp peaks at 188.3 and 192.8 K, between which the crystal is known to be incommensurate. Thermodynamic quantities of the transitions were determined and compared with those of Ether molecular crystals showing incommensurate phases. Molar thermodynamic functions are tabulated. (C) 1999 Elsevier Science Ltd. All rights reserved.
Title:
Boron trichloride graphite intercalation compound studied by selected area
electron diffraction and scanning tunneling microscopy
Authors:
Walter J. Shioyama H.
Source:
(list of journals)
Journal of Physics & Chemistry of Solids. 60(6):737-741, 1999 Jun.
Abstract:
Boron trichloride was intercalated from a 1.0 M solution of BCl3 in heptane at 65 degrees C. A mixture of a stage-2 and a stage-3 graphite intercalation compound without unreacted graphite was estimated from an X-ray diffraction pattern. A scanning tunneling microscope study showed the occurrence of a Moire structure. This pattern can be interpreted as a commensurate supperlattice to the underlying graphene lattice. This hexagonal in-plane structure formed by guest particles shows the following relationship to the pristine graphite lattice as well as to the pristine BCl3 lattice: a((Moire)) = 5 x a((graphite)) = 2 x a((BCl3)) = 1225 pm. The structure is rotated by 29 degrees +/- 0.3 degrees in respect to the carbon lattice. This surface structure was confirmed by selected area electron diffraction data. (C) 1999 Elsevier Science Ltd. All rights reserved.
Title:
Modes selection in polymer mixtures undergoing phase separation by
photochemical reactions
Authors:
Tran-Cong Q. Kawai J. Endoh K.
Source:
(list of journals)
Chaos. 9(2):298-307, 1999 Jun.
Abstract:
Phase separation kinetics and morphology of binary polymer mixtures (A/B) in the presence of photochemical reactions were investigated by using phase-contrast optical microscopy combined with digital image analysis. The polymers were chemically designed in such a way that two types of chemical reactions, intermolecular photodimerization and intramolecular photoisomerization, of polymer segments can be induced and controled by irradiation with ultraviolet light. Unlike the conventional case, the phase separation in the presence of these reactions is spontaneously frozen due to the suppression of the long-wavelength instabilities, resulting in stationary spatial structures with intrinsic periodicities. These characteristic length scales are determined by the competition between the two antagonistic interactions: phase separation as a relatively short-range activation and the photochemical reaction as a long- range inhibition. Furthermore, it was found that the spatial symmetry breaking of concentration fluctuations can emerge from the elastic stress associated with the nonhomogeneous kinetics of the reactions. Experimental data obtained with three types of reactions: A-A only cross-link, A-A and B-B simultaneous cross-links and the reversible A double left right arrow B photoisomerization are described. These results do not only indicate that combination of chemical reactions and phase separation could provide a novel method to control the morphology of multiphase polymer materials, but also suggest that photoreactive polymers can be used as a chemical system to study the mode-selection process in polymers far from thermodynamic equilibrium. (C) 1999 American Institute of Physics. .
Title:
Growth modes and surface structures of Te overlayers
deposited on Au(111) surfaces
Authors:
Nagashima S.
Source:
(list of journals)
Applied Surface Science. 145:73-77, 1999 Apr.
Abstract:
The growth modes and surface structures of Te overlayers deposited on Au(111) surfaces have been studied by Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and electron energy loss spectroscopy (EELS). The Au(111) single crystal surfaces were formed in situ by vacuum deposition on an air-cleaved MoS2 at 590 K in an ultrahigh vacuum. The Auger data obtained at 298 K suggest that the Te overlayer grows in the monolayer plus simultaneous multilayers growth mode at an early stage of Te deposition. LEED results show that the first monolayer of Te is arranged with an incommensurate Au(111)-(root 3 x root 3)R30 degrees-Te structure, and that after the completion of the first monolayer, a (3 x 3)-Te structure appears. However, the (3 x 3) structure fades out during growth of multilayers. Furthermore, EELS and LEED results represent that no reaction such as surface alloying is occurring during Te deposition. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Irradiation-induced growth of nanoquasicrystals from
amorphous matrix in the equilibrium immiscible Fe-Cu system
Authors:
Yang GW. Lai WS. Lin C. Liu BX.
Source:
(list of journals)
Applied Physics Letters. 74(22):3305-3307, 1999 May 31.
Abstract:
A microstructure of nanosized quasicrystals embedded in an amorphous matrix was formed in the Fe70Cu30 multilayered films upon room temperature 200 keV xenon ion irradiation. The initial Fe and Cu crystalline phases in the as-deposited multilayers transformed into a unique amorphous phase at a dose of 8 X 10(14) Xe+ cm(-2) and further irradiation, i.e., up to a dose of 5 X 10(15) Xe+ cm(-2) induced the growth of the quasicrystals in some local areas in the amorphous matrix. High-resolution electron microscopy examination revealed that the compositions of the quasicrystals and amorphous matrix were close to Fe50Cu50 and Fe70Cu30, respectively. Apparently, the above microstructure was formed through a two-step phase transition along the increase of ion dose and the amorphous-to-quasicrystal transition was discussed in terms of the similarity in the atomic configuration between the icosahedral and amorphous short-range orders. (C) 1999 American Institute of Physics. .
Title:
Crystal structure and
crystal-chemical features of a new Ti-rich member of the
eudialyte family
Authors:
Rastsvetaeva RK. Khomyakov AP. Chapuis G.
Source:
(list of journals)
Zeitschrift fur Kristallographie. 214(5):271-278, 1999.
Abstract:
The trigonal structure of a new member of the eudialyte group was established from X-ray single-crystal diffraction, lambda(MoKalpha) = 0.71073 Angstrom; space group R3m; a = 14.153(9) Angstrom, c = 60.72(5) Angstrom, V = 10546.1 Angstrom(3); M = 3050; D-x = 2.88g/cm(3); Z = 3; mu = 28 cm(-1); R(hkl) = 0.068 for 3402 reflections. Due to the ordered replacement of Zr with Ti, the new mineral is characterized by a doubling of c and an alternation along [001] of two microdomains, containing (Zr, Ti) or (Ti, Zr)-octahedra, respectively. The key positions on the triad axis are accommodated by Si, Mn and Al atoms. Mn is four-fold coordinated and dominates in one nine-membered ring of the Ti microdomain while Al is six-fold coordinated in the ring of the Zr microdomain. The second key sites are related to Fe atoms which are situated in a slightly aplanar oxygen squares similarly to other relevant examples. These two positions are completed with some neighbour subsites. The axial Al octahedron is connected with three Ti octahedra around the triad axis forming a polyhedral cluster. The splitting and isomorphic substitution of the Na dominant positions are similar to other eudialyte minerals. It was also reported for kentbrooksite. The Na(8b) and Na(9b) atoms are the most disordered around the 18c site with 25% occupancy. The unusual doubling of the structure in the new mineral may be interpreted as a commensurate modulation with wave displacements along the c axis. Other original features of this new representative in the eudialyte family are also discussed.
Title:
Adsorption of Ho on Mo(112) crystal face
Authors:
Losovyj YB. Dubyk NT.
Source:
(list of journals)
Vacuum. 54(1-4):25-29, 1999 Jul-Sep.
Abstract:
Growth and atomic structure of Ho submonolayers deposited on the Mo(1 1 2) crystal face were investigated with the use of AES and LEED techniques. It is well known that various species of alkali metal, alkaline-earth and rare-earth adatoms adsorbed on the furrow faces form linear chain structures across the atomic rows of Mo(1 1 2) and W(1 1 2) surfaces, In contrast to this case Ho deposited on the Mo(1 1 2) face does not reveal an ordered structure in the annealed adlayers at low coverage. Upon further deposition of Ho, the adlayer undergoes one-dimensional compression in the [(1) over bar 1 1] direction and incommensurate (1 x 4) and (1 x 5) structures are formed. This behavior of Ho adlayers is similar to that of Gd adlayers adsorbed on the Mo(1 1 2) face and essentially different from that for Gd-, and Ho-W(1 1 2) adsystems. This fact is connected with the different nature of the indirect interaction between atoms adsorbed on Mo and W substrates at low coverages. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.
Title:
Mechanical properties of quasicrystals investigated by
indentation and scanning probe microscopes
Authors:
Wolf B. Paufler P.
Source:
(list of journals)
Surface & Interface Analysis. 27(5-6):592-599, 1999 May-Jun.
Abstract:
Hardness, elastic modulus and crack propagation were studied using micro- and nanoindentation, atomic force microscopy and scanning acoustic microscopy. We present measurements performed on icosahedral AlPdMn (three-dimensional quasicrystal) and decagonal AlCuCoSi (two-dimensional quasicrystal) from room temperature to 550 degrees C. Additionally, YMgZn was impressed at room temperature. The surface of icosahedral specimens became fractured into segments exhibiting steps in height along shear cracks. Quantity of piling up as well as number and extension of cracks are smaller for the two-dimensional quasicrystalline material, which also displays a hardness anisotropy between different surface orientations. Quantitative hardness measurements revealed a strong indentation size effect exhibiting a hardness increase with decreasing load at room temperature, and the inverse behaviour for higher temperatures. Copyright (C) 1999 John Wiley & Sons, Ltd.
Title:
Comment on "Direct imaging of local chemical disorder and columnar vacancies
in ideal decagonal Al-Ni-Co quasicrystals"
Authors:
Coddens G.
Source:
(list of journals)
Physical Review Letters. 82(21):4366, 1999 May 24.
Title:
Comment on "Direct imaging of local chemical disorder and columnar vacancies
in ideal decagonal Al-Ni-Co quasicrystals" - Yan, Pennycook,
and Pang reply
Authors:
Yan YF. Pennycook SJ. Tsai AP.
Source:
(list of journals)
Physical Review Letters. 82(21):4367, 1999 May 24.
Title:
Theory for the bending anisotropy of lipid membranes and tubule formation
Authors:
Chen CM.
Source:
(list of journals)
Physical Review E. 59(5 Part B):6192-6195, 1999 May.
Abstract:
We study the spontaneous symmetry breaking of the bending rigidity of lipid membranes in two Principal directions by a Landau mean-field theory, When the temperature is below the tilting temperature (T-c), the coupling between molecullar orientation and membrane local curvature square leads to an increase of the bending rigidity in the tilting direction and therefore a spontaneous symmetry breaking in two principal directions. The asymmetry (Delta) of the bending rigidity undergoes;a continuous change upon cooling and grows as T-c- T for T<T-c. We discuss this anisotropical effect on the tilt structure of the ripple phase P-beta, of a nearly hat membrane and the sphere-to-tubule transition in a dilute solution of lipids. The transition between the spherical vesicle phase and the tubular phase is predicted to be first order. .
Title:
Monte Carlo study of dense monolayer and bilayer films on the (100) plane of
face-centered cubic crystals
Authors:
Patrykiejew A. Sokolowski S. Zientarski T. Binder K.
Source:
(list of journals)
Langmuir. 15(10):3642-3652, 1999 May 11.
Abstract:
A Monte Carlo simulation method in the canonical and in the grand canonical ensembles is used to study the behavior and properties of dense monolayer and bilayer films formed on the (100) plane of model face-centered cubic crystals. Systems with different effects due to the periodicity of the gas-solid potential are considered, and the mechanism of melting in the first and the second adsorbed layer is discussed. It is demonstrated that the film structure is very sensitive to the gas-solid potential corrugation, as well as to the temperature and the surface coverage. In particular, it is shown that monolayer films formed on weakly corrugated surfaces exhibit the incommensurate (dense) phase at sufficiently low temperatures, and the two-dimensional liquid phase of lower density, when the temperature: is higher than a certain transition temperature, which depends on the surface corrugation. In the case of intermediate corrugation, the incommensurate solid coexists with the registered (1 x 1) phase, while for highly corrugated surfaces only the registered monolayers are stable. It is also shown that the melting temperature for the first layer is very sensitive to the surface corrugation, while in the second layer we do not observe such strong effects.
Title:
Phase relations in the system In2O3-TiO2-Fe2O3 at 1100 degrees C in air
Authors:
Brown F. Flores MJR. Kimizuka N. Michiue Y. Onoda M. Mohri T. Nakamura M. Ishizawa N.
Source:
(list of journals)
Journal of Solid State Chemistry. 144(1):91-99, 1999 Apr.
Abstract:
Phase relations in the system In2O3-TiO2-Fe2O3 at 1100 degrees C in air are determined by means of a classic quenching method, There exist In2TiO5:Fe2TiO5 having a pseudo-Brookite-type phase and a new phase, In3Ti2FeO10 having a solid solution range from In2O3:TiO2:Fe2O3 = 4:6:1 to In2O3:TiO2:Fe2O3 = 0.384:0.464:0.152 (mole ratio) on the line "InFeO3"-''In2Ti2O7.'' The crystal structures of In3Ti2FeO10 are pyrochlore related with a(m) = 5.9171 (5) Angstrom, b(m) = 3.3696 (3) Angstrom, c(m) = 6.3885 (6) Angstrom, and beta = 108.02 (1)degrees in a monoclinic crystal system at 1100 degrees C, and a(o) = 5.9089 (5) Angstrom, b(o) = 3.3679 (3) Angstrom, and c(o) = 12.130 (1) Angstrom in an orthorhombic system at 1200 degrees C, The relationship between the lattice constants of these phases and those of the cubic pyrochlore type are approximately as follows: a(m) = -1/4 a(p) +(- 1/2)b(p) + (-1/4) c(p), b(m) = -1/4 a(p) +(0) b(p) + (1/4) c(p), c(m) = 1/4 a(p) + (- 1/2)b(p) + (1/4)c(p) and beta = 109.47 degrees in the monoclinic system, and a(o) =- 1/4 a(p) + (- 1/2) b(p) + (- 1/4) c(p), b(o) = - 1/4 a(p) + (0) b(p) + (1/4) c(p), and c(o) = 2/3 a(p) + (- 2/3) b(p) + (2/3) c(p) in the orthorhombic system, where a(p) = b(p) = c(p) = 9.90 (Angstrom) are the lattice constants of "In2Ti2O7" having the cubic pyrochlore type. All solid solutions of In3Ti2FeO10 have incommensurate structures with a periodicity of q x b* (q = 0.281-0.356) along the b* axis and the stoichiometric phase has q = 1/3. InFeO3 having a layered structure type is unstable between 750 and 1100 degrees C. (C) 1999 Academic Press.
Title:
Structural properties and thermal stability of Bi8Pb5O17 fast ion conducting
phases
Authors:
Santarosa M. Righi L. Gemmi M. Speghini A. Migliori A. Calestani G. Bettinelli M.
Source:
(list of journals)
Journal of Solid State Chemistry. 144(2):255-262, 1999 May.
Abstract:
Samples with Bi8Pb5O17 stoichiometry were synthesized by ceramic techniques at temperatures ranging from 200 to 640 degrees C. Their structural properties and relative stabilities were investigated using X-ray and electron diffraction, differential scanning calorimetry, and Raman spectroscopy. The tetragonal beta(2) phase is described by an incommensurately modulated structure, whose modulation depends on the firing temperature. Heat treatments in the 200-300 degrees C range lead to the formation of a new tetragonal phase, chi, which is converted back to beta(2) above 300 degrees C, The intermediate phi phase can be obtained without the previous formation of beta(2), and its X-ray powder diffraction pattern is indexed using a triclinic cell. The present data suggest that the beta(2) phase is the low-temperature polymorph of this composition. (C) 1999 Academic Press.
Title:
Raman spectroscopy of KAl(MoO4)(2) and NaAl(MoO4)(2) single
crystals
Authors:
Maczka M. Kojima S. Hanuza J.
Source:
(list of journals)
Journal of Raman Spectroscopy. 30(4):339-345, 1999 Apr.
Abstract:
Polarized Raman spectra were obtained for KAl(MoO4)(2) and NaAl(MoO4)(2) crystals at ambient temperature, Raman studies of NaAl(MoO4)(2) were also performed over a wide temperature range, 100-930 K. The assignment of the observed bands to the respective stretching, bending and lattice modes was proposed. The temperature dependence of the Raman spectra showed that NaAl(MoO4)(2) remains in the monoclinic structure up to the melting temperature. However, the monoclinic distortion from the trigonal D-3d(3) structure is relatively small at high temperatures and increases continuously with decreasing temperature. Copyright (C) 1999 John Wiley & Sons, Ltd.
Title:
The crystal structure of oxides grown on
Zr-20Nb alloy
Authors:
Woo OT. Lin YP.
Source:
(list of journals)
Journal of Nuclear Materials. 270(3):376-381, 1999 Apr.
Abstract:
Oxides that were grown on Zr-20Nb in water at 300 degrees C for 3 d, or in air at 400 degrees C for less than or equal to 2 h were characterized by analytical electron microscopy. In both oxides. a similar microstructure was observed and similar electron diffraction patterns and high resolution lattice images were obtained. Analyses of the results showed that the crystal structure of the oxides was identical to that of an incommensurate modulated Nb2Zrx-2O2x+1 phase, with x approximate to 10. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Title:
Icosahedral phase growth in chill cast Ti68Fe28Si4 alloy
Authors:
Liu YC. Song GS. Yang GC. Zhou YH.
Source:
(list of journals)
Journal of Crystal Growth. 203(1-2):131-135, 1999 May.
Abstract:
Phase selection during growth involving the icosahedral quasicrystal and metastable crystalline beta-Ti phases was investigated by means of chill cast. The metastable beta-Ti phase was found near the chilling plate, while the icosahedral quasicrystal phase in the upper part. The X-ray, TEM, optical microscopy techniques were used to investigate the microstructure and identify the types of phases. The icosahedral quasicrystal phase grew in rounded dendritic pattern continuously. Aligned dendritic growth facilitated the massive transformation from metastable beta-Ti phase to icosahedral quasicrystal-phase. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Title:
Domain size effects in neutron and SR powder diffraction studies of some
oxides
Authors:
Przenioslo R. Sosnowska I. Zoltek M. Wroblewski T. Shiojiri M. Hohlwein D. Troyanchuk IO.
Source:
(list of journals)
Journal of Alloys & Compounds. 286(1-2):180-183, 1999 May 5.
Abstract:
We discuss the properties of synchrotron radiation (SR) and neutron powder diffraction investigations of the crystal and magnetic structure of solids. Special emphasis is paid to the analysis of the full width at half maximum (FWHM) of the observed Bragg reflections and its relation with the size of the coherently ordered regions of the material. Two specific examples are discussed: a SR powder diffraction study of the crystal structure of the hexaferrite BaSn2Fe4O11 and a neutron powder diffraction study of the magnetic ordering of the magnetic moments of manganese ions in the distorted perovskite system CaMn7O12. (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
Anisotropic X-ray anomalous scattering by incommensurately
modulated crystals
Authors:
Ovchinnikova EN. Dmitrienko VE.
Source:
(list of journals)
Journal of Alloys & Compounds. 286(1-2):236-240, 1999 May 5.
Abstract:
The possibility of the ATS (anisotropy of the tensor of susceptibility) reflections appearance in X-ray anomalous anisotropic diffraction near the absorption edges is considered for the crystals with incommensurate modulation. The superspace groups are used to describe symmetry properties of the susceptibility tensor for incommensurately modulated crystals. It is shown that the modulation can change both the resonant spectra and the tensorial properties of susceptibility. No ATS reflections may appear in the incommensurately modulated crystals owing to the modulation of the resonant spectra, but the modulation of the angular part of the susceptibility tensor can lead to the appearance of the ATS main reflections and ATS satellites. The incommensurate modulation can violate the reflection extinctions which correspond to the glide planes, the screw axes and to the centering translations. The possibility of the ATS reflections near the K-edge of Ni in the diffraction pattern of La2NiO4+x is considered. (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
Temperature dependence of fullerene electroabsorption spectra - model
calculations
Authors:
Petelenz P. Andrzejak M. Kazaoui S. Minami N.
Source:
(list of journals)
Chemical Physics. 243(1-2):149-157, 1999 May 1.
Abstract:
As demonstrated in recent experiments, the electroabsorption spectra of fullerene thin films exhibit rather strong temperature dependence in the energy regions where the signal is attributed to the eigenstates of CT parentage. This is difficult to rationalize in terms of a purely electrostatic model where the CT excitons are viewed as localized charge pairs. In the present paper, a simple dimer model is used to account for the main features of the off-diagonal CT interaction that gives rise to charge delocalization. The results demonstrate that the strong temperature dependence of the EA signal may be explained by disorder-modulated orientational dependence of charge-transfer integrals, and highlight the role of the off-diagonal CT coupling in organic molecular crystals. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
The crystal chemistry of sogdianite, a milarite-group
mineral
Authors:
Cooper MA. Hawthorne FC. Grew ES.
Source:
(list of journals)
American Mineralogist. 84(5-6):764-768, 1999 May-Jun.
Abstract:
The crystal structure of sogdianite, hexagonal, a = 10.053(1), c = 14.211(2) Angstrom, V = 1243.8(4) Angstrom(3), space group = P6/mcc, Z = 2, has been refined to an R index of 2.0% using 607 observed (\F-o\ > 5 sigma\F\) reflections collected with an automated four-circle diffractometer using MoK alpha X-radiation. Site-scattering refinement and electron-microprobe analysis indicate the composition (Zr0.76Ti0.384+Fe0.733+Al0.13)(Sigma=2)(square(1.15)Na(0.85))(Sigma=2)K[Li3Si 12O30]. The T2 tetrahedron is completely occupied by Li, and all Al occurs at the octahedrally coordinated A site. The <A-O> bond length is compatible with all Fe bring in the trivalent stale. There is no significant positional disorder of the A-group cations, in accord with the absence of H2O in sogdianite. Single-crystal X-ray precession photographs of sogdianite show the presence of diffractions that are incommensurate with the sogdianite diffraction pattern. The relative intensity of the incommensurate diffractions increases with the degree of apparent alteration of sogdianite (clear --> turbid --> murky), suggesting that sogdianite is altering to, or possible exsolving, a second phase, probably zektzerite.
Title:
The morphology of quasicrystals,
incommensurate composite crystals and
modulated crystals derived from the
broken-bond model
Authors:
van Smaalen S.
Source:
(list of journals)
Acta Crystallographica - Section a - Foundations of
Crystallography. 55(Part 3):401-412, 1999 May 1.
Abstract:
The broken-bond model for the surface free energy of crystals is considered. The consequences are derived for the morphology of periodic crystals, quasicrystals, incommensurately modulated crystals and intergrowth compounds. It is found that low-index facets on periodic crystals and quasicrystals are the result of finding an optimized position along the vector normal to the surface of the surface plane. The same principle explains the normal facets on modulated crystals and intergrowth crystals. The so-called satellite facets are the result of surface pinning of the phase of the modulated wave. On intergrowth compounds, facets may be found that are stabilized by a combination of both mechanisms. It is shown that the most stable facets on intergrowth crystals are the normal facets that are common to the subsystems, independent of the details of the structure.
Title:
X-ray phase determination by the principle of minimum charge
Authors:
Elser V.
Source:
(list of journals)
Acta Crystallographica - Section a - Foundations of
Crystallography. 55(Part 3):489-499, 1999 May 1.
Abstract:
When the electron density in a crystal or a quasicrystal is reconstructed from its Fourier modes, the global minimum value of the density is sensitively dependent on the relative phases of the modes. The set of phases that maximizes the value of the global minimum corresponds, by positivity of the density, to the density having the minimum total charge that is consistent with the measured Fourier amplitudes. Phases that minimize the total electronic charge (i.e. the average electron density) have the additional property that the lowest minima of the electron density become exactly degenerate and proliferate within the unit cell. The large number of degenerate minima have the effect that density maxima are forced to occupy ever smaller regions of the unit cell. Thus, by minimization of the electronic charge, the atomicity of the electron density is enhanced as well. Charge minimization applied to simulated crystalline and quasicrystalline diffraction data successfully reproduces the correct phases starting from random initial phases.
Title:
Quasiperiodic patterns generated by mixing lattices derived from a
dodecahedral star and an icosahedral star
Authors:
Soma T. Watanabe Y.
Source:
(list of journals)
Acta Crystallographica - Section a - Foundations of
Crystallography. 55(Part 3):508-511, 1999 May 1.
Abstract:
A 3D quasiperiodic pattern by projection from an nD lattice can be defined by an orthonormal n x n lattice matrix which produces basis vectors in pattern space with a prescribed arrangement and basis vectors in perpendicular or test space satisfying the quasicrystallographic condition. A 16 x 16 lattice matrix is derived which produces basis vectors in pattern space as a combination or mixing of dually positioned dodecahedral star and icosahedral star. It is shown that the mixed star constitutes a eutactic star. Since the module generated by the mixed eutactic star is totally irrational, patterns generated by projection using the lattice matrix are quasicrystallographic and the equilateral pattern is generated for 1:1 mixing.
Title:
Positive-definite conditions of elastic constants of two-dimensional
quasicrystals with noncrystallographic
symmetries
Authors:
Wang JB. Zhang RK. Ding DH. Wang RH.
Source:
(list of journals)
Acta Crystallographica - Section a - Foundations of
Crystallography. 55(Part 3):558-560, 1999 May 1.
Abstract:
In the present work, the positive-definite conditions of the elastic constants of two-dimensional (2D) quasicrystals with non-crystallographic symmetries have been derived. These results are necessary for studying elastic and mechanical properties of two-dimensional quasicrystals both in theory and in experiment.
Title:
Interdiffusion in nanometer-scale multilayers investigated by in situ
low-angle x-ray diffraction
Authors:
Wang WH. Bai HY. Zhang M. Zhao JH. Zhang XY. Wang WK.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(16):10811-10822, 1999 Apr 15.
Abstract:
An iii situ low-angle x-ray diffraction technique is used to investigate interdiffusion phenomena in various metal-metal and metal-amorphous Si nanometer-scale compositionally modulated multilayers (ML's). The temperature-dependent interdiffusivities are obtained by accurately monitoring the decay of the first-order modulation peak as a function of annealing time. Activation enthalpies and preexponential factors for the interdiffusion in the Fe-Ti, Ag-Bi, Fe-Mo, Mo-Si, Ni-Si, Nb-Si, and Ag-Si ML's are determined. Activation enthalpies and preexponential factors for the interdiffusion in the ML's are very small compared with that in amorphous alloys and crystalline solids. The relation between the atomic-size difference and interdiffusion in the ML's are investigated. The observed interdiffusion characteristics are compared with that in amorphous alloys and crystalline alpha-Zr, alpha-Ti, and Si. The experimental results suggest that a collective atomic-jumping mechanism govern the interdiffusion in the ML's, the collective proposal involving 8-15 atoms moving between extended nonequilibrium defects by thermal activation. The role of the interdiffusion in the solid-state reaction in the ML's is also discussed. .
Title:
The effect of Mn and Al contents on the solvus of kappa phase in austenitic
Fe-Mn-Al-C alloys
Authors:
Li MC. Chang H. Kao PW. Gan D.
Source:
(list of journals)
Materials Chemistry & Physics. 59(1):96-99, 1999 Apr 30.
Abstract:
It is known that the precipitation of the kappa phase has significant effect on the mechanical properties of Fe-Mn-Al-C alloys. The kappa phase may be present along the grain boundaries tinter-granular) or within the grains (intra-granular). The effect of Al and Mn contents on the solvus of both inter- and intra-granular kappa phase was investigated for a composition range of Fe-(21-32 wt.%)Mn-(2-10 wt.%)Al-1C. The results clearly indicate that the addition of Al raises the solvus of both inter- and intra-granular kappa phases significantly, while the addition of Mn only causes slight reduction of the solvus. The implication of this result on the development of this alloy is also discussed. (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
Periodical magnetic effects in FexSi1-x/Si multilayers, depending upon the
modulation length
Authors:
Perez GT. Salas FH. Morales R. Alvarez-Prado LM. Alameda JM.
Source:
(list of journals)
Journal of Magnetism & Magnetic Materials. 197:20-22, 1999 May.
Abstract:
Magnetic properties of compositionally modulated FexSi1-x/Si amorphous and crystalline multilayers are reported. From SQUID magnetometry and transverse magneto-optic Kerr effect measurements, we detected noticeable lambda-related structure in both magnetization and relative reflectivity. A systematic oscillation is found for lambda < 16 Angstrom. On the contrary, in samples with definite multilayered structure (lambda greater than or equal to 16 Angstrom), a significant reduction in magnetization is found as lambda decreases. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Structural and magnetic properties of Ni2In type (Mn1-xNix)(65)Ga-35
compounds
Authors:
Shiraishi H. Niida H. Iguchi Y. Mitsudo S. Motokawa M. Ohayama K. Miki H. Onodera H. Hori T. Kanematsu K.
Source:
(list of journals)
Journal of Magnetism & Magnetic Materials. 197:660-662, 1999 May.
Abstract:
New intermetallic compounds (Mn1-xNix)(65)Ga-35 of Ni2In type structure are found in the range of 0.15 less than or equal to x less than or equal to 0.45. In the higher x range, the magnetization-temperature curves show Curie-Weiss type behaviors, but those with x less than or equal to 0.35 suggest another type ferromagnet. The magnetic ordering temperature T-c decreases for x less than or equal to 0.2 and then increases with increasing x. The curves of 0.25 less than or equal to x less than or equal to 0.3 show a hump and then slightly decrease with decreasing temperature. In the neutron diffraction experiment for x = 0.275, the (0 0 1) reflection appears for 165 K less than or equal to T < 218 K indicating the presence of an antiferromagnetic component lying in basal plane. For T < 165 K, the satellite lines of(0 0 1) suggest an appearance of incommensurate phase, perhaps of a helical spin structure, changing the pitch of helix from 5.78C to 8.47C with temperature. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Magnetic structures of Ce(AgxCu1-x)(1.8)Sb-2 Kondo compounds
Authors:
Guzik A. Pierre J. Kaczmarska K. Ouladdiaf B.
Source:
(list of journals)
Journal of Magnetism & Magnetic Materials. 197:891-892, 1999 May.
Abstract:
The magnetic structures of the Ce(AgxCu1-x)(1.8)Sb-2 compounds have been refined from neutron diffraction. The transition from the CeCu1.8Sb2 commensurate frustrated antiferromagnetic structure to the CeAg1.8Sb2 incommensurate one occurs through ferromagnetic and spin-glass states. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Composition of inflation rules for aperiodic
structures with nine-fold symmetry
Authors:
Escudero JG.
Source:
(list of journals)
International Journal of Modern Physics B. 13(4):363-373, 1999 Feb 10.
Abstract:
Deterministic aperiodic planar patterns with nine-fold symmetry have been interpreted recently in terms of a class of formal grammars known as DOL systems. A wider class of patterns with the same symmetry can be generated by composing two inflation rules. They are described with the help of ETOL systems. From the formal language theory point of view this corresponds to a selective approach, due to the fact that we need to introduce nonterminal symbols in the alphabet. From the point of view of quasicrystal structures, instead of having only one pattern of a given size and shape, we now have a finite number of them. This allows to construct nondeterministic models of aperiodic structures.
Title:
Low-temperature electrical conductivity and dielectric properties of
TlInS2(1-x)Se2x crystals
Authors:
Sheleg AU. Iodkovskaya KV.
Source:
(list of journals)
Inorganic Materials. 35(5):444-447, 1999 May.
Abstract:
The electrical conductivity, dielectric loss tangent, and permittivity of TlInS2 and TlInS2(1-x)Se2x (x = 0.1, 0.2, 0.3) crystals were measured in the temperature range 100-250 K. Around the incommensurate commensurate phase transition, the temperature dependences show anomalies whose shape and position depend on Se content. With increasing x, the transition temperature decreases sharply, and the anomalies become broader and nearly vanish at x = 0.3. The properties studied exhibit hysteretic behavior in cooling-heating cycles.
Title:
Electronic and magnetic structure of the undoped two and
three-leg ladder cuprates in an itinerant electrons model
Authors:
Germain P. Lagues M.
Source:
(list of journals)
European Physical Journal B. 8(4):497-505, 1999 Apr.
Abstract:
We study the electronic and magnetic structure of the undoped ideal two and three-leg ladder cuprates by assuming a moderate on site coulombic repulsion. This analysis is an extension of the Fermi liquids studies proposed for the CuO2 plane in view to explain the high T-c superconductivity and the competition with the antiferromagnetic phase. At zero doping, the quasi-one-dimensionality of the structure results in SDW correlations with different (commensurate) vectors according to the number of legs, which contrasts with the predictions made from the Heisenberg model. At mean field, and for n = 3 (Sr2Cu3O5), we predict a magnetic ordered state, detected by mu Sr and NMR measurements with critical temperatures consistent with our assumptions on the physical parameters, the modulation vector being pi/2. The presence of several bands at the Fermi level explains why there is no observable gap in the static susceptibility measurements. For n = 2, we predict a gap consistent with experimental Curie susceptibility. But the expected magnetic instability is detected only in La2Cu2O5, where the interladder coupling is stronger. In every case the one-dimensional van Hove singularities are far from the Fermi level, making difficult the obtaining of high T-c superconductivity.
Title:
Pseudocritical NMR frequency shift above the
normal-incommensurate phase transition
Authors:
Decker F. Holzer KP. Mischo P. Petersson J. Schussler D.
Source:
(list of journals)
European Physical Journal B. 8(4):507-510, 1999 Apr.
Abstract:
The NMR satellite frequencies were measured as a function of temperature in the normal high-temperature phase for Rb-87 in Rb2ZnBr4 and Rb2ZnCl4 and for Cl-35 in betaine calciumchloride dihydrate. Approaching the respective normal-incommensurate phase transition an anomalous shift of the NMR frequency is observed for the first two cases. This effect is ascribed to the increasing order parameter fluctuations. The experimental data are compared to calculations which relate the observed behaviour of the NMR frequencies to the non-classical critical behaviour of the substances under investigation.
Title:
Disorder driven roughening transitions of elastic manifolds and periodic
elastic media
Authors:
Emig T. Nattermann T.
Source:
(list of journals)
European Physical Journal B. 8(4):525-546, 1999 Apr.
Abstract:
The simultaneous effect of both disorder and crystal-lattice pinning on the equilibrium behavior of oriented elastic objects is studied using scaling arguments and a functional renormalization group technique. Our analysis applies to elastic manifolds, e.g., interfaces, as well as to periodic elastic media, e.g., charge-density waves or flux-line lattices. The competition between both pinning mechanisms leads to a continuous, disorder driven roughening transition between a flat state where the mean relative displacement saturates on large scales and a rough state with diverging relative displacement. The transition can be approached by changing the impurity concentration or, indirectly, by tuning the temperature since the pinning strengths of the random and crystal potential have in general a different temperature dependence. For D dimensional elastic manifolds interacting with either random-field or random-bond disorder a transition exists for 2 < D;< 4, and the critical exponents are obtained to lon;est order in epsilon = 4 - D. At the transition, the manifolds show a superuniversal logarithmic roughness. Dipolar interactions render lattice effects relevant also in the physical case of D = 2. For periodic elastic media, a roughening transition exists only if the ratio p of the periodicities of the medium and the crystal lattice exceeds the critical value p, = 6/pi root epsilon. For p < p, the medium is always flat. Critical exponents are calculated in a double expansion in p = p(2)/p(c)(2) - 1 and epsilon = 4 - D and fulfill the scaling relations of random field models.
Title:
A high temperature furnace for in situ and time-resolved x-ray diffraction
studies
Authors:
Capitan MJ. Thouin N. Rostaing G.
Source:
(list of journals)
Review of Scientific Instruments. 70(5):2248-2252, 1999 May.
Abstract:
A high temperature furnace has been built and mounted on a six-circle goniometer for in situ diffraction studies of polycrystalline and powder samples. Temperatures up to 1400 K are controlled with a stability better than +/-0.05 K in a vacuum better than 10(-7) atm. The furnace is also able to work in oxidizing or reducing atmosphere and is mounted on a chi circle table using the phi circle as a driver for precise translation of the sample in the z direction. The sample can be rotated continuously via a mechanical feedthrough. The temperature is measured by means of a thermocouple placed at the sample holder (0.5 mm from the sample position). The temperature has been calibrated up to 1073 K by following the known thermal expansion of an AlCuFe quasicrystal. (C) 1999 American Institute of Physics. .
Title:
Study of Mn2+ EPR spectra in the incommensurate phase of
Rb2ZnCl4
Authors:
Trubitsyn MP.
Source:
(list of journals)
Physics of the Solid State. 41(4):624-626, 1999 Apr.
Abstract:
An EPR study of Mn2+ centers in the incommensurate phase of rubidium tetrachlorozincate crystals is reported. It is shown that the temperature dependence of the high-field hyperfine line group M-S = 3/2<->5/2 can be described in terms of a simple "local'' model.(1) The data obtained support the nonclassical type of critical behavior in Rb2ZnCl4 crystals corresponding to the three-dimensional Heisenberg model for a two-component order parameter. (C) 1999 American Institute of Physics. .
Title:
Incommensurate structure of a spin density
wave in the one-dimensional t-J model
Authors:
Caprara S. Avignon M. Tugushev V.
Source:
(list of journals)
Physics Letters A. 255(1-2):98-102, 1999 May 3.
Abstract:
We make use of the slave-boson approach to investigate the magnetic properties of the one-dimensional I - J model in the weak-coupling limit J < t(1 - n), where n is the number of electrons per unit cell. In the mean-field approximation at zero temperature we find that the helix spin-density-wave phase has a lower energy than the Neel phase. This latter disappears below a critical electron density n(c), whereas the helix phase persists for all ra, The hole-doping dependence of the spin-density-wave amplitude Delta and of the helix wave-vector q(0) are calculated. The temperature vs hole doping phase diagram in the mean-field approximation is also determined. It is shown that for n above a certain value n* the helix state transforms into the Neel stare by increasing the temperature as q(0) is reduced to zero. The Neel phase evolves towards the paramagnetic phase at higher temperatures. For n below n* the helix phase transforms directly into the paramagnetic phase by increasing the temperature. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Hillock growth phenomena during post-indentation annealing of
quasicrystalline AlPdMn
Authors:
Wolf B. Baunack S. Paufler P.
Source:
(list of journals)
Physica Status Solidi A-Applied Research. 172(2):317-327, 1999 Apr 16.
Abstract:
Single-quasicrystalline icosahedral AlPdMn was subject to Vickers microindentations at room temperature, annealed up to 750 degrees C in vacuum, and then inspected using optical microscopy, atomic force microscopy (AFM), wavelength dispersive microanalysis (WDX) and Auger spectroscopy (AES). At temperatures above 600 degrees C the whole sample surface became increasingly rough, exhibiting holes and small elevations, whereas the vicinity of the impressions remained free of surface alterations. The growth of large hillocks out of the impressions was observed at temperatures above 700 degrees C in the presence of oxygen. No growth of high elevations was noted for an oxygen partial pressure below 3 x 10(-6) Pa. AES and WDX revealed an enrichment of manganese and the depletion of aluminium in the hillocks. The results are discussed in the frame of indentation induced defects and their impact on diffusion and surface migration.
Title:
Mechanical properties of icosahedral AlPdMn probed by indentation at variable
temperatures
Authors:
Wolf B. Paufler P.
Source:
(list of journals)
Physica Status Solidi A-Applied Research. 172(2):341-361, 1999 Apr 16.
Abstract:
Hardness and elastic modulus of the icosahedral quasicrystal Al70Pd21Mn9 (in the following simply denoted as AlPdMn) have been probed by micro- and nanoindentation in the temperature range from room temperature to 820 K. Pronounced indentation size effects (ISE) were found that,result in a hardness increase with decreasing force at room temperature and in the inverse behaviour for elevated temperatures. Furthermore, considerable indentation creep was observed for temperatures above 670 K. Atomic force microscopy (AFM) was utilised to both quantify the impression contact area and to study the development of surface modifications and crack propagation around the indents. The elastic modulus exhibits a linear decrease with raising temperature which is considerably smaller than observed for metals, but somewhat higher than in case of elemental semiconductors.
Title:
Polarization analysis of low-energy excitations in single-domain Cr
Authors:
Boni P. Lorenzo JE. Roessli B. Shirane G. Werner SA. Wildes A.
Source:
(list of journals)
Physica B. 268:255-258, 1999 Jun.
Abstract:
The longitudinal and transverse spin fluctuations in single-domain Cr have been investigated in the transverse spin-density-wave phase using constant energy scans with 4 less than or equal to E less than or equal to 25 meV and polarization analysis. The transverse excitations show well-defined peaks centered at the incommensurate satellite positions (1 +/- delta 0 0) and a broad peak at the commensurate (1 0 0) position. The longitudinal fluctuations exhibit a much more complicated structure due to the additional appearance of magnetic excitations below 9 meV (Fincher-Burke modes). The fluctuations with longitudinal polarization show a pronounced renormalization between 136 and 230 K raising the possibility that the Fincher-Burke modes are responsible for the phase transition at T-N. Above E similar or equal to 18 meV, the longitudinal fluctuations decrease with increasing E at T = 230 K in contrast to the transverse fluctuations. Our results indicate that unpolarized beam data is not really useful for making comparisons with existing theories. There is an urgent need to extend polarization analysis to higher neutron energies. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Minute splitting of magnetic excitations due to dipolar interactions in
CsFeCl3 and RbFeCl3 observed with polarised neutrons
Authors:
Dorner B. Petitgrand D. Gudel HU.
Source:
(list of journals)
Physica B. 268:263-265, 1999 Jun.
Abstract:
The splitting due to dipolar interactions was investigated for the hexagonal [1 1 0] direction (y-direction). The S-x and S-y fluctuations were exclusively visible in the non-spin-flip and the spin-flip channels, respectively. The splitting creates minima in the dispersion curves away from the commensurate K-point (1/3 1/3 0). In CsFeCl3, which does not exhibit long-range order, the excitations are temperature independent at low temperature. In RbFeCl3 a soft mode behaviour is observed and the new minima in the dispersion curves correspond to the observed incommensurate structures. In the commensurate phase of RbFeCl3 below 1.95 K an acoustic and an optic mode were observed. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Pentagonal Al-Co-Ni quasicrystal with a
superstructure
Authors:
Ritsch S. Beeli C. Luck R. Hiraga K.
Source:
(list of journals)
Philosophical Magazine Letters. 79(5):225-232, 1999 May.
Abstract:
A one-dimensionally periodic pentagonal quasicrystal with a superstructure has been found in the Al-Co-Ni system in a sample quenched from 1160 degrees C at the composition Al71.5Co25.5Ni3. Its electron diffraction patterns are characterized by a fivefold rotation axis as a unique symmetry element as well as superstructure reflections similar to those of a related decagonal phase. The presence of this symmetry in electron diffraction patterns originates from strong dynamical scattering effects of electrons in relatively thick regions of the sample, in combination with the unique parallel arrangement of fivefold symmetric atom clusters. Differently, the superstructure reflections are caused by the long-range order of this new state which can be described by a random variant of a Penrose rhomb tiling.
Title:
Effects of charge density modulation on incommensurate
antiferromagnetism: Ginzburg-Landau study
Authors:
Yamase H. Kohno H. Fukuyama H. Ogata M.
Source:
(list of journals)
Journal of the Physical Society of Japan. 68(4):1082-1085, 1999 Apr.
Abstract:
In the vicinity of hole density 1/8, La-based high-T-c cuprates exhibit long-range order of incommensurate antiferromagnetism (IC-AF). Motivated by this observation, we explore the possible stabilization of IC-AF ordering due to the existence of static charge density modulation (CDM). We use Ginzburg-Landau free energy based on the mean field theory of the t-J model. We show numerically that three kinds of CDMs, including a stripe pattern, can stabilize static IC-AF ordering. We also argue that such CDMs can cause the saturation of the degree of incommensurability (eta) for IC-AF fluctuation as a function of hole density. In our framework, the effects of the low-temperature tetragonal (LTT) structure only appear as a slight increase of eta for the stripe pattern.
Title:
A model for supersymmetry - An extension of the Chen-Walker's model
Authors:
Mashiyama H. Mashiyama KT.
Source:
(list of journals)
Journal of the Physical Society of Japan. 68(4):1273-1276, 1999 Apr.
Abstract:
A model for incommensurate transitions proposed by Chen and Walker [Phys. Rev. B 43 (1991) 5634] has been extended to describe a sub-lattice model which possesses supersymmetry. If a zone boundary mode freezes, a superstructure with supersymmetry can appear and may transform into a superstructure without supersymmetry at lower temperature. Although both superstructures belong to the same space group, the transition is either second or first order one with accompanying a definite anomaly in specific heat and susceptibility.
Title:
Far-infrared spectroscopy investigation of commensurate and
incommensurate Cs2CdBr4 crystal
Authors:
Shchur Y. Kamba S. Petzelt J.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(17):3601-3613, 1999 May 3.
Abstract:
Far-infrared reflectivity measurements of Cs2CdBr4 crystal were performed over the frequency region 15-600 cm(-1) and temperature region 10-297 K. All transverse lattice modes have frequencies below 230 cm(-1) because of the heavy atoms in the Cs2CdBr4 crystal. A sequence of phase transitions can be identified on the basis of the activation of new modes below the phase transition temperatures due to the lowering of the crystal symmetry on cooling. Factor-group analysis was carried out and selection rules found for the infrared activity of phonon modes in the incommensurate and commensurate phases, and the results were compared with the experimental data.
Title:
Lattice dynamics simulation of Cs2CdBr4 crystal
Authors:
Shchur Y. Kamba S. Petzelt J.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(17):3615-3628, 1999 May 3.
Abstract:
Lattice dynamics calculations for the Cs2CdBr4 crystal in the high-temperature orthorhombic phase (Pnma) and in the monoclinic phase (P2(1)/n11) at similar to 195 K were carried out. The model was based on the atom-atom potential function which comprised the long-range Coulombic, short-range and covalent interactions. Comparison of the calculated phonon frequencies with the experimental ones obtained from far-infrared reflectivity and Raman scattering measurements gives a reasonable agreement in most cases. A possible origin of the incommensurate phase transition was discussed on the basis of a coupling between low-lying Sigma(2) phonon branches. Using group-theory analysis and the calculated phonon dispersion branches, it is shown that the P2(1)/n 1 1-P (1) over bar phase transition is very probably induced by the condensation of a phonon mode at the Brillouin zone boundary.
Title:
Modulated ferroelectrics
Authors:
Blinc R.
Source:
(list of journals)
Ferroelectrics. 220(1-2):105-136, 1999.
Abstract:
Modulated ferroelectrics represent a class of materials where the spontaneous polarization and/or some other characteristic physical property varies in space in a regular manner. The presence of one or more modulation waves gives rise to a number of new phenomena which are not found in homogeneous ferroelectrics. Here we review the properties of: (a) incommensurate ferroelectrics with one, two or three independent modulation waves, (b) ferroelectric and antiferroelectric liquid crystals in external fields and confined geometries where a crossover exists between a plane wave and a soliton-type modulation wave, (c) composite and multiple layer type materials. The importance of some of these systems for applications will be also discussed.
Title:
The structures and variation of vacancy ordering in
epitaxial DySi2-x thin films on (111)Si
Authors:
Shen GH. Chen JC. Chen LJ.
Source:
(list of journals)
Applied Surface Science. 142(1-4):300-304, 1999 Apr.
Abstract:
Epitaxial DySi2-x films were grown in a-Si (15 nm)/Dy (30 nm)/(111)Si samples annealed at 700 degrees C for 10 min in an ultrahigh vacuum chamber. From the electron diffraction pattern analysis, the structure of the epitaxial DySi2-x thin films were determined to consist of a superstructure of an root 3 X root 3 R 30 degrees vacancy ordering structure with an out-of-step structure. The three-dimensional structure of the root 3 X root 3 R 30 degrees vacancy ordering was determined to be (root 3 X root 3 R 30 degrees 2c). The periodicity along the c-axis of the out-of-step vacancy ordering structure with M = 2 was also analyzed to be 2c. The intrinsic structure was found to transform to various modulated structures by ion bombardment during cross-sectional transmission electron microscope (TEM) sample preparation. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Epitaxial growth and interface structure of PbS on InP(110)
Authors:
Preobrajenski AB. Chasse T.
Source:
(list of journals)
Applied Surface Science. 142(1-4):394-399, 1999 Apr.
Abstract:
We have investigated layer growth mode, interface chemistry and morphology of PbS layers on InP(110) using XPS and LEED. AL room temperature, the interface has been observed to be abrupt and non-reactive. The growth mode is layer-like but proceeds in a multilayer fashion. Epitaxial PbS layers have been grown with the (001) face parallel to InP(110) and good lattice match along the [1 (1) over bar 0] orientation of the substrate surface. Along the [001] surface direction, an incommensurate. lattice match has been observed. Upon heating of the substrate during PbS deposition 3D island growth occurs beyond an initial multilayer stage of growth. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Growth of thin Ti films on Al single-crystal surfaces at
room temperature
Authors:
Smith RJ. Kim YW. Shivaparan NR. White GA. Teter MA.
Source:
(list of journals)
Surface & Interface Analysis. 27(4):185-193, 1999 Apr.
Abstract:
The growth of thin Ti films on Al(001), Al(110) and Al(111) surfaces at room temperature has been studied using high-energy Rutherford backscattering spectroscopy (RBS) and channeling, x-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED). Our results show that Ti atoms form a thin, metastable, fee overlayer on Al(110) and Al(001) surfaces. The primary evidence for this conclusion is the reduced backscattering that occurs as the Ti atoms shadow the Al atoms in the fee structure of the Al substrate. For the Al(111) surface the Al surface peak area in ion channeling, measured as a function of Ti coverage, shows a small decrease for the first monolayer (ML) of Ti coverage but then increases gradually with coverage, a characteristic of alloy formation. However, XPS and low-energy ion scattering (LEIS) results are generally consistent with overlayer growth of Ti on the Al(111) surface, and the LEED pattern indicates an ordered overlayer for Ti coverages from 2 to 12 ML, at which point the Al surface was completely covered by Ti, The results suggest the growth of incommensurate, ordered islands of hcp Ti on Al(111) in a Stranski-Krastanov growth mode, in remarkable contrast to the pseudomorphic fee Ti overlayer growth observed for Ti films on Al(001) and Al(110). Copyright (C) 1999 John Whey & Sons, Ltd.
Title:
Anatomy of a structural phase transition: theoretical analysis of the
displacive phase transition in quartz and other silicates
Authors:
Dove MT. Gambhir M. Heine V.
Source:
(list of journals)
Physics & Chemistry of Minerals. 26(4):344-353, 1999 Apr.
Abstract:
A theoretical analysis and computer modelling of quartz gives a picture of the alpha-beta phase transition in terms that would appear to be widely applicable to other silicate framework structures. The picture is based upon the fact that the structure of the beta-phase can distort to the alpha form through the rotations of the SiO4 tetrahedra without necessitating any distortions of the individual tetrahedra. A simple model based upon this premise and augmented by lattice energy calculations of the ordering potential gives a value for the phase transition temperature that is in semi-quantitative agreement with experiment. The reasons for the success of this model are then explored using a full anharmonic lattice dynamics calculation of the phase transition using renormalised phonon theory, highlighting the particular significance of the soft phonon blanch compared to all the other phonon branches. The basic picture also explains the variation of the transition temperature with cation concentration in other aluminosilicates, and gives further insight into the validity of the mean-field description in these phase transitions.
Title:
Acentric low-temperature superstructure of NaV2O5
Authors:
Ludecke J. Jobst A. van Smaalen S. Morre E. Geibel C. Krane HG.
Source:
(list of journals)
Physical Review Letters. 82(18):3633-3636, 1999 May 3.
Abstract:
The low-temperature superstructure of alpha'-NaV2O5 is determined by synchrotron radiation x-ray diffraction. The high-temperature structure is confirmed to be centrosymmetric, but the modulated structure is found to be acentric Fmm2 on the 2a X 2b X 4c supercell. An analysis using superspace symmetry shows that there are modulated and nonmodulated chains of vanadium atoms, tentatively assigned to magnetic and nonmagnetic chains. The arrangement of these chains is different from any model previously considered. .
Title:
Suppression of superconductivity by nonmagnetic impurities, structural
properties and magnetic ordering in HoxLa1-xNi2B2C
Authors:
Freudenberger J. Kreyssig A. Ritter C. Nenkov K. Drechsler SL. Fuchs G. Muller KH. Loewenhaupt M. Schultz L.
Source:
(list of journals)
Physica C. 315(1-2):91-98, 1999 Apr 1.
Abstract:
Superconducting and magnetic properties as well as the lattice structure of polycrystalline HoxLa1-xNi2B2C samples have been studied by susceptibility, X-ray, and neutron diffraction measurements, respectively. A miscibility gap has been found between x = 0.4 and x = 0.7 if the samples are prepared by standard are-melting. Samples in this concentration range have been successfully prepared by melt-spinning. All samples exhibit the LuNi2B2C-type structure and the lattice parameters depend linearly on the La content. Already a low lanthanum concentration of about 10% leads to a rapid depression of T-c from 8.5 K to 2 K. Furthermore this concentration leads to a complete depression of the a-axis modulated incommensurate antiferromagnetic structure. Two other magnetic structures, one with commensurate (0 0 1) and one with incommensurate wave vector (0 0 0.915) were found to be less sensitive to the La concentration. The neutron-diffraction peak intensities connected to these structures decrease with increasing La content and disappear at x = 0.75 (commensurate structure) and x = 0.55 (incommensurate structure). A comparison with HoxR1-xNi2B2C compounds (R = Y, Lu) shows that these two magnetic structures are influenced in different way by the size of the nonmagnetic rare-earth ion R. No size effect was observed for the magnetic ordering temperature of the commensurate antiferromagnetic structure, whereas the incommensurate spiral structure along c-axis was found to be sensitive to the difference in the size of the R and the Ho ions, (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Experimental verification of the quasi-unit-cell model of
quasicrystal structure (vol 396, pg 55,
1998)
Authors:
Steinhardt PJ. Jeong HC. Saitoh K. Tanaka M. Abe E. Tsai AP.
Source:
(list of journals)
Nature. 399(6731):84, 1999 May 6.
Title:
Microhardness and fracture toughness studies of decagonal
quasicrystal in Al-Cu-Co system
Authors:
Murthy GVS. Ray AK. Minz RK. Mukhopadhyay NK.
Source:
(list of journals)
Journal of Materials Science Letters. 18(3):255-258, 1999 Feb 1.
Title:
Iodo-oxyapatite, the first example from a new class of
modulated apatites
Authors:
Henning PA. Lidin S. Petricek V.
Source:
(list of journals)
Acta Crystallographica - Section B, Structural Science.
55(Part 2):165-169, 1999 Apr 1.
Abstract:
Iodo-oxyapatite [pentadecacalcium iodide oxide nonaphosphate, Ca-15(PO4)(9)IO] was synthesized by a flux method and the structure was solved from single-crystal X-ray data. The crystal structure was refined in the space group P6(3)/m [a = 9.567 (1), c = 20.754 (2) Angstrom and Z = 2] to wR on F of 0.0459. Iodo-oxyapatite has a typical hexagonal apatite structure but the unit cell is tripled along the hexad owing to ordering of the iodide and oxide ions along this direction.
Title:
Novel type of dislocation in an Al-Pd-Mn quasicrystal
approximant
Authors:
Klein H. Feuerbacher M. Schall P. Urban K.
Source:
(list of journals)
Physical Review Letters. 82(17):3468-3471, 1999 Apr 26.
Abstract:
A single crystal of the xi'-AlPdMn phase was plastically deformed in a three-point bending geometry. The deformed crystal shows a periodic lattice of phason lines. In a high-resolution electron microscopy (HREM) study a novel dislocation type, termed metadislocation, was observed fur the first time. The magnitude of its Burgers vector is 171 Angstrom. At the core of the metadislocation a dislocation of the xi' structure is found. For the first time its structure and Burgers vector were determined by HREM. in magnitude and direction it is equivalent to the most common Burgers vector in the icosahedral quasicrystal. The structural relationship between the dislocation and the metadislocation is discussed.
Title:
Level fluctuations in quantum systems with multifractal eigenstates
Authors:
Zhong JX. Geisel T.
Source:
(list of journals)
Physical Review E. 59(4):4071-4074, 1999 Apr.
Abstract:
The relationship between universality of level fluctuation laws and multifractality of eigenstates is studied by analyzing energy spectra of tight-binding models of quantum billiards with multifractal eigenstates. We show that level fluctuations in our models are well described by the universal statistical laws such as Poisson statistics for integrable systems and statistics for the Gaussian orthogonal random matrix ensemble as long as the energy levels are located in bandlike spectra, which indicates that level statistics is irrelative to the multifractal properties of eigenstates. Our results are further confirmed by statistical properties of energy spectra in tight-binding models of two-dimensional quasicrystals.
Title:
Role of the coupling between strains and order parameter gradient in
crystals
Authors:
Saint-Gregoire P.
Source:
(list of journals)
Phase Transitions. 67(4 Part B):587-615, 1999.
Abstract:
The manifestation and the role of coupling between order parameter gradient and strains, or equivalently between order parameter and gradient of strains, is reviewed. Dynamical phenomena occurring in perovskites, and in particular in quantum paraelectric phases, evidenced as a coupling between phonon branches at q not equal 0, and also in several other systems (quartz, Sn2P2Se6, Cs2HgBr4, and other systems satisfying the Lifshitz criterion) in relation with the formation of an incommensurate phase, are presented. Besides, the consequences in relation with domain walls, structure of incommensurate phases, and defects are also discussed.
Title:
Characterization of NixFe1-x(0.10 < x < 0.95) electrodeposition from a family
of sulfamate-chloride electrolytes
Authors:
Leith SD. Ramli S. Schwartz DT.
Source:
(list of journals)
Journal of the Electrochemical Society. 146(4):1431-1435, 1999 Apr.
Abstract:
The characteristics of a nickel sulfamate/iron chloride plating bath suitable for high rate electrodeposition of NiFe alloys are described. The effects of current density, electrolyte agitation, and Ni+2/Fe+2 content on deposit composition and plating current efficiency are explored via stripping voltammetry using a rotating ring-disk electrode. Specific plating bath formulations and operating conditions for depositing a wide range of alloy compositions at a variety of growth rates are illustrated. Special attention is given to determination of polarization and electrolyte mixing conditions for plating Permalloy and Invar. X-ray diffraction studies are used to investigate relationships between alloy composition and crystal structure. The implications for using the plating bath to electroplate composition-modulated alloys and 3D microstructures are discussed. (C) 1999 The Electrochemical Society. S0013-4651(98)07-040-2. All rights reserved.
Title:
Raman and infrared hard mode spectroscopy of the internal vibrations in
Sn2P2Se6
Authors:
Eijt S. Maior MM.
Source:
(list of journals)
Journal of Physics & Chemistry of Solids. 60(5):631-643, 1999 May.
Abstract:
The high frequency internal valence vibrations of the P2Se6 molecular units in Sn2P2Se6 are studied by Raman and infrared hard mode spectroscopy. These internal modes reflect the structural changes on a local bond length scale, related to the phase transition sequence paraelectric-incommensurate-ferroelectric. Clear frequency and intensity changes are observed in relationship to the phase transitions, in quantitative agreement with mode coupling theory and symmetry selection rules. The relationship to the structural changes is discussed. Additional Raman activity is observed in the incommensurate phase related to phonon folding processes, and in the ferroelectric phase because of deviations from a centro-symmetric structure. (C) 1999 Elsevier Science Ltd. All rights reserved.
Title:
Low-temperature ordered phase of methylthiolate monolayers on Au(111)
Authors:
Kondoh H. Nozoye H.
Source:
(list of journals)
Journal of Physical Chemistry B. 103(14):2585-2588, 1999 Apr 8.
Abstract:
Low-temperature phases of methylthiolate (CH3S) monolayers on Au(lll) have been investigated by using cryogenic scanning tunneling microscopy. The methylthiolate monolayers have a structure with a (root 3 x root 3)R30 degrees lattice at room temperature, while at 110 K it is transformed into a one-dimensional "chain structure" near step edges and a two-dimensionally ordered structure with an anisotropic lattice on terraces. The latter structure has an oblique commensurate (3 x 4) unit cell (8.6 x 11.5 Angstrom) in which four methylthiolates are located as a "tetramer". This temperature-dependent phase transition is reversible. The formation of tetramers is interpreted as evidence of an important role of a clustering of sulfur species in forming the ordered structure of the thiolate monolayers.
Title:
Monolayer epitaxy of a triangular molecule on graphite
Authors:
Irie S. Isoda S. Kuwamoto K. Miles MJ. Kobayashi T. Yamashita Y.
Source:
(list of journals)
Journal of Crystal Growth. 199(Part 2):939-944, 1999 Mar.
Abstract:
2,4,6-Tris(1,3-dithiol-2-ylidene)-1,3,5-cyclohexanetrione (C-15 H-6 O-3 S-6, abbreviated; TDTCHTO) has a shape of triangular propeller-like structure, and is known to crystallize as an orthorhombic structure (orthorhombic-I) by solution-growth process. In this study, monolayer of TDTCHTO was grown on a graphite (0 0 1) surface by vacuum-deposition, and was studied on its structure and epitaxy by STM. The observed two-dimensional lattice of TDTCHTO monolayer is hexagonal with a = 1.77 nm, in which the two molecules stack with their triangular molecular planes parallel onto the graphite surface. As a result, the monolayer of TDTCHTO forms a different layer structure from the known orthorhombic structure, and therefore the molecular packing with hexagonal symmetry may be promoted by the symmetry of graphite surface. From the STM observation, the epitaxy is concluded as commensurate, not point-on-line coincidence, which means that an interaction between TDTCHTO and graphite is stronger comparing with side-by-side intermolecular interaction in the monolayer. The a-axis of the monolayer TDTCHTO makes an angle of 14 degrees with the a-axis of graphite, and every molecule is coordinated on equivalent lattice point of graphite. This monolayer structure is discussed in relation with the orthorhombic-II observed with TEM for a thicker film grown on graphite. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Multiply twinned C-60 and C-70 nanoparticles
Authors:
Pauwels B. Bernaerts D. Amelinckx S. Van Tendeloo G. Joutsensaari J. Kauppinen EI.
Source:
(list of journals)
Journal of Crystal Growth. 200(1-2):126-136, 1999 Apr.
Abstract:
Nanoparticles of C-60 and C-70 prepared by aerosol flow reactor method show a well developed morphology when produced at sufficiently high temperatures. Hexagonal plate shaped, icosahedral and decagonal particles of C-60 and C-70 are formed. Morphology and internal structure are studied by scanning and transmission electron microscopy. The plate-like particles are lamellar-twinned and grow preferentially on the side-faces by nucleation of new molecular layers along re-entrant corners. The decagonal multiply twinned nanoparticles are strained and show a distinct deviation from cubic symmetry. Some of the C-70 particles exhibit a modulated structure to accommodate the internal stress; this is possible because of the ellipsoidal shape of the C-70 molecule. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Magnetoelasticity of Cr-Ga alloy single crystals at high
pressures
Authors:
Prinsloo ARE. Alberts HL. Smit P.
Source:
(list of journals)
Journal of Applied Physics. 85(8 Part 2A):4747-4749, 1999 Apr 15.
Abstract:
Measurements are reported of the pressure dependences of the elastic constants of Cr+0.16 at. % Ga and Cr+0.88 at. % Ga alloy single crystals through the Neel temperature of both crystals and through the incommensurate-commensurate transition temperature of the latter crystal. The long-wavelength acoustic-mode Gruneisen parameters, gp, which quantify the lattice vibrational anharmonicity, are calculated from the measurements. Both alloys show, depending on the temperature, unusually large positive and negative values of gp which are ascribed to strong coupling of the spin-density wave to the acoustic phonons. The nature of these interactions differs for the two alloys. (C) 1999 American Institute of Physics. .
Title:
Evidence of tetragonal to orthorhombic distortion of HoNi2B2C in the
magnetically ordered state
Authors:
Kreyssig A. Loewenhaupt M. Freudenberger J. Muller KH. Ritter C.
Source:
(list of journals)
Journal of Applied Physics. 85(8 Part 2B):6058-6060, 1999 Apr 15.
Abstract:
Using high resolution neutron scattering on a powder sample of HoNi2 (B2C)-B-11 magnetoelastic effects are observed in this compound for the first time. At low temperatures the tetragonal lattice is distorted along the [110] direction, in which the long-range ordered Ho moments are aligned. The length of the unit cell in [110] direction is shortened by about 0.19% compared to its length in [(1) over bar 10] direction. This lattice distortion is considered to be related to the existence of the commensurate c-axis modulated antiferromagnetic structure. (C) 1999 American Institute of Physics. .
Title:
Probing the structure of accreting compact sources through
X-ray time lags and spectra
Authors:
Hua XM. Kazanas D. Cui W.
Source:
(list of journals)
Astrophysical Journal. 512(2 Part 1):793-803, 1999 Feb 20.
Abstract:
We exhibit, by compiling all data sets we can acquire, that the Fourier-frequency-dependent, hard X-ray lags, first observed in the analysis of aperiodic variability of the light curves of the black hole candidate Cyg X-l, appear to be a property shared by several other accreting black hole candidate sources and also by the different spectral states of this source. We then present both analytic and numerical models of these time lags resulting by the process of Comptonization in a variety of hot electron configurations. We argue that, under the assumption that the observed spectra are due to Comptonization, the dependence of the lags on the Fourier period provides a means for mapping the spatial density profile of the hot electron plasma, while the period at which the lags eventually level off provides an estimate of the size of the scattering cloud. We further examine the influence of the location and spatial extent of the soft photon source on the form of the resulting lags for a variety of configurations; we conclude that the study of the X-ray hard lags can provide clues about these parameters of the Comptonization process, too. Fits of the existing data with our models indicate that the size of the Comptonizing clouds are quite large in extent (similar to 1 lt-s) with inferred radial density profiles that are in many instances inconsistent with those of the standard dynamical models, whereas the extent of the source of soft photons appears to be much smaller than those of the hot electrons by roughly 2 orders of magnitude and its location consistent with the center of the hot electron corona.
Title:
X-ray diffraction study of C2F3Cl physisorbed on graphite
Authors:
Ackermann R. Knorr K.
Source:
(list of journals)
Surface Science. 424(2-3):290-298, 1999 Apr 1.
Abstract:
Monolayers of the planar molecule C2F3Cl, a polar haloethen, physisorbed on exfoliated graphite have been investigated by X-ray diffraction. At a lower coverage, the molecules lie flat on the surface, and at a higher coverage, they stand on the FCl dipod. The coverage-temperature phase diagram has been established and the structures of the three 2D crystalline phases determined. One of the two crystalline phases of the low coverage regime is commensurate root 7 x root 7 and orientationally disordered. The second phase of this regime is incommensurate and goes through a sequence oblique-rectangular-triangular with increasing temperature. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
A new modelling approach to superconductor layered
structures
Authors:
Depero LE. Sangaletti L. Allieri B. Bontempi E.
Source:
(list of journals)
Solid State Communications. 110(7):387-392, 1999.
Abstract:
The analysis of the structural data of high T-c superconducting cuprates (HTSCs) shows that large differences exist in X-ray diffraction (XRD) patterns collected from powders and thin films with respect to the single crystal case, depending in many cases on the synthesis routes and material treatments. These differences are often disregarded and the assessment on the purity of the crystalline phase is made on the basis of XRD pattern indexing only. However, when relative intensities of XRD reflections belonging to. the same family (e.g. (001)) differ from those obtained from the single crystal structure, the simple pattern indexing is not sufficient for the structural characterization and important structural features are missed. These might be helpful for discussing magnetic or electrical behaviour of specimens, as the related properties may depend on the structural correlation along the c axis. In this article a structural modelling of cuprates of the Bi-Sr-Ca-Cu-O family is proposed by considering the electronic density in the projection perpendicular to the layers of the structure. In particular, the structures of Bi-2201, Bi-2212 and Bi-2223 HTSCs were reduced to monomers and intergrowth effects are simulated by generating polymers with different percentages of these phases. By using this model, much information in terms of intergrowth and site occupancy can be gained from a careful analysis of intensities and widths of 001 reflections. (C) 1999 Elsevier Science Ltd. All rights reserved.
Title:
Neutron diffraction study of the ZrMn6Ge6, LuMn6Ge6 and ScMn6Ge6 compounds
Authors:
Mazet T. Welter R. Venturini G. Ressouche E. Malaman B.
Source:
(list of journals)
Solid State Communications. 110(7):407-412, 1999.
Abstract:
The new hexagonal HfFe6Ge6-type ZrMn6Ge6 compound orders antiferromagnetically below T-N = 640 K and undergoes a second transition at T-t = 50 K. Neutron diffraction experiments were performed on the three ZrMn6Ge6, LuMn6Ge6 and ScMn6Ge6 compounds. At 300 K, they exhibit collinear easy-axis antiferromagnetic arrangements and the magnetic structure consists of ferromagnetic (001) Mn planes antiferromagnetically coupled along the c-axis with a ( + - - +) sequence (mu(Mn) approximate to 2.06, 1.86 and 1.94 mu(B) for Zr-, Lu- and ScMn6Ge6, respectively). At low temperature, spin reorientation processes occur, yielding incommensurate antiferromagnetic arrangements. Below T-t, in both ZrMn6Ge6 and LuMn6Ge6 (T-t similar to 30 K), the Mn moments form a double-cone structure (mu(Mn) approximate to 2.1 mu(B), semi-cone angle alpha approximate to 6 degrees) as already found in YMn6Ge6 (T-t similar to 80 K) whereas only preliminary results are available for ScMn6Ge6 below T-t = 255 K. These results lead us to strongly revise previous conclusions concerning LuMn6Ge6 and ScMn6Ge6 with more reasonable Mn magnetic moment values (similar to 2 mu(B) against the similar to 1 mu(B) value previously published). (C) 1999 Elsevier Science Ltd. All rights reserved.
Title:
Relaxation processes in the incommensurate phase of a
crystal with defects
Authors:
Kallaev SN. Kamilov IK.
Source:
(list of journals)
Physics of the Solid State. 41(3):460-461, 1999 Mar.
Abstract:
The nature of the relaxation of the incommensurate superstructure of a ferroelectric to the equilibrium state is investigated experimentally. It is shown that near a phase transition the temperature dependence of the relaxation time of the incommensurate phase of the defective crystal is exponential. This law agrees qualitatively with the notion of domain wall motion in an inhomogeneous medium containing "random local phase-transition temperature'' type defects. (C) 1999 American Institute of Physics. .
Title:
Shift of the apical oxygen of the CuO6 octahedron and the superconductivity
in Bi1.8Pb0.2Sr2-xCuOy systems
Authors:
Yan HJ. Mao ZQ. Xu GJ. Zhang YH.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(13):8459-8462, 1999 Apr 1.
Abstract:
The Raman scattering, electron diffraction (ED), and resistivity are measured for a nominal composition of Bi1.8Pb0.2Sr2-xCuOy system. It is found that the peaks of A(tg) vibrational modes of the oxygen atom in a SrO layer along the c axis are broadened, the intensity is reduced, and the position of the peak shifts toward low frequency in Raman spectra as Sr content decreases. The reduction of the incommensurate modulation wavelength is observed by ED measurements with the decrease in Sr content. This suggests that the results in Raman spectra and ED are attributed to the shift of the apical oxygen in CuO6 octahedron induced by the decrease of Sr content in Bi1.8Pb0.2Sr2-xCuOy system. The resistivity measurements show that the shift of the apical oxygen not only brings about the disappearance of superconductivity, but also induces a metal-semiconductor transition. .
Title:
Scanning tunneling microscope studies on the atomic
structures in Bi2Sr2CaCu2O8+delta highly doped with Pb
Authors:
Nishiyama M. Ogawa K. Chong I. Hiroi Z. Takano M.
Source:
(list of journals)
Physica C. 314(3-4):299-307, 1999 Mar 20.
Abstract:
Highly doped high-T-c Bi compounds, i.e., Bi2.2-xPbxSr1.8CaCu2O8+delta (x = 0.7) (denoted by Bi(Pb)-2212) were recently found to have dramatically improved critical current J(c) [I. Chong, Z. Hiroi, M. Izumi, J. Shimoyama, Y. Nakayama, K. Kishio, T. Terashima, Y. Bando, and M. Takano, Science 276 (1997) 770; J. Shimoyama, Y. Nakayama, K. Kitazawa, K. Kishio, Z. Hiroi, I. Chong, M. Takano, Physica C 281 (1997) 69]. To elucidate atom structures of the Bi(Pb)-2212, ultrahigh vacuum scanning tunneling microscope (UHV-STM) studies have been performed. We observed, for the first time, defected alpha-phase with fragmented modulation of lambda = 7 nm. Observed defects are amorphous regions of a few nanometer size embedded in the alpha-phase and edge dislocations with Burgers vector (1/2) [110]. Both the defects are suggested potentially to be effective pinning centers in Bi(Pb)-2212. Annealing in vacuum at temperatures up to 630 degrees C for 19 h was found sufficient enough to evaporate all the Pb atoms in the surface layers of Bi(Pb)-2212 and consequently to transform Bi(Pb)-2212 with lambda = 7 nm to pure Bi-2212 with lambda = 2.7 nm. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Spin dynamics in i-R8Mg42Zn50 quasicrystals (R = Gd, Tb, Dy)
Authors:
Charrier B. Cotrell S. Schmitt D.
Source:
(list of journals)
Physica B. 266(3):165-172, 1999 May.
Abstract:
Spin dynamics has been investigated in icosahedral R8Mg42Zn50 quasicrystals (R = Gd, Tb, Dy) by means of muon spin relaxation experiments. Two distinct components are clearly observed, one of them being a fast relaxing signal with a stretched exponential form as in some disordered systems. The corresponding depolarization rate strongly increases when the temperature approaches the ordering temperature T-N defined by neutron diffraction experiments. Crystal held effects seem to be noticeable, especially in the dysprosium compound. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Tiling theory applied to the surface structure of
icosahedral AlPdMn quasicrystals
Authors:
Kramer P. Papadopolos Z. Teuscher H.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(13):2729-2748, 1999 Apr 5.
Abstract:
Surfaces of i-Al-68 Pd-23 Mn-9 as observed in scanning tunnelling microscopy (STM) and low-energy electron diffraction (LEED) experiments show atomic terraces in a Fibonacci spacing. We analyse them in a bulk tiling model due to Elser which incorporates many experimental data. The model has dodecahedral Bergman clusters within an icosahedral tiling T*((2F)) and is projected from the six-dimensional face-centred hypercubic lattice. We derive the occurrence and Fibonacci spacing of atomic planes perpendicular to any fivefold axis, compute the variation of planar atomic densities, and determine the (auto-) correlation functions. Upon interpreting the planes as terraces at the surface, we And quantitative agreement with the STM experiments.
Title:
Band structure and electronic properties of the
incommensurate misfit compound (LaS)(1.18)VS2
Authors:
Cario L. Rouxel J. Meerschaut A. Moelo Y. Corraze B. Chauvet O.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(14):2887-2900, 1999 Apr 12.
Abstract:
The electronic properties of the incommensurate misfit compound (LaS)(1.18)VS2 are investigated by different methods. Linear muffin-tin orbital atomic-sphere approximation bandstructure calculation shows that this material should be a metal with a Fermi level located near a minimum of the density of states. Experimentally, the electrical resistivity is hopping-like while the magnetic susceptibility is metallic-like with a strong enhancement. We suggest that these paradoxical properties can be reconciled by taking into account the effects of incommensurability and electronic correlations. A comparison with commensurate LiVS2 and with Ti or Cr incommensurate misfit derivatives is discussed.
Title:
RGe2-x compounds (R = Y, Gd-Ho) with new ordered ThSi2-defect
structures
Authors:
Venturini G. Ijjaali I. Malaman B.
Source:
(list of journals)
Journal of Alloys & Compounds. 285(1-2):194-203, 1999 Mar 30.
Abstract:
The R-Ge systems (R = Y, Gd-Ho) have been investigated in the composition range 60-65 Ge at.% and the ThSi,-type RGe2-x compounds have been checked by X-ray powder diffraction. Besides the well-known Y3Ge5-type R3Ge5 compounds, 14 new ordered ThSi2-defect derivatives have been characterized. Some structural hypothesis are made and the crystal structures of the Dy11Ge18, Ho14Ge23, Gd(17)Ge(29 )have been refined from powder X-ray diffraction. The evolution in the structural series is discussed and compared with the evolution in the AlB2 defect derivatives. (C) 1999 Elsevier Science S.A. all rights reserved.
Title:
The microstructure analysis of Al-Cu-Cr phases in
Al65Cu20Cr15 quasicrystalline particles Al base composites
Authors:
Qi YH. Zhang ZP. Hei ZK. Dong C.
Source:
(list of journals)
Journal of Alloys & Compounds. 285(1-2):221-228, 1999 Mar 30.
Abstract:
The microstructures of Al65Cu20Cr15 as-cast and as-quenched master alloys and Al-Cu-Cr phases in Al65Cu20Cr15 particles/Al base composites after hot-pressing are investigated by transmission electron microscope and electron probe microanalyser. Two icosahedral quasicrystals SIQC and FIQC, two approximants to icosahedral quasicrystal IIA and FIA, one decagonal quasicrystal DQC, three approximants to decagonal quasicrystal DA1, DA2 and Theta, a new Al-Cu phase xi that have a monoclinic structure with lattice parameter a=1.2 nm, b=0.9 nm, c=0.8 nm, beta=130" and three tau type phases tau(2), tau(4), and tau(7), were found. The composition-structure diagram in the Al-Cu-Cr system was drawn from phases above, in which there are two ela-constant lines: one is the icosahedral quasicrystalline line with e/a=1.86; the other is the decagonal quasicrystalline line with e/a=2.09. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Influence of a magnetic field on the magnetoelasticity of
commensurate spin-density-wave Cr-Ru and Cr-Si alloy single
crystals
Authors:
Dawe AM. Alberts HL. Smit P.
Source:
(list of journals)
Journal of Alloys & Compounds. 285(1-2):L12-L15, 1999 Mar 30.
Abstract:
Previously reported attempts to produce a single-Q commensurate (C) spin-density-wave (SDW) state in a dilute Cr alloy by magnetic held cooling through the Neel temperature (T-N), were unsuccessful. In the present study the influence of a cooling field of 4.5 T on the magnetoelasticity of Cr + 0.3 at.% Ru and Cr + 1.6 at.% Si alloy single crystals, both having CSDW phases below T-N, are reported. The results show that cooling the Cr + 0.3 at.% Ru crystal through T-N in a field of 4.5 T has no influence on the first-order commensurate-incommensurate SDW magnetic phase transition. On the other hand, cooling the Cr + 1.6 at.% Si crystal in a field of 4.5 T through T-N noticeably affects the elasticity in the CSDW state, suggesting a condensation of part of this crystal into a single-Q CSDW phase. (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
Strain affected properties of icosahedral Al-Pd-Mn single ingot
Authors:
Yokoyama Y. Yamada Y. Fukaura K. Sunada H. Note R. Inoue A. Sugiyama K. Hiraga K.
Source:
(list of journals)
Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes &
Review Papers. 38(3A):1495-1499, 1999 Mar.
Abstract:
Some physical properties of the Al-Pd-Mn icosahedral quasicrystal are drastically changed by inhomogeneous strain distribution, as exemplified for the electrical resistivity and the Vickers hardness. In order to reveal the intrinsic properties of the Al-Pd-Mn icosahedral alloy, the study on the relation between the strain and the properties was investigated. By the full anneal treatment (1000 K, 50 h), the anisotropies bf the electrical resistivity and the Vickers hardness are found to annihilate significantly with decreasing anisotropic strain distribution. And the intrinsic properties are estimated by the extrapolation from the relation between the strain and the physical property to the no strain state.
Title:
Crystal chemistry and defect structure of
ekmanite: new data from transmission electron microscopy and Mossbauer
spectroscopy
Authors:
Ferrow EA. Wallenberg LR. Holtstam D.
Source:
(list of journals)
European Journal of Mineralogy. 11(2):299-308, 1999 Mar-Apr.
Abstract:
Ekmanite is a member of the 2:1 type modulated layer silicates such as ganophyllite and bannisterite. Its chemical composition can be represented by K(M-20)(OH)(16) (M = Fe2+, Mg2+ Mn2+) where three of eight Si-tetrahedra are inverted across the interlayer sharing an apical oxygen with similarly inverted tetrahedra from the adjacent layers. The arrangement of the regular, D, and inverted, R, tetrahedra has the configuration 4D2R1D1R4D... along the b-axis. In local regions of possibly high Mg/(Mn+Fe) ratio, this configuration is interrupted by the absence of inverted tetrahedra. Ekmanite typically contains a multitude of defects; twinning and both regular and irregular stacking arrangements are the most common ones. Ekmanite is sensitive to oxidation and an unidentified phase, chemically related to it, is always found lining its grain boundaries. This texture results in intergrown rods defining polygons where the central parts do not contain ekmanite. The Mossbauer spectrum consists of Fe2+ and Fe3+ absorption doublets with the Fe2+ absorption composed of two Gaussian line pairs and the Fe3+ absorption of a single but broad line pair.
Title:
Light-induced modification of 3D photonic band structure
detected by means of photoreflection
Authors:
Kapitonov AM. Kachan SM. Ponyavina AN. Gaponenko SV. Bogomolov VN. Prokofiev AV. Sitarek P. Misiewicz J.
Source:
(list of journals)
Acta Physica Polonica A. 95(3):335-342, 1999 Mar.
Abstract:
Porous synthetic opal possessing a three-dimensional photonic band structure of semimetallic type was impregnated with polycrystalline CdS. The photonic stop band in (111) direction was examined by means of photoreflection technique. Under cw laser excitation of semiconductor inclusions the reflectance of the system changes indicating a modification of photonic band structure. A possible mechanism is discussed. Numerical simulations within the framework of quasicrystalline approximation are given.
Title:
Investigation of a resonance structure in the system of two
K-S mesons in the mass region around 1775 MeV
Authors:
Grygor'ev VK. Baloshin ON. Barkov BP. Batalova NV. Vladimirsky VV. Erofeeva ON. Katinov YV. Korol'kov IY. Luzin VN. Sokolsky VV. Tikhomirov GD. Uzunyan SA. Skurenko YP.
Source:
(list of journals)
Physics of Atomic Nuclei. 62(3):470-478, 1999 Mar.
Abstract:
The system of two K-S mesons has been analyzed in the mass interval 1600-1950 MeV. Relevant events from pi(-)p interactions at 40 GeV were recorded by the 6-m MIS spectrometer developed at the Institute of Theoretical and Experimental Physics (Moscow). The use of a neutral trigger in the experiment being reported made it possible to suppress both charged particles and photons. By using the constraint \t\ > 0.23 GeV2, a maximum of width about 30 MeV was discovered near the KSKS invariant mass of 1775 MeV. An investigation of this maximum revealed that it is likely to be explained by the existence of two narrower states whose widths are commensurate with the spectrometer mass resolution of about 5 MeV. Data on these states, whose masses have been found to be 1768 and 1787 MeV, are compatible with the quantum-number values of J(PC) = 2(++). The product of the cross section and the relevant branching ratio has been estimated at about 1.5 and 2.5 for, respectively, the first and the second state.
Title:
Dynamical diffraction and x-ray standing waves from atomic planes normal to a
twofold symmetry axis of the quasicrystal AlPdMn
Authors:
Jach T. Zhang Y. Colella R. de Boissieu M. Boudard M. Goldman AI. Lograsso TA. Delaney DW. Kycia S.
Source:
(list of journals)
Physical Review Letters. 82(14):2904-2907, 1999 Apr 5.
Abstract:
We have observed dynamical diffraction in the [0240 (2) over bar 4] and [0460 (4) over bar 6] reflections of the icosahedral quasicrystal AlPdMn in the back-reflection geometry (theta(B) = 90 degrees). The x-ray fluorescence From the AI and Pd atoms exhibits strong standing wave behavior, similar to that observed in crystalline materials. The data indicate a long-range order of each species of atoms, with the coherent positions attributable to distributions of the Al and Pd, which we compare to a centrosymmetric model. We observe deviations from the model which imply small departures from inversion symmetry along the twofold symmetry asis and from the expected coherent fractions for Al. .
Title:
Interlayer coupling and superconducting critical temperature of
Bi2Sr1.5La0.5CuO6+delta and Bi2Sr2CaCu2O8+delta:
Incommensurate effects of pressure
Authors:
Yurgens A. Winkler D. Claeson T. Murayama T. Ando Y.
Source:
(list of journals)
Physical Review Letters. 82(15):3148-3151, 1999 Apr 12.
Abstract:
The c-axis interlayer coupling of Bi2Sr1.5La0.5CuO6+delta and Bi2Sr2CaCu2O8+delta single crystals was changed by means of hydrostatic pressure P < 1 GPa resulting in a drastic increase of the c-axis critical current I-c (up to 270% GPa(-1)) and decrease of the normal state resistance R-n (down to -60% GPa(-1)). The superconducting critical temperature only slightly increases with a rate of approximate to 2%-6% GPa(-1). The much stronger effect of pressure on I-c and R-n in Bi2Sr1.5La0.5CuO6+delta implies that the CuO-interlayer coupling has little effect on T-c in this compound.
Title:
The decagonal superstructure Al71Co13Ni16 and its relation
to the basic decagonal phase Al71Co7Ni22
Authors:
Haibach T. Cervellino A. Estermann MA. Steurer W.
Source:
(list of journals)
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical
Properties. 79(4):933-942, 1999 Apr.
Abstract:
Stable Al71Co13Ni16 represents a commensurate quasiperiodic superstructure of decagonal Al71Co7Ni22 .The structure was analysed with a large X-ray diffraction data set. All Bragg peaks observable on an imaging plate detector were recollected on a six-circle diffractometer at the synchrotron source Hasylab. The Bragg peak positions were determined with high accuracy and the resolution in perpendicular space was optimized by collecting all observable reflections including the weak satellite reflections. The five-dimensional Bravais lattice was determined uniquely by a novel Patterson technique. The 'translation' vectors of the 'quasilattice' were separated from the decoration vectors and the proper metric was derived. Consequences of misindexing the diffraction pattern, especially with respect to scaling, are discussed. A comparison of the superstructure metric with its average structure revealed the structural relationships.
Title:
In situ STM study of self-assembled mercaptopropionic acid monolayers for
electrochemical detection of dopamine
Authors:
Giz MJ. Duong B. Tao NJ.
Source:
(list of journals)
Journal of Electroanalytical Chemistry. 465(1):72-79, 1999 Apr 6.
Abstract:
An Au(lll) electrode coated with a self-assembled monolayer of 3-mercaptopropionic acid (MPA) has been investigated by square-wave voltammetry for electrochemical detection of dopamine in the presence of ascorbic acid and characterized by in situ STM. The electrode is found to shift selectively the unwanted oxidation of ascorbic acid to higher potentials while leaving the oxidation of dopamine unchanged. The selectivity is lost below similar to - 0.5 V (Ag \ AgCl \ 3 M KCl) due to a reductive desorption of MPA, and also above similar to 1.2 V where the Au electrode begins to oxidize. STM shows that even a brief oxidation results in large change in the molecular packing structure of the MPA monolayer. Before the oxidation, the MPA molecules in the monolayer pack into several phases. The most dominant phase is an incommensurate p x root 3 structure, while commensurate phases, 5 x root 3, 6 x root 3, 8 x root 3 and 10 x root 3 have also been observed frequently. In some areas, the molecules pack into a superlattice 3 x 4 root 3 that can be attributed to a periodic mixing of two discrete conformations of MPA. After cycling the potential to the oxidation potentials, the ordered structures transform into a less compact disordered structure. The exposed bare Au electrode in the disordered structure is believed to be responsible for the loss of the electrode selectivity. (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
Quasicrystalline and dynamic planforms in nonlinear optics
Authors:
Pismen LM. Rubinstein BY.
Source:
(list of journals)
Chaos Solitons & Fractals. 10(4-5):761-776, 1999 Apr-May.
Abstract:
A variety of stationary and wave patterns that show a complicated spatial structure but are ordered in the Fourier space can be constructed by considering interaction of non-collinear modes near a symmetry breaking bifurcation point. The planform selection is particularly rich in the presence of resonant (phase-dependent) interactions among degenerate modes. We consider the problem of pattern selection for two optical systems: a cavity with two nonlinear elements and a cavity with a rotated optical field. Complex quasicrystalline patterns sustained by resonant interactions arise under conditions when wave and Turing modes are excited simultaneously. The excited patterns may be saturated even by the action of quadratic (three-wave) interactions only, and may exhibit periodic amplitude modulation on a slow time scale. (C) 1999 Elsevier Science Ltd. All rights reserved.
Title:
Toward the crystal structure of nagyagite,
[Pb(Pb,Sb)S-2][(Au,Te)]
Authors:
Effenberger H. Paar WH. Topa D. Culetto FJ. Giester G.
Source:
(list of journals)
American Mineralogist. 84(4):669-676, 1999 Apr.
Abstract:
Synthetic nagyagite was grown from a melt as part of a search for materials with high-temperature superconductivity. Electron microprobe analyses of synthetic nagyagite and of nagyagite from the type locality Nagyag, Transylvania (now Sacarimb, Romania) agree with data from literature. The crystal chemical formula [Pb(Pb,Sb)S-2] [(Au,Te)] was derived from crystal structure investigations. Nagyagite is monoclinic pseudotetragonal. The average crystal structure was determined from both synthetic and natural samples and was refined from the synthetic material to R = 0.045 for 657 single-crystal X-ray data: space group P2(1)/m, a = 4.220(1) Angstrom, b = 4.176(1) Angstrom, c = 15.119(3) Angstrom, beta = 95.42(3)degrees, and Z = 2. Nagyagite features a pronounced layer structure: slices of a two slabs thick SnS-archetype with formula Pb(Pb,Sb)S-2 parallel to (001) have a thickness of 9.15 Angstrom. Te and Au form a planar pseudo-square net that is sandwiched between the SnS-archetype layers; it is assumed that planar (AuTe4)-Te-[4te] configurations are edge connected to chains and that Te atoms are in a zigzag arrangement. Ordering within the SnS-archetype and gold-tellurium layers, intense twinning and/or stacking variants are responsible for the often observed superstructure reflections. For buckhornite, [(Pb2Bi)(Sigma 3)S-3] [(AuTe2)(Sigma 3)] a structure model is proposed considering a homologous series with nagyagite, [(Pb-3(Pb,Sb)(3))(Sigma 6)S-6][(Au,Te)(3)].
Title:
A moving screw dislocation in a one-dimensional hexagonal
quasicrystal
Authors:
Fan TY. Li XF. Sun YF.
Source:
(list of journals)
Acta Physica Sinica-Overseas Edition. 8(4):288-295, 1999 Apr.
Abstract:
This paper extends a moving screw dislocation theory in a conventional crystal to a one-dimensional hexagonal quasicrystal in the framework of the Landau theory. By introducing two functions phi and psi which satisfy wave equations, respectively, a general solution is suggested in terms of phi and psi. The analytical expressions for displacement and stress fields induced by a moving screw dislocation as well as the energy are found. The results obtained here when imposing the condition that the phason fields is absent reduce to those for a moving screw dislocation in a crystal.
Title:
Friction between single-grain Al70Pd21Mn9 quasicrystal
surfaces
Authors:
Ko JS. Gellman AJ. Lograsso TA. Jenks CJ. Thiel PA.
Source:
(list of journals)
Surface Science. 423(2-3):243-255, 1999 Mar 10.
Abstract:
An UHV tribometer was used to make measurements of friction between the five-fold surfaces of two single-grain Al70Pd21Mn9 quasicrystals. The surfaces of these quasicrystal samples were either truly clean or modified by controlled adsorption of desired species. The results of many (similar to 200) single-pass friction measurements using clean quasicrystal surfaces indicate that the average static friction coefficient is mu(s) = 0.60 +/- 0.08. The friction coefficient of the perfectly clean quasicrystal surfaces is lower than those reported for the perfectly clean surfaces of many pure metals but is higher than those measured on quasicrystal surfaces exposed to air. Under shear the quasicrystal surfaces slide over one another without exhibiting stick-slip behavior or adhesion. This behavior differs from clean metal surfaces that often exhibit adhesion after being brought into contact in ultra-high vacuum. Studies were performed to determine the effects of surface oxidation, surface structure and surface composition on quasicrystal friction. During the early stages of oxidation the static friction coefficient decreased to a limit of mu(s) = 0.35 +/- 0.05. More subtle changes to the quasicrystal surfaces such as adsorption of sulfur or formation of a thin Al-Pd-Mn alloy of CsCl structure produced no significant changes in the static friction coefficient. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Magnetic phases in quasi-binary (Fe1-xCox)Ge-2 intermetallic compounds
Authors:
Men'shikov AZ. Dorofeev YA. Teplykh AE.
Source:
(list of journals)
Physics of the Solid State. 41(2):253-258, 1999 Feb.
Abstract:
Magnetic neutron diffractometry revealed the existence in (Fe1-xCox)Ge-2 solid solutions (x<0.5) with C16 structure of only two magnetic phases, namely, low-temperature (AFI) and high-temperature (AFII). A third magnetic phase, AFIII, suggested by earlier magnetic measurements, has not been found. The AFI and AFII phases have a commensurate and an incommensurate antiferromagnetic structure with the wave vectors k(0) = 2 pi/a (1,0,0) and k = k(0) + delta k, respectively. The regions of their existence are shown in the magnetic phase diagram. Neutron diffraction measurements yielded the concentration dependence of the average magnetic moment per atom in the antiferromagnetic sublattice of a 3d metal, which, similarly to the dependence of the Neel point on x, was found to be nonlinear. An analysis of these dependences suggests that substitution of cobalt for iron is accompanied, on the one hand, by a decrease of the local spin density on the iron atoms in the nearest environment of a cobalt atom and, on the other hand, by an increase of the effective exchange integral between the nearest-neighbor iron atoms located along the tetragonal axis. (C) 1999 American Institute of Physics. .
Title:
Quasicontinuous mechanism of the
quasicrystal-to-crystal phase transition
Authors:
Rochal SB.
Source:
(list of journals)
Physics Letters A. 253(5-6):327-332, 1999 Mar 29.
Title:
Anisotropic thermal transport of 2D quasicrystals of
decagonal Al-Ni-Co system
Authors:
Matsukawa M. Yoshizawa M. Noto K. Yokoyama Y. Inoue A.
Source:
(list of journals)
Physica B. 263:146-148, 1999 Mar.
Abstract:
The anisotropic thermal conductivity of 2D quasicrystals of the decagonal Al-Ni-Co system has been measured over a wide range of temperature. The thermal conductivity value along the periodic axis shows the nearly same behavior as the dirty alloy system. The quasiperiodic thermal conductivity exhibits a typical plateau dependence similar to that of the disordered system. The anisotropic behavior of the measured thermal conductivity is discussed on the basis of phonon relaxation time approximation. The main contributions of phonon scattering processes in the periodic and quasiperiodic directions are phonon-electron interaction and point-defect-like scattering effect arising from Penrose tiling, respectively. A small increase above the plateau region in the quasiperiodic transport indicates hopping conduction of localized vibration modes assisted by phonons such as fracton excitations in the disordered system. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Linear analysis of pattern formation in nematics in oblique magnetic fields
Authors:
Casquilho JP.
Source:
(list of journals)
Liquid Crystals. 26(4):517-524, 1999 Apr.
Abstract:
The dynamics of nematic director field reorientation in non-Freedericksz geometries, after a magnetic field H is applied at an oblique angle relatively to the initial homogeneous director n(0) (H not normal to n(0)), is studied considering a magnetic reorientation driven by hydrodynamic instabilities (with backflow). This study is carried out for bounded samples between two parallel plates with planar boundary conditions and with rigid anchoring. Linear stability and wave vector selection analysis predict that, when the angle of the magnetic to the initial director field is increased, for a given magnetic field intensity, two transitions from a homogeneous to a transient distorted director field reorientation can occur: a transition at a first critical angle to an aperiodic distorted director field and a transition at a second critical angle to a periodic distorted director field. It is shown that the periodic mode is cut off at a higher reduced field when the magnetic field acts away from the normal direction.
Title:
Influence of the molecular length on the occurrence of
incommensurate low ordered smectic phases for non-symmetric
dimesogenic compounds
Authors:
Hardouin F. Achard MF. Laguerre M. Jin JI. Ko DH.
Source:
(list of journals)
Liquid Crystals. 26(4):589-599, 1999 Apr.
Abstract:
Systematic physical chemistry studies are in progress concerning the occurrence of incommensurate low ordered smectic phases (S-ic)dagger in non-symmetric dimesogens with molecular parameters varying from those of the standard compound KI-5(4). In the present study, the selected molecules possess the same cholesteryl unit and the same spacer length, but the terminal chain of the aromatic mesogenic part is varied. Up to a critical molecular length, a competition between two incommensurate lengths is observed and the dimesogenic compounds respond to the frustration connected to this competition with the formation either of an incommensurate phase S-ic or of a two dimensional modulated phase. For longer dimesogens, a commensurate lock-in of the two characteristic lengths systematically occurs.
Title:
Recurrence times in quasi-periodic motion: Statistical properties, role of
cell size, parameter dependence
Authors:
Theunissen M. Nicolis C. Nicolis G.
Source:
(list of journals)
Journal of Statistical Physics. 94(3-4):437-467, 1999 Feb.
Abstract:
We investigate the probabilistic properties of recurrence times for the simplest form of aperiodic deterministic dynamics, quasi-periodic motion. Previous results using number theory techniques predict two fundamental recurrence times for uniform quasi-periodic motion on a two-dimensional torus, while no analogous analytic result seems to exist for higher dimensional tori. The two-dimensional uniform case is reanalyzed From a more geometric point of view and new, workable expressions are derived that enable us Fully to understand and predict the recurrence phenomenon and to analyze its parameter dependence. Emphasis is placed on the statistical properties and, in particular, on the variability of recurrence times around their mean, in relation to local Farey tree structure. Higher-dimensional tori are considered, and seen to also display a high variability in their finite-time recurrence behavior. The results are finally extended to the non-uniform quasi-periodic case.
Title:
Magnetic susceptibility and characteristic features of the electronic
structure of quasicrystalline alloys
Authors:
Prekul AF. Kuz'min NY. Shchegolikhina NI.
Source:
(list of journals)
JETP Letters. 69(3):221-226, 1999 Feb 10.
Abstract:
Experiments are performed to determine the magnetic susceptibility of the icosahedral phase itself in the alloy Al62Cu25.5Fe12.5 in the temperature range 3.9- 1100 K. A new regularity is observed - the curves of the temperature dependences of the susceptibility and electrical conductivity are congruent. (C) 1999 American Institute of Physics.
Title:
Anisotropic diamagnetic susceptibility of AlNiCo
quasi-crystal
Authors:
Yamada Y. Yokoyama Y. Matono K. Fukaura K. Sunada H.
Source:
(list of journals)
Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes &
Review Papers. 38(1A):52-55, 1999 Jan.
Abstract:
We have carried out magnetization measurements of a single decagonal Al72Ni12CO16 quasi-crystal for the cases of the magnetic field parallel and perpendicular to the periodic axis with a torsion-type magnetic balance in various magnetic fields up to 10 kOe from 4.2 K to room temperature. Anisotropic diamagnetic susceptibility was observed, which is closely correlated to the electron motions in the quasi-crystal.
Title:
Electronic structure of quasi-one dimensional models
Authors:
Wang HY.
Source:
(list of journals)
Communications in Theoretical Physics. 31(1):65-72, 1999 Jan 30.
Abstract:
Ladder models are studied as quasi-one dimensional tight binding systems. A set of iteration formula is derived for calculating local densities of states for various ladders including periodic, quasiperiodic and disordered ones. Band structures are analyzed.
Title:
Transverse elastic waves in Fibonacci superlattices
Authors:
Zarate JE. Fernandez-Alvarez L. Velasco VR.
Source:
(list of journals)
Superlattices & Microstructures. 25(3):519-526, 1999 Mar.
Abstract:
We study the transverse elastic waves propagating in 6-mm class hexagonal crystals forming Fibonacci superlattices. These are formed by repetitions of CdS and ZnO slabs in A and B constituent blocks following the Fibonacci sequence. We study the periodic superlattices formed by the infinite repetition of a given Fibonacci generation together with the finite Fibonacci generations having stress-free surfaces, in order to compare the effects introduced by the different boundary conditions. We have also considered the effects of piezoelectricity when all the interfaces are metallized and kept at a fixed potential. We use the surface Green function matching method for N nonequivalent interfaces to obtain the dispersion relations and the density of states of these systems. We have studied the influence of the increasing order of the Fibonacci generations on the dispersion relation of the transverse elastic modes. The Fibonacci spectrum is clearly seen even for low-order Fibonacci generations and is almost not modified by the piezoelectric coupling when the interfaces are metallized. (C) 1999 Academic Press.
Title:
Positron-annihilation studies of stable Al-based icosahedral
quasicrystals
Authors:
Sato K. Takahashi Y. Uchiyama H. Kanazawa I. Tamura R. Kimura K. Komori F. Suzuki R. Ohdaira T. Takeuchi S.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(10):6712-6716, 1999 Mar 1.
Abstract:
The positron-annihilation lifetime spectra in the Al-Pd-Re alloy system, the positron-annihilation Doppler-broadening spectra by slow variable monoenergetic positron beam in Al70.7Pd21.34Re7.96 and Al71.5Pd20.3Mn8.2 alloys, and positron-annihilation lifetime spectra by slow positron beam in Al71.5Pd20.3Mn8.2 were measured. These measurements indicate that every sample contains a dense distribution of structural vacancy-type sites. This result is consistent with our previous expectation of the relationship between the presence of vacant centers in clusters and the stability of icosahedral quasicrystals. Furthermore, the structural vacancy densities in icosahedral quasicrystals of Al70.7Pd21.34Re7.96 and Al71.5Pd20.3Mn8.2 have been estimated to be 7.7x10(20) and 5.0x10(20) cm(-3), respectively. .
Title:
Spin-Peierls order parameter and antiferromagnetism in the dimerized and
incommensurate phases of Zn-doped CuGeO3
Authors:
Buchner B. Lorenz T. Walter R. Kierspel H. Revcolevschi A. Dhalenne G.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(10):6886-6907, 1999 Mar 1.
Abstract:
Measurements of the thermal-expansion coefficient, the magnetostriction, and the specific heat of Zn-doped CuGeO3 single crystals (x less than or equal to 3.3%) in magnetic fields up to 16 T are presented. Measuring the lattice constant as a function of temperature, magnetic field, and doping concentration allows us to determine the concentration and field dependence of the averaged spin-Peierls order parameter. A strong reduction upon doping is observed and interpreted in terms of solitonlike defects of the dimerization. From these data the relationship between the averaged spin-Peierls order parameter in doped CuGeO3 and the transition temperature T-SP is extracted. The specific heat at low temperatures is dominated by doping induced low-energy excitations. The temperature and field dependence of the corresponding contribution to the specific heat is discussed in a model with random magnetic exchange constants. Studying the thermodynamic properties as a function of an external field, we determine the magnetic field vs temperature phase diagrams of Cu1-xZnxGeO3. Several systematic changes upon doping are revealed. In particular, we find a strong enhancement of disorder in doped CuGeO3, when entering the incommensurate phase with increasing field which we attribute to an additional randomness of the order-parameter phase. Moreover, this field-induced phase transition between dimerized and incommensurate phases is accompanied by a pronounced increase of the antiferromagnetic ordering temperature T-N. A phenomenological description assuming a coupling between the spin-Peierls and the antiferromagnetic order parameters is presented, which allows us to interpret simultaneously both field and concentration dependences of TN .
Title:
Influence of nearest-neighbor Coulomb interactions on the phase diagram of
the ferromagnetic Kondo model
Authors:
Malvezzi AL. Yunoki S. Dagotto E.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(10):7033-7042, 1999 Mar 1.
Abstract:
The influence of a nearest-neighbor Coulomb repulsion of strength V on the properties of the ferromagnetic Kondo model is analyzed using computational techniques. The Hamiltonian studied here is defined on a chain using localized S=1/2 spins, and one orbital per site. Special emphasis is given to the influence of the Coulomb repulsion on the regions of phase separation recently discovered in this family of models, as well as on the double-exchange-induced ferromagnetic ground state. When phase separation dominates at V = 0, the Coulomb interaction breaks the large domains of the two competing phases into small "islands" of one phase embedded into the other. This is in agreement with several experimental results, as discussed in the text. Vestiges of the original phase separation regime are found in the spin structure factor as incommensurate peaks, even at large values of V. In the ferromagnetic regime close to density n = 0.5, the Coulomb interaction induces tendencies to charge ordering without altering the fully polarized character of the state. This regime of "charge-ordered ferromagnetism" may be related with experimental observations of a similar phase by Chen and Cheong [Phys. Rev. Lett. 76, 4042 (1996)]. Our results reinforce the recently introduced notion [see, e.g., S. Yunoki et al., Phys. Rev. Lett. 80, 845 (1998)] that in realistic models for manganites analyzed with unbiased many-body techniques, the ground state properties arise from a competition between ferromagnetism and phase-separation-charge-ordering tendencies. .
Title:
Commensurately modulated
structure of 4H(b)-TaSe2 determined by x-ray
crystal-structure refinement
Authors:
Ludecke J. van Smaalen S. Spijkerman A. de Boer JL. Wiegers GA.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(9):6063-6071, 1999 Mar 1.
Abstract:
The (root 13ax root 13axc) superstructure of 4H(b)-TaSe2 at room temperature has been determined by x-ray crystal-structure refinement using (3+2)-dimensional superspace. The resulting modulation has its largest amplitudes for a longitudinal displacement of the Ta atoms in the octahedrally coordinated (T) layers, thus leading to a superstructure of hexagram-shaped clusters containing thirteen Ta atoms each. The atoms in the corresponding planes of Se atoms show a transversal modulation, which can be interpreted as the relaxation of these layers to the modulation of the Ta layers. Forming a similar pattern, modulations were found of the atoms in the layers with Ta in trigonal prismatic coordination (H layers), with amplitudes of about 1/10 of the sizes of the modulations in the T layers. These results confirm the presence of a charge-density wave in the T layers, while the modulations of the H layer can be assigned to elastic coupling between the two types of layers. The observation of nonzero displacements of the atoms of the H layers provides an interpretation for recent observations by scanning tunneling microscope (STM): the superstructure features observed by STM on the H layers is a direct consequence of the atomic displacements in this layer. .
Title:
A straight dislocation in one-dimensional hexagonal
quasicrystals
Authors:
Li XF. Fan TY.
Source:
(list of journals)
Physica Status Solidi B-Basic Research. 212(1):19-26, 1999 Mar.
Abstract:
The elastic field induced by a straight dislocation in a one-dimensional hexagonal quasicrystal with its line parallel to the quasiperiodic axis is obtained by superposition of the elastic fields of a pure edge part and a pure screw part. By extending the Peach-Koehler force to quasicrystals, the force between two parallel screw dislocations is given. For a screw dislocation in this quasicrystal of general cross-section, the elastic field and the image force on the dislocation are given via the conformal mapping method.
Title:
New mu SR results on the magnetic structure of CeAl2
Authors:
Schenck A. Andreica D. Pinkpank M. Gygax FN. Ott HR. Amato A. Heffner RH. MacLaughlin DE. Nieuwenhuys GJ.
Source:
(list of journals)
Physica B. 261:14-15, 1999 Jan.
Abstract:
Zero field mu SR measurements on a high-quality single crystal of CeAl2 provides, in contrast to earlier mu SR studies, evidence for a single-k incommensurate, sinusoidally modulated AFM-phase below 3.8 K in qualitative agreement with neutron results. Below 1 K we find a drastic change in the mu SR signal which may indicate a further change in the magnetically ordered phase, however, preserving its incommensurately modulated structure, (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Magnetic structure of the antiferromagnetic Kondo stannide
Ce2Ni2Sn
Authors:
Laffargue D. Bouree F. Chevalier B. Etourneau J. Roisnel T.
Source:
(list of journals)
Physica B. 261:46-47, 1999 Jan.
Abstract:
Magnetization and electrical resistivity measurements on the Ce2Ni2Sn ternary stannide suggest the occurrence of antiferromagnetic ordering below TN = 4.7 K. Neutron powder diffraction (NPD) shows that Ce2Ni2Sn is magnetically ordered at T = 1.5 K: magnetic Bragg peaks can then be indexed with a commensurate wave vector, k = (0 0 1/2), and the Ce,Ni,Sn magnetic structure described as a collinear arrangement of Ce-moments. Two components of the Ce-magnetic moment M only are obtained from NPD, which are respectively parallel (M) and perpendicular (Mperpendicular to) to k (Mperpendicular to = 0.335(10) muB) The value of the resulting magnetic moment M is a function of the orientation of Mperpendicular to within (a, b) plane and lies in the interval 0.41(5) less than or equal to M less than or equal to 0.53(5)muB/Ce3+, far below gjJ = 2.14 muB/Ce3+. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Title:
Magnetic structures of UNiAl in magnetic fields
Authors:
Prokes K. Bourdarot F. Burlet P. Olsovec M. Sechovsky V. Javorsky P. Bruck E. Goukassov A. de Boer FR. Menovsky AA.
Source:
(list of journals)
Physica B. 261:246-247, 1999 Jan.
Abstract:
UNiAl orders antiferromagnetically (AF) below T-N = 19.3 K with a propagation vector q = (0.1, 0.1, 0.5). U moments oriented along the c-axis of the hexagonal structure are modulated sinusoidally within the basal plane with an amplitude of 1.24 mu(B)/U. The magnetic structure consists of three U moments (U-1, U-2, U-3) coupled ferromagnetically within the basal plane. U-1 and U-2 are substantially larger than II, and invariant with held, whereas U-3 becomes enhanced in a held along c. The vector q remains intact in fields lower than the critical metamagnetic field (B-c = 11.4 T at 1.5 K). Above B-c, UNiAl orders ferromagnetically with equal Umoments of 0.91 mu(B) in 11.8 T at 1.7 K. When decreasing field below B-c, the original propagation vector is lost and a new AF structure with q ' = (0.17, 0.03, 0.5) is established. The original q is recovered only by warming far above T-N and subsequent zero-field cooling. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Correlations between crystallographic and physical
properties in (Bi,Pb)(2)Sr-2(Ca,Y)Cu2O8+Delta superconductors
Authors:
Manifacier L. Collin G. Blanchard N.
Source:
(list of journals)
Physica B. 261:562-563, 1999 Jan.
Abstract:
Efforts were made to synthesize pure and single-phased samples of the (Bi, Pb)(2)Sr-2(Ca, Y)Cu2O8 (+ j) system. Systematic X-ray incommensurate Rietveld refinements along with AC susceptibility measurements wen performed. The basic yttrium substitution reveals strong internal structural changes on the modulation parameters. In the mean time, diamagnetic shielding in the samples vanishes before T-c, does, suggesting a 3D-2D crossover. It is proposed that Y3+ creates correlated domains in the CuO2 planes and localizes charges, thus diminishing the diamagnetic screening. Such a localization could be accompanied by the heavy structural changes observed. Adding lead in the structure would then restore the mobility of the charges. Indeed, without affecting T-c, (i.e. without affecting the carrier concentration), Pb substitution enhances diamagnetic shielding and even restores superconductivity in the otherwise insulating Bi2Sr2(Ca-0.4,Y-0.6)Cu2O8 (+ Delta) sample. We then conclude that carrier concentration is very little affected by cationic substitution (small T-c, variations) and that Y and Pb rather affect the mobility of the charges, destroying and restoring 3D correlations, respectively. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Rare earth magnetic order in RNi2B2C and RNiBC
Authors:
Skanthakumar S. Lynn JW.
Source:
(list of journals)
Physica B. 261:576-581, 1999 Jan.
Abstract:
A review of neutron diffraction experiments on the magnetic order in the RNi2B2C and RNiBC (R - rare earth) systems is given. The RNi2B2C materials exhibit a R-ide variety of commensurate and incommensurate magnetic structures for different rare earths, along with superconductivity that is coupled to the magnetism. Simple commensurate antiferromagnetic structures are observed for R = Pr (T-N = 4.0 K), Nd (T-N = 4.8 K), Ho (T-N = 8.5 K) and Dy (T-N = 11 K). In addition, HoNi2B2C exhibits a c-axis spiral and an a-axis modulated incommensurate structure above 5 K, while both structures collapse in favor of the commensurate structure at low T. A transversely polarized spin density wave (SDW) type incommensurate structure is observed for Er (T-N = 6.8 K) and Tm (T-N = 1.5 K), while a longitudinally polarized SDW structure is observed for Tb (T-N = 15 K) No magnetic ordering of any type is detected for Y, Ce and Yb. HoNiBC is an antiferromagnet (T-N = 9.8 K), ErNiBC is ferromagnetic (T-C = 4.6 K), while TbNiBC and DyNiBC exhibit both ferromagnetic and antiferromagnetic ordering at 17 K and similar to 12 K, respectively. Published by Elsevier Science B.V. All rights reserved.
Title:
Permutation representations defined by G-clusters with application to
quasicrystals
Authors:
Cotfas N.
Source:
(list of journals)
Letters in Mathematical Physics. 47(2):111-123, 1999 Jan.
Abstract:
Starting from each finite union of orbits (called G-cluster) of an R-irreducible orthogonal representation of a finite group G, we define a representation of G in a higher-dimensional space (called permutation representation), and we prove that it can be decomposed into an orthogonal sum of two representations such that one of them is equivalent to the initial representation. This decomposition allows us to use the strip projection method and to obtain some patterns useful in quasicrystal physics. We show that certain self-similarities of such a pattern can be obtained by using the decomposition into R-irreducible components of the corresponding permutation representation, and we present two examples.
Title:
Laser cladding of aluminium-base quasicrystalline alloys
Authors:
Audebert F. Colaco R. Vilar R. Sirkin H.
Source:
(list of journals)
Scripta Materialia. 40(5):551-557, 1999 Feb 5.
Title:
Structure and mechanical properties of (Mo, Re)Si-2 alloys
Authors:
Mitchell TE. Misra A.
Source:
(list of journals)
Materials Science & Engineering A-Structural Materials Properties
Microstructure & Processing. 261(1-2):106-112, 1999 Mar 15.
Abstract:
Hot hardness tests have been performed on are-melted (Mo, Re)Si-2 alloys at temperatures from ambient to 1300 degrees C. Re is found to be a potent solution hardening addition to MoSi2 over the entire temperature range, much more than would be expected from their atomic size mismatch or modulus mismatch. In addition ReSi2-x has about twice the hardness of pure MoSi2 at all temperatures. This may be related to the structure of ReSi2-x which nominally has the same tetragonal C11(b) structure as MoSi2 but is Si-deficient (x = 0.25, i.e. the composition is Re4Si7). The Si deficiency is accompanied by some unusual incommensurate periodicities in the structure which themselves give rise to orthorhombic and monoclinic distortions. The resulting microstructure probably explains the high strength of Re4Si7 and the potent hardening effect of Re in MoSi2 may be due to the accompanying Si vacancies. (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
Designing banana-shaped liquid crystals without Schiff's
base units: m-terphenyls, 2,6-diphenylpyridines and V-shaped tolane
derivatives
Authors:
Shen D. Diele S. Pelzl G. Wirth I. Tschierske C.
Source:
(list of journals)
Journal of Materials Chemistry. 9(3):661-672, 1999 Mar.
Abstract:
This paper reports attempts to obtain (anti)ferroelectric switchable achiral banana-shaped molecules without Schiff's base units. For this purpose we have synthesized novel V-shaped molecules consisting of rigid angular central units [1,3-disubstituted benzene, 2,7-disubstituted naphthalene, 1,3-diphenylbenzene, 2,6-diphenylnitrobenzene, 2,6-diphenylpyridine, 1,3-bis(phenylethynyl)benzene, 1-phenyl-3-(phenylethynyl)benzene] connected via ester linkages to two rigid cores (1,4-disubstituted benzenes, biphenyls, 2-phenylpyrimidines, phenylbenzoates). Most compounds have rather high melting points. Only molecules with seven aromatic rings show liquid crystalline properties. Two-dimensional modulated smectic phases (rectangular columnar phases) were found for molecules with phenylbenzoate rigid units. Intercalated fluid smectic phases were detected for the corresponding 2-phenylpyrimidine derivatives. For the first time in the case of banana-shaped molecules a nematic phase was observed for a 2'-nitro-m-terphenyl-4,4 "-diyl bisbenzoate. However, none of the synthesized compounds exhibit the typical texture of the (anti) ferroelectric switchable mesophases, known from the Schiff's base derivatives.
Title:
Unified structure in Quaternary climate
Authors:
Gauthier JH.
Source:
(list of journals)
Geophysical Research Letters. 26(6):763-766, 1999 Mar 15.
Abstract:
The Quaternary climate record exhibits a structure of superimposed, aperiodic oscillations starting at the 11-yr sunspot cycle and spaced by powers of 2 in period through the major 90,000-yr glacial cycle. Climate cycles that do not fall in this structure typically correspond to harmonics of the structure oscillations. The inclusion of the known solar cycles and the presence of increased abundances of cosmogenic radionuclides at many structure periods suggest that the structure is related to long-period solar variability.
Title:
Interfaces in the XY model and conformal invariance
Authors:
Zhang DG. Chen ZJ. Li BZ.
Source:
(list of journals)
Chinese Physics Letters. 16(1):44-46, 1999.
Abstract:
The one-dimensional XY model with n arbitrarily placed interfaces is investigated. The energy spectrum is shown to have a tower structure only for a commensurate configuration of the critical parameters. The interfacial critical exponents in such cases are determined from conformal invariance theory. The underlying algebra generating the conformal spectrum is the shifted SO(4c) Kac-Moody algebra, the central charge is 2c, which is exactly two times of that in the Ising model with the same structure of interfaces.
Title:
Barium hollandite-type compounds BaxFe2xTi8-2xO16 with x = 1.143 and 1.333
Authors:
Loezos JM. Vanderah TA. Drews AR.
Source:
(list of journals)
Powder Diffraction. 14(1):31-35, 1999 Mar.
Abstract:
Experimental X-ray powder diffraction patterns and refined unit cell parameters for two barium hollandite-type compounds, BaxFe2xTi8-2xO16, with x=1.143 and 1.333, are reported here. Compared to the tetragonal parent structure, both compounds exhibit monoclinic distortions that increase with Ba content [Ba1.333Fe2.666Ti5.334O16: a=10.2328(8), b=2.9777(4), c=9.899(1) Angstrom, beta=91.04(1)degrees, V=301.58(5) Angstrom(3), Z=1, rho(calc)= 4.64 g/cc; Ba1.143Fe2.286Ti5.714O16: a=10.1066(6), b=2.9690(3), c=10.064(2) Angstrom, beta=90.077(6)degrees, V=301.98(4) Angstrom(3), 1=i, rho(calc)=4.48 g/cc]. The X-ray powder patterns for both phases contain a number of broad, weak superlattice peaks attributed to ordering of the Ba2+ ions within the tunnels of the hollandite framework structure. According to the criteria developed by Cheary and Squadrito [Acta Crystallogr. B 45, 205 (1989)], the observed positions of the (0k1)/(1k0) superlattice peaks are consistent with the nominal x-values of both compounds, and the k values calculated from the corresponding d-spacings suggest that the Ba ordering within the tunnels is commensurate for x = 1.333 and incommensurate for x = 1.143. High-temperature X-ray diffraction data indicate that the 1.333 compound undergoes a monoclinic-->tetragonal phase transition between 310 and 360 degrees C. (C) 1999 International Centre for Diffraction Data. .
Title:
Wolf prize honours quasicrystal pioneer
Authors:
Janot C.
Source:
(list of journals)
Physics World. 12(3):45, 1999 Mar.
Title:
On the growth of decagonal Al-Ni-Co quasicrystals from the
ternary melt
Authors:
Fisher IR. Kramer MJ. Islam Z. Ross AR. Kracher A. Wiener T. Sailer MJ. Goldman AI. Canfield PC.
Source:
(list of journals)
Philosophical Magazine B-Physics of Condensed Matter Structural Electronic
Optical & Magnetic Properties. 79(3):425-434, 1999 Mar.
Abstract:
High-quality, single-grain samples of decagonal Al-Ni-Co quasicrystals with volumes of up to 0.8 cm(3) and an approximate composition of Al72Ni11Co17 have been grown from the ternary melt. The precise growth methods and conditions are discussed in detail. X-ray diffraction patterns of crushed single grains and of single-grain samples are exceptionally sharp indicating a high degree of structural order with no evidence of second phases. Transmission electron micrographs also reveal sharp diffraction patterns in the even it layers but diffuse scattering in the odd n layers, indicative of a structure intermediate between the Al73Co27 and Al69Ni31 end members. The electrical resistivity measured directly from cut bars for currents flowing perpendicular to the crystalline direction (i.e. perpendicular to the c axis) is non-metallic, with a broad maximum around 180 K, and a value of approximately 310 mu Omega cm at 300 K. The resistivity for currents flowing parallel to the c axis is metallic and is almost an order of magnitude smaller in value than for i perpendicular to c.
Title:
Chemical-twinning mode of the B2 structure in relation to
Al-Cu approximants
Authors:
Dong C. Zhang QH. Wang D. Wang YM.
Source:
(list of journals)
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical
Properties. 79(3):501-510, 1999 Mar.
Abstract:
Complex structures can be regarded as bring derived from a few basic structures via the local twinning at the atomic level. Although quasicrystals and approximants are believed to be the B2 derivatives, the related B2 twinning mode is not known. This paper addresses this problem by analysing the twinning property of Al-Cu approximants in an Al3Cu4 sample. Such an analysis leads to the recognition of the B2 chemical-twinning mode as 180 degrees/[111]B-2, which is responsible for the pentagonal atomic configuration in the Al-Cu approximants as well as for the pseudofivefold B2 twinning observed on quasicrystal surfaces.
Title:
Determination of the tiling type and phason strain analysis of decagonal
quasicrystals in Al-Ni-Co alloys
Authors:
Hory R. Pohla C. Ryder PL.
Source:
(list of journals)
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical
Properties. 79(3):549-560, 1999 Mar.
Abstract:
From high-resolution electron micrographs of the decagonal phases of the Al72.5Co11Ni16.5 and Al70Co15Ni15 alloys, tilings are produced by connecting prominent structural features. Indexing the tiling vertices as the projection of a five-dimensional periodic lattice and investigation of the distribution of the vertices in orthogonal space gives information about the tiling model and possible phason strains. The technique also reveals domain boundaries which separate regions differing only in the amounts of linear phason strain.
Title:
Bond-valence analysis of the structure of
(Ba0.875Sr0.125)RuO3
Authors:
Santoro A. Sora IN. Huang Q.
Source:
(list of journals)
Journal of Solid State Chemistry. 143(1):69-73, 1999 Feb 15.
Abstract:
The structure of TRuO3(T = Ba0.875Sr0.125) has been analyzed using the bond valence procedures developed by Brown [e.g., Acta Crystallogr, Sect, B 48, 553 (1992)] and O'Keeffe [Structure and Bonding 71, 161 (1989)], The experimental results, which show "overbonded" and "underbonded" T and Ru cations, respectively, are explained by the fact that the theoretical T-O and Ru-O distances that completely satisfy the valence requirements of the atoms are incommensurate under the constraints imposed by the site symmetries of the special positions occupied by the atoms. Starting from a model derived from sphere packing geometry and the theoretical bond lengths, it is possible to evaluate the lattice parameters and the atomic shifts that minimize the strains introduced into the structure by the incommensurability of the theoretical Ru-O and T-O distances, and to arrive at a model quite close to the experimental results without making use of any prior knowledge of the structure. According to this analysis, therefore, the observed structure is interpreted as resulting from a compromise between the different bond distance requirements of the Ru and T cations.
Title:
Modulated structures in oxidized cerium
niobates
Authors:
Thompson JG. Withers RL. Brink FJ.
Source:
(list of journals)
Journal of Solid State Chemistry. 143(1):122-131, 1999 Feb 15.
Abstract:
Three previously reported oxidized cerium niobate phases CeNbO4+x (x = 0.08, 0.25, and 0.33) have been synthesized and characterized by X-ray powder and electron diffraction. All three phases display structures which are modulated variants of a parent fergusonite-type (CeNbO4)-Nb-III structure (I2/a, a = 5.5342 (2) Angstrom b = 11.4016(6) Angstrom, c = 5.1583 (3) Angstrom, beta = 94.600(5)degrees). The x = 0.08 phase with parent unit cell (I2/a, a = 5.3029(8) Angstrom, b = 11.483(2) Angstrom, c = 5.2515(8) Angstrom, beta = 91.32(2)degrees) is a two-dimensional, incommensurately modulated phase characterized by incommensurate primary modulation wavevectors q(1) similar to [0.345, 0, 0.1381](p)* and q(2) similar to [-0.069, 0, 0.172](p)* (p for parent). The x = 0.25 phase with parent unit cell (I2/a, a = 5.3522(8) Angstrom, b = 11.374(3) Angstrom, c = 5.116(1) Angstrom, beta = 93.34(2)degrees) is a commensurately modulated superstructure phase characterized by the reciprocal space unit cell a(r)* = 1/12[402](p)*, b(r)* = 1/4[020](p)*, and c(r)* = 1/3[(1) over bar 01](p)* (r for resultant). The x = 0.33 phase with parent unit cell (I1, a = 5.4374(8) Angstrom, b = 11.189(2) Angstrom, c = 5.1458(8) Angstrom, alpha = 90.56(1), beta = 94.37(1), gamma = 88.19(1)degrees) is again commensurately modulated with q = 1/3[101](p)*. The close structural relationship between the three oxidized phases and possible interstitial oxygen sites in the (CeNbO4)-Nb-III structure are discussed. (C) 1999 Academic Press.
Title:
Waves in a time-dependent magnetized electron-positron plasma
Authors:
Rowe ET.
Source:
(list of journals)
Journal of Plasma Physics. 61(Part 1):135-150, 1999 Jan.
Abstract:
Waves in a magnetized electron-positron plasma, supporting a large-amplitude electric field E-0 of superluminal phase speed, are considered. The case of perturbations with the same phase speed as the large-amplitude wave can he treated exactly, and we restrict our attention to tills case, obtaining analytical results. The exact analytical results provide insight into the effect of the magnetic field and the large-amplitude wave on the harmonic structure of the perturbations. Three solutions are found for waves polarized perpendicular to E-0. Waves are amplitude modulated for weak magnetic fields (relative to the strength of the large-amplitude wave) and frequency-modulated for strong magnetic fields. This suggests that frequency modulation may be relevant to pulsars.
Title:
The absence of a discommensuration lattice in the
incommensurate phase of Rb2ZnCl4
Authors:
Babkevich AY. Cowley RA.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(7):1639-1655, 1999 Feb 22.
Abstract:
X-ray scattering close to the lock-in temperature T-L has been measured as a function of temperature to investigate whether the discommensuration lattice is a useful description of the structure of Rb2ZnCl4. We review different models for the incommensurate structure and discuss how they might be distinguished by a scattering experiment. Our results are compared with earlier published x-ray measurements and with those obtained from nuclear spin-resonance techniques. All of the x-ray results suggest that higher harmonics of the scattering measured in the a*/c* and b*/c* planes are much weaker than predicted by the abrupt-discommensuration model. We conclude from the measurements that this theory does not provide an adequate description of the experimental results close to the lock-in transition.
Title:
A study of the new HfFe6Ge6-type ZrMn6Sn6 and HfMn6Sn6 compounds by
magnetization and neutron diffraction measurements
Authors:
Mazet T. Welter R. Malaman B.
Source:
(list of journals)
Journal of Alloys & Compounds. 284(1-2):54-59, 1999 Mar 4.
Abstract:
Bulk magnetization and neutron diffraction measurements have been performed on the new HfFe6Ge6-type (Pb/mmm) ZrMn6Sn6 and HfMn6Sn6 compounds. These compounds order antiferromagnetically below 580(5) and 575(5) K for R=Zr and Hf, respectively. At 300 K, both compounds exhibit a collinear easy-plane antiferromagnetic arrangement and the magnetic structure consists of ferromagnetic (001) Mn planes antiferromagnetically coupled along the c-axis with the (+ - - +) sequence, i.e. a doubling of the c-axis of the chemical cell (mu(Mn)=1.98(7) mu(B) and mu(Mn)=2.05(6) mu(B) for ZrMn6Sn6 and HfMn6Sn6, respectively). At approximately 60 K, a commensurate-incommensurate transition occurs for both compounds, yielding an helical magnetic structure characterized by a thermal dependent k=[00q(z)] wave vector. At 2 K, q(z)=0.491(1) and 0.481(1) r.l.u., while eta(Mn)=2.11(3) mu(B) and 2.18(2) mu(B) for ZrMn6Sn6 and HfMn6Sn6, respectively. A comparison with other RMn6Sn6 compounds involving a non-magnetic R element (R=Mg, Sc, Lu, Y) allows us to underline the influence of the R valency on the magnetic behavior of the Mn sublattice in this class of materials. (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
Effects of cross-linked structure on temperature-responsive
hydrophobic interaction of poly(N-isopropylacrylamide) hydrogel-modified
surfaces with steroids
Authors:
Yakushiji T. Sakai K. Kikuchi A. Aoyagi T. Sakurai Y. Okano T.
Source:
(list of journals)
Analytical Chemistry. 71(6):1125-1130, 1999 Mar 15.
Abstract:
Cross-linked poly(N-isopropylacrylamide) (PIPAAm) hydrogel-modified surfaces were prepared to investigate the effects of a three-dimensionally cross-linked structure of PIPAAm layers on both wettability changes and hydrophobic interactions with hydrophobic solutes in response to temperature changes. The temperature-responsive surface was prepared by polymerization of IPAAm in the presence of cross-linker on the substrates on which an azo polymerization initiator was covalently bonded. The PIPAAm hydrogel-modified surface showed temperature-responsive hydrophilic/hydrophobic surface property alterations as demonstrated by a large and discontinuous wettability changes in a range of 27-32 degrees C, a slightly lower temperature range than the phase transition temperature for soluble PIPAAm in aqueous media. This implies that the dynamic motion in response to temperature for PIPAAm segments in the modified hydrogel is restricted due to the cross-linked structure. The effect of the three-dimensional PIPAAm structure on the separation of hydrophobic steroids was investigated by high-performance liquid chromatography with an aqueous mobile phase. The retention times for steroids with different hydrophobicities were increased as the temperature was raised. Cortisone and prednisolone, those showing close hydrophobicity, were successfully separated at an elevated temperature above 25 degrees C owing to the amplified hydrophobic interaction of prednisolone compared to that of cortisone with the hydrophobic gel surfaces. The separation of relatively hydrophobic steroids was achieved even at lower temperature. The expanded network of the highly hydrated gel layer allowed the penetration of steroid molecules within the hydrogel layer which resulted in the changes in peak width. The cross-linked structure of PIPAAm hydrogels on substrates strongly influences both surface wettability changes and interaction with hydrophobic steroids in response to temperature due to the restricted dynamic motion of PIPAAm segments in the gel.
Title:
High-resolution electron-microscope images of crystals with
correlated atomic displacements
Authors:
Etheridge J.
Source:
(list of journals)
Acta Crystallographica - Section a - Foundations of
Crystallography. 55(1 Part 2):143-159, 1999 Mar 1.
Abstract:
A coordinate-space multislice description of the scattering of high-energy electrons is constructed from consecutions of differential operators acting upon atomic potentials. It is used to find expressions for the intensity distribution in high-resolution electron-microscope images of crystals whose atoms are periodically displaced relative to a reference lattice according to a modulation wave. Both static correlated displacements, such as occur in modulated structures, and time-dependent correlated displacements, as are generated by phonons, are considered. Two aspects of the image are examined in detail; its translational symmetry and its dependence upon the correlations between the atomic displacements. It is shown that the intensity distribution due to scattering from static correlated displacements has the translational symmetry of the modulated structure in that projection, as determined by the component of the modulation wavevector perpendicular to the incident beam, whereas that due to scattering from phonons has the translational symmetry of the reference lattice in that projection. The former is a consequence of higher-order Laue-zone interactions. The intensity distribution due to scattering from static displacements depends upon the absolute phase of the displacement at each scattering atomic site whereas that due to scattering from phonons depends only upon the relative phase of the displacements between different scattering sites, both within the same atomic column parallel to the beam and in adjacent columns. In both cases, the influence of the component of the correlation wavevector parallel to the incident beam is different to that perpendicular to the beam; the former affects the intensity mostly at the atomic sites whilst the latter affects the intensity mostly between the atomic sites. It is also observed that, as a consequence of the periodic nature of the polarization-vector function, the interference terms are small, both relative to the noninterference term and in an absolute sense, particularly for phonon scattering. For this reason, the contribution to the image due to scattering from correlated atomic displacements will have greater and sharper atomic contrast than that due to scattering from the reference structure without displacements. In addition, this component of the intensity distribution will not exhibit strong contrast reversal when the objective-lens defocus is changed.
Title:
Incommensurate state and spin-induced Peierls instability
Authors:
Koshibae W. Yamanaka M. Oshikawa M. Maekawa S.
Source:
(list of journals)
Physical Review Letters. 82(10):2119-2122, 1999 Mar 8.
Abstract:
We propose a novel incommensurate spin state induced by the motion of doped carriers in the one-dimensional double exchange model. The state has an energy gap in the charge excitation caused by the 2k(F) instability and an incommensurate structure in the localized spins with k(F) periodicity accompanied by continuous degeneracy. A metal-insulator transition is proposed in an applied magnetic held. These electronic and magnetic properties are consistent with the experimental data in the hole doped one-dimensional nickelate Y2-xCaxBaNiO5.
Title:
An investigation of the momentum dependence of the electronic spectrum for a
disordered system
Authors:
Yildiz AK. Beeby JL.
Source:
(list of journals)
Philosophical Magazine Letters. 79(3):129-136, 1999 Mar.
Abstract:
The spectral properties of disordered systems are investigated using two-dimensional examples in the tight-binding approximation. The spectra are examined as functions of the momentum wavevector for two-dimensional systems. A particular example is the directional dependence of the spectrum for a quasicrystal, represented by a two-dimensional Penrose lattice. The spectrum changes dramatically, as expected, when the momentum vector moves off a symmetry axis of the system. The value of this approach for analysing the electronic properties of structurally disordered systems is discussed.
Title:
Lattice dynamics and structural instabilities in biphenyl sulfone derivatives
Authors:
Schneider J. Panepucci HC. dos Santos MC. Meriles CA. Nunes LAO.
Source:
(list of journals)
Journal of the Physical Society of Japan. 68(2):493-507, 1999 Feb.
Abstract:
Bis(4-chlorophenyl)sulfone (BClPS) is one of the few organic molecular solids which exhibits a displacive normal-incommensurate phase transition involving spatial modulations of conformational parameters. In the present work, the room temperature phase of BClPS was taken as a prototype, in order to investigate the structural stability of a group of related solids. Lattice dynamics calculations were performed in order to detect possible soft mode instabilities in the phonon dispersion branches. An atomistic semiempirical approach was adopted in lattice calculations, in addition to a semirigid molecular model considering the possibility of coupling between lattice and low lying internal degrees of freedom. Also, free-molecule equilibrium structure and dynamics calculations were performed using ab initio 3-21G* methods, to evaluate the extent of conformational distortions of the molecule in solid phase. The contribution of the internal potential and the molecular packing on the lattice instability of BClPS and related derivatives are discussed. The results suggest that a possible new group of unstable molecular solids with a common prototype packing at high temperature could be identified, in a situation resembling the A(2)BX(4) family of ionic solids.
Title:
Arithmetic properties of spectra produced by Farey hierarchies of
approximants
Authors:
Radulescu O. Janssen T.
Source:
(list of journals)
Journal of Mathematical Physics. 40(3):1317-1333, 1999 Mar.
Abstract:
We discuss the consequences of the hierarchical nature of series of approximants of aperiodic crystals on their diffraction patterns and spectra of elementary excitations. We show how a linear form defined on Z(3) can be used to order Bragg reflections in diffraction patterns according to their amplitudes, and gaps in spectra of elementary excitations according to their widths, for all the structures in the hierarchy. Bragg peaks amplitudes and gap widths are projective functions on P(Z(3)), recursively defined on 2D Farey sets (generalization of Farey series). (C) 1999 American Institute of Physics. .
Title:
Magnetic behavior in the incommensurate phase similar to
LaCrS3: effect of the partial substitution of Cr by Ti on the magnetic
properties
Authors:
Lafond A. Cody JA. Moelo Y. Meerschaut A. Rouxel J.
Source:
(list of journals)
Journal of Magnetism & Magnetic Materials. 192(3):490-498, 1999 Mar.
Abstract:
Dilution of the magnetic interactions between Cr3+ ions by Ti3+ ions was observed in the CrS2 layer of the misfit-layer compound similar to LaCrS3. Pure similar to LaCrS3 has complex magnetic properties which are reminiscent of spin glass behavior. This magnetic behavior comes from both the modulated character of the structure and the magnetic frustration of the planar-antiferromagnetic-triangular network of Cr3+ ions. Thus, there is a large hysteresis between the zero field cooled and the field cooled magnetic susceptibility curves below the transition temperature ( approximate to 75 K). Formation of a solid solution similar to LaCr1-xTixS3 by the addition of Ti3+ ions results in the decrease of transition temperature up to a doping level of x approximate to 0.5, where the transition is no longer observed. The magnetic behavior of the phase with x approximate to 0.5 is similar to that of several random exchange antiferromagnetic compounds. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Transitions between modulated phases in an Ising model with
third-neighbour inter-actions (mean-field approximation)
Authors:
Massidda V.
Source:
(list of journals)
Journal of Magnetism & Magnetic Materials. 192(3):505-515, 1999 Mar.
Abstract:
We study order-disorder transitions in a three-dimensional Ising lattice in which all the spins belonging to the same xq, plane have the same degree of disorder, so that the structure can be effectively reduced to a chain of layers. The layers interact with each other up to third neighbours. Employing the mean-field approximation, we find the different configurations that undergo the transition to total disorder in terms of the interaction constants and work our a diagram displaying the possible sequences of modulated phases that can be found when the temperature goes from 0 to the order-disorder transition point. At intermediate temperatures the average values of the spins of the layers for periodic structures are found by solving an equation system. Substitution of these values into the expression of the free energy allows one to determine the most stable structure for each set of interaction constants and for each temperature. The model predicts a transition between two modulated structures with the same wavelength but different unit cells, for suitable values of the interaction constants. The formalism is also applied to substances like UNi2Si2, with only a partial agreement with experiment. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Title:
Development of stochastic oscillations in a one-dimensional dynamical system
described by the Korteweg de Vries equation
Authors:
Gurevich AV. Zybkin KP. El GA.
Source:
(list of journals)
Journal of Experimental & Theoretical Physics. 88(1):182-195, 1999 Jan.
Abstract:
The behavior of the solution of the Korteweg-de Vries equation for large-scale oscillating aperiodic initial conditions prescribed on the entire x axis is considered. It is shown that the structure of small-scale oscillations arising in a Korteweg-de Vries system as t --> infinity loses its dynamical properties as a consequence of phase mixing. This process can be called the generation of soliton turbulence. The infinite system of interacting solitons with random phases developing under these conditions leads to oscillations having a stochastic character. Such a system can be described using the terms applied to a continuous random process, the probability density and correlation function. It is shown that for this it suffices to determine from the prescribed initial conditions amplitude distribution function of the solitons and their mean spatial density. The limiting stochastic characteristics of the mixed state for problems with initial data in the form of an infinite sequence of isolated small-scale pulses are found. Also, the problem of stochastic mixing under arbitrary initial conditions in the dispersionless limit (the Hopf equation) is completely solved. (C) 1999 American Institute of Physics. .
Title:
X-ray and electrochemical studies of Cu upd on single
crystal electrodes in the presence of bromide: comparison
between Au(111) and Pt(111) electrodes
Authors:
Herrero E. Glazier S. Buller LJ. Abruna HD.
Source:
(list of journals)
Journal of Electroanalytical Chemistry. 461(1-2):121-130, 1999 Jan 29.
Abstract:
Results from electrochemical and in-situ surface X-ray scattering studies of Cu underpotential deposition (upd) on Au(111) and Pt(111) surfaces in the presence of bromide anions are compared. On Au(111) two different ordered structures have been found by GIXD. At the initial stages of Cu deposition, an enhancement of bromide adsorption is observed resulting in the formation of a bromide incommensurate hexagonal structure, which compresses when the potential is scanned in the negative direction. At +0.32 V, there is a phase transition giving rise to the formation of a commensurate (4 x 4) bromide structure. This phase transition coincides with the appearance of a very sharp peak in the voltammetric profile. In this structure, copper adatoms are probably sandwiched between the electrode surface and the bromide adlayer. Unlike Cu upd on Pt(111) electrodes, no ordered CuBr adlayer is observed. The differences in behavior of Cu upd on Au(111) and Pt(111) electrodes is ascribed not to energetic considerations, but rather to geometric constraints imposed by the lattice structure of the metal relative to the deposited adlayer. The stability (to rinsing) and kinetics of the adlayers formed on Pt(111) electrodes in the presence of bromide have also been examined. (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
Solid-liquid interface in the growth of a decagonal Al-72 Co-16 Ni-12
quasicrystal
Authors:
Guo JQ. Sato TJ. Hirano T. Tsai AP.
Source:
(list of journals)
Journal of Crystal Growth. 197(4):963-966, 1999 Mar.
Abstract:
To understand growth mechanism of a decagonal Al-72 Co-16 Ni-12 single quasicrystal, solid-liquid interface during crystal growth was investigated. When a single quasicrystal was grown at a growth rate of 0.5 mm/h, the solid-liquid interface is flat. At steady growth state it was found that Al is enriched, while Co and Ni are depleted in front of the interface. Solute partition ratios of Al, Co and Ni were determined to be about 0.91, 1.57 and 1.08, respectively. The change of the solute partition ratio and redistribution process during the crystal growth has been discussed. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Adsorption of PF3 on Cu(001): Ordered overlayer structures
and frustrated translational modes
Authors:
Braun J. Bishop GG. Ermakov AV. Goncharova LV. Hinch BJ.
Source:
(list of journals)
Journal of Chemical Physics. 110(11):5337-5345, 1999 Mar 15.
Abstract:
The adsorption of PF3 on Cu(001) was studied by means of high resolution helium atom scattering (HAS) and SPALEED. PF3 adsorbs at surface temperatures below 210 K and forms a lattice gas at exposures less than 0.8 L. Saturation is reached for exposures greater than 3 L. At these coverages PF 3 forms an ordered c(4 x 2) layer for surface temperatures above 145 K. For temperatures below 145 K an incommensurate, hexagonal PF 3 layer was observed that necessarily excludes uniquely on-top site PF3 molecule to surface coordination. A new vibrational mode in the thermal energy regime corresponding to the frustrated translation parallel to the surface was identified; the energies of excitation were 3.3 meV and 3.5 meV, respectively, for the isolated molecules and the c(4 x 2) structure. No dispersion of the frustrated translation in the ordered c(4 x 2) phase was found. The results are discussed in terms of adsorbate-adsorbate and adsorbate-substrate interactions. (C) 1999 American Institute of Physics. .
Title:
Inelastic neutron scattering study of the dynamics of the AlNiCo decagonal
phase
Authors:
Dugain F. de Boissieu M. Shibata K. Currat R. Sato TJ. Kortan AR. Suck JB. Hradil K. Frey F. Tsai AP.
Source:
(list of journals)
European Physical Journal B. 7(4):513-516, 1999 Feb.
Abstract:
The dynamics of the decagonal AlNiCo phase has been investigated on a single-grain quasicrystalline sample using inelastic neutron scattering. The decagonal structure can be viewed as a periodic stacking of quasiperiodic planes. The anisotropy between the modes propagating in the periodic and quasiperiodic directions is found to be much weaker than theoretically predicted. A strong resonance splitting is observed at an energy transfer of 15 meV for transverse modes polarized in the quasiperiodic plane.
Title:
An analysis of nanoparticle stability [Russian]
Authors:
Dolgushev NV. Suvorov SA.
Source:
(list of journals)
Doklady Akademii Nauk. 364(3):342-344, 1999 Jan.
Title:
Elastic model of the primary stripe texture in free-standing chiral smectic C
films
Authors:
Lejcek L.
Source:
(list of journals)
Czechoslovak Journal of Physics. 49(2):233-252, 1999 Feb.
Abstract:
In paper E. Gorecka et al.: Phys. Rev. Lett. 75 (1995) 4047 the modulations of the director inside smectic layers of chiral smectic C: free-standing film were identified as a periodic system of domain walls on which the director orientation changes by pi. Domain walls were terminated in the film bulk. An improved model, in which domain walls are terminated by (+/-pi)-disclinations, is proposed. The model is an extension of the model of Meyer and Pershan for the case of chiral smectic C: films. The experimental dependence of the periodicity of the system on the film thickness is used to estimate the model parameters.
Title:
Dynamics of autowaves in a one-dimensional crystal model
Authors:
Dmitriev SV. Shigenari T. Volkova SM. Vasiliev AA. Abe K.
Source:
(list of journals)
Computational Materials Science. 13(4):227-231, 1999 Jan.
Abstract:
A mechanism of the phase transition between two modulated structures with different wave vectors was proposed and investigated numerically. The phase transition occurs through the mechanism of nucleation and growth of the new phase. The role of the nucleus is played by an unstable domain wall and the domain of a new low energy phase grows due to the motion of autowaves. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Title:
Intrinsic pinning, commensurability, and reentrant behavior on
superconducting Mo/Si multilayers
Authors:
Fogel NY. Mikhailov MY. Bomze YV. Yuzephovich OI.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(5):3365-3368, 1999 Feb 1.
Abstract:
A reentrance phenomenon is found on Mo/Si multilayers which occurs in parallel to the layers and slightly inclined magnetic fields. This effect may be explained in terms of the intrinsic pinning and vortex lattice (VL) commensurability with the underlying layered structure. The locations of the zero-resistance regions correspond to stable VL configurations or to the transitions between two commensurate lattices. It is suggested that this resistive method may be used as a tool to study VL structure in layered superconductors. .
Title:
Structural study of approximant phases of Al-Cu-Fe
quasicrystals under high pressure
Authors:
Joulaud JL. Capitan MJ. Hausermann D. Lefebvre S. Calvayrac Y.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(5):3521-3526, 1999 Feb 1.
Abstract:
X-ray-diffraction experiments under high-pressure conditions were performed on two high-order approximant phases of the icosahedral Al-Cu-Fe quasicrystal. The rhombohedral and pentagonal samples were compressed under quasihydrostatic conditions up to 35 GPa. We did not observe clear evidence for structural transformation in either sample. The most prominent feature observed was a broadening of the Bragg peaks with increasing pressure. This behavior has been compared with the one exhibited by the parent related structure (i-Al-Cu-Fe) and by a low-order cubic approximant structure (a-Al-Cu-Fe-Si). The modifications in the diffraction patterns are preserved after pressure release. The peak broadening has been related with the development of a particular phason-strain field. This kind of interaction is explained with the help of group-theoretical arguments proposed by Ishii. .
Title:
Path-integral Monte Carlo simulation of the second layer of He-4 adsorbed on
graphite
Authors:
Pierce M. Manousakis E.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(5):3802-3814, 1999 Feb 1.
Abstract:
We have developed a path-integral Monte Carlo method for simulating helium Alms and apply it to the second layer of helium adsorbed on graphite. We use helium-helium and helium-graphite interactions that are found from potentials which realistically describe the interatomic interactions. The Monte Carlo sampling is over both particle positions and permutations of particle labels. From the particle configurations and static structure factor calculations, we find that this layer possesses, in order of increasing density, a superfluid liquid phase, a root 7 x root 7 commensurate solid phase that is registered with respect to the first layer, and an incommensurate solid phase. By applying the Maxwell construction to the dependence of the low-temperature total energy on the coverage, we are able to identify coexistence regions between the phases. From these, we deduce an effectively zero-temperature phase diagram. Our phase boundaries are in agreement with heat capacity and torsional oscillator measurements, and demonstrate that the experimentally observed disruption of the superfluid phase is caused by the growth of the commensurate phase. We further observe that the superfluid phase has a transition temperature consistent with the two-dimensional value. Promotion to the third layer occurs for densities above 0.212 atom/Angstrom (2), in good agreement with experiment. Finally, we calculate the specific heat for each phase and obtain peaks at temperatures in general agreement with experiment. .
Title:
Transmission properties of light through the Fibonacci-class multilayers
Authors:
Yang XB. Liu YY. Fu XJ.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(7):4545-4548, 1999 Feb 15.
Abstract:
We study the transmission properties of light through the Fibonacci-class quasiperiodic multilayers. The trace map of the propagation matrices, its invariant of motion, and the expression for the transmission coefficient are obtained. For the normal incidence of light, the transmission coefficient exhibits a switchlike property in a family of the Fibonacci-class multilayers, while a six-cycle feature in another family is found. .
Title:
Synthesis, thermal stability, structural features, and electromagnetic
properties of Bi2+xSr2-xCuO6+delta (0 <= x <= 0.4)
Authors:
Niinae T. Ikeda Y. Bando Y. Takano M. Kusano Y. Takada J.
Source:
(list of journals)
Physica C. 313(1-2):29-36, 1999 Feb 10.
Abstract:
The thermal stability and structural modulation were studied systematically in a wide range of 0 less than or equal to x less than or equal to 0.4 for the 2201 phase in the Bi-Sr-Cu-O system, Bi2 + x Sr2-xCUO6 + 8, and it was found that these properties varied remarkably at x approximate to 0.1. Compositions 0 less than or equal to x < 0.1 remained stable only in a narrow low-T high-P-O2 region and their modulation period changed stepwisely, not continuously, and reversibly between 4.9b (oxidized) and 5.5b (reduced) when the oxygen content was changed only by 0.65%. In relation to this we propose for 0 less than or equal to x < 0.1 specifically that the change in oxygen content induces the exchange of small amounts of Bi and Sr ions between the 'BiO' and 'SrO' sheets. The superconductivity of the cation-stoichiometric composition (x = 0) was also studied as a function of oxygen content. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Magnetic helix in MnO2
Authors:
Kovalev OV.
Source:
(list of journals)
Low Temperature Physics. 25(2):115-121, 1999 Feb.
Abstract:
The paper pursues the following two goals: to demonstrate the principle of concordance of the basic sets of representations and to investigate possible incommensurate magnetic structures proceeding from the previously developed theory of induced representations. The methods and the results obtained differ essentially from those obtained on the basis of Lifshitz invariants. The effect of exchange energy spectrum smoothing as a result of inclusion of a nonexchange interaction is established The role of dipole interaction in the magnetic helix orientation is elucidated. (C) 1999 American Institute of Physics. .
Title:
Visual signal detection with two-component noise: low-pass spectrum effects
Authors:
Burgess AE.
Source:
(list of journals)
Journal of the Optical Society of America A-Optics & Image Science.
16(3):694-704, 1999 Mar.
Abstract:
Detection of signals in natural images and scenes is limited by both noise and structure. The purpose of this study is to investigate phenomenological issues of signal detection in two-component noise. One component had a broadband (white) spectrum designed to simulate image noise. The other component was filtered to simulate two classes of low-pass background structure spectra: Gaussian-filtered noise and power-law noise. Measurements of human and model observer performance are reported for several aperiodic signals and both classes of background spectra. Human results are compared with two classes of observer models and are fitted very well by suboptimal prewhitening matched filter models. The nonprewhitening model with an eye filter does not agree with human results when background-noise-component power spectrum bandwidths are less than signal energy bandwidths. (C) 1999 Optical Society of America .
Title:
Crystal growth of large icosahedral Zn-Mg-Y single grains by
a liquid encapsulated top seeded solution growth method
Authors:
Langsdorf A. Assmus W.
Source:
(list of journals)
Crystal Research & Technology. 34(2):261-265, 1999.
Abstract:
In this paper we present our work on the single crystal growth of the icosahedral phase in the system Zn-Mg-Y. Taking into account the results of our previous systematic investigation of the phase diagram Zn-Mg-Y we have been able to grow single grains of the icosahedral phase with a diameter of nearly 1cm. We apply a Liquid Encapsulated Top Seeded Solution Growth method (LE-TSSG) in order to prevent Mg- and Zn-losses during growth.
Title:
On the commensurate-incommensurate
transition in adsorbed monolayers
Authors:
Patrykiejew A. Sokolowski S. Zientarski T. Binder K.
Source:
(list of journals)
Surface Science. 421(3):308-319, 1999 Feb 11.
Abstract:
A Monte Carlo simulation method is used to study the commensurate-incommensurate phase transition in monolayers and the formation of bilayer films on the (100) face of an fee crystal. The phase diagram for the system which forms the registered(1x1)and high density incommensurate phases in the monolayer has been determined. It is shown that the registered phase undergoes the transition to a denser incommensurate solid phase when the film density increases. The mechanism of melting of the monolayer film is found to depend on the film density. In particular, the melting of dense incommensurate solid monolayer film is found to be accompanied by the transfer of adsorbed molecules into the second layer. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Title:
Stability of colloidal quasicrystals (vol 81, pg 469, 1998)
Authors:
Denton AR. Lowen H.
Source:
(list of journals)
Physical Review Letters. 82(7):1610, 1999 Feb 15.
Title:
Defect and transmission properties of two-dimensional quasiperiodic photonic
band-gap systems
Authors:
Cheng SSM. Li LM. Chan CT. Zhang ZQ.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(6):4091-4099, 1999 Feb 1.
Abstract:
It has recently been demonstrated that two-dimensional photonic band gaps can be realized in systems comprising of a quasiperiodic arrangement of dielectric cylinders. We show that waveguides crafted out of such photonic ''quasicrystals'' can be used to guide light around sharp corners, just as in the case of periodic photonic band-gap systems, but the quasiperiodic systems tend to be more frequency selective. Because of the absence of translational symmetry, these quasiperiodic photonic band-gap structures also display richer defect properties. Spectral gaps for both the TM and TE polarizations in the same frequency range can be realized in metallodielectric configurations. .
Title:
Amorphization and recrystallization of covalent tetrahedral
networks
Authors:
Bolse W.
Source:
(list of journals)
Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions
with Materials & Atoms. 148(1-4):83-92, 1999 Jan.
Abstract:
In the present paper recent studies on the amorphization and recrystallization of the light covalent ceramics SiC, Si3N4 and SiO2 (and in comparison Si) shall be reviewed. By combining long and short range order sensitive analysis techniques new insights into the disordering/reordering mechanisms and the structure of the disordered materials were gained. The results will be discussed in the light of a topological approach of the transition between periodic and aperiodic networks. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Structure of freshly formed and low-temperature aged Fe-N
austenites
Authors:
Han KH. Song YK.
Source:
(list of journals)
Materials Science & Engineering A-Structural Materials Properties
Microstructure & Processing. 260(1-2):246-251, 1999 Feb.
Abstract:
A transmission electron microscopy (TEM) study has been carried out to investigate the structural state of freshly formed and aged Fe-8.6 at.% N austenites. The experimental alloys were prepared by gas nitriding of iron foils under NH3/H-2 mixture, followed by direct quenching into iced-brine. The observation has shown that the freshly formed Fe-8.6 at.% N alloy is essentially composed of a single austenite which does not contain the long-range atomic order of the interstitial nitrogen atoms. The results rather indicated that the as-nitrided Fe-N austenite would contain local atomic order to form isolated Fe4N-type and/or N-Fe-N (100)gamma dumbbell-type atomic configuration in a short-range, as suggested by previous Mossbauer spectroscopy studies. Aging at low temperatures, i.e. 373 and 473 K, allowed further segregation of nitrogen atoms to result in the formation of the fine structure, resembling the (100) modulated structure by the spinodal decomposition. The resulting microstructure consisted of the N-enriched regions and the N-depleted regions, where the former further contained Fe4N-type long-range atomic order. (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
Cation deficiency in (Ba,Sr)Co1-xOy hexagonal perovskite related oxides: New
members of the A(n+2)B ' BnO3n+3 homologous series
Authors:
Boulahya K. Parras M. Gonzalez-Calbet JM.
Source:
(list of journals)
Journal of Solid State Chemistry. 142(2):419-427, 1999 Feb 1.
Abstract:
The new phases (Ba0.5Sr0.5)(7)Co6O18, Ba8Co7O21, and Ba9Co8O12 have been shown by electron diffraction and high-resolution electron microscopy to be three new members (n = 5, n = 6, and n = 7) of the 2H hexagonal perovskite-related A(n+2)B'BnO3n+3 homologous series. Their modulated structures are made up of chains, running along the c direction and separated by Ba(Sr) ions, containing a succession of one Co atom in prismatic trigonal sites and it Co atoms in octahedral coordination sharing faces. The strategy to synthesize different terms of this family is discussed in terms of the distance between AO(3) layers, (C) 1999 Academic Press.
Title:
Anion ordering in fluorinated La2CuO4
Authors:
Abakumov AM. Hadermann J. Van Tendeloo G. Shpanchenko RV. Oleinikov PN. Antipov EV.
Source:
(list of journals)
Journal of Solid State Chemistry. 142(2):440-450, 1999 Feb 1.
Abstract:
La2CuO4 has been fluorinated using XeF2 as a soft fluorinating agent at temperatures ranging from 200 to 400 degrees C, The structure of the fluorinated samples was studied by a combination of X-ray diffraction (XRD), electron diffraction (ED), high-resolution electron microscopy (HREM), and microanalysis. XRD shows the sequential changes with increasing temperature of the XeF2 treatment. A significant structural rearrangement, associated with the formation of a tetragonal K2NiF4-type structure (I-centered lattice with cell parameters a 4.0383(6) A, c = 13.093(3) Angstrom) occurs at 250 degrees C. Samples annealed at 300 and 400 degrees C reveal the formation of a new monoclinic phase (a approximate to 17.36 Angstrom, b approximate to 5.62 Angstrom, c approximate to 10.59 Angstrom, beta approximate to 91.5 degrees; SG, C2/m). The structural model, deduced from ED and HREM, involves the filling of part of the interstitial positions by fluorine atoms with removal of the neighboring oxygen, resulting in the formation of a fluorite-like arrangement of the La(O, F) layers. The fluorite-type and NaCl-type slabs alternate along the [110] direction of the K2NiF4 subcell in an ordered array. Several crystallites also show an incommensurate superstructure which is explained as a pseudoperiodic arrangement of shear planes. (C) 1999 Academic Press.
Title:
Helimagnetic order in ferric arsenate, FeAsO4
Authors:
Forsyth JB. Wright JP. Marcos MD. Attfield JP. Wilkinson C.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(6):1473-1478, 1999 Feb 15.
Abstract:
High-resolution time of flight neutron powder diffractometry has been used to determine the antiferromagnetic structure of ferric arsenate at 4.2 K. The structure is incommensurate with a magnetic propagation vector (0.04994(3), 0, -0.24725(2)) in the a*-c* plane of the monoclinic unit cell. The spins of 4.01(2) mu(B) On the Fe3+ ions rotate in a plane containing b* and making an angle of 34.1(7)degrees to [001] in beta obtuse. The structure shows that the dominant antiferromagnetic coupling is between Fe3+ ions which are linked through tetrahedral arsenate groups giving a frustrated exchange network.
Title:
Molecular dynamics study of crystallization of supercooled
liquid sodium
Authors:
Galashev AE. Chernysheva IP.
Source:
(list of journals)
Inorganic Materials. 35(1):42-48, 1999 Jan.
Abstract:
Crystallization of supercooled liquid sodium containing a spheroidal bce nucleus was studied by molecular dynamics simulations. The degree of supercooling and the critical nucleus size are determined. After solidification, the system exhibits elasticity of shear. Nucleus growth is accompanied by self-sustained aperiodic temperature oscillations. The radial distribution function is computed and Voronoi polyhedra are constructed for the system immediately before and after the transition. It is shown by the projection method that the crystallized system contains structural defects and Features a long-range order.
Title:
Hard Mode Infrared Spectroscopy of plagioclase feldspars
Authors:
Atkinson AJ. Carpenter MA. Salje EKH.
Source:
(list of journals)
European Journal of Mineralogy. 11(1):7-21, 1999 Jan-Feb.
Abstract:
Local states of order and the character of phase transitions in a suite of natural and heat-treated plagioclase feldspars have been examined by Hard Mode Infrared Spectroscopy at room temperature. Autocorrelation analysis has been used to determine variations of average linewidths of groups of peaks in the primary IR spectra. Changes in frequency of selected peaks and an autocorrelation parameter from the frequency range 500-650 cm(-1) scale with the square of the macroscopic order parameter for the C (1) over bar <-> I (1) over bar transition. Combining the autocorrelation data, which provide information relating to the local (unit-cell) scale behaviour, with lattice strain, which indicates the average macroscopic behaviour, leads to a qualitative differentiation between the two incommensurate phases, e(1) (An-rich) and e(2) (Ab-rich). Within individual domains of the e(1) structure in crystals of composition similar to An70, the local homogeneity and Al/Si ordering conformation appear to be indistinguishable from IT structural states. The degree of I (1) over bar order diminishes with increasing Ab-content and would extrapolate to zero somewhere between similar to An40 and similar to An50. The e(2) structures appear to relate to the Al/Si ordering of albite but retain a degree of heterogeneity on a phonon length scale which is comparable to that found in disordered C (1) over bar crystals. On the length scale of the IR experiments, there is an abrupt cut off for the formation of P (1) over bar domains between similar to An86 and similar to An90 as Ab-component is added to anorthite. Transitions of the type C (1) over bar <-> I (1) over bar, I (1) over bar <-> P (1) over bar and I (1) over bar <-> e(1) appear to be continuous as a function of composition at a local structural scale. Deviations from ideal mixing in the heat-treated series arise from Al/Si ordering at An-rich compositions.
Title:
Electrochemical, in-situ surface EXAFS and CTR studies of Co monolayers
irreversibly adsorbed onto Pt(111)
Authors:
Herrero E. Li J. Abruna HD.
Source:
(list of journals)
Electrochimica Acta. 44(14):2385-2396, 1999.
Abstract:
Irreversibly adsorbed Co adlayers with surface coverages of about 0.6 and 1 ML can be deposited onto Pt(lll) from CoSO4 in 0.1 M H2SO4 and CoCl2 in 0.1 M NaOH solutions. Once adsorbed, the adlayers were studied in 0.1 M H2SO4 and 0.1 M NaOH solutions respectively, by electrochemical, surface EXAFS (SEXAFS) and crystal truncation rod (CTR) measurements. In 0.1 M H2SO4, an irreversible oxidation with a peak potential value of +1.00 V (vs. Ag/AgCl) corresponding to the oxidation of the cobalt adlayer as well as the Pt substrate was observed. There was also a reduction wave present at -0.29 V and which was ascribed to, at least in part, the evolution of hydrogen and which resulted in the displacement of the cobalt adlayer. In 0.1 M NaOH two redox processes were also observed at formal potential values of -0.355 and -1.04 V. The former, which exhibited significant kinetic limitations, was ascribed to a Co-III(OH)(3)/Co-II(OH)(2) redox process. The latter was ascribed to the generation of Co-0. SEXAFS measurements in sulfuric acid (at an applied potential of 0.0 V) and in 0.1 M NaOH (at applied potential values of -0.06 and -0.75 V) were consistent with the presence of an oxidized cobalt layer with Co, O and Pt near neighbors. CTR data were also consistent with the presence of an oxidized cobalt bi-layer structure. In 0.1 M NaOH and at a coverage of ca. 1 ML, the deposited cobalt appears to form a 1 x 1 structure with the cobalt atoms occupying three-fold hollow sites. Relative changes in the number of oxygen near neighbors with applied potential (derived from EXAFS data) were also consistent with electrochemical data. In 0.1 M H2SO4 (at an applied potential of 0.0 V) and at a cobalt coverage of about 0.6 ML, the deposited cobalt appears to form an incommensurate monolayer with an expanded lattice (Co-Co distance of 2.96 Angstrom) likely involving co-adsorbed (bi)sulfate. (C) 1999 Elsevier Science Ltd. All rights reserved.
Title:
Phenomenological theory of phase diagrams involving
incommensurate phase [Review]
Authors:
Sannikov DG.
Source:
(list of journals)
Crystallography Reports. 44(1):148-164, 1999 Jan-Feb.
Abstract:
A phenomenological approach to the construction of phase diagrams with multiple phase transitions (including incommensurate ones) is presented. The diagrams containing the Lifshitz point are considered. The theoretical temperature-pressure and temperature-electric field phase diagrams for deuterated theourea and betaine calcium chloride dihydrate are found to be consistent with the diagrams obtained in experiments.
Title:
Critical slowing of local fluctuations near the
paraelectric-incommensurate phase transition in Rb2ZnCl4
Authors:
Trubitsyn MP. Pastukhov VI. Bochkova TM.
Source:
(list of journals)
Physics of the Solid State. 41(1):108-111, 1999 Jan.
Abstract:
A study is reported of the anomalous broadening of Mn2+ EPR lines on the high-temperature side of the paraelectric-incommensurate phase transition in Rb2ZnCl4 crystals. It is shown that the resonant-line broadening is inhomogeneous and due to the contribution of low-frequency fluctuations corresponding to the central peak in the elementary-excitation spectrum. The data obtained have permitted us to obtain the critical correlation-length exponent nu=0.64+/-0.02 corresponding to the 3d XY model of Heisenberg. (C) 1999 American Institute of Physics. .
Title:
The invar effect and phase transitions in Cs(2)Znl(4)
crystals
Authors:
Bagautdinov BS. Shekhtman VS.
Source:
(list of journals)
Physics of the Solid State. 41(1):123-127, 1999 Jan.
Abstract:
An in situ x-ray diffraction study of Cs2ZnI4 crystals performed in the 4.2-300 K temperature range is reported. The lattice parameter measurements have revealed three anomalies corresponding to phase transitions. The thermal expansion coefficient along the c axis was found to vanish in the region of incommensurate and commensurate modulated phases, 120-96 K (the invar effect). A possible crystallographic model relating modulated atomic displacements to the invar effect is discussed. (C) 1999 American Institute of Physics. .
Title:
Phase transitions in the (Cs1-xRbx)(2)Znl(4) system
Authors:
Sukhovskii AA. Lisin VV. Aleksandrova IP. Voronov VN. Melero JJ.
Source:
(list of journals)
Physics of the Solid State. 41(1):128-131, 1999 Jan.
Abstract:
(Cs1-xRbx) 2ZnI4 crystals were grown by two different methods with Rb concentrations varying from x=0 to 2.5%. I-127 NQR and calorimetric measurements showed that crystals grown by the Bridgman technique contain residual impurities (similar to 0.5%) for all x. While x=0 crystals grown from solution do not contain detectable impurities, they allow incorporation only of a low Rb concentration, not above 0.5%. A transition-temperature-concentration (x) phase diagram has been constructed for Bridgman-grown crystals from NQR data. Rb doping shifts the normal-incommensurate and incommensurate-ferroelastic phase-transition points toward higher temperatures with different rates. The P2(1)/m<->P1 first-order transition shifts toward lower temperatures. The region of low Rb concentrations lies closest to the critical point. (C) 1999 American Institute of Physics. .
Title:
Tunneling spectroscopy in AlNiCo decagonal quasicrystals
Authors:
Li GH. He HF. Wang YP. Lu L. Li SL. Jing XN. Zhang DL.
Source:
(list of journals)
Physical Review Letters. 82(6):1229-1232, 1999 Feb 8.
Abstract:
Tunneling spectroscopy of Al73Ni17Co10 decagonal single quasicrystals has been measured at ultralow temperatures. In addition to the wide pseudogap observed in previous photoemission experiments. very rich fine structures in the density of states around the Fermi energy were discovered. The fine structures strongly depend on the applied magnetic field and disappear above similar to 4 T. The zero-bias resistance of the junction varies with magnetic fields in a complicated way, which is suggested to be related to the hierarchy structure of quasicrystals. A puzzling hysteretic phenomenon was observed in some bias ranges in zero magnetic field, the origin of which needs to be clarified in the future. .
Title:
Coexistence of charge-density wave and spin-Peierls orders in quarter-filled
quasi-one-dimensional correlated electron systems
Authors:
Riera J. Poilblanc D.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(4):2667-2675, 1999 Jan 15.
Abstract:
Charge and spin-Peierls instabilities in quarter-filled (n = 1/2) compounds consisting of coupled ladders and/or zigzag chains are investigated. Hubbard and t-J models including local Holstein and/or Peierls couplings to the lattice are studied by numerical techniques; Next nearest-neighbor hopping and magnetic exchange, and short-range Coulomb interactions are also considered. We show that, generically, these systems undergo instabilities towards the formation of charge-density waves, bond order waves, and (generalized) spin-Peierls modulated structures. Moderate electron-electron and electron-lattice couplings can lead to a coexistence of these three types of orders. In the ladder, a zigzag pattern Is stabilized by the Holstein coupling and the nearest-neighbor Coulomb repulsion. In the case of an isolated chain, bond-centered and site-centered 2k(F) and 4k(F) modulations are induced by the local Holstein coupling. In addition, we show that, in contrast to the ladders, a small charge ordering in the chains strongly enhances the spin-Peierls instability. Our results are applied to the NaV2O5 compound (trellis lattice) and various phases with coexisting charge disproportionation and spin-Peierls order are proposed and discussed in the context of recent experiments. The role of the long-range Coulomb potential is also outlined. .
Title:
Electronic structure calculations of Al-Cu alloys:
comparison with experimental results on Hume-Rothery phases
Authors:
Fournee V. Mazin I. Papaconstantopoulos DA. Belin-Ferre E.
Source:
(list of journals)
Philosophical Magazine B-Physics of Condensed Matter Structural Electronic
Optical & Magnetic Properties. 79(2):205-221, 1999 Feb.
Abstract:
Electronic band-structure calculations for a set of hypothetical Al-Cu alloys are presented. The influence of the local order and of the Cu concentration on the local density of states is analysed. The Als states are repelled towards the bottom of the occupied band by the interaction with the more localized Cud states lying about 4 eV below the Fermi lever. Bonding and antibonding Al p states also appear, located on each side of the Cud band. The coupling between the more extended states of Al with the d band of Cu is well described by a Fano-like effect. Two calculations performed for real Al-Cu phases of the Hume-Rothery type allow direct comparison with experimental results obtained by soft-X-ray spectroscopies. A pseudogap induced by the interaction between the Fermi sphere and the Brillouin zone is observed in agreement with the experiment. The availability of the Hume-Rothery criterion in the formation of the pseudogap observed in quasicrystalline phases is also discussed.
Title:
Modulated phases and proton centring in ice observed by
X-ray diffraction up to 170 GPa
Authors:
Loubeyre P. LeToullec R. Wolanin E. Hanfland M. Husermann D.
Source:
(list of journals)
Nature. 397(6719):503-506, 1999 Feb 11.
Abstract:
Because of its open hydrogen-bonded structure, ice shows many structural changes between different crystalline forms under high pressure. Crystallographic studies of these transitions have been pursued largely by neutron scattering, which allows the positions of the hydrogen atoms to be identified(1,2). Such studies have previously been extended to pressures of up to 20 GPa, which is however insufficient tea permit the investigation of ice X, a 'symmetric ice' in which the protons are thought to reside midway between the oxygen atoms(3-5). So far, information about ice X has therefore come from indirect methods such as infrared(6,7) or Brillouin(8) spectroscopy. Here we show that single-crystal X-ray diffraction is able to reveal the signature of hydrogen-bond symmetrization. The 111 reflection can be assigned to the hydrogen atoms alone, and we can measure it up to 170 GPa in a diamond anvil cell. This diffraction line (normalized against the intensity of the 222 line, which is due mostly to oxygen atoms) indicates that the proton centring in ice X occurs from about 60 to 150 GPa; at this latter pressure the intensity increases sharply, signalling a further structural change. At lower pressures, we see ice VII ordering in a sequence of spatially modulated phases between 2.2 and 25 GPa, which suggests an analogy with the incommensurate phases of the frustrated Ising model(9).
Title:
Magnetic-field-induced phase transitions between helical
structures in noncentrosymmetric uniaxial antiferromagnets
Authors:
Bogdanov AN. Shestakov AA.
Source:
(list of journals)
Low Temperature Physics. 25(1):76-78, 1999 Jan.
Abstract:
Two symmetrically different types of one-dimensional modulated structures (cycloids and conical helicoids) can exist in noncentrosymmetric uniaxial antiferromagnets. An applied magnetic field induces a first-order phase transition between these phases. The equilibrium parameters of the modulated structures are determined from the solution of the corresponding differential equations, and the phase diagram of the antiferromagnet in a bias magnetic field is calculated numerically. An analysis of experimental results leads to the conclusion that the predicted phase transition occurs in Ba2CuGe2O7. (C) 1999 American Institute of Physics. .
Title:
Modulated structures with field-controlled
direction and periodicity in SmC* liquid crystals
Authors:
Subacius D. Voloschenko D. Bos P. Lavrentovich OD.
Source:
(list of journals)
Liquid Crystals. 26(2):295-298, 1999 Feb.
Abstract:
A stable modulated structure in the form of stripes occurs in SmC* liquid crystal cells well below the SmA-SmC* transition point, without any applied or pre-applied electric field. The periodicity of the modulations is much smaller than the cell thickness. The stripes are tilted away from the rub direction of the cell. A low applied voltage changes both the periodicity and orientation of the stripes, allowing for electric field control of optical diffraction at the stripes.
Title:
Tunnelling and point contact spectroscopy of the density of states in
quasicrystalline alloys
Authors:
Escudero R. Lasjaunias JC. Calvayrac Y. Boudard M.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(2):383-404, 1999 Jan 18.
Abstract:
Point contact and tunnelling experiments performed at low temperatures were used to study the electronic behaviour of the icosahedral quasicrystalline alloys AlPdRe, AlCuFe, and AlPdMn. With samples of high quality we observed at low temperatures a zero-bias anomaly that we related to the decrease of the electronic density of states (DOS) due to the electron-electron interaction. This interaction tends to diminish the DOS at the Fermi level and can be seen as the energy pseudogap of the alloy. Our experiments indicate that the DOS is strongly modified near EF and consists of a spiky feature in abroad pseudogap, with the width of the feature of the order of 100 meV or even larger for the AlPdRe, whereas it is as small as 20-22 meV for Al-Cu-Fe and 17-20 meV for Al-Pd-Mn. The broad pseudogap has widths larger than 400 meV for AlPdRe, whereas for AlCuFe it is about 80-90 meV and for AlPdMn it is of the order of 110-122 meV. The studies were performed on three samples of the compositions Al70.5Pd21Re8.5, Al68.2Pd22.8Mn9.0, and Al63Cu25Fe12 The junctions were of the types alloy-Au(ln, Al) and alloy-insulator-Au(In, Al), and were studied at different temperatures between that of liquid nitrogen and 2 K, and even to 400 mK for the AlCuFe alloy.
Title:
X-ray study of the incommensurate phase of TlInS2
Authors:
Kashida S. Kobayashi Y.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(4):1027-1035, 1999 Feb 1.
Abstract:
The successive structural phase transitions in the layer compound TllnS(2) have been studied using single-crystal x-ray diffraction. The intermediate phase between 194 K and 214 K is found to be incommensurate; the satellite maps show that the modulation mode which characterizes the intermediate phase has q(i) = (delta, 0, 0.25) (delta approximate to 0.044). It is shown that the previously reported satellite reflections at q = (delta, delta, 0.25) are ascribable to twins. A structure model is presented for the incommensurate phase. In the low-temperature phase below 197 K, the satellite reflections are shifted to a commensurate position, q(c) = (0, 0, 0.25).
Title:
Diffuse scattering from octagonal quasicrystals
Authors:
Lei JL. Hu CZ. Wang RH. Ding DH.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(5):1211-1223, 1999 Feb 8.
Abstract:
Explicit formulae for thermal diffuse scattering from octagonal quasicrystals have been derived in terms of elastic constants. Contours of constant diffuse scattering intensity are calculated. The anisotropic peak shapes vary greatly even for Bragg spots aligned with a given direction in reciprocal space. Diffuse scattering patterns in the plane perpendicular to a given zone axis are associated with corresponding specific elastic constants. Analysis of peak shapes can be used to acquire numerical values of elastic constants if diffuse scattering patterns can be measured precisely.
Title:
Incommensurate phases in the Ba-Mn-Pd-O system
Authors:
Battle PD. Burley JC. Cussen EJ. Darriet J. Weill F.
Source:
(list of journals)
Journal of Materials Chemistry. 9(2):479-483, 1999 Feb.
Abstract:
Polycrystalline samples of bulk composition Ba5Mn3PdO12, Ba6Mn4PdO15, and Ba7Mn5PdO18 have been synthesised and characterised by X-ray diffraction, electron diffraction and magnetometry. These compounds adopt a 2H-related crystal structure consisting of [001] chains of MnO6 and PdO6 polyhedra, with Ba2+ cations separating the chains. The three compounds, each of which is commensurate in the xy plane but incommensurate along the z axis, differ in the ratio of octahedra to trigonal prisms in the chains (3 : 1, 4 : 1 and 5 : 1 respectively). The lattice parameters of the four dimensional trigonal unit cell are typically a approximate to 10.02 Angstrom, c(1) approximate to 4.3 Angstrom, c(2) approximate to 2.61 Angstrom. The homogeneity and crystallinity of the samples increases with the ratio of octahedra to trigonal prisms and is greater in the xy plane than parallel to z. The magnetic susceptibility of all three phases deviates from the Curie-Weiss law below 100 K, but no magnetic phase transition is apparent above 5 K.
Title:
Electron microscopy studies of the long-range ordering in alpha, beta and
gamma phases of BiLaxSr3-O-x(5.5-y)
Authors:
Wolcyrz M. Kepinski L.
Source:
(list of journals)
Journal of Alloys & Compounds. 283(1-2):139-145, 1999 Feb 1.
Abstract:
Selected area electron diffraction and high-resolution transmission electron microscopy together with the crystallographic image processing procedure allowed us to characterize the superstructures of all three phases existing along the BiSr3-xLaxO5.5-y line of the Bi-Sr-La-O system and denoted as beta (x=0), a (x=0.2) and gamma (x=0.833). Their superstructure unit cells were determined in relation to the basic perovskite lattice and the superstructure unit cell parameters were estimated basing on the X-ray powder diffraction data. For beta-phase: a=20.03 Angstrom, b=30.63 Angstrom, c=17.90 Angstrom, alpha=90 degrees, beta=90 degrees, gamma=100.22 degrees. For a-phase: a=12.08 A, b=16.63 A, c=12.13 A, a=90", beta=90.18 degrees, gamma=90 degrees. For gamma-phase: a=14.67 Angstrom, b=10.39 Angstrom, c=11.98 A, alpha=89.82 degrees, beta=89.73 degrees, gamma=90.20 degrees. It is supposed that the superstructure of the beta-phase is a slightly deformed rhombohedral stacking of the basic perovskite blocks. The superstructure unit cell of the alpha-phase is a monoclinic modification of the multiplied perovskite cell. The gamma-phase exhibits triclinic deformation of the perovskite lattice but for some crystallites a complex displacively modulated or even composite-type structure was observed. All samples appeared to be more or less sensitive to the focused electron beam. (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
Resonant X-ray diffraction in incommensurately
modulated crystals. Symmetry consideration
of anisotropic anomalous scattering
Authors:
Ovchinnikova EN. Dmitrienko VE.
Source:
(list of journals)
Acta Crystallographica - Section a - Foundations of
Crystallography. 55(Part 1):20-29, 1999 Jan.
Abstract:
Symmetry restrictions on the intensities and polarization properties of main reflections and their satellites are found for incommensurately modulated crystals in the case of anisotropic anomalous X-ray diffraction near absorption edges. It is shown that the modulation becomes a source of additional anisotropy for each resonant scatterer and induces a modulated behaviour of the susceptibility tensor. The four-dimensional approach is used to calculate the set of possible reflections. It is found that additional ('forbidden') reflections may appear both in the system of main reflections and in the system of satellites. The anisotropy also results in complex azimuthal and polarization properties of each reflection. The displacive modulation is discussed in detail. The ATS reflections corresponding to the resonant X-ray diffraction near the K-edge of iron in pyrrhotite-5.5C are considered.
Title:
The periodic average structure of particular
quasicrystals
Authors:
Steurer W. Haibach T.
Source:
(list of journals)
Acta Crystallographica - Section a - Foundations of
Crystallography. 55(Part 1):48-57, 1999 Jan.
Abstract:
The non-crystallographic symmetry of d-dimensional (dD) quasiperiodic structures is incompatible with lattice periodicity in do physical space. However, dD quasiperiodic structures can be described as irrational sections of no (n > d) periodic hypercrystal structures. By appropriate oblique projection of particular hypercrystal structures onto physical space, discrete periodic average structures can be obtained. The boundaries of the projected atomic surfaces give the maximum distance of each atom in a quasiperiodic structure from the vertices of the reference lattice of its average structure. These maximum distances turn out to be smaller than even the shortest atomic bond lengths. The metrics of the average structure of a 3D Ammann tiling, for instance, with edge lengths of the unit tiles equal to the bond lengths in elemental aluminium, correspond almost exactly to the metrics of face-centred-cubic aluminium, This is remarkable since most stable quasicrystals contain aluminium as the main constitutent. The study of the average structure of quasicrystals can be a valuable aid to the elucidation of the geometry of quasicrystal-to-crystal transformations. It can also contribute to the derivation of the physically most relevant Brillouin (Jones) zone.
Title:
Spin-orbit electric field gradient in cubic ferromagnets: Strong
magnetization-direction dependence of the field gradient distribution
Authors:
Seewald G. Hagn E. Zech E. Kleyna R. Voss M. Forkel-Wirth D. Burchard A.
Source:
(list of journals)
Physical Review Letters. 82(5):1024-1027, 1999 Feb 1.
Abstract:
The electric quadrupole interaction of Pt-191 (I-pi = 3/2(-); T-1/2 = 2.9 d) in an Fe single crystal was measured for magnetization M parallel to the crystallographic [100], [110], and [111] axes. For M parallel to [111] and [110] the distribution of the electric field gradient (EFG) is relatively sharp. For M parallel to [100] the EFG distribution is by a factor of 2.8(6) broader than for M parallel to [111]. data on Os, Re, Ir, and Au in Fe indicate that this behavior seems to be of general nature: In all cases the EFG distribution for M parallel to [100] is considerably broader than for M parallel to [110] and [111].
Title:
Dislocation migration and phason strain relaxation in a
quasicrystal
Authors:
Takeuchi S. Shinoda K. Edagawa K.
Source:
(list of journals)
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical
Properties. 79(2):317-327, 1999 Feb.
Abstract:
Phason flips accompanying the glide of a perfect dislocation has been examined using the Burkov model of the decagonal quasicrystal which is a pseudobinary alloy of Al and transition metals. It is shown that the glide of a perfect dislocation is difficult without producing chemical disorder. There are three extreme cases in the glide of a dislocation in quasicrystal: firstly conservative glide at a very high temperature where the complete phason relaxation occurs; secondly, glide producing chemical disorder; thirdly glide producing a stacking fault with the fault vector of the phason component of the Burgers vector.
Title:
Domain wall solutions for EHM model of crystal
Authors:
Shigenari T. Dmitriev SV. Vasiliev AA. Abe K.
Source:
(list of journals)
Journal of the Physical Society of Japan. 68(1):117-125, 1999 Jan.
Abstract:
For a one-dimensional discrete model of a crystal the solution of the form of a moving domain wall in an odd-periodic commensurate structure was derived in the continuum approximation. The energy of the commensurate odd-periodic structure; the width and the energy of domain wall were expressed in terms of the amplitudes of harmonics of carrying commensurate structure. With the use of the result by Ishibashi, the relation between domain wall solutions in odd-periodic and even-periodic commensurate structures Tvas established. The applicability and the accuracy of the solutions were also discussed. The obtained solutions were found to he more accurate and general than those by other authors.
Title:
Phenomenological description of the sevenfold phase of betaine calcium
chloride dihydrate. I. Coupling to the electric field
Authors:
Hlinka J. Iwata M. Ishibashi Y.
Source:
(list of journals)
Journal of the Physical Society of Japan. 68(1):126-133, 1999 Jan.
Abstract:
The sevenfold phase of Betaine Calcium Chloride Dihydrate (q(c)/c* = 2/7) is analyzed in the framework of the conventional phenomenological model for the type I commensurate phase. Parameters of the potential are determined from a set of selected experimental data. Quantitative results are obtained for various physical properties, including the relaxation frequency of the ("pseudo") phason gap and the mobility of the domain walls in the commensurate phase, the thickness and mutual distance of the phase solitons in the incommensurate phase, field-temperature phase diagram and the amplitude of the order parameter.
Title:
A note on the long period commensurate
structures - Comment
Authors:
Massidda V.
Source:
(list of journals)
Journal of the Physical Society of Japan. 68(1):315, 1999 Jan.
Title:
A note on the long period commensurate
structures - Reply
Authors:
Ishibashi Y.
Source:
(list of journals)
Journal of the Physical Society of Japan. 68(1):316, 1999 Jan.
Title:
Antiphase modulated structure of
Fe2O3(ZnO)(15) studied by high-resolution electron microscopy
Authors:
Li CF. Bando Y. Nakamura M. Kimizuka N.
Source:
(list of journals)
Journal of Solid State Chemistry. 142(1):174-179, 1999 Jan.
Abstract:
As one of our systematic studies of the modulated structures of a series of new homologous compounds RMO3(ZnO)(m) (R = Sc, In, Y, and La; M = In, Fe Ga, and AI; nl = integer), this paper reports the modulated structure of Fe2O3(ZnO)(15) (R=Fe; M= Fe) studied by high-resolution electron microscopy. It is found that the main and satellite spots in the diffraction patterns can be indexed as ha*+kb*+lc*+mq by considering a mono-clinic unit cell of a = 0.57 nm, b = 0.33 nm, c = 3.5 nm, and beta = 92 degrees and a modulation wave vector of q = b*/34.8+c*/2. The possible space groups for the basic structure are Ct, Cm, and C2/m, and the possible four-dimensional superspace groups for the modulated structure are C-1(C2), C-(1 over bar)(Cm), and C-1 (1 over bar)(C2/m). The crystal structure of Fe2O3(ZnO)(15) consists of Fe-O layers interleaved with 16 Fe/Zn-O layers. In the high-resolution image, the modulated structure appeared as zigzag-shaped contrasts among the Fe/Zn-O layers, where Fe is in high concentration. Compared with those of InMO3(ZnO)(m) (R = In; M= In, Fe and Ga) reported in our earlier paper, the special features of the present modulated structure are the half-periodicity relative shift of the neighboring zigzag-shaped contrasts and the appearance of modulation within the Fe-O layers. (C) 1999 Academic Press.
Title:
Atomic and electronic structure of quasiperiodic and
crystalline Mg-61 at.% Al alloys
Authors:
Fournee V. Belin-Ferre E. Donnadieu P. Flank AM. Muller H.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(1):191-208, 1999 Jan 11.
Abstract:
Mg-Al alloys with composition Mg-61 at.% Al display two types of structure: a stable crystalline state (the so-called beta-Mg2Al3) and a metastable one showing both quasiperiodicity and inflation symmetry. The atomic as well as electronic structures of stable crystalline beta- Mg2Al3 and a metastable Mg39Al61 phase that exhibits quasiperiodicity and inflation symmetry have been studied thanks to x-ray spectroscopy techniques. Extended x-ray absorption finestructure experiments performed above the Al and Mg K absorption edges have probed the local atomic order around Mg as well as Al atoms. X-ray emission and absorption spectroscopies have investigated occupied and unoccupied electronic states around Mg and Al. The local order has been found to be the same around Al atoms in both alloys, whereas around Mg atoms differences are seen for higher shells than first neighbours. This suggests that the same clusters must be involved in both phases and that the quasiperiodicity is connected with modification of the Mg atom environment forming the linkage between large clusters. On the other hand, the electronic distributions show differences from beta-Mg2Al3 to the quasiperiodic phase that are consistent with the local order studies. A pseudogap is observed in the Mg and Al electronic structures which is more marked in the quasiperiodic phase than the crystalline alloy. By analogy to quasicrystals, we suggest the enhancement observed is due to the occurrence of an inflation mechanism in the arrangement of the clusters in the quasiperiodic alloy with respect to the beta-Mg2Al3 crystal.
Title:
Elastic field for a straight dislocation in a decagonal
quasicrystal
Authors:
Li XF. Duan XY. Fan TY. Sun YF.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 11(3):703-711, 1999 Jan 25.
Abstract:
A straight dislocation line in a decagonal quasicrystal is considered. For a decagonal quasicrystal of point groups 10, <(10)over bar> and 10/m with a straight dislocation parallel to the periodic direction, the basic governing equations are solved by decoupling this problem into a plane elasticity problem and an antiplane elasticity problem. For the latter, the solution is known; for the former, it is reduced to a single equation, Delta(4)F(x, y) = 0, Delta being the harmonic operator, by introducing a displacement function F. A general solution is formulated. Using a general solution and the Fourier transform, the explicit expressions for the dislocation-induced elastic field in a decagonal quasicrystal are obtained and the energy per unit length on the dislocation is given.
Title:
New boron based nanostructured materials
Authors:
Boustani I. Quandt A. Hernandez E. Rubio A.
Source:
(list of journals)
Journal of Chemical Physics. 110(6):3176-3185, 1999 Feb 8.
Abstract:
Based on a series of ab initio studies we have pointed out the remarkable structural stability of nanotubular and quasiplanar boron clusters, and postulated the existence of novel layered, tubular, and quasicrystalline boron solids built from elemental subunits. The present study illustrates and predicts qualitative structural and electronic properties for various models of nanotubular and layered boron solids, and compares them to well-known tubular and layered forms of pure carbon and mixed boron compounds. (C) 1999 American Institute of Physics. .
Title:
Superconductivity in two-leg spin ladders [A(2)Cu(2)O(3)](5)[CuO2](7) (A =
Sr, Ca, Bi, Y, Pb)
Authors:
Leonyuk L. Babonas GJ. Szymczak R. Szymczak H. Baran M. Reza A. Maltsev V. Shvanskaya L. Rybakov V.
Source:
(list of journals)
Europhysics Letters. 45(3):387-392, 1999 Feb 1.
Abstract:
The single crystals with two-leg spin-ladder-type structure were investigated. According to the structural, magnetic, optical and resistivity data obtained, the studied crystals [A(2)Cu(2)O(3)](5)[CuO2](7) were shown, for the first time, to be high-T-c superconductors (T-c=80 K) which belong to the class of cuprates with incommensurate-type structure.
Title:
High-strength materials produced by precipitation of icosahedral
quasicrystals in bulk Zr-Ti-Cu-Ni-Al amorphous alloys
Authors:
Xing LQ. Eckert J. Loser W. Schultz L.
Source:
(list of journals)
Applied Physics Letters. 74(5):664-666, 1999 Feb 1.
Abstract:
Zr62-xTixCu20Ni8Al10(3 less than or equal to x less than or equal to 5) amorphous alloys crystallize via precipitation of icosahedral quasicrystals in the primary crystallization step, leading to nano-sized quasicrystals embedded in an amorphous matrix. Ti is the decisive component favoring the precipitation of quasicrystals. The mechanical properties of the crystallized alloys with different amounts of quasicrystalline phase were measured by compression and bending tests. If the volume fraction of quasicrystalline precipitates is below about 50%, the strength increases with an increasing amount of quasicrystalline precipitates, but the ductility does not decrease significantly in comparison with the amorphous counterpart. The fracture stress reaches 1835 MPa for 50 vol % of quasicrystals. Quasicrystalline precipitates of more than 60 vol % lead to reduction of ductility and strength. This shows a way of producing bulk quasicrystalline materials of high strength by crystallization of bulk amorphous alloys. (C) 1999 American Institute of Physics. .
Title:
Charge-density waves and surface Mott insulators for adlayer
structures on semiconductors: Extended Hubbard modeling
Authors:
Santoro G. Scandolo S. Tosatti E.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(3):1891-1901, 1999 Jan 15.
Abstract:
Motivated by the recent experimental evidence of commensurate surface charge-density waves (CDW) in Pb/Ge(lll) and Sn/Ge(lll) root 3-adlayer structures, as well as by the insulating states found on K/Si(lll):B and SiC(0001), we have investigated the role of electron-electron interactions, and also of electron-phonon coupling, on the narrow surface-state band originating from the outer dangling-bond orbitals of the surface. We model the root 3 dangling-bond lattice by an extended two-dimensional Hubbard model at half filling on a triangular lattice. The hopping integrals are calculated by fitting first-principle results for the surface band. We include an on-site Hubbard repulsion U and a nearest-neighbor Coulomb interaction V, plus a long-ranged Coulomb tail. The electron-phonon interaction is treated in the deformation potential approximation. We have explored the phase diagram of this model including the possibility of commensurate 3 X 3 phases, using mainly the Hartree-Fock approximation. For U larger than the bandwidth we find a noncollinear antiferromagnetic spin-density wave (SDW) insulator, possibly corresponding to the situation on the SiC and K/Si surfaces. For U comparable or smaller, a rich phase diagram arises, with several phases involving combinations of charge and spin-density-waves (SDW), with or without a net magnetization. We find that insulating, or partly metallic 3 X 3 CDW phases can be stabilized by two different physical mechanisms. One is the intersite repulsion V, which together with electron-phonon coupling can lower the energy of a charge modulation. The other is a magnetically-induced Fermi-surface nesting, stabilizing a net cell magnetization of 1/3, plus a collinear SDW, plus an associated weak CDW. Comparison with available experimental evidence, and also with first-principle calculations is made. .
Title:
Gold-induced faceting on a Si(001) vicinal surface: Spot-profile-analyzing
LEED and reflection-electron-microscopy study
Authors:
Minoda H. Yagi K. Heringdorf FJMZ. Meier A. Kahler D. von Hoegen MH.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(3):2363-2375, 1999 Jan 15.
Abstract:
Au-induced faceting on a 40 off Si(001) vicinal surface at temperatures between 750 and 880 degrees C was studied by in situ high-resolution low-energy electron diffraction and ultrahigh vacuum reflection electron microscopy. The formation of an Au-induced incommensurate 5x3.2 reconstruction on (001) terraces triggers the transformation of the initial regular step train of the vicinal surface into a "hill-and-valley" structure composed of very wide (001) terraces and step bands. With further increasing Au coverage the step bands transform to well-ordered (119) facets, which also exhibit the Au-induced reconstruction. For,adsorption temperatures below 800 degrees C the transformation to the well-ordered (119) facet is kinetically hindered: an irregular mixture of (115), (117), and (119) facets is observed. The (001) terraces and facets are alternately arranged to form;a hill-and-valley structure with an average period of similar to 400 nm and terrace lengths of more than several hundreds of mu m. Driving force for the large-scale morphological transformation into the hill-and-valley structure is the decrease of surface free energy of the (001) and the (119) surface due to the formation of Au-induced reconstruction on (119) facets as well as on (001) areas. .
Title:
Cubic superspace symmetry and inflation rules in metastable MgAl alloy
Authors:
Elcoro L. Perez-Mato JM.
Source:
(list of journals)
European Physical Journal B. 7(1):85-89, 1999 Jan.
Abstract:
The diffraction properties of a quenched Al-Mg alloy which has been recently termed as a "cubic quasicrystal" are quantitatively reanalyzed. It is shown that the phase can be interpreted within the superspace formalism as an ordinary incommensurately modulated structure. The cubic six-dimensional superspace group that describes its symmetry properties has been determined. The additional inflation symmetry features exhibited by the diffraction diagram can be summed up by its invariance for the inflation factor (2 + root 3), but this property has its origin in the specific value of the modulus of the modulation wave vectors, which is composition dependent. Other particular values of this modulus can give rise to similar scaling properties. Further experiments are required to ellucidate if the mentioned inflation symmetry is a fortuitous situation in a composition dependent wave vector, or has indeed the physical significance which would allow to describe the system as a "cubic quasicrystal".
Title:
Mossbauer study of superconducting Bi2Sr2Ca2Cu3(1-x)Fe3xO10
Authors:
Bhargava SC. Chakrabarty JS. Singh S.
Source:
(list of journals)
Solid State Communications. 109(5):311-316, 1999.
Abstract:
A Mossbauer study of Fe in the Bi2Sr2Ca2Cu3(1-x)Fe3xO10 superconductor is described. Fe is found to have a strong preference for the square-planar site. This enables study of the characteristics of this site in the superconductor. (C) 1999 Published by Elsevier Science Ltd.
Title:
Decagonal epilayers on the icosahedral quasicrystal
Al70Pd20Mn10
Authors:
Bolliger B. Erbudak M. Vvedensky DD. Kortan AR.
Source:
(list of journals)
Physical Review Letters. 82(4):763-766, 1999 Jan 25.
Abstract:
The pentagonal surface of the icosahedral quasicrystal Al70Pd20Mn10 becomes decagonal upon sputtering with Ar+ ions at elevated temperatures. This decagonal surface has a vastly different chemical composition (Al22Pd56Mn22) than bulk decagonal quasicrystals (Al70Pd10Mn20) and is coherent with the icosahedral substrate across the entire macroscopic sample. The transformation of this surface back to the original icosahedral structure and composition during annealing is followed in real space and in real time with secondary-electron imaging. The structural changes during this transformation are discussed in light of current models of decagonal and icosahedral quasicrystals.
Title:
Interaction between magnetic order and the vortex lattice in HoNi2B2C
Authors:
Dewhurst CD. Doyle RA. Zeldov E. Paul DM.
Source:
(list of journals)
Physical Review Letters. 82(4):827-830, 1999 Jan 25.
Abstract:
Local Hall probe array magnetization measurements have been made on single crystals of the magnetic superconductor HoNi2B2C. Measured flux profiles show that surface barriers dominate the hysteresis below T-c(similar or equal to 8.9K) except in a narrow temperature range between 5 and 5.75 K where superconductivity is strongly suppressed due to the onset of an a-axis incommensurate ordering of the Ho moments. The data presented show that the magnetic order also has a profound influence on the nonequilibrium (vortex-pinning) properties of the superconducting state.
Title:
Interaction of foreign macrodroplets in a nematic liquid
crystal and induced supermolecular
structures
Authors:
Lev BI. Tomchuk PM.
Source:
(list of journals)
Physical Review E. 59(1 Part A):591-602, 1999 Jan.
Abstract:
The behavior of a system of macroscopic particles introduced in a nematic liquid crystal is studied theoretically. The energy of the pair interparticle interaction associated with the director elastic field deformation is found. The interaction intensity and character are studied as functions of the distance, the geometric parameters of foreign macroparticles, and the value of their anchoring to the mesophase. The interparticle interaction can cause nontrivial collective behavior that results in the formation of new spatially modulated structures in the macroparticle system. The periodic arrangement of chiral particles that induces a helical structure can give rise to two incommensurable periods in the average orientation distribution of macroparticles. .
Title:
Diffuse scattering from decagonal quasicrystals
Authors:
Lei JL. Wang RH. Hu CZ. Ding DH.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(2):822-828, 1999 Jan 1.
Abstract:
General formulas for both thermal and quenched diffuse scattering from quasicrystals are applied to the case of decagonal quasicrystals from corresponding elasticity theory. Contours of constant diffuse scattering intensity are illustrated. The anisotropic peak shapes vary greatly even for Bragg spots aligned with a given direction in reciprocal space. Diffuse scattering patterns in the plane perpendicular to a given zone axis are associated with corresponding specific elastic constants. Quantitative examination of diffuse scattering patterns may yield numerical values of the elastic constants. .
Title:
Influence of phason flips on electronical properties of
quasicrystalline model systems
Authors:
Schwabe H. Kasner G. Bottger H.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(2):861-870, 1999 Jan 1.
Abstract:
The influence of single phason flips on the electronic properties of quasicrystalline model systems is investigated instead of using random tiling models. In a tight binding model of the Penrose lattice there are seven different types of possible phason flips according to the involved vertex stars. Tolerating a random number of flips of only one type simultaneously and avoiding multiple flips the spectrum, the eigenstates and the de conductance of this model system as a function of the flip type are calculated. Every flip in the lattice leads to a defect state localized at the flipped atom sites with an eigenenergy outside the spectrum of the unflipped lattice. All types of flips result in smoothing out the density of states and very strong fluctuations of the conductance in most of the energy regions. But the strength of this effect at a given energy depends strongly on the type of the flips in the lattice. A certain quasicrystalline pattern showing resonance at this energy can be more or less influenced by the flips, resulting in a strong or weak effect to the conductance. So the investigation of the conductance under the influence of special flips offers the possibility to study the relevance of several local configurations to the electronic properties at a given energy. .
Title:
Multiple-scattering x-ray-absorption fine-structure
Debye-Waller factor calculations
Authors:
Poiarkova AV. Rehr JJ.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(2):948-957, 1999 Jan 1.
Abstract:
An efficient local equation-of-motion method is introduced for calculations of the mean-square half-pathlength fluctuations sigma(j)(2) in multiple-scattering x-ray-absorption fine-structure Debye-Waller factors in aperiodic systems. Given a few local force constants, the method yields sigma(j)(2) via projected densities of modes or via the displacement-displacement correlation function in real time, over a few vibration cycles. The calculation scales linearly with the system size and does not rely on any symmetry considerations. Sample applications are presented for crystalline Cu and Ge, and zinc tetraimidazole. .
Title:
Surface oxidation of Al-Cu-Fe alloys: a comparison of
quasicrystalline and crystalline phases
Authors:
Pinhero PJ. Anderegg JW. Sordelet DJ. Besser MF. Thiel PA.
Source:
(list of journals)
Philosophical Magazine B-Physics of Condensed Matter Structural Electronic
Optical & Magnetic Properties. 79(1):91-110, 1999 Jan.
Abstract:
We have used X-ray photoelectron spectroscopy and Auger electron spectroscopy to examine the characteristics of oxide surfaces on a family of Al-Cu-Fe alloys. The alloys studied are compositionally similar but structurally different: two are crystalline and one is quasicrystalline. The samples all are formed by consolidation of powders, resulting in multiple grains with random surface orientations. They are oxidized to saturation in a variety of environments at room temperature. Under the conditions of our experiments, there is no detectable difference in the oxidation characteristics of the three phases. That is, there is no difference in the elemental constituents which oxidize, or in the relative extent of oxygen-induced Al segregation, or in the depth of the oxide formed. Hence, the oxidation chemistry of these alloys is determined by their Al-rich chemical composition, and not by their atomic or electronic bulk structure, under these conditions.
Title:
Heterophase quasicrystalline interfaces and their
characterization
Authors:
Mandal RK.
Source:
(list of journals)
Philosophical Magazine B-Physics of Condensed Matter Structural Electronic
Optical & Magnetic Properties. 79(1):157-161, 1999 Jan.
Abstract:
The characterization of heterophase interfaces in icosahedrally related systems cannot be accomplished by the available three-dimensional crystalline terms owing to lack of periodicity of at least one of the phases constituting the boundary. The purpose of this communication is to show that the existing method of interface characterization in terms of registry of the two underlying lattices can be recovered for quasiperiodic cases by extending the concept to six-dimensional hyperspace. This has been demonstrated by the method of characterizing the interface between icosahedral and decagonal quasicrystals found in Al-Pd-Mn system.
Title:
Gas-sensing properties of spinodally decomposed (Ti,Sn)O-2 thin films
Authors:
Arakawa S. Mogi K. Kikuta K. Yogo T. Hirano S.
Source:
(list of journals)
Journal of the American Ceramic Society. 82(1):225-228, 1999 Jan.
Abstract:
The gas-sensing properties of spinodally decomposed (Ti,Sn)O-2 thin films on sapphire substrates were investigated for CO, C3H8, and C2H5OH, and hydrogen gases at a temperature of 500 degrees C. The variation in the d-spacing of the (101) plane of (Ti0.5Sn0.5)O-2 films showed behavior that was typical of spinodal decomposition during annealing at a temperature of 900 degrees C, Transmission electron micrographs of the spinodally decomposed (Ti,Sn)O-2 films on sapphire (01 (1) over bar 2) substrates revealed the characteristic modulated structure. The modulated lamella microstructure consisted of TiO2- and SnO2-rich regions at intervals of similar to 10 nm. The films were very sensitive to hydrogen gas and revealed anisotropic electrical conduction that was influenced by the modulated microstructure, which is characteristic of spinodal decomposition.
Title:
Quantum waveguide theory of serial stub structures
Authors:
Jin GJ. Wang ZD. Hu A. Jiang SS.
Source:
(list of journals)
Journal of Applied Physics. 85(3):1597-1608, 1999 Feb 1.
Abstract:
The electronic behaviors in quantum wires with serial stubs are studied. A general theory of quantum waveguide based on transfer matrix method is developed and is used to treat periodic stub structures, serial stub structures with a defect stub, and Fibonacci stub structures. A number of interesting physical properties in connection with electronic transmission, energy spectra, and charge density distributions in these structures, are found theoretically. In particular, we find that whether there are periodicity and symmetry in the transmission and energy spectra depends on the commensurability of the length parameters. If one length ratio is incommensurate, then the transmission and energy spectra do not exhibit periodicity and symmetry even for periodic stub structures. In particular, the quasiperiodic behaviors are shown in Fibonacci stub structures proposed by us whenever the length parameters are commensurate. The experimental relevance is also addressed briefly. (C) 1999 American Institute of Physics. .
Title:
Non-orthogonal tight-binding new method for alloys, including Slater-Friedel
screening corrections
Authors:
Abramovici G.
Source:
(list of journals)
Solid State Communications. 109(4):253-256, 1999.
Abstract:
We have built a new Tight-Binding model for (first series) transition metal alloys, in which no adjustable parameter is needed. We take screening charge corrections and overlapping two-center terms into account and calculate for the first time an explicit expression of the effective Hamiltonian. Charge transfer is a parameter, which provides a simple description of the electronic structure. We get an analytical equation of the charge transfer and resolve it numerically by a self-consistent method, for an approximant of a quasicrystal. (C) 1998 Elsevier Science Ltd. All rights reserved.
Title:
Self-diffusion in icosahedral Al72.4Pd20.5Mn7.1 and phason percolation at low
temperatures studied by Al-27 NMR
Authors:
Dolinsek J. Apih T. Simsic M. Dubois JM.
Source:
(list of journals)
Physical Review Letters. 82(3):572-575, 1999 Jan 18.
Abstract:
Aluminum self-diffusion in a monodomain icosahedral quasicrystal Al72.4Pd20.5Mn7.1 has been studied at temperatures between 4 and 400 K by Al-27 NMR measurements of the decay of transverse nuclear spin magnetization in a spatially inhomogeneous electric field gradient. Temperature dependence of the renormalized diffusion constant can be explained in the framework of the Kalugin-Katz phason-assisted diffusion model where the atomic jumps occur as a result of the presence of matching-rules violation defects. The observed self-diffusion process resembles a percolation transition with the percolation threshold at 72 K. .
Title:
Activation parameters of plastic flow in icosahedral Al-Cu-Fe
Authors:
Giacometti E. Baluc N. Bonneville J.
Source:
(list of journals)
Philosophical Magazine Letters. 79(1):1-7, 1999 Jan.
Abstract:
Poly-quasicrystalline samples of an icosahedral Al-Cu-Fe alloy have been deformed in compression tests under constant-strain-rate conditions at temperatures ranging from room temperature up to 1020 K (m approximate to 1150 K, where T-m is the melting temperature). The activation volumes, which were measured by performing load relaxation experiments, were found to be small and reveal that two different thermally activated mechanisms belonging to two different temperature regimes, are responsible for plastic flow of icosahedral Al-Cu-Fe; the first mechanisms operates between 770 and 960 K, and the second at higher temperatures. The activation enthalpy Delta H has been determined for the low-temperature regime. Under the assumption that the entropy term arises mainly from the variation in the shear modulus with temperature, the activation Gibbs free energy Delta G has been deduced for the corresponding rate-controlling mechanism.
Title:
Synthesis, characterization and hydrogenation behaviour of composite hydrogen
storage alloys, LaNi (5)/La2Ni7, LaNi3
Authors:
Srivastava S. Srivastava ON.
Source:
(list of journals)
Journal of Alloys & Compounds. 282(1-2):197-205, 1999 Jan 15.
Abstract:
The present study deals with investigations on the composite hydrogen storage materials LaNi5/La2Ni7, LaNi3, for efficient, high energy density Ni-MH batteries. To achieve this goal extensive investigations were carried out to study the effect of presence of secondary phases on the main phase LaNi5 with reference to hydrogenation behaviour and structural-microstructural characterizations using XRD, TEM and SEM techniques. Alloys were synthesized through melt-casting with varying concentrations of secondary phases like La2Ni7, LaNi3, Ni (minor phases), i.e., 55%, 30%, 5% and 0% by a special technique of pellet encapsulation. Structural characterizations using the XRD technique confirmed the formation of secondary phases together with the major phase LaNi5,. The diffraction patterns after hydrogenation did not exhibit secondary phase diffraction peaks, instead the resulting phase was found to be single phasic, exhibiting LaNi5 like diffraction patterns with an unusual intensity distribution. TEM investigations showed the presence of two types of modulated phases; one of which corresponds to a approximate to 1.5a(o), c approximate to c(o), and the other to a approximate to 1.3a(o), c approximate to c(o), together with the parent phase (LaNi5), in the as-synthesized and hydrogenated/dehydrogenated versions, corresponding to alloy with secondary phase concentration upto 30%, (a(o) and c(o) being lattice constants of the parent LaNi5 structure). The signature of the modulated phases were not present in XRD patterns, but could be seen in the selected area electron diffraction patterns, suggesting that modulation has taken place in local areas of the basal plane, due to ordering of hydrogen atoms. These modulated unit cells can be modeled in terms of the original lattice of LaNi5, by inserting and ordering of hydrogen atoms at viable interstitial sites. Microstructural evaluations through SEM revealed that secondary phases suppressed pulverization. Investigations of the hydrogenation behaviour of these alloys showed that hydrogen storage capacity and desorption kinetics did not decrease for minor concentrations of secondary phases, but a decrease was found for the alloys having higher concentrations of secondary phases. Similar results were obtained for alloy MmNi(5), where secondary phases corresponded to Mm(2)Ni(7) and MmNi. (C) 1999 Elsevier Science S.A. All rights reserved.
Title:
Neutron diffraction study of the magnetic structure of
U0.1Np0.9Ru2Si2
Authors:
Dervenagas P. Hiess A. Lander GH. Wastin F. Rebizant J.
Source:
(list of journals)
Solid State Communications. 109(1):35-39, 1999.
Abstract:
The magnetic structure of the U0.1NP0.9Ru2Si2 solid solution was studied using neutron diffraction techniques on a single crystal. At T-N = 25 K this compound orders magnetically into an incommensurate longitudinally modulated structure which is very similar to the one reported for pure NpRu2Si2. At T-com approximate to 13 K, however, an incommensurate to commensurate transition takes place and the low temperature magnetic structures is the same as the one observed in URu2Si2. The calculated value of the magnetic moment is consistent with the published neutron diffraction and Mossbauer results. (C) 1998 Elsevier Science Ltd. All rights reserved.
Title:
Magnetic and electrical properties of a stable Zn-Mg-Ho icosahedral
quasicrystal
Authors:
Kashimoto S. Matsuo S. Nakano H. Shimizu T. Ishimasa T.
Source:
(list of journals)
Solid State Communications. 109(1):63-67, 1999.
Abstract:
We investigated the electrical resistivity and the magnetism of heavy-rare-earth-based Zn60Mg30Ho10 F-type icosahedral quasicrystals in the temperature region between 2 K and room temperature below 80 kOe in magnetic field. The maximum value of the electrical resistivity is 159 mu Omega cm which is comparatively lower than other quasicrystal systems. Below 15 K, the magnetic-field dependence exhibits a magnetoresistance maximum which has not been observed in quasicrystals studied to date, and the temperature dependence shows a resistance minimum. The temperature dependence of the magnetic susceptibility follows, a Curie-Weiss law between 10 K and room temperature corresponding to the effective number of Bohr magneton 10.6 for every Ho atom in the sample. The earlier mentioned anomalies are considered to be related to the dense and large magnetic moments located at the quasiperiodic lattice. (C) 1998 Elsevier Science Ltd. All rights reserved.
Title:
Monte Carlo simulations of icosahedral quasicrystal growth
and melting
Authors:
Dmitrienko VE. Astaf'ev SB. Kleman M.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(1):286-293, 1999 Jan 1.
Abstract:
Three-dimensional Monte Carlo simulations for atomic growth and melting of icosahedral quasicrystals an presented. It is supposed that the atoms can be locally ordered both icosahedrally and dodecahedrally, and the preferred ordering arises during the growth according to statistical and energetical criteria. All the waiting positions (where an atom could be in principle added) are generated on the cluster surface at every stage of the growth. The binding energies of all atoms and all waiting positions are computed with an oscillating Friedel potential. Then an object, chosen at random from the joined list of surface atoms and waiting positions, is treated according to the Metropolis criterion. The suggested growth process is completely local. It is found that the speed and sign of the process and the resulting structures depend strongly on the growth parameters. Most frequently, the main structural motif of grown clusters is the dodecahedral local ordering (DLO) whereas the icosahedral local ordering (ILO) is usually rare. However, the latter becomes dominant for rather exotic interatomic potentials or for high growth rates. The phenomenon of critical seed size is observed: for those parameters, for which large clusters grow, small enough seeds stop to grow and may even melt, The grown quasicrystals are faceted and their sizes in perpendicular space are rather close to those predicted theoretically and observed experimentally. .
Title:
Existence and localization of surface states on Fibonacci
quasicrystals: A tight-binding study
Authors:
Zijlstra ES. Fasolino A. Janssen T.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(1):302-307, 1999 Jan 1.
Abstract:
Surface states of the Fibonacci chain are studied within the tight binding off-site model for clusters and approximants by numerical and transfer matrix methods. In each gap of the bulk spectrum a surface stale can exist. The existence and energy of a surface state depend on the boundary conditions at the surface. The exponential envelope of surface states is used to define a localization length, which is shown to depend only on the energy of a specific state. .
Title:
Magnetic and transport properties of single-grain R-Mg-Zn icosahedral
quasicrystals [R = Y, (Y1-xGdx), (Y1-xTbx), Tb, Dy, Ho, and
Er]
Authors:
Fisher IR. Cheon KO. Panchula AF. Canfield PC. Chernikov M. Ott HR. Dennis K.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(1):308-321, 1999 Jan 1.
Abstract:
We report measurements of the de magnetization, the low-held ac magnetic susceptibility, and the electrical resistivity of large (up to 0.5 cm(3)) single-grain samples of icosahedral R-Mg-Zn (R = Y, Tb, Dy, Ho, and Er). The dc magnetization and ac magnetic susceptibility data both indicate that icosahedral Tb-Mg-Zn and Dy-Mg-Zn undergo a transition to a spin-glass state at T-f = 5.8 and 3.6 K, respectively, while low-temperature ac susceptibility measurements show that T-f = 1.95 and 1.3 K for Ho-Mg-Zn and Er-Mg-Zn, respectively. For the series of solid solutions (Y1-xTbx)-Mg-Zn, the freezing temperature T-f varies approximately as x(2/3). The (Y1-xGdx)-Mg-Zn solid solutions have lower T-f values than (Y1-xTbx)-Mg-Zn for the same magnetic rare-earth concentrations (x), indicating that local moment anisotropy caused by crystalline electric-field effects plays a significant role in increasing T-f. On the other hand, angular-dependent studies show that the de magnetization for T > T-f is isotropic within the experimental uncertainty. The electrical resistivity rho(T) of the single-grain samples is only weakly temperature dependent, with a small, negative d rho/dT. Absolute values of the resistivity fall in the range between 150 and 200 mu Omega cm, which is distinctly lower than the values previously reported for other thermodynamically stable icosahedral quasicrystals. .
Title:
Partial phonon density of states of Fe in an icosahedral
quasicrystal (Al62Cu25.5Fe12.5)-Fe-57 by inelastic
nuclear-resonant absorption of 14.41-keV synchrotron radiation
Authors:
Brand RA. Coddens G. Chumakov AI. Calvayrac Y.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(22):R14145-R14148, 1999 Jun 1.
Abstract:
We use a recently developed method based on inelastic nuclear-resonant absorption of x rays to measure the iron-partial vibrational density of states (VDOS) in a quasicrystal. The results differ from those obtained by inelastic neutron scattering in an astounding way: whereas the neutron results exhibit a very smooth and featureless behavior, the iron-partial VDOS is strongly peaked at one energy value.
Title:
Antiferromagnetic properties of ternary silicides RNiSi (R = Tb-Er)
Authors:
Szytula A. Balanda M. Hofmann M. Leciejewicz J. Kolenda M. Penc B. Zygmunt A.
Source:
(list of journals)
Journal of Magnetism & Magnetic Materials. 191(1-2):122-132, 1999 Jan.
Abstract:
Neutron diffraction and magnetometric measurements show that RNiSi (R = Tb-Er) compounds are antiferromagnetic at low temperatures. At 1.5 K, TbNiSi exhibits a square-modulated order of magnetic moments which transforms at 9 K into a sine-modulated magnetic structure stable up to the Neel point at 16 K. The same magnetic behavior was found in DyNiSi with the magnetic phase transition at 3 K and the Neel point at 8.8 K. At 1.5 K, the antiferromagnetic order in HoNiSi is collinear described by the wave vector \1/2, 0, 1/2\. The ordering changes to a sine-modulated structure with the wave vector \0.53, 0.18, 0.336\ at 3.2 K and vanishes at the Neel point at 4.1 K. A collinear antiferromagnetic structure with the wave vector \0, 1/2, 1/4\ was found at 1.5 K in ErNiSi. It transforms at 2.2 IC. into a sine-modulated order described by the wave vector \0.197, 0.515, 0.154\. The Neel point is at 3.3 K. In RNiSi (R = Tb, Dy, Ho) the magnetic moment was found to be aligned along the b-axis, while in ErNiSi it is localized in the (a-c) plane. In all compounds the magnitude of the ordered magnetic moment at 1.5 K amounts nearly to the free ion values for the respective R3+ ions. (C) 1999 Elsevier Science B.V. All rights reserved.
Title:
Short-term X-ray variability of black hole candidates: Ginga results
Authors:
Negoro H.
Source:
(list of journals)
Nuclear Physics B-Proceedings Supplements. 69(1-3):344-347, 1999 Jan.
Abstract:
The superposition technique is a new analysis method to obtain average properties of certain kinds of aperiodic time variations. Real average profiles of X-ray shots in Cyg X-l, GS 339-4, GS 2023+338 and GS 1124-68 in the hard state are obtained in detail by applying the technique to rapid time Variations of these sources observed by Ginga. The shot profiles obtained are consistent with structures of power spectral densities and phase (time) lags below a few Hz. Soft energy spectra of the S-ray shots are thought to be the origin of soft excess components in time-averaged energy spectra. The shot profiles imply that the X-ray shots arise from aperiodic mass accretion in the advection dominated disk. These results are briefly described.
Title:
Four-component intergrowth structures of the metal-ion cage complexes
fac-(1,5,9,13,20-pentamethyl-3,7,11,15,18,22-hexaazabicyclo[7.7.7]tricosane)M
-II diperchlorate hydrate, [M(C22H48N6)](ClO4)(2)xH(2)O, M = Ni, Zn
Authors:
Haller KJ. Rae AD. Bygott AMT. Hockless DCR. Ralph SF. Geue RJ. Sargeson AM.
Source:
(list of journals)
Acta Crystallographica - Section B, Structural Science. 55(Part 3):380-388,
1999 Jun 1.
Abstract:
The crystal structures of (1,5,9,13,20-pentamethyl-3,7,11,15,18,22-hexaazabicyclo [7.7.7]tricosane-kappa(6)N,N',- N ",N''',N"",N''''')nickel(II) diperchlorate-x(water) (x = 0.530), [Ni(C22H48N6)](ClO4)(2). 0.530H(2)O, and (1,5,9,13,20-pentamethyl-3,7,11,15,18,22-hexaazabicyclo- [7.7.7]tricosane-kappa(6)N,N',N ",N''',N"'',N"''')zinc(II) diperchlorate-x(water) (x = 0.608), [Zn(C22H48N6)](ClO4)(2).-. 0.608H(2)O, are isomorphic and each is described as an intergrowth of four substructures, consistent with different modulations of an idealized parent structure of space group C2/c. Two substructures correspond to alternative orientations of a C (1) over bar structure for which x = 0 in the general formula [M(C22H48N6)](ClO4)(2). xH(2)O. and two substructures correspond to alternative origins of a P2(1)/n structure for which x = 1. Twinning also occurs. An analysis of the pseudosymmetry, a description of the refinement and a description of the refined structures are presented. The MN6 coordination geometry is essentially octahedral, in contrast to the trigonal-prismatic geometry observed for the Cd-II and Hg-II complexes of the same ligand.
Title:
Extension of three-dimensional space-group generators to the (3+1) case
Authors:
Stroz K.
Source:
(list of journals)
Journal of Applied Crystallography. 32(Part 3):452-455, 1999 Jun 1.
Abstract:
A method of building up the generators of 775 (3+1)-dimensional superspace groups is proposed. The generators are based on the conventional space-group generators selected by Wondratschek and applied in the International Tables for Crystallography (1995, Vol. A). By the method, the generation of (3+1) space groups is found to be easier, the description of symmetry operations is closer to that used for the conventional space groups, and ambiguities in the (3+1) group notation are avoided.
Title:
Comments on the characteristics of incommensurate modulation in quartz:
discussion about a neutron scattering experiment
Authors:
Aslanyan TA. Shigenari T. Abe K.
Source:
(list of journals)
Acta Crystallographica - Section a - Foundations of Crystallography. 55(Part
1):65-69, 1999 Jan.
Abstract:
From analysis of the elastic neutron scattering data of Dolino et al. [J. Phys. (Paris) (1984), 45, 361-371], it is shown that, besides the well identified components u(x) and u(y) of the acoustic displacements in the incommensurate (IC) phase of quartz, there also exists a strong component of the u(z) vector of the modulation. The existence of the large u(z) is not consistent with the currently accepted model for the IC transition in quartz, since the long-period IC modulation observed in quartz cannot induce any noticeable acoustic component u(z). The need for a new model is keenly felt in order to understand the origin of the IC modulation in quartz.
Title:
Superordering in Ni-rich and Ni-poor decagonal Al-Co-Ni phases
Authors:
Hradil K. Weidner E. Neder RB. Frey F. Grushko B.
Source:
(list of journals)
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical
Properties. 79(8):1963-1976, 1999 Aug.
Abstract:
Single-crystal X-ray diffraction was carried out on a decagonal Ni-rich phase in the Al-Co-Ni system with a nominal composition of Al72.5CO11Ni16.5. Apart from sharp Bragg reflections, satellite scattering was observed in Al72.5Co11Ni16.5 which is different from the satellite scattering observed in a Ni-poor phase with nominal composition Al72.5Co16.5Ni11. The two types of superorder scattering are interpreted in an unified way by periodic order superimposed on the quasiperiodic averaged substructure. This periodic regimes have a limited correlation length (short-range ordering). While the modulation period stays almost constant over a wide range of compositions in these decagonal alloys, the modulation Vector is rotated by pi/10 if passing from Ni-rich (S satellites) to Ni-poor (C satellites) compositions. Arguments are given in favour of this interpretation which is also supported by computer simulations.
Title:
Quasiperiodic packings of fibres with icosahedral symmetry
Authors:
Duneau M. Audier M.
Source:
(list of journals)
Acta Crystallographica - Section a - Foundations of Crystallography. 55(Part
4):746-754, 1999 Jul 1.
Abstract:
Different icosahedral packings of fibres have been experimentally realized. A packing construction with straight fibres of the same circular cross section, only parallel to fivefold icosahedral axes and respecting the closest packing condition, is reported. Its characteristics of point-group symmetry and related two-dimensional tilings are analysed. But for determining unambiguously all the fibre positions it appears that a mathematical construction has to be made from the cut and projection of a five-dimensional space. Through such a method, the volume fraction of fibrous reinforcement in a composite material can be calculated. The related two-dimensional tiling can be proved to be different from a Penrose tiling. Finally, the characteristics of other icosahedral packings where fibres are parallel to threefold axes or to both threefold and fivefold axes are briefly discussed and a few further experiments on their elasticity properties and photonic band-gap structure are suggested.
Title:
Formalism for the computation of the RKKY interaction in aperiodic systems
Authors:
Roche S. Mayou D.
Source:
(list of journals)
Physical Review B-Condensed Matter. 60(1):322-328, 1999 Jul 1.
Abstract:
A numerical method to investigate the Rudermann-Kittel-Kasuya-Yosida (RKKY) interaction between localized spins in aperiodic materials is presented. Based on an expansion df the spectral measure on orthogonal polynomials, this approach leads to an effective framework to analyze linear response formula for the RKKY coupling in complex systems. Particularly useful in the tight-binding scheme it is used in this Paper to understand the role of the local environment and the quasiperiodic potential on the interaction between magnetic spins. Interesting features are revealed and discussed within the. context of anomalous localization and transport. .
Title:
High-temperature expansion for Ising models on quasiperiodic
tilings
Authors:
Repetowicz P. Grimm U. Schreiber M.
Source:
(list of journals)
Journal of Physics A-Mathematical & General. 32(24):4397-4418, 1999 Jun 18.
Abstract:
We consider high-temperature expansions for the free energy of zero-field Ising models on planar quasiperiodic graphs. For the Penrose and the octagonal Ammann-Beenker tiling, we compute the expansion coefficients up to 18th order. As a by-product, we obtain exact vertex-averaged numbers of self-avoiding polygons on these quasiperiodic graphs. In addition, we analyse periodic approximants by computing the partition function via the Kac-Ward determinant. It turns out that the series expansions alone do not yield reliable estimates of the critical exponents. This is due to the limitation on the order of the series caused by the number of graphs that have to be taken into account, and, more seriously, to rather strong fluctuations in the behaviour of the coefficients. Nevertheless, our results are compatible with the commonly accepted conjecture that the models under consideration belong to the same universality class as those on periodic two-dimensional lattices.
Title:
Long-term stability of a quasiperiodic Ta Al multilayer:
Disintegration at room temperature analyzed by grazing angle x-ray scattering
and photoelectron spectroscopy
Authors:
Yang P. Klemradt U. Tao Y. Peisl J. Peng RW. Hu A. Jiang SS.
Source:
(list of journals)
Journal of Applied Physics. 86(1):267-274, 1999 Jul 1.
Abstract:
A three-component Fibonacci (3CF) Ta/Al multilayer has been reinvestigated by specular and diffuse x-ray reflectivity and x-ray photoelectron spectroscopy (XPS) after 41 months of storage at room temperature. The specular reflectivity shows drastically suppressed diffraction peaks, whose positions and intensities are explained by severe interdiffusion of the Ta/Al bilayers building the 3CF sequence. Nonspecular reflectivity scans still indicate a high degree of interfacial roughness correlation in the growth direction that is attributed to the long spatial Fourier components of the interface profiles, which are substantially less affected by interdiffusion. The angle-resolved XPS spectra show that the Ta capping layer is completely oxidized and interdiffused by Al, whereas below the oxide layer Ta and Al coexist in metallic form in the same film. Both x-ray reflectivity and XPS yield an oxide layer of similar to 30 Angstrom thickness. Despite the severe structural disintegration, the multilayer diffraction spectrum can still be indexed by means of the projection theory for quasiperiodic sequences, which points to a remarkable stability of quasiperiodic properties against significant disorder. We conclude that Ta/Al bilayers are apparently unsuitable for multilayer applications due to the lack of thermal stability even at room temperature, with grain boundary diffusion pointed out as a possible disintegration mechanism. The design of improved 3CF Ta/Al multilayers is discussed with regard to applications in x-ray optics. (C) 1999 American Institute of Physics. .
Title:
Twelvefold quasiperiodic patterns in a nonlinear optical
system with continuous rotational symmetry
Authors:
Herrero R. Westhoff EG. Aumann A. Ackemann T. Logvin YA. Lange W.
Source:
(list of journals)
Physical Review Letters. 82(23):4627-4630, 1999 Jun 7.
Abstract:
Twelvefold quasiperiodic structures are observed in an autonomous optical pattern forming system with continuous rotational symmetry. These quasipatterns arise from a primary hexagonal structure. In dependence on the experimental parameters the bifurcation can be sub- or supercritical. In the supercritical case, the transition is mediated by a new kind of patterns with different amplitudes in its fundamental modes. It is proven by an optical Fourier filtering technique that the observed quasipatterns can exist only in the presence of harmonics of the fundamental unstable modes. .
Title:
Magnetostatic modes in quasiperiodic Fibonacci magnetic
superlattices
Authors:
Anselmo DHAL. Cottam MG. Albuquerque EL.
Source:
(list of journals)
Journal of Applied Physics. 85(8 Part 2B):5774-5776, 1999 Apr 15.
Abstract:
The magnetostatic modes are studied in multilayer structures that exhibit deterministic disorders. Some models that have attracted particular attention are the quasiperiodic magnetic multilayers that obey a substitutional sequence of the Fibonacci type. The spin wave spectra are evaluated in the geometry where the magnetization is perpendicular to the surfaces of the layers of the superlattice by using a transfer-matrix approach. Numerical results are presented for the ferromagnets EuS and Fe and for the antiferromagnet MnF2. (C) 1999 American Institute of Physics. .
Title:
Formation of quasiperiodic patterns within a simple
two-dimensional model system
Authors:
Quandt A. Teter MP.
Source:
(list of journals)
Physical Review B-Condensed Matter. 59(13):8586-8592, 1999 Apr 1.
Abstract:
We present a simple two-dimensional model system which tends to organize itself in the form of a quasiperiodic state. The system is composed of one sort of particles only, with mutual interactions that strongly deviate from the standard Lennard-Jones-type of potentials at intermediate distances. The dynamics of this system are simulated by using standard molecular dynamics methods for classical systems. .
Title:
The periodic average structure of particular quasicrystals
Authors:
Steurer W. Haibach T.
Source:
(list of journals)
Acta Crystallographica - Section a - Foundations of Crystallography. 55(Part
1):48-57, 1999 Jan.
Abstract:
The non-crystallographic symmetry of d-dimensional (dD) quasiperiodic structures is incompatible with lattice periodicity in do physical space. However, dD quasiperiodic structures can be described as irrational sections of no (n > d) periodic hypercrystal structures. By appropriate oblique projection of particular hypercrystal structures onto physical space, discrete periodic average structures can be obtained. The boundaries of the projected atomic surfaces give the maximum distance of each atom in a quasiperiodic structure from the vertices of the reference lattice of its average structure. These maximum distances turn out to be smaller than even the shortest atomic bond lengths. The metrics of the average structure of a 3D Ammann tiling, for instance, with edge lengths of the unit tiles equal to the bond lengths in elemental aluminium, correspond almost exactly to the metrics of face-centred-cubic aluminium, This is remarkable since most stable quasicrystals contain aluminium as the main constitutent. The study of the average structure of quasicrystals can be a valuable aid to the elucidation of the geometry of quasicrystal-to-crystal transformations. It can also contribute to the derivation of the physically most relevant Brillouin (Jones) zone.
Title:
Quasipatterns in second-harmonic generation
Authors:
Longhi S.
Source:
(list of journals)
Physical Review E. 59(1 Part A):R24-R27, 1999 Jan.
Abstract:
A cascade of two-dimensional quasipatterns is predicted in intracavity optical frequency doubling due to a polarization instability at the fundamental frequency. Amplitude equations derived from a microscopic model of the frequency conversion process show that quasiperiodic structures of arbitrary orientational order can be spontaneously selected due to bulk nonlinear effects when detuned operation for both fundamental and second: harmonic fields occurs. Multistability and coexistence of patterns and quasipatterns is also discussed. .
Title:
Self-consistent treatment of copolymers with arbitrary sequences
Authors:
Kuznetsov YA. Timoshenko EG.
Source:
Nuovo Cimento della Societa Italiana di Fisica D-Condensed Matter Atomic
(list of journals) Molecular & Chemical Physics Fluids Plasmas Biophysics. 20(12BIS):2265-2288,
1998 Dec.
Abstract:
Using the Gaussian Ansatz for the monomer-monomer correlation functions ae derive a set of the self-consistent equations for determination of the conformational state in the bead-and-spring copolymer model. The latter is based on the Edwards-type effective free-energy functional with arbitrary two-body interaction matrix. The rate of conformational changes in kinetics may be expressed via the instantaneous gradients of the variational free-energy functional in the space of the averaged dynamical variables. We study the equilibrium and kinetics for some periodic and random aperiodic amphiphilic sequences in infinitely diluted solution. Typical equilibrium phase diagrams are elucidated and the conformational structure of different states is discussed. The kinetics of compaction of an amphiphilic copolymer to the globular state proceeds through formation of locally frustrated non-equilibrium structures. This leads to a rather complicated multistep kinetic process. We observe that even a small modification in the primary sequence of a copolymer may significantly change its kinetic folding properties.
Title:
Diffuse scattering data acquisition techniques
Authors:
Estermann MA. Steurer W.
Source:
(list of journals)
Phase Transitions. 67(1 Part B):165-195, 1998.
Abstract:
Techniques are presented for acquiring and reducing X-ray diffuse scattering data from disordered crystalline materials. These methods are part of a comprehensive approach to study disorder in novel quasicrystalline phases as a function of temperature, but can be applied without further adaptation to periodic crystalline systems. By fully exploiting the possibilities of modern two-dimensional X-ray detector systems - using imaging plates or charge coupled devices (CCD) - large volumes of reciprocal space can be measured in a quantitative and rapid way. For this purpose, the classical rotation method for collecting integrated Bragg intensities is extended for acquiring quasi-continuous diffuse diffraction data. A new high-temperature furnace and helium beam path, designed for the diffraction geometry of the rotation method, are integral parts of the diffraction system. New methods are presented for handling the reduction of diffuse diffraction data from area detectors. One of the key techniques is the reconstruction of arbitrary slices and volumes in reciprocal space from a single series of rotation images taken from an arbitrarily oriented single-crystal (reciprocal space mapping).
Title:
Diffuse scattering. X-rays vs. neutrons
Authors:
Boysen H. Frey F.
Source:
(list of journals)
Phase Transitions. 67(1 Part B):197-217, 1998.
Abstract:
Fundamental and experimental differences between X-ray and neutron scattering methods are outlined and the advantages of either radiation for the study of disorder in crystals are described. Special emphasis is laid on their complementarity, e.g. to identify the atomic species involved in the disorder or to decide between the elastic or inelastic nature of the diffuse scattering (static or dynamic disorder). This is illustrated by three examples: LiNbO3 (dynamic nature of chain-like disorder), doped ZrO2 (identification of cationic and anionic disorder components) and decagonal quasicrystals (distinction between quasi-isoelectronic elements).
Title:
Kinetics of phase transitions in modulated ferroelectrics:
Time-resolved neutron diffraction from Rb2ZnCl4
Authors:
Eckold G. Hagen M. Steigenberger U.
Source:
(list of journals)
Phase Transitions. 67(1 Part B):219-244, 1998.
Abstract:
The kinetics of the ferroelectric phase transition between modulated phases in Rb2ZnCl4 at about 190 K has been investigated by time-resolved neutron scattering. Observing the time dependence of satellite spectra, it is found that the structural changes associated with the field-induced transformation proceed on a millisecond time scale. Under the influence of fast cycling strong electric fields unusual non-equilibrium states are obtained which are modulated in space as well as in time and characterised by the presence of internal mechanical strains.
Title:
Diffuse scattering and order in quasi-one-dimensional molecular
crystals
Authors:
Van Smaalen S. Lamfers HJ. De Boer JL.
Source:
(list of journals)
Phase Transitions. 67(1 Part B):277-294, 1998.
Abstract:
The order and disorder in quasi-one-dimensional organic conductors is reviewed from a structural point of view. The qualitative features are discussed of the diffuse scattering and of superstructure reflections. The possibilities are considered to obtain structural information from a quantitative analysis of the diffuse scattering. Two examples are presented in detail. For C1TET-TTF(AuI2)(0.8) it is shown that the partially ordered AuI2 substructure can be determined from the maxima within the diffuse sheets. For (Perylene)Co(mnt)(2) a quantitative description of the first-order satellite reflections requires a saw-tooth shaped modulation function of large amplitude (0.7 Angstrom).
Title:
Disorder diffuse scattering from quasicrystals
Authors:
Steurer W. Frey F.
Source:
(list of journals)
Phase Transitions. 67(1 Part B):319-361, 1998.
Abstract:
Very sharp Bragg reflections accompanied by diffuse scattering phenomena are typical for most stable quasicrystals. The correlation length of the quasiperiodic average structure can reach several micrometers as proved by high-resolution X-ray diffraction experiments. This corresponds to a structural perfection of some quasicrystals similar to that of silicon. Nevertheless, the omnipresent diffuse scattering indicates significant deviations from a strictly ordered quasiperiodic structure especially in the case of decagonal phases. These structural deviations may be caused by phason fluctuations, by disorder in the packing of the basic atomic clusters, by the formation of nanodomains, by chemical disorder, or by superstructure formation on a short-range scale. Characteristic examples of different types of structural disorder present in icosahedral and decagonal quasicrystals are reported. The diffuse scattering phenomena in decagonal Al-Co-Ni as a function of composition and temperature are discussed in more detail.
Title:
On the thickness of domain walls in ferroelectrics and ferroelastics
Authors:
Ishibashi Y. Salje EKH.
Source:
(list of journals)
Phase Transitions. 67(1 Part B):363-372, 1998.
Abstract:
Ferroelastic and ferroelectric domain walls are commonly described by wall profiles of the tanh(x/w)-type. We argue that this profile is still a good approximation if higher-order gradient energies are considered. Such energies are relevant for phase transitions close to structural incommensurations and also for phase transitions with dominant elastic interactions. Their effect on the wall profile is to influence the effective wall thickness. Positive gradient energies tend to widen domain walls beyond the values predicted in classic Landau-Ginzburg theory.
Title:
Thermal hysteresis and memory effects in TlInS2
Authors:
Allakhverdiev KR. Mikailov FA. Kulibekov AM. Turetken N.
Source:
(list of journals)
Phase Transitions. 67(2 Part A):457-465, 1998.
Abstract:
The dielectric susceptibility of layered TlInS2 was studied in the temperature range of successive phase transitions. Thermal hysteresis was observed in the incommensurate phase. It was shown that after annealing the crystal at a fixed temperature within the incommensurate phase, the existing temperature interval of this phase reveals noticeable broadening. The thermal memory effect is discussed using a defect density wave model.
Title:
Structural phase transitions in ionic molecular solids
Authors:
Hardy JR.
Source:
(list of journals)
Phase Transitions. 67(3 Part B):521-537, 1998.
Abstract:
An overview is presented of our studies on the nature of structural instabilities in relatively complex ionic solids. These are based on parameter-free interionic potentials based on the Gordon-Kim modified electron gas formalism extended to molecular ions. We describe the manner in which there emerge from these studies quite general concepts of "size" and "shape" as structural determinants. In particular, we discuss how these, and the approximate symmetries that they can produce, can provide a relatively simple structure-based explanation of the origins of incommensurate phases in these systems. However, we also emphasize that the existence of such symmetries does nor guarantee an incommensurate phase. This can only be realized if long-range correlations are sufficiently strong to overcome random local disordering. Thus, either the molecular units are partially linked and/or there exist long-range Coulomb interactions between individual units.
Title:
Modulated structures associated with
charge-density waves [Review]
Authors:
Ghorayeb AM.
Book Editors
Boulesteix C
Source:
(list of journals)
OXIDES : PHASE TRANSITIONS, NON STOICHIOMETRY, SUPERCONDUCTORS. 155-1 PG.
159-197. 1998 [Figures] [Plates].
Abstract:
In this work, we report on the occurrence of periodic lattice distortions associated with charge-density waves in low-dimensional metallic structures. After presenting a brief theoretical background concerning the conditions under which such distortions may occur, we consider a few examples of low-dimensional conductors that undergo such periodic distortions. In particular, we discuss, on the one hand, some of the transition-metal dichalcogenides and, on the other hand, some of the oxide bronzes. Emphasis is particularly put on showing how the transition to a charge-density-wave state may be followed not only by structural studies, but also by studies of some of the electronic properties of these compounds, particularly their transport properties.
Title:
Structure and superconductivity of the Bi-, Tl- and
Hg-cuprates
Authors:
Bordet P.
Book Editors
Boulesteix C
Source:
(list of journals)
OXIDES : PHASE TRANSITIONS, NON STOICHIOMETRY, SUPERCONDUCTORS. 155-1 PG.
383-412. 1998 [Figures] [Plates].
Abstract:
We present a comparison of the crystal-chemical properties of the Bi-, Tl-, and Hg-based superconducting cuprates, in relation to their physical properties. Despite the global similarity of their layered structures, the different crystal-chemical nature of these three cations leads to quite different structural properties for the three series. The present knowledge of the relationships between crystal-chemical and superconducting properties in these systems is presented, with emphasis on the different doping mechanisms observed.
Title:
High-resolution electron microscopy of quasicrystals
[Review]
Authors:
Hiraga K.
Book Editors
Hawkes PW
Source:
(list of journals)
ADVANCES IN IMAGING AND ELECTRON PHYSICS, VOL. 101. 101 PG. 37-98. 1998
[Figures].
Title:
Correlations between physical and crystallographic
parameters in the (Bi, Pb)(2)Sr-2(Ca, Y)Cu2O8+delta superconductors
Authors:
Manifacier L. Collin G. Blanchard N.
Source:
(list of journals)
International Journal of Modern Physics B. 12(29-31):3306-3312, 1998 Dec 20.
Abstract:
Systematic studies of the lead and yttrium substituted Bi-2212 phase were performed on various compositions ranging between 0 and 0.8 for Pb and between 0 and 0.9 for Y. Crystallographic measurements reveal that the two modulations observed in unleaded and highly Pb-substituted samples are closely linked, the main differences being that the commensurate component disappears in type II (lead type) modulation, along with the modulation of the Bi3+ ion. We argue that this is due to a covalent bonding between Bi-O planes. The study of internal parameters, including modulation amplitudes, of the Bi2Sr2(Ca1-x, Y-x)Cu2O8+x/2+delta system reveals three distinct regimes with very different behaviors, corresponding to the overdoped, underdoped and insulating regimes. By comparing these results to the variation of the diamagnetic shielding with Y and Pb contents, we conclude that yttrium and lead affect more the mobility of the holes than the hole concentration itself. Y seems to induce, rather than a metal/insulator transition, a switch from a three-dimensional to a two-dimensional regime with a hole localization in the CuO2 planes.
Title:
Icosahedral phase in laser-remelted Ti68Fe26Si6 alloy
Authors:
Liu YC. Yang GC. Song GS. Zhou YH.
Source:
(list of journals)
Journal of Materials Science Letters. 17(22):1875-1876, 1998 Nov 15.
Title:
Equilibrium composition-modulated
structures in alloy epitaxial films
Authors:
Shchukin VA. Starodubtsev AN.
Source:
(list of journals)
Physics of Low-Dimensional Structures. 12:203-224, 1998.
Abstract:
The global thermodynamic stability of an alloy film against fluctuations of alloy composition is studied. The non-linear problem of finding the final structure of a decomposing alloy is solved by using a Ginzburg-Landau expansion of the free energy in the vicinity of the critical point of the alloy instability. The exact phase diagram in the variables "temperature - average composition" is constructed, containing regions of absolutely unstable, metastable, and stable alloys. The period of the equilibrium structure, being of the order of the film thickness, exhibits a logarithmic dependence on temperature near the critical point. A composition-modulated structure with a one-dimensional periodicity in the surface plane is proved to be the equilibrium one.
Title:
Slow stage in the evolution of an incommensurate
ferroelectric superlattice
Authors:
Kallaev SN. Glushkov VF.
Source:
(list of journals)
Physics of the Solid State. 40(11):1904-1905, 1998 Nov.
Abstract:
The nature of the slow evolution of a soliton system in an incommensurate phase of a ferroelectric is investigated experimentally. It is shown that the duration of the time interval in which the anomalous permittivity and the corresponding soliton spacings are governed by a logarithmic law increases from a few minutes to several hours as the ferroelectric phase transition is approached. (C) 1998 American Institute of Physics. .
Title:
Investigation of progesterone loaded poly(D,L-lactide) microspheres using
TMDSC, SEM and PXRD
Authors:
Hill VL. Passerini N. Craig DQM. Vickers M. Anwar J. Feely LC.
Source:
(list of journals)
Journal of Thermal Analysis. 54(2):673-685, 1998.
Abstract:
Poly(d,l-lactide) microspheres with progesterone loadings of 0, 10, 20, 30 and 50% w/w were manufactured using an interrupted solvent evaporation process. Spherical microspheres with loadings close to the theoretical values were produced. The glass transition of the polymer could be identified by a step change in the heat capacity measured by TMDSC. Progesterone was found to plasticise the glass transition temperature at contents of 20% w/w or less. At a 30% loading, cold crystallisation of progesterone was seen indicating that an amorphous form of the drug was present; these microspheres were found to exhibit a pitted surface. TMDSC of the 50% progesterone samples suggested that most of the drug was present as crystals. This was supported by the SEM and PXRD results.
Title:
Alkaline-earth overlayers on furrowed transition metal surfaces: An example
of tailoring the surface properties
Authors:
Yakovkin IN. Katrich GA. Loburets AT. Vedula YS. Naumovets AG.
Source:
(list of journals)
Progress in Surface Science. 59(1-4):355-365, 1998 Sep-Dec.
Abstract:
Alkaline-earth (AE) layers adsorbed on furrowed transition metal surfaces are remarkable for a variety of their atomic structures thus offering a good possibility for exploring the interplay between atomic and electronic structures as well as dynamic properties of surfaces. As the coverage increases, the commensurate-incommensurate transition in the AE layers is accompanied by the nonmetal-to-metal transition (NMT) in the films which leads to dramatic changes in characteristics of photoemission and surface diffusion thus enabling one to tailor the surface properties. The calculations for one-dimensionally compressing monolayers elucidate some important features of the NMT in such adsorbed films. These findings have been exploited to develop effective Mg-Ba alloy photocathodes.
Title:
Low-temperature phases (phase II) of ionic conductors Ag7TaS6 and Ag7NbS6
Authors:
Onoda M. Wada H. Tansho M. Ishii M.
Source:
(list of journals)
Solid State Ionics. 115(Special Issue SI):515-519, 1998 Dec.
Abstract:
The crystal structures of low-temperature forms of argyrodite-type superionic conductors, namely Ag7TaS6 II (between approx. 280 K and approx. 170 K) and Ag7NbS6 II (between approx. 280 K and approx. 140 K), analyzed based on powder X-ray diffraction data have been compared with each other. The crystal structure of Ag7TaS6 II could be described on the basis of a space group Pc with the lattice constants a = 7.453, b = 7.403, c = 12.806 Angstrom and beta = 124.62 degrees. In the Rietveld analysis of Ag7NbS6 II, a commensurately modulated structure approach was adopted to obtain a smooth convergence. The crystal data of Ag7NbS6 II are expressed as a(1) = 7.368, a(2) = 14.770, a(3) = 12.768 Angstrom, sigma = (0.25 0 0), beta = 124.28 degrees in a four-dimensional formalism with a superspace-group Pc(alpha 1/2 gamma), that is A = 29.47, B = 14.770, C = 12.768 Angstrom, beta = 124.28 degrees in a three-dimensional formalism with a space group Cc. In Ag7TaS6 II and Ag7NbS6 II, almost a half of Ag ions are in distorted tetrahedrons and the other Ag ions are in triangular faces shared by two tetrahedrons. A split model of mobile Ag ions in the room-temperature phase I is discussed in connection with Ag sites in the low-temperature phase II. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
Spin-density-wave effects on the vibrational anharmonicity of acoustic
phonons in Cr-Ir alloy single crystals
Authors:
Martynova J. Alberts HL. Smit P.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 10(50):11731-11742, 1998 Dec 21.
Abstract:
Measurements are reported of the dependences on hydrostatic pressure (p) of the elastic constants (c(ij)) of Cr-Ir alloy single crystals containing 0.07 at.% and 0.20 at.% Ir. For the former concentration the alloy exhibits a transition from an incommensurate (I) spin-density-wave (SDW) to a paramagnetic state at the Neel temperature (T-N). dc(ij)/dp was studied as a function of temperature through T-N. The concentration of the Cr0.998Ir0.002 crystal is larger than the triple-point concentration on the Cr-lr magnetic phase diagram and for this crystal there appears a phase transition from an ISDW to a commensurate (C) SDW at T-IC. dc(ij)/dp was measured for this crystal as a function of temperature through T-IC. The acoustic mode Gruneisen parameters were calculated for the two crystals as a function of temperature through T-N (for Cr0.9993Ir0.0007) and through T-IC (for Cr0.998Ir0.002). Large negative Gruneisen parameters are observed in the ISDW and CSDW phases of Cr0.998Ir0.002. The results indicate stronger magnetoelastic interactions in the CSDW than in the ISDW phase of this crystal. It is shown that the strong magnetoelastic coupling in the ISDW and CSDW antiferromagnetic phases of the Cr-Ir system takes mainly place through volume effects.
Title:
Neutron diffraction study of the magnetic ordering in the Ho(Mn1-xAlx)(2)
system
Authors:
Dubenko IS. Golosovsky IV. Markosyan AS. Mirebeau I.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 10(50):11755-11764, 1998 Dec 21.
Abstract:
The magnetic and crystal structure of the as-cast cubic Ho(Mn1-xAlx)(2) compounds (x less than or equal to 0.1) was studied using neutron powder diffraction. The samples showed substantial inhomogeneity and consisted of at least two C15-type crystal phases. In the first phase predominating in HoMn2 (96.3%) ferrimagnetic long range order is stable. The second phase with the cell parameter lying within the narrow range 7.49-7.52 Angstrom shows an incommensurate magnetic structure with a wave vector k approximate to [0.18, 0.18, 0.08] weakly dependent on x. Short range correlations of an antiferromagnetic type along with long range ordering were observed. The diffuse maxima lie at the positions corresponding to the Bragg reflections with half-integer indices and are ascribed to short range correlations based on the MnO-type antiferromagnetic structure developed within clusters of similar to 25 Angstrom in size. No volume effect associated with the onset of Mn magnetism was observed up to x = 0.1.
Title:
Phase transitions in LiKSO4 between 1.5 K and 850 K: an infrared
spectroscopic study
Authors:
Zhang M. Salje EKH. Putnis A.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 10(50):11811-11827, 1998 Dec 21.
Abstract:
A systematic infrared spectroscopic investigation of the sequence of phase transitions in LiKSiO4 at temperatures between 1.5 K and 850 K in the region of 50-1500 cm(-1) is reported. IR powder spectra show phase transitions near 35 K, 60 K, 140 K, 190 K, 240 K and 708 K on heating. The transitions are characterized either by the appearance of new IR bands, IR band splitting or a change in the temperature dependence of spectral profiles. The numbers of internal bands show that the phases in the temperature regions of 140-190 K and 190-240 K consist of a monoclinic (space group Cc) and a trigonal (space group P31c) structure, respectively. The observation of two nu(2) IR modes between 140 and 190 K rules out the orthorhombic structure of C-2 upsilon(12) (Cmc2(1)). Symmetry changes occur at the phase transitions at 135 K and 60 K.
Title:
Magnetic order in RAgGe (R=Gd-Er) intermetallic compounds
Authors:
Baran S. Hofmann M. Leciejewicz J. Penc B. Slaski M. Szytula A.
Source:
(list of journals)
Journal of Alloys & Compounds. 281(2):92-98, 1998 Dec 18.
Abstract:
Polycrystalline samples of the ternary intermetallics RAgGe (R=Tb-Er) were investigated by means of magnetization and neutron diffraction measurements. For GdAgGe compounds only magnetic measurements were performed. They crystallize in the hexagonal ZrNiAl-type structure. Magnetic measurements show antiferromagnetic ordering at Neel temperatures between 15.6 K for R-Gd and 3.6 K for R=Er. For TbAgGe the neutron diffraction data reveal a complicated sine modulated magnetic structure which is affected by temperature changes. For DyAgGe and HoAgGe the square modulated magnetic ordering is described by the wave vector k=(1/3 1/3 0) while for ErAgGe by k=(1/2 1/2 0). With increasing number of 4f-electrons one observes a change of the direction of magnetic moment from parallel to the c-axis for R = Tb via one which forms an angle phi with the c-axis for R = Dy, to one which lies in the basal plane for R = Ho and Er. (C) 1998 Elsevier Science S.A. All rights reserved.
Title:
An EXAFS investigation of the local structure of R8Mg42Zn50
icosahedral quasicrystals (R=Y, Dy)
Authors:
Charrier B. Hazemann JL. Schmitt D.
Source:
(list of journals)
Journal of Alloys & Compounds. 281(2):117-122, 1998 Dec 18.
Abstract:
EXAFS experiments have been performed on the icosahedral quasicrystals R8Mg42Zn50 (R=Y, Dy) at the Y K, Dy L-III and Zn K edges. Isomorphism of Y- and Dy-based quasicrystals is clearly evidenced. The rare earth is found to be essentially surrounded by Zn atoms with a small amount of Mg atoms. The surrounding of Zn appears less spherical than that of the rare earth and includes the three elements in almost stoichiometric proportion. The relation between structure and magnetic properties is discussed. (C) 1998 Elsevier Science S.A. All rights reserved.
Title:
A reinterpretation of the NH4Cu7S4 structure
Authors:
Noren L. Berger R. Lidin S. Eriksson L. Huster J.
Source:
(list of journals)
Journal of Alloys & Compounds. 281(2):186-195, 1998 Dec 18.
Abstract:
The structure of NH4Cu7-xS4 has been investigated using X-ray single crystal diffraction at varying temperatures. The room temperature structure is best described as a tetragonal crystalline framework with channels incorporating some of the copper atoms in a disordered, almost amorphous, manner. The crystallographic description based primarily on the framework renders the space group I4/m and a unit cell with a = 10.2695(5) Angstrom and c = 3.8094(3) Angstrom. Upon cooling below 270 K, the copper atoms in the channels start to order. To begin with, the compound adopts the CsAg7S4 structure type with the unit-cell parameters a = 10.289(1) Angstrom and c = 7.704(1) Angstrom. Upon further cooling. incommensurate orderings occur, in accordance with the fact that a copper deficient sample was used in the investigation (x approximate to 0.16). (C) 1998 Elsevier Science S.A. All rights reserved.
Title:
Liquid-solid equilibria in the Al-rich corner of the Al-Mn-Cr system
Authors:
Schenk T. Durand-Charre M. Audier M.
Source:
(list of journals)
Journal of Alloys & Compounds. 281(2):249-263, 1998 Dec 18.
Abstract:
The aspect of the Al-Mn-Cr phase diagram related to liquid-solid equilibria in the subsection Al4Cr-Al4Mn-Al was investigated. It is shown that ternary Al4MnxCr1-x compounds (0 less than or equal to x less than or equal to 1) whose structure correspond to that of the hexagonal mu Al4Mn phase, previously identified as a periodic approximant of Al-Mn and Al-Cr quasicrystalline phases, are in equilibrium with a liquidus phase field extending between both binary Al-Mn and Al-Cr limits. A new ternary Al-Mn-Cr phase, called Psi is also found and characterised. Its structure is monoclinic with cell parameters a(Psi) = 17.48 Angstrom, b(Psi) = 30.31 Angstrom, c(Psi) = 24.695 Angstrom, beta = 135 degrees and a space group of either C2/c or Cc symmetry. But as peculiar structural faults are observed in this monoclinic Psi-phase, its formation is assumed to be the result of an allotropic transformation of an orthorhombic structure which would first solidify. Besides, from structural relationships observed between the mu and Psi structures, it is suggested that the atomic structure of Psi could also be typical of an arrangement of icosahedral clusters as, for instance, those defined in both the mu Al4Mn and lambda Al4.5Mn structures. (C) 1998 Elsevier Science S.A. All rights reserved.
Title:
Aging characteristics of thermomechanically processed Cu-9Ni-6Sn alloy
Authors:
Kim SS. Rhu JC. Jung YC. Han SZ. Kim CJ.
Source:
(list of journals)
Scripta Materialia. 40(1):1-6, 1998 Dec 4.
Abstract:
Cu-Ni-Sn alloys have gathered a considerable amount of interests over the past 20 years, since the strength level of Cu-Ni-Sn alloys with a proper thermomechanical processing equals to those obtained by high-strength, precipitation-hardened Cu-Be alloys (1-3). The aging response of Cu-Ni-Sn alloys is known to be extremely sensitive to aging temperature, aging time and prior processing history (1-4). When Cu-Ni-Sn alloys are aged below 400 degrees C after solution heat treatment, for example, the supersaturated solid solution ct is reported to follow the three stages of decomposition. In the first stage, the modulated structure with Sn-rich and Sn-poor regions forms along the [100]alpha direction as a result of spinodal decomposition. In the second stage, the metastable gamma' precipitates with D0(22) type structure nucleate from the modulated structure, and the highest strength occurs in this stage. In the final stage of transformation, the gamma' phases decompose into the cellular structures, consisted of equilibrium a and gamma phases, and the strength ceases to increase. The effect of cold working prior to aging practice on tensile properties of Cu-Ni-Sn alloys is significant, but still controversial (1,2,5). In the present study, aging characteristics of heavily swaged Cu-9Ni-6Sn alloy, the composition of which is known to have the best combination of mechanical and physical properties, were examined. The hardening behaviors of Cu-9Ni-6Sn alloys, either solutionized and aged or directly aged, are discussed with SEM fractographic studies and TEM micrographic observations.
Title:
Linear continuous inhomogeneous strains of a quasicrystal
lattice
Authors:
Rochal SB. Lebedyuk IV.
Source:
(list of journals)
Physics Letters A. 250(1-3):152-156, 1998 Dec 21.
Abstract:
Linear continuous inhomogeneous strains are shown to occur in a quasicrystalline lattice. Their symmetry analysis is given for a dodecagonal case. At such strains, the magnitudes of position displacements are proportional to the strain value and the flip-flaps of positions are absent. (C) 1998 Elsevier Science B.V.
Title:
Superlattice patterns in surface waves
Authors:
Kudrolli A. Pier B. Gollub JP.
Source:
(list of journals)
Physica D. 123(1-4):99-111, 1998 Nov 15.
Abstract:
We report novel superlattice wave patterns at the interface of a fluid layer driven vertically. These patterns are described most naturally in terms of two interacting hexagonal sublattices. Two frequency forcing at very large aspect ratio is utilized in this work. A superlattice pattern ("superlattice-I") consisting of two hexagonal lattices oriented at a relative angle of 22 degrees is obtained with a 6:7 ratio of forcing frequencies. Several theoretical approaches that may be useful in understanding this pattern have been proposed. In another example, the waves are fully described by two superimposed hexagonal lattices with a wavelength ratio of root 3, oriented at a relative angle 30 degrees. The time dependence of this "superlattice-II" wave pattern is unusual. The instantaneous patterns reveal a time-periodic stripe modulation that breaks the sixfold symmetry at any instant, but the stripes are absent in the time average. The instantaneous patterns are not simply amplitude modulations of the primary standing wave. A transition from the superlattice-II state to a 12-fold quasi-crystalline pattern is observed by changing the relative phase of the two forcing frequencies. Phase diagrams of the observed patterns (including superlattices, quasicrystalline patterns, ordinary hexagons, and squares) are obtained as a function of the amplitudes and relative phases of the driving accelerations. Copyright (C) 1998 Elsevier Science B.V.
Title:
The effect of Pb on the behavior of structure modulation in
Bi2-xPbxSr3Fe2Oy isostructural with Bi2Sr2CaCu2O8
Authors:
Sedykh V. Bagautdinov BS. Suvorov EV. Smirnova IS. Dubovitskii AV. Shekhtman VS.
Source:
(list of journals)
Physica C. 309(3-4):175-186, 1998 Dec 20.
Abstract:
The complex investigation of the behavior of the structure modulation has been carried out on single crystals of the Bi2-xPbxSr3FexOy compound (isostructural with 2212Cu) depending on the Pb content (x = 0.12, 0.15, 0.20, 0.25) by X-ray diffraction methods, Mossbauer spectroscopy, and electron microscopy. It has been shown that the modulated structure exists in all the studied specimens with x < 0.25. Beginning from the Pb concentration x = 0.12 the modulated structure is no longer continuous over the specimen as in the free-Pb compound and becomes 'island' one combining the regions with modulation and without it. At x = 0.25 the modulation disappears practically, however, the structure is distorted because of, probably, a high Pb concentration. (C) 1998 Published by Elsevier Science B.V. All rights reserved.
Title:
Distortion of the microstructure in Bi1.8Pb0.2Sr2-xCuOy
system
Authors:
Yan HJ. Mao ZQ. Xu GJ. Shi L. Tian ML. Zhang YH.
Source:
(list of journals)
Physica C. 309(3-4):263-268, 1998 Dec 20.
Abstract:
We investigate the Raman scattering and electron diffraction (ED) for the nominal composition of Bi1.8Pb0.2Sr2-xCuOy samples. It is found that the Sr vacancies bring about the distortion of Sr-O bond as well as the reduction of the incommensurate modulation with decreasing Sr content in Bi1.8Pb0.2Sr2-xCuOy. samples. Our analysis indicates that the characteristics in Raman scattering spectra can be explained well by the crystal misfit model. (C) 1998 Published by Elsevier Science B.V. All rights reserved.
Title:
Partially disordered phase in frustrated triangular lattice antiferromagnet
CuFeO2
Authors:
Mitsuda S. Kasahara N. Uno T. Mase M.
Source:
(list of journals)
Journal of the Physical Society of Japan. 67(12):4026-4029, 1998 Dec.
Abstract:
We reinvestigated successive magnetic phase transitions (TN1 similar to 14.0 K, TN2 similar to 10.5 K) in a frustrated triangular lattice antiferromagnet (TLA) CuFeO2 by neutron diffraction measurements using single crystals. The magnetic structure of the intermediate temperature phase between TN1 and TN1 is found to be a quasi-long range ordered sinusoidally amplitude-modulated structure with a temperature dependent propagation wave vector (q q 0). These features of successive phase transitions are well explained by reinvestigated Monte-Carlo simulation of a 2D Ising TLA with competing exchange interactions up to 3rd neighbors, in spite of the Heisenberg spin character of orbital singlet Fe3+ magnetic ions.
Title:
The structural phase transitions in LiK0.50Rb0.50SO4 mixed
crystal
Authors:
Righi A. Bourson P. Ayala AP. Pimenta MA. Moreira RL.
Source:
(list of journals)
Journal of the Physical Society of Japan. 67(12):4285-4290, 1998 Dec.
Abstract:
The structural phase transitions of the LiK0.50Rb0.50SO4 mixed crystal were investigated by Raman spectroscopy and neutron powder diffraction up to 800 K. The results show two first order structural transitions, quite analogous to the transitions in LiKSO4. Raman spectra and diffraction profiles were compatible with average symmetries C-3v(4), C-6(6) and D-2h(16) for the three observed phases, with increasing temperature. The transitions, both reconstructive, are smeared over large temperature intervals, leading to the coexistence of Raman bands and neutron peaks of the different phases and to an anomalous behavior of the lattice parameters into these intervals. In the hexagonal phase, the cell Volume presents a hysteretic behavior depending on the sample thermal history. Raman spectra of the orthorhombic phase shows the high rotational disorder of the SO4 ions, associated with the high Li positional disorder in this high conducting phase.
Title:
Feasibility of covalent quasicrystals
Authors:
Borodin VA. Manichev VM.
Source:
(list of journals)
Journal of Experimental & Theoretical Physics. 87(6):1191-1194, 1998 Dec.
Abstract:
An algorithm for constructing a quasicrystalline structure based on atoms with tetrahederal coordination of covalent atomic bonds (the typical coordination for group IV atoms) is proposed. The algorithm is used to construct a computer model of a cluster with icosahedral symmetry. The model is used to estimate the energy parameters of the structure and the distributions of bonds over interatomic bond lengths and interbond angles. The distributions obtained correlate well with the analogous results for silicon glasses and do not impose any fundamental constraints on the implementation of such structures in practice. (C) 1998 American Institute of Physics. .
Title:
Magnetic structures of the triangular lattice magnets
AFe(SO4)(2) (A = K, Rb, Cs)
Authors:
Serrano-Gonzalez H. Bramwell ST. Harris KDM. Kariuki BM. Nixon L. Parkin IP. Ritter C.
Source:
(list of journals)
Journal of Applied Physics. 83(11 Part 2):6314-6316, 1998 Jun 1.
Abstract:
In the crystal structures of CsFe(SO4)(2), RbFe(SO4)(2), and KFe(SO4)(2), the magnetic Fe3+ ions form a triangular array in well separated layers. CsFe(SO4)(2) and RbFe(SO4)(2) may be regarded as realizations of the highly frustrated triangular lattice antiferromagnet, whereas KFe(SO4)(2) is a suspected realization of the row model. The latter model is characterized by two couplings J' and J, and for J'/J>0.5 forms a helical spin structure with an incommensurate repeat distance. The regular triangular lattice magnet may be described by the row model with J'=J, and its "120 degrees" spin Structure may be regarded as a special case of this helical structure. We have determined the low temperature (1.3 K) magnetic structures adopted by CsFe(SO4)(2), RbFe(SO4)(2), and KFe(SO4)(2) by powder neutron diffraction. CsFe(SO4)(2) and RbFe(SO4)(2) adopt the expected 120 degrees helical spin structure of the triangular lattice magnet, but KFe(SO4)(2) does not adopt the expected incommensurate helical structure of the row model. Rather, it adopts a sine wave modulated structure. Possible reasons for this behavior are discussed. (C) 1998 American Institute of Physics. .
Title:
Atomic self-diffusion in dodecagonal quasicrystals
Authors:
Roth J. Gahler F.
Source:
(list of journals)
European Physical Journal B. 6(4):425-445, 1998 Dec.
Abstract:
A molecular dynamics study of atomic self-diffusion in Frank-Kasper type dodecagonal quasicrystals is presented. It is found that the quasicrystal-specific flip mechanism for atomic diffusion, predicted by Kalugin and Katz, indeed occurs in this system. However, in order to be effective, this mechanism needs to be catalyzed by other defects, such as half-vacancies. For this reason, it is difficult to distinguish from standard vacancy diffusion.
Title:
Evidence of the "memory" effect of amorphous aluminosilicate gel precursors
by simulation of zeolite crystallization processes using the
population balance method
Authors:
Antonic T. Subotic B.
Source:
(list of journals)
Croatica Chemica Acta. 71(4):929-948, 1998 Dec.
Abstract:
There is abundant experimental evidence that most, or even all zeolite nuclei are formed in the aluminosilicate gel and/or gel/liquid interface by a linking of specific subunits during gel precipitation and/or ageing. Since the nuclei (particles of quasicrystalline phase) cannot grow inside the gel matrix, they start to grow after being >>released<< from the gel dissolved during the crystallization, i.e. when they are in full contact with the liquid phase (autocatalytic nucleation). Based on these findings it was assumed that the rate of autocatalytic nucleation depends on the rate of gel dissolution as well as on the number and distribution of nuclei in the gel matrix, but that crystal size distribution in the crystalline end product depends exclusively on the number and distribution of nuclei in the gel matrix and not on the crystallization conditions, or even on the treatment of aluminosilicate gel precursor prior to crystallization. This so called >>memory<< effect of amorphous aluminosilicate precursors was evidenced by simulation of zeolite crystallization under different conditions, using the population balance method.
Title:
Elastic properties of Cs2HgBr4 and Cs2CdBr4 crystals
Authors:
Kityk AV. Zadorozhna AV. Shchur YI. Martynyuk-Lototska IY. Burak Y. Vlokh OG.
Source:
(list of journals)
Australian Journal of Physics. 51(6):943-957, 1998.
Abstract:
Using ultrasonic velocity measurements, all components of the elastic constant matrix C-ij, elastic compliances matrix S-ij, and linear compressibility constants matrix K-ij of orthorhombic Cs2HgBr4 and Cs2CdBr4 crystals have been determined over a wide temperature range, including the region of the phase transition from the normal to the incommensurate phase. Results obtained are considered within the framework of the phenomenological theory. Preliminary analysis of the acoustical properties at room temperature clearly indicates that both crystals are relatively important materials for acousto-optical applications.
Title:
Optical variability in active galactic nuclei: Starbursts or disk
instabilities?
Authors:
Kawaguchi T. Mineshige S. Umemura M. Turner EL.
Source:
(list of journals)
Astrophysical Journal. 504(2 Part 1):671-679, 1998 Sep 10.
Abstract:
Aperiodic optical variability is a common property of active galactic nuclei (AGNs), though its physical origin is still open to question. To study the origin of the optical-ultraviolet variability in AGNs, we compare light curves of two models to observations of quasar 0957 + 561 in terms of a structure function analysis. In the starburst (SB) model, random superposition of supernovae in the nuclear starburst region produces aperiodic luminosity variations, while in the disk-instability (DI) model, variability is caused by instabilities in the accretion disk around a supermassive black hole. We calculate fluctuating light curves and structure functions, V(tau), by simple Monte Carlo simulations on the basis of the two models. Each resultant V(tau) possesses a power-law portion, [V(tau)](1/2) proportional to tau(beta), at short time lags (tau). The two models can be distinguished by the logarithmic slope beta; beta similar to 0.74-0.90 in the SB model and beta similar to 0.41-0.49 in the DI model, while the observed light curves exhibit beta similar to 0.35. Therefore, we conclude that the DI model is favored over the SE model in explaining the slopes of the observational structure function in the case of 0957 + 561, though this object is a radio-loud object and thus is not really a fair test for the SE model. In addition, we examine the time asymmetry of the light curves by calculating V(tau) separately for the brightening and the decaying phases. The two models exhibit opposite trends of time asymmetry to some extent, although the present observation is not long enough to test this prediction.
Title:
Structures of fluoroarsenates KAsF6-n(OH)(n), n = 0, 1, 2:
Application of the heavy-atom method for modulated
structures
Authors:
Peterkova J. Dusek M. Petricek V. Loub J.
Source:
(list of journals)
Acta Crystallographica - Section B, Structural Science.
54(Part 6):809-818, 1998 Dec 1.
Abstract:
Structures of KAsF6-n(OH)(n), n = 0, 1, 2, have been determined from single-crystal X-ray diffraction data. Potassium hexafluoroarsenate, KAsF6, has a standard structure, potassium hydroxopentafluoroarsenate. KAsF5(OH), has a superstructure, and potassium dihydroxotetrafluoroarsenate, KAsF4(OH)(2), has an incommensurate modulated structure. The superstructure has been solved both in the supercell by standard methods and in the basic cell as a commensurate modulated structure, giving the same results in both cases. The heavy-atom method for modulated structures has been developed and applied to identify a good starting point for the refinement of strongly modulated KAsF4(OH)(2). Moreover, the influence of hydrogen bonding on a regular disturbance of simple translation symmetry of the structure is discussed.
Title:
Zussmanite in ferruginous metasediments from southern central Chile
Authors:
Massonne HJ. Herve F. Medenbach O. Munoz V. Willner AP.
Source:
(list of journals)
Mineralogical Magazine. 62(6):869-876, 1998 Dec.
Abstract:
Zussmanite KFe13[AlSi17O42](OH)(14), a modulated 2:1 layer silicate, has so far been found only in iron-rich metasediments from Laytonville, California (Agrell ct al., 1965). A new occurrence is reported here from Punta Nihue north of Valdivia, Chile, in banded stilpnomelane-schists. These are intercalated in the 'Western Series', a complex of low-grade metamorphic rocks with local high-pressure, low-temperature overprint (e.g, blueschists). The rock contains conspicuous porphyroblasts of zussmanite of mm size and is composed of chemically distinct bands with the subsequent assemblages: (1) zussmanite-stilpnomelane-quartz, (2) siderite-quartz +/- stilpnomelane (3) apatite-stilpnomelane-quartz +/- siderite. The chemical composition of zussmanite, (K0.80Na0.05B0.01)(Fe11.292+Mg1.11Mn0.25Fe0.143+Cr0.01Al0.19Ti0.01)[Al1.23Si1 6.77O42](OH)(14), its optical properties and X-ray data correlate well with the Californian occurrence. Additionally, we present new IR data. In type (2) bands of fine-grained crystals of a K,Al poor mineral formed from siderite and quartz. Its chemical composition is close to that of zussmanite. A similar phase was also reported from Laytonville, California (Muir Wood, 1980). The rarity of rock-forming zussmanite can be explained by its occurrence in strongly Fe-rich and reduced rocks, as well as, by a possibly narrow P-T stability field.
Title:
Influence of epitaxial stress on spinodal decomposition in binary alloys with
large size effects: Application to the Au-Ni system
Authors:
Abadias G. Marty A. Gilles B.
Source:
(list of journals)
Acta Materialia. 46(18):6403-6419, 1998 Nov 20.
Abstract:
Within the framework of Cahn's pioneering theory of spinodal decomposition, the effect of the epitaxial stress on the stability of a binary alloy solid solution against infinitesimal compositional fluctuations is revisited. It is shown that the elastic energy term due to a coherent lattice mismatch with a substrate modifies the linearised diffusion equation. This term is particularly high when size effects between the two constituents are strong. It is then necessary to take into account anharmonic terms in the expression of the elastic energy. From the modified diffusion equation, a new spinodal curve, called the epitaxial coherent spinodal, may be calculated for different substrate lattice parameters. The results of the model are compared with recent experiments on coherently grown (001) Au-Ni alloys. A modulated structure has been evidenced upon annealing which is in good agreement with our calculations. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
Internal and external quasicrystal inflation center and
their scaling factors
Authors:
Masakova Z. Patera J. Pelantova E.
Source:
(list of journals)
Physics of Atomic Nuclei. 61(11):1978-1982, 1998 Nov.
Abstract:
The properties of quasicrystals of the cut and project type-namely, self-similarities or so-called inflation properties-are studied. A complete description is given for centers of the scaling symmetry of a quasicrystal, and the relevant scaling factors are determined for each "inflation center." If the center is a quasicrystal point, it is called an "internal inflation center"; otherwise, it is an "external" one. It turns out that, for any quasicrystal point u, the set of appropriate scaling factors is a u-dependent one-dimensional quasicrystal. There are infinitely many scaling factors common to all internal inflation centers. The description of external inflation centers, which are plentiful in any quasicrystal, is a slight modification of a similar description for the internal ones.
Title:
Modulations in incommensurate (Ca1-xSrx)(2)MgSi2O7 single
crystals
Authors:
Jiang JC. Schosnig M. Schaper AK. Ganster K. Rager H. Toth L.
Source:
(list of journals)
Physics & Chemistry of Minerals. 26(2):128-134, 1998 Dec.
Abstract:
Single crystals of (Ca1-xSrx)(2)MgSi2O7 slightly doped with 1000 ppm Mn2+ and with x ranging from 0.04 to 0.32 were grown from the melt in a mirror furnace applying the Czochalski technique. Transmission electron microscopy (TEM) revealed incommensurately modulated structures at room-temperature for all compositions in accordance with earlier studies by electron paramagnetic resonance (EPR). Electron diffraction patterns clearly show satellite reflections typical for two-dimensional modulation, and their successive destabilization with increasing Sr content. The modulation is of tartan-like appearance. Beyond a Sr/(Sr+Ca) ratio of about 0.32 the synthesis of stable solid solution akermanite type crystals was proved not to be feasible, indicating the existence of a miscibility gap in the Sr akermanite system. As presumed from the diffuse scattering around the satellite reflections, and suggested more conclusively by crystallographic processing of high resolution EM images the Sr ions incorporated into the incommensurate crystal phase are distributed in an ordered fashion and are partly adapted to the displacive modulation of the pure akermanite. This means, occupational modulation even makes a contribution to the overall modulation characteristics in (Ca1-xSrx)(2) MgSi2O7.
Title:
On the sequence of phase transitions in tridymite
Authors:
Pryde AKA. Dove MT.
Source:
(list of journals)
Physics & Chemistry of Minerals. 26(2):171-179, 1998 Dec.
Abstract:
We consider the phase transitions in tridymite from the perspective of the rigid unit mode model. The rigid unit modes are the low-frequency phonons of a crystal structure that consists of an infinite framework of tetrahedra linked at corners, that can propagate without the tetrahedra distorting. Because they give distortions of the structure with a low energy cost they are the natural soft modes for displacive phase transitions. We consider the normal phase transition sequence in tridymite on cooling, HP LHP ..., as a successive condensation of rigid unit modes acting as soft modes. Some of the low-temperature phases (e.g. MX-1) arise as rigid unit mode distortions of the high-temperature structure and do not follow the sequence of phases found at higher temperatures. We are able to account for all the commensurate phases and some of the modulated phase within the framework of the rigid unit mode model.
Title:
Atom cluster arrangements in cubic approximant phases of icosahedral
quasicrystals
Authors:
Hiraga K. Sugiyama K. Ohsuna E.
Source:
(list of journals)
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical
Properties. 78(5):1051-1064, 1998 Nov.
Abstract:
Structural characteristics of six cubic approximant phases, alpha-(AlPdMnSi), beta-(AlPdMnSi), gamma-(AlCuRuSi), (Al,Zn)(49)Mg-32, alpha-(AlMnSi) and Al12Mn, of icosahedral quasicrystals are discussed systematically in terms of atom cluster arrangements. The structures of those approximants can be classified into two groups: firstly, that characterized as a simple-cubic packing of atom clusters with icosahedral symmetry or a 'CsCl'-type packing of two types of atom clusters, and, secondly, a body-centred packing of one type of atom cluster with icosahedral symmetry. The former, alpha-(AlPdMnSi), beta-(AlPdMnSi) and gamma-(AlCuRuSi), is suggested to be approximant phases of F-type icosahedral phases, and the latter, (Al,Zn)(49)Mg-32, alpha-(AlMnSi) and Al12Mn, to be those of P-type icosahedral phases. Atomic arrangements of the atom clusters with icosahedral symmetry in the approximant phases are characterized by the existence of a fundamental icosahedral cluster and are classified into two groups by the manner of the packing of atoms on the fundamental icosahedral cluster: namely, the so-called octahedral (alpha-(AlMnSi) and Al12Mn) and tetrahedral (alpha-(AlPdMnSi), beta-(AlPdMnSi), gamma-(AlCuRuSi) and (Al,Zn)(49)Mg-32) packings.
Title:
Icosahedral quasicrystal formation in Ti-Zr-based alloys and
a new classification technique
Authors:
Kim WJ. Gibbons PC. Kelton KF.
Source:
(list of journals)
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical
Properties. 78(5):1111-1124, 1998 Nov.
Abstract:
Until recently, icosahedral phase (i-phase) formation was studied primarily in Al-transition metal alloys. The Al-based i-phases generally fall into one of two classes; those believed to be based on the Pauling triacontahedron, fundamental to the Bergman 1/1 phase, and those based on the double-shell Mackay icosahedra found in the 1/1 alpha-(Al-Mn-Si) phase. Notable Bergman-type quasicrystals include i-(Al-Li-Cu) and i-(Al-Mg-Zn); i-(Al-Mn-Si) forms the best known Mackay-type i-phase. The large number of Ti-based i-phases now known, and the differences in their diffraction features raise the question of their fundamental structural units. To address this partially, results of X-ray and electron microscopy studies of Ti-Zr-Ni alloys, where Ni is replaced by Fe and Co, are reported. The character of the i-phases varies smoothly from the Ti-Zr-Ni quasicrystals, which probably are Bergman-type i-phases. to the Ti-Zr-Fe quasicrystals, which probably are Mackay types. A new classification method for icosahedral quasicrystals based on the ratio of the quasilattice constant a(q) to the average atomic separation [a(s)], computed from the measured density, is introduced and applied to both Al- and Ti-based quasicrystals. On the basis of this scheme, most Ti-based i-phases, including the Ti-3d transition metal-Si-O phases and Ti-Zr-Fe, form a third group, different from the Al-based Mackay and Bergman groups. Ti-Zr-Ni and Ti-Zr-Co quasicrystals fall into the same class as the Bergman-type Al-based i-phases.
Title:
Investigation of structural defects and inhomogeneities in Al-Pd-Mn
icosahedral quasicrystals by combined synchrotron X-ray
topography and phase radiography
Authors:
Mancini L. Reinier E. Cloetens P. Gastaldi J. Hartwig J. Schlenker M. Baruchel J.
Source:
(list of journals)
Philosophical Magazine A-Physics of Condensed Matter Defects & Mechanical
Properties. 78(5):1175-1194, 1998 Nov.
Abstract:
Phase-sensitive radiography, made possible by the lateral coherence of the beams from third-generation synchrotron-radiation sources, has been combined with monochromatic X-ray topography in an investigation of structural defects and inhomogeneities in the bulk of Al-Pd-Mn icosahedral single quasicrystal grains. Loop-shaped defects previously observed by X-ray topography are thus related with holes and second phase precipitates revealed by phase radiography. The evolution of these defects after annealing provides clues on their nature and formation.
Title:
Phenyl ring flips in crystals of
bis-(4-chlorophenyl)-sulphone and a binary criterion for distinguishing
chemical exchange from spin diffusion in deuteron exchange nuclear magnetic
resonance
Authors:
Speier P. Muller A. Meinel C. Haeberlen U.
Source:
(list of journals)
Molecular Physics. 95(5):859-870, 1998 Dec 10.
Abstract:
We demonstrate by selective saturation deuteron NMR experiments on a deuterated crystal of bis-(4-chlorophenyl)-sulphone (BCPS, the 'butterfly molecule') that, in the crystalline state, the two phenyl rings of this molecule are flipping through 180 degrees. This process is thermally activated, the kinetic parameters are Delta E = (71 +/- 5) kJ mol(-1) and k(0) = 10(15.5+/-0.8) s(-1). Our spectra also indicate a slow magnetization transfer, on a time scale of 50 s at room temperature, between deuterons located on different wings of the molecule. Flips of the molecule as a whole about a crystal and molecular twofold axis would account for this magnetization transfer. An alternative explanation is spin diffusion. To discriminate between these two possibilities we develop and apply a new criterion. It exploits the fact that the sign of quadrupolar order transferred between two I = 1 spin ensembles with quadrupole splittings of opposite sign depends on whether the quadrupolar order transfer occurs via chemical exchange or via spin diffusion. This criterion thus allows one, in a single experiment, to discriminate between chemical exchange and spin diffusion in a yes/no fashion. We therefore call it binary quadrupolar order criterion. Its application to BCPS yields the result that the observed slow magnetization transfer is due to spin diffusion and that the BCPS molecules are not flipping as a whole on a time scale of 50 s at room temperature.
Title:
Surface reactivity of a sputter-annealed Al-Pd-Mn
quasicrystal
Authors:
Jenks CJ. Lograsso TA. Thiel PA.
Source:
(list of journals)
Journal of the American Chemical Society. 120(48):12668-12669, 1998 Dec 9.
Title:
Structural studies of the fast oxygen ion conductor BICOVOX.15 by
single-crystal neutron diffraction at room temperature
Authors:
Muller C. Anne M. Bacmann M. Bonnet M.
Source:
(list of journals)
Journal of Solid State Chemistry. 141(1):241-247, 1998 Nov 15.
Abstract:
The room temperature crystal structure of the fast oxygen ion conductor Bi-4(V0.85Co0.15)(2)O11-delta (BICOVOX.15) was refined within the average tetragonal unit cell from single-crystal neutron diffraction data, The unit cell dimensions are a(T) = 3.929(2) Angstrom and c(T) = 15.476(9) Angstrom in space group I4/mmm with Z = 1. The conventional R-w factor is 0.067. The structure consists of intergrowth, along the c-axis, of alternating (Bi2O2)(2+) sheets and (VO(3.5)square(0.5))(2-) oxygen-deficient perovskite-like layers. The compound, which exhibits a high ionic conductivity at moderate temperatures, undergoes a phase transition around 780 K between the disordered high-temperature gamma-phase and the lower temperature gamma'-phase, showing a modulated superstructure. Oxygen vacancies are localized in the perovskite-like layers, oxygen stoichiometry is derived, and oxygen diffusion paths are proposed for the gamma'-phase at room temperature, (C) 1998 Academic Press.
Title:
General models for the distributions of electric field gradients in
disordered solids [Review]
Authors:
Le Caer G. Brand RA.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 10(47):10715-10774, 1998 Nov 30.
Abstract:
Hyperfine studies of disordered materials often yield the distribution of the electric field gradient (EFG) or related quadrupole splitting (QS). The question of the structural information that may be extracted from such distributions has been considered for more than fifteen years. Experimentally most studies have been performed using Mossbauer spectroscopy, especially on Fe-57. However, NMR, NQR, EPR and PAC methods have also received some attention. The EFG distribution for a random distribution of electric charges was for instance first investigated by Czjzek et al [1] and a general functional form was derived for the joint (bivariate) distribution of the principal EFG tensor component V-zz and the asymmetry parameter eta. The importance of the Gauss distribution for such rotationally invariant structural models was thus evidenced. Extensions of that model which are based on degenerate multivariate Gauss distributions for the elements of the EFG tensor were proposed by Czjzek. The latter extensions have been used since that time, more particularly in Mossbauer spectroscopy, under the name 'shell models'. The mathematical foundations of all the previous models are presented and critically discussed as they are evidenced by simple calculations in the case of the EFG tensor. The present article only focuses on those aspects of the EFG distribution in disordered solids which can be discussed without explicitly looking at particular physical mechanisms. We present studies of three different model systems. A reference model directly related to the first model of Czjzek, called the Gaussian isotropic model (GIM), is shown to be the limiting case for many different models with a large number of independent contributions to the EFG tensor and not restricted to a point-charge model. The extended validity of the marginal distribution of eta in the GIM model is discussed. It is also shown that the second model based on degenerate multivariate normal distributions for the EFG components yields questionable results and has been exaggeratedly used in experimental studies. The latter models are Further discussed in the light of new results. The problems raised by these extensions are due to the fact that the consequences of the statistical invariance by rotation of the EFG tensor have not been sufficiently taken into account. Further difficulties arise because the structural degrees of freedom of the disordered solid under consideration have been confused with the degrees of freedom of QS distributions. The relations which are derived and discussed are further illustrated by the case of the EFG tensor distribution created at the centre of a sphere by m charges randomly distributed on its surface. The third model, a simple extension of the GIM, considers the case of an EFG tensor which is the sum of a fixed part and of a random part with variable weights. The bivariate distribution f(V-zz, eta) is calculated exactly in the most symmetric case and the effect of the random part is investigated as a function of its weight. The various models are more particularly discussed in connection with short-range order in disordered solids. An ambiguity problem which arises in the evaluation of bivariate distributions of centre lineshift (isomer shift) and quadrupole splitting from 1/2 <->> 3/2: Mossbauer spectra is finally quantitatively considered.
Title:
Matrix element effects in the angle-resolved photoemission spectrum of BISCO
Authors:
Bansil A. Lindroos M.
Source:
(list of journals)
Journal of Physics & Chemistry of Solids. 59(10-12):1879-1883, 1998 Oct-Dec.
Abstract:
We report first-principles angle-resolved photointensity (ARPES) simulations in Bi2212 in order to assess the importance of matrix element effects in the ARPES spectra. Our calculations properly account for the photoemission process and include full crystal wavefunctions of the initial and final states in the presence of the surface. The spectral weight of the ARPES feature associated with the CuO2 plane bands is found to be strongly anisotropic in the (k(x), k(y)) plane. These results indicate that the relationship between the ARPES intensities and the underlying electronic structure can be quite complicated and that caution should be exercised in interpreting detailed features of the ARPES intensities in terms of the properties of the theoretical one-particle spectral density functions. (C) 1998 Elsevier Science Ltd. All rights reserved.
Title:
Structural transitions in 2,2 '-bipyridine adlayers on Au(111) - an in-situ
STM study
Authors:
Dretschkow T. Lampner D. Wandlowski T.
Source:
(list of journals)
Journal of Electroanalytical Chemistry. 458(1-2):121-138, 1998 Oct 30.
Abstract:
The adsorption and phase formation of 2,2'-bipyridine on the Au(lll) \ aqueous electrolyte interface has been studied using ac-voltammetry and in-situ scanning tunneling microscopy. At positive charge densities 2,2'-bipyridine forms in neutral and acidic solutions an ordered monolayer of 'molecular chains' (phase I) determined by directional substrate-adsorbate coordination and lateral pi-stacking. The distance between adjacent parallel rows is 9.6 +/- 0.5 Angstrom. Molecules are tilted from the normal to the chain axis by an angle of 28 +/- 2 degrees. The rotation angle gamma = 30 degrees between the stacking rows and the [11 (2) over bar]-direction of the former Au(lll)-(p x root 3) reconstruction lines was obtained, and a commensurate (4 x 2 root 3) unit cell is proposed. A second ordered 'stacking phase' of 2,2'-bipyridine, which is incommensurate with the underlying substrate surface, was found at negative charge densities in acidic solutions (phase V). Nearly defect-free molecular rows decorate the reconstruction lines of Au(lll)-(p x root 3) at an angle of 86 degrees; each molecule is tilted from the chain axis by either + 23 or - 16 degrees. Identical tilt angles repeat every other row. The dynamics of film formation and dissolution as well as the substrate stability were investigated by in-situ STM as a function of electrode potential and temperature. It was found that both formation and dissolution of phase I are governed by nucleation and growth processes. Several metastable adlayer structures were found during these transitions. Their appearance and characteristic properties depend strongly on the applied substrate potential perturbation, accompanied by structural changes of the electrode surface. The 2,2'-bipyridine phase I stabilizes the Au(lll)-(p x root 3) reconstruction only in neutral solutions, but inhibits, in general, the onset of gold oxidation at more positive potentials. The 'break-off' of the adlayer starts with a broadening of domain boundaries, the formation of channels, holes and smaller adlayer patches until the organic phase can no longer be resolved at E>1.25 V. Remarkably, the entire process is fairly reversible. (C) 1998 Elsevier Science S.A. All rights reserved.
Title:
Modulated structure of orthorhombic
lazurite
Authors:
Evsyunin VG. Rastsvetaeva RK. Sapozhnikov AN. Kashaev AA.
Source:
(list of journals)
Crystallography Reports. 43(6):999-1002, 1998 Nov-Dec.
Abstract:
The structure of the orthorhombic modification of lazurite from the deposit of the southwestern Pamirs is determined (sp, gr. Pnaa, R-hkl = 0.068, 1460 reflections). The character of the commensurate modulations of the displacements and the replacements of all the atoms in the structure is studied. Three types of sulfur radicals that replaced chlorine atoms in the sodalite-type structure are established.
Title:
Scanning tunneling microscopy study of a BiCl3-graphite intercalation
compound
Authors:
Walter J. Shioyama H. Sawada Y.
Source:
(list of journals)
Carbon. 36(12):1811-1814, 1998.
Abstract:
In the presence of chlorine gas, BiCl3 was intercalated from the gas phase into highly oriented pyrolytic graphite; second-stage compounds were obtained. The surface structure in air was determined with a scanning tunneling microscope. A long-periodical rectangular structure was observed with an a-axis of 1429 pm and a b-axis of 1841 pm. This commensurate structure fits very well with X-ray diffraction data for a superlattice in BiCl3 graphite intercalation compounds published by another group. (C) 1998 Elsevier Science Ltd. All rights reserved.
Title:
Noncentrosymmetric structure of a decagonal Al70Mn17Pd13
quasicrystal
Authors:
Weber S. Yamamoto A.
Source:
(list of journals)
Acta Crystallographica - Section a - Foundations of
Crystallography. 54(Part 6 Special Issue 2):997-1005, 1998
Nov 1.
Abstract:
A noncentrosymmetric structure of decagonal Al70Mn17Pd13 With the space group P10(5)mc was determined for the first time on the basis of a single-crystal X-ray data set. This analysis gave a considerable improvement over the corresponding centrosymmetric model [Weber & Yamamoto (1997). Philos. Mag. A76, 85-106]. For 1428 independent reflections, R-w = 0.119 (R = 0.167) and a reasonable chemical composition of Al69.1Mn18.5Pd12.4 was obtained by the introduction of the shift from an ideal atom position. The structure loses the inversion center mainly by the breakdown of the mirror plane perpendicular to the tenfold axis which is caused by the asymmetric chemical arrangement.
Title:
Average unit cell of the Fibonacci chain
Authors:
Wolny J.
Source:
(list of journals)
Acta Crystallographica - Section a - Foundations of
Crystallography. 54(Part 6 Special Issue 2):1014-1018, 1998
Nov 1.
Abstract:
An average unit cell for the Fibonacci chain has been constructed in physical space. The positions of atoms have been replaced by a statistical probability function of atomic displacements from the nearest point of the reference lattice. An analytical expression for diffraction peak intensities has been derived.
Title:
Negative thermal expansion in beta-quartz
Authors:
Welche PRL. Heine V. Dove MT.
Source:
(list of journals)
Physics & Chemistry of Minerals. 26(1):63-77, 1998 Nov.
Abstract:
Computer modelling and theoretical analysis are used to explain the nearly zero and slightly negative coefficients of thermal expansion in beta-quartz well above the alpha-beta phase transition temperature. Quartz was selected for study as an archetypal material with a framework structure of stiff units, namely SiO4 tetrahedra, linked through shared oxygen atoms as very flexible hinges. The contributions of the soft mode, the Vallade mode, the TA(z) phonon branch and the phonon spectrum as a whole are discussed in detail. The results fully support and illustrate a recent theory of the negative contribution to thermal expansion in framework structures. It is a geometrical effect due to the rotation of the tetrahedral units, folding together as they vibrate. The very rapid increase in the lattice parameters for about 20 K above the transition temperature is well accounted for within quasiharmonic theory, and is therefore not evidence for critical fluctuations or fluctuating patches of alpha(+), alpha(-) structure.
Title:
Direct imaging of local chemical disorder and columnar vacancies in ideal
decagonal Al-Ni-Co quasicrystals
Authors:
Yan Y. Pennycook SJ. Tsai AP.
Source:
(list of journals)
Physical Review Letters. 81(23):5145-5148, 1998 Dec 7.
Abstract:
Atomic-resolution Z-contrast images provide direct images of chemical disorder and columnar vacancies in an ideal Al-Ni-Co decagonal quasicrystal. Chemical disorder occurs in the central ring of the 2 nm clusters and involves both Al and Ni(Co) atoms. Columnar vacancies are observed in the form of closely spaced, half-occupied atomic columns in specific rings within the clusters. This structure, derived from real space images, differs significantly from previous atomic models. .
Title:
Transport properties of the hierarchical model for stretched polymers
Authors:
Zhu CP. Xiong SJ. Chen T.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(19):12848-12852, 1998 Nov 15.
Abstract:
We prove that the hierarchical fractal model recently proposed for describing the stretched polymers [A. N. Samukhin et at, Phys. Rev. Lett. 78, 326 (1997)] is equivalent to a one-dimensional chain with hierarchical aperiodic structure. By use of the transfer matrix technique we calculate the electronic transmission and the de conductance. We find that there exist sharp-edged transmission subbands and gaps, but that the transmission subbands are rich in substructures that show self-similarity. The temperature dependence of conductance g(T) is sensitive to the variation of the Fermi level and to the structure parameters transmission and variation of the original fractal structure. The relationship of the obtained results to the experimental data and other theoretical works is discussed. .
Title:
Exact eigenstates of tight-binding Hamiltonians on the Penrose tiling
Authors:
Repetowicz P. Grimm U. Schreiber M.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(20):13482-13490, 1998 Nov 15.
Abstract:
We investigate exact eigenstates of tight-binding models on the planar rhombic Penrose tiling. We consider a vertex model with hopping along the edges and the diagonals of the rhombi. For the wave functions, we employ an ansatz, first introduced by Sutherland, which is based on the arrow decoration that encodes the matching rules of the tiling. Exact eigenstates are constructed for particular values of the hopping parameters and the eigenenergy. By a generalized ansatz that exploits the inflation symmetry of the tiling, we show that the corresponding eigenenergies are infinitely degenerate. Generalizations and applications to other systems are outlined. .
Title:
Superstructure formation of large organic adsorbates on a
metal surface: A systematic approach using oligothiophenes on Ag(111)
Authors:
Soukopp A. Glockler K. Kraft P. Schmitt S. Sokolowski M. Umbach E. Mena-Osteritz E. Bauerle P. Hadicke E.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(20):13882-13894, 1998 Nov 15.
Abstract:
A series of "end-capped" oligothiophenes ECnT with different chain lengths n (n = 3-6)were vapor deposited onto the Ag(lll) surface. The adsorption and structural ordering was investigated by thermal desorption spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy. For all molecules we observe highly ordered monolayers with flat-lying molecules and long-range ordered domains of several hundred Angstrom diameter. For the two smaller oligomers (EC3T and EC4T), two phases-a commensurate (relaxed) and an incommensurate (compressed)-are found, whereas the two longer molecules (EC5T and EC6T) form only incommensurate phases. The six unit cells exhibit significantly different symmetries, containing 1, 2, or 4 molecules. The formation of the geometric structures is discussed under the aspect of molecular size, molecular symmetry, and interplay of the molecule-substrate and molecule-molecule interactions. The last aspect was also investigated by concomitant force-field calculations. .
Title:
Isolated magnetic moments in icosahedral Al-Pd-Mn alloys
Authors:
Krajci M. Hafner J.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(21):14110-14112, 1998 Dec 1.
Abstract:
We present ab initio calculations of the formation of magnetic moments in a large approximant to icosahedral Al-Pd-Mn quasicrystals. It is shown that large magnetic moments can form on a small number of Mn sites characterized by a loose coordination by Al atoms and some close Pd neighbors. d-d hybridization is shown to play an important role. .
Title:
Structural transformations at the surface of the decagonal
quasicrystal Al70Co15Ni15
Authors:
Zurkirch M. Bolliger B. Erbudak M. Kortan AR.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(21):14113-14116, 1998 Dec 1.
Abstract:
By using Auger electron spectroscopy and secondary-electron imaging, we show that, as a result of bombardment with 1.5-keV Ar+ ions, Al is preferentially sputtered and the surface structure of a decagonal Al70Co15Ni15 quasicrystal transforms to body-centered cubic. Annealing the sample at 700 It restores the Al concentration at the surface and, thereby, the quasicrystalline structure. Real-time observations establish the orientational relationship between the quasicrystalline and cubic surface structures, which we use to propose an atomic model of their interface. .
Title:
Growth defects in BSCCO (2212) single crystal whiskers
Authors:
Timofeev VN. Gorlova IG.
Source:
(list of journals)
Physica C. 309(1-2):113-119, 1998 Dec 1.
Abstract:
The defect structure of superconducting single crystal whiskers BSCCO (2212) was studied by high voltage transmission electron microscopy. Dislocations, twins, growth steps, antiphase domains associated with a commensurate modulation and antiphase boundaries of incommensurate modulation were found. The latter are inherent to all whiskers in contrast to any other defects. The defect structures of the whiskers and BSCCO (2212) plate-like single crystals are compared. The influence of some defects on superconducting properties of the material is discussed. (C) 1998 Published by Elsevier Science B.V. All rights reserved.
Title:
X-ray analysis of the structure of a copoly(ester-imide)
Authors:
Cho JD. Blackwell J. Chvalun SN. Jin JG. Ni YS.
Source:
(list of journals)
Journal of Polymer Science Part B-Polymer Physics. 36(17):3137-3145, 1998
Dec.
Abstract:
The structure of a thermotropic liquid crystalline copoly(ester-imide) prepared from p-hydroxybenzoic acid (48 mol %), 4,4'-dihydroxybenzophenone (26 mol %), and N,N'-bis(trimellitimide)hexane (26 mol %) has been investigated by X-ray diffraction. X-ray fiber diagrams of as-spun and annealed fibers contain a series of aperiodic layer lines reminiscent of those seen for fibers of other copolymers that have extended chain conformations and completely random monomer sequences. The positions of these layer lines were reproduced approximately in simulation of the X-ray scattering by a fully extended chain of completely random sequence, and the match was improved to within experimental error when we considered a stereochemically acceptable sinuous chain. This agreement was lost when the sequence statistics deviated were completely random. (C) 1998 John Wiley & Sons, Inc.
Title:
Crystal and magnetic structure of a novel
compound UCu5Al. Structural stability with Th-substitution
Authors:
Troc R. Tran VH. Wolcyrz M. Andre G. Bouree F.
Source:
(list of journals)
Journal of Magnetism & Magnetic Materials. 190(3):251-256, 1998 Dec.
Abstract:
The antiferromagnetically ordered, moderate heavy fermion UCu5Al, crystallises in the original tetragonal I4/mmm structure, which remains unchanged in the U1 - xThxCu5Al solid solutions up to x approximate to 0.35. Above this composition, other solid solutions with general chemical formula (U1 - xThx)(Cu1 - yAly)(5) are formed, having a different type of structure, namely the hexagonal CaCu5-type. Below T-N = 18 K UCu5Al orders with a sine-modulated, incommensurate magnetic structure described by a wave vector k = (0, 0, 0.55) and the moment amplitude of 1.45(5) mu(B) at 1.4 K. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
Low-temperature dynamics of incommensurate biphenyl as
probed by spectral hole burning
Authors:
Suisalu A. Zazubovich V. Kikas J. Friebel J. Friedrich J.
Source:
(list of journals)
Europhysics Letters. 44(5):613-619, 1998 Dec 1.
Abstract:
We have measured the temperature dependence of the homogeneous width of spectral holes in the incommensurate phase III of chlorin-doped biphenyl from 60 mK to 10 K. Below 2 K a power law (similar to T-alpha, alpha = 1.36, 1.74 for different spectral peaks) prevails. Above 2 K a strong coupling to low-energy (5 and 9 cm(-1)) vibrational modes dominates. No indication of a low-temperature lock-in transition was found.
Title:
Electrical and optical investigations of Rb2ZnCl4 crystals
in the vicinity of the incommensurate phase
Authors:
Abu El-Fadl A.
Source:
(list of journals)
European Physical Journal-Applied Physics. 4(1):5-9, 1998 Oct.
Abstract:
Temperature dependence of the dielectric constant epsilon and the electrical resistivity rho of Rb2ZnCl4 (RZC) along the three crystallographic axes were measured between 260 and 360 K. The electrical measurements clearly reveal the paraelectric incommensurate phase around 303 K. Peaks in the dielectric constants epsilon(a) and epsilon(b) were observed at this transition temperature. The results of the electrical resistivity were analyzed and the activation energies of conduction at different temperature regions were evaluated. The dependence of the absorption coefficient alpha on the photon energy and on temperature near the fundamental absorption edge was measured. Exponential dependence of that coefficient according to the Urbach's rule was observed and the Urbach parameters were determined and their temperature dependence was investigated. The temperature gradient of the band gap (partial derivative E-g/partial derivative T) reveals an anomaly at the incommensurate paraelectric phase. The indirect band gap was shifted towards the longer wavelength (red shift) with increasing temperature. This behaviour could be interpreted in terms of electron lattice interaction and crystal field splitting.
Title:
Al-Cu approximants in the Al3Cu4 alloy
Authors:
Dong C. Zhang QH. Wang DH. Wang YM.
Source:
(list of journals)
European Physical Journal B. 6(1):25-32, 1998 Nov.
Abstract:
The Al3Cu4 composition, with an e/a ratio of 1.86 being close to ternary Al-Cu-TM (Transition Metal) quasicrystals, has been chosen for the search of AI-Cu approximants. Phase structures and compositions were studied using TEM, ii-ray diffraction and EPMA techniques. Two new phases were found: face-centered orthorhombic oF-Al43.2Cu56.8 (a = 0.816(6), b = 1.414(9), c = 0.999(5) nm) and body-centered orthorhombic oI-Al41.3Cu58.7 (oI, a = 0.408(3), b = 0.707(4), c = 0.999(5) nm). Their e/a ratios are the same as that of the Al-Cu-Fe icosahedral quasicrystal. Their space groups are probably oF-Fmm2 and oI-Imm2. Both are B2 vacancy-containing superstructures; unit cell compositions can be expressed approximately as oF-Al(36)Cu(48)square(12) and oI-Al(8)Cu(12)square(4) (square: vacancies). They both exist in twinning variants of the types 120 degrees/[001] and 180 degrees/[310]. Such twinning modes indicate that these orthorhombic phases are the decomposition products of a high-temperature parent phase epsilon 2-Al2Cu3, the atomic structure of which contains pentagonal atomic arrangements. Therefore the of, oI, and epsilon 2 phases are all B2-based approximants corresponding to the Al-Cu-TM quasicrystals.
Title:
Charge transfers in complex transition metal alloys (Ti2Fe)
Authors:
Abramovici G.
Source:
(list of journals)
European Physical Journal B. 6(1):39-44, 1998 Nov.
Abstract:
We introduce a new Non-Orthogonal Tight-Binding model, for complex alloys, in which electronic structure is characterized by charge transfers. We give the analytic calculation of a charge transfer, in which overlapping two-center terms are rigorously taken into account. Then, we apply numerically this result to an approximant phase of a quasicrystal of Ti2Fe alloy. This model is more particularly adapted to transition metals, and gives realistic densities of states.
Title:
Thermal behaviour of dimesogenic liquid crystal compounds
under pressure
Authors:
Maeda Y. Yun YK. Jin JI.
Source:
(list of journals)
Thermochimica Acta. 322(2):101-116, 1998 Nov 25.
Abstract:
Thermal behaviour of two dimesogenic liquid crystal compounds, KI5 and KI5A, was investigated under atmospheric and hydrostatic pressure by a differential scanning calorimeter and a high-pressure DTA apparatus. The enantiotropic phase transitions of crystal - multiple mesophases - isotropic liquid for both compounds were observed under atmospheric pressure. On the other hand, only two major peaks of crystal - smectic (melting) and cholesteric - isotropic (isotropization) transitions were observed under hydrostatic pressure up to 300 MPa. Not all the multiple mesophasic transitions of the KI5 compound between the incommensurate smectic A (S-Ainc) and cholesteric (N*) phases could be detected because of their very small heat of transitions and the low sensitivity of the high-pressure DTA apparatus. A pressure-induced crystal polymorph of the KI5 compound appears at pressure above about 20 MPa and the crystal polymorph is formed preferentially under pressure above 100 MPa. The polymorph has a melting temperature higher than that of the normal crystal and it is thermodynamically stable. Enantiotropic phase transitions of crystal - S-Ainc-(TGB-N*)-I of the KI5A compound is unchanged at pressures up to 160 MPa, but double or triple peaks are observed at the crystal - S-Ainc transition under high pressure above about 180 MPa. This phenomenon is ascribed to the formation of a pressure-induced crystal polymorph and a high-pressure mesophase. The incomplete T vs. P phase diagrams of the KI5 and KI5A compounds were constructed. (C) 1998 Elsevier Science B.V.
Title:
Lattice instability of Cs2HgCl4 crystals - I. Elastic
properties
Authors:
Kityk AV. Zadorozhna AV. Shchur YI. Martynyuk-Lototska IY. Vlokh OG.
Source:
(list of journals)
Physica Status Solidi B-Basic Research. 210(1):35-45, 1998 Nov.
Abstract:
Using ultrasonic velocity measurements all components of the elastic constant matrix C-ij, elastic compliance matrix S-ij and matrix of linear compressibility constants K-ij of orthorhombic C2HgCl4 crystals have been determined in a wide temperature range including the phase transition region from the normal to incommensurate phase. The obtained results are considered within the framework of the phenomenological theory.
Title:
One-dimensional Hamiltonian for columnar liquid crystals
Authors:
D'hulst R. Caille A.
Source:
(list of journals)
Journal of Statistical Physics. 92(5-6):865-889, 1998 Sep.
Abstract:
A one-dimensional Hamiltonian is derived upon microscopic considerations to model the columnar phases of a liquid crystal made of molecules of discrete rotational symmetry. The study deals with the ground state of this Hamiltonian, only the orientational degrees of freedom being taken into account. The intracolumnar interaction is described by the natural cantedness of an isolated column, while interaction parameters H and G characterize the amplitude of the local crystal field at a site originating from the other surrounding columns. The phase diagrams of the orientational ordering along the column are numerically investigated and a previous analytical approach is briefly recalled. A new perturbation development is proposed. This allows us to analyse a multiphase point and to explain the appearance of an infinity of phases in the vicinity of this point. The anisotropy of the columnar lattice is then investigated with the use of the same perturbation development, and some of the properties of a complex phase diagram are examined numerically as well as analytically.
Title:
Reinvestigation and structural approach of the Ba-Pt-O system for 4/3 <
Y=Ba/Pt < 5/2
Authors:
Grasset F. Weill F. Darriet J.
Source:
(list of journals)
Journal of Solid State Chemistry. 140(2):194-200, 1998 Nov 1.
Abstract:
A reinvestigation of the Ba-rich region of the Ba-Pt-O system has been undertaken. The existence of a solid solution, already mentioned, has been confirmed, and its true formulation has been determined: Ba-12[BaxPt3-x]Pt6O27 with 0 less than or equal to x less than or equal to 3. The structure of these phases can be schematically considered as being built up from the periodic stacking along the c direction of one close-packing [Ba3O9] layer, similar to those of the hexagonal perovskite, and three [Ba(3)A'O-6] layers, with A' = Ba, Pt. The stacking of these mixed layers is of hexagonal type, and then columns parallel to c are formed. They consist of octahedra and trigonal prisms, sharing faces, which are occupied by A' cations. For 0 less than or equal to x less than or equal to 1, the structure appears to be incommensurate and should be described as a composite crystal based on two subsystems: [Ba] and [(Ba, Pt)O-3]. For x > 1, the X-ray diffraction pattern can be explained using a three-dimensional cell, but the structure refinement attempts as well as the electron diffraction patterns seem to indicate these phases are commensurate modulated structufes. (C) 1998 Academic Press.
Title:
Diffraction and DAFS studies of a Ba-4(BaxPt1-x2+)Pt24+O9 twinned
crystal, a member of the Ba-p(BaxPt1-x2+)Ptp-24+O3p-3 series
Authors:
Vacinova J. Hodeau JL.
Source:
(list of journals)
Journal of Solid State Chemistry. 140(2):201-218, 1998 Nov 1.
Abstract:
Crystallographic studies of the Ba-Pt-O system have been undertaken using X-ray and electron diffraction techniques. The system is described by means of a Ba-p(BaxPt1-x2+)Ptp-24+O3p-3 formula which corresponds to a BaO3 hexagonal based framework with Pt chains, where p represents the oxygen deficiency and the presence of both Pt4+ and Pt2+ cations in the compounds, and x a possible substitution of Pt4+ by Ba2+ in trigonal prismatic sites. The structure of a Ba-4(Ba0.04Pt0.962+)Pt24+O9 crystal has been solved by using 5548 X-ray difraction reflections collected on a twinned crystal, Refinements were performed with two distinct models: an "average" P321 space group and an "orthorhombic" Ct space group with cell parameters a = 17.460(4) Angstrom, b = 10.085(2) Angstrom, c = 8.614(3) Angstrom. In this structure, two Pt4+ and one Pt2+ cations are distributed over four Ba planes and form chains along the c axis, consisting of two face-sharing Pt4+O6 octahedra connected with one Pt2+O6 trigonal prism. A lattice misfit occurs between the rigid barium lattice and the PtO3 chains, giving rise to a composite structure. Twinning and domain configurations are described and taken into account in the refinement. This twinning is related to the presence of Pt2+ cations, whose positions break the threefold axis symmetry. A diffraction anomalous fine structure (DAFS) study was also performed on this twinned single crystal. Anomalous scattering factors f' and f " for platinum in this crystal were refined near the LmPt absorption edge. They confirm the weak barium occupancy of the trigonal prismataic site and the Pt4+ valence of the octahedral sites. Reflection overlaps, due to twinning, flatten the DAFS sensitivity to Pt atoms in the prismatic sites and did not allow their clear valence determination, but Pt-O bond lengths agree with the presence of Pt2+ cations at the center of prismatic faces. Electron diffraction patterns of powders having slightly different composition show a continuous evolution of incommensurate Bragg peaks and a weak correlation between the PtO3 chains. They also confirm the composite nature and the one-dimensionality of the Ba-p(BaxPt1-x2+)Pp-24+O3p-3 series, which can produce highly anisotropic physical properties. (C) 1998 Academic Press.
Title:
Diffractive point sets with entropy
Authors:
Baake M. Moody RV.
Source:
(list of journals)
Journal of Physics A-Mathematical & General. 31(45):9023-9039, 1998 Nov 13.
Abstract:
After a brief historical survey, this paper introduces the notion of entropic model sets (cut and project sets), and, more generally, the notion of diffractive point sets with entropy. Such sets may be thought of as generalizations of lattice gases. We show that taking the site occupation of a model set stochastically results, with probabilistic certainty, in well-defined diffractive properties augmented by a constant diffuse background. We discuss both the case of independent, but identically distributed (i.i.d.) random variables and that of independent, but different (i.e. site dependent) random variables. Several examples are shown.
Title:
Octagonal quasicrystals and a formula for shelling
Authors:
Morita J. Sakamoto K.
Source:
(list of journals)
Journal of Physics A-Mathematical & General. 31(46):9321-9325, 1998 Nov 20.
Abstract:
Octagonal quasicrystals will be realized in a cyclotomic field, and a formula for shelling will be given using number theory.
Title:
High-order incommensurate modulations and
incommensurate superstructures in
transparent Sr0.6Ba0.4Nb2O6 (SBN40) ceramics
Authors:
Lee HY. Freer R.
Source:
(list of journals)
Journal of Applied Crystallography. 31(Part 5):683-691, 1998
Oct 1.
Abstract:
Ceramics of strontium barium niobate (Sr0.6Ba0.4Nb2O6, SBN40), having the tetragonal tungsten bronze (TTB) structure, were prepared by a conventional processing route; sintering at temperatures in the range 1573-1723 K yielded products with three types of microstructure. Incommensurate superstructures were investigated by transmission electron microscopy (TEM). Modulation of the incommensurate superstructure (ICS) depended on microstructural development. The lowest-order ICS modulation was a common feature in all the SBN40 ceramics, regardless of microstructure. (h+1/2,h+1/2,l) reflections and unusually low delta (incommensurability parameter) were observed in SBN40 specimens having abnormally large grains and thus a certain degree of A-site ordering was expected. Transparent SBN40 ceramics which exhibited large homogeneous grains were characterized by a shortened c axis, intense [001] X-ray diffraction reflections, a multiplication of (110) and (001) cell spacings and the appearance of higher-order ICS reflections. Planar defects, having the thickness of one d(110) spacing, were observed aligned along {110}. The development of a higher-order structural modulation and of ICS reflections is believed to reduce the structural energy; the development of planar defects appears to stabilize the incommensurate phase.
Title:
Evidence for variable range hopping conductivity in the ordered
quasicrystal i-AlPdRe
Authors:
Delahaye J. Brison JP. Berger C.
Source:
(list of journals)
Physical Review Letters. 81(19):4204-4207, 1998 Nov 9.
Abstract:
We Show that the conductivity of the quasicrystal i-AlPdRe follows a Mott's variable range hopping conduction law sigma(T) = sigma(0) exp -(T-0/T)(1/4) in the temperature range 20-600 mK. The i-AlPdRe phase thus behaves like disordered insulators at very low temperature. We find a very low activation term T-0 similar to 1 mK, which is an indication of a large localization length xi, in accordance with the vicinity to the metal-insulator transition. This is the first time that a pure Mott's law is observed at very low temperature in a structurally ordered compound made of metallic elements.
Title:
Magnetic incommensurability in tetragonal DyRu2Ge2
Authors:
Garnier A. Gignoux D. Ouladdiaf B. Schmitt D. Shigeoka T.
Source:
(list of journals)
Physica B. 254(3-4):166-171, 1998 Nov.
Abstract:
Magnetization measurements on a single crystal as well as neutron diffraction experiments on powder and a single crystal of the tetragonal DyRu2Ge2 compound are presented. They allowed to evidence a huge uniaxial anisotropy and to build up the field-temperature magnetic phase diagram along the easy [0 0 1] magnetization direction below T-N = 20 K. We did not observe a change of behaviour at the transition temperature T-l = 3 K at which a peak appears in the thermal variation of the specific heat. Such a transition, also observed in other RRu2Ge2 and RRu2Si2 (R = Tb or Dy) compounds, is likely to be associated with the onset of a mixed magnetic structure at low temperature. Contrary to these compounds where the low-temperature magnetic propagation vector is long-range commensurate, in DyRu2Ge2, from our experiments, we can assert that the propagation vector is truly incommensurate. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
An in situ STM study of sulphate adsorption on copper(111) in acidic aqueous
electrolytes
Authors:
Li WH. Nichols RJ.
Source:
(list of journals)
Journal of Electroanalytical Chemistry. 456(1-2):153-160, 1998 Sep 30.
Abstract:
Ordered structures have been observed by STM over a wide potential range for sulphate adsorbed on a Cu(111) electrode from aqueous acidic media. The structures observed are complex having large unit cells and showing both short-range and long-range periodicity, with Moire pattern formation. The short-range periodicity gives rise to a parallelogram sub-structure of dimensions b = (0.70 +/- 0.03) nm, b' = (0.47 +/- 0.03) nm and beta = (72 +/- 5)degrees. Three 120 degrees rotational domains are seen for this structure. This sub-structure has dimensions similar to the unit cell for the (root 3a x root 7a) structure, which has been previously observed for sulphate adsorbed on Au(111), Rh(111) and Pt(111). We propose that the sub-structure observed on Cu(111) arises also from an adsorbed sulphate ad-layer, with co-adsorbed water or cations, similar to that observed on the other metals. However, by contrast, we observe a distinct Moire pattern for sulphate/Cu(111), while no such Moire pattern has been observed for the sulphate/Rh(111) or Au(111) or Pt(111) systems. The measured 'lattice' constants for the Moire pattern, which has a distorted hexagonal structure, are c = (2.9 +/- 0.3) nm, c' = (3.7 +/- 0.3) nm and chi = (57 +/- 5)degrees. The Moire pattern arises from the superposition of the incommensurate adsorbate superstructure with the underlying copper substrate, which itself may also be reconstructed in the presence of the adsorbate. The fact that a complex incommensurate ad-layer is formed, which does not appear to lie along any high symmetry directions of the Cu(111) substrate, indicates that strong adsorbate-adsorbate interactions override the substrate-adsorbate interactions. This gives further credence to the model in which the very similar (root 3a x root 7a) structures previously observed on Au(111), Rh(111) and Pt(111) incorporate 'structured water', which hydrogen bonds with adjacent sulphate chains, forming a particular stable ad-layer structure. (C) 1998 Elsevier Science S.A. All rights reserved.
Title:
Effect of n=1 buffer layers on n=2 and n=3 thin films of Bi2Sr2Can-1CunOy
Authors:
Oku T. Ajisaka O. Inuzuka H. Horie Y. Nomiyama T. Miyazaki T.
Source:
(list of journals)
Japanese Journal of Applied Physics Part 2-Letters. 37(11A):L1304-L1307, 1998
Nov 1.
Abstract:
The effect of n = 1(2201) buffer layers on it = 2(2212) and n = 3(2223) thin films of Bi2Sr2Can-1CunOy was investigated to reduce the strain caused by the lattice mismatch between the films and the substrates. The bilayer thin films of 2213/2201 and 2212/2201 were grown epitaxially on SrTiO3 (100) substrates by de sputtering. When the thickness of the buffer layer was 10-25 nm, the superconducting transition temperature increased by similar to 20 K for 2223/2201 and by similar to 6 K for 2212/2201. The increase was attributed to the reduction of the strain from the experimental results of the full width at half-maximum of X-ray diffraction peaks, the length along the c-axis and the roughness of the film surface.
Title:
Microphase separation and modulated phases in a Coulomb
frustrated Ising ferromagnet
Authors:
Viot P. Tarjus G.
Source:
(list of journals)
Europhysics Letters. 44(4):423-428, 1998 Nov 15.
Abstract:
We study a 3-dimensional Ising model in which the tendency to order due to short-range ferromagnetic interactions is frustrated by competing long-range (Coulombic) interactions. Complete ferromagnetic ordering is impossible for any nonzero Value of the frustration parameter, but the system displays a variety of phases characterized by periodically modulated structures. We have performed extensive Monte Carlo simulations which provide strong evidence that the microphase separation transition between paramagnetic and modulated phases is a fluctuation-induced first-order transition. Additional transitions to various commensurate phases may also occur when further lowering the temperature.
Title:
Prediction and verification of the structural chemistry of new
one-dimensional barium/copper/iridium oxides
Authors:
Blake GR. Sloan J. Vente JF. Battle PD.
Source:
(list of journals)
Chemistry of Materials. 10(11):3536-3547, 1998 Nov.
Abstract:
We propose a classification scheme for the commensurate phases in the family of pseudo one-dimensional structures formed from the mixed hcp stacking of A(3)O(9) and oxygen-deficient A(3)A'O-6 layers. We envisage these compounds as composites of two substructures having common a and b unit cell parameters but different parameters c(1) and c(2). Use of the ratio c(1)/c(2) facilitates the prediction of new commensurate structures while allowing for the commonly incommensurate nature of materials in this family. The structures of the new commensurate phases Ba5CuIr3O12, Ba14Cu3Ir8O33, Ba16Cu3Ir10O39, and Ba9Cu2Ir5O21 are predicted and subsequently verified by powder X-ray diffraction and HRTEM. Ba5CuIr3O12 has a 10 layer structure with space group P321, a = 10.14382(8) Angstrom, c = 21.6553(2) Angstrom; Ba14Cu3Ir8O33 has a 14 layer structure with space group P321, a = 10.14585(8) Angstrom, c = 29.9574(3) Angstrom; Ba16Cu3Ir10O39 has a 16 layer structure with space group P321, a = 10.13643(7) Angstrom; c = 35.0616(3) Angstrom; Ba9Cu2Ir5O21 has an 18 layer structure with space group R32, a = 10.14464(11) Angstrom, c = 38.2455(6) Angstrom. Sequences of trigonal prismatic sites and octahedral sites run in chains parallel to z, with Ba cations located between the chains; the distribution of iridium and copper cations in the octahedral and trigonal prismatic sites is disordered in each case. Electron diffraction patterns and lattice images show evidence for modulation in the structures of Ba5CuIr3O12, Ba14Cu3Ir8O33, and Ba16Cu3Ir10O39 but not in that of Ba9Cu2Ir5O21. The magnetic susceptibilities of all four phases obey a modified Curie-Weiss law above 150 K,with no long-range magnetic order observed between 5 and 300 K. They are all electrical insulators.
Title:
Conductivity and magnetoconductivity of a new series of
Al70Pd22.5(Re1-xRux)(7.5) quasicrystals
Authors:
Wang CR. Su ZY. Lin ST.
Source:
(list of journals)
Solid State Communications. 108(9):681-686, 1998.
Abstract:
A series of Al70Pd22.5(Re1-xRux)(7.5) quasicrystals with x = 0.13, 0.2, 0.4, 0.6, 0.8 have been prepared. Replacement of Re by Ru is seen to decrease the resistivity and the resistivity ratio r = rho(4.2) (K)/rho(300) (K). The magnetoconductivity (MC) of the samples with r less than or equal to 10.3 was analyzed using the quantum interference theory. The obtained results suggest that a more resistive sample suppresses not only the weak localization contribution but also the electron-electron interaction contribution through the reduction of the g* value. For the samples with x = 0.2(a) and 0.4(a), the observed positive MC at low fields and low temperatures indicates that these samples are already in the hopping regime. However, the anomalous behavior concerning the decrease in the magnitude of positive MC with decreasing temperature is in contradiction with the theoretical predictions. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.
Title:
Magnetic order and transport in the heavy-fermion system CeCu6-xAux
Authors:
von Lohneysen H. Neubert A. Pietrus T. Schroder A. Stockert O. Tutsch U. Loewenhaupt M. Rosch A. Wolfle P.
Source:
(list of journals)
European Physical Journal B. 5(3):447-455, 1998 Oct.
Abstract:
We report on extensive elastic neutron scattering to determine the wave vector of the magnetic order in CeCu6-xAux single crystals for x > 0.1. For all values of x investigated (0.2, 0.3, 0.5, 1.0) we find long-range incommensurate antiferromagnetic order with an ordering vector Q approximate to (0.625 0 0.275) for x = 0.2, nearly unchanged for x = 0.3, and Q approximate to (0.59 0 0) for x = 0.5, staying roughly the same for x = 1.0. In addition, short-range correlations are observed for x = 0.2, reminiscent of those found previously for a = 0.1. The ordered magnetic moment is found to increase rapidly for small a, and more slowly for the larger a: values. The increase of the specific-heat anomaly at the ordering temperature with x is in qualitative accord with this behavior. Finally, data of the electrical resistivity for current how along the three crystallographic directions are presented, showing a clear signature of the magnetic order. A theoretical interpretation of the interplay of magnetic order and transport in terms of (i) the partial suppression of the Kondo effect by the staggered magnetization and (ii) the anisotropic band structure induced by the staggered field is shown to account well for the data, provided the ordering vector Q is close to 2k(F), where k(F) is a typical Fermi momentum.
Title:
Metal dot structure buried in semiconductor quantum wires
fabricated by STM electrically induced modifications
Authors:
Yamada S. Kikutani T. Aoki N. Hong C. Hori H.
Source:
(list of journals)
Applied Physics a (Materials Science Processing). 66(Part 2 Suppl
S):S1095-S1099, 1998 Mar.
Abstract:
We have made a ferromagnetic (Ni) dot structure buried in semiconductor quantum wires by two-step surface modifications with STM. The wire was a type of split-gate, and the hole in which the Ni was buried was in the form of a small reversed cone (200 nm upper diameter and 100 nm depth). This size was selected in order to observe strong spin-selected transports, because we adopted a pseudomorphic heterojunction which has a two-dimensional electron gas layer at 60 nm depth from the surface. In low-temperature tranport measurements, we observed two distinct magnetization-dependent features. Before magnetization, aperiodic conductance oscillations against gate voltage sweep were observed: after magnetization, periodic and reproducible oscillations were recorded. In studying the current-voltage characteristics, we observed Coulomb blockade-like features. The Coulomb gap is reduced to about a half when external magnetic fields of +/-5000 Gs are applied, which seems to indicate expansion of the dot size. To study the origin of those transport features, magnetic force microscopy (MFM) measurements have been made for similar Ni dot samples at ambient conditions. MFM observation suggests preliminary domain wall formation inside the dot before magnetization. This then disappears after magnetization, implying a single domain formation for the entire dot. On the basis of those results, we propose a domain-related transport model which essentially interprets the observed transport properties.
Title:
Effect of gamma irradiation on the hysteresis phenomena at the
incommensurate-commensurate phase
transition in Rb2ZnBr4
Authors:
Sheleg AU. Iodkovskaya KV. Kurilovich NF.
Source:
(list of journals)
Physics of the Solid State. 40(10):1734-1737, 1998 Oct.
Abstract:
The effect of gamma irradiation on the temperature hysteresis in dielectric permittivity epsilon and loss tangent tan delta of crystalline Rb2ZnBr4 has been studied in the vicinity of the incommensurate-commensurate phase transition. The epsilon(T) and tan delta(T) curves were found to exhibit anomalies in the form of maxima. Hysteresis was observed in the measured properties, including the transition temperature T-c (Delta T = T-c(h) - T-c(c)), in both unirradiated and irradiated samples. It is shown that, as the radiation dose increases the extent of the hysteresis Delta T increases, the values of epsilon(max) and tan delta(max) at the transition point decrease, and the anomalies wash out. (C) 1998 American Institute of Physics. .
Title:
Pr-doping effect on the structure and superconductivity of
Bi2Sr2Ca1-xPrxCu2Oy single crystals
Authors:
Sun XF. Zhao X. Wu WB. Fan XJ. Li XG. Ku HC.
Source:
(list of journals)
Physica C. 307(1-2):67-73, 1998 Oct 1.
Abstract:
Effect of Pr-doping on the structure and superconductivity of Bi2212 system was studied for Bi2Sr2Ca1-xPrxCu2Oy single crystals with x = 0-0.78. The a- and b-axis lengths increase with increasing Pr concentration, while the c-axis length and the period of modulation decrease with Pr-doping. These can be explained by the higher valence of Pr ion substituting at Ca site, the extra oxygen in BiO bilayers and the lattice mismatch between perovskite layer and BiO bilayer. In addition, the changes in lattice parameters are more dramatic in the Pr-rich region than those in the Ca-rich region, which can be attributed to the difficulty in the intercalation of extra oxygen in the BiO bilayer at high-doping level. The superconducting transition temperature increases slightly at first and then drops gradually upon Pr doping and the complete suppression of superconductivity occurs when the Pr content reaches 0.60. The superconducting volume faction also decreases with Pr content and is proportional to 1 - ax(2). (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
Highly faceted growth shape of microvoids in icosahedral Al-Mn-Pd
Authors:
Beeli C. Godecke T. Luck R.
Source:
(list of journals)
Philosophical Magazine Letters. 78(5):339-348, 1998 Nov.
Abstract:
Faceted microholes in icosahedral Al-Mn-Pd quasicrystals form by condensation of thermal vacancies; typically during annealing in the temperature range above approximately 700 degrees C. Prolonged annealing at temperatures between 750 and 830 degrees C leads to the growth of large and highly faceted microholes through a classical Ostwald ripening process. The indexing of all facets of such a microhole is presented. The idealized morphology is found to correspond to an icosahedral polyhedron with 302 facets.
Title:
The mesoscopic structure of disordered dodecagonal tantalum
telluride: a high-resolution transmission electron microscopy study
Authors:
Krumeich F. Conrad M. Nissen HU. Harbrecht B.
Source:
(list of journals)
Philosophical Magazine Letters. 78(5):357-367, 1998 Nov.
Abstract:
A disordered dodecagonal quasicrystalline tantalum-rich telluride was prepared at the upper thermal stability limit of the related quasicrystalline phase by application of conventional high-temperature synthesis techniques. The structure of the disordered telluride was studied on a mesoscopic scale by means of high-resolution transmission electron microscopy (HRTEM). A selective imaging technique was employed in order to produce HRTEM images which allow a square-triangle tiling underlying the structure on a length scale of about 2 nm to be recognized The tiling was analysed with regard to specific deviations from a perfectly ordered quasicrystalline dodecagonal telluride and various crystalline approximants. The application of a general construction principle derived from the structures of two well characterized approximants allows the reconstruction of a realistic structural model for the disordered dodecagonal phase and the calculation of its composition. The disordered phase is interpreted as an intergrowth of nuclei of various crystalline approximants with interspersed relies of the dodecagonal phase. The tantalum mole fraction of the disordered phase deviates by about 5 ppm from that of a truly dodecagonal telluride Ta3+2x31/2Te4 containing the two components in an irrational ratio.
Title:
Dislocations in quasicrystals and their interaction with
cluster-like obstacles
Authors:
Mikulla R. Gumbsch P. Trebin HR.
Source:
(list of journals)
Philosophical Magazine Letters. 78(5):369-376, 1998 Nov.
Abstract:
A dislocation moving through a quasicrystal leaves in its wake a fault denoted a phason wall. For a two-dimensional model quasicrystal the disregistry energy of this phason wall is studied to determine possible Burgers vectors of the quasicrystalline structure. Unlike periodic crystals, the disregistry energy is an average quantity with large fluctuations on the atomic scale. Therefore the dislocation core structure and mobility cannot be linked to this quantity, e.g. by a Peierls-Nabarro model. Atomistic simulations show that dislocation motion is controlled by local obstacles inherent to the atomic structure of the quasicrystal.
Title:
Quasicrystals - From tilings to coverings
Authors:
Urban KW.
Source:
(list of journals)
Nature. 396(6706):14-15, 1998 Nov 5.
Title:
Experimental verification of the quasi-unit-cell model of
quasicrystal structure
Authors:
Steinhardt PJ. Jeong HC. Saitoh K. Tanaka M. Abe E. Tsai AP.
Source:
(list of journals)
Nature. 396(6706):55-57, 1998 Nov 5.
Abstract:
The atomic structure of quasicrystals(1)-solids with long-range order, but non-periodic atomic lattice structure-is often described as the three-dimensional generalization of the planar two-tile Penrose pattern(2). Recently, an alternative model has been proposed(3-5) that describes such structures in terms of a single repeating unit(3-5)-the three-dimensional generalization of a pattern composed of identical decagons. This model is similar in concept to the unit-cell description of periodic crystals, with the decagon playing the role of a 'quasi-unit cell'. But, unlike the unit cells in periodic crystals, these quasi-unit cells,overlap their neighbours, in the sense that they share atoms. Nevertheless, the basic concept of unit cells in both periodic crystals and quasicrystals is essentially the same: solving the entire atomic structure of the solid reduces to determining the distribution of atoms in the unit cell. Here we report experimental evidence for the quasi-unit-cell model by solving the structure of the decagonal quasicrystal Al72Ni20Co8. The resulting structure is consistent with images obtained by electron and X-ray diffraction, and agrees with the measured stoichiometry, density and symmetry of the compound. The quasi-unit-cell model provides a significantly better fit to these results than all previous alternative models, including Penrose tiling.
Title:
A neutron diffraction study of the low-temperature magnetic phase of DyRu2Si2
Authors:
Gignoux D. Schmitt D. Shigeoka T.
Source:
(list of journals)
Europhysics Letters. 44(3):374-378, 1998 Nov 1.
Abstract:
The low-field, low-temperature magnetic phase of the tetragonal compound DyRu2Si2 is studied by neutron diffraction on a single crystal. The analysis of all the harmonies of the fundamental long-period commensurate propagation vector is consistent with the (40(4) over bar) magnetic structure in which one ninth of the moments of the magnetic unit cell vanish. The origin of such a non-usual structure is discussed.
Title:
Quasicrystals: pentagonal order and electronic localisation.
[French]
Authors:
Roche S.
Source:
(list of journals)
Annales de Chimie-Science des Materiaux. 23(7-8):953-968, 1998 Oct-Dec.
Abstract:
This article concerns the current state of fundamental and applied research of quasicrystalline materials. Potential technological applications are also addressed.
Title:
Incommensurate magnetism in PrBa2Cu3O6.92
Authors:
Hill JP. Boothroyd AT. Andersen NH. Brecht E. Wolf T.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(17):11211-11214, 1998 Nov 1.
Abstract:
We report resonant x-ray magnetic scattering and high-resolution neutron-diffraction studies of the Pr site magnetism in high quality single crystals of PrBa2Cu3O6.92. These studies reveal that the Pr sublattice orders at 19 K in a well correlated, long period incommensurate structure with probable wave vector (0.5+/-delta,0.5,0) or (0.5,0.5+/-delta,0) with delta=0.006 r.l.u. The observed x-ray scattering results from dipole transitions, demonstrating the existence of an ordered 5d Pr moment and implying a large 4f moment at the Pr site. A spin reorientation transition to a commensurate antiferromagnetic structure of wave vector (0.5,0.5,0.5) is observed at lower temperatures. .
Title:
Landau model for uniaxial systems with complex order parameter
Authors:
Latkovic M. Bjelis A.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(17):11273-11284, 1998 Nov 1.
Abstract:
We study the Landau model for uniaxial incommensurate-commensurate systems of class I by keeping umklapp terms of third and fourth order in the expansion of the free energy. It applies to systems in which the soft-mode minimum lies between the corresponding commensurate wave numbers. The minimization of the Landau functional leads to the sine-Gordon equation with two nonlinear terms, equivalent to the equation of motion for the well-known classical mechanical problem of two mixing resonances. We calculate the average free energies for periodic, quasiperiodic, and chaotic solutions of this equation, and show that in the regime of finite strengths of umklapp terms only periodic solutions are absolute minima of the free energy, so that the phase diagram contains only commensurate configurations. The phase transitions between neighboring configurations are of the first order, and the wave number of ordering goes through a harmless staircase with a finite number of steps. These results are the basis for the interpretation of phase diagrams for some materials from class I of incommensurate-commensurate systems, in particular of those for A(2)BX(4) and betaine-calciumchloride-dihydrate compounds. Also, we argue that chaotic barriers which separate metastable periodic solutions represent an intrinsic mechanism for observed memory effects and thermal hystereses. .
Title:
Fermi surfaces and anomalous transport in quasicrystals
Authors:
Roche S. Fujiwara T.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(17):11338-11344, 1998 Nov 1.
Abstract:
Electronic transport properties of quasicrystals are discussed theoretically. By means of nb initio linear muffin tin orbitals calculations, electronic band structure and corresponding Fermi surfaces of several quasicrystalline approximants are obtained. A criterion for distinguishing between metallic and anomalous transport properties in intermetallics is proposed. Unconventional temperature dependence of conductivity of quasicrystals and approximants is addressed in a second part. It is shown that power law exponents can be directly deduced from scaling analysis of the Kubo formula. Finally in relation to our results, we briefly summarize actual knowledge on low temperature transport regimes. .
Title:
Local atomic structure and the valence band
structure of the rhombic-triacontahedral
quasicrystal, its 1/1 approximant, and the
Mackay-icosahedral quasicrystal in the Al-Mg-Pd alloy system
Authors:
Takeuchi T. Mizutani U. Yamaguchi S. Fukunaga T. Mizuno T. Tanaka N.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(17):11345-11353, 1998 Nov 1.
Abstract:
The rhombic-triacontahedral-type quasicrystal (RT-QC), its (1/1, 1/1, 1/1) approximant (RT-1/1) and the Mackay-icosahedral-type quasicrystal (MI-QC) can be formed in the Al-Mg-Pd system. The radial distribution function RDF(r) spectra of the three compounds is derived from neutron diffraction experiments. Powdered x-ray diffraction Rietveld refinement is also carried out to determine the atomic structure of the RT-1/1, and the refined data are converted to the RDF(r). The interatomic distance of the AI-Pd pair in the RT-1/1 and RT-QC is found to be remarkably shortened relative to that calculated from the hard sphere model with Goldschmidt radii. In the MI-QC, the interatomic distance of the AI-Pd pair is further shortened. In addition, the shortening of the interatomic distance is also observed in the Mg-Pd pair. The valence band spectra studied by the x-ray photoemission spectroscopy and soft x-ray spectroscopy clearly show the formation of the bonding and antibonding states associated with the Al-Pd and Mg-Pd atomic pairs in the MI-QC. The results are consistent with the shortening of the interatomic distances derived from the structure analysis. The reason for the possession of the highest resistivity in the MI-QC among the three compounds is attributed to the formation of the covalent bonding between AI-Pd and Mg-Pd atomic pairs. .
Title:
Abrasive wear behavior of Al-Cu-Fe quasicrystalline
composite coatings
Authors:
Sordelet DJ. Besser MF. Logsdon JL.
Source:
(list of journals)
Materials Science & Engineering A-Structural Materials Properties
Microstructure & Processing. 255(1-2):54-65, 1998 Oct 31.
Abstract:
Quasicrystals are a relatively new class of materials which exhibit unusual atomic structure and useful physical and chemical properties. The inherent brittleness of quasicrystals has limited their potential use to primarily surface coating applications. This study examined the effect on abrasive wear behavior of Al-Cu-Fe quasicrystalline coatings through the addition (e.g. 0-100 v/o) of a relatively ductile Fe-Al phase. Coatings were deposited by plasma are spraying techniques. The incorporation of discrete Fe-Al particles into the quasicrystalline coating matrix improves the abrasive wear resistance. Moreover, it is observed that low-level additions of the Fe-Al phase (e.g. 1 v/o) produce the most abrasive wear-resistant coating. The wear behavior of the quasicrystalline and composite coatings is discussed in terms of wear mode and coating hardness. (C) 1998 Elsevier Science S.A. All rights reserved.
Title:
Rippled commensurate phases in DIFFOUR model: Continuum
approximation
Authors:
Hlinka J. Orihara H. Ishibashi Y.
Source:
(list of journals)
Journal of the Physical Society of Japan. 67(10):3488-3492, 1998 Oct.
Abstract:
Landau potential functional is derived for type-I commensurate- incommensurate phase transitions that appear in the phase diagram of a simple discrete model with fourth order anharmonicity (DIFFOUR model). Coefficients of the lowest order terms (including the usual Lifshitz and lock-in terms) are given explicitly for the rippled (polar) phases with the period p = 3, 5 and 7 sites.
Title:
Thermal properties at the
commensurate-incommensurate transition of
K2ZnCl4
Authors:
Ahn HY. Jeong HT. Cho YC. Jeong SY. Jeong YH.
Source:
(list of journals)
Journal of the Physical Society of Japan. 67(10):3500-3504, 1998 Oct.
Abstract:
The heat capacity of the K2ZnCl4 single crystal was measured between 330 K and 415 K using an adiabatic calorimeter. A distinct anomaly of the commensurate-incommensurate transition was observed at 403.64 +/- 0.05 K for the first time by the adiabatic calorimetry, where the enthalpy change is Delta H = 9.990 J . mol(-1) and the entropy change is Delta S = 0.025 J . K-1 mol(-1) . The anomaly of the heat capacity is demonstrated by the behavior of the phase soliton or the domain wall near the transition point. The heat capacity was simulated numerically by using the phenomenological Landau theory and compared with the experimental results. The anomaly of the thermal expansion near T-C measured by TMA is related with a structural phase transition accompanied by the entropy change. We discuss the influence of the anomalous change of the thermal expansion compared with the heat capacity near T-C.
Title:
Ferroelectric phase transitions in Sn2P2S6 and Sn2P2Se6
crystals
Authors:
Moriya K. Kuniyoshi H. Tashita K. Ozaki Y. Yano S. Matsuo T.
Source:
(list of journals)
Journal of the Physical Society of Japan. 67(10):3505-3511, 1998 Oct.
Abstract:
Heat capacities of Sn2P2S6 and Sn2P2Se6 single crystals were measured at temperatures between 10 and 380 K for the farmer and between 10 and 350 K for the latter using an adiabatic calorimeter. The heat capacity anomaly due to the ferroelectric-paraelectric phase transition occurred at 337.25 +/- 0.10 K in Sn2P2S6. The anomalies corresponding to the ferroelectric-incommensurate and incommensurate-paraelectric phase transitions occurred at 193.24 +/- 0.10 and 220.07 +/- 0.15 K in Sn2P2Se6. The normal heat capacities for the compounds were estimated by least squares fitting of the Debye and Einstein functions to the experimental data. supplemented by spectroscopic normal mode frequencies. The anomalous heat capacities,pave the phase transition entropies of 8.6 JK(-1) mol(-1) for Sn2P2S6 and 8.5 and 1.5 JK(-1) mol(-1) for Sn2P2Se6. The large transition entropies are consistent with an order-disorder mechanism for the ferroelectric-paraelectric phase transitions in Sn2P2S6 and Sn2P2Se6.
Title:
Formation of F- and P-type icosahedral quasicrystals in the
Zn-Mg-Ho alloy system
Authors:
Shimizu T. Ishimasa T.
Source:
(list of journals)
Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes &
Review Papers. 37(10):5691-5696, 1998 Oct.
Abstract:
Two types of icosahedral quasicrystals, F- and P-types, formed at 563 degrees C in the Zn60Mg40-xHox alloy depending on Ho content. In the composition range of 6 less than or equal to x less than or equal to 10, F-type icosahedral quasicrystal formed as a major phase in these alloys. The intensity of superlattice reflections which occurred due to F-type ordering became weaker in the alloys with lower Ho content. At x = 5, P-type icosahedral quasicrystal formed, coexisting with MgZn2-type Laves phase at 563 degrees C and 503 degrees C. Some electron diffraction patterns of the P-type icosahedral quasicrystal exhibited diffuse scattering intensity at positions corresponding to F-type superlattice reflections. By annealing at 403 degrees C, a mixture of the P-type icosahedral quasicrystal and the MgZn2-type phase changed to a mixture of the F-type quasicrystal and a decagonal quasicrystal. The former state was reversibly obtained by additional annealing at 503 degrees C. These experimental results support the interpretation that the three types of quasicrystals form as a thermodynamically stable state in the Zn-Mg-Ho alloy system.
Title:
Electron diffraction study of alpha-AlMnSi crystals along
non-crystallographic zone axes
Authors:
Song GL. Bursill LA.
Source:
(list of journals)
International Journal of Modern Physics B. 12(22):2279-2303, 1998 Sep 10.
Abstract:
The structure of crystalline alpha-AlMnSi is examined by electron diffraction. Six distinct Bone axes are examined, including both normal crystallographic and non-crystallographic zone axes, allowing the space group symmetry of alpha-AlMnSi to be studied. a method for indexing the non-crystallographic zone axis diffraction patterns, which involve reflections from several nearby crystallographic zone axes, is described and applied to electron diffraction patterns of the quasi-5-fold, 3-fold and a-fold axes of the icosahedral building units of cubic alpha-AlMnSi. These are compared with electron diffraction patterns from the corresponding 5-fold, 3-fold and a-fold axes of the quasicrystalline phase i-AlMnSi, from which we may make some conclusions concerning the occupancies of the icosahedral units in i-AlMnSi. Electron diffraction patterns characteristic of Pm (3) over bar were obtained for thicker specimens. However, for thin specimens, as used for HRTEM imaging, the electron diffraction patterns were characteristic of Im (3) over bar space group symmetry. This unusual behaviour arises because the structural basis for the Pm (3) over bar to Im (3) over bar phase transition is a weak effect, involving changes in occupancy of the icosahedral structural elements located at the corners (double-MacKay icosahedra) and body-centers (MacKay icosahedra) of the cubic unit cell. The effects of changing the occupancies of the outer shells of the MI and DMI structural units on the diffraction intensities of the weak reflections were examined. Thus, calculation of the dynamical diffraction amplitudes shows that in fact the weak reflections characteristic of Pm (3) over bar only develop sufficient intensity if two conditions are satisfied: namely (1) the crystal thickness exceeds approx. 50 nn and (2) if a significant proportion of Im (3) over bar occupancies are included in the structural model. By fitting the observed thickness variation of the diffraction intensities we propose a new set of occupancies for alpha-AlMnSi, which is consistent with the electron, X-ray and neutron diffraction data.
Title:
Incommensurate versus commensurate
description of the A(x)BX(3) hexagonal perovskite-type
structure. Sr1.2872NiO3 incommensurate
composite compound example
Authors:
Evain M. Boucher F. Gourdon O. Petricek V. Dusek M. Bezdicka P.
Source:
(list of journals)
Chemistry of Materials. 10(10):3068-3076, 1998 Oct.
Abstract:
We report a new structure determination of the Sr1.2872NiO3 incommensurate composite hexagonal perovskite compound. Three different refinement strategies are presented: (i) a 3D supercell approximation with a nonharmonic development of the atomic displacement factor, (ii) an original (3+1)D incommensurate composite description with the use of crenel functions, and (iii) a (3+1)D commensurate composite model. The three strategies are discussed and compared to previous refinements carried out for the hexagonal perovskites in a classical way or with the superspace group formalism. Out of the three methods, the incommensurate composite approach gives slightly better results with a final global R value of 2.89% for 635 independent reflections (at a I/sigma(I) > 2 level) and only 60 parameters (R (3) over bar m(00 gamma)Os superspace group;a = 9.5177(7) Angstrom, c = 2.5739(2) Angstrom, q = 0.64359(4)c*, V = 201.93(4) Angstrom(3), and Z = 3). The use of crenel functions notably improves previously reported results. New structural features are evidenced for Sr1.2872NiO3: (i) an incommensurate character, (ii) a splitting of the trigonal prismatic nickel atoms over 5 positions, (iii) a definite stoichiometry which induces a perfect charge balance, and (iv) a nonharmonic behavior of some Sr atoms. Those characteristics seem general to most hexagonal perovskite compounds and essential for correctly interpreting their interesting magnetic properties. Finally, a new generic formulation is proposed, which explains the various stoichiometries observed and suggests a new compound possibility.
Title:
Cristobalite-related phases in the NaAlO2-NaAlSiO4 system. II. A
commensurately modulated cubic
structure
Authors:
Withers RL. Thompson JG. Melnitchenko A. Palethorpe SR.
Source:
(list of journals)
Acta Crystallographica - Section B, Structural Science.
54(Part 5):547-557, 1998 Oct 1.
Abstract:
The crystal structure of a new cubic cristobalite-related sodium aluminosilicate Na1.45Al1.45Si0.55O4 [P2(1)3, a = 14.553 (1) Angstrom] has been modelled using a modulation wave approach and the model tested against X-ray powder diffraction data using the Rietveld method. Owing to there being 64 independent positional parameters and eight independent Na sites, refinement of the tetrahedral framework atom positions and Na occupancies was not possible. The framework was modelled successfully in terms of q(1) = 1/4[020](p)*-type (p = parent) modulation waves with the requirement that the MO4 (M = Al0.725Si0.275) tetrahedra be as close to regular as possible. Na/vacancy ordering was modelled successfully in terms of q(2) = 1/4[220](p)* modulation waves. Only the Na-atom positions were refined. The significance of this unique modulated cubic cristobalite-related structure and the possible insight it provides to understanding beta-cristobalite are discussed.
Title:
Disorder in the crystal structure of
Cs2HgCl4 studied by the maximum entropy method
Authors:
Bagautdinov B. Luedecke J. Schneider M. van Smaalen S.
Source:
(list of journals)
Acta Crystallographica - Section B, Structural Science.
54(Part 5):626-634, 1998 Oct 1.
Abstract:
The disorder at room temperature in crystalline Cs2HgCl4, dicaesium mercury tetrachloride, is studied by the Maximum Entropy Method (MEM). X-ray scattering up to theta = 30 degrees (Mo K alpha radiation) revealed the orthorhombic space group Pnma, with a = 9.8136(9), b = 7.6018(6) and c = 13.4201 (9) Angstrom. Refinement converged to R = 0.032 for 1046 observed unique reflections. The structure model involves unphysically short distances between Cs and Cl atoms. The MEM applied to the Bragg intensity data shows that both Cs(1) and Cl(1) exhibit strong anharmonic displacements out of the mirror plane. The relation is shown between these displacements, the soft phonons at room temperature and the static modulations at low temperatures of several A(2)BX(4) compounds. A comparision of the MEM with a refinement of anharmonic displacements parameters shows the MEM to be less affected by unwanted correlations between parameters than the refinement of anharmonic displacement parameters.
Title:
Intermediate phases in the Ca-rich part of the system
(Ca1-xSrx)8[Al12O24](WO4)(2)
Authors:
Tobbens DM. Depmeier W.
Source:
(list of journals)
Zeitschrift fur Kristallographie. 213(10):522-531, 1998.
Abstract:
The Ca-rich part of the cation substitution series of aluminate sodalites (Ca1-xSrx)(8)[Al12O24](WO4)(2) has been studied as a function of temperature and composition. The intermediate beta-phase of pure calcium tungstate aluminate sodalite was found to have a (3 + 2)-dimensional commensurately modulated structure with an isometric unit cell. The probable superspace group is Abm2(alpha 0 gamma) 0s0, 000 with alpha = 1/4, gamma = 1/4, a = b = root 2.9.301(1) Angstrom, c = 9.301(1) Angstrom, at 636 K. Its average structure was found to be similar to that of the room-temperature gamma-phase. In crystals with 0 < x less than or equal to 0.18 the existence of a new intermediate phase could be confirmed. At variance with the otherwise very similar room-temperature phase with x = 0, this gamma'-phase has an incommensurate modulation vector. Its proposed superspace group is Abm2(1/2 0 gamma) 0ss with gamma = 0.05(1). Within the precision of our TEM-experiments gamma does not change with temperature or composition. The average structure of the gamma'-phase could be refined and was found closely related with the average structure of gamma-CAW.
Title:
The magnetic structures of DyNi2Ge2
Authors:
Islam Z. Detlefs C. Goldman AI. Bud'ko SL. Canfield PC. Zheludev A.
Source:
(list of journals)
Solid State Communications. 108(6):371-376, 1998.
Abstract:
In this paper we report the results of neutron diffraction measurements of the magnetic structures of a single crystal of DyNi2Ge2 in zero applied magnetic field. There are two distinct magnetic transitions in this material; one is from the paramagnetic phase to an amplitude modulated (AM) antiferromagnetic phase at the Neel temperature, T-N = 8.3+/-0.1 K, and the other is at a lower temperature, T-t = 3.1+/-0.2 K, from this phase to an equal moment (EM) antiferromagnetic structure. The EM structure is described by a set of three wave vectors, namely, tau(1) = (0 0 3/4), tau(2) = (1/2 1/2 0) and tau(3) = (1/2 1/2 1/2). A weak third harmonic, tau(1) = (0 0 1/4), related to tau(1), also appears indicating that the magnetic structure is not purely sinusoidal. In this phase Dy moments have their full saturation value of mu(s) = 10 mu(B). The AM phase is described by a single propagation vector tau(1). In both the phases there is an ordered component of the Dy moments in the basal plane. The angle between the ordered Dy moments and the the (c) over bar axis is estimated to be 17 degrees+/-6 degrees at 1.5 K. These results are consistent with the de susceptibility as a function of temperature data which shows weak anisotropy and two transitions. (C) 1998 Elsevier Science Ltd. All rights reserved.
Title:
Diffuse scattering from pentagonal quasicrystals
Authors:
Lei JL. Wang RH. Hu CZ. Ding DH.
Source:
(list of journals)
Physics Letters A. 247(4-5):343-352, 1998 Oct 19.
Abstract:
Explicit formulae for thermal diffuse scattering from pentagonal quasicrystals have been derived in terms of elastic constants. Isointensity contours of diffuse scattering are illustrated. Unlike ordinary crystals, shapes of isointensity contours are much more complicated and vary even among the collinear Bragg spots. Information about elastic constants can be extracted from a quantitative analysis of diffuse scattering patterns. (C) 1998 Elsevier Science B.V.
Title:
Direct observation of a phason gap in an incommensurate
molecular compound
Authors:
Ollivier J. Etrillard J. Toudic B. Ecolivet C. Bourges P. Levanyuk AP.
Source:
(list of journals)
Physical Review Letters. 81(17):3667-3670, 1998 Oct 26.
Abstract:
We report the results of an inelastic neutron scattering study of the lattice vibration spectra in the normal and incommensurate phases of (ClC6D4)(2)SO2. Because of unusually low soft mode damping, a finite value of the phason frequency at the satellite position is observed for the first time. The soft mode frequency saturation in the normal phase and this phason gap are consistent with the dynamical nature of the observed central peak. .
Title:
Atomic motion in quasicrystalline Al70Re8.6Pd21.4: A
two-dimensional exchange NMR study
Authors:
Dolinsek J. Ambrosini B. Vonlanthen P. Gavilano JL. Chernikov MA. Ott HR.
Source:
(list of journals)
Physical Review Letters. 81(17):3671-3674, 1998 Oct 26.
Abstract:
Al-27 2D exchange NMR experiments on an icosahedral Al70Re8.6Pd21.4 quasicrystal have detected slow atomic motions in the sub-kHz range at temperatures between 0.16 and 130 K. The observed motion is limited in space and can be associated with local phason fluctuations at very low energies, involving quantum tunneling at very low temperatures. It may thus be regarded as an atomic motion acting as a precursor to bulk self-diffusion. .
Title:
Thermodynamical fingerprints of fractal spectra
Authors:
Vallejos RO. Anteneodo C.
Source:
(list of journals)
Physical Review E. 58(4):4134-4140, 1998 Oct.
Abstract:
We investigate the thermodynamics of model systems exhibiting two-scale fractal spectra. In particular, we present both analytical and numerical studies on the temperature dependence of the vibrational and electronic specific heats. For phonons, and for bosons in general, we show that the average specific heat can be associated to the average (power law) density of states. The corrections to this average behavior are log-periodic oscillations, which can be traced back to the self-similarity of the spectral staircase. In the electronic problem, even if the thermodynamical quantities exhibit a strong dependence on the particle number, regularities arise when special cases are considered. Applications to substitutional and hierarchical structures are discussed. .
Title:
Topological modeling of cascade amorphization in network
structures using local rules
Authors:
Hobbs LW. Jesurum CE. Pulim V. Berger B.
Source:
(list of journals)
Materials Science & Engineering A-Structural Materials Properties
Microstructure & Processing. 253(1-2):16-29, 1998 Sep 30.
Abstract:
A local rules-based assembly procedure was used to erect large periodic and aperiodic models of the tetrahedral network compounds SiO2, Si3N4 and SiC, whose topological properties were assessed in a prior investigation. Several hundred tetrahedra in central regions of the models were disconnected and randomly rotated, then allowed to reconnect according to an imposed set of the same or different rules, in order to simulate radiation disordering within a dense collision cascade. Alterations in the rebonded cascade region were characterized by assessment of density, underconnection, tetrahedral distortion, inter-tetrahedral bond angle, radial correlations and local topology. While SiO2 networks amorphize easily and acceptably in this way, Si3N4 and SiC networks do not. It is concluded that the experimental difficulty in amorphizing Si3N4 is due to the topological difficulty in tetrahedral reconnection from random orientations according to the applicable local rules for Si3N4, while the observed ease of amorphizing SiC must arise from the potential for chemical disorder in that compound. (C) 1998 Elsevier Science S.A. All rights reserved.
Title:
Nonlinear dielectric constant of thiourea
crystal
Authors:
Kim YH. Kim JJ.
Source:
(list of journals)
Journal of the Korean Physical Society. 33(4):494-500, 1998 Oct.
Abstract:
The nonlinear dielectric constants of the thiourea crystal were measured up to the 5(th) nonlinear order (n=5) in the region of the commensurate phase transition. Odd harmonic responses (n=1, 3, 5) could be well explained by recent theories, but the even harmonic responses (n=2, 4) were found to be in disagreement with the available theories. Furthermore, the harmonic dielectric constants were observed even to change sign, depending on the thermodynamic hysteresis of the sample, that is, the sign of the spontaneous polarization at the time of the measurement. Increasing dispersions in the nonlinear dielectric responses were observed with increasing harmonic order n even when the linear response was in the region free of dispersion.
Title:
Dynamical and irreversible magnetic effects in i-R8Mg42Zn50
quasicrystals (R = Tb, Dy)
Authors:
Charrier B. Schmitt D.
Source:
(list of journals)
Journal of Magnetism & Magnetic Materials. 189(2):165-172, 1998 Nov.
Abstract:
Dynamical and irreversible properties of i-R8Mg42Zn50 quasicrystals (R = Tb, Dy) have been investigated through AC susceptibility, non-linear magnetic susceptibility and time-dependent magnetization measurements. Neither relaxation times nor non-linear susceptibility diverge at the ordering temperature TN or at the critical temperature T-c where time-dependent phenomena appear. These irreversible effects exist in magnetic fields much higher than in other disordered systems. The positional and orientational disorder of the magnetic moments, specific of quasicrystals, should influence the observed properties. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
The double nature of the ErNiSi2 magnetic structure neutron
diffraction and magnetic measurements
Authors:
Schobinger-Papamantellos P. Buschow KHJ. Wilkinson C. Fauth F. Ritter C.
Source:
(list of journals)
Journal of Magnetism & Magnetic Materials. 189(2):214-224, 1998 Nov.
Abstract:
The magnetic phase diagram of the compound ErNiSi2 of CeNiSi2 structure type (Cmcm, space group) has been studied by neutron diffraction and magnetic measurements. The paramagnetic neutron data confirmed the sample homogeneity. The analysis of the data collected in the magnetically ordered regime (T-N = 3.4 K) showed the existence of two distinct types of magnetic ordering associated with the wave vectors q(1) = (1/2, 0, 0) and q(2) = (q(x), q(y), q(z)) which are not related by symmetry. The q(1) phase corresponds to a uniaxial antiferromagnetic arrangement of the Er moments along b associated with a 2a cell enlargement. The refined moment value at 1.5 K is mu(Er) = 7.6(1) mu(B). This Ordering is stable only below T-1 = 1.8 K. Above T-1, a first-order transition accompanied by hysteresis effects, leads to the appearance of a second set of magnetic reflections. These reflections are associated with a wave vector in a general reciprocal lattice position q(2) = (q(x), q(y), q(z)) that has a temperature dependent length and orientation. At T-1 the two phases coexist and are present in equal amounts. The wave vector components of the q, phase at T-1 are q(x) = 0.1262(3), q(y) = 0.022(2) and q(z) = 0.2273(3) r.l.u. The structure corresponds to a sine wave modulated structure with an amplitude of 5.31 mu(B) polarized along b. This structure dominates the high-temperature region, T > T-1, Below T-1 it is still present as a metastable phase but its relative amount decreases with decreasing temperature. The same holds for the q(1) phase which exists as a metastable phase above T-1. The coexistence region on heating spans the interval T-1 +/- 0.45 K. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
Stability study of icosahedral phases in diblock copolymer melt
Authors:
Roan JR. Shakhnovich EI.
Source:
(list of journals)
Journal of Chemical Physics. 109(17):7591-7611, 1998 Nov 1.
Abstract:
The stability of three possible icosahedral phases (called here vertex, edge, and face models, respectively) in a diblock copolymer melt is examined, with higher harmonics included in the density-wave mean field theory developed by Leibler. Two cases are examined: (1) diblock copolymer melt with constant coupling vertices, and (2) diblock copolymer melt with general coupling vertices in which, unlike all the previous studies on the effect of higher order harmonics in diblock copolymer melt, the calculation is performed exactly. We find that icosahedral phases are always metastable and the mean-field phase diagram of the diblock copolymer is unchanged. (C) 1998 American Institute of Physics. .
Title:
Physical properties of GdNiGa
Authors:
Canepa F. Cirafici S. Merlo F. Palenzona A.
Source:
(list of journals)
Journal of Alloys & Compounds. 279(2):L11-L12, 1998 Oct 2.
Abstract:
Electrical resistivity (4.2-300 K range) and magnetization measurements (4.2-300 K and 0-1 T) were performed on GdNiGa, TiNiSi type. Onset of ferromagnetism is observed at T-c=30.5 K, with a magnetic moment saturation value (H=1 T) at 4.2 K of 7.2 mu(B). A Curie-Weiss like behaviour is observed above T-c, with a paramagnetic Curie temperature theta(p)=32 K and a magnetic moment mu(eff)=7.85 mu(B). (C) 1998 Elsevier Science S.A. All rights reserved.
Title:
Transition between periodic and quasiperiodic structures in
Al-Ni-Co
Authors:
Grushko B. Holland-Moritz D. Wittmann R. Wilde G.
Source:
(list of journals)
Journal of Alloys & Compounds. 280(1-2):215-230, 1998 Oct 23.
Abstract:
A series of Al-Ni-Co alloys forming stable decagonal (D-ANC) quasicrystals was studied in as-cast and annealed states. It was shown that under certain conditions periodic structures with pseudodecagonal (PD) symmetry can be produced at the same compositions as stable decagonal quasicrystals. Different variants of D-ANC and PD were observed in a compositional range of 70-72.5 at.% Al and 13-18 at.% Co. As-cast D-ANC can be transformed to single-phase PD of the same local composition. Single-phase PDs can be transformed to D-ANC of the same composition by heating to a temperature higher than the formation temperature of these PDs. The transition between PD and D-ANC was studied in more detail in Al71Ni14.5Co14.5 and Al70Ni15Co15 by electron microscopy, powder X-ray diffractometry and differential thermal analysis. The results of this study do not confirm the thermodynamic stability of this PD structure. (C) 1998 Elsevier Science S.A. All rights reserved.
Title:
Soft modes and phonon interactions in Sn2P2S6 studied by neutron scattering
Authors:
Eijt SWH. Currat R. Lorenzo JE. Saint-Gregoire P. Hennion B. Vysochanskii YM.
Source:
(list of journals)
European Physical Journal B. 5(2):169-178, 1998 Sep.
Abstract:
The low frequency lattice dynamics and its relationship to the second order paraelectric-to-ferroelectric transition in Sn2P2S6 is studied. The dispersion branches of the acoustic and lowest lying optical phonons in the a*-c* plane have been obtained in the ferroelectric phase, for x-polarized phonons. Close to the phase transition a considerable softening is found for the lowest optical mode (P-x), comparable to the behaviour observed in previous Raman investigations. As found previously in Sn2P2Se6, a strong coupling between the TO(P-x) and TA(u(xz)) phonons is observed, although, apparently, not strong enough to lead to an incommensurate phase. The sok TO(P-x) mode at the zone center is observed. The temperature dependence of its frequency and damping shows that the transition is not entirely displacive. At low temperatures an unusual apparent negative LO-TO splitting is observed which is shown to arise from the coupling of the x-polarized soft mode to the nearby z-polarized optical phonon. For comparison, the soft TO(P-x) dispersion in the a*-b* plane is measured in both the paraelectric and ferroelectric phases. Consistent frequency changes and LO-TO splitting are observed, revealing a significant interaction between the TA(u(yx)) and LA(u(xx)) acoustics branches and the TO and LO soft optic branches, respectively. In contrast, the nearby y-polarised optic branch shows almost no temperature dependence. Finally, the influence of piezoelectric effects on the limiting acoustic slopes in the ferroelectric phase is discussed.
Title:
LEED for complex surface structures [Review]
Authors:
Heinz K.
Source:
(list of journals)
Current Opinion in Solid State & Materials Science. 3(5):434-438, 1998 Oct.
Abstract:
The past year has seen new developments in the application of low energy electron diffraction to complex surfaces. Atomic images of part of the unit cell can be reconstructed from conventional, that is, discrete, spot intensities. Global searches are designed to find the best-fit structures in the parameter space chosen. Incommensurate and quasicrystalline structures have also been approached by intensity analyses.
Title:
Thermodynamic properties of the spin-Peierls systems
Authors:
Houzet M. Buzdin AI.
Source:
(list of journals)
Solid State Communications. 108(5):307-312, 1998.
Abstract:
We calculate the specific heat and magnetization in the dimerized and incommensurate phases of a spin-Peierls system, in the Hartree-Fock scheme. We demonstrate that in the incommensurate phase, the pinning of soliton walls on the crystal structure may lead to the step-like behavior of the specific heat as a function of magnetic field. Such behavior has been indeed observed in the experiments on the spin-Peierls compound CuGeO3. (C) 1998 Elsevier Science Ltd. All rights reserved.
Title:
Analysis of the incommensurately modulated
OS phase of SiO2 tridymite
Authors:
Pryde AKA. Heine V.
Source:
(list of journals)
Physics & Chemistry of Minerals. 25(8):603-610, 1998 Sep.
Abstract:
The structure, symmetry and origin of the incommensurately modulated OS phase of tridymite (SiO2) and its lock-in to the OP three-fold superlattice structure are discussed in a computational study. The structure of the OS phase (which has not been determined experimentally) is deduced as the only geometrically possible structure derived from the parent OC phase by rotation and translation of the SiO4 tetrahedra without significant distortion of these units. It can be visualised conveniently in terms of the McConnell formalism of two component difference structures C-1 and C-2 whose space group symmetries are derived. The results are in accordance with the known lock-in structure at wave vector Q=1/3a*. In the latter, the +/-C-1 regions expand and the structure can square up in a very general way to take advantage of the lost symmetries (lost compared with the OC phase).
Title:
Crack propagation in quasicrystals
Authors:
Mikulla R. Stadler J. Krul F. Trebin HR. Gumbsch P.
Source:
(list of journals)
Physical Review Letters. 81(15):3163-3166, 1998 Oct 12.
Abstract:
Crack propagation is studied in a two dimensional decagonal model quasicrystal. The simulations reveal the dominating role of highly coordinated atomic environments as structure-intrinsic obstacles for both dislocation motion and crack propagation. For certain overloads, these obstacles and the quasiperiodic nature of the crystal result in a specific crack propagation mechanism: The crack tip emits a dislocation followed by a phason wall, along which the material opens up. .
Title:
Behavior of charge density waves in a one-dimensional organic conductor
visualized by scanning tunneling microscopy
Authors:
Nishiguchi T. Kageshima M. Ara-Kato N. Kawazu A.
Source:
(list of journals)
Physical Review Letters. 81(15):3187-3190, 1998 Oct 12.
Abstract:
Charge density waves (CDW) in a tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) single crystal have been studied with molecular resolution using a low temperature scanning tunneling microscope (STM). For the first time the periodicities of the CDW along both the a and b axes have been observed and were found to be coincident with those of the 2k(F) CDW. The influence of crystal singularities on the ordering of the CDW along the a axis was also revealed. .
Title:
Origin of magnetism in crystalline and
quasicrystalline AlMn and AlPdMn phases
Authors:
Simonet V. Hippert F. Audier M. de Laissardiere GT.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(14):R8865-R8868, 1998 Oct 1.
Abstract:
The existence of localized moments on a small fraction of the Mn atoms in the mu - Al4MnxCr1-x hexagonal phase, closely related to AlMn quasicrystals, is shown by magnetization and nuclear magnetic resonance studies. Deviations from a Curie behavior observed in the mu phase, as well as in the AlMn, AlMnSi, and AlPdMn quasicrystals, can be interpreted by a Kondo effect. The crystallographic site leading to magnetic Mn in the mu phase is identified and the moment formation is justified by theoretical calculations. These results shed light on the origin of magnetism in quasicrystalline phases where a similar site must also exist. .
Title:
First-principles interatomic potentials for transition-metal aluminides. II.
Application to Al-Co and Al-Ni phase diagrams
Authors:
Widom M. Moriarty JA.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(14):8967-8979, 1998 Oct 1.
Abstract:
Aluminum-rich intermetallic compounds and alloys are important for their technological applications and scientifically interesting for their complex structures such as quasicrystals. Detailed knowledge of interatomic interactions can help explain structural and mechanical properties of these systems. The first paper of this series [Phys. Rev. B 56, 7905 (1997)] derived first-principles interatomic potentials for alloys of aluminum with first row transition metals from generalized pseudopotential theory (GPT). This paper assesses the ability of those potentials to reproduce and elucidate the binary alloy phase diagrams of Al1-xCox and Al1-xNix. When the full theory is taken into account, we successfully reproduce the phase diagrams up to x = 0.3. While many of the general features of the phase diagrams can be obtained with x = 0 GPT pair potentials alone, the volume and composition-dependence of the total energy become important by x = 0.25. In addition, for certain complex structures, we introduce partial aluminum occupancy and demonstrate its importance. At high transition-metal concentration x > 0.25, we must further include three- and four-body transition-metal interactions to account for the stability of Al5Co2 in the Al1-xCox phase diagram. .
Title:
Crystalline surface structures induced by
ion sputtering of Al-rich icosahedral quasicrystals
Authors:
Shen Z. Kramer MJ. Jenks CJ. Goldman AI. Lograsso T. Delaney D. Heinzig M. Raberg W. Thiel PA.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(15):9961-9971, 1998 Oct 15.
Abstract:
Low-energy electron diffraction patterns, produced from quasicrystal surfaces by ion sputtering and annealing to temperatures below similar to 700 K, can be assigned to various terminations of the cubic CsCl structure. The assignments are based upon ratios of spot spacings, estimates of surface lattice constants, bulk phase diagrams vs surface compositions, and comparisons with previous work. The CsCl overlayers are deeper than about five atomic layers, because they obscure the diffraction spots from the underlying quasicrystalline substrate. These patterns transform irreversibly to quasicrystalline(like) patterns upon annealing to higher temperatures, indicating that the cubic overlayers are metastable. Based upon the data for three chemically identical, but symmetrically inequivalent surfaces, st model is developed for the relation between the cubic overlayers and the quasicrystalline substrate. The model is based upon the related symmetries of. cubic close-packed and icosahedral-packed materials. The model explains not only the symmetries of the cubic surface terminations, but also the number and orientation of domains. .
Title:
Crystallography and microstructural studies of phase
transformations in the Dy2O3 system
Authors:
Kim YJ. Kriven WM.
Source:
(list of journals)
Journal of Materials Research. 13(10):2920-2931, 1998 Oct.
Abstract:
The crystallography, microstructures, and phase transformation mechanisms in dysprosia (DY2O3) have been studied. The lattice parameters of B and C phases were refined by x-ray diffraction (XRD). The modulated structures and decomposed structures in the CaO-doped samples were characterized by transmission electron spectroscopy (TEM). A new twin was observed in the modulated B phase. Contrary to the previous studies, the B to C transformation was induced by grinding. The A to B transformation was considered to be ferroelastic and the spontaneous strain was calculated. The major driving force for the B (monoclinic) to C (cubic) transformation is suggested to be the release of lattice strains and cation charge repulsions in the B structure, which is analogous to the beta (monoclinic) to gamma (orthorhombic) transformation in Ca2SiO4. This transformation can be displacive, if some conditions are provided to overcome the bonding energy of the interlayer oxygens in the B structure.
Title:
Preparation and dielectric property of BaTiO3-SrTiO3 artificially
modulated structures
Authors:
Tsurumi T. Miyasou T. Ishibashi Y. Ohashi N.
Source:
(list of journals)
Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes &
Review Papers. 37(9B):5104-5107, 1998 Sep.
Abstract:
In order to elucidate the origin of the asymmetry observed in the D-E or C-V hysteresis loops of BaTiO3 (BTO)-SrTiO3 (STO) epitaxial films, "artificially modulated structures" (AMSs), where the chemical composition was continuously changed along the direction of film thickness, were prepared and their dielectric properties were measured. A fully automatic molecular beam epitaxy system was developed to fabricate AMSs. Two kinds of AMS, (BTO<--STO) and (STO<--BTO) where Ba/Sr ratios were changed from the film/substrate interface to the film surface in the reverse direction, were prepared on Nb-doped STO single crystals. The simulation of XRD profiles indicated that a relaxation of the crystal lattice occurred along the a-axis in the two AMSs, and the degree of the relaxation was more significant in (BTO<--STO)AMS. It was observed that the asymmetry of the C-V hysteresis loop was changed by the modulation of chemical composition, and that the origin of the asymmetry was attributed to the lattice relaxation rather than the asymmetry of the stress field.
Title:
Effect of cooling rate on the precipitation of quasicrystals
from the Zr-Cu-Al-Ni-Ti amorphous alloy
Authors:
Xing LQ. Eckert J. Loser W. Schultz L.
Source:
(list of journals)
Applied Physics Letters. 73(15):2110-2112, 1998 Oct 12.
Abstract:
The Zr57Cu20Al10Ni8Ti5 alloy solidifies into an amorphous phase upon rapid quenching or casting at low cooling rates. However, the amorphous alloys formed at different cooling rates exhibit different crystallization behavior. The slowly cooled bulk amorphous alloys prepared by copper mold casting reveal a first crystallization peak at 715 K upon heating at 0.33 K/s and crystallize via precipitation of an icosahedral quasicrystalline phase in the first crystallization step. The rapidly quenched ribbons exhibit a first crystallization peak at 720 K and crystallize by simultaneous precipitation of the quasicrystalline phase together with Zr2Cu and Zr2Ni intermetallic phases in the first stage of crystallization. It is supposed that the undercooled Zr57Cu20Al10Ni8Ti5 melt has a tendency to develop an icosahedral short-range order, which is favored by low cooling rate. As a result, the bulk amorphous alloy has a short-range order close to a quasicrystalline phase. In contrast, the structure of the ribbon is more similar to that of the melt at high temperature and the atoms are oriented more randomly. (C) 1998 American Institute of Physics. .
Title:
Bulk, surface, and annealing properties of grown quasiperiodic tilings
Authors:
Joseph D.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(13):8347-8354, 1998 Oct 1.
Abstract:
Entropically stabilized quasicrystals are usually modeled as equilibrium ensembles of random tilings although the corresponding kinetics may be very slow. In a recently published model we showed how to circumvent this problem by a growth process with reversible dynamics. In the limit of vanishing growth velocity the grown samples are representative of the equilibrium ensemble. Here, we consider bulk and surface properties of this model, an annealing procedure that heals tears, as well as the extension to other symmetries.
Title:
Heisenberg model on the (1)/(5)-depleted square lattice and the CaV4O9
compound
Authors:
Manuel LO. Micheletti MI. Trumper AE. Ceccatto HA.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(13):8490-8494, 1998 Oct 1.
Abstract:
We investigate the ground-state structure of the Heisenberg model on the 1/5-depleted square lattice for arbitrary values of the first- and second-neighbor exchange couplings. By using a mean-field Schwinger-boson approach we present a unified description of the rich ground-slate phase diagram, which includes the plaquette and dimer resonant-valence-bond phases, long- and short-range Neel orders, an incommensurate phase: and other magnetic orders with complex magnetic unit cells. We also discuss some implications of our results for the experimental realization of this model in the CaV4O9 compound.
Title:
Neutron diffraction and x-ray resonant exchange-scattering studies of the
zero-field magnetic structures of TbNi2Ge2
Authors:
Islam Z. Detlefs C. Goldman AI. Bud'ko SL. Canfiield PC. Hili JP. Gibbs D. Vogt T. Zheludev A.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(13):8522-8533, 1998 Oct 1.
Abstract:
The zero-field magnetic structures of the rare-earth intermetallic compound TbNi2Ge2 have been determined using conventional magnetic neutron diffraction and high-resolution x-ray resonant exchange scattering techniques. There are two distinct magnetic phase transitions in this material: one is from the high-temperature paramagnetic state to a long period antiferromagnetic phase at the Neel temperature (T-N=16.8 K), and the other is at a lower temperature (T-t= 9.3 K), where the system locks into a commensurate phase. The structure above T-t is described by a longitudinal, amplitude modulated, sinusoidal wave with propagation vector tau(1) approximate to(000.758+/-0.002) in reciprocal-lattice units (r.l.u.). As the temperature is lowered below T-t, tau(1) locks at (0 0 3/4) and additional magnetic Bragg reflections corresponding to tau(2) =(1/2 1/2 0) and tau(3) = (1/2 1/2 1/2) develop. A weak modulation tau(1)' = (0 0 1/4), related to tau(1) also appears indicating a squaring-up of the low-temperature structure. In this equal moment structure all Tb moments have the saturation value of mu(s) = 9.0 +/- 0.2 mu(B). Both the phases are uniaxial with Tb moments parallel to the (c) over cap axis of the tetragonal unit cell.
Title:
Structural modulation in Bi-2(Sr0.9La0.1)(2)Cu1-xCoxOy (x = 0.2, 0.6, 1.0)
Authors:
Jiang H. Li FH. Liu W. Zhang Y. Mao ZQ.
Source:
(list of journals)
Physica C. 305(3-4):202-208, 1998 Sep 1.
Abstract:
Three specimens of Bi-2(Sr0.9La0.1)(2)Cu1-xCoxOy with x = 0.2, 0.6, 1.0, respectively, were investigated by transmission electron microscopy to explore the influences of Co substitution for Cu on the structural modulation. They have in common orthorhombic modulated structures. But the modulation periodicity decreases gradually with the increase of Co content. Its ratio to the corresponding lattice parameter of basic structure equals 4.28 for I = 0.2, 4.18 for x = 0.6 and 4.00 for x = 1.0. Consequently, the modulated structures of the former two phases are incommensurate: while it is commensurate for the last one. The stacking disorder due to the weak bonding connection between two adjacent Bi-O layers has been observed in the two incommensurate modulated phases. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
Symmetrical staircase in the profile of lattice-modulation period versus
pr-concentration in Bi2Sr2(Ca1-x,Prx,) Cu2O8+delta
Authors:
Onozuka T. Niizeki K.
Source:
(list of journals)
Journal of the Physical Society of Japan. 67(9):2984-2987, 1998 Sep.
Abstract:
Variation of the lattice-modulation period p(a) of the "incommensurate" phase Bi2Br2(Ca1-xPrx)Cu2O8+delta (0 less than or equal to x less than or equal to 0.72) with Pr-concentration x was examined by electron diffraction. The plot of p(a) versus a: exhibits roughly a linear decrease but it has a staircase structure. The period of each stair, p(a), agrees with a value expected for a commensurate structure. Mie observed nine stairs which are symmetrically arranged; the central stair corresponds to the primary structure with a simple modulation, and a stair on the left (or right) corresponds to a structure which is derived from the primary structure by introducing an advanced (or delayed) discommensuration. The observed structures cover a full range of commensurate structures predicted theoretically.
Title:
Structural modulation and charge distribution in the spin-ladder
Ca-13.6Sr0.4CU24+yO41+z
Authors:
Isobe M. Takayama-Muromachi E.
Source:
(list of journals)
Journal of the Physical Society of Japan. 67(9):3119-3124, 1998 Sep.
Abstract:
In order to find the most stable distribution of hole carriers, the bond-valence-sum (BVS) and the electrostatic energy for a composite crystal Ca13.6Sr0.4Cu24+yO41+z (y = -0.017 and z = -0.035) were calculated using modulated structure data at ambient pressure and room temperature. The BVS calculation suggests that at least four holes per molecule stay in the 1-D chain. The lowest Madelung energy was given from a hole distribution in which all of the self doped holes occupy the sites in the 1-D chain. However, transfer of one hole to the ladder per molecule costs only about 0.7 eV/mol. Considering experimental uncertainties in the structural parameters or contribution of other terms such as kinetic energy to the total energy it is implied that a small number of holes can be transferred into the ladder. In the 1-D chain. the hole tend to be localized in every other copper site or its adjacent oxygen sites by the structural modulation reflecting the Coulomb interaction between them.
Title:
Phenomenological theory of the linear and nonlinear dielectric
susceptibilities in the type-II incommensurate phase
Authors:
Iwata M. Orihara H. Ishibashi Y.
Source:
(list of journals)
Journal of the Physical Society of Japan. 67(9):3130-3136, 1998 Sep.
Abstract:
The linear and third-order nonlinear dielectric susceptibilities in the type-II incommensurate phase were investigated oil the basis of the Landau-type thermodynamic potential. The expression for the frequency dependence of the third-order susceptibility in the incommensurate phase, for which the thermodynamic potential includes no Lifshitz invariant, was obtained. II was found that the third-order nonlinear susceptibility shows a jump with the change of its sign at the incommensurate transition point even in the second order transition; which is caused by the contribution from the amplitude mode of the modulated structure. We found that the third-order susceptibility reflects the behavior of the amplitude mode in the incommensurate phase. As a result. it has turned out that the measurement of third-order nonlinear dielectric susceptibility becomes a powerful method as a probe for the amplitude mode in the modulated structure.
Title:
Representation analysis and spin-slip model of the
incommensurate structure of the kondo
antiferromagnets CePdSn and CePtSn
Authors:
Kadowaki H.
Source:
(list of journals)
Journal of the Physical Society of Japan. 67(9):3261-3266, 1998 Sep.
Abstract:
Representation analysis of the neutron diffraction data of the Kondo antiferromagnets CePdSn and CePtSn shows that the incommensurate magnetic structures of the single-k type belong to the Gamma(3) irreducible representation of the space group. The contradicting mu SR observation supporting commensurate structures and the neutron data are shown to be explained semiquantitatively by spin-slip structures which are derived by the Gamma(3) incommensurate structures.
Title:
Simulation studies of ZrW2O8 at high pressure
Authors:
Pryde AKA. Dove MT. Heine V.
Source:
(list of journals)
Journal of Physics-Condensed Matter. 10(38):8417-8428, 1998 Sep 28.
Abstract:
The negative thermal expansion recently observed over a wide range of temperatures in the ambient pressure phase alpha-ZrW2O8 was attributed to the existence of low-frequency phonon modes which propagate with minimal distortion of the WO4 tetrahedra and ZrO6 octahedra, the so-called 'rigid unit modes'. The flexibility afforded this structure by these modes raises questions about the structure's behaviour with pressure. Further experiments found a high-pressure phase gamma-ZrW2O8 which also exhibited negative thermal expansion. Calculations using the rigid unit mode model have shown that the mechanism described earlier in the context of alpha-ZrW2O8 is consistent with the negative thermal expansion in gamma-ZrW2O8. Atomistic simulations have been used to calculate further properties of these two phases (e.g. transition pressure, compressibilities) using interatomic potentials derived for the earlier work on alpha-ZTW(2)O(8). The reproduction of the cell parameters and bond lengths measured for gamma-ZrW2O8 does not imply a substantial change in the bonding character of the W-O interactions.
Title:
Observations of silicon surfaces exposed to inductively coupled CHF3 and
C4F8/H-2 plasmas using Fourier transform infrared ellipsometry
Authors:
Lee HJ. Motomura H. Tachibana K.
Source:
(list of journals)
Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes &
Review Papers. 37(8):4522-4526, 1998 Aug.
Abstract:
In situ Fourier transform infrared ellipsometry has been used to investigate the characteristics of fluorocarbon films deposited in inductively coupled CHF3 and C4F8/H-2 plasmas. Chemical composition and thickness of the films have been studied as a function of process parameters. For the CHF3 plasma, the mode strength of CF2 bond group increases monotonically with pressure varying from 3 to 20 mTorr. The mode strength ratio of hydrogen-containing fluorocarbon bond groups (CHFx) to CF2 bond group increases with decreasing pressure. If He gas is admired to CHF3, the CHFx/CF2 ratio also increases. Changes in the film structure have been discussed in terms of the relationship between electron temperature and CHF3 dissociation. As the discharge power is increased, the deposition rate increases linearly without considerable changes in the chemical composition of the film. For the C4F8/H-2 plasma, relative concentration of CHFx species increases linearly with H-2 mixing ratio.
Title:
Incommensurate modulated
structure study of a Cu-Zn-Al-Zr phase
Authors:
Chung CY. Zou WH. Han XD. Lam CWH. Gao M. Duan XF. Lai JKL.
Source:
(list of journals)
Acta Materialia. 46(15):5541-5555, 1998 Sep 18.
Abstract:
Zr was added to Cu-Zn-Al shape memory alloy as a grain refinement element. There are two new phases, Cu50.2Zr24.6Al17.3Zn7.9 (at%) (Z(1) phase) and Cu57.4Zr20.4Zn10.3Al11.9 (at%) (Z(2) phase), in the Cu-19.0Zn-13.1Al-1.1Mn-0.3Zr (at%) alloy. The structure of the Cu57.4Zr20.4Zn10.3Al11.9 (at%) (Z(2)) phase is studied in detail in the present paper. The results of electron diffraction and high-resolution electron microscopy (HREM) investigations indicated a one-dimensional incommensurate modulated structure in the Z(2) phase. The average structure of the phase is base-centred orthorhombic. The systematic reflection conditions associated with the main and satellite reflections demonstrate that the Bravais class of the Z(2) phase is P-11 (1 over bar)(Cmmm) type in a (3 + 1) dimensional space for the incommensurate modulated structure. The substitution modulation effects of the Al and Zr elements are revealed by energy-filtered transmission electron microscopy (EFTEM). {1 (3) over bar (2) over bar} compound-type twins are observed in the Z(2) phase. The relationship between the Z(1) and Z(2) phases in the alloy is discussed, (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
Coverage-dependent superstructures in chemisorbed NTCDA
monolayers: a combined LEED and STM study
Authors:
Stahl U. Gador D. Soukopp A. Fink R. Umbach E.
Source:
(list of journals)
Surface Science. 414(3):423-434, 1998 Sep 19.
Abstract:
The long-range order and local geometric arrangement of 1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA) monolayers on Ag(111) have been studied with low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Two distinct superstructures are detected which appear separately or may even coexist, depending on coverage. Moreover, the unit cells of these two phases are correlated to each other, leading to an arrangement of parallel stripes of alternating superstructures. The structures can reversibly be transferred into one another by additional dosing or by thermal description. For certain tunneling conditions it is possible to image the substrate through the monolayer without disturbing it. Thus, for one structure, the exact adsorption site could be determined by the simultaneous observation of contrast from substrate and adsorbate. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
Crystalline oxides on silicon: The first five monolayers
Authors:
McKee RA. Walker FJ. Chisholm MF.
Source:
(list of journals)
Physical Review Letters. 81(14):3014-3017, 1998 Oct 5.
Abstract:
The long-standing problem of growing a commensurate crystalline oxide interface with silicon has been solved. Alkaline earth and perovskite oxides can be grown in perfect registry on the (001) face of silicon, totally avoiding the amorphous silica phase that ordinarily forms when silicon is exposed to an oxygen containing environment. The physics of the heteroepitaxy lies in establishing a sequenced transition that uniquely addresses the thermodynamics of a layer-by-layer energy minimization at the interface. A metal-oxide-semiconductor capacitor using SrTiO3 as an alternative to SiO2 yields the extraordinary result of t(eq) < 10 Angstrom.
Title:
Real-space multiple-scattering calculation and interpretation of
x-ray-absorption near-edge structure
Authors:
Ankudinov AL. Ravel B. Rehr JJ. Conradson SD.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(12):7565-7576, 1998 Sep 15.
Abstract:
A self-consistent real-space multiple-scattering (RSMS) approach for calculations of x-ray-absorption near-edge structure (XANES) is presented and implemented in an ab initio code applicable to arbitrary aperiodic or periodic systems. This approach yields a quantitative interpretation of XANES based on simultaneous, self-consistent-field (SCF) calculations of local electronic structure and x-ray absorption spectra, which include full multiple scattering from atoms within a small cluster and the contributions of high-order MS from scatterers outside that cluster. In addition, the code includes a SCF estimate of the Fermi energy and an account of orbital occupancy and charge transfer. We also present a qualitative, scattering-theoretic interpretation of XANES. Sample applications are presented for cubic BN, UF6, Pu hydrates, and distorted PbTiO3. Limitations and various extensions are also discussed. .
Title:
Surface acoustic waves in two-dimensional periodic elastic
structures
Authors:
Tanaka Y. Tamura S.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(12):7958-7965, 1998 Sep 15.
Abstract:
Acoustic waves localized at the surface of two-dimensional (2D) periodic elastic structures, or 2D phononic crystals, are studied theoretically by taking account of the elastic anisotropy of constituent materials. The surface considered is perpendicular to the axis of aperiodic array of cylinders embedded in a background material. The dispersion relations of the surface modes are calculated for circular cylinders of AlAs which form a square lattice in a GaAs matrix. The folding and anisotropy of the surface wave branches, as well as the existence of pseudusurface waves, are found. The stop band distributions of the surface, pseudosurface, and bull; waves are plotted in a form relevant for comparison with ultrasound imaging experiments. .
Title:
Scanning tunneling microscopy of the misfit-layer compound (SmS)(1).19NbS2
Authors:
Ohno Y.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(12):8042-8049, 1998 Sep 15.
Abstract:
Scanning tunneling microscopy (STM) images with atomic resolution have been obtained from the top SmS layer in (SmS)(1.19)NbS2, one of a large family of misfit-layer compounds that consist of two layer sets with different geometry and lattice constants. They show a rectangular or a nearly rectangular lattice of light spots. One of the images has the same periodicity as each atomic species in the [11] direction and half the periodicity in the [1 (1) over bar] direction. The other image shows light spots that are mismatched with the atomic positions over a wide area and have the periodicity of three times of the lattice constant along the a and b axes. The images are analyzed, using a Fourier transformation (FT) technique. They are reproduced within the experimental errors of +/-7 percent. A standing wave model for a charge density on a surface is proposed, which indicates that there are a clear distinction between the a and b axes and an asymmetry between the [11]and [1<(1)over b>] directions. It is found that no Sm atoms are imaged and interlayer interaction more or less affects the STM images. Point defects and a modulated structure have been observed, which are discussed in relation to charge transfer from SmS to NbS2 layers and incommensurabiliry of the crystal. .
Title:
High-temperature in situ straining experiments in the high-voltage electron
microscope
Authors:
Messerschmidt U. Baither D. Bartsch M. Baufeld B. Geyer B. Guder S. Wasilkowska A. Czyrska-Filemonowicz A. Yamaguchi M. Feuerbacher M. Urban K.
Source:
(list of journals)
Microscopy & Microanalysis. 4(3):226-234, 1998 May-Jun.
Abstract:
Design rules are described here for high-temperature straining stages for transmission electron microscopy. Temperatures above 1000 degrees C can be attained by electron bombardment of the specimen grips. Thermal equilibrium can be reached in a short time by carrying off the heat by water cooling. Some applications of this stage are described. Ferroelastic deformation was observed at 1150 degrees C in t' and partially stabilized zirconia, which changes the microstructure for successive dislocation plasticity. In the oxide-dispersion-strengthened alloy INCOLOY MA 956, dislocations are impeded by oxide particles and move smoothly between the particles. At high temperatures, both the resting and traveling times control the average dislocation velocity. In MoSi2 single crystals of a soft orientation, dislocations with 1/2[111] Burgers vectors are created in localized sources and move on {110} planes in a viscous manner. The dislocations in Al-Pd-Mn single quasicrystals are oriented in preferred crystallographic directions and move in a viscous way as well. On the basis of in situ observations, conclusions are drawn for interpreting macroscopic deformation behavior at high temperatures.
Title:
Spontaneous incommensurate crystal phase in
the Jahn-Teller KDy(MoO4)(2) crystal?
Authors:
Kharchenko NF. Kharchenko YN. Szymczak R. Baran M.
Source:
(list of journals)
Low Temperature Physics. 24(9):689-692, 1998 Sep.
Abstract:
Investigations of magnetic and spontaneous birefringence properties of a KDy(MoO4)(2) crystal under the Jahn-Teller phase transformation reveal some features indicating the existence of two spontaneous phase transitions at temperatures close to 14.3 and 11.0 K. The characteristic changes in birefringence in these transitions suggest that the crystal of KDy molybdate has a modulated incommensurate lattice structure in the temperature range from 11.0 to 14.3 K. (C) 1998 American Institute of Physics. .
Title:
Modulated-crystal model for the twelvefold
quasicrystal Ta62Te38
Authors:
Uchida M. Horiuchi S.
Source:
(list of journals)
Journal of Applied Crystallography. 31(Part 4):634-637, 1998
Aug 1.
Abstract:
A transmission electron microscopy study reveals that the so-called twelvefold quasicrystal Ta62Te38 is a crystal subjected to structure modulation. It is composed of two incommensurate layers rotated by 30 degrees to each other about their normal. High-resolution electron microscope images show the formation of commensurate domains and their discommensuration. The observed electron diffraction patterns may be explained by a kinematical calculation for the commensurate cell, designated as a 7 x 7 cell. The modulation is considered to be due to the rearrangement of atomic vacancies in response to the occurrence of charge-density waves.
Title:
Formation of well-ordered surface compounds by coadsorption of thallium and
bromide on the Au(111) electrode surface
Authors:
Wang JX. Robinson IK. Adzic RR.
Source:
(list of journals)
Surface Science. 413:374-383, 1998 Sep 3.
Abstract:
The structures of the adlayers formed on Au(111) in acid solution containing thallium and bromide have been investigated by using in situ surface X-ray diffraction. At the most positive potentials, where Br forms close-packed rotated-hexagonal monolayers, the surface is free of Tl. The Br adlayer disorders at the potential where thallium starts to coadsorb. With further decreasing potential, two well-ordered commensurate and one weakly-ordered incommensurate phases appear over a 0.7 V potential region prior to the formation of the close-packed rotated-hexagonal Tl monolayer, The structure factor analysis for the commensurate phases shows the formation of TlBr2 and TlBr surface compounds in the 3-(root 13 x root 13) and 2-(3 x root 5) phases, respectively. In addition, an adlayer-induced subsurface relaxation has been observed. Under the 2TlBr-(3 x root 3) adlayer, where bromide ions are at the bridge sites and thallium ions are situated near the hollow sites, the top layer of Au atoms displaces laterally along the root 3 direction. This results in more uniform spacings between T1 and the three neighboring gold atoms, as well as an increase of the Br-Au separation. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
Structural and magnetic ordering of chromium in Ag/Cr multilayers
Authors:
Demuynck S. Meersschaut J. Dekoster J. Swinnen B. Moons R. Vantomme A. Cottenier S. Rots M.
Source:
(list of journals)
Physical Review Letters. 81(12):2562-2565, 1998 Sep 21.
Abstract:
We studied the influence of the lattice structure on the chromium magnetism in Ag/Cr multilayers by combining structural characterization techniques and perturbed angular correlation spectroscopy. Chromium in Ag/Cr multilayers orders as an incommensurate longitudinal spin-density wave (SDW) with the spins oriented out of plane. A size effect induces the instability of the SDW below a critical chromium thickness. The absence of the spin-flip transition, the position of the Neel temperature, and the actual character of the SDW are attributed to the specific structural properties. .
Title:
Anisotropy-driven dynamics of cellular fronts in directional solidification
in thin samples
Authors:
Akamatsu S. Faivre G.
Source:
(list of journals)
Physical Review E. 58(3 Part B):3302-3315, 1998 Sep.
Abstract:
We present an experimental investigation of the influence of interfacial anisotropy on the cellular growth patterns observed in directional solidification of the CBr4-8 mol % C2Cl6 alloy at pulling velocities less than twice the cellular-threshold velocity. The experiments ate performed with single-crystal samples about 8 mm wide and 12 mu m thick. In such samples, the solidification dynamics is essentially two dimensional, and the effective anisotropy of the system can be varied by changing the orientation of the (face centered cubic) crystal with respect to the solidification setup, as was previously established by S. Akamatsu, G. Faivre, and T. Ihle [Phys. Rev. E, 51, 4751 (1995)]. We find that the cellular pattern is unstable at all values of the spacing lambda for crystal orientations corresponding to a vanishing effective interfacial anisotropy. For the other crystal orientations, i.e., for a nonvanishing effective interfacial anisotropy, stable cellular patterns are found over a finite width lambda range. The various modes of instability limiting this range are described. In particular, we show that a homogeneous tilt bifurcation exists for some orientations of the "degenerate" type (i.e., such that a {110} plane of the crystal is parallel to the growth direction and perpendicular to the sample plane). This bifurcation is not spontaneous, however, but a consequence of the particular symmetry of the effective interfacial anisotropy of the system for this crystal orientation.
Title:
Noise-induced coherent oscillations in randomly connected neural networks
Authors:
Pham J. Pakdaman K. Vibert JF.
Source:
(list of journals)
Physical Review E. 58(3 Part B):3610-3622, 1998 Sep.
Abstract:
We study the dynamics of randomly connected excitatory networks of excitable spike-response neuron models. Large networks can exhibit a nonmonotonic collective response to a stimulation when the coupling strength between neurons lies within an appropriate range. With such a coupling, noise imposed upon neurons induces synchronization of the units and oscillations of the network activity, consisting of a succession of bursts. Furthermore, the regularity of this rhythmic activity goes through a maximum as the noise amplitude is increased. This nonmonotonic dependence on the noise amplitude relies on the fact that noise acts in two antagonistic ways. Noise of low amplitude shortens the interval between two successive bursts, lending to an increase of the dynamics regularity, whereas noise of strong amplitude deteriorates the regularity of the dynamics during a burst. In order to study the influence of the noise amplitude and the coupling on the generation of collective oscillations quantitatively, we consider a simpler network model of excitable units. We derive a discrete map, including the noise amplitude and the coupling strength as parameters, which describes the network dynamics in the limit of a large number of neurons. This map reproduces all characteristic features of the activity dynamics obtained with simulated networks. From the analysis of the bifurcation structure of this map, we obtain parameter regions where noise-induced oscillations occur. Using this map we also study the effect of the network connectivity on the generation of oscillations. We show that such noise-induced coherent oscillations in fully connected networks are related to special initial conditions, and are sensitive to perturbations, whereas they can be the only asymptotically stable regime in sparsely connected networks.
Title:
Local order and magnetism in liquid Al-Pd-Mn alloys
Authors:
Simonet V. Hippert F. Klein H. Audier M. Bellissent R. Fischer H. Murani AP. Boursier D.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(10):6273-6286, 1998 Sep 1.
Abstract:
We report neutron scattering experiments on several Al-Pd-Mn liquid alloys with Mn content between 3.5 and 7.2 at. % which are in thermodynamical equilibrium with icosahedral quasicrystalline or approximant phases. The results reveal an overall similarity between the structure factor in the solid and in the liquid states, suggesting the presence of a strong icosahedral local order in the liquid state. Simulations of the structure factor at large momentum transfer support this interpretation. In addition, a marked increase of the neutron scattering cross section at small momentum transfer occurs on melting, revealing the appearance of paramagnetic scattering in the liquid state. A comparison with susceptibility measurements combined with additional neutron scattering experiments using polarized neutrons, demonstrates that magnetic moments are present in the liquid state and not in the solid state. In the liquid state, at a given temperature, the same spin value can be extracted from the paramagnetic scattering and the susceptibility data. The link between the evolution of the magnetic properties and that of the short- and medium-range order at the melting point is discussed. Surprisingly, the paramagnetism continues to increase with temperature in the liquid state. This remarkable behavior might be due either to an increase of the spin value with temperature as a consequence of thermal expansion or to the coexistence of magnetic and nonmagnetic Mn in temperature-dependent proportions. The origin of this behavior is discussed in relation to the evolution of the liquid structure.
Title:
Magnetic phase diagram of the spin-Peierls compound CuGeO3 doped with Al and
Sn
Authors:
Demishev SV. Weckhuysen L. Vanacken J. Trappeniers L. Herlach F. Bruynseraede Y. Moshchalkov VV. Pronin AA. Sluchanko NE. Samarin NA.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(10):6321-6329, 1998 Sep 1.
Abstract:
The magnetic phase diagram of the doped inorganic spin-Peierls compound CuGe1-xYxO3 (Y = Sn or Al) is studied in magnetic fields up to B similar to 50 T at temperatures 0.32-20 K. The comparative analysis of the magnetization data and the resonant magnetoabsorption spectra for the frequency range 20-120 GHz shows that the spin-Peierls phase is not destroyed up to x(Sn) = 0.01 and x(Al) = 0.02. The strong effects of doping on the magnetic phase transition between the spin-Peierls (D) and the incommensurate (M) phases are observed. The temperature dependence of the transition field B-DM(T) demonstrates a nonmonotonous behavior with a maximum at T similar to 9 K. Doping by Sn and Al reduces the amplitude of the B-DM(T) maximum by a factor of 2 with respect to the undoped crystal. The magnetic hysteresis width Delta B(T) at T<1 K increases substantially in both the Al- and Sn-doped crystals. The magnitude chi of the magnetic transition along the phase boundary B-DM(T) follows a critical behavior similar to that of the superlattice peak: chi = chi(0)[1-(T/T*)](beta), where T* approximate to 12 K is the temperature of the triple point and beta = 0.75 +/- 0.04. A model of the magnetic hysteresis in the spin-Peierls compounds based on a universal scaling of the magnetic phase diagram and g-factor renormalization in the transition region B similar to B-DM, is suggested. The influence of disorder on the properties of the CuGeO3 crystals is discussed.
Title:
Magnetic structure of (SmMn2Ge2)-Sm-154 as a function of
temperature and pressure
Authors:
Tomka GJ. Ritter C. Riedi PC. Kapusta C. Kocemba W.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(10):6330-6338, 1998 Sep 1.
Abstract:
Neutron scattering, ac susceptibility, and NMR measurements have been made on isotopically enriched (SmMn2Ge2)-Sm-154. All the magnetic states are characterized from much clearer neutron-diffraction spectra than in previous works, in which natural abundance Sm was used. A temperature versus pressure magnetic phase diagram is proposed, consisting of six distinct magnetic states, including previously undetected incommensurate cone structures at low temperatures and pressures. The noncollinear magnetic structures of these magnetic phases are such that a larger antiferromagnetic component appears within (001) planes in the ferromagnetic states than in the antiferromagnetic states. This observation provides an explanation for the anisotropic changes in the lattice constant and the anomalous magnetoresistance of SmMn2Ge2. Previously unexplained susceptibility and NMR measurements are interpreted in terms of changes to the cone structure. Changes in the Mn-Mn spacing and magnetic coupling are consistent with previous observations on related systems.
Title:
Comparison of potential calculations with helium diffraction and thermal
desorption data of CF4 and CF3Cl adsorbed on Cu(110)
Authors:
Marmier A. Girardet C. Diercks V. David R. Zeppenfeld P.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(11):7420-7427, 1998 Sep 15.
Abstract:
Helium atom scattering and thermal desorption spectroscopy an used to determine the adsorption properties of the tetrahedral and pyramidal molecules CF4 and CF3Cl, respectively, on the Cu(110) surface. High-order commensurate structures with large unit cells are obtained for CF4 and CF3Cl. The thermal desorption spectra reveal a zero-order desorption process for both species. A "leading edge" analysis yields monolayer adsorption energies of 161+/-6 meV for CF4 and 260+/-6 meV for CF3Cl. Semiempirical potential calculations corroborate these values and show that the shape of the potential energy maps for the two molecules is not very different, leading to tripod-down equilibrium configurations. The calculations also indicate some trends for an orientationally ordered structure for CF3Cl along the Cu troughs which could be at the origin of a ferroelectric phase.
Title:
An X-ray scattering and simulation study of the ordering kinetics in CuAu
Authors:
Elder KR. Malis O. Ludwig K. Chakraborty B. Goldenfeld N.
Source:
(list of journals)
Europhysics Letters. 43(6):629-634, 1998 Sep 15.
Abstract:
A detailed numerical and experimental study of the ordering of the low-temperature tetragonal phase of CuAu is presented. The numerical simulations are based on a coarse-grained free energy derived from electronic structure calculations of CuAu, while the experimental results are obtained from in situ. X-ray scattering. Both theoretical and experimental work indicate a subtle kinetic competition between the ordered tetragonal phase and the metastable modulated phase.
Title:
Symmetry description of OD crystal
structures in group theoretical terms
Authors:
Grell J.
Source:
(list of journals)
Acta Applicandae Mathematicae. 52(1-3):261-269, 1998 Jul.
Abstract:
OD structures of layers are the geometric models of a certain class of crystal structures - so-called polytypes - with local order and generally global disorder. The set of all partial and total symmetry operations of an OD structure does not form a space group, but a groupoid. Here a group-theoretical ansatz is made for an OD symmetry description showing the relation between the set of symmetry operations of an OD structure and some symmetry groups which is based on considerations of cosets and double cosets with respect to the symmetry groups of certain periodic parts of the structure.
Title:
Diophantine equations related to quasicrystals: A note
Authors:
Pelantova E. Perelomov AM.
Source:
(list of journals)
Theoretical & Mathematical Physics. 115(3):737-739, 1998 Jun.
Abstract:
We give the general solution of three Diophantine equations in the ring of integers of the algebraic number field Q[root 5]. These equations are related to the problem of determining the minimum distance in quasicrystals with fivefold symmetry.
Title:
Anisotropic spin correlations in the Zn-Mg-Ho icosahedral
quasicrystal
Authors:
Sato TJ. Takakura H. Tsai AP. Shibata K.
Source:
(list of journals)
Physical Review Letters. 81(11):2364-2367, 1998 Sep 14.
Abstract:
Neutron scattering experiments have been performed on the Zn-Mg-Ho icosahedral quasicrystal using powder and single-crystalline samples. In contrast to a previous Letter [Charrier ct al., Phys. Rev. Lett. 78, 4637 (1997)], the magnetic long-range order could not be detected in the icosahedral quasicrystal. It instead exhibits highly anisotropic diffuse scattering, which appears as satellite ridges of intense nuclear Bragg reflections, running parallel to the fivefold axis. The result suggests that quasi-five-dimensional spin correlations develop on a six-dimensional hypercubic lattice.
Title:
Coherence-domain methods in tissue and cell optics [Review]
Authors:
Tuchin VV.
Source:
(list of journals)
Laser Physics. 8(4):807-849, 1998 Jul-Aug.
Abstract:
Effects that accompany the propagation of laser radiation in tissues and interaction of laser radiation with cell flows are considered. These effects include diffraction, formation of speckle structures, interference of speckle fields, scattering from moving particles, etc. We discuss coherent optical methods that hold much promise for applications in biomedicine, such as photon-correlation spectroscopy; speckle interferometry; coherent topography and tomography; diffusion wave spectroscopy; phase, confocal, and Doppler microscopy; and low-coherence interferometry and tomography.
Title:
Incommensurately modulated polar
structures in antiferroelectric tin-modified lead zirconate
titanate: II, dependence of structure-property relations on
tin content
Authors:
Forst D. Li JF. Xu ZK.
Source:
(list of journals)
Journal of the American Ceramic Society. 81(9):2225-2236, 1998 Sep.
Abstract:
Studies of the structure-property relations in Pb0.98Nb0.02-[(Zr1-xSnx)(0.97)Ti-3](1-z)O-3 (PZST x/3/2) were performed for 0 < x < 0.50 by transmission electron microscopy, dielectric spectroscopy, and electrically induced polarization and strain methods. As the tin content increased, a general sequence of changes in phase stability was observed, including (i) a ferroelectric rhombohedral (FEr) phase (x < 0.15), (ii) a coexistence of FEr and antiferroelectric incommensurate (AFE(in)) states (x = 0.15), and (iii) an AFE(in) state (x > 0.15), Evidence will be presented that incommensurately modulated structures become pinned into long-lived metastable states by quenched tin impurities, rather than evolving toward a commensurate phase. Maximum electrically induced strains (epsilon) and polarizations (P) were found in the compositional range of x approximate to 0.15, where FEr and AFE(in) regions coexisted, Values of epsilon as large as 0.5% were found at field strengths of <80 kV/cm, In addition, these studies demonstrated evidence for two electrically induced phase transitions (x = 0.15): (i) an antiferroelectric-ferroelectric (AFE-FE) transition near 40 kV/cm, and (ii) a secondary ferroelectric-ferroelectric (FE-FE) transition near 60-80 kV/cm, The dominate contribution to epsilon was associated with the secondary transition, whereas the dominate contribution to P was associated with the first. For x < 0.15, evidence of an induced FE-FE transition was found, For x > 0,15, an induced AFE-FE transition was evident, However, no indications of a secondary FE-FE transition were observed. Large epsilon values were not induced until field levels significantly greater than that required to induced polarization saturation were obtained, which indicates a decoupling of epsilon and P.
Title:
Analysis of a solid solution formed by magnesium tungstate and magnesium
tellurate: Pb2MgWxTe(1-x)O6 [French]
Authors:
Rivezzi N. Sciau P.
Source:
(list of journals)
Journal of Solid State Chemistry. 139(2):332-341, 1998 Sep.
Abstract:
The solid solutions Pb2MgWxTe(1-x)O-6 was prepared and investigated by dielectric measurements, DSC, X-ray, and neutron powder diffraction. A phase diagram is proposed, Above 312 K the structure is cubic (space group Fm (3) over bar m) for all x values (0 less than or equal to x less than or equal to 1), Around 190 K and for x less than or equal to 0.4, the incommensurate phase transition of Pb2MgTeO6 is observed, It is little affected in this range by the W rate. The compositions x greater than or equal to 0.8 undergo the orthorhombic/commensurate phase transition of Pb2MgWO6. This transition is very sensitive to the amount of Te present, The transition temperature and the orthorhombic distortion decrease quickly with increasing Te content, For 0.6 < x < 0.8 the transition is partial, In the range 0.4 < x < 0.6 the situation is more complex, both commensurate and incommensurate phases being observed at low temperature, The structure corresponding to x = 0.4 has been determined by neutron powder diffraction at 12 K, It is isostructural to the incommensurate phase of Pb2Mg TeO6, The orthorhombic/commensurate structures (space group Pmcn) of x = 0.5, 0.7, and 0.9 were determined by X-ray powder diffraction at 80 K, The atomic displacements from the cubic positions decrease with increasing Te content, (C) 1998 Academic Press.
Title:
Modulated structures of homologous
compounds InMO3(ZnO)(m) (M = In, Ga; m = integer) described by
four-dimensional superspace group
Authors:
Li CF. Bando Y. Nakamura M. Onoda M. Kimizuka N.
Source:
(list of journals)
Journal of Solid State Chemistry. 139(2):347-355, 1998 Sep.
Abstract:
The modulated structures appearing in the homologous compounds InMO3(ZnO)(m) (M = In, Ga; m = integer) were observed by using a high-resoultion transmission electron microscope and are described based on a four-dimensional superspace group, The electron diffraction patterns for compounds with m larger than 6 reveal extra spots, indicating the formation of a modulated structure. The subcell structures for m = odd and even numbers are assigned to be either monoclinic or orthorhombic, respectively, On the other hand, extra spots can be indexed by one-dimensional modulated structure, The possible space groups for the subcell structure are Cm, C2, and C2/m for m = odd numbers, while those for m = even numbers are Ccm2(1) and Ccmm, respectively, Then, corresponding possible superspace groups are assigned to be P-s(C2), P-(1 over bar)(Cm), and P-s (1 over bar)(C2/m) for odd rn numbers and P(<1(11)over bar%gt;)(Ccm21) and P-1(1 over bar 1)(Ccmm) for even m numbers, Based on the superspace group determination, a structure model for a one-dimensional modulated structure is proposed. (C) 1998 Academic Press.
Title:
A new binary system exhibiting simultaneous crystallization
and spinodal decomposition: poly(ethylene-2,6-naphthalenedicarboxylate)
poly(ether imide) blend
Authors:
Chen HL. Hwang JC. Wang RC.
Source:
(list of journals)
Polymer. 39(24):6067-6072, 1998 Nov.
Abstract:
The phase behaviour and crystallization of poly(ethylene-2,6-naphthalenedicarboxylate) (PEN)/poly(ether imide) (PEI) blends were investigated. PEN and PEI were miscible in the melt over the entire composition range. A PEI-rich phase containing ca. 80 wt.% of PEI was identified after the crystallization of PEN below 240 degrees C. This observed composition deviated from the composition calculated by assuming a simple liquid-solid phase separation. Morphological observation by optical microscopy revealed simultaneous occurrence of spinodal decomposition and crystallization, where modulated structure was locked in by the crystallization of PEN. A UCST phase diagram with the binodal line located below the equilibrium melting point was identified. Investigation on the multiple melting behaviour showed that recrystallization of PEN following the initial melting was hindered due to the remixing between PEN and PEI. Despite the occurrence of spinodal decomposition, the crystallization rate of PEN still dropped with increasing initial PEI composition. (C) 1998 Elsevier Science Ltd. All rights reserved.
Title:
Quasicrystal Lie algebras
Authors:
Patera J. Pelantova E. Twarock R.
Source:
(list of journals)
Physics Letters A. 246(3-4):209-213, 1998 Sep 14.
Abstract:
A family of new infinite-dimensional Lie algebras over the real and complex number fields, closely related to the Witt (or Virasoro) algebra, is introduced and some unusual properties are pointed out. Generators of the Lie algebras are in a one-to-one correspondence with the points of a one-dimensional quasicrystal. (C) 1998 Published by Elsevier Science B.V.
Title:
ac Stark effect in a doubly driven three-level atom
Authors:
Wei CJ. Suter D. Windsor ASM. Manson NB.
Source:
(list of journals)
Physical Review A. 58(3):2310-2318, 1998 Sep.
Abstract:
In this paper we present a detailed treatment of the ac Stark effect of a three-level atom driven by two strong laser fields in a cascade scheme. We consider two situations where there is a weak laser field probing a new transition starting from one of the three levels to a fourth level. In one case the initial level of the probed transition is the ground state and in the other case the initial level is the intermediate state. For both situations we derive an analytical expression for the absorptive and dispersive responses of the weak probe field and present the spectrum obtained from numerical calculation. The general feature of the spectrum has a three-peak structure. The positions and relative intensities of the three spectral components are affected strongly by the driving field intensities and detunings. An account of the spectrum is given in terms of the dressed-state formalism.
Title:
Magnetic structures of RNiSb compounds (R = rare earths)
investigated by neutron diffraction
Authors:
Karla I. Pierre J. Ouladdiaf B.
Source:
(list of journals)
Physica B. 253(3-4):215-221, 1998 Oct.
Abstract:
The magnetic structures of RNiSb compounds (R = Ce, Nd, Tb, Dy, Ho) have been investigated by neutron diffraction. At low temperatures, the hexagonal compound NdNiSb shows a ferromagnetic order, whereas CeNiSb has a modulated structure with a ferromagnetic component. The cubic compounds Tb-, Dy-, and HoNiSb order antiferromagnetically with a propagation vector Q = (0.5, 0.5, 0.5). In the latter semiconducting phases, negative superexchange interactions between nearest neighbours should dominate. The crystal electric field plays an important role in all compounds. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
A triple point in an alloy with modulated compositional
order
Authors:
Massidda V.
Source:
(list of journals)
Physica B. 253(3-4):313-319, 1998 Oct.
Abstract:
We consider a triangular lattice whose sites can be occupied by atoms A or B, which interact with each other up to second neighbours. The concentration of A atoms, x, is fixed. Using the mean-field approximation the free energy is written in terms of the occupation probabilities of the sites, which are evaluated by a classical statistical formalism. In this way, the free energies of different configurations can be compared with each other. It is found that in a certain range of values of the interaction constants a triple-point exists in the (x,T) phase diagram, where the disordered phase (D) coexists with a commensurate (C) and an incommensurate (I) modulated phase. This triple point is not of the Lifshitz type. The C-D and the C-I transitions are discontinuous, while the I-D transition is continuous. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
Growth of crystals, composite crystal
structures and electrical resistance of high-pressure phases
of Mg2B1+x (B=Sn,Ge)
Authors:
Bolotina NB. Dyuzheva TI. Bendeliani NA. Petricek V. Petrova AE. Simonov VI.
Source:
(list of journals)
Journal of Alloys & Compounds. 278(1-2):29-33, 1998 Aug 21.
Abstract:
Single crystals of high-pressure phases of Mg2B1+x (B=Sn, Ge; x similar to 0.1) were grown at 5.8 GPa within the temperature range 600-1500 K. The composite crystal structures were investigated by the X-ray technique. Both structures are found to be closely related and each is composed of two incommensurate atomic subsystems. Two identically oriented hexagonal subcells are characterized by a common period a and an irrational value of the ratio gamma=c(I)/c(II) between incommensurate periods. The values of the cell parameters an, for Mg2Sn1+x a=13.245(3) Angstrom, c(I)=4.450(2) Angstrom, c(II)=3.273(3) Angstrom, gamma similar to 1.36, and for Mg2Ge1+x, a=12.53(1) Angstrom, c(I)=4.175(3) Angstrom, c(II)=3.037(3) Angstrom, gamma similar to 1.375. All Mg atoms and most of the Sn(Ge) atoms form subsystem I close to the alpha-PbCl2 structure type (cotunnite). Both the structure type and the stoichiometry of the compounds are disturbed by Sn(Ge) atoms which form incommensurate subsystem II of the composite. Resistance measurements at low temperature confirm conduction of metallic character for both compounds. (C) 1998 Elsevier Science S.A. All rights reserved.
Title:
X-ray crystal structures of
high-temperature, incommensurate, and ferroelectric
modifications of Rb2CoCl4
Authors:
Novikova MS. Tamazyan RA.
Source:
(list of journals)
Crystallography Reports. 43(2):175-188, 1998 Mar-Apr.
Abstract:
The X-ray crystal structures of three phase modifications of Rb2CoCl4-high-temperature, incommensurate, and ferroelectric-are determined for the first time. A split-atom model was proposed for the structure of the high-temperature phase at 295 K. The structural changes that accompany two phase transitions are discussed. The anomalous behavior of thermal parameters is the ferroelectric phase transition is revealed. Variations of the modulation vector q, the unit-cell parameters, and the satellite-reflection intensities with temperature were studied for the modulated phases. The calculated, value of spontaneous polarization in the ferroelectric phase (0.12 mu C/cm(2)) is typical of the beta-K2SO4-type ferroelectrics.
Title:
On the theory of incommensurately modulated
quasicrystals: the Frenkel-Kontorova model of a Fibonacci
quasilattice
Authors:
Belyaev OA.
Source:
(list of journals)
Crystallography Reports. 43(3):360-361, 1998 May-Jun.
Abstract:
The Frenkel-Kontorova model is applied to a Fibonacci chain. The nature of formation of incommensurate phases in quasicrystals is considered in terms of this model.
Title:
Defect density waves and specific manifestations of the memory effect in
crystals with incommensurate phases
Authors:
Shmyt'ko IM. Bagautdinov BS.
Source:
(list of journals)
Crystallography Reports. 43(4):631-639, 1998 Jul-Aug.
Abstract:
The X-ray diffraction studies of SC(NH2)(2), TMA-ZnCl4, and Ag3AsS3 crystals revealed specific manifestations of the memory effect associated with defect density waves: the appearance of additional modulation waves and their interactions with the ordinary wave, an increase of the temperature range corresponding to the incommensurate phase, the superposition of several modulated phases, and the reverse temperature hysteresis characterizing the transition from the normal to the incommensurate one phase.
Title:
On relaxation of dielectric constant in the range of phase transition from
incommensurate to commensurate polar phase
in Rh2ZnCl4 crystals
Authors:
Gladkii VV. Kirikov VA. Ivanova ES.
Source:
(list of journals)
Crystallography Reports. 43(4):661-666, 1998 Jul-Aug.
Abstract:
Slow relaxation of the dielectric constant epsilon of an inhomogeneous structure transformed into the nonequilibrium state in a jumpwise manner has been studied in both incommensurate and commensurate polar phases of a Br2ZnCl4 crystal. It is shown that in both phases, relaxation obeys the logarithmic temporal law characteristic of numerous inhomogeneous systems with uniform distributions of energies of the barriers separating metastable and thermodynamically equilibrium states. The relaxation times and energy barriers, which have the maximum values at the point of the structural phase transition, are evaluated.
Title:
The surface structure of a beta-Al(Cu1-xFex)-(110) film
formed on an AlCuFe quasicrystal substrate, analyzed by
dynamical LEED
Authors:
Shi F. Shen Z. Delaney DW. Goldman AI. Jenks CJ. Kramer MJ. Lograsso T. Thiel PA. Van Hove MA.
Source:
(list of journals)
Surface Science. 411(1-2):86-98, 1998 Aug 11.
Abstract:
In order to understand the unique properties of quasicrystalline surfaces, it is paramount to compare quasicrystalline and crystalline surfaces of similar chemical composition. To that end, the fivefold surface of an AlCuFe quasicrystal substrate was transformed, by ion bombardment and annealing, into a film with the beta-Al(Cu1-xFex) bulk structure. This is a CsCl structure with Fe and Cu atoms randomly occupying the body-center sites, and Al atoms at the corner sites. The film exposes a (110) free surface: its external structure was analyzed by dynamical low-energy electron diffraction in terms of atomic positions and layer-wise composition. The best fit between theory and experiment slightly favors a copper-rich composition in the surface layers (x = 0), although the sensitivity to the value of x is low, because Cu and Fe are very similar electron scatterers. The Al atoms in the surface layer buckle outward by 0.12 +/- 0.04 Angstrom relative to the Cu or Fe atoms in the same layer, while other relaxations from the bulk structure are small. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
Effect of gamma irradiation on the low-temperature electrical conductivity
and dielectric properties of TlGaSe2 crystals
Authors:
Sheleg AU. Iodkovskaya KV. Kurilovich NF.
Source:
(list of journals)
Physics of the Solid State. 40(7):1208-1210, 1998 Jul.
Abstract:
Electrical conductivity and dielectric properties of single-crystal TlGaSe2 have been studied as a function of gamma irradiation dose in the 100-280 K range including the existence of an incommensurate phase. Anomalies in the form of maxima have been observed in the sigma=f(T), tan delta=f(T), and epsilon=f(T) curves at the points of transition from the paraphase to incommensurate (IC) phase, T-i, and from the IC to commensurate phase, T-c. The increase in the quantities sigma, tan delta,and epsilon observed initially with increasing irradiation dose is followed by their strong decrease and disappearance of the anomalies. It has been established that gamma irradiation does not affect the phase transition temperatures T-i and T-c. (C) 1998 American Institute of Physics.
Title:
Vortex states in antiferromagnetic crystals
Authors:
Bogdanov A. Shestakov A.
Source:
(list of journals)
Physics of the Solid State. 40(8):1350-1356, 1998 Aug.
Abstract:
It is shown that axially symmetric two-dimensional nonuniform states can exist in easy-axis and cubic antiferromagnets lacking inversion symmetry, in the form of two-dimensional spatially modulated structures (magnetic vortex lattices) and isolated two-dimensional structures (vortices). The structure and equilibrium dimensions of the lattices and vortices have been determined by numerical solution of differential equations. (C) 1998 American Institute of Physics. .
Title:
High-temperature magnetic order in the singlet-ground-state compound PrCu2
Authors:
Schenck A. Andreica D. Gygax FN. Pinkpank M. Onuki Y. Ahmet P. Abliz M. Settai R. Amato A. Kaplan N.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(9):5205-5208, 1998 Sep 1.
Abstract:
It is known that PrCu2 shows a modulated antiferromagnetic structure below T-N=(50-60) mK that is claimed to be of a cooperative nuclear-electronic nature . Here we report on an observation by muon spin-rotation spectroscopy that this order seems to persist on a short-range scale with an apparently unchanged structure up to 60 K, i.e., up by three orders of magnitude as compared with T-N. We conjecture that the apparent magnetic order is of a secondary nature and the primary mechanism involves quadrupolar effects.
Title:
Highly anisotropic electronic structure in decagonal
quasicrystals and approximants
Authors:
Krajci M. Hafner J.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(9):5378-5383, 1998 Sep 1.
Abstract:
We present detailed ab initio calculations of the electronic structure in decagonal quasicrystals and approximants and in crystalline compounds in the Al-Cu-Co and Al-Mn systems. The observed anisotropy of the electronic structure is discussed in relation to the anomalous transport properties of the decagonal quasicrystals. Our results can explain the appearance of large transport anisotropies in the quasicrystalline and approximant phases. The effect of disorder on the anisotropies has been investigated.
Title:
Crystal structure of a hexagonal phase and
its relation to a quasicrystalline phase in Zn-Mg-Y alloy
Authors:
Takakura H. Sato A. Yamamoto A. Tsai AP.
Source:
(list of journals)
Philosophical Magazine Letters. 78(3):263-270, 1998 Sep.
Abstract:
The crystal structure of a Zn-Mg-Y hexagonal phase, considered to be related to that of the quasicrystalline phase, has been determined by single-crystal X-ray diffraction. The atomic model, refined to a final R value of 0.027, has the composition Zn65.22Mg27.92Y6.86 and 92 atoms in a unit cell with lattice constants a = 14.579(2) Angstrom and c = 8.687(1) Angstrom and the space group P6(3)/mmc. The Y atoms are situated at two different sites; one is fully occupied by Y atoms, while the other is shared with Mg atoms. The structure can be characterized by a layer structure stacked along the c axis, and also viewed as a columnar structure composed of fused Friauf polyhedras sharing hexagonal rings. The similarity of this hexagonal phase to the MgZn2 phase is shown. The structural relationship between this hexagonal phase and the icosahedral phase is also discussed.
Title:
New structural model of an Al72Ni20Co8 decagonal
quasicrystal
Authors:
Saitoh K. Tsuda K. Tanaka M.
Source:
(list of journals)
Journal of the Physical Society of Japan. 67(8):2578-2581, 1998 Aug.
Abstract:
A new structural model of an Al72Ni20Co8 decagonal quasicrystal is constructed on the basis of high-angle annular dark-field images and high-resolution electron microscope images. The model is composed of two types of atom clusters with about a 0.4nm radius as basic structural units, which are similar to the unit existing in the Al13Fe4 monoclinic approximant. The two clusters are located at the lattice points of the rhombic Penrose lattice. The model satisfies the symmetry of space group P10(5)/mmc. High-resolution electron microscope images calculated from the, model agree well with the experimental ones.
Title:
Mossbauer spectroscopy of [N(CH3)(4)](2)FeCl4
Authors:
Hikita T. Itoh K. Gesi K.
Source:
(list of journals)
Journal of the Physical Society of Japan. 67(8):2780-2783, 1998 Aug.
Abstract:
Mossbauer spectrum of Fe-57 of [N(CH3)(4)](2)FeCl4 was measured as a function of temperature in the temperature range 20 similar to 290 K. Single doublet was observed in the orthorhombic phase (phase I). The spectrum is almost the same in the incommensurate phase (phase II) and in the phase II' where the structure is modulated in the z-direction with the wavenumber 3/7. These modulation seems to raise no large EFG (electric field gradient) modulation to cause noticeable change in the spectrum. A new doublet appears in the phase III where the structure is commensurate with the cell tripling along the c axis. This doublet persists even to the phase IV where the structure is monoclinic with Z = 4. If we consider the crystal symmetry, the extra doublet is prohibited in this phase. The extra EFG is interpreted as the peculiarity to the powder sample.
Title:
Electrochemical deposition of metals onto silicon [Review]
Authors:
Oskam G. Long JG. Natarajan A. Searson PC.
Source:
(list of journals)
Journal of Physics D-Applied Physics. 31(16):1927-1949, 1998 Aug 21.
Abstract:
The general concepts governing the electrochemical deposition of metal films onto semiconductors are discussed. Deposition onto semiconductor surfaces is complicated due to the band structure of the semiconductor, which affects both the thermodynamics and the kinetics of metal deposition processes. The influence of the potential distribution at the semiconductor/solution interface on the charge transfer mechanisms involved in deposition of metals is discussed. Models for electrochemical nucleation and growth are described and the influence of the unique physical properties of semiconductors is analysed. Finally, we present recent results for electrochemical deposition of gold, copper and platinum onto n-type silicon.
Title:
Magnetoelectric effect and field-induced
'incommensurate-homogeneous' phase transitions in EuMn2O5
Authors:
Popov YF. Kadomtseva AM. Vorob'ev GP. Sanina VA. Tehranchi MM. Zvezdin AK.
Source:
(list of journals)
Journal of Magnetism & Magnetic Materials. 188(1-2):237-240, 1998 Sep.
Abstract:
The magnetoelectric effect and phase transitions induced by a strong magnetic field (up to 200 kOe) in single crystals EuMn2O2 have been investigated. It is known that these compounds have an incommensurate magnetic structure. The electric polarization of the single crystals were measured, along the a, b-, and c-axes of the crystals, and the magnetic field was oriented along the c-axis. At low magnetic fields (H < 100 kOe), the dependencies of the electric polarization on the magnetic field are practically quadratic ones which correlate well with the above mentioned incommensurate magnetic structure of the compounds. The jump-like anomalies of the curves 'the electric polarization-magnetic field' were discovered. The critical fields H-ef of these jumps are of 100 kOe order and depend more on the temperature. There is in general, a large linear contribution of the electric polarization into the magnetic field dependence at H > H-ef. This favors that the field induced 'incommensurate-homogeneous' phase transition probably takes place at the critical field. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
Growth of large single grains of the icosahedral
quasicrystal ZnMgY
Authors:
Langsdorf A. Assmus W.
Source:
(list of journals)
Journal of Crystal Growth. 192(1-2):152-156, 1998 Aug.
Abstract:
In this paper we report on the growth of icoshedral (i-)ZnMgY single quasicrystals by a liquid encapsulated (LE) top seeded solution growth (TSSG) method. This method meets both main requirements for the growth of i-ZnMgY: to avoid the peritectic growth reaction and to deal with the high vapour pressure of the component Zn. We obtain high quality single grains of i-ZnMgY with dimensions of a few mm in each direction. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
Magnetic structure of TbIrSi3 compound
Authors:
Bazela W. Stusser N. Szytula A. Zygmunt A.
Source:
(list of journals)
Journal of Alloys & Compounds. 277:578-582, 1998 Jul 24.
Abstract:
The paper reports on neutron diffraction and magnetic measurements of TbIrSi3. The compound crystallizes in the tetragonal BaNiSn3-type of structure. Below 16 K, the Tb-magnetic moments order antiferromagnetically. In the temperature region 1.6-7.4 K, a collinear antiferromagnetic structure of AFI-type with the moment in the basal plane is observed. With increasing temperature, the magnetic structure changes into a transversal sine-wave modulated structure. In the temperature region 7.8-11 K, a collinear and a sine-modulated structure coexist whereas in the region 11-16 K, a sine-modulated one is detected. The data are briefly discussed in terms of the RKKY theory and electric-field model. (C) 1998 Elsevier Science S.A.
Title:
Self-propagating high-temperature synthesis and formation of
quasicrystals in Al/Mn bilayer thin films
Authors:
Myagkov VG. Bykova LE. Bondarenko GN.
Source:
(list of journals)
JETP Letters. 68(2):131-134, 1998 Jul 25.
Abstract:
Self-propagating high-temperature synthesis in Al/Mn bilayer thin films was investigated. It was found that a quasicrystalline phase forms after the passage of self-propagating high-temperature synthesis through the sample. It is shown that after multiple initiation (n>5) of self-propagating high-temperature synthesis in a sample the quasicrystalline phase transforms into a stable Al6Mn phase. It is conjectured that self-propagating high-temperature synthesis can play the main role in the formation of quasicrystals in other film systems as well. (C) 1998 American Institute of Physics.
Title:
Light scattering by low-frequency excitations in quasi-periodic n-alkane/urea
adducts
Authors:
Ollivier J. Ecolivet C. Beaufils S. Guillaume F. Breczewski T.
Source:
(list of journals)
Europhysics Letters. 43(5):546-551, 1998 Sep 1.
Abstract:
High-resolution light scattering spectroscopy has been performed on a series of n-alkane CnH2n+2/urea inclusion compounds with n = 12, 14, 17-19. The elastic constants of these incommensurate composite crystals have been determined and found to be independent of the chain length of the guest molecules. In addition, no extraneous acoustic-like mode appeared in all spectra. Hen-ever, quasi-elastic components with different widths are observed for different polarizations. In one of them the characteristics of the scattered light suggest that the quasi-elastic broadening could be generated by a sliding mode, whereas the other detected component is assigned to the reorientational motions of the n-alkane chains about their long axis.
Title:
Elastic Green's function of icosahedral quasicrystals
Authors:
Bachteler J. Trebin HR.
Source:
(list of journals)
European Physical Journal B. 4(3):299-306, 1998 Aug.
Abstract:
The elastic theory of quasicrystals considers, in addition to the "normal" displacement field, three "phason" degrees of freedom. Mie present an approximative solution for the elastic Green's function of icosahedral quasicrystals, assuming that the coupling between the phonons and phasons is small.
Title:
Novel morphology of voids in single-quasicrystalline
icosahedral Al70.5Pd21.0Mn8.5
Authors:
Waseda Y. Suzuki S. Urban K.
Source:
(list of journals)
Zeitschrift fur Naturforschung Section A-A Journal of Physical Sciences.
53(8):679-683, 1998 Aug.
Abstract:
This paper deals with the morphology and surface chemistry of faceted voids existing in single-quasicrystalline icosahedral Al70.5Pd21.0Mn8.5. By observation with a scanning electron microscope of surfaces obtained by cleavage of the quasicrystal, the habit planes of the dodecahedral voids were identified. The chemical surface composition of the void surface was determined by Auger electron spectroscopy after cleavage in ultra-high vacuum.
Title:
Characterization by electrolyte electroreflectance and X-ray photoelectron
spectroscopy of amorphous Ni59Nb40Pt1-xSnx alloys and their activation by HF
solutions
Authors:
Sistiaga M. Cuesta A. Pierna AR. Gutierrez C.
Source:
(list of journals)
Surface Science. 410(2-3):312-320, 1998 Aug 1.
Abstract:
The influence of chemical etching with HF on the nature of the surface of amorphous Ni59Nb40Pt1-xSnx alloys has been studied in situ by electrolyte electroreflectance (EER) and ex situ by X-ray photoelectron spectroscopy (XPS). The EER spectrum of the untreated alloy in 0.5 M H2SO4 shows a bipolar band, which disappears after the HF treatment yielding a structureless EER spectrum similar to that of Pt, but reappears after several hours in the 0.5 M H2SO4 electrolyte. This process of dissolution by HF of an oxide species and its reappearance after a few hours cannot be followed by XPS, since the time interval between sample withdrawal from the electrolyte and actual measurement is of a few hours as well. XPS spectra showed the presence of metallic Nb before and after the HF treatment, and that niobium pentoxide was the main species in the as-quenched alloy, but that after treatment with HF it became a minor component, the main one being NbO. The main effect of the I-IF treatment is to produce a platinum enrichment of the surface, as unequivocally determined by cyclic voltammetry, XPS and EER. After Ar sputtering for 9 min the XPS spectrum of the untreated alloy showed metallic Nb only, while in the HF-treated alloy the peaks of metallic Nb were swamped by those of NbO and some Nb2O5. We interpret this difference as being due to the formation by the HF attack of a porous Nb film which becomes oxidized in the electrolyte and/or during transfer to the spectrometer, and so thick that it is not eliminated by Ar sputtering for 9 min. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
Self-similarity in the bifurcation structure involving
period tripling, and a suggested generalization to period n-tupling
Authors:
Goswami BK.
Source:
(list of journals)
Physics Letters A. 245(1-2):97-109, 1998 Aug 10.
Abstract:
We compute the bifurcation structure in the parameter space of the periodically forced Toda oscillator model of class B lasers. The substructures, born in the process of period tripling, appear in a self-similar manner within the main bifurcation structure. Next, our observations suggest that, similar to period tripling, the birth of an n-tupled saddlenode (n = 4,5,...) around a given stable periodic orbit is also a generic phenomenon of this oscillator. These n-tupling processes create substructures as in the case of period tripling. Taking into account all such n-tupling processes, the composite bifurcation structure apparently exhibits a new self-similar feature. (C) 1998 Elsevier Science B.V.
Title:
Lowest energy structures of gold nanoclusters
Authors:
Garzon IL. Michaelian K. Beltran MR. Posada-Amarillas A. Ordejon P. Artacho E. Sanchez-Portal D. Soler JM.
Source:
(list of journals)
Physical Review Letters. 81(8):1600-1603, 1998 Aug 24.
Abstract:
The lowest energy structures of Au-n, (n = 38, 55. 75) nanoclusters are obtained by unconstrained dynamical and genetic-symbiotic optimization methods, using a Gupta II-body potential. A set of amorphous structures, nearly degenerate in energy, are found as the most stable configurations. Some crystalline or quasicrystalline isomers are also minima of the cluster potential energy surface with, similar energy. First principles calculations using density functional theory confirm these results and give different electronic properties for the ordered and disordered gold cluster isomers.
Title:
X-ray study of CHF3 and CH3Cl monolayers on boron nitride
Authors:
Morishige K. Komura T.
Source:
(list of journals)
Langmuir. 14(17):4887-4890, 1998 Aug 18.
Abstract:
The structures of CHF3 and CH3Cl monolayers adsorbed on the basal plane of boron nitride have been examined by X-ray diffraction. For CHF3, orientationally disordered, triangular, incommensurate high-temperature and orientationally ordered low-temperature incommensurate phases were observed. The latter phase has antiferroelectric ordering of an electric dipole moment and is uniaxially compressed. On the other hand, CH3Cl molecules form only one crystalline monolayer of an antiferroelectric structure, independent of temperature and coverage. These results are compared with the monolayers of these molecules on graphite.
Title:
Structural and microstructural aspects of Si-x(Ta,Nb)Te-2
Authors:
Frangis N. Van Tendeloo G. Manolikas C. Amelinckx S.
Source:
(list of journals)
Journal of Solid State Chemistry. 139(1):105-123, 1998 Aug.
Abstract:
The modulated structures of the compounds of the type A(x)MTe(2) (M = Nb, Ta; A = Si, Ge) are discussed, and the electron diffraction patterns and high-resolution electron microscopy images are analyzed in terms of interface modulated structures. The structure of SixTaTe2 (x approximate to 1/3) is of particular interest; it results from the presence of periodic interfaces of two types leading to an incommensurately looking diffraction pattern with a q-vector slightly larger than c(0)*/3. A domain microstructure consisting of three orientation variants and three translation variants is revealed and interpreted in terms of the crystal structure, The domains are assumed to result from an order-disorder transition. In SixNbTe2(x = 3/7), different long period structures with long periods 7c(0), 8c(0) and 9c(0) are formed. Possible models are discussed. (C) 1998 Academic Press.
Title:
Bi3+ electronic lone pair configuration in the modulated
Bi-2212 type oxides
Authors:
Jakubowicz N. Perez O. Grebille D. Leligny H.
Source:
(list of journals)
Journal of Solid State Chemistry. 139(1):194-199, 1998 Aug.
Abstract:
The Bi3+ ion is characterized by the electronic configuration [Xe] 4f(14)5d(10)6s(2), and its 6s(2) lone pair plays an important role in the environment of the ion. A program of localization of the lone pair was successively applied to several bismuth oxides, Different Bi environments were then evidenced and a comparison between simple Bi oxides and more complex phases (modulated and collapsed phases in the family of the so-called Bi-2212 oxides or related compounds) was carried out. All these environments are characterized by Bi-Lp distances ranging from 0.5 to 1 Angstrom and O-Lp distances above 2.4 Angstrom. They can always be described as a more or less important distortion of an ideal BiO(3)Lp tetrahedron, The possible role of this lone pair in the accommodation of the modulation in some phases is outlined. (C) 1998 Academic Press.
Title:
Bromide adsorption induced formation of thallium bromide adlayers with
varying composition and structure on the Au(111) electrode
surface
Authors:
Adzic RR. Wang JX.
Source:
(list of journals)
Journal of Physical Chemistry B. 102(33):6305-6308, 1998 Aug 13.
Abstract:
The underpotential deposition of Tl on Au(111) in 0.1 M HClO4 solution containing 1 mM Tl+ and 1 mM Br- has been investigated by using cyclic voltammetry, in situ X-ray scattering, and rotating disk-ring techniques. Three interesting phenomena for the UPD of metals in the presence of adsorbed anions are reported, viz., (i) an increase of the underpotential shift for deposition of Tl on Au(111) in the presence of Br- in solution, (ii) a formation of two mixed adlayers, surface compounds, with the stoichiometry Tl-Br-2 and Tl-Br, and (iii) an exceptionally complex structural behavior of this system with five ordered phases. Bromide and thallium form incommensurate rotated-hexagonal close-packed phases at ca. 0.85 and -0.3 V, respectively. In the intermediate potential region three mixed phases exist, identified as 3TlBr(2)-(root 13 x root 13), 2TlBr-(3 x root 3), and TlBr-c(p x root 3).
Title:
Simple physical generation of aperiodic
structures
Authors:
Janot C. Patera J.
Source:
(list of journals)
Journal of Non-Crystalline Solids. 234:234-238, 1998 Jul.
Abstract:
Space-filling tiling is difficult when local symmetries are not compatible with periodicity. Alternatively space covering may be obtained by adding individual atoms or small clusters according to local rules which force bonding directions and fix a shortest distance between pairs of atom. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
Short-range order in undercooled liquid metals
Authors:
Jacobs G. Egry I. Holland-Moritz D. Platzek D.
Source:
(list of journals)
Journal of Non-Crystalline Solids. 234:396-402, 1998 Jul.
Abstract:
Undercooled liquid metals are a metastable slate of matter with properties which fan be investigated by electromagnetic levitation. To obtain insight into the short-range order of undercooled liquid metals, we have installed an electromagnetic levitation facility at a synchrotron source. In this paper, we report the results obtained by a combination of electromagnetic levitation and the extended X-ray absorption fine structure (EXAFS) technique. Measurements have been carried out on potentially ferromagnetic Liquid Co-Pd alloys, and on Al-Cu-Co alloys of quasicrystal forming composition. In spite of the experimental difficulties, spectra could be obtained over a wide temperature range and the relevant physical parameter, such as the nearest-neighbour distance: could be determined quantitatively. At the melting point, the Go-Co nearest neighbour distance is 2.50 Angstrom, while the Co-Pd nearest neighbour distance is 2.69 Angstrom. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
Discovery of a new boron-rich phase by electron
crystallography
Authors:
Steeds JW. Wilson JA.
Source:
(list of journals)
Journal of Applied Crystallography. 31(Part 3):373-378, 1998
Jun 1.
Abstract:
In examining a supply of supposedly amorphous, high-purity, boron powder, a significant proportion of the particles were found to be well crystallized. Examination of these crystalline particles by convergent-beam electron diffraction revealed that they were orthorhombic with space group Pnma (a = 16.7, b = 17.7, c = 10.3 Angstrom). Contaminating impurities are thought to be responsible for the formation of this crystal structure but the authors were unable to identify them by analytical transmission electron microscopy. Some remarkable electron diffraction effects resulted from the dense reciprocal lattice of Bragg reflection and these are described. Noncrystalline particles in the powder were, in fact, found to be quasicrystalline in nature with planar disorder.
Title:
Crystallography and solidification behaviour of nanometric
Pb particles embedded in icosahedral and decagonal
quasicrystalline matrix
Authors:
Singh A. Tsai AP.
Source:
(list of journals)
Acta Materialia. 46(13):4641-4656, 1998 Aug 10.
Abstract:
Solidification behaviour of lead particles embedded in icosahedral and decagonal quasicrystalline matrix has been studied. Differential scanning calorimetry traces for the icosahedral matrix show a sharp lead melting peak but a very Aat solidification exotherm with several peaks, while lead in the decagonal matrix shows sharp melting and solidification peaks. Transmission electron microscopy shows that lead particles are Faceted on major planes of the matrix. The solidified lead particles show well defined orientation relationships with the matrix. Three relationships were observed in the case of the icosahedral matrix in all of which there is a tendency for the lead {022} planes to align with icosahedral {211111} and {221001} planes. In the decagonal matrix a single relationship is observed. The calculated contact angles for nucleation show that lead solidification on quasicrystalline surfaces occur at higher undercoolings for the same contact angles, as compared to solidification on crystals. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.
Title:
The yttrium oxide fluoride solid solution described as a composite
modulated system
Authors:
Schmid S.
Source:
(list of journals)
Acta Crystallographica - Section B, Structural Science.
54(Part 4):391-398, 1998 Aug 1.
Abstract:
Single-crystal X-ray diffraction data (Mo K alpha radiation) are used to determine the structure of the Delta = 0.174 member of a (YO1 - DeltaFDelta)F1 + Delta, 0.12 less than or equal to Delta less than or equal to 0.22, wide-range non-stoichiometric solid solution in the yttrium oxide fluoride system. The structure is refined as a composite modulated structure composed of two mutually incommensurable Q and H substructures with overall superspace-group symmetry Acmm(0,0,1.174..)0s0. The Q substructure has lattice parameters a = 5.415 (2), b(Q) = 5.534 (2) and c(Q) = 5.525 (2) Angstrom, and superspace-group-symmetry Acmm(0,0,1.174..)0s0. The H substructure has lattice parameters a = 5.415 (2), b(H) = 1/2b(Q) = 2.767(1) and c(H) = 4.696(2) Angstrom, and superspace-group symmetry Pmcm(0,1/2,0.8518...)s00. Refinement on 338 unique reflections converged to R = 0.025, while a previous conventional superstructure refinement led to R = 0.101. This lowering of the R factor goes hand-in-hand with a substantial reduction in the number of refined parameters.
Title:
Structural refinement of monoclinic low tridymite MC with diffraction
intensities of a twin crystal [German]
Authors:
Kato K. Nukui A. Jarchow O. Lons J.
Source:
(list of journals)
Zeitschrift fur Kristallographie. 213(7-8):392-398, 1998.
Abstract:
The crystal structure of the monoclinic low tridymite MC, a polymorph of SiO2, has been re-refined using the unpublished as-measured intensities of a twinned crystal collected by Kato and Nukui [Acta Crystallogr. B32 (1976) 2486-2491]. Crystal data: space group Cc, a = 18.494(8) Angstrom, b = 4.991(2) Angstrom, c = 25.832(8) Angstrom, beta = 117.75(2)degrees, z = 48. R = 0.071, R-w = 0.071 based on 6453 F-o's for 325 variable parameters. The Si-O distances are between 1.575(6) Angstrom and 1.620(7) Angstrom; mean 1.598 Angstrom. Except for an extreme value of 178.8(6)degrees, the Si-O-Si angles range from 142.9(4)degrees to 156.3(6)degrees; mean 148.6 degrees. The structure was refined also as a commensurate modulated structure based on the high-tridymite structure.
Title:
Thermal stability of amorphous and crystalline multilayers
produced by magnetron sputtering
Authors:
Beke DL. Langer GA. Kis-Varga M. Dudas A. Nemes P. Daroczi L. Kerekes G. Erdelyi Z.
Source:
(list of journals)
Vacuum. 50(3-4):373-383, 1998 Jul-Aug.
Abstract:
For the demonstration of the high diversity of different applications of the magnetron sputtering technique in the fabrication of multilayers the production, characterisation and investigations on the thermal stability of epitaxial metallic Mo/V as well as amorphous Si/Ge semiconductor multilayers are presented. It is demonstrated, that combination of low and high angle X-ray diffraction as well as TEM is a very essential tool for the characterisation of the modulated structures and it is also very useful in the investigation of the thermal stability. The experimental results are also compared with numerical calculations made by finite element method for the diffusional homogenisation, controlled by bulk diffusion. It was shown, that in the case of the amorphous Si/Ge system the intermixing is possible in amorphous state, and diffusional stresses do not ca use a significant curvature on the thermal decay curves of the first order peak of the low angle Bragg reflection In(I/I-0) vs t, but they play an important role in the strong porosity formation in the silicon side. Furthermore it was illustrated, that the initial curvature on the In(I/I-0) vs t curve is due to the strong concentration dependence of the intrinsic diffusion coefficients. In epitaxial Mo/V multilayers the thermal behaviour is different. There is a fast transformation of the layered structure into a heterogeneous partly reacted structure, which consists of regions of a reacted Mo(V) alloy and the remaining Mo/V layers. This can not be interpreted by bulk diffusion, but rather by the formation of grain-boundaries inside the Mo layer and probably by a grain-boundary motion induced alloying. (C) 1998 Elsevier Science Ltd. All rights reserved.
Title:
We present a revision for the existing theories on diffraction of
electromagnetic waves by volume gratings. [Review]
Authors:
Cheben P. Calvo ML.
Source:
(list of journals)
Revista Mexicana de Fisica. 44(4):323-332, 1998 Aug.
Abstract:
We present a revision for the existing theories on diffraction of electromagnetic waves by volume gratings. We have focused our attention to the following groups of theories: coupled waves theories, modal theories, multiple dispersion theories, and electromagnetic theories of gratings, provided they were appropriate to analysis of volume diffraction gratings. We also include a revision of some other theories and methods having minor impact in this field as: effective medium theory, boundary diffraction method, finite element method, and micro genetics algorithms. We include a total of 225 selected references covering a period of approximately one hundred years: 1891-1997.
Title:
Phase behavior of a system of particles with core collapse
Authors:
Jagla EA.
Source:
(list of journals)
Physical Review E. 58(2 Part A):1478-1486, 1998 Aug.
Abstract:
The pressure-temperature phase diagram of a one-component system, with particles interacting through a spherically symmetric pair potential in two dimensions, is studied. The interaction consists of a hard core plus an additional repulsion at low energies. It is shown that at zero temperature, instead of the expected isostructural transition due to core collapse occurring when increasing pressure, the system passes through a series of ground states that are not triangular lattices. In particular, depending on parameters, structures with squares, chains, hexagons, and even quasicrystalline ground states are found. At finite temperatures the solid-fluid coexistence line presents a zone with negative slope (which implies melting with decreasing in volume) and the fluid phase has a temperature of maximum density, similar to that in water.
Title:
Low-temperature thermal and optical properties of single-grained decagonal
Al-Ni-Co quasicrystals
Authors:
Bianchi AD. Bommeli F. Felder E. Kenzelmann M. Chernikov MA. Degiorgi L. Ott HR. Edagawa K.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(6):3046-3056, 1998 Aug 1.
Abstract:
We report measurements of the specific heat C-p(T) and of the thermal conductivities lambda(p)(T) along the periodic direction and lambda(q)(T) along a direction in the quasiperiodic plane for decagonal Al-Ni-Co at low temperatures. The coefficient gamma=0.63 mJ mol(-1) K-2 of the linear term to C-p(T) indicates a low density of electronic states at E-F. The magnitude of the cubic-in-T term to the low-temperature specific heal is in fair agreement with the acoustic contribution to C-p(T) calculated from the results of low-temperature measurements of the elastic stiffness constants c(ij). The phonon contribution to lambda(p)(T) shows a distinct maximum at 25 K, typical for periodic crystals. The dominant feature in the phonon contribution to lambda(q)(T) is an extended plateau between 30 and 70 K, in agreement with the concept of generalized Umklapp processes in quasicrystals. This distinct difference between the phonon contributions to lambda(p)(T) and lambda(q)( T) is similar to that previously observed for Al65CU20Co15 The optical conductivity sigma(1)(omega) is obtained from reflectivity data in the frequency range between 1 meV and 12 eV. At low frequencies the optical conductivity sigma(1)(omega) is characterized by an anisotropic Drude contribution. Al high frequencies an additional absorption for the periodic and the quasiperiodic direction is observed centered at approximately 1 and 2 eV, respectively, which can be associated with electronic excitations across a pseudogap.
Title:
Domain excitations in spin-Peierls systems
Authors:
Dobry A. Ibaceta D.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(6):3124-3128, 1998 Aug 1.
Abstract:
We study a model of a spin-Peierls material consisting of a set of antiferromagnetic Heisenberg chains coupled with phonons and interacting among them via an interchain elastic coupling. The excitation spectrum is analyzed by bosonization techniques and the self-harmonic approximation. The elementary excitation is the creation of a localized domain structure where the dimerized order is the opposite to the one of the surroundings. It is a triplet excitation whose formation energy is smaller than the magnon ap. Magnetic internal excitations of the domain an possible and give the further excitations of the system. We discuss these results in the context of recent experimental measurements on the inorganic spin-Peierls compound CuGeO3.
Title:
Generation of non-equilibrium random tilings and their characterization
Authors:
Ebinger W. Roth J. Trebin HR.
Source:
(list of journals)
Physica Status Solidi B-Basic Research. 208(2):353-366, 1998 Aug.
Abstract:
This paper deals with generation and structural properties of icosahedral quasicrystalline tilings consisting of the canonical rhombohedra. First, we characterize the plane and slab structure of ideal and random quasicrystals and discuss their implications for experiment. Second, we present a new method for generating non-equilibrium random tilings called the addition method.
Title:
Complementary observations of defects in quasicrystals by
X-ray topography and electron microscopy
Authors:
Reinier E. Mancini L. Gastaldi J. Baluc N. Hartwig J. Baruchel J.
Source:
(list of journals)
Physica B. 253(1-2):61-67, 1998 Oct.
Abstract:
Further information on defects previously [J. Gastaldi et al. Phil. Mag. Lett. 72 (1995) 311.] observed by X-ray topography in quasicrystalline grains, and that show a loop-shaped contrast, was obtained by combining this technique with electron microscopic observations and chemical analyses. The experiments, carried out either at room temperature or during in situ and real-time high temperature annealing, allowed to get clues on the relationships between these loop-shaped defects, the growth process of the quasicrystal grains and the defect behaviour under the annealing treatment. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
Edge dislocations in nanoquasicrystalline materials
Authors:
Gutkin MY. Ovid'ko IA.
Source:
(list of journals)
Nanostructured Materials. 10(3):493-501, 1998 Apr.
Abstract:
A theoretical model is proposed which describes energetic characteristics and behavioral features of edge dislocations in coarse-grained and nanostructured quasicrystals. The key point of the model is representation of dislocation-induced phason imperfections as centers of isotropic dilatation (flexes). The special attention in this paper is paid to the influence of the nanoscale structure on both energetic characteristics and behavioral features of edge dislocations in nanostructured quasicrystals (nanoquasicrystalline materials). It is shown, in particular, that the basic grain-size-sensitive contribution of dislocation-induced phason imperfections to the total energy of an edge dislocation varies directly with grain size, in which case the formation of edge dislocations is not suppressed in nanoquasicrystalline materials tin contrast to coarse-grained quasicrystalline materials. (C) 1998 Acta Metallurgica Inc.
Title:
Thermal expansion and cooling rate dependence of transition temperature in
ZrTiO4 single crystal
Authors:
Park Y.
Source:
(list of journals)
Materials Research Bulletin. 33(9):1325-1329, 1998 Sep.
Abstract:
Thermal expansion in ZrTiO4 single crystal was investigated in the temperature range covering the normal, incommensurate, and commensurate phases. Remarkable change was found at the normal-incommensurate phase transition (T-I) in all thermal expansion coefficients a, b, and c. The spontaneous strains chi(as) and chi(bs) along the a and b axes show linear temperature dependence, while the spontaneous strain chi cs along the c axis shows a nonlinear temperature dependence. Small discontinuity along the c direction was observed at the incommensurate-commensurate transition temperature, T-c = 845 degrees C. dT(I)/dP and dT(c)/dP depend on the cooling rate. (C) 1998 Elsevier Science Ltd.
Title:
Breakdown of de Gennes scaling in HoxLu1-xNi2B2C
Authors:
Freudenberger J. Fuchs G. Nenkov K. Handstein A. Wolf M. Kreyssig A. Muller KH. Loewenhaupt M. Schultz L.
Source:
(list of journals)
Journal of Magnetism & Magnetic Materials. 187(3):309-317, 1998 Sep.
Abstract:
The temperature dependence of magnetic ordering and the superconducting transition have been studied for polycrystalline HoxLu1-xNi2B2C compounds by susceptibility and resistivity measurements as well as neutron diffraction. For Ho concentrations in the range 0 less than or equal to x less than or equal to 0.7, the superconducting transition temperature, T-c, decreases from 16.5 K at x = 0 linearly with increasing x and, consequently, with increasing effective de Gennes factor. This is in accordance with a generalized Abrikosov-Gor'kov theory. At x = 0.7, T-c reaches 8.5 K i.e. the value of HoNi2B2C. Pair breaking by the Ho magnetic moments is stronger in HoxLu1-xNi2B2C compared to HoxY1-xNi2B2C. This is attributed to the difference between the lattice constants of the Ho-Y and the Ho-Lu systems resulting in different electronic structure parameters. A complete breakdown of the scaling behaviour of T-c occurs for x > 0.7, where T-c becomes independent of the effective de Gennes factor. In this range of x re-entrant behaviour and the presence of an incommensurate a-axis, modulated antiferromagnetic structures have been observed below a characteristic temperature T-m. Commensurate and incommensurate c-axis modulated antiferromagnetic structures that are observed both in the Ho-Y and the Ho-Lu systems coexist with superconductivity. (C) 1998 Elsevier Science B.V. All rights reserved.
Title:
Densities, minimal distances, and coverings of quasicrystals
Authors:
Moody RV. Patera J.
Source:
(list of journals)
Communications in Mathematical Physics. 195(3):613-626, 1998 Aug.
Abstract:
Quasicrystals are generalizations of lattices. In this spirit, we consider here three kinds of geometric properties of mathematical models of quasicrystals: minimal distances between quasicrystal points, covering radii of quasicrystals, and the densities of quasicrystal points. A closed formula for the density of points in quasicrystals with local symmetries of types H-2, H-3, and H-4 is derived. Using this we determine the planes of maximal density in 3-dimensional icosahedral (i.e. H3) quasicrystals. Under fairly mild conditions on the acceptance window, these turn out to be the planes orthogonal to the 5-fold axes of the H-3-symmetry, revealing that the symmetry is already implicit in the quasicrystal, even when it is not explicit. We show how to determine the minimal distances and covering radii in particular quasirystals. In particular we derive the covering radius of the canonical H-2 quasicrystal Sigma(2) and derive an interesting covering result and estimate for the quasicrystal C-4.
Title:
Mechanisms of transition between 1q and 2q incommensurate
phases in a two-dimensional crystal model
Authors:
Dmitriev SV. Shigenari T. Abe K.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(5):2513-2522, 1998 Aug 1.
Abstract:
The two-dimensional elastically hinged molecule model of a crystal which contains two anharmonic terms was studied numerically. The results show that the Iq or 2q incommensurate phase can be stable depending on the parameters of the model. For example, in the sinusoidal incommensurate regime the Iq (2q) phase can be globally stable but in the domain-wall regime the situation can be opposite and the 1q <-> 2q (2q <-> 1q) transition can be expected. Another mechanism of the 1q <-> 2q phase transition stems from the softening of the dispersion surface simultaneously at two points of the Brillouin zone, (kappa(x),0) and (0,kappa(y)) In this case the 2q modulated phase can appear as a linear combination of the two Iq modulated phases. Under the assumption that the dispersion surface is slightly perturbed for some reason, the softening first occurs at one of the two points resulting in the Iq phase formation. Further changing of the external parameters leads to the softening at the second point and the 1q <-> 2q transition can take place. Both these mechanisms of the 1q <-> 2q phase transition were revealed and studied. .
Title:
Interpretation of the temperature dependence of Mn2+ high-field ESR spectra
in the first incommensurately modulated
phase of betaine calcium chloride dihydrate
Authors:
Metz H. Heidler R. Michel D. Windsch W.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(5):2556-2562, 1998 Aug 1.
Abstract:
By a combination of X-band and e-band ESR investigations it was possible to distinguish between effects of first and second order in the critical behavior, which are influenced in different ways by the dynamics of the order-parameter fluctuations. The theoretical analysis is based on a Fourier expansion of the ESR fine-structure elements in terms of the harmonics of the incommensurate modulation. Second-order perturbation theory for the evaluation of the ESR spectra was applied. The splitting between thr edge singularities should show a temperature dependence given by the superposition of two different critical contributions: Delta B-ES=a(T-i-T)(<(beta)over bar>)+b(T-i-T)(2 beta). The second contribution depends on the strength of the external magnetic held. This could be clearly revealed in the comparison between Q- and X-band measurements. The influence of the Mn content c(Mn) or of the gamma-irradiation dose c(gamma) on the splitting of the edge singularities was analyzed. .
Title:
Structural refinement of 1/1 bcc approximants to
quasicrystals: Bergman-type W(TiZrNi) and Mackay-type
M(TiZrFe)
Authors:
Kim WJ. Gibbons PC. Kelton KF. Yelon WB.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(5):2578-2585, 1998 Aug 1.
Abstract:
We report the structural refinement of large-unit-cell bcc crystalline phases found in Ti-Zr-Ni and Ti-Zr-Fe alloys, which are 1/1 rational approximants of icosahedral quasicrystals in the same alloys. The structure of the stable 1/1 phase W(TiZrNi), lattice constant a(o) = 14.317 Angstrom, determined by a Rietveld analysis of x-ray and neutron powder diffraction data, is closely related to that of the 1/1 phases R(AlLiCu) and Bergman(AlMgZn), containing Bergman-type icosahedral clusters of atoms. Despite the similar chemistry of the 1/1 phases in Ti-Zr-Ni and Ti-Zr-Fe alloys, the 1/1 phase M(TiZrFe) contains double-shell Mackay icosahedra, Like those found in the 1/1 phase alpha(TiCrSiO). These results provide starting structures for six-dimensional refinements of the related quasicrystals. .
Title:
Antiferromagnetic structure of UNiAl
Authors:
Prokes K. Bourdarot F. Burlet P. Javorsky P. Olsovec M. Sechovsky V. Bruck E. de Boer FR. Menovsky AA.
Source:
(list of journals)
Physical Review B-Condensed Matter. 58(5):2692-2698, 1998 Aug 1.
Abstract:
UNiAl crystallizes in the hexagonal ZrNiAl-type structure. Magnetic, transport, and thermal properties of UNiAl point to an antiferromagnetic (AF) ordering below T-N= 19.3 K. Below this temperature UNiAl orders with propagation vector q=(0.1,0.1,0.5). U magnetic moments are oriented along the hexagonal axis and modulated sinusoidally within the basal plane. The modulation is not even partially squared-up down to 1.7 K. The maximum size of U moment is (1.24+/-0.03)mu(B)/U. However, the three U atoms that are crystallographically equivalent do not carry the same moment within the crystallographic unit cell. The propagation vector of AF structure does not change in the whole temperature range. AF correlations that propagate also with q =(0.1,0.1,0.5) can be traced at temperatures up to 30 K showing the critical scattering near T-N. .
Title:
Commensurate columnar composite compounds: Synthesis and
structure of Ba15Zr14Se42 and Sr21Ti19Se57
Authors:
Tranchitella LJ. Fettinger JC. Dorhout PK. Van Calcar PM. Eichhorn BW.
Source:
(list of journals)
Journal of the American Chemical Society. 120(30):7639-7640, 1998 Aug 5.
Authors:
Destainville N.
Title:
Entropy and boundary conditions in random rhombus tilings
Source:
(list of journals)
Journal of Physics A-Mathematical & General. 31(29):6123-6139, 1998 Jul 24.
Abstract:
The tilings of rhombi in two dimensions and of rhomboedra in three dimensions are studied when they are constrained by Bred boundary conditions. We establish a link between those conditions and free or periodic boundary ones: the entropy is written as a functional integral which is treated via a saddle-point method. We can exhibit the dominant states of the statistical ensemble of tilings and show that they can display a strong structural inhomogeneity caused by the boundary. This inhomogeneity is responsible for a difference of entropy between the studied fixed boundary tilings and free boundary ones. This method uses a representation of tilings by membranes embedded in a higher-dimensional hypercubic lattice. It is illustrated in the case of 60 degree rhombus tilings.
Title:
Beta-integers as natural counting systems for quasicrystals
Authors:
Burdik C. Frougny C. Gazeau JP. Krejcar R.
Source:
(list of journals)
Journal of Physics A-Mathematical & General. 31(30):6449-6472, 1998 Jul 31.
Abstract:
Recently, discrete sets of numbers, the beta-integers Z(beta), have been proposed as numbering tools in quasicrystalline studies. Indeed, there exists a unique numeration system based on the irrational beta > 1 in which the beta-integers are all real numbers with no fractional part. These beta-integers appear to be quite appropriate for describing some quasilattices relevant to quasicrystallography when precisely beta is equal to 1 + root 5/2 (golden mean tau), to 1 + root 2, or to 2 + root 3, i.e, when beta is one of the self-similarity ratios observed in quasicrystalline structures. As a matter of fact, beta-integers are natural candidates for coordinating quasicrystalline nodes, and also the Bragg peaks beyond a given intensity in corresponding diffraction patterns: they could play the same role as ordinary integers do in crystallography. In this paper, we prove interesting algebraic properties of the sets Z(beta) when beta is a 'quadratic unit PV number', a class of algebraic integers which includes the quasicrystallographic cases. We completely characterize their respective Meyer additive and multiplicative properties Z(beta) + Z(beta) subset of Z(beta) + F Z(beta)Z(beta) subset of Z(beta) + G where F and G are finite sets, and also their respective GaIois conjugate sets Z(beta)'. These properties allow one to develop a notion of a quasiring Z(beta). We hope that in this way we will initiate a sort of algebraic quasicrystallography in which we can understand quasilattices which be 'module on a quasiring' in R-d : Lambda(beta) = Sigma(i) Z(beta ei). We give also some two-dimensional examples with beta = tau.
Title:
Benzotriazole adsorption and inhibition of Cu(100) corrosion in HCl: A
combined in situ STM and in situ FTIR spectroscopy study
Authors:
Vogt MR. Nichols RJ. Magnussen OM. Behm RJ.
Source:
(list of journals)
Journal of Physical Chemistry B. 102(30):5859-5865, 1998 Jul 23.
Abstract:
The adsorption and the corrosion inhibiting effect of benzotriazole (BTAH) on Cu(100) electrodes in 0.1 M HCl were investigated using in situ STM, in situ FTIR spectroscopy, and electrochemical measurements. In the double-layer range up to potentials of -0.6 V vs SCE a Cu surface morphology with extended, atomically flat terraces, separated by almost randomly oriented steps, and a low Cu surface mobility are observed by STM. High-resolution STM images reveal a commensurate superstructure in this potential range, which is attributed to a chemisorbed adlayer of BTAH molecules. At potentials around -0.6 V this structure is replaced by a c(2 x 2) Cl- adlayer, which has the same atomic and long-range structure as found in BTAH-free HCl solution. Upon further potential increase to potentials >-0.35 V STM experiments and polarization measurements indicate the onset of Cu dissolution, while the surface is still covered by the c(2 x 2) Cl- adlayer. At slightly higher potentials (>-0.3 V) STM, IR, and electrochemical data point to the formation of a thick, inhibiting Cu(I)BTA film on the Cu surface. The pronounced differences of the BTAH adsorption behavior to that found in H2SO4 solution provide a microscopic explanation for the reduced inhibition efficiency of BTAH in the presence of chloride.
Title:
A femtosecond snapshot of crystalline order in molecular
liquids
Authors:
Ratajska-Gadomska B. Gadomski W. Wiewior P. Radzewicz C.
Source:
(list of journals)
Journal of Chemical Physics. 108(20):8489-8498, 1998 May 22.
Abstract:
A theoretical model of ultrafast dynamics in the optical Kerr effect in molecular liquids is developed. It assumes that for short times there exist dynamic quasicrystalline structures including a central molecule and its nearest neighbors. The interaction of such structures with a femtosecond laser pulse leads to excitation of vibrational modes (local phonons) which are responsible for subpicosecond nonlinear polarizability of the liquid. The results of numerical calculations performed for benzene show a very good agreement with the experimental data. The lifetime of the dynamic quasicrystalline structures in benzene, at room temperature, is estimated to be about 200 fs. (C) 1998 American Institute of Physics.
Title:
Effects of quenched disorder on La-modified lead zirconate titanate: Long-
and short-range ordered structurally incommensurate phases,
and glassy polar clusters
Authors:
Viehland D. Dai XH. Li JF. Xu Z.
Source:
(list of journals)
Journal of Applied Physics. 84(1):458-471, 1998 Jul 1.
Abstract:
Structure-property relationship studies have been performed in the La-modified lead zirconate titanate (PLZT) solution as a function of quenched La impurity content and Zr/Ti ratio by transmission electron microscopy, lattice imaging, and dielectric spectroscopy. Investigations were performed for 65/35 less than or equal to Zr/Ti less than or equal to 90/10. These investigations have demonstrated a general trend in domain structure and polar order with increasing quenched impurity concentration. For Zr/Ti ratios of 90/10 and 85/15, a structurally incommensurate antiferroelectric (AFE(in)) state was found to be stabilized with increasing La. Temperature dependent investigations demonstrated that the incommensurate structure becomes pinned into long-time metastable states, rather than transforming to a commensurate phase. Also, the modulation wavelength (lambda) was found to increase significantly with increasing Ti. When lambda increased to similar to 40 Angstrom, polar clusters began to condense from the AFE(in) order. For Zr/Ti ratios of 80/20 and 65/35, increasing quenched disorder was found to result in the evolution of polar order through a common sequence of domainlike states including polar clusters, tweedlike structures, and normal micron-sized polydomain structures. These results, in conjunction with dielectric spectroscopy, demonstrate a crossover between a long-period incommensurately modulated state and a relaxer ferroelectric state with increasing quenched disorder. Clearly, both quenched disorder (i.e., random fields) and competing polar orderings (i.e., frustration) underlay the unique behaviors of PLZT. (C) 1998 American Institute of Physics.
Title:
The electronic spectrum of a three-dimensional quasicrystal
Authors:
Olenev DV. Isaev EI. Slobodianiuk PV. Vekilov YK.
Source:
(list of journals)
JETP Letters. 67(8):589-594, 1998 Apr 25.
Abstract:
The electronic spectrum of an icosahedral quasicrystal with a central-atom decoration of the Amman-Mackay network is investigated in the tight-binding approximation. The quasicrystal is described as a structural limit of the optimal cubic approximants with increasing period. The electronic spectra for the first four optimal cubic approximants do not contain the hierarchical gap structure which is typical for the Canter set of the spectrum of a one-dimensional quasicrystal. At the same time, as the order of the approximant increases, the spectrum becomes singular throughout the entire energy scale. (C) 1998 American Institute of Physics.
Title:
Synthesis of porphyrin nanometer material by a new method [Chinese]
Authors:
Wang XQ. Gao S. Yu LX. Miao CJ. Li HB. Cao XZ. Wang LP.
Source:
(list of journals)
Chemical Journal of Chinese Universities-Chinese. 19(6):854-857, 1998 Jun.
Abstract:
Nanometer particles have tremendous application potency in the fields of photoelectricity conversion, information storage and photocatalysis, etc.. However, it has not been reported that preparation of nanometer material was carried out from porphyrin compounds with a structure which can be modulated and have a higher chemical activity. At present, the preparation methods of nanometer material include liquid-phase method, gas-phase method and physical method. The liquid phase method also covers coprecipatation method and solvent evaporation method. The coprecipatation method has some drawback, for instancd, being difficult to wash and filtrate and easy to retain entrained precipitant. For gasphase method, solvent evaporation method and physical method, it needs special equipment and exacting technology conditions, as well as a high processing temperature which results in decomposition of most organic compounds, including porphyrin compounds. In this work, a new method was used to synthesize porphyrin nanometer material. By using this simple method, liquid molecules can be easily embedded in the pores of diatomaceous earth pores. The synthesized porphyrin nanometer material was characterized by the methods of UV-Vis, IR, surface photovoltage spectroscopy and transmission electron microscope. According to the photograph of transmission elecrton microscope, the diameter of crystalline grain of porphyrin molecules aggregated in the pores of diatomaceous earth pores estimated td be 20 nm.
Title:
Imaging and identification of atomic planes of cleaved Bi2Sr2CaCu2O8+delta by
high resolution scanning tunneling microscopy
Authors:
Pan SH. Hudson EW. Ma J. Davis JC.
Source:
(list of journals)
Applied Physics Letters. 73(1):58-60, 1998 Jul 6.
Abstract:
Imaging of the surface of a cleaved Bi2Sr2CaCu2O8+delta (BSCCO) single crystal with a scanning tunneling microscope reveals a series of repeating terraces, whose separations are then used to identify the atomic planes which are exposed. On each of the exposed planes, the incommensurate modulation is also clearly resolved with atomic resolution. The measured separations between the terraces lead to the deduction that any atomic layer can be exposed by mechanical cleavage of BSCCO. We, therefore, suggest that the identity of atomic planes, and the direction of tunneling should always be taken into consideration when interpreting tunneling spectra obtained on such cleaved BSCCO crystals. (C) 1998 American Institute of Physics.